Variable valve timing

Details Variable valve timing Variable valve timing

1996-06-05

1997-09-30

Lo, Weilun

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

123 9031, 74568R, 251251, F01L 1300, F01L 1344

Patent

active

056717067

DESCRIPTION:

BRIEF SUMMARY
The present invention relate to a valve train for an internal combustion engine that permits the crank angles at which the valves open and close to be varied. The invention can be applied both to achieve an equal phase shift of the opening and closing crank angles so as not to change the duration of the valve event, or to bring about a relative change in the phases of the opening and closing times of a valve so as to vary the duration of the valve event.
As is well known, valve timing has a significant effect on engine performance and the optimum setting varies with engine operating conditions. To optimise performance under different operating conditions, it is necessary to be able to vary the valve timing.
The simplest form of variable valve timing is achieved by varying the phase of the inlet valves relative to the exhaust valves. More complex systems seek to vary the duration of valve events, which is equivalent to using a cam with a different profile.
Various variable valve timing systems have been proposed in the past that achieve either variable phase shift or variable valve event duration. These systems have suffered from various problems. Some, though feasible, have been costly to implement and some have developed excessive friction or not proved to be reliable. Furthermore, many could not be fitted as a modification to existing engines and required much of the valve train and cylinder head to be redesigned.
The most relevant prior art known to the Applicants is GB-A-2,247,061. This shows a cam formed on a sleeve that may rotate relative to the driven camshaft. Coupling between the cam sleeve and the camshaft is by means of a spring biased plunger that engages in a recess in the cam sleeve to act as a form of spring biased lost motion coupling. This permits the cam sleeve to be moved by the reaction forces exerted by the valve spring to allow the duration of the valve event to be collapsed under certain operating conditions.
According to the present invention, there is provided a valve operating mechanism comprising a hollow shaft, a sleeve journalled on the hollow shaft and fast in rotation with a cam, a coupling yoke connected by a first pivot pin to the hollow shaft and by a second pivot pin to the sleeve and means for moving the yoke radially to effect a phase change between the hollow shaft and the sleeve, wherein the means for moving the yoke radially comprise an actuating rod slidably received in the hollow shaft, a cam surface on the actuating rod and a plunger passing through a generally radial bore in the hollow sleeve to cause the yoke to move radially in response to axial movement of the actuating rod.
Preferably two plungers are provided to move the yoke in opposite directions.
If the two plungers drive the yoke without any free play, then a variable phase shift is achieved by moving the actuating rod. On the other hand, if there is free play between the ends of the plungers and the yoke, then this free play allows the yoke to accelerate once the lobe of the cam passes the full lift position of the valve, thereby allowing the valve opening event to be collapsed.
The invention will now be described further, by way of example, with reference to the accompanying drawings, in which:
FIG. 1 is a section through a camshaft along the section plane I--I in FIG. 2 for an engine with variable event timing,
FIG. 2 is a section through the plane II--II in FIG. 1, passing through the axis of the camshaft, showing both plungers in their fully extended position,
FIG. 3 is a section similar to that of FIG. 2, showing an alternative embodiment of the invention,
FIGS. 4 and 5 show sections similar to that of FIG. 2 that demonstrate the manner in which variable event timing is achieved by moving the plungers,
FIGS. 6 and 7 show the movement of the plungers by the actuating rod in order to achieve the desired variation of the valve event in FIGS. 4 and 5,
FIG. 8 is a view similar to that of FIG. 1 of an embodiment achieving only variable phasing without modifying the duration of the valve event,
FIGS. 9 a

REFERENCES:
patent: 3144009 (1964-08-01), Goodfellow et al.
patent: 4771742 (1988-09-01), Nelson et al.
patent: 5199393 (1993-04-01), Baldassini
patent: 5361736 (1994-11-01), Phoenix et al.
patent: 5365896 (1994-11-01), Hara et al.
patent: 5417186 (1995-05-01), Elrod et al.

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