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Discussion Starter #1
I'd like to retrofit brake activating TC (not ignition cutoff like oem). What's entailed in doing this with our cars?

I imagine with 4 channel ABS this shouldn't be a huge ordeal. But what do I know?:confused: I'll tell you what I know. My inside wheels spin incessantly on at least one turn on every track I drive and I think LSD is the wrong approach to solving that. Brake activating TC seems like the perfect solution.
 

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A possible solution to your problem is to just lightly left-foot brake while you're on the throttle exiting such a turn.

xtn
 

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I'm fairly sure that all brake-managed systems also use throttle management as part of the entire package -- at least, the ones in Jags, Mercs, and Fords do. And I've driven C63's with and without LSD back to back -- believe me, LSD *is* the right answer.

Steve
 

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confused...

I am not sure I understand.

You are in a tight turn, with the inside wheel carrying less weight than the outside. The inside is still carrying some weight and has not lifted off the ground. (I wonder if that is possible since most of the weight in the car is biased towards the rear.)

So, now you apply throttle and the inside wheel spins. You want to apply the brake. The result will be to apply most of the torque to the outside wheel, thus accelerating you through the corner.

Good idea, but the implementation is beyond current technology as far as I can tell.

Consider anti-lock braking for a minute. The ABS controllers can only apply full brake, release it, apply it and cycle. Granted it can do this quickly but there is no partial braking. Partial braking would be ideal because then the control could apply the brake only enough to have non-sliding friction, much better to stop than the aforementioned cycling, which results in sliding friction.

On to trying to control the torque application by applying the brake on the inside wheel. It will clearly not work if you try and cycle the inside brake as you will actually cause the car to slow when the brake is locked. I wonder what the car dynamics will feel like with the outside tire driving forward and the inside locking and unlocking? I might hazard a guess as to dramatic oversteer, with a spin, since you are probably on the limit of lateral acceleration anyway.

I think the ideal you are looking for is to partially brake the inside to prevent the spinning wheel, but still allow it to turn at car speed. Allowing car speed will help with cornering. Maybe if it even impeded the rotation to slightly more(!) than car speed will counteract understeer but that is not possible since you already have minimal traction.

Unfortunately I do not know of any servo systems that allow for careful control of partial braking.

Having just experienced the inability of the normally amazing Lotus ABS to control the locking characteristics of the AP brakes, I am pessimistic. But my wife is the mechanical engineer in the family and she has no interest in analyzing the dynamics involved. (I still love her.)

Michael
 

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Good idea, but the implementation is beyond current technology as far as I can tell.
BMW has been using it with open diff cars for years - it used to be called "ADB" and now appears to be called "ADB-X." What's being described is exactly how the E46 worked.

The BMW uses only proprtional rear braking for ADB. Throttle management only comes into play if DSC is also enabled (they can be disabled separately although ADB is always enabled when DSC is).

http://www.bmw.com/com/en/insights/technology/technology_guide/articles/automatic_differential_brake.html

Note, this is not traction control. ADB is merely a solution to an open diff.

I'd bet a system such as this would be nearly impossible to implement in the Lotus without completely replacing the braking system.
 

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BMW has been using it with open diff cars for years - it used to be called "ADB" and now appears to be called "ADB-X." What's being described is exactly how the E46 worked.

...snip...

I'd bet a system such as this would be nearly impossible to implement in the Lotus without completely replacing the braking system.
Unless you are a very inclined mechanic and software tinkerer, with a high tolerance for failure until success, my guess is simply buying a car that had this feature would be the only practical method.

On the other hand, it would seem to me that Lotus could put something like this into production via the ECU via electronic throttle ABS management--but it would seem like a good idea to solve the reported issues with the braking system first, or at least in concert with any upgrade effort.

By the way, I have no solid foundation for these thoughts other than speculation.
 

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Unless you are a very inclined mechanic and software tinkerer, with a high tolerance for failure until success, my guess is simply buying a car that had this feature would be the only practical method.

On the other hand, it would seem to me that Lotus could put something like this into production via the ECU via electronic throttle ABS management--but it would seem like a good idea to solve the reported issues with the braking system first, or at least in concert with any upgrade effort.

By the way, I have no solid foundation for these thoughts other than speculation.
Yup.

I believe Kelsey-Hayes, aka LucasVarity, aka TRW already has a somewhat similar differential braking implementation in their "VSC" (ESC on Saab, Renault, GM, etc.) but don't think they go so far as to openly claim it as an LSD replacement the way BMW has.

In other words, Lotus could probably spec. it that way (the ABS system is/was Kelsey-Hayes) but I seriously doubt they'd ever implement it without handling the software themselves.

Initially, the sporting BMW crowd was concerned that it would lead to accelerated rear pad wear but it proved to not be the case. Regardless, the car is still applying the brake(s) and I'd take an LSD over that.
 

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Traction control on the Vette is brake-based. A less intrusive setting is called "Competition Mode" and allows some tail-out fun but puts the "brakes" on when overdone. The way it works is by applying the inside rear brake...and this is in addition to the stock supplied clutch-pack LSD. The end result is that it sometimes wears down rear brakes to the point of premature failure of pads and leads to slower lap times. A skilled driver will perform better without it engaged. This is used ONLY because the car is oversteering to an unsafe (as perceived by the ECU) level.

Now your application is calling for the TCS to limit inside wheel spin, caused by unweighting of the inside wheel in a turn/exiting a turn and there not being enough traction ofthe tire...resutant wheel spin limits your drive/application of power.
That, and I am aware of your reluctance to employ one, is a textbook symptom of not having an LSD.

The only question comes down to which one will work for your use. If it's just that the wheel is unweighted and the tire can't handle the power given, then a Torsen/Quaife/Factory LSD will work.
If you are bumping a curb and lifting your wheel off the ground...then a clutch-pack is required.

Know this, that a Quaife/Torsen does not promote understeer on corner entry like a clutch-pack because it operates as an open diff when not on the gas. It's the clutch-pack that still operates in LSD mode even when off the gas...and it's that function that allows cars equipped with them to trail-brake MUCH later without swapping ends.

The negatives of running with an LSD can be easily overcome. The negatives of not running with an LSD, when one is needed, is not easily overcome. Sure, you could limit your application of throttle...but wouldn't planting it be much more fun?

Good luck,
TomK
 

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Discussion Starter #9
From what I understand, there is a factory option for a clutch pack LSD for the cup cars, but the others get the torsen LSD as an option. I still don't completely understand why one would opt for one or the other. regardless, IMO the car should not have anything hindering the open diff unless there is severe differential wheel speed and whatever it is should be very reliable and light. IMO brake-based TC is the ticket for our cars since, presumably, such a system would answer to all that criteria. It really shouldn't take much brake pressure to control wheel spin so I don't imagine the brake pad life would be greatly effected.

Does anyone understand the basic system components in the BMW or GM (Vette) systems and how the Lotus ABS system differs?
 
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