David - please explain "cogging" as you see it, I just found this Wiki. The motors are "AC" not DC if that matters. Thanks. -John

Found this Wiki: http://en.wikipedia.org/wiki/Cogging_torque

Cogging torque of electrical motors is the torque due to the interaction between the permanent magnets and the stator slots of a Permanent Magnet (PM) machine. Also termed as detent or 'no-current' torque, it is an undesirable component for the operation of such a motor. It is especially prominent at lower speeds, with the symptom of jerkiness.

A summary of techniques used for reducing cogging torque:

* Odd - Even number of stator coils (15) and magnets (16) - See Muller Motor
* Skewing stator stack or magnets
* Using fractional slots/pole
* Modulating drive current waveform
* Optimizing the magnet pole arc or width

Almost all the techniques used against cogging torque also reduce the motor Back emf and so the resultant running torque.

Here to mention, a slotless PM motor does not have any cogging torque.

 

These motors have permanent magnets fixed to the rotor. Wire coils (electromagnets) are evenly spaced on the stator. Each coil having a permeable core.

If the motor is DC, a commutator (brush or brushless) switches the DC to each coil (or set of coils) in turn to make the motor turn.

For AC motors, each phase connects to a coil, and the next phase to the next. (three phase). The electro-magnets attract the permanent magnet on the rotor, and pull it into position. When current is switched, or phased to the next pole, the rotor continues to turn to the next.

When the rotor is turned without power, a resistance occurs as the magnets pass each pole.

Depending on design, this cogging can be heavy or light. (Multiple pole motors seem to have less cogging).

I expect our hybrids have light cogging and just ignore the drag. Or, a very slight current is applied to counter the cogging.

Or, Ford has a better idea!!!

Google Brushless DC motors, GE ECM motors, Sensorless DC motors, Permanent Magnet AC motors. Brushless Permanent magnet DC motors.

There is a fine line between AC and DC motors when they are brushless and permanent magnet.

Maybe the distinction is in the drive, more than the motor.

Some drives are variable frequency AC drives, while others PWM (pulse width modulate) the drive to each coil. (Similar to a stepper motor control).

 

The motors in the FEH are 3 phase AC. And brush less, otherwise you could weld the brushes under high demand, this is a problem on the older diesel electric locomotives

 

...Other posts indicate the motors are permanent magnet. (They can still be three phase).

Are they permanent magnet, or three pahse motors with a VFD (Variable Frequency Drive)?

 

My technical data says they are 3 phase AC electric motors I dont know if they have magnets or not. I would copy and paste but that is not allowed from the data service. They do not have brushes though. One of my friends is a locomotive tech and he was worried about the brushes arching under heavy load like the old train engines did.

 

Brushless designs use semiconductors and microcontrollers in place of the brushes and commutator. ...maybe not on locomotoves as that would be a lot of current!

A three phase motor (not PM) is efficient, controllable, and existing technology. And that makes sense in our hybrid application. theory says a PM motor is more efficient, but tests I have seen do not show a significant improvement.

If it is a three phase induction motor, there would not be any cogging.

I would like to know for sure if it is PM, or not!

 

The FEH eCVT uses a permanent magnet AC synchronous machine for its lower losses, higher torque density, and reliability. That's what I've read anyway.

GaryG

 

What about the traction motor? PM or induction???

 

They are the same motors, just different sizes David. So yes, there both PM. They both are motors and generators and can turn in both directions.

GaryG