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Global TrainingTP95850 3

General Information

The expression power transfer system is a collective one that covers the clutch, gearbox,

propeller shaft and rear axle.

These components have the task of transferring the engine power to the driving wheels.

The components in the power transfer system are:

1. Clutch

2. Gearbox

3. Propeller shaft4. Rear axle

When both the engine (5) and the power transfer system are described as a single unit, we talk

about the power train.

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Clutch

A clutch is a transmission component whose purpose is to let the engine run without the driving

wheels being affected. Examples are when the vehicle has to be stopped or started or when the

driver has got to change gear. In cases like this the power transfer system has to be disengaged

from the engine. This is called declutching.

The major component of a clutch consist of a plate (1), release bearing (2) and a disc (3). All are

mounted between the engine and the gearbox.

The clutch is operated by a servo-aided system that consists of:A. Master cylinder connected to the clutch pedal.

B. Clutch servo connected to release bearing.

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Gearbox:

A gearbox makes the necessary conversions to the driving power transferred from the engine to

the driving wheels with aid of various power ratios.

There are three basic gearboxes:

1. Manual gearbox

2. Automatic gearbox

3. Semi-automatic gearbox

- In a Manual gearbox, the driver selects the gear to be shifted.

- In an Automatic gearbox, the driver selects a driving program and the gear selection is carried

out by an electronic system and the actual gear changes are performed by a internal hydraulic

control system.

- In a Semi-automatic gearbox, the driver selects a driving program and the gear selection is

carried out by an electronic system and the actual gear changes are performed by external

pneumatic cylinders.

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Power take-off

Some trucks require driving power for different types of auxiliary equipment. If the truck is

equipped with a tipper platform, concrete mixer or a crane, a power take-off is required to

operate the hydraulic pump.

Power take-off is divided into two main categories, those that are dependent upon the clutch and

those that are independent of it.

- The power take-off dependent on a clutch (1) is driven by the gearbox and is used for tippers

and cranes.

- The power take-off independent on a clutch (2) is driven by the flywheel and is usually used forrefrigerator trucks and concrete mixers.

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Propeller shaft

Propeller shaft

The purpose of the propeller shaft is to transfer the driving power from the transmission to the

final drive.

The most common type of propeller shaft consists of:

Driving flange (1) with spider (2) mounted in needle bearings.

Thanks to the universal joint the propeller shaft can turn to various angels caused by the

movement between the transmission and rear axle.

Propeller shafts (3) (4) is made of strong tubular steel, which has been design to stand up to the

maximum torque that is transferred to the rear axle.

The propeller shafts is furnished with sliding splines _ at the tube end (3) and sleeve end (4) to

absorb the movement between the transmission and rear axle.

Support bearing (5)

If the vehicle has more than one propeller shaft a support bearing is used to suspend the

propeller shafts on the vehicles cross member.

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Final Drive

The main task of the rear axle is to transmit driving power from the engine out to the wheels.

The rear axle consists of:

Rear axle-housing (1), which is made of cast iron and is to support and protect all axle

components.

Differential (2) with helical gears that transfer the driving power through an angel of 90.

Driving shafts (3) that transmit the driving power on to the wheels.

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