Experimental and Numerical Study of an Electro-Hydraulic Camless VVA System

This paper presents the current research activity about an electro-hydraulic camless valve actuation system for internal combustion engines. From a general point of view, this system (Hydraulic Valve Control - HVC) is an open loop device for engine valve fully flexible camless actuation. In the HVC system, the valve actuation timing and duration are controlled by varying the driving signal of the pilot stage, which is governed by a solenoid, fast-acting, three-way valve; the valve lift is adjusted by varying the oil pressure of the power stage. This system uses hydraulic forces to open the engine valve while a mechanical spring is used for its closure. The HVC key element is a spool valve, which operates as a three way / three position valve. This element is designed in order to ensure the synchronization of its own motion with that of the poppet valve mass-spring system. This mechanism, which will be more thoroughly illustrated in the paper, has a significant role in the energy balance of the HVC system.

In the present paper, an experimental and numerical analysis of the HVC actuator behavior (mainly in terms of engine valve lift, pressure histories and energy consumption) is shown including the effects of cylinder back-pressure. A specific analysis of valve landing is also presented. Using this experimental data, a further validation of the HVC 1-D numerical model is performed in order to obtain a fully predictive design tool.