How do the Traction Control System (TCS) and Limited Slip Differential (LSD) work?

As described in Honda’s technical literature on the NSX:

 
"The torque control differential is designed to help maintain traction when    driving over split friction surface conditions and maintain vehicle stability at speed and    in crosswinds. It employs a multi-plate clutch and planetary gearset design. Like many    conventional LSD (Limited Slip Differential) systems, this unit resists the rotational    speed difference between the rear wheels and attempts to maintain the same rate of    rotation at both wheels. But unlike most units, the amount of additional torque resisting    the rotational difference is limited to 16 kg-m. This reduces understeer by not trying to    keep the car from going towards the direction in which it is being steered. In a cornering    situation, too much torque transfer to the inside rear wheel tends to oppose the turning    moment from the front wheels, thereby increasing understeer. 

 
If the NSX should be disturbed from its intended direction in a crosswind, the    differential will detect the rotational difference between the two rear wheels and    transfer torque to the slower rotating wheel. This has the effect of helping to keep the    car on the desired path. 

 
Compared to both conventional open differentials and limited slip differentials,    straight line tracking is improved, especially in crosswinds. On a split friction road    surface, the acceleration time is reduced compared to a conventional open    differential." 

[BJ] The stability in crosswinds is an irrelevant and uneducated statement which was probably used for marketing purposes. LSD units simply resist wheel speed differences by the clutch plates locking together. When the tires and torque are equally distributed and locked together (like a spool), the car wants to go in a straight line, thus giving the car stability. More detail on differentials from my article (for an NSX) on MotoIQ.com:
Differentials are used in a car so that the driven wheels can rotate at different speeds through a turn. This is important because while in a turn, the outside wheels have a longer path to travel (due to a larger radius) and make more revolutions than the inside wheel. A differential allows this to happen without resistance using engine driven orbiting spider gears that are in mesh with bevel gears which are attached to the axles. In vehicles without a differential such as a kart, the axle is solid and locked (aka: spool) with both driving wheels forced to rotate at exactly the same speed, pushing the car straight. By nature a differential wants to put all of the engine’s power to the wheels with the least amount of traction–the path of least resistance. The side effect of this is unwanted inside wheel-spin out of corners, and even single wheel spin on straight-aways (aka: peg-legging, one-tire-fire, etc…). This greatly affects acceleration since the power is not able to be put to the ground efficiently and is lost through the inside unloaded tire. When accelerating out of a corner, the inside tire represents less than half of the available grip compared to the outside loaded tire. Under aggressive driving conditions, this wheel spin also makes a car difficult to steer with the throttle because the inside tire will spin and the car will not rotate under acceleration, or slide/drift. Because of the shortcomings of conventional ‘open’ differentials, they are not desirable for either fast lap times or ability to rotate and throttle-steer cars.
A limited slip differential fixes this problem by resisting the differentials tendency to deliver all of the power to the free spinning wheel. It accomplishes this by reducing the difference in speed between the two driven wheels and thus delivering the engines torque to both wheels. 1991-1994 NSX’s like our project NSX have conventional clutch-type limited slips. These limited slips use driven and drive clutch plates preloaded with a cone-spring (Bellville Washer) to provide a resistance to the bevel gears spinning against each other at different speeds. This resistance helps keep the driven wheels spinning at closer speeds to each other rather than the big discrepancies between the two wheels like in an open differential. The amount of limited slip resistance is controlled solely by the preload of the cone-spring which in the case of the stock NSX is pretty light. This is fine for the output of the stock engine with soft stock suspension and small tires but as you increase the power and grip, the locking ability is not strong enough and inside wheel spin rears its ugly head again. While the stock LSD unit can be preloaded to be ‘tighter’ and more aggressive, it still has shortcomings in locking ability, design, and tune-ability. For our turbocharged engine, and planned bigger and stickier tires, this was not going to cut it.
The OS Giken “Super Lock” LSD is a more advanced design of a limited slip called a Salisbury differential. The Salisbury diff is one of the most common designs in racing cars and uses cone-spring (bellville washer) preloaded clutch packs to provide the limited slip action just like a conventional limited slip but with a twist. The cross shaft of the spider gears is actually a cam that rides in a hole between two half’s of a split carrier that is driven by the ring gear of the differential. As the ring gear applies torque to the differential case and the carrier, the cross shaft cam which is coupled to the wheels is wedged into the carrier’s “ramps”, applying force that wants to split the two halves apart. This force squeezes the differential’s clutch packs. As more torque applied to the differential, the more the clutch plates lock together and prevent differences in wheel speed. The OS Giken LSD has been reliable with over 1,000whp under road racing uses without any issues.[BJ]

TCS is not affected when you upgrade wheel/tire sizes as long as you keep the same size ratio. This is because it looks at the ratio of the speeds of the front and rear (and left/right) wheels.

The TCS systems tolerance for the ratio is reported to be 5%. As long as you keep the ratio within 5% of stock TCS should work with any size wheels you can mount on the car. See section 4.4 for a list of wheel sizes that NSX owners have tried and the appropriate tire sizes to use with them.

TCS Comments

[NM] I experimented with Dan O. at a soapy skidpad with the TCS on – as well as separately in a wet and empty parking lot. I have a 91 so I can’t speak for later models which may or may not have updated systems.

My experience on the skidpad was that TCS worked very well. Even if I floored it and increased wheel angle, the car just started to predictably understeer at an predictable rate. The TCS was not obtrusive at all.

On a damp, empty parking lot I would accelerate with TCS on in a straight line then take a very sharp 70 to 90 deg turn with lots of throttle. The TCS did little to control the wheel spin in a straight line (seems to kick in a little unpredictably) – but when I would turn the TCS came on rather abruptly in the turn and it was very disorienting. So disorienting it is almost irresistible to hit the breaks and then the fun really begins!!! Once I got the hang of it and was comfortable with the "kick in" it became much more predicable and manageable.

IMO – if you have invested in driving schools and are an alert and confident driver, you will be better off without the TCS in the dry. In the wet, I would definitely use it, but only after going to a parking lot and getting used to it so you know how your car will react to TCS. At the track I only run TCS when it is raining and I have my R1’s on (R1’s stick in the LIGHT rain better then most people think!). Most good instructors with knowledge of the NSX will ask you to turn it off (in the dry) and will evaluate your driving style, experience, and conditions when recommending TCS in the rain.

[CA] I was driving the NSX after work yesterday, taking in moment and enjoying the idea of keeping it, I was at a stop light, the light turned green and I (believe it or not) slowly accelerated the TCS light started to blink and the power was effectively cut, I was barely rolling and could not accelerate, nor could I turn the TCS off (????) after about 7-8 seconds it cleared and have not been able to duplicate the problem.

I want to reiterate that I was not hot rodding (I have found new inner peace with merely driving normally!) and that this was the softest accerealtion I possibly could have done.

[SS] The only two times I have spun my car [’95 -T]is with TCS on, in dry conditions. My experience: With TCS off, the car slides like any other car, and you just simply steer into the slide and GENTLY let off the gas to line everything back up. Just like you were taught in drivers ed. Just like every other car without TCS.

With TCS on, when the rear looses traction, starts to slide, then TCS kicks in and effectively brakes the rear, trying to put it back in place. Meanwhile, I was steering into the slide as usual, and the car tail whipped in the opposite direction of the slide, and spun. This snap-oversteer condition is very fast, and virtually unrecoverable. I have never fought so hard to recover from a slide. The TCS computer sucks in the dry.

Yeah, OK the initial slides were my fault, but the TCS computer SHOULD NOT INTERFERE with my ability to recover. The owners manual states something to the extent that driving with the TCS on does not require any special technique than driving with TCS off. Total CRAP. With TCS on, and in dry conditions, you continue to steer INTO the curve, not the slide, nail the gas, and let the computer sort out the rear end. Is this Hondas definition of ‘no special technique’?

I very much dislike the TCS computer in the dry. And I wish Honda would pay for $10K of suspension and steering damage due to my last spin, with TCS on.

ICBW, but I think they modified the TCS computer in 97+ years to help correct this.

[RKB] Althought the TCS was updated in the 97+ cars to keep the car under power in corners where it’s already too deep and a lift would cause oversteer – too many people including myself have noticed some strange throttle behaviour.

[RBA] I know from my TCS experimentation you can get away with a fairly decent rear-end slide and still line it out – just stay on the throttle and don’t try to countersteer. One of my rear rims found this out the hard way. 😉 In my ’93 I found that TCS could still recover from sliding the back-end about 3 feet from a standing still pull-out and hard left onto a roadway. Much further around and you get real cozy with the grill of the guy behind you…

Technical Information