Motor vehicles – Including one or more ski-like or runner members – With at least one surface-engaging propulsion element
Patent
1990-07-06
1992-03-31
Hill, Mitchell J.
Motor vehicles
Including one or more ski-like or runner members
With at least one surface-engaging propulsion element
280 91, B62D 900
Patent
active
050999397
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a multi-axle steering system with a mechanical hydraulic steering gear having a booster pressure steering cylinder to augment the manual steering force for front steering and a hydrostatic steering cylinder for rear steering and having a locking device to lock the rear steering wherein the locking device is arranged in the rear steering rod linkage. The locking device has a piston rod with a lockable piston and couples to the rear steering linkage which is locked mechanically by a locking piston on a piston rod which is part of a centering device wherein locking holds the rear axle in straight ahead position.
BACKGROUND OF THE INVENTION
Such a steering mechanism is described, for example, in DE-OS (German Patent application laid open to inspection) 36 15 720 (U.S. Pat. No. 4,884,647 to Mimuro) which has mechanical locking when the rear steering linkage is in straight ahead steering position.
The disadvantage is that as a result of valve leakages or other sealing defects leakage of a hydrostatic system causes displacement of the hydrostatic steering power cylinder as a result of which the positions of the front and rear steering linkages are not synchronized. Thus, it is necessary by means of a manual procedure, to turn off a selector switch for the purpose of engaging the second (rear) axle or several axles. During the next following overtravelling of the now additionally connected axle, the latter was then centered and blocked in the straight ahead position. After that, it was possible to control the axle again for steering purposes.
The prior art illustrates a manually operated valve with a centering device, whereby the centering function is performed only by a biasing spring acting to lock a piston rod in centered position. The disadvantage is that only a certain spring characteristic is available and that there is always a counterpressure. Besides, the characteristic of the device is limited.
SUMMARY OF THE INVENTION
The purpose of the present invention is to create a multi-axle steering system wherein synchronization of the steered axles with respect to each other will be possible during continuous operation.
By means of the centering device disclosed, especially by means of pressure forces on centering pistons, renewed synchronization or a synchronizing impulse is always provided continually during operations. During an overtravel of the straight ahead position of the front axle which is returned by the vehicle driver, force is applied to the steering linkage as a reversing impulse to the centering pistons.
This return of the front steering to straight ahead by the vehicle driver, controls the rear steering linkage to change direction back and forth until a centered position is reached to coincide with the straight ahead position of the front steering linkage. Thus, leakage which causes displacement of the power steering cylinder of the hydrostatic system is synchronized for straight ahead position for front and rear steering linkages.
The centering device of the invention facilitates a return of the rear steering linkage into the straight ahead position in every situation.
Yet another advantage is represented by the connection with the locking device which generally is so designed that it can be overridden in an emergency so that, especially in the case of all terrain vehicles, there cannot be any breakages in mechanical parts and the centering device acts as counterpressure in this forced steering deflection. A buffer, e.g., shock absorber, is thus created.
For example, once an overload has disappeared, there will be an automatic return to the straight-ahead position by providing pressure to the centering piston chambers.
In this way, the pressure required for centering and return is always present. This means that, even in case of failure of the hydraulic steering system, return and centering can take place via the pressure force. For safety reasons, the system can be so connected that, for example, in case of a pressure drop and upon the attainment of a certain min
REFERENCES:
patent: 4702333 (1987-10-01), Lippert
patent: 4884647 (1989-12-01), Mimuro et al.
Elser Dieter
Kogel Walter
Hill Mitchell J.
Zahnradfabrik Friedrichshafen AG
Zalkind Albert M.
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