The active valve control system (AVCS) is an automobile

variable valve timing Variable valve timing (VVT) is the process of altering the timing of a Poppet valve, valve lift event in an internal combustion engine, and is often used to improve performance, fuel economy or emissions. It is increasingly being used in combina ...

technology used by

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. It varies the timing of the valves by using

hydraulic Hydraulics () is a technology and applied science using engineering, chemistry, and other sciences involving the mechanical properties and use of liquids. At a very basic level, hydraulics is the liquid counterpart of pneumatics, which concer ...

oil An oil is any nonpolar chemical substance that is composed primarily of hydrocarbons and is hydrophobic (does not mix with water) and lipophilic (mixes with other oils). Oils are usually flammable and surface active. Most oils are unsaturate ...

pressure to rotate 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 syst ...

, known as "phasing", in order to provide optimal valve timing for engine load conditions. The system is closed loop using the camshaft sensors, crankshaft sensors, air flow meter, throttle position as well as oxygen sensors and/or Air-Fuel ratio sensors in order to calculate engine load. The ECU is programmed to operate control valves that adjust the delivery of the hydraulic pressure in order to move the camshaft into the position that will provide the engine with the best performance while meeting emissions standards. AVCS is used on the Version 7 and up EJ207 engines, the EJ204, EJ254, EJ255, EJ257, the second generation EZ30D (2005+ in the USA market) found in the

Legacy Legacy or Legacies may refer to: Arts and entertainment Comics * " Batman: Legacy", a 1996 Batman storyline * '' DC Universe: Legacies'', a comic book series from DC Comics * ''Legacy'', a 1999 quarterly series from Antarctic Press * ''Legacy ...

Outback The Outback is a remote, vast, sparsely populated area of Australia. The Outback is more remote than Australian bush, the bush. While often envisaged as being arid, the Outback regions extend from the northern to southern Australian coastli ...

, Legacy 2.0R, 3.0R and the B9

Tribeca Tribeca ( ), originally written as TriBeCa, is a neighborhood in Lower Manhattan in New York City. Its name is a syllabic abbreviation of "Triangle Below Canal Street". The "triangle" (more accurately a quadrilateral) is bounded by Canal Str ...

. A dual AVCS system phases both the intake and exhaust camshafts on the EZ36 found in the 2008+ Tribeca, 2009+ Outback 3.6R, 2009+ Legacy 3.6R, and on the 2008+ STi EJ257 (W25 heads). Dual AVCS is present on the new FA20 engines in the 2015+ WRX, Forester and BRZ and the FB20 engines in the 2012+ Impreza / Crosstrek, though they actuate with a different method than those of the older engines. Dual AVCS is also found on Japanese-spec engines, notably the late model EJ207s in the WRX STI.

AVCS

The implementation of AVCS is quite different from AVLS. The latter only changes the cam profile that's operating the two valves. In AVCS, the engine computer (ECU) can command a solenoid which advances or retards the camshaft rotation by up to 35 degrees. By retarding the cams at idle or very low engine loads, a smoother, easier idle can be achieved. From idle through medium engine loads, AVCS advances the intake valves to begin opening during the last part of the exhaust stroke, when the exhaust valves are still slightly open. Some of the pressure created during the exhaust stroke flows into the intake manifold, having the effect of

exhaust gas recirculation In internal combustion engines, exhaust gas recirculation (EGR) is a nitrogen oxide () emissions reduction technique used in petrol engine, petrol/gasoline, diesel engines and some hydrogen internal combustion engine vehicle, hydrogen engines. ...

(EGR). The intake valves also close earlier during the intake stroke. This helps with engine efficiency and fuel economy. At very high engine loads, AVCS advances the intake valves further to open even sooner during the exhaust stroke. This produces a scavenging effect – that is, intake airflow helps clear the cylinder of exhaust gas. It also closes the intake valves sooner on the compression stroke. This results in improved volumetric efficiency, increased dynamic compression, and helps to generate higher power output.

References

External links

*Subaru Drive Magazine articles
AVCSSubaru AVCS Explained
{{subaru Variable valve timing Subaru it:AVCS

AVCS

See also

References

External links