Running Alt. from the gearbox?

[hat_man]

I was recently watching the 24 Hours of LeMans and they said some of the cars run their alternators from the gearbox. The idea I guess is to not have as much drag on the engine to help with HP. I realize these cars do run 24 hours straight and not stop and go like ours, but not knowing anything about anything, wouldn't the drag on the gearbox be nearly the same as the drag on the engine? I mean, aren't they physically connected?

In my completely non-mechanical mind, if this is a better set-up, then why couldn't we run an Alt. or P/S pump from the driveshaft in some kind of mechanical/magical way?

I say this somewhat in jest as I know using the gearbox(trans/driveshaft) has to be super expensive and highly technical, but it is an interesting idea. A toothed ring (perfectly balanced mind you) around the driveshaft with a smaller gear on an Alt. or P/S pump mounted under the bed of a pick-up. I assume that there would be the same drag on the driveline no matter where you put the Alt in this mythical system. Would this actually "free up" HP for any kind of FE increase? Hypothetically not in actuality.

Maybe this should be in the Unicorn section.

[hat_man]

Another thought just went through my pea sized brain.

How about a 4WD set up with some different gearing (more efficient) running the rear "output" to a 2WD rear-end and using the front "output" to drive the Alt. and P/S, etc. Maybe everything except the water pump?

Just another thought from the guy who thinks too much.

[ChazInMT]

Yeah, No. The further down the line you put stuff the less efficient it is due to having to be driven through an inefficient component. It isn't like a huge loss, but if the gearbox is 95% efficient at driving something, and it is pulling the alternator the whole time, than there is a 5% loss to the power required to drive the alternator as opposed to when it is driven directly by the engine.

Not to mention what it would do to your pulse & glide performance if you were to factor that in.

And mechanically speaking, do we really want the high amperage electric thingy hanging in the wind/rain/dirt/mud stream that is the underside of our cars.

I suspect that they drive it from the gear box on the race cars because it's 1 less belt to worry about, they don't care about pulse & glide, and if engineered well, I bet it's a bullet proof connection to drive the alternator with. I bet a ham sandwich though that the thing is sticking up half way into the foot well of the front passenger seat if it is a hopped up version of a Aston, Vette, or Beemer....Never mind that honey, just keep your feet off it, it's probably a little warm.

[Daox]

It shouldn't make a difference HP wise. Its a load on the engine no matter where it is.

[hat_man]

That's kind of what I thought. I was just musing more than anything. Keeps me thinking outside the box.

[justme1969]

Yes and No. Ive never seen one hung from a gear box but have seen it set to yoke of the drive shaft.
It is more efficient than you think driven by the weight of the rotating assemblies there is negligable resistance.
Normal mounting will be atop or beside the rear axle.
Added benefits are weight transfer to rear and close proximity to rear mounted Batt.

[ConnClark]

Like ChazInMT said You would want it before the transmission. The best solution would be to incorporate the alternator into the fly wheel. The next best thing would be a gear drive. Then probably a toothed belt.

Of course all of this power savings would be dwarfed by just improving the efficiency of the alternator.

[oil pan 4]

Originally Posted by justme1969

Normal mounting will be atop or beside the rear axle.
Added benefits are weight transfer to rear and close proximity to rear mounted Batt.

It cleans up the mess under the hood, might be handy to not have the alt in the way if you have to make a repair while on the side of the track.

[AntiochOG]

An alternator connected to the driveshaft would continue to charge the battery (at a cost to coasting distance) during EOC.

[oil pan 4]

Originally Posted by AntiochOG

An alternator connected to the driveshaft would continue to charge the battery (at a cost to coasting distance) during EOC.

I think it would solve part of the problem of EOCing and having the lights on (at night), engine off and running down the battery.

So long as you are using a rear wheel drive vehicle.