Pneumatic valve gear
Encyclopedia
Pneumatic valve springs are metal bellows
filled with compressed air used as an alternative to the metal wire spring
s used to close valve
s in high-speed internal combustion engine
s. This system was introduced in the mid-1980s in Renault
turbocharged 1.5 litre Formula One
engines.
as a result. Pneumatic systems, sharing a common reservoir of pressure retain a more static level of force, controlling the valve effectively, without any attendant peak lift load increase.
Bellows is a misleading word, since this would suggest some sort of concertina shaped cylinder. This is not the case, and a bellows of this design would fail due to metal fatigue at the roots and crests. Instead, it is simply a piston and cylinder, similar to a small pneumatic ram. Where the tappet bore where a hydraulic tappet would normally reside, becomes the cylinder, and the retainer assembly becomes the piston. Pressurised air(nitrogen) is pumped into this cylinder which then causes the piston/ retainer to rise to the top of cylinder, causing the valve to form an airtight seal with the seat. The compressed gas then becomes the spring so to speak, and does not have the same traits as springs do at elevated rpm.
A small light spring is sometimes fitted between the piston, and retainer so that when the system is switched off, the spring forces the piston down against the bottom of bore, and forces the retainer upwards. This ensures that no crown to valve contact occurs when shut down.
engines, often said to be the most powerful. However, reliability and poor handling of their chassis kept the cars from success until 1989 when Renault provided Williams
with its V10 engine to begin a winning streak. Renault won the constructors' championship with Williams in 1992, 1993, 1994, 1996 and 1997, and with Benetton
in 1995. Nigel Mansell
, Alain Prost
, Michael Schumacher
, Damon Hill
and Jacques Villeneuve
each won a Driver's championship in the 1990s with Renault engines.
Pneumatic valve springs are also found in several Moto GP
motorcycle engines, debuting in 2002 with the Aprilia RS3 Cube
. In 2005, Team Roberts was the first to use pneumatic valves full time in their uncompetitive KTM
powered bike. Today, almost all of the MotoGP teams use pneumatic valve technology on their bikes, including Yamaha, Suzuki and Honda. Ducati uses a desmodromic design.
, to reduce moving parts while improving valve control.
Bellows
A bellows is a device for delivering pressurized air in a controlled quantity to a controlled location.Basically, a bellows is a deformable container which has an outlet nozzle. When the volume of the bellows is decreased, the air escapes through the outlet...
filled with compressed air used as an alternative to the metal wire spring
Spring (device)
A spring is an elastic object used to store mechanical energy. Springs are usually made out of spring steel. Small springs can be wound from pre-hardened stock, while larger ones are made from annealed steel and hardened after fabrication...
s used to close valve
Poppet valve
A poppet valve is a valve consisting of a hole, usually round or oval, and a tapered plug, usually a disk shape on the end of a shaft also called a valve stem. The shaft guides the plug portion by sliding through a valve guide...
s in high-speed internal combustion engine
Internal combustion engine
The internal combustion engine is an engine in which the combustion of a fuel occurs with an oxidizer in a combustion chamber. In an internal combustion engine, the expansion of the high-temperature and high -pressure gases produced by combustion apply direct force to some component of the engine...
s. This system was introduced in the mid-1980s in Renault
Renault F1
Lotus Renault GP, formerly the Renault F1 Team, is a British Formula One racing team. The Oxfordshire-based team can trace its roots back through the Benetton team of the late 1980s and 1990s to the Toleman team of the early 1980s. Renault had also competed in various forms since , before taking...
turbocharged 1.5 litre Formula One
Formula One
Formula One, also known as Formula 1 or F1 and referred to officially as the FIA Formula One World Championship, is the highest class of single seater auto racing sanctioned by the Fédération Internationale de l'Automobile . The "formula" designation in the name refers to a set of rules with which...
engines.
Concept
Racing engines often fail at high rotational speeds because mechanical springs are unable to retract the valves quickly enough to provide clearance for the piston. Renault's pneumatic valve technology replaced steel springs with light weight compressed air bellows. These could retract valves more quickly and reduce the possibility of piston-valve interference as long as pressure could be maintained. Additionally, the amount of seat tension required to keep a coil sprung valve under control results in greater peak lift loading, with added stress to the entire valvetrainValvetrain
Valvetrain is an all-encompassing term used to describe the mechanisms and parts which control the operation of the valves. A traditional reciprocating internal combustion engine uses valves to control air and fuel flow into and out of the cylinders, facilitating combustion.-Layout:Valvetrain: The...
as a result. Pneumatic systems, sharing a common reservoir of pressure retain a more static level of force, controlling the valve effectively, without any attendant peak lift load increase.
Bellows is a misleading word, since this would suggest some sort of concertina shaped cylinder. This is not the case, and a bellows of this design would fail due to metal fatigue at the roots and crests. Instead, it is simply a piston and cylinder, similar to a small pneumatic ram. Where the tappet bore where a hydraulic tappet would normally reside, becomes the cylinder, and the retainer assembly becomes the piston. Pressurised air(nitrogen) is pumped into this cylinder which then causes the piston/ retainer to rise to the top of cylinder, causing the valve to form an airtight seal with the seat. The compressed gas then becomes the spring so to speak, and does not have the same traits as springs do at elevated rpm.
A small light spring is sometimes fitted between the piston, and retainer so that when the system is switched off, the spring forces the piston down against the bottom of bore, and forces the retainer upwards. This ensures that no crown to valve contact occurs when shut down.
Pneumatic valve technology in racing
Pneumatic valve springs gave Renault an advantage with its turbochargedTurbocharger
A turbocharger, or turbo , from the Greek "τύρβη" is a centrifugal compressor powered by a turbine that is driven by an engine's exhaust gases. Its benefit lies with the compressor increasing the mass of air entering the engine , thereby resulting in greater performance...
engines, often said to be the most powerful. However, reliability and poor handling of their chassis kept the cars from success until 1989 when Renault provided Williams
WilliamsF1
Williams Grand Prix Engineering Limited, trading as AT&T Williams, is a British Formula One motor racing team and constructor. It was founded and run by Sir Frank Williams and Patrick Head...
with its V10 engine to begin a winning streak. Renault won the constructors' championship with Williams in 1992, 1993, 1994, 1996 and 1997, and with Benetton
Benetton Formula
Benetton Formula Ltd., commonly referred to simply as Benetton, was a Formula One constructor that participated from to . The team was owned by the Benetton family who run a worldwide chain of clothing stores of the same name. In 2000 the team was purchased by Renault, but competed as Benetton for...
in 1995. Nigel Mansell
Nigel Mansell
Nigel Ernest James Mansell OBE is a British racing driver who won both the Formula One World Championship and the CART Indy Car World Series...
, Alain Prost
Alain Prost
Alain Marie Pascal Prost, OBE, Chevalier de la Légion d'honneur is a French racing driver. A four-time Formula One Drivers' Champion, Prost has won more titles than any driver except for Juan Manuel Fangio , and Michael Schumacher . From 1987 until 2001 Prost held the record for most Grand Prix...
, Michael Schumacher
Michael Schumacher
Michael Schumacher is a German Formula One racing driver for the Mercedes GP team. Famous for his eleven-year spell with Ferrari, Schumacher is a seven-time World Champion and is widely regarded as the greatest F1 driver of all time...
, Damon Hill
Damon Hill
Damon Graham Devereux Hill OBE is a retired British racing driver. In 1996 Hill won the Formula One World Championship. As the son of the late Graham Hill, he is the only son of a world champion to win the title...
and Jacques Villeneuve
Jacques Villeneuve
Jacques Joseph Charles Villeneuve, , is a Canadian musician and automobile racing driver. He is the son of the late Formula One driver Gilles Villeneuve, and is the namesake of his uncle...
each won a Driver's championship in the 1990s with Renault engines.
Pneumatic valve springs are also found in several Moto GP
Grand Prix motorcycle racing
Road Racing World Championship Grand Prix is the premier championship of motorcycle road racing currently divided into three distinct classes: 125cc, Moto2 and MotoGP. The 125cc class uses a two-stroke engine while Moto2 and MotoGP use four-stroke engines. In 2010 the 250cc two-stroke was replaced...
motorcycle engines, debuting in 2002 with the Aprilia RS3 Cube
Aprilia RS3 Cube
The RS3 Cube is a prototype race motorcycle that was developed by Aprilia to compete in the 2002 until 2004 MotoGP seasons. It was unveiled at the Bologna Motor Show in December 2001 by Aprilia's president, Ivano Beggio, and their race boss, Jan Witteveen...
. In 2005, Team Roberts was the first to use pneumatic valves full time in their uncompetitive KTM
KTM
KTM Sportmotorcycle AG is an Austrian motorcycle, bicycle and moped manufacturer.The company was founded in 1934 by engineer Hans Trunkenpolz in Mattighofen. It started out as a metal working shop and was named Kraftfahrzeuge Trunkenpolz Mattighofen...
powered bike. Today, almost all of the MotoGP teams use pneumatic valve technology on their bikes, including Yamaha, Suzuki and Honda. Ducati uses a desmodromic design.
Future valve technology
While pneumatic valve springs have become standard in Formula One engines, Renault has been researching computer controlled electro hydraulic valves using no camshaftCamshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
, to reduce moving parts while improving valve control.