In-wheel motors (IWMs) have been around since the world got serious about electric propulsion. GM’s Autonomy of 2002 concept was an FCEV with a skateboard chassis propelled by IWMs. GM had working demonstrators, including a Chevrolet S-10 pick-up with IWMs driving the rear wheels plus a single motor at the front.
For the past 15 years, Protean Electric has worked on nothing else. Since we first reported on the Farnham-based company back in 2017, it has continued to develop the technology and amassed extensive knowledge along the way.
The latest Gen 5 Proteandrive IWM (PD18 Gen 5) has completed a validation programme and, claims the company, sets a new industry standard for IWMs, producing 1106lb ft and 138bhp and weighing 39kg.
Two motors in a front- or rear-wheel-drive configuration give peak power of 276bhp, while four-wheel drive gives 553bhp. Maximum speed with the motors is 140mph.
The IWM has an integrated disc brake, fits in an 18in wheel and is validated for use in mainstream cars and light commercials, meeting 15-year and 186,000-mile durability requirements. The motors were subjected to severe shock, vibration, thermal cycles, sand, dust, water and chemical contamination during tests.
The appeal of IWMs lies mainly in the packaging. In this case the entire drive unit fits inside the wheel, including the inverter, which manages energy in and out and handles the transition between AC and the DC current from and to the battery.
A conventional e-axle set-up with motor and transmission on the car’s centreline and driveshafts to each wheel creates an incompressible package that can’t be part of a front or rear crumple zone, and the same applies to ICE cars.
By removing these packages the wheels can be moved closer to the car’s corners, freeing up space inside. The other plus point is improved efficiency and range, because there are no losses from reduction transmissions or drivetrain components.
Protean has spent years commissioning and studying independent analysis of potential issues such as unsprung weight, but an early study by Lotus Engineering concluded that unsprung weight isn’t an issue at all.
Essentially, the heavier a car is the less of an effect it poses, and any effects of unsprung weight can be compensated for with suspension and damper tuning.
The first PD18 is designed for 400V architectures, and the company expects to have an 800V version ready by the end of the year.
The PD18 is compatible with cars, SUVs, vans and autonomous pods weighing up to 5.2 tonnes; the smaller, 107bhp PD16 is for cars, vans and pods up to 3.2 tonnes.
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Anyone familiar with the vintage Technics 1200 turntables will know that the record platter forms an integral part of the motor structure, although I think it uses DC. Japanese direct drive turntables as opposed to belt drive types in the olden days had a similar set-up, although their designs drove the centre spindle like an axle rather than the entire platter. They also apply back emf to stop/brake the Technics 1200 turntable quickly for professional use such as queuing etc. One of the reasons it's stood the test of time and is so robust.
Although I do indeed love the idea of IWMs, the fact that you need at multiples of 2 per 4 wheel vehicle is surely the factor that is limiting car manufacture interest. I would guess that the motor is the most expensive part of an EV drivetrain, so doubling the motor while removing the driveshafts and other assosiated parts is probably still more expensive than the current EV setup.
Maybe there will be a point when battery tech becomes cheap enough, it could offset the cost increase of IWMs as their efficiency, let alone their packaging benefits must be what car manufacturers are craving right now so they can reduce car sizes and provide the greater range customers are after.
Why would you want 2 EV motors when one and a cheap simple drivetrain would suffice. Longevity, would they like to see what a pot hole did to my wheel last winter. As to Lotus saying unsprung weight isn't an issue, that's just being dismissive of a fundamental enginnering problem and doesn't sound like Lotus.
To some up, still no production after 7 years and the only stated working example is a truck, 20 inch wheels no doubt.
Well two motors would save the cost and weight of driveshafts and differential.
And most combustion cars have three or four cylinders when one might technically do the job.
It's just a question of whether electric motors could be made cheap enough which admittedly the article does not address!
Emm one cylinder cars, not even remotely comparable.
As to 'just a question of whether it would be cheap enough', nope there's far more to it than that.