A Study of the Performance of a SI Engine Incorporating a Hydraulically Controlled Variable Valve Timing System

The present paper deals with the valve lift curves that can be obtained by the use of a variable valve timing system (early valve closure type), and with the performance that can be expected from an engine with such a system. In the first stage of the work, the hydraulic mechanism which controls the anticipated closure, has been designed by means of a mathematical model, adjusted with empirical data obtained from laboratory tests about the hydraulic behaviour of the main components: flow coefficients and time dependent behaviour of the electrical-hydraulic ports. A computational study of realistic variable valve timing engine performance was carried out by means of a wave action model based on the method of characteristics. These results were compared with the ones corresponding to a conventional throttled engine and with those that can be obtained by the use of an ideal variable valve timing system in which the closure of the valve occurs instantaneously.