Variable phase coupling

Details Variable phase coupling Variable phase coupling

2000-01-28

2001-04-10

Lo, Weilun (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090310, C074S56800M, C464S002000, C464S160000

Reexamination Certificate

active

06213071

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a variable phase coupling.
BACKGROUND OF THE INVENTION
The optimum angles at which the inlet and exhaust valves of an internal combustion engine should open and close, both in relation to one another and in relation to the engine crankshaft, vary with the engine speed and load conditions. In an engine with a fixed valve timing, a compromise setting must be adopted in which different performance parameters are traded off one against the other.
To achieve improved performance over a range of engine speeds and loads, it has already been proposed to use variable phase couplings to vary the phase of a camshaft in relation to the crankshaft and in relation to another camshaft.
Several variable phase couplings are known from the prior art, each having its own advantages and disadvantages. Noise and wear are particularly serious common problems that are caused by the fact that camshafts are subjected to torque reversal during operation. While a valve is being opened by a cam on the camshaft, torque has to be applied to the camshaft in one direction to overcome the resistance of the valve spring. On the other hand, while a valve is closing, its spring attempts to accelerate the camshaft and the camshaft experiences a torque reaction from the valve train acting in the opposite direction.
A further problem with some known designs is that they cannot be retro-fitted to an existing engine because they require major modification to the engine block, cylinder head or valve train.
EP-A-0723094, which is believed to represent the closest prior art to the present invention, discloses a variable phase coupling for adjusting the phase between first and second rotatable members that addresses many of the above problems. The coupling comprises a first rotatable member within which there is coaxially mounted a second rotatable member, the two rotatable members being relatively axially displaceable with respect to one another. Helical grooves are formed on an inner cylindrical surface of the first rotatable member and on the outer cylindrical surface of the second rotatable member. Balls that are held in position relative to one another by means of a cage are engaged in the helical grooves of the two members. Adjustment means are provided for bringing about a phase change by causing relative axial displacement of the first and second rotatable members.
The second rotatable member may be formed as an intermediate cylinder or sleeve between an inner rotatable shaft and the first rotatable member, the inner rotatable shaft and the intermediate cylinder or sleeve being coupled for rotation together by a coupling with allows relative axial displacement thereof, or the first rotatable member may be formed as an intermediate sleeve or cylinder between the second rotatable member and an outer rotatable member, the outer rotatable member and the intermediate cylinder being coupled for rotation together by a coupling which allows relative axial displacement thereof.
In EP-A-0723094, the coupling between the intermediate member and one of the inner rotatable shaft or the outer rotatable member, that is to say one of the drive and driven members, is by means of axial grooves which simply allow the intermediate member to move axially without brining about any relative phase shift. Furthermore, it is essential in this earlier proposal to use cages for each set of balls.
OBJECT OF THE INVENTION
The present invention seeks to provide a variable phase coupling that can be retro-fitted to an engine and that is robust and quiet in operation.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a variable phase coupling for connecting a crankshaft to a camshaft, the coupling comprising a drive member for connection to the crankshaft having helical grooves of a first pitch, a driven member for connection to the engine camshaft having helical grooves of a different pitch facing towards the grooves in the drive member, an intermediate member disposed between the drive and driven members having helical grooves on its inner and outer surfaces, a first set of balls engaging in the pairs of helical grooves comprising the helical grooves in the driven member and the facing grooves on one surface of the intermediate member, a second set of balls engaging in the pairs of helical grooves that comprise the grooves in the drive member and the facing grooves on the other surface of the intermediate member, and means for axially displacing the intermediate member relative to the drive and driven members, the displacement of the intermediate member serving to move the balls relative to the helical grooves in the drive and driven members so as to vary the phase between the drive and driven members, wherein, in order to reduce backlash, the grooves in each pair have a slightly different pitch from one another and two balls are provided between each pair of grooves, the balls being biased apart.
The fact that all the grooves are helical means that for a given degree of phase change, a smaller axial displacement of the intermediate member is required to bring about a given change of phase. In this respect, it is preferred that the helical grooves in the drive and driven members should have the same helical angle but opposite pitch.
A serious limitation of the proposal in EP-A-0723094 is the requirement for cages and absence of means for limiting or avoiding backlash. In order to suppress the noise resulting from torque reversals in the prior art, it is necessary either to make the couplings very accurately or to employ some form of active backlash control. Such active backlash control conventionally contributes to an increase in sliding friction and increases the force required to bring about a change in phase. As a result, it is necessary to resort to a larger actuator and, if a hydraulic actuator is used, this also means a slower response because of the small diameter of the drillings in the camshaft that feed oil to the actuator.
The problem of backlash is overcome by forming the grooves in each pair of a slightly different pitch from one another and placing two balls between each pair of grooves, the balls being biased apart, for example by a spring or hydraulically.


REFERENCES:
patent: 2197155 (1940-04-01), Nardone
patent: 3807243 (1974-04-01), Yada
patent: 5078647 (1992-01-01), Hampton
patent: 5152263 (1992-10-01), Danieli
patent: 5172661 (1992-12-01), Brune et al.
patent: 5172662 (1992-12-01), Hampton
patent: 5219313 (1993-06-01), Danieli
patent: 5803030 (1998-09-01), Cole
patent: 0 723 094 (1996-07-01), None

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