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Homework Help: Engine - Drive Shaft Coupling Torque

  1. Dec 26, 2011 #1
    1. The problem statement, all variables and given/known data

    A solid drive shaft is connected to an engine by a coupling, which has drive pins located on a pitch circle diameter of 80 mm (Note: the diameter of the pitch circle is greater than the diameter of the drive shaft). If the maximum power output of the engine is 90kW at 5000 rev/min, the shear stress in drive pins is not to exceed 60 MN/m2, and the shear stress in drive shaft is not to exceed 70 MN/m2, determine:

    (i) The minimum acceptable diameter of the shaft
    (ii) If the minimum number of solid drive pins that are required is 5 determine the diameter of each pin

    2. Relevant equations



    3. The attempt at a solution

    I worked out the torque of the engine to be 47.12 MNm by using P=Tω but can I just put this value into T/J=[itex]\tau[/itex]/r to find the answer to (i)?
  2. jcsd
  3. Dec 26, 2011 #2


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    123321: Your value for torque, T, currently looks incorrect. Try again, paying attention to units and correct unit conversions. After you obtain T, yes, you can use T in your first relevant equation.

    By the way, MN/m^2 is called MPa. Always use the correct, special name for a unit. E.g., 60 MPa, not 60 MN/m^2.
  4. Dec 26, 2011 #3
    Thanks for answering this question too nvn, I think I'm going to skip the I beam question. I've got no clue. Haha!

    To convert rpm to rad/sec you times by 2[itex]\Pi[/itex]/60 right? Which give me 523.6 rad/sec. Then multiplying this by the power to give me T, which gives me the same answer.
  5. Dec 26, 2011 #4


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    123321: Should you not divide this into power? Check your algebra, and try again.
  6. Dec 26, 2011 #5
    Haha! That was embarassing...
  7. Dec 27, 2011 #6
    I worked out the torque of the engine to be 171.89 and then I was going to put it into T/J=τ/r the problem is that J = 2I = Πd^4/32 so do I use 40 mm as the radius or am I supposed to have two unknowns?
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