The whine in my 08 MMH 4WD is not exactly as described here - no one's yet commented on what it might be, so all guesses welcome.

It happens in specific speed bands - regardless of load, regardless of whether accelerating or braking, ICE on or off or speakers on or off. 35-40 miles per hour, 55-65 miles per hour are two of the bands. It's a high-pitched whine that's pretty obvious in those bands, even more so with the front windows rolled down; pressing the accelerator changes the pitch, though sometimes the pitch goes down with the accelerator being pressed. Seems to originate somewhere underneath the vehicle between the front seats and front wheels.

Anyone else have this? Our '06 FEH 4WD doesn't make these sounds.

 

Its coming from the transmisssion's electric motor/generators. Its simply a matter of RPM and load. No mystery. At some RPMs it will whine a bit like many electric motors you've heard. As for going up or down in pitch, that probably depends on how the system decides is the best way to power the wheels at the speed/load you are going... sometimes its going to let the generator turn faster, sometimes slower... if you want to go faster and the generator sounds like its going slower then the power is coming from a different source (I would guess that its allowing the ICE to drive the wheels more rather than drive the generator, but I'm certainly no expert on that planetary system).

I have worked with lots of eletric motors and that whine is a distinctive motor/generator sound.

 

Thanks, Tim. It's actually related to speed, not RPMs, and is 100% consistent - so I'm betting it's something more in the transmission. There are other whines that the FEH makes as well, and which are clearly the motor/generators. This one is different.

 

The traction motor is permanently attached to the wheels in a fixed gear ratio.

Thus speed of the wheels is directly proportional to speed of the motor.
Thus the whine pitch of the motor would change with vehicle speed.
But also the intensity of sound will change with load put upon the generator/motor.
No load = no sound. More load = louder sound.

The smaller generator/motor changes RPM when the engine changes RPM and vise-versa.

 

As I understand it there isn't much in the transmission but the planetary and the two motors actually...

 

Well, it remains a mystery, then; the 08 MMH 4WD does it, and the 06 FEH 4WD doesn't...

 

Next time just leave your wife at home.

 

stevedebbi,

That sounds very much like the electric motor in generator mode. Especially since you say you're hearing it going down a hill: this is prime time for the motor to switch to charging the batteries. Our Honda Civic Hybrid (similarly) has a distinctive whine every time we decelerate, coupled with in-dash charging indication.