JP2001058577A - Steering system for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a vehicle steering system that can realize a fine helm maneuver responding to the operation of operational measure. SOLUTION: A helm control part 50 sets a voltage command value based input signals from a vehicle speed sensor 60, steering position sensor 15 and a rotary encoder 34, and then controls the output of a helm motor 40 by giving a control signal to a driving circuit 42 in response to a settled voltage command value D. As for the voltage command value, first, a target steering position is decided based on the handle amount of a steering wheel 10 that is detected by the rotary encoder 34, and the voltage command value is set corresponding to the sum of the two values; one is obtained by multiplying the first factor by the deviation between target steering position and the steering position of wheel W that is detected by the steering position sensor 15, and the other is obtained by multiplying the handling speed of the steering wheel 20 by the second factor.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a vehicle steering system in which operating means is provided mechanically separated from steering wheels.

[0002]

2. Description of the Related Art A steering wheel and a steering wheel are mechanically separated from each other to detect an operation direction and an operation amount of the steering wheel. On the basis of the detection result, a driving force from a steering actuator such as an electric motor is used. 2. Description of the Related Art There has been proposed a vehicle steering system in which wheels are steered. The vehicle steering system having such a configuration is provided with a steering control unit including, for example, a microprocessor. The steering control unit sets a target turning position of the wheel based on the operation direction and the operation amount of the steering wheel, and the actual turning position of the wheel (actual turning position of the wheel) approaches the target turning position. The steering actuator is controlled as follows.

[0003]

In the control of the steering actuator by the steering control section, it is preferable to turn the wheels without delaying the operation of the steering wheel. That is, as shown in FIG.
When the steering wheel 1 is operated in the + θ direction, the steering shaft 3 for turning the wheel 2 is moved in the A direction,
When the steering wheel 1 is operated in the -θ direction, it is preferable to move the steering shaft 3 in the direction B opposite to the direction A.

However, for example, when the steering wheel 1 is operated in the + θ direction and then continuously turned back in the −θ direction, that is, when the so-called turning operation is performed quickly, the operation of the steering wheel is not affected by the operation of the steering wheel. There is a possibility that a delay (response delay) may occur in turning. For example, as shown in FIG. 5A, when the turning operation of the steering wheel 1 from the + θ direction to the −θ direction is performed quickly, if the driving force of the steering actuator is small, the steering wheel 1 moves in the −θ direction. There is a possibility that the actual turning position of the wheel 2 may not have reached the target turning position before the turning operation by the time t when the operation is started. At this time,
Since the actual turning position of the wheel 2 has not reached the target turning position, the steering actuator is controlled to move the steering shaft 3 in the A direction even though the steering wheel 1 is operated in the -θ direction. You. As a result, FIG.
As shown in (1), there is a response delay of time T1 from the start of the operation of the steering wheel 1 in the -θ direction until the actual turning position of the wheel 2 coincides with the target turning position.

After the actual turning position of the wheel 2 coincides with the target turning position, a control signal is output to the steering actuator to move the steering shaft 3 in the B direction. However, the steering shaft 3 does not immediately move in the B direction due to the inertial force acting on the steering actuator and the steering shaft 3 in the A direction. Thereby, as shown in FIG. 5B, a response delay of time T2 occurs after the actual turning position of the wheel 2 matches the target turning position. As described above, a response delay of time (T1 + T2) occurs from the start of the operation of the steering wheel 1 in the -θ direction to the start of the movement of the steering shaft 3 in the B direction. Despite being operated in the θ direction, a situation occurs in which the wheels 2 are further steered in a direction opposite to the desired steering direction.

SUMMARY OF THE INVENTION It is an object of the present invention to solve the above-mentioned technical problems and to provide a steering apparatus for a vehicle which can realize a good steering operation in response to an operation of an operation means.

[0007]

According to the first aspect of the present invention, there is provided a steering actuator for generating a torque for turning a steering wheel, and a steering actuator for generating a torque. Mechanically separated
Operating means operated to input the turning direction of the wheel; operating speed detecting means for detecting an operating speed when the operating means is operated; and operating speed detected by the operating speed detecting means. And a drive control means for controlling the drive of the steering actuator so as to generate a torque in the turning direction inputted from the operation means based on the operation means.

According to the present invention, the steering actuator is controlled so as to generate a torque in the steering direction input from the operation means based on the operation speed detected by the operation speed detection means. Accordingly, if the torque output from the steering actuator is increased in accordance with the operation speed of the operation means, a response delay caused when the operation means is quickly operated (the turning of the wheel in response to the operation of the operation means). Delay) can be reduced, and a steering operation satisfactorily responding to the operation of the operation means can be realized.

The invention according to claim 2 further includes a turning position detecting means for detecting a turning position of the wheel, and an operation amount detecting means for detecting an operation amount of the operating means. The steering actuator is an electric motor, and the drive control means determines a target turning position based on the operation amount of the operation means detected by the operation amount detection means, and detects the target turning position and the turning position detection. A value obtained by multiplying a deviation from the turning position of the wheel detected by the means by a first coefficient, and a value obtained by multiplying the operation speed detected by the operation speed detecting means by a second coefficient. 2. The vehicle steering system according to claim 1, wherein an applied voltage to said electric motor is set in accordance with a sum of the following.

According to the present invention, the voltage applied to the electric motor as the steering actuator determines the target turning position based on the operation amount of the operating means detected by the operation amount detecting means. A value obtained by multiplying a deviation from the steered position of the wheel detected by the steered position detecting means by a first coefficient, and a value obtained by multiplying the operating speed detected by the operating speed detecting means by a second coefficient. It is set according to the sum with the value. For example, in a conventional vehicle steering system in which operating means is mechanically separated from wheels, a deviation between a target steered position and a steered position of a wheel is multiplied by a value obtained by multiplying the deviation by a first coefficient. The voltage applied to the electric motor is set. In this conventional control, if the operation of the operating means is fast, the change in the steered position of the wheel cannot follow the change in the target steered position, and the change in the steered position of the wheel is later than the change in the target steered position. Stand up. Therefore, after turning the wheel in one direction, if the switching operation of the operating means is quickly performed to steer in the other direction opposite to this one direction, even if the operating direction of the operating means is changed. Regardless, the voltage applied to the electric motor may be set to a value that causes the wheels to turn in one direction.

On the other hand, according to the second aspect of the present invention, the value obtained by multiplying the deviation between the target steered position and the steered position of the wheel detected by the steered position detecting means by a first coefficient is obtained. The voltage applied to the electric motor is set in accordance with the sum of the operation speed detected by the operation speed detection means and a value obtained by multiplying the second coefficient by the second coefficient. Since the value obtained by multiplying the operation speed by the second coefficient has a sign corresponding to the operation direction of the operation means, the change in the steered position of the wheel is delayed with respect to the change in the target steered position. Is applied, the voltage applied to the electric motor is set to such a value as to turn the wheel in the other direction immediately after the switching operation. Therefore, it is possible to prevent the wheels from being steered in the one direction even though the operating means is operated in the direction to steer the wheels in the other direction. Therefore, it is possible to reduce the delay of the turning of the wheels with respect to the operation of the operation unit, and to realize a steering operation satisfactorily responding to the operation of the operation unit.

Further, the value of the voltage applied to the electric motor for turning the wheel in the other direction is set to a larger value as the operating speed of the operating means is increased. Steering operation can be realized. According to a third aspect of the present invention, there is provided a steering actuator for generating a driving force for turning a steering wheel, and a steering actuator mechanically separated from the wheel, and operated to input a turning direction of the wheel. Operating means to be turned, and a turning operation for detecting that the turning operation of the operating means has been performed to steer the wheel in one direction and then to turn the wheel in the other direction opposite to the one direction. Detecting means, and drive control means for driving and controlling the steering actuator so that the torque in the other direction is immediately generated when the turning operation is detected by the turning operation detecting means. It is a vehicle steering device characterized by the following.

According to the present invention, after the wheel is steered in one direction, when the operating means is turned back to steer in the other direction opposite to the one direction, the steering actuator is turned in the other direction. Immediate torque is generated. As a result, a response delay occurring at the time of the switching operation can be reduced, and a good steering operation in response to the operation of the operation means can be realized. The invention according to claim 4 further includes a turning position detecting means for detecting a turning position of the wheel, and an operation amount detecting means for detecting an operation amount of the operating means. An electric motor, wherein the drive control means determines a target turning position based on an operation amount of the operation means detected by the operation amount detection means, and sets the target turning position, the target turning position, and the target turning position. A voltage applied to the electric motor is set based on a value obtained by multiplying a deviation from a virtual turning position determined based on the turning position of the wheel detected by the position detecting means by a predetermined coefficient. The vehicle steering system according to claim 3, wherein:

According to the present invention, by setting the virtual steering position near the target steering position, the electric motor as the steering actuator is generated so that the torque in the other direction is generated immediately after the turning operation. Can be set. The virtual turning position is a turning position of the wheel detected by the turning position detecting means at the same time as a target turning position determined at the time when the turning operation is detected by the turning operation detecting means. Is preferably determined by multiplying the ratio of the wheel by the steered position of the wheel detected by the steered position detecting means.

The drive control means determines a target steering position based on the operation amount of the operation means detected by the operation amount detection means while the turning operation of the operation means is being performed. Based on a value obtained by multiplying a deviation between a target steered position, a target steered position and a virtual steered position determined based on the steered position of the wheel detected by the steered position detecting means by a predetermined coefficient, It is preferable to set a voltage applied to the electric motor.

The period during which the switching operation of the operating means is being performed may be a period from the start of the switching operation of the operating means to the end of the switching operation, or It may be a period during which operation is performed in a direction to return to the neutral position from a state where the operation is performed to one side from the neutral position. Note that the neutral position of the operation means refers to the position of the operation means in a straight traveling state of the vehicle.

[0017]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. FIG. 1 is a conceptual diagram showing a configuration of a vehicle steering system according to one embodiment of the present invention. The vehicle steering system includes a steering mechanism 10 for causing a pair of steering wheels (usually front wheels) W to perform a steering operation, a steering wheel 20 mechanically separated from the steering mechanism 10, and A reaction force actuator 30 for applying a reaction force to the steering wheel 20 is provided.

The steering mechanism 10 includes a steering shaft 11 extending in the left-right direction of the vehicle body, and knuckles connected to both ends of the steering shaft 11 through tie rods 12, 12 to support wheels W, W. Arms 13 and 13 are provided. The steering shaft 11 is supported by the housing 14 so as to be movable in the axial direction, and a steering motor 40 as a steering actuator is coaxially incorporated in a middle portion thereof. When the steering motor 40 is driven, the rotation of the steering motor 40 is converted into movement of the steering shaft 11 by a movement conversion mechanism including a ball screw or the like, and the movement of the steering shaft 11 achieves steering of the wheels W and W. .

The reaction force actuator 30 is constituted by an electric motor (for example, a three-phase brushless motor) having a rotating shaft 31 protruding from both sides, and a casing thereof is fixed to an appropriate position on the vehicle body. The steering wheel 20 is coaxially fixed to a protruding end on one end side of the rotating shaft 31. On the other hand, the protruding end on the other end side of the rotating shaft 31 is connected to an appropriate position of the vehicle body by a torsion screw 32 having a predetermined elasticity. If twisted, the steering wheel 20
When the rotation operation is stopped, the rotation shaft 31 is rotated by its elasticity to return the steering wheel 20 to a predetermined neutral position. Thereby, the wheels W,
With the return operation of W in the straight traveling direction, the steering wheel 20 can be returned to the neutral position.

The reaction force actuator 30 and the steering motor 40 include a steering control unit 50 including a microprocessor and the like.
Is controlled by the More specifically, the reaction force actuator 30 is provided with a torque sensor 33 for detecting an operation torque input from the steering wheel 20 and a rotary encoder 34 for detecting an operation position of the steering wheel 20. These detection signals are input to the steering control unit 50.

The steering control unit 50 creates a control signal based on the detection signals of the torque sensor 33 and the rotary encoder 34, and supplies the created control signal to the drive circuit 35. As a result, a current corresponding to the control signal is supplied from the drive circuit 35 to the reaction force actuator 30. As a result, an appropriate reaction force in the direction opposite to the operation direction of the steering wheel 20 is applied from the reaction force actuator 30 to the steering wheel 20. Granted. Therefore, when rotating the steering wheel 20, it is necessary to apply an operation torque against the reaction force generated by the reaction force actuator 30.

On the other hand, a rotary encoder 41 for detecting the rotational position of the steering motor 40 is disposed in association with the steering motor 40.
Is input to the steering control unit 50. The steering shaft 11 is related to the steering shaft 11.
A turning position sensor 15 for detecting the axial position (actual turning position) of the vehicle is provided. This steering position sensor 15
Is also input to the steering control unit 50. Further, the steering control unit 50 receives detection signals from a vehicle speed sensor 60 for detecting a vehicle speed and a current sensor 70 for detecting a current flowing through the steering motor 40.

The steering control unit 50 sets a voltage command value D based on the input signals from the sensors, and supplies a control signal corresponding to the set voltage command value D to the drive circuit 42. As a result, a current corresponding to the control signal is supplied from the drive circuit 42 to the steering motor 40, and as a result, a torque for moving the steering shaft 11 in a direction corresponding to the operation direction of the steering wheel 20 is output from the steering motor 40. Is done. For example, when the steering wheel 20 is operated in the + θ direction, a torque that moves the steering shaft 11 in the A direction is output from the steering motor 40, and when the steering wheel 20 is operated in the −θ direction, A torque is output from the steering motor 40 in such a direction as to move the steering shaft 11 in the direction B opposite to the direction A.

The voltage command value D is set based on the following equation (1). D = K · (Xm−Xr) + K2 · dθ (1) where K, K2: coefficient Xm = Map (θn, V): target steering Position Map: Function θn: Numerical value representing the operating position of the steering wheel V: Vehicle speed Xr: Numerical value representing the actual steering position dθ .. Operating speed of the steering wheel That is, the steering control unit 50 first controls the steering wheel 20 detected by the rotary encoder 34.
Is determined based on the numerical value θn representing the operating position of the vehicle and the vehicle speed V detected by the vehicle speed sensor 60. Further, based on the detection signal of the rotary encoder 34, an operation speed dθ which is an operation amount of the steering wheel 20 per unit time is obtained. The difference between the numerical value Xm representing the target turning position and the numerical value Xr representing the actual turning position detected by the turning position sensor 15 is represented by a coefficient K
And the value obtained by multiplying the operating speed dθ of the steering wheel 20 by the coefficient K2 is set as the voltage command value D.

FIG. 2 shows an example of a time change of the numerical value Xm representing the target steered position, the numerical value Xr representing the actual steered position, the proportional term K · (Xm−Xr), the differential term K2 · dθ, and the voltage command value D. FIG. For example, it is assumed that after the steering wheel 20 is quickly operated in the + θ direction, the steering wheel 20 is rapidly turned back in the opposite direction (direction approaching the neutral position of the steering wheel 20) in the −θ direction. At this time, in a state where the steering wheel 20 is turned on the + θ side with respect to the neutral position, the numerical value Xm representing the target turning position takes a positive value, and the steering wheel 20 is shifted on the −θ side with respect to the neutral position. If the numerical value Xm representing the target turning position takes a negative value in the rotating state, the numerical value Xm representing the target turning position responds to the operation of the steering wheel 20 as shown in FIG. Shows the changes made.

Conventionally, in a vehicle steering system in which the steering wheel 20 and the steering mechanism 10 are mechanically separated,
The value of the proportional term K · (Xm−Xr) is set as the voltage command value D. In this conventional control, if the operation of the steering wheel 20 is fast, the change in the actual turning position cannot follow the change in the target turning position, and the numerical value Xr representing the actual turning position cannot be obtained.
Is a numerical value X representing the target turning position, as shown in FIG.
It rises later than the change in m.

As a result, if the coefficient K is a positive value, the proportional term K · (Xm−Xr) is calculated by changing the numerical value Xr representing the actual turning position to the target turning position, as shown in FIG. Takes a positive value until time t2, which coincides with the numerical value Xm representing the value, and after that time t2, the numerical value Xr representing the actual turning position becomes negative until time t3 when the steering wheel 20 returns to the neutral position (= 0). Take a value. Therefore, the voltage command value D takes a positive value from time t1 when the turning back of the steering wheel 20 is started to time t2 even though the steering wheel 20 is operated in the direction approaching the neutral position. As a result, a torque for moving the steering shaft 11 in the direction A shown in FIG.

On the other hand, in this embodiment,
As represented by the equation (1), a value obtained by adding the derivative term K2 · dθ to the proportional term K · (Xm−Xr) is set as the voltage command value D. If the coefficient K2 is a positive value, the derivative term K2 · dθ
2D, the voltage command value D is set to a negative value immediately after the time t1 at which the turning of the steering wheel 20 is started, as shown in FIG. 2E. . Accordingly, it is possible to prevent the torque for moving the steering shaft 11 in the direction A from being output from the steering motor 40 even when the steering wheel 20 is operated in a direction approaching the neutral position. Therefore, the response delay of the operation of the steering mechanism 10 to the operation of the steering wheel 20 can be reduced, and a favorable steering operation in response to the operation of the steering wheel 20 can be realized.

Although the above description does not take into account the rising characteristic of the numerical value Xr representing the actual turning position with respect to the operation of the steering wheel 20 in the + θ direction, the derivative of the numerical value Xr into the proportional term K · (Xm−Xr) is not considered. By setting the value obtained by adding the term K2 · dθ to the voltage command value D,
As shown in FIG. 2 (e), the +
Since a large voltage is applied to the steering motor 40 during the operation in the θ direction, the rising characteristics of the actual turning position Xr are improved. Thereby, the response delay of the operation of the steering mechanism 10 to the operation of the steering wheel 20 can be further reduced.

Next, according to a second embodiment of the present invention,
Description will be made with reference to FIG. 1 again. In this embodiment, the steering control unit 50 sets the voltage command value D based on the following equation (2). D = K · (Xm−Kg · Xr) (2) where K, Kg ····· Coefficient Kg = Xm1 / Xr1 Xm1 ····· Target rotation at the start of switching back Numerical value representing steering position Xr1 Numerical value representing actual steering position at the start of turning back Xm = Map (θn, V) Numerical value representing target steering position Map Function θn: Numerical value representing the operating position of the steering wheel V: Vehicle speed Xr: Actual turning position The steering control unit 50 turns on the ignition switch of the vehicle. During this time, it is repeatedly checked whether or not the turning operation of the steering wheel 20 is performed based on the detection signal of the rotary encoder 34. Whether or not this switching operation has been performed is determined based on a code attached to the numerical value θn indicating the operation position of the steering wheel 20 and a code indicating the operation direction of the steering wheel 20 (for example, a code of the operation speed dθ). I can judge. For example, when the numerical value θn representing the operation position of the steering wheel 20 is a positive value, and the steering wheel 20
When operated in the θ direction, the steering wheel 20
Can be determined to have been performed. That is, if the sign given to the numerical value θn indicating the operation position of the steering wheel 20 does not match the sign indicating the operation direction of the steering wheel 20, the steering wheel 20
Can be determined to have been performed.

When the turning of the steering wheel 20 is detected, the ratio of the numerical value Xm1 representing the target turning position at the start of turning and the numerical value Xr1 representing the actual turning position is calculated, and the calculated value is calculated. Is defined as a coefficient Kg. While the turning of the steering wheel 20 is being performed, the position represented by the numerical value Kg · Xr obtained by multiplying the numerical value Xr representing the actual turning position detected by the turning position sensor 15 by the coefficient Kg is steered. Assuming that this is the turning position of the shaft 11, a numerical value Kg representing this virtual turning position
A difference between Xr and a numerical value Xm representing the target steered position is obtained, and a value obtained by multiplying the difference by a coefficient K is set as a voltage command value D.

While the steering wheel 20 is not being turned back, the coefficient Kg is set to 1 and
According to the equation (2), a difference between a numerical value Xr representing the actual turning position detected by the turning position sensor 15 and a numerical value Xm representing the target turning position is obtained, and a value obtained by multiplying the difference by a coefficient K is obtained. Set as voltage command value D. FIG. 3 is a diagram illustrating an example of a time change of the numerical value Xm representing the target turning position, the numerical values Kg · Xr representing the virtual turning position, and the voltage command value D. When the steering wheel 20 is quickly operated in the + θ direction from the neutral position and then quickly turned back in the −θ direction, the numerical value Xm representing the target steered position becomes:
If it is set as shown in FIG. 3A, the numerical value Xr representing the actual turning position changes as shown by a two-dot chain line in FIG. 3B.

Since the numerical value Xm1 representing the target steered position at the time t1 at which the steering wheel 20 is turned back is larger than the numerical value Xr1 representing the actual steered position, the numerical value Xm1 representing the target steered position and the numerical value Xm1 representing the actual steered position are shown. The coefficient Kg, which is a ratio with the numerical value Xr1, becomes larger than 1. Therefore, the numerical value Kg · Xr representing the virtual steered position is larger than the numerical value Xr representing the actual steered position, and changes as shown by the solid line in FIG. Therefore, if the coefficient K is a positive value,
The voltage command value D is, as shown by the solid line in FIG.
The value is set to a negative value immediately after the time t1 at which the turning of the steering wheel 20 is started. Thus, as in the first embodiment described above, the steering wheel 2
Even if 0 is operated in the direction approaching the neutral position, it is possible to prevent the torque for moving the steering shaft 11 in the A direction from being output from the steering motor 40. Therefore, the steering mechanism 10 for the operation of the steering wheel 20
Can be reduced, and a good steering operation in response to the operation of the steering wheel 20 can be realized.

Although the two embodiments of the present invention have been described above, the present invention can be embodied in modes other than the above-described two embodiments. For example, instead of the steering wheel, another configuration such as a pedal or a lever can be adopted as the operation means. Also,
The steering speed detecting means may be a steering speed sensor or a means for differentiating the steering angle.

In addition, various design changes can be made within the scope of the matters described in the claims.

[Brief description of the drawings]

FIG. 1 is a conceptual diagram showing a configuration of a vehicle steering system according to an embodiment of the present invention.

FIG. 2 is a diagram illustrating an example of a temporal change of a target steered position, an actual steered position, a proportional term, a differential term, and a voltage command value.

FIG. 3 is a diagram showing an example of a temporal change of a target steered position, a virtual steered position, and a voltage command value in another embodiment of the present invention.

FIG. 4 is an illustrative view for explaining an operation of the vehicle steering system in which the steering wheel and the steering mechanism are mechanically separated.

FIG. 5 is a diagram for explaining a response delay occurring in the operation of the steering mechanism.

[Explanation of symbols]

15 Steering position sensor (steering position detecting means) 20 Steering wheel (operating means) 34 Rotary encoder (operating amount detecting means, operating speed detecting means) 40 Steering motor (steering actuator, electric motor) 42 Drive circuit 50 Control unit ( Drive control means) 60 vehicle speed sensor K coefficient (first coefficient, predetermined coefficient) K2 coefficient (second coefficient) Xm value representing target turning position Xr value representing actual turning position dθ operation speed

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) B62D 119: 00 (72) Inventor Nobuyoshi Sugitani 1 Toyota Town, Toyota City, Aichi Prefecture Toyota Motor Corporation F Terms (reference) 3D032 CC12 DA03 DA04 DA09 DA15 DA20 DA23 DA64 DC01 DC03 DC09 DC40 DD02 EA01 EB04 EB11 EB12 EC24 EC29 GG01 3D033 CA13 CA16 CA17 CA18 CA19 CA20 CA21

Claims (4)

[Claims] 1. A steering actuator for generating torque for turning a steering wheel, and operating means provided mechanically separated from the wheel and operated to input a turning direction of the wheel. Operating speed detecting means for detecting an operating speed when the operating means is operated; and a torque in the steering direction input from the operating means based on the operating speed detected by the operating speed detecting means. And a drive control means for controlling the drive of the steering actuator so as to generate the steering error. 2. The vehicle according to claim 1, further comprising: a steering position detecting means for detecting a steering position of the wheel; and an operation amount detecting means for detecting an operation amount of the operating means, wherein the steering actuator is an electric motor. The drive control means determines a target turning position based on an operation amount of the operation means detected by the operation amount detection means, and detects the target turning position and the target turning position detected by the turning position detection means. According to the sum of a value obtained by multiplying the deviation from the steered position of the wheel by a first coefficient and a value obtained by multiplying the operation speed detected by the operation speed detection means by a second coefficient, 2. The vehicle steering apparatus according to claim 1, wherein an applied voltage to said electric motor is set. 3. A steering actuator for generating a driving force for turning a steering wheel, and an operation mechanically separated from the wheel and operated to input a turning direction of the wheel. Means, after turning the wheel in one direction, turning operation detecting means for detecting that a turning operation of the operating means has been performed to steer in the other direction opposite to the one direction; Drive control means for driving and controlling the steering actuator so as to immediately generate the torque in the other direction when the turning operation is detected by the turning operation detecting means. Vehicle steering system. 4. The vehicle further includes a turning position detecting means for detecting a turning position of the wheel, and an operation amount detecting means for detecting an operation amount of the operating means, wherein the steering actuator is an electric motor. The drive control means determines a target turning position based on the operation amount of the operation means detected by the operation amount detection means, and determines the target turning position, the target turning position, and the turning position detection means. A voltage applied to the electric motor is set based on a value obtained by multiplying a deviation from a virtual steering position determined based on the steering position of the wheel detected by a predetermined coefficient. The vehicle steering system according to claim 3, wherein