Acoustic Control Induction System, or ACIS, is an implementation of a variable-length intake manifold system designed by Toyota.
Simply put, the ACIS system uses a single intake air control valve located in the intake to vary the length of the intake tract in order to optimize power and torque, as well as provide better fuel efficiency and reduce intake "roar".
The engine control unit (ECU) controls the position of one or more air control valves based on input signals from throttle angle and engine RPM. The vacuum switching valve (VSV) which controls the vacuum supply to the actuator is normally closed and passes vacuum to the actuator when it is energized by the ECU. By energizing the VSV vacuum is passed to the actuator, closing the air control valve. This effectively lengthens the intake manifold run. By de-energizing the VSV, vacuum to the actuator is blocked and trapped vacuum is bled off of the actuator diaphragm. Toyota ACIS is an On/Off system. The valve (or valves in newer models with multiple valves to create more than 2 lengths) is either fully opened or fully closed. An example of early single-valve ACIS programming would be the 3.0L 3VZ-FE engine. The ECU actuates the VSV to close the valve when the throttle position is 60% or greater and engine speed is 3,900 RPM or more.[ citation needed ]
Applications:
In internal combustion engines, a variable-length intake manifold (VLIM),variable intake manifold (VIM), or variable intake system (VIS) is an automobile internal combustion engine manifold technology. As the name implies, VLIM/VIM/VIS can vary the length of the intake tract in order to optimise power and torque across the range of engine speed operation, as well as to help provide better fuel efficiency. This effect is often achieved by having two separate intake ports, each controlled by a valve, that open two different manifolds – one with a short path that operates at full engine load, and another with a significantly longer path that operates at lower load. The first patent issued for a variable length intake manifold was published in 1958, US Patent US2835235 by Daimler Benz AG.
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