Variator (variable valve timing)
Encyclopedia
Variable valve timing
(VVT) is a system for varying the valve opening of an internal combustion engine. This allows the engine to deliver high power, but also to work tractably and efficiently at low power.Volkswagen, Fluted variator, pp. 4-5 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
and valves. This simple system cannot change the duration of the valve opening, or their lift.'Lift' is the the distance by which the valves open. Later VVT systems, such as the helical camshaft
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.
and FIAT
variable valve timing
(VVT) device.
Alfa Romeo first applied VVT in 1980 to the long-established Twin Cam engine
used in the Alfa Romeo Spider
. It is best known for its use throughout the Twin Spark engine
introduced with the Alfa 75
. The technique derives from work carried in the 1970s by Ing. Giampaolo Garcea.
In Italian the device is termed variatore de fase. Unlike systems that vary the duration of valve opening, the Alfa system varies the phase
relationship between a camshaft and crankshaft (i.e. piston position). The Alfa system, on their twin cam engine, is only applied to the inlet camshaft, the exhaust camshaft being unaffected.
Alfa Romeo's variator is a cylindrical chamber that contains a pressure chamber and piston along with helical splines. Engine oil pressure, moves the internal piston which rotates slightly due to the helical splines and advances the inlet valve timing by 25 degrees. Oil flow to the variator is controlled by a solenoid valve
. When engine speed reaches a certain speed, normally 1500-2000 rpm in the Twin Spark
application, the solenoid
energises, causing pressurised oil to be directed through the inlet camshaft into the variator. The inlet camshaft position is advanced 25 degrees, thus increasing valve overlap. It remains in this advanced state until about 5000 rpm when the solenoid switches off, and the variator piston returns the valve timing to its natural state. The variable timing increases the engine's mid-range flexibility and reduces emissions. Exact changeover points depend on version. It is notable that this relatively early system only has two settings: unchanged and fully advanced.
Alfetta Gold Cloverleaf in 1985. The next engine to employ a variator was the 75
Twinspark of 1988. These engines had 8 valve heads on the classic all alloy block and not the 1990s Fiat
/Alfa cast iron block engine which is the subject here.
The Fiat Stilo
with the 1.8l or 2.4l engines and Alfa Romeo
1.6l, 1.8l and 2.0l use a variator with the only exception being the Alfa Romeo 147
Junior. This has tthe 105 bhp engine, not the 120 bhp version.
If the petrol engine sounds like a diesel briefly after starting, it means that the variator splines are worn and should be replaced. This was a regular occurrence for the 16 valve Twin Spark
. When worn, the noise remains until about 1500 rpm - the variator is usually quieter when in the advanced position. Variators are best replaced at the same time as the timing belt. They will only cause noise, and not fail completely.
s, and also to the W8 and W12 engines. The multiple-bank
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 one one side of these paddles, a phase shift is achieved. The hydraulic fluid is engine oil, controlled by a solenoid valve mounted on the cylinder head and controlled by the ECU
. A Hall effect
sensor also monitors the camshaft position.
Variable valve timing
In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...
(VVT) is a system for varying the valve opening of an internal combustion engine. This allows the engine to deliver high power, but also to work tractably and efficiently at low power.Volkswagen, Fluted variator, pp. 4-5 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
Camshaft
A camshaft is a shaft to which a cam is fastened or of which a cam forms an integral part.-History:An early cam was built into Hellenistic water-driven automata from the 3rd century BC. The camshaft was later described in Iraq by Al-Jazari in 1206. He employed it as part of his automata,...
and valves. This simple system cannot change the duration of the valve opening, or their lift.'Lift' is the the distance by which the valves open. Later VVT systems, such as the helical camshaft
Helical camshaft
A helical camshaft is a type of mechanical variable valve actuation 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 being at full valve lift.In this article a “variable duration...
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.
Alfa Romeo system
Variator is the name for the Alfa RomeoAlfa Romeo
Alfa Romeo Automobiles S.p.A. is an Italian manufacturer of cars. Founded as A.L.F.A. on June 24, 1910, in Milan, the company has been involved in car racing since 1911, and has a reputation for building expensive sports cars...
and FIAT
Fiat
FIAT, an acronym for Fabbrica Italiana Automobili Torino , is an Italian automobile manufacturer, engine manufacturer, financial, and industrial group based in Turin in the Italian region of Piedmont. Fiat was founded in 1899 by a group of investors including Giovanni Agnelli...
variable valve timing
Variable valve timing
In internal combustion engines, variable valve timing , also known as Variable valve actuation , is a generalized term used to describe any mechanism or method that can alter the shape or timing of a valve lift event within an internal combustion engine...
(VVT) device.
Alfa Romeo first applied VVT in 1980 to the long-established Twin Cam engine
Alfa Romeo Twin Cam engine
The all alloy Alfa Romeo Twin Cam engine series was an inline-4 cylinder engine produced by Alfa Romeo from 1954 to 1994. For earlier Alfa Romeo engines featuring twin camshafts, refer to the main Alfa Romeo page...
used in the Alfa Romeo Spider
Alfa Romeo Spider
The Alfa Romeo Spider is a roadster produced by the Italian manufacturer Alfa Romeo from 1966 to 1993 . Widely regarded as a design classic, it remained in production for almost three decades with only minor aesthetic and mechanical changes...
. It is best known for its use throughout the Twin Spark engine
Alfa Romeo Twin Spark engine
Alfa Romeo Twin Spark technology was used first time in Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars to enable it to achieve a higher power output from its engines...
introduced with the Alfa 75
Alfa Romeo 75
The Alfa Romeo 75, sold in North America as the Milano, was a compact sports saloon / compact executive car produced by the Italian automaker Alfa Romeo between 1985 and 1992...
. The technique derives from work carried in the 1970s by Ing. Giampaolo Garcea.
In Italian the device is termed variatore de fase. Unlike systems that vary the duration of valve opening, the Alfa system varies the phase
Phase
-In physics:*Phase , a physically distinctive form of a substance, such as the solid, liquid, and gaseous states of ordinary matter**Phase transition is the transformation of a thermodynamic system from one phase to another*Phase...
relationship between a camshaft and crankshaft (i.e. piston position). The Alfa system, on their twin cam engine, is only applied to the inlet camshaft, the exhaust camshaft being unaffected.
Alfa Romeo's variator is a cylindrical chamber that contains a pressure chamber and piston along with helical splines. Engine oil pressure, moves the internal piston which rotates slightly due to the helical splines and advances the inlet valve timing by 25 degrees. Oil flow to the variator is controlled by a solenoid valve
Solenoid valve
A solenoid valve is an electromechanical valve for use with liquid or gas. The valve is controlled by an electric current through a solenoid: in the case of a two-port valve the flow is switched on or off; in the case of a three-port valve, the outflow is switched between the two outlet ports...
. When engine speed reaches a certain speed, normally 1500-2000 rpm in the Twin Spark
Alfa Romeo Twin Spark engine
Alfa Romeo Twin Spark technology was used first time in Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars to enable it to achieve a higher power output from its engines...
application, the solenoid
Solenoid
A solenoid is a coil wound into a tightly packed helix. In physics, the term solenoid refers to a long, thin loop of wire, often wrapped around a metallic core, which produces a magnetic field when an electric current is passed through it. Solenoids are important because they can create...
energises, causing pressurised oil to be directed through the inlet camshaft into the variator. The inlet camshaft position is advanced 25 degrees, thus increasing valve overlap. It remains in this advanced state until about 5000 rpm when the solenoid switches off, and the variator piston returns the valve timing to its natural state. The variable timing increases the engine's mid-range flexibility and reduces emissions. Exact changeover points depend on version. It is notable that this relatively early system only has two settings: unchanged and fully advanced.
Applications
The variable valve timing was first commercially used in the Alfa RomeoAlfa Romeo
Alfa Romeo Automobiles S.p.A. is an Italian manufacturer of cars. Founded as A.L.F.A. on June 24, 1910, in Milan, the company has been involved in car racing since 1911, and has a reputation for building expensive sports cars...
Alfetta Gold Cloverleaf in 1985. The next engine to employ a variator was the 75
Alfa Romeo 75
The Alfa Romeo 75, sold in North America as the Milano, was a compact sports saloon / compact executive car produced by the Italian automaker Alfa Romeo between 1985 and 1992...
Twinspark of 1988. These engines had 8 valve heads on the classic all alloy block and not the 1990s Fiat
Fiat
FIAT, an acronym for Fabbrica Italiana Automobili Torino , is an Italian automobile manufacturer, engine manufacturer, financial, and industrial group based in Turin in the Italian region of Piedmont. Fiat was founded in 1899 by a group of investors including Giovanni Agnelli...
/Alfa cast iron block engine which is the subject here.
The Fiat Stilo
Fiat Stilo
The Fiat Stilo is a small family car available as a 3-door and a 5-door hatchback, as well as an estate , produced by the Italian automaker Fiat Automobiles. The Stilo 3-door and 5-door were launched in 2001 to replace the Fiat Bravo/Brava, with the Stilo MultiWagon following in 2002...
with the 1.8l or 2.4l engines and Alfa Romeo
Alfa Romeo
Alfa Romeo Automobiles S.p.A. is an Italian manufacturer of cars. Founded as A.L.F.A. on June 24, 1910, in Milan, the company has been involved in car racing since 1911, and has a reputation for building expensive sports cars...
1.6l, 1.8l and 2.0l use a variator with the only exception being the Alfa Romeo 147
Alfa Romeo 147
The Alfa Romeo 147 is a small family car produced by Italian automaker Alfa Romeo from 2000 to 2010. The 147 was voted European Car of the Year for 2001, beating the Ford Mondeo and the Toyota Prius....
Junior. This has tthe 105 bhp engine, not the 120 bhp version.
Reliability
Although the variator rarely fails outright, it developed a poor reputation for unreliability and requiring a relatively expensive repair. This reputation was made worse by the perception of the variator as a component that over cars managed entirely without, and Alfa's previous reputation for mechanical reliability already made them susceptible to such criticism.If the petrol engine sounds like a diesel briefly after starting, it means that the variator splines are worn and should be replaced. This was a regular occurrence for the 16 valve Twin Spark
Alfa Romeo Twin Spark engine
Alfa Romeo Twin Spark technology was used first time in Alfa Romeo Grand Prix car in 1914. In the early 1960s it was used in their race cars to enable it to achieve a higher power output from its engines...
. When worn, the noise remains until about 1500 rpm - the variator is usually quieter when in the advanced position. Variators are best replaced at the same time as the timing belt. They will only cause noise, and not fail completely.
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 engineVR6 engine
The VR6 engine is an internal combustion engine configuration, consisting of six cylinders. It was developed by the Volkswagen Group in the late 1980s, and evolutions of the original variant are still produced by them....
s, and also to the W8 and W12 engines. The multiple-bank
Cylinder bank
Internal combustion piston engines are usually arranged so that the cylinders are in lines parallel to the crankshaft. Where they are in a single line, this is referred to as an inline or straight engine....
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 one one side of these paddles, a phase shift is achieved. The hydraulic fluid is engine oil, controlled by a solenoid valve mounted on the cylinder head and controlled by the ECU
ECU
ECU may refer to:Automotive terms* Electronic control unit, a generic term for any embedded system that controls one or more of the electrical systems or subsystems in a motor vehicle...
. A Hall effect
Hall effect
The Hall effect is the production of a voltage difference across an electrical conductor, transverse to an electric current in the conductor and a magnetic field perpendicular to the current...
sensor also monitors the camshaft position.