Internal-combustion engines – Adjustable combustion chamber – Piston in head adjusted
Patent
1991-03-11
1992-04-07
Okonsky, David A.
Internal-combustion engines
Adjustable combustion chamber
Piston in head adjusted
123 78D, F02B 7504
Patent
active
051017768
DESCRIPTION:
BRIEF SUMMARY
The invention relates to an engine in which the compression ratio is variable.
It is well known that the selection of compression ratio is a design compromise in any engine with fixed compression ratio. In particular, the efficiency under part load operation is improved by increasing the compression ratio but a high compression ratio cannot be used under high load conditions because of the tendency for the engine to knock on account of the high temperatures and pressures occurring in the combustion chamber. In view of the damage caused to the engine by knock under high load conditions, the compression ratio in an engine of fixed compression ratio is limited to the lowest safe value for high load operation, which leads to a corresponding sacrifice in efficiency under part load operation. Any conventional engine can thus be rendered more efficient if the compression ratio is increased only during part load operation.
It is particularly desirable to be able to vary the effective compression ratio in engines in which late or early inlet valve closing is used as a means of regulating the intake charge to achieve part load operation. Such regulation is done to reduce pumping losses in the engine but has the adverse effect of reducing the effective compression ratio even further during part load operation.
Various suggestions for varying the compression ratio are to be found in the prior art. These proposals are intended to vary the geometry of combustion chamber or the cranking mechanism while the engine is running. To date, none of these suggestions has been commercially feasible for a variety of reasons, amongst them cost, complexity, reliability and bulk.
GB-A-2,122,251 proposes an auxiliary chamber connected to the main combustion chamber by a valve which is opened at a variable instant in the compression stroke. The valve in this proposal needs to be actuated during each engine combustion cycle and is intended to remove part of the charge from the combustion, re-introducing that part of the charge into the next combustion cycle.
U.S. Pat. No. 3,889,646 describes a variable compression ratio cylinder head in which an auxiliary volume is connected to the main combustion chamber by a conventional poppet valve. Such an arrangement is not practicable because during low compression operation, that is under high load, the valve stem and head (which are poorly cooled) are fully exposed to the elevated temperatures within the combustion chamber and will cause pre-ignition. The valve will also not seal the combustion chamber effectively during such low compression operation because of leakage through the valve guide. For these reasons, the proposal in the above patent is intended only to facilitate the starting of a high compression ratio engine and once started, the auxiliary volume is permanently isolated from the combustion chamber.
A still further proposal, described in JP-A-60-27742, includes a rotor in the cylinder head which has a cut away portion to increase the residual volume when in one position. A serious problem with this, and other proposals relying on rotary valves, is that sealing around the rotor is not adequate. The increased clearance gap is a source of hydrocarbon emissions and furthermore deposits in this gap around the rotor eventually interfere with its operation.
GB-A-715,274 and other prior art patents, propose an auxiliary chamber connected to the combustion chamber permanently during low compression ratio operation and isolated from the combustion chamber during high compression ratio operation by a valve which tends to be raised off its seat by the combustion pressure. In such an engine, it is necessary to provide a valve which can effectively seal the two chambers from one another against this high pressure and for this a large external force is required. Also, once the valve is seated, the auxiliary chamber takes no further part in the engine operation and the chamber is vented to atmosphere either intentionally or by taking no special provisions to seal the stem of the valve.
According
REFERENCES:
patent: 1983351 (1934-12-01), Edwards
patent: 1994000 (1935-03-01), Lang
patent: 2042969 (1936-06-01), Snyder
patent: 2890688 (1959-06-01), Goiot
Drouillard Jerome R.
Ford Motor Company
Okonsky David A.
Sadler Clifford L.
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