4wheel drive ppt presentation

1. Four-Wheel-Drive

2. Why Four-Wheel-Drive?
Advantages
Improved traction and handling
Able to transmit torque to all four wheels
Disadvantages
Higher initial cost and weight
Requires special service and maintenance

3. 4X4 = Four wheeled vehicle, four wheels
can receive torque.
4X2 = Four wheeled vehicle, two wheels
can receive torque.
Definitions

4. 4WD Designs
RWD vehicles equipped with an added
transfer case, a front drive shaft, a front
differential, and front drive axles

5. 4WD Designs
 FWD vehicles with an added transfer case, a rear drive
shaft, and a rear axle

6. Transfer case - An
auxiliary
transmission
mounted to the side
or rear of the main
transmission.
No differential
action is provided.
4WD Definitions

7. 4WD Components
 Transfer case
Transmits power from the transmission to the front and rear
drive shafts

8. 4WD Components
 Transfer case
Will typically be a gear or chain type

9. Types of Transfer Cases
Drive chain design
Has less weight to
improve fuel economy
Is usually used with
planetary gearsets
Is the most common
design

10. Types of Transfer Cases
Gear-type
Uses only gear-sets to transfer power
Stronger & more durable

11. Center
differential -
serves the
same purpose
as a transfer
case but allows
for differential
operation.
4WD Definitions

12. Limited-slip center
differential. Controls
differential operation
through a disc or
cone-type clutch.
Later designs are
computer operated.
4WD Definitions

13. 4WD Components
Drive shafts
Connect to the front and rear differentials

14. 4WD Components
 Universal joints or CV-joints
Are used to connect front axles to the wheel hubs

15. Part-time 4WD - Typically systems that
operate in two-wheel drive until the driver
commands four-wheel drive operation.
Torque is then divided (50/50 fixed)
between the front and rear drive-shaft.
They do not corner well on dry pavement.
Selection of two- or four-wheel-drive is done
by a shifter, electric switch and/or locking
hubs.
4WD Definitions

16. Part-Time 4WD Shift Controls
Electric switch or shift lever
Allows the driver to select which
axles receive power
Power can be directed to:
all four wheels
two wheels
none (neutral)
Some vehicles have a
low-speed range that can
be selected

17. Older designs may have different drive-
axle gear ratios.
This will result in a push-pull type action if
the vehicle is driven on dry pavement.
This phenomenon is called drive-line windup.
Part-Time 4WD

18. Part-Time 4WD Shift Controls
Manual Shift lever
Some vehicles
have a
low-speed range
that can
be selected

19. Part-Time 4WD
Locking Hubs
Manual or automatic operation

20. Part-Time 4WD
Locking Hubs
manual operation

21. Part-Time 4WD
Locking Hubs
automatic operation - vacuum or electro-
magnetically operated.

22. Part-Time 4WD
 Locking Axles - final differential will be of an “open”
design. When one axle is disconnected from the wheel
the spider gears rotate freely, neither axle receives
torque.
 Used with an open differential

23. Part-Time 4WD
Locking Axles - Toyota’s Automatic
Disconnecting Differential (ADD)

24. Transfer Case Modes of
Operation
 Ranges available with a part-time transfer case:
Neutral

25. Transfer Case Modes of
Operation
 Ranges available with a part-time transfer case:
Two-wheel-drive—high

26. Transfer Case Modes of
Operation
 Ranges available with a part-time transfer case:
Four-wheel-drive—high

27. Transfer Case Modes of
Operation
 Ranges available with a part-time transfer case:
Four-wheel-drive—low

28. Full-time four-wheel drive (4wd) -
Constantly provides power to all four
wheels. These systems typically do NOT
have a provision for “low” operating
range.
Axles and differentials are constantly locked.
Usually equipped with a center “differential”
instead of a transfer-case.
All-wheel drive - see above
4WD Definitions

29. 4WD Systems
Full-time systems
Cannot be selected
out of four-wheel-
drive
May have an open
or limited-slip center
differential.

30. Full-time 4WD
Open Center Differential - If the wheels
on either final differential loose traction,
maximum torque is delivered to the axle
with the LEAST traction.
For this reason, limited-slip center
differentials are far more common today.

31. Full-time 4WD
Newer computer-controlled designs allow
for different operational modes.
Ford Automatic Four-wheel-drive (A4WD)
Navigator and Expedition
4WD AUTO - full power to the rear wheels.
The front wheels receive power as required.
4WD High - Full power to both wheels, no
center gear-reduction.
4WD Low - Low gear ratio in center
differential for (2:1 ratio) for slow, high
torque driving

32. On-demand four-wheel drive -
Automatically controlled 4WD. One axle is
driven until slip is detected or anticipated.
Computer controlled
uses wheel speed sensors and/or axle speed
sensors to detect slippage.
When slippage is detected, torque is sent to
the opposite axle. The amount sent depends
on the amount of slippage.
4WD Definitions

33. On-demand four-wheel drive
4WD Definitions

34. Viscous coupling in a center differential
4WD Definitions

35. Viscous coupling in a center differential
4WD Definitions

36. On-demand four-wheel
drive
Ford’s control-trac system
normal operation - 96% of torque is sent to
the rear wheels.
Upon slippage a computer energizes an
electro-magnetic clutch in the transfer case.
Up to 96% of torque can be sent to the front
wheels.

37. 4WD Systems
Four-wheel drive systems without a center
differential.
Tire sizes must all be the same (this holds true for
any 4WD application)
Tread wear must be similar
Tire changes on an all-wheel drive must be done
in sets of four
Gear ratios should be the same in the front and
rear differentials.

38. Front Axle and Hub Service
Guidelines
 Most front axles are
serviced like those
in 2WD systems
 Follow the recommended
procedure for servicing
4WD hubs
 Some hubs are not
serviceable and must
be replaced

39. Effects of Vehicle
Modifications
Installing larger tires and lift kits
Alters vehicle handling by changing unsprung weight
Increases steering effort
Causes a rough ride
May cause vehicle to wander and vibrate
Possible driveshaft working angle issues
Possible Vehicle Speed sensor issues
May necessitate computer programming

40. Maintenance Tips
 Check the fluid level often
 Check for fluid contamination any time the
vehicle has been driven through deep water
 Use only the recommended lubricant
 Always follow
the proper
towing
procedures