Spark Ignition Type Internal Combustion Engine

Abstract

A spark ignition type internal combustion engine comprises a variable compression ratio mechanism able to change a mechanical compression ratio, an actual compression action start timing changing mechanism able to change a start timing of an actual compression action, and an exhaust valve. At the time of engine low load operation, the mechanical compression ratio is maximized to obtain a maximum expansion ratio, and the actual compression ratio is set so that no knocking occurs. The maximum expansion ratio is 20 or more. The closing timing of the exhaust valve at the time of engine low load operation is made substantially intake top dead center. Due to this, even if operating the internal combustion engine in a state of a large expansion ratio, the temperature of the exhaust purification catalyst can be maintained at a relatively high temperature.

Description

TECHNICAL FIELD[0001]The present invention relates to a spark ignition type internal combustion engine.BACKGROUND ART[0002]Known in the art is a spark ignition type internal combustion engine provided with a variable compression ratio mechanism able to change a mechanical compression ratio and a variable valve timing mechanism able to control a closing timing of an intake valve, performing a supercharging action by a supercharger at the time of engine medium load operation and engine high load operation and, in the state holding an actual compression ratio fixed at the time of engine medium and high load operation, increasing the mechanical compression ratio and retarding the closing timing of the intake valve as the engine load becomes lower (for example, see Japanese Patent Publication (A) No. 2004-218522).[0003]However, in general, in an internal combustion engine, the larger the expansion ratio, the longer the period in an expansion stroke where a downward force acts on the pist...

AI Technical Summary

Benefits of technology

[0028]According to the present invention, since as much exhaust gas as possible is discharged from the combustion chamber to the exhaust purification catalyst, even if

Problems solved by technology

However, if increasing the expansion ratio in this way, most of the heat energy produced in the combustion chamber is converted to kinetic energy, so the exhaust gas falls in temperature.

Further, along with this, the pressure of the exhaust gas in the combustion chamber at the end of the expansion stroke also becomes lower and accordingly the exhaust gas becomes harder to exhaust from the combustion chamber.

On the other hand, if the engine exhaust purification catalyst provided in the engine exhaust passage is not

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