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Discussion Starter #1
From reading elsewhere, I gather that the Volt will have a single large electrical engine with a transmission connecting to a "traditional" driveshaft. Does anyone have insights into why GM is doing this rather than using two (or four) in-hub motors?
 

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Hub motors are expensive. One motor, drive shafts and differential is cheaper.
 

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Discussion Starter #4
I expect those will show up in later models, starting with high price / high performance models. The Lightning GT offers in-hub motors, but it costs $300K.
So if the in-hub motors cost so much $$$, why is the Mitsubishi iMiEV Sport (showcased in late 2007) listed on Wikipedia as having "in-wheel motors for the front wheels, while a single motor powers the rears"?

I think the styling of the iMiEV Sport is rather horrible, but I imagine that it will be targeted for sale at the cheaper end of the spectrum.
 

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David, you are going to have to trust the engineers to decide what is best in this case. They have to weigh many variables from cost to production issues. I'm sure GM has advanced programs on-going that are either designing wheel-hub motors or are dealing with venders that do. Wheel-hub motors are coming because they offer so many advantages from ease of maintenance to the ability to control each wheel in anyway the computer sees fit. I'm also looking forward to seeing them on my car in the near future. The possibilities are endless.
 

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So if the in-hub motors cost so much $$$, why is the Mitsubishi iMiEV Sport (showcased in late 2007) listed on Wikipedia as having "in-wheel motors for the front wheels, while a single motor powers the rears"?

I think the styling of the iMiEV Sport is rather horrible, but I imagine that it will be targeted for sale at the cheaper end of the spectrum.
Good question. I suspect that they were trying to eek as much mileage out of the NiMH batteries as possible, and need the regenerative braking capabilities of all 4 wheels. If they just switch to Li-Ion, they could dump the front wheel motors and have a much longer range vehicle at a much cheaper price.
 

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Good question. I suspect that they were trying to eek as much mileage out of the NiMH batteries as possible, and need the regenerative braking capabilities of all 4 wheels. If they just switch to Li-Ion, they could dump the front wheel motors and have a much longer range vehicle at a much cheaper price.
Jason, You lost me on this one. Why would it matter if there was just one motor or four absorbing the regen energy? It's the same about of energy in both cases. If you have one big motor or four smaller ones it won't make much of a difference. If anything the one big motor would be slightly more efficient at converting the regen energy.

I will wait to see what wheel-hub motors they end up using. I would love to see a modern design EV with wheel-hub motors getting real road time. Great for R&D.
 

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Jason, You lost me on this one. Why would it matter if there was just one motor or four absorbing the regen energy? It's the same about of energy in both cases. If you have one big motor or four smaller ones it won't make much of a difference. If anything the one big motor would be slightly more efficient at converting the regen energy.

I will wait to see what wheel-hub motors they end up using. I would love to see a modern design EV with wheel-hub motors getting real road time. Great for R&D.
Texas, you are right, if the RAV-4 had a 4WD transmission connecting all 4 wheels to one motor, that too would allow regenerative breaking, or 4 wheels to 2 motors, or 4 wheels to 4 motors. My only point was having all 4 wheels attached to motors to harvest energy from all brakes was probably the driving factor to include them in the RAV-4.
 

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Sorry Jason, You missed my point. You could have one motor on one wheel and it will still absorb all the energy. Think of it like applying the brake to only one wheel in a car. It will stop right? If it can stop the car then it absorbed all the energy of the moving car. That is just the physics of the problem. Now if you are stopping hard or the surface is slippery then of course it is better to have four brakes with ABS or something even better, four-wheel computer controlled traction control. With four wheel-hub motors it will be possible to do all kinds of advanced things. You can apply a little more power to the front right wheel while stopping the spin on the back right wheel, etc. After a few years (decades?) of programming the cars will feel alive.
 

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Jason wrote: I suspect that they were trying to eek as much mileage
out of the NiMH batteries as possible...

The Mitsu i-MiEV uses Li-ion battery pack developed by GS Yuasa.
It is said to have a nominal capacity of 16KWH (same as the volt).

The purpose of using smaller in-hub motors instead of one large
motor is, I think, to distribute the burden of high current when
starting from standstill. With a given voltage the current is highest
when the motor is not rotating. This could cause frying of the motor.
For example, Keio University's Eliica has 8 in-hub motors (it needs
8 wheels to avoid motor over-heat).

From the standpoint of driving dynamics the added unsprung
weight of in-hub motor is not desirable, though.
 

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Texas, yes you can stop solely with breaking one wheel or two but not nearly as fast. If only the front wheels are used you could recover a significant amount of "recoverable" energy in real world driving but would still need 4 wheel breaking some of the time.

Hub motors will be slightly more efficient and allow better control of power to each wheel. But, they will always cost more, have unsprung weight issues, and most importantly reliability issue. Reliability issues stem from their position ahead of the suspension. They won't be cushioned from all of the potholes, curbs, rocks, etc that wheels get battered with.
 

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Jason, You lost me on this one. Why would it matter if there was just one motor or four absorbing the regen energy? It's the same about of energy in both cases. If you have one big motor or four smaller ones it won't make much of a difference. If anything the one big motor would be slightly more efficient at converting the regen energy.

I will wait to see what wheel-hub motors they end up using. I would love to see a modern design EV with wheel-hub motors getting real road time. Great for R&D.
The biggest advantage i can think of with wheel hub motors is the elimination of gears. Gears offer friction. Friction converts energy into waste heat, which ultimately uses more electicity and and produces less miles per kilowatt.
 

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Motors are pretty heavy, and if they are in the Hub that would be unsprung weight. which is very bad for handling and stability of the vehicle.

Some smart engineer could probably come up with a way to use short driveshafts, so each motor could still be mounted inside the suspension but drives only one wheel.

As others have pointed out could lead to interesting traction control to be able to not only brake wheels individually but power them differently also.
 

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Ah, I see some of you have not seen the following. Enjoy!

Mini Cooper - Wheel hub motors:
http://www.caranddriver.com/reviews/hot_lists/car_shopping/green_machines/pml_flightlink_electric_mini_cooper_car_news

PML Flightlink:
http://www.pmlflightlink.com/

“PML's specialty is flat "pancake" brushless electric motors it makes them for various military, marine, and construction applications and in the Mini these motors are entirely contained inside the 19-inch wheels. Each wheel contains an identical motor, each rated at 160 horsepower, which makes this an all-wheel-drive 640-horsepower Mini. Top speed is estimated to be in excess of 150 mph, with a 0-to-60 time of 4.5 seconds. The figures are estimated because, as this is written, the PML QED (for "quad electric drive") Mini has not run with electric power; its creators have been too busy drumming up interest at the British International Motor Show and the Electric Vehicle Symposium in Japan.

But the company is confident that it has a better solution amid the electric-and-hybrid-vehicle debate. Hub motors are not new, but PML claims its motors have the best power-to-weight ratio in the industry. PML's motor unit, including the miniature Hi-Pa drive inverter, weighs 53 pounds, and the complete wheel assembly, including the tire, is only 4.4 pounds heavier than a regular Mini's, so the effect on unsprung weight is small. “
 

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For purposes of cabin design, performance and range, eventually, all cars will have 2 or 4 in-hub motors. Batteries, caps, fuel cells will be distributed throughout the floor of the vehicle for the same reason. Only an ICE generator (and passengers) will remain a large bulk item that will require it's own cubic volume.
 

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Hey, if you use the word eventually then I would have to say that even the ICE will be gone. All that weight and complexity can be replaced with more nanotech batteries. ;)

I wonder if we will adopt a plan like Project Better Place anytime soon. The basic concept is that you need the charging infrastructure for fast recharge (or swap) before people can comfortably eliminate the range extender. When that happens we can forget about the gas, oil, maintenance, etc. that is associated with the ICE. I wonder how far we could get with 1.5 Trillion dollars worth of smart grid infrastructure. Probably a very good start. Hummm.

http://www.projectbetterplace.com/ I read that over 30 countries are trying to duplicate the model.
 

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Discussion Starter #17
From the standpoint of driving dynamics the added unsprung weight of in-hub motor is not desirable, though.
I've read elsewhere that the additional weight is only about 35 kg (80 lbs.) per in-hub motor. Apparently the lower center of gravity (due to the battery pack) helps with various issues of having additional unsprung weight.
 

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I've read elsewhere that the additional weight is only about 35 kg (80 lbs.) per in-hub motor. Apparently the lower center of gravity (due to the battery pack) helps with various issues of having additional unsprung weight.
If you read my previous post the additional weight is just 4.4 lbs. In addition, these are not even in mass production yet. Wait until all the major automotive companies and their vendors start optimizing the design. I predict that in 10 years 4-wheel-hub motor configurations will be standard on all cars and that their un-sprung wheel weight will be of no concern.
 

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If you read my previous post the additional weight is just 4.4 lbs. In addition, these are not even in mass production yet. Wait until all the major automotive companies and their vendors start optimizing the design. I predict that in 10 years 4-wheel-hub motor configurations will be standard on all cars and that their un-sprung wheel weight will be of no concern.
I believe it will be a high percentage of vehicles, but there will be some who try 2 wheel and 4 wheel transmissions (unless companies overspec the 2 - 4 wheel motors to stay in maximum torque range at all speeds).
 
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