Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1991-10-25
1992-11-10
Argenbright, Tony M.
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9031, 464 1, 464160, F01L 134
Patent
active
051614936
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The invention relates to a phase change mechanism for varying the phase of a driven member relative to a drive member. The invention can be used for the camshaft of an internal combustion engine for varying the relative phase of opening and closing of the inlet and exhaust valves in a dual overhead camshaft internal combustion engine.
The optimum times for opening and closing the inlet and exhaust valves in an internal combustion engine vary with operating parameters such as engine load and speed. In any engine with fixed angles for opening and closing the valves for all engine operating conditions, the valve timing is a compromise which detracts from the engine efficiency in all but a limited range of operating conditions. For this reason, control systems have been proposed which vary the valve timing during engine operation.
BACKGROUND ART
Most of the prior art proposals employ a linear actuator to set the desired phase shift and they rely on converting the linear movement of the actuator into a rotary movement of the camshaft relative to its drive pulley or gear. One such example has been to include a helical gear on the camshaft and to move the helical gear axially to cause the phase of the camshaft to change.
Phase change mechanisms which convert linear actuation movement into an angular phase shift have certain disadvantages which have prevented their being generally adopted in engine designs intended for mass production. Their space requirements are difficult to satisfy and even more serious problems are presented by the cost, complexity and size of the linear actuating system which they require.
Most previous attempts at actuation have required an external power source. Amongst the proposed sources of force for actuating the phase change mechanism have been electro-mechanical actuators (motors or solenoids), or hydraulic actuators. One complexity resulting from such designs is that supplying current or hydraulic fluid to a rotating actuator is troublesome. If the prime mover is stationarily mounted, then this problem is avoided but creates a new problem in how to couple the force from the prime mover to the phase change mechanism. All such proposals also involve friction losses, exacerbate the packaging problem and add to the manufacturing cost.
To mitigate the foregoing problems, there has been described in co-pending Application No. PCT/GB 89/01256 an actuating system for a phase change mechanism which uses a brake acting on a reaction member to bring about a phase change. Thus, whereas most prior art attempts at adjusting the position of the actuator have employed external active sources of power, the invention in the above application relies on the use of the rotation of the phase change mechanism to bring about the desired operation of the actuator, the only external force required being friction.
The preferred embodiment described in the above application enables continuous control over the phase change over a large range and though this is required for some complex applications, in simpler applications a two position control is quite adequate.
The present invention seeks to provide a phase change mechanism, which can be controlled by an actuating system and allows two position control to be achieved simply and inexpensively.
SUMMARY OF THE INVENTION
According to the present invention, there is provided a phase change mechanism for a camshaft of an internal combustion engine, as hereinafter set forth in claim 1.
The phase change mechanism comprises a drive member to be connected to the camshaft drive, a driven member to be connected to the camshaft; and a coupling element interposed between and movable relative to the drive and driven members. The coupling element is connected for rotation with the drive and driven members in such a manner that the phase of the driven member relative to the drive member is dependent upon the position of the coupling element. The means connecting the coupling element to the drive and driven members permit the coupling element to move bet
REFERENCES:
patent: 4305352 (1981-12-01), Oshima et al.
patent: 5056478 (1991-10-01), Ma
patent: 5117784 (1992-06-01), Schechter et al.
Argenbright Tony M.
Drouillard Jerome R.
Ford Motor Company
Lo Weilun
May Roger L.
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