The differential system allows the rear wheels of a tractor to rotate at different speeds when turning. It contains a pinion gear, crown wheel, and differential gears that connect to left and right axles. This allows the outer wheel to turn faster than the inner wheel during a turn. The final drive further reduces speed coming from the gearbox before powering the rear wheels. Common final drive types are bull gear, hub reduction, and straight/solid axles, each providing different torque multiplication and load handling abilities.

1. Working principle of differential
system and final drive
Presented by
GEETA PATEL

3. Differential unit is a special arrangement of
gears to permit one of the rear wheels of the
tractor to rotate slower or faster than the
other.
• While turning the tractor on a curved path, the
inner wheel has to travel lesser the tractor to
move faster than the other at the turning point.
Differential unit

4. • The output shaft coming from the gear box is
provided with a bevel pinion at the end of the
shaft.
• The bevel pinion is in mesh with a large bevel
wheel known as crown wheel.
• The main functions of crown wheel assembly
are:
• (i) to transmit power through right angle drive
to suit the tractor wheels.
• (ii) to reduce the speed of rotation.

5. Main Functions of Differential
• Further reduces the rotations coming from the gear
box before the same are passed on to the rear axles.
• Changes the direction of axis of rotation of the power
by 90 degree i.e. from being longitudinal to transverse
direction.
• To distribute power equally to both the rear driving
axles when the tractor is moving in straight ahead
direction.
• To distribute the power as per requirement to the
driving axles during turning i.e. more rotations are
required by the outer wheel as compared to the inner
wheel – during turns.

6. The main components of the differential are:
1. Input pinion gear
2. Crown wheel gear
3. Differential cage
4. Differential star
5. Differential axle (sun) gear

10. WORKING
• The differential casing is rigidly attached with the
crown wheel and moves like one unit.
• Two pinions are provided inside the differential
casing, such that they are carried round by the crown
wheel but they are free to rotate also on their own shaft
or stud.
• There are two or more bevel gears in mesh with
differential pinion.
• One bevel pinion is at the end of each half shaft,
which goes to the tractor rear wheel

11. • Thus instead of crown wheel being keyed directly
to a solid shaft between the tractor wheels, the
drive is taken back from the indirect route through
differential casing, differential pinion and half
shaft of the tractor
• When the tractor is moving in a straight line, the
differential pinion do not rotate on the stub shaft
but are solid with the differential casing.
• They drive the two bevel gears at the same speed
and in the same direction as the casing and the
crown wheel.

12. Differential lock:
• Differential lock is a device to join both half
axles of the tractor so that even if one wheel
is under less resistance, the tractor comes out
from the mud etc as both wheels move with
the same speed and apply equal traction.

13. FINAL DRIVE
• Final drive is a gear reduction unit in the power trains
between the differential and the drive wheels.
• Final drive transmits the power finally to the rear axle and
the wheels.
• The tractor rear wheels are not directly attached to the half
shafts but the drive is taken through a pair of spur gears.
• Each half shaft terminates in a small gear, which meshes
with a large gear called bull gear.
• The bull gear is mounted on the shaft, carrying the tractor
rear wheel.
• The device for final speed reduction, suitable for tractor
rear wheels is known as final drive mechanism.

15. Types of final drive
•Bull gear type
•Hub reduction axles
•Straight axle
• Planetary
Ring Gear
• The ring gear is a large circular gear that forms the outer part of the final drive
assembly.
• It is connected to the differential unit or planetary gear set and rotates with the
movement of the tractor's wheels.
• The ring gear engages with other gears in the final drive, transferring power and
torque to the wheels.
Pinion Gear
• The pinion gear is a small gear that meshes with the ring gear.
• It is connected to the tractor's transmission output shaft or axle shaft and rotates with
the transmission's input speed.
• As the pinion gear engages with the ring gear, it transmits the rotational force to the
final drive, thereby turning the tractor's wheels.

16. The bull gear final drive system consists of a set of gears and shafts that
transmit power from the tractor's transmission to the rear wheels. The gears
are called bull gears, which mesh with small pinions attached to the axle shafts.
This system provides high torque and power to the wheels, making it suitable
for heavy-duty applications. Bull gear final drives are commonly found in larger
and older tractors.

17. Hub reduction axles employ a planetary gear system within the wheel hub to
enhance torque and load-carrying capacity. These axles reduce rotational speed
while significantly increasing torque, crucial for heavy-duty tasks like pulling or
carrying substantial loads.
They bolster the off-road capabilities of a tractor to improve the traction in
challenging terrains.
Additionally, they distribute the load among multiple components, reducing axle
stress and enhancing longevity.

18. A straight axle, also known as a solid axle or live axle, is a common type of axle used
in many tractors and other heavy-duty vehicles. It offers simplicity, durability, load
distribution, and excellent traction, making it suitable for heavy-duty agricultural
tasks and off-road operations.
Tractors with straight axles typically employ other mechanisms for steering while
relying on the solid axle for load bearing and stability.

19. The planetary final drive system utilises a set of planetary gears to transmit power
from the transmission to the wheels. These gears are compact and provide a higher
gear reduction. It results in increased torque and traction.
Planetary final drives offer better manoeuvrability. It makes them ideal for smaller
tractors and those used in agricultural applications. Planetary rear axle is also
known as epicyclic reduction.

20. 1. Power Transmission: It transfers power from the tractor's transmission
to the wheels. It ensures efficient power delivery, enabling the tractor to
move with the required torque and speed.
2. Gear Reduction: It helps convert the high-speed, low-torque output from the
transmission into the necessary low-speed, high-torque output at the wheels.
As a result, tractor generates more pulling power to handle heavy loads.
3. Speed Control: It alters the gear ratios within the final drive to help the
operator adjust the speed at which the tractor moves ensuring precise control
and operation in various conditions.
4. Direction Control: It engages different drive shafts and gears to help the
operator determine the direction the tractor moves, whether forward, reverse,
or turning.
5. Traction: Good traction is essential for preventing slippage and ensuring
efficient operation, particularly in challenging terrain.
6. Torque Multiplication: In the case of planetary final drives, they offer
torque multiplication, which is crucial for tasks that require significant pulling
or pushing force, such as tilling or pulling heavy loads.
Functions of the Final Drive in Tractors

23. PROBLEM