Gear box

 Gear box: Necessity for gear ratios in
transmission, Synchronous gear boxes, 3, 4
and 5 speed gear boxes, Free Wheeling
mechanism, Planetary gears systems, over
drives, fluid coupling and torque converters,
Epicyclic gear box, principle of automatic
transmission, calculation of gear ratios

Automotive Gears: Gears play an important role in trucks, car, buses,
motor bikes and even geared cycles. These gears control speed and include
gears like ring and pinion, spiral gear, hypoid gear, hydraulic gears,
reduction gearbox.

Depending on the size of the
vehicles, the size of the gears also
varies. There are low gears
covering a shorter distance and
are useful when speed is low.
There are high gears also with
larger number of teeth.

 To provide the high torque at the time of
starting, hill climbing, accelerating and
pulling a load since high tractive effort is
needed
 It permits engine crankshaft to revolve at
high speed, while the wheels turn at slower
speeds
 Variable torque by set of gears
 Vehicle speed can be changed keeping engine
speed same with certain limit

 The transmission also provides a neutral
position so that the engine and the road
wheels are disconnected even with the
clutch in the engaged position
 A means to back the car by reversing the
direction of rotation of the drive is also
provided by the transmission

 Variation of resistance to the vehicle motion
at various speeds
 Variation of tractive effort of the vehicle
available at various speeds

 Manual Transmission
 Sliding Mesh Gear box
 Constant Mesh Gear box
 Synchromesh Gear box
 Automatic Transmission
o Over drive (semi-automatic)
o Fluid drive or Fluid coupling
o Fully automatic
 Epicyclic gear box
 Free Wheeling unit
 Torque Convertor

A fluid coupling is a hydrodynamic device used to
transmit rotating mechanical power. It has been used
in automobile transmission as an alternative to a
mechanical clutch

Fluid coupling consists of three components, plus the
hydraulic fluid:
 The housing, also known as the shell (which must have
an oil tight seal around the drive shafts), contains the
fluid and turbines.
 Two turbines:
 One connected to the input shaft; known as the pump
or impellor, primary wheel, input turbine, driving
member
 The other connected to the output shaft, known as
the turbine, output turbine, secondary wheel or
runner or driven member

 The driving turbine, known as the 'pump', (or driving torus) is
rotated by the prime mover, which is typically an internal
combustion engine or electric motor. The impellor's motion imparts
both outwards linear and rotational motion to the fluid.
 The hydraulic fluid is directed by the 'pump' whose shape forces the
flow in the direction of the 'output turbine' (or driven torus). Here,
any difference in the angular velocities of 'input stage' and 'output
stage' result in a net force on the 'output turbine' causing a torque;
thus causing it to rotate in the same direction as the pump.
 The motion of the fluid is effectively toroidal - travelling in one
direction on paths that can be visualised as being on the surface of
a torus:
 If there is a difference between input and output angular velocities
the motion has a component which is circular (i.e. round the rings
formed by sections of the torus)
 If the input and output stages have identical angular velocities
there is no net centripetal force - and the motion of the fluid is
circular and co-axial with the axis of rotation (i.e. round the edges
of a torus), there is no flow of fluid from one turbine to the other.

The figure shows the power transmission system of an
automobile . The motion of the crank shaft is transmitted
through the clutch to the gear box. From the gear box the
motion is transmitted to the propeller shaft through the
universal joint and then to differential through another
universal joint. Finally power transmitted to the rear
wheels
through the rear axle.

Gear box

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