JPH0825479B2 - Rear wheel steering system for automobiles - Google Patents

Description

TECHNICAL FIELD The present invention relates to a rear wheel steering system for an automobile.

2. Description of the Related ArtVarious types of automobiles have been developed in the past, in which the rear wheels are simultaneously steered along with the steering operation of the front wheels by the steering operation of the steering wheel, for example, Japanese Patent Laid-Open No. 55-91457. It has already been made public.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention In the conventional rear wheel steering device as described above, the left and right rear wheels are connected, and the left and right rear wheels are combined depending on the steering angle (or steering force) of the front wheels and the vehicle speed at that time. It is common to use the method of steering to.

However, when the running vehicle turns, a load shift occurs on the left and right wheels depending on the degree of the turning, and the ground load of the outer turning wheel increases, but the ground load of the inner turning wheel decreases and the cornering force decreases. Therefore, in order to maximize the tire performance of the left and right rear wheels (that is, the drag force against the sideways movement), it is necessary to determine the steering angle of the rear wheels according to the load. Since the rear wheels are connected and steered together, there is a problem that the tire characteristics cannot be maximized because the wheels have to be steered based on the average load of the left and right rear wheels. are doing.

The present invention mainly aims to address the above-mentioned problems of the conventional rear wheel steering system.

Means for Solving the Problems According to the present invention, a left rear wheel steering mechanism and a right rear wheel steering mechanism are provided independently of each other, and the left and right rear wheels can be steered separately by an output signal of a control circuit. In addition to the above configuration, the left and right axle load sensors that detect the axle loads of the left and right rear wheels and input the axle load signals to the control circuit are provided. The difference between the left and right axle loads is calculated from the input left and right axle load signals, and the steering angle at which the left and right rear wheels should be steered based on the axle load difference is set to the steering angle of the outer turning wheel as the axle load difference increases. It is characterized in that the left and right steering wheels are determined separately so that the turning angle of the turning inner wheel is large, and output signals are separately issued to the left and right rear wheel steering mechanisms.

Action From the above, the left and right rear wheels are steered in the same direction as the front axle by steering the front wheels.However, if there is a difference in axial load between the left and right rear wheels due to load movement caused by the degree of turning, the difference in axial load will occur. The larger is the turning inner wheel side steered more than the turning outer wheel side, and the reduction of the cornering force on the turning inner wheel side due to the reduction of the ground contact load on the turning inner wheel side due to the load movement is due to the increase of the cornering force due to the increase of the steering angle. It is compensated, and it is possible to maximize the tire performance for both the inner and outer wheels of the rear wheel and improve the steering stability.

Embodiment One embodiment of the present invention will be described below with reference to the accompanying drawings.

In FIG. 1, 1 is a steering wheel,
By rotating the steering handle 1 to the right or left, a well-known front wheel steering device such as a rack and pinion type steering device (not shown) is activated to steer the front wheels to the right or left. .

Reference numeral 2 is a front wheel steering angle sensor that detects a front wheel steering angle by steering operation of the steering wheel 1 and issues a front wheel steering angle signal.
Is a vehicle speed sensor that emits a vehicle speed signal. The control circuit 4 determines whether or not the vehicle is turning by the front wheel steering angle signal of the front wheel steering angle sensor 2 and the vehicle speed signal of the vehicle speed sensor 3.
When it is determined that the vehicle is turning, the control circuit 4 determines the steering angle (including the steering direction) at which the rear wheels should be steered based on the input of signals from the axle load sensors 15 for the left and right rear wheels, which will be described later. To output an output signal.

The left and right rear wheels 14L and 14R are independent steering mechanisms L
And R are steered separately.

The steering mechanisms L and R are actuators controlled by output signals of the control circuit 4, for example, an electric motor 5
And a cylindrical worm 6 fixed to the output shaft of the electric motor 5.
And a worm wheel 7 that meshes with the cylindrical worm 6,
A pinion gear 8 that rotates integrally with the worm wheel 7, and a rack shaft 9 that meshes with the pinion gear 8.
Each rack shaft 9 comprises a tie rod 12 and a knuckle arm 13.
The left and right rear wheels 14L and 14R are connected to each other via the rack shaft 9 by the rotation of the electric motor 5 so that the rear wheels 14L and 14R can be steered separately. There is.

Each of the steering mechanisms L and R is provided with a rear wheel steering angle sensor 10 which detects the respective rear wheel actual steering angles and issues respective actual steering angle signals of the left and right rear wheels to the control circuit 4.

Reference numeral 15 is a left and right axial load sensor for detecting the vertical load acting on each shaft of the left and right rear wheels 14L and 14R, that is, the axial load and individually inputting the axial load signals to the control circuit 4, for example, an air suspension. In an equipped vehicle, a pressure sensor that detects the air pressure of each of the left and right rear wheel suspensions can be used as the axle load sensor 15.

The relationship between the axial load difference between the left and right rear wheels and the optimum steering angles of the left and right rear wheels is preset in the control circuit 4 as a map, and the left and right rear wheels input by the left and right axle load sensors 15 are set. The left and right axial load difference is calculated from the axial load information of the left and right, and the steering angles of the left and right rear wheels are calculated based on the map according to the change of the left and right axial load difference. Is approximately the same steering angle, and when the left and right axial load difference is large, the steering angle of the left and right rear wheels on the turning inner wheel side is made larger than the turning angle of the turning outer wheel side, and the turning angle difference of the turning inner and outer wheels is the left and right axial load. It is decided to increase as the difference increases, and output signals are output to the electric motors 5 and 5 of the left and right rear wheel steering mechanisms L and R to steer the left and right rear wheels 14L and 14R respectively. ,
The left and right rear wheels are steered individually according to the steering angle determined by the control circuit 4 by feedback control based on the rear wheel actual steering angle signals input from the left and right rear wheel steering angle sensors 10, 10.

In the above, the turning direction of the left and right rear wheels is the same as the turning direction of the front wheels.

Generally, when a vehicle turns, a load shift occurs on the left and right wheels depending on the degree of turning, and the axial load on the inner wheel side is reduced to a small extent, so that the drag force against sideways, that is, the cornering force is reduced. On the other hand, the cornering force of the tire increases as the turning angle in the turning direction increases.

Therefore, as described above, the steered angle of the rear wheels in the same direction as the steered direction of the front wheels is made larger on the turning inner wheel side than on the turning outer wheel side, and the steering angle difference between the turning inner and outer wheels becomes larger as the left and right axial load difference increases. By controlling so that the decrease in the axial load of the turning inner wheel causes a decrease in the cornering force to be compensated by the increase in the cornering force due to the increase in the steering angle of the turning inner wheel, the tire performance of both the turning inner wheel and the outer wheel is reduced. It is possible to maximize the controllability and significantly improve the steering stability.

In the above embodiment, the optimum steering angles of the left and right rear wheels are determined by the axle load sensor 1.
Although an example is shown in which the left and right shaft load information input from 5, 15 is used to make a determination based on a map that has been set in advance, in the present invention, other than the above, the control circuit 4 uses the front wheel steering angle sensor 2 Based on the front wheel steering angle information obtained from the vehicle speed information and the vehicle speed information obtained from the vehicle speed sensor 3, the conventional average steering angles of the left and right rear wheels are first determined, and then the control circuit 4 obtains the axis load sensors 15 and 15 from the axes. From the load difference information, for example, based on the characteristics of the inner / outer wheel steering angle difference with respect to the inner / outer wheel shaft load difference as shown in FIG. 2 (this is set in the advance control circuit 4), the average steering angle is determined. The values may be modified to determine the respective steering angles of the inner and outer wheels to appropriate values such that the inner wheel side has a larger steering angle than the outer wheel side, and output signals are issued.

In this case, the method of determining the average rear wheel steering angle from the front wheel steering angle and the vehicle speed is, for example, in the low speed range, the rear wheels are slightly steered in the direction opposite to the front wheel steering direction (reverse phase steering), From the medium speed to the high speed range, the rear wheel steering direction is set in the same direction as the front wheel steering direction (in-phase steering) and the rear wheel steering angle is increased as the vehicle speed increases. The method may be adopted, or the average rear wheel rudder angle determination method is adopted in which all the rear wheels are steered in the same phase from the low speed region to the high speed region and the rear wheel steering angle is gradually increased as the vehicle speed increases. Is also good.

In the low speed range, the rear wheels are reverse-phase steered, while in the high speed range, the rear wheels are in-phase steered. The load difference is almost zero, and it is during the in-phase steering that controls the inner and outer wheel steering angle differences due to the left and right axial load differences. The decrease of the axial load of the turning inner wheel can be compensated by the increase of the cornering force based on the increase of the steering angle of the turning inner wheel in the in-phase direction to maximize the tire performance and improve the steering stability.

In the illustrated embodiment, an electric motor is used as an actuator for steering the rear wheels, and the rotation of the electric motor is used to steer the rear wheels via a reduction gear mechanism, a pinion gear, a rack shaft, and the like. However, the rear wheel steering actuator, the mechanism for transmitting the steering force from the actuator to the rear wheels, and the like are different from those in the illustrated embodiment.
For example, an arbitrary structure such as a mechanism for steering the rear wheels by the hydraulic pressure of the hydraulic actuator can be adopted.

As described above, according to the present invention, the axial load of each of the left and right rear wheels is detected during steering by rotating the steering handle, and the axial load is determined according to the difference between the axial loads of the left and right rear wheels. The larger the difference is, the larger the steering angle is given to the turning outer wheel to the turning inner wheel, so that the turning angles of the left and right rear wheels are controlled separately. The decrease in cornering force due to the decrease can be compensated by increasing the steering angle of the turning inner wheel to maximize the performance of the tire, and it is possible to significantly improve the maneuverability accuracy and stability. It can bring about a great effect.

[Brief description of drawings]

FIG. 1 is an explanatory plan view showing an embodiment of the present invention, and FIG. 2 is a diagram showing a control characteristic of a difference in steering angle between inner and outer wheels with respect to a difference in axial load between inner and outer wheels. 1 ... Steering handle, 2 ... Front wheel steering angle sensor,
3 ... Vehicle speed sensor, 4 ... Control circuit, L, R ... Rear wheel steering mechanism, 10 ... Rear wheel steering angle sensor, 14L, 14R ... Rear wheel, 15 ...
… Axial load sensor.

Claims (2)

[Claims] 1. A control circuit according to a turning operation of a front wheel by a turning operation of a steering wheel, determines a direction and a steering angle at which a rear wheel should be turned, and outputs an output signal to operate a rear wheel steering mechanism. In a rear wheel steering system for an automobile adapted to perform wheel steering, a left rear wheel steering mechanism and a right rear wheel steering mechanism, which should steer the left and right rear wheels separately, are provided separately and The left and right axle load sensors that detect the axle load of each rear wheel and input the axle load signal to the control circuit are provided, and the front wheel steering operation control circuit inputs each from the left and right axle load sensors. The left and right axial load difference is calculated from the generated axial load signal, and the steering angle at which the left and right rear wheels should be steered based on the axial load difference. Determined separately for the left and right to maximize the steering angle,
A rear wheel steering device for an automobile, wherein the rear wheel steering device for an automobile is configured to generate output signals for operating the left and right rear wheel steering mechanisms separately. 2. The rear wheel steering system for a vehicle according to claim 1, wherein the steering direction of the rear wheels determined by the control circuit is the same as the steering direction of the front wheels.