Locking Differentials

7/28/2019 Locking Differentials

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AGM 240

Power Frames

Mr. Conrado

Locking Differentials


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Introduction

This lesson discusses methods

employed to override undesirable

differential action.

When the differential is locked up,

both of the axles will be driven at the

same speed regardless of wheelconditions.


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This differential can be locked or

unlocked with the differential switch

in the cab.

The operator should lock the

differential anytime the machine is

being operated in a straight line. This transfers all of the torque to all

wheels under all traction conditions.

The differential can be unlocked for

turns in order to reduce the turning

radius and tire wear.


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The differential has a clutch between

the left side gear and the differential

housing.

When the differential is locked, a

solenoid will allow oil flow behind the

clutch piston to engage the clutch.

The clutch will be engaged and left sidegear will rotate at the speed of the

rotating housing.

The differential pinion gears will not

rotate on their axes because the spider

and the side gear rotate at the same

speed.

The differential pinion gears will hold

the other side gear.

Both of the axle shafts will turn at the

speed of the rotating housing.


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When the differential is unlocked, the

solenoid will block the flow to the

clutch pack and both of the side

gears can turn freely.

Locking differentials force one of the

side gears to rotate with thedifferential housing.

This causes the differential to act like

a solid axle and transmit all of the

torque to both of the wheels.

This causes both wheels to rotate at

the same speed, regardless of

traction.


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Jaw Clutch

Some locking differentials use jaw

clutches.

The operator engages the jaw clutch

when a wheel is slipping.

By using a pedal or a switch to lock

the differential.

The operator determines when the

differential lock is needed.

Jaw Clutch


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Jaw Clutch

The operator should lower the

engine speed and not spin the wheel

while engaging the differential lock.

Engaging the jaw clutch at high

speeds can cause damage to the

differential. The operator should not attempt to

turn while the jaw clutch is engaged.

Sometimes the operator will hear

the jaw clutches hitting each other.

If that happens, the operator shouldlower the engine speed to let the jaw

clutches engage.


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Jaw Clutch

The jaw clutch connects one of the

side gears to the differential housing.

The differential pinion gears will not

rotate on their axes because the

spider and the side gear rotate at the

same speed. The differential pinion gears will hold

the other side gear.

Both of the axle shafts will turn at the

speed of the rotating housing.

When the differential is unlocked,springs will push the jaw clutch apart

and both of the side gears can turn

freely.


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Backhoe Loaders

In Backhoe Loaders, the jaw clutch is

engaged by pushing down on a foot

pedal.

This motion is transmitted through a

mechanical linkage and results in a

constant torque on a lock lever. The lock lever causes a fork to push

the coupling on the side gear into the

adapter on the differential housing.

When the two halves of the jaw

clutch are pushed together, one side

gear will be locked to the differential

housing.


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Backhoe Loaders

After full engagement has occurred,

the differential lock pedal should be

released.

The power that is transferred from

one wheel to the other wheel results

in a side force. This side force will keep the jaw

clutch engaged.

When the power becomes more

equally distributed, the side force will

reduce. The jaw clutch will disengage

automatically due to the reduced

side force.


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Wheel Tractor Scrapers

In Wheel Tractor Scrapers, air is used

to engage the jaw clutch.

One half of the jaw clutch is splined

to the differential housing. The other

half of the jaw clutch is fastened to

the left axle shaft. In older Wheel Tractor Scrapers, the

operator can engage the jaw clutch

by pushing down on a foot pedal.

In newer Wheel Tractor Scrapers, the

operator engages the jaw clutch by

pushing a switch.

When the pedal or switch is released,

the jaw clutch will release.


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Wheel Tractor Scrapers

When the pedal is depressed or theswitch is pushed, a differential lockvalve will allow air to flow behind apiston.

The piston will push the jaw that isconnected to the axle shaft so that it

contacts the jaw that is connected tothe differential housing.

When the two halves of the jawclutch are pushed together, one axleshaft will be locked to the differentialhousing.

When the pedal is released or whenthe switch is released, the pressureair will not flow behind the piston.

The spring will push the two halves ofthe jaw clutch apart.


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Limited Slip Differential

A limited slip differential is designedto provide equal power to bothwheels until the ground conditionscause a variance in traction betweenthe left and right wheel.

It contains two multidisc clutches.

Each clutch connects a side gear tothe rotating housing.

A small clearance is specified duringthe assembly of the limited slipdifferential to ensure proper clutchengagement.

Both wheels will be driven at equaltorque and speed during straightoperation if good traction is availablebeneath both wheels.


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In a standard differential, if the machine

is jacked up and one wheel is held or

braked, the other wheel turnscorrespondingly faster.

With a limited slip differential, the

clutches make this more difficult by a

factor that increases proportionally tothe input torque.

The locking effect happens due tointernal friction of the differential.

When a speed difference at the axles

occurs, the separating forces inside the

differential will cause the compression

of the clutch packs.

This causes torque in the faster wheel

to be redirected to the wheel with

better traction.


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When a turn is needed, the forces

from the wheels are sufficient to

overcome the clutch packs.

This design is used due to space

limitations.

In this design, the gear toothseparating forces are used to apply

the clutches.


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Spider

The spider shown consists of three

shafts.

The long shaft holds two differential

pinion gears.

Two half length shafts each hold one

differential pinion gear.


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Connector

The ends of the three shafts meet at

a connector.

Internal slack is present because this

type of connection is used instead of

a direct connection, and allows gear

tooth separating forces to be felt.


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Spider

Each spider shaft is inserted into the

connector through the rotating

housing and through the differential

pinion gears.

Three dowels are used to fasten the

shafts to the rotating housing.


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Side Gear

One side gear sits on top of the

connector and differential pinion

gears.

The other sits below the connector

and differential pinion gears.

The differential pinion gears meshwith the side gears.

The face of the side gear shown is the

contact surface for the clutch pack.

When a speed difference is present,

gear tooth separating forces push theside gears axially toward the clutch

packs.

The axial forces compress the clutch

packs.


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Discs and Plates

The discs are splined to the side gears.

The plates are connected to the

rotating housing.

The amount of torque used to

compress the clutch packs is called the

braking torque.

The braking torque is load dependentand is proportional to the amount ofinput torque.

When the clutch is engaged on the

faster axle, the total input torque will

increase.

All torque above the braking torque istransferred to the slower wheel.

Therefore, the limited slip differential

provides a torque split when the

clutches are engaged.


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Shims

Shims are used to set clearance when

necessary.


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Lab

Homework

Locking Differentials

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