Pumps – Expansible chamber type – Valved piston
Patent
1998-05-18
2000-08-29
Yuen, Henry C.
Pumps
Expansible chamber type
Valved piston
417554, 1375195, F04B 3910, F16K 1500
Patent
active
061098965
DESCRIPTION:
BRIEF SUMMARY
PRIOR ART
The invention is based on a piston pump for pumping hydraulic fluid, particularly for vehicle brake systems.
In a known piston pump of this type (German Patent Disclosure DE 44 07 978 A1), the stepped piston is produced as a one-piece turned part, in which a plurality of annular grooves are punched to make pump chambers and for receiving seals. Such a pump piston, because of the expense for machining, is very cost-intensive. The stepped piston has one region with a larger diameter and another region with a smaller diameter. In order to obtain a clearly apparent distinction between these two diameters, a great deal of material has to be removed from the stepped piston, which involves considerable labor. The stepped piston is also supported axially displaceably in the region of its smaller diameter. Because of this support, the stepped piston must also have good shape and surface quality in this region as well. Because the diameter of the stepped piston is reduced at this bearing point, the requisite shape and surface quality can be achieved only with increased effort.
In another known piston pump of this type (French Patent Disclosure FR 1 218 349 A1), the stepped piston is embodied in two parts and comprises a piston cylinder, which is guided in the larger-diameter portion of a stepped bore and which defines one pump chamber with each of its end faces facing away from one another, and a piston rod, guided in the smaller-diameter portion of the bore, and this rod is passed through a pump chamber and with a collar on its end form-lockingly engages a recess machined into the end face of the piston cylinder. This two-part nature of the pump again entails high production costs, especially since the piston cylinder and the piston rod require separate guides for their axial motion. Because the piston cylinder and the piston rod are each guided separately, this means overall a long structural length, because of the requisite minimum guide lengths.
ADVANTAGES OF THE INVENTION
The piston pump of the invention has the advantage over the prior art that the stepped piston can be produced very economically and has a marked cost advantage over a one-piece turned part or a stepped piston divided into two parts, that is, a piston rod and a piston cylinder. Thus, for the piston pump of the invention, with the advantage, dictated by the stepped nature of the pump piston, of higher pumping capacity even at low temperatures, the market for more-economical brake systems for vehicles of the lower price class is also opened up, which can help improve the braking performance in this class.
BRIEF DESCRIPTION OF THE DRAWINGS
The invention is described in further detail in the ensuing description in terms of exemplary embodiments shown in the drawing. Shown are:
FIG. 1, a fragmentary longitudinal section through a piston pump for a vehicle brake system;
FIG. 2, an enlarged view of detail II in FIG. 1 for a modified piston pump;
FIGS. 3a and 3b, a longitudinal section of the bush, press-fitted onto the solid cylinder, to illustrate the stepped piston of the piston pump of FIG. 2, in accordance with two exemplary embodiments.
DESCRIPTION OF THE EXEMPLARY EMBODIMENTS
The piston pump shown in fragmentary longitudinal section in FIG. 1 for pumping hydraulic fuel is intended particularly as a pump in a vehicle brake system and is used for controlling the pressure in wheel brake cylinders. Depending on the type of brake system, the abbreviations ABS, ASR, FDR and EHB are used for such brake systems. In the brake system, the pump serves for instance to feed back brake fluid from one or more wheel brake cylinders to a master cylinder (ABS), and/or for pumping brake fluid out of a supply container into one or more wheel brake cylinders (ASR, FDR and EHB). The pump is required for instance in a brake system with wheel slip control (ABS or ASR) and/or in a brake system serving as a steering aide (FDR) and/or in an electrohydraulic brake system (EHB). With the wheel slip control (ABS or ASR), for instance, locking of the wheel
REFERENCES:
patent: 5086738 (1992-02-01), Kubis et al.
patent: 5123819 (1992-06-01), Schuller et al.
patent: 5199860 (1993-04-01), Stegmaier
patent: 5577896 (1996-11-01), Harada
patent: 5823639 (1998-10-01), Zinnkann et al.
Alaze Norbert
Schuller Wolfgang
Gimie Mahmoud M
Greigg Edwin E.
Greigg Ronald E.
Robert & Bosch GmbH
Yuen Henry C.
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