Patent ID: 8316639

Claim:
An internal combustion engine comprising: a combustion chamber including an exhaust port; an exhaust valve arranged to open or close the exhaust port; an exhaust device including an exhaust path arranged to guide exhaust gas discharged from the combustion chamber via the exhaust port; and an exhaust cleaning device provided in the exhaust path and including a catalyst; wherein the exhaust device includes: a convergent section including a flow path cross-sectional area that is smaller at a downstream end thereof than at an upstream end thereof; a divergent section provided downstream with respect to the convergent section and including a flow path cross-sectional area that is larger at a downstream end thereof than at an upstream end thereof; and a branch section arranged to branch a shock wave generated by the exhaust gas discharged from the combustion chamber and propagating in a downstream direction in the exhaust path at a higher velocity than the exhaust gas that generated the shock wave and is flowing into the exhaust path from the combustion chamber when the exhaust port is opened, from a portion of the exhaust path which is upstream with respect to the divergent section, and to propagate the shock wave back to the exhaust path; the exhaust path is arranged to cause the exhaust gas that generated the shock wave and is flowing into the exhaust path from the combustion chamber to pass the convergent section and to collide against the shock wave, which has propagated in the branch section, between the branch section and the divergent section, so as to increase the pressure of the exhaust gas in the convergent section; the exhaust gas is caused to pass the divergent section to generate a new shock wave and thus to decrease the temperature of the exhaust gas; and the catalyst of the exhaust cleaning device is provided in a portion of the exhaust path which is downstream with respect to the divergent section.