JP2015071345A - Electric power steering device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an electric power steering device capable of relaxing impact force during end collision, without addition of a steering angle sensor or the like.SOLUTION: Torque command value saturation degree P is detected based on a steering assistance command value Iref_preLim, motor angle speed ω, and vehicle speed Vs. When the torque command value saturation degree P is equal to or more than a threshold Pth, the steering assistance command value Iref_preLim is limited with a limitation value I_Lim. Then based on the steering assistance command value Iref_Lim after limitation, an electric motor 13 is driven and controlled.

Description

  The present invention relates to an electric power steering apparatus including an electric motor that generates a steering assist torque to be applied to a steering mechanism, and more particularly to an electric power steering apparatus for reducing an impact at the time of end contact.

2. Description of the Related Art Conventionally, as a steering device, an electric power steering device that gives a steering assist force to a steering mechanism by driving an electric motor in accordance with a steering torque by which a driver steers a steering wheel has become widespread.
In general, in a steering mechanism, the steering wheel continues to steer in either direction from the neutral position, and when the steering wheel operation amount reaches a maximum steering angle corresponding to the maximum value, the steering mechanism comes into contact with the mechanical stopper. The steering limit is such that no further steering is possible. This end limit is referred to as end contact when the steering limit is reached.

When the steering wheel is operated quickly, that is, when the steering speed is high, the steering assist force generated by the electric power steering device is also increased, and the impact force generated at the time of the end application is also increased. As a result, the durability of the steering mechanism may decrease, or the driver may feel uncomfortable during the steering operation.
Therefore, as an electric power steering device for reducing the impact at the time of end contact, there is a technique described in Patent Document 1, for example. This technique reduces and corrects the auxiliary steering torque of the electric motor when the steering angle exceeds a predetermined steering angle near the maximum steering angle. Here, as the steering speed is faster, the steering assist torque reduction correction amount is increased and corrected.

  Moreover, as another electric power steering apparatus, there exists a technique of patent document 2, for example. In this technique, when it is detected that the steered wheel has approached a predetermined maximum steering angle and exceeds the attenuation start steering angle, the driving force of the electric motor is attenuated. Here, the attenuation start steering angle is set according to the load of the steered wheels and the steering speed of the steered wheels.

Japanese Patent No. 3560024 Japanese Patent No. 4132439

However, the technique described in Patent Document 1 requires a sensor that detects the rudder angle. In addition, when the steering speed is high, there is a case where the impact at the time of the end contact cannot be sufficiently alleviated due to the inertia of the electric motor.
Further, in the technology described in Patent Document 2, the attenuation start steering angle is set according to the load of the steered wheel and the steering speed of the steered wheel, and the steering speed is high. Increases the difference between the maximum steering angle and the attenuation start steering angle (accelerates the point of time when the driving force of the electric motor is attenuated) to prevent the motor inertia from generating a large impact at the time of contact. Yes. However, in this case as well, a sensor for detecting the steering angle is separately required as in the technique described in Patent Document 1.

  Therefore, an object of the present invention is to provide an electric power steering device that can reduce the impact force at the time of end contact without adding a steering angle sensor or the like separately.

  In order to solve the above problems, an aspect of an electric power steering apparatus according to the present invention includes a steering torque detection unit that detects a steering torque input to a steering mechanism, and a steering torque detected by at least the steering torque detection unit. A torque command value calculation unit that calculates a steering assist torque command value based on the electric motor, an electric motor that generates a steering assist torque to be applied to a steering shaft of the steering mechanism, and drive control of the electric motor based on the steering assist torque command value An electric power steering device comprising: a motor control unit that detects a motor angular speed of the electric motor; a vehicle speed detection unit that detects a vehicle speed of the host vehicle; and the torque command value calculation unit Steering assist torque command value calculated in step, motor angular velocity detected by the motor angular velocity detection unit, When the saturation detection unit detects the saturation of the steering assist torque command value based on the vehicle speed detected by the vehicle speed detection unit, and when the saturation detected by the saturation detection unit is greater than or equal to a preset threshold value A torque command value limiting unit that limits the steering assist torque command value calculated by the torque command value calculation unit as compared to when the saturation detected by the saturation detection unit is less than the threshold value, When the saturation detected by the saturation detection unit is equal to or greater than a preset threshold, the motor control unit controls the electric motor based on the steering assist torque command value after being limited by the torque command value limiting unit. It is characterized by drive control.

  Thus, when the degree of saturation of the steering assist torque command value is equal to or greater than the threshold value, the steering assist torque command value is limited, so that the output of the electric motor can be limited. Therefore, the impact force transmitted to the torque transmission member such as the intermediate shaft at the time of end contact that becomes the steering limit can be reduced. Further, since it is possible to determine whether the torque command value limit condition is satisfied based on the steering assist torque command value, the motor angular velocity, and the vehicle speed, it is not necessary to add a steering angle sensor or the like that detects the steering angle. .

  In the above, the saturation detection unit multiplies the steering assist torque command value calculated by the torque command value calculation unit by the motor angular velocity detected by the motor angular velocity detection unit, and the motor power of the electric motor A motor power calculation unit that calculates a motor power reference value that is a reference value of the motor power based on the vehicle speed detected by the vehicle speed detection unit, and the motor A power deviation calculation unit for calculating a power deviation by subtracting the motor power reference value set by the motor power reference value setting unit from the motor power calculated by the power calculation unit, and the power deviation calculation It is preferable to include a saturation calculation unit that calculates the saturation of the steering assist torque command value by integrating the power deviation calculated by the unit with time.

Thus, since the actual motor work amount and the target motor work amount are compared, the saturation degree of the steering assist torque command value can be appropriately calculated. Therefore, it is possible to appropriately determine whether or not the limiting condition for the steering assist torque command value is satisfied, and it is possible to effectively reduce the impact force at the time of contact.
Furthermore, in the above, it is preferable that the motor power reference value setting unit sets the motor power reference value to be smaller as the vehicle speed detected by the vehicle speed detection unit is faster. Since the steering assist torque command value is calculated to be smaller even with the same steering torque as the vehicle speed is faster, the saturation level of the steering assist torque command value is appropriately detected by setting the motor work rate reference value smaller as the vehicle speed is faster. The steering assist torque command value can be appropriately limited.

Further, in the above, when the saturation detected by the saturation detection unit is greater than or equal to the threshold value, the torque command value limiting unit calculates the torque command value as the saturation detected by the saturation detection unit increases. It is preferable to increase the limit amount of the steering assist torque command value calculated by the unit.
As a result, the greater the degree of saturation of the steering assist torque command value, the stronger the limit of the steering assist torque command value can be made, and the impact force at the time of end contact can be weakened more reliably.

  Furthermore, in the above, a saturation correction for correcting the saturation by multiplying the saturation detected by the saturation detection unit by a power supply voltage sensitive gain corresponding to the power supply voltage applied to the electric motor. It is preferable to provide a part. In this way, since the power supply voltage applied to the electric motor is taken into account, the saturation degree of the steering assist torque command value can be detected more appropriately.

In the above, it is preferable that the saturation correction unit sets a power supply voltage sensitive gain to be higher as the power supply voltage is higher. As a result, the higher the power supply voltage applied to the electric motor, the greater the degree of saturation of the steering assist torque command value, making it easier to limit the steering assist torque command value.
Further, in the above, a switchback operation detection unit that detects a switchback operation of the steering wheel by the driver based on the steering torque detected by the steering torque detection unit and the motor angular velocity detected by the motor angular velocity detection unit. The saturation detection unit preferably sets the saturation to zero when the switchback operation detection unit detects a steering wheel switchback operation by the driver.

  In this way, since the degree of saturation of the steering assist torque command value is set to zero during the switchback operation, it is possible not to limit the steering assist torque command value during the switchback operation. That is, since the motor output is limited only during the turning operation, it is possible to prevent the steering assist force from becoming insufficient when the steering wheel is turned back from the vicinity of the maximum steering angle toward the neutral position. it can. Therefore, at the time of such a switching back operation, the driver is not given a feeling that the steering wheel sticks near the maximum steering angle, and deterioration of the steering feeling can be prevented.

  According to the present invention, when the degree of saturation of the steering assist torque command value is equal to or greater than the threshold value, the steering assist torque command value can be limited and the generated motor torque can be limited. Therefore, the impact force transmitted to the torque transmitting member such as the intermediate shaft when the steering limit position at the time of end contact is reached can be reduced without adding a separate steering angle sensor or the like.

1 is an overall configuration diagram showing an electric power steering apparatus according to the present invention. It is a block diagram which shows the specific structure of a controller. It is a block diagram which shows the specific structure of a torque command value limiting part. It is a calculation map of motor work rate reference value W_t. It is a calculation map of limit value I_Lim. It is a flowchart which shows the torque command value restriction | limiting process procedure performed in a torque command value restriction | limiting part. It is a block diagram which shows the specific structure of the torque command value limiting part of 2nd Embodiment. It is a calculation map of power supply voltage gain G_Vr. It is a block diagram which shows the specific structure of the torque command value limiting part of 3rd Embodiment. It is a flowchart which shows the increase / switchback determination processing procedure performed by a switch / switchback processing unit.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
(First embodiment)
FIG. 1 is an overall configuration diagram showing an electric power steering apparatus according to the present invention.
In the figure, reference numeral 1 denotes a steering wheel of a vehicle, and a steering force applied to the steering wheel 1 from a driver is transmitted to the steering shaft 2. The steering shaft 2 has an input shaft 2 a and an output shaft 2 b, one end of the input shaft 2 a is connected to the steering wheel 1, and the other end of the input shaft 2 a is connected to one end of the output shaft 2 b via the steering torque sensor 3. It is connected to.

  The steering force transmitted to the output shaft 2 b is transmitted to the intermediate shaft 5 via the universal joint 4 and further transmitted to the pinion shaft 7 via the universal joint 6. The steering force transmitted to the pinion shaft 7 is transmitted to the tie rod 9 via the steering gear 8 and steers steered wheels (not shown). Here, the steering gear 8 is configured in a rack and pinion type having a pinion 8a connected to the pinion shaft 7 and a rack 8b meshing with the pinion 8a, and the rotational motion transmitted to the pinion 8a is linearly moved by the rack 8b. It has been converted to movement.

A steering assist mechanism 10 for transmitting a steering assist force to the output shaft 2b is connected to the output shaft 2b of the steering shaft 2. The steering assist mechanism 10 includes a reduction gear 11 connected to the output shaft 2b, and an electric motor 13 connected to the reduction gear 11 and generating an auxiliary steering force for the steering system.
The steering torque sensor 3 detects the steering torque applied to the steering wheel 1 and transmitted to the input shaft 2a. For example, the steering torque sensor 3 converts the steering torque into a torsion angle displacement of a torsion bar (not shown) interposed between the input shaft 2a and the output shaft 2b, detects this torsion angle displacement with a magnetic signal, and converts it into an electric signal. Is configured to convert. The steering torque T detected by the steering torque sensor 3 is input to the controller 14.

The controller 14 operates by being supplied with power from a battery 15 that is a vehicle-mounted power source. Here, the negative electrode of the battery 15 is grounded, and the positive electrode thereof is connected to the controller 14 via an ignition switch 16 that starts the engine, and is directly connected to the controller 14 without passing through the ignition switch 16.
In addition to the steering torque T, the vehicle speed Vs detected by the vehicle speed sensor 17 is input to the controller 14. Then, steering assist control (steering assist) is performed to apply a steering assist force corresponding to these to the steering system. Specifically, a steering assist command value (steering assist torque command value) for generating the steering assist force by the electric motor 13 is calculated by a known procedure, and the electric motor 13 is operated based on the calculated steering assist command value. Calculate the current command value. The drive current supplied to the electric motor 13 is feedback-controlled based on the calculated current command value and the detected motor current value.

Next, a specific configuration of the controller 14 will be described.
As shown in FIG. 2, the controller 14 includes a command value calculation unit 21 that calculates a steering assist command value based on the steering torque T and the vehicle speed Vs, a command value compensation unit 22 that compensates the steering assist command value, and a command value. A torque command value limiting unit 23 that limits the steering assist command value Iref_preLim compensated by the compensation unit 22 and a motor control unit 24 that drives and controls the electric motor 13 based on the steering assist command value Iref_Lim after the limitation. .

The command value calculation unit 21 includes a steering assist command value calculation unit 31, a phase compensation unit 32, and a torque differentiation circuit 33.
The steering assist command value calculation unit 31 calculates a steering assist command value with reference to the steering assist command value calculation map based on the steering torque T and the vehicle speed Vs. Here, the steering assist command value calculation map is composed of a characteristic diagram with the steering torque T on the horizontal axis, the steering assist command value on the vertical axis, and the vehicle speed Vs as a parameter. The steering assist command value is set so that the steering assist command value increases relatively slowly at first with respect to the increase of the steering torque T, and further increases with the increase of the steering torque T. Yes. The slope of this characteristic curve is set so as to decrease as the vehicle speed Vs increases. Each characteristic curve has an upper limit value.

The phase compensation unit 32 performs phase compensation on the steering assist command value calculated by the steering assist command value calculation unit 31, and outputs the steering assist command value after phase compensation to the adder 48. Here, for example, a transfer characteristic such as (T ₁ s + 1) / (T ₂ s + 1) is applied to the steering assist command value.
The torque differentiating circuit 33 calculates a compensation value for the steering torque T based on the steering torque change rate obtained by differentiating the steering torque T, and outputs the compensation value to the adder 48.

The command value compensation unit 22 includes at least an angular velocity computation unit 41, an angular acceleration computation unit 42, a convergence compensation unit 43, an inertia compensation unit 44, and a SAT estimation feedback unit 45.
The angular velocity calculation unit 41 differentiates the motor rotation angle θ detected by the rotation angle sensor 13a to calculate the motor angular velocity ω. The angular acceleration calculation unit 42 differentiates the motor angular velocity ω calculated by the angular velocity calculation unit 41 to calculate the motor angular acceleration α.

The convergence compensator 43 receives the motor angular velocity ω calculated by the angular velocity calculator 41 and converges the brake so as to brake the operation of the steering wheel 1 in order to improve the yaw convergence of the vehicle. The compensation value Ic is calculated.
The inertia compensator 44 calculates an inertia compensation value Ii for compensating for the torque equivalent generated by the inertia of the electric motor 13 and preventing deterioration of the sense of inertia or control responsiveness.

The SAT estimation feedback unit 45 inputs the steering torque T, the motor angular velocity ω, the motor angular acceleration α, and the steering assist command value calculated by the command value calculation unit 21, and estimates and calculates the self-aligning torque SAT based on these.
The adder 46 adds the inertia compensation value Ii calculated by the inertia compensation unit 44 and the self-aligning torque SAT calculated by the SAT estimation feedback unit 45, and outputs the result to the adder 47.

The adder 47 adds the addition result of the adder 46 and the convergence compensation value Ic calculated by the convergence compensation unit 43 and outputs the result to the adder 48 as a command compensation value Icom.
The adder 48 adds the compensation value output from the torque differentiating circuit 33 and the command compensation value Icom output from the command value compensation unit 22 to the steering assist command value after phase compensation output from the phase compensation unit 32. The compensated steering assist command value Iref_preLim is output. The compensated steering assist command value Iref_preLim is input to the torque command value limiter 23.

The torque command value limiting unit 23 inputs the compensated steering assist command value (pre-limit steering assist command value) Iref_preLim output from the adder 48, executes the torque command value limiting process shown below, A steering assist command value Iref_Lim is output.
FIG. 3 is a block diagram showing a specific configuration of the torque command value limiting unit 23. As shown in FIG. 3, the torque command value limiting unit 23 includes a power calculation unit 23a, a target power setting unit 23b, a subtractor 23c, a torque command value saturation calculation unit (time integration) 23d, A torque command value restriction processing unit 23e.

The power calculation unit 23 a multiplies the steering assist command value Iref_preLim output by the adder 48 and the motor angular speed ω calculated by the angular speed calculation unit 41 to calculate a motor work amount W that is a power of the electric motor 13. .
The target power setting unit 23b refers to the map shown in FIG. 4 and sets the motor power reference value W_t based on the vehicle speed Vs. Here, the motor power reference value W_t is a value smaller than the target value of the motor power by a certain value, and becomes maximum when the vehicle speed Vs = 0, and becomes 0 as the vehicle speed Vs increases as shown in FIG. Set so that it becomes smaller. The map shown in FIG. 4 can be tuned for each electric motor.

The subtracter 23c subtracts the motor power reference value W_t set by the target power setting unit 23b from the motor power W calculated by the power calculation unit 23a, and outputs the result as a power deviation ΔW.
The torque command value saturation calculation unit 23d integrates the power deviation ΔW output from the subtractor 23c with time, and outputs the result as the torque command value saturation P.

  First, the torque command value limit processing unit 23e refers to the map shown in FIG. 5 based on the torque command value saturation P calculated by the torque command value saturation calculation unit 23d, and the limit value I_Lim of the steering assist command value Iref_preLim. Is calculated. Here, as shown in FIG. 5, the limit value I_Lim is set so as to become smaller as the torque command value saturation degree P becomes larger. The map shown in FIG. 5 can be tuned for each electric motor.

  Next, the torque command value limit processing unit 23e determines whether or not the torque command value saturation degree P is equal to or greater than a threshold value Pth for determining a preset steering limit. If it is determined that P ≧ Pth, the steering assist value is determined. The command value Iref_preLim is limited with the limit value I_Lim as the upper limit. Then, the limited result is output to the motor control unit 24 as a post-restricted steering assist command value Iref_Lim.

That is, the process executed by the torque command value limiting unit 23, which is a characteristic part in the present embodiment, is summarized as follows.
FIG. 6 is a flowchart showing a torque command value limiting process procedure executed by the torque command value limiting unit 23.
First, in step S1, the torque command value limiting unit 23 reads the steering assist command value Iref_preLim, the motor angular speed ω, and the vehicle speed Vs, and proceeds to step S2.

In step S2, the torque command value limiting unit 23 (power calculation unit 23a) multiplies the steering assist command value Iref_preLim read in step S1 by the motor angular velocity ω to calculate the motor power W, and the process proceeds to step S3. Transition.
In step S3, the torque command value limiting unit 23 (target power setting unit 23b) sets the motor power reference value W_t based on the map shown in FIG. 4 based on the vehicle speed Vs read in step S1. .

  Next, in step S4, the torque command value limiter 23 (subtractor 23c) subtracts the motor power reference value W_t set in step S3 from the motor power W calculated in step S2 to obtain a power deviation. ΔW is calculated (ΔW = W−W_t). Here, a limiter having a lower limit value of 0 is provided for the power deviation ΔW. That is, when the motor power W is smaller than the motor power reference value W_t and (W−W_t) is a negative value, the power deviation ΔW = 0 is calculated. Accordingly, when the motor power W is smaller than the motor power reference value W_t, the following integration process is not performed.

  In step S5, the torque command value limiting unit 23 (torque command value saturation calculation unit 23d) integrates the power deviation ΔW calculated in step S4 with time to calculate the torque command value saturation P (P = P + ΔW). ). Here, since the motor power reference value W_t is set to a value smaller than the target value of the motor power, a value obtained by integrating the power deviation ΔW over time (torque command value saturation P) This is a value indicating the degree to which the actual motor work is saturated with respect to the target value of the work. That is, the larger the value of the torque command value saturation P is, the more the actual motor work is saturated with respect to the target value.

  In step S6, the torque command value limiting unit 23 (torque command value limiting processing unit 23e) determines whether or not the torque command value saturation P calculated in step S5 is 0 or more. If P ≧ 0, the process proceeds to step S7, where the torque command value saturation P calculated in step S5 is set as the final torque command value saturation P as it is, and the process proceeds to step S9 described later. . On the other hand, if it is determined in step S6 that P <0, the process proceeds to step S8, the final torque command value saturation P is set to 0, and then the process proceeds to step S9.

  In step S9, the torque command value limiting unit 23 (torque command value limiting processing unit 23e) determines whether or not the torque command value saturation P is equal to or greater than a preset threshold value Pth. If P <Pth, it is determined that the torque command value limiting condition is not satisfied, and the torque command value limiting process is terminated as it is. On the other hand, if P ≧ Pth, it is determined that the torque command value restriction condition is satisfied, and the routine goes to Step S10.

In step S10, the torque command value limiting unit 23 (torque command value limiting processing unit 23e) calculates the limit value I_Lim of the steering assist command value Iref_preLim based on the torque command value saturation P based on the map shown in FIG. Set, and proceed to step S11.
In step S11, the torque command value limiting unit 23 (torque command value limiting processing unit 23e) determines whether or not the absolute value of the steering assist command value Iref_preLim read in step S1 is greater than or equal to the limit value I_Lim. If | Iref_preLim | ≧ I_Lim, it is determined that the steering assist command value Iref_preLim needs to be limited, and the process proceeds to step S12.

  In step S12, the torque command value limiting unit 23 (torque command value limiting processing unit 23e) sets Sign (Iref_preLim) · I_Lim as the post-restricted steering assist command value Iref_Lim, and ends the torque command value limiting process. Here, Sign (Iref_preLim) is 1 when the steering assist command value Iref_preLim is positive, and is -1 when it is negative.

  If it is determined in step S11 that | Iref_preLim | <I_Lim, it is determined that there is no need to limit the steering assist command value Iref_preLim, and the process proceeds to step S13. In step S13, the torque command value limiting unit 23 (torque command value limiting processing unit 23e) sets the steering assist command value Iref_preLim as the post-limit steering assist command value Iref_Lim, and ends the torque command value limiting process.

Returning to FIG. 2, the motor control unit 24 includes a current detector 60 that detects the actual current of the electric motor 13, a current command value calculation unit 61, a subtractor 62, a current control unit 63, and a motor drive unit 64. And comprising.
The current command value calculator 61 calculates the current command value Iref of the electric motor 13 from the post-limit steering assist command value Iref_Lim output from the torque command value limiter 23.

The subtractor 62 calculates a current deviation between the current command value Iref output from the current command value calculation unit 61 and the motor current detection value (actual current) detected by the current detector 60, and supplies this to the current control unit 63. Output.
The current control unit 63 performs feedback control that performs a proportional integration (PI) operation on the current deviation and outputs a voltage command value.

The motor drive unit 64 calculates a duty based on the voltage command value output from the current control unit 63 and calculates a duty ratio that is a drive command for the electric motor 13. Then, the electric motor 13 is driven based on the duty ratio.
In FIG. 1, the steering torque sensor 3 corresponds to the steering torque detector, and the vehicle speed sensor 17 corresponds to the vehicle speed detector. In FIG. 2, the command value calculation unit 21 corresponds to the torque command value calculation unit, and the subtractor 62, the current control unit 63, and the motor drive unit 64 correspond to the motor control unit. Further, the angular velocity calculation unit 41 corresponds to a motor angular velocity detection unit.

  In FIG. 3, a power calculation unit 23a, a target power setting unit 23b, a subtractor 23c, and a torque command value saturation calculation unit 23d correspond to a saturation detection unit, of which the power calculation unit 23a is a motor work. Corresponding to the rate calculator, the target power setting unit 23b corresponds to the motor power target value setting unit, the subtractor 23c corresponds to the power deviation calculator, and the torque command value saturation calculator 23d calculates the saturation. Corresponds to the department. Further, the torque command value limiting processing unit 23e corresponds to the torque command value limiting unit.

Next, the operation of the first embodiment will be described.
When the driver turns on the ignition switch 16, control power is supplied from the battery 15 to the controller 14, and the controller 14 is activated. At this time, the controller 14 performs steering assist control based on the steering operation by the driver.
For example, when the driver starts the vehicle and is turning on a curved road, the controller 14 calculates a steering assist command value Iref_preLim based on the steering torque T and the vehicle speed Vs.

  At this time, when the steering torque T is relatively small, the motor power W calculated based on the steering assist command value Iref_preLim and the motor angular speed ω is set to the motor power reference value W_t set based on the vehicle speed Vs. Smaller than. That is, the power deviation ΔW (= W−W_t) is a negative value. Therefore, the torque command value saturation P obtained by time integration of the power deviation ΔW is also a negative value, and the final torque command value saturation P is set to 0 (step S8 in FIG. 6).

Since the torque command value saturation P = 0 is smaller than the threshold value Pth (No in step S9), the torque command value restriction condition is not satisfied in this case. Therefore, the steering assist command value Iref_preLim is not limited, and the electric motor 13 is rotationally driven using the steering assist command value Iref_preLim as it is as the limited steering assist command value Iref_Lim.
As a result, the steering assist torque corresponding to the steering torque T and the vehicle speed Vs is generated by the electric motor 13, and this is transmitted to the output shaft 2 b of the steering shaft 2 via the reduction gear 11. This reduces the driver's steering burden.

When the driver turns and operates the steering wheel 1 and detects a relatively large steering torque T from the state where the normal steering assist control is performed, the motor power W increases the motor power reference value W_t. Exceed. That is, the power deviation ΔW> 0, and the torque command value saturation P obtained by time integration of the power deviation becomes a value equal to or greater than the threshold value Pth (Yes in step S9).
Then, the controller 14 sets a limit value I_Lim that becomes smaller as the torque command value saturation P becomes larger, in accordance with the torque command value saturation P. Further, the steering assist command value Iref_preLim is limited by the limit value I_Lim set in this way.

Then, the controller 14 drives the electric motor 13 to rotate based on the limited steering assist command value (restricted steering assist command value) Iref_Lim. As a result, the output of the electric motor 13 is limited compared to before the steering assist command value is limited.
Therefore, in this case, the assist torque when the driver steers the steering wheel 1 to the vicinity of the rack end can be limited. Therefore, the impact force transmitted to the torque transmission member such as the intermediate shaft at the time of end contact that becomes the steering limit can be reduced, and the durability of the steering mechanism can be maintained.

  Thus, by integrating the deviation between the motor power W and the motor power reference value W_t over time, the degree to which the actual motor work is saturated with respect to the target value of the motor work (torque command value saturation) Degree P) can be detected. Therefore, it is possible to easily determine whether or not the torque command value restriction condition is satisfied by comparing the torque command value saturation P with a preset threshold value Pth. Furthermore, since it is possible to determine whether or not the torque command value limiting condition is satisfied based only on the steering assist command value Iref_preLim, the motor angular velocity ω, and the vehicle speed Vs, it is necessary to provide a steering angle sensor that detects the steering angle. Absent.

  The motor power reference value W_t is set to a smaller value as the vehicle speed Vs increases. As the vehicle speed Vs increases, the steering assist torque command value Iref_preLim is calculated to be smaller even with the same steering torque T. Therefore, the torque command value saturation P can be appropriately calculated by setting the motor power reference value W_t to be smaller (the target value of the motor power is set to be smaller) as the vehicle speed Vs is higher.

Furthermore, since the limit value I_Lim of the steering assist torque command value Iref_preLim is set smaller as the torque command value saturation P is larger, the limit amount of the steering assist torque command value Iref_preLim is increased as the torque command value saturation P is larger. be able to. Therefore, the impact force at the time of end contact can be weakened more reliably.
(Second Embodiment)
Next, a second embodiment of the present invention will be described.

In the second embodiment, the magnitude of the torque command value saturation P is set according to the power supply voltage of the electric motor 13.
FIG. 7 is a block diagram showing a specific configuration of the torque command value limiting unit 23 in the second embodiment.
The torque command value limiting unit 23 has the same configuration as the torque command value limiting unit 23 shown in FIG. 3 except that a power supply voltage gain setting unit 23f and a gain multiplication unit 23g are added. Therefore, here, the description will focus on the different parts.

The power supply voltage gain setting unit 23f receives the power supply voltage Vr of the electric motor 13, and sets the power supply voltage gain G_Vr with reference to the power supply voltage gain calculation map shown in FIG. Here, the power supply voltage gain G_Vr is set to a larger value as the power supply voltage Vr becomes higher, as shown in FIG.
The gain multiplication unit 23g multiplies the torque command value saturation P calculated by the torque command value saturation calculation unit 23d by the power supply voltage gain G_Vr set by the power supply voltage gain setting unit 23f, and the result is the final torque command. The value saturation P is output to the torque command value restriction processing unit 23e.

  Thus, since the power supply voltage Vr applied to the electric motor 13 is taken into consideration, the torque command value saturation P can be calculated more appropriately. At this time, the higher the power supply voltage Vr, the larger the power supply voltage sensitive gain G_Vr is set. Therefore, the higher the power supply voltage Vr, the larger the torque command value saturation P is set, and the steering assist command value Iref_preLim is limited. Can be made easier.

In FIG. 7, the power supply voltage gain setting unit 23f and the gain multiplication unit 23g correspond to a saturation correction unit.
(Third embodiment)
Next, a third embodiment of the present invention will be described.
In the third embodiment, the steering state (addition / return) of the driver is determined, and the torque command value saturation P is set according to the result.

FIG. 9 is a block diagram showing a specific configuration of the torque command value limiting unit 23 in the third embodiment.
The torque command value limiting unit 23 has the same configuration as that of the torque command value limiting unit 23 shown in FIG. 3 except that a rounding / switching back processing unit 23h is added. Therefore, here, the description will focus on the different parts.

Based on the steering assist command value Iref_preLim and the motor angular speed ω, the increase / return processing unit 23h determines whether or not the driver is operating the steering wheel 1 to be switched back. Torque command value saturation P is set.
FIG. 10 is a flowchart showing the increase / return determination processing procedure executed by the increase / return processing unit 23h.

First, in step S21, the increase / return processing unit 23h determines whether or not the steering assist command value Iref_preLim and the motor angular velocity ω have the same sign. If Sign (Iref_preLim) = Sign (ω), it is determined that the driver is turning and operating the steering wheel 1, and the process proceeds to step S22.
In step S22, the increase / return processing unit 23h uses the torque command value saturation P calculated by the torque command value saturation calculation unit 23d as the final torque command value saturation P as it is as a torque command value restriction processing unit. 23e, and the addition / return determination process is completed.

On the other hand, if it is determined in step S21 that Sign (Iref_preLim) ≠ Sign (ω), it is determined that the driver is turning back the steering wheel 1, and the process proceeds to step S23.
In step S23, the increase / return processing unit 23h outputs the final torque command value saturation P = 0 to the torque command value restriction processing unit 23e, and ends the increase / switchback determination processing.

  Thus, when the driver is turning back the steering wheel 1, the torque command value saturation P = 0 is set regardless of the steering assist command value Iref_preLim and the motor angular velocity ω. Therefore, the torque command value saturation P becomes equal to or less than the threshold value Pth (No in step S9 in FIG. 6), and the steering assist command value Iref_preLim can be prevented from being limited.

  In this way, the steering assist command value Iref_preLim is limited only when the driver is performing a turning operation, and is not performed when the driver is performing a switching operation. Therefore, when the steering wheel 1 is turned back from the vicinity of the maximum steering angle toward the neutral position, it is possible to prevent a feeling of sticking in the vicinity of the maximum steering angle of the steering wheel 1 due to a lack of steering assist force. And good steering feeling can be maintained.

Here, step S21 in FIG. 10 corresponds to the switch back operation detection unit.
In the third embodiment, a process for setting the torque command value saturation P according to the power supply voltage Vr of the electric motor 13 may be further added as in the second embodiment. Good.

  DESCRIPTION OF SYMBOLS 1 ... Steering wheel, 2 ... Steering shaft, 3 ... Steering torque sensor, 8 ... Steering gear, 10 ... Steering assist mechanism, 13 ... Electric motor, 14 ... Controller, 15 ... Battery, 16 ... Ignition switch, 17 ... Vehicle speed sensor, DESCRIPTION OF SYMBOLS 18 ... Steering angle sensor, 21 ... Command value calculating part, 22 ... Command value compensating part, 23 ... Torque command value limiting part, 23a ... Work rate calculating part, 23b ... Target work rate setting part, 23c ... Subtractor, 23d ... Torque command value saturation calculation unit, 23e ... torque command value restriction processing unit, 23f ... power supply voltage gain setting unit, 23g ... gain multiplication unit, 23h ... increase / return processing unit, 24 ... motor control unit, 31 ... steering Auxiliary command value calculation unit, 32 ... phase compensation unit, 33 ... torque differentiation circuit, 41 ... angular velocity calculation unit, 42 ... angular acceleration calculation unit, 43 ... convergence convergence compensation unit, 44 Inertia compensation unit, 45 ... SAT estimation feedback portion, 46 to 48 ... adder, 61 ... current command value calculating section, 62 ... subtractor, 63 ... current controller, 64 ... motor driving unit

Claims (7)

A steering torque detector for detecting a steering torque input to the steering mechanism; a torque command value calculator for calculating a steering assist torque command value based on at least the steering torque detected by the steering torque detector; An electric power steering apparatus comprising: an electric motor that generates a steering assist torque to be applied to a steering shaft; and a motor control unit that drives and controls the electric motor based on the steering assist torque command value.
A motor angular velocity detector for detecting a motor angular velocity of the electric motor;
A vehicle speed detector for detecting the vehicle speed of the host vehicle;
The degree of saturation of the steering assist torque command value based on the steering assist torque command value calculated by the torque command value calculation unit, the motor angular speed detected by the motor angular velocity detection unit, and the vehicle speed detected by the vehicle speed detection unit. A saturation detection unit for detecting
When the saturation detected by the saturation detection unit is equal to or greater than a preset threshold, the saturation detected by the saturation detection unit is less than the threshold when the steering assist torque command value calculated by the torque command value calculation unit is detected. A torque command value limiter for limiting the torque compared to when
When the saturation detected by the saturation detection unit is equal to or greater than a preset threshold, the motor control unit controls the electric motor based on the steering assist torque command value after being limited by the torque command value limiting unit. An electric power steering apparatus characterized by controlling driving. The saturation detector is
A motor power calculation unit that calculates the motor power of the electric motor by multiplying the steering assist torque command value calculated by the torque command value calculation unit by the motor angular speed detected by the motor angular speed detection unit;
Based on the vehicle speed detected by the vehicle speed detector, a motor power reference value setting unit that sets a motor power reference value that is a reference value of the motor power;
A power deviation calculating unit for subtracting the motor power reference value set by the motor power reference value setting unit from the motor power calculated by the motor power calculation unit, and calculating a power deviation;
The saturation calculation part which calculates the saturation of the said steering assist torque command value by time-integrating the work deviation calculated by the said work deviation deviation part, The said calculation part is provided. Electric power steering device.   The electric power steering apparatus according to claim 2, wherein the motor power reference value setting unit sets the motor power reference value to be smaller as the vehicle speed detected by the vehicle speed detection unit is faster. The torque command value limiter is
When the saturation detected by the saturation detection unit is equal to or greater than the threshold, the amount of steering assist torque command value calculated by the torque command value calculation unit increases as the saturation detected by the saturation detection unit increases. The electric power steering apparatus according to claim 1, wherein the electric power steering apparatus is increased.   A saturation correction unit that corrects the saturation by multiplying the saturation detected by the saturation detection unit by a power supply voltage sensitivity gain corresponding to the power supply voltage applied to the electric motor. The electric power steering device according to any one of claims 1 to 4, wherein The saturation correction unit is
6. The electric power steering apparatus according to claim 5, wherein the power supply voltage sensitive gain is set to be larger as the power supply voltage is higher. Based on the steering torque detected by the steering torque detector and the motor angular velocity detected by the motor angular velocity detector, a switchback operation detector that detects a steering wheel switchback operation by the driver is provided.
The saturation detector is
The electric motor according to any one of claims 1 to 6, wherein when the switchback operation detection unit detects a switchback operation of a steering wheel by a driver, the saturation is set to zero. Power steering device.

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