Explanation of Drivetrain loss needed

[MSRP]

Okay, I've searched this site but not ONE thread actually explained 'what' actually causes drivetrain loss. Everyone knows that All-wheel-drives lose more horsepower when compared to FWD and RWDs but can anyone actually explain what causes the hp loss?

-- The best explanation so far that i found is "The vehicle's ability to turn this roller is measured and calculated to come up with a figure that represents how much horsepower is actually available to move the vehicle around. Because a frictional loss between the engine and the driven wheels is unavoidable, wheel-driven horsepower will always be less than net horsepower." http://forums.yellowworld.org/archive/index.php/t-8524.html

However where exactly is this frictional loss coming from? Is something not strong enough and momentarily 'twisting' or rubbing, and therefore expending horsepower unnecessarily?

I'm just curious and I can't really figure this out..

Thanks for your time...

BTW if you're just going to respond with "Because that's just is" DON'T...
This thread is for educated people that would like to learn, not an argument between nit-wits, so please don't reply if you have nothing to say! Thanks

 

[Attoir]

I'm not an expert, but this is my understanding.

It's the same principal when you're using a ratchet with an extension on it. One extension, and you can't feel too much slack in the whole assembly. Add in three more extensions and you're going to feel a lot of slack before any actual torque / power is applied to the bolt.

In ANY joint, between a gear, in a bearing, anything where two moving parts connect, kinetic energy (power) will convert itself into some amount of heat (which means a loss of power). Between one gear and another, at 10,000rpm, (all figuratively speaking), after 5 minutes, I'm sure you'd be able to feel a significant amount of heat being produced.

Say those gears get too hot. You can sit them in a pool of oil while they're spinning in order to cool them off. That oil is also going to add resistance, as it takes more effort for the gears to make their way through oil than air. One of the main places this occurs is with your crankshaft.

Another is all the gears in your transmission are pretty much submerged in trans fluid.

Think about exactly how many joints / gears / bearing / whatever the energy produced in the cylinders go through before it reaches the wheels. There's a lot. A significant amount of power can be, and is lost.

Now, let's say the number of joints in a FWD car between the cylinder and wheels is... 300. (No clue what the actual number is)

Now think about an AWD car. You add a transfer case, driveshaft, more bearings, rear differential (whose gears are also submerged in fluid), axles, hubs, wheel bearings, etc.

You're of course going to have more loss in the AWD car.

Makes sense to me.

 

[slugsgomoo]

it's not only frictional loss, but also rotating mass. There is simply more weight to rotate with the additional parts.

The really interesting thing is that drivetrain loss is not linear- if you look at curves on a motor that has been dynoed on a stand at different levels, and then in a car, at those same levels, you'll see that the percentage of power lost is smaller at higher power, even though you may actually continue increase the number of horsepower lost. If that makes sense.

 

[98RedGs]

http://www.dsmtuners.com/forums/showthread.php?t=57651&highlight=Drivetrain+loss
http://www.dsmtuners.com/forums/showthread.php?t=137345&highlight=Drivetrain+loss

Both of these threads have some good information in them that could help you with your question. But drivetrain loss is usually blamed on the amount of frictional loss, but also rotating mass. These two factors plus the weight of the car can play a role in the drivetrain power loss calculation.

http://www.dsmtuners.com/forums/showthread.php?t=94188&highlight=drivetrain
Another thread I just remembered.



Thank you
John

 

[-silencer-]

Okay, I've searched this site but not ONE thread actually explained 'what' actually causes drivetrain loss. Everyone knows that All-wheel-drives lose more horsepower when compared to FWD and RWDs but can anyone actually explain what causes the hp loss?

The majority of it is extra rotating weight. Think of it this way..
You can pedal a bike with normal wheels fairly easily. How much harder would it be if you filled those wheels with lead? It's extra rotating weight and it takes more effort to get moving. However, there's the law of inertia, so it takes less extra % of effort to increase the speed once you get it moving. Why do people buy a lightened flywheel? Less rotational weight means quicker acceleration and deceleration.