Most four-stroke piston engines today employ one or more camshafts to operate poppet valves. The lobes on the camshafts operate cam followers which in turn open the poppet valves. A camless (or, free valve engine) uses electromagnetic, hydraulic, or pneumatic actuators to open the poppet valves instead. Actuators can be used to both open and 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 is fixed. The camshaft runs at half the engine speed. Although many modern engines use camshaft phasing, adjusting the lift and valve duration in a working engine is more difficult. Some manufacturers use systems with more than one cam lobe, but this is still a compromise as only a few profiles can be in operation at once. This is not the case with the camless engine, where lift and valve timing can be adjusted freely from valve to valve and from cycle to cycle. It also allows multiple lift events per cycle and, indeed, no events per cycle—switching off the cylinder entirely.
Camless engines are not without their problems though. Common problems include high power consumption, accuracy at high speed, temperature sensitivity, weight and packaging issues, high noise, high cost, and unsafe operation in case of electrical problems.
Camless valve trains have long been investigated by several companies, including Renault, BMW, Fiat, Valeo, General Motors, Ricardo, Lotus Engineering, Ford, Koenigsegg, and Cargine. Camless systems are commercially available, although not in production road vehicle engines.
A helical camshaft is a type of mechanical variable valve actuation (VVA) system. More specifically it is a camshaft that allows the valve opening duration to be varied over a wide, continuous, step-less, range, with all of the added duration being at full valve lift.
In this article a "variable duration camshaft" refers to a camshaft with a design that is intended to eliminate a conventional camshaft in a cylinder head and operate the valves independently to engine load and economy requirements. Further qualifications are:
The duration range is step-less and continuous
All the added range is at full valve lift
The range is wide enough to allow full torque/power at even extremely high RPM
The range is wide enough to allow engine load control by late inlet valve closing (LIVC)
The rates of valve opening/closing, acceleration, jerk etc. are within acceptable limits at all duration settings
Camless engines in production
MAN B&W Diesel are producing ship engines which make use of electrohydraulic valve control rather than camshafts, rocker arms and pushrods. The advantages of the engine the camless system gives is comprehensive:
Superior performance parameters due to variable electronically controlled timing of fuel injection and exhaust valves at any load.
Improved emissions with lower NOx and smokeless operation.
Easy change of operating mode during engine operation.
Simplified mechanical system with well-proven traditional fuel injection technology.
A Control system with more precise timing, giving superior engine balance with equalized thermal load in and between cylinders.
Monitoring and diagnostics of engine for longer overhaul intervals.
Lower rpm possible for ship maneuvering.
Superior acceleration, and crash stop performance
Up-gradable to software development over the lifetime of the engine
The Swedish Koenigsegg car company are developing a camless system and have successfully implemented the system on an existing SAAB car engine.The company aims to introduce the system on their sports car range.