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AUT 242 – Automotive Electricity II

AUT 242 – Automotive Electricity II. Chapter 19 Cranking System. OBJECTIVES. After studying Chapter 19, the reader will be able to: Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “C” (Starting System Diagnosis and Repair).

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AUT 242 – Automotive Electricity II

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  1. AUT 242 – Automotive Electricity II Chapter 19 Cranking System

  2. OBJECTIVES After studying Chapter 19, the reader will be able to: • Prepare for ASE Electrical/Electronic Systems (A6) certification test content area “C” (Starting System Diagnosis and Repair). • Describe how the cranking circuit works. • Discuss how a starter motor converts electrical power into mechanical power. • Describe the hold-in and pull-in windings of a starter solenoid.

  3. Armature Brush-end housing Brushes CEMF Commutator-end housing Commutator segments Compression spring Drive-end housing Field coils Field housing Field poles Ground brushes Hold-in winding Insulated brushes Mesh spring Neutral safety switch Overrunning clutch PM starter Pole shoes Pull-in winding RVS Starter drive Starter solenoid Through bolts KEY TERMS

  4. CRANKING CIRCUITPARTS INVOLVED • Modern cranking circuits include the following: • Starter motor • Battery • Starter solenoid or relay • Starter drive • Ignition switch

  5. CRANKING CIRCUITPARTS INVOLVED • Some column-mounted ignition switches act directly on the electrical ignition switch itself, whereas others use a link from the lock cylinder to the ignition switch

  6. CRANKING CIRCUITCONTROL CIRCUIT PARTS AND OPERATION • The engine is cranked by an electric motor that is controlled by a key-operated ignition switch. • The ignition switch will not operate the starter unless the automatic transmission is in neutral or park, or the clutch pedal is depressed on manual transmission/transaxle vehicles. • This is to prevent an accident that might result from the vehicle moving forward or rearward when the engine is started.

  7. CRANKING CIRCUITCONTROL CIRCUIT PARTS AND OPERATION • To prevent the engine from cranking, an electrical switch is usually installed to open the circuit between the ignition switch and the starter solenoid.

  8. COMPUTER-CONTROLLED STARTINGOPERATION • Some key-operated ignition systems and most push-button-to-start systems use the computer to crank the engine. • The ignition switch start position on the push-to-start button is used as an input signal to the powertrain control module (PCM). • Before the PCM cranks the engine, the following conditions must be met. • The brake pedal is depressed. • The gear selector is in park or neutral. • The correct key fob (code) is present in the vehicle.

  9. COMPUTER-CONTROLLED STARTINGOPERATION • Instead of using an ignition key to start the engine, some vehicles are using a start button which is also used to stop the engine, as shown on this Jaguar.

  10. COMPUTER-CONTROLLED STARTINGREMOTE STARTING • Remote starting, sometimes called remote vehicle start (RVS) , is a system that allows the driver to start the engine of the vehicle from inside the house or a building at a distance of about 200 ft (65 m).


  12. STARTER MOTOR OPERATIONPRINCIPLES • This series-wound electric motor shows the basic operation with only two brushes: one hot brush and one ground brush. • The current flows through both field coils, then through the hot brush and the loop winding of the armature, before reaching ground through the ground brush.

  13. STARTER MOTOR OPERATIONPRINCIPLES • The interaction of the magnetic fields of the armature loops and field coils creates a stronger magnetic field on the right side of the conductor, causing the armature loop to move toward the left.

  14. STARTER MOTOR OPERATIONPRINCIPLES • The armature loops rotate due to the difference in the strength of the magnetic field. • The loops move from a strong magnetic field strength toward a weaker magnetic field strength.

  15. STARTER MOTOR OPERATION • Magnetic lines of force in a four-pole motor.

  16. STARTER MOTOR OPERATIONPRINCIPLES • A pole shoe and field winding.

  17. STARTER MOTOR OPERATION • This wiring diagram illustrates the construction of a series-wound electric motor. • Notice that all current flows through the field coils, then through the armature (in series) before reaching ground. • This winding produces maximum torque at 0-RPM. • This wiring diagram illustrates the construction of a shunt-type electric motor, and shows the field coils in parallel (or shunt) across the armature.

  18. STARTER MOTOR OPERATION • A compound motor is a combination of series and shunt types, using part of the field coils connected electrically in series with the armature and some in parallel (shunt).


  20. HOW THE STARTER MOTOR WORKS • Pole shoes and field windings installed in the housing.

  21. HOW THE STARTER MOTOR WORKS • A typical starter motor armature. • The armature core is made from thin sheet metal sections assembled on the armature shaft, which is used to increase the magnetic field strength.

  22. HOW THE STARTER MOTOR WORKS • An armature showing how its copper wire loops are connected to the commutator.

  23. HOW THE STARTER MOTOR WORKS • A cutaway of a typical starter motor showing the commutator, brushes, and brush spring.

  24. Don’t Hit That Starter! • In the past, it was common to see service technicians hitting a starter in their effort to diagnose a no-crank condition. • Often the shock of the blow to the starter aligned or moved the brushes, armature, and bushings. • Many times, the starter functioned after being hit, even if only for a short time.

  25. Don’t Hit That Starter! • However, most starters today use permanent magnet fields, and the magnets can be easily broken if hit. • A magnet that is broken becomes two weaker magnets. • Some early PM starters used magnets that were glued or bonded to the field housing. • If struck with a heavy tool, the magnets could be broken with parts of the magnet falling onto the armature and into the bearing pockets, making the starter impossible to repair or rebuild.

  26. Don’t Hit That Starter! • This starter permanent magnet field housing was ruined when someone used a hammer on the field housing in an attempt to “fix” a starter that would not work. • A total replacement is the only solution in this case.

  27. GEAR-REDUCTION STARTERSPURPOSE AND FUNCTION • Gear-reduction starters are used by many automotive manufacturers. • The purpose of the gear reduction (typically 2:1 to 4:1) is to increase starter motor speed and provide the torque multiplication necessary to crank an engine.

  28. STARTER DRIVESPURPOSE AND FUNCTION • A starter drive includes small pinion gears that mesh with and rotate the larger gear on the engine flywheel or flex plate for starting. • The pinion gear must engage with the engine gear slightly before the starter motor rotates, to prevent serious damage to either the starter gear or the engine, but must be disengaged after the engine starts.

  29. STARTER DRIVESPURPOSE AND FUNCTION • A cutaway of a typical starter drive showing all of the internal parts.


  31. STARTER DRIVESGear Ratio • The ring gear to pinion gear ratio is usually 15:1 to 20:1.

  32. STARTER DRIVESOperation • Operation of the overrunning clutch. • (a) Starter motor is driving the starter pinion and cranking the engine. The rollers are wedged against spring force into their slots. • (b) The engine has started and is rotating faster than the starter armature. Spring force pushes the rollers so they can rotate freely.

  33. What Is a Bendix? • Older-model starters often used a Bendix drive mechanism, which used inertia to engage the starter pinion with the engine flywheel gear. • Inertia is the tendency of a stationary object to remain stationary, because of its weight, unless forced to move. • On these older-model starters, the small starter pinion gear was attached to a shaft with threads, and the weight of this gear caused it to be spun along the threaded shaft and mesh with the flywheel whenever the starter motor spun. • If the engine speed was greater than the starter speed, the pinion gear was forced back along the threaded shaft and out of mesh with the flywheel gear. • The Bendix drive mechanism has generally not been used since the early 1960s, but some technicians use this term when describing a starter drive.

  34. POSITIVE-ENGAGEMENT STARTERS • Positive-engagement starters, used on many older Ford engines, utilize the shunt coil winding and a movable pole shoe to engage the starter drive.

  35. POSITIVE-ENGAGEMENT STARTERS • The movable pole shoe is held down (which keeps the starter drive engaged) by a smaller coil on the inside of the main drive coil. A circuit diagram of a Ford system using a movable-pole-shoe starter.

  36. SOLENOID-OPERATED STARTERS • Wiring diagram of a typical starter solenoid. • Notice that both the pull-in winding and the hold-in winding are energized when the ignition switch is first turned to the “start” position. • As soon as the solenoid contact disk makes electrical contact with both the B and M terminals, the battery current is conducted to the starter motor and electrically neutralizes the pull-in winding.

  37. Small hold-in winding holds plunger in after it has been pulled in. • Plunger pushes on contact. • Contact completes connection from battery to starter motor.

  38. How Are Starters Made So Small? • Starters and most components in a vehicle are being made as small and as light in weight as possible to help increase vehicle performance and fuel economy. • A starter can be constructed smaller due to the use of gear reduction and permanent magnets to achieve the same cranking torque as a straight drive starter, but using much smaller components.

  39. How Are Starters Made So Small? • A palm-size starter armature.

  40. SUMMARY • All starter motors use the principle of magnetic interaction between the field coils attached to the housing and the magnetic field of the armature. • The control circuit includes the ignition switch, neutral safety (clutch) switch, and solenoid. • The power circuit includes the battery, battery cables, solenoid, and starter motor. • The parts of a typical starter include the main field housing, commutator-end (or brush-end) housing, drive-end housing, brushes, armature, and starter drive.

  41. REVIEW QUESTIONS • What is the difference between the control circuit and the power (motor) circuit sections of a typical cranking circuit? • What are the parts of a typical starter? • Why does a gear-reduction unit reduce the amount of current required by the starter motor? • What are the symptoms of a defective starter drive?

  42. CHAPTER QUIZ 1. Starter motors operate on the principle that ________ . • The field coils rotate in the opposite direction from the armature • Opposite magnetic poles repel • Like magnetic poles repel • The armature rotates from a strong magnetic field toward a weaker magnetic field

  43. CHAPTER QUIZ 2. Series-wound electric motors ________ . • Produce electrical power • Produce maximum power at 0 RPM • Produce maximum power at high RPM • Use a shunt coil

  44. CHAPTER QUIZ 3. Technician A says that a defective solenoid can cause a starter whine. Technician B says that a defective starter drive can cause a starter whining noise. Which technician is correct? • Technician A only • Technician B only • Both Technicians A and B • Neither Technician A nor B

  45. CHAPTER QUIZ 4. The neutral safety switch is located ________. • Between the starter solenoid and the starter motor • Inside the ignition switch itself • Between the ignition switch and the starter solenoid • In the battery cable between the battery and the starter solenoid

  46. CHAPTER QUIZ 5. The brushes are used to transfer electrical power between ________ . • Field coils and the armature • The commutator segments • The solenoid and the field coils • The armature and the solenoid

  47. CHAPTER QUIZ 6. The faster a starter motor rotates, ________ . • The more current it draws from the battery • The less CEMF is generated • The less current it draws from the battery • The greater the amount of torque produced

  48. CHAPTER QUIZ 7. Normal cranking speed of the engine is about ________ . • 2000 RPM • 1500 RPM • 1000 RPM • 200 RPM

  49. CHAPTER QUIZ 8. A starter motor rotates about ________ times faster than the engine. • 18 • 10 • 5 • 2

  50. CHAPTER QUIZ 9. Permanent magnets are commonly used for what part of the starter? • Armature • Solenoid • Field coils • Commutator

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