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Torque calculation on drive half shaft in coast downshift condition

  1. Feb 9, 2015 #1


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    I want to calculate the torque coming onto a half shaft in a very particular event.

    The event is I let's say I am in 3rd gear and have reached my max torque zone after which I have taken my foot of the acc pedal...nw I m letting the the vehicle coast as soon as it reaches say 60% of max power rpm I downshift to 2st gear and after downshift m still not pressing the acc pedal..m just letting the vehicle drive by its momentum..

    Now during my downshift as soon as I engage the clutch I will have a very high amount of torque cmng onto the shaft...
    Pls guide me how to proceed to calculate this torque..!
    Thanx in advance... :)
  2. jcsd
  3. Feb 9, 2015 #2


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    Science Advisor

    As always, draw a free body diagram.
    The braking torque depends on the motor characteristics.
    You need to calculate how much torque is required to run the engine against a closed throttle.... No easy task....
    Do you know the fluid friction across the butterfly etc?
  4. Feb 9, 2015 #3


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    Thanx billy for your reply...
    It is basically a fuel in injected engine...I had some some data regarding the drag torque of the engine... If I multiply that value to the gear ratios the torque which is coming is to the tune of 200 Nm per shaft..the wheel slip torque if I consider .8 coefficient of friction comes up to 830 Nm but the incident which I mentioned above the values of torque varies from 1300 Nm to 1700 Nm depending upon the way clutch is released...1300 for gradual & 1700 for sudden...
  5. Apr 21, 2015 #4


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    Gold Member

    Also include the force needed to accelerate the flywheel and rotating/reciprocating mass of the engine.
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