transfer cases chapter 8 page 175
DESCRIPTION
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 systemsTRANSCRIPT
CBCAUTO
JH
TRANSFER CASES
CHAPTER 8Page 175
CBCAUTO
JH
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
CBCAUTO
JH
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
CBCAUTO
JH
TYPICAL 4WD
SYSTEM 2 WHEEL
CBCAUTO
JH
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
CBCAUTO
JH
NEUTRAL Power flows
into Transfer case with no output.
CBCAUTO
JH
2 WHEEL HIGH
Power flow to rear wheels only.
No reduction
CBCAUTO
JH
4 WHEEL HIGH Power flows to
both front & rear axles.
No reduction
CBCAUTO
JH
4 WHEEL LOW Power flows to
both front & rear axles.
In reduction
CBCAUTO
JH
TRANSFER CASE DESIGNS
GEAR DRIVEN (pg. 191) CHAIN DRIVEN (pg. 192) PLANETARY GEAR DRIVES (Pg.
193) ELECTRONICALLY CONTROLLED
PLANETARY GEARSETS (Pg. 194)
CBCAUTO
JH
GEAR DRIVEN POWER FLOW
Page 191
CBCAUTO
JH
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)
CBCAUTO
JH
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
CBCAUTO
JH
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)
CBCAUTO
JH
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)
CBCAUTO
JH
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
CBCAUTO
JH
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