Camless

Camless

Most piston engines today employ a camshaft to operate poppet valves. This consists of a cylindrical rod running the length of the cylinder bank with a number of oblong "lobes" or "cams" protruding from it, one for each valve. The cams force the valves open by pressing on the valve, or on some intermediate mechanism, as they rotate.

There is sliding friction between the surface of the cam and the cam follower which rides upon it. There have been attempts to reduce this such as a roller follower valvetrain which has significantly less friction and allows for concave cam lobes.

In addition to mechanical friction, force is required to overcome the valve springs used to close the engine's valves. This force is usually very minimal though since the compressed spring will return most of the force to compress it back to the valvetrain when it decompresses. Nevertheless, these losses may reduce overall efficiency.

Another problem seen with camshaft/spring operation is the valvetrain weight and the RPM limits inherent on this setup.

One of the approaches designed to overcome these problems, but which has proved difficult to implement, is Camless valvetrains using solenoids or magnetic systems which have long been investigated by BMW and Fiat, and are currently being prototyped by Valeo and Ricardo. The new Fiat Nuova 500 is supposed to have this kind of enginecite news|url=http://www.autoblog.com/2008/01/07/camless-engine-may-debut-on-2009-fiat-500-alfa-junior/ |title=Camless engine may debut on 2009 Fiat 500, Alfa Junior |publisher=Autoblog |date=2008-01-07 |accessdate=2008-08-29] .

The earliest proposed system was on the Tucker Torpedo in 1947, which was planned use oil pressure to open the valves. However, the engine didn't reach production due to legal problems.

Camless engines would not only be more efficient in terms of mechanical energy, they would also be more flexible, as the valves could be computer-controlled and free up more power to the wheels. Infinitely variable valve timing would be possible, though variable valve lift would be more difficult. Valeo estimates that the efficiency of a camless engine would be 20% greater than a comparable camshaft-operated engine, though Ricardo is more conservative. These companies are positioning this technology as an alternative to hybrid engines currently used to increase fuel economy.

References

*
*
*


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • Camless — Un moteur à explosion Camless (littéralement « sans cames ») utilise une nouvelle technologie, dont le principe consiste à piloter individuellement, à partir d un calculateur, chaque soupape sans arbres à cames. Ces derniers sont… …   Wikipédia en Français

  • Variable valve actuation — Variable Valve Actuation, or 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,… …   Wikipedia

  • Multiair — (or Uniair) is an electro hydraulic variable valve actuation technology controlling air intake (without a throttle valve) in petrol or diesel engines [1]. It is compatible with both naturally aspirated and forced induction engines. Multiair… …   Wikipedia

  • Valvetrain — A traditional reciprocating internal combustion engine uses valves to control air and fuel flow into and out of the cylinders, facilitating combustion.Valvetrain is an all encompassing term used to describe the mechanisms and parts which control… …   Wikipedia

  • Vehicle acronyms and abbreviations — *A4: 4 speed automatic transmission *A5: 5 speed automatic transmission *A6: 6 speed automatic transmission *A/C: Air conditioning *AdvHEV: Advanced hybrid *AMT: Automated Manual Transmission *ATLS: Automated Truck Loading Systems *Autogas: LPG… …   Wikipedia

  • Arbre a cames — Arbre à cames Animation d un arbre à 2 cames actionnant 2 soupapes Un arbre à cames est un dispositif mécanique permettant de transformer un mouvement rotatif en mouvement longitudinal et réciproquement. L’arbre à cames est une découverte du… …   Wikipédia en Français

  • Arbre a cames en tete — Arbre à cames Animation d un arbre à 2 cames actionnant 2 soupapes Un arbre à cames est un dispositif mécanique permettant de transformer un mouvement rotatif en mouvement longitudinal et réciproquement. L’arbre à cames est une découverte du… …   Wikipédia en Français

  • Arbre À Cames — Animation d un arbre à 2 cames actionnant 2 soupapes Un arbre à cames est un dispositif mécanique permettant de transformer un mouvement rotatif en mouvement longitudinal et réciproquement. L’arbre à cames est une découverte du moyen âge pendant… …   Wikipédia en Français

  • Arbre À Cames En Tête — Arbre à cames Animation d un arbre à 2 cames actionnant 2 soupapes Un arbre à cames est un dispositif mécanique permettant de transformer un mouvement rotatif en mouvement longitudinal et réciproquement. L’arbre à cames est une découverte du… …   Wikipédia en Français

  • Arbre à came — Arbre à cames Animation d un arbre à 2 cames actionnant 2 soupapes Un arbre à cames est un dispositif mécanique permettant de transformer un mouvement rotatif en mouvement longitudinal et réciproquement. L’arbre à cames est une découverte du… …   Wikipédia en Français

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”