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Traction control of a spinning wheel

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I'm sure this has been asked before but I just can't find it, sorry.

Imagine one front wheel is in the air. One rear wheel probably will be too. Car is stuck, fair enough, that's what happens without axle LSD or diff lockers.

That lifted front wheel just spins. Does the traction control brake the spinning wheel at all, or just cut engine power? In my experience it does not brake the spinning wheel. Is that to be expected on the 2008 Limited?

You can use the handbrake gently to slightly brake a spinning rear wheel, mixed success. Two handbrake levers, one for each rear wheel, would be helped in the absence of a diff lock. Not likely though... Any other tips to move on from this situation, rather than more entry speed? Thanks.
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You can have mixed situations, I had situations were the engine cuts power and it just stalls on my manual 5-speed, or situations were I had a very muddy place to go out and you literally feel the horrible braking on the spinning wheel... is terrible really, make the whole car shake and vibrates but gets the job done.
 

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That lifted front wheel just spins. Does the traction control brake the spinning wheel at all
On a 2WD RAV4, the spinning front wheel is locked by braking and you can move (simulates a locked diff). Now, if both are spinning on ice or grass, you are stuck.
On a 4WD RAV4, because there is no central differential, braking one wheel is OK, but braking two opposite axle wheels, with different speeds on the remaining wheels, will just lock the driveshaft. So, in my experience, Toyota doesn't do it. I think it will brake ONE wheel if it loses traction, but not TWO (have not tested this).
This is a split of 55% front drive and 45% rear drive. It is disconnected at speed above 25MPH or by use of braking.
Highlander and Sienna have an open central differential and can apply brake on any wheels that lose traction:
Full-Time 4WD/AWD All Wheel Drive Sienna and Highlander gas System This systems sends variable power to both axles. It incorporates the front differential, center differential and transfer case into one compact unit. Rear differential is located at rear axle. Operation AWD system relies on a specialized Electronic Control Unit (ECU) to control wheel spin by applying the brakes to that wheel therefore directing power to other wheels with traction. Benefits This is a light duty system that allows a vehicle exceptional traction at all times while utilizing all the features of VSC and TRAC.
 

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oh yea it is that time of the year in the usa to think on snow and ice.
make sure not to shock the system with hard grip. that spin and sudden grip thing.
things tend to break if spin and sudden stop.
that inertia thing and medium duty parts.

cool stuff here on the non locker diff setups.
lots of tricks for when you are stuck or close to stuck.

if you can one of the best rules is not to stop on slick.
hard to do at times.
but to stay in motion is always a good plan.
 

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On a 2WD Rav4 it will apply the brake to a (undriven) front wheel and that will get you unstuck? 🙇‍♂️
Yes. That call that "LSD".
For a second I was thinking a 2WD Rav4 was RWD
LOL, yeah RAV4 is basically a FWD car, even the "4WD" one.
No, it has an Limited Slip Differential, it will lock both front wheels together
It is not a true LSD (differential inside transmission is still open), it is simulated via braking.
 

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Is that to be expected on the 2008 Limited?
Correct me if I'm wrong, but does not the Limited with AWD have full time AWD? That means it has a center differential. At one time I thought the full time Limited AWD had a Torsen center differential (Torque Sensing) which is an elegant limited slip that sends the torque to the wheel that is NOT spinning. Traction control can still brake selected wheels depending on various factors.

But your case is different. When diagonal wheels don't have traction (spinning) no amount of center differential magic will solve the problem. (I call that the teetter-totter mode). I often encounter that with my 4Runner in off road situations. Higher levels of 4Runners have locking front/rear differentials which solves the problem, but my lowly SR5 does not, but it does have what is called "Atrac" mode which simulates, via the traction control system, a locking front/rear differential. I can't count how many times the Atrac mode has gotten me out of trouble.

In difficult off road scenarios, you can't just enter the difficult section faster to coast through it; you have to go slow due to the bad terrain; no way around that.

One solution, not mentioned so far, is to have weight shift to one side or the other of your car (ask your passengers to move to one side or the other), so one of the spinning wheels may get traction. Doesn't always solve the problem, but may help.
 

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Discussion Starter · #11 ·
You can have mixed situations, i had situations were the engine cuts power and it just stalls on my manual 5-speed, or situations were i had a very muddy place to go out and you literally feel the horrible breaking on the spinning wheel... is terrible really, make the whole car shake and vibrates but gets the job done.
Thanks, knowing the reaction can be mixed is useful.
 

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Discussion Starter · #12 ·
On a 4WD RAV4, because there is no central differential, braking one wheel is OK, but braking two opposite axle wheels, with different speeds on the remaining wheels, will just lock the driveshaft. So, in my experience, Toyota doesn't do it. I think it will brake ONE wheel if it loses traction, but not TWO (have not tested this).

Highlander and Sienna have an open central differential and can apply brake on any wheels that lose traction:
Thanks, good to know. An old RWD car I had had great traction control. Open rear diff but great grip in the snow unless both rear wheels broke traction.

Your 4WD rav4 explanation makes sense. Sounds like the traction control will get it moving if one wheel is on ice etc (although with a locked centre diff that's a bit unnecessary). Sounds like it won't help with two lifted wheels. Either need a rear diff lock (no), more articulation (no) or something else (handbrake or left for braking to control the spin a bit).
 

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Discussion Starter · #13 ·
oh yea it is that time of the year in the usa to think on snow and ice.
make sure not to shock the system with hard grip. that spin and sudden grip thing.
things tend to break if spin and sudden stop.
that inertia thing and medium duty parts.

cool stuff here on the non locker diff setups.
lot's of tricks for when you are stuck or close to stuck.

if you can one of the best rules is not to stop on slick.
hard to do at times.
but to stay in motion is always a good plan.
Yes, noted about avoiding shock loads. Controlling the spin with left foot braking (manual car) or dragging the handbrake should help with that. It's only the 4 cylinder so not tons of torque.

Did you post a link I couldn't see? You mentioned "lots of tricks for when you are stuck."
 

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Thanks, good to know. An old RWD car I had had great traction control. Open rear diff but great grip in the snow unless both rear wheels broke traction.

Your 4WD rav4 explanation makes sense. Sounds like the traction control will get it moving if one wheel is on ice etc (although with a locked centre diff that's a bit unnecessary). Sounds like it won't help with two lifted wheels. Either need a rear diff lock (no), more articulation (no) or something else (handbrake or left for braking to control the spin a bit).
The center clutch is completely necessary on this car, when you decide to lock it, it will really lock front and back and not wait for a spin to act and lock rear wheels... they will be already locked... this helps a lot and is even more noticeable when you drift on snow and mud, the car tends to turn into the corner when the center locked instead of under steering and then locking and then the traction control becomes crazy, start to beep and cuts power... this car with the center clutch locked is more effective and fun
 

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Discussion Starter · #15 ·
Correct me if I'm wrong, but does not the Limited with AWD have full time AWD? That means it has a center differential. At one time I thought the full time Limited AWD had a Torsen center differential (Torque Sensing) which is an elegant limited slip that sends the torque to the wheel that is NOT spinning. Traction control can still brake selected wheels depending on various factors.

But your case is different. When diagonal wheels don't have traction (spinning) no amount of center differential magic will solve the problem. (I call that the teetter-totter mode). I often encounter that with my 4Runner in off road situations. Higher levels of 4Runners have locking front/rear differentials which solves the problem, but my lowly SR5 does not, but it does have what is called "Atrac" mode which simulates, via the traction control system, a locking front/rear differential. I can't count how many times the Atrac mode has gotten me out of trouble.

In difficult off road scenarios, you can't just enter the difficult section faster to coast through it; you have to go slow due to the bad terrain; no way around that.

One solution, not mentioned so far, is to have weight shift to one side or the other of your car (ask your passengers to move to one side or the other), so one of the spinning wheels may get traction. Doesn't always solve the problem, but may help.
Thanks. As said, it's not full time 4WD. The electromagnetic 'centre diff' is at the rear. The prop shaft spins full time I think, but the coupling to the rear axle is at the rear diff. When this locks it is 4WD, but it locks on/off automatically depending on what the car senses. You can manually lock it upto 30mph or something like that. Easy to test. Jack up a front wheel, ignition off, that front wheel will turn easily by hand. Now turn ignition on, enable diff lock, that front wheel will not turn because the back axle is on the ground. I'm not sure how much load you can apply before the electromagnetic coupling will slip.

I understand a centre diff won't get you going if both axles have a spinning wheel. Your tip of weight distribution is worth remembering, thanks.
 

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Discussion Starter · #17 ·
The center clutch is completely necessary on this car, when you decide to lock it, it will really lock front and back and not wait foe a spin to act and lock rear wheels... they will be already locked... this helps a lot and is even more noticeable when you drift on snow and mud, the car tends to turn into the corner when the center locked instead of under steering and then locking and then the traction control becomes crazy, start to beep and cuts power... this car with the center clutch locked is more effective and fun
Yes agreed, that's great on flat surfaces. It's when a bit of articulation is needed that I'm asking about. With no rear diff, and the traction control not braking two spinning wheels (one on each axle) then alternative ideas are needed! Thanks.
 

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There is no "central clutch".
Only one electromagnetic coupler at the rear diff.
that electro magnetic coupler, is not a bunch of discs that are compressed together?

EDIT:

After some research and investigation, is, an centre clutch and this is how it looks like:
Automotive tire Camera lens Automotive design Motor vehicle Engineering


Source: Toyota all-wheel drive. ATC / DTC coupling


es agreed, that's great on flat surfaces. It's when a bit of articulation is needed that I'm asking about. With no rear diff, and the traction control not braking two spinning wheels (one on each axle) then alternative ideas are needed! Thanks.
You are asking too much, two oposite wheels on the air is more than you should be handling with this tall car.
 

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that electro magnetic coupler, is not a bunch of discs that are compressed together?
Rectangle Font Schematic Slope Parallel

Rectangle Building Font Parallel Schematic

Font Line Rectangle Parallel Auto part

Rectangle Font Line Parallel Engineering



Electromagnetic coupling
The outer part of the main clutch is attached together with the front housing. The inner part of the main clutch is attached together with the shaft. The control clutch is attached together with the control cam. The activation energy from the transfer is transferred from the propeller shaft to the front housing. However, when the linear solenoid is not operating, the main clutch and control clutch are in a free state, and the activation energy from the transfer is not transferred to the rear wheels.
If current is applied to the linear solenoid, the solenoid magnetizes, and the electromagnet pull force causes the armature to attach to the control clutch side. Or, if there is a difference between the rotation speed of the front and rear wheels and the control clutch attaches, a difference occurs in the rotation of the main cam attached to the shaft and the control cam attached to the front housing. As a result, each ball pushes its cam, and the main clutch attaches. The activation energy from the front housing passes through main clutch to the shaft, and then to the rear differential. Then the activation energy is transferred to the rear wheels.
Depending on the rotation difference between the front and rear wheels, the system controls the current flowing to the linear solenoid. Then the activation energy applied to the rear wheels is smoothly controlled. Depending on the amount of current, the restraint energy of the outer and inner side of the main clutch changes, and the activation energy from the propeller shaft is smoothly controlled from a limited condition to condition that is nearly a direct-link 4WD condition.
 
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