Mechanical Design - Please Consider Using "In-Wheel" Motor

[Anonymous]

I believe that the ultimate future of electric vehicles will be to use the "In-Wheel" motor design, much like the Protean Motor units. This will save a tremendous amount of engine and power train weight, free up interior space, provide very simply "two wheel" or "four wheel" drive ability along with making maintenance and repair work extremely easy - just replace the wheel/hub motor. As much as I love the Bolt, General Motors should take this car to the next level of this technology!

 

[Anonymous]

As I understand it, in-wheel motors are a significant engineering challenge due to the increase weight of each wheel.

 

[Anonymous]

General Motors should take this car to the next level of this technology!

The in-wheel motor technology is simply not advantageous enough to be used, otherwise it would be. The advantage of having the motor and power electronics located together is shorter power wires (cheaper) and easier to cool by running coolant loops near the AC equipment which is also in the middle of the car.

 

[jas]

Plus, and this has been discussed for years in electric vehicle forums, having motors exposed like this would not make maintenance easier but would require more repairs.

 

[Anonymous]

Wheel motors make for lousy handling.
One 100KW motor and one VFD drive is more efficient and lighter than two 50KW motors and two VFD's.

 

[charge]

Wheel motors create too much unsprung mass, meaning Isaac Newton' F=MA physics tell us the ride will be rougher with in-wheel motors.
I like the summaries above too.
Also, consider the extra shock loading and lack of protection from the elements (dirt, dust, water) in a wheel.

One slight variation of this concept (OK, not the same as being "in the wheel", but bear with me): You could do without a differential completely and run 2 motors total, one on each half-shaft. The turning differential action would be commanded on each wheel by the computer or other local sensing device.
You could use UQM's controlled motors interfaced to one another for AWD or 2WD systems, with steering and slip sensing.

 

[marta]

Wheel motors create too much unsprung mass, meaning Isaac Newton' F=MA physics tell us the ride will be rougher with in-wheel motors.
I like the summaries above too.
Also, consider the extra shock loading and lack of protection from the elements (dirt, dust, water) in a wheel.

One slight variation of this concept (OK, not the same as being "in the wheel", but bear with me): You could do without a differential completely and run 2 motors total, one on each half-shaft. The turning differential action would be commanded on each wheel by the computer or other local sensing device.
You could use UQM's controlled motors interfaced to one another for AWD or 2WD systems, with steering and slip sensing.

What would the advantage of 2 smaller motors (one on each half shaft) be? Vs just one large electric motor with a differential...

 

[DucRider]

What would the advantage of 2 smaller motors (one on each half shaft) be? Vs just one large electric motor with a differential...

More precise control of the the power delivered to each wheel.
I suspect until you get into very high performance applications, the cost/weight/complexity cons outweigh the benefits of such a system. Even the PP03 that was designed solely for the Pikes Peak Hillclimb (and overall winner) used limited slip differentials, even with 3 electric motors per axle. 1,368 hp and 1,593 lb/ft of torque. http://www.topspeed.com/cars/others/2015-drive-eo-pp03-ar170210.html#main
Second overall was the Rimac which did use one motor per wheel. It features the Rimac All Wheel Torque Vector Vectoring system, which can vary the torque on each wheel depending on the steering angle, speed, longitudinal and lateral forces, yaw-rates, and several other variables.
http://www.topspeed.com/cars/rimac-automobile/2015-tajima-rimac-e-runner-concept_one-ar169695.html

 

[charge]

One slight variation of this concept (OK, not the same as being "in the wheel", but bear with me): You could do without a differential completely and run 2 motors total, one on each half-shaft. The turning differential action would be commanded on each wheel by the computer or other local sensing device.
You could use UQM's controlled motors interfaced to one another for AWD or 2WD systems, with steering and slip sensing.

What would the advantage of 2 smaller motors (one on each half shaft) be? Vs just one large electric motor with a differential...

.

More precise control of the the power delivered to each wheel.........................It features the Rimac All Wheel Torque Vector Vectoring system, which can vary the torque on each wheel depending on the steering angle, speed, longitudinal and lateral forces, yaw-rates, and several other variables. http://www.topspeed.com/cars/rimac-automobile/2015-tajima-rimac-e-runner-concept_one-ar169695.html

More precise control, more directly commanded control.
Anti-skid stability control on modern cars works on the same sensor inputs DucRider described for the Rimac. New cars are demanding in performance these days.
Also, each of the two motors can be smaller and cheaper individually than one big motor since you only need about half-power going thru each motor.
Differentials are heavy and we'd be glad to not have one.
Being smaller motors means they lie flatter and lower beneath a trunk or load floor.
Being smaller motors means they have less rotational inertia (respond quicker).
In addition, it avoids using braking commands to do traction control and anti-skid (yaw) control as most cars do now with differentials.

DucRider, I didn't know about the Rimac system, as I've spent my years doing Aero Engineering with software/mechanical off and on, so thanks for the reference. Here is a picture of the two-motor (one on each half-shaft) system, which Rimac claims saves space and weight.

Granted a single motor plus one differential would be cheaper overall (even though each smaller motor is cheaper than a bigger motor). There is a lot of emphasis on weight, space, and performance in Stability Control (anti-skid, yaw control), so it might be a decent approach for a passenger vehicle.

 

[marta]

I'm not sorry I asked, but wow, that got over my head fast!

Thanks for taking the time to outline the advantages. I guess my initial thought was that simpler is cheaper, and in theory, that's what the Bolt EV's main function is supposed to be - EV range at a decent cost.

After reading your explanations it does make sense to increase power/decrease power for steering and traction control vs using the brakes and actually burning power into heat loss (friction).