Engineering news
To reduce carbon emissions, car manufacturers are striving to produce relatively small-capacity engines able to operate very economically at low and high speeds. These would produce low levels of carbon and other emissions in urban traffic and at cruising speeds, while still having power in reserve for overtaking manoeuvres.
Paul Chatten believes his “discrete valve event timing system” could do just that. He claims he could create naturally aspirated engines – whose air intake depends solely on atmospheric pressure – in excess of 197bhp, while reducing car emissions. Further increases in power could be obtained by using forced induction, such as turbocharging or supercharging.
Raising the operating speed of an engine will increase its power output, enabling even smaller engines using natural aspiration or forced induction. However, volumetric efficiency and operation at high engine speeds requires the valves to open earlier and close later to help accommodate high gas inertia and the pressure waves present in the inlet and exhaust systems.
Chatten explains: “Unfortunately high-speed cam profiles result in very inefficient operation and poor emission control during low-speed operation.”
Variable valve timing can help to mitigate against this, and many engines today employ a form of mechanism that can vary the time the valve opens. According to Chatten, many of these mechanisms are only partially effective at varying the time the valve remains open.
An example of Chatten’s patented invention uses a simple co-axial planetary gear mechanism to provide “infinite discrete control of all the valve events” including the exhaust valve opening (EVO), exhaust valve closing (EVC), inlet valve opening (IVO) and inlet valve closing (IVC). This enables variable valve timing, valve dwell (how long the valve remains open) and ability to vary the exhaust valve and inlet valve overlap. In this example, each valve is operated by two independent cams, one to open and another to close the valve. “The closing cam is profiled to prevent closing phase reciprocal valve loading at all times,” says Chatten.
Another patented design offers an alternative where an independent cam operates each valve, enabling valves to open and close independently of each other. Varying the opening sequence for each valve within a cylinder promotes swirl and supports good fuel mixing and exhaust “hydrocarbon scavenging”. This effect could be further enhanced by employing one inlet and one exhaust on each side of the cylinder.
The cams which act directly on the cam followers or bucket tappets do not increase the valve actuating mechanism reciprocating mass and do not rely on electrical or hydraulic systems to control the valve events. This means the mechanism does not limit the operating speed of the engine. Efficient operation at rotational operating speeds in excess of 12,000rpm (currently common motorcycle practice) could be possible subject to engine design, says Chatten. The design could be used for any engine speed but would be most effective when valve event control is optimised for all different engine speeds and load conditions.
“The ability to accurately and discretely vary all the valve events EVO, EVC, IVO and IVC could be utilised to support internal exhaust gas recirculation, yielding reductions in NOx, hydrocarbons and CO,” says Chatten.
Considerable torque increases could also be achieved using variable event timing, most significantly at the extremes of the engine speed range where fixed valve timing and traditional valve phaser systems are most compromised.
“This invention could create naturally aspirated engines in excess of 197bhp while contributing to CO2, NOx, CO and particulate air pollution emissions control,” explains Chatten.
“This would reduce the requirement for external exhaust gas circulation and electric hybridisation and could provide considerable cost benefits when compared with current practice.”