Gears%20and%20Transmissions

1
Gears and Transmissions
2
Why Is a Transmission Necessary?

• Provide torque multiplication at low speeds
• Reduce engine RPM at highway speeds
• Allow the engine to operate within its most
  efficient RPM range
• Allows the engine to be disengaged from the rear
  wheels while the vehicle is not moving (torque
  converter clutch)

3
What Does a Transmission Do?

• The basic purpose of a transmission breaks down
  into 3 parts
• Ability to alter shaft RPM
• Ability to multiply torque
• Ability to reverse the direction of shaft rotation

4
How Does the Transmission Produce Torque
Multiplication And/or RPM Reduction

• Transmissions use gears
• Spur
• Helical
• Planetary
• Gears are able to change the RPM and the torque
  of the power moving through the transmission as
  well as the direction of rotation

5
Planetary Gears
How Stuff Works
6
Helical Gears
7
Spur Gears
8
Types of Gears

• Spur
• Simplest gear design
• Straight cut teeth
• Noisy operation
• Helical
• Spiral cut teeth
• At least two teeth are in mesh at any time
• Distributes the tooth load
• Quieter operation
• Planetary
• Most complex design
• Used in almost all automatic transmissions
• Contains three parts
• Sun gear
• Planet gears
• Internal gear (ring gear)

9
Power Vs. Torque
How Stuff Works

• Torque measurement of twisting force
• Power measurement of how quickly work can be
  done
• Power is dependent on torque and RPM
• Horsepower Torque x RPM

5252
Mustang Cobra VS. Caterpillar Diesel
10
Gear Ratios
How Stuff Works

• When two gears are in mesh, a gear ratio exists
• Driven Gear Ratio
• Example
• Drive gear has 14 teeth
• Driven gear has 28 teeth
• 28 ? 14 21 ratio (two to one ratio)
• The drive gear must rotate twice to make the
  driven gear rotate once

Drive Gear
11
Reversal of Direction

• When two gears are in mesh one will spin the
  opposite direction of the other
• Idlers are used to reverse direction

12
Speed Change

• The change in RPM from the input gear to the
  output gear is directly proportional to the gear
  ratio
• Example 31 gear ratio
• Input gear turns at 900 RPM
• Output gear turns at 300 RPM

13
Torque Multiplication

• The change in torque from the input gear to the
  output gear is directly proportional to the gear
  ratio
• Example 31 gear ratio
• Engine turns input gear at 900 RPM with 50 lb/ft
  of force
• Output gear turns driveshaft at 300 RPM with 150
  lb/ft of force

14
Torque Multiplication
1 inch 3 inches
15
Multiple Gear Ratios

• Individual gear ratios can be multiplied to
  calculate a total gear ratio
• Example Chevy caprice with a TH-350 transmission
  and a 305 engine
• By removing the differential cover and inspecting
  the gearset you are able to count 10 teeth on the
  input gear and 41 teeth on the output gear
• 41 ? 10 4.11
• You are able to find the 1st gear ratio of the
  TH-350 in a manual which is listed as 2.521

16
Multiple Gear Ratios

• Rear end ratio x 1st gear ratio total gear
  ratio
• 4.1 x 2.52 10.331
• This tells us that the engine turns 10.33
  revolutions for every 1 revolution of the tires
  (speed reduction)
• Torque multiplication can also be calculated
• The 305 engine produces 245 lb/ft of torque at
  3200 RPM
• _at_ 3200 RPM in 1st gear the torque acting on the
  rear tires 230 lb/ft x 10.33 2375.9 lb/ft
  torque !!!

17
Gear Engine Output Torque Engine Speed Gear Ratio Transmission Output Torque Transmission Output Speed
1 200 ft/lbs 2000 RPM 41 800 ft/lbs 500 RPM Underdrive
2 200 ft/lbs 2000 RPM 21 400 ft/lbs 1000 RPM Underdrive
3 200 ft/lbs 2000 RPM 11 200 ft/lbs 2000 RPM Direct Drive
4 200 ft/lbs 2000 RPM .51 100 ft/lbs 4000 RPM Overdrive
18
Automatic Transmission I.D.

• Most automatics are identified by the oil pan.
• Look at the shift indicator to determine if the
  transmission is a 3-speed, 4-speed etc.
• Different transmissions may have been installed
  in otherwise identical vehicles.
• Shopkey and other manuals list transmission
  application by vehicle.

19
Automatic Transmission I.D.
20
Automatic Transmission I.D.
GM I.D.
21
Planetary Gearsets

• Simple planetary gearsets contain three
  components
• Internal (ring) gear / (annulus gear)
• Planet gears (and carrier)
• Sun gear
• One component will be the drive member, one the
  driven, and one will be held (except direct drive
  and neutral)
• Unlike other types of gears, planetary gears are
  able to operate on one single axis

22
Planetary Action

• Direct Drive
• Any two of the components are driven
• 11 Ratio

23
Planetary Action

• Underdrive
• Planet carrier is the output
• Minimum reduction
• Ring gear is held
• Sun gear is the input
• Maximum reduction
• Ring gear is input
• Sun gear is held

24
Planetary Action

• Overdrive
• Planet carrier is the input
• Minimum overdrive
• Ring gear is the input
• Sun gear is held
• Maximum overdrive
• Ring gear is held
• Sun gear is the input

25
Planetary Action

• Reverse
• Planet carrier is held
• Underdrive
• Ring gear is the output
• Sun gear is the input
• Overdrive
• Ring gear is the input
• Sun gear is output

26
Sun Carrier Internal Speed Torque Direction
Input Output Held Maximum Reduction Maximum Increase Same as Input
Held Output Input Minimum Reduction Minimum Increase Same as Input
Output Input Held Maximum Increase Maximum Reduction Same as Input
Held Input Output Minimum Increase Minimum Reduction Same as Input
Input Held Output Reduction Increase Opposite as Input
Output Held Input Increase Reduction Opposite as Input
27
(No Transcript)
28
Calculating Planetary Gear Ratios

• Direct Drive 11
• Underdrive
• Carrier is output
• of sun gear teeth of ring gear teeth

Ratio
of teeth on the driving member
29
Calculating Planetary Gear Ratios

• Overdrive
• Carrier is input
• of teeth on the driven member .

Ratio
of sun gear teeth of ring gear teeth
30
Calculating Planetary Gear Ratios

• Underdrive
• Carrier is held
• of teeth on driven gear

Ratio
of teeth on driving gear