JP4231430B2 - Vehicle steering device - Google Patents

Description

  The present invention relates to a steering handle that is operated by a driver to steer a vehicle, a reaction force actuator that applies a reaction force to the steering handle, a turning actuator for turning steered wheels, and a steering handle. The present invention relates to a steering-by-wire vehicle steering apparatus including a steering control device that drives and controls a steering actuator according to an operation to steer a steered wheel.

  In recent years, the development of steering devices that employ this type of steering-by-wire system has been actively carried out. For example, Patent Document 1 below detects a steering angle and a vehicle speed, calculates a transmission ratio that decreases as the steering angle increases and increases as the vehicle speed increases, and divides the steering angle by this transmission ratio, thereby dividing the front wheel A steering device is shown in which a turning angle (amount of rack shaft displacement) is calculated and the front wheels are turned to the calculated turning angle. Further, in this steering device, the steering response and followability of the front wheels are improved by correcting the calculated turning angle in accordance with the steering speed obtained by time-differentiating the detected steering angle. Further, by calculating the target yaw rate using the detected vehicle speed and the detected steering angle, and correcting the calculated turning angle according to the difference between the calculated target yaw rate and the detected actual yaw rate, the vehicle behavior state Steering control that takes into account is realized.

  Further, in Patent Document 2 below, the steering torque and the steering angle of the steering wheel are detected, two turning angles that increase as the steering torque and the steering wheel steering angle increase are calculated, and these calculated turning angles are added. A steering device is shown in which the front wheels are steered at the steered angle. In this steering apparatus, the vehicle speed is also detected, the both turning angles are corrected based on the detected vehicle speed, and the turning characteristics are changed according to the vehicle speed.

  However, in any of the above-described conventional devices, the steering angle and the steering torque, which are the operation input values for the steering wheel by the driver for steering the vehicle, are detected, and the front wheels are detected using the detected steering angle and steering torque. The steering angle is directly calculated, and the front wheels are steered to the calculated steering angle. However, although the steering control of these front wheels has removed the mechanical connection between the conventional steering wheel and the steered wheels, the response of the steering of the front wheels to the operation of the steering wheel is the operation position of the steering wheel. Alternatively, the basic technical idea of determining the front wheel turning angle according to the operating force is exactly the same, and in these turning methods, the front wheel turning angle is determined according to human sensory characteristics. It was difficult to drive the vehicle.

  That is, in the above-described conventional device, the turning angle that cannot be perceived by the driver is determined directly in response to the operation of the steering wheel, and the vehicle turns by turning the front wheels according to the turning angle. . The driver senses the lateral acceleration, yaw rate, and turning curvature of the vehicle due to the turning of the vehicle by touch or vision, and feeds back to the operation of the steering handle to turn the vehicle in a desired manner. In other words, since the turning angle of the front wheels with respect to the steering wheel operation by the driver is a physical quantity that cannot be perceived by humans, the turning angle that is directly determined by the driver's steering operation is the driver's perception. It was not determined according to the characteristics, and this made it difficult to drive the vehicle.

  Further, in the above-described conventional apparatus, the determined turning angle is corrected according to the difference between the target yaw rate calculated using the detected vehicle speed and the detected steering wheel angle, and the detected actual yaw rate. This is merely correction of the turning angle in consideration of the behavior state of the vehicle, and does not determine the turning angle according to the yaw rate that the driver will perceive by operating the steering wheel. Accordingly, in this case as well, the turning angle determined for the driver's steering operation is not determined in accordance with the driver's perceptual characteristics, making it difficult to drive the vehicle.

  Further, in the above-described conventional device, a steering characteristic suitable for traveling from a low speed region to a high speed region is obtained by continuously changing a transmission ratio representing a ratio of the steering angle and the turning angle according to the detected vehicle speed. I try to get it. By the way, for example, in the case where the vehicle is parked in a garage or in parallel parking, the driver operates the steering wheel while moving the vehicle at a low speed (slow speed). In this way, when the vehicle is moving at a low speed (slow speed), the driver determines the steering angle of the front wheel that cannot be perceived by humans by operating the steering wheel based on the surrounding situation obtained from vision. This makes it difficult to drive the vehicle. For this reason, when the vehicle is moving at a low speed (slow speed), it is desired that the front wheels (steered wheels) steer with good responsiveness to the steering operation of the steering wheel.

JP 2000-85604 A Japanese Patent Laid-Open No. 11-124047

  In order to cope with the above problem, the present inventors have worked on research on a vehicle steering apparatus that can steer a vehicle in accordance with human perceptual characteristics in response to a steering wheel operation by a driver. Regarding such human perception characteristics, according to Weber-Fechner's law, it is said that the human sensory quantity is proportional to the logarithm of the physical quantity of the given stimulus. In other words, if the physical quantity of a stimulus given to a human being is changed exponentially with respect to the human operating quantity, the relationship between the operating quantity and the physical quantity can be matched to the human perceptual characteristics. The present inventors have applied the Weber-Hefner's law to a vehicle steering system and discovered the following.

  When driving a vehicle, the vehicle turns by operating the steering handle, and the vehicle's motion state quantities such as lateral acceleration, yaw rate, and turning curvature change as the vehicle turns, and the driver senses the motion state quantity of the vehicle. And it feels more visually. Accordingly, if the amount of motion state of the vehicle that can be perceived by the driver is changed exponentially with respect to the driver's operation on the steering wheel, the driver's operation on the steering wheel is not changed by the driver. The vehicle can be operated according to the perceptual characteristics.

  The present invention is based on the above discovery, and its purpose is to make the vehicle easier to drive by steering the vehicle in accordance with human perceptual characteristics in response to the operation of the steering wheel by the driver, and at low speed. Accordingly, it is an object of the present invention to provide a vehicle steering apparatus that can improve steering response.

In order to achieve the above object, the present invention is characterized in that a steering handle operated by a driver to steer a vehicle, a reaction force actuator that applies a reaction force to the steering handle, and a steered wheel is steered. A steering-by-wire vehicle steering apparatus comprising: a steering actuator for controlling the steering wheel to steer a steered wheel by drivingly controlling the steering actuator according to an operation of the steering handle. The rudder control device relates to a displacement amount sensor for detecting a displacement amount of the steering handle, an operation force converting means for converting the detected displacement amount to an operation force applied to the steering handle, and turning of the vehicle. if the driver represents the operation state quantity of the vehicle that may be perceived Te, a predetermined Weber ratio relating to the motion state quantity predetermined for said operating force Weber Expect the anticipated motion state quantity of the vehicle that is defined as a power function of the operating force, the motion state quantity calculating means for calculating using the converted operation force, which is the calculated to index a value obtained by dividing the ratio Steering angle calculation means for calculating the turning angle of the steered wheels necessary for the vehicle to move with the motion state quantity using the calculated expected motion state quantity, and vehicle speed detection means for detecting the vehicle speed of the vehicle Vehicle speed determination means for determining whether or not the detected vehicle speed is equal to or lower than a predetermined vehicle speed, and when the vehicle speed determination means determines that the vehicle speed of the vehicle is equal to or lower than a predetermined vehicle speed, the amount of displacement relative to the steering handle And a linear turning angle calculation means for calculating a turning angle having a predetermined linear relationship using the detected displacement amount , and controlling the turning actuator according to the calculated turning angle. The steered wheel It lies in the configuration with a steering control means for steering the steering angle which is the calculated.

In this case, the predetermined linear relationship is a linear relationship in which the turning angle is the maximum turning angle at which the steered wheels can be steered with respect to the maximum amount of displacement that can be input to the steering handle of the driver. There should be. Moreover, anticipated motion state quantity calculated by the pre Kiun dynamic state quantity changing means, the lateral acceleration of the vehicle, may is one of a yaw rate and turning curvature.

In the present invention configured as described above, first, when the vehicle is traveling at a vehicle speed greater than a predetermined vehicle speed (during normal traveling), the operating force of the driver with respect to the steering wheel is related to the turning of the vehicle. The operation force representing a vehicle motion state that can be perceived by the driver and having an index obtained by dividing a predetermined Weber ratio related to the motion state amount by a predetermined Weber ratio related to the operation force. It is converted into a predicted motion state quantity (lateral acceleration, yaw rate, turning curvature, etc.) of the vehicle defined as a power function of . Then, based on the converted expected motion state quantity, the turning angle of the steered wheel necessary for the vehicle to move with the expected motion state quantity is calculated, and the steered wheel is added to the calculated turning angle. Steered. Therefore, when the vehicle turns by turning the steered wheels, the driver is given the expected motion state quantity as the “physical quantity of the applied stimulus” according to the Weber-Hefner law. Then, the anticipated motion state quantity, since it is intended to change in the base Ki-th power relationship to the operation force of the steering wheel, the driver, while perceiving the motion state quantity that matches the human perception characteristics, steering The handle can be operated. The lateral acceleration and yaw rate can be sensed tactilely by the driver in contact with each part in the vehicle. Further, the turning curvature can be visually perceived by the driver due to changes in the situation within the field of view of the vehicle. As a result, according to the present invention, the driver can operate the steering wheel in accordance with human perceptual characteristics, so that driving of the vehicle is simplified.

Further, when the vehicle is moving at a predetermined vehicle speed or lower, for example, when the driver is moving the vehicle at a low speed (slow speed) for garage parking or parallel parking , A steered angle is calculated based on the amount of displacement and a predetermined linear relationship, and the steered wheels are steered to the calculated steered angle. As a result, it is possible to ensure good responsiveness of the turning operation with respect to the displacement amount of the steering wheel of the driver, which is required when the vehicle is moving at a low speed (slow speed). That is, the turning angle of the steered wheels can be changed linearly with respect to the displacement amount of the steering wheel by calculating the turning angle with respect to the displacement amount of the steering wheel by the driver based on a predetermined linear relationship. it can. Accordingly, the driver can easily estimate the turning angle based on the amount of displacement with respect to the steering wheel, so that driving is easy even when the vehicle is moving at a low speed (slow speed). .

In addition, when the vehicle is moving at a low speed (slow speed), if the turning angle is calculated based on the Weber-Hefner's law as in normal driving, the steering with respect to the operating force is performed as described above. the change Gabe-out power of the relationship of the corner. For this reason, depending on the amount of displacement input by the driver, a turning angle smaller than the turning angle requested by the driver may be calculated. On the other hand, the turning angle is calculated based on a predetermined linear relationship, in particular, a linear relationship in which the turning angle of the steered wheels is the maximum value with respect to the maximum displacement amount of the steering wheel by the driver. Thus, the steered wheels can be steered at a steered angle larger than that during normal travel with the same displacement . Accordingly, the amount of steering wheel operation by the driver is reduced, and the steered wheels can be steered with high responsiveness (quickly), and the vehicle can be easily driven during low speed (slow speed) movement.

  Hereinafter, a vehicle steering apparatus according to an embodiment of the present invention will be described with reference to the drawings. FIG. 1 schematically shows a vehicle steering apparatus according to this embodiment.

  The steering apparatus includes a steering handle 11 as an operation unit that is turned by a driver to steer left and right front wheels FW1 and FW2 as steered wheels. The steering handle 11 is fixed to the upper end of the steering input shaft 12, and the lower end of the steering input shaft 12 is connected to a reaction force actuator 13 including an electric motor and a speed reduction mechanism. The reaction force actuator 13 applies a reaction force to the turning operation of the steering handle 11 by the driver.

  In addition, the steering device includes a steering actuator 21 including an electric motor and a speed reduction mechanism. The turning force by the turning actuator 21 is transmitted to the left and right front wheels FW1 and FW2 via the turning output shaft 22, the pinion gear 23, and the rack bar 24. With this configuration, the rotational force from the steering actuator 21 is transmitted to the pinion gear 23 via the steering output shaft 22, and the rack bar 24 is displaced in the axial direction by the rotation of the pinion gear 23. Due to the displacement in the axial direction, the left and right front wheels FW1, FW2 are steered left and right.

  Next, an electric control device that controls the operation of the reaction force actuator 13 and the steering actuator 21 will be described. The electric control device includes a steering angle sensor 31, a turning angle sensor 32, a vehicle speed sensor 33, and a lateral acceleration sensor 34.

  The steering angle sensor 31 is assembled to the steering input shaft 12, detects the rotation angle from the neutral position of the steering handle 11, and outputs it as the steering angle θ. The steered angle sensor 32 is assembled to the steered output shaft 22, detects the rotational angle from the neutral position of the steered output shaft 22, and corresponds to the actual steered angle δ (the steered angle of the left and right front wheels FW1, FW2). ). Note that the steering angle θ and the actual turning angle δ are represented by setting the neutral position to “0”, the left rotation angle as a positive value, and the right rotation angle as a negative value. The vehicle speed sensor 33 detects and outputs the vehicle speed V. The lateral acceleration sensor 34 detects and outputs the actual lateral acceleration G of the vehicle. The actual lateral acceleration G also represents leftward acceleration as positive and rightward acceleration as negative.

  These sensors 31 to 34 are connected to the electronic control unit 35. The electronic control unit 35 includes a microcomputer including a CPU, a ROM, a RAM, and the like as main components, and controls the operations of the reaction force actuator 13 and the turning actuator 21 by executing a program. The ROM stores in advance a steering characteristic changing program, which will be described later, and the electronic control unit 35 (specifically, the CPU) executes each step of the program and changes the steering characteristic according to the vehicle speed V. . Drive circuits 36 and 37 for driving the reaction force actuator 13 and the steering actuator 21 are connected to the output side of the electronic control unit 35, respectively. In the drive circuits 36 and 37, current detectors 36a and 37a for detecting a drive current flowing through the electric motor in the reaction force actuator 13 and the steering actuator 21 are provided. The drive current detected by the current detectors 36a and 37a is fed back to the electronic control unit 35 in order to control the drive of both electric motors.

  Next, regarding the steering device of the present embodiment configured as described above, first, regarding the steering operation of the device, the function block of FIG. 2 representing functions realized by computer program processing in the electronic control unit 35. This will be described with reference to the drawings. The electronic control unit 35 includes a reaction force control unit 40 for controlling the reaction force applied to the steering handle 11, and the left and right front wheels FW1 and FW2 corresponding to the driver's sensory characteristics based on the turning operation of the steering handle 11. A sensory adaptation control unit 50 for determining the target turning angle δd and a steering control unit 60 for controlling the steering of the left and right front wheels FW1, FW2 based on the target turning angle δd.

When the steering handle 11 is turned by the driver, the steering angle sensor 31 detects the steering angle θ, which is the rotation angle of the steering handle 11, and uses the detected steering angle θ as the reaction force control unit 40 and the sense. Each is output to the matching control unit 50. In the reaction force control unit 40, the displacement-torque conversion unit 41 calculates a reaction force torque Tz that is an exponential function of the steering angle θ by using the following equation (1).
Tz ＝ To ・ exp (K1 ・ θ)… Formula 1
However, To and K1 in the formula 1 are constants, and these values will be described in detail when the sensory adaptation control unit 50 described later is described. Further, the steering angle θ in the equation 1 represents the absolute value of the detected steering angle θ. If the detected steering angle θ is positive, the constant To is set to a negative value, and the detected steering angle θ is If negative, the constant To is a positive value having the same absolute value as the negative constant To. Here, it is also possible to calculate the reaction force torque Tz using a conversion table having characteristics as shown in FIG. 3 in which the reaction force torque Tz with respect to the steering angle θ is stored, instead of the calculation of the equation (1). For this reason, in the description of the steering characteristic change program described in detail later in this specification, the conversion table will be used.

  The calculated reaction force torque Tz is supplied to the drive control unit 42. The drive control unit 42 inputs a drive current flowing from the drive circuit 36 to the electric motor in the reaction force actuator 13 and feedback-controls the drive circuit 36 so that a drive current corresponding to the reaction force torque Tz flows through the electric motor. . By the drive control of the electric motor in the reaction force actuator 13, the electric motor applies a reaction force torque Tz to the steering handle 11 via the steering input shaft 12. Therefore, the driver feels the reaction force torque Tz that changes exponentially with respect to the steering angle θ, in other words, while applying a steering torque equal to the reaction force torque Tz to the steering handle 11, It will rotate. The relationship between the steering angle θ and the reaction torque Tz also follows the above-mentioned Weber-Hefner law, and the driver rotates the steering handle 11 while receiving a sense from the steering handle 11 that matches human perception characteristics. Can be operated.

On the other hand, with respect to the steering angle θ input to the sensory adaptation control unit 50, the displacement-torque conversion unit 51 calculates the steering torque Td according to the following equation 2 similar to the equation 1.
Td ＝ To ・ exp (K1 ・ θ)… Formula 2
Also in this case, To and K1 in the formula 2 are constants similar to those in the formula 1. However, the steering angle θ in Equation 2 represents the absolute value of the detected steering angle θ. If the detected steering angle θ is positive, the constant To is set to a positive value, and the detected steering angle is If θ is negative, the constant To is a negative value having the same absolute value as the positive constant To. Here, in this case as well, the steering torque Td may be calculated using a conversion table having characteristics as shown in FIG. 3 in which the steering torque Td with respect to the steering angle θ is stored, instead of the calculation of the expression 2. Good. For this reason, in the description of the steering characteristic change program described in detail later in this specification, the conversion table will be used.

The calculated steering torque Td is supplied to the torque-lateral acceleration conversion unit 52. If the absolute value of the steering torque Td is less than a predetermined positive value To, the torque-lateral acceleration conversion unit 52 calculates the expected lateral acceleration Gd that the driver expects by turning the steering wheel 11 as follows: Thus, when the absolute value of the steering torque Td is not less than a predetermined positive value To, the expected lateral acceleration Gd, which is a power function of the steering torque Td, is calculated according to the following equation 4.
Gd = 0 (| Td | <To)… Formula 3
Gd = C · Td ^K2 (To ≦ | Td |) Equation 4
However, C and K2 in Formula 4 are constants. Further, the steering torque Td in the equation 4 represents the absolute value of the steering torque Td calculated using the equation 2, and if the calculated steering torque Td is positive, the constant C is a positive value. If the calculated steering torque Td is negative, the constant C is set to a negative value having the same absolute value as the positive constant C. In this case as well, the steering torque Td may be calculated using a conversion table having characteristics as shown in FIG. 4 in which the expected lateral acceleration Gd with respect to the steering torque Td is stored, instead of the calculations of the equations 3 and 4. Is possible. For this reason, in the description of the steering characteristic change program described in detail later in this specification, the conversion table will be used.

Here, Formula 4 will be described. When the steering torque Td is eliminated using the above equation 2, the following equation 5 is obtained.
Gd = C (To · exp (K1 · θ)) ^K2 = C · To ^K2 · exp (K1, K2 · θ) = Go · exp (K1, K2 · θ)
In Equation 5, Go is a constant C · To ^K2 , and Equation 5 indicates that the expected lateral acceleration Gd varies exponentially with respect to the steering angle θ of the steering wheel 11 by the driver. The expected lateral acceleration Gd is a physical quantity that can be perceived by the driver due to the contact of a part of the driver's body with a predetermined part in the vehicle, and follows the aforementioned Weber-Hefner law. Therefore, if the driver can turn the steering handle 11 while perceiving a lateral acceleration equal to the expected lateral acceleration Gd, the relationship between the turning operation of the steering handle 11 and the steering of the vehicle can be expressed by human perception characteristics. It can be made to correspond.

As described above, the expected lateral acceleration Gd shown in the equation 4 (that is, the equation 5) changes exponentially with respect to the steering angle θ, which is the operation amount of the steering wheel 11, and thus the human perception specification is performed. It is suitable for. Further, the simplest method for the turning operation of the steering handle 11 by the driver is to turn the steering handle 11 at a constant speed ω (θ = ω · t). The acceleration Gd changes exponentially with respect to time t as shown in the following equation (6). Therefore, it will be understood that if the steering handle 11 can be rotated while perceiving a lateral acceleration equal to the expected lateral acceleration Gd, the driver can easily rotate the steering handle 11.
Gd = Go · exp (K0 · ω · t) ... Equation 6
However, K0 is a constant having a relationship of K0 = K1 · K2.

Further, as shown in Equation 3, when the steering torque Td is less than the predetermined value To, the expected lateral acceleration Gd is kept at “0”. This is because, even when the steering angle θ is “0”, that is, when the steering wheel 11 is kept at the neutral position, the steering torque Td becomes a positive predetermined value To by the calculation of the above equation 2, and this steering torque Td If (= To) is applied to the calculation of Equation 4, the expected lateral acceleration Gd becomes a positive value C · To ^K2 , which is not realistic. However, as described above, if the steering torque Td is less than the predetermined value To, the expected lateral acceleration Gd is “0”, so this problem is solved.

In this case, the minimum steering torque that can be perceived by the driver is the predetermined value To, the minimum perceived lateral acceleration that the driver can perceive is Go, and the predetermined value To has a relationship of Go = C · To ^K2. By doing so, the expected lateral acceleration Gd of the vehicle until the steering torque Td reaches a predetermined value To, that is, until the driver feels the lateral acceleration generated in the vehicle by turning the vehicle by operating the steering handle 11. Is kept at “0”. According to this, only when the steering handle 11 is steered at the minimum steering torque To or more, the left and right front wheels FW1, FW2 are steered by the steered angle required to generate the expected lateral acceleration Gd. Will correspond exactly to the steering of the vehicle.

  Next, how to determine the parameters K1, K2, and C (predetermined values K1, K2, and C) used in the expressions 1 to 6 will be described. In the description of how to determine the parameters K1, K2, and C, the steering torque Td and the expected lateral acceleration Gd in the expressions 2 to 6 are handled as the steering torque T and the lateral acceleration G. According to the aforementioned Weber-Hefner law, “the ratio ΔS / S between the minimum physical quantity change ΔS perceivable by humans and the physical quantity S at that time is constant regardless of the value of the physical quantity S, and the ratio ΔS / S is called the Weber ratio. The present inventors confirmed that the above-mentioned Weber-Hefner's law is established with respect to steering torque and lateral acceleration, and in order to determine the Weber ratio, the following experiments were conducted for men and women, age, and vehicle driving. I went to various people with different histories.

  Regarding the steering torque, a torque sensor is assembled to the steering handle of the vehicle, a test torque is applied to the steering handle from the outside, and the test torque is changed in various manners, and a human being resists this test torque. Measured the human's ability to adjust the steering torque to adjust the steering handle so that it does not rotate by applying an operating force to the steering handle. That is, in the above situation, when the detected operation torque at a certain time is T, and the minimum steering torque change amount that can be perceived as a change from the detected steering torque T is ΔT, the ratio value ΔT / T, that is, Weber The ratio was measured for various humans. According to this experimental result, the Weber ratio ΔT / T was approximately constant 0.03 regardless of the operation direction of the steering wheel, the state of the hand holding the steering wheel, and the magnitude and direction of the inspection torque. .

  Regarding the lateral acceleration, a wall member is provided on the side of the driver's seat, and a force sensor for detecting the pressing force of the human shoulder is assembled to the wall member. The wall member is made to contact the wall member against the inspection force while applying the inspection force to the wall member from the outside in the lateral direction and changing the inspection force in various modes. It was adjusted so that the wall member does not move by pushing, that is, the human side force adjustment ability to maintain the posture was measured. That is, under the above situation, F is the detection force that can withstand lateral force from the outside at a certain time and maintain the posture, and the minimum force change amount ΔF that can perceive the change from the detection force F The ratio value ΔF / F, the Weber ratio, was measured for various humans. According to the results of this experiment, the Weber ratio ΔF / F was a substantially constant value of about 0.09 regardless of the magnitude and direction of the reference force applied to the wall member.

On the other hand, when the formula 2 is differentiated and the formula 2 is considered in the differentiated formula, the following formula 7 is established.
ΔT ＝ To ・ exp (K1 ・ θ) ・ K1 ・ Δθ = T ・ K1 ・ Δθ
When the equation 7 is modified and the Weber ratio ΔT / T related to the steering torque obtained by the experiment is Kt, the following equation 8 is established.
K1 = ΔT / (T · Δθ) = Kt / Δθ Equation 8

If the maximum steering torque is Tmax, the following formula 9 is established from the above formula 2.
Tmax ＝ To ・ exp (K1 ・ θmax) ... Equation 9
If Equation 9 is modified, the following Equation 10 is established.
K1 = log (Tmax / To) / θmax Equation 10
Then, the following formula 11 is derived from the formula 8 and the formula 10.
Δθ = Kt / K1 = Kt · θmax / log (Tmax / To) (Formula 11)
In Equation 11, Kt is the Weber ratio of the steering torque T, θmax is the maximum value of the steering angle, Tmax is the maximum value of the steering torque, and To is the minimum steering torque that can be perceived by humans as described above. Since these values Kt, θmax, Tmax, and To are constants determined by experiments and systems, the differential value Δθ can be calculated using the equation (11). Then, a predetermined value (coefficient) K1 can also be calculated based on Equation 8 using the differential value Δθ using the Weber ratio Kt.

In addition, when the expression 4 is differentiated and the expression 4 is considered in the differentiated expression, the following expression 12 is established.
ΔG = C ・ K2 ・ T ^K2-1 ΔT = G ・ K2 ・ ΔT / T
When Expression 12 is modified and the Weber ratio ΔT / T related to the steering torque obtained by the experiment is set to Kt and the Weber ratio ΔF / F related to the lateral acceleration is set to Ka, the following Expressions 13 and 14 are established.
ΔG / G = K2 · ΔT / T Equation 13
K2 = Ka / Kt ... Formula 14
In this equation 14, Kt is the Weber ratio related to the steering torque, and Ka is the Weber ratio related to the lateral acceleration, both of which are given as constants. Therefore, using these Weber ratios Kt and Ka, the above equation is used. 14 can also calculate the coefficient K2.

If the maximum value of the lateral acceleration is Gmax and the maximum value of the steering torque is Tmax, the following equation 15 is derived from the equation 4.
C = Gmax / Tmax ^K2 Equation 15
In Equation 15, Gmax and Tmax are constants determined by experiments and systems, and K2 is calculated by Equation 14, so that a constant (coefficient) C can also be calculated.

  As described above, the maximum value θmax of the steering angle θ, the maximum value Tmax of the steering torque T, the maximum value Gmax of the lateral acceleration G, the minimum steering torque To, the minimum sensed lateral acceleration Go, the Weber ratio Kt and the lateral acceleration relating to the steering torque T. If the Weber ratio Ka is determined by experiment and system, the coefficients K1, K2, and C in the equations 1 to 5 can be determined in advance by calculation. Accordingly, in the displacement-torque conversion units 41 and 51 and the torque-lateral acceleration conversion unit 52, the reaction force torque Tz, the steering torque Td, and the expected lateral acceleration that match the driver's perceptual characteristics are obtained using the equations 1-5. Gd can be calculated.

  Returning to the description of FIG. 2 again, the expected lateral acceleration Gd calculated by the torque-lateral acceleration conversion unit 52 is supplied to the turning angle conversion unit 53. The turning angle conversion unit 53 calculates the target turning angle δd of the left and right front wheels FW1 and FW2 necessary for generating the expected lateral acceleration Gd, and changes according to the vehicle speed V as shown in FIG. And a table representing a change characteristic of the target turning angle δd with respect to the expected lateral acceleration Gd. This table is a set of data collected by running the vehicle while changing the vehicle speed V and actually measuring the turning angle δ and the lateral acceleration G of the left and right front wheels FW1, FW2. Then, the turning angle conversion unit 53 refers to this table and calculates a target turning angle δd corresponding to the input expected lateral acceleration Gd and the detected vehicle speed V input from the vehicle speed sensor 33. Further, the lateral acceleration G (expected lateral acceleration Gd) and the target turning angle δd stored in the table are both positive, but the expected lateral acceleration Gd supplied from the turning angle conversion unit 53 is negative. In this case, the output target turning angle δd is also negative.

Since the target turning angle δd is a function of the vehicle speed V and the lateral acceleration G as shown in the following formula 16, it can be calculated by executing the calculation of the following formula 16 instead of referring to the table. it can.
δd = L · (1 + A · V ² ) · Gd / V ² Equation 16
However, L in said Formula 16 is a predetermined value which shows the wheel base of a vehicle, and A is a predetermined value which was decided beforehand.

The calculated target turning angle δd is supplied to the turning angle correction unit 61 of the turning control unit 60. The turning angle correction unit 61 receives the expected lateral acceleration Gd from the torque-lateral acceleration conversion unit 52 and also the actual lateral acceleration G detected by the lateral acceleration sensor 34, and calculates the following equation (17). The corrected target turning angle δda is calculated by correcting the inputted target turning angle δd.
δda = δd + K3 · (Gd−G) Equation 17
However, the coefficient K3 is a predetermined positive constant. When the actual lateral acceleration G is less than the expected lateral acceleration Gd, the coefficient K3 is corrected so that the absolute value of the corrected target turning angle δda is increased. . When the actual lateral acceleration G exceeds the expected lateral acceleration Gd, the absolute value of the corrected target turning angle δda is corrected to be smaller. By this correction, the target turning angle δd of the left and right front wheels FW1, FW2 necessary for the expected lateral acceleration Gd is ensured with higher accuracy.

  The calculated corrected target turning angle δda is supplied to the drive control unit 62. The drive control unit 62 inputs the actual turning angle δ detected by the turning angle sensor 32, and electrically drives the turning actuator 21 so that the left and right front wheels FW1, FW2 are turned to the corrected target turning angle δda. Feedback control of motor rotation. The drive control unit 62 also receives a drive current that flows from the drive circuit 37 to the electric motor in the steering actuator 21, and drives the electric motor so that a drive current having a magnitude corresponding to the steering torque flows appropriately. The circuit 37 is feedback controlled. By the drive control of the electric motor in the steering actuator 21, the rotation of the electric motor is transmitted to the pinion gear 23 via the steering output shaft 22, and the rack bar 24 is displaced in the axial direction by the pinion gear 23. As the rack bar 24 is displaced in the axial direction, the left and right front wheels FW1 and FW2 are steered to the corrected target turning angle δda.

  Next, a steering characteristic change program for changing the steering characteristic based on the vehicle speed V input from the vehicle speed sensor 33 by the electronic control unit 35 will be described in detail with reference to the flowchart shown in FIG. When the driver turns an ignition switch (not shown) into an “ON” state, the steering characteristic changing program starts executing in step S10 and is repeatedly executed every predetermined short time.

  Then, the electronic control unit 35 inputs the vehicle speed V of the vehicle from the vehicle speed sensor 33, and determines whether or not the current vehicle speed V is higher than a predetermined vehicle speed in step S11. That is, in step S11, if the vehicle speed V of the current vehicle is higher than the predetermined vehicle speed, it is determined as “Yes”, each step after step S12 is executed, and the driver's steering sensation characteristics during normal traveling are determined. Steering characteristics compatible with Since the steering characteristics during normal running are steering characteristics according to the above-mentioned Weber-Hefner law, detailed description from step S12 to step S14 shown below is omitted.

  In step S <b> 12, the electronic control unit 35 calculates a steering torque Td (reaction torque Tz) with respect to the steering angle θ of the steering handle 11 detected by the steering angle sensor 31. That is, the electronic control unit 35 calculates the steering torque Td (reaction force torque Tz) with respect to the steering angle θ using the conversion table shown in FIG. 3, and proceeds to step S13. In step S13, the electronic control unit 35 calculates the expected lateral acceleration Gd expected by the driver based on the steering torque Td calculated in step S12. That is, the electronic control unit 35 calculates the expected lateral acceleration Gd with respect to the steering torque Td using the conversion table shown in FIG. 4, and proceeds to step S14.

  In step S14, the electronic control unit 35 calculates a target turning angle δd corresponding to the expected lateral acceleration Gd calculated in step S13 and the vehicle speed V input from the vehicle speed sensor 33. That is, the electronic control unit 35 uses the conversion table shown in FIG. 5 to calculate the target turning angle δd for the expected lateral acceleration Gd, proceeds to step S16, and temporarily ends the execution of the steering characteristic changing program. Then, the electronic control unit 35 corrects the calculated target turning angle δd to calculate the corrected target turning angle δda, and the left and right front wheels FW1, FW1, so that the actual turning angle δ becomes the corrected target turning angle δda. Steering control of FW2 is performed.

  On the other hand, if the current vehicle speed V is equal to or lower than the predetermined vehicle speed in step S11, the electronic control unit 35 determines “No”, proceeds to step S15, and changes the steering characteristic to the steering characteristic suitable for the low speed region. change. Hereinafter, the steering characteristic changing process in step S15 will be described in detail.

  When the vehicle is moving in a very low speed region that is equal to or lower than a predetermined vehicle speed, for example, the driver may be placing the vehicle in a garage or performing parallel parking. As the steering characteristics required when the vehicle is moving in this way, the left and right front wheels FW1 and FW2 as steered wheels are steered with high responsiveness (so-called, quickly) to the driver's operation of the steering handle 11. Steering characteristics. In other words, in the slow speed region, a steering characteristic is required in which the actual turning angle δ is larger than the actual turning angle δ during normal traveling with respect to the steering angle θ input by the driver via the steering handle 11. .

  For this reason, when the steering characteristic at the time of normal driving is applied while the vehicle is moving in the slow speed region, the steering characteristic is not adapted to the driver's steering feeling. That is, the steering characteristic during normal driving is a steering characteristic in which the actual turning angle δ varies exponentially (or exponentially) with respect to the steering angle θ according to the Weber-Hefner law. Becomes smaller than the actual turning angle δ required by the driver, and does not conform to the steering feeling of the driver. More specifically, the target turning angle δd during normal running changes exponentially (or exponentially) and increases as the vehicle speed V decreases, as is apparent from Equation 16 and FIG. It has characteristics.

  For this reason, the corrected target turning angle δda (actual turning angle δ) calculated based on the target turning angle δd also changes exponentially (or exponentially) and increases as the vehicle speed V decreases. Have Then, in a low speed region (including the very low speed region) smaller than a certain vehicle speed V, the actual turning angle δ is set to the maximum steering angle θmax (hereinafter, this maximum value is maximized) on the steering wheel 11 as shown in FIG. When the steering angle θmax is input, the maximum value δmax of the actual turning angle (hereinafter, this maximum value is referred to as the maximum actual turning angle δmax) can be obtained. However, if the driver turns the steering wheel 11 until the maximum steering angle θmax is reached, the left and right front wheels FW1 and FW2 are steered so as to have the maximum actual steering angle δmax, but the maximum steering angle θmax is exceeded. When a small steering angle θ1 is input, the actual turning angle δ1 is exponentially small (exponential function).

  For this reason, if the electronic control unit 35 determines that the current vehicle speed V is in the low speed region, particularly the slow speed region, the electronic control unit 35 employs a proportional map in which the steering angle θ and the actual turning angle δ have a linear relationship. This proportional map has a characteristic that the actual turning angle δ increases as the steering angle θ increases, and can be expressed as δ = Kθ. Here, the proportional constant K is K = δmax / θmax because the left and right front wheels FW1, FW2 are steered so as to have the maximum actual turning angle δmax when the steering handle 11 rotates to the maximum steering angle θmax. It is represented by As a result, it is possible to obtain a steering characteristic in which the actual turning angle δ changes linearly to the maximum actual turning angle δmax as the steering handle 11 is turned to the maximum steering angle θmax.

  In addition, by adopting this proportional map, when the steering angle θ1 is input, the actual turning angle δ can be set to an actual turning angle δ2 that is larger than the actual turning angle δ1. Here, as shown in FIG. 7, if the steering characteristics during normal travel are applied when the vehicle speed V is in the very low speed region, the steering angle δ2 is set to the actual turning angle δ2. It is necessary to rotate the steering handle 11 until the steering angle θ2 becomes larger than the steering angle θ1. Therefore, by adopting the proportional map in the slow speed region, the turning angle δ with respect to the same steering angle θ can be increased as compared to during normal travel, and the steering characteristics required by the driver in the slow speed region can be obtained. it can. Further, the amount of operation of the steering wheel 11 by the driver can be reduced.

  Thus, when the electronic control unit 35 adopts the proportional map in step S15, the execution of the steering characteristic changing program is once terminated in step S16. Then, the electronic control unit 35 calculates the actual turning angle δ that is linearly related to the steering angle θ input by the driver based on the proportional map that has been adopted, and the actual rotation that has calculated the left and right front wheels FW1, FW2. The steering is controlled so that the steering angle δ is obtained.

  That is, when the steering angle θ is input from the steering angle sensor 31, the electronic control unit 35 determines the actual turning angle δ based on the proportional map. Then, the electronic control unit 35 operates the turning actuator 21 via the drive circuit 37 so that the left and right front wheels FW1 and FW2 are steered to the actual turning angle δ determined. With the operation of the steering actuator 21, the rotational force of the actuator 21 is transmitted to the steering output shaft 22, the pinion gear 23, and the rack bar 24 so that the left and right front wheels FW1, FW2 become the actual steering angle δ. Steered.

  As can be understood from the above description, according to the present embodiment, the steering angle θ as an operation input value of the driver with respect to the steering handle 11 is converted into the steering torque Td by the displacement-torque conversion unit 51 during normal traveling. At the same time, the converted steering torque Td is converted into the expected lateral acceleration Gd by the torque-lateral acceleration conversion unit 52, and the left and right front wheels are converted by the turning angle conversion unit 53, the turning angle correction unit 61, and the drive control unit 62. FW1 and FW2 are steered to the corrected target turning angle δda necessary for generating the expected lateral acceleration Gd.

  In this case, since the steering torque Td is equal to the reaction force torque Tz, it is a physical quantity that can be perceived by the driver from the steering wheel 11 due to the action of the reaction force actuator 13 and changes exponentially with respect to the steering angle θ. Therefore, the driver can turn the steering handle 11 according to human perceptual characteristics while feeling a reaction force according to Weber-Hefner's law. The actual lateral acceleration G generated in the vehicle by turning the left and right front wheels FW1 and FW2 is a physical quantity that can be perceived, and the actual lateral acceleration G is controlled to be equal to the expected lateral acceleration Gd. Further, the expected lateral acceleration Gd also changes exponentially with respect to the steering angle θ input by the driver (exponentially by changing Expression 4 to Expression 5). Accordingly, the driver can turn the steering wheel 11 by turning the steering handle 11 according to the human perceptual characteristic while feeling the lateral acceleration according to the Weber-Hefner law. As a result, the driver can operate the steering handle 11 in accordance with human perceptual characteristics, and thus driving of the vehicle is simplified.

  Further, the turning angle correction unit 61 corrects the target turning angle δd so that the actual lateral acceleration G actually generated in the vehicle accurately corresponds to the steering angle θ of the steering handle 11, so that the vehicle An actual lateral acceleration G accurately corresponding to the steering angle θ of the steering handle 11 is generated. As a result, the driver can operate the steering wheel 11 while perceiving the lateral acceleration more accurately according to the human perceptual characteristics, so that the driving of the vehicle becomes easier.

  When the vehicle is moving at a predetermined vehicle speed or less, the turning angle δ with respect to the steering angle θ input by the driver can be calculated based on a predetermined linear relationship, that is, a proportional map. Accordingly, the turning angle δ of the left and right front wheels FW1, FW2 can be linearly changed with respect to the input steering angle θ. As a result, the driver can easily estimate the turning angle δ based on the steering angle θ input to the steering handle 11, so that driving of the vehicle in the very low speed region is simplified.

  Further, since the proportional map is determined to be the maximum turning angle δmax that can steer the left and right front wheels FW1 and FW2 with respect to the maximum steering angle θmax that can turn the steering handle 11, the same steering angle The left and right front wheels FW1, FW2 can be steered at θ with a larger turning angle δ than when traveling normally. Accordingly, the amount of operation of the steering wheel 11 by the driver can be reduced, the left and right front wheels FW1, FW2 can be steered with high responsiveness, and the driving when the vehicle moves at a low speed can be simplified.

First Modification The steering characteristic changing program in the above embodiment is applied to a steering apparatus that employs lateral acceleration as a motion state quantity. Instead of this, the steering characteristic changing program can be applied to a steering apparatus that employs a yaw rate as a motion state quantity. Hereinafter, this first modification will be described. In the first modification, as shown by a broken line in FIG. 1, the steering device detects an actual yaw rate γ, which is a motion state quantity that can be perceived by the driver, instead of the lateral acceleration sensor 34 in the above embodiment. A yaw rate sensor 38 is provided. Other configurations are the same as those in the above embodiment, but the computer program executed by the electronic control unit 35 is slightly different from that in the above embodiment with respect to the turning operation. Further, the steering characteristic change program applied to the steering device that uses the yaw rate according to the first modification as the motion state quantity is the same as the steering characteristic change program of the above-described embodiment, and thus detailed description thereof is omitted.

  In the first modification, the computer program executed by the electronic control unit 35 with respect to the steering operation is shown in the functional block diagram of FIG. In this case, in the sensory adaptation control unit 50, the displacement-torque conversion unit 51 functions in the same manner as in the above embodiment, but a torque-yaw rate conversion unit 54 is provided instead of the torque-lateral acceleration conversion unit 52 in the above embodiment. ing.

The torque-yaw rate conversion unit 54 uses the steering torque Td calculated by the displacement-torque conversion unit 51 to calculate the expected yaw rate γd that the driver expects from the turning operation of the steering handle 11 to the steering torque Td. If the absolute value is less than the positive small predetermined value To, the value is set to “0” as shown in the following equation 18;
γd = 0 (| Td | <To) Equation 18
γd = C · Td ^K2 (To ≦ | Td |) Equation 19
However, C and K2 in Equation 19 are constants as in the above embodiment. Also in this case, the steering torque Td in the equation 19 represents the absolute value of the steering torque Td calculated using the above equation 2. If the calculated steering torque Td is positive, the constant C Is a positive value, and if the calculated steering torque Td is negative, the constant C is a negative value having the same absolute value as the positive constant C. In this case, the expected yaw rate γd may be calculated using a conversion table having characteristics as shown in FIG. 9 in which the expected yaw rate γd with respect to the steering torque Td is stored instead of the calculations of the equations 18 and 19. Good.

  Further, the turning angle conversion unit 55 calculates the target turning angle δd of the left and right front wheels FW1 and FW2 necessary for generating the expected yaw rate γd, and changes according to the vehicle speed V as shown in FIG. And a table representing the change characteristic of the target turning angle δd with respect to the expected yaw rate γd. This table is a set of data collected by actually measuring the turning angle δ and the yaw rate γ of the left and right front wheels FW1 and FW2 while running the vehicle while changing the vehicle speed V. Then, the turning angle conversion unit 55 calculates the target turning angle δd corresponding to the input expected yaw rate γd and the detected vehicle speed V input from the vehicle speed sensor 33 with reference to this table. Further, the yaw rate γ (expected yaw rate γd) and the target turning angle δd stored in the table are both positive, but if the expected yaw rate γd supplied from the turning angle conversion unit 55 is negative, The output target turning angle δd is also negative.

Since the target turning angle δd is a function of the vehicle speed V and the yaw rate γ as shown in the following equation 20, it can be calculated by executing the calculation of the following equation 20 instead of referring to the table. .
δd = L · (1 + A · V ² ) · γd / V Equation 20
In Equation 20, L is a predetermined value indicating the wheel base, and A is a predetermined value.

The calculated target turning angle δd is supplied to the turning angle correction unit 63 of the turning control unit 60. The turning angle correction unit 63 receives the expected yaw rate γd from the torque-yaw rate conversion unit 54 and also the actual yaw rate γ detected by the yaw rate sensor 38, and executes the calculation of the following equation (21). The corrected target turning angle δda is calculated by correcting the input target turning angle δd.
δda = δd + K4 · (γd−γ) Equation 21
However, the coefficient K4 is a predetermined positive constant, and when the actual yaw rate γ is less than the expected yaw rate γd, the coefficient K4 is corrected so that the absolute value of the corrected target turning angle δda becomes larger. When the actual yaw rate γ exceeds the expected yaw rate γd, the absolute value of the corrected target turning angle δda is corrected. By this correction, the turning angles of the left and right front wheels FW1, FW2 necessary for the expected yaw rate γd are more accurately ensured.

  Also in the first modified example, if the steering characteristic changing program shown in FIG. 6 is executed and the vehicle speed V is equal to or lower than the predetermined vehicle speed, the electronic control unit 35 adopts a proportional map in step S15. Here, when the yaw rate is employed as the motion state quantity, the target turning angle δd during normal traveling changes exponentially as apparent from the above equation 20 and FIG. It has a characteristic of increasing as the vehicle speed V increases, and is different from the characteristic of the target turning angle δd of the above embodiment. However, by determining that the vehicle is in the slow speed region in step S11, in order to adopt the proportional map in step S15, the actual turning angle δ determined in the slow speed region is the target turning during normal travel. It is not related to the characteristics of the steering angle δd. Therefore, also in the first modification, the same steering characteristic changing program as that in the above embodiment can be executed.

  The other program processing executed by the electronic control unit 35 is the same as that in the above embodiment. And in the functional block diagram of FIG. 8, the same code | symbol as FIG. 2 of the said embodiment is attached | subjected, and the description is abbreviate | omitted.

  In the first modified example described above, the steering angle θ as an operation input value of the driver with respect to the steering handle 11 is converted into the steering torque Td by the displacement-torque converter 51, and the converted steering torque is also converted. Td is converted to the expected yaw rate γd by the torque-yaw rate conversion unit 54, and the left and right front wheels FW1, FW2 are corrected to generate the expected yaw rate γd by the turning angle conversion unit 55, the turning angle correction unit 63, and the drive control unit 62. The vehicle is steered to the target turning angle δda. Also in this case, since the steering torque Td is equal to the reaction force torque Tz, it is a physical quantity that can be perceived by the driver from the steering handle 11 by the action of the reaction force actuator 13, and changes exponentially with respect to the steering angle θ. Therefore, the driver can turn the steering handle 11 according to the human perceptual characteristic while feeling the reaction force according to the Weber-Hefner law.

  Further, the yaw rate γ generated in the vehicle by the steering of the left and right front wheels FW1 and FW2 is a physical quantity that can be perceived, and the yaw rate γ is controlled to be equal to the expected yaw rate γd. It changes exponentially with respect to θ (exponentially by changing equation 19 in the same way as changing from equation 4 to equation 5 in the above embodiment). Therefore, the driver can turn the steering wheel 11 by turning the steering handle 11 according to the human perception characteristic while feeling the yaw rate according to the Weber-Hefner law. As a result, the driver can operate the steering handle 11 in accordance with the human perceptual characteristics, as in the case of the above-described embodiment, so that the driving of the vehicle is simplified.

  Further, the turning angle correction unit 61 corrects the target turning angle δd so that the actual lateral acceleration G actually generated in the vehicle accurately corresponds to the steering angle θ of the steering handle 11, so that the vehicle An actual lateral acceleration G accurately corresponding to the steering angle θ of the steering handle 11 is generated. As a result, the driver can operate the steering wheel 11 while perceiving the lateral acceleration more accurately according to the human perceptual characteristics, so that the driving of the vehicle becomes easier.

  When the vehicle is moving at a predetermined vehicle speed or less, the turning angle δ with respect to the steering angle θ input by the driver can be calculated based on a predetermined linear relationship, that is, a proportional map. Accordingly, the turning angle δ of the left and right front wheels FW1, FW2 can be linearly changed with respect to the input steering angle θ. As a result, the driver can easily estimate the turning angle δ based on the steering angle θ input to the steering handle 11, so that the driving of the vehicle in the slow speed region is simplified.

  Further, since the proportional map is determined to be the maximum turning angle δmax that can steer the left and right front wheels FW1 and FW2 with respect to the maximum steering angle θmax that can turn the steering handle 11, the same steering angle The left and right front wheels FW1, FW2 can be steered at θ with a larger turning angle δ than when traveling normally. Accordingly, the amount of operation of the steering wheel 11 by the driver can be reduced, the left and right front wheels FW1, FW2 can be steered with high responsiveness, and the driving when the vehicle moves at a low speed can be simplified.

Second Modification The steering characteristic change program in the above embodiment is applied to a steering apparatus that employs lateral acceleration as a motion state quantity. Further, the steering characteristic changing program in the first modified example is applied to a steering apparatus that employs a yaw rate as a motion state quantity. Instead of these, the present invention can also be applied to a steering apparatus that employs a turning curvature as a motion state quantity. Hereinafter, this second modification will be described. Also in the second modification, the steering device is configured as shown in FIG. 1 as in the above embodiment. However, regarding the turning operation, the computer program executed by the electronic control unit 35 is slightly different from that in the above embodiment. Further, the steering characteristic change program applied to the steering device having the turning curvature as the motion state quantity according to the second modification is the same as the steering characteristic change program of the above-described embodiment, and thus detailed description thereof is omitted. .

  In the second modification, the computer program executed by the electronic control unit 35 with respect to the steering operation is shown in the functional block diagram of FIG. In this case, in the sensory adaptation control unit 50, the displacement-torque conversion unit 51 functions in the same manner as in the above embodiment, but a torque-turning curvature conversion unit 56 is provided instead of the torque-lateral acceleration conversion unit 52 in the above embodiment. It has been.

The torque-turning curvature conversion unit 56 uses the steering torque Td calculated by the displacement-torque conversion unit 51 to calculate the expected turning curvature ρd that the driver expects by turning the steering handle 11 as the steering torque. If the absolute value of Td is less than a small positive predetermined value To, it is set to “0” as shown in Equation 22 below, and if the absolute value of the steering torque Td is greater than or equal to a positive small predetermined value To, it is calculated according to Equation 23 below.
ρd = 0 (| Td | <To) Equation 22
ρd = C · Td ^K2 (To ≦ | Td |) Equation 23
However, C and K2 in Equation 23 are constants as in the above embodiment. Also in this case, the steering torque Td in the equation 23 represents the absolute value of the steering torque Td calculated using the above equation 2. If the calculated steering torque Td is positive, the constant C Is a positive value, and if the calculated steering torque Td is positive, the constant C is a negative value having the same absolute value as the positive constant C. In this case, the expected turning curvature ρd is calculated using a conversion table having characteristics as shown in FIG. 12 in which the expected turning curvature ρd with respect to the steering torque Td is stored instead of the calculations of the equations 22 and 23. May be.

  Further, the turning angle conversion unit 57 calculates the target turning angle δd of the left and right front wheels FW1 and FW2 necessary for generating the expected turning curvature ρd, according to the vehicle speed V as shown in FIG. There is a table that changes and represents the change characteristic of the target turning angle δd with respect to the expected turning curvature ρd. This table is a set of data collected by actually measuring the turning angle δ and the turning curvature ρ of the left and right front wheels FW1 and FW2 while the vehicle is running while changing the vehicle speed V. Then, the turning angle conversion unit 57 refers to this table and calculates the target turning angle δd corresponding to the input expected turning curvature ρd and the detected vehicle speed V input from the vehicle speed sensor 33. The turning curvature ρ (expected turning curvature ρd) and the target turning angle δd stored in the table are both positive, but the expected turning curvature ρd supplied from the torque-turning curvature conversion unit 56 is negative. If so, the output target turning angle δd is also negative.

Since the target turning angle δd is a function of the vehicle speed V and the turning curvature ρ as shown in the following equation 24, the target turning angle δd can be calculated by executing the operation of the following equation 24 instead of referring to the table. it can.
δd = L · (1 + A · V ² ) · ρd Equation 24
However, also in the formula 24, L is a predetermined value representing the wheel base, and A is a predetermined value.

The calculated target turning angle δd is supplied to the turning angle correction unit 64 of the turning control unit 60. The turning angle correction unit 64 receives the expected turning curvature ρd from the torque-turning curvature conversion unit 56 and also receives the actual turning curvature ρ from the turning curvature calculation unit 65. The turning curvature calculation unit 65 uses the lateral acceleration G detected by the lateral acceleration sensor 34 or the yaw rate γ detected by the yaw rate sensor 38 and the vehicle speed V detected by the vehicle speed sensor 33 to calculate the following Expression 25. The actual turning curvature ρ is calculated by execution and output to the turning angle correction unit 64.
ρ = G / V ² or ρ = γ / V Equation 25

And the turning angle correction | amendment part 64 performs the calculation of following formula 26, correct | amends the input target turning angle (delta) d, and calculates corrected target turning angle (delta) da.
δda = δd + K5 · (ρd−ρ) Equation 26
However, the coefficient K5 is a positive constant determined in advance, and when the actual turning curvature ρ is less than the expected turning curvature ρd, the coefficient K5 is corrected so that the absolute value of the corrected target turning angle Δda is increased. When the actual turning curvature ρ exceeds the expected turning curvature ρd, the absolute value of the corrected target turning angle δda is corrected to be smaller. By this correction, the turning angles of the left and right front wheels FW1, FW2 necessary for the expected turning curvature ρd are more accurately ensured.

  Also in the second modified example, if the steering characteristic changing program shown in FIG. 6 is executed and the vehicle speed V is equal to or lower than the predetermined vehicle speed, the electronic control unit 35 adopts a proportional map in step S15. Here, when the turning curvature is adopted as the motion state quantity, the target turning angle δd during normal traveling changes exponentially as apparent from the above equation 24 and FIG. At the same time, it has a characteristic of increasing as the vehicle speed V increases, and is different from the characteristic of the target turning angle δd of the above embodiment. However, by determining that the vehicle is in the slow speed region in step S11, in order to adopt the proportional map in step S15, the actual turning angle δ determined in the slow speed region is the target turning during normal travel. It is not related to the characteristics of the steering angle δd. Therefore, also in the second modification, the same steering characteristic changing program as that in the above embodiment can be executed.

  The other program processing executed by the electronic control unit 35 is the same as that in the above embodiment. And in the functional block diagram of FIG. 11, the code | symbol same as FIG. 2 of the said embodiment is attached | subjected, and the description is abbreviate | omitted.

  Also in the second modified example described above, the steering angle θ as the operation input value of the driver with respect to the steering handle 11 is converted into the steering torque Td by the displacement-torque converter 51, and the converted steering torque is also converted. Td is converted to the expected turning curvature ρd by the torque-turning curvature conversion unit 56, and the left and right front wheels FW1, FW2 generate the expected turning curvature ρd by the turning angle conversion unit 57, the turning angle correction unit 64, and the drive control unit 62. To the corrected target turning angle δda required for Also in this case, since the steering torque Td is equal to the reaction force torque Tz, it is a physical quantity that can be perceived by the driver from the steering handle 11 by the action of the reaction force actuator 13, and changes exponentially with respect to the steering angle θ. Therefore, the driver can turn the steering handle 11 according to the human perceptual characteristic while feeling the reaction force according to the Weber-Hefner law.

  Further, the turning curvature due to the turning of the left and right front wheels FW1 and FW2 is also a physical quantity that can be visually perceived, and this turning curvature ρ is controlled to be equal to the expected turning curvature ρd, and the expected turning curvature ρd is also steered. It changes exponentially with respect to the angle θ (exponentially by changing Expression 23 in the same manner as changing from Expression 4 to Expression 5 in the above embodiment). Accordingly, the driver can turn the vehicle by turning the steering handle 11 according to human perceptual characteristics while visually perceiving the turning curvature according to the Weber-Hefner's law. As a result, the driver can operate the steering wheel 11 in accordance with the human perceptual characteristics as in the case of the above-described embodiment, so that the driving of the vehicle is simplified.

  Further, the turning angle correction unit 64 corrects the target turning angle δd so that the actual turning curvature ρ actually generated in the vehicle accurately corresponds to the steering angle θ of the steering handle 11, so that the vehicle is steered. The vehicle turns with an actual turning curvature ρ that accurately corresponds to the steering angle θ of the handle 11. As a result, the driver can operate the steering wheel 11 while perceiving a turning curvature that more accurately matches the human perceptual characteristics, and thus the driving of the vehicle is further simplified. Further, the specific operational effects are the same except that the lateral acceleration of the above embodiment is changed to the turning curvature.

  Further, the turning angle correction unit 61 corrects the target turning angle δd so that the actual lateral acceleration G actually generated in the vehicle accurately corresponds to the steering angle θ of the steering handle 11, so that the vehicle An actual lateral acceleration G accurately corresponding to the steering angle θ of the steering handle 11 is generated. As a result, the driver can operate the steering wheel 11 while perceiving the lateral acceleration more accurately according to the human perceptual characteristics, so that the driving of the vehicle becomes easier.

  When the vehicle is moving at a predetermined vehicle speed or less, the turning angle δ with respect to the steering angle θ input by the driver can be calculated based on a predetermined linear relationship, that is, a proportional map. Accordingly, the turning angle δ of the left and right front wheels FW1, FW2 can be linearly changed with respect to the input steering angle θ. As a result, the driver can easily estimate the turning angle δ based on the steering angle θ input to the steering handle 11, so that the driving of the vehicle in the slow speed region is simplified.

  Further, since the proportional map is determined to be the maximum turning angle δmax that can steer the left and right front wheels FW1 and FW2 with respect to the maximum steering angle θmax that can turn the steering handle 11, the same steering angle The left and right front wheels FW1, FW2 can be steered at θ with a larger turning angle δ than when traveling normally. Accordingly, the amount of operation of the steering wheel 11 by the driver can be reduced, the left and right front wheels FW1, FW2 can be steered with high responsiveness, and the driving when the vehicle moves at a low speed can be simplified.

Third Modification In the above embodiment, the steering angle θ is used as the operation input value of the steering wheel 11 even during normal travel. In addition to this, it is also possible to carry out the modification by using the steering torque T as the operation input value of the steering wheel 11 during normal traveling. Hereinafter, this third modification will be described. In the third modification, a steering torque sensor 39 is connected to the electronic control unit 35 as indicated by a broken line in FIG. The steering torque sensor 39 is assembled to the steering input shaft 12 and detects and outputs the steering torque T applied to the steering handle 11. Moreover, in this 3rd modification, the displacement-torque conversion part 51 is not provided in the functional block diagram of FIG. 2 showing the computer program regarding steering operation, The torque-lateral acceleration conversion part 52 is the said implementation. Instead of the steering torque Td calculated by the displacement-torque conversion unit 51 in the embodiment, the expected lateral acceleration Gd is calculated by executing the calculations of equations 3 and 4 using the steering torque T detected by the steering torque sensor 39. . In this case as well, the expected lateral acceleration Gd may be calculated using a conversion table representing the characteristics shown in FIG. The other program processing executed by the electronic control unit 35 is the same as in the above embodiment.

  According to the third modification, the steering torque T as the driver's operation input value for the steering handle 11 is converted into the expected lateral acceleration Gd by the torque-lateral acceleration conversion unit 52, and the turning angle conversion unit 53, the steering By the angle correction unit 61 and the drive control unit 62, the left and right front wheels FW1, FW2 are steered to the corrected target turning angle δda necessary for generating the expected lateral acceleration Gd. Also in this case, the steering torque T is a physical quantity that can be perceived by the driver from the steering handle 11, and the expected lateral acceleration Gd changes exponentially with respect to the steering torque T. Therefore, the driver can turn the steering handle 11 according to the human perceptual characteristic while feeling the reaction force according to the Weber-Hefner law. Accordingly, also in this third modified example, as in the case of the above-described embodiment, the driver rotates the steering handle 11 according to the human perceptual characteristics while feeling the lateral acceleration according to the Weber-Hefner law, Since the vehicle can be turned, the same effect as the above-described embodiment is expected.

  Further, during normal travel, the vehicle steering control according to the above embodiment and the vehicle steering control according to the third modification may be switchable. That is, both the steering angle sensor 31 and the steering torque sensor 39 are provided, and the estimated lateral acceleration Gd is calculated using the target turning torque Td calculated by the displacement-torque converter 51 as in the above embodiment. It is also possible to switch between the case where the expected lateral acceleration Gd is calculated using the steering torque T detected by the steering torque sensor 39 and to make it usable. In this case, the switching may be performed automatically according to the driver's intention or according to the motion state of the vehicle.

  Furthermore, in carrying out the present invention, the present invention is not limited to the above-described embodiments and modifications, and various modifications can be made without departing from the object of the present invention.

  Moreover, in the said embodiment and each modification, in order to steer a vehicle, the steering handle 11 rotated is used. However, instead of this, for example, a joystick-type steering handle that is linearly displaced may be used, or any other one that can be operated by the driver and instructed to steer the vehicle is used. May be.

  For example, in the above embodiment and each modification, the left and right front wheels FW1 and FW2 are steered by rotating the steered output shaft 22 using the steered actuator 21. However, instead of this, the left and right front wheels FW1, FW2 may be steered by linearly displacing the rack bar 23 using the steered actuator 21.

  Further, in the above-described embodiment and each modified example, lateral acceleration, yaw rate, and turning curvature are each independently used as the amount of vehicle motion state that can be perceived by humans. However, the vehicle steering control may be performed by switching the amount of motion state of these vehicles by a selection operation by the driver or by automatically switching according to the traveling state of the vehicle. When switching automatically according to the running state of the vehicle, for example, the turning curvature is used as the motion state quantity when the vehicle is running at low speed, the yaw rate is used as the motion state quantity when the vehicle is running at medium speed, and the vehicle is running at high speed. Sometimes, lateral acceleration is used as the motion state quantity. According to this, appropriate steering control of the vehicle is performed according to the running state of the vehicle, and the driving of the vehicle becomes easier.

It is the schematic of the steering apparatus of the vehicle which concerns on embodiment and each modification of this invention. FIG. 2 is a functional block diagram functionally representing a computer program process of steering control executed by the electronic control unit of FIG. 1 according to the embodiment of the present invention. It is a graph which shows the relationship between a steering angle and a steering torque. It is a graph which shows the relationship between steering torque and estimated lateral acceleration. It is a graph which shows the relationship between a prospective lateral acceleration and a target turning angle. 2 is a flowchart showing a steering characteristic changing program executed by the electronic control unit of FIG. 1 according to the embodiment of the present invention. 6 is a graph for explaining a linear relationship between a steering angle and a turning angle according to an embodiment of the present invention. It is a functional block diagram functionally showing the computer program process of the steering control performed in the electronic control unit of FIG. 1 according to the first modification of the present invention. It is a graph which shows the relationship between steering torque and estimated yaw rate. It is a graph which shows the relationship between an expected yaw rate and a target turning angle. FIG. 10 is a functional block diagram functionally representing a computer program process of turning control executed by the electronic control unit of FIG. 1 according to a second modification of the present invention. It is a graph which shows the relationship between steering torque and prospective turning curvature. It is a graph which shows the relationship between a prospective turning curvature and a target turning angle.

Explanation of symbols

FW1, FW2 ... front left and right wheels, 11 ... steering handle, 12 ... steering input shaft, 13 ... reaction force actuator, 21 ... steering actuator, 22 ... steering output shaft, 31 ... steering angle sensor, 32 ... steering angle sensor, 33 ... Vehicle speed sensor, 34 ... Lateral acceleration sensor, 35 ... Electronic control unit, 38 ... Yaw rate sensor, 39 ... Steering torque sensor, 40 ... Reaction force control unit, 50 ... Sensory adaptation control unit, 51 ... Displacement-torque conversion unit, 52 ... Torque-lateral acceleration conversion unit, 53, 55, 57 ... Steering angle conversion unit, 54 ... Torque-yaw rate conversion unit, 56 ... Torque-turning curvature conversion unit, 60 ... Steering control unit, 61, 63, 64 ... steering angle correction unit,

Claims (3)

A steering handle that is operated by a driver to steer the vehicle, a reaction force actuator that applies a reaction force to the steering handle, a steering actuator that steers the steered wheel, and an operation of the steering handle In a steering by wire type vehicle steering apparatus provided with a steering control device that drives and controls the steering actuator to steer the steered wheels, the steering control device includes:
A displacement amount sensor for detecting a displacement amount of the steering wheel;
An operating force converting means for converting the detected displacement amount into an operating force applied to the steering handle;
A vehicle driving state quantity that can be perceived by the driver in relation to the turning of the vehicle, and a value obtained by dividing a predetermined Weber ratio related to the movement state quantity by a predetermined Weber ratio related to the operating force. A motion state quantity calculating means for calculating a predicted motion state quantity of the vehicle, which is defined as a power function of the operating force as an index , using the converted operating force ;
A turning angle calculation means for calculating a turning angle of the steered wheels necessary for the vehicle to move with the calculated expected motion state quantity, using the calculated expected motion state quantity;
Vehicle speed detecting means for detecting the vehicle speed of the vehicle;
Vehicle speed determination means for determining whether or not the detected vehicle speed is equal to or lower than a predetermined vehicle speed;
When the vehicle speed determining means determines that the vehicle speed is equal to or lower than a predetermined vehicle speed, a linearity for calculating a turning angle that has a predetermined linear relationship with the displacement amount with respect to the steering handle using the detected displacement amount. Turning angle calculation means,
A steering-by-wire system comprising: a steering control unit configured to control the steering actuator according to the calculated turning angle and to turn the steered wheels to the calculated turning angle. Vehicle steering device. The steering apparatus for a steering-by-wire vehicle according to claim 1,
The predetermined linear relationship is a steering-by-wire relationship in which the turning angle is the maximum turning angle at which the steered wheels can be steered with respect to the maximum amount of displacement that can be input to the steering handle of the driver. Type vehicle steering device. In the steering apparatus for a steering-by-wire vehicle according to claim 1 or 2,
Before anticipated motion state quantity calculated by Kiun dynamic state quantity computing means of the vehicle steering system of the steering-by-wire system is any one of a lateral acceleration, yaw rate and turning curvature of the vehicle.

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