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.
See also
References
- ^ "United States Patent: 6871618". Patft.uspto.gov. http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&p=1&u=%2Fnetahtml%2FPTO%2Fsearch-bool.html&r=1&f=G&l=50&co1=AND&d=PTXT&s1=6,871,618&OS=6,871,618&RS=6,871,618. Retrieved 2009-10-02.
- ^ "Valeo tests camless system for gas engines; supplier hopes to produce fuel-saving technology by '08: AutoWeek Magazine". Autoweek.com. 2009-02-06. http://www.autoweek.com/apps/pbcs.dll/article?AID=/20051014/FREE/510140701. Retrieved 2009-10-02.
- ^ "View Item : » Managed Content » Lotus". Grouplotus.com. http://www.grouplotus.com/managedcontent/view/24. Retrieved 2009-10-02.
- ^ "Cargine". Cargine. http://www.cargine.com/. Retrieved 2009-10-02.
External links
- "EVIC Engine Home Page". Home.cogeco.ca. 2009-03-25. http://home.cogeco.ca/~davebowesevic/. Retrieved 2009-06-06.
- "Valeo tests camless system for gas engines; supplier hopes to produce fuel-saving technology by '08". AutoWeek. http://www.autoweek.com/apps/pbcs.dll/article?AID=/20051014/FREE/510140701. Retrieved October 14, 2005.
- "Advanced Actuators Research Group, Department of Mechanical Engineering, University of South Carolina". http://www.me.sc.edu/research/AARG/.
- "Valeo signs up 'several global automakers' for camless engine". http://www.autoweek.com/apps/pbcs.dll/article?AID=/20061221/FREE/61218008/1024/rss01&rssfeed=rss01.
- "Study of a Pneumatic Hybrid aided by a FPGA Controlled Free Valve Technology System". http://luur.lub.lu.se/luur?func=downloadFile&fileOId=1218738.
- "ME Engines – the New Generation of Diesel Engines" (PDF). http://www.mandiesel.com/files/news/filesof2810/p412-0503.pdf.
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