Variable valve timing In internal combustion engines, variable valve timing (VVT) is the process of altering the timing of a valve lift event, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combination with varia ...

(VVT) is a system for varying the valve opening of an

internal combustion engine An internal combustion engine (ICE or IC engine) is a heat engine in which the combustion of a fuel occurs with an oxidizer (usually air) in a combustion chamber that is an integral part of the working fluid flow circuit. In an internal combus ...

. This allows the engine to deliver high power, but also to work tractably and efficiently at low power. There are many systems for VVT, which involve changing either the relative timing, duration or opening of the engine's inlet and exhaust valves. One of the first practical VVT systems used a variator to change the phasePhase refers to the relative timing between the inlet and exhaust camshafts, expressed as an angular measure. of the

camshaft A camshaft is a shaft that contains a row of pointed cams, in order to convert rotational motion to reciprocating motion. Camshafts are used in piston engines (to operate the intake and exhaust valves), mechanically controlled ignition systems ...

and valves. This simple system cannot change the duration of the valve opening, or their lift.'Lift' is the distance by which the valves open. Later VVT systems, such as the

helical camshaft A helical camshaft is a type of mechanical variable valve actuation (VVA) system. More specifically it is a camshaft that allows the valve opening duration to be varied over a wide, continuous, step-less range, with all of the added duration bein ...

or the movable fulcrum systems, could change these factors too. Despite this limitation, the variator is a relatively simple device to add to an existing engine and so they remain in service today. As the benefit of the variator relies on changing the relative timing between inlet and exhaust, variator systems are only applied to

double overhead camshaft An overhead camshaft (OHC) engine is a piston engine where the camshaft is located in the cylinder head above the combustion chamber. This contrasts with earlier overhead valve engines (OHV), where the camshaft is located below the combustion cha ...

engines. A variator system that moved a single camshaft for both inlet and exhaust would be possible, but would have no performance benefit.

Alfa Romeo system

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 US. Later this was also used in the 1983 Alfetta 2.0 Quadrifoglio Oro models as well as other cars. The technique derives from work carried in the 1970s by Alfa Romeo engineer Giampaolo Garcea and in Italian the device is termed ''variatore di fase''. The

Alfa Romeo Twin Spark engine Alfa Romeo Twin Spark (TS) technology was used for the first time in the Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars ( GTA, TZ) to enable it to achieve a higher power output from its engines. And in the ea ...

, introduced in the 1987

Alfa Romeo 75 The Alfa Romeo 75 (Type 161, 162B), sold in North America as the Milano, is a compact executive car produced by the Italian automaker Alfa Romeo between 1985 and 1992. The Alfa 75 was commercially quite successful: in only three years, 236,907 c ...

, also uses variable valve timing. The Alfa system varies the

phase Phase or phases may refer to: Science *State of matter, or phase, one of the distinct forms in which matter can exist *Phase (matter), a region of space throughout which all physical properties are essentially uniform * Phase space, a mathematic ...

(not the duration) of the cam timing and operates on the inlet camshaft.

Applications

* 1980

Alfa Romeo Spider The Alfa Romeo Spider (105/115 series) is a two-seater, front engine, rear drive roadster manufactured and marketed by Alfa Romeo from 1966 to 1994 in four distinct generations, or ''Series'', each with modifications ranging from modest to exte ...

* 1987

Twinspark * 1991

Alfa Romeo 155 The Alfa Romeo 155 (Type 167) is a compact executive car produced by Italian automobile manufacturer Alfa Romeo between 1992 and 1998. It was unveiled in January 1992 at Barcelona, with the first public launch in March 1992, at the Geneva Motor S ...

1.8l and 2.0l petrol engines * 1997

Alfa Romeo 156 The Alfa Romeo 156 (Type 932) is a compact executive car produced by the Italian automobile manufacturer Alfa Romeo. It was introduced at the 1997 Frankfurt Motor Show as the replacement for the Alfa Romeo 155. The 156 received a positive recep ...

with the 1.6l, 1.8l and 2.0l petrol engines * 1998

Alfa Romeo GTV and Spider The Alfa Romeo GTV and the Alfa Romeo Spider (Type 916) were sports cars produced by the Italian manufacturer Alfa Romeo from 1993 to 2004. The GTV is a 2+2 coupé, and the Spider is a two-seater roadster version of the GTV. Around 39,000 Spid ...

with the 1.8l and 2.0l petrol engines * 2000

Alfa Romeo 147 The Alfa Romeo 147 (Type 937) is a small family car produced by the Italian automaker Alfa Romeo from 2000 to 2010. The 147 was voted European Car of the Year in 2001. The 147 was launched at the Turin Motor Show in June 2000 as a replacement fo ...

with the 1.6l and 2.0l petrol engines, except for the model with the 105 bhp engine *2004

Alfa Romeo GT The Alfa Romeo GT (Type 937) is a coupe automobile that was produced by the Italian automaker Alfa Romeo between 2003 and 2010. The GT was introduced in March 2003 at the Geneva Motor Show.Fiat Chrysler Automobiles EMEA PressNEW ALFA GT COUPÉ, W ...

with the 1.8l and 2.0l petrol engines * 2001

Fiat Stilo The Fiat Stilo (Type 192) is a small family car available as a three- and a five-door hatchback, as well as an estate (Fiat Stilo Multi Wagon), produced by Italian automaker Fiat. The Stilo hatchbacks were presented in March 2001, at the Bologna ...

with the 1.8l or 2.4l engines

Volkswagen system

Volkswagen use a variator system with two variators, one for each camshaft. Like the Alfa Romeo system, these are electrically-controlled hydraulic units, mounted in the camshaft's timing belt pulley. These systems are fitted to the Volkswagen VR5 and VR6 engines, and also to the W8 and

W12 engine A W12 engine is a twelve-cylinder piston engine where three banks of four cylinders are arranged in a W configuration around a common crankshaft. W12 engines with three banks of four cylinders were used by several aircraft engines from 1917 unt ...

s. The multiple-

bank A bank is a financial institution that accepts deposits from the public and creates a demand deposit while simultaneously making loans. Lending activities can be directly performed by the bank or indirectly through capital markets. Because ...

W engines have four variators in total, one for each camshaft. The Volkswagen variator is referred to as a 'fluted variator', owing to the shape of the hydraulic components. Unlike the Alfa Romeo system with its helical splines and indirect actuation,Hydraulic action in the Alfa Romeo is axial, using helical splines to then cause a rotation of the variator. the Volkswagen system has a direct rotational action. The internal components of the variator resemble a paddle wheel inside a loose casing, so that it is free to move a few degrees from side to side. By applying hydraulic pressure on one side of these paddles, a phase shift is achieved. The

hydraulic fluid A hydraulic fluid or hydraulic liquid is the medium by which power is transferred in hydraulic machinery. Common hydraulic fluids are based on mineral oil or water. Examples of equipment that might use hydraulic fluids are excavators and backhoe ...

is engine oil, controlled by a solenoid valve mounted on the cylinder head and controlled by the ECU. A

Hall effect The Hall effect is the production of a voltage difference (the Hall voltage) across an electrical conductor that is transverse to an electric current in the conductor and to an applied magnetic field perpendicular to the current. It was disco ...

sensor also monitors the camshaft position.

Other variator-based VVT systems

Variable Cam Timing Variable Camshaft Timing (VCT) is an automobile variable valve timing technology developed by Ford. It allows for more optimum engine performance, reduced emissions, and increased fuel efficiency compared to engines with fixed camshafts. It uses ...

, Ford *

VANOS VANOS is a variable valve timing system used by BMW on various automotive petrol engines since 1992. The name is an abbreviation of the German words for ''variable camshaft timing'' (german: variable Nockenwellensteuerung). The initial version ...

, BMW

References

{{Reflist, colwidth=35em Variable valve timing Engine technology