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AMCs Improve Power Density of Electric Motors

  • Tuesday, 9th July 2019
  • Reading time: about 4 minutes

Alvant has published research on the performance of rotors in electric vehicle motors. 

This shows that AMCs can increase the strength and stiffness of high-speed rotors, reduce overall motor weight, reduce inertia to improve the motor’s transient responses, and multiply power density by a factor of two to three. These are the kinds of gains vehicle manufacturers are seeking to improve the efficiency and responsiveness of their hybrid and electric engines.

AMCs are a family of materials in which aluminium is reinforced with high-performance ceramics. Such matrix composites can be precisely tailored for stiffness, strength, density, thermal properties, and electrical properties. It is also possible, by using Alvant’s unique Advanced Liquid Pressure Forming (ALPF) method, to selectively reinforce areas of a mechanical component with these high-performance materials in a near net shape manufacturing approach. Alternatively, Alvant’s materials can be cost-effectively applied as discrete inserts into a component where an array of similar inserts meets the performance requirements.

Latest research – commissioned by Alvant but conducted independently – shows that if rotors in axial flux motors (AFMs) suitable for passenger cars were made from AMCs, rather than following the current convention of making them from steel, mass and inertia would be reduced by anything from 45 to 73 per cent. This means overall motor weight would typically be reduced by 19 to 25kg.

The precise extent of the weight savings made possible by AMC rotors depends on the type of axial flux motor. In AFMs with electrical steel cores, the weight saving would be 45 per cent per motor; in AFMs with soft magnetic cores the saving is 50%; and in AFMs with a Halbach Array the saving is 73%. 

A typical electric variant of a combustion engine vehicle is ~125% heavier and so there is a need to reduce weight and increase driving range from a single battery charge. For an average electric vehicle, a 6 per cent weight saving provides an additional 3 km of range. Alternatively, it can facilitate a smaller battery leading to a ~£300 reduction in battery production costs and ~£450 per annum reduction in ownership costs.

Electric motor performance can also be enhanced because of the higher specific strength and stiffness of a rotor made from AMCs rather than steel. The latest research indicates that rotor speeds of 15,000 rpm would be reliably sustainable. Manufacturing rotors from AMCs would also have the advantage of reducing the number of parts required on the assembly line. 

This weight reduction and ability to increase the rotor speed increases the power density, a holy grail of electric motor development, by a massive 225 to 300 percent. In the simulated tests, transient response was also seen to improve when typical torque available at 8,000 rpm was applied to the rotor.

Alvant’s Commercial Director, Richard Thompson, commented, “These latest research findings are potentially good news for vehicle manufacturers who face the new engineering challenges posed by hybrid and electric engines. The research data also affirms that AMCs are a more suitable material than polymer composites for components such as motor shafts, the drivetrain, fans, flywheels, energy recovery systems, and batteries. Looking beyond the automotive industry, AMCs also have great potential for other rotational components, such as wind turbines.”

By releasing this new data, Alvant has added to the publicly-shared findings of the 2014 ‘Make it Lighter with Less’ R&D competition run by Innovate UK, part of the UK Research and Innovation (UKRI) funding agency. Research submitted to this competition by Alvant in collaboration with GE Aviation, YASA Motors, and the National Composites Centre, established that AMCs can achieve a 40 per cent rotor weight saving on an axial flux electric motor suitable for passenger cars, significantly increasing the rotor’s potential power-to-inertia ratio and improving engine efficiency and responsiveness.

Richard Thompson will speak about the applications of AMCs in hybrid and electric vehicles at the Advanced Materials Show, which takes place at the Telford International Centre, Shropshire, on 10-11 July 2019. This free-to-attend exhibition offers expert insights into current and future materials development.

Image provided by Alvant

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