asymmetrical rotors in vane pumps

[GMautotech]

I hope I don't get kicked off here, because I am not a professional engineer. I am an automotive technician, and work at a GM car dealership. The question I have has to do with design theory of a positive displacement, vane type pump.

The pump in question is used in automatic transmissions. It is a positive, variable displacement pump, with the variable displacement accomplished by movement of the cam ring.

Over the years, I have noticed that pumps of this type often have vanes which are irregularly-spaced around the circumference of the rotor. I suspect that this is for noise reduction, as the irregular spacing would prevent the pump from producing a constant frequency that might cause some other component in the vehicle to resonate.

Also, I have noticed that this type of pump typically has a prime number of vanes, i.e., 7, 11, 13. I suspect that this has something to do with noise reduction also, but I don't understand the principle behind it.

The reason for my post is that I am very interested in this concept, but I cannot find information on the web that will answer my questions. I also wish to write a paper on the topic, the intended audience being other automotive techs like myself, with no formal engineering background.

Could someone suggest a good place to look to do research on this topic?

Thanks!

 

[unclesyd]

A little late. Missed several days due to Ivan.

Your pump is a variation of the "walking ring" pump here is a little information about this type pump.
I would contact Continental and see if they have more information on same.

http://www.memagazine.org/backissues/december98/marketplace/tech_focus/techfocus2.html

http://www.continentalhydraulics.com/vanepumps.htm

I’ve seen a good description of this type pump and it’s workings and it may have been here.

http://www.wiley.com/WileyCDA/WileyTitle/productCd-0764571168.html