Camless

 Most four-stoke piston engines today employ one or more camshafts to operatepoppet valves. The lobes on the camshafts operate cam followers which in turn open thepoppet valves. A camless(or，free valve engine) uses electromagnetic，hydraulic，orpneumatic actuators to open the poppet valves instead. Actuators can be used to both openand close the valves, or an actuator opens the valve while a spring closes it.

    As a camshaft normally has only one lobe per valve, the valve duration and lift isfixed. The camshaft runs at half the engine speed. Although many modern engines usecamshaft phasing，adjusting the lift and valve duration in a working engine is moredifficult. Some manufacturers use systems with more than one cam lobe, but this is still acompromise as only a few profiles can be in operation at once. This is not the case with thecamless engine, where lift and valve timing can be adjusted freely from valve to valve andfrom cycle to cycle. It also allows multiple lift events per cycle and, indeed，no events percycle-switching off the cylinder entirely.

    Camless engines are not without their problems though. Common problems includehigh power consumption, accuracy at high speed，temperature sensitivity, weight andpackaging issues，high noise，high cost, and unsafe operation in case of electricalproblems.

    Camless valve trains have long been investigated by several companies， includingRenault, BMW，Fiat, Valeo, General Motors，Ricardo, Lotus Engineering，Ford andCargine.  Some systems are commercially available, although not in production carengines.

    Notably, Formula One cars do not use camless valve trains, but pneumatic valvesprings together with conventional camshafts and followers instead, this is howeverprimarily due to the regulations teams must follow for engine development.