reduced cogging torque in ndfeb motors 1

[uppili11]

we are using bonded ndfeb magnets for our dc motors.but we could not
introduce this motor to several automotive application because of high cogging torque.
can anybody share their experience on reduction of cogging torque using bonded ndfeb magnets

 

[UKpete]

uppili11 - sorry, it's me again.

Firstly can I recommend two text books on brushless DC:
D Hanselman "Brushless Permanent-Magnet Design"
and
JR Hendershot, TJE Miller "Design of Brushless Permanent-magnet Motors"

I don't think the type of magnet material will have a very strong influence on cogging torque, except of course that high energy rare-earth types may appear worse simply because they have higher flux.

Hanselman describes the following 5 techniques on cogging torque reduction:
1. Make the tooth tips thick enough so they don't saturate.
2. Use a fractional pitch winding (ie number of slots per magnet pole per phase should not be an integer)
3. Increase the airgap (though to compensate the magnet volume must be increased to maintain flux constant)
4. Skew the stator slots
5. Shape the rotor magnets - make them thinner near the pole transitions.

Of course the ultimate method to eliminate cogging torque is to go slotless i.e. and airgap winding.

 

[UKpete]

I've assumed that you are using a brushless motor in the above post, but maybe you have a commutator motor. However, the above rules still apply, except that the magnets are on the stator of course.

 

[jbartos]

Suggestion: Visit

http://link.springer-ny.com/link/se...contents/02/00144/s00202-002-0144-4ch002.html

for: the reduction of cogging torque

http://www.me.berkeley.edu/PREM/publicat.htm

for: G.H. Jang and J.W. Yoon, "The Spindle Motor with Low Cogging Torque and High Torque Efficiency", Proceeding of the 25th Incremental Motion Control Systems and Devices, San Jose CA, June, 1996, pp. 175-180

http://em4-si.eng.hokudai.ac.jp/compumag99/C.html

for: Chen Shi Xin - Singapore (PH3)
Robust Design for Cogging Torque Reduction of PM Electric Motors Using Response Surface Methodology and Taguchi Method

http://www.thingap.com/index.htm

for: ThinGap(TM) coils, modern electric motors with zero cogging or ripple torque,
also at

http://www.thingap.com/technology.htm

 

[uppili11]

many thanks.the motor is not brushless but as UK pete mentioned the techinques are common viz skewed slots/increase air gap etc.The flux per pole what we talk is about
38000 maxwell which is pretty high compared to standrad wet permanent magnet motors and so is the cogging torque.the issue of reduction cogging torque is mainly to have much reduced noise level of motors so that it can replace the conventional
PMDC motor but with much reduced size .(example:a bonded ndfeb motor can have a frame size of 36mm but can replace a 42mm motor)the reason why this is not so popular yet in automotive is because of this high cogging and high noise.any modification of the existing design should be production friendly and economical for mass production.am looking for suggestion whether any suitable magnetization technique will help in reduction in cogging torque without loosing much flux

 

[janderson2]

In some cases, the cogging is due to an imbalance in the magnetic fields. This is especially true on canstack type steppers where the stator and rotor poles are equal numbered.

I agree with the suggestion of increasing the pole tips, but this will detract from positional control if this is needed.

If torque can be reduced, you can open the airgap. A few .000's will make a big difference.

 

[uppili11]

the idea of going for high energy magnets is to get much better performance.in this case the number of rotor slots are 5(odd) and the stator has two poles.the cogging torque is over 12mNm.Where as a normal motor has got around 6mNm.
Am still looking for some good suggestion on magnetizing/experience of any expert in this field /or any research paper on this

 

[jbartos]

Suggestion: Visit

http://www.maintenance.org.uk/PEOPLE/BSP_PUBS.html

for Transverse Flux Motor by Rolls-Royce
Also, reference:
S. Huang, J. Luo, T.A. Lipo, "Analysis and Evaluation of
the Transverse Flux Circumferential Current Machine,"
Conference Record of the 1997 IEEE Industry Applications
Society, Oct. 5-9, 1997, New Orleans, Louisiana, Volume 1,
pp. 378-384

 

[uppili11]

Thanks for the responses.Am going thru the various websites suggested for a
readymade solution which is still far away.Many thanks.