Internal-combustion engines – Poppet valve operating mechanism – Lubrication
Reexamination Certificate
2000-03-02
2001-06-19
Lo, Weilun (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
Lubrication
C123S090170, C123S1950HC
Reexamination Certificate
active
06247436
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to a front cover for an internal combustion engine.
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, and optimum valve lift all vary with the engine speed and load conditions. In an engine with fixed camshafts, a compromise setting must be adopted in which the different performance parameters are traded off one against the other.
To achieve performance improvements over a range of engine speeds and loads, it has already been proposed to vary the cam phase, duration, lift or a combination of these parameters in relation to the crankshaft by the introduction of variable valve actuation mechanisms.
Several variable valve actuation mechanisms are known from the prior art each having its own advantages and disadvantages. The majority of these mechanisms use oil pressure to control their operation via a control valve to which the oil is supplied by way of drillings in the camshaft and/or the cylinder head. A problem that is encountered with this approach is that the rate at which oil can be supplied to the control valve is restricted by the size of the drillings. Furthermore, there will be a drop in oil pressure due to the cylinder head being far removed from the oil pump in the case of many engines. Consequently, the variable valve actuation mechanism can only respond slowly when a change to its current setting is required.
A still further disadvantage is that the requirement for oil passages in the engine block, cylinder head and valve train can make it difficult to retro-fit the variable valve actuation mechanism into an existing engine.
EP-A-0,704,605 discloses an internal combustion engine having a crankshaft and a camshaft the ends of which project from a front end of the engine, a hydraulically operable variable valve actuation mechanism at the front end of the engine for driving the camshaft, an engine driven pump located at the front end of the engine and drive means located at the front end of the engine for transmitting torque from the crankshaft to the variable valve actuation mechanism. The engine is fitted with a front cover which covers the front end of the camshaft but does not reach down as far as the crankshaft nor the engine oil pump.
OBJECT OF THE INVENTION
The present invention accordingly seeks to provide a more convenient means of supplying oil under pressure to a hydraulic variable valve actuation mechanism, that achieves a more plentiful supply of oil under pressure and that can be retrofitted to some existing engines without major modification.
SUMMARY OF THE INVENTION
According to the present invention, there is provided an internal combustion engine having a crankshaft and a camshaft the ends of which project from a front end of the engine, a hydraulically operable variable valve actuation mechanism at the front end of the engine for driving the camshaft, an engine driven oil pump located at the front end of the engine and drive means located at the front end of the engine for transmitting torque from the crankshaft to the variable valve actuation mechanism, characterised by a front cover overlying the variable valve actuation mechanism, the end of the crankshaft projecting from the front end of the engine and the torque transmitting drive means, and by oil supply passages formed in the front cover and directly connected to the engine driven oil pump and to the variable valve actuation mechanism, to enable the resistance to oil flow of the hydraulic circuit connecting the engine drive oil pump to the variable valve actuation mechanism to be reduced.
In the present invention, oil is supplied to the variable valve actuation mechanism without the need for the oil to flow through the drillings in the camshaft. The oil passages in the front cover can therefore be sized as required and no restriction is placed on them by such considerations as the diameter of the camshaft and the dimensions of the camshaft bearings. Furthermore, because few modifications are required in the engine block, cylinder head and valve train, the invention allows variable valve actuation to be retrofitted to existing engines.
An engine driven oil pump can conveniently be located either at the front end of the engine or within the engine cover, allowing a relatively short passage of large diameter to be mounted on, or formed in, the front cover to transfer oil from the engine pump to the variable valve actuation mechanism. Hence, a large oil flow rate can readily be established and there will not be a serious drop in the pressure in the oil reaching the valve actuation mechanism.
It is also preferred that the cover should incorporate a regulating valve for controlling the oil supply to the valve actuation mechanism.
The actuation mechanism may include a cylindrical working chamber mounted for the rotation with the engine camshaft and the front cover may include an end closure for the working chamber sealed against the cylindrical wall of the chamber by means of rotary seals. As an alternative to rotary seals, the passages in the cover may communicate with short large diameter bores formed in the engine block or cylinder head and connected directly to the variable valve actuation mechanism without passing through drillings in camshaft.
It will be appreciated that the invention is not restricted to any particular valve actuation mechanism and may be used with any mechanism that is hydraulically operated.
In a further development of the invention, a water pump may be mounted on the engine front cover and driven by a pulley mounted on the crankshaft. The coolant circuit of the water pump may in this case comprise further passages formed in the front cover and connecting the water pump to coolant galleries in the engine block and/or the engine cylinder head.
REFERENCES:
patent: 5301639 (1994-04-01), Satou
patent: 5474038 (1995-12-01), Golovatai-Schmidt et al.
patent: 5566651 (1996-10-01), Strauss et al.
patent: 5718196 (1998-02-01), Uchiyama et al.
patent: 5797363 (1998-08-01), Nakamura
patent: 5842451 (1998-12-01), Eisebeck et al.
patent: 196 47 299 (1998-04-01), None
patent: 0 704 605 (1996-04-01), None
patent: 0 863 297 (1998-09-01), None
Lancefield Timothy Mark
Methley Ian
Lo Weilun
Mechadyne PLC
Smith-Hill and Bedell
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