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-   -   Driving all four wheels: how is it done? (https://www.team-bhp.com/forum/4x4-technical/90454-driving-all-four-wheels-how-done-25.html)

A very good question. Can I seek another answer, that probably is known to the experts here.

How is the condition of a free spinning wheel determined? And once the vehicle has moved, say a delta amount, what does the systems interpret as? What happens to the torque split right at that point.

On a Locking differential (by mechanical means - I dont necessarily mean MLD) one has the choice of keeping the diff locked till one can anticipate having no more need of keeping it locked.

Wont that jugglery be controlled by a CPU?

Yes, the concept is same. Individual brake control. Do it manually and you need jugglery, but have a CPU do it, its seamless

I would like to make a correction to the above : It should read .... (depends on the pitch angle of the teeth of the meshing worm-to-worm internals),...

With apologies to the mods.
Shashanka


The question was "If you have brake control over individual wheels...". It seemed to me that perhaps Sutripto meant manual control rather than having a CPU (EBD) do it for you.

Detecting, and handling the transitions is where you show (off) your engineering prowess.

+1. (But do check out fiddle brakes . Needs a navigator though, and only two wheels.)

Regards
Sutripta

Shouldn't that read driving prowess rather than "engineering prowess"!:D

Thanks for mentioning fiddle brakes. Read about it. Learnt something new today. Reading continues. :thumbs up

Fiddle Brakes or Fiddling with Individual Brakes:

It should be easy enough to determine and operate when you are clearly stuck, thus knowing which wheel has traction and which not!

But, what do you do, when for example, you are going up a steep incline, and need a 50-50 Torque split, to ensure that there is some available to whichever wheel needs the same. I don't think any contraption involving individual brakes will give a 50-50 split, will it?

Please correct me, if I have got it all wrong.

No, engineering it is. Was talking of an automated system.

Easier said than done.

That is why I said

Or talk to the marketing/ engineering team of say the Mercedes M series!

Regards
Sutripta

The wisdom of keeping your engine in optimum power band answers question of why gypsy with momentum is able to take the incline.

Or perhaps Alan Wenbourne of meccanoscene, who, though not as exalted as the M series team, is sufficiently lucid on the esoteric nature of the Torsen and the Ferrari diffs!

Regards,
Shashanka

Hear hear Dirty Dan !

Never heard a truer word! I am 63+ and I am all for "awing de womens"!
Tho' most of them - specially the new rally participants awe de hell outa me!

And to be frank, so much hair-splitting & semantics over torque-wind-up & center diffs & torque-splitting is getting a bit long in the tooth! Apart from folks like 1100D, Blackpearl and a few other genuinely brave enthusiasts in these columns, I suspect most others are like me - Sunday off-roaders, for whom the weekly jaunt to Naukuchiatal & surrounds give me bragging rights!
Regards,
Shashanka

And consequences would be...?

I mean, can some one please explain this a bit? :)

Hello Sheel,
Since so many others before this have discussed the topic threadbare, it may be presumptuous of me to butt in - but there is really no great mystery to it.

With the 3rd diff. (or central differential) in place the problem of drive-line or transmission wind-up (very noticeable on smooth tarmac, particularly while making steering-lock turns, and caused by the different rotational speeds of the front & rear prop. shafts/drive-lines) is eliminated. The central differential allows for different relative input speeds to the front/rear differentials, while still maintaining torque to both front & rear.
In place of the 3rd/central diff. there are also different kinds of couplings (viscous/hydraulic) used which fulfil the same function - allowing different input speeds to front/rear diffs while maintaining torque.
All this nuclear science allows the vehicle to be labelled "AWD", meaning it has permanently engaged 4WD. In addition to this basic set up one can have all sorts of fancy frills as discussed ad nauseum earlier in the thread.

A 4WD vehicle without the central/3rd diff (Scorpio, Thar and a whole army of others) is hugely competent in off-road conditions where its 4WD capability is quite apparent. And on smooth tarmac, as mentioned earlier, it is not advisable to engage 4WD and let it continue as a normal 2WD highway cruiser.

Comments and corrections to the above - from all pundits in the forum - are always welcome.

Why? Because of design or any limitation?

Design limitation governed by cost factor.