Variable compression ratio engine

Internal-combustion engines – Four-cycle – Having subcharger associated with the cylinder

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Details

123432, 123568, F02M 2507, F01L 112

Patent

active

056828543

DESCRIPTION:

BRIEF SUMMARY
TECHNICAL FIELD

The present invention relates to a variable compression ratio engine, and more particularly, to a variable compression ratio engine which can convert between an ordinary cycle and a Miller cycle.


BACKGROUND ART

In order to reduce NOx contained in exhaust gas, exhaust gas recirculation (EGR), by which exhaust gas, which is an inert gas, is recirculated into an intake gas and by which the combustion temperature is lowered, has been conventionally conducted in vehicle engines. Regarding this exhaust gas recirculation, when the load on an engine is heavy, the volume efficiency is improved as the temperature of EGR gas becomes lower, and the combustion temperature becomes lower and the NOx decreases as there is a larger amount of EGR gas. On the other hand, when the load on an engine is light, the combustion is not stable when the temperature of the EGR gas is low, so that an EGR gas with a high temperature is preferable. For this reason, a method of controlling the EGR gas to be cooled when the load is heavy and of controlling the EGR gas so that the EGR gas is not cooled when the load is light, by providing an EGR gas cooling means, is already known (for example, refer to Japanese Patent Application Laid-open No. 4-175453 and Japanese Patent Application Laid-open No. 4-301172).
However, when the EGR is conducted with a heavy load, disadvantages of increased fuel consumption, reduced output, etc., are brought about.
In other conventional art, many of the compression ratios of engines, for example, direct injection type diesel engines are set in the vicinity of 15 to 17. This compression ratio is required for securing starting efficiency and a good combustion state when a load is light, for example, a combustion state without blue and white smoke including hydrocarbon compounds, etc. The times for opening and closing an intake valve are fixed in order that the aforementioned compression ratio is obtained. When the compression ratio is determined, the pressure within a cylinder chamber at the end of the compression stroke is determined, and the pressures within the cylinder chamber at ignition, explosion, etc., are also determined. Meanwhile, a maximum allowable pressure within a cylinder chamber is determined in accordance with the engine, and the higher the compression ratio is, the higher the pressure within a cylinder chamber becomes at the end of compression. Accordingly, the difference between this pressure within a cylinder chamber and the maximum allowable pressure within a cylinder chamber lessens, and this is the main factor which prevents an engine from outputting high power.
The aforementioned compression ratio is desired to be in the vicinity of 11 to 13, from the viewpoint of combustion efficiency and high power output. As an example, average axial effective pressures, which can be achieved with the compression ratios at 17 and 12, are shown in FIG. 27. A unit of pressure in FIG. 27 is kgf/cm.sup.2. For example, in the case of an engine with a maximum allowable pressure within the cylinder, Pmax, of 150 kgf/cm.sup.2 or less (Pmax.ltoreq.150 kgf/cm.sup.2), the average axial effective pressure stays at 21 kgf/cm.sup.2 with the compression ratio of 17; but with the compression ratio of 12, the average axial effective pressure can be 34 kgf/cm.sup.2, that is, high power can be outputted.
However, since it is an absolutely necessary condition to obtain an excellent starting and an excellent combustion state when the load is light, in the current state, the compression ratio is set in the vicinity of 15 to 17 and high power output is sacrificed. This is also the case in gasoline engines, and though the compression ratio is desired to be 11 to 13 as in the diesel engines from the view of combustion efficiency (thermal efficiency), the compression ratio is set at 8 to 10 in order to prevent the occurrence of knocking when the load is heavy. As a result, there are disadvantages of increasing fuel consumption and of generating a large amount of CO.sup.2.
As the art which improves thermal

REFERENCES:
patent: 4552112 (1985-11-01), Nagao et al.
patent: 5070824 (1991-12-01), Morishita
patent: 5233948 (1993-08-01), Boggs et al.
patent: 5253620 (1993-10-01), Dohn et al.
patent: 5603292 (1997-02-01), Hakansson

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