Exhaust flow rate control valve

An exhaust flow rate control valve comprising:

• an exhaust pipe which is provided in an exhaust system for an engine and which includes an inner pipe member through which exhaust gas is passed and an outer pipe member surrounding the inner pipe member;
• an on-off valve provided in the inner pipe member and switched between a closed state in which a flow passage sectional area of the inner pipe member is decreased, and an opened state in which the flow passage sectional area is increased;
• and
• a resilient member disposed between the inner pipe member and the outer pipe member so as to bias the on-off valve in a closing direction,
• the on-off valve being switched from the closed state to the opened state by an increase in pressure of the exhaust gas acting on the on-off valve against a biasing force of the resilient member,
• wherein the on-off valve comprises an upper portion and a lower portion, the upper portion of the on-off valve having a surface area which is less than the surface area of the lower portion of the on-off valve,
• and wherein in the vicinity of the on-off valve,
• the inner pipe member comprises a cross sectional shape which substantially corresponds to the peripheral shape of the on-off valve, such that the inner pipe member is formed so that a sectional area of an upper half of the inner pipe member is smaller than that of a lower half of the inner pipe member, and
• the outer pipe member comprises a circular cross section, such that a space is formed between the upper half of the inner pipe member and the outer pipe member, and the resilient member is disposed in the space formed between the inner pipe member and the outer pipe member.