Toyota COMPUTER-CONTROLLED SYSTEM Training Manual page 116

a
NOTE -
Duty
Ratio
ISC - ISC Valv e
The "duty ratio" is the ratio of the interval
during which current flows to the interval
during which current does not flow in one
cycle of a signal . The figure below shows the
time in one cycle during which current flows
and does not flow .
A : Current flows (on )
B : Current does not flow (off )
(On )
1
0
(Off)
B
Duty ratio (% )
= A+AB x 10 0
1 cycl e
LOW DUTY RATIO HIGH DUTY RATIO
(On) (On)
1 n n n 1
0 ~
(Off)
~ 0 J
U
u U
(Off)
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3 . DUTY-CONTROL ACV TYP E
The construction of this type of ISC valve is as
shown in the following figure . While current
flows according to signals from the Engine ECU,
the coil becomes excited and the valve moves .
This changes the gap between the solenoid
valve and the valve body, controlling the idle
speed . (Note, however, that the fast-idle speed
is controlled using an air valve . )
From air cleane r
♦
♦
To air intake chambe r
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In actual operation, current to the coil is
switched on and off each 100 msec ., so the
position of the solenoid valve is determined by
the proportion of time that the signal is on as
compared to the time it is off (i .e ., by the duty
ratio) . In other words, the valve opens wider the
longer current flows to the coil .
4 . ON-OFF CONTROL VSV TYP E
The construction of this type of ISC valve is as
shown in the figure below . Signals from the
Engine ECU cause current to flow to the coil .
This excites the coil, which opens the valve,
increasing the idle speed by approximately 100
rpm . (Fast-idle speed is controlled using an air
valve .)
Solenoid coil
From air
cleaner
~ To air intake
chambe r
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