Steering control device and steering control method

Abstract

This steering control device is configured to execute offset amount calculation processing, offset compensation processing, and offset reduction processing. The offset amount calculation processing is processing for calculating an offset amount which is a difference equivalent amount between a target turning equivalent angle and an actual turning equivalent angle with satisfaction of a predetermined condition as a trigger. The offset compensation processing is processing for correcting the target turning equivalent angle by an offset correction amount corresponding to the offset amount. The predetermined condition includes a plurality of types of conditions. The offset amount calculation processing and the offset compensation processing are provided separately for each of the plurality of types of conditions. The offset reduction processing is processing for reducing the magnitude of the offset correction amount, and when two or more mutually different offset compensation processing instances are executed, includes cooperative processing for cooperatively setting a reduction rate of the offset correction amount used in the two or more offset compensation processing instances.

Description

Steering control device and steering control method

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

[0002] For example, Patent Document 1 listed below describes a steering control device for a system in which the transmission of power between the steering wheel and the steered wheels is interrupted. This steering control device sets a target value for the steered angle of the steered wheels in accordance with the steering angle. This steering control device also corrects the target value of the steered angle in accordance with the difference between the previous and current values ​​of the target value of the steered angle set in accordance with the steering angle, and then executes a process to gradually change the correction amount to zero. Furthermore, when the steering angle is not changing while the vehicle is stopped, this steering control device executes a process to bring the target value of the steered angle closer to the actual steered angle in order to reduce the current of the motor that steers the steered wheels. Note that the target value changed by this process is gradually returned to its original value when the steering angle changes.

[0003] Japanese Patent Application Laid-Open No. 2022-129218

[0004] As described above, when there are multiple types of processes for gradually changing the target value, if these processes are executed simultaneously, there is a risk that the target value will suddenly change.

[0005] One aspect of the present disclosure provides a steering control device. The steering control device is configured to execute a target steering equivalent angle setting process, an operation process, an offset amount calculation process, an offset compensation process, and an offset reduction process in a state in which the steered wheels and the steering shaft are mechanically disconnected. The target steering equivalent angle setting process is a process for setting a target steering equivalent angle. The target steering equivalent angle is a target value of the steering equivalent angle, which is a variable indicating the steering angle of the steered wheels. The operation process is a process for operating a motor that steers the steered wheels in accordance with a control operation amount in which the target steering equivalent angle is a target value of a control amount. The offset amount calculation process is a process for calculating an offset amount that is an amount equivalent to the difference between the target steering equivalent angle and the actual steering equivalent angle, triggered by the satisfaction of a predetermined condition. The offset compensation process is a process for correcting the target steering equivalent angle by an offset correction amount that corresponds to the offset amount. The predetermined condition includes a plurality of types of conditions. The offset amount calculation process and the offset compensation process are provided separately for each of the plurality of types of conditions. The offset reduction process is a process for reducing the magnitude of the offset correction amount, and when two or more different offset compensation processes are being executed, includes a collaborative process for collaboratively setting the reduction rate of the magnitude of the offset correction amount used in the two or more offset compensation processes.

[0006] Another aspect of the present disclosure provides a steering control method. The steering control method includes, in a state in which the steered wheels and the steering shaft are mechanically disconnected, executing a target steering equivalent angle setting process, executing an operation process, executing an offset amount calculation process, executing an offset compensation process, and executing an offset reduction process. The target steering equivalent angle setting process is a process for setting a target steering equivalent angle. The target steering equivalent angle is a target value of a steering equivalent angle, which is a variable indicating the steering angle of the steered wheels. The operation process is a process for operating a motor that steers the steered wheels in accordance with a control operation amount in which the target steering equivalent angle is a target value of a control amount. The offset amount calculation process is a process for calculating an offset amount that is an amount equivalent to the difference between the target steering equivalent angle and the actual steering equivalent angle, triggered by the satisfaction of a predetermined condition. The offset compensation process is a process for correcting the target steering equivalent angle by an offset correction amount that corresponds to the offset amount. The predetermined condition includes a plurality of types of conditions. The offset amount calculation process and the offset compensation process are provided separately for each of the plurality of types of conditions. The offset reduction process is a process for reducing the magnitude of the offset correction amount, and includes, when two or more different offset compensation processes are being executed, a cooperative process for cooperatively setting the reduction rates of the magnitudes of the offset correction amounts used in the two or more offset compensation processes.

[0007] FIG. 1 is a diagram showing a configuration of a vehicle according to an embodiment. FIG. 2 is a block diagram showing a part of the processing executed by the steering control device shown in FIG. 1. FIG. 3 is a flowchart showing the procedure of the processing executed by the steering control device shown in FIG. 1. FIG. 4 is a flowchart showing the procedure of the processing executed by the steering control device shown in FIG. 1. FIG. 5 is a flowchart showing the procedure of the processing executed by the steering control device shown in FIG. 1. FIG. 6 is a time chart showing the effect of the processing shown in FIG. 7. FIG. 8 is a time chart showing the effect of the processing shown in FIG.

[0008] An embodiment will be described below with reference to the drawings. "Configuration of steering control system" As shown in Figure 1, a vehicle steering device 10 is a steer-by-wire type steering device. The steering device 10 includes a reaction force actuator Ar and a turning actuator At. The steering device 10 of this embodiment has a structure in which the power transmission path between the steering wheel 12 and the steered wheels 44 is mechanically disconnected.

[0009] 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.

[0010] Reaction motor 20 is, for example, a three-phase brushless motor. The rotation shaft of reaction motor 20 is connected to steering shaft 14 via speed reducer 16. Meanwhile, steered shaft 40 extends along the vehicle width direction, which is the left-right direction in FIG. 1 . Left and right steered wheels 44 are connected to both ends of steered shaft 40 via tie rods 42, respectively. The steered angle of steered wheels 44 is changed by linear movement of steered shaft 40.

[0011] The steering actuator At includes a reduction gear mechanism 56, a steering motor 60, and a steering inverter 62. As an example, the steering motor 60 is a three-phase surface permanent magnet synchronous motor. The rotating shaft of the steering motor 60 is connected to a pinion shaft 52 via the reduction gear mechanism 56. The pinion teeth of the pinion shaft 52 mesh with rack teeth 54 of the steering shaft 40. The pinion shaft 52 and the steering shaft 40 provided with the rack teeth 54 form a rack-and-pinion mechanism 50. The torque of the steering motor 60 is applied as a steering force to the steering shaft 40 via the pinion shaft 52. In response to the rotation of the steering motor 60, the steering shaft 40 moves in the vehicle width direction, which is the left-right direction in FIG. 1 .

[0012] The steering control device 70 includes a PU 72 and a storage device 74. The PU 72 is a software processing device such as a CPU or a GPU. The storage device 74 may be an electrically non-rewritable non-volatile memory. Alternatively, the storage device 74 may be an electrically rewritable non-volatile memory or a storage medium such as a disk medium. The steering control device 70 controls the control amount by the PU 72 executing a program stored in the storage device 74.

[0013] The control object of steering control device 70 is steering wheel 12. Steering control device 70 operates 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. Also, the control object of steering control device 70 is steered wheels 44. Steering control device 70 operates 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.

[0014] In order to control the control variable, steering control device 70 refers to steering torque Th, which is the input torque to steering shaft 14, detected by torque sensor 80. Steering control device 70 also refers to rotation angle θa of the rotation shaft of reaction force motor 20, detected by rotation angle sensor 82. Steering control device 70 also 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. Steering control device 70 also refers to rotation angle θb of the rotation shaft of turning motor 60, detected by rotation angle sensor 84. Steering control device 70 also 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. The steering control device 70 also refers to the vehicle speed V detected by the vehicle speed sensor 92 .

[0015] "Control" Fig. 2 shows part of the processing executed by the steering control device 70. Steering angle calculation processing M10 is processing for calculating a steering angle θh, which is the rotation angle of the steering wheel 12, based on a rotation angle θa as an input variable. The steering angle calculation processing M10 includes processing for converting the rotation angle θa into an integrated angle including a range exceeding 360° 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 processing M10 includes processing for multiplying the converted integrated angle by a conversion coefficient based on the rotational speed ratio of the reduction mechanism 16 to calculate the steering angle θh. Note that the steering angle θh is set to a positive value when the steering angle is to the right of the steering neutral position, and a negative value when the steering angle is to the left of the steering neutral position, for example.

[0016] The steering equivalent angle calculation process M12 calculates the steering equivalent angle θp based on the rotation angle θb as an input variable. The steering equivalent angle θp is a variable that indicates the steering angle of the steered wheels 44. The steering equivalent angle calculation process M12 includes, for example, a process of counting the number of rotations of the steering motor 60 from a rack neutral position, which is the position of the steering shaft 40 when the vehicle is traveling straight, and converting the counted number of rotations into an integrated angle that includes a range exceeding 360°. The steering equivalent angle calculation process M12 includes a process of multiplying the converted integrated angle by a conversion coefficient based on the rotational speed ratio of the reduction mechanism 56 to calculate the steering equivalent angle θp. That is, in this embodiment, as an example, the steering equivalent angle θp is set to a value equal to the actual rotation angle of the pinion shaft 52. Note that the steering equivalent angle θp may be set to a positive value when the angle is to the right of the rack neutral position and a negative value when the angle is to the left of the rack neutral position.

[0017] Target reaction force calculation process M14 is a process for calculating target reaction force Tr* corresponding to the steering reaction force to be applied to steering wheel 12, based on input variables including steering torque Th, vehicle speed V, steering equivalent angle θp, and q-axis current iqt. Here, q-axis current iqt is the q-axis current flowing through steering motor 60. q-axis current iqt is a variable indicating the torque of steering motor 60. q-axis current iqt is calculated by PU 72 based on currents iu2, iv2, iw2 and rotation angle θb. More specifically, target reaction force calculation process M14 includes a process for changing target reaction force Tr* in accordance with the magnitude of the torque of steering motor 60 under the following condition. This condition is a condition that the magnitude of target reaction force Tr* when the torque of steering motor 60 is large is equal to or greater than the magnitude of target reaction force Tr* when the torque of steering motor 60 is small. The target reaction force calculation process M14 also includes a process for changing the target reaction force Tr* in accordance with the steering equivalent angle θp as an input variable under the following condition: The magnitude of the target reaction force Tr* when the steering equivalent angle θp is large is equal to or greater than the magnitude of the target reaction force Tr* when the steering equivalent angle θp is small.

[0018] The target reaction force Tr* is actually a command value for the reaction force motor 20. The steering reaction force is obtained by multiplying the target reaction force Tr* by a coefficient corresponding to the reduction ratio of the reduction mechanism 16. Note that in descriptions such as "changing B according to A under the condition that when A is large, B is equal to or larger than B when A is small," the case where A is large and the case where A is small refer to a relative magnitude relationship when comparing the two. For example, "when A is large" corresponds to "A is a first value," and "when A is small" corresponds to "A is a second value smaller than the first value." The above description also means that, depending on the settings of the first and second values, B when A is the first value may be larger than B when A is the second value. The above description also means that B is changed according to A so that A when B is large is larger than A when B is small.

[0019] The reaction force operation process M16 is a process for outputting an operation signal MSs for the reaction force inverter 22 based on input variables such as target reaction force Tr*, currents iu1, iv1, iw1, and rotation angle θa. The reaction force operation process M16 includes a process for calculating d-axis and q-axis current command values ​​based on the target reaction force Tr*. The reaction force operation process M16 also includes a process for calculating d-axis and q-axis currents based on the currents iu1, iv1, iw1, and rotation angle θa. The reaction force operation process M16 then includes a process for calculating an operation signal MSs for operating the reaction force inverter 22 so that the d-axis and q-axis currents approach the command values.

[0020] The target steering equivalent angle setting process M18 is a process for calculating a target steering equivalent angle θp*0 based on the input variables of steering angle θh and vehicle speed V. The target steering equivalent angle θp*0 is a target value of the steering equivalent angle θp according to the operation of the steering wheel 12 by the driver. The target steering equivalent angle setting process M18 includes a process for changing the target steering angle ratio, which is the ratio between the steering angle θh and the target steering equivalent angle θp*0, according to the vehicle speed V, etc.

[0021] The offset correction amount calculation process M20 is a process for calculating an offset correction amount Δθpa of the target equivalent turning angle θp*0 based on the equivalent turning angle θp and the target equivalent turning angle θp*0 as input variables.

[0022] Offset correction process M22 is a process for calculating target steering equivalent angle θp*1 by subtracting offset correction amount Δθpa from target steering equivalent angle θp*0. Residual current suppression process M24 is a process for calculating offset correction amount Δθpb for suppressing residual current. Residual current refers to the current that flows to steering motor 60 when steering angle θh is fixed, for example, while the vehicle is stopped. In other words, if steering equivalent angle θp deviates from target steering equivalent angle θp*, which is set based on steering angle θh as an input variable, steering motor 60 generates torque to bring steering equivalent angle θp closer to target steering equivalent angle θp*. However, if this torque is smaller than the frictional force between steered wheels 44 and the road surface, the deviation between target steering equivalent angle θp* and steering equivalent angle θp is not resolved, and current continues to flow to steering motor 60. Residual current suppression process M24 includes a process for calculating an offset correction amount Δθpb as a correction amount for the target steering equivalent angle θp*1 so as to bring the target steering equivalent angle θp* closer to the steering equivalent angle θp under such circumstances.

[0023] Residual correction process M26 is a process for calculating target steering equivalent angle θp* by subtracting offset correction amount Δθpb from target steering equivalent angle θp*1. Steering feedback process M30 is a process for calculating steering torque command value Tt*, which is a command value for the torque of steering motor 60, in accordance with the manipulated variable of feedback control in which steering equivalent angle θp is the controlled variable and target steering equivalent angle θp* is the target value of the controlled variable. In more detail, steering feedback process M30 is a process for, as an example, substituting the sum of the output value of the proportional element, the output value of the integral element, and the output value of the derivative element for steering torque command value Tt*. The proportional element is a value obtained by multiplying the difference between target steering equivalent angle θp* and steering equivalent angle θp by proportional gain Kp. The integral element is an integrated value of the value obtained by multiplying the difference by integral gain Ki. The derivative element is a value obtained by multiplying the first-order time derivative of the difference by derivative gain Kd. It should be noted that when the steering torque command value Tt* is set in accordance with the output value of the integral element, if the deviation between the target steering equivalent angle θp* and the steering equivalent angle θp is not eliminated as described above, the absolute value of the steering torque command value Tt* will gradually increase.

[0024] The offset reduction rate setting process M28 is a process for setting the reduction rate of the absolute values ​​of the offset correction amounts Δθpa and Δθpb. The steering operation process M32 is a process for outputting an operation signal MSt for the steering inverter 62 based on the input variables of the steering torque command value Tt*, currents iu2, iv2, iw2, and rotational angle θb. The steering operation process M32 includes a process for calculating current command values ​​for the d and q axes based on the steering torque command value Tt*. The steering operation process M32 also includes a process for calculating currents for the d and q axes based on the currents iu2, iv2, iw2 and rotational angle θb. The steering operation process M32 then includes a process for calculating an operation signal MSt for operating the steering inverter 62 so that the currents for the d and q axes become the command values.

[0025] "Details of Offset Correction Amount Calculation Process" Fig. 3 shows a detailed procedure of part of the offset correction amount 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 number of each process is represented by a number preceded by "S."

[0026] 3, the PU 72 first determines whether the offset flag Fo is "1" (S10). The value of the offset flag Fo is set to "1" when the absolute value of the offset correction amount Δθpa is set to a value greater than zero. The value of the offset flag Fo is set to "0" when the absolute value of the offset correction amount Δθpa is zero.

[0027] When the PU 72 determines that the offset flag Fo is "0" (S10: NO), it determines whether a predetermined condition is met under which the absolute value of the offset correction amount Δθpa is set to a value greater than zero (S14). The predetermined condition is a condition under which the deviation between the target steering equivalent angle θp* and the steering equivalent angle θp becomes large. The predetermined condition may be the following first condition or second condition. The first condition is a condition under which the target steering equivalent angle θp*0 is discontinuously changed.

[0028] Specifically, the first condition may be, for example, a condition that an abnormality has occurred in vehicle speed sensor 92. In other words, if vehicle speed sensor 92 is configured with sensors that detect the speeds of a plurality of wheels, the method of calculating vehicle speed V may be changed if an abnormality occurs in any one of the wheel speed sensors. In such a case, the target steering equivalent angle θp*0 changes discontinuously due to discontinuous changes in vehicle speed V. Also, for example, the first condition may be a condition that steering intervention by steering control device 70 is started. When steering intervention is started, target steering equivalent angle θp*0 changes discontinuously because the target steering equivalent angle θp*0 is set independently of steering angle θh and vehicle speed V.

[0029] The second condition is a condition that the target equivalent steering angle θp*0 deviates from the equivalent steering angle θp even though the steered wheels 44 can be steered. The second condition may be, for example, a condition that the vehicle's start switch is switched from an off state to an on state. When the steering wheel 12 is rotated with the start switch in the off state, the steering angle θh and the equivalent steering angle θp become inconsistent. Therefore, at the time of the start switch switching, even though the steered wheels 44 can be steered, the target equivalent steering angle θp*0 deviates significantly from the equivalent steering angle θp. Alternatively, for example, the second condition may be a condition that the current limit of the steering motor 60 is released. Specifically, for example, if the steered wheels 44 hit an obstacle such as a curb while the current of the steering motor 60 is limited, it becomes difficult to steer the steered wheels 44 toward the obstacle. In this state, if the steering wheel 12 is steered toward the side that hits the obstacle, the target equivalent steering angle θp*0 changes as the steering angle θh changes. In contrast, the equivalent steering angle θp is maintained at a constant value. If the current limitation of the steering motor 60 is released in this state, the target equivalent steering angle θp*0 and the equivalent steering angle θp will differ significantly, even though the steered wheels 44 can be controlled to be steered.

[0030] When the PU 72 determines that a predetermined condition is met (S12: YES), it assigns "1" to the offset flag Fo (S14). Then, the PU 72 calculates an offset amount Δθpa0, which is an amount equivalent to the difference between the target steering equivalent angle θp* and the actual steering equivalent angle θp (S16). More specifically, when the first condition is met, the PU 72 assigns a value obtained by subtracting the previous value "θp*0(n-1)" of the target steering equivalent angle θp*0 from the current value "θp*0(n)" of the target steering equivalent angle θp*0 to the offset amount Δθpa0. Note that the steering equivalent angle θp immediately before the first condition is met is considered to be approximately equal to the target steering equivalent angle θp*0. Therefore, when the first condition is met, the "value obtained by subtracting the previous value from the current value of the target steering equivalent angle θp*0" can be considered to be the difference between the target steering equivalent angle θp* and the actual steering equivalent angle θp. In other words, when the first condition is met, the "value obtained by subtracting the previous value from the current value of the target steering equivalent angle θp*0" can be regarded as an amount equivalent to the difference between the target steering equivalent angle θp* and the actual steering equivalent angle θp. On the other hand, when the second condition is met, the PU 72 assigns the value obtained by subtracting the steering equivalent angle θp from the target steering equivalent angle θp*0 to the offset amount Δθpa0.

[0031] Next, the PU 72 assigns the offset amount Δθpa0 to the offset correction amount Δθpa (S18). On the other hand, if the PU 72 determines that the predetermined condition is not met (S12: NO), it assigns zero to the offset amount Δθpa0 (S20).

[0032] 3 when the PU 72 completes the processes of S18 and S20 or when a positive determination is made in the process of S10. "Details of Residual Current Suppression Process M24" Fig. 4 shows a detailed procedure of a part of the residual current suppression process M24. The process shown in Fig. 4 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval.

[0033] 4, the PU 72 determines whether the residual flag FL is "1" (S30). The value of the residual flag FL is set to "1" when the absolute value of the offset correction amount Δθpb is set to a value greater than zero. The value of the residual flag FL is set to "0" when the absolute value of the offset correction amount Δθpb is zero.

[0034] When the PU 72 determines that the remaining flag FL is "0" (S30: NO), the PU 72 determines whether the logical product of the following conditions A to C is true (S32). Condition A is a condition that indicates that the vehicle is stopped.

[0035] Condition B is a condition that the absolute value of the q-axis current iqt of the steering motor 60 is equal to or greater than the threshold value Ith. Condition C is a condition that the maximum value of the magnitude of the steering torque Th in a predetermined period is equal to or less than a predetermined value. Here, the predetermined value is set to a value smaller than the magnitude of the steering torque Th when the driver turns the steering wheel 12. Condition C is a condition for determining that the driver has no intention of turning the steering wheel 12.

[0036] If the PU 72 determines that the logical product is true (YES in S32), it assigns "1" to the residual flag FL (S34). On the other hand, if the PU 72 determines that the residual flag FL is "1" (YES in S30), it determines whether steering has started (S36). For example, the PU 72 may determine that steering has started when the absolute value of the rate of change of the steering angle θh is equal to or greater than a predetermined rate. Alternatively, for example, the PU 72 may determine that steering has started when the absolute value of the steering torque Th is equal to or greater than a predetermined value.

[0037] When PU 72 determines that steering has not started (S36: NO), it calculates an offset correction amount Δθpb for bringing target steering equivalent angle θp* closer to steering equivalent angle θp (S38). As an example, when the absolute value of the difference between steering equivalent angle θp and target steering equivalent angle θp* is equal to or greater than a predetermined amount ΔIL, PU 72 subtracts from offset correction amount Δθpb a value having the sign of the value obtained by subtracting target steering equivalent angle θp* from steering equivalent angle θp and the magnitude of the predetermined amount ΔIL. The predetermined amount ΔIL is set to a change in steering angle per predetermined time that is difficult for the driver to perceive. Here, the predetermined time is the cycle of the processing shown in FIG. 4.

[0038] On the other hand, if the PU 72 determines that steering has started (S36: YES), it assigns "0" to the residual flag FL (S40), the PU 72 assigns the offset correction amount Δθpb to the offset amount Δθpb0 (S42), and the PU 72 assigns "1" to the recovery flag FI (S44).

[0039] On the other hand, if the determination in step S32 is negative, the PU 72 assigns zero to the offset correction amount Δθpb (S46). When the processes of steps S34, S38, S44, and S46 are completed, the PU 72 temporarily ends the series of processes shown in FIG.

[0040] "Details of Offset Reduction Speed ​​Setting Process M28" Fig. 5 shows a detailed procedure of part of the offset reduction speed setting process M28. 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.

[0041] In the series of processes shown in FIG. 5 , the PU 72 determines whether the logical product of the first cooperative control being stopped and the second cooperative control being stopped is true (S50). If the logical product is true (S50: YES), the PU 72 determines whether the values ​​of both the offset flag Fo and the recovery flag FI are "1" (S52). If the PU 72 determines that both values ​​are "1" (S52: YES), the PU 72 determines whether the signs of the offset amounts Δθpa0 and Δθpb0 are equal (S54). If the signs are equal (S54: YES), the PU 72 executes the first cooperative control (S56). On the other hand, if the signs are opposite (S54: NO), the PU 72 executes the second cooperative control (S58).

[0042] The PU 72 temporarily terminates the series of processes shown in Fig. 5 when it completes the processes of S56 and S58 or when it makes a negative determination in the processes of S50 and S52. Fig. 6 shows a detailed procedure of the first cooperative control. The series of processes shown in Fig. 6 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval.

[0043] In the series of processes shown in FIG. 6 , the PU 72 first calculates a decrease amount Δ that determines the decrease rate of the magnitudes of the offset correction amounts Δθpa and Δθpb (S60). Specifically, the PU 72 first calculates a steering angular velocity sensitive base value Δωb based on the target steering equivalent angular velocity ωp*0 as an input variable. The target steering equivalent angular velocity ωp*0 is the rate of change of the target steering equivalent angle θp*0. The target steering equivalent angular velocity ωp*0 is calculated by the PU 72 based on the target steering equivalent angle θp*0 as an input variable. Specifically, the PU 72 calculates the steering angular velocity sensitive base value Δωb based on the target steering equivalent angular velocity ωp*0 as an input variable. More specifically, the PU 72 changes the steering angular velocity sensitive base value Δωb based on the target steering equivalent angular velocity ωp*0 as an input variable under the following conditions: The condition is that the steering angular velocity sensitive base value Δωb when the absolute value of the target steering equivalent angular velocity ωp*0 is large is equal to or greater than the steering angular velocity sensitive base value Δωb when the absolute value of the target steering equivalent angular velocity ωp*0 is small. This processing may be processing in which the steering angular velocity sensitive base value Δωb is calculated using map data based on the target steering equivalent angular velocity ωp*0 as an input variable. Here, the map data is data in which the target steering equivalent angular velocity ωp*0 is an input variable and the steering angular velocity sensitive base value Δωb is an output variable.

[0044] Note that map data is a set of data consisting of discrete values ​​of input variables and values ​​of output variables corresponding to each of the input variable values. Furthermore, map calculation may be a process in which, when the value of an input variable matches one of the input variable values ​​in the map data, the value of the corresponding output variable in the map data is the calculation result. Furthermore, map calculation may be a process in which, when the value of an input variable does not match any of the input variable values ​​in the map data, the calculation result is a value obtained by interpolating the values ​​of multiple output variables included in the map data. Alternatively, map calculation may be a process in which, when the value of an input variable does not match any of the input variable values ​​in the map data, the calculation result is the value of the output variable in the map data that corresponds to the closest value of the multiple input variables included in the map data.

[0045] The PU 72 also multiplies the steering angular velocity-sensitive base value Δωb, which is an input variable, by a gain Gv and assigns the resulting value to the steering angular velocity-sensitive decrease amount Δω. The gain Gv is calculated by the PU 72 based on the vehicle speed V, which is an input variable. This process may be a map calculation using map data in which the vehicle speed V is an input variable and the gain Gv is an output variable. The PU 72 also calculates the vehicle speed-sensitive decrease amount Δv based on the vehicle speed V, which is an input variable. This process may be a map calculation using map data in which the vehicle speed V is an input variable and the vehicle speed-sensitive decrease amount Δv is an output variable. The PU 72 then assigns the smaller of the steering angular velocity-sensitive decrease amount Δω and the vehicle speed-sensitive decrease amount Δv to the decrease amount Δ.

[0046] Next, the PU 72 multiplies the decrease amount Δ by the remaining amount gain Gθ and assigns the resulting value to the decrease amount Δ (S62). The remaining amount gain Gθ is calculated by the PU 72 according to the absolute value of the sum of the offset correction amounts Δθpa and Δθpb as input variables.

[0047] If the absolute value of the sum is greater than a predetermined value Δθp1, the PU 72 assigns "1" to the remaining amount gain Gθ. If the absolute value of the sum is equal to or less than the predetermined value Δθp1, the PU 72 changes the remaining amount gain Gθ according to the absolute value under the following condition: the remaining amount gain Gθ when the absolute value of the sum is large must be equal to or greater than the remaining amount gain Gθ when the absolute value of the sum is small. The PU 72 also sets the minimum gain Gmin, which is the remaining amount gain Gθ when the absolute value of the sum is zero, to a value greater than "0."

[0048] For example, the remaining amount gain Gθ is calculated by the PU 72 using a map, with map data stored in advance in the storage device 74. Here, the map data is data in which the absolute value of the above sum is an input variable and the remaining amount gain Gθ is an output variable.

[0049] The PU 72 determines whether the absolute value of the offset correction amount Δθpa is zero (S64). If the PU 72 determines that the absolute value of the offset correction amount Δθpa is not zero (S64: NO), the PU 72 determines whether the offset amount Δθpa0 is positive (S66). If the PU 72 determines that the offset amount Δθpa0 is positive (S66: YES), the PU 72 assigns the smaller of either zero or a value obtained by subtracting the decrease amount Δ from the offset correction amount Δθpa to the offset correction amount Δθpa (S68). On the other hand, if the PU 72 determines that the offset amount Δθpa0 is not positive (S66: NO), the PU 72 assigns the larger of either zero or a value obtained by adding the decrease amount Δ to the offset correction amount Δθpa to the offset correction amount Δθpa (S70).

[0050] As is clear from the processes of S68 and S70, the decrease amount Δ is a decrease variable that defines the decrease rate of the magnitude of the offset correction amount Δθpa. Incidentally, the decrease rate of the magnitude of the offset correction amount Δθpa is expressed as "Δ / Tc" using the cycle Tc of the series of processes shown in FIG.

[0051] On the other hand, if the PU 72 determines that the offset correction amount Δθpa is zero (S64: YES), it assigns "0" to the offset flag Fo (S72). Then, the PU 72 determines whether the offset correction amount Δθpb is zero (S74). If the PU 72 determines that the offset correction amount Δθpb is not zero (S74: NO), it determines whether the offset correction amount Δθpb is positive (S76). If the PU 72 determines that the offset amount Δθpb0 is positive (S76: YES), it assigns the smaller of the value obtained by subtracting the decrease amount Δ from the offset correction amount Δθpb or zero to the offset correction amount Δθpb (S78). On the other hand, if the PU 72 determines that the offset amount Δθpb0 is not positive (S76: NO), it assigns the smaller of the value obtained by adding the decrease amount Δ to the offset correction amount Δθpb or zero to the offset correction amount Δθpb (S80).

[0052] As is clear from the processes of S78 and S80, the decrease amount Δ is a decrease variable that defines the decrease rate of the magnitude of the offset correction amount Δθpb. The decrease rate of the magnitude of the offset correction amount Δθpb is expressed as "Δ / Tc" using the cycle Tc of the series of processes shown in FIG.

[0053] On the other hand, if the PU 72 determines that the offset correction amount Δθpb is zero (YES in S74), the PU 72 sets the recovery flag FI to “0” (S82). Then, the PU 72 determines that the first cooperative control has been completed (S84).

[0054] When the PU 72 completes the processes of S68, S70, S78, S80, and S84, it temporarily terminates the series of processes shown in Fig. 6. Fig. 7 shows a detailed procedure of the second cooperative control. The series of processes shown in Fig. 7 are realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval. For convenience, the same step numbers are assigned to processes in Fig. 7 that correspond to those shown in Fig. 6.

[0055] 7 , when completing the process of S60, the PU 72 multiplies the decrease amount Δ by the remaining amount gain Gθ and assigns the result to the decrease amounts Δa and Δb (S62a). Specifically, the PU 72 multiplies the decrease amount Δ by the remaining amount gain Gθ calculated according to the absolute value of the offset correction amount Δθpa as an input variable, and assigns the result to the decrease amount Δa. Furthermore, the PU 72 multiplies the decrease amount Δ by the remaining amount gain Gθ calculated according to the absolute value of the offset correction amount Δθpb as an input variable, and assigns the result to the decrease amount Δb.

[0056] When the PU 72 completes the process of S62a, it proceeds to the process of S64. When the PU 72 determines that the offset correction amount Δθpa is positive (YES in S66), it assigns the smaller of either zero or a value obtained by subtracting the decrease amount Δa from the offset correction amount Δθpa to the offset correction amount Δθpa (S68a). On the other hand, when the PU 72 determines that the offset amount Δθpa0 is not positive (NO in S66), it assigns the larger of either zero or a value obtained by adding the decrease amount Δa to the offset correction amount Δθpa to the offset correction amount Δθpa (S70a).

[0057] As is clear from the processes of S68a and S70a, the decrease amount Δa is a decrease variable that defines the decrease rate of the magnitude of the offset correction amount Δθpa. Incidentally, the decrease rate of the magnitude of the offset correction amount Δθpa is expressed as "Δa / Tc" using the cycle Tc of the series of processes shown in FIG.

[0058] After completing the processes of S68a, S70a, and S72, the PU 72 determines whether the offset correction amount Δθpb is zero (S74). If the PU 72 determines that the offset correction amount Δθpb is not zero (S74: NO), the PU 72 determines whether the offset correction amount Δθpb is positive (S76). If the PU 72 determines that the offset amount Δθpb0 is positive (S76: YES), the PU 72 assigns the smaller of either zero or a value obtained by subtracting the decrease amount Δb from the offset correction amount Δθpb (S78a). On the other hand, if the PU 72 determines that the offset amount Δθpb0 is not positive (S76: NO), the PU 72 assigns the larger of either zero or a value obtained by adding the decrease amount Δb to the offset correction amount Δθpb (S80a).

[0059] As is clear from the processes of S78a and S80a, the decrease amount Δb is a decrease variable that defines the decrease rate of the magnitude of the offset correction amount Δθpb. The decrease rate of the magnitude of the offset correction amount Δθpb is expressed as "Δb / Tc" using the cycle Tc of the series of processes shown in FIG.

[0060] When the PU 72 completes the process of S82, it determines whether the offset flag Fo is "0" (S83). When it determines that the offset flag Fo is zero (S83: YES), it determines that the second cooperative control is completed (S84a).

[0061] The PU 72 temporarily terminates the series of processes shown in FIG. 7 when it completes the processes of S78a, S80a, and S84a or when a negative determination is made in S83. The process of setting the reduction rate at which the offset correction amounts Δθpa and Δθpb are reduced in the offset reduction rate setting process M28 is not limited to the first cooperative control and the second cooperative control. The offset reduction rate setting process M28 also includes a process of setting the reduction rate at which one of the offset correction amounts Δθpa and Δθpb is reduced. This process is executed when a negative determination is made in S50 or S52 and only one of the offset flag Fo and the recovery flag FI is set to "1." This process sets the reduction rate at which one of the offset correction amounts Δθpa and Δθpb is reduced by a reduction amount Δ. Here, the reduction amount Δ is set by the same process as in S60 or S62. More specifically, in the process of S62, the remaining amount gain Gθ is set in accordance with either one of the offset correction amounts Δθpa and Δθpb.

[0062] <Functions and Effects of the Present Embodiment> Fig. 8 shows a situation in which a positive determination is made in the processing of S54. The right side of Fig. 8 shows a case in which the first cooperative control is executed. The left side of Fig. 8 shows a comparative example in which the first cooperative control is not executed.

[0063] In the upper part of Fig. 8, the dashed dotted line indicates the transition of the target steering equivalent angle θp*0. Also, in the upper part of Fig. 8, the solid line indicates the transition of the target steering equivalent angle θp*. Also, in the upper part of Fig. 8, the two-dotted line virtually indicates the transition of the target steering equivalent angle θp* in the case where the magnitudes of the offset correction amounts Δθpa, Δθpb are not reduced.

[0064] 8, after time t1, the absolute values ​​of the offset correction amounts Δθpa and Δθpb simultaneously gradually decrease. In this case, the rate of change of the target steering equivalent angle θp* becomes excessively large until time t2 when the offset correction amount Δθpb becomes zero.

[0065] 8, in this embodiment, the PU 72 first gradually decreases only the absolute value of the offset correction amount Δθpa after time t1. Then, after time t4 when the offset correction amount Δθpa becomes zero, the PU 72 gradually decreases the offset correction amount Δθpb. This makes it possible to prevent the absolute value of the rate of change of the target steering equivalent angle θp* from becoming excessively large.

[0066] Figure 9 shows a situation in which a negative determination is made in the processing of S54. Figure 9 shows a case in which second cooperative control is executed. In the upper part of Figure 9, the dashed dotted line indicates the transition of the target steering equivalent angle θp*0. Also in the upper part of Figure 9, the solid line indicates the transition of the target steering equivalent angle θp*. Also in the upper part of Figure 9, the two-dotted line virtually indicates the transition of the target steering equivalent angle θp* in the case in which the offset correction amounts Δθpa, Δθpb are not reduced.

[0067] After time t1, the absolute values ​​of the offset correction amount Δθpa and the offset correction amount Δθpb gradually decrease simultaneously, so that the target steering equivalent angle θp* is hardly affected by the gradual decrease until time t2 when the offset correction amount Δθpb becomes zero. Strictly speaking, when the absolute value of the offset correction amount Δθpb is greater than a predetermined value Δθp1, there is no effect of the gradual decrease. When the absolute value of the offset correction amount Δθpb becomes equal to or less than the predetermined value Δθp1, a difference occurs between the rate of decrease of the absolute value of the offset correction amount Δθpa and the rate of decrease of the absolute value of the offset correction amount Δθpb due to the remaining amount gain Gθ. Therefore, the change in the target steering equivalent angle θp* is slightly affected by the gradual decrease. Then, after time t2 when the offset correction amount Δθpb becomes zero, the rate of change of the target steering equivalent angle θp* is a rate of change determined by the decrease amount Δ superimposed on the rate of change of the target steering equivalent angle θp*0.

[0068] According to the present embodiment described above, the following further actions and effects can be obtained. (1) The PU 62 sets the rate of decrease of the magnitude of the offset correction amount Δθpa and the rate of decrease of the magnitude of the offset correction amount Δθpb to be the same by defining them by the same decrease amount Δ. This makes it possible to suppress fluctuations in the rate of change of the target steering equivalent angle θp* due to the gradual decrease process of the offset correction amounts Δθpa and Δθpb.

[0069] (2) The processes for setting the reduction rates of the magnitudes of the two offset correction amounts Δθpa and Δθpb, which are different from each other, share a single offset reduction rate setting process M28. This reduces the calculation load.

[0070] 6 and 7, it is particularly easy to adopt logic that continues the processing of S60, S62, and S66 to S70 even when the offset correction amounts Δθpa and Δθpb become zero. In this case, even when cooperative control is not being performed, the computational load is greater than when a single offset reduction rate setting process M28 is provided. That is, regardless of whether cooperative control is being performed, the offset correction amount calculation process M20 and the residual current suppression process M24 each perform processes similar to the processes of S60, S62, and S66 to S70, so the computational load is constantly large.

[0071] (3) In the gradual decrease process of the absolute values ​​of the offset correction amounts Δθpa, Δθpb, when the remaining absolute value to be gradually decreased falls below a predetermined value Δθp1, PU 72 sets the remaining amount gain Gθ to a value smaller than "1." Therefore, the decrease amount Δ is smaller than when the absolute value was greater than the predetermined value Δθp1. Therefore, the rate at which the absolute value decreases due to the gradual decrease process is slower. Therefore, at the end of the gradual decrease process, the absolute value of the second-order derivative of the target steering equivalent angle θp* can be prevented from becoming excessively large. Therefore, it is possible to prevent the output value of the derivative element in steering feedback process M30 from becoming excessively large as the gradual decrease process ends.

[0072] (4) When the offset correction amounts Δθpa and Δθpb have the same sign, the PU 62 calculates the remaining gain Gθ based on the absolute value of the sum of the offset correction amounts Δθpa and Δθpb as input variables. This allows the gradual decrease speed of the offset correction amounts Δθpa and Δθpb to be appropriately reduced only near the end of the gradual decrease process.

[0073] (5) When the signs of the offset correction amounts Δθpa and Δθpb are different from each other, the PU 62 calculates the remaining amount gain Gθ based on the offset correction amount Δθpa as an input variable, and calculates the remaining amount gain Gθ based on the offset correction amount Δθpb as an input variable. This allows the remaining amount gain Gθ to be set simply.

[0074] <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.

[0075] Regarding Collaborative Processing In the above embodiment, when the offset correction amounts Δθpa and Δθpb have the same sign, the offset correction amount Δθpa is reduced to zero and then the offset correction amount Δθpb is reduced to zero. However, this is not limiting. For example, when the offset correction amounts Δθpa and Δθpb have the same sign, the offset correction amount Δθpb may be reduced to zero and then the offset correction amount Δθpa may be reduced to zero.

[0076] The collaborative processing is not limited to a processing in which, when the offset correction amounts Δθpa and Δθpb have the same sign, the first offset correction amount is reduced to zero and then the second offset correction amount is reduced. For example, the collaborative processing may be a processing in which both the offset correction amounts Δθpa and Δθpb are simultaneously reduced even when the offset correction amounts Δθpa and Δθpb have the same sign. However, in this case, for example, when both the offset correction amounts Δθpa and Δθpb are non-zero, the respective reduction rates are set to "1 / 2" of the reduction rate when only one of the offset correction amounts Δθpa and Δθpb is non-zero. However, it is not necessary that the reduction rates of the offset correction amounts Δθpa and Δθpb be equal. For example, the reduction rate of the offset correction amount Δθpa may be twice the reduction rate of the offset correction amount Δθpb. In this case, it is sufficient that the rate of decrease of each of the offset correction amounts is less than the rate of decrease when only one of the offset correction amount Δθpa and the offset correction amount Δθpb is non-zero.

[0077] The cooperative process for cooperatively setting the reduction rates of the offset correction amounts used in each of the multiple types of offset compensation processes is not limited to cooperatively setting the reduction rates of the offset correction amounts Δθpa and Δθpb. For example, the cooperative process may be a process for cooperatively setting the reduction rates of two types of correction amounts: one of the offset correction amounts Δθpa and Δθpb, and another correction amount that can be set simultaneously with the offset correction amount. Furthermore, for example, the cooperative process may be a process for cooperatively setting the reduction rates of three or more types of offset correction amounts that can be set simultaneously.

[0078] "Regarding operation processing" The operation amount of the closed-loop control does not necessarily have to be the sum of the output value of the proportional element, the output value of the derivative element, and the output value of the integral element. For example, the operation amount of the closed-loop control may be the sum of the output value of the proportional element and the output value of the derivative element. Also, for example, the operation amount of the closed-loop control may be the sum of the output value of the derivative element and the output value of the integral element.

[0079] The manipulated variable of the closed-loop control does not necessarily have to consist of only the manipulated variable of the classical control. For example, the manipulated variable of the closed-loop control may include a disturbance estimated by a disturbance observer.

[0080] The operation of the motor according to the manipulated variable of the closed-loop control is not limited to the operation of the motor according to only the manipulated variable of the closed-loop control. For example, the operation of the motor according to the sum of the manipulated variable of the closed-loop control and the manipulated variable of the open-loop control may be used.

[0081] The motor operation according to the differential manipulated variable is not limited to the motor operation according to the manipulated variable of closed-loop control in which the target steering equivalent angle is the target value of the controlled variable. For example, the controlled variable does not have to include the steering equivalent angle.

[0082] Regarding the Decrease Variable Setting Process The decrease amount Δ is not limited to the value obtained by multiplying the steering angular velocity sensitive base value Δωb by the gain Gv that depends on the vehicle speed V. For example, the gain Gv may be a fixed value.

[0083] With map data stored in storage device 74, PU 72 may perform map calculations to determine the decrease amount Δ in accordance with the target steering-equivalent angular velocity ωp*0 and vehicle speed V. Here, the map data is data in which the target steering-equivalent angular velocity ωp*0 and vehicle speed V are input variables and the decrease amount Δ is an output variable.

[0084] The decrease amount Δ may be the sum of the steering angular velocity-sensitive decrease amount Δω and the vehicle speed-sensitive decrease amount Δv. Here, the PU 72 may calculate the steering angular velocity-sensitive decrease amount Δω in accordance with the target steering equivalent angular velocity ωp*0 under the following condition. The condition is that the magnitude of the steering angular velocity-sensitive decrease amount Δω when the absolute value of the target steering equivalent angular velocity ωp*0 is large is equal to or greater than the magnitude of the steering angular velocity-sensitive decrease amount Δω when the absolute value of the target steering equivalent angular velocity ωp*0 is small. Furthermore, the PU 72 may calculate the vehicle speed-sensitive decrease amount Δv in accordance with the vehicle speed V under the following condition. The condition is that the vehicle speed-sensitive decrease amount Δv when the vehicle speed V is large is equal to or greater than the vehicle speed-sensitive decrease amount Δv when the vehicle speed V is small.

[0085] The decrease variables set by the decrease variable setting process are not limited to the decrease amounts Δ, Δa, and Δb. Regarding the reduction process: When the offset correction amounts Δθpa and Δθpb are zero, it is not essential that the remaining amount gain Gθ be greater than "0."

[0086] It is not essential that the value of the remaining amount gain Gθ be "1" when the absolute values ​​of the offset correction amounts Δθpa, Δθpb, etc. are larger than the predetermined value Δθp1. For example, when the gradual reduction process of the offset correction amount is started when the absolute value is larger than the predetermined value Δθp1, the remaining amount gain Gθ may be temporarily increased gradually from a value smaller than "1" to "1" as the absolute value decreases. This makes it possible to limit the magnitude of the rate of change of the target steering equivalent angle θp* associated with the start of the gradual reduction process to a small value.

[0087] The value of the remaining amount gain Gθ does not necessarily have to be "1" when the absolute values ​​of the offset correction amounts Δθpa, Δθpb or their sum are greater than the predetermined value Δθp1. For example, the value of the remaining amount gain Gθ may be "0.9" when the absolute values ​​of the offset correction amounts Δθpa, Δθpb or their sum are greater than the predetermined value Δθp1. The point is that the value of the remaining amount gain Gθ when the absolute values ​​of the offset correction amounts Δθpa, Δθpb or their sum are greater than the predetermined value Δθp1 must be a constant value and must be greater than the value when the absolute values ​​of the offset correction amounts Δθpa, Δθpb or their sum are equal to or less than the predetermined value Δθp1.

[0088] - If the signs of the offset correction amounts Δθpa and Δθpb are opposite and the value obtained by subtracting the smaller of their absolute values ​​from the larger is equal to or greater than a predetermined value Δθp1, only the larger absolute value may be multiplied by the remaining amount gain Gθ.

[0089] Regarding the offset reduction process, it is not essential that the reduction process be a process of multiplying the reduction amount Δ, which is the value of the reduction variable set by the reduction variable setting process, by the remaining amount gain Gθ. The offset reduction process may be a process of calculating the reduction amount using map data in which the variables used to calculate the remaining amount gain Gθ in the above embodiment, the vehicle speed V, and the target steering equivalent angular velocity ωp*0 are input variables and the reduction amount is an output variable.

[0090] "Regarding the steering control device" The steering control device is not limited to one that executes various processes using a PU. For example, it may be equipped with a dedicated hardware circuit, such as an ASIC, that executes at least part of the processes executed in the above embodiments. That is, the steering control device may be equipped with any of the following processing circuits (a) to (c). (a) A processing circuit that includes a processing device that executes all of the above processes in accordance with a program, and a program storage device such as a memory device that stores the program. (b) A processing circuit that includes a processing device and program storage device that executes part of the above processes in accordance with a program, and a dedicated hardware circuit that executes the remaining processes. (c) A processing circuit that includes a dedicated hardware circuit that executes all of the above processes. Here, there may be multiple software execution devices that include a processing device and a program storage device, and multiple dedicated hardware circuits.

[0091] Regarding the steering actuator: As the steering actuator At, for example, one in which steering motor 60 is arranged coaxially with steering shaft 40 may be used. Alternatively, for example, one connected to steering shaft 40 via a belt-type reducer using a ball screw mechanism may be used.

Claims

1. A system is configured to execute a target steering equivalent angle setting process, an operation process, an offset amount calculation process, an offset compensation process, and an offset reduction process when the steered wheels and the steering shaft are mechanically disconnected, wherein the target steering equivalent angle setting process is a process for setting a target steering equivalent angle, the target steering equivalent angle being a target value of the steering equivalent angle which is a variable indicating the steering angle of the steered wheels, the operation process is a process for operating a motor that steers the steered wheels in accordance with a control operation amount for which the target steering equivalent angle is a target value of the control amount, the offset amount calculation process is a process for calculating an offset amount which is an amount equivalent to the difference between the target steering equivalent angle and the actual steering equivalent angle when a predetermined condition is met as a trigger, and the offset compensation process is a process for correcting the target steering equivalent angle by an offset correction amount which is in accordance with the offset amount, the predetermined condition includes a plurality of types of conditions, and the offset amount calculation process and the offset compensation process are provided separately for each of the plurality of types of conditions, The offset reduction process is a process for reducing the magnitude of the offset correction amount, and when two or more different offset compensation processes are being executed, the steering control device includes a cooperative process for cooperatively setting the reduction rate of the magnitude of the offset correction amount used in the two or more offset compensation processes.

2. A steering control device as described in claim 1, wherein the offset reduction process includes a reduction variable setting process, the reduction variable setting process is a process for setting a value of a reduction variable, the reduction variable is a variable indicating a reduction rate of the magnitude of the offset correction amount, and the reduction variable setting process is shared for setting the reduction rate of the magnitude of the offset correction amount in each of the two or more offset compensation processes.

3. A steering control device as described in claim 1, wherein the two or more mutually different offset compensation processes include a first offset compensation process and a second offset compensation process, and the cooperative process includes a process of reducing the magnitude of the offset compensation amount used in the first offset compensation process prior to a process of reducing the magnitude of the offset compensation amount used in the second offset compensation process when the offset compensation amount used in the first offset compensation process and the offset compensation amount used in the second offset compensation process have the same sign.

4. A steering control device as described in claim 3, wherein the cooperative processing is a processing for executing a processing for reducing the magnitude of the offset correction amount used in the second offset compensation processing after the processing for reducing the magnitude of the offset correction amount used in the first offset compensation processing is completed, and includes a processing for setting the rate of reduction of the magnitude of the offset correction amount used in the first offset compensation processing and the rate of reduction of the magnitude of the offset correction amount used in the second offset compensation processing to be the same.

5. A steering control device according to claim 4, wherein the offset reduction process includes a reduction process, which is a process for changing the reduction rate in accordance with the magnitude of the offset correction amount as an input variable when the magnitude of the offset correction amount is equal to or less than a predetermined value, on the condition that the reduction rate of the magnitude of the offset amount when the magnitude of the offset correction amount is large is equal to or greater than the reduction rate when the magnitude of the offset correction amount is small, and which includes a process for setting the input variable to the sum of the offset correction amount used in the first offset compensation process and the offset correction amount used in the second offset compensation process when the offset correction amount used in the first offset compensation process and the offset correction amount used in the second offset compensation process have the same sign.

6. A steering control device as described in claim 1, wherein the two or more mutually different offset compensation processes include a first offset compensation process and a second offset compensation process, and the cooperative process includes a process of simultaneously executing a process of decreasing the magnitude of the offset compensation amount used in the first offset compensation process and a process of decreasing the magnitude of the offset compensation amount used in the second offset compensation process when the offset compensation amount used in the first offset compensation process and the offset compensation amount used in the second offset compensation process have opposite signs.

7. A steering control method applied when the steered wheels and the steering shaft are mechanically disconnected, the steering control method comprising the steps of: executing a target steering equivalent angle setting process; executing an operation process; executing an offset amount calculation process; executing an offset compensation process; and executing an offset reduction process; the target steering equivalent angle setting process is a process for setting a target steering equivalent angle; the target steering equivalent angle is a target value of the steering equivalent angle which is a variable indicating the steering angle of the steered wheels; the operation process is a process for operating a motor which steers the steered wheels in accordance with a control operation amount for which the target steering equivalent angle is a target value of a control amount; the offset amount calculation process is a process for calculating an offset amount which is an amount equivalent to the difference between the target steering equivalent angle and the actual steering equivalent angle when a predetermined condition is met as a trigger; and the offset compensation process is a process for correcting the target steering equivalent angle by an offset correction amount which is in accordance with the offset amount; the predetermined condition comprises a plurality of types of conditions; and the offset amount calculation process and the offset compensation process are provided separately for each of the plurality of types of conditions. The offset reduction process is a process for reducing the magnitude of the offset correction amount, and when two or more different offset compensation processes are being executed, the steering control method includes a cooperative process for cooperatively setting the reduction speed of the magnitude of the offset correction amount used in the two or more offset compensation processes.

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