Desmodromic cam driven variable valve timing mechanism

Details Desmodromic cam driven variable valve timing mechanism Desmodromic cam driven variable valve timing mechanism

2000-01-13

2001-11-06

Denion, Thomas (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

Valve driven closed

C123S090150, C123S090160, C123S090170, C123S090250

Reexamination Certificate

active

06311659

ABSTRACT:

TECHNICAL FIELD
The invention relates to variable valve timing mechanisms and, more particularly, to valve actuating mechanisms for varying the lift and timing of engine valves.
BACKGROUND OF THE INVENTION
U.S. Pat. No. 5,937,809, issued Aug. 17, 1999, discloses cam driven variable valve timing (VVT) mechanisms which are relatively compact, and are applicable for operating individual or multiple valves. In these mechanisms, an engine valve is driven by an oscillating rocker cam that is actuated by a linkage driven by a rotary eccentric, preferably a rotary cam. The linkage is pivoted on a control member that is, in turn, pivotably about the axis of the rotary cam and angularly adjustable to vary the orientation of the rocker cam and thereby vary the valve lift and timing. The rotary cam may be carried on a cams haft. The oscillating cam is pivoted on the rotational axis of the rotary cam.
U.S. patent application Ser. No. 09/129,270, filed Aug. 5, 1998, discloses a similar cam actuated VVT mechanism having various additional features, including a variable ratio pin and slot control member drive providing advantageous control characteristics and a worm drive for the control shaft designed to prevent backdrive forces from overcoming the actuating force of the small drive motor. A particular embodiment of flat spiral mechanism return springs is also disclosed.
SUMMARY OF THE INVENTION
The present invention provides improved VVT mechanisms wherein dual desmodromic rotating cams are provided for actuating oscillating cam drive mechanisms. The dual rotating cam drive includes both opening and closing cams that actuate the mechanisms in both valve opening and valve closing directions. The desmodromic cams thus avoid the need to provide return springs which are required in previous cam driven VVT mechanisms to bias the mechanisms toward a valve closed position. The dual cams may be located at axially adjacent positions on a single cams haft. A single rocker with dual arms may carry separate followers, one engaging each cam to provide the positive opening and closing action needed to eliminate mechanism return springs without requiring extended motion of the oscillating cams as in a crank driven mechanism.
A mechanism lash adjuster or a semi-compliant return follower arm may be used to take up lash between the dual cam followers of the rotary cams.
The advantages of control by a variable ratio slide and slot control lever drive as well as a back force limiting worm drive for the control shaft may be combined with the dual cam mechanism to provide additional system advantages comparable to those designed for single cam actuated mechanisms requiring return springs.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.


REFERENCES:
patent: 1671973 (1928-06-01), Anderson
patent: 1740790 (1929-12-01), Stanton
patent: 4364341 (1982-12-01), Holtmann
patent: 5988125 (1999-11-01), Hara et al.

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