[dadu]

Great job SS, quite good and technical thread.

[sudev]

The old horse drawn carriages achieved direction control by turning the front complete axle and wheels on a central pivot. This way the need for differential was all but eliminated.
However (there are always however's) this also meant quite a lot of steering effort which was being passed on to the horse. When steering was moved to hands of driver it became unmanageable to move to entire axle around central pivot. So now two pivots were designed on either side of the chassis which were then connected to the steering.
Now take this forward to why differential comes in....

[ex670c]

Originally Posted by sudev

The old horse drawn carriages achieved direction control by turning the front complete axle and wheels on a central pivot. This way the need for differential was all but eliminated.

Hi Sudev,

A differential is required in a Live Axle.

Horse drawn carriages have a Free Wheel, each wheel rotates independent of the other wheel.

Regards,

Arka

[Samurai]

Differential is required when torque has to be transmitted to an axle whose wheels could turn in different speeds. An open differential always delivers equal amount of torque to each wheel, whether driving straight or turning (ideally).

Open Diff: Equal torque to both wheels, but allows different speeds.
Locked Diff (or no diff): Equal torque to both wheels, doesn't allow different speeds.
Limited slip diff: Allows unequal torque, allows different speeds.

[ex670c]

Originally Posted by Samurai

Differential is required when torque has to be transmitted to an axle whose wheels could turn in different speeds. An open differential always delivers equal amount of torque to each wheel, under all circumstances.

Open Diff: Equal torque to both wheels, but allows different speeds.
Closed Diff (or no diff): Equal torque to both wheels, doesn't allow different speeds.
Limited slip diff: Allows unequal torque, allows different speeds.

Hi Sharath,

You have described Locked Differential/ Spool and LSD quite well, but Open Differential needs to be described in detail, it will transfer equal amount of torque, but traction will depending on the weight of the vehicle, gradient of the road, and Drag & Friction.

It has been better explained by Differential (mechanical device) - Wikipedia, the free encyclopedia

under Loss of Traction

Regards,

Arka

[Samurai]

Oh yeah, you are right. I meant to say while driving straight or turning, but not under loss of traction. Let me fix that.

[Sutripta]

@SS Finally the experts (faculty) are chipping in. Without their active contribution, this thread is not going to go anywhere. Maybe each can write the lead post on his area of expertise. And still waiting for whether this whole section is of interest, and useful. Look at the lopsided views to responses ratio. Also, if it is not interesting and useful, what will make it so.

Originally Posted by headers

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.

I don't think the puffing and sweating 0.1 HP engine is going to like this solution!
See post #25/ 26.

@tejas Theoretically, I suppose if it can be arranged that the rear tyre always follows the track of the front, the central diff can be avoided. Haven't thought through the case of initiating and getting out of the turn, and what effect different slip angles will have. The solution (4 wheel steering) is likely to be more problematic than the problem (transmission windup).

Regards
Sutripta

[Sutripta]

Originally Posted by Sutripta

Maybe each can write the lead post on his area of expertise.

I have been thinking this thought right from day 1, but am finding that the experts are too modest, and not coming forward on their own. Just to get the ball rolling, may I suggest (of the top of my head)
A) Arka to pen the lead article on Jeep (and Offroaders in general) drivetrains.
B) Suresh Stephen for explaining the Torsen
C) Prateesh for general engineering comments. (eg. why the Traction Avant used UJs)

Regards
Sutripta

Note to mods:- If this post is inappropriate, pls. delete it.

[Samurai]

Sutripta,

The trouble here is calling for experts to comment. Who is an expert? Most of us here have only fringe knowledge, picked up over weekend activities. That doesn't make one an expert.

Only a professional, who has done it for a living for a few years can be called an expert. Rest of the people only have circumstantial knowledge, which could be correct or incorrect. Our theories are often half-baked, practical knowledge mostly anecdotal. Unlike academicians who are comfortable being called expert thanks to their various degrees, we weekend warriors are wary of such titles.

Therefore, as long as you use titles like faculty, experts, etc., most people here will be uncomfortable in sharing what little they know. At least, that is my feeling.

[ex670c]

Originally Posted by Sutripta

I have been thinking this thought right from day 1, but am finding that the experts are too modest, and not coming forward on their own. Just to get the ball rolling, may I suggest (of the top of my head)
A) Arka to pen the lead article on Jeep (and Offroaders in general) drivetrains.
B) Suresh Stephen for explaining the Torsen
C) Prateesh for general engineering comments. (eg. why the Traction Avant used UJs)

Hi Sutripta,

I think DB & UBS Sir can write a much better article of JEEP & 4x4 Drive Train.

Regards,

Arka

[anb]

Originally Posted by SS-Traveller

Part-time 4WD provides better traction on slippery surfaces because the front and rear sets of wheels are locked together.

What is mean by locking together of front and rear set of wheels ? can you explain?

What is the difference between transfer case and center differential? are they same?

[Sutripta]

^^^^ (Oops. point to post #54)
Point taken. But here it was meant in a lighthearted way, used amongst an essentially closed user group, who have interacted for some time.

Let us dispense with the terms expert, faculty, etc. and say the set of people generally respected by the majority here, the people who will be called on by other members of this group for their opinion, arbitration, and last word on specific subjects.

Let this be our own wiki.

Over to you, SS.

@Arka: I don't think ANYONE will object to yours writing the lead. OTOH, can you get DB or UBS to write the lead? But I'm sure they (and others) will chip in once the ball starts rolling.

Regards
Layman Sutripta

[DirtyDan]

Originally Posted by anb

What is mean by locking together of front and rear set of wheels ? can you explain?

In a four wheel drive vehicle there is a mechanical connection between front and rear axles via the 2 drive shafts, transmission and other components. A center differential can break this connection allowing the front and rear to travel and track at different speeds without friction. This is particularly vital on curves where front and rear wheels do not take the same track and speed.

Originally Posted by anb

What is the difference between transfer case and center differential? are they same?

Not the same. Transfer case is the switch that gives you four wheel or two wheel drive. It transfers power by engaging/disengaging the drive shaft to one axle (usually the front one).

Center differential compensates for the difference in speed and course between the front and rear wheels. Most 4x4 vehicles do not have a center differential. Hence if they are operated on hard dry pavement in 4 wheel drive they are subject to "drive train windup" that can break drive shafts and cook transmissions among other things. Off road or on slippery surfaces the tyres of 4x4 vehicles slip enough on the surface to reduce drive train windup to an acceptable level.

There's your quick dirty answer. You can find a lot more info on the web and by looking around in this forum.

[roadie_swift]

Originally Posted by ex670c

Hi Guys,

A nice video explaining the differential.

Regards,

Arka

Hey, this is really cool! This is one of the best and simplest (to understand) illustrations about the Differential that I have come across. Thanks a lot.

Although, I still have one query. In the video, they have (maybe for the sake of simplicity) addressed only the scenario where one wheel is stopped completely, and the other has to move. In this case, the central gear mounted on a pivot would obviously enable movement of the one wheel which is not stopped.

But, what would happen in case one wheel is moving normally, and the other, instead at being stopped, is moving at half the speed of the normal. In that case, how would the illustrated system work?

Ok, since the teeth on all wheels are equally spaced, may be at exactly half the speed, it will just skip the alternate teeth and keep moving. But what if the speed of one wheel is, say, Pi times the other wheel. How does the central wheel accommodate the irregular speeds?

Thanks again for the sharing of your knowledge.

Cheers,
R_S

Note from Team-BHP Support: Please do not quote large text, video, pictures as it inconveniences our mobile and low bandwidth users. Thanks for your understanding !!!

[sudev]

The video shows variation from zero differential to total differential - wheel moving in sync to one wheel completely stopped.

The central differential gears start spinning and take what ever the difference and can vary from zero (both wheel in sync) to total (one wheel stopped) and to anything in between.