An Analysis of Valve Train Friction in Terms of Lubrication Principles

Friction losses in a motored 1.6L valve train can be reduced by roller tappets, by needle bearing inserts placed in the rocker arm/fulcrum contact and in the cam journals and by reducing spring tension. Friction reducing engine oil additives reduce valve train friction substantially, but oil viscosity has only a limited effect. These results can be quantitatively accounted for by a simple friction model based on lubrication theory. Both the model and the experimental results are consistent with the idea that the friction losses in the valve train are mainly due to boundary and mixed lubrication.