Variable Valve - Control Systems for Spark Ignition Engine 2001-01-0671

The present paper presents the results of both theoretical and experimental research carried out on a mono cylinder engine equipped with an original hydraulically actuating distribution system, which determines variable valve timing (VVT). There are presented the construction and the operation of the hydraulic system for which a mathematical and physical simulation pattern was created. The variable timing system enables permanent variation of both valve's timing and lifting. The results obtained by using the mathematical and physical simulation pattern are presented by simulating VVT engine operation and load control through the inlet valve. When the VVT engine is running, the fresh charge admission velocity into the cylinder is maintained at a high level for the entire range of load variation. The admission velocity is high under small part-loads and the turbulence intensity level is also highly maintained which enables the development of the combustion process. Simultaneously in small part-loads by load control through the inlet valve the pumping losses decrease. Thus a 10% up to 29% increase of the efficiency of the VVT engine is obtained comparatively to the case when the classic engine (the throttled one) is used.

Valve timing improvement when using model mentioned above was based on the decrease of residual exhausted gases and pumping losses.

The VVT system designed by the authors was tested on a mono cylinder engine with the following characteristics: S (stroke) / D (bore) = 81/76 [mm/mm].