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Old 21st July 2015, 15:14   #376
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Default Re: Driving all four wheels: how is it done?

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Why? Because of design or any limitation?
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Originally Posted by SS-Traveller View Post
Design limitation governed by cost factor.
Doesn't a part time 4WD with central differential become a full time 4WD?
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Old 21st July 2015, 20:52   #377
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Default Re: Driving all four wheels: how is it done?

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Why? Because of design or any limitation?
"Vehicles with part-time 4WD systems do not have a centre differential."

Actually this is because there's no need for one / advantage to one, since 4wd is in that case disengage-able and would not have to be used on hard/non-slippery surfaces that would otherwise cause windup (mechanical binding - described elsewhere in the thread) in the drive system.
A center diff. is used in full-time systems to eliminate this possibility since they are not disengage-able, and must be used on every kind of surface.

Benefit of the part-time system is that it is absolutely locked in (when engaged), so that you don't have the wheels of one axle taking "the path of least resistance" and spinning when the axle at the other end has better traction: Some have noted that with "open" [non-LSD] diffs at center and both ends, some so-called full-time "4wd" systems can actually leave you with something like 1wd (!) at points - three wheels stuck when the fourth happens to be spinning on a slippery surface! The best way around this is to have the center diff a LSD unit. Better yet when the front/rears also are, as in Jeep (USA)'s old "Quadratrac" system - but in that case, frictional losses related to the constant running of four axles, two propeller shafts, and THREE LSD's, made for frighteningly poor FE (a friend's 1976 J10 pickup, with 5.9L V-8, managed only 3kmpl!)

Electronically sensing / engaging locking diffs are the best economy/performance solution - but then you've got complex electronics involved, that eventually will cost more than the car's worth to fix.

As usual... no perfection in the earthly realm.

-Eric

Last edited by ringoism : 21st July 2015 at 21:08.
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Old 1st August 2015, 17:32   #378
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Default Re: Driving all four wheels: how is it done?

I shall once again stick out my neck and push for a comprehensive, high-competence, high-reliability EBD system to tackle this whole issue of wheel-slip/wheel-spin.
Quite a while back (at the height of the Iran-Iraq war) where the Hummer proved its cojones, among the many write-ups on it one highlight which stuck in my mind was its rudimentary EBD at the time.
Regardless of how many wheels had lost traction (if all 4 wheels were on an oilslick on tarmac, then of course you were on your own & God took the hindmost!) the EBD would sense (via the normal accelerometer route) which wheel(s) still had traction. And would then selectively, progressively, apply brake force to the spinning wheels, transferring torque to the other wheels and hopefully, enable one to wriggle out of a sticky situation. It was certainly rudimentary at the time, with limited input channels and, relatively speaking, lethargic response times.
A good deal of water has flown under the bridge since then and, arguably, technology has galloped the fastest & farthest.
Is it inconceivable that we haven't yet come to the stage where a high reliability, high durability, sufficiently quick responding and comprehensive EBD cannot replace all the limited slip hardware that one has at the moment?
Would it not put an undoubtedly cheaper alternative within reach of the average motorist with average means?

Leaving the dedicated gearheads (with their no doubt, unlimited budgets) to continue playing around with all the hardware (read Torsens, Haldex's, Eatons, Giovanni-Ferrari's et al) available?
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Old 1st August 2015, 18:26   #379
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Default Re: Driving all four wheels: how is it done?

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...EBD system to tackle this whole issue of wheel-slip/wheel-spin.
EBD = Electronic Brakeforce Distribution.

I believe you mean TC (Traction Control).
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Old 2nd August 2015, 04:59   #380
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by SS-Traveller View Post
EBD = Electronic Brakeforce Distribution.

I believe you mean TC (Traction Control).
No, I believe traction control is a more elaborate programme. I dont mean something elaborate. EBD could be adapted to be a simpler substitute for such acronyms (traction control, stability control etc). A more pocket friendly add-on for mere mortals like me, which would aid wheel spin/slip control, without burning a hole in the pocket!
I also have the sneaking suspicion that mfrs indulge in bandying these acronyms to differentiate themselves from each other while providing the same fundamental driving aids.
The idea is to avoid heavy, expensive, power hungry mechanicals / hydraulics and revert to a more economical, PLC based device for controlling wheel-spin. Retain the essential fore & aft differentials (normal open types),
and utilize the EBD for all wheel spin control function. Obviously this vehicle would be a standard 4WD - without the luxury of permanent AWD with its central diff/viscous coupling requirement. But it would put wheel spin control - of a kind - within the reach of the average motorist.
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Old 2nd August 2015, 09:43   #381
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Default Re: Driving all four wheels: how is it done?

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No, I believe traction control is a more elaborate programme.
No. EBD and TC essentially use the same primary set of hardware, i.e. wheel lock sensors, to execute different functions. In addition, EBD uses other sensors (measuring g-forces, brake pedal pressure) than what TC uses (A-pedal input sensor, engine rpm, gear position), to carry out different tasks. EBD per se is quite an elaborate and complicated set-up too, and does add substantial cost to any vehicle. A combination 0f EBD and TC in a single car would naturally be cheaper than EBD and TC in two separate cars, because of some shared hardware.
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Old 2nd August 2015, 16:53   #382
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Default Re: Driving all four wheels: how is it done?

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A good deal of water has flown under the bridge since then and, arguably, technology has galloped the fastest & farthest.
Oh, it has... consider this one.

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Old 3rd August 2015, 00:34   #383
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Default Re: Driving all four wheels: how is it done?

Pendulum tilt could work for you or against you depending on how radical the curve/turn is or how radical the traversed slope is. There are many times, I think, when you would do better to have the weight on the inside wheels in a curve or the upslope side in a traverse of a slope. I don't think there is an easy mechanical answer to this which means there is probably not an easy software solution either.

I am also thinking that the very first original WWII jeep could handle most of what is in this film and most of what we want to do off road.

Interesting concept though, the pendulum vehicle.
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Old 3rd August 2015, 09:53   #384
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Default Re: Driving all four wheels: how is it done?

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Our Storme & Scorpios do not come with MLD? What about others, Pajero Sports, Fortuner & Thar, Gypsy.
None of the vehicles you have mentioned here come with an MLD.

The older SFX/GLX had LSDs as OE fitment but the Sport has open diffs, front and rear.

M&M fits MLDs as OE fitment on Scorpio SCDC (Single Cab and Double Cab) but does not offer it here in India.



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How much will the cost be to fit the Eaton MLD on my Scorpio? Will it be helpful? I do not have any plans to off road purposely on my Scorpio.
Fitting an MLD is definitely helpful. Hariya (My Scorpio CRDe 2WD) had an MLD and it did pull me out of situations where an open diff would have given up, and none of them were OTR excursions.

However, the MLD has an issue as well.

You see, like the others have explained, the MLD locks the driveshafts the moment the difference in the rpms of both the driveshafts exceeds 100. While this enables the wheel that is stuck/has traction to get some torque, Once that wheel gets moving, the MLD disengages instantly and your differential behaves like a normal, open diff.

While this is good in situations where one push is enough to get the vehicle out, in situations like a slush patch, a snowed out incline etc, it makes the MLD lock and unlock many times within a few metres and hence renders progress minimal and a lot of shocks to the drivetrain as well.
Keep this in mind.

The MLD costed me around 23k INR to procure and fit. Let me know if you need the M&M part number for it.
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Old 3rd August 2015, 11:21   #385
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Oh, it has... consider this one.
Samurai, this throws out the window all pre-concieved notions regarding off-roading - it is most definitely the amateur off-roader's dream ! The only drawback as far as I an see is the lack of a canopy - which I'm certain can be rectified.
Cheers

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Originally Posted by SS-Traveller View Post
No. EBD and TC essentially use the same primary set of hardware, i.e. wheel lock sensors, to execute different functions. In addition, EBD uses other sensors (measuring g-forces, brake pedal pressure) than what TC uses (A-pedal input sensor, engine rpm, gear position), to carry out different tasks. EBD per se is quite an elaborate and complicated set-up too, and does add substantial cost to any vehicle. A combination 0f EBD and TC in a single car would naturally be cheaper than EBD and TC in two separate cars, because of some shared hardware.
Like I said, technology has come a long way - sticking to wheel spin/slip sensing in the EBD (the additional inputs - pedal sensors, gear posn sensors, engine rpm/torque sensors etc would be bonus icing on the cake) would still make it a good deal more economical than having torsens /haldex' on board. Which is what mfrs should be aiming for - instead of leading the average motorist up the garden path with marketing hype and acronyms and passing it of as high-cost hi-tech.

Last edited by Gannu_1 : 5th August 2015 at 08:52. Reason: Removing youtube URL from quoted post.
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Old 5th August 2015, 08:39   #386
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Default Re: Driving all four wheels: how is it done?

I must admit that Samurai's Swincar Spider video is eye-popping - for me certainly. Apart from the other bits and pieces (in themselves fascinating) what really catches the imagination is the wheel articulation. Independent articulation of each wheel in all 3 axes - vertical, transverse and longitudinal - does away with the idea of a fixed wheelbase and track. A truly remarkable device, using the principal variable (driver weight) as a plumbline to keep the C.G. always low & within the vehicle parameters. This is perfect in the world of ATVs (but not for regular road-users in India!) and as I mentioned earlier, the lack of that canopy...........
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Old 5th August 2015, 09:03   #387
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Default Re: Driving all four wheels: how is it done?

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How much will the cost be to fit the Eaton MLD on my Scorpio? Will it be helpful? I do not have any plans to off road purposely on my Scorpio.
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Originally Posted by n.devdath View Post
The MLD costed me around 23k INR to procure and fit. Let me know if you need the M&M part number for it.
According to this (Eaton MLD (M-Locker) now available off the shelf) post, it seems the Eaton MLD doesn't fit the new generation Scorpio. Don't know how accurate this info is, though.

Cheers,
Vikram

Last edited by comfortablynumb : 5th August 2015 at 09:04.
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Old 8th August 2015, 20:19   #388
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Default Re: Driving all four wheels: how is it done?

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Originally Posted by mallumowgli View Post
Doesn't a part time 4WD with central differential become a full time 4WD?
Just so! But adding the centre diff/viscous coupling also adds to the cost (as SS-Traveler mentioned succinctly earlier) & complexity & also to the no. of items that can potentially go wrong!

Another reason to stick to the tried and trusted Thars, Boleros, Scorpios et al.
Ah! - if only someone would come up with that super-competent EBD to take care of the wheel-spin, wheel-slip issues.........
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Old 15th November 2015, 19:13   #389
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Default Re: Driving all four wheels: how is it done?

Can the Duster AWD or a Yeti AWD be towed to some distance with all 4 wheels on ground & engine running?

I know it is not recommended to tow it or move it without a flat-bed, but still..if need be?
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Old 15th November 2015, 20:48   #390
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Default Re: Driving all four wheels: how is it done?

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Can the Duster AWD or a Yeti AWD be towed to some distance with all 4 wheels on ground & engine running?

I know it is not recommended to tow it or move it without a flat-bed, but still..if need be?
Both vehicles have manual transmissions, so I am not sure why either cannot be towed in neutral, with engine switched off too.

What does the owner's manual say?
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