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This paper describes an investigation of a method of implementing VVT with the use of a secondary valve in series with the conventional intake valve of the engine. The secondary valve is not required to withstand the temperatures and pressures of combustion, and therefore can be of relatively lightweight design, so that it is easier to adjust the timing of the secondary valve than that of the main valve. Experiments with such a valve installed in a production engine indicate that benefits of variable valve timing such as overlap optimisation and throttleless load control (4% Fuel benefits at 980 rpm and 1.5 bar IMEP) are attainable with this system.

This paper describes an investigation of implementing variable valve timing with the use of a secondary valve in the intake tract The secondary valve acts in series with the conventional poppet valve of the engine, which is actuated in the conventional manner and with fixed timing It is significantly easier to adjust the timing of the secondary valve than that of the main valve There are two possible modes of operation of this device One is to control valve overlap, improving low speed low load performance The other is to use it as a load control mechanism, replacing the conventional throttle and therefore reducing the ‘pumping losses’ associated with conventional throttling We have implemented such a system on a motored single-cylinder research engine using pneumatic actuation Our experiments have demonstrated successful load control, significant pumping loss reduction, and control of backflow from the exhaust to the intake manifold