| 摘要 |
PROBLEM TO BE SOLVED: To secure negative pressure of a master bag while protecting a supercharger by a simplified system. SOLUTION: Negative pressure is generated and increased between a throttle valve 5 of an air intake passage 2 and a supercharger by closing a by-pass valve 10 of a by-pass passage 9 to by-pass a mechanical supercharger 8 at the time of brake working operation and in the case where engine rotating speed is lower than specified engine rotating speed. Consequently, it is possible to restrain a pressure ratio of the supercharger upstream side and the supercharger downstream side of the air intake passage low and to restrain temperature of delivery air delivered to the supercharger downstream side of the air intake passage from the supercharger lower than specified temperature by closing the by-pass valve at lower than the specified engine rotating speed. Accordingly, it is possible to restrain influence to the supercharger by heat of the delivery air.
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