Power plants – Pressure fluid source and motor – Expansible chamber type volumetric responsive measuring...
Patent
1990-04-18
1991-12-17
Kwon, John T.
Power plants
Pressure fluid source and motor
Expansible chamber type volumetric responsive measuring...
60452, 180132, F16D 3102
Patent
active
050725866
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
This invention relates to a hydrostatic auxiliary power steering mechanism, especially for motor vehicles. The auxiliary power steering mechanism contains a metering device and a control valve which channels the pressure medium which is fed to a steering motor by a variable displacement or a constant pump via a current divider valve. In the pressure line, there is provided an orifice by virtue of whose pressure difference one can activate an adjusting device of the variable displacement pump or of the current divider valve. The feed from the pressure into the valve borehole is guided via a central piston collar which is arranged on a valve piston that is movably positioned in the valve borehole.
BRIEF DESCRIPTION OF THE PRIOR ART
Such a hydrostatic auxiliary power steering mechanism is known, for example from German Patent No. 31 32 342. The pressure medium is supplied in a load-dependent fashion to the privileged steering gear by means of such a steering mechanism. Here the orifice is made with a constant cross-section for load-dependent output allocation. A constant pilot flow is delivered via the orifice when the control valve is in the neutral position. In case of adjustment of the control valve, the connections to the metering device and to the steering motor are already controlled after a small valve adjustment. The pilot flow must then be choked so that one can set a pressure that will correspond to the steering resistance. The pressure rises as the valve adjustment increases. When the set pressure overcomes the steering resistance, pressure medium is branched off in front of the orifice and is supplied to the steering motor via the metering device. As a result, the pressure difference over the orifice is altered so that the adjustment of the variable pump will occur. In case of high steering resistances, the variable pump will receive a regulating signal only when the control valve is completely deflected. The late regulating signal leads to dynamic problems such as oscillations in the steering system. The purpose of the invention is to improve the known hydrostatic auxiliary power steering mechanism so that a regulating signal is supplied early on to the adjusting pump independently of the steering resistance. The new mechanism is to be housed within the dimensions of the known control valve.
SUMMARY OF THE INVENTION
The hydrostatic auxiliary power steering mechanism of the invention includes a orifice having a crosssection that can be altered as a function of the setting position of the control valve and that has its smallest value when the control valve is in the neutral middle position. The orifice can be enlarged in both directions in case of an adjustment of the valve. This is achieved by forming the orifice between the discharge cross-section of the pressure line into the valve borehole and the central piston collar. Because the valve piston is made symmetrically in both directions with respect to the orifice, the alteration of the orifice cross-section will be the same in both directions of steering. The adjustable orifice and its control mechanism can be housed within the dimensions of the known control valve device. By virtue of the arrangement and design of the orifice according to the invention, the variable pump receives a regulating signal after the control valve has traveled a very small adjustment distance so that oscillation-free regulation of the adjusting pump is possible.
If the central piston collar is made wider than the maximum axial extent of the discharge-cross-section of the pressure line into the valve borehole, then the pressure line is closed when the control valve is in the neutral middle position. In this position, the smallest cross-section of the orifice has the value zero. In a practical manner, the segment of the pressure line located behind the orifice and the control line are connected to the piston borehole by a common connection which is located in the area of the central piston collar. If, in the process, the width of the ce
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Denion Thomas
Kwon John T.
Zahnradfabrik Friedrichshafen AG.
Zalkind Albert M.
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