Camless

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Most piston engines today employ a camshaft to operate poppet valves. This consists of a cylindrical rod running the length of the cylinder bank with a number of oblong lobes or cams protruding from it, one for each valve. The cams force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.

There is sliding friction between the surface of the cam and the cam follower which rides upon it. There have been attempts to reduce this such as a roller follower valvetrain which has significantly less friction and allows for concave cam lobes.

In addition to mechanical friction, force is required to overcome the valve springs used to close the engine's valves. This force is usually very minimal though since the compressed spring will return most of the force to compress it back to the valvetrain when it decompresses. Nevertheless, these losses may reduce overall efficiency.

Another problem seen with camshaft/spring operation is the valvetrain weight and the RPM limits inherent on this setup.

One of the approaches designed to overcome these problems, but which has proved difficult to implement, is Camless valvetrains using solenoids or magnetic systems which have long been investigated by BMW and Fiat, and are currently being prototyped by Valeo and Ricardo. The new Fiat Nuova 500 is supposed to have this kind of engine.

The earliest proposed system was on the Tucker Torpedo in 1947, which was planned use oil pressure to open the valves. However, the engine didn't reach production due to legal problems.

Camless engines would not only be more efficient in terms of mechanical energy, they would also be more flexible, as the valves could be computer-controlled. Infinitely variable valve timing would be possible, though variable valve lift would be more difficult. Valeo estimates that the efficiency of a camless engine would be 20% greater than a comparable camshaft-operated engine, though Ricardo is more conservative. These companies are positioning this technology as an alternative to hybrid engines currently used to increase fuel economy.

[edit] References

• Valeo tests camless system for gas engines; supplier hopes to produce fuel-saving technology by '08. AutoWeek. Retrieved on October 14, 2005.

• Advanced Actuators Research Group, Department of Mechanical Engineering, University of South Carolina.

• Valeo signs up 'several global automakers' for camless engine.

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