Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1994-06-02
1996-09-17
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9017, F01L 104, F01L 118, F02D 1302
Patent
active
055558607
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention relates to a valve control mechanism for internal combustion engines.
BACKGROUND OF THE INVENTION
Reciprocating valves in internal combustion engines are typically actuated by a rotating cam operating a push rod, the push rod pressing a rocker arm thereby to depress the valve or alternatively in an overhead camshaft system a rotating camshaft over the engine block engages an intermediate portion of a rocker arm pivoted at one end, the other end depressing the valve. Thus the shape of the cam lobe serves to determine the duration and rate of opening and closing of the valve and the valve stroke length.
A number of systems have been previously proposed, for instance in Australian Patent Application No. 82878/82, to provide a second rotating cam operating on a rocker arm which second cam can be actuated to provide further control over operation of an engine valve. Such systems, however, are quite limited in their application as only a small number of control parameters can be altered to affect operation of the valve. This limitation severely restricts the ability to make adjustments to the system when it is desired to optimise engine performance under different operating conditions.
SUMMARY OF THE INVENTION
According to the present invention there is provided a control mechanism for an engine valve comprising two rotatable cams which engage a lever at two follower regions at different positions, the lever having a zone of application linked to the valve whereby rocking movement of the lever consequent on rotation of the cams causes opening and closing of the valve, wherein one of the two cams is in constant engagement with the lever and the other cam is in periodic engagement with the lever, a gap being provided between the other cam and its respective follower region when the other cam is not in constant engagement with the lever, the width of the gap affecting the duration of opening and closing of the valve and its stroke length.
Advantageously, the zone of application of the lever is movable longitudinally along the lever to thereby vary the stroke length of the valve.
Advantageously, the lever is movable transversely with respect to the axis of the cams and is profiled so that the gap width is varied by said transverse movement of the lever to thereby vary the timing of the valve.
Each of the cams may be of a different shape and/or size and thereby allow a very wide choice of the duration of valve opening and closing and of the valve stroke length, commonly referred to as lift. As with normal single camshaft driven valves, the shape and size of the first cam determines the position of the valve, its stroke length and its duration of opening or closing. However by the combination of the two cams operating on a pivoted lever, the pivoted lever serving to actuate the valve, there is provided the ability to alter the valve control mechanism to optimise engine performance under specific operating conditions. Further, the gap provided between the lever and the other cam gives the ability to time the cams so that the valve will open and close over a small portion of the piston stroke, this being achieved by timing the cams so that as one cam is about to lift the valve the other cam is nearing the end of its lift thereby giving a brief opening and shutting of the valve.
Further, the gap provided between the lever and the other cam eliminates the requirement to provide a heat expansion gap as the cam and the lever only engage during a part of each cycle. Also, as the contact of the other cam and its respective region is periodic, the amount of wear on these respective surfaces is significantly reduced.
The lever can be of any appropriate shape to allow the cams to engage the respective follower regions. A further variation may, for example, have a lever in which the or each of the follower regions is tapered such that the surface which contacts the or each cam is inclined obliquely to it. Alternative constructions of the lever, in addition to the various configurations of cam
REFERENCES:
patent: 1885796 (1932-11-01), Boulet
patent: 3313280 (1967-04-01), Arutunoff et al.
patent: 3888216 (1975-06-01), Miokovic
patent: 4138973 (1979-02-01), Luria
patent: 4459946 (1984-07-01), Burandt
patent: 4535733 (1985-08-01), Honda
patent: 4714057 (1987-12-01), Wichart
patent: 5052350 (1991-10-01), King
patent: 5113813 (1992-05-01), Rosa
patent: 5178105 (1993-01-01), Norris
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