Thread: What went wrong....

Originally Posted by KarlB

Can somebody explain how ETC kills momentum in a sand driving situation?

In this case for simplicity we will say the centre diff lock is engaged that way you can consider each axle as operating without transferring torque to the other axle.

A break of traction results in the application of the brakes to the spinning wheel, when the brake is applied to the spinning wheel that wheel stops spinning forcing the wheel on the other end of the axle to break traction if it is not already spinning. The cycle repeats over and over again. Each time the brakes are released if there is enough traction for the torque applied then the vehicle will move forward but in the case of sand it is likely to have insufficient traction and the wheel spin will just help to dig you in further.

In order to maintain your momentum you must deliver enough power to overcome the friction of the sand, if you don't get it right you slow down and stay on top of the sand without breaking traction or you break traction and start digging in. Even the short application of the brakes as is done by the TC system (over and over again) converts energy out of the system into heat in the brake pads/rotors. Every time the brakes are released the sudden rotation of the wheel breaks traction and starts digging in.

Originally Posted by slug_burner

A break of traction results in the application of the brakes to the spinning wheel, when the brake is applied to the spinning wheel that wheel stops spinning forcing the wheel on the other end of the axle to break traction if it is not already spinning.

No it doesn't, the wheel that has drive transferred to it will normally be stationary or turning much slower than the spinning wheel and when it gets drive it bites and pulls the vehicle. If the it looses traction (no drive) and it starts to spin faster than the other wheel, drive is transferred to the other wheel and so on.

At no stage is any wheel that has traction braked - only those wheels, that not only have no traction but are spinning faster than another wheel with traction are braked.

Cheers

Garry

Originally Posted by camel_landy

To cover the initial question, it sounds as though you have selected too low a gear.

Wheel spin is caused by torque... The lower the gear, the greater the torque.

When climbing, you need to select a higher gear, not lower. That will increase momentum as well as reduce the amount of torque at the wheels.

If you're in soft sand, dropping the tyre pressures will help too.

Anti-Stall
Anti-Stall is available in all gears... It is actually more a feature of ANY engine with EFi, not just Land Rover engines. The engine ECU on any car will monitor the engine speed, if the engine speed drops, it adjusts to maintain the steady engine speed. Hence why TD5 has 'anti-stall' too.

All that Land Rover do, is take this effect, get it to operate within different parameters and call it a 'feature'.

Idle Jack
1st gear, lo-range... When the car is moving, the idle speed is raised slightly to prevent the car from providing too much engine brakeing and reducing the chances of the car sliding on steep descents.

M

Idle Jack, never head of it. That is not what Land Rover called it. My car will stall in all gears but low 1. In low 1 it may brake traction but will keep spinning regardless of what it's up against. I'd imagine for just about everyone, common sense would prevail and the clutch disengaged before any drive line components could be damaged. But it acts like a hand throttle.

I have head what you are calling Anti Stall is required by modern motors to maintain anti pollution requirements. Not sure how that helps when I change gears the motor runs on for a half second, but I don't make the rules.

T.c fault code question:- In regards to the code on the e.c.u. Does it record it as a single fault or multiple i.e. switch of the traction control ten times ten recorded faults or does one override the other?

Allan

The car ONLY does it on steep dunes - not in any other sand driving condition as has been said on a number of times now...

As Slug Burner explained - on a steep dune the TC functions correctly in stopping the wheel with least traction, but if there is no traction for any of the 4 wheels what would you expect to happen...? The TC does at that point apply brakes to all 4 wheels thus slowing the car and eventually stalling it pretty violently. This is not just a theory, but something I've seen on many occations on a number of Pumas.

The solution is the basics of sand driving taken as far as you dare - VERY soft tyres and a LOT of momentum.

Originally Posted by Loubrey

but if there is no traction for any of the 4 wheels what would you expect to happen...? The TC does at that point apply brakes to all 4 wheels thus slowing the car and eventually stalling it pretty violently.

That is not the case - TC only works on wheels that are spinning faster than its opposite wheel. If all four wheels have lost traction and are spinnning at roughly the same speed then TC will not activate. If one of the wheels gains a bit more traction and slows it down so the other wheel is spinning faster then TC will momentarily brake that wheel and transfer power to the wheel that has traction.

TC cannot brake all four wheels at once.

Garry

Originally Posted by slug_burner View Post
A break of traction results in the application of the brakes to the spinning wheel, when the brake is applied to the spinning wheel that wheel stops spinning forcing the wheel on the other end of the axle to break traction if it is not already spinning.

Originally Posted by garrycol

No it doesn't (that is a pretty emphatic no), the wheel that has drive transferred to it will normally be stationary or turning much slower than the spinning wheel and when it gets drive it bites and pulls the vehicle (it can also bite and brake the surface of the sand and start digging in until the the TC applies the brake to that wheel). If the it looses traction (no drive) and it starts to spin faster than the other wheel, drive is transferred to the other wheel and so on. (Therefore digging with one wheel at a time on each axle unless there is enough traction to allow the vehicle to move on)

At no stage is any wheel that has traction braked - only those wheels, that not only have no traction but are spinning faster than another wheel with traction are braked.

Cheers

Garry

On dunes where the sand is expansive enough sand has pretty uniform traction properties, if one wheel brakes traction, forcing all the drive over to the other wheel will also result in a loss of traction.

This is a known issue and much has been written about it before.

To all who have posted so far.......really good to get advice when needed !I will expand on my experience and get back to basics.....

I was attempting to start in low 3rd with diff lock........and am aware that any gear lower is just too slow, but did not attempt high as on a previous day a mate had informed me that I was getting a lot of spin for no reward. This time the sand was pretty rutty and plenty soft after so many attempts up the dune by all drivers.....it was like a traffic light at some points with all comers lining up for a go !!

I did notice the TC light coming on and off intermittantly.....and found that I just could not get a run up. And we are not talking "ultra steep" at all.....just the usual steeper longer dune which I would certainly expect the defender to blow away.

I do believe that lowering the tyres would have been a option....I did get out and check them at 14psi (on the better gauge i have). But maybe 12 psi next time.

I am having Daniel at MULGO install a hard wired compressor on Friday morning so now am not so worried about going down the extra few psi.....(but rolling over the rim does not sound like fun !!) I will go back to Stocko on Sunday and attempt the same dune....and get back to you !!

As for operator error........absolutely 100 percent probability...... I really do need to get myself some lessons, and believe it would assist my skills in all areas of using my machine. Does any one know of a local mob (Newcastle) that do it ?

Cheers to all.