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HomeOff Topics › Automotive: How to split torque 33% / 66%?
01-18-2009 02:30 PM  9 years agoPost 1
gigi

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Port-au-Prince, Haiti

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I'm trying to find a good drawing of the inside of the kind of device which is used in certain high-performance all-wheel drive sports cars [like a 911 turbo] or some AWD small SUV's [like a Honda CR-V] that splits torque between the front and wheel axle in any fashion other than 50-50.

I totally understand how differentials of all kinds work, whether open, limited slip, lockers, Etc. I am very familiar with how a regular differential only sends the same amount of torque to each one of its outputs, whether they're turning at the same rpm or not. But I haven't understood yet how you can have a 40/60 front-rear split, or any ratio that's other than even. But I know it can be done.

Can anyone shed some light on this subject? Ideally, please provide a picture or a link, but otherwise I'll be happy with a written explanation of HOW this is accomplished.

Thanks,

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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01-18-2009 02:52 PM  9 years agoPost 2
03fomoco

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Tucson AZ

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Clutch
Most use a Fluid Clutch of some type. Like the 4x4 on demand uses a fluid clutch for initial engagement. I am guessing for a 60/40 split it would come down to the design of the stators and rotors in a torque converter type of device between the front and rear driveshafts. I am also guessing that the more fancy and expensive ones could me modulated like a modern torque converter. Someone smart will come along shortly...

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01-18-2009 02:53 PM  9 years agoPost 3
AAKEE

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Boden, Sweden

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Don´t know about any links showing it, but for example a regaular differential, but You differ the size of the 4 internal gearwheels. If you make the size of the gearwheel that put power out to the front wheels smaller than the one for the rear wheels, then you made the torque different.

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01-18-2009 04:41 PM  9 years agoPost 4
gigi

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Port-au-Prince, Haiti

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Same wheel speed required
No problem understanding that if the speed of the output shaft is increased or decreased via gearing, the torque will decrease or increase accordingly. But evidently all the wheels on the vehicle must turn at the same speed, not counting going around bends... That's where I don't get it. I'm not saying the explanantion is wrong, however.

I think the fluid coupling is used to connect and disconnect the drive to the other axle whenever wheelspin occurs, but I don't think it does the actual torque splitting I am talking about. Yes, it will vary the torque output from 0 up to a certain maximum, but the device I am talking about is mechanical, as in gears, and doles torque out in a fixed ratio. I just wish I could understand it better and see an actual picture of it.

Thanks for any additional help,

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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01-18-2009 04:54 PM  9 years agoPost 5
Brokenlink

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Oakdale

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01-18-2009 09:15 PM  9 years agoPost 6
AAKEE

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Boden, Sweden

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Hi!

The different size wont make the wheels differ in speed. As the speed of the wheels will still be the same, only thing that differs is torque. Remember: when running straight ahead, the 'whole' differential will rotate and the internal gears will not ( = same speed for both axes, but different torque).

I would guess that its rather common to use planet gears( not sure of the english expression, could be planetarium gear ?) to make the torque between axes differ.

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01-18-2009 09:23 PM  9 years agoPost 7
Brokenlink

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Oakdale

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The different size wont make the wheels differ in speed
Sure it will.

Jamie Griffith

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01-24-2009 02:17 PM  9 years agoPost 8
gigi

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Port-au-Prince, Haiti

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Thanks!
Brokenlink, thanks for the working link It's funny, I had seen that very page a couple of years ago.

Somehow, I still don't think I've found what I'm looking for, however... And I don't see how to do it other than how AAKEE has proposed it, but it still doesn't add up in my head.

Ah well, we'll keep looking and hopefully resolve this matter someday.

Thanks for the help, everybody!

Gigi

My heli spending has gone way down since I got a Honda 919 :-)

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01-24-2009 05:31 PM  9 years agoPost 9
AAKEE

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Boden, Sweden

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how a differential works
Quote
--------------------------------------------------------------------------------

The different size wont make the wheels differ in speed
--------------------------------------------------------------------------------

Sure it will.
The way a differential works, it allows the wheels or axles to rotate at different speeds, still pushing torque through.
With a differential on one axle or between two axles the speed of the wheels will be the same as that wheel has "on ground".
When running straight forward the speed of the wheels (or axles) will be the same...so the whole differential housing rotates, but not the internal gears. If the internal gears are different size then torque will differ to the two output shafts.
When running through a bend/corner the speed will differ automatically and the internal gears of the differential will rotate, still putting out the same torque as before.

So with a differential on a car its the speed of the wheel vs the ground that determine the speed of the wheel and the differential only 'allows' this. If the differential internal gears have different size then the torque will be different between output shafts. This gives us for example the 60/40 split.

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