Cam Roller Contact

The automotive industry and the design of engines are strongly ruled by performance andlegislation demands. First order aspects defining the main functions of a component are wellknown and new challenges appear at a lower scale. Wear reduction is defined as a second orderproblem and requires decreasing the scale of observation of components down to roughness.This thesis work and its aim lie within the scope of wear improvements and are focusedon the injection cam/roller contact of heavy duty diesel engines. In order to reach the aimseveral material and methods are used: a valve train rig test, roughness characterisation anddifferent manufacturing processes.It is shown by experiments that the flank and nose of injection cams are specific areas withspecific roughness (higher density of summits Sds) compared to the rest of the cam. The wearis characterized by rounded-off of summits (Ssc). From those results and since wear processesare strongly linked to the pressure generated between the mating surfaces, the development ofa rough contact model is of great interest.An elastic rough contact model is implemented and improved later on by an elasto-plasticdescription of materials. The simulations are validated by a wear test and are used to rankthe ability of surfaces (both cam and roller) to face wear problems. The ratio of plasticallydeformed peaks shows that the flank and nose of the cam are reacting badly to pressures. Additionallythe rough contact allows ranking/optimization of different machining processes withrespect to their expected functional contact performance.Future work will be to use such a model to choose a good combination of surfaces (camand roller) in order to reduce wear