Lightweight rotor sleeve technology

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New lightweight rotor sleeve technology drives sustainability, explains Richard Thompson

Post COP26, the urgent need for action on carbon emissions could not be clearer. As the automotive industry faces escalating pressure to improve performance and reduce weight in the pursuit of net zero, new, innovative materials technology harnessing aluminium matrix composites (AMCs) is proving a dynamic, sustainable solution for engineers.

The technology is based on the convergence of advanced materials and a novel manufacturing process to produce AlXal (pronounced Al-Zal), a highly versatile aluminium composite, cited for its exceptional mechanical properties and its significant potential in the automotive sector. What Alvant’s developmental work has uncovered is AlXal’s compatibility with rotor sleeve applications, owing to its preferential electromagnetic, mechanical performance and thermal conductivity for electric motors. It offers high strength and stiffness up to 350°C, the potential for lower magnet operating temperatures compared to carbon composite sleeves and enhanced damage and fatigue tolerance. Adding to its appeal is its lightweight capabilities – more than 50% lighter than steel and up to 40% lighter than titanium – making the material a compelling proposition for OEM electric machine manufacturers that are pursuing increased efficiency and power density (kW/kg).

Rotor sleeve innovation 

So how does this low loss rotor technology work to improve the performance of permanent magnet radial flux motors? Surface-mounted permanent magnet electric motors typically require a magnet retention system that can includes a mechanical rotor sleeve, which generates unwanted eddy currents and/or acts a thermal insulator depending on material. Alternatively, interior mounted permanent magnet machines use slotted steel laminates to retain the magnets limiting the proximity of the magnets to the stator. This can lead to increasing losses and higher temperatures, reducing the overall efficiency and limiting the power of the electric machine. In addition, manufacturing and assembly costs can be high with the use of carbon fibre composites, adhesives and heat shrink metallic sleeves. Typical rotor sleeve materials include stainless steel, titanium, Inconel and carbon fibre composite, all of which can add to the detrimental impact on the effectiveness of the machine. Alvant’s core technology can be applied to create surface-mounted magnet rotors and interior mounted permanent magnet rotors which minimise the magnetic bridge element of the laminates.

This all equates to potential gains and savings in key areas compared to typical metallic and carbon composite solutions. These include up to a 20% increase in peak power, 60% reduction in rotor losses when compared to carbon composite at high speed and around 50% efficiency improvement versus stainless steel. The overall improvements in the efficiency at which it converts electrical energy to mechanical energy also translate to further benefits that place engineers and manufacturers at a competitive advantage, such as reduced manufacturing and operating costs.

Partnership to advance technology

Alvant’s recent collaborative agreement with 3M signals its growing position in the sector as an influential materials innovation and technology partner. The partnership will focus on advancing core technology in the areas of electric machines (motor and generator) and lightweight metallic components that require enhanced performance characteristics. Through harnessing Alvant’s expertise in the design, development, testing and manufacture of AMC materials and components, the partnership will enable both parties to jointly develop applications that will bring energy and cost-saving benefits to manufacturers and engineers across sectors including automotive and industrial.

Multi-sector benefits

The compelling benefits of AMCs means they have potential uses in a wide range of engineering applications. Where safety and reliability are essential, AMCs could find use applications in high-pressure seals, aircraft landing gear and seats. Where performance, efficiency and precision are vital, use cases include robotics, electric motors and automotive suspensions. And it is their lightweight high strength and stiffness characteristics that provide the automation industry with a method for increased productivity through increased speed and reduced maintenance. The list of possibilities doesn’t stop there - AMCs’ capability of withstanding extreme temperatures makes them suitable for components in high-voltage battery systems and vehicle powertrains.

The road ahead

As industries try to navigate their way through a multitude of obstacles – the global pandemic, climate change, shortages and rising fuel costs – they face an uphill challenge of finding suitable materials that will reduce weight whilst maintaining reliability and lowering whole-life ownership costs. Alvant firmly believes that AMCs offer an exciting potential to industries that need a step change in performance to meet ever stringent market and legislative demands. During what is the growth stages of an age of New Materials, now is the time for the industry to stop relying on traditional technologies and embrace change.

Richard Thompson is with Alvant

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