Magnomatics' top gear

Sheffield University spin-out Magnomatics, which develops novel high-torque magnetic gearboxes, motors and generators, is leading a consortium to produce high torque density electric drives for commercial vehicles.

The company says its technology is also suitable for applications such as wind turbines, hybrid cars, aircraft and domestic equipment, and is being applied in the government-backed Low Carbon Vehicles Integrated Delivery Programme.

The aim of the project is to produce a novel brushless permanent- magnet electrical machine incorporating integral magnetic gearing for traction in hybrid trucks, buses and construction vehicles.

The consortium, which includes Kollmorgan Corporation, Magnet Applications and the Volvo Group, will build and evaluate two demonstrator vehicles.

Magnomatics said its pseudo-direct-drive (PDD) can overcome the shortcomings of mechanical gearing on electrical machines. Conventionally, it is only possible to achieve a relatively low torque for a given volume due to limits on the magnetic and electric loadings. So mechanical gearing is often needed to match the machine to its load.

But Magnomatics’ technology, combines torque production and magnetic gearing within a single integrated machine, giving a very high torque density. The company claims it has the highest torque density of any known electrical machine, up to 120kN/m3.

Typical torque densities are said to be eight times greater than a standard naturally-cooled permanent magnet machine and about double a transverse flux machine, although without the usual penalty of a low-power factor.

It is also possible to realise pseudo-direct-drives with both a low-speed/high-torque output and a high-speed/low-torque output.

Other advantages over conventional machines include reduced size and maintenance, improved reliability and higher efficiency. The low electrical loading can also remove the need for forced or liquid cooling.

Magnomatics said the drive technology also has inherent torque overload protection, a high-power factor and the possibility of having two output shafts with different rotational speeds.

It employs high-energy rare-earth magnets. The magnetic gears transmit torque between two rotating shafts across an airgap. The physical airgap between the input and output shafts creates a number of advantages over mechanical gears.

These include less wear, no need for lubrication and cooling on the torque-carrying components, the absence of vibration and acoustic noise and a relative immunity to damage from overload torques or the presence of debris between the gear wheels.

To achieve this, Magnomatics uses an arrangement of three concentric cylindrical shapes: two rotors with differing numbers of permanent magnet poles, and an intermediate ring with stationary magnetic pole-pieces that modulate the magnetic fields to link the rotors’ movement. A magnetic gear uses permanent magnets to transmit torque between an input and output shaft.

The gear ratio of the transmission is dependent on the design of the magnetic circuit. Typically, a magnetic gear has an efficiency of 99 per cent, with torque densities of up to 150kN/m3, which is comparable with two and three-stage helical gearboxes. Since there is no mechanical contact between moving parts, wear is negligible.

Another benefit is that magnetic gears protect against overloading. The gear simply slips if an overload torque is applied, only re-engaging when input torque falls below the limiting threshold. They can be realised in radial, axial or linear topologies and optimal designs have been developed to realise both low (2 to 30:1) and high (30 to 1000:1) ratios in a single stage.

The company believes magnetic gears have the potential for a wide range of applications ranging from high-speed, lightweight components for F1 cars to low-speed, massive, utility scale wind turbine powertrains. The ultimate goal in each case is to provide a highly efficient and reliable torque transmission system.

The inventor of high-torque magnetic gears, company co-founder and technical director Dr Kais Atallah, has applied for 12 patents on behalf of Magnomatics.

Among the company’s recent backers is Fusion IP, which invested £150,000 in the funding round that was led by the White Rose Technology Seedcorn Fund. The company will have a 48 per cent share in Magnomatics. A recent funding round brought a further cash boost of £500,000.

David Baynes, Fusion IP chief executive, said that he expects the technology to have a major impact in the hybrid car and wind turbine industries.

Max Glaskin