Turbocharger with annular rotary bypass valve for the turbine, and catalyst disposed in the bypass channel of the turbine housing

A turbocharger includes a turbine wheel (54) mounted within a turbine housing (52) and connected to a compressor wheel (34) by a shaft (36). The turbine housing defines an exhaust gas inlet (56) connected to a volute (58) that surrounds the turbine wheel, and an axial bore (62) through which exhaust gas that has passed through the turbine wheel is discharged from the turbine housing. The turbine housing further defines an annular bypass passage (60) surrounding the bore and arranged to allow exhaust gas to bypass the turbine wheel. An annular bypass valve (70) is disposed in the bypass passage. The bypass valve comprises a fixed annular valve seat (72) and a rotary annular valve member (74) arranged coaxially with the valve seat. A catalyst (120) is disposed in the annular bypass passage (60). The catalyst is formed of spaced-apart, undulating metal fins (122) coated with a catalyst material and contained in a generally annular cage (130).