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Modern Automotive Technology

Modern Automotive Technology. by Russell Krick. Publisher The Goodheart-Willcox Co., Inc. Tinley Park, Illinois. PowerPoint for. Chapter 55. Manual Transmission Fundamentals. Contents. (8 Topics). Basic transmission parts Purpose of a manual transmission Gear fundamentals

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Modern Automotive Technology

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  1. Modern Automotive Technology by Russell Krick PublisherThe Goodheart-Willcox Co., Inc.Tinley Park, Illinois PowerPoint for

  2. Chapter 55 Manual Transmission Fundamentals

  3. Contents (8 Topics) • Basic transmission parts • Purpose of a manual transmission • Gear fundamentals • Manual transmission construction

  4. Contents (continued) • Transmission types • Transmission power flow • Speedometer drive • Manual transmission switches

  5. Input shaft Gears Synchronizers Shift forks Shift linkage Gear shift lever Output shaft Transmission case Basic Transmission Parts

  6. Basic Transmission Parts

  7. Purpose of a Manual Transmission A manual transmission is designed to change the vehicle’s drive wheel speed and torque in relation to enginespeed and torque

  8. Transmission Features • A manual transmission should: • be able to increase torque to the drive wheels for quick acceleration • supply different gear ratios to match load conditions • provide a reverse gear • provide an easy means of shifting gears • operate quietly with minimum power loss

  9. Gear Fundamentals • Gears are round wheels with teeth machined on their perimeters • They transmit turning effort from one shaft to another • When gears are different sizes, output speed and torque change

  10. Gear Drive Small gear driving a larger gear

  11. Gear Drive Large gear driving a smaller gear

  12. Gear Ratio • The number of revolutions a drive gear must turn before the driven gear completes one revolution • Calculated by dividing the number of teeth on the driven gear by the number of teeth on the drive gear Gear Ratio = # of driven gear teeth # of drive gear teeth

  13. Gear Ratio If the drive gear has 12 teeth and the driven gear has 24 teeth, the gear ratio is two-to-one Gear Ratio = # of driven gear teeth # of drive gear teeth = 24 12 = 2 or written 2:1

  14. Gear Ratio

  15. Transmission Gear Ratios • First gear 3:1 • Second gear 2:1 • Third (high) gear 1:1 • Reverse gear 3:1

  16. Gear Reduction • Occurs when a small gear drives a larger gear • Increases turning force (torque) • Used in lower transmission gears

  17. Overdrive Ratio • Results when a larger gear drives a smaller gear • Output gear speed increases • Output torque is reduced

  18. Gear Types • Two gear types are commonly used in automotive transmissions: • spur gears • helical gears

  19. Spur Gears • Somewhat noisy • Teeth are cut parallel to the centerline of the gear shaft • Used for sliding gears such as reverse gear

  20. Helical Gears • Teeth are machined at an angle to the centerline • Quieter and stronger than spur gears • Used for main drive gears which are in constant mesh

  21. Gear Types

  22. Gear Backlash • Distance between the meshing gear teeth • Allows lubricating oil to enter the high-friction area between the gear teeth • Allows the gears to expand during operation

  23. Manual Transmission Lubrication • Bearings, shafts, and gears are lubricated by oil splash lubrication • As gears rotate, they sling oil around inside the transmission • Typically, 80W or 90W gear oil is used

  24. Transmission Bearings • Bearings reduce the friction between the surfaces of rotating parts • Three basic types are used: • ball bearings • roller bearings • needle bearings • Used between shafts and housing, or between gears and shafts

  25. Transmission Bearings Three types of antifriction bearings used

  26. Manual Transmission Construction

  27. Transmission Case • Supports the bearings and shafts • Provides an enclosure for gear oil • Made of cast iron or aluminum • Drain plug and fill plug are provided • typically, the oil level should be level with the bottom of the fill plug hole at operating temperature

  28. Extension Housing • Bolts to the rear of the transmission case • Encloses the output shaft • Holds the rear oil seal

  29. Front Bearing Hub • Covers the front transmission bearing • Acts as a sleeve for the release bearing

  30. Manual Transmission

  31. Transmission Shafts • At least four shafts are commonly used: • input shaft • countershaft • reverse idler shaft • output shaft

  32. Input Shaft • Transfers rotation from the clutch disc to the countershaft gears • Anytime the clutch disc turns, the input shaft gear turns

  33. Countershaft • Holds the countershaft gears into mesh with the input gear and other gears • Located slightly below and to one side of the input shaft • Normally, it is locked in the case and does not turn

  34. Reverse Idler Shaft • Supports the reverse idler gear, • Allows reverse idler gear to mesh with gears on both the countershaft and output shaft

  35. Output Shaft • Holds the output gears and synchronizers • Connects to the drive shaft to turn the wheels • Gears are free to revolve on the shaft, but the synchronizers are locked on the shaft by splines

  36. Transmission Shafts

  37. Transmission Gears Input shaft gear turns countershaftgears. Countershaft gears turnoutput shaft gears

  38. Gear Ranges Gear reduction Direct drive Output shaft rotation is reversed

  39. Input Gear Machined part of the steel input shaft

  40. Countershaft Gear Several gears machined from a single piece of steel

  41. Reverse Idler Gear Assembly

  42. Output Shaft Gears

  43. Synchronizers • Synchronizers have two functions: • prevent the gears from clashing (grinding) during engagement • lock the output gear to the output shaft

  44. Synchronizer Theory • When the synchronizer is away from an output gear, the gear freewheels (spins freely) on the output shaft • When the synchronizer slides against the output gear, it is locked to the synchronizer and to the output shaft • Power flows through the output shaft to the drive wheels

  45. Synchronizer Construction Hub is splined to the output shaft

  46. Synchronizer Operation • When the driver shifts gears, the synchronizer sleeve slides on its splined hub toward the output gear • Blocking ring cone rubs on the side of the drive gear cone, causing friction between the two • Output gear, synchronizer, and the output shaft begin to spin at the same speed

  47. Synchronizer Operation

  48. Synchronizer Operation • As soon as the speed is equalized, the sleeve can slide over the blocking ring and spur gear teeth on the output gear • This locks the output gear to the synchronizer hub and to the shaft • Power flows through that gear to the drive wheels

  49. Synchronizer Operation

  50. Fully Synchronized Transmission • All the forward output gears use a synchronizer • Allows the driver to downshift into any lower gear (except reverse) while the vehicle is moving

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