Internal-combustion engines – Poppet valve operating mechanism – Valve driven closed
Patent
1985-10-31
1986-06-17
Cline, William R.
Internal-combustion engines
Poppet valve operating mechanism
Valve driven closed
123 9027, F01L 130
Patent
active
045949727
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a valve mechanism.
In a conventional valve train, a spring is used to return the valve after opening. The spring must be relatively stiff to counteract the inertia of the valve so as to allow the engine to run at a safe maximum design speed without valve bounce. This limits the rate of acceleration of the valve, which it is desirable to increase in order to improve the time lift integral of the valve opening period, that is to say to increase the breathing efficiency of the engine. Higher valve acceleration requires a stiffer spring which increases the stresses and causes excessive wear. Valve train friction is also increased and the torque required to drive the valve train fluctuates widely as the springs are compressed and relaxed.
There have been proposed in the past so called desmodromic valve mechanisms in which the valve is returned by positive mechanical action and does not require the use of a stiff return spring. Such a mechanism therefore has the potential of giving better breathing efficiency at high engine speed, less valve train friction and less fluctuations in the driving torque. However, most known designs are complicated, expensive to implement and require very accurate dimensional control.
The present invention seeks to provide an operating mechanism for a valve in which the closing movement of the valve is effected or else at least assisted by positive cam action but which can be implemented in a less costly and complex manner.
In accordance with the present invention, there is provided a vaive operating mechanism for an internal combustion engine, comprising a cam driven in synchronism with the engine crankshaft, a cam follower acted upon by an opening profile of the cam and operative to move a valve in an opening direction and a movable closing member having two profiles thereon the first interacting with the cam and the second with the cam follower, closure of the valve being effected by the opening profile of the cam acting on the first cam profile of the closing member to move the closing member in such a direction that the second cam profile of the closing member acts on the cam follower to close the valve.
Preferably, the closing member has a generally V-shaped edge of which one side constitutes the first cam profile and the other constitutes the second cam profile. The closing member may either be pivotable or slidable relative to the cam shaft.
Advantageously, a light spring is provided to move the closing member in a direction to close the valve but this spring need not be very stiff and serves merely to support the weight of the valve and to take up the small tolerances when the valve is nearly closed.
It is possible for the cam follower to consist of a roller mounted directly in line with the valve stem. Alternatively, the cam follower may comprise an intermediate member, such as a pivoted lever, having a first cam surface engageable by the cam and carrying a roller acting as a follower for the second cam profile of the closing member. The valve in the latter case may either be coupled to an extension of the lever or may be mounted directly in line with the roller.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a schematic view of a first embodiment of the invention shown with the valve in a closed position,
FIG. 2 is a view of the same embodiment as shown FIG. 1 with the valve in an open position,
FIG. 3 is a schematic view of a second embodiment shown with the valve about to begin to open,
FIG. 4 is a view of the same embodiment as shown in FIG. 3 with the valve fully open,
FIG. 5 shows the embodiment of FIGS. 3 and 4 when the valve is fully closed, and
FIG. 6 is a perspective view of a further embodiment of the invention.
In FIG. 1, there is shown a valve 10 which is connected by means of a collet arrangement generally designated 12 to a guide 14. The guide 14 is connected to a fork 16, of which only one limb is shown, carrying a cam follower roller 18 at its
REFERENCES:
patent: 1227812 (1917-05-01), MacPherson
patent: 1444857 (1923-02-01), Taub
patent: 1503384 (1924-07-01), Sewell
patent: 2015135 (1935-09-01), Brady
patent: 2833258 (1958-05-01), Lorscheidt et al.
patent: 2954017 (1960-09-01), Forstner
Cline William R.
Ford Motor Company
McCollum Robert E.
Neils Peggy
Sadler Clifford L.
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