Running Alt. from the gearbox?

[MetroMPG]

Originally Posted by AntiochOG

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

This was my first thought as well.

Logical extension: take control of the field to increase charging output for light "regen" braking when desired.

[tjts1]

Also power steering pumps.

[RedDevil]

Why would a racing car run the alt from the gearbox instead of the engine, and where in the gearbox could it hook up?

Well, not having the alt in before the clutch means that the rotating mass on the engine gets less. It could rev up or down quicker between gears.
The input shaft will have to change speed too though. The alterrnator could double as a motor to speed up, or draw extra to slow down the input gear shaft when shifting gear.

If the alternator is on the output shaft then its speed would equal that of the car, and possibly it would only provide full power at top speed while at lower speed the lesser drag means quicker acceleration.

Neither setup seems particularly fit to reduce fuel consumption in a road going car.

The Insight has an electric motor/generator that doubles as a fly wheel. But the Prius has electric motors and generators incorporated in its 'e-CVT' planetary gearbox system. The racing Prius.

[DucFanDan]

I'm guessing the announcer misspoke.

On many mid-engined, rear drive race cars (think Le Mans prototypes), the alternator is run off the axle shaft where it comes out of the transaxle. High-end modern race cars *may* have the alternator bolted to the transaxle and be driven by internal gears... but I have not seen that in-person.

In older times, it was done as a space-saving measure... as the engine bays on these cars are very cramped, and there is typically more room next to or above the transaxle.

As far as efficiency, it's not going to be more efficient, academically speaking. It is, however, better for a rev-happy race engine. The wheels/tires (and by extension, the CV axles) do not accelerate and decelerate as much as the engine does (which runs up and down with each gear change). By attaching the alternator to the axle shaft, you no longer have to waste energy revving the alternator up and down.

This might make a few HP difference on a 700-HP prototype race car that is being run through the entire rev range repeatedly over the course of a race. It is not, however, going to make a measurable difference in your daily driver... which, if you are driving for fuel economy, you are *not* trying to rev up and down quickly/repeatedly. Also note that on a race car averaging 150mph or so around Le Mans, the axle speed is enough to keep the minimalist electrical system going just fine. On your street car, running the alternator that slowly may present you with the problem of inadequate electrical power to keep the car running and the battery charged.

[user removed]

I think the Alfa alfetta 159 grand prix engine was two 4 cylinder blocks bolted nose to nose, with everything gear driven from the meeting point of the two engines. Both engines drove the car as a single straight eight while the front engine drove a two stage supercharger.
Good for 390 HP at a fuel consumption of 2 MPG under racing conditions. 1500 CC displacement.

No fan belts to break.

[justme1969]

Originally Posted by DucFanDan

I'm guessing Also note that on a race car averaging 150mph or so around Le Mans, the axle speed is enough to keep the minimalist electrical system going just fine. On your street car, running the alternator that slowly may present you with the problem of inadequate electrical power to keep the car running and the battery charged.

I need to rais B/s flag here. Unless you drive an electric car perhaps.
The only mods to the alternator on a scca club car were the pulley Diameters.
Also most were not trailer queens though not daily drivers they were street legal play things. Ive seen electronic packages in race cars that resemble an aircraft cockpit though Lap tops have changed most of that.