Steering control device and steering control method

Abstract

The invention relates to a steering control device (1) and a steering control method. A vehicle steering system (2) has a power transmission path cut off between a steering unit (4) steered by a steering wheel (3) of a vehicle and a turning unit (6) operated to turn a turning wheel (5) of the vehicle. A steering control device (1) for a vehicle steering system (2) includes a processor (60) that controls operation of a turning unit (6). A processor (60) executes a target rotation angle calculation process that calculates a target rotation angle, which is a target of a rotation angle indicating a rotation position of a rotating wheel (5) and is a control amount for operating a rotating unit (6), on the basis of a steering angle indicating a rotation position of a steering wheel (3).

Description

Technical Field

[0001] The present disclosure relates to a steering control device and a steering control method. Background Art

[0002] There is a steer-by-wire steering device installed in a vehicle. Such a steer-by-wire steering device has an advantage in that the relationship between the steering angle indicating the rotational position of the steering wheel and the rotation angle indicating the rotational position of the turning wheel can be freely changed. However, freely changing the relationship between the steering angle and the rotation angle will have an impact on the response characteristics of the yaw rate as the behavior of the vehicle. As a technology that can cope with such an impact, for example, a steering control device described in Japanese Unexamined Patent Application Publication No. 2023-12120 (JP 2023-12120A) has been proposed.

[0003] In the aforementioned JP 2023-12120A, phase compensation is performed to cope with the influence of the freely changing relationship between the steering angle and the turning angle on the responsiveness of the yaw rate as the behavior of the vehicle. Such phase compensation compensates for the component that acts to freely change the relationship between the steering angle and the turning angle.

[0004] Incidentally, it can be considered that the influence of freely changing the relationship between the steering angle and the turning angle is not limited to the influence on the responsiveness of the yaw rate as the behavior of the vehicle, but also affects the control stability. Therefore, in the case where the relationship between the steering angle and the turning angle changes freely, it is expected to alleviate the reduction in control stability. Summary of the invention

[0005] One aspect of an implementation of the present disclosure is a steering control device for a vehicle steering system having a power transmission path cut off between a steering unit steered by a steering wheel of the vehicle and a rotation unit operated to rotate a rotating wheel of the vehicle. The steering control device includes a processor configured to control the operation of the rotation unit. The processor is configured to perform a target rotation angle calculation process, which calculates a target steering angle based on a steering angle representing a rotation position of the steering wheel, the target rotation angle being a target of a rotation angle representing a rotation position of the rotating wheel and being a control amount for operating the rotation unit. The target rotation angle calculation process includes: a conversion calculation process, which receives an input of a steering angle in order to change the relationship between the steering angle and the rotation angle, and uses the input to calculate a conversion component obtained by converting the steering angle; a compensation calculation process, which receives an input of a conversion component in order to adjust the influence on the behavior of the vehicle, and uses the input to calculate a compensation component obtained by performing phase compensation on the conversion component; and a component reflection process, which calculates the target rotation angle so as to reflect the compensation component. The conversion calculation process includes calculating the conversion component according to a conversion characteristic that specifies the relationship between the steering angle and the conversion component. The compensation calculation process includes calculating the compensation component according to a compensation characteristic that specifies a relationship between the conversion component and the compensation component. At least a first process between the conversion calculation process and the compensation calculation process includes a characteristic change process that changes a characteristic in the first process based on a characteristic of a second process between the conversion calculation process and the compensation calculation process so as to ensure control stability of the vehicle steering system.

[0006] According to this configuration, the characteristic change processing changes the characteristics in the corresponding processing based on the characteristics of other processing. Therefore, in the conversion calculation processing and the compensation calculation processing, the characteristics of these processing can be associated with each other from the viewpoint of ensuring the control stability of the vehicle steering system. That is, in the case where the relationship between the steering angle and the turning angle changes, the control stability of the vehicle steering system can also be ensured. Therefore, the reduction in control stability can be alleviated.

[0007] In the conversion calculation process and the compensation calculation process, the compensation calculation process may include a characteristic change process. The characteristic change process in the compensation calculation process may change the compensation characteristic based on the conversion characteristic.

[0008] According to this configuration, in a case where the conversion component obtained by changing the steering angle is further subjected to phase compensation, the compensation characteristic in the compensation calculation process is changed so as to mitigate the reduction in control stability of the vehicle steering system. Therefore, by simply including the characteristic change process in the compensation calculation process, the reduction in control stability can be mitigated.

[0009] The conversion calculation process may convert the steering angle into a conversion component using a steering angle variable value indicating a ratio of a change in the rotation angle relative to a change in the steering angle. The conversion characteristic may be based on a steering angle variable value that changes according to a state of at least either the vehicle or the vehicle steering system. The compensation calculation process may be a phase lag filter process that performs phase lag compensation on the conversion component. The compensation characteristic may indicate a constant of a transfer function that is a characteristic of the phase lag filter process.

[0010] According to this configuration, also in the case where the steering angle variable value changes according to a state change of at least either the vehicle or the vehicle steering system, control stability of the vehicle steering system can be ensured regardless of the state change.

[0011] With respect to the conversion calculation process and the compensation calculation process, the conversion calculation process may include a characteristic change process. The characteristic change process in the conversion calculation process may change the conversion characteristic based on the compensation characteristic.

[0012] According to this configuration, in a case where the compensation characteristic in the compensation calculation process changes according to the running of the vehicle, the conversion characteristic in the conversion calculation process is changed so as to mitigate the reduction in control stability of the vehicle steering system. Therefore, by simply including the characteristic change process in the conversion calculation process, the reduction in control stability can be mitigated.

[0013] The compensation calculation process may be a phase lag filter process that performs phase lag compensation on the conversion component. The compensation characteristic may indicate a constant of a transfer function of a characteristic of the phase lag filter process that changes according to a state of at least any one of a vehicle or a vehicle steering system. The conversion calculation process may convert the steering angle into the conversion component using a steering angle variable value indicating a ratio of a change amount of the turning angle relative to a change amount of the steering angle. The conversion characteristic may be based on the steering angle variable value.

[0014] According to this configuration, also in a case where the constant of the transfer function changes according to a state change of at least either the vehicle or the vehicle steering system, control stability of the vehicle steering system can be ensured regardless of the state change.

[0015] The conversion calculation process may include a steering angle variable value calculation process that calculates a steering angle variable value using the steering angle as an input. The characteristic based on the steering angle variable value may be a change amount of the conversion component or a change amount of the steering angle variable value relative to a change amount of the steering angle input into the steering angle variable value calculation process.

[0016] According to this configuration, adjustment of the change gradient obtained in association with the steering angle variable value becomes possible. This is effective for ensuring control stability of the vehicle steering system.

[0017] Another aspect of the present disclosure is a steering control method for a vehicle steering system having a power transmission path cut off between a steering unit steered by a steering wheel of the vehicle and a rotating unit operated to rotate a rotating wheel of the vehicle. The steering control method includes a control process for performing a control operation of the rotating unit. The control process includes a target rotation angle calculation process, which calculates a target rotation angle based on a steering angle representing a rotation position of the steering wheel, the target rotation angle being a target of a rotation angle representing a rotation position of the rotating wheel and being a control amount for operating the rotating unit. The target rotation angle calculation process includes: a conversion calculation process, which receives an input of a steering angle in order to change the relationship between the steering angle and the rotation angle, and uses the input to calculate a conversion component obtained by converting the steering angle; a compensation calculation process, which receives an input of a conversion component in order to adjust the influence on the behavior of the vehicle, and uses the input to calculate a compensation component obtained by performing phase compensation on the conversion component; and a component reflection process, which calculates the target rotation angle so as to reflect the compensation component. The conversion calculation process includes calculating the conversion component according to a conversion characteristic that specifies the relationship between the steering angle and the conversion component. The compensation calculation process includes calculating the compensation component according to a compensation characteristic that specifies a relationship between the conversion component and the compensation component. At least a first process between the conversion calculation process and the compensation calculation process includes a characteristic change process that changes a characteristic in the first process based on a characteristic of a second process between the conversion calculation process and the compensation calculation process so as to ensure control stability of the vehicle steering system.

[0018] According to the present disclosure, the reduction in control stability can be alleviated. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals denote like elements, and in which:

[0020] Figure 1 is a view showing the configuration of a vehicle steering system according to a first embodiment;

[0021] Figure 2 It is shown Figure 1 A block diagram of the functions of the steering control device;

[0022] Figure 3 It shows the calculation Figure 1 A block diagram of the function of the angular axial force in the steering control device;

[0023] Figure 4 It is shown Figure 2A block diagram of the functions of a steering angle ratio variable control unit;

[0024] Figure 5 is a block diagram showing the functions of a steering angle ratio variable control unit according to a second embodiment;

[0025] Figure 6 is a block diagram showing the functions of a steering angle ratio variable control unit according to a third embodiment;

[0026] Figure 7 is a block diagram showing the function of a steering angle ratio variable control unit according to a fourth embodiment; and

[0027] Figure 8 : is a block diagram showing the function of a steering angle ratio variable control unit according to the fifth embodiment. DETAILED DESCRIPTION

[0028] First embodiment

[0029] The first embodiment of the present disclosure will be described below. Figure 1 As shown, the vehicle steering system 2 includes a steering control device 1. The vehicle steering system 2 includes a steering unit 4 and a turning unit 6. The steering unit 4 is steered by the driver through a steering wheel 3 of the vehicle as a steering member. The turning unit 6 operates to turn the left and right turning wheels 5 of the vehicle according to the steering input into the steering unit 4 by the driver. The vehicle steering system 2 of the present embodiment has, for example, the following structure, in which the power transmission path between the steering unit 4 and the turning unit 6 is always mechanically cut off. In this structure, the power transmission path between the steering actuator 12 to be described later and the turning actuator 31 to be described later is always mechanically cut off. Therefore, the vehicle steering system 2 includes a steer-by-wire steering device.

[0030] The steering unit 4 includes a steering shaft 11 and a steering actuator 12. The steering shaft 11 is connected to the steering wheel 3. The steering actuator 12 has a steering side motor 13 and a steering side reduction mechanism 14. The steering side motor 13 is a reaction force motor that applies a steering reaction force, which is a force acting against steering, to the steering wheel 3 through the steering shaft 11. The steering side motor 13 is connected to the steering shaft 11 through a steering side reduction mechanism 14 formed of, for example, a worm and a worm wheel. For the steering side motor 13 of the present embodiment, for example, a three-phase brushless motor is used.

[0031] The rotating unit 6 includes a pinion shaft 21, a rack shaft 22 as a rotating shaft, and a rack housing 23. The pinion shaft 21 and the rack shaft 22 are coupled together at a predetermined crossing angle. Pinion teeth 21a formed in the pinion shaft 21 and rack teeth 22a formed in the rack shaft 22 mesh with each other to form a rack and pinion mechanism 24. The pinion shaft 21 corresponds to a rotation axis that allows conversion into a rotation angle θi representing a rotation position of the rotating wheel 5. The rack housing 23 accommodates the rack and pinion mechanism 24.

[0032] One end of the pinion shaft 21 on the side opposite to the side coupled to the rack shaft 22 protrudes from the rack housing 23. Both ends of the rack shaft 22 protrude from both ends in the axial direction of the rack housing 23. At both ends of the rack shaft 22, a tie rod 26 is coupled through a rack end 25 formed by a ball joint. The front end of the tie rod 26 is coupled to a steering knuckle (not shown) on which the left and right turning wheels 5 are mounted, respectively.

[0033] The rotating unit 6 includes a rotating actuator 31. The rotating actuator 31 includes a rotating side motor 32, a transmission mechanism 33, and a conversion mechanism 34. The rotating side motor 32 applies a rotating force for rotating the rotating wheel 5 to the rack shaft 22 through the transmission mechanism 33 and the conversion mechanism 34. The rotating side motor 32 transmits the rotation to the conversion mechanism 34 through the transmission mechanism 33 formed by, for example, a belt transmission mechanism. The transmission mechanism 33 converts the rotation of the rotating side motor 32 into a reciprocating motion of the rack shaft 22 through the conversion mechanism 34 formed by, for example, a ball screw mechanism. For the rotating side motor 32 of the present embodiment, for example, a three-phase brushless motor is used.

[0034] In the vehicle steering system 2, when the motor torque is applied as a rotational force from the rotation actuator 31 to the rack shaft 22 according to the steering operation of the driver, the rotation angle θi of the rotation wheel 5 changes. At the same time, a steering reaction force acting against the steering of the driver is applied from the steering actuator 12 to the steering wheel 3. Therefore, in the vehicle steering system 2, the steering torque Th required to steer the steering wheel 3 is changed as a steering reaction force of the motor torque applied from the steering actuator 12.

[0035] The reason for providing the pinion shaft 21 is to support the rack shaft 22 together with the pinion shaft 21 in the rack housing 23. By a supporting mechanism (not shown) provided in the vehicle steering device 2, the rack shaft 22 is supported so as to be movable in its axial direction and simultaneously pressed toward the pinion shaft 21. Therefore, the rack shaft 22 is supported inside the rack housing 23. However, another supporting mechanism that supports the rack shaft 22 in the rack housing 23 without using the pinion shaft 21 may be provided.

[0036] Electrical configuration of vehicle steering system

[0037] like Figure 1 As shown, the steering-side motor 13 and the turning-side motor 32 are connected to the steering control device 1. The steering control device 1 controls the operation of each of the motors 13,32.

[0038] Detection results of the various sensors are input into the steering control device 1. Examples of the various sensors include a torque sensor 41, a steering-side rotation angle sensor 42, a turning-side rotation angle sensor 43, and a vehicle speed sensor 44.

[0039] The torque sensor 41 is provided in the steering shaft 11 at a portion between the steering wheel 3 and the steering-side speed reduction mechanism 14. The torque sensor 41 detects a steering torque Th, which is a value indicating a torque applied to the steering shaft 11 by the driver's steering operation. The steering torque Th is detected in association with the twisting of a torsion bar 41a, which is a middle portion of the steering shaft 11 and is provided in the steering shaft 11, between the steering wheel 3 and the steering-side speed reduction mechanism 14. The steering-side rotation angle sensor 42 is provided in the steering-side motor 13. The steering-side rotation angle sensor 42 detects a rotation angle θa, which is an angle of the rotation shaft of the steering-side motor 13 within a range of 360 degrees. The turning-side rotation angle sensor 43 is provided in the turning-side motor 32. The turning-side rotation angle sensor 43 detects a rotation angle θb, which is an angle of the rotation shaft of the turning-side motor 32 within a range of 360 degrees. The vehicle speed sensor 44 detects a vehicle speed V as a traveling speed of the vehicle.

[0040] Function of the steering control

[0041] like Figure 2 As shown, the steering control device 1 has a reaction force control unit 50 and a rotation control unit 60. The reaction force control unit 50 performs a control process for controlling the steering wheel 3 as a control target. The reaction force control unit 50 controls the driving of the steering actuator 12, more particularly the steering side motor 13, to control the steering reaction force of the control amount as the control target. The rotation control unit 60 performs a control process for controlling the rack shaft 22 as the control target. The rotation control unit 60 controls the driving of the rotation actuator 31, more particularly the rotation side motor 32, to control the rotation force of the control amount as the control target. The reaction force control unit 50 and the rotation control unit 60 send information to each other and receive information from each other through a local network such as a serial communication network. The reaction force control unit 50 is combined with the steering unit 4 to form a reaction force system RS. The rotation control unit 60 is combined with the rotation unit 6 to form a rotation system TS. In the present embodiment, the rotation control unit 60 is an example of a control unit.

[0042] The reaction force control unit 50 includes a central processing unit (hereinafter referred to as "CPU") and a memory. When the CPU executes a program stored in the memory with a predetermined calculation cycle, the reaction force control unit 50 performs various processes. The rotation control unit 60 includes a central processing unit (hereinafter referred to as "CPU") and a memory. When the CPU executes a program stored in the memory with a predetermined calculation cycle, the rotation control unit 60 performs various processes. The CPU and the memory constitute a microcomputer as a processing circuit. The memory includes a computer-readable medium, such as a random access memory (RAM) and a read-only memory (ROM). However, it is an example that various processes are implemented by software. The processing circuits possessed by the reaction force control unit 50 and the rotation control unit 60 can be configured to implement at least some of the processes by hardware circuits such as logic circuits.

[0043] Figure 2 Some of the processes performed by the reaction force control unit 50 and the rotation control unit 60 are shown. Figure 2 The processes shown in are some of the processes implemented when the CPU executes the program stored in the memory, and are depicted by the type of processing to be implemented.

[0044] The reaction force control unit 50 has a current sensor 54. The current sensor 54 detects an actual current value Ia obtained from the value of the current in each phase of the steering side motor 13, which flows through a connection line between the reaction force control unit 50 and the motor coil in each phase of the steering side motor 13. The current sensor 54 acquires a voltage drop of a shunt resistor as a current, the shunt resistor being connected to the source side of each of the switching elements in an inverter (not shown) that is provided to correspond to the steering side motor 13. Figure 2 In the drawings, for convenience of description, connection lines for corresponding phases and current sensors for corresponding phases are collectively illustrated as one connection line and one current sensor.

[0045] The rotation control unit 60 has a current sensor 65. The current sensor 65 detects an actual current value Ib obtained from a current value in each phase of the rotation side motor 32, which current flows through a connection line between the rotation control unit 60 and a motor coil in each phase of the rotation side motor 32. The current sensor 65 acquires a voltage drop of a shunt resistor connected to a source side of each of the switching elements in an inverter (not shown) provided to correspond to the rotation side motor 32 as a current. Figure 2 In the drawings, for convenience of description, connection lines for corresponding phases and current sensors for corresponding phases are collectively illustrated as one connection line and one current sensor.

[0046] Reaction force control unit

[0047] like Figure 2 As shown, the reaction force control unit 50 controls the power supply to the steering side motor 13 by receiving the input of the steering torque Th, the vehicle speed V, the rotation angle θa, the axial force rotation angle θpf and the current axial force Tai. The axial force rotation angle θpf and the current axial force Tai are components calculated in the rotation control unit 60.

[0048] The reaction force control unit 50 has a steering angle calculation unit 51, a target reaction force torque calculation unit 52, and a current application control unit 53. The steering angle calculation unit 51 calculates the steering angle θs by receiving an input of the rotation angle θa. The steering angle calculation unit 51 converts the rotation angle θa into a cumulative angle including a range exceeding 360°, for example, by counting the number of rotations of the steering side motor 13 from the steering neutral position, which is the rotation position of the steering wheel 3 when the vehicle is traveling straight forward. The steering angle calculation unit 51 calculates the steering angle θs by multiplying the cumulative angle obtained by the conversion by a conversion factor based on the rotation speed ratio of the steering side reduction mechanism 14. The steering angle θs thus obtained is used for calculation in the target reaction torque calculation unit 52. The steering angle θs is output to the rotation control unit 60.

[0049] The target reaction torque calculation unit 52 calculates the target reaction torque command value Ts* by receiving the input of the steering torque Th, the vehicle speed V, the axial force rotation angle θpf, the current axial force Tai and the steering angle θs. The target reaction torque command value Ts* is a reaction force control amount used as a target of the steering reaction force of the steering wheel 3 that should be generated by the steering side motor 13. The target reaction torque command value Ts* thus obtained is used for control in the current application control unit 53.

[0050] The current application control unit 53 calculates the current command value Ia* by receiving the input of the target reaction force torque command value Ts*. The current command value Ia* is the target value of the torque to be generated by the steering side motor 13. The current application control unit 53 calculates the converted current value Iae by receiving the input of the actual current value Ia and the rotation angle θa. The converted current value Iae is a conversion value obtained by converting the actual current value Ia into a current value in the dq coordinate system. The current application control unit 53 controls the power supply to the steering side motor 13 by performing feedback control on the converted current value Iae so as to adapt the converted current value Iae to the current command value Ia*. As a result, the steering side motor 13 generates torque according to the target reaction force torque command value Ts*. Therefore, appropriate steering feedback can be provided to the driver according to the reaction force from the road surface.

[0051] Rotation control unit

[0052] like Figure 2 As shown, the turning control unit 60 controls the power supply to the turning-side motor 32 by receiving inputs of the vehicle speed V, the turning angle θb, and the steering angle θh. The steering angle θs is a component calculated in the reaction force control unit 50.

[0053] The rotation control unit 60 includes a pinion angle calculation unit 61, a steering angle ratio variable control unit 62, a pinion angle feedback control unit (in Figure 2 , which are “pinion angle F / B control unit” 63, current application control unit 64, axial force rotation angle calculation unit 66 and current axial force calculation unit 67.

[0054] The pinion angle calculation unit 61 calculates the pinion angle θp by receiving an input of the rotation angle θb. The pinion angle calculation unit 61 converts the rotation angle θb into a cumulative angle including a range exceeding 360° by, for example, counting the number of rotations of the rotation-side motor 32 from the rack neutral position, which is the position of the rack shaft 22 when the vehicle is traveling straight ahead. The pinion angle calculation unit 61 calculates the pinion angle θp, which is the actual rotation angle of the pinion shaft 21, by multiplying the cumulative angle obtained by the conversion by a conversion factor based on the speed ratio of the transmission mechanism 33, the lead of the conversion mechanism 34, and the speed ratio of the rack and pinion mechanism 24. The pinion angle θp thus obtained is used for calculation in the pinion angle feedback control unit 63.

[0055] The steering angle ratio variable control unit 62 performs a target rotation angle calculation process of calculating a target pinion angle θp* by receiving inputs of the vehicle speed V and the steering angle θs. The target pinion angle θp* is a rotation control amount serving as a target of the pinion angle θp obtained by rotating the turning wheel 5. The target pinion angle θp* thus obtained is used for calculation in the pinion angle feedback control unit 63.

[0056] The pinion angle feedback control unit 63 calculates the turning force command value Tp* by receiving the input of the target pinion angle θp* and the pinion angle θp. The turning force command value Tp* is a turning control amount used as a target of the turning force of the turning wheel 5 that should be generated by the turning side motor 32. The pinion angle feedback control unit 63 calculates the turning force command value Tp* by performing feedback control on the pinion angle θp so that the pinion angle θp is adapted to the target pinion angle θp*. The turning force command value Tp* thus obtained is used for control in the current application control unit 64.

[0057] The current application control unit 64 calculates the current command value Ib* by receiving the input of the turning force command value Tp*. The current command value Ib* is the target value of the torque to be generated by the rotating side motor 32. The current application control unit 64 calculates the converted current value Ibe by receiving the input of the actual current value Ib and the rotation angle θb. The converted current value Ibe is a converted value obtained by converting the actual current value Ib into a current value on the dq coordinate system. The current application control unit 64 controls the power supply to the rotating side motor 32 by performing feedback control on the converted current value Ibe to adapt the converted current value Ibe to the current command value Ib*. As a result, the rotating side motor 32 generates torque according to the turning force command value Tp*. Therefore, the rotating wheel 5 can be rotated according to the angle of the turning force.

[0058] The axial force rotation angle calculation unit 66 calculates the axial force rotation angle θpf by receiving the input of the steering angle θs and the conversion component θvg. The conversion component θvg is an intermediate component obtained in the process of calculating the target pinion angle θp* by the steering angle ratio variable control unit 62. The axial force rotation angle calculation unit 66 calculates the axial force rotation angle θpf by adding the steering angle θs and the conversion component θvg. The axial force rotation angle θpf thus obtained is output to the reaction force control unit 50.

[0059] For example, Figure 3 As shown, the target reaction force torque calculation unit 52 of the reaction force control unit 50 has an angular axial force calculation unit 52a. The angular axial force calculation unit 52a includes a process for calculating the angular axial force Taf by receiving an input of the axial force rotation angle θpf. The angular axial force Taf is an estimated value of the axial force acting on the rack shaft 22 specified by an arbitrarily set vehicle model or the like, and is a component reflected in the target reaction force torque command value Ts*.

[0060] The current axial force calculation unit 67 calculates the current axial force Tai by receiving the input of the actual current value Ib. The current axial force Tai is an estimated value of the axial force actually acting on the rack shaft 22 as the rotating wheel 5 rotates, and is a component reflected in the target reaction force torque command value Ts*. The current axial force Tai thus obtained is output to the reaction force control unit 50.

[0061] Steering angle ratio variable control unit

[0062] like Figure 4 As shown, the steering angle ratio variable control unit 62 has a static component calculation unit 70 , a dynamic component calculation unit 80 , and a reflection calculation unit 90 .

[0063] The static component calculation unit 70 performs a conversion calculation process of calculating a conversion component θvg by receiving inputs of the steering angle θs and the vehicle speed V. More specifically, the static component calculation unit 70 has a steering angle variable value calculation unit 71 and a conversion component calculation unit 72 .

[0064] The steering angle variable value calculation unit 71 includes a process for calculating the speed increasing ratio G and the characteristic change component Cvg by receiving inputs of the steering angle θs and the vehicle speed V. More specifically, the steering angle variable value calculation unit 71 has a speed increasing ratio calculation unit 71a and a characteristic change calculation unit 71b.

[0065] The speed increasing ratio calculation unit 71a includes a steering angle variable value calculation process for calculating the speed increasing ratio G by receiving the input of the steering angle θs and the vehicle speed V. The speed increasing ratio G is a steering angle variable value obtained by subtracting "1" from a value indicating a relationship in a case where the steering angle θs is the denominator and the target pinion angle θp* is the numerator. The value indicating a relationship in a case where the steering angle θs is the denominator and the target pinion angle θp* is the numerator is used as an index indicating a ratio of a change amount of the target pinion angle θp* relative to a change amount of the steering angle θs. Such an index is called, for example, a transmission ratio, a steering angle ratio, a gear ratio, etc., and specifies a relationship between the steering angle θs and the pinion angle θp or a relationship between the steering angle θs and the rotation angle θi. That is, the speed increasing ratio G is a value indicating a difference compared to a case where the steering angle θs corresponds to the target pinion angle θp* at a ratio of 1:1. The speed increasing ratio G thus obtained is used for calculations in the characteristic change calculation unit 71b and the conversion component calculation unit 72.

[0066] For example, the speed increasing ratio G is set so that the value becomes smaller as the steering angle θs becomes larger, and the value becomes smaller as the vehicle speed V becomes larger. The speed increasing ratio G is a positive value including "0". Therefore, the index indicating the ratio of the change amount of the target pinion angle θp* relative to the change amount of the steering angle θs is equal to or greater than "1".

[0067] The characteristic change calculation unit 71b includes a process for calculating the characteristic change component Cvg by receiving the input of the steering angle θs and the speed increasing ratio G. The characteristic change component Cvg is a value of a change gradient obtained by dividing the denominator by the steering angle change value Δθs which is the change amount of the steering angle θs, and the numerator by the conversion component change value Δθvg which is the change amount of the conversion component θvg. For example, in the case where the speed increasing ratio G is calculated based on a mapping using the steering angle θs as an input, such a change gradient may be a value obtained as a gradient between points before the change of the mapping and after the change of the mapping, that is, where the denominator is the steering angle change value Δθs, and the numerator is the speed increasing ratio change value ΔG which is the change amount of the speed increasing ratio G. The characteristic change component Cvg thus obtained is used for calculation in the dynamic component calculation unit 80.

[0068] The conversion component calculation unit 72 includes a process for calculating the conversion component θvg by receiving the input of the steering angle θs and the speed increasing ratio G. The conversion component calculation unit 72 is a multiplier, and calculates the conversion component θvg by multiplying the steering angle θs by the speed increasing ratio G. The conversion component θvg is a static component for increasing the amount of change in the steering angle θs by reflecting the speed increasing ratio G. That is, the conversion component θvg is a static component that reflects a stable characteristic in the behavior characteristics of the vehicle due to reflecting the speed increasing ratio G.

[0069] For example, since the steering angle θs is converted into the conversion component θvg, the conversion component calculation unit 72 has a characteristic specified by the characteristic change component Cvg obtained based on the speed increase ratio G so as to change the stable characteristic in the behavior characteristic of the vehicle. In the present embodiment, the characteristic change component Cvg is an example of the conversion characteristic.

[0070] The dynamic component calculation unit 80 performs a process of calculating the compensation component θvgc by receiving the input of the steering angle θs and the conversion component θvg. In addition, the dynamic component calculation unit 80 performs a characteristic change process of changing the characteristics of the compensation calculation process by receiving the input of the characteristic change component Cvg. More specifically, the dynamic component calculation unit 80 has a compensation calculation unit 81 and a characteristic change processing unit 82.

[0071] The compensation calculation unit 81 includes a process of calculating the compensation component θvgc by receiving an input of the conversion component θvg. The compensation component θvgc is obtained by compensating for a dynamic component that reflects a response characteristic in the behavior characteristics of the vehicle and has an influence due to the conversion calculation process performed on the steering angle θs. The compensation calculation unit 81 is, for example, a phase lag filter having a zero-order / first-order, i.e., first-order lag transfer function, and calculates the compensation component θvgc by performing phase compensation on the conversion component θvg. The compensation component θvgc thus obtained is used to reflect the calculation in the calculation unit 90.

[0072] For example, the phase lag filter is a low-pass filter, and has a characteristic that is specified by a transfer function having a predetermined cutoff frequency in order to adjust a response characteristic in the behavior characteristic of the vehicle, and that has an influence due to the conversion calculation process performed on the steering angle θs. The cutoff frequency corresponds to the filter constant K set when a discrete control system is implemented as the compensation calculation unit 81. For example, the filter constant K is set so that the value becomes smaller as the steering angular velocity ωs obtained by differentiating the steering angle θs becomes larger. In the present embodiment, the filter constant K is an example of a compensation characteristic.

[0073] The characteristic change processing unit 82 includes a process of calculating a characteristic change value Kc by receiving an input of a characteristic change component Cvg. The characteristic change value Kc is a component for changing the filter constant K. The characteristic change value Kc thus obtained is used for calculation in the compensation calculation unit 81. For example, the compensation calculation unit 81 uses the filter constant K obtained by adding or subtracting the characteristic change value Kc to the filter constant K after reflecting the characteristic change value Kc in phase compensation. The characteristic change value Kc in this case is an adjustment operation value for performing adjustment so as to change the filter constant K.

[0074] For example, the characteristic change value Kc is a value that changes according to the characteristic change component Cvg, and has a characteristic of changing the filter constant K so as to alleviate the degradation of the control stability of the vehicle steering system 2. For example, the characteristic change value Kc is set so that the value becomes smaller as the characteristic change component Cvg becomes larger.

[0075] The reflection calculation unit 90 performs a component reflection process of calculating the target pinion angle θp* by receiving input of the steering angle θs and the compensation component θvgc. The reflection calculation unit 90 is an adder and calculates the target pinion angle θp* by adding the compensation component θvgc to the steering angle θs.

[0076] How the implementation works

[0077] For example, in a case where the filter constant K does not change based on the characteristic variation component Cvg, in response to a change in the speed increasing ratio G, the range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation in the compensation calculation unit 81 is limited.

[0078] On the other hand, the characteristic change processing unit 82 in the dynamic component calculation unit 80 performs processing for changing the filter constant K of the compensation calculation unit 81 according to the characteristic based on the speed increase ratio G, that is, the characteristic change component Cvg. In the case where the filter constant K is thus changed according to the characteristic change component Cvg, in response to the change in the speed increase ratio G, the range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation in the compensation calculation unit 81 changes. That is, in the case where the conversion component θvg obtained by converting the steering angle θs is further subjected to phase compensation, the filter constant K in the compensation calculation unit 81 is changed so as to mitigate the reduction in the control stability of the vehicle steering system 2.

[0079] Advantages of the implementation method

[0080] (1-1) From the viewpoint of ensuring the control stability of the vehicle steering system 2, changing the filter constant K according to the characteristic change component Cvg can associate the speed increase ratio G and the filter constant K with each other in the conversion component calculation unit 72 and the compensation calculation unit 81. Therefore, even in the case where the relationship between the steering angle θs and the target pinion angle θp* changes, the control stability of the vehicle steering system 2 can be ensured. Therefore, the reduction in control stability can be alleviated.

[0081] (1-2) Of the static component calculation unit 70 and the dynamic component calculation unit 80, the dynamic component calculation unit 80 includes the characteristic change processing unit 82. Therefore, by simply including the characteristic change processing unit 82 in the dynamic component calculation unit 80, the reduction in control stability can be alleviated.

[0082] (1-3) The static component calculation unit 70 performs a process of converting the steering angle θs into the conversion component θvg using the speed increase ratio G. The speed increase ratio G varies according to the steering angle θs and the vehicle speed V. The dynamic component calculation unit 80 performs a phase lag filter process of performing phase lag compensation on the conversion component θvg. Therefore, in the case where the speed increase ratio G varies according to the steering angle θs and the vehicle speed V, the control stability of the vehicle steering system 2 can be ensured regardless of these steering angles θs and the vehicle speed V.

[0083] (1-4) The static component calculation unit 70 performs processing for calculating the speed increasing ratio G using the steering angle θs as an input. The characteristic change component Cvg is a conversion component change value Δθvg relative to the steering angle change value Δθs. The characteristic change component Cvg may be a speed increasing ratio change value ΔG relative to the steering angle change value Δθs. Therefore, adjustment of a change gradient obtained in association with the speed increasing ratio G becomes possible. This is effective for ensuring control stability of the vehicle steering system.

[0084] Second embodiment

[0085] The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. For ease of description, the same components as those in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and their description will be omitted.

[0086] Steering angle ratio variable control unit

[0087] like Figure 5 As shown, in the steering angle ratio variable control unit 62 of the present embodiment, the contents of the processing executed by the static component calculation unit 70 and the dynamic component calculation unit 80 are different.

[0088] More specifically, the static component calculation unit 70 has a characteristic change processing unit 73 in addition to a steering angle variable value calculation unit 74 and a conversion component calculation unit 72 as components corresponding to the steering angle variable value calculation unit 71 described in the first embodiment above. The dynamic component calculation unit 80 has a compensation calculation unit 81, but does not have a characteristic change processing unit 82. Therefore, the filter constant K in the present embodiment is set to change based on the steering angle velocity ωs obtained by differentiating the steering angle θs, and in addition, for example, does not change based on the characteristic change value Kc described in the first embodiment above. The filter constant K of the compensation calculation unit 81 is used for calculation in the characteristic change processing unit 73.

[0089] The characteristic change processing unit 73 of the static component calculation unit 70 includes a process of calculating the characteristic change component Cvg by receiving an input of the filter constant K. The characteristic change component Cvg thus obtained is used for calculation in the characteristic change calculation unit 74b.

[0090] The characteristic change calculation unit 74b is a component corresponding to the characteristic change calculation unit 71b described in the first embodiment above, and includes a process for calculating an adjusted speed increase ratio Gc by receiving inputs of the steering angle θs and the characteristic change component Cvg. The adjusted speed increase ratio Gc is a value for obtaining a speed increase ratio G that should satisfy the conversion component change value Δθvg of the characteristic change component Cvg relative to the steering angle change value Δθs. For example, in a case where the speed increase ratio G is calculated based on a mapping using the steering angle θs as an input, such an adjusted speed increase ratio Gc may be a value for obtaining a speed increase ratio G that should satisfy the speed increase ratio change value ΔG of the characteristic change component Cvg relative to the steering angle change value Δθs. The adjusted speed increase ratio Gc thus obtained is used for calculation in the speed increase ratio calculation unit 74a.

[0091] The speed increasing ratio calculation unit 74a is a component corresponding to the speed increasing ratio calculation unit 71a described in the first embodiment above, and includes a process for calculating the adjusted speed increasing ratio Gc as the speed increasing ratio G. The process for calculating such a speed increasing ratio G may be, for example, a process for obtaining the speed increasing ratio G by adding, subtracting or multiplying the adjusted speed increasing ratio Gc. The speed increasing ratio G thus obtained is used for calculation in the conversion component calculation unit 72. The characteristic change component Cvg, i.e., the adjusted speed increasing ratio Gc in this case, is an adjustment operation value for performing adjustment so as to change the speed increasing ratio G.

[0092] For example, the characteristic variation component Cvg is a value that varies according to the filter constant K, and has a characteristic of changing the speed increasing ratio G in order to alleviate the degradation of the control stability of the vehicle steering system 2. For example, the characteristic variation component Cvg is set so that the value becomes smaller as the filter constant K becomes smaller.

[0093] How the implementation works

[0094] For example, in a case where the speed increasing ratio G does not change based on the filter constant K, due to the change in the filter constant K, the speed increasing ratio G falls outside the range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation in the compensation calculation unit 81.

[0095] On the other hand, the characteristic change processing unit 73 in the static component calculation unit 70 performs processing for changing the speed increasing ratio G of the steering angle variable value calculation unit 74 based on the filter constant K. In the case where the speed increasing ratio G is thus changed based on the filter constant K, in response to the change in the filter constant K, the speed increasing ratio G is changed so as to remain within a range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation in the compensation calculation unit 81. Therefore, in the case where the conversion component θvg obtained by converting the steering angle θs is further subjected to phase compensation, the speed increasing ratio G in the steering angle variable value calculation unit 74 is changed so as to mitigate the reduction in the control stability of the vehicle steering system 2.

[0096] Advantages of the implementation method

[0097] The present embodiment which has been described above can produce the following advantages in addition to the advantages equivalent to the advantages (1-1) and (1-4) of the above-mentioned first embodiment.

[0098] (2-1) With respect to the static component calculation unit 70 and the dynamic component calculation unit 80, the static component calculation unit 70 includes the characteristic change processing unit 73. Therefore, by simply including the characteristic change processing unit 73 in the static component calculation unit 70, the reduction in control stability can be mitigated.

[0099] (2-2) The dynamic component calculation unit 80 performs a phase lag filter process for performing phase lag compensation on the conversion component θvg. The filter constant K varies according to the steering angle θs. The static component calculation unit 70 performs a process for converting the steering angle θs into the conversion component θvg using the speed increase ratio G. Therefore, in the case where the filter constant K varies according to the steering angle θs, the control stability of the vehicle steering system 2 can also be ensured regardless of the steering angle θs.

[0100] Third embodiment

[0101] The third embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. For ease of description, the same components as those in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and their description will be omitted.

[0102] Steering angle ratio variable control unit

[0103] like Figure 6 As shown, in the steering angle ratio variable control unit 62 of the present embodiment, the contents of the processing executed by the static component calculation unit 70 and the dynamic component calculation unit 80 are different.

[0104] More specifically, the steering angle ratio variable control unit 62 has a characteristic change processing unit 100 in addition to the static component calculation unit 70 and the dynamic component calculation unit 80. The dynamic component calculation unit 80 has a compensation calculation unit 81, but does not have a characteristic change processing unit 82. Therefore, the filter constant K in the present embodiment is set to change based on the steering angular velocity ωs obtained by differentiating the steering angle θs, and in addition, for example, does not change based on the characteristic change value Kc described in the above-mentioned first embodiment. The filter constant K of the compensation calculation unit 81 is used for calculation in the characteristic change processing unit 100.

[0105] The characteristic change processing unit 100 includes a process of calculating an adjusted conversion component θvgc0 by receiving input of a conversion component θvg, a characteristic change component Cvg, and a filter constant K. The adjusted conversion component θvgc0 is a value that changes according to the conversion component θvg, the characteristic change component Cvg, and the filter constant K, and has a characteristic of changing the conversion component θvg so as to alleviate the deterioration of the control stability of the vehicle steering system 2. For example, the adjusted conversion component θvgc0 is set so that the value becomes smaller as the characteristic change component Cvg becomes larger or as the filter constant K becomes smaller. The adjusted conversion component θvgc0 thus obtained is used for the calculation in the compensation calculation unit 81. In this case, the adjusted conversion component θvgc0 is an adjustment operation value for performing adjustment so as to change the conversion component θvg. Therefore, changing the conversion component θvg is equivalent to performing adjustment so as to change the filter constant K or equivalent to performing adjustment so as to change the characteristic change component Cvg, that is, the speed increase ratio G.

[0106] How the implementation works

[0107] For example, in a case where the conversion component θvg is not adjusted, the range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation in the compensation calculation unit 81 is limited in response to the change in the speed increasing ratio G. In this case, due to the change in the characteristic change component Cvg and the filter constant K in response to the change in the speed increasing ratio G, the speed increasing ratio G falls outside the range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation in the compensation calculation unit 81.

[0108] On the other hand, the characteristic change processing unit 100 performs processing for changing the conversion component θvg based on the characteristic change component Cvg and the filter constant K. In the case where the conversion component θvg is thus changed, in response to the change in the speed increasing ratio G, the conversion component θvg is changed so as to remain within a range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation in the compensation calculation unit 81. Therefore, in the case where the conversion component θvg obtained by converting the steering angle θs is further subjected to phase compensation, the conversion component θvg which is the target of the phase compensation is changed so as to mitigate the reduction in the control stability of the vehicle steering system 2.

[0109] Advantages of the implementation method

[0110] The present embodiment which has been described above can produce the following advantages in addition to the advantages equivalent to the advantages (1-1) and (1-4) of the above-mentioned first embodiment.

[0111] (3-1) The steering angle ratio variable control unit 62 includes a characteristic change processing unit 100 in addition to the static component calculation unit 70 and the dynamic component calculation unit 80. Therefore, by simply including the characteristic change processing unit 100 separately from the static component calculation unit 70 and the dynamic component calculation unit 80 in the steering angle ratio variable control unit 62, the reduction in control stability can be alleviated.

[0112] (3-2) The static component calculation unit 70 performs a process of converting the steering angle θs into the conversion component θvg using the speed increasing ratio G. The dynamic component calculation unit 80 performs a phase lag filtering process of performing phase lag compensation on the conversion component θvg. The conversion component θvg is affected by changes in the speed increasing ratio G and the filter constant K. Thus, in the case where the conversion component θvg is affected by changes in the speed increasing ratio G and the filter constant K, the control stability of the vehicle steering system 2 can be ensured regardless of the changes in these speed increasing ratios G and the filter constant K.

[0113] Fourth embodiment

[0114] The fourth embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. For ease of description, the same components as those in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and their description will be omitted.

[0115] Steering angle ratio variable control unit

[0116] like Figure 7 As shown, in the steering angle ratio variable control unit 62 of the present embodiment, the contents of the processing executed by the static component calculation unit 70 and the dynamic component calculation unit 80 are different.

[0117] More specifically, the static component calculation unit 70 has a speed-increasing ratio calculation unit 71a but does not have a characteristic change calculation unit 71b. The characteristic change processing unit 82 of the dynamic component calculation unit 80 includes a process of calculating the characteristic change value Kc by receiving an input of the speed-increasing ratio G.

[0118] For example, the characteristic change value Kc is a value that changes according to the speed increase ratio G, and has a characteristic of changing the filter constant K in order to reduce the degradation of the control stability of the vehicle steering system 2. For example, the characteristic change value Kc is set so that the value becomes smaller as the speed increase ratio G becomes higher. The characteristic of changing the filter constant K can make the filter constant K change according to the change of the speed increase ratio G, that is, the speed increase ratio change value ΔG. In this case, the process of calculating the speed increase ratio change value ΔG should be included in the process of either the speed increase ratio calculation unit 71a or the characteristic change processing unit 82.

[0119] The present embodiment which has been described above can produce effects equivalent to those of the above-described first embodiment, and advantages equivalent to the advantages (1-1) and (1-4) of the above-described first embodiment.

[0120] Fifth embodiment

[0121] The fifth embodiment will be described below with reference to the drawings, focusing on the differences from the second embodiment. For ease of description, the same components as those in the second embodiment will be denoted by the same reference numerals as those in the second embodiment, and their description will be omitted.

[0122] Steering angle ratio variable control unit

[0123] like Figure 8 As shown, in the steering angle ratio variable control unit 62 of the present embodiment, the content of the processing executed by the static component calculation unit 70 is different.

[0124] More specifically, the static component calculation unit 70 has a speed-increasing ratio calculation unit 74a and a characteristic change processing unit 73, but does not have a characteristic change calculation unit 74b. The characteristic change processing unit 73 includes a process for calculating the adjusted speed-increasing ratio Gc by receiving an input of the filter constant K. The adjusted speed-increasing ratio Gc thus obtained is used for calculation in the speed-increasing ratio calculation unit 74a.

[0125] For example, the adjusted speed increasing ratio Gc is a value that changes according to the filter constant K, and has a characteristic of changing the speed increasing ratio G in order to reduce the degradation of the control stability of the vehicle steering system 2. For example, the adjusted speed increasing ratio Gc is set so that the value becomes smaller as the filter constant K becomes smaller. The manner in which the speed increasing ratio G is changed in order to change the speed increasing ratio G change, i.e., the speed increasing ratio change value ΔG, may be specified. In this case, the processing of performing the calculation involved in changing the speed increasing ratio change value ΔG should be included in the processing of either the speed increasing ratio calculation unit 74a or the characteristic change processing unit 73.

[0126] The present embodiment described above can produce effects equivalent to those of the above-mentioned second embodiment, as well as advantages equivalent to the advantages (1-1) and (1-4) of the above-mentioned first embodiment and advantages equivalent to the advantages (2-1) and (2-2) of the above-mentioned second embodiment.

[0127] Other Implementations

[0128] Each of the above-described embodiments can be changed as follows: The following other embodiments can be combined with each other within the scope that no technical contradiction occurs.

[0129] In the first embodiment, when calculating the characteristic change value Kc, the characteristic change processing unit 82 may receive input of the steering angle θs and the vehicle speed V, i.e., parameters for calculating the speed increasing ratio G. In addition, the characteristic change processing unit 82 may use the conversion component θvg. The other embodiments described herein may also be applied to the fourth embodiment.

[0130] In the first embodiment, it is not important whether the form of the change in the characteristic change value Kc is linear or nonlinear. The other embodiments described herein can also be applied to the fourth embodiment.

[0131] In the first embodiment, the characteristic change value Kc should at least be set to be able to mitigate the reduction in control stability of the vehicle steering system 2 according to the characteristics of stability. For example, according to the characteristics of control stability of the vehicle steering system 2, the characteristic change value Kc may be set so that the value becomes larger as the speed increase ratio G becomes higher. The other embodiments described herein may also be applied to the fourth embodiment.

[0132] In the first embodiment, the compensation calculation unit 81 may use the filter constant K reflecting the characteristic change value Kc obtained by multiplying the filter constant K by the characteristic change value Kc in the phase compensation. The other embodiments described herein may also be applied to the fourth embodiment.

[0133] In the first embodiment, the filter constant K may be set to change only according to the characteristic change value Kc. The other embodiments described herein may also be applied to the fourth embodiment.

[0134] When the characteristic change processing unit 82 is provided, the first embodiment may also further include the characteristic change processing unit 73 as in the second embodiment. That is, the static component calculation unit 70 and the dynamic component calculation unit 80 may include the characteristic change processing units 73 and 82 for changing the characteristic of each unit in the unit based on the characteristics of the processing of the other units so as to ensure the control stability of the vehicle steering system 2. The other embodiments described herein may also be applied to the fourth embodiment.

[0135] In the second embodiment, the adjusted speed increasing ratio Gc should at least be set to be able to mitigate the reduction in control stability of the vehicle steering system 2 according to the characteristics of stability. For example, according to the characteristics of control stability of the vehicle steering system 2, the adjusted speed increasing ratio Gc may be set so that the value becomes larger as the filter constant K becomes smaller. The other embodiments described herein may also be applied to the fifth embodiment.

[0136] In each of the embodiments, the speed-increasing ratio calculation unit 71a may calculate an index indicating a ratio of a change in the target pinion angle θp* relative to a change in the steering angle θs as the speed-increasing ratio G. That is, the speed-increasing ratio G is a value equal to or greater than "1". In other embodiments described herein, the compensation component θvgc calculated by the dynamic component calculation unit 80 is used as the target pinion angle θp*. In this case, the dynamic component calculation unit 80 performs processing corresponding to the reflection calculation unit 90, and thus the reflection calculation unit 90 may be omitted.

[0137] In each of the embodiments, the steering angle variable value calculation unit 71, 74 should at least be able to reflect the state change of at least any one of the vehicle steering system 2 or the vehicle on the speed increase ratio G. For example, when calculating the speed increase ratio G, the steering angle variable value calculation unit 71, 74 may use only one of the steering angle θs or the vehicle speed V, or may use other elements in combination. Examples of other elements include the steering angular velocity ωs and the rotational angular velocity ωt obtained by the differential value of the pinion angle θp or the target pinion angle θp*.

[0138] In each of the embodiments, the speed-increasing ratio G can be arbitrarily changed, such as, for example, setting the speed-increasing ratio G to change linearly as the value becomes smaller as the steering angle θs becomes larger, or setting the speed-increasing ratio G to make the value become larger as the steering angle θs becomes larger. In addition, the speed-increasing ratio G can be a negative value.

[0139] In each of the embodiments, the compensation calculation unit 81 should at least be able to reflect the state change of at least any one of the vehicle steering system 2 or the vehicle on the phase compensation, that is, the filter constant K. For example, when performing phase compensation, the compensation calculation unit 81 may use the filter constant K according to the vehicle speed V, or may use both the steering angular velocity ωs and the vehicle speed V, or may use other elements in combination. Examples of other elements include the aforementioned rotational angular velocity ωt.

[0140] In each of the embodiments, for example, the filter constant K may be set such that, for example, the value becomes larger as the steering angular speed ωs becomes higher.

[0141] In each of the embodiments, for the compensation calculation unit 81, for example, a low-pass filter having a high-order transfer function, such as a second-order lag transfer function, can be adopted as long as the low-pass filter is a phase lag filter. The compensation calculation unit 81 can be, for example, a phase advance filter as long as it is finally appropriately made in the steering angle ratio variable control unit 62.

[0142] In each of the embodiments, the current axial force calculation unit 67 may be a function of the reaction force control unit 50, i.e., the target reaction force torque calculation unit 52. In this case, the target reaction force torque calculation unit 52 should at least include a process of calculating the current axial force Tai by receiving an input of the actual current value Ib.

[0143] In each of the embodiments, the axial force rotation angle calculation unit 66 may be a function of the reaction force control unit 50, i.e., the target reaction force torque calculation unit 52. In this case, the target reaction force torque calculation unit 52, i.e., the angular axial force calculation unit 52a should at least include a process of calculating the axial force rotation angle θpf by receiving inputs of the steering angle θs and the conversion component θvg.

[0144] In each of the embodiments, at least some of the functions of the steering angle ratio variable control unit 62 may be functions of the reaction force control unit 50 .

[0145] In each of the embodiments, when calculating the target reaction torque command value Ts*, the target reaction torque calculation unit 52 does not need to use either the vehicle speed V or the steering torque Th, or may use other elements in combination.

[0146] In each of the embodiments, the target reaction torque calculation unit 52 may calculate, as the target reaction torque command value Ts*, a value calculated by execution of torque feedback control that adapts the steering torque Th to the target steering torque calculated based on the steering torque Th.

[0147] In each of the embodiments, the steering angle calculation unit 51 may calculate the steering angle θs by considering the twist amount of the steering shaft 11 according to the steering torque Th.

[0148] In each of the embodiments, the steering angle θs may be a detection value of a steering angle sensor that directly detects the rotation angle of the steering shaft 11. The steering angle sensor may be provided in the steering shaft 11 between the steering wheel 3 and the torque sensor 41, for example.

[0149] In each of the embodiments, the steering actuator 12 does not necessarily have to include the steering-side speed reduction mechanism 14 .

[0150] In each of the embodiments, the steering side motor 13 is not limited to a three-phase brushless motor. For example, the steering side motor 13 may be a brushed DC motor. Other embodiments described herein may also be applied to the rotation side motor 32.

[0151] In each of the embodiments, the pinion angle θp can be obtained by converting the detection value of the movement amount of the rack shaft 22. In this case, the control amount related to the pinion angle θp and the like is converted from the detection value of the movement amount of the rack shaft 22.

[0152] In each of the embodiments, the operating member operated by the driver to steer the vehicle is not limited to the steering wheel 3. For example, the operating member may be a joystick. In each of the embodiments, the rotating unit 6 transmits the rotation of the rotating side motor 32 to the conversion mechanism 34 through the transmission mechanism 33. However, without being limited thereto, the rotating unit 6 may be configured to transmit the rotation of the rotating side motor 32 to the conversion mechanism 34, for example, through a gear mechanism. Or the rotating unit 6 may be configured so that the rotating side motor 32 directly rotates the conversion mechanism 34. In addition, the rotating unit 6 may be configured to include a second rack and pinion mechanism, and the rotating unit 6 may be configured so that in the second rack and pinion mechanism, the rotation of the rotating side motor 32 is converted into the reciprocating motion of the rack shaft 22.

[0153] In each of the embodiments, the configuration of the rotating unit 6 is not limited to the configuration in which the right rotating wheel 5 and the left rotating wheel 5 operate in conjunction with each other. In other words, the configuration may enable the right rotating wheel 5 and the left rotating wheel 5 to be independently controlled.

[0154] In each of the embodiments, the vehicle steering system 2 has a linkless structure in which the steering unit 4 and the rotating unit 6 are always mechanically disconnected from each other. However, without being limited thereto, the vehicle steering system 2 may have a structure in which the steering unit 4 and the rotating unit 6 may be mechanically disconnected from each other by a clutch, for example.

[0155] In each of the embodiments, for the rotation side motor 32, for example, a motor provided on the same axis as the rack shaft 22 or a motor connected to a pinion shaft forming a rack and pinion mechanism together with the rack shaft 22 through a worm and a worm gear may be used.

Claims

1. A steering control device (1), the steering control device (1) being used for a vehicle steering system (2), the vehicle steering system (2) having a power transmission path cut off between a steering unit (4) steered by a steering wheel (3) of the vehicle and a rotating unit (6) operated to rotate a rotating wheel (5) of the vehicle, The steering control device (1) comprises a processor (60) configured to control the operation of the rotation unit (6), characterized in that: The processor (60) is configured to execute a target rotation angle calculation process, the target rotation angle calculation process calculating a target rotation angle based on a steering angle representing a rotation position of the steering wheel (3), the target rotation angle being a target of a rotation angle representing a rotation position of the rotating wheel (5) and being a control amount for operating the rotating unit (6); The target rotation angle calculation process includes: a conversion calculation process that receives an input of the steering angle and calculates a conversion component obtained by converting the steering angle using the input of the steering angle in order to change the relationship between the steering angle and the rotation angle; a compensation calculation process that receives an input of the conversion component and calculates a compensation component obtained by performing phase compensation on the conversion component using the input of the conversion component in order to adjust the influence on the behavior of the vehicle; and a component reflection process for calculating the target rotation angle so as to reflect the compensation component; The conversion calculation process includes calculating the conversion component according to a conversion characteristic that specifies a relationship between the steering angle and the conversion component; The compensation calculation process includes calculating the compensation component according to a compensation characteristic that specifies a relationship between the conversion component and the compensation component; and At least a first process between the conversion calculation process and the compensation calculation process includes a characteristic change process, which changes the characteristics in the first process based on the characteristics of a second process between the conversion calculation process and the compensation calculation process so as to ensure the control stability of the vehicle steering system (2).

2. The steering control device (1) according to claim 1, characterized in that: In the conversion calculation process and the compensation calculation process, the compensation calculation process includes the characteristic change process; and The characteristic changing process in the compensation calculation process changes the compensation characteristic based on the conversion characteristic.

3. The steering control device (1) according to claim 2, characterized in that: the conversion calculation process converts the steering angle into the conversion component using a steering angle variable value indicating a ratio of a change amount of the rotation angle relative to a change amount of the steering angle; The conversion characteristic is based on the steering angle variable value that changes according to the state of at least either the vehicle or the vehicle steering system (2); The compensation calculation process is a phase lag filtering process that performs phase lag compensation on the conversion component; and The compensation characteristic indicates a constant of a transfer function as a characteristic of the phase lag filtering process.

4. The steering control device (1) according to claim 1, characterized in that: In the conversion calculation process and the compensation calculation process, the conversion calculation process includes the characteristic change process; and The characteristic changing process in the conversion calculation process changes the conversion characteristic based on the compensation characteristic.

5. The steering control device (1) according to claim 4, characterized in that: The compensation calculation process is a phase lag filtering process that performs phase lag compensation on the conversion component; The compensation characteristic indicates a constant of a transfer function as a characteristic of the phase lag filtering process that changes according to a state of at least either the vehicle or the vehicle steering system (2); the conversion calculation process converts the steering angle into the conversion component using a steering angle variable value indicating a ratio of the amount of change in the rotation angle relative to the amount of change in the steering angle; and The conversion characteristic is based on the steering angle variable value.

6. The steering control device (1) according to claim 3 or claim 5, characterized in that: the conversion calculation process includes a steering angle variable value calculation process that calculates the steering angle variable value using the steering angle as an input; and The characteristic based on the steering angle variable value is the amount of change of the conversion component or the amount of change of the steering angle variable value relative to the amount of change of the steering angle input into the steering angle variable value calculation process.

7. A steering control method, the steering control method being used for a vehicle steering system (2), the vehicle steering system (2) having a power transmission path cut off between a steering unit (4) steered by a steering wheel (3) of the vehicle and a rotating unit (6) operated to rotate a rotating wheel (5) of the vehicle, The steering control method comprises executing a control process for controlling the operation of the rotation unit (6), characterized in that: The control process includes a target rotation angle calculation process, the target rotation angle calculation process calculates a target rotation angle based on a steering angle representing a rotation position of the steering wheel (3), the target rotation angle being a target rotation angle representing a rotation position of the rotating wheel (5) and being a control amount for operating the rotating unit (6); The target rotation angle calculation process includes: a conversion calculation process that receives an input of the steering angle and calculates a conversion component obtained by converting the steering angle using the input of the steering angle in order to change the relationship between the steering angle and the rotation angle; a compensation calculation process that receives an input of the conversion component and calculates a compensation component obtained by performing phase compensation on the conversion component using the input of the conversion component in order to adjust the influence on the behavior of the vehicle; and a component reflection process for calculating the target rotation angle so as to reflect the compensation component; The conversion calculation process includes calculating the conversion component according to a conversion characteristic that specifies a relationship between the steering angle and the conversion component; The compensation calculation process includes calculating the compensation component according to a compensation characteristic that specifies a relationship between the conversion component and the compensation component; and At least a first process between the conversion calculation process and the compensation calculation process includes a characteristic change process, which changes the characteristics in the first process based on the characteristics of a second process between the conversion calculation process and the compensation calculation process so as to ensure the control stability of the vehicle steering system (2).

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