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Comments
For a center differential? Can it be locked? If not, I don't agree with that statement. If it can, I can't wait to get one. I am checking on the availability of a torsen diff for the front diff of my 99 Landcruiser, which is open.
For instance, the totally open diff'l in the pre-04 RXes has a VC in parallel, mechanically, with the differential. That open diff'l could have just as well been a torsen, and the VC could have just as well been an electrically actuated clutch.
believe me the beers help
"Equally impressive is the Cruiser's ABS system, which is operational even in low-range 4WD while the center differential is locked. The system is designed to enhance off-road braking performance, allowing ABS control on poor traction surfaces, while avoiding early activation on steep slopes. It does so by determining road conditions according to changes in vehicle acceleration and road roughness. As road roughness increases, ABS influence will decrease. The system also will determine the slope of the road. As the slope increases, ABS influence decreases."
BMW recommends turning off the DSC, Dynamic Stability Control, during maneuvers such rocking back and forth to get unstuck in a mud "wallow". Turning it off prevents the dethrottling of the engine so one might actually get out of that mud.
On the other hand it also says that in this mode, DSC off, the brake modulation for left/right torque apportioning might result in an automatic "masking out" of the brake application capability to prevent brake overheating due to allowing high rates of wheelspin.
Next year's "feature" for Toyota/Lexus AWD systems?
Due to the rain, I had engaged 4WD Hi. My VSC was on. The center differential definitely was not locked.
While going down a moderate grade on an interstate with a light rain but a very wet road, my 4Runner's rear began swinging out counterclockwise. I believe I lifted my foot from the accelerator (although it's possible that I didn't change my accelerator pedal position; it's hard to remember) and turned the front wheels into the spin (i.e., to the right).
Basically, the 4Runner just kept rotating around - turning into the spin did absolutely nothing. After spinning 3/4 around the rear of the vehicle slammed into the concrete center divide, I did another full rotation so that the rear hit the divide again, and I ended up nearly facing forward again as I stopped. Thank God I was not harmed in any way in this high-speed accident.
I used to drive in snow and ice conditions as a matter of course and I've successfully recovered more than once from my vehicle's rear swinging out by turning into the spin exactly as I did in my accident. However, I was in a FWD vehicle in those other instances and it did not have VSC.
Did my being in 4WD with VSC engaged help or hurt my recovery efforts in this accident? Looking at some of the earlier postings that describe braking being applied to up to three wheels in slippery conditions has me wondering...
Thanks for your insight. Thanks also to Toyota for making a vehicle in which I crashed so hard that my driver's seatback was bent backwards by the force of my body against it, but in which I was otherwise so protected that I walked away with only a few sore muscles.
Or else the e-throttle(??) and/or VSC wasn't very quick in shutting down the engine...
Or the VSC malfunctioned and after initially applying the right front brake to counteract the inital "spin" and then it never released it.
I want to correct any notion that I was attempting a turn at highway speed. I was driving straight when the rear end drifted out to my right. The only turning I did was in response to the spin to try to recover control.
I don't believe vehicle safety systems should compensate for every driver error, such as going to fast, but I would like to understand why, when I tried what had always worked previously, it didn't work this time. Thanks.
4500 pound is a lot of weight, maybe your FWD cars are much less. SUVs have a tendency to roll, your wheels may have left ground. Coupled with wet road no traction on maybe all 4 wheels. Too much for the VSC.
I think your choice of drivetrain modes and actions in the incident were correct. Maybe braking would have helped, but I suspect not. In previous vehicles I've very occasionally encountered a sudden patch (usually ice or polished snow) of near-zero-friction and even on the flat there was little I could do. In these cases my car began to spin, and only a combination of luck and eventual traction (and just a little skill) saved me from big problems. You do't have to do anything (such as braking or turning) to cause the spin if conditions are slippery enough, and the failure of the system plus your wheel turning to stop the spin would suggest that things really were slippery, at least for a brief time.
There are other possibilities, though. The system should have at least been blinking its yellow dash light at you, and probably beeping to indicate it had lost control. You didn't mention anything like that. Perhaps there was indeed a VSC malfunction.
The system should have been braking the right side wheels (I don't know the precise combination or balance), but you might not have noticed in all the excitement. I've experienced the right-side-only braking and it wasn't terribly dramatic.
The de-throttling and throttle response is instant in my experience, so I don't think that was it.
We can all make mistakes from time to time, no matter how careful we are, but sometimes stuff just happens that's outside all reasonable bounds of caution.
I have done my own testing in 4Runners TLCs all equiped with atleast VSC and ABS. The Idea of VSC and ABS is to keep the wheels spinning the same speed as the road is passing, ABS is to prevent lock up, VSC is to prevent overspining the tires. You did everything in the situation right, but you should have had you foot still on the throttle, thats why VSC did not do anything noticable... If you would have left it on it would have instantly cut the power to what it should have been to keep the tires spinnign aproxomitly as fast as the road, which is designed for ultimate traction. But since you pulled your foot off the accelerator you did what the system was going to do but you took all power away where as the system would take what was dangerous away. this mostlikly caused the read tires to spen slower than the road thus no traction was created. Applying Brakes in this type of a slide would have possibly rolled your car, the brakes would have gripeed the front and spun the front more out as the center of weight is not and probably rolled depending on the grade. The absolute right thing you could have done was steer into it, keep your foot on the gas, and pray. two of which im sure you were doing. I know how hard it is to react in that situation, ive been in it too many times. But when an SUV nearing 5000 lbs goes Sideways on flat land it takes a skilled driver to recover, going downhill you need a few angels... Anywho glad you OK.
Will apply moderate braking to the front wheel toward the outside of the spin or overstear. If the spin or overstear still continues to the point that the "moment" line of the vehicle is outside the "line" of that outside wheel, then the braking will stop and only then will the engine be dethrottled.
So if the rear is coming around counter-clockwise, then the right front brake will be moderately applied, rapid on and off modulation. If the rear of the car continues to swing out such that more than 50% of the weight/inertia is outside the "line" of that front tire, then the braking is now detrimental to spin recovery and so the VSC will release them.
Back when, or immediately before, the spin began if the Trac system detected rear wheelspin then the Traction control system would have applied rear braking to prevent wheelspin and to maintain traction.
Since about 2000 the Lexus systems were changed, delaying the onset of dethrottling due to wheelspin, to give the driver recovery time, time to lift/feather the throttle if Trac activated due to power.
The other activity wherein VSC is involved is understear, "pushing" and in that case the standard procedure is to apply braking to the rear wheel to the inside of the "turn". In this case dethrottling is also immediately enabled.
It helps to keep in mind that the two primary sensor inputs to the VSC system is the stearing wheel position, "what direction (and how much)does the driver want the vehicle to turn?", and the yaw sensor "which way/direction (and how rapidly)is the vehicle actually turning?"
As long as the two sensors agree then VSC does not come into play.
The Trac system has responsibility for maintaining traction and therefore its primary inputs are the 4 ABS wheelspeed sensors.
EBD is electronic brake force distribution, sort of a replacement/update on the old mechanical brake pressure front/rear proportioning valve. During braking it monitors braking effects at all wheels and modulates individual wheel braking pressure to equalize overall braking forces.
Trac was simply traction control and now A-trac incorporates LSD capability.
BA is brake assist supposedly to help some of us keep the the brakes applied more adequately in an emergency braking circumstance.
To say one or the other is the master would be like saying the lead programmer did not understand realtime multi-tasking programming.
One can certainly say that ABS, Anti-lock Braking System laid the eggs from which all of these others were "hatched".
The shop manual for my 01 AWD RX300 indicates that for understearing both rear brakes are applied (moderately??) and the engine is dethrottled.
I have become very well familiar that with overstearing the outside front brake is applied.
And if I try to really push it in snow or on ice, turning or straight, the brakes go crazy and if I persist with a heavy throttle foot the engine is dethrottled.
Hank My manual says and its possible this is a missprint Vehicle SKID control VSC (introduced for 2000) and in my experiance of off roading it acts mutch like my wifes BMW DSC control, which dethrottles the engine. Ill go to the Toyotay site and reread the info on the systems i could be wrong, but then that would make my manual wrong too..
http://www.toyota.com/landcruiser/key_features/star_safety_system- .html
everything you need to know about ABS, TRAC, EBD, BA, and VSC, it even runs through scenarios for you
To clean up just a few issues: I honestly can't say whether the VSC lights flashed or not. My brain was zooming along trying to figure out if there was anything else I could do to recover control, and then I was just waiting for what was going to happen next. To address another point, a friend at work who traveled the same route that morning said he saw other vehicles fishtail in that same area, so I take it there was a particularly bad section of road that contributed to my skid.
And finally, as you might have guessed from my sign-on (between4rnrs), I intend to get a new 4Runner to replace my totaled vehicle ($17.6k repair estimate: frame bent down 6-8 inches in the back, rear quarter panels and roof buckled, even the hood was misaligned (but the rear doors still open and close!)). As much as I loved my 2001 model, the new version seems better still, and how can I turn away from a vehicle that took all that damage but left me unharmed?
thats what i said, and i ended up with a wonderful used 2003 TLC.
Good luck in you search, (note; new 4Runners have more power than the TLC. V-8 runs around 277hp V-6 runs 240.... LC V-8 runns 235... arg...)
BJC
I don't consider it a big deal, however, and haven't encountered anything that explains why the RWD mode wasn't made available on the V8s. Interestingly, I think you get the highest towing capacity and fastest 0-60 performance in a RWD-only V8.
But if you just have to have more horsepower, wait a month or so for the variable-valve version to start shipping.
Not surprisingly, neither plain HP or torque numbers tell the story very well. Chevy bragged about the 270 HP of its new 6 cyl. in the Trailblazer, etc. and yet these vehicles are slower than some lesser-powered equivalents. In the most reliable comparisons of the V6 and (non VVT-i) V8 0-60 times I've seen, they usually come out about even. That makes sense, as the V6 has more horsepower, is lighter, and has a 2WD mode, while the V8 has more torque. Torque is handy (it's generally easier to translate the power of a higher-torque engine into good acceleration) but in the end it's POWER (measured, say, in horsepower or kW and not lb-ft.) that does the work of accelerating a vehicle. Check your physics textbook if you're interested in the details. With perfect transmissions, a 245 HP vehicle would always out-accelerate an otherwise-equivalent 235 HP vehicle.
Money wasn't a factor in my V6/V8 decision, as I could easily afford either one, and actually changed my mind several times over several months. In the end, I drove both types a few times and liked the way the V6 felt and handled. The RWD-only mode and a front end that is 150 lbs lighter probably explain the "feel" element, though the two were pretty close overall, and I liked them both. I'll do some towing, but not enough to need the V8. That's my situation, and others made different choices that they're happy with, too.
As for differences in noise and vibration levels at cruise or while accelerating, I didn't feel or hear much during test drives. I think I may have felt a slight difference (V8 might have been smoother) under heavy acceleration, but it was hard to be sure. The engine sounds under significant acceleration are somewhat *different* but they were equally quiet otherwise and so I suppose that is a matter of taste.
The new V8 should clearly be faster than the V6 because it has both more torque and horsepower, but unless the V8 badge in the grille and/or bragging rights are decisive for buyers, I always recommend testing them both. Drive, drive, drive, and then buy what you like.
I am a new owner of '05 Sequoia 4WD SR5, I tried to read throught all threads in this forum, with so many discussions on Toyota's 4WD system, I am still very confused.
Could someone give me a quick summary on what kind of 4WD system is in '05 Sequoia? can I always engage in the 4HI mode even in high speed driving? would that harm the drivetrain or engine doing so?
Thanks you in advance for any advice!
Thanks!
Wrong!!! Tacomas are and have been shift on the fly at 60mph or below. Lever or electronic.
2WD....is rear drive only
4WD-HI...braking apportioned AWD, brakes are applied to individual slipping wheel(s) to simulate LSDs, front, rear, and center 98and dethrottling to prevent brake over-heating.
4WD-LO...Locked center differential and disabled VSC, Trac, ABS, etc.
So, the salesperson was likely correct, full stop to shift into 4-lo, locked center differential, binding stearing on high traction surfaces.
The brake proportioned AWD system is likely more than adequate 99.99% of the time on-road, and having to put it into low range for off road use, locked diff'l, would not be a serious handicap for off-roaders.
I have no doubt that all of the confusion we are seeing about multi-mode drivelines via some of the poster's questions is resulting in one hell of a lot of needless repairs to these systems due to inadvertant misuse.
http://www.toyota.com/landcruiser/key_features/star_safety_system- .html
Center Differential
Rear-wheel-drive cars need a rear differential to power the right and left rear wheels and let them turn at different rates of speed when cornering. Front-wheel-drive cars need a front differential for the same reasons.
Vehicles with full-time or permanenet four-wheel-drive, or with all-wheel drive, require a center differential (or similar device, such as a viscous coupling unit or VCU). In a tight turn, all four wheels travel at different speeds.
A center differential receives power (or more correctly, torque) from the transmission (or transfer box) and sends this torque to the front and rear differentials, while allowing the front and rear wheels to travel at different rates.
Differential Lock
The main disadvantage of an "open" differential is that the usable torque is restricted by the wheel with the least traction. A differential lock literally locks out the differential action and forces torque to be split equally between each wheel (or each axle)for maximum traction. In a rear-wheel drive vehcile, for instance, locking the rear differential locks the left and right rear wheels together so that both receive equal torque.
In a full-time or permanent four-wheel drive wehcile, locking the center differential locks the front and rear drive-shafts together, sending equal torque to the front and rear axles. While locking a differential helps increase traction, it makes steering more difficult on high-traction surfaces because it tends to force the vehcile to travel in a straight line.