Lecture Notes on Automotive Starting Motor

Overview of Starting Systems

• Historical Method: Cars used to start by hand-cranking, risking injury (e.g., breaking an arm).
• Modern Method: Starting motors handle heavy work, allowing for easier ignition of the engine.

Starting Motor Functionality

• Mechanism:
  • Pressing the starting motor switch connects it to the flywheel.
  • Electric current from the battery powers the starting motor, causing the armature to rotate.
  • The armature is geared to the flywheel via a pinion gear.

Relationship Between Magnetism and Electricity

• Flowing current produces a magnetic field around a conductor (similar to a bar magnet).
• Stronger current = stronger magnetic field.
• Movement of a conductor within a magnetic field can induce current flow.

Electromagnetism Principles

• Characteristics of Magnets:

  • Every magnet has a north and south pole.
  • Unlike poles attract; like poles repel.

• Electromagnet Formation:

  • A conductor loop becomes an electromagnet with current flow.
  • Direction of current changes the polarity of the electromagnet.

Armature Rotation

• Magnetic Interaction:

  • Current causes the loop's polarity to change, leading to continuous rotation.
  • Initial attraction turns into repulsion as the loop aligns with the magnet.

• Segments and Brushes:

  • Segments are copper conductors that rotate with the loop.
  • Brushes remain stationary, wired to the battery.
  • Switching brushes allows current direction to change at the right moment for continuous rotation.

Energy Conversion

• The starting motor converts electrical energy to mechanical energy through rotation.
• Multiple Loops Required:
  • A single wire loop is insufficient; multiple windings create an armature for sufficient power.
  • Proper winding arrangement maximizes current flow when in correct alignment with pole pieces.

Magnetic Field Components

• Pole Pieces and Field Windings:
  • Pole pieces replace large bar magnets, with conductors wound around them to enhance magnetic fields.
  • Increased magnetic field significantly boosts armature turning power.

Summary of Starting Motor Operation

• Closing the starter switch completes the circuit between the battery and motor.
• Current polarity influences armature and field coil windings.
• The armature rotates while trying to align with field poles but changes polarity through the segments at the brushes.
• Rotary power is transmitted to the flywheel, cranking the engine.

Conclusion

• Despite its simplicity, the starting motor was a significant advancement in automotive technology.