Pumps – Expansible chamber type – Valved piston
Patent
1999-05-28
2000-06-27
Freay, Charles G.
Pumps
Expansible chamber type
Valved piston
417470, 92129, 92248, F04B 104
Patent
active
060799617
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The invention relates to a piston pump for a brake of a vehicle.
A piston pump of this kind for a hydraulic, slip-controlled vehicle brake system has been disclosed by DE 41 07 979 A1. The known piston pump has a pump housing with a cylinder bore in which a piston is contained so that the piston can move axially. A cam element that can be driven to rotate is provided for driving the piston into a reciprocating stroke motion in the axial direction; this cam element is disposed against an end face of the piston and the piston includes an end face that rests against a circumference which constitutes a strike surface. The piston of the known piston pump is a costly, multiple-step work piece that is manufactured in a cutting fashion by means of turning and boring. A circumference surface of the piston must be ground since it constitutes a bearing surface of the piston.
ADVANTAGES OF THE INVENTION
The piston pump according to the invention, has a piston made of plastic, which is manufactured, for example, by means of injection molding. In order for the end face of the piston, which constitutes the strike surface and which rests against the cam element, to be able to durably withstand the stresses occurring between the cam element and the strike surface predominantly due to friction, the piston has a cam strike piece made of wear resistant material on its strike surface. The cam strike piece is for example disk shaped, it is preferably inserted into an injection molding tool before the piston is injection molded, and the plastic of the piston is injection molded around the cam strike piece, wherein the strike face provided for contacting the cam element is not covered with plastic. The cam strike piece can, for example, be comprised of a metal such as hardened steel, or of ceramic, for example sintered ceramic.
Firstly, the piston pump according to the invention has an advantage that its piston can be simply, rapidly, and inexpensively manufactured in one work cycle by means of injection molding. A finishing, for example by means of grinding the piston circumference or shaping a valve seat disposed in the piston, can be eliminated. Fluid conduits possibly required in the piston for the fluid inlet into the piston pump or for the fluid outlet from the piston pump are produced with forming cores inserted into the injection molding tool so that finishing is not required for the inlet or outlet cores.
Other advantages of the invention are positive sliding properties of the piston in the pump housing due to the fact that the piston is made of plastic. In order to improve the sliding properties and to reduce wear, the plastic of the piston can have TEFLON components added to it. If a valve that controls the fluid inlet or the fluid outlet is attached to the piston, whose valve seat is embodied on the piston, the elasticity behavior of the piston made of plastic improves the closing behavior and tightness of the valve, particularly with increasing pressure.
The piston can also be used to produce a seal between the piston and the pump housing. This has the advantage that a sealing ring can be omitted.
Another advantage of the invention is that without additional expense, a stepped piston can be produced in which one end of the piston has a greater diameter than the other end of the piston.
Advantageous embodiments and improvements of the invention disclosed are a subject of the invention disclosed hereinafter.
With an embodiment of the invention, the cam strike piece has positive engagement elements on an outside which produce a positive engagement with the piston in order to improve the securing of the cam strike piece in the piston. Positive engagement elements of this kind can be continuous or interrupted ribs, grooves, or the like.
The piston pump according to the invention is provided in particular as a pump in a brake system of a vehicle and is used to control the pressure in wheel brake cylinders. The abbreviations ABS, ASR, FDR, or EHB are used for such brake systems, depending on
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Eckstein Ursula
Schuller Wolfgang
Evora Robert Z.
Freay Charles G.
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
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