Steering control device and steering control method

Abstract

In the present invention, a steering control device (50) is configured to execute a reaction force command value setting process and an operation process. The reaction force command value setting process includes a process of: calculating a reaction force torque command value, which is a command value of a torque variable indicating a reaction force; and superimposing, on the reaction force torque command value, a correction amount having a negative correlation with the amount of variation in steering torque, which is torque that a driver imparts to the steering shaft (14). In the operation process, the reaction force actuator is operated in accordance with the reaction force torque command value.

Description

Steering control device and steering control method

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

[0002] Japanese Patent Application Laid-Open Publication No. 2006-109494 (Patent Document 1) describes a device for mechanically limiting the rotational range of a steering shaft in a steer-by-wire system. Specifically, the device includes a first rotating member that rotates in conjunction with the steering shaft and a second rotating member that rotates with the first rotating member. The device also includes a restricting member that contacts the second rotating member to prevent rotation of the second rotating member when the second rotating member reaches a predetermined rotation angle. When the first rotating member rotates a predetermined amount from the steering angle at which rotation of the second rotating member is prevented by the restricting member, the first rotating member and the second rotating member come into contact with each other, preventing rotation of the first rotating member. This prevents rotation of the first rotating member.

[0003] Japanese Patent Application Laid-Open No. 2020-69844

[0004] However, in the above device, the magnitude of the torque that impedes the rotation of the steering shaft differs between a state in which the second rotating member is rotated by the rotation of the first rotating member and a state in which only the first rotating member rotates. Therefore, when switching from one of the above two states to the other, the torque applied to the steering shaft changes stepwise, which may cause a deterioration in the steering feel for the driver.

[0005] According to one aspect of the present disclosure, there is provided a steering control device that operates a reaction force actuator that applies a reaction force to a steering shaft that is rotated in response to steering by a driver while power transmission to steered wheels is interrupted. The reaction force actuator includes a first rotating member that rotates in conjunction with the steering shaft, a second rotating member that rotates along with the first rotating member, and a restricting member that contacts the second rotating member to prevent rotation of the second rotating member when the second rotating member reaches a predetermined rotation angle. The first rotating member and the second rotating member are configured to contact each other such that the second rotating member prevents rotation of the first rotating member when the first rotating member rotates a predetermined amount from the angle at which rotation of the second rotating member is prevented. The steering control device is configured to execute a reaction force command value setting process and an operation process. The reaction force command value setting process calculates a reaction force torque command value, which is a command value of a torque variable indicating the reaction force, and includes a process of superimposing a correction amount, which is negatively correlated with a fluctuation amount of steering torque, which is torque input to the steering shaft by the driver, on the reaction force torque command value. The operation process is a process of operating the reaction force actuator in accordance with the reaction torque command value.

[0006] Another aspect of the present disclosure provides a steering control method for operating a reaction force actuator that applies a reaction force to a steering shaft that is rotated in response to steering by a driver while power transmission to steered wheels is interrupted. The reaction force actuator includes a first rotating member that rotates in conjunction with the steering shaft, a second rotating member that rotates along with the first rotating member, and a restricting member that contacts the second rotating member to prevent rotation of the second rotating member when the second rotating member reaches a predetermined rotation angle. The first rotating member and the second rotating member are configured to contact each other such that the second rotating member prevents rotation of the first rotating member when the first rotating member rotates a predetermined amount from the angle at which rotation of the second rotating member is prevented. The steering control method includes executing a reaction force command value setting process and an operation process. The reaction force command value setting process is a process of calculating a reaction force torque command value, which is a command value of a torque variable indicating the reaction force, and includes a process of superimposing a correction amount, which has a negative correlation with a fluctuation amount of a steering torque, which is a torque input to the steering shaft by a driver, on the reaction force torque command value. The operation process is a process of operating the reaction force actuator in accordance with the reaction force torque command value.

[0007] FIG. 1 is a diagram showing the configuration of a steering system according to a first embodiment. FIG. 2 is an exploded perspective view showing the configuration of a portion of a reaction force actuator according to the embodiment. FIG. 3 is an exploded perspective view showing the configuration of a portion of a reaction force actuator according to the embodiment. FIG. 4 is a cross-sectional view showing the configuration of a portion of a reaction force actuator according to the embodiment. FIG. 5 is a diagram showing the operation of a stopper function of the reaction force actuator according to the embodiment. FIG. 6 is a block diagram showing processing executed by a control device according to the embodiment. FIG. 7 is a block diagram showing details of a portion of processing executed by the control device according to the embodiment. FIG. 8 is a diagram showing the relationship between the operation of the stopper function of the reaction force actuator and torque. FIG. 9 is a flowchart showing the procedure of processing executed by a control device according to a second embodiment. FIG. 10 is a block diagram showing details of a portion of processing executed by a control device according to a third embodiment. FIG. 11 is an exploded perspective view showing the configuration of a portion of a reaction force actuator according to a modified example.

[0008] First Embodiment A first embodiment will be described below with reference to the drawings. "Prerequisite Configuration" A vehicle steering device 10 shown in FIG. 1 is a steer-by-wire device. The steering device 10 includes a steering wheel 12, a steering shaft 14, a reaction force actuator 20, and a turning actuator 30. The steering shaft 14 is connected to the steering wheel 12. The reaction force actuator 20 applies a force that resists the force exerted by the driver when operating the steering wheel 12. The reaction force actuator 20 includes a reaction force motor 22, a reaction force inverter 24, and a reaction force reduction mechanism 26. The reaction force motor 22 applies a steering reaction force, which is a force that resists steering, to the steering wheel 12 via the steering shaft 14. The reaction force motor 22 is connected to the steering shaft 14 via the reaction force reduction mechanism 26. As an example, a three-phase synchronous motor is used for the reaction force motor 22. The reaction force reduction mechanism 26 is, for example, a worm and wheel.

[0009] The steering actuator 30 steers the steerable wheels 34 in accordance with the driver's steering intention, as indicated by the driver's operation of the steering wheel 12. The steering actuator 30 includes a rack shaft 32, a steering motor 42, a steering inverter 44, a steering transmission mechanism 46, and a conversion mechanism 48. As an example, a three-phase surface permanent magnet synchronous motor (SPM) is used for the steering motor 42. The steering transmission mechanism 46 is made up of a belt transmission mechanism. The steering transmission mechanism 46 transmits the rotational power of the steering motor 42 to the conversion mechanism 48. The conversion mechanism 48 converts the transmitted rotational power into axial displacement power of the rack shaft 32. The axial displacement of the rack shaft 32 causes the steerable wheels 34 to turn.

[0010] The steering control device 50 controls the control amount of the steering wheel 12 and the steered wheels 34, which are the control objects. That is, the steering control device 50 controls the steering reaction force that resists the steering by the driver, which is the control amount of the steering wheel 12, which is the control object. The steering control device 50 also controls the steering angle, which is the control amount of the steered wheels 34, which are the control object. The steering angle is the turning angle of the tires, which are the steered wheels 34.

[0011] To control the controlled variable, the steering control device 50 refers to the steering torque Th detected by the torque sensor 60. The steering torque Th is the torque applied to the steering shaft 14 by the driver through operation of the steering wheel 12. To control the controlled variable, the steering control device 50 refers to the rotation angle θa, which is the angle of the rotation shaft of the reaction force motor 22, detected by the steering-side rotation angle sensor 62. To control the controlled variable, the steering control device 50 also refers to the currents ius, ivs, and iws flowing through the reaction force motor 22. The currents ius, ivs, and iws may be detected, for example, as the amount of voltage drop across a shunt resistor provided in each leg of the reaction force inverter 24. To control the controlled variable, the steering control device 50 refers to the rotation angle θb, which is the angle of the rotation shaft of the turning motor 42, detected by the turning-side rotation angle sensor 64. Furthermore, in order to control the control variables, steering control device 50 refers to currents iut, ivt, and iwt flowing through steering motor 42. Currents iut, ivt, and iwt may be detected, for example, as voltage drops across shunt resistors provided in each leg of steering inverter 44. Steering control device 50 refers to vehicle speed V detected by vehicle speed sensor 66.

[0012] The steering control device 50 includes a PU 52 and a storage device 54. The PU 52 is a software processing device such as a CPU, a GPU, or a TPU. The storage device 54 may be an electrically non-rewritable non-volatile memory. Alternatively, the storage device 54 may be an electrically rewritable non-volatile memory or a storage medium such as a disk medium.

[0013] "Configuration of Reaction Force Actuator 20" Figure 2 shows the configuration of part of the reaction force actuator 20. As shown in Figure 2, the reaction force actuator 20 includes a housing 70 that is fixed to the vehicle. The steering shaft 14 is inserted into the housing 70. The housing 70 supports the steering shaft 14 so that it can rotate. The steering shaft 14 is inserted into a plurality of ring-shaped members. The ring-shaped members include a washer 80, an intermediate stopper 90, a washer 82, an end stopper 100, a wave washer 84, and a C-shaped retaining ring 86.

[0014] The housing 70 is provided with a protrusion 72 that serves as a restricting member for restricting the rotation of the intermediate stopper 90. As shown in Fig. 3, the intermediate stopper 90 is provided with a protrusion 92 whose rotation is restricted by the protrusion 72. An O-ring 94 is fitted onto the protrusion 92.

[0015] FIG. 4 shows a partial cross-sectional view of the reaction force actuator 20. As shown in FIG. 4, an elastic force acting in the right direction in the figure is applied to the end stopper 100 by the wave washer 84. As a result, an elastic force acting in the right direction in the figure is applied to the intermediate stopper 90 via the washer 82. Meanwhile, the steering shaft 14 has a reduced diameter portion at the end on the left side in the figure. The washer 80, the intermediate stopper 90, and the washer 82 are disposed in the reduced diameter portion of the steering shaft 14. Therefore, displacement of the washer 80 to the right in the figure is restricted. Therefore, an elastic force acting in the right direction in the figure is applied to the intermediate stopper 90 by the washer 82, and an elastic force acting in the left direction in the figure is applied to the intermediate stopper 90 by the washer 80.

[0016] The end stopper 100 is fixed to the steering shaft 14. Therefore, as the steering shaft 14 rotates, the end stopper 100 rotates integrally with the steering shaft 14. As the end stopper 100 rotates, the intermediate stopper 90 rotates as well.

[0017] "Rotation restriction of steering shaft 14" The upper part of Fig. 5 shows a case where the steering shaft 14 rotates to the right turning side. The left end of the upper part of Fig. 5 shows a state where the steering angle θs, which is the rotation angle of the steering shaft 14, is a value corresponding to the end of the left turning side. The upper part of Fig. 5 also shows a state where the steering shaft 14 rotates to the right turning side as it moves to the right in the figure. In particular, the right end of the upper part of Fig. 5 shows a state where the steering angle θs is a value corresponding to the end of the right turning side.

[0018] As shown in the upper part of Figure 5, when the steering shaft 14 turns right from the end on the left turning side, the intermediate stopper 90 rotates as the end stopper 100 rotates. The center of the upper part of Figure 5 shows a state in which the protrusion 92 of the intermediate stopper 90 contacts the protrusion 72 of the housing 70 via the O-ring 94. This prevents the intermediate stopper 90 from turning further to the right. Therefore, the end stopper 100 rotates independently as the steering shaft 14 rotates. Then, as the steering shaft 14 rotates further, the protrusion 102 of the end stopper 100 contacts the protrusion of the intermediate stopper 90 via the O-ring 94, preventing the end stopper 100 from turning further to the right. This state is shown at the right end of the upper part of Figure 5. In this state, the steering shaft 14 cannot rotate further to the right. The steering angle θs at this time is the upper limit on the right turning side.

[0019] The lower part of Fig. 5 shows a case where the rotation angle of the steering shaft 14 rotates to the left turning side. The left end of the lower part of Fig. 5 shows a state where the steering angle θs is a value corresponding to the end of the right turning side. The lower part of Fig. 5 also shows a state where the steering shaft 14 rotates to the left turning side as it moves to the right in the figure. In particular, the right end of the lower part of Fig. 5 shows a state where the steering angle θs is a value corresponding to the end of the left turning side.

[0020] As shown in the lower part of Figure 5, when the steering shaft 14 turns left from the end on the right-turning side, the intermediate stopper 90 rotates as the end stopper 100 rotates. The center of the lower part of Figure 5 shows a state in which the protrusion 92 of the intermediate stopper 90 contacts the protrusion 72 of the housing 70 via the O-ring 94. This prevents the intermediate stopper 90 from turning left any further. Therefore, the end stopper 100 rotates independently as the steering shaft 14 rotates. Then, as the steering shaft 14 rotates further, the protrusion 102 of the end stopper 100 contacts the protrusion of the intermediate stopper 90 via the O-ring 94, preventing the end stopper 100 from turning left any further. This state is shown at the right end of the lower part of Figure 5. In this state, the steering shaft 14 cannot rotate further to the left. The steering angle θs at this time is the upper limit on the left-turning side.

[0021] "Outline of Control" Fig. 6 shows the processing executed by the steering control device 50. The processing shown in Fig. 6 is realized by the PU 52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined interval.

[0022] The steering angle calculation process M10 includes a process of converting the rotation angle θa into an integrated angle including a range exceeding 360 degrees by, for example, counting the number of rotations of the reaction force motor 22 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 of calculating the steering angle θs by multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotational speed ratio of the reaction force reduction mechanism 26.

[0023] The steering equivalent angle calculation process M12 includes a process of converting the rotation angle θb into an integrated angle including a range exceeding 360 degrees, for example, by counting the number of rotations of the steering motor 42 from a rack neutral position, which is the position of the rack shaft 32 when the vehicle is traveling straight. The steering equivalent angle calculation process M12 includes a process of calculating a steering equivalent angle θp corresponding to the steering angle of the steered wheels 34 by multiplying the integrated angle obtained by the conversion by a conversion coefficient corresponding to the reduction ratio of the steering transmission mechanism 46 and the lead of the conversion mechanism 48, etc. The steering equivalent angle θp is a quantity that is proportional to the steering angle. Note that, as an example, the steering equivalent angle θp is positive when it is an angle to the right of the rack neutral position, and negative when it is an angle to the left of the rack neutral position.

[0024] The target steering equivalent angle calculation process M18 is a process for calculating the target steering equivalent angle θp* in accordance with the steering angle θs and the vehicle speed V. The assist amount setting process M20 is a process for calculating the assist amount Ta using the steering torque Th and the vehicle speed V as inputs. The assist amount Ta is an amount in the same direction as the steering direction of the driver. The magnitude of the assist amount Ta is set to a large value when the force assisting the steering by the driver is to be increased.

[0025] The axial force setting process M22 is a process that calculates the axial force F acting on the rack shaft 32 through the steered wheels 34 using the vehicle speed V, the q-axis current iqt of the steering motor 42, and the target steering equivalent angle θp* as inputs. The axial force F is a value that expresses the force acting on the rack shaft 32 through the steered wheels 34 through control. However, the axial force F does not necessarily have to be intended to estimate the force acting on the rack shaft 32 with high accuracy. The axial force F may be, for example, a virtually determined force acting on the rack shaft 32. The axial force F is converted into a torque applied to the steering shaft 14. In other words, it is converted into a torque applied to the steering shaft 14 assuming that power transmission between the steered wheels 34 and the steering shaft 14 is possible. The axial force F is an amount acting in the direction opposite to the steering direction of the driver. The axial force setting process M22 may be a process that calculates the axial force F so that the absolute value of the axial force F increases as the absolute value of the target steering equivalent angle θp* increases. Further, for example, the axial force setting process M22 may be a process of calculating the axial force F so that the absolute value of the axial force F increases as the vehicle speed V increases. Furthermore, the axial force setting process M22 may be a process of calculating the axial force F so that the absolute value of the axial force F increases as the absolute value of the q-axis current iqt increases. Here, the q-axis current iqt is calculated by the PU 52 in accordance with the steering equivalent angle θp and the currents iut, ivt, and iwt.

[0026] The subtraction process M24 is a process of substituting the value obtained by subtracting the axial force F from the assist amount Ta into the target reaction torque Ts. The target reaction torque Ts is a target value of the torque that the reaction motor 22 applies to the steering shaft 14.

[0027] The reaction force operation signal generation process M26 is a process for generating an operation signal MSs for the reaction force inverter 24 in order to control the torque of the reaction force motor 22 so that the torque applied to the steering shaft 14 becomes the target reaction force torque Ts. Specifically, the reaction force operation signal generation process M26 includes a process for converting the target reaction force torque Ts into a target torque of the reaction force motor 22. The reaction force operation signal generation process M26 also includes a process for calculating an operation signal MSs for the reaction force inverter 24 in order to bring the current flowing through the reaction force motor 22 closer to a current determined from the target reaction force torque Ts through current feedback control. Note that the operation signal MSs is actually an operation signal for each of the six switching elements of the reaction force inverter 24. By setting the torque of the reaction force motor 22 to the target reaction force torque Ts, the steering reaction force that resists the force that tries to rotate the steering wheel 12 becomes "(-1)·Ts".

[0028] The steering feedback process M30 is a process for substituting the manipulated variable of feedback control, in which the steering equivalent angle θp is used as a control variable and the target steering equivalent angle θp* is used as a target value of the control variable, into the target steering torque Tt*. The target steering torque Tt* has a fixed ratio to the torque of the steering motor 42.

[0029] The steering operation signal generation process M32 is a process for generating an operation signal MSt for the steering inverter 44 in order to control the torque of the steering motor 42 so that the torque of the steering motor 42 becomes a value having a constant ratio with respect to the target steering torque Tt*. In more detail, the steering operation signal generation process M32 includes a process for converting the target steering torque Tt* into a target torque of the steering motor 42. The steering operation signal generation process M32 also includes a process for calculating an operation signal MSt for the steering inverter 44 in order to bring the current flowing through the steering motor 42 close to a current determined from the target torque by current feedback control. Note that the operation signal MSt is actually an operation signal for each of the six switching elements of the steering inverter 44.

[0030] "Assist Amount Setting Process" Fig. 7 shows details of the assist amount setting process M20. The phase lag compensation process M60 is a process for delaying the phase of the steering torque Th. This may be a process for compensating the phase of the steering torque Th in order to adjust the frequency characteristics of the phase difference between both sides of a torsion bar provided in the torque sensor 60, for example. The phase-compensated steering torque Th, which is the output value of the phase lag compensation process M60, is the steering torque Thr. The phase lag compensation process M60 includes a filter process M62 and a filter coefficient setting process M64.

[0031] The filter processing M62 includes a phase lag filter and a low-pass filter. The transfer function of the phase lag filter is "(1+α·T1·s) / (1+T1·s)". The transfer function of the low-pass filter is "1 / (1+T2·s)". The value obtained by processing the steering torque Th through the phase lag filter and the low-pass filter is the steering torque Thr.

[0032] The filter coefficient setting process M64 sets the filter coefficients α and T1 of the phase lag filter and the filter coefficient T2 of the low-pass filter in accordance with the vehicle speed V and the assist gradient R, which will be described later.

[0033] The basic assist amount setting process M66 is a process for setting a basic assist amount Tab using the steering torque Thr and the vehicle speed V as inputs. The basic assist amount setting process M66 sets the basic assist amount Tab to a value that has a positive correlation with the steering torque Thr. This process may be, for example, a process in which the PU 52 calculates the basic assist amount Tab from a map in a state in which map data is pre-stored in the storage device 54. The map data is data that uses the steering torque Thr and the vehicle speed V as input variables and the basic assist amount Tab as an output variable.

[0034] Here, map data refers to 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, the 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 output variable in the corresponding map data is used as the calculation result. Furthermore, when the value of an input variable does not match any of the input variable values ​​in the map data, the map calculation may be a process in which the value obtained by interpolating the values ​​of multiple output variables included in the map data is used as the calculation result. Alternatively, when the value of an input variable does not match any of the input variable values ​​in the map data, the map calculation may be a process in which the value of the output variable in the map data that corresponds to the closest value of the input variable values ​​included in the map data is used as the calculation result.

[0035] The basic assist amount setting process M66 includes a process of calculating and outputting an assist gradient R. The assist gradient R indicates the ratio of the change in the basic assist amount Tab to the change in the steering torque Thr.

[0036] The phase lead compensation process M70 is a process for advancing the phase of the assist amount Ta. This may be intended to perform phase compensation on the assist amount Ta in order to adjust the response delay of the steering wheel 12 in response to a change in the steering torque Th. The phase lead compensation process M70 includes a differential operation M72, a gain setting process M74, and a multiplication process M76.

[0037] The differential calculation M72 is a process for calculating a first-order time differential value dTh of the steering torque Th. The gain setting process M74 is a process for setting the gain Gad using the assist gradient R and the vehicle speed V as inputs. The gain setting process M74 may be a process for calculating the gain Gad from a map in a state where map data is pre-stored in the storage device 54. This map data is data that uses the assist gradient R and the vehicle speed V as input variables and the gain Gad as an output variable.

[0038] The multiplication process M76 is a process of multiplying the time differential value dTh by a gain Gad. The product of the time differential value dTh and the gain Gad is the lead compensation amount Tad as the output of the phase lead compensation process M70.

[0039] The torque differentiation process M80 is a process that calculates a derivative correction amount Td using the steering torque Th as an input. The torque differentiation process M80 includes a derivative calculation M82 and a correction amount calculation process M84. The derivative calculation M82 is a process that calculates a first-order time derivative dTh of the steering torque Th as an input. The correction amount calculation process M84 is a process that calculates a derivative correction amount Td using the time derivative dTh as an input. The correction amount calculation process M84 changes the derivative correction amount Td in accordance with the time derivative dTh under the condition that the derivative correction amount Td when the absolute value of the time derivative dTh is large is equal to or greater than the derivative correction amount Td when the absolute value of the time derivative dTh is small. The derivative correction amount Td has a sign that suppresses changes in the steering torque Th. This can be achieved, for example, by making the sign of the derivative correction amount Td equal to the sign of the time derivative dTh.

[0040] In the description of this specification, "changing B according to A while satisfying the condition that when A is large, B is equal to or greater 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." This 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.

[0041] More specifically, the correction amount calculation process M84 is a process in which the PU 52 calculates the differential correction amount Td using map data stored in advance in the storage device 54. Here, the map data is data in which the time differential value dTh is an input variable and the differential correction amount Td is an output variable.

[0042] The synthesis process M90 is a process of adding the lead compensation amount Tad and the differential correction amount Td to the basic assist amount Tab. The value calculated in this way is the assist amount Ta. <Functions and Effects of the First Embodiment> Figure 8 shows the transition of the load torque, which is the torque that tries to prevent the rotation of the steering shaft 14. Note that Figure 8 corresponds to the operation in the upper part of Figure 5.

[0043] 8, when the state in which the intermediate stopper 90 is rotated along with the rotation of the end stopper 100 changes to the state in which the end stopper 100 rotates independently, the load torque increases stepwise. This is because a new frictional force with the intermediate stopper 90 is applied when the end stopper 100 rotates.

[0044] Here, the PU 52 repeatedly calculates the assist amount Ta in accordance with the differential correction amount Td at a predetermined cycle. When the load torque increases stepwise, the differential correction amount Td serves as an amount that compensates for the stepwise increase in the load torque. This suppresses fluctuations in the steering torque Th. This suppresses the driver from feeling a stepwise increase in the load torque when operating the steering wheel 12.

[0045] The first embodiment further provides the following advantages: (1-1) An O-ring 94 is provided on the protrusion 92 of the intermediate stopper 90. This reduces the impact of contact compared to when the protrusion 92 comes into direct contact with the protrusion 72.

[0046] Second Embodiment A second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment.

[0047] Fig. 9 shows the procedure of the synthesis process M90 according to this embodiment. The series of processes shown in Fig. 9 is realized by the PU 52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined interval. Note that, below, the step number of each process is represented by a number preceded by "S."

[0048] 9, the PU 52 first acquires the steering angle θs (S10). The PU 52 then determines whether the steering angle θs is within a region (predetermined angle range) that is equal to or greater than the first angle θsL and equal to or less than the second angle θsH (S12). This region includes the steering angle θs at the time when the intermediate stopper 90 switches from being rotated by the end stopper 100 to not being rotated by the end stopper 100. It is desirable to set this region as narrow as possible while still including tolerance-related variations in the steering angle θs at the time of the switch.

[0049] If the PU 52 determines that the amount of assist is within the above range (S12: YES), it assigns the value obtained by adding the basic assist amount Tab to the advance compensation amount Tad and the differential correction amount Td to the assist amount Ta (S14).On the other hand, if the PU 52 determines that the amount of assist is outside the above range (S12: NO), it assigns the value obtained by adding the basic assist amount Tab to the advance compensation amount Tad to the assist amount Ta (S16).

[0050] When the PU 52 completes the processes of S14 and S16, it temporarily ends the series of processes shown in Fig. 9. <Functions and Effects of Second Embodiment> In this embodiment, the processes of S10, S12, and S16 in Fig. 9 are added to the first embodiment, so that the differential correction amount Td can be reflected in the assist amount Ta only in the vicinity of the steering angle where the load torque increases in a stepwise manner.

[0051] Third Embodiment Hereinafter, a third embodiment will be described with reference to the drawings, focusing on differences from the first embodiment.

[0052] Fig. 10 shows details of the assist amount setting process M20 according to this embodiment. For convenience, the same reference numerals are used in Fig. 10 to designate processes corresponding to those shown in Fig. 7.

[0053] As shown in FIG. 10 , the torque differentiation process M80 includes a filtering process M86 that receives the time differential value dTh as an input. The filtering process M86 extracts, from the time differential value dTh, frequency components associated with the step increase in the load torque. That is, the time differential value dTh0 output by the filtering process M86 indicates the magnitude of the frequency components associated with the step increase in the load torque in the time differential value dTh. The correction amount calculation process M84 receives the time differential value dTh0 as an input and calculates the differential correction amount Td. More specifically, the correction amount calculation process M84 is a process in which the PU 52 performs map calculations to calculate the differential correction amount Td using map data previously stored in the storage device 54. Here, the map data is obtained by substituting the time differential value dTh as an input variable of the map data described above with the time differential value dTh.

[0054] <Functions and Effects of the Third Embodiment> In this embodiment, a filter process M86 is added to the first embodiment, so that the differential correction amount Td can be selectively reflected in the assist amount Ta when the load torque increases stepwise.

[0055] <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.

[0056] Regarding the correction amount calculation process, the correction amount calculation process does not necessarily have to be a process of calculating the differential correction amount Td using map data in which the time differential value dTh is an input variable and the differential correction amount Td is an output variable. For example, the correction amount calculation process may be a process in which the time differential value dTh is multiplied by a gain and the resulting value is assigned to the differential correction amount Td.

[0057] "Regarding the correction amount" The correction amount is not limited to the differential correction amount Td. For example, the correction amount may be a value obtained by multiplying the output value of a high-pass filter that receives the steering torque Th as an input by a gain. Furthermore, for example, the correction amount may be a predetermined fixed value. In this case, for example, a process may be executed to determine whether the absolute value of the difference between the previous value of the steering torque Th and the current value is equal to or greater than a threshold value, and if the absolute value is equal to or greater than the threshold value, the assist amount Ta may be calculated using the correction amount.

[0058] Regarding the Assist Amount Setting Process The assist amount setting process is not limited to a process in which the assist amount Ta is calculated by adding the sum of the correction amount for compensating for a step in the load torque and the phase lead compensation amount Tad to the basic assist amount Tab. For example, a hysteresis correction amount, which is a correction amount for making the assist amount Ta different between turning the steering wheel 12 back and forth, may be added to the basic assist amount Tab. Also, for example, a damping correction amount, which is a correction amount negatively correlated with the rotation speed of the steering wheel 12, may be added to the basic assist amount Tab. Also, for example, a return correction amount, which is a correction amount for returning the steering wheel 12 to the neutral position, may be added to the basic assist amount Tab.

[0059] The input to the basic assist amount calculation process does not necessarily have to be the steering torque Thr, which is the output of the phase lag compensation process M60. For example, the input to the basic assist amount calculation process may be the steering torque Th.

[0060] The phase lead compensation process M70 does not necessarily have to be a process of multiplying the time differential value dTh by the gain Gad and assigning the result to the lead compensation amount Tad. For example, the phase lead compensation process M70 may be a process of calculating the lead compensation amount Tad from a map using map data in which the time differential value dTh is an input variable and the lead compensation amount Tad is an output variable.

[0061] The phase lead compensation process M70 does not necessarily use the time derivative value dTh. For example, the phase lead compensation process M70 may be a process in which the steering torque Th is filtered and used as the lead compensation amount Tad.

[0062] The assist amount setting process does not necessarily include the phase lead compensation process M70. Regarding the Cushioning Member: While the O-ring 94 is shown in FIG. 3 as an example of a cushioning member for absorbing impact when the intermediate stopper 90 comes into contact with the housing 70, this is not limiting. For example, the cushioning member may be made of rubber.

[0063] It is not essential that the intermediate stopper 90 be provided with a buffer member for absorbing impact when the intermediate stopper 90 comes into contact with the housing 70. Figure 11 shows an example in which an O-ring 74 is provided on the protrusion 72 of the housing 70. In this case, the restricting member provided on the housing 70 for restricting rotation of the intermediate stopper 90 includes the protrusion 72 and the O-ring 74. Note that rubber may be provided instead of the O-ring 74.

[0064] It is not necessary to provide a buffer member to absorb the impact when the intermediate stopper 90 contacts the housing 70. "Regarding the Device for Restricting Rotation of the Steering Shaft 14" The device for restricting the rotation of the steering shaft 14 is not limited to the device illustrated in the above embodiment. For example, the device may include multiple intermediate stoppers that are rotated by the end stopper 100. Here, an example will be described in which a first intermediate stopper and a second intermediate stopper are provided. In this case, the first intermediate stopper and the second intermediate stopper are rotated as the end stopper 100 rotates. Then, the protrusion of the first intermediate stopper comes into contact with the protrusion 72 of the housing 70, preventing the first intermediate stopper from rotating. As a result, only the second intermediate stopper is rotated as the end stopper 100 rotates. Then, the protrusion of the second intermediate stopper comes into contact with the protrusion of the first intermediate stopper, preventing the second intermediate stopper from rotating. As a result, the end stopper 100 rotates independently. Then, the protrusion 102 of the end stopper 100 comes into contact with the protrusion of the second intermediate stopper, thereby preventing rotation of the end stopper 100. In other words, further rotation of the steering shaft 14 is prevented.

[0065] "Regarding the steering control device" The steering control device is not limited to one that executes software processing. For example, it may be provided with a dedicated hardware circuit, such as an ASIC, that executes at least a portion of the processing executed in the above embodiment by hardware processing. That is, the steering control device may include a processing circuit having any of the following configurations (a) to (c): (a) A processing circuit that includes a processing device that executes all of the above processing 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 processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing. (c) A processing circuit that includes a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices that include a processing device and a program storage device. Also, there may be multiple dedicated hardware circuits.

[0066] "Regarding the Controlling Entity" The entity that executes the control does not necessarily have to be a single steering control device. For example, the above-described processing may be executed in cooperation with the steering control device and a mobile terminal of the user. Specifically, for example, the axial force setting processing M22 may be executed by the mobile terminal of the user.

[0067] "Others" - In each of the above embodiments, the steering device 10 has a linkless structure in which the steering wheel 12 and the steered wheels 34 are mechanically separated at all times, but this is not limited to this, and the steering device 10 may have a structure in which the steering wheel 12 and the steered wheels 34 can be mechanically separated by a clutch. <Notes> A rotation restricting device that restricts the rotation of a steering shaft that is rotated in response to steering by a driver while power transmission to steered wheels is cut off, comprising: a first rotating member that rotates in conjunction with the steering shaft; a second rotating member that is rotated along with the first rotating member; and a restricting member that contacts the second rotating member to hinder the rotation of the second rotating member when the rotation angle of the second rotating member reaches a predetermined angle, wherein the first rotating member and the second rotating member come into contact with each other such that the second rotating member hinders the rotation of the first rotating member when the first rotating member rotates a predetermined amount from the angle at which rotation of the second rotating member is hindered, and the restricting member has a buffer material at a portion that contacts the second rotating member when the rotation angle of the second rotating member reaches the predetermined angle.

Claims

1. A steering control device that operates a reaction force actuator that applies a reaction force to a steering shaft that is rotated in response to the driver's steering input while power transmission to the steering wheels is interrupted, The reaction actuator comprises a first rotating member that rotates in conjunction with the steering shaft, a second rotating member that is rotated along with the first rotating member, and a restricting member that contacts the second rotating member and hinders its rotation when the rotation angle of the second rotating member reaches a predetermined angle. The first rotating member and the second rotating member are configured to come into contact with each other such that the second rotating member obstructs the rotation of the first rotating member when the first rotating member rotates by a predetermined amount from an angle that hinders the rotation of the second rotating member. The steering control device is configured to perform reaction force command value setting processing and operation processing, The reaction force command value setting process includes a process for calculating a reaction force torque command value, which is the command value of the torque variable indicating the reaction force, and a process for superimposing a correction amount having a negative correlation with the amount of fluctuation of the steering torque, which is the torque input to the steering shaft by the driver, onto the reaction force torque command value. The aforementioned operation process is a process of operating the reaction actuator according to the reaction torque command value, The reaction force command value setting process includes a torque derivative calculation process and a correction amount calculation process, The torque derivative calculation process is a process for calculating the time derivative value of the steering torque, The steering control device is a steering control device in which the correction amount calculation process is a process that changes the correction amount according to the time derivative value as an input variable, under the condition that the absolute value of the correction amount when the absolute value of the time derivative value of the steering torque is large is greater than or equal to the absolute value of the correction amount when the absolute value of the time derivative value is small.

2. The steering control device according to claim 1, wherein the torque derivative calculation process and the correction amount calculation process are repeatedly performed at predetermined intervals.

3. The steering control device according to claim 1, wherein the steering control device performs the correction amount calculation process only within a predetermined angular range of the steering shaft that includes the rotation angle at which the steering control device switches from one state in which the first rotating member rotates along with the second rotating member, to the other state in which the first rotating member rotates without rotating along with the second rotating member.

4. The steering control device according to claim 1, wherein the correction amount calculation process is a process that calculates the correction amount according to the value obtained by filtering the time derivative value.

5. The reaction force command value setting process includes a phase lead compensation process, separate from the correction amount calculation process. The steering control device according to claim 1, wherein the phase lead compensation process is a process that uses the time derivative of the steering torque to reflect a lead compensation amount for advancing the phase of the reaction torque command value into the reaction torque command value.

6. A steering control method that operates a reaction force actuator which applies a reaction force to a steering shaft that is rotated in response to the driver's steering input while power transmission to the steering wheels is interrupted, The reaction actuator comprises a first rotating member that rotates in conjunction with the steering shaft, a second rotating member that is rotated along with the first rotating member, and a restricting member that contacts the second rotating member and hinders its rotation when the rotation angle of the second rotating member reaches a predetermined angle. The first rotating member and the second rotating member are configured to come into contact with each other such that the second rotating member obstructs the rotation of the first rotating member when the first rotating member rotates by a predetermined amount from an angle that hinders the rotation of the second rotating member. The steering control method includes performing a reaction force command value setting process and performing an operation process, The reaction force command value setting process includes a process for calculating a reaction force torque command value, which is the command value of the torque variable indicating the reaction force, and a process for superimposing a correction amount having a negative correlation with the amount of fluctuation of the steering torque, which is the torque input to the steering shaft by the driver, onto the reaction force torque command value. The aforementioned operation process is a process of operating the reaction actuator according to the reaction torque command value, The reaction force command value setting process includes a torque derivative calculation process and a correction amount calculation process, The torque derivative calculation process is a process for calculating the time derivative value of the steering torque, The steering control method is a process in which the correction amount calculation process modifies the correction amount according to the time derivative value as an input variable, provided that the absolute value of the correction amount when the absolute value of the time derivative value of the steering torque is large is greater than or equal to the absolute value of the correction amount when the absolute value of the time derivative value is small.