JPH0357773A - Rear wheel steering device for vehicle - Google Patents

Abstract

PURPOSE:To improve the turning performance by installing a control means for setting the steering characteristic to the same phase only in the case when the front wheels are steered in a small angle, if the car speed is smaller than a prescribed value. CONSTITUTION:When the car speed is a prescribed value, e.g., 10Km/h or less, and each front wheel 2 has a small steering angle, in other words, when a vehicle starts from a road shoulder parking position, a CPU 40 detects the front wheel starting angle thetaF at present, and rear wheels 4 and 4 are steered with the map characteristic (g) of a ROM 34 on the basis of the front wheel steering angle thetaF. In other words, when the above-described front wheel steering angle thetaF is larger than the previously set small steering angle thetaF1, the rear wheels 4 and 4 are set in the reverse phase for the front wheels 2 and 2, while, if the front wheel steering angle thetaF is smaller than the above-described small steering angle thetaF1, as in the start from the road shoulder parking position, the rear wheels 4 and 4 are set in the same phase for the front wheels 2 and 2. Therefore, the bulging-out of the rear part of the car body on start is prevented, and the turning performance can be improved.

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention provides a vehicle speed-sensitive 4W system that changes the rear wheel steering characteristic from the in-phase side to the opposite-phase side with respect to the front wheels in accordance with the vehicle speed, for example.
This invention relates to a rear wheel steering system for a vehicle such as a S.

(Prior Art) Conventionally, as the rear wheel steering device of the above-mentioned vehicle, for example,
There is an apparatus described in Japanese Patent Application Laid-Open No. 193771/1983.

That is, a front wheel steering mechanism that steers the front wheels, a rear wheel steering mechanism that steers the rear wheels, a steering mechanism linked to the above-mentioned front wheel steering mechanism, and a steering ratio (θ / θ
,) for changing the steering ratio, for example, when the vehicle speed is 20 to 50 km/h.
In this case, the rear wheel steering angle is set to zero (2WS), and at low vehicle speeds, the rear wheel steering characteristics are changed to the opposite phase side with respect to the front wheels, and at high vehicle speeds, the rear wheel steering characteristics are changed to the same phase side with respect to the front wheels. This is a four-wheel steering system for a vehicle.

However, such conventional devices have the following problems.

For example, when the above-mentioned 4WS vehicle is parked on the road shoulder and started from this parking position by turning the steering wheel to the opposite side of the road, the rear wheels are steered to the opposite phase side due to the above-mentioned rear wheel steering characteristic. There was a problem in that the rear part of the vehicle protruded onto the road shoulder when the vehicle started moving.

(Object of the Invention) An object of the present invention is to provide a rear wheel steering device for a vehicle that can prevent the rear part of the vehicle from protruding when starting from a parking position, etc., and improve maneuverability. .

(Structure of the Invention) The present invention is a rear wheel steering device for a vehicle that changes the rear wheel steering characteristic from the in-phase side to the opposite phase side with respect to the front wheels in accordance with the vehicle speed, and when the vehicle speed is below a predetermined value, The present invention is characterized in that the rear wheel steering device for a vehicle is equipped with a control means that sets the steering characteristic to the in-phase side only when the front wheels have a small steering angle.

(Effects of the Invention) According to the present invention, when the vehicle speed is below a predetermined value and the front wheels have a small steering angle, for example when starting from a roadside parking position, the above-mentioned control means sets the steering characteristic to the in-phase side. When the steering wheel is turned to the opposite side of the road, both the front wheels and the rear wheels are steered to the opposite side of the road.

As a result, it is possible to prevent the rear part of the vehicle from protruding when starting from a parking position as described above, thereby improving maneuverability.

(Example) An embodiment of the present invention will be described in detail below based on the drawings.

The drawing shows a four-wheel steering system for a vehicle, and in FIG. a rear wheel steering device 5 that steers the rear wheels 4, 4 in response to the steering of the vehicle, a power steering mechanism 6 that assists the steering force of the front wheel steering device 3 described above, and a rear wheel steering characteristic that responds to the vehicle speed. The 4WS control unit 7 changes the phase from the same phase side to the opposite phase side with respect to the front wheels 2.2.

The front wheel steering device 3 described above includes a rack shaft 8 extending in the vehicle width direction.
And ball joints 9, 9 are attached to both ends of this rack shaft 8.
Left and right tie rods 10.1 each connected via
0 and knuckle arms 11, 11, and a steering shaft l4 having a pinion 13 attached to its tip end that meshes with the rack 12 of the rack shaft 8, and this steering shaft 14 is rotationally driven via the steering wheel 1. As a result, the rack shaft 8 slides left and right, thereby steering the front wheels 2, 2 in the left and right directions about the king bin.

On the other hand, the above-mentioned rear wheel steering device 5 is a rear wheel steering rod whose both ends are connected to the rear wheels 4.4 via knuckles 15, 15, knuckle arms 16, 16, tie rods 17.17, and ball joints 18.18. 19, a motor 20 serving as an operating unit for slidingly displacing the rear wheel steering rod 19 in the vehicle width direction, and a reduction gear mechanism 2■ for transmitting the driving force of the motor 20 to the rear wheel steering rod 19 described above. There is.

The above-mentioned rear wheel steering rod 19 is provided with the following functions: when the clutch 22 is turned off when a failure occurs in the rear wheel steering device 5,
A neutral position biasing means 23 is installed as a fail-safe mechanism for biasing the rear wheels 4, 4 to a neutral position (2WS state where the rear wheel steering angle is zero).

As shown in FIG. 2, this neutral position biasing means 23 includes a locking holder 24, 24 which is spaced and fixed to a predetermined portion of the rear wheel steering rod 19, and a slide which is loosely fitted into the rear wheel steering rod 19. It is equipped with possible retainers 25, 25, a centering spring 26 stretched between these left and right retainers 25, and a stopper tube 27 fixed to the rear steering control box, and the rear wheels 4, 4 are in a neutral position. At times, the left and right retainers 25, 25 are kept in contact with the stopper tubes 27, respectively, and when the rear wheel steering rod 19 is slid to either the left or right and the rear wheels 4, 4 are steered, the rotation is reversed. The retainer 25 on the steering direction side is spaced apart from the stopper tube 27, and the compression reaction force of the centering spring 26 is used to bias the rear wheel steering rod 19 to the neutral position.

A rotary encoder 28 for detecting the rotation angle of the motor 20 is attached to one side of the motor 20, while a brake 30 is disposed between the motor rotation shaft 29 and the clutch 22 on the other side of the motor 20. When the rear wheels 4, 4 are steered at a predetermined angle, the brake 30 is activated and the motor 20 is stopped to reduce the load on the motor 20.

A plurality of reduction gears and a pawl screw 32 are provided between the output shaft 31 of the clutch 22 and the rear wheel steering rod 19.
A reduction gear mechanism 21 including the above-mentioned motor 20 is interposed, and the rotational force of the above-mentioned motor 20 is converted into a slide driving force by the above-mentioned ball screw 32 to drive the rear wheel steering rod 19.

For the above-mentioned deceleration, a gear sensor 33 is disposed near the wheel mechanism 21 to detect the amount of operation of the mechanism 21.

By the way, the above-mentioned 4WS control unit 7 is CP
Equipped with U40, ROM34, RAM35, and the above CP
U40 is a steering angle signal from a wheel steering angle sensor 36 that detects the operating amount of the steering wheel 1, and a steering angle signal from a front wheel steering angle sensor 37 that detects a front wheel steering angle according to the operating amount of the front wheel rack shaft 8. a vehicle speed signal from a first vehicle speed sensor 38 that detects the vehicle speed according to the rotational speed of the front wheels 2.2, and a vehicle speed signal from the second vehicle speed sensor 39 that detects the vehicle speed according to the rotational speed of the thrust shaft. , the motor 20, the brake 30, and the clutch 22 according to the program stored in the ROM 34 based on input signals including feedback signals from the rotary encoder 28 and the gear sensor 33. 2. Vehicle speed data to change to the same phase side with respect to 2, vehicle speed data to change the same characteristic to the opposite phase side, rear wheel steering angle to zero (2W
S) Stores necessary data such as vehicle speed data.

Furthermore, the above-mentioned ROM 34 stores a map of rear wheel steering characteristics using vehicle speed as a parameter, as shown in FIG.

In the map shown in Fig. 3, the horizontal axis shows the front steering angle θ, the vertical axis shows the rear steering angle θ1, characteristics a to f show normal vehicle speed-sensitive rear wheel steering characteristics, and characteristic g shows the vehicle speed V. is less than a predetermined value, for example 10 km/h, and the front wheels 2.2 have a small steering angle θ,
It shows the characteristics at the time of starting with the steering characteristics being on the in-phase side at 1 o'clock.

Here, when the vehicle speed is below a predetermined value, the CPU 40 described above
And the steering characteristics are set to 3rd level only when the front wheel 2 and 2 are at the small steering angle θF1.
This is a control means having the characteristic g shown in the figure.

The operation of the four-wheel steering system for a vehicle configured as described above will be explained with reference to the flowchart shown in FIG.

When the ignition switch is turned on in the first step 41, the CPU 40 turns on the RAM in the next second step 42.
Flags are set in 35 predetermined areas.

Next, in a third step 43, the CPU 40 determines the current vehicle speed V
It is determined whether V is smaller than a predetermined value, for example 10 km/h, and when V>10 km/h, the process moves to the next fourth step 44.

In this fourth step 44, the CPU 40 detects the current front wheel steering angle θ.

Next, in a fifth step 45, the CPU 40 determines the current vehicle speed V
and the current front wheel steering angle θ, after steering the rear wheels 4.4 at any one of the characteristics a to f shown in FIG. 6th step 4
At step 6, the CPU 40 sets down the flag.

Here, the above-mentioned characteristics a to f show an example, and specifically, control is performed to linearly change between these characteristics a to f according to the vehicle speed.

Normal vehicle speed sensitive 4WS control is performed in the first step 41 to the sixth step 46 described above.

By the way, when the vehicle speed ■ is less than a predetermined value, for example 10 km/h,
The control when the front wheels 2, 2 are at a small steering angle, that is, when the vehicle starts from the roadside parking position, is as follows.

That is, in the third step 43 described above, the CPU 40
When it is determined that the speed is 10 km/h, the next seventh step 47
to move to.

In this seventh step 47, the CPU 40 determines whether a flag is set in a predetermined area of the RAM 35, that is, whether F=1 or not, and when F=O, the process proceeds to the above-mentioned fourth step 44, while F; When the value is 1, the process moves to the next eighth step 48.

In this eighth step 48, the CPU 40 detects the current front wheel steering angle θ.

Next, in a ninth step 49, the CPU 40 uses the characteristic g (third
(see figure) to steer the rear wheels 4,4.

As is clear from the characteristic g in FIG. However, as when starting from a roadside parking position, the front wheel steering angle θ
When F is smaller than the above-mentioned small steering angle θFl, the rear wheels 4, 4 are in the same phase as the front wheels 2, 2.

That is, when the steering wheel 1 is turned to the opposite road side when starting from a roadside parking position, the rear wheels 4, 4 are steered to the opposite roadside side, which is in phase with the front wheels 2, 2.

As a result, it is possible to prevent the rear part of the vehicle body from protruding when starting as described above, and it is possible to improve maneuverability.

Note that the above-mentioned control to the in-phase side is executed only once at the time of oscillation, as is clear from the flowchart of FIG.

Regarding the correspondence between the structure of this invention and the above-described embodiment, the control means of this invention corresponds to the CPU 40 of the embodiment, but this invention is not limited to the structure of the above-described embodiment. do not have.

[Brief explanation of drawings]

The drawings show an embodiment of the present invention, FIG. 1 is a system diagram showing a four-wheel steering system, FIG. 2 is a system diagram showing a rear wheel steering system of a vehicle, and FIG. 3 is a system diagram showing vehicle speed-sensitive rear wheel steering characteristics. FIG. 4 is a flowchart showing 4WS control. 2... Front wheel 4... Rear wheel 5... Rear wheel steering device 40... CPU 2... Figure 3 of the previous section

Claims (1)

[Claims] (1) A rear wheel steering device for a vehicle that changes the rear wheel steering characteristic from the in-phase side to the opposite phase side with respect to the front wheels in accordance with the vehicle speed, and when the vehicle speed is below a predetermined value, the front wheels are turned at a small steering angle. A rear wheel steering device for a vehicle, which is equipped with a control means that sets only the steering characteristics to the in-phase side.