Steering control device

Abstract

To provide a turning control device that can suppress discomfort given to a driver due to change of a vehicle speed for controlling.SOLUTION: A PU 72 calculates target values of turning angles of turning wheels 44 on the basis of a steering angle which is a rotation angle of a steering wheel 12 and a vehicle speed. The PU 72 determines that a state where the steering angle does not vary is a steering-retaining state, and switches the vehicle speed that is used for calculating the target value of the turning angle to a fixed vehicle speed. When the steering angle varies, the PU 72 switches the vehicle speed that is used for calculating the target value from the fixed vehicle speed to a vehicle speed which is renewed accordingly. The PU 72 gradually changes the target value, when switching the vehicle speed.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, Patent Document 1 listed below describes a steering control device that performs feedback control of the steering angle to a target steering angle. This device calculates the target steering angle according to the steering angle. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent Publication No. 2021-30838 Summary of the Invention [Problem to be solved by the invention]

[0004] Incidentally, the control vehicle speed may be used as an input to calculate an operation variable, such as the target steering angle, which is a variable for determining the operation amount of the steering system. Furthermore, several variables may be selectively used as the control vehicle speed. When the variable used as the control vehicle speed is changed, the control vehicle speed may suddenly change. In this case, the operation amount of the steering system may suddenly change, which may cause the driver to feel uncomfortable. [Means for solving the problem]

[0005] The means for solving the above problems and their effects will be described below. 1. A steering control device applied to a vehicle equipped with a steering system in which the relationship between a steering angle and a turning angle can be changed, the steering angle being the rotation angle of a steering wheel and the turning angle being the turning angle of steered wheels of the vehicle, the steering control device being configured to execute an operation variable calculation process, a selection process, an operation process, a gradual change process, and an operation amount calculation process, the operation variable calculation process being a process of variably setting the value of an operation variable for determining the operation amount of the steering system using a control vehicle speed as an input, the operation amount being an amount for controlling the turning angle, the selection process being a process of selecting a control vehicle speed from a plurality of control vehicle speeds to be used as an input for the operation variable calculation process, the operation process being a process of operating the steering system in accordance with the operation amount, the gradual change process being a process of gradually changing, when the control vehicle speed selected by the selection process is changed, a change in the value of the operation variable caused by a change in the value of the control vehicle speed accompanying the change, and the operation amount calculation process being a process of calculating the operation amount using as an input the value of the operation variable gradually changed by the gradual change process.

[0006] In the above configuration, when the control vehicle speed selected by the selection process is changed, the control vehicle speed also changes accordingly. This may result in a large change in the value of the operation variable. Therefore, in the above configuration, the change in the value of the operation variable caused by the change in the control vehicle speed is gradually changed. This makes it possible to prevent a sudden change in the operation amount of the steering system caused by the change in the control vehicle speed. Therefore, it is possible to prevent the driver from feeling uncomfortable due to the change in the control vehicle speed.

[0007] 2. A steering control device as described in 1 above, configured to execute a change detection process that detects a change in the control vehicle speed selected by the selection process, and the gradual change process is a process that gradually changes the value of the operating variable when the change is detected by the change detection process.

[0008] In the above configuration, the gradual change of the value of the operating variable is triggered by the change detection process, and therefore, it is possible to prevent the gradual change of the value of the operating variable from being caused by the gradual change process even when the control vehicle speed has not been changed.

[0009] 3. A steering control device as described in 1 or 2 above, configured to execute an angular velocity acquisition process to acquire the value of an angular velocity variable which is a variable indicating the rate of change of the steering angle, wherein the gradual change process includes a process of variably setting a gradual change rate from the value of the operating variable corresponding to the control vehicle speed before the change to the value of the operating variable corresponding to the control vehicle speed after the change according to the value of the angular velocity variable, and a process of setting the gradual change rate when the value of the angular velocity variable is large to be equal to or higher than the gradual change rate when the value of the angular velocity variable is small.

[0010] When the magnitude of the steering angular velocity is large, the driver desires to quickly change the steering to a desired state. The desired state is considered to correspond to the state at the end of the gradual change process. Therefore, by increasing the gradual decrease rate when the magnitude of the steering angular velocity is large, the desired state can be reached more quickly when the magnitude of the steering angular velocity is large. Therefore, the driver can have a good steering feeling.

[0011] 4. A steering control device as described in any one of 1 to 3 above, configured to execute a vehicle speed acquisition process for acquiring a vehicle speed, which is the traveling speed of the vehicle, wherein the gradual change process is a process for variably setting a gradual change speed from the value of the operating variable corresponding to the control vehicle speed before the change to the value of the operating variable corresponding to the control vehicle speed after the change, according to the vehicle speed, and includes a process for setting the gradual change speed when the vehicle speed is high to be equal to or higher than the gradual change speed when the vehicle speed is low.

[0012] When the vehicle speed is high, the rate of change of the operating variable is high, but the driver tends to feel less uncomfortable compared to when the vehicle speed is low. Therefore, in the above configuration, by increasing the gradual change rate when the vehicle speed is high, the value of the operating variable can be set to a value corresponding to the changed control vehicle speed as quickly as possible while suppressing the driver from feeling uncomfortable.

[0013] 5. A steering control device as described in any one of 1 to 4 above, configured to execute a vehicle speed acquisition process for acquiring a vehicle speed, which is the traveling speed of the vehicle, and a storage process for storing and retaining the vehicle speed acquired at a predetermined timing by the vehicle speed acquisition process as a fixed vehicle speed, wherein the plurality of control vehicle speeds include the vehicle speed acquired each time by the vehicle speed acquisition process and the fixed vehicle speed, and the gradual change process includes a process for gradually changing the value of the operating variable corresponding to the control vehicle speed before the change to the value of the operating variable corresponding to the control vehicle speed after the change, when the vehicle speed selected by the selection process is changed from the fixed vehicle speed to the vehicle speed acquired each time.

[0014] When the vehicle speed is changed from a fixed speed to a vehicle speed acquired on an ongoing basis, the control vehicle speed tends to change significantly. Therefore, if the control vehicle speed is not changed gradually when the vehicle speed is changed from a fixed speed to a vehicle speed acquired on an ongoing basis, the value of the operation variable will change suddenly, which is likely to cause discomfort to the driver. Therefore, the gradual change process is particularly useful in the above configuration.

[0015] 6. A steering control device as described in 5 above, configured to execute a steering determination process for determining whether or not the steering angle is being maintained, wherein the selection process includes a steering upon holding process for changing the control vehicle speed from the vehicle speed acquired each time to the fixed vehicle speed, with the timing of transition from a state determined by the steering upon holding process to a state determined to be the steering upon holding, as the predetermined timing, and a steering release process for changing the control vehicle speed from the fixed vehicle speed to the vehicle speed acquired each time when the state determined by the steering upon holding process to a state determined to be the steering upon holding is transitioned from a state determined to be the steering upon holding to a state determined not to be the steering upon holding while the steering upon holding process is being executed.

[0016] In a fixed steering state, if the value of the operation variable changes due to acceleration or deceleration of the vehicle speed, the driver may perform steering unintentionally. Therefore, in the above configuration, in the fixed steering state, the operation variable is calculated based on a fixed vehicle speed. Then, when the fixed steering state is released, the fixed steering release process switches the control vehicle speed to the vehicle speed acquired each time. This makes it possible to calculate an appropriate value of the operation variable according to the vehicle speed.

[0017] 7. A steering control device as described in 5 or 6 above, configured to execute a boundary determination process to determine whether or not the state is in a boundary state where the difference between the magnitude of the value of a steering angle variable and an upper limit value is equal to or less than a predetermined value, wherein the steering angle variable is a variable indicating the steering angle, and the selection process includes an end process that changes the control vehicle speed from the vehicle speed obtained each time to the fixed vehicle speed, with the predetermined timing being the timing of transition from a state determined by the boundary determination process to a state determined to be the boundary state, and an end release process that changes the control vehicle speed from the fixed vehicle speed to the vehicle speed obtained each time when the state transitions from a state determined by the boundary determination process to a state determined not to be the boundary state while the end process is being executed.

[0018] In a boundary state, if the value of the operation variable changes due to acceleration or deceleration of the vehicle speed, the driver may perform steering unintended by the driver. Therefore, in the above configuration, in the boundary state, the value of the operation variable is calculated based on a fixed vehicle speed. Then, when the boundary state is resolved, the end release process switches the control vehicle speed to the vehicle speed acquired each time. This makes it possible to calculate an appropriate value of the operation variable according to the vehicle speed.

[0019] 8. A steering control device as described in any one of 1 to 4 above, wherein the plurality of control vehicle speeds include a first wheel speed which is the speed of a first wheel of the vehicle, and a second wheel speed which is the speed of a second wheel of the vehicle, and the selection process includes a process of selecting the second wheel speed as the control vehicle speed when an abnormality is detected in one of the wheel speeds of the vehicle while the first wheel speed is selected as the control vehicle speed.

[0020] In the above configuration, if an abnormality is detected in one of the vehicle's wheel speeds, the second wheel speed is selected. This allows the value of the manipulated variable to be calculated using the second wheel speed as the control vehicle speed. Furthermore, a sudden change in the value of the manipulated variable caused by changing the control vehicle speed from the first wheel speed to the second wheel speed is suppressed by the gradual change process.

[0021] 9. A steering control device according to any one of 1 to 8 above, wherein the steering system includes a steering actuator that steers the steered wheels, the operation amount is the operation amount of the steering actuator, and the operation variable is a target steering angle that is a target value of the steering angle.

[0022] According to the above configuration, the gradual change process can suppress a sudden change in the target steering angle due to a change in the control vehicle speed. 10. The steering control device according to claim 9, wherein the gradual change processing includes processing for correcting the target steering angle output by the operation variable calculation processing in accordance with the changed control vehicle speed.

[0023] In the above configuration, the target steering angle output by the operation variable calculation process is corrected, so that a sudden change in the target steering angle can be reliably suppressed. 11. A steering control device as described in claim 9, wherein the gradual change processing includes processing for gradually changing the control vehicle speed used by the operation variable calculation processing to calculate the target steering angle from the control vehicle speed before the change to the control vehicle speed after the change when the control vehicle speed is changed by the selection processing.

[0024] In the above configuration, by gradually changing the control vehicle speed from the pre-change control vehicle speed to the changed control vehicle speed, it is possible to suppress a sudden change in the target steering angle due to a change in the control vehicle speed. [Brief explanation of the drawings]

[0025] [Figure 1] 1 is a diagram showing a configuration of a vehicle according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing a part of the processing executed by the steering control device according to the embodiment. [Figure 3] 3 is a flowchart showing a procedure of processing executed by the steering control device according to the embodiment. [Figure 4] 3 is a flowchart showing a procedure of processing executed by the steering control device according to the embodiment. [Figure 5] 6 is a flowchart showing the procedure of processing executed by a steering control device according to a second embodiment. [Figure 6] 10 is a flowchart showing the procedure of processing executed by a steering control device according to a third embodiment. [Figure 7] FIG. 10 is a block diagram showing part of the processing executed by a steering control device according to a fourth embodiment. [Figure 8] 3 is a flowchart showing a procedure of processing executed by the steering control device according to the embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0026] First Embodiment A first embodiment of the steering control device will be described below with reference to the drawings. "Prerequisite configuration" As shown in Fig. 1, vehicle steering device 10 is a steer-by-wire type steering device. Steering device 10 includes a reaction force actuator Ar and a turning actuator At. Steering device 10 of this embodiment has a structure in which the power transmission path between steering wheel 12 and steered wheels 44 is mechanically disconnected.

[0027] A steering shaft 14 is connected to the steering wheel 12. The reaction force actuator Ar is an actuator for applying a steering reaction force to the steering wheel 12. The steering reaction force is a force that acts in the opposite direction to the direction of operation of the steering wheel 12 by the driver. By applying the steering reaction force to the steering wheel 12, it is possible to give the driver an appropriate sense of responsiveness. The reaction force actuator Ar includes a reduction mechanism 16, a reaction force motor 20, and a reaction force inverter 22.

[0028] The reaction motor 20 is a three-phase brushless motor. The rotation shaft of the reaction motor 20 is connected to the steering shaft 14 via a reduction gear mechanism 16. Meanwhile, steering shaft 40 extends along the vehicle width direction, which is the left-right direction in Figure 1. Left and right steered wheels 44 are connected to both ends of steering shaft 40 via tie rods 42. The linear movement of steering shaft 40 changes the steering angle of steered wheels 44.

[0029] Steering actuator At includes speed reduction mechanism 56, steering motor 60, and steering inverter 62. Steering motor 60 is a three-phase brushless motor. The rotating shaft of steering motor 60 is connected to pinion shaft 52 via speed reduction mechanism 56. Pinion teeth of pinion shaft 52 mesh with rack teeth 54 of steering shaft 40. Pinion shaft 52 and steering shaft 40 provided with rack teeth 54 form rack-and-pinion mechanism 50. Torque of steering motor 60 is applied as a steering force to steering shaft 40 via pinion shaft 52. In response to the rotation of steering motor 60, steering shaft 40 moves along the vehicle width direction, which is the left-right direction in FIG. 1 .

[0030] The steering device 10 is equipped with a steering ECU 70. The steering ECU 70 controls steering wheel 12. The steering ECU 70 operates a reaction force actuator Ar to control the steering reaction force as a control variable of the control object. Fig. 1 shows an operation signal MSs to reaction force inverter 22. The steering ECU 70 also controls steered wheels 44. The steering ECU 70 operates a steering actuator At to control the steering angle of steered wheels 44 as a control variable of the control object. Fig. 1 shows an operation signal MSt to steering inverter 62.

[0031] In order to control the control variable, steering ECU 70 refers to steering torque Th, which is input torque to steering shaft 14, detected by torque sensor 80. Also, steering ECU 70 refers to rotation angle θa of the rotation shaft of reaction force motor 20, detected by rotation angle sensor 82. Also, steering ECU 70 refers to currents iu1, iv1, iw1 flowing through reaction force motor 20. Currents iu1, iv1, iw1 are quantified as voltage drops across shunt resistors provided in each leg of reaction force inverter 22. In order to control the control variable, steering ECU 70 refers to rotation angle θb of the rotation shaft of turning motor 60, detected by rotation angle sensor 84. Also, steering ECU 70 refers to currents iu2, iv2, iw2 flowing through turning motor 60. Currents iu2, iv2, iw2 are quantified as voltage drops across shunt resistors provided in each leg of turning inverter 62.

[0032] The steering ECU 70 also refers to the wheel speeds ωwa to ωwd output from the braking ECU 90. The braking ECU 90 acquires the wheel speed ωwa of the right steered wheel 44 detected by the wheel speed sensor 100. The braking ECU 90 also acquires the wheel speed ωwb of the left steered wheel 44 detected by the wheel speed sensor 102. The braking ECU 90 also acquires the wheel speed ωwc of the right wheel 46 detected by the wheel speed sensor 104. The braking ECU 90 also acquires the wheel speed ωwd of the left wheel 46 detected by the wheel speed sensor 106.

[0033] The steering ECU 70 includes a PU 72, a storage device 74, and peripheral circuits 76. The PU 72 is a software processing device such as a CPU, a GPU, and a TPU. Here, the peripheral circuits 76 include a circuit that generates a clock signal that regulates internal operation, a power supply circuit, a reset circuit, etc. The steering ECU 70 controls the control amount by the PU 72 executing a program stored in the storage device 74.

[0034] "control" FIG. 2 shows part of the processing executed by the steering ECU 70. The vehicle speed calculation process M10 is a process for calculating the vehicle speed V based on the wheel speeds ωwa to ωwd.

[0035] The steering angle calculation process M12 is a process that uses the rotation angle θa as an input and calculates the steering angle θh, which is the rotation angle of the steering wheel 12. The steering angle calculation process M12 includes a process that converts the rotation angle θa into an integrated angle that includes a range exceeding 360°, for example, by counting the number of rotations of the reaction force motor 20 from a steering neutral position, which is the position of the steering wheel 12 when the vehicle is traveling straight. The steering angle calculation process M12 includes a process that calculates the steering angle θh by multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotational speed ratio of the speed reduction mechanism 16. Note that the steering angle θh may be positive when it is an angle to the right of the steering neutral position, and negative when it is an angle to the left of the steering neutral position, for example.

[0036] Pinion angle calculation process M14 is a process that uses rotation angle θb as an input and calculates pinion angle θp, which is the rotation angle of pinion shaft 52. Pinion angle calculation process M14 includes, for example, a process of counting the number of rotations of steering motor 60 from a rack neutral position, which is the position of steering shaft 40 when the vehicle is traveling straight, and converting it into an integrated angle that includes a range exceeding 360°. Pinion angle calculation process M14 includes a process of multiplying the converted integrated angle by a conversion coefficient based on the rotational speed ratio of speed reduction mechanism 56 to calculate pinion angle θp, which is the actual rotation angle of pinion shaft 52. Note that pinion angle θp may be positive when it is an angle to the right of the rack neutral position and negative when it is an angle to the left of the rack neutral position, for example. Steering motor 60 and pinion shaft 52 are linked via speed reduction mechanism 56. For this reason, there is a correlation between rotation angle θb of steering motor 60 and pinion angle θp. Using this correlation, pinion angle θp can be found from rotation angle θb of steering motor 60. Furthermore, pinion shaft 52 is meshed with steered shaft 40. Therefore, there is also a correlation between pinion angle θp and the amount of movement of steered shaft 40. In other words, pinion angle θp is a value that reflects the steering angle of steered wheels 44.

[0037] The steering reaction force command value calculation process M16 is a process that calculates a steering reaction force command value Tr* according to the steering reaction force to be applied to the steering wheel 12 using the steering torque Th, vehicle speed V, and pinion angle θp as inputs. The steering reaction force command value calculation process M16 includes a process that particularly increases the magnitude of the steering reaction force command value Tr* when the magnitude of the pinion angle θp is near its maximum value. This is intended to prevent the driver from displacing the steering wheel 12 in a direction that increases the pinion angle θp. The steering reaction force command value Tr* is actually a command value for the reaction force motor 20. The steering reaction force is calculated by multiplying the steering reaction force command value Tr* by a coefficient according to the reduction ratio of the reduction mechanism 16.

[0038] The reaction force operation process M18 is a process that receives the steering reaction force command value Tr*, currents iu1, iv1, iw1, and rotation angle θa as inputs and outputs an operation signal MSs for the reaction force inverter 22. The reaction force operation process M18 includes a process of calculating dq-axis current command values ​​based on the steering reaction force command value Tr*. The reaction force operation process M18 also includes a process of calculating dq-axis currents based on the currents iu1, iv1, iw1 and the rotation angle θa. The reaction force operation process M18 then includes a process of calculating an operation signal MSs for operating the reaction force inverter 22 so that the dq-axis currents become command values.

[0039] The target pinion angle calculation process M20 is a process for calculating the target pinion angle θp*0 using the steering angle θh and the vehicle speed V as inputs. The offset amount calculation process M22 is a process for calculating an offset amount Δθp of the target pinion angle θp*0 using the steering angle θh and the vehicle speed V as inputs.

[0040] The offset process M24 is a process for calculating the target pinion angle θp* by subtracting the offset amount Δθp from the target pinion angle θp*0. The pinion angle feedback process M26 is a process for calculating a steering torque command value Tt*, which is a command value for the torque of the steering motor 60, in order to feedback-control the pinion angle θp to the target pinion angle θp*.

[0041] The steering operation process M28 is a process that receives as input the steering torque command value Tt*, currents iu2, iv2, iw2, and rotation angle θb, and outputs an operation signal MSt for the steering inverter 62. The steering operation process M28 includes a process that calculates current command values ​​for the dq axes based on the steering torque command value Tt*. The steering operation process M28 also includes a process that calculates currents for the dq axes based on the currents iu2, iv2, iw2 and the rotation angle θb. The steering operation process M28 then includes a process that calculates an operation signal MSt for operating the steering inverter 62 so that the currents for the dq axes become the command values.

[0042] Fig. 3 shows the procedure of the target pinion angle calculation process M20. The process shown in Fig. 3 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval. Note that, hereinafter, the step numbers of each process are represented by numbers preceded by "S."

[0043] In the series of processes shown in FIG. 3, the PU 72 first acquires the steering angular velocity ωh and the vehicle speed V (S10). The steering angular velocity ωh is a first-order time differential value of the steering angle θh. The steering angular velocity ωh is calculated by the PU 72 based on the steering angle θh. Then, the PU 72 determines whether the flag F is "1" (S12). If the flag F is "1", this means that the vehicle speed V used to calculate the target pinion angle θp*0 is a fixed vehicle speed V0. If the flag F is "0", this means that the vehicle speed V, which is updated each time, is used to calculate the target pinion angle θp*0.

[0044] When the PU 72 determines that the flag F is "0" (S12: NO), it determines whether the state in which the absolute value of the steering angular velocity ωh is equal to or less than the threshold value ωhL has continued for a predetermined time (S14). This process is a process for determining whether the driver is in a so-called fixed steering state in which the steering wheel 12 is fixed. When the PU 72 determines that this has continued for the predetermined time (S14: YES), it assigns "1" to the flag F and assigns the vehicle speed V obtained in the process of S10 to the fixed vehicle speed V0 (S16).

[0045] On the other hand, when the PU 72 determines that the flag F is "1" (S12: YES), it determines whether the absolute value of the steering angular velocity ωh is greater than a threshold value ωhH (S18). The threshold value ωhH is a value equal to or greater than the threshold value ωhL. The threshold value ωhH is preferably set to a value greater than the threshold value ωhL. When the PU 72 determines that the absolute value is equal to or less than the threshold value ωhH (S18: NO) or when the processing of S16 is completed, it assigns the fixed vehicle speed V0 to the control vehicle speed Vc (S20).

[0046] On the other hand, if the PU 72 determines that the vehicle speed ωhH is greater than the threshold value ωhH (S18: YES), it assigns "0" to the flag F (S22). If the processing of S22 is completed or if a negative determination is made in the processing of S14, the PU 72 assigns the latest vehicle speed V obtained in the processing of S10 to the control vehicle speed Vc (S24).

[0047] When completing the processes of S20 and S24, the PU 72 assigns a value obtained by adding a predetermined amount Δ to the steering angle θh to the target pinion angle θp*0 (S26). Here, the PU 72 variably sets the predetermined amount Δ according to the steering angle θh and the control vehicle speed Vc. This process may be, for example, a process in which the PU 72 calculates the predetermined amount Δ using a map while map data is stored in the storage device 74. Here, the map data is data in which the steering angle θh and the control vehicle speed Vc are input variables and the predetermined amount Δ is an output variable. Note that the map data is a set of data consisting of discrete values ​​of the input variables and values ​​of the output variables corresponding to each of the input variable values. Furthermore, the map calculation may be a process in which, when the value of an input variable matches any of the values ​​of the input variables in the map data, the value of the output variable in the corresponding map data is used as the calculation result. Furthermore, the map calculation may be a process in which, when the value of an input variable does not match any of the values ​​of the input variables in the map data, a value obtained by interpolating the values ​​of multiple output variables contained in the map data is used as the calculation result. Alternatively, when the value of an input variable does not match any of the values ​​of the input variables in the map data, the map calculation may be a process in which, when the value of an input variable does not match any of the values ​​of the input variables in the map data, the value of the output variable in the map data that corresponds to the closest value among the values ​​of the output variables contained in the map data is used as the calculation result.

[0048] When the process of S26 is completed, the PU 72 temporarily ends the series of processes shown in FIG. The offset calculation process M22 is performed as follows: The offset calculation process M22 is performed as follows: The PU 72 executes a program stored in the storage device 74 repeatedly at predetermined intervals, for example.

[0049] 4, the PU 72 first acquires the pinion angle θp, the steering angular velocity ωh, and the vehicle speed V (S30). The steering angular velocity ωh is calculated by the PU 72 in accordance with the steering angle θh.

[0050] The PU 72 determines whether the flag F has been switched from "1" to "0" (S32). In other words, the PU 72 determines whether the input for calculating the target pinion angle θp*0 has been switched from the fixed vehicle speed V0 to the latest vehicle speed V, which is updated each time. If the PU 72 determines that the input has been switched (S32: YES), the PU 72 assigns a value obtained by subtracting the target pinion angle θp*0 from the target pinion angle θp* to the offset amount initial value Δθpb, and also assigns the offset amount initial value Δθpb to the offset amount Δθp (S34).

[0051] When the processing of S34 is completed or when a negative determination is made in the processing of S32, the PU 72 calculates a decrement base value Δ0 in accordance with the magnitude of the steering angular velocity ωh (S36). The PU 72 sets the decrement base value Δ0 when the magnitude of the steering angular velocity ωh is large to be equal to or greater than the decrement base value Δ0 when the magnitude of the steering angular velocity ωh is small. This processing can be realized, for example, by having the PU 72 calculate the decrement base value Δ0 using a map while map data is stored in the storage device 74. Here, the map data is data that uses the absolute value of the steering angular velocity ωh as an input variable and the decrement base value Δ0 as an output variable.

[0052] Next, the PU 72 calculates the gain G according to the vehicle speed V (S38). The PU 72 sets the gain G when the vehicle speed V is high to be equal to or greater than the gain G when the vehicle speed V is low. This process can be realized, for example, by having the PU 72 calculate the gain G using a map while map data is stored in the storage device 74. Here, the map data is data that uses the vehicle speed V as an input variable and the gain G as an output variable.

[0053] Next, the PU 72 multiplies the decrement base value Δ0 by the gain G and assigns the result to the offset decrement Δ1 (S40). Then, the PU 72 determines whether the offset decrement Δ1 is smaller than a lower limit value ΔL (S42). The PU 72 calculates the lower limit value ΔL according to the vehicle speed V. The PU 72 sets the lower limit value ΔL when the vehicle speed V is high to be equal to or greater than the lower limit value ΔL when the vehicle speed V is low. This process can be implemented, for example, by having the PU 72 calculate the lower limit value ΔL using a map while map data is stored in the storage device 74. Here, the map data is data that uses the vehicle speed V as an input variable and the lower limit value ΔL as an output variable.

[0054] If the PU 72 determines that the offset decrease amount Δθpb is smaller than the lower limit value ΔL (S42: YES), it assigns the lower limit value ΔL to the offset decrease amount Δ1 (S44). If the PU 72 completes the process of S44 or if the process of S42 makes a negative determination, it determines whether the offset amount initial value Δθpb is positive (S46). If the PU 72 determines that the offset amount initial value Δθpb is positive (S46: YES), it assigns the larger of zero or a value obtained by subtracting the offset decrease amount Δ1 from the offset amount Δθp (S48). On the other hand, if the PU 72 determines that the offset amount initial value Δθpb is equal to or smaller than zero (S46: NO), it assigns the smaller of zero or a value obtained by adding the offset decrease amount Δθp to the offset amount Δθp (S50).

[0055] When the PU 72 completes the processes of S48 and S50, it temporarily ends the series of processes shown in FIG. "Actions and Effects of the Present Embodiment" When the control vehicle speed Vc is switched from the fixed vehicle speed V0 to the vehicle speed V that is updated each time, the PU 72 gradually changes the target pinion angle θp* from a value determined from the fixed vehicle speed V0 to a value determined according to the vehicle speed V that is updated each time. This makes it possible to prevent the pinion angle θp from changing suddenly, and therefore to prevent the steering angle of the steered wheels 44 from changing suddenly.

[0056] According to the present embodiment described above, the following actions and effects can be further obtained. (1-1) The PU 72 gradually changes the target pinion angle θp* when the flag F changes from "1" to "0." In other words, the PU 72 gradually changes the target pinion angle θp* when the control vehicle speed Vc is changed. This prevents the rate of change of the target pinion angle θp* from decreasing even when the control vehicle speed Vc is not changed.

[0057] (1-2) When the magnitude of the steering angular velocity ωh is large, the driver desires to quickly change the steering to a desired state. The desired state is considered to correspond to a state in which the offset amount Δθp is zero. Therefore, the PU 72 sets the reduction rate of the offset amount Δθp according to the steering angular velocity ωh. This allows the desired state to be reached more quickly when the magnitude of the steering angular velocity ωh is large. Therefore, the driver can have a good steering feeling.

[0058] (1-3) When the vehicle speed V is high, the rate of change of the target pinion angle θp* is faster than when the vehicle speed V is low, but the driver tends to feel less uncomfortable. Therefore, by increasing the rate of decrease of the offset amount Δθp when the vehicle speed V is high, the PU 72 can set the target pinion angle θp* to a value corresponding to the changed control vehicle speed Vc as quickly as possible while minimizing the driver's discomfort.

[0059] (1-4) If the magnitude of the steering angular velocity ωh is small for a predetermined time, the PU 72 determines that the driver is in a fixed steering state, where the steering wheel 12 is fixed. If the PU 72 determines that the driver is in a fixed steering state, it calculates the target pinion angle θp* according to the fixed vehicle speed V0. This makes it possible to prevent the target pinion angle θp* from changing even when the driver is in a fixed state.

[0060] <Second embodiment> The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0061] Fig. 5 shows the procedure of the target pinion angle calculation process M20 according to this embodiment. The process shown in Fig. 5 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval. For convenience, the processes in Fig. 5 corresponding to those shown in Fig. 3 are given the same step numbers, and their description will be omitted.

[0062] In the series of processes shown in FIG. 5, when the PU 72 determines that the flag F is "0" (S12: NO), it determines whether the magnitude of the pinion angle θp is equal to or greater than an end threshold value θpthH (S14a). The end threshold value θpthH is set according to the maximum possible magnitude of the pinion angle θp. The end threshold value θpthH is a value within a predetermined region. The predetermined region is a region of the pinion angle θp when the steering reaction force command value Tr* is set to a value intended to prevent the pinion angle θp from being displaced in an increasing direction. When the PU 72 determines that the pinion angle θp is equal to or greater than the end threshold value θpthH (S14a: YES), the PU 72 proceeds to the process of S16. On the other hand, when the PU 72 determines that the pinion angle θp is less than the end threshold value θpthH (S14a: NO), the PU 72 proceeds to the process of S24.

[0063] On the other hand, when the PU 72 determines that the flag F is "1" (S12: YES), it determines whether the magnitude of the pinion angle θp is smaller than the release threshold θpthL (S18a). The release threshold θpthL is equal to or smaller than the end threshold θpthH. The release threshold θpthL is preferably smaller than the end threshold θpthH. When the PU 72 determines that the pinion angle θp is smaller than the release threshold θpthL (S18a: YES), it proceeds to processing of S22. On the other hand, when the PU 72 determines that the pinion angle θp is equal to or larger than the release threshold θpthL (S18a: NO), it proceeds to processing of S20.

[0064] In this embodiment, the process of S32 in FIG. 4 is a process in which the value of flag F determined by the process of FIG. 5 is input. <Third embodiment> The third embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0065] As described above, vehicle speed calculation process M10 is a process for calculating vehicle speed based on wheel speeds ωw1 to ωw4. If an abnormality occurs in any one of wheel speeds ωw1 to ωw4, braking ECU 90 notifies steering ECU 70 of this. In this case, vehicle speed calculation process M10 calculates vehicle speed V by a process different from that used before the notification.

[0066] The procedure of the vehicle speed calculation process M10 is shown in Fig. 6. The process shown in Fig. 6 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at predetermined intervals.

[0067] In the series of processes shown in FIG. 6, the PU 72 acquires wheel speeds ωw1 to ωw4 (S70). When newly acquiring wheel speeds ωw1 to ωw4 in the process of S70, the PU 72 determines whether or not the brake ECU 90 has determined that the detected value of one wheel is invalid (S72). This process is processing to determine whether or not the brake ECU 90 has notified the steering ECU 70 that there is an abnormality in any one of the wheel speeds ωw1 to ωw4. If the PU 72 determines that there is no invalid determination (S72: NO), it assigns the wheel speed ωwT to the vehicle speed V (S74). The wheel speed ωwT is the third largest value among the wheel speeds ωw1 to ωw4. On the other hand, if the PU 72 determines that an invalid determination has been made (S72: YES), it assigns the wheel speed ωwS to the vehicle speed V (S76). The wheel speed ωwS is the second largest value among the wheel speeds ωw1 to ωw4.

[0068] When the processing of S74 and S76 is completed, the PU 72 determines whether the vehicle speed V has switched from one of the wheel speed ωwT and the wheel speed ωwS to the other (S78). Figure 6 shows an example of a logical expression that becomes logical H when the vehicle speed V has switched.

[0069] When the PU 72 determines that a switch has occurred (S80: YES), it assigns "0" to flag F (S82). On the other hand, when the PU 72 determines that a switch has not occurred (S80: NO), it assigns "1" to flag F (S84).

[0070] When the PU 72 completes the processes of S82 and S84, it temporarily ends the series of processes shown in FIG. According to the present embodiment described above, the following actions and effects can be further obtained.

[0071] (3-1) When an abnormality occurs in any of the wheel speeds ωw1 to ωw4, the PU 72 selects the wheel speed ωwS instead of the wheel speed ωwT. The PU 72 then gradually changes the target pinion angle θp* when triggered by switching from one of the two states, where the wheel speed ωwT is set to the vehicle speed V and where the wheel speed ωwS is set to the vehicle speed V, to the other. This makes it possible to suppress changes in the target pinion angle θp* caused by the above switching.

[0072] <Fourth embodiment> The fourth embodiment will be described below with reference to the drawings, focusing on the differences from the third embodiment.

[0073] Fig. 7 shows part of the processing executed by the steering ECU 70 according to this embodiment. Of the processing shown in Fig. 7, the processing corresponding to the processing shown in Fig. 2 is denoted by the same reference numerals for convenience.

[0074] In this embodiment, the target pinion angle calculation process M20 is a process for calculating the target pinion angle θp*, which is input to the pinion angle feedback process M26. On the other hand, the offset amount calculation process M22a is a process for calculating an offset amount ΔV of the vehicle speed V. Furthermore, the offset process M24a is a process for subtracting the offset amount ΔV from the vehicle speed output by the vehicle speed calculation process M10 and outputting the result as the vehicle speed V. The vehicle speed V output by the offset process M24a is input to the steering reaction force command value calculation process M16 and the target pinion angle calculation process M20.

[0075] The procedure of the offset amount calculation process M22a is shown in Figure 8. The process shown in Figure 8 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval. For convenience, the processes in Figure 8 that correspond to those shown in Figure 4 are given the same step numbers, and their explanations will be omitted.

[0076] 8, if the PU 72 makes a positive determination in the process of S32, the PU 72 proceeds to the process of S34a. In the process of S34a, the PU 72 assigns a value obtained by subtracting the previous value "V(n-1)" of the vehicle speed V from the current value "V(n)" to the offset amount initial value ΔVb, and also assigns the offset amount initial value ΔVb to the offset amount ΔV. If the process of S34a is completed, the PU 72 proceeds to the process of S36.

[0077] Furthermore, when the PU 72 makes a negative determination in the process of S42 or when it completes the process of S44, it determines whether the offset amount initial value ΔVb is positive (S46a). If it determines that the offset amount initial value ΔVb is positive (YES in S46a), it assigns the larger of zero or a value obtained by subtracting the offset decrease amount Δ1 from the offset amount ΔV to the offset amount ΔV (S48a). On the other hand, if the PU 72 determines that the offset amount initial value ΔVb is equal to or less than zero (NO in S46a), it assigns the smaller of zero or a value obtained by adding the offset decrease amount Δ1 to the offset amount ΔV to the offset amount ΔV (S50a).

[0078] When the PU 72 completes the processes of S48a and S50a, it temporarily ends the series of processes shown in FIG. According to the present embodiment described above, the following actions and effects can be further obtained.

[0079] (4-1) The PU 72 inputs the vehicle speed V output by the offset processing M24a to the steering reaction force command value calculation processing M16 and the target pinion angle calculation processing M20. This makes it possible to suppress a sudden change in the target pinion angle θp* caused by switching from one of the two states, where the wheel speed ωwT is set to the vehicle speed V and where the wheel speed ωwS is set to the vehicle speed V, to the other. Furthermore, it is possible to suppress a sudden change in the steering reaction force command value Tr* caused by this switching.

[0080] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problem" section above is as follows. Below, the correspondence is shown for each number of the solving means described in the "Means for Solving the Problem" section. [1] The manipulated variable calculation process corresponds to target pinion angle calculation process M20. The manipulated variable corresponds to target pinion angle θp*. The manipulated variable corresponds to steering torque command value Tt*. The selection process corresponds to the processes of S12 to S24 in FIG. 3, the processes of S12, S14a, S16, S18a, and S20 to S24 in FIG. 5, and the processes of S72 to S76 in FIG. 6. The gradual change process corresponds to part of offset amount calculation process M22 and offset process M24 in FIG. 2, and part of offset amount calculation process M22a and offset process M24a in FIG. 7. The manipulated variable calculation process corresponds to pinion angle feedback process M26. The operation process corresponds to steering operation process M28. [2] The change detection process corresponds to the process of S32. [3] The angular velocity acquisition process corresponds to the process of S30. The angular velocity variable corresponds to the steering angular velocity ωh. The gradual change speed corresponds to the decrease speed determined by the offset decrease amount Δ1. [4] The vehicle speed acquisition process corresponds to the process of S30. The gradual change speed corresponds to the decrease speed determined by the offset decrease amount Δ1. [5] The vehicle speed acquisition process corresponds to the process of S10 in Figure 3. The storage process corresponds to the process of S16. [6] The fixed steering determination process corresponds to the process of S14. The fixed steering process corresponds to the process of S20 in Figure 3. The fixed steering release process corresponds to the process of S24 in Figure 3. [7] The boundary determination process corresponds to the process of S14a. The end process corresponds to the process of S20 in Figure 5. The end release process corresponds to the process of S24 in Figure 5. [8] The first wheel speed corresponds to the wheel speed ωwT. The second wheel speed corresponds to the wheel speed ωwS. The selection process corresponds to the process of S72. [9] The steering actuator corresponds to the steering actuator At.

[10] Corresponds to the process of FIG. 2.

[11] Corresponds to the process of FIG. 7.

[0081] <Other embodiments> This embodiment can be modified as follows: This embodiment and the following modifications can be combined and implemented within the scope of technical compatibility.

[0082] "Angular velocity acquisition process" The angular velocity variable used as an input for calculating the gradual decrease rate of the offset amounts Δθp and ΔV is not limited to the steering angular velocity ωh. For example, it may be the rate of change of the target pinion angle θp*. Or, for example, it may be the rate of change of the pinion angle θp. Or, for example, if the reaction force operation process M18 includes a process of feedback-controlling the steering angle θh to its target value, it may be the rate of change of the target value.

[0083] "About vehicle speed acquisition processing" The vehicle speed used as an input for calculating the rate at which the offset amounts Δθp and ΔV are gradually decreased is not limited to the values ​​of the variables exemplified in the above embodiment, and may be, for example, the average value of the wheel speeds ωwa to ωwd.

[0084] "About gradual change processing" The processes of S42 and S44 may not be provided. The process of calculating the gradual decrease rate of the offset amounts Δθp, ΔV in accordance with the value of the angular velocity variable and the vehicle speed V is not limited to the process exemplified in Figures 4 and 8. For example, instead of the process of S36 to S40, a process of calculating the offset decrease amount Δ1 from a map using map data in which the value of the angular velocity variable and the vehicle speed V are input variables and the offset decrease amount Δ1 is an output variable may be included.

[0085] It is not necessary to calculate the gradual decrease rate of the offset amounts Δθp and ΔV according to the value of the angular velocity variable and the vehicle speed. For example, with regard to the two variables, the value of the angular velocity variable and the vehicle speed, the gradual decrease rate may be calculated based on only one of them. Also, for example, with regard to the two variables, the gradual decrease rate may be calculated without depending on either of them. This can be achieved, for example, by dividing the initial offset amount value Δθpb by N and setting the value as the offset decrease amount Δ1. Furthermore, the gradual decrease rate may be a fixed value.

[0086] "About boundary determination processing" The boundary determination process for determining whether or not the difference between the magnitude of the steering angle variable and the upper limit is equal to or less than a predetermined value is a boundary state, and is not limited to the process of S14a. For example, it may be a process for determining whether or not the magnitude of the steering angle θh is equal to or greater than a predetermined value. That is, since the target pinion angle θp*0 is determined according to the steering angle θh, the pinion angle θp is determined according to the steering angle θh. Therefore, the steering angle θh is a steering angle variable that indicates the steering angle.

[0087] "About the first wheel speed and second wheel speed" The first and second wheel speeds are not limited to the second and third largest values ​​among the wheel speeds ωwa to ωwd. For example, they may be the third and fourth largest values ​​among the wheel speeds ωwa to ωwd.

[0088] "Operation volume calculation process" In the above embodiment, pinion angle feedback process M26 calculates steering torque command value Tt* as an operation amount for feedback-controlling pinion angle θp to target pinion angle θp*, but this is not limited to this. For example, it may include a process of calculating damping torque, which is torque in the opposite direction to the direction of change in pinion angle θp over time, and adding this to steering torque command value Tt*. This process may further receive as input at least one of pinion angular velocity, which is a change in pinion angle θp over time, and target pinion angular velocity, which is a change in target pinion angle θp* over time. Furthermore, by including vehicle speed V as an input, damping torque may be variably set in accordance with vehicle speed V.

[0089] Instead of the pinion angle feedback process M26, a process may be used in which a detected value of the movement amount of the steered shaft 40 is feedback-controlled to a target value. In this case, in the above embodiment, the control amount and the like related to the pinion angle θp are replaced with the control amount and the like related to the movement amount of the steered shaft 40.

[0090] The operation amount calculation process is not limited to a process of calculating an operation amount for feedback control of a quantity indicating a steering angle, such as pinion angle θp. For example, it may be a process of calculating an operation amount for open-loop control of a quantity indicating a steering angle to a target value. Also, for example, it may be a process of calculating the sum of an operation amount for open-loop control and an operation amount for feedback control.

[0091] "About Instrumental Variables" As described in the section "Regarding the operation amount calculation process," when feedback control is performed on the movement amount of the steered shaft 40, the target value of the movement amount may be set as the operation variable.

[0092] "About the instrumental variable calculation process" The target pinion angle calculation process M20 may be a process for variably setting the steering angle ratio in accordance with the detection value of the yaw rate sensor in addition to the control vehicle speed Vc.

[0093] "About operation processing" The control method for steering motor 60 is not limited to dq-axis current feedback processing. For example, if a DC motor is used as steering motor 60 and the drive circuit is an H-bridge circuit, it is sufficient to simply control the current flowing through steering motor 60.

[0094] "About steering control devices" The steering control device is not limited to a device in which a device for operating the steering actuator At and a device for operating the reaction force actuator Ar are integrated together. For example, the device for operating the steering actuator At and the device for operating the reaction force actuator Ar may be devices housed in separate housings that are capable of communicating with each other.

[0095] The steering control device is not limited to one that includes the PU 72 and the storage device 74 and executes software processing. For example, it may include a dedicated hardware circuit, such as an ASIC, that performs hardware processing on at least a portion of what was processed by software in the above embodiments. That is, the control device may have any of the following configurations (a) to (c): (a) includes a processing device that executes all of the above processing in accordance with a program, and a program storage device, such as a storage device, that stores the program. (b) includes a processing device and program storage device that executes a portion of the above processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing. (c) includes a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices that include a processing device and a program storage device, and multiple dedicated hardware circuits.

[0096] "About steering actuators" The steering actuator At may be, for example, one in which steering motor 60 is arranged coaxially with steering shaft 40. Alternatively, for example, one in which steering motor 60 is connected to steering shaft 40 via a belt-type reducer using a ball screw mechanism may be used.

[0097] "About the steering system" The steering system capable of changing the relationship between the steering angle and the turning angle is not limited to a steering system in which the transmission of power between the steering wheel 12 and the steered wheels 44 is cut off. For example, a steering system capable of changing the relationship between the steering angle and the turning angle may be configured by using a variable gear as the gear that enables the transmission of power between the steering wheel 12 and the steered wheels 44. [Explanation of symbols]

[0098] 10...Steering device 12...Steering wheel 14...Steering shaft 16...Reduction mechanism 20...Reaction motor 22...Reaction force inverter 40...Steering shaft 42...Tie rod 44...Steering wheel 46...Wheel 52...Pinion shaft 56…Reduction mechanism 60...Steering motor 62...Steering inverter 70…Steering ECU 80...Torque sensor 82, 84...Rotation angle sensor 90…Brake ECU 100, 102, 104, 106...Wheel speed sensors

Claims

1. The present invention is applied to a vehicle equipped with a steering system capable of changing the relationship between the steering angle and the turning angle, The steering angle is a rotation angle of a steering wheel, The steering angle is a turning angle of a steered wheel of the vehicle, configured to execute an operation variable calculation process, a selection process, an operation process, a gradual change process, and an operation amount calculation process; the operation variable calculation process is a process of variably setting values ​​of operation variables for determining an operation amount of the steering system using a control vehicle speed as an input, the operation amount is an amount for controlling the steering angle, the selection process is a process of selecting the control vehicle speed to be input to the operation variable calculation process from among a plurality of control vehicle speeds; the operation processing is processing for operating the steering system in accordance with the operation amount, the gradual change processing is processing for, when the control vehicle speed selected by the selection processing is changed, gradually changing a change in the value of the operation variable caused by a change in the value of the control vehicle speed associated with the change, the manipulated variable calculation process is a process of calculating the manipulated variable using, as an input, the value of the manipulated variable gradually changed by the gradual change process; The steering angle change rate is determined based on the angular velocity of the steering wheel. The gradual change processing is a processing for variably setting a gradual change speed from the value of the operating variable corresponding to the control vehicle speed before the change to the value of the operating variable corresponding to the control vehicle speed after the change according to the value of the angular velocity variable, and includes a processing for setting the gradual change speed when the value of the angular velocity variable is large to be equal to or higher than the gradual change speed when the value of the angular velocity variable is small.

2. a change detection process for detecting a change in the control vehicle speed selected by the selection process, 2. The steering control device according to claim 1, wherein the gradual change process is a process for gradually changing the value of the manipulated variable, triggered by the change being detected by the change detection process.

3. a vehicle speed acquisition process for acquiring a vehicle speed, which is a traveling speed of the vehicle; 3. The steering control device according to claim 1, wherein the gradual change processing includes processing for variably setting a gradual change speed from the value of the operating variable corresponding to the control vehicle speed before the change to the value of the operating variable corresponding to the control vehicle speed after the change in accordance with the vehicle speed, and processing for setting the gradual change speed when the vehicle speed is high to be equal to or higher than the gradual change speed when the vehicle speed is low.

4. a vehicle speed acquisition process for acquiring a vehicle speed, which is a traveling speed of the vehicle; a storage process of storing and holding the vehicle speed acquired at a predetermined timing by the vehicle speed acquisition process as a fixed vehicle speed, the plurality of control vehicle speeds include the vehicle speed acquired each time by the vehicle speed acquisition process and the fixed vehicle speed; A steering control device according to any one of claims 1 to 3, wherein the gradual change processing includes a process of gradually changing the value of the operating variable corresponding to the control vehicle speed before the change to the value of the operating variable corresponding to the control vehicle speed after the change when the vehicle speed selected by the selection processing is changed from the fixed vehicle speed to the vehicle speed obtained each time.

5. The system is configured to execute a steering determination process for determining whether the steering angle is maintained at a predetermined angle, The selection process includes a steering-holding process for changing the control vehicle speed from the vehicle speed acquired each time to the fixed vehicle speed, with the timing at which the steering-holding determination process transitions from a state determined not to be the steering-holding state to a state determined to be the steering-holding state as the predetermined timing; 5. A steering control device as described in claim 4, which includes a steering release process that changes the control vehicle speed from the fixed vehicle speed to the vehicle speed obtained each time when the state transitions from a state determined to be the steering state by the steering determination process to a state determined not to be the steering state while the steering during processing is being performed.

6. The system is configured to execute a boundary determination process for determining whether or not a difference between the magnitude of the steering angle variable value and the upper limit value is equal to or less than a predetermined boundary state, the steering angle variable is a variable indicating the steering angle, The selection process includes an end process for changing the control vehicle speed from the vehicle speed acquired each time to the fixed vehicle speed, with the predetermined timing being a transition from a state determined not to be the boundary state by the boundary determination process to a state determined to be the boundary state. A steering control device as described in claim 4 or 5, which includes an end release process that changes the control vehicle speed from the fixed vehicle speed to the vehicle speed obtained each time when the end process is being executed and the state transitions from a state determined to be the boundary state by the boundary determination process to a state determined not to be the boundary state.

7. the plurality of control vehicle speeds include a first wheel speed that is a speed of a first wheel of the vehicle, and a second wheel speed that is a speed of a second wheel of the vehicle; 4. The steering control device according to claim 1, wherein the selection process includes a process of selecting the second wheel speed as the control vehicle speed when an abnormality is detected in any of the wheel speeds of the vehicle while the first wheel speed is selected as the control vehicle speed.

8. the steering system includes a steering actuator that steers the steered wheels, the operation amount is an operation amount of the steering actuator, 8. The steering control device according to claim 1, wherein the manipulated variable is a target steering angle that is a target value of the steering angle.

9. 9. The steering control device according to claim 8, wherein the gradual change process includes a process of correcting the target steering angle output by the operation variable calculation process in accordance with the changed control vehicle speed.

10. 9. The steering control device according to claim 8, wherein the gradual change processing includes processing for gradually changing the control vehicle speed used by the operation variable calculation processing to calculate the target steering angle from the control vehicle speed before the change to the control vehicle speed after the change when the control vehicle speed is changed by the selection processing.

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