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This work deals with valve motion measurements on cylinder heads of Ducati racing motorbikes, by means of high speed laser Doppler vibrometer. The experimental apparatus is described and some measurement results are presented.The results confirm that the effects of the dynamic phenomena are very important, especially at high speeds, and that thedynamic response gets worse with the increment of backlashes in the cam kinematic pairs. In addition, the measurements make it possible to analyse the valve bumping phenomena. The information retrieved from measurements provides insight into the cam system dynamics and helps the development of elastodynamic predictive models.Keywords: valve train, laser Doppler vibrometer, motorbike engine, test bench. 1. INTRODUCTION Nowadays tests on the dynamic performances of valve trains in reciprocating engines are becoming more and more important. In fact, this kind of devices operates at very high speed and, as a consequence, it is not possible to neglect theeffects of link elastic flexibility and mass distribution, as well as the effects of backlashes and friction in joints, on thedynamic response of the mechanism. In particular, the valve motion can be so affected by the above mentioned effects,that it may fail to perform its tasks adequately, e.g. leading to alterations of the engine's fluid dynamics. In addition, highaccelerations and dynamic stress levels take place and may cause serious functional troubles, such as wear, fatigue andbreakage of mechanical components (see Fig. 1 and 2).This work deals with a desmodromic valve train of the twincylinder 'L' engine of Ducati racing motorbikes. This timing |
