The invention aims to provide a valve
cam provided with a cosine-
constant speed type buffer section and used for an internal
combustion machine and a lift curve determination method of the valve
cam.The cosine-
constant speed type buffer section is composed of two segments, namely the acceleration curve of the first segment is a
cosine curve, and the acceleration curve of the second segment is a constant-speed curve; the expression of the lift curve of the valve
cam used for the internal
combustion machine is that when 0<=alpha<=alpha1, hC(alpha)=C1(1-cosomega alpha); when alpha1<=alpha<=alpha0, hC(alpha)=E0+E1alpha; and the undetermined constants C1, E0 and E1 of the cosine-
constant speed type buffer section are worked out according to the boundary conditions and the continuity conditionat the position where alpha=alpha1, namely C1=h0 / [1+cos(omegaG alpha0)+
omega alpha0(1-G)sin(omegaG alpha0)], E1=C1.
omega.sin(omegaG alpha0), and E0=h0 / alpha0 E1. According to the valve cam provided with the cosine-constant speed type buffer section and used for the internal
combustion machine and the lift curve determination method of the valve cam, the third derivative of the
tail end of the buffer section can be kept zero, the discontinuity of the segments of the buffer section can be avoided, and thus
impact, vibration and
noise, caused by the cam profile, of a valve mechanism can be reduced easily.