09-08-2012, 12:29 PM
Advanced Four-Wheel-Drive Systems
Advanced Four-Wheel-Drive Systems.ppt (Size: 500 KB / Downloads: 140)
Objectives
Use the correct terminology when discussing 4WD systems.
Describe the different designs of 4WD systems and their applications.
Compare and contrast the components of part-and full-time 4WD systems.
Discuss the purpose of an interaxle differential and the design variations used by the industry.
Discuss the purpose, operation, and application of a viscous coupling in 4WD systems.
SAE Terminology and Definitions
All-wheel-drive (AWD)
A system that constantly sends power to all four wheels
Part-time 4WD systems
Manually-controlled systems
Full-time 4WD
Permanently all-wheel-drive
On-Demand 4WD Systems
This system will drive one axle until slip is detected
A varied amount of torque is automatically sent to the other axle when slip is detected
Some systems allow the driver to select 2WD only
Design Variations
Open center differential
Uses differential action to compensate for differences in speed between the axles
Limited-slip center differential
Allows more torque to be delivered to the axle with the most traction
All-Wheel-Drive System Features
These systems always drive all wheels
Most AWD systems are based on a FWD system with an added transfer case or center differential
Some systems are computer-controlled
Some are on-demand systems
Center Differentials
Are used to prevent drive line windup
Some systems use a viscous clutch to transfer power to the other axle
Some systems allow the driver to control the amount of torque going to each wheel
Some systems are computer-controlled
Viscous Clutches or Couplings
Are self-contained and not serviceable
Can be installed inside or outside the transaxle housing
Consist of two sets of steel plates in a drum of thick fluid
Split the engine torque according to the needs of each axle
Viscous Coupling Construction
One set of steel plates is splined to the input shaft
The other set is splined to a drum
The output shaft is attached to the drum
The drum contains silicone fluid