Patent ID: 7426979

Claim:
An exhaust gas control valve which shifts exhaust gas passages connectable between plural rooms in a muffler according to engine speed, the exhaust gas control valve comprising: a valve seat formed with a valve seat surface and provided with a wall portion projecting from the valve seat surface, the valve seat having an opening to pass exhaust gas through the valve seat; a valve plate formed with a valve plate surface and provided with a wall portion arranged along the wall portion of the valve seat, the valve plate surface having a first exhaust gas pressure receiving area which corresponds to an area of the opening and is contactable with the valve seat surface so that the exhaust gas control valve can prevent leakage of the exhaust gas through the opening and a second exhaust gas pressure receiving area which is larger than the first exhaust gas pressure receiving area; and a spring pressing the valve plate toward the valve seat, and wherein the exhaust valve is shiftable among at least a closed state where pressure of the exhaust gas generated in a low engine speed operation acts on only the first exhaust gas pressure receiving area and the first exhaust gas pressure receiving area is in contact with the valve seat surface to shut the opening, an intermediate state where the pressure generated in a middle engine speed operation acts on the first exhaust gas pressure receiving area and the second exhaust gas pressure receiving area and the valve plate surface is apart from the valve seat surface to open the opening while the wall portions of the valve plate and the valve seat overlap with each other to keep the exhaust gas control valve closed, and an opening state where the pressure generated in a high engine speed operation acts on the first exhaust gas pressure receiving area and the second exhaust gas pressure receiving area and at least a part of the wall portions are apart from each other to form a gap through which the exhaust gas can pass, wherein the valve seat has a seat body portion having the valve seat surface, a tip wall portion projecting from a tip end of the seat body portion, and side wall portions projecting from side edges of the seat body portion and contacting both ends of the tip wall portion, and the valve plate has a valve body portion having the valve plate surface, a tip portion and side wall portions which are arranged along the tip portion and the side wall portions of the valve seat and insertable within an area surrounded by the tip portion and the side wall portions of the valve seat. wherein the valve plate is rotatable around a shaft relative to the valve seat, and wherein a shaft side portion of the seat body portion and a shaft side portion of the valve body portion have guide portions with circular-arc shaped inner surfaces centered on the shaft and facing with each other for preventing a leakage of the exhaust gas therebetween.