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Why not in-wheel hub engines?

I have read about the Brabus All Electric 4wd , and now it seems it is in production.
Brabus uses wheel hub engines. 4 of them for a whopping 4 x 110 hp. 440 HP. Grip on all wheels. Must be fun. Even in wintertime.

As we know there is no plan for a 4wd Tesla S any time soon.
But wouldn't it be possible for Tesla also to use those Protean Electric motors?
Sure bolting 2 of them in front corners must be cost friendly way to give Tesla S 4wd?

I do see the obvious, that those 2 electric motors will increase the unsprung weight. Are there others?

Maybe possible to do an personal upgrade to the front wheels, slightly modification maybe but should be doable?

Here you can see those In-wheel motors

In-wheel hub engines are a bad idea. I had this discussion with a friend of mine (who happens to work for Tesla). You want to reduce the un-sprung weight as much as possible for handling purposes. Heavy wheels won't handle the bumps and whatnot as well as light-weight wheels.

Not to mention any shocks not dampened by the tires will affect the stator, rotor, gears, inverter, etc. in integrated in-hub systems.

I don't think 'why not' is the place to start. The question is 'why'? I think the current setup is very efficient and 4WD can be achieved the way they have proposed in the model X - with a similar drive-train in the front of the car.

They show a range of 350km vs MS of 480km. They show 0-100km in 6.9sec vs MS of 4.2. They don't show a price but it looks like half the car the MS is so when I can buy one 40K USD I might think about, but they don't show a price.

Hub motors are weak generally speaking. You need four to get same result as Model S gets with one. Add one more and hub-motors lose.

In addition to adding unsprung weight, hub motors increase the distance between the wheel and the king pin linkages. This has implications that make proper suspension geometry more difficult and will generally increase stresses in all of the suspension components.

With hub motors, there is the advantage of better natural air cooling, but the disadvantage of being more exposed to the elements.

Another consideration, more motors=more motor housings=higher overall motor weight.

" You want to reduce the un-sprung weight as much as possible for handling purposes. Heavy wheels won't handle the bumps and whatnot as well as light-weight wheels."

Zigackly. Which is why I had asked tesla for a smaller diameter wheel than even the 19". Alas, no go.

I'd love light 17" or 18" wheels to be the std equipment. I know, I know car is big, won't look good, etc etc..

@Redshift - what's the weight of a wheel compared to a tire? For every inch reduction in wheel diameter you need to increase the tire wall by half an inch. There must be little marginal weight saving...?

In addition to the unsprung weight issues (which Lotus did some work on and found that for the most part you could work around the issues by tuning the rest of the suspension), a hub motor means that the bearings in the motor itself support the weight of the car, so they are more likely to wear out than if the motor isn't weight-bearing.

See http://en.wikipedia.org/wiki/Unsprung_mass for reasons why you want as little mass as possible in the wheels.

Nitpicky engineer note:

An ENGINE is a prime mover- it contains its own energy source. Rocket engine. Internal combustion engine. Jet engine.

a MOTOR is a device that converts energy generated elsewhere to kinetic energy. Hydraulic motor. Pneumatic motor. Electric MOTOR.

There is no such thing as an electric 'engine.'

With left/right hub motors I suspect a mechanical failure or software bug would result would have very very bad consequences.

Overall weight savings are better when you reduce the wheel weight. I went for 15" wheels (a lighter alloy than the OEM 16") for my first car, and I recall that the per wheel weight was down by almost 5 lbs. 20 lbs overall may not sound like much, but it made the handling noticeably tighter. The rotational unsprung mass reduction gives you the maxim bang for bucks.

It also makes you feel all the bumps onto road. Larger wheel doesn't notice small bumps, smaller does. Larger wheel makes smoother ride.

DTsea
Thank you, in Italian there is no such distinction, and I could not tell if there was a real difference in the English language. Now I know

gianni;
in casual speech, there is less distinction drawn. E.g., to "go motoring" is to go for a pleasure drive (in your engine-driven car). The electric starter in a car is always called a 'motor', but no one would be confused if you referred to the V-6 as a motor. Except engineers, who might get slightly red in the face for a moment.

Timo - he's talking smaller wheel (rim) plus larger tire = external diameter remains the same. I know this is probably a language issue, often "wheel" means the whole thing in many languages :-).

So the effect is quite the opposite: less bumpy with the smaller rim + bigger tire.

You will lose, but it is a gain: the reduction gear, the differential, the semiaxis and omocinetic joints
  You gain, but it is a loss: 31Kg per wheel and all power and signal connections to each wheel. The 4 motors have to work under extreme acceleration and in contact with the dirt of the road.
It will be interesting to see the developments

Personally, I think in-wheel motors are perfect for small, non-performance EVs. You use up less space in the body of the car, which is most at a premium in small cars, and non-performance car buyers won't care as much about unsprung weight. Lighter cars also lessen the weight being born by the motor spindles as well.

All - I have to jump in here on in-wheel motors. Don't get me wrong, the Tesla powertrain is fantastic. But we make in-wheel motors so I wanted to say something.

Each of our in-wheel motors is 80kW so it would take four (not two) to get us to the Model S (310 kW) for power. But,each of our motors is 800 N.m peak torque and more torque feels better.
We can also provide torque and regen on each wheel individually, so torque vectoring around corners is doable.

Unsprung mass is legit, but can be overcome the added 31kg per corner with conventional ride engineering work on shock damping, springs, etc. Here's a study from Lotus you can read if you wish: http://www.proteanelectric.com/wp-content/uploads/2012/10/The-Effect-of-...

We use a conventional automotive bearing so we have an answer for road loads without creating load paths through the motor itself.

Besides, I would like to free up the space occupied by in-board motors, drive shafts and stuff and put in more battery (range), more people space and make the car look completely different.

We are still in the prototype stages so I'm not "selling" here. I just want to add some more to the conversation.
Ken

I see.. increased complexity, increased cost, minimal "if any" gains in efficiency as far as range propulsion etc. While I'm sure there are specialized platforms that might benefit from such an arrangement. It does not appear to be a setup that would drive down costs significantly towards a goal of a viable affordable to the masses mass produced "on road" BEV.

I dont see in wheel becoming the norm anytime soon, people need to swap their tire for winter wheel, please like to change the look of their car with new wheel, people don't want their crazy expensive in wheel motor to be stole with a few bolt out, etc...

Protean:

I think in wheel motors are perfect for all wheel drive applications like off roaming vehicles.
Even though the added unsprung weight can be somewhat offset by suspension design and spring rates, it's
Not 'ideal' for a sports car/sedan.

IMHO.

Gianni- Anch'io parlo la bella lingua Italiana. (Dopo un anno a Foggia). Vero, pensando un attimo, che si usa la stessa parola. C'e' un convergenza bella pero' dicendo 'ingeniere' (con la radice che sarebbe in inglese 'ingenious' oppure 'gene' significando il momento di creativita, di nascita; in America, i primi ingenieri erano quelli progettando motori di vapore- quindi 'engine' mentre 'motor' scende dalla radice 'muovimento.'

ciao-

That's easy for you to say.

Well nickjhowe, it makes more sense in Italian but I will try.

The word for engineer in Italian is ingegnere which comes from the same root word as gene, genius, ingenius- relating to creation, or maybe birth. The first American engineers were guys who designed or operated steam engines. Back then an 'engine' was any designed machine but steam engines became so prevalent that 'engine' took its modern sense. However the root word of 'motor' is the same as the root of 'movement' so you could say that a motor is anything that makes motion, but an engine is the real spark- the prime mover- and that the juxtaposition of those words is pleasing and meaningful.

So I don't get red in the face about it, as Brian H suggested... I just like using the right word because of the compact and beautiful historical connotations.

Ingenious, I meant. Engineers, as all know, are poor spellers.

Protean,
Did you not have 120kw wheel motors under development at one time. That would be about 630 hp if installed on all wheels.
Also, how much breaking can be done with these motors? If all of breaking can be done through regen (using resistors if battery / supercapacitors can't take it) then we save some of the unsprung weight here.

lph;
breaking is to be avoided at all costs. Very expensive to repair. It's best to brake before they break.

Opps, should had checked before sending.


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