JP2025111978A - Steering control device - Google Patents

Abstract

[Problem] To provide a steering control device that can shorten the time required for processing to learn the midpoint. [Solution] A PU (52) operates a reaction motor (22) to displace a steering shaft (14) to the right-turning side as far as possible. When the steering angle no longer changes, the PU (52) sets the steering angle at that time as the upper limit value for the right-turning side. The PU (52) calculates the upper limit value for the left-turning side based on the upper limit value for the right-turning side and the mechanical end distance. The PU (52) sets "1/2" of the sum of the upper limit value for the right-turning side and the upper limit value for the left-turning side as the midpoint. [Selected Figure] Figure 1

Description

The present invention relates to a steering control device.

Patent Document 1 below describes a steer-by-wire system in which power transmission between the steered wheels and the steering shaft is cut off. The control device described in the document calculates the midpoint based on the steering angle when the steering shaft is displaced to the maximum left and the maximum right.

Japanese Patent Application Laid-Open No. 2021-195084

In the case of the above device, the steering shaft needs to be displaced to the maximum extent possible in both the right-turning and left-turning directions in order to calculate the midpoint, which increases the processing time required to calculate the midpoint.

The means for solving the above problems and their effects will be described below.
1. A steering control device in which a reaction motor that applies a reaction force to the steering shaft is an operation target when power transmission between steered wheels and a steering shaft is interrupted, the steering control device being configured to execute an end hitting process, an end determination process, a maximum displacement variable acquisition process, and a midpoint learning process, the end hitting process being a process of displacing the steering shaft to the maximum extent to either the right turning side or the left turning side by operating the reaction motor, the end determination process being a process of determining whether the steering shaft has been displaced to the maximum extent, the maximum displacement variable acquisition process being a process of acquiring a value of a maximum displacement variable, the maximum displacement variable being a variable obtained based on the determination by the end determination process that the maximum displacement has been reached, and the midpoint learning process being a process of learning a midpoint of the rotation angle of the steering shaft based on the value of the maximum displacement variable.

The range over which the steering shaft can be displaced can be determined in advance. Therefore, the value of the maximum displacement variable obtained when the steering shaft is displaced to the maximum can also be used to determine the variable value indicating the steering angle resulting from maximum displacement in either direction. This means that the upper limit of the steering angle in both directions can be determined based on the value of the maximum displacement variable. Therefore, in the above configuration, the midpoint is learned based on the value of the maximum displacement variable. This reduces the time required for the midpoint learning process compared to when processing is performed to displace the steering shaft to the maximum in both directions.

2. A steering control device as described in paragraph 1, wherein the value of the maximum displacement variable is the integrated value of the rotation angle of the reaction motor when the end determination process determines that the maximum displacement has occurred, and the midpoint learning process is a process for learning the midpoint based on a predetermined rotatable angle of the steering shaft and the integrated value as an input variable.

The integrated value indicates the upper limit of the steering angle for either of the above. Therefore, the maximum rotation angle of the steering shaft and the integrated value can be used to determine the upper limit or midpoint of the other steering angle.

3. A steering control device as described in claim 1 above, configured to execute an initial value acquisition process, wherein the end contact process includes a process for controlling the rotational speed of the reaction motor to a target rotational speed, the maximum displacement variable is the elapsed time until the end contact process determines that the maximum displacement has occurred, the initial value acquisition process is a process for acquiring an integrated value of the rotational angle of the reaction motor at the start of measuring the elapsed time, and the midpoint learning process is a process for learning the midpoint based on the value of the maximum displacement variable as an input variable and the integrated value at the start.

The amount of steering shaft displacement can be determined based on the target rotational speed and elapsed time. Therefore, the steering angle when either of the above displacements occurs can be determined based on the elapsed time and the value acquired by the initial value acquisition process. Therefore, with the above configuration, the midpoint can be learned.

4. The steering control device according to claim 3, wherein the target rotational speed is a constant value.
In the above configuration, by setting the target rotation speed to a constant value, the amount of displacement of the steering shaft can be more easily determined from the elapsed time than when the target rotation speed is changed.

5. A steering control device described in any one of items 1 to 4 above, which is configured to execute a midpoint control process, in which the midpoint control process displaces the steering shaft from a state in which it has been displaced to the maximum extent in one of the directions by the end contact process to a learned midpoint position without displacing the steering shaft to the other of the right-turning side and the left-turning side to the maximum extent.

With the above configuration, the steering angle can be quickly shifted to the midpoint after midpoint learning is completed.

1 is a diagram illustrating a configuration of a steering system according to a first embodiment. FIG. 2 is an exploded perspective view showing a configuration of a part of a reaction force actuator provided in the steering system shown in FIG. 1 . 2 is a cross-sectional view showing a configuration of a part of a reaction force actuator included in the steering system shown in FIG. 1. 3A and 3B are diagrams illustrating the operation of the stopper function of the reaction force actuator shown in FIG. 2. 2 is a flowchart showing a procedure of processing executed by the steering control device shown in FIG. 1 . 2 is a flowchart showing a procedure of processing executed by the steering control device shown in FIG. 1 . 10 is a flowchart showing a procedure of a process executed by a steering control device according to a second embodiment.

First Embodiment
Hereinafter, the first embodiment will be described with reference to the drawings.
"Prerequisite configuration"
The 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 surface permanent magnet synchronous motor. The reaction force reduction mechanism 26 is, for example, a worm and wheel.

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. The steering motor 42 is, for example, a three-phase synchronous motor. The steering transmission mechanism 46 is composed 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.

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

The control target of the reaction force control device 50 is the steering wheel 12. The reaction force control device 50 controls the steering reaction force that resists the driver's steering, which is the control amount of the steering wheel 12.

To control the control amount, the reaction force control device 50 references the steering torque Th detected by the torque sensor 56. 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 control amount, the reaction force control device 50 references 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 58. To control the control amount, the reaction force control device 50 also references 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 voltage drop across shunt resistors provided in each leg of the reaction force inverter 24.

The steering control device 60 includes a PU 62 and a storage device 64. The PU 62 is a software processing device such as a CPU or GPU. The storage device 64 may be electrically non-rewritable non-volatile memory. Alternatively, the storage device 64 may be electrically rewritable non-volatile memory or a storage medium such as a disk medium.

The control target of the steering control device 60 is the steered wheels 34. The steering control device 60 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 serve as the steered wheels 34.

To control the control amount, the steering control device 60 references the rotation angle θb, which is the angle of the rotation shaft of the steering motor 42, detected by the steering-side rotation angle sensor 66. To control the control amount, the steering control device 60 also references the currents iut, ivt, and iwt flowing through the steering motor 42. The currents iut, ivt, and iwt may be detected, for example, as the voltage drop across shunt resistors provided in each leg of the steering inverter 44.

"Configuration of reaction force actuator 20"
FIG. 2 shows a partial configuration 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 rotatably supports the steering shaft 14. 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.

The housing 70 is provided with a protrusion 72 that acts as a restricting member to restrict rotation of the intermediate stopper 90. The intermediate stopper 90 is provided with a protrusion 92 whose rotation is restricted by the protrusion 72.

Figure 3 shows a partial cross-sectional view of the reaction force actuator 20. As shown in Figure 3, an elastic force acting in the right direction in the figure is exerted on the end stopper 100 by the wave washer 84. As a result, an elastic force acting in the right direction is exerted on 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, intermediate stopper 90, and 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 exerted on the intermediate stopper 90 by the washer 82, and an elastic force acting in the left direction in the figure is exerted by the washer 80.

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.

"Restricting rotation of steering shaft 14"
FIG. 4 shows the movement of the intermediate stopper 90 as the steering shaft 14 rotates.
The upper part of Fig. 4 shows a case where the steering shaft 14 rotates to the right-hand side. The left end of the upper part of Fig. 4 shows a state where the steering angle θh, 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 Fig. 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 Fig. 4 shows a state where the steering angle θh is at a value corresponding to the end of the right-hand side.

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 the 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 θh at this time is the upper limit on the right turning side.

The bottom part of Figure 4 shows the case where the rotation angle of the steering shaft 14 rotates to the left turning side. The left end of the bottom part of Figure 4 shows the state where the steering angle θh is at a value corresponding to the end of the right turning side. The bottom part of Figure 4 also shows the 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 bottom part of Figure 4 shows the state where the steering angle θh is at a value corresponding to the end of the left turning side.

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 the 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 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 to the 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 θh at this time is the upper limit on the left-turning side.

"N-point learning value"
As shown in FIG. 1 , the storage device 54 of the reaction force control device 50 stores steering side N-point learning data 54a indicating the N-point learning value, which is the learned value of the steering angle θh when traveling straight. The storage device 64 of the turning control device 60 stores steering side N-point learning data 64a indicating the N-point learning value, which is the learned value of the steering angle when traveling straight. As an example, the turning side N-point learning data 64a is stored in the storage device 64 before the steering device 10 is shipped. Meanwhile, in this embodiment, the reaction force control device 50 executes a process to acquire the N-point learning value when the reaction force control device 50 is started for the first time after shipping. The reaction force control device 50 also executes a process to acquire the N-point learning value when the turning control device 60 is started immediately after the steering side N-point learning data 54a is lost in the storage device 54 due to, for example, battery replacement. The conditions under which the reaction force control device 50 and the turning control device 60 start communication for steering the vehicle include a condition that each of them holds the N-point learning value.

The process in which the reaction force control device 50 acquires the N-point learning value is performed, for example, by displacing the steering angle θh up to its upper limit value on the right-turning side. This will be described below.
"N-point learning process"
Figure 5 shows the processing procedure at the time of startup of the reaction force control device 50. The processing shown in Figure 5 is realized by the PU 52 executing a program stored in the storage device 54, triggered by startup of the reaction force control device 50. Note that, below, the step number of each process is represented by a number preceded by "S."

In the series of processes shown in FIG. 5, the PU 52 first determines whether steering side N-point learning data 54a is stored (S10). If the PU 52 determines that steering side N-point learning data 54a is not stored (S10: NO), it sets the control mode to N-point learning mode (S12). On the other hand, if the PU 52 determines that steering side N-point learning data 54a is stored (S10: YES), it sets the control mode to normal control mode (S14). The normal control mode is a mode in which processing related to steering of the vehicle is performed in cooperation with the steering control device 60. However, when the normal control mode is started, initial check processing, such as whether communication with the steering control device 60 can be performed normally, is performed.

When the PU 52 completes the processes of S12 and S14, the PU 52 temporarily ends the series of processes shown in FIG.
6 shows a processing procedure for acquiring the steering-side N-point learning data 54a. The series of processing steps 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.

In the series of processes shown in FIG. 6, the PU 52 first determines whether the N-point learning mode is in effect (S20). If the PU 72 determines that the N-point learning mode is in effect (S20: YES), it determines whether the operation mode in the N-point learning mode is in right turn mode (S22). The operation mode is set to right turn mode when the control mode switches to N-point learning mode. If the PU 52 determines that the right turn mode is in effect (S22: YES), it assigns a value obtained by adding a predetermined amount Δ to the target steering angle θh* to the target steering angle θh* (S24). Then, the PU 72 determines whether the logical product of the following conditions (A) to (C) remains true for a certain period of time (S26).

Condition (A) is a condition that the absolute value of the steering torque Th is equal to or less than a predetermined value, that is, that the driver is not operating the steering wheel 12.
Condition (B) is a condition that the previous value "θh(n-1)" of the steering angle θh matches the current value "θh(n)." The steering angle θh is calculated by the PU 52 based on the rotation angle θa as an input variable. The calculation process of the steering angle θh by the PU 52 includes the following processes. That is, the calculation process includes converting the rotation angle θa into an integrated angle that includes a range exceeding 360° by 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 calculation process also includes multiplying the converted integrated angle by a conversion coefficient based on the rotational speed ratio of the reaction force reduction mechanism 26 to calculate the steering angle θh. Note that the steering angle θh is positive when it is an angle to the right of the steering neutral position, and negative when it is an angle to the left of the steering neutral position.

Condition (C) is a condition that the absolute value of the q-axis current iqs flowing through the reaction motor 22 is equal to or greater than the threshold value Ith. The threshold value Ith is set to a value greater than the expected absolute value of the q-axis current iqs when changing the steering angle θh when the steering angle is in the intermediate region between the upper limit value on the right-hand side and the upper limit value on the left-hand side. For example, if the feedback control in the processing of S34 described below includes a proportional term, the threshold value Ith may be set to be equal to or greater than the output value of the proportional term when the absolute value of the difference between the target steering angle θh* and the steering angle θh becomes a predetermined amount Δ. Furthermore, if the feedback control in the processing of S34 includes an integral term, the threshold value Ith may be a value that determines whether a windup phenomenon of the integral term is occurring. The q-axis current iqs is calculated by the PU 52 based on the rotation angle θa and the currents ius, ivs, and iws as input variables.

The condition for determining that the steering angle has reached its upper limit on the right-turn side is true when the above logical product is true. In other words, if condition (A) is true, it is understood that the driver is not preventing the reaction force motor 22 from rotating the steering shaft 14. Therefore, if the upper limit on the right-turn side is reached when condition (A) is true, condition (B) is true. Furthermore, if the upper limit on the right-turn side is reached, the absolute value of the difference between the target steering angle θh* and the steering angle θh cannot be reduced, so the absolute value of the torque of the reaction force motor 22 increases, and condition (C) is true.

If the PU 52 determines that the logical product of conditions (A) to (C) remains true for a certain period of time (S26: YES), it assigns the current value of the steering angle θh, "θh(n)," to the target steering angle θh* (S28). It then assigns the current value, "θh(n)," to the right upper limit value θhR (S30).

The PU 72 switches the operation mode to the midpoint movement mode (S32).
When the processing of S32 is completed or when a negative determination is made in the processing of S26, the PU 52 calculates a target torque Ts* corresponding to the operation amount by feedback control, in which the steering angle θh is the control amount and the target steering angle θh* is the target value of the control amount (S34). The target torque Ts* is a target value of the torque of the reaction force motor 22.

Then, the PU 52 outputs to the reaction force inverter 24 an operation signal MSs for the reaction force inverter 24 to bring the torque of the reaction force motor 22 closer to the target torque Ts* (S36).
On the other hand, if the determination in S22 is negative, the PU 52 subtracts the mechanical end interval θLR from the right upper limit value θhR and assigns the result to the left upper limit value θhL (S38). The mechanical end interval θLR indicates the size of the angular range in which the steering angle θh can change. This angular range is the range in which the steering angle θh changes from the state shown at the left end to the state shown at the right end in the upper part of Figure 4. The PU 52 obtains the mechanical end interval θLR by reading out the mechanical end interval data 54b stored in the storage device 54.

The PU 52 assigns "1/2" of the sum of the right upper limit value θhR and the left upper limit value θhL to the midpoint θhmd (S40).
The PU 52 determines whether the steering angle θh coincides with the midpoint θhmd (S42). If the PU 52 determines that the steering angle θh does not coincide with the midpoint θhmd (S42: NO), the PU 52 subtracts a predetermined amount Δ from the target steering angle θh* and assigns the result to the target steering angle θh* (S44). Then, the PU 52 proceeds to the process of S34.

On the other hand, when the PU 72 determines that the steering angle θh coincides with the midpoint θhmd (S42: YES), the PU 72 ends the N-point learning mode (S46).
The PU 72 temporarily terminates the series of processes shown in FIG. 6 when it completes the processes of S36 and S46 or when it makes a negative determination in the process of S20.

"Actions and Effects of the Present Embodiment"
If the steering-side N-point learning data 54a is not stored at startup, the PU 52 sets the control mode to the N-point learning mode. In the N-point learning mode, the PU 52 increases the target steering angle θh* at a speed determined by a predetermined amount Δ. This controls the steering angle θh to follow the target steering angle θh*. When the steering angle θh reaches the right upper limit, the steering angle θh no longer increases. Therefore, the PU 52 recognizes the steering angle θh at that time as the right upper limit θhR.

Then, the PU 52 calculates the left upper limit value θhL based on the right upper limit value θhR and the mechanical end distance θLR. The PU 52 then calculates the midpoint θhmd based on the right upper limit value θhR and the left upper limit value θhL.

In this way, the PU 52 calculates the midpoint θhmd by only performing the process of displacing the steering shaft 14 to the right as far as possible. Therefore, the processing time required to calculate the midpoint θhmd can be reduced compared to when both the process of displacing the steering shaft 14 to the right and the process of displacing it to the left are performed.

According to the present embodiment described above, the following actions and effects can be further obtained.
(1) The PU 52 determines whether the steering shaft 14 has been displaced to its maximum extent based on whether the logical product of the above conditions (A) to (C) is true. This allows for highly accurate determination of whether the steering shaft 14 has been displaced to its maximum extent.

In other words, if the maximum displacement is determined to have occurred when the logical product of the above conditions (B) and (C) is true, there is a risk that the system will erroneously determine that the maximum displacement has occurred if the driver applies force to the steering wheel 12 so as not to change the steering angle θh. Also, if the maximum displacement is determined to have occurred when the logical product of the above conditions (A) and (B) is true, there is a risk that the system will erroneously determine that the maximum displacement has occurred if there is an abnormality in the power supply to the reaction force motor 22.

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

Figure 7 shows the processing steps involved in acquiring steering-side N-point learning data 54a. The series of processes shown in Figure 7 are 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 Figure 7 for processes corresponding to those shown in Figure 6.

In the series of processes shown in FIG. 7, if the PU 72 makes a positive determination in the processing of S22, it determines whether this is the first cycle in the right turn mode (S50). If the PU 52 determines that this is the first cycle (S50: YES), it assigns the steering angle θh to the initial value θh0 (S52). If the PU 52 completes the processing of S52 or makes a negative determination in the processing of S50, it proceeds to the processing of S24. Upon completing the processing of S24, the PU 52 adds the cycle Tc to the counter T (S54). The cycle Tc is the execution cycle of the series of processes shown in FIG. 7. The counter T is a variable that measures the period during which the processes of S34 and S36 are executed in accordance with the processing of S24. The PU 52 then proceeds to the processing of S26.

If a negative determination is made in the process of S22, the PU 52 assigns the following value to the midpoint θhmd (S40a).
[Δ・{T-(certain time)}/Tc+θh0]-θLR/2
Here, "T - (fixed time)" can be considered to be the time during which the steering angle θh has changed. It is preferable that the "fixed time" here be a fixed time from the point in time when condition (B) is satisfied, rather than a fixed time as the duration during which conditions (A) to (C) are satisfied. Furthermore, "Δ/Tc" indicates the rate of change of the steering angle θh. Therefore, "Δ·{T - (fixed time)}/Tc" is the amount by which the steering angle θh has turned to the right. Furthermore, "Δ·{T - (fixed time)}/Tc + θh0" indicates the right upper limit value θhR. Furthermore, the value obtained by subtracting the mechanical end distance θLR from "Δ·{T - (fixed time)}/Tc + θh0" indicates the left upper limit value θhL. Therefore, referring to the processing of S40, the above equation can be interpreted as the midpoint θhmd.

When the PU 72 completes the process of S40a, the PU 72 proceeds to the process of S42.
<Correspondence>
The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problem" column is as follows. Below, the correspondence is shown for each number of the means for solving the problem described in the "Means for Solving the Problem" column. [1] The end contact process corresponds to the process of S34 and S36 when the processes of S22 to S24 are being executed. The end determination process corresponds to the process of S26. The maximum displacement variable acquisition process corresponds to the process of S30 in FIG. 6 and the process of S54 when a positive determination is made in the process of S26 in FIG. 7. The midpoint learning process corresponds to the processes of S40 and S40a. [2] The midpoint learning process corresponds to the process of S40. The integrated value corresponds to the steering angle θh. The "predetermined rotatable angle of the steering shaft" corresponds to the mechanical end interval θLR. [3] The initial value acquisition process corresponds to the process of S52. The value of the maximum displacement variable corresponds to the value of the counter T when a positive determination is made in the process of S26 in FIG. 7. The target steering angular velocity corresponds to "Δ/Tc." [4] This corresponds to the target steering angle θh* changing by a predetermined amount Δ per cycle Tc. [5] The midpoint control process corresponds to the processes of S34 and S36 when the process of S44 is being executed.

<Other embodiments>
This embodiment can be modified as follows: This embodiment and the following modifications can be combined with each other within the scope of technical compatibility.

"About end contact processing"
The end contact process is not limited to a process in which the target steering angular velocity is set to a constant value. For example, the target steering angular velocity may be reduced during the end contact process. This makes it possible to achieve a good compromise between reducing the impact when the right upper limit value is reached and quickly reaching the right upper limit value. Furthermore, the number of times the target steering angular velocity is changed during the end contact process does not necessarily have to be once, and may be two or more times.

- The condition for determining that PU 52 has reached the right upper limit is not limited to the condition that the logical product of the above conditions (A) to (C) remains true for a certain period of time. The condition for determining that PU 52 has reached the right upper limit may be, for example, that the above conditions (A) and (B) are true for a certain period of time. Also, for example, the condition for determining that PU 52 has reached the right upper limit may be that the above conditions (B) and (C) are true for a certain period of time. Furthermore, for example, if threshold value Ith is used as a value for determining whether integral term windup has occurred, the condition for determining that PU 52 has reached the right upper limit may be that the above conditions (A) and (C) are true.

- When PU 52 determines that the right upper limit value has been reached, it is not necessary to execute the process of substituting steering angle θh for target steering angle θh*. For example, when PU 52 determines that the right upper limit value has been reached, it may gradually decrease target steering angle θh* according to a predetermined amount Δ.

- The control variable of the feedback control in the end contact processing does not necessarily have to be the steering angle θh. For example, the control variable of the feedback control in the end contact processing may be the rate of change of the steering angle θh.

- The end contact process does not necessarily have to be a process of turning the steering shaft 14 to the right. For example, the end contact process may be a process of turning the steering shaft 14 to the left.

"About midpoint learning processing"
6 illustrates an example in which the PU 52 repeats the processes of S38 and S40 in the midpoint movement mode until a positive determination is made in the process of S42, but this is not limiting. For example, when executing the process of S30, the PU 52 may execute the processes of S38 and S40 only once and store the values thereof in the storage device 54.

- Figure 7 illustrates an example in which the PU 52 repeats the process of S40a in midpoint movement mode until a positive determination is made in the process of S42, but this is not limited to this. For example, when executing the process of S30, the PU 52 may execute the process of S40a only once and store the value in the storage device 54.

- In the processing of FIG. 6, the PU 52 may execute the following processing instead of the processing of S38 and S40. That is, the PU 52 may execute processing to substitute "θhR - θLR/2" for the midpoint θhmd.

- The midpoint learning process does not necessarily have to be a process of learning the midpoint of the steering angle θh obtained by integrating the rotation angle θa. For example, if a dedicated sensor is provided to detect the rotation angle of the steering shaft 14, the process may instead learn that midpoint.

"About steering control devices"
The reaction force control device 50 and the steering control device 60 may be integrally formed.
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 through 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 according to a program, and a program storage device, such as a memory device, that stores the program. (b) A processing circuit that includes a processing device and program storage device that executes part of the above processing according to 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.

"Device for restricting rotation of 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 intermediate stopper that rotates with the end stopper 100 does not have to be provided.

DESCRIPTION OF SYMBOLS 10... Steering device 12... Steering wheel 14... Steering shaft 16... Reduction mechanism 20... Reaction force actuator 22... Reaction force motor 24... Reaction force inverter 26... Reaction force reduction mechanism 30... Steering actuator 32... Rack shaft 34... Steering wheel 42... Steering motor 44... Steering inverter 46... Steering transmission mechanism 48... Conversion mechanism 50... Reaction force control device

Claims (5)

A steering control device in which a reaction motor that applies a reaction force to a steering shaft when power transmission between steered wheels and a steering shaft is interrupted,
configured to execute end contact processing, end determination processing, maximum displacement variable acquisition processing, and midpoint learning processing;
the end contact process is a process of displacing the steering shaft to the maximum extent toward either the right-turning side or the left-turning side by operating the reaction motor,
the end determination process is a process for determining whether the steering shaft has been displaced to the maximum extent,
the maximum displacement variable acquisition process is a process of acquiring a value of a maximum displacement variable,
the maximum displacement variable is a variable obtained based on the determination that the maximum displacement has occurred in the end determination process,
A steering control device, wherein the midpoint learning process is a process for learning the midpoint of the rotation angle of the steering shaft based on the value of the maximum displacement variable. the value of the maximum displacement variable is an integrated value of the rotation angle of the reaction motor when it is determined by the end determination process that the maximum displacement has occurred,
2. The steering control device according to claim 1, wherein the midpoint learning process is a process for learning the midpoint based on a predetermined rotatable angle of the steering shaft and the integrated value as an input variable. configured to execute an initial value acquisition process;
the end contact process includes a process of controlling a rotation speed of the reaction motor to a target rotation speed,
the maximum displacement variable is the elapsed time until it is determined that the maximum displacement has occurred by the end contact process,
the initial value acquisition process is a process of acquiring an integrated value of the rotation angle of the reaction force motor at the start of measuring the elapsed time,
2. The steering control device according to claim 1, wherein the midpoint learning process is a process for learning the midpoint based on the value of the maximum displacement variable as an input variable and the integrated value at the start. A steering control device as described in claim 3, wherein the target rotational speed is a constant value. configured to perform a midpoint control process;
2. The steering control device according to claim 1, wherein the midpoint control process is a process for displacing the steering shaft from the state in which the steering shaft has been displaced to the maximum extent in either one of the directions by the end contact process to a learned midpoint position without displacing the steering shaft to the other of the right-turning side and the left-turning side to the maximum extent.