Active Valve Control System
Encyclopedia
Active Valve Control System (AVCS) is an automobile
variable valve timing
technology used by Subaru
. It varies the timing of the intake valves by using hydraulic oil
pressure to rotate the camshaft
in order to provide optimal air flow in and out of the engine. The system is closed loop using 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 minding emissions standards.
AVCS is used on the Version 7 and up EJ207 engines, the EJ255 and EJ257, the second generation EZ30D (2005+ in the USA Market) found in the Legacy
Outback
, Legacy 3.0R and the B9 Tribeca
. A Dual AVCS system utilizes both the intake and exhaust camshafts on the EZ36 found in the 2008 Tribeca. Dual AVCS is also found on Japanese Spec engines, although a complete list of the engines with Dual AVCS has yet to be compiled.
At low engine speeds, each of the two intake valves for a given cylinder run on a different camshaft profile (the engines are 4-valve per cylinder type). One valve is operated by a low-lift, low-duration lobe, while the other is actuated by a high-lift, high-duration lobe. This increases air speed causing a smooth idle, while at the same time promoting a swirl factor, increasing efficiency.
At high speeds, the ECU (Engine Control Unit
) computer signals a solenoid to let oil pressure move a pin which locks the two lobes together. This means at high speed both intake valves are effectively driven by the high-speed camshaft lobe. This increases high-RPM power due to increased valve lift, duration and overall timing.
Cam locking is done by moving a pin with hydraulic pressure. As with other variable valve timing
systems, it allows the engine to have a quiet low-speed operation with a smooth idle, while also using a camshaft lobe profile similar to "race cam" at high engine RPMs.
Widespread use of AVLS began with non-turbocharged Subaru 2.5 liter four-cylinder engines in Model year
2006. AVLS was first used in the 2005 six-cylinder 3.0 liter Subaru Outback. Turbocharged engines and Subaru's six-cylinder engines continue to use Subaru's AVCS (variable cam phasing) system instead of AVLS. Reports generally agree the new engine feels like a brand new engine with flatter torque curve compared to previous non-AVLS, non-AVCS 2.5 liter engines. Initial applications raised maximum power from 165 hp to 175 hp, but more significantly raised the power at most RPM levels. The goal is better fuel economy, improved driveability and increased power.
Model year
s:
Automobile
An automobile, autocar, motor car or car is a wheeled motor vehicle used for transporting passengers, which also carries its own engine or motor...
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...
technology used by Subaru
Subaru
; is the automobile manufacturing division of Japanese transportation conglomerate Fuji Heavy Industries .Subaru is internationally known for their use of the boxer engine layout popularized in cars by the Volkswagen Beetle and Porsche 911, in most of their vehicles above 1500 cc as well as...
. It varies the timing of the intake valves by using hydraulic oil
Motor oil
Motor oil or engine oil is an oil used for lubrication of various internal combustion engines. The main function is to lubricate moving parts; it also cleans, inhibits corrosion, improves sealing, and cools the engine by carrying heat away from moving parts.Motor oils are derived from...
pressure to rotate 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,...
in order to provide optimal air flow in and out of the engine. The system is closed loop using 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
Engine control unit
An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...
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 minding emissions standards.
AVCS is used on the Version 7 and up EJ207 engines, the EJ255 and EJ257, the second generation EZ30D (2005+ in the USA Market) found in the Legacy
Subaru Legacy
The Subaru Legacy is a mid-size car built by the Japanese company Fuji Heavy Industries, and manufactured by its division Subaru since 1989, and is available as a sedan or wagon. Part of the original design goals for the Legacy model was to provide Subaru a vehicle in which they could compete in...
Outback
Subaru Outback
The Subaru Outback is a station wagon manufactured by Fuji Heavy Industries since 1995. Its original concept originated with Subaru of America, which was suffering from slumping sales in the mid-1990s partly due to a lack of an entry in the then-burgeoning sport utility vehicle market...
, Legacy 3.0R and the B9 Tribeca
Subaru Tribeca
The Subaru Tribeca is a mid-size crossover SUV sold since 2005 by Subaru, the automobile manufacturing division of Japanese transportation conglomerate Fuji Heavy Industries . Released in some markets as the Subaru B9 Tribeca, the name "Tribeca" derives from the TriBeCa neighborhood of New York City...
. A Dual AVCS system utilizes both the intake and exhaust camshafts on the EZ36 found in the 2008 Tribeca. Dual AVCS is also found on Japanese Spec engines, although a complete list of the engines with Dual AVCS has yet to be compiled.
i-AVLS
i-Active Valve Lift System (i-AVLS) is a version that supports variable valve lift. It includes 2 intake lift profiles depending on engine speeds. AVLS-equipped Subaru engines have 2 intake valves per cylinder, but AVLS only controls one of them, leaving the other in high-lift mode at all times.At low engine speeds, each of the two intake valves for a given cylinder run on a different camshaft profile (the engines are 4-valve per cylinder type). One valve is operated by a low-lift, low-duration lobe, while the other is actuated by a high-lift, high-duration lobe. This increases air speed causing a smooth idle, while at the same time promoting a swirl factor, increasing efficiency.
At high speeds, the ECU (Engine Control Unit
Engine Control Unit
An engine control unit is a type of electronic control unit that determines the amount of fuel, ignition timing and other parameters an internal combustion engine needs to keep running...
) computer signals a solenoid to let oil pressure move a pin which locks the two lobes together. This means at high speed both intake valves are effectively driven by the high-speed camshaft lobe. This increases high-RPM power due to increased valve lift, duration and overall timing.
Cam locking is done by moving a pin with hydraulic pressure. As with other 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...
systems, it allows the engine to have a quiet low-speed operation with a smooth idle, while also using a camshaft lobe profile similar to "race cam" at high engine RPMs.
Applications
It was introduced with 2007 model year with 2.5-liter naturally aspirated Subaru engines.Widespread use of AVLS began with non-turbocharged Subaru 2.5 liter four-cylinder engines in Model year
Model year
The model year of a product is a number used worldwide, but with a high level of prominence in North America, to describe approximately when a product was produced, and indicates the coinciding base specification of that product....
2006. AVLS was first used in the 2005 six-cylinder 3.0 liter Subaru Outback. Turbocharged engines and Subaru's six-cylinder engines continue to use Subaru's AVCS (variable cam phasing) system instead of AVLS. Reports generally agree the new engine feels like a brand new engine with flatter torque curve compared to previous non-AVLS, non-AVCS 2.5 liter engines. Initial applications raised maximum power from 165 hp to 175 hp, but more significantly raised the power at most RPM levels. The goal is better fuel economy, improved driveability and increased power.
Model year
Model year
The model year of a product is a number used worldwide, but with a high level of prominence in North America, to describe approximately when a product was produced, and indicates the coinciding base specification of that product....
s:
- 2005: 3.0 liter naturally aspirated H6 Subaru engines (used along with AVCS)
- 250 hp, 219 lbft torque in 2005 3.0-liter Subaru Outback
- 2006: all 2.5 liter naturally aspirated Subaru engines
- 173 hp, 166 lbft torque in 2006 Subaru ForesterSubaru ForesterThe Subaru Forester is an all-wheel drive crossover wagon manufactured since 1997 by Fuji Heavy Industries and sold under the Subaru brand...
and Impreza 2.5iSubaru ImprezaIntroduced in November 1993, the Impreza was offered in either front-wheel drive or all-wheel drive versions and as a four-door sedan/saloon or five-door station wagon/estate. According to a Motor Trend article written March 1992 on page 26, the name of Subaru's new compact was, initially, to be...
models - 175 hp, 169 lbft torque in 2007 Subaru LegacySubaru LegacyThe Subaru Legacy is a mid-size car built by the Japanese company Fuji Heavy Industries, and manufactured by its division Subaru since 1989, and is available as a sedan or wagon. Part of the original design goals for the Legacy model was to provide Subaru a vehicle in which they could compete in...
model
- 173 hp, 166 lbft torque in 2006 Subaru Forester
- 2007-: all 2.5-liter naturally aspirated Subaru engines
External links
- Subaru Drive Magazine articles: AVCS (dead), i-AVLS (dead)