Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2002-11-05
2004-06-08
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090170, C123S090150
Reexamination Certificate
active
06745736
ABSTRACT:
This invention relates to a valve control mechanism for an internal combustion engine, to engines containing such mechanisms and to a method of operating the valves of an internal combustion engine.
Our British Patent No. 2 190 140 describes and claims a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in a cam carrier and being arranged for a limited degree of axial movement and having associated with it means for effecting such movement, each of the cam surfaces having an outline, in a section plane containing the axis of the camshaft, which is not parallel to that axis, whereby in use the valve action is a function of the axial location of the camshaft within the range of permitted axial movement, the mechanism also comprising a cam follower for each cam, the cam follower comprising a one-piece body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem through only a shim and has at the opposite extremity a trough of part-circular cross-section which receives a member in the form of a segment of a circular cylinder, the curved surface of which faces the interior surface of the trough, so that said member can turn with respect to said body, whilst a planar side surface of the member faces the cam surface. The present invention offers developments derived from this earlier valve control mechanism.
Our British Patent Application No. 2 341 659A (published Mar. 22, 2000) describes and claims, in or for use in an internal combustion engine, a valve control mechanism which comprises: a camshaft carrying a plurality of cams, the camshaft being mounted in, or being adapted to be mounted in, a cylinder head or cam carrier, the valve control mechanism further including means for relatively advancing and retarding the rotation of the camshaft, said advance/retard means comprising a piston housed and axially displaceable within a cylinder, the axial position of said piston being under hydraulic control, and a mechanical coupling between said piston and the camshaft, said mechanical coupling serving to translate the axial movement of said piston into relative rotational movement of said camshaft.
The present invention is concerned with a valve control mechanism of the type disclosed in GB 2 190 140B, with or without the additional features disclosed in GB 2 341 659A. The disclosure of GB 2 190 140B and of GB 2 341 659A is incorporated herein by reference thereto.
More particularly, the present invention provides in or for use in an internal combustion engine, a valve control mechanism including a camshaft carrying a plurality of cams, the cams cooperating with and thereby serving to actuate valves which control the induction of fluids into, and the exhaust of fluids from, a combustion cylinder during the operating cycle of the engine; wherein:
(i) said camshaft is arranged to be movable axially within a predetermined range of movement;
(ii) at least one of the cams has a profile which, when viewed in a plane perpendicular to the axis of the camshaft, varies as a function of the position along the camshaft axis; and
(iii) the profile of said one cam is such that, when the camshaft is moved axially to one extreme of its permitted movement, interaction between the cam and the valve with which it is associated generates no valve movement when the cam is rotated.
In one embodiment of this invention, the profile of said one cam is such that, when the camshaft is moved axially to one extreme of its permitted movement, interaction between the cam and the valve with which it is associated generates no valve lift, thereby preventing opening of the valve.
In another embodiment, the profile of said one cam is such that, when the camshaft is moved axially to one extreme of its permitted movement, interaction between the cam and the valve with which it is associated maintains the valve in an open condition.
Valve control mechanisms in accordance with this invention may be used to disable one or more of the combustion cylinders in an engine; such disablement provides benefits in terms of fuel economy.
The systems described in GB 2 341 659A allow considerable variation in the valve operating cycles; controlled variation of valve lift, valve timing and the duration of the “valve open” and “valve closed” phases are possible. Appropriate design of the cam profile used in such a system thus makes it possible to operate the engine with almost any predetermined valve/cam lift plot, and to adjust the operating conditions during running of the engine as desired. Systems of this sort will be termed herein VVLDT systems (“variable valve lift/duration/timing”).
It will be appreciated that the features described in GB 2 341 659A permit control of the valve lift and duration with different cam profiles varying infinitely within two limits (through the axial displacement of the camshaft) and of the valve timing (through the rotational adjustment of the camshaft). When these three functions operate together, the duration of valve opening, their angular shift and the envelope of the curve obtained by plotting valve position against time can also be adjusted.
In a valve control mechanism in accordance with the invention, each cam generally has associated therewith a cam follower. Preferably, each cam follower comprises a body which reciprocates within a slideway and at one extremity acts upon the end of a valve stem, the cam follower having at its opposite extremity a trough of curved cross-section which receives a member in the form of a segment having on one side thereof a surface curved correspondingly to that of said trough, and having on the other side thereof a planar surface, whereby the curved surface of the segment enables said member to turn with respect to said body, while the planar surface of the member cooperates with the cam surface.
Preferably, the cam followers are disposed relative to the valve stems such that the zone of action between the each cam follower and the end of its respective valve stem is located away from the mid-point (measured in a direction parallel to the axis of the camshaft) of a section through the cam follower in a plane which contains the axis of the camshaft and the axis of the valve stem. A particularly preferred arrangement is where said end of the valve stem is partly recessed within the body of the cam follower.
In the present invention, the profile of each cam may be such that a line connecting the points of maximum radial extent of the cam at opposite ends (in the direction of the camshaft axis) thereof is non-parallel to the axis of the camshaft. Cams of this type of profile are described as swashed cams. When viewed in the direction of the camshaft axis, cams of this sort display a phase angle between the camshaft axis and the line marking the “noses” of the cam profile. Using cams of this structure allows more extended control of valve action, in particular timing, when the camshaft undergoes axial displacement.
REFERENCES:
patent: 6474281 (2002-11-01), Walters
patent: 4229186 (1994-03-01), None
patent: 1296157 (1970-08-01), None
patent: 2203489 (1988-10-01), None
patent: 2341659 (2000-03-01), None
LandOfFree
Valve control mechanism does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Valve control mechanism, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Valve control mechanism will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3345220