Steering control device, steering control system, and steering control method

Abstract

Provided is a steering control device (70) in which a steering wheel is a control target and in which a motor that steers the steering wheel is an operation target. The steering control device carries out a right turn operation process, a left turn operation process, and a midpoint calculation process. The right turn operation process is for operating the motor to displace the steering wheel, at a right turn speed, to the right turn side to the maximum degree. The left turn operation process is for operating the motor to displace the steering wheel, at a left turn speed, to the left turn side to the maximum degree. The midpoint calculation process is for calculating the midpoint of the maximum value of the steering angle of the steering wheel on the right turn side in the right turn operation process and the maximum value of the steering angle on the left turn side in the left turn operation process. The right turn operation process includes a process for changing the right turn speed partway through the right turn operation process.

Description

Steering control device, steering control system, and steering control method

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

[0002] Japanese Patent Application Laid-Open No. 2006-101094 describes a vehicle steering system that calculates the center position of a steering wheel. This system controls a reaction motor to steer the steering wheel to the right, thereby obtaining a maximum right-side steering angle. This system also controls a reaction motor to steer the steering wheel to the left, thereby obtaining a maximum left-side steering angle. This system then determines the center point between the maximum right-side steering angle and the maximum left-side steering angle as the neutral position of the steering wheel.

[0003] JP 2023-22874 A

[0004] There is a demand for reducing the time required for the process of calculating the midpoint.

[0005] One aspect of the present disclosure provides a steering control device. In the steering control device, steered wheels are controlled and a motor that steers the steered wheels is operated. The steering control device is configured to execute a right turn operation process, a left turn operation process, and a midpoint calculation process. The right turn operation process is a process for maximally displacing the steered wheels to the right at a right turning speed by operating the motor. The left turn operation process is a process for maximally displacing the steered wheels to the left at a left turning speed by operating the motor. The midpoint calculation process is a process for calculating a midpoint between a maximum value of the turning angle of the steered wheels on the right turning side in the right turn operation process and a maximum value of the turning angle on the left turning side in the left turn operation process. The right turn operation process includes a process for changing the right turning speed during the right turn operation process. The left turn operation process includes a process for changing the left turning speed during the left turn operation process.

[0006] Another aspect of the present disclosure provides a steering control method. In the steering control method, steered wheels are controlled and a motor that steers the steered wheels is operated. The steering control method includes steps of executing a right turn operation process, a left turn operation process, and a midpoint calculation process. The right turn operation process is a process of displacing the steered wheels to the right side at a right turning speed by operating the motor. The left turn operation process is a process of displacing the steered wheels to the left side at a left turning speed by operating the motor. The midpoint calculation process is a process of calculating a midpoint between a maximum value of the turning angle of the steered wheels on the right turning side in the right turn operation process and a maximum value of the turning angle on the left turning side in the left turn operation process. The right turn operation process includes a process of changing the right turning speed during the right turn operation process. The left turn operation process includes a process of changing the left turning speed during the left turn operation process.

[0007] Fig. 1 is a block diagram showing a steering system according to one embodiment. Fig. 2 is a flowchart showing the procedure of processing executed by the steering control device shown in Fig. 1. Fig. 3 is a flowchart showing the procedure of processing executed by the steering control device shown in Fig. 1. Fig. 4 is a block diagram showing a manufacturing process of the steering system of Fig. 1. Fig. 5 is a flowchart showing the procedure of processing executed by the steering control device shown in Fig. 4. Fig. 6 is a flowchart showing the procedure of processing executed by the steering control device shown in Fig. 4. Fig. 7 is a diagram showing an example of control in the manufacturing process shown in Fig. 4.

[0008] An embodiment will be described below with reference to the drawings. "Configuration of Steering System" Fig. 1 shows the configuration of a vehicle steering system 10. Steering system 10 includes a steering device 20, a turning device 30, a reaction force control device 60, and a turning control device 70.

[0009] The steering device 20 includes a steering wheel 12 and a steering shaft 14 mechanically connected to the steering wheel 12. A reaction motor 16 is mechanically connected to the steering shaft 14. The reaction motor 16 is used to apply a reaction force that resists the operation of the steering wheel 12 by the driver. The output voltage of an inverter 18 is applied to the terminals of the reaction motor 16.

[0010] The steering device 30 includes a rack shaft 32 and a pinion shaft 34. Rack teeth 32a are formed on the rack shaft 32. Pinion teeth 34a are formed on the pinion shaft 34. The rack teeth 32a and the pinion teeth 34a are engaged with each other to form a rack and pinion mechanism 36.

[0011] Steering device 30 includes steering actuator ACT. Steering actuator ACT includes steering motor 40, inverter 42, transmission mechanism 44, and conversion mechanism 46. Transmission mechanism 44 transmits the rotation of steering motor 40 to conversion mechanism 46, for example, via a belt. Conversion mechanism 46 includes, as an example, a ball screw mechanism. Conversion mechanism 46 converts the rotational displacement from transmission mechanism 44 into axial displacement of rack shaft 32. Transmission mechanism 44 and conversion mechanism 46 are conversion devices that convert the rotational power of steering motor 40 into axial displacement power of rack shaft 32.

[0012] The steerable wheels 50 are steered by the axial displacement of the rack shaft 32. The range of axial displacement of the rack shaft 32 is determined by the rack housing 48. In other words, the maximum value of the steering angle of the steerable wheels 50 on the right-turning side and the maximum value on the left-turning side are determined by the position at which the displacement of the rack shaft 32 is prevented by the rack housing 48.

[0013] The reaction force control device 60 includes a PU 62 and a storage device 64. The control object of the reaction force control device 60 is the steering device 20, and the operation object is the reaction force motor 16. The reaction force control device 60 controls the control amount of the control object by the PU 62 executing a program stored in the storage device 64.

[0014] Steering control device 70 includes PU 72 and storage device 74. The control object of steering control device 70 is steered wheels 50, and the operation object is steering actuator ACT. Steering control device 70 controls the control amount of the control object by PU 72 executing a program stored in storage device 74. To control the control amount, steering control device 70 references the rotation angle of steering motor 40 detected by rotation angle sensor 82. To control the control amount, steering control device 70 references absolute angle θa detected by absolute angle sensor 84. Absolute angle θa is the rotation angle of pinion shaft 34. Absolute angle θa is a variable that has a one-to-one correspondence with the steering angle. For example, absolute angle θa has a positive value in the case of a right-turning side, and a negative value in the case of a left-turning side. For example, if the maximum value of the steering angle on the right-turning side is greater than one rotation of pinion shaft 34, absolute angle θa can be an angle exceeding 360°. The steering control device 70 refers to the currents iut, ivt, and iwt that flow through the steering motor 40. Note that the currents iut, ivt, and iwt may be detected as the amount of voltage drop across a shunt resistor provided in each leg of the inverter 42.

[0015] Reaction force control device 60 and steering control device 70 are capable of communicating with each other. "Processing of steering control device" Figure 2 shows the procedure of processing that is executed when steering control device 70 is started up as a trigger. The processing shown in Figure 2 is realized by PU 72 repeatedly executing a program stored in storage device 74, for example, at a predetermined interval. Note that below, the step number of each processing step is represented by a number preceded by "S".

[0016] In the series of processes shown in FIG. 2 , the PU 72 first determines whether the power supply of the steering control device 70 has been switched from off to on (S10). If the PU 72 determines that the power supply has been switched (S10: YES), the PU 72 determines whether correction data 74a is stored in the storage device 74 (S12). If the PU 72 determines that correction data 74a is stored (S12: YES), the PU 72 sets the operation mode to the normal control mode (S14). The normal control mode is a mode in which normal control is performed in which the steering angle is the control variable. On the other hand, if the PU 72 determines that correction data 74a is not stored (S12: NO), the PU 72 sets the operation mode to the inspection mode (S16). The inspection mode is a mode in which processing such as acquiring the correction data 74a is performed.

[0017] PU 72 temporarily terminates the series of processes shown in Figure 2 when the processes of S14 and S16 are completed or when a negative determination is made in the process of S10. Figure 3 shows the procedure of the processes executed by steering control device 70. The processes shown in Figure 3 are realized by PU 72 repeatedly executing a program stored in storage device 74, for example at a predetermined interval, in the normal control mode.

[0018] In the series of processes shown in Fig. 3, the PU 72 first determines whether the processing mode in the normal control mode is the initial check mode (S20). The initial check mode is a mode in which predetermined processing is executed when the steering control device 70 is started. If the PU 72 determines that the processing mode is the initial check mode (S20: YES), the PU 72 determines whether a consistency check of information related to the steering angle acquired by the steering control device 70 has not been completed (S22). The consistency check is part of the predetermined processing. If the PU 72 determines that the consistency check has not been completed (S22: YES), the PU 72 acquires the latest absolute angle θa detected by the absolute angle sensor 84 (S24).

[0019] The PU 72 assigns the value obtained by adding the correction amount Δa to the acquired absolute angle θa to the absolute angle θa (S26). The correction amount Δa is a value indicated by the correction data 74a stored in the storage device 74. Next, the PU 72 acquires the steering equivalent angle θp (S28). The steering equivalent angle θp is a variable having a one-to-one correspondence with the steering angle of the steered wheels 50. The steering equivalent angle θp is, for example, the rotation angle of the pinion shaft 34. The steering equivalent angle θp is calculated by the PU 72 based on a process of integrating the rotation angle θt. For example, the steering equivalent angle θp has a positive value when turning to the right and a negative value when turning to the left. In this embodiment, the resolution of the steering equivalent angle θp is higher than the resolution of the absolute angle θa. In other words, the steering equivalent angle θp can express a smaller steering angle than the absolute angle θa.

[0020] The PU 72 determines whether the absolute value of the difference between the steering equivalent angle θp and the absolute angle θa is greater than a threshold value Δth (S30). The processing of S30 is a process for evaluating the reliability of the steering equivalent angle θp used for controlling the steering angle. If the PU 72 determines that the absolute value of the difference is greater than the threshold value Δth (S30: YES), it determines that there is an abnormality in the steering equivalent angle θp (S32). On the other hand, if the PU 72 determines that the absolute value of the difference is equal to or less than the threshold value Δth (S30: NO), it determines that the steering equivalent angle θp is normal (S34).

[0021] The PU 72 temporarily terminates the series of processes shown in FIG. 3 when it completes the processes of S32 and S34 or when a negative determination is made in the processes of S20 and S22. If the above processes determine that an abnormality exists, the PU 72 may notify the driver of the abnormality by operating the user interface 78 shown in FIG. 1. On the other hand, if no abnormality is determined in predetermined processes including the above processes, the PU 72 executes normal control in which the steering angle is the control variable. That is, the initial check mode is a mode for determining whether or not to transition to a processing mode in which normal control in which the steering angle is the control variable is executed. In the processing mode in which normal control in which the steering angle is the control variable is executed, the control variable is the steering equivalent angle θp.

[0022] As described above, in the initial check mode, the absolute angle θa corrected by the correction amount Δa is referenced. Therefore, the processing mode for executing normal control using the steering angle as the controlled variable is a process that uses the steering equivalent angle θp, the reliability of which is guaranteed by the absolute angle θa corrected by the correction amount Δa. In other words, the correction amount Δa is referenced by PU 72 to execute normal control using the steering angle as the controlled variable.

[0023] "Acquisition of Correction Data 74a" The correction data 74a is stored in the storage device 74 before the steering device 30 is mounted on the vehicle.

[0024] Figure 4 shows the hardware configuration when correction data 74a is acquired. As shown in Figure 3, steering control device 70 is connected to facility-side terminal 90. Facility-side terminal 90 comprises PU 92 and storage device 94. Facility-side terminal 90 causes PU 92 to execute a program stored in storage device 94, thereby causing steering control device 70 to execute processing to acquire correction data 74a.

[0025] The procedure for the process for acquiring the correction data 74a is shown in Fig. 5. The process shown in Fig. 5 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at predetermined intervals.

[0026] In the series of processes shown in FIG. 5 , the PU 72 first determines whether the operation mode is the inspection mode (S40). If the PU 72 determines that the operation mode is the inspection mode (S40: YES), it determines whether the end contact process is being executed (S42). If the PU 72 determines that the end contact process is not being executed (S42: NO), it determines whether an end contact command has been input from the facility-side terminal 90 to the steering control device 70 (S44). If the PU 72 determines that a command has been input (S44: YES), it receives data indicating the guard values ​​Δ1 to Δ3 output from the facility-side terminal 90 (S46). The PU 72 also receives the change angles θp1 and θp2 output from the facility-side terminal 90 (S48). The PU 72 then starts the end contact process (S50).

[0027] Next, PU 72 acquires the steering equivalent angle θp (S52). Then, PU 72 calculates a target steering equivalent angle θp*, which is a target value of the steering equivalent angle θp (S54). Next, PU 72 calculates a target torque Tt* corresponding to the operation amount by feedback control, in which the steering equivalent angle θp is the control amount and the target steering equivalent angle θp* is the target value of the control amount (S56). Target torque Tt* is the torque of steering motor 40.

[0028] Then, PU 72 outputs to inverter 42 an operation signal MSt for inverter 42 to bring the torque of steering motor 40 closer to target torque Tt* (S58). On the other hand, if PU 72 determines that end contact processing is being executed (S42: YES), it determines whether end contact processing has been completed (S60). If PU 72 determines that end contact processing has not yet been completed (S60: NO), it proceeds to processing of S52.

[0029] On the other hand, if the PU 72 determines that the end contact process has been completed (S60: YES), if a negative determination is made in the processes of S40 and S44, or if the process of S58 is completed, the PU 72 temporarily terminates the series of processes shown in FIG. 5.

[0030] Fig. 6 shows details of the processing of S54. In the series of processing shown in Fig. 6, the PU 72 determines whether the control mode of the steered wheels 50 in the end contact processing is the right turn mode (S70). The right turn mode is a mode in which processing is executed to steer the steered wheels 50 to the right turn side. As an example, the PU 72 sets the right turn mode at the start of the processing of S70.

[0031] When the PU 72 determines that the vehicle is in the right turn mode (S70: YES), it determines whether the target steering equivalent angle θp* is equal to or greater than the change angle θp1 (S72). When the PU 72 determines that the target steering equivalent angle θp* is less than the change angle θp1 (S72: NO), it assigns a guard value Δ1 to the change amount Δ (S74). The change amount Δ determines the amount of change in the target steering equivalent angle θp* per predetermined time. In other words, the change amount Δ determines the rate of change of the target steering equivalent angle θp*. On the other hand, when the PU 72 determines that the target steering equivalent angle θp* is equal to or greater than the change angle θp1 (S72: YES), it assigns a guard value Δ2 to the change amount Δ (S76). The guard values ​​Δ1 and Δ2 are set to positive values, and the guard value Δ1 is set to a value greater than the guard value Δ2.

[0032] When the processing of S74 and S76 is completed, the PU 72 assigns a value obtained by adding the amount of change Δ to the target steering equivalent angle θp* to the target steering equivalent angle θp* (S78).The PU 72 then determines whether the logical product of the following conditions (A) and (B) remains true for a certain period of time (S80).

[0033] Condition (A) is a condition that the previous value "θp(n-1)" of steering equivalent angle θp and the current value "θp(n)" match. Condition (B) is a condition that the absolute value of q-axis current iqt flowing through steering motor 40 is equal to or greater than threshold value Ith. Threshold value Ith is set to a value greater than the expected absolute value of q-axis current iqt when steered wheels 50 are turned when the steering angle is in an intermediate region between the upper limit value on the right-turning side and the upper limit value on the left-turning side.

[0034] The above conditions (A) and (B) are conditions for determining that the steering angle has reached the upper limit value on the right-turn side. If the PU 72 determines that the logical product of conditions (A) and (B) remains true for a certain period of time (S80: YES), the PU 72 assigns the current value "θp(n)" of the steering equivalent angle θp to the target steering equivalent angle θp* (S82). The PU 72 then determines whether the control mode is the right-turn mode (S84). If the PU 72 determines that the control mode is the right-turn mode (S84: YES), the PU 72 assigns the current value "θp(n)" to the right-side upper limit value θpR and sets the control mode to the left-turn mode (S86).

[0035] On the other hand, if the PU 72 determines that the control mode is not the right turn mode (S70: NO), it determines whether or not the control mode is the left turn mode (S88). If the PU 72 determines that the control mode is the left turn mode (S88: YES), it determines whether or not the target steering equivalent angle θp* is equal to or less than the change angle θp2 (S90). If the PU 72 determines that the target steering equivalent angle θp* is greater than the change angle θp2 (S90: NO), it assigns "(-1)·Δ1" to the change amount Δ (S92). On the other hand, if the PU 72 determines that the target steering equivalent angle θp* is equal to or less than the change angle θp2 (S90: YES), it assigns "(-1)·Δ2" to the change amount Δ (S94).

[0036] The PU 72 also proceeds to the process of S78 when the processes of S92 and S94 are completed. The process of S80, which is executed upon completion of the processes of S92 and S94, is a process for determining whether the steering angle has reached the upper limit value on the left turning side.

[0037] Thereafter, if the determination in S84 is negative, the PU 72 assigns the current value "θp(n)" to the left upper limit value θpL and sets the control mode to the midpoint movement mode (S96).Then, the PU 72 assigns "½" of the sum of the right upper limit value θpR and the left upper limit value θpL to the midpoint θpmd (S98).

[0038] Thereafter, the PU 72 determines whether the steering equivalent angle θp coincides with the midpoint θpmd by making a negative determination in the processing of S88 (S100). When the PU 72 determines that the steering equivalent angle θp does not coincide with the midpoint θpmd (S100: NO), it assigns a guard value Δ3 to the change amount Δ (S102). The guard value Δ3 is a positive value and is set to a value greater than the guard value Δ2. The guard value Δ3 may be equal to the guard value Δ1. Then, the PU 72 assigns a value obtained by adding the change amount Δ to the target steering equivalent angle θp* to the target steering equivalent angle θp* (S104).

[0039] On the other hand, if the PU 72 determines that the steering equivalent angle θp coincides with the midpoint θpmd (S100: YES), it acquires the latest absolute angle θa detected by the absolute angle sensor 84 (S106). Next, the PU 72 determines whether the absolute value of the absolute angle θa is equal to or less than the threshold value θath (S108). The process of S108 is a process for determining whether the absolute angle θa has been acquired normally. That is, if the process of S100 returns a positive determination, it is considered that the absolute angle θa is close to zero. Therefore, if the absolute angle θa deviates significantly from zero, it is considered that some kind of abnormality exists.

[0040] When the PU 72 determines that the absolute value is equal to or smaller than the threshold value θath (YES in S108), it substitutes the absolute angle θa for the correction amount Δa and then stores the correction amount Δa in the storage device 74 (S110). As a result, the storage device 74 transitions from a state in which the correction data 74a, which is data indicating the correction amount Δa, is not stored to a state in which the correction data 74a is stored.

[0041] The PU 72 then completes the end contact process (S112). Note that the PU 72 temporarily ends the series of processes shown in FIG. 6 when it completes the processes of S86, S98, S104, and S112, or when it makes a negative determination in the processes of S80 and S108.

[0042] <Actions and Effects of the Present Embodiment> Figure 7 illustrates the end contact processing. As shown in Figure 7, when an end contact command is input from facility-side terminal 90 to steering control device 70, from time t1 onwards, PU 72 increases target steering equivalent angle θp* at a rate defined by guard value Δ1. As a result, steering equivalent angle θp, which indicates the steering angle of steered wheels 50, is controlled to follow target steering equivalent angle θp*. At time t2, when target steering equivalent angle θp* reaches change angle θp1, PU 72 changes the rate of change of target steering equivalent angle θp* to a rate defined by guard value Δ2. Thereafter, when target steering equivalent angle θp* reaches right upper limit value θpR at time t3, steering equivalent angle θp no longer increases. Therefore, at time t4, PU 72 reduces target steering equivalent angle θp* to steering equivalent angle θp.

[0043] The PU 72 then decreases the target steering equivalent angle θp* at a speed defined by the guard value Δ1. When the target steering equivalent angle θp* reaches the change angle θp2 at time t5, the PU 72 changes the rate of decrease of the target steering equivalent angle θp* to a speed defined by the guard value Δ2. When the steering equivalent angle θp reaches the left upper limit value θpL at time t6, the steering equivalent angle θp stops changing. Therefore, at time t7, the PU 72 increases the target steering equivalent angle θp* to the steering equivalent angle θp. Thereafter, the PU 72 increases the target steering equivalent angle θp* at a speed defined by the guard value Δ3. When the steering equivalent angle θp reaches the midpoint θpmd, the PU 72 acquires the absolute angle θa. When the absolute value of the absolute angle θa is equal to or less than the threshold value θath, the PU 72 stores the absolute angle θa as the correction amount Δa in the storage device 74.

[0044] In this way, PU 72 changes the steering angular velocity midway while causing the steering equivalent angle to reach the right upper limit value θpR and the left upper limit value θpL. This makes it possible to advantageously achieve both a reduction in the time required for processing to obtain the correction amount Δa and suppression of impact on the steering device 30. That is, if PU 72 changes the target steering equivalent angle θp* at a speed defined by guard value Δ1, a large impact occurs when the steering equivalent angle θp reaches the right upper limit value θpR and the left upper limit value θpL. In contrast, if PU 72 changes the target steering equivalent angle θp* at a speed defined by guard value Δ2, the impact when the steering equivalent angle θp reaches the right upper limit value θpR and the left upper limit value θpL can be mitigated. However, in this case, the time required for processing to obtain the correction amount Δa increases.

[0045] The above embodiment also provides the following advantages and benefits: (1) The guard value Δ3 is set to a value greater than the guard value Δ2. This reduces the time required to reach the midpoint θpmd compared to when the guard value Δ2 is used in the midpoint movement mode.

[0046] (2) In this embodiment, a system is employed in which guard values ​​Δ1 to Δ3 are input to steering control device 70 from facility-side terminal 90. This makes it possible to flexibly set the right turning speed and the like to appropriate values ​​in accordance with requirements such as the schedule of the manufacturing process of steering device 30.

[0047] (3) In this embodiment, a system is employed in which change angles θp1, θp2 are input to steering control device 70 from facility-side terminal 90. This makes it possible to flexibly set the required time for right turn mode, etc., to an appropriate value in accordance with requirements such as the schedule for the manufacturing process of steering device 30.

[0048] (4) In this embodiment, the steering equivalent angle θp, which is determined by integrating the rotation angle θt of steering motor 40, is used as the control variable for feedback control in the midpoint movement mode. The steering equivalent angle θp has a higher resolution than the absolute angle θa. Therefore, the steering angle of steered wheels 50 can be controlled to the midpoint with high precision.

[0049] (5) On the condition that the absolute value of the absolute angle θa when the steering equivalent angle θp reaches the midpoint θpmd is equal to or less than the threshold value θath, the PU 72 stores the absolute angle θa as the correction data 74a in the storage device 74. This prevents the absolute angle θa from being stored when the steering angle of the steered wheels 50 is not at the midpoint due to some abnormality.

[0050] <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.

[0051] Regarding the Right Turn Operation Processing: In the right turn operation processing, the number of times the right turn speed is changed does not necessarily have to be once, but may be two or more times.

[0052] The condition for determining that the PU 72 has reached the right upper limit value θpR is not limited to the condition that the logical product of the above conditions (A) and (B) remains true for a certain period of time. The condition for determining that the PU 72 has reached the right upper limit value θpR may be, for example, the condition that the above condition (A) remains true for a certain period of time. Furthermore, the condition for determining that the PU 72 has reached the right upper limit value θpR may be, for example, the condition that the above condition (B) remains true for a certain period of time.

[0053] When the PU 72 determines that the right upper limit value θpR has been reached, it is not necessary to execute the process of substituting the steering equivalent angle θp for the target steering equivalent angle θp*. For example, when the PU 72 determines that the right upper limit value θpR has been reached, the PU 72 may gradually decrease the target steering equivalent angle θp* in accordance with the guard value Δ1.

[0054] The control amount of the feedback control in the right turn operation processing does not necessarily have to be the steering equivalent angle θp. For example, the control amount of the feedback control in the right turn operation processing may be the rate of change of the steering equivalent angle θp. Also, for example, the control amount of the feedback control in the right turn operation processing may be the absolute angle θa.

[0055] Regarding Left Turn Operation Processing In the left turn operation processing, the number of times the left turn speed is changed does not necessarily have to be once, but may be two or more times.

[0056] The condition for determining that the PU 72 has reached the left upper limit value θpL is not limited to the condition that the logical product of the above conditions (A) and (B) remains true for a certain period of time. The condition for determining that the PU 72 has reached the left upper limit value θpL may be, for example, the condition that the above condition (A) remains true for a certain period of time. Furthermore, the condition for determining that the PU 72 has reached the left upper limit value θpL may be, for example, the condition that the above condition (B) remains true for a certain period of time.

[0057] It is not essential that the PU 72 executes the process of substituting the steering equivalent angle θp for the target steering equivalent angle θp* when it determines that the left upper limit value θpL has been reached. For example, when it determines that the left upper limit value θpL has been reached, the PU 72 may gradually decrease the target steering equivalent angle θp* in accordance with the guard value Δ1.

[0058] The control amount of the feedback control in the left turn operation processing does not necessarily have to be the steering equivalent angle θp. For example, the control amount of the feedback control in the left turn operation processing may be the rate of change of the steering equivalent angle θp. Also, for example, the control amount of the feedback control in the left turn operation processing may be the absolute angle θa.

[0059] "Midpoint Calculation Process" The process of S108 is not essential to the midpoint calculation process. For example, if the control variable of the feedback control in the right turn operation process and the left turn operation process is the absolute angle θa, the PU 72 may determine the right upper limit value θpR and the left upper limit value θpL as the value of the absolute angle θa. In this case, the PU 72 may store the midpoint θpmd, which is "½" of the sum of the right upper limit value θpR and the left upper limit value θpL, in the storage device 74 as the correction data 74a.

[0060] "Regarding the end contact processing" It is not essential that the end contact processing be performed before the steering device 30 is mounted on the vehicle. For example, the end contact processing may be performed immediately after the steering device 30 is mounted on the vehicle. In that case, for example, if the steering control device 70 is mounted on the vehicle and is capable of communicating with the facility-side terminal 90, the end contact processing can be performed in the same manner as in the above embodiment.

[0061] Regarding the absolute angle sensor: The absolute angle sensor, which detects a quantity that corresponds one-to-one to the steering angle of the steered wheels 50, is not limited to the sensor exemplified in the above embodiment. For example, it may be a linear stroke sensor that directly detects the amount of displacement of the rack shaft 32 in the axial direction.

[0062] It is not essential that the resolution of the absolute angle θa be lower than the resolution of the steering equivalent angle θp. "Regarding the Reference Processing" The reference processing is not limited to the processing shown in FIG. 3. For example, the PU 72 may substitute "θa + Δa" for the steering equivalent angle θp every time the power is switched from the off state to the on state. As a result, the initial value of the steering equivalent angle θp at the time the power is switched from the off state to the on state is set to "θa + Δa".

[0063] Regarding the steering control device: It is not essential that the guard values ​​Δ1, Δ2, Δ3 are input to the steering control device 70 from the facility-side terminal 90. For example, the guard values ​​Δ1, Δ2, Δ3 may be stored in advance in the storage device 74 of the steering control device 70.

[0064] It is not essential that the change angles θp1, θp2 are input to the steering control device 70 from the facility-side terminal 90. For example, the change angles θp1, θp2 may be stored in advance in the storage device 74 of the steering control device 70.

[0065] 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 by hardware processing. In other words, the steering control device may include a processing circuit having any of the following configurations (a) to (c): (a) A processing circuit that includes a processing device that executes all of the above processing in accordance with a program, and a program storage device, such as a memory device, that stores the program. (b) A processing circuit that includes a processing device and program storage device that executes part of the above processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing. (c) A processing circuit that includes a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices that include a processing device and a program storage device. Also, there may be multiple dedicated hardware circuits.

[0066] "Regarding the steering control system" When the facility-side terminal 90 does not input the guard values ​​Δ1, Δ2, Δ3 and the change angles θp1, θp2 to the steering control device 70, the facility-side terminal 90 may only have the function of outputting a command to the steering control device 70 to execute the end contact processing.

[0067] Regarding the steering control method: It is not essential that all of the processes illustrated in Figures 2 to 6 be executed by the computer installed in steering control device 70. For example, some of the processes may be executed by the computer of facility-side terminal 90.

Claims

1. A steering control device in which steered wheels are the control object and a motor that steers the steered wheels is the operation object, configured to execute a right turning operation process, a left turning operation process, and a midpoint calculation process, wherein the right turning operation process is a process for maximally displacing the steered wheels to the right at a right turning speed by operating the motor, the left turning operation process is a process for maximally displacing the steered wheels to the left at a left turning speed by operating the motor, the midpoint calculation process is a process for calculating the midpoint between the maximum value of the turning angle of the steered wheels on the right turning side in the right turning operation process and the maximum value of the turning angle on the left turning side in the left turning operation process, the right turning operation process includes a process for changing the right turning speed in the middle of the right turning operation process, and the left turning operation process includes a process for changing the left turning speed in the middle of the left turning operation process.

2. A steering control device as described in claim 1, wherein the right turning speed before and after the change and the left turning speed before and after the change can be input from outside the steering control device, the right turning operation processing is processing that utilizes the input right turning speed, and the left turning operation processing is processing that utilizes the input left turning speed.

3. A steering control device as described in claim 1, wherein the value of a steering angle variable that changes the right turning speed in the right turning operation processing and the value of a steering angle variable that changes the left turning speed in the left turning operation processing can be input from outside the steering control device, the right turning operation processing is a process that utilizes the input value of the steering angle variable, the left turning operation processing is a process that utilizes the input value of the steering angle variable, and the steering angle variable is a variable that indicates the steering angle.

4. A steering control device as claimed in claim 1, comprising a storage device and configured to execute a steering equivalent angle calculation process, an absolute angle acquisition process, a midpoint movement process, a storage process, and a reference process, wherein the steering equivalent angle calculation process is a process of calculating a steering equivalent angle in response to a detection value of a rotation angle of the motor, the steering equivalent angle being a variable indicating the steering angle of the steered wheel, the absolute angle acquisition process is a process of acquiring an absolute angle detected by an absolute angle sensor, the absolute angle sensor being a sensor that detects an angle having one-to-one correspondence with the steering angle, the midpoint calculation process is a process in which the steering equivalent angle is an input and the midpoint is an output, the midpoint movement process is a process of operating the motor to control the steering equivalent angle to the midpoint, the storage process is a process of storing in the storage device the absolute angle acquired when the steering equivalent angle becomes the midpoint by the midpoint movement process, and the reference process is a process of referencing the absolute angle stored in the storage device for a process of controlling the steering angle after a steering actuator including the motor is mounted on a vehicle.

5. A steering control device as described in claim 4, wherein the storage process is a process for storing the absolute angle in the storage device on the condition that the absolute angle acquired when the steering equivalent angle becomes the midpoint by the midpoint movement process is within a predetermined range.

6. A steering control device according to claim 4, wherein the right turn operation process, the left turn operation process, the midpoint calculation process, and the storage process are processes executed before the steering actuator is mounted on the vehicle.

7. A steering control system comprising: a steering control device as described in claim 2; and an equipment side device capable of communicating with the steering control device, the equipment side device being configured to execute input processing, the input processing being processing for inputting the right turning speed before and after the change and the left turning speed before and after the change to the steering control device.

8. A steering control method in which steered wheels are the control object and a motor for steering the steered wheels is the operation object, the steering control method having steps of executing a right turning operation process, a left turning operation process, and a midpoint calculation process, wherein the right turning operation process is a process for maximally displacing the steered wheels to the right at a right turning speed by operating the motor, the left turning operation process is a process for maximally displacing the steered wheels to the left at a left turning speed by operating the motor, the midpoint calculation process is a process for calculating the midpoint between the maximum value of the turning angle of the steered wheels on the right turning side in the right turning operation process and the maximum value of the turning angle on the left turning side in the left turning operation process, the right turning operation process includes a process for changing the right turning speed in the middle of the right turning operation process, and the left turning operation process includes a process for changing the left turning speed in the middle of the left turning operation process.

Images