starting system fundamentals

© 2012 Delmar, Cengage Learning

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

– 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 motor – 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

starting system fundamentals

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