Steering control device and steering control method

Abstract

This steering control device is configured to execute a steering angle acquisition process, a target turning equivalent angle setting process, a turning operation process, a determination process, and a gradual change process. The target turning equivalent angle setting process is a process for setting a target turning equivalent angle according to a selected driving mode among a plurality of driving modes on the basis of a steering angle as an input variable. The plurality of driving modes are set such that the gear ratio, which is the ratio of the target turning equivalent angle to the steering angle, can be different in each of the driving modes. The determination process is a process for assessing, on the basis of whether a vehicle is in a stopped state or a traveling state, whether or not to execute the gradual change process when a request to switch the driving mode occurs. The gradual change process is a process for gradually bringing the target turning equivalent angle corresponding to the driving mode before switching closer to the target turning equivalent angle corresponding to the driving mode after switching.

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 that changes the gear ratio, which is the ratio of the turning angle to the steering angle, in accordance with the value of a mode variable that indicates the driver's preference for the steering feel of the vehicle. When the value of the mode variable is changed, this steering control device executes a process that gradually shifts the target value of the variable that indicates the turning angle from the target value corresponding to the value of the mode variable before the change to the target value corresponding to the value of the mode variable after the change.

[0003] Japanese Patent Application Laid-Open No. 2023-135038

[0004] However, depending on the circumstances in which a request to change the mode variable occurs, even if the target value is gradually changed, there is a risk of causing inconvenience such as an inappropriate sudden change in the steering angle.

[0005] One aspect of the present disclosure provides a steering control device. A control object of the steering control device is a steering device that can change the relationship between the steering angle of the steered wheels of a vehicle and the steering angle, which is the rotation angle of a steering shaft. The steering device includes a steering actuator that steers the steered wheels. The steering control device is configured to execute a steering angle acquisition process, a target steering equivalent angle setting process, a steering operation process, a determination process, and a gradual change process. The steering angle acquisition process is a process for acquiring the steering angle. The target steering equivalent angle setting process is a process for setting a target steering equivalent angle in accordance with a selected driving mode from among a plurality of driving modes, based on the steering angle as an input variable. The target steering equivalent angle is a target value of the steering equivalent angle, which is a variable indicating the steering angle. The plurality of driving modes are modes in which a gear ratio, which is the ratio of the target steering equivalent angle to the steering angle, can differ from one another. The driving modes are configured so that the gear ratio, which is the ratio of the target steering equivalent angle to the steering angle, can differ. The steering operation process is a process of operating the steering actuator so as to bring the steering equivalent angle closer to the target steering equivalent angle. The determination process is a process of determining whether to execute the gradual change process when a request to switch the driving mode is made, using whether the vehicle is in a stopped state or a traveling state as one of the conditions for determining whether to execute the gradual change process. The gradual change process is a process of gradually bringing the target steering equivalent angle corresponding to the driving mode before switching closer to the target steering equivalent angle corresponding to the driving mode after switching.

[0006] Another aspect of the present disclosure provides a steering control device. A control object of a steering control method is a steering device that can change the relationship between a steering angle, which is a rotation angle of a steering shaft, and a steering angle of steered wheels of a vehicle. The steering device includes a steering actuator that steers the steered wheels. The steering control method includes executing a steering angle acquisition process, a target equivalent steering angle setting process, a steering operation process, a determination process, and a gradual change process. The steering angle acquisition process is a process that acquires the steering angle. The target equivalent steering angle setting process is a process that sets a target equivalent steering angle in accordance with a selected driving mode from among a plurality of driving modes, based on the steering angle as an input variable. The target equivalent steering angle is a target value of the equivalent steering angle, which is a variable that indicates the steering angle. The plurality of driving modes are modes in which gear ratios, which are the ratio of the target equivalent steering angle to the steering angle, can differ from one another. The steering operation process is a process that operates the steering actuator so as to bring the equivalent steering angle closer to the target equivalent steering angle. The determination process is a process for determining whether to execute the gradual-change process when a request for switching the driving mode is made, using whether the vehicle is in a stopped state or a traveling state as one of the conditions for determining whether to execute the gradual-change process. The gradual-change process is a process for gradually approaching the target steering equivalent angle corresponding to the driving mode before switching to the target steering equivalent angle corresponding to the driving mode after switching.

[0007] It is a diagram showing the configuration of a vehicle according to one embodiment. It is a block diagram showing part of the processing executed by the steering control device shown in Fig. 1. It is a flowchart showing the procedure of the processing executed by the steering control device shown in Fig. 1. It is a flowchart showing the procedure of the processing executed by the steering control device shown in Fig. 1.

[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. The steering angle calculation process M10 is a process for calculating the steering angle θh, which is the rotation angle of the steering wheel 12, based on the rotation angle θa as an input variable. The steering angle calculation process M10 includes a process 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 process M10 includes a process 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 may be 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 steering angle θh and the vehicle speed V as input variables. 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 a 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. The target steering equivalent angle setting process M18 also includes a process for separately setting a target steering angle ratio for each of a plurality of driving modes. The driving mode is selected by the driver by operating the user interface 94 shown in FIG. 1 . The plurality of driving modes include, for example, a normal mode and a sport mode.

[0021] The offset correction amount calculation process M20 is a process for calculating an offset correction amount Δθp of the target steering equivalent angle θp* 0. The offset correction process M22 is a process for calculating the target steering equivalent angle θp* by subtracting the offset correction amount Δθp from the target steering equivalent angle θp* 0.

[0022] The steering feedback process M24 is a process for calculating the steering torque command value Tt*, which is the command value of the torque of the steering motor 60, in accordance with the operation amount of the feedback control in which the steering equivalent angle θp is the control amount and the target steering equivalent angle θp* is the target value of the control amount.

[0023] The steering operation process M26 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 rotation angle θb. The steering operation process M26 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 M26 also includes a process for calculating currents for the d and q axes based on the currents iu2, iv2, iw2 and the rotation angle θb. The steering operation process M26 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 approach the command values.

[0024] "Details of Offset Correction Amount Calculation Process M20" Fig. 3 shows a detailed procedure 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."

[0025] In the series of processes shown in Fig. 3, the PU 72 first acquires the vehicle speed V, the steering equivalent angle θp, and the target steering equivalent angle θp*0 (S10). Next, the PU 72 determines whether or not the flag F is "1" (S12). The value of the flag F is set to "1" when the absolute value of the offset correction amount Δθp is set to a value greater than zero. The value of the flag F is set to "0" when the absolute value of the offset correction amount Δθp is zero.

[0026] When the PU 72 determines that the flag F is "0" (S12: NO), the PU 72 determines whether a gradual change request, which will be described later, has been generated (S14). The gradual change request is a request to gradually change the target steering equivalent angle θp* in a situation where there is a large deviation between the target steering equivalent angle θp* and the steering equivalent angle θp.

[0027] When the PU 72 determines that a gradual change request has been generated (S14: YES), it assigns "1" to flag F (S16). Then, the PU 72 calculates an offset amount Δθp0, which is an amount equivalent to the difference between the target steering equivalent angle θp* and the actual steering equivalent angle θp (S18). More specifically, the PU 72 executes the following process A or process B.

[0028] Process A: The PU 72 assigns the 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 Δθp0. The steering equivalent angle θp immediately before a gradual change request, which will be described later, is considered to be approximately equal to the target steering equivalent angle θp*0. Therefore, when a gradual change request is made, 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 a gradual change request is made, 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 amount equivalent to the difference between the target steering equivalent angle θp* and the actual steering equivalent angle θp.

[0029] Process B: The PU 72 substitutes the value obtained by subtracting the steering equivalent angle θp from the target steering equivalent angle θp*0 into the offset amount Δθp0. Next, the PU 72 substitutes the offset amount Δθp0 into the offset correction amount Δθp (S20).

[0030] On the other hand, if the PU 72 determines that the flag F is "1" (S12: YES), it determines whether the offset correction amount Δθp is zero (S22). If the PU 72 determines that the offset correction amount Δθp is greater than zero (S22: NO), it calculates the target steering equivalent angular velocity ωp*0 (S24). The target steering equivalent angular velocity ωp*0 is the rate of change of the target steering equivalent angle θp*. The PU 72 calculates the target steering equivalent angular velocity ωp*0 based on the target steering equivalent angle θp*0 as an input variable.

[0031] The PU 72 calculates a decrease amount Δ that determines the decrease rate of the magnitude of the offset correction amount Δθp (S26). 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. 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 condition: 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 process may be a process of map-calculating the steering angular velocity sensitive base value Δωb 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.

[0032] 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.

[0033] 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.

[0034] The PU 72 determines whether the offset amount Δθp0 is positive (S28). If the PU 72 determines that the offset amount Δθp0 is positive (S28: YES), the PU 72 assigns the larger of either zero or a value obtained by subtracting the decrease amount Δ from the offset correction amount Δθp to the offset correction amount Δθp (S30). On the other hand, if the PU 72 determines that the offset amount Δθp0 is not positive (S28: 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 Δθp to the offset correction amount Δθp (S32).

[0035] On the other hand, if the PU 72 determines that the offset correction amount Δθp is zero (S22: YES), it sets the flag F to "0" (S34). If the determination in S14 is negative, the PU 72 sets the offset correction amount Δθp to zero (S36).

[0036] When the PU 72 completes the processes of S20 and S30 to S36, it temporarily ends the series of processes shown in Fig. 3. "Processing when a mode switching request is made" Fig. 4 shows the procedure of the process when a request to switch the driving mode is made. The series of processes 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.

[0037] 4, the PU 72 first determines whether a mode switching request has occurred (S40). The PU 72 determines that a mode switching request has occurred when the driver operates the user interface 94 to select a driving mode different from the currently selected driving mode.

[0038] When the PU 72 determines that a mode switching request has occurred (S40: YES), the PU 72 acquires the vehicle speed V (S42). Then, the PU 72 determines whether the vehicle is in a traveling state based on the vehicle speed V (S44). This process may be a process of determining that the vehicle is in a stopped state when the vehicle speed V is equal to or less than a threshold speed. Here, the threshold speed may be zero.

[0039] When the PU 72 determines that the vehicle is in a traveling state (S44: YES), it determines whether the absolute value of the steering angle θh is equal to or less than a predetermined value θth (S46). In other words, it determines whether the absolute value of the difference between the steering angle θh and the neutral angle exceeds the predetermined value θth. This process determines whether the change in vehicle behavior falls within an acceptable range even if the target steering angle ratio changes due to switching the driving mode. When the PU 72 determines that the steering angle θh is equal to or less than the predetermined value θth (S46: YES), it switches the driving mode (S48). Then, it generates a gradual change request (S50). When the PU 72 executes the process of S50 in conjunction with the execution of the process of S48, it executes process A in the process of S18.

[0040] On the other hand, if the PU 72 determines that the absolute value of the steering angle θh is greater than the predetermined value θth (S46: NO), it decides not to execute mode switching and notifies the user that mode switching is not possible by operating the user interface 94 (S52). For example, if the user interface 94 has a speaker, the process of S52 may be a process of outputting an audio signal. Also, for example, if the user interface 94 has a display device, the process of S52 may be a process of outputting visual information.

[0041] On the other hand, if the PU 72 determines that the vehicle is stopped (S44: NO), it executes a drive mode switch (S54). The PU 72 then determines whether the absolute value of the steering angle θh is equal to or less than the end angle θen after the drive mode switch (S56). This process determines whether the target steering equivalent angle θp*0 can be set when the drive mode is switched. That is, an upper limit is set for the magnitude of the steering equivalent angle θp. The steering angle θh when the magnitude of the steering equivalent angle θp is equal to the upper limit is the end angle θen. The steering angle θh when the absolute value of the target steering equivalent angle θp*0 is the upper limit changes depending on the target steering angle ratio. Therefore, when the drive mode is changed, the target steering equivalent angle θp*0 corresponding to the steering angle θh before the change may exceed the upper limit. In other words, the absolute value of the current steering angle θh may exceed the end angle θen.

[0042] When the PU 72 determines that the absolute value of the steering angle θh is equal to or less than the end angle θen after the drive mode is switched (YES in S56), the PU 72 determines whether the absolute value of the difference between the target steering equivalent angle θp*0 and the steering equivalent angle θp is equal to or less than a predetermined value Δθpth (S58). The predetermined value Δθpth is the allowable upper limit value of the amount of displacement of the steering equivalent angle θp.

[0043] When the PU 72 determines that the absolute value of the difference between the target steering equivalent angle θp*0 and the steering equivalent angle θp is equal to or less than the predetermined value Δθpth (S58: YES), the PU 72 proceeds to the process of S50. When the PU 72 executes the process of S50 because the determination of S58 is affirmative, the PU 72 executes the process B in the process of S18.

[0044] On the other hand, when it is determined that the absolute value of the difference between the target steering equivalent angle θp*0 and the steering equivalent angle θp exceeds the predetermined value Δθpth (S58: NO), or when the determination in the processing of S56 is negative, the PU 72 calculates a corresponding steering angle θhr (S60). The corresponding steering angle θhr is a steering angle θh whose ratio with the current steering equivalent angle θp matches the target steering angle ratio after switching of the driving mode.

[0045] The PU 72 executes synchronization processing, which is processing for operating the reaction force inverter 22 so as to bring the steering angle θh closer to the corresponding steering angle θhr (S62). The PU 72 then determines whether the absolute value of the difference between the steering angle θh and the corresponding steering angle θhr is equal to or less than a predetermined value Δθh (S64). The predetermined value Δθh is the allowable upper limit value for the amount of displacement of the steering equivalent angle θp. This processing determines whether the amount of change in the target steering equivalent angle θp*0 when a gradual change request is generated is equal to or less than the allowable upper limit value. The PU 72 continues processing in S62 until the absolute value of the difference between the steering angle θh and the corresponding steering angle θhr becomes equal to or less than the predetermined value Δθh. If the PU 72 determines that the absolute value of the difference between the steering angle θh and the corresponding steering angle θhr is equal to or less than the predetermined value Δθh (S64: YES), the PU 72 proceeds to processing in S50. When the PU 72 executes the process of S50 as a result of a positive determination being made in the process of S64, the PU 72 executes the process B in the process of S18.

[0046] The PU 72 temporarily terminates the series of processes shown in FIG. 4 when it completes the processes of S50 and S52 or when it makes a negative determination in S40. <Functions and Effects of the Present Embodiment> When a request to switch the driving mode is generated, the PU 72 determines whether the vehicle is in a driving state. If the PU 72 determines that the vehicle is in a driving state, the PU 72 executes a driving mode switch on the condition that the absolute value of the steering angle θh is equal to or less than a predetermined value θth. Then, the PU 72 generates a gradual change request to gradually bring the target steering equivalent angle θp* closer to the value after the switch from the value before the switch. On the other hand, if the PU 72 determines that the vehicle is in a driving state and the absolute value of the steering angle θh exceeds the predetermined value θth, the PU 72 does not execute a driving mode switch. This prevents a sudden change in vehicle behavior due to a driving mode switch.

[0047] When a request to switch the driving mode is generated and the PU 72 determines that the vehicle is stopped, the PU 72 executes a switching of the driving mode. The PU 72 then determines whether the absolute value of the steering angle θh is equal to or less than the end angle θen. When the PU 72 determines that the absolute value of the steering angle θh is equal to or less than the end angle θen and the absolute value of the difference between the target steering equivalent angle θp* after the switching of the driving mode and the current steering equivalent angle θp is equal to or less than a predetermined value Δθpth, the PU 72 generates a gradual change request. This causes the PU 72 to gradually approach the target steering equivalent angle θp* from its value before the switching to its value after the switching.

[0048] On the other hand, if PU 72 determines that the absolute value of steering angle θh is equal to or less than end angle θen and determines that the absolute value of the difference between the target steering equivalent angle θp* after the driving mode switch and the current steering equivalent angle θp is greater than predetermined value Δθpth, it executes the following process. That is, PU 72 operates reaction force inverter 22 so as to bring steering angle θh closer to corresponding steering angle θhr. Then, when the absolute value of the difference between the target steering equivalent angle θp* after the driving mode switch and the current steering equivalent angle θp becomes equal to or less than predetermined value Δθpth, PU 72 generates a gradual-change request and gradually brings target steering equivalent angle θp* closer to the value after the switch from the value before the switch.

[0049] <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.

[0050] Regarding the Synchronization Process: The PU 72 may execute a process similar to that of S58 instead of S64. The synchronization process is not limited to a process that is completed when a positive determination is made in S64. For example, the synchronization process may be completed when the steering angle θh matches the corresponding steering angle θhr. In this case, it is not necessary to generate a gradual change request after the synchronization process is completed.

[0051] Regarding the determination process: (a) Regarding the generation of a gradual change request: When the absolute value of the steering angle θh is greater than a predetermined value θth in a traveling state, it is not essential not to generate a gradual change request. For example, when a gradual change request is generated even though the absolute value of the steering angle θh is greater than the predetermined value θth in a traveling state, the decrease amount Δ may be set to a smaller value than when the absolute value of the steering angle θh is equal to or less than the predetermined value θth.

[0052] Alternatively, instead of issuing a gradual-change request when both S44 and S46 are determined to be positive, the PU 72 may execute the following process. That is, the PU 72 may issue a gradual-change request when the absolute value of the steering angle θh is equal to or less than a determination value. Here, the PU 72 changes the determination value in accordance with the vehicle speed V under the condition that the determination value when the vehicle speed V is high is equal to or less than the determination value when the vehicle speed V is low.

[0053] (b) Regarding the execution of driving mode switching: When a mode switching request occurs during driving, the PU 72 may uniformly decide not to execute the driving mode switching process.

[0054] "Regarding Driving Modes" The multiple driving modes in which the gear ratio, which is the ratio of the target steering equivalent angle to the steering angle, can differ from one another do not necessarily have to be a sport mode and a normal mode. The multiple driving modes may include a mode in which the target steering angle ratio is larger than that of the sport mode. Also, the multiple driving modes may include a mode in which the target steering angle ratio is smaller than that of the normal mode. Also, the multiple driving modes may include a mode in which a target steering angle ratio freely set by the driver is used instead of a predetermined target steering angle ratio.

[0055] Regarding the Gradual Change Process: The steering angular velocity variable, which is an input variable in the process of calculating the steering angular velocity sensitive base value Δωb, is not limited to the target steering equivalent angular velocity ωp*0. The steering angular velocity variable may be, for example, the rate of change of the steering angle θh.

[0056] 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.

[0057] 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 rate of change of the target steering equivalent angle θp*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 rate of change of the target steering equivalent angle θp*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.

[0058] "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.

[0059] 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 steering control device in which a steering device that can change the relationship between the steering angle of the steered wheels of a vehicle and the steering angle, which is the rotation angle of a steering shaft, is a control object, the steering device is equipped with a steering actuator that steers the steered wheels, and is configured to execute a steering angle acquisition process, a target steering equivalent angle setting process, a steering operation process, a determination process, and a gradual change process, the steering angle acquisition process is a process for acquiring the steering angle, the target steering equivalent angle setting process is a process for setting a target steering equivalent angle in accordance with a driving mode selected from a plurality of driving modes based on the steering angle as an input variable, the target steering equivalent angle is a target value of the steering equivalent angle, which is a variable indicating the steering angle, the plurality of driving modes are modes in which a gear ratio, which is the ratio of the target steering equivalent angle to the steering angle, can differ from one another, and the steering operation process is a process for operating the steering actuator so as to bring the steering equivalent angle closer to the target steering equivalent angle, The decision process is a process for determining whether or not to execute the gradual change process when a request to switch the driving mode occurs, using whether the vehicle is in a stopped state or a running state as one of the conditions for determining whether or not to execute the gradual change process, and the gradual change process is a steering control device that gradually approaches the target steering equivalent angle corresponding to the driving mode before switching to the target steering equivalent angle corresponding to the driving mode after switching.

2. A steering control device as described in claim 1, wherein the gradual change processing is executed on condition that the driving mode is switched, and the decision processing includes a process for deciding not to execute the gradual change processing by deciding not to execute the driving mode switching when a request to switch the driving mode occurs, on condition that the vehicle is in a traveling state.

3. A steering control device as described in claim 2, wherein the decision process includes: a process for deciding not to execute the gradual change process by deciding not to execute the driving mode switching when the absolute value of the difference between the steering angle and the neutral angle as input variables exceeds a predetermined value when the vehicle is in a driving state; and a process for deciding to execute the driving mode switching and the gradual change process when the vehicle is in a driving state, on the condition that the absolute value of the difference between the steering angle and the neutral angle as input variables is equal to or less than the predetermined value.

4. A steering control device as described in claim 1, wherein the determination process includes a process of determining to execute the gradual change process when the absolute value of the difference equivalent amount is equal to or less than a predetermined value in the stopped state, and the difference equivalent amount is an amount indicating the difference between the target steering equivalent angle and the actual steering equivalent angle according to the driving mode after switching.

5. A steering control device as described in claim 4, wherein the steering device is equipped with a steering actuator that rotates the steering shaft and is configured to execute synchronization processing, wherein the synchronization processing is processing that operates the steering actuator so that the steering angle approaches a corresponding steering angle when a request to switch the driving mode occurs in the stopped state and the absolute value of the difference equivalent amount is greater than the predetermined value, and the corresponding steering angle is the steering angle that satisfies the relationship between the gear ratio in the selected driving mode and the actual steering equivalent angle.

6. A steering control device according to claim 5, wherein the synchronization process is completed by changing the steering angle by a predetermined amount, and the decision process includes a process for deciding to execute the gradual change process when the synchronization process is completed.

7. A steering control device as described in claim 4, wherein an end angle, which is an upper limit value of the absolute value of the steering angle, is set separately for each of a plurality of driving modes, and the decision process includes a process of deciding not to execute the gradual change process when a request to switch the driving mode occurs in the stopped state and the absolute value of the steering angle exceeds the end angle corresponding to the selected driving mode, even if the absolute value of the difference equivalent amount is equal to or less than a predetermined value.

8. A steering control device according to claim 1, wherein the steering device is equipped with a steering actuator that rotates the steering shaft, an end angle that is an upper limit value of the absolute value of the steering angle is set separately for each of a plurality of driving modes, and is configured to execute a synchronization process, wherein the synchronization process is a process of operating the steering actuator so as to reduce the absolute value of the steering angle to less than or equal to the end angle when a request to switch the driving mode occurs in the stopped state and the absolute value of the steering angle is greater than the end angle corresponding to the selected driving mode, and the determination process includes a process of determining not to execute the gradual change process when the synchronization process is executed.

9. A steering control device according to claim 8, wherein the synchronization process is completed by changing the steering angle by a predetermined amount, and the determination process includes a process for determining to execute the gradual change process when the synchronization process is completed.

10. A steering control method in which a steering device capable of changing the relationship between the steering angle of steered wheels of a vehicle and the steering angle, which is the rotation angle of a steering shaft, is a control object, the steering device is equipped with a steering actuator that steers the steered wheels, and the method includes execution of a steering angle acquisition process, execution of a target steering equivalent angle setting process, execution of a steering operation process, execution of a determination process, and execution of a gradual change process, the steering angle acquisition process is a process of acquiring the steering angle, the target steering equivalent angle setting process is a process of setting a target steering equivalent angle in accordance with a driving mode selected from a plurality of driving modes based on the steering angle as an input variable, the target steering equivalent angle is a target value of the steering equivalent angle, which is a variable indicating the steering angle, the plurality of driving modes are modes in which a gear ratio, which is the ratio of the target steering equivalent angle to the steering angle, can differ from one another, and the steering operation process is a process of operating the steering actuator so as to bring the steering equivalent angle closer to the target steering equivalent angle, The decision process is a process for determining whether or not to execute the gradual change process when a request to switch the driving mode occurs, using whether the vehicle is in a stopped state or a running state as one of the conditions for determining whether or not to execute the gradual change process, and the gradual change process is a steering control method for gradually approaching the target steering equivalent angle corresponding to the driving mode before switching to the target steering equivalent angle corresponding to the driving mode after switching.

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