JP2006103527A - Electric steering device for vehicle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To make steering stability and steering feeling at the time of backward traveling compatible. <P>SOLUTION: The electric steering device for a vehicle comprises a steering torque sensor 16 detecting steering input of a driver, a steering control device 20 calculating a target current of a steering assist force generating motor 10 on the basis of the steering input detected by at least the steering torque sensor 16, and a drive circuit 21 driving the motor 10 according to the target current calculated by the steering control device 20. A yaw rate correcting portion 34 at the time of backward traveling is provided, which changes steering assist force according to a yaw rate generated on a vehicle at the time of backward traveling of the vehicle. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an electric steering apparatus for a vehicle.

  An electric power steering device is known as a vehicle steering device. In the electric power steering apparatus, a steering shaft coupled to a steering wheel and a steering mechanism that steers the steered wheels are mechanically coupled, and an electric motor for assisting a steering force is linked to the steering mechanism. In general, the drive current of the electric motor is controlled such that the steering assist force increases as the steering input (for example, steering torque) of the driver applied to the steering wheel increases.

By the way, the vehicle generally has different turning responsiveness with respect to the turning angle of the steered wheel when moving forward and backward, so if the control of the steering assist force is the same between forward and backward, the steering stability and steering feeling during backward movement are reduced. It will decline. An electric power steering device that solves this problem is disclosed in Patent Document 1 or Patent Document 2.
The electric power steering apparatus disclosed in Patent Document 1 includes a steering feel setting map for reverse operation, and when the reverse operation is performed, the steering force is heavier than that at the time of forward operation, thereby preventing excessive steering at the time of reverse operation and stabilizing the steering. Improves steering and steering wheel return.

However, steering may be performed with an insufficient posture while confirming the rear or the like when reversing, and operability when reversing at a low vehicle speed is deteriorated only by increasing the steering force when reversing. Since the vehicle behavior is gentle even if the steering is somewhat large in the low vehicle speed range when reversing, it is better to be able to steer with a light steering force. Conversely, in the high vehicle speed region, the influence of the steering on the vehicle behavior is large. There is a need to increase sex.
Therefore, the electric power steering device disclosed in Patent Document 2 improves steering performance as a light steering force setting in the low vehicle speed region during reverse, and improves steering stability as a heavy steering force in the high vehicle speed region. Yes.
JP-A-6-144262 JP-A-10-297517

However, simply increasing the steering force in the high vehicle speed range at the time of reverse does not change the tendency of the vehicle to have a large influence on the vehicle behavior with respect to the steering angle at the time of reverse movement. This easily cuts the vehicle and leads to an unstable vehicle state.
In addition, steering torque is less likely to occur due to the suspension geometry when moving backward than when moving forward, and it is difficult to obtain good straight running stability and steering stability when moving backward only by setting the steering force.
Accordingly, the present invention provides an electric steering device capable of achieving both steering stability and steering feeling during reverse travel.

In order to solve the above-mentioned problem, the invention according to claim 1 includes a steering input detection means (for example, a steering torque sensor 16 in an embodiment described later) for detecting a driver's steering input, and at least the steering input detection means. A target current calculating means (for example, a steering control device 20 in an embodiment to be described later) for calculating a target current of a steering assist force generating motor (for example, a motor 10 in an embodiment to be described later) based on the detected steering input; A yaw rate generated in a vehicle when the vehicle moves backward in an electric steering apparatus for a vehicle comprising driving means for driving the motor according to the target current calculated by the target current calculating means (for example, a drive circuit 21 in an embodiment described later). Steering assist force changing means for changing the steering assist force in accordance with (for example, reverse yaw in the embodiment described later) Characterized in that it comprises a chromatography preparative correcting unit 34).
With this configuration, it is possible to change the steering assist force in a direction that suppresses the generation of the yaw rate during reverse.

The invention according to claim 2 is characterized in that, in the invention according to claim 1, the steering assist force changing means reduces the steering assist force in accordance with an increase in yaw rate.
With this configuration, the steering assist force at the time of reverse can be made smaller than that at the time of forward movement, and when the yaw rate generated at the time of reverse is small, the steering assist force is increased and the yaw rate generated at the time of reverse is large. Sometimes the steering assist force can be reduced. Further, since the degree of reduction of the steering assist force is small when the yaw rate generated at the time of reverse is small, even in the high vehicle speed region, if the generated yaw rate is small, it is possible to obtain a steering assist force that is almost equivalent to the usual.

The invention according to claim 3 is the invention according to claim 2, further comprising a yaw rate region in which no output is made from the steering assist force changing means, and the yaw rate region is set larger as the vehicle speed is lower. And
With this configuration, the yaw rate region (hereinafter referred to as the dead zone) where no output from the steering assist force changing means can be changed according to the vehicle speed, the dead zone is increased when the vehicle speed is low, and the vehicle speed is high. Sometimes the dead zone can be reduced.

The invention according to claim 4 is characterized in that, in the invention according to claim 2 or 3, the output gain of the steering assist force changing means is set smaller as the vehicle speed is lower.
With this configuration, the steering assist force can be increased by reducing the output gain when the vehicle speed is low during reverse, thereby reducing the steering, and when the vehicle speed is high, the steering assist force can be increased by increasing the output gain. The steering can be made heavier and the yaw rate at the time of reverse when the vehicle speed is high can be suppressed.

The invention according to claim 5 is characterized in that, in the invention according to any one of claims 2 to 4, no output is made from the steering assist force changing means when the vehicle speed is a predetermined vehicle speed or less. .
With this configuration, the steering assist force can be prevented from being reduced when the vehicle speed is equal to or lower than the predetermined vehicle speed.

The invention according to claim 6 is based on steering input detection means (for example, a steering torque sensor 16 in an embodiment to be described later) for detecting a driver's steering input, and steering based on at least the steering input detected by the steering input detection means. A target current calculation means (for example, a steering control device 20 in an embodiment described later) for calculating a target current of an auxiliary force generation motor (for example, a motor 10 in an embodiment described later), and a target calculated by the target current calculation means. In an electric steering apparatus for a vehicle comprising driving means for driving the motor in accordance with an electric current (for example, a driving circuit 21 in an embodiment to be described later), the target current calculating means is a target current of the motor when the vehicle moves backward A reverse target current map is calculated, and the reverse target current map indicates that the steering assist force increases as the yaw rate increases. Is fence set, and characterized in that the higher the vehicle speed is high steering assist force is set small.
With this configuration, the steering assist force at the time of reverse can be made smaller than that at the time of forward movement, and the steering assist force is increased when the yaw rate generated at the time of reverse is small, and when the yaw rate generated at the time of reverse is large. The steering assist force can be reduced, and the steering assist force can be increased when the vehicle speed during reverse is low, and the steering assist force can be decreased when the vehicle speed during reverse is high.

According to the first aspect of the present invention, since the steering assist force is controlled to change according to the yaw rate during reverse travel, excessive vehicle cuts can be suppressed during reverse travel, and steering stability during reverse travel can be suppressed. Can be improved.
According to the second aspect of the present invention, the control for reducing the steering assist force is performed in accordance with the increase in the yaw rate during reverse travel, so that excessive vehicle cut-in during reverse travel can be suppressed, and steering during reverse travel is possible. Stability can be improved. Further, since the degree of reduction of the steering assist force is small when the yaw rate generated at the time of reverse is small, even in the high vehicle speed region, if the generated yaw rate is small, it is possible to obtain a steering assist force that is almost equivalent to the usual.

  According to the third aspect of the invention, the dead zone of the yaw rate can be increased when the vehicle speed is low, and the dead zone of the yaw rate can be reduced when the vehicle speed is high. It can be increased to obtain a light steering feeling, and a stable steering feeling can be obtained by reducing the steering assist force from the time when the yaw rate is small at high vehicle speeds that have a large influence on the vehicle behavior. Therefore, it is possible to achieve both steering stability and steering feeling during reverse travel.

  According to the invention of claim 4, when the vehicle speed is low during reverse, the steering assist force can be increased to obtain a light steering feeling, and when the vehicle speed is high, the steering assist force can be reduced to obtain a stable steering feeling. Can do. Therefore, it is possible to achieve both steering stability and steering feeling during reverse travel. In addition, since the yaw rate can be prevented from being generated when the vehicle speed is high, which greatly affects vehicle behavior, excessive cuts and wobbling of the vehicle can be suppressed, and straight running stability and steering stability can be reduced. improves.

  According to the fifth aspect of the present invention, the steering assist force can be prevented from being reduced when the vehicle speed is lower than the predetermined vehicle speed when the vehicle is traveling backward, so that the steering feeling at low speed is lightened and a good steering feeling is achieved. Obtainable.

According to the sixth aspect of the present invention, the steering assist force can be increased when the yaw rate during reverse travel is small, and the steering assist force can be decreased when the yaw rate during reverse travel is large. Incision can be suppressed, and the steering stability during reverse travel can be improved.
Moreover, when the vehicle speed during reverse is low, the steering assist force is increased so that a light steering feeling can be obtained, and when the vehicle speed during reverse is high, the steering auxiliary force is reduced so that a stable steering feeling can be obtained. Can do. Therefore, it is possible to achieve both steering stability and steering feeling during reverse travel. In addition, since the yaw rate can be prevented from being generated when the vehicle speed is high, which greatly affects vehicle behavior, excessive cuts and wobbling of the vehicle can be suppressed, and straight running stability and steering stability can be reduced. improves.

Hereinafter, an embodiment of an electric steering apparatus according to the present invention will be described with reference to the drawings of FIGS. In the following embodiments, the present invention will be described in an aspect applied to an electric power steering apparatus.
First, the configuration of the electric power steering apparatus will be described with reference to FIG. The electric power steering apparatus includes a manual steering force generating mechanism 1, and the manual steering force generating mechanism 1 includes a connecting shaft 5 in which a steering shaft 4 integrally coupled to a steering wheel (operator) 3 has a universal joint. And is connected to the pinion 6 of the rack and pinion mechanism. The pinion 6 meshes with the rack teeth 7a of the rack shaft 7 that can reciprocate in the vehicle width direction, and left and right front wheels 9, 9 as steered wheels are connected to both ends of the rack shaft 7 via tie rods 8, 8. Has been. With this configuration, a normal rack and pinion type steering operation can be performed when the steering wheel 3 is steered, and the direction of the vehicle can be changed by turning the front wheels 9 and 9. The rack shaft 7 and the tie rods 8 and 8 constitute a steering mechanism.

  A motor (steering assist force generating motor) 10 that generates a steering assist force for reducing the steering force generated by the manual steering force generating mechanism 1 is disposed coaxially with the rack shaft 7. The steering assist force supplied by the motor 10 is converted into thrust via a ball screw mechanism 12 provided substantially parallel to the rack shaft 7 and is applied to the rack shaft 7. For this purpose, a driving-side helical gear 11 is integrally provided on the rotor of the motor 10 through which the rack shaft 7 is inserted, and a driven-side helical gear 13 that meshes with the driving-side helical gear 11 is provided at one end of the screw shaft 12 a of the ball screw mechanism 12. The nut 14 of the ball screw mechanism 12 is fixed to the rack 7.

  The steering shaft 4 is provided with a steering speed sensor 15 for detecting the steering speed (angular speed) of the steering shaft 4, and is provided in a steering gear box (not shown) that houses the rack and pinion mechanism (6, 7a). Is provided with a steering torque sensor (steering input detecting means) 16 for detecting a steering torque acting on the pinion 6. The steering speed sensor 15 outputs an electrical signal corresponding to the detected steering speed, and the steering torque sensor 16 outputs an electrical signal corresponding to the detected steering torque to the steering control device (target current calculation means) 20, respectively.

A shift position sensor 17 that detects a shift position of a transmission (not shown) of the vehicle outputs an electrical signal corresponding to the detected shift position to the steering control device 20.
Further, a yaw rate sensor (yaw rate detecting means) 18 for detecting the yaw rate of the vehicle and a vehicle speed sensor 19 for outputting an electric signal corresponding to the vehicle speed are attached at appropriate positions of the vehicle body. The yaw rate sensor 18 outputs an electric signal corresponding to the detected yaw rate, and the vehicle speed sensor 19 outputs an electric signal corresponding to the vehicle speed to the steering control device 20, respectively.

  The steering control device 20 determines a target current to be supplied to the motor 10 based on a control signal obtained by processing the input signals from these sensors 15, 16, 17, 18, and 19, and a drive circuit (drive means). The output torque of the motor 10 is controlled by supplying it to the motor 10 via 21, and the steering assist force in the steering operation is controlled.

Next, current control for the motor 10 in this embodiment will be described with reference to the control block diagram of FIG.
The steering control device 20 includes a base current determination unit 31, an inertia correction unit 32, a damper correction unit 33, and a reverse yaw rate correction unit (steering assist force changing unit) 34.
The base current determination unit 31 determines a base current value corresponding to the steering torque and the vehicle speed with reference to a base current map (not shown) based on the output signals of the steering torque sensor 16 and the vehicle speed sensor 19. Here, the base current map is set so that the base current increases as the steering torque increases, and the base current decreases as the vehicle speed increases.
The inertia correction unit 32 performs inertia mass compensation of the motor 10 for the base current determined by the base current determination unit 31.
The damper correction unit 33 calculates a first correction current based on the steering speed, and subtracts the first correction current from the current after inertia mass compensation.

The reverse yaw rate correction unit 34 calculates the second correction current Im2 based on the yaw rate generated in the vehicle during reverse, and subtracts the second correction current Im2 from the current output from the damper correction unit 33 to the motor 10. Calculate the target current.
This target current is output to the drive circuit 21, and the drive circuit 21 controls the supply current to the motor 10 to be the target current, supplies current to the motor 10, and controls the output torque of the motor 10. .

The calculation of the second correction current Im2 in the reverse yaw rate correction unit 34 will be described in detail. First, the low-pass filter (LPF) 35 performs low-pass filter processing on the output signal of the yaw rate sensor 18 to remove the high-frequency component of the yaw rate, and this signal is used as the yaw rate after LPF processing.
Further, the offset yaw rate amount corresponding to the vehicle speed is calculated with reference to the offset map 36 based on the output signal of the vehicle speed sensor 19. The offset map 36 is set so that the offset yaw rate amount increases when the vehicle speed is low, and the offset yaw rate amount gradually decreases as the vehicle speed increases.

Then, the post-offset yaw rate is obtained by subtracting the offset yaw rate amount from the post-LPF yaw rate. When the result of subtracting the offset yaw rate amount from the yaw rate after LPF processing is negative, the yaw rate after offset is set to “0”.
Based on the post-offset yaw rate, the basic correction current map 37 is calculated with reference to the basic correction current map 37 according to the post-offset yaw rate. The basic correction current map 37 is set so that the basic correction current Imb is “0” when the post-offset yaw rate is “0”, and the basic correction current Imb gradually increases as the post-offset yaw rate increases. .

Further, a vehicle speed ratio (output gain) G corresponding to the vehicle speed is calculated based on the output signal of the vehicle speed sensor 19 with reference to the vehicle speed ratio map 38. The vehicle speed ratio map 38 is set smaller as the vehicle speed is lower. More specifically, the vehicle speed ratio G is set to “0” at the vehicle speed “0”, and the vehicle speed ratio G is set to gradually increase as the vehicle speed increases in a low vehicle speed region lower than the predetermined vehicle speed. The vehicle speed ratio G is set to be constant in a high vehicle speed range equal to or higher than the vehicle speed.
A product obtained by multiplying the basic correction current Imb calculated from the basic correction current map 37 by the vehicle speed ratio G calculated from the vehicle speed ratio map 38 is defined as a second correction current Im2 (Im2 = Imb · G).

  Next, the second correction current Im2 is subtracted from the current output from the damper correction unit 33 to calculate the target current. However, this subtraction process is performed only when the vehicle is moving backward, not when the vehicle is moving forward. The switching of the presence / absence of the subtraction processing is performed by the switching means 39 that opens and closes based on the output signal from the shift position sensor 17, and the switching means 39 is turned on when the shift position is reverse, and is turned off at other positions. Become.

In this way, the reverse yaw rate correction unit 34 calculates the second correction current Im2 based on the yaw rate generated in the vehicle during reverse, and subtracts the second correction current Im2 from the current output from the damper correction unit 33. Since the target current for the motor 10 is calculated, the steering assist force at the time of reverse can be made smaller than that at the time of forward movement.
In particular, in this embodiment, the second correction current Im2 based on the yaw rate at the time of reverse movement is basically set to be small when the yaw rate is small, so that the second correction current Im2 is small when the yaw rate generated at the time of reverse movement is small. Thus, the target current is increased, the steering assist force can be increased, and the steering can be lightened. In other words, since the degree of reduction of the steering assist force is small when the yaw rate generated at the time of reverse is small, even in the high vehicle speed region, if the generated yaw rate is small, the steering assist force can be made substantially equal to that at the normal time.
On the other hand, the second correction current Im2 is basically set to increase as the yaw rate increases. Therefore, when a large yaw rate occurs during reverse, the second correction current Im2 increases, the target current decreases, and steering is performed. The assisting force can be reduced, and the generation of the yaw rate when retreating can be suppressed. Thereby, excessive cutting of the vehicle at the time of reverse travel can be suppressed, and the steering stability at the time of reverse travel is improved.

  Further, the second correction current Im2 is calculated by multiplying the basic correction current Imb by a vehicle speed ratio G that changes according to the magnitude of the vehicle speed, so that the second correction current Im2 can also be calculated according to the vehicle speed even when the yaw rate during reverse is the same. 2 The correction current Im2 can be changed. In particular, in this embodiment, the vehicle speed ratio G is set to be small when the vehicle speed is low and to increase as the vehicle speed increases. Therefore, when the vehicle speed is low, the second correction current Im2 is small and the target current is The steering assist force can be increased and the steering can be lightened. On the other hand, when the vehicle speed is high, the second correction current Im2 becomes large, the target current becomes small, the steering assist force can be reduced, the steering can be made heavy, and the generation of the yaw rate at the time of reverse when the vehicle speed is high is suppressed. can do. As a result, it is possible to suppress excessive cuts and wobbling of the vehicle during reverse travel when the vehicle speed having a large influence on the vehicle behavior is high, and straight running stability and steering stability are improved.

  Further, the basic correction current Imb is calculated based on the offset yaw rate obtained by subtracting the offset yaw rate amount from the LPF processed yaw rate, and when the result obtained by subtracting the offset yaw rate amount from the LPF processed yaw rate is negative The basic correction current Imb is set to “0” when the post-yaw rate is “0” and the post-offset yaw rate is “0”. Therefore, even if the yaw rate is generated during reverse, the reverse yaw rate correction unit 34 2 A yaw rate region (hereinafter referred to as a dead zone) where the correction current Im2 is not output can be provided.

  In particular, in this embodiment, since the yaw rate offset amount is set to decrease as the vehicle speed increases, the dead zone can be increased when the vehicle speed is low, and the dead zone can be reduced as the vehicle speed increases. it can. The fact that the dead zone becomes large when the vehicle speed is low means that when the vehicle speed is low, the second correction current Im2 does not occur unless a large yaw rate is generated during reverse, and therefore the target current increases when the vehicle speed is low and the yaw rate is small. A large steering assist force can be obtained, and the steering can be lightened. On the other hand, when the vehicle speed is high, the dead zone becomes small. When the vehicle speed is high, the second correction current Im2 is generated from the time when the yaw rate generated at the time of reverse is small, and the target current becomes small, so the steering assist force becomes small. Thus, the steering can be made heavy, and the generation of the yaw rate at the time of reverse when the vehicle speed having a large influence on the vehicle behavior is high can be suppressed.

As described above, according to the electric power steering apparatus of this embodiment, the control for reducing the steering assist force according to the increase in the yaw rate during the reverse travel (the control for changing the steering assist force according to the yaw rate) is performed. Excessive vehicle notches during reverse travel can be suppressed, and steering stability during reverse travel can be improved.
In addition, the yaw rate offset amount is set to be large when the vehicle speed is low and small as the vehicle speed increases. Therefore, at low vehicle speeds, the steering assist force can be increased from when the yaw rate is small to obtain a light steering feeling. At a high vehicle speed that has a great influence on the vehicle behavior, the steering assist force can be reduced from the time when the yaw rate is small, and a stable steering feeling can be obtained.
Further, since the vehicle speed ratio G is set to be small when the vehicle speed is low and large as the vehicle speed increases, the steering assist force can be increased at a low vehicle speed to obtain a light steering feeling. At high vehicle speeds that have a large influence, the steering assist force can be reduced to obtain a stable steering feeling.
As a result, it is possible to achieve both steering stability and steering feeling during reverse travel.

  In the vehicle speed ratio map 38 in this embodiment, the vehicle speed ratio G is set to increase gradually as soon as the vehicle speed exceeds “0”. However, the vehicle speed ratio from the vehicle speed “0” to a predetermined vehicle speed value is set. G may be set to “0” and the vehicle speed ratio G may be set to gradually increase when the vehicle speed exceeds the predetermined vehicle speed value. When the vehicle speed ratio G is set in this way, output from the yaw rate correction unit 34 can be prevented from being performed below the predetermined vehicle speed value, and the steering assist force can be prevented from being reduced. As a result, the steering feeling at low speed becomes light and a good steering feeling can be obtained.

  Further, in the above-described embodiment, the yaw rate correction unit 34 for reverse operation is added to the basic control line of the target current for the motor 10 (in this embodiment, the base current determination unit 31, the inertia correction unit 32, and the damper correction unit 33). The steering control device 20 is configured as described above, but instead of adding the reverse yaw rate correction unit 34 in this way, the steering control device 20 uses the forward target current map and the reverse target current map (reverse target current). Current map), and the target current may be calculated by changing the target current map in accordance with forward and backward movement of the vehicle. In this case, the reverse target current map is set such that the steering assist force decreases as the yaw rate increases, and the steering assist force decreases as the vehicle speed increases. Of course, a table may be used instead of the map.

Even when the steering control device is configured in this manner, the steering assist force can be increased when the yaw rate during reverse travel is small, and the steering assist force can be decreased when the yaw rate during reverse travel is large. The vehicle can be prevented from being cut and the steering stability during reverse running can be improved.
Moreover, since the steering assist force can be increased when the vehicle speed during reverse is low, a light steering feeling can be obtained, and when the vehicle speed during reverse is high, the steering assist force can be reduced, so that a stable steering feeling can be obtained. Can be obtained. Therefore, it is possible to achieve both steering stability and steering feeling during reverse travel. In addition, since the yaw rate can be prevented from being generated when the vehicle speed is high, which greatly affects vehicle behavior, excessive cuts and wobbling of the vehicle can be suppressed, and straight running stability and steering stability can be reduced. improves.

[Other Examples]
The present invention is not limited to the embodiment described above.
In the embodiment, the steering assist force is decreased as the yaw rate increases, that is, the steering is performed in the direction in which the yaw rate is increased. For example, although the yaw rate is generated, the yaw rate is decreased by turning back or the like. When steering is performed in the direction, control for adding the steering assist force may be performed.
Further, the electric steering apparatus according to the present invention is not limited to the application to the electric power steering apparatus of the above-described embodiment, but can also be applied to a steering apparatus of a steering-by-wire system.
The steering-by-wire system consists of a steering wheel and other controls that are mechanically separated from the steering mechanism, a reaction force motor that applies a reaction force to the controls, and a steering mechanism. And a steering motor that generates a force for turning the steered wheels.

It is a lineblock diagram of the electric steering device concerning this invention. It is a block diagram of the current control with respect to the motor of the said electric steering device.

Explanation of symbols

10 Motor (steering assist force generation motor)
16 Steering torque sensor (steering input detection means)
20 Steering control device (target current calculation means)
21 Drive circuit (drive means)
34 Backward yaw rate correction unit (steering assist force changing means)

Claims (6)

Steering input detection means for detecting the steering input of the driver;
Target current calculation means for calculating a target current of the steering assist force generating motor based on at least the steering input detected by the steering input detection means;
Drive means for driving the motor in accordance with the target current calculated by the target current calculation means;
In an electric steering apparatus for a vehicle comprising:
An electric steering apparatus for a vehicle, comprising: steering assist force changing means for changing the steering assist force in accordance with a yaw rate generated in the vehicle when the vehicle moves backward.   The electric steering apparatus according to claim 1, wherein the steering assist force changing unit reduces the steering assist force in accordance with an increase in yaw rate.   3. The electric steering apparatus for a vehicle according to claim 2, further comprising a yaw rate region in which no output is output from the steering assist force changing means, wherein the yaw rate region is set to increase as the vehicle speed decreases.   The electric steering apparatus for a vehicle according to claim 2 or 3, wherein the output gain of the steering assist force changing means is set to be smaller as the vehicle speed is lower.   The electric steering apparatus for a vehicle according to any one of claims 2 to 4, wherein when the vehicle speed is equal to or lower than a predetermined vehicle speed, no output is performed from the steering assist force changing means. Steering input detection means for detecting the steering input of the driver;
Target current calculation means for calculating a target current of the steering assist force generating motor based on at least the steering input detected by the steering input detection means;
Drive means for driving the motor in accordance with the target current calculated by the target current calculation means;
In an electric steering apparatus for a vehicle comprising:
The target current calculation means includes a reverse target current map for calculating a target current of the motor at the time of reverse of the vehicle, and the reverse target current map has a smaller steering assist force as the yaw rate increases, and the vehicle speed The electric steering device for a vehicle is characterized in that the steering assist force is set to be smaller as the value is higher.

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