Center diff engineering explained? (1 Viewer)

[Number6]

I was reading on another elsewhere forum that the CDL and the ATRAC system are really just another AWD system. Here, there was an ok, if brief and general description of how the center diff works and how it differs from a Torsen or fluid coupling, buried somewhere in a forum topic, but I cant recall where it is.

The description told me enough to know that the full time system in 100's is not just AWD. AWD drive systems, to my knowledge do not offer 50/50 torque splits, do not lock, nor offer any kind of 4L/4H range option. AWD systems are fully automatic with no input available at all from the driver (although recently some systems allow to disconnect the AWD and go to 2WD). They do not have the versatility or control of Toyota's full time 4wd

AWD systems, as I understand, use a fluid coupling or Torsen as a center diff- with Torsens usually found on higher end vehicles. Land Cruisers use an entirely different center diff design that makes it a "true" full time 4wd with a full time 60/40(?) torque split.

Please explain- and if I'm wrong on something correct me- the 100's center diff design and operation. Feel free to go in the weeds here.

 

[Skidoo]

The 100 center diff is just like the diffs in front and rear with spider gears, so torque split depends on tire traction. If a tire looses traction more torque goes there. Below shows pinion gears of spider in transfer case. Once center diff is locked you have the 50/50 split. ATRAC brakes slipping wheel trying to keep torque balanced.

 

[bucfl]

Love full time 4wd here in Florida especially now in rainy season.

 

[BullElk]

I think Fulltime 4WD is one of the best things vehicle manufacturers have ever done (with DRLs a close second). The Land Cruiser was sporting the fulltime 4WD in 1990 if not sooner. Now nearly every car has it like they invented it.

 

[Somebodyelse5]

I don't think the LC's center diff has a 60/40 split, I believe it is essentially on open diff that will send power along path of least resistance. Once the diff is locked, it is a true 50/50 split.

 

[uHu]

To call a locked diff a 50/50% split is debatable. If it's locked, there is no split, it's actually 100%/100%. That is: if the CDL is locked, and the RDL is locked, you can get 100% of the power to one rear wheel in the most extreme case. If both the CDL and RDL were 50/50, you would get only 25% to that one wheel.

 

[Number6]

I should clarify some. The split I bring up would be between the axles, not the wheels. By 60/40 I mean a 60% rear axle/40% front axle split.

I'm here to learn, so I'm glad to be corrected on anything.

 

[BullElk]

Seems like even front to back would still be 50/50. The CDL is just joining the two into one happy contraption. No??

It still boggles my mind why Toyota ever made a 4WD system to send all power to the very wheel you don't want to spin....the one with NO traction.

 

[bucfl]

Isn’t that what limited slip is unless you have a locker.

 

[Njck22]

The 100 does not have a viscous coupler. No 60/40 split.

The 80 T-case does, along with locking. For the 80 series that means with the center diff unlocked, you still will get power to both front and rear axles(unequal), but the coupler makes slipping possible to drive on-road without damage. Lock it, and both the driveshafts get equal power (locked together).

For the 100, it is an open center differential normally, meaning one drive shaft can stop or slip without any limit. Locking the center diff links to two axles, hence equal power.

Seems like even front to back would still be 50/50. The CDL is just joining the two into one happy contraption. No??

It still boggles my mind why Toyota ever made a 4WD system to send all power to the very wheel you don't want to spin....the one with NO traction.

That is really just the nature of robust mechanical 4wd systems. Wheels and driveshafts have to be able to slip to allow the vehicles to corner on grippy surfaces. The 80 series used the coupler to eliminate this problem, while the 100 uses electronic braking systems.

Other vehicle manufactures use more complex transfer cases, made possible by electronics, but I reckon that none are as reliable and robust as the Toyota systems.

Here's a video I found that shows the 100 series on various tests to see if the electronic aids really work.

 

[BullElk]

The 80 series used the coupler to eliminate this problem, while the 100 uses electronic braking systems.

Except for the '98-99 correct?

 

[Njck22]

Except for the '98-99 correct?

Yes, but they had rear diff locks correct? I think the electronic system works well enough to where the rear diff lock was no longer a necessity.

 

[BullElk]

Agree but how does the '98-99 system without CDL and rear locker engaged compare to the 80's design without CDL engaged?

 

[white_lx]

This is a great 'engineering' video. Mostly talks about the Torsen LSD center diff (as in the GX470), but at around 29min into the video the open center diff and ATRAC are discussed.

 

[Njck22]

Agree but how does the '98-99 system without CDL and rear locker engaged compare to the 80's design without CDL engaged?

Without the center differential locked, The 80 series design would be superior in an off road or slippery surface comparison. The 80 would send power to both driveshafts, but it would still be limited by the open front and rear differentials. If one wheel or two wheels on the same axle of the 80 did not have traction, it could get out. If one wheel on each axle did not traction, the 80 would be stuck.

The 100 without CDL but with rear locked would mean if one or both front wheels lost traction, or both rear wheels, it would be stuck.
If one rear wheel lost traction, then it would not be stuck.

A 100 without CDL and without rear lock and without Atrac would be stuck as soon as one wheel lost traction.

But, this seems a bit unrealistic as simply locking the center diff would prevent the above situations

 

[krice118]

Best way to underatand this is to go drive in loose dirt, mud or snow with CDL off. Then do it again with cdl on.

With CDL on you have much better control. I agree with the above, there is no split when the cdl is off (power goes to wheels with least resistance) and when loked, fromt and rear axle are split 50/50

 

[084runnerltd]

Agree but how does the '98-99 system without CDL and rear locker engaged compare to the 80's design without CDL engaged?

98-99” have CDL and offered rear locker as an option. Unfortunately my 99, doesn’t have the rear locker ;(....and my 80 was superior off-road.....til I sold it.