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

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Discussion Overview

The discussion centers around the relationship between torque, engine speed (rpm), and vehicle acceleration, particularly in the context of a car operating at a steady speed and the mechanics of increasing speed from that state. Participants explore the implications of torque curves, throttle position, and gearbox behavior, with a focus on a hypothetical older vehicle with a manual transmission.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant describes the scenario of maintaining a steady speed and questions how to apply more torque to accelerate, presenting two potential explanations: (a) the torque curve represents maximum torque at full throttle, or (b) the gearbox has buffering that allows for increased rpm without immediate speed increase.
  • Another participant suggests focusing on "throttle" rather than "accelerator" as a key concept in understanding the situation.
  • A third participant asserts that power curves from a dynamometer are typically measured at wide open throttle, implying that part throttle results in lower torque values than those shown on torque curves.
  • A later reply supports the first explanation (a), stating it is the correct understanding of the torque curve's representation.

Areas of Agreement / Disagreement

Participants express differing views on the mechanics of torque application and the role of throttle versus accelerator. While some support the idea that torque curves reflect maximum torque at full throttle, others introduce alternative perspectives, indicating that the discussion remains unresolved with competing explanations.

Contextual Notes

The discussion does not clarify the assumptions underlying the torque curve interpretation or the specifics of how throttle position affects torque output. There is also a lack of consensus on the impact of gearbox behavior in this context.

jjolla
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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:
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jjolla said:
...
Great ... now, how do i accelerate to increase speed? Put my foot further down on the accelerator ...
Hint: Think "throttle" instead of "accelerator".
 
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.
 
jjolla said:
(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 ;

This is the correct explanation.
 

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