Chapter 7 Diesel Engine Sart Ting Systems

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chapter 7Diesel Engine Starting SystemsLearning ObjectivesKey TermsAfter reading this chapter, the student shouldArmature 220Hold in 240be able to:Field coil 220Starter interlock 234Brushes 220Starter relay 225Commutator 223Disconnect switch 2371. Identify all main components of a diesel enginestarting system2. Describe the similarities and differencesPull in 240 between air, hydraulic, and electric startingsystems3. Identify all main components of an electricstarter motor assembly4. Describe how electrical current flows throughan electric starter motor5. Explain the purpose of starting systemsinterlocks6. Identify the main components of a pneumaticstarting system7. Identify the main components of a hydraulicstarting system8. Describe a step-by-step diagnostic procedurefor a slow cranking problem9. Describe a step-by-step diagnostic procedurefor a no crank problem10. Explain how to test for excessive voltage dropin a starter circuit216M07 HEAR3623 01 SE C07.indd 21607/01/15 8:26 PM

IntroductionSafety Firstable to get the job done. Many large diesel engines will use a24V starting system for even greater cranking power. SeeSome specific safety concerns related todiesel engine starting systems are as follows:Figure 7–2 for a typical arrangement of a heavy-duty electricstarter on a diesel engine.A diesel engine needs to rotate between 150 and 250 rpm Battery explosion riskto start. The purpose of the starting system is to provide the Burns from high current flow through battery cablestorque needed to achieve the necessary minimum cranking Strain injuries from lifting heavy starters and batteries(some are over 65 lb)speed. As the starter motor starts to rotate the flywheel, thecrankshaft is turned, which then starts piston movement. Fora small four-cylinder engine, there doesn’t need to be a great Burns from battery electrolyte Fire hazards from sparks and hot wires Unexpected cranking or starting of engineneeded to get the required cranking speed. Some heavy-duty Injuries from sudden release of stored energy (electrical,24V starters will create over 200 ft-lb of torque. This torquehydraulic, air pressure)then gets multiplied by the gear reduction factor between thedeal of torque generated by a starter. But as engines get morecylinders and bigger pistons, a huge amount of torque will bestarter motor pinion gear and ring gear on the engine’s fly-The Importance of Starting SystemsA func-tional machine needs a running engine, and if the enginewheel. This is usually around 20:1. See Figure 7–3 for howa starter assembly pinion engages with the flywheel ring gear.doesn’t crank, it doesn’t start. A properly operating and reliable starting system is a must for keeping a machine productive. For many years, diesel engines have mostly used electricmotors to crank them over to start the combustion process.For some applications, an air or hydraulic motor will create thetorque needed to turn the engine over.Many years ago, diesel engines were sometimes startedwith a smaller gas engine called a pup engine. See Figure7–1 for a pup engine on an older diesel engine. Another way toget a diesel engine started was to start it on gasoline and thenswitch it over to run on diesel fuel. This was a complex solutionto a simple task because the engine had to have a way to varyits compression ratio, and it needed a spark ignition systemand a carburetor. As 12V electrical systems became more popular and electric motor design improved, electric starters wereFigure 7–1 A pup engine starter motor.Figure 7–2 A typical arrangement of a heavy-duty electricstarter on a diesel engine.Figure 7–3 A starter assembly engaging with a flywheel ringgear.D iese l E n g i n e S t a rtin g S y st em sM07 HEAR3623 01 SE C07.indd 21721707/01/15 8:26 PM

This engine cranking task is much more difficult in coldertemperatures especially if the engine is directly driving othermachine components such as hydraulic pumps, a torque converter, or a PTO (power take-off) drive shaft. Cold engine oiladds to the load on the starter, and this load may increaseby three to four times what it would normally be in warmerweather. Engine oil that is the wrong viscosity (too thick) for thetemperature will greatly increase the engine’s rolling resistance.Adding to this problem is the fact that a battery is less efficientin cold temperatures.When engineers design a cranking system, they must takeinto account cold weather cranking conditions and will quiteoften offer a cold weather starting option. This would likely include one or more of the following: bigger or more batteries,higher output starter, larger battery cables, battery blankets,oil heaters, diesel fired coolant heater, electric immersion coolant heater (block heater), and one or more starting aids like anether injection system or an inlet heater.One more recent difficulty added to starting systems isa result of electronic controls on some engines. Some ECMsmay need to see a minimum number of engine revolutions ata minimum speed before it will energize the fuel system. Thisequates to longer cranking times and more strain on the cranking system. Some electronic engines will crank for five secondsFigure 7–4 A double starter assembly arrangement.or longer even when the engine is warm before the ECM startsto inject fuel and the engine starts.It’s important that a machine’s starting system worksSome larger engines will need two or more startersproperly and you should be aware of how the main compo-to do this. Some starters for large diesel engines will createnents of a system work. This will give you the knowledgeover 15 kW or 20 hp! See Figure 7–4 for a double starterneeded to make a proper diagnosis when you get a complaintarrangement.of an engine cranking slowly or not at all.When a starter motor starts to turn the engine over, itsIf an engine doesn’t start, then a machine isn’t working,pistons start to travel up in the cylinders on compressionand instead of making money, it’s costing money. The betterstroke. There needs to be between 350 and 600 psi of pressureyou know how to diagnose and repair a starting system prob-created on top of the piston. This is the main resistance thatlem, the more valuable you will be as an HDET. There are lotsthe starter has to overcome. This pressure is what is neededof technicians who are good at changing starters whether theto create the necessary heat in the cylinder so that when fuelstarter is faulty or not. Many times the cause of a starting com-is injected it will ignite. If the starting system can’t crank theplaint is something other than the starter.engine fast enough, then the compression pressure and heatIf a starter is used properly, it will last for well over 10,000won’t be high enough to ignite the fuel. If the pistons are mov-starts. The biggest factor in reducing the life of an electricing too slowly, there will be time for the compression to leak bystarter is overheating from over-cranking. Never run the starterthe piston rings. Also the rings won’t get pushed against thefor more than a 30-second stretch, and if it does run that long,cylinder, which again allows compression pressure to leak intothen wait at least two minutes between cranks to allow thethe crankcase. When this happens, the engine won’t start orstarter to cool.it starts with incomplete combustion. Incomplete combustionFor engines up to 500 hp, electric starting systems willequals excessive emissions. This is another reason to have abe used for 99% of the applications. For any size engine, airproperly operating starting system.and hydraulic starting systems are an option; however, they willThe faster a starter can crank a diesel engine, the faster itstarts and the quicker it runs clean.218likely only be used for special applications and usually for engines over 500 hp.Chapte r 7M07 HEAR3623 01 SE C07.indd 21807/01/15 8:26 PM

We’ll first examine the different electric starter motor de-Tech Tipsigns, next discuss air and hydraulic starter motors, and thenThis chapter focuses on diesel engine starting sys-look at the control circuit for starters.tems because at this time they are the most populartype of engine used for heavy equipment. However,there may be some other types of engines used in thefuture such as natural gas–powered engines.Natural gas engines are used for many stationaryElectric StarterMotor Assemblypower applications, and many are similar to dieselengines but with lower compression ratios, differentAn electric starter will take stored electrical energy from a bat-fuel system, and a spark ignition system. Becausetery (or sometimes a capacitor) and convert it into torque atof the lower compression ratio, they will put a lowerthe starter’s pinion gear. The pinion then engages with the ring demand on the starting system.gear that is part of the engine’s flywheel and turns the flywheelthat rotates the engine’s crankshaft. See Figure 7–5 for acutaway of a starter and its main parts.There are two main types of electric starter motorThe job of any starter motor assembly is to take a storedassemblies:energy (electric, air, or hydraulic) and convert it into mechanicalDirect drive (pinion is driven directly by the arma-rotation to crank the engine fast enough to begin the engine’sture): A direct drive electric starter has a motor thatignition sequence.is designed to generate high torque at low speed andoperate at high speed with low torque (the motor willsometimes exceed 5000 rpm) for a short length of time.Need to KnowIt will use a solenoid actuated shift lever to push outthe pinion to engage it with the ring gear before or justas the armature (rotating shaft in the motor assembly)The most common type of starting system uses electrical en-starts turning.ergy; however, compressed air and hydraulic energy can beGear reduction (higher speed motor output to a gearused as well.reduction and then to pinion): A gear reductionThe following are the main comparable components ofstarter (planetary or pinion reduction) is designed tothe three main types of starting systems:use a smaller higher speed electric motor to producehigher cranking torque with the same or less electricalElectric Starting Air StartingSystemSystemHydraulicStarting Systempower consumed. The heaviest and bulkiest part of aElectric starter motor assemblyAir motor starterassemblyHydraulic motorstarter assemblysize and weight the engineers have saved space andBattery cablesAir linesHydraulic hosesas a comparable output gear reduction starter. Al-Starter relayRelay valveDirectional controlvalveStarter interlocksystemStarter interlocksystemStarter interlocksystemBattery(ies) orcapacitorAir tankHydraulicaccumulatorStarter switchStarter switch orvalveStarter switch orvalveWiring harnessWiring harness(optional)Wiring harness(optional)direct drive starter is the motor so by reducing motorweight. Some direct drive starters are twice the weightthough this isn’t a big concern for a large machine, youwill be thankful for the lighter weight whenever it comestime to change the starter.Gear reduction starter motor assemblies can havetheir motor offset from the output shaft or use planetarygears and have the motor shaft in-line with the outputshaft.Direct Drive Starter Components Starter housing: Center section that holds the pole shoesand field coils in place.D iese l E n g i n e S t a rtin g S y st em sM07 HEAR3623 01 SE C07.indd 21921907/01/15 8:26 PM

Figure 7–5 An electric starter cutaway (Halderman, Automotive Technology, 5th ed.,Fig. 52–18). Nose piece: The drive end of the starter where the pinion gear is located. Holds the shift lever in place and supports the armature shaft with a bushing. magnetic field when current flows through them. End cap: Opposite end of the starter from the nose piece.Supports brush holder assembly and the other armature Pole shoes: Iron cores for the field coils that help to increase magnetism. shaft bushing. Field coils: Heavy copper windings that create a strongSolenoid: Has two windings (pull-in and hold-in) that getenergized by the starter control circuit and magneticallyArmature: The rotating part of the motor that has severalmove a plunger. The plunger is connected to a heavywindings that have each of their ends loop to a commu-contact disc that is a switch. The switch will send currenttator bar. It will have splines to drive the starter drive.from the battery terminal to the field coils. The plungerBrushes: Contact the commutator bars and transfercould also be connected to a shift lever that will move theelectrical current to the armature.pinion.Brush holders: Spring loaded to keep the brushes in contact with the armature.220 Pinion gear: The starter output that engages with the flywheel and cranks the engine.Chapte r 7M07 HEAR3623 01 SE C07.indd 22007/01/15 8:26 PM

Overrunning clutch: Drives the pinion from the armature shaft output that will drive an intermediate gear that drives theShift lever: Used to push the pinion out to engage withpinion gear shaft.the ring gear. Motor components (armature, brushes, brush holder,field coils, pole shoes) are the same as a direct drivestarter.Solenoid: The solenoid performs the same electrical functions as the direct drive starter but may directly pushGear Reduction Starter Components Gear reduction: The armature shaft will have a gearbut will not allow the armature to be driven by the ring gear.the pinion gear out. Overrunning clutch: Same as direct drive. SeeFigure 7–6 for a gear reduction starter.Figure 7–6 A gear reduction starter (Halderman, Automotive Technology, 5th ed.,Fig. 52–20).D iese l E n g i n e S t a rtin g S y st em sM07 HEAR3623 01 SE C07.indd 22122107/01/15 8:26 PM

Figure 7–7 Current flow causing opposing magnetic fields(Halderman, Automotive Technology, 5th ed., Fig. 47–11 or52–8).Electric Motor Operation The action of the motor section of the electric starter assembly is the same as anybrush-type motor used on a heavy equipment machine. Someother applications of motors that use brushes could be supplementary steering or brake pump motors, windshield wipermotors, and hood lift motors.The basic principle behind any electric motor operation is the arranging of opposing magnetic fields so that rotation is created. This is the same force that will try to keeptwo like poles of permanent magnets apart. If you have everplayed with magnets, you will be familiar with this force. See Figure 7–7 for how current flow can cause opposing magnetic fields.As discussed in Chapter 5, if current is flowing through aconductor, then there will be a magnetic field created aroundthe conductor. If you want to build a stronger magnetic field,then loop an insulated wire into coils, put an iron core throughthe middle of the coil, and increase the current flow throughthe wire.If opposing or attracting magnetic fields can be arrangedbetween two components, then relative motion occurs. This ofcourse can only happen if the magnetic forces are strong enoughto overcome the resistance that it is opposing. Opposing magnetic fields are also used to make solenoid plungers move.We’ll start to look at a simple motor with one pair of fieldcoils and an armature with one loop of wire. In a simple DCelectric starter motor, one magnetic field is created in the stationary motor housing and is generated between a pair of fieldcoil/pole shoe electromagnets. See Figure 7–8 for the fieldcoils/pole shoes in a starter motor housing. The pole shoes areFigure 7–8 The field coils/pole shoes in a starter motorhousing (Halderman, Automotive Technology, 5th ed., Fig.52–6).the iron core of the electromagnet, and when the field coils areenergized, a strong magnetic field is created. One field coil willwith a thin varnish to keep the loops insulated from itself andact like a north pole and the field coil opposite will act like afrom the pole shoe. If this insulation fails, there will be a shortsouth pole. This magnetic field is like the field occurring be-circuit fault.tween the ends of a horseshoe magnet. The field windings areThe other magnetic field in the simple starter motor isheavy flat copper and appear to be bare wire but are coatedcreated in a loop of wire (winding) that is the armature. The222Chapte r 7M07 HEAR3623 01 SE C07.indd 22207/01/15 8:26 PM

Web ActivitySearch the Internet for homemade electric motorsand you will see a variety of simple designs. Why notsee if you can make your own motor. Hopefully curiosity will get the better of you. This will also help youto understand how magnetism and electricity worktogether to make mechanical movement.It’s not hard to make an electric motor. SeeFigure 7–10 for a simple homemade motor. Thefield magnets are permanent magnets but could bemade stronger with field coils.Figure 7–9 How do the armature winding interact with thefield poles (Halderman, Automotive Technology, 5th ed., Fig.52–6)?armature operates inside the magnetic field that has been created by the field coil/pole shoes. When the armature winding isenergized, its surrounding magnetic field interacts with the poleshoe/field coil magnetic field. The armature shaft is supportedon two bearings in each end of the motor assembly to allowrotation. When the two opposing magnetic fields create an unbalance, the armature will rotate to try to become magneticallybalanced. If the magnetic fields are timed correctly to opposeeach other at the proper location, then the armature will rotate.In other words, as the loop of armature winding is energized,Figure 7–10 A simple homemade electric motor.it will have a surrounding magnetic field on each of the twolongest sections of the winding that run parallel to the armatureshaft. These sections of the winding will react to the field coils’ Seemagnetic fields and the reacting force will try to push the ar-of wire are embedded into the core. Each end of an armaturemature winding away. As the armature rotates, the winding willwinding is connected to one commutator bar. The commuta-have its direction of current flow reverse as soon as the endstor bars are insulated from each other but are exposed on theirof the winding swap places with the brushes feeding it current.outer surface to allow connection to the motor brushes. YouThis allows the same loop of wire to be continuously pushedshould also note that the windings are offset to the commuta-away from the field coil magnetic field. See Figure 7–9 fortor bars that they connect to. This is to place the winding at thehow the armature winding interacts with the field poles.correct location relative to the field coil magnetic field so thatThe armature shaft is the rotating output of any electricmotor. The armature windings are embedded into grooves thatFigure 7–11 for a typical armature and how the loopsmaximum torque is created on the armature by the opposingmagnetic fields.run along the length of the armature core. The armature coreYou’ve probably noticed by looking at the photo of theserves the same purpose as the field coils/pole shoes—thatarmature that there is more than one loop of wire and moreis, to increase the magnetic field surrounding the energizedthan one set of commutator bars. To provide continuous and windings. The windings are insulated from each other and fromsteady rotation of an electric motor, there needs to be a con-the core by a thin coat of varnish. Shorts and grounds maystant opposing magnetic field. As more windings are addedoccur if this varnish coating fails and exposes the bare copper.to the armature, it’s possible to do this. As one loop of wire’sD iese l E n g i n e S t a rt in g S y st em sM07 HEAR3623 01 SE C07.indd 22322307/01/15 8:26 PM

Figure 7–11 A typical armature and how the loops of wireare embedded into the core.Web ActivitySearch the Internet for commutation and see if youcan find an animation of an electric motor working.Figure 7–13 A set of brusher leads.This should help you understand the interaction between the armature windings, commutato

ular and electric motor design improved, electric starters were able to get the job done. many large diesel engines will use a 24V starting system for even greater cranking power. see Figure 7–2 for a typical arrangement of a heavy-duty electric starter on a diesel engine. A diesel engine needs to rotate between 150 and 250 rpm

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