Traction control does work

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4ePajero
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Re: Traction control does work

Wed Mar 09, 2011 3:48 pm

Mcnoogle wrote:Also, how does the TC react with water crossing-with a slippery riverbed, surely when your wheels start spinning, you will lose all torque to that wheel, and thus stop dead?
TC brakes only the wheel that loses traction (the spinning one).
It then "BSs" the system that that wheel has traction again, albeit "traction against the brake".
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Re: Traction control does work

Wed Mar 09, 2011 3:51 pm

Aaaahh,

Now it starts making sense, same as one would use handbrake for same on rear LSD.
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Re: Traction control does work

Wed Mar 09, 2011 4:03 pm

the interesting part is that while the TC braked wheel(s) is still spinning (while the brakes are trying to stop it) only a part of the engine power is going to the wheel(s) with traction. The rest is lost via heat generation from the brakes.

As soon as the wheel(s) stops dead the losses are marginal as no heat is generated (no energy loss except for the vacuum system powering the brakes) and all the power of the engine (that was lost to heat) goes to the wheel(s) with traction.
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Re: Traction control does work

Fri Mar 11, 2011 1:12 pm

Yes I also agree TC works well provided that the driver uses a very steady right foot.
A technique that I use with TC is the old “left foot braking” one, as in rallying. TC and ordinary braking is not mutually exclusive. I select a reasonable throttle opening before I go into the obstacle and hold that steady Then I control the vehicle speed via the brake pedal with the left foot. Its easier with automatic and quite quick to get used to. Yes your first few attempts will be hair raising, but once you master that it is a good way to keep the traction steady and the TC unconfused by holding a steady throttle. As a matter of fact I am so used to left foot braking now that I use it all the time. Think of parking or three point turning for instance.
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Gerrit Loubser
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Re: Traction control does work

Sat Mar 12, 2011 8:31 am

Whether electronic traction control or a mechanical difflock system is “best“ is a great question and a very tricky one to answer, because the variety of systems is so large and because “best“ can be defined in so many different ways.

Why did the motor industry embrace electronic traction control? There are a few good reasons:
* Cost. The system allows the control of spin-out by mostly using hardware that is already on board (for the ABS system)
* Idiot-proofing. Traction control readily integrates with vehicle electronic systems and allows the vehicle and indeed the driver/occupants to be protected from driver mistakes (e.g. generating wind-up by leaving diffs locked on high grip surfaces or skidding off a track due to steering interference from locked diffs).

Absolute vehicle mobility was not the reason for the rise in popularity of traction control. If the goal is mobility over terrain where spin-out is likely (whether that is due to terrain undulations or variability in underfoot conditions), there is no substitute for a system that uses mechanical differential locks at all inter-axle locations and in all axles under full control of a driver that knows what he is doing.

As a gross generalisation, but based on the current state of the art of electronic traction control, I would judge a system with traction control at all four wheels and a center diff lock (if full time 4x4) to have approximately equal mobility to a system with mechanical rear and center diff locks only, all else being equal. Each of these systems will have the upper hand under certain specific conditions, though: traction control on all four wheels might come out on top in slow rock crawling where the traction control system has the time to react, whereas the rear diff lock system will win in the sand or on a loose hill climb where momentum has to be used and where things happen to fast for the electronics. The moment another axle diff lock is added to the latter system, the traction control system is blown out of the water.

The primary advantages of mechanical diff locks are:
* Nothing can beat the speed at which they can alter the torque split between the diff's output shafts.
* They can transfer 100% of the torque via one output shaft, i.e. they have the largest possible torque bias ratio.
* All of the engine's power is always available for propulsion.
* Torque is transmitted in a smooth manner without interfering with gear ratios.

The primary disadvantages of mechanical locks are:
* They can lead to driveline abuse in the hands of the inexperienced.
* They can lead to steering interference.
* They are expensive to fit, because they require dedicated hardware. This also adds mass.
* They are expensive to fully integrate. into an electronic control system
* They can generate large loads in driveline components due to their large torque bias ability.


The primary advantages of electronic traction control have been alluded to:
* Cost
* Easy integration into control and protection schemes.
* Ability to act on all wheels
* Ability to prevent steering interference by electronic means

The primary disadvantages of electronic traction control are:
* The system is reactive, because it has to determine that slip has already occurred by means of wheel speed readings instead of preventing slip from ocurring in the first place. Until traction control systems can use wheel torque readings to determine what is about to happen, this disadvantage will remain.
* It is fundamentally flawed to apply brakes when propulsion is the objective. In a perfect traction control system, the wheel speeds on an axle will be regulated to be identical and equal torque will be transmitted via each side shaft. This means that 50% of the power transmitted via that axle is dissipated as heat. Brake wear is also accelerated.
* Real traction control systems are not able to equalise wheel speeds perfectly and pulse the application of the brakes at the slipping wheel. If that wheel is actually brought to rest, the gear ratio of that axle is halved due to diff action, which plays havoc with the tractive effort available. In practice the wheel is not brought to a complete standstill, but the effective gear ratio still pulsates.
* Traction control systems depend on a hydraulic brake booster for their actuation energy. These components were developed for ABS and typically have a short activation duty cycle capability. If they are called upon to operate continuously for a longer time (long difficult climb) they generate excessive heat and switch themselves off in the interest of self preservation, leaving the vehicle with open diffs.


So what is the ultimate system? That is not easy to answer, but I think it would be very hard to beat a fulltime 4x4 system with center and rear mechanical diff locks in conjunction with electronic traction control that can operated simultaneously with the diff locks...
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Re: Traction control does work

Sat Mar 12, 2011 11:56 am

Gerrit is generally right in saying:
It is fundamentally flawed to apply brakes when propulsion is the objective. In a perfect traction control system, the wheel speeds on an axle will be regulated to be identical and equal torque will be transmitted via each side shaft. This means that 50% of the power transmitted via that axle is dissipated as heat. Brake wear is also accelerated.
Agreed. Why would you as general rule apply brakes while trying to maintain propulsion. However if you watch the video and for those that can recall climbing up a river bed with large rocks, you will be aware that after pushing hard and getting over a rock or other hill the car takes off. What you do instinctly is to get off the accelerator and onto the brake so stopping the car racing for the next rock. So far so good, but now you approach the next rock. You get back onto the accelerator but your engine is sitting at idling speed, you have zero turbo boost and hardly any drive from the torque converter. By the time all these systems gets back into play the car has stopped and you get this jerky motion that you see on the video. If you had kept your right foot partly down and stopped the car from storming the next rock at speed using your left foot on the brake, you have solid continuous power to the wheels when you need it. At the correct time you only have to release the brake. No engine speed catch-up, no turbo lagg and no torque converter delay will be noticed. This is a technique for those of us who have TC as a given. I am not saying it makes TC better than DL or anything like that. It certainly works for me.
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Re: Traction control does work

Sat Mar 12, 2011 12:55 pm

Gerrit Loubser wrote: * It is fundamentally flawed to apply brakes when propulsion is the objective.
I seldom argue with Gerrit, especially if it concerns drive train matters.
I have a problem with the above.
TC brakes only the wheel spinning (not contributing to propulsion), so to "apply brakes" to a spinning wheel cannot effect propulsion.
Gerhard Fourie
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Re: Traction control does work

Sat Mar 12, 2011 1:59 pm

Bigwill, you are right that driving through the brakes can be a very useful rock crawling technique, but then this is performed by the driver at will and he is able to judge whether it is appropriate and desist from doing it if not..

Gerhard, you are right that the slipping wheel might not be contributing to propulsion, but what I am referring to is that a significant amount of power that might have been available for propulsion is now turned into heat at the brakes. Sometimes in serious dune climbs the vehicle has barely enough power to make a climb in a high enough gear to generate the necessary momentum and any effort that channels some of that power away from propulsion is undesireable. This scenario is rather less relevant if you have a 5 liter V10 TDi under the bonnet, of course :mrgreen: .
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Re: Traction control does work

Sat Mar 12, 2011 2:29 pm

Exactly my point! And drivers must get used to using the left foot for when this needed.
Willie from Jo'burg
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Re: Traction control does work

Sun Mar 13, 2011 11:21 am

Vehicles are becoming more technically advanced. Some people hate it and will avoid buying such vehicles and others like the idea of tech advancement and will choose their next vehicle with that in mind. We have come a long way from having to drive up to the obstacle, then stop and getting out in the mud and rain, turning the hub-locks (that are now tough to turn and dirty and slippery), only then selecting the required 4x4 option before continuing.

Modern vehicles get most of the things done on the fly and without too much intervention from the driver.

If the going gets really tough on a track that is designed to challenge car and driver, I'll put my money on the experienced driver with mechanical devises to operate at his experienced demand.

I stay away from 4x4 challenges and enjoy the comfort and ease with which my Pajero goes through the outback terrain. I also remain of the opinion that the petrol engine is better mated to the auto box and electronic controls than the diesel engine is. Whether this is due to the system being designed for the petrol engine or just chance or just my warped sense of observation, is open to debate.
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