Abstract: A turbine impeller to be driven for rotation by exhaust gas of an internal combustion engine is fixed to a turbine shaft. The turbine shaft is supported by a radial bearing in radial directions and mounted to a bearing housing. The turbine shaft includes a stepped part which is formed between the turbine impeller and the radial bearing so that the outer diameter of the turbine shaft is greater at the turbine impeller side than at the radial bearing side. The bearing housing includes an oil drain for discharging oil which has lubricated the radial bearing. The distance L from a side face of the radial bearing to the stepped part is set to a value at which oil moving from an end of the radial bearing does not reach the stepped part when a turbine-revolution speed Nt is higher than that Nti which is produced by an idling operation of the internal combustion engine.

Abstract: In order to activate a catalyst in a short time in an internal combustion engine having a turbine, an exhaust bypass flow passage and an exhaust bypass valve and its valve seat provided in the exhaust bypass flow passage are set to sizes large enough to be able to make almost all the amount of the exhaust gas bypass the turbine, and the exhaust bypass valve is controlled by a driving actuator using a motor or a solenoid. Rapid activation of the catalyst is implemented by totally opening the exhaust bypass valve during the starting period of operation of the internal combustion engine to make almost all the amount of exhaust gas flow into the catalyst by bypassing the turbine.

Abstract: A turbine impeller to be driven for rotation by exhaust gas of an internal combustion engine is fixed to a turbine shaft. The turbine shaft is supported by a radial bearing in radial directions and mounted to a bearing housing. The turbine shaft includes a stepped part which is formed between the turbine impeller and the radial bearing so that the outer diameter of the turbine shaft is greater at the turbine impeller side than at the radial bearing side. The bearing housing includes an oil drain for discharging oil which has lubricated the radial bearing. The distance L from a side face of the radial bearing to the stepped part is set to a value at which oil moving from an end of the radial bearing does not reach the stepped part when a turbine-revolution speed Nt is higher than that Nti which is produced by an idling operation of the internal combustion engine.