Working principle of electric starting motor

    The four electromagnetic field winding being connected in series-parallel motor with a wave wound armature of heavy section conductors.
    The solenoid switch is mounted at the commutator end of the starter motor and has two windings one for engagement and one for holding. The solenoid switch functions in two stages.

(i) First stage: In the first stage the top contacts close and complete the battery circuit through the drive pinion engagement and the filed coil of the starter motor.

(ii) Second stage: In the second stage which is controlled by the drive pinion engagement mechanism, the lower contacts close, short-circuiting the engagement coil and applying the full battery power to the motor through the holding coil.

Description: When is starter push contact closed. The top contacts closed of the solenoid switch and complete battery circuit through the engagement coil of the drive pinion and field coil at that time preventing full operation of the starter motor. The movement is obtained through a trip plunger, push rod with a shock spring.

    The starter motor is transmitted through a spring-clutch which assists enjoyment and dis-engagement of the drive pinion. The drive pinion is thus brought into mesh with flywheel ring gear by an axle movement and a slow rotation of the armature. The shock of a buffer spring position between the push rods, safeguards the drive pinion against jamming should the drive pinion and flywheel ring gear meet tooth to tooth.

    Near the position of full drive pinion engagement, the lower contacts closed of the switch are released by the movement of the engaging solenoid. The action short circuits the engaging coil and puts into the circuit the holding coil, responsive to variations in load on the starter motor. At the same time, full voltage is applied to the starter motor circuit and maximum power is available to rotate the engine in full motion and the engine starts. The drive pinion is then smartly returned to the free position by the spring when the push button is released. 


For Larger Engine: The starter motor is designed for use on the larger type of engine, because of the high inertia of the flywheel, it is necessary for the starter pinion to engage with the flywheel ring gear before the starter develops full rotation.

    The field windings of the machine consist of a main series winding, an auxiliary series winding, and a shunt winding.

Description: The solenoid switch operated in two-stage, and used to control the starting cycle.

(i) First stage: When the switch is operated the first stage contacts on the solenoid switch closed and a small current passing through the auxiliary field winding causing, the armature to rotate slowly. Simultaneously the complete armature assembly is drawn towards the driving end of the machine by the magnetic field. The drive pinion is brought into mesh with the flywheel ring gear. The drive pinion near the flywheel ring gear pushes the tripping disc which operates the trip-arm or trigger on the solenoid switch.

(ii) Second stage: The second stage contacts to closed and complete the circuit through the main series winding. The starter exerts by full-electric power and to rotate the engine on full motion and start. When the starter button is released, the armature returns to the disengaged position by the coiled spring of the armature plunger.

Note: The starter is provided with a multiple disc clutch for transmitting torque from the armature shaft to drive the pinion apart. The acts as a freewheel protecting the armature from running at excessively high speeds. This also protects the drive pinion and armature shaft against overload.