JPH10315998A - Steering controller for vehicle - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a steering controller for vehicle which can improve the steering property of a vehicle while ensuring the stability in the steering of the vehicle. SOLUTION: A steering controller for vehicle which controls a rolling amount of a wheel 3 in accordance with a turning amount of a handle 21 is provided with a steering sensor 24 which detects a steering amount of the handle 21, a car speed sensor 51 which detects a speed of a vehicle, and an ECU 4 which changes and controls a turning amount of the wheel 3 for a steering amount of the handle 21 so that a yaw rate gain of the vehicle becomes substantially constant and increases a steering load of the handle 21 when the vehicle exceeds a transverse acceleration limit by the turning of the wheel 3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a steering control device for a vehicle.

[0002]

2. Description of the Related Art In order for a vehicle to run stably, it is important that the yaw rate (yaw angular velocity) and lateral acceleration of the vehicle do not exceed their limits. A steering device described in Japanese Patent Application Laid-Open No. 6-144270 is known as one that aims to improve the driving stability of the vehicle as well as the running stability of the vehicle. This steering device calculates a steering gear ratio (steering ratio: ratio between a steering wheel angle and an actual steering angle) based on an operation angle signal of a steering rotation shaft and a vehicle speed signal of a vehicle speed sensor. When the vehicle speed is low, the lateral acceleration of the vehicle is calculated. Is set so as to be constant, and the steering gear ratio is set so that the yaw rate of the vehicle is constant when the vehicle speed is high. By setting such a steering gear ratio, the stability of the vehicle is ensured at a high speed, and the agility of the vehicle is improved at a low speed.

[0003]

However, the conventional steering apparatus has a problem that the steering range is limited in order to ensure the running stability of the vehicle. That is, in the relationship between the turning angle of the vehicle and the vehicle speed, the yaw rate limit is generally reached before the lateral acceleration limit by steering when the vehicle is running at a low speed, and the yaw rate limit is more than the yaw rate limit by steering when the vehicle is running at a high speed. The lateral acceleration limit is reached first.
However, in the steering device described above, the steering gear ratio is controlled based on the lateral acceleration during low-speed running and the yaw rate during high-speed running. The steering range is limited even though there is a margin in either the limit or the lateral acceleration limit.

Further, in the above-described steering apparatus, the steering gear ratio is varied to ensure the steering stability of the vehicle. However, it is not the steering gear ratio but the actual steering angle that affects the actual behavior of the vehicle. (Steering angle of the wheel), even if only the steering gear ratio is changed according to the vehicle speed, the running stability of the vehicle is not necessarily ensured.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned problems, and it is an object of the present invention to provide a vehicle steering system capable of ensuring the stability of vehicle steering and improving the steerability of the vehicle. It is an object to provide a control device.

[0006]

In order to achieve the above object, a vehicle steering control device according to the present invention is directed to a vehicle steering control device for controlling a wheel turning amount in accordance with a steering amount of a steering wheel. A steering amount detecting means for detecting a steering amount of the steering wheel, a vehicle speed detecting means for detecting a speed of the vehicle, and a wheel for the steering amount of the steering wheel so that a yaw rate gain of the vehicle becomes substantially constant with respect to a change in the speed of the vehicle. It is characterized by comprising transmission ratio variable means for varying the amount of steering, and steering reaction force control means for increasing the steering reaction force of the steering wheel when the vehicle exceeds the lateral acceleration limit by turning the wheels.

Further, in the vehicle steering control device according to the present invention, the transmission ratio variable means makes the turning amount of the wheel constant with respect to the steering amount of the steering wheel at the time of stationary steering and traveling at an extremely low speed. Also, when the vehicle is not running at extremely low speed, the amount of wheel turning relative to the amount of steering of the steering wheel is varied so that the yaw rate gain of the vehicle is constant.

According to these inventions, the steering amount of the wheel with respect to the steering wheel operation is controlled so as to maintain a constant yaw rate gain, and the transmission ratio of the steering wheel with respect to the steering wheel operation during high-speed running is greatly changed. Absent. Therefore, the driver can easily operate the steering wheel. Also,
Since the steering reaction force of the steering wheel increases when the vehicle exceeds the lateral acceleration limit due to the turning of the wheels, the driver can reliably recognize the vehicle state through the operation of the steering wheel. Further, the steering wheel can be operated even in a region exceeding the lateral acceleration limit of the vehicle.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the accompanying drawings. In the drawings, the same elements are denoted by the same reference numerals, and the description is omitted. Also,
The dimensional ratios in the drawings do not always match those described.

(First Embodiment) FIG. 1 is a schematic diagram showing the configuration of a vehicle steering control device according to this embodiment. In FIG. 1, a steering control device 1 is of a steer-by-wire type in which a steering amount of a steering wheel 21 is converted into an electric signal and transmitted to a steering mechanism such as a tie rod. A reaction force actuator 22 that applies a reaction force to the handle 21 when the handle 21 is operated is provided. The reaction force actuator 22
For example, it is composed of an electric motor and a gear mechanism. The reaction force actuator 22 is mechanically connected to the handle 21 via a steering shaft 23, and applies a steering reaction force to the handle 21 according to the operation state of the handle 21.

As shown in FIG. 1, the steering shaft 23 is provided with a steering position sensor 24 for detecting a steering angle θ (steering position) of the steering wheel 21. The steering position sensor 24 outputs a steering signal corresponding to the steering angle θ of the steering wheel 21 to the ECU 4. The ECU 4 controls the steering control device 1
It is a control unit that performs overall control, and outputs drive signals to the reaction force actuator 22 and the steering actuator 25. The steering actuator 25 operates upon receiving a drive signal from the ECU 4, and steers the wheels 4 via a relay rod 26, a tie rod 27, and a knuckle arm 28.
As described above, according to the steering control device 1, the steering actuator 2 is controlled via the ECU 4 in response to the operation of the steering wheel 21.
5 is operated, and the wheels 3, 3 are steered.

The steering control device 1 is provided with a vehicle speed sensor 51 and a turning sensor 52. The vehicle speed sensor 51 detects the speed of the vehicle, and uses the detected vehicle speed information as an electrical signal, that is, a vehicle speed signal. Output to ECU4. The turning sensor 52 detects the amount of turning of the wheels 3 and outputs the detected turning angle information to the ECU 4 as an electric signal, that is, a turning signal.

The ECU 4 functions as a transmission ratio variable unit of the steering control device 1. That is, the ECU 4 has a function of varying the amount of turning of the wheels 3 with respect to the amount of steering of the steering wheel 21 so that the yaw rate gain of the vehicle becomes substantially constant. For example, the ECU 4 outputs a drive signal to the steering actuator 25 based on information such as the vehicle speed and the steering angle of the steering wheel, and sets the vehicle speed detected by the vehicle speed sensor 51 to V,
When the yaw rate gain ((yaw rate γ) / (steering wheel steering angle θ)) is Kr, the stability factor is A, and the wheelbase of the vehicle is L, the transmission ratio Zh ((handle 21) (Steering angle θ) / (steering angle ηh of wheel 3), driving control of steering actuator 25 is performed so that wheel 3 is steered at steering angle ηh with respect to steering angle θ of steering wheel 21. .

[0014]

(Equation 1)

That is, in this case, the transmission ratio Zh of the steering angle ηh of the wheel 3 to the steering angle θ of the steering wheel 21 is determined by the ECU
4 is set so as to satisfy Equation (1) based on a drive signal from the steering actuator 25 to the steering actuator 25, a gear ratio in the steering actuator 25, and the like. When the transmission ratio Zh is set based on this equation (1) and the vehicle is controlled so that the yaw rate gain is constant, the relationship between the vehicle speed V and the transmission ratio Zh is shown in FIG. 2 (solid line in the figure). become that way. That is, in a low-speed region of the vehicle, the transmission ratio Zh changes largely with an increase in the vehicle speed V, but in a high-speed region, the transmission ratio Zh does not change much with an increase in the vehicle speed V. Further, in FIG. 2, in the stationary region and the extremely low speed region, the transmission ratio Zh
The lower limit is set so that the steering wheel speed does not fall below a certain value, so that the steering operation does not become excessive in these speed ranges. In the stationary region and the extremely low speed region, the transmission ratio may be controlled based on the equation (1) so that the yaw rate gain of the vehicle is constant. In this case,
The transmission ratio is varied so that the yaw rate gain of the vehicle is constant regardless of the speed change of the vehicle.

The broken line in FIG. 2 shows the relationship between the vehicle speed V and the transmission ratio Zm when the lateral acceleration gain is fixed. When the lateral acceleration gain ((lateral acceleration α) / (steering wheel steering angle θ)) is Ka, the transmission ratio Zm is expressed by the following equation (2).

[0017]

(Equation 2)

Assuming that the lateral acceleration gain is constant, the transmission ratio Zm
It can be seen that, when the transmission ratio Zh is set with the yaw rate gain being constant, the change in the transmission ratio during high-speed running is smaller than when the transmission ratio is set.

On the other hand, the ECU 4 functions as a steering reaction force control means of the steering control device 1. That is, the ECU 4
It has a function of increasing the steering reaction force of the steering wheel 21 when the vehicle exceeds the lateral acceleration limit due to the turning of the wheels 3.

For example, in equation (1), (steering wheel steering angle θ) / (steering angle ηh of wheel 3) is substituted for transmission ratio Zh to solve for steering angle ηh, and the maximum yaw rate at which the vehicle can run stably is obtained. (Yaw rate limit value) is γx,
The relationship between the vehicle speed V and the limit turning angle ηx is given by the following equation (3).

[0021]

(Equation 3)

In the equation (2), (steering wheel steering angle θ) / (steering angle ηm of the wheel 3) is substituted for the transmission ratio Zm to solve for the steering angle ηm, and the maximum lateral angle at which the vehicle can run stably is obtained. Assuming that the acceleration (lateral acceleration limit value) is αy, the relationship between the vehicle speed V and the limit turning angle ηy is expressed by the following equation (4). The lateral acceleration limit value αy is determined by the position of the center of gravity of the vehicle, the wheel tread, and the like.

[0023]

(Equation 4)

FIG. 3 shows the relationship between the vehicle speed and the steering angle based on these equations (3) and (4). The solid line in FIG.
The relationship between the vehicle speed V reaching the yaw rate limit of the vehicle and the turning angle ηx is shown. When the turning angle becomes larger than this solid line (in FIG. 3, the upper right region from the solid line), the running stability decreases. The dashed line in FIG. 3 indicates the limit of the lateral acceleration of the vehicle. If the steering angle is larger than this dashed line (the upper right region in FIG. 3), the running stability is reduced.

In FIG. 3, it can be seen that generally, when the vehicle speed during traveling of the vehicle increases to some extent, the steering of the wheels 3 reaches the lateral acceleration limit before the yaw rate limit of the vehicle. When the steering of the wheel 3 is controlled so that the yaw rate gain of the vehicle is constant, the steering angle of the wheel 3 may exceed the lateral acceleration limit steering angle ηy (the oblique line in FIG. 3). region). In this case, the running stability of the vehicle with respect to the lateral acceleration cannot be ensured. Therefore,
The ECU 4 calculates a vehicle speed signal input from the vehicle speed sensor 51 and a steering signal input from the steering sensor 52 based on the vehicle speed signal.
It is determined whether or not the vehicle has exceeded the lateral acceleration limit value αy, and when the wheel 3 is steered beyond the lateral acceleration limit value αy, the reaction force actuator 22 is driven to increase the steering load of the steering wheel 21. Output a signal.

As a result, the relationship between the steering angle θ of the steering wheel 21 and the steering load for steering the steering wheel 21 when the vehicle is traveling at a certain vehicle speed is as shown in FIG. 4, for example. In FIG. 4, when the steering angle θ of the steering wheel 21 is gradually increased from a neutral state (vehicle straight traveling state), the steering load increases in proportion thereto, and the wheel 3 is moved to the limit steering angle ηy (the vehicle Steering angle θ exceeding lateral acceleration limit value αy)
At the time point y, the increasing rate of the steering load increases. Therefore, the driver can reliably recognize the state of the vehicle through the operation of the steering wheel.

Next, the operation of the steering control device 1 will be described.

In FIG. 1, when the driver operates the steering wheel 21 while the vehicle is running, the steering position sensor 24 outputs a steering signal corresponding to the steering amount of the steering wheel 21, and the steering signal is input to the ECU 4. EC receiving steering signal
U4 outputs a drive signal corresponding to the steering signal to the steering actuator 25 and the reaction force actuator 22, respectively. Therefore, the reaction force actuator 22 and the steering actuator 25 operate in response to the drive signals, and a steering reaction force is given to the steering wheel 21 through the steering shaft 23 by the reaction force actuator 22, and the steering actuator 25 The wheel 3 is steered through the tie rod 27, the knuckle arm 28, and the like.

At this time, the relationship between the steering angle θ of the steering wheel 21 and the steering angle η of the wheels 3 is controlled so that the transmission ratio Zh shown in the above equation (1) is obtained. The transmission ratio (solid line in FIG. 2) changes according to V, and the yaw rate gain of the vehicle is kept constant regardless of the magnitude of vehicle speed V. Therefore, the driver can easily operate the steering wheel while the vehicle is running. For example, if the transmission ratio between steering wheel operation and wheel steering is set as a constant yaw rate gain,
As shown in FIG. 2, the change in the transmission ratio in the high-speed region is smaller than when the lateral acceleration gain is set to be constant (broken line in FIG. 2). Therefore, the steering amount of the steering wheel 21 for turning the wheels 3 during high-speed running does not become very large as compared with low-speed running, and the steering operation can be performed without discomfort.

In general, the driver does not frequently steer the steering wheel 21 during high-speed running, so that the driver has few chances to feel the transmission ratio during high-speed running, and it is difficult for the driver to get used to the change in the transmission ratio. That is, in a high-speed region, it is easier to drive the vehicle if the change in the transmission ratio is made as small as possible. Further, when the transmission ratio between the steering wheel operation and the wheel turning is set as a constant yaw rate gain, even if the vehicle is accelerated or decelerated while maintaining the steering wheel 21, the vehicle travels so that the yaw rate is constant. . Therefore, at this time, it is not necessary to steer the steering wheel 21 in accordance with the turning direction of the vehicle, and it is extremely easy to drive. As described above, the operability of the vehicle can be improved by changing the amount of turning of the wheels with respect to the amount of steering of the steering wheel so that the yaw rate gain of the vehicle becomes substantially constant.

On the other hand, in FIG. 1, when the steering angle of the wheels 3 exceeds the lateral acceleration limit of the vehicle when the driver turns the steering wheel 21 while the vehicle is running, a signal is output from the steering sensor 52. Based on the steering signal and the vehicle speed signal output from the vehicle speed sensor 51, the ECU 4 detects that the lateral acceleration limit of the vehicle has been exceeded. At this time, the ECU 4 outputs a drive signal to the reaction force actuator 22 to increase the increase ratio of the steering reaction force. Upon receiving this drive signal, the reaction force actuator 22 increases the increasing rate of the steering load of the steering wheel 21 as shown in FIG. As a result, the steering load of the steering wheel 21 increases when the vehicle exceeds the lateral acceleration limit, so that the driver can easily recognize through the steering wheel 21 that the vehicle has exceeded the lateral acceleration limit.

Further, it is possible to steer the wheel 3 using an area exceeding the lateral acceleration limit (the shaded area in FIG. 3).

As described above, according to the steering control device 1 according to the present embodiment, the steering angle η of the wheel 3 with respect to the operation angle θ of the steering wheel 21 is varied so that the yaw rate gain of the vehicle becomes substantially constant. When the vehicle exceeds the lateral acceleration limit due to the turning of the wheels, the steering reaction force of the steering wheel 21 is increased. For this reason, during normal running, the vehicle is very easy to drive without exceeding the yaw rate limit. When the lateral acceleration limit is exceeded, the driver can easily and reliably recognize the state of the vehicle through the operation of the steering wheel. Further, the steering wheel 21 exceeds the lateral acceleration limit.
Can be steered. Therefore, the vehicle can be driven in accordance with the driver's intention to drive while making the driver recognize the state of the vehicle.

(Second Embodiment) Next, a vehicle steering control device according to a second embodiment will be described.

FIG. 5 shows a steering control device 1a according to this embodiment.
Is shown. In FIG. 5, a steering control device 1a is used in an electric power steering system that applies an assist force to a rack bar 31. In this power steering system, a pinion 30 provided on a steering shaft 23 connected to a steering wheel 21 is mounted on a rack bar 3.
1 and the steering force of the steering wheel 21 is mechanically transmitted as a turning force. On the other hand, the steering force T1 of the steering wheel 21 is detected by the torque sensor 29. Upon receiving the output signal of the torque sensor 29, the ECU 4 outputs a drive signal corresponding to the steering torque of the steering wheel 21 to the assisting actuator 32. Then, the assisting actuator 32 is driven in response to the drive signal to drive the rack bar 31.
Is moved, and the wheel 3 is steered via the tie rod 27 and the knuckle arm 28.

As shown in FIG. 5, the steering control device 1a has a variable transmission ratio mechanism 61 disposed in the middle of the steering shaft 23. The transmission ratio variable mechanism 61 includes the ECU 4
The rotation amount of the steering shaft 23 on the handle 21 side and the rack bar 31 side is varied based on the drive signal of the steering shaft 23, and is constituted by, for example, a transmission, a variable gear ratio motor, a differential motor, and the like. The variable transmission ratio mechanism 61 and the ECU 4 function as transmission ratio variable means of the steering control device 1a. That is, the ECU 4 outputs a drive signal to the transmission ratio variable mechanism 61 so that the yaw rate gain of the vehicle becomes substantially constant with respect to the steering amount of the wheel 3 with respect to the steering amount of the steering wheel 21 and receives the signal to change the transmission ratio variable mechanism. Reference numeral 61 appropriately changes the rotation speed of the steering shaft 23 on the handle 21 side and the rack bar 31 side. The transmission ratio in this case is controlled so as to be the transmission ratio Zh shown in the above-described equation (1).

On the other hand, the ECU 4 functions as a steering reaction force control means of the steering control device 1a. That is, the ECU 4
Has a function of increasing the steering reaction force of the steering wheel 21 when the vehicle exceeds the lateral acceleration limit due to the turning of the wheels 3. For example, the ECU 4 determines whether or not the vehicle has exceeded the lateral acceleration limit value αy based on the vehicle speed signal input from the vehicle speed sensor 51 and the turning signal input from the turning sensor 52, Wheel 3 beyond limit value αx
When the vehicle is steered, a drive signal is output to the steering actuator 25 so as to increase the steering load of the steering wheel 21. As a result, the relationship between the steering angle θ of the steering wheel 21 and the steering load for steering the steering wheel 21 when the vehicle is traveling at a certain vehicle speed is, for example, as shown in FIG.
That is, when the steering angle θ of the steering wheel 21 is gradually increased from the neutral state (the vehicle is in a straight running state), the steering load increases in proportion thereto, and the wheel 3 is moved to the limit steering angle ηy (the lateral acceleration limit value of the vehicle). At the time of the steering angle θy exceeding αy), the increasing rate of the steering load increases.

In the steering control device 1a using such an electric power steering system, the same operation and effect as those of the steering control device 1 according to the first embodiment can be obtained. That is, the steering angle of the wheel 3 with respect to the operation angle θ of the steering wheel 21 is changed so that the yaw rate gain of the vehicle becomes substantially constant, and when the vehicle exceeds the lateral acceleration limit due to the steering of the wheel, the steering angle of the steering wheel 21 is reduced. The power is increased. Therefore, during normal traveling, the vehicle can be easily driven without exceeding the yaw rate limit. When the lateral acceleration limit is exceeded, the driver can easily and reliably recognize the state of the vehicle through the operation of the steering wheel. Further, the steering wheel 21 can be steered beyond the lateral acceleration limit. Therefore, the vehicle can be driven in accordance with the driver's intention to drive while making the driver recognize the state of the vehicle.

(Third Embodiment) Next, a vehicle steering control device according to a third embodiment will be described.

FIG. 6 shows a steering control device 1b according to this embodiment.
Is shown. In FIG. 6, a steering control device 1b is used for a hydraulic power steering system that applies an assist force to a rack bar 31. In this power steering system, a pinion 30 provided on a steering shaft 23 connected to a steering wheel 21 is mounted on a rack bar 3.
1 and the steering force of the steering wheel 21 is mechanically transmitted as a turning force. On the other hand, a hydraulic circuit equipped with a pump is provided, and a part of the steering force of the steering wheel 21 is converted to the assist force of the rack bar 31 via the hydraulic circuit. The steering force of the steering wheel 21 and the hydraulic cylinder 6
The rack bar 31 is moved by the assist force of 2, and the wheels 3 are steered via the tie rod 27 and the knuckle arm 28 and the like.

As shown in FIG. 6, in the steering control device 1a, a hydraulic adjustment valve 63 for controlling the supply and discharge of the hydraulic oil to and from the hydraulic cylinder 62 is provided on the steering shaft 23. The hydraulic adjustment valve 63 is provided with a hydraulic reaction mechanism that adjusts the reaction oil pressure in accordance with the output signal from the ECU 4. Is controlled. For this reason, the ECU
4 and the hydraulic adjustment valve 63 function as steering reaction force control means of the steering control device 1b. For example, the ECU 4 determines whether or not the vehicle has exceeded the lateral acceleration limit value αy based on the vehicle speed signal input from the vehicle speed sensor 51 and the turning signal input from the turning sensor 52, Limit value α
When the wheel 3 is steered beyond y, the hydraulic adjustment valve 63
In order to increase the steering load of the steering wheel 21, a driving signal is output so as to increase the steering reaction force. as a result,
The relationship between the steering angle θ of the steering wheel 21 and the steering load for steering the steering wheel 21 when the vehicle is traveling at a certain vehicle speed is, for example, as shown in FIG. That is, when the steering angle θ of the steering wheel 21 is gradually increased from the neutral state (the vehicle is traveling straight), the steering load increases in proportion to the steering angle θ, and the wheel 3 moves to the limit steering angle ηy (the lateral acceleration of the vehicle). At the time of the steering angle θy exceeding the limit value αy), the increasing rate of the steering load increases.

In the steering control device 1b using such a hydraulic power steering system, the same operation and effect as those of the steering control device 1 according to the first embodiment or the steering control device 1b according to the second embodiment are obtained. can get. That is, the steering angle of the wheel 3 with respect to the operation angle θ of the steering wheel 21 is changed so that the yaw rate gain of the vehicle becomes substantially constant, and when the vehicle exceeds the lateral acceleration limit due to the steering of the wheel, the steering angle of the steering wheel 21 is reduced. The power is increased. For this reason, during normal running, the vehicle is very easy to drive without exceeding the yaw rate limit. When the lateral acceleration limit is exceeded, the driver can easily and reliably recognize the state of the vehicle through the operation of the steering wheel. Further, the steering wheel 21 can be steered beyond the lateral acceleration limit. Therefore, the vehicle can be driven in accordance with the driver's intention to drive while making the driver recognize the state of the vehicle.

[0043]

As described above, according to the present invention, the following effects can be obtained.

[0044] The vehicle can be driven in accordance with the driver's intention to drive while making the driver aware of the state of the vehicle.
It is possible to achieve both driving safety and maneuverability of the vehicle.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a vehicle steering control device.

FIG. 2 is a diagram showing a relationship between a vehicle speed and a transmission ratio in a vehicle steering control device.

FIG. 3 is a diagram illustrating a relationship between a vehicle speed and a turning angle in the vehicle steering control device;

FIG. 4 is a diagram illustrating a relationship between a steering wheel angle and a steering load in the vehicle steering control device;

FIG. 5 is an explanatory diagram of a vehicle steering control device according to a second embodiment.

FIG. 6 is an explanatory diagram of a vehicle steering control device according to a third embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Steering control device, 21 ... Steering wheel, 24 ... Steering sensor, 3 ... Wheel, 4 ... ECU, 51 ... Vehicle speed sensor

Claims (2)

[Claims] 1. A vehicle steering control device for controlling a turning amount of a wheel according to a steering amount of a steering wheel, a steering amount detecting means for detecting a steering amount of the steering wheel, a vehicle speed detecting means for detecting a speed of the vehicle. A transmission ratio variable means for varying a steering amount of the wheel with respect to a steering amount of the steering wheel so that a yaw rate gain of the vehicle becomes substantially constant with respect to a speed change of the vehicle; A steering reaction control device for increasing a steering reaction force of the steering wheel when the vehicle exceeds a lateral acceleration limit. 2. The transmission ratio varying means makes the steering amount of the wheel relative to the steering amount of the steering wheel constant at the time of stationary steering and extremely low speed running, and at the time other than the stationary steering and extremely low speed running. 2. The vehicle steering control device according to claim 1, wherein a steering amount of the wheel with respect to a steering amount of the steering wheel is varied such that a yaw rate gain of the vehicle is constant. 3.