[urq] Alternator Whine and Airflow Direction

Buchholz, Steven Steven.Buchholz at kla-tencor.com
Tue Nov 7 14:34:11 EST 2006

... we're just talking about cooling the alternator, not trying to draw air across a radiator.  The "fan" on the alternator is a radial impeller, that is the fan's exhaust is intended to be moving outward radially from the axle of the fan.  This means that the air would be at right angles to any air coming into the engine compartment due to the motion of the vehicle.  It seems odd, but it is probably likely that in most cases (not just Audis) that the airflow internal to the alternator would be considered backward (i.e. toward the front of the car in a longitudinal engine configuration).  On the T44s there is a "Ram air" duct which connects to a shroud on the back of the alternator housing.  On the V8Q the duct to the "back" of the alternator attaches to the front brake cooling duct in the belly pan.  The RAM air should accentuate any flow from the fan.

Steve B
San José, CA (USA)
> But the direction of the airflow would have to be from the front of the car to
> the rear! If the fan pushes the air out the front at speed it wouldn't be able
> to exit, because the fan would be pushing against whatever air speed the car
> had. And the car would overheat, but only at speed, idling it would come back
> down to normal temps....

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