Operation Control - Honda GL1800 Service Manual

TECHNICAL FEATURES
When electric current flows through the coil turning the iron core into an electro-magnet, the N and S poles of the magnet
and the N and S poles of the electro-magnet attract each other causing the magnet on the valve shaft to rotate. To change
the rotating direction of the valve, current flow is reversed. This switches the N and S poles of the electro-magnet and the
rotating direction of the valve reverses.
Current flow direction
irection of
magnetic force

OPERATION CONTROL

The IAC's drive signal is output from the ECM to turn the IAC valve side voltage on and off.
As the IAC valve is required to control the intake air flow volume by continuously changing its valve angle, the digital drive
signal turns the voltage on and off at a constant frequency, with the signal being a PWM (Pulse Width Modulation) type
that changes the on time ratio per cycle. This is referred to as the duty ratio (duty cycle). The average current changes
smoothly, just as the analog type does, in accordance with the changes of the duty ratio.
The IAC valve has a built-in drive circuit. With the 50% of the duty ratio used as a reference point of 0 (zero), the drive cir-
cuit judges the duty ratio below the reference point as the close-circuit direction and the duty ratio (duty cycle) above the
reference point as the open-circuit direction. The IAC switches the open and close circuit direction by changing the direc-
tion of the current flow through the coil.
F GN RELAY
AC VALVE
ECM
DR VE C RCU T
ON
VER GE
Constant voltage
OFF
Valve close open
Duty Ratio (duty cycle)
24-3