Dynamic analysis of a car engine valve train system

Abstract

In this paper, a multibody model of a car engine valve train system was developed, by using LMS Virtual.Lab software, in order to analyse its resonant vibrational behaviour. The model complexity is the result of a compromise between the need to obtain accurate results (with acceptable run times) and the requirement of an easy integration of subcomponent models into a virtual assembly. The cam-follower contact was modelled using appropriate tools of the adopted code (Generator Cam, Cam Contact). Model validation was realised by comparing the kinematic laws of the valve motion, obtained from the numerical simulation, against those obtained from the experimental tests performed by FCA Group. Then, the dynamics of the valve train system was analysed, applying a ramp to the crankshaft with a variable engine speed (1,000 to 6,000 rpm) and considering the motion unsmoothness deriving from the inertia and combustion pressure loads. The camshaft is considered rigidly connected to the crankshaft by a mechanism with a transmission ratio equal to 0.5. Such analyses allow to assess the valve bounce, the disengagement phenomena of the cam-follower system, the resultant forces acting on the camshaft bearings, and the resisting torque on the camshaft.