Diff-lockers with traction control
I intend installing ARB air-lockers in a Defender with traction control. I can't see any reason for this to be a problem - the traction control will simply never detect a wheel-spin, and therefore won't engage.
But it did make me wonder if there are any strange effects if TC is used in conjunction with automatic lockers, or limited slip diffs of either the torque-sensing or the speed-sensing types? (Not that I can see the point of having that combination - just wondered if it would misbehave).
No problems with LSD - the brakes would suffer less wear. A different thing are detroit lockers and similar systems: As these are no differentials in a classic understanding but sort of an overriding cluth allowing the faster wheel to override, I expect serious problems.
It seems like the perfect set up to me, locker in the rear and TC up front, minimising the chance of totaling CV joints etc as can be the case with a front locker.
The only potential problem I could think of is if the ETC compares front and rear wheel speed, it might confuse things if only one front wheel had traction, but can`t see it hurting anything.
I would make a post an www.aulro.com it is an Australian LR forum, nearly all the later model defenders over there have ABS/ETC so I would be suprised if someone over there had`nt done something similar.
Well, you raise an interesting point, Col.
In principle, TCS works best when all diffs (centre included) are *unlocked*. In an ideal TC system, the brakes should be applied independently to each wheel, and progressively. With all open diffs, only one wheel will spin when traction is lost. The ideal TCS would progressively retard that wheel to the point where next wheel will also start to spin (or of course, the vehicle moves forward). TCS will then progressively apply the brake to that new spinning wheel, starting at low pressure, while still maintaining the higher pressure on the first wheel. And so on, until all four wheels are turning. This all happens in an instant, and can be repeated several times per second.
This ideal system would minimize the total amount of braking force applied, so maximizing the useful engine power, and minimizing brake wear.
Any locked diff would potentially mean that the TCS is trying to stop a wheel from turning when it has to turn. For example, with the rear and centre diff lcoked, and good traction only under one front wheel, a TCS would try to hold the rear wheels, until the front wheel with grip started to turn. But the transmission
must turn the rear wheels if rear and centre diffs are locked.
(In practice, TCSs tend to substitute independently progressive braking with a series of momentary "grabs" at a wheel. The frequency of these grabs does much the same thing as progressive braking, but a bit more sloppily. A system with independent braking pressures at each wheel would be hugely complex, I imagine. But the overall effect of the simpler system is very similar to what I described.)
Locking all the diffs avoids any problems - the TCS isn't activated, because all the wheels are turning. Locking only the centre diff makes TCS a little less efficient, but seldom creates a serious tussle between brakes and transmission. And the benefits of locking the centre diff almost certainly outweigh the disadvantages.
I'm not a big fan of TCS. It has two advantages - it's pretty much idiot-proof, and it's very cheap to add to an ABS system, as all almost all the hardware is there already.
But it can sap a huge amount of power (contributing to overheating if the car's already working hard in hot weather), it wears out your brakes, and even the fastest system are reactive - a wheel has to stop before TCS kicks in.
Actually, I can't see the point of anything other than a full manual locker http://www.horizonsunlimited.com/ubb/smile.gif
Hello Michael, it's been a while.
You've pretty much closed your own argument, just a few precisions:
TCS involves a speed sensor on each wheel, and works on differences, trying to slow the faster wheels down to the speed of the slowest, which logically has the most grip.
It doesn't wait for you to grind to a halt to do this, the best application is on snowy roads, but it always allows for ther speed difference experienced in the tightest of manoeuvres. Consequently it will never be able to replace the locked effect.
It uses a hybrid algorithm somewhere between the emergency brake assist and the ABS system; and is almost invariably linked into the engine's ECU. The good old cable between your foot and the injection pump is becoming quite rare. Hence no overheat problem as the ECU reduces power when the TCS applies the brakes.
The ABS has to disactivate when you lock the standard (centre) diff on a LR, I wouldn't be surprised if the CTS did the same. Aftermarket difflocks might mess up the ABS system because they don't send a "locked" signal to the system's brain. Putting a line onto the centre diff's "locked" sensor/switch should get round that.
Stop the car with a wheel in the air, and then set off again. The CTS changes its logic; and rather than pulse braking it releases little bursts of torque to the wheel, until all wheels are turning at about the same speed.
LRs are designed to cope with constantly changing surfaces, Farmer Brown doesn't want to have to stop, lock hubs, pull levers, disconnect roll bers etc. before,er, stopping to open the gate and head off the road into his field, any more than the average squaddy (the two principal markets for real 4x4s). Permanent 4x4 and TCS is almost the ideal solution to this particular design challenge.
Considering how much time an overlaner's vehicle spends in difficult terrain, and how that terrain is distributed (days of good road, and days of bad. You have to stop anyway to let down the tyres etc)) I'm for part time 4wd, with good old diff locks and lockable hubs.
The fuel saving is noticeable, remember that a diff is only 93% efficient, and that you're turning a lot of metal without a real reason.
Your reflections imply that you've ditched Nyathi for a new defender. Perhaps a bit long for going shopping.
Hi Luke - how are you?
I stand corrected on how LR's TCS is actually implemented - thanks for the info! I assume, though, that the brake pressure applied doesn't vary from wheel to wheel? (Other than being zero on the slower-moving wheels). It really *is* still a bit sloppy, even though it sounds more sophisticated than I originally thought. Incidentally, my understanding is that the LR TCS does continue to operate when the centre diff is locked, though I can't find any specific refernce to back that up.
My point, of course, was that using the brakes is a clever but inherently flawed way of adding traction, even if they get the algorithms perfect. In theory, at the extreme, it can sap 75% of the available power! So it's not a good time for the ECU to cut power, either.
I do have sympathy with manufacturers who provide TC instead of lockers. It is more convenient, and you can't break things as easily as you can with lockers. And it does work.
Actually, though I was interested in how Detroit Lockers, limited slip diffs, and other unpredictable devices would co-exist with a TCS.
I'm for permanent 4WD, with user-controlled lockable diffs, operable while moving http://www.horizonsunlimited.com/ubb/smile.gif
Regarding Nyathi, we still have her - she is being put through her MOT, and then, reluctantly, we will have to sell her. I am working on another project, though! http://www.horizonsunlimited.com/ubb/smile.gif
Good to see you still around - how're your plans going?
Hi Luke, hows it going ?...Just to stick my two pennies worth in and clean a couple of points up....
On a Defender or any LR product the TC is dormant until we get wheelspin.
As mentioned it used the ABS wheel speed sensors to determine differences in speed firstly between wheels on the same axle - THEN wheels on different axles.
Open diffs allow power to take the line of least resistance - if one wheel is on ice and one is on concrete it will put all available power to that wheel, thats there drawback, but we need to run in this configuration on road in permanant 4 wheel drive or we will get wind up and tyre scrub.
So if you have a light wheel or its in the air or on a slippery surface and turning faster than the other wheel on that axle or faster than the wheels on the other axle, The TC cuts in and pulse brakes only that wheel that is spinning, between 4-7 times a second.
This pulse braking provides resistance - so that the spinning wheel is no longer the line of least resistance.
As its not so easy to turn that wheel any more there is torque transfer back through the open diff to the other wheel which hopefully has traction.
It pulse brakes only to prevent engine stall in higher gears or with low throttle openings.
The ECU does not cut power on the LR systems, if it did the wheelspin would cease and the TC would think that traction has been found and cut out.
As for the TC using 75% of the engines power.....
You are actually losing 50% of your power through a spinning wheel and 100% if a wheel is spinning at either end, on the contrary the TC is preventing this loss and doing it rather effeciently too.
How we have to react as the driver is when we get wheelspin is to add progressive throttle, lifting the rpm, encouraging the already spinning wheel to turn faster, the TC pinches the brakes more aggresively causing more resistance and beceause there is more torque to transfer through the open diff to the wheel with grip, this is what gets us through.
So now differences between CDL engaged/disenged....
With the CDL disengaged if we get wheel spin all availabe power is lost through the spinning wheel. As TC is reactive there is a slight delay before it cuts in and pinches the spinning wheel, this delay can mean you lose quite a bit of momentum and then the transferred torque has to push back though 3 open diffs to get to where it is needed, it all takes time.
With the CDL engaged we are splitting the power 50% to the front axle and 50% to the rear so if we get wheelspin on say a front wheel as long as the rear wheels have grip they with push you - vice versa.
This is our normal Defender configuration if we are likely to lose traction.
So now if we get wheelspin the torque transfer only has to go through 1 open diff - on the same axle and beceause TC works on all four wheels on the LR this is nice and quick - each end isolated, you get further before wheelspin and when it does happen the TC is more effective and quicker.
Make sense Guys ?
As mentioned, with a rear air locker engaged as you always get 100% drive (but not always traction with wheel spin)- theres no difference in speed between the wheels on the same axle - so the TC will never cut in, at the front end it will still be doing its thing between those wheels if theres a speed differential - definitely the best set up as you can still turn.
Great as 100% drive to the front axle is with a FDL - the steering wheel becomes rather redundant when engaged.
With a Limited slip or a self locking system as long as it cuts in before the TC no problem, if it doesnt though they will be fighting each other - potentially - the locker engaging then the TC cutting in and disengaging the locker - ad infinitum, Luke, you know more than me on that, any thoughts, how quick do they cut in ?
Michael, you mentioned using the braking as better than TC....
I take it you mean using left foot cadence braking as we throttle to mimick TC ? its something lots of us do trials driving (and turn off the brake lights with a switch, so the competition cant see when you are doing it!!!)
The TC is braking the spinning wheel only, 4-7 times a second - with left foot braking we are braking the all the wheels, fine if we are not moving - as long as you cadence brake - the power gets transferred to the wheel with grip and the gaps in braking allow the vehicle to move forward. But I cant tap my foot on the brake as quick as TC - maybe Michael Flatley could !!!
But if we have momentum its detrimental - slowing our wheels down with grip -much less chance of keeping going.
TC is a great system and on a Discovery 3 with a rear locking diff and 3rd generation TC - probably the most capable PROCUCTION 4x4 I've ever driven, it works a treat - you can drive up hills you can hardly walk up, without having to putting a hand down, at a crawl.
You mentioned brake wear, a Defender - especially a 110, has even more wheel travel than the Discovery, it keeps its wheels on the ground so well, the TC rarely cuts in unless you are doing some severe cross axles or lots of slippery terrain.
The price of a front air locker buys a lot of brake pads.....
Add a rear air locker to a ABS equipped Defender and youve got an awesomely capable vehicle.
I'll get my spelling right one day...
[This message has been edited by Gipper (edited 08 November 2005).]
[This message has been edited by Gipper (edited 08 November 2005).]
[This message has been edited by Gipper (edited 08 November 2005).]
Hi Grif, this is getting to look like a little club.
To polish off the discussion, I don't think anyone would put a self locker onto a car with TCS as they work towards the same thing. The means of varying the braking power to each wheel is by varying the frequency of applying the brake, which is very quick to kick in. I've got a Detroit locker on another vehicle and it's a lumpy bugger around tight corners, I wouldn't like to combine the two.
Brake wear, who cares? It helps keep the dealer network alive, replacing pads.
Michaels's original question implies that the TCS isn't quite what he's looking for, because drivers have different preferences and styles no car will be exactly what's needed.
The enormous advantage of cars like the defender is that one can modify them to suit, well, almost...
I'm very happy with the size of my Iveco 4x4 camper, which is surprisingly capable. It's fitted out for two, and we are three now (she's absolutely gorgeous, but I'm bound to say that; another one to follow I hope).
LRs are too small for us (her), even Nyathi doesn't have a shower inside; here's the dilemma: Do I find another Iveco and rig it up for four (add an axle perhaps), or for the SAME price do I stop farting around with modest sized vehicles and get a Tatra 815 or MAN KAT so that everyone has their permanant bed? (a real advantage when you're touring)
What I love about the Tatra is its central tyre inflation system, an enormous help to traction, and its independant suspension. Lockable this and that (even the doors) All it needs is a recent watercooled engine, not difficult to do really. Madness? Oh yes, but that's since birth.
I've gone off topic but you did ask http://www.horizonsunlimited.com/ubb/wink.gif
see you out there
My Point with the TC is that the system is actually quite simple in how it works and it works very well.
Yes even I am looking at getting a 110 - youve got the excuse of an extra pair of feet for needing the room - I'm just getting old !!!
Whats your fuel consumption with the Iveco ?...thats the big difference to running a full size truck, you'll get around 3 ish /kpl depending on engine size.
It gets a bit expensive driving around Europe and you find yourself heading through Ceuta or the Middle East alot...with 900 litre tanks !!!
Though thats probably where you were heading anyway....
Ok, Grif, I am a little confused - did I say braking was better than TC?? I think I said (or at least I intended to say!) that any system that uses the brakes to help gain traction is very inefficient.
Regarding the 75% potential torque wastage, here's why:
One of the big misconceptions of a differential is that when a wheel spins, all the "power" goes to that wheel.
An open diff always equalises the torque on both its outputs shafts (internal friction ignored). Torque is the twisting force that results from the engine turning (or trying to turn) a shaft against the resistance provided by the wheels. Therefore (assuming that the transmission can supply unlimited force), the torque on any side-shaft is purely a function of the traction at that wheel. For any given set of load conditions, a vehicle needs a certain level of torque to start moving.
So, to use the simple case of a 4x2 with an open diff, if one wheel lifts into the air, the torque on that shaft becomes (nearly) zero, and therefore the torque on the other shaft is also (nearly) zero. On the other hand, if the wheel is in mud instead of in the air, there will be some resistance as it spins, and therefore some torque. There will be an equal torque on the other wheel too.
Let's assume the car needs 2000Nm total torque to drag itself up the hill. If the muddy ground under the left wheel is capable of supporting 1000Nm without allowing the wheel to spin, then we have no problem - each wheel will provide 1000Nm.
But if the "muddy" wheel can only provide, say 400Nm, then the diff will exert a corresponding maximum of 400Nm on the "solid" wheel. With only a total of 800Nm, the vehicle is stuck. Only one wheel is spinning, but each wheel is contributing an equal amount. We need a further 1200Nm from somewhere.
What TC would do, in principle, is to apply the brake to the spinning wheel, and "artificially" raise its torque. I say artificially, because whatever torque is added by the brake is not part of the 2000Nm total required. In the case above, the brake will be applied until the torque on the spinning "muddy" wheel reaches 1600Nm, made up of 400Nm useful "traction torque", and 1200Nm "braking torque". The open diff equalises the torque on both shafts, so the "solid" wheel also provides 1600Nm. The total torque is therefore 3200Nm, of which 1200Nm is needed to overcome the brakes, leaving the necessary 2000Nm total to move the car.
The cunning part of TC is that it doesn't have to work this out. It just brakes the spinning wheel, until the other one starts to turn. But the torque-equalising effect of the open diff makes it inevitable that the TCS must supply 1200Nm of braking before the total usable torque reaches the necessary 2000Nm.
The downside is that the engine and transmission need to supply 3200Nm of torque to go up a 2000Nm hill. The theoretical 75% wastage is when a permanent 4x4 (3 open diffs) has one wheel with good traction, and the other three wheels with no traction at all. If 2000Nm is required to move the car, the TC brakes all three other wheels to 2000Nm each, so that the last wheel can get its 2000Nm. The engine has to supply 8000Nm for a 2000Nm hill. It's an unlikely real-world situation, but it illustrates the huge additional torque requirements of TC when there are big differences in traction under each wheel.
This is all in contrast with a locker. A locker forces each wheel to turn, but their torques can vary. In the 4x2 example above, locking the diff would result in 400Nm (the maximum) on the "muddy" wheel and 1600Nm on the "solid" wheel. Voilà. No waste. Of course, you can break a shaft more easily, because the torque is distributed unevenly. With TC, the torque is always the same on each shaft - the engine/transmission's maximum will be reached before any one component reaches breaking point.
Anyway, getting back to the original question, I think you hit the nail on the head, Grif - it will all depend on how quickly the LSDs or auto-lockers engage, versus the TCS. I guess on some LSDs TC might actually help provide the necessary activation, instead of using the hadbrake to do it? But overall, it's all a bit too unpredictable for my liking...
Well, thanks for all the interesting posts - I had no idea there were so many of us diff-heads about!
What is more disappointing is all the places you can't go in a big truck. If you like exploring little back roads and tracks, a truck is a real problem. Rickety bridges, narrow roads, and picturesque little villages don't mix well with big trucks.
Also, although you can be very self-contained, you are very restricted about where you can camp. Discrete bushcamps aren't so discrete, and it's physically harder to find places you can fit into. Hotels and guest-houses will not be as willing to let you camp (or even park) in their car parks, and often you can't fit into courtyards, or under arches, or through gateways.
We are also thinking of going up a size or two for our next trip(s), but just wanted to point out some of the snags!
[This message has been edited by SandyM (edited 09 November 2005).]
Excellent! we are geeting involved, You've nailed it Michael, your sums are a bit strange but the principle is spot on.
The ground under the 'solid' wheel will probably give under the extra torque, but that happens under either systems.
LSDs are just that, there is always slip. You have to give more gas to get the lesser slipping wheel up to the torque necessary. Heavy footed drivers apply here.
They're also higher maintenance because there are clutches involved in the diff. (I believe Detrit make a torque biasing diff but I read that it's not very solid)
Auto lockers are clunky, by their very nature there's no half measure. You're either locked or unlocked, whether it's done by software or by a Detroit locker type the result is still clunky.
TC is evidently a 'convenience' solution: by that I mean that you no longer have to prepare for a tricky passage, and it kicks in without much ado.
IMHO there will be more hapless drivers getting stuck in fields because of a blind faith in their TC than before; when they were instructed to pull this, push that, turn whatever. By the time they finally get to the edge of a soft bit they've forgotten all the instructions so think better of it.
If you know you're heading into a tricky patch you generally prepare for it, hence the validity of Michael's initial observation:
"I can't see the point of anything other than a full manual locker"
Grif, you're right about Europe, my camper is 6m long and turns tighter than a defender (and some small cars too).
For its meagre 100hp it averaged 13.8 litres per 100km over our 30000km jaunt around WA, including the dunes in the Banc d'Arguin (little but soft) and a few other hideous roads. I think that's excellent for 5.5 tonnes of vehicle.
The next one will NOT use 12mm marine ply for the box.
Apparently I can get it up to 130hp by fiddling with the Bosch injection pump.
I really like having a huge range and living inside. Mosquitoes and cities are much easier to cope with. That's less easy to do in a smaller vehicle, and the economy of the Iveco is excellent for what it is capable of. But I did notice the limitations of 16 inch wheels, and would love to upsize on that count without being penalized on overall height.
A scaled up version of a VW T3 4x4 transporter would be ideal as a base vehicle except that it doesn't exist (Well there is the GAZ 37391 Vodnik and the OT 65 which are about the right size compromise but not really accessible (not to mention the spares problem)
Frequently a big truck can get into those tight alleys, or up that mountain pass, (2.5 metres wide isn't prohibitive) but at the risk of having to do several kilometres in reverse because you can't find space to turn around.
Grif in a LWB, that's something! I know of a super 6x6 defender that's just got back from a RTW, fully equipped well maintained etc.etc. bla bla http://www.horizonsunlimited.com/ubb/smile.gif
Michael, tell me about your upsizing plans, as there's so little on the market in terms of base vehicles I'm intrigued.
p.s. looking back this thread contains some relatively long posts; is everybody's job as boring as mine?
A bit off topic, but can I ask you about the availability of Iveco engine spares and/or workshops in west africa? And the rest of africa for that matter if you know. We still have our trans-africa Defender, but I'm thinking of upsizing somehow in the next few years due to our expanding family (now 3 and soon to be 4).
Erik, you're in exactly the same family situation as me; wonderful isn't it?
What do you need a mechanic for? We're not talking about LRs here :-)
There's a dealership in Morocco, and Iveco claim to have dealers in quite a few countries, but with African shipping speeds it's not worth the wait.
I set off with the usual spares; bushes etc. and the Iveco parts CD just in case (lovely to have anyway) You agree with your favorite dealer that he'll DHL if necessary and off you go.
I did use that system not because of poor preparation but poor numbering (right box, right number, wrong part inside, thank you Iveco) Works a treat.
The ancilliaries are all Bosch or Magnetti Marelli with very standard mounting points. The injection pump is a standard Bosch, parts available everywhere.
I got my rear springs replaced in Ghana with customised Merc ones for a fraction of the price of Iveco springs.
Take all the filters you'll need for the whole trip, you can change the oil at any garage. I'm still curious about that system that cleans the oil to a point where you don't need to change it, sound ideal but I'm dubious.
I might add that we found a super guy in the north of Italy who did us a complete engine rebuild for a good price, after asking us why because the engine was still absolutely fine at 180000km (what price peace of mind?)
They're a great little truck.
I think my personal mail's in my profile, if you want to find out more, I am a bit of a fan of the Daily 4x4
The international handling of spare parts is quite good, but that also depends on the local availability (and knowledge) of a specific model. As parts hardly ordered are the classic "bad luck", a home-based dealer who could be contacted e.g. by e-mail and will send parts via courier service is a perfect backup - this system it really working worldwide. It's the same with modern Landrovers: No problem with Series models, but engine parts for a td5?
@ LSD and ETC
The worm-type torsen differentials in ETC-equipped Rovers deliver a terrible performance: As they work with a torque differential, the necessary braking force is lower saving brake overheating.
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