Section 8.Theory of Operation Travel

turn the traction motor in the correct direction.

c.Simultaneously an analog voltage, that represents and is proportional to the throttle command, is output from the Steer/Tractor Manage r and sent to the traction power amplifier. This voltage (TRAVEL REQ) ranges from 0 to about +4.25VDC depending on throttle input WRT TRAVEL REF. Based on this, the TPA controls the strength of the field and armature to obtain the correct travel speed in the appropriate amount of time. The higher the voltage, the faster the TPA makes the lift truck travel.

NOTE: Travel speed is limited until the operator initializes steering and the Steer/Tractor Manager detects the request.

2.The TRAVEL REQ voltage is used by the traction power amplifier to drive the armature and field transistors to meet the throttle request. The armature transistor is, in effect, connecting terminal M- to B(in varying amounts) allowing current to flow through the traction motor armature. The traction power amplifier also drives its internal field transistors that, in turn, controls the amount and direction of flow through the traction motor field winding. When a plug is requested, the Steer/Tractor Manager changes the direction request to the traction power amplifier and changes the speed request output (TRAVEL REQ) to reflect the requested plugging strength. Current now flows from B+ through:

•FU3

•Traction motor armature

•M-

•B- (TP4)

•To battery negative

3.During operation, the traction power amplifier monitors for:

•Armature current*

•Field current*

•M- shorted to B-*

Publication Number: 1043922B, Revised: 2 Sept 2015