Posted on 06/26/2008 5:33:11 AM PDT by Red Badger
Fig. 1. Dyson's switched reluctance motor features a rotor without coils and a stator with two sets of coils that are switched s
Almost all domestic vacuum cleaners utilise an ac series wound electric motor to spin the fan that generates suction and airflow.
This has remained the case for decades, even though this type of motor has significant drawbacks. First among these is the combination of carbon brushes and commutator that wears and leads to motor failures. Furthermore, the carbon dust tends to be exhausted to atmosphere, acting as a potentially harmful pollutant. In addition, because of the speed at which the typical motor runs - in the order of 35000 rpm - the fan is of a relatively large diameter and inefficient. As well as leading to unnecessary wastage of energy, the motor and fan combination is also noisy. Dyson's engineers recognised that the scope to make further improvements to the AC series wound motor was limited, so decided to take a step back and develop a better alternative. Seven years and £8million (E11.7million) later, a production line has been established in Singapore, less than 10km from the company's manufacturing plant in Malaysia, to produce motors that will be used in future Dyson vacuum cleaners. With annual production running at 2 million vacuum cleaners per year, the motor production facility may well reach similar output levels in the future. Economies of scale will also benefit from the fact that only two models of motor are required to cope with all mains electricity voltages around the world, which is a significant improvement over the present situation. Once volume production is underway, the cost of the motor and controller will be closer to the cost of a conventional motor, though the increased complexity inevitably means that the cost will be higher initially. Life expectancy for a conventional vacuum cleaner motor is only around 500 - 600 hours and the intention was to develop a motor with double the life. This meant eliminating the commutator and brushes, which led the engineers to investigate switched reluctance (SR) motors. These feature a rotor without coils and a stator with two sets of coils that are switched so as to alternately attract the poles on the stator (Fig. 1). Because of the asymmetric design of the rotor poles and the momentum of the rotor, the rotor turns rather than oscillating. In the Dyson design, referred to as the Dyson digital motor (DDM), the rotor consists of a stack of iron laminations and the stator windings are wound on iron laminations that give only minimal clearance with the rotor so as to maximise efficiency. An opto-electronic switch senses the position of a flag on the rotor so as to provide the positional information required for the control electronics to switch the stator phases with the correct timing.
Faster and smaller
Because there are no contacting components, the motor is able to run at 100000 rpm, which is much faster than conventional motors. The advantage of a faster motor is that the fan can be made smaller and more efficient. Dysons's engineers started by looking at turbo impellers from automotive turbochargers and the current design is certainly similar in concept. However, to perform reliably at such speeds, the fan is moulded from PEEK, which is remarkably tough (Fig. 2). Thanks to the more efficient design, a 1500W Dyson digital motor generates 400AW (airwatts) as opposed to 300AW for a comparable conventional motor. High speeds require specialist bearings and, with nothing suitable available off-the-shelf, Dyson worked with a German bearing company to develop special ball bearings. These have steel balls and races, with cages moulded from PEEK. Another issue resulting from the exceptionally high speed is that the rotor runs super-critically, that is to say, above its resonant frequency. In order to reach this speed without resonance causing damage to the rotor, stator or bearings, the motor has to accelerate past the critical speed so that the critical speed is only experienced for three to four revolutions (patent-pending anti-vibration bearing mounts are also incorporated). Needless to say, to achieve this level of control requires some sophisticated electronics. In addition to ramping up the speed of the motor so as to reduce in-rush currents, the electronics must ensure that the critical speed is passed quickly. But once a device incorporates electronics, there is scope to add more functionality. For example, Dyson vacuum cleaners only require infrequent filter changes, which are easily forgotten by most owners; as the filter starts to block, this can be sensed and the electronics can signal that the filter needs changing.
Onboard memory
Dyson is also planning to store data on the onboard memory, such as the motor's serial number, build date and information relating to usage and operation. Going a step further, this data can be transmitted back to the company's service facility by telephone to enable problems to be diagnosed remotely. While the main consumer benefits will be seen as smaller, lighter, better performing products, the digital technology could also enable other innovations relating to customer service. For instance, warranty terms could relate to running hours rather than the length of time elapsed since purchase.
Noise cancellation
So far the motor has been developed purely for use in Dyson's own vacuum cleaners, with the stator being overmoulded and the fan and ducting being designed as part of the same assembly. Included in the fan ducting are two Helmholtz resonators that act as noise cancellation devices to eliminate the peaks that detract from the noise quality. These, coupled with the fact that the motor spins faster and the noise peaks are narrower, mean that the motor and fan is quieter than a conventional motor and fan and the noise quality is improved (though noise quality is always subjective). But despite the specialist nature of this development, Dyson has already received enquiries from other organisations interested in high-speed motors with no wearing parts. Aerospace companies have expressed an interest and it is possible that licences to use the technology - much of which has patents pending - could be issued. Dyson is claiming that the motor will last 1000hours, or twice as long as a conventional alternative, but life tests have been terminated after 2000 hours because the test rigs are required for more motors. We are told that we can expect to see products being launched with the new motor possibly in 2004, and it will be interesting to watch where future developments take this concept - and whether Dyson decides to develop its own motors for other domestic appliances.
James Dyson is a GENIUS! I’ve owned a Dyson vacuum for nearly 2 years. Love it! It sucks like a drunk prom queen.
Ho Hum.....
Dyson working on new generation of fast, green cars
“It sucks like a drunk prom queen”
A queen or a queen?
Why are we seeing such an old article?
I would be more interested in a 100000 RPM electric turbo diesel than an electric car.
Hint! Dyson. Hint!
The only thing I question in this article is just how much potentially polluting carbon gets released from less than one inch carbon brushes that last ten or twenty years.
The Brits have always been superbly creative... who choose to leave liberal-land for more fertile pastures. Soon, the island will be left with only Muslims and liberals. Good combination - should prove v-interesting. The intelligent Brits will be there in other (hopefully non liberal) countries continuing to contribute real improvements to our life.
I was working for a company in Connecticut that wanted to use one of these motors in a turbo expander product, making compressed gasses with this motor while spun on air foil bearings
If you use it, it will kill you.......
My lad is in America...and I have encouraged him all the way. I'm a bit old in the tooth and will stay with the sinking ship. Having said that my little pasture isn't on the frontline of anything except beautiful mountains!
Interesting. Thanks for posting.
So when a sock gets caught inside, it will replicate the force of a frag grenade going off.
Refrigeration/air conditioning is where most electrons go to die (yes, I know that death is greatly exaggerated) so maybe these motors can help there?
Your wish is their command. See his thread: "Vacuum King, Sir James Dyson, wants to create an electric car"
Ping me when they can get this thing to put a starship into hyperspace so we conservatives can all get aboard and leave this place for the Muzzies and the Luddites.
They can eat the liberals.
Me too. I also have an Oreck, but the Dyson offers twice the performance at half the price. The cheap Dirt Devil and Hoover junk isn't even in the running.
So this is a five year old press release? Implying these motors have been in their products all this time? Pardon me if I’m slow here........
Why do all of the green cars look like something that Shriners would drive in a Labor Day Parade? I’d buy a green Hummer or Pickup, or Mustang, but not one of these hotwheels-looking toys.
Yes, the motors are in production and being used. I posted the article as a prelude to the story of Dyson setting his sights on a larger version for a automobile.................
The early Model T cars and such were thought to be ugly, too...........
I'm sitting here laughing my whatever off over that remark.
But, to quote the late great Slim Pickens, could it suck the chrome off a trailer hitch?
OMG, I'm a lady, I'm not supposed to speak or post that way. < still choking with laughter>
If I still lived in DC i’d be very tempted given how awful parking can be in a lot of places and the price of gas. If I wasn’t on the highway much i’d love something small. Small doesn’t eqaul bad to drive anymore. The mini is as much a root to drive as anything i’ve driven in a long time and the knew Honda Fit is supposed to handle amazingly well. CD had it doing better than the Corvette in a slalom test.
SR motors have been around a long time. Electronics to control them have improved a lot in the last 10 yrs.
High speed allows high power density but it’ll be eaten alive by the transmission. Direct drive wheel motors are a better sol’n. The problem remains; battery technology.
Well, McCain's offering $300-400 MIL.......................
I once made that remark to a female friend of mine about a woman of dubious reputation and I thought my friend would wet herself she was laughing so hard. She said, “I’ll never look at a trailer hitch the same way again.”
I guess he won’t need public campaign financing if he can foot that bill.
That’s $300-400 MIL of OUR tax money he wants to give away!...............
BTW, HP pen plotters (pen and paper move) were designed to use the same motor tech.
But, alas, have never fully understood the concept of electricity.
< /former MG owner>
Or a tennis ball through a garden hose?
unnecessary wastage of energy=Broom
I’m looking at one right this minute.......
“...But, alas, have never fully understood the concept of electricity.
< /former MG owner>...”
Q: Why do the Brits drink warm beer?
A: Lucas refrigerators
“The advantage of a faster motor is that the fan can be made smaller and more efficient.”
Your comment, “High speed allows high power density but it’ll be eaten alive by the transmission”, is on target.
Wheel rpm on a car is closer to 1000 rpm at cruising speeds. And not only does the motor have to have super bearings but so does the bearings on the high side of any gearbox. Gas turbines have the same problem.
The reason these SR motors can turn so fast is because back EMF does not limit the speed, as i does on a brushless DC motor. For a vacuum cleaner that needs a high speed impeller I could see the advantage, but for a vehicle that uses low speed wheels, brushless DC seems like it would have an advantage.
And, Brushless DC motors approach 90 % efficiency already anyway so where’s the gain?
Better batteries are indeed the ticket for electric vehicles.
Hey, they gotta start somewhere! The Toyota Pious was the forerunner of the modern hybrids, but now they’re getting into the small and mid-sized SUV market. I kinda like the looks of the Mercury Mariner, but the electric part of it still doesn’t have the range I want. Guess I’ll have to wait for someone to market the ultra-capacitor batteries made by using carbon nanotubes, so they’ll be smaller and more powerful!
The National Science Foundation funds scientific research all the time. I'd prefer it be spent on something USEFUL, rather than more inane research on 'global warming'. Come to think of it, some enterprising professor could submit a grant for research and couch it in global warming terms. The greenies would love it, and we'd get our good batteries. A Win-Win, I'd say.
OFS
You've got to think 'outside the box'. With the size of electric cars that are being proposed, the solution is to buy two of them - one for each foot. That way the wheels can be made much smaller, and turn at 10,000 rpm.
airwatts??????
“They’re iron and copper; no (rare earth) magnets. They’re the least expensive motor...”
No, Brushless DC motors always have permeant magnets in the armature.
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