Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Patent
1990-10-22
1991-10-15
Cross, E. Rollins
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
123 9031, F01L 134
Patent
active
050564781
DESCRIPTION:
BRIEF SUMMARY
The invention relates to a mechanism for varying the phase of a camshaft of an internal combustion engine and in particular to 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, inter alia, with engine 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. It has been proposed previously for this reason to vary the valve timing during engine operation.
In other systems, variation of the valve timing has been proposed as a means for regulating the engine output power. For example, if the inlet valve is allowed to remain open for part of the compression stroke, the volumetric efficiency of the engine can be reduced. Such a system requires an even greater range of control over the phase of the camshaft and the control needs to be continuous over the full adjustment range.
Various proposals have been made for adjustment of the camshaft phase angle relative to the crankshaft but these systems have all been complex on account of the need to withstand the considerable torque fluctuations experienced by a camshaft during normal operation. The system must also supply the force required to rotate the camshaft against the resistance offered by the valve springs which need to be compressed.
For example, it has been suggested to include a helical gear on the camshaft and to provide some form of mechanism, be it hydraulic or electro-mechanical, for axially moving the helical gear to cause the phase of the camshaft to change.
The prior art systems have therefore all involved considerable expense and many have created packaging problems on account of their size. Generally, these mechanism have only permitted a limited degree of phase adjustment, typically 15.degree. at the camshaft, which is not sufficient for regulation of the engine output power.
Bearing in mind the cost of the phase changing mechanism and the additional load which it creates to derive the necessary power for rotating the camshaft, it has not hitherto proved generally commercially viable.
The invention seeks to mitigate at least some of the above disadvantages and to provide a variable camshaft phasing mechanism which is relatively compact, inexpensive, and does not add significantly to the engine load.
According to the present invention, there is provided a variable camshaft phasing mechanism, comprising concentric drive and driven members rotatable respectively with a drive pulley and a camshaft, the members being coupled to one another by means of an eccentric cranking element on one of the members engaged by hydraulic jacks on the other member and valve means for controlling the flow of the hydraulic fluid from the chambers of the hydraulic jacks to lock the members against rotation relative to one another in different relative angular positions of the members, characterised in that the eccentric element is tightly gripped between two hydraulic jacks acting on opposite sides of the eccentric element in order to avoid backlash, and in that the hydraulic circuit connected to the two jacks comprises a three position valve means serving to maintain the jacks isolated from one another in one position, and to provide communication between the two jacks in each of the two directions of fluid flow in each of the respective two other positions.
The use of hydraulics to alter the phase of rotation of two members is already known from GB-A-2 121 917 and GB A-2 066 986 which relate to automatic devices for advancing diesel injection pumps. Both these prior art references use two hydraulic jacks acting together to advance the phase angle and each opposed by a spring.
In the present invention, two hydraulics jacks are used to effect the phase change but they act in opposition to one another
REFERENCES:
patent: 4858572 (1989-08-01), Shirai et al.
patent: 4903650 (1990-02-01), Ohlendorf et al.
patent: 5002023 (1991-03-01), Butterfield et al.
Cross E. Rollins
Drouillard Jerome R.
Ford Motor Company
Lo Weilun
May Roger L.
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