Experimental and Modeled Effects of Camshaft Manufacturing Errors on the Dynamics of High Speed Valve Trains

Abstract

The idea of harnessing combustion to perform mechanical work is by no means anew one. The internal combustion engine, as we know it today, has its origins in the lastcentury, however the idea for controlling combustion to perform mechanical work datesback to the Renaissance. Even with the advent of alternative sources of power forcommerce and personal applications, the internal combustion engine represents a largeportion of the power generation available in this country.There are numerous types of internal combustion engines, each with a variety ofsubsystems. While all of these types and corresponding subsystems are equally important,this investigation is focused on the valve train dynamics of a pushrod type internalcombustion engine. Operating this type of engine at too high of an engine speed usuallycauses dynamic malfunctions such as spring surge, lifter/cam pair separation, valvebounce, etc. in the valve train. Although the interaction of each of the valve traincomponents contributes to the limit speed, the shape of the cam plays a critical role.Therefore, this investigation will look at how small changes in the cam profile due tomanufacturing errors change the dynamics of a valve train in a pushrod type engine.Automotive cams can be manufactured as copied or original parts. Copied partsare typically produced on a rocker type cam grinder and the original parts are produced on a computer numerical control grinder. Therefore, various errors associated with thesemanufacturing techniques are studied herein.Installing cams with profile errors in an engine may result in the dynamicmalfunction of its valve train. In order to study the effect of these profile errors, some ofthe error cam profiles that were predicted for the rocker grinder were manufactured andtested in an actual valve train. In addition, the effects of error cam profiles wereinvestigated by using an existing valve train simulation model. It was found by bothexperimentation and simulation that camshaft errors on the order of typical shoptolerances had little impact on the dynamics of high speed valve trains.