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Old 14th October 2010, 09:51   #31
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Originally Posted by SS-Traveller View Post

Thanks, Spike - you're a genius! At one stroke, with one document, you've actually said all that this thread was trying to convey!
Dada, I can share only these little things which I know :-)

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Originally Posted by Sutripta View Post
Why are the experts picking on me. I'm getting paranoid
Dada, you calling me an expert

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Originally Posted by DirtyDan View Post
Drivetrain windup gives testimony as to just how much traction tyres really give you on pavement. -------
Shortly thereafter bearings in the tranny melt and fuse. When you open such a transmission all the gear oil will be gone, vaporized and/or turned to tar and soot. The traction of tyres on a hard surface is enough to melt tranny bearings, and relatively quickly, too, say, 60K.
Very very well said DD. Bearings are designed to work at a particular operating temperature (maximum worst case scenario), if this temperature is exceeded bearings will give away. The weakest link in the transmission is usually targeted, usually this happens to be the bearings and oil seals.

Spike
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Old 14th October 2010, 10:35   #32
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Originally Posted by Samurai View Post
I have a question to the experts. Even in our humble Jeep/Gypsy, one can move from 2H -> 4H -> 2H while the vehicle is moving. Let's assume the hubs are locked or have a flange. Why don't we call this shift-on-fly?

Why only SUV which can do the same are known to have shift-on-fly?

Is auto-locking hub qualifying it to be called as shift-on-fly?
Interesting question, so did not fire from the hip.
On the fly should mean engagement and disengagement possible at any point in conventional usage pattern. In a dog engaged TC, it means one shaft has to be free/ unpowered during engagement. In our simpler systems, one side is 'powered' by the rear wheels, the other by the front wheels. If we do not have a means of breaking this power flow, its not shift on the fly. My opinion only.

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My Invader is invincible off road because I have tow hooks front and rear and a good mobile with which I can call Rahoon and his intrepid M&M tractor .
You are a person after my own heart. To your list I would add
A) lots of small denomination currency notes to entice/ reward the locals after they manhandle your vehicle out of trouble.
B) Slush bars for use by the said locals.
C) If travelling, the Bradshaw.

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Originally Posted by sudev View Post
One question: Does Gypsy have a fixed central transfer case or with differential?
No central diff. I think rally gypsies unwind their transmissions by raising wheels of the ground!

@SST: I've an idea on how this thread can be structured (teaching plan ) and you can choose your course contents! Should be a separate post, so after the 'no back to back post' time limit.

Regards
Sutripta

Last edited by Sutripta : 14th October 2010 at 10:37.
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Old 14th October 2010, 10:43   #33
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Originally Posted by SS-Traveller View Post
Sorry, Arka, I missed this post earlier. To elaborate: Part-time or full-time 4WD systems, especially those with a dual-range transfer case offering low-ratio drive, certainly are more invincible (but obviously not totally so) in no-road conditions. But all-wheel drive / automatic 4WD / on-demand 4WD systems without low-range gears are not as good at tackling no-road situations as part-time or full-time 4WD vehicles. When the not-so-discerning owner of a CR-V / Tucson / Aria learns that his car has AWD - which he equates with full-time 4WD - he dares to venture off-road, only to be sorry for it. (No doubt, though, on-demand 4WD would still do better than a 2WD of comparable specs.) Hope you'll agree with me on that.
Hi SS_Traveller,

I agree with you totally, I have come across many cases of CR-V owners confusing their vehicles to be 4WD, and getting stuck on the beach.

I had to once winch out a New Model CR-V (2007) from a pit, its front wheels had dug in, after winching the vehicle out, there was no way of towing her to the road, so I decided to drive her back on to the road.

Put her in 1st Gear and kept varying the engine rpm between 3-5K to create some wheel spin for the LSD to engage the rear wheels and the CR-V was flying, I almost forgot that she was an On Demand 4WD, my biggest worry was damaging her curves. The guy driving my MM540, took sometime to catch up.

The cross-over SUV and soft-roaders are obviously not Off-Road Vehicles, but Luxury Bad-Road Vehicles.

Also the design and the ADR Angle and other attributes generally discourage them from more deliberate off-roading.

Regards,

Arka


Last edited by ex670c : 14th October 2010 at 10:52.
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Old 14th October 2010, 10:58   #34
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After all these questions of torque windup and SUV's I'd like some knowledge shed for a street junkie like me!

I want to know about the 4wd systems from the hallowed evo's and skylines.

The only thing I have some small knowlegde about is the shaft in shaft system of the *ALL HAIL* audi QUATTRO coming from the 70's RS quattro rally car. But elaboration on that would help. It started as a mechanical and finally dropped down to the realm of electro-mechanical.

Would you'll kindly bless me with some gyaan!

Last edited by valhallen.282 : 14th October 2010 at 11:01.
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Old 14th October 2010, 11:03   #35
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Originally Posted by Sutripta View Post
@SST: I've an idea on how this thread can be structured (teaching plan ) and you can choose your course contents!
Well, my plan was to talk about driving all four wheels - and how we can do that without using much of jargon/tech terms, while explaining the differences between the different types of systems that help to drive all 4 wheels. But you're the course administrator, I'm just the class teacher!
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Originally Posted by Sutripta View Post
Re: cycle rickshaw.
One driven wheel. So no differential. And it works! Zillions on the road.
So now we want to design an autorickshaw. What do we do, and why?
We build a differential! But the differential also provides one-wheel drive at most given points of time (the difference versus a cycle rickshaw is that now it's one-wheel drive on either the left or right side - unlike the cycle rick's solitary wheel drive only), until the autorickshaw is travelling dead straight like an arrow - which, of course, it never does. But then, autoriskshaws travel with all wheels planted on terra firma - and lie down peacefully when they lift their wheels up!

OTOH, when we talk about 4WD vehicles, the imagery of wheels in the air or buried in mud is the most persistent one
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- and either way, we find that one wheel in the air leaves all the other wheels quite, quite useless in moving the vehicle.
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Originally Posted by DirtyDan View Post
I have tow hooks front and rear and a good mobile with which I can call Rahoon and his intrepid M&M tractor .
Yes! The mobile phone moves the vehicle better than the wheels!!! And remember this (A Tractor for OTR Excursions - would it be fun?)???

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Originally Posted by DirtyDan View Post
Drivetrain windup...
Yes, that's where the whole problem lies - either we separate out left and right wheels, front and back axles through differentials, and lose movement as soon as one wheel is spinning free, or we end up with transmission windup when we lock those diffs up. And there are enough mechanically challenged folks in the world, who can melt bearings all so easily. This thread is targeted at them.
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Originally Posted by SPIKE ARRESTOR View Post
The weakest link in the transmission is usually targeted, usually this happens to be the bearings and oil seals.
Along with bearing meltdown, there's bank balance meltdown too!
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Old 14th October 2010, 11:04   #36
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I have newbie question:

Wouldn't Torque on demand is killer for Tires?

Some tires would rotating more and some tires would be less and all tires engaged some how. If on 'not so good Tarmac' or on 'bad roads' if rear tire rotation is more and front tire rotation is less then rear tires would wear out faster than front due to excessive rotation.

Last edited by aah78 : 17th February 2015 at 20:26. Reason: Spell-check.
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Old 14th October 2010, 12:11   #37
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First of all, Puja greetings to all.

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Originally Posted by SS-Traveller View Post
Well, my plan was to talk about driving all four wheels - and how we can do that without using much of jargon/tech terms, while explaining the differences between the different types of systems that help to drive all 4 wheels. But you're the course administrator, I'm just the class teacher!
And course administrators are generally derided by the actual teaching staff on the ground!

I thought of it not as a purely 4x4 thread, but as a 'what vehicle benefits most from what drivetrain' section. Remember starting point was the Aria's choice of 4x4.

Going through the evolution of the automobile would be a good strategy. Why initially RWD. Then the shift to FWD, which is almost universal today. Modern thinking on these two systems. Differentials (normal simple open types. Locked = no diff)

Then maybe a short discussion on ABS, and a longer one on ESP.

And only then need for (not implementation of) specialised 4x4 systems. Off road, and high performance. A short discussion on the Jensen FF, and a longer one on the Audi Quattro. And of course the Jeeps.

Only then a discussion on limited slip, and torque splits. (We will still gloss over its implementations. We will discuss more the needs, and their tying in with modern ABS/ EBD/ ESP/ add any other acronym you feel like).

Implementation of locking diffs.

Last stage would be discussion of implementation of limited slip and torque splits. Clutches, viscous coupling, torsens etc. for both 2wd and 4wd applications.

What do the experts think?


Quote:
We build a differential!
Why. We had just seen that our simple cycle rik worked without one. How different is the autorik?

Quote:
OTOH, when we talk about 4WD vehicles, the imagery of wheels in the air or buried in mud is the most persistent one
Isn't the most common image 'parked in upscale shopping mall/ cruising up and down the mall'.

Regards
Sutripta
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Old 14th October 2010, 12:22   #38
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Hooked to this very interesting thread.

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Originally Posted by DirtyDan View Post
There is always a difference in speed between front axle and rear axle in a 4 wheel drive vehicle even on a straightaway. Either the front drags the rear or the rear pushes the front.
DD et al,
Can you elaborate on how and why the speeds would always be different between front and rear axles on a straight? Given that the crown pinion ratios and tyre sizes are the same at the front and rear (safe assumption), why would this happen?

Cheers,
Adi
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Old 14th October 2010, 12:28   #39
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Originally Posted by fazalaliadil View Post
I am learning.
Thanks,
Hope you enjoy more, Fazal-sahab!

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Originally Posted by sudev View Post
@SST: Thanks for starting this very interesting topic
The example....needs to understood...
Thank YOU for explaining Ragul's question!
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Originally Posted by 4x4addict View Post
In a Full T ime 4WD vehicle like the Toyota Fortuner/Land Cruiser/Mitsubishi Pajero the Center differential needs to maintain a 50:50 torque split between the front and rear axles. This can be done manually by engaging the center differential lock. When the manual lock is not engaged the differential need some way to maintain the torque transfer between the front and rear differentials.
....If either off these systems are not used, then a center differential pretty much makes a vehicle 2WD (either front or rear only) unless it is manually locked.
Very true. As I said,
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Originally Posted by SS-Traveller View Post
...one wheel in the air leaves all the other wheels quite, quite useless in moving the vehicle.
But locking & unlocking differentials manually was a cumbersome process at worst, and even in the best of times, it never was effortless for some - for people who will not drive a car with manual gearshift, you expect them to lock differentials manually??! and oh, forgetting to unlock later on was even more trouble! So came the need to invent those limited slip differentials.

But then, LSDs were never as good in transferring rotational forces the other side (left to right, front to back, or vice versa), as locked differentials. Watch the video below of an Audi Quattro with both its left wheels off the ground (on rollers) - note the speed that has to be built up before LSD activates and pulls the car out.

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Originally Posted by valhallen.282 View Post
Would you'll kindly bless me with some gyaan!
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Originally Posted by anujmishra View Post
I have newbiew question:
You know what, guys? This thread was specifically started to explain & answer your questions about 4WD. There are so many folks who are utterly confused about 4WD, and here we have in India for the first time, an indigenous brand new vehicle called the Aria being rolled out - and folks imagining this is a car like the Gypsy/Thar, only its 7-star variant. Read what ex670c says about CR-Vs in sand above, or the comparo video between the Panda and a Rangie... Only problem here is, the Panda was far less expensive than the Rangie, but the Aria/CR-V are a whole lot more expensive than the Thar/Gypsy/Safari in this country.
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Originally Posted by valhallen.282 View Post
I want to know about the 4wd systems from the hallowed evo's and skylines.
Mitsu Evos and Nissan Skylines are AWD vehicles, like the Audi Quattro, with every new generation incorporating more and more electronic wizardry to put down the phenomenal power their engines generate, on to the road. But in the end, they are best suited for smooth tarmac or at most, bad-road/snowy-road situations, not mud-plugging or rock-climbing. Watch this video and imagine a Thar there - where the Quattro struggles, the basic Thar would move like a Sunday walk in the park.


Remember, any car with all 4 wheels being driven, is not always an offroader. That's why the classification of different types of 4WD in vehicles, at the beginning of this thread.
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Originally Posted by anujmishra View Post
Wouldn't Torque on demand is killer for Tires?
Some tires would rotating more and some tires would be less and all tires engaged some how. If on 'not so good Tarmac' or on 'bad roads' if rear tire rotation is more and front tire rotation is less then rear tires would wear out faster than front due to excessive rotation.
To an extent, you're right. To produce torque on demand in an LSD, wheelspin HAS to be created first. So one wheel /axle scrabbles for grip before transferring the torque to the other wheel / axle. In the process of wheelspin occurring on gravel, yes, there can be some wearing out or nicks & cuts on the spinning tyre. If you didn't want any damage to tyres at all, avoid driving on bad roads at all!

Finally, here's a video of how a Torsen LSD works - it's in French, but the animations are self-explanatory.
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Old 14th October 2010, 12:46   #40
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Originally Posted by SS-Traveller View Post
Finally, here's a video of how a Torsen LSD works - it's in French, but the animations are self-explanatory.
In my way of looking at things, these animations show the the torsen works as a differential. Dont see how animations can show how changing the angles will change the characteristics of the drive. And to really get a feel of that, you have to turn different worms by hand.

Once again, leave torsens for last.

Regards
Sutripta
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Old 14th October 2010, 17:23   #41
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Quote:
Originally Posted by Sutripta View Post
Going through the evolution of the automobile would be a good strategy. Why initially RWD. Then the shift to FWD, which is almost universal today. Modern thinking on these two systems. Differentials (normal simple open types. Locked = no diff).

Only then a discussion on limited slip, and torque splits. (We will still gloss over its implementations. We will discuss more the needs, and their tying in with modern ABS/ EBD/ ESP/ add any other acronym you feel like).

Implementation of locking diffs.

Last stage would be discussion of implementation of limited slip and torque splits. Clutches, viscous coupling, torsens etc. for both 2wd and 4wd applications.
What do the experts think?
Your course syllabus certainly looks interesting. Expert opinions highly sought after over here.
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Originally Posted by Sutripta View Post
Why. We had just seen that our simple cycle rik worked without one. How different is the autorik?
That will be step one! Why do we need a differential at all if the cycle rickshaw can do without one?
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Originally Posted by SS-Traveller View Post
We build a differential! But the differential also provides one-wheel drive at most given points of time (the difference versus a cycle rickshaw is that now it's one-wheel drive on either the left or right side - unlike the cycle rick's solitary wheel drive only), until the autorickshaw is travelling dead straight like an arrow - which, of course, it never does.
Right, basic engineering class #1 coming up: so why was the differential (which we talk about like we know all about it but actually don't) invented at all?
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Old 15th October 2010, 08:08   #42
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Originally Posted by SS-Traveller View Post
That will be step one! Why do we need a differential at all if the cycle rickshaw can do without one?
One does not need a differential if the speeds are low.i.e speed < say 20 kph. The vehicle & tyres will manage the frictional issues.

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Right, basic engineering class #1 coming up: so why was the differential (which we talk about like we know all about it but actually don't) invented at all?
The differential as the name suggests was invented to accommodate the difference in the wheel speeds that arise due to different radii each wheel takes during a turn.

Guess this was illustrated in the initial posts [page 1]
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Old 15th October 2010, 10:38   #43
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Hi Guys,

A nice video explaining the differential.



Regards,

Arka
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Old 15th October 2010, 11:06   #44
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So theoretically, if a car has an all wheel steering (the back wheels move in opposite direction to the front), then the wheels will move in the exact same distance and there will be no transmission wind up?
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Old 15th October 2010, 11:22   #45
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Originally Posted by Tejas@perioimpl View Post
So theoretically, if a car has an all wheel steering (the back wheels move in opposite direction to the front), then the wheels will move in the exact same distance and there will be no transmission wind up?
Hi Tejas,

Even with a Rear Steer, there will be transmission Windup if there is no Differential action between the Front and Rear Axle.

In the Above Case
i) Front Wheels will be slightly faster than the rear wheels as in all vehicles.

ii) The Outer wheels will be faster than the inner wheels.

Rear Steer improves the turning radius and maneuverability.

Regards,

Arka
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