20% Drivetrain loss doesn't make sense to my brain.

Exactly what I'm saying...an umbrella concept cannot account for everything, it is, at best, guesswork...an approximation.
However, YES...its a good way to estimate, or at least the best/only way. I also understand that much better now, too. But, I think that to some engineers, an estimate probably amounts to a guess...which, to some, amounts to not much. If your guessing a bridge needs to be 15 ft. high for a truck to pass under it, and the truck is 14 ft. high, and your margin for error is plus or minus 4 ft., you can't take that to the bank, ya' know?
But, I DIDN'T WRITE THE ARTICLE!!!! Nor, am I endorsing it, OR debunking it...
I...merely posted it, for discussions sake.
It IS fun to try to wrap your head around it...
Again...I'm NOT A SCIENTIST.

 

Forces being exponential in general terms gives us an idea to calculate what we're looking for, like a 'rule of thumb' way of looking at things. I was glad to see the use of 'work over time' which is what it's really about. Force, friction, parasitic drag, centrifugal force, wind resistance (in the gear cases and in the crankcase). Every component takes work to get through. Easy if you don't over-think it. I like how they figure CVT drive systems. Very close to the topic but backwards in some ways. As in 'x' grams at a radius of 3"= 'y' force @ 'a' RPM. Increasing 'a' by 50% can yield 250% more force if not more. I actually have those formulae in the home shop and they're helpful in many ways. Too much info no doubt, but I find these topics fun and informative.

 

Hey, I am not trying to make it sound like you don't have an interest in this. Just trying to drive home the point that there are so many variables in what you are trying to understand. You are trying to get your brain around something that Engineers with PHD's sometimes don't understand. I my self don't understand, hell I don't understand Quantum Physics and I know I don't, thats why I am not turning my hair gray tryng to understand something that is beyond me.

Here is somethings the think about.

From a oil point of view a transmission that is cold will consume more HP than one that is hot. That is because the the oil will get thinner and cause less drag as the oil moves past the gears due to thinner viscosity. But as the oil gets warmer it will also loose it viscosity and become less efficient to reduce the effects of friction. So as the transmission gets warmer the oils flows better causing less HP loss and more HP loss at the same time but at different rates. So how can you calculate this?

Also a new transmission will consume more HP than one that is older. The faces of the teeth of the gears will become more polished as the transmission is used. This will cause the Coefficient of friction to go down which results in less energy consumed in the transfer of energy. But at the same time the wear that is happening on the gears is also taking place on the shafts and bearings. As the bearings and shaft wear they become less efficient in transferring energy again at different rates. Again how do you calculate this?

I guess what I am trying to show you is that there is too much going on to make a clear decisive number to use when calculating the losses. In order to get an exact number you must examine every component in the system for a valid number. This is usually done in a new out of the box condition. But that number is not valid for the same system of components that that have been well used. On any given day and circumstance the number will change. That is why the rule of thumb.

Change the lubrication, changes the efficiency.
Change the HP input, changes the efficiency.
Change the operating temp, changes the efficiency.
Change the gear material, changes the efficiency.
Change the gear selections, changes the efficiency.
Change the gear pitch, changes the efficiency.
And ON
And ON

 

My Brain hurts.



Excellent thread.

 

Now here's a puzzle -
Horsepower lost in the transmission - where does it go?
HEAT - but 20% of 200 at the flywheel is 40HP.
1HP is 746 watts so 40HP is almost 30 kilowatts.
Hmmm, my transmission doesn't get THAT hot.
And then go up to 1000HP - 150KW?
Does not compute.
Somebody out there got a rational answer to this?
Onwards and upwards,
Neil.

 

Exactly. Refering back to the original posters example of comparing a 100 hp flathead to the 1000hp at the crank engine, it's easy to imagine that if the flathead's drivetrain was put behind a 1000hp engine, the loss would be 100% because parts would be scattered all over the ground! More power, bigger bits in the drivetrain = more power loss.

Bob

 

Look at the Ford numbers above; very little loss in trans in high, lots in lower gears, so in situations where lower gear use is essentially momentary there would be litttle cooking going on there. In high, I think they guessed about 13%, mostly in rear end.
Trans would presumably get real damn warm in a long second gear climb.

 

This looks like a fun discussion I missed out on when I was out on the salt....

Yeah, friction is a percentage thing. Yeah, friction in a manual trans in high gear (straight thru) is pretty low. Yeah, rearends get hot under high power use!

Anyone who claims that some transmission or rearend always uses XX hp is nuts. I have that trans and that rearend in my car, and it'll creep in Drive at idle with no problem.

Driveline inertia will show up in chassis dyno testing if there is acceleration involved (such as on a dyno pull where the engine speed is increasing)...but not during steady state testing.

Remember, the frictional equation is pretty damn simple:

F = u N

(frictional force equals the coefficient of friction times the normal force)

so don't be surprised at all if you find the percent loss is pretty much a constant. It is a fact that was discovered a long time ago, and aint gonna change.