Piston pump

Details Piston pump Piston pump

1992-05-04

1993-10-05

Bertsch, Richard A.

Pumps

Motor driven

Electric or magnetic motor

92 60, F04B 2100

Patent

active

052499359

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The present invention relates to a piston pump, more particularly for use in a hydraulic brake slip control apparatus, comprising a pump housing with at least one working chamber which is connectible to supply lines via an inlet valve and an output valve, and comprising a working piston movable into the working chamber and drivable to perform stroke movements.
A piston pump of the mentioned type is known from German published patent application 38 08 901. In various cases control of the flow rate supplied to the pump is performed on the suction side. It may occur as a result that the pressure fluid supply on the suction side is less that the delivery rate of the pump so that cavitation in the working chamber of the pump is encountered and, consequently, there is a risk of air being sucked in through the piston clearance.
It is an object of the present invention to provide a piston pump of the type referred to, the flow rate of which is dependent on the pressure fluid supply on the suction side.


SUMMARY OF THE INVENTION

This object is achieved according to the present invention by a charging piston which confines the working chamber and is freely movable between two end positions defined by stops, the stroke volume of which corresponds to the stroke volume of the working piston. The charging piston of the piston pump according to this invention compensates for the lack of fluid supply by its stroke movement during the suction stroke of the working piston so that merely that quantity of pressure fluid is sucked in which propagates via the suction valve into the working chamber. The quantity of pressure fluid sucked in during a suction stroke of the working piston may thus range between zero and the stroke volume of the working piston. Cavitation in the working chamber is avoided this way. Depending on the resistance to a change in position of the charging piston, at most a small pressure below atmospheric pressure will occur in the working chamber, however, without there being the risk of air intake.
When pressure below atmospheric pressure in the working chamber is to be avoided during the suction stroke, the charging piston can be movable into the working chamber by resilient means supported on the pump housing according to another feature of this invention. Owing to the force of the resilient means, the resistance to a change in position of the charging piston can be made up for and, in addition, a suction pressure can be determined which must prevail in the suction-side supply line in order to permit the piston pump to receive and deliver pressure fluid.
For employing the piston pump in a brake slip control apparatus, the charging piston is adapted to be retained in its retracted end position on the stop of the pump housing by a pressure in the working chamber of roughly 1 to 2 bar. In this design the pressure in the brake system can be decreased sufficiently, and the risk of air intake after de-activation is reliably avoided.
It can be provided in a favorable improvement of this invention that the operating cross-sections of charging piston and working piston are of equal size and that the working piston forms the stop for an end position of the charging piston. This accomplishes a simple structure, and the charging piston can be moved into its retracted end position by mechanical contact with the working piston, the reliability being enhanced thereby.
Further, it is expedient that the charging piston is sealed in relation to the cylinder bore by a ring seal. The resistance to a change in position of the charging piston can be effectively increased by means of the ring seal.
Simplification of the piston pump can be achieved further in that the working piston and the charging piston are accommodated in one common cylinder bore. It is suitable when the charging piston and/or the working piston includes on its end face close to the working chamber, an extension, the peripheral surface of which has such a distance from the wall of the cylinder bore that the flow route to the

REFERENCES:
patent: 3168045 (1965-02-01), Sebastiani

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