Steering operation control device

Abstract

The present disclosure discloses a steering operation control device. The steering operation control device (1) controls a steering operation device (2) as a controlled object, and the steering operation device (2) has a structure for cutting off the power transmission between a steering operation unit (4) and a steering unit (6). The steering operation control device (1) includes a central processing unit. The central processing unit is configured to perform a reduction process when at least one of a driving state quantity and a steering operation state is a state quantity indicating that a target steering corresponding angle does not change. The reduction process is a process of reducing the drive current to be supplied to a steering motor (33).

Description

Technical Field

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

[0002] Japanese Unexamined Patent Application Publication No. 2019-59392 (JP 2019-59392A) describes a steer-by-wire type steering operation device. The steer-by-wire type steering operation device is configured such that power transmission between a steering operation unit and a steering unit is cut off. The steering operation unit is connected to a steering wheel, and the steering unit is configured to steer a steering wheel in response to a steering input to the steering operation unit. The steering operation control device is configured to control the steer-by-wire type steering operation device as a controlled object, and the steering operation control device includes a steering control unit configured to control an operation of a steering motor that applies a steering force to the steering unit. The steering force is a force that steers the steering wheel. The steering control unit calculates a target value of a drive current supplied to the steering motor by performing steering angle feedback control that causes a steering angle of the steering wheel to follow a target steering angle calculated based on a driver's steering. The steering control unit controls the operation of the steering motor based on the target value of the drive current to be supplied to the steering motor. Summary of the Invention

[0003] The steering wheel remains stationary at a position where the force that steers the steering wheel balances with the frictional force of the road surface. The frictional force of the road surface changes according to the road surface condition. Therefore, the steering angle at which the force that steers the steering wheel balances with the frictional force of the road surface may deviate from the target steering angle. In this case, a difference is generated between the target steering angle and the steering angle. For example, even when the vehicle temporarily stops and the steering wheel is in a steering operation holding state or a hands-off state, the steering control unit calculates a target value for the drive current that reduces the difference between the target steering angle and the steering angle. However, when the difference is small, assume such a situation: even when the drive current is supplied to the steering motor according to the difference, the position of the steering wheel that remains stationary does not change. In this case, due to the continuously generated difference between the target steering angle and the steering angle, the drive current may continuously flow into the steering motor.

[0004] The present invention provides a steering operation control device capable of reducing power consumption.

[0005] The steering operation control device according to one aspect of the present invention is a steering operation control device configured to control a steering operation device as a controlled object. The steering operation device has a structure that cuts off the power transmission between the steering operation unit and the steering unit. The steering operation unit is connected to the steering wheel, and the steering unit is configured to turn the steering wheel in response to the steering input to the steering operation unit. The steering operation control device includes a central processing unit configured to: control the operation of a steering motor configured to apply a steering force to the steering unit, the steering force being a force for turning the steering wheel; calculate a steering target current value, which is a target value of the drive current to be supplied to the steering motor, by performing steering angle feedback control so that an actual steering corresponding angle follows a target steering corresponding angle that is a target value of the steering angle of the steering wheel; control the operation of the steering motor based on the steering target current value; perform a reduction process of reducing the drive current to be supplied to the steering motor; and perform the reduction process when at least one of a running state quantity and a steering operation state quantity is a state quantity indicating that the target steering corresponding angle does not change, the running state quantity indicating the running state of the host vehicle, and the steering operation state quantity indicating the steering operation state of the host vehicle.

[0006] When the running state quantity indicates that the target steering corresponding angle does not change, or when the steering operation state quantity indicates that the target steering corresponding angle does not change, the steering corresponding angle does not change when the force for turning the steering wheel balances with the frictional force of the road surface. At this time, a difference may occur between the target steering corresponding angle and the steering corresponding angle. In this regard, it is assumed that the state where the target steering corresponding angle does not change is a state where the demand for the steering motor to apply a steering force to the steering wheel to turn the steering wheel is low. In the above configuration, when the running state quantity indicates that the target steering corresponding angle does not change, or when the steering operation state quantity indicates that the target steering corresponding angle does not change, a reduction process of reducing the drive current to be supplied to the steering motor is performed. Thereby, it is possible to suppress the drive current supplied to the steering motor when the force for turning the steering wheel balances with the frictional force of the road surface, and this drive current is generated when the steering angle deviates from the target steering angle.

[0007] In the above aspect, when the vehicle speed as the running state quantity is a low vehicle speed including the stopped state of the host vehicle, the central processing unit may be configured to determine that the running state quantity corresponds to a state quantity indicating that the target steering corresponding angle does not change, and the central processing unit may be configured to perform the reduction process.

[0008] In the above configuration, compared with the case where the vehicle speed is a high vehicle speed, it may be difficult for the steering motor to enter a state where the steering motor applies a steering force to the steering wheel to turn the steering wheel when the vehicle speed is a low vehicle speed. Therefore, when the vehicle speed is a low vehicle speed, it is possible to make the state for performing the reduction process more appropriate.

[0009] In the above aspect, when the value of the steering operation state quantity indicates that the steering wheel is in the steering operation holding state or the steering wheel is in the released state, the central processing unit can be configured to determine that the steering operation state quantity corresponds to a state quantity indicating that the target steering corresponding angle does not change, and the central processing unit can be configured to perform a reduction process.

[0010] In the above configuration, when the value of the steering operation state quantity indicates that the steering wheel is in the steering operation holding state or the steering wheel is in the released state, it is assumed that the driver does not input a steering to change the steering corresponding angle to the steering operation unit. In this case, compared with a situation such as when the driver cuts into the steering wheel, it may be difficult for the steering wheel to enter a state where the steering wheel is steered by receiving a steering force from the steering motor. Therefore, when the value of the steering operation state quantity indicates that the steering wheel is in the steering operation holding state or the steering wheel is in the released state, the state of performing the reduction process can be made more appropriate.

[0011] In the above aspect, the central processing unit can be configured to calculate a target steering corresponding angle based on the steering input of the steering operation unit, and the central processing unit can be configured to make the target steering corresponding angle approach the actual steering corresponding angle in the reduction process.

[0012] In the above configuration, when the target steering corresponding angle approaches the steering corresponding angle, the difference between the target steering corresponding angle and the steering corresponding angle can be reduced. In the above configuration, the central processing unit can be configured to calculate an offset angle based on the target steering corresponding angle and the actual steering corresponding angle, and the offset angle is the amount by which the target steering corresponding angle approaches the actual steering corresponding angle. The central processing unit can be configured to correct the target steering corresponding angle by adding the offset angle to the target steering corresponding angle or subtracting the offset angle from the target steering corresponding angle. The central processing unit can be configured to calculate a steering target current value based on the corrected target steering corresponding angle.

[0013] In the above configuration, the central processing unit can be configured to correct the offset angle calculated in the current calculation cycle based on the driving state quantity and the steering operation state quantity. The central processing unit can be configured to correct the target steering corresponding angle by adding the corrected offset angle to the target steering corresponding angle or subtracting the offset angle corrected thereby from the target steering corresponding angle.

[0014] In the above configuration, the frictional force of the road surface changes according to the road surface condition, and therefore, the difference between the target steering corresponding angle and the steering corresponding angle changes each time. Therefore, it is assumed that an appropriate offset angle for reducing the difference between the target steering corresponding angle and the steering corresponding angle changes each time. In view of this, the offset angle correction unit corrects the offset angle in each calculation cycle. Thereby, the target steering corresponding angle can be appropriately corrected so that the target steering corresponding angle approaches the steering corresponding angle.

[0015] In the above configuration, the central processing unit may be configured to change a correction amount for reducing an offset angle based on at least one of a driving state quantity and a steering operation state quantity.

[0016] For example, in the case of a driving state quantity indicating that the vehicle is traveling at a relatively high vehicle speed, or in the case of a steering operation state quantity indicating that a steering unit configured to steer a steering wheel is steering the steering wheel, even when the correction amount for reducing the offset angle becomes large and the increased correction amount appears as an unexpected movement of the steering unit to the driver, it can be said that such movement is difficult to be transmitted to the driver as a sense of discomfort. In view of this, the above configuration takes into account the driving state quantity or the steering operation state quantity, and thus, the above configuration can effectively design a way to eliminate the offset angle as soon as possible while suppressing the driver's discomfort.

[0017] In the above configuration, in a state where a reduction process is being executed, when at least one of the driving state quantity and the steering operation state quantity is a state quantity indicating a change in a target steering corresponding angle, the central processing unit may be configured to end the execution of the reduction process. When the state of executing the reduction process changes to a state of not executing the reduction process, the central processing unit may be configured to gradually reduce the absolute value of the offset angle.

[0018] In the above configuration, by gradually reducing the absolute value of the offset angle that makes the target steering corresponding angle approach the steering corresponding angle, the target steering corresponding angle changes slowly. This enables a slow transition from a state of executing the reduction process to a state of not executing the reduction process.

[0019] With the above aspects, power consumption can be reduced. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The features, advantages, and technical and industrial significance of exemplary embodiments of the present invention will be described below with reference to the accompanying drawings, in which like reference numerals represent like elements, and in the accompanying

[0021] In the drawings:

[0022] Figure 1 is a diagram showing a schematic configuration of a steer-by-wire type steering operation device;

[0023] Figure 2 is a block diagram showing a schematic configuration of a steering operation control device;

[0024] Figure 3 is a block diagram showing a schematic configuration of an axial force calculation unit;

[0025] Figure 4 is a block diagram showing a schematic configuration of a reduction processing unit; and

[0026] Figure 5 is a block diagram showing a schematic configuration of an offset angle correction unit. DETAILED DESCRIPTION

[0027] An embodiment of a steering operation control device will be described with reference to the accompanying drawings. As Figure 1 shown, a steering operation device 2, which is a controlled object to be controlled by a steering operation control device 1, is configured as a steer-by-wire type steering operation device. The steering operation device 2 includes a steering operation unit 4 and a steering unit 6. The steering operation unit 4 is configured to be steered by a driver via a steering wheel 3, and the steering unit 6 is configured to steer a steering wheel 5 in response to the steering input by the driver to the steering operation unit 4.

[0028] The steering operation unit 4 includes a steering operation shaft 11 and a steering operation actuator 12. The steering wheel 3 is fixed to the steering operation shaft 11. The steering operation actuator 12 applies a steering operation reaction force to the steering wheel 3 via the steering operation shaft 11. The steering operation reaction force is a force that resists the driver's steering. The steering operation actuator 12 includes a steering operation motor 13 and a steering operation speed reducer 14. The steering operation motor 13 serves as a drive source, and the steering operation speed reducer 14 is configured to reduce the rotation of the steering operation motor 13 and transmit the rotation to the steering operation shaft 11. As the steering operation motor 13 of the present embodiment, for example, a three-phase brushless motor is employed.

[0029] The steering unit 6 includes a first pinion shaft 21 and a rack shaft 22. The rack shaft 22 is connected to the first pinion shaft 21. The first pinion shaft 21 and the rack shaft 22 are placed at a predetermined crossing angle. A first rack and pinion mechanism 23 is constituted by meshing a pinion tooth 21a formed on the first pinion shaft 21 with a first rack tooth 22a formed on the rack shaft 22. The first pinion shaft 21 is a rotating shaft capable of converting its rotation into a steering angle of the steering wheel 5. Corresponding tie rods 24 are connected to opposite ends of the rack shaft 22. The respective distal ends of the tie rods 24 are respectively connected to corresponding steering knuckles (not shown) to which the right and left steering wheels 5 are assembled.

[0030] The steering unit 6 includes a steering actuator 31 that applies a steering force for steering the steering wheel 5 to the rack shaft 22. The steering actuator 31 applies a steering force to the rack shaft 22 via a second pinion shaft 32. The steering actuator 31 includes a steering motor 33 and a steering speed reducer 34. The steering motor 33 serves as a drive source, and the steering speed reducer 34 is configured to reduce the rotation of the steering motor 33 and transmit the rotation to the second pinion shaft 32. The second pinion shaft 32 and the rack shaft 22 are placed at a predetermined crossing angle. A second rack and pinion mechanism 35 is constituted by meshing a second pinion tooth 32a formed on the second pinion shaft 32 with a second rack tooth 22b formed on the rack shaft 22.

[0031] In the steering operation device 2 configured as described above, in response to the driver's steering operation, the steering angle of the steering wheel 5 changes, such that the second pinion shaft 32 is driven to rotate by the steering actuator 31, and the rotation of the second pinion shaft 32 is converted into the axial movement of the rack shaft 22 via the second rack and pinion mechanism 35. At this time, a reaction force against the driver's steering operation is applied from the steering operation actuator 12 to the steering wheel 3.

[0032] The electrical configuration of the steering operation device 2 will be described below. The steering operation control device 1 is connected to the steering operation motor 13 and the steering motor 33. The steering operation control device 1 controls the operations of the steering operation motor 13 and the steering motor 33. The steering operation control device 1 includes a central processing unit (CPU) and a memory (not shown). The steering operation control device 1 performs various controls such that the CPU executes a program stored in the memory in each predetermined calculation cycle.

[0033] A torque sensor 41 for detecting the steering operation torque Th applied to the steering operation shaft 11 is connected to the steering operation control device 1. The torque sensor 41 is provided closer to the steering wheel 3 than the connection portion of the steering operation shaft 11 and the steering operation reduction gear 14. The torque sensor 41 detects the steering operation torque Th based on the deformation of a torsion bar spring provided in the middle of the steering operation shaft 11. A steering rotation angle sensor 42 and a steering rotation angle sensor 43 are connected to the steering operation control device 1. The steering rotation angle sensor 42 detects the rotation angle θs of the steering operation motor 13 as a detection value indicating the steering amount of the steering operation unit 4 in a relative angle within 360 degrees. The steering rotation angle sensor 43 detects the rotation angle θt of the steering motor 33 as a detection value indicating the steering amount of the steering unit 6 in a relative angle. A vehicle speed sensor 44 is connected to the steering operation control device 1. The vehicle speed sensor 44 detects the vehicle speed V as the traveling speed of the vehicle. Note that when steering is performed in the right direction, the steering operation torque Th and the rotation angles θs and θt are detected as positive values, and when steering is performed in the left direction, the steering operation torque Th and the rotation angles θs and θt are detected as negative values.

[0034] The steering operation control device 1 performs reaction force control such that a steering operation reaction force is generated according to the steering operation torque Th by controlling the drive of the steering operation motor 13. In addition, the steering operation control device 1 performs steering control such that the steering wheel 5 is steered according to the steering operation state by controlling the drive of the steering motor 33.

[0035] The configuration of the steering operation control device 1 will be described below. The steering operation control device 1 includes a central processing unit (CPU) and a memory (not shown), and the CPU executes a program stored in the memory in each predetermined calculation cycle. Thereby, various processes are executed.

[0036] Figure 2 Some of the respective processes executed by the steering operation control device 1 are shown. In Figure 2 it, some of the respective processes realized by the CPU executing the program stored in the memory are described for each type of process to be realized.

[0037] As Figure 2 shown, the steering operation control device 1 includes a steering operation control unit 50 and a steering control unit 60. The steering operation control unit 50 is configured to execute reaction force control, and the steering control unit 60 is configured to execute steering control. The steering operation control unit 50 includes a steering operation side current sensor 54. The steering operation side current sensor 54 detects a steering operation side actual current value Is obtained from the current value of each phase of the steering operation motor 13 in a connection line between the steering operation control unit 50 and the motor coil of each phase of the steering operation motor 13. The steering operation side actual current value Is indicates the value of the actual drive current supplied to the steering operation motor 13. The steering operation side current sensor 54 obtains the voltage drop of a shunt resistor as a current, and the shunt resistor is connected to the source side of each switching element in an inverter (not shown) provided for the steering operation motor 13. Note that in Figure 2 it, for the purpose of description, the connection lines of each phase and the current sensors of each phase are collectively shown as one connection line and one current sensor.

[0038] The steering control unit 60 includes a steering side current sensor 65. The steering side current sensor 65 detects a steering side actual current value It obtained from the current value of each phase of the steering motor 33 in a connection line between the steering control unit 60 and the motor coil of each phase of the steering motor 33. The steering side actual current value It indicates the value of the actual drive current supplied to the steering motor 33. The steering side current sensor 65 obtains the voltage drop of a shunt resistor as a current, and the shunt resistor is connected to the source side of each switching element in an inverter (not shown) provided for the steering motor 33. Note that in Figure 2 it, for the purpose of description, the connection lines of each phase and the current sensors of each phase are collectively shown as one connection line and one current sensor.

[0039] The configuration of the steering operation control unit 50 will be described below. The steering operation torque Th, vehicle speed V, rotation angle θs, actual current value It on the steering side, and pinion angle θp (described later) are input to the steering operation control unit 50. The steering operation control unit 50 controls the power supply to the steering operation motor 13 based on the steering operation torque Th, vehicle speed V, rotation angle θs, actual current value It on the steering side, and pinion angle θp. Note that the pinion angle θp is calculated based on the rotation angle θt.

[0040] The steering operation control unit 50 includes a steering operation angle calculation unit 51, a target reaction force torque calculation unit 52, and a current application control unit 53. The rotation angle θs is input to the steering operation angle calculation unit 51. The steering operation angle calculation unit 51 converts the rotation angle θs into an accumulated angle including a range exceeding 360° by counting the number of rotations of the steering operation motor 13 from the steering neutral position, which is the position of the steering wheel 3 when the vehicle is going straight, for example. The steering operation angle calculation unit 51 calculates the steering operation angle θh by multiplying the accumulated angle obtained by the conversion by a scale factor based on the rotation speed ratio of the steering operation reduction gear 14. Note that, for example, when the steering operation angle θh is an angle on the right side of the steering neutral position, the steering operation angle θh is positive, and when the steering operation angle θh is an angle on the left side of the steering neutral position, the steering operation angle θh is negative. The obtained steering operation angle θh is output to the steering control unit 60.

[0041] The steering operation torque Th, vehicle speed V, actual current value It on the steering side, and target pinion angle θp* (described later) are input to the target reaction force torque calculation unit 52. The target reaction force torque calculation unit 52 calculates the target reaction force torque T* as the reaction force control amount based on the steering operation torque Th, vehicle speed V, actual current value It on the steering side, and target pinion angle θp*. The target reaction force torque T* as the reaction force control amount is the target value of the steering operation reaction force of the steering wheel 3 that should be caused by the steering operation motor 13.

[0042] More specifically, the target reaction force torque calculation unit 52 includes a steering operation reaction force calculation unit 55 and an axial force calculation unit 56. The steering operation torque Th and the vehicle speed V are input to the steering operation reaction force calculation unit 55. The steering operation reaction force calculation unit 55 calculates a steering operation reaction force component Tb* based on the steering operation torque Th and the vehicle speed V. The steering operation reaction force component Tb* indicates the motor torque that rotates the steering wheel 3 in the direction in which the driver steers, that is, the assisting force that assists the driver in steering the steering wheel 3. As the absolute value of the steering operation torque Th becomes larger or when the vehicle speed V becomes smaller, the steering operation reaction force calculation unit 55 calculates a steering operation reaction force component Tb* with a larger absolute value. The obtained steering operation reaction force component Tb* is output to the subtracter 57.

[0043] The vehicle speed V, the actual current value It on the steering side, and the target pinion angle θp* (described later) are input to the axial force calculation unit 56. The axial force calculation unit 56 calculates the axial force to be applied to the rack shaft 22 through the steering wheel 5 based on the vehicle speed V, the actual current value It on the steering side, and the target pinion angle θρ*. The axial force calculation unit 56 calculates the steering operation reaction force corresponding to the axial force, that is, the torque conversion value obtained by converting the axial force into torque, as the axial force component Fd. The obtained axial force component Fd, and the target reaction force torque T* obtained by subtracting the axial force component Fd from the steering operation reaction force component Tb* by the subtracter 57 is output to the current application control unit 53.

[0044] The target reaction force torque T*, the actual current value Is on the steering operation side, and the rotation angle θs are input to the current application control unit 53. The current application control unit 53 supplies a drive current corresponding to the target reaction force torque T* to the steering operation motor 13. The current application control unit 53 calculates the target current value on the steering operation side of the steering operation motor 13 based on the target reaction force torque T*. Then, the current application control unit 53 obtains the difference between the target current value on the steering operation side and the current value on the dq coordinate, which is obtained by converting the actual current value Is on the steering operation side detected by the steering operation side current sensor 54 based on the rotation angle θs, and the current application control unit 53 controls the power supply to the steering operation motor 13 to eliminate this difference. The steering operation motor 13 generates a torque corresponding to the target reaction force torque T*. Thus, it is possible to give the driver an appropriate reaction force feeling corresponding to the road surface reaction force.

[0045] The configuration of the steering control unit 60 will be described below. The steering operation torque Th, the vehicle speed V, the steering operation angle θh, and the rotation angle θt are input to the steering control unit 60. The steering control unit 60 controls the power supply to the steering motor 33 based on the steering operation torque Th, the vehicle speed V, the steering operation angle θh, and the rotation angle θt.

[0046] The steering control unit 60 includes a pinion angle calculation unit 61, a target pinion angle calculation unit 62, a pinion angle feedback control unit (referred to as "pinion angle F / B control unit" in the figure) 63, and a current application control unit 64.

[0047] The rotation angle θt is input to the pinion angle calculation unit 61. The pinion angle calculation unit 61 converts the rotation angle θt into an accumulated angle including a range exceeding 360° by counting the number of rotations of the steering motor 33 from the rack neutral position, which is the position of the rack shaft 22 when the vehicle is going straight, for example. The pinion angle calculation unit 61 calculates the pinion angle θp, which is the actual rotation angle of the second pinion shaft 32, by multiplying the accumulated angle obtained by the conversion by a scale factor based on the rotation speed ratio of the steering reduction gear 34. Note that, for example, when the pinion angle θp is an angle on the right side of the rack neutral position, the pinion angle θp is positive, and when the pinion angle θp is an angle on the left side of the rack neutral position, the pinion angle θp is negative. The steering motor 33 and the second pinion shaft 32 operate together via the steering reduction gear 34. Therefore, there is a correlation between the rotation angle θt of the steering motor 33 and the pinion angle θp. By using this correlation, the pinion angle θp can be obtained from the rotation angle θt of the steering motor 33. In addition, the second pinion shaft 32 meshes with the rack shaft 22. Therefore, there is also a correlation between the pinion angle θp and the movement amount of the rack shaft 22. That is, the pinion angle θp is a value reflecting the steering angle of the steering wheel 5. The pinion angle θp thus obtained is output to the pinion angle feedback control unit 63. In the present embodiment, the pinion angle is an example of a steering corresponding angle.

[0048] The vehicle speed V, the steering operation angle θh, the steering operation torque Th, and the actual current value It on the steering side are input to the target pinion angle calculation unit 62. The target pinion angle calculation unit 62 calculates the target pinion angle θp*, which is the target steering corresponding angle as the target of the pinion angle θp, based on the vehicle speed V, the steering operation angle θh, the steering operation torque Th, and the actual current value It on the steering side. In the present embodiment, the target pinion angle calculation unit 62 is an example of a target steering corresponding angle calculation unit.

[0049] The target pinion angle calculation unit 62 includes a steering operation angle ratio variable calculation unit 66 and a reduction processing unit 67. The vehicle speed V and the steering operation angle θh are input to the steering operation angle ratio variable calculation unit 66. The steering operation angle ratio variable calculation unit 66 calculates the converted angle θvg by adding the adjustment amount Δθ to the steering operation angle θh. The steering operation angle ratio variable calculation unit 66 changes the adjustment amount Δθ according to the vehicle speed V. The adjustment amount Δθ is used to change the steering operation angle ratio that is the ratio of the converted angle θvg to the steering operation angle θh. For example, the adjustment amount Δθ is changed so that the change of the converted angle θvg with respect to the change of the steering operation angle θh is larger when the vehicle speed V is lower than when the vehicle speed V is higher. The steering operation angle θh and the converted angle θvg are correlated. In addition, the converted angle θvg is an angle that is the basis for the target pinion angle θp*. Therefore, the steering operation angle θh and the target pinion angle θp* are correlated. In addition, the pinion angle θp is controlled based on the target pinion angle θp*. Therefore, the steering operation angle θh and the pinion angle θp are also correlated. The steering operation angle θh is a value that reflects the steering angle of the steering wheel 5.

[0050] The vehicle speed V, the steering operation torque Th, the converted angle θvg, and the actual steering side current value It are input to the reduction processing unit 67. The reduction processing unit 67 calculates the offset angle θofst based on the vehicle speed V, the steering operation torque Th, the converted angle θvg, and the actual steering side current value It. The offset angle θofst is a compensation amount when calculating the target pinion angle θp*. The offset angle θofst is an amount that makes the target pinion angle θp* approach the pinion angle θp. The offset angle θofst will be described in detail later.

[0051] 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 calculates the steering operation force command value Tp* as the target control amount by feedback control of the pinion angle θp so that the pinion angle θp follows the target pinion angle θp*. The target control amount is the target of the steering force.

[0052] The steering force command value Tp*, the actual current value It on the steering side, and the rotation angle θt are input to the current application control unit 64. The current application control unit 64 calculates the target current value It* on the steering side of the steering motor 33 based on the steering operation force command value Tp*. Then, the current application control unit 64 obtains the difference between the target current value It* on the steering side and the current value on the dq coordinate, which is obtained by converting the actual current value It detected by the steering side current sensor 65 based on the rotation angle θt, and the current application control unit 64 controls the power supply to the steering motor 33 to eliminate this difference. The steering motor 33 generates a torque corresponding to the steering force command value Tp*. Thus, the steering wheel 5 can be steered by an angle corresponding only to the steering force command value Tp*. Note that the target current value It* on the steering side obtained by controlling the power supply to the steering motor 33 is output to the target pinion angle calculation unit 62. The target current value It* on the steering side corresponds to the target current value on the steering side. In addition, the current application control unit 64 corresponds to the steering target current value calculation unit.

[0053] The target pinion angle θp* is calculated as a control amount corresponding to the converted angle θvg obtained from the steering operation angle θh. The steering wheel 5 remains stationary at a position where the force that steers the steering wheel 5 balances the frictional force of the road surface. The force that steers the steering wheel 5 includes the steering force applied by the steering motor 33 or the force that returns the steering wheel 5 to its neutral position. The mechanical error of the steering unit 6 varies according to the steering operation device 2. In addition, the frictional force of the road surface varies according to the road surface condition. Therefore, the steering angle when the force that steers the steering wheel 5 balances the frictional force of the road surface may deviate from the target steering angle corresponding to the target pinion angle. In this case, a difference appears between the target steering angle and the steering angle. When this difference is small, assume such a situation: even if a drive current is supplied to the steering motor 33 according to this difference, the position where the steering wheel 5 remains stationary does not change. In this case, according to the difference between the target pinion angle θp* and the pinion angle θp, which is constantly generated in the pinion angle feedback control unit 63, the drive current may continuously flow into the steering motor 33. To solve this problem, the steering operation control device 1, that is, the steering control unit 60 includes a reduction processing unit 67.

[0054] The axial force calculation unit 56 is described below. As Figure 3 shown, the axial force calculation unit 56 includes a current axial force calculation unit 81, an angular axial force calculation unit 82, a distribution gain calculation unit 83, multipliers 84, 85, and an adder 86.

[0055] The actual current value It on the steering side of the steering motor 33 is input to the current axial force calculation unit 81. The current axial force calculation unit 81 calculates a current axial force Fer based on the actual current value It on the steering side. The current axial force Fer is an estimated value of the axial force to be applied to the rack shaft 22 through the steering wheel 5. Here, when a difference occurs between the target pinion angle θp* and the actual pinion angle θp due to a disturbance acting on the steering wheel 5, the actual current value It on the steering operation side of the steering motor 33 changes. The disturbance corresponds to the road surface condition, that is, the frictional resistance of the road surface. That is, the actual current value It on the steering side of the steering motor 33 reflects the actual road surface reaction force acting on the steering wheel 5. Therefore, it is possible to calculate the current axial force Fer that reflects the influence of the road surface condition based on the actual current value It on the steering side of the steering motor 33. The current axial force calculation unit 81 calculates the current axial force Fer having a larger absolute value when the absolute value of the actual current value It on the steering side is larger.

[0056] The target pinion angle θp* is input to the angular axial force calculation unit 82. The angular axial force calculation unit 82 calculates an angular axial force Fib based on the target pinion angle θp*. The angular axial force Fib is an ideal value of the axial force to be applied to the rack shaft 22 through the steering wheel 5. The angular axial force calculation unit 82 calculates the axial force Fib having a larger absolute value when the absolute value of the target pinion angle θp* is larger.

[0057] The vehicle speed V is input to the distribution gain calculation unit 83. The distribution gain calculation unit 83 includes a map that defines the relationship between the vehicle speed V and the distribution gains Gib, Ger. The distribution gain calculation unit 83 calculates the distribution gains Gib, Ger corresponding to the vehicle speed V by referring to the map. As indicated by the solid line, the value of the distribution gain Gib when the vehicle speed V is high is lower than the value of the distribution gain Gib when the vehicle speed V is low. In addition, as indicated by the dashed line, the distribution gain Ger when the vehicle speed V is high is higher than the distribution gain Ger when the vehicle speed V is low. Note that in the present embodiment, the distribution gain Gib and the distribution gain Ger are set to corresponding values such that their sum is "1". More specifically, when the vehicle speed V is equal to or less than a predetermined vehicle speed threshold V0, the distribution gain Gib is set to "1", and the distribution gain Ger is set to "0".

[0058] The value obtained by multiplying the current axial force Fer by the distribution gain Ger in the multiplier 84 and the value obtained by multiplying the angular axial force Fib by the distribution gain Gib in the multiplier 85 are input to the adder 86. The adder 86 calculates the axial force component Fd by adding the value obtained by multiplying the current axial force Fer by the distribution gain Ger and the value obtained by multiplying the angular axial force Fib by the distribution gain Gib.

[0059] The configuration of the reduction processing unit 67 is described below. As Figure 4 shown, the reduction processing unit 67 includes a basic offset angle calculation unit 101, a switching unit 102, a determination unit 103, an accumulated offset angle calculation unit 104, a previous value holding unit 105, a differentiator 106, a switching unit 107, an offset angle correction unit 108, and an adder 109.

[0060] The target pinion angle θp* and the actual steering side current value It are input to the basic offset angle calculation unit 101. The basic offset angle calculation unit 101 includes a map that defines the relationship between the basic offset angle θo1 and the target pinion angle θp*. The basic offset angle calculation unit 101 performs map calculation based on the target pinion angle θp* by referring to the map to obtain the basic offset angle θo1. As the absolute value of the target pinion angle θp* becomes larger, the basic offset angle calculation unit 101 calculates a basic offset angle θo1 with a larger absolute value. In addition, the basic offset angle calculation unit 101 sets the sign of the basic offset angle θo1 in the direction in which the actual steering side current value It decreases, based on the actual steering side current value It. More specifically, when the actual steering side current value It is positive, the basic offset angle calculation unit 101 sets the sign of the basic offset angle θo1 to negative, and when the actual steering side current value It is negative, the basic offset angle calculation unit 101 sets the sign of the basic offset angle θo1 to positive. Note that when the actual steering side current value It is "0", the basic offset angle calculation unit 101 sets the basic offset angle θo1 to "0".

[0061] The actual steering side current value It, the basic offset angle θo1, and the minimum offset angle θmin are input to the switching unit 102. The minimum offset angle θmin is set to the minimum angle to be output when no offset is performed. In the present embodiment, the minimum offset angle θmin is set to "0". The basic offset angle θo1 is input to the first input N1 of the switching unit 102. The minimum offset angle θmin is input to the second input N2 of the switching unit 102.

[0062] When the actual steering-side current value It input in this way is greater than the current threshold value I0, the switching unit 102 controls the selection state so that the basic offset angle θo1 input to the first input N1 is output to the cumulative offset angle calculation unit 104. When the actual steering-side current value It input in this way is equal to or less than the current threshold value I0, the switching unit 102 controls the selection state so that the minimum offset angle θmin input to the second input N2 is output to the cumulative offset angle calculation unit 104. In the present embodiment, when the determination flag Fc is input to the switching unit 102, the switching unit 102 changes to a state in which a reduction process for reducing the drive current is to be executed, and when the determination flag Fc is not input to the switching unit 102, the switching unit 102 changes to a state in which the reduction process is not executed. The current threshold value I0 is set to the value of the actual steering-side current value It such that when the actual steering-side current value It is lower than this value, it is considered that the drive current to be supplied to the steering motor 33 is small enough.

[0063] The target pinion angular velocity ωp* obtained by differentiating the vehicle speed V, the steering operation torque Th, and the target pinion angle θp* by the differentiator 106 is input to the determination unit 103. The determination unit 103 generates a determination flag Fc based on the vehicle speed V, the steering operation torque Th, and the target pinion angular velocity ωp*, and switches whether to execute a reduction process for reducing the drive current based on the determination flag Fc. When the vehicle speed V is a low vehicle speed including the stop state of the host vehicle, and when the steering wheel 3 is in the steering operation holding state or the steering wheel 3 is in the released state, the determination unit 103 generates a determination flag Fc indicating that the reduction process for reducing the drive current is to be executed. On the other hand, when the vehicle speed V is not a low vehicle speed or when the steering wheel 3 is not in the steering operation holding state and the steering wheel 3 is not in the released state, the determination unit 103 does not generate a determination flag Fc.

[0064] When the vehicle speed V is equal to or less than the vehicle speed threshold value V0, the determination unit 103 determines that the vehicle speed V is a low vehicle speed including the stop state of the host vehicle. The vehicle speed threshold value V0 is a value based on which it is considered that the host vehicle is traveling at a low speed, and more specifically, the vehicle speed threshold value V0 is set to the value of the vehicle speed V that does not include road surface information. That is, the vehicle speed threshold value V0 is set to the value of the vehicle speed V when the distribution gain Gib is "1" and the distribution gain Ger is "0". In the present embodiment, the vehicle speed V is an example of a driving state quantity.

[0065] When the steering operation torque Th is equal to or greater than the steering operation holding torque threshold Th0, and the target pinion angular velocity ωp*, which is the change amount of the target pinion angle θp*, is equal to or less than the steering operation holding angular velocity threshold ω0, the determination unit 103 determines that the steering wheel 3 is in the steering operation holding state. The steering operation holding torque threshold Th0 is set to a value with respect to the steering operation torque Th, based on which it is considered that the driver inputs a steering to the steering wheel 3. The steering operation holding angular velocity threshold ω0 is set to a value approximately equal to the target pinion angular velocity ωp*, based on which it is considered that the steering angle of the steering wheel 5 does not change. That is, the steering operation holding angular velocity threshold ω0 is set to a value approximately equal to the target pinion angular velocity ωp* when the steering angle does not change due to the balance between the force for steering the steering wheel 5 and the frictional force of the road surface. In the present embodiment, the steering operation torque Th and the target pinion angular velocity ωp* are examples of the steering operation state quantities.

[0066] When the steering operation torque Th is equal to or less than the release torque threshold Th1 and the target pinion angular velocity ωp* is equal to or less than the release angular velocity threshold ω1, the determination unit 103 determines that the steering wheel 3 is in the release state. The release torque threshold Th1 is set to a value with respect to the steering operation torque Th, based on which it is considered that the driver does not input a steering to the steering wheel 3. The release angular velocity threshold ω1 is set to a value approximately equal to the target pinion angular velocity ωp* when the steering wheel 5 returns to its neutral position by the self-aligning torque. The release angular velocity threshold ω1 is set to be smaller than the value of the target pinion angular velocity ωp* when the driver cuts in or cuts back the steering wheel. Note that the release angular velocity threshold ω1 may be the same value as the steering operation holding angular velocity threshold ω0, or may have a value different from the steering operation holding angular velocity threshold ω0.

[0067] The determination flag Fc, the value output from the switching unit 102, and the offset angle θofst(-) in the previous calculation cycle are input to the cumulative offset angle calculation unit 104, and the offset angle θofst(-) is held by a previous value holding unit 105 (described later). The cumulative offset angle calculation unit 104 calculates the cumulative offset angle θto based on the determination flag Fc, the value output from the switching unit 102, and the offset angle θofst(-) in the previous calculation cycle. The cumulative offset angle calculation unit 104 includes an adder 110 and a previous value holding unit 111.

[0068] The determination flag Fc, the offset angle θofst(-) in the previous calculation cycle, and the cumulative offset angle θto(-) in the previous calculation cycle are input to the previous value holding unit 111. When the state changes from not inputting the determination flag Fc in the previous calculation cycle to inputting the determination flag Fc in the previous calculation cycle, the previous value holding unit 111 controls the selection state so that the offset angle θofst(-) is output to the adder 110. The selection state of outputting the offset angle θofst(-) occurs at the moment when the state changes from not inputting the determination flag Fc to inputting the determination flag Fc.

[0069] When the state of not inputting the determination flag Fc in the previous calculation cycle does not change to inputting the determination flag Fc, the previous value holding unit 111 controls the selection state so that the cumulative offset angle θto(-) is output to the adder 110. The selection state of outputting the cumulative offset angle θto(-) occurs when the determination flag Fc is continuously input, when the determination flag Fc is not input, and when the state changes from inputting the determination flag Fc in the previous calculation cycle to not inputting the determination flag Fc in the previous calculation cycle.

[0070] In this way, when the state changes from not inputting the determination flag Fc in the previous calculation cycle to inputting the determination flag Fc in the previous calculation cycle, the offset angle θofst(-) is output to the adder 110. In addition, when the determination flag Fc is continuously input, when the determination flag Fc is not input, or when the state changes from inputting the determination flag Fc in the previous calculation cycle to not inputting the determination flag Fc in the previous calculation cycle, the cumulative offset angle θto(-) is output to the adder 110.

[0071] The value output from the switching unit 102 and the value held by the previous value holding unit 111 are input to the adder 110. The adder 110 calculates the cumulative offset angle θto by adding the value input from the switching unit 102 and the value held by the previous value holding unit 111. Therefore, when the state changes from not inputting the determination flag Fc in the previous calculation cycle to inputting the determination flag Fc in the previous calculation cycle, the target to be accumulated is changed to the offset angle θofst(-), and the process of reducing the offset angle θofst is performed for the offset angle θofst(-). Thus, the accumulation of the cumulative offset angle θto is reset.

[0072] The cumulative offset angle θto calculated by the adder 110, the offset angle θofst(-) in the previous calculation cycle held by the previous value holding unit 105, and the determination flag Fc are input to the switching unit 107. The cumulative offset angle θto is input to the first input N11 of the switching unit 107. The offset angle θofst(-) is input to the second input N12 of the switching unit 107.

[0073] When the determination flag Fc is input, the switching unit 107 controls the selection state so that the cumulative offset angle θto is output to the offset angle correction unit 108 as the uncorrected offset angle θofstb. When the determination flag Fc is not input, the switching unit 107 controls the selection state so that the offset angle θofst(-) is output to the offset angle correction unit 108 as the uncorrected offset angle θofstb. In the present embodiment, when the determination flag Fc is input to the switching unit 107, the switching unit 107 shifts to the state of executing the reduction process, and when the determination flag Fc is not input to the switching unit 107, the switching unit 107 shifts to the state of stopping the execution of the reduction process. Therefore, the switching unit 107 switches between the state of executing the reduction process and the state of stopping the execution of the reduction process according to whether the determination flag Fc is input.

[0074] The vehicle speed V, the target pinion angular velocity ωp*, the determination flag Fc, and the uncorrected offset angle θofstb output from the switching unit 107 are input to the offset angle correction unit 108. The offset angle correction unit 108 calculates the offset angle θofst based on the vehicle speed V, the target pinion angular velocity ωp*, the determination flag Fc, and the uncorrected offset angle θofstb.

[0075] As Figure 5 shown, the offset angle correction unit 108 includes a vehicle speed gain map calculation unit 121, a reduction amount map calculation unit 122, a minimum amount holding unit 123, a lower limit protection processing unit 124, a multiplier 125, a sign processing unit 126, a multiplier 127, a switching unit 128, and a switching unit 129.

[0076] The vehicle speed V is input to the vehicle speed gain map calculation unit 121. The vehicle speed gain map calculation unit 121 includes a map that defines the relationship between the vehicle speed V and the vehicle speed gain G. The vehicle speed gain map calculation unit 121 performs map calculation based on the vehicle speed V by referring to the map to obtain the vehicle speed gain G. The vehicle speed gain G is a gain for gradually reducing the offset angle θofst so that the target pinion angle θp* does not suddenly change due to the reduction of the offset angle θofst. Using the vehicle speed gain G, when the offset target pinion angle θp* is made to approach the non-offset target pinion angle θp*, the offset angle θofst can be reduced without giving discomfort to the driver. The vehicle speed gain map calculation unit 121 calculates the vehicle speed gain G having a larger absolute value as the vehicle speed V is higher.

[0077] The target pinion angular velocity ωp*, which is the change amount of the target pinion angle θp*, is input to the reduction amount map calculation unit 122. The reduction amount map calculation unit 122 includes a map that defines the relationship between the absolute value of the target pinion angular velocity ωp* and the reduction basic amount θdb of the reduction basic amount θd. The reduction amount map calculation unit 122 performs map calculation based on the absolute value of the target pinion angular velocity ωp* by referring to the map to obtain the reduction basic amount θdb. The reduction basic amount θdb is a component for gradually reducing the offset angle θofst so that the target pinion angle θp* does not suddenly change due to the reduction of the offset angle θofst. As the absolute value of the target pinion angular velocity ωp* is larger, that is, the change amount of the steering angle of the steering wheel 5 is larger, the reduction amount map calculation unit 122 calculates the reduction basic amount θdb with a larger absolute value.

[0078] The minimum amount holding unit 123 is a predetermined storage area of a memory (not shown), in which the minimum amount θdmin of the reduction amount θd is stored. The minimum amount θdmin is a component for reducing the offset angle θofst so that the offset angle θofst does not remain constant. The minimum amount θdmin is set to a value within the range indicated by experiments to ensure that even when the reduction amount θd output from the multiplier 125 is less than the minimum amount θdmin, the minimum amount is the reduction amount θd.

[0079] The reduction amount θd output from the multiplier 125 and the minimum amount θdmin output from the minimum amount holding unit 123 are input to the lower limit protection processing unit 124. The reduction amount θd is input to the first input M1 of the lower limit protection processing unit 124. The minimum amount θdmin is input to the second input M2 of the lower limit protection processing unit 124.

[0080] The lower limit protection processing unit 124 determines whether the reduction amount θd input to the first input M1 is equal to or greater than the minimum amount θdmin. Then, when the reduction amount θd input to the first input M1 is equal to or greater than the minimum amount θdmin, the lower limit protection processing unit 124 controls the selection state of the lower limit protection processing unit 124 so that the reduction amount θd input to the first input M1 is output as the final reduction amount θd. At the same time, when the reduction amount θd input to the first input M1 is less than the minimum amount θdmin, the lower limit protection processing unit 124 controls the selection state of the lower limit protection processing unit 124 so that the minimum amount θdmin is output as the final reduction amount θd. That is, the lower limit protection processing unit 124 operates to reduce the offset angle θofst by at least the minimum amount θdmin so that the offset angle θofst does not remain constant. Thus, it is possible to suppress the offset angle θofst from remaining constant.

[0081] The uncorrected offset angle θofstb output from the switching unit 107 is input to the sign processing unit 126. The sign processing unit 126 determines the sign of the uncorrected offset angle θofstb and calculates a value of "1" or "-1" corresponding to the sign. When the uncorrected offset angle θofstb has a positive value, the sign processing unit 126 calculates "1", and when the uncorrected offset angle θofstb has a negative value, the sign processing unit 126 calculates "-1".

[0082] The final reduction amount θd output from the lower limit protection processing unit 124 and the sign output from the sign processing unit 126 are input to the multiplier 127. The multiplier 127 calculates the processed reduction amount θdp as the correction amount by multiplying the final reduction amount θd by the sign output from the sign processing unit 126.

[0083] The uncorrected offset angle θofstb output from the switching unit 107 and the processed reduction amount θdp calculated by the multiplier 127 are input to the switching unit 128. The uncorrected offset angle θofstb is input to the first input M11 of the switching unit 128. The processed reduction amount θdp is input to the second input M12 of the switching unit 128. When the uncorrected offset angle θofstb is greater than the processed reduction amount θdp, the switching unit 128 controls the selection state so that the value obtained by subtracting the processed reduction amount θdp from the uncorrected offset angle θofstb is output as the unprocessed offset angle θofstp. Further, when the unprocessed offset angle θofstp is equal to or less than the processed reduction amount θdp, the switching unit 128 determines the processed reduction amount θdp as the uncorrected offset angle θofstb, and the switching unit 128 controls the selection state so that the value obtained by subtracting the processed reduction amount θdp from the uncorrected offset angle θofstb is output as the unprocessed offset angle θofstp. In this case, the unprocessed offset angle θofstp is "0". Thus, when the processed reduction amount θdp is greater than the unprocessed offset angle θofstp, the offset angle θofst is completely eliminated by reducing the offset angle θofst. In this case, the switching unit 128 operates so that the sign of the uncorrected offset angle θofstb is not inverted as a result of reflecting the reduction amount θd.

[0084] The uncorrected offset angle θofstb output from the switching unit 107, the unprocessed offset angle θofstp output from the switching unit 128, and the determination flag Fc are input to the switching unit 129. The uncorrected offset angle θofstb is input to the first input M21 of the switching unit 129. The unprocessed offset angle θofstp is input to the second input M22 of the switching unit 129. When the determination flag Fc is input, the switching unit 129 controls the selection state so that the uncorrected offset angle θofstb is output as the offset angle θofst. In this case, the process of reducing the offset angle θofst is stopped so that the offset target pinion angle θp* approaches the non-offset target pinion angle θp*. When the determination flag Fc is not input, the switching unit 129 controls the selection state so that the unprocessed offset angle θofstp is output as the offset angle θofst. In this case, the process of reducing the offset angle θofst is executed so that the offset target pinion angle θp* approaches the non-offset target pinion angle θp*.

[0085] In this way, when the unprocessed offset angle θofstp has a value other than zero, the offset angle correction unit 108 operates so that the reduction amount θd output from the lower limit protection processing unit 124 is reflected on the unprocessed offset angle θofstp. At the same time, when the unprocessed offset angle θofstp has a value of zero, the offset angle correction unit 108 operates so that the reduction amount θd output from the lower limit protection processing unit 124 is not reflected on the unprocessed offset angle θofstp. As a result, the offset angle θofst for correcting the converted angle θvg gradually changes.

[0086] Return reference Figure 4 , the converted angle θvg calculated by the steering operation angle ratio variable calculation unit 66 and the offset angle θofst calculated by the offset angle correction unit 108 are input to the adder 109. The adder 109 calculates the target pinion angle θp* by adding the offset angle θofst to the converted angle θvg. Therefore, the corrected target pinion angle θp* is calculated by adding the offset angle θofst to the converted angle θvg corresponding to the original target pinion angle. Therefore, when the vehicle speed V is a low vehicle speed including the stop state of the host vehicle, and when the steering wheel 3 is in the steering operation holding state or the steering wheel 3 is in the released state, the difference between the corrected target pinion angle θp* and the pinion angle θp is equal to or less than the difference between the converted angle θvg and the pinion angle θp. As a result, the reduction processing unit 67 performs the reduction processing. The target steering corresponding angle correction unit described in the claims corresponds to the adder 109. In addition, the offset angle calculation unit described in the claims corresponds to the basic offset angle calculation unit 101, the switching unit 102, the determination unit 103, the cumulative offset angle calculation unit 104, the previous value holding unit 105, the differentiator 106, and the switching unit 107.

[0087] The operations in this embodiment will be described below. When the driving state quantity such as the vehicle speed V indicates that the target pinion angle θp* does not change, or when the steering operation state quantity such as the steering operation torque Th indicates that the target pinion angle θp* does not change, when the force for turning the steering wheel 5 is balanced with the frictional force of the road surface, the pinion angle θp, that is, the steering angle, does not change. At this time, a difference may occur between the target pinion angle θp* and the pinion angle θp. In this regard, it is assumed that the state where the target pinion angle θp* does not change is a state where the demand for the steering motor 33 to apply a steering force to the steering wheel 5 to turn the steering wheel 5 is low.

[0088] In this embodiment, when the driving state quantity indicates that the target pinion angle θp* does not change, or when the steering operation state quantity indicates that the target pinion angle θp* does not change, a reduction process for reducing the drive current supplied to the steering motor 33 is performed. More specifically, when the vehicle speed V is a low vehicle speed including the stop state of the host vehicle, and when the steering wheel 3 is in the steering operation holding state or the steering wheel 3 is in the released state, the reduction process is performed. The reduction processing unit 67 calculates the corrected target pinion angle θp* by adding the offset angle θofst to the converted angle θvg corresponding to the original target pinion angle. Thereby, the difference between the target pinion angle θp* and the pinion angle θp is made smaller than the difference between the converted angle θvg and the pinion angle θp. In this case, the pinion angle feedback control unit 63 calculates a steering force command value Tp* having an absolute value smaller than the absolute value before the reduction process is performed. The current application control unit 64 calculates the steering side target current value It* of the steering motor 33 such that the steering side target current value It* becomes smaller. The steering side target current value It* is calculated based on the steering force command value Tp*. Therefore, the drive current supplied to the steering motor 33 is made smaller based on the steering side target current value It*. Thereby, it is possible to suppress the drive current supplied to the steering motor 33, which is generated when the pinion angle θp deviates from the target pinion angle θp* when the force for turning the steering wheel 5 is balanced with the frictional force of the road surface.

[0089] The effects of this embodiment will be described below.

[0090] (1) It is possible to suppress the drive current supplied to the steering motor 33, which is generated when the pinion angle θp deviates from the target pinion angle θp* when the force for turning the steering wheel 5 is balanced with the frictional force of the road surface. Therefore, power consumption can be reduced.

[0091] (2) Compared with the case where the vehicle speed V is a high vehicle speed, in the case where the vehicle speed V is a low vehicle speed, it may be difficult for the steering motor 33 to enter a state where the steering motor applies a steering force to the steering wheel 5 to steer the steering wheel 5. In particular, when the vehicle is stopped, even if the driving current is reduced by preferentially temporarily stopping the steering force applied by the steering motor 33 rather than continuing to apply the steering force by the steering motor 33, it can be assumed that the driver will hardly feel discomfort or any inconvenience. Therefore, in the case where the vehicle speed V is a low vehicle speed, the state in which the reduction process is executed can be made more appropriate.

[0092] (3) When the steering operation state quantity has a value indicating that the steering wheel 3 is in a steering operation holding state or the steering wheel 3 is in a released state, it is assumed that the driver does not input a steering to change the pinion angle θp to the steering operation unit 4. In this case, compared with a situation such as when the driver cuts the steering wheel, it may be difficult for the steering wheel 5 to enter a state where the steering wheel 5 is steered by receiving a steering force from the steering motor 33. Therefore, even if the driving current is reduced by preferentially temporarily stopping the steering force applied by the steering motor 33 rather than continuing to apply the steering force by the steering motor 33, it can be assumed that the driver will hardly feel discomfort or any inconvenience. From this point, in the case where the steering operation state quantity has a value indicating that the steering wheel 3 is in a steering operation holding state or the steering wheel 3 is in a released state, the state in which the reduction process is executed can be made more appropriate.

[0093] (4) When the target pinion angle θp* approaches the pinion angle θp, the difference between the target pinion angle θp* and the pinion angle θp can be reduced. (5) The frictional force of the road surface varies according to the road surface condition, and therefore, the difference between the target pinion angle θp* and the pinion angle θp varies each time. Therefore, it is assumed that the appropriate offset angle θofst for reducing the difference between the target pinion angle θp* and the pinion angle θp varies each time. In view of this, the offset angle correction unit 108 corrects the uncorrected offset angle θofstb in each calculation cycle. Thereby, the target pinion angle θp* can be appropriately corrected so that the target pinion angle θp* approaches the pinion angle θp.

[0094] (6) The offset angle correction unit 108 gradually reduces the offset angle θofst that makes the target pinion angle θp* approach the pinion angle θp by calculating the reduction amount θd for reducing the uncorrected offset angle θofstb. By gradually reducing the offset angle θofst, the target pinion angle θp* changes slowly. This enables a slow transition from the state in which the reduction process is executed to the state in which the reduction process is not executed.

[0095] (7) Since power consumption can be reduced, overheating of the steering operation control device 1 and the steering operation device 2 can be suppressed. In addition, since power consumption can be reduced, energy saving of the steering operation device 2 can be achieved.

[0096] The above-described embodiment can be modified as follows. In addition, as long as there is no technical inconsistency in the other embodiments described below, they can be combined with each other. For example, as the driving state quantity, instead of or in addition to the vehicle speed V, the yaw rate detected by the yaw rate sensor of the vehicle can be used, the distribution ratio between the distribution gains Ger and Gib can be used, or other state quantities can be used in combination.

[0097] For example, as the steering operation state quantity, instead of or in addition to the steering operation torque Th and the pinion angular velocity ωp, the steering operation angle θh or the steering operation angular acceleration can be used, or other state quantities can be used in combination. In addition, only one of the steering operation torque Th and the pinion angular velocity ωp can be used.

[0098] The determination unit 103 may generate a determination flag Fc only when it is determined that the vehicle speed V is a low vehicle speed including the host vehicle stop state. In addition, the determination flag Fc may be generated only when it is determined that the steering wheel 3 is in the steering operation holding state, or the determination flag Fc may be generated only when it is determined that the steering wheel 3 is in the released state. That is, the determination unit 103 may generate the determination flag Fc when at least one of the driving state quantity and the steering operation state quantity is a state quantity indicating that the target pinion angle θp* does not change.

[0099] The determination unit 103 generates a determination flag Fc based on driving state quantities such as the vehicle speed V, the steering operation torque Th, and the pinion angular velocity ωp, and the steering operation state quantity. However, the present invention is not limited thereto. For example, in addition to these state quantities, the determination unit 103 may also generate the determination flag Fc based on a self-driving state signal indicating the operation state of the automatic driving control function and a gear state signal indicating the position state of the gear. In this case, the determination unit 103 further generates the determination flag Fc under the condition that the operation state of the self-driving control function is not turned on and the gear is not within the reverse gear range. On the other hand, in the case where the operation state of the self-driving control function is turned on or the shift position is within the reverse gear range, the determination unit 103 does not generate a determination flag Fc. Thus, it is possible to suppress the execution of the self-driving control from being interfered by the reduction process. In addition, in the case where the shift position is within the reverse gear range, a so-called rear guide monitoring function may be provided according to the product specifications. The rear guide monitoring function is a function that assists the backward operation of the vehicle such as reverse parking or parallel parking, so that a camera device is attached to the rear of the vehicle, and the video image captured by the camera device and the predicted route of the vehicle are displayed on a display provided inside the vehicle compartment. When performing the backward operation at a low vehicle speed based on this function, the driver may feel uncomfortable when the reduction process is performed. In the case where the determination flag Fc is not generated when the gear is within the reverse gear range, it is possible to suppress the driver from feeling uncomfortable.

[0100] For the case where the steering wheel 3 is in the released state and the case where the steering wheel 3 is in the steering operation holding state, the determination unit 103 may output different determination flags Fc. In this case, for example, the basic offset angle calculation unit 101 may calculate different offset angles θofst in the released state and the steering operation holding state by calculating different basic offset angles θo1, etc. for the released state and the steering operation holding state.

[0101] The switching units 102, 107, 129, and the lower limit protection processing unit 124 each use the same value as the value for determining which signal to output from the signals input to the first input and the second input, but they may use different values. For example, the determination unit 103 may set a vehicle speed threshold V0 used when determining that the vehicle speed V is a low vehicle speed including the stop state of the host vehicle in a state where the determination flag Fc is not output, such that the vehicle speed threshold V0 is greater than the vehicle speed threshold V0 used when determining the state of outputting the determination flag Fc.

[0102] A constant value such as “0” can be input into the second input N12 of the switching unit 107. The adder 109 calculates the target pinion angle θp* by adding the offset angle θofst to the converted angle θvg. However, depending on the setting of the sign of the offset angle θofst, the adder 109 can calculate the target pinion angle θp* by subtracting the offset angle θofst from the converted angle θvg.

[0103] In addition to the converted angle θvg, the basic offset angle calculation unit 101 can also calculate the basic offset angle θo1 based on the pinion angle θp. The reduction processing unit 67 reduces the drive current by performing reduction processing on the target pinion angle θp*. However, the reduction processing unit 67 can reduce the drive current by performing reduction processing on the steering force command value Tp*, or can reduce the drive current by performing reduction processing on the steering-side target current value It*.

[0104] The reduction processing unit 67 can be added as a component of the steering operation control unit 50. This is effective when calculating the target reaction force torque T* to follow the pinion angle θp. The offset angle correction unit 108 may not have the configuration of the lower limit protection processing unit 124. In addition to this, the offset angle correction unit 108 can be used to substantially reduce the offset angle θofst by a minimum amount θdmin. In this case, the vehicle speed gain map calculation unit 121 and the reduction amount map calculation unit 122 can be omitted. Furthermore, the offset angle correction unit 108 can reduce the offset angle θofst by multiplying the uncorrected offset angle θofstb by a gain. The gain in this case can be determined considering a state similar to that of the vehicle speed gain map calculation unit 121 and the reduction amount map calculation unit 122.

[0105] The offset angle correction unit 108 reduces the offset angle θofst by adding the processed reduction amount θdp that varies according to the vehicle speed V and the pinion angular velocity ωp to the uncorrected offset angle θofstb, but the present invention is not limited to this. For example, when the vehicle speed V is a low vehicle speed including the stopped state of the host vehicle, and when the steering wheel 3 is in the steering operation holding state or the steering wheel 3 is in the released state, the offset angle correction unit 108 can reduce the offset angle θofst by adding a constant value to the uncorrected offset angle θofstb.

[0106] When the vehicle speed V is not a low vehicle speed including the stopped state of the host vehicle, or when the steering wheel 3 is not in the steering operation holding state or in the released state, the offset angle correction unit 108 may not reduce the offset angle θofst.

[0107] The reduction processing unit 67 may be configured without the offset angle correction unit 108. In this case, the uncorrected offset angle θofstb is output to the adder 109. In addition to the vehicle speed gain corresponding map calculation unit 121 and the reduction map amount calculation unit 122, the offset angle correction unit 108 may additionally include a calculation unit that considers other states. Further, the offset angle correction unit 108 may additionally include a calculation unit that considers other states, rather than only considering either one or both of the vehicle speed gain map calculation unit 121 and the reduction amount map calculation unit 122. Other states may be, for example, the current angle of the offset angle θofst, i.e., the remaining amount. In this case, as the remaining amount becomes smaller, the degree of reduction should become gentler. Further, as other states, the offset angle θofst(-) in the previous calculation cycle may be used.

[0108] In the vehicle speed gain map calculation unit 121, the change mode of the vehicle speed gain G can be appropriately modified. For example, the vehicle speed V can be classified into a low vehicle speed, a medium vehicle speed, a high vehicle speed, etc., and different change modes of the vehicle speed gain G can be set for each vehicle speed. For example, the vehicle speed gain G is made constant in the case of a low vehicle speed.

[0109] In the reduction amount map calculation unit 122, the change mode of the reduction basic amount θdb can be appropriately modified. For example, the pinion angular velocity ωp can be classified into a low steering speed, a medium steering speed, a high steering speed, etc., and different change modes of the reduction basic amount θdb can be set for each steering speed. For example, the reduction basic amount θdb is made constant in the case of a low steering speed.

[0110] The minimum amount θdmin having a fixed value may be stored in the minimum amount holding unit 123. Further, the minimum amount holding unit 123 may calculate a variable minimum amount θdmin based on the input value. For example, the target pinion angle θp* and the vehicle speed V are input to the minimum amount holding unit 123. The minimum amount holding unit 123 includes a first map that defines the relationship between the target pinion angle θp* and a first component and a second map that defines the relationship between the vehicle speed V and a second component. The minimum amount holding unit 123 performs map calculation based on the target pinion angle θp* by referring to the first map to obtain the first component. Further, the minimum amount holding unit 123 performs map calculation based on the vehicle speed V to obtain the second component. The minimum amount holding unit 123 calculates the value obtained by multiplying the first component by the second component as the minimum amount θdmin. The minimum amount θdmin calculated in this way is output to the lower limit protection processing unit 124.

[0111] If the accumulation of the offset angle θofst is not considered, the adder 110 can be omitted in the reduction processing unit 67. The control of the steering motor 33 can be performed based on the movement amount of the rack shaft 22 by directly detecting the movement amount instead of controlling the pinion angle θp. In this case, various control amounts related to the pinion angle θp in the above-described embodiment are replaced with various control amounts related to the movement amount of the rack shaft 22.

[0112] In addition to the vehicle speed V, the steering operation angle ratio variable calculation unit 66 can also change the steering operation angle ratio according to the yaw rate detected by the yaw rate sensor of the vehicle. When the steering operation reaction force calculation unit 55 calculates the steering operation reaction force component Tb*, the steering operation reaction force calculation unit 55 should at least use the steering operation torque Th, and the steering operation reaction force calculation unit 55 may not use the vehicle speed V or may use other elements in combination.

[0113] In the above-described embodiment, the steering operation angle ratio can be fixed. In this case, the steering operation angle ratio variable calculation unit 66 can be omitted. In the above-described embodiment, as the steering motor 33, for example, the steering motor 33 can be arranged coaxially with the rack shaft 22, or the steering motor 33 can be connected to the rack shaft 22 via a belt reducer using a ball screw mechanism.

[0114] In the above-described embodiment, the steering operation control device 1 can be constituted by a processing circuit, which includes: 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) configured to execute at least one of various processes, or 3) a combination of the above two. The processor includes a CPU and a memory such as a RAM or a ROM, and the program code or command configured to cause the CPU to execute the process is stored in the memory. The memory (i.e., the non-transitory computer-readable medium) includes all available media that can be accessed by a general or dedicated computer.

[0115] In the above-described embodiment, the steering operation device 2 has a linkless structure in which the steering operation unit 4 is always mechanically separated from the steering unit 6. However, the present invention is not limited to this. As Figure 1 indicated by the alternating long and short dashed lines, the steering operation device 2 has a structure in which the steering operation unit 4 is mechanically separated from the steering unit 6 by a clutch 25.

Claims

1. A steering operation control device (1) configured to control a steering operation device (2) as a controlled object, the steering operation device (2) having a structure that cuts off power transmission between a steering operation unit (4) and a steering unit (6), the steering operation unit (4) being connected to a steering wheel (3), the steering unit (6) being configured to steer a steering wheel (5) in response to a steering operation input to the steering operation unit (4), wherein the steering operation control device (1) is characterized by including a central processing unit configured to: Control the operation of a steering motor (33) configured to apply a steering force to the steering unit (6), the steering force being a force for steering the steering wheel (5); Calculate a steering target current value as a target value of a drive current to be supplied to the steering motor (33) by performing steering angle feedback control so that an actual steering corresponding angle follows a target steering corresponding angle that is a target value of the steering angle of the steering wheel (5); Control the operation of the steering motor (33) based on the steering target current value; Perform a reduction process for reducing the drive current to be supplied to the steering motor (33); Perform the reduction process when at least one of a running state quantity and a steering operation state quantity is a state quantity indicating that the target steering corresponding angle does not change, the running state quantity indicating the running state of the host vehicle, and the steering operation state quantity indicating the steering operation state of the host vehicle; Calculate the target steering corresponding angle according to the steering operation input to the steering operation unit (4); Make the target steering corresponding angle approach the actual steering corresponding angle in the reduction process; Calculate an offset angle based on the target steering corresponding angle and the actual steering corresponding angle, the offset angle being an amount for making the target steering corresponding angle approach the actual steering corresponding angle; Correct the target steering corresponding angle by adding the offset angle to the target steering corresponding angle or subtracting the offset angle from the target steering corresponding angle; Calculate the steering target current value based on the corrected target steering corresponding angle; Correct the offset angle calculated in the current calculation cycle based on the running state quantity and the steering operation state quantity; And Correct the target steering corresponding angle by adding the corrected offset angle to the target steering corresponding angle or subtracting the corrected offset angle from the target steering corresponding angle.

2. The steering operation control device (1) according to claim 1, characterized in that, The central processing unit is configured to: change a correction amount based on at least one of the running state quantity and the steering operation state quantity to reduce the offset angle.

3. A steering operation control device (1) configured to control a steering operation device (2) as a controlled object, the steering operation device (2) having a structure that cuts off power transmission between a steering operation unit (4) and a steering unit (6), the steering operation unit (4) being connected to a steering wheel (3), the steering unit (6) being configured to steer a steering wheel (5) in response to a steering operation input to the steering operation unit (4), the steering operation control device (1) being characterized by including a central processing unit configured to: Control the operation of a steering motor (33) configured to apply a steering force to the steering unit (6), the steering force being a force for steering the steering wheel (5); Calculate a steering target current value as a target value of a drive current to be supplied to the steering motor (33) by performing steering angle feedback control so that an actual steering corresponding angle follows a target steering corresponding angle that is a target value of the steering angle of the steering wheel (5); Control the operation of the steering motor (33) based on the steering target current value; Perform a reduction process of reducing the drive current to be supplied to the steering motor (33); Perform the reduction process when at least one of a driving state quantity and a steering operation state quantity is a state quantity indicating that the target steering corresponding angle does not change, the driving state quantity indicating the driving state of the host vehicle, and the steering operation state quantity indicating the steering operation state of the host vehicle; Calculate the target steering corresponding angle according to the steering operation input to the steering operation unit (4); In the reduction process, make the target steering corresponding angle approach the actual steering corresponding angle; Calculate an offset angle based on the target steering corresponding angle and the actual steering corresponding angle, the offset angle being an amount for making the target steering corresponding angle approach the actual steering corresponding angle; Correct the target steering corresponding angle by adding the offset angle to the target steering corresponding angle or subtracting the offset angle from the target steering corresponding angle; Calculate the steering target current value based on the corrected target steering corresponding angle; In a state where the reduction process is being performed, when at least one of the driving state quantity and the steering operation state quantity is a state quantity indicating that the target steering corresponding angle changes, the central processing unit is configured to end the execution of the reduction process; And When the state of performing the reduction process transitions to a state of not performing the reduction process, the central processing unit is configured to gradually reduce the absolute value of the offset angle.

4. The steering operation control device (1) according to any one of claims 1 to 3, characterized in that, When the vehicle speed as the driving state quantity is a low vehicle speed including the stop state of the host vehicle, the central processing unit is configured to determine that the driving state quantity corresponds to a state quantity indicating that the target steering corresponding angle does not change, and the central processing unit is configured to perform the reduction process.

5. The steering operation control device (1) according to any one of claims 1 to 3, characterized in that, In the case where the value of the steering operation state quantity indicates that the steering wheel (3) is in the steering operation holding state or the steering wheel (3) is in the hand - off state, the central processing unit is configured to determine that the steering operation state quantity corresponds to a state quantity indicating that the target steering corresponding angle does not change, and the central processing unit is configured to perform the reduction process.

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