The input shaft spring and the mechanical guard
spring oppose movement in the throttle open
direction, and provide the "feel" of the accelerator
pedal. The throttle valve spring and the drive gear
spring oppose movement in the throttle closed
The design of the input shaft and the mechanical
guard, and the bias of their respective springs,
means that, except in cruise control, they always
rotate together. The throttle cable turns them in
the open direction; the springs keep their
adjacent levers locked together and turn them in
the closed direction.
The ECM monitors the position of the input shaft
and mechanical guard using the inputs from the
accelerator pedal and mechanical guard position
sensors. During normal operation, when the ECM
detects any movement it signals the dc motor to
turn the throttle valve and follow the input shaft
and mechanical guard, maintaining a constant
gap between the adjacent levers of the throttle
valve and mechanical guard. The dc motor drive
gears turn the throttle valve in the closed
direction; the throttle valve spring turns the
throttle valve in the open direction and keeps the
throttle valve in contact with the drive gear.
Inputs from the throttle valve position sensor
enable the ECM to exercise closed loop control.
The arrangement of the throttle valve drive
prevents the ECM from exceeding driver
demand, since if the motor is driven fully open
the throttle valve engages the mechanical guard
and disengages from the dc motor drive gears.
The arrangement of the mechanical guard to
throttle valve interface allows the ECM to reduce
throttle opening to less than driver demand, eg.
during stability/traction control or engine power
dc Motor Coolant