Oxford YASA Motors Shows Specific Torque Above 30Nm/kg

A picture of the YASA topology. Source: Woolmer and McCulloch 2007. Click to enlarge.

Recent results from certified dynamometer testing has demonstrated that the 23 kg Oxford YASA motor produces a peak torque of 700 N&iddot;m (516 lb-ft), pushing its specific torque to more than 30N&iddot;m/kg. The company has also received the second tranche of £1.45-million (US$2.3 million) investment funding.

The Yokeless And Segmented Armature (YASA) topology is a new type of axial flux motor that has no stator yoke, a high fill factor and short end windings which all increase torque density and efficiency of the machine. The topology is based around a series of magnetically separated segments that form the stator of the machine. The novel design is enabled by using powdered iron materials that enable complex magnetic parts to be manufactured easily.

The YASA motor shows a step change improvement in torque density—initially with 20N&iddot;m/kg, or typically at least 2 times better than the best alternatives, according to the company. The improvement in specific torque comes from the combination of patented improvements in the magnetics, the cooling and the packaging of the motor.

We already have our sights set on the next generation YASA motor, which will push specific torque towards 40N&iddot;m/kg. This will enable the company to deliver a range of exciting direct-drive products with unparalleled performance.

—Nick Farrant, CEO of Oxford YASA Motors

Direct-drive electric motors are increasingly viewed in motor racing as the most efficient method of delivering quick acceleration as well as capturing a high percentage of energy from braking, th company said. Over the next 12 months, Oxford YASA Motors will be installing systems into new racing vehicles and TTXGP motorcycles.

The company is continuing to develop new markets for hybrid and electric vehicles, through ongoing collaborations with Delta Motorsport and Morgan Motor Cars in the UK, plus Electroengine in Sweden.

Oxford YASA Motors was founded in September 2009 to commercialize the YASA electric motor, developed by Dr. Malcolm McCulloch and Dr. Tim Woolmer at OXford University. McCulloch, head of the Department’s Electronic Power Group and Woolmer, then a PhD student in the group, originally devised the electric motor for the 2008 Morgan Lifecar.


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