Steering control device and steering control method

Abstract

In a state where a steered wheel and a steering shaft are mechanically disconnected, this steering control device is configured to execute a resistance force applying process and a resistance force limiting process. The resistance force applying process is a process for applying a resistance torque to the steering shaft by operating a motor, the resistance torque being a torque that prevents the driver from rotating the steering shaft. The resistance force limiting process is a process for limiting the magnitude of the resistance torque to a smaller value when the force applied to the steering shaft by the driver decreases while the resistance force applying process is being executed.

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 No. 2006-124494 describes a control device that controls the torque applied by a motor to the steering shaft when power transmission between the steering shaft and the steered wheels is interrupted. When the rotation angle of the steering wheel approaches an upper limit, this control device executes a process in which the motor applies a torque to the steering shaft that prevents the driver from further increasing the steering angle.

[0003] JP 2023-19704 A

[0004] However, if the driver takes his or her hands off the steering wheel while the blocking torque is being applied to the steering shaft as described above, the steering wheel may be displaced at an excessively high speed.

[0005] One aspect of the present disclosure provides a steering control device. The steering control device is configured to execute a blocking force application process and a blocking force limiting process when the steered wheels and the steering shaft are mechanically disconnected. The blocking force application process is a process of applying a blocking torque to the steering shaft by operating a motor, which is a torque that prevents the driver from rotating the steering shaft. The blocking force limiting process is a process of limiting the magnitude of the blocking torque to a smaller value if the force applied by the driver to the steering shaft weakens while the blocking force application process is being executed.

[0006] Another aspect of the present disclosure provides a steering control method. The steering control method includes steps of executing a blocking force application process and a blocking force limiting process in a state in which the steered wheels and the steering shaft are mechanically disconnected. The blocking force application process is a process of applying a blocking torque to the steering shaft by operating a motor, the blocking torque being a torque that prevents the driver from rotating the steering shaft. The blocking force limiting process is a process of limiting the magnitude of the blocking torque to a smaller value if the force applied by the driver to the steering shaft weakens while the blocking force application process is being executed.

[0007] FIG. 5 is a diagram showing the configuration of a steering system according to a first embodiment. FIG. 6 is an exploded perspective view showing the configuration of a portion of a reaction force actuator provided in the steering system shown in FIG. 1. FIG. 7 is a cross-sectional view showing the configuration of a portion of a reaction force actuator provided in the steering system shown in FIG. 1. FIG. 8 is a diagram showing the operation of a stopper function of the reaction force actuator shown in FIG. 2. FIG. 9 is a block diagram showing details of a portion of the processing executed by the control device shown in FIG. 1. FIG. 10 is a block diagram showing details of the axial force setting processing shown in FIG. 5. FIG. 6 is a flowchart showing the procedure of the axial force setting processing according to a second embodiment. FIG. 7 is a flowchart showing the procedure of the axial force setting processing according to the second embodiment. FIG. 8 is a flowchart showing the procedure of the axial force setting processing according to a third embodiment. FIG. 9 is a flowchart showing the procedure of the axial force setting processing according to the third embodiment. FIG. 10 is a diagram showing a method of limiting an end blocking torque according to a modified example of the above embodiment. FIG. 11 is a diagram showing a method of limiting a deviation blocking torque according to a modified example of the above embodiment.

[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. The reaction force motor 22 is, for example, a three-phase synchronous motor. 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, which is 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. The steering motor 42 is, for example, a three-phase surface permanent magnet synchronous motor (SPM). 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 includes a PU 52 and a storage device 54. The PU 52 is a software processing device such as a CPU and a GPU. 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.

[0011] The control objects of the steering control device 50 are the steering wheel 12 and the steered wheels 34. 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. The steering control device 50 also controls the steering angle, which is the control amount of the steered wheels 34. The steering angle is the turning angle of the tires, which are the steered wheels 34.

[0012] 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, the steering control device 50 references the currents iut, ivt, and iwt flowing through the steering motor 42 to control the control variables. The currents iut, ivt, and iwt may be detected, for example, as voltage drops across shunt resistors provided in each leg of the steering inverter 44. The steering control device 50 references the vehicle speed V detected by the vehicle speed sensor 66. The steering control device 50 references the yaw rate γ detected by the yaw rate sensor 68. The steering control device 50 references a detection signal from a contact detection sensor 69 that detects whether or not a person's hand is touching the steering wheel 12. The contact detection sensor 69 may be a sensor that detects a change in a physical quantity related to the steering wheel 12. Here, the physical quantity may be capacitance, load, or the like. The contact detection sensor 69 may also be a sensor that captures an image of the area around the steering wheel 12. In this case, the detection signal from the contact detection sensor 69 is image data.

[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 as a restricting member that restricts the rotation of the intermediate stopper 90. The intermediate stopper 90 is provided with a protrusion 92 whose rotation is restricted by the protrusion 72.

[0015] FIG. 3 shows a partial cross-sectional view of the reaction force actuator 20. As shown in FIG. 3, 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] "Restriction of Rotation of Steering Shaft 14" Figure 4 shows the operation of the intermediate stopper 90 in response to the rotation of the steering shaft 14. The upper part of Figure 4 shows the case where the steering shaft 14 rotates to the right-hand side. The left end of the upper part of Figure 4 shows a state where the steering angle θs, which is the rotation angle of the steering shaft 14, is at a value corresponding to the end of the left-hand side. The upper part of Figure 4 also shows a state where the steering shaft 14 rotates to the right-hand side as it moves to the right in the figure. In particular, the right end of the upper part of Figure 4 shows a state where the steering angle θs is at a value corresponding to the end of the right-hand side.

[0018] As shown in the upper part of Figure 4, 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 4 shows a state in which the protrusion 92 of the intermediate stopper 90 contacts the protrusion 72 of the housing 70. 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 92 of the intermediate stopper 90, 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 4. 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. 4 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. 4 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. 4 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. 4 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 4, 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 4 shows a state in which the protrusion 92 of the intermediate stopper 90 contacts the protrusion 72 of the housing 70. This prevents the intermediate stopper 90 from turning further left. 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 92 of the intermediate stopper 90, preventing the end stopper 100 from turning further left. This state is shown at the right end of the lower part of Figure 4. 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. 5 shows the processing executed by the steering control device 50. The processing shown in Fig. 5 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. The assist amount setting process M20 is a process for map-calculating the assist amount Ta by the PU 52 in a state where map data M20a is stored in the storage device 54. The map data M20a is data using the steering torque Th and the vehicle speed V as input variables and the assist amount Ta as an output variable.

[0025] 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.

[0026] The angular velocity calculation process M21 is a process in which the steering angle θs is input and the steering angular velocity ωs is output. The angular velocity calculation process M21 may be a process in which the amount of change in the steering angle θs per unit time is substituted for the steering angular velocity ωs, for example.

[0027] The reaction force setting process M22 calculates a reaction force F, which is a force that resists the force applied by the driver to the steering wheel 12. The subtraction process M24 substitutes the value obtained by subtracting the reaction force F from the assist amount Ta into a target reaction torque Tr*. The target reaction torque Tr* is a target value of the torque that the reaction force motor 22 applies to the steering shaft 14.

[0028] The steering operation signal generation process M26 generates an operation signal MSs for the reaction force inverter 24 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 Tr*. Specifically, the steering operation signal generation process M26 includes a process of converting the target reaction force torque Tr* into a target torque of the reaction force motor 22. The steering operation signal generation process M26 also includes a process of calculating an operation signal MSs for the reaction force inverter 24 by current feedback control so that the current flowing through the reaction force motor 22 approaches a current determined from the target reaction force torque Tr*. 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 Tr*, the absolute value of the steering reaction force resisting the rotational force applied to the steering wheel 12 becomes equal to the absolute value of the target reaction force torque Tr*. Furthermore, the sign of the steering reaction force that resists the rotational force applied to the steering wheel 12 is usually opposite to the sign of the assist amount Ta, because the absolute value of the reaction force F is usually greater than the absolute value of the assist amount Ta.

[0029] The steering feedback process M30 is a process for substituting the manipulated variable of feedback control, in which the steering equivalent angle θp is the controlled variable and the target steering equivalent angle θp* is the target value of the controlled variable, into the target steering torque Tt*. The target steering torque Tt* has a fixed ratio to the torque of the steering motor 42.

[0030] 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.

[0031] "Details of Reaction Force Setting Process" Figure 6 shows details of the reaction force setting process M22. The axial force setting process M40 calculates the axial force Fa 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 Fa is a value that expresses the force acting on the rack shaft 32 through the steered wheels 34 through control. However, the axial force Fa does not necessarily have to be intended to estimate the force acting on the rack shaft 32 with high accuracy. For example, the axial force Fa may be a virtually determined force acting on the rack shaft 32. The axial force Fa is converted into a torque applied to the steering shaft 14. In other words, it is converted into a torque that would be applied to the steering shaft 14 if it were assumed that power transmission between the steered wheels 34 and the steering shaft 14 were possible. The axial force Fa is an amount that acts in the direction opposite to the steering direction of the driver.

[0032] The axial force setting process M40 includes a process of substituting the weighted average value of the angle axial force Fθ and the current axial force Fi for the axial force Fa. Here, the angle axial force Fθ is calculated by the PU 52 in accordance with the target steering equivalent angle θp* and the vehicle speed V. The current axial force Fi is calculated by the PU 52 in accordance with the q-axis current iqt.

[0033] The axial force setting process M40 may be a process of changing the angular axial force Fθ in accordance with the target steering equivalent angle θp* under the condition that the absolute value of the angular axial force Fθ when the absolute value of the target steering equivalent angle θp* is large is equal to or greater than the absolute value of the angular axial force Fθ when the absolute value of the target steering equivalent angle θp* is small. The axial force setting process M40 may be a process of changing the angular axial force Fθ in accordance with the vehicle speed V under the condition that the absolute value of the angular axial force Fθ when the vehicle speed V is large is equal to or greater than the absolute value of the angular axial force Fθ when the vehicle speed V is small. Furthermore, the axial force setting process M40 may be a process of changing the current axial force Fi in accordance with the q-axis current iqt under the condition that the absolute value of the current axial force Fi when the absolute value of the q-axis current iqt is large is equal to or greater than the absolute value of the current axial force Fi when the absolute value of the q-axis current iqt is small. 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.

[0034] In the description "changing B according to A under 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." According to the above description, 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. Furthermore, the above description means that B is changed according to A so that A when B is large is larger than A when B is small.

[0035] The end-blocking torque setting process M42 sets the end-blocking torque Fen, which is a torque that prevents the driver from rotating the steering shaft 14 so that the absolute value of the steering angle θs becomes excessively large. The end-blocking torque setting process M42 sets the magnitude of the end-blocking torque Fen to a value greater than zero when the absolute value of the steering angle θs is equal to or greater than the end threshold θen. The end-blocking torque setting process M42 changes the end-blocking torque Fen in accordance with the steering angle θs under the following condition when the absolute value of the steering angle θs is equal to or greater than the absolute value of the end-blocking torque Fen when the absolute value of the steering angle θs is large. This condition is a condition under which the absolute value of the end-blocking torque Fen when the absolute value of the steering angle θs is large is equal to or greater than the absolute value of the end-blocking torque Fen when the absolute value of the steering angle θs is small. The end threshold θen is set to a value smaller than the absolute values ​​of the right-side upper limit of the steering angle θs shown in the upper part of FIG. 4 and the left-side upper limit of the steering angle θs shown in the lower part of FIG. 4.

[0036] The converted steering angle calculation process M44 is a process in which the vehicle speed V and the steering equivalent angle θp are input and the converted steering angle θse is output. The converted steering angle θse is the steering angle θs as an input to the target steering equivalent angle calculation process M18 when the target steering equivalent angle θp* is set to the steering equivalent angle θp by the target steering equivalent angle calculation process M18.

[0037] The deviation preventing torque setting process M46 is a process in which the steering angle θs and the converted steering angle θse are input and the deviation preventing torque FΔ is output. The deviation preventing torque FΔ is a torque that prevents the absolute value of the deviation between the steering angle θs and the converted steering angle θse from becoming excessively large when the driver rotates the steering shaft 14. The deviation preventing torque setting process M46 includes a process of calculating a deviation Δθ, which is the value obtained by subtracting the converted steering angle θse from the steering angle θs. The deviation preventing torque setting process M46 is a process that increases the absolute value of the deviation preventing torque FΔ above zero when the absolute value of the deviation Δθ is equal to or greater than a threshold value Δth. In other words, the deviation preventing torque setting process M46 is a process that increases the absolute value of the deviation preventing torque FΔ above zero when the absolute value of the difference between the target steering angle determined by the target steering equivalent angle θp* and the steering angle of the steered wheels 34 is equal to or greater than a threshold value. The deviation preventing torque setting process M46 is a process for changing the deviation preventing torque FΔ in accordance with the deviation Δθ when the absolute value of the deviation Δθ is equal to or greater than the threshold value Δth under the following condition: The absolute value of the deviation preventing torque FΔ when the absolute value of the deviation Δθ is large is equal to or greater than the absolute value of the deviation preventing torque FΔ when the absolute value of the deviation Δθ is small.

[0038] The selection process M48 is a process of substituting the smaller of the end blocking torque Fen and the deviation blocking torque FΔ for the blocking torque Fpr0. The steering gain setting process M50 is a process in which the steering torque Th is an input and the steering gain Gs is an output. The steering gain setting process M50 includes a process of setting the steering gain Gs to "1" when the absolute value of the steering torque Th is equal to or smaller than the first threshold T1. The steering gain setting process M50 includes a process of setting the steering gain Gs to "0" when the absolute value of the steering torque Th is equal to or larger than the second threshold T2. The steering gain setting process M50 includes a process of changing the steering gain Gs in accordance with the absolute value of the steering torque Th under the following conditions when the absolute value of the steering torque Th is greater than the first threshold T1 and less than the second threshold T2. This condition is a condition in which the steering gain Gs when the absolute value of the steering torque Th is large is equal to or smaller than the steering gain Gs when the absolute value of the steering torque Th is small.

[0039] The speed gain setting process M52 is a process in which the steering angular velocity ωs is an input and the speed gain Gω is an output. The speed gain setting process M52 includes a process of setting the speed gain Gω to "0" when the absolute value of the steering angular velocity ωs is equal to or less than the first threshold value ω1. The speed gain setting process M52 includes a process of setting the speed gain Gω to "1" when the absolute value of the steering angular velocity ωs is equal to or greater than the second threshold value ω2. The speed gain setting process M52 includes a process of changing the speed gain Gω in accordance with the absolute value of the steering angular velocity ωs under the following condition when the absolute value of the steering angular velocity ωs is greater than the first threshold value ω1 and less than the second threshold value ω2. This condition is a condition in which the speed gain Gω when the absolute value of the steering angular velocity ωs is large is equal to or less than the speed gain Gω when the absolute value of the steering angular velocity ωs is small.

[0040] The multiplication process M54 calculates the product of the steering gain Gs and the speed gain Gω. The blocking gain calculation process M56 subtracts the product of the steering gain Gs and the speed gain Gω from "1" and assigns the result to the blocking gain Gpr.

[0041] The blocking torque calculation process M58 is a process of multiplying the blocking torque Fpr0 by the blocking gain Gpr and assigning the result to the blocking torque Fpr. The reaction force calculation process M60 is a process of adding the blocking torque Fpr to the axial force Fa and assigning the result to the reaction force F.

[0042] The blocking force application process corresponds to the steering operation signal generation process M26 when the absolute value of the blocking torque Fpr is greater than zero. The blocking force limiting process corresponds to the steering gain setting process M50, the speed gain setting process M52, the multiplication process M54, the blocking gain calculation process M56, and the blocking torque calculation process M58.

[0043] "Functions and Effects of the Present Embodiment" The PU 52 executes control to prevent the absolute value of the steering angle θs from further increasing beyond the end threshold value θen, which is the upper limit value for control. That is, when the absolute value of the steering angle θs becomes equal to or greater than the end threshold value θen, the PU 52 superimposes an end prevention torque Fen on the reaction force F. Therefore, if the driver operates the steering wheel 12 in a direction that further increases the absolute value of the steering angle θs in a region where the absolute value of the steering angle θs is equal to or greater than the end threshold value θen, the absolute value of the end prevention torque Fen becomes large. If the driver releases his or her hands from the steering wheel 12 in this state, the steering wheel 12 may be displaced toward the neutral position at an excessively high speed if the steering gain Gs and the speed gain Gω are not used.

[0044] In contrast, in this embodiment, when the driver releases his / her hands from the steering wheel 12, the PU 52 sets the steering gain Gs to a value greater than "0." Furthermore, when the speed at which the steering wheel 12 changes to the neutral position due to the blocking torque Fpr increases, the PU 52 sets the speed gain Gω to a value greater than "0." As a result, the blocking gain Gpr becomes a value smaller than "1." Therefore, the magnitude of the blocking torque Fpr is limited to a value smaller than the magnitude of the blocking torque Fpr0.

[0045] Furthermore, PU 52 executes control to prevent converted steering angle θse from deviating significantly from steering angle θs. That is, when the absolute value of deviation Δθ is equal to or greater than threshold value Δth, PU 52 superimposes deviation prevention torque FΔ on reaction force F. Therefore, if the torque of steering motor 42 is not sufficient to steer steered wheels 34 according to target steering equivalent angle θp* due to, for example, a curb or the like, the absolute value of deviation prevention torque FΔ becomes large. In this state, if the driver releases his or her hands from steering wheel 12, steering wheel 12 may be displaced at an excessively high speed if steering gain Gs and speed gain Gω are not used.

[0046] In contrast, in this embodiment, when the driver releases his / her hands from the steering wheel 12, the PU 52 sets the steering gain Gs to a value greater than "0." Furthermore, when the speed at which the steering wheel 12 changes due to the blocking torque Fpr increases, the PU 52 sets the speed gain Gω to a value greater than "0." As a result, the blocking gain Gpr becomes a value smaller than "1." Therefore, the magnitude of the blocking torque Fpr is limited to a value smaller than the magnitude of the blocking torque Fpr0.

[0047] According to the present embodiment described above, the following further actions and effects can be obtained. (1-1) When the absolute value of the steering torque Th is greater than the first threshold value T1 and less than the second threshold value T2, the PU 52 changes the blocking gain Gpr in accordance with the absolute value of the steering torque Th under the following condition. That is, the PU 52 changes the blocking gain Gpr under the condition that the blocking gain Gpr when the absolute value of the steering torque Th is small is equal to or less than the blocking gain Gpr when the absolute value of the steering torque Th is large. As a result, the absolute value of the blocking torque Fpr is changed in accordance with the absolute value of the steering torque Th under the condition that the absolute value of the blocking torque Fpr when the absolute value of the steering torque Th is small is equal to or less than the absolute value of the blocking torque Fpr when the absolute value of the steering torque Th is large. As a result, a sudden change in the blocking torque Fpr can be suppressed compared to when the blocking gain Gpr is switched stepwise between "0" and "1."

[0048] (1-2) When the absolute value of the steering angular velocity ωs is greater than the first threshold value ω1 and less than the second threshold value ω2, the PU 52 changes the blocking gain Gpr in accordance with the absolute value of the steering angular velocity ωs under the following condition. That is, the PU 52 changes the blocking gain Gpr under the condition that the blocking gain Gpr when the absolute value of the steering angular velocity ωs is large is equal to or greater than the blocking gain Gpr when the absolute value of the steering angular velocity ωs is small. As a result, the blocking torque Fpr is changed in accordance with the absolute value of the steering angular velocity ωs under the condition that the absolute value of the blocking torque Fpr when the absolute value of the steering angular velocity ωs is large is equal to or less than the absolute value of the blocking torque Fpr when the absolute value of the steering angular velocity ωs is small. As a result, a sudden change in the blocking torque Fpr can be suppressed compared to when the blocking gain Gpr is switched stepwise between "0" and "1" in accordance with the absolute value of the steering angular velocity ωs.

[0049] Second Embodiment A second embodiment will be described below with reference to the drawings, focusing on differences from the first embodiment.

[0050] In this embodiment, the PU 52 executes a process upstream of the selection process M48 to limit the end-stop torque Fen and the deviation-stop torque FΔ using gains. FIG. 7 shows the procedure for the process of limiting the magnitude of the end-stop torque Fen according to this embodiment. The process shown in FIG. 7 is implemented by the PU 52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined interval. Note that, hereinafter, the step numbers of each process are represented by numbers preceded by "S."

[0051] In the series of processes shown in FIG. 7 , the PU 52 first acquires the detection value of the contact sensor 69 (S10). Next, the PU 52 determines whether the restriction flag FL is “1” (S12). When the restriction flag FL is “1,” this indicates that processing to reduce the magnitude of the blocking torque Fpr is being executed. When the restriction flag FL is “0,” this indicates that processing to reduce the magnitude of the blocking torque Fpr is not being executed. If the PU 52 determines that the restriction flag FL is “0” (S12: NO), the PU 52 determines whether the detection value acquired in the processing of S10 indicates that the driver has released his / her hands from the steering wheel 12 (S14). If the PU 52 determines that the detection value indicates that the driver has released his / her hands from the steering wheel 12 (S14: YES), the PU 52 assigns “1” to the restriction flag FL (S16).

[0052] Then, the PU 52 acquires the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the end excess amount Δθen (steering angle θs) (S18). Here, the current axial force Fi is a variable indicating the force applied to the steered wheels 34. The current axial force change amount ΔFi is the amount of change in the current axial force Fi per unit time. The current axial force change amount ΔFi is calculated by the PU 52. The end excess amount Δθen indicates the amount by which the absolute value of the steering angle θs exceeds the end threshold value θen. The end excess amount Δθen is zero when the absolute value of the steering angle θs is equal to or less than the end threshold value θen. The end excess amount Δθen is calculated by the PU 52 when the PU 52 acquires the end excess amount Δθen instead of the steering angle θs in the processing of S18.

[0053] The PU 52 calculates an end gain Gen according to the values ​​of the variables acquired by the process of S18 (S20). The end gain Gen is a value greater than or equal to 0 and less than 1. The PU 52 may change the end gain Gen according to the steering angular velocity ωs under the condition that the end gain Gen when the absolute value of the steering angular velocity ωs is large is equal to or less than the end gain Gen when the absolute value of the steering angular velocity ωs is small. The process of S20 may be a process in which the PU 52 calculates the end gain Gen using a map while map data is stored in the storage device 54. Here, the map data is data in which the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the end excess amount Δθen (steering angle θs) are input variables, and the end gain Gen is an output variable.

[0054] The PU 52 multiplies the end blocking torque Fen set in the end blocking torque setting process M42 by the end gain Gen, and assigns the resulting value to the end blocking torque Fen (S22).

[0055] On the other hand, if the PU 52 determines that the restriction flag FL is "1" (S12: YES), it determines whether the detection value acquired in the processing of S10 indicates that the driver has his / her hands on the steering wheel 12 (S24). If the PU 52 makes a negative determination in the processing of S24, it proceeds to the processing of S18. On the other hand, if the PU 52 determines that the detection value indicates that the driver has his / her hands on the steering wheel 12 (S24: YES), it assigns "0" to the restriction flag FL (S26).

[0056] The PU 52 temporarily terminates the series of processes shown in Fig. 7 when it completes the processes of S22 and S26 or when a negative determination is made in the process of S14. Fig. 8 shows the procedure for the process of limiting the magnitude of the deviation preventing torque FΔ according to this embodiment. The process shown in Fig. 8 is realized by the PU 52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined interval. For convenience, the same step numbers are used in Fig. 8 for processes corresponding to those shown in Fig. 7.

[0057] 8, when the PU 52 completes the processing of S16, it acquires the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the deviation Δθ (S18a). Then, the PU 52 uses the values ​​of the variables acquired in the processing of S18a as inputs to calculate the deviation gain GΔ (S20a). The deviation gain GΔ is a value equal to or greater than "0" and less than "1."

[0058] The PU 52 may change the deviation gain GΔ in accordance with the steering angular velocity ωs under the condition that the deviation gain GΔ when the absolute value of the steering angular velocity ωs is large is equal to or smaller than the deviation gain GΔ when the absolute value of the steering angular velocity ωs is small. The process of S20a may be a process in which the PU 52 calculates the deviation gain GΔ using map data stored in the storage device 54. Here, the map data is data in which the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the deviation Δθ are input variables and the deviation gain GΔ is an output variable.

[0059] The PU 52 multiplies the deviation blocking torque FΔ set by the deviation blocking torque setting process M46 by the deviation gain GΔ and assigns the resulting value to the deviation blocking torque FΔ (S22a). When the PU 52 completes the process of S22a, it temporarily ends the series of processes shown in FIG. 8. The blocking force limiting process corresponds to the processes of S18 to S22 and S18a to S22a. The contact detection process corresponds to the processes of S14 and S24.

[0060] "Functions and Effects of the Present Embodiment" (2-1) The PU 52 sets the end gain Gen in accordance with the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the end excess amount Δθen (steering angle θs). This allows the end gain Gen to be set to a more appropriate value than when the end gain Gen is set independently of the values ​​of these variables.

[0061] (2-2) The PU 52 sets the deviation gain GΔ in accordance with the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the deviation Δθ. This allows the deviation gain GΔ to be set to a more appropriate value than when the deviation gain GΔ is set independently of the values ​​of these variables.

[0062] Third Embodiment A third embodiment will be described below with reference to the drawings, focusing on differences from the second embodiment.

[0063] In this embodiment, whether or not to execute the process of limiting the magnitudes of the end blocking torque Fen and the deviation blocking torque FΔ to the small side is determined without using the detection value of the contact detection sensor 69 .

[0064] 9 shows the procedure for the process of limiting the magnitude of the end prevention torque Fen according to this embodiment. The process 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. For convenience, the same step numbers are used in FIG. 9 to designate processes corresponding to those shown in FIG. 7.

[0065] 9, the PU 52 first acquires the steering angle θs, the steering torque Th, and the reaction force F (S10a). If the determination in S12 is negative, the PU 52 then determines whether the logical sum of the following conditions (A) to (F) is true (S14a). The logical sum of conditions (A) to (F) being true is a condition for determining that the driver has released his / her hands from the steering wheel 12 in a situation where the absolute value of the end prevention torque Fen set by the end prevention torque setting process M42 is greater than zero.

[0066] Condition (A): The absolute value of the time differential of the steering torque Th is equal to or greater than a threshold value dTh. Condition (B): The absolute value of the time differential of the reaction force F is equal to or greater than a threshold value dF.

[0067] Condition (C): A condition that the amount of change over time Δ|Th| of the absolute value of the steering torque Th is smaller than a threshold value ΔTth. Here, the threshold value ΔTth is set to a value equal to or less than zero. Condition (D): A condition that the amount of change over time Δ|F| of the absolute value of the reaction force F is smaller than a threshold value ΔFth. Here, the threshold value ΔFth is set to a value equal to or less than zero.

[0068] Condition (E): The absolute value of the time derivative of the steering angular velocity ωs is equal to or greater than a threshold value ωsth. Condition (F): The amount of change d|θs| over time in the absolute value of the steering angle θs is smaller than a threshold value dθth. Here, the threshold value dθth is set to a value equal to or less than zero.

[0069] If the PU 52 determines that the logical sum of the above conditions (A) to (F) is true (S14a: YES), the PU 52 proceeds to the process of S16. If the PU 52 determines that the logical sum of the above conditions (A) to (F) is false (S14a: NO), the PU 52 temporarily ends the series of processes shown in FIG.

[0070] On the other hand, if the PU 52 makes a positive determination in the processing of S12, it determines whether the logical sum of the following conditions (G) to (J) is true. If the logical sum of conditions (G) to (J) is true, this is the condition for determining that the driver has touched the steering wheel 12 in a situation where the absolute value of the end prevention torque Fen set by the end prevention torque setting processing M42 is greater than zero.

[0071] Condition (G): The absolute value of the steering angular velocity ωs is equal to or less than a threshold value ωsth. Condition (H): The absolute value of the yaw rate γ is equal to or less than a threshold value γth. The PU 52 may set the threshold value γth according to the vehicle speed V. Specifically, the PU 52 may change the threshold value γth according to the vehicle speed V under the condition that the threshold value γth when the vehicle speed V is high is equal to or greater than the threshold value γth when the vehicle speed V is low.

[0072] Condition (I): The absolute value of the steering torque Th is equal to or greater than a threshold value Thth. Condition (J): The absolute value of the steering angle θs is equal to or less than a threshold value θsth. The threshold value θsth may be equal to the end threshold value θen.

[0073] If the PU 52 determines that the logical sum of the conditions (G) to (J) is true (S24a: YES), the PU 52 proceeds to the process of S26. On the other hand, if the PU 52 determines that the logical sum of the conditions (G) to (J) is false (S24a: NO), the PU 52 proceeds to the process of S18.

[0074] 10 shows the procedure for the process of limiting the magnitude of the deviation preventing torque FΔ according to this embodiment. The process shown in FIG. 10 is realized by the PU 52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined interval. For convenience, the same step numbers are used in FIG. 10 to designate processes corresponding to those shown in FIGS. 8 and 9.

[0075] 10, if the PU 52 determines that the restriction flag FL is "0" (S12: NO), the PU 52 determines whether the logical sum of the above conditions (A) to (E) is true (S14b). The logical sum of the conditions (A) to (E) being true is a condition for determining that the driver has released the steering wheel 12 in a situation where the absolute value of the deviation preventing torque FΔ set by the deviation preventing torque setting process M46 is greater than zero.

[0076] If the PU 52 determines that the logical sum of the conditions (A) to (E) is true (14b: YES), the PU 52 proceeds to the process of S16. If the PU 52 determines that the logical sum of the conditions (A) to (E) is false (14b: NO), the PU 52 temporarily ends the series of processes shown in FIG.

[0077] On the other hand, when the PU 52 determines that the restriction flag FL is "1" (S12: YES), the PU 52 determines whether the logical sum of the above conditions (G) to (I) is true. The logical sum of the conditions (G) to (I) being true is a condition for determining that the driver has touched the steering wheel 12 in a situation where the absolute value of the deviation preventing torque FΔ set by the deviation preventing torque setting process M46 is greater than zero.

[0078] If the PU 52 determines that the logical sum of the conditions (G) to (I) is true (S24b: YES), the PU 52 proceeds to the process of S26. On the other hand, if the PU 52 determines that the logical sum of the conditions (G) to (I) is false (S24b: NO), the PU 52 proceeds to the process of S18.

[0079] "Functions and Effects of the Present Embodiment" (3-1) When the absolute value of the end prevention torque Fen set by the end prevention torque setting process M42 is greater than zero, and the logical sum of conditions (A) to (F) is true, the PU 52 sets the end gain Gen to a value less than "1." This makes it possible to limit the magnitude of the end prevention torque Fen to a smaller value at an appropriate timing, regardless of the detection value of the contact sensor 69.

[0080] (3-2) When the absolute value of the end blocking torque Fen set by the deviation blocking torque setting process M46 is greater than zero, and the logical sum of conditions (A) to (E) is true, the PU 52 sets the deviation gain GΔ to a value less than 1. This makes it possible to limit the magnitude of the deviation blocking torque FΔ to a smaller value at an appropriate timing, regardless of the detection value of the contact sensor 69.

[0081] (3-3) When the PU 52 determines that the logical sum of the conditions (G) to (J) is true while the end gain Gen is set to a value smaller than 1, the PU 52 stops limiting the end blocking torque Fen by the end gain Gen. This makes it possible to stop the process of limiting the magnitude of the end blocking torque Fen to a smaller value at an appropriate timing, regardless of the detection value of the contact detection sensor 69.

[0082] (3-4) When the PU 52 determines that the logical sum of the conditions (G) to (I) is true while the deviation gain GΔ is set to a value smaller than 1, it stops limiting the deviation preventing torque FΔ by the deviation gain GΔ. This makes it possible to stop the process of limiting the magnitude of the deviation preventing torque FΔ to a smaller value at an appropriate timing, regardless of the detection value of the contact detection sensor 69.

[0083] <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.

[0084] Regarding the Blocking Force Application Process (a) Regarding the Deviation Blocking Torque Setting Process The deviation blocking torque setting process is not limited to the process illustrated in Fig. 6. The deviation blocking torque setting process may be, for example, a process in which a value obtained by multiplying the deviation Δθ by a proportionality coefficient is assigned to the deviation blocking torque FΔ.

[0085] (b) Regarding the End Blocking Force Setting Process The end blocking force setting process is not limited to the process illustrated in Fig. 6. For example, the end blocking force setting process may be a process in which a value obtained by subtracting the end threshold value θen from the steering angle θs is multiplied by a proportionality coefficient and assigned to the end blocking torque Fen.

[0086] (c) Others The blocking force application process is not limited to a process in which the larger of the deviation blocking torque FΔ and the end blocking torque Fen is assigned to the blocking torque Fpr. For example, the blocking force application process may be a process in which the sum of the deviation blocking torque FΔ and the end blocking torque Fen is assigned to the blocking torque Fpr. Furthermore, for example, the blocking force application process may be configured solely by the deviation blocking torque setting process. Furthermore, for example, the blocking force application process may be configured solely by the end blocking force setting process.

[0087] Regarding the blocking force limiting process: In Fig. 6, the blocking force limiting process may be changed to a process of switching maps in the end blocking torque setting process M42. That is, as shown by the dashed-dotted line in Fig. 11, when the absolute value of the steering torque Th is small or when the absolute value of the steering angular velocity ωs is large, the end blocking torque Fen may be set to a small value. Note that the dashed-dotted line illustrates a polygonal line whose slope increases as the absolute value of the steering angle θs becomes greater than a predetermined value that is greater than the end threshold value θen, but it may also be a downwardly convex curve.

[0088] In Fig. 6, the blocking force limiting process may be changed to a process of switching maps in the deviation blocking torque setting process M46. That is, as shown by the dashed-dotted line in Fig. 12, when the absolute value of the steering torque Th is small or when the absolute value of the steering angular velocity ωs is large, the deviation blocking torque FΔ may be set to a small value. Note that the dashed-dotted line illustrates a polygonal line whose slope increases as the absolute value of the deviation Δθ becomes greater than a predetermined value that is greater than the threshold value Δth, but a downwardly convex curve may also be used.

[0089] While Fig. 6 illustrates an example in which the blocking gain Gpr is multiplied by the blocking torque Fpr0, this is not limiting. For example, a gain equivalent to the blocking gain Gpr may be multiplied by both the end blocking torque Fen and the deviation blocking torque FΔ. In this case, the gain by which the end blocking torque Fen is multiplied may be different from the gain by which the deviation blocking torque FΔ is multiplied.

[0090] The process of S14 is not limited to a process in which the output value of a single contact detection sensor 69 is input. For example, the process of S14 may be a process in which the values ​​of multiple variables corresponding to the detection values ​​of multiple sensors are input. Here, the values ​​of the multiple variables may include, for example, the steering angle θs, the steering torque Th, the vehicle speed V, the steering angular velocity ωs, etc.

[0091] The process of S24 is not limited to a process in which the output value of a single contact detection sensor 69 is input. For example, the process of S24 may be a process in which the values ​​of multiple variables corresponding to the detection values ​​of multiple sensors are input. Here, the values ​​of the multiple variables may include, for example, the steering angle θs, the steering torque Th, the vehicle speed V, the steering angular velocity ωs, etc.

[0092] The process of S14a is not limited to a process of determining whether the logical sum of conditions (A) to (F) is true. For example, the process of S14a may be a process of determining whether the logical sum of two to five conditions selected from the six conditions (A) to (F) is true. Furthermore, for example, the process of S14a may be a process of determining whether any one condition selected from the six conditions (A) to (F) is satisfied.

[0093] The process of S14a may be a process of determining whether the logical product of conditions (A) to (F) is true. Also, for example, the process of S14a may be a process of determining whether the logical product of some or more of conditions (A) to (F) is true.

[0094] The process of S24a is not limited to a process of determining whether the logical sum of conditions (G) to (J) is true. For example, the process of S24a may be a process of determining whether the logical sum of two or three conditions selected from the four conditions (G) to (J) is true. Furthermore, for example, the process of S24a may be a process of determining whether any one condition selected from the four conditions (G) to (J) is satisfied.

[0095] The process of S24a may be a process of determining whether the logical product of conditions (G) to (J) is true. Also, for example, the process of S24a may be a process of determining whether the logical product of some or more of conditions (G) to (J) is true.

[0096] The process of S14b is not limited to a process of determining whether the logical sum of conditions (A) to (E) is true. For example, the process of S14b may be a process of determining whether the logical sum of two to four conditions selected from the five conditions (A) to (E) is true. Furthermore, for example, the process of S14b may be a process of determining whether any one condition selected from the five conditions (A) to (E) is true.

[0097] The process of S14b may be a process of determining whether or not the logical product of conditions (A) to (E) is true. Also, for example, the process of S14b may be a process of determining whether or not the logical product of some or more of conditions (A) to (E) is true.

[0098] The process of S24b is not limited to a process of determining whether the logical sum of conditions (G) to (I) is true. For example, the process of S24b may be a process of determining whether the logical sum of any two conditions selected from the three conditions (G) to (I) is true. Furthermore, for example, the process of S24b may be a process of determining whether any one condition selected from the three conditions (G) to (I) is true.

[0099] The process of S24b may be a process of determining whether the logical product of conditions (G) to (I) is true. Also, for example, the process of S24b may be a process of determining whether the logical product of any two conditions of conditions (G) to (I) is true.

[0100] 7 and 9 show an example in which the process for setting the end gain Gen is a process in which the values ​​of five variables, namely, the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the end excess amount Δθen (steering angle θs), are input, but the present invention is not limited to this. The process for setting the end gain Gen may be a process in which the values ​​of any one to four variables selected from the five variables, namely, the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the end excess amount Δθen (steering angle θs), are input.

[0101] 8 and 10 show an example in which the process for setting the deviation gain GΔ is a process in which the values ​​of five variables, namely, the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the deviation Δθ, are input, but this is not limiting. For example, the process for setting the deviation gain GΔ may be a process in which the values ​​of any one to four variables selected from the five variables, namely, the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, the vehicle speed V, and the deviation Δθ, are input.

[0102] The blocking gain Gpr by which the blocking torque Fpr0 is multiplied is not limited to the variable value calculated by the process shown in Fig. 6. For example, the blocking gain Gpr by which the blocking torque Fpr0 is multiplied may be a variable value calculated from the values ​​of four variables, namely, the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, and the vehicle speed V. Furthermore, the blocking gain Gpr by which the blocking torque Fpr0 is multiplied may be a variable value calculated from the values ​​of any one to three variables selected from the four variables, namely, the steering angular velocity ωs, the current axial force Fi, the current axial force change amount ΔFi, and the vehicle speed V.

[0103] In the above case, the process of multiplying the blocking gain Gpr may be triggered by the logical sum of two to five conditions selected from the five conditions (A) to (E) being true. Here, the logical sum may be interpreted as the logical product. Furthermore, for example, the process of multiplying the blocking gain Gpr may be triggered by the establishment of any one of the five conditions.

[0104] In the above case, the process of multiplying the blocking gain Gpr may be terminated when the logical sum of two or three conditions selected from the three conditions (G) to (I) is true. Here, the logical sum may be interpreted as the logical product. For example, the process of multiplying the blocking gain Gpr may be terminated when any one of the three conditions (G) to (I) is satisfied.

[0105] Regarding the device for restricting the rotation of the steering shaft 14: The device for restricting the rotation of the steering shaft 14 is not limited to the device exemplified in the above embodiment. For example, the end stopper 100 does not necessarily have to have an intermediate stopper that rotates along with it.

[0106] "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 part of the processing executed in the above embodiment. 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.

[0107] "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.

Claims

1. A steering control device configured to execute a blocking force application process and a blocking force limitation process in a state where the steering wheel and the steering shaft are mechanically disconnected. The blocking force application process is a process of applying a blocking torque, which is a torque that prevents a driver from rotating the steering shaft, to the steering shaft by operating a motor. The blocking force limitation process is a process of limiting the magnitude of the blocking torque to a lower level when the rotational force applied by the driver to the steering shaft weakens while the blocking force application process is being executed.

2. The steering control device according to claim 1, wherein the blocking force limitation process has a steering torque as an input, and is configured to be executed when the magnitude of the steering torque is equal to or less than a predetermined value while the blocking force application process is being executed.

3. The input variable of the blocking force limitation process includes a predetermined variable, and the blocking force limitation process is configured to be executed triggered by the magnitude of the value of the predetermined variable being equal to or greater than a predetermined value while the blocking force application process is being executed. The predetermined variable is any one of three variables: the steering angular velocity, the time derivative of the steering torque, and the time derivative of the torque applied by the blocking force application process.

4. A steering control device configured to execute a contact detection process. The contact detection process is a process of obtaining a detection value of a sensor that detects whether or not a driver's hand is touching a steering wheel connected to the steering shaft. The blocking force limitation process includes a process of limiting the magnitude of the blocking torque to a lower level when the detection value of the sensor is input and it is detected that the driver's hand is not touching the steering wheel.

5. The steering control device according to claim 1, wherein the blocking force limitation process includes a process of changing the degree of limiting the magnitude of the blocking torque in response to an input of at least one variable among four variables: the steering angular velocity, the vehicle speed, the force applied to the steering wheel, and the time derivative value of the force applied to the steering wheel.

6. A steering control device according to claim 1, configured to execute a contact detection process, wherein the contact detection process is a process of acquiring a detection value of a sensor that detects whether a driver's hand is touching a steering wheel connected to the steering shaft, and when it is detected that the driver's hand is touching the steering wheel, the braking force limitation process is stopped.

7. The steering control device according to claim 1, wherein the braking force limitation process includes a process of setting the braking torque to zero when the magnitude of the steering torque is equal to or less than a predetermined torque and the magnitude of the steering angular velocity is equal to or greater than a predetermined speed.

8. The steering control device according to claim 7, wherein the braking force limitation process includes a process of restricting the magnitude of the braking torque to the smaller side according to the magnitude of the steering torque under the condition that when the steering torque is greater than the predetermined torque, the magnitude of the braking torque when the magnitude of the steering torque is small is equal to or less than the magnitude of the braking torque when the magnitude of the steering torque is large, and a process of restricting the magnitude of the braking torque to the smaller side according to the magnitude of the steering angular velocity under the condition that when the steering angular velocity is less than the predetermined speed, the magnitude of the braking torque when the magnitude of the steering angular velocity is large is equal to or less than the magnitude of the braking torque when the magnitude of the steering angular velocity is small.

9. The steering control device according to claim 1, wherein the braking force application process is configured to be executed when the magnitude of the steering angle is equal to or greater than an end threshold value.

10. The steering control device according to claim 1, wherein the braking force application process is configured to be executed when the absolute value of the difference between the target steering angle and the steering angle of the steered wheels is equal to or greater than a threshold value.

11. The steering control device according to claim 9, wherein the braking force limitation process includes a process of changing the degree of restricting the braking torque to the smaller side according to either the steering angle or the amount by which the steering angle exceeds the end threshold value when the magnitude of the steering angle is equal to or greater than the end threshold value.

12. A steering control method having a step of executing a blocking force application process and a blocking force limitation process in a state where the steering wheel and the steering shaft are mechanically blocked, the blocking force application process being a process of applying a blocking torque, which is a torque that prevents a driver from rotating the steering shaft, to the steering shaft by operating a motor, and the blocking force limitation process being a process of limiting the magnitude of the blocking torque to a smaller side when the force applied by the driver to the steering shaft weakens while the blocking force application process is being executed.

Images