Go Back   Team-BHP > Buckle Up > 4x4 & Off-Roading > 4x4 Technical


Reply
 
Thread Tools Search this Thread
Old 6th April 2015, 16:20   #346
BHPian
 
adisag's Avatar
 
Join Date: Feb 2010
Location: Gurgaon
Posts: 132
Thanked: 42 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by lal79 View Post
Consider a scenario, one wheel from both front and rear axle doesn't have traction. Power will flow to the wheels with least traction. In this scenario, one wheel from front and rear axle doesn't have traction, and those wheels only will spin and the wheels having traction won't spin. Now you have one wheel each from both front and rear axle spinning freely and you are stuck. This will happen even for a 4X4 with Open differential(regardless of whether there is a low ratio transfer case).
I managed to get my Yeti stuck in a unlikely position a few days back, the front right tire went into a ditch, and the weight of the car was directly on the chassis. The rear left wheel was airborne due to the weight distribution.

Basically, only two diagonally opposite wheels (front left and rear right) had grip, the other two were incapacitated. Given that my Yeti is a 4wd, what should have happened? Shouldn't the two wheels with grip been able to pull the car out of the ditch?
What ended up happening was that the two wheels in the air were spinning, but there was no torque going to the two wheels with grip. :O The car was stuck. Another thing I noticed was that every time the RPM would hit ~2000 RPM, the power would cut-off for a few seconds.
Finally got the car out by getting a friend to put some weight on the rear left side. The moment that wheel touched the ground, the car jumped out (in reverse gear) with utmost ease.
The whole scene from getting into the ditch to getting out took maybe 5 minutes, so I did'nt have the presence (or the time) to document the situation for better understanding. The next morning, I got the car onto a car lift to double check the 4wd works, all 4 wheels spin on acceleration, so I guess everything is in order (?)

The Yeti in question is a 2010 Ambiente 4x4 (No Off Road Button), I did try this with the traction control on as well as off, similar results in both conditions, but since we were out in less than 5 minutes, I may have missed some critical details.

Thoughts would be appreciated - is this normal behavior?

Last edited by adisag : 6th April 2015 at 16:27.
adisag is offline   Reply With Quote
Old 6th April 2015, 16:24   #347
Senior - BHPian
 
Join Date: Dec 2009
Location: Ghaziabad
Posts: 1,003
Thanked: 753 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by adisag View Post
Basically, only two diagonally opposite wheels (front left and rear right) had grip, the other two were incapacitated. Given that my Yeti is a 4wd, what should have happened? Shouldn't the two wheels with grip been able to pull the car out of the ditch?
And this is exactly why Lockers are such a lovely thing. Either that, or insane Articulation, that is.
Yes, your Yeti is fine, if it behaved this way.
roy_libran is offline   Reply With Quote
Old 6th April 2015, 16:37   #348
Team-BHP Support
 
.anshuman's Avatar
 
Join Date: Dec 2004
Location: Good-Gaon
Posts: 7,702
Thanked: 8,918 Times
Default Re: Driving all four wheels: how is it done?

As Roy commented it is perfectly normal for the Yeti Ambiente with 2 x open axles to behave like this.

The situation would have been have handled better with Electronic Differential Lock equipped (part of ESP package) Elegance variant, though nowhere as effective as the manual lockers but good enough to divert some power back although in jerks by braking the free spinning wheels.
.anshuman is offline   (1) Thanks Reply With Quote
Old 7th April 2015, 00:26   #349
BHPian
 
Join Date: Jun 2010
Location: Mumbai
Posts: 25
Thanked: 7 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by .anshuman View Post
As Roy commented it is perfectly normal for the Yeti Ambiente with 2 x open axles to behave like this.

The situation would have been have handled better with Electronic Differential Lock equipped (part of ESP package) Elegance variant, though nowhere as effective as the manual lockers but good enough to divert some power back although in jerks by braking the free spinning wheels.
I was wondering how effective will it be to try driving through the brakes in this situation - basically press on the brake pedal and the accelerator at the same time. Will this provide torque to the wheel with traction?
gragusha is offline   Reply With Quote
Old 7th April 2015, 10:33   #350
Team-BHP Support
 
.anshuman's Avatar
 
Join Date: Dec 2004
Location: Good-Gaon
Posts: 7,702
Thanked: 8,918 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by gragusha View Post
I was wondering how effective will it be to try driving through the brakes in this situation - basically press on the brake pedal and the accelerator at the same time. Will this provide torque to the wheel with traction?
I have not suggested to use the brakes, the EDL function in the ESP package will do that for you automatically without any manual intervention.
.anshuman is offline   Reply With Quote
Old 12th April 2015, 13:00   #351
BHPian
 
Join Date: Jun 2010
Location: Mumbai
Posts: 25
Thanked: 7 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by .anshuman View Post
I have not suggested to use the brakes, the EDL function in the ESP package will do that for you automatically without any manual intervention.
Hi - understand that - but I was thinking of a simpler system like a Fortuner - I understand that the rear diff is open in that. In this case what will be possible solution for getting out (apart from putting more weight or trying to stuff rocks etc under the free wheeling wheel... does applying brakes and pressing accelerator pedal at the same time help at all?

Also ESP may not work well in automatically applying brakes to the slipping wheels, as in the above example. In that situation, weight had to redistributed for giving traction to the slipping wheel.

Thanks for the help.
gragusha is offline   Reply With Quote
Old 21st May 2015, 09:43   #352
Distinguished - BHPian
 
dhanushs's Avatar
 
Join Date: Oct 2009
Location: Bathery/BLR
Posts: 3,440
Thanked: 4,042 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by gragusha View Post
does applying brakes and pressing accelerator pedal at the same time help at all?
Yes, it'll help. The wheel with traction now, has torque needed to overcome the braking and get the free wheel spinning.
dhanushs is offline   Reply With Quote
Old 15th June 2015, 09:09   #353
Distinguished - BHPian
 
Sheel's Avatar
 
Join Date: Jul 2006
Location: Purnea(Bihar)
Posts: 5,182
Thanked: 4,764 Times
Default Re: Driving all four wheels: how is it done?

In 4H at very low speeds and steering at full lock, does it provide some resistance? It gets sluggish, low, crawling speeds.
Sheel is offline   Reply With Quote
Old 15th June 2015, 10:50   #354
Distinguished - BHPian
 
Tejas@perioimpl's Avatar
 
Join Date: Sep 2008
Location: Bombay
Posts: 3,962
Thanked: 4,867 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by Sheel View Post
In 4H at very low speeds and steering at full lock, does it provide some resistance? It gets sluggish, low, crawling speeds.
Yes, your steering would want to return to centre. On paved roads in 4H (locked), and while turning you are effectively dragging one wheel or hopping it (called chirping also).
Tejas@perioimpl is offline   (1) Thanks Reply With Quote
Old 15th June 2015, 14:16   #355
Distinguished - BHPian
 
dhanushs's Avatar
 
Join Date: Oct 2009
Location: Bathery/BLR
Posts: 3,440
Thanked: 4,042 Times
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by Sheel View Post
In 4H at very low speeds and steering at full lock, does it provide some resistance? It gets sluggish, low, crawling speeds.
Yes. Drivetrain wind up is the reason. Technically, you shouldnt be driving on surfaces with good traction, in 4WD with center diff locked. If at all you are driving, hold the steering wheel freely. Dont push it.
dhanushs is offline   (1) Thanks Reply With Quote
Old 25th June 2015, 22:32   #356
BANNED
 
Join Date: Jan 2014
Location: mum,lko,kolkata
Posts: 704
Thanked: 672 Times
Infractions: 0/2 (14)
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by Sutripta View Post
This is a topic meant for experts. As a not foolish (I hope) layman, do you think I should rush in!? .....Lets start with the basics. Maybe the experts can answer a simpler question for us: -
If you were the vehicle designer, what would be your thought process which lead you to choose one of the drive configuration from all those (RWD, FWD, Full time 4x4, part time 4x4 .........., and options of LSDs and MLDs) available.
Regards
Sutripta

Sutripta, as another aspirant to the discussion, I'd say the primary control would be the cost of the sytem and the target customer.
Thereafter being given a free hand, I'd prefer the full-time AWD with the three Torsen diffs to take advantage of its inbuilt limited slip capabilities. Without the bother of external hydro-electrics(Haldex) or the speed sensitive mechanicals of the Eaton type.

The Torsen takes great advantage of the relative/partial irreversibility of the worm/wormwheel drive and incorporates it into its limited slip function. The one drawback of the Torsen is its relatively higher power absorption and of course its higher cost.

But as I mentioned earlier, the target customer is important, as witness the Quattro's almost total domination of the rally scene at the time of its introduction.
shashanka is offline   Reply With Quote
Old 26th June 2015, 06:23   #357
BANNED
 
Join Date: Jan 2014
Location: mum,lko,kolkata
Posts: 704
Thanked: 672 Times
Infractions: 0/2 (14)
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by Samurai View Post
I could be totally mistaken here. But I remember reading this long time back. A torque sensitive LSD won't work if one ........... free wheel under brakes may need 20% of available torque to keep spinning, there by transmitting 5X or 100% of available torque to the other side.

Spot on, Samurai - this is the reason for the name, Torsen. It doesn't really sense wheel spin or slip. The degree of torque on the spinning wheel is sensed and if the internal bias of the torsen diff. is 5X (depends on the pitch of the teeth of the meshing worm-to-worm internals), then five times the torque is sent to the stuck wheel - which may not be enough to get that wheel moving. Therefore the application of the brakes to multiply the available torque.
I wonder why this relatively simple method - EBD I mean - has not been incorporated with the function of the standard diff. as a cheaper (though less effective perhaps) way of getting around this whole wheel slip issue.

Surely, with the kind of software development expertise that is available in the country, it can't be an insurmountable problem to integrate the two functions - the differential and the EBD.
Leaving aside the issues of robustness, durability, reliability etc, surely it would put the benefits of limited slip performance - of a kind - within the reach of enthusiasts with limited means !
shashanka is offline   Reply With Quote
Old 26th June 2015, 21:16   #358
Distinguished - BHPian
 
Join Date: Jul 2009
Location: Kolkata
Posts: 3,489
Thanked: 2,036 Times
Default Re: Driving all four wheels: how is it done?

^^^
If you have brake control over individual wheels, do you need a LSD?

Regards
Sutripta
Sutripta is offline   Reply With Quote
Old 26th June 2015, 21:58   #359
Senior - BHPian
 
Join Date: Dec 2009
Location: Ghaziabad
Posts: 1,003
Thanked: 753 Times
Default

Quote:
Originally Posted by Sutripta View Post
^^^
If you have brake control over individual wheels, do you need a LSD?

Regards
Sutripta
I think the answer is No. But, usability would be adversely impacted, would it not?
Imagine the jugglery you'd need to do the moment you're unstuck!
roy_libran is offline   Reply With Quote
Old 27th June 2015, 05:18   #360
BANNED
 
Join Date: Jan 2014
Location: mum,lko,kolkata
Posts: 704
Thanked: 672 Times
Infractions: 0/2 (14)
Default Re: Driving all four wheels: how is it done?

Quote:
Originally Posted by roy_libran View Post
I think the answer is No. But, usability would be adversely impacted, would it not?
Imagine the jugglery you'd need to do the moment you're unstuck!

Yes, absolutely - it would probably need a fair amount of orientation time (days perhaps) to familiarize oneself and start applying the brakes at the right time to avoid trouble.

An EBD with the necessary input bandwidth (to encompass commonly faced situations) and response time could provide a cheaper, simpler, tho' less competent, alternative (to the massive overkill of the full Quattro system) for the average motorist with average means - me, in other words !
shashanka is offline   (1) Thanks Reply With Quote
Reply


Thread Tools Search this Thread
Search this Thread:

Advanced Search


Similar Threads
Thread Thread Starter Forum Replies Last Post
All Hail Crusoe! Fiat Linea T-Jet+ : Four years and 47,000 kms done Biraj Long-Term Ownership Reviews 258 8th June 2017 16:18
Does ABS require disk brakes on all the four wheels? abhilashvk Technical Stuff 26 23rd February 2010 00:36
News: Car loses all four wheels on highway DriverR Street Experiences 10 10th July 2009 13:52
Two sets of four wheels uy663z SUVs, MUVs & 4x4s 37 3rd December 2007 09:39
Four Wheels under 3 Lakhs gemithomas Hatchbacks 33 16th April 2007 13:21


All times are GMT +5.5. The time now is 03:10.

Copyright 2000 - 2017, Team-BHP.com
Proudly powered by E2E Networks