1. Copyright © 2014 Delmar, Cengage Learning DC Motors Instructor Name: (Your Name) 8 CHAPTER

2. Copyright © 2014 Delmar, Cengage Learning Learning Objectives List the components of a typical starting (cranking) motor Describe how interacting magnetic fields cause the armature in an electric motor to rotate Explain why a starter motor draws less current as motor speed increases List the advantages and disadvantages of a gear reduction starter motor

3. Copyright © 2014 Delmar, Cengage Learning Learning Objectives Measure cranking circuit resistance using the voltage drop method Troubleshoot the cause of a no-crank problem Disassemble a starter motor, test the internal components, and reassemble Perform a rapid assessment of a trucks electrical system Explain how rotational direction is reversed with a permanent magnet motor

4. Copyright © 2014 Delmar, Cengage Learning Introduction Electric motors are used extensively on modern trucks, windshield wipers, heating and A/C, some hydraulic ABS systems The starting or cranking motor is the largest Electric motors convert electrical energy into mechanical energy Almost all motors used on trucks uses brushes to contact the rotating elements, hence the name brushed DC motors

5. Copyright © 2014 Delmar, Cengage Learning Important Facts Two magnetic fields that interact with each other combine to form a single magnetic field. If the arrows on the magnetic lines of force of both magnetic fields are pointing in the same direction, the resulting magnetic field is strengthened. If the arrows on the magnetic lines of force are pointing in opposite direction, the resulting magnetic field is weakened.

6. Copyright © 2014 Delmar, Cengage Learning Interaction of Current Carrying Conductor in a Magnetic Field Figure 8-3 (A) Current-carrying conductor placed in magnetic field causes an interaction between magnetic fields; conductor is compelled to move from strong magnetic field to weak field. (B) Current-carrying conductor formed into a loop is compelled to rotate around its axis to move from strong field to weak field.

7. Copyright © 2014 Delmar, Cengage Learning Important Facts Conductors that are carrying current are compelled (want) to move out of a stronger magnetic field into a weaker magnetic field.

8. Copyright © 2014 Delmar, Cengage Learning Components of a Simple Electric Motor Armature – The conductive loop that rotates inside an electric motor Split Ring Commutator – Provides connection to both ends of the armature loop through brushes and allow it to rotate. Pole Shoes – Electromagnets that surround the armature. Field Coils – Copper wire wrapped around pole shoes that create the electromagnet

9. Copyright © 2014 Delmar, Cengage Learning Brushed DC Motor Figure 8-4 Brushed DC motor; current flow through armature reverses directions every 180 degrees of rotation.

10. Copyright © 2014 Delmar, Cengage Learning Magnetic Field Developed By Pole Shoes Figure 8-5 Magnetic field developed by pole shoes.

11. Copyright © 2014 Delmar, Cengage Learning Armature Windings and Commutator Segments Figure 8-6 Armature windings and commutator segments.

12. Copyright © 2014 Delmar, Cengage Learning Cutaway View of Starter Motor Figure 8-8 Cutaway view of a starter motor.

13. Copyright © 2014 Delmar, Cengage Learning Four Insulated Field Coils with Brushes Figure 8-11 Four insulated field coils with brushes.

14. Copyright © 2014 Delmar, Cengage Learning Pole Shoes and Field Coil Inside Iron Housing Figure 8-12 Pole shoes and field coils installed in iron housing.

15. Copyright © 2014 Delmar, Cengage Learning Interaction of Magnetic Fields Results in Armature Rotation Figure 8-13 Interaction of magnetic fields results in armature rotation.

16. Copyright © 2014 Delmar, Cengage Learning Series Wound Motor Figure 8-14 Series-wound motor.

17. Copyright © 2014 Delmar, Cengage Learning Shunt Wound Motor Figure 8-15 Shunt- wound motor.

18. Copyright © 2014 Delmar, Cengage Learning Compound Wound Motor Figure 8-16 Compound motor.

19. Copyright © 2014 Delmar, Cengage Learning Starter Drive Components Pinion Gear – Small diameter gear that acts as the starter output gear Ring Gear – Part of the engine fly wheel, pinion gear engages the ring gear to rotate the engine One Way or Over Riding Clutch – Prevents destruction of the armature due to rapid acceleration by ring gear Solenoid – An electromechanical device used to engage the pinion gear to the ring gear

20. Copyright © 2014 Delmar, Cengage Learning Figure 8-17 Solenoid with coil not energized. Solenoid Figure 8-18 Solenoid with coil energized.

21. Copyright © 2014 Delmar, Cengage Learning Shift Lever Type Drive Figure 8-19 Shift-lever-type drive.

22. Copyright © 2014 Delmar, Cengage Learning Drive Mechanism Figure 8-20 Drive mechanism.

23. Copyright © 2014 Delmar, Cengage Learning Roller Clutch Permits One-Way Drive Figure 8-21 Roller clutch permits one-way drive.

24. Copyright © 2014 Delmar, Cengage Learning Crank Inhibit Circuit Figure 8-22 Crank inhibit circuit.

25. Copyright © 2014 Delmar, Cengage Learning Gear Reduction Starter Motor Cut-Away Figure 8-23 Gear-reduction starter motor cutaway.

26. Copyright © 2014 Delmar, Cengage Learning Testing Cranking System Resistance Connect carbon pile resistor across starter B+ and ground terminal Connect DMM across battery terminals Briefly load carbon pile to 500A, note battery terminal voltage Connect DMM across the starter B+ and ground terminal. Do not connect to carbon pile clamps. Briefly load carbon pile to 500A, note starter terminal voltage

27. Copyright © 2014 Delmar, Cengage Learning Testing Cranking System Resistance (continued) Subtract the loaded starter terminal voltage from the loaded battery terminal voltage. The result is the amount of voltage that is dropped on the positive and negative cranking circuit battery cables.

28. Copyright © 2014 Delmar, Cengage Learning Measuring Cranking System Resistance Figure 8-24 Measuring cranking circuit resistance by loading to 500A and measuring voltage drop on circuit.

29. Copyright © 2014 Delmar, Cengage Learning Determining the Source of Excessive Voltage Drop in a Cranking Circuit Connect carbon pile resistor across starter motor B+ and ground terminal Connect DMM across battery positive and starter positive terminals. Do not connect to carbon pile clamps. Briefly load carbon pile to 500A and note positive circuit voltage drop

30. Copyright © 2014 Delmar, Cengage Learning Determining the Source of Excessive Voltage Drop in a Cranking Circuit (continued) Connect DMM across battery negative and starter negative terminals. Do not connect to carbon pile clamps. Briefly load carbon pile to 500A and note negative circuit voltage drop The positive and negative circuit voltage drops should each be about half the maximum allowable voltage drop or 0.25V

31. Copyright © 2014 Delmar, Cengage Learning Finding Source of High Cranking System Resistance Figure 8-25 Finding the source of the high cranking circuit resistance.

32. Copyright © 2014 Delmar, Cengage Learning Basic Electrical/Electronic Diagnostic Procedure Flowchart Figure 8-29 Diagnostic flowchart.

33. Copyright © 2014 Delmar, Cengage Learning Cranking Circuit Diagram Figure 8-30 Cranking circuit diagram.

34. Copyright © 2014 Delmar, Cengage Learning DMM Measuring High and Low Side of Magnetic Switch During Cranking Figure 8-31 DMM measuring high and low side of magnetic switch coil during crank.

35. Copyright © 2014 Delmar, Cengage Learning Voltage Measurements at Neutral Start Switch Figure 8-32 Voltage measurements at neutral start switch.

36. Copyright © 2014 Delmar, Cengage Learning Starter No-Load Bench-Test Setup Figure 8-33 Starter no-load bench-test setup.

37. Copyright © 2014 Delmar, Cengage Learning Testing For Open Field Coils Figure 8-35 Testing for open field coils.

38. Copyright © 2014 Delmar, Cengage Learning Testing For Shorted-to-Ground Field Coils Figure 8-36 Testing for a shorted-to- ground field coil.

39. Copyright © 2014 Delmar, Cengage Learning Testing Armature For Shorts-to-Ground Figure 8-39 Testing armature for shorted-to-ground windings.

40. Copyright © 2014 Delmar, Cengage Learning Testing Armature For Open Circuits Figure 8-40 Testing armature for open circuits.

41. Copyright © 2014 Delmar, Cengage Learning Energizing the Starter to Measuring Pinion Clearance Figure 8-42 Energizing the starter motor solenoid to measure pinion gear clearance.

42. Copyright © 2014 Delmar, Cengage Learning View Looking into a Single Loop Armature Figure 8-46 View looking into a single-loop armature.

43. Copyright © 2014 Delmar, Cengage Learning Armature Rotating Due to Magnetic Field Interaction and Commutation Figure 8-47 Armature rotating due to magnetic field interactions and commutation.

44. Copyright © 2014 Delmar, Cengage Learning CEMF in Stationary Motor and Motor at Full Speed Figure 8-48 CEMF with motor stationary (top) and motor rotating at full speed (bottom) and the effect on current drawn by the motor.

45. Copyright © 2014 Delmar, Cengage Learning Starter Solenoid Pull-In and Hold-In Windings Figure 8-50 Starter solenoid hold-in and pull-in windings.

46. Copyright © 2014 Delmar, Cengage Learning Summary Electric motors convert electric energy into mechanical energy. Most electric motors used on trucks are a brushed DC-type motor. A brushed DC motor has spring loaded brushes that make contact with the commutator segments. The commutator segments are attached to loops of wire that make up the armature assembly. The armature is the rotating component of the starter.

47. Copyright © 2014 Delmar, Cengage Learning Summary (continued) The pole shoes are the stationary electromagnets bolted to the motor frame. Field coils surround the pole shoes. Current flow through the field coils causes the pole shoes to be magnetized. This set up a stationary magnetic field. The stationary magnetic field interacts with the magnetic field surrounding the armature windings. The interaction causes areas of weak and strong magnetic fields inside the motor. The armature rotates to escape the strong fields.

48. Copyright © 2014 Delmar, Cengage Learning Summary (continued) The commutation process describes the reversal of current flow through the armature winding at just the right time to keep the armature in a location of strong magnetic field. The current reversal causes the armature to continually rotate in an attempt to escape the strong magnetic fields.

49. Copyright © 2014 Delmar, Cengage Learning Summary (continued) Counter-electromagnetic force (CEMF) is the voltage that is induced in the armature windings as they pass through the magnetic fields set up by the pole shoes. The CEMF acts as a series-opposing voltage to the battery voltage. The CEMF increases as the motor speed increases. This causes the current drawn by the starter to decrease as the motor speed increases. The highest level of current draw is when the starter motor is stationary.

50. Copyright © 2014 Delmar, Cengage Learning Summary (continued) The starter motor assembly contains the pinion gear. The drive assembly assembly causes the pinion gear to be meshed with the engine ring gear when the motor solenoid is energized. The drive assembly contains a one-way clutch that permits the starter motor to drive the engine but prevent the engine from driving the starter motor.

51. Copyright © 2014 Delmar, Cengage Learning Summary (continued) A positive engagement starter motor is designed not to rotate until the pinion gear is in full mesh with the ring gear. This reduces the likelihood of ring gear milling. The starter motor causes the drive with pinion gear to slide into mesh with ring gear and also causes the high current contacts for the starter motor to close.

52. Copyright © 2014 Delmar, Cengage Learning Summary (continued) Cranking circuit resistance is determined by causing a steady known amount of current flow through the battery cables using a carbon pile resistor. The voltage dropped on the cables with the known current flowing is used to determine if cranking circuit resistance is acceptable. Low cranking circuit resistance is vital for proper engine cranking speed.

53. Copyright © 2014 Delmar, Cengage Learning Summary (continued) Many smaller motors found on trucks are permanent magnet motors. The term permanent magnet refers to the pole shoes, which are constructed of material that has been magnetized. The direction of these motors can be reversed by changing the direction of current flow through the armature windings through motor voltage polarity reversal.