Smaller and cleaner electric motor spins at 100000rpm (Dyson)

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.

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.

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.

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.

PRESS RELEASE from 2003: X020 - Dyson SR Motor 06 October, 2003 DYSON REINVENTS THE ELECTRIC MOTOR Dyson Engineers Develop Small, High-Speed, Intelligent, and Carbon-Free Motor – “X020” Dyson engineers have developed a fast, intelligent and carbon-free motor codenamed X020. With a power-to-weight ratio equal to that of a Ferrari sports car engine, X020 is the first ultra-high speed switched reluctance motor to incorporate turbocharger aerodynamics and aerospace materials. X020 has no brushes, no magnets and no commutator. It is up to three-times faster and much smaller than a typical vacuum cleaner motor. Though on a smaller scale, X020’s development is comparable to the step-change of the jet engine over the propeller in the aerospace industry. X020’s embedded software gives it diagnostic capabilities and allows the motor to manage energy efficiently and safely – much like an engine management system in a car. The software also houses the motor’s ‘DNA’ – for example, build date, usage and owner information, all of which can be simply and quickly communicated to a call centre by holding a telephone handset to the device port or via the internet. “We wanted to overcome the problems associated with existing motors, specifically brush, commutator and magnet failures,” said Simeon Jupp, Director of Research, Design and Development at Dyson. “X020 has its origins in switched reluctance motor technology, but with its speed, size and diagnostic capabilities, it takes the science to a new level - X020 has the potential to be the brain and the brawn behind Dyson innovations of the future.” X020 was developed over six years by a team of UK mechanical, electrical, electronic, aeronautical, materials and software engineers. X020 has several patents pending and has innovative features and advantages over conventional switched reluctance motors: Speed: * At 100,000 rpm, X020 is spinning over five times faster than a Formula 1 engine (19,000 rpm) * X020 is the fastest and highest power density motor ever developed for domestic appliances * X020 derives efficiency from its high tolerances. For example, its impeller spins at over 600mph with only 0.3mm – around the thickness of a business card - between the blade tip and the impeller housing * The motor makes up to 1,666 revolutions every second. At this speed, the X020 control system needs to pulse the motor with energy four times per revolution: this translates into over 400,000 signals, decisions and power pulses every minute or 6,666 every second * It uses a three-dimensional compressor fan similar to those used in turbochargers, and runs at 2½-3 times the speed of a conventional centrifugal fan * X020 has increased Airwatts compared to conventional domestic appliance motors – from 300 AW to 400 AW, a 33% increase Intelligence: * X020 has a 128 byte memory chip to run diagnostic tests and enhance performance * Dyson is currently researching the use of X020 technology in future innovations. For example, if X020 were to be used in a Dyson appliance, data could be transferred from the machine to Dyson via a telephone or Internet connection. Information including serial data, warranty status and usage data could be downloaded immediately ensuring even more efficient customer service for Dyson owners * 2,000 lines of code are used in the control software developed by Dyson engineers Greener: * Being brushless, X020 has no polluting carbon emissions Reliable: * Long life – X020 has a working life of over 1000 hours of constant use and is able to operate in ambient temperatures of up to 35 degrees Celsius * Soft Start – X020’s full speed is reached in 1.5 seconds, reducing in-rush current and preventing blown trips * Fault diagnosis and protection features ensure safety and longevity Lightweight: * X020 weighs 1000g compared to 1300g for a typical vacuum motor, giving it an excellent power to weight ratio * During development, Dyson engineers reduced the X020’s rotor by 50%, making the rotating assembly weigh less than 100g Materials and Manufacturing Techniques: * X020 has a turbocharger style-3D impeller optimised for performance * X020’s impeller is made from PEEK, a material made with carbon fibre reinforcement and normally used in aerospace engineering. PEEK™ has been used in the wing construction of fighter aircraft * The impeller is aerodynamic. Its blades are continuously curving in all three dimensions. There is barely a straight 2D section to any part of the blade surface. Even previous aerospace & automotive 3D style impellers have had straight sections towards the exit of the impeller, i.e. radial blade tips * X020 has a square motor core, saving material and giving a stronger structure * To reach such high tolerances Dyson engineers have worked jointly with a bearing manufacturer to develop an exclusive ball bearing for high-speed applications similar to those used in precision measuring equipment and guidance systems * Dyson engineers spent 18 months researching aerodynamics, mechanical structure, vibration, electronic control, software, and manufacturing techniques. This relied on computer simulation to optimise the design Notes to Editors: * Dyson has a team of over 350 engineers, scientists and industrial designers based in the UK who are innovating continually to develop new technology for the home * PEEK™ is a trademark of Victrex PLC For further information please contact the Dyson Press Office: T: 0207 833 8244 E: press.office@dyson.com W: www.dyson.co.uk ENDS

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