Steering control device

Abstract

To provide a turning control device which inhibits sudden change of a turning wheel caused by cancellation of restriction with respect to control of a control amount.SOLUTION: A PU 72 feedback-controls a turning angle to a target turning angle. The PU 72 executes current limitation if a temperature of a turning motor 60 is equal to or higher than a prescribed temperature. The PU 72 gradually changes the target turning angle from the turning angle to the target turning angle when cancelling current limitation.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] For example, Patent Document 1 listed below describes a steering control device that controls steered wheels. This control device executes a process to limit the output of a steering motor to protect the steering motor for turning the steered wheels from overheating. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-83059 Summary of the Invention [Problem to be solved by the invention]

[0004] When the output is limited as described above, there is a risk that the control amount indicating the steering angle will suddenly change to the target value when the limit is released. [Means for solving the problem]

[0005] The means for solving the above problems and their effects will be described below. 1. A steering control device applied to a vehicle equipped with a steering system in which the relationship between a steering angle and a turning angle can be changed, the steering angle being the rotation angle of a steering wheel and the turning angle being the turning angle of steered wheels of the vehicle, the device being configured to execute a target control variable calculation process, an operation process, a judgment process, and a gradual change process, the target control variable calculation process being a process of calculating a target control variable that is a target value of a control variable of the steering system, the control variable being a quantity that indicates an angle variable that is correlated with the turning angle of the steered wheels, the operation process being a process of operating the steering system in order to control the control variable to the target control variable, the judgment process being a process of determining whether or not a constraint has occurred in control of the control variable, and the gradual change process being a process of gradually changing the target control variable that is an input to the operation process from the control variable to the target control variable calculated by the target control variable calculation process when the state in which it is determined by the judgment process that the constraint has occurred is switched to a state in which it is determined that the constraint has not occurred.

[0006] When the above constraint exists, there is a risk that the difference between the control amount and the target control amount will become large. If the constraint is resolved when the difference between the control amount and the target control amount is large, there is a risk that the control amount will suddenly change to the target control amount. Therefore, in the above configuration, the target control amount, which is input to the operation processing, is gradually changed from the control amount to a value calculated by the target control amount calculation processing. This makes it possible to prevent a sudden change in the control amount caused by the resolution of the constraint. Therefore, with the above configuration, it is possible to prevent a sudden change in the steered wheels caused by the resolution of the constraint.

[0007] 2. A steering control device as described in 1 above, wherein the steering system includes a motor for steering the steered wheels, and includes a current limiting process for limiting the current of the motor when the temperature of the steering system is equal to or higher than a predetermined temperature, and the judgment process includes a process for determining that the constraint has occurred when the current limiting process is being executed.

[0008] In the above configuration, by limiting the motor current when the steering system temperature is high, it is possible to prevent the steering system temperature from becoming excessively high. Then, when the temperature drops due to the current limit, the constraint is removed. In this case, by using gradual change processing, it is possible to prevent a sudden change in the control variable.

[0009] 3. A steering control device as described in 1 or 2 above, wherein the determination process includes a speed variable acquisition process for acquiring a value of a steering angle speed variable, and a process for determining that the constraint has occurred when a logical product of the magnitude of the value of the steering angle speed variable being equal to or less than a predetermined value and the magnitude of the difference between the control amount and the target control amount being equal to or greater than a difference threshold is true, and the steering angle speed variable is a variable indicating the rate of change of the steering angle.

[0010] When the difference between the control amount and the target control amount is large, control is performed to eliminate the difference. Therefore, the value of the steering angular velocity variable tends to increase. Therefore, when the difference is large but the value of the steering angular velocity variable is small, there is a possibility that a constraint has occurred in the control of the control amount, such as an excessively large torque being required to steer the steered wheels. Therefore, in the above configuration, it is determined that a constraint has occurred in such a case.

[0011] 4. A steering control device as described in 3 above, wherein the judgment process includes an acquisition process for acquiring steering torque, and a process for determining that the constraint exists when the logical product of the magnitude of the value of the steering angular velocity variable is equal to or less than a predetermined value, the magnitude of the difference between the control amount and the target control amount is equal to or greater than a difference threshold, and the magnitude of the steering torque is equal to or greater than a threshold is true, and the steering torque is a torque input to the steering wheel.

[0012] When the steering torque is large, the driver intends to steer the steered wheels. Nevertheless, when the difference between the control amount and the target control amount is large and the value of the steering angular velocity variable is small, there is a possibility that a constraint has occurred in the control of the control amount, such as the torque required to steer the steered wheels being excessively large. Therefore, in the above configuration, it is determined that a constraint has occurred in such a case.

[0013] 5. A steering control device as described in any one of 1 to 4 above, wherein the steering system is equipped with a motor for steering the steered wheels and is configured to execute a voltage limiting process that limits the voltage applied to the motor to a smaller value, and the determination process includes a process that determines that the constraint has occurred when the voltage limiting process is being executed.

[0014] When the voltage limiting process is performed, the magnitude of the current flowing through the motor is limited to a small value. As a result, the torque that can be generated by the motor is limited to a small value. Therefore, when the voltage limiting process is performed, there is a possibility that a restriction has been imposed on the control of the controlled variable. Therefore, in the above configuration, when the voltage limiting process is performed, it is determined that a restriction has been imposed on the control of the controlled variable.

[0015] 6. The steering control device according to any one of 1 to 5 above, wherein the control amount is a steering angle variable that is a variable indicating the steering angle. [Brief explanation of the drawings]

[0016] [Figure 1] 1 is a diagram showing a configuration of a vehicle according to a first embodiment. [Figure 2] FIG. 2 is a block diagram showing a part of the processing executed by the steering control device according to the embodiment. [Figure 3] 3 is a flowchart showing a procedure of processing executed by the steering control device according to the embodiment. [Figure 4] 3 is a flowchart showing a procedure of processing executed by the steering control device according to the embodiment. [Figure 5] 4 is a time chart showing the operation of the embodiment. [Figure 6] 6 is a flowchart showing the procedure of processing executed by a steering control device according to a second embodiment. [Figure 7] 10 is a flowchart showing the procedure of processing executed by a steering control device according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0017] First Embodiment A first embodiment of the steering control device will be described below with reference to the drawings. "Prerequisite configuration" As shown in Fig. 1, vehicle steering device 10 is a steer-by-wire type steering device. Steering device 10 includes a reaction force actuator Ar and a turning actuator At. Steering device 10 of this embodiment has a structure in which the power transmission path between steering wheel 12 and steered wheels 44 is mechanically disconnected.

[0018] A steering shaft 14 is connected to the steering wheel 12. The reaction force actuator Ar is an actuator for applying a steering reaction force to the steering wheel 12. The steering reaction force is a force that acts in the opposite direction to the direction of operation of the steering wheel 12 by the driver. By applying the steering reaction force to the steering wheel 12, it is possible to give the driver an appropriate sense of responsiveness. The reaction force actuator Ar includes a reduction mechanism 16, a reaction force motor 20, and a reaction force inverter 22.

[0019] The reaction motor 20 is a three-phase brushless motor. The rotating shaft of the reaction motor 20 is connected to the steering shaft 14 via a reduction gear mechanism 16. The reaction inverter 22 is a power conversion circuit that converts the voltage of a battery 24, which serves as a DC voltage source, into AC voltage and applies it to the reaction motor 20.

[0020] Meanwhile, steering shaft 40 extends along the vehicle width direction, which is the left-right direction in Figure 1. Left and right steered wheels 44 are connected to both ends of steering shaft 40 via tie rods 42. The linear movement of steering shaft 40 changes the steering angle of steered wheels 44.

[0021] Steering actuator At includes speed reduction mechanism 56, steering motor 60, and steering inverter 62. Steering motor 60 is a three-phase brushless motor. The rotating shaft of steering motor 60 is connected to pinion shaft 52 via speed reduction mechanism 56. Pinion teeth of pinion shaft 52 mesh with rack teeth 54 of steering shaft 40. Pinion shaft 52 and steering shaft 40 provided with rack teeth 54 form rack-and-pinion mechanism 50. Torque of steering motor 60 is applied as a steering force to steering shaft 40 via pinion shaft 52. In response to the rotation of steering motor 60, steering shaft 40 moves along the vehicle width direction, which is the left-right direction in FIG. 1 .

[0022] The steering device 10 is equipped with a steering ECU 70. The steering ECU 70 controls steering wheel 12. The steering ECU 70 operates a reaction force actuator Ar to control the steering reaction force as a control variable of the control object. Fig. 1 shows an operation signal MSs to reaction force inverter 22. The steering ECU 70 also controls steered wheels 44. The steering ECU 70 operates a steering actuator At to control the steering angle of steered wheels 44 as a control variable of the control object. Fig. 1 shows an operation signal MSt to steering inverter 62.

[0023] In order to control the control variable, steering ECU 70 refers to steering torque Th, which is input torque to steering shaft 14, detected by torque sensor 80. Also, steering ECU 70 refers to rotation angle θa of the rotation shaft of reaction force motor 20, detected by rotation angle sensor 82. Also, steering ECU 70 refers to currents iu1, iv1, iw1 flowing through reaction force motor 20. Currents iu1, iv1, iw1 are quantified as voltage drops across shunt resistors provided in each leg of reaction force inverter 22. In order to control the control variable, steering ECU 70 refers to rotation angle θb of the rotation shaft of turning motor 60, detected by rotation angle sensor 84. Also, steering ECU 70 refers to currents iu2, iv2, iw2 flowing through turning motor 60. Currents iu2, iv2, iw2 are quantified as voltage drops across shunt resistors provided in each leg of turning inverter 62.

[0024] The turning ECU 70 refers to the terminal voltage Vb of the battery 24 detected by a voltage sensor 86. The turning ECU 70 also refers to the charge / discharge current Ib of the battery 24 detected by a current sensor 88. The turning ECU 70 also refers to the outside air temperature TO, which is the temperature around the vehicle, detected by an outside air temperature sensor 90. The turning ECU 70 also refers to the vehicle speed V detected by a vehicle speed sensor 92.

[0025] The steering ECU 70 includes a PU 72, a storage device 74, and peripheral circuits 76. The PU 72 is a software processing device such as a CPU, a GPU, and a TPU. Here, the peripheral circuits 76 include a circuit that generates a clock signal that regulates internal operation, a power supply circuit, a reset circuit, etc. The steering ECU 70 controls the control amount by the PU 72 executing a program stored in the storage device 74.

[0026] "control" FIG. 2 shows part of the processing executed by the steering ECU 70. The steering angle calculation process M10 is a process that uses the rotation angle θa as an input and calculates the steering angle θh, which is the rotation angle of the steering wheel 12. The steering angle calculation process M10 includes a process that converts the rotation angle θa into an integrated angle that includes a range exceeding 360°, for example, by counting the number of rotations of the reaction force motor 20 from a steering neutral position, which is the position of the steering wheel 12 when the vehicle is traveling straight. The steering angle calculation process M10 includes a process that calculates the steering angle θh by multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotational speed ratio of the speed reduction mechanism 16. Note that the steering angle θh is positive when it is an angle to the right of the steering neutral position, and negative when it is an angle to the left of the steering neutral position, for example.

[0027] Pinion angle calculation process M12 is a process that uses rotation angle θb as an input and calculates pinion angle θp, which is the rotation angle of pinion shaft 52. Pinion angle calculation process M12 includes, for example, a process of counting the number of rotations of steering motor 60 from a rack neutral position, which is the position of steering shaft 40 when the vehicle is traveling straight, and converting it into an integrated angle that includes a range exceeding 360°. Pinion angle calculation process M12 includes a process of multiplying the converted integrated angle by a conversion coefficient based on the rotational speed ratio of speed reduction mechanism 56 to calculate pinion angle θp, which is the actual rotation angle of pinion shaft 52. Note that pinion angle θp is, for example, positive when it is an angle to the right of the rack neutral position and negative when it is an angle to the left of the rack neutral position. Steering motor 60 and pinion shaft 52 are linked via speed reduction mechanism 56. For this reason, there is a correlation between rotation angle θb of steering motor 60 and pinion angle θp. Using this correlation, pinion angle θp can be found from rotation angle θb of steering motor 60. Furthermore, pinion shaft 52 is meshed with steered shaft 40. Therefore, there is also a correlation between pinion angle θp and the amount of movement of steered shaft 40. In other words, pinion angle θp is a value that reflects the steering angle of steered wheels 44.

[0028] Target reaction force calculation process M14 is a process that uses steering torque Th, vehicle speed V, pinion angle θp, and q-axis current iqt as inputs to calculate target reaction force Tr* corresponding to the steering reaction force to be applied to steering wheel 12. Here, q-axis current iqt is the q-axis current flowing through turning motor 60. q-axis current iqt is calculated by PU 72 based on currents iu2, iv2, iw2 and rotation angle θb. Target reaction force calculation process M14 includes a process that calculates target reaction force Tr* in accordance with the torque applied to steered wheels 44, based on q-axis current iqt. More specifically, target reaction force calculation process M14 includes a process that calculates target reaction force Tr* to a larger value as the magnitude of the torque applied to steered wheels 44 increases. Here, q-axis current iqt is used as a variable that indicates the torque of turning motor 60. Target reaction force Tr* is actually a command value for reaction force motor 20. The value obtained by multiplying the target reaction force Tr* by a coefficient according to the reduction ratio of the reduction mechanism 16 becomes the steering reaction force.

[0029] The reaction force operation process M16 is a process that receives the target reaction force Tr*, currents iu1, iv1, iw1, and rotation angle θa as inputs and outputs an operation signal MSs for the reaction force inverter 22. The reaction force operation process M16 includes a process of calculating dq-axis current command values ​​based on the target reaction force Tr*. The reaction force operation process M16 also includes a process of calculating dq-axis currents based on the currents iu1, iv1, iw1 and the rotation angle θa. The reaction force operation process M16 then includes a process of calculating an operation signal MSs for operating the reaction force inverter 22 so that the dq-axis currents become command values.

[0030] The target pinion angle calculation process M18 is a process for calculating the target pinion angle θp*0 using the steering angle θh and the vehicle speed V as inputs. The target pinion angle θp*0 is a target value of the pinion angle θp according to the operation of the steering wheel 12 by the driver.

[0031] The offset amount calculation process M20 is a process for calculating an offset amount Δθp of the target pinion angle θp*0 using the steering angle θh and the vehicle speed V as inputs. The offset correction process M22 is a process for calculating the target pinion angle θp* by subtracting the offset amount Δθp from the target pinion angle θp*0.

[0032] The pinion angle feedback process M24 is a process for calculating a steering torque command value Tt*, which is a command value for the torque of the steering motor 60, in order to feedback-control the pinion angle θp to the target pinion angle θp*.

[0033] The steering operation process M26 is a process that receives as input the steering torque command value Tt*, currents iu2, iv2, iw2, and pinion angle θp, and outputs an operation signal MSt for the steering inverter 62. The steering operation process M26 includes a process that calculates current command values ​​for the dq axes based on the steering torque command value Tt*. The steering operation process M26 also includes a process that calculates currents for the dq axes based on the currents iu2, iv2, iw2 and the rotation angle θb. The steering operation process M26 then includes a process that calculates an operation signal MSt for operating the steering inverter 62 so that the currents for the dq axes become the command values.

[0034] "Current limiting process" In principle, steering operation process M26 is a process for controlling the torque of steering motor 60 to steering torque command value Tt*. However, if there is a limit to the output of battery 24, the upper limit of the current flowing to steering motor 60 is limited.

[0035] Fig. 3 shows the procedure for determining whether or not to execute the current limiting process. The process shown in Fig. 3 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at a predetermined interval. Note that, below, each process step number will be assigned by a number prefixed with "S."

[0036] In the series of processes shown in FIG. 3, the PU 72 first acquires the outside air temperature TO and the q-axis current iqt (S10). Next, the PU 72 calculates the motor temperature Tm, which is the temperature of the steering motor 60, based on the outside air temperature TO and the q-axis current iqt (S12). Here, the PU 72 updates the motor temperature Tm by adding a predetermined update amount to the previous value of the motor temperature Tm. The PU 72 calculates the update amount according to the q-axis current iqt. When the magnitude of the q-axis current iqt is large, the PU 72 sets the update amount to be equal to or greater than the update amount when the magnitude of the q-axis current iqt is small. In particular, when the magnitude of the q-axis current iqt is equal to or greater than a predetermined value, the PU 72 sets the update amount to a positive value. In other words, the motor temperature Tm is increased. The PU 72 also calculates the predetermined value according to the outside air temperature TO. Here, the PU 72 sets the predetermined value when the outside air temperature TO is high to be equal to or less than the predetermined value when the outside air temperature TO is low.

[0037] Next, the PU 72 determines whether or not the flag F is "1" (S14). If the flag F is "1", it indicates that the current limiting process is being executed. If the flag F is "0", it indicates that the current limiting process is not being executed.

[0038] When the PU 72 determines that flag F is "0" (S14: NO), it determines whether motor temperature Tm is equal to or greater than a restriction lower limit value TthH (S16). Restriction lower limit value TthH may be set, for example, according to a lower limit value at which the temperature of steering motor 60 increases as the magnetic flux density of the permanent magnet of steering motor 60 decreases. When the PU 72 determines that motor temperature Tm is equal to or greater than restriction lower limit value TthH (S16: YES), it assigns "1" to flag F (S18). Then, the PU 72 executes current limiting processing (S20).

[0039] On the other hand, if the PU 72 determines that the flag F is "1" (S14: YES), it determines whether the motor temperature Tm is equal to or lower than the release upper limit value TthL (S22). The release upper limit value TthL is set to a value smaller than the restriction lower limit value TthH. If the PU 72 determines that the motor temperature Tm is equal to or lower than the release upper limit value TthL (S22: YES), it sets the flag F to "0" (S24). Then, the PU 72 releases the current limitation (S26).

[0040] The PU 72 temporarily terminates the series of processes shown in FIG. 3 when it completes the processes of S20 and S26 or when it makes a negative determination in the processes of S16 and S22. The procedure of the offset amount calculation process M20 is shown in Fig. 4. The process shown in Fig. 4 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at predetermined intervals.

[0041] In the series of processes shown in FIG. 4, the PU 72 first acquires the steering angular velocity ωh and the vehicle speed V (S30). The steering angular velocity ωh is a first-order time differential value of the steering angle θh. The steering angular velocity ωh is calculated by the PU 72 based on the steering angle θh. The PU 72 then determines whether or not the flag F has been switched from "1" to "0" (S32). The PU 72 determines that the timing has changed if the flag F was "1" when the series of processes shown in FIG. 4 was previously executed and the flag F is "0" when the series of processes shown in FIG. 4 is currently executed. If the PU 72 determines that the timing has changed (S32: YES), the PU 72 acquires the target pinion angle θp*0 and the pinion angle θp (S34). Then, the PU 72 substitutes the value obtained by subtracting the pinion angle θp from the target pinion angle θp* into the initial offset amount value Δθpb, and also substitutes the initial offset amount value Δθpb into the offset amount Δθp (S36).

[0042] The PU 72 calculates a decrement base value Δ0 when the processing of S36 is completed or when a negative determination is made in the processing of S32 (S38). The PU 72 sets the decrement base value Δ0 when the magnitude of the steering angular velocity ωh is large to be equal to or greater than the decrement base value Δ0 when the magnitude of the steering angular velocity ωh is small. This processing can be realized, for example, by having the PU 72 calculate the decrement base value Δ0 using a map while map data is stored in the storage device 74. Here, the map data is data that uses the absolute value of the steering angular velocity ωh as an input variable and the decrement base value Δ0 as an output variable.

[0043] Map data is a set of data consisting of discrete values ​​of input variables and values ​​of output variables corresponding to each of the input variable values. Furthermore, the map calculation may be a process in which, when the value of an input variable matches one of the input variable values ​​in the map data, the value of the corresponding output variable in the map data is used as the calculation result. Furthermore, when the value of an input variable does not match any of the input variable values ​​in the map data, the map calculation may be a process in which the value obtained by interpolating the values ​​of multiple output variables included in the map data is used as the calculation result. Alternatively, when the value of an input variable does not match any of the input variable values ​​in the map data, the map calculation may be a process in which the value of the output variable in the map data that corresponds to the closest value among the multiple output variable values ​​included in the map data is used as the calculation result.

[0044] Next, the PU 72 calculates the gain G according to the vehicle speed V (S40). The PU 72 sets the gain G when the vehicle speed V is high to be equal to or greater than the gain G when the vehicle speed V is low. This process can be realized, for example, by having the PU 72 calculate the gain G using a map while map data is stored in the storage device 74. Here, the map data is data that uses the vehicle speed V as an input variable and the gain G as an output variable.

[0045] Next, the PU 72 multiplies the decrement base value Δ0 by the gain G and assigns the result to the offset decrement Δ1 (S42). Then, the PU 72 determines whether the offset decrement Δ1 is smaller than a lower limit value ΔL (S44). The PU 72 calculates the lower limit value ΔL according to the vehicle speed V. The PU 72 sets the lower limit value ΔL when the vehicle speed V is high to be equal to or greater than the lower limit value ΔL when the vehicle speed V is low. This process can be implemented, for example, by having the PU 72 calculate the lower limit value ΔL using a map while map data is stored in the storage device 74. Here, the map data is data that uses the vehicle speed V as an input variable and the lower limit value ΔL as an output variable.

[0046] If the PU 72 determines that the offset decrease amount Δθpb is smaller than the lower limit value ΔL (S44: YES), it assigns the lower limit value ΔL to the offset decrease amount Δ1 (S46). If the PU 72 completes the process of S46 or if the process of S44 makes a negative determination, it determines whether the offset amount initial value Δθpb is positive (S48). If the PU 72 determines that the offset amount initial value Δθpb is positive (S48: YES), it assigns the larger of zero or a value obtained by subtracting the offset decrease amount Δ1 from the offset amount Δθp to the offset amount Δθp (S52). On the other hand, if the PU 72 determines that the offset amount initial value Δθpb is equal to or smaller than zero (S48: NO), it assigns the smaller of zero or a value obtained by adding the offset decrease amount Δθp to the offset amount Δθp (S50).

[0047] When the PU 72 completes the processes of S50 and S52, it temporarily ends the series of processes shown in FIG. "Actions and Effects of the Present Embodiment" FIG. 5 illustrates transitions of target pinion angle θp* and pinion angle θp. As shown in FIG. 5, flag F is "0" before time t1. That is, current limiting processing is not executed before time t1. Therefore, pinion angle θp increases in accordance with an increase in target pinion angle θp*. On the other hand, current limiting processing is executed in the period from time t1 to time t2. Therefore, the actual torque generated by steering motor 60 falls short of steering torque command value Tt* for controlling pinion angle θp to target pinion angle θp*. As a result, pinion angle θp deviates from target pinion angle θp*.

[0048] After that, at time t2, when the current limiting process is released, the PU 72 first sets the target pinion angle θp* to the pinion angle θp. Then, the PU 72 gradually increases the target pinion angle θp* to the target pinion angle θp*0 output by the target pinion angle calculation process M18. This makes it possible to prevent the pinion angle θp from suddenly changing when the current limiting process is released.

[0049] In contrast to this, the behavior of the pinion angle θp in the case where the process of shifting the target pinion angle θp* by the offset amount Δθp from the target pinion angle θp*0 is not executed is shown by the two-dot chain line. <Second embodiment> The second embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0050] In the above embodiment, after a deviation occurs between target pinion angle θp* and pinion angle θp due to the current limiting process, when the deviation can be eliminated, target pinion angle θp* is shifted from target pinion angle θp*0. However, the situation in which a deviation occurs between target pinion angle θp* and pinion angle θp is not limited to this. For example, there may be a situation in which the magnitude of the torque of steering motor 60 required to make pinion angle θp follow target pinion angle θp* becomes excessively large. This occurs, for example, when the vehicle runs over a curb.

[0051] Therefore, in this embodiment, when it is detected that the above situation is resolved, a process is executed to shift the target pinion angle θp* from the target pinion angle θp*0. The procedure for the process of detecting the above situation is shown in Fig. 6. The process shown in Fig. 6 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at predetermined intervals.

[0052] In the series of processes shown in FIG. 6, PU 72 first acquires steering angular velocity ωh, vehicle speed V, steering torque Th, target pinion angle θp*, and pinion angle θp (S60). Next, PU 72 determines whether flag F is "1" or not (S62). When flag F is "1," this indicates that a situation exists in which the magnitude of the torque of steering motor 60 required to cause pinion angle θp to follow target pinion angle θp* becomes excessively large. When flag F is "0," this indicates that the situation does not exist. In this way, flag F according to this embodiment differs from that shown in FIG. 3. However, this flag F is used in the process of S32 in FIG. 4.

[0053] When the PU 72 determines that the flag F is not "1" (S62: NO), it determines whether the logical product of the following conditions (A) to (D) is true (S64). Condition (A): The absolute value of the steering angular velocity ωh is equal to or less than a predetermined velocity ωth. The predetermined velocity ωth is set to be less than the minimum value of the steering angular velocity ωh that is realized by feedback control using the pinion angle feedback process M24 when the absolute value of the difference between the target pinion angle θp* and the pinion angle θp is large.

[0054] Condition (B): The vehicle speed V is equal to or less than a predetermined vehicle speed Vth. Condition (C): The condition that the magnitude of the steering torque Th is equal to or greater than a predetermined torque Tth. The predetermined torque Tth is set to a value that occurs when the driver intends to steer the steered wheels 44 to a large extent.

[0055] Condition (D): The condition that the absolute value of the difference between the target pinion angle θp* and the pinion angle θp is equal to or greater than a threshold value Δth. The threshold value Δth may be set to, for example, equal to or greater than the maximum value of the difference between the target pinion angle θp* and the pinion angle θp that can occur when feedback control by the pinion angle feedback process M24 is performed normally.

[0056] If the logical product is determined to be true (S64: YES), the PU 72 assigns "1" to flag F (S66). On the other hand, if the PU 72 determines that the flag F is "1" (S62: YES), it determines whether the logical product of the above conditions (A) to (D) is false (S68). If the PU 72 determines that the logical product is false (S68: YES), it assigns "0" to the flag F (S70).

[0057] The PU 72 temporarily terminates the series of processes shown in FIG. 6 when it completes the processes of S66 and S70 or when it makes a negative determination in the processes of S64 and S68. "Actions and Effects of the Second Embodiment" If PU 72 determines that the logical product of the above conditions (A) to (D) is true, it assigns "1" to flag F. Here, if condition (D) is satisfied, the magnitude of the difference between target pinion angle θp* and pinion angle θp should decrease due to feedback control by pinion angle feedback process M24. However, if the magnitude of the torque of steering motor 60 required to cause pinion angle θp to follow target pinion angle θp* is excessively large, the state in which condition (D) is satisfied continues. In that case, the magnitude of the torque of steering motor 60 increases. Meanwhile, target reaction force calculation process M14 shown in FIG. 2 includes a process for calculating target reaction force Tr* in accordance with the torque applied to steered wheels 44. Therefore, if the magnitude of the torque of steering motor 60 is large, target reaction force Tr* is also set to a large value. As a result, it becomes difficult to change steering angle θh. This causes condition (A) to be satisfied. Therefore, when the above conditions (A) and (D) are met, it is considered that the magnitude of the torque of steering motor 60 required to make pinion angle θp follow target pinion angle θp* becomes excessively large.

[0058] Therefore, under such circumstances, the PU 72 assigns "1" to flag F. When such circumstances are resolved, the PU 72 assigns "0" to flag F. When such circumstances are resolved, the pinion angle θp follows the target pinion angle θp*. Here, the PU 72 gradually changes the target pinion angle θp* from the pinion angle θp to the target pinion angle θp*0. This suppresses a sudden change in the pinion angle θp.

[0059] According to the present embodiment described above, the following actions and effects can be further obtained. (2-1) Condition (C) is included in the conditions for determining that a situation exists in which the magnitude of the torque of steering motor 60 required to make pinion angle θp follow target pinion angle θp* becomes excessively large. When the magnitude of steering torque Th is large, it is considered that the driver is attempting to steer steered wheels 44. Nevertheless, when condition (D) is met, it is highly likely that a situation exists in which the magnitude of the torque of steering motor 60 required to make pinion angle θp follow target pinion angle θp* becomes excessively large. Therefore, by including condition (C) above, it is possible to more accurately determine the situation.

[0060] (2-2) A situation in which the magnitude of the torque of steering motor 60 required to make pinion angle θp follow target pinion angle θp* becomes excessively large usually tends to occur when vehicle speed V is low. Therefore, by including condition (B) in the conditions for determining whether the above situation exists, it can be determined with higher accuracy whether the above situation exists.

[0061] <Third embodiment> The third embodiment will be described below with reference to the drawings, focusing on the differences from the first embodiment.

[0062] In this embodiment, voltage limiting processing is executed to limit the magnitude of the output voltage of steering inverter 62 to a smaller value depending on the state of battery 24. When voltage limiting processing is executed, there is a risk that the actual torque generated by steering motor 60 will be insufficient for steering torque command value Tt* for controlling pinion angle θp to target pinion angle θp*. If the actual torque is insufficient, pinion angle θp will deviate from target pinion angle θp*. In that case, there is a risk that pinion angle θp will suddenly change when voltage limiting processing is released.

[0063] Therefore, in this embodiment, when the voltage limiting process is released, a process is executed to shift the target pinion angle θp* from the target pinion angle θp*0. The procedure for determining whether or not to execute the voltage limiting process is shown in Fig. 7. The process shown in Fig. 7 is realized by the PU 72 repeatedly executing a program stored in the storage device 74, for example, at predetermined intervals.

[0064] In the series of processes shown in FIG. 7, the PU 72 first acquires the terminal voltage Vb, the outside air temperature TO, and the state of charge SOC of the battery 24 (S80). Next, the PU 72 determines whether or not the flag F is "1" (S82). When the flag F is "1," it indicates that the voltage limiting process is being executed. When the flag F is "0," it indicates that the voltage limiting process is not being executed. In this way, the flag F according to this embodiment differs from that shown in FIG. 3. However, this flag F is used in the process of S32 in FIG. 4.

[0065] When the PU 72 determines that the flag F is "0" (S82: NO), it determines whether the logical sum of the following conditions (E) to (G) is true (S84). Condition (E): Terminal voltage Vb is equal to or less than specified voltage Vth. Specified voltage Vth is set according to the upper limit of terminal voltage Vb when the torque that can be generated by steering motor 60 is limited to a small value.

[0066] Condition (F): The outside air temperature TO is equal to or lower than a predetermined temperature TOth. The predetermined temperature TOth is set based on the upper limit of the outside air temperature TO at which the output power of the battery 24 is limited to a small value.

[0067] Condition (G): The charging rate SOC of the battery 24 is equal to or lower than a predetermined value SOCth. The predetermined value SOCth is set based on the upper limit of the charging rate SOC at which the output power of the battery 24 cannot be sufficiently increased. The charging rate SOC is calculated by the PU 72 based on an integration process of the charging / discharging current Ib. In addition, the terminal voltage Vb when the magnitude of the charging / discharging current Ib is small may be regarded as an open circuit voltage and added as an input to the calculation process of the charging rate SOC.

[0068] If the PU 72 determines that the logical sum is true (S84: YES), it assigns "1" to flag F (S86), and then executes voltage limiting processing (S88). On the other hand, if the PU 72 determines that the flag F is "1" (S82: YES), it determines whether the above logical sum is false (S90). If the PU 72 determines that the above logical sum is false (S90: YES), it assigns "0" to the flag F (S92). Then, the PU 72 cancels the voltage limiting process (S94).

[0069] The PU 72 temporarily terminates the series of processes shown in FIG. 7 when it completes the processes of S88 and S94 or when it makes a negative determination in the processes of S84 and S90. "Actions and Effects of the Third Embodiment" PU 72 executes voltage limiting processing in a situation where the output of battery 24 is restricted. This makes it possible to prevent the power required of battery 24 from becoming excessively large. However, in this case, the magnitude of the torque generated by steering motor 60 is restricted to a small value. This can increase the difference between target pinion angle θp* and pinion angle θp. Therefore, when voltage limiting processing is released, PU 72 gradually changes target pinion angle θp* from pinion angle θp to target pinion angle θp*0. This makes it possible to prevent a sudden change in pinion angle θp.

[0070] <Correspondence> The correspondence between the matters in the above embodiment and the matters described in the "Means for Solving the Problem" column is as follows. Below, the correspondence is shown for each number of the means for solving the problem described in the "Means for Solving the Problem" column. [1,6] Target control amount calculation processing corresponds to target pinion angle calculation processing M18. The control amount corresponds to pinion angle θp. The operation processing corresponds to pinion angle feedback processing M24 and steering operation processing M26. The gradual change processing corresponds to part of offset amount calculation processing M20 and offset correction processing M22 in FIG. 2. The determination processing corresponds to the processing of S14 to S24, the processing of S62 to S70, and the processing of S82 to S92. [2] Current limiting processing corresponds to the processing of S20. [3,4] Determination processing corresponds to the processing of S62 to S70. [5] Voltage limiting processing corresponds to the processing of S88.

[0071] <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.

[0072] "About the judgment process" In the process shown in Fig. 6, flag F is switched from "1" to "0" when the logical product of the above conditions (A) to (D) becomes false, but this is not limiting. For example, flag F may be switched from "1" to "0" when at least one of conditions (A), (C), and (D) is no longer satisfied. Also, for example, flag F may be switched from "1" to "0" when at least one of conditions (A) and (D) is no longer satisfied.

[0073] The validity of the above condition (A) does not presuppose that the target reaction force calculation process M14 is a process that inputs a variable indicating the torque of the steering motor 60. For example, as described in the section "Regarding the target reaction force calculation process," the condition (A) is valid even if the target reaction force calculation process M14 is a process that inputs the steering angle θh. The point is that it is sufficient if control is performed so that the steering angle θh changes in accordance with changes in the steering angle of the steered wheels 44.

[0074] The condition that the magnitude of the value of the steering angle velocity variable is equal to or less than a predetermined value is not limited to condition (A). For example, the condition may be that the magnitude of the rate of change of the pinion angle θp is equal to or less than a predetermined value.

[0075] "About the target reaction force calculation process" 2, target reaction force calculation process M14 is shown as a process for calculating target reaction force Tr* based on q-axis current iqt, but this is not limited to this. Instead of q-axis current iqt, the process may input an estimated value of the torque of steering motor 60 itself as a variable indicating the torque of steering motor 60. Alternatively, for example, the process may input steering angle θh. In this case, target reaction force calculation process M14 may be a process for calculating target reaction force Tr* so as to prevent displacement of steering angle θh in a direction that would destroy the consistency between steering angle θh and pinion angle θp.

[0076] "About gradual change processing" The process of FIG. 4 may be modified so that, when a positive determination is made in the process of S32, the offset amount Δθp output by the offset amount calculation process M20 is set to the offset amount initial value Δθpb.

[0077] The processes of S44 and S46 may not be provided. The process for calculating the gradual decrease rate of the offset amount Δθp in accordance with the steering angular velocity and the vehicle speed is not limited to the process illustrated in Fig. 4. For example, map calculation may be performed using map data in which the steering angular velocity and the vehicle speed are input variables and the offset decrease amount Δ1 is an output variable.

[0078] It is not necessary to calculate the rate at which the offset amount Δθp is gradually decreased depending on the steering angular velocity and the vehicle speed. For example, with respect to the two variables of the steering angular velocity and the vehicle speed, the rate at which the offset amount Δθp is gradually decreased may be calculated based on only one of these variables. Also, for example, with respect to the two variables, the rate at which the offset amount Δθp is gradually decreased may be calculated independently of either one of these variables.

[0079] "Regarding control amount calculation processing" The target pinion angle calculation process M18 may be a process for variably setting the steering angle ratio in accordance with the detection value of the yaw rate sensor in addition to the vehicle speed V.

[0080] "About operation processing" In the above embodiment, pinion angle feedback process M24 calculates steering torque command value Tt* as an operation amount for feedback-controlling pinion angle θp to target pinion angle θp*, but this is not limited to this. For example, it may include a process of calculating damping torque, which is torque in the opposite direction to the direction of change in pinion angle θp over time, and adding this to steering torque command value Tt*. This process may further receive as input at least one of the pinion angular velocity, which is the change in pinion angle θp over time, and the target pinion angular velocity, which is the change in target pinion angle θp* over time. Furthermore, by including vehicle speed V as an input, the damping torque may be variably set in accordance with vehicle speed V.

[0081] Instead of the pinion angle feedback process M24, a process may be used in which a detected value of the movement amount of the steered shaft 40 is feedback-controlled to a target value. In this case, in the above embodiment, the control amount and the like related to the pinion angle θp are replaced with the control amount and the like related to the movement amount of the steered shaft 40.

[0082] The operation processing does not necessarily have to include a process of calculating a manipulated variable for feedback control of a control variable indicating a steering angle, such as pinion angle θp. For example, the operation processing may include a process of calculating a manipulated variable for open-loop control of a control variable indicating a steering angle to a target value. Furthermore, for example, the operation processing may include a process of calculating the sum of the manipulated variable for open-loop control and the manipulated variable for feedback control.

[0083] The control method for steering motor 60 is not limited to dq-axis current feedback processing. For example, if a DC motor is used as steering motor 60 and the drive circuit is an H-bridge circuit, it is sufficient to simply control the current flowing through steering motor 60.

[0084] "About target control amount" As described in the section "Regarding Operation Processing," when feedback control is performed on the amount of movement of the steered shaft 40, the target value of the amount of movement may be set as the target control amount.

[0085] "About steering system temperature" In the above embodiment, the q-axis current iqt is used as an input to calculate the motor temperature Tm, but this is not limiting. For example, the square root of the sum of the squares of the d-axis current and the q-axis current may be used as an input. This square root is proportional to the amplitude of the currents iu2, iv2, and iw2.

[0086] Motor temperature Tm is not limited to an estimated value. For example, steering motor 60 may be provided with a temperature sensor such as a thermistor and the temperature measured thereby may be used. The temperature of the steering system is not limited to the temperature of the steering motor 60. For example, it may be the temperature of the steering inverter 62.

[0087] "About steering control devices" The steering control device is not limited to a device in which a device for operating the steering actuator At and a device for operating the reaction force actuator Ar are integrated together. For example, the device for operating the steering actuator At and the device for operating the reaction force actuator Ar may be devices housed in separate housings that are capable of communicating with each other.

[0088] The steering control device is not limited to one equipped with PU 72 and storage device 74 and executing software processing. For example, it may be equipped with a dedicated hardware circuit such as an ASIC that performs hardware processing on at least a portion of what was processed by software in the above embodiment. That is, the control device may have any of the following configurations (a) to (c): (a) equipped with a processing device that executes all of the above processing in accordance with a program, and a program storage device such as a storage device that stores the program; (b) equipped with a processing device and program storage device that executes a portion of the above processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing; (c) equipped with a dedicated hardware circuit that executes all of the above processing. Here, there may be multiple software execution devices equipped with a processing device and program storage device. Also, there may be multiple dedicated hardware circuits.

[0089] "About steering actuators" The steering actuator At may be, for example, one in which steering motor 60 is arranged coaxially with steering shaft 40. Alternatively, for example, one in which steering motor 60 is connected to steering shaft 40 via a belt-type reducer using a ball screw mechanism may be used.

[0090] "About the steering system" The steering system capable of changing the relationship between the steering angle and the turning angle is not limited to a steering system in which the transmission of power between the steering wheel 12 and the steered wheels 44 is cut off. For example, a steering system capable of changing the relationship between the steering angle and the turning angle may be configured by using a variable gear as the gear that enables the transmission of power between the steering wheel 12 and the steered wheels 44. [Explanation of symbols]

[0091] 10...Steering device 12...Steering wheel 14...Steering shaft 16...Reduction mechanism 20...Reaction motor 22...Reaction force inverter 24...Battery 40...Steering shaft 42...Tie rod 44...Steering wheel 50...Rack and pinion mechanism 52...Pinion shaft 54...Rack teeth 56…Reduction mechanism 60...Steering motor 62...Steering inverter 70…Steering ECU

Claims

1. The present invention is applied to a vehicle equipped with a steering system capable of changing the relationship between the steering angle and the turning angle, The steering angle is a rotation angle of a steering wheel, The steering angle is a turning angle of a steered wheel of the vehicle, configured to execute a target control amount calculation process, an operation process, a determination process, and a gradual change process; the target control amount calculation process is a process of calculating a target control amount that is a target value of a control amount of the steering system, the control amount is a quantity indicating an angle variable having a correlation with the steering angle of the steered wheels, the operation processing is processing for operating the steering system in order to control the control amount to the target control amount, the determination process is a process for determining whether or not a constraint is imposed on control of the controlled variable, the gradual change process is a process of gradually changing the target control amount, which is an input of the operation process, from the control amount to the target control amount calculated by the target control amount calculation process when the state in which it is determined that the constraint exists is switched to the state in which it is determined that the constraint does not exist by the determination process, the determination process includes a speed variable acquisition process for acquiring a value of a steering angle speed variable, and a process for determining that the constraint exists when a logical product of a value of the steering angle speed variable being equal to or smaller than a predetermined value and a value of a difference between the control amount and the target control amount being equal to or larger than a difference threshold is true, A steering control device, wherein the steering angle velocity variable is a variable that indicates a rate of change of the steering angle.

2. the steering system includes a motor for steering the steered wheels, a current limiting process for limiting a current of the motor when the temperature of the steering system is equal to or higher than a predetermined temperature; The turning control device according to claim 1 , wherein the determination process includes a process of determining that the restriction exists when the current limiting process is being executed.

3. the determination process includes an acquisition process for acquiring a steering torque, and a process for determining that the constraint exists when a logical product of the magnitude of the value of the steering angular velocity variable being equal to or less than a predetermined value, the magnitude of the difference between the control amount and the target control amount being equal to or greater than a difference threshold, and the magnitude of the steering torque being equal to or greater than a threshold is true, 3. A steering control device according to claim 1, wherein the steering torque is a torque input to the steering wheel.

4. the steering system includes a motor for steering the steered wheels, The motor is configured to execute a voltage limiting process for limiting a voltage applied to the motor to a smaller value, 4. The steering control device according to claim 1, wherein the determination process includes a process of determining that the restriction exists when the voltage limiting process is being executed.

5. 5. The steering control device according to claim 1, wherein the control amount is a steering angle variable that is a variable indicating the steering angle.

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