Freelander 1 So... tell me about Traction Control...

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Avocet1

Well-Known Member
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In the recent snow, I had to undertake a "necessary journey", which gave me the chance to see what it could do in snow. I'm on Event ML698 tyres, with a reasonable amount of tread on them. As anticipated, they were "OK" on the virgin snow, but nothing special on the hard-packed stuff. (In fact, "a bit rubbish", really).

Anyway, during the drive, I noticed the yellow TC light coming on. As far as I could ascertain, this doesn't seem to actually do anything, apart from telling me that one or more wheels has lost traction. I already know this from the rev counter and the feel of the car, however. On more modern cars, I can feel the ABS pump cut in when the Traction Control light comes on, and / or feel the throttle closing to reduce power. As far as I could tell, (including a few experiments in dire provocation), the FL1 Traction Control system appears to do none of this. It just seems to be a "loss-of-traction warning light".

Is that what they're supposed to be like?
 
The amount of sensation of the ABS/TC/ESC intervention is proportional to the size of input the vehicle's systems are having to apply to keep the vehicle on course, so if it's only having to make minor adjustments the intervention will b almost imperceptible which is probably why you don't feel it.
 
I was thinking more just about TC than the other systems. (To be honest, I didn't even think it had ESC)? However, it's true that the car was going in a (fairly) straight line at the time. In a few places, I did boot it and spin the wheels up to pretty ludicrous speeds, thinking it would throttle back, but (OK, I wasn't bouncing it off the rev limiter) it didn't. If we get some more snow or ice, I'll maybe try and hoof it sideways to see what it does then, if I can find somewhere safe to do it. Pulling out of a few junctions, the back end did step out of line slightly, but this was sub 10 MPH, so I wouldn't have expected an ESC intervention anyway.
 
It has 4 systems, Hill Descent Control, Electronic Stability Control, Traction Control and Antilock Braking System - all of which are effectively just computer programs that modulate the ABS block to varying degrees. HDC is electronic workaround for descending steep hills off road without the use of low ratio transfer box. Antilock Braking System, y'all know what that does. Traction Control and Electronic Stability Control are where the magic is. In the event of one wheel spinning, detected by the different relative speed/acceleration of the ABS sensors, the TC system simultaneously modulates the brake on the spinning wheel and may ask the engine ECU to reduce power (not 100% on this point). By braking the spinning wheel, some torque is transferred across the diff to the other wheel which presumably has grip in essence our Traction Control works like moder performance car's "E-Diff", in that it uses electronics to emulate the function of a limited slip diff and transfer torque to tyres with grip. Stability control, works just as a normal car, steering column has a sensor for steering angle, ABS sensors are monitored for wheel speed, and in the nook between the headlining and sheet metal of the roof, is located a "yaw sensor". I think that as it's mounted so high it's it's not just a yaw sensing gyro, but that it's also got roll axis and maybe accelerometer as well?

But yeah, the ESC reads steering angle, yaw sensor, ABS sensor wheel speeds and makes the ABS block do "Kingy!Toing!KingeyKingy Toing!" nises of varying amplitude as it dendeavours to brake wheels to find grip / negate slip / prevent skidding / prevent spinning as required to save you from the road coniditons / terrain / yourself. And the amplitude of the noises is directly proportional to the magnitude of the inputs the system is having to make, and that in itself is a function of the severity of the impending emergency the system(s) are trying to mitigate. So, since you were going in a fairly straight line, the system wouldn't have been working too hard, only having to apply little minor modulations here or there, which is probably why you didn't feel/hear it. I can tell you from experience, that if you do something stupid with the car, like when making up time as you were late for work, throw it into a hairpin the way you normally do you in your MR2, you will be acutely aware of the ESP working the ABS block really hard to save you from your own, well my own, stupidity.
 
Avocet1 said:
I'm on Event ML698 tyres, with a reasonable amount of tread on them. As anticipated, they were "OK" on the virgin snow, but nothing special on the hard-packed stuff. (In fact, "a bit rubbish", really).
Click to expand...

Those tyres are a low tech AT tyre, so will be less than satisfactory in hard packed snow/ice. Good grip in winter conditions requires tyres with lots of sipes, not just 1 token sipe per tread block. In icy winter conditions, in my experience, M&S rated road tyres are second only to true winter tyres. Large blocked low tech AT tyres, are well out of their depth, when it comes to these slippy winter conditions.

As for the TC, it's complicated. However it doesn't alter the engine torque like normal car TC systems, as that's not what is needed when conditions are tough.
The FL1 TC works as described above, basically applying the brakes on the spinning wheels, which sends torque across the differential, to the wheels which aren't spinning. For this system to work, the engine power needs to remain constant, or be increased slightly while TC is active. The idea being, the more torque the engine makes, the more torque there is to send across the diff to the wheels that aren't spinning. There is some power loss in the brakes, so increased torque from the engine is helpful to maintain progress. This is why the light comes on, so to warn the driver to increase engine power when it's active.

The FL2 system is a lot more advanced, and is able to actually lock the spinning wheels, forcing the torque across the differential, to the wheels with grip.

Unfortunately the FL1 can't do this, but it can slow down the spinning wheels, so increasing throttle will help send more power to where its needed.
 
Jayridium said:
It has 4 systems, Hill Descent Control, Electronic Stability Control, Traction Control and Antilock Braking System - all of which are effectively just computer programs that modulate the ABS block to varying degrees. HDC is electronic workaround for descending steep hills off road without the use of low ratio transfer box. Antilock Braking System, y'all know what that does. Traction Control and Electronic Stability Control are where the magic is.
Click to expand...
Yes, to be fair the HDC worked pretty well. I tried that too, and felt pretty reassured. But do they REALLY have ESC???! (It's a 2001 TD4). There's no ESC light on the dash, nothing about ESC in the handbook?

Jayridium said:
In the event of one wheel spinning, detected by the different relative speed/acceleration of the ABS sensors, the TC system simultaneously modulates the brake on the spinning wheel and may ask the engine ECU to reduce power (not 100% on this point). By braking the spinning wheel, some torque is transferred across the diff to the other wheel which presumably has grip in essence our Traction Control works like moder performance car's "E-Diff", in that it uses electronics to emulate the function of a limited slip diff and transfer torque to tyres with grip. Stability control, works just as a normal car, steering column has a sensor for steering angle, ABS sensors are monitored for wheel speed, and in the nook between the headlining and sheet metal of the roof, is located a "yaw sensor". I think that as it's mounted so high it's it's not just a yaw sensing gyro, but that it's also got roll axis and maybe accelerometer as well?
Click to expand...

Yaw Rate Sensors are the bane of my life at work. I've never seen one up in the roof of a car though. They tend to be at the pitch and roll centres. This means somewhere on the floor, between the front seats, on most vehicles I deal with. They're a pain because when you try to cut the floor out and lower it to get wheelchairs in, the YRS gets in the way. Even more annoyingly, some manufacturers have started to combine it with the airbag trigger too. Early ones were gyros, but I think the modern ones are all solid state now. I could see why an off-road manufacturer might want to put it up above the headlining out of the way of any water, but that would be tricky programming (and probably make it very dangerous if someone then alters spring / roll rates and fits a lift kit, etc). I've had the headlining out of mine (usual reason!) and don't remember seeing anything that looked like a YRS? (I did once have some discussions with Bosch about moving one. They wanted €380,000 just for the feasibility study into moving it)! I don't remember seeing a steering angle sensor either, on my various trips into the footwell, but admit, I've never had the column apart. It certainly has throttle-by-wire, so it could close the throttle to reduce power if it wanted to.

Jayridium said:
But yeah, the ESC reads steering angle, yaw sensor, ABS sensor wheel speeds and makes the ABS block do "Kingy!Toing!KingeyKingy Toing!" nises of varying amplitude as it dendeavours to brake wheels to find grip / negate slip / prevent skidding / prevent spinning as required to save you from the road coniditons / terrain / yourself. And the amplitude of the noises is directly proportional to the magnitude of the inputs the system is having to make, and that in itself is a function of the severity of the impending emergency the system(s) are trying to mitigate. So, since you were going in a fairly straight line, the system wouldn't have been working too hard, only having to apply little minor modulations here or there, which is probably why you didn't feel/hear it. I can tell you from experience, that if you do something stupid with the car, like when making up time as you were late for work, throw it into a hairpin the way you normally do you in your MR2, you will be acutely aware of the ESP working the ABS block really hard to save you from your own, well my own, stupidity.
Click to expand...
Lovin' that ABS noise description! That definitely wasn't happening though. I don't know if it can "do it gently" though. I think it either has an ABS intervention or it doesn't? Traction control is mentioned in the handbook, and the write-up is as you describe. Must admit, I haven't tried taking real liberties with it though. Maybe I need to try harder! It says the TC doesn't work about 30 MPH. I can't remember if I was doing more than 30 at the time, I must admit. Further "research" needed, methinks!
 
Nodge68 said:
Those tyres are a low tech AT tyre, so will be less than satisfactory in hard packed snow/ice. Good grip in winter conditions requires tyres with lots of sipes, not just 1 token sipe per tread block. In icy winter conditions, in my experience, M&S rated road tyres are second only to true winter tyres. Large blocked low tech AT tyres, are well out of their depth, when it comes to these slippy winter conditions.
Click to expand...

Yeah... but... £100 for 4 of them with wheels in them and I'm a tightwad! OK, having heard the bloody racket they make, I can see why the seller was getting rid of them with very few miles on - serve me right! My daughter's Mazda 2 is on proper Winter tyres and they are a revelation. Unfortunately, she's in Scotland or it would have been handy to do a back-to-back on the same stretch of road, but I bet she'd have been little or no worse than the Landy. Don't get me wrong, there were 2WD cars just crabbing sideways and slowly sliding down some of the steeper hills that the Landy got up (when I say "steeper", maybe 8-10% gradients). Nothing really steep. But she's done good things up in Scotland on them!

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Nodge68 said:
As for the TC, it's complicated. However it doesn't alter the engine torque like normal car TC systems, as that's not what is needed when conditions are tough.
The FL1 TC works as described above, basically applying the brakes on the spinning wheels, which sends torque across the differential, to the wheels which aren't spinning. For this system to work, the engine power needs to remain constant, or be increased slightly while TC is active. The idea being, the more torque the engine makes, the more torque there is to send across the diff to the wheels that aren't spinning. There is some power loss in the brakes, so increased torque from the engine is helpful to maintain progress. This is why the light comes on, so to warn the driver to increase engine power when it's active.

The FL2 system is a lot more advanced, and is able to actually lock the spinning wheels, forcing the torque across the differential, to the wheels with grip.

Unfortunately the FL1 can't do this, but it can slow down the spinning wheels, so increasing throttle will help send more power to where its needed.
Click to expand...

That's interesting. Mrs. Avocet's late X-Trail (2006) used to do the same thing, but it was very noticeable. Almost to the point of being aggressive. And it certainly reduced engine power. I guess, forgetting snow for the moment, maybe with sand or mud, there's a bit of a traction benefit to "some" wheelspin? As I mentioned to Jay, I wasn't conscious of the ABS doing anything, but maybe it was!

Thanks both, for your thoughts!
 
Hi Avo, nice pics :D

You're right of course F1 does not have ESC - just the functions that work when the 3 Amigos are not lit ;)

As said, TC monitors the sensors and if 1 wheel on an axle is spinning faster than the other - then it will pulse the brake to put torque through the other 1. As an 'addendum' to this, it would never only pulse 1 wheel, it would be pulsing 2 wheels as the props and VCU in effect lock the axle speeds together, so you'd have to lose grip on 2 wheels. TC is normally demonstrated on axle twisters, so it is pulsing 1 wheel on each side. In on road conditions, I'd imagine it is more likely to pulse both wheels on the same side, my thoughts being that 1 side of the road has more compromised grip. However, I suppose in that compacted snow conditions - it could be either.

With my Wabco ABS unit, you know the TC is kicking in by the sound and feel of the pump kicking into life, if the Teves unit is more 'refined', maybe you would not hear/feel it - but I doubt it. It is in effect doing the same as HDC - ie pulsing the brakes. So the sound/feel should be similar if you feel HDC is working fine.

I get TC kicking in a lot more frequently having changed to 2WD. It doesn't have traction from the back axle keeping a front wheel from spinning away. So on uneven gravelly river beds a front will spin and the TC kick in briefly. I never feel the wheel spin, the first I know that it has slipped is the TC kicking in and the car generally drives as if it hadn't slipped at all.

As an aside, it does not matter how good traction is, there is only so much grip to be had before physics simply says "that's enough". It also very difficult to predict some times. We took a drive over the 'Port Hills' about 10 years ago in the Discovery. It was a fine day, but turned as we headed home. By the time we got to the top of the hill to begin the decent back into Christchurch, there was at least 2" of snow and temps were dropping like a stone. We crawled down the hill following a big Merc saloon. It was slow, but no real problems until we got quite close to the bottom (probably less than 2km left) when everything froze. The Merc lost virtually all control. I can remember having a bit of a giggle at the bloke's expense, until shortly after when I was in the same position with the Disco. I only needed to think about touching the brakes and the car was sliding. So I had very little control going down the hill, but if I put it in reverse to 'power' back up the slope, it had zero problems, grip was fine. In the end I managed to just point the car into the curb and use that to restrict our free fall down the hill :D
 
GrumpyGel said:
Hi Avo, nice pics :D

You're right of course F1 does not have ESC - just the functions that work when the 3 Amigos are not lit ;)

As said, TC monitors the sensors and if 1 wheel on an axle is spinning faster than the other - then it will pulse the brake to put torque through the other 1. As an 'addendum' to this, it would never only pulse 1 wheel, it would be pulsing 2 wheels as the props and VCU in effect lock the axle speeds together, so you'd have to lose grip on 2 wheels. TC is normally demonstrated on axle twisters, so it is pulsing 1 wheel on each side. In on road conditions, I'd imagine it is more likely to pulse both wheels on the same side, my thoughts being that 1 side of the road has more compromised grip. However, I suppose in that compacted snow conditions - it could be either.

With my Wabco ABS unit, you know the TC is kicking in by the sound and feel of the pump kicking into life, if the Teves unit is more 'refined', maybe you would not hear/feel it - but I doubt it. It is in effect doing the same as HDC - ie pulsing the brakes. So the sound/feel should be similar if you feel HDC is working fine.

I get TC kicking in a lot more frequently having changed to 2WD. It doesn't have traction from the back axle keeping a front wheel from spinning away. So on uneven gravelly river beds a front will spin and the TC kick in briefly. I never feel the wheel spin, the first I know that it has slipped is the TC kicking in and the car generally drives as if it hadn't slipped at all.

As an aside, it does not matter how good traction is, there is only so much grip to be had before physics simply says "that's enough". It also very difficult to predict some times. We took a drive over the 'Port Hills' about 10 years ago in the Discovery. It was a fine day, but turned as we headed home. By the time we got to the top of the hill to begin the decent back into Christchurch, there was at least 2" of snow and temps were dropping like a stone. We crawled down the hill following a big Merc saloon. It was slow, but no real problems until we got quite close to the bottom (probably less than 2km left) when everything froze. The Merc lost virtually all control. I can remember having a bit of a giggle at the bloke's expense, until shortly after when I was in the same position with the Disco. I only needed to think about touching the brakes and the car was sliding. So I had very little control going down the hill, but if I put it in reverse to 'power' back up the slope, it had zero problems, grip was fine. In the end I managed to just point the car into the curb and use that to restrict our free fall down the hill :D
Click to expand...

Not sure which ABS pump I have, but it's definitely working. Jayiridium's "Kingy!Toing!KingeyKingy Toing!" noises are quite evident when locking a wheel under braking or when the HDC is "doing its thing". I did wonder whether I had all 4 wheels spinning, so it didn't think anything was amiss, but then the TC light wouldn't have been flashing.

I've heard that in certain off-road situations, quite a lot of wheelspin can be beneficial, so I'm wondering whether the FL1 TC system is simply designed to allow a lot of it before actually doing anything?
 
The FL1 TC will allow the wheels to spin, but will slow the rotational velocity of the faster wheels. The sound you hear is the motor in the ABS modulator, and the noise of the brake grabbing on several times a second.

The FL2 TC system is well ahead of the FL1 system, the FL2 can actually lock the spinning wheels, but the FL1 system, can only reduce the spinning.
 
Nodge68 said:
The FL1 TC will allow the wheels to spin, but will slow the rotational velocity of the faster wheels. The sound you hear is the motor in the ABS modulator, and the noise of the brake grabbing on several times a second.

The FL2 TC system is well ahead of the FL1 system, the FL2 can actually lock the spinning wheels, but the FL1 system, can only reduce the spinning.
Click to expand...

That's odd, because "locking" a spinning wheel can't serve any useful function when it comes to getting you moving. You'd have thought it would be the more primitive system that locked the wheel, and the more advanced system that could just reduce the speed of it, so as to match it to the speed of the rotating wheel on the other side of the same axle?
 
Avocet1 said:
That's odd, because "locking" a spinning wheel can't serve any useful function when it comes to getting you moving. You'd have thought it would be the more primitive system that locked the wheel, and the more advanced system that could just reduce the speed of it, so as to match it to the speed of the rotating wheel on the other side of the same axle?
Click to expand...
It wouldn't know when to stop either.
 
GrumpyGel said:
It wouldn't know when to stop either.
Click to expand...
When you say "wouldn't know when to stop", do you mean, it wouldn't know when to stop braking the wheel that was turning faster? I haven't really thought this through, but surely it wouldn't be that hard for the software to check that both wheels were within "X" RPM of each other and then start easing the braking pressure off the one that was being braked? Mrs Avocet's late X-Trail had something similar (I forget what they called it but "electronic diff lock" or somesuch). It would brake whichever wheel was turning faster on that axle. However, it would also shut the throttle (in fact, it would do so quite early on - too early, IMO).
 
Avocet1 said:
When you say "wouldn't know when to stop", do you mean, it wouldn't know when to stop braking the wheel that was turning faster? I haven't really thought this through, but surely it wouldn't be that hard for the software to check that both wheels were within "X" RPM of each other and then start easing the braking pressure off the one that was being braked? Mrs Avocet's late X-Trail had something similar (I forget what they called it but "electronic diff lock" or somesuch). It would brake whichever wheel was turning faster on that axle. However, it would also shut the throttle (in fact, it would do so quite early on - too early, IMO).
Click to expand...
Yeh, if you lock it up, how do you then know when it has regained grip?

I wouldn't think the ABS modulator in a Freelander could offer variable breaking force, its probably just an applied pressure to the system that it pulses. I suppose frequency of the pulses creates a net combined force, so it could pulse quicker or slower. I dunno.

The reduced throttle, as Nodge says, sounds a bit wrong to me, cos you still want drive through the wheel with traction. Lots of reasons to do it though I suppose, may be to try and stop that other wheel losing traction, possibly protect the drive line while brakes are being applied, maybe a wheel spinning without traction with high throttle would turn real quick I suppose - brakes might burn or over rev the engine. I dunno.
 
Avocet1 said:
That's odd, because "locking" a spinning wheel can't serve any useful function when it comes to getting you moving.
Click to expand...

Of course it does. A spinning wheel serves very little in the way of motive force, and none at all if the the wheel is in the air.
By locking the spinning wheel on say the front axle, then the differential sends power to the opposite wheel, which by the assumption that its not spinning, means it has some useful grip.

This process is repeated many times a second sending power back and forth across the axles, which means momentum can be maintained.
 
Nodge68 said:
Of course it does. A spinning wheel serves very little in the way of motive force, and none at all if the the wheel is in the air.
By locking the spinning wheel on say the front axle, then the differential sends power to the opposite wheel, which by the assumption that its not spinning, means it has some useful grip.

This process is repeated many times a second sending power back and forth across the axles, which means momentum can be maintained.
Click to expand...
I don't think Avo was questioning pulsing the brake - but locking it would not be a good idea if it was not in the air - eg slipping on ice or a hollow in loose ground - because if the other wheel, or the car's momentum, takes the car over that patch the locked wheel would stop the car from moving forward. You would need sensors for suspension being at the limits of its travel if you were to lock the wheel.
 
GrumpyGel said:
I don't think Avo was questioning pulsing the brake - but locking it would not be a good idea if it was not in the air - eg slipping on ice or a hollow in loose ground - because if the other wheel, or the car's momentum, takes the car over that patch the locked wheel would stop the car from moving forward. You would need sensors for suspension being at the limits of its travel if you were to lock the wheel.
Click to expand...

Don't forget that the ABS ECU or Terrain Response (TR) system on the FL2 doesn't just monitor 1 wheel at a time. The system monitors all wheel sensors simultaneously, along with pump pressure, brake line pressure, vehicle motion and angle via the yaw sensor, torque output of the engine and a many other things.

The system uses all this information to determine which wheel to apply the brakes on, and for how long and how hard.

The FL1 is pretty basic by comparison to the FL2, so isn't able to lock a non-contributing wheel, but it is able to slow the spinning wheel down to the average rotational speed of the other 3.
The FL2 is much more advanced, being able to actually lock a spinning wheel like I said, but it's not relevant in this case.
 
The FL2 doesn't lock wheels but it does have the ability to pulse brake them faster than the FL1. Both vehicles are doing the same thing but the FL2 has the ability to vary the rate it pulse brakes wheels. It can hold gears for higher revs for settings like sand mode. Also switch on the haldex permanently to give 4x4 instead of switching it on only when initially pulling away or when it senses loss of grip, in normal driving mode. The rate at which it takes action varies depending on the terrain response setting chosen.
 
Filmed me FL2 doing the same test but not put it up yet. Ere's some other examples. Where you can see the wheel stopped while its moving its because the drivers gently applying the brakes, on an auto gearbox crawling slowly to keep the speed down.



 
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