Analysis of Cam/Roller Follower Friction and Slippage in Valve Train Systems

In order to predict and understand the slippage between the cam and roller follower, the Cummins L-10 engine valve train was modeled. A mixed lubrication model was developed to investigate the friction and oil film thickness since the valve train is operated in very severe conditions. First, the roller follower pin friction was studied because it is a significant friction source for a valve train with a roller follower.⁽¹³⁾ Using similarity analysis of the roller pin friction from the experimental data, the correlation between the friction coefficient and the Sommerfeld variable was obtained. Second, the interface friction between the cam and roller follower was studied. Oil film thickness and the asperity load were obtained based on the mixed lubrication model. Finally, the total friction force at each cam angle was calculated and roller slippage was predicted by comparing the tractive force and the friction force. Experimental results were used to model friction parameters and to compare against the calculated values.⁽¹⁾