Motor vehicles – Surface effect vehicles – Dynamic seal or fluid curtain
Patent
1991-03-26
1993-03-16
Focarino, Margaret A.
Motor vehicles
Surface effect vehicles
Dynamic seal or fluid curtain
180134, 91 34, B62D 512
Patent
active
051936372
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a hydraulic steering system for an automotive vehicle comprising two halves which are mutually articulated and can be swung by two cylinder-piston devices one of which is disposed on each side of the vehicle.
The invention relates primarily to steering systems for heavy automotive vehicles such as the types of machine used by contractors or entrepeneurs and being of the kind which have two mutually articulated vehicle-halves. The relative positions of these vehicle-halves are adjusted with the aid of two piston-cylinder devices to which pressure oil is pumped via a control valve, which may be manipulated by means of the vehicle steering wheel or with the aid of a steering stick. The pump rotates at the same speed as the engine of the vehicle, and has a selected displacement which is sufficiently large to ensure that the quantity of oil delivered each minute will result in satisfactory adjustment of the mutual relative positions of the two vehicle halves to a desired steering position. In the case of known steering systems of this kind, the piston-cylinder devices are double-acting and cross-connected, so that when the first chamber of one cylinder device is connected to the pump, the second chamber of the other cylinder device is also connected to the pump. This arrangement is chosen so that whenever applicable, considerable resistance can be overcome when steering the vehicle in terrain where the ground is soft, and in other instances when the steering torque is unusually large. The drawback with this arrangement, however, is that the system becomes overdimensioned for those operating conditions which occur most often in practice, i.e. conditions in which the vehicle is often on relatively firm ground or very firm ground, such as a road surface, and the steering resistance is relatively slight.
Consequently, one of the drawbacks of the known steering systems resides in the need to dimension the pump in a manner to satisfy the requirement of a relatively large flow of pressure oil in conditions where large steering torques prevail. In the case of control valves which are connected to the steering wheel of the vehicle, the valve is normally of such construction as to make it necessary to choose larger valves for larger flows of pressure oil. An example of the steering system under consideration is known from SE-B-407 545.
Accordingly, the object of the present invention is to provide a steering system which enables a considerably smaller and considerably less expensive pump to be used, and also a considerably smaller and less expensive control valve, while still maintaining satisfactory steering possibilities, both when steering resistance is normally relatively low and when said resistance is abnormally high.
This object is achieved with a steering system of the aforedescribed kind having, in accordance with the invention, the characterizing features set forth below.
In short, it can be said that in the case of the inventive steering system, the two steering cylinders are connected together with the aid of a directional valve such as to function as single-acting piston-cylinder devices during normal steering conditions, resulting in approximately half the flow of pressure oil to the first chamber of one or the other of said cylinder devices compared with cross-connected piston-cylinder devices, at the same time as the second chambers of the two piston-cylinder devices are connected to the return tank of the system. Consequently, the pump and the control valve can be made correspondingly smaller, which in turn results in considerably reduced purchase costs.
If, in an exceptional case, the steering torque should be abnormally high, the pressure in the pump line to the first chamber of one cylinder will rise and when this pressure has increased to a level above a pre-determined value, the inventive directional valve will be adjusted under the influence of said pressure to a position in which it connects the second chamber of the second piston-cylinder device to the pump, such
REFERENCES:
patent: 4081961 (1978-04-01), Dwyer
Boehler Anne Marie
Focarino Margaret A.
VME Industries Sweden AB
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