Companies look to develop alternatives to rare earth motors
Supply and demand is a fact of life and very much at the heart of business. For many engineers, the cost of materials and components can encourage innovation as much as it can restrict it. For most, cost remains the biggest driver and any dramatic or sustained spike in component pricing will likely see many look elsewhere for lower-cost alternatives.
That is the view largely echoed by electric motor manufacturers and users at the moment. The cost of the rare earth materials used to make the powerful magnets has gone up six times in the last few years alone, giving OEMs and their suppliers serious cause for concern.
To date, China has produced around 95% of the world's supply of rare earth elements. However, it is putting an ever-tightening stranglehold on the supply of these materials, reducing exports and preciptating a worldwide shortage. Naturally, this has dramatically increased price.
Conspiracists might suggest this is a concerted effort by China to control supply so it can hike up prices of the materials and exploit the increasing demand from the lucrative wind energy and electric/hybrid car markets, both of which are expected to grow massively in coming years.
Whatever the motives, the result is the same; the price of the commonly used elements neodymium and dysprosium are skyrocketing. But this is having another effect on industry, as engineers struggle to keep costs under control, more companies are seeking and developing alternatives.
Dr Sab Safi, a consultant to SDT Drive Technology, says: "There is a possibility that rare earth magnets may become unavailable or too expensive and this justifies efforts to develop innovative designs for permanent magnet motors that do not use rare earth magnets."
SDT Drive Technology in Southampton has been considering and exploring the need for different types of electric motors that do away with the need for rare earth materials, particularly for use in hybrid and electric vehicles. It suggests that both induction motors and switched reluctance motors have the potential to offer similar performance without using rare earth metals.
Induction motors are relatively low cost and lightweight, but are generally bigger than equivalent rare earth motors. In practice, many electric vehicle designs employ induction motors, yet induction motors for hybrid electric vehicles have to date not been so popular. There is an opportunity for enhanced induction motor designs that utilise advanced manufacturing technologies, materials, and control methods. And while research on hybrid permanent magnet motors and switchedreluctance motors, in addition to comparisons of both is available, it sometimes ignores induction motors as a suitable alternative.
Switched reluctance (SR) motors are similar to stepper motors except the stator phase currents are switched based on rotor positions, hence the name. Although the technology is pretty well established, it is only recently that advances in power electronics, digital control and sensing technology have allowed SR technology to compete. As a result the technology is gaining popularity within the automotive sector. "SR motors are especially well suited for rugged applications or high-speed applications where high power density is needed," says Dr Safi. "They also offer a long constant power range which makes them highly favourable for vehicle traction applications.
However, higher speed operation may cause high mechanical losses due to aerodynamic drag and viscosity losses."
SR motors are increasingly being made commercially available by a number of companies that are rolling them out to the automotive sector. This situation has also prompted a consortium of UK technology companies to undertake a research programme to allow better design and modelling capability of SR motors. Headed by Oxford based Cobham Technical Services and co-funded by the TSB, the group includes Jaguar Land Rover and
Ricardo. It will also be looking at developing the next generation of switched reluctance motors that avoid the inherent expense of rare earth magnets, and provide tools to enable engineers to take up the technology.
Cobham will develop multi-physics software, and capture the other partners' methodology in order to design, simulate and analyse the performance of high-efficiency, lightweight electric traction motors that eliminate the use of expensive magnetic materials. Using the software tools JLR and Ricardo will be able to rapidly design, develop and manufacture a prototype switched reluctance motor that addresses the requirements of luxury hybrid vehicles.
Kevin Ward, a director at Cobham Technical Services, says: "Cobham will also develop its existing SR motor capabilities to provide the consortium with enhanced tools based on the widely-used Opera suite for design, finite element simulation and analysis.
"In addition to expanding various facets of the Opera electromagnetic simulator capabilities, we will investigate advanced integration with our other multi-physics software to obtain more accurate evaluation of model related performance parameters such as vibration."
However, for many applications there is simply not a realistic alternative in the market for rare earth magnets just yet. They still offer the best power density-to-size ratio and for more bespoke applications, performance still largely outweighs cost at the moment.
Maxon Motors uses three types of magnets in its motors; Neodymium, Alnico and some ferrites. Neodymium is more common for precision types of products and is rare earth derived. Although it is the most expensive, it does give the best performance. The other alternatives are Alnico, an aluminium nickel, and some ferrites. These cost less, but have much lower performance.
Paul Williams, sales engineer with Maxon Motors, says: "What we have found is the cost of rare earth magnets has gone through the roof. So people have started to move, if they can, to an Alnico magnet. But this means the sizes go up. For a lot of our applications, we need that performance but in a small size. If size isn't important to you, you can obviously use a lower-cost magnet."
Around 60% of Maxon Motor applications are bespoke in some way, so it uses a high degree of application knowledge and can modify the motor to suit the application.
"For us it is quite a significant cost of the motor," says Williams. "We have had to put a rare-earth surcharge on the magnets at the moment and this has an impact on the cost of the motor.
"The major cause for concern in the market is within the automotive industry with hybrid and electric cars relying on the superior power density provided by rare-earths. Can they find suitable alternatives or will the market for rare earth stabilise pricing? The fact is that the volatile price changes rare earth magnets will not be able to sustained within the automotive industry."
This is also of particular concern for Japanese manufacturers who rely on a continuous supply from China to export their cars abroad. Japan has neither the raw materials or enough in its recycling waste stream to support the demand of its local markets. This is therefore prompting similar moves across the Pacific by electronics powerhouse Hitachi. It, too, is developing motors that don't use rare earth elements, no doubt to satisfy demand from companies such as Toyota, which uses around 1.4kg of neodymium in every Prius.
Hitachi has recently announced an 11kW, highly-efficient permanent magnet, synchronous motor that does not use magnetic material containing rare earth metals such as neodymium or dysprosium. Instead, the motor uses an iron-based amorphous metal in the core. The key challenges were technologies such as structural optimisation and minimising losses in the core.
Compared to conventional motors of the same class, the motor is smaller and achieves an energy efficiency of approximately 93% which fulfils the highest standard of IE4(2) efficiency guideline.
Hitachi also developed technology to optimise the structure of the axial gap motor to efficiently use low-magnetic ferrite material and a stratified core structure, which efficiently draws out the low energy loss characteristic of the amorphous metal.
Most electric motor companies are concerned about the increasing scarcity of rare earth elements and it is clear that many industries are actively seeking alternatives. While some more bespoke applications continue to use the rare earth metal motors, if the trend of rising prices continues, there will be a crossover sooner rather than later when the trade-off between cost and performance swings the other way.
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