Electronic Throttle
The electronic throttle enables the ECM to
control the flow of air into the engine. It includes:
an input shaft that receives driver inputs from
the accelerator pedal via a conventional
throttle cable
a mechanical guard, to prevent throttle valve
position exceeding driver demand and to
operate the throttle valve mechanically if the
electronic system fails
a vacuum actuator, to operate the mechanical
guard in the cruise control mode of operation
a throttle valve, to regulate the air flow
a thermostatic air valve, to control a bypass
flow around the throttle valve
a dc motor, to operate the throttle valve in
response to inputs from the ECM
three position sensors, to supply the ECM
with the position's of the input shaft (ie.
accelerator pedal), the mechanical guard and
the throttle valve
springs connected to the input shaft, the
mechanical guard, the throttle valve and the
drive gear of the dc motor.
Vacuum Actuator
On vehicles with cruise control, the vacuum
actuator is connected to manifold vacuum and
controlled by the ECM. On vehicles without
cruise control, the vacuum actuator is open to
atmosphere and the actuator is inoperative.
Thermostatic Air Valve
The thermostatic air valve is a wax capsule
operated valve that enables engine starting at
low engine temperatures (with the accelerator
pedal in the idle position, the degree of throttle
valve movement available between fully closed
and the mechanical guard is insufficient to start
the engine at low temperatures). The
thermostatic air valve is fully open at a coolant
temperature of approximately -30°C (-22˚F) and
progressively closes until it is fully closed at
+40 °C (+104˚F). A flow of engine coolant
through the throttle body provides the
temperature source to operate the thermostatic
air valve.
Throttle Valve
Position Sensor
Mechanical Guard
Mechanical Guard
Position Sensor
Accelerator Pedal
Position Sensor
Spring Force
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