To favorably discharge blow-by gas in a crankcase to an intake system, in a spark ignition internal combustion engine which controls an intake air amount through the change of intake valve closing timing by fully opening a throttle valve at least when the intake air amount is a set amount or more and control a mechanical compression ratio so as to make an actual compression ratio constant with respect to the intake valve closing timing.
A variable compression mechanism contains a first discharge path 91 for discharging the blow-by gas to an upstream side of an intake system supercharger 28 and a second discharge path 92 for discharging the blow-by gas to a downstream side of an intake system throttle valve 17, operates the supercharger and delays intake valve closing timing to maintain the intake air amount in comparison to before operation of the supercharger by a variable valve timing mechanism B when a throttle valve is fully opened and the supercharger is in an operation region, and to heighten the mechanical compression ratio by the variable compression ratio mechanism (A) so as to make the actual compression ratio constant with respect to delayed intake valve closing timing.
Jun Tsuruta
Tetsuro Shimada
Shinji Mitsuhashi
Koichi Ito
Tatsuki Sone
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