Steering control apparatus and steering control method

Abstract

To provide a steering control apparatus and a steering control method which can suppress deterioration in control stability.SOLUTION: A steering control apparatus is applied to a vehicle steering system having a configuration in which a power transmission path between a steering unit and a turning unit is separated. A turning control unit comprises a steering angle ratio variable control section 62 calculating a target pinion angle θp* based on a steering angle θs. The steering angle ratio variable control section 62 includes a static component calculation section 70, a dynamic component calculation section 80 and a reflection calculation section 90. The static component calculation section 70 includes processing of calculating a transform component θvg obtained by transforming the steering angle θs based on a speed increase ratio G. The dynamic component calculation section 80 includes processing of calculating a compensated component θvgc obtained by phase-compensating the transform component θvg based on a filter constant K. The dynamic component calculation section 80 includes a characteristic change processing section 82 for changing the filter constant K so as to secure the control stability of the vehicle steering system based on the speed increase ratio G.SELECTED DRAWING: Figure 4

Description

[Technical field]

[0001] The present invention relates to a steering control device and a steering control method. [Background technology]

[0002] Conventionally, there is a steer-by-wire type steering device mounted on a vehicle. Such a steer-by-wire type steering device has an advantage that the relationship between the steering angle, which is the rotation position of the steering wheel, and the turning angle, which is the turning position of the steered wheels, can be freely changed. However, freely changing the relationship between the steering angle and the turning angle affects the response characteristics of the yaw rate, which is the behavior of the vehicle. As a technology that makes it possible to deal with such effects, for example, a steering control device described in Patent Document 1 has been proposed.

[0003] In the above-mentioned Patent Document 1, phase compensation is applied to deal with the effect on the yaw rate response, which is the behavior of the vehicle, caused by freely changing the relationship between the steering angle and the turning angle. Such phase compensation compensates for the component that acts to freely change the relationship between the steering angle and the turning angle. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2023-12120 Summary of the Invention [Problem to be solved by the invention]

[0005] However, the influence of freely changing the relationship between the steering angle and the turning angle is not limited to the influence on the yaw rate responsiveness, which is the behavior of the vehicle, but is also thought to affect the stability of control. In other words, when the relationship between the steering angle and the turning angle is freely changed, it is desired to suppress the deterioration of the stability of control. [Means for solving the problem]

[0006] A steering control device capable of solving the above-mentioned problems is applied to a vehicle steering system having a structure in which a power transmission path between a steering unit steered by a steering wheel of a vehicle and a steering unit operating to steer the steered wheels of the vehicle is separated. The steering control device includes a control unit that controls the operation of the steering unit, and the control unit is configured to execute a target steering angle calculation process that calculates a target steering angle that is a steering position of the steered wheels, which is a control amount for operating the steering unit, based on a steering angle that is a rotational position of the steering wheel, and the target steering angle calculation process includes a conversion calculation process that inputs the steering angle to calculate a conversion component obtained by converting the steering angle in order to change the relationship between the steering angle and the steering angle, and a conversion calculation process that inputs the conversion component to phase compensate the conversion component in order to adjust the influence on the behavior of the vehicle. and a component reflection process that calculates the target steering angle so as to reflect the compensated component, wherein the conversion calculation process includes a process of calculating the conversion component according to a conversion characteristic that defines a relationship between the steering angle and the conversion component, and the compensation calculation process includes a process of calculating the compensated component according to a compensation characteristic that defines the relationship between the conversion component and the compensated component, and at least one of the conversion calculation process and the compensation calculation process includes a characteristic change process that changes a characteristic in the corresponding process based on a characteristic in the other process so as to ensure stability in control of the vehicle steering system.

[0007] According to the above configuration, the characteristic change process changes the characteristic in the corresponding process based on the characteristic of the other process. This allows the characteristics of the conversion calculation process and the compensation calculation process to be associated with each other in terms of ensuring the control stability of the vehicle steering system. In other words, even when the relationship between the steering angle and the turning angle is changed, the control stability of the vehicle steering system can be ensured. Therefore, a decrease in the control stability can be suppressed.

[0008] More specifically, in the above-mentioned steering control device, the compensation calculation processing of the conversion calculation processing and the compensation calculation processing includes the characteristic change processing, and the characteristic change processing in the compensation calculation processing is a processing that changes the compensation characteristic based on the conversion characteristic.

[0009] According to the above configuration, when the transformation component obtained by changing the steering angle is further phase-compensated, the compensation characteristics in the compensation calculation process are changed so as to suppress a decrease in the stability of the control of the vehicle steering system. As a result, the decrease in the stability of the control can be suitably suppressed simply by including the characteristic change process in the compensation calculation process.

[0010] In the above steering control device, it is preferable that the conversion calculation process is a process of converting the steering angle into the conversion component using a steering angle variable value indicating a ratio of a change in the steering angle to a change in the steering angle, the conversion characteristic is a characteristic based on the steering angle variable value corresponding to a change in the state of at least one of the vehicle and the vehicle steering system, the compensation calculation process is a phase lag filter process that performs phase lag compensation on the conversion component, and the compensation characteristic is a value indicating a constant of a transfer function which is a characteristic of the phase lag filter process.

[0011] According to the above configuration, even if the steering angle variable value changes in response to a change in the state of at least one of the vehicle and the vehicle steering system, control stability of the vehicle steering system can be ensured regardless of the change in state.

[0012] Further, in the above steering control device, the conversion calculation process of the conversion calculation process and the compensation calculation process includes the characteristic change process, and the compensation characteristic in the compensation calculation process is configured to be changed based on a change in the state of the vehicle, and the characteristic change process in the conversion calculation process is a process that changes the conversion characteristic based on the compensation characteristic.

[0013] According to the above configuration, when the compensation characteristic in the compensation calculation process changes due to the running of the vehicle, the conversion characteristic in the conversion calculation process is changed so as to suppress the deterioration of the stability of the control of the vehicle steering system. In other words, by simply including the characteristic change process in the conversion calculation process, the deterioration of the stability of the control can be suitably suppressed.

[0014] In the above steering control device, it is preferable that the compensation calculation process is a phase lag filter process that performs phase lag compensation on the conversion component, the compensation characteristic is a value indicating a constant of a transfer function that is a characteristic of the phase lag filter process in response to a state change of at least one of the vehicle and the vehicle steering system, the conversion calculation process is a process that converts the steering angle into the conversion component using a steering angle variable value that indicates the ratio of a change in the steering angle to a change in the steering angle, and the conversion characteristic is a characteristic based on the steering angle variable value.

[0015] According to the above configuration, even if the constant of the transfer function changes in response to a change in the state of at least one of the vehicle and the vehicle steering system, control stability of the vehicle steering system can be ensured regardless of the change in state.

[0016] In the above steering control device, it is preferable 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 change in the conversion component or the change in the steering angle variable value relative to the change in the steering angle input to the steering angle variable value calculation process.

[0017] According to the above-mentioned configuration, it is possible to adjust the gradient of change obtained in relation to the steering angle variable value, which is effective in ensuring the control stability of the steering system for a vehicle brake. A steering control method capable of solving the above-mentioned problems is a method applied to a vehicle steering system having a structure in which a power transmission path between a steering unit steered by a steering wheel of a vehicle and a steering unit operating to steer the steered wheels of the vehicle is separated. The steering control method includes executing a control process for controlling the operation of the steering unit, the control process including a target steering angle calculation process for calculating a target steering angle, which is a target of the steering angle, which is a steering position of the steered wheels, which is a control amount for operating the steering unit, based on a steering angle, which is a rotational position of the steering wheel, and the target steering angle calculation process includes a conversion calculation process for inputting the steering angle to change the relationship between the steering angle and the steering angle, and a conversion calculation process for converting the steering angle to calculate a conversion component obtained by inputting the conversion component to adjust the influence on the behavior of the vehicle. The steering system includes a compensation calculation process that calculates a compensated component obtained by compensation, and a component reflection process that calculates the target steering angle so as to reflect the compensated component, wherein the conversion process includes a process that calculates the converted component according to a conversion characteristic that defines the relationship between the steering angle and the converted component, and the compensation process includes a process that calculates the compensated component according to a compensation characteristic that defines the relationship between the converted component and the compensated component, and at least one of the conversion process and the compensation process includes a characteristic change process that changes the characteristic in the process based on the characteristic of the other process so as to ensure control stability of the vehicle steering system. Effect of the Invention

[0018] According to the present invention, it is possible to suppress a decrease in stability in control. [Brief description of the drawings]

[0019] [Figure 1] 1 is a diagram showing a configuration of a vehicle steering system according to a first embodiment. [Diagram 2] FIG. 2 is a block diagram showing the functions of the steering control device of FIG. 1. [Diagram 3] FIG. 2 is a block diagram showing a function for calculating an angular axial force in the steering control device of FIG. 1. [Figure 4] 3 is a block diagram showing the functions of a steering angle ratio variable control unit in FIG. 2. [Diagram 5] FIG. 11 is a block diagram showing the functions of a steering angle ratio variable control unit according to a second embodiment. [Figure 6] FIG. 11 is a block diagram showing the functions of a steering angle ratio variable control unit according to a third embodiment. [Figure 7] FIG. 11 is a block diagram showing the functions of a steering angle ratio variable control unit according to a fourth embodiment. [Figure 8] FIG. 13 is a block diagram showing the functions of a steering angle ratio variable control unit according to a fifth embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0020] <First embodiment> A first embodiment of the present invention will now be described. As shown in FIG. 1, 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 a driver via a steering wheel 3 of the vehicle, which is a steering member. The turning unit 6 operates to turn left and right steered wheels 5 of the vehicle in response to a steering input to the steering unit 4 by the driver. The vehicle steering system 2 of this embodiment has a structure in which, for example, a power transmission path between the steering unit 4 and the turning unit 6 is mechanically separated at all times. A power transmission path between a steering actuator 12 described later and a turning actuator 31 described later is mechanically separated at all times. That is, the vehicle steering system 2 includes a steer-by-wire type steering device.

[0021] 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 includes a steering-side motor 13 and a steering-side reduction mechanism 14. The steering-side motor 13 is a reaction motor that applies a steering reaction force, which is a force resisting steering, to the steering wheel 3 via the steering shaft 11. The steering-side motor 13 is connected to the steering shaft 11 via the steering-side reduction mechanism 14, which is made of, for example, a worm and wheel. For the steering-side motor 13 of this embodiment, for example, a three-phase brushless motor is adopted.

[0022] The steering unit 6 includes a pinion shaft 21, a rack shaft 22 as a steering shaft, and a rack housing 23. The pinion shaft 21 and the rack shaft 22 are connected with a predetermined cross angle. A rack-and-pinion mechanism 24 is formed by meshing pinion teeth 21a formed on the pinion shaft 21 with rack teeth 22a formed on the rack shaft 22. The pinion shaft 21 corresponds to a rotation axis that can be converted into a steering angle θi, which is the steering position of the steered wheels 5. The rack housing 23 accommodates the rack-and-pinion mechanism 24.

[0023] One end of the pinion shaft 21 opposite to the end connected to the rack shaft 22 protrudes from a rack housing 23. Both ends of the rack shaft 22 protrude from both axial ends of the rack housing 23. Tie rods 26 are connected to both ends of the rack shaft 22 via rack ends 25 made of ball joints. The ends of the tie rods 26 are connected to knuckles (not shown) to which the left and right steered wheels 5 are respectively attached.

[0024] The steering unit 6 includes a steering actuator 31. The steering actuator 31 includes a steering side motor 32, a transmission mechanism 33, and a conversion mechanism 34. The steering side motor 32 applies a steering force for steering the steered wheels 5 relative to the rack shaft 22 via the transmission mechanism 33 and the conversion mechanism 34. The steering side motor 32 transmits rotation to the conversion mechanism 34 via the transmission mechanism 33, which is, for example, a belt transmission mechanism. The transmission mechanism 33 converts the rotation of the steering side motor 32 into reciprocating motion of the rack shaft 22 via the conversion mechanism 34, which is, for example, a ball screw mechanism. For the steering side motor 32 of this embodiment, for example, a three-phase brushless motor is used.

[0025] In vehicle steering system 2, the steering angle θi of steered wheels 5 is changed by applying a motor torque as a steering force from steering actuator 31 to rack shaft 22 in response to steering by the driver. At this time, a steering reaction force resisting the steering by the driver is applied to steering wheel 3 from steering actuator 12. As a result, in vehicle steering system 2, the steering torque Th required for steering steering wheel 3 is changed by the steering reaction force, which is the motor torque applied from steering actuator 12.

[0026] The pinion shaft 21 is provided in order to support the rack shaft 22 together with the pinion shaft 21 inside the rack housing 23. The rack shaft 22 is supported movably along its axial direction and is pressed toward the pinion shaft 21 by a support mechanism (not shown) provided in the vehicle steering system 2. As a result, the rack shaft 22 is supported inside the rack housing 23. However, another support mechanism for supporting the rack shaft 22 in the rack housing 23 may be provided without using the pinion shaft 21.

[0027] <Electrical configuration of vehicle steering system> 1, the steering-side motor 13 and the steered-side motor 32 are connected to a steering control device 1. The steering control device 1 controls the operation of each of the motors 13, 32.

[0028] Detection results of various sensors are input to the steering control device 1. The various sensors include, for example, a torque sensor 41, a steering side rotation angle sensor 42, a turning side rotation angle sensor 43, and a vehicle speed sensor 44.

[0029] The torque sensor 41 is provided on the steering shaft 11 between the steering wheel 3 and the steering side 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. The steering torque Th is detected in relation to the twist of a torsion bar 41a provided on the steering shaft 11 between the steering wheel 3 and the steering side reduction mechanism 14, in the middle of the steering shaft 11. The steering side rotation angle sensor 42 is provided on the steering side motor 13. The steering side rotation angle sensor 42 detects a rotation angle θa, which is an angle of a rotation shaft of the steering side motor 13, within a range of 360 degrees. The turning side rotation angle sensor 43 is provided on the turning side motor 32. The turning side rotation angle sensor 43 detects a rotation angle θb, which is an angle of a rotation shaft of the turning side motor 32, within a range of 360 degrees. The vehicle speed sensor 44 detects a vehicle speed V, which is the traveling speed of the vehicle.

[0030] <Functions of the steering control device> As shown in FIG. 2, the steering control device 1 has a reaction force control unit 50 and a turning control unit 60. The reaction force control unit 50 executes a control process for controlling the steering wheel 3, which is an object of control. The reaction force control unit 50 controls the driving of the steering actuator 12, more specifically the steering-side motor 13, in order to control the steering reaction force, which is the control amount of the object of control. The turning control unit 60 executes a control process for controlling the rack shaft 22, which is an object of control. The turning control unit 60 controls the driving of the turning actuator 31, more specifically the turning-side motor 32, in order to control the steering force, which is the control amount of the object of control. The reaction force control unit 50 and the turning control unit 60 transmit and receive information to each other via a local network such as serial communication, for example. The reaction force control unit 50 constitutes a reaction force system RS in combination with the steering unit 4. The turning control unit 60 constitutes a steering system TS in combination with the steering unit 6. In this embodiment, the turning control unit 60 is an example of a control unit.

[0031] The reaction force control unit 50 is equipped with a central processing unit (hereinafter referred to as "CPU") and a memory. The reaction force control unit 50 executes various processes by the CPU executing a program stored in the memory at a predetermined calculation cycle. The steering control unit 60 is equipped with a central processing unit (hereinafter referred to as "CPU") and a memory. The steering control unit 60 executes various processes by the CPU executing a program stored in the memory at a predetermined calculation cycle. The CPU and the memory constitute a microcomputer, which is a processing circuit. The memory includes computer readable media such as RAM (Random Access Memory) and ROM (Read Only Memory). However, it is one example that various processes are realized by software. The processing circuits of the reaction force control unit 50 and the steering control unit 60 may be configured to realize at least a part of the processes by a hardware circuit such as a logic circuit.

[0032] Fig. 2 shows a part of the processing executed by the reaction force control unit 50 and the steering control unit 60. The processing shown in Fig. 2 is a part of the processing realized by the CPU executing a program stored in the memory, and is described for each type of processing realized.

[0033] The reaction force control unit 50 has a current sensor 54. The current sensor 54 detects an actual current value Ia obtained from a current value of each phase of the steering-side motor 13 flowing through a connection line between the reaction force control unit 50 and a motor coil of each phase of the steering-side motor 13. The current sensor 54 obtains, as a current, a voltage drop across a shunt resistor connected to the source side of each switching element in an inverter (not shown) provided corresponding to the steering-side motor 13. Note that, for convenience of explanation, in FIG. 2, the connection lines of each phase and the current sensors of each phase are illustrated as one unit.

[0034] The steering control unit 60 has a current sensor 65. The current sensor 65 detects an actual current value Ib obtained from the current value of each phase of the steering-side motor 32 flowing through a connection line between the steering control unit 60 and the motor coil of each phase of the steering-side motor 32. The current sensor 65 obtains, as a current, a voltage drop across a shunt resistor connected to the source side of each switching element in an inverter (not shown) provided corresponding to the steering-side motor 32. Note that, for ease of explanation, in FIG. 2, the connection lines of each phase and the current sensors of each phase are illustrated as one each.

[0035] <About the reaction force control unit> 2, reaction force control unit 50 controls power supply to steering-side motor 13 by inputting steering torque Th, vehicle speed V, rotation angle θa, axial force turning angle θpf, and current axial force Tai. The axial force turning angle θpf and current axial force Tai are components calculated in steering control unit 60.

[0036] The reaction force control unit 50 has a steering angle calculation unit 51 , a target reaction force torque calculation unit 52 , and an electricity supply control unit 53 . Steering angle calculation unit 51 calculates steering angle θs by inputting rotation angle θa. Steering angle calculation unit 51 converts rotation angle θa into an integrated angle including a range exceeding 360°, for example, by counting the number of rotations of steering-side motor 13 from a steering neutral position, which is the rotation position of steering wheel 3 when the vehicle is moving straight. Steering angle calculation unit 51 calculates steering angle θs by multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotation speed ratio of steering-side reduction gear mechanism 14. Steering angle θs obtained in this way is used for calculation in target reaction force torque calculation unit 52. In addition, steering angle θs is output to steering control unit 60.

[0037] Target reaction torque calculation unit 52 calculates target reaction torque command value Ts* by inputting steering torque Th, vehicle speed V, axial force turning angle θpf, current axial force Tai, and steering angle θs. Target reaction torque command value Ts* is a reaction force control amount that is a target for the steering reaction force of steering wheel 3 to be generated through steering-side motor 13. Target reaction torque command value Ts* thus obtained is used for control in current supply control unit 53.

[0038] The energization control unit 53 calculates a current command value Ia* by inputting the target reaction torque command value Ts*. The current command value Ia* is a target value of the torque to be generated in the steering-side motor 13. The energization control unit 53 calculates a converted current value Iae by inputting the actual current value Ia and the rotation angle θa. The converted current value Iae is a converted value obtained by converting the actual current value Ia into a current value on the dq coordinates. The energization control unit 53 controls the power supply to the steering-side motor 13 by executing a feedback control of the converted current value Iae so that the converted current value Iae follows the current command value Ia*. As a result, the steering-side motor 13 generates a torque according to the target reaction torque command value Ts*. That is, it is possible to give the driver a suitable sense of response according to the road surface reaction force.

[0039] <About the steering control unit> 2, the steering control unit 60 receives the vehicle speed V, the rotation angle θb, and the steering angle θs to control the power supply to the steering-side motor 32. The steering angle θs is a component calculated in the reaction force control unit 50.

[0040] The steering control unit 60 has a pinion angle calculation unit 61, a steering angle ratio variable control unit 62, a pinion angle feedback control unit ("pinion angle F / B control unit" in the figure) 63, an energization control unit 64, a steering angle calculation unit for axial force 66, and a current axial force calculation unit 67.

[0041] The pinion angle calculation unit 61 calculates the pinion angle θp by inputting the rotation angle θb. The pinion angle calculation unit 61 converts the rotation angle θb into an integrated angle including a range exceeding 360°, for example, by counting the number of rotations of the steered-side motor 32 from a rack neutral position, which is the position of the rack shaft 22 when the vehicle is traveling straight. The pinion angle calculation unit 61 multiplies the integrated angle obtained by the conversion by a conversion coefficient based on the rotation speed ratio of the transmission mechanism 33, the lead of the conversion mechanism 34, and the rotation speed ratio of the rack and pinion mechanism 24, to calculate the pinion angle θp, which is the actual rotation angle of the pinion shaft 21. The pinion angle θp obtained in this way is used for calculation in the pinion angle feedback control unit 63.

[0042] Steering angle ratio variable control unit 62 executes target steering angle calculation processing to calculate target pinion angle θp* by inputting vehicle speed V and steering angle θs. Target pinion angle θp* is a steering control amount that is a target for pinion angle θp obtained as a result of steering steered wheels 5. Target pinion angle θp* obtained in this manner is used for calculation in pinion angle feedback control unit 63.

[0043] The pinion angle feedback control unit 63 calculates a steering force command value Tp* by inputting the target pinion angle θp* and the pinion angle θp. The steering force command value Tp* is a steering control amount that is a target for the steering force of the steered wheels 5 to be generated through the steered-side motor 32. The pinion angle feedback control unit 63 calculates the steering force command value Tp* by executing feedback control of the pinion angle θp so as to make the pinion angle θp follow the target pinion angle θp*. The steering force command value Tp* obtained in this manner is used for control in the current supply control unit 64.

[0044] The energization control unit 64 calculates a current command value Ib* by inputting the steering force command value Tp*. The current command value Ib* is a target value of the torque to be generated in the steered-side motor 32. The energization control unit 64 calculates a converted current value Ibe by inputting 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 coordinates. The energization control unit 64 controls the power supply to the steered-side motor 32 by executing feedback control of the converted current value Ibe so that the converted current value Ibe follows the current command value Ib*. This causes the steered-side motor 32 to generate a torque according to the steering force command value Tp*. That is, it is possible to rotate the steered wheels 5 by an angle according to the steering force.

[0045] Axial force turning angle calculation section 66 calculates axial force turning angle θpf by inputting steering angle θs and conversion component θvg. Conversion component θvg is an intermediate component obtained in the process in which steering angle ratio variable control section 62 calculates target pinion angle θp*. Axial force turning angle calculation section 66 calculates axial force turning angle θpf by adding steering angle θs and conversion component θvg. The axial force turning angle θpf obtained in this manner is output to reaction force control section 50.

[0046] For example, as shown in Fig. 3, target reaction force torque calculation section 52 of reaction force control section 50 has angle axial force calculation section 52a. Angular axial force calculation section 52a includes a process of calculating angular axial force Taf by inputting axial force turning angle θpf. The angular axial force Taf is an estimated value of the axial force acting on rack shaft 22, which is defined by an arbitrarily set vehicle model or the like, and is a component reflected in target reaction force torque command value Ts*.

[0047] The current axial force calculation unit 67 calculates the current axial force Tai by inputting the actual current value Ib. The current axial force Tai is an estimated value of the axial force that actually acts on the rack shaft 22 in association with the steering of the steered wheels 5, and is a component reflected in the target reaction torque command value Ts*. The current axial force Tai thus obtained is output to the reaction force control unit 50.

[0048] <About the variable steering angle ratio control unit> As shown in FIG. 4, the steering angle ratio variable control section 62 has a static component calculation section 70, a dynamic component calculation section 80, and a reflection calculation section 90.

[0049] The static component calculation unit 70 executes a conversion calculation process to calculate the conversion component θvg by inputting 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.

[0050] The steering angle variable value calculation unit 71 includes a process of calculating a speed increase ratio G and a characteristic change component Cvg by inputting the steering angle θs and the vehicle speed V. More specifically, the steering angle variable value calculation unit 71 has a speed increase ratio calculation unit 71a and a characteristic change calculation unit 71b.

[0051] The speed increase ratio calculation unit 71a includes a steering angle variable value calculation process that calculates the speed increase ratio G by inputting the steering angle θs and the vehicle speed V. The speed increase ratio G is a steering angle variable value obtained by subtracting "1" from a value indicating a relationship when the steering angle θs is the denominator and the target pinion angle θp* is the numerator. The value indicating the relationship when the steering angle θs is the denominator and the target pinion angle θp* is the numerator is an index indicating the ratio of the change in the target pinion angle θp* to the change in the steering angle θs. Such an index is called, for example, a transmission ratio, a steering angle ratio, a gear ratio, etc., and specifies the relationship between the steering angle θs and the pinion angle θp, or the relationship between the steering angle θs and the turning angle θi. In other words, the speed increase ratio G is a value indicating the difference with respect to the case where the steering angle θs and the target pinion angle θp* correspond to each other at 1:1. The speed increase ratio G thus obtained is used in the calculations in the characteristic change calculation section 71b and the conversion component calculation section 72.

[0052] For example, the speed increase ratio G is set to decrease as the steering angle θs increases and to decrease as the vehicle speed V increases. The speed increase ratio G is a positive value including "0." In other words, the index indicating the ratio of the amount of change in the target pinion angle θp* to the amount of change in the steering angle θs is "1" or greater.

[0053] The characteristic change calculation unit 71b includes a process of calculating the characteristic change component Cvg by inputting the steering angle θs and the speed increase ratio G. The characteristic change component Cvg is a value of a change gradient obtained by using the steering angle change value Δθs, which is the amount of change in the steering angle θs, as the denominator and the conversion component change value Δθvg, which is the amount of change in the conversion component θvg, as the numerator. For example, when the speed increase ratio G is calculated using a map with the steering angle θs as the input, such a change gradient may be a value obtained by using the gradient between points before and after the change in the map, that is, the steering angle change value Δθs as the denominator and the speed increase ratio change value ΔG, which is the amount of change in the speed increase ratio G, as the numerator. The characteristic change component Cvg obtained in this way is used for calculation in the dynamic component calculation unit 80.

[0054] The conversion component calculation unit 72 includes a process for calculating the conversion component θvg by inputting the steering angle θs and the speed increase ratio G. The conversion component calculation unit 72 is a multiplier that calculates the conversion component θvg by multiplying the steering angle θs by the speed increase ratio G. The conversion component θvg is a change amount for increasing the steering angle θs by reflecting the speed increase ratio G. In other words, the conversion component θvg is a static component that reflects the speed increase ratio G and thus reflects the steady-state characteristics of the vehicle behavior.

[0055] For example, the conversion component calculation unit 72 has a characteristic that is defined by a characteristic change component Cvg that is obtained based on the speed increase ratio G so as to change the steady-state characteristics of the vehicle behavior due to conversion of the steering angle θs into the conversion component θvg. In this embodiment, the characteristic change component Cvg is an example of a conversion characteristic.

[0056] The dynamic component calculation unit 80 receives the steering angle θs and the transformed component θvg to execute a process of calculating a compensated component θvgc. The dynamic component calculation unit 80 also receives the characteristic change component Cvg to execute a characteristic change process of changing the characteristics of the compensation calculation process. More specifically, the dynamic component calculation unit 80 has a compensation calculation unit 81 and a characteristic change processing unit 82.

[0057] The compensation calculation unit 81 includes a process of calculating a compensated component θvgc by inputting the transformation component θvg. The compensated component θvgc is obtained by compensating for a dynamic component that reflects the response characteristics of the vehicle behavior, which is affected by the steering angle θs due to the transformation calculation process. The compensation calculation unit 81 is, for example, a phase lag filter having a zeroth order / first order, i.e., a first-order lag transfer function, and calculates the compensated component θvgc by phase compensating the transformation component θvg. The compensated component θvgc obtained in this manner is used for calculation in the reflection calculation unit 90.

[0058] For example, the phase lag filter is a low-pass filter, and has a characteristic defined by a transfer function having a predetermined cutoff frequency so as to adjust the response characteristic of the vehicle behavior that is affected by applying a conversion calculation process to the steering angle θs. The cutoff frequency corresponds to a filter constant K set when implementing a discrete control system as the compensation calculation unit 81. For example, the filter constant K is set so that the value decreases as the steering angular velocity ωs obtained by differentiating the steering angle θs increases. In this embodiment, the filter constant K is an example of a compensation characteristic.

[0059] The characteristic change processing unit 82 includes a process of calculating a characteristic change value Kc by inputting the 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 after reflecting the characteristic change value Kc, which is obtained by adding or subtracting the characteristic change value Kc to the filter constant K, in phase compensation. The characteristic change value Kc in this case is an adjustment operation value for making an adjustment to change the filter constant K.

[0060] 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 suppress deterioration of the stability in the control of the vehicle steering system 2. For example, the characteristic change value Kc is set so that the larger the characteristic change component Cvg, the smaller the value becomes.

[0061] The reflection calculation unit 90 executes a component reflection process for calculating the target pinion angle θp* by inputting the steering angle θs and the compensated component θvgc. The reflection calculation unit 90 is an adder, and calculates the target pinion angle θp* by adding the compensated component θvgc to the steering angle θs.

[0062] <Action of this embodiment> For example, if the filter constant K is not changed based on the characteristic change component Cvg, the range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation of the compensation calculation unit 81 in response to changes in the speed increase ratio G will be limited.

[0063] In response to this, the characteristic change processing unit 82 in the dynamic component calculation unit 80 executes a process of changing the filter constant K of the compensation calculation unit 81 according to the characteristic based on the speed increase ratio G, i.e., the characteristic change component Cvg. In this way, when the filter constant K is changed according to the characteristic change component Cvg, the range in which the stability in control of the vehicle steering system 2 can be ensured by the phase compensation of the compensation calculation unit 81 changes in response to the change in the speed increase ratio G. In other words, when the conversion component θvg obtained by converting the steering angle θs is further phase compensated, the filter constant K in the compensation calculation unit 81 is changed so as to suppress a decrease in the stability in control of the vehicle steering system 2.

[0064] <Effects of this embodiment> (1-1) By changing the filter constant K according to the characteristic change component Cvg, the conversion component calculation unit 72 and the compensation calculation unit 81 can associate the speed increase ratio G with the filter constant K from the viewpoint of ensuring stability in controlling the vehicle steering system 2. In other words, even when the relationship between the steering angle θs and the target pinion angle θp* is changed, it is possible to ensure stability in controlling the vehicle steering system 2. Therefore, it is possible to suppress a decrease in stability in controlling.

[0065] (1-2) Of the static component calculation unit 70 and the dynamic component calculation unit 80, the dynamic component calculation unit 80 includes a characteristic change processing unit 82. As a result, by simply including the characteristic change processing unit 82 in the dynamic component calculation unit 80, deterioration of stability in control can be suitably suppressed.

[0066] (1-3) The static component calculation unit 70 executes a process of converting the steering angle θs into a conversion component θvg using the speed increase ratio G. The speed increase ratio G changes according to the steering angle θs and the vehicle speed V. The dynamic component calculation unit 80 executes a phase lag filter process that performs phase lag compensation on the conversion component θvg. This ensures the stability of the control of the vehicle steering system 2, regardless of the steering angle θs and the vehicle speed V, even if the speed increase ratio G changes according to the steering angle θs and the vehicle speed V.

[0067] (1-4) The static component calculation unit 70 executes a process of calculating the speed increase ratio G by inputting the steering angle θs. The characteristic change component Cvg is set to be a conversion component change value Δθvg for the steering angle change value Δθs. The characteristic change component Cvg may also be a speed increase ratio change value ΔG for the steering angle change value Δθs. This makes it possible to adjust the change gradient obtained in relation to the speed increase ratio G. This is effective in ensuring the stability of the control of the vehicle steering system.

[0068] <Second embodiment> Hereinafter, the second embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment. For convenience of explanation, the same components as those in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and the explanation thereof will be omitted.

[0069] <About the variable steering angle ratio control unit> As shown in FIG. 5, in the steering angle ratio variable control section 62 of this embodiment, the static component calculation section 70 and the dynamic component calculation section 80 execute different processes.

[0070] More specifically, the static component calculation unit 70 has a steering angle variable value calculation unit 74, which is configured to correspond to the steering angle variable value calculation unit 71 described in the first embodiment, and a conversion component calculation unit 72, as well as a characteristic change processing unit 73. The dynamic component calculation unit 80 does not have a characteristic change processing unit 82, but has a compensation calculation unit 81. That is, the filter constant K in this embodiment is set so as not to change based on the characteristic change value Kc described in the first embodiment, for example, in addition to changing based on the steering angular velocity ωs obtained by differentiating the steering angle θs. The filter constant K of the compensation calculation unit 81 is used for calculation in the characteristic change processing unit 73.

[0071] The characteristic change processing unit 73 of the static component calculation unit 70 includes a process for calculating the characteristic change component Cvg by inputting a filter constant K. The characteristic change component Cvg thus obtained is used for calculation by the characteristic change calculation unit 74b.

[0072] The characteristic change calculation unit 74b has a configuration corresponding to the characteristic change calculation unit 71b described in the first embodiment, and includes a process of calculating an adjusted speed increase ratio Gc by inputting the steering angle θs and the characteristic change component Cvg. The adjusted speed increase ratio Gc is a value of the speed increase ratio G for obtaining a conversion component change value Δθvg that satisfies the characteristic change component Cvg for the steering angle change value Δθs. For example, when the speed increase ratio G is calculated using a map with the steering angle θs as an input, the adjusted speed increase ratio Gc may be a value of the speed increase ratio G for obtaining a speed increase ratio change value ΔG that satisfies the characteristic change component Cvg for 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.

[0073] The speed increase ratio calculation unit 74a corresponds to the speed increase ratio calculation unit 74a described in the first embodiment, and includes a process of calculating the adjusted speed increase ratio Gc as the speed increase ratio G. The process of calculating the speed increase ratio G may be, for example, a process of obtaining the speed increase ratio G by adding, subtracting, or multiplying the adjusted speed increase ratio Gc. The speed increase ratio G obtained in this manner is used for calculation in the conversion component calculation unit 72. In this case, the characteristic change component Cvg, i.e., the adjusted speed increase ratio Gc, is an adjustment operation value for adjusting the speed increase ratio G to change it.

[0074] For example, the characteristic change component Cvg is a value that changes according to the filter constant K, and has a characteristic of changing the speed increase ratio G so as to suppress deterioration of the stability in the control of the vehicle steering system 2. For example, the characteristic change component Cvg is set so that its value decreases as the filter constant K decreases.

[0075] <Action of this embodiment> For example, if the speed increase ratio G is not changed based on the filter constant K, the filter constant K will change, resulting in the speed increase ratio G falling outside the range in which the phase compensation of the compensation calculation unit 81 can ensure control stability of the vehicle steering system 2.

[0076] In response to this, the characteristic change processing unit 73 in the static component calculation unit 70 executes a process of changing the speed increase ratio G of the steering angle variable value calculation unit 74 based on the filter constant K. In this way, when the speed increase ratio G is changed based on the filter constant K, the speed increase ratio G is changed so as to fall within a range in which the stability of the control of the vehicle steering system 2 can be ensured by the phase compensation of the compensation calculation unit 81 in response to the change in the filter constant K. In other words, when the conversion component θvg obtained by converting the steering angle θs is further phase compensated, the speed increase ratio G in the steering angle variable value calculation unit 74 is changed so as to suppress a decrease in the stability of the control of the vehicle steering system 2.

[0077] <Effects of this embodiment> According to the present embodiment described above, in addition to the effects (1-1) and (1-4) of the first embodiment, the following effects can be obtained.

[0078] (2-1) Of the static component calculation unit 70 and the dynamic component calculation unit 80, the static component calculation unit 70 includes a characteristic change processing unit 73. As a result, by simply including the characteristic change processing unit 73 in the static component calculation unit 70, it is possible to suitably suppress deterioration in stability in control.

[0079] (2-2) The dynamic component calculation unit 80 executes a phase lag filter process that performs phase lag compensation on the conversion component θvg. The filter constant K changes according to the steering angle θs. The static component calculation unit 70 executes a process that converts the steering angle θs into the conversion component θvg using the speed increase ratio G. This ensures stability in the control of the vehicle steering system 2, regardless of the steering angle θs, even if the filter constant K changes according to the steering angle θs.

[0080] <Third embodiment> Hereinafter, the third embodiment will be described with reference to the drawings, focusing on the differences from the first embodiment. For convenience of explanation, the same components as those in the first embodiment will be denoted by the same reference numerals as those in the first embodiment, and the explanation thereof will be omitted.

[0081] <About the variable steering angle ratio control unit> As shown in FIG. 6, in the steering angle ratio variable control section 62 of this embodiment, the contents of the processes executed by the static component calculation section 70 and the dynamic component calculation section 80 are different.

[0082] More specifically, the steering angle ratio variable control section 62 has a static component calculation section 70 and a dynamic component calculation section 80, as well as a characteristic change processing section 100. The dynamic component calculation section 80 does not have a characteristic change processing section 82, but has a compensation calculation section 81. That is, the filter constant K in this embodiment is set so as not to change based on the steering angular velocity ωs obtained by differentiating the steering angle θs, for example, based on the characteristic change value Kc described in the first embodiment. The filter constant K of the compensation calculation section 81 is used for calculation in the characteristic change processing section 100.

[0083] The characteristic change processing unit 100 includes a process of calculating the adjusted conversion component θvgc0 by inputting the conversion component θvg, the characteristic change component Cvg, and the 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 suppress deterioration of the stability of the control 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 the filter constant K becomes smaller. The adjusted conversion component θvgc0 obtained in this manner is used for the calculation of the compensation calculation unit 81. The adjusted conversion component θvgc0 in this case is an adjustment operation value for adjusting the conversion component θvg to change it. Changing the conversion component θvg in this manner corresponds to adjusting the filter constant K to change it, or adjusting the characteristic change component Cvg, i.e., the speed increase ratio G to change it.

[0084] <Action of this embodiment> For example, if 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 of the compensation calculation unit 81 in response to a change in the speed increase ratio G is limited. In this case, the characteristic change component Cvg and the filter constant K also change in response to a change in the speed increase ratio G, and as a result, the speed increase ratio G falls outside the range in which the control stability of the vehicle steering system 2 can be ensured by the phase compensation of the compensation calculation unit 81.

[0085] In response to this, the characteristic change processing unit 100 executes a process of changing the conversion component θvg based on the characteristic change component Cvg and the filter constant K. When changing the conversion component θvg in this manner, the conversion component θvg is changed so as to fall within a range in which the stability in control of the vehicle steering system 2 can be ensured by the phase compensation of the compensation calculation unit 81 in response to a change in the speed increase ratio G. In other words, when the conversion component θvg obtained by converting the steering angle θs is further phase compensated, the conversion component θvg that is the target of the phase compensation is changed so as to suppress a decrease in the stability in control of the vehicle steering system 2.

[0086] <Effects of this embodiment> According to the present embodiment described above, in addition to the effects (1-1) and (1-4) of the first embodiment, the following effects can be obtained.

[0087] (3-1) The steering angle ratio variable control section 62 has a static component calculation section 70 and a dynamic component calculation section 80, and also includes a characteristic change processing section 100. As a result, by simply including the characteristic change processing section 100 that is separate and independent from the static component calculation section 70 and the dynamic component calculation section 80 in the steering angle ratio variable control section 62, deterioration of control stability can be suitably suppressed.

[0088] (3-2) The static component calculation unit 70 executes a process of converting the steering angle θs into a conversion component θvg using the speed increase ratio G. The dynamic component calculation unit 80 executes a phase lag filter process that performs phase lag compensation on the conversion component θvg. The conversion component θvg is affected by changes in the speed increase ratio G and the filter constant K. As a result, even if the conversion component θvg is affected by changes in the speed increase ratio G and the filter constant K, it is possible to ensure stability in the control of the vehicle steering system 2 regardless of the changes in the speed increase ratio G and the filter constant K.

[0089] <Fourth embodiment> The fourth embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment. For convenience of explanation, the same components as those in the first embodiment are denoted by the same reference numerals as those in the first embodiment, and the explanation thereof will be omitted.

[0090] <About the variable steering angle ratio control unit> As shown in FIG. 7, in the steering angle ratio variable control section 62 of this embodiment, the contents of the processes executed by the static component calculation section 70 and the dynamic component calculation section 80 are different.

[0091] More specifically, the static component calculation unit 70 does not have a characteristic change calculation unit 71b, but has a speed increase ratio calculation unit 71a. The characteristic change processing unit 82 of the dynamic component calculation unit 80 includes a process for calculating a characteristic change value Kc by inputting the speed increase ratio G.

[0092] 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 so as to suppress deterioration of the stability of the control 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 increases. The characteristic of changing the filter constant K may change according to the change in the speed increase ratio G, i.e., the speed increase ratio change value ΔG. In this case, the process of calculating the speed increase ratio change value ΔG may be included in the process of either the speed increase ratio calculation unit 71a or the characteristic change processing unit 82.

[0093] According to the present embodiment described above, it is possible to obtain actions similar to those of the first embodiment, and also to obtain effects similar to the effects (1-1) and (1-4) of the first embodiment. <Fifth embodiment> Hereinafter, the fifth embodiment will be described with reference to the drawings, focusing on the differences from the second embodiment. For convenience of explanation, the same components as those in the second embodiment will be denoted by the same reference numerals as those in the second embodiment, and the explanation thereof will be omitted.

[0094] <About the variable steering angle ratio control unit> As shown in FIG. 8, in the steering angle ratio variable control section 62 of this embodiment, the contents of the processing executed by the static component calculation section 70 are different.

[0095] More specifically, the static component calculation section 70 does not have a characteristic change calculation section 74b, but has a speed increase ratio calculation section 74a and a characteristic change processing section 73. The characteristic change processing section 73 includes a process of calculating an adjusted speed increase ratio Gc by inputting a filter constant K. The adjusted speed increase ratio Gc thus obtained is used for calculation in the speed increase ratio calculation section 74a.

[0096] For example, the adjusted speed increase ratio Gc is a value that changes according to the filter constant K, and has a characteristic of changing the speed increase ratio G so as to suppress deterioration of the stability of the control of the vehicle steering system 2. For example, the adjusted speed increase ratio Gc is set to have a smaller value as the filter constant K decreases. Also, changing the speed increase ratio G can be specified to change the change in the speed increase ratio G, i.e., the speed increase ratio change value ΔG. In this case, the process of performing the calculation related to changing the speed increase ratio change value ΔG may be included in the process of either the speed increase ratio calculation unit 74a or the characteristic change processing unit 73.

[0097] According to the present embodiment described above, it is possible to obtain an action similar to that of the second embodiment, as well as effects similar to the effects (1-1) and (1-4) of the first embodiment and effects similar to the effects (2-1) and (2-2) of the second embodiment.

[0098] <Other embodiments> The above-described embodiments may be modified as follows. In addition, the following other embodiments may be combined with each other to the extent that there is no technical contradiction.

[0099] In the first embodiment, the characteristic change processing unit 82 may input the steering angle θs and the vehicle speed V, that is, the parameters used in calculating the speed increase ratio G, when calculating the characteristic change value Kc. Alternatively, the characteristic change processing unit 82 may use the conversion component θvg. The other embodiments described herein can be similarly applied to the fourth embodiment.

[0100] In the first embodiment, the change in the characteristic change value Kc may be linear or nonlinear. The other embodiments described herein can be similarly applied to the fourth embodiment.

[0101] In the first embodiment, the characteristic change value Kc may be set to suppress a decrease in stability in accordance with the characteristics of the stability in control of the vehicle steering system 2. For example, the characteristic change value Kc may be set to a larger value as the speed increase ratio G increases, depending on the characteristics of the stability in control of the vehicle steering system 2. The other embodiments described herein can be similarly applied to the fourth embodiment.

[0102] In the first embodiment, the compensation calculation unit 81 may use the filter constant K after reflecting the characteristic change value Kc, which is obtained by multiplying the filter constant K by the characteristic change value Kc, in phase compensation. The other embodiments described herein can be similarly applied to the fourth embodiment.

[0103] In the first embodiment, the filter constant K may be set to change only depending on the characteristic change value Kc. The other embodiments described herein can be similarly applied to the fourth embodiment.

[0104] The first embodiment may have the characteristic change processing unit 82 and may further have the characteristic change processing unit 73 as in the second embodiment. In other words, the static component calculation unit 70 and the dynamic component calculation unit 80 may each include a characteristic change processing unit 73, 82 for changing the characteristic in each unit based on the characteristic of the other processing so as to ensure the stability of control of the vehicle steering system 2. The other embodiments described herein can be similarly applied to the fourth embodiment.

[0105] In the second embodiment, the adjusted speed increase ratio Gc may be set to suppress a decrease in stability in accordance with the characteristics of the stability in control of the vehicle steering system 2. For example, the adjusted speed increase ratio Gc may be set to a larger value as the filter constant K becomes smaller, depending on the characteristics of the stability in control of the vehicle steering system 2. The other embodiments described herein can be similarly applied to the fifth embodiment.

[0106] In each embodiment, the speed increase ratio calculation unit 71a may calculate an index indicating the ratio of the amount of change in the target pinion angle θp* to the amount of change in the steering angle θs as the speed increase ratio G. In other words, the speed increase ratio G is a value of "1" or more. In the other embodiments described herein, the compensated 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 executes the process corresponding to the reflection calculation unit 90, so that the reflection calculation unit 90 can be eliminated.

[0107] In each embodiment, the steering angle variable value calculation units 71, 74 need only be able to reflect state changes of at least one of the vehicle steering system 2 and the vehicle in the speed increase ratio G. For example, when calculating the speed increase ratio G, the steering angle variable value calculation units 71, 74 may use only one of the steering angle θs and the vehicle speed V, or may use a combination of other elements. The other elements include the steering angular velocity ωs, and the steering angular velocity ωt obtained from the differential value of the pinion angle θp or the target pinion angle θp*.

[0108] In each embodiment, the speed increase ratio G can be changed as appropriate, for example, by setting it to change linearly as the steering angle θs increases and its value decreases, or by setting it to increase as the steering angle θs increases. In addition, the speed increase ratio G may be a negative value.

[0109] In each embodiment, the compensation calculation unit 81 only needs to be able to reflect state changes of at least one of the vehicle steering system 2 and the vehicle in the phase compensation, i.e., in the filter constant K. For example, when performing phase compensation, the compensation calculation unit 81 may use a filter constant K corresponding to the vehicle speed V, may use either the steering angular velocity ωs or the vehicle speed V, or may use a combination of other elements. The other elements include the above-mentioned steering angular velocity ωt, etc.

[0110] In each embodiment, the filter constant K may be set to a larger value as the steering angular velocity ωs increases, for example. In each embodiment, the compensation calculation unit 81 may be a low-pass filter having a higher-order transfer function, such as a second-order lag filter, if the compensation calculation unit 81 is a phase lag filter. Also, the compensation calculation unit 81 may be a phase lead filter, if the compensation calculation unit 81 is eventually made proper within the steering angle ratio variable control unit 62.

[0111] In each embodiment, the current axial force calculation unit 67 may be a function of the reaction force control unit 50, that is, the target reaction force torque calculation unit 52. In this case, the target reaction force torque calculation unit 52 may include a process for calculating the current axial force Tai by inputting the actual current value Ib.

[0112] In each embodiment, steering angle for axial force calculation section 66 may be a function of reaction force control section 50, i.e., target reaction force torque calculation section 52. In this case, target reaction force torque calculation section 52, i.e., angle axial force calculation section 52a, may include a process for calculating steering angle for axial force θpf by inputting steering angle θs and transformation component θvg.

[0113] In each embodiment, at least a part of the functions of the steering angle ratio variable control section 62 may be the functions of the reaction force control section 50 . In each embodiment, when calculating the target reaction force torque command value Ts*, the target reaction force torque calculation unit 52 may not use either the vehicle speed V or the steering torque Th, or may use a combination of other elements.

[0114] In each embodiment, the target reaction torque calculation unit 52 may calculate, as the target reaction torque command value Ts*, a value calculated by executing torque feedback control that causes the steering torque Th to follow a target steering torque calculated based on the steering torque Th.

[0115] In each embodiment, the steering angle calculation unit 51 may calculate the steering angle θs by taking into account the amount of torsion of the steering shaft 11 that corresponds to the steering torque Th. In each embodiment, 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. Note that the steering angle sensor may be provided, for example, on the steering shaft 11 between the steering wheel 3 and the torque sensor 41.

[0116] In each embodiment, the steering actuator 12 does not necessarily have to include the steering side reduction mechanism 14. In each embodiment, the steering-side motor 13 is not limited to a three-phase brushless motor. For example, it may be a DC motor with brushes. The other embodiments described herein can be similarly applied to the steered-side motor 32.

[0117] In each embodiment, the pinion angle θp may be obtained by converting a detection value of the movement amount of the rack shaft 22. In this case, the control amount and the like related to the pinion angle θp are converted by the detection value of the movement amount of the rack shaft 22.

[0118] In each embodiment, the operating member operated by the driver to steer the vehicle is not limited to the steering wheel 3. For example, it may be a joystick. In each embodiment, the steering unit 6 transmits the rotation of the steering-side motor 32 to the conversion mechanism 34 via the transmission mechanism 33, but the present invention is not limited to this. For example, the steering unit 6 may be configured so that the rotation of the steering-side motor 32 is transmitted to the conversion mechanism 34 via a gear mechanism. The steering unit 6 may also be configured so that the steering-side motor 32 directly rotates the conversion mechanism 34. Furthermore, the steering unit 6 may be configured to include a second rack-and-pinion mechanism, and the rotation of the steering-side motor 32 is converted into reciprocating motion of the rack shaft 22 by the second rack-and-pinion mechanism.

[0119] In each embodiment, the steering unit 6 is not limited to a configuration in which the right steered wheels 5 and the left steered wheels 5 are linked together. In other words, the right steered wheels 5 and the left steered wheels 5 may be independently controlled.

[0120] In each embodiment, the vehicle steering system 2 has a linkless structure in which the steering unit 4 and the turning unit 6 are mechanically separated at all times, but this is not limited to the above, and the vehicle steering system 2 may have a structure in which the steering unit 4 and the turning unit 6 can be mechanically separated by a clutch, for example.

[0121] In each embodiment, the steered-side motor 32 may be, for example, one that is arranged coaxially with the rack shaft 22, or one that is connected to a pinion shaft that constitutes a rack-and-pinion mechanism on the rack shaft 22 via a worm and wheel. [Explanation of symbols]

[0122] 1...Steering control device 2...Vehicle steering system 3. Steering wheel 4…Steering unit 5…Steering wheel 6...Steering unit 60...Steering control unit (control unit) 62...Steering angle ratio variable control unit 70...Static component calculation section 71...Steering angle variable value calculation unit 71a...Speed-up ratio calculation unit 71b...characteristic change calculation section 72...Transform component calculation unit 73...Characteristic change processing section 74...Steering angle variable value calculation unit 74a...Speed-up ratio calculation unit 74b...Characteristic change calculation section 80...Dynamic component calculation section 81...Compensation calculation section 82...Characteristic change processing section 90…Reflection calculation section 100...characteristic change processing section

Claims

1. A steering control device applied to a vehicle steering system having a structure in which a power transmission path between a steering unit steered by a steering wheel of a vehicle and a steering unit that operates to steer the steered wheels of the vehicle is separated, A control unit for controlling the operation of the steering unit, the control unit is configured to execute a target steering angle calculation process for calculating a target steering angle, which is a target of a steering angle, which is a steering position of the steered wheels, which is a control amount for operating the steering unit, based on a steering angle, which is a rotational position of the steering wheel; The target steering angle calculation process includes: a conversion calculation process for calculating a conversion component obtained by inputting the steering angle so as to change a relationship between the steering angle and the turning angle; a compensation calculation process for calculating a compensated component obtained by inputting the conversion component and performing phase compensation on the conversion component in order to adjust the influence on the behavior of the vehicle; A component reflection process for calculating the target steering angle so as to reflect the compensated component, the conversion calculation process includes a process of calculating the conversion component according to a conversion characteristic that defines a relationship between the steering angle and the conversion component, the compensation calculation process includes a process of calculating the compensated component according to a compensation characteristic that defines a relationship between the converted component and the compensated component, A steering control device in which at least one of the conversion calculation process and the compensation calculation process includes a characteristic change process for changing the characteristics of the one process based on the characteristics of the other process so as to ensure control stability of the vehicle steering system.

2. the compensation calculation process of the conversion calculation process and the compensation calculation process includes the characteristic change process, The steering control device according to claim 1 , wherein the characteristic changing process in the compensation calculation process is a process for changing the compensation characteristic based on the conversion characteristic.

3. the conversion calculation process is a process of converting the steering angle into the conversion components using a steering angle variable value indicating a ratio of a change amount of the steering angle to a change amount of the steering angle, the conversion characteristic is a characteristic based on the steering angle variable value in response to a change in a state of at least one of the vehicle and the vehicle steering system, the compensation calculation process is a phase lag filter process that performs phase lag compensation on the conversion component, 3. The steering control device according to claim 2, wherein the compensation characteristic is a value indicating a constant of a transfer function which is a characteristic of the phase lag filtering process.

4. the conversion calculation process of the conversion calculation process and the compensation calculation process includes the characteristic change process, The steering control device according to claim 1 , wherein the characteristic changing process in the conversion calculation process is a process for changing the conversion characteristic based on the compensation characteristic.

5. the compensation calculation process is a phase lag filter process that performs phase lag compensation on the conversion component, the compensation characteristic is a value indicating a constant of a transfer function that is a characteristic of the phase lag filtering process in response to a state change of at least one of the vehicle and the vehicle steering system, the conversion calculation process is a process of converting the steering angle into the conversion components using a steering angle variable value indicating a ratio of a change amount of the steering angle to a change amount of the steering angle, The steering control device according to claim 4 , wherein the conversion characteristic is a characteristic based on the steering angle variable value.

6. 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, 6. The steering control device according to claim 3, wherein the characteristic based on the steering angle variable value is a change in the conversion component or a change in the steering angle variable value relative to a change in the steering angle input to the steering angle variable value calculation process.

7. A steering control method applied to a vehicle steering system having a structure in which a power transmission path between a steering unit steered by a steering wheel of a vehicle and a steering unit that operates to steer steered wheels of the vehicle is separated, comprising: The steering control method includes executing a control process for controlling an operation of the steering unit, the control process includes a target steering angle calculation process for calculating a target steering angle, which is a target of a steering angle, which is a steering position of the steered wheels, which is a control amount for operating the steering unit, based on a steering angle, which is a rotational position of the steering wheel; The target steering angle calculation process includes: a conversion calculation process for calculating a conversion component obtained by inputting the steering angle so as to change a relationship between the steering angle and the turning angle; a compensation calculation process for calculating a compensated component obtained by inputting the conversion component and performing phase compensation on the conversion component in order to adjust the influence on the behavior of the vehicle; A component reflection process for calculating the target steering angle so as to reflect the compensated component, the conversion calculation process includes a process of calculating the conversion component according to a conversion characteristic that defines a relationship between the steering angle and the conversion component, the compensation calculation process includes a process of calculating the compensated component according to a compensation characteristic that defines a relationship between the converted component and the compensated component, A steering control method in which at least one of the conversion calculation process and the compensation calculation process includes a characteristic change process for changing the characteristics of the conversion calculation process based on the characteristics of the other process so as to ensure control stability of the vehicle steering system.

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