[RedTerrano]

Originally Posted by ruzbehxyz

Before we move on to the 4WD Endeavour, lets understand difference between various driving aids and fitments in an AWD or 4WD vehicle.

EPIC compilation of knowledge, especially for someone like me, who has never driven a 4WD but has always been curious. Hats off to you @ruzbehxyz for your effort.

If ever, TBHP comes out with a "Everything you need to know about driving", this article deserves to be the top in the 4WD for dummies section.

Voted an absolutely deserved 5 stars.

[Sheel]

Originally Posted by Tejas@perioimpl

So traction control sensitivity goes down. But ATRAC is the name given specially for offroad use.

So until there are x number of wheel spins without the vehicle moving forward and that too at a constant rpm it won’t activate. And when it does, it’s quite seamless.

Want to ask one thing specifically related to A-TRAC, is it specific to front wheels only?

[Tejas@perioimpl]

Originally Posted by Sheel

Want to ask one thing specifically related to A-TRAC, is it specific to front wheels only?

No. All wheels.

In New 2020 Thar, the similar BTC system is for front wheels and the rear is an Automatic difflock.

The new fortuner, the Diff Lock is selectable. So ATRAC works on all wheels till you engage the rear difflock.

I assume (not sure) that once the rear diff lock is engaged, the system would then act only on the front wheels.

In a way I'm happy that most cars are not giving front diff locks. Incorrect use of the front ones will snap the axle. They are more unforgiving that rear ones.

[ruzbehxyz]

Originally Posted by Tejas@perioimpl

I assume (not sure) that once the rear diff lock is engaged, the system would then act only on the front wheels.

For most 4WD vehicles, the BTC switches off once the differentials are locked eg. Toyota Fortuner. However for the Everest / Endeavour, the front wheels still get BTC (sensitivity reduced) when the rear lockers are engaged. Confirmed the same in Robert Pepper's lecture as well.

All 4X4 Everests, 4X4 Rangers and even Hi-Rider Rangers have a manually lockable cross-axle differential (“locker”). When that is engaged the ESP, BTC and ETC systems are changed. They are all active, but BTC sensitivity is reduced.

Source: https://motofomo.com.au/advice/ford-...tms-explained/

[Sheel]

Originally Posted by Tejas@perioimpl

I assume (not sure) that once the rear diff lock is engaged, the system would then act only on the front wheels.

This is specifically what I wanted to ask you . That once rear diff lock is engaged, I see / have felt, the A-TRAC being activated for front wheels, but since I could not comment with authority, wanted to ask this with you.

Thanks :-).

Absolutely super thread rubehxyz. Thanks for sharing .

[real_koolkrish]

ruzbehxyz Thanks for taking your time and compiling all this information into a post. I learnt many new things from your post and this will surely be helpful to many Car Enthusiasts like me.Cheers !!

[Tejas@perioimpl]

Originally Posted by Sheel

This is specifically what I wanted to ask you . That once rear diff lock is engaged, I see / have felt, the A-TRAC being activated for front wheels

It's quite common sense actually. Once the difflock is engaged you are theoretically with a single shaft at the rear. The ATRAC/BTC works by braking one wheel. On a single shaft if you brake one wheel, the other wheel would also technically stop and thereby negate the function.

So ATRAC at the back needs to go off when the rear differential locker is engaged.

[rkv_2401]

Thanks @ruzbehxyz for your efforts in compiling this. Just what I needed to read.

I went to a hill station recently in my Vento TSi, and I decided to go visit a resort that was under construction. The road was steep and almost non-existent, and while coming back up there was a big rock at a steep place. I stopped behind the rock. When I accelerated and released the handbrake (I didn't need to do this, just wanted to preserve the clutch a bit more ), one of my wheels started spinning while the other one was stationary. The car started bucking and kicked up a lot of dust before it could get moving, which was unnerving. Rolled back and tried it again with no throttle and it made it up with far less fuss, although it's likely the underbody took a hit during the fiasco.

I supposed there was a differential, so no damage would have been done - still. It was relieving to read about the open differential used in passenger cars.

[SS-Traveller]

Originally Posted by ruzbehxyz

Modern 4WD or 4x4 vehicles are equipped with various driving aids, which help the driver in many ways. Although this ruins the driving skill, this is the present and future, and almost all modern 4WD’s come with various bells and whistles which are electronically controlled. How is this achieved?

Thanks for a detailed update on the electronic aids that make a 4wd vehicle progressively more invincible in off-road terrain. However, the basics of how all the 4 wheels are driven, remain the same in case of 4x4 vehicles powered by internal combustion engines. So, for reference of those who are discovering the joys of going off the tarmac, here's a link to the thread that explains the basics of transferring power from engine to wheels - https://www.team-bhp.com/forum/4x4-t...-how-done.html (Driving all four wheels: how is it done?).

Originally Posted by ruzbehxyz

Manual vs Automatic for off road:

This is a debatable topic and many old school off roaders prefer Manual transmission. However with the newer Auto transmissions and driving aids, the Auto transmissions are easier to drive offroad. Many Aussie websites have rated the modern Automatic transmissions as a better option.

Some pros of the Automatic transmission :-

Not all automatic transmissions are better than manual transmissions. However, those types of AT 'boxes that connect between the engine and the gearbox with a torque converter unit (usually the 'boxes with planetary gears, sometimes those with CVT systems) are helped by the fact that the torque converter can multiply the engine's (not so great) torque output at low RPMs by a factor of 2 - 2.5x, or even more. This offers a major advantage over manual transmissions in off-road situations where larger torque delivery to the wheels is necessary. Shifting to low range helps multiply the torque in MT, but with an automatic transmission with planetary gears and a torque converter, the need to shift to low range can be reduced or delayed.

[shashanka]

A veritable smorgasbord of technology and hardware @ruzbehxyz! But a question still remains in my mind. I have asked this earlier on another thread here (Driving all four wheels: how is it done? - SS-traveller) and today with the giant leaps in AI and software technology, it seems even more relevant. Why haven't we been able to develop a brake-activated limited slip mechanism (something on the lines of the new Thar's BLD, but obviously more comprehensive).

All the other devices you have mentioned (apart from the Torsen and its derivatives) need external inputs (electro/hydro/mechanical) with their unavoidable delays & lags and the inevitable niggles. The Torsen alone works without any external inputs and in real time. But it too has its drawbacks, among them being its high power absorption and high machining tolerances during manufacture and the consequent high cost. Plus the fact that it senses torque differences to the wheels and not wheel slip. No doubt the need for a 3rd differential or VC remains for AWD applications to avoid torque wind-up, but just think of the saving in weight and complexity that such a brake activated mechanism would entail. One could continue with normal open differentials.

A brake activated slip-limiting device, with high sensitivity and near real-time response capability. Plus the abuse-friendly reliability that is a given in off-road use.
Aaah.....if only such a device were available of the shelf today, it would bring smiles to pocket-sensitive enthusiasts like me! No need for high investments in power absorbing and niggle-prone hardware.

[dhanushs]

Originally Posted by ruzbehxyz

For most 4WD vehicles, the BTC switches off once the differentials are locked eg. Toyota Fortuner. However for the Everest / Endeavour, the front wheels still get BTC (sensitivity reduced) when the rear lockers are engaged. Confirmed the same in Robert Pepper's lecture as well.

It's basically a cheap substitute for lockers (Since it helps on road as well). So, when lockers are ON there is no reason to brake an individual wheel, for whatever reason it might be.

[SS-Traveller]

Originally Posted by shashanka

...a question still remains in my mind
...
Why haven't we been able to develop a brake-activated limited slip mechanism (something on the lines of the new Thar's BLD, but obviously more comprehensive).

The Thar's BLD, or Toyota's A-TRAC system, or for that matter, dhanushs' home-grown system, does exactly that. Equipping all common cars with such a system adds to manufacturing cost, and offers no advantage on tarmac.

[ruzbehxyz]

Originally Posted by dhanushs

It's basically a cheap substitute for lockers

Not its not. The ever improving technology of BTC, is slowly killing the locking differential.

Read this article for more details: https://unsealed4x4.com.au/electroni...-differential/

[shashanka]

Originally Posted by SS-Traveller

The Thar's BLD, or Toyota's A-TRAC system, or for that matter, dhanushs' home-grown system, does exactly that. Equipping all common cars with such a system adds to manufacturing cost, and offers no advantage on tarmac.

The point is well taken. But would all common cars have AWD/4WD? Taking the example of an earlier Mahindra Commander with 4WD and without any add-on frills. If it were to be retro-fitted with such a system today, assuming it was available off-the-shelf, I'd feel that it would add good value to its off-road capability, without huge expense (once again assuming the ongoing trend of falling prices and reduced sizes with increasing capability of software as it proliferates).

Is technology really so incompetent today or is it another case of automotive 7-Sisters hegemony - a bias against more economical technology research.

[dhanushs]

Originally Posted by ruzbehxyz

Not its not. The ever improving technology of BTC, is slowly killing the locking differential.

Read this article for more details: https://unsealed4x4.com.au/electroni...-differential/

Umm.. Sorry, I would humbly agree to disagree and wouldn't go by an article or online information on the same.

Braking (Reducing torque to a wheel) so that the other wheel gets more torque can never be same as a locked differential. May be for overlanding/expedition and soft offroading it works seamlessly, but in hardcore off-roading the concept of braking for traction will get you laughs.

Brake locking takes away your control on throttle, and the level of control you get in locked differentials is waayy more. Try driving over huge boulders stretch and you will know.

Originally Posted by ruzbehxyz

....Endeavour, the front wheels still get BTC (sensitivity reduced) when the rear lockers are engaged. ....
...

Can you please elaborate on how the sensitivity is reduced?
What are the parameters ECU take into account?
How is it modulated for different terrains?
What is the effect on the driver? (Driver feel)