THEORY OF OPERATION - TM-9-2920-232-34-P0017

TM 9- 2920- 232- 34&P / TO 38X14- 2- 32

- -

THEORY OF OPERATION

0003 00

THIS WORK PACKAGE COVERS:

Theory of Operation

DETAILED OPERATION

a. When 24 VDC power source is properly connected to ground terminal of starter motor and to BAT terminal of

the solenoid assembly, any circuit which will apply this same voltage to terminal S on the solenoid assembly

will energize the solenoid windings. Pull--in winding will initially be grounded through the motor windings and

commutator (a low resistance path); the hold--in winding is connected direct to ground by the electrical lead

assembly.

b. Current flow through the solenoid windings creates a magnetic field which pulls the plunger into the solenoid

assembly. This movement linked through the shift lever slides drive clutch assembly nearer to drive end of the

armature shaft (engaging pinion gear with an engine drive gear, if starter were mounted on an engine).

As the plunger bottoms in the solenoid assembly, it presses switch contact assembly against the motor

terminal stud and the battery terminal stud inside the solenoid assembly case. The power circuit is completed

to the starter motor when this switch is closed and the solenoid pull--in winding is shorted. The solenoid

hold--in winding maintains switch closed against spring pressure until start control circuit is opened.

d. At any given armature position, power applied to the starter motor will provide current flow simultaneously

through each of three paths to ground. Each path routes current through one pair of series--connected field

coils, through a brush--to--commutator contact, through two armature windings, and through the

brush--to--commutator contact of an adjacent brush to ground. When current flows, each path generates an N

and an S magnetic pole on the armature and an N and S magnetic pole on a pair of adjacent pole shoes in

the frame assembly. Magnetic fields between these armature poles and pole shoes provide the starter's

output torque.

e. At output end of the starter, drive torque of the armature shaft is coupled through the clutch rolls (no slip

direction) to the drive pinion.

If the drive pinion could not engage a drive gear because of gear tooth misalinement, the helical spline would

be pushed through the drive pinion by overpowering the compression spring as necessary. This movement

along the helical spline allows switch contacts in the solenoid assembly to be closed and armature to start

rotation. The compression spring engages drive pinion with drive gear as soon as gear tooth alinement

permits.

g. The overrunning action provided by the clutch rolls prevents an engine from driving the armature. At normal

engine speeds, the ratio between the engine drive gear and the starter drive pinion would produce destructive

rates of rotation for the starter armature were it not for the protection afforded by the overrunning clutch.

h. Operator should not hold start switch on (hold--in winding energized) longer than 30 seconds at one time and

should allow two minutes for starter to cool before engaging the starter again. Start switch should be released

(turned off) as soon as an engine starts.

When start circuit is opened and while solenoid switch is still closed, solenoid windings are connected in a

series circuit. Current flows through pull--in winding in a reverse direction to that in hold--in winding. This

makes mutually canceling magnetic fields. With overall solenoid magnetic field thus neutralized, the return

spring pressures open the solenoid switch and pull drive clutch assembly away from pinion--engaged position.

END OF WORK PACKAGE

0003 00-032 0-ank

00-1/ 0bl-1