Pumps – Expansible chamber type – Valved piston
Reexamination Certificate
2000-04-24
2001-11-20
Koczo, Michael (Department: 3746)
Pumps
Expansible chamber type
Valved piston
C137S860000
Reexamination Certificate
active
06318979
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a piston pump which is intended for use in a hydraulic, slip-controlled vehicle brake system.
Such piston pumps are known per se. Reference may be made for instance to German Patent Disclosure DE 41 07 979 A1. The known piston pump has a piston that is axially displaceably guided in a pump housing and that can be driven by a rotationally drivable cam to execute an axially reciprocating stroke motion. As a result of the reciprocating motion, the piston increases and decreases the volume of a positive displacement chamber, which adjoins the piston on one face end and is defined by a face end of the piston. The change in volume of the positive displacement chamber causes the pumping of fluid by the piston pump in a manner known per se.
For controlling a flow of the pumped fluid through the piston pump, the piston pump has one inlet valve and one outlet valve, both of them embodied as check valves.
OBJECT AND SUMMARY OF THE INVENTION
The piston of the piston pump is embodied as a hollow piston. The positive displacement chamber of the piston pump of the invention is located inside the piston embodied as a hollow piston. Embodying the piston as a hollow piston, which makes it possible to shift the positive displacement chamber of the piston pump into the piston itself, makes a short, compact piston pump possible. The invention has the advantage of reducing the required installation space and in particular of shortening the requisite structural length of the piston pump.
At least one of the check valves of the piston pump of the invention that control the flow through the piston pump has a bandlike valve closing body of a spring-elastic material. For example, the valve closing body can be spring-elastic strip of metal (sheet-metal strip) or some other material. A valve hole is made in the piston and is covered by the bandlike valve closing body. Through the valve hole, a flow of fluid in one direction is possible, that is, into the piston embodied as a hollow piston or out of it; the bandlike valve closing body is lifted from the valve hole by the flow. In the opposite direction, the bandlike valve closing body that covers the valve hole closes the valve hole; a flow through the valve hole in the opposite direction is therefore not possible. The bandlike valve closing body and the valve hole form a check valve; the valve closing body of a spring-elastic material simultaneously forms a valve spring element. Embodying the check valve of the piston pump with a bandlike valve closing body in accordance with the invention has the advantage of a simple valve design and makes economical production of the check valve possible. The check valve furthermore has a single moving part, namely the bandlike valve closing body, making both a separate valve spring element and guidance of the valve closing body unnecessary; the valve closing body is self-guiding because of its bandlike embodiment. Another advantage is that the check valve of the piston pump of the invention can be mounted in a space-saving way on the inside or outside of the piston and requires virtually no additional installation space. Combining the check valve, which has the bandlike valve closing body, with the hollow piston makes a short, compact piston pump possible, which is furthermore simple in its design and simple to produce.
The valve closing body is channel-like; it encloses a hollow chamber between itself and the piston. The valve closing body rests with its longitudinal edges, and at points spaced apart from one another in its longitudinal direction, on the piston, so that the enclosed hollow chamber extends over a portion or virtually the entire length valve closing body and is laterally bounded along the longitudinal edges. The valve hole and piston discharges into the hollow chamber enclosed between the piston and the valve closing body. Because of the channel-like embodiment of the valve closing body, the valve closing body is subjected with fluid not only in the region of the valve hole, or in other words over the relatively small cross-sectional area of the valve hole, but instead over a relatively large area, which extends over a portion or the entire length of the bandlike valve closing body. Thus, a pressure in the valve hole acts upon the valve closing body over a relatively large area, so that even a slight overpressure suffices to lift the valve closing body from the valve hole and thus to open the check valve. In the embodiment of claim
6
, even a slight opening pressure thus suffices to open the check valve. The check valve has an improved opening behavior, and the efficiency of the piston pump is improved. Particularly when the check valve is used as an inlet valve, the piston pump of the invention has the advantage of improved aspiration performance and better filling of its positive displacement chamber.
The piston pump of the invention is intended in particular as a pump in a vehicle brake system and is used in controlling the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS (for anti-lock brake system), TCS (traction control system), ESP (electronic stability program) and EHB (electrohydraulic brake system) are used for such brake systems. In the brake system, the pump serves for instance to return brake fluid from a wheel brake cylinder or a plurality of wheel brake cylinders to a master cylinder (ABS) and/or to pump brake fluid out of a supply container into a wheel brake cylinder or a plurality of wheel brake cylinders (TCS or ESP or EHB). The pump is needed for instance in a brake system with wheel slip control (ABS or TCS) and/or a brake system serving as a steering aid (ESP) and/or an electrohydraulic brake system (EHB). With wheel slip control (ABS or TCS), locking of the wheels of the vehicle during a braking event involving strong pressure on the brake pedal (ABS) and/or spinning of the driven wheels of the vehicle in the event of strong pressure on the gas pedal (TCS) can for instance be prevented. In a brake system serving as a steering aid (ESP), a brake pressure is built up in one or more wheel brake cylinders independently of an actuation of the brake pedal or gas pedal, for instance to prevent the vehicle from breaking out of the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB), in which the pump pumps the brake fluid into the wheel brake cylinder or wheel brake cylinders if an electric brake pedal sensor detects an actuation of the brake pedal, or in which the pump is used to fill a reservoir of the brake system.
The invention will be better understood and further objects and advantages thereof will become more apparent from the ensuing detailed description of an exemplary embodiment taken in conjunction with the drawings.
REFERENCES:
patent: 474365 (1892-05-01), Carlin
patent: 1674718 (1928-06-01), Eisenhauer
patent: 2887961 (1959-05-01), Hawley
patent: 3787145 (1974-01-01), Keyes et al.
patent: 5232273 (1993-08-01), Eckstein et al.
patent: 2043002 (1970-08-01), None
patent: 2647768 A1 (1976-10-01), None
patent: 4017956 A1 (1990-06-01), None
patent: 4107979 A1 (1991-03-01), None
patent: 2021682 A (1978-07-01), None
patent: WO 90/15247 (1990-06-01), None
Greigg Ronald E.
Koczo Michael
Robert & Bosch GmbH
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