POWERTRAIN TECHNOLOGY Electric motors redefined

Jonathan Newell talks to Advanced Electric Machines about the advantages of motors without permanent magnets in hybrid powertrains for commercial vehicles.

from Newcastle set about redefining the construction of electrical machines to meet the requirements for more power, reduced cost and a sustainable life cycle. Commercial vehicle manufacturer, Cummins was the driving force behind changes needed to provide hybrid power for trucks. The US powertrain giant wanted a hybrid plug-and-play motor for a 7.5 tonne truck to replace its existing permanent magnet (PM) motor using the same power electronics and a reduced Bill-of-Materials cost.


UNIVERSITY SPIN OUT A team at the University of Newcastle led by Dr James Widner had been working on hybrid motors at the Centre for Advanced Electrical Drives and saw the potential for the switched reluctance motor at the heart of their work.. As a result, Advanced Electric

Machines (AEM) was spun out from the University in March 2017 producing two motors for passenger cars and commercial vehicles respectively. Since then, the company has been working with important users of electric motors in both the automotive and aerospace sectors including such exciting new market entrants as Tevva Motors, a company that couldn’t find a better motor for commercial vehicles than AEM’s HDSRM unit.

REDEFINITION OF SWITCHED RELUCTANCE MACHINES Switched reluctance motors have been in existence since the mid 19th century although they largely gave way to the dominance of rare earth PMs from the mid 1980s. Now, SRMs could fall back into the limelight as a more sustainable alternative. According to Mike Woodcock, Strategy

ith increasing demand for hybrid powertrain electric motors, a group of entrepreneurs

❱ ❱ The HDSRM was developed as a plug-and-play replacement for Permanent Magnet Motors

Director at AEM, motors without PMs have significant environmental benefits. “Rare earths are in the critical materials list and are difficult to find. Once extracted, they need a lot of energy to process them, they suffer from a loss of efficiency in service and there are end-of- life issues due to difficulties in recycling,” he explains.

With the HDSRM. AEM is

redefining the Switch Reluctance Motor and overcoming the traditional disadvantages of them. According to Woodcock, the peak efficiency zone of the HDSRM is wider than PM motors, it can operate at higher temperatures and can use the normal vehicle cooling system. One of the main disadvantages of

SRMs is the phenomenon of “torque ripple”, which affects the smoothness of the motor. AEM has overcome this with 6-phase technology within the motor that uses the same power electronics as PM motors, a crucial aspect in matching the Cummins “plug-and-play” requirements.

COMMERCIAL VEHICLE ADVANTAGES I asked Woodcock about the driving cycles commercial vehicles are exposed

❱ ❱ The HDSRM switched reluctance motor from AEM is making hybrid powertrains for commercial vehicles a sustainable reality

to and whether the motor was optimised to any cycle in particular. “For long driving cycles, the HDSRM

is better than PM motors as it has a wider efficiency zone and runs hotter for longer. PMs tend to demagnetise with heat,” he explains. He went on to say that for shorter “last mile” driving cycles, the HDSRM has equivalent performance to PM motors but has the advantage of reduced cost and ease of recycling. The plug-and-play element is also of importance to commercial vehicle manufacturers as it gives them both good flexibility in the design and reduces the system complexity of a hybrid vehicle, without the significant costs associated with having to use different power electronics, which traditional SRMs require. The HDSRM is modular and can be

integrated into the same package space as other motors, increasing the flexibility of its deployment. AEM showcased its innovative technology earlier this year at the JSAE Spring Congress in Japan and Engine Expo in Germany, with support from the Advanced Propulsion Centre.

Automotive Test & Validation 2018 /// 5

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