1. Field of the Invention
The present invention relates to an internal combustion engine provided with an exhaust secondary air introduction assembly and valve rest mechanisms.
2. Background Art
Guiding of exhaust secondary air into an exhaust path is a well known way of oxidizing unburned components of HC and CO in exhaust gas expelled from a combustion chamber of an internal combustion engine. An air suction-type exhaust secondary introduction assembly employing a reed valve is a well known assembly for introducing exhaust secondary air.
Internal combustion engines exist having valve rest mechanisms for resting the opening and closing operation of some of the inlet valves of a plurality of inlet valves, or resting the opening and closing of some of the exhaust valves of a plurality of exhaust valves, as in Japanese Patent Laid-open Publication No. Hei. 10-184.327. This operation is carried out when the engine is running at a low number of revolutions, or under a low load, so that only a small amount of air is taken in.
There are, however, problems associated with exhaust secondary air introduction assemblies for internal combustion engines having valve rest mechanisms. When one or more of the exhaust valves are stopped, the flow of exhaust gases at the exhaust port is deflected so that exhaust gas is not expelled from the exhaust outlets provided for the exhaust valves that are stopped. It is, however, necessary to maintain a spacing using the position of the exhaust secondary air introduction inlet of the exhaust port for the deflected flow so that there is sufficient mixing of the exhaust gas and the exhaust secondary air by the time the exhaust gas reaches an exhaust purification assembly.
The air suction-type exhaust secondary air introduction assembly also has to ensure, with the position of the exhaust secondary air introduction opening of the exhaust port, that the pulsation pressure of the exhaust gas operates on the exhaust secondary air introduction opening when one or more exhaust valves are stopped.