Steering control device

Abstract

To provide a steering control device which can suppress the lowering of a steering feeling.SOLUTION: A steering control device sets a steering device as a control object, and comprises a target reaction force torque calculation part for calculating target reaction force torque. The target reaction force torque calculation part has an angle axial force calculation part 101 for calculating an angle axial force Fr corresponding to a target pinion angle θp*. The angle axial force calculation part 101 has a hysteresis component calculation part for adding a vehicle-stop hysteresis component Fhy2 on a calculation so as to possess a hysteresis characteristic with respect to the steering agent θs. The hysteresis component calculation part calculates a correction zero point Pc corresponding to an original point of the hysteresis characteristic when calculating the vehicle-stop hysteresis component Fhy2 which can maintain a value of the vehicle-stop hysteresis component Fhy2 at the timing of a transition at a second vehicle speed after being transited from a first vehicle speed, and calculates the vehicle-stop hysteresis component Fhy2 with the calculated correction zero point Pc as an original point.SELECTED DRAWING: Figure 9

Description

[Technical field]

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

[0002] Conventionally, as one type of steering device, there is a steer-by-wire type steering device in which a power transmission path between a steering section steered by a driver and a steering section that steers the steered wheels in response to the driver's steering is separated. In this type of steering device, road surface information such as a road surface reaction force received by the steered wheels is not mechanically transmitted to the steering wheel. Therefore, some steering control devices that control this type of steering device control a steering side actuator provided in the steering section so as to apply a steering reaction force to the steering wheel that takes into account the road surface information, thereby controlling the road surface information to be transmitted to the driver.

[0003] For example, in the steering control device of Patent Document 1, the axial force acting on the steering shaft provided in the steering unit is taken into consideration when determining the steering reaction force. In the steering control device of Patent Document 1, an angle axial force based on a target steering angle for controlling the steering angle of the steered wheels, which is calculated based on the steering angle of the steering wheel, is exemplified as one of the axial forces to be taken into consideration. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2020-142596 A Summary of the Invention [Problem to be solved by the invention]

[0005] The relationship between the steering angle on which the target steering angle is based and the axial force actually acting on the steering shaft changes depending on the vehicle speed. When the vehicle is stopped, the axial force gradient, which is the rate of change of the axial force with respect to the steering angle, becomes small, and the hysteresis width of the axial force with respect to the change in the steering angle becomes large. On the other hand, when the vehicle is traveling at a medium to high speed, the axial force gradient becomes large, and the hysteresis width becomes small. The angle axial force may be calculated by adding a calculated hysteresis component so as to have a hysteresis width that reflects the actual hysteresis state of the axial force with respect to such a change in the steering angle.

[0006] However, if a situation arises in which the addition of a calculation hysteresis component causes the hysteresis width to change more than expected, this may result in an uncomfortable feeling in the movement of the steering wheel or in the sensation obtained from the steering wheel.

[0007] In addition, this problem is not limited to the angular axial force calculated as a component of the steering reaction force, but may occur in any component of the steering reaction force calculated by adding a calculated hysteresis component so as to have a hysteresis width in order to reflect the actual hysteresis situation. [Means for solving the problem]

[0008] A steering control device that solves the above problem has as its control target a steering device that varies the steering torque required for steering a steering wheel by a motor torque applied by an actuator using a motor as a drive source, and includes a torque command value calculation unit that calculates a torque command value that 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 having a torque component calculation unit that calculates a torque component used when calculating the torque command value based on a state variable that changes in response to the operation of the steering device, and the torque component calculation unit includes an operation unit that calculates a hysteresis characteristic for the change in a specific state variable, which is obtained by using a value set at a predetermined timing of the specific state variable that changes in response to the steering of the steering device as an origin, to the torque component. The torque component calculation unit has a hysteresis component calculation unit that calculates a mathematical hysteresis component, the hysteresis component calculation unit including a first calculation state that calculates the mathematical hysteresis component to add a first hysteresis characteristic to the torque component, and a second calculation state that calculates the mathematical hysteresis component to add a second hysteresis characteristic having a hysteresis width larger than that of the first hysteresis characteristic to the torque component, and in the second calculation state after transition from the first calculation state, a value corresponding to an origin in the second hysteresis characteristic when calculating the mathematical hysteresis component that can maintain the value of the mathematical hysteresis component at the timing of the transition is calculated, and the mathematical hysteresis component is calculated with the calculated value as the origin.

[0009] In the above configuration, the origin when the calculated hysteresis component is calculated is corrected according to the situation, so that the calculated hysteresis component can be calculated. For example, a situation in which the first calculation state changes to the second calculation state is a situation in which the hysteresis width is expected to change more significantly than expected before and after the transition when the calculated hysteresis component is calculated. In response to this, the origin when the calculated hysteresis component is calculated is corrected on the condition that the state transitions from the first calculation state to the second calculation state. As a result, in the case of the transition, even if a specific state variable is maintained at a value at the timing of the transition, a sudden change in the hysteresis width between the calculated hysteresis component before the transition and the calculated hysteresis component after the transition can be suppressed. Therefore, the existence of a situation in which the hysteresis width suddenly changes for the calculated hysteresis component is suppressed, so that it is possible to suppress the occurrence of an uncomfortable feeling in the movement of the steering wheel and the sensation obtained from the steering wheel. Therefore, it is possible to improve the steering feel.

[0010] In the above steering control device, the torque component calculation unit can be embodied as an angle axial force calculation unit having an axial force basic component calculation unit that calculates, as the torque component, a basic component of an angular axial force which is an axial force that is determined according to an angle that can be converted into a steering angle of a steered wheel of a vehicle and does not reflect road surface information, and a hysteresis component calculation unit that calculates a calculation hysteresis component to be added to the basic component and the calculation hysteresis component.

[0011] In the above steering control device, it is preferable that the hysteresis component calculation unit is configured to reflect the calculated hysteresis component obtained by calculation of the first calculation state in the torque component when the vehicle is in a first state in which it can be determined that the vehicle is in a running state that does not include a stopped state, and to reflect the calculated hysteresis component obtained by calculation of the second calculation state in the torque component when the vehicle is in a second state in which it can be determined that the vehicle is in a running state that includes a stopped state.

[0012] According to the above configuration, when the first state is changed to the second state, the value of the calculated hysteresis component at the timing of the change can be maintained. This makes it possible to improve the steering feel even in a situation where the first state is changed to the second state. From the viewpoint of conveying the friction of the steered wheels of the vehicle to the driver, it is advantageous to greatly change the hysteresis width in the second state between the first state and the second state. In other words, when calculating the calculated hysteresis component, a situation in which the hysteresis width is expected to change significantly corresponds to a case where the first state is changed to the second state. Therefore, it is possible to improve the steering feel while realizing a specification that is advantageous from the viewpoint of conveying the friction of the steered wheels of the vehicle to the driver.

[0013] In the above steering control device, it is preferable that the hysteresis component calculation unit is configured to calculate the calculated hysteresis component capable of maintaining the value of the calculated hysteresis component at the timing of the transition when the vehicle speed is a second vehicle speed defined as corresponding to the second state after transition from a first vehicle speed defined as corresponding to the first state.

[0014] According to the above configuration, the conditions for maintaining the value of the calculated hysteresis component can be optimized through an approach that uses the vehicle speed. In the above steering control device, it is preferable that the torque component calculation unit further has a coefficient calculation unit that calculates a vehicle speed coefficient that changes based on the vehicle speed to take the vehicle speed into account when adding the first hysteresis characteristic or the second hysteresis characteristic to the torque component, and the hysteresis component calculation unit is configured to calculate the calculated hysteresis component that can maintain the value of the calculated hysteresis component at the timing of the transition when the vehicle speed coefficient calculated through the coefficient calculation unit is a second vehicle speed coefficient calculated in the case of a second vehicle speed defined as corresponding to the second state after a transition from a first vehicle speed coefficient calculated in the case of a first vehicle speed defined as corresponding to the first state.

[0015] According to the above configuration, the conditions under which the value of the calculated hysteresis component is maintained can be optimized through an approach using a vehicle speed coefficient that varies based on the vehicle speed. Effect of the Invention

[0016] According to the steering control device of the present invention, deterioration in steering feel can be suppressed. [Brief description of the drawings]

[0017] [Figure 1] 1 is a diagram showing a schematic configuration of a steer-by-wire steering device in a first embodiment. [Diagram 2] FIG. 2 is a block diagram showing the functions of the steering control device in the first embodiment. [Diagram 3] FIG. 2 is a block diagram showing functions of a steering force calculation unit in the first embodiment. [Figure 4] FIG. 4 is a block diagram showing functions of an axial force calculation unit in the first embodiment. [Diagram 5] FIG. 4 is a block diagram showing functions of a distribution axial force calculation unit in the first embodiment. [Figure 6] FIG. 4 is a block diagram showing the function of a running hysteresis component calculation unit in the first embodiment. [Figure 7] 4A is a graph showing the relationship between the steering angle and the hysteresis component during forward steering, and FIG. 4B is a graph showing the relationship between the steering angle and the hysteresis component during return steering. [Figure 8] 5 is a graph showing the relationship between vehicle speed and a running vehicle speed gain. [Figure 9] FIG. 4 is a block diagram showing functions of an angle and axial force calculation unit in the first embodiment. [Figure 10] 6 is a graph showing the relationship between the steering angle during a stop and a stopping vehicle speed gain. [Figure 11] 6 is a graph showing the relationship between the steering angle and the hysteresis component for stopping in a situation where the vehicle speed has changed from a first vehicle speed to a second vehicle speed; [Figure 12]2A is a graph showing the relationship between steering angle and steering torque while the vehicle is moving, and FIG. 2B is a graph showing the relationship between steering angle and steering torque while the vehicle is stopped. [Figure 13] FIG. 11 is a block diagram showing the function of an angle and axial force calculation unit in the second embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0018] First Embodiment A first embodiment of a steering control device will be described with reference to the drawings. As shown in Fig. 1, the steering device 2 of the vehicle to be controlled by the steering control device 1 is configured as a steer-by-wire type steering device. The steering device 2 includes a steering unit 4 that is steered by a driver via a steering wheel 3, and a turning unit 6 that steers steered wheels 5 in response to the steering input to the steering unit 4 by the driver.

[0019] The steering unit 4 includes a steering shaft 11 and a steering side actuator 12. The steering shaft 11 is connected to the steering wheel 3. The steering side actuator 12 includes a steering side motor 13, which is a drive source, and a steering side reduction mechanism 14. The steering side motor 13 applies a steering reaction force, which is a force resisting steering, to the steering wheel 3 via the steering shaft 11. The steering side motor 13 is connected to the steering shaft 11 via the steering side reduction mechanism 14, which is made of, for example, a worm and wheel. For the steering side motor 13 in this embodiment, for example, a three-phase brushless motor is adopted.

[0020] The steered portion 6 includes a pinion shaft 21, a rack shaft 22 as a steered shaft connected to the pinion shaft 21, and a rack housing 23. The pinion shaft 21 and the rack shaft 22 are connected with a predetermined cross angle. A rack and pinion mechanism 24 is formed by meshing pinion teeth 21a formed on the pinion shaft 21 with rack teeth 22a formed on the rack shaft 22. The rack housing 23 accommodates the rack and pinion mechanism 24. An end of the pinion shaft 21 opposite to the end connected to the rack shaft 22 protrudes from the rack housing 23. Both ends of the rack shaft 22 protrude from both ends in the axial direction of the rack housing 23. Tie rods 26 are connected to both ends of the rack shaft 22 via rack ends 25 made of ball joints. The ends of the tie rods 26 are connected to knuckles (not shown) to which the left and right steered wheels 5 are assembled.

[0021] The steering unit 6 includes a steering-side actuator 31 that applies a steering force to the rack shaft 22 to turn the steered wheels 5. The steering-side actuator 31 includes a steering-side motor 32 that is a drive source, a transmission mechanism 33, and a conversion mechanism 34. The steering-side motor 32 applies a steering force to the rack shaft 22 to turn the steered wheels 5 via the transmission mechanism 33 and the conversion mechanism 34. The steering-side motor 32 transmits rotation to the conversion mechanism 34 via the transmission mechanism 33, which is, for example, a belt transmission mechanism. The transmission mechanism 33 converts the rotation of the steering-side motor 32 into reciprocating motion of the rack shaft 22 via the conversion mechanism 34, which is, for example, a ball screw mechanism.

[0022] In the steering device 2 configured in this manner, the steering angle of the steered wheels 5 is changed by applying a motor torque as a steering force from the steering-side actuator 31 to the rack shaft 22 in response to steering by the driver. At this time, a steering reaction force that resists the steering by the driver is applied to the steering wheel 3 from the steering-side actuator 12. That is, in the steering device 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-side actuator 12.

[0023] Incidentally, 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. In other words, the rack shaft 22 is supported movably along its axial direction and is pressed toward the pinion shaft 21 by a support mechanism (not shown) provided in the steering device 2. In this way, the rack shaft 22 is supported inside the rack housing 23. However, another support mechanism for supporting the rack shaft 22 in the rack housing 23 may be provided without using the pinion shaft 21.

[0024] <Electrical configuration of steering device 2> 1, the steering side motor 13 and the turning side motor 32 are connected to a steering control device 1. The steering control device 1 controls the operation of the steering side motor 13 and the turning side motor 32.

[0025] To the steering control device 1, a torque sensor 41, a steering side rotation angle sensor 42, a turning side rotation angle sensor 43, and a vehicle speed sensor 44 are connected. 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. The torque sensor 41 is provided on a portion of the steering shaft 11 closer to the steering wheel 3 than the steering side reduction mechanism 14. The torque sensor 41 detects the steering torque Th based on the twist of a torsion bar 41a provided midway on the steering shaft 11. Note that the steering torque Th is detected as a positive value when the vehicle is steered to the right, for example, and as a negative value when the vehicle is steered to the left.

[0026] The steering side rotation angle sensor 42 detects the rotation angle θa, which is the angle of the rotation shaft of the steering side motor 13, within a range of 360 degrees. The steering side rotation angle sensor 42 is provided in 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 linked via the steering side reduction mechanism 14. For this reason, there is a correlation between the rotation angle θa of the steering side motor 13 and the rotation angle of the steering shaft 11, and furthermore, the steering angle θs, which is the rotation angle of the steering wheel 3. Therefore, the steering angle θs can be obtained based on the rotation angle θa of the steering side motor 13. Note that the rotation angle θa is detected as a positive value when steering to the right, for example, and as a negative value when steering to the left.

[0027] The turning-side rotation angle sensor 43 detects the rotation angle θb, which is the angle of the rotation shaft of the turning-side motor 32, within a range of 360 degrees. The turning-side rotation angle sensor 43 is provided in the turning-side motor 32. The rotation angle θb of the turning-side motor 32 is used to calculate the pinion angle θp. The turning-side motor 32 and the pinion shaft 21 are linked via the transmission mechanism 33, the conversion mechanism 34, and the rack-and-pinion mechanism 24. Therefore, there is a correlation between the rotation angle θb of the turning-side motor 32 and the pinion angle θp, which is the rotation angle of the pinion shaft 21. Therefore, the pinion angle θp can be obtained based on the rotation angle θb of the turning-side motor 32. In addition, the pinion shaft 21 is meshed with the rack shaft 22. Therefore, there is also a correlation between the pinion angle θp and the amount of movement of the rack shaft 22. In other words, the pinion angle θp is a value that reflects the turning angle of the steered wheels 5. The rotation angle θb is detected as a positive value when the vehicle is steered to the right, and as a negative value when the vehicle is steered to the left.

[0028] The vehicle speed sensor 44 detects the vehicle speed V, which is set as information indicating the traveling speed of the vehicle. <Functions of the steering control device 1> The steering control device 1 includes a central processing unit and a memory (not shown). In the steering control device 1, the CPU executes a program stored in the memory at each predetermined calculation cycle. This executes various types of control.

[0029] As shown in FIG. 2, the steering control device 1 includes a steering side control unit 50 that controls 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 current value of each phase of the steering side motor 13 flowing through a connection line between the steering side control unit 50 and a motor coil of each phase of the steering side motor 13. The steering side current sensor 54 obtains, as a current, a voltage drop of a shunt resistor connected to each source side of a switching element in an inverter (not shown) provided corresponding to the steering side motor 13. Note that, in FIG. 2, for convenience of explanation, the connection lines of each phase and the current sensors of each phase are illustrated as one.

[0030] The steering control device 1 also includes a turning-side control unit 60 that controls power supply to the turning-side motor 32. The turning-side control unit 60 includes a turning-side current sensor 65. The turning-side current sensor 65 detects a turning-side actual current value Ib obtained from a current value of each phase of the turning-side motor 32 that flows through a connection line between the turning-side control unit 60 and the motor coil of each phase of the turning-side motor 32. The turning-side current sensor 65 obtains, as a current, a voltage drop across a shunt resistor connected to each source side of a switching element in an inverter (not shown) provided corresponding to the turning-side motor 32. Note that, for convenience of explanation, in FIG. 2, the connection lines of each phase and the current sensors of each phase are illustrated as one.

[0031] <Steering side control unit 50> The steering torque Th, the vehicle speed V, the rotation angle θa, the steered side actual current value Ib, the pinion angle θp, and the target pinion angle θp* 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 steered side actual current value Ib, the pinion angle θp, and the target pinion angle θp*.

[0032] The steering side control unit 50 has a steering angle calculation unit 51, a target reaction force torque calculation unit 52, and an electricity supply control unit 53. The steering angle calculation unit 51 receives the rotation angle θa. The steering angle calculation unit 51 converts the rotation angle θa into an integrated angle including a range exceeding 360 degrees, for example, by counting the number of rotations of the steering side motor 13 from a steering neutral position, which is the position of the steering wheel 3 when the vehicle is moving straight. The steering angle calculation unit 51 calculates the steering angle θs by multiplying the integrated angle obtained by the conversion by a conversion coefficient based on the rotation speed ratio of the steering side reduction gear 14. The steering angle θs obtained in this manner is output to the target reaction force torque calculation unit 52. The steering angle θs is also output to the steered side control unit 60, that is, a steering angle ratio variable control unit 62 described later.

[0033] The target reaction torque calculation unit 52 receives as input the steering torque Th, vehicle speed V, steered side actual current value Ib, steering angle θs, pinion angle θp, and target pinion angle θp* described below. The target reaction torque calculation unit 52 calculates the target reaction torque Ts* based on the steering torque Th, vehicle speed V, steered side actual current value Ib, steering angle θs, pinion angle θp, and target pinion angle θp*. The target reaction torque Ts* is a reaction force control amount that is a target value of the steering reaction force of the steering wheel 3 to be generated through the steering side motor 13. 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.

[0034] Specifically, the target reaction force torque calculation unit 52 has a steering force calculation unit 55 and an axial force calculation unit 56 . The steering torque Th, the steering angle θs, 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, the steering angle θs, and the vehicle speed V. The steering force Tb* acts in the same direction as the steering direction of the driver.

[0035] Specifically, as shown in FIG. 3, the steering force calculation unit 55 has a basic control amount calculation unit 71 and a compensation amount calculation unit 72. The basic control amount calculation unit 71 receives the steering torque Th and the vehicle speed V. The basic control amount calculation unit 71 calculates the basic control amount I1* based on the steering torque Th and the vehicle speed V. The basic control amount I1* is a control amount calculated in relation to the steering of the steering wheel 3. The basic control amount I1* is a basic component of the steering force Tb*, and is set so that the steering of the steering wheel 3 exhibits a desired characteristic. For example, the basic control amount calculation unit 71 calculates the basic control amount I1*, which has a larger absolute value as the absolute value of the steering torque Th increases and the vehicle speed V decreases, taking into account the assist gradient, which is the rate of change of the basic control amount I1* with respect to the change of the steering torque Th. The basic control amount I1* thus obtained is output to the adder 73.

[0036] The compensation amount calculation unit 72 receives the steering torque Th, the vehicle speed V, and the steering angle θs. The compensation amount calculation unit 72 calculates the following return compensation amount I2*, the driving hysteresis compensation amount (hereinafter referred to as the "driving hysteresis compensation amount") I3*, the damping compensation amount I4*, and the inertia compensation amount I5* based on the steering torque Th, the vehicle speed V, and the steering angle θs. The various compensation amounts include, in addition to the specific compensation amounts of the compensation amounts I2* to I5*, a phase lag compensation amount (not shown) for phase compensation to delay the phase of the steering torque Th and a phase lead compensation amount for phase compensation to lead the phase of the basic control amount I1*. The phase lag compensation amount is for adjusting the assist gradient. The phase lead compensation amount is for suppressing the resonance characteristics and stabilizing the system. The various compensation amounts are compensation amounts for compensating so that the operation of the steering wheel 3 realized based on the basic control amount I1* shows the desired characteristics.

[0037] The compensation amount calculation unit 72 has a return compensation amount calculation unit 81, a driving hysteresis compensation amount calculation unit (hereinafter referred to as the “driving hysteresis compensation amount calculation unit”) 82, a damping compensation amount calculation unit 83, and an inertia compensation amount calculation unit 84.

[0038] The return compensation amount calculation unit 81 receives the steering torque Th, the vehicle speed V, the steering angle θs, and the steering speed ωs obtained by differentiating the steering angle θs through a differentiator 85. The return compensation amount calculation unit 81 calculates the return compensation amount I2* based on the steering torque Th, the vehicle speed V, the steering angle θs, and the steering speed ωs. The return compensation amount I2* compensates for the return operation of the steering wheel 3 that returns the steering wheel 3 to the neutral steering position. The return operation of the steering wheel 3 is related to the self-aligning torque of the steered wheels 5, and the excess or deficiency of the self-aligning torque is compensated for by the return compensation amount I2*. The return compensation amount I2* is for generating a torque in a direction that returns the steering wheel 3 to the neutral steering position. The return compensation amount I2* thus obtained is output to the adder 73.

[0039] The vehicle speed V and the steering angle θs are input to the traveling hysteresis compensation amount calculation unit 82. The traveling hysteresis compensation amount calculation unit 82 calculates the traveling hysteresis compensation amount I3* based on the vehicle speed V and the steering angle θs. The traveling hysteresis compensation amount I3* is used to optimize the hysteresis characteristics caused by friction when the steering wheel 3 is in operation. The hysteresis characteristics caused by the friction when the steering wheel 3 is in operation involve the mechanical friction components of the vehicle on which the steering device 2 is mounted, and the optimization of the hysteresis characteristics caused by the mechanical friction components is compensated for by the traveling hysteresis compensation amount I3*. In this embodiment, the traveling hysteresis compensation amount I3* is used to optimize the hysteresis characteristics caused by friction when the steering wheel 3 is in operation, particularly in the case of a traveling state in which the vehicle does not include a stopped state. The traveling state in which the vehicle does not include a stopped state is, for example, a state in which the vehicle is traveling at a medium to high speed, such as 10 kilometers per hour or more. The running hysteresis compensation amount I3* has a hysteresis characteristic with respect to the change in the steering angle θs. The running hysteresis compensation amount I3* thus obtained is output to the adder 73.

[0040] The vehicle speed V and the steering speed ωs are input to the damping compensation amount calculation unit 83. The damping compensation amount calculation unit 83 calculates the damping compensation amount I4* based on the vehicle speed V and the steering speed ωs. The damping compensation amount I4* compensates for the reduction of the micro-vibrations occurring in the steering wheel 3. The viscosity components of the steering device 2, particularly the viscosity components of the steered side actuator 31, are involved in reducing the micro-vibrations occurring in the steering wheel 3, and the damping compensation amount I4* compensates for the reduction of the micro-vibrations occurring in the steering wheel 3. The damping compensation amount I4* is intended to generate a torque in the opposite direction to the direction in which the steering speed ωs occurs at that time. The damping compensation amount I4* obtained in this manner is output to the adder 73.

[0041] The inertia compensation amount calculation unit 84 receives the vehicle speed V and the steering acceleration αs obtained by differentiating the steering speed ωs through a differentiator 86. The inertia compensation amount calculation unit 84 calculates the inertia compensation amount I5* based on the vehicle speed V and the steering acceleration αs. The inertia compensation amount I5* compensates for the feeling of sticking when the steering wheel 3 starts to be steered and the feeling of flow when the steering is finished. The inertia component of the steering device 2 is involved in suppressing the feeling of sticking when the steering wheel 3 starts to be steered and the feeling of flow when the steering is finished, and the inertia compensation amount I5* compensates for the suppression of the feeling of sticking when the steering wheel 3 starts to be steered and the feeling of flow when the steering is finished. The inertia compensation amount I5* generates a torque in the direction in which the steering acceleration αs is generated when the absolute value of the steering acceleration αs increases when the steering wheel 3 starts to be steered, etc. The inertia compensation amount I5* is used to generate a torque in the opposite direction to the direction in which the steering acceleration αs is generated when the absolute value of the steering acceleration αs decreases, such as when the steering of the steering wheel 3 ends. The inertia compensation amount I5* thus obtained is output to the adder 73.

[0042] The adder 73 calculates the steering force Tb* by adding each of the compensation amounts I2* to I5* to the basic control amount I1*. In addition to each of the compensation amounts I2* to I5*, the phase lag compensation amount and the phase lead compensation amount are also added to and reflected in the basic control amount I1*. As shown in FIG. 2, the steering force Tb* thus obtained is output to the subtractor 57. The steering force Tb* acts in the same direction as the steering direction of the driver. The steering force Tb* is calculated as a value in the dimension of torque (N m).

[0043] As shown in FIG. 2, the axial force calculation unit 56 receives inputs of the vehicle speed V, steering angle θs, the steered side actual current value Ib, the pinion angle θp, and the target pinion angle θp* described below. The axial force calculation unit 56 calculates the axial force F acting on the rack shaft 22 through the steered wheels 5 based on the vehicle speed V, the steering angle θs, the steered side actual current value Ib, the pinion angle θp, and the target pinion angle θp*. The axial force F is calculated as a value in the dimension of torque (N·m). The axial force F acts in the opposite direction to the steering direction of the driver. The subtractor 57 subtracts the axial force F from the steering force Tb* to calculate the target reaction torque Ts*. The target reaction torque Ts* thus obtained is output to the current control unit 53.

[0044] The current supply control unit 53 receives the target reaction torque Ts*, the rotation angle θa, and the steering side actual current value Ia. The current supply control unit 53 calculates a current command value Ia* for the steering side motor 13 based on the target reaction torque Ts*. The current supply control unit 53 obtains a deviation between the current command value Ia* and a current value on the dq coordinate 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 so as to eliminate the deviation. The steering side motor 13 generates a torque according to the target reaction torque Ts*. This makes it possible to provide the driver with an appropriate sense of responsiveness.

[0045] <Steering side control unit 60> 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.

[0046] The steering side control unit 60 has a pinion angle calculation unit 61, a steering angle ratio variable control unit 62, a pinion angle feedback control unit ("pinion angle F / B control unit" in FIG. 2) 63, and an energization control unit 64.

[0047] 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 an integrated angle including a range exceeding 360 degrees, for example, by counting the number of rotations of the steering-side motor 32 from a rack neutral position, which is the position of the rack shaft 22 when the vehicle is moving straight. 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 integrated angle obtained by conversion by a conversion coefficient based on the reduction 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. Note that the pinion angle θp is positive when it is, for example, an angle to the right of the rack neutral position, and negative when it is an angle to the left of the rack neutral position. The pinion angle θp obtained in this manner is output to the pinion angle feedback control unit 63. The pinion angle θp is also output to the steering-side control unit 50, that is, the axial force calculation unit 56 of the target reaction torque calculation unit 52.

[0048] The steering angle ratio variable control unit 62 receives the vehicle speed V and the steering angle θs. The steering angle ratio variable control unit 62 calculates the target pinion angle θp* by adding an adjustment amount to the steering angle θs. The steering angle ratio variable control unit 62 varies the adjustment amount for varying the steering angle ratio, which is the ratio of the target pinion angle θp* to the steering angle θs, according to the vehicle speed V. For example, the adjustment amount is varied so that the change in the target pinion angle θp* relative to the change in the steering angle θs is larger when the vehicle speed V is slow than when the vehicle speed V is fast. There is a correlation between the steering angle θs and the target pinion angle θp*. In addition, 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.

[0049] 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 executes PID control using a proportional term, an integral term, and a differential term as feedback control of the pinion angle θp so that the pinion angle θp follows the target pinion angle θp*. That is, the pinion angle feedback control unit 63 obtains a deviation between the target pinion angle θp* and the pinion angle θp, and calculates a steering force command value T* as a target control amount that is a target for the steering force so as to eliminate the deviation.

[0050] The energization control unit 64 receives as input the steering force command value T*, the rotation angle θb, and the turning side actual current value Ib. The energization control unit 64 calculates a current command value Ib* for the turning side motor 32 based on the turning force command value T*. The energization control unit 64 then determines the deviation between the current command value Ib* and a current value on the dq coordinates obtained by converting the turning side actual current value Ib based on the rotation angle θb, and controls the power supply to the turning side motor 32 so as to eliminate the deviation. As a result, the turning side motor 32 rotates by an angle corresponding to the turning force command value T*.

[0051] <Axial force calculation section 56> Here, the function of the axial force calculation unit 56 will be described in detail. As shown in FIG. 4, the axial force calculation section 56 has a distribution axial force calculation section 91, an end axial force calculation section 92, a deviation axial force calculation section 93, and an axial force selection section 94.

[0052] The distributed axial force calculation unit 91 calculates a distributed axial force Fd according to the axial force acting on the rack shaft 22. The distributed axial force Fd corresponds to a calculated axial force estimated by distributing an angle axial force Fr and a current axial force Fi, which will be described later, at their respective distribution ratios so that the axial force acting on the rack shaft 22 through the steered wheels 5 is suitably reflected. The distributed axial force Fd thus obtained is output to an adder 95. In this embodiment, the distributed axial force Fd is an example of a torque component.

[0053] The end axial force calculation unit 92 calculates an end axial force Fie for informing the driver of a situation in which the steering limit of the steering wheel 3, i.e., the steering limit of the steered wheels 5, is reached. When the absolute value of the steering angle θs approaches a steering angle limit corresponding to the steering limit, the end axial force Fie corresponds to a force that resists the steering of the steering wheel 3 in order to restrict further steering of the steering wheel 3 beyond the steering angle limit.

[0054] The end axial force calculation unit 92 receives an input of a target pinion angle θp*. The end axial force calculation unit 92 calculates the end axial force Fie based on the target pinion angle θp*. Specifically, the end axial force calculation unit 92 is provided with an end axial force map that defines the relationship between the target pinion angle θp* and the end axial force Fie, and calculates the end axial force Fie from the map using the target pinion angle θp* as an input. When the absolute value of the target pinion angle θp* is equal to or smaller than the threshold angle θie, the end axial force calculation unit 92 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 92 calculates an end axial force Fie with an absolute value greater than "0", assuming that the steering angle θs will exceed the steering angle limit. The end axial force Fie is set so that when the absolute value of the target pinion angle θp* exceeds the threshold angle θie and becomes large to a certain extent, the absolute value becomes so large that the steering wheel 3 cannot be further steered by hand. The end axial force Fie obtained in this manner is output to the axial force selection unit 94.

[0055] The deviation axial force calculation unit 93 calculates the deviation axial force Fv that notifies the driver of a situation in which a deviation occurs in the relationship considering the steering angle ratio between the steering state of the steering wheel 3 and the steering state of the steered wheels 5. A situation in which the steered wheels 5 hit an obstacle such as a curb is an example of a situation in which a deviation occurs in the relationship considering the steering angle ratio between the steering state of the steering wheel 3 and the steering state of the steered wheels 5. In this case, even though the steered wheels 5 cannot be steered in one direction toward the obstacle, there is a possibility that the steered wheels 5 will be steered in that one direction beyond the stop position of the steering wheel 3 corresponding to the stop position of the steered wheels 5. This is because the power transmission path between the steering unit 4 and the steered unit 6 is separated. Another example of a situation in which a deviation occurs in the relationship considering the steering angle ratio between the steering state of the steering wheel 3 and the steering state of the steered wheels 5 is a situation in which the correlation between the steering angle θs and the steered angle is lost as a result of the operation of the steered side motor 32 being restricted for overheat protection. This is because it becomes difficult for the pinion angle θp to follow the target pinion angle θp*. The deviation axial force Fv corresponds to a force that resists further steering of the steering wheel 3 in order to restrict the further steering of the steering wheel 3 when the steered wheels 5 hit an obstacle such as a curb. Also, when the operation of the steered-side motor 32 is limited for overheat protection, the deviation axial force Fv corresponds to a force that resists the further steering of the steering wheel 3 in order to ensure the tracking of the pinion angle θp to the target pinion angle θp*.

[0056] The deviation axial force calculation unit 93 receives the steering angle θs, the pinion angle θp, and the steered-side actual current value Ib as inputs. The deviation axial force calculation unit 93 calculates a conversion angle obtained by converting the pinion angle θp, which is expressed as a steering angle index value, into a value expressed as a steering angle index value according to the steering angle ratio by adding an adjustment amount to the pinion angle θp. The deviation axial force calculation unit 93 varies the adjustment amount according to the vehicle speed V so as to obtain a calculation rule in which the relationship between the input and the output is reversed with respect to the calculation rule defined by the steering angle ratio variable control unit 62. The deviation axial force calculation unit 93 calculates the deviation axial force Fv based on the deviation obtained by subtracting the conversion angle from the steering angle θs. Specifically, the deviation axial force calculation unit 93 is provided with a deviation axial force map that defines the relationship between the absolute value of the deviation and the deviation axial force Fv, and calculates the deviation axial force Fv from the map using the deviation as an input. Then, the deviation axial force calculation unit 93 sets the sign of the deviation axial force Fv based on the turning side actual current value Ib. That is, the deviation axial force calculation unit 93 sets the deviation axial force Fv to be positive when the turning side actual current value Ib is a positive value including zero, and sets the deviation axial force Fv to be negative when the turning side actual current value Ib is a negative value. The deviation axial force Fv obtained in this manner is output to the axial force selection unit 94.

[0057] The end axial force Fie and the deviation axial force Fv are input to the axial force selection unit 94. The axial force selection unit 94 selects the axial force having the largest absolute value from the end axial force Fie and the deviation axial force Fv, and calculates the selected axial force as the selected axial force Fsl. The adder 95 adds the selected axial force Fsl to the distributed axial force Fd to calculate the axial force F. As shown in FIG. 2, the axial force F thus obtained is output to the subtractor 57. The subtractor 57 subtracts the axial force F from the steering force Tb* to calculate the target reaction torque Ts*. The target reaction torque Ts* thus obtained is output to the current control unit 53.

[0058] <Distribution axial force calculation unit 91> Next, the function of the distribution axial force calculation unit 91 will be described in detail. As shown in FIG. 5, the distribution axial force calculation section 91 has an angle axial force calculation section 101, a current axial force calculation section 102, and an axial force distribution ratio calculation section 103.

[0059] The angle axial force calculation unit 101 receives the target pinion angle θp*, the steering angle θs, and the vehicle speed V. The angle axial force calculation unit 101 calculates the angle axial force Fr based on the target pinion angle θp*, the steering angle θs, and the vehicle speed V. The angle axial force Fr is an ideal value of the axial force defined by an arbitrarily set vehicle model. The angle axial force Fr is calculated as an axial force that does not reflect road surface information. The road surface information is information such as minute irregularities that do not affect the lateral behavior of the vehicle and steps that affect the lateral behavior of the vehicle. For example, the angle axial force calculation unit 101 calculates the angle axial force Fr so that the absolute value of the angle axial force Fr increases as the absolute value of the target pinion angle θp* increases. In addition, the angle axial force calculation unit 101 calculates the angle axial force Fr so that the absolute value of the angle axial force Fr increases as the vehicle speed V increases. The angle axial force Fr is calculated as a value in the dimension (N·m) of torque. The angular axial force Fr thus obtained is output to the multiplier 104. In this embodiment, the angular axial force Fr is an example of a torque component, and the angular axial force calculation unit 101 is an example of a torque component calculation unit.

[0060] The current axial force calculation unit 102 receives the turning side actual current value Ib as input. The current axial force calculation unit 102 calculates the current axial force Fi based on the turning side actual current value Ib. The current axial force Fi is an axial force that actually acts on the rack shaft 22 that operates to turn the steered wheels 5, i.e., an estimated value of the axial force actually transmitted to the rack shaft 22. The current axial force Fi is calculated as an axial force that reflects the above road surface information. For example, the current axial force calculation unit 102 calculates the current axial force Fi on the assumption that the torque applied to the rack shaft 22 by the turning side motor 32 and the torque corresponding to the force applied to the rack shaft 22 through the turning wheels 5 are balanced. That is, the current axial force calculation unit 102 calculates the current axial force Fi so that the absolute value of the current axial force Fi increases as the absolute value of the turning side actual current value Ib increases. The current axial force Fi is calculated as a value in the dimension (N·m) of the torque. The current axial force Fi thus obtained is output to the multiplier 105.

[0061] The vehicle speed V is input to the axial force distribution ratio calculation unit 103. The axial force distribution ratio calculation unit 103 calculates the axial force distribution gain Di based on the vehicle speed V. The axial force distribution gain Di is a 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 distributed axial force Fd. The axial force distribution ratio calculation unit 103 is provided with an axial force distribution gain map that defines the relationship between the vehicle speed V and the axial force distribution gain Di. The axial force distribution ratio calculation unit 103 inputs the vehicle speed V and calculates the axial force distribution gain Di from the map. The axial force distribution gain Di thus obtained is multiplied by the current axial force Fi and output to the adder 108 as the final current axial force Fim obtained through the multiplier 105. The subtractor 106 subtracts the axial force distribution gain Di from "1" stored in the storage unit 107 to calculate the axial force distribution gain Dr. The axial force distribution gain Dr thus obtained is output to the multiplier 104. The axial force distribution gain Dr is the distribution ratio of the angular axial force Fr when obtaining the distributed axial force Fd. In other words, the value of the axial force distribution gain Dr is calculated so that the sum of the axial force distribution gain Dr and the axial force distribution gain Di is "1 (100%)". The distribution ratio includes the concept of a zero value in which only either the angular axial force Fr or the current axial force Fi is distributed to the distributed axial force Fd. The storage unit 107 is a predetermined storage area of ​​a memory not shown.

[0062] The axial force distribution gain Dr thus obtained is multiplied by the angular axial force Fr obtained by the angular axial force calculation unit 101, and is output to an adder 108 as a final angular axial force Frm obtained through a multiplier 104. The angular axial force Frm and the current axial force Fim are added in the adder 108 to calculate a distributed axial force Fd. The distributed axial force Fd acts in the direction opposite to the steering direction of the driver. The distributed axial force Fd is calculated as a value in the dimension of torque (N·m). As shown in FIG. 4, the distributed axial force Fd thus obtained is output to an adder 95.

[0063] <Driving hysteresis compensation amount calculation unit 82> Next, the running hysteresis compensation amount calculation unit 82 will be described. As shown in FIG. 6, the driving hysteresis compensation amount calculation unit 82 has a driving zero point calculation unit 111, a driving hysteresis component calculation unit (hereinafter referred to as the “driving hysteresis component calculation unit”) 112, and a driving vehicle speed gain calculation unit 113.

[0064] A steering angle θs is input to the driving zero point calculation unit 111. The driving zero point calculation unit 111 calculates a driving zero point Pr based on the steering angle θs when the driving hysteresis component calculation unit 112 calculates a driving hysteresis component Fhy1 described later. Specifically, when the driving zero point calculation unit 111 determines the start of turning steering or the start of return steering, it calculates the steering angle θs at the start position as the driving zero point Pr. The driving zero point calculation unit 111 determines the start of turning steering or the start of return steering based on an increase or decrease in the steering angle θs, that is, the sign of the steering speed ωs obtained by differentiating the steering angle θs. In other words, the driving zero point calculation unit 111 updates the driving zero point Pr every time it determines the start of turning steering or the start of return steering.

[0065] In this embodiment, the turning steering is a steering in which the steering direction is the same and the steering is continued in one direction. The return steering is a steering for a steering angle θs within a small predetermined range after the steering direction is changed. For example, the running zero point calculation unit 111 judges the start of turning steering as the time when the steering angle θs starts to increase or decrease from a state where it is not increasing or decreasing, that is, when the steering speed ωs starts to change from a zero value to either positive or negative. The running zero point calculation unit 111 judges the start of return steering as the time when the state of the increase or decrease of the steering angle θs starts to change between increasing and decreasing during turning steering, that is, when the sign of the steering speed ωs starts to change between positive and negative. The running zero point calculation unit 111 judges the start of return steering as the time when the steering angle θs has changed by an amount corresponding to a predetermined range after it has been judged to be the start of return steering.

[0066] The thus obtained running zero point Pr is output to the running hysteresis component calculation unit 112. The steering angle θs and the driving zero point Pr are input to the driving hysteresis component calculation unit 112. The driving hysteresis component calculation unit 112 calculates a driving hysteresis component (hereinafter referred to as "driving hysteresis component") Fhy1, which is a component to be added to the basic control amount I1* so that the steering force Tb* has a hysteresis characteristic, based on the steering angle θs and the driving zero point Pr.

[0067] 7(a) and (b), the driving hysteresis component calculation unit 112 is provided with hysteresis maps (hereinafter referred to as "hismaps") MA1 and MA2 that define the relationship between the steering angle θs and the driving hysteresis component Fhy1. The driving hysteresis component calculation unit 112 calculates the driving hysteresis component Fhy1 using either the hismaps MA1 and MA2 depending on whether the steering is forward steering or backward steering, as determined in the same manner as the driving zero point calculation unit 111. In the hismaps MA1 and MA2, "θs" indicates the steering angle θs at the start position of the forward steering or backward steering, that is, the amount of change in the steering angle θs when the driving zero point Pr is set as the origin, that is, the angle deviation θhs.

[0068] Specifically, during turning steering, driving hysteresis component calculation unit 112 uses histmap MA1 to calculate driving hysteresis component Fhy1. In this case, the driving hysteresis component Fhy1 is calculated so that the greater the absolute value of the angle deviation θhs, the greater the absolute value of the driving hysteresis component Fhy1 becomes, and the smaller the absolute value of the hysteresis gradient, which is the rate of change of the driving hysteresis component Fhy1 at the rise time relative to the angle deviation θhs, becomes. In this case, the absolute value of the driving hysteresis component Fhy1 is calculated so that it saturates when the angle deviation θhs is in a predetermined range or more, and the maximum value at that time is equal to or less than the maximum value Fmax.

[0069] When steering to the right, the driving hysteresis component calculation unit 112 uses the value shown in the first quadrant with the driving zero point Pr at the start position of the steering as the origin of the histmap MA1. When steering to the left, the driving hysteresis component calculation unit 112 uses the value shown in the third quadrant with the driving zero point Pr at the start position of the steering as the origin of the histmap MA1.

[0070] On the other hand, during return steering, the driving hysteresis component calculation unit 112 uses the hiss map MA2 to calculate the driving hysteresis component Fhy1. In this case, the driving hysteresis component Fhy1 is calculated so as to be proportional to the angle deviation θhs. In this case, the driving hysteresis component Fhy1 is calculated only when the angle deviation θhs is within a predetermined range from the driving zero point Pr.

[0071] When steering back to the right, the driving hysteresis component calculation unit 112 sets the driving zero point Pr at the start position of the steering back as the origin of the histmap MA2, and uses the value shown in the first quadrant only while the angle deviation θhs is within a predetermined range from the origin. When steering back to the left, the driving hysteresis component calculation unit 112 sets the driving zero point Pr at the start position of the steering back as the origin of the histmap MA2, and uses the value shown in the third quadrant only while the angle deviation θhs is within a predetermined range from the origin.

[0072] In this embodiment, the histmaps MA1 and MA2 are configured to change the running hysteresis component Fhy1 according to the vehicle speed V. The histmaps MA1 and MA2 change the running hysteresis component Fhy1 according to the vehicle speed V in order to realize a desired steering feeling. In this embodiment, for example, the running hysteresis component Fhy1 is changed so that the hysteresis gradient increases as the vehicle speed V decreases. The histmaps MA1 and MA2 change the running hysteresis component Fhy1 so that the maximum value Fmax increases as the vehicle speed V increases. For example, the maximum value Fmax is set to a value up to 10 times larger when the vehicle speed V is an extremely low speed that includes a stopped state, such as less than 6 kilometers per hour, compared to a medium to high speed that does not include a stopped state, such as 10 kilometers per hour or more. The running hysteresis component Fhy1 may be changed according to the steering speed ωs, which is a differential value of the steering angle θs. In this case, for example, the driving hysteresis component Fhy1 may be changed so that the hysteresis gradient decreases as the steering speed ωs increases.

[0073] As a result, when the steering wheel 3 is sine-steered by periodically repeating turning steering and returning steering at a constant frequency, the driving hysteresis component calculation unit 112 calculates the driving hysteresis component Fhy1 so that it has hysteresis characteristics with respect to changes in the steering angle θs. The driving hysteresis component Fhy1 obtained in this manner is output to the multiplier 114.

[0074] The vehicle speed V is input to the traveling vehicle speed gain calculation unit 113. The traveling vehicle speed gain calculation unit 113 calculates a traveling vehicle speed gain Dv1 based on the vehicle speed V. As shown in Fig. 8, the running vehicle speed gain calculation unit 113 includes a vehicle speed gain map M11 that defines the relationship between the vehicle speed V and the running vehicle speed gain Dv1, and calculates the running vehicle speed gain Dv1 using the map with the vehicle speed V as an input. When the vehicle speed V is, for example, the extremely low speed, that is, less than the first threshold value V1, the running vehicle speed gain calculation unit 113 calculates the running vehicle speed gain Dv1 as "zero value (0%)". When the vehicle speed V is, for example, the medium to high speed, that is, equal to or greater than the second threshold value V2, the running vehicle speed gain calculation unit 113 calculates the running vehicle speed gain Dv1 as "1 (100%)". When the vehicle speed V is, for example, a low speed between a very low speed and a medium to high speed, that is, equal to or greater than a first threshold value V1 and less than a second threshold value V2, the traveling vehicle speed gain calculation unit 113 calculates the traveling vehicle speed gain Dv1 so that there is a linear connection between "zero value" and "1." In this embodiment, a vehicle speed V less than the first threshold value V1 corresponds to a second vehicle speed determined to correspond to the second state, and a vehicle speed V equal to or greater than the first threshold value, that is, equal to or greater than the second threshold value V2, corresponds to a first vehicle speed determined to correspond to the first state.

[0075] The traveling vehicle speed gain Dv1 thus obtained is multiplied by the traveling hysteresis component Fhy1 and is output to the adder 73 as the traveling hysteresis compensation amount I3* obtained through a multiplier 114. <Angle axial force calculation section 101> Next, the angle and axial force calculation unit 101 will be described.

[0076] As shown in FIG. 9, the angle axial force calculation unit 101 has an axial force basic component calculation unit 121, an extremely low speed determination unit 122, a stopping zero point calculation unit 123, a stopping hysteresis component calculation unit (hereinafter referred to as the "stopping hysteresis component calculation unit") 124, a stopping vehicle speed gain calculation unit 125, and a zero point inverse calculation unit 126.

[0077] The target pinion angle θp* is input to the axial force basic component calculation unit 121. The axial force basic component calculation unit 121 calculates the axial force basic component Frb, which is a basic component of the angular axial force Fr, based on the target pinion angle θp*. Specifically, the axial force basic component calculation unit 121 performs calculations such that the absolute value of the axial force basic component Frb increases as the absolute value of the target pinion angle θp* increases. The axial force basic component Frb is calculated as a value in the dimension of torque (N m). The axial force basic component Frb obtained in this manner is output to an adder 127.

[0078] The vehicle speed V is input to the very low speed determination unit 122. When the very low speed determination unit 122 detects that the vehicle speed V has crossed the first threshold value V1 and transitioned to less than the first threshold value V1, the very low speed determination unit 122 generates a determination FLG indicating the detection. In this embodiment, the situation in which the vehicle speed V has crossed the first threshold value V1 and transitioned to less than the first threshold value V1 corresponds to the situation in which the vehicle speed V has changed from the first vehicle speed to the second vehicle speed. The determination FLG obtained in this manner is output to the stopping zero point calculation unit 123.

[0079] The parking zero point calculation unit 123 receives the steering angle θs, the judgment FLG, and a correction zero point Pc, which will be described later. The parking zero point calculation unit 123 calculates a parking zero point Ps, based on the steering angle θs, for use when the parking hysteresis component calculation unit 124 calculates a parking hysteresis component (hereinafter referred to as a "parking hysteresis component") Fhy2, which will be described later. When the parking zero point calculation unit 123 determines the start of turning-in steering or the start of returning steering, it calculates the steering angle θs at the start position as the parking zero point Ps, in the same way as the running zero point calculation unit 111 calculates the running zero point Pr.

[0080] Then, when the determination FLG is not input, the stopping zero point calculation unit 123 calculates the stopping zero point Ps obtained by the calculation as the final stopping zero point Ps. In other words, when the determination FLG is not input, the stopping zero point calculation unit 123 updates the stopping zero point Ps every time it determines the start of turning steering or the start of returning steering.

[0081] On the other hand, when the judgment FLG is input, the stopping zero point calculation unit 123 calculates the stopping zero point Ps after correcting the calculated stopping zero point Ps to become the corrected zero point Pc as the final stopping zero point Ps. The corrected zero point Pc is obtained through the zero point inverse calculation unit 126. In other words, when the judgment FLG is input, the stopping zero point calculation unit 123 updates the stopping zero point Ps to become the corrected zero point Pc obtained through the zero point inverse calculation unit 126 while not determining the start of turning steering or the start of turning back steering. The calculation of the corrected zero point Pc will be described in detail later. The final stopping zero point Ps obtained in this manner is output to the stopping hysteresis component calculation unit 124.

[0082] The steering angle θs, the stopping zero point Ps, and the vehicle speed V are input to the stopping hysteresis component calculation unit 124. The stopping hysteresis component calculation unit 124 calculates a stopping hysteresis component Fhy2, which is a component to be added to the axial force basic component Frb so that the angular axial force Fr has a hysteresis characteristic, based on the steering angle θs, the stopping zero point Ps, and the vehicle speed V.

[0083] 7(a) and (b), the stopping hysteresis component calculation unit 124 includes histmaps MB1 and MB2 that define the relationship between the steering angle θs and the stopping hysteresis component Fhy2. The histmaps MB1 and MB2 are basically the same as the histmaps MA1 and MA2 included in the running hysteresis component calculation unit 112.

[0084] The stopping hysteresis component calculation unit 124 calculates the stopping hysteresis component Fhy2 in the same manner as the running hysteresis component calculation unit 112 calculates the running hysteresis component Fhy1. That is, when steering to the right, the stopping hysteresis component calculation unit 124 uses the value shown in the first quadrant with the stopping zero point Ps at that time as the origin of the histmap MB1. When steering to the left, the stopping hysteresis component calculation unit 124 uses the value shown in the third quadrant with the stopping zero point Ps at that time as the origin of the histmap MB1. When steering back to the right, the stopping hysteresis component calculation unit 124 uses the value shown in the first quadrant with the stopping zero point Ps at that time as the origin of the histmap MB2 only while the angle deviation θhs is within a predetermined range from the origin. In addition, when steering back to the left, the stopping hiss component calculation unit 124 uses the stopping zero point Ps at that time as the origin of the hiss map MB2, and uses the value shown in the third quadrant only while the angle deviation θhs is within a specified range from the origin.

[0085] As a result, when the steering wheel 3 is sine steered by periodically repeating forward steering and backward steering at a constant frequency, the parking hysteresis component calculation unit 124 calculates the parking hysteresis component Fhy2 so that it has hysteresis characteristics with respect to changes in the steering angle θs. The parking hysteresis component Fhy2 obtained in this manner is output to the multiplier 128 and the zero point inverse calculation unit 126.

[0086] In this embodiment, the characteristic exhibited by the stopping hysteresis component Fhy2 calculated when the vehicle speed V is the above-mentioned medium to high speed is an example of a first hysteresis characteristic. That is, the state in which the stopping hysteresis component Fhy2 is calculated when the vehicle speed V is the above-mentioned medium to high speed is an example of a first calculation state. Moreover, the characteristic exhibited by the stopping hysteresis component Fhy2 calculated when the vehicle speed V is the above-mentioned extremely low speed is an example of a second hysteresis characteristic. That is, the state in which the stopping hysteresis component Fhy2 is calculated when the vehicle speed V is the above-mentioned extremely low speed is an example of a second calculation state.

[0087] The vehicle speed V is input to the stopping vehicle speed gain calculation unit 125. The stopping vehicle speed gain calculation unit 125 calculates a stopping vehicle speed gain Dv2 based on the vehicle speed V. As shown in FIG. 10, the stopping vehicle speed gain calculation unit 125 includes a vehicle speed gain map M12 that defines the relationship between the vehicle speed V and the stopping vehicle speed gain Dv2, and calculates the stopping vehicle speed gain Dv2 using the map with the vehicle speed V as an input. When the vehicle speed V is, for example, the above-mentioned low speed and medium-high speed, that is, equal to or higher than the first threshold value V1, the stopping vehicle speed gain calculation unit 125 calculates the stopping vehicle speed gain Dv2 as a "zero value (0%)". When the vehicle speed V is, for example, a zero value, the stopping vehicle speed gain calculation unit 125 calculates the stopping vehicle speed gain Dv2 as "1 (100%)". When the vehicle speed V is, for example, an extremely low speed, that is, less than the first threshold value V1, the stopping vehicle speed gain calculation unit 125 calculates the stopping vehicle speed gain Dv2 so that the "zero value" and "1" are linearly connected.

[0088] Further, the stopping vehicle speed gain calculation unit 125 limits the amount of change in the stopping vehicle speed gain Dv2 per calculation cycle to a predetermined limit value while the vehicle speed V increases from zero to the above-mentioned medium to high speed, i.e., the second threshold value V2. When the amount of change in the stopping vehicle speed gain Dv2 per calculation cycle exceeds the limit value, the stopping vehicle speed gain calculation unit 125 limits the amount of change in the stopping vehicle speed gain Dv2 per calculation cycle to the limit value. As a result, the stopping vehicle speed gain calculation unit 125 gradually changes the stopping vehicle speed gain Dv2 with respect to the immediately preceding cycle (one cycle before) while the vehicle speed V increases from zero to the above-mentioned medium to high speed, i.e., the second threshold value V2. In other words, the stopping vehicle speed gain calculation unit 125 has a function of compensating the stopping vehicle speed gain Dv2 so as to suppress a sudden change in the stopping vehicle speed gain Dv2 while the vehicle speed V increases from zero to the above-mentioned medium to high speed, i.e., the second threshold value V2. In this embodiment, as shown by the two-dot chain line in Fig. 10, for example, the limit value is changed so as to become larger as the vehicle speed V increases. The limit value is set based on tests, simulations, etc., from the viewpoint of realizing the change in stiffness of the steered wheels 5 that occurs while the vehicle speed V increases from zero to the above-mentioned medium to high speed, i.e., toward the second threshold value V2.

[0089] The stopping vehicle speed gain Dv2 thus obtained is multiplied by the stopping hysteresis component Fhy2 and input to the adder 127 as the angle axial force hysteresis component (hereinafter referred to as the "angle axial force hysteresis component") Fhyr obtained through the multiplier 128. The angle axial force Fr obtained by adding the angle axial force hysteresis component Fhyr to the axial force basic component Frb in the adder 127 is output to the multiplier 104.

[0090] In this embodiment, the stopping vehicle speed gain Dv2 is an example of a vehicle speed coefficient, and the stopping vehicle speed gain calculation unit 125 is an example of a coefficient calculation unit. In addition, the stopping vehicle speed gain Dv2 calculated when the vehicle speed V is less than the first threshold value V1 corresponds to the second vehicle speed coefficient, and the stopping vehicle speed gain Dv2 calculated when the vehicle speed V is equal to or greater than the first threshold value V1 corresponds to the first vehicle speed coefficient.

[0091] In this embodiment, the running hysteresis compensation amount I3* is compensated to optimize the hysteresis characteristic due to friction during operation of the steering wheel 3, particularly in a running state in which the vehicle does not include a stopped state. A running state in which the vehicle does not include a stopped state refers to a state in which the vehicle is running at a medium to high speed, such as 10 kilometers per hour or more. The running hysteresis compensation amount I3* has a hysteresis characteristic with respect to a change in the steering angle θs. The running hysteresis compensation amount I3* thus obtained is output to the adder 73.

[0092] As shown in FIG. 9, the zero-point inverse calculation unit 126 receives the parking hiss component Fhy2 and the steering angle θs. Based on the parking hiss component Fhy2 and the steering angle θs, the zero-point inverse calculation unit 126 calculates the corrected zero point Pc. The zero-point inverse calculation unit 126 includes the hiss maps MB1 and MB2 provided in the parking hiss component calculation unit 124, particularly the hiss maps MB1 (V < V1) and MB2 (V < V1) when the vehicle speed V is the above-mentioned extremely low speed. In addition, when the zero-point inverse calculation unit 126 determines the start of the cut-in steering or the start of the cut-back steering in the same manner as the parking zero-point calculation unit 123 calculates the parking zero point Ps, it calculates the steering angle θs at the start position as the parking zero point Ps. In this case, the zero-point inverse calculation unit 126 calculates the change amount of the steering angle θs, that is, the angle deviation θhs, with the parking zero point Ps as the origin based on the steering angle θs.

[0093] Then, the zero-point inverse calculation unit 126 calculates the angle deviation θhs corresponding to the origin in the hiss maps MB1 (V < V1) and MB2 (V < V1) when calculating the parking hiss component Fhy2 with the same value as the input value of the parking hiss component Fhy2. In this case, when performing the cut-in steering to the right, the zero-point inverse calculation unit 126 uses the value shown in the first quadrant of the hiss map MB1 (V < V1). When performing the cut-in steering to the left, the zero-point inverse calculation unit 126 uses the value shown in the third quadrant of the hiss map MB1 (V < V1). When performing the cut-back steering to the right, the zero-point inverse calculation unit 126 uses the value shown in the first quadrant of the hiss map MB2 (V < V1). When performing the cut-back steering to the left, the zero-point inverse calculation unit 126 uses the value shown in the third quadrant of the hiss map MB2 (V < V1).

[0094] For example, as shown in FIG. 11, assuming a cut-in steering operation to the right, for a coordinate system with the horizontal axis being the angle deviation θhs and the vertical axis being the parking hysteresis component Fhy2, let the point representing the input [parking hysteresis component Fhy2, angle deviation θhs] be coordinate P1. Here, in FIG. 11, for the values shown in the first quadrant of the hysteresis map MB1 (V < V1) indicated by the two-dot chain line, the hysteresis map MB1 (V < V1) is offset so as to be shifted entirely to the right, that is, to the side where the angle deviation θhs increases on the positive value side, until it overlaps with coordinate P1. Then, for the offset hysteresis map MB1 (V < V1) indicated by the solid line in FIG. 11, the value of the steering angle θs corresponding to the value of the angle deviation θhs on the horizontal axis becomes the correction zero point Pc. In this case, the correction zero point Pc is obtained as a value obtained by subtracting the value of the angle deviation θhs on the horizontal axis from the steering angle θs corresponding to the parking zero point Ps. For the angle deviation θhs obtained by updating the origin to the correction zero point Pc, as the parking hysteresis component Fhy2 calculated by the hysteresis map MB1 (V < V1), the same value as the value of the parking hysteresis component Fhy2 input to the zero point inverse calculation unit 126 at that time is obtained. This is the same for the values shown in the third quadrant of the hysteresis map MB1 (V < V1), assuming a cut-in steering operation to the left, and the values shown in the third quadrant are offset to the left, that is, to the side where the angle deviation θhs increases on the negative value side. Also, when performing a cut-back steering operation to the right, the same applies to the values shown in the first quadrant of the hysteresis map MB2 (V < V1), and the values shown in the first quadrant are offset to the right, that is, to the side where the angle deviation θhs increases on the positive value side. Also, when performing a cut-back steering operation to the left, the same applies to the values shown in the third quadrant of the hysteresis map MB2 (V < V1), and the values shown in the third quadrant are offset to the left, that is, to the side where the angle deviation θhs increases on the negative value side. The correction zero point Pc thus obtained is output to the parking zero point calculation unit 123. In the present embodiment, the extremely low speed determination unit 122, the parking zero point calculation unit 123, the parking hysteresis component calculation unit 124, the parking vehicle speed gain calculation unit 125, the zero point inverse calculation unit 126, and the multiplier 128 are examples of the hysteresis component calculation unit.

[0095] The operation of the first embodiment will be described. In this embodiment, the hysteresis component Fhy2 for stopping can be calculated by correcting the origin in the hysteresis maps MB1 and MB2 according to the situation of whether the vehicle speed V is extremely low. For example, the situation of detecting that the vehicle speed V has changed from medium-low speed to low speed and then to extremely low speed is a situation where it is assumed that the hysteresis width changes greatly before and after the transition to extremely low speed when calculating the hysteresis component Fhy2 for stopping. This is because, for the hysteresis map MB1 (V≥V1, V2) used before the transition to extremely low speed, the maximum value Fmax of the hysteresis component Fhy2 for stopping is set large for the hysteresis map MB1 (V<V1) used after the transition to extremely low speed. The same applies to the hysteresis maps MB2 (V≥V1, V2) and MB2 (V<V1, V2).

[0096] In this embodiment, it can be determined by the determination FLG in the zero-point calculation unit 123 for stopping that the vehicle speed V has changed from medium-high speed to low speed and then to extremely low speed. Then, when the determination FLG is input, the zero-point calculation unit 123 for stopping updates the obtained zero point Ps for stopping to be the corrected zero point Pc obtained through the zero-point inverse calculation unit 126.

[0097] For example, assuming that the situation shown in FIG. 11 shows the moment when the vehicle speed V has changed from medium-high speed to low speed and then to extremely low speed on the premise of a cut-in steering operation to the right. At this moment, when the angle deviation θhs is the first deviation value θhs1, the hysteresis component Fhy2 of the first component value Fhy21 corresponding to the coordinate P1 is calculated based on the hysteresis map MB1 (V≥V1, V2).

[0098] Subsequently, immediately after the vehicle speed V changes to an extremely low speed, when calculating the parking hysteresis component Fhy2, the state changes to using the hysteresis map MB1 (V < V1) shown by the two-dot chain line in FIG. 11. If immediately after the vehicle speed V changes to an extremely low speed is not the start of cut-in steering or the start of cut-back steering, the parking zero point Ps (\"Ps1\" in FIG. 11) at the moment when the vehicle speed V changes from medium-high speed to low speed and then to extremely low speed is maintained. In this case, if the angle deviation θhs is maintained at the first deviation value θhs1 immediately after the vehicle speed V changes to an extremely low speed, based on the hysteresis map MB1 (V < V1), the parking hysteresis component Fhy2 of the second component value Fhy22 corresponding to the coordinate P2 is calculated. The situation where the angle deviation θhs is maintained at the first deviation value θhs1 corresponds to, for example, the steering wheel 3 not being held by the driver, a released state, etc. That is, immediately after the vehicle speed V changes to an extremely low speed, due to the change to the state of using the hysteresis map MB1 (V < V1) shown by the two-dot chain line in FIG. 11, the hysteresis width of the parking hysteresis component Fhy2 may change suddenly.

[0099] In contrast, as shown by the arrow in FIG. 11, in this embodiment, even if immediately after the vehicle speed V changes to an extremely low speed is not the start of cut-in steering or the start of cut-back steering, on the condition that the vehicle speed V has changed to an extremely low speed, the parking zero point Ps is updated to the corrected zero point Pc. As a result, as shown by the arrow in FIG. 11, the parking zero point Ps is updated from \"Ps1\" to the corrected zero point Pc (\"Ps2\" in FIG. 11). In this case, even if the angle deviation θhs was maintained at the first deviation value θhs1, based on the hysteresis map MB1 (V < V1) shown by the solid line in FIG. 11, the parking hysteresis component Fhy2 of the first component value Fhy21 corresponding to the coordinate P1 is calculated.

[0100] Thereby, when the vehicle speed V changes from medium-high speed to low speed and then to extremely low speed, a sudden change in the hysteresis width between the parking hysteresis component Fhy2 before the change and the parking hysteresis component Fhy2 after the change can be suppressed.

[0101] Therefore, the characteristics in Fig. 12(a) represent steering characteristics for driving, which are indicated by the relationship between the steering angle θs and the steering torque Th when the steering wheel 3 is sign-steered at a low vehicle speed V or a medium to high vehicle speed V. In contrast, the characteristics in Fig. 12(b) represent steering characteristics for stopping, which are indicated by the relationship between the steering angle θs and the steering torque Th when the steering wheel 3 is sign-steered at an extremely low vehicle speed V.

[0102] Then, while the steering characteristics for driving and stopping change according to the vehicle speed V, when the vehicle speed V changes from a medium to high speed to a very low speed, the steering characteristics change from those for driving to those for stopping. In this case, the hysteresis width changes significantly between the steering characteristics when the steering wheel 3 is sine-steered as described above, but a sudden change in the hysteresis width is suppressed during the change process.

[0103] The effects of this embodiment will be described. (1-1) In the present embodiment, the situation in which the hysteresis width of the stopping hysteresis component Fhy2 changes suddenly is suppressed, and therefore it is possible to suppress an uncomfortable feeling appearing in the movement of the steering wheel 3 and in the sensation obtained from the steering wheel 3. Therefore, it is possible to improve the steering feel.

[0104] (1-2) According to this embodiment, when the vehicle speed V changes from a medium-high speed to a very low speed across a low speed, the value of the stopping hysteresis component Fhy2 at the timing of the change can be maintained. This makes it possible to improve the steering feel even in a situation where the vehicle speed V changes from a medium-high speed to a very low speed across a low speed. From the viewpoint of conveying the friction of the steered wheels 5 to the driver, it is advantageous to greatly change the hysteresis width in the very low speed driving state between a low speed or medium-high speed driving state and a very low speed driving state. In other words, when calculating the stopping hysteresis component Fhy2, a situation where the hysteresis width is expected to change greatly corresponds to a case where the vehicle speed V changes from a medium-high speed to a very low speed across a low speed. Therefore, it is possible to improve the steering feel while realizing a specification that is advantageous from the viewpoint of conveying the friction of the steered wheels 5 to the driver.

[0105] (1-3) According to this embodiment, the conditions for maintaining the value of the stopping hysteresis component Fhy2 can be optimized through an approach that uses the vehicle speed V. <Second embodiment> A second embodiment of the steering control device will be described with reference to the drawings. The differences from the first embodiment will be mainly described. The same components as those in the first embodiment will be denoted by the same reference numerals, and the duplicated description will be omitted.

[0106] <Angle axial force calculation section 101> 13, the angle axial force calculation unit 101 has a configuration that is modified from the configuration described in the above-mentioned first embodiment by deleting the very low speed determination unit 122. In the angle axial force calculation unit 101 of this embodiment, with the deletion of the very low speed determination unit 122, changes are made to the stopping zero point calculation unit 123 and the zero point inverse calculation unit 126 of the above-mentioned first embodiment.

[0107] Specifically, the steering angle θs and the corrected zero point Pc are input to the stopping zero point calculation unit 123a corresponding to the stopping zero point calculation unit 123 of the first embodiment. The stopping zero point calculation unit 123a calculates the stopping zero point Ps in the same manner as the stopping zero point calculation unit 123 of the first embodiment. When the corrected zero point Pc is not input, the stopping zero point calculation unit 123a calculates the stopping zero point Ps obtained by calculation as the final stopping zero point Ps. On the other hand, when the corrected zero point Pc is input, the stopping zero point calculation unit 123 calculates the stopping zero point Ps obtained by correction so that the stopping zero point Ps becomes the corrected zero point Pc as the final stopping zero point Ps.

[0108] Further, a zero point inverse calculation unit 126a corresponding to the zero point inverse calculation unit 126 of the first embodiment receives the stopping hysteresis component Fhy2, the steering angle θs, and the stopping vehicle speed gain Dv2. When the zero point inverse calculation unit 126a does not detect that the value of the stopping vehicle speed gain Dv2 has changed from the "zero value", i.e., has started to increase, in other words, when the zero point inverse calculation unit 126a detects that the value does not change or has started to decrease from "1" to the "zero value", it does not calculate or output the corrected zero point Pc. On the other hand, when the zero point inverse calculation unit 126a detects that the value of the stopping vehicle speed gain Dv2 has changed from the "zero value", i.e., has changed to a state where it starts to increase, it calculates the corrected zero point Pc in the same manner as the zero point inverse calculation unit 126 of the first embodiment and outputs it to the stopping zero point calculation unit 123. In other words, when the zero point inverse calculation unit 126a detects that the value of the stopping vehicle speed gain Dv2 has changed from the "zero value" to a state where it starts to increase, it calculates and outputs the corrected zero point Pc so that the stopping zero point Ps is updated in the stopping zero point calculation unit 123a without determining the start of turning steering or the start of turning back steering.

[0109] According to this embodiment, in addition to the actions and effects according to the first embodiment, the following effects are achieved. (2-1) According to this embodiment, the situation in which the value of the stopping hysteresis component Fhy2 is maintained can be optimized through an approach that uses the stopping vehicle speed gain Dv2.

[0110] The above-described embodiments may be modified as follows. In addition, the following other embodiments may be combined with each other to the extent that there is no technical contradiction. In the first embodiment, the function of the extremely low speed determination unit 122 may be realized as a function of the stopping zero point calculation unit 123. That is, the stopping zero point calculation unit 123 may be configured to receive the vehicle speed V. Alternatively, the function of the extremely low speed determination unit 122 may be realized as a function of the zero point inverse calculation unit 126. In this case, the zero point inverse calculation unit 126 may be configured to receive the vehicle speed V. Then, the stopping zero point calculation unit 123 may be configured to receive the corrected zero point Pc only in a situation where it is necessary, as in the second embodiment. In these cases, the function of the extremely low speed determination unit 122 can be deleted.

[0111] In the second embodiment, the function of the zero point inverse calculation unit 126a that detects that the value of the stopping vehicle speed gain Dv2 has changed from the "zero value" to a state where it starts to increase may be realized as a function of the stopping zero point calculation unit 123a. In other words, the stopping zero point calculation unit 123a may be configured to input the vehicle speed V. In this case, the zero point inverse calculation unit 126a may basically be configured to calculate and output the corrected zero point Pc. Then, when detecting that the value of the stopping vehicle speed gain Dv2 has changed from the "zero value" to a state where it starts to increase, the stopping zero point calculation unit 123a may reflect the correction by the input corrected zero point Pc. In addition, the angle axial force calculation unit 101 may be configured to add a calculation unit having the function of the zero point inverse calculation unit 126a that detects that the value of the stopping vehicle speed gain Dv2 has changed from the "zero value" to a state where it starts to increase.

[0112] In the first embodiment, the zero point inverse calculation unit 126 may be configured to input the angular axial force hysteresis component Fhyr. In this case, the zero point inverse calculation unit 126 may be configured to input the stationary vehicle speed gain Dv2, and the stationary vehicle speed gain Dv2 may be used to calculate the corrected zero point Pc. The zero point inverse calculation unit 126 may also calculate an angle deviation θhs corresponding to the origin when calculating the angular axial force hysteresis component Fhyr having the same value as the inputted angular axial force hysteresis component Fhyr for the corrected zero point Pc. In this case, the zero point inverse calculation unit 126 may also calculate an angle deviation θhs corresponding to the origin when calculating the stationary vehicle hysteresis component Fhy2 having the same value as the inputted angular axial force hysteresis component Fhyr for the corrected zero point Pc. This is also true for the second embodiment.

[0113] In each of the above embodiments, in the portion where the target pinion angle θp* is used, various components may be calculated based on state variables correlated with the target pinion angle θp* instead of the target pinion angle θp*. Examples of state variables correlated with the target pinion angle θp* include the pinion angle θp, steering angle θs, rotation angle θa, and rotation angle θb, which are examples of state variables that change according to the operation of the steering device 2. These target pinion angles θp* and these angles correlated with the target pinion angle θp* are angles that can be converted into the steering angle of the steered wheels 5. In other words, the axial force basic component Frb and the end axial force Fie may be calculated based on the pinion angle θp, for example. Even in the case of this modified example, the same effects as those of each of the above embodiments can be obtained. This is also true for state variables correlated with the target pinion angle θp*, such as the steering angle θs and the pinion angle θp. In other words, the running hysteresis component Fhy1 and the stopping hysteresis component Fhy2 may be calculated based on the pinion angle θp or the target pinion angle θp* instead of the steering angle θs, for example.

[0114] In each of the above embodiments, when the steering force calculation unit 55 calculates the steering force Tb*, it is sufficient to use at least a state variable related to the operation of the steering wheel 3, and the vehicle speed V may not be used, or other elements may be used in combination. As a state variable related to the operation of the steering wheel 3, instead of the steering torque Th exemplified in each of the above embodiments, the steering angle θs or other elements may be used.

[0115] In each of the above embodiments, the axial force basic component calculation unit 121 needs to use at least the target pinion angle θp* when calculating the axial force basic component Frb, and may use other elements such as the vehicle speed V in combination.

[0116] In each of the above embodiments, when calculating the driving hysteresis component Fhy1, the driving hysteresis component calculation unit 112 needs to use at least the steering angle θs, and does not need to use the vehicle speed V. In this case, the driving vehicle speed gain Dv1 is used to adjust the magnitude of the maximum value Fmax in accordance with the vehicle speed V of the hismaps MA1 and MA2. This is also true when the stopping hysteresis component calculation unit 124 calculates the stopping hysteresis component Fhy2. In this case, the stopping vehicle speed gain Dv2 is used to adjust the magnitude of the maximum value Fmax in accordance with the vehicle speed V of the hismaps MB1 and MB2.

[0117] In each of the above embodiments, when calculating the driving hysteresis component Fhy1, the driving hysteresis component calculation unit 112 may use other elements in combination with the steering angle θs and the vehicle speed V. This also applies to when the stopping hysteresis component calculation unit 124 calculates the stopping hysteresis component Fhy2.

[0118] In each of the above embodiments, the axial force distribution ratio calculation unit 103 needs only to use the vehicle speed V when calculating the axial force distribution gain Di, and may use other elements in combination. In each of the above embodiments, the end axial force calculation unit 92 and the deviation axial force calculation unit 93 may be deleted from the axial force calculation unit 56. In this case, the axial force selection unit 94 and the adder 95 may be deleted. The distributed axial force Fd calculated by the distributed axial force calculation unit 91 is output to the subtractor 57.

[0119] In each of the above embodiments, the traveling vehicle speed gain calculation unit 113 may use the vehicle speed V in calculating the traveling vehicle speed gain Dv1, or may use other elements in combination. This also applies to the stopping vehicle speed gain calculation unit 125 calculating the stopping vehicle speed gain Dv2.

[0120] In each of the above embodiments, when gradually changing the stopping vehicle speed gain Dv2, the stopping vehicle speed gain calculation unit 125 may gradually change the stopping vehicle speed gain Dv2 over elapsed time, or may take into consideration the steering state of the steering unit 4, such as the steering angle θs, and the steering state of the steering unit 6, such as the pinion angle θp.

[0121] In each of the above embodiments, other situations may be assumed for the situation in which the value of the stopping hysteresis component Fhy2 is maintained. As another situation, for example, a situation in which the rotation of the steered wheels 5 becomes locked while the vehicle is traveling can be considered. In a situation in which the rotation of the steered wheels 5 becomes locked while the vehicle is traveling, the vehicle speed V may become extremely slow due to the rotation of the steered wheels 5 becoming locked. This can be estimated, for example, from the deviation between the vehicle speed V and a state variable such as the yaw rate occurring in the vehicle. As another situation, a situation in which the road on which the vehicle is traveling changes from a high μ road to a low μ road can be assumed.

[0122] In each of the above embodiments, the target to which the calculated hysteresis component is added is not limited to the angular axial force Fr. The target to which the calculated hysteresis component is added can be changed as appropriate as long as it has a hysteresis characteristic that is convenient for operating the steering device 2, such as an axial force obtained by considering at least one of the yaw rate and the lateral acceleration. In this case, even if a problem similar to that of each of the above embodiments occurs, the problem can be solved by applying a configuration similar to each of the above embodiments.

[0123] In each of the above embodiments, the vehicle speed V is very low, i.e., the value of the first threshold value V1 may be changed as appropriate as long as it includes the stopped state. For example, the first threshold value V1 may be set to a low speed such as 3 km / h, or may be set to a low speed such as 10 km / h.

[0124] The steering control device 1 of each of the above embodiments may be configured to reflect command values ​​of an automatic driving system that realizes various driving assistance functions and automatic driving functions in the operation of the steering device 2. In this case, even if a problem similar to that of each of the above embodiments occurs, the problem can be solved by applying a configuration similar to that of each of the above embodiments.

[0125] In each of the above embodiments, the steering side control unit 50 may be added as a function of the steered side control unit 60. In each of the above embodiments, the steered-side motor 32 may be, for example, one that is arranged coaxially with the rack shaft 22, or one that is connected to the rack shaft 22 via a worm and wheel to a pinion shaft that constitutes a rack-and-pinion mechanism.

[0126] In each of the above embodiments, the steering control device 1 can be configured by a processing circuit including: 1) one or more processors that operate according to a computer program (software); 2) one or more dedicated hardware circuits such as an application specific integrated circuit (ASIC) that executes at least some of the various processes; or 3) a combination thereof. The processor includes a CPU and memory such as RAM and ROM, and the memory stores program code or instructions configured to cause the CPU to execute processes. The memory, i.e., a non-transitory computer-readable medium, includes any available medium that can be accessed by a general-purpose or special-purpose computer.

[0127] In each of the above embodiments, the steering device 2 has a linkless structure in which the steering unit 4 and the steered unit 6 are mechanically separated at all times, but the present invention is not limited to this, and may have a structure in which the steering unit 4 and the steered unit 6 can be mechanically separated by a clutch. The steering device 2 may also be an electric power steering device that applies an assist force, which is a force for assisting the driver in steering. In this case, the steering wheel 3 is mechanically connected to the pinion shaft 21 via the steering shaft 11. The assist force may reflect a component equivalent to the angular axial force hysteresis component Fhyr in each of the above embodiments. In this case, even if a problem similar to that of each of the above embodiments occurs, the problem can be solved by applying a configuration similar to that of each of the above embodiments. [Explanation of symbols]

[0128] 1...Steering control device 2...Steering gear 3. Steering wheel 5…Steering wheel 12...Steering actuator (actuator) 13...Steering side motor (motor) 52...Target reaction torque calculation unit (torque command value calculation unit) 101...Angle axial force calculation unit (torque component calculation unit) 121...Axial force basic component calculation section 122...Extremely low speed judgment section (judgment section) 123, 123a...Stopping zero point calculation unit (hysteresis component calculation unit) 124...Stopping hysteresis component calculation unit (hysteresis component calculation unit) 125...Stopping vehicle speed gain calculation unit (hysteresis component calculation unit) 126, 126a...Zero point inverse calculation unit (hysteresis component calculation unit)

Claims

1. The steering device is a control target that varies a steering torque required for steering a steering wheel by a motor torque applied by an actuator using a motor as a drive source, and the control target includes a torque command value calculation unit that calculates a torque command value that 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 has a torque component calculation unit that calculates a torque component used when calculating the torque command value based on a state variable that changes in response to an operation of the steering device, the torque component calculation unit has a hysteresis component calculation unit that calculates a hysteresis component for adding a hysteresis characteristic to the torque component with respect to a change in a specific state variable obtained with a value set at a predetermined timing of the specific state variable that changes in response to steering of the steering device as an origin, The hysteresis component calculation unit is a first calculation state for calculating the calculated hysteresis component for adding a first hysteresis characteristic to the torque component, and a second calculation state for calculating the calculated hysteresis component for adding a second hysteresis characteristic having a hysteresis width larger than that of the first hysteresis characteristic to the torque component, In the second calculation state after transition from the first calculation state, a value corresponding to an origin in the second hysteresis characteristic when calculating the calculated hysteresis component capable of maintaining a value of the calculated hysteresis component at the timing of the transition is calculated, and the calculated hysteresis component is calculated with the calculated value as an origin, The hysteresis component calculation unit is When the vehicle is in a first state in which it can be determined that the vehicle is in a traveling state not including a stopped state, the hysteresis component in the calculation obtained in the first calculation state is reflected in the torque component, A steering control device configured to reflect the computational hysteresis component obtained by computing the second computational state in the torque component when the vehicle is in a second state in which it can be determined that the vehicle is in a traveling state including a stopped state.

2. The torque component calculation unit an axial force fundamental component calculation unit that calculates, as the torque component, a fundamental component of an angular axial force, which is an axial force that is determined according to an angle that can be converted into a steering angle of a steering wheel of a vehicle and does not reflect road surface information; 2. The steering control device according to claim 1, further comprising an angle axial force calculation unit having a hysteresis component calculation unit that calculates the calculated hysteresis component to be added to the base component.

3. The steering control device according to claim 1 or 2, wherein the hysteresis component calculation unit is configured to calculate the calculated hysteresis component capable of maintaining the value of the calculated hysteresis component at the timing of the transition when the vehicle speed is a second vehicle speed defined as corresponding to the second state after transitioning from a first vehicle speed defined as corresponding to the first state.

4. the torque component calculation unit further includes a coefficient calculation unit that calculates a vehicle speed coefficient that changes based on a vehicle speed so as to add the vehicle speed to the calculated hysteresis component when the first hysteresis characteristic or the second hysteresis characteristic is added to the torque component, The steering control device according to claim 1 or 2, wherein the hysteresis component calculation unit is configured to calculate a calculated hysteresis component that can maintain the value of the calculated hysteresis component at the timing of the transition when the vehicle speed coefficient calculated through the coefficient calculation unit is a second vehicle speed coefficient calculated at a second vehicle speed defined as corresponding to the second state after transition from a first vehicle speed coefficient calculated at a first vehicle speed defined as corresponding to the first state.

5. The coefficient calculation unit gradually changes the vehicle speed coefficient according to a limit value while the vehicle speed is increasing, The steering control device according to claim 4 , wherein the vehicle speed coefficient is changed so that the limit value becomes larger as the vehicle speed increases.

Images