CH-3-Gear Box

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Fundamentals of automobilesystem

CH : 3

AUTOMOBILE TRANSMISSION

SYSTEM


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Gear Box

A transmission or gearbox provides

speed and torque conversions from arotating power source to another

device using gear ratios.


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Transmission:

To vary the engine torque as per the driving needs and

transfer it to wheels.

Lower gear (1st, 2nd etc) for more torque (turning force)& less speed. For example at starting, climbing etc

Higher gears for more speed but less torque like highway

driving

Two types of transmissions are used.

Manual Transmissions

Automatic Transmissions

Transmission (Gearbox)


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Gear Ratios

The gear ratio can be determined by counting the teeth on

both gears.


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Advantages:

Cheaper to manufacture than A/T

Economical on fuel

Easy to maintain

Lighter than A/T units

Benefits: Lower vehicle cost

Fuel efficient

Lower maintenance cost


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Automatic Transmissions

In automatic transmission, the gearbox changes gear ratios

automatically as the vehicle moves, thus freeing the driver

from having to shift gears manually.


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Sliding Mesh Gear Box


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Contd

The various spur-type gears are mounted on

three shafts.

Primary shaft (alternative names clutch orfirst motion shaft)

Lay shaft (countershaft)

Main shaft (third motion shaft)


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Constant Mesh Gear Box


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In this design, the main shaft pinions revolves

freely on bushes or needle-roller bearings and

are all in constant engagement with the

corresponding lay shaft wheels. The gearoperation is obtained by locking the

respective gear to the main shaft by means of

a dog clutch.

The quieter-running helical gears can be

employed, and during gear changing the noise

and wear are reduced

Contd


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DOUBLE DECLUTCHING

Used for smooth engagement and disengagementof gears in constant mesh gear box.

Procedure: for higher gear to lower gear:1. Press clutch pedal and shift gear to neutral

2. Release clutch pedal and press accelerator pedal to

increase speed of main shaft, so speed of mainshaft and dog clutch can be same.

3. Again press clutch pedal and shift from neutral to

lower gear


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Synchromesh Gear Box


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Fundamentally the box is laid out in samemanner as a constant-mesh, with theexception that a cone clutch is fitted betweenthe dog and gear members.

The initial movement of the selector a sleevecarries the hub towards the gear and allowsthe cones adjusts the speed of the gearwheel

to suit the hub and main shaft. Extra pressure on the lever will allow the

sleeve to override the spring-loaded balls, andpositively engage with the dogs on the gear.

Contd


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Epicyclic Gear Train

Epicyclic means one gear revolving upon andaround another.

The design involves planet and sun gears as one

orbits the other like a planet around the sun. Here is a picture of a typical gear box.

This design can produce large gear

ratios in a small space and are used

on a wide range of applications

from marine gearboxes to electric

screw drivers.


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Epicyclic Gear train

A small gear at the center called the sun, several

medium sized gears called the planets and a large

external gear called the ring gear.


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Epicyclic Gear train

It is the system of epicyclic gears in which at leastone wheel axis itself revolves around another fixed

axis.


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Torque convertor


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CVT


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CH-3-Gear Box

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