Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 113

ISC - ISC Valve
ISC VALV E
1 . STEPPER MOTOR TYPE
The ISC valve is mounted on the air intake
chamber or throttle body . In order to control the
speed at which the engine idles, it increases or
decreases (based upon signals from the Engine
ECU) the amount of intake air that is allowed to
bypass the throttle valve .
The idle speed adjusting screw* is set to the fully
closed position at the factory, because the idle
speed is controlled by the ISC valve .
The use of the idle speed adjusting screw has
been discontinued in recent models .
Air flow meter
Idle speed adjusting screw *
Engine
ECU
ISC
valve
Thro
tt
le valv e
To cylinder s
OHP 7 0
CONSTRUCTIO N
A stepper motor is built into the ISC valve . This
motor rotates the rotor clockwise or
counterclockwise, moving the valve in or out .
This in turn increases or decreases the clearance
between the valve and valve seat, regulating
the amount of air that is allowed to pass
through . The ISC valve has 125 steps from the
fully closed to the fully open position .
Since the air flow capacity of the stepper motor
type ISC valve is large, it is also used for
controlling fast idle . It is not necessary to use it
in combination with an air valve .
Roto r
Stator
®
To air intake
♦ chambe r
Valve sea t
Valve shaf t
Stopper plat e
OHP 7 0
it
From air flow mete r
Small
-
Number of steps
-
Large
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• Rotor . . . constructed of a 16-pole perma-
nent magnet . (The number of poles
differs depending on the engine . )
• Stator . . . two sets of 16-pole cores, each of
which is staggered by half a pitch
in relation to the other . Two coils
are wound around each core, each
coil being wound in opposite
directions . (The number of poles
differs depending on the engine . )
OHP 7 0
OPERATIO N
Current flows through one of the four coils of
the stator in turn in accordance with the output
from the ECU . The flow of current in coil S1 is as
shown in the following illustration :
101