PURPOSE: To maintain favourable output performance by setting cam surfaces of driving cams and oscillating cams so that composite acceleration of valve lift before and after variable operation of valve timing.
CONSTITUTION: Shapes of cam surfaces 7a, 8a of driving cams 7, 8 and cam surfaces 41, 51 of oscillating cams 4, 5 are set so that a positive acceleration compound on the cam surfaces 41, 51 of the oscillating cams 4, 5 and a positive acceleration compound on the cam surfaces 7a, 8a of the driving cams 7, 8 are not overlapped in a valve lift process and the positive acceleration compound of the driving cams 7, 8 precede the positive acceleration compound of the oscillating cams 4, 5. Consequently, change of valve lift acceleration before and after variation at the time of valve timing variation by way of moving a camshaft 6 in the axial direction and change to the side of reduction are restrained. Accordingly, it is possible to maintain favourable output performance without lowering of engine output.
NISHIDA MASAMI
ASAI AKIRA
