History Of VVT (Variable Valve Timing) Technology

History of VVT Technology

Steam Engines Application

The first variable valve timing systems came into existence in the nineteenth century on steam engines. Stephenson valve gear, as used on early steam locomotives, supported variable cutoff, that is, changes to the time at which the

admission of steam to the cylinders is cut off during the power stroke. 

Early approaches to variable cutoff coupled variations in admission cutoff with variations in exhaust cutoff. Admission and exhaust cutoff were decoupled with the development of the Corliss valve. These were widely used in constant speed variable load stationary engines, with admission cutoff, and therefore torque, mechanically controlled by a centrifugal governor and trip valves. As poppet valves came into use, simplified valve gear using a camshaft came into use. With such engines, variable cutoff could be achieved with variable profile cams that were shifted along the camshaft by the governor.this is now coming in system.

Aircraft Application

Some versions of the Bristol Jupiter radial engine of the early 1920s incorporated variable valve timing gear, mainly to vary the inlet valve timing in connection with higher compression ratios. The Lycoming R-7755 engine had a Variable Valve Timing system consisting of two cams that can be selected by the pilot. One for take off, pursuit and escape, the other for economical cruising.

Automotive Application

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 3,641,988). 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&nsp;L had a mechanical VVT system in SPICA fuel injected cars sold in the United States. 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.

Honda’s REV motorcycle engine employed on the Japanese market-only Honda CBR400F in 1983 provided a technology base for VTEC.

In 1986, Nissan developed their own form of VVT with the VG30DE(TT) engine for their MID4 Concept. Nissan chose to focus their NVCS (Nissan Valve-Timing Control System) mainly on torque production at low to medium engine speeds, because, the vast majority of the time, automobile engines will not be operated at extremely high speeds. The NVCS system can produce a smooth idle and high amounts of torque at low to medium engine speeds. TheVG30DE engine was first used in the 300ZX (Z31) 300ZR model in 1987. It was the first production car to use electronically controlled VVT technology. In 1987 Nissan also sold the Gloria, Leopard, and Cedric, all of which could come powered by the VG20DET engine which also utilized Nissans NVCS valve timing system.

The next step was taken in 1989 by Honda with the VTEC system. Honda had started production of a system that gives an engine the ability to operate on two completely different cam profiles, eliminating a major compromise in engine design. One profile designed to operate the valves at low engine speeds provides good road manners, low fuel consumption and low emissions output. The second is a high lift, long duration profile and comes into operation at high engine speeds to provide an increase in power output. The VTEC system was also further developed to provide other functions in engines designed primarily for low fuel consumption. The first VTEC engine Honda produced was the B16A which was installed in the Integra, CRX, and Civic hatchback available in Japan and Europe. In 1991 the Acura NSX powered by the C30A became the first VTEC equipped vehicle available in the US. VTEC can be considered the first “cam switching” system and is also one of only a few currently in production.

In 1991, Clemson University researchers patented the Clemson Camshaft which was designed to provide continuously variable valve timing independently for both the intake and exhaust valves on a single camshaft assembly. This ability makes it suitable for both pushrod and overhead cam engine applications.

In 1992, Porsche introduced VarioCam its 968 model which provided continuously variable valve timing for the intake valves.

BMW VANOS system.

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.

Ford began using Variable Cam Timing in 1998 for the Ford Sigma engine and the Ford Zetec engine. Ford became the first manufacturer to use variable valve timing in a pickup-truck, with the top-selling Ford F-series in the 2004 model year. The engine used was the 5.4 L 3-valve Triton.

In 1999, Porsche introduced VarioCam Plus on its 911 Turbo which combined continuous valve timing and two stage valve lift on the intake 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 athrottle valve and greatly reducing pumping loss. The reduction of pumping loss accounts for more than a 10% increase in power output and fuel economy.

Toyota VVT-i engine.

In 2005, General Motors offered the first Variable Valve timing system for pushrod V6 engines, LZE and LZ4.

In 2007, DaimlerChrysler became the first manufacturer to produce a cam-in-block engine with independent control of exhaust cam timing relative to the intake. The 2008 Dodge Viper uses Mechadyne’s concentric camshaft assembly to help boost power output to 600 bhp (450 kW).

In 2009, Fiat Powertrain Technologies introduced the Multiair system in Geneva Motor Show. The Multiair is a hydraulically-actuated variable valve timing system, which gives full control over valve lift and timing. The new technology will be available in Alfa Romeo MiTo starting from September 2009.

In 2009, Porsche introduced an enhanced version of VarioCam Plus on its 911 GT3 including the previous variable valve timing and two stage valve lift on the intake valves but with additional variable timing of the exhaust valves.

Diesel Engines Application

In 2010, Mitsubishi developed and started mass production of its 4N13 1.8 L DOHC I4 world’s first passenger car diesel engine that features a variable valve timing system.

VVT Implementations

• Aftermarket modifications — Conventional hydraulic tappet can be engineered to rapidly bleed-down for variable reduction of valve opening and duration.
• Alfa Romeo
  • Twin Cam — some versions are equipped with Variable Valve Timing technology.
  • Twin Spark — is equipped with Variable Valve Timing technology.
  • JTS — is equipped with Variable Valve Timing technology, both intake and exhaust.
  • Multiair continuously varies the timing of the inlet valve by changing oil pressure.
• BMW
  • Valvetronic — Provides continuously variable lift for the intake valves; used in conjunction with Double VANOS.
  • VANOS — Varies intake timing by rotating the camshaft in relation to the gear.
  • Double VANOS — Continuously varies the timing of the intake and exhaust valves.
• Daihatsu
  • DVVT — Daihatsu Variable Valve Timing. Continuously varies the timing of the intake camshaft, or both the intake and exhaust camshafts (depending on application).
• Fiat
  • “StarJet” FIRE-based engine.
• Ford
  • VCT Variable Cam Timing — Varies valve timing by rotating the camshaft.
  • Ti-VCT Twin Independent Variable Camshaft with two fully variable camshafts used in Ford Sigma engine andFord Duratec engine.
• Chrysler — Varies valve timing through the use of concentric camshafts developed by Mechadyne enabling dual-independent inlet/exhaust valve adjustment on the 2008 Dodge Viper.
• General Motors Corporation (GM)
  • VVT — Varies valve timing continuously throughout the RPM range for both intake and exhaust for improved performance in both overhead valve and overhead cam engine applications.(See also Northstar System).
  • DCVCP (Double Continuous Variable Cam Phasing) — Varies intake and exhaust camshaft timing continuously with hydraulic vane type phaser; available on Family 1, Family 0, and Family II engines.
  • Alloytec — Continuously variable camshaft phasing for inlet cams; continuously variable camshaft phasing for inlet cams and exhaust cams (High Output Alloytec).
• Honda
• VTEC — Varies duration, timing and lift by switching between two different sets of cam lobes.
• VTEC-E — This system is designed solely for the purpose of improving fuel economy. A variation of the VTEC mechanism is used to create an offset of lift between the two intake valves, one valve opening only slightly to prevent accumulation of fuel in the intake port. The asymmetrical opening of the intake valves creates a powerful swirl in the combustion chamber and allows for a very lean intake charge to be used under certain conditions. Under normal operation the two intake valve rocker arms are locked together and both valves follow the normal lift cam profile.



Honda VTEC engine.

• i-VTEC — In high-output DOHC 4 cylinder engines, the i-VTEC system adds continuous intake cam phasing (timing) to traditional VTEC. In economy-oriented SOHC and DOHC 4-cylinder engines the i-VTEC system increases engine efficiency by delaying the closure of the intake valves under certain conditions and by using an electronically controlled throttle valve to reduce pumping loss. In SOHC V6 engines the i-VTEC system is used to provide Variable Cylinder Management which deactivates one bank of three cylinders during low demand operation.
• Advanced VTEC — This is the latest Honda VVT system and is the most unusual of all the VTEC systems. Rather than switching between cam lobes the Advanced VTEC system uses intermediate rocker arms with a variable fulcrum to continuously vary intake valve timing, duration and lift.
• Hyundai MPI CVVT — Varies power, torque, exhaust system, and engine response.
• Kawasaki — Varies position of cam by changing oil pressure thereby advancing and retarding the valve timing,2008 Concours 14 (also known as the 1400GTR).
• Lexus VVT-iE — Continuously varies the intake camshaft timing using an electric actuator.
• Mazda S-VT — Continually varies intake timing and crank angle using an oil control valve actuated by the ECU to control oil pressure.
• Mitsubishi MIVEC — Varies valve timing, duration and lift by switching between two different sets of cam lobes.
  • The 4B1 engine series uses a different variant of MIVEC which varies timing (phase) of both intake and exhaust camshafts continuously.
  • The 4N1 engine family is the world’s first to feature a variable valve timing system applied to passenger car diesel engines.
• Nissan
  • N-VCT — Varies the rotation of the cam(s) only, does not alter lift or duration of the valves.
  • VVL — Varies timing, duration, and lift of the intake and exhaust valves by using two different sets of camlobes.
  • CVTC introduced with the HR15DE, HR16DE, MR18DE and MR20DE new engines in September 2004 on theNissan Tiida and North American version named Nissan Versa (in 2007); and finally the Nissan Sentra (in 2007).
  • VVEL introduced with the VQ37VHR Nissan VQ engine engine in 2007 on the Infiniti G37.
• Porsche
  • VarioCam — Varies intake timing by adjusting tension of a cam chain.
  • VarioCam Plus — Varies intake valve timing by rotating the cam in relation to the cam sprocket as well as duration, timing and lift of the intake and exhaust valves by switching between two different sets of cam lobes.
• Proton
  • Campro CPS — Varies intake valve timing and lift by switching between two sets of cam lobes without using rocker arms as in most variable valve timing systems. Debuted in the 2008 Proton Gen-2 CPS^[8][9] and the 2008 Proton Waja CPS.
  • VVT introduced in the Waja 1.8′s F4P renault engine (Toyota supplies the VVT to renault)
• PSA Peugeot Citroën CVVT — Continuous variable valve timing.
• Renault Clio Renault Sport 172, 172 Cup, 182, 182 Cup, Trophy, 197, 197 Cup, 200, and Clio V6 Mk2 VVT — Megane 1.6 vvt variable valve timing.
• Rover VVC — Varies timing with an eccentric disc.
• Suzuki — VVT — Suzuki M engine
• Subaru
  • AVCS — Varies timing (phase) with hydraulic pressure, used on turbocharged and six-cylinder Subaru engines.
  • AVLS — Varies duration, timing and lift by switching between two different sets of cam lobes (similar to Honda VTEC). Used by non-turbocharged Subaru engines.
• Toyota
  • VVT — Toyota 4A-GE 20-Valve engine introduced VVT in the 1992 Corolla GT-versions.
  • VVT-i — Continuously varies the timing of the intake camshaft, or both the intake and exhaust camshafts (depending on application).
  • VVTL-i — Continuously varies the timing of the intake valves. Varies duration, timing and lift of the intake and exhaust valves by switching between two different sets of cam lobes.
  • Valvematic
• Vauxhall – VVT used in the facelift Vectra 1.8 engines.
• Volkswagen Group — VVT introduced with later revisions of the 1.8t engine, and the 30-valve 2.8 L V6. Similar toVarioCam, the intake timing intentionally runs advanced and a retard point is calculated by the ECU. A hydraulic tensioner retards the intake timing. Most modern VW Group petrol engines now include VVT on either the inlet cam, or both inlet and exhaust cams, as in their V6, V8 and V10 engines.
• Volvo
  • CVVT — Continuous variable valve timing on intake and/or exhaust camshafts (depending on application).
  • CPS — Changes valve timing, duration and lift of the intake valves by switching between two different sets of cam lobes. Same basic technology as Porsches VarioCam Plus with switching direct-acting tappets. To date this is only used on Volvos short inline-6 (SI6) naturally-aspirated 3.2 L engine.

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