Want a quiet ride? Acoustic noise in motors:cause & solutio.

[lostrack]

http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F7090%2F19100%2F00882782.pdf%3Farnumber%3D882782&authDecision=-203

ABSTRACT

This paper deals with the causes of acoustic noise in induction motors and presents methods to reduce the noise before and after the motor is manufactured. The acoustic noise in induction motors has three main sources:

The first one is the ventilating system which is responsible for the noise level of 2 and 4 pole-motors due to the fan speed.

The second is the magnetic noise, generated by vibration of the core due to the electromagnetic forces in the airgap.

The third is the noise generated by the bearings.

The influence of the PWM frequency inverters on the magnetic noise is also considered and results of tests performed on motors are also presented. It is shown that a reduction in the fan diameter decreases the noise emitted by the ventilating system.

Related to the magnetic noise, solutions have been adopted during design stage by stator/rotor slot design.

Finally, the paper presents advantages, disadvantages and general comments about each solution and comparing noise level with parameters described in standards


Now, does anyone have an IEEE Explore login?

[Doctorbass]

http://ieeexplore.ieee.org/Xplore/login.jsp?url=http%3A%2F%2Fieeexplore.ieee.org%2Fiel5%2F7090%2F19100%2F00882782.pdf%3Farnumber%3D882782&authDecision=-203

ABSTRACT

This paper deals with the causes of acoustic noise in induction motors and presents methods to reduce the noise before and after the motor is manufactured. The acoustic noise in induction motors has three main sources:

The first one is the ventilating system which is responsible for the noise level of 2 and 4 pole-motors due to the fan speed.

The second is the magnetic noise, generated by vibration of the core due to the electromagnetic forces in the airgap.

The third is the noise generated by the bearings.

The influence of the PWM frequency inverters on the magnetic noise is also considered and results of tests performed on motors are also presented. It is shown that a reduction in the fan diameter decreases the noise emitted by the ventilating system.

Related to the magnetic noise, solutions have been adopted during design stage by stator/rotor slot design.

Finally, the paper presents advantages, disadvantages and general comments about each solution and comparing noise level with parameters described in standards


Now, does anyone have an IEEE Explore login?

For teh fan speed, there is always a dominant frequency and few harmonics. The dominant frequency wich is corresponding to the exact number of time each blade are moving in one sec, can be solved with a Helmotz resonnant device wich is an empty cavity with a determined volume and input that is placed close to the sound source. It will act by cancelling that frequency with the positive and the negative phase together

The second noise source wich is the vibration of the motor can be solved by improoving the magnetic shield around the motor and also adding some mechanical damper to the right locations ( often obtained by computer simulations.


the third oen from teh bearing is more difficult. But it can be damped by adding some elastomer material to the surface aruond teh bearing holder and will damp these vibrations. What is difficult is to find a way that these added material are flameproof.. like 94-V material ad that dont degrade the performances and cost of these motor.

Ex: The 9C motor can be modified with the elastomer on the isid eo fthe side cover wich will reduce alot the szzzzz noise.

Doc

[Kingfish]

Dynamat on the inside. Although it would also inhibit motor cooling. However I bet just a few small strips would be enough to attentuate the ringing. I have some left over from completely sealing the inside of my 4x4, so maybe I can give that a shot.

Cheers, KF

[fechter]

A lot of the noise from typical ebike motors comes from the square wave drive of the controller. By using a sine or rounded trapezoid wave, the noise would be greatly reduced.

[XLR8]

To reduce a sound coming from my hub motor I put a dob of silicon sealer where the spokes cross each other to dampen the resonance. It works rather well.

[Doctorbass]

Dynamat on the inside. Although it would also inhibit motor cooling. However I bet just a few small strips would be enough to attentuate the ringing. I have some left over from completely sealing the inside of my 4x4, so maybe I can give that a shot.

Cheers, KF

Yeah Dynamat work pretty well on car body... as well as on hub motor

Doc

[liveforphysics]

Sinus current makes hubmotors virtually silent in my experience.

[Kingfish]

Sinus would be sweet, but who sells one that we can mod? I thought we were let to our own to come up with something

Sinuously ~ KF

[John in CR]

I don't want to mod one. I just want Luke to get hooked on a motor I like to use.

BTW Luke, we popped Hubmonster open today for beefing up and ventilating that big diameter long stator motor. It's going to be able to handle a whole lot more controller than I've ever gotten my mitts on.

On the topic of silence, the high efficiency hubbies are by far my quietest yet. There's just a hint of that non-sinus phase pulsing on the first couple of revolutions and then nothing. The scooter tire I have on it is much quieter than my other larger tires too, so it's a unique ride.

John

[Miles]

Found this one in my library:

[lostrack]

Found this one in my library:

You're the man!