"This paper seeks to provide an overview of the basic parameters used in the specification of valve timing in spark ignition engines. The effect of these parameters on engine performance and emissions will be discussed in general terms rather than with reference to any particular engine or type of engine. Some of the current industry trends will be discussed in terms of their impact on the engine valve timing parameters."

"It is becoming more widely understood that advanced VVA systems will be required for future diesel engines to enable advanced combustion strategies such as HCCI. The cost, however, of implementing such systems is commonly seen as a problem. Affordable VVA systems require low engineering, investment and piece costs to achieve a high costbenefit ratio.

Engineering and investment costs can be minimised by the use of modular, interchangeable systems that allow maximum commonality between the major engine component assemblies, such as the cylinder head and covers. These systems allow the valve train type to be specified at build time, such that a standard valve train or various levels of VVA can be built into the engine as legislation and product differentiation dictate.

This paper describes a modular, camshaft-operated family of valve train solutions that range from a standard valve train through to advanced VVA systems for both intake and exhaust. Such a family has been built into a common cylinder head package, to give various levels of functionality. Variable valve lift, variable open period and modulated secondary valve openings and the practical combinations of these functions are presented along with their potential uses.

This type of modular design is relatively simple, whilst still meeting all the packaging constraints imposed on modern diesel engines."

"Simulation has been used to investigate how variable duration VVA can influence the transient torque rise of a modern light-duty diesel engine. The base engine examined employed a variable geometry turbo-charger with air to air inter-cooling, cooled EGR and common rail fuel injection. The VVA system investigated was variable duration, applied to both intake and exhaust valves, controlling primarily exhaust opening and intake closing events.

This paper describes the assumptions and methods used to deal with transient combustion, the interaction of the VGT and EGR sub-systems, the VVA, VGT and the EGR controllers, and contrasts the behaviour of the standard engine with that using VVA by presenting result to explain the phenomena that lead to the differences in torque rise profile."

This was initially written as an SAE paper, but was never published.

"An investigation has been carried out to identify how variable valve actuation (VVA) can be used to improve the part load fuel economy of a modern light-duty diesel engine. The base engine examined employed a variable geometry turbo-charger (VGT) with air to air inter-cooling, cooled exhaust gas re-circulation (EGR) and common rail fuel injection. The VVA system investigated was of the variable duration type, controlling primarily exhaust valve opening and intake valve closing events.

This paper describes how the fuel economy of the base engine was affected by the interactions of the VGT and EGR systems. It then presents simulation data that shows the methods by which fuel economy can be improved by the use of VVA, explains the phenomena that lead to this improvement and quantifies the extent to which it can be improved: Indicated and brake specific fuel consumption improvements of up to 6% and 19% respectively, were found during the course of this work."

"DaimlerChrysler and Mechadyne have undertaken a piece of work to investigate the opportunities for improving the operation of light duty diesel engines using variable valve timing. The very high compression ratios used in this type of engine make it essential to be able to alter the valve open periods to affect exhaust valve opening and intake valve closing, whilst leaving the valve motions largely unchanged around overlap top dead centre to avoid valve to piston contact.

This paper presents an overview of the design solution, a description of the simulation model used, performance and economy data predicted by the model and a discussion of other areas of opportunity where improvements may be possible."