Valve drive of an internal combustion engine

Details Valve drive of an internal combustion engine Valve drive of an internal combustion engine

1996-08-02

1998-01-13

Lo, Weilun

Internal-combustion engines

Poppet valve operating mechanism

Rocker

123 9036, 74559, F01L 118

Patent

active

057067708

DESCRIPTION:

BRIEF SUMMARY
DESCRIPTION

The invention concerns valve drive of an internal combustion engine whose finger lever (2) or rocker arm (9) is pivoted by a bore (7) on a shaft (8) for pivoting relative to a cylinder head.
Such an arrangement is known, for example, from the textbook: Bosch: Kraftfahrtechnisches Taschenbuch, 20th Edition, VDI-Verlag (1987). FIG. 1 on page 318 of this book shows a rocker arm drive which is contacted indirectly at one end by a control cam acting through a tappet rod while being held in position centrally relative to a cylinder head by means of a pedestal and a shaft. A drawback of this type of device considered to be generic is that an axial positional fixing of the rocker arm on the shaft is effected as a rule by using spacing bushes or other stops between the lever concerned and the adjacent pedestal. It is also known in the art to support the rocker arm on the pedestal with the help of at least one compression spring. Such arrangements are not only relatively complicated from the manufacturing point of view but also cause additional frictional wear.
In case a finger lever is used as a cam follower in the drive, it is known in the art to provide fixing means at the valve-proximate end of the finger lever. Thus, for example, at its end facing the associated gas exchange valve, the finger lever can comprise cheeks which extend away from the cam and prevent a lateral excursion of the finger lever. A disadvantage of this arrangement is that the axial dimension of the cheeks required in valve direction reduces the available design space for at least one valve spring by which the gas exchange valve is loaded in closing direction. Another known solution is to arrange adjusting discs having a guiding profile for the finger lever on the spring retainer of the gas exchange valve. Due to these adjusting discs, additional forces come to act on the valve stem and lead to increased friction in the guideway of the valve stem and to premature wear.
The object of the invention is therefore to create an improved cam follower of the initially cited type in which the aforesaid disadvantages and drawbacks are eliminated and which, in particular, can be fixed in an exact position relative to its pivoting axis by simple means and at low manufacturing costs.
The invention achieves this object wherein a simple axial fixing of the finger lever or rocker arm, as the case may be, on its associated shaft is obtained. Additional friction-increasing stops for the shaft on the pedestal and other complicated measures such as, for example, shoulders on the shaft can thus be dispensed with. The configuration of the invention provides a pivoting of the cam follower with particularly low friction while, at the same time, simplifying assembly.
The solution of the invention is also applicable when using hydraulic or mechanical clearance compensation elements, not specified further here, which are integrated in both embodiments in the valve-proximate end of the cam follower.
Positional fixing is achieved by a circlip which is pretensioned in an outward or an inward direction. This circlip constitutes a particularly simple means for a positional fixing of the finger lever or rocker arm because it is available as a mass product and all that is still required is to provide the necessary grooves on the housing and the shaft.
However, it is also possible to make the recess of the bore of the finger lever or rocker arm in the form of a radial bore with a rolling element arranged therein which, to achieve fixing, extends at the same time beyond an annular surface situated between the two elements (cam follower and shaft). The use of a screw as a fixing means leads to the formation of an easily disengageable connection between the cam follower and the shaft. The invention equally covers fixing means other than the aforesaid rolling elements, for instance, cylindrical or pin-type fixing means and the like.
The region of the shaft surrounded by the bore of the finger lever or rocker arm comprises a radial bore in which, to achieve an axial f

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