Camless piston engine

A camless or free-valve piston engine has poppet valves operated by means of electromagnetic, hydraulic, or pneumatic actuators instead of cams. Actuators can be used to both open and close valves, or to open valves closed by springs or other means.

As a camshaft normally has only one lobe per valve, the valve duration and lift is fixed. The camshaft rotates at the rate of the crankshaft. 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 development

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, Gongda, and Koenigsegg's subsidiary FreeValve. Camless systems are commercially available, although not yet in production road vehicle engines. In the spring of 2015 Christian von Koenigsegg told reporters that the technology pursued by his company is "getting ready for fruition", but said nothing specific about the time-table.

Camless engines in marine and power stations

MAN Diesel & Turbo are producing engines which make use of electrohydraulic valve control rather than camshafts, rocker arms and pushrods. As well, many Wärtsilä engines have electronically controlled common-rail systems for fuel injection and valve actuation.

The advantages of the engine the camless system gives are 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.
• Upgradeable with software development over the lifetime of the engine.
• A lighter and shorter engine as the camshaft timing belt, sprockets and camshaft are eliminated.

Camless engines in car

The Swedish company Freevalve AB (formerly Cargine) are developing a camless system and have successfully implemented the system on an existing SAAB car engine.

See also

• Helical camshaft
• Multiair