How the heck does LSD+Traction control work!??!

[Popinski]

I know some rear wheel drive cars with both LSD and traction control. How the heck do they both work together?

if the LSD is spinning both tires.. then what's the job of the traction control system? I know both the Dodge Challenger and Hyundai Genesis Coupe have this weird system.

 

[Audi Junkie]

It's *not* spinning the tires.

 

[Colt45ws]

A LSD is not 100% effective. The traction control can give some assist, also part of the traction control methodology is to reduce engine power electronically, this helps as well. I have heard from people that Helical Gear differentials work well with TC, becase of the way they are setup.

 

[Captain_Klink]

I've had them, and they don't. u need to get a subaru, that actually DOES work. the others just do a tiny little bit of something. i find in any serious kind of snow, neither lsd nor tc hardly do squat. meanwhile the subaru is going around almost saying "what's the big deal?", passing everyone by going in the curb lane, which is piled high with snow, everyone is going in the passing lane ultra slow, except subaru barreling through snow like
it's on dry pavement.

wow..."squat" doesn't get [censored]

 

[Saturn_Fan]

The traction control on the 06' Saturn VUE I had sucked. I actually got stuck more with it on in deep snow than without it. Traction control on some models, depending on how it works, is overrated.

 

[Colt45ws]

Originally Posted By: Saturn_Fan
The traction control on the 06' Saturn VUE I had sucked. I actually got stuck more with it on in deep snow than without it. Traction control on some models, depending on how it works, is overrated.

I know in the Ford manuals it says to disable T/C in deep snow. I never got stuck last winter in my Vic, with RWD, open diff and no T/C. Just a set of studless snows.

 

[chevrofreak]

The traction control monitors all 4 wheels, and when there is a variance (from one side to the other, or from front to rear) it will cut power and/or apply brakes to the drive wheels, because it believes that they have lost traction. If it detects a that it's from one side to the other, your LSD is slipping rather than grabbing, and the traction control engaging may help prevent wear of your clutches.

My car (96 Crown Vic Police Interceptor) has traction assist, which only applies the brakes. I installed a limited slip differential, and since I don't want the brakes cutting in, I removed my ABS fuse.

 

[92saturnsl2]

LSD helps some, but in production vehicles the torque differential proves useless in snow and ice.

Most modern traction control systems apply the brake to a wheel that is spinning, effectively moving torque to the wheel that has traction. GM's early traction control would actually shift into second gear and retard timing lowering engine output to help combat wheel spin.

I see no reason why the two can't play nice together.

 

[d00df00d]

Originally Posted By: Popinski
I know some rear wheel drive cars with both LSD and traction control. How the heck do they both work together?

if the LSD is spinning both tires.. then what's the job of the traction control system? I know both the Dodge Challenger and Hyundai Genesis Coupe have this weird system.

The answer is slightly different for different kinds of diffs.

Clutch-type diffs are made to start locking up when you apply gas or brakes. Usually, they will only lock up to a certain point; more locking gives better traction, less locking gives better drivability and a more forgiving nature. My car, for example, has a 25% lock. This is way on the drivable/forgivable side of the spectrum, which is nice; on the flip side, it will still permit a fair amount of slip under extreme conditions (e.g. one wheel on ice while the other is on pavement). This can overheat and wear out the clutch packs. A traction control system can prevent that by applying a brake or limiting the throttle.

Some modern diffs are computer controlled. They can vary the amount of lock they provide, and usually can also send the torque to one wheel or the other. For those cars, that torque split/lockup control is part of the traction control system. However, the computer still might apply a brake if one wheel is way out of control.

Viscous diffs act like very loose clutch-type diffs. Not only are they prone to overheating in extreme circumstances, but they also don't provide as much of a traction advantage. A traction control system can prevent overheating and improve traction.

Torque vectoring (a.k.a. helical or "Torsen" type) diffs basically manage torque split on their own. The catch is that they only work if both wheels have at least some traction. If one wheel is spinning freely (e.g. on ice or in the air), all bets are off. A traction control system can cut in if that happens, applying just a little bit of brake to the spinning wheel to make everything work again.

 

[d00df00d]

A couple more points:

Sometimes, "traction control" systems include launch control to manage revs and throttle on a hard launch. Also, stability control systems use brakes to keep the car from spinning out while cornering. These are independent of driving the wheels.

 

[OVERKILL]

LSD's of the clutch-type can also be modified to increase the clamping. It is not uncommon for Mustang guys to cram a few extra clutches in each side, which makes the action much heavier; many will chirp the inside tire under tight cornering.

Ford also varied their clutch use depending on the vehicle. Trucks got a heavier LSD. My Expedition has a very heavy clutch setup and even with one tire on ice, still drives forward.

 

[Colt45ws]

Originally Posted By: OVERK1LL
LSD's of the clutch-type can also be modified to increase the clamping. It is not uncommon for Mustang guys to cram a few extra clutches in each side, which makes the action much heavier; many will chirp the inside tire under tight cornering.

Ford also varied their clutch use depending on the vehicle. Trucks got a heavier LSD. My Expedition has a very heavy clutch setup and even with one tire on ice, still drives forward.

Yes, you can buy a truck preload spring for the clutches, it is heavier.

 

[Popinski]

Thanks for the replies, however, my real question was: How do both LSD and TCS work in conjunction with each other?

 

[Rhymingmechanic]

On my 2WD Silverado, the locking (not limited slip) rearend was required in order to get traction control. That model, 2001, has wheel speed sensors in front, but uses the vehicle speed sensor in the trans as a third sensor. My guess is that the computer compares the VSS reading against the front wheels to determine whether the back wheels are spinning. It would assume both rear tires are spinning at the same rate since the rear is a locker. (That's where the setup doesn't exactly match your question. A limited slip might need wheel speed sensors all around, since the rear tires could spin at different speeds.)

The ABS control module is different for a truck with traction control, so there must be some braking action involved. The effect I've noticed is reducing power. You can floor the throttle on snow and the truck will slowly creep forward, adding or pulling power. Traction control makes the thing surprisingly drivable in the winter.

 

[OVERKILL]

LSD allows both wheels to spin at the same time, whilst TC by itself will try and retard power and shift it to the wheel with some grip.

The two together would allow the retarding of power to aide in traction, whilst applying power to both drive-wheels simultaneously.

 

[d00df00d]

Originally Posted By: Popinski
Thanks for the replies, however, my real question was: How do both LSD and TCS work in conjunction with each other?

See my response above...

 

[Popinski]

I apologize. Thank you for your post.

 

[SteveSRT8]

Challenger's equipped with the LSD have a getrag clutch type. A very well proven design, and a huge upgrade from the old 215MM open diff with Brake Lock Differential (mercedes style).

On the late model Chrysler vehicles, the ESP is an integrated system. It's actually quite sophisticated, and it really works well in almost any conditions.

All the LSD really does is make it easier on the rear brakes as they will rarely be trying to match wheel speeds. Many earlier models wore the rear brake pads early as a result of the BLD use during aggressive driving.

 

[mechtech2]

Popinski - In general, you have a good observation. LSD and traction control don't work well together.
Many supposed 4 wheel drive vehicles are really 2 wheel drive, with open differentials.
Traction controls are either/both brake control or throttle control. Not much else has input to drive or stop a corner/wheel of the car.