TABLE OF CONTENTS Figure 20.1 a is a cross-sectional view showing the overhead valve arrangement in an automobile engine. In analyzing the dynamics of this or any other cam system, we would expect to determine the contact force at the cam surface, the spring force, and the cam-shaft torque, all for a complete rotation of the cam. In one method of analysis the entire cam-follower train, consisting of the push rod, the rocker arm, and the valve stem together with the cam shaft, are considered rigid. If the members are in fact fairly rigid and if the speed is moderate, such an analysis will usually produce quite satisfactory results. In any event, such rigid-body analysis should always be made first.
Sometimes the speeds are so high or the members are so elastic (perhaps because of extreme length) that an elastic-body analysis must be used. This fact is usually discovered when troubles are encountered with the cam system. Such troubles are usually evidenced by noise, chatter, unusual wear, poor product quality, or perhaps fatigue failure of some of the parts. In other cases, laboratory investigation of the performance of a prototype cam system may reveal substantial differences between the theoretical and the observed performance.
Figure 20.1 b is a mathematical model of an elastic-body cam system. Here m 3 is the mass of the cam and a portion of the cam shaft. The motion machined...
