JP7792277B2 - Steering control device - Google Patents

Description

The present invention relates to a steering control device.

For example, Patent Document 1 below describes a steering control device that controls steered wheels. This control device executes processing to limit the output of the steering motor, which steers the steered wheels, to protect the motor from overheating.

Japanese Patent Application Laid-Open No. 2020-83059

When the above output limit is applied, there is a risk that the control variable indicating the steering angle will suddenly change to the target value when the limit is released.

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 capable of changing the relationship between a steering angle and a turning angle, 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 determination 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 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 determination process being a process of determining whether or not a constraint is occurring 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 a state in which it is determined by the determination process that the constraint is occurring is switched to a state in which it is determined that the constraint is not occurring.

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, with 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 due to the resolution of the constraint. Therefore, with the above configuration, it is possible to prevent a sudden change in the steered wheels due to the resolution of the constraint.

2. The steering system is a steering control device as described in paragraph 1, in which the steering system includes a motor for steering the steered wheels, and includes a current limiting process that limits the current to the motor when the temperature of the steering system is equal to or higher than a predetermined temperature, and the determination process includes a process that determines that the constraint has occurred when the current limiting process is being executed.

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 rising excessively. Then, when the temperature drops due to the current limit, the constraint is resolved. In that case, by using gradual change processing, it is possible to prevent sudden changes in the control variable.

3. The steering control device according to claim 1 or 2, wherein the determination process includes a speed variable acquisition process for acquiring the value of a steering angle speed variable, and a process for determining that the constraint exists when the 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.

When the difference between the control amount and the target control amount is large, control is performed to eliminate that difference. Therefore, the value of the steering angular velocity variable tends to increase. Therefore, if the difference is large but the value of the steering angular velocity variable is small, there may be constraints on the control of the control amount, such as an excessively large torque being required to steer the steered wheels. Therefore, the above configuration determines that a constraint has occurred in such a case.

4. The steering control device according to claim 3, wherein the determination 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 the torque input to the steering wheel.

When the steering torque is large, the driver intends to steer the steered wheels. However, if 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 may be constraints on the control of the control amount, such as an excessively large torque being required to steer the steered wheels. Therefore, the above configuration determines that constraints have occurred in such cases.

5. The steering system is a steering control device according to any one of items 1 to 4 above, wherein the steering system includes 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 lower value, and the determination process includes a process of determining that the constraint has occurred when the voltage limiting process is being executed.

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 the motor can generate is limited to a small value. Therefore, when voltage limiting process is performed, there is a possibility that restrictions have been placed on the control of the controlled variable. Therefore, with the above configuration, when voltage limiting process is performed, it is determined that restrictions have been placed on the control of the controlled variable.

6. The steering control device according to any one of items 1 to 5 above, wherein the control variable is a steering angle variable that indicates the steering angle.

1 is a diagram illustrating a configuration of a vehicle according to a first embodiment. FIG. 2 is a block diagram showing a part of the processing executed by the steering control device according to the embodiment. 3 is a flowchart showing a procedure of processing executed by the steering control device according to the embodiment. 3 is a flowchart showing a procedure of processing executed by the steering control device according to the embodiment. 4 is a time chart showing the operation of the embodiment. 10 is a flowchart showing a procedure of a process executed by a steering control device according to a second embodiment. 10 is a flowchart showing a procedure of a process executed by a steering control device according to a third embodiment.

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

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. A steering reaction force is a force that acts in the opposite direction to the direction in which the driver operates the steering wheel 12. By applying a 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.

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 the battery 24, which serves as a DC voltage source, into AC voltage and applies it to the reaction motor 20.

On the other hand, the 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 the steering shaft 40 via tie rods 42. The steering angle of the steered wheels 44 is changed by the linear movement of the steering shaft 40.

The steering actuator At includes a reduction gear mechanism 56, a steering motor 60, and a steering inverter 62. The steering motor 60 is a three-phase brushless motor. The rotating shaft of the steering motor 60 is connected to a pinion shaft 52 via the reduction gear mechanism 56. The pinion teeth of the pinion shaft 52 mesh with rack teeth 54 of the steering shaft 40. The pinion shaft 52 and the steering shaft 40, on which the rack teeth 54 are provided, form a rack-and-pinion mechanism 50. The torque of the steering motor 60 is applied as a steering force to the steering shaft 40 via the pinion shaft 52. As the steering motor 60 rotates, the steering shaft 40 moves along the vehicle width direction, which is the left-right direction in FIG. 1.

The steering device 10 is equipped with a steering ECU 70 .
The steering ECU 70 controls the 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 the 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.

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

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

The steering ECU 70 comprises a PU 72, a storage device 74, and peripheral circuits 76. The PU 72 is a software processing device such as a CPU, GPU, or TPU. Here, the peripheral circuits 76 include circuits that generate clock signals that regulate internal operation, power supply circuits, reset circuits, etc. The steering ECU 70 controls control variables by having the PU 72 execute programs stored in the storage device 74.

"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 of converting 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 of multiplying the integrated angle obtained by conversion by a conversion coefficient based on the rotational speed ratio of the speed reduction mechanism 16 to calculate the steering angle θh. Note that the steering angle θh is positive when it is an angle to the right of the steering neutral position, and negative when it is an angle to the left of the steering neutral position, for example.

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

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

The reaction force operation process M16 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 for calculating d-axis and q-axis current command values based on the target reaction force Tr*. The reaction force operation process M16 also includes a process for calculating d-axis and q-axis currents based on the currents iu1, iv1, iw1, and rotation angle θa. The reaction force operation process M16 then includes a process for calculating an operation signal MSs to operate the reaction force inverter 22 so that the d-axis and q-axis currents become the command values.

The target pinion angle calculation process M18 is a process that calculates the target pinion angle θp*0 using the steering angle θh and vehicle speed V as input. The target pinion angle θp*0 is the target value of the pinion angle θp in response to the operation of the steering wheel 12 by the driver.

The offset amount calculation process M20 is a process in which the steering angle θh and the vehicle speed V are input to calculate the offset amount Δθp of the target pinion angle θp*0.
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.

Pinion angle feedback processing M24 is processing that calculates the steering torque command value Tt*, which is the torque command value for the steering motor 60, in order to feedback control the pinion angle θp to the target pinion angle θp*.

The steering operation process M26 receives the steering torque command value Tt*, currents iu2, iv2, iw2, and pinion angle θp as inputs and outputs an operation signal MSt for the steering inverter 62. The steering operation process M26 includes a process for calculating dq-axis current command values based on the steering torque command value Tt*. The steering operation process M26 also includes a process for calculating dq-axis currents based on the currents iu2, iv2, iw2 and the rotation angle θb. The steering operation process M26 then includes a process for calculating an operation signal MSt to operate the steering inverter 62 so that the dq-axis currents become the command values.

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

Figure 3 shows the procedure for determining whether or not to execute current limiting processing. The processing shown in Figure 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 processing step will be numbered with a number preceded by "S."

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). 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 based on 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 based on 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.

Next, the PU 72 determines whether flag F is "1" (S14). If flag F is "1", it indicates that current limiting processing is being performed. If flag F is "0", it indicates that current limiting processing is not being performed.

If PU 72 determines that flag F is "0" (S14: NO), it determines whether motor temperature Tm is equal to or greater than limit lower limit value TthH (S16). Limit 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. If PU 72 determines that the temperature is equal to or greater than limit lower limit value TthH (S16: YES), it assigns "1" to flag F (S18). Then, PU 72 executes current limiting processing (S20).

On the other hand, if the PU 72 determines that flag F is "1" (S14: YES), it determines whether the motor temperature Tm is equal to or less 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 less than the release upper limit value TthL (S22: YES), it assigns "0" to flag F (S24). Then, the PU 72 releases the current limit (S26).

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 offset 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.

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 the 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 timing has come when flag F has switched from "1" to "0" (S32). The PU 72 determines that a switch has occurred if flag F was "1" during the previous execution of the series of processes shown in FIG. 4 and flag F is "0" during the current execution. If the PU 72 determines that a switch has occurred (S32: YES), it 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 value Δθpb, and also substitutes the initial offset value Δθpb into the offset amount Δθp (S36).

When the processing of S36 is completed or when a negative determination is made in the processing of S32, the PU 72 calculates the decrement base value Δ0 (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 perform map calculations to determine the decrement base value Δ0 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.

Map data is a set of data consisting of discrete values of input variables and values of output variables corresponding to each input variable value. Furthermore, a map operation 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, a map operation 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, a map operation 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.

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 achieved, for example, by having the PU 72 perform map calculations to calculate the gain G 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.

Next, the PU 72 multiplies the decrement base value Δ0 by the gain G and assigns the result to the offset decrement Δ1 (S42). The PU 72 then determines whether the offset decrement Δ1 is smaller than the lower limit ΔL (S44). The PU 72 calculates the lower limit ΔL based on the vehicle speed V. The PU 72 sets the lower limit ΔL when the vehicle speed V is high to be equal to or greater than the lower limit ΔL when the vehicle speed V is low. This process can be implemented, for example, by having the PU 72 perform map calculations to determine the lower limit ΔL 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 ΔL as an output variable.

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

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 changes in 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 response to an increase in target pinion angle θp*. On the other hand, current limiting processing is executed during 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*.

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 prevents the pinion angle θp from suddenly changing when the current limiting process is released.

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.

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

Therefore, in this embodiment, when it is detected that the above situation has been resolved, a process is executed to shift the target pinion angle θp* from the target pinion angle θp*0.
The procedure for 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.

In the series of processes shown in FIG. 6, the PU 72 first obtains the steering angular velocity ωh, vehicle speed V, steering torque Th, target pinion angle θp*, and pinion angle θp (S60). Next, the PU 72 determines whether flag F is "1" (S62). If flag F is "1," this indicates that the magnitude of the torque of the steering motor 60 required to cause the pinion angle θp to follow the target pinion angle θp* is excessively large. If flag F is "0," this indicates that this is not the case. In this way, flag F in this embodiment differs from that shown in FIG. 3. However, this flag F is used in the process of S32 in FIG. 4.

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.

Condition (B): The vehicle speed V is equal to or less than a predetermined vehicle speed Vth.
Condition (C): 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.

Condition (D): 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, for example, to a value 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.

If the PU 72 determines that the logical product is true (YES at S64), it sets flag F to "1" (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).

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, feedback control by pinion angle feedback process M24 should reduce the magnitude of the difference between target pinion angle θp* and pinion angle θp. 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 this 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. This makes it difficult to change steering angle θh. As a result, condition (A) is 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.

In such a situation, the PU 72 assigns "1" to flag F. When such a situation is resolved, the PU 72 assigns "0" to flag F. When such a situation is resolved, the pinion angle θp follows the target pinion angle θp*. Here, the PU 72 gradually changes the target pinion angle θp* from pinion angle θp to target pinion angle θp*0. This prevents sudden changes in the pinion angle θp.

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. If the magnitude of steering torque Th is large, it is considered that the driver is attempting to turn steered wheels 44. Nevertheless, if condition (D) is satisfied, 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.

(2-2) A situation in which the magnitude of the torque of the steering motor 60 required to cause the pinion angle θp to follow the target pinion angle θp* becomes excessively large typically tends to occur when the vehicle speed V is low. Therefore, by including condition (B) in the conditions for determining whether the above situation exists, it is possible to more accurately determine whether the above situation exists.

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

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

Therefore, in this embodiment, when the voltage limiting process is released, a process is executed to shift the target pinion angle θp* with respect to 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.

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 charging rate SOC of the battery 24 (S80). Next, the PU 72 determines whether the flag F is "1" (S82). If the flag F is "1," it indicates that the voltage limiting process is being executed. If the flag F is "0," it indicates that the voltage limiting process is not being executed. In this way, the flag F in this embodiment differs from that shown in FIG. 3. However, this flag F is used in the process of S32 in FIG. 4.

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 a 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.

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.

Condition (G): This condition states that 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 the integration process of the charging and discharging current Ib. In addition, the terminal voltage Vb when the magnitude of the charging and discharging current Ib is small may be considered as the open circuit voltage and added as an input to the calculation process of the charging rate SOC.

If the PU 72 determines that the logical sum is true (YES at S84), it sets flag F to "1" (S86).Then, the PU 72 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 logical sum is false (S90). If the PU 72 determines that the logical sum is false (S90: YES), it assigns "0" to the flag F (S92). Then, the PU 72 cancels the voltage limiting process (S94).

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 demand on 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.

<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] The target control amount calculation process corresponds to the target pinion angle calculation process M18. The control amount corresponds to the pinion angle θp. The operation process corresponds to the pinion angle feedback process M24 and the steering operation process M26. The gradual change process corresponds to part of the offset amount calculation process M20 and the offset correction process M22 in FIG. 2. The determination process corresponds to the processes of S14 to S24, S62 to S70, and S82 to S92. [2] The current limiting process corresponds to the process of S20. [3, 4] The determination process corresponds to the processes of S62 to S70. [5] The voltage limiting process corresponds to the process of S88.

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

"About the judgment process"
6, the 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 limited to this. For example, the flag F may be switched from "1" to "0" when at least one of the conditions (A), (C), and (D) is no longer satisfied. Also, for example, the flag F may be switched from "1" to "0" when at least one of the conditions (A) and (D) is no longer satisfied.

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 "Regarding the target reaction force calculation process" section, condition (A) is valid even if the target reaction force calculation process M14 is a process that inputs the steering angle θh. The key is that control is performed so that the steering angle θh changes in accordance with changes in the steering angle of the steered wheels 44.

- The condition that the magnitude of the steering angle velocity variable value 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.

"About the target reaction force calculation process"
2, target reaction force calculation process M14 is 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 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 disrupt the consistency between steering angle θh and pinion angle θp.

"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.

The processes of S44 and S46 do not have to 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.

- It is not necessary to calculate the rate at which the offset amount Δθp is gradually decreased in accordance with the steering angular velocity and vehicle speed. For example, with respect to the two variables of steering angular velocity and 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 these two variables, the rate at which the offset amount Δθp is gradually decreased may be calculated without depending on either of them.

"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.

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

Instead of pinion angle feedback processing M24, processing may be used that feedback controls the detected value of the amount of movement of the steered shaft 40 to a target value. In this case, in the above embodiment, the control amount related to the pinion angle θp is replaced with the control amount related to the amount of movement of the steered shaft 40.

- It is not essential that the operation processing include processing for calculating a manipulated variable for feedback control of a control variable indicating the steering angle, such as pinion angle θp. For example, it may include processing for calculating a manipulated variable for open-loop control of a control variable indicating the steering angle to a target value. Also, for example, it may include processing for calculating the sum of the manipulated variable for open-loop control and the manipulated variable for feedback control.

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

"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.

"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 amplitudes of the currents iu2, iv2, and iw2.

The motor temperature Tm is not limited to an estimated value. For example, a temperature sensor such as a thermistor may be provided in the steering motor 60 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.

"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.

The steering control device is not limited to one equipped with a PU 72 and a 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) 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) A processing device and program storage device that executes part of the above processing in accordance with a program, and a dedicated hardware circuit that executes the remaining processing. (c) A 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. There may also be multiple dedicated hardware circuits.

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

"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 that enables the transmission of power between the steering wheel 12 and the steered wheels 44.

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

Claims (5)

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 . 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. 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. 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,
The turning control device according to any one of claims 1 to 3 , wherein the determination process includes a process of determining that the restriction exists when the voltage limiting process is being executed. 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.