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Automotive How to apply more torque to increase speed from steady-state

  1. Dec 2, 2012 #1
    If I am traveling along at a steady 60 kph in top gear ... and say my tacho is showing 2000rpm,
    then my "torque curve" says for this rpm the engine is outputting a specific torque - as I understand it, this is what is needed to zero out the forces from wind resistance and other frictional forces. Thus the net force will be zero and i maintain a steady speed.

    Great ... now, how do i accelerate to increase speed? Put my foot further down on the accelerator ... but how does the car experience a higher torque at my starting 2000rpm? (assuming i stay in the same gear). Remember, at 2000rpm, the Torque curve tells me I have a specific torque value .. so in order for me to have more torque, i need more rpm ... but this means i need more speed. (this is a chicken/egg scenario)

    I am assuming one of two explanations:

    (a) the Torque curve actually represents the Max torque at Full throttle ... so anything less than full throttle means you get smaller torque (than the graphs we see) at any given rpm ; or

    (b) the gearbox has some buffering/damping ... so when I put my foot down the revs go up even athought the speed of the wheels follow more slowly behind.

    Of course, new cars have auto self-adjusting everything (valves, continuous transmission ratios, etc) ... but let's answer the question assuming I have a stick-shift jalopy from the 60's ... so which is it? (a) or (b) or (c) both or (d) something else?
    Last edited: Dec 2, 2012
  2. jcsd
  3. Dec 3, 2012 #2
    Hint: Think "throttle" instead of "accelerator".
  4. Dec 3, 2012 #3
    It's a. Power curves as seen from a dyno are typically at wide open throttle.
    Part throttle will give some value less than this.
  5. Jan 18, 2013 #4
    This is the correct explanation.
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