Pumps – Expansible chamber type – Plural pumping chambers
Patent
1993-10-28
1994-11-01
Gluck, Richard E.
Pumps
Expansible chamber type
Plural pumping chambers
184 24, 92240, 92153, F04B 3714, F04B 3902, F04B 3904, F04B 3912
Patent
active
053603249
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a reciprocating pump, more particularly though not exclusively a reciprocating vacuum pump of the kind used to evacuate a vehicle braking servo predominantly on vehicles driven by diesel engines.
Such vacuum pumps or so-called exhausters are usually mounted on the cylinder head or the crankcase of the engine to be operated by an engine-driven cam acting on the piston or push-rod. For the purpose of lubrication, oil from the crankcase may be led or allowed to leak into the pumping chamber and by virtue of the convenient engine crankcase mounting discharged directly into the crankcase.
However, the necessary orientation and/or disposition of the pump in any particular application is not always conducive to adequate lubrication, so that a special oil supply has to be provided.
Another consideration in the manufacture of such pumps is to facilitate the control of component tolerances, and in this and other ways to avoid or minimise high cost machining and assembly operations. More specifically, it would be highly advantageous to avoid accurate machining of the cylinder bore and the piston rod bearing concentric therewith; indeed, in the ideal, to enable construction of a pump from cast, forged or stamped elements not requiring machining. It will be understood that such considerations also go to the need for adequate lubrication and sealing, at least to the extent required to compensate for deviations in concentricity and surface finish as a result of using unmachined components.
It is particularly important to ensure adequate lubrication in automotive applications because the vacuum pump is usually driven by the vehicle camshaft and may reciprocate at 2000 to 2500 strokes per minute. The problem of adequate lubrication is exacerbated when pumps having a large bore/stroke ratio are employed, typically greater than 2, because of the need to ensure a low profile pump body on overhead camshaft engines.
According to one aspect of the invention there is provided a reciprocating vacuum pump having a cylinder, a substantially disc shaped piston reciprocal in the cylinder and said piston being driven axially by a rod running in a lubricated bearing, said piston having a peripheral seal of resilient material and said seal having peripheral skirt portions extending radially outwardly and in opposite directions, characterized in that a lubrication flowpath is provided between said bearing and the cylinder space on the side of said piston remote from the bearing. The skirt portions thus provide substantially conical sealing lands directed axially of the piston in opposite directions and providing a substantially uni-directional sealing action. The seal is formed of a low friction material, preferably an ethylene/acrylic elastomer such as VAMAC (registered trademark). Such a seal is able to accommodate taper and ovality and the flexibility and the self generating capabilities of the seal can be made appropriate to the hardness grade of the material, the hardness grade being selected to suit the surface texture and abrasive properties of the cylinder bore.
The seal may be generally Y-shaped and fitted to float in a groove around the piston but in a preferred embodiment is bonded directly to the piston. One advantageous feature arising from the use of such bonded seals is that the seal may have projecting portions moulded integrally with the seal and shaped to fit into cylinder end spaces so filling otherwise "dead" spaces and yielding an improved compression ratio.
Reciprocating vacuum pumps for automotive applications are generally mounted directly on the engine, oil spilling from the camshaft lubrication system serving to lubricate the piston rod bearing of the pump. In the absence of any specific supply, the only oil available for lubrication of the seal enters the pump through the piston rod bearing. Thus it is essentially marginal and enters only the space on the said one side of the piston. The lip of the peripheral skirt portion extending to the said one side of the piston allows sufficient o
REFERENCES:
patent: 2188106 (1940-01-01), Caldwell
patent: 2216353 (1940-10-01), Park
patent: 2668656 (1954-02-01), Booth et al.
patent: 4055950 (1977-11-01), Grossman
patent: 4214507 (1980-07-01), Hock et al.
patent: 4694734 (1987-09-01), Nomura et al.
patent: 4976591 (1990-12-01), Rivas et al.
Earle Stephen R.
Levington Henry J.
Gluck Richard E.
WABCO Automotive (UK) Limited
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