Crawl control discussion

[bloc]

To add to this technically running without CDL we aren't in 4wd but awd hi or lo. Is the bind really that drastic to warrant not having it engaged though? Especially since the higher mileage 200s tend to have a mind of their own when trying to engage CDL and don't always engage when asked. So for certain terrain it might be smart to engage ahead of time if you know you'll need it (IMO).
I do agree though that our rigs are more than capable with CDL not engaged and just letting ATRAC do its thing. I've been on trail rides where CDL wouldn't engage and I didn't have too many issues because the computer was smart enough to keep traction where I needed it.

The bind probably won’t damage anything on the traction surfaces we are usually using if, but it definitely impacts turning radius, and that is the primary reason I leave it off most of the time.

Then again I also have had no problems with my CDL.. I guess if someone dealt with this a lot leaving it on would have merit. Or leave it off and let atrac handle things

Also since I didn’t see it answered directly TA= turn assist, which isn’t on all years of 200.

I’m curious what differential in percentage outside the 70/30 (or 60/40) specification the torsen will allow before it begins to bind and lock.

anyone know?

I don’t think our torsen-c diff does actually lock without the CDL. It is just a torque biasing diff, with the afformentioned percentages.

 

[highfructose]

The bind probably won’t damage anything on the traction surfaces we are usually using if, but it definitely impacts turning radius, and that is the primary reason I leave it off most of the time.

Then again I also have had no problems with my CDL.. I guess if someone dealt with this a lot leaving it on would have merit. Or leave it off and let atrac handle things

Also since I didn’t see it answered directly TA= turn assist, which isn’t on all years of 200.



I don’t think our torsen-c diff does actually lock without the CDL. It is just a torque biasing diff, with the afformentioned percentages.

I’d be curious to know if this is true...I assumed all torsen diffs are torsen diffs because they are automatically engaging differentials using worm gears to slowly bind and then lock when the difference between two shafts exceeds a certain parameter.

I also assumed that part of the reason our diff has a “locking feature” and not a lock is that it probably does something along the lines of applying a brake of some sort to one of the shafts, thereby causing that differential in speed between them, thereby causing the torsen differential to bind and then lock.

by the same token, if, absent the “locking feature” being engaged, should the differential in speed between the front and rear driveshaft exceed a certain parameter, one would assume our center torsen differential would automatically begin to bind and then lock...since that’s what torsen differentials are designed to do.

I believe old audis, and perhaps newer ones, have such a torsen center differential.

 

[afgman786]

I’d be curious to know if this is true...I assumed all torsen diffs are torsen diffs because they are automatically engaging differentials using worm gears to slowly bind and then lock when the difference between two shafts exceeds a certain parameter.

I also assumed that part of the reason our diff has a “locking feature” and not a lock is that it probably does something along the lines of applying a brake of some sort to one of the shafts, thereby causing that differential in speed between them, thereby causing the torsen differential to bind and then lock.

by the same token, if, absent the “locking feature” being engaged, should the differential in speed between the front and rear driveshaft exceed a certain parameter, one would assume our center torsen differential would automatically begin to bind and then lock...since that’s what torsen differentials are designed to do.

I believe old audis, and perhaps newer ones, have such a torsen center differential.

I can personally say my 200 does not do that. I have had all traction aids off and the center diff unlocked and power was only going to the path of least resistance. I got myself into a situation where only 1 tire did not have traction and all the power went there. Even with increasing wheel speed the rear diff never engaged because all my traction aids were turned off so there was nothing to apply resistance to the front wheel that had no traction.

 

[highfructose]

I can personally say my 200 does not do that. I have had all traction aids off and the center diff unlocked and power was only going to the path of least resistance. I got myself into a situation where only 1 tire did not have traction and all the power went there. Even with increasing wheel speed the rear diff never engaged because all my traction aids were turned off so there was nothing to apply resistance to the front wheel that had no traction.

Interesting. It may be the case that the center torsen diff allows quite a bit of differential speed between the driveshafts before it will engage. Maybe it never automatically locks even though, technically, torsen diffs are supposed to have that capability.

 

[M1911]

Theoretically I would tend to agree.

Also at issue is that, technically, the center diff is a torsen...meaning even if you don’t engage it via the “locking feature,” there is only a certain amount of slip that it will allow before it “automatically” locks itself at least somewhat...unless I misunderstand the nature of our torsen center differential.

No, that's not how a Torsen works.

The Torsen tries to send torque to both output shafts. If resistance on one shaft reduces (i.e., both front tires are on a slippery surface), it will try to send torque to the other output shaft. However, limited slip diffs are "limited". That is, they can muster up a limited amount of torque differential. If the difference in torque is too much, they end up behaving like an open diff. So if you lift both front wheels off the ground, an unlocked Torsen center diff isn't going to get you moving.

No, Torsen diffs don't "automatically" lock themselves. A Torsen diff in normal operation always sends torque to both output shafts. It isn't like a typical AWD center coupling that has electric clutches. In those center couplings, typically one shaft isn't turning at all until the system senses the front wheels slip. Then it locks up and sends power to the rear shaft, but only after the front has slipped. A Torsen is different -- it sends power to both axles in normal operation. But a Torsen doesn't automatically lock.

 

[M1911]

I’m curious what differential in percentage outside the 70/30 (or 60/40) specification the torsen will allow before it begins to bind and lock.

anyone know?

You misunderstand Torsens. Torsens do not automatically lock. They only lock when you press the button.

 

[M1911]

Interesting. It may be the case that the center torsen diff allows quite a bit of differential speed between the driveshafts before it will engage. Maybe it never automatically locks even though, technically, torsen diffs are supposed to have that capability.

No, that is not how Torsen's work. Torsens are ALWAYS engaged. But they only lock when you press the button.

 

[TeCKis300]

Couple characteristics of Torsens
- not capable of fully locking so it will never transfer 100% torque, hence the ability to manually lock the center diff enabling 4x4 funciton
- If no load at all on one axle, it functions as an open diff. It's tor-sen or torque-sensing, and needs some load in order to bias any torque.

 

[linuxgod]

Couple characteristics of Torsens
- not capable of fully locking so it will never transfer 100% torque, hence the ability to manually lock the center diff enabling 4x4 funciton
- If no load at all on one axle, it functions as an open diff. It's tor-sen or torque-sensing, and needs some load in order bias any torque.

Interesting. I thought the torsen center diff was limited slip? I thought if you break a CV and pull the front driveshaft you lock the center diff because you didn't want to overheat the torsen center diff, but I thought you'd still move (just with most of the power being dumped into the front shaft). I didn't realize it actually operated like an open diff at that point when there's no resistance.

No video handy but I suspect locking the center diff is similar to a rear elocker. In the transfer case it's driven by the actuator rod which locks the gears together, whereas in the latter case it's a smaller version in which the pin (actuator) pops out and engages when electrified.

 

[TeCKis300]

Interesting. I thought the torsen center diff was limited slip? I thought if you break a CV and pull the front driveshaft you lock the center diff because you didn't want to overheat the torsen center diff, but I thought you'd still move (just with most of the power being dumped into the front shaft). I didn't realize it actually operated like an open diff at that point when there's no resistance.

No video handy but I suspect locking the center diff is similar to a rear elocker. In the transfer case it's driven by the actuator rod which locks the gears together, whereas in the latter case it's a smaller version in which the pin (actuator) pops out and engages when electrified.

You're still correct that It is a type of limited slip. Just pointing out that it needs some load in order to function as such. The more load and speed differential there is, the more torque it will bias.

 

[slowride]

I am a physicist, but only undergrad. Nothing interesting happens until post-doc.

I did hear a tree fall in the forest last time I was there.

At some point if you open your mind and eyes you will discover, we humans are no smarter than your favorite pet poodle compared to the intelligence of the universe.

Harness /control gravity and travelling to the other side of the universe will be quicker than a McDonald's drive thru.

That's why UFO's don't have bathrooms.

Peace.

 

[M1911]

Interesting. I thought the torsen center diff was limited slip? I thought if you break a CV and pull the front driveshaft you lock the center diff because you didn't want to overheat the torsen center diff, but I thought you'd still move (just with most of the power being dumped into the front shaft). I didn't realize it actually operated like an open diff at that point when there's no resistance.

Limited slip differentials can only handle a certain range of torque difference between the two output shafts. Once that difference is exceeded, all the torque goes to the output shaft with the least resistance. This is true in the Torsen as well. That is why our Torsen's are lockable. If the Torsen could automatically lock, forcing the front and rear driveshafts to spin at the same speed automatically, then there might be no need for a manual lock.

See: Torsen - https://www.awdwiki.com/en/torsen/#:~:text=They%20limit%20high%20differential%20rotation,to%20one%20of%20the%20axles.

 

[bloc]

On top of all of this, a Torsen type 3 is different than what goes into axle differentials, and is often designed to bias more torque to the rear than the front. An analogy would be if you put this type into an axle diff it could send more torque to the right tire than the left under acceleration.

Also @bjowett would probably be the expert here but many toyota e-lockers don’t technically lock both axle shafts together, they usually lock one axle shaft to the diff carrier and the spider gears transmit the torque to the other axle shaft. This is much more common than actually locking both shafts to each other. I’m assuming our CDL works the same way, but not totally sure.

 

[TeCKis300]

On top of all of this, a Torsen type 3 is different than what goes into axle differentials, and is often designed to bias more torque to the rear than the front. An analogy would be if you put this type into an axle diff it could send more torque to the right tire than the left under acceleration.

Yup, and I was trying to find documentation on what the standard torque split was. Still trying to find it and there was some bits that suggested 40:60, but need to confirm. Also there could be some documentation that states max torque bias.

 

[JohnPW]

Limited slip differentials can only handle a certain range of torque difference between the two output shafts. Once that difference is exceeded, all the torque goes to the output shaft with the least resistance. This is true in the Torsen as well. That is why our Torsen's are lockable. If the Torsen could automatically lock, forcing the front and rear driveshafts to spin at the same speed automatically, then there might be no need for a manual lock.

See: Torsen - https://www.awdwiki.com/en/torsen/#:~:text=They%20limit%20high%20differential%20rotation,to%20one%20of%20the%20axles.

Yes but in that case the ATRAC would brake the free spinning wheels and you would move. You don’t need to lock the center diff as MTS would prevent the problem. Maybe that was obvious but I had to think it through. I still don’t understand the scenario where a locked CDL is offering an advantage over MTS/Crawl.

Yup, and I was trying to find documentation on what the standard torque split was. Still trying to find it and there was some bits that suggested 40:60, but need to confirm. Also there could be some documentation that states max torque bias.

Toyota brochures for the 200 claim a 40/60 rear bias. I can’t find much in the owners manual

 

[grinchy]

40/60 split is confirmed

Transfer section of the 2009 new car guide for the LX570 attached.

 

[linuxgod]

 

[M1911]

Yes but in that case the ATRAC would brake the free spinning wheels and you would move.

I was only commenting on the behavior of the center diff. The traction control system is an independent system from the center diff.

 

[kcjaz]

The bind probably won’t damage anything on the traction surfaces we are usually using if, but it definitely impacts turning radius, and that is the primary reason I leave it off most of the time.

Then again I also have had no problems with my CDL.. I guess if someone dealt with this a lot leaving it on would have merit. Or leave it off and let atrac handle things

Also since I didn’t see it answered directly TA= turn assist, which isn’t on all years of 200.



I don’t think our torsen-c diff does actually lock without the CDL. It is just a torque biasing diff, with the afformentioned percentages.

CDL impact to turn radius confirmed: Turn assist test. I tend to leave my CDL locked on a trail and only unlock if I really need to for a turn. My CDL is sometime a little finicky and doesn't want to go back in. 4L but CDL unlocked is just AWD and doesn't cut it when loosing traction on a one or the wheels.

 

[M1911]

CDL impact to turn radius confirmed: Turn assist test. I tend to leave my CDL locked on a trail and only unlock if I really need to for a turn. My CDL is sometime a little finicky and doesn't want to go back in. 4L but CDL unlocked is just AWD and doesn't cut it when loosing traction on a one or the wheels.

On the beach, I lock the center diff right away. But on off-road trails, I don't lock the center diff unless I think I will need it. When offroad at a couple LCDCs, I can remember only once or twice that I needed to lock the center diff.