Exhaust-flow-rate control valve, and two-stage supercharging system provided with same

Abstract

An exhaust-flow-rate control valve for controlling a flow rate of exhaust gas flowing through an exhaust flow passage includes: a valve rod; a valve body having a flat plate shape and configured to rotate about the valve rod; and a valve housing having a cylindrical shape and defining a part of the exhaust flow passage inside the valve housing. A valve seat surface extending along a direction intersecting with an axial direction of the exhaust flow passage and being configured to make contact with an outer peripheral portion of the valve body in a fully-closed state in which an opening degree of the valve body is zero degree, and a flow passage surface extending along the axial direction of the exhaust flow passage and defining a passage region R through which the exhaust gas passes between the flow passage surface and the outer peripheral portion of the valve body in a valve-open state in which the opening degree of the valve body is greater than zero degree are formed on an inner peripheral surface of the valve housing. The passage region R of exhaust gas increases slowly while the valve body transitions from the fully-closed state to a predetermined valve-open state in which the separation distance between the valve body and the end portion of the flow passage surface is shortest.