Steering controls

Abstract

The steering control device (1) includes a torque command value calculation unit (52) configured to calculate a torque command value, which is a target value of the motor torque when controlling the operation of the motor so as to generate the motor torque. The torque command value calculation unit (52) includes a first component calculation unit configured to calculate a first component, a second component calculation unit configured to calculate a second component, and a torque component calculation unit configured to calculate the torque component. The first component calculation unit is configured to add a calculation hysteresis component to the first component so as to provide a hysteresis characteristic with respect to a change in a specific state variable. The torque component calculation unit (52) is configured to perform calculations in a first calculation case and calculations in a second calculation case.

Description

Technical Field

[0001] The present invention relates to a steering control device. Background Art

[0002] In the related art, a steer-by-wire system in which the power transmission path between a steering unit (for steering by the driver) and a rotation unit (for rotating the wheels in response to the driver's steering) is disconnected is known as a steering system. In this steering system, road surface information, such as the road surface reaction force applied to the wheels, is not mechanically transmitted to the steering wheel. Therefore, a steering control device controlling this steering system controls the steering-side actuator provided in the steering unit to apply a steering reaction force to the steering wheel that takes into account the road surface information, thereby transmitting road surface information to the driver.

[0003] For example, the steering control device described in Japanese Unexamined Patent Application Publication No. 2020-142596 (JP 2020-142596A) determines the steering reaction force in consideration of the axial force acting on the rotating shaft provided in the rotating unit, and uses a distributed axial force in which a plurality of types of axial forces are added at a predetermined distribution ratio and regarded as one axial force. In JP 2020-142596A, an angular axial force based on a target rotation angle for controlling the rotation angle of a rotating wheel calculated according to the steering angle of a steering wheel, a current axial force based on a driving current of a rotating side motor serving as a driving source of a rotating side actuator, and the like are exemplified as the plurality of types of axial forces. The steering control device described in JP 2020-142596 A calculates the steering reaction force based on the distributed axial force in which the angular axial force and the current axial force are distributed. Summary of the Invention

[0004] The relationship between the steering angle, which serves as the basis for the target steering angle, and the axial force actually acting on the rotating shaft varies depending on vehicle speed. When the vehicle is stopped, the axial force gradient, which represents the rate of change of the axial force relative to the steering angle, decreases, and the hysteresis width of the axial force relative to the change in steering angle increases. On the other hand, when the vehicle is traveling at medium or high speeds, the axial force gradient increases and the hysteresis width decreases. The angular axial force can be calculated by adding a calculated hysteresis component to achieve a hysteresis width that reflects the actual hysteresis of the axial force relative to the change in steering angle.

[0005] To more accurately convey road conditions, such as the road surface reaction force, to the driver, adjustments can be made to increase the axial force gradient of the distributed axial force. This is effective when the current axial force distribution ratio is high. On the other hand, when the angular axial force distribution ratio is high and adjustments are made to increase the axial force gradient of the distributed axial force, the gradient of the added calculation hysteresis component becomes larger than expected, potentially leading to oscillatory control behavior.

[0006] This problem is not limited to the angular axial force calculated as a component of the steering reaction force, and may similarly be caused as long as there is a component of the steering reaction force calculated by adding a calculation hysteresis component so as to achieve a hysteresis width reflecting the actual hysteresis state.

[0007] Aspects of the present invention provide a steering control device. The steering control device controls a steering system in which the steering torque required to steer a steering wheel is changed using motor torque applied from an actuator driven by a motor. The steering control device includes a torque command value calculation unit configured to calculate a torque command value, which is a target value of the motor torque when controlling the operation of the motor so as to generate the motor torque. The torque command value calculation unit includes: a first component calculation unit configured to calculate a first component based on a first state variable that changes according to the operation of the steering system; a second component calculation unit configured to calculate a second component based on a second state variable that changes with the operation of the steering system; and a torque component calculation unit configured to calculate a torque component used to calculate the torque command value based on at least one of the first component and the second component. The torque command value calculation unit is configured to set the first state variable to a state variable that does not have a hysteresis characteristic with respect to changes in a specific state variable that changes according to the operation of the steering system, and to set the second state variable to a state variable that has a hysteresis characteristic with respect to changes in the specific state variable. The first component calculation unit is configured to add a calculation hysteresis component to the first component when calculating the first component, thereby providing a hysteresis characteristic relative to changes in a specific state variable. The torque component calculation unit is configured to perform calculations in a first calculation case and a second calculation case. The first calculation case is a calculation for adjusting the gradient of the second component relative to changes in the specific state variable. The second component is obtained by the second component calculation unit, and the adjusted second component is used to calculate the torque component. The second calculation case is a calculation for adjusting the gradient of the torque component relative to changes in the specific state variable. The torque component is obtained through calculation based on at least one of the first component and the second component, and the adjusted torque component is calculated as the final torque component.

[0008] With this configuration, the final torque component can be calculated using the first and second calculation scenarios, respectively, depending on the situation. For example, if the hysteresis gradient of the calculated hysteresis component added to the first component when using the second calculation scenario is assumed to be larger than expected, the first calculation scenario can be used to increase the gradient of the second component relative to changes in a specific state variable while suppressing the oscillation characteristics of the control caused by the larger-than-expected increase in the hysteresis gradient associated with the first component. This improves control stability.

[0009] In the steering control device, the first component calculation unit may be an angular axial force calculation unit configured to calculate an angular axial force as a first component, the angular axial force being determined based on an angle that can be converted into a rotation angle of a rotating wheel of the vehicle, and being an axial force in which road surface information is not reflected. The second component calculation unit may be a current axial force calculation unit configured to calculate a current axial force as a second component, the current axial force being determined based on a current supplied to the motor, and being an axial force in which road surface information is reflected.

[0010] In the steering control device, the torque component calculation unit may be configured to reflect, in the torque command value, a torque component obtained by calculation in a first calculation case when the vehicle has a first vehicle speed including a stopped state. The torque component calculation unit may be configured to reflect, in the torque command value, a torque component obtained by calculation in a second calculation case when the vehicle has a second vehicle speed including a running state.

[0011] With this configuration, in a stopped state, it is possible to suppress the oscillating characteristics of control caused by a larger-than-expected increase in the hysteresis gradient associated with the first component while increasing the gradient of the second component relative to the change in the specific state variable using the first calculation. From the perspective of conveying road surface conditions, such as road surface reaction force, to the driver, it is more preferable to increase the gradient of the torque component relative to the change in the specific state variable in the stopped state and the stopped state of the driving state. That is, the hysteresis gradient of the calculated hysteresis component added to the first component is assumed to be larger than expected for the stopped state and the stopped state of the driving state. Therefore, from the perspective of conveying road surface conditions, such as road surface reaction force, to the driver, it is possible to achieve improved control stability by implementing the preferred mode.

[0012] In the steering control device, the torque component calculation unit may include a mediation unit configured to mediate which torque component, among torque components obtained by calculation in the first calculation case and calculation in the second calculation case, is to be reflected in the torque command value when the calculation in the first calculation case and the calculation in the second calculation case are performed in parallel. The mediation unit may be configured to reflect the torque component obtained by calculation in the first calculation case in the torque command value when the vehicle has a first vehicle speed including a stopped state. The mediation unit may be configured to reflect the torque component obtained by calculation in the second calculation case in the torque command value when the vehicle has a second vehicle speed including a running state.

[0013] With this configuration, the torque component obtained by the calculation in the first calculation case and the torque component obtained by the calculation in the second calculation case can be reflected in the torque command value, taking into account the situation as close as possible. Therefore, the situation in which improvement in control stability is to be achieved can be determined more accurately.

[0014] In a steering control device, the mediation unit can be configured to compensate for the torque component so that when the component to be reflected in the torque command value switches between the torque component obtained by calculation in a first calculation case and the torque component obtained by calculation in a second calculation case, a sudden change in the torque component between before and after the switching is suppressed.

[0015] With this configuration, when the component to be reflected in the torque command value switches between the torque component obtained by calculation in the first calculation case and the torque component obtained by calculation in the second calculation case, it is possible to suppress a sudden change in the torque component before and after the switching. This is effective in achieving improved control stability.

[0016] With the steering control device according to the present invention, an improvement in control stability can be achieved. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, wherein like symbols represent like elements, and in which:

[0018] Figure 1 is a diagram schematically showing the configuration of a steer-by-wire system;

[0019] Figure 2 is a block diagram showing the functions of a steering control device;

[0020] Figure 3 is a block diagram illustrating the functionality of an axial force calculation unit;

[0021] Figure 4is a block diagram illustrating the functionality of a distributed axial force calculation unit;

[0022] Figure 5A is a graph showing the relationship between the steering angle and the hysteresis component when turning the steering wheel;

[0023] Figure 5B is a graph showing the relationship between the steering angle and the hysteresis component at the time of return steering;

[0024] Figure 6 is a graph showing an example of a gradient adjustment map when the vehicle is parked; and

[0025] Figure 7 : is a graph showing an example of a gradient adjustment map during driving. DETAILED DESCRIPTION

[0026] Hereinafter, a steering control device according to an embodiment will be described with reference to the accompanying drawings. Figure 1 As shown, a vehicle steering system 2 controlled by a steering control device 1 is configured as a steer-by-wire system. The steering system 2 includes a steering unit 4 that is steered by a driver using a steering wheel 3 and a turning unit 6 that turns a turning wheel 5 according to the steering input to the steering unit 4 by the driver.

[0027] 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 motor 13 serving as a drive source and a steering reduction gear mechanism 14. The steering motor 13 applies a steering reaction force, which acts as a force opposing the steering, to the steering wheel 3 via the steering shaft 11. The steering motor 13 is connected to the steering shaft 11 via the steering reduction gear mechanism 14, which is configured as a worm and worm wheel, for example. For example, a three-phase brushless motor is employed as the steering motor 13 according to this embodiment.

[0028] The rotating unit 6 includes a pinion shaft 21, a rack shaft 22 serving as a rotating shaft connected to the pinion shaft 21, and a rack housing 23. The pinion shaft 21 and the rack shaft 22 are connected to each other at a predetermined intersection angle. The rack and pinion mechanism 24 is configured by meshing the pinion teeth 21a formed in the pinion shaft 21 and the rack teeth 22a formed in the rack shaft 22 with each other. The rack and pinion mechanism 24 is housed in the rack housing 23. The end opposite to the end of the pinion shaft 21 connected to the rack shaft 22 protrudes from the rack housing 23. Both ends of the rack shaft 22 protrude from both ends of the rack housing 23 in the axial direction. A tie rod 26 is connected to both ends of the rack shaft 22 via a rack end 25 formed by a ball joint. The distal end of the tie rod 26 is connected to a steering knuckle (not shown) to which the right and left turning wheels 5, 5 are assembled.

[0029] The rotating unit 6 includes a rotating actuator 31 that applies a rotational force to the rack shaft 22 to rotate the rotating wheel 5. The rotating actuator 31 includes a rotating motor 32 as a drive source, a transmission mechanism 33, and a conversion mechanism 34. The rotating motor 32 applies a rotational force to the rack shaft 22 to rotate the rotating wheel 5 via the transmission mechanism 33 and the conversion mechanism 34. The rotating motor 32 transmits rotation to the conversion mechanism 34 via the transmission mechanism 33, which is configured as, for example, a belt transmission mechanism. The transmission mechanism 33 converts the rotation of the rotating motor 32 into reciprocating motion of the rack shaft 22 via the conversion mechanism 34, which is configured as, for example, a ball screw mechanism.

[0030] In the steering system 2 having the aforementioned configuration, the rotation angle of the turning wheel 5 is changed by applying the motor torque as a turning force from the turning-side actuator 31 to the rack shaft 22 in response to the driver's steering operation. At this time, a steering reaction force opposing the driver's steering is applied to the steering wheel 3 from the steering actuator 12. That is, in the steering system 2, the steering torque Th required to steer the steering wheel 3 is changed by the steering reaction force, which is the motor torque applied from the steering actuator 12.

[0031] The reason for providing the pinion shaft 21 is that the rack shaft 22 is supported in the rack housing 23 together with the pinion shaft 21. Specifically, the rack shaft 22 is supported so as to be movable in its axial direction and pressed toward the pinion shaft 21 by a support mechanism (not shown) provided in the steering system 2. Therefore, the rack shaft 22 is supported in the rack housing 23. Instead of using the first pinion shaft 21, another support mechanism for supporting the rack shaft 22 in the rack housing 23 may be provided.

[0032] Electrical configuration of steering system 2

[0033] like Figure 1 As shown, the steering-side motor 13 and the rotating-side motor 32 are connected to the steering control device 1. The steering control device 1 controls the operations of the steering-side motor 13 and the rotating-side motor 32.

[0034] A torque sensor 41, a steering-side rotational angle sensor 42, a turning-side rotational angle sensor 43, and a vehicle speed sensor 44 are connected to the steering control device 1. The torque sensor 41 detects the steering torque Th, which indicates the torque applied to the steering shaft 11 in response to the driver's steering operation. The torque sensor 41 is located in a portion of the steering shaft 11 closer to the steering wheel 3 than the steering-side reduction gear mechanism 14. The torque sensor 41 detects the steering torque Th based on the amount of twisting of a torsion bar 41a located in the middle of the steering shaft 11. For example, when steering right, the steering torque Th is calculated as a positive value, and when steering left, the steering torque Th is calculated as a negative value.

[0035] The steering-side rotational angle sensor 42 detects the rotation angle θa, which is the angle of the rotation shaft of the steering-side motor 13, as a relative angle within a 360-degree range. The steering-side rotational angle sensor 42 is provided within the steering-side motor 13. The rotation angle θa of the steering-side motor 13 is used to calculate the steering angle θs. The steering-side motor 13 and the steering shaft 11 are interlocked via the steering-side reduction gear mechanism 14. Therefore, the rotation angle θa of the steering-side motor 13 is correlated with the rotation angle of the steering shaft 11 or the steering angle θs, which is the rotation angle of the steering wheel 3. Therefore, the steering angle θs can be calculated based on the rotation angle θa of the steering-side motor 13. For example, when turning right, the rotation angle θa is detected as a positive value, and when turning left, the rotation angle θa is detected as a negative value.

[0036] The rotating-side rotational angle sensor 43 detects the rotational angle θb, which is the angle of the rotation axis of the rotating-side motor 32, as a relative angle within a 360-degree range. The rotating-side rotational angle sensor 43 is provided in the rotating-side motor 32. The rotational angle θb of the rotating-side motor 32 is used to calculate the pinion angle θp. The rotating-side motor 32 and the pinion shaft 21 are interlocked via the transmission mechanism 33, the conversion mechanism 34, and the rack and pinion mechanism 24. Therefore, the rotational angle θb of the rotating-side motor 32 is correlated with the pinion angle θp, which is the rotational angle of the pinion shaft 21. Therefore, the pinion angle θp can be calculated based on the rotational angle θb of the rotating-side motor 32. The pinion shaft 21 meshes with the rack shaft 22. Therefore, the pinion angle θp also correlates with the amount of movement of the rack shaft 22. In other words, the pinion angle θp is a value that reflects the rotational angle of the rotating wheel 5. For example, when right turning is performed, the rotation angle θb is detected as a positive value, and when left turning is performed, the rotation angle θb is detected as a negative value.

[0037] Function of the steering controls

[0038] The vehicle speed sensor 44 detects the vehicle speed V, which is set as information indicating the vehicle's travel speed. The steering control device 1 includes a central processing unit (CPU) and a memory (not shown). The steering control device 1 performs various types of control by causing the CPU to execute a program stored in the memory at intervals of a predetermined calculation cycle.

[0039] like Figure 2As shown, the steering control device 1 includes a steering side control unit 50 that controls the power supply to the steering side motor 13. The steering side control unit 50 includes a steering side current sensor 54. The steering side current sensor 54 detects a steering side actual current value Ia obtained from a phase current value of the steering side motor 13, which flows in a connection line between the steering side control unit 50 and the phase motor coil of the steering side motor 13. The steering side current sensor 54 obtains a 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 side motor 13 as a current. Figure 2 , for the purpose of convenience of description, the connected wiring and one of each of the phase current sensors are shown together.

[0040] The steering control device 1 includes a rotating side control unit 60 that controls the power supply to the rotating side motor 32. The rotating side control unit 60 includes a rotating side current sensor 65. The rotating side current sensor 65 detects a rotating side actual current value Ib obtained from a phase current value of the rotating side motor 32, which flows in a connection line between the rotating side control unit 60 and the phase motor coil of the rotating side motor 32. The rotating side current sensor 65 obtains a voltage drop of a shunt resistor connected to the source side of each switching element in an inverter (not shown) provided corresponding to the rotating side motor 32 as a current. Figure 2 , for the purpose of convenience of description, the connected wiring and one of each of the phase current sensors are shown together.

[0041] Steering control unit

[0042] The steering torque Th, the vehicle speed V, the rotation angle θa, the actual turning-side current value Ib, the pinion angle θp, and a target pinion angle θp* to be described later are input to the steering-side control unit 50. The steering-side control unit 50 controls the power supply to the steering-side motor 13 based on the steering torque Th, the vehicle speed V, the rotation angle θa, the actual turning-side current value Ib, the pinion angle θp, and the target pinion angle θp*.

[0043] The steering side control unit 50 includes a steering angle calculation unit 51, a target reaction torque calculation unit 52, and a power supply control unit 53. The rotation angle θa is input to the steering angle calculation unit 51. The steering angle calculation unit 51 calculates the rotation angle θa as a total angle within a range exceeding 360 degrees by, for example, counting the number of rotations of the steering side motor 13 starting from the steering midpoint (which is the position of the steering wheel 3 when the vehicle moves straight forward). The steering angle calculation unit 51 calculates the steering angle θs by multiplying a conversion factor based on the rotation speed ratio of the steering side reduction gear mechanism 14 by the total angle obtained by the conversion. The obtained steering angle θs is output to the target reaction torque calculation unit 52. The steering angle θs is output to the turning side control unit 60, that is, the steering angle ratio change control unit 62 to be described later.

[0044] The steering torque Th, vehicle speed V, actual turning current value Ib, steering angle θs, pinion angle θp, and target pinion angle θp*, which will be described later, are input to a target reaction torque calculation unit 52. The target reaction torque calculation unit 52 calculates a target reaction torque Ts*, which is a target reaction control value of the steering reaction force of the steering wheel 3 generated by the steering-side motor 13, based on the steering torque Th, vehicle speed V, actual turning current value Ib, steering angle θs, pinion angle θp, and target pinion angle θp*. In this embodiment, the target reaction torque Ts* is an example of a torque command value, and the target reaction torque calculation unit 52 is an example of a torque command value calculation unit.

[0045] Specifically, the target reaction torque calculation unit 52 includes a steering force calculation unit 55 and an axial force calculation unit 56. The steering torque Th and the vehicle speed V are input to the steering force calculation unit 55. The steering force calculation unit 55 calculates the steering force Tb* based on the steering torque Th and the vehicle speed V. The steering force Tb* acts in the same direction as the driver's steering direction. The steering force calculation unit 55 calculates the steering force Tb* so that the absolute value of the steering force Tb* increases as the absolute value of the steering torque Th increases and the vehicle speed V decreases. The steering force Tb* is calculated as a value having the dimension of torque (N·m). The obtained steering force Tb* is output to the subtractor 57.

[0046] The vehicle speed V, the steering angle θs, the actual current value Ib on the rotating side, the pinion angle θp, and the target pinion angle θp* to be described later are input to the axial force calculation unit 56. The axial force calculation unit 56 calculates the axial force F applied to the rack shaft 22 via the turning wheel 5 based on the vehicle speed V, the steering angle θs, the actual current value Ib on the rotating side, the pinion angle θp, and the target pinion angle θp*. The axial force F is calculated as a value having the dimension of torque (N·m). The axial force F acts in a direction opposite to the steering direction of the driver. The subtractor 57 calculates the target reaction torque Ts* by subtracting the axial force F from the steering force Tb*. The acquired target reaction torque Ts* is output to the power supply control unit 53.

[0047] The target reaction torque Ts*, the rotation angle θa, and the steering-side actual current value Ia are input to the power supply control unit 53. Based on the target reaction torque Ts*, the power supply control unit 53 calculates the current command value Ia* for the steering-side motor 13. The power supply control unit 53 calculates the difference between the current command value Ia* and the current value on the dq coordinate system obtained by converting the steering-side actual current value Ia based on the rotation angle θa, and controls the power supply to the steering-side motor 13 to eliminate the difference. The steering-side motor 13 generates a torque corresponding to the target reaction torque Ts*. This provides the driver with an appropriate sense of responsiveness.

[0048] Rotating side control unit

[0049] The steering angle θs, the vehicle speed V, and the rotation angle θb are input to the turning-side control unit 60. The turning-side control unit 60 controls the power supply to the turning-side motor 32 based on the steering angle θs, the vehicle speed V, and the rotation angle θb.

[0050] The turning side control unit 60 includes a pinion angle calculation unit 61, a steering angle ratio change control unit 62, a pinion angle feedback control unit ( Figure 2 “Pinion angle F / B control unit” in ) 63 and power supply control unit 64.

[0051] The rotation angle θb is input to the pinion angle calculation unit 61. The pinion angle calculation unit 61 converts the rotation angle θb into a total angle encompassing a range exceeding 360 degrees by, for example, counting the number of rotations of the rotation-side motor 32 starting from the rack midpoint (the position of the rack shaft 22 when the vehicle is traveling straight ahead). The pinion angle calculation unit 61 calculates the pinion angle θp, which is the actual rotation angle of the pinion shaft 21, by multiplying the total angle obtained by the conversion by a conversion factor based on the reduction ratio of the transmission mechanism 33, the lead of the conversion mechanism 34, and the rotational speed ratio of the rack and pinion mechanism 24. For example, when the pinion angle θp is to the right of the rack midpoint, the pinion angle θp is calculated as a positive value, and when the pinion angle θp is to the left of the rack midpoint, the pinion angle θp is calculated as a negative value. The obtained pinion angle θp is output to the pinion angle feedback control unit 63. The pinion angle θp is output to the steering-side control unit 50 , that is, the axial force calculation unit 56 of the target reaction torque calculation unit 52 .

[0052] The vehicle speed V and the steering angle θs are input to the steering angle ratio change control unit 62. The steering angle ratio change control unit 62 calculates the target pinion angle θp* by adding an adjustment amount to the steering angle θs. The steering angle ratio change control unit 62 changes the adjustment amount according to the vehicle speed V to change the steering angle ratio, which is the ratio of the target pinion angle θp* to the steering angle θs. For example, the adjustment amount is changed so that the target pinion angle θp* changes more with respect to the change in the steering angle θs when the vehicle speed V is low than when the vehicle speed V is high. 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*. Therefore, there is also a correlation between the steering angle θs and the pinion angle θp.

[0053] The target pinion angle θp* and the pinion angle θp are input to the pinion angle feedback control unit 63. The pinion angle feedback control unit 63 performs PID control as feedback control of the pinion angle θp using a proportional term, an integral term, and a differential term, so that the pinion angle θp matches the target pinion angle θp*. Specifically, the pinion angle feedback control unit 63 calculates the difference between the target pinion angle θp* and the pinion angle θp, and calculates the turning force command value T* as the target control value for the turning force so that the difference is eliminated.

[0054] The turning force command value T*, the rotation angle θb, and the actual turning-side current value Ib are input to the power supply control unit 64. The power supply control unit 64 calculates the current command value Ib* for the turning-side motor 32 based on the turning force command value T*. The power supply control unit 64 calculates the difference between the current command value Ib* and the current value on the dq coordinate system obtained by converting the actual turning-side current value Ib based on the rotation angle θb, and controls the power supply to the turning-side motor 32 so that the difference is eliminated. As a result, the turning-side motor 32 rotates by an angle corresponding to the turning force command value T*.

[0055] Axial force calculation unit

[0056] The function of the axial force calculation unit 56 will be described in more detail below. Figure 3 As shown, the axial force calculation unit 56 includes a distribution axial force calculation unit 71 , an end axial force calculation unit 72 , a difference axial force calculation unit 73 and an axial force selection unit 74 .

[0057] The distributed axial force calculation unit 71 calculates the distributed axial force Fd based on the axial force acting on the rack shaft 22. The distributed axial force Fd corresponds to a calculated axial force obtained by estimating the axial force acting on the rack shaft 22 by distributing the angular axial force Fr and the current axial force Fi (described later) according to their distribution ratio so that the axial force acting on the rack shaft 22 via the rotating wheel 5 is appropriately reflected. The obtained distributed axial force Fd is output to the adder 75. In this embodiment, the distributed axial force Fd is an example of a torque component.

[0058] The end axial force calculation unit 72 calculates the end axial force Fie to inform the driver that the steering limit of the steering wheel 3, that is, the rotation limit of the turning wheels 5, has been reached. The end axial force Fie corresponds to a force that opposes the turning of the steering wheel 3 so as to restrict additional turning of the steering wheel 3 beyond the steering angle limit corresponding to the steering limit when the absolute value of the steering angle θs approaches the steering angle limit.

[0059] The target pinion angle θp* is input to the end axial force calculation unit 72. The end axial force calculation unit 72 calculates the end axial force Fie based on the target pinion angle θp*. Specifically, the end axial force calculation unit 72 includes an end axial force map that defines the relationship between the target pinion angle θp* and the end axial force Fie. Using the target pinion angle θp* as input, the end axial force calculation unit 72 calculates the end axial force Fie as "0." When the absolute value of the target pinion angle θp* is equal to or less than the threshold angle θie, the end axial force calculation unit 72 calculates the end axial force Fie as "0." When the absolute value of the target pinion angle θp* is greater than the threshold angle θie, the end axial force calculation unit 72 determines that the steering angle θs exceeds the steering angle limit and calculates the end axial force Fie so that its absolute value is greater than "0." The end axial force Fie is set so that when the absolute value of the target pinion angle θp* increases above the threshold angle θie, the absolute value of the end axial force Fie becomes so large that additional manual steering of the steering wheel 3 becomes impossible. The acquired end axial force Fie is output to the axial force selection unit 74 .

[0060] The differential axial force calculation unit 73 calculates the differential axial force Fv to notify the driver of any changes in the relationship between the steering state of the steering wheel 3 and the rotational state of the turning wheels 5 based on the steering angle ratio. An example of a situation in which the relationship between the steering state of the steering wheel 3 and the rotational state of the turning wheels 5 based on the steering angle ratio changes is when the turning wheels 5 come into contact with an obstacle (e.g., a curb). In this situation, the turning wheels 5 cannot turn toward the obstacle, but there is a possibility that the steering wheel 3 will turn toward the obstacle beyond the stop position of the steering wheel 3 corresponding to the stop position of the turning wheels 5. This is because the power transmission path between the steering unit 4 and the turning unit 6 is disconnected. Another example of a situation in which the relationship between the steering state of the steering wheel 3 and the rotational state of the turning wheels 5 based on the steering angle ratio changes is when the operation of the turning-side motor 32 is restricted to prevent overheating, resulting in a loss of correlation between the steering angle θs and the pinion angle θp. This is because the pinion angle θp is unlikely to coincide with the target pinion angle θp*. The differential axial force Fv corresponds to a force opposing the turning of the steering wheel 3, so that additional turning of the steering wheel 3 is restricted when the turning wheel 5 comes into contact with an obstacle (e.g., a curb). The differential axial force Fv corresponds to a force opposing the turning of the steering wheel 3, so that the turning of the steering wheel 3 is restricted to ensure consistency of the pinion angle θp with the target pinion angle θp* when the operation of the turning-side motor 32 is restricted to prevent overheating.

[0061] The steering angle θs, the pinion angle θp, and the actual current value Ib on the rotating side are input to the differential axial force calculation unit 73. The differential axial force calculation unit 73 calculates the converted angle obtained by converting the pinion angle θp by adding an adjustment amount to the pinion angle θp according to the steering angle ratio, so that the pinion angle θp is expressed as an index value of the rotating angle, so that it is expressed as an index value of the steering angle. The differential axial force calculation unit 73 changes the adjustment amount according to the vehicle speed V, so that the calculation rule defined by the steering angle ratio change control unit 62 is changed to a calculation rule in which the relationship between its input and output is reversed. The differential axial force calculation unit 73 calculates the differential axial force Fv based on the difference obtained by subtracting the converted angle from the steering angle θs. Specifically, the differential axial force calculation unit 73 includes a differential axial force map in which the relationship between the absolute value of the difference and the differential axial force Fv is defined, and calculates the differential axial force Fv using the difference as input. The differential axial force calculation unit 73 sets the sign of the differential axial force Fv based on the actual rotating-side current value Ib. Specifically, the differential axial force calculation unit 73 sets the differential axial force Fv to positive when the actual rotating-side current value Ib is positive, including zero, and sets the differential axial force Fv to negative when the actual rotating-side current value Ib is negative. The obtained differential axial force Fv is output to the axial force selection unit 74.

[0062] The end axial force Fie and the differential axial force Fv are input to the axial force selection unit 74. The axial force selection unit 74 selects the axial force having the larger absolute value between the end axial force Fie and the differential axial force Fv, and calculates the selected axial force as the selected axial force Fs1. The adder 75 calculates the axial force F by adding the selected axial force Fs1 to the distributed axial force Fd. Figure 2 As shown, the acquired axial force F is output to the subtractor 57. The subtractor 57 calculates the target reaction torque Ts* by subtracting the axial force F from the steering force Tb*. The acquired target reaction torque Ts* is output to the power supply control unit 53.

[0063] Distributed axial force calculation unit

[0064] The function of the distributed axial force calculation unit 71 will be described in more detail below. Figure 4 As shown, the distribution axial force calculation unit 71 includes an angular axial force calculation unit 81, a current axial force calculation unit 82, a distribution ratio calculation unit 83, a stop gradient adjustment unit 84, a stop distribution axial force calculation unit 85, a driving distribution axial force calculation unit 86, a driving gradient adjustment unit 87 and an axial force mediation unit 88.

[0065] Specifically, the angular axial force calculation unit 81 includes an axial force base component calculation unit 91 and a hysteresis component calculation unit 92. The target pinion angle θp* is input to the axial force base component calculation unit 91. The axial force base component calculation unit 91 calculates the axial force base component Frb, which is the base component of the angular axial force Fr, based on the target pinion angle θp*. The angular axial force Fr is an ideal value of the axial force defined by a model arbitrarily set for the vehicle. The angular axial force Fr is calculated as an axial force in which road surface information is not reflected. Road surface information includes information such as subtle bumps and depressions that do not affect the vehicle's behavior in the lateral direction or stepped portions that affect the vehicle's behavior in the lateral direction. Specifically, the axial force base component calculation unit 91 calculates the axial force base component Frb so that its absolute value increases as the absolute value of the target pinion angle θp* increases. The axial force base component Frb is calculated as a value having the dimension of torque (N·m). The obtained axial force base component Frb is output to the adder 93.

[0066] The steering angle θs is input to the hysteresis component calculation unit 92. The hysteresis component calculation unit 92 calculates the hysteresis component Fhy, which is a component to be added to the axial force base component Frb so that the angular axial force Fr has a hysteresis characteristic, based on the steering angle θs.

[0067] like Figure 5A and Figure 5B As shown, the hysteresis component calculation unit 92 includes hysteresis maps M1 and M2 that define the relationship between the steering angle θs and the hysteresis component Fhy. The hysteresis component calculation unit 92 uses one of the hysteresis maps M1 and M2 to map and calculate the hysteresis component Fhy based on the turning direction or return direction determined based on the sign and change of the steering angle θs. In this embodiment, turning direction refers to steering in which the steering direction remains constant. In this embodiment, return direction refers to steering within a predetermined small range of the steering angle θs after the steering direction has changed. In the hysteresis maps M1 and M2, "θs" represents the rate of change of the steering angle θs, with the steering angle θs at the start position of the turning direction or return direction defined as the origin.

[0068] Specifically, the hysteresis component calculation unit 92 calculates the hysteresis component Fhy using the hysteresis map M1 when the steering wheel is turned. In this case, the hysteresis component Fhy is calculated so that its absolute value increases as the absolute value of the steering angle θs increases, and the absolute value of the hysteresis gradient (the rate of change of the hysteresis component Fhy relative to the steering angle θs as the absolute value of the steering angle θs increases) decreases as the absolute value of the steering angle θs increases. In this case, the absolute value of the hysteresis component Fhy saturates within the range where the steering angle θs is equal to or greater than a predetermined value, and is calculated so that the maximum value at this time is equal to or less than the maximum value Fmax.

[0069] When the steering wheel is turned right, the hysteresis component calculation unit 92 uses a value that appears in the first quadrant with the steering angle θs at the start position of the steering wheel as the origin of the hysteresis map M1. When the steering wheel is turned left, the hysteresis component calculation unit 92 uses a value that appears in the third quadrant with the steering angle θs at the start position of the steering wheel as the origin of the hysteresis map M1.

[0070] On the other hand, the hysteresis component calculation unit 92 calculates the hysteresis component Fhy using the hysteresis map M2 when returning to the steering position. In this case, the hysteresis component Fhy is calculated to be proportional to the steering angle θs. In this case, the hysteresis component Fhy is calculated only when the steering angle θs is within a predetermined range from the origin.

[0071] In the case of a rightward return turn, the hysteresis component calculation unit 92 uses a value appearing in the first quadrant only when the steering angle θs is within a predetermined range from the origin, with the steering angle θs at the start position of the return turn as the origin of the hysteresis map M2. In the case of a leftward return turn, the hysteresis component calculation unit 92 uses a value appearing in the third quadrant only when the steering angle θs is within a predetermined range from the origin, with the steering angle θs at the start position of the return turn as the origin of the hysteresis map M2.

[0072] In this embodiment, hysteresis maps M1 and M2 are configured to vary hysteresis component Fhy according to vehicle speed V. To achieve a desired steering feel, hysteresis components Fhy are varied according to vehicle speed V. In this embodiment, for example, hysteresis component Fhy is varied such that the hysteresis gradient increases as vehicle speed V decreases. Hysteresis component Fhy can also be varied according to steering speed, which is a derivative of steering angle θs. In this case, for example, hysteresis component Fhy can be varied such that the hysteresis gradient decreases as steering speed increases.

[0073] Therefore, when performing sinusoidal steering, in which the steering wheel 3 is periodically rotated and returned at a constant frequency, the hysteresis component calculation unit 92 calculates the hysteresis component Fhy so as to provide a hysteresis characteristic relative to changes in the steering angle θs. The obtained hysteresis component Fhy is output to the adder 93. The adder 93 calculates the angular axial force Fr by adding the hysteresis component Fhy to the axial force base component Frb. The obtained angular axial force Fr is output to the stop distribution axial force calculation unit 85 and the running distribution axial force calculation unit 86.

[0074] In this embodiment, the pinion angle θp and the target pinion angle θp* are examples of a first state variable that changes in response to the operation of the steering mechanism 2. When the steering angle θs is used as an example of a specific state variable that changes in response to the operation of the steering mechanism 2, the pinion angle θp and the target pinion angle θp* are correlated with the steering angle θs and change in a manner interlocked with the steering angle θs. Therefore, the pinion angle θp and the target pinion angle θp* exhibit essentially no hysteresis characteristics relative to the steering angle θs. In other words, the angular axial force calculation unit 81 is an example of a first component calculation unit. The angular axial force Fr is an example of a first component.

[0075] The actual current value Ib on the rotating side is input to the current axial force calculation unit 82. The current axial force calculation unit 82 calculates the current axial force Fi based on the actual current value Ib on the rotating side. The current axial force Fi is an estimated value of the axial force actually acting on the rack shaft 22 that operates to rotate the rotating wheel 5, that is, the axial force actually transmitted to the rack shaft 22. The current axial force Fi is calculated as an axial force in which road surface information is reflected. Specifically, the current axial force calculation unit 82 calculates the current axial force Fi based on the following assumption: the torque applied to the rack shaft 22 by the rotating side motor 32 and the torque corresponding to the force applied to the rack shaft 22 via the rotating wheel 5 are balanced, so that the absolute value of the current axial force Fi increases as the absolute value of the actual current value Ib on the rotating side increases. The current axial force Fi is calculated as a value having the dimension of torque (N·m). The calculated current axial force Fi is output to the stop gradient adjustment unit 84 and the driving distribution axial force calculation unit 86.

[0076] In the present embodiment, the actual current value Ib on the rotating side is an example of a second state variable that changes with the operation of the steering system 2. When the steering angle θs is set as an example of a specific state variable that changes according to the operation of the steering system 2, the actual current value Ib on the rotating side changes together with the axial force actually acting on the rotating wheel 5 according to the pinion angle θp related to the steering angle θs. The axial force actually acting on the rotating wheel 5 has a hysteresis characteristic relative to the change in the pinion angle θp. Therefore, the actual current value Ib on the rotating side basically has a hysteresis characteristic relative to the steering angle θs. That is, the current axial force calculation unit 82 is an example of a second component calculation unit. The current axial force Fi is an example of a second component.

[0077] The target pinion angle θp* and the vehicle speed V are input to the distribution ratio calculation unit 83. The distribution ratio calculation unit 83 calculates the distribution gain D based on the target pinion angle θp* and the vehicle speed V. The distribution gain D is the distribution ratio of the current axial force Fi when the angular axial force Fr and the current axial force Fi are distributed to obtain the distribution axial force Fd. Specifically, the distribution ratio calculation unit 83 includes a distribution gain map that defines the relationship between the target pinion angle θp* and the vehicle speed V and the distribution gain D, and uses the target pinion angle θp* and the vehicle speed V as input to calculate the distribution gain D. The obtained distribution gain D is output to the stop distribution axial force calculation unit 85 and the running distribution axial force calculation unit 86.

[0078] When the vehicle speed V approaches a zero value within a first vehicle speed range (e.g., lower than 6 km / h) which is a low vehicle speed including a stopped state, the distribution gain D changes to a value close to "1 (100%)". In this case, at the first vehicle speed, the angular axial force Fr and the current axial force Fi are distributed so that the influence of the current axial force Fi on the distributed axial force Fd is dominant. When the vehicle speed V increases within a second vehicle speed range (e.g., equal to or higher than 6 km / h) which includes a medium or high speed driving state, the distribution gain D changes to a value close to "zero value (0%)". In this case, at the second vehicle speed, the angular axial force Fr and the current axial force Fi are distributed so that the influence of the angular axial force Fr on the distributed axial force Fd is dominant.

[0079] The distribution gain D is changed so that the value of the distribution gain D becomes larger when the target pinion angle θp* is larger than when the target pinion angle θp* is smaller. On the other hand, the distribution gain D is changed so that the value of the distribution gain D becomes smaller when the target pinion angle θp* is smaller than when the target pinion angle θp* is larger. In this case, at the first vehicle speed, the tendency for the current axial force Fi to dominate the distributed axial force Fd becomes stronger as the target pinion angle θp* increases. On the other hand, at the first vehicle speed, the tendency for the current axial force Fi to dominate the distributed axial force Fd becomes weaker as the target pinion angle θp* decreases.

[0080] In some cases, the distribution gain D may be "1 (100%)" or "zero (0%)", where only one of the angular axial force Fr and the current axial force Fi is distributed to the distribution axial force Fd. That is, the distribution gain D in this embodiment includes the concept of zero value.

[0081] The current axial force Fi is input to the stop gradient adjustment unit 84. The stop gradient adjustment unit 84 calculates the adjusted current axial force Fia obtained by adjusting the current axial force Fi so that the magnitude of the axial force gradient indicating the change pattern of the current axial force Fi changes. Here, the adjustment of the axial force gradient of the current axial force Fi corresponds to the adjustment of the axial force gradient indicating the change pattern of the current axial force Fi relative to the steering angle θs. Specifically, the stop gradient adjustment unit 84 includes a gradient adjustment map M11 in which the relationship between the current axial force Fi and the adjusted current axial force Fia is defined, and the adjusted current axial force Fia is mapped and calculated with the current axial force Fi as input. The obtained adjusted current axial force Fia is output to the stop distribution axial force calculation unit 85.

[0082] like Figure 6 As shown, compared to the proportional shape M0 indicating a proportional relationship between input and output, the gradient adjustment map M11 is configured to have an amplified shape indicating a relationship in which the output value is greater than the input value. That is, the adjusted current axial force Fia is calculated as a value obtained by amplifying the absolute value of the current axial force Fi relative to the current axial force Fi. When the absolute value of the current axial force Fi approaches zero, the amplification ratio of the adjusted current axial force Fia relative to the current axial force Fi is maximized, and the amplification ratio decreases as the absolute value of the current axial force Fi increases, and saturates within a range where the absolute value of the current axial force Fi is equal to or greater than a predetermined value. The maximum value of the adjusted current axial force Fia when the amplification ratio of the adjusted current axial force Fia relative to the current axial force Fi is saturated is calculated as the maximum value F0. In this case, when the absolute value of the current axial force Fi approaches zero, the axial force gradient of the adjusted current axial force Fia is greater than the current axial force Fi before adjustment. From the perspective of suppressing the vibration characteristics in the control and ensuring the control stability even when the control is continuously performed using the adjusted current axial force Fia, the amplification ratio of the adjusted current axial force Fia relative to the current axial force Fi or the gradient adjustment mapping M11 associated with the maximum value F0 is set through experiments, simulations, etc.

[0083] Return to reference Figure 4, the angular axial force Fr, the adjusted current axial force Fia and the distribution gain D are input to the stop distribution axial force calculation unit 85. The stop distribution axial force calculation unit 85 calculates the stop distribution axial force Fd1 by adding the value obtained by multiplying the adjusted current axial force Fia by the distribution gain D and the value obtained by multiplying the adjusted angular axial force Fr by the gain obtained by subtracting the distribution gain D from "1". That is, the stop distribution axial force Fd1 is calculated as a component in which the axial force gradient of only the current axial force Fi in the distributed angular axial force Fr and the current axial force Fi has been adjusted. On the other hand, the stop distribution axial force Fd1 is calculated as a component in which the hysteresis gradient of the angular axial force Fr in the distributed angular axial force Fr and the current axial force Fi has not yet been adjusted. The obtained stop distribution axial force Fd1 is output to the axial force mediation unit 88.

[0084] In this embodiment, the calculation implemented by the functions of the stop gradient adjustment unit 84 and the stop distribution axial force calculation unit 85 corresponds to a first calculation case, in which the adjusted current axial force Fia obtained by adjusting the axial force gradient of the current axial force Fi is used to calculate the distribution axial force Fd.

[0085] The angular axial force Fr, the current axial force Fi, and the distribution gain D are input to the running distribution axial force calculation unit 86. The running distribution axial force calculation unit 86 calculates the running distribution axial force Fd2 by adding the value obtained by multiplying the current axial force Fi by the distribution gain D and the value obtained by multiplying the angular axial force Fr by the gain obtained by subtracting the distribution gain D from "1". The obtained running distribution axial force Fd2 is output to the running gradient adjustment unit 87.

[0086] The driving distributed axial force Fd2 is input to the driving gradient adjustment unit 87. The driving gradient adjustment unit 87 calculates an adjusted driving distributed axial force Fd2a by adjusting the driving distributed axial force Fd2 so as to change the magnitude of the axial force gradient indicating the variation pattern of the driving distributed axial force Fd2. Adjustment of the driving distributed axial force Fd2 corresponds to adjustment of the hysteresis gradient, which indicates the variation pattern of the angular axial force Fr included in the driving distributed axial force Fd2 relative to the steering angle θs. Adjustment of the axial force gradient of the driving distributed axial force Fd2 corresponds to adjustment of the axial force gradient indicating the variation pattern of the current axial force Fi included in the driving distributed axial force Fd2 relative to the steering angle θs. Specifically, the driving gradient adjustment unit 87 includes a gradient adjustment map M12 defining the relationship between the driving distributed axial force Fd2 and the adjusted driving distributed axial force Fd2a. The driving gradient adjustment unit 87 uses the driving distributed axial force Fd2 as input to calculate the adjusted driving distributed axial force Fd2a. That is, the adjusted running distributed axial force Fd2a is calculated as the following components: the hysteresis gradient of the distributed angular axial force Fr has been adjusted, and the axial force gradient of the distributed current axial force Fi has been adjusted. The obtained adjusted running distributed axial force Fd2a is output to the axial force adjustment unit 88.

[0087] like Figure 7As shown, compared to the proportional shape M0, which indicates a proportional relationship between input and output, the gradient adjustment map M12 is configured with an amplified shape, indicating a relationship in which the output value is greater than the input value. Specifically, the adjusted running distribution axial force Fd2a is calculated as a value obtained by amplifying the absolute value of the running distribution axial force Fd2 relative to the running distribution axial force Fd2. When the absolute value of the running distribution axial force Fd2 approaches zero, the amplification ratio of the adjusted running distribution axial force Fd2a relative to the running distribution axial force Fd2 is maximized. This amplification ratio decreases as the absolute value of the running distribution axial force Fd2 increases, and saturates within a range where the absolute value of the running distribution axial force Fd2 is equal to or greater than a predetermined value. The maximum value of the adjusted running distribution axial force Fd2a at which the amplification ratio of the adjusted running distribution axial force Fd2a relative to the running distribution axial force Fd2 saturates is calculated as the maximum value F1. In this case, when the absolute value of the running distribution axial force Fd2 approaches zero, the axial force gradient of the adjusted running distribution axial force Fd2a is greater than that of the running distribution axial force Fd2 before adjustment. The amplification factor of the adjusted running distribution axial force Fd2a relative to the running distribution axial force Fd2 is set to be smaller than the amplification factor when the absolute value of the current axial force Fi in the gradient adjustment map M11 approaches zero. The maximum value F1 is set to be smaller than the maximum value F0 in the gradient adjustment map M11. From the perspective of suppressing vibration characteristics during control and ensuring control stability even when control is continuously executed using the adjusted running distribution axial force Fd2a, the amplification factor of the adjusted running distribution axial force Fd2a relative to the running distribution axial force Fd2, or the gradient adjustment map M12 associated with the maximum value F1, is set through experiments, simulations, and the like.

[0088] In this embodiment, the calculation implemented by the functions of the driving distribution axial force calculation unit 86 and the driving gradient adjustment unit 87 corresponds to the second calculation situation: in the second calculation situation, the adjusted driving distribution axial force Fd2a obtained by adjusting the hysteresis gradient of the angular axial force Fr and adjusting the axial force gradient of the current axial force Fi is used to calculate the distribution axial force Fd.

[0089] The stop-distributed axial force Fd1, the adjusted running-distributed axial force Fd2a, and the vehicle speed V are input to the axial force mediation unit 88. In the distributed axial force calculation unit 71, a first calculation performed by the functions of the stop gradient adjustment unit 84 and the stop-distributed axial force calculation unit 85 and a second calculation performed by the functions of the running-distributed axial force calculation unit 86 and the running gradient adjustment unit 87 are performed in parallel, and the stop-distributed axial force Fd1 and the adjusted running-distributed axial force Fd2a are obtained. The stop-distributed axial force Fd1 and the adjusted running-distributed axial force Fd2a are input to the axial force mediation unit 88 in parallel. The axial force mediation unit 88 performs mediation based on the vehicle speed V while adding the stop-distributed axial force Fd1 and the adjusted running-distributed axial force Fd2a at a predetermined distribution ratio.

[0090] Specifically, when the vehicle speed V indicating the first vehicle speed is input, the axial force mediation unit 88 calculates the distributed axial force Fd by setting the distribution ratio of the stop distribution axial force Fd1 to "100%" and the distribution ratio of the adjusted running distribution axial force Fd2a to "zero value". In this case, the axial force mediation unit 88 mediates so that the stop distribution axial force Fd1 is output as the distributed axial force Fd. On the other hand, when the vehicle speed V indicating the second vehicle speed is input, the axial force mediation unit 88 calculates the distributed axial force Fd by setting the distribution ratio of the stop distribution axial force Fd1 to "zero value" and the distribution ratio of the adjusted running distribution axial force Fd2a to "100%". In this case, the axial force mediation unit 88 mediates so that the adjusted distribution axial force Fd2a is output as the distributed axial force Fd. As Figure 3 As shown, the obtained distributed axial force Fd is output to the adder 75 .

[0091] like Figure 4 As shown, the axial force adjustment unit 88 has the following function: when the vehicle speed V changes between the first and second vehicle speeds in the immediately preceding cycle (the previous cycle), it gradually changes the distribution ratio between the stop distribution axial force Fd1 and the adjusted running distribution axial force Fd2a. When the vehicle speed V changes between the first and second vehicle speeds in the immediately preceding cycle (the previous cycle), the component output as the distribution axial force Fd—that is, the component reflected in the target reaction torque Ts*—switches between the stop distribution axial force Fd1 and the adjusted running distribution axial force Fd2a. When the vehicle speed V changes between the first and second vehicle speeds in the immediately preceding cycle (the previous cycle), the axial force adjustment unit 88 performs a process of gradually changing the distribution ratio between the stop distribution axial force Fd1 and the adjusted running distribution axial force Fd2a over time.

[0092] For example, when the vehicle speed V changes from a first vehicle speed to a second vehicle speed, the axial force adjustment unit 88 slowly changes the distribution ratio of the stop-distributed axial force Fd1 over time while switching the distribution ratio from "100%" to "zero." In this case, the axial force adjustment unit 88 slowly changes the distribution ratio of the adjusted running-distributed axial force Fd2a over time while switching the distribution ratio from "zero" to "100%." That is, when the component output as the distributed axial force Fd—i.e., the component reflected in the target reaction torque Ts*—switches between the stop-distributed axial force Fd1 and the adjusted running-distributed axial force Fd2a, the axial force adjustment unit 88 functions to compensate for the distributed axial force Fd, thereby suppressing any sudden changes in the distributed axial force Fd before and after the switch.

[0093] As a method of slowly changing the distribution ratio of the stop distribution axial force Fd1 to the adjusted running distribution axial force Fd2a, for example, the axial force mediation unit 88 can obtain the difference between a distribution ratio before and after switching and calculate the difference as an offset value. In this case, the axial force mediation unit 88 changes the distribution ratio after switching to the distribution ratio before switching by the offset value, so that the distribution ratio after switching quickly becomes the initial post-switching value by slowly reducing the offset value over time. The stop gradient adjustment unit 84, the stop distribution axial force calculation unit 85, the running distribution axial force calculation unit 86, the running gradient adjustment unit 87, and the axial force mediation unit 88 are examples of torque component calculation units.

[0094] The operation of this embodiment will be described below. In this embodiment, the distributed axial force Fd is calculated using the stop distributed axial force Fd1 and the adjusted running distributed axial force Fd2a, respectively, depending on the situation. In particular, when the vehicle speed V is the first vehicle speed, the stop distributed axial force Fd1 is used as the distributed axial force Fd. That is, when the vehicle is moving slowly forward in a straight line at the vehicle speed V indicating the first vehicle speed, the target pinion angle θp* is small, the influence of the current axial force Fi on the distributed axial force Fd is weak, and adjustment using the gradient adjustment map M11 is performed, so that the axial force gradient of the current axial force Fi is increased to compensate for this influence. In this case, since the vehicle speed V is the first vehicle speed, the hysteresis gradient of the angular axial force Fr is increased, and adjustment using the gradient adjustment map M11 is not performed, so that the hysteresis gradient is not greater than expected.

[0095] For example, it is assumed that the vehicle is traveling slowly and straight ahead on a driving road having a stepped portion (i.e., a groove with slight bumps and recesses) at a vehicle speed V indicating a first vehicle speed. In this case, even when the rotating wheel 5 passes over the stepped portion of the grooved driving road, the absolute value of the current axial force Fi is considered to be small due to the small stepped portion. On the other hand, even if the absolute value of the current axial force Fi is a small value close to zero, the adjusted current axial force Fia adjusted using the gradient adjustment map M11 is calculated as a value obtained by amplifying the absolute value of the current axial force Fi. That is, in a case where the vehicle is traveling slowly and straight ahead on a grooved driving road having a small stepped portion, the driver can be accurately notified that the rotating wheel 5 passes over the stepped portion of the grooved driving road. In this case, the hysteresis gradient of the angular axial force Fr that is not adjusted using the gradient adjustment map M11 is prevented from becoming larger than expected.

[0096] On the other hand, when the adjusted running distributed axial force Fd2a is used as the distributed axial force Fd when the vehicle speed V is the first vehicle speed, even if the absolute value of the current axial force Fi is small and close to zero, the adjusted current axial force Fia adjusted using the gradient adjustment map M12 is calculated as a value obtained by amplifying the absolute value of the current axial force Fi. In this case, since the vehicle speed V is the first vehicle speed, the hysteresis gradient of the angular axial force Fr increases, and adjustment using the gradient adjustment map M12 is performed such that the hysteresis gradient is greater than expected. In other words, the hysteresis gradient of the angular axial force Fr adjusted using the gradient adjustment map M12 is greater than expected.

[0097] The advantages of this embodiment will be described below. In this embodiment, when vehicle speed V is the first vehicle speed, while increasing the axial force gradient of the current axial force Fi using the stop-distributed axial force Fd1 as the distributed axial force Fd, it is possible to suppress the oscillation characteristics of control caused by an unexpected increase in the hysteresis gradient of the angular axial force Fr. Consequently, improved control stability can be achieved.

[0098] In the stopped state, the axial force gradient of the current axial force Fi can be increased using the stopped distributed axial force Fd1 as the distributed axial force Fd, while suppressing the vibration characteristics in the control caused by the increase in the hysteresis gradient of the angular axial force Fr exceeding expectations. From the perspective of conveying the road surface conditions, such as the road surface reaction force, to the driver, it is more preferable to increase the axial force gradient of the distributed axial force Fd in the stopped state and the stopped state in the running state. That is, the hysteresis gradient of the calculated hysteresis component Fhy added to the angular axial force Fr is assumed to be greater than expected corresponding to the stopped state and the stopped state in the running state. Therefore, from the perspective of conveying the road surface conditions, such as the road surface reaction force, to the driver, it is possible to achieve improvement in control stability by implementing the preferred mode.

[0099] The stop-distribution axial force Fd1 and the adjusted travel-distribution axial force Fd2a obtained through parallel calculation are then reflected in the target reaction torque Ts* through mediation by the axial force mediation unit 88. In this manner, the stop-distribution axial force Fd1 and the adjusted travel-distribution axial force Fd2a are reflected in the target reaction torque Ts*, taking into account the most recent circumstances possible. This allows for more accurate determination of the circumstances under which control stability improvement is to be achieved.

[0100] By using the function of the axial force mediation unit 88, when the distributed axial force Fd reflected in the target reaction torque Ts* switches between the stop distributed axial force Fd1 and the adjusted driving distributed axial force Fd2a, the sudden change of the distributed axial force Fd between before and after the switching can be suppressed.

[0101] The aforementioned embodiment can be modified as follows. Unless a technical conflict arises, the following modified examples can be combined. In the aforementioned embodiment, the unit using the target pinion angle θp* can calculate various components based on state variables related to the target pinion angle θp*, rather than the target pinion angle θp*. Examples of state variables related to the target pinion angle θp* include the pinion angle θp, the steering angle θs, the rotation angle θa, and the rotation angle θb, which are examples of state variables that change depending on the operation of the steering system 2. The target pinion angle θp or an angle related to the target pinion angle θp* is an angle that can be converted into the rotation angle of the turning wheel 5. That is, for example, the axial force base component Frb or the end axial force Fie can be calculated based on the pinion angle θp. This modified example achieves the same advantages as the aforementioned embodiment. This applies to the steering angle θs or state variables related to the target pinion angle θp*, such as the pinion angle θp. That is, for example, the hysteresis component Fhy can be calculated based on the target pinion angle θp*, rather than the steering angle θs.

[0102] As long as at least a state variable related to the operation of the steering wheel 3 is used to calculate the steering force Tb*, the steering force calculation unit 55 may not use the vehicle speed V or may use a combination with another element. As the state variable related to the operation of the steering wheel 3, the steering angle θs may be used instead of the steering torque Th described in the aforementioned embodiment, or another element may be used.

[0103] The hysteresis component calculation unit 92 may use another element such as the vehicle speed V in combination as long as at least the steering angle θs is used to calculate the hysteresis component Fhy.

[0104] As long as at least the target pinion angle θp* is used to calculate the axial force base component Frb, the axial force base component calculation unit 91 may use another element such as the vehicle speed V in combination.

[0105] As long as at least one of the vehicle speed V and the target pinion angle θp* is used to calculate the distribution gain D, the distribution ratio calculation unit 83 may use another element in combination.

[0106] The end axial force calculation unit 72 and the difference axial force calculation unit 73 may be deleted from the axial force calculation unit 56. In this case, the axial force selection unit 74 and the adder 75 may be deleted. The distributed axial force Fd calculated by the distributed axial force calculation unit 71 is output to the subtractor 57.

[0107] The gradient adjustment map M11 can also be used for map calculations using, in addition to the current axial force Fi, another element (e.g., vehicle speed V) as input. In this case, in the gradient adjustment map M11, the magnification of the adjusted current axial force Fia relative to the current axial force Fi can be changed, for example, so that it decreases as the vehicle speed V increases.

[0108] In addition to the running distribution axial force Fd2, the gradient adjustment map M12 can be used for map calculation using a combination with another element (e.g., vehicle speed V) as input. In this case, in the gradient adjustment map M12, the magnification ratio of the adjusted running distribution axial force Fd2a relative to the running distribution axial force Fd2 can be changed, for example, so that it decreases as the vehicle speed V increases, or the map can be configured to have a decaying shape indicating a relationship in which the output value is smaller than the input value, compared to the proportional shape M0.

[0109] Instead of or in addition to the vehicle speed V, the axial force mediation unit 88 may mediate the axial force reflected in the target reaction torque Ts* between the stop-distributed axial force Fd1 and the travel-distributed axial force Fd2a, taking into account the steering state of the steering unit 4 (e.g., steering angle θs) or the rotational state of the rotation unit 6 (e.g., pinion angle θp). For example, the longitudinal acceleration of the vehicle, from which the stop state and travel state of the vehicle can be determined, or the accelerator or brake operation state of the vehicle may be considered as state variables to be used instead of the vehicle speed V.

[0110] The axial force mediation unit 88 slowly changes the distribution ratio in consideration of the steering state of the steering unit 4 (eg, steering angle θs) or the rotation state of the rotation unit 6 (eg, pinion angle θp) instead of or in addition to the elapsed time.

[0111] The axial force mediation unit 88 may be configured to select one of the stop distribution axial force Fd1 and the adjusted running distribution axial force Fd2 a as the distribution axial force Fd, or to switch the selected state based on the vehicle speed V.

[0112] The calculation situations may be switched so that only one of the first calculation situation implemented by the functions of the stop gradient adjustment unit 84 and the stop distribution axial force calculation unit 85 and the second calculation situation implemented by the functions of the travel distribution axial force calculation unit 86 and the travel gradient adjustment unit 87 functions based on the vehicle speed V. In this case, the axial force mediation unit 88 may be deleted.

[0113] As a component to which the hysteresis component is added for calculation, in addition to the angular axial force Fr, a component such as the steering force Tb* or an axial force component obtained by taking into account the yaw rate or lateral acceleration can be appropriately used, as long as it is a component that facilitates operation of the steering system 2 due to its hysteresis characteristics. As a component based on a state variable having a hysteresis characteristic with respect to changes in the steering angle θs, in addition to the current axial force Fi, a component such as an axial force obtained by taking into account the actual axial force acting on the rack shaft 22 or an axial force obtained by taking into account the tire force acting on the turning wheel 5 can be appropriately used. Even if the same problem as that in the previously mentioned embodiment arises in the appropriately used component, the problem can be solved by adopting the configuration according to this embodiment.

[0114] The hysteresis gradient or axial force gradient is not limited to changes in the steering angle θs, but can be modified as appropriate for changes in the pinion angle θp or the target pinion angle θp* related to the steering angle θs, state variables that change in accordance with the operation of the steering system 2 without any correlation with the steering angle θs, and the like. Even when the same problem as that in the previously mentioned embodiment arises in the appropriately changed hysteresis gradient or axial force gradient, the problem can be solved by adopting the configuration according to this embodiment.

[0115] For example, in addition to the stop distributed axial force Fd1 and the adjusted running distributed axial force Fd2a, a function for calculating the axial force by adjusting the hysteresis gradient of the angular axial force Fr may be added to the distributed axial force calculation unit 71. By adopting a configuration in which the axial force calculated by the added function is correlated with the appropriate situation, the same advantages as those in the previously mentioned embodiment can be achieved.

[0116] The first vehicle speed range can be set to a wider range, such as less than 10 km / h, or a narrower range, such as less than 3 km / h, as long as it includes a stopped state. The same applies to the second vehicle speed range. In other words, the second vehicle speed range can be appropriately changed as long as it includes a running state.

[0117] In the aforementioned embodiment, the steering-side control unit 50 may be provided as a function of the turning-side control unit 60. In the aforementioned embodiment, the turning-side motor 32 may adopt, for example, a configuration in which the turning-side motor 32 is coaxially arranged with the rack shaft 22, or a configuration in which a pinion shaft constituting a rack and pinion mechanism is connected to the rack shaft 22 via a worm and a worm gear.

[0118] In the aforementioned embodiment, the steering control device 1 can be configured as a processing circuit that includes (1) one or more processors operating according to a computer program (software), (2) one or more dedicated hardware circuits such as application-specific integrated circuits (ASICs) that perform at least some of the various processes, or (3) a combination thereof. The processor includes a CPU and a memory such as RAM and ROM, and the memory stores program code or commands configured to cause the CPU to perform the processes. The memory, i.e., non-transitory computer-readable media, includes all available media that can be accessed by a general-purpose or special-purpose computer.

[0119] In the aforementioned embodiment, the steering system 2 employs a non-linked structure in which the steering unit 4 and the rotation unit 6 are normally mechanically disconnected from each other. However, the present invention is not limited thereto, and the steering system may employ a structure in which the steering unit 4 and the rotation unit 6 can be mechanically disconnected via a clutch. The steering system 2 may be an electric power steering system that applies an assist force in the form of assisting the driver's steering operation. In this case, the steering wheel 3 is mechanically connected to the pinion shaft 21 via the steering shaft 11.

Claims

1. A steering control device (1) for controlling a steering system (2) in which a steering torque required for steering a steering wheel is changed using motor torque applied from an actuator having a motor as a drive source, the steering control device (1) being characterized by comprising: a torque command value calculation unit (52) configured to calculate a torque command value that is a target value of the motor torque when controlling the operation of the motor so that the motor torque is generated; wherein the torque command value calculation unit (52) includes: a first component calculation unit configured to calculate a first component based on a first state variable that changes according to the operation of the steering system; a second component calculation unit configured to calculate a second component based on a second state variable that changes with the operation of the steering system; and a torque component calculation unit configured to calculate a torque component for calculating the torque command value based on at least one of the first component and the second component, wherein the torque command value calculation unit (52) is configured to set the first state variable to a state variable having no hysteresis characteristics with respect to a change in a specific state variable that changes according to an operation of the steering system, and to set the second state variable to a state variable having a hysteresis characteristics with respect to a change in the specific state variable, wherein the first component calculation unit is configured to add a calculation hysteresis component to the first component when calculating the first component so as to provide a hysteresis characteristic with respect to a change in the specific state variable, wherein the torque component calculation unit is configured to perform calculations in a first calculation case and calculations in a second calculation case, The first calculation condition is used to adjust the calculation of the gradient of the change of the second component relative to the specific state variable, the second component is obtained by the second component calculation unit, and the adjusted second component is used to calculate the torque component, and The second calculation case is a calculation for adjusting the gradient of the torque component relative to the change of the specific state variable, the torque component is obtained by calculation based on at least one of the first component and the second component, and the adjusted torque component is calculated as the final torque component.

2. The steering control device (1) according to claim 1, characterized in that The first component calculation unit is an angular axial force calculation unit (81) configured to calculate an angular axial force as the first component, the angular axial force being determined based on an angle that can be converted into a rotation angle of a rotating wheel of a vehicle, and being an axial force in which road surface information is not reflected, and Wherein, the second component calculation unit is a current axial force calculation unit (82), and the current axial force calculation unit (82) is configured to calculate the current axial force as the second component, the current axial force is determined according to the current supplied to the motor, and the current axial force is an axial force in which road surface information is reflected.

3. The steering control device (1) according to claim 1 or 2, characterized in that The torque component calculation unit is configured to reflect the torque component obtained by calculation in the first calculation case in the torque command value when the vehicle has a first vehicle speed including a stopped state, and Here, the torque component calculation unit is configured to reflect the torque component obtained by calculation in the second calculation case in the torque command value when the vehicle has a second vehicle speed including a running state.

4. The steering control device (1) according to claim 1 or 2, characterized in that The torque component calculation unit includes a mediation unit (88) configured to mediate which of the torque components obtained by the calculation in the first calculation case and the calculation in the second calculation case is to be reflected in the torque command value when the calculation in the first calculation case and the calculation in the second calculation case are performed in parallel, The mediation unit (88) is configured to reflect the torque component obtained by calculation in the first calculation case in the torque command value when the vehicle has a first vehicle speed including a stopped state, and The mediation unit (88) is characterized in that, when the vehicle has a second vehicle speed including a running state, the torque component obtained by calculation in the second calculation case is reflected in the torque command value.

5. The steering control device (1) according to claim 4, characterized in that The mediation unit (88) is configured to compensate the torque component so that when the component to be reflected in the torque command value switches between the torque component obtained by calculation in the first calculation case and the torque component obtained by calculation in the second calculation case, a sudden change in the torque component between before and after the switching is suppressed.

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