Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1997-04-29
1998-05-05
Lo, Weilun
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9017, 123 9055, F01L 114, F01L 1300
Patent
active
057461651
DESCRIPTION:
BRIEF SUMMARY
The invention concerns a valve drive of an internal combustion engine wherein the cams contact at least one cam follower (1), at least one high lift cam (5) and one low lift cam (4) situated next to the high lift cam (5) in axial direction of the camshaft and being arranged out-of-phase with each other, said cams (4, 5) actuating the cam follower (1) in opening and closing directions of a gas exchange valve (51), the cam follower (1) being comprised of at least a first and a second unit (3, 2) which are displaceable relative to each other, the low lift cam (4) being in contact with the first unit (3) and the high lift cam (5) being in contact with the second unit (2).
A valve drive of the aforesaid type known from DE-42 02 506, comprises a cam follower having an annular bottom portion and a circular bottom portion concentric thereto. A low lift cam actuates the circular bottom portion, while the annular bottom portion is actuated by a cam of higher lift arranged on each side of the low lift cam in camshaft direction. The two bottom portions can be coupled to each other by hydraulic coupling means to achieve a maximum stroke of the tappet. As viewed in camshaft direction, the contour of the low lift cam is situated entirely within the projected contour of the high lift cam but slightly out-of-phase therewith. However, to obtain a more optimum filling of fuel-air mixture, it is advantageous, at a certain speed and loading of the internal combustion engine not only to lay the valve opening time point of the low lift cam in advance of the valve opening time point of the high lift cam but also to shift the lift of the low lift cam partially out of the lift of the high lift cam. At the same time, the hydraulic coupling of the units known from the generic prior art document proves to be unfavorable due to its compressibility arising from leakage losses, oil foaming and the like.
It is therefore an object of the invention to create a valve drive comprising at least one cam follower of the initially described species in which the mentioned drawbacks are eliminated, and in which, more particularly, a shifting of the valve opening time point of the low lift cam is achieved without influencing the valve opening time point of the high lift cam by simple means, and a reliable coupling of the two units of the cam follower is assured.
By virtue of the displaceble piston, the excess lift of the low lift cam is neutralized by a simple axial movement as long as the cam follower is coupled to the high lift cam. Because of said piston, which can also be locked in place for coupling the cam follower to the low lift cam, the load reversal potential of the cam follower can be exploited more optimally than in the cited prior art. Thus, it is no problem to advance the timing point of opening of the gas exchange valve when the engine is running at low speed and low load. However, a configuration, not specified here, is also conceivable with which, by an appropriate arrangement of the cams, the valve opening time point of the low lift cam lags behind that of the high lift cam.
In an advantageous embodiment of the invention, the cam follower is configured as a tappet.
Due to the fact that, in this preferred embodiment, the circular bottom portion protrudes beyond the annular bottom portion during the base circle phase of the control cams and in the coupled state of the elements, it is possible to configure the low lift cam so that it does not protrude beyond the outer contour of the high lift cam as viewed in camshaft direction although its lift is in excess of the lift of the high lift cam. However, a further embodiment, in which the two bottom portions are flush with one another during the base circle phase of the control cams, is both conceivable and intended. In such an embodiment, it is possible as set forth initially, to have the tip of the low lift cam protrude beyond the outer contour of the high lift cam as viewed in an axial direction of the camshaft.
Further developments of the invention are directed to the arrangement of t
REFERENCES:
patent: 5287830 (1994-02-01), Dopson et al.
patent: 5343833 (1994-09-01), Shirai
patent: 5603294 (1997-02-01), Kawai
patent: 5651335 (1997-07-01), Elendt et al.
Maas Gerhard
Speil Walter
INA Walzlager Schaeffler KG
Lo Weilun
LandOfFree
Valve drive of an internal combustion engine 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 drive of an internal combustion engine, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Valve drive of an internal combustion engine will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-45667