mr henderson
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| posted on 11/11/08 at 03:51 PM |
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quote:
Originally posted by v8kid
John read the bit where I said the friction losses were proportional to the applied load. Think about pushing heavy versus light loads across a gravel
drive.
David
Where in the rolling road situation would you expect most of the increased losses due to friction to be?
(I'm sure you read my bit where I explained how the tyre losses were already accounted for) (and the other bit where I explained that there were
no speed increases to be allowed for)
John
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MikeRJ
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| posted on 11/11/08 at 04:19 PM |
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quote:
Originally posted by mr henderson
Well then it's a good job that the rolling road measures the tyre losses too!
The problem is that during a power run the tyres will be heavily loaded, hence distorting more and absorbing more power. During the coast down run
where transmission losses are measured, the tyre has far less load and will look like a lower loss.
There are so many factors that a coast down measurement of loss can only be an approximation.
quote:
Originally posted by mr henderson
Why would a more powerful engine show higher losses throught the same transmission? I'm not saying that it wouldn't, but I see no inherent
reason why it would, so would be interested to hear your thoughts about that.
Think about the measurement of power; Torque x RPM. A more powerful engine is going to be producing more of either or both. High RPM will always
give more frictional losses, especial viscous friction loss through churning the oil. More torque gives higher loads on both gear teeth and bearings,
again increasing frictional losses.
For any given RPM, it will take a certain amount of power just to turn a gearbox/final drive with no load on it's output. Once you start
loading the gearbox, the losses will increase as more torque is put through the box. This gives you a fixed and a variable component of the power
loss.
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v8kid
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| posted on 11/11/08 at 04:48 PM |
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John I'm afraid thats just the way it is! More power at the same speed means more torque. More torque means more sideload on the gears and
bearings. More load means higher frictional losses.
Can't change the way things are!!
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C10CoryM
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| posted on 11/11/08 at 06:34 PM |
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Sorry, I'd have to say that the flywheel numbers given from a chassis dyno are no more accurate than using a percentage.
As David says, the harder you load gears the more friction it takes to slide the helical gears over each other. Also applies to tire loading
(deformation), and alignment changes. Way too many variables to be accurate.
There is no real standard for measuring HP here. Racers use rwhp because that's all that really matters. The automakers use SAEnet hp which
is flywheel power with accesories,exhaust, air cleaner, and emmisions.
"Our watchword evermore shall be: The Maple Leaf Forever!"
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