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Front-Wheel-Drive (Transaxle and CV Joint) Fundamentals

Front-Wheel-Drive (Transaxle and CV Joint) Fundamentals. Chapter 77. Objectives. Describe differences between front- and rear-wheel drivetrains Tell the names of parts of a transaxle Trace the power flow through four- and five-speed transaxles. Introduction.

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Front-Wheel-Drive (Transaxle and CV Joint) Fundamentals

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  1. Front-Wheel-Drive (Transaxle and CV Joint) Fundamentals Chapter 77

  2. Objectives • Describe differences between front- and rear-wheel drivetrains • Tell the names of parts of a transaxle • Trace the power flow through four- and five-speed transaxles

  3. Introduction • Most automobiles today have front-wheel drive • FWD car has transaxle • Drive axles extend to front wheels out of each side of transaxle • Each end of the drive axle is a CV joint • Transaxle can be either manual or automatic

  4. Front-Wheel Drive • Advantages • More efficient drivetrain • Better fuel economy • Combined with MacPherson struts: less unsprung weight for better handling • Transmission hump is eliminated • A few FWD engines have been mounted longitudinally • Most transaxles mounted sideways

  5. Manual Transaxle • Manual transaxles and transmissions • Use same kind of clutch • Three parallel paths for power flow • Input shaft located above intermediate shaft • Input shaft gears directly drive output shaft gears • Differential assembly • Gear shafts • Supported by larger ball, roller, or tapered roller bearings • End play is controlled by thrust washers

  6. Shift Linkage • Transverse transaxles • Shifted by cables or shift linkage • Two shift cables or rods • One moves a selector on transaxle • Other moves shift fork back and forth • Advantage • Engine shake is not transmitted back to driver’s hand on shift lever

  7. Transaxle Differential • Allows wheels to turn at different speeds when rounding corners • Same as rear-wheel-drive differential • Ordinary helical gearset • Used instead of bevel gears • Power from differential side gears is transmitted to front drive axles through axle shafts

  8. Transaxle Power Flow • Five-speed power flow • Fixed gears for first, second, and reverse on input shaft • Fixed gears for third, fourth, fifth on intermediate shaft • Power flow leaves transmission intermediate shaft • Continues through drive pinion to axles • Engine is mounted sideways • Axles run parallel to input shaft

  9. Automatic Transaxle • Combination of automatic transmission and differential • Same parts and operation apply • Transverse engine • Power flow is through gears or sprocket and chain • Chain drive • Allows transaxle to be mounted slightly below and to the side of the engine

  10. Front Drive Axles • Difference between rear-wheel drive and front-wheel drive axles • Front-wheel drive axles have CV joints at ends • Axles driven at sharper angles • Allow steering front wheels during power transmission • Universal joint changes output speed twice in every revolution when run at an angle • Rear-wheel drive vehicle drive shaft turns very fast • Positioned before gear reduction of differential

  11. Axle Shaft Parts • Drive axle is called half shaft or axle shaft • Stub shaft (stub axle) • Short shaft at outside end • Splined to front hub so it can drive front wheels • CV joint classifications • Inboard and outboard • Fixed and plunge • Ball and tripod

  12. CV Joint Construction • Most common joint combination • Rzeppa joint for outside fixed joint and a tripod for inside plunge joint • Fixed joints • Rzeppa joint: ball-and-socket type • Types of plunge joints • Tripod tulip • Double offset plunge joint • Cross groove plunge joint

  13. Axle Shafts • Characteristics • May be solid or hollow • May have damper weights to absorb vibration • Turn much slower than rear-wheel drive shaft • Balance not as important • When different lengths: long one twists and lags before puts its torque to the wheel • Torque steer is prevented by longer axle shaft of larger diameter tubing

  14. CV Joint Boots • Boots at each end of axle contain grease • Protect joint from the elements • CV joint boot • Attached to axle and stub shafts with plastic or steel bands or straps • Made of natural rubber, neoprene, silicone, or urethane

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