jokerx7

Well, I posted this over on my Jeep forum, and thought I might as well see how all of you guys liked it, enjoy:





Call this a thought exercise, or maybe even a trolling attempt to start a worthwhile discussion. After taking a semester of strengths of materials, I'd like to think I have at least a rudimentary of the theory behind the basic underlying principles of cars.... So, I thought I'd try and figure out exactly where those ponies are going between the flywheel and the road.



It seems logical to assume that a fair amount of this power is consumed in getting all of the rotating mass up to speed. And for the most part, these should be simple calculations. Driveshafts, and halfshafts are pretty much uniform cylinders, while the flywheel, and all the gears in the tranny and differential(s). As I am dealing with powertrain loss, I won't go into discussion about the engine itself, but the same principles apply, and undoubtedly account for the high hp/L that my little wankel puts out.



As it is possible to physically calculate the loss due to rotational inertia (moment of inertia for you engineer types...), it would likewise seem possible to find a happy medium between strength and this inertia. I would imagine that auto-companies put some thought into this, but I am guessing that for anything but sports cars, the considerations are more along the lines of building the components with a fairly small factor of safety in the interests of saving money on manufacturing, ie snapping halfshafts when an engine begins to put out more max torque (not horsepower mind you).



There are obviously other power drains, including the gaps between gears, u-joints, cv joints, and that ever present pain phenomenon, friction, plus a little drag from the oil in the cases. The problem is, eliminating these is impossible, so they can only be minimized. Though, it would seem to me that friction could be minimized quite well. Ideally, there would be no sliding or rolling friction in the system, but only static friction. If this were so, no "work," ie horsepower would have to be exerted to overcome it. But as there is really no way around the gaps between machined objects, friction will stay.



But, much of the realm of friction is based on machining precision, and rests heavily upon the fluid mechanics of the lubricating components in the system.



And finally back to the easier stuff; rotation. There's probably not a lot that can be done for a reasonable price to reduce rotational inertia. Using exotic materials would surely help, but is prohibitively expensive. Whereas, something like an aluminum flywheel could net you a few ponies. Beyond that though, there's not a whole lot to do.



Though I will give one case example. The propellor shaft of a U.S. carrier stretches some 600 ft, weighs something like 300,000 pounds. But this is not the whole story, this shaft is not solid steel, but a tube filled with some substance. If the shaft was solid, it would weigh somewhere around 1.3 million pounds, but only be able to withstand something like ~1.5 times more torsional force.





Well, that is my rant. I guess I didn't really solve any real problems, but maybe I at least gave some insight into the subject for at least one of you peoples out there...



Edit: Wheels, tires, brakes, clutches, torque convertors, etc all apply too, I just got too involved in writing and forgot them

jarroyo

Ummmmmm Okay. I have just one question though, was there a point that i missed while reading that? Or was it just a bit of insight?