Steering control device

Abstract

To provide a steering control device that is able to highly accurately grasp whether or not a turning motor approaches a turning angle at which the turning motor cannot turn a turning wheel, according to a condition at that time, such as a friction coefficient between the turning wheel and a road surface.SOLUTION: A PU calculates an assist amount Ta in accordance with a steering torque Th. The PU calculates an axial force F in accordance with a target turning equivalent angle θp*, a vehicle speed V, and a q-axis current iqt. The PU controls torque of a reaction motor so that a value obtained by subtracting the assist amount Ta from the axial force F becomes a force against the rotation of a steering wheel. When an absolute value of the q-axis current iqt is equal to or larger than a threshold value, the PU determines that a turning motor approaches a situation in which a turning angle cannot be further increased even if a steering angle θs is increased. Then, by increasing the magnitude of the axial force F, the PU prevents steering from being performed so as to increase the magnitude of the steering angle.SELECTED DRAWING: Figure 2

Description

Technical Field

[0001] The present invention relates to a steering control device.

Background Art

[0002] Patent Document 1 below describes a steering control device in a steer-by-wire system in which the power transmission between the steering shaft and the steered wheels is interrupted. This device limits the target steering angle before the steering angle cannot be further increased by the steering motor for steering the steered wheels.

Prior Art Document

Patent Document

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] Incidentally, the steering angle at which the steering motor cannot further increase the steering angle is determined by various factors such as the friction coefficient of the road surface. Therefore, in the case of the above device, there is a possibility that a limit is applied prematurely even though the steering angle can actually be increased by the steering motor.

Means for Solving the Problems

[0005] Hereinafter, means for solving the above problems and their effects will be described. 1. In a state where the steering wheel and the steering shaft are mechanically disconnected, a steering control device is configured to execute a steering process, a reaction force application process, an axial force variable acquisition process, and an increase process, wherein the steering process is a process of operating a steering motor to steer the steering wheel according to a steering angle, the steering angle being the rotation angle of the steering shaft, the reaction force application process is a process of operating a reaction force motor to apply a reaction force against the driver's rotation of the steering shaft, the axial force variable acquisition process is a process of acquiring a value of an axial force variable based on a detected value of a physical quantity, the axial force variable being a variable indicating a force applied to the steering wheel and preventing the steering wheel from being steered, and the increase process is a process of increasing the reaction force based on the value of the axial force variable as an input variable to prevent the steering angle from becoming an angle at which the steering motor cannot steer the steering wheel.

[0006] With the above configuration, by increasing the reaction force, it is possible to suppress the steering angle from becoming an angle at which the steering wheel cannot be steered. In particular, with the above configuration, it is possible to increase the reaction force while grasping whether the steering angle is approaching an angle at which the steering motor cannot steer the steering wheel based on the value of the axial force variable. Therefore, it is possible to accurately grasp whether the steering angle is approaching an angle at which the steering motor cannot steer the steering wheel according to the conditions at that time, such as the friction coefficient between the steering wheel and the road surface.

[0007] 2. The increase process includes a determination process, the determination process is a process of determining whether the steering angle is approaching an angle at which the steering motor cannot steer the steering wheel based on the value of the axial force variable as an input variable, and the increase process is a process of increasing the reaction force when it is determined that the angle is approaching. The steering control device according to 1 above.

[0008] With the above configuration, by providing a determination process, it is easy to manage whether the increase process is executed. 3. The steering control device according to 1 or 2 above, wherein the increase process is configured to be executed on the condition that the vehicle speed is equal to or lower than a predetermined speed.

[0009] When the vehicle speed is low, the torque of the steering motor required to steer the steered wheels tends to be greater than when the vehicle speed is high. Also, when restricting the change in the steering angle at high vehicle speeds, there is a concern that it may interfere with driving.

[0010] Therefore, in the above configuration, by performing the increase process on the condition that the vehicle speed is below a predetermined speed, it is possible to limit the steering while suppressing as much as possible the limitation of the steering, only when approaching the steering angle at which it becomes impossible to steer the steered wheels.

[0011] 4. The reaction force application process includes an assist amount setting process and an axial force setting process. The axial force setting process is a process of setting an axial force that is a force resisting the rotation operation of the steering shaft by the driver. The assist amount setting process is a process of setting an assist amount that is an amount for assisting the driver in rotating the steering shaft. The reaction force application process includes a process of determining the reaction force according to a value obtained by subtracting the assist amount from the axial force. The increase process is a process of increasing and correcting the axial force. The steering control device according to any one of 1 to 3 above.

[0012] In the above configuration, the reaction force can be increased by increasing and correcting the axial force. 5. The reaction force application process includes an assist amount setting process and an axial force setting process. The axial force setting process is a process of setting an axial force that is a force resisting the rotation operation of the steering shaft by the driver. The assist amount setting process is a process of setting an assist amount that is an amount for assisting the driver in rotating the steering shaft. The reaction force application process includes a process of determining the reaction force according to a value obtained by subtracting the assist amount from the axial force. The axial force setting process includes a process of superimposing a blocking torque that prevents the steering angle from becoming larger than that on the axial force when the magnitude of the steering angle is equal to or greater than a threshold value. The increase process includes a process of reducing the magnitude of the threshold value. The steering control device according to any one of 1 to 3 above.

[0013] In the above configuration, a limit can be set on the range within which the steering angle can be taken by control using the blocking torque. Moreover, an increase process can be realized by changing the threshold value. 6. The reaction force application process includes an assist amount setting process and an axial force setting process. The axial force setting process is a process of setting an axial force, which is a force resisting the rotation operation of the steering shaft by the driver. The assist amount setting process is a process of setting an assist amount, which is the amount of assisting the driver in rotating the steering shaft. The reaction force application process includes a process of determining the reaction force according to a value obtained by subtracting the assist amount from the axial force. The increase process is the steering control device according to any one of 1 to 3 above, which is a process of decreasing and correcting the assist amount.

[0014] In the above configuration, the reaction force can be increased by decreasing and correcting the assist amount. 7. The physical quantity is the current flowing through the steering motor in the steering control device according to any one of 1 to 6 above.

[0015] The current flowing through the steering motor is a variable indicating the force that hinders the steering of the steered wheels. Therefore, in the above configuration, the value of the axial force variable can be obtained using the detected value of the easily obtainable physical quantity.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Mode for Carrying Out the Invention

[0017] <First Embodiment> Hereinafter, the first embodiment will be described with reference to the drawings. 「Premise Configuration」 The steering device 10 of the vehicle shown in FIG. 1 is a steer-by-wire type device. The steering device 10 includes a steering wheel 12, a steering shaft 14, a reaction force actuator 20, and a steering actuator 30. The steering shaft 14 is connected to the steering wheel 12. The reaction force actuator 20 is an actuator that applies a force that resists the force with which the driver operates the steering wheel 12. The reaction force actuator 20 includes a reaction force motor 22, a reaction force inverter 24, and a reaction force reduction mechanism 26. The reaction force motor 22 applies a steering reaction force, which is a force that resists steering, to the steering wheel 12 via the steering shaft 14. The reaction force motor 22 is connected to the steering shaft 14 via the reaction force reduction mechanism 26. As an example, a three-phase synchronous motor is adopted for the reaction force motor 22. The reaction force reduction mechanism 26 is composed of, for example, a worm and wheel.

[0018] The steering actuator 30 is an actuator having a use for steering the steered wheels 34 according to the driver's steering intention indicated by the operation of the steering wheel 12 by the driver. The steering actuator 30 includes a rack shaft 32, a steering motor 42, a steering inverter 44, a steering transmission mechanism 46, and a conversion mechanism 48. As an example, a three-phase surface magnet synchronous motor (SPM) is adopted for the steering motor 42. The steering transmission mechanism 46 is composed of a belt transmission mechanism. The rotational power of the steering motor 42 is transmitted to the conversion mechanism 48 by the steering transmission mechanism 46. The conversion mechanism 48 converts the transmitted rotational power into displacement power in the axial direction of the rack shaft 32. The steered wheels 34 are steered by the displacement of the rack shaft 32 in the axial direction.

[0019] 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 a non-volatile memory that cannot be electrically rewritten. The storage device 54 may also be a non-volatile memory that can be electrically rewritten and a storage medium such as a disk medium.

[0020] The control targets of the steering control device 50 are the steering wheel 12 and the steered wheels 34. That is, the steering control device 50 controls the steering reaction force against the driver's steering, which is the control amount of the steering wheel 12 as the control target. Further, the steering control device 50 controls the steering angle, which is the control amount of the steered wheels 34 as the control target. The steering angle is the slip angle of the tire as the steered wheel 34.

[0021] The steering control device 50 refers to the steering torque Th detected by the torque sensor 60 for controlling the control amount. The steering torque Th is the torque applied to the steering shaft 14 by the driver through the operation of the steering wheel 12. The steering control device 50 refers to the rotation angle θa, which is the angle of the rotation shaft of the reaction motor 22, detected by the steering-side rotation angle sensor 62 for controlling the control amount. Further, the steering control device 50 refers to the currents ius, ivs, iws flowing through the reaction motor 22 for controlling the control amount. The currents ius, ivs, iws may be detected, for example, as the voltage drop amounts of shunt resistors provided in each leg of the reaction inverter 24. The steering control device 50 refers to the rotation angle θb, which is the angle of the rotation shaft of the steering motor 42, detected by the steered-side rotation angle sensor 64 for controlling the control amount. Further, the steering control device 50 refers to the currents iut, ivt, iwt flowing through the steering motor 42 for controlling the control amount. The currents iut, ivt, iwt may be detected, for example, as the voltage drop amounts of shunt resistors provided in each leg of the steering inverter 44. The steering control device 50 refers to the vehicle speed V detected by the vehicle speed sensor 66.

[0022] "Outline of Control" Fig. 2 shows the processes executed by the steering control device 50. The processes shown in Fig. 2 are realized by the PU 52 repeatedly executing, for example, at a predetermined cycle, the program stored in the storage device 54.

[0023] 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, for example, by counting the number of rotations of the reaction force motor 22 from the steering neutral position, which is the position of the steering wheel 12 when the vehicle is going straight. The steering angle calculation process M10 includes a process of calculating the steering angle θs by multiplying the converted integrated angle by a conversion coefficient based on the rotation speed ratio of the reaction force reduction mechanism 26.

[0024] The equivalent steering 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 the rack neutral position, which is the position of the rack shaft 32 when the vehicle is going straight. The equivalent steering angle calculation process M12 includes a process of calculating the equivalent steering angle θp corresponding to the steering angle of the steering wheel 34 by multiplying the converted integrated angle by a conversion coefficient according to the reduction ratio of the steering transmission mechanism 46 and the lead of the conversion mechanism 48. The equivalent steering angle θp is a quantity in a proportional relationship with the steering angle. Note that, as an example, the equivalent steering angle θp is positive when it is an angle on the right side of the rack neutral position and negative when it is an angle on the left side.

[0025] The target equivalent steering angle calculation process M18 is a process of calculating the target equivalent steering angle θp* based on the steering angle θs and the vehicle speed V as input variables. The assist amount setting process M20 is a process of calculating the assist amount Ta based on the steering torque Th and the vehicle speed V as input variables. The assist amount Ta is a quantity 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 increasing the force assisting the driver's steering.

[0026] The axial force setting process M22 is a process of setting the axial force F based on the vehicle speed V as an input variable, the q-axis current iqt of the steering motor 42, and the target steering equivalent angle θp*. The axial force F is a value that represents, by control, the force acting on the rack shaft 32 through the steering wheel 34. However, it is not necessary for the axial force F to be intended to accurately estimate the force acting on the rack shaft 32. The axial force F may be, for example, a virtual determination of the force acting on the rack shaft 32. The axial force F is converted into the torque applied to the steering shaft 14. That is, it is converted into the torque applied to the steering shaft 14 assuming a state where power transmission between the steering wheel 34 and the steering shaft 14 is possible. Here, the q-axis current iqt is calculated by the PU52 according to the rotation angle θb and the currents iut, ivt, iwt.

[0027] The subtraction process M24 is a process of substituting the value obtained by subtracting the axial force F from the assist amount Ta into the target reaction torque Ts. The target reaction torque Ts is the target value of the torque that the reaction motor 22 applies to the steering shaft 14. The target reaction torque Ts usually has the opposite sign to the assist amount Ta. The reaction force against the rotational power of the steering shaft 14 by the driver is an amount corresponding to the value obtained by subtracting the assist amount Ta from the axial force F.

[0028] The reaction force operation signal generation process M26 is a process of generating an operation signal MSs for the reaction force inverter 24 to control the torque of the reaction motor 22 so that the torque applied to the steering shaft 14 becomes the target reaction torque Ts. Specifically, the reaction force operation signal generation process M26 includes a process of converting the target reaction torque Ts into the target torque of the reaction motor 22. Further, the reaction force operation signal generation process M26 includes a process of calculating the operation signal MSs for the reaction force inverter 24 so as to bring the current flowing through the reaction motor 22 close to the current determined from the target reaction torque Ts by current feedback control. Note that the operation signal MSs is actually the operation signal for each of the six switching elements of the reaction force inverter 24.

[0029] The steering feedback process M30 is a process of substituting the operation amount of feedback control, where the equivalent steering angle θp is the control amount and the target equivalent steering angle θp* is the target value of the control amount, into the target steering torque Tt*. The target steering torque Tt* has a fixed ratio with the torque of the steering motor 42.

[0030] The steering operation signal generation process M32 is a process of generating an operation signal MSt for the steering inverter 44 to control the torque of the steering motor 42 so that the torque of the steering motor 42 becomes a value having a fixed ratio with the target steering torque Tt*. Specifically, the steering operation signal generation process M32 includes a process of converting the target steering torque Tt* into the target torque of the steering motor 42. Further, the steering operation signal generation process M32 includes a process of calculating the operation signal MSt for the steering inverter 44 so as to bring the current flowing through the steering motor 42 closer to the current determined from the target torque by current feedback control. Note that the operation signal MSt is actually the operation signal for each of the six switching elements of the steering inverter 44.

[0031] "Axial force setting process" Fig. 3 shows the details of the axial force setting process M22. The angle axial force setting process M40 is a process of calculating the angle axial force Fr based on the target steering equivalent angle θp* and the vehicle speed V as input variables. The angle axial force Fr is an estimated value of the axial force defined by an arbitrarily set vehicle model or the like. However, the angle axial force Fr is converted into the torque of the steering shaft 14. The angle axial force Fr is calculated as an axial force that does not reflect road surface information. Road surface information is information such as minute unevenness that does not affect the lateral behavior of the vehicle and steps that affect the lateral behavior of the vehicle. The angle axial force setting process M40 is, for example, a process of calculating the angle axial force Fr according to the target steering equivalent angle θp* under the condition that the absolute value of the angle axial force Fr when the absolute value of the target steering equivalent angle θp* is large is equal to or greater than the angle axial force Fr when the absolute value of the target steering equivalent angle θp* is small. Also, for example, the angle axial force setting process M40 is, for example, a process of changing the angle axial force Fr according to the vehicle speed V under the condition that the absolute value of the angle axial force Fr when the vehicle speed V is large is equal to or greater than the absolute value of the angle axial force Fr when the vehicle speed V is small.

[0032] In addition, in the description such as "changing B according to A while satisfying the condition that B when A is large is equal to or greater than B when A is small", the case where A is large and the case where A is small mean the relative magnitude relationship when the two are compared. For example, the case where "A is large" corresponds to the case where "A is the first value", and the case where "A is small" corresponds to the case where "A is the second value smaller than the first value". Also, the above description means that depending on the setting of the first value and the second value, B when A is the first value may be larger than B when A is the second value. Also, the above description means changing B according to A so that A when B is large is larger than A when B is small.

[0033] Specifically, the angle axial force setting process M40 is a process of performing map calculation on the angle axial force Fr in a state where the map data is stored in the storage device 54. The map data is data in which the target steering equivalent angle θp* and the vehicle speed V are input variables and the angle axial force Fr is an output variable.

[0034] Here, the map data is paired data consisting of discrete values of the input variable and the values of the output variable corresponding to each value of the input variable. Also, the map operation may be any process that sets the value of the output variable of the corresponding map data as the operation result when the value of the input variable matches any of the values of the input variable of the map data. Further, the map operation may be any process that sets, as the operation result, a value obtained by interpolating the values of a plurality of output variables included in the map data when the value of the input variable does not match any of the values of the input variable of the map data. Alternatively, the map operation may be any process that sets, as the operation result, the value of the output variable of the map data corresponding to the closest value among the values of a plurality of input variables included in the map data when the value of the input variable does not match any of the values of the input variable of the map data.

[0035] The current axial force setting process M42 is a process of calculating the current axial force Fi based on the q-axis current iqt of the steering motor 42 as the input variable. The current axial force Fi is an estimated value of the axial force actually acting on the rack shaft 32 that operates to steer the steering wheel 34, that is, the axial force actually transmitted to the rack shaft 32. However, the current axial force Fi is converted into the torque of the steering shaft 14. The current axial force Fi is calculated as the axial force reflecting the road surface information. For example, the current axial force setting process M42 may be a process of calculating the current axial force Fi on the assumption that the torque applied to the rack shaft 32 by the steering motor 42 and the torque corresponding to the force applied to the rack shaft 32 through the steering wheel 34 are balanced. The current axial force setting process M42 is a process of calculating the current axial force Fi according to 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.

[0036] Specifically, the current axial force setting process M42 is a process of performing a map operation on the current axial force Fi by the PU52 in a state where the map data is stored in advance in the storage device 54. The map data is data in which the q-axis current iqt is the input variable and the current axial force Fi is the output variable.

[0037] The distribution ratio calculation process M46 is a process of calculating the ratio D based on the vehicle speed V and the target steering equivalent angle θp* as input variables. The ratio D is the ratio of the current axial force Fi to the sum of the angular axial force Fr and the current axial force Fi. The ratio D has a value between 0 and 1. The distribution ratio calculation process M46 may be, for example, a process of performing a map operation on the ratio D by the PU52 with the map data stored in the storage device 54. Here, the map data is data in which the vehicle speed V and the target steering equivalent angle θp* are input variables and the ratio D is an output variable.

[0038] The second distribution ratio calculation process M48 is a process of calculating the second ratio "1 - D" by subtracting the ratio D from "1". The second ratio is the ratio of the angular axial force Fr to the sum of the angular axial force Fr and the current axial force Fi.

[0039] The first ratio multiplication process M50 is a process of multiplying the current axial force Fi by the ratio D. The second ratio multiplication process M52 is a process of multiplying the angular axial force Fr by the second ratio. The end stop torque setting process M60 is a process of setting the end stop 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 stop torque setting process M60 is a process of setting the magnitude of the end stop torque Fen to a value greater than zero when the absolute value of the steering angle θs is greater than or equal to the end threshold value θen. The end stop torque setting process M60 is a process of changing the end stop torque Fen according to the steering angle θs under the following conditions when the absolute value of the steering angle θs is greater than or equal to the end threshold value θen. This condition is that the absolute value of the end stop torque Fen when the absolute value of the steering angle θs is large is greater than or equal to the absolute value of the end stop torque Fen when the absolute value of the steering angle θs is small.

[0040] The addition process M62 is a process of substituting the value obtained by adding the output value of the first ratio multiplication process M50, the output value of the second ratio multiplication process M52, and the end stop torque Fen into the axial force F. That is, the axial force F is the sum of the weighted average processing value of the angular axial force Fr and the current axial force Fi and the end stop torque Fen.

[0041] "Steering Limit" When PU52 is near the output limit of the steering motor 42, it increases the force resisting the rotation of the steering shaft 14 by the driver to prevent steering that exceeds the output limit of the steering motor 42.

[0042] Figure 4 shows the procedure of the process for increasing the force resisting the rotation of the steering shaft 14 by the driver. The series of processes shown in Figure 4 is realized by PU52 repeatedly executing a program stored in the storage device 54, for example, at a predetermined cycle. Hereinafter, the step numbers of each process are represented by numbers preceded by "S".

[0043] In the series of processes shown in Figure 4, first, PU52 acquires the vehicle speed V and the q-axis current iqt (S10). Next, PU52 determines whether the flag FL is "1" (S12). The flag FL indicates that control for preventing steering that exceeds the output limit of the steering motor 42 is being executed when it is "1". The flag FL indicates that control for preventing steering that exceeds the output limit of the steering motor 42 is not being executed when it is "0". When PU52 determines that the flag FL is "0" (S12: NO), it determines whether the logical product of the following condition (A) and condition (B) is true (S14).

[0044] Condition (A): It is a condition that the vehicle speed V is equal to or less than a predetermined speed Vth. The predetermined speed Vth may be a value of 10 km / h or less. The predetermined speed Vth may be a value of 5 km / h or less. The predetermined speed Vth may be zero.

[0045] Condition (B): It is a condition that the magnitude of the q-axis current iqt is equal to or greater than a threshold value Ith. The threshold value Ith may be set according to, for example, the allowable maximum current of the steering inverter 44. When determining that the logical product is true (S14: YES), PU52 assigns "1" to flag FL (S16). Then, PU52 executes correction to increase the magnitude of axial force F (S18). That is, when the axial force F output by addition process M62 is positive, PU52 sets, as the input variable of subtraction process M24, a value obtained by correcting the axial force F to a larger value. Also, when the axial force F output by addition process M62 is negative, PU52 sets, as the input variable of subtraction process M24, a value obtained by correcting the axial force F to a smaller value.

[0046] When determining that flag FL is "1" (S12: YES), PU52 determines whether the logical product of the above conditions (A) and (B) is false (S20). When determining that the logical product is false (S20: YES), PU52 assigns "0" to flag FL (S22).

[0047] Note that when PU52 completes the processes of S18 and S22 and when making a negative determination in the process of S14, PU52 once terminates the series of processes shown in FIG. 4. "Operations and Effects of the Present Embodiment" PU52 calculates assist amount Ta according to steering torque Th. PU52 calculates axial force F according to target steering equivalent angle θp*, vehicle speed V, and q-axis current iqt. PU52 controls the torque of reaction motor 22 so that the value obtained by subtracting assist amount Ta from axial force F becomes the force resisting the rotation of steering wheel 12.

[0048] When determining that the above condition (B) is satisfied, PU52 determines that the situation is approaching where the steering angle cannot be further increased by steering motor 42 even if steering angle θs is increased. Then, by increasing the magnitude of axial force F, PU52 prevents steering that expands the magnitude of the steering angle. Thereby, it is possible to suppress steering that cannot be realized by steering motor 42.

[0049] According to the present embodiment described above, the operations and effects described below can be obtained. (1)PU52 includes the condition that the above condition (A) is satisfied in addition to the above condition (B) being satisfied as the execution condition for the process of increasing and correcting the magnitude of the axial force F. When the vehicle speed V is high, the force required to steer the steering wheel 34 tends to be smaller than the force required to steer the steering wheel 34 when the vehicle speed V is low. Therefore, by including the above condition (A) in the above execution condition, it is possible to more accurately grasp that the situation where the steering angle cannot be further increased by the steering motor 42 even if the steering angle θs is expanded is approaching. In addition, by not increasing and correcting the axial force F when the vehicle speed V is high, it is possible to suppress the steering from being hindered during the running of the vehicle.

[0050] <Second Embodiment> Hereinafter, the second embodiment will be described with reference to the drawings, centering on the differences from the first embodiment.

[0051] In the present embodiment, the magnitude of the threshold value θen is decreased in order to prevent steering that exceeds the output limit of the steering motor 42. FIG. 5 shows the procedure of the process for increasing the force resisting the rotation of the steering shaft 14 by the driver. The series of processes shown in FIG. 5 is realized by the PU52 repeatedly executing, for example, at a predetermined cycle, the program stored in the storage device 54. In FIG. 5, for the processes corresponding to the processes shown in FIG. 4, the same step numbers are given for convenience.

[0052] In the series of processes shown in FIG. 5, the PU52 decreases and corrects the threshold value θen (S18a) when the process of S16 is completed and when a negative determination is made in the process of S20. When the process of S18a is completed, the PU52 temporarily ends the series of processes shown in FIG. 5.

[0053] When the threshold value θen is decreased and corrected by the PU52, the magnitude of the steering angle θs easily reaches the threshold value θen. When the magnitude of the steering angle θs reaches the threshold value θen, the end stop torque Fen becomes greater than zero. Therefore, the absolute value of the axial force F increases as compared with the case where the threshold value θen is not changed.

[0054] <Third Embodiment> The following describes the third embodiment, focusing on the differences from the first embodiment, with reference to the drawings.

[0055] In this embodiment, the assist amount Ta is decreased to prevent steering that exceeds the output limit of the steering motor 42. Fig. 6 shows the procedure of the process for increasing the target reaction torque Ts. The series of processes shown in Fig. 6 is realized by the PU52 repeatedly executing, for example, at a predetermined period, a program stored in the storage device 54. In Fig. 6, for the processes corresponding to the processes shown in Fig. 4, the same step numbers are given for convenience.

[0056] In the series of processes shown in Fig. 6, when the PU52 completes the process of S16 and when a negative determination is made in the process of S20, the magnitude of the assist amount Ta is decreased and corrected (S18b). That is, when the assist amount Ta output by the assist amount setting process M20 is positive, the PU52 sets, as the input variable of the subtraction process M24, a value obtained by correcting the assist amount Ta to a smaller value. Also, when the assist amount Ta output by the assist amount setting process M20 is negative, the PU52 sets, as the input variable of the subtraction process M24, a value obtained by correcting the assist amount Ta to a larger value.

[0057] When the PU52 completes the process of S18b, the PU52 temporarily ends the series of processes shown in Fig. 6. When the assist amount Ta output by the assist amount setting process M20 by the PU52 is decreased and corrected, the absolute value of the target reaction torque Ts becomes larger. Therefore, the reaction force against the steering on the side of expanding the steering angle becomes larger.

[0058] <Corresponding Relationship> The correspondence between the matters in the above-described embodiment and the matters described in the column of "Means for Solving the Problems" is as follows. Below, the correspondence is shown for each number of the solution means described in the column of "Means for Solving the Problems". [1] The steering process corresponds to the target steering equivalent angle calculation process M18, the steering feedback process M30, and the steering operation signal generation process M32. The reaction force application process corresponds to the assist amount setting process M20, the axial force setting process M22, the subtraction process M24, and the reaction force operation signal generation process M26. The axial force variable acquisition process corresponds to the process of S10. The axial force variable corresponds to the q-axis current iqt. The increase process corresponds to the processes of S14, S18, S18a, and S18b. [2] The determination process corresponds to the process of S14. [3] It corresponds to the above condition (A). [4] The increase process corresponds to the process of S18. [5] The increase process corresponds to the process of S18a. [6] The increase process corresponds to the process of S18b.

[0059] <Other Embodiments> Note that this embodiment can be implemented with the following modifications. This embodiment and the following modification examples can be implemented in combination with each other within a technically non-conflicting range.

[0060] "Regarding the Axial Force Variable" · The axial force variable is not limited to the q-axis current iqt. For example, it may be the torque of the steering motor 42 calculated by multiplying the q-axis current iqt by a predetermined coefficient. Further, when the steering motor 42 is a permanent magnet synchronous motor, the axial force variable may be the torque of the steering motor calculated by the d-axis current and the q-axis current.

[0061] · It is not essential that the axial force variable is a variable indicating the torque of the steering motor 42. For example, it may be the detection value of a dedicated sensor that detects the force acting in the axial direction of the rack shaft 32. "Regarding the Determination Process" · The determination process is not limited to determining whether the logical product of the above conditions (A) and (B) is true. For example, it may be a process of determining whether the above condition (B) is true. Here, the threshold Ith in condition (B) may be changed according to the vehicle speed V.

[0062] · The condition for stopping the increase process is not limited to the condition that the logical sum of the non - establishment of the above condition (A) and the non - establishment of the above (B) is true. For example, it may be a condition that the logical product of the vehicle speed V being greater than or equal to a specified speed and the absolute value of the q - axis current iqt being less than or equal to a predetermined value is true. Here, the specified speed is greater than the predetermined speed Vth. Also, the predetermined value is less than the threshold Ith. In this way, by providing hysteresis in the control, it is possible to suppress the hunting of the execution and stop of the increase process.

[0063] "Regarding the axial force setting process" · It is not essential that the input variables of the angular axial force setting process M40 are the target equivalent steering angle θp* and the vehicle speed V. For example, the vehicle speed V may not be included in the input variables of the angular axial force setting process M40. Also, for example, as the angular variable of the steering system as an input variable of the angular axial force setting process M40, it is not limited to the target equivalent steering angle θp*. For example, the angular variable of the steering system may be the equivalent steering angle θp. Also, for example, the angular variable of the steering system may be the steering angle θs.

[0064] · The input variable of the current axial force setting process M42 is not limited to the q - axis current iqt. For example, the input variables of the current axial force setting process M42 may be the q - axis current iqt and the vehicle speed V. Also, for example, the input variables of the current axial force setting process M42 may include angular variables of the steering system such as the target equivalent steering angle θp*, the equivalent steering angle θp, and the steering angle θs.

[0065] ·It is not essential that the input variables of the distribution ratio calculation process M46 be the target equivalent steering angle θp* and the vehicle speed V. For example, the vehicle speed V may not be included in the input variables of the distribution ratio calculation process M46. Also, for example, the angular variable of the steering system as an input variable of the distribution ratio calculation process M46 is not limited to the target equivalent steering angle θp*. For example, the angular variable of the steering system may be the equivalent steering angle θp. Also, for example, the angular variable of the steering system may be the steering angle θs.

[0066] ·It is not essential that the axial force setting process include both of the two processes of the angular axial force setting process M40 and the current axial force setting process M42. For example, for the two processes of the angular axial force setting process M40 and the current axial force setting process M42, it may include only one of them.

[0067] ·It is not essential that the axial force setting process include the end stop torque setting process M60. "Regarding the reaction force application process" ·It is not essential that the reaction force application process include the assist amount setting process M20 and the axial force setting process M22. For example, in a state where map data is stored in the storage device 54, a process of map-calculating the target reaction force torque Ts by the PU52 according to the steering torque Th, the q-axis current iqt, and the vehicle speed V as input variables may be used.

[0068] "Regarding the steering control device" ·The steering control device is not limited to one that executes various processes by a PU. For example, it may include a dedicated hardware circuit such as an ASIC that executes at least a part of the processes executed in the above embodiment. That is, the control device may include any of the following processing circuits (a) to (c). (a) A processing circuit including a processing device that executes all of the above processes according to a program, and a program storage device such as a storage device that stores the program. (b) A processing circuit including a processing device and a program storage device that execute a part of the above processes according to a program, and a dedicated hardware circuit that executes the remaining processes. (c) A processing circuit including a dedicated hardware circuit that executes all of the above processes. Here, there may be a plurality of software execution devices including a processing device and a program storage device, and dedicated hardware circuits.

[0069] "Regarding the steering actuator" ·As the steering actuator 30, for example, one that transmits the rotational power of the steering motor 42 to the steering wheel 34 via a rack and pinion mechanism may be adopted.

Explanation of symbols

[0070] 10... Steering device 12... Steering wheel 14... Steering shaft 20... Reaction force actuator 22... Reaction force motor 24... Inverter for reaction force 26... Reduction mechanism for reaction force 30... Steering actuator 32... Rack shaft 34... Steering wheel 42... Steering motor 44... Inverter for steering 46... Steering transmission mechanism 48... Conversion mechanism 50... Steering control device

Claims

1. configured to execute a steering process, a reaction force application process, an axial force variable acquisition process, and an increase process in a state where the steering wheel and the steering shaft are mechanically disconnected; The steering process is a process of operating a steering motor to steer the steering wheel according to a steering angle; The steering angle is the rotation angle of the steering shaft; The reaction force application process is a process of operating a reaction force motor to apply a reaction force against the driver's rotation of the steering shaft; The axial force variable acquisition process is a process of acquiring a value of an axial force variable based on a detected value of a physical quantity; The axial force variable is a variable indicating a force applied to the steering wheel and preventing the steering wheel from being steered; The increase process is a steering control device that increases the reaction force based on the value of the axial force variable as an input variable to prevent the steering angle from reaching an angle at which the steering motor cannot steer the steering wheel.

2. The increase process includes a determination process; The determination process is a process of determining whether the steering angle is approaching an angle at which the steering motor cannot steer the steering wheel based on the value of the axial force variable as an input variable; The increase process is the steering control device according to claim 1, which increases the reaction force when it is determined that the angle is approaching.

3. The steering control device according to claim 1, wherein the increase process is configured to be executed on the condition that the vehicle speed is equal to or lower than a predetermined speed.

4. The reaction force application process includes an assist amount setting process and an axial force setting process; The axial force setting process is a process of setting an axial force that is a force against the driver's rotation operation of the steering shaft; The assist amount setting process is a process of setting an assist amount that is an amount for assisting the driver in rotating the steering shaft; The reaction force application process includes a process of determining the reaction force according to a value obtained by subtracting the assist amount from the axial force; The increase process is the steering control device according to claim 1, which is a process of increasing and correcting the axial force.

5. The reaction force application process includes an assist amount setting process and an axial force setting process; The axial force setting process is a process of setting an axial force that is a force against the driver's rotation operation of the steering shaft; The assist amount setting process is a process of setting an assist amount that is an amount for assisting the driver in rotating the steering shaft; The reaction force application process includes a process of determining the reaction force according to a value obtained by subtracting the assist amount from the axial force. The axial force setting process includes a process of superimposing a blocking torque that prevents the steering angle from becoming larger than the threshold value on the axial force when the magnitude of the steering angle is equal to or greater than the threshold value. The increasing process includes a process of reducing the magnitude of the threshold value. The steering control device according to claim 1.

6. The reaction force application process includes an assist amount setting process and an axial force setting process. The axial force setting process is a process of setting an axial force that is a force resisting the rotational operation of the steering shaft by the driver. The assist amount setting process is a process of setting an assist amount that is an amount for assisting the driver in rotating the steering shaft. The reaction force application process includes a process of determining the reaction force according to a value obtained by subtracting the assist amount from the axial force. The increasing process is a process of reducing and correcting the assist amount. The steering control device according to claim 1.

7. The physical quantity is the current flowing through the steering motor. The steering control device according to claim 1.

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