Internal-combustion engines – Four-cycle – Variable clearance
Patent
1997-08-28
1999-06-01
McMahon, Marguerite
Internal-combustion engines
Four-cycle
Variable clearance
123 48B, G05G 100
Patent
active
059080140
DESCRIPTION:
BRIEF SUMMARY
This invention relates to a reciprocating piston type internal combustion engine with a variable compression ratio according to the preamble of the patent claim. The great majority of internal combustion engines in use today are reciprocating piston type engines. In a reciprocating piston engine of this type, the compression ratio is the ratio between the combustion space that remains free when the piston is at the top dead-centre and the total cylinder volume when the piston is at the bottom dead-centre. The combustion processes in such reciprocating piston engines and in internal combustion engines in general are very complex and are influenced by several parameters. This is just as true of petrol engines as it is of diesel engines or indeed engines which run on other types of fuels. Optimum fuel combustion and hence maximum engine efficiency basically depend on the volume of air sucked or taken in, its temperature, humidity and compression, on the type and quality of the fuel injected into the engine, on the way the fuel mixes with the air and on the ignition of the mixture. Hence the quality of the fuel/air mixture and the precise timing and manner in which it is ignited also affect the movement of the piston. The pressure pattern during combustion also plays a major role, as does the timing of combustion per se. When an engine is running under a high load, the combustion pressures are higher than when it runs idle. If the engine is run at a high speed, there is far less time for combustion than if the engine is allowed to run at a low speed. In addition to these variables, which depend on the way the engine is operated, external climatic conditions also influence the way the engine runs and the efficiency of the combustion. Hence it is not all one and the same whether an engine is operated at sea level or at high altitudes where the air pressure is low. The external temperature and the weather-related air humidity also play a role.
Over the last few years, great advances have been made in relation to optimizing engine combustion processes; these are essentially due to the constantly expanding capabilities of the available microprocessor controls on the one hand, and to the achievements made in the field of materials engineering on the other hand. In many engines, the composition of the fuel/air mixture is now controlled by a microprocessor. The quantity of air sucked in, its temperature and humidity are measured, for example, and the volume of fuel injected is recalculated and optimized for each injection in line with these parameters. Furthermore, the instant of ignition and the timing and duration of the fuel injection are recalculated each time by a microprocessor which also takes the engine speed into account. Improved materials have also made it feasible to use 4-valve technology in engines for everyday use whereas earlier on this costly technology was used exclusively for high performance engines. Improved fuels, i.e. improved grades of petrol in particular, plus better materials allow higher combustion temperatures and pressures and have hence tended to lead to a higher compression coefficient in modern engines in comparison with the past. Compression is also a factor with a crucial impact on the combustion of the fuel/air mixture and hence the efficiency of the engine. As a general rule, the higher the compression ratio, the better the efficiency of combustion. The limit of maximum compression is defined by the knock resistance rating, in that if it is compressed too much, the air/fuel mixture self-ignites and hence uncontrolled combustions occur at the wrong times. The engine then knocks and sustains damage.
All the above-mentioned parameters are involved in a complex interplay. A vehicle engine is driven at constantly changing speeds and under different loads. On top of that there are all the various external factors such as fluctuating air temperature, air pressure and humidity. Hence a conventional engine with a fixed compression ratio can never run ideally or to optimum effect. The engine
REFERENCES:
patent: 1553009 (1925-09-01), Stuke
patent: 4044629 (1977-08-01), Clarke
patent: 5158047 (1992-10-01), Schaal et al.
McMahon Marguerite
Schindler Edwin D.
TK Design AG
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