Diesel Engnine Cam and Roller Follower Tribology

Abstract: Surfaces subjected to rolling and sliding contacts may suffer from contact fatigue. The cam and roller follower mechanism is a typical rolling and sliding contact. This thesis deals with the running in aspects to avoid high stress variation that leads to fatigue wear and the aspect of what happens to indentation damages that occurs on the surface if there are any particles in the lubricant. The particles can be both self generated and be present from dirt. This thesis also deals with how the oil and the additives in the oil affect the contact properties. The thesis contains six papers. One of the papers that presents the test apparatus used for all the experiments is already published on the Nordtrib conference in June 2004 and the other papers, which deal with all the experiments done, are sent in for publication. The experiment of the running in behaviour with steel rollers has also been presented at the Leeds-Lyon-conference in August 2005. It is seen from the results that the running in occurs fast and there is a difference in the running in behaviour depending on if steel rollers or ceramic rollers are used. The ceramic roller has lower inertia that makes the roller easier to accelerate to get higher percentage of rolling in the contact. Higher amount of rolling and smoother surfaces, as the ceramic rollers have, give better lubrication properties and therefore the running in wear is smaller. The damage progress experiments show better ?healing? of the surface if there is some hardness difference. When combustion gases were used around the contacts, less visible tribolfilms were created on the cam surface. The tribofilms that were created consisted of Ca, P and Zn. The possible states of Zn inside the tribofilms are many, including zinc-phosphate, zinc-iron-phosphate, zinc-oxide and zinc-sulfide. The contact conditions had not been so tough that pure EP-films, mainly consisting of FeS, were formed. The tribofilms shown were blue and brown and the blue marks withstood a longer period of sputtering time until a clear iron signal, originating from the cam substrate, was detected than in the case of the brown marks.