THE DIRTY LITTLE SECRETS ABOUT CAMSHAFT …（对凸轮轴的肮脏的小秘密u2026）.pdfVIP

09/07 THE DIRTY LITTLE SECRETS ABOUT CAMSHAFT DESIGN EVERY ENGINE BUILDER SHOULD KNOW Jim Wolf Valve motion is probably the least understood element of a successful performance engine. Kinematics, fluid dynamics and metallurgy must all be mastered by any engineer that sets out to design a successful valve motion profile for a high performance engine and ultimately translate this motion onto a camshaft that will accurately produce the same motion at the valves. This is not always the level of engineering you will get when choosing a camshaft for your engine. Unfortunately there is a dirty little secret in cam design that is still practiced today by some manufacturers that either “don’t know what they don’t know” or choose to ignore the learning curve required to engineer a modern high performance camshaft. “Morphing” or master tweaking is when a cam grinder takes an existing profile master (a large lobe shaped disc followed by a cam grinding machine) and tweaks the grinding machine (including CNC grinders) causing it to stretch or distort the actual grinding path of the master to achieve a “morphed” cam lobe and then builds a second master from the morphed lobe. This is not cam design by any stretch of the imagination, yet many cam grinders unfortunately still use morphing to develop new profiles! Hertzian contact stress, spring harmonics, maximum follower wear path length, component mass and flex, and cam drive feed back are examples of just a few of the constraints that cannot be directly address by morphing. Modern lobe design is no longer primarily done in the displacement domain or physical shape of the lo