gears and transmissions. why is a transmission necessary? provide torque multiplication at low...
TRANSCRIPT
Gears and Transmissions
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)
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
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
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)
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
How Stuff Works
5252
Mustang Cobra VS. Caterpillar Diesel
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
How Stuff Works
Reversal of Direction
• When two gears are in mesh one will spin the opposite direction of the other
• Idlers are used to reverse direction
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
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
Torque Multiplication
1 inch 3 inches
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 = 4.1:1• You are able to find the 1st gear ratio of the TH-350
in a manual which is listed as 2.52:1
Multiple Gear Ratios
• Rear end ratio x 1st gear ratio = total gear ratio• 4.1 x 2.52 = 10.33:1
– 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
– @ 3200 RPM in 1st gear the torque acting on the rear tires = 230 lb/ft x 10.33 = 2375.9 lb/ft torque !!!
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
2 200 ft/lbs 2000 RPM
2:1 400 ft/lbs 1000 RPM Underdrive
3 200 ft/lbs 2000 RPM
1:1 200 ft/lbs 2000 RPM Direct Drive
4 200 ft/lbs 2000 RPM
.5:1 100 ft/lbs 4000 RPM Overdrive
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.
Automatic Transmission I.D.
Automatic Transmission I.D.
1 Aluminum Powerglide 14 bolts
2 TH200 Metric 11 bolts
3 TH350 13 bolts
4 TH400 13 bolts
5 TH200-4R 16 bolts
6TH700-R4, 4L60, 4L60E
16 bolts
7 4L80E 17 bolts
GM I.D.
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
Planetary Action
• Direct Drive– Any two of the components are driven– 1:1 Ratio
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
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
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
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
Calculating Planetary Gear Ratios
• Direct Drive = 1:1
• Underdrive– Carrier is output
# of sun gear teeth + #of ring gear teeth# of teeth on the driving member
= Ratio
Calculating Planetary Gear Ratios
• Overdrive– Carrier is input
# of teeth on the driven member .# of sun gear teeth + #of ring gear teeth
= Ratio
Calculating Planetary Gear Ratios
• Underdrive– Carrier is held
# of teeth on driven gear= Ratio# of teeth on driving gear