Drive line loss

[joe117]

Why would drive line loss be a percentage of the total power being transmitted through it?

Seems like the loss might go up a little when higher torque is going through it but I don't see how a constant percentage is going to give the right answer.

Calculating the flywheel hp by using a constant percentage of loss on the way to the wheels, will give a bigger number.
Perhaps that's why it's popular to use a fixes percentage.

 

[ViperRay]

Joe, check this out:

http://www.superstang.com/horsepower.htm#whyauto

 

[joe117]

That's a good article but it doesn't really answer the question.

If you look at the heat energy that 18% of your hp represents, It's hard to see where all that heat is going.

I'm not sure that the load on gears or bearings has a linear effect on frictional losses.

Loss through bearings or gears probably goes up when more torque is transmitted,
I don't see why the loss must be linear.

 

[ViperRay]

I'm not sure that it's a linear relationship either... unless someone wants to somehow measure driveline heat output vs. torque, we'll not know.

A percentage is probably an oversimplification... how close to the truth it comes is questionable and in my mind only suggests that driveline loss is not fixed.

 

[RedGTS]

While the amount of driveline loss (power, not percentage) will rise somewhat with increases in power, the truth is that driveline loss is closer to a fixed amount for a given car than it is a fixed percentage of total power. Because it is really neither, and because there is no ready way to measure a fixed amount without removing the engine from the car, it is easier to approximate as a fixed percentage. The percentage will go down some as power goes up though.

 

[joe117]

Yup,
I believe there is an almost fixed amount of power that it takes to run the drivetrain.

Gear mesh, roller and ball bearings probably don't increase friction in a linear manner as torque goes up.

The amount of heat that would be generated by 80 or 100 hp loss in a drivetrain is very large. I just don't see that heat being generated.

I believe that people like to have a big % number for loss calculation.
That way they can claim a bigger number for engine hp.

I also believe that a number of car guys are going to favor the dyno that shows the biggest hp.
I'm sure that the folks who sell dyno time have thought about this.

 

[Viper X]

Ditto RedGTS