GEARBOX
Gearbox is a speed and torque
changing device.
It changes speed and torque between
engine and driving wheels.
The mechanism through which the
driving torque of the engine is transmitted to the driving wheel is the
gearbox.
PURPOSES/ FUNCTIONS OF GEAR BOX
It helps the engine to disconnect
from driving wheels.
It helps the running engine to be
connected to the driving wheel smoothly and without shock.
It provides the leverage between
engine and driving wheels to be varied.
It helps the driving wheel to be
driven at different speeds.
It gives the relative movement
between engine and driving wheels due to flexing of the road springs.
TRACTIVE EFFORT
The torque available on the wheel produces
a driving force which is parallel to the road known as “Tractive effort”.
TYPES OF GEARBOX
1. Manual transmission
i)
sliding mesh gearbox
ii)
Constant mesh gearbox
iii)
Synchromesh gearbox
2. Automatic transmission
i)
Hydromantic gearbox
ii)
Torque converter gearbox
3. Epicyclical gearbox
SLIDING MESH GEAR BOX
Simple in construction, Simplest
type of gearbox.
In this gearbox, spur gears are
used.
It consist of following parts.
1.
output shaft
2.Low
and reverse sliding gear
3.
Second sliding gear
4.
clutch
5.
Input shaft
6. Clutch gear
7. Counter shaft drive gear
8.
Counter shaft
9.Low
speed gear
10.
Second gear
11.
reverse gear
12.
Reverse idler gear
13.
Gear shift fork
There are three gears (1,6 and 5)
attached on the main shaft and four gears (2,3,4 and 7) are on the lay shaft.
The two gears on the main shaft (6
and 5) can be slide by a shifting yoke and mesh with the gears (3 and 4) on lay
shaft.
Therefore it is called “sliding
mesh gearbox”. A separated idler gear (8) is mounted on the idler shaft.
GEARS IN NEUTRAL
When the engine is running and the
clutch is engaged, the counter shaft is driven by the clutch gear.
The clutch gear rotates in opposite
direction to the counter shaft.
The low speed and high speed gears
that are fitted on the transmission main shaft or gearbox shaft do not rotate
because they are not engaged with any driving gears.
Therefore there is no motion
transmitted from clutch to output shaft.
Hence the vehicle is stationary.
CONSTANT MESH GEARBOX
All gears are constantly mesh and
dog clutches are used for engaging and disengaging the gears.
Helical and double helical gear
teeth can be used for the gears.
This type gears having less
damaging during meshing because the gear diameter are smaller with few numbers
of teeth.
So this type has more defects when
compared o synchronous type.
ADVANTAGES OF CONSTANT MESH GEARBOX
OVER SLIDING MESH GEARBOX
Quicker gearing can be achieved
Only damage occurs on dog clutch
teeth not teeth of gear wheels.
Synchronizing devices can be used
for smooth engagement of gears.
Once the dog clutches are engaged
there is no motion between their teeth but the power is transmitted through the
sliding action on teeth on one wheel on those of other when the gear teeth are
engaged.
To transmit the motion properly,
the teeth are suitably shaped.
SYNCHROMESH GEARBOX
To simplify the operations of
changing gears without the occurrence of clashes and their consequent damage, a
synchromesh gearbox is used in different type of motor vehicles.
Helical gears are used
It has synchromesh unit instead of
dog clutch.
The synchronizer helps to
synchronize the speeds of two gears to be engaged.
ADVANTAGES
Gear changing is very much
simplified
Less wear in gears
Quiet
DISADVANTAGES:
Design is very much complex
Initial cost is high
Quick change of gears occurs due to
noise of crashing
TORQUE CONVERTER
Constructional features are similar
to fluid flywheel.
The only difference is that it has
an ordinary stationary member called “stator or reaction member”.
All the members have blades or
vanes of specified shape.
But the operation is not similar.
In fluid flywheel same torque is
transmitted as given by the engine shaft.
But the torque converter increases
the torque in the ratio of about 2:1 to 3:1
