INJECTION - IGNITION
9
Stepper motor
The throttle body incorporates an automatic choke function performed by a stepper motor (1).
The stepper motor shaft is fitted with a valve which opens a communicating passage between two
ports; one of these ports (2) is connected to the intake manifold of the vertical cylinder while the
other (4) is connected to the intake manifold of the horizontal cylinder. A third port (3) is connected
to the airbox.
The stepper motor simultaneously controls two by-pass ports having an air flow capacity of around
6 kg/h. The by-pass ports with adjuster screws are present because it is necessary to balance the
air flow to the two cylinders.
In order to compensate for the quantity of supplementary air supplied by the stepper motor and
consequently deliver the correct amount of fuel, the ECU converts the stepper motor steps into
angular degrees of the throttle: this system means that opening the stepper motor is equivalent to
opening the throttle.
NOTES
The influence of the stepper motor air flow is present to approximately 30° throttle angle; no
correction is required for greater angles.
The opening of the stepper motor is controlled by the engine temperature (the opening or closing
of the stepper is determined by the engine temperature).
Sub 9-7
To Next Page
Loading...
