The ACIS (Acoustic Control Induction System) changes the effective length of the intake manifold to increase power over a wide range from low speed to high speed. This system uses an intake air control valve to divide the intake manifold into two stages that make it possible to change the effective length of the intake manifold to match the engine speed and throttle valve opening. There are several types of ACIS. The example used here is that for the 3UZ-FE engine.
The main components of the system are described below.
(1) Intake air control valve
The intake air control valve is in the intake air chamber, and is opened and closed to change the effective length of the intake manifold in two stages.
(2) VSV (Vacuum Switching Valve)
According to the ACIS signal from the engine ECU, the VSV control the vacuum, which is the power source for operating the actuator of intake air control valve.
(3) Vacuum tank
The vacuum tank has a built-in check valve. And it stores the vacuum applied to the actuator so that the intake air control valve can be fully closed even in the low-vacuum condition.
(1) When the air intake control valve closes (VSV ON)
When the engine ECU turns ON the VSV to match the long pulsation cycle, a vacuum is applied to the actuator diaphragm chamber. This closes the control valve. This in turn, lengthens the effective length of the intake manifold, which improves the air intake effect and power in the low- and medium-speed ranges due to the intake air pulsation effect.
(2) When the air intake control valve open (VSV OFF)
When the engine ECU turns OFF the VSV to match the short pulsation cycle, atmospheric pressure is applied to the actuator diaphragm chamber, opening the control valve. When the control valve opens, the effective length of the intake manifold is shortened, which provides maximum air intake effectiveness to increase power in the high-speed range.