Experimental measurement of roller slip in end-pivoted roller follower valve train

Direct-acting tappets and end-pivoted roller followers are the two main types of valve train configurations widely used in passenger car engines. Considerable theoretical and experimental work has been carried out on the direct-acting valve train. However, due to complex nature of the end-pivoted rollers, limited work has been carried out in this area. In roller follower valve train, the roller rotation has a direct impact on the performance in terms of component durability and friction. Roller rotation minimizes the chances of fatigue failure by even distribution of wear, improves the lubrication, and influences the valve train power loss. In this research work, the effect of lubricant rheology and operating conditions on the performance of end-pivoted roller follower has been studied experimentally in detail. Tests have been carried out on real production engine, avoiding any major modification to the components under investigation. The tests revealed presence of roller slip at certain operating conditions. Lubricant viscosity played a key role in the slippage of roller at lower temperatures, however, at high temperatures, negative slip was observed indicating that component inertia has a role to play in roller slip. High camshaft operating speeds and roller inertia increased the tendency of slippage. The study of roller slip was not possible without the development of a new method of measuring roller performance, also reported in this paper. The experimental set up, roller rotation measurement system, test procedure, and results are presented and discussed in detail.