cate ceva despre istoria vvt-ului(adica a axelor cu came care deschid admisiile/evacuarile de aer si carburant in functie de turatie: cu cat turatia e mai mare, cu atat e nevoie ca amestecul carburant sa fie mai bogat in aer, deci deschide supapele de aer mai mult timp, si cu cat e mai mica turatia, cu atat amestecul e necesar sa fie mai bogat in carburant, deci deschide supapele de admisie la aer mai putin timp, si pe cele de evacuare in functie de ele), se pare ca italienii au fost primii care au folosit-o la automobile, desi ea exista de pe vremea motoarelor cu aburi...
Fiat was the first auto manufacturer to patent a functional automotive variable valve timing system which included variable lift. Developed by Giovanni Torazza in the late 1960s, the system used hydraulic pressure to vary the fulcrum of the cam followers (US Patent 3,641,98
. The hydraulic pressure changed according to engine speed and intake pressure. The typical opening variation was 37%.
In September 1975,
General Motors (GM) patented a system intended to vary valve lift. GM was interested in throttling the intake valves in order to reduce emissions. This was done by minimizing the amount of lift at low load to keep the intake velocity higher, thereby atomizing the intake charge. GM encountered problems running at very low lift, and abandoned the project.
Alfa Romeo was the first manufacturer to use a variable valve timing system in production cars (US Patent 4,231,330). The 1980
Alfa Romeo Spider 2.0 L had a mechanical VVT system in
SPICA fuel injected cars sold in the
USA. Later this was also used in the 1983
Alfetta 2.0 Quadrifoglio Oro models as well as other cars. The system was engineered by Ing Giampaolo Garcea in the 1970s.
[2]
Honda's
REV motorcycle engine employed on the Japanese market-only Honda CBR400F in 1983 provided a technology base for
VTEC.
Germanii abia tarziu se trezesc, cu sistemul vanos la bmw, in 92
In 1992
BMW introduced the
VANOS system. Like the Nissan NVCS system it could provide timing variation for the intake cam in steps (or phases), the VANOS system differed in that it could provide one additional step for a total of three. Then in 1996 the
Double Vanos system was introduced which significantly enhances emission management, increases output and torque, and offers better idling quality and fuel economy. Double Vanos was the first system which could provide electronically controlled, continuous timing variation for both the intake and exhaust valves. In 2001 BMW introduced the
Valvetronic system. The Valvetronic system is unique in that it can continuously vary intake valve lift, in addition to timing for both the intake and exhaust valves. The precise control the system has over the intake valves allows for the intake charge to be controlled entirely by the intake valves, eliminating the need for a
throttle valve and greatly reducing
pumping loss. The reduction of pumping loss accounts for more than a 10% increase in power output and fuel economy.