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9StartingSystemOperation

LEARNINGOBJECTIVESUpon completion and review of this chapter, youshould be able to:

• Define the two circuits of the automotivestarting system.

• Identify the basic starting systems parts andexplain their function in the system.

• Define the different designs of startingsystems used by the different automotivemanufacturers.

• Identify the internal components of anautomotive starter motor and explain theiroperation.

• Define the term magnetic repulsion andexplain how a DC starter motor operates.

• Define the terms series, shunt (parallel),and compound (series-parallel) as theyapply to starter motor internal circuitry.

• Explain the operation of the armature andfields.

• Define starter motor drives and explain theiroperation.

• Define the different designs of startingmotors used by the different automotivemanufacturers.

• Explain the operation of the overrunningclutch.

KEY TERMSArmatureBrushesClutch Start SwitchCompound MotorDetentedIgnition SwitchLap WindingMagnetic RepulsionMagnetic SwitchOverrunning ClutchPinion GearSeries MotorShunt MotorSolenoidSolenoid-Actuated StarterStarter DriveStarting Safety SwitchTorque

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Figure 9-1. In this diagram of the starting system, thestarter circuit is shown as a solid line and the controlcircuit is shown as a dashed line. (Delphi AutomotiveSystems)

INTRODUCTIONThe engine must be rotated before it will start andrun under its own power. The starting system is acombination of mechanical and electrical compo-nents that work together to start the engine. Thestarting system is designed to change electricalenergy that is being stored in the battery intomechanical energy. To accomplish this conver-sion, a starter motor is used. This chapter willexplain how the starting system and it compo-nents operate.

STARTING SYSTEMCIRCUITSThe starting system draws a large amount ofcurrent from the battery to power the startermotor. To handle this current safely and with aminimum voltage loss from resistance, thecables must be the correct size, and all connec-tions must be clean and tight. The driverthrough the ignition switch controls the startingsystem. If the heavy cables that carry current tothe starter were routed to the instrument paneland the switch, they would be so long that thestarter would not get enough current to operateproperly. To avoid such a voltage drop, the start-ing system has the following two circuits, asshown in Figure 9-1:

• Starter circuit• Control circuit

Starter CircuitThe starter circuit, or motor circuit, (shown as thesolid lines of Figure 9-1) consists of the following:

• Battery• Magnetic switch• Starter motor• Heavy-gauge cables

The circuit between the battery and the startermotor is controlled by a magnetic switch (a relayor solenoid). Switch design and function varyfrom system to system. A gear on the starter motorarmature engages with gear teeth on the engineflywheel. When current reaches the starter motor,it begins to turn. This turns the car’s engine, whichcan quickly fire and run by itself. If the startermotor remained engaged to the engine flywheel,the starter motor would be spun by the engine at avery high speed. This would damage the startermotor. To avoid this, there must be a mechanismto disengage the starter motor from the engine.There are several different designs that will dothis, as we will see in this chapter.

Control CircuitThe control circuit is shown by the dashed lines inFigure 9-1. It allows the driver to use a smallamount of battery current, about three to fiveamperes, to control the flow of a large amount ofbattery current to the starter motor. Control cir-cuits usually consist of an ignition switch con-nected through normal-gauge wiring to the batteryand the magnetic switch. When the ignition switchis in the start position, a small amount of currentflows through the coil of the magnetic switch.This closes a set of large contact points within themagnetic switch and allows battery current toflow directly to the starter motor. For more infor-mation about control circuits, see the “StarterControl Circuit Devices” section in Chapter 9 ofthe Shop Manual.

BASIC STARTINGSYSTEM PARTSWe have already studied the battery, which is animportant part of the starting system. The othercircuit parts are as follows:

• Ignition switch• Starting safety switch (on some systems)

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Figure 9-2. This ignition switch acts directly on the con-tact points. (Reprinted by permission of Robert Bosch GmbH)

Figure 9-3. Column-mounted switches act directlyon the contact points.

• Relays or solenoids (magnetic switches)• Starter motor• Wiring

Ignition SwitchThe ignition switch has jobs other than controllingthe starting system. The ignition switch normallyhas at least four positions:

• ACCESSORIES• OFF• ON (RUN)• START

Switches on late-model cars also have a LOCKposition to lock the steering wheel. All positionsexcept START are detented. That is, the switchwill remain in that position until moved by thedriver. When the ignition key is turned to STARTand released, it will return to the ON (RUN) posi-tion. The START position is the actual starterswitch part of the ignition switch. It applies bat-tery voltage to the magnetic switch.

There are two types of ignition switches in use.On older cars, the switch is mounted on the instru-ment panel and contains the contact points (Figure9-2). The newer type, used on cars with lockingsteering columns, is usually mounted on the steer-ing column. Many column-mounted switches oper-ate remotely mounted contact points through a rod.Other column-mounted switches operate directlyon contact points (Figure 9-3). Older domestic andimported cars sometimes used separate push-buttonswitches or cable-operated switches that controlledthe starting system separately from the ignitionswitch.

Starting Safety SwitchThe starting safety switch is also called a neutralstart switch. It is a normally open switch thatprevents the starting system from operating whenthe automobile’s transmission is in gear. If the carhas no starting safety switch, it is possible to spin

the engine with the transmission in gear. Thismakes the car lurch forward or backward, whichcould be dangerous. Safety switches or interlockdevices are now required by law with all auto-matic and manual transmissions.

Starting safety switches can be connected in twoplaces within the starting system control circuit.The safety switch can be placed between the igni-tion switch and the magnetic switch, as shown inFigure 9-4, so that the safety switch must be closedbefore current can flow to the magnetic switch. Thesafety switch also can be connected between themagnetic switch and ground (Figure 9-5), so thatthe switch must be closed before current can flowfrom the magnetic switch to ground. Where thestarting safety switch is installed depends upon thetype of transmission used and whether the gearshiftlever is column-mounted or floor-mounted.

Automatic Transmissions/TransaxlesThe safety switch used with an automatic trans-mission or transaxle can be either an electricalswitch or a mechanical device. Electrical/elec-tronic switches have contact points that are closedonly when the gear lever is in PARK or NEUTRAL,as shown in Figure 9-4. The switch can be mountednear the gearshift lever, as in Figures 9-6 and 9-7, oron the transmission-housing, as in Figure 9-8. The

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Figure 9-6. An electrical safety switch installed nearthe floor-mounted gearshift lever. (GM Service and PartsOperations)

Figure 9-4. This starting safety switch must be closed before battery current can reach the magnetic switch.(GM Service and Parts Operations)

Figure 9-5. The clutch switch must be closed beforebattery current can flow from the magnetic switch toground. (DaimlerChrysler Corporation)

contacts are in series with the control circuit, so thatno current can flow through the magnetic switchunless the transmission is out of gear.

Mechanical interlock devices physicallyblock the movement of the ignition key when thetransmission is in gear, as shown in Figures 9-9and 9-10. The key can be turned only whenthe gearshift lever is in PARK or NEUTRAL.Some manufacturers use an additional circuit inthe neutral start switch to light the backup lamps

when the transmission is placed in REVERSE(Figures 9-7 and 9-8).

Ford vehicles equipped with an electronicautomatic transmission or transaxle use an addi-tional circuit in the neutral safety switch to inform

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Figure 9-8. Transmission-mounted safety switch.(DaimlerChrysler Corporation)

Figure 9-7. Column-mounted neutral safety switch near gearshift tube. (GM Service and Parts Operations)

Figure 9-9. A mechanical device within the steeringcolumn blocks the movement of the ignition switch.

the microprocessor of the position of the manuallever shaft. This signal is used to determine thedesired gear and electronic pressure control. Theswitch is now called a manual lever positionswitch (MLPS).

General Motors has done essentially the sameas Ford, renaming the PARK/NEUTRAL switchused on its 4T65E and 4T80E transaxles. Itnow is called either a PRNDL switch or aPARK/NEUTRAL position switch and providesinput to the PCM regarding torque converterclutch slip. This input allows the PCM to make

the necessary calculations to control clutch applyand release feel.

Manual Transmissions/TransaxlesThe starting safety switch used with a manualtransmission on older vehicles is usually an elec-trical switch similar to those shown in Figures 9-7and 9-8. A clutch start switch (also called aninterlock switch) is commonly used with manual

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Figure 9-11. The clutch pedal must be fully depressedto close the clutch switch and complete the control circuit.

transmissions and transaxles on late-model vehi-cles. This is an electric switch mounted on thefloor or firewall near the clutch pedal. Its contactsare normally open and close only when the clutchpedal is fully depressed (Figure 9-11).

Relays and SolenoidsA magnetic switch in the starting system allowsthe control circuit to open and close the startercircuit. The switch can be either of the following:

• A relay, which uses the electromagnetic fieldof a coil to attract an armature and close thecontact points

• A solenoid, which uses the electromagneticfield of a coil to pull a plunger into the coiland close the contact points

In addition to closing the contact points, solenoid-equipped circuits often use the movement of the sole-noid to engage the starter motor with the engineflywheel. We will explain this in Chapter 10. The ter-minology used with relays and solenoids is oftenconfusing. Technically, a relay operates with ahinged armature and does only an electrical job; asolenoid operates with a movable plunger and usu-ally does a mechanical job. Sometimes, a solenoidis used only to open and close an electric circuit;the movement of the plunger is not used for anymechanical work. Manufacturers sometimes callthese solenoids “starter relays.” Figure 9-12 shows acommonly used Ford starter relay. We will continueto use the general term magnetic switch, and will tellyou if the manufacturer uses a different name for thedevice.

For more information about magnetic switches,see the following sections in Chapter 9 of the ShopManual: “Inspection and Diagnosis,” “StarterControl Circuit Devices,” and “Unit Removal.”

WiringThe starter motor circuit uses heavy-gauge wiringto carry current to the starter motor. The controlcircuit carries less current and thus uses lighter-gauge wires.

SPECIFIC STARTINGSYSTEMSVarious manufacturers use different starting sys-tem components. The following paragraphs brieflydescribe the circuits used by major manufacturers.

Delco-Remy (Delphi)and BoschDelco-Remy and Bosch starter motors are usedby General Motors. The most commonly usedDelco-Remy and Bosch automotive starter motordepends upon the movement of a solenoid both tocontrol current flow in the starter circuit and toengage the starter motor with the engine flywheel.This is called a solenoid-actuated starter. The

Figure 9-10. A lever on the steering wheel blocks themovement of the ignition key when the transmission isin gear.

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Figure 9-12. The Ford starter relay or magnetic switch.

Figure 9-13. GM Starter circuit. (Delphi AutomotiveSystems)

solenoid is mounted on, or enclosed with, themotor housing (Figure 9-13).

The type and location of starting safety switchesvary within the GM vehicle platforms. Larger-sizeGM cars use a mechanical blocking device in thesteering column (Figure 9-9). The intermediate andsmaller cars with automatic transmissions have elec-trical switches mounted near the shift lever. Theseare either on the column, as shown in Figure 9-7, oron the floor (Figure 9-6). On front-wheel-drive

(FWD) cars with automatic transmissions, thePARK/NEUTRAL or PRNDL switch is an electri-cal switch mounted on the transaxle case manuallever shaft (Figure 9-14). GM cars with floor-shiftmanual transmissions use a clutch pedal-operatedsafety switch. With column-shift manual transmis-sions, an electric switch is mounted on the column.

Ford MotorcraftFord has used three types of starter motors, andtherefore has several different starting systemcircuits. The Motorcraft positive engagementstarter has a movable-pole shoe that uses electro-magnetism to engage the starter motor with theengine. This motor does not use a solenoid to moveanything, but it uses a solenoid to open and close thestarter circuit as a magnetic switch (Figure 9-15).Ford calls this solenoid a starter relay.

The Motorcraft solenoid-actuated starter is verysimilar to the Delco-Remy unit and depends uponthe movement of a solenoid to engage the startermotor with the engine. The solenoid is mountedwithin the motor housing and receives battery cur-rent through the same type of starter relay used inthe positive engagement system. Although themotor-mounted solenoid could do the job of thisadditional starter relay, the second relay is installed

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Figure 9-14. GM PRNDL/Park-neutral switch on a GMTransaxle. (GM Service and Parts Operations)

Figure 9-15. The Ford starting system circuit with thepositive engagement starter.

on many Ford automobiles to make the cars easierto build. Motorcraft solenoid-actuated starterswere used on Ford cars and trucks with large V8engines. The Motorcraft permanent magnet gear-reduction (PMGR) starter is a solenoid-actuateddesign that operates much like the Motorcraftsolenoid-actuated starter previously described.However, the starter circuit may or may not use astarter relay, depending on the car model.

Rear-wheel-drive (RWD) Ford automobileswith manual transmissions have no starting safety

switch. Front-wheel-drive (FWD) models withmanual transaxles have a clutch interlock switch.If a Ford car with an automatic transmission has acolumn-mounted shift lever, a blocking interlockdevice prevents the ignition key from turningwhen the transmission is in gear. If the automatictransmission shift lever is mounted on the floor,an electrical switch prevents current from flowingto the starter relay when the transmission is ingear. The switch may be mounted on the trans-mission case or near the gearshift lever.

DaimlerChryslerChrysler uses a solenoid-actuated starter motor.The solenoid is mounted inside the motor hous-ing and receives battery current through astarter relay, as shown in Figure 9-16. Chryslerstarter relays used prior to 1977 have fourterminals, as shown in Figure 9-17A. In 1977, asecond set of contacts and two terminals wereadded (Figure 9-17B). The extra contacts andterminals allow more current to flow throughthe relay to the ignition system and to theexhaust gas recirculation (EGR) timer. This hasno effect on the operation of the relay within thestarting system. These starter relays generallywere mounted on the firewall.

Current Chrysler starting systems use a standardfive-terminal Bosch relay (Figure 9-18) but onlyfour terminals are used in the circuit (Figure 9-19).The relay is located at the front of the driver’s-sidestrut tower in a power distribution center or cluster.

Chrysler automobiles with manual transmis-sions have a clutch interlock switch, as shownin Figure 9-20. Current from the starterrelay can flow to ground only when the clutchpedal is fully depressed. Cars with automatictransmissions have an electrical neutral startswitch mounted on the transmission housing(Figure 9-21). When the transmission is out ofgear, the switch provides a ground connectionfor the starter control circuit.

Toyota and NissanToyota and Nissan use a variety of solenoid-actuated direct drive and reduction-gear starterdesigns manufactured primarily by Hitachi andNippondenso, as shown in Figures 9-22 and 9-23.The neutral start switch (called an inhibitorswitch by the Japanese automakers) incorporatesa relay in its circuit.

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Figure 9-17. Comparison of the terminals on a pre-1977 starter relay (A) and a 1977 or later relay (B).(DaimlerChrysler Corporation)

Figure 9-18. DaimlerChrysler starting system with afive-terminal relay. (DaimlerChrysler Corporation)

Figure 9-16. Typical DaimlerChrysler starting system. (DaimlerChrysler Corporation)

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Figure 9-19. Only four of the five relay terminals areused when the Bosch relay is installed. (DaimlerChryslerCorporation)

Figure 9-23. A typical Nissan diesel starting system.(Courtesy of Nissan North America, Inc.)

Figure 9-20. DaimlerChrysler clutch switch.(DaimlerChrysler Corporation)

Figure 9-21. When the automatic transmission is inPARK or NEUTRAL, a transmission lever touches thecontact and completes the control circuit to ground.(DaimlerChrysler Corporation)

STARTER MOTORSStarter Motor PurposeThe starter motor converts the electrical energyfrom the battery into mechanical energy forcranking the engine. The starter is an electricmotor designed to operate under great electricalloads and to produce very high horsepower. Thestarter consists of housing, field coils, an arma-ture, a commutator and brushes, end frames, anda solenoid-operated shift mechanism.

FRAME AND FIELDASSEMBLYThe frame, or housing, of a starter motor(Figure 9-24) encloses all of the moving motorparts. It supports the parts and protects themfrom dirt, oil, and other contamination. The partof the frame that encloses the pole shoes andfield windings is made of iron to provide a pathfor magnetic flux lines (Figure 9-25). To reduceweight, other parts of the frame may be made ofcast aluminum.

Figure 9-22. Typical Nissan starting system used ongasoline engines. (Courtesy of Nissan North America, Inc.)

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Figure 9-25. The motor frame is a path for flux lines.

Figure 9-24. Starter motor housing.

Figure 9-26. Brush end and end housing.

armature shaft turns. It also encloses the gearthat meshes with the engine flywheel. This iscalled the drive end housing. The drive endhousing often provides the engine-to-motormounting points. These end pieces may be madeof aluminum because they do not have to con-duct magnetic flux.

The magnetic field of the starter motor isprovided by two or more pole shoes and fieldwindings. The pole shoes are made of iron andare attached to the frame with large screws(Figure 9-27). Figure 9-28 shows the paths ofmagnetic flux lines within a four-pole motor.The field windings are usually made of a heavy

One end of the housing holds one of the twobearings or bushings in which the armature shaftturns. On most motors, it also contains thebrushes that conduct current to the armature(Figure 9-26). This is called the brush, or com-mutator, end housing. The other end housingholds the second bearing or bushing in which the

Figure 9-27. Pole shoes and field windings in housing.

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Figure 9-28. Flux path in a four-pole motor.

Figure 9-29. Pole shoe and field winding removedfrom housing.

copper ribbon (Figure 9-29) to increase theircurrent-carrying capacity and electromagneticfield strength. Automotive starter motors usuallyhave four-pole shoes and two to four field wind-ings to provide a strong magnetic field withinthe motor. Pole shoes that do not have fieldwindings are magnetized by flux lines from thewound poles.

Torque is the force of a starter motor, a forceapplied in a rotary, or circular direction. Thetorque, speed, and current draw of a motor

are related. As speed increases in most automotivestarter motors, torque and current draw decrease.These motors develop maximum torque just beforethe engine begins to turn. Once the engine beginsto turn, the motor speed increases and torquedecreases. The maximum amount of torque pro-duced by a motor depends upon the strength of itsmagnetic fields. As field strength increases, torqueincreases.

DC STARTER MOTOROPERATIONDC starter motors (Figure 9-30) work on theprinciple of magnetic repulsion. This principlestates that magnetic repulsion occurs when astraight rod conductor composed of the armature,commutator, and brushes is located in a magneticfield (field windings) and current is flowingthrough the rod. This situation creates two sepa-rate magnetic fields: one produced by the magnet(pole shoes of the magnetic field winding) andanother produced by the current flowing throughthe conductor (armature/commutator/brushes).

Figure 9-30 shows the magnet’s magnetic fieldmoving from the N pole to the S pole and the con-ductor’s magnetic field flowing around the con-ductor. The magnetic lines of force have arubber-band characteristic. That is, they stretchand also try to shorten to minimum length.

Figure 9-30 shows a stronger magnetic fieldon one side of the rod conductor (armature/commutator/brushes) and a weak magnetic fieldon the other side. Under these conditions, theconductor (armature) will tend to be repulsed bythe strong magnetic field (pole shoes and fieldwinding) and move toward the weak magneticfield. As current in the conductor (armature) andthe strength of the magnet (field windings)increases, the following happens:

• More lines of magnetism are created on thestrong side.

• More repulsive force is applied to the con-ductor (armature).

• The conductor tries harder to move toward theweak side in an attempt to reach a balancedneutral state.

• A greater amount of electrical heat isgenerated.

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Figure 9-30. Motor principle.

NOTE: The combination of the U-shaped conductor loop and the split copper ring are calledthe commutator because they rotate together.Together they become the armature.

Current flows from the positive ( � ) batteryterminal through the brush and copper ringnearer the N pole, through the conductor (arma-ture) to the copper ring and brush nearer theS pole and back to the negative (�) battery ter-minal. This electrical flow causes the portion ofthe loop near the S pole to push downward andthe N pole to push upward. With a strong fieldon one side of the conductor and a weak field onthe other side, the conductor will move from thestrong to the weak. Put another way, the weakermagnetic field between the S and N poles onone side of the conductor is repulsed by thestronger magnetic field on the other side of theconductor. The commutator then rotates. As itturns, the two sides of the conductor loopreverse positions and the two halves of thesplit copper ring alternately make contact withthe opposite stationary brushes. This causes theflow direction of electrical current to reverse(alternating current) through the commutatorand the commutator to continue to rotate in thesame direction.

In order to provide smooth rotation and tomake the starter powerful enough to start theengine, many armature commutator segments areused. As one segment rotates past the stationarymagnetic field pole, another segment immedi-ately takes its place.

When the starter operates, the current passingthrough the armature produces a magnetic field ineach of its conductors. The reaction between themagnetic field of the armature and the magneticfields produced by the field coils causes the arma-ture to rotate.

Motor Internal CircuitryBecause field current and armature current flowto the motor through one terminal on the housing,the field and armature windings must be con-nected in a single complete circuit. The internalcircuitry of the motor (the way in which the fieldand armature windings are connected) gives themotor some general operating characteristics.

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Figure 9-31. Basic motor circuitry.

Figure 9-32. Torque output characteristics of series,shunt, and compound motors.

initial torque (Figure 9-32), but are used topower other automotive accessories.

The compound motor, shown in Figure 9-31C,has both series and shunt field windings. It com-bines both the good starting torque of the series-type and the relatively constant operating speed ofthe shunt-type motor (Figure 9-32). A compoundmotor is often used as an automotive starter.Figure 9-33 shows the actual relationships of fieldand armature windings in different types of motors.

Figure 9-33. Actual relationships of field and arma-ture windings in different types of motors.

Figure 9-31 shows the three general types ofmotor internal circuitry, as follows:

• Series• Shunt (parallel)• Compound (series-parallel)

All automotive starter motors in use today arethe series type or the compound type. The seriesmotor (Figure 9-31A) has only one path forcurrent. As the armature rotates, its conductorscut magnetic flux lines. A counter-voltage isinduced in the armature windings, opposing theoriginal current through them. The counter-voltage decreases the total current through boththe field and the armature windings, becausethey are connected in series. This reduction ofcurrent also reduces the magnetic field strengthand motor torque. Series motors produce agreat amount of torque when they first begin tooperate, but torque decreases as the enginebegins to turn (Figure 9-32). Series motors workwell as automotive starters because cranking anengine requires a great amount of torque at first,and less torque as cranking continues.

The shunt motor (Figure 9-31B) does notfollow the increasing-speed/decreasing-torquerelationship just described. The counter-voltagewithin the armature does not affect field current,because field current travels through a separatecircuit path. A shunt motor, in effect, adjusts itstorque output to the imposed load and operatesat a constant speed. Shunt motors are not usedas automotive starters because of their low

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Figure 9-34. Motor armature.

ARMATURE ANDCOMMUTATORASSEMBLYThe motor armature (Figure 9-32) has a lami-nated core. Insulation between the laminationshelps to reduce eddy currents in the core. Forreduced resistance, the armature conductors aremade of a thick copper wire. Motor armatures areconnected to the commutator in one of two ways.In a lap winding, the two ends of each conductorare attached to two adjacent commutator bars(Figure 9-35). In a wave winding, the two ends ofa conductor are attached to commutator bars thatare 180 degrees apart (on opposite sides of thecommutator), as shown in Figure 9-36. A lap-wound armature is more commonly used becauseit offers less resistance.

The commutator is made of copper bars insulatedfrom each other by mica or some other insulatingmaterial. The armature core, windings, and commu-tator are assembled on a long armature shaft. Thisshaft also carries the pinion gear that meshes withthe engine flywheel ring gear (Figure 9-37). Theshaft is supported by bearings or bushings in the endhousings. To supply the proper current to the arma-ture, a four-pole motor must have four brushes rid-ing on the commutator (Figure 9-38). Mostautomotive starters have two grounded and twoinsulated brushes. The brushes are held against thecommutator by spring force.

PERMANENT-MAGNET FIELDSThe permanent magnet, planetary-drive startermotor is the first significant advance in starterdesign in decades. It was first introduced on some1986 Chrysler and GM models, and in 1989 byFord on Continental and some Thunderbird models.Permanent magnets are used in place of the electro-magnetic field coils and pole shoes. This eliminates

Figure 9-35. Armature lap winding. (Delphi AutomotiveSystems)

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Figure 9-36. Armature wave winding.

Figure 9-37. The pinion gear meshes with the fly-wheel ring gear.

Figure 9-38. A four-brush motor. (Delphi AutomotiveSystems)

the motor field circuit, which in turn eliminates thepotential for field wire-to-frame shorts, field coilwelding, and other electrical problems. The motorhas only an armature circuit. Because the smallerarmature in permanent magnet starters uses rein-forcement bands, it has a longer life than the arma-ture in wound-field starter motors.

The magnetic field of the starter motor is pro-vided by four or six small permanent magnets.These magnets are made from an alloy of iron andrare-earth materials that produces a magnetic fieldstrong enough to operate the motor without relyingon traditional current-carrying field coil windingsaround iron pole pieces. Removing the field circuitnot only minimizes potential electrical problems,the use of permanent-magnet fields allows engi-neers to design a gear-reduction motor half the sizeand weight of a conventional wound-field motorwithout compromising cranking performance.

See Chapter 9 of the Shop Manual for serviceand testing.

STARTER MOTORAND DRIVE TYPESStarter motors, as shown in Figure 9-39 aredirect-current (DC) motors that use a greatamount of current for a short time. The startermotor circuit is a simple one containing just the

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Figure 9-40. The Chrysler reduction-gear startermotor. (DaimlerChrysler Corporation)

starter motor and a solenoid or relay. This circuitis a direct path for delivering the momentaryhigh current required by the starter motor fromthe battery.

The starter motor cranks the engine through apinion gear that engages a ring gear on theengine flywheel. The pinion gear is drivendirectly off the starter armature (Figure 9-39) orthrough a set of reduction gears (Figure 9-40)that provides greater starting torque, although ata lower rpm.

For the starter motor to be able to turn theengine quickly enough, the number of teeth on theflywheel ring gear, relative to the number of teethon the motor pinion gear, must be between 15 and20 to 1 (Figure 9-41).

When the engine starts and runs, its speedincreases. If the starter motor were permanentlyengaged to the engine, the motor would be spunat a very high speed. This would throw armaturewindings off the core. Thus, the motor must bedisengaged from the engine as soon as the engineturns more rapidly than the starter motor hascranked it. This job is done by the starter drive.

Four general kinds of starter motors are used inlate-model automobiles:

• Solenoid-actuated, direct drive• Solenoid-actuated, reduction drive• Movable-pole shoe• Permanent-magnet, planetary drive

Figure 9-39. Starter motor cutaway.

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Figure 9-43. The solenoid has a heavy-gauge pull-inwinding and a lighter-gauge hold-in winding. (DelphiAutomotive Systems)

Solenoid-Actuated,Direct DriveThe main parts of a solenoid-actuated, direct-drive starter (Figure 9-42), are the solenoid, theshift lever, the overrunning clutch, and the starterpinion gear. The solenoid used to actuate a starterdrive has two coils: the pull-in winding and thehold-in, or holding, winding (Figure 9-43). Thepull-in winding consists of few turns of a heavywire. The winding is grounded through the motorarmature and grounded brushes. The hold-in

winding consists of many turns of a fine wire andis grounded through the solenoid case.

When the ignition switch is turned to the startposition, current flows through both windings.The solenoid plunger is pulled in, and the contactsare closed. This applies battery voltage to bothends of the pull-in winding, and current through itstops. The magnetic field of the hold-in winding isenough to keep the plunger in place. This circuitryreduces the solenoid current draw during crank-ing, when both the starter motor and the ignitionsystem are drawing current from the battery.

The solenoid plunger action, transferredthrough the shift lever, pushes the pinion gear intomesh with the flywheel ring gear (Figure 9-44).When the starter motor receives current, itsarmature begins to turn. This motion is trans-ferred through the overrunning clutch and piniongear to the engine flywheel.

The teeth on the pinion gear may not immedi-ately mesh with the flywheel ring gear. If this hap-pens, a spring behind the pinion compresses so thatthe solenoid plunger can complete its stroke. Whenthe motor armature begins to turn, the pinion teethline up with the flywheel, and spring force pushesthe pinion to mesh.

The Delco-Remy MT series, as shown inFigure 9-45, is the most common example of thistype of starter motor and has been used fordecades on almost all GM cars and light trucks.While this motor is manufactured in different sizes

Figure 9-41. The ring-gear-to-pinion-gear ratio isabout 20 to 1.

Figure 9-42. A typical solenoid-actuated drive.

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Figure 9-44. The movement of the solenoid plungermeshes the pinion gear and the flywheel ring gear.

RETURN SPRING

PLUNGERRUBBERGASKET

GROMMET

BUSHING

SOLENOID

SHIFT LEVER

PINIONSTOP

OVERRUNNINGCLUTCH

ASSISTSPRING

FIELDCOIL

ARMATURE

Figure 9-45. The Delco-Remy solenoid-actuated drivemotor. (Delphi Automotive Systems)

Figure 9-46. Delco-Remy provides differently con-nected starter motors for use with various engines.(GM Service and Parts Operations)

for different engines (Figure 9-46), the most com-mon application is a four-pole, four-brush design.

The solenoid plunger action, in addition toengaging the pinion gear, closes contact pointsto complete the starter circuit. To avoid closingthe contacts before the pinion gear is fullyengaged, the solenoid plunger is in two pieces(Figure 9-47). When the solenoid windings aremagnetized, the first plunger moves the shiftlever. When the pinion gear reaches the fly-wheel, the first plunger has moved far enough totouch the second plunger. The first plunger con-

tinues to move into the solenoid, pushing thesecond plunger against the contact points.

A similar starter design has been used by Fordon diesel engines and older large-displacementV8 gasoline engines. It operates in the same wayas the starter just described. The solenoid actioncloses a set of contact points.

Because Ford installs a remotely mountedmagnetic switch in all of its starting circuits, thesolenoid contact points are not required to con-trol the circuit. The solenoid contact points arephysically linked, so that they are always“closed.”

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Figure 9-48. Circuit diagram of a system using amovable-pole-shoe starter.

Figure 9-47. The Delco-Remy solenoid plunger is intwo pieces. (Delphi Automotive Systems)

In the early 1970s, Chrysler also manufacturedfully enclosed direct-drive starter motor. It works inthe same way as the solenoid-actuated starters pre-viously described. The solenoid plunger closes con-tact points to complete the motor circuitry, but thesystem also has a remotely mounted starter relay.Reduction-drive starters are usually compoundmotors. Most Bosch and all Japanese starter motorsoperate on the same principles.

Solenoid-Actuated,Reduction DriveThe Chrysler solenoid-actuated, reduction-drivestarter uses a solenoid to engage the pinion with theflywheel and close the motor circuit. The motorarmature does not drive the pinion directly, how-ever; it drives a small gear that is permanentlymeshed with a larger gear. The armature-gear-to-reduction-gear ratio is between 2 and 3.5 to 1,depending upon the engine application. This allowsa small, high-speed motor to deliver increasedtorque at a satisfactory cranking rpm. Solenoid andstarter drive operation is basically the same as asolenoid-actuated, direct-drive starter.

Movable-Pole-Shoe DriveManufactured by the Motorcraft Division of Ford,the movable-pole-shoe starter motor is used on

most Ford automobiles (Figure 9-48). One of themotor-pole shoes pivots at the drive end housing.The field winding of this shoe also contains aholding coil, wired in parallel and independentlygrounded. When the starter relay is closed, batterycurrent flows through the field windings and theholding coil of the pole shoe to ground. This cre-ates a strong magnetic field, and the pole shoe ispulled down into operating position. The motion istransferred through a shift lever, or drive yoke, tomesh the pinion gear with the ring gear.

When the pole shoe is in position, it opens a setof contacts. These contacts break the ground con-nection of the field windings. Battery current isallowed to flow through the motor’s internal cir-cuitry, and the engine is cranked. During crank-ing, a small amount of current flows through theholding coil directly to ground to keep the shoeand lever assembly engaged.

An overrunning clutch prevents the startermotor from being turned by the engine. When theignition switch moves out of the start position,current no longer flows through the windings ofthe movable pole shoe or the rest of the motor.Spring force pulls the shoe up, and the shift leverdisengages the pinion from the flywheel.

Permanent-MagnetPlanetary DriveThe high-speed, low-torque permanent-magnetplanetary-drive motor operates the drive mecha-nism through gear reduction provided by a simpleplanetary gearset. Figure 9-49 shows the Boschgear reduction design, which is similar to thatused in Chrysler starters. Figure 9-50 shows the

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Starting System Operation 203

Figure 9-50. Delco-Remy permanent-magnet, gear-reduction starter components. (Delphi AutomotiveSystems)

Figure 9-49. Bosch permanent-magnet gear-reduction starter components. (Reprinted by permissionof Robert Bosch GmbH)

drive pinion. An internal ring gear is keyed to thefield frame and held stationary in the motor. Thearmature shaft drives the sun gear for the plane-tary gearset. The sun gear meshes with three plan-etary pinions, which drive the pinion carrier inreduction as they rotate around the ring gear. Thestarter driveshaft is mounted on the carrier anddriven at reduced speed and increased torque.This application of internal gear reductionthrough planetary gears delivers armature speedsin the 7,000-rpm range. The armature and drive-shaft ride on roller or ball bearings rather thanbushings.

Permanent-magnet, planetary-drive startersdiffer mechanically in how they do their job, buttheir electrical wiring is the same as that used inthe field-coil designs (Figure 9-51).

Although PMGR motors are lighter in weightand simpler to service than traditional designs,they do require special handling precautions. Thematerial used for the permanent magnet fields isquite brittle. A sharp impact caused by hitting ordropping the starter can destroy the fields.

OVERRUNNINGCLUTCHRegardless of the type of starter motor used, whenthe engine starts and runs, its speed increases. Themotor must be disengaged from the engine assoon as the engine is turning more rapidly thanthe starter motor that has cranked it. With amovable-pole-shoe or solenoid-actuated drive,however, the pinion remains engaged until powerstops flowing to the starter. In these applications,

Figure 9-51. Field coils and permanent-magnetstarters use the same electrical wiring.

gear reduction design used in the Delco-Remypermanent-magnet, gear-reduction (PMGR)starter. All PMGR starter designs use a solenoidto operate the starter drive and close the motorarmature circuit. The drive mechanism is identi-cal to that used on other solenoid-actuated startersalready described. Some models, however, uselightweight plastic shift levers.

The planetary gearset between the motor arma-ture and the starter drive reduces the speed andincreases the torque at the drive pinion. The com-pact gearset is only 1/2 to 3/4 inch (13 to 19 mm)deep and is mounted inline with the armature and

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Figure 9-53. The operation of an overrunning clutch.

Figure 9-52. Cutaway view of an overrunning clutch.

the starter is protected by an over-running clutch(Figure 9-52).

The overrunning clutch consists of rollersthat ride between a collar on the pinion gear andan outer shell. The outer shell has tapered slotsfor the rollers so that the rollers either ride freelyor wedge tightly between the collar and the shell.Figure 9-53 shows the operation of an overrun-ning clutch. In Figure 9-53A, the armature isturning, cranking the engine. The rollers arewedged against spring force into their slots. InFigure 9-53B, the engine has started and is turn-ing faster than the motor armature. Spring forcepushes the rollers so that they float freely. Theengine’s motion is not transferred to the motorarmature. These devices are sometimes calledone-way clutches because they transmit motionin one direction only.

Once the engine starts, the ignition switch is tobe released from the start position. The solenoidhold-in winding is demagnetized, and a returnspring moves the plunger out of the solenoid. Thismoves the shift lever back so that the overrunningclutch and pinion gear slide away from the fly-wheel. For more information about overrunningclutches, see the following sections of Chapter 9in the Shop Manual, “Bench Tests” and “StarterMotor Overhaul Procedure.”

SUMMARYElectrical starting systems consist of a high-current starter circuit controlled by a low-currentcontrol circuit. The ignition switch includes con-tacts that conduct battery current to the magneticswitch. The magnetic switch may be a relay or asolenoid and may have other jobs besides con-trolling the starter circuit current flow. Thestarter motor and connecting wires are alsoincluded in the system. Variations are commonamong the starting systems used by the variousmanufacturers. Magnetic repulsion occurs whena straight-rod conductor composed of the arma-ture, commutator, and brushes is located in amagnetic field (field windings) and current isflowing through the rod.

When the starter operates, the current passingthrough the armature produces a magnetic field ineach of its conductors. The reaction between themagnetic field of the armature and the magneticfields produced by the field coils causes the arma-ture to rotate.

Traditional starter motors have pole pieceswound with heavy copper field windings attachedto the housing. A new design, the permanent-magnet planetary drive, uses small permanentmagnets to create a magnetic field instead of polepieces and field windings.

One end housing holds the brushes; the otherend housing shields the pinion gear. The motorarmature windings are installed on a laminatedcore and mounted on a shaft. The commutatorbars are mounted on, but insulated from, the shaft.

The solenoid-actuated drive uses the move-ment of a solenoid to engage the pinion gear withthe ring gear. Delco-Remy, Chrysler, Motorcraft,and many foreign manufacturers use this type ofstarter drive. The movable-pole-shoe drive, usedby Ford, has a pivoting pole piece that is movedby electromagnetism to engage the pinion gear

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with the ring gear. In the planetary-gear driveused by Chrysler, Ford, and GM, an armature-shaft sun gear meshes with the planetary pinions,which drive the pinion carrier in reduction asthey rotate around the ring gear. The starter

driveshaft is mounted on the carrier and driven atreduced speed and increased torque. An overrun-ning clutch is used with all starter designs to pre-vent the engine from spinning the motor anddamaging it.

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206 Chapter Nine

Review Questions1. All of these are part of the control circuit

except:a. A starting switchb. An OCP thermostatc. A starting safety switchd. A magnetic switch

2. Which of the following is a component of astarting circuit?a. Magnetic switchb. Ballast resistorc. Voltage regulatord. Powertrain control module (PCM)

3. Two technicians are discussing theoperation of a DC automotive starter.Technician A says the principle of magneticrepulsion causes the motor to turn.Technician B says the starter uses amechanical connection to the engine thatturns the armature. Who is right?a. A onlyb. B onlyc. Both A and Bd. Neither A nor B

4. All of these are part of a starter motorexcept:a. An armatureb. A commutatorc. Field coilsd. A regulator

5. The starting system has _________ circuitsto avoid excessive voltage drop.a. Twob. Threec. Fourd. Six

6. The starter circuit consists of which of thefollowing?a. Battery, ignition switch, starter motor,

large cablesb. Battery, ignition switch, relays or

solenoids, large cablesc. Battery, magnetic switch, starter motor,

primary wiringd. Battery, magnetic switch, starter motor,

large cables

7. Which of the following is not part of thestarter control circuit?a. The ignition switchb. The starting safety switch

c. The starter relayd. The starter motor

8. The ignition switch will not remain in whichof the following positions?a. ACCESSORIESb. OFFc. ON (RUN)d. START

9. The starting safety switch is also called a:a. Remote-operated switchb. Manual-override switchc. Neutral-start switchd. Single-pole, double-throw switch

10. Safety switches are most commonly usedwith:a. Automatic transmissionsb. Imported automobilesc. Domestic automobilesd. Manual transmissions

11. Starting safety switches used with manualtransmissions are usually:a. Electricalb. Mechanicalc. Floor-mountedd. Column-mounted

12. Which of the following is not true ofsolenoids?a. They use the electromagnetic

field of a coil to pull a plunger intothe coil.

b. They are generally used to engagethe starter motor with the engineflywheel.

c. They operate with a movableplunger and usually do amechanical job.

d. They send electronic signals to thecontrol module and have nomoving parts.

13. Starter motors usually have how many poleshoes?a. Twob. Fourc. Sixd. Eight

14. The rotational force of a starter motor is:a. Polarizedb. Rectified

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Starting System Operation 207

(Delphi Automotive Systems)

c. Torqued. Current

15. Which of the following is true of a shuntmotor?a. It has high initial torque.b. It operates at variable speed.c. It has only one path for current flow.d. It is not often used as a starting motor.

16. Which of the following is true of acompound motor?a. It has low initial torque.b. It operates at variable speeds.c. It has only one path for current flow.d. It is often used as a starting motor.

17. In a lap-wound motor armature, thetwo ends of each conductor areattached to commutator segmentsthat are:a. Adjacentb. 45 degrees apartc. 90 degrees apartd. 180 degrees apart

18. Most automotive starters have ________grounded and ________ insulatedbrushes.a. 2, 2b. 2, 4c. 4, 4d. 4, 8

19. The ratio between the number of teeth onthe flywheel and the motor pinion gear isabout:a. 1:1b. 5:1c. 20:1d. 50:1

20. The overrunning clutch accomplishes whichof the following?a. Separates the starter motor from the

starter solenoidb. Brings the starter motor into contact with

the ignition circuitc. Lets the starter motor rotate in either

directiond. Protects the starter motor from spinning

too rapidly

21. A starting motor must have ____________brushes as poles.a. The same number ofb. Twice as many

22. The preceding illustration shows a:a. Permanent-magnet planetary-gear

starterb. Movable-pole-shoe starterc. Direct-drive, solenoid-actuated starterd. Reduction-gear drive, solenoid-actuated

starter

23. Which type of starter drive is not used onlate-model cars?a. Direct driveb. Bendix drivec. Reduction drived. Planetary drive

24. A solenoid uses two coils. Their windingsare called:a. Push-in and pull-outb. Pull-in and push-outc. Push-in and hold-outd. Pull-in and hold-in

25. Which of the following is true of a reductiondrive?a. The motor armature drives the pinion

directly.b. The sun gear is mounted on the

armature shaft.c. The overrunning clutch reduces battery

current.d. The small gear driven by the armature

is permanently meshed with a largergear.

c. One-half as manyd. Three times as many

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208 Chapter Nine

26. The planetary drive starter uses:a. Permanent magnetsb. Field coilsc. Both A and Bd. Neither A nor B

27. Which of the following is not required of apermanent magnet starter?a. Brush testingb. Commutator testingc. Field circuit testingd. Armature testing

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