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Sorry but you are wrong here, when a differential is “locked” the torque goes equally to both wheels, both wheels turn at the rate of the wheel with most traction (slower wheel). That is where the term “locked” comes from. It is for this reason a locked differential, or locked transfer case as well, cannot be used on hard surfaces roads, because in a turn the outside wheel is forced to revolve faster than the inside wheel, when locked this becomes impossible so the outside wheel skids. To address this limited slip differentials were invented, many of which are a form of mechanical inboard brake (using clutch Plates) on the differential but they are a compromise as is the electronically braked differential that we have.
 

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I had a 1973 Dodge Dart with a standard open rear differential, if you jacked the rear of the car up and held one of the wheels with your hand, when you put the car in gear the other wheel would spin. No torque at all applied to the wheel you are holding. Now if brake were to be applied to the spinning wheel torque proportional to that force is returned to the other side.
 

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I’d also like to add that the system limits torque by reducing the injector output. You might have the accelerator floored but the computer overrides your input to determine how much fuel the engine receives to keep the torque output within its designed limit. The system also considers wheelspeed in the equation. More torque can be applied to a wheel/drivetrain already in motion than one at standstill without damage. So if you are completely stopped the system will reduce initial available torque even more than if the the drivetrain was turning. This is why in a mud situation it’s able to power through if you keep momentum. If you stop then there will be even less power available to get going again.
Keep in mind that the total engine output, particularly the diesel, of this vehicle is more than some V-8 engines during the 70’s and 80’s. It is not a question of how much torque the motor can make, it’s a question of how much torque the computer will allow to the drivetrain.
Great post! Couldn't have said it better.


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Sorry but you are wrong here, when a differential is “locked” the torque goes equally to both wheels, both wheels turn at the rate of the wheel with most traction (slower wheel). That is where the term “locked” comes from. It is for this reason a locked differential, or locked transfer case as well, cannot be used on hard surfaces roads, because in a turn the outside wheel is forced to revolve faster than the inside wheel, when locked this becomes impossible so the outside wheel skids.
Sorry, but you are wrong. Locked differentials transmit equal movement to each side, not equal torque. An open differential is the opposite - it allows unequal movement but in the process delivers equal torque.

For an open diff with both wheels off the ground virtually no torque is applied because the wheel(s) spin freely. Holding one with your hands just makes the other rotate twice as fast. If only one wheel is off the ground and spinning and you try to hold it (trying to is Darwin Award material) then some torque, equal to your strength, would be generated on both wheels.
This is why when a car with open diff is stuck in the mud/snow with one wheel spinning you put your mat or whatever under the spinning wheel, not the one that is still gripping.
 

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From Car and Driver:
The humble open center differential*—simple, reliable, cheap—has been driven to near extinction by electromechanical alternatives that offer more control and greater efficiency. An open differential, a variation of the common planetary gearset found in automatic transmissions, splits a single torque input (the transmission) into two outputs (the front and rear axles) but allows them to rotate at different speeds. Yet open diffs have no means of limiting the speed variation between the two outputs, so torque is free to follow the path of least resistance. Hence, it’s possible for a vehicle to become stuck with one wheel spinning furiously while the others remain stationary. Most modern vehicles compensate with a cheap but effective combination of software and existing hardware that uses the brakes to create a reaction torque at the slipping wheel, closing the path of least resistance and thus increasing the torque applied to the wheels with more traction.

https://www.caranddriver.com/features/a15102281/best-all-wheel-drive-system/
 

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I think we are disagreeing over semantics the equal movement you describe produces torque when the wheel is braked, “reaction torque’ as it is described in the above C&D article, the torque then flows to the “path of least resistance” via the open differential (the un-braked wheel). Since that wheel has traction the torque supplied allows the vehicle to move.
Regardless of how you want to describe how or where the torque exists or what constitutes torque the fundamental point here is that the computer in this vehicle will reduce engine output so the torque does not exceed the capacity of any structure in the driveline system, the differential itself, the clutchpacks or the individual CV joints. This is the important point because there are many who think the vehicle is stuck because the engine has insufficient power to turn the wheels when in deep mud, rocks, sand ect...
 

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I think we are disagreeing over semantics
To a large extent, yes.
That Car and Driver item is not a bad description though the idea of torque following the path of least resistance is interesting. Torque is a force and always exists as action and reaction - you can't push with any force on something that doesn't resist. If a slipping wheel only needs X torques to spin it then X torques is what you'll get on the other side of an open diff.

My main point is that with open diffs there is no way to apply more torque to drive-train components by braking individual wheels than in normal operation, such as flooring it when the lights go green, as torque is always distributed equally. The caveat to that is that in normal driving 1st gear/low range is not used - when it is used the available torque is substantially increased, which is possibly why management of engine output is needed at such times.
 

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The system also considers wheelspeed in the equation. More torque can be applied to a wheel/drivetrain already in motion than one at standstill without damage. So if you are completely stopped the system will reduce initial available torque even more than if the the drivetrain was turning. This is why in a mud situation it’s able to power thro
 

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On steep hills, the vehicle (like a Jeep Renegade TrailHawk) appear to run out of power and can no longer move forward - even when there are no spinning tires.
 

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On steep hills, the vehicle (like a Jeep Renegade TrailHawk) appear to run out of power and can no longer move forward - even when there are no spinning tires.
The computer is programed to cut power to save drivetrain components from failing.

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That isn't actually correct.
Just considering one axle:
When both wheels grip the diff applies equal torque to both half-shafts - half the propshaft torque to each.
f there is a locking diff and one wheel has no traction the full torque from the propshaft will be applied to the gripping wheel's half-shaft.
With a braked system with open diff the two half-shafts always get half the torque - the slipping wheel is prevented from spinning by the brake, which from the drive line's point of view is the same as being on the ground.
Exactly. People here are confusing traction control with Selectrain functions. When the system applies the brake to a wheel off the ground, the differential sees that as a wheel with perfect traction against an unmovable object (like a straight vertical brick wall) and sends the torque to the other end of the axle.

This concept is not new, its just been re-engineered with modern technology. Porsche used this idea on the 959 which now costs $1,100,000.00 . Once a wheel comes off the ground or loses traction, whats important is that power to that wheel be redirected elsewhere for maximum ability. How you achieve that can be many different ways.
 

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To a large extent, yes.
That Car and Driver item is not a bad description though the idea of torque following the path of least resistance is interesting. Torque is a force and always exists as action and reaction - you can't push with any force on something that doesn't resist. If a slipping wheel only needs X torques to spin it then X torques is what you'll get on the other side of an open diff.
I understand what you're saying but you absolutely can apply torque to something that doesn't resist, as long as it has mass. Otherwise gyroscopes couldn't be used to change angles on satellites.

The reality is that as soon as one tire in a open differential system loses traction then the load is removed from the system, and that force is then transferred into increasing the RPM of the engine and the rest of the driveline. The force is still there it's just being used in a way that is not useful to us.
 

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People need to realize that the Renegade is NOT an "off roader". It IS "trail rated" ("trail" is not OFF ROAD, Trail is what's considered in the off road community as "soft road"). The Renegade is also NOT a "4x4" (I don't care what jeep plasters on it, it's false advertising at the least) it is a AWD based system (GKN produced) using torque bias (wet clutch based) electronically controlled.
AWD (such that the Renegade IS), is fantastic on road (since the substructure remains solid) and is preferred for snow.
However, AWD is terrible for off road since it relies on loss of traction in order to send to power to other wheels. When in dirt (non solid substructure), a wheel will dig itself a hole as the system finally decides to send power to another wheel. By this time, not only does that "other" wheel bear the burden of powering the vehicle out (entirely), but ALSO has to power it out while overcoming a completely dug in/rutted wheel that just buried itself thus more than quadrupling the force needed to power out). It's not a proper system for any "real" off roading to say the least.
It is, however GREAT on paved roads since it never has to power out of any "dug hole". These systems exist because people want max fuel economy, at least a smidgen of off road ability (and a smidgen is all you'll get), and excellent inclement weather traction (which AWD excels at).
While the Renegade DOES have an aggressive AWD system (much better than Subaru's) which acts fairly quickly (still not quick enough to prevent the downfalls of AWD off road), it is a lightweight system (again, MPG being the prime target) so it is programmed to "save itself" under load (in other words, the system, mechanically, is not designed to handle any serious stress anyway... so it will cut power to prevent any serious stress to the components).
So... you have a system that biases off the front wheels. Then, when it senses a front wheel spinning itself into a hole (off road), it will eventually (IMO, Jeeps IS the quickest for this, to their credit) transfer power to other wheels. The main problem is: Now the power needed to unstuck the vehicle is massive as it's got at least one wheel dug in a hole, and the mechanicals of the system are not up to the task. Thus it cuts power and you go nowhere (as is seen in multiple videos of the vehicle). All you have to do it google roller tests of this system (Renegade) to see that it lets wheels spin for quite a while until it transfers power (easily enough to bury a wheel). Still... it IS probably the most aggressive AWD system out there (to Jeeps credit).
That being said, The Renegade is easily better than most AWD CUV's (car based utility vehicles) out there with it's aggressive AWD.
What I have issue with is Jeeps audacity to label it as "4x4" (which is CLEARLY is not, even by GKN who makes the system for them), In the Trailhawk, you have a "4-low" which is simply 1st gear (NOT a real "low range"), and all have the "4-lock" button which does nothing but engage the real driveline (but NOT the rear wheels since it has a wet clutch disconnect at the rear differential). So even in "4-lock), NO, you are not getting any power to rear wheels until the system senses power loss at the front wheels and transfers power (via that rear wet clutch differential) to the rear. The only reason Jeep calls it a "4x4" is because, technically, it DOES sent power to the rear when you hit that "4-lock" button.... but they don't tell you that NONE of it goes to the rear wheels (disconnected via wet clutch at the rear diff) unless slippage is sensed at the FRONT. So the "4x4" badging is based on technicality alone, and Jeep knows this (and they should be ashamed of misleading people that way).
While it's a GREAT system for what it is (an inclement weather system), it is NOT a great choice for any serious off roading (though will suffice for mild trails).
I have a "17 Renegade TH and actually love it for what it is. It's a great commuter, easy to city park, gets decent MPG, and will easily handle the mild off roading I'd through at it. That being said... I wish Jeep would stop with the nonsense fake badging/advertising (it's misleading at least, and false advertising at most).
 

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open front & rear diffs with computer traction control is not same as locking diffs

open front & rear diffs with computer traction control is not same as locking diffs - and the difference is not even close !!!

I assume many of you have watched some videos of a Jeep Renegade (or any other 4x4 with open differentials with computer traction control) climbing a hill , where one tire in the front and one tire in the rear are up in the air or touching the ground with almost no traction. On steep hills, the vehicle (like a Jeep Renegade TrailHawk) appear to run out of power and can no longer move forward - even when there are no spinning tires.

Here is the reason why:
A 4x4 vehicle with front & rear locking differentials can apply all of the torque to any tire. Thus if 1 tire has traction and 3 tires have no traction, the one tire with traction can get all of the torque to turn the tire to move the vehicle.
However - A 4x4 vehicle with open front and rear differentials can not apply all of the torque to any single tire (even with computer traction control applying full locking brake action to any tires in the air). With this type of a vehicle (like a Jeep Renegade TrailHawk), when the computer applies a traction control brake force to a slipping tire, the remaining tire with traction will now have 1/2 of the available maximum torque to turn the tire. This condition with one front and one rear tire in the air with computer traction control effectively results in a engine to torque ratio of half - and it thus behaves similar to having a 2x taller gear ratio.

Thus - if you have a choice of locking front & rear differentials verses computer traction control , and you absolutely need the torque pulling power, then always use a locking differential.


So, a Jeep Renegade TrailHawk with a 20:1 crawl ratio with one front and one rear tire in the air actually has the torque equivalent of a 10:1 crawl ratio. This explains why in some videos where a Jeep Renegade appears to run out of power when climbing a steep hill where one or two tires are in the air.

Now if the Jeep Renegade TrailHawk had front & rear electronic locking differentials (in addition to computer traction control) , the vehicle would possibly be a much more capable vehicle off road.

The problem is not the diffs. The problem is the throttle control signal coming from the gas pedal. I installed a Pedal Commander and put it in performance mode to restore active control of the accelerator and performance went through the roof. I scramble up inclines I couldn't touch before. I go places my buddies in their Rubicons wont follow me. The important factor in off road performance is overcoming forces that are trying to stop you with power and traction that overcomes those. There are a lot of ways to achieve that. The Jeep Renegade Trailhawk does that, but just like other Jeeps, they need a little modification to reach their true potential. The ground clearance of a 2 door Wrangler and a Renegade Trailhawk are the same. The weight of the vehicle is significantly lower than the Wrangler so you are overcoming less resistance to climb and move forward on a Renegade than a Wrangler. The 4WD system on a Trailhawk is state of the art and works very well. I am extremely happy with the off road performance of my Trailhawk and it proves its ability every time I take it out.

2396347924
 

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People need to realize that the Renegade is NOT an "off roader". It IS "trail rated" ("trail" is not OFF ROAD, Trail is what's considered in the off road community as "soft road"). The Renegade is also NOT a "4x4" (I don't care what jeep plasters on it, it's false advertising at the least) it is a AWD based system (GKN produced) using torque bias (wet clutch based) electronically controlled.
AWD (such that the Renegade IS), is fantastic on road (since the substructure remains solid) and is preferred for snow.
However, AWD is terrible for off road since it relies on loss of traction in order to send to power to other wheels. When in dirt (non solid substructure), a wheel will dig itself a hole as the system finally decides to send power to another wheel. By this time, not only does that "other" wheel bear the burden of powering the vehicle out (entirely), but ALSO has to power it out while overcoming a completely dug in/rutted wheel that just buried itself thus more than quadrupling the force needed to power out). It's not a proper system for any "real" off roading to say the least.
It is, however GREAT on paved roads since it never has to power out of any "dug hole". These systems exist because people want max fuel economy, at least a smidgen of off road ability (and a smidgen is all you'll get), and excellent inclement weather traction (which AWD excels at).
While the Renegade DOES have an aggressive AWD system (much better than Subaru's) which acts fairly quickly (still not quick enough to prevent the downfalls of AWD off road), it is a lightweight system (again, MPG being the prime target) so it is programmed to "save itself" under load (in other words, the system, mechanically, is not designed to handle any serious stress anyway... so it will cut power to prevent any serious stress to the components).
So... you have a system that biases off the front wheels. Then, when it senses a front wheel spinning itself into a hole (off road), it will eventually (IMO, Jeeps IS the quickest for this, to their credit) transfer power to other wheels. The main problem is: Now the power needed to unstuck the vehicle is massive as it's got at least one wheel dug in a hole, and the mechanicals of the system are not up to the task. Thus it cuts power and you go nowhere (as is seen in multiple videos of the vehicle). All you have to do it google roller tests of this system (Renegade) to see that it lets wheels spin for quite a while until it transfers power (easily enough to bury a wheel). Still... it IS probably the most aggressive AWD system out there (to Jeeps credit).
That being said, The Renegade is easily better than most AWD CUV's (car based utility vehicles) out there with it's aggressive AWD.
What I have issue with is Jeeps audacity to label it as "4x4" (which is CLEARLY is not, even by GKN who makes the system for them), In the Trailhawk, you have a "4-low" which is simply 1st gear (NOT a real "low range"), and all have the "4-lock" button which does nothing but engage the real driveline (but NOT the rear wheels since it has a wet clutch disconnect at the rear differential). So even in "4-lock), NO, you are not getting any power to rear wheels until the system senses power loss at the front wheels and transfers power (via that rear wet clutch differential) to the rear. The only reason Jeep calls it a "4x4" is because, technically, it DOES sent power to the rear when you hit that "4-lock" button.... but they don't tell you that NONE of it goes to the rear wheels (disconnected via wet clutch at the rear diff) unless slippage is sensed at the FRONT. So the "4x4" badging is based on technicality alone, and Jeep knows this (and they should be ashamed of misleading people that way).
While it's a GREAT system for what it is (an inclement weather system), it is NOT a great choice for any serious off roading (though will suffice for mild trails).
I have a "17 Renegade TH and actually love it for what it is. It's a great commuter, easy to city park, gets decent MPG, and will easily handle the mild off roading I'd through at it. That being said... I wish Jeep would stop with the nonsense fake badging/advertising (it's misleading at least, and false advertising at most).

As a retired engineer, I dont even know where to start with your sypnosis. Four wheel drive refers to the fact that both axles are capable of applying torque to the ground. Almost every "four wheel drive" vehicle ever made has the characteristics of distribution of torque issues that you describe, INCLUDING THE JEEP WRANGLER.
 
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