ATRAC vs other AWD differential systems

[JosephD05]

How does the technology other manufacturers use, such as BMW X or Subaru, which apparently tranfer torque to the slipping wheels, compare to ATRAC which needs to apply the brakes on the slipping wheel in order to transfer torque to the opposite wheel? Is ATRAC an older or inferior technology? If so, why is it still used on the 80+K LX570? Sorry if this is a total noob question.

 

[CJ3Flyr]

ATRAC in conjuction with VSC is pretty much at the top of the heap. The other manufacturers use other names but it boils down to very similar technology. The new Mercedes adds a Torsen limited slip in the axle to augment its' "ATRAC" but again very similar technology.

All the systems involve reducing engine output, processing the speed inputs from the wheels and trying to force the power to the slow wheel and away from the fast wheel.

What's of greatest significance, in the end game, is not the technology but the implementation of it. Sometimes it's more desirable to have a highly evolved technology rather than the latest and greatest (Windows XP vs. Windows Vista as an example). Some of the manufacturers have awesome technology for AWD (Honda) but it doesn't work when the vehicle is stuck. The system can't transfer enough torque to get the job done. On the road the "more advanced" system may have .01% more refinement in terms of feel and efficiency but is it worth such little gain? Toyota's system in addition to being technologically advanced actually works! :bigok:

Does that help?
:cheers:

 

[JosephD05]

Seems like there are different types of AWD systems, some are far superior. Are there any systems that actually tranfer full torque to slipping wheels without having to brake other wheels? Systems that come to mind are SH-AWD, Jeeps select trak or whatever their top end system is, Subaru's symetrical AWD, etc. I saw a video on youtube that showed the CRV, highlander amongst others all having problems going up a hill inch which two tires only had traction, while the subaru was able to get teh car up with only ONE tire. Quite impressive. I am sure most of you have seen this video:

http://www.youtube.com/watch?v=t09ExAUgtyE&feature=related

 

[CJ3Flyr]

I saw the same video...

That SH-AWD is to my point... They advertise and show animations of 100% of the torque being transferred, it seems that the real world is a different place than where they film the ads. SH-AWD is very technologically advanced but, when stuck, it doesn't work. Subaru's system DOES actively vary the F to R bias, the Toyota doesn't. So in that sense it's more advanced sort of... With active transfer of torque (F to R) such as the Subaru you get power sent to the axle that needs it the most and then the axle deals with the right to left aspect. In the 4Runner (with the center diff unlocked and in 4wd) the end result is similar but the methodology isn't quite as eloquent. In a non-controlled or Torsen center diff the torque bias goes towards the slipping axle, unlike the Subaru. Now here's where the playing field levels... Assume it's the rear axle with low traction. The rear wheels will be slowed by application of the rear brakes. The brakes will equalize the the right to left wheel speed and the extra power (what's being "held back" by the brakes) will be forced to the front axle. Is there energy loss because of brake application rather than directing the power forward with other technology? Yes. Does it matter? To a rally racer, yes. To most of us it's far more important to drive the car in foul weather or off-road and not get stuck.

As for the Highlander not making the hill. IMHO that has more to do with the lack of agressiveness on the part of traction control in that application. The brakes don't apply hard enough or the power is cut too much or...

In the case of the 4Runners system most would lock the center diff in very slippery, slow conditions. The center lock is a geared lock meaning it's mechanically impossible for the front wheels to get more or less power than the rear wheels. The aggressively programmed ATRAC then handles the right to left traction issues very effectively. Even with the center diff open I suspect the 4Runner would handle the test in the video, center diff locked, no question!

Again, the Toyota 4Runners technology is very good. Is it at the pinnacle of technology? No. Does it work? Does it work smoothly and efficiently? YES! :bigok:

:cheers:

 

[JosephD05]

I saw the same video...

That SH-AWD is to my point... It's very technoloigically advanced but, when stuck, it doesn't work. Subaru's system DOES actively vary the F to R bias, the Toyota doesn't. So in that sense it's more advanced sort of... With active transfer of torque (F to R) such as the Subaru you get power sent to the axle that needs it the most and then the axle deals with the right to left aspect. In the 4Runner (with the center diff unlocked and in 4wd) the end result is similar but the methodology isn't quite as eloquent. In a non-controlled or Torsen center diff the torque bias goes towards the slipping axle, unlike the Subaru. Now here's where the playing field levels... Assume it's the rear axle with low traction. The rear wheels will be slowed by application of the rear brakes. The brakes will equalize the the right to left wheel speed and the extra power (what's being "held back" by the brakes) will be forced to the front axle. Is there energy loss because of brake application rather than directing the power forward with other technology? Yes. Does it matter? To a rally racer, yes. To most of us it's far more important to drive the car in foul weather or off-road and not get stuck.

As for the Highlander not making the hill. IMHO that has more to do with the lack of agressiveness on the part of traction control in that application. The brakes don't apply hard enough or the power is cut too much or...

In the case of the 4Runners system most would lock the center diff in very slippery, slow conditions. The center lock is a geared lock meaning it's mechanically impossible for the front wheels to get more or less power than the rear wheel. The aggressively programmed ATRAC then handles the right to left traction issues very effectively. Even with the center diff open I suspect the 4Runner would handle the test in the video, center diff locked, no question!

Again, the Toyota 4Runners technology is very good. Is it at the pinnacle of technology? No. Does it work? Does it work smoothly and efficiently? YES! :bigok:

:cheers:

Excellent explanation. Well I would say the torsen video on toyota 4runner page is misleading then. It shows the diff actively sending more torque to the axle with more traction. Not that I am complaining, I find the traction of the 4runner to be amazing, espeically with full time 4wd. It's nice to be able to pound your foot on the gas in the rain and just go..no wheel slippage at all.

 

[CJ3Flyr]

It shows the diff actively sending more torque to the axle with more traction. ...I find the traction of the 4runner to be amazing...

I think the misleading aspect of the video is the 'middle' step is left out. That middle step being the rear brakes pinching and the extra power being sent forward (in my example).


:iagree:The end result of the 4Runner system is awesome! I love it! :bigok:

 

[JosephD05]

Now, if only they can make seats comfortable for people over 6ft tall, I would have the perfect vehicle. :dancin:

 

[CJ3Flyr]

Now, if only they can make seats comfortable for people over 6ft tall, I would have the perfect vehicle. :dancin:

Me too brother! Have a good one...
:cheers:

 

[Falls]

An all wheel drive vehicle is NOT the same as a 4wheel drive vehicle or for that matter a full time 4x4 vehicle.

Every time I use my ATRAC is exceeds my expectations. This weekend I was pulling some stumps out. My front 2 wheels were on the dry grass and the back 2 were on asphalt driveway. The diff. was NOT locked but was in 4lo. I had no choice but to pull in reverse. We hooked up the straps , wrapped them in blankets to prevent whiplashing...lol and I started to lightly pull to tighten my strap. To my surprise my front 2 tires as well as my back 2 tires were all turning and left me 2 divots and 2 rubber skid marks on the drive.

Operations was a success without and issue .

Amazing truck the more and more I push it the more it surprises me . Try that with a Subaru

 

[CJ3Flyr]

I saw the same video...

That SH-AWD is to my point... They advertise and show animations of 100% of the torque being transferred, it seems that the real world is a different place than where they film the ads.

I have been thinking about a disconnect in my explanation... I have said certain, high tech systems "just don't work in the real world". That sentiment centers on being stuck. The 100% torque transfer thing: I believe the ads. Too much at stake to lie. What they don't emphasize is 100% of AVAILIBLE torque. 100% AVAILIBLE is nowhere near the torque rating of the engine as the traction control system has it held WAY BACK, as in not enough to move the mass of the vehicle.

I just forgot to emphasize that point sufficiently as I was talking about the systems that "didn't work in the real world".

Hope that ads some clarity.
:cheers:

 

[RunnerUp]

Now, if only they can make seats comfortable for people over 6ft tall, I would have the perfect vehicle. :dancin:

hmmm, maybe its because i grew up in 4runners ( family has had them ever since i was in 8th grade) but when im in my 02 and the 07 im perfectly comfortable... i actually dont even have to put the 07 seat all the way back... and im 6'3" and 225lbs... are you guys really having that much difficulty??

 

[Falls]

hmmm, maybe its because i grew up in 4runners ( family has had them ever since i was in 8th grade) but when im in my 02 and the 07 im perfectly comfortable... i actually dont even have to put the 07 seat all the way back... and im 6'3" and 225lbs... are you guys really having that much difficulty??

I'm 6'2" 190 and am totally comfortable. My father is 6'11" and is ok with it or at least just as comfortable if not more than their Trailblazer for short little around town trip's , but I'm sure he would not want to drive cross country in it ....lol