New operating strategies afforded by fully variable valve trains

Electrohydraulic and electromechanical valve train technologies for four-stroke engines are emerging which allow much greater flexibility and control of the valve events than can be achieved using mechanically-based systems. Much of the work done on exploiting the benefits of these systems has been directed towards improving engine fuel economy and reducing emissions. In the present work a study has been made, using an engine simulation program, in to some of the possible benefits to engine performance that may be facilitated by the flexibility of fully variable valve train (FVVT) systems. The simulation study indicates that FVVT systems, limited by realistic opening and closing rates, provide sufficient range in the valve event duration and timing to enable the engine to produce very high specific outputs whilst achieving a high level of torque in the low- and mid-speed range. It is also shown that an FVVT system makes it possible to modify the basic intake manifold tuning mechanism by modifying the engine firing order, without recourse to variable geometry manifold systems. Additionally, the operation of a 'pneumatic hybridisation' concept are investigated and a range of further operating strategies, including Differential Cylinder Loading, which become viable upon the adoption of FVVT systems are also discussed. Copyright © 2004 SAE International.