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

[0007]Therefore, an object of the present invention is to provide a spark ignition type internal combustion engine able to maintain an exhaust purification catalyst at a relatively high temperature even when operating the internal combustion engine in the state of a large expansion ratio.

[0017]In another aspect of the present invention, the higher the engine speed, the higher the actual compression ratio.

[0020]In another aspect of the present invention, the closing timing of the intake valve is shifted as the engine load becomes lower to a direction away from intake bottom dead center until a limit closing timing enabling control of the amount of intake air fed into the combustion chamber.

[0024]In another aspect of the present invention, in a region of a load lower than the engine load when the closing timing of the intake valve reaches the limit closing timing, the lower the load, the larger the air-fuel ratio is made.

[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 operating the internal combustion engine in the state of a large expansion ratio, the exhaust purification catalyst can be maintained at a relatively high temperature.

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 raised to a certain temperature or more, generally it cannot exhibit its excellent exhaust purification action.

Further, if increasing the expansion ratio, the exhaust gas becomes harder to be exhausted from the combustion chamber, so the flow rate of the exhaust gas flowing into the exhaust purification catalyst becomes smaller.

For this reason, if operating the internal combustion engine in the state of a large expansion ratio, maintaining the exhaust purification catalyst at a high temperature becomes difficult.

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