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OBJECTIVES

OBJECTIVES. After studying Chapter 18, the reader should 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.

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OBJECTIVES

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  1. OBJECTIVES After studying Chapter 18, the reader should 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.

  2. CRANKING CIRCUIT • For any engine to start, it must first be rotated, using an external power source. • It is the purpose and function of the cranking circuit to create the necessary power and transfer it from the battery to the starter motor that rotates the engine.

  3. CRANKING CIRCUIT • Modern cranking circuits include the following: • Starter motor. • Battery. • Starter solenoid or relay. • Starter drive. • Ignition switch. FIGURE 18-1 A typical solenoid-operated starter.

  4. CRANKING CIRCUIT FIGURE 18-2 Some column-mounted ignition switches act directly on the contact points, whereas others use a link from the lock cylinder to the ignition switch.

  5. CRANKING CIRCUITControl Circuit • Many automobile manufacturers use an electric switch called a neutral safety switch that opens the circuit between the ignition switch and the starter to prevent starter motor operation unless the gear selector is in neutral or park. FIGURE 18-3 A typical wiring diagram of a starter circuit.

  6. COMPUTER-CONTROLLED STARTING • 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.

  7. COMPUTER-CONTROLLED STARTING • Computer-controlled starting is almost always part of the system if a push button start is used. FIGURE 18-4 Instead of 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.

  8. COMPUTER-CONTROLLED STARTING • This feature allows the heater or air conditioning system to start before the driver arrives. FIGURE 18-5 The top button on this key fob is the remote start button.

  9. HOW THE STARTER MOTOR WORKS • A starter consists of the main structural support of a starter called the main field housing, one end of which is called a commutator-end (or brush-end) housing and the other end a drive-end housing.

  10. HOW THE STARTER MOTOR WORKS • The commutator-end plate supports the end containing the starter brushes. • Through bolts hold the three components together. FIGURE 18-6 A typical starter motor.

  11. HOW THE STARTER MOTOR WORKS • The starter uses four brushes—two brushes to transfer the current from the field coils to the armature, and two brushes to provide the ground return path for the current that flows through the armature. FIGURE 18-7 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 through the loop winding of the armature before reaching ground through the ground brush.

  12. HOW MAGNETIC FIELDS TURN AN ARMATURE • One basic principle of electromagnetism is that a magnetic field surrounds every conductor carrying a current. • Inside the starter housing is a strong magnetic field created by the field coil magnets.

  13. HOW THE STARTER MOTOR WORKS • Inside the starter housing is a strong magnetic field created by the field coil magnets. FIGURE 18-8 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. HOW THE STARTER MOTOR WORKS FIGURE 18-9 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. HOW THE STARTER MOTOR WORKS • The magnetic field of the starter motor is provided by two or more pole shoes and field windings. • The pole shoes are made of iron and are attached to the frame with large screws. FIGURE 18-10 Pole shoes and field windings installed in the housing.

  16. HOW THE STARTER MOTOR WORKS • Paths of magnetic flux lines within a four-pole motor. FIGURE 18-11 Magnetic lines of force in a four-pole motor.

  17. HOW THE STARTER MOTOR WORKS • The field windings are usually made of a heavy copper ribbon to increase their current-carrying capacity and electromagnetic field strength. FIGURE 18-12 A pole shoe and field winding.

  18. TYPES OF STARTER MOTORS • Starter motors must provide high power at low starter motor speeds to crank an automotive engine at all temperatures and at the cranking speed required for the engine to start (60 to 250 engine RPM). • Many starter motors are series wound, which means that the current flows first through the field coils, then in series through the armature, and finally to a ground through the ground brushes. FIGURE 18-13 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.

  19. TYPES OF STARTER MOTORSSeries Motors • A series motor develops its maximum torque at the initial start (0 RPM) and develops less torque as the speed increases. • Because the power (torque) of the starter depends on the strength of the magnetic fields, the torque of the starter decreases as the starter speed increases.

  20. TYPES OF STARTER MOTORSShunt Motors • Shunt-type electric motors have the field coils in parallel (or shunt) across the armature. FIGURE 18-14 This wiring diagram illustrates the construction of a shunt-type electric motor. Shunt-type electric motors have the field coils in parallel (or shunt) across the armature as shown.

  21. TYPES OF STARTER MOTORSCompound Motors • A compound-wound, or compound, motor has the operating characteristics of a series motor and a shunt-type motor, because some of the field coils are connected to the armature in series and some (usually only one) are connected directly to the battery in parallel (shunt) with the armature. FIGURE 18-15 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).

  22. ARMATURE AND COMMUTATOR ASSEMBLY • The motor armature has a laminated core. FIGURE 18-16 A typical starter motor armature.

  23. ARMATURE AND COMMUTATOR ASSEMBLY • Motor armatures are connected to the commutator in one of two ways. • In a lap winding, the two ends of each conductor are attached to two adjacent commutator bars. FIGURE 18-17 An armature lap winding.

  24. ARMATURE AND COMMUTATOR ASSEMBLY • The armature core, windings, and commutator are assembled on a long armature shaft. • This shaft also carries the pinion gear that meshes with the engine flywheel ring gear. FIGURE 18-18 The pinion gear meshes with the flywheel ring gear.

  25. ARMATURE AND COMMUTATOR ASSEMBLY • Most automotive starters have two grounded and two insulated brushes, which are held against the commutator by spring force. FIGURE 18-19 A cutaway of a typical starter motor.

  26. PERMANENT-MAGNET FIELDS • The permanent-magnet, planetary-drive starter motor is the first significant advance in starter design in decades. • This eliminates the motor field circuit, which in turn eliminates the potential for field wire-to-frame shorts, field coil welding, and other electrical problems.

  27. DON’T HIT THAT STARTER! • 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. FIGURE 18-20 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.

  28. GEAR-REDUCTION STARTERS • 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. FIGURE 18-22 Many gear-reduction starters use a planetary gear reduction assembly similar to that used in an automatic transmission. FIGURE 18-21 Chrysler was one of the first vehicle manufacturers to use a gear-reduction starter.

  29. STARTER DRIVES • A starter drive includes a small pinion gear that meshes with and rotates the larger gear on the engine for starting. • The ends of the starter pinion gear are tapered to help the teeth mesh more easily without damaging the flywheel ring gear teeth. FIGURE 18-23 A cutaway of a typical starter drive.

  30. STARTER DRIVES • If the engine starts and is accelerated to 2000 RPM (normal cold engine speed), the starter will be destroyed by the high speed (36,000 RPM) if the starter was not disengaged from the engine. FIGURE 18-24 The ring gear to pinion gear ratio is usually 15:1 to 20:1.

  31. A BIT OF HISTORYA Bendix Drive Is Now Called a Starter Drive • Older-model starters often used a Bendix drive mechanism, which used inertia to engage the starter pinion with the engine flywheel gear. • The overrunning clutch, which is built in as a part of the starter drive unit, uses steel balls or rollers installed in tapered notches. FIGURE 18-25 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.

  32. A BIT OF HISTORYA Bendix Drive Is Now Called a Starter Drive • The spring between the drive tang or pulley and the overrunning clutch and pinion is called a mesh spring and it helps to cushion and control the engagement of the starter drive pinion with the engine flywheel gear. FIGURE 18-26 Cutaway of a solenoid-activated starter showing the solenoid, shift lever, and starter drive assembly that includes the starter pinion and overrunning clutch with a mesh spring in one unit.

  33. STARTER DRIVE OPERATION • A starter drive is generally a dependable unit and does not require replacement unless defective or worn. • Intermittent starter drive failure (starter whine) is often most noticeable during cold weather.

  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. FIGURE 18-27 A Ford movable-pole-shoe starter.

  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. FIGURE 18-28 A circuit diagram of a Ford system using a movable-pole-shoe starter.

  36. SOLENOID-OPERATED STARTERS • A starter solenoid is an electromagnetic switch containing two separate, but connected, electromagnetic windings. FIGURE 18-29 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. HOW ARE STARTERS MADE SO SMALL? • A starter can be constructed smaller due to the use of gear reduction to achieve the same cranking torque as a straight drive starter, but using much smaller components. FIGURE 18-30 A palm-sized starter armature.

  38. 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.

  39. REVIEW QUESTIONS • What parts are included in the starter control circuit? • List the parts of a typical starter. • Explain why a gear-reduction unit reduces the amount of current required by the starter motor. • Describe the symptoms of a defective starter drive.

  40. CHAPTER QUIZ • 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

  41. CHAPTER QUIZ • 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

  42. 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

  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 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

  46. 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

  47. 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

  48. 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

  49. 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

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