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Toyota 4WD systems explained

2487 messages,  Last post on Apr 28, 2012 at 12:48 PM

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What is this discussion about? Toyota Sequoia, Toyota Highlander, Toyota 4Runner, Toyota Land Cruiser, Toyota RAV4, Toyota Tacoma, Truck, SUV

Messages Page 214 of 250

#2122 of 2487 Re: RAV4 .vs. Subaru AWD [hdfatboy] by 2toyotas

Jan 14, 2008 (10:59 pm)

Replying to: hdfatboy (Jan 14, 2008 9:03 am)
You should really know more about Toyotas 4WD Systems before commenting. First, the Torsen Center Differential has been in the 4Runner since 2003, and in the Sequoia since 2005. Second ALSD only operates in 2WD, and is engaged by pressing a button. All other times TRAC is on, and works at any speed. TRAC will brake the slipping wheel and cut engine power for stability, which is what you would want above 35 mph. ALSD will brake the slipping wheel to give equal power to each wheel. When these vehicles are in 4WD ATRAC operates at all speeds on both axles. When the center diff is unlocked the Torsen will split power 40 front and 60 rear in normal driving, and up to 53% of power can go to the front, and 71% can go to the rear. ATRAC will brake spinning wheels and cut engine power for stability. When the Center Diff is locked power is split 50/50 and ATRAC will just brake spinning wheels, it does not cut engine power. When LOW range is engaged ATRAC does not cut engine power, and brakes wheels to keep driveability, instead of stability. This is on both front and rear axles, and is said to be equal to a vehicle with the center and rear diffs locked. A Sequoia, 4Runner, or Land Cruiser/LX570 will go farther without getting stuck than any Cadillac,Denali,Audi, or Subaru.

#2123 of 2487 rav4 by kurtamaxxxguy

Jan 15, 2008 (8:37 am)

To recap, 2toyotas, how does the RAV4s' 4WD system work?
Is it similar to the 4runner?

#2124 of 2487 Re: RAV4 .vs. Subaru AWD [hdfatboy] by nedzel

Jan 15, 2008 (9:27 am)

Replying to: hdfatboy (Jan 14, 2008 9:03 am)
"The new system in the 2008 LC, Sequoia, LX570, 4Runner and LS600h uses a mechanical LSD for the center differential which is not the case in the 4wd systems of Toyota's lower priced vehicles or last year's models.
  
This newer system does not exist on most of their older models (I think it was on the older 4Runner models)."
 
All of the 4th generation 4Runners (from 2003 on) have a lockable Torsen center differential. The same is true of the GX470. I believe that the previous generation LandCruiser and LX470 also used the same lockable Torsen center diff.

#2125 of 2487 Re: rav4 [kurtamaxxxguy] by nedzel

Jan 15, 2008 (9:30 am)

Replying to: kurtamaxxxguy (Jan 15, 2008 8:37 am)
No, it is NOT similar at all to the 4Runner. The 4Runner has a lockable Torsen center differential and a low-range. The RAV4 is a FWD vehicle until the rears slip...

#2126 of 2487 Re: RAV4 .vs. Subaru AWD [2toyotas] by hdfatboy

Jan 15, 2008 (11:45 am)

Replying to: 2toyotas (Jan 14, 2008 10:59 pm)
2toyotas,
Exactly what references did I make that were incorrect? I stated that the 4Runner had a Torsen Center differential prior to 2008. According to Toyota's press releases on the '08 Sequoia, the Torsen Center Differential was added to the Sequoia this year. I would welcome any information suggesting the Sequoia had a Torsen Ctr Differential since 2005 as I have been unable to find such information.
 
I made no reference to ALSD or TRAC. I simply stated that the Toyota system does not transfer torque across the rear axle upon slippage above 35mph. This is an accurate statement however I would again welcome any resource you have suggesting otherwise.
 
The addition of the mechanical center differential to the Sequoia, LX570, Land Cruiser and LS600h are an acknowledgement by Toyota that it is a better system than they used in the previous year's 4wd system. Why do you suppose they added a mechanical center differential when most of Toyota's 4wd systems have had open diffs in the front, center and rear prior to 2008? It clearly is a more expensive design however its also a better design for on-road 4wd operation.
 
I'm quite familiar with the system in the Sequoia and I believe the '08 design is a far better system than the previous design. The fact that the new system maintains a variable but minimum amount of torque to the front wheels when in 4wd hi (center diff unlocked) is only possible because they added the Torsen Center Differential which did not exist on any other vehicle in the Toyota lineup prior to 2008 (other than the 4Runner). This "AWD" mode with a minimum amount of torque always going to the front wheels could not have been achieved without a mechanical center differential.
 
My point regarding the new Toyota 4wd design was specific to on-road traction and that most of the top-line brands have had a mechanical center differential for years. Toyota's addition to the list is a good thing. For the same reason they added a mechanical center diff to their system, I wish they had also added a mechanical limited slip diff to the rear. As I shared earlier, most if not all of the major brands include a limited slip differential on the rear of their higher end 4wd vehicles. Most engineers consider a liquid viscous diff., mech. LSD and electronically locking rear differentials as all being superior to an open differential with TRAC or any other type of system that utilizes the braking system solely to distribute torque.
 
I would much rather have a system that starts with a mechnical LSD and fine-tunes traction with an electronic reverse braking system such as ATRAC. Toyota added a mechanical center differential because with the 5.7 they have added 105hp to the Sequoia/LX570/LC drivetrain that did not exist in prior years. Trying to manage over 400ft/lbs of torque with an electronic system is not practical which explains Toyota's conversion to a system used by most other brands. I just wish they had taken it to the next step and added a second Torsen to the rear differential.
 
BTW, I hope your appraisal of the Sequoia's ability to "go farther without getting stuck" is accurate as I just ordered a Black/Red Rock Platinum Sequoia with delivery expected in early Feb.
 
Here’s an interesting video on the rear differential and A-LSD in operation on the 2wd Tundra as compared to a 2wd Chevy with a locking rear differential. Its an exaggeration to some degree however it does highlight the limitations of a rear open diff with A-LSD vs a mechanical locking rear diff.
http://www.youtube.com/watch?v=Z8PpZF77tgk
 
Here’s the press release on the new Sequoia drivetrain.
http://www.pressroom.toyota.com/Releases/View?id=TYT2007110908452

#2127 of 2487 Re: RAV4 .vs. Subaru AWD [nedzel] by hdfatboy

Jan 15, 2008 (12:57 pm)

Replying to: nedzel (Jan 15, 2008 9:27 am)
Based on the recent announcements from Toyota, the Torsen center diff has been newly added to the LX570, Land Cruiser, Sequoia and LS400h for 2008. The LX570, LC and Sequoia had (lockable) open center differentials prior to 2008. If anyone can provide a resource suggesting these vehicles had mechanical center LSDs before 2008...please share. (The only Toyota vehicle I have found information on that included a lockable center Torsen LSD prior to 2008 is the 4Runner).
 
Prior to 2008 the Sequoia, LC and LX470 had locking center differentials, however when the ctr diff was unlocked it was essentially an open diff. This design is significantly different from the 2008 design which is a locking design that still retains a limited slip capability when it is unlocked.
 
2008 LS400h http://pressroom.toyota.com/presstxt/2008lexuskit/2008LS600hL_sf.pdf
2008 Sequoia http://www.pressroom.toyota.com/Releases/View?id=TYT2007110908452
2008 LX570 http://jalopnik.com/336324/details-out-for-2008-lexus-lx-570-ndash-the-classy-wa- y-to-overcompensate
2008 LC http://www.caranddriver.com/previews/14080/first-drive-2008-toyota-land-cruiser-- high-tech-suspension-page3.html
 
Here’s a technical paper from Toyota on why they designed LC 4WD transfer case – VF4AM - for 2008 to incorporate a Torsen-C limited slip differential. This is the same transfer case used in the Sequoia, LX570 and LC. I believe the LS400h and the 4Runner use a different center Torsen unit from the 2008 LC, LX570 and Sequoia. As outlined in the article, the previous LC had an open center differential and relied solely on A-TRC for front/rear torque distribution. The article points out that traction is enhanced when A-TRC is used in combination with a Torsen differential. This means that torque transfer has been improved when transferring front to rear with the new design. Unfortunately it also means that the current design with an open rear diff using only A-TRC is not as good at transferring torque from left to right compared to a system that would have combined a Torsen rear diff with A-TRC.
http://www.cuneoclub4wd.it/fram1/rubriche/toyota/toy2/trasmissione.pdf
 
A Torsen rear diff would have added cost but would have resulted in a better 4wd system for on-road use. Namely… 2sp transfer case + lockable Torsen Ctr Diff. + Torsen rear diff. + A-TRC. The Chevy system includes the 2sp transfer case + lockable torsen ctr diff + auto-locking rear diff + electronic traction control. IMO the Chevy design is still a somewhat better 4wd setup for flexibility and road use, however the new Toyota 4WD system is definitely better than the prior year’s models used in the LC, LX470 and Sequoia with open center differentials (as their own technical paper confirms).

#2128 of 2487 e by trebor129

Jan 15, 2008 (3:20 pm)

The 1997 and newer Hummer H1s have 3 LSDs *and* also have an electronic slippage and wheel braking system. This sounds like the ultimate in design.
 
Toyota claims having an open diff front and back is more reliable as LSDs fail more often. Perhaps, or perhaps it was just to save money.
 
I would like to have 3 Torsen units. Torsen is a family of systems and you can get them in various designs with different behaviors.
 
We had 6 inches of snow yesterday and I tested the new 2008 Sequoia up our driveway. Our 2006 Honda minivan cannot get up it. The Sequoia had a lot of trouble in 2WD mode but I could probably get it up with skill and momentum.
 
I could detect no difference in performance between 4WD and 4WD with the center-diff fully locked.
 
I also tried to wiz around corners on icy roads and also doing hard braking while turning, and the truck never spun out. I think that was the stability control working. I unfortunately did not try it with it turned off.

#2129 of 2487 Re: e [trebor129] by hdfatboy

Jan 15, 2008 (5:30 pm)

Replying to: trebor129 (Jan 15, 2008 3:20 pm)
I've had 4 vehicles with mechanical rear LSDs. Each of these vehicles were driven between 80K & 120K miles. I've never had a failed mechanical LSD and never had to have any service work to them. There is no scheduled maintenance on any mechanical LSDs in the Chevy line-up for 100K miles. I've also never even met anyone that's had a failed LSD or heard of anyone with a failed mechanical LSD although I'm sure it has happened,
 
While I'm confident the failure rate of a LSD is higher than an open diff, I believe failure of any modern differential is nominal when used in normal road conditions (not off-roading, snowing plowing or extreme towing).

#2130 of 2487 Re: e [trebor129] by wwest

Jan 15, 2008 (6:06 pm)

Replying to: trebor129 (Jan 15, 2008 3:20 pm)
"....*and* also have an electronic slippage and wheel braking system."
 
Does it make any sense to have both? I would think the virtaul (braking) LSD would be so quick acting that a mechanical LSD would NEVER come into play...
 
When a manufacturer says a vehicle has LSD but doesn't define the type how do you know which it is?
 
Spring-loaded friction clutch pak?
 
Viscous fluid?
 
Torsen?
 
Electronic via brakes?
 
Not talking LOCKING diff'l here, only LIMITED slip.

#2131 of 2487 Re: e [hdfatboy] by wwest

Jan 15, 2008 (6:09 pm)

Replying to: hdfatboy (Jan 15, 2008 5:30 pm)
For probably 99% of owners a rear LSD could fail and they would never know, notice. Maybe even greater than 99% since you have to have a need for a rear LSD in order to notice it isn't working and just how often does the average owner really NEED a rear LSD..??

Messages Page 214 of 250

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