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-mike
The wheel that is spinning has zero torque, while the wheel on the ground has 100% of the torque.
I think about it like this with a locker. If you have one wheel in the air and the other on the ground, which one is twisting its axle more? The one on the ground will twist its axle more because its tire has resistance. The tire in the air won't twist its axle because it doesn’t have any resistance to turning.
I don't think torque is split 50/50 all of the time with a locker like it is with an open diff. Perhaps it is split 50/50 when both are on pavement (I know that you know this is bad, so I'll avoid that conversation).
I hope one of my examples can make sense :-)
-mike
Yes
'where does the torque from the engine go'
This is the puzzling question most of the time.
If all the wheels are in the air the torque generated by the engine will go into drive train losses (as it always does heat/noise). It will also go into rotational inertia when it spins the tires/drive train up to speed. This can take fractions of a second before the engine will reach it's redline (since there is not much resistance to turning it). Once the engine is redlining, WOT or otherwise, fuel will be cutoff to the system with today’s electronics so that damage is not done to the engine. So the engine actually creates a small amount of torque to spin the drive train up, and after that it just stops making torque. An engine can be rated at 100 hp, but that doesn't mean it is always making that amount. The engine can make anywhere between 100 hp, and probably a couple of negative horses (engine brake), so there is a wide variation possible whether the driver wants it or not.
-mike
Since I don't know the inner workings of these particular devices, I'll just ask how does this sound to you? Since the wheel is not spinning, the viscosity of the transmission fluid changes and alters the amount of torque delivered.
tidester
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SUVs
-mike
TRAC only comes into play if one rear wheel begins to slip and then TRAC will instantly apply, release, apply, release, etc, the brake to that wheel, using the on/off cycling of the brake to modulate the frictional coefficient of that wheel such that it's rotational rate roughly equals that of the opposite wheel.
If this condition persists for more than a few hundred milliseconds and the operator does not react quickly and lift the throttle then the TRAC ecu will itself dethrottle the engine.
The Sequoia, ML, and I think the new LC, AWD systems work the same way except TRAC will use the brakes on any wheel or wheel to alleviate wheelspin.
Three open diff'ls with TRAC to insure true AWD operation on most surfaces, dry, slippery, snow, ice, etc.
The Sequoia only locks the center diff'l in L4 and with the transmission shifter in "low", otherwise it uses TRAC to apportion torque in AWD mode if slippery conditions are encountered.
tidester
Host
SUVs
Almost no (acknowledging that there are exceptions) AWD or 4WD vehicle has an LSD or anything equivalent for the front wheels.
For FWD TRAC my suspicion has been that alternate on/off application of brakes on only one front wheel would feed back to the steering wheel in much the same way ABS does to the brake pedal and that might provoke an improper reaction on the part of the driver.
So I suspect that dethrottling is the only action that can reasonably be chosen for FWD TRAC implementation.
-mike
Paisan, I think your descriptions of the difference between a "posi" rear and an open rear diff are not correct. Also I do not believe the tire that rotates must be on the inside of a vehicle with an open diff.
If you did a burn out with a vehicle having an open diff (either rear or front) only one tire would leave a mark. It could be either side depending on the tread of the tire and the traction provided by the road surface under each tire. The tire facing the least resistance will begin rotating and as it out acclerates the opposite wheel on the open diff, more power will be directed to the wheel already spinning causing it to spin even faster causing even more of a "burn-out" until traction on that tire is achieved.
A posi-rear will have an entirely different effect during a burnout. (I know as I recall the burnouts in a 69 GTO back in highschool with a posi rear). The tracks on the road will be from both wheels however one will typically be greater than the other. A posi rear will, by its design, assure that some of the engine's power will go to both wheels under all conditions regardless of traction (ie the two burnout marks from both tires spinning).
having a posi rear for this reason alone was part of the "cool" factor.
An LSD wouks in a similar fashion but less agressively ensuring that some power is directed to both wheels attached to it while still ensuring smooth operations around turns.
That downside of a posi rear was its tendency to hop if accelerated to hard in turns.
Are you saying that a open diff DOES split torque 50/50?
I'm only asking because I read different opinions just about everyday.
Open diff'l, RWD:
If you could limit the level of engine torque to just below "burn-out" (the point at which either rear wheel starts "slipping", {BURNING OUT!}) would you agree that in this case equal torque is being delivered to both rear wheels?
a locker can split torque from 0/100 to 50/50 to 100/0 and anywhere in-between. It all depends upon the traction conditions of the wheels though.
:-)
Yes, up to the point of slippage an open differential will equally distribute power to both wheels receiving their power from that diff. All of the designs from Toyota, GM and every manufacturer are trying to meet the demands of multiple requirements.
Keep the power coming, prevent power from overtaking traction, transfer power when traction is lacking, keep the vehicle moving in the direction the operator intends, design the drivetrain to accomodate all speeds, angles and radius of turns and I'm sure there are more. A pretty healthy list of requirements.
Some designs are good at achieving some objectives, some make sacrifices to be better at others, some are compromises across the board. Its my opinion that an awd system, deliverying some power to all wheels under all circumstances at all speeds, utilizing mechanical differentials to distribute and transfer power across the drivetrain combined with the electronics and computerization to minimize or prevent slippage when the power exceeds the traction is the best of all worlds. Offer it with the ability to turn the traction control off for very rare occaisions and the ability to lock any differential for those really rare events and off-roading and you got all the bases covered.
Throw in 4wd lo and you'd even make paisan a happy 4 wheelin guy:)
-mike
The position that an open diff is always in a 50/50 mode is correct (even with a spinning tire)but what is reaching the ground is not the potential torque output of the engine (at the running rpm).
In the situation of a open diff vehicle sitting on ice, spinning one wheel and not moving, you can go from idle to redline and all you do is spin the one tire faster. You could then replace the engine with a hand crank and you would be able to spin the tire also (although slower).
The question of where did the torque go? The little bit required to spin the tire is all that was generated. You could spin the tire with a hand crank. (but but... I had a supercharged 454 at 5000 rpm...)lol
As you can conclude (it was touched on in previous posts), measuring torque output from rotating machinery (including jet engines, etc) requires a resisting torque up to the capacity of the engine.
In the context of the open diff and spinning tires the torque is limited by the available friction between the spinning tire and road surface. The engine torque didn't go anywhere, it just wasn't generated.
-mike
I'm disappointed. It's a Trailblazer XL clone, with the GMC look. Isuzu has a longer warranty and a V8 option, so I'd pick that over the GMC or Chevy, but I can't imagine it'll bring many new buyers.
-juice
The vehicle is now out of warranty and the dealer understands that I am willing to pay for another repair, but they are telling me that the popping noise is just pressure release on the front axle and while it is kind of loud and disconcerting, it is normal operation and not to worry. I feel like I am being handed a line of bull. Any other Suzuki owners have similar experiences? I hear Toyotas (the older ones) make some noise too, and I was told by a 4wd specialty shop, who did test my vehicle, that the dealer may be right.
Be assured that I have never driven my 4wd L or H on dry pavement and I usually don't even use the 4wd off-road unless I have to. However, some of the steep, dry dirt hills I have climbed have been hard-packed (lots of friction for dirt).
Any opinions?
Living here in a Northern climate I swore to myself that I would NEVER own a FWD car and the AWD RX (70/30 F/R torque bias) seemed a good compromise. It's a compromise alright, but their's, not mine.
Isn't there a Lexus version of the 4Runner? Maybe that would fit your needs.
Good luck
The Rav, HL and RX get a center viscous with a 50/50 torque split IIRC.
-mike
The Highlander has optional traction control, and the RX300 makes it standard along with stability control. Highlander and RAV4 also offer an optional LSD.
-juice
I have a 325xi sedan and I know it feels stable. I haven't had the opportunity to drive it in snow or any adverse weather. Could somebody describe to me with some detail as to what will happen when it gets in the snow and wheels start losing grip? I know it has a 68/32 split rear/front, but will it shift that ratio around if wheels slip?
Thanks,
Paul
-mike
-mike
The #s that they give you for torque split on VC units is the "standard" or the % split which it strives to achive. Unless you have a center locking diffy, (One of the only regular cars I've found this in is the XT6 manual tranny model) it will vary the power. Even with a center locking diffy you can't engage it on dry pavement.
-mike
The base viscosity determines the "normal" (non-heated) coupling co-efficient. The rate at which the fluid expands determines the "attack" rate, the rate at which the coupling co-efficient increases due to heating from the disparate rotational rates of the two sets of clutch plates.
Some manufacturers also add a gas "bubble" of a controlled size to initially delay the onset of high coupling and still have a high rate of "attack" once the size of the bubble is minmized by increasing fluid pressure.
My 911 only applies 10% of the drive power to the front wheels because the base viscosity of the fluid determines that factor.
I suppose that if I were to run it in tight circles continuously then what you say would be true, but in normal use the VC will not "tighten" above 10% until the expanding fluid "volume" overcomes the volume of the gas bubble.
So in "normal" use, "standard" turns, the VC's coupling co-efficient remains at 10%
Oh, by the way, most manufacturers will tell you that the "attack" rate of their VC is on the order of hundreds of milliseconds.
-mike
No, a properly set up VC will vary the ratio, dynamically, shortly after the onset and duration of disparate rotational rates of the two sets of clutch plates.
For instance the factory quotes the RX300 as 70/30 F/R while in reality 30% is the absolute most torque, at best, it will ever transfer to the rear. The RX, and likely the HL, are predominantly FWD vehicles with virtually no torque (maybe 5%) transferred to the rear on initial front axle slippage.
Subarus:
4EAT AWD: 80/20 up to 60/40 during slippage
MT AWD: 50/50 up to 20/80 and 80/20 during slippage
4EAT AWD w/VTD: 45/55 up to 60/40 and 40/60 during slippage
Isuzu TOD:
2wd mode: 0/100 locked
TOD mode: 15/85 >5mph with slippage: up to 50/50
4wd low mode: 50/50 low range gearset
-mike
They, Lexus, (acurately) quote torque split as 50/50 and that is likely the truth on high traction surfaces, low traction surfaces are yet another story.
I reside in a hilly, rural area of Michigan with a moderate amount of snowfall. Can someone explain how the Selec-trac (Full-time 4 wheel drive) option works on the Liberty and how good is this system? Also, how would the optional Trac-Lok rear differential fit into the workings? Does it make sense to have a limited slip rear end bolted on with this option?
Scott
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-mike
I've gotten what appear to be conflicting answers on this subject. I'm not sure if that's because the people who have bought these vehicles don't know how and when it works, or if they even care.