The active valve control system (AVCS) is an automobile
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 var ...
technology used by
Subaru
( or ; ) is the automobile manufacturing division of Japanese transportation conglomerate Subaru Corporation (formerly known as Fuji Heavy Industries), the twenty-first largest automaker by production worldwide in 2017.
Subaru cars are ...
. It varies the timing of the valves by using
hydraulic
Hydraulics (from Greek: Υδραυλική) 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 counte ...
oil 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 systems ...
, 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
In law, a legacy is something held and transferred to someone as their inheritance, as by will and testament. Personal effects, family property, marriage property or collective property gained by will of real property.
Legacy or legacies may refer ...
Outback
The Outback is a remote, vast, sparsely populated area of Australia. The Outback is more remote than the bush. While often envisaged as being arid, the Outback regions extend from the northern to southern Australian coastlines and encompass a ...
, 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 Stree ...
.
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 just 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, you achieve a smoother, easier idle. 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/gasoline, diesel engines and some hydrogen engines. EGR works by recirculating a portion of an engine's exhaust ...
(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.
See also
*
AVLS
References
External links
*Subaru Drive Magazine articles
AVCSSubaru AVCS Explained
{{subaru
Variable valve timing
Subaru
it:AVCS