Motor vehicles – Steering gear – With alternate emergency power means
Patent
1996-09-03
1998-12-22
Johnson, Brian L.
Motor vehicles
Steering gear
With alternate emergency power means
180441, 180442, B62A 506
Patent
active
058508880
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a hydraulic steering system.
Such steering systems are employed in particular in slow-moving vehicles with high axle loads.
Steering systems of this kind have been known for a long time and are employed in a multitude of embodiments.
The steering systems comprise mainly a rotary slide control valve and an orbital displacement system. The rotary slide control valve is formed by an outer control sleeve, fitted into the casing, and an inner concentrically disposed control piston. The control piston is connected, on the one hand, by a gear hub to the steering wheel and, on the other hand, relatively movable by a pin connection to the control sleeve. The control sleeve is rigidly connected to the rotor gear wheel of the orbital displacement system with a pin connection and a drive shaft. The control piston is centered in its position by a way of a spring element relative to the control sleeve. The control piston and the control sleeve are rotatable relative to each other by a limited amount against the force of this spring element. A hydraulic connection exists between the rotary slide control valve and the orbital displacement system through commutator boreholes.
The hydraulic steering system is furnished with connections for a feed, for a return, and for two cylinder lines for the control cylinder.
These steering devices are characterized by a high volume of displacement without translation ratio between servo operation and emergency operation.
This means, however, that in case of a possible failure of the supply pump the steering system switches instantaneously to emergency operation, and that therefore all of the required steering power has to be supplied manually at the steering wheel. This is a safety risk in particular in road traffic.
Therefore, it has been a long-time endeavor to provide steering systems, which switch automatically to another translation ratio in the concrete situation of the change from servo operation to emergency operation.
Thus, the German printed patent document DE 22 28 531 C2 is known, which shows the possibility for changing the displacement volume for each rotation of the steering wheel.
This steering system is furnished with an orbital displacement system with two parallel-connected displacement units, wherein the movable gear wheels of the displacement unit are mechanically connected to each other by a gear shaft. Switching valves are disposed in the hydraulic connection lines between the two displacement units, wherein the switching valves connect the two displacement units in the presence of compression oil, i.e. in the servo steering operation, and render a displacement unit ineffective in emergency steering operation, i.e. in case of failure of the supply pump.
The number of the necessary rotations of the steering wheel for reaching a certain locking angle or steering lock of the steered wheels becomes necessarily higher based on the decreased displacement volume. However, the required steering power remains substantially constant in case of a corresponding construction of the steering and thus manageable by the operator of the vehicle.
However, the constructive expenditure and thus the cost expenditure is relatively large. Based on the complicated structure, the steering system is very much subject to interferences. Thus, the steering system does not eliminate the safety risk in road traffic.
A rotary piston machine has become known from the German printed patent document DE 21 40 569, which rotary piston machine operates in particular as an engine. The rotary slide control valve of the rotary piston machine is furnished with a switching device, wherein the switching device connects selectively each fourth of twelve valve openings of the outer control sleeve to the feed or to the discharge.
Thus, the rotary piston machine operates in one of the two operational stages with a decreased chamber volume on the pressure side and thus with a decreased torque and with an increased rotational speed. The switching device is op
REFERENCES:
patent: 4131177 (1978-12-01), Goodbary et al.
patent: 4470260 (1984-09-01), Miller et al.
patent: 4838314 (1989-06-01), Gage
patent: 4942935 (1990-07-01), Lech
patent: 5050696 (1991-09-01), McGovern et al.
patent: 5056311 (1991-10-01), Tischer
Bergmann Erhard
Schildmann Manfred
Voss Gerhard
Hydraulik Nord GMBG
Johnson Brian L.
Kasper Horst M.
Savitt Gary
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