To prevent knocking by maximizing a mechanical compression ratio to secure an internal EGR gas in a wide operating area.
The valve gear of this engine comprises a first intake cam 41b opening an intake valve in an intake stroke, a second intake cam 41c opening the intake valve at least in an exhaust stroke before the intake valve is opened in the intake stroke and closing, at the latest, the intake valve before a top dead center in the exhaust stroke, and a controller controlling the valve gear according to the operating conditions of the engine. The controller performs the opening/closing operations of the intake valve by the second intake cam 41c in addition to the opening/closing operations of the intake valve by the first intake cam 41b at least in the high load operating area of the engine. Also, the controller controls the valve gear so that an intake valve closing timing by the first intake cam 41b is delayed by a prescribed amount from a bottom dead center so that an effective compression ratio becomes smaller than an expansion ratio.
COPYRIGHT: (C)2006,JPO&NCIPI
Keiji Araki
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Takao Ito
Jiro Higuchi