Transcript Gears and Transmissions

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
• Spur
– Simplest gear design
– Straight cut teeth
– Noisy operation
Types of Gears
• 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)
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
How Stuff Works
Gear Ratios
• When two gears are in mesh, a gear ratio exists
• Driven Gear = Ratio
Drive Gear
• 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
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 Transmission
Output Torque 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.
GM 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
6
TH700-R4, 4L60,
4L60E
16 bolts
7
4L80E
17 bolts
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 = Ratio
# of teeth on the driving member
Calculating Planetary Gear
Ratios
• Overdrive
– Carrier is input
# of teeth on the driven member
. = Ratio
# of sun gear teeth + #of ring gear teeth
Calculating Planetary Gear
Ratios
• Underdrive
– Carrier is held
# of teeth on driven gear
# of teeth on driving gear = Ratio