PURPOSE: To raise the charging efficiency of intake air over the entire operational range of an engine, by differentiating the valve opening period of a pair of intake valves provided for each cylinder, and changing the valve opening and closing timing of one intake valve having a longer valve opening period according to the operational conditions of the engine.
CONSTITUTION: A pair of intake ports and intake valves and a pair of exhaust ports and exhaust valves are provided for each cylinder. The intake valves are combined with cams formed on a cam shaft 38, and a cam 42 is so formed that one (24) of the intake valves has a longer valve opening period and a larger opening area than the other. A variable mechanism 56 consisting of a motor 64, a rotatable member 58, etc. is provided for varying the valve opening and closing timing of the intake valve 24. By driving the motor 64 according to the operational conditions of an engine, and actuating member 62 is moved to the right and left and the rotatable member 58 is turned around the cam shaft 38 by a driving shaft 60. At the same time, a tappet 66 is also moved and the positional relationship between the tappet 66 and the cam 44 is changed, so that the valve opening and closing timing of the intake valve 24 can be changed.
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TAKAHASHI KOUICHI
NAGAO AKIO
FUJIMOTO MISAO
NISHIKAWA TOSHIO
