Motor vehicles – Including one or more ski-like or runner members – With at least one surface-engaging propulsion element
Patent
1990-11-02
1992-02-11
Marmor, Charles A.
Motor vehicles
Including one or more ski-like or runner members
With at least one surface-engaging propulsion element
92 131, 92 136, B62D 506
Patent
active
050868632
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a steering system for motor vehicles.
In such steering systems, the vehicle's rear wheels can be turned in the opposite direction with respect to the front wheels while the vehicle is moving slowly and in the same direction when the vehicle is moving fast. For this purpose, a steering valve is provided which activates both the front-axle steering and the rear axle steering. U S. Pat. No. 4,669,567 discloses an additional adjusting motor for the rear wheels which can be activated via a directional valve in accordance with the driving speed. In the extension of the housing of the working piston, the adjusting motor includes a housing segment with two steering pistons that act as stroke limitation pistons and that are spaced by a spring. The steering pistons can be shifted on a piston rod that simultaneously carries the working piston and comes to rest against the shoulders of the housing segment by virtue of the force of the spring. In the area of the steering pistons, the piston rod has a reduced diameter whose axial extent is larger, by a small amount, than the maximum interval between the two steering pistons. When the working piston is in the mid-point position, there are provided equally large intervals between sections of the piston rod into which the elastic forces are inserted. The spring chamber located between the two steering pistons functions as a pressure chamber and is connected to a pressure line of the pump. A branch of the pressure line leads to a tank. A throttle valve, that can be influenced by a driving speed sensor, is provided in the branch.
The known steering system is operated as follows. If the driver, in case of higher speed, performs a steering motion, then the driving speed sensor causes the throttle valve to close. A pressure is built up in the pressure chamber and that pressure holds the steering pistons so that they will rest against the shoulders of the housing segment. Simultaneously, the directional valve of the adjusting motor is switched due to the influence of yet another driving speed sensor so that the rear wheels will perform an equidirectional steering motion with the front wheels. Because both steering pistons are fixed axially, the piston rod can be shifted only in the area of small intervals, whereby the elastic bodies are compressed. This results in a steering angle deflection of the rear wheels amounting to about 8.degree.. Driving stability is increased as a result of this steering process. If the driver, on the other hand, while driving slowly, performs a steering motion, then the driving speed sensor will open the throttle valve, whereby no pressure is generated in the pressure chamber. Only the spring forces the steering pistons against the housing shoulders. Simultaneously, the other driving speed sensor switches the directional valve into a position in which the rear wheels will be engaged so that they will be in a steering direction opposite to the front wheels. Depending on the steering direction, the piston rod steers one of the steering pistons against the force of the spring, away from its shoulder, as a result of which a considerably greater shifting distance for the piston rod and thus also a greater steering engagement for the rear wheels is provided. This arrangement is intended to facilitate stable steering behavior during fast driving speeds and a tight turning circle in case of slower driving speeds. In case of failure of the hydraulic system and because the piston rod is freely movable in the straight-ahead driving position, the rear wheels are inclined to a self-steering behavior pattern, especially when driving rapidly on an uneven road. This signifies an unfavorable change in the vehicle's driving behavior because uncontrolled wheel-turning and axle-shimmying will impair directional and driving stability. Moreover, in the known steering system, when the vehicle is being driven slowly, high pressures are required because one must overcome not only the friction force of the wheels to be st
REFERENCES:
patent: 4669567 (1987-06-01), Nakamura et al.
patent: 4781262 (1988-11-01), Nakamura et al.
patent: 4798256 (1989-01-01), Fassbender
patent: 4914913 (1990-04-01), St. Germain et al.
Boehler Anne Marie
Marmor Charles A.
Zahnradfabrik Friedrichshafen AG.
Zalkind Albert M.
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