Starting and Motor Systems Chapter 18 Starting and Motor Systems

Types of Electric Motors Electric motors are used to start the engine In hybrid electric vehicles (HEVs), electric motors can used to propel the vehicle Smaller electric motors are DC Traction or drive motors are AC

Basics of Electromagnetism

Electromagnets Natural magnets from magnetite Artificial magnets rearrange molecules to align along North and South poles Artificial magnets can be temporary or permanent Current carrying wire generates a magnetic field

Coils

Magnetic Circuits and Reluctance Lines of flux can only occupy a closed magnetic circuit The resistance to the passage of flux lines is called reluctance Inserting an iron core into a coil increases the strength of the magnetic field

Magnetic Circuits and Reluctance (Cont.) Electromagnetic field is directly proportional to the number of turns and current flow The number of magnetic lines is proportional to the ampere-turns divided by the reluctance

Magnetic Field Strength Magnetic polarity depends on the direction of current flow Field strength increases if current increases Field strength increases if coil turns increase If reluctance increases, field strength decreases

Motors Convert electric energy into mechanical energy Use interactions of magnetic fields An electromagnet is fitted to a shaft Shaft surrounded by stationary fields Polarity of fields are switched Shaft rotation can do work

Basic Motor

Starting Motors Great amounts of torque for short periods All starting motors of same basic design Housing or frame contains internal parts Field coils produce strong stationary fields Polarity switching fields from rotating armature Brushes and commutator switch polarity End frame supports armature

Housing

Field Coils

Armature

Brushes and End Frame

Knowledge Check Describe the basic operating principles of a DC electric motor. The interaction between stationary magnetic fields and magnetic fields around the armature cause the armature to spin. The fields generated around the armature switch polarity to keep the interaction with the stationary fields attracting and repelling to keep the rotation going.

Operating Principles

Operating Principles (Cont.) Many armature segments are used The number of coils and brushes differ between models Three styles of motor windings: Series motors Parallel or shunt motors Compound or combination motors

Operating Principles (Cont.) Series motors develop maximum torque at start-up Shunt motors develop less start-up torque but maintain constant speed under load Compound motors have good starting torque with constant speed Shunt coils are used to limit free speed

Permanent Magnet Motors Replaces field coils with permanent magnets Current supplied directly to armature Function same as other motor designs Use planetary gear assembly for gear reduction Gear reduction increases torque

Gear Reduction Starter

Counter EMF Starter motor torque dependant on: Current draw The slower the armature turns the more current it will draw More torque needed to crank a difficult engine

Counter EMF (Cont.) CEMF is produced when armature loops pass through magnetic fields This voltage opposes battery supplied voltage The faster the spin, the more voltage is induced

Brushless Motors Removes brush contacts and wear Use permanent magnet motor and electromagnet field windings Used in some HEVs

Starting System Turns the crank until the engine can operate under its own power Starter motor engages and spins flywheel Only purpose is to crank engine fast enough to start

Starting System Components Battery Ignition switch Cable and wires Starter solenoid or relay Starter motor Starter safety switch

Typical Starting System

Starter Circuit Carries the high current flow within the system Supplies power for engine cranking Components are: Battery and battery cables Magnetic switch or solenoid Starter motor

Battery and Cables Starter circuit requires two or more heavy-gauge cables Negative cable connects to engine or transmission Positive cable connects to starter solenoid or relay

Magnetic Switches Enables control circuit to open and close starter circuit Can be either a solenoid or a relay: Solenoid is most common Relays is similar to a solenoid but does not mesh starter drive gear with flywheel

Solenoids Meshes drive gear with flywheel Energizes starter motor through contacts

Starter Relay Used as an electrical relay to the starter Provides an alternate electrical path for ignition coil during cranking Some vehicles use both a relay and a starter solenoid to reduce current through the ignition switch

Ford Starter Relay

Knowledge Check What are the functions of the starter solenoid? The solenoid connects the battery to the starter motor and engages the drive gear with the flywheel.

Starter Drives Meshes armature to flywheel Pinion meshes with flywheel before the armature spins An overrunning clutch is used to prevent starter damage when the engine starts

Pinion gear is locked to the armature shaft in one direction

Pinion freewheels when turned opposite drive direction by the flywheel

Gear Reduction Drives

Control Circuit Allows a small amount of current to control the high current starter circuit Consists of ignition switch, safety switch, and starter solenoid or relay Starting safety switch Prevents vehicle from starting unless in park or neutral or with clutch disengaged

Starting Safety Switch Neutral safety or clutch safety switch Prevents starter operation if transmission is not in Park or Neutral of if clutch pedal is not fully depressed

Starting System Testing Do not crank the engine for longer than 15 seconds Allow at least two minutes in between cranking cycles for starter to cool

Preliminary Checks Check the battery and charge as needed Check wiring and cable connections Check to make sure the cables are the correct size Check any fusible links in the wiring Ensure engine has correct weight oil

Preliminary Checks (Cont.)

Safety Precautions Starting tests performed with engine cranking Bypass ignition to prevent engine from starting Make sure transmission is out of gear and parking brake is set

No-Crank Problems Verify battery and cable condition. Test for voltage at solenoid S terminal May need to connect scan tool to check starter circuit signal and anti-theft system

Starter Solenoid Problems Typical complaint is a clicking noise when attempting to start the engine Anything that reduces current flow will affect solenoid operation Solenoids can often be replaced separately or as a starter assembly

Starting Safety Switches Can be checked with a voltmeter or ohmmeter With transmission in park or clutch depressed, switch should be closed May need adjusted if not closing circuit

Battery Load Test Slow cranking is often caused by insufficient battery current The battery must be able to crank engine under all load conditions

Cranking Tests Cranking voltage test measures available voltage during cranking Refer to service manual for voltage specifications, normally at least 9.6 volts Cranking current test measures starter current draw during cranking Watch voltage and amperage and compare to specifications

Insulated Circuit Resistance Tests Insulated circuit contains all high current cables and connections Disable or bypass the ignition Typical reading specifications 0.2 - 0.6 volts Higher readings indicated resistance in either the insulated positive or negative circuits

Starter Relay Bypass Test Simple way to determine if relay is operational Disable the ignition Connect a heavy jumper between the battery positive terminal and relay’s starter terminal

Control Circuit Voltage Drop High resistance in solenoid switch circuit reduces current flow through solenoid windings Disable the ignition system Test between battery positive and starter switch terminal on solenoid or relay Normally less than 0.5 volts

Control Circuit Voltage Drop (Cont.)

Starter Drive Test Checks for a slipping starter drive Bypass or disable the ignition Crank engine for several seconds Repeat at least three times If engine stops cranking but starter is still spinning, the starter drive is slipping

Knowledge Check Technician A says a faulty Park/Neutral switch can cause a no-crank complaint. Technician B says a poor battery cable connection can cause a no-crank condition. Who is correct? Both Technicians A and B

Removing the Starter Motor Disconnect battery negative cable Disconnect solenoid wiring and mark as necessary Loosen starter mounting bolts Support the starter and remove bolts Lift starter away from flywheel

Free Speed (No-Load) Test Every starter should be bench tested when removed and before being installed Firmly clamp starter in a vice Connect ammeter to battery cable and starter to a battery Check current draw and motor speed

No-Load Testing

Starter Motor Service Field coil tests Refer to a wiring diagram Check for opens and shorts in coil feeds

Starter Motor Service (Cont.) Armature tests Inspect commutator Check for continuity between commutator segments

Starter Motor Service (Cont.) Brush inspection Ohm check brush holder Measure brush length Bearings and bushings Check for loose, tight, or rough bearings and bushings

Starter Motor Service (Cont.) Starter drives and clutches Inspect teeth on drive gear Check flywheel teeth Check operation of overrunning clutch

Starter Motor Reassembly Reverse disassembly procedures Lubricate splines on armature shaft that the drive gear rides on Lubricate bearings and/or bushings with high-temperature grease Apply sealant to solenoid flange Check pinion depth clearance Perform a no-load bench test

Installation Sand paint from mounting point Check starter clearance on starters that use shims