Ytskadors utveckling på kamaxlar

Sammanfattning: The background for this master thesis is the stricter emission control requirement in heavyduty diesel engines at the same time as the demands for improved diesel engine efficiency are getting stronger. One approach to meet these demands is to increase the fuel injector pressure. A higher fuel injector pressure makes the fuel spray more finely dispersed into the cylinder and a better combustion is achieved. This high pressure requires higher contact loads between the camshaft and roller. Higher working loads increase the risk for surface damage and fatigue of the camshaft and roller. This requires that a thorough investigation of which parameters that affect the contact between the camshaft and roller is done. The aim of this master thesis is thus to investigate how the hardness difference between camshaft and roller influences the damage propagation of surface damage. More aspects are how the shape and the position of the surface damage affect the propagation. To simplify the documentation of the surface damage, a method is evaluated using silicon replicas. To be able to follow the damage development on the camshaft and rollers three camshafts with artificial indents are run in a test apparatus. Each one of the camshafts is run in five different intervals of time. Between each interval the engine was dismantled and the camshaft and rollers were examined. This examination was done with a light microscope and replicas of interesting surface indents were made using silicone. The silicone replicas were then also scanned with a Wyko- topometer so 3D measurements over the surface could be achieved. When the examination was finished the parts were reassembled and the next interval was run. The silicone Master Exact that was evaluated in the paper can be used to replicate a very fine surface. The silicone is also easy to use and the method can be adopted for simplifying the documentation and analysis of different surface damages and surface profile parameters. The results shows that the damage development mainly depends on which hardness the camshaft has and if the surface damages have occurred on the camshaft or roller. The damage development of the artificial indents can generally be sorted into three different phases. The main reason for surface damage in phase one is plastic deformation, in the second face wear, and in the last phase fatigue. Earlier experiments shows that the best way of avoiding wear and fatigue is to use the same hardness in the contacting surfaces. When initial surface damage is taken to consideration, and not only damage caused by contaminants in the lubricant, this is not always true.