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The calculation of the contact stress between cam and cam follower is an important step in the valve train design process. Unacceptably high contact stresses result in excessive wear at the running surfaces. The established analytical methods for calculation of contact stress are limited by assumptions. The Finite Element Analysis (FEA) offers an advanced tool with fewer limitations than the analytical equations. This paper compares these two calculation methods. In a first step, the FEA is used to confirm the analytically calculated results with the standard Hertz equations. Then some special cases, which cannot be calculated by the standard equations, are investigated by FEA, like the limited width of one contact partner, or a non-circular roller profile.

Reduction of exhaust emissions, increase of power output and fuel economy, and engine brake systems with higher performance, are the most important factors within the development of Heavy Duty Diesel engines. All of these issues result in an increase in loading for the entire valve train. To fulfill the increasing requirements, modern Heavy Duty Diesel engines are using valve train configurations with roller followers, designed as roller tappets or roller levers. While these roller followers are well-known engine components, there is a great demand for the enhancement of functional properties and simultaneous cost reduction. Main areas for the design work are the base design of body or lever with roller chamber, push rod area and lever geometry and especially the roller bearing together with the assembling technology.