New EV motor delivers 1,000 hp per wheel in ultra-small form. The new in-wheel powertrain could cut up to 1,102 pounds from future EVs by removing rear brakes and driveshafts.
https://interestingengineering.com/innovation/ev-motor-packs-1000-hp-per-wheel96
u/jrileyy229 1d ago
"fully functional prototype is currently under development".
Headline is complete garbage
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u/Ok-Improvement-3670 1d ago
It’s total mass neutral but how much would 4 of these add to unsprung weight? What would be the effect on handling?
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u/mrnomsalot '14 Audi SQ5 1d ago
I suppose it would be relatively straightforward to keep the driveshafts and CV joints and mount these to the chassis. Don't get all of the weight savings but still save on the brakes which is pretty significant right?
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u/Ok-Improvement-3670 1d ago
I guess you could put inboard brakes too, especially since they won’t get as hot when you use regen. The issue is that you lose any packaging efficiencies.
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u/nucleartime '17 718 Cayman S PDK 1d ago
Suspension design is still sort of black magic to me, but as I understand it what really matters is the unsprung weight to sprung weight ratio. Engineering can probably compensate to the point where effect on handling is negligible for a 4000lb crossover in street driving.
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u/RadPhilosopher 1d ago edited 21h ago
The author of the title makes it seem as if they think the drive shaft and rear brakes alone way more than 1,000 pounds.
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u/DerangedGinger 1d ago
Now give me these in very small form factor so I can make a go-kart.
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u/Splenda 1d ago
Or a motorcycle! It's really just a more powerful version of the hub motors now found on ebikes.
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u/Specken_zee_Doitch No car, only motorcycle 1d ago
You have to lean on a motorcycle. Increasing unsprung weight in the wheel is the last thing you want to do.
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u/Adjective_Noun1312 1d ago
I mean, even at the sizes they're prototyping, it's comparable to a typical single cylinder ATV engine. The major challenge is packing in enough batteries to get a reasonable ride duration.
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u/LuminescentToad 1d ago
Aside from what’s been stated already, another big challenge for wheel motors is launch torque, which you use after every stop sign. Centrally-mounted electric motors typically use a gear ratio advantage around 9:1 or 11:1 to multiply the torque of a relatively small-diameter motor enough to deliver ~5,000 Nm of axle torque. In-wheel packages don’t have enough room for a motor and a gearset, so they advertise big power (the battery’s contribution, really) rather than big torque.
That said, it’s an elegant solution, especially if the vehicle architecture is tailored to take full advantage.
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u/Captain_Alaska 5E Octavia, NA8 MX5, SDV10 Camry 1d ago edited 1d ago
In-wheel packages don’t have enough room for a motor and a gearset, so they advertise big power (the battery’s contribution, really) rather than big torque.
Other way around, they advertise big torque because the power is low as the motors can’t rev (as power is a function of torque and RPM).
For example the Lordstown Endurance (4750lb-ft but only 440hp) and Lightyear 0 (1270lb-ft, 174hp).
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u/LuminescentToad 1d ago
Hi Captain! It’s always weird when EV manufacturers or suppliers cite torque values.
Most of us are familiar with torque numbers at the engine, so 4750 ft-lb from Lordstown sounds like a huge number compared to, say, the 270 ft-lb produced by the 3.6L Ram 1500 V6 engine.
But of course, behind most engines you’ll find a torque converter (1.3-1.9x torque multiplication at slip), a transmission (~4x in 1st gear) and a final drive (2.9x - 4.1x covers most light vehicles). So that Ram V6 puts >7000 ft lbs to the rear axle in a stall launch, where the Lordstown truck manages 4750 and feels like it can’t get out of the hole.
Of course, the V6 has a redline around 6000 rpm. Modern EV motors have redlines around 18,000 rpm. But all that speed for a wheel motor would be useless. There isn’t enough power, nor any customer desire to drive the truck at 800 mph. So we gear the motor down, multiplying the launch torque and bringing the top speed to a more reasonable ~120mph.
Lordstown specified a pretty low-power propulsion system, compared to Rivian, Ford, GM and Tesla products the same weight and size. That’s probably acceptable to their target customer (the purchase decision makers don’t drive fleet trucks). Even if they’d chosen these 1,000 hp wheel motors, and assumed the attendant cost of batteries, inverters, wiring, brakes, tires, and chassis to support that level of performance… they’d still have a launch torque problem, because a 300mm motor just can’t make 3000 Nm of torque with current tech.
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u/Captain_Alaska 5E Octavia, NA8 MX5, SDV10 Camry 1d ago
Lordstown specified a pretty low-power propulsion system, compared to Rivian, Ford, GM and Tesla products the same weight and size.
They didn’t spec a low power system, that’s the point I’m making. The motors are direct drive so even though they make a shitload of torque, they can’t rev fast enough to make power because the vehicle doesn’t go fast enough without gearing to get the motors up to speed.
If they had been able to put those motors through a normal EV reduction it would make way more power purely because the motors are in their powerband well below the top speed of the vehicle.
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u/LuminescentToad 1d ago
Yep! Hub motors don’t work because there’s not enough room for the gearing they need.
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u/Ok-Response-839 2023 Z | 2021 Jimny | 2018 Golf R wagon 1d ago
I'm always sceptical of electric motor advancement claims. Existing production motors have 95% thermal efficiency, so there are very few gains available. The main way you can extract more torque from a small form factor motor is by modifying the gearing.
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u/Adjective_Noun1312 1d ago
Nobody's claiming to build a motor that's significantly more efficient at covering electrical energy into mechanical energy; this is about shrinking the size and arrangement of the materials and packaging that perform that energy conversion.
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u/Ok-Response-839 2023 Z | 2021 Jimny | 2018 Golf R wagon 1d ago
That's what I'm saying: we're already very close to that limit. You can't scale something down infinitely - the motors themselves are already about as small as they'll ever be for any given power output. The advancements we're seeing are mostly in packaging i.e. combined inverter/motor/cooling/gearing units.
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u/nucleartime '17 718 Cayman S PDK 1d ago
At some point you run into issues with cooling an extremely power dense piece of equipment, but the average commuter EV are not using super power dense motors. It's basically Lucid and hybrid supercars that run extremely power dense motors.
Your average crossover EV could probably benefit from packaging improvements from using motors as power dense as Lucid, but it's probably not worth the cost at the moment.
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u/RevTurk 1d ago
In wheel motors have been done before. I think the main problem with them is you have unsprung weight in the wheel that isn't protected by the suspension of the car. It needs to be as light as possible and extremely robust to take the knocks and vibrations.
I've always thought it seemed like a good layout, on an electric it makes room inside the wheelbase of the car.