Lotus leads way with clean engine

A unique hydraulic valve system has been developed by luxury car manufacturer Lotus, which it claims could cut fuel consumption by 20 per cent and revolutionise the family saloon.

Using the new system when a car hits traffic, its engine automatically shuts down two of its four cylinders, reducing power, increasing fuel economy and cutting exhaust emissions by up to 90 per cent.

But once the road clears, the car regains full thrust by reverting to firing on all four cylinders. Research manager Jamie Turner said the technology was a big step towards the development of the cleanest-possible combustion engine.

‘Our model will combine performance on the open road and economy in town traffic,’ he said.

The Lotus electrohydraulic, multi-ignition Active Valve Train (AVT) has taken around 10 years to develop.

While most engines have a camshaft that controls all the cylinder valves simultaneously, this is replaced in the Lotus engine with a system of hydraulics, which allows the valves to be managed independently of each other.

The mechanism consists of a hydraulic piston attached to each engine cylinder valve. Movement of the piston is controlled by the flow of synthetic low-viscosity hydraulic fluid.

The hydraulic flow itself is regulated by a high-frequency servo valve operating at 400Hz, which enables accurate control of the cylinder valve and so-called soft-touchdown to ensure quiet operation.

The electrohydraulic valve actuation system has full control over valve timing, lift and velocity. The movement of the hydraulic pistons is monitored by a central processing unit which will correct the valve profiles from cycle to cycle.

Each individual valve can therefore be controlled separately and operate on different profiles, allowing the engine to shut down one or more of its cylinders completely to save fuel.

Lotus says the AVT system has an advantage over electromagnetic valves currently under development as these do not allow lift to be varied and require a 42-volt power operating system.

Other benefits of AVT include reduced idle speed, optimised engine braking and traction control, and the possibility of linking hydraulic capacity to the gearshift and clutch mechanisms.

Lotus has already sold 10 single-cylinder test models to interested clients and estimates that the new engine should be ready for commercial use by 2007.

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