TRANSFER CASES CHAPTER 8 Page 175

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

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

TYPICAL 4WD SYSTEM 2 WHEEL

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

NEUTRAL Power flows into Transfer case with no output.

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

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

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

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

GEAR DRIVEN POWER FLOW Page 191

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)

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

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)

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)

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

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