Section 8. Theory of Operation Model 8210/8250 Maintenance Manual
Traction System
8-6 Publication: 1146945/001, Revised: 25 Sep 2018
Traction System
Vehicle Manager
The VM is also sometimes referred to as the
Electronic Tiller Arm Card (ETAC). The
programmable motor control functions are
performed by the electronic circuitry housed
within the VM in the control handle. The basic
functions of the VM include:
• Monitor relative positioning of the thumb
controls to eighteen hall effect sensors for
speed and direction control.
• Monitor the position of the emergency
reverse button for emergency reversing of
the truck direction.
• Monitor truck performance and provide
input data and commands to the operator
display.
• Provide lift/lower input commands to the
traction amplifier.
• Monitor horn switches S18-1 and S18-2
for horn operation.
• Monitor and determine operation based on
truck performance parameter settings.
Traction Amplifier
The basic functions of the traction amplifier
include:
• The direction control section controls the
traction motor direction by manipulating
the traction motor polarity according to
the directional inputs from the Vehicle
Manager.
• The speed control section controls the
traction motor speed and torque by
monitoring the information received from
the Vehicle Manager via the CAN Bus.
• The control circuit section that controls all
truck inputs and outputs (excluding
handle head inputs).
Direction/Speed Control
The following descriptions assume the battery is
charged and connected, and the truck is ON.
Control Handle Positioning
When the control handle is in the upright
position, the parking brake is engaged. When
the control handle is within 6 to 78 degrees of
the upright position, the Arm Angle Proximity
Switch closes and enables travel, the main
contactor closes, and the brake is allowed to
disengage (when travel is requested). When the
control handle is placed in the bottom 8 degrees
of its operating range, the Arm Angle Proximity
Switch opens, engaging the parking brake.
When the control handle is returned to the full
upright position, the main contactor remains
closed for approximately 20 seconds then
opens.
Travel Request
When the thumb controls are rotated from
neutral:
• A forward travel signal is detected via hall
effect sensors, by the Vehicle Manager
(VM). The VM determines if the request is
for forward (tractor-first) direction or
reverse (forks-first) direction based on
which set of hall effect sensors are
activated.
• The VM verifies that the emergency reverse
button is not activated.
• The VM verifies the state of the Arm Angle
Proximity Switch via a CAN message from
the TA. Based on its position, the VM
sends the travel request via the CAN to the
TA.
• If the main contactor (MPC) is not closed,
the TA supplies B– to pin J1-6, closing the
main contactor (MPC).
• The TA releases the brake.
• The TA then controls the voltage at U, V,
and W of the traction motor. Voltage will
vary from 24V to –24V. The voltage is
proportional to the position of the thumb
controls.
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