JPH0328075A - Rear wheel steering device for car - Google Patents

Abstract

PURPOSE:To enhance the response at cornering without impairing the running stability in straight running by setting the reference value for the rear wheel steering angle when the front wheel steering angle is zero, to a certain point on the toe-out side. CONSTITUTION:For the front wheel steering angle thetaH, No.1, No.2 specific value theta1, theta2 are selected in accordance with the car speed sensed by a car speed sensor S1. The operating amount of a steering wheel 6, i.e., the front wheel steering angle thetaH, is sensed by a steering angle sensor S4. The reference value for the rear wheel steering angle when the front wheel steering angle thetaH is 0, i.e., the initial toe, is set to a certain point slightly on the toe-out side. When the steering angle thetaH is smaller than the No.1 specific value theta1, a drive means E shall remain out of operation while the revolution is continued with the toe- out condition held as it is, to provide a high revolving characteristic. Further, when the steering angle thetaH exceeds the No.1 specific value theta1, the drive means E is actuated to control the rear wheels into the toe-in direction, and the neg. toe-in amount is approached to zero, that shall be attained when the No.2 specific value theta2 is reached. When this No.2 specific value theta2 is exceeded, the pos. toe-in amount is increased.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a rear wheel steering device for a vehicle.

[Prior art]

As a four-wheel steering device that steers the rear wheels according to the steering angle of the front wheels, for example, as described in Japanese Patent Application Laid-Open No. 60-193780, It is known that the wheels are simultaneously steered in the toe-in direction.

This is achieved by installing cylinder devices between the left and right suspension arms that support the rear wheels and the vehicle body, and using these left and right cylinder devices, for example, within the range of conformance (elastic deformation of elastic push in the suspension), When the front wheels are steered, both the left and right rear wheels are controlled in the toe-in direction. In this way, in a vehicle in which both the left and right rear wheels are steered in the toe-in direction, the rear wheel that becomes the inner wheel when turning (which becomes the outer wheel in the next turn in the opposite direction) is steered in the opposite direction. Toe-in can be set in advance in preparation for turning.

Therefore, even on a running road with continuous left and right curves, it is possible to obtain toe-in of the rear wheels, which are the outer wheels, in a responsive manner when turning, which is preferable in terms of ensuring running stability of the vehicle.

[Problem to be solved by the invention]

In the conventional four-wheel steering device described above, the left and right rear wheels are simultaneously steered in the toe-in direction in response to the steering of the front wheels.
Controlling the wheels in the toe-in direction in this way is a control direction that increases the running stability of the vehicle.In other words, while it improves the running stability when driving straight, it may reduce the response when turning. There was a problem.

SUMMARY OF THE INVENTION An object of the present invention is to provide a rear wheel steering system for a vehicle that solves the above-mentioned problems and can improve responsiveness when turning without impairing running stability when traveling straight.

[Means to solve the problem]

In order to achieve the above object, a rear wheel steering device for a vehicle according to the present invention is a rear wheel steering device that steers both rear wheels in a toe-in direction in response to an increase in a steering angle of the front wheels. is zero,
In other words, the reference value of the rear wheel steering angle when traveling straight is set to the predetermined value on the toe-out side. [Function] The rear wheel steering device of the present invention configured as described above sets the reference value of the rear wheel steering angle to a predetermined value on the toe-out side when the front wheel steering angle is zero, so that This means that the rear wheels, especially the rear wheels located on the outside during the turn, are held toe-out at the start of the turn, improving turning performance at the beginning of the turn. Furthermore, as the steering angle of the front wheels increases, both the rear wheels are controlled in the toe-in direction, thereby ensuring the running stability of the vehicle body.

Here, since controlling the wheels in the toe-out direction is a control direction that improves the turning performance of the vehicle, the vehicle rear wheel steering system of the present invention improves the turning performance at the initial stage of turning. be.

〔Example〕

Embodiments of the present invention will be described based on the drawings.

In the system diagram of the control system according to the embodiment of the present invention shown in FIG. 1, the left front wheel IL and the right front wheel IR are linked by a front wheel steering mechanism A, and the left rear wheel 2L and the right rear wheel 2R are connected to each other by a rear wheel steering mechanism A. It is linked by mechanism B. The front wheel steering mechanism A includes two pairs of left and right knuckle arms 3L,
3R and a pair of left and right tie rondos 4L connected to it,
4R, and a relay rod 5 that connects left and right tie rods 4L and 4R, and is linked to a steering mechanism C. The steering device IIC is shown as a rack-and-pinion type, and when the steering wheel 6 is rotated to the right in the figure, the relay rod 5 is displaced to the left in the figure, and the amount of rotational displacement of the steering wheel 6, That is, the left and right front wheels IL and IR are steered to the right in the figure by an amount corresponding to the steering angle. Similarly, when the steering wheel 6 is rotated to the left, the left and right front wheels ILSIR are steered to the left.

The rear wheel steering mechanism B includes a pair of left and right knuckle arms 7L,
7R and a pair of left and right Tyrosods 8L connected to it,
8R and the connecting mechanism D that connects the left and right tie rods 8L and 8R. The coupling mechanism D has 1N swinging pieces 9L and 9R attached between the left and right rear wheels 2L and 2R so as to be movable in the left-right direction with respect to the vehicle body, and the outer end is attached to the left tie rod 8L. The inner end of the left relay rod IOL is connected to the left swinging piece 9L, and the inner end of the right relay rod IORO, whose outer end is connected to the right tie rod 8R, is connected to the right t1 moving piece 9R. ing.

Furthermore, the outer ends of a pair of left and right connecting rods IIL, IIR are connected to the left and right moving pieces 9L, 9R, and the inner ends of the connecting rods 11L, 11R are connected to the ball nut 2. ．． The ball nut 12 is supported so as to be displaceable in the longitudinal direction with respect to the vehicle body, and is driven by a step motor l serving as a driving means E.
The screw rod inserted into the ball nut 12 is rotated in accordance with the forward and reverse rotations of 3, and the ball nut l2 is displaced in the front-rear direction, causing the left and right connecting rods ILL and 11R to move inward or outward in the vehicle width direction at the same time. By displacing it, the left and right rear wheels 2L and 2R are steered in the toe-in or toe-out direction.

The control unit 14 is constituted by a microcomputer, has a built-in control means 15 for controlling the rotational speed of the step motor 13, and receives signals from the sensors S1 to S6 manually.

Here, sensor S1 is a vehicle speed detection sensor, sensor S2 is a throttle position detection sensor, sensor S3 is a brake switch that detects depression of the brake pedal, sensor S4 is a steering angle detection sensor of the steering wheel 6, and sensor S5 is a wiper switch sensor. Does S6 detect rotational displacement of step motor l3? It is an encoder.

Note that the toe-in ilTi of the wheels refers to the distance between the left wheel L and the right wheel R at the rear end, as shown in Fig. 2.
The distance A between the center lines of and the distance B between the center lines at the tip
The difference between T. It is expressed as =A-B, and when T,>0, the toe-in state occurs, and when T,<O, the toe-out state occurs.

Next, details of control for rear wheel steering will be explained.

Figure 3 shows the toe-in amount T of the rear wheels relative to the steering angle θ of the front wheels.
．． is an explanatory diagram showing a change in the steering angle of the rear wheels when the front wheel steering angle θ9=0, that is, the reference value of the rear wheel steering angle, i.e., initial}-to, is set to a slight toe-out (for example, to=2 to -3am+), When the steering angle 0■ of the front wheels is smaller than the l-th predetermined value θ1 (θ8<θI), the driving means E is not operated and the vehicle continues turning with the toe-out state, thereby obtaining high turning performance. .

When the steering angle θi of the front wheels exceeds a first predetermined value θ1, the drive means E is operated to control the rear wheels in the toe-in direction, and the negative toe-in amount T1 (toe-out amount) approaches zero. ,
When the second predetermined value θ is reached, T+=O, and when the second predetermined value θ2 is exceeded (θ,>θt), the positive toe-in is 3.
jlT. This increases the

Here, since the negative toe-in amount TI, that is, the toe-out amount, is a small value, it is necessary to install a fail-safe mechanism by providing a bar on the toe-out l side and adopting an irreversible structure on the drive means. will disappear.

The above-mentioned structure improves the initial turning ability when the vehicle turns, and improves the handling feeling. In addition, it is desirable that the first predetermined value θ and the second predetermined value θ2 be changed according to the vehicle speed ■, since running stability becomes more necessary than turning performance as the vehicle speed increases. , the first predetermined value θ and the second predetermined value θ2 are made smaller as the vehicle speed ■ increases, thereby making the toe-out state short and switching to the toe-in state early. As a result, it is possible to maintain good turning performance when turning at low speeds, while maintaining good steering ability when turning at high speeds. It is possible to improve the linear feel of the vehicle.

Note that when the vehicle speed V is lower than a predetermined value and the vehicle is running at low speed, the first
The predetermined value θ1 may be set to infinity, that is, the vehicle may run only in the toe-out state without switching to the toe-in state.

The operation of the embodiment of the present invention described above will be explained based on the flowchart of FIG. 4. First, the vehicle speed detection sensor S
1, the vehicle speed V is detected, and a first predetermined value θ and a second predetermined value θ2 are selected according to the detected vehicle speed .

Next, the steering angle of the steering wheel 6, that is, the steering angle θ■ of the front wheels is detected by the steering angle detection sensor S4, and the detected steering angle θ8 of the front wheels is set to a first predetermined value θ and a second predetermined value. Compared with θ2, 0. When θ, the rear wheel toe-in amount T is set to an initial toe of 10 (-2 to -3 tra).
Hold it in place and turn with toe-out to improve turning performance at the beginning of the turn.

At θ1<θ■>θ2, the toe-in ffiTi is shifted from the initial toe of 10 to zero.

? ■〉At θ2, the toe-in amount T. Let be a positive value,
Drive with toe-in.

Furthermore, as shown in FIG. 5, when the front wheels are steered to a third predetermined value θ3 that is larger than the second predetermined value θ2, it is preferable to switch to toe-out again.

With this structure, it is possible to improve turning performance when the front wheels are turned at a large steering angle (not used at high speeds) when turning while driving at medium to low speeds. [Effects of the Invention] Since the present invention is configured as described above, it produces the effects described below.

Since the reference value of the rear wheel steering angle when the front wheel steering angle is zero is set as a predetermined value on the toe-out side, the rear wheels, especially the rear wheels located on the outside during the turn, are held in toe-out at the start of a turn. As a result, it is possible to improve the turning performance at the beginning of a turn and also to improve the steering feeling.

[Brief explanation of drawings]

The figures show an embodiment of the present invention. Fig. 1 is a system diagram of a control system according to an embodiment of the invention, Fig. 2 is an explanatory diagram of the amount of toe-in, and Fig. 3 shows the amount of toe-in relative to the front wheel turning angle. FIG. 4 is a flowchart of the control operation, and FIG. 5 is a graph showing changes in toe-in amount for different front wheel turning angles. IL, IR... Left and right front wheels, 2L, 2R... Left and right rear wheels, B... Rear wheel steering mechanism, D... Connection mechanism, E... Drive means, l3・・・・・・Steep motor, l4・・・・
Control unit, 15... Control means for the step motor.

Claims (1)

[Claims] (1) A rear wheel steering device that steers the rear wheels in the toe-in direction in response to an increase in the front wheel steering angle, which sets the reference value of the rear wheel steering angle when the front wheel steering angle is zero to the toe-out side. A rear wheel steering device for a vehicle, characterized in that the steering device has a predetermined value.