Design and Analysis of a Roller Follower Variable Valve Timing System

A Variable Valve Timing system has been designed and rig tested for application on a high speed marine diesel engine. It has been demonstrated that inlet valve phasing is an appropriate way of reducing the flow of exhaust gas residuals, particularly at light loads, into the inlet manifold during valve overlap.

The system described controls the position of the roller follower by means of an eccentric to allow the inlet valve events to be retarded by up to 40° crank angle. A kinematic model has been constructed to examine the tappet motion, and comparisons are made with measured values. Modelling of the lubrication regime at the roller, cam and tappet contact points is presented, to examine the system wear characteristics. Roller follower speed is measured to examine the prevailing lubrication regime. Rig results show that the VVT system is reliable and that the desired phasing of the valve events is obtained.