| 摘要 |
PURPOSE:To prevent valve stick from happening before hand by controlling an exhaust changeover valve to open for a specified time forcibly, when a valve stick condition of the exhaust changeover valve for varying the operation number of turbochargers is predicted by a prediction means. CONSTITUTION:In an engine, a large volume turbine 3 of low pressure and a small volume turbine 4 of high pressure are provided at an exhaust passage in series. Only the turbocharger 3 of the low pressure is operated by closing an exhaust changeover valve 24 provided at an exhaust bypass passage 14, and also a compressor 4 in the high pressure is operated by closing the valve. In this case, in a control computer 51, a ratio K between pressure of outlets of a high pressure compressor and a low pressure compressor are calculated so that it is compared with a standard pressure ratio Ko. When the condition is K>Ko, since the space between the exhaust changeover valve 24 and a housing 60 becomes narrow, occurrence of valve stick is estimated, and the exhaust changeover valve 24 is opened only for a specified time. |
