Modal Analysis of Valve train Test Rig Support Structure

Improvement of fuel economy is one of the most important development targets of modern passenger car engines. Modern solutions such as Direct Injection, Variable Valve Trains, or Cylinder Deactivation help to obtain this requirement. Each one of these techniques optimize the thermodynamic efficiency of the engine. However, the mechanical structure of combustion engines shows many areas of possible optimization regarding the mechanical efficiency.

Engine friction affects the overall fuel consumption, mainly under low speed conditions combined with part load. Low speed/part load conditions are relevant for the real life fuel consumption of an engine, as well as friction improvements have significant effects on the fuel economy. The valve train drive produces the dominant friction portion under these conditions. Hence the friction optimization of this engine subsystem is one of the key issues regarding mechanical efficiency.

The valve train friction consists mainly of friction produced by the contact between cam and cam follower, e.g. tappet or finger lever. The introduction of a roller contact to the cam, is a known optimization method. However the cam shaft bearings need to be optimized as well. This paper explains the influence of the cylinder head structure on the behavior of the cam shaft bearings. The modal analysis method shows the test rig structure influence on the valve train components during vibrational analysis. Conclusions and suggestions for the system are presented.