h a l f b a k e r yContrary to popular belief
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EV (Electric Vehicle) Hub wheels have several drawbacks:
a. Because they revolve, even the smallest weight is
translated into a large addition to the moment (equivalent
to adding a much larger weight to the car).
b. Adding weight in the wheel system is generally less good
for the total stability
and maneuverability of the car.
c. Hub motors must withstand harsher conditions of hits,
bumps, jolts, dirt, water and corrosion near the road, as
opposed to a motor stored inside the car.
d. One of the features making an electric motor for
vehicles more expensive is that it must run at a high range
of variant speeds, and work with variant torques.
My proposal is this:
For about 90 HP (70 kW) standard motor on many private
cars I would do as follows: (a) Remove the main motor and
put a low cost 30 HP motor which runs at a small range of
constant high speed low torque for distance driving. Divide
the remaining 40 kW to each of the four wheels with low
cost common 10 kW hub motors, built for slow speeds,
starting the car, and stopping it (with regenerative
energy).
For trucks with a 320 HP (~240 kW) and at least 10 wheels,
put 12 kW hub motors in the wheels = 120 and a 120 kW
motor replacement for the main motor.
Then rent the batteries.
[link]
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Or convert your existing car to burn hydrogen. |
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I thought that the main advantage of hub motors was in getting rid of the mechanical power distribution system (axles, differential, CV /universal joints etc). If you have to have all this for your large motor anyway, why have any of your motors in the hubs? |
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//Or convert your existing car to burn hydrogen// which helps how ? Zero'ish emissions at the vehicle perhaps, but the H2 has to come from somewhere and you have to get it to the car in the first place. |
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If you've electrics then getting power from a company that burns hydrogen is more efficient than burning it in the vehicle. |
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//regenerative breaking// my vehicle has that... expensive. |
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You don't want to actually stop the car with regenerative brakes, as you are essentially reversing the motor voltage, (which will eventually pull you backwards), and regenerative brakes get a little squirrely with anti-lock braking functions, especially on dirt roads. They take a lot of behind-the-scenes management to fade in and fade out to conventional brakes under specific vehicle / engine speed / throttle position / transmission conditions, as demanded by the chassis controller and/or driver demand. |
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There's no reason not to use hub motors for all tractive force (acceleration). As mentioned above, using hub motors removes the need for mechanical powertrain. |
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The braking problem is one of peak energy transfer. While a truck might be able to accelerate at 0.2G, it will still be expected to brake at the limit of grip, approaching 1G. To achieve all this with regenerative braking requires very large hub motors, so braking is shared with conventional brakes. It is the mixing of regen and conventional braking that causes headaches. |
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The durability requirements of automotive engine bay components are no different to suspension or powertrain components (in terms of vibration, contamination, corrosion etc.) A chassis mounted motor needs to be just as tough as a hub motor. |
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One of the benefits of electric motors is that they produce maximum torque at zero rpm. The speed limits of motors are the same whether they are driving or being driven, so the argument for high and low speed motors is not valid. |
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//You don't want to actually stop the vehicle with regenerative braking...//
Actually this idea might help with that to an extent. You can use field-coil motors (if that's the right word) for braking, which are marvellously controllable but not that efficient, then use a permanent magnet motor (which are finicky to control but quite efficient) for the main motive force. (I could have this wrong, but that's how I understand electric motors). |
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//peak energy transfer//
My own idea on the matter (not contrary to this post) is to have a separate pedal which controls the amount of electric-motor interaction; in this post it would control the amount of hub-motor interaction. Resting the foot on (or pressing) the gas or brake pedal determines the polarity, and the third pedal controls the amount of interaction. In an emergency or a situation requiring all the driver's concentration, they can just use the (normal)brakes. |
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I'm afraid that third pedal would be a layer of window dressing. The motor and engine must balance eachother out in dealing with what's happening behind the scenes too often with the battery state of charge and the transmission range selection, a direct connection control system would lose those elements. |
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Anybody who wants to take a serious jab at regenerative
braking on small commuter vehicles should first look at
freight locomotives. Point #1: all that heat has to go
somewhere. Power units (sorry, rr slang for locos) have
giant exchangers and radiators that by themselves weigh
more than a Prius... |
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Of course, my time w/ the roads was spent in the car
shops, so my knowledge of units is limited. Somebody like
the esteemed [FlyingToaster] may have more enlightening
things to say about this. |
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Alterother - the regenerative braking on a battery carrying vehicle is used to recharge the battery. Locomotives don't carry large batteries, so they just dump the energy as heat. |
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F1 cars run electric KERS systems which are small and light enough for racing and can store enough energy that they're worth carrying. They are only harvesting energy from rear axle braking, so a road car with front drive & KERS has the potential for more energy recovery. |
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// Locomotives don't carry large batteries, so they just
dump the energy as heat. //
Actually, they carry batteries about the same size as a
washing machine. Several of them, as a matter of fact, and
when they're done recharging them through regenerative
braking (which they do *very* efficiently) they dump the
waste heat. I may have been just a dumb f#%ckin'
carknocker, as we liked to call ourselves (in my shop, at
least) but I've crawled around inside a unit or two. |
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My time on the rr's was in passenger service, so I've never even seen the business end of a train :( However I'm thinking supercaps because in a theoretical car which weighs 2 tonnes you need about 0.4kWh to decelerate from 100kph to 0, and that's maybe only 40-50kg worth. Batteries aren't as efficient, though much lighter. Unlike a battery, a voltage converter would be needed, dunno how efficient those are. |
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[RS] True a directly connected pedal without any voltage-regulation/conversion or whatever might not be optimum, but I think it's almost necessary because the driver is the one who can see road, traffic and trip conditions, not the computer. So, like driving stickshift, it would take a bit of getting used to but the end result would be better mileage. Unlike a stick you don't *have to* use it. though that results in much slower acceleration and no regen braking. |
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OK, so the idea was discussed thoroughly. Anybody
for fish? |
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Forgot to say that the lower kW motors are
commonplace, no need to develop anything, and
easily fit in the respective wheels. |
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[FT] I'd think another advantage of supercaps is that they
can take a charge really fast, avoiding the issue of
resistance build-up when braking down steep hills (this, as
I understand it, is why power units shed so much heat; not
that the batteries are full, necessarily, but that they just
can't take the charge fast enough). |
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