Correct in all respects. You probably know, but neglected to say that in practice the forces at work are not static. The battery SOC is not a constant, but is changing as the ECU alternately uses current to maintain the dynamic relationship between the MGs and then switches to recharge it. Its the same thing that you can observe on either display when cruising down the road with the battery topped up. The ECU will attempt to use some assist, just so that it can top it again.

I think this would be a natural application for a super capacitor at some point in the future. Such short-term exchanges of current could be buffered by the supercap to reduce battery cycles and keep the battery cooler. The same setup could handle high, instantaneous power changes and serve as a buffer for the battery system, including hard regenerative braking (which is the only way to keep this on topic).

Regarding the open stator, I agree, which is why I never bought into the argument that the AC side is open when the vehcile is placed in "N". That would be a fast way to either go out of business serving warranty claims, or to put a disclaimer in the warranty and lose lots of customers. (Not to even mention the PCM issues.)

 

FastMover you had it closer to right the first time. Now you are both completely wrong.

Thought experiment:

What is the lowest (non-negative) speed a motor or generator can turn? How about zero RPMs? Max torque for a motor is at the locked rotor condition.

Generation mode is completely different! How much power/current/whatever is going to come out of a generator at zero rpm? It does not take a rocket scientist to figure out that a stalled generator is putting out zilch, zero, nothing, nada, nil, etc.

 

That is exactly what I was trying to say in my second post:

Quote:

This is frequency independent up to a point, but at very low RPM the frequency period becomes too long to sustain the DC ouput at a constant voltage given the maximum design amplitude.)

I just didn't say it very well. At low frequencies the induced field decays as it is converted to current, and the period is so long that another cycle does not occur to re-excite the field, so it collapses or drops to levels below what is required to support the charging current.

 

"Sorry, but if you open the stator output of "these" motors while they're still rotating the voltage output will rise as high as need be to find, or open, a current flow path."

No: a moving wire in a magnetic field produces a finite voltage that depends on the flux swept by the wire per unit of time. In an open circuit, the voltage will be finite, and the current zero.

Experiment: find a cheap DC motor from a battery powered toy. Disconnect the leads and spin the shaft by hand. Observe that no sparks fly between the leads.

 

Now hold one bare motor lead in each hand and spin the motor rapidly..

Hint: Have a doctor close by.

 

Here's a hand drill powering a good-sized DC motor: It puts out a "killer" 15 volts:

http://www.youtube.com/watch?v=1bAcVVBxHj0

All I'm saying is that an open-circuit generator is a voltage source, not a current source. An open circuit voltage source is very happy, but an open circuit current source (like a Van de Graff generator) will build up charge until it sparks.

So, as voltage sources, MG1 and MG2 can, if desired by the ECU, be electrically disconnected without harm, so long as their open-circuit voltage is less than the breakdown voltage of the power electronics, a value that is easily calculated by the design engineers.

 

Aside from the physics of motors as generators, I do have an on-point question:

Does "B" mode also engage the rear brakes, as described in normal braking?

 

Based on the size of the DC motor in the video it seems unlikely that it would have a permanent magnet "stator". So the voltage generator will be only a function of the residual magnetism of the stator.

But the more important point is that as the drill motor RPMs declined the output voltage closely followed. That would indicate to me that should the drill motor been able to turn 2500 RPM then the motor voltage would have risen accordingly.

The motor/generators in these hybrids MUST be capable of charging a ~200 volt battery set throughout a wide RPM range. If it is possible to do that then what do you suppose the open circuit voltage might become at maximum RPM.

I am given to understand that the FEH has an electric clutch that disenages the entire driveline unless the ignition is on or if the inertia switch indicates a sharp forward movement indicative of being struck from behind, a rear-ender.

The purpose I was given, read, was that in the event of a rear-ender unless the MGs are disenaged from the driveline their surge voltage might easily go high enough to damage the electrics.

The existence of this clutch is also why the FEH can be towed 4-down.

 

It is my understanding that the only purpose for switching into "B" mode "switch is to enable of engine compression braking. Completely independent of your use, or not, of frictional and/or regen braking.

 

Sorry if I misunderstood. The way you said it in you second post seemed fine to me. It was later when you agreed with wwest (who was wrong for sure) that you seemed to be off track. I'm sure I just read it wrong.