Variator (variable valve timing)

Last updated

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. [1] There are many systems for VVT, which involve changing either the relative timing, duration or opening of the engine's inlet and exhaust valves.

Contents

One of the first practical VVT systems used a variator to change the phase [note 1] of the camshaft and valves. This simple system cannot change the duration of the valve opening, or their lift. [note 2] 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.

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 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. [2] The Alfa Romeo Twin Spark engine, introduced in the 1987 Alfa Romeo 75, also uses variable valve timing. [3] [4]

The Alfa system varies the phase (not the duration) of the cam timing and operates on the inlet camshaft. [5]

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.[ citation needed ]

Applications

Volkswagen system

'Fluted variators' on a transparent model of a Hyundai T-GDI engine Vane phasers T-GDI.JPG
'Fluted variators' on a transparent model of a Hyundai T-GDI engine

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. [11] These systems are fitted to the Volkswagen VR5 and VR6 engines, 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, [note 3] 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. [11] 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.

Other variator-based VVT systems

Related Research Articles

<span class="mw-page-title-main">VTEC</span> Automobile variable valve timing technology

VTEC is a system developed by Honda to improve the volumetric efficiency of a four-stroke internal combustion engine, resulting in higher performance at high RPM, and lower fuel consumption at low RPM. The VTEC system uses two camshaft profiles and hydraulically selects between profiles. It was invented by Honda engineer Ikuo Kajitani. It is distinctly different from standard VVT systems which change only the valve timings and do not change the camshaft profile or valve lift in any way.

<span class="mw-page-title-main">Variable valve timing</span> Process of altering the timing of a valve lift event

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 variable valve lift systems. There are many ways in which this can be achieved, ranging from mechanical devices to electro-hydraulic and camless systems. Increasingly strict emissions regulations are causing many automotive manufacturers to use VVT systems.

<span class="mw-page-title-main">VVT-i</span> Automobile variable valve timing technology

VVT-i, or Variable Valve Timing with intelligence, is an automobile variable valve timing technology developed by Toyota. It was first introduced in 1995 with the 2JZ-GE engine found in the JZS155 Toyota Crown and Crown Majesta.

<span class="mw-page-title-main">VANOS</span> BMW variable valve timing system

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.

<span class="mw-page-title-main">Variable Cam Timing</span> Automobile variable valve timing technology

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 electronically controlled hydraulic valves that direct high pressure engine oil into the camshaft phaser cavity. These oil control solenoids are bolted into the cylinder heads towards the front of the engine near the camshaft phasers. The powertrain control module (PCM) transmits a signal to the solenoids to move a valve spool that regulates the flow of oil to the phaser cavity. The phaser cavity changes the valve timing by rotating the camshaft slightly from its initial orientation, which results in the camshaft timing being advanced or retarded. The PCM adjusts the camshaft timing depending on factors such as engine load and RPM.

The GM Ecotec engine, also known by its codename L850, is a family of all-aluminium inline-four engines, displacing between 1.4 and 2.5 litres. While these engines were based on the GM Family II engine, the architecture was substantially re-engineered for the new Ecotec application produced since 2000. This engine family replaced the GM Family II engine, the GM 122 engine, the Saab H engine, and the Quad 4 engine. It is manufactured in multiple locations, to include Spring Hill Manufacturing, in Spring Hill, Tennessee while the engine block and cylinder heads are cast at Saginaw Metal Casting Operations in Saginaw, Michigan.

Variable displacement is an automobile engine technology that allows the engine displacement to change, usually by deactivating cylinders, for improved fuel economy. The technology is primarily used in large, multi-cylinder engines. Many automobile manufacturers have adopted this technology as of 2005, although the concept has existed for some time prior to this.

<span class="mw-page-title-main">Common rail</span> Engine fuel delivery method

Common rail direct fuel injection is a direct fuel injection system built around a high-pressure fuel rail feeding solenoid valves, as opposed to a low-pressure fuel pump feeding unit injectors. High-pressure injection delivers power and fuel consumption benefits over earlier lower pressure fuel injection, by injecting fuel as a larger number of smaller droplets, giving a much higher ratio of surface area to volume. This provides improved vaporization from the surface of the fuel droplets, and so more efficient combining of atmospheric oxygen with vaporized fuel delivering more complete combustion.

<span class="mw-page-title-main">Fully Integrated Robotised Engine</span> Motor vehicle engine

The FIRE is a series of automobile engines from Fiat Powertrain Technologies, built in FCA's Termoli, Betim and also in Dundee, MI plants. It was designed by Italian design firm Rodolfo Bonetto. It is constructed by robot assembly plants ("Robogate") to reduce costs.

<span class="mw-page-title-main">Alfa Romeo Twin Spark engine</span> Motor vehicle 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 to enable it to achieve a higher power output from its engines. And in the early and middle 1980s, Alfa Romeo incorporated this technology into their road cars to enhance their performance and to comply with stricter emission controls.

The Family 1 is a straight-four piston engine that was developed by Opel, a former subsidiary of General Motors and now a subsidiary of PSA Group, to replace the Opel cam-in-head engines for use on mid-range cars from Opel/Vauxhall. Originally produced at the Aspern engine plant, production was moved to the Szentgotthárd engine plant in Hungary with the introduction of the DOHC version. GM do Brasil at São José dos Campos, GMDAT at Bupyeong and GM North America at Toluca also build these engines.

A camless or free-valve piston engine is an engine that has poppet valves operated by means of electromagnetic, hydraulic, or pneumatic actuators instead of conventional cams. Actuators can be used to both open and close valves, or to open valves closed by springs or other means.

<span class="mw-page-title-main">Alfa Romeo Twin Cam engine</span> Motor vehicle engine

The Alfa Romeo Twin Cam engine is an all-alloy inline-four engine series produced by Alfa Romeo from 1954 to 1994. In Italian it is known as the "bialbero" ("twin-shaft"), and has also been nicknamed the "Nord" (North) engine in reference to its being built in Arese, close to Milan, in the North of Italy and to distinguish it from the Alfa Romeo Boxer engine built in the South (Sud) for the Alfasud.

<span class="mw-page-title-main">Alfa Romeo JTS engine</span> Motor vehicle engine

The JTS engine is a gasoline direct injection engine produced by Alfa Romeo. It exists in two forms, straight-4 and V6, and was introduced into the Alfa lineup in 2002.

<span class="mw-page-title-main">MultiAir</span> Automobile variable valve timing technology

MultiAir or Multiair is a hydraulically-actuated variable valve timing and variable valve lift engine technology enabling "cylinder by cylinder, stroke by stroke" control of intake air directly via a gasoline engine's inlet valves. Developed by Fiat Powertrain Technologies, the technology bypasses a primary engine inefficiency: pumping losses caused by restriction of the intake passage by the throttle plate, used to regulate air feeding the cylinders.

Variable valve lift (VVL) is an automotive piston engine technology which varies the height a valve opens in order to improve performance, fuel economy or emissions. There are two main types of VVL: discrete, which employs fixed valve lift amounts, and continuous, which is able to vary the amount of lift. Continuous valve lift systems typically allow for the elimination of the throttle valve.

<span class="mw-page-title-main">Fiat Pratola Serra modular engines</span> Motor vehicle engine

The Fiat Pratola Serra modular engines are a family of engines produced by the Fiat Group since 1994 and used in Fiat, Alfa Romeo, Lancia and Jeep vehicles. They are named after the Pratola Serra municipality in which they're being produced.

<span class="mw-page-title-main">Fiat 124 Spider (2016)</span> Motor vehicle

The Fiat 124 Spider, nicknamed the Fiata, is a front-engine, rear-drive, two-passenger roadster manufactured by Mazda for FCA, having debuted at the 2015 LA Auto Show for model year 2016.

References

  1. Phase refers to the relative timing between the inlet and exhaust camshafts, expressed as an angular measure.
  2. 'Lift' is the distance by which the valves open.
  3. Hydraulic action in the Alfa Romeo is axial, using helical splines to then cause a rotation of the variator.
  1. Volkswagen, Fluted variator, pp. 4-5
  2. 1 2 "Alfa Romeo Spider FAQ".
  3. re (2005-10-17). "Alfa Romeo". italiaspeed.com. Retrieved 2018-03-31.
  4. "The History of ALFA Romeo 75".
  5. "Variable Valve Timing (VVT)". Austincc.edu. Retrieved 2018-03-31.
  6. "Alfa Romeo 156 Variator". Alfaworkshop.co.uk. Retrieved 2018-03-31.
  7. "Alfa Romeo GTV Variator". Alfaworkshop.co.uk. Retrieved 2018-03-31.
  8. "Alfa Romeo 147 Variator". Alfaworkshop.co.uk. Retrieved 2018-03-31.
  9. "Fiat Stilo Variator". Fiatworkshop.co.uk. Retrieved 2018-03-31.
  10. "Technical: stilo variator solenoid part number". The FIAT Forum. Retrieved 2018-03-31.
  11. 1 2 "Variable Valve Timing with fluted variator" (PDF). Volkswagen Self-study programme.