AUTO LSD (or Not) for added traction in 2WD?

I deleted my post. I misread his post so my response was not really applicable.

 

Possibly... But I still made it out. My post probably doesn't belong in the AUTO LSD thread but just wanted to share my experiences.

 

oh...

Yeah, I saw the video too and honestly wasn't too impressed. Those don't look like donuts to me. It looks like he's driving in circles. If those are donuts in the video posted, I can do donuts in my mom's mini-van.

 

Mechanically, if you have one wheel in the air, a rear locker will transfer 100% of the available torque to the wheel with traction. The rear locker forces both wheels to spin at the same speed.

If you completely stop the free-air wheel, then the differential acts like a 2:1 overdrive. With the fully braked free-air wheel not moving, the driven wheel will have half the torque but twice the rotational speed as it would with a locker.

Auto-LSD seems to pulse the brake on the free-air wheel, right? I am inclined to think that perhaps this falls somewhere in-between the locker and fully-braked examples above. I would like to see a torque graph for each rear wheel when A-LSD is in operation...I suspect that you would see the torque on the driven wheel pulsing from less-than-half to more-than-half of the available torque. There's a lot of factors that would have to be taken into account to model the torque in a simulation...

 

I'd bet you wouldn't. I'm betting that at any instance in time you would find the same amount of torque at both wheels. It is still an open differential, so both wheels receive the same rotational force, regardless of their respective angular velocities.

 

When one wheel is braked, the differential is a 2:1 gear set. Half torque, double speed.

The reason I think it will spike above the "half torque" level is that when you unbrake the low-traction wheel, the drivetrain speeds up. When you brake the low-traction wheel, the rotational inertia of the drivetrain (other than the braked wheel and axle) would be dumped into the wheel with traction.

 

That's if you happen to have no traction at both sides. ALSD is not about magically creating traction, it's about using what is available. ALSD makes a huge difference in daily driving, especially in the land of 5 months of snow...... BTW I don't carry sandbags either, BFG's AT's and ALSD will get you just about anywhere there is a road, (in the winter).

 

Angular momentum is not torque. The torque that has been converted into rotational momentum, in say the driveshaft, will be reduced by any opposite torque, like the sudden braking of the wheel. If you look at the changing angular momentum over a fixed amount of time as a vector, it would be opposite of the torque produced by the wheel being braked. Angular momentum is conserved only until outside torque is introduced.
Besides that, any additional resistance experienced by the spinning wheel is going to instantly increase the total available torque in the system, and it is going to be split equally by the differential.

 

Well yes... that's exactly what I was saying.

Dude I've lived in Montana for 3 years, I think I know a thing or two about snow. The fact is I highly doubt a 5 lugger has A/Ts on them. The post said, he saw no difference and I'm inclined to agree based on my experience.

Where I live, once it snows, the roads don't get plowed and you will not get anywhere without weights in the bed. ALSD or Lockers don't help at all since most of the time you are on packed snow or snow covered ice.

You are probably lucky enough to live in a place where they actually plow roads after heavy snow storms or not get storms that last for days. "Just about anywhere" is not everywhere. I was responding to a comment about situations/locations where ALSD makes no difference. (i.e. "when stuck in snow")

I'm not saying ALSD doesn't work, just saying 4x4 is the way to be on packed snow/ice if you have an empty bed.

 

Angular momentum produces torque when opposed, which is what happens when the spinning wheel is braked. The force that slows the driveshaft and engine comes from the ring gear and carrier. If one side gear is held in place by a brake, then all of the torque applied to the carrier will be split, resulting in torque on the driven wheel. The total torque available to that wheel will be half of the engine output torque plus half of the torque required to reduce the angular momentum of the drivetrain from its previous level.

This is why I think you would see a pulse of torque to the driven wheel higher than simply half of engine output torque.

 

Yeah, I see what your saying. There would be a difference in the net torque at each wheel due to the one being braked deducting what it sees from the rotating mass of the ring gear and carrier. I think if you were operating at a fixed torque level it would happen. But the applied torque is going up the instance it sees an increased opposition. I think this would cover up any spike because that spike could only equal the applied torque and the relatively small amount of torque from opposing the rotating mass of the carrier and ring gear. IDK and could be totally wrong. I don't know if you could measure it either. Good discussion either way.

 

It is great when techies begin to discuss the science and mechanics involved!
I may be slow to learn, but once I 'get it', I think I am good for life!

IF all the torque coming to the back differential is diverted to one wheel (because the other is braked)... would that one wheel have 100% torque if the other wheel is 100% braked? If not, is torque frozen by a braked wheel simply 'lost'?

Another question... Are there any more of you 2WD Tacomans who became stuck or stalled, but got free by turning on the AUTO LSD? This question could be answered by 4WD Tacomans who stayed in 2WD.

Thanks for all the replies!

 

And what I'd like to do more than anything else on the topic is to team up with you and go Mythbusters on it.

 

With one wheel totally braked, the differential is like a 2:1 overdrive for the remaining wheel. It cuts the applied torque in half, but doubles the rotational speed.

 

Thank you!

 

seems to follow, trac is just what you're trying to do with auto LSD. Its just helping regulate your foot. If you're trying for brute spinning force, you can either hit the auto lsd button or just keep your foot in it.
The end result would be very similar and downright untestable in the real world.

and yea.. don't try to destroy energy.

 

This is what I was doing on my ATV and I can confirm that it works.

Didn't try on Tacoma, but I don't see why it wouldn't work.

 

I'm going to do you a favor and clear up the "poor man's locker" aka the ebrake for offroading. among other things.

it was developed for people with torsen (torque sensing) differentials. torsens work by tansfering torque by multiplying, lets say 5. so it sends 5 times the available torque to the wheel with the most traction. if your wheel goes in the air, 5 times 0 is 0 and the torsen is now a open diff. pull the ebrake or apply the brake and the torsen will now send power to both wheels with more going to the wheel with the most resistance (traction)

also, a locker is far superior to a alsd. one, the locker locks both wheels together so in order to spin one wheel you need to brake it's traction and the traction of the other. it will always send 50% of engine torque to both wheels and doesn't really hurt turning radius imho.

I always use it as it disables all the electro crud that causes accidents offroad. I've used it at 70mph. the 5mph warning is to protect toyota if you brake something on your truck as a locker will put severe stress on parts when traction on both wheels is present.

as for sand, my truck with tires aired up will go through deep sand, glamis, in 2wd locked (gotta love locker mod). trac and atrac work great on dirt, but are severely flawed in sand.

to drive sand you need momentom, wheel spin, and always on throttle. trac stops wheel spin fast and digs you in. my truck does way better in deep sand with vsc disabled 4x4 than it does with it enabled. even my old silverado with its autolocking rear diff would go through sand in 2wd as long as you kept speed up and power flowing.

trac's flaw is that it slows down your tire to send power and that will dig you in, it is no where near a replacement for a true LSD which can keep power transfering without interferring with momentum. a torsen differential would be much better as it does not affect steering, nor momentum, wich is why hmmwv's use them on all 3 diffs. my old jeep used hydraulic pumps in each wheel to send pressure to a center clutch to apply power away from the wheel that is spinning, it had this in all 3 diffs, it was called quadra drive and it worked amazing if you knew how to use it (needs a bit of wheelspin to work, open diff'ness of take off, keep pedal down and it will find traction almost immediately)

actually, by completely stopping a wheel from moving, you would redirect 100% of engine torque to the opposite wheel.

think about it this way, one wheel on road, and one on ice. no brakes, give it gas, will you move? no. there for, 0% of engine torque is applied to the wheel with the traction, otherwise you would have moved.

this is how open differentials work. and if you know how a open diff works, you would know that by stopping a wheel, you are making the spider gears rotate around the axle shaft and completely bypassing the wheel with more traction

oh, and a little afternote, a locker in sand kind of sucks. when turning the inside tire will spin at the same rate as the outside one thus making it dig into the sand and sink.

if you use a locker in deep sand, please refrain from slow sharp turns

 

What I discovered the first time I took my 2010 truck to Baja was that (with TRAC in 4WD) I could drive the deep beach sand without lowering my tire pressure. My previous two Tacomas (open differentials) could not do this at 32 psi. It was crystal clear that TRAC offered a true traction improvement over open differentials in that situation.

As you may know, TRAC in 4WD-High has no engine regulation as it does in 2WD. So, I will presume your research is all in 2WD.

AUTO LSD is simply TRAC in 2WD with no engine regulation. The way it gets both tires to have torque is if one does begin to spin faster than the other, brakes are applied to the free tire enough to equalize them.

Since I can only lock the rear end in L4, as a 4WD Tacoma I cannot compare AUTO LSD and a rear locker in 2WD. (unless I do the relay mod)

I can only compare the three: Open Differntial (VSC OFF Mode) to TRAC (standard mode) to AUTO LSD (TRAC OFF Mode).

I have done this in sand and found the AUTO LSD caused BOTH rear tires to kick up rooster tails and it was quite impressive.

 

Then there was something wrong. There are plenty of trucks with open diffs that manage to drive fine with out tire deflation.