Patent attributes
To provide a waste-gate valve device with a good flow-rate controllability. A waste-gate valve device 1 includes: a turbine housing 3 provide with a waste-gate channel 2 through which exhaust gas bypasses a turbine; and a waste-gate valve 4 to open and close an outlet of the waste-gate channel 2. The waste-gate valve 4 includes a valve body 7 to open and close the outlet of the waste-gate channel 2, and a protrusion 8 to be housed in the waste-gate channel 2 when the valve body 7 closes the outlet of the waste-gate channel 2. The waste-gate channel 2 ensures a maximum flow rate of exhaust gas at a time when the waste-gate valve is fully open. An area ratio of a flow-path cross-sectional area A1 of the waste-gate channel 2 to a flow-path cross-sectional area A2 of a merging portion is not more than 0.2, the merging portion being a part at which exhaust gas having passed through the turbine merges. A widened portion 2A at which the flow-path cross-sectional area increases is disposed on the outlet of the waste-gate channel.
