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Wheel Hub Motor on future vehicles and its effects

Wheel Hub Motor on future vehicles and its effects

Wheel Hub Motor on future vehicles and its effects

(OP)
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.

RE: Wheel Hub Motor on future vehicles and its effects

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

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Wheel Hub Motor on future vehicles and its effects


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?

RE: Wheel Hub Motor on future vehicles and its effects

(OP)
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?

RE: Wheel Hub Motor on future vehicles and its effects

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

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Wheel Hub Motor on future vehicles and its effects

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

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Wheel Hub Motor on future vehicles and its effects

(OP)
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).

RE: Wheel Hub Motor on future vehicles and its effects

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)

RE: Wheel Hub Motor on future vehicles and its effects

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

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Wheel Hub Motor on future vehicles and its effects

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.

RE: Wheel Hub Motor on future vehicles and its effects

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

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Wheel Hub Motor on future vehicles and its effects

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 smile

RE: Wheel Hub Motor on future vehicles and its effects

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

Regards

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Wheel Hub Motor on future vehicles and its effects

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%208x8%20AHED%2027.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.

RE: Wheel Hub Motor on future vehicles and its effects


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

RE: Wheel Hub Motor on future vehicles and its effects

(OP)
kenvlach,

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

RE: Wheel Hub Motor on future vehicles and its effects

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.smile

Rod

RE: Wheel Hub Motor on future vehicles and its effects

(OP)
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?

RE: Wheel Hub Motor on future vehicles and its effects

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

eng-tips, by professional engineers for professional engineers
Please see FAQ731-376 for tips on how to make the best use of Eng-Tips Fora.

RE: Wheel Hub Motor on future vehicles and its effects

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

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Wheel Hub Motor on future vehicles and its effects

Just to add to the frey... The motors could turn in the
opposite direction (planetary).

 I haven't thought of this until now but could you counter balance for added weight?

I know something is wrong with that statement but it works on our large tools.

Cheers  

I don't know anything but the people that do.

RE: Wheel Hub Motor on future vehicles and its effects

thundair,
that's fine, for straightaways! bigsmile

RE: Wheel Hub Motor on future vehicles and its effects

LeTourneau did the wheel motor in large earth moving vehicles many years ago. What was in their favor was large diameter wheels, which worked effectively in electric motors. The principle seems to apply to small, light vehicles with relatively large wheel hubs.

RE: Wheel Hub Motor on future vehicles and its effects

(OP)
plasgear.  YUP!  Seems to me in order to make the idea work you would have to put larger (proportionally) wheels on a vehicle in order to incorporate wheel hub motors.

RE: Wheel Hub Motor on future vehicles and its effects

How big were the wheels on the Mitsubishi 4wd electric drive demonstartor? They may have been 18s from memory. There again they were 50 kW motors.

Cheers

Greg Locock

Please see FAQ731-376 for tips on how to make the best use of Eng-Tips.

RE: Wheel Hub Motor on future vehicles and its effects

Our electric car with 50kW (cant remember torque numbers, but over 200Nm each for the whole rev range) electric motors has 17 inch wheels, but the bigger the better to allow more room for larger wire in the windings (more current = more torque) etc.

Smaller cars dont need the huge amounts of torque, so smaller motors (and therfore wheels) would work.

Ryan

RE: Wheel Hub Motor on future vehicles and its effects

Hi Rod,
Our car website is www.nzeco.net We are working with Hybrid Auto in Brisbane who are supplying us with the 2 in-wheel electric motors and allowing us to use many components they have developed and helping us with their outstanding expertise and knowledge of electric cars.

Regards,
Ryan

RE: Wheel Hub Motor on future vehicles and its effects

Hi Ryan,

I would like to know more about these in-wheel electric motors from Hybrid Auto. Could you give me a clue how to find more information about that? The link www.nzeco.net does not say nothing about hybrid cars or in-wheel electric motors. I called Hybrid Auto but a man that I contacted said he do not know that they supply nz company with in-wheel electric motors.

Regards,
Dimitar

RE: Wheel Hub Motor on future vehicles and its effects

Hi Dimitar,

Forgot to mention the project is for the University of Waikato, not a company and our website expired, so we are working on another one.

Hybrid Auto works out of Brisbane.

Cheers,
Ryan

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