Steering control device and steering control method

Abstract

To provide a steering control device and steering control method that are capable of more smoothly steering turning wheels.SOLUTION: A steering control device is applied to a vehicle steering system that has a structure in which a power transmission path between a steering unit and a turning unit is separated. The turning unit includes: a turning shaft that rotates a turning wheel; a turning motor that generates turning force, which is the torque applied to the turning shaft to rotate a rack wheel; and a turning control unit that controls the turning motor. The turning control unit controls the turning motor so that a pinion angle θp follows a target pinion angle θp* and includes a correction processing unit 72 that corrects the pinion angle θp to be an angle within a defined angular range where the turning force that can be generated by the turning motor and the axial force generated on the rack shaft can maintain balance. The correction processing unit 72 includes a control amount restriction processing unit 82 related to the restriction of a current command value Ib*.SELECTED DRAWING: Figure 4

Description

Technical Field

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

Background Art

[0002] Conventionally, there is a so-called steer-by-wire type steering device in which the power transmission path between the steering wheel and the steered wheels is separated. For example, the steering device described in Patent Document 1 has a reaction force motor that is a source of the steering reaction force applied to the steering shaft, and a steering motor that is a source of the steering force for steering the steered wheels. When the vehicle is running, the control device of the steering device generates a steering reaction force through power supply control for the reaction force motor, and steers the steered wheels through power supply control for the steering motor.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In a conventional general steer-by-wire type steering device including the steering device described in Patent Document 1, when the steering wheel is operated by a driver, the steered wheels steer while maintaining the balance between the steering force generated by the steering motor and the axial force generated on the steering shaft.

[0005] However, when an axial force exceeding the maximum steering force that can be generated by the steering motor is generated, it becomes difficult to maintain the balance between the steering force generated by the steering motor and the axial force acting on the steering shaft depending on the axial force characteristics of the vehicle. For this reason, there is a possibility that it becomes difficult to smoothly steer the steered wheels according to the steering state of the steering wheel.

[0006] For example, when so-called "standing cut" is performed, that is, when the steering wheel is steered while the vehicle is in a stopped state, a larger axial force is likely to be generated. Depending on the axial force characteristics of the vehicle, the following events may occur. That is, at the time when the standing cut is performed, the steering wheel does not move, and the steering wheel starts to move after the axial force decreases as the vehicle starts moving. There is concern that the driver may feel discomfort due to the occurrence of such events.

Means for Solving the Problem

[0007] The steering control device capable of solving the above problem 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 that operates to steer the steering wheels of the vehicle is separated. In the steering control device, the steering unit includes a steering shaft that steers the steering wheels, a steering motor that generates a steering force, which is a torque applied to the steering shaft to steer the steering wheels, and a control unit that controls the steering motor. The control unit controls the steering motor so that a conversion angle convertible to the steering angle of the steering wheels follows a target angle calculated according to the steering state of the steering wheel, and corrects the conversion angle so that the angle is within an angle range determined such that the steering force that can be generated by the steering motor and the axial force generated on the steering shaft can maintain a balance of forces. The correction process includes a control amount limitation process related to the limitation of the control amount for commanding the steering force generated in the steering motor to the steering motor.

[0008] The above configuration focuses on the fact that restricting the control amount for the steering motor leads to correcting the conversion angle. That is, restricting the control amount for the steering motor realizes correcting the conversion angle so that the angle is within the angular range defined such that the steering force that can be generated by the steering motor and the axial force generated on the steering shaft can maintain a balance of forces. Thereby, it is suppressed that the conversion angle deviates from the angular range in which it is difficult to maintain the balance of forces between the steering force generated by the steering motor and the axial force generated on the steering shaft. That is, it is suppressed that a situation occurs in which an axial force exceeding the steering force that can be generated by the steering motor is generated. Therefore, the steering wheel can be steered more smoothly according to the steering state of the steering wheel.

[0009] In the above steering control device, the correction process preferably includes a limit angle calculation process for calculating a limit angle for defining an angular range in which the steering force generated by the steering motor and the axial force generated on the steering shaft can maintain a balance of forces, and the control amount restriction process preferably includes a process for calculating a restriction component related to the restriction of the control amount based on the limit angle and the conversion angle.

[0010] According to the above configuration, in the control amount restriction process, optimization of the restriction of the control amount can be achieved. In the above steering control device, the limit angle calculation process preferably includes a process for calculating the limit angle for defining an angular range restricted with respect to the angular range in design based on the state of the vehicle including at least the vehicle speed.

[0011] According to the above configuration, in the limit angle calculation process, for example, it is possible to take into account the situation of a parking state or an extremely low speed range in which a situation where the steering wheel is steered in a larger range is likely to occur. This is particularly effective in including the vehicle speed, which is considered to have a large influence on the change in the axial force generated on the steering shaft according to the state of the vehicle, in the state of the vehicle. Therefore, it is possible to appropriately determine the situation in which the control amount should be restricted.

[0012] In the above-described steering control device, it is preferable that the limit angle calculation process includes a process of calculating the limit angle based on, in addition to the vehicle speed, the state regarding the steering force generated by the steering motor.

[0013] According to the above configuration, in the limit angle calculation process, for example, the remaining force of the steering force that the steering motor can generate can be taken into account. Therefore, it is possible to appropriately determine the situation where the control amount should be limited.

[0014] In the above-described steering control device, the control amount limiting process includes a steering condition determination process of determining whether or not a cut-in steering condition indicating that the steered wheels are cut in toward the limit side of the angle region is satisfied, and when it is determined that the cut-in steering condition is satisfied, it is preferable that the control amount limiting process executes a process related to the limitation of the control amount.

[0015] According to the above configuration, in the control amount limiting process, for example, it is possible to take into account a situation where it is assumed that the converted angle deviates from an angle region where it is difficult to maintain the balance between the steering force of the steering motor and the axial force generated on the steering shaft. Therefore, it is possible to appropriately determine the situation where the control amount should be limited.

[0016] In the above-described steering control device, it is preferable that the control unit is configured to execute a compensation process of compensating the control amount so as to suppress a sudden change in the control amount before and after the limitation when the control amount is limited through the control amount limiting process.

[0017] According to the above configuration, in the compensation process, when the control amount is limited, the control amount can be changed more gently from before the limitation to after the limitation. Therefore, it is possible to reduce the driver's discomfort with respect to the vehicle behavior that appears due to the limitation of the control amount.

[0018] In the above-described steering control device, it is preferable that the compensation process is a filter process using a low-pass filter. This is effective for facilitating the implementation of the compensation process. The steering control method capable of solving the above 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 that operates to steer the steered wheels of the vehicle is separated. The steering control method includes executing a control process for controlling a steering motor that generates a steering force, which is a torque applied to a steering shaft for steering the steered wheels to steer the steered wheels. The control process controls the steering motor so that a conversion angle convertible to a steering angle of the steered wheels follows a target angle calculated according to a steering state of the steering wheel, and includes a correction process for correcting the conversion angle so that an angle within an angle range determined to be able to maintain a balance between the steering force that can be generated by the steering motor and an axial force generated on the steering shaft. The correction process includes a control amount limitation process related to a limitation of a control amount for commanding the steering force generated in the steering motor to the steering motor.

Effects of the Invention

[0019] According to the present invention, the steered wheels can be steered more smoothly.

Brief Description of the Drawings

[0020]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Modes for Carrying Out the Invention

[0021] <First Embodiment> Hereinafter, a first embodiment of the present invention will 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 steering wheel 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 steering wheel unit 6 operates to steer the left and right steering wheels 5 of the vehicle in response to the steering input by the driver to the steering unit 4. The vehicle steering system 2 of the present embodiment has a structure in which the power transmission path between the steering unit 4 and the steering wheel unit 6 is mechanically separated at all times. The power transmission path between the steering actuator 12 described later and the steering wheel actuator 31 described later has a structure in which it is mechanically separated at all times. That is, the vehicle steering system 2 includes a steer-by-wire type steering device.

[0022] 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 motor 13 and a steering side reduction mechanism 14. The steering motor 13 is a reaction force motor that applies a steering reaction force, which is a force resistant to steering, to the steering wheel 3 via the steering shaft 11. That is, the steering unit 4 is a reaction force unit. The steering motor 13 is connected to the steering shaft 11 via a steering side reduction mechanism 14 composed of, for example, a worm and wheel. For the steering motor 13 of the present embodiment, for example, a three-phase brushless motor is adopted.

[0023] The steering wheel 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 crossing angle. A rack and pinion mechanism 24 is configured by meshing a pinion tooth 21a formed on the pinion shaft 21 and a rack tooth 22a formed on the rack shaft 22. The pinion shaft 21 corresponds to a rotation shaft that can be converted into a steering angle θi, which is the steering position of the steering wheel 5. The rack housing 23 houses the rack and pinion mechanism 24.

[0024] One end of the pinion shaft 21 on the side opposite to the side connected to the rack shaft 22 protrudes from the 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 each consisting of a ball joint. The tips of the tie rods 26 are respectively connected to knuckles (not shown) to which the left and right steering wheels 5 are assembled.

[0025] The steering unit 6 includes a steering actuator 31. The steering actuator 31 includes a steering motor 32, a transmission mechanism 33, and a conversion mechanism 34. The steering motor 32 applies a steering force for steering the steering wheels 5 to the rack shaft 22 via the transmission mechanism 33 and the conversion mechanism 34. The steering motor 32 transmits rotation to the conversion mechanism 34 via a transmission mechanism 33 consisting of, for example, a belt transmission mechanism. The transmission mechanism 33 converts the rotation of the steering motor 32 into a reciprocating motion of the rack shaft 22 via a conversion mechanism 34 consisting of, for example, a ball screw mechanism. In this embodiment, a three-phase brushless motor is, for example, adopted as the steering motor 32.

[0026] In the vehicle steering system 2, the steering angle θi of the steering wheels 5 is changed by applying motor torque as a steering force from the steering actuator 31 to the rack shaft 22 in response to a steering operation by the driver. At this time, a steering reaction force against the driver's steering is applied from the steering actuator 12 to the steering wheel 3. Thereby, in the vehicle steering system 2, the steering torque Th required for steering the steering wheel 3 is changed by the steering reaction force, which is the motor torque applied from the steering actuator 12.

[0027] The reason for providing the pinion shaft 21 is to support the rack shaft 22 together with the pinion shaft 21 inside the rack housing 23. By a support mechanism (not shown) provided in the vehicle steering system 2, the rack shaft 22 is supported so as to be movable along its axial direction and is pressed toward the pinion shaft 21. Thereby, the rack shaft 22 is supported inside the rack housing 23. However, other support mechanisms for supporting the rack shaft 22 in the rack housing 23 without using the pinion shaft 21 may be provided.

[0028] <Electrical Configuration of Vehicle Steering System> As shown in FIG. 1, the steering motor 13 and the steering angle change motor 32 are connected to the steering control device 1. The steering control device 1 controls the operation of each motor 13, 32.

[0029] 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 steering angle change-side rotation angle sensor 43, and a vehicle speed sensor 44.

[0030] The torque sensor 41 is provided at a portion between the steering wheel 3 and the steering-side speed reduction mechanism 14 on the steering shaft 11. The torque sensor 41 detects a steering torque Th, which is a value indicating the torque applied to the steering shaft 11 by the driver's steering operation. The steering torque Th is detected in relation to the twist of a torsion bar 41a provided midway along the steering shaft 11 between the steering wheel 3 and the steering-side speed reduction mechanism 14 on the steering shaft 11. The steering-side rotation angle sensor 42 is provided on the steering motor 13. The steering-side rotation angle sensor 42 detects a rotation angle θa, which is the angle of the rotation shaft of the steering motor 13, within a range of 360 degrees. The steering angle change-side rotation angle sensor 43 is provided on the steering angle change motor 32. The steering angle change-side rotation angle sensor 43 detects a rotation angle θb, which is the angle of the rotation shaft of the steering angle change 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.

[0031] <Functions of Steering Control Device> As shown in FIG. 2, the steering control device 1 includes a reaction force control unit 50 and a steering control unit 60. The reaction force control unit 50 executes control processing for controlling the steering wheel 3 that is the control target. The reaction force control unit 50 controls the drive of the steering actuator 12, more specifically, the steering motor 13, in order to control the steering reaction force that is the control amount of the control target. The steering control unit 60 executes control processing for controlling the rack shaft 22 that is the control target. The steering control unit 60 controls the drive of the steering actuator 31, more specifically, the steering motor 32, in order to control the steering force that is the control amount of the control target. The reaction force control unit 50 and the steering control unit 60 mutually transmit and receive information via a local network such as serial communication. The reaction force control unit 50 constitutes a reaction force system RS in combination with the steering unit 4. The steering control unit 60 constitutes a steering system TS in combination with the steering unit 6.

[0032] The reaction force control unit 50 includes 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 the programs stored in the memory at a predetermined operation cycle. The steering control unit 60 includes a central processing unit (hereinafter referred to as “CPU”) and a memory. The steering control unit 60 executes various processes by the CPU executing the programs stored in the memory at a predetermined operation cycle. The CPU and the memory constitute a microcomputer that is a processing circuit. The memory includes computer-readable media such as RAM (Random Access Memory) and ROM (Read Only Memory). However, the realization of various processes by software is an example. The processing circuits included in the reaction force control unit 50 and the steering control unit 60 may be configured to realize at least part of the processes by a hardware circuit such as a logic circuit.

[0033] FIG. 2 shows a part of the processes executed by the reaction force control unit 50 and the steering control unit 60. The processes shown in FIG. 2 describe, for each type of realized process, a part of the processes realized by the CPU executing the programs stored in the memory.

[0034] The reaction force control unit 50 has a current sensor 54. The current sensor 54 detects an actual current value Ia obtained from the current values of each phase of the steering motor 13 flowing through the connection lines between the reaction force control unit 50 and the motor coils of each phase of the steering motor 13. The current sensor 54 acquires, as current, the voltage drop of a shunt resistor connected to the source side of each switching element in an inverter (not shown) provided corresponding to the steering motor 13. In FIG. 2, for convenience of explanation, the connection lines of each phase and the current sensors of each phase are shown collectively as one each.

[0035] The steering control unit 60 has a current sensor 65. The current sensor 65 detects an actual current value Ib obtained from the current values of each phase of the steering motor 32 flowing through the connection lines between the steering control unit 60 and the motor coils of each phase of the steering motor 32. The current sensor 65 acquires, as current, the voltage drop of a shunt resistor connected to the source side of each switching element in an inverter (not shown) provided corresponding to the steering motor 32. In FIG. 2, for convenience of explanation, the connection lines of each phase and the current sensors of each phase are shown collectively as one each.

[0036] <Regarding the reaction force control unit> As shown in FIG. 2, the reaction force control unit 50 controls the power supply to the steering motor 13 by inputting the steering torque Th, the vehicle speed V, and the rotation angle θa.

[0037] The reaction force control unit 50 includes a steering angle calculation unit 51, a steering reaction force command value calculation unit 52, and a power supply control unit 53. The steering angle calculation unit 51 calculates the steering angle θs by inputting the rotation angle θa. The steering angle calculation unit 51 converts the rotation angle θa into an integrated angle including a range exceeding 360° by, for example, counting the number of rotations of the steering motor 13 from the steering neutral position, which is the rotation position of the steering wheel 3 when the vehicle is moving straight ahead. The steering angle calculation unit 51 calculates the steering angle θs by multiplying the converted integrated angle by a conversion coefficient based on the rotation speed ratio of the steering side reduction mechanism 14. The thus obtained steering angle θs is used in the calculation by the steering reaction force command value calculation unit 52. Further, the steering angle θs is output to the steering control unit 60.

[0038] The steering reaction force command value calculation unit 52 calculates the steering reaction force command value Ts* by inputting the steering torque Th and the vehicle speed V. The steering reaction force command value Ts* is a reaction force control amount that is the target of the steering reaction force of the steering wheel 3 to be generated through the steering motor 13. The thus obtained steering reaction force command value Ts* is used in the control by the energization control unit 53.

[0039] The energization control unit 53 controls the energization to the steering motor 13 by executing current feedback control for the actual current value Ia by inputting the steering reaction force command value Ts*, the rotation angle θa, and the actual current value Ia. Thereby, the steering motor 13 generates a torque corresponding to the steering reaction force command value Ts*. That is, it is possible to give the driver an appropriate feeling of feedback according to the road surface reaction force.

[0040] <Regarding the steering control unit> As shown in FIG. 2, the steering control unit 60 controls the power supply to the steering motor 32 by inputting the vehicle speed V, the steering angle θs, and the rotation angle θb.

[0041] The steering control unit 60 includes a pinion angle calculation unit 61, a target pinion angle calculation unit 62, a pinion angle feedback control unit (referred to as "pinion angle F / B control unit" in the figure) 63, and an energization control unit 64.

[0042] 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° by, for example, counting the rotation speed of the steering motor 32 from the rack neutral position, which is the position of the rack shaft 22 when the vehicle is moving straight ahead. The pinion angle calculation unit 61 multiplies the obtained integrated angle 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 thus obtained is used in the calculation by the pinion angle feedback control unit 63.

[0043] Note that the pinion angle θp is positive when it is, for example, an angle on the right side rather than the rack neutral position, and negative when it is an angle on the left side. The steering motor 32 and the pinion shaft 21 are interlocked via the transmission mechanism 33, the conversion mechanism 34, and the rack shaft 22. Therefore, there is a correlation between the rotation angle θb of the steering motor 32 and the pinion angle θp. Using this correlation, the pinion angle θp can be obtained from the rotation angle θb of the steering motor 32. The pinion shaft 21 meshes with the rack shaft 22. Therefore, there is also a correlation between the pinion angle θp and the movement amount of the rack shaft 22. That is, the pinion angle θp is a conversion angle that can be converted into the steering angle θi of the steering wheel 5, that is, the steering position.

[0044] The target pinion angle calculation unit 62 calculates the target pinion angle θp* by inputting the steering angle θs and the vehicle speed V. The target pinion angle θp* is a steering control amount that is the target angle of the pinion angle θp obtained as a result of steering the steering wheel 5. The target pinion angle θp* thus obtained is used in the calculation by the pinion angle feedback control unit 63.

[0045] The target pinion angle calculation unit 62 calculates a target pinion angle θp* by adding an adjustment amount to the steering angle θs. The adjustment amount is an operation amount for changing the steering angle ratio of the target pinion angle θp* with respect to the steering angle θs. The steering angle ratio includes "1" and is changed to be larger than "1". On the premise that the vehicle speed V is faster, it is a value that increases smoothly and non-linearly, for example. That is, the adjustment amount changes according to the vehicle speed V so that the change in the target pinion angle θp* with respect to the change in the steering angle θs is larger when the vehicle speed V is slow than when it is fast. For this reason, there is a correlation between the steering angle θs and the target pinion angle θp*. The pinion angle θp is controlled based on the target pinion angle θp*. For this reason, there is also a correlation between the steering angle θs and the pinion angle θp. That is, the pinion angle θp is a value that reflects the steering angle θs. Therefore, changing the steering angle ratio changes the relationship between the steering angle θs and the pinion angle θp.

[0046] 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 the target of the steering force of the steered wheels 5 to be generated through the steering motor 32. The pinion angle feedback control unit 63 calculates the steering force command value Tp* by performing feedback control of the pinion angle θp so that the pinion angle θp follows the target pinion angle θp*. The steering force command value Tp* thus obtained is used for control in the energization control unit 64.

[0047] The energization control unit 64 controls the energization of the steering motor 32 by inputting the steering force command value Tp*, the rotation angle θb, and the actual current value Ib and performing current feedback control on the actual current value Ib. As a result, the steering motor 32 generates torque corresponding to the steering force command value Tp*. That is, it is possible to rotate the steered wheels 5 by an angle corresponding to the steering force.

[0048] <Regarding the energization control unit in the steering control unit> As shown in FIG. 3, the energization control unit 64 in the steering control unit 60 includes a current command value calculation unit 71, a correction processing unit 72, a reflection processing unit 73, and a current feedback control unit (referred to as "current F / B control unit" in the figure) 74.

[0049] A steering force command value Tp* is input to the current command value calculation unit 71. The current command value calculation unit 71 calculates a current command value Ib* based on the steering force command value Tp*. The current command value Ib* thus obtained is used in the calculation by the reflection processing unit 73.

[0050] The vehicle speed V, the pinion angle θp, and the actual current value Ib are input to the correction processing unit 72. The correction processing unit 72 calculates a limit gain Ki based on the vehicle speed V, the pinion angle θp, and the actual current value Ib. The limit gain Ki is a limiting component for limiting the current command value Ib*, and is, for example, a value of 1 or less greater than "0". That is, when the limit gain Ki is less than "1", the current command value Ib* is limited so that its absolute value becomes smaller. This means that the pinion angle θp is corrected so as to limit the angle range that can be changed, that is, the target pinion angle θp* is corrected. The limit gain Ki thus obtained is used in the calculation by the reflection processing unit 73. In the present embodiment, the process executed by the correction processing unit 72 is an example of correction processing.

[0051] The current command value Ib* and the limit gain Ki are input to the reflection processing unit 73. The reflection processing unit 73 calculates a final current command value Ib* (Ib* × Ki) by multiplying the current command value Ib* by the limit gain Ki. For example, the reflection processing unit 73 is a multiplier. The final current command value Ib* becomes the value of the current command value Ib* obtained through the calculation in the current command value calculation unit 71 when the limit gain Ki is "1". The final current command value Ib* becomes a value obtained by limiting the current command value Ib* obtained through the calculation in the current command value calculation unit 71 when the limit gain Ki is a value other than "1". The final current command value Ib* thus obtained is used in the calculation by the current feedback control unit 74.

[0052] The final current command value Ib*, the rotation angle θb, and the actual current value Ib are input to the current feedback control unit 74. Based on the final current command value Ib*, the rotation angle θb, and the actual current value Ib, the current feedback control unit 74 generates a motor control signal Smp through the execution of current feedback control so that the actual current value Ib follows the final current command value Ib*. The motor control signal Smp thus obtained is used to drive an inverter provided corresponding to the steering motor 32.

[0053] <Regarding the correction processing calculation unit> As shown in FIG. 4, the correction processing unit 72 includes a limit angle calculation processing unit 81, a control amount limit processing unit 82, and a compensation processing unit 83.

[0054] The vehicle speed V and the actual current value Ib are input to the limit angle calculation processing unit 81. The limit angle calculation processing unit 81 calculates a limit angle θplim based on the vehicle speed V and the actual current value Ib. The limit angle θplim is a value calculated in an angle dimension that is the unit of the pinion angle θp, and is the upper and lower control limit values on the left and right sides based on the rack neutral position when changing the pinion angle θp. For example, the limit angle θplim may be a positive or negative value, or an absolute value. These upper and lower limit values on the left and right sides are angles for defining the angle range in which the pinion angle θp can change, and will determine the range of values that the target pinion angle θp* can take. The limit angle θplim thus obtained is used in the calculation by the control amount limit processing unit 82. In the present embodiment, the processing executed by the limit angle calculation processing unit 81 is an example of limit angle calculation processing.

[0055] More specifically, the limit angle calculation processing unit 81 includes a process of calculating the magnitude of the axial force generated in the rack shaft 22 at the vehicle speed V at that time based on the axial force characteristics of the vehicle showing the relationship with the vehicle speed V for the axial force generated in the rack shaft 22. Further, the limit angle calculation processing unit 81 includes a process of calculating the remaining force of the steering force that can be generated by the steering motor 32 at that time based on the actual current value Ib for the steering force generated by the steering motor 32. Then, the limit angle calculation processing unit 81 includes a process of calculating the limit angle θplim by comparing the magnitude of the axial force generated in the rack shaft 22 at the vehicle speed V with the remaining force of the steering force that can be generated by the steering motor 32.

[0056] The remaining force of the steering force that can be generated by the steering motor 32 corresponds to the difference between the maximum output of the steering motor 32 and the steering force actually generated by the steering motor 32. The steering force actually generated by the steering motor 32 correlates with the actual current value Ib. The axial force generated in the rack shaft 22 during the steering of the steering wheel 5 correlates with the vehicle speed V such that it increases as the vehicle speed V decreases.

[0057] Therefore, the limit angle calculation processing unit 81 calculates the limit angle θplim so that the pinion angle θp is within the angle range defined such that the steering force generated by the steering motor 32 and the axial force generated in the rack shaft 22 can maintain a balance of forces.

[0058] For example, when the remaining force of the steering force that can be generated by the steering motor 32 is sufficient for the axial force generated in the rack shaft 22 at the vehicle speed V, the limit angle calculation processing unit 81 calculates the limit angle θplim, which is the maximum value as the design limit value. In this case, the angle range in which the pinion angle θp can change is not restricted with respect to the design angle range.

[0059] On the other hand, when there is a shortage of the remaining force of the steering force that the steering motor 32 can generate with respect to the axial force generated in the rack shaft 22 at the vehicle speed V, the limit angle calculation processing unit 81 calculates a limit angle θplim that is smaller than the maximum value, which is the design limit value. When there is a shortage of the remaining force of the steering force that the steering motor 32 can generate, the larger the shortage, the more the limit angle θplim deviates from the maximum value, which is the design limit value, that is, the value approaches the rack neutral position. In this case, the angle range in which the pinion angle θp can change is restricted with respect to the design angle range.

[0060] The pinion angle θp and the limit angle θplim are input to the control amount limiting processing unit 82. The control amount limiting processing unit 82 calculates a limit gain Ki based on the pinion angle θp and the limit angle θplim. The limit gain Ki thus obtained is used in the calculation by the compensation processing unit 83. In the present embodiment, the processing executed by the control amount limiting processing unit 82 is an example of the control amount limiting processing.

[0061] More specifically, the control amount limiting processing unit 82 includes a process of comparing the pinion angle θp and the limit angle θplim. The control amount limiting processing unit 82 calculates the difference between the absolute values of these by comparing the absolute values of the pinion angle θp and the limit angle θplim. Further, the control amount limiting processing unit 82 includes a steering condition determination process of determining whether or not the cut-in steering condition is satisfied. The steering condition determination process is a process of determining whether or not the steering wheel 5 is in a state of being cut in toward the limit side of the angle region based on the change state of the pinion angle θp, for example, the pinion angular velocity ωp obtained by differentiating the pinion angle θp. When the signs of the pinion angle θp and the pinion angular velocity ωp match each other, the control amount limiting processing unit 82 determines that the steering wheel 5 is in a state of being cut in toward the limit side of the angle region (hereinafter referred to as the "cut-in steering state"), that is, the cut-in steering condition is satisfied. On the other hand, when the signs of the pinion angle θp and the pinion angular velocity ωp do not match, the control amount limiting processing unit 82 determines that the steering wheel 5 is in a state of being cut back toward the rack neutral position side (hereinafter referred to as the "cut-back steering state"), that is, the cut-in steering condition is not satisfied. Note that when the pinion angular velocity ωp is "0", the control amount limiting processing unit 82 determines that it is not in the cut-in steering state, that is, the cut-in steering condition is not satisfied.

[0062] Then, when the cut-in steering condition is satisfied, the control amount limiting processing unit 82 includes a process of calculating a limit gain Ki for preventing the steering wheel 5 from being steered when the pinion angle θp exceeds the limit angle θplim. That is, when the cut-in steering condition is satisfied, the control amount limiting processing unit 82 calculates a limit gain Ki for preventing the absolute value of the pinion angle θp from exceeding the absolute value of the limit angle θplim.

[0063] For example, when the difference between the absolute values of the pinion angle θp and the limit angle θplim is sufficiently large, the control amount limiting processing unit 82 calculates a limit gain Ki of "1" on the assumption that it can be determined that the steering wheel 5 will not be steered when the pinion angle θp exceeds the limit angle θplim. Calculating a limit gain Ki of "1" means not correcting the pinion angle θp, that is, not limiting the current command value Ib*.

[0064] On the one hand, when the difference between the absolute value of the pinion angle θp and the limit angle θplim is small, the control quantity limiting processing unit 82 calculates a limit gain Ki less than "1" on the assumption that it can be determined that the pinion angle θp exceeds the limit angle θplim and the steering wheel 5 is steered. Calculating a limit gain Ki less than "1" means limiting the current command value Ib*, that is, correcting the pinion angle θp. In this case, the control quantity limiting processing unit 82 calculates a smaller limit gain Ki as the difference between the absolute value of the pinion angle θp and the limit angle θplim becomes smaller. That is, when the difference between the absolute value of the pinion angle θp and the limit angle θplim is small, the limit gain Ki increases the limiting amount of the current command value Ib* as the difference becomes smaller.

[0065] Note that when the cut-in steering condition is not satisfied, the control quantity limiting processing unit 82 includes a process of calculating a limit gain Ki of "1" regardless of the difference between the absolute value of the pinion angle θp and the limit angle θplim. This is because when the cut-in steering condition is not satisfied, the steering wheel 5 cannot be steered with the pinion angle θp exceeding the limit angle θplim, so there is little need to limit the current command value Ib*, that is, correct the pinion angle θp.

[0066] The limit gain Ki is input to the compensation processing unit 83. The compensation processing unit 83 is a process for gradually changing the limit gain Ki. For example, the compensation processing unit 83 is a filter process using a low-pass filter. When the value of the limit gain Ki changes, the compensation processing unit 83 suppresses a sudden change in the change. The limit gain Ki obtained by performing such filter processing is reflected in the current command value Ib* through the reflection processing unit 73. In the present embodiment, the process executed by the compensation processing unit 83 is an example of compensation processing.

[0067] <Operation of this Embodiment> For example, when an axial force exceeding the maximum steering force that can be generated by the steering motor 32 is generated, depending on the axial force characteristics of the vehicle, it becomes difficult to maintain the balance between the steering force generated by the steering motor 32 and the axial force acting on the rack shaft 22.

[0068] In contrast, the present embodiment focuses on the fact that restricting the current command value Ib* leads to correcting the pinion angle θp. That is, restricting the current command value Ib* realizes correcting the pinion angle θp so that it becomes an angle within an angular range determined such that the steering force that can be generated by the steering motor 32 and the axial force generated in the rack shaft 22 can maintain a balance of forces.

[0069] Therefore, the correction processing unit 72 includes a control amount restriction processing unit 82 related to the restriction of the current command value Ib*. The restriction of the current command value Ib* aims to correct the pinion angle θp so that it becomes an angle within an angular range determined such that the steering force that can be generated by the steering motor 32 and the axial force generated in the rack shaft 22 can maintain a balance of forces. Thereby, it is suppressed that the pinion angle θp deviates from an angular range in which it is difficult to maintain the balance of forces between the steering force of the steering motor 32 and the axial force generated in the rack shaft 22.

[0070] <Effects of the present embodiment> (1-1) By restricting the current command value Ib*, it is suppressed that the pinion angle θp deviates from an angular range in which it is difficult to maintain the balance of forces between the steering force of the steering motor 32 and the axial force generated in the rack shaft 22. That is, it is suppressed that a situation occurs in which an axial force exceeding the steering force that can be generated by the steering motor 32 is generated. Therefore, the steering wheel 5 can be steered more smoothly according to the steering state of the steering wheel 3.

[0071] (1-2) The correction processing unit 72 includes a limit angle calculation processing unit 81 that calculates a limit angle θplim. Further, the control amount restriction processing unit 82 in the correction processing unit 72 includes a process of calculating a limit gain Ki based on the limit angle θplim and the pinion angle θp. Thereby, in the control amount restriction processing unit 82, the optimization of the restriction of the current command value Ib* can be achieved.

[0072] (1-3) The limit angle calculation processing unit 81 is configured to include a process of calculating a limit angle θplim for defining a limited angle region with respect to the designed angle region based on the vehicle speed V. Thereby, in the limit angle calculation processing unit 81, for example, it is possible to take into account a situation in a parking state or a very low speed range where the steering wheel 5 is likely to be steered in a larger range. This is because the axial force generated in the rack shaft 22 changes according to the state of the vehicle, and it is particularly effective to include the vehicle speed V, which is considered to have a great influence, in the state of the vehicle. Therefore, it is possible to appropriately determine the situation where the current command value Ib* should be limited.

[0073] (1-4) The limit angle calculation processing unit 81 is configured to include a process of calculating the limit angle θplim based on the actual current value Ib in addition to the vehicle speed V. Thereby, in the limit angle calculation processing unit 81, for example, it is possible to take into account the remaining force of the steering force that the steering motor 32 can generate. Therefore, it is possible to appropriately determine the situation where the current command value Ib* should be limited.

[0074] (1-5) The control amount limiting processing unit 82 is configured to include a steering condition determination process for determining whether or not the cut-in steering condition is satisfied. And when it is determined through the steering condition determination process that the cut-in steering condition is satisfied, the control amount limiting processing unit 82 is configured to execute a process related to the limitation of the current command value Ib*. Thereby, in the control amount limiting processing unit 82, for example, it is possible to take into account a situation where it is assumed that the pinion angle θp deviates from an angle region where it is difficult to maintain the balance between the steering force of the steering motor 32 and the axial force generated in the steering shaft. Therefore, it is possible to appropriately determine the situation where the current command value Ib* should be limited. In this case, for example, even if the steering wheel 5 reaches the position corresponding to the limit angle θplim, the momentum at that time, that is, the acceleration, will also be alleviated. This is effective for suppressing the generation of abnormal noise when the steering wheel 5 reaches the position corresponding to the limit angle θplim.

[0075] (1-6) The correction processing unit 72 includes a compensation processing unit 83 that gradually changes the limiting gain Ki. As a result, in the compensation processing unit 83, when the limiting gain Ki changes, the limiting gain Ki can be gradually changed. That is, when the current command value Ib* is limited, the steering control unit 60 can gradually change the final current command value Ib* from before the limitation to after the limitation. Thereby, it is possible to reduce the discomfort of the driver with respect to the vehicle behavior that appears due to the limitation of the current command value Ib*.

[0076] (1-7) The compensation processing unit 83 employs a filter process using a low-pass filter. This is effective for facilitating the implementation of the compensation processing unit 83. <Second Embodiment> Hereinafter, the second embodiment will be described with reference to the drawings, centering on the differences from the first embodiment. For the sake of convenience of explanation, the same components as those in the first embodiment are denoted by the same reference numerals as in the first embodiment, and the description thereof is omitted.

[0077] As shown by the dashed two-dot line in FIG. 2, the steering control unit 60 of this embodiment has a correction processing unit 91 related to the limitation of the steering force command value Tp*. Instead of the correction processing unit 72 of the first embodiment calculating the limiting gain Ki, the correction processing unit 91 calculates the limiting gain Kt. In this case, in the steering control unit 60, by eliminating the reflection processing unit 73, the current command value Ib* obtained through the current command value calculation unit 71 is used in the calculation by the current feedback control unit 74.

[0078] As shown in FIG. 5, the correction processing unit 91 calculates a limit gain Kt based on the vehicle speed V, the pinion angle θp, and the actual current value Ib. The limit gain Kt is a component for limiting the steering force command value Tp*, and is, for example, a value of 1 or less that is greater than 0. That is, when the limit gain Kt is less than 1, the steering force command value Tp* is limited so that its absolute value becomes smaller. This means that the pinion angle θp is corrected so as to limit the angle range that can be changed, that is, the target pinion angle θp* is corrected. The thus obtained limit gain Kt is reflected in the steering force command value Tp* through the reflection processing unit 92.

[0079] The reflection processing unit 92 calculates the final steering force command value Tp* (Tp* × Kt) by multiplying the steering force command value Tp* by the limit gain Kt. For example, the reflection processing unit 92 is a multiplier, similar to the reflection processing unit 73.

[0080] Note that the correction processing unit 91 has a configuration corresponding to the limit angle calculation processing unit 81, the control amount limit processing unit 82, and the compensation processing unit 83 in the correction processing unit 72 of the first embodiment. That is, the limit gain Kt is subjected to a filter process.

[0081] According to the present embodiment described above, the operations and effects similar to those of the first embodiment can be obtained. <Other Embodiments> The above embodiments may be modified as follows. Also, the following other embodiments can be combined with each other as long as there is no technical contradiction.

[0082] ·In each embodiment, the limit angle calculation processing unit 81 may be configured to perform map calculation of the limit angle θplim using, for example, a map that defines the relationship between the vehicle speed V, the actual current value Ib, and the limit angle θplim.

[0083] ·In each embodiment, when calculating the limit angle θplim, the limit angle calculation processing unit 81 may consider, in addition to the vehicle speed V and the actual current value Ib, the yaw rate or the like generated in the vehicle. For example, the yaw rate is one of the parameters indicating the state of the vehicle. In addition, the limit angle calculation processing unit 81 may consider the load capacity of the vehicle. For example, the difference in the load capacity of the vehicle is a factor that changes the axial force characteristics of the vehicle. Further, the limit angle calculation processing unit 81 may consider the drive mode of the steering motor 32. For example, when the steering motor 32 is redundantly designed, the difference in the drive mode as to whether all systems are driven or only one of the systems is driven is a factor that changes the maximum output of the steering motor 32.

[0084] ·In each embodiment, instead of the actual current value Ib, the limit angle calculation processing unit 81 may be configured to input the detection result of the axial force sensor. The axial force sensor is a sensor that detects the axial force generated in the rack shaft 22 and can be provided, for example, on the rack shaft 22. In addition, instead of the actual current value Ib, the limit angle calculation processing unit 81 may be configured to input the final current command value Ib*.

[0085] ·In each embodiment, instead of the limit angle θplim, the limit angle calculation processing unit 81 may calculate the angle range in which the pinion angle θp can change. In addition, instead of the limit angle θplim, the limit angle calculation processing unit 81 may calculate the change range based on the current pinion angle θp.

[0086] ·In each embodiment, instead of the pinion angle θp, the control amount limit processing unit 82 may be configured to input the steering angle θs. For example, the control amount limit processing unit 82 can obtain the pinion angle θp or a corresponding value by taking into account the adjustment amount in the steering angle θs.

[0087] ·In each embodiment, the control amount limiting processing unit 82 may consider, in addition to the cut-in steering condition, whether or not the steering wheel 5 is in a state of hitting an obstacle such as a curb where the rack shaft 22 cannot move when hitting an obstacle such as a curb. For example, the control amount limiting processing unit 82 can determine whether or not it is in a state of hitting an obstacle such as a curb based on whether the vehicle speed V is in a stopped state or an extremely low speed range, and whether the change gradient of the actual current value Ib is greater than a threshold value.

[0088] ·In each embodiment, when executing the steering condition determination process, the control amount limiting processing unit 82 may consider the steering torque Th in addition to the pinion angle θp. Alternatively, when executing the steering condition determination process, the control amount limiting processing unit 82 may input the steering torque Th instead of the pinion angle θp.

[0089] ·In each embodiment, the control amount limiting processing unit 82 may not include a steering condition determination process for determining whether or not the cut-in steering condition is satisfied. ·In each embodiment, the compensation processing unit 83 may change its implementation method. For example, when the value of the limit gain Ki or the limit gain Kt changes, a method such as obtaining the deviation before and after the change and gradually changing the deviation may be adopted.

[0090] ·In the first embodiment, the correction processing unit 72 may not include the compensation processing unit 83. For example, the compensation processing unit 83 may be included in the steering control unit 60. The other embodiments described herein can be similarly applied to the second embodiment.

[0091] ·In each embodiment, the configuration corresponding to the compensation processing unit 83 may be omitted. ·In each embodiment, the target pinion angle calculation unit 62 may set the target pinion angle θp* to the same value as the steering angle θs. That is, the steering angle ratio, which is the ratio of the steering angle θs to the steering angle θi, may be "1:1".

[0092] ·In each embodiment, when calculating the steering reaction force command value Ts*, the steering reaction force command value calculation unit 52 may not use either the vehicle speed V or the steering torque Th, or may use a combination of other elements.

[0093] ·In each embodiment, the steering reaction force command value calculation unit 52 may calculate, as the steering reaction force command value Ts*, a value calculated by executing torque feedback control that causes the steering torque Th to follow the target steering torque calculated based on the steering torque Th.

[0094] ·In each embodiment, the steering angle calculation unit 51 may calculate the steering angle θs by taking into account the twist of the steering shaft 11 corresponding 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. The steering angle sensor may be provided, for example, between the steering wheel 3 and the torque sensor 41 on the steering shaft 11.

[0095] ·In each embodiment, it is not essential for the steering actuator 12 to include the steering side reduction mechanism 14. ·In each embodiment, the steering motor 13 is not limited to a three-phase brushless motor. For example, it may be a DC motor with brushes. Other embodiments described herein can be similarly applied to the steering motor 32.

[0096] ·In each embodiment, the pinion angle θp may be obtained by converting the 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 will be converted by the detection value of the movement amount of the rack shaft 22.

[0097] ·In each embodiment, the operating member that the driver operates 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 is not limited to a configuration in which the right steering wheel 5 and the left steering wheel 5 are interlocked. In other words, the right steering wheel 5 and the left steering wheel 5 may be independently controllable.

[0098] ·In each embodiment, the vehicle steering system 2 has a linkless structure in which the steering unit 4 and the steering unit 6 are mechanically separated at all times, but it is not limited to this. For example, a structure in which the steering unit 4 and the steering unit 6 can be mechanically separated by a clutch may be used.

[0099] ·In each embodiment, the steering motor 32 may be, for example, arranged coaxially with the rack shaft 22, or connected to the pinion shaft constituting the rack and pinion mechanism of the rack shaft 22 via a worm and wheel.

Explanation of Reference Numerals

[0100] 1... Steering control device 2... Vehicle steering system 3... Steering wheel 4... Steering unit 5... Steering wheel 6... Steering unit 22... Rack shaft (steering shaft) 32... Steering motor 60... Steering control unit (control unit) 72... Correction processing unit 81... Limit angle calculation processing unit 82... Control amount limit processing unit 83... Compensation processing unit 91... Correction processing unit

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 steered wheels of the vehicle is separated, wherein the steering unit includes a steering shaft that steers the steered wheels, a steering motor that generates a steering force, which is a torque applied to the steering shaft to steer the steered wheels, and a control unit that controls the steering motor, the control unit controls the steering motor so that a conversion angle convertible to a steering angle of the steered wheels follows a target angle calculated according to a steering state of the steering wheel, and executes a correction process for correcting the conversion angle so that the angle is within an angle range defined as being able to maintain a balance between the steering force that can be generated by the steering motor and an axial force generated in the steering shaft, the correction process including a control amount limitation process related to limitation of a control amount for commanding the steering force to be generated in the steering motor, the steering control device.

2. The correction process includes a limit angle calculation process for calculating a limit angle for defining an angle range in which the steering force generated by the steering motor and the axial force generated in the steering shaft can maintain a balance, the control amount limitation process including a process for calculating a limitation component related to limitation of the control amount based on the limit angle and the conversion angle, the steering control device according to claim 1.

3. The limit angle calculation process includes a process for calculating the limit angle for defining an angle range limited with respect to a design angle range based on a state of the vehicle including at least a vehicle speed, the steering control device according to claim 2.

4. The limit angle calculation process includes a process for calculating the limit angle based on a state related to the steering force generated by the steering motor in addition to the vehicle speed, the steering control device according to claim 3.

5. The control amount limitation process includes a steering condition determination process for determining whether or not a cut-in steering condition indicating that the steered wheels are cut in toward a limit side of the angle range is satisfied, the control amount limitation process executing a process related to limitation of the control amount when it is determined that the cut-in steering condition is satisfied, the steering control device according to any one of claims 1 to 4.

6. The control unit according to any one of claims 1 to 4, which is configured to execute a compensation process for compensating the control amount so as to suppress a sudden change in the control amount before and after the restriction when the control amount is restricted through the control amount restriction process.

7. The steering control device according to claim 6, wherein the compensation process is a filter process using a low-pass filter.

8. 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, wherein the steering control method includes executing a control process for controlling a steering motor that generates a steering force, which is a torque applied to a steering shaft that steers the steered wheels to steer the steered wheels, the control process controls the steering motor so that a conversion angle convertible to a steering angle of the steered wheels follows a target angle calculated according to a steering state of the steering wheel, and the conversion angle is corrected so as to be an angle within an angle range determined such that the steering force that can be generated by the steering motor and an axial force generated on the steering shaft can maintain a balance of forces, the correction process includes a control amount restriction process related to restriction of a control amount for commanding the steering force to be generated in the steering motor.

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