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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.

The contact behavior between camshaft and follower is effected by pressure, lubrication and temperature. Regarding the camshaft, steel is the usual material for Heavy Duty Diesel engines, but also chilled ductile iron can be applied. There is a greater variety in design and material of the follower. For gliding contact chilled cast iron tappets offer an optimal compromise between performance and price; for higher loading, steel is a suitable material. A roller-tappet is required for maximum load conditions; if gliding contact is essential, carbide metal plated steel tappets can be used. Important design features for the roller tappet are concerning the pushrod pan, the roller chamber, the bearing between roller and pin and the prevention of twisting.

In 1990 the Ministry of Research and Technology in the FRG proposed a comprehensive concept to sponsor biotechnical and energetical use of agricultural materials. Within this concept various modern Diesel engines have been investigated with respect to performance, fuel consumption, exhaust emissions and durability characteristics using neat (100%) rapeseed oil as fuel. Energy consumption and engine performance are similar to operation with Diesel fuel, exhaust emissions are higher with rapeseed oil. Diesel engines with divided combustion chambers and big cylinder units are suited for continuous operation with rapeseed oil.

Emission standards in the European Community are based on the ECE city-cycle. In the future legislation will be extended to emissions on country roads and highways. Due to low speeds and accelerations only 13 % of the total engine operating range are used during the ECE driving cycle in a car equipped with an engine of less than 1,4 1 displacement. The future European extra-urban driving cycle covers in combination with the ECE city-cycle the engine operating range up to speeds of n = 3500 rpm. The mean values of engine speed and load agree quite well with real driving conditions on country roads and highways in France and the FRG.