| 摘要 |
PROBLEM TO BE SOLVED: To prevent a fluid leakage from between a valve and a valve seat in a double poppet type valve device. SOLUTION: In the whole operation region of an engine, the conditions for increasing an elongation amount of a valve shaft 11 to the maximum extent are that a temperature of exhaust gas is high and a flow rate of exhaust gas is high in an EGR region. When operation plunges into the outside of EGR region where load is high from the EGR region, for example, operation is accelerated from the EGR region, there are possibilities that both of two valves are not seated on valve seats together, EGR gas leaks from a clearance between the valve on one side and the valve seat on one side, and output performance is worsened and a PM amount increases due to the mixture of EGR gas into suctioned air. In this case, a differenceΔL between a dimension L1 between the valve seats 14 and 15 and a dimension L2 between the valves 12 and 13 (ΔL=L1-L2)[L1>L2] when the valves are fully closed at normal temperature is set to 0.15 mm, and a clearance C of 0.15 mm is provided between the valve 12 on upper side (the valve positioned on a rear side in the direction of opening valve) and the valve seat on upper side (the valve seat positioned on a rear side in the direction of opening valve) at normal temperature.
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