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David K
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About Differentials and Traction Control
Inspired by a Nomad's u2u, here is a brief explanation of 2WD vs. 4WD and Open Differentials vs. Limited Slip Differentials, Locked Differentials,
Traction Control and A-TRAC.
Differentials: Transfer torque (engine power) from the driveshaft to both tires on that axle equally UNTIL one tire needs to rotate more than the
other... This happens when turning, and is the reason for a differential (to allow the outside tire to rotate more than the inside). Otherwise, there
would be binding and scuffing on hard surfaces. These are normal 'open differentials'.
The negative part of an open differential when off roading is that the tire that rotates the easiest gets the engine torque and spins. The tire that
has traction on firm ground does nothing. A 2WD gets stuck the easiest because of this... only one of the 4 tires will spin. The movie 'My Cousin
Vinny' does a great job explaining this.
4WD has front and rear differentials so you double the possibility of moving through difficult terrain... Usually that is enough, but not always as
4WDs get stuck too, but is worse places!
If one front tire and one rear tire have no traction (on ice, mud, etc.), you will be stuck, as torque goes automatically to those two, low traction
tires. You will notice that only one front and one rear tire will spin when stuck. Lowering the tires' air pressure is one way to increase traction.
This is how we cross deep, loose sand.
LIMITED SLIP differentials have clutches or other mechanisms inside them that will brake the faster spinning side so more torque will be shared with
the opposite tire. Posi-traction is one brand of limited slip differentials.
TRACTION CONTROL is newer technology that uses rotation sensors on each tire, and the car's brakes, to slow down a free spinning tire. This action
will transfer torque to the traction tire. In 4WD, this is a big help in soft terrain or hill climbing.
LOCKING DIFFERENTIALs are now standard on many 4WD vehicles, most often on the rear differential only. Sometimes on the front, too as on Jeep
Rubicons. When you 'lock' the differential, a gear goes into place that connects both sides of the differential (both tires) together. This divides
torque 50-50. The loose tire rotates no more than the traction tire... you will move ahead with just one of these tires on firm ground.
The negative part of lockers is that steering is very difficult on hard ground, so lockers are recommended to be used only for emergency conditions
and only at slow speed.
A-TRAC (Active Traction Control) is available on some Toyota and Lexus models (and under different names by some other companies perhaps). A-TRAC is
big step up from basic TRACTION CONTROL in that the braking of a non-traction tire is much firmer and basically locks its rotation to the opposite
traction tire. A-TRAC provides the traction of front and rear lockers, but without the steering issues. No speed or safety concerns with A-TRAC. It
does only work in LOW RANGE, however. The A-TRAC does make noise, but works!
In the Off Road TRD 4WD Tacoma of 2009+ there is TRAC (traction control) in 2WD and 4WD High, and A-TRAC in 4WD Low.
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sanquintinsince73
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Great information, DK. So basically when I switch to 4x4 on my suburban only 1 front and 1 rear are spinning. Years ago I had a Toyota where I had to
get out and manually lock the front hubs. That vehicle handled off-road situations a heck of alot better than anything I've used since. With my
suburban I do alot of sand dunes in San Quintin and it handles just ok.
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baron
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AWD
Good info
Now can someone explain how my 2007 GMC Savana AWD van drive train works? Muchas gracias
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Sherman
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| Quote: | Originally posted by sanquintinsince73
Great information, DK. So basically when I switch to 4x4 on my suburban only 1 front and 1 rear are spinning. Years ago I had a Toyota where I had to
get out and manually lock the front hubs. That vehicle handled off-road situations a heck of alot better than anything I've used since. With my
suburban I do alot of sand dunes in San Quintin and it handles just ok. |
My understanding of locking hubs is that they free the front axle and differential from being driven by the forward motion of the vehicle's front
wheels when the transfer case is in 2WD mode. This saves wear & tear on the front drive shaft, universal joints and bearings, and gives a slight
increase in MPG. If I recall from owners manuals from the Travel-All's, Jeeps, and Toyota's I've owned, it was recommended to engage the hubs from
time to time to ensure lubrication of those parts that would stay idle if in 2WD mode with hubs disengaged. Once engaged, the front drive on these
would perform as described above, if not limited slip, only one wheel would spin in a stuck situation. Putting the trans in reverse, would reverse the
wheel that spins, thus the trick of "rocking" a vehicle to un-stick it, by quickly shifting back and forth from forward to reverse.
[Edited on 12-28-2010 by Sherman]
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TMW
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| Quote: | Originally posted by sanquintinsince73
Great information, DK. So basically when I switch to 4x4 on my suburban only 1 front and 1 rear are spinning. Years ago I had a Toyota where I had to
get out and manually lock the front hubs. That vehicle handled off-road situations a heck of alot better than anything I've used since. With my
suburban I do alot of sand dunes in San Quintin and it handles just ok. |
Not necessarily. Most GM trucks and large SUVs come with a locking differental in the rear that was locked below 25mph and unlocked above. You can
test by raising one side in the rear and try to turn the wheel.
[Edited on 12-28-2010 by TW]
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TMW
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Sherman manually locking hubs disconecct the wheel from the drive axle at the wheel. Self locking front hubs are disconected in the differential and
the transfer case disconnects the drive to the front differential in both cases.
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David K
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| Quote: | Originally posted by baron
Good info
Now can someone explain how my 2007 GMC Savana AWD van drive train works? Muchas gracias |
AWD 'All Wheel Drive' (Full Time 4WD) has a third or center differential that allows the front and rear driveshaft to turn at different speeds (when
turning). 4WD (Part Time 4WD) vehicles when in 4WD have the front and rear driveshafts locked and should NOT be driven on dry pavement as any turning
will cause a bind between the two driveshafts.
Some AWDs have a center differential lockout for true 4WD when off roading. Otherwise the split in torque is not even between the front and rear in
AWD.
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David K
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| Quote: | Originally posted by TW
Sherman manually locking hubs disconecct the wheel from the drive axle at the wheel. Self locking front hubs are disconected in the differential and
the transfer case disconnects the drive to the front differential in both cases. |
Originally, there were 'self locking hubs'... my dad had them on the Wagoneer... The only issues was to go back into 2WD and unlock the hubs, you
needed to drive in reverse a bit.
Today, to free up the front drive components, an 'ADD' is used instead of hubs. ADD is Automatic Disconnecting Differential... my Tacoma has this...
and allows shift-on-the-fly engaging of 4WD up to 55 mph and disengaging, too... No backing up required. A 'fork' is applied to one side of the
differential for 4WD, and when it is retracted, as when an open differential has no traction on one side, neither side gets any torque.
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David K
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| Quote: | Originally posted by sanquintinsince73
Great information, DK. So basically when I switch to 4x4 on my suburban only 1 front and 1 rear are spinning. Years ago I had a Toyota where I had to
get out and manually lock the front hubs. That vehicle handled off-road situations a heck of alot better than anything I've used since. With my
suburban I do alot of sand dunes in San Quintin and it handles just ok. |
Well... if one side of the vehicle is on firmer ground than the other... then the tries on the loose soil side will spin.
In soft sand or mud, etc. where all the surface is loose and you no longer have forward movement (too much air in the tires, perhaps)... You may see
one rear and one front tire spinning... The other two are getting torque, just not enough to rotate. It makes it seem that 4WD is really just 2WD (one
front and one back working) and 2WD is just 1WD.
Either tire will get torque, depends which one has more traction... torque goes to the tire with LESS traction with standard/ open differentials. This
is great when turning on dry roads... but terrible when trying to go through bad terrain or up steep hills with loose rocks.
New cars and trucks are getting tracion control and VSC (Vehicle Stability Control) along with it. VSC used on my truck was invented by Bosch.
VSC has been said to be the greatest safety feature to come to automobiles since the seat belt!
VSC automatically straightens your vehicle out if it begins to go into a spin on the highway should you make a sudden sweve to avoid hitting
something.
Every Toyota now has TRAC and VSC... as well as many other car companies.
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bigboy
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David, return to engineering school as soon as possible! Open diffs always have equal torque applied to both wheels. The wheel that is spinning on mud
or ice has the same amount of torque as the wheel that is on firm ground. Just imagine a one wheel drive vehicle. When power is applied to one wheel
only, the car would rotate around that drive wheel. A better way to picture this is to think what would happen if you only had braking on one wheel.
Upon breaking even moderately, the car would spin or severely pull every time the brakes are applied.
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David K
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big boy... I didn't go to 'engineering school', I tried to write it in non-mechanical terms... if I used "torque" incorrectly, then what is the
correct word for the rotation energy from the engine that is diverted to the low traction tire from the differential?
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bigboy
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David.....open difs will work as well as any differential as long as the traction is the same for both wheels or in the case of four wheel drive, all
wheels. In a 4X4 situation in sand on level ground, open differentials will work as well as the other difs mentioned. All four wheels will be driven
and no slippage will be incurred if both wheels, per axle, have the same weight and surface conditions. Where they don't work as well is off road
situations where one wheel, on that axle, is in the air or on a slippery surface and the other wheel is on a hard surface with more traction.
In the case where one wheel is in the air, the power delivered to both wheels on that axle will be nothing since the torque will be equal on a open
differential. This is where the other kinds of differentials shine that you mentioned in your post.
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David K
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| Quote: | Originally posted by bigboy
David.....open difs will work as well as any differential as long as the traction is the same for both wheels or in the case of four wheel drive, all
wheels. In a 4X4 situation in sand on level ground, open differentials will work as well as the other difs mentioned. All four wheels will be driven
and no slippage will be incurred if both wheels, per axle, have the same weight and surface conditions. Where they don't work as well is off road
situations where one wheel, on that axle, is in the air or on a slippery surface and the other wheel is on a hard surface with more traction.
In the case where one wheel is in the air, the power delivered to both wheels on that axle will be nothing since the torque will be equal on a open
differential. This is where the other kinds of differentials shine that you mentioned in your post. |
Yes, that's the point about limited slip transfering 'torque' or instead of a spinning tire in the air, you get a tire pushing against the ground to
move you ahead. You rarely have equal traction conditions under all four tires at the same time when you are off the highway. Even when the surface is
the same... torque/ power/ whatever you want to call it is biased to just one tire per axle.
In sand, if I bog down (from too much air in the tires)... even though the surface condition is equal... you still will have one front and one
opposite side rear tire spinning more than the other on each axle. This may be due to the vehicle weight distribution, but is the case with open
differentials.
I discovered last January that Traction Control (automatic limited slip) allowed me to wheel all over the beach at Bahia Santa Maria without
deflating... which was a first after years and years of four wheeling there.
To test it and see if it wasn't just some kind of fluke... I de-activated the traction control and had only open differentials in 4WD High... and the
truck bogged down and got stuck...
Without letting any air out or clearing away the sand from the tires... I turned on the A-TRAC (in 4WD Low) and the truck climbed out of the stuck! I
went back into High Range with standard TRAC back on, and drove about again, with ease!
I was totally blown away by the new Toyota system and have continued 'testing' it ever since!
In the summer, with a heavy load, I did need to lower the tire pressure so as to not dig in so much... Temperature does affect sand driving. However,
on many other occaisions the limited slip of TRAC and the 'automatic lockers' of A-TRAC have shown me what a big step forward technology has made in
traction ability.
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David K
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from Wikipedia
>>>So far, the word torque seems correct... (I still would like to be corrected if there is a better word to describe the power that turns a
wheel on a vehicle)<<<
Torque, also called moment or moment of force (see the terminology below), is the tendency of a force to rotate an object about an
axis,[1] fulcrum, or pivot. Just as a force is a push or a pull, a torque can be thought of as a twist....
Understanding the relationship between torque, power and engine speed is vital in automotive engineering, concerned as it is with transmitting power
from the engine through the drive train to the wheels.
--------------------------------------------------------------------------------
Differential:
A vehicle's wheels rotate at different speeds, mainly when turning corners. The differential is designed to drive a pair of wheels with equal torque
while allowing them to rotate at different speeds.
In vehicles without a differential, such as karts, both driving wheels are forced to rotate at the same speed, usually on a common axle driven by a
simple chain-drive mechanism.
When cornering, the inner wheel needs to travel a shorter distance than the outer wheel, so with no differential, the result is the inner wheel
spinning and/or the outer wheel dragging, and this results in difficult and unpredictable handling, damage to tires and roads, and strain on (or
possible failure of) the entire drivetrain.
Input torque is applied to the ring gear (blue), which turns the entire carrier (blue). The carrier is connected to both the side gears (red and
yellow) only through the planet gear (green) (visual appearances in the diagram notwithstanding). Torque is transmitted to the side gears through the
planet gear. The planet gear revolves around the axis of the carrier, driving the side gears. If the resistance at both wheels is equal, the planet
gear revolves without spinning about its own axis, and both wheels turn at the same rate.
If the left side gear (red) encounters resistance, the planet gear (green) spins as well as revolving, allowing the left side gear to slow down, with
an equal speeding up of the right side gear (yellow).
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Loss of Traction:
The torque applied to each driving wheel is a result of the engine, transmission and drive axles applying a twisting force against the resistance of
the traction at that roadwheel.
Unless the load is exceptionally high, the drivetrain can usually supply as much torque as necessary, so the limiting factor is usually the traction
under each wheel. It is therefore convenient to define traction as the amount of torque that can be generated between the tire and the road surface,
before the wheel starts to slip.
If the torque applied to drive wheels does not exceed the threshold of traction, the vehicle will be propelled in the desired direction; if not, then
one or more wheels will simply spin.
To illustrate how a conventional "open" (non-locked or otherwise traction-aided) differential can limit torque applied to the driving wheels, imagine
a simple rear-wheel drive vehicle, with one rear roadwheel on asphalt with good grip, and the other on a patch of slippery ice. With the load,
gradient, etc. The vehicle requires a certain amount of torque applied to the drive wheels to move forward. If the two roadwheels were driven without
a differential, each roadwheel would be supplied with an equal amount of torque, and would push against the road surface as hard as possible. The
roadwheel on ice would quickly reach the limit of traction, but would be unable to spin because the other roadwheel has good traction. The traction of
the asphalt plus the small extra traction from the ice exceeds the minimum requirement, so the vehicle will be propelled forward.
*** With an open differential, however, as soon as the "ice wheel" exceeds the threshold of traction available (which varies depending on tire size,
type, and inflation pressure, vehicle weight and proportioning, temperature, etc.), it will start to spin, further reducing traction (the amount of
torque required to spin the wheel against traction lowers after the threshold is initially broken).
Since an open differential limits total torque applied both drive wheels as the amount utilized by the lower traction wheel multiplied by a factor of
2, when one wheel is on a slippery surface, the total torque applied to the driving wheels will be lower than the minimum torque required for vehicle
propulsion. thus, the vehicle will not be propelled. 
--------------------------------------------------------------------------------------
Many newer vehicles feature traction control, which partially mitigates the poor traction characteristics of an open differential by using the
anti-lock braking system to limit or stop the slippage of the low traction wheel, thus transferring more torque to the wheel with good traction. While
not as effective in propelling a vehicle under poor traction conditions as a traction-aided differential, it is better than a simple mechanical open
differential with no electronic traction assistance.
--------------------------------------------------------------------------------------
There are various devices for getting more usable traction from vehicles with differentials.
One solution is the Positive Traction (Posi), the most well-known of which is the clutch-type. With this differential, the side gears are coupled to
the carrier via a multi-disc clutch which allows extra torque to be sent to the wheel with higher resistance then available at the other driven
roadwheel when the limit of friction is reached at that other wheel. Below the limit of friction more torque goes to the slower (inside) wheel.
A limited slip differential (LSD) or anti-spin is another type of traction aiding device that uses a mechanical system that activates under
centrifugul force to positively lock the left and right spider gears together when one wheel spins a certain amount faster than the other. This type
behaves as an open differential unless one wheel begins to spin and exceeds that threshold.
While positraction units can be of varying strength, some of them with high enough friction to cause an inside tire to spin or outside tire to drag in
turns like a spooled differential, the LSD will remain open unless enough torque is applied to cause one wheel to loose traction and spin, at which
point it will engage.
A LSD can use clutches like a posi when engaged, or may also be a solid mechanical connection like a locker or spool. It is called limited slip
because it does just that; it limits the amount that one wheel can "slip" (spin).
A locking differential, such as ones using differential gears in normal use but using air or electrically controlled mechanical system, which when
locked allow no difference in speed between the two wheels on the axle. They employ a mechanism for allowing the axles to be locked relative to each
other, causing both wheels to turn at the same speed regardless of which has more traction; this is equivalent to effectively bypassing the
differential gears entirely.
Other locking systems may not even use differential gears but instead drive one wheel or both depending on torque value and direction. Automatic
mechanical lockers do allow for some differntiation under certain load conditions, while a selectable locker typically couples both axles with a solid
mechanical connection like a spool when engaged.
Electronic traction control systems usually use the anti-lock braking system (ABS) roadwheel speed sensors to detect a spinning roadwheel, and apply
the brake to that wheel. This progressively raises the reaction torque at that roadwheel, and the differential compensates by transmitting more torque
through the other roadwheel—the one with better traction.
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DENNIS
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| Quote: | Originally posted by bigboy
David, return to engineering school as soon as possible! |
 What a
nice, civilized way to say something else.
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TMW
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According to my copy of Manual Transmissions and Transaxles 4th addition by Jack Erjavec page 177 it says When a car is stuck in mud or snow, one
drive wheel spins while the other remains stationary. In this example, the differential is transferring all of the torque and rotary motion to the
drive wheel with the least resistance. Resistance, in this case, means traction. Applying torque to the wheel without traction does little good while
trying to move the car
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David K
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| Quote: | Originally posted by TW
According to my copy of Manual Transmissions and Transaxles 4th addition by Jack Erjavec page 177 it says When a car is stuck in mud or snow, one
drive wheel spins while the other remains stationary. In this example, the differential is transferring all of the torque and rotary motion to the
drive wheel with the least resistance. Resistance, in this case, means traction. Applying torque to the wheel without traction does little good while
trying to move the car |
BINGO!  (thanks for that TW... it is what I have been saying...
and I didn't need to go back to engineering school  )
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4x4abc
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David,
I admire your work! You know so much more about Baja than I - but I know differentials better.
4x4 has been my field for 25 years.
You are a little off about what's happening with torque in a wheel spin situation.
Even though the web and books are full of "all torque goes to the slipping wheel" - physics books tell a different story.
And when you checked wikipedia it was right in front of your eyes: "A vehicle's wheels rotate at different speeds, mainly when turning corners. The
differential is designed to drive a pair of wheels with equal torque while allowing them to rotate at different speeds"
So, the open (no lockers, no limited slip) differential always sends equal torque to both wheels. Always!
Always, as in a straight line, in turns, with a wheel on slippery surface - even with one wheel in the air.
The wiki article has a decent description of what's happening when the two connected wheels encounter unequal traction. Let me paraphrase it: A
vehicle needs a certain amount of torque to me moved. On high traction surfaces it will be almost impossible to get a tire to slip and spin - the
amount of torque generated on both tires is very high = the vehicle can accelerate quickly.
If the driven axle would encounter a mixed surface (asphalt/sand) the tire on sand might slip and spin. However, the amount of torque to get a tire to
spin on sand requires a certain amount of torque (called threshold - see wiki above). Since the rule is that an open differential always distributes
torque equally - the tire with more traction will get the same amount as the slipping tire. Threshold times two. And in this case the vehicle might
still be moving, because twice the amount of low torque might be sufficient to move the car. Depends.
A slipping and spinning tire by itself is not an indicator that the car will not move. Think of high HP cars laying rubber with slipping and spinning
tires - they do indeed move.
Here is where Baja and off-road comes in. Sometimes one tire has so little traction that the threshold torque generated is so low that even doubling
it (remember, the other tire gets the same amount) will not be sufficient to move the truck. 2 times a very low amount is still a very low amount.
But drive system might be just missing an additional 20 lb-ft. So your friend's strong shoulder (threshold torque times two plus friend's torque) is
enough to move the car.
Now, the description so far was only for a one axle 2WD - but most of have 4WD, so we are safe, right? Not necessarily.
Almost always (the "why" would be too lengthy in one post) if one tire slips and spins the diagonally opposed wheel on the other axle will also slip
and spin. Those two diagonally opposed wheels will slip and spin later than the one wheel on a 2WD. Because each tire of a 4WD will have to generate
only half the amount of torque as the wheels on a 2WD (given that both cars are of equal weight)
But since we usually drive where no 2WD dares to go, we get stuck due to low threshold torque.
Don't feel to badly about not knowing exactly how the differential does its work. Even the wiki contributors goof on occasion. In the 'Loss of
traction' section above you copied from their site: " If the two roadwheels were driven without a differential, each roadwheel would be supplied with
an equal amount of torque, and would push against the road surface as hard as possible."
That is dead wrong.
When no differential is present, the tire with more traction will generate the most torque - the one with less traction will generate less. So there
will be higher mechanical stress on the axle shaft going to the wheel with more traction.
Rule for axles with differential locks engaged (equal to not having a differential) is: Wheel rotations are equal - torque is unequal.
To repeat open differential: Wheel rotations are unequal - torque is equal.
more: http://www.4x4abc.com/4WD101/
I'll be happy to outline some of the measures that can be taken if one does not have limited slip, traction control or selectable lockers.
Harald Pietschmann
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David K
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Thank you Harald... so what is the best way to describe the effect of slowing the spinning tire down so the traction tire can move the vehicle (as
with limited slip).
I can picture the process... but using 'torque' was technically wrong, yet most understand what is happening...
Both tires get 'torque' when one is spinning freely in the air or on ice... But the tire on firm ground does nothing to move the vehicle until the
spinning tire is braked (limited slip or locker) to slow it down or match its rotation with the other tire.
Until the spinner is slowed or stopped, the energy is lost to it... When it is slowed or stopped the 'energy' (what I called torque) then goes to turn
the tire on fiorm ground.
What is the correct term I need to answer this in simple to understand terms?
Muchas Gracias!
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4x4abc
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David,
you were absolutely correct when you used 'torque' - you were only off by saying torque only goes to the spinning wheel.
Follow me on this little excursion:
rules first
The traction each tire has on the ground is the counterforce for torque - without a counterforce (traction or resistance) no torque can be created.
In order to avoid spinning tires, you have to have an equal or higher amount of traction than the amount of torque applied.
An open differential always distributes torque equally while allowing both wheels to rotate at a proportional different rate (if one goes 10 rpm
faster, the other one will slow down 10 rpm - if one stops, the other will rotate twice as fast as before).
Just for arguments sake, lets say a car needs 100 units of torque to start moving.
At the beginning of our experiment the car is on high traction asphalt. 100 units of traction under each wheel. So when I step on the gas, increasing
the torque, the car will start moving when each tire generates at least 50 units of torque (50 + 50). I still have 50 units of traction on each wheel
to spare (we need some of it for lateral stability).
New test. One wheel on dry asphalt, one wheel on sand. Sand has about 40% of the traction dry asphalt has. So, 100 units of traction at the wheel on
asphalt - 40 units of traction at the wheel on sand. When I step on the gas and reach the threshold torque of 40 units at the wheel on sand, that tire
will start slipping. Since the rule is, that the open diff apportions torque equally, the wheel on asphalt also get 40 units of torque. 40 + 40 = 80
80 units of torque is not enough to move the car - we need 100.
Someone willing to push the car would easily be able to generate additional 20 units of torque and get the car moving.
Here is what traction control would do. The computer would send a signal to apply the brake (pulsating like ABS) at the wheel that is starting to
slip. The brake will have to create additional 20 units of resistance. 20 + 40 is 60 at the wheel on sand - so the other wheel will also get 60,
together that's 120 (20 of the will turn into heat due to the brake friction) and the car starts moving.
The advantage is that traction control always only adds as much resistance (friction) as needed at the wheel(s) that slip. Disadvantage is that the
system is reactive. You have to get the wheel(s) slipping first before traction control steps in to save your tush.
Limited slip. By installing clutch plates inside the differential the internal parts are much harder to move. They put up resistance. This amount of
"preload" is fixed when first installed. So, lets say, each axle half puts up a resistance of 30 units, then your wheel on sand would not even slip
because I have a total counter force of 40 + 30 at that wheel. 70 at the other wheel. 140 in total - of which 110 are usable (30 turn into heat).
So, advantage is that this system is proactive - it keeps the wheels from slipping in the first place. Disadvantage is that the threshold is fixed and
might not be sufficient for really slippery stuff. Also, clutch plates wear out and the effectiveness of limited slip is going away over time.
There are some other limited slip concepts I will not go into to keep things easy. They have all one thing in common - they limit slip, but they do
not prevent it entirely.
Another test. One wheel on dry asphalt, one wheel on ice. Ice has about 10% of the traction dry asphalt has. So, 100 units of traction at the wheel
on asphalt - 10 units of traction at the wheel on ice. Will my limited slip (30 preload) save me?
Lets see - 10 + 30 = 40 at the wheel on ice - 40 as well at the high traction wheel. Meaning I can't generate enough torque to get moving. The wheel
on ice will slip.
This shows you that limited slip is an acceptable assistant for some conditions, but not for all.
were you able to follow?
this might help to illustrate:
http://www.youtube.com/watch?v=iAlro4aKPWM&feature=playe...
[Edited on 1-19-2011 by 4x4abc]
[Edited on 1-19-2011 by 4x4abc]
Harald Pietschmann
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