26SI Series Alternator – Normal Operation

General Information

A DC series wound motor is used as the starting motor. The starting motor has field winding (11) and armature (14). The excitation and armature windings are connected in series. The pinion end of the armature shaft has splines for pinion drive (12) .

The solenoid is an integral part of the starting motor. The solenoid pushes the pinion drive (12) with the pinion (13) forward through the shift lever (10) and the plunger. The end of the plunger is a spool which is connected to the shift lever. Return spring (1) helps return pinion drive (12) and shift lever (10) to the rest position after key start switch (7) is released and solenoid contacts (8) have been opened. A semi-solid link mechanism prevents welding of the solenoid contacts.

The starting motor has a two-stage mechanical pinion drive (12) that protects armature (14) from an overspeed condition. The pinion drive also allows a smooth engagement of pinion (13) into the flywheel ring gear. The pinion drive is held on the splines of the armature shaft. The pinion drive is connected to the pinion (13) through the teeth of the integral overrunning clutch. Shift lever (10) moves the pinion drive (12) axially in the direction of the ring gear.

37-MT And 41-MT Operation

When the key start switch (7) is closed, the following components are energized: start (S)terminal (4), pull-in winding (3) and hold-in winding (5). The solenoid plunger pulls the shift lever (10) against the force of the spring (1). The shift lever pushes the pinion drive (12) toward the engine flywheel. The armature (14) has not yet turned. The solenoid contacts (8) have not closed. This sends starting motor current to the excitation windings and the armature windings. If the pinion (13) can immediately engage the flywheel ring gear, the pinion moves forward. When the pinion reaches the end of the drive pinion shaft and the solenoid contacts (8) close. The starting motor is now in partial engagement.

If a pinion tooth meets a ring gear tooth, the pinion cannot immediately mesh with the ring gear. The solenoid contacts (8) close as the meshing spring is compressed through the shift lever (10). The starting motor is now turned on. The operation turns the pinion (13). The pinion initially meshes with the teeth of the ring gear. The pressure from the meshing spring causes the pinion (13) to fully mesh. The pressure from the meshing spring causes the ring gear to fully mesh.

At the end of solenoid armature travel, solenoid contacts (8) close. This allows full battery voltage to be applied to battery (Bat) terminal (6) and motor (Mtr) terminal (9). The starting motor current energizes the field winding (11). The starting motor current powers the starting motor. Armature (14) now begins to rotate and the helical spline forces the pinion farther into the ring gear until the pinion contacts the stop ring of the armature shaft.

The pull-in winding (3) is turned off when the starting circuit is closed. Hold-in winding (5) remains energized. The hold-in winding magnetic force is enough to hold the solenoid plunger in the pull-in position until the engine is started.

When the engine starts and the ring gear turns pinion (13) faster than the starting motor, the clutch section of the pinion drive (12) breaks the connection between the pinion and the armature shaft. This prevents damage to the armature from being rotated too fast. The pinion remains meshed with the ring gear while the shift lever (10) is held in the engaged position. The shift lever assembly and pinion drive are returned to the rest position by the return spring (1) only when the key start switch is released. The return spring also keeps the pinion in the rest position until the starting motor is again operated.

42-MT Operation

When the key start switch (7) is closed, the following components are energized: start terminal (4), pull-in winding (3) and hold-in winding (5). The activation of the pull-in winding (3) and the hold-in winding (5) produces a magnetic force. The magnetic force will pull the plunger to the right. The plunger will pull the shift lever (10) which will compress the return spring (1). The shift lever will push the pinion assembly along the armature shaft toward the flywheel ring gear.

The pinion gear (13) may meet a tooth of the flywheel ring gear as the pinion gear tries to move forward. The other drive components will continue to be pushed forward. The helical spline of the overrunning clutch portion of the pinion drive assembly (12) rotates the pinion gear in the cranking direction. The spring of the pinion drive assembly is being compressed. The pinion tooth will slide past the tooth on the flywheel ring gear until the next gap is found. The pinion gear will then engage onto the flywheel due to the pressure that is built up in the compressed spring. At the same time, the overrunning clutch rotates in the overspeed direction.

The pinion gear may also meet a damaged ring gear tooth or a notched ring gear tooth. While the pinion drive assembly (12) is being pushed forward, the armature assembly (14) is being rotated in the opposite direction. This is due to the helical spline. The spring of the pinion drive assembly is also becoming compressed. Due to the forces that are being applied to the drive components onto the damaged tooth, the starting motor current may not have force enough to turn the armature. The starting attempt must be stopped. When the key start switch is released, the pinion drive assembly will release the compression of the spring. This will cause the pinion gear to rotate. The pinion gear is now ready to mesh with the flywheel ring gear. The starting attempt can now be retried.

When the pinion gear (13) meshes completely with the flywheel ring gear, solenoid contacts (8) close. Full battery voltage is then applied to the battery terminal “Bat” (6) and the motor terminal “Mtr” (9). Starting motor current will then energize the field winding (11) and the armature (14). The pull-in winding (3) will become de-energized. The hold-in winding (5) will still have enough force to hold in the plunger assembly until the solenoid contacts (8) are open. The starting motor starts to crank the engine with full torque.

As soon as the engine starts, the flywheel ring gear turns the pinion gear (13) faster than the starting motor’s normal speed. The overrunning clutch breaks the mechanical connection between the two gears. The pinion gear turns on the helical spline which will compress the spring in the pinion drive assembly. The pinion gear will then be pulled from the flywheel gear. Flyweights also help to break the mechanical connection between the two gears. This process must take place in order to prevent the starting motor from being rotated at speeds higher than maximum permissible speed. When the key start switch (7) is released, the shift lever assembly and pinion drive assembly will return to the rest position. The solenoid contacts open and the starting motor turns off. The rotating armature is quickly stopped by a mechanical brake disc.