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Published byHaylie Percell Modified over 2 years ago

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Gears and Transmissions

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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)

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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

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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

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Planetary Gears How Stuff Works

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Helical Gears

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Spur Gears

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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)

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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

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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

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

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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

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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

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Torque Multiplication 1 inch 3 inches

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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 1 st gear ratio of the TH-350 in a manual which is listed as 2.52:1

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Multiple Gear Ratios Rear end ratio x 1 st 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 1 st gear the torque acting on the rear tires = 230 lb/ft x 10.33 = 2375.9 lb/ft torque !!!

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GearEngine Output Torque Engine Speed Gear Ratio Transmission Output Torque Transmission Output Speed 1200 ft/lbs2000 RPM 4:1800 ft/lbs500 RPMUnderdrive 2200 ft/lbs2000 RPM 2:1400 ft/lbs1000 RPMUnderdrive 3200 ft/lbs2000 RPM 1:1200 ft/lbs2000 RPMDirect Drive 4200 ft/lbs2000 RPM.5:1100 ft/lbs4000 RPMOverdrive

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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.

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Automatic Transmission I.D.

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1 Aluminum Powerglide14 bolts 2 TH200 Metric11 bolts 3 TH35013 bolts 4 TH40013 bolts 5 TH200-4R16 bolts 6 TH700-R4, 4L60, 4L60E 16 bolts 7 4L80E17 bolts GM I.D.

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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

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

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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

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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

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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

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SunCarrierInternalSpeedTorqueDirection InputOutputHeldMaximum Reduction Maximum Increase Same as Input HeldOutputInputMinimum Reduction Minimum Increase Same as Input OutputInputHeldMaximum Increase Maximum Reduction Same as Input HeldInputOutputMinimum Increase Minimum Reduction Same as Input InputHeldOutputReductionIncreaseOpposite as Input OutputHeldInputIncreaseReductionOpposite as Input

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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

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Calculating Planetary Gear Ratios Overdrive –Carrier is input # of teeth on the driven member. # of sun gear teeth + #of ring gear teeth = Ratio

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Calculating Planetary Gear Ratios Underdrive –Carrier is held # of teeth on driven gear = Ratio # of teeth on driving gear

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