The active valve control system ( AVCS ) is a variable valve timing technology used by Subaru. This varies the time from the valve by using hydraulic oil pressure to rotate the cam shaft, known as "phasing", to provide optimum valve time for machine load conditions. The system closes the loop using a camshaft sensor, crankshaft sensor, air flow meter, throttle position and oxygen sensor and/or Air-Fuel ratio sensor to calculate engine load. The ECU is programmed to operate a control valve that adjusts the hydraulic pressure delivery to move the cam shaft to a position that will provide the best performing engine while measuring emission standards.
AVCS is used in Version 7 and the EJ207, EJ204, EJ254, EJ255 and EJ257 engines, the second generation EZ30D (2005 in US Market) are found in Legacy Outback, Legacy 2.0R and 3.0R and B9 Tribeca.
A Dual AVCS system phase both intake and exhaust camshafts on EZ36 found in Tribeca 2008, 2009 Outback 3.6R, 2009 Legacy 3.6R, and on 2008 STi EJ257 (head W25). Dual AVCS is present on the new FA20 engine in 2015 WRX and BRZ and FB20 engines in 2012 Impreza/Crosstrek, although they move with different methods compared to older machines. Dual AVCS is also found on the Japanese Spec machine, especially the final model EJ207 on the WRX STI.
Video Active valve control system
AVCS
Implementation of AVCS is very different from AVLS. The latter only changes which cam operates one of the two valves.
In AVCS, machine computers (ECUs) may order a solenoid that advances or slows the rotation of the cam shaft by up to 35 degrees.
By slowing cams when idle or very low engine load, you will get a smoother and easier idle. From idle to medium machine load, the AVCS boosts the intake valve to begin opening during the last part of the exhaust, when the exhaust valve is still slightly open. Some of the pressure created during the exhaust flows into the intake manifold, which has an exhaust gas recirculation (EGR) effect. The intake valve also closes early during the intake step. It helps with engine efficiency and fuel savings.
At very high engine loads, the AVCS increases the intake valve further to open faster during the exhaust stroke. This produces a scavenging effect - that is, incoming airflow helps clean the exhaust gas cylinder. It also closes the intake valve faster in the compression step. This results in increased volumetric efficiency, increased dynamic compression, and helps generate higher output power.
Maps Active valve control system
See also
- AVLS
References
External links
- Subaru Drive Magazine articles: AVCS, i-AVLS
- Subaru AVCS Explained
Source of the article : Wikipedia
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