Brake Traction Control System

[CapnBoost]

A differential distributes the power, if it slips it sends it somewhere else. Traction control eliminates the power, either by using a central clutch, the brakes, or by limiting the power that the engine is producing.

While they both manage torque they are doing it in very different ways and not always accomplishing the same task. A fully locked up truck is not in any way similar to a torque biasing center diff which isn't at all similar to the focus's traction control.

When I look up specs on the ST170 I only see traction control and 4 wheel abs.

[RacingManiac]

What about a spool/welded diffs?

they aren't technically "diff" anymore......

A diff not not just send the power somewhere else if it slips. If both wheel slips(by the same amount), you spin the tires(note the plural), one wheel slip, an open diff keeps sending the power to that wheel, and it spins on and on. A spool spins both wheel(or if the tire has too much traction, it burns out the clutch, or stall the engine). A LSD will create some kind of resistance on the spinning wheel, and redistribute the power to another wheel. This happens with or without traction control.

[TheScrutineer]

Hi, I have just looked in the log book and found this listed seperate to traction control...

"Brake Traction Control System (BTCS)

This system minimises cross-axle wheel slip to enhance traction at lower speeds"

While I understand this and an LSD are completely different systems, if the slipping driving wheel on one axel slips the brake will engage on this wheel. Then the open differential will transfer the power to the other driving wheel. So in essence, this is achieving exactly the same as an LSD. Curiously it says 'at lower speeds' which maybe a disadvantage of this limited system?

[RacingManiac]

I think at lower speed there is a greater chance of you being able to overwhelm 1 wheel especially at higher steering lock due to the steering geometry effect(caster, for instance), higher speed you are unlikely to have the power or the cornering force to induce the wheel to unload itself to have the need for that correction....

http://www.fordtransituk.co.uk/fordt...ngdynamics.htm

also available on transit van....

"BTCS continues to be available on Transit as an option and is particularly useful on those vehicles that encounter a wide range of slippery surfaces where traction might be problematic – which is generally the case around construction sites. Ford's BTCS-system comes into effect as soon as wheel slip is detected, using the brake to slow the wheel until it regains grip. It doesn't throttle back torque from the engine, but transfers the torque to the wheel with the most grip."

That is a limited slip diff function basically....

[CapnBoost]

It doesn't throttle back torque from the engine, but transfers the torque to the wheel with the most grip."

That is a limited slip diff function basically....

Except that this would be useless racing, and a limited slip would be useless on ice. While they accomplish a similar function their uses are entirely different. Additionally, if the brake is involved then the torque isn't making it to the tire. That torque is eliminated, not distributed.

[RacingManiac]

The spinning wheel when braked, does not continually receive the same amount of power from the engine, because the open diff will now at this point, will not see the spinning wheel(now no longer free-spinning) as a path of least resistance, and the power will be redistributed. The amount of brake applied I imagined is proportional to the amount of wheel speed difference. No argument that some power will be lost because you are indeed braking one wheel, but idea is apply enough brake to allow the power to go to the opposing wheel, not to stop the wheel.

Its a transit van, its not supposed to be raced(though some might suggest otherwise), and a ST170 is still a road car at the end of the day. You can always fit an actual limited slip diff to the car afterall. Limited slip diff would be useless on ice, if both wheels are on ice, if single wheel on ice the other on something with more traction, then you would have some forward momentum....

[CapnBoost]

The spinning wheel when braked, does not continually receive the same amount of power from the engine, because the open diff will now at this point, will not see the spinning wheel(now no longer free-spinning) as a path of least resistance, and the power will be redistributed. The amount of brake applied I imagined is proportional to the amount of wheel speed difference. No argument that some power will be lost because you are indeed braking one wheel, but idea is apply enough brake to allow the power to go to the opposing wheel, not to stop the wheel.

Its a transit van, its not supposed to be raced(though some might suggest otherwise), and a ST170 is still a road car at the end of the day. You can always fit an actual limited slip diff to the car afterall. Limited slip diff would be useless on ice, if both wheels are on ice, if single wheel on ice the other on something with more traction, then you would have some forward momentum....

That's what I'm saying. They have other purposes. No amount of traction control will perform the duties of a LSD, and no LSD will perform all of the functions of traction control. I don't think that it's factually accurate to say that traction control acts like a LSD because it doesn't.

[RacingManiac]

BTCS is not a "traction control" as Ford's own press document says, it does not limit torque to the wheel, which is what fundamentally a traction control does. It does infact performs the function that emulates a LSD at low speed.....

[CapnBoost]

BTCS is not a "traction control" as Ford's own press document says, it does not limit torque to the wheel, which is what fundamentally a traction control does. It does infact performs the function that emulates a LSD at low speed.....

Their press document calls it Brake Traction Control System (BTCS)
"Ford's BTCS-system comes into effect as soon as wheel slip is detected, using the brake to slow the wheel until it regains grip. It doesn't throttle back torque from the engine, but transfers the torque to the wheel with the most grip." They say it works particularly well when one wheel is slipping but the other is on dry tarmac. That implies that it also works when both wheels are slipping. So yes, it does allow an open diff to function like a limited slip diff.

I don't know if Ford's system is similar to Jeep but Jeep's system (also BTCS) can individually brake any wheel that is slipping, a LSD cannot do that.

[RacingManiac]

I just read the press release posted on the hideout section here at UCP on the new McLaren MP4-12C....it eliminated the LSD altogether(for a 600bhp, RWD, mid engine super car)and uses an active controlled rear brakes to emulate LSD function, amongst other thing....

[Matra et Alpine]

I;m not so sure this braking instead of an LSD is a good idea.

Reason ? An Audi was takn for one fast lap of the 'ring and they didnt' turn of it's "stability control" ... this meant the computer was applying braking forece at almmost every corner as the car fought for grip .... the disks and pads wre DESTROYED and had to be replaced having over-heated.

I hate to think what the brake wear woudl be like when this is pushed REALLy hard with it braking the inside rear wheel on entry to corners and braking on that wheel AGAIN when powering out of it. Gonna be a REALL bummer on trackdays . Lots of orders for one disk and one pair of pads I predict

"clever" -- but is it really "better" ?

[Ferrer]

I;m not so sure this braking instead of an LSD is a good idea.

Reason ? An Audi was takn for one fast lap of the 'ring and they didnt' turn of it's "stability control" ... this meant the computer was applying braking forece at almmost every corner as the car fought for grip .... the disks and pads wre DESTROYED and had to be replaced having over-heated.

I hate to think what the brake wear woudl be like when this is pushed REALLy hard with it braking the inside rear wheel on entry to corners and braking on that wheel AGAIN when powering out of it. Gonna be a REALL bummer on trackdays . Lots of orders for one disk and one pair of pads I predict

"clever" -- but is it really "better" ?

Apparently something similar happened to autoblog while testing the new Mk VI Golf GTI. And they weren't even on a track.

[RacingManiac]

Matra that's what I thought as well, there are more stories of stuff like that for cars with a brake emulating LSD doing track work. I am surprised McLaren is going that far to do that on their 600bhp supercar....I can see the brake steer since I'd imagine the duration of the application to 'steer' the car into the corner is actually minute portion of the turn-in phase, but LSD will be acting for much longer during as the power is being applied....granted a mid-engine car probably will have more robust rear brake due to the rear weight bias allowing the rear doing more work(thus maybe with more pad material and braking power), they are still not meant to pull that kind of duty I'd think...

[wwgkd]

Since most of this seems to have been resolved I'd just like to point out that LSDs are not in fact useless on ice. Most serious offroaders prefer a LSD or better yet full locking diff to the electronic systems. If you're on ice the LSD will keep you from sitting there with one wheel spinning and the other doing nothing, thus accomplishing it's job just as well as the electric system.

If you're retarded enough to punch the throttle all the way and spin both tires without stopping, then no form of traction management is going to save you from a date with a ditch or worse. The reason a lot of offroaders don't like the electronic forms of managing traction is that the early versions especially got confused easily and would often result in somebody getting stuck 6 feet from where the pavement ended and sand/snow began. This is largely due to the fact that in sand or snow quite often all four tires are slipping and it would cause the system to brake all of the tires at the same time and immobilize the vehicle. Toyota 4runners were particularly notorious for this.

[Alastor]

"clever" -- but is it really "better" ?

Mclaren seems to think it is better. They obviously considered multiple paths and choose to go with the BTCS. The only real benefit I can see is cost. If they were already going to develop/use a traction control system, then it seems like minimal additional development is required to emulate the LSD. As well, you end up with essentially zero recurring costs, since it presumably uses the same hardware as the basic TCS.

The downside as you mentioned is an increase in brake disc and pad wear. But they just may consider those consumables and the trade off acceptable. Also, I wonder what they expect the average customer will do with the car. If one hard lap can destroy a set of discs and pads, then they must not expect much track use. Seems like a curious conclusions when selling a supercar, but maybe that is true.

But the cost savings only seems really significant over developing a new LSD from scratch. I would have to imagine that there are COTS LSD solutions that they could make work with a moderate about of engineering. You still have recurring costs, but it seems like it shouldn’t be significant compared to the price of the car and it would be much more robust for a performance orientated vehicle.