Variable valve timing

Hello Guys first i will tell you what are valves and how they work, and also tell you about VVT.

There is basically 4 valves per cylinder 2 for intake and 2 for exhaust. The main purpose of the valves are to breathe air in or out into the engine. When the intake valve is open using a cam shaft the mixture of air and fuel enters the cylinder and after the power generation process the exhaust valve are opened again using the cam shaft the gases are released of the cylinder. But this valve work exactly same on all rpm range which is not good for power, fuel economy or emission, hence VVT(Variable valve timing) is used.

Variable Valve timing (VVT) is the process of altering the valve timing and valve lift and valve duration, and this process is used to improve performance, fuel economy and emission.

Valve Timing decides at what rpm the valves open and close.

Valve Duration decides how long the valves stays open.

Valve Lift decides how far the valve lifts of its original position.

These all process is controlled by a computer which can constantly change according to the situation.

Lets see and example if an exhaust valve is open for long in one stroke all the exhaust gas would leave the cylinder creating more area for new air and fuel mixture to breathe in next stroke, which can generate more power. On the other hand if the exhaust valve is opened for a short period there could be some gas left on the cylinder for next stroke, this create a small engine displacement for a moment which can give you better fuel economy.

There are various companies who have their own name for this system. Though Fiat was the first to patent VVT in 1960, but Alfa Romeo was the first to use VVT in the production car called as CVVT. Most famous is Honda’s Vtech. There are numerous ways all the companies use this system for eg fiat Multiair uses hydraulic pressure.

  • AVLS (Subaru)
  • CPS (Proton) but proton use vvt engine for their new model of 2016
  • CVTCS (Nissan, Infiniti)
  • CVVT (Alfa Romeo, Citroën, Geely, Hyundai, Iran Khodro, Kia, Peugeot, Renault, Volvo)
  • DCVCP – dual continuous variable cam phasing (General Motors)
  • DVVT (Daihatsu) (Perodua)
  • MIVEC (Mitsubishi)
  • MultiAir (Fiat)
  • N-VCT (Nissan)
  • S-VT (Mazda)
  • Ti-VCT (Ford)
  • Valvetronic (BMW)
  • VarioCam (Porsche)
  • VCT (Ford, Yamaha)
  • VTEC, i-VTEC (Honda, Acura)
  • VVC (MG Rover)
  • VVL (Nissan)
  • Valvelift (Audi)
  • VVEL (Nissan, Infiniti)
  • VVT (Chrysler, General Motors, Proton, Suzuki, Isuzu, Volkswagen Group)
  • VVT-i, VVTL-i (Toyota, Lexus)
  • VTVT (Hyundai, Kia)

List from Wikipedia page :

Variable Valve timing is must in all the new cars and this technology has brought a revolution in automobile technology.

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