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. Types of Gears Spur Helical Planetary 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)
Types of Gears

6. Power Vs. Torque Torque – measurement of twisting force
How Stuff Works
Power Vs. Torque
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

7. Gear Ratios When two gears are in mesh, a gear ratio exists
How Stuff Works
Gear Ratios
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 = 2:1 ratio (two to one ratio)
The drive gear must rotate twice to make the driven gear rotate once
Drive Gear

8. Reversal of Direction
When two gears are in mesh one will spin the opposite direction of the other
Idlers are used to reverse direction

9. Speed Change
The change in RPM from the input gear to the output gear is directly proportional to the gear ratio
Example: 3:1 gear ratio
Input gear turns at 900 RPM
Output gear turns at 300 RPM

10. Torque Multiplication
The change in torque from the input gear to the output gear is directly proportional to the gear ratio
Example: 3:1 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

11. Torque Multiplication
1 inch inches

12. 1 200 ft/lbs 2000 RPM 4:1 800 ft/lbs 500 RPM Underdrive 2 2:1
Gear
Engine Output Torque
Engine Speed
Gear Ratio
Transmission Output Torque
Transmission Output Speed 1
200 ft/lbs
2000 RPM
4:1
800 ft/lbs
500 RPM
Underdrive 2
2:1
400 ft/lbs
1000 RPM 3
1:1
Direct Drive 4
.5:1
100 ft/lbs
4000 RPM
Overdrive

13. 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

14. Planetary Action Direct Drive Any two of the components are driven
1:1 Ratio