PASSAGE VARIABLE EXHAUST PIPE

摘要

PROBLEM TO BE SOLVED: To early activate a catalyst just after an engine is stared, to suppress a rise in back pressure at the normal operation and to prevent high temperature deterioration of the catalyst at the engine high load. SOLUTION: When an exhaust gas temperature is in a low temperature region, exhaust gas led to a catalytic device is sufficiently high in temperature and the catalyst is early activated because a control device 60 controls an opening/closing valve 40 so that exhaust gas passes through only a first passage R1 with high heat insulation property. When the exhaust gas temperature is in a middle temperature region, cross sectional area of the passable passage of exhaust gas is increased and the rise in back pressure of exhaust gas is suppressed because the control device 60 controls the opening/closing valve 40 so that exhaust gas passes through not only the first passage R1 having high insulation property but also a second passage R2 having low heat insulation property. When the exhaust gas is in a high temperature region, temperature of exhaust gas led to the catalytic device is hat so high as to deteriorate the catalyst and performance of the catalyst can be excellently maintained because the catalytic device controls the opening/closing valve 40 so that exhaust gas passes through only the second passage R2 with low heat insulation property.