RE: Detroit '09: Fisker Karma S

[just me]

Aston needs to hurry up and start churning out the Rapide, and follow up with a second generation version that's a hybrid. Fisker is stealing their thunder. I really like this car, but the front grille is hideous!

[theluckyman]

zcacogp said:

theluckyman said:

A question - I'm an energy analyst/engineer not an automotive engineer. I suspect quite a few of you are though. What would the implications be of putting an electric motor on each wheel? Would it necessarily affect unsprung mass?

Interesting Q. Little known fact - this is where a car-making company called Porsche started, around 100 years ago ... (not what you think tho'.)

It would be possible. The unsprung mass issue would depend upon whether you put the motor outside of the suspension (in which case it would be part of the unsprung mass), or inside driving through a CV joint or similar (in which case it wouldn't be part of the unsprung mass.)

What's behind the question?


Oli.

Thanks for getting back Oli. I'll presume existing CV joints are strong enough since the MiEV and Mini EV use them. I had an idea, but it would have been a bad compromise if it affected handling (apologies to Jensen Interceptor owners).

I was thinking about the Audi A8 - heavy because of the quattro system they use, which got me thinking about how you'd package 4WD with a plug-in. Advantages of having the elec motor connected to all wheels is a big increase in the amount of energy you recover when you slow down or break. If you could have a motor on each wheel it would reduce complexity - you don't need diffs or the weight of the mechanical system - and you could set it up to alter the car's handling pretty much at will with the right software.

So what's this Porsche story? I like little-known facts

Cheers, George

[theluckyman]

mitch78 said:

BlueCello said:

Looks a bit like the DB9 Volante. This is a good thing.

It would, Henrik Fisker designed the DB9 and the Vantage.

I thought the DB9 had been pretty much signed off as a Callum design before Fisker arrived?

[fairplay101]

Certainly one of the best looking cars of the moment, genuinely gorgeous looking thing. And like many others have said, I too just hope they come up with a few other more choice permutations that actually get it moving!

[skwdenyer]

zcacogp said:

theluckyman said:

A question - I'm an energy analyst/engineer not an automotive engineer. I suspect quite a few of you are though. What would the implications be of putting an electric motor on each wheel? Would it necessarily affect unsprung mass?

Interesting Q. Little known fact - this is where a car-making company called Porsche started, around 100 years ago ... (not what you think tho'.)

It would be possible. The unsprung mass issue would depend upon whether you put the motor outside of the suspension (in which case it would be part of the unsprung mass), or inside driving through a CV joint or similar (in which case it wouldn't be part of the unsprung mass.)

Wheel motors are quite common, and getting more and more efficient. As to whether they increase the unsprung mass, it all depends upon the level of integration of the motor into the upright, the size of the motor and its technology, the size of the driveshaft and CV joint being usurped, and so on. It is conceivably possible to design a wheel motor which has no appreciable effect upon unsprung mass, but it is not certain it would be possible. Adding a discreet motor to an existing vehicle as a wheel motor would almost certainly increase unsprung mess, yes.