chapter 23 bennet

8/10/2019 Chapter 23 Bennet

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Chapter 23

Heavy-Duty

Truck Axles


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Objectives (1 of 3)

Identify the types of axles used on trucks and

trailers.

Define the terms dead axle, live axle, pusher

axle, and tag axle.

Outline the construction of a drive axle carrier

assembly.

Explain how a pinion and crown gearsetchange the direction of powerflow.


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Objectives (2 of 3)

Describe differential action and list the

reasons it is required.

Identify the components required to create

differential action.

Describe the operation of the various drive

axle configurations.

Identify the components used in an interaxledifferential or power divider.


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Objectives (3 of 3)

Explain how an interaxle differential lock

functions.

Define the term spinout and explain how it is

caused.

Trace the powerflow path through different

types of differential carriers.


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Examples of Heavy-duty Axles


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Typical Steering Axle


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Trailer Axle


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Single Rear Drive Axle


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Cutaway Differential Carrier


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Shop Talk

Each OEM tends to use different words to describe the samecomponents, but in this text we will try to use the most commonterm.

A crown gear is also a ring gear, but we usually will use the firstterm.

An axle shaft also can be known as a half-shaft or drive shaft;once again, we usually will use the first term.

A drive shaft connects a drive wheel to a differential, whereas adriveshaft is a propeller shaft that delivers input torque to thefinal drive carrier. Confused? You bet, but, nevertheless, you

should try to become familiar with all the OEM terms so that youcan accurately interpret service literature.


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Typical Differential Components


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Differential Action


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Tandem Drive Axles


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Final Drive Axle Configurations

A single-reduction axle

A planetary double-reduction axle

A two-speed axle assembly

A tandem drive axle


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Bevel Gears


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Hypoid, Amboid,

and Spiral Bevel Gears


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Single-reduction Carrier


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Differential Lock


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Hypoid Double-reduction Carrier

Pl t


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Planetary

Double-reduction Gearing


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Forward Tandem Drive Axle


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Torque Distribution

with Power Divider Unlocked


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Torque Distribution

with Power Divider Locked

P Di id


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Power Divider

with External Lube Pump


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Disengaged Power Divider


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Torque Distribution

with Normal Traction Conditions


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Power Divider Engaged

T Di t ib ti


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Torque Distribution

When One Axle Loses Traction

D i A l Sh ft


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Drive Axle Shaft

Configurations

Two drive axle shaft configurations are used

to provide support between the axle hub and

the vehicle wheels.

Semi-floating axle shaft Full floating axle shaft


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Non-driving Axles

There are three categories of non-driving or

dead axles.

Steering axles

Lift and tag axles

Trailer axles


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Summary (1 of 6)

Axles can be divided into live axles and dead

axles.

Live axles are drive axles; they house the

gearing required to change the direction ofpowerflow and produce differential action.

Dead axles are designed to support chassis

loads. Dead axles include steering axles, tag

axles, pusher axles, and various types of

trailer axles.


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Summary (2 of 6)

The drive axles in trucks are known asdifferential carriers and are mounted in abanjo housing.

Driveshafts deliver driveline torque to thedifferential carrier that uses pinion and crowngearing to change the direction of powerflowand transmit it to the drive wheels.

Differential gearing is required in drive axlesand enables an outboard wheel to turn fasterthan an inboard wheel through a turn.


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Summary (3 of 6)

The critical differential components are a four

shaft spider with pinion gears on each shaft

that mesh to side gears on either side. The

side gears are splined to the axle shaftresponsible for driving the wheels.

During differential action, the slowdown of

one side gear is inversely proportional to the

increase in speed of its opposite side gear.


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Summary (4 of 6)

Most single-reduction axles are splash-

lubricated by gear oil as the geared

components rotate, but many differential

carriers with power dividers and multiple-reduction gearing use oil pumps to help

lubricate the assembly.

Tandem drive trucks require an inter-axle

differential or power divider to divide driveline

torque between the two drive axles.


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Summary (5 of 6)

In a tandem drive axle arrangement, differentialaction in the differential carriers and power divider

can cause spinout, in which a one-wheel spin can

produce fourfold velocities.

Most inter-axle differentials can be temporarily

locked out by a driver-activated switch.

This can help provide traction in slippery conditions

and reduce the potential for spinout.


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Summary (6 of 6)

Two-speed differential carrier gearing can beused on both single and tandem drive axlevehicles; control is by the driver.

A double-reduction differential carrier canproduce two ratio reductions. The firstreduction takes place at the crown and piniongearing, the second at a planetary gearset.

Torque proportioning power dividers reducespinouts by biasing torque transfer to thedrive axle with the most traction.

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