Suzuki DF200 Service Manual page 90

IAC VALVE
• The IAC valve uses a stepper type motor.
• The IAC valve is installed on the intake collector assembly.
• The IAC valve controls the volume of bypass air to stabilize the idling/trolling speed.
• The transistor driving the IAC is inside the ECM and turns ON/OFF when a signal (command) is received
from the CPU.
This signal operates the stepper motor inside the IAC valve, causing it to be driven equal to the number of
command signal steps. Through this procedure, the system is able to attain a very precise target
idling/trolling speed.
• The stepper motor rotates by means of magnetic attraction between the stator and rotor. More specifi-
cally, shifting the stator excitation in State (1) of below illustration to that in State (2) will develop a mag-
netic torque to cause the rotor to rotate and then stabilize in State (3). (The illustration at below shows the
operating principle of a simple stepper motor. This example differs slightly from the 2-phase excitation
method used in the actual application). This operation is repeated equal to the number of command signal
steps from the ECM resulting in rotation of the rotor. With the screw shaft installed, this rotation is con-
verted to a linier motion of the valve pintle that changes the volume of IAC air flow.
• Battery voltage is applied to the center tap of each coil through the ECM main relay when the ignition
switch is turned on. The Each coil end connects to one of the ECM terminals "IAC 1-4".
The terminal voltage at ECM terminals "IAC 1-4" is 1 V MAX when current flows and battery voltage at all
other times.
3
2
1. Valve pintle
2. Screw shaft
1
3. Rotor
4. Coil
5. Bearing
6
N
S
N
Attraction
7
S
6
State 1
6. Stator
7. Rotor
8. IAC valve
9. Throttle valve
4
5
Air flow
Attraction
S
S N S
N
State 2
Pole shifting
+12 V
Gr
IAC valve
N S N
State 3
Rotor rotation
ENGINE CONTROL SYSTEM
ECM
W/B
55 IAC1
R/G 58 IAC3
W/Bl
57 IAC4
R/Y 56 IAC2
8
9
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