Steering control device and steering control method

Abstract

To provide a steering control device capable of maintaining stability of a steering system even when gradual reduction processing of magnitude of an offset correction amount is executed.SOLUTION: The PU sets the target steered corresponding angle θ p * 0 in accordance with the steering angle as an input variable. A PU calculates an offset amount which is a difference between a target turning corresponding angle θ p * 0 and a turning corresponding angle θ p by using a predetermined condition that the target turning corresponding angle θ p * 0 changes discontinuously as a trigger. The PU calculates a target turning corresponding angle θ p * by subtracting an offset correction amount Δ θ p corresponding to the offset amount from the target turning corresponding angle θ p * 0. The PU performs guard processing on a decrease speed of the offset correction amount Δ θ p so that a change speed of the target turning corresponding angle θ p * is equal to or less than an upper limit guard value ω th.SELECTED DRAWING: Figure 3

Description

[Technical Field]

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

[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. Under predetermined conditions, this device corrects the target value of the steered angle of the steered wheels in accordance with the difference between the target value and the actual steered angle, and then gradually changes the correction amount to zero. This device sets the speed of the gradual change in accordance with the vehicle speed and the steering angular velocity. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Publication No. 2022-37763 Summary of the Invention [Problem to be solved by the invention]

[0004] As described above, by setting the gradual change speed according to the vehicle speed and angular velocity, it is possible to prevent the driver from feeling uncomfortable when steering. However, there is a risk that stability may be impaired by executing the gradual change process. [Means for solving the problem]

[0005] The means for solving the above problems and their effects will be described below. 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 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 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 turns the steered wheels in accordance with an operation amount of control in which the target steering equivalent angle is a target value of a control amount, and the offset amount calculation process is a process for calculating an offset equivalent which is an amount equivalent to the difference between the target steering equivalent angle and the actual steering equivalent angle, triggered by the establishment of a predetermined condition. a set amount calculating section for calculating a set amount of the offset compensation process, the offset compensation process being a process for correcting the target steering equivalent angle as an input variable of the operation process by an offset correction amount corresponding to the offset amount, the offset reduction process being a process for reducing the magnitude of the offset correction amount, the offset reduction process including a guard process, the guard process being a process for limiting the magnitude of the reduction rate of the offset correction amount based on the value of a steering angular velocity variable as an input variable, so as to limit the magnitude of the rate of change of the target steering equivalent angle corrected by the offset compensation process to an upper limit guard value or less, and the steering angular velocity variable being a variable indicating the rate of change of the target steering equivalent angle.

[0006] The rate of change of the target steering equivalent angle corrected by the offset compensation process is determined according to the rate of change of the target steering equivalent angle before correction and the offset correction amount. Therefore, the steering angle velocity variable is a variable necessary for grasping the rate of change of the target steering equivalent angle corrected by the offset compensation process. In the above configuration, because the input variable of the guard process is the steering angle velocity variable, it is possible to set the magnitude of the rate of decrease of the offset correction amount when limiting the magnitude of the rate of change of the target steering equivalent angle corrected by the offset compensation process to be equal to or less than the upper guard value. Therefore, by setting the upper guard value to a value that ensures the stability of the control of the steering system, the stability of the steering system can be maintained even when the offset compensation process is executed.

[0007] 2. A steering control device as described in 1 above, configured to execute a rate of change calculation process, wherein the rate of change calculation process is a process of calculating a rate of change related to the target steering equivalent angle set by the target steering equivalent angle setting process as the value of the steering angular velocity variable, the offset reduction process includes a reduction variable setting process, the reduction variable setting process is a process of setting a value of a reduction variable, the reduction variable being a variable indicating a rate of reduction in the magnitude of the offset correction amount, and the guard process includes a process of calculating, based on the rate of change of the target steering equivalent angle and the value of the reduction variable as input variables, a rate of change of the target steering equivalent angle in the case where the magnitude of the target steering equivalent angle changes at the rate of reduction indicated by the value of the reduction variable, and when the absolute value of the calculated rate of change exceeds the upper limit guard value, correcting the value of the reduction variable calculated by the reduction variable setting process in accordance with the amount of the excess.

[0008] In the above configuration, the rate of change of the target steering equivalent angle when the magnitude of the target steering equivalent angle changes according to the rate of decrease indicated by the value of the decrease variable is calculated, so the value of the decrease variable can be appropriately corrected. Also, in the above configuration, the value of the decrease variable set by the decrease variable setting process is corrected, so even if the value of the decrease variable set by the decrease variable setting process contains noise, the influence of the noise can be reduced.

[0009] 3. The steering control device according to 1 or 2 above, wherein the guard processing includes processing for changing the upper limit guard value in accordance with vehicle speed. In the above configuration, the upper limit guard value is set according to the vehicle speed, so compared to when the upper limit guard value is a fixed value, it is easier to set the upper limit guard value as large as possible while ensuring the stability of the steering system.

[0010] 4. A steering control device according to claim 3, wherein the guard processing includes processing for setting the upper limit guard value to a value for abnormality when an abnormality occurs in the detection of the vehicle speed. In the above configuration, if an abnormality occurs in the detection of the vehicle speed, the upper limit guard value is set to a value for the abnormality, thereby making it possible to appropriately deal with the abnormality in the detection of the vehicle speed.

[0011] 5. A steering control device described in any one of 1 to 4 above, wherein the offset reduction processing includes a reduction variable setting processing, the reduction variable setting processing is processing for setting the value of a reduction variable, the reduction variable being a variable indicating the reduction rate of the magnitude of the offset correction amount, and the reduction variable setting processing includes processing for changing the value of the reduction variable in accordance with the rate of change under the condition that when the magnitude of the rate of change of the target steering equivalent angle as an input variable is large, the rate of change is equal to or greater than the rate of change when the magnitude of the rate of change is small.

[0012] In the above configuration, the value of the decrease variable is set according to the rate of change of the target turning equivalent angle. However, even if the value of the decrease variable is the same, if the relationship between the sign of the offset correction amount and the sign of the rate of change of the target turning equivalent angle is different, whether or not the value exceeds the upper limit guard value may differ. Therefore, even when the value of the decrease variable is set according to the rate of change, it is effective to perform the above guard process. [Brief explanation of the drawings]

[0013] [Figure 1] 1 is a diagram illustrating a configuration of a vehicle according to an embodiment. [Figure 2] FIG. 2 is a block diagram showing part of the processing executed by the steering control device shown in FIG. [Figure 3] 2 is a flowchart showing a procedure of processing executed by the steering control device shown in FIG. [Figure 4] 4 is a time chart showing the effect of the process shown in FIG. 3. DETAILED DESCRIPTION OF THE INVENTION

[0014] Hereinafter, an embodiment will be described with reference to the drawings. "Configuration of steering control system" As shown in Fig. 1, vehicle steering device 10 is a steer-by-wire type steering device. Steering device 10 includes a reaction force actuator Ar and a turning actuator At. Steering device 10 of this embodiment has a structure in which the power transmission path between steering wheel 12 and steered wheels 44 is mechanically disconnected.

[0015] 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.

[0016] 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.

[0017] Steering actuator At includes speed reduction mechanism 56, steering motor 60, and steering inverter 62. Steering motor 60 is, as an example, a three-phase surface permanent magnet synchronous motor. The rotating shaft of steering motor 60 is connected to pinion shaft 52 via speed reduction mechanism 56. Pinion teeth of pinion shaft 52 mesh with rack teeth 54 of steering shaft 40. Rack-and-pinion mechanism 50 is formed by pinion shaft 52 and steering shaft 40, on which rack teeth 54 are provided. Torque of steering motor 60 is applied as a steering force to steering shaft 40 via pinion shaft 52. In response to the rotation of steering motor 60, steering shaft 40 moves along the vehicle width direction, which is the left-right direction in FIG. 1 .

[0018] 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.

[0019] 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 the control amount of the control object. Fig. 1 shows an operation signal MSs to reaction force inverter 22. Furthermore, 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 the control amount of the control object. Fig. 1 shows an operation signal MSt to steering inverter 62.

[0020] In order to control the control variable, steering control device 70 refers to steering torque Th, which is 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 .

[0021] "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 a 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°, for example, by counting the number of rotations of the reaction force motor 20 from a steering neutral position, which is the position of the steering wheel 12 when the vehicle is traveling straight. The steering angle calculation process M10 includes a process for multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotational speed ratio of the speed reduction mechanism 16, to calculate the steering angle θh. Note that the steering angle θh is set to a positive value when the angle is to the right of the steering neutral position, and a negative value when the angle is to the left of the steering neutral position, for example.

[0022] The steering equivalent angle calculation process M12 is a process for calculating 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 for 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 for 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.

[0023] 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 such as 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 to 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. Furthermore, the target reaction force calculation process M14 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 condition is that 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.

[0024] The target reaction force Tr* is actually a command value for the reaction force motor 20. A value obtained by multiplying the target reaction force Tr* by a coefficient according to the reduction ratio of the reduction mechanism 16 becomes the steering reaction force. In the description "changing B according to A on the condition that B when A is large 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 the relative relationship of magnitude when comparing the two. For example, "when A is large" corresponds to the case where "A is a first value," and "when A is small" corresponds to the case where "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.

[0025] 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 dq-axis current command values ​​based on the target reaction force Tr*. The reaction force operation process M16 also includes a process for calculating dq-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 dq-axis currents approach the command values.

[0026] 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 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 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.

[0027] The offset correction amount calculation process M20 is a process for calculating the offset correction amount Δθp of the target turning equivalent angle θp*0. The offset correction process M22 is a process for calculating the target turning equivalent angle θp* by subtracting the offset correction amount Δθp from the target turning equivalent angle θp*0.

[0028] 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.

[0029] 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 dq-axis current command values ​​based on the steering torque command value Tt*. The steering operation process M26 also includes a process for calculating dq-axis currents 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 dq-axis currents approach the command values.

[0030] "Offset correction amount calculation process M20" Fig. 3 shows the 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, below, the step number of each process is represented by a number preceded by "S."

[0031] 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.

[0032] When PU 72 determines that flag F is "0" (S12: NO), it determines whether a predetermined condition is met under which the absolute value of offset correction amount Δθp is set to a value greater than zero (S14). The predetermined condition is a condition under which the deviation between target turning equivalent angle θp* and turning 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 target turning equivalent angle θp*0 is discontinuously changed.

[0033] 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 by sensors that detect the speeds of each 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.

[0034] The second condition is a condition that the target equivalent turning angle θp*0 and the equivalent turning angle θp deviate by a predetermined amount or more, 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 turning angle θp become mismatched. Therefore, even though the steered wheels 44 can be steered and controlled at the time of the start switch switching, the target equivalent turning angle θp*0 deviates significantly from the equivalent turning angle θp. Alternatively, for example, the second condition may be a condition that the current limitation 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 steering wheel 12 is steered toward the side that hits the obstacle, target equivalent steering angle θp*0 changes as steering angle θh changes. In contrast, equivalent steering angle θp is maintained at a constant value. If the current limitation on steering motor 60 is released in this state, there will be a large deviation between target equivalent steering angle θp*0 and equivalent steering angle θp, even though steered wheels 44 can be controlled to be steered.

[0035] When the PU 72 determines that a predetermined condition is met (S14: YES), it assigns "1" to flag F (S16). Then, the PU 72 calculates an offset amount Δθp0 that is an amount equivalent to the difference between the target steering equivalent angle θp* and the actual steering equivalent angle θp (S18). 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 Δθp0. 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 the 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 Δθp0.

[0036] Next, the PU 72 substitutes the offset amount Δθp0 into the offset correction amount Δθp (S20). On the other hand, when the PU 72 determines that the flag F is "1" (S12: YES), it determines whether or not the offset correction amount Δθp is zero (S22). When 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*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.

[0037] 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 according to the target steering equivalent angular velocity ωp*0 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.

[0038] 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.

[0039] Furthermore, the PU 72 multiplies the steering angular velocity-sensitive base value Δωb as an input variable by the 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 as an input variable. This processing may be map calculation using map data in which the vehicle speed V is an input variable and the gain Gv is an output variable. Furthermore, the PU 72 calculates the vehicle speed-sensitive decrease amount Δv based on the vehicle speed V as an input variable. This processing may be 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. Then, the PU 72 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.

[0040] The PU 72 determines whether or not there is an abnormality in the vehicle speed V (S28). If the PU 72 determines that there is an abnormality in the vehicle speed V (S28: YES), it assigns an abnormality value ωthf to an upper limit guard value ωth (described later) (S32). On the other hand, if the PU 72 determines that there is no abnormality in the vehicle speed V (S28: NO), it calculates the upper limit guard value ωth based on the vehicle speed V as an input variable (S30). In detail, the processing of S30 may be processing in which the PU 72 calculates the upper limit guard value ωth using a map, with map data stored in the storage device 74. Here, the map data is data in which the vehicle speed V is an input variable and the upper limit guard value ωth is an output variable.

[0041] When the processes of S30 and S32 are completed, the PU 72 determines whether the offset amount Δθp0 is positive (S34). When the PU 72 determines that the offset amount Δθp0 is positive (S34: YES), the PU 72 assigns the smaller of zero or a value obtained by subtracting the decrease amount Δ from the offset correction amount Δθp to the offset correction amount Δθp (S36). Then, the PU 72 determines whether the absolute value of the value obtained by adding "Δ / Tc" to the target steering-equivalent angular velocity ωp*0 is greater than the upper limit guard value ωth (S38).

[0042] The processing of S38 is processing to determine whether or not the rate of change of the target steering equivalent angle θp* exceeds the upper limit guard value ωth when the target steering equivalent angle θp*0 is corrected by the offset correction amount Δθp calculated by the processing of S36. That is, as is clear from the processing of S36, the decrease amount Δ is a decrease variable that defines the decrease rate of the magnitude of the offset correction amount Δθp. The decrease rate of the magnitude of the offset correction amount Δθp is expressed as "Δ / Tc" using the period Tc of the series of processing shown in FIG.

[0043] When the PU 72 determines that the absolute value of the above-mentioned added value is larger than the upper limit guard value ωth (S38: YES), it executes processing to limit the absolute value of the rate of change of the target steering equivalent angle θp* to the upper limit guard value ωth (S40). That is, the PU 72 assigns a value having the magnitude of the value obtained by subtracting the absolute value of the target steering equivalent angular velocity ωp*0 from the upper limit guard value ωth and multiplying the result by the period Tc and having the sign of the target steering equivalent angular velocity ωp*0 to the offset correction amount Δθp.

[0044] On the other hand, if the PU 72 determines that the offset amount Δθp0 is not positive (S34: NO), it assigns the smaller of the value obtained by adding the decrease amount Δ to the offset correction amount Δθp or zero to the offset correction amount Δθp (S42).Then, the PU 72 determines whether the absolute value of the value obtained by subtracting "Δ / Tc" from the target steering equivalent angular velocity ωp*0 is larger than the upper limit guard value ωth (S44).

[0045] The processing of S44 is processing to determine whether or not the rate of change of the target steering equivalent angle θp* exceeds the upper limit guard value ωth when the target steering equivalent angle θp*0 is corrected by the offset correction amount Δθp calculated by the processing of S42. That is, as is clear from the processing of S42, the decrease amount Δ is a decrease variable that defines the decrease rate of the magnitude of the offset correction amount Δθp. The decrease rate of the magnitude of the offset correction amount Δθp is expressed as "Δ / Tc" using the period Tc of the series of processing shown in FIG.

[0046] When the PU 72 determines that the absolute value of the subtracted value is greater than the upper limit guard value ωth (S44: YES), the PU 72 proceeds to the process of S40. On the other hand, if the PU 72 determines that the offset correction amount Δθp is zero (S22: YES), it assigns "0" to flag F (S48). If the determination in the process of S14 is negative, the PU 72 assigns zero to the offset correction amount Δθp (S46).

[0047] The PU 72 temporarily ends the series of processes shown in FIG. 3 when it completes the processes of S40, S46, and S48, or when it makes a negative determination in the processes of S38 and S44. "Actions and Effects of the Present Embodiment" Fig. 4 shows an example of the transition of the target steering equivalent angle θp* after a predetermined condition is met. The right side of Fig. 4 shows the transition of the target steering equivalent angle θp* according to this embodiment. The left side of Fig. 4 shows a comparative example in which the processes of S38, S40, and S44 are not executed.

[0048] In the comparative example shown in Fig. 4, after time t1 when a predetermined condition is met, the rate of change of target steering equivalent angle θp* becomes excessively large due to the gradual decrease process of the magnitude of offset correction amount Δθp. On the other hand, in the present embodiment, even after time t1 when a predetermined condition is met, the absolute value of the rate of change of target steering equivalent angle θp* is limited to be equal to or less than the upper limit guard value ωth. This makes it possible to maintain the stability of the steering system even when the gradual decrease process of the magnitude of offset correction amount Δθp is executed.

[0049] According to the present embodiment described above, the following actions and effects can be further obtained. (1) In the processes of S38 and S44, the PU 72 calculates the rate of change of the target steering equivalent angle θp* when the target steering equivalent angle θp*0 is corrected by the offset correction amount Δθp calculated in the processes of S36 and S42. This makes it possible to appropriately determine whether the magnitude of the rate of change of the target steering equivalent angle θp* exceeds the upper limit guard value ωth.

[0050] (2) The PU 72 corrects the offset correction amount Δθp so as to limit the magnitude of the rate of change of the target turning equivalent angle θp* to the upper limit guard value ωth or less. This makes it possible to reduce the influence of noise even if the decrease amount Δ set by the processing of S26 contains noise.

[0051] (3) The PU72 changes the upper limit guard value ωth according to the vehicle speed V. This makes it easier to set the upper limit guard value ωth as large as possible while ensuring the stability of the steering system, compared to when the upper limit guard value ωth is set to a fixed value.

[0052] (4) When an abnormality occurs in the detection of the vehicle speed V, the PU 72 sets the upper limit guard value ωth to the abnormal value ωthf. This allows appropriate action to be taken when an abnormality occurs in the detection of the vehicle speed V. (5) PU72 changed the decrease amount Δ in accordance with the target steering equivalent angular velocity ωp*0 under the condition that the decrease amount Δ when the magnitude of the target steering equivalent angular velocity ωp*0 is large is equal to or greater than the decrease amount Δ when the magnitude of the target steering equivalent angular velocity ωp*0 is small. However, even if the decrease amount Δ is the same, whether or not it exceeds the upper limit guard value ωth may differ if the relationship between the sign of the offset correction amount Δθp and the sign of the target steering equivalent angular velocity ωp*0 is different. Therefore, even if the decrease amount Δ is set in accordance with the target steering equivalent angular velocity ωp*0, it is effective to execute the processing of S38 and S44.

[0053] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for solving the problem" column is as follows. Below, the correspondence is shown for each number of the solving means described in the "Means for solving the problem" column. [1] Operation processing corresponds to steering feedback processing M24 and steering operation processing M26. Offset amount calculation processing corresponds to the processing of S18. Offset compensation processing corresponds to offset correction amount calculation processing M20 and offset correction processing M22. Offset reduction processing corresponds to the processing of S34 to S44. Guard processing corresponds to the processing of S38, S40, and S44. [2] Change rate calculation processing corresponds to the processing of S24. The change rate of the target steering equivalent angle corresponds to the target steering equivalent angular velocity ωp*0. Decrease variable setting processing is the processing of S26. [3] Corresponds to the processing of S30. [4] Corresponds to the processing of S32. [5] Corresponds to the fact that the decrease amount Δ is set in accordance with the steering angular velocity sensitive decrease amount Δω.

[0054] <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.

[0055] "About guard processing" The upper limit guard value ωth does not necessarily have to be changed in accordance with the vehicle speed V. The guard process does not necessarily have to include a process of comparing the magnitude of the target steering equivalent angular velocity ωp*0 corrected based on the decrease amount Δ with the upper limit guard value ωth. In other words, the guard process does not necessarily have to include the processes of S38 and S44. For example, the guard process may include a process of comparing the magnitude of the value of the decrease variable with a threshold value set in accordance with the target steering equivalent angular velocity ωp*0. Here, the threshold value may have a magnitude of, for example, "ωth - |ωp*0|".

[0056] In the processing of S40, processing is performed on the premise that the magnitude of the target steering equivalent angular velocity ωp*0 does not exceed the upper guard value ωth, but this is not limiting. For example, the magnitude of the rate of change of the target steering equivalent angle θp*0 may exceed the upper guard value ωth, and the guard processing may limit the rate of change of the final target steering equivalent angle θp* to be equal to or less than the upper guard value ωth.

[0057] "About the decreasing 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.

[0058] 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.

[0059] 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 change 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. Also, the PU 72 may change 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.

[0060] "About steering control devices" 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 according to 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 according to 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.

[0061] "About steering actuators" The steering actuator At may be, for example, one in which steering motor 60 is arranged coaxially with steering shaft 40. Alternatively, for example, one in which steering motor 60 is connected to steering shaft 40 via a belt-type reducer using a ball screw mechanism may be used. [Explanation of symbols]

[0062] 10...Steering device 12...Steering wheel 14...Steering shaft 16...Reduction mechanism 20...Reaction motor 22...Reaction force inverter 40...Steering shaft 42...Tie rod 44...Steering wheel 50...Rack and pinion mechanism 52...Pinion shaft 54...Rack teeth 56…Reduction mechanism 60...Steering motor 62...Steering inverter 70...Steering control device

Claims

1. The 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 in a state where 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 a steering equivalent angle which is a variable indicating the steering angle of the steered wheels, the operation processing is processing for operating a motor that steers the steered wheels in accordance with an operation amount of control in which the target steering equivalent angle is a target value of a control amount, the offset amount calculation process is a process of calculating an offset amount that is an amount equivalent to a difference between the target steering equivalent angle and the actual steering equivalent angle, when a predetermined condition is satisfied as a trigger, the offset compensation process is a process of correcting the target steering equivalent angle as an input variable of the operation process by an offset correction amount corresponding to the offset amount, the offset reduction process is a process of reducing the magnitude of the offset correction amount, the offset reduction process includes a guard process, the guard processing is processing for limiting the magnitude of the rate of decrease of the offset correction amount so as to limit the magnitude of the rate of change of the target steering equivalent angle corrected by the offset compensation processing to an upper limit guard value or less, based on the value of a steering angular velocity variable as an input variable, A steering control device, wherein the steering angle velocity variable is a variable indicating the rate of change of the target steering equivalent angle.

2. configured to execute a rate of change calculation process, the change rate calculation process is a process for calculating a change rate regarding the target steering equivalent angle set by the target steering equivalent angle setting process as a value of the steering angular velocity variable, the offset reduction process includes a reduction variable setting process, the decrease variable setting process is a process of setting a value of a decrease variable, the decrease variable is a variable indicating a decrease rate of the magnitude of the offset correction amount, 2. A steering control device according to claim 1, wherein the guard processing includes a process of calculating, based on the rate of change of the target steering equivalent angle as input variables and the value of the decrease variable, a rate of change of the target steering equivalent angle when the magnitude of the target steering equivalent angle changes according to a rate of decrease indicated by the value of the decrease variable, and, if the absolute value of the calculated rate of change exceeds the upper limit guard value, correcting the value of the decrease variable calculated by the decrease variable setting processing in accordance with the amount by which the upper limit guard value is exceeded.

3. The steering control device according to claim 1 , wherein the guard process includes a process for changing the upper limit guard value in accordance with a vehicle speed.

4. 4. The steering control device according to claim 3, wherein the guard process includes a process of setting the upper limit guard value to a value for abnormality when an abnormality occurs in the detection of the vehicle speed.

5. the offset reduction process includes a reduction variable setting process, the decrease variable setting process is a process of setting a value of a decrease variable, the decrease variable is a variable indicating a decrease rate of the magnitude of the offset correction amount, 2. The steering control device according to claim 1, wherein the reduction variable setting process includes a process of changing the value of the reduction variable in accordance with the rate of change of the target steering equivalent angle as an input variable, under the condition that the rate of decrease when the rate of change of the target steering equivalent angle is large is equal to or greater than the rate of decrease when the rate of change of the target steering equivalent angle is small.

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