Frictional Differences between Rolling and Sliding Interfaces for Passenger Car Switching Roller Finger Followers

The demand for improving fuel economy in passenger cars is continuously increasing. Eliminating energy losses within the engine is one method of achieving fuel economy improvement. Frictional energy losses account for a noticeable portion of the overall efficiency of an engine. Valvetrain friction, specifically at the camshaft interface, is one area where potential for friction reduction is evident. Several factors can impact the friction at the camshaft interface. Some examples include: camshaft lobe profile, rocker arm interface geometry, valve spring properties, material properties, oil temperature, and oil pressure. This paper discusses the results of a series of tests that experimented the changes in friction that take place as these factors are altered. The impact of varying testing conditions such as oil pressure and oil temperature was evaluated throughout the duration of the testing and described herein. Test data quantifying the effect of utilizing friction reducing surface treatment methods, specifically diamond-like carbon, is also provided. However, the main focus of the study is on the frictional differences that take place at the camshaft interface for a switching roller finger follower equipped with a roller bearing vs. a switching roller finger follower equipped with a slider pad. An analysis was performed, using brake specific fuel consumption, in order to predict the approximate fuel economy benefit that would result from transitioning from a slider pad design to roller only design for a switching roller finger follower application. Test results suggest that making the switch from a slider-style switching roller finger follower to a roller-style switching roller finger follower has a noticeable improvement on the overall fuel consumption of an engine.