Model 4700 Maintenance Manual Travel
Section 8. Theory of Operation Traction System
compared to its previously Learned value and the VM converts the voltage value into a percentage-of-request. The VM converts travel direction and percentage-of-request into a message that is sent via the CAN-Bus to the Traction Power Amplifier (TPA) and Operator Display (OD). The TPA sends the RPM request to the Traction Motor(s) to satisfy the direction and speed request received by the VM. The TPA monitors the Encoder(s) (EN1 for single traction motor trucks; EN1 and EN2 for dual traction motor trucks) to verify that actual travel direction and speed matches what was requested. The VM constantly monitors the travel request and updates the information to the TPA as changes occur. All operational parameters that affect motor torque and speed are controlled by the TPA. The TPA also monitors the Temperature switch(es) (TS1 for single traction motor trucks; TS1 and TS2 for dual traction motor trucks). The temperature switch(es) are normally closed. They open when an overtemperature condition exists in the motor, causing a reduction in travel speed to allow the motor to cool. An icon on the Operator Display is also illuminated to alert the operator. When the truck is moving and the travel pedal is released or travel direction is reversed, the same sequence of events takes place. The VM does not request plugging or regeneration: it just requests travel in the opposite direction at a particular speed. The VM communicates this information to the TPA via the CAN-Bus. The TPA calculates both direction and speed and determines whether the request from the VM must be met with a travel, a plug, or a regeneration control output to the traction motor. The VM energizes the Braking Lights. The brake pedal may be depressed to apply the hydraulic brake, aiding in slowing the truck. NOTE: The Braking Lights are not energized just by depressing the brake pedal alone. The lights are energized when the truck is traveling and a change in requested direction is sensed by the TPA and relayed to the VM via the CAN-Bus.
Publication 1160093, Issued: 20 May 2013
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