Positive-displacement pump

Details Positive-displacement pump Positive-displacement pump

2000-04-14

2001-07-03

Walberg, Teresa (Department: 3742)

Pumps

With condition responsive pumped fluid control

Pressure responsive relief or bypass valve

C417S300000

Reexamination Certificate

active

06254358

ABSTRACT:

FIELD OF THE INVENTION
The invention relates to a positive-displacement pump for conveying a pressure medium from a container to a consumer, in particular a power steering gear for motor vehicles. A pump package, consisting of a rotor, a cam ring and several operating slides has been inserted into the interior of a housing. The operating slides can be embodied as vanes of a vane cell pump, or as rollers of a roller cell pump, for example. Work chambers are formed between the cam ring and the rotor, which are divided by the operating slides and which are limited in the axial direction by control plates. A bypass flow control valve is used for controlling the actual flow. A throttle of the bypass flow control valve is formed by an orifice having an adjustable cross-sectional surface. In this case the cross-sectional surface can be adjusted as a function of the displacement of a piston, which can be displaced against the force of a spring.
BACKGROUND OF THE INVENTION
Such a positive-displacement pump is known from DE-A1-41 01 210. The throttle orifice of the bypass flow control valve of this pump is arranged on a movable piston. Because of this, the flow control valve controls the positive-displacement pump with a dropping flow characteristic. This means that at an increasing number of revolutions the flow conveyed by the pump is governed. The reduced conveyed flow causes a reduced throughput pressure in the steering system and therefore a reduction of the power consumption.
In another known positive-displacement pump (DE-A1-44 33 598 or U.S. Pat. No. 5,810,565), a control throttle is displaced as a function of the conveyed flow. This means that the regulation takes place independently of the pressure. In this case, the adjustment signal is a pulse. Regulation as a function of the pressure is not possible.
However, with pumps of this type the effect of the reduced power consumption only occurs at increased numbers of revolutions.
BRIEF SUMMARY OF THE INVENTION
The invention is based on the object of creating a positive-displacement pump by simple means, wherein a regulation toward an increased governed flow takes place very rapidly in case of a pressure increase. In particular, the regulation should occur also at lower numbers of revolution.
This object is attained by means of the positive-displacement pump having a pump package and a bypass flow control valve. A throttle for the flow control valve includes an orifice-like throttle opening having an adjustable cross-sectional surface. To this end, the cross-sectional surface of the orifice-like throttle opening is designed so it can be increased in case of an increasing pressure at the orifice-like throttle opening. By means of a pressure occurring at the orifice-like throttle opening, the piston can be exclusively displaced against the force of the spring, so that the cross-sectional surface of the orifice-like throttle opening can be changed as a function of the pressure. Because of this, the piston can be easily and rapidly adjusted as a function of the conveying pressure. At lower pressures, for example at 4 bar, the piston is in a position in which the cross-sectional surface of the orifice-like throttle opening is partially closed off. With increasing pressure the piston begins to be displaced against the force of the spring. In the process the open cross-sectional surface of the orifice-like throttle opening is increased.
Advantageous and useful embodiments of the invention are recited here after. It is particularly useful if the orifice-like throttle opening is arranged so it cannot be displaced in relation to the housing. In this case the piston is designed as a control pin and works together with the orifice-like throttle opening. Here, the control pin becomes displaceable in relation to the orifice-like throttle opening and independently of the piston of the bypass flow control valve. On its one end, the control pin has a profiled tip, and the spring acts on its other end, on the side remote from the profiled tip, in the direction toward a reduction of the cross-sectional surface of the orifice. The tip is usefully designed in the form of a frustum.
In another exemplary embodiment, the orifice is also arranged so it cannot be displaced with respect to the housing. However, the piston is designed as a control piston and works together with the orifice. On its end facing the orifice, the control piston has an essentially flat front face with a recess which connects its front face with its circumferential surface. Usefully, the recess of the control piston is designed in the shape of a transverse slit.
For removing possibly generated leakage oil from the space containing the spring, this space is connected by means of a conduit with a low pressure chamber. The low pressure chamber can be constituted by the surroundings of the pump, or by a suction chamber of the positive-displacement pump.


REFERENCES:
patent: 4251193 (1981-02-01), Minnis et al.
patent: 5098259 (1992-03-01), Ohtaki et al.
patent: 5236315 (1993-08-01), Hamao et al.
patent: 5810565 (1998-09-01), Eppli

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