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  1. TRANSFER CASES CHAPTER 8 Page 175

  2. OBJECTIVES • Describe operation and controls of transfer cases • Compare components of Full time and part time 4WD • Discuss purpose of interaxle differential and variations • Discuss purpose and operation of viscous coupling in 4WD systems

  3. Purpose of Transfer Cases • Transfers torque to both front and rear drive axle assemblies (Gear or Chain) • Normally connected to each axle by two drive shafts. • Provides Direct drive (high) or torque multiplication (Low) • Is a “auxiliary transmission” Page 187

  4. TYPICAL 4WD SYSTEM • 2 WHEEL

  5. CLASSIFICATIONS • Three Types • Part-Time: Has neutral, 2WD High, 4WD High and 4WD Low. • Full Time: 4WD High and 4WD Low, 4WD High Lock and 4WD Low lock • Part-Time/Full time: 2WD High, Full time 4WD High and part time 4WD Low. Page 187

  6. NEUTRAL • Power flows into Transfer case with no output.

  7. 2 WHEEL HIGH • Power flow to rear wheels only. • No reduction

  8. 4 WHEEL HIGH • Power flows to both front & rear axles. • No reduction

  9. 4 WHEEL LOW • Power flows to both front & rear axles. • In reduction

  10. TRANSFER CASE DESIGNS • GEAR DRIVEN (pg. 191) • CHAIN DRIVEN (pg. 192) • PLANETARY GEAR DRIVES (Pg. 193) • ELECTRONICALLY CONTROLLED PLANETARY GEARSETS (Pg. 194)

  11. GEAR DRIVEN POWER FLOW Page 191

  12. OPERATION • Most transfer cases have two levers. One for 2wd/4wd and one for range (Hi, Low) • Oil Pump • “Shift on Fly” Uses magnetic clutch to bring shafts, differentials axles to same speed. Electric motor makes actual shift when components are synchronized. (Page 192)

  13. OPERATION • Some Transfer cases are two speed i.e. allow a low range and a high range • Some Transfer cases are single speed i.e. only between 2WD and 4WD • Some are computer controlled

  14. CHAIN DRIVEN • Today’s transfer cases are made of aluminum, have chains and planetary gearsets to reduce weight and improve efficiency • Simple Planetary Gearsets are made up of three gears (Pg. 188)

  15. Chain Driven Power Flow • Planetary Gearset allows for different gear positions. • Power flow through most transfer cases equipped with planetarys is the same. • Shift mechanism moves planetary gearset along splined section of the input shaft. (Power flow Pg. 189-190)

  16. CENTER DIFFERENTIALS • Prevents Driveline wind-up • Used in Full Time 4WD and AWD systems (Can disengage operation on some cars to lock all four wheel direct) • Can be external between transmission and axles (page 177 and 182) • Can be located inside transfer case (page 183 and 198) Page 198

  17. VISCOUS COUPLINGS • Drum filled with thick silicone fluid • Houses several thin steel discs • Splits engine torque according to the needs of each axle. • Prevents wheel scuffing along pavement. • Used on 4WD and AWD Page 199