Last post on Mar 03, 2013 at 8:13 AM
You are in the Toyota Highlander
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Toyota Highlander, SUV
#9465 of 10987 Re: Highlander is AWD 50/50 (wwest) [nimrod99]
Jul 21, 2004 (5:43 am)
The following is a quote from Edmunds 2003 review:
"The Toyota's full-time all-wheel-drive system is always on, splitting power 50/50 front and rear via a viscous-coupled center differential. The system overcame every limited traction scenario we encountered without difficulty. Judging by its performance, we believe the Highlander could easily handle a rutted or snowy road to a vacation home, trailhead or remote beach. Ask more of it than that and you may be calling for roadside assistance."
#9466 of 10987 AWD.....
Jul 21, 2004 (7:34 am)
It is my understanding that with the advent of the 04 MY the Toyota Sienna, HL, and the RX330 all share the same AWD system. For 04 the viscous clutch has been eliminated entirely in favor of s simple open center diff'l and the use of the brakes to apportion engine torque when necessary.
The brake apportioning system will not activate unless the ABS wheelspeed sensors indicate one wheel or wheels is turning, spinning, faster than others.
Note that wheelspin must occur before the torque apportioning system comes on-line. A clear indication that the instant a wheel looses traction the 50/50, 25/25/25/25, torque distribution "rule" becomes "null".
The same is true of VC use in prior years.
Prior to 04 the HL and RX shared the same AWD system using a viscous clutch ACROSS the open center diff'l to eliminate extended periods of disparate front/rear rotational rates.
And pardon me, but I don't think any automotive magazine writer knows "beans" about the actual design and/or implementation of any of the modern day systems, ALL inclusive, they generally just parrot the propaganda put out by the factories.
And yes, it is a 2001 AWD RX300 I have.
And now to those four divots....
Wouldn't you agree that any FWD or RWD vehicle would have driven away from that spot just as quickly as you did?
Assuming your experience was with a MY prior to 04 and ignoring the VC for the moment the center differential in the Toyota AWD system will act exactly like the normal rear or front open differential as long as the effort required to turn both of the differentials output shafts are roughly equal.
How many times have you seen a RWD or FWD non-turning vehicle spin a wheel on one side and not the other when the roadbed is NOT slippery. Sand and loose dirt and "fine", pea gravel surfaces DO NOT constitute a slippery roadbed.
By it's very design the VC cannot come into play and provide any substantial level of locking of the center diff'l in a constant or instantaneous manner. To do so would result in long term damage to the driveline each and every time you turn a corner, especially so for accelerating tight turns.
The "viscous" fluid is formulated to have a very high volumetric expansion ratio with temperature. When the two output shafts of the center diff'l start to turn at disparate rates the fluid between the tightly spaced interspersed clutch plates is rapidly heated by the shearing forces and since the volume of the hermetically sealed VC container is FIXED the pressure between the clutch plates increases dramatically thereby increasing the coupling coefficient between the clutch plates.
We're talking about hundreds of milliseconds for the VC to reach even a low lock level and several seconds for it to reach a locking level of any real benefit. As one can readily see, it cannot sustain anything close to 100% locking of the center diff'l, thus the 70/30 measurement I obtained with sustained "slippage" on a 4 wheel dyno.
One of the things I discovered during the winter snowstorm this past year was that my RX's Trac system dethrottles the engine long before the VC has an opportunity to react to wheelspin. That's very likely the reason the VC was eliminated, the Trac system made it useless anyway.
#9467 of 10987 Re: Memory Seats [junepug]
Jul 21, 2004 (7:35 am)
The only Toyota vehicle available with memory seats is the Avalon XLS and even then only with the optional "Premium Luxury Package". Maybe this will become more main-stream one day, but Toyota needs to keep these luxury distinctions between HL & RX to justify the price gradient.
#9468 of 10987 To be sure...
Jul 21, 2004 (8:15 am)
Not sure how many know why the center diff'l MUST "initially" be OPEN for AWD systems. These are basically systems which automatically add some level of locking to the center diff'l during extended periods of wheelspin.
When you enter a turn the front wheels turn at a different rate than the rear, the tighter the turn the greater the difference in F/R rotational rates will be.
Anyone who has driven a 4WD "part-time" system while actually engaged on a high traction surface can describe the effect. With the center diff'l locked (RIDGID mechanical coupling/linkage) the front and rear drivelines MUST turn at equal rates. With no slippery roadbed surface to provide the "give" or "slack" while turning, the driveline winds up until the windup torque exceeds the tires' traction coefficient, and then the tires "scrub", slip, to release the mechanical windup.
Probably not just a few busted fingers and knuckles as a result of the feedback to the steering wheel during this effect. 4WD owners are taught, or else quickly learn, to keep fingers on the outside of the steering wheel when the 4WD system is engaged.
So, the problem for automotive design engineers was how to provide an "automatically" engaging all wheel drive system. A system that ONLY engaged with actual wheelspin, and not the apparent wheelspin resulting from simply entering a tight turn.
I admit that I'm a bit surprised that some enterprising young engineer hasn't come to the realization that steering wheel position "off-center" could be used as an indicator to disengage the center diff'l "lock".
You can probably get a good idea of how effective a VC implemented AWD system is, how quickly it comes "on-line" and how ridgid it becomes, by driving your vehicle on a high traction surface in a tight circle as fast as your comfort level allows. But be sure and keep your fingers on the outside of the steering wheel since a good system will quickly begin to scrub the tires and just might jerk the steering wheel from your grasp.
#9469 of 10987 Memory seats...
Jul 21, 2004 (8:16 am)
The early ES300s had "self-contained" driver seat memory and sometimes show up on EBAY.
Jul 21, 2004 (8:19 am)
I understand all about VC.
But have you considered that in the HL the engine output drives both sides of the drivetrain simultaneously through the automatic transmission?
In your scenario - the engine drives the front axle, while the rear axle is connected to the front by a center VC. This is not the case.
Both front and rear axles are connected to the VC which is part of the automatic transmission. This is how they can get each side to be 50/50 split and it doesn't rely upon the front drive train to drive the rear through a slipping center VC
You can say whatever - the HL is 50/50 split front rear.
#9471 of 10987 According to...
Jul 21, 2004 (10:29 am)
the 00 and/or 01 AWD RX300 Lexus shop manuals (I have both), tranny volume:
The transmission (not "technically" transaxle)output directly drives the input to the center diff'l (drives the center diff'l outer case in actuality) then one output "shaft" of the center differential drives the front differential and the other the rear driveline and thereby the rear differential.
The two input shafts of the VC are connected, one each, to an output shaft of the center diff'l. There is NO locking of the center diff'l unless or until the viscous fluid can react to differential turning rates of the two output shafts of the center diff'l.
Think about it, seriously, if the system had full time or instantaneous 50/50 coupling that would be an exact equivalent to an engaged 4WD part-time system and the driveline would be destroyed in short order due to the continual windup stress during turns.
#9472 of 10987 So Toyota is lying to us?
Jul 21, 2004 (12:20 pm)
According to all the public information - the HL is AWD with 50/50 split.
And NO - the drive line would not wind-up as I said - front and rear are connected through a VC in parallel to the automatic transmission (not in series).
I have the 03 Highlander shop manuals - which describes the HL drive line better than the RX300 shop manual (which is a different vehicle.
#9473 of 10987 Re: Extended Manufacturers Warranty-2004 V6 Highlander [bandit1]
Jul 21, 2004 (12:34 pm)
i paid 1000 for mine
#9474 of 10987 I'll give ya 50/50...
Jul 21, 2004 (12:42 pm)
That Willard will be hard to convince...even if Mr. Toyoda himself sent in the actual Toyota explanation.
And please, don't mention front window fog-up to Willard!