Starter Motor: Principles, Components, and Operation
Starter Motor Principles
A conductor carrying an electric current within a magnetic field tends to move perpendicular to the magnetic field lines. The starter motor acts as an electromagnet due to the current flow, creating magnetic properties. This interaction with the stator poles results in circular motion.
Starter Motor Components
The starter motor assembly includes a DC electric motor and a gear mechanism. The electric motor has an armature that rotates within the stator, supported at both ends of the shaft. The front end features a pinion gear that engages with the flywheel’s crown gear.
Coupling Pinion Gear
Rotation is transmitted from the starter to the combustion engine through gears. A small sliding gear shaft, coupled to the starter motor, is moved by a relay on a forked pivot. This engages with a larger gear on the engine’s crankshaft flywheel. A free wheel mechanism ensures torque is transmitted to the crankshaft gear, but prevents the starter from being driven by the engine.
Engines Starting with Induced or Sliding
Starter motors with induced slip have a field winding connected in series, plus an assistant and a support winding. When the engine reaches full turn, the magnetic field decreases. The clamp winding keeps the crown gear engaged with the pinion. Releasing the ignition switch disengages the pinion via a spring, returning the armature to its resting position.
Flywheel
The flywheel contains rollers and springs that maintain coupling with the engine flywheel’s crown. Once the engine starts, the pinion rotates freely due to the bearing but remains interlocked as long as the key is engaged.
Reduction System
The rotor does not directly drive the pinion. Instead, it uses a gear system where the rotor gear is smaller than the driving pinion shaft. This reduces the pinion’s rotation speed and multiplies the engine’s power.
Casing or Motor Body
The steel body encloses the inductor magnetic field, formed by the polar icecaps and created by the spools. The armature or rotor moves within this casing.
Rotor or Induced
The rotor consists of a shaft with a cylinder made of slotted magnetic sheets. These slots house the coils that create the magnetic field. The collector, mounted on one side of the shaft, has insulated copper foils that connect to the rotor conductors. Brushes rub against these segments, feeding power to the motor. The shaft has helical grooves for the drive mechanism.
Collector Side Cover
This lid supports one side of the motor assembly and the armature shaft, which rests on a bronze bearing. Brush holders are mounted, one isolated and one grounded, with graphitized carbon brushes that allow the passage of the engine’s current. Springs ensure correct contact pressure of the brushes against the commutator.
Tapa Share Obtained
This steel or aluminum casting serves as a closure on the other side of the assembly. It has a brass cap that rests on the shaft, a housing for the contactor or control relay, and a flange with holes for mounting the engine.
Starter Relay
The starter relay, directly incorporated into the engine, serves to activate the motor circuit and move the drive mechanism for coupling the starter pinion to the vehicle engine’s crown. It consists of an electromagnet with two coils, powered directly from the battery via the ignition key. The solenoid plunger moves, closing the switch terminals and moving a coupling bracket to control the fork.