Phase change coupling

Details Phase change coupling Phase change coupling

2000-05-31

2001-10-30

Denion, Thomas (Department: 3748)

Internal-combustion engines

Poppet valve operating mechanism

With means for varying timing

C123S090150, C123S090160, C123S090170, C123S090310, C464S001000, C464S002000, C464S160000, C074S56800M

Reexamination Certificate

active

06308669

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a phase change coupling for an engine camshaft.
BACKGROUND OF THE INVENTION
Phase change couplings are known for engine camshafts that allow the phase of intake and exhaust camshafts to be changed relative to one another or relative to the crankshaft in dependence upon the operating conditions of the engine. All such couplings require power to change the camshaft phase and this is derived directly or indirectly from the engine. In particular, if the phase change coupling is fluid pressure operated, the engine is required to run normally in order to provide the necessary fluid pressure.
Most of the camshaft phase change couplings currently in use have no means of locking the camshaft in a known angular position when there is insufficient actuation pressure to control the position of the phase change coupling.
The camshaft phasing couplings incorporating locking mechanisms that are known generally take the form of a locking pin that engages in a slot or hole when the phase change coupling is in its “start-up” position. In the case of an uncontrolled engine shut down, the phase change coupling may not be able to return to the start-up position and so the lock will not operate. With these existing types of phase change coupling, no amount of engine cranking will allow the phase change coupling to move to the correct position if there is insufficient control pressure because the cranking will always tend to retard the camshaft timing.
If the engine attempts to start while the phase change coupling is incorrectly positioned, poor emissions may result, or in the worst case the engine may not start at all. On account of recent emissions legislation, the risk of high pollutant levels upon engine start-up may not be tolerated.
SUMMARY OF THE INVENTION
With a view to mitigating the foregoing problems, the present invention provides a phase change coupling for an engine, comprising first means driven by an engine generated hydraulic pressure for varying the angular position of a drive member of the engine camshaft in relation to the camshaft, characterised by a locking mechanism that is operative only during cranking of the engine to lock the drive member mechanically to the camshaft in one direction of relative rotation and to permit the drive member and the camshaft to be rotated relative to one another in the opposite direction by the reaction torque of the camshaft on the drive member, whereby, when the engine generated hydraulic pressure is insufficient to drive the first means, the drive member and the camshaft are moved by the reaction torque of the camshaft towards a predetermined relative position suitable for starting the engine.
It is preferred to provide means for disabling the fuel supply to the engine until said predetermined relative position of the drive member and the camshaft is reached. Because the locking mechanism in the present invention will ensure that the camshaft will ultimately be driven into its correct phase for starting, one can afford to wait for the camshaft timing to be correct before any fuel is injected, thus avoiding any emissions concerns resulting from incorrect camshaft timing.
The invention may be applied to any fluid pressure operated phase change coupling, a suitable example being described in WO99/06675.
The locking mechanism may comprise a one-way clutch that is released when the fluid pressure used to actuate the phase change coupling reaches a sufficiently high level. Alternatively, the locking mechanism may comprise an electrically or centrifugally released clutch that only acts as a one-way clutch while the engine is being cranked below idling speed.


REFERENCES:
patent: 5040651 (1991-08-01), Hampton
patent: 5117784 (1992-06-01), Schechter
patent: 5235941 (1993-08-01), Hampton
patent: 5870983 (1999-02-01), Sato

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