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Description of intake system
The air filtered by the air cleaner flows into the surge tank but only by such amount according to the opening of the throttle
in the throttle body as well as the engine speed.
The throttle valve in the throttle body regulates the air amount into the engine by its opening. The air from the throttle
body goes into the surge tank and is distributed to the intake manifold of each cylinder to be drawn into the combustion
chamber.
When the engine is cold, as the engine cooling water temperature is low, the air regulator opens and the air bypasses the
throttle valve and flows into the surge tank. Due to such function, even when the throttle valve is completely closed, the
air flows into the surge tank, increasing the idle speed by that amount and warm–up operation is improved.
After the engine has been warmed up, the ISC solenoid valve regulates the air bypassing the throttle valve, thereby
stabilizing the idle speed.
Throttle body
The main components of
the throttle body are: a throttle valve which regulates the amount of
intake air, a throttle sensor
which detects throttle valve opening, a bypass passage to allow a small amount of air during idling and a thermo–wax
type air regulator which boosts the engine warm–up at a low temperature.
Idle speed control (ISC)
The idle speed control uses a linear solenoid type ISC solenoid valve to stabilize the idle speed by changing the amount
of
air flow bypassing the ISC solenoid valve according to the ECM.
ISC solenoid valve
Shown at the right is this type of ISC
solenoid valve.
When electricity flows according to the signal from the ECM, the coil
is excited, causing the valve shaft to move. Due to this movement, the
clearance between the solenoid valve and the valve body changes to
control the idle speed although the fast idle speed is controlled by the
air regulator.
The ECM controls ON/OFF of electricity flow to the coil by using the
XHz frequency and controls the ISC solenoid valve position by using
its duty ratio. That is, the longer the ON time is (or the larger the ISC
duty ratio is), the larger the valve opening becomes, resulting in more
amount of the bypassing air. This duty ratio can be expressed as fol-
lows.
IDLE SPEED CONTROL (ISC)
The ISC duty ratio is calculated by using the following equation.
ISC duty ratio = (Basic value + Correction at engine start + Electric load
compensation + D range compensation
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