An axial flux mo­tor to put the EV world in a spin

Wheels (Australia) - - Contents -

What is it?

A pro­to­type elec­tric driv­e­train un­der de­vel­op­ment by Bri­tish elec­tric mo­tor spe­cial­ist Equipmake. While most tra­di­tional EV mo­tors use ra­dial flux mo­tors, this ap­pli­ca­tion em­ploys a less con­ven­tional axial flux mo­tor. And un­like some con­cep­tual EV driv­e­trains, the Equipmake de­sign is des­tined for a re­al­world ap­pli­ca­tion, mak­ing its de­but in Bri­tish bou­tique sportscar man­u­fac­turer Ariel’s new ‘Hiper­car’ in 2019.

How does it work?

While ra­dial flux mo­tors have proven their worth in EV pow­er­trains, the axial flux mo­tor has an in­her­ently more com­pact de­sign and the po­ten­tial to pro­vide more torque than a sim­i­larly sized ra­dial de­sign. There are also ef­fi­ciency ad­van­tages of­fered by a shorter and sin­gled­i­men­sion flux path – a fun­da­men­tal force nec­es­sary for mo­tor ro­ta­tion.

At the heart of the sys­tem, Equipmake’s own APM200 axial mo­tor pro­vides 220kw and 450Nm with a max­i­mum speed of 10,000rpm and sends power to ei­ther a sin­gle axle or both for four-wheel-drive trac­tion. An epicyclic gear­box al­lows the out­put shaft to be con­nected di­rectly to the wheel hub for a more com­pact and light­weight end prod­uct.

Power is pro­vided by a 56kwh bat­tery for emis­sions-free driv­ing but if elec­tric­ity re­serves are low, a 35kw ‘mi­cro-tur­bine’ gas tur­bine range-ex­ten­der en­gine cuts in to gen­er­ate elec­tric­ity.

Why does it mat­ter?

Put sim­ply – power density. Equipmake claims its APM200 mo­tor has a power to weight ra­tio of 7kw per kilo­gram – about the same as a mid-2000s V10 For­mula 1 en­gine, which made about 700kw from 3.0 litres. The com­bi­na­tion with a jet en­gine range-ex­ten­der, which also has a high power density, max­imises the over­all sys­tem density fig­ure.

While large bat­tery packs, ra­dial flux mo­tors and pis­ton-en­gine hy­brid pow­er­trains are prov­ing the fea­si­bil­ity of range-ex­tended EVS, the Equipmake/ariel ap­proach scales down the size and weight of a long-range elec­tric driv­e­train with­out compromising power and per­for­mance. That means the pow­er­train can be squeezed into a car that’s light and small enough to up­hold Ariel’s rep­u­ta­tion for ban­tamweight ma­chines with su­per­carde­stroy­ing per­for­mance.

If it’s suc­cess­ful, the Equipmake so­lu­tion marks another sig­nif­i­cant mile­stone in the evo­lu­tion of EVS that are fun and ef­fi­cient.

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