Rotating Cylinder Valve (RCV) engine unveiled

Reduced emissions

The stability and efficiency of the combustion system also lends itself to naturally low engine-out emissions. These benefits are likely to be greatest when an RCV four-stroke is used in substitution for a piston ported two-stroke engine, given the latter’s much higher hydrocarbon and CO2 emissions. The physically compact and high revving nature of RCV technology offers the emissions performance of a well engineered four stroke while retaining some of the practical advantages typical of a small two stroke. As such RCV technology is an ideal four-stroke choice for the substitution of crankcase scavenged two strokes for applications such as scooters and hand held forest and garden equipment.

Cylinder drive system

While the RCV engine does not require a valve train, a gear or toothed belt drive system is needed in order to rotate the cylinder and cylinder valve at exactly half crankshaft rotational speed. In the 125cc RCV engine developed for MPI, the cylinder is driven via an advanced face gear drive similar to those found in many helicopter and machine tool applications. The system uses a three dimensional gear tooth profile which enables the drive to be transferred through a 90 degree contact with the cylinder. With the ability to include a counter-balance weight within the idler gear, this arrangement offers exceptionally high standards of vibrational refinement, facilitating improved handling and driver comfort in scooter and ATV applications. With the use of sintered gear blanks, it also offers a considerable production cost advantage over alternatives such as bevel gear drives. Additionally, the face gear drive affords much greater tolerance to the high levels of component thermal expansion typically found with engine components.

Valve sealing – a fundamental challenge solved

While many previous sleeve and rotary valve engines delivered benefits in terms of breathing and performance, a common and fundamental problem was that of effective valve sealing. Typically, close tolerances were relied upon in order to achieve sealing during engine operation. Such engines were hence both relatively expensive to manufacture and required lengthy and controlled engine warm-up procedures to avoid seizure. With thermal expansion of the cylinder and reciprocating components typically two orders of magnitude greater than the tolerances required for sealing, the need for an effective, robust and low cost means of valve sealing was a fundamental challenge which prevented more widespread and practical application of such engines.

With its patented technology RCV Engines Ltd has solved this challenge through a highly innovative and yet fundamentally very simple cylinder valve sealing system which employs essentially the same basic principles as used in piston rings:

In order to accommodate the thermal expansions typical of engine operation, the valve has an ‘active’ sprung sealing mechanism, referred to by RCV Engines Ltd as a ‘sliding seal’.

...continued