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 and Cargine.[1][2][3][4] Some systems are commercially available, although not in production car engines.
Notably, Formula One cars do not use camless valve trains, but pneumatic valve springs together with conventional camshafts and followers instead, this is however primarily due to the regulations teams must follow for engine development.
Variable valve actuation (VVA) is a generalised term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems.
The valves within an internal combustion engine are used to control the flow of the intake and exhaust gasses into and out of the combustion chamber. The timing, duration and lift of these valve events has a significant impact on engine performance. In a standard engine, the valve events are fixed, so performance at different loads and speeds is always a compromise between driveability (power and torque), fuel economy and emissions. An engine equipped with a variable valve actuation system is freed from this constraint, allowing performance to be improved over the engine operating range.
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 and Cargine.[1][2][3][4] Some systems are commercially available, although not in production car engines.
Notably, Formula One cars do not use camless valve trains, but pneumatic valve springs together with conventional camshafts and followers instead, this is however primarily due to the regulations teams must follow for engine development.
Variable valve actuation (VVA) is a generalised term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems.
The valves within an internal combustion engine are used to control the flow of the intake and exhaust gasses into and out of the combustion chamber. The timing, duration and lift of these valve events has a significant impact on engine performance. In a standard engine, the valve events are fixed, so performance at different loads and speeds is always a compromise between driveability (power and torque), fuel economy and emissions. An engine equipped with a variable valve actuation system is freed from this constraint, allowing performance to be improved over the engine operating range.
Strictly speaking, the history of the search for a method of variable valve opening duration goes back to the age of steam engines when the valve opening duration was referred to as “steam cut-off”. Almost all steam engines had some form of variable cut-off. That they are not in wide use is a reflection that they are all lacking in some aspect of variable valve actuation.
The desirability of being able to vary the valve opening duration to match an engine’s rotational speed first became apparent in the 1920s when maximum allowable RPM limits were generally starting to rise. Up until about this time an engine’s idle RPM and its operating RPM were very similar, meaning that there was little need for variable valve duration.
It was in the 1920s that the first patents for variable duration valve opening started appearing – for example United States patent U.S. Patent 1,527,456. A surprising fact is that from these first patents up until the appearance of the helical camshaft there has never been a really practical and useful variable duration camshaft.
Multiair (or Uniair) is an electro-hydraulic variable valve actuation technology controlling air intake (without a throttle valve) in petrol or diesel engines. It is compatible with both naturally-aspirated and forced-induction engines. Multiair technology was patented by Fiat in 2002; it was launched at the 2009 Geneva Motor Show to be available in the Alfa Romeo MiTo. The new engines will be produced in Termoli, Italy at the Fiat Powertrain Technologies factory..........
The desirability of being able to vary the valve opening duration to match an engine’s rotational speed first became apparent in the 1920s when maximum allowable RPM limits were generally starting to rise. Up until about this time an engine’s idle RPM and its operating RPM were very similar, meaning that there was little need for variable valve duration.
It was in the 1920s that the first patents for variable duration valve opening started appearing – for example United States patent U.S. Patent 1,527,456. A surprising fact is that from these first patents up until the appearance of the helical camshaft there has never been a really practical and useful variable duration camshaft.
Multiair (or Uniair) is an electro-hydraulic variable valve actuation technology controlling air intake (without a throttle valve) in petrol or diesel engines. It is compatible with both naturally-aspirated and forced-induction engines. Multiair technology was patented by Fiat in 2002; it was launched at the 2009 Geneva Motor Show to be available in the Alfa Romeo MiTo. The new engines will be produced in Termoli, Italy at the Fiat Powertrain Technologies factory..........
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