Traccontrol or lsd in 4wd?

Nah this is incorrect. 4wd means two wheel on the back, the spare wheel and the steering wheel are receiving torque.

 

That's 5wd. Only available if you opted in for the dual trans package.

 

Still it doesn't have a LSD, it has a locking differential. LSD function in OR is still break actuated.

 

While in 4wd, power is split 50/50 between front and rear differentials. Both differentials are open (slip) differentials so, on each axle, the power would go to the wheel with least traction. However, traction control uses breaks on each wheel to simulate LSD function and sends power to the wheel that has more traction. If you turn the traction control off on a low traction surface, the truck would practically be 2wd where one wheel on the front and one in the back gets power. Traction control ensures at least some of the power goes to all the wheels under those conditions. OR and Pro also have a mechanically locking rear diff, when locked two wheels on the back also receive 50% of the power that goes to the read diff. So with that the overall power split becomes 50/(25/25).

Theoretically speaking, the truck can never be 4wd since the front diff is open, for it to truly be 4wd, you would need to have a locking front diff. If you put the truch in 4wd and lock the rear diff, it becomes something like 3.5 wd with the traction control . OR and Pro have a more "intense" break actuated power distribution, so they are probably closer to having a true 4wd than other trims.

 

Maybe I missed it, but you are comparing
2wd no button presses (what you are calling TRAC)
And
2wd short VSC press to give AutoLSD
?

And you are wondering why autolsd is more effective than normal TRAC On and VSC On?

Or am I misunderstanding ?

 

I’m questioning whether Auto LSD mode is simply TRAC with VSC off or if there are other differences. Many times I have been temporarily stuck and TRAC was doing nothing (no ABS brake noises), I switched to Auto LSD mode with a short press of the button, and then heard ABS noises and got unstuck. Maybe I was being impatient or doing something different with the throttle. I’ll find some place to experiment. Just need a hill with some ice and dry pavement.

Edit: I was also once stuck in snow with 3 wheels in snow and one rear wheel on concrete. In reverse and 4wd I was going no where. TRAC was not doing anything. I put it in 2wd Auto LSD mode and got unstuck. It’s possible I had everything disabled when in 4wd, but I don’t remember.

 

Got it
Some people think autolsd is 'stronger'.

I dont have enough natural low traction conditions to really be able to effectively test.
On bench tests I dont think it is 'stronger' in its brake applications.

I do THINK autolsd has less throttle intervention and is quicker to engage the brakes, compared to 'no button press modes', but I have not done enough techstream data logging to be 100% sure of the nuances between the two.

Sounds like you have great natural conditions... get a copy of techstream and we might learn something.

Careful datalogging of wheel speed and throttle is something I never did under sloppy conditions, as I was primarily developing 2wheel low and working on anytime locker.

 

Ok I did some experiments late last night where I paid close attention to the TRAC/LSD operation indicator, throttle position, and engine output. First I found a nearby hill and drove up onto a snow covered curb such that the passenger side wheels were in about 6” of plowed snow and the driver side wheels were on semi-dry pavement. Stuck she was.

In 2wd normal mode the TRAC operation indicator flashed constantly as the passenger rear wheel spun. The driver side wheel did nothing or very very little. I could not feel any forward motion. I also noticed that engine output was dramatically limited even though there was no yaw. I stayed stuck.

In Auto LSD mode the Auto LSD operation indicator flashed repeatedly as the passenger side rear wheel spun. The driver side rear wheel pushed the truck forward in a quick on-off pattern. Engine power was not limited. The more I pushed the throttle down (up to a point) the faster the truck moved forward. I got unstuck.

I tried the same thing in reverse with basically the same results.

Conclusions:

TRAC does operate when stuck. It just doesn’t do a good job of getting the truck unstuck.

TRAC operates in reverse.

TRAC and/or VSC limits engine output even when there is no yaw. The wheels just need to be spinning. Maybe that was obvious to others, but it wasn’t to me until now. I’m not sure if it’s TRAC or VSC doing this. Or maybe they are really just two modes of the same system.

Auto LSD seems to be a bit more aggressive at applying the brakes in addition to not limiting engine output.

 

Beautiful work.
(Guess I was going in the right direction, but we know even better now. I really do think the VSC is super aggressive in limiting throttle, even when there is no yaw rate. I think it acts when it sees that the longitudinal acceleration measured by the accelerometers don't match the drive train speed change it is seeing...)

You have gone this far, you have to do just a bit more.
First try your test again in 4hi. Interestingly, in 4hi the default mode is VSC and TRAC both ON, and then with short VSC-Button press you get VSC ON and TRAC OFF (unlike 2hi)... So in your testing you probably will find 4hi-default to be not too effective, and 4hi-short button press to be even less effective. You have to try and see if you can duplicate the predictions...

You are an OR, so your 4Lo testing will generally not be applicable to the Sport/SR/SR5/Limited trims and you need to keep that in mind. 4Lo for you will default to VSC OFF and TRAC OFF, unless you use Atrac, MTS, etc.... where the other trims get TRAC ON and VSC OFF as the default 4Lo mode.

Then, get all the data together and post it to the traction control sticky.
Come on, DO IT.

 

I’m going to need a steeper hill to test 4wd. And if I can’t get unstuck, will you winch me out? Hah!

 

yes I will, but from Florida, so my winch cable might be a bit short.

Just try it on the existing hill, you might be surprised... (if just to prove me wrong)

 

I tried 3 different hills but I couldn't find one that caused the wheels to spin in 4hi. I was even plowing snow with the bottom of the truck in one case. I'm really amazed how good the TRD OR is in snow compared to the SR5. I assume it's the tires that make the difference.

We're supposed to get 12" of snow on Friday. Hopefully that will present a challenge for the Taco.

 

Oof, so much wrong I’m not sure it’s worth the effort to correct, hopefully people just skip over.

 

Lol which part is wrong?

 

OP, I'm also in Florida. 4HI without my locker engaged has never given me any issues, even on sugar sand with factory tires.

To my understanding, you want to make sure traction control is OFF so that if a wheel starts to slip it doesn't cut power and make you slow down enough to get stuck in a rut. It's happened to me before.

 

The relationship between torque and speed is not equivalent. The torque distribution front to rear in 4wd is unknown but the speed to each diff is equal. Because the tcase outputs front to rear are "locked" it is possible to send 100% of the torque to the front or the rear alone.

Same deal. A locked diff (spool) does not split torque equally left to right on the axle. It has equal speeds left to right, but is capable of sending 100% of the torque to either wheel. In other words, if the diff is locked and the left tire is in the air, the right tire will receive 100% of the torque and apply it to the ground if it can handle it without beginning to slip.

 

TRAC seems to be most active at higher speeds and stopping power induced wheel spin under those conditions. It will intervene to limit power induced wheel slip by cutting engine power and/or braking the slipping wheel/s. IMO, it behaves like traction control without launch control meaning it is not very active at speeds near 0. TRAC will work by referencing the speed of the front wheels and it doesn't seem to like being active with no front wheel speed and one rear wheel with no speed.

The auto LSD is basically more of an all-time anti-wheel slip device that has functionality similar to traction control with launch control by utilizing brakes only with no throttle intervention. Basically it's mimicking a mechanical limited slip diff that does not care about wheel speed at the opposite axle, just wheel speed differential across the axle.

So TRAC in 2wd references front wheel speed to determine rear wheel slip. I believe TRAC in 4wd is just referencing differences in speed across each axle, acting like auto LSD across the front and across the rear. ATRAC is doing the same and looks for wheel speed differential across each axle individually.

 

And to reiterate, an open diff always splits TORQUE equally, ignoring small frictional effects. (If one axle can only receive very small torque because it is slipping, the other axle receives the same small torque).

If both axles have similar angular velocity, power is split nearly equally across an open diff. (Higher speed axle will recieve more power, as power is torque x angular velocity)

 

Just now seeing this thread. I'll add some mentions of these findings to the sticky OP when I get a chance.