Pumps – Expansible chamber type – Valved piston
Reexamination Certificate
1999-01-11
2001-01-09
Look, Edward K. (Department: 3745)
Pumps
Expansible chamber type
Valved piston
C092S171100
Reexamination Certificate
active
06171083
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a piston pump, for use in a hydraulic vehicle brake system.
Piston pumps of this kind are known in and of themselves. They have a for example cylindrical piston, which is guided so that it can move axially in a liner. The liner can be of one piece with a liner bottom on its one end face. The liner in known piston pumps is comprised of steel and is produced by machining or also by shaping, for example by cold pressing. The liner is inserted into a pump housing. A cam drive, for example, can be provided for driving the piston into a reciprocating stroke motion. It is also possible to guide the piston so that it can move axially in a pump housing without a liner. In this instance, the pump housing is comprised of steel. When a liner is used, the pump housing is frequently made of die-cast aluminum.
OBJECT AND SUMMARY OF THE INVENTION
The pump piston according to the invention, has a plastic liner or, if the piston is guided directly in the pump housing, has a plastic pump housing made. If there is a liner, then the pump housing can likewise be made of plastic or for example can also be made of die-cast aluminum or also of steel. A liner made of plastic or a pump housing made of plastic, i.e. making the part of the piston pump that axially guides the piston out of plastic, yields a considerable cost advantage over the manufacture of this part put of steel. Another advantage is the elimination of work cycles that are required when the part that guides the piston is made of steel, for example machining and/or shaping surface work of a running surface that guides the piston and belongs to the part guiding the piston, or the production of undercuts, recesses, or openings. Moreover, favorable sliding properties of the plastic with low friction and low wear are produced, as well as an elastic behavior of the liner that is improved in relation to steel. The improved elastic behavior has the advantage that for example an inlet or outlet valve of the piston pump, which valve is embodied as a check valve, whose valve seat is disposed on a liner bottom, seals better and closes faster. Furthermore, a striking of a valve closing body against the valve seat is damped when a valve of this kind closes, which reduces noise generation and wear. In addition, the plastic liner or plastic pump housing, by virtue of its elastic behavior, damps pressure vibrations, pressure pulsations, and pressure peaks that are caused by the discontinuous manner in which the piston pump feeds. Another advantage of the manufacture of the part guiding the piston out of plastic is the possibility of producing virtually any geometry desired. As a result, points of the part guiding the piston that are acted on by the flowing fluid during the fluid delivery by means of the piston pump, i.e. for example an inflow region and an outflow region, can be embodied using flow technology with a view to low noise generation and low flow resistance.
According to the invention, the liner is of one piece with a filter. This has the advantage that no separate filter is required, which saves on both manufacturing costs and assembly expenditures. Another advantage is that with an equal length of the liner, a filter surface can be embodied as larger as a result of the one-piece embodiment than with a liner that has a filter placed onto it.
In one embodiment of the invention the liner has a valve seat part so that the valve seat can be simply embodied in a wear resistant manner. The valve seat part can be made of one piece with the liner, for example by means of injection molding it with the plastic that constitutes the liner.
In another embodiment of the invention the liner has a reduced diameter in an axially defined region which, together with a pump bore of the pump housing into which the liner is inserted, constitutes an annular conduit encompassing the liner. An inflow or outflow of the piston pump according to the invention takes place by means of this annular conduit. The annular conduit has the advantage that it assures an inflow or outflow of the piston pump independent of an angular position in which the liner is inserted into the pump housing; therefore, the angular alignment does not have to be observed when installing the liner into the pump housing. Embodying the annular conduit by means of a diameter narrowing of the liner has the advantage that a diameter widening of the pump bore in the pump housing does not have to be embodied, for example by means of turning, which would bring about a considerable manufacturing expense.
The piston pump according to the invention is provided in particular as a pump in a brake system of a vehicle and is used in the control of the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS, ASR, FDR, or EHB are used for brake systems of this kind. In the brake system, the pump is used, for example, to return brake fluid from a wheel brake cylinder or from a number of wheel brake cylinders into a master cylinder (ABS) and/or to feed brake fluid from a reservoir into a wheel brake cylinder or a number of wheel brake cylinders (ASR, FDR, or EHB). The pump is required, for example, in a brake system with a wheel slip regulation (ABS or ASR) and/or in a brake system used as a steering aid (FDR), and/or in an electrohydraulic brake system (EHB). With the wheel slip regulation (ABS or ASR), for example a locking of the wheels of the vehicle can be prevented during a braking operation when there is a powerful pressure on the brake pedal (ABS) and/or an excess rotation of the driven wheels of the vehicle can be prevented when there is a powerful pressure on the gas pedal (ASR). In a brake system used as a steering aid (FDR) a brake pressure is built up in one or more wheel brake cylinders independent of an actuation of the brake pedal or gas pedal in order, for example, to prevent the vehicle from swerving off the track desired by the driver. The pump can also be used in an electrohydraulic brake system (EHB) in which the pump feeds the brake fluid into the wheel brake cylinder or cylinders when an electrical 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 preferred embodiments taken in conjunction with the drawings.
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Greigg Edwin E.
Greigg Ronald E.
Lazo Thomas E.
Look Edward K.
Robert & Bosch GmbH
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