Starting System Fundamentals Chapter 28

Objectives Explain electric motor principles Describe starter parts Understand the operation of a solenoid Discuss starter drive operation

Introduction Starter system Without a starter Important part of the automotive electrical system Without a starter Car would have to be push started Henry Ford's Model T had a hand crank for the engine

Starter Motor Starter circuit includes: Starter operates at a high rpm Starter drive Battery Ignition switch Solenoid Starter operates at a high rpm Has a small pinion gear on end of starter drive Meshes with a large gear on the flywheel

Starter Motor (cont'd.) Gear ratio Provides starter with leverage needed Gear ratio between the two gears is about 18:1 Crank engine at normal cranking speed Starter motor must be turned 3,600 rpm

Starter Motor Fundamentals Starters use electromagnetism to convert electrical energy to mechanical power Two separate magnetic fields Produced by horseshoe Resulting from current flowing through the conductor Push-pull effect on armature Causes conductor to move from stronger to weaker magnetic field

Starter Motor Fundamentals (cont'd.) Conductor is formed into a loop Loop wire is placed between two electromagnetic pole shoes Ends of the wires have commutator bars Multiple loops make up an armature Armature has a soft iron core Field coils made of heavy copper ribbons Wound around soft iron cores called pole shoes

Starter Motor Fundamentals (cont'd.) Some starter motors don't have field coils Have permanent magnets instead Simpler Weigh less Create less heat Brushes, usually made of carbon, are lightly held against the commutator by springs Usually four brushes, which are together in pairs

Starter Drives Have an overrunning, or one-way clutch Transmits motion from starter to flywheel Disengages from the engine at startup Teeth on the starter drive gear are tapered

Starter Electrical Circuit Starter motor requires a large amount of current Battery must be in good enough condition to provide sufficient current Starter switched on by ignition switch and key Most cars use a solenoid Engages starter drive pinion with flywheel ring gear When a coil in the solenoid is energized, a magnetic field draws the piston into the coil

Starter Electrical Circuit (cont'd.) Ignition switch: opens and closes the circuit to the starter Electricity can take two paths in the starter Safety switches Circuit on newer cars with automatic transmissions has a neutral safety switch Late-model vehicles with manual transmissions have a starter/clutch interlock switch

Gear Reduction Starters Some manufacturers use gear reduction starters Lighter Use less current Small in size Lower gear ratio gives them enough torque Smaller battery cables can also be used

Brushless DC Motors Hybrid vehicles use brushless motors No commutator or brushes Arcing cannot occur Permanent magnets are part of the rotor Electromagnets are part of the stator Electronic circuitry Takes the place of brushes and commutator bars

Brushless DC Motors (cont'd.) Rotor position Sensed either by: Hall switch Magnetic field strength in unexcited field windings Magnetic strength in windings Varies with changes in the duty cycle Pulse-width modulation With longer pulses, the motor turns faster