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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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Manual Transmissions
Manual Transmissions
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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