Power plants – Pressure fluid source and motor – Expansible chamber type volumetric responsive measuring...
Patent
1990-05-31
1991-12-17
Look, Edward K.
Power plants
Pressure fluid source and motor
Expansible chamber type volumetric responsive measuring...
60387, 180132, F16D 3102
Patent
active
050725858
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a hydrostatic auxiliary-power steering device.
In such steering mechanisms, what is involved are oscillatory systems that tend toward pressure oscillation without damping measures. These pressure oscillations are kept stationary even when the operating condition is unchanged. Pressure oscillations can be eliminated by various measures, with a result of pressure losses or with an unfavorable effect on the synchronization characteristics of the steering mechanism. In the same way, the automatic steering reverse motion can deteriorate.
BRIEF DESCRIPTION OF THE PRIOR ART
In a steering mechanism known from DE-PS 28 07 464, the control slide of the steering valve is shaped in such a way that the damping effect remains small in the neutral position of the slide. In that way, the automatic steering reverse motion is almost unhindered. However, since a damping effect occurs in the displacement positions of the control slide, the steering reverse motion can already be hindered very strongly when there is a relatively small torque at the steering wheel. This is attributable to the fact that the control slide is shifted by the torque, with guiding edges forming a restrictor acting as a damping means. The pressure oil that is driven out of the steering motor must then flow back through this restrictor. Furthermore, big losses of pressure occur at high steering speeds since a large stream of oil has to flow through the restrictor. These pressure losses simulate a high steering resistance at the metering pump that is capable of being driven by the steering wheel, so that, when the steering motor leads with respect to the steering wheel rotation, no corresponding reaction of the steering valve can occur to counteract the disturbance of synchronization.
A steering valve for a hydrostatic steering mechanism also is known from DE-PS 23 34 365 in which control collars, control grooves and guiding edges serve the purpose of sealing and throttling the pressure oil. That steering valve has the task of generating a certain pressure-regulating characteristic curve. The pressure oscillations that occur are supposed to be broken up by a flat ascent of the characteristic curve. A disadvantage of such a design lies in the fact that not any degree of flatness at all can be selected for the ascent of the characteristic curve. That is only possible through an enlargement of the steering valve piston stroke, as a result of which the steering precision deteriorates. Since the steering mechanisms in question are frequently supplied with a stream of pressure oil whose height changes with the rate of rotation of the pump, the desired flat ascent is automatically possible only for a certain working point of the apparatus.
Therefore it is the object of the invention to provide a damping device for a hydrostatic steering mechanism that does not generate high pressure losses or influence the steering mechanism's synchronization characteristics disadvantageously. Furthermore, the suggested damping is intended to be effective at any working point of the steering mechanism.
SUMMARY OF THE INVENTION
According to the invention, a damping valve is provided for the hydrostatic steering mechanism in the intake conduit. A piston valve of the damping valve blocks a branch conduit leading from the intake conduit to the metering pump in its midposition centered by the biasing forces of a sparing. When pressure is applied as a result of adjusting movement of the steering valve, a flow cross-section to the metering pump's branch conduit opens at the piston valve. By this arrangement, only a delayed development in the branch conduit of a quick change of pressure in the intake conduit when there is a pickup of volume in the metering pump is possible. As a result, oscillations in the steering mechanism can be reliably dampened. If pressure fluctuations take place without rotational movements at the steering wheel, the damping is infinitely high since the piston valve remains in the blocked mid-position i
REFERENCES:
patent: 4462209 (1984-07-01), Thomsen et al.
patent: 4495769 (1985-01-01), Tischer et al.
patent: 4548035 (1985-10-01), Thomsen et al.
patent: 4553389 (1985-11-01), Tischer et al.
Fassbender Rolf
Ilg Bernd
Look Edward K.
Nguyen Hoang
Zahnradfabrik Friedrichshafen AG
Zalkind Albert M.
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