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Gear ratios

Gear ratios. OBJECTIVES. To understand and calculate gear ratios To understand and demonstrate the relationship of torque and rotational speed To understand and properly express the relationship between the driving and driven gears.

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Gear ratios

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  1. Gear ratios

  2. OBJECTIVES • To understand and calculate gear ratios • To understand and demonstrate the relationship of torque and rotational speed • To understand and properly express the relationship between the driving and driven gears

  3. How do you get 4000 lbs of wheels and steel moving from a stop and keep it going without over revving the engine? • Gears! They are used to keep the engine in its ideal RPM range for any given condition • What can be done to get a race car to the end of the ¼ mile faster? • Use a set of low gears (numerically higher ratios) • What would you do to a vehicle to achieve a higher top speed? • Use a set of high gears (numerically lower ratios)

  4. If you have 20 apples and 10 oranges, what is the ratio of oranges to apples ? • 10/20=2:1

  5. Money in the stock market (2004) • Write a sentence about the graph to the left. • The graph has a positive return. When you put money in, you get more money out. • What is the ratio of output to input? (Show Work!)

  6. Money in the Stock Market (2009) • Write a sentence about the graph to the left. • What is the ratio of output to input? (Show Work!)

  7. Torque Relationship Torque Output (ft/lb) Torque Input (ft/lb) Write a sentence about the blue and red line? What is the gear ratio of the blue and red line? Under Drive Direct Drive

  8. Speed Relationship Engine Output RPM Write a sentence about the blue and red line? What is the gear ratio of the blue and red line? Engine Input RPM Under Drive Direct Drive

  9. Calculating Gear Ratios and Torque • Always divide the driven gear by the drive gear • 2 divided by 1 = 2:1 ratio • This ratio is used to calculate the output torque • 25 ft-lb x 2= 50 ft-lb

  10. Calculating Output Rpm • Divide the input rpm by the gear ratio • 1000 rpm divided by 2= 500 rpm

  11. Calculating TransmissionGear Ratios (multiple gear sets) 1. Calculate the ratio of the first set of gears by dividing the driven (output) gear by the drive (input) gear 2. Do the same for the second set of gears 3. Multiply the answer from the first calculation with the answer from the second calculation

  12. Divide the driven by the drive gear 44 divided by 11= 4:1

  13. How many times will the drive gear turn to rotate the driven gear once with a ratio of 4:1? • 4 times • 100 ft-lb of torque is input to a gear ratio of 4:1, how much is output? • 400 ft-lb • 1000 rpm is input to a gear ratio of 4:1, what is the output? • 250 rpm

  14. Torque Relationship (ft/lbs) Write a sentence about the blue and red line? What is the gear ratio of the blue and red line? Overdrive Direct Drive

  15. Speed Relationship (RPM) Write a sentence about the blue and red line? What is the gear ratio of the blue and red line? Overdrive Direct Drive

  16. If the input torque is 150 ft-lbs and the output torque is 450 ft-lbs, is this is under, direct, or over drive? What is the ratio • Under drive • 3:1 • If the input rpm is 1000 and the output rpm is 400, is this under, direct, or overdrive? What is the gear ratio? • Under drive • 2.5:1

  17. Two or more sets of gears in mesh- calculate the first set, then the second and multiply together for final ratio 3.63 x 3.52=12.78:1

  18. Gear Ratio Formula Driven gear (A) divided by Drive gear (A) multiplied by Driven gear (B) divided by Drive gear (B) equals Final transmission gear ratio

  19. Gear set A-drive gear has 20 teeth, driven has 40, Gear set B drive gear has 30 teeth, driven gear has 40. What is the drive ratio? • 2:1 x 1.33:1=2.66:1

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