Wheel Hub Motor on future vehicles and its effects

[xLeadxSledx]

I have been researching future trends in vehicle design lately and there seems to be a clear trend that most major manufacturers believe wheel hub motors will be used almost exclusively.

I can see the benefit in doing this because you are able to use the large wheel diameters to reduce motor currents, among other things.

The one side-effect I can see is the additional weight of a wheel/hub motor design compared to a traditional wheel/rim design and the effect of this extra weight on the suspension. Specifically the increased un-sprung weight versus the reduce body weight of a future vehicle (reduce body weight that would be needed to make an electric vehicle really viable).

Electric motors have come a long way, but so far, you cannot escape the need for lots of copper for high power/current designs that would be needed for a vehicle drivetrain.

I am more or less interested in what you folks have to say on this topic. I work in the robotics field but have always been interested in vehicle design.

Thank you up-front for your opinions.

 

[patprimmer]

I have seen wheel designs where the spokes are shaped to act as springs. I imagine that there are lateral compliance and dampening issues to be resolved, but in this case the hub could be sprung and a very low unsprung weight could be obtained for the tyre, rim and a portion of the spokes but sans hub and axles.

Regards

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[Fabrico]

Various forms of "sprung hubs" have been around for nearly a century. Problem is, when they run out of travel, the situation becomes worse than ever.

It would be nice to come up with some kind of progressive and powerful compounding for re-generation. That way the brakes could finally be almost eliminated.

In a fashion somewhat similar to hydraulics, why can't powerful magnetic pulses be sent through the upper and lower control arms?

 

[xLeadxSledx]

the one reason i can see for not sending magnetic (electrical) pulses through the a-arms is the abount of EMI that would create. You would be generating major magnetic fields and have very little options for proper shielding.

Another thing comes to mind. If you have the suspention built into the wheel hub itself, then you would essentially be reducing the available volume of which to package your motor/gears. Isn't this counter productive? Whatever the amount of suspension travel you have would take-away from your motor diameter?

 

[GregLocock]

To be honest for commuter type vehicles there is very little penalty in increasing the unsprung mass, and any competent mechanical engineer can design an electric motor that will cope with the vibration and so on that a wheel motor sees.

Cheers

Greg Locock

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[patprimmer]

How is running out of travel on a sprung hub worse than running out of travel on a normal suspension?

Regards

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[xLeadxSledx]

patprimmer,

the are equally bad. The point i was was trying to make is that whatever suspension travel you have with a wheel hub motor/suspension design takes away from the max diameter you can have for a motor.

Assume a 20" Wheel ID and 5" of total suspension travel. With a conventional suspension you could have a max motor OD of 20". With a wheel hub/suspension design the max motor OD would be 15".

Motor OD, or more specifically working diameter of the stator/magnets, is a direct function of motor output torque and therefore motor current. Motor diameter is important because the less motor current you have the high effciency you have (in most cases).

 

[glantman]

We are using some electric motors in our car this year. We have eliminated rear brakes (regen only) and moved the park brake to the front wheels.

The guys that designed the motors are really worried about the unsprung mass of the motors, so we are working on using very lightweight materials to lighten them.

I guess we will have to wait a few months until it is rolling to see what affect the extra unsprung mass will have

Ryan (New Zealand)

 

[GregLocock]

You might want to quiz them politely, or do the FORBIDDEN EXPERIMENT - bolt a 5 kg mass to the spindle of each wheel and see if you care about the difference. If anyone mentions gyroscopic effects, give them 1 point for effort and then tell them to go away and do the work.





Cheers

Greg Locock

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[glantman]

The motors are going to weigh approx. 13kg each (yes large, but they have a lot of power) which may affect the sprung to unsprung mass ratio a lot, especially since the car will hopefully weigh 600kg.

The only way that we figure to counteract this is to use active damping, which is coming on leaps and bounds recently. This should hopefully elleviate all handling problems, and allow the suspension to handle as you desire.

 

[GregLocock]

13 kg is not that much in the context of a typical unsprung mass, particularly since you'll be losing the CV joints, halfshafts and hopefully downsizing the brakes.

How are you going to get the power to drive the active dampers? What makes you think that you can resolve all handling issues (eg aforesaid gyroscopic effects) with dampers? Do you really have a source for them in the timeframe of your project?

I've made a suggestion, instead of chasing rainbows, why not try the experiment and see if it matters?

Cheers

Greg Locock

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[glantman]

What do you mean by gyroscopic effects? I have never heard of them when refering to suspension.

The project is an ongoing one, so we have no timeframes, but at this stage we do not have any active dampers avaliable, although there is a lot of R&D into them at the moment. I dont believe that active damping will solve all problems but will be able to solve the large majority of problems.

As per the experiment, I will see what I can do, hopefully we will be able to get something like that working to test it out.

Cheers,
Ryan

 

[patprimmer]

I have never seen a car suspension system where the wheels don't turn.

Regards

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[kenvlach]

xLeadxSledx,
Can you give a website link to your design?

I found a few, interesting in-hub motor designs, ranging from mopeds avaialble for sale:

http://www.electricrider.com/crystalyte/index.htm

to an 8-wheel drive vehicle from General Dynamics & the US Army (very skimpy details on page 4):

http://www.dodsbir.net/SITIS/view_pdf.asp?id=HE 8x8 AHED 27.pdf

and a DARPA-funded 4-wheeler (General Dynamics, Boeing, US Navy, Magnet Motors):

http://www.dtic.mil/ndia/ewc/Kennedy.pdf

The latter two were apparently tested in 2002.

 

[WGJ]

Gyroscopic effects - lift the front wheel of an adult bicycle off the ground and spin it vigorously, then move the handlebars left and right and feel the reactions.

It's called precession. See

http://en.wikipedia.org/wiki/Precession

Bill

 

[xLeadxSledx]

kenvlach,

I have not published my design. I do have a bunch of ideas though.

 

[evelrod]

Pat.
LOL!!! I've just gotta make it to OZ one of these days. I have a feeling that I'll be right at home.

Rod

 

[xLeadxSledx]

greg locock,

what is the typical unsprug weight of a modern passenger sedan? (or better yet sprung/unsprung ratio) at what point would that weight effect ride/handling?

 

[patprimmer]

Rod

Sometimes the chin is just to far out for me to resist the temptation. I know, self discipline and discretion are desirable traits I sometimes lack.

I am sure you would fit right in here.

Regards

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[GregLocock]

small car 30 large car 50 kg.

I have never done the FORBIDDEN EXPERIMENT, directly, but I invented it due to the repeated mantra about unsprung mass.

We used to have a beam axle and an IRS in the same car, with the same tyres, and the same front suspension. The difference in usprung mass was perhaps 10-15 kg per wheel.

There were certain circumstances in which a difference was easily detectable, but for the vast majority of the time, on the vast majority of road surfaces, the differences were unimportant.




Cheers

Greg Locock

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