Mechanical cup pushrod for an internal combustion engine's valve

Details Mechanical cup pushrod for an internal combustion engine's valve Mechanical cup pushrod for an internal combustion engine's valve

1997-12-04

1999-03-23

Lo, Wellun

Internal-combustion engines

Poppet valve operating mechanism

Tappet

F01L 114

Patent

active

058845950

DESCRIPTION:

BRIEF SUMMARY
FIELD OF THE INVENTION

The invention concerns a method of adjusting valve clearance with a mechanical cup tappet for a valve gear of an internal combustion engine comprising a hollow cylindrical skirt guided in a reception bore of a cylinder head, a cam-proximate end of the skirt being defined by a disc-shaped bottom, said bottom comprising on a cam-proximate side, an upper, wear-resistant contact disc for the cam, said contact disc extending over a major part of a diameter of the bottom, said bottom comprising on a cam-distal side, a lower contact disc for a stem of a gas exchange valve, a diameter of the lower contact disc being substantially smaller than a diameter of the upper contact disc.


BACKGROUND OF THE INVENTION

Valve tappets of the pre-cited type are used in valve gears of internal combustion engines and serve to transmit a lifting motion of a control cam to a gas exchange valve. It is known in this connection, for example, from U.S. Pat. No. 4,909,198, to arrange both upper and lower contact discs in the region of the bottom of the tappet. In this document, which is considered as species-defining, the lower contact disc serves as a wear protection disc because the tappet housing as a whole is made of a light weight material such as aluminium. The upper contact disc of this prior art document, which has a substantially larger diameter than the lower contact disc, serves not only for an initial adjustment of valve clearance during assembly of the internal combustion engine but also for an adjustment of valve clearance in accordance to the operating periods of the internal combustion engine proposed by the manufacturer. During an initial mounting of the cup tappet already, adjusting ranges of, for instance, up to 3.5 mm fluctuations in thickness have to be realized. Thus, the force of the valve spring which loads the cup tappet towards the cam has to match the highest conceivable mass of the tappet and is thus higher than desirable. These possibly, relatively high oscillating masses of the tappet cause an unnecessary increase of friction work in the valve gear. In the case of subsequent adjustment of valve clearance during maintenance work on the internal combustion engine, the valve clearance is likewise corrected via the upper contact disc which therefore has a solid configuration. This means that upper contact discs in a large number of different thicknesses have to be kept in store by engine manufacturers and servicing stations. The main drawback of the prior art tappet of U.S. Pat. No. 4,909,198, however, is that it has a relatively large mass despite its light weight housing because valve clearance has to be compensated through its upper contact disc which is relatively "solid" compared to the lower contact disc and because it has a large adjusting range.


OBJECT OF THE INVENTION

The object of the invention is to provide a method of adjusting valve clearance with a cup tappet of the pre-cited type in which the mentioned drawbacks are eliminated and, in particular, to reduce the mass of the tappet further, while simultaneously improving ease of mounting and servicing.


SUMMARY OF THE INVENTION

The invention achieves this object by the fact that identical upper contact discs are used in an initial mounting of the cup tappet in the valve gear of all internal combustion engines of a particular type, a valve clearance occurring before the initial mounting of the cup tappet is adjusted to a desired value by lower contact discs having an appropriate thickness, the upper contact disc has an extremely small thickness in keeping only with the required strength properties, and a variation of valve clearance occurring during operation of the internal combustion engine is compensated by upper contact discs having an appropriate thickness. The invention achieves its object alternatively by the fact that valve clearance in an internal combustion engine is adjusted through upper and lower contact discs wherein the ratio between a clearance adjusting range H.sub.SW of the lower contact disc and a cle

REFERENCES:
patent: 2863432 (1958-12-01), O'Brien
patent: 4909198 (1990-03-01), Shiraya et al.
patent: 5267538 (1993-12-01), Speil et al.
patent: 5289804 (1994-03-01), Mori
patent: 5372099 (1994-12-01), Matsunuma et al.
patent: 5445119 (1995-08-01), Regueiro
JP 58-101204 A, Patent Abstracts of Japan; M-241, Sep. 8, 1983, vol. 7, No. 203.

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