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.
Sliding friction between the surface of the cam and the cam follower which rides upon it is considerable. In addition to mechanical friction, considerable force is required to overcome the valve springs used to close the engine's valves. This can amount to an estimated 25% of an engine's total output at idle, reducing overall efficiency. A roller follower valve train has significantly less friction and allows for concave cam lobes.
Cam less 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. It has been estimated that the efficiency of a cam less engine would be 20% greater than a comparable camshaft-operated engine. This technology is an alternative to hybrid engines currently used to increase fuel economy.
In general, the fuel is sent into the combustion chamber by using valves which are governed by the rotation of the cam shaft. This rotation of the cam shaft, the speed of which is proportional to the engine’s speed, determines the timing of the engine valves. This will reduce the power output of the engine as some power is lost in the rotation of the cam shaft. The engine will either have powerful performance or increased fuel economy, but with the existing technology it is difficult to achieve both simultaneously.
In response to the needs of improved engines, there have been designed some mechanical devices to achieve some variable valve timing. These...