Last post on Aug 21, 2013 at 5:16 PM
You are in the Toyota Sequoia
What is this discussion about?
Toyota Sequoia, Toyota Highlander, Toyota 4Runner, Toyota Land Cruiser, Toyota RAV4, Toyota Tacoma, Truck, SUV
#2160 of 2493 Re: Guess what... [nedzel]
Feb 06, 2008 (9:05 am)
Yes, I know what all the advertising says, hardcopy and on the internet.
Clearly, I may be wrong but the information at techinfo.toyota.com is pretty detailed, detailed well enough that a good mechanic could use it to overhaul the transfer system.
The word "torsen" is not used beyond 2003 in any of the documentation and I have no idea why that would be unless it isn't used or there is some legality involved.
Additionally if you read the document ion for traction control it appears that a torsen diff'l would be of no use since the TRAC system would quickly brake any wheel (and dethrottle the engine simultaneously) that exhibits spin or slip.
As somewhat of a parallel, I bought a 2001 AWD RX300 because it had HID VSC/TRAC and a viscous clutch across the center diff'l to provide torque to the rear driveline if front slippage occurred.
I quickly discovered that the VC was probably useless since the TRAC system activated at the first sign, seemingly the very instant, wheelspin developed.
Apparently Lexus discovered the same thing as the VC was discontinued for the RX330 series as was announced in NCF, New Car Features for the new 2004 RX330.
But guess what....??
Lexus continued to advertise, hardcopy sales brochures, on the internet, and in various PR pieces, that the RX330 had a VC, Viscous Clutch when the shop/repair manual indicated otherwise.
Lexus finally admitted, in writing (email), that the RX330 did not use a VC and apologized for the mis-information.
And now here I am arguing with Lexus as to whether or not the new(er) RX350 uses the VC. The advertising says yes but the shop/repair manuals say not and the TRAC use indicates it might be useless even if it is installed.
Sorta of like the issue of a torsen with TRAC in the 4runner.
#2161 of 2493 Re: Guess what... [nedzel]
Feb 06, 2008 (9:11 am)
Read the material, however sparse, on TC, Traction Control, on the provided link.
If you have a torsen diff'l in the 4runner wouldn't you need to disable TC in order to put it to use...??
#2163 of 2493 Re: Guess what... [wwest]
Feb 11, 2008 (12:15 pm)
A torsen center diff, compared to an open center diff, enhances brake TC by multiplying the effect of a slipping, braked wheel by more than 1:1 across the axle diff to the other wheel. The amount depends on the bias ratio of the torsen.
#2164 of 2493 Re: Guess what... [green]
Feb 11, 2008 (1:15 pm)
Yes, but doesn't that seem counter-productive...??
The front wheels are already slipping (abet at a rate limited by TC) an obvious indication of a slippery roadbed surface, and the Torsen will MULTIPLY the torque at the rear wheels (torque sustained via TC braking), or vice versa.
I would think one would want LESS torque at the opposite wheels, not MORE.
#2166 of 2493 Re: How is F/AWD accomplished? [wwest]
Feb 11, 2008 (2:58 pm)
All 3 of these "4wd" vehicles (Highlander AWD, RX330 and Sienna AWD) are built off a variation of the Toyota Camry drivetrain which is FWD. All 3 of these vehicles have open center and rear differentials (unless someone has any new information on the '08's that they now have a LSD ctr diff)
In reality these are FWD vehicles that transfer power when there is slippage using the brakes from the front wheels that are slipping to the rear one's that aren't. Generally these systems cannot transfer torque over a certain speed such as 35mph. Once you're over this speed, the brakes can no longer be applied to transfer torque to wheels that are not slipping and you essentially have a FWD vehicle.
This type of system will generally use up brake pads more than a vehicle with a center LSD or Viscous liquid ctr diff. While Toyota refers to the system as "AWD", it would not meet the definition of AWD by most other manufacturer's that use this term such as Subaru, Audi, MB, Volvo or GM, however it is nice marketing even if its not a very effective 4wd drivetrain.
Unless Toyota has added a Viscous Liquid center differential or a limted slip differential to these 3 vehicles, they would generally not meet the definition of AWD used by all other manufacturers of AWD vehicles.
Since there's no operator controls it wouldn't meet the definition of a typical 4wd system either. Best way to think about this system is that its a FWD vehicle with traction control that transfers power to the rear wheels when the front wheels slip, but only at lower speeds and only a small amount of the available torque as shown in the video. Better than FWD alone but not nearly as good as a real AWD system or a 4wd system.
#2167 of 2493 Re: How is F/AWD accomplished? [hdfatboy]
Feb 11, 2008 (3:48 pm)
But I would think that TRAC could brake the front wheels enough to "force" enough torque to the rear to get the car in motion even with the obstacle blocking the rera wheels.
Or is it just a matter of poor or inadequate TRAC design?
#2168 of 2493 Re: How is F/AWD accomplished? [wwest]
Feb 11, 2008 (4:46 pm)
Using brakes to transfer torque is a very delicate balancing act. Braking too much will stop your momentum before the rear wheels have picked up the torque to keep the vehicle going. Therefore the software has its limitations and will only reduce the front wheel torque to a certain amount and only under a certain speed.
The video shows the significant limitations of using braking to transfer torque across an open differential. As the video shows, a system such as Toyota's that is solely based on braking to transfer torque is a poor substitute for a mechanical LSD or viscous liquid CTR diff.. That's why the RX330/350 can't climb a slippery incline even when the front wheels slip and the rear has traction.
If the vehicle was moving at speed, the system wouldn't even attempt to transfer torque in order to avoid causing an unstable driving situation, not to mention how much additional wear and tear would be place on the front brakes if the system attempted to use front wheel braking to transfer torque at higher speeds such as a highway ramp or even a high speed curve in a major highway.
This type of system is simply Toyota's way of keeping drivetrain costs down and giving the marketing department a "claim" that most consumer's will never understand or see the difference with real AWD and 4wd drivetrains. Their approach allows for higher prices with lower costs and a better margin on their "AWD" vehicles. Smart buyers will know the difference and see this drivetrain as nothing more than a glorified traction system for limited road situations.
Toyota loyalists will undoubtedly have a different perspective however the videos tell the real world story. Here's another example showing the difference between the Tundra's rear open diff with "electronic torque transfer via the brakes" vs the mechanical auto-locking rear differential in a Chevy pickup. A rear LSD would perform somewhere between the 2wd Tundra and the 2wd Chevy in this video. http://www.youtube.com/watch?v=Z8PpZF77tgk The video was filmed at the Eaton proving grounds which makes the Eaton auto-locking differential used in the 2wd Silverado pickup.
#2169 of 2493 Re: Guess what... [wwest]
Feb 11, 2008 (5:27 pm)
You may or may not want more depending on conditions, but the torsen-C center will require less frequent TC engagement and less brake pressure when it does engage, compared to an open center.