JP5083661B2 - Electric power steering device - Google Patents

Description

  The present invention relates to an electric power steering apparatus that assists steering by an assist force of a motor.

2. Description of the Related Art Conventionally, as an electric power steering apparatus that assists steering by the assist force of a motor, for example, an electric power steering apparatus shown in Patent Document 1 is known. This electric power steering apparatus determines whether or not the electric motor is in an overload state based on the current value of the motor current actually flowing through the electric motor. And, for example, in order to prevent a large motor current from flowing through the electric motor when it is determined that the electric motor is in an overload state by locking the steering wheel against a curb or the like during steering, The command current value determined according to the steering torque is limited by a predetermined value to avoid an overheated state of the electric motor and protect the electric motor.
JP 2001-322555 A

  By the way, for example, when one of the steered wheels of the front wheel drive vehicle falls into the side groove and derails, when the driver steers the steered wheel to return from this derailed state, the side surface of the steered wheel in the derailed state becomes the side groove. Abuts the side of When the driver further steers the steered wheel from this contact state, the command current value is limited as described above in order to avoid and protect the overload state of the electric motor, and the assist torque by the electric motor is limited.

  Depending on the derailed state, the steered wheel may be driven as a drive wheel by a wheel drive device such as an engine while pressing the side surface of the steered wheel toward the side surface of the side groove with the assist force of the electric motor. Thus, it is assumed that the vehicle can escape from the derailed state.

  However, if the assist torque of the electric motor is limited in order to avoid the overload state of the electric motor and protect it even in such a derailed state, the possibility of return from the derailed state is significantly reduced. Resulting in.

  The present invention has been made in order to solve the above-described problems, and an object of the present invention is to determine whether or not to return from the wheel and to improve the possibility of returning from the wheel. Is to provide.

In order to achieve the above object, the electric power steering apparatus according to claim 1 outputs an assist force capable of assisting steering of both steered wheels (41, 42) which are also drive wheels of the vehicle. A wheel load detection means (P ₁ , P ₂ , P ₃ , P ₄ ) for detecting the wheel load (P ₁ , P ₂ , P ₃ , P ₄ ) of all the wheels (41, 42, 43, 44) including both the steering wheels. 41b, 42b, 43b, 44b) and whether one of the two steered wheels is in a derailed state where it falls into the stepped portion (D) of the road surface and derails is determined based on each wheel load. A motor for generating a maximum wheel removal return force (φ), which is a maximum wheel return return force that can be generated in order to cause the steering wheel in the wheel-out state to return from the wheel-removed state. maximum assist force is the maximum assist force may make (FS _m) Of the maximum rotational driving force that is the maximum rotational driving force that can be generated when both the steering wheels are rotationally driven by the wheel driving device (50), the estimation is based on the pressing force acting in the vertical direction on the side surface of the stepped portion. To determine whether or not to return from the derailed state based on the maximum derailed return force estimating means and the wheel load of the steered wheel in the derailed state. Derailment means for determining whether or not the derailment return from the derailment state is impossible when the maximum derailment return force does not exceed the wheel load of the steered wheel in the derailment state. A return enable / disable determining means; and a motor control means (30) for controlling the assist force by the motor to gradually increase when it is not determined by the return wheel return enable / disable determination means that the return to wheel release is impossible. The technical features to provide To.

  In the first aspect of the present invention, based on each wheel load, it is determined whether any one of the two steered wheels that are also drive wheels is in a disengaged state. It is determined that the steered wheel has been removed when it is greater than or equal to a value set larger than the average value of the wheel load. When it is determined that the wheel has been derailed, the maximum assist force that can be generated by the motor is the maximum derailing return force that can be generated to return the steered wheel that is in the derailed state from the derailed state. In addition, it is estimated based on the pressing force acting in the vertical direction on the side surface of the step portion of the maximum rotational driving force that can be generated by rotating both the steering wheels by the wheel driving device. Based on this maximum derailment return force and the wheel load of the steered wheel in the derailed state, it is determined whether or not the derailment can be returned, and when it is not determined that the derailment is impossible (derailing is possible). When it is determined that the assist force by the motor is gradually increased by the motor control means.

  In order to return a steered wheel in a derailed state, it is necessary to apply a derailing return force that exceeds the wheel load of the steered wheel to the steered wheel. Accordingly, it is determined that the wheel return return is impossible when the maximum wheel return return force estimated as described above does not exceed the wheel load of the steered wheel in the wheel release state. When the return force exceeds the wheel load of the steered wheel in the derailed state, it is determined that the derailment return is possible. When it is determined that the wheel return can be returned, the assist force of the motor is gradually increased.

As a result, when it is determined that the wheel return can be returned, even if it has a motor protection function that avoids an overload condition of the motor, the wheel return return is performed until the motor protection function is activated. This assist force is gradually increased while generating the assist force for. For this reason, it is possible to lengthen the period for generating the assist force for returning from the wheel removal, so that the possibility of wheel return returning is improved. Furthermore, since the assist force is gradually increased without suddenly increasing, the assist force ensures that the side surface of the steered wheel in the derailed state is pressed against the side surface of the stepped portion, and the assist force is returned to derailment. Can be optimized for.
Accordingly, it is possible to determine whether or not the wheel return can be returned and improve the possibility of the wheel return return.

  In the invention of claim 2, the motor control means controls the motor so as to temporarily stop the output of the assist force when it is determined by the wheel removal return possibility determination means that the wheel release return is impossible. Thereby, when it is determined that wheel return return is impossible, generation of unnecessary assist force by the motor can be avoided.

  In the invention of claim 3, the motor control means controls the motor so as to gradually decrease the assist force when it is determined by the wheel release return availability determination means that wheel return return is impossible. As a result, it is possible to avoid unnecessary assist force from being generated by the motor without deteriorating the steering feeling due to the sudden decrease of the assist force when it is impossible to return from the wheel.

  In the invention of claim 4, the notifying means notifies the driver or the like of the result of determining whether or not to return to the derailment determined by the means for determining whether or not to return to the derailment. As a result, when either one of the steered wheels is derailed, it is recognized in advance whether or not the steered wheels in the derailed state can be de-returned without actually driving the steered wheels and trying the derailed return. can do. In addition, as described above, since it is possible to recognize in advance whether or not the derailment return is possible without trying the derailment return, the motor or the like can be operated by steering unnecessarily until there is no possibility of the derailment return. There is no overload.

  In the invention of claim 5, the wheel load detecting means is a strain sensor which is mounted on the arm interposed between the vehicle body and each wheel and is mounted in the vicinity of each wheel, and based on the strain of the arm in the mounting portion. To detect each wheel load. Thereby, the wheel load of each wheel can be reliably detected.

  In the invention of claim 6, the wheel load detecting means is a relative distance sensor provided in the vicinity of each wheel for detecting the relative distance between the vehicle body and each wheel, and each relative distance detected by each relative distance sensor. For example, the degree of inclination of the vehicle body with respect to the road surface is calculated, and the wheel load of each wheel is estimated and detected from the degree of inclination.

  For this reason, for example, a sensor for detecting the wheel load of each wheel by detecting the relative distance between the vehicle body and each wheel with a relative distance sensor such as a vehicle height sensor of an active suspension provided in advance in the vehicle. It is possible to estimate and detect each wheel load without providing a wheel.

  In the invention of claim 7, the wheel-removal judging means is configured to set a wheel load on both steered wheels to be equal to or greater than a first wheel load threshold that is set to be larger than an average value of wheel loads on all other wheels. When the average value is 110% or more of the average value, it is determined that the steered wheel is in a disengaged state.

  If either one of the steered wheels falls into the stepped portion of the road surface and derails and some of the steered wheels come into contact with the side of the stepped portion, etc., the vehicle body weight of the vehicle is deviated compared to the other wheels. It acts more greatly on the steering wheel in the wheel state. For this reason, the wheel load of the steered wheel that is in the wheel-removed state becomes larger than the average value of the wheel loads of all other wheels. Therefore, by comparing the wheel loads of the two steered wheels with the first wheel load threshold value, it is possible to appropriately determine whether or not the vehicle is in the derailed state.

  In the invention of claim 8, is the wheel-removal determining means in a wheel-removed state when the vehicle speed is not more than a predetermined speed threshold value determined to be stopped, for example, 0 (zero) km / h or less? Whether or not is determined based on the wheel load.

  Usually, since a vehicle that has derailed cannot move, the vehicle speed at the time of derailment is equal to or less than the speed at which it is determined that the vehicle is stopped. Therefore, it is possible to more reliably determine whether or not the vehicle is in the wheel-out state by considering the vehicle speed.

In the invention of claim 9, the maximum derailing return force φ is set to FS _m , the maximum assist force is set to be smaller than the maximum rotational driving force, and the maximum rotational driving force during derailing that can be generated by the wheel driving device is FD. _m is the relative angle between the direction along the side surface of the steered wheel in the derailed state and the direction along the side surface of the stepped portion, and the friction coefficient at the contact surface between the side surface of the steered wheel and the side surface of the stepped portion in the derailed state When the predetermined coefficient corresponding to is μ, it is estimated by the following equation.
φ = μ × (FS _m + FD _m × sin δ)

The contact surface between the side surface of the steered wheel and the side surface of the stepped portion in the derailed state is a push that acts on the side surface of the stepped portion in the vertical direction among the maximum assist force FS _m and the maximum rotational drive force FD _m during derailment The pressure, that is, FD _m × sin δ acts as the maximum force for returning to derailment. Therefore, when the friction coefficient on the contact surface is μ, the maximum derailing return force φ can be calculated appropriately and specifically using the above equation.

At this time, the maximum rotational drive force FD _m at the time of wheel removal is smaller than the maximum rotational drive force that can be generated on the steered wheels by the wheel drive device, and is set to, for example, about 1/3 of the maximum rotational drive force. There is no excessive load on the wheel drive.

  In the tenth aspect of the invention, the relative angle detection means detects the actual steering angle of the steered wheel, which is the angle at which the steered wheel is steered with respect to the traveling direction of the vehicle, as the relative angle. In order to detect the relative angle between the direction along the side surface of the steered wheel in the derailed state and the direction along the side surface of the stepped portion on the road surface, a dedicated sensor or the like for detecting the shape of the stepped portion is required. On the other hand, the relative angle between the direction corresponding to the traveling direction of the vehicle in the derailed state and the direction along the side surface of the stepped portion is generally the same. Therefore, by using the actual steering angle of the steered wheel as a relative angle between the direction along the side surface of the steered wheel and the direction along the stepped portion, the relative angle is estimated without providing a dedicated sensor or the like. obtain.

  In the eleventh aspect of the present invention, the derailment return availability determination means determines whether or not the derailment return is possible when the current value flowing through the motor becomes equal to or greater than a predetermined current threshold at which the motor is determined to be overloaded. .

  In order to more accurately determine whether or not return from wheel removal is possible, it is necessary to estimate the maximum wheel release return force in a state where the side surface of the steered wheel that is in a wheel removal state is pressed against the side surface of the stepped portion. Immediately after derailment, it is assumed that the side surface of the steered wheel is not pressed against the side surface of the stepped portion, and in this case, the maximum derailment return force cannot be effectively applied for the derailment return. It is.

  When the side surface of the steered wheel in the derailed state is pressed against the side surface of the stepped portion, the motor that assists the steering of the steered wheel is overloaded, and the value of the current flowing through the motor increases. Therefore, when the steering wheel is removed, the value of the current flowing to the motor increases and the motor is overloaded, so it is estimated that the side surface of the steering wheel is pressed against the side surface of the stepped portion. In this case, it is possible to make a more accurate determination by determining whether or not the wheel return can be returned based on the maximum wheel return return force and the wheel load of the steered wheel that is in the wheel release state.

  According to a twelfth aspect of the present invention, when the maximum derailing return force is equal to or smaller than a second wheel load threshold set to be equal to or smaller than a wheel load on the steered wheel in the derailed state, the derailing return possibility determination means It is determined that recovery is impossible.

  When the maximum derailing return force is equal to or less than the wheel load of the steered wheel in the derailing state, there is a possibility that the derailing cannot be performed. Therefore, the maximum derailing return force is equal to or less than a second wheel load threshold set to be equal to or less than the wheel load on the steered wheel in the derailed state, for example, 90% or less of the wheel load on the steered wheel in the derailed state. In this case, it is determined that derailment is impossible. As a result, it is possible to appropriately determine that the wheel-return return is impossible.

  According to the thirteenth aspect of the present invention, when it is determined by the wheel-removal determining means that either one of the two steered wheels is in the wheel-removed state, the overload protection of the motor is stopped or the protection condition is eased. Thereby, even when there is a limit to protect the motor by avoiding overload of the motor, by temporarily stopping or relaxing the limit on motor overload protection in order to give priority to the return from the derailed state, The possibility of return from wheel removal can be improved.

  According to a fourteenth aspect of the present invention, the electric power steering apparatus includes vehicle height adjusting means capable of adjusting the height of the vehicle body with respect to each wheel. Then, when it is determined that either one of the two steered wheels is in the derailed state by the derailing determination means, the vehicle height adjusting means determines the height of the vehicle body relative to the “steered wheel in the derailed state” The height is adjusted to be higher than the height of the vehicle body with respect to “the wheel that is farthest from the steered wheel in the wheeled state”.

  In general, a wheel that has been removed comes in contact with the bottom or side surface of the side groove, and its position is lower than other wheels. If it does so, compared with the normal state before dewheeling, the posture of the vehicle will incline in the direction of the derailed steering wheel, and the wheel load of the steered wheel will be increased.

  Therefore, by adjusting the height of the vehicle body relative to the “steering wheel in the derailed state” by the vehicle height adjusting means to be higher than the height of the vehicle body relative to the “wheel most distant from the steered wheel in the derailed state” The wheel load of the steered wheels can be reduced. As a result, the wheel load of the steered wheels in the derailed state is reduced, so that the force required for the derailed return is reduced, and the possibility of the derailed return can be improved.

  According to a fifteenth aspect of the present invention, the electric power steering apparatus includes vehicle height adjusting means capable of adjusting the height of the vehicle body with respect to each wheel. Then, when it is determined that either one of the two steered wheels is in the derailed state by the derailing determination means, the vehicle height adjustment means determines the height of the vehicle body relative to the “steered wheel in the derailed state” as “ Adjust the height higher than the height of the vehicle body relative to the wheel that is farthest away from the steered wheel and the wheel that is different from the wheel that is farthest away from the steered wheel and the wheel that is farthest away from the steered wheel. Based on the degree of change in the wheel load of the steered wheel in the detached state when the height of the vehicle body is changed with respect to each wheel, the wheel load of the steered wheel in the detached state is reduced. adjust.

  In this way, the vehicle height adjustment means can adjust the height of the vehicle body with respect to each wheel so that the wheel load of the steered wheels in the derailed state is reduced. Will be reduced, and the possibility of wheel-out return can be further improved.

  In the invention according to claim 16, the electric power steering apparatus includes an air pressure detecting means for detecting the air pressure of each wheel, an air pressure adjusting means capable of adjusting each air pressure, and a removal by the friction force between the air pressure and each wheel and the road surface. And a map in which a frictional force evaluation value indicating the possibility of wheel return is associated in advance. Then, when it is determined that either one of the two steered wheels is in a wheel-removed state by the wheel-removal determining means, the air pressure adjusting means increases the frictional force evaluation value on the basis of the map to restore the wheel removal. Adjust each air pressure individually to increase the possibility.

  The frictional force generated between the elastic wheel and the rigid road surface increases as the ground contact area increases if the wheel air pressure is the same, and increases as the wheel air pressure increases if the ground contact area is the same. . On the other hand, the ground contact area increases as the wheel air pressure decreases, so if the wheel air pressure is too high, it is disadvantageous from the viewpoint of the ground contact area. Therefore, it is considered that the wheel air pressure that can increase the possibility of return from the wheel in terms of frictional force exists between the minimum air pressure and the maximum air pressure of the wheel.

  Therefore, a map in which the air pressure of the wheel is associated with the evaluation value of the frictional force indicating the possibility of returning from the wheel by the frictional force between the wheel and the road surface is experimentally set and stored in advance. This frictional force evaluation value is set, for example, such that the closer to 1, the higher the possibility of wheel release return. And, at the time of derailment, based on the map in which the air pressure and the frictional force evaluation value are associated with each other, the air pressure of each wheel is adjusted by the air pressure adjusting means so as to increase the frictional force evaluation value. The possibility of returning from the wheel removal can be increased by appropriately increasing the friction force generated therebetween.

  In the invention according to claim 17, the electric power steering apparatus includes an air pressure detecting means for detecting the air pressure of each wheel, an air pressure adjusting means capable of adjusting each air pressure, and a removal by the friction force between the air pressure and each wheel and the road surface. And a map in which a frictional force evaluation value indicating the possibility of wheel return is associated in advance. Then, when it is determined that either one of the two steered wheels is in a derailed state by the derailment determining means, the steering wheel in the derailed state when each air pressure is changed by the air pressure adjusting means. Each air pressure is adjusted so as to increase the possibility of return from wheel removal based on both the degree of change in wheel load and the degree of change in the frictional force evaluation value obtained from the map when each air pressure is changed.

  As described above, both the degree of change in the wheel load of the steered wheel when each air pressure is changed and the degree of change in the frictional force evaluation value obtained from the map when each air pressure is changed. Therefore, each air pressure is adjusted so as to increase the possibility of returning from the wheel, so that each air pressure is adjusted only in accordance with the frictional force evaluation value as in the invention described in claim 16. As a result, a more optimal air pressure can be set, and the possibility of return from wheel removal can be further increased.

[First Embodiment]
Hereinafter, a first embodiment of the present invention will be described with reference to the drawings. First, the configuration of the electric power steering apparatus 20 according to the first embodiment will be described based on FIGS. 1 (A) and 1 (B).
FIG. 1A is a configuration diagram showing an example of the overall configuration of the electric power steering apparatus 20 according to the first embodiment. The electric power steering apparatus 20 mainly includes a steering wheel 21, a steering shaft 22, a pinion shaft 23, an EPS actuator 24, a rod 25, a torque sensor 26, an ECU 30, wheel load sensors 41b to 44b, and the like.

  As shown in FIG. 1, one end of a steering shaft 22 is connected to the steering wheel 21, and the input side of a torque sensor 26 is connected to the other end of the steering shaft 22. Further, one end side of the pinion shaft 23 is connected to the output side of the torque sensor 26.

  The torque sensor 26 includes a torsion bar (not shown) and two resolvers attached to both ends of the torsion bar so as to sandwich the torsion bar. The input / output receives one end of the torsion bar and outputs the other end. By detecting the twist amount of the torsion bar between the two resolvers, the steering torque Ts and the steering angle θ by the steering wheel 21 are detected. Then, the torque sensor 26 generates a detection signal corresponding to the steering torque Ts and the steering angle θ and outputs the detection signal to the ECU 30.

  The input side of the EPS actuator 24 is connected to the other end side of the pinion shaft 23. The EPS actuator 24 converts the rotational motion input from the pinion shaft 23 into the axial motion of the rod 25 by the rack and pinion gear. In addition, the assist torque Tm generated by the assist motor 24a is controlled by the ECU 30 to generate an assist force corresponding to the steering state.

  A right front wheel 41 is attached to the right end of the rod 25, and a left front wheel 42 is attached to the left end of the rod 25. The actual steering angle δ of the right front wheel 41 and the left front wheel 42, which are the steered wheels, is varied by the axial movement of the rod 25, and the traveling direction of the vehicle is changed. The vehicle in the first embodiment is front wheel drive, and the right front wheel 41 and the left front wheel 42 are driven and rotated as drive wheels by torque output from a wheel drive device 50, for example, an engine or the like. Hereinafter, at least one of the right front wheel 41 and the left front wheel 42 is also referred to as a steering wheel. In addition to the right front wheel 41 and the left front wheel 42, a right rear wheel 43 and a left rear wheel 44, which will be described later, are also referred to as wheels 41 to 44, respectively. Further, the vehicle in the first embodiment is four-wheel drive, and each wheel 41 to 44 may be driven as a drive wheel to rotate.

The wheel load sensor 41b is a strain sensor mounted on the arm 41a interposed between the vehicle body and the right front wheel 41 and in the vicinity of the right front wheel 41. The wheel load sensor 41b is based on the distortion of the arm 41a at the mounting portion. to detect the wheel load _{P 1.} Similarly to the wheel load sensor 41b, the wheel load sensors 42b to 44b are mounted on the arms 42a, 43a, 44a interposed between the vehicle body and the left front wheel 42, the right rear wheel 43, and the left rear wheel 44, respectively. The wheel loads P ₂ , P ₃ , and P ₄ of the left front wheel 42, the right rear wheel 43, and the left rear wheel 44 are detected based on the distortion of the arms 42 a, 43 a, and 44 a at each mounting portion. Each wheel load sensor 41b~44b, respectively, and outputs to the ECU30 and generates a detection signal corresponding to the wheel load _P 1 to P _4.

  FIG. 1B is a circuit block diagram illustrating a configuration example of the ECU 30 and the like. The ECU 30 mainly includes an input / output interface I / F 32 capable of inputting / outputting various sensor information by an MPU (Micro Processor Unit) 31 having a peripheral LSI such as an A / D converter, a memory, and the like, a torque sensor 26, and the like. And a motor drive circuit 33 capable of supplying a motor current by PWM control to the assist motor 24a based on a motor current command value output from the MPU 31. Reference numeral 34 shown in FIG. 1B is a current sensor 34 that can detect a motor current value i that actually flows through the assist motor 24a. Sensor information relating to the motor current value i detected by the current sensor 34 is as follows. The motor current signal can be input to the MPU 31 via the input / output interface I / F 32.

  With this configuration, the electric power steering apparatus 20 detects the steering torque Ts by the steering wheel 21 by the torque sensor 26, and sets the assist motor 24a to generate an assist force corresponding to the steering torque Ts. It is controlled by the ECU 30.

  Further, as shown in FIG. 1A, a wheel drive device 50 is electrically connected to the ECU 30, and the wheel drive device 50 outputs a wheel drive stop signal output from the ECU 30 as will be described later. Accordingly, the rotational drive of the right front wheel 41 and the left front wheel 42 is stopped, and the stop of the rotational drive is released according to the wheel drive stop release signal.

  In addition, a vehicle speed sensor 60 and a warning device 70 are electrically connected to the ECU 30. The vehicle speed sensor 60 detects the traveling speed of the vehicle (vehicle speed V) and outputs a detection signal corresponding to the vehicle speed V to the ECU 30. The warning device 70 is provided, for example, on an instrument panel in the vehicle interior, and information corresponding to a derailment return possible signal, a derailment nonreturnable signal, or a treatment information presentation signal output from the ECU 30 as will be described later. As a display notification means for displaying on the monitor 71.

FIG. 2 is an explanatory view exemplifying a wheel removal return force that is applied to the left front wheel 42 and the like in order to return the left front wheel 42 that is in a wheel removal state.
As illustrated in FIG. 2, when the left front wheel 42 falls into a stepped portion on the road surface, for example, the side groove D, the side surface of the steered wheel 42 faces the side surface of the side groove D depending on the state of the wheel removal. There is a possibility that the steering wheel 41 and 42 are driven by the wheel driving device 50 while being pressed with a sufficient force by the assisting force of the assist motor 24a, thereby returning from the dewheeling state. However, if the assist torque is limited by the motor protection function even in the above-described derailed state, the possibility of return from derailment is reduced.

  Therefore, in the first embodiment, when the wheel is returned to the side groove D or the like by the process of improving the possibility of return from wheel removal described below, whether or not the wheel return can be returned is determined according to the state of the wheel removal. By performing processing according to this determination result, the possibility of return from wheel removal is improved.

  Hereinafter, the wheel release return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the first embodiment will be described with reference to FIGS. 3 and 4. FIG. 3 and FIG. 4 are flowcharts showing the flow of the derailment return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the first embodiment.

First, in step S101 in FIG. 3, vehicle speed V, wheel loads P _{1 to} P ₄ , motor current value i, steering angle θ, and the like detected by each sensor are read. Next, in step S103, the vehicle speed V is determined whether or not it is less than the speed threshold value V ₀ is determined to be stopped. In the first embodiment, V ₀ is set to 0 (zero) km / h, for example.

If the vehicle speed V is not less than or equal to the speed threshold V ₀ , it is determined No in step S103 and the processing from step S101 is repeated. In such a situation, when the vehicle speed V is less than the speed threshold _{V 0} (in S103 Yes), in step S105, the wheel load _{P 1} of the right front wheel 41 is greater than the wheel load average value of each wheel other than the right front wheel 41 It is determined whether or not the wheel load threshold P _A1 is set or more. Here, the wheel load threshold value _PA1 is calculated by the following equation (1).
P _A1 = K ₁ × (P ₂ + P ₃ + P ₄ ) / 3 (1)
Here, when a part of the right front wheel 41 right front wheel 41 is derailing depressed the groove D is in contact with the side surface or the like of the groove D, wheel load P ₁ is the wheel load of each wheel other than the right front wheel 41 since larger than a predetermined value than the average value, _{K 1,} for example, it is set to 1.1 (110%).

If wheel load _{P 1} in step S105 is the wheel load threshold _{P A1} above, (Yes in S105) it is determined that the right front wheel 41 is derailing depressed to ditch D, the determination in step S109 Processing is done. Note that the determination processing in step S105 and step S107 described later corresponds to “derailing determination means” described in the claims.

On the other hand, if the wheel load _{P 1} is not the wheel load threshold _{P A1} or (No in S105), in step S107, the wheel load _{P 2} of the left front wheel 42 is, from the wheel load average value of each wheel other than the left front wheel 42 It is determined whether or not the wheel load threshold value _{PA2 is} greater than or equal to a large value. Here, the wheel load threshold value _PA2 is calculated by the following equation (2).
P _A2 = K ₂ × (P ₁ + P ₃ + P ₄ ) / 3 (2)
Here, _{K 2,} similar to _{K 1} described above, for example, is set to 1.1 (110%).

When the wheel load _{P 2} in the step S107 is the wheel load threshold _{P A2} above, the left front wheel 42 is determined to be derailing depressed to ditch D (Yes in S107), the processing in step S109 Is made.

On the other hand, if the wheel load _{P 2} is not wheel load threshold _{P A2} more (No in S107), the right front wheel 41 and the left front wheel 42 is determined not to derailing, the processing from step S101 is repeated.

  If it is determined Yes in step S105 or step S107, in step S109, whether or not the motor current value i is greater than or equal to the overload current value io determined that the assist motor 24a is in an overload state. Determined. Hereinafter, the case where the left front wheel 42 is removed will be described.

  Here, for example, when the side surface of the left front wheel 42 is not pressed against the side surface of the side groove D immediately after the wheel is removed, an excessive load is not generated on the assist motor 24a. Then, the processing from step S101 is repeated.

  In such a situation, if the side surface of the left front wheel 42 is pressed against the side surface of the side groove D by steering for return from the wheel removal, the assist motor 24a is overloaded, and the motor current value i becomes equal to or higher than the overload current value io. In step S109, “Yes” is determined.

  In step S111, motor overload protection stop processing is performed. By this stop processing, the restriction for avoiding motor overload and protecting the assist motor 24a is temporarily stopped. In the stop process, the above limitation may be relaxed without stopping. Further, the limitation for overheating protection of the assist motor 24a may not be stopped or relaxed.

  Next, in step S113, the actual steering angle δ (see FIG. 2), which is the angle at which the right front wheel 41 and the left front wheel 42 are steered with respect to the traveling direction of the vehicle, becomes the steering angle θ detected by the torque sensor 26. Calculated based on Note that the processing in step S113 corresponds to “relative angle detection means” recited in the claims.

In step S115, the maximum derailing return force φ that can be generated by the assist motor 24a and the wheel drive device 50 in order to restore the left front wheel 42 in the derailing state from the derailing state is expressed by the following equation (3). Is calculated by
φ = μ × (FS _m + FD _m × sin δ) (3)

Here, μ is a predetermined coefficient corresponding to the friction coefficient in the contact surface S between the side surface of the left front wheel 42 and the side surface of the side groove D (see FIG. 2), and is set to 0.1, for example. FS _m is the maximum assist force that can be generated by the assist motor 24a. Further, FD _m is the maximum rotational driving force at the time of derailing set to be smaller than the maximum rotational driving force that can be generated when the right front wheel 41 and the left front wheel 42 are rotationally driven by the wheel driving device 50, and the wheel driving device. In order to suppress an excessive load at 50, for example, it is set to 1/3 of the maximum rotational driving force. Note that the processing in step S115 corresponds to “maximum derailing return force estimating means” described in the claims.

  The basis of the above formula (3) will be described with reference to FIG. 2. After the left front wheel 42 is derailed and falls into the side groove D, the side surface of the left front wheel 42 becomes the side surface of the side groove D by steering for return from the derailment. The actual steering angle δ becomes constant by being pressed by the contact surface S. At this time, on the contact surface S, the assist force FS generated by the assist motor 24a, the rotational drive force FR of the right front wheel 41 by the wheel drive device 50, and the rotational drive force FL of the left front wheel 42 are added values. Of the rotational driving force FD, the pressing force (FD × sin δ) acting in the vertical direction on the side surface of the side groove D acts as a force for returning from the wheel removal.

Further, when steering is performed so as to press the side surface of the left front wheel 42 against the side surface of the side groove D, the contact surface S has a maximum assist force FS _m by the assist motor 24a and a maximum rotation drive during wheel removal by the wheel drive device 50. Of the force FD _m , the pressing force (FD _m × sin δ) acting in the vertical direction on the side surface of the side groove D acts as the maximum force for returning from the wheel removal. When the predetermined coefficient corresponding to the friction coefficient of the contact surface S is μ, the maximum derailing return force φ is calculated by the above equation (3).

If the maximum derailing return force φ is calculated as described above in step S115, in step S117 of FIG. 4, the maximum derailing return force φ is from wheel loads P ₂ in the left front wheel 42 is derailing state a determination is made whether small or less wheel load threshold P _B is set. Here, when the left front wheel 42 is removed, the wheel load threshold P _B is calculated by the following equation (4).
P _B = K ₃ × P ₂ (4)
Referring to grounds of the above formula (4), when the maximum derailing return force φ is below the wheel load P ₂ of the left front wheel 42 is derailed state may not be derailing return. Therefore, in this first embodiment, the K _3, 1 the following values, for example, by setting 0.9, the wheel load threshold P _B is set smaller than the wheel load P _2, the maximum derailing return force φ determines whether it is less than this wheel load threshold P _B. Note that the processing in step S117 corresponds to “derailing return availability determination means” described in the claims.

FIG. 5 (A) is an explanatory diagram showing an example in which it is displayed on the monitor 71 of the warning device 70 that it is impossible to return the wheel, and FIG. It is explanatory drawing which shows an example by which it is displayed that a wheel return is possible.
In step S117 described above, when the maximum wheel release return force φ is equal to or less than the wheel load threshold P _B (Yes in S117), it is determined that the wheel return return is impossible, and in step S121, the wheel return return is determined. A disabling signal is output to the warning device 70. As a result, the warning device 70 displays on the monitor 71 that it is impossible to return from the wheel release, as illustrated in FIG.

  Next, in step S123, an assist motor drive temporary stop process is performed, and the generation of the assist force by the assist motor 24a is temporarily stopped. As a result, it is possible to suppress an unnecessary load from being applied to the assist motor 24a even though it is impossible to return from the wheel.

  In step S125, a wheel drive stop signal is output to the wheel drive device 50. For this reason, the rotation driving of the right front wheel 41 and the left front wheel 42 by the wheel driving device 50 is stopped, and thus an unnecessary load is applied to the wheel driving device 50 even though it is impossible to return the wheel. Can be suppressed.

FIG. 6 is an explanatory diagram showing an example of treatment information displayed on the monitor 71 of the warning device 70, and FIG. 6 (A) shows a coefficient of friction between the left front wheel 42 and the side groove D that are in a wheel-removed state. FIG. 6B is an explanatory diagram illustrating first treatment information that promotes improvement, and FIG. 6B is an explanatory diagram illustrating second treatment information that prompts a decrease in the height of the side groove D to be returned.
After the process of step S125, a treatment information presentation signal is output to the warning device 70 in step S127. As a result, the warning device 70, as illustrated in FIGS. 6 (A) and 6 (B), uses the monitor 71 to add information indicating that it is impossible to recover from the above-described derailment, and to take action information for returning from the derailment. For example, the first treatment information for promoting the improvement of the coefficient of friction between the left front wheel 42 and the side groove D by laying a cloth or a sheet between the left front wheel 42 and the side groove D in the derailed state (see FIG. 6A). ) Or second treatment information that promotes a decrease in the height of the side groove D to be returned by installing stones, blocks, other instruments, etc. between the lower side of the left front wheel 42 and the side groove D in the derailed state ( (See FIG. 6B).

Incidentally, for example, it may set the priority for displaying the action information in accordance with the wheel load P ₂ of the front left wheel 42 in derailing state. Specifically, when the wheel loads P ₂ hardly changes may display the first treatment information on the monitor 71 since the friction of the side surface of the groove D is insufficient. On the other hand, if the wheel load P ₂ had been steadily reduced halfway through processing of from step S131 to be described later, the second treatment data since the friction of the side surface of the groove D is sufficient to monitor 71 indicate. After the process of step S127, the process from step S101 of FIG. 3 is repeated.

On the other hand, when the maximum derailment return force φ is not less than or equal to the wheel load threshold P _B (No in S117), it is determined that the derailment return is possible. Then, in step S131, a wheel removal return enable signal is output to the warning device 70. As a result, the warning device 70 displays on the monitor 71 that it is possible to return from the wheel removal as illustrated in FIG. 5B.

  Next, in step S133, assist torque gradual increase processing is performed. In this process, the assist motor 24a is driven and controlled so that the assist torque Tm for assisting steering is gradually increased from the current assist torque Tm by a predetermined torque regardless of the driver's steering. In step S <b> 135, a wheel drive stop cancellation signal is output to the wheel drive device 50. Thereby, when the rotation drive of the right front wheel 41 and the left front wheel 42 by the wheel drive device 50 is stopped in step S125 described above, the stop of the rotation drive is released.

  In step S137, the motor current value i exceeds the overload current value io, and is less than the current limit value is, which is a limit current value that can be supplied to the assist motor 24a for return from the wheel removal. It is determined whether or not.

  Here, if the motor current value i is equal to or greater than the current limit value is (No in S137), it is determined that the wheel return return cannot be performed with the assist torque Tm that can be generated by the assist motor 24a, and the above-described step S121 is performed. Process from.

  On the other hand, if the motor current value i is less than the current limit value is (Yes in S137), it is determined in step S139 whether or not the motor current value i is greater than or equal to the overload current value io.

Here, if the motor current value i is equal to or greater than the overload current value io (Yes in S139), it is determined that the wheel removal has not been returned, and the processing from step S101 of FIG. 3 described above is performed. Further, (No in S139) even when the motor current value i is not the overload current value io above, if the wheel load _{P 1} is the wheel load threshold _{P A1} or (Yes in S141) or the wheel load _{P 2} are wheels If it is a load threshold value P _A2 above (Yes in S143), it is determined as not derailing returning those not occur an excessive load on the assist motor 24a, the processing from step S101 of FIG. 3 described above Do.

On the other hand, (No in S139) even when the motor current value i is not the overload current value io or not the wheel load _{P 1} is the wheel load threshold _{P A1} or (No in S141) and the wheel load _{P 2} is the wheel load If not the threshold P _A2 more (no in S143), since the excessive load on the assist motor 24a is vehicle weight of the vehicle does not occur, acts substantially uniformly on each wheel 41-44, derailing It is determined that the return has been completed, and the derailment return possibility improving process is completed.

As described above, in the electric power steering apparatus 20 according to the first embodiment, the ECU 30 determines whether any one of the right front wheel 41 and the left front wheel 42 which are also drive wheels is in a derailed state. Based on the wheel loads P _{1 to} P ₄ , if the wheel load P ₁ of the right front wheel 41 is equal to or greater than the wheel load threshold P _A1 set larger than the wheel load average value of each wheel other than the right front wheel 41, the right determines that the front wheel 41 is derailed, the left when the wheel load P ₂ of the front left wheel 42 is the wheel load threshold P _A2 than is larger than the wheel load average value of each wheel other than the left front wheel 42 It is determined that the front wheel 42 is removed.

When it is determined that one of the right front wheel 41 and the left front wheel 42 has been derailed, the assist motor 24a generates a maximum derailing return force φ that can be generated to return from the derailed state. vertical to the side surface of the groove D of the maximum assist force FS _m plus derailing derailing at the maximum rotational driving force front right wheel 41 and the left front wheel 42 by a wheel drive device 50 can be generated by driving the rotation during FD _m to obtain It is estimated based on the pressing force acting on the.

Then, for example, when the left front wheel 42 is determined to be derailed, wheel load threshold P for the maximum derailing return force φ is set below the wheel load P ₂ of the left front wheel 42 is derailing state If it is less than or equal to _B, it is determined that wheel return return is impossible, and if the maximum wheel return return force φ is not less than or equal to the wheel load threshold P _B , it is determined that wheel return return is possible. . When it is determined that the wheel return can be returned, the assist torque Tm (assist force) by the assist motor 24a is gradually increased from the current assist torque Tm by a predetermined torque.

As a result, if it is determined that the wheel return can be returned, even if there is a limitation that the motor current value i that can be supplied to the assist motor 24a as a motor protection function is less than the current limit value is, Until the motor current value i of the motor 24a reaches the current limit value is, the assist force is gradually increased while generating the assist force for returning from the wheel removal. For this reason, it is possible to lengthen the period for generating the assist force for returning from the wheel removal, so that the possibility of wheel return returning is improved. Furthermore, since the assist force is gradually increased without suddenly increasing, the side surface of the steered wheel in the derailed state is reliably pressed against the side surface of the side groove D by this assist force, and the assist force is returned to derailment. Can be optimized for.
Accordingly, it is possible to determine whether or not the wheel return can be returned and improve the possibility of the wheel return return.

  Further, in the electric power steering apparatus 20 according to the first embodiment, the ECU 30 sets the assist motor 24a so as to temporarily stop the output of the assist force when it is determined that the wheel return return is impossible. Control. Thereby, when it is determined that the wheel return return is impossible, it is possible to avoid generation of unnecessary assist force by the assist motor 24a.

  Further, in the electric power steering apparatus 20 according to the first embodiment, the ECU 30 notifies the driver or the like by displaying the determination result of whether or not the wheel removal return is possible on the monitor 71 of the warning device 70. As a result, when either one of the steered wheels is derailed, it is recognized in advance whether or not the steered wheels in the derailed state can be de-returned without actually driving the steered wheels and trying the derailed return. can do. In addition, as described above, since it is possible to recognize in advance whether or not the derailing return is possible without trying the derailing return, the assist motor 24a can be operated by unnecessary steering even when there is no possibility of the derailing return. Etc. are not overloaded.

  Further, in the electric power steering apparatus 20 according to the first embodiment, the ECU 30 determines that the first and second described above are displayed on the monitor 71 of the warning device 70 when it is determined that the wheel removal return is impossible. The treatment information for returning to derailment such as the treatment information of 2 is displayed. The possibility that the driver or the like returns from the derailed state can be improved by appropriately performing the work for returning from the derailment based on the displayed treatment information.

Moreover, in the electric power steering device 20 according to the first embodiment, the wheel load sensors 41b to 44b are on the arms 41a to 44a interposed between the vehicle body and the wheels 41 to 44, respectively. It is a strain sensor attached to each of the wheels 41 to 44, and detects each wheel load P _{1 to} P ₄ based on the respective strains of the arms 41 a to 44 a at each attachment portion. Thereby, the wheel loads P _{1 to} P ₄ of the wheels 41 to 44 can be reliably detected.

In the electric power steering apparatus 20 according to the first embodiment, the ECU 30 causes the wheel load P ₁ at the right front wheel 41 to be set larger than the wheel load average value of each wheel other than the right front wheel 41. threshold P _A1 above, for example, determines that the right front wheel 41 is in derailing state when at least 110% of the wheel load average value, the wheel load P ₂ in the left front wheel 42, the wheels other than the front left wheel 42 It is determined that the left front wheel 42 is in a disengaged state when the wheel load threshold value _PA2 is set to be greater than the wheel load average value, for example, 110% or more of the wheel load average value.

When any one of the right front wheel 41 and the left front wheel 42 falls into the side groove D of the road surface and part of the wheel comes in contact with the side surface of the side groove D or the like, It is because it becomes larger than the average value of the wheel load in all the other wheels. Therefore, wheel load P ₁ and wheel load threshold P _{A1 or,} by comparing each wheel load P ₂ and wheel load threshold P _A2, it is possible to properly determine whether a derailing state.

Further, in the electric power steering apparatus 20 according to the first embodiment, the ECU 30 determines whether or not the vehicle is in the derailed state when the vehicle speed V is equal to or less than the speed threshold value V ₀ determined to be stopped. Is determined based on the wheel load.

  Normally, a vehicle that has been derailed cannot move, so the vehicle speed V at the time of derailment is less than or equal to the speed at which it is determined that the vehicle is stopped. Therefore, it is possible to more reliably determine whether or not the vehicle is in the derailed state by considering the vehicle speed V.

In the electric power steering apparatus 20 according to the first embodiment, the ECU 30 sets the maximum derailing return force φ, the maximum assist force FS _m , and smaller than the maximum rotational driving force by the wheel driving device 50. FD _m , the actual steering angle of the steered wheel is δ, and the friction coefficient μ of the contact surface S between the side surface of the steered wheel and the side surface of the side groove D in the disengaged state is described above. (3) is calculated.

The contact surface S between the side surface of the steered wheel and the side surface of the side groove D that is in the derailed state acts in the vertical direction on the side surface of the side groove D among the maximum assist force FS _m and the maximum rotational driving force FD _m during derailment. The pressing force, that is, FD _m × sin δ acts as the maximum force for returning to the wheel removal. Therefore, when the friction coefficient on the contact surface S is μ, the maximum derailing return force φ can be calculated appropriately and specifically using the above equation.

At this time, the maximum rotational driving force FD _m at the time of wheel removal is smaller than the maximum rotational driving force that can be generated on the steered wheels by the wheel driving device 50, and is set to, for example, about 1/3 of the maximum rotational driving force. The wheel drive device 50 is not excessively loaded.

Further, when calculating the pressing force acting in the vertical direction on the side surface of the side groove D out of the maximum rotational driving force FD _m at the time of derailment, the direction along the side surface of the steered wheel in the derailed state and the side surface of the side groove D As a relative angle with respect to the direction, calculation is performed using an actual steering angle δ of the steering wheel, which is an angle at which the steering wheel is steered with respect to the traveling direction of the vehicle.

  In order to detect the relative angle between the direction along the side surface of the steered wheel and the direction along the side surface of the side groove D, a dedicated sensor or the like for detecting the shape of the side groove D is required. On the other hand, normally, the relative angle between the direction corresponding to the traveling direction of the vehicle in the derailed state and the direction along the side surface of the side groove D substantially coincides. Therefore, by using the actual steering angle δ as a relative angle between the direction along the side surface of the steered wheel in the derailed state and the direction along the side groove D, the relative angle can be estimated without providing a dedicated sensor or the like. A dedicated sensor or the like may be provided to accurately detect the relative angle between the direction along the side surface of the steered wheel in the derailed state and the direction along the side surface of the side groove D.

  Further, in the electric power steering apparatus 20 according to the first embodiment, the ECU 30 causes the motor current value i to be greater than or equal to the overload current value io that is determined that the assist motor 24a is in an overload state. Judgment is made on whether or not derailment is possible.

Thereby, for example, when the left front wheel 42 is removed, the motor current value i flowing to the assist motor 24a increases to become the overload current value io or more, so that the assist motor 24a is in an overload state and left The state in which the side surface of the front wheel 42 is pressed against the side surface of the side groove D is estimated, and in this pressed state, the wheel release return is performed based on the maximum wheel release return force φ and the wheel load P ₂ of the left front wheel 42 in the wheel release state. More accurate determination can be performed by determining whether or not it is possible.

Further, in the electric power steering apparatus 20 according to the first embodiment, the ECU 30 has the wheel load P _{1 on the} right front wheel 41 or the wheel load P on the left front wheel 42 in which the maximum derailing return force φ is in the derailed state. _{When the} wheel load threshold value P _B is set to ₂ or less, it is determined that the wheel removal return is impossible.

For example, if the maximum derailing return force φ is the wheel load P ₂ less in the front left wheel 42 is a derailed state may not be derailing return. Therefore, it is determined that the maximum derailing return force φ is impossible to Datsuwa return if less wheel load threshold P _B is set below the wheel load P _2. As a result, it is possible to appropriately determine that the wheel-return return is impossible.

  In the electric power steering apparatus 20 according to the first embodiment, when it is determined that one of the right front wheel 41 and the left front wheel 42 is in the wheel-removed state, the ECU 30 sets the assist motor 24a. Stop overload protection or relax its protection conditions. As a result, even when there is a limit to protect the assist motor 24a by avoiding an overload of the assist motor 24a, the limit on the motor overload protection is temporarily stopped or relaxed in order to give priority to the return from the derailed state. By doing so, the possibility of return from wheel removal can be improved.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIGS. FIG. 8 is an explanatory diagram showing a main part of the electric power steering apparatus 20 according to the second embodiment of the present invention. FIG. 9 is a part of a flowchart showing a flow of the wheel return return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the second embodiment.

The electric power steering apparatus 20 according to the second embodiment is a vehicle height adjusting means capable of adjusting the height of the vehicle body B with respect to the wheels 41 to 44 (hereinafter also referred to as vehicle heights H _{1 to} H ₄ ). The fact that the active suspension 80 is newly adopted and the processing for improving the possibility of return from wheel removal is calculated based on the flowcharts shown in FIGS. 9 and 4 instead of the flowcharts shown in FIGS. It is different from the electric power steering apparatus according to one embodiment. Therefore, substantially the same components as those of the electric power steering apparatus of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

As shown in FIG. 8, the active suspension 80 is hydraulic and has a reservoir 81 for storing oil, an oil pump 82 for discharging (supplying) the oil in the reservoir 81 at a high pressure, and a pressure from the oil pump 82. depending on the amount of oil and a suspension device 83a~83d for adjusting respectively the height _H 1 to H ₄ in respective wheels 41 to 44. The oil pump 82 may be driven by an engine or may be driven by an electric motor dedicated to the oil pump 82. Further, the reservoir 81 and the oil pump 82 may be provided for each of the suspension devices 83a to 83d, or may be provided at two locations for the front wheel and the rear wheel.

Suspension system 83a is one that has a function of adjusting are supported by the arm 41a interposed by the vehicle height H ₁ between the vehicle body B and the right front wheel 41. The suspension device 83 b, 83c, 83d is, the vehicle body B and the left front wheel 42, the right rear wheel 43, the arms 42a interposed between the left rear wheel 44, 43a, the vehicle height _H 2 are respectively supported by the 44a, H ₃ and H ₄ are adjusted. The suspension devices 83a to 83d have the same mechanical configuration, and the suspension device 83a will be described below as a representative.

  As shown in FIG. 8, the suspension device 83a includes a switching valve 84, a switching valve drive circuit 85 that drives the switching valve 84, a shock absorber 86, and a coil spring provided around a piston rod 86b of the shock absorber 86. 87. A hydraulic chamber 86d is formed between the piston 86c and the power cylinder 86a of the shock absorber 86.

  The switching valve 84 has a state in which the oil in the reservoir 81 is increased in pressure by the oil pump 82 and supplied to the hydraulic chamber 86d through the pressure oil hole 86e of the shock absorber 86 (hereinafter also referred to as a pressure oil supply state), and the hydraulic chamber 86d. The state in which the pressure oil is discharged to the reservoir 81 through the pressure oil hole 86e (hereinafter also referred to as the pressure oil discharge state) and the state in which the oil amount in the hydraulic chamber 86d is maintained (hereinafter also referred to as the oil amount maintenance state). It plays the role of switching.

  Based on an instruction from the ECU 30, the switching valve drive circuit 85 drives and controls the switching valve 84 to switch to any one of a pressure oil supply state, a pressure oil discharge state, and an oil amount maintenance state.

Derailment return possibility improvement processing by the ECU 30 of the electric power steering apparatus 20 according to the second embodiment configured as described above will be described with reference to FIGS. 9 and 4.
Similarly to the first embodiment, if it is determined that any of the steered wheels 41 and 42 has been removed during the repeated processing of steps S101 to S109 in FIG. 9 (Yes in S103, Yes in S105, or S107). In step S200, vehicle height adjustment processing is performed.

In this process, among the right front wheel 41 and the left front wheel 42 that are the steering wheels, the vehicle height with respect to the steered wheel in the derailed state is adjusted to the highest level, and the vehicle height with respect to the wheel that is farthest from the steered wheel in the derailed state is set to the highest. Adjust low. Specifically, when the left front wheel 42 is removed, the vehicle height H _{2 with} respect to the left front wheel 42 is set by driving the switching valve drive circuit 85 of the suspension device 83b to bring the switching valve 84 into a pressure oil supply state. To the highest position. Further, by the switching valve drive circuit 85 switching valve 84 by driving the suspension device 83d to the pressure oil discharge state, to adjust the vehicle height H ₃ for the right rear wheel 43 in the lowest state. In this case, the vehicle height H ₄ for vehicle height H ₁ and the left rear wheel 44 for the right front wheel 41 may be maintained at a height of current, the height of the intermediate position which is intermediate between the highest position and the lowest position It may be adjusted. Incidentally, it may be the highest and lowest adjusted vehicle height H ₃ of the vehicle height H ₂ as described above, may be higher to adjust than the vehicle height H ₂ of the vehicle height H _3.

Thus, by increasing adjustment than the vehicle height H ₃ for the right rear wheel 43 of the vehicle height H ₂ to the left front wheel 42 of the derailed state, it is possible to reduce the wheel load P ₂ of the left front wheel 42. Therefore, since the wheel load P ₂ of the left front wheel 42 is derailing state decreases the maximum derailing return force phi, will be the force required for derailing the return is reduced, the derailing return The possibility can be improved.

After the vehicle height adjustment process in step S200 described above, the process from step S111 is performed as in the first embodiment. In particular, the determination of the step S117 of FIG. 4, and since the wheel load P ₂ of the left front wheel 42 is derailing state decreases, so decreases as well wheel load threshold P _B, derailing return is possible It can be seen that (No in S117) is easily performed.

As described above, the electric power steering apparatus 20 according to the second embodiment includes the active suspension 80 that can adjust the vehicle heights H _{1 to} H ₄ for the wheels 41 to 44. When it is determined that either the right front wheel 41 or the left front wheel 42 that is the steered wheel is in the derailed state, the vehicle height with respect to the “steered wheel in the derailed state” is the highest state by the active suspension 80. The vehicle height with respect to the “wheels most distant from the steered wheels in the derailed state” is adjusted to the lowest state.

As a result, the wheel load of the steered wheels in the derailed state is reduced, so that the force required for the derailed return is reduced, and the possibility of the derailed return can be improved.
The vehicle height adjusting means is not limited to adopting a hydraulic suspension device. For example, a means capable of adjusting the vehicle height, such as an extendable piezo element, may be adopted.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIGS. FIG. 10 and FIG. 11 are flowcharts showing a subroutine of the vehicle height adjustment process during the process for improving the possibility of return from wheel removal by the ECU 30 of the electric power steering apparatus 20 according to the third embodiment of the present invention.

  The electric power steering apparatus 20 according to the third embodiment performs an arithmetic processing based on the flowcharts shown in FIGS. 10 and 11 in addition to the flowcharts shown in FIGS. This is different from the electric power steering apparatus according to the second embodiment. Therefore, substantially the same components as those of the electric power steering apparatus of the second embodiment are denoted by the same reference numerals, and description thereof is omitted.

Hereinafter, the wheel return return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the third embodiment will be described with reference to FIGS. 9 to 11 and FIG. 4.
Similarly to the second embodiment, if it is determined that any of the steered wheels 41 and 42 has been removed during the repeated processing of steps S101 to S109 in FIG. 9 (Yes in S103, Yes in S105, or S107). In step S200, vehicle height adjustment processing is performed.

  In the third embodiment, the vehicle height adjustment process in step S200 is performed based on the subroutine shown in FIGS. This vehicle height adjustment process will be described in detail below.

As shown in FIG. 10, an initial height setting process is performed in step S201. In this process, among the right front wheel 41 and the left front wheel 42 that are the steering wheels, the vehicle height with respect to the steered wheel in the derailed state is adjusted to the highest level, and the vehicle height with respect to the wheel that is farthest from the steered wheel in the derailed state is set to the highest. Adjust low. Here, each height H ₁ to H ₄ is adjustable in height by the N stages, defines the lowest state h _1, the highest state h _N, the state of the intermediate position and h _m . Further, the wheel load of the steered wheel in the wheel-out state is defined as a wheel-out load P _obj .

Specifically, when the left front wheel 42 is removed, the vehicle height H _{2 with} respect to the left front wheel 42 is set by driving the switching valve drive circuit 85 of the suspension device 83b to bring the switching valve 84 into a pressure oil supply state. It is adjusted to _{h N.} Further, by the switching valve drive circuit 85 switching valve 84 by driving the suspension device 83d to the pressure oil discharge state, to adjust the vehicle height H ₃ for the right rear wheel 43 to h _1. Further, to adjust the vehicle height _{H 4} for the left rear wheel 44 to _{h m} with adjusting the height _{H 1} for the right front wheel 41 to _{h m.}

Next, in step S203, d _a1 calculation processing is performed. In this process, a de-wheel load _{P lower} in a state in which lower the vehicle height _{H 1} of the front right wheel 41 by _{Δh (H 1 = h lower)} , the height _{H 1} of the front right wheel 41 only Delta] h high state (H ₁ = h _upper ) and the wheel removal load P _upper is acquired. In the d _a1 calculation process and the d _a2 calculation process, d _a3 calculation process, and d _a4 calculation process, which will be described later, after the vehicle height adjustment, the derailed load P _obj is stabilized, and then P _lower and P _upper are acquired. It is assumed that the vehicle heights H _{1 to} H ₄ are readjusted to the height before each calculation process after each calculation process. Further, Δh corresponds to the height of one stage in the vehicle height N stage.

Then, d _a1 which is the degree of change in the wheel removal load P _obj resulting from the vehicle height adjustment of the right front wheel 41 is calculated by the following equation (5).
d _a1 = (P _upper −P _lower ) / (h _upper −h _lower )
... (5)

Here, d _a1 indicates a change in the wheel removal load P _obj when the vehicle height H ₁ is set higher than the present, as can be seen from the equation (5), and d _a1 is a positive value. If means that when increasing the height H ₁ derailing load P _obj is increased, this case better to set lower the vehicle height H ₁ is favors derailing return. On the other hand, if d _a1 is a negative value, increasing the vehicle height H ₁ means that the wheel removal load P _obj decreases. In this case, setting the vehicle height H ₁ higher is advantageous for returning to the wheel removal. Act on. The same applies to d _a2 , d _a3 , and d _a4 calculated based on equations (6) to (8) described later.

Next, in step S205, d _a2 calculation processing is performed. In this process, a de-wheel load _{P lower} in a state in which lower the vehicle height of _{H 2} left front wheel 42 by _{Δh (H 2 = h lower)} , the highest state of the vehicle height of _{H 2} left front wheel 42 _{(H 2} = _Deletion load P _upper at h _N ). Since the height of H ₂ left front wheel 42 is set so as already the highest, rather than the state in which a higher height H ₂ only Delta] h, de-wheel load in the state of the vehicle height H _{2 =} h _N It is assumed that P _upper is acquired.

Then, d _a2 that is the degree of change in the wheel removal load P _obj resulting from the vehicle height adjustment of the left front wheel 42 is calculated by the following equation (6).
d _a2 = (P _upper −P _lower ) / (h _N −h _lower ) (6)

Next, in step S207, d _a3 calculation processing is performed. In this process, the derailing load P _lower when the vehicle height H ₃ of the right rear wheel 43 is the lowest (H ₃ = h ₁ ) and the vehicle height H ₃ of the right rear wheel 43 are increased by Δh ( The wheel removal load P _upper at H ₃ = h _upper ) is acquired. Since the vehicle height H ₃ of the right rear wheel 43 is already set to be the lowest, the vehicle is not removed in the state where the vehicle height H ₃ is lowered by Δh, and the vehicle is removed in a state where the vehicle height H ₃ = h _1. It is assumed that the load P _lower is acquired.

Then, d _a3 that is the degree of change in the wheel removal load P _obj resulting from the vehicle height adjustment of the right rear wheel 43 is calculated by the following equation (7).
d _a3 = (P _upper −P _lower ) / (h _upper −h ₁ ) (7)

Next, in step S209, d _a4 calculation processing is performed. State In this process, which was high and de wheel load _{P lower} in a state in which lower the vehicle height _{H 4} of the left rear wheel 44 by _{Δh (H 4 = h lower)} , the vehicle height _{H 4} of the left rear wheel 44 only Delta] h A wheel removal load P _upper at (H ₄ = h _upper ) is acquired.

Then, d _a4 that is the degree of change in the wheel removal load P _obj resulting from the vehicle height adjustment of the left rear wheel 44 is calculated by the following equation (8).
d _a4 = (P _upper −P _lower ) / (h _upper −h _lower )
... (8)

Next, in step S211, a vehicle height adjustment amount setting process is performed. In this process, a set of vehicle height adjustment amounts respectively corresponding to the vehicle heights H _{1 to} H ₄ for reducing the wheel removal load P _obj is A _a = (a _a1 , a _a2 , a _a3 , a _a4 ). Then, a _a1 , a _a2 , a _a3 , a _a4 are set based on D _a = (d _a1 , d _a2 , d _a3 , d _a4 ) calculated in steps S203 to S209.

Specifically, the corresponding a _a1 is set as follows based on d _a1 , which is the degree of change regarding a wheel whose vehicle height is not set to the highest (h _N ) or the lowest (h ₁ ). That is, when d _a1 is a positive value, lowering the vehicle height has an advantageous effect on the return from derailment, so the corresponding a _a1 is set to a negative value with respect to d _a1 . On the other hand, when d _a1 is a negative value, increasing the vehicle height has an advantageous effect on the return from derailment, so the corresponding a _a1 is set to a positive value with respect to d _a1 . Similarly, a _a4 is set based on d _a4 . However, for d _a2 and d _a3 where the vehicle height has already been set to the highest (h _N ) and the lowest (h ₁ ), the corresponding a _a2 and a _a3 are set to 0 (zero).

The vehicle height adjustment amount A _{s is} obtained by normalizing each component of A _a = (a _a1 , a _a2 , a _a3 , a _a4 ) with a norm and multiplying by a predetermined coefficient G _{1 according} to the following equation (9). Set.
A _s = G ₁ · A / || A _a || (9)
However, || A _a || = (a _a1 ² + a _a2 ² + a _a3 ² + a _a4 ² ) ^1/2 . The predetermined coefficient G ₁ is, for example, is set to 2.

Incidentally, the vehicle height adjustment amount A _s in place of Equation (9) may be set based on the following equation (10).
A _s = G ₁ · A / || D _a || (10)
However, || D _a || = (d _a1 ² + d _a2 ² + d _a3 ² + d _a4 ² ) ^1/2 . In this case, even if a component that is set to a = 0 (zero) is included due to restrictions on the maximum value and the minimum value of the vehicle height, the absolute value of the vehicle height adjustment amount is prevented from greatly changing in each repetition process. can do.

The predetermined coefficient G ₁ may be variable, for example,. But the minimum value 1 to a small value (typically 1/2 every fixed number of iterations (typically 5 times) )), The vehicle height can be finely adjusted. Thus, the vehicle heights H _{1 to} H ₄ that minimize the wheel removal load P _obj can be calculated more accurately.

Then, at step S213, temporarily adjusting the height _H 1 to H ₄ based on the value obtained by adding respectively the values of the current vehicle height _H 1 to H ₄ of the vehicle height adjustment amount _{A s.} In this case, each value of the vehicle height adjustment amount A _s is higher by adjusting the corresponding height in the case of a positive value, in the case of a negative value is adjusted corresponding to the vehicle height lower. As described above, the vehicle height adjustment amount is not limited to setting the vehicle height adjustment amount in step S211 after all the change degrees d _{a1 to} d _a4 are calculated, and the vehicle height adjustment amount is set for each change degree d _{a1 to} d _a4. It may be set.

Here, the processing from step S201 to step S213 will be described in detail by taking specific values as an example when the left front wheel 42 is removed. In the following description, the vehicle heights H _{1 to} H ₄ can be adjusted by 10 steps (h _{1 to} h ₁₀ ) every 1 cm by the suspension devices 83 a to 83 d of the active suspension 80.

First, H ₁ = h ₅ , H ₂ = h ₁₀ , H ₃ = h ₁ , and H ₄ = h ₅ are set by the initial height setting process in step S201. Next, in step S203, P _lower = 3540N acquired when H ₁ = h ₄ is adjusted and P _upper = 3480N acquired when H ₁ = h ₆ is adjusted (5) By substituting into, d _a1 = (3480-3540) / (6-4) = − 30 is calculated.

Then, in steps S205, S207, and S209, calculation is performed as d _a2 = 80, d _a3 = −60, and d _a4 = 40, respectively. Next, in step S211, a _a1 = 30, a _a2 = 0, a _a3 = 0, a _a4 = −40 set based on d _{a1 to} d _{a4 and the} like are substituted into equation (9), and A _f = (1.2, 0, 0, −1.6) is set. As described above, since each suspension device 83a to 83d is adjusted in 10 steps every 1 cm, in step S213, H ₁ = h ₆ , H ₂ = h ₁₀ , H ₃ = h ₁ , H ₄ = h ₃ . Is set. Each suspension device 83a~83d is continuously vehicle height H ₁ to H ₄ may be adopted as adjustable without being adjusted stepwise.

When the vehicle heights H _{1 to} H ₄ set in step S213 are temporarily adjusted as described above, the wheel removal load P _obj is acquired in step S215 of FIG.

In step S217, it is determined whether or not the wheel removal load _Pobj is less than the minimum wheel removal load _Pmin . Here, under the initial conditions, the minimum wheel removal load P _min is set to a value sufficiently larger than the wheel removal load P _obj acquired in step S215. At this stage, it is determined Yes in step S217. The

Next, in step S219, R ₁ = 0 (zero) is set. In step S221, the minimum wheel removal load P _min is set to be equal to the wheel removal load P _obj acquired in step S215.

Next, in step S223, R ₁ = R ₁ +1 is set, and in step S225, R ₂ = R ₂ +1 is set. Here, R ₁ and R ₂ will be described. R ₁ indicates the number of times that the processing of steps S203 to S215 has been repeated since the minimum wheel removal load P _min is updated. On the other hand, _{R 2} represents the number of times the process is repeated in steps S203~S215 regardless updating the minimum de-wheel load _{P min.}

Next, in step S227, _{R 1} is judged whether it is smaller than Ra. Ra is set to 5 times, for example. Here, it is immediately after the minimum de-wheel load _{P min} is updated, _{R 1} is determined as Yes at step S227 is less than Ra.

In step S229, it is determined whether R ₂ is less than Rb. Note that Rb is a larger value than Ra, and is set to 20 times, for example. Here, it is immediately after the processing after step S201 is performed, it is less than _{R 2} is Rb (Yes in S229), the processing from step S203 in FIG. 10 are repeated.

On the other hand, No in repeating the processing from step S203, if the minimum de-wheel load _{P min} is not updated _{R 1} is equal to or greater than Ra (No in S227), or, in the case _{where R 2} is equal to or greater than Rb (S229 ), The vehicle height adjustment processing is terminated assuming that the vehicle heights H _{1 to} H ₄ set in step S213 are the optimum values that minimize the wheel removal load P _obj .

After the vehicle height adjustment process in step S200 of FIG. 9 is completed in this way, step S111 is performed in the vehicle height state in which the wheel removal load P _obj adjusted in step S213 is minimized as in the second embodiment. Is processed.

As described above, in the electric power steering apparatus 20 according to the third embodiment, when it is determined that one of the right front wheel 41 and the left front wheel 42 that are the steered wheels is in the dewheeling state, the active power steering apparatus 20 is active. The suspension 80 adjusts the vehicle height with respect to the “steering wheel in the derailed state” to the highest state, and adjusts the vehicle height with respect to the “wheel farthest away from the steered wheel in the derailed state” to the lowest state. When the vehicle heights H _{1 to} H ₄ with respect to the wheels 41 to 44 are changed, respectively, with respect to the wheels different from the “steering wheels in the derailed state” and the “wheels most distant from the steered wheels in the derailed state”. the de-wheel load _{P obj} is adjusted to be smaller on the basis of the change degree _d a1 _{to d a4} of derailing load _{P obj.}

As described above, the active suspension 80 can adjust the vehicle heights H _{1 to} H ₄ for the wheels 41 to 44 so that the wheel removal load P _obj becomes small. The force will be reduced, and the possibility of return from wheel removal can be further improved.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described with reference to FIGS. FIG. 12 is an explanatory view showing a main part of an electric power steering apparatus 20 according to the fourth embodiment of the present invention. FIG. 13 is a part of a flowchart showing the flow of the derailment return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the fourth embodiment. FIG. 14 is an explanatory diagram showing an example of an air pressure-friction force evaluation value map used in the air pressure adjustment process of FIG.

The electric power steering apparatus 20 according to the fourth embodiment newly employs an air pressure adjusting device 90 that is an air pressure adjusting means capable of adjusting the air pressure t _{1 to} t ₄ of each of the wheels 41 to 44, and derails. The point that the return possibility improvement processing is calculated based on the flowcharts shown in FIGS. 13 and 4 instead of the flowcharts shown in FIGS. 3 and 4 is the same as the electric power steering apparatus according to the first embodiment. Different. Therefore, substantially the same components as those of the electric power steering apparatus of the first embodiment are denoted by the same reference numerals, and description thereof is omitted.

The air pressure adjusting device 90 is a known device that can adjust the air pressures t _{1 to} t ₄ of the wheels 41 to 44. As shown in FIG. 12, the air pressure adjusting device 90 includes, for example, an air pressure supply device 91 that can supply high-pressure air, and air valves 41 c to 44 c provided on the wheels 41 to 44, respectively.

  The air pressure supply device 91 includes an unillustrated pump, a motor, a motor drive circuit, and the like, and supplies high-pressure air to the wheels 41 to 44 through tubes and air valves 41c to 44c and the like based on instructions from the ECU 30. To play a role.

Air valve 41c~44c, based on an instruction from the ECU 30, and the pressure increasing state in which the high-pressure air supplied from the air pressure supply device 91 is supplied to each wheel 41-44 pressure increase each pneumatic _t 1 ~t ₄ respectively Further, it plays a role of switching between a reduced pressure state in which the air of each of the wheels 41 to 44 is discharged to reduce the pressure of each of the air pressures t _{1 to} t ₄ .

In addition, each wheel 41 to 44, capable of detecting air pressure sensor 41d~44d is provided each pneumatic _t 1 ~t _4.

Derailment return possibility improvement processing by the ECU 30 of the electric power steering apparatus 20 according to the fourth embodiment configured as described above will be described with reference to FIGS. 13 and 4.
Similarly to the first embodiment, if it is determined that any of the steered wheels 41 and 42 has been removed during the repeated processing of steps S101 to S109 in FIG. 13 (Yes in S103, Yes in S105, or S107). In step S300, the air pressure adjustment process is performed.

In this process, each pneumatic _t 1 ~t ₄ a frictional force evaluation value indicating the likelihood of derailing recovery by frictional force between the respective wheels 41 to 44 and the road surface _v 1 to v ₄ of the wheels 41 to 44 Adjust to increase.

Specifically, based on the air pressure-friction force evaluation value map shown in FIG. 14, target air pressures ta _{1 to} ta ₄ that set the friction force evaluation values v _{1 to} v ₄ to the highest are set. Then, each air valve 41c~44c the high pressure air from the air pressure supply device 91 is supplied to the pressure increasing state or a reduced pressure state, the air pressure _t 1 ~t ₄ detected by the pressure sensor 41D～44d, these above It is adjusted to be equal to the target air pressure ta _{1 to} ta ₄ . As a result, the frictional force generated between the wheels 41 to 44 and the road surface can be appropriately increased to increase the possibility of return from wheel removal.

Here, the air pressure-friction force evaluation value map of FIG. 14 described above will be described. The frictional force generated between the elastic wheel and the rigid road surface increases as the ground contact area increases if the wheel air pressure is the same, and increases as the wheel air pressure increases if the ground contact area is the same. . On the other hand, the ground contact area increases as the wheel air pressure decreases, so if the wheel air pressure is too high, it is disadvantageous from the viewpoint of the ground contact area. Therefore, it is considered that the target air pressures ta _{1 to} ta ₄ of the wheels 41 to 44 that can increase the possibility of return from the wheel from the viewpoint of frictional force exist between the minimum air pressure t _min and the maximum air pressure t _max of the wheels. It is done.

  Therefore, a map in which the wheel air pressure t is associated with the frictional force evaluation value v indicating the possibility of return from the wheel due to the frictional force between the wheel and the road surface is experimentally set and stored in advance. For example, the frictional force evaluation value v is set such that the closer to 1, the higher the possibility of wheel-return return.

  After the air pressure adjustment process in step S300 described above, the process from step S111 is performed in the same manner as in the first embodiment.

As described above, the electric power steering apparatus 20 according to the fourth embodiment, the air pressure _t 1 ~t ₄ pressure sensor 41d~44d and each pneumatic _t 1 ~t ₄ detects the respective wheel 41-44 And an air pressure adjusting device 90 capable of adjusting the air pressure, and the air pressure-friction force evaluation in which the air pressure t and the frictional force evaluation value v indicating the possibility of return from wheel removal due to the frictional force between the wheels and the road surface are associated in advance. Has a value map. When it is determined that either the right front wheel 41 or the left front wheel 42 that is the steered wheel is in a wheel-out state, the air pressure adjusting device 90 performs the friction force based on the air pressure-friction force evaluation value map. The air pressures t _{1 to} t ₄ of the wheels 41 to 44 are adjusted so as to increase the evaluation value v and increase the possibility of return from wheel removal.

In this way, at the time of derailment, the wheels 41 to 41 are adjusted by the air pressure adjusting device 90 so as to increase the friction force evaluation value v based on the air pressure-friction force evaluation value map in which the air pressure t and the friction force evaluation value v are associated. By adjusting the air pressure t _{1 to} t ₄ of 44, the frictional force generated between the wheel and the road surface can be appropriately increased to increase the possibility of return from the wheel removal.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described with reference to FIGS. FIG. 15 is a part of a flowchart showing the flow of the wheel return return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the fifth embodiment. 16 and 17 are flowcharts showing a subroutine of the air pressure adjustment process of FIG.

  The electric power steering apparatus 20 according to the fifth embodiment employs the active suspension 80 described in the second embodiment and the air pressure adjusting apparatus 90 described in the fourth embodiment, and returns to the derailment. The possibility improvement processing is performed based on the flowcharts shown in FIGS. 15 and 4 and FIGS. 10, 11, 16, and 17 instead of the flowcharts shown in FIGS. 3 and 4. It is different from the electric power steering apparatus according to one embodiment. Therefore, the same reference numerals are given to the components described in the above embodiments, and description thereof is omitted.

Hereinafter, the wheel-release return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the fifth embodiment will be described with reference to FIGS. 15, 4, 10, 11, 16, and 17. To do.
Similarly to the first embodiment, if it is determined that any of the steered wheels 41 and 42 has been removed during the repeated processing of steps S101 to S109 in FIG. 15 (Yes in S103, Yes in S105, or S107). In step S200, vehicle height adjustment processing is performed. This vehicle height adjustment process is performed based on the subroutine shown in FIGS. 10 and 11 as in the third embodiment. In the vehicle height adjustment process in step S200, as in the second embodiment, the vehicle height for the steered wheel in the derailed state is adjusted to the highest level, and the vehicle height for the wheel most distant from the steered wheel in the derailed state is adjusted. May be adjusted to the lowest, and the vehicle height relative to the other wheels may be adjusted to the height of the intermediate position.

  In step S300, air pressure adjustment processing is performed. In the fifth embodiment, this process is performed based on the subroutine shown in FIGS. This air pressure adjustment process will be described in detail below.

As shown in FIG. 16, in step S301, an initial air pressure setting process is performed. In this process, the air pressure _t 1 ~t ₄ of the wheels 41 to 44 are respectively set by adjusting each air valve 41c~44c to be equal to the initial air pressure _{t 0} is set as an initial pressure. Here, it is assumed that the air pressures t _{1 to} t ₄ can be adjusted in N stages between the minimum air pressure t _min and the maximum air pressure t _max by the air pressure adjusting device 90.

Next, in step S303, _db1 calculation processing is performed. In this process, the state where the de-wheel load _{P lower} in a state where the air pressure _{t 1} of the right front wheel 41 and lowered by _{Δt (t 1 = t lower)} , the air pressure _{t 1} of the right front wheel 41 is made higher by Delta] t _(t 1 = The _dewheeling load P _upper at t _upper ) is acquired. In the d _b1 calculation process and the d _b2 calculation process, the d _b3 calculation process, and the d _b4 calculation process, which will be described later, P _lower and P _upper are acquired after the wheel removal load P _obj is stabilized after the air pressure adjustment. There, after each operation processing, the pneumatic t ₁ ~t ₄ shall be readjusted to pressure before each operation process. Further, Δt corresponds to a one-stage pressure difference in the N-stage air pressure, and is set to 0.1, for example, in the fifth embodiment.

Then, d _b1 , which is the degree of change in the wheel removal load P _obj due to the air pressure adjustment of the right front wheel 41, is calculated by the following equation (11).
d _b1 = (P _upper −P _lower ) / (t _upper −t _lower )
(11)

Here, d _b1 indicates a change in the wheel removal load P _obj when the air pressure t ₁ is set higher than the present value, as can be seen from the equation (11), and d _b1 is a positive value. higher air pressure t ₁ is the means that de-wheel load P _obj is increased, this case better to set lower the air pressure t ₁ is favors derailing return. On the other hand, when _db1 is a negative value, increasing the air pressure t ₁ means that the wheel removal load P _obj is reduced. In this case, setting the air pressure t ₁ higher has an advantage in returning to the wheel removal. To do. The same applies to d _b2 , d _b3 , and d _b4 calculated based on formulas (12) to (14) described later.

Next, in step S305, _db2 calculation processing is performed. In this process, similarly to the step S303, and de wheel load _{P lower} in a state in which lower the air pressure _{t 2} of the left front wheel 42 by _{Δt (t 2 = t lower)} , the air pressure _{t 2} of the left front wheel 42 Delta] t only The _dewheeling load P _upper in the raised state (t ₂ = t _upper ) is acquired.

Then, _{db 2} , which is the degree of change in the wheel removal load P _obj due to the air pressure adjustment of the left front wheel 42, is calculated by the following equation (12).
_{d b2 = (P upper -P lower} ) / (t upper -t lower)
(12)

Next, in step S307, _db3 calculation processing is performed. In this process, similarly to the step S303, and de wheel load _{P lower} the air pressure _{t 3} of the right rear wheel 43 in a state of being lowered by _{Δt (t 3 = t lower)} , the air pressure _{t 3} of the right rear wheel 43 A wheel removal load P _upper in a state where it is increased by Δt (t ₃ = t _upper ) is acquired.

Then, _{db 3} , which is the degree of change in the wheel removal load P _obj due to the air pressure adjustment of the right rear wheel 43, is calculated by the following equation (13).
_{d b3 = (P upper -P lower} ) / (t upper -t lower)
... (13)

Next, in step S309, _db4 calculation processing is performed. In this process, similarly to the step S303, and de wheel load _{P lower} in a state in which lower the air pressure _{t 4} of the left rear wheel 44 by _{Δt (t 4 = t lower)} , the air pressure _{t 4} of the left rear wheel 44 A wheel removal load P _upper in a state where it is increased by Δt (t ₄ = t _upper ) is acquired.

Then, _{db 4} , which is the degree of change in the wheel removal load P _obj resulting from the adjustment of the air pressure of the left rear wheel 44, is calculated by the following equation (14).
_{d b4 = (P upper -P lower} ) / (t upper -t lower)
(14)

Next, in step S311, a first air pressure adjustment setting process is performed. In this process, a set of first air pressure adjustment amounts respectively corresponding to the air pressures t _{1 to} t ₄ of the wheels 41 to 44 for reducing the wheel removal load P _obj is A _b = (a _b1 , a _b2 , a _b3. , A _b4 ), a _b1 , a _b2 , a _b3 , a _b4 are set based on D _b = (d _b1 , d _b2 , d _b3 , d _b4 ) calculated in steps S303 to S309 To do.

Specifically, when d _b1 is a positive value, lowering the air pressure has an advantageous effect on the return to wheel release, so the corresponding a _b1 is set to a negative value with respect to d _b1 . On the other hand, when d _b1 is a negative value, increasing the air pressure has an effect on the return to wheel release, so the corresponding a _b1 is set to a positive value with respect to d _b1 . set based on _d b2 _{to d b4} are similarly for a _b2 ~a _b4.

Then, the first air pressure adjustment amount _Ah is set by normalizing each component of A _b = (a _b1 , a _b2 , a _b3 , a _b4 ) with a norm according to the following equation (15). The first air pressure adjustment amount A _h corresponds to the degree of change in the wheel removal load P _obj when the air pressures t _{1 to} t ₄ are changed.
A _h = A / || A _b || (15)
However, || A _b || = (a _b1 ² + a _b2 ² + a _b3 ² + a _b4 ² ) ^1/2 .

Next, in step S313, _dc1 calculation processing is performed. In this process, the friction force evaluation value _{v lower} in a state where the air pressure _{t 1} of the right front wheel 41 and lowered by _{Δt (t 1 = t lower)} , a state where the air pressure _{t 1} of the right front wheel 41 is made higher by Delta] t _{(t 1} The frictional force evaluation value v _upper at = t _upper ) is acquired from the air pressure-friction force evaluation value map of FIG.

Then, the d _c1 is a degree of change in the frictional force evaluation value v due to air pressure adjustment of the front right wheel 41 is calculated by the following equation (16).
d _c1 = (v _upper −v _lower ) / (t _upper −t _lower )
... (16)

Here, d _c1 indicates the change in the frictional force evaluation value v when the air pressure t ₁ is set higher than the current value, as can be seen from the equation (16), and when d _c1 is a positive value. means that the frictional force evaluation value v and increasing the air pressure t ₁ is increased, this case better to set a high pressure t ₁ is favors derailing return to. On the other hand, if d _c1 is a negative value, it means that if the air pressure t ₁ is increased, the frictional force evaluation value v decreases, and in this case, setting the air pressure t ₁ low has an advantage in returning to the wheel removal. To do. The same applies to d _c2 , d _c3 , and d _c4 calculated based on equations (17) to (19) described later.

Next, in step S315, _dc2 calculation processing is performed. In this process, similarly to the step S313, the frictional force evaluation value _{v lower} in a state of low air pressure _{t 2} of the left front wheel 42 by _{Δt (t 2 = t lower)} , the air pressure _{t 2} of the left front wheel 42 Delta] t The frictional force evaluation value v _upper is obtained in a state where it is only increased (t ₂ = t _upper ).

Then, the d _c2 is a degree of change in the frictional force evaluation value v due to air pressure adjustment of the front left wheel 42 is calculated by the following equation (17).
d _c2 = (v _upper −v _lower ) / (t _upper −t _lower )
... (17)

Next, in step S317, _dc3 calculation processing is performed. In this process, similarly to the step S313, the frictional force evaluation value _{v lower} in a state where the air pressure _{t 3} of the right rear wheel 43 and lowered by _{Δt (t 3 = t lower)} , air pressure _{t 3} of the right rear wheel 43 And the frictional force evaluation value v _upper in a state where t is increased by Δt (t ₃ = t _upper ).

Then, the d _c3 is a degree of change in the frictional force evaluation value v due to air pressure adjustment of the right rear wheel 43 is calculated by the following equation (18).
d _c3 = (v _upper −v _lower ) / (t _upper −t _lower )
... (18)

Next, in step S319, a _dc4 calculation process is performed. In this process, similarly to the step S313, the frictional force evaluation value _{v lower} in a state of low air pressure _{t 4} of the left rear wheel 44 by _{Δt (t 4 = t lower)} , air pressure _{t 4} of the left rear wheel 44 And the frictional force evaluation value v _upper in a state where t is increased by Δt (t ₄ = t _upper ).

Then, calculates a d _c4 is a degree of change in the frictional force evaluation value v due to air pressure adjustment of the left rear wheel 44, the following equation (19).
d _c4 = (v _upper −v _lower ) / (t _upper −t _lower )
... (19)

Next, in step S321, a second air pressure adjustment setting process is performed. In this process, the second air pressure adjustment amount set corresponding respectively to the air pressure _t 1 ~t ₄ of the wheels 41 to 44 to increase the frictional force evaluation value _{v A c = (a c1,} a c2, a c3 , A _c4 ), a _c1 , a _c2 , a _c3 , a _c4 are set based on D _c = (d _c1 , d _c2 , d _c3 , d _c4 ) calculated in steps S313 to S319 To do.

Specifically, when d _c1 is a positive value, lowering the air pressure has an advantageous effect on the return from the wheel removal, so the corresponding a _c1 is set to a negative value with respect to d _c1 . On the other hand, if d _c1 is a negative value, increasing the air pressure has an effect on the return to wheel release, so the corresponding a _c1 is set to a positive value with respect to d _c1 . Similarly, a _{c2 to} a _c4 are set based on d _c2 to d _c4 .

Then, each component of A _c = (a _c1 , a _c2 , a _c3 , a _c4 ) is normalized by a norm by the following equation (20) to set the second air pressure adjustment amount A _f . The second air pressure adjustment amount _Af corresponds to the degree of change in the frictional force evaluation value v when the air pressures t _{1 to} t ₄ are changed.
A _f = A / || A _c || (20)
However, || A _c || = (a _c1 ² + a _c2 ² + a _c3 ² + a _c4 ² ) ^1/2 .

Next, in step S323, a comprehensive air pressure adjustment setting process is performed. In this process, based on the second air pressure adjustment amount A _f set by the first air pressure adjustment amount A _h and step S321 which is set at step S311, both the change and the change in the frictional force of the wheel load the overall air pressure adjustment amount a _t is a pneumatic adjustment amount to increase the likelihood of considering to derailing return is calculated by the following equation (21).
_{A t = G 2 × (C} h × A h + C f × A f) ··· (21)
Note that _Ch and _Cf are coefficients for weighting the relationship between the effect due to the change in the wheel load and the effect due to the change in the frictional force, and are set so as to satisfy _Ch + _Cf = 1. In the fifth embodiment, for example, C _h = 0.25 and C _f = 0.75 are set for the purpose of emphasizing the effect due to the change in frictional force. Also, G ₂ is a coefficient for controlling the air pressure adjustment amount, the in the fifth embodiment, for example, is set to 0.1.

Then, in step S325, based on the current value obtained by adding to each pneumatic _t 1 ~t ₄ the values of the total pressure adjustment amount _{A t,} temporarily adjust the air pressure _t 1 ~t _4. In this case, each value of the total air pressure adjustment amount A _t is higher by adjusting the corresponding pressure in the case of a positive value, the corresponding pressure is adjusted lower in the case of a negative value.

When the air pressures t _{1 to} t ₄ of the wheels 41 to 44 are temporarily adjusted in this way, the wheel removal load P _obj that is the wheel load of the steered wheel in the wheel removal state is acquired in step S327 in FIG. . In step S329, a frictional force evaluation value calculation process is performed. In this process, based on the friction force evaluation values v _{1 to} v ₄ set by the air pressure-friction force evaluation value map of FIG. 14 described above from the air pressures t _{1 to} t ₄ detected by the air pressure sensors 41d to 44d. Then, a frictional force evaluation value _Vf indicating the possibility of return from wheel removal due to the frictional force between all the wheels 41 to 44 and the road surface is calculated by the following equation (22).
V _f = C ₁ × v ₁ + C ₂ × v ₂ + C ₃ × (v ₃ + v ₄ ) (22)
Here, C ₁ , C ₂ , and C ₃ are coefficients for weighting the relationship between the drive wheel in the de-wheeled state, the drive wheel in the non-de-wheeled state, and the non-drive wheel, and this fifth embodiment. In, for example, C ₁ = 0.5, C ₂ = 0.3, and C ₃ = 0.1 are set. The equation (22) is an equation based on the assumption that the right front wheel 41 is removed. When the left front wheel 42 is removed, the frictional force evaluation value _Vf is calculated by the following equation (22 ′).
_{V f = C 1 × v 2} + C 2 × v 1 + C 3 × (v 3 + v 4) ··· (22 ')

Next, in step S331, comprehensive evaluation value calculation processing is performed. In this process, a comprehensive evaluation value for comprehensively evaluating the possibility of return from the wheel release based on the wheel removal load P _obj acquired in step S327 and the frictional force evaluation value V _f calculated in step S329. I is calculated by the following equation (23).
_{I = C p × P obj +} C v × V f ··· (23)
C _p and C _v are coefficients for weighting the relationship between the effect due to the change in wheel load and the effect due to the change in frictional force.

Here, as the wheel removal load P _obj decreases, the possibility of wheel return return increases, while as the frictional force evaluation value V _f increases, the possibility of wheel release return increases. Therefore, by setting C _p to a negative number, the overall evaluation value I indicates that the possibility of return from the wheel removal increases as the overall evaluation value I increases. In addition, when the frictional force between each wheel and the road surface is increased, the derailing return force that can be generated by the assist motor 24a and the wheel driving device 50 can be used effectively. In the fifth embodiment, for example, C _p = −1 and C _v = 10000 are set.

Here, the processing from step S301 to S331 will be described in detail by taking specific values as an example for the case where the left front wheel 42 is removed. In the following description, it is assumed that the air pressures t _{1 to} t ₄ can be adjusted every 0.01 kgf / cm ² by the air pressure adjusting device 90.

First, t ₁ = t ₀ , t ₂ = t ₀ , t ₃ = t ₀ , and t ₄ = t ₀ are set by the initial height setting process in step S301. Next, in step S303, the _P lower = 3402N acquired when adjusted to pneumatic _t 1 _{= t} 0 _-Δt, and _P upper = 3398N acquired when adjusted to pneumatic _t 1 = _{t 0} + _Δt Is substituted into equation (11) to calculate d _b1 = (3398-3402) /0.2=−20.

In steps S305, S307, and S309, calculation is performed as d _b2 = −10, d _b3 = 10, and d _b4 = 30, respectively. Next, in step S311, a _a1 = 20, a _a2 = 10, a _a3 = −10, and a _a4 = −30 set based on d _{b1 to} d _{b4 and the} like are substituted into equation (15), A _h = (0.51, 0.26, −0.26, −0.77) is set.

In step S313, v _lower = 0.81 acquired when the air pressure is adjusted to t ₁ = t ₀ -Δt and v _upper = 0 acquired when the air pressure is adjusted to t ₁ = t ₀ + Δt. By substituting .77 into the equation (16), d _c1 = (0.81−0.77) /0.2=0.2 is calculated.

Then, in steps S315, S317, and S319, calculation is performed with d _c2 = 0.2, d _c3 = 0.2, and d _c4 = 0.2, respectively. Next, in step S321, a _c1 = −0.2, a _c2 = −0.2, a _c3 = −0.2, a _c4 = −0.2 set based on d _{c1 to} d _{c4 and the} like. Is substituted into equation (20), and A _f = (− 0.5, −0.5, −0.5, −0.5) is set.

Then, when A _t = (0.05, 0.044, 0.031, −0.004) is set by substituting A _h and A _f into equation (21) in step S323, based on the value obtained by adding respectively each value in the current of each pneumatic _t 1 ~t ₄ of _{a t} at S325, pneumatic _t 1 ~t ₄ is temporarily adjusted.

In step S327, the wheel removal load P _obj = 3395N is acquired. In step S329, the friction force evaluation values v _{1 to} v ₄ set by the air pressure-friction force evaluation value map from the air pressures t _{1 to} t ₄ (= t ₀ ) detected by the air pressure sensors 41d to 44d. Is substituted into the equation (22) to calculate the frictional force evaluation value V _f = 0.82. Then, the overall evaluation value I = −1 × 3395 + 10000 × 0.82 = 4805 is calculated by substituting the wheel removal load P _obj and the frictional force evaluation value V _f into the equation (23) in step S331.

Overall evaluation value I is calculated in step S331 as described above, in step S333, the overall evaluation value I is determined whether more than the maximum evaluation value I _max. Here, under the initial conditions, the maximum evaluation value I _max is set to a value sufficiently smaller than the comprehensive evaluation value I acquired in step S331. At this stage, it is determined as Yes in step S333.

Next, in step S335, R ₃ = 0 (zero) is set. Then, at step S337, the maximum evaluation value _{I max} is set equal to the total evaluation value I calculated in step S331.

Next, in step S339, R ₃ = R ₃ +1 is set, and in step S341, R ₄ = R ₄ +1 is set. Here, R ₃ and R ₄ will be described. R ₃ represents the number of times the process is repeated in steps S303~S331 from when the maximum evaluation value _{I max} is updated. On the other hand, _{R 4} represents the number of times the process is repeated in regardless step S303~S331 to update the maximum evaluation value _{I max.}

Next, in step S343, _{R 3} is determined if it is less than Rc. Rc is set to 5 times, for example. Here, it is immediately after the maximum evaluation value _{I max} is updated, _{R 3} is judged Yes in step S343 is less than Rc.

Then, in step S345, it is determined whether _{R 4} is less than Rd. Note that Rd is larger than Rc, and is set to 20 times, for example. Here, it is immediately after the processing after step S301 is performed, it is less than _{R 4} is Rd (Yes in S345), the processing from step S303 in FIG. 16 are repeated.

On the other hand, in the repeating processes from step S303, when the maximum evaluation value _{I max} is not updated _{R 3} is equal to or greater than Rc (No in S343), or _{when R 4} is equal to or greater than Rd (No in S345) The air pressure adjustment processing is terminated assuming that the air pressures t _{1 to} t ₄ temporarily adjusted in step S325 are optimum values that maximize the overall evaluation value I.

  After the air pressure adjustment process in step S300 in FIG. 15 is completed in this way, the process from step S111 is performed in the air pressure state in which the total evaluation value I adjusted in step S325 is maximized, as in the first embodiment. Is made.

As described above, the electric power steering apparatus 20 according to the fifth embodiment, the air pressure _t 1 ~t ₄ pressure sensor 41d~44d and each pneumatic _t 1 ~t ₄ detects the respective wheel 41-44 And an air pressure adjusting device 90 capable of adjusting the air pressure, and the air pressure-friction force evaluation in which the air pressure t and the frictional force evaluation value v indicating the possibility of return from wheel removal due to the frictional force between the wheels and the road surface are associated in advance. Has a value map. When it is determined that one of the right front wheel 41 and the left front wheel 42 as the steered wheels is in the dewheeling state, the air pressure adjusting device 90 removes the air pressures t _{1 to} t _{4 when} they are changed. The degree of change of the friction force evaluation value v obtained from the air pressure-friction force evaluation value map when the first air pressure adjustment amount A _h corresponding to the degree of change of the wheel load P _obj and the air pressures t _{1 to} t ₄ are respectively changed. The air pressures t _{1 to} t ₄ are adjusted based on both the second air pressure adjustment amount A _f corresponding to the above and so as to increase the possibility of the wheel return return.

Thus, derailing the degree of change of the load P _obj, air pressure when the respective pneumatic t ₁ ~t ₄ was varied each time of changing each pneumatic t ₁ ~t ₄ respectively - from the friction force evaluation value map The air pressures t _{1 to} t ₄ are adjusted to increase the possibility of return from wheel removal based on both the degree of change in the frictional force evaluation value v obtained, and therefore the frictional force as in the fourth embodiment. Compared with the case where each of the air pressures t _{1 to} t ₄ is adjusted according to only the evaluation value v, a more optimal air pressure can be set, and the possibility of returning from the wheel removal can be further increased.

  The present invention is not limited to the above embodiments, and may be embodied as follows. Even in this case, the same operations and effects as those of the above embodiments can be obtained.

(1) The above-described disengagement return possibility improving process is not limited to being performed based on the flowcharts shown in FIGS. 3 and 4, and may be performed based on the flowcharts shown in FIGS. 3 and 7. The flowchart in FIG. 7 is obtained by replacing the assist motor drive temporary stop process in step S123 of the flowchart in FIG. 4 with the assist torque gradual decrease process in step S124. In this gradual decrease process, the assist motor 24a generates the assist force. The current assist torque Tm is gradually decreased by a predetermined torque. Thus, when it is impossible to return from the wheel, unnecessary assist force generated by the assist motor 24a can be avoided without impairing the steering feeling due to the sudden decrease of the assist force.

(2) The warning device 70 is not limited to displaying and notifying the determination result of whether or not the wheel return can be returned on the monitor 71, but may be displayed and notified on a car navigation monitor mounted on the vehicle. Further, a warning light may be provided separately, and the warning light may be turned on according to the determination result of whether or not the wheel removal return is possible.

(3) The warning device 70 responds to the determination result of whether or not to return to the derailment instead of notifying the driver or the like by a visual display by displaying the determination result on whether or not to return to the derailment on the monitor 71. For example, a notification sound generating means for generating a notification sound may be provided, and a notification sound such as a buzzer sound or a sound may be generated by the notification sound generating means. As a result, it is possible to recognize with the auditory notification sound whether or not the derailment can be returned.
In addition, the warning device 70 may display the determination result on whether or not the wheel release return is possible on the monitor 71 and generate the notification sound. In this way, by notifying whether or not the wheel return can be returned by combining the visual display and the auditory notification sound, it is possible to more reliably recognize whether or not the wheel return can be returned.

(4) If it is determined in step S117 that it is impossible to return from the wheel removal, it is difficult for the driver alone to return from the wheel removal. It may be displayed on 70 monitors 71. At the time of the display, a contact information for requesting support may be displayed at the same time.
In addition, in a vehicle having a data communication device that can transmit and receive predetermined information through an Internet connection by wireless communication or the like, if it is determined in step S117 that return from wheel removal is impossible, the data communication device is used. You may be made to request support automatically.

(5) Instead of the wheel load sensor, the following sensor may be used.
A wheel load sensor composed of a load cell that outputs load detection values corresponding to the wheel loads of the front wheels and the rear wheels, disclosed in Japanese Patent Laid-Open No. 05-024422.
A wheel load sensor for detecting a load at a suspension upper mount portion of a vehicle disclosed in Japanese Patent Laid-Open No. 05-072065.
A load sensor that is disposed at the upper end of a shock absorber and detects a load related to each wheel, as disclosed in JP-A-08-198131.
A wheel load sensor that is provided in a suspension device that supports each wheel and that detects a wheel load acting on each wheel, as disclosed in Japanese Patent Application Laid-Open No. 10-024819, and is provided in the suspension device. A magnetostrictive sensor that detects distortion, a sensor that detects distortion of an axle, or a sensor that detects the internal pressure of an air spring of an air suspension.
A sensor for detecting the wheel load of a vehicle equipped with a McPherson strut type wheel suspension mechanism disclosed in Japanese Patent Application Laid-Open No. 2005-106596, with a built-in shock absorber and a lower end supported on the top of the knuckle A stress sensor attached to a strut that is a suspension member whose upper end is supported by the vehicle body.
A displacement sensor disclosed in JP-A-2006-058254, which is provided at a position facing the side surface of the brake rotor and measures a gap between the brake rotor and a wheel based on a displacement amount detected by the displacement sensor A wheel load detection device comprising load calculation means for detecting a load applied to the vehicle.
-Magnetostriction provided between the crimping portion provided at the end portion of the hub wheel having the wheel mounting flange and the end surface facing outward at the outer ring of the constant velocity joint, disclosed in JP-A-2006-064650 A change in the amount of strain acting on the ring-shaped load detection portion made of a material and the magnetostrictive layer of the load detection portion is detected as a magnetoresistance change, and a load applied to the wheel bearing device is detected based on the magnetoresistance change amount. A wheel load detection device comprising a load detection unit.
-The distance between the displacement sensor and the magnetized portion is changed by the deformation of the angle formed between the cylindrical portion and the flange portion of the vehicle body side raceway member disclosed in Japanese Patent Application Laid-Open No. 2003-336652, and is generated by the magnetized portion. A sensor device comprising: a magnetic sensor that detects a fluctuation amount of a magnetic field that is applied; and a processing unit that obtains a fluctuation amount of a tire ground contact load from a fluctuation amount of a distance output as the magnetic field fluctuation amount.
-Disclosed in Japanese Patent Application Laid-Open No. 2007-024550, which is composed of a strain gauge or the like provided between the bumper rubber disposed below the coil spring and the vehicle body so as not to contact the coil spring. Spring sensor force determined based on the detection value of the displacement sensor, comprising a load sensor for detecting the bumper rubber reaction force generated by the vehicle and a displacement sensor for detecting the distance between the suspension arm following the vertical movement of the wheel and the vehicle body Wheel load detection device that calculates and detects wheel load using a bumper rubber reaction force detected by a load sensor.

(6) Instead of detecting the wheel loads P _{1 to} P ₄ by the wheel load sensors 41 b to 44 b, for example, a relative height sensor such as a vehicle height sensor of an active suspension provided in advance in the vehicle or a sensor described below. The degree of inclination of the vehicle body relative to the road surface is calculated based on the relative distance between the vehicle body and each wheel detected, and the wheel loads P _{1 to} P ₄ of the wheels 41 to 44 are estimated and detected from the inclination degree. May be.
A stroke sensor disclosed in Japanese Patent Application Laid-Open No. 07-276956, which is incorporated in a hydraulic cylinder of each suspension device and detects the length of the hydraulic cylinder, that is, the relative position of each wheel from the body frame.
A vehicle height sensor that is disposed between the front and rear shafts and the vehicle body and detects a relative vehicle height, which is disclosed in JP-A-08-282320.
Alternatively, the degree of inclination of the vehicle body may be calculated by an acceleration sensor, an infrared sensor, an image camera, or the like, and the wheel loads P _{1 to} P ₄ of the wheels 41 to 44 may be estimated and detected from the degree of inclination. Thus, the wheel loads P _{1 to} P ₄ can be estimated and detected without providing the wheel load sensors 41 b to 44 b for detecting the wheel loads P _{1 to} P ₄ .

(7) Instead of detecting the wheel loads P _{1 to} P ₄ with the wheel load sensors 41b to 44b, for example, the air pressure of each of the wheels 41 to 44 is detected with an air pressure sensor disclosed in Japanese Patent Laid-Open No. 08-156539. Then, the wheel loads P _{1 to} P ₄ of the wheels 41 to 44 may be estimated and detected from the air pressure.
Further, the wheel loads P _{1 to} P ₄ of the wheels 41 to 44 may be estimated and detected in consideration of the air pressure of the wheels 41 to 44 and the deflection of the wheels 41 to 44.

(8) The friction coefficient μ on the contact surface S between the side surface of the steered wheel and the side surface of the side groove D that is in the wheel-removed state is not limited to a predetermined value in advance, and a certain amount of wheel-return return force is actually applied. The friction coefficient μ may be estimated on the basis of the wheel load of the steered wheel that is in a disengaged state that decreases when output.

(9) The maximum rotational drive force FD _m at the time of derailment that can be generated by rotationally driving the steered wheels that are in the derailed state by the wheel drive device 50 is the maximum that can be generated by rotationally driving both steered wheels that are not in the derailed state. It is not limited to 1/3 of the rotational driving force, but is set to be equal to the limit value of the pressing force when the limit value of the pressing force that can be applied to the side surface of the steered wheel is known in advance. May be.

(10) In step S109, since the motor current value i is equal to or greater than the overload current value io, it is determined that the side surface of the left front wheel 42 is pressed against the side surface of the side groove by steering for return from the wheel removal. If the change amount of the actual rudder angle δ is equal to or smaller than the angle difference at which the actual rudder angle δ is determined to be a constant value, the left front wheel is steered by steering for returning from the wheel. It may be determined that the side surface of 42 is pressed against the side surface of the side groove, and it may be determined Yes in step S109.

(11) In each of the above embodiments, as illustrated in FIG. 1, a so-called rack type electric power steering apparatus that can transmit the assist force output from the assist motor 24 a to the rack mechanism has been described as an example. The present invention is not limited to this. For example, the present invention is applied to a so-called column-type electric power steering apparatus that can transmit the assist force output from the assist motor to the pinion shaft 23 via the speed reducer. Also good.
Also, a so-called rack parallel type electric power steering device in which the rack shaft and the motor are arranged in parallel, a so-called pinion type electric power steering device in which the motor is arranged in the pinion portion having the pinion shaft 23, or a so-called You may apply to a dual pinion type electric power steering device.

FIG. 1A is a block diagram showing an overall configuration example of the electric power steering apparatus according to the first embodiment, and FIG. 1B is a circuit block diagram showing a configuration example of an ECU and the like. It is explanatory drawing which illustrated the derailment return force which acts on the said left front wheel etc. in order to return the left front wheel which is a derailment state. It is a part of flowchart which shows the flow of the derailment return possibility improvement process by ECU of the electric power steering device which concerns on this 1st Embodiment. It is a part of flowchart which shows the flow of the derailment return possibility improvement process by ECU of the electric power steering device which concerns on this 1st Embodiment. FIG. 5 (A) is an explanatory diagram showing an example in which it is displayed on the monitor of the warning device in FIG. 1 that it is impossible to return the wheel, and FIG. 5 (B) is a monitor of the warning device in FIG. It is explanatory drawing which shows an example by which it is displayed that a derailment return is possible. FIG. 6A is an explanatory diagram illustrating an example of treatment information displayed on the monitor of the warning device in FIG. 1, and FIG. 6A is a first diagram that promotes an improvement in the coefficient of friction between a steered wheel and a side groove that are in a derailed state. FIG. 6B is an explanatory diagram illustrating second treatment information that promotes a decrease in the groove height of the side groove to be returned. It is a part of flowchart which shows the flow in the modification of the derailment return possibility improvement process by ECU of the electric power steering device which concerns on this 1st Embodiment. It is explanatory drawing which shows the principal part of the electric power steering device which concerns on 2nd Embodiment of this invention. It is a part of flowchart which shows the flow of the derailment return possibility improvement process by ECU of the electric power steering device which concerns on this 2nd Embodiment. It is a part of flowchart which shows the subroutine of the vehicle height adjustment process in the wheel drive reset possibility improvement process by ECU of the electric power steering device which concerns on 3rd Embodiment of this invention. It is a part of flowchart which shows the subroutine of the vehicle height adjustment process in the wheel drive reset possibility improvement process by ECU of the electric power steering device which concerns on 3rd Embodiment of this invention. It is explanatory drawing which shows the principal part of the electric power steering device 20 which concerns on 4th Embodiment of this invention. FIG. 10 is a part of a flowchart showing a flow of a wheel return return possibility improving process by the ECU 30 of the electric power steering apparatus 20 according to the fourth embodiment. It is explanatory drawing which shows an example of the air pressure-friction force evaluation value map used for the air pressure adjustment process of FIG. It is a part of flowchart which shows the flow of the derailment return possibility improvement process by ECU30 of the electric power steering device 20 which concerns on this 5th Embodiment. It is a part of flowchart which shows the subroutine of the air pressure adjustment process of FIG. It is a part of flowchart which shows the subroutine of the air pressure adjustment process of FIG.

Explanation of symbols

20 ... Electric power steering device 24a ... Assist motor 26 ... Torque sensor (relative angle detection means)
30 ... ECU
41 ... Right front wheel (steering wheel, driving wheel, wheel)
42 ... Left front wheel (steering wheel, driving wheel, wheel)
43 ... Right rear wheel
44 ... Left rear wheel (wheel)
41b to 44b ... wheel load sensor (wheel load detecting means)
50 ... Wheel drive device 60 ... Vehicle speed sensor 70 ... Warning device (notification means)
71 ... Monitor 80 ... Active suspension (vehicle height adjustment means)
83a to 83d ... Suspension device (vehicle height adjusting means)
90 ... Air pressure adjusting device (air pressure adjusting means)
D ... Gutter (stepped part of road surface)
FS m _... maximum assist force FD m _... derailing at the maximum rotational driving force _H 1 to H 4 _... vehicle height i ... motor current value is ... the current limit value io ... overload current value (a predetermined current threshold value)
P ₁ to P 4 _... wheel load _P A1, _{P A2 ...} wheel load threshold (first wheel load threshold)
P _B ... wheel load threshold (second wheel load threshold)
t _{1 to} t ₄ ... air pressure δ ... actual steering angle (relative angle)
θ: Steering angle φ: Maximum derailment return force V: Vehicle speed V ₀ ... Speed threshold

Claims (17)

A motor that outputs assist force capable of assisting steering of both steered wheels that are also drive wheels of the vehicle;
Wheel load detecting means for detecting wheel loads of all wheels including both the steered wheels;
A wheel removal determining means for determining whether one of the two steered wheels is in a wheel-removed state in which the wheel falls into a stepped portion of the road surface and dewheels;
The maximum assist force that can be generated by the motor is the maximum derailment return force that is the maximum derailment return force that can be generated to return the steered wheel that is in the derailment state from the derailment state. Based on the pressing force acting in the vertical direction on the side surface of the stepped portion of the maximum rotational driving force that is the maximum rotational driving force that can be generated by rotating both the steering wheels by the wheel driving device in addition to the assisting force. Means for estimating the maximum derailment return force to be estimated;
A derailment return availability determination means for determining whether or not the derailment return from the derailed state is possible based on the maximum derailment return force and the wheel load of the steered wheel in the derailed state, A wheel-return-return availability determination means for determining that wheel-return return from the wheel-removed state is impossible when the wheel-returning force does not exceed the wheel load of the steered wheel in the wheel-removed state;
Motor control means for controlling so as to gradually increase the assist force by the motor when it is not determined by the wheel return return availability determination means that wheel return return is impossible;
An electric power steering apparatus comprising:   The motor control means performs control so as to temporarily stop the output of the assist force by the motor when it is determined that the return to wheel removal is impossible by the return wheel return availability determination means. The electric power steering apparatus according to claim 1.   The motor control means performs control so as to gradually reduce the assist force by the motor when the wheel removal return possibility determination means determines that wheel return return is impossible. Item 2. The electric power steering apparatus according to Item 1.   The electric power steering apparatus according to any one of claims 1 to 3, further comprising notifying means for notifying a result of determining whether or not to return to wheel removal determined by the means for determining whether or not to return to wheel removal.   The wheel load detection means is a strain sensor that is mounted on an arm that is interposed between a vehicle body and each wheel and that is attached in the vicinity of each wheel, and that each wheel is based on the distortion of the arm at the mounting portion. The electric power steering apparatus according to any one of claims 1 to 4, wherein a load is detected.   The wheel load detection means is a relative distance sensor that is provided in the vicinity of each wheel and detects a relative distance between the vehicle body and each wheel, and based on each relative distance detected by each relative distance sensor. The electric power steering apparatus according to any one of claims 1 to 4, wherein each wheel load is estimated and detected.   The wheel-removal determination means is in the case where any one of the wheel loads on the two steered wheels is equal to or greater than a first wheel load threshold value set larger than an average value of the wheel loads on all other wheels. The electric power steering apparatus according to any one of claims 1 to 6, wherein it is determined that the steered wheel is in a derailed state. It has a vehicle speed sensor that detects the vehicle speed,
When the vehicle speed is equal to or less than a predetermined speed threshold that is determined to be stopped, the wheel removal determination means determines whether the vehicle is in a wheel removal state based on the wheel load. The electric power steering apparatus as described in any one of Claims 1-7. Relative angle detection means for detecting a relative angle between the direction along the side surface of the steered wheel in the derailed state and the direction along the side surface of the stepped portion,
The maximum derailing return force estimating means is configured such that the maximum derailing return force (φ) is set such that the maximum assist force is FS _m and smaller than the maximum rotational driving force and can be generated by the wheel driving device. When the maximum rotational driving force is FD _m , the relative angle is δ, and a predetermined coefficient corresponding to the friction coefficient on the contact surface between the side surface of the steered wheel and the side surface of the stepped portion is μ The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is estimated by the following expression.
φ = μ × (FS _m + FD _m × sin δ)   10. The electric power steering apparatus according to claim 9, wherein the relative angle detection means detects an actual steering angle of the steered wheel as the relative angle.   The wheel removal return availability determination means determines whether wheel release return is possible when the value of a current flowing through the motor is equal to or greater than a predetermined current threshold value at which the motor is determined to be in an overload state. The electric power steering apparatus according to any one of claims 1 to 10.   The wheel-return return enable / disable determining means is not capable of wheel-return return when the maximum wheel-return return force is equal to or less than a second wheel load threshold set to be equal to or less than the wheel load on the steered wheel in the wheel-removed state. It determines with having, The electric power steering device as described in any one of Claims 1-11 characterized by the above-mentioned.   The overload protection of the motor is stopped or the protection condition is relaxed when one of the two steered wheels is determined to be in a derailed state by the derailing determining means. The electric power steering apparatus as described in any one of 1-12. Vehicle height adjustment means capable of adjusting the height of the vehicle body for each wheel;
The height of the vehicle body relative to “the steered wheels in the derailed state” is determined by the vehicle height adjusting means when one of the two steered wheels is determined to be in the derailed state by the derailed determining means. The electric power steering apparatus according to any one of claims 1 to 13, wherein the height of the vehicle body is adjusted to be higher than a height of the vehicle body with respect to a "wheel most distant from the steered wheel in the derailed state". Vehicle height adjustment means capable of adjusting the height of the vehicle body for each wheel;
The height of the vehicle body relative to “the steered wheels in the derailed state” is determined by the vehicle height adjusting means when one of the two steered wheels is determined to be in the derailed state by the derailed determining means. Is adjusted to be higher than the height of the vehicle body with respect to the “wheel most distant from the steering wheel in the derailed state”, and “mostly separated from the steered wheel in the derailed state” and “the steered wheel in the derailed state” The height of the vehicle body with respect to the wheels other than “wheels” is determined based on the degree of change in the wheel load of the steered wheels in the wheeled state when the height of the vehicle body with respect to each wheel is changed. It adjusts so that the wheel load of a steering wheel may become small, The electric power steering device as described in any one of Claims 1-13 characterized by the above-mentioned. Air pressure detecting means for detecting the air pressure of each wheel;
An air pressure adjusting means capable of adjusting each air pressure;
A map in which the air pressure and a frictional force evaluation value indicating the possibility of derailing return due to the frictional force between each wheel and the road surface are associated in advance;
When one of the steered wheels is determined to be in a wheel-out state by the wheel-out determining unit, the air pressure adjusting unit increases the frictional force evaluation value based on the map and returns to the wheel-out. The electric power steering apparatus according to any one of claims 1 to 15, wherein each of the air pressures is adjusted so as to increase the possibility. Air pressure detecting means for detecting the air pressure of each wheel;
An air pressure adjusting means capable of adjusting each air pressure;
A map in which the air pressure and a frictional force evaluation value indicating the possibility of derailing return due to the frictional force between each wheel and the road surface are associated in advance;
When any one of the two steered wheels is determined to be in the derailed state by the derailing determination unit, the steered wheel in the derailed state when the air pressure is changed by the air pressure adjusting unit. Based on both the degree of change in wheel load and the degree of change in the frictional force evaluation value obtained from the map when each of the air pressures is changed, the air pressure is increased so as to increase the possibility of return from wheel removal. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is adjusted.

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