The Third Generation of Valvetrains - New Fully Variable Valvetrains for Throttle-Free Load Control

The SI-engine has a disadvantage in fuel economy compared with a DI-Diesel engine. One of the major effects is the throttle-driven load control with its pumping losses. The main target is to reduce these losses in the thermodynamic process with a throttle-free load control. BMW has developed fully variable valve trains as a possible technical solution to realise a load control by regulating the valve lift and the closing time of the inlet valve. The essential variability can be achieved by fully variable mechanical valve trains or mechatronic systems both showing a robust running behavior in emissions and cyclic fluctuations.

The camshaft driven mechanical system is based on the technology of the BMW Double-VANOS system. An additional variability makes it possible to shift the valve lift continuously in order to control the valve closing.

The highest variability is given by a system with each valve being controlled seperatly. The electromechanical valve train enables the optimised timing of the individual valve offering a reduction in fuel consumption by about 10 per cent and a additional peak torque of 5 per cent. The required energy is supplied by an Starter/Alternator with high efficiency mounted directly on the crankshaft.

Fully variable valve train systems provide significantly better fuel consumption without major compromises in emissions and performance - a promising concept for future engine development