Torque Density. Saturation Curve.

[dArsonval]

Having long been a fan of the Advance Patent Search feature via Google to research old patent numbers found on equipment I’ve worked on
over the years and the site providing a wealth of insight for me in understanding why an item was constructed the way it was designed,
(Reliance Electric and General Electric patents have been especially helpful for me at times for example), the recent news of Tesla Motors
offering all their patents in good faith to those interested in utilizing them… prompted me to look ‘em up to see what’s there.

Torque Density, and Saturation Curve seem to be a reoccurring theme designers are wrestling with.

Torque Density.
Saturation Curve.

Is/are the root of these problems in the physical/mechanical aspects of a motor design, or the power supply driving the motor?

John

 

[7anoter4]

If we compare torque density [Nm/m^3] with tangential stress [N/m^2] used once upon a time to calculate the electrical machine main dimensions, it seems to be the same units: [Nm/m^3=N/m^2].
The correct rotor size for torque production can easily be estimated with the tangential stress. The size of the rotor depends explicitly on the torque, not the output power of the machine.
As a basis for machine design, the machine constant C [kWs/m^3] of a well-designed electric machine is an alternative to the tangential stress of the air gap.
For synchronous and induction machine C=π^2/sqrt(2)*kW*A*Bm where:
A=linear current density [no.of conductors*current/(*Dgap)].
Bm =magnetic flux density ; kw=winding factor
Then rotor volume Vr=π/4*Si/C/no no=freq./p 2*p=number of poles.
Where: Si=m*Em*Is
Em=EMF in stator; Is=stator current; m=stator no.of phases.
See:
-Richter, Rudolf, 1963. Electrische Maschinen, Band II, Synchronmaschinen und Einankerumformer. Dritte Auflage. Birkhäuser Verlag, Basel und Stuttgart, Germany. 707 p. (In German).
-Design of Rotating Electrical Machines by Juha Pyrhönen Professor and others.

 

[mikekilroy]

In simplistic terms, possible torque goes up by the square of the diam and linearly with the length. Not sure how this relates to the question.

On similar note, motor Kt (AKA Kb, Ke) can be changed on the fly to allow voltage limited motors to go much faster... Past 'torque angle control' seemed limited to about 30% dynamic change; recent DRIVE algoriths have allowed EV PM motors to get 200-300-400% changes.

In case either comment are of any value to the discussion.

http://www.KilroyWasHere<dot>com