max torque and maximum power

[ernestopeña]

hello:

can someone help me understand why maximum power and maximum torque in an engine are not at the same rpm?

i assume this:
since torque= force* distance, the maximum torque should come with the maximum force and therefore maximum force is when there is maximum power,,,,

please correct me and make me understand

thank you..

[pompelmo]

You think correctly, but you forgot
that torque=J*acceleration/distance(radius)
F=force
r=distance(radius)
J="holding up" moment of all the spinning parts
a=acceleration

SO

F*r=J*(a/r)

[rodders]

for your information, here in Australia FORD have produced an engine that is supplied in the normal road car with a TORQUE figure that is constant from I think 2,400 RPM to maximium RPM !! That is it the Torque does not drop off as the revs Increases !!

[Chuck E]

Horsepower is equal to the product of torque x rpm x constant. If torque were constant from 2400 rpm to say 6000 rpm, then the horsepower would increase over that entire range. If on the other hand torque peaks at some value of rpm and then decreases, the picture is more complicated. If torque decreases slowly as the rpm’s rise, horsepower might still rise. A little more rapid drop in torque with rpm and horsepower might remain constant over the range. Finally, when torque drops faster than the rpm’s rise horsepower will begin to decrease. Since the torque verses rpm curve usually tails off slowly it is highly unlikely that torque and horsepower will peak at the same rpm.

[crystalclear]

I just finished helping a friend unload a truck. He's moved house.
Don't confuse weightlifter STRENGTH with POWER, rate of doing work.

Did we lift the absolute maximum we could on each trip?
No.
We could work faster by doing quick light trips. At a pinch, I can carry a bed matress on my own. But two of us carrying it can go more than twice as fast as me on my own, so we are working faster (POWER) doing more return trips (RPM), even if we are using less FORCE.

Torque is twisting force. Your not necessarily working faster if you twist harder but have to rotate slowly as a result. Empty a well as fast as you can with a bucket on a rope and a handle to turn. Would you use the biggest bucket you could possible lift and use maximum torque? No, you'd use a biggish bucket that you could still wind up quickly.

Take a horse like James Watt studied. He thought it could pull a pulley with 180 pounds weight on it and walk round in a 12 foot circle 2.4 times per minute. Torque=Force*distance=Force*radius=12*180=2160 foot pounds of torque.

Work=Force*distance=Force*circumference=force*radius*2*pi=180*12=2160*2*pi=13571 pound feet of work for every revolution

And since the horse would go 2.4 times round in a minute he thought a horse power was
2.4*13571 =32572 pounds feet of work every minute.
And he rounded this up to 33000.
And that is now the definition of horsepower 33000 pounds feet per minute.

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Now speculation on my part, I bet the same horse could have pulled 300 pounds and gone round once a minute.
Torque=300*12=3600 foot pounds of torque

Power=3600*2*pi=22619

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So even if the maximum torque the horse can give is 3600 foot pounds, at one RPM, it would still be giving about 2/3 of the power it would give at 2.4 RPM.

[acastval]

The theory reason which maximum power and maximum torque are not at the same rpm is: Each engine has an angular velocity which, the mass of the "work fluid" (the gas-air mixture that full the cylinder in one cycle) is the max.Then the area of the real cycle and the torque are the max values.At this point the power increase with the rpm because it depends of velocity although the the "work fluid" is down and the torque too.
Excuse me for my level of english, i need practice.