Vehicle with steerable front and rear wheels

Details Vehicle with steerable front and rear wheels Vehicle with steerable front and rear wheels

1996-07-11

1998-08-25

Louis-Jacques, Jacques

Data processing: vehicles, navigation, and relative location

Vehicle control, guidance, operation, or indication

Vehicle subsystem or accessory control

701 42, 701 36, 180412, 180415, 280707, G06G 776, B62D 6110

Patent

active

057992592

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a vehicle with steerable front and rear wheels. The steering angle of the rear wheels of such vehicles is set as a function of the steering angle of the front wheels and of further parameters.
2. Description of the Prior Art
At low speeds during forward travel, the rear wheels are angled opposite the front wheels in order to increase the maneuverability of the vehicle by decreasing the diameter of the turning circle. In vehicles with long wheel bases, particularly with buses, the rear of the vehicle swings out far. It is possible for the rear wheels to run over the curb when starting from a bus stop. Obstacles can be caught by the rear of the vehicle.
Because of these problems it has been proposed in connection with a known vehicle (DE-C2-35 06 048) to gradually adapt the angle of steering lock of the rear wheels as a function of the distance traveled by the vehicle to the set value determined by the steering angle of the front wheels.
It is the object of the invention to further improve the steering characteristics of a known vehicle.


SUMMARY OF THE INVENTION

This object is attained in the vehicle wherein displacement of the rear wheels when starting and steering out of forward travel follows the steering movement of the front wheels with a time delay. By means of this it is assured that the rear of the vehicle initially moves almost parallel in respect to a curb or other obstacle. The rear wheel at the outside of the turn moves inside the path of travel of the front wheel at the outside of the turn. In this way the rear wheel on the outside of the turn cannot run over an obstacle with which the front wheel on the outside of the turn should already have collided.
Practical and advantageous embodiments of the invention ensue from the dependent claims.
The time delay in displacing the rear wheels in respect to the steering movement of the front wheels is fixed in such a way that the delay is greater at low vehicle speeds than at high vehicle speeds and equals zero above a limit value of 20 km/h, for example. This results in advantages in running dynamics, such as an immediate increase in lateral force during running speeds above the limit value.
With a vehicle intended for right-hand traffic it suffices to set the time delay only in connection with a steering angle in the direction of a left turn. For example, with a bus, the bus stop is always approached from only one side, i.e. only on this side can the curb or an obstacle be run over when leaving the bus stop. A small loss in maneuverability at low running speeds can be accepted in left turns, since left turns are always made in the outside lane of the curve, i.e. in the lane with the greater radius. With vehicles intended for left-hand traffic this characteristic is provided in a reversed sense.
The control and regulating device for steering the rear wheels can be simplified in that the time delay only takes place during forward travel and not during travel in reverse.
The invention will be explained in detail below by means of an exemplary embodiment represented in the drawings.


BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a steering process of the vehicle with several positions of the vehicle.
FIG. 2 shows a flow chart diagram of a preferred method in accordance with the present invention.


DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 show a schematically represented vehicle 1 having steerable front wheels 2 and steerable rear wheels 3. The vehicle is shown in several positions during a steering process. In the initial position the vehicle is parallel with a linear lateral boundary line 4, for example a curb or a wall. In this position as well as in the end position shown, the outer contour of the vehicle is represented by heavy lines.
When moving away from the boundary line 4, initially the front wheels 2 alone are angled. Taking into consideration the starting speed, the rear wheels 3 are only angled after a time delay, i.e. after a defined time int

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