When to lock the Torsen center differential (H4L)?

[Bilbo]

I think they've confused themselves. What they're describing is the function of the diff when used on an axle, I think. When used on the tcase, as in your 4Runner, it's not seeing the wheels, it sees the driveshafts. Ergo, it can't direct power to the wheel with the most grip.

How it knows which driveshaft has the most resistance (or "grip"), and what the existence of two wheels on the other side of each open diff does to what the T3 "sees", is beyond me. Reading your blurb, it may be more effective than I thought. But it's still not AWD in the sense that I laid out above. It's not biasing power away from individual wheels that have lost traction.

[MENTION=49649]KidVermicious[/MENTION] I agree with you - the T-3 has no way to sense individual wheel traction or rotation. That was sloppy writing on their part. I think they should have used the term "wheels" or "axle, as in "shifting power to the wheels with the most traction." Elsewhere they correctly describe torque management and differentiation as for the axles, not wheels. And the overall message is clear: the T-3 CD does not behave like a limited slip axle differential.

Whatever the T-3 does, it is torque-based and it is "instantaneously" responsive. And given the alternatives:

1. We have this great new product that increases torque to the axle with less traction, or
2. We have this great new product that increases torque to the axle with greater traction

My money is on #2.

Would you be comfortable if I changed my original post to read "... increase torque distribution to the axle with greater traction"? Maybe there is a better term? Would that leave any further problems in the description of how it operates?

As for the AWD issue, I never used that term nor did I intend to. But perhaps I did imply it. I tried to make it clear that the CD only manages torque distribution and differentiation between the two axles. The axle differentials and the myriad of wheel sensors and such have their own roles to play in managing wheel-on-axle performance.

Ultimately, this will all lead back to thinking about why I would ever lock the CD unless I'm stuck in a ditch. Solutions follow from problem descriptions, or at least I've read that's true. lol

 

[KidVermicious]

... why I would ever lock the CD unless I'm stuck in a ditch. Solutions follow from problem descriptions, or at least I've read that's true. lol

Regardless of of exactly how the T3 works, I think this is a perfectly viable approach, especially if you're not out on four wheeling trails looking for trouble.

 

[KidVermicious]

Your description of "AWD" refers only to a specific type of AWD, which isn't consistent with the majority of AWD systems, as most can't actively transfer power 100%. The multimode awd with the torsen CD is a more capable "awd" system than many other claimed "awd" systems out there.

Ultimately it's semantics. The fact that Toyota has a system that it calls "All Wheel Drive" that is not available on the 4Runner tells me that the 4Runner doesn't have All Wheel Drive. And regardless of what you call it, the otherwise very capable 4Runner with multimode and Torsen center diff is not as capable of maintaining traction on ice as a true All Wheel Drive system, which I will let Wikipedia explain to you:

All wheel drive (AWD) or "permanent multiple-wheel drive" refers to a drive train system that includes a differential between the front and rear drive shafts. This is normally coupled with some sort of anti-slip technology that will allow differentials to spin at different speeds, but still maintain the ability to transfer torque from one wheel in case of loss of traction at that wheel.

Emphasis mine. I maintain that the ability to actively bias power away from a wheel that has lost traction is the defining difference between full time 4WD and standard AWD systems, regardless of what the various marketing gurus at various car companies decide to call their product.

Obviously Wikipedia is not an authority on anything, so if you've got a more authoritative cite defining AWD your way instead of mine, I'll happily defer.

 

[bimrunner]

There's a huge amount of variation between AWD systems, and it's often hard to get good information about how they physically work. Honda/Acura has at least three systems. The lightest is used on the CR-V, and IIRC it used a clutch to send some power to the rear axle, but I don't think it can choose which side it goes to. They call it Realtime 4WD, and it might be useful to keep from getting stuck in some situations, but other than that it's not very useful, and the car is basically FWD. The Pilot and Ridgeline are called 4WD even though they are really AWD, and their system is called VTM-4. It used a pair of clutches in the rear to send power to either the right or left side. From what I've read, it can work well, but sometimes it doesn't activate when you need it. It only works up to a certain speed. Some Acuras have SH-AWD, which can actively split power between the rear wheels to improve handling, even before slipping is detected. I think it's a mechanical system. It sounds like it works really well on the road, but I don't think it's intended for driving off road trails. Subaru has several different systems, and I haven't been able to find good information about which models use which type. Some use clutches and run mostly FWD, and some use viscous coupling, and some might use something else. A lot of small crossovers use a lightweight system like Honda's realtime, but it's hard to find information about how they work, and whether they have anything to control a spinning wheel using the brakes like our 4runners do. Most of them buy the technology from a company like Bosch, so many of them are the same, but they wont tell you. The Highlander hybrid (used to?) have a motor in the rear to make it AWD, which is ideal since there is no mechanical coupling to worry about, but it was only like 60hp, and it tended to overheat. The upcoming Tesla X looks really good.


Here's a thread with some info about the limited slip center (4th gen, but it works basically the same as the 5th Limited) http://www.toyota-4runner.org/4th-gen-t4rs/181476-limited-slip-center-differential.html

I have a 2014 MDX with SH-AWD and it does in fact move power from front to rear and side to side before slippage. It is really only designed to improve cornering on road. I would not take the Acura off-road... as if my wife would let me anyway... It would not be a great off-road vehicle in any sense of term. Acura was designed for a little more performance driven, unibody, semi-luxury family hauler. It competes with Lexus RX350 and Infinity QX60... all of which are crossovers. Works great on road though! Even has a cool indicator as to which wheels are getting the most power real-time. Most of the time it is biased to the front wheels.

 

[crackiswack]

Ultimately it's semantics. The fact that Toyota has a system that it calls "All Wheel Drive" that is not available on the 4Runner tells me that the 4Runner doesn't have All Wheel Drive. And regardless of what you call it, the otherwise very capable 4Runner with multimode and Torsen center diff is not as capable of maintaining traction on ice as a true All Wheel Drive system, which I will let Wikipedia explain to you:



Emphasis mine. I maintain that the ability to actively bias power away from a wheel that has lost traction is the defining difference between full time 4WD and standard AWD systems, regardless of what the various marketing gurus at various car companies decide to call their product.

Obviously Wikipedia is not an authority on anything, so if you've got a more authoritative cite defining AWD your way instead of mine, I'll happily defer.

What you'll notice is that in the video you posted that they all fall under the 4wd label, and the defining feature of the toyota "AWD" is that the system applies brakes to the wheel that loses traction to prevent the loss of power to the other wheel, but thats exactly what the TRAC system does in the 4runner, so again its just an argument in semantics, but regardless of what they call it, its an AWD system. A torsen T3 unit variation is used in many audi quattro awd systems as well.

 

[crackiswack]

BTW, here is a better site that explains the differences between awd systems regardless of is they are referred to as awd or 4wd systems.
All Wheel Drive Explained | awd cars, 4x4 vehicles, 4wd trucks, 4motion, quattro, xDrive, SH-AWD, Haldex, Torsen, wiki - How it works

 

[m85476585]

Ultimately it's semantics. The fact that Toyota has a system that it calls "All Wheel Drive" that is not available on the 4Runner tells me that the 4Runner doesn't have All Wheel Drive. And regardless of what you call it, the otherwise very capable 4Runner with multimode and Torsen center diff is not as capable of maintaining traction on ice as a true All Wheel Drive system, which I will let Wikipedia explain to you:



Emphasis mine. I maintain that the ability to actively bias power away from a wheel that has lost traction is the defining difference between full time 4WD and standard AWD systems, regardless of what the various marketing gurus at various car companies decide to call their product.

Obviously Wikipedia is not an authority on anything, so if you've got a more authoritative cite defining AWD your way instead of mine, I'll happily defer.

A lot of cars they are selling as AWD might not meet that definition. I don't think there is one definition, anyway, except that any of the wheels could possibly be used as drive wheels at some point. Some companies even label their small crossovers AWD or 4WD interchangeably. If I remember right, both the RAV4 and CR-V have been called 4WD or AWD at some point in the past, but they are both called AWD right now.

The system in these crossovers is really very similar to 4runners with a limited slip center differential. The crossovers generally use a clutch to transfer some power to the rear axle sometimes. 4runners use a Torsen center differential which accomplishes the same thing, but works slightly differently. The 4runner uses the brakes to control slipping wheels, which effectively transfers power to the other wheels through the differentials. I don't know if crossovers use the brakes to do the same thing, but they generally don't have mechanical limited slip differentials (some do, but most don't for price reasons). Since most of them use clutches which are electronically controlled, there is some reaction delay after the wheels start slipping. The manufacturers claim there isn't, but there is! 4runners have mechanical limited slip, so front-rear power transfer happens almost instantly (if the rotating parts flex that would add a very slight delay). So our 4runners are more capable than these crossovers.

I test drove a 2005 CR-V on snow, and from a stop the front wheels would definitely spin a bit before the back wheels would do anything. They've probably gotten a bit better since then, but for efficiency they don't connect the rear unless it's needed.

Honda calls their VTM-4 system 4WD, but it's closer to that AWD definition than a lot of the others. The rear propeller shaft always rotates, and two clutches in the rear can send power either to the left or right rear wheel. The front has an open differential, and I don't know if the brakes can be used to control slipping like in Toyotas. It's an elegant, lightweight design, but unfortunately from what I've read the electronics that control it leave something to be desired. They don't react fast enough, and it only works up to a certain speed. The SH-AWD system is similar, but as far as I know it also only works on the rear differential. I believe they also have a hybrid SH-AWD system that uses motors.

From what I've read, our 4runners should work as well or better on snow and ice than most small SUVs. They won't work as well as luxury brands that use mechanical limited slip differentials front and/or rear and have drivetrains and suspension set up for performance and handling. If you care about snow and ice handling, get some winter tires and you will be better off than most cars out there for a lot less money than getting the best drive system. If you want even better than that, you probably need a German car or an Acura.

 

[NoDak]

1. awd will never have a 4L
2. most awd/4wd (Im looking at you rav4) are hybrid designs. they are primarily fwd mode until slip then transfer power to the other wheels
3. the LE is a FT 4wd system
4. Subaru asym awd is like the LE system w/o the 4L
5. the wrx sti is the perfect marriage of 4wd and awd, iirc, they have lockable CD and RD.

this is what I remember from numerous readings across a lot of different post and articles.

 

[JB.]

I don't see how it could be better unlocked especially turning...

I'm making two assumptions, first roads are fully snow packed as stated and second you are on the gas driving through the turn. If it's slick enough for the front to slide the rear would slide just as easy, ie sure a front wheel drive can slide right though but so would a rear wheel drive when it swings out the back end. Isn't the 50/50 split ideal because the wheels are all pushing equally providing the pull traction from the front and the push from the rear? In the 40/60 split it would seam the extra power to the rear axle could increase the chance of kicking out the rear. Please expand if incorrect?

After seeing kidvermicious post, I am thinking in terms of driving through the city not blasting down the road at 55mph+. Is there a difference?

I was just pointing out how it could be better.

What can be said with certainty is that during an unlocked turn, the front wheels will trace a tighter, more precise path within the range of what would be considered a normal, acceptable turn. When the turn starts to get into the range of what might be considered lost control, the comparison gets more complicated.

Given that oversteer is often more dangerous than understeer, it's not a given that center locked will under-perform unlocked during turns in all conditions with all drivers. Ultimately what matters is how the vehicle behaves in each mode under given driving inputs, but the rigid coupling of the front and rear drive shafts that limits front/rear wheel independence during turns is a physical fact with no ambiguity. The real world results of that physical fact can probably be debated until the cows come home considering how many variables are involved.

 

[crackiswack]

1. awd will never have a 4L
2. most awd/4wd (Im looking at you rav4) are hybrid designs. they are primarily fwd mode until slip then transfer power to the other wheels
3. the LE is a FT 4wd system
4. Subaru asym awd is like the LE system w/o the 4L
5. the wrx sti is the perfect marriage of 4wd and awd, iirc, they have lockable CD and RD.

this is what I remember from numerous readings across a lot of different post and articles.

1. Ok, this is an argument in semantics then.
2. Yes, there are a lot of hybrid systems out there, some that work extremely well, see SH-AWD
3. Ok, semantics. So you're saying the only thing that makes is a FT 4wd instead of a AWD is the 4L?
4. So then the LE is AWD with a 4L
5. SOME Stis have a center lock. None had a rear locker, some had an LSD rear.

 

[crackiswack]

I was just pointing out how it could be better.

What can be said with certainty is that during an unlocked turn, the front wheels will trace a tighter, more precise path within the range of what would be considered a normal, acceptable turn. When the turn starts to get into the range of what might be considered lost control, the comparison gets more complicated.

Given that oversteer is often more dangerous than understeer, it's not a given that center locked will under-perform unlocked during turns in all conditions with all drivers. Ultimately what matters is how the vehicle behaves in each mode under given driving inputs, but the rigid coupling of the front and rear drive shafts that limits front/rear wheel independence during turns is a physical fact with no ambiguity. The real world results of that physical fact can probably be debated until the cows come home considering how many variables are involved.

Yep, the problem with locking the front and rear together in turns is more understeer, whereas the unlocked torsen is much more neutral handling in turns. In the case of the 4runner it doesn't oversteer when unlocked or in 2wd at all ime so an unlocked differential performs better in slippery on road conditions and even on dirt roads compared to a lock differential. Locked works better in slow crawling/mud etc

 

[Jhalko]

I was just pointing out how it could be better.

What can be said with certainty is that during an unlocked turn, the front wheels will trace a tighter, more precise path within the range of what would be considered a normal, acceptable turn. When the turn starts to get into the range of what might be considered lost control, the comparison gets more complicated.

Given that oversteer is often more dangerous than understeer, it's not a given that center locked will under-perform unlocked during turns in all conditions with all drivers. Ultimately what matters is how the vehicle behaves in each mode under given driving inputs, but the rigid coupling of the front and rear drive shafts that limits front/rear wheel independence during turns is a physical fact with no ambiguity. The real world results of that physical fact can probably be debated until the cows come home considering how many variables are involved.

I don't totally follow you on some of that, you sound like [MENTION=66316]1engineer[/MENTION], haha. I'm just trying to understand so I can go with whatever is going to give me the best traction generally speaking for the low speed driving around town on snow. Most of my comments come from the thought that leaving the center diff unlocked is going to increase the chance that the rear end can kick out since there is a bias of torque there. When I'm on the highway I never lock it as I'm either moving fast or sitting in traffic. Honestly I drive somewhat conservative so it probably doesn't matter for me, but I want to understand.

 

[Jhalko]

Excluding solid sheet ice, has there ever been a time up in Nort Dakooota when VSC or TRAC have not kept you pointing in the direction you want to go? I find it almost impossible with VSC on to mess it up on normal snow covered roads. Sure, you get the initial beginnings of a slide or push but all of a sudden *poof* (magic happens) and you are not in a guardrail or over the hill, you are going around the turn, albeit slower, because TRAC killed your acceleration.

I'd like to add, the 4Runner traction system is "tuned" so much better then the JGC I owned before, in some ways it's less active, but definitely there. I know some complain about it on the 4Runner and maybe Jeep has improved theirs in the last few years, but man it was scary a couple times driving that Jeep when it kicked in, the rare occasion I notice it on the 4Runner seems helpful. We don't get a ton of ice here in CO though, mostly champagne powder you know.

:trophy:

 

[rigtec]

"This question comes up so often, and there's a lot of confusion about how exactly the multimode 4WD works and when you should be in what mode...

...Does that make a little more sense?..."

"Yes it does KV!"

I always enjoy reading an EXCELLENT essay addressing some of the myths, folklore, and grapevine hearsay that plague our technical community. Thanks for doing that! Rgds,

PS: "Hoping to hear more of that from you!"

rigtec, cheers!

 

[NoDak]

1. Ok, this is an argument in semantics then.
2. Yes, there are a lot of hybrid systems out there, some that work extremely well, see SH-AWD
3. Ok, semantics. So you're saying the only thing that makes is a FT 4wd instead of a AWD is the 4L?
4. So then the LE is AWD with a 4L
5. SOME Stis have a center lock. None had a rear locker, some had an LSD rear.

1. have you ever seen an awd with a 4L
2. I don't consider the Subaru, audi and I forgot the sh-awd. those don't compare to the normal awd/4wd designation that most have where they are primarily fwd until slippage. I blame Toyota with that stupid 4wd plate on the back of the rav4 until they removed it and put awd in its place. they have these hybrids to save gas. if they had a real 4wd system, the mpg would suck.
3. typically 4wd vehicles that have 4L are not considered awd
4. see 3
5. I stand corrected, I guess I misread the dccd on the sti's, for some odd reason I thought I had read they had 2 diffs.

if you put those hybrid awd/4wd systems up against a real 4wd vehicle, guess who usually wins. even on some of the cheaper Subaru's they don't have the same awd system compared to the higher end models. same goes for the audi's, if they have the Quattro drive instead of the haldex systems.

the only downside to the sh-awd is that it was primarily for enhancing cornering on dry pavement and has no center diff. it works without one, but the complexity of doing the same thing as a cheaper center diff is over kill, but that's just me.

but as you said its all semantics in the end, I just look at differently than you.

 

[crackiswack]

I don't totally follow you on some of that, you sound like [MENTION=66316]1engineer[/MENTION], haha. I'm just trying to understand so I can go with whatever is going to give me the best traction generally speaking for the low speed driving around town on snow. Most of my comments come from the thought that leaving the center diff unlocked is going to increase the chance that the rear end can kick out since there is a bias of torque there. When I'm on the highway I never lock it as I'm either moving fast or sitting in traffic. Honestly I drive somewhat conservative so it probably doesn't matter for me, but I want to understand.

Leave it unlocked. The torque biasing won't matter in lower speed conditions because the torque shift is essentially instantaneous. The car will not tend to oversteer when unlocked

 

[JayceeP]

it depends on the road conditions and your level of experience in snow.....

in a slide with 4wd locked you point the wheels in the direction you want to go in a slide, with vsc, this hinders that whereas in a 4hL I just give some gas and go and it pulls me back on my line.

with vsc on, when the brakes kick and adjusts, sometimes this amplifies the slide since that one wheel is locked on ice/snow which doesnt help.

I completely agree. I actually didn't learn until reading another thread a couple of weeks ago that a locked center diff = same as putting a 2wd vehicle in 4wd manually. This is how my Jeep Wrangler 4door worked and I felt it had noticeably more bite in the snow. This year, I will be locking the center diff on snowy days.

itsometimes its better to have vsc and sometimes its not. but only experience would give you the idea of when each applies.

when I first started driving these smart systems, I used them exclusively, but over the last 20-30 years in North Dakota winters, I have learn to work with them and adjust.

I still vehemently tell my wife and daughter to leave those systems on and don't tell them how to disable them between starts. I do show them how to lock the center diff (rav4 or turn off the nannies in the Tacoma) to get up those areas in town that are slick at stop lights/signs, but since its the temp solution, it re-engages after 25-30 mph.

When I had my Jeep I preferred no traction control most of the time when in 4wd. I found it worked really well in 2wd however. I do notice that traction control re-engages in the 4R at those speeds. Is there any way to fully disable the system? In the Jeep if you pushed the traction control button, it turned off. But if you held it for 5 seconds, it turned off everything. That equalled a LOT of fun.

 

[BlackWorksInc]

Most AWD systems don't have a true dedicated transfer case, they just have a tacked on differential. Some of the higher end vehicles actually have a planetary gear set/electronically controlled transfer case to act as a LSD, but that all still falls under AWD.

The reason 4WD and AWD are mainly different is because of the fact that 4WDs have a gear reduction set in them. Most commercial 4WD vehicles only have 4Hi and 4Lo, but some older designs had a gear reduction in 4Hi as well as 4Lo. Aftermarket Transfercases can have additional gearing to further differentiate ratios and become like smaller manual/automatic transmissions.

This is what mainly differentiates 4WD from AWD, is that there are additional gear reductions availible to power all 4 wheels; were as most AWD systems lack this completely or can only provide LSD functionality to try and make up for it.

Sorry if the post is a bit short and vague, but I didn't have a lot of time to fully explain it, I may expand on it later.

 

[ScoMey]

I don't totally follow you on some of that, you sound like [MENTION=66316]1engineer[/MENTION], haha. I'm just trying to understand so I can go with whatever is going to give me the best traction generally speaking for the low speed driving around town on snow. Most of my comments come from the thought that leaving the center diff unlocked is going to increase the chance that the rear end can kick out since there is a bias of torque there. When I'm on the highway I never lock it as I'm either moving fast or sitting in traffic. Honestly I drive somewhat conservative so it probably doesn't matter for me, but I want to understand.

Try as I might, I've never really been able to get the back end of my Limited to really kick out while applying power and turning ... and the one time I did, the VSC nanny kicked in and ended the fun pretty quick. :zoom:

 

[1000MPH]

This is a great post.
:thumb:

it depends on the road conditions and your level of experience in snow.

if the roads have had a few days/weeks of maintenance on them from the city I will leave it off. the first few days is the worse and I will lock the CD and turn off vsc since most of the time I use the 4wd system to pull me into the direction I want to go (it goes back to basics of slides in a fwd, rwd, awd-hybrid, awd-subaru/audi, or 4wd and 4wd-locked).

in a slide with 4wd locked you point the wheels in the direction you want to go in a slide, with vsc, this hinders that whereas in a 4hL I just give some gas and go and it pulls me back on my line.

with vsc on, when the brakes kick and adjusts, sometimes this amplifies the slide since that one wheel is locked on ice/snow which doesnt help.

on the flip side, dropping down gears going down a long steep hill helps slow you down and not slide, whereas using the brakes can engage the abs and cause ever so slight sliding of the rear or whole vehicle out of your line. I had this happen back in the 90's coming down a hill to a set of railroad tracks and only going 15-20 mph, ended up sliding 1/2 down the hill for that move until I figured it out.

last year the warden figured that out finally in her Tacoma, so now she drops down 2-3 gear coming down the hill from work to home.

sometimes its better to have vsc and sometimes its not. but only experience would give you the idea of when each applies.

when I first started driving these smart systems, I used them exclusively, but over the last 20-30 years in North Dakota winters, I have learn to work with them and adjust.

I have driven rwd sedans (no accidents, but fun as hell to slide in an open field), fwd cars (1 slide off the road due to spring slush), Subaru (no accidents), and 4runners (no accidents). now I have had accidents but never due to snow, always during the dam summer months. someone opened a car door as I was driving by (me and warden), backed into the DQ pole (warden, son), forgot to lock the hitch on the uhaul while loading, school riding lawn mower slid into the rear quarter panel of the 98 4runner.

I still vehemently tell my wife and daughter to leave those systems on and don't tell them how to disable them between starts. I do show them how to lock the center diff (rav4 or turn off the nannies in the Tacoma) to get up those areas in town that are slick at stop lights/signs, but since its the temp solution, it re-engages after 25-30 mph.

all the above is first and foremost, dependent on driving for the conditions. doing 70 on a ice covered road, yeah seeya in the ditch or hospital. and if it gets too bad, stay the hell home. which I have done several times and just took vacation time.

good example. back in 1994, I was driving down to texas for USAF cross training. left just before turkey day and headed to I-29 to drive to texas. sometime after hitting the SD border at night, the road had a funny look to it. slowed down to about 20mph, hit the brakes and promptly slid. freaked me out. so I ended up doing about 25-35 mph until I hit watertown, which took about 3-4 hours. during this time frame, one person passed me, guess what he was doing probably 55 mph and all I could think was, that person was crazy driving at that speed on that black ice road.