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GEARBOXES IN AUTOMOBILES
By
P. MOHAN BHARATHY
MECHANICAL “C”
INTRODUCTION…
 As the output shaft of a gearbox rotates at slower rate
than the input shaft, and this reduction in speed will
produce a mechanical advantage, causing an increase
in torque.
 Usually found near motors of some sort, gearboxes are
used to reduce the load on the motor.
 This reduces wear on the engine, allows more control,
and allows greater speeds.
 In other words, if when the motor is turning 2500 rpm the
output shaft is turning 500, the gearbox is reducing the
number of revolutions from input to output.
 Torque converters, hydraulics, electrical power and hybrid
configurations may also be used for the same purpose.
TYPES OF GEARBOXES
Types of Gearboxes:
 Sliding Mesh Gear box
 Constant Mesh Gear Box
 Synchromesh Gear Box
 Epicyclic Gear Box
An engine may consist of one or more gearbox.
There may be gearboxes which are a mixture of these types.
SLIDING MESH GEARBOX
 In this type of gear box, gears are engaged and disengaged by sliding
of the gear wheels.
 Gear wheels on the main shaft engage with gear wheels on the lay
shaft or counter shaft by sliding themselves.
1.main drive gear
2.counter shaft
3.main shaft
4.I gear
5.II gear
6.III gear
7.top speed engaging
dogs
SLIDING MESH GEARBOX
CONSTANT MESH GEARBOX
 In this case, gear wheels on the main shaft and lay
shafts are constantly engaged and the rotary motion is
transmitted to the main shaft by engaging dog clutches.
1.I speed gear
2.II speed gear
3.main shaft
4.III speed gear
5.top and III speed engaging
dogs
6.top gear
7.primary shaft or main drive
gear
8.counter shaft/cluster gear
CONSTANT MESH GEARBOX
CONSTANT MESH GEARBOX
CONSTANT MESH GEARBOX
Advantages of Constant mesh gearbox over Sliding mesh
Gearbox:
 Helical and herringbone gear can be employed in these gearboxes
and, therefore, constant mesh gearboxes are quieter.
 Since the gears are engaged by dog clutches, if any damage occurs
while engaging the gears, the dog unit members get damaged and
not the gear wheels.
 By suitably designing the dog clutch, the gear changing can be
made easier.
 Damage to the dog clutch is less likely because all the teeth are
engaged at a time.
SYNCHROMESH GEARBOX
 If the car is moving, the output shaft is always turning (because
ultimately it is connected to the wheels).
 The layshaft is usually connected to the engine, but it is free-
spinning once the clutch has been operated.
 Because the gears are meshed all the time, the synchro brings the
layshaft to the right speed for the dog gear to mesh.
 This means that the layshaft is now spinning at a different speed to
the engine, the clutch gently equalises the speed of the engine and
the layshaft, either bringing the engine to the same speed as the
layshaft or vice versa depending on engine torque and vehicle
speed.
 The green cone-shaped area
is the syncho collar. It's
attached to the red dog gear
and slides with it.
 As it approaches the helical
gear, it makes friction contact
with the conical hole.
 The more contact it makes,
the more the speed of the
output shaft and free-spinning
helical gear are equalized
before the teeth engage.
SYNCHROMESH GEARBOX
EPICYCLIC GEARBOX
 In such gear boxes
epicyclic gear trains are
employed to get the
various gear ratios.
 The characteristic feature
of an epicyclic gearing is
that at least one wheel not
only rotates about its own
axis but also rotates about
some other axis.
EPICYCLIC GEARBOX
Automatic gearboxes
typically use one or more
compound planetary gear
sets instead of chaining
regular gear sets together.
They look just like a regular
planetary gear set from the
outside, but inside there are
two sun gears and two sets of
intermeshing planet gears.
There is still only one ring
gear though.
EPICYCLIC GEARBOX
OVERDRIVE…
 The highest gears may be "overdrive" types that increase the output
speed.
 The overdrive consists of an electrically or hydraulically operated
epicyclic gear train bolted behind the transmission unit.
 It can either transfer the input drive shaft directly to the output shaft,
called a propshaft (1:1), or increase the propshaft speed so that it
turns faster than the input shaft (1:1 + n). Thus, in overdrive the gear
ratio is less than unity, i.e., propeller shaft rotates at a speed higher
than the engine speed.
 Thus the propshaft may be "overdriven" relative to the input shaft.
 It is actuated by a knob or button, often incorporated into the
gearshift knob, and does not require operation of the clutch.
OVERDRIVE
3-synchro overdrive gearbox
of an MGB Roadster 1968
model
TYPES OF TRANSMISSIONS
Common Types include:
 Manual Transmission
 Semi-Automatic Transmission
 Automatic Transmission
Uncommon Types include:
 Dual clutch transmission
 Continuously Variable Transmission [CVT]
 Infinitely Variable Transmission [IVT]
 Electric Variable Transmission [EVT]
 Hydrostatic
 Hydrodynamic
 Electric
MANUAL TRANSMISSION
 A simple but rugged sliding-mesh or unsynchronized / non-
synchronous system found in racing cars, older heavy-duty
trucks, and some agricultural equipment.
 Here straight-cut spur gear sets are spinning freely, and must be
synchronized by the operator matching engine revs to road speed,
to avoid noisy and damaging "gear clash.
 When the driver engages the clutch, the sliding gear disengages
from its existing position and can slide up and down the gearbox to
re-engage in a higher or lower gear.
MANUAL TRANSMISSION
SEQUENTIAL GEARBOX
 Manual transmissions use the standard "H"
pattern in the shifter. The manual transmission in
a motorcycle is nothing like this.
 On a motorcycle, you shift gears by clicking a
lever up or down with your toe. It is a much
faster way to shift. This type of transmission is
called a sequential gearbox or a sequential
manual transmission.
 It turns out that most race cars use sequential
gearboxes as well
SEQUENTIAL GEARBOX
 There are three forks
controlled by three rods
that are engaged by the
shift lever.
 There is still a set of gear
selector forks that move
collars that engage gears.
 The only difference is the
way the control rods are
manipulated.
 The "H" pattern is
eliminated and replaced
with a different motion.
 In a race car, the motion of
the shift lever is either
"push forward" to up-shift
or "pull backward" to
downshift.
SEMI-AUTOMATIC TRANSMISSION
AUTOMATIC TRANSMISSION
 Epicyclic Gearing or Planetary Gearing
are as used in an automatic transmission. An
Automatic transmission will select an
appropriate gear ratio without any operator
intervention.
 They primarily use hydraulics to select gears,
depending on pressure exerted by fluid within
the transmission assembly.
AUTOMATIC TRANSMISSION
Cutaway view of a typical 3-speed
automatic transmission
ADVANTAGES
Here are some of the features of an automatic
transmission:
 If the car is in overdrive (on a four-speed
transmission), the transmission will automatically
select the gear based on vehicle speed and
throttle pedal position.
 If you accelerate gently, shifts will occur at lower
speeds than if you accelerate at full throttle.
 If you floor the gas pedal, the transmission will
downshift to the next lower gear.
ADVANTAGES
Advantages of Automatic Transmission over Manual Transmission:
 Better fuel efficiency upto 15% increase.
 No loss of torque transmission from the engine to the driving wheels
during gear shifts.
 Very smooth gear-shift operations
 Appeals to drivers due to overall fast shifts and rapid responses, along
with the latest technology.
DISADVANTAGES
Disadvantages of Automatic Transmission over Manual Transmission:
 Its mechanical efficiency is very less than that of a manual transmission
type.
 Its requires a specialized transmission fluid/lubricants which is
expensive and need to be changed regularly.
 Its expensive to manufacture.
 It is heavier than an conventional manual transmission gearbox.
 It has much higher rate of failure due to complexity.
THANK YOU

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Automobile transmission - Gear Box

  • 1. GEARBOXES IN AUTOMOBILES By P. MOHAN BHARATHY MECHANICAL “C”
  • 2. INTRODUCTION…  As the output shaft of a gearbox rotates at slower rate than the input shaft, and this reduction in speed will produce a mechanical advantage, causing an increase in torque.  Usually found near motors of some sort, gearboxes are used to reduce the load on the motor.  This reduces wear on the engine, allows more control, and allows greater speeds.  In other words, if when the motor is turning 2500 rpm the output shaft is turning 500, the gearbox is reducing the number of revolutions from input to output.  Torque converters, hydraulics, electrical power and hybrid configurations may also be used for the same purpose.
  • 3. TYPES OF GEARBOXES Types of Gearboxes:  Sliding Mesh Gear box  Constant Mesh Gear Box  Synchromesh Gear Box  Epicyclic Gear Box An engine may consist of one or more gearbox. There may be gearboxes which are a mixture of these types.
  • 4. SLIDING MESH GEARBOX  In this type of gear box, gears are engaged and disengaged by sliding of the gear wheels.  Gear wheels on the main shaft engage with gear wheels on the lay shaft or counter shaft by sliding themselves. 1.main drive gear 2.counter shaft 3.main shaft 4.I gear 5.II gear 6.III gear 7.top speed engaging dogs
  • 6. CONSTANT MESH GEARBOX  In this case, gear wheels on the main shaft and lay shafts are constantly engaged and the rotary motion is transmitted to the main shaft by engaging dog clutches. 1.I speed gear 2.II speed gear 3.main shaft 4.III speed gear 5.top and III speed engaging dogs 6.top gear 7.primary shaft or main drive gear 8.counter shaft/cluster gear
  • 9. CONSTANT MESH GEARBOX Advantages of Constant mesh gearbox over Sliding mesh Gearbox:  Helical and herringbone gear can be employed in these gearboxes and, therefore, constant mesh gearboxes are quieter.  Since the gears are engaged by dog clutches, if any damage occurs while engaging the gears, the dog unit members get damaged and not the gear wheels.  By suitably designing the dog clutch, the gear changing can be made easier.  Damage to the dog clutch is less likely because all the teeth are engaged at a time.
  • 10. SYNCHROMESH GEARBOX  If the car is moving, the output shaft is always turning (because ultimately it is connected to the wheels).  The layshaft is usually connected to the engine, but it is free- spinning once the clutch has been operated.  Because the gears are meshed all the time, the synchro brings the layshaft to the right speed for the dog gear to mesh.  This means that the layshaft is now spinning at a different speed to the engine, the clutch gently equalises the speed of the engine and the layshaft, either bringing the engine to the same speed as the layshaft or vice versa depending on engine torque and vehicle speed.
  • 11.  The green cone-shaped area is the syncho collar. It's attached to the red dog gear and slides with it.  As it approaches the helical gear, it makes friction contact with the conical hole.  The more contact it makes, the more the speed of the output shaft and free-spinning helical gear are equalized before the teeth engage. SYNCHROMESH GEARBOX
  • 12. EPICYCLIC GEARBOX  In such gear boxes epicyclic gear trains are employed to get the various gear ratios.  The characteristic feature of an epicyclic gearing is that at least one wheel not only rotates about its own axis but also rotates about some other axis.
  • 13. EPICYCLIC GEARBOX Automatic gearboxes typically use one or more compound planetary gear sets instead of chaining regular gear sets together. They look just like a regular planetary gear set from the outside, but inside there are two sun gears and two sets of intermeshing planet gears. There is still only one ring gear though.
  • 15. OVERDRIVE…  The highest gears may be "overdrive" types that increase the output speed.  The overdrive consists of an electrically or hydraulically operated epicyclic gear train bolted behind the transmission unit.  It can either transfer the input drive shaft directly to the output shaft, called a propshaft (1:1), or increase the propshaft speed so that it turns faster than the input shaft (1:1 + n). Thus, in overdrive the gear ratio is less than unity, i.e., propeller shaft rotates at a speed higher than the engine speed.  Thus the propshaft may be "overdriven" relative to the input shaft.  It is actuated by a knob or button, often incorporated into the gearshift knob, and does not require operation of the clutch.
  • 16. OVERDRIVE 3-synchro overdrive gearbox of an MGB Roadster 1968 model
  • 17. TYPES OF TRANSMISSIONS Common Types include:  Manual Transmission  Semi-Automatic Transmission  Automatic Transmission Uncommon Types include:  Dual clutch transmission  Continuously Variable Transmission [CVT]  Infinitely Variable Transmission [IVT]  Electric Variable Transmission [EVT]  Hydrostatic  Hydrodynamic  Electric
  • 18. MANUAL TRANSMISSION  A simple but rugged sliding-mesh or unsynchronized / non- synchronous system found in racing cars, older heavy-duty trucks, and some agricultural equipment.  Here straight-cut spur gear sets are spinning freely, and must be synchronized by the operator matching engine revs to road speed, to avoid noisy and damaging "gear clash.  When the driver engages the clutch, the sliding gear disengages from its existing position and can slide up and down the gearbox to re-engage in a higher or lower gear.
  • 20. SEQUENTIAL GEARBOX  Manual transmissions use the standard "H" pattern in the shifter. The manual transmission in a motorcycle is nothing like this.  On a motorcycle, you shift gears by clicking a lever up or down with your toe. It is a much faster way to shift. This type of transmission is called a sequential gearbox or a sequential manual transmission.  It turns out that most race cars use sequential gearboxes as well
  • 21. SEQUENTIAL GEARBOX  There are three forks controlled by three rods that are engaged by the shift lever.  There is still a set of gear selector forks that move collars that engage gears.  The only difference is the way the control rods are manipulated.  The "H" pattern is eliminated and replaced with a different motion.  In a race car, the motion of the shift lever is either "push forward" to up-shift or "pull backward" to downshift.
  • 23. AUTOMATIC TRANSMISSION  Epicyclic Gearing or Planetary Gearing are as used in an automatic transmission. An Automatic transmission will select an appropriate gear ratio without any operator intervention.  They primarily use hydraulics to select gears, depending on pressure exerted by fluid within the transmission assembly.
  • 24. AUTOMATIC TRANSMISSION Cutaway view of a typical 3-speed automatic transmission
  • 25. ADVANTAGES Here are some of the features of an automatic transmission:  If the car is in overdrive (on a four-speed transmission), the transmission will automatically select the gear based on vehicle speed and throttle pedal position.  If you accelerate gently, shifts will occur at lower speeds than if you accelerate at full throttle.  If you floor the gas pedal, the transmission will downshift to the next lower gear.
  • 26. ADVANTAGES Advantages of Automatic Transmission over Manual Transmission:  Better fuel efficiency upto 15% increase.  No loss of torque transmission from the engine to the driving wheels during gear shifts.  Very smooth gear-shift operations  Appeals to drivers due to overall fast shifts and rapid responses, along with the latest technology.
  • 27. DISADVANTAGES Disadvantages of Automatic Transmission over Manual Transmission:  Its mechanical efficiency is very less than that of a manual transmission type.  Its requires a specialized transmission fluid/lubricants which is expensive and need to be changed regularly.  Its expensive to manufacture.  It is heavier than an conventional manual transmission gearbox.  It has much higher rate of failure due to complexity.