JP2019010966A - Steering control device - Google Patents

Abstract

To provide a steering control device configured to perform a lane keep assist control and capable of maintaining steering feeling of a driver at the time of overheat restriction of a motor of the steering control device.SOLUTION: When an upper limit value Imax of a current supplied to a motor is equal to or lower than a first lane keep assist stop threshold Isth1 at the time of overheat restriction of the motor, a lane keep assist control is stopped by not outputting a correction current command value I2* for returning a vehicle to a target course. When the upper limit value Imax of a current supplied to the motor is higher than the first lane keep assist stop threshold Isth1, the correction current command value I2* for returning the vehicle to the target course is output to perform the lane keep assist control. Therefore, whether the lane keep assist control is performed or stopped at the time of overheat restriction of the motor can be clearly determined. Consequently, at the time of overheat restriction of the motor, the lane keep assist control can be appropriately performed.SELECTED DRAWING: Figure 6

Description

  The present invention relates to a steering control device.

  Conventionally, as described in Patent Document 1, there is known a steering assist device that performs so-called lane keep assist control for returning a vehicle to a target travel line when the vehicle deviates from the target travel line.

  The steering assist device described above is a target current value calculated by adding a steering assist current value calculated based on the vehicle speed and steering torque and a lane keep assist current value calculated based on an image captured by the camera. The assist force is generated from the motor by controlling the motor based on the above.

JP 2017-1626 A JP 2010-260469 A

  In the above steering assist device, there may be a case where the motor cannot output the original output for some reason. For example, as described in Patent Document 2, in order to limit overheating of the motor, it is conceivable to limit the output of the motor by limiting the upper limit of the current value supplied to the motor (assist limitation). When the lane keep assist control is performed in the state where the motor output is limited, the motor may not be able to output the output for the lane keep assist current value by limiting the upper limit of the current value due to the overheat limit. That is, there is a possibility that the lane keep assist control is not properly performed.

  An object of the present invention is to provide a steering control device that can appropriately perform lane keep assist control when overheating of a motor is limited.

  A steering control device that can achieve the above object is premised on a steering control device that controls a motor that generates an assist force in accordance with a steering state and a traveling state of a vehicle. The steering control device calculates a basic current command value that is a basis for calculating a target current command value that is a target value of a current to be supplied to the motor based on a state quantity corresponding to a steering state and a running state of the vehicle. A calculation unit that determines whether or not to perform lane keep assist control that suppresses the vehicle from deviating from the lane when the vehicle is running, and determines that the lane keep assist control is to be performed; When a correction value for correcting the command value is output and it is determined that the lane keep assist control is not performed, a correction value output determination unit that does not output the correction value and an output result from the correction value output determination unit A correction unit that calculates the target current command value by correcting the basic current command value, and overheating of the motor based on the temperature of the motor as the state quantity A state determination unit that calculates a limit value for the current supplied to the motor for a limit, and a current control that sets the limit value to the target current command value when the target current command value is equal to or greater than the limit value And a section. The correction value output determination unit is configured such that the limit value is equal to or less than a specified value set in consideration of a maximum value of the target current command value calculated by correcting the basic current command value with the correction value. It is determined that the lane keep assist control is not performed, and when the limit value is larger than the specified value, it is determined that the lane keep assist control is performed.

  When the motor drive is limited due to motor overheating limitation, if the motor is driven based on the target current command value calculated by correcting the basic current command value with the correction value, the state determination unit calculates The target current command value may be limited to the limit value due to the limit value. In this case, the correction value for the lane keep assist control in the target current command value may not be reflected in the driving of the motor. That is, there is a possibility that the lane keep assist control may not be properly performed.

  In that respect, according to the above configuration, the correction value output determination unit may not apply the correction value of the target current command value to the motor drive when the limit value is equal to or less than the specified value. It is determined that control is not performed, and no correction value is output. On the other hand, when the limit value becomes larger than the specified value, the correction value output determination unit has a surplus power with respect to the limit value, and the correction value portion of the target current command value is reflected in driving the motor. Therefore, it is determined that the lane keep assist control is performed, and a correction value is output. Therefore, it is possible to clearly distinguish between execution and stop of the lane keep assist control when the motor is overheat limited. Therefore, the lane keep assist control can be appropriately performed when the motor is overheat limited.

  In the above steering control device, the specified value is changed according to the vehicle speed as the state quantity, and the specified value is preferably smaller as the vehicle speed becomes faster.

  In general, as the vehicle speed increases, the assist force generated by the motor decreases, and the basic current command value for driving the motor and the correction value for performing lane keep assist control also decrease. That is, comparing the case where the vehicle speed is low and the case where the vehicle speed is high, the motor output is more powerful when the vehicle speed is high. For this reason, when the specified value is constant with respect to the vehicle speed and the vehicle speed is high, the limit value becomes equal to or less than the specified value regardless of whether the motor output has sufficient power, and the correction value output determination unit sets the correction value. May be stopped, and the lane keep assist control may be stopped. That is, the timing at which the lane keep assist control stops is almost the same between the case where the vehicle speed V is the medium vehicle speed state and the case where the vehicle speed V is the high vehicle speed state.

  In that respect, according to the above configuration, since the specified value is set to be smaller as the vehicle speed increases, the time until the limit value becomes equal to or less than the specified value when the vehicle output is fast and the motor output has sufficient capacity. By increasing the length, the lane keep assist control can be performed for a longer time even when the motor is overheat limited. Therefore, the frequency at which the lane keep assist control stops when the motor is overheat limited can be reduced.

  It is preferable that a correction value calculation unit that calculates the correction value is provided, and the correction value calculation unit calculates the correction value based on a command from a higher-level control unit that is an upper level of the steering control device.

  According to the steering control device of the present invention, the lane keep assist control can be appropriately performed when the overheating of the motor is limited.

1 is a schematic diagram of an electric power steering device in an embodiment. FIG. The functional block diagram of EPSECU in 1st Embodiment. The control flowchart which showed the process sequence of the lane keep assist control of the correction value output determination part in 1st Embodiment. Schematic which shows the behavior of the vehicle in the case of implementing lane keep assist control in embodiment. The figure which showed the change of the lane keep assist stop threshold with respect to the change of the vehicle speed in 2nd Embodiment. The timing chart figure in which the lane keep assist control stops when the motor of the first embodiment is overheat limited. The timing chart figure in which the lane keep assist control stops when the motor of the second embodiment is overheat limited.

<First Embodiment>
Hereinafter, a first embodiment in which the steering control device is embodied as a control device of a column assist type electric power steering device (hereinafter referred to as “EPS”) will be described.

  As shown in FIG. 1, the EPS 10 includes a steering mechanism 20, an assist torque applying mechanism 30, a control device 50, and a lane keep ECU 60. The lane keep ECU 60 is an upper ECU for the control device 50, and the control device 50 is a lower ECU for the lane keep ECU 60. The lane keep ECU 60 is an example of a host control unit.

  The steering mechanism 20 turns the steered wheels 26 and 26 based on the operation of the driver's steering wheel 21. The steering mechanism 20 includes a steering shaft 22 that rotates integrally with the steering wheel 21 and a rack shaft 23. The steering shaft 22 includes a column shaft 22a connected to the steering wheel 21, an intermediate shaft 22b connected to the lower end portion of the column shaft 22a, and a pinion shaft 22c connected to the lower end portion of the intermediate shaft 22b. doing. A lower end portion of the pinion shaft 22 c is connected to the rack shaft 23 via a rack and pinion mechanism 24. The rack and pinion mechanism 24 is formed by meshing the pinion teeth provided at the lower end portion of the pinion shaft 22c with the rack teeth on the rack shaft 23. Therefore, the rotational motion of the steering shaft 22 is converted into a reciprocating linear motion in the axial direction of the rack shaft 23 (the left-right direction in FIG. 1) via the rack and pinion mechanism 24. The reciprocating linear motion is transmitted to the left and right steered wheels 26 and 26 via tie rods 25 and 25 respectively connected to both ends of the rack shaft 23, whereby the steered angles of the steered wheels 26 and 26 are changed. .

  The assist torque applying mechanism 30 includes a speed reduction mechanism 32 connected to the column shaft 22a and a motor 31 having a rotating shaft 31a. The rotational force of the rotating shaft 31a of the motor 31 is transmitted to the column shaft 22a via the speed reduction mechanism 32. The motor 31 is used as a source of assist force that assists the operation of the steering wheel 21. As the motor 31, for example, a three-phase brushless motor is employed.

  The lane keep ECU 60 instructs the control device 50 to execute lane keep assist control that causes the vehicle to travel without departing from the lane. The lane keep ECU 60 sets a target course of the vehicle based on the image data captured by the in-vehicle camera 72, and calculates a lane keep assist command value LK * for causing the vehicle to travel along the target course.

  As shown in FIG. 4, the lane keep ECU 60 recognizes a pair of lane boundary lines (white lines) L1 and Lr that form a lane based on image data taken by the in-vehicle camera 72, and recognizes a lane in which the vehicle is traveling. To do. The lane keep ECU 60 sets a target course Ls as a lane reference line in the lane. The target course Ls is set at the center of the lane width, for example. The lane keep ECU 60 instructs the controller 50 to return the vehicle course to the target course Ls (arrow in FIG. 4) when the vehicle is displaced from the target course Ls (arrow in FIG. 4). LK * is calculated. The vehicle is less likely to be displaced from the target route Ls as the vehicle speed V increases. For this reason, the lane keep assist command value LK * decreases as the vehicle speed V increases.

  The control device 50 controls the driving of the motor 31 based on the lane keep assist command value LK * and outputs from various sensors. The various sensors are provided for detecting a state quantity corresponding to the traveling state or steering state of the vehicle. Examples of the various sensors include a vehicle speed sensor 70, a torque sensor 71, and a temperature sensor 73. The vehicle speed sensor 70 detects a vehicle speed V that is the traveling speed of the vehicle. The torque sensor 71 is provided between the steering wheel 21 and the assist torque applying mechanism 30 in the column shaft 22a. The torque sensor 71 periodically detects the steering torque Th generated in the steering shaft 22 by the driver's operation of the steering wheel 21. The temperature sensor 73 is attached to the motor 31. The temperature sensor 73 detects the internal temperature Tmp of the motor 31.

  As shown in FIG. 2, the control device 50 includes an assist torque calculation unit 51 as a basic current command value calculation unit, a lane keep assist torque calculation unit 52 as a correction value calculation unit, a current limiting unit 53 as a state determination unit, Correction value output determination unit 54, adder 55 as a correction unit, current feedback control unit (hereinafter referred to as “current F / B control unit”) 56 as a current control unit, drive signal generation unit 57, drive circuit unit 58 , And a current sensor 59.

The current sensor 59 detects the actual current Im supplied to the motor 31.
The assist torque calculator 51 calculates a basic current command value I1 * for driving the motor 31 based on the steering torque Th and the vehicle speed V. The assist torque calculation unit 51 includes a map showing the relationship between the steering torque Th and the basic current command value I1 * according to the vehicle speed V. The assist torque calculator 51 calculates a larger basic current command value I1 * as the absolute value of the steering torque Th increases and the vehicle speed V decreases.

  The lane keep assist torque calculation unit 52 calculates a corrected current command value I2 * as a correction value for correcting the basic current command value I1 * based on the lane keep assist command value LK *. As described above, the lane keep assist command value LK * decreases as the vehicle speed V increases, so the correction current command value I2 * decreases as the vehicle speed V increases.

  The current limiting unit 53 includes a map that defines the relationship between the upper limit value Imax of the actual current Im supplied to the motor 31 and the internal temperature Tmp of the motor 31. The current limiter 53 receives the internal temperature Tmp detected by the temperature sensor 73 as an input, and calculates a map of the upper limit value Imax of the actual current Im supplied to the motor 31 at a predetermined period. The map has a threshold value Tth for the internal temperature Tmp. This threshold value Tth is set as a timing at which the upper limit value Imax of the actual current Im supplied to the motor 31 starts to be limited from the viewpoint of suppressing overheating of the motor 31. When the internal temperature Tmp exceeds the set threshold value Tth, the current limiting unit 53 limits the upper limit value Imax of the actual current Im supplied to the motor 31 to gradually decrease as the internal temperature Tmp increases. The motor 31 may be overheated when, for example, the vehicle is traveling on a winding road such as a mountain road. It can be considered that the driver is likely to be in an overheated state because the motor 31 is overloaded by frequently repeating steering of the steering wheel 21. The motor 31 is overheated particularly when the vehicle speed V is in the middle vehicle speed state. The medium vehicle speed state is a vehicle speed V that is frequently used when the vehicle travels on a lane. The upper limit value Imax is an example of a limit value.

  Based on the vehicle speed V detected by the vehicle speed sensor 70 and the upper limit value Imax calculated by the current limiting unit 53, the correction value output determination unit 54 calculates the corrected current command value I2 * calculated by the lane keep assist torque calculating unit 52. It is determined whether or not to output to the adder 55. That is, the correction value output determination unit 54 determines whether or not to perform lane keep assist control of the vehicle. When it is determined that the lane keep assist control is to be performed, the correction value output determination unit 54 outputs the correction current command value I2 * to the adder 55. When determining that the lane keep assist control is not performed, the correction value output determination unit 54 outputs “0” to the adder 55 (does not output the correction current command value I2 *).

Next, the correction value output determination unit 54 will be described in detail.
The correction value output determination unit 54 determines whether or not the vehicle speed V is equal to or higher than a predetermined value. The predetermined value is set from the viewpoint of determining whether or not the control device 50 has reached the vehicle speed V at which the lane keep assist control is performed. Further, the predetermined value can be appropriately changed according to vehicle specifications. The correction value output determination unit 54 does not output the correction current command value I2 * when determining that the vehicle speed V is not equal to or higher than the predetermined value. When determining that the vehicle speed V is equal to or higher than the predetermined value, the correction value output determination unit 54 determines whether or not the upper limit value Imax calculated by the current limiting unit 53 is greater than the first lane keep assist stop threshold Isth1. When the correction value output determination unit 54 determines that the upper limit value Imax is greater than the first lane keep assist stop threshold Isth1, the correction value output determination unit 54 outputs a correction current command value I2 *. The correction value output determination unit 54 does not output the correction current command value I2 * when it is determined that the upper limit value Imax is equal to or less than the first lane keep assist stop threshold Isth1. The first lane keep assist stop threshold Isth1 is an example of a specified value.

Here, a method of setting the first lane keep assist stop threshold value Isth1 will be described.
The first lane keep assist stop threshold Isth1 is set in view of whether or not the lane keep assist control can be appropriately performed in a state where the motor 31 is overheat limited. Specifically, when the first lane keep assist stop threshold Isth1 is set, the vehicle 31 travels on a mountain road or the like where the motor 31 is likely to be overheated for a predetermined time. While the vehicle is running, the actual current Im supplied to the motor 31 is experimentally detected, and the maximum value of the actual current Im supplied to the motor 31 when the vehicle runs on a mountain road or the like is verified. This verification is performed a plurality of times, and the first lane keep assist stop threshold value Isth1 is set in consideration of the maximum value for a plurality of times. Note that verifying the maximum value of the actual current Im is synonymous with verifying the maximum value of the target current command value I *, which is a target value of current supplied to the motor 31 described later.

The functional significance of setting the first lane keep assist stop threshold Isth1 will be described.
When the upper limit value Imax when the overheating of the motor 31 is limited is less than or equal to the first lane keep assist stop threshold value Isth1, the motor 31 may not be able to sufficiently output the correction current command value I2 * for the lane keep assist control. There is. If the motor 31 cannot output the correction current command value I2 * sufficiently, the vehicle may not return to the lane target course Ls, that is, the lane keep assist control may not be appropriately executed.

  On the other hand, when the upper limit value Imax when the overheating of the motor 31 is limited becomes larger than the first lane keep assist stop threshold value Isth1, the motor 31 outputs the correction current command value I2 * for the lane keep assist control. Since there is remaining power up to the upper limit value Imax, the lane keep assist control is appropriately performed.

  Accordingly, when the upper limit value Imax is equal to or less than the first lane keep assist stop threshold value Isth1, the lane keep assist control is stopped by not outputting the correction current command value I2 *, and the upper limit value Imax is set to the first lane keep assist stop threshold value Isth1. When it becomes larger, it is preferable to output the corrected current command value I2 * and execute the lane keep assist control.

  The adder 55 adds the basic current command value I1 * calculated by the assist torque calculation unit 51 and the correction value (correction current command value I2 * or “0”) output from the correction value output determination unit 54. Thus, the target current command value I *, which is the target value of the current supplied to the motor 31, is calculated. Note that the target current command value I * considered in the setting method of the first lane keep assist stop threshold value Isth1 is obtained by adding the correction current command value I2 * to the basic current command value I1 *.

  Current F / B control unit 56 takes in target current command value I *, upper limit value Imax, and actual current Im. Current F / B control unit 56 compares target current command value I * and upper limit value Imax. That is, the current F / B control unit 56 compares the target current command value I * from the viewpoint of preventing the target current command value I * from exceeding the upper limit value Imax set from the viewpoint of limiting overheating of the motor 31. If the target current command value I * is equal to or higher than the upper limit value Imax as a result of comparing the two, the current F / B control unit 56 sets the target value of the current supplied to the motor 31 to the upper limit value Imax. If the target current command value I * is less than the upper limit value Imax, the current F / B control unit 56 uses the target current command value I * supplied from the adder 55 as the target value of the current supplied to the motor 31 as it is. use. The current F / B control unit 56 performs feedback control so that the actual current Im detected by the current sensor 59 matches the target value of the current supplied to the motor 31 (target current command value I * or upper limit value Imax). Run. The current F / B control unit 56 calculates the voltage command value V * so as to eliminate the difference between the target value of the current supplied to the motor 31 and the actual current Im.

  The drive signal generation unit 57 calculates a motor control signal Sm for driving the drive circuit unit 58 based on the voltage command value V * calculated by the current F / B control unit 56. The drive circuit unit 58 is a three-phase inverter, and generates three-phase AC power by operating based on the motor control signal Sm. The motor 31 is rotated by being supplied with power through the drive circuit unit 58. The rotational force of the motor 31 is transmitted as assist torque to the column shaft 22a, so that the driver's operation of the steering wheel 21 is assisted.

Next, a processing procedure of lane keep assist control executed by the correction value output determination unit 54 will be described.
As shown in FIG. 3, the correction value output determination unit 54 takes in the vehicle speed V and the upper limit value Imax (step S101), and determines whether the vehicle speed V is equal to or higher than a predetermined value (step S102). When it is determined that the vehicle speed V is not equal to or higher than the predetermined value, the correction value output determination unit 54 does not output the correction current command value I2 * to the adder 55 (step S103). When it is determined that the vehicle speed V is equal to or higher than the predetermined value, the correction value output determination unit 54 determines whether or not the upper limit value Imax is greater than the first lane keep assist stop threshold Isth1 (step S104). When the correction value output determination unit 54 determines that the upper limit value Imax is not greater than the first lane keep assist stop threshold Isth1, the process proceeds to step S103. When determining that the upper limit value Imax is greater than the first lane keep assist stop threshold value Isth1, the correction value output determination unit 54 outputs the correction current command value I2 * to the adder 55 (step S105).

As described above in detail, according to the present embodiment, the following effects can be obtained.
(1) The correction value output determination unit 54 does not output the correction current command value I2 * to the adder 55 when the upper limit value Imax is equal to or less than the first lane keep assist stop threshold value Isth1. This is because the correction current command value I2 * of the target current command value I * may not be reflected in the driving of the motor 31. On the other hand, the correction value output determination unit 54 outputs the correction current command value I2 * to the adder 55 when the upper limit value Imax is larger than the first lane keep assist stop threshold value Isth1. This is because the target current command value I * has a surplus with respect to the upper limit value Imax, and the correction current command value I2 * portion of the target current command value I * is reflected in the driving of the motor 31. Therefore, when the overheating of the motor 31 is limited, it is possible to clearly distinguish between execution and stop of the lane keep assist control. Accordingly, the lane keeping control can be appropriately performed when the motor 31 is overheat limited.

<Second Embodiment>
Hereinafter, a second embodiment of the steering control device will be described. The main difference from the first embodiment is that the lane keep assist stop threshold changes according to the vehicle speed. In addition, about the structure similar to 1st Embodiment, the same code | symbol is attached | subjected and detailed description is omitted.

  As shown in FIG. 5, the lane keep assist stop threshold value Isth varies between the second lane keep assist stop threshold value Isth2 and the first lane keep assist stop threshold value Isth1 according to the vehicle speed V. The lane keep assist stop threshold value Isth decreases as the vehicle speed V increases. When the lane keep assist stop threshold Isth is equal to or less than the second lane keep assist stop threshold Isth2, the second lane keep assist stop threshold Isth2 is set to be constant regardless of the vehicle speed V. The first lane keep assist stop threshold value Isth1 is the same as that in the first embodiment.

Here, the setting of the second lane keep assist stop threshold value Isth2 will be described.
The second lane keep assist stop threshold Isth2 is set from the viewpoint of whether or not the lane keep assist control can be appropriately performed in a state where the motor 31 is overheat limited when the vehicle speed V is in a high speed state. Specifically, when the second lane keep assist stop threshold value Isth2 is set, the motor 31 is caused to travel on a mountain road or the like where the motor 31 is likely to be overheated. Let it run. When the vehicle travels, the current supplied to the motor 31 is experimentally detected, and when the motor 31 is overheat limited, the maximum value of the current supplied to the motor 31 when the vehicle travels on a highway or the like is verified. This verification is performed a plurality of times, and the second lane keep assist stop threshold value Isth2 is set in consideration of the maximum value for a plurality of times.

According to the present embodiment, the following effects can be obtained.
(2) Generally, as the vehicle speed V increases, the assist force that the motor 31 needs to generate decreases, and the basic current command value I1 * for driving the motor 31 and the correction for performing the lane keep assist control. The current command value I2 * is also reduced. That is, comparing the case where the vehicle speed V is slower and the case where the vehicle speed V is faster, the output of the motor 31 has more power when the vehicle speed V is higher.

  As shown in FIG. 6, in the first embodiment, the first lane keep assist stop threshold Isth1 is constant with respect to the vehicle speed V. When the vehicle speed V is a high vehicle speed state, the upper limit value Imax is equal to or lower than the first lane keep assist stop threshold value Isth1 regardless of whether the output of the motor 31 has sufficient power, and the correction value output determination unit 54 There is a risk of stopping the output of the command value I2 *. That is, the timing at which the lane keep assist control stops is almost the same between the case where the vehicle speed V is the medium vehicle speed state and the case where the vehicle speed V is the high vehicle speed state. As described above, the motor 31 is frequently overheated when the vehicle speed V is in the middle vehicle speed state. Comparing the case where the vehicle speed V is the medium vehicle speed state and the case where the vehicle speed V is the high vehicle speed state, the internal temperature Tmp of the motor 31 is more likely to rise when the vehicle speed V is the medium vehicle speed state. Therefore, as shown in FIG. 6, the rate of change in which upper limit value Imax decreases with time tends to be greater in the middle vehicle speed state than in the case where vehicle speed V is in the high speed state.

  As shown in FIG. 7, according to the control device 50 of the present embodiment, the lane keep assist stop threshold Isth is set smaller as the vehicle speed V increases. When the vehicle speed V increases and the output of the motor 31 has a surplus capacity, the time until the upper limit value Imax becomes equal to or less than the lane keep assist stop threshold value Isth is made longer, even when the overheating of the motor 31 is limited. Lane keep assist control can be implemented for a long time. Therefore, when the motor 31 is overheat limited, the frequency at which the lane keep assist control stops can be reduced.

Note that the present embodiment may be modified as follows within a technically consistent range.
In the first and second embodiments, the column assist type electric power steering device has been specifically described. For example, the rack shaft 23 is configured to assist the rack shaft 23 using a motor 31 and a speed reduction mechanism. The present invention may also be applied to a steering device such as a direct assist type.

  In the first and second embodiments, the correction current command value I2 * is calculated by the lane keep assist torque calculation unit 52 based on the lane keep assist command value LK * of the lane keep ECU 60, but is not limited thereto. . For example, the lane keep assist torque calculator 52 may be omitted, and the lane keep ECU 60 may calculate the corrected current command value I2 *.

DESCRIPTION OF SYMBOLS 31 ... Motor, 51 ... Assist torque calculating part, 53 ... Current limiting part, 54 ... Correction value output determination part, Th ... Steering torque, V ... Vehicle speed, Tmp ... Internal temperature, Im ... Actual current, I1 * ... Basic current command Value, I2 * ... corrected current command value, I * ... target current command value, Imax ... upper limit value, Isth ... lane keep assist stop threshold, Isth1 ... first lane keep assist stop threshold, Isth2 ... second lane keep assist stop threshold , Ls ... Target course.

Claims (3)

In a steering control device that controls a motor that generates an assist force according to a steering state and a traveling state of a vehicle,
A basic current command value calculation unit that calculates a basic current command value that is a calculation base of a target current command value that is a target value of a current supplied to the motor based on a state quantity according to a steering state and a running state of the vehicle;
It is determined whether or not to perform lane keep assist control that suppresses the vehicle from deviating from the lane when the vehicle travels. When it is determined that the lane keep assist control is to be performed, the basic current command value is corrected. A correction value output determination unit that does not output the correction value when it is determined that the lane keep assist control is not performed.
A correction unit that calculates the target current command value by correcting the basic current command value according to an output result from the correction value output determination unit;
A state determination unit that calculates a limit value for the current supplied to the motor for limiting overheating of the motor based on the temperature of the motor as the state quantity;
A current control unit that sets the limit value to the target current command value when the target current command value is equal to or greater than the limit value;
The correction value output determination unit is configured such that the limit value is equal to or less than a specified value set in consideration of a maximum value of the target current command value calculated by correcting the basic current command value with the correction value. A steering control device that determines that the lane keep assist control is not performed and determines that the lane keep assist control is performed when the limit value is larger than the specified value. The specified value is changed according to the vehicle speed as the state quantity,
The steering control device according to claim 1, wherein the specified value becomes smaller as the vehicle speed increases. A correction value calculation unit for calculating the correction value;
The steering control device according to claim 1, wherein the correction value calculation unit calculates the correction value based on a command from a higher-level control unit that is a higher level of the steering control device.