In

video of the Yeti at 5.38 and 5.53 you see one back wheel coming off the ground. Sometimes the wheel is stopped from spinning and in the other shot it keeps spinning...

In the Yeti brochure it says:

EDL off-road

• Maintains permanent traction of the car

• Can work diagonally across axles

• Brakes the slipping wheel(s)

• Helps maintain driver control and vehicle stability

And in the glossary for EDL it states:

EDL:

the Electronic Differential Lock continually compares the rpm of the drive wheels, and if it identifies a difference between them which could lead to an individual wheel spinning, for example if the two wheels are on different types of surface or accelerating on wet leaves, the system brakes the wheel affected until uniform rpm of all drive wheels is restored.

So why did this wheel in the video keep spinning? Is there a difference in how the EDL works depending on if the OFF ROAD button is pressed or not?

Edited 13 April, 201016 yr by 900000

The Yetis don't have mechanical locking diffs so it has to rely on the EDL function.

It doesn't always apply maximum braking power to the spinning wheel, just enough to 'trick' the differential into thinking that both wheels have grip and it will put power to the other wheel as well at the spinning one.

Wot James said!!

It is a characturistic of all these "brake" based traction control systems.

Unlike the above posters, I dont fully understsand the technicalities of the system but, having seen lots of Yeti off roading footage I do know that it seems to be very effective!

Unlike the above posters, I dont fully understsand the technicalities of the system but, having seen lots of Yeti off roading footage I do know that it seems to be very effective!

Basically:

one wheel goes into the air and spins.

brakes come on that wheel

drive transferred to other wheel on that axle

car drives on

In off-road terms it is known as being cross-axled, and is the perfecr way to stop old Land Rovers!!

Drive / power will always go towards the path of least resistance. A spinning wheel is where it will go - always. The same is true for any mechanical system also, unless you have locking differentials.

Braking the wheel - even momentarily - will 'divert' drive back to the other wheels allowing forward motion (in theory and dependant on actual traction of course).

Dabbing the brake with your foot will also 'kid' the system into diverting power to any spinning wheel... i.e. if your cross axled. Any electronic system can be fooled by the terrain and make no progress even though two or more wheels are touching the ground, using the foot brake will lock all the wheels and even out power distribution momentarily. This can have the effect of regaining drive to the wheels with grip.

A handy trick on the Discovery 3 with no rear locking eDiff (the diff locks are not mechanical like Defender).

If you dab the brakes in the Yeti then expect the power to be cut altogether.

A handy trick on the Discovery 3 with no rear locking eDiff (the diff locks are not mechanical like Defender).

I didn't realise the Discovery3 doesn't have a locking diff, I presumed it would have done!

from reading about the 4x4 system on the Haldex website (who makes the 4wd system in these vehicles, along with Audi, Merc etc etc). The system can't determine what the vehicle is doing by its physical location - i.e. it doesn't know when a wheel is lifted off the ground. The only way it senses motion or slippage is from the relative rotation of the wheels. It said the system reacts within 1/7th of whee rotation. So if it detects slippage on one wheel (i.e. its spinning faster than the rest), it attempts to stop that wheel by applying the brake to it and diverting the power to the slowest rotating wheel(s) (i.e. those with greatest grip). Obviously it can't lock the slipping wheel forever as it could end up dragging the wheel along when the vehicle gains forward motion when the as the other weels grip. Therefore it will pulse the brakes to see if the what was slipping wheel is still slipping or whether it can now rotate at the same speed as the rest.

Therefore it does look like its just spinning all the time when its lifted off the ground. I suspect in a cross axled and on slippy ground the vehicles is dancing power all over the place to try and get some wheels to grip. It must be quite clever to do all of this so quickly such that forward motion is maintained as much as crapy road tires allow (i.e. when all 4 wheels are spiinning in the mud you're gonna need to fetch a land rover, land cruiser or unimog to pull you out).

Wikipedia Haldex Traction System. We're on the 4th generation in Yetis.

"

Fourth generation - 2007

Saab introduces a unique combination of Haldex Couplings on its 9-3 Turbo-X in late 2007. Called XWD (Cross-Wheel Drive), it allows enhanced traction, safer driving, and better control.^[1] The main components of the new Haldex system are the Power Take-Off Unit (PTU), Limited Slip Coupling (LSC) and eLSD (Electronic Limited Slip Differential). The PTU is the final drive unit at the front of the vehicle that transmits power to the front wheels and sends power down the driveshaft to the rear wheels. It is not a Haldex design, but is required to adapt the system to a front-wheel drive vehicle. The LSC sits at the rear of the vehicle in-line with the driveshaft. It controls the torque split between the front and rear wheels of the vehicle. The LSC sends torque to the eLSD that sits between the rear wheels. The eLSD transfers torque to the two rear wheels. Like with XWD, previous generation Haldex systems also included an LSC and an LSD. However, with the new system Haldex significantly redesigned the workings of their LSC. The LSC is still a clutch pack that adjusts torque split depending on hydraulic pressure. It is the method of fluid flow through the device that has changed.

A large complaint about the old system was its lagging response time. LSC versions 3.0 and earlier used a built-in pump to create hydraulic pressure on the clutch pack to increase the torque drive to the rear wheels. While efforts were made on Haldex's part to create pre-emptive torque by adding a check valve and feeder pump to provide some instant pressure when triggered by wheel slippage, it was still limited in capacity. That is why for version 4.0 Haldex made an effort to improve response time by eliminating the hydraulic pump built in to the LSC, which also reduced its overall packaging size. Instead they have added a proportional pressure release valve with an accumulator that is kept filled by a detached feeder pump. This provides more instant response by holding the valve open to limit the torque drive to the rear wheels and keeping the hydraulic fluid flowing through the system. That way when rear torque is demanded, the valve closes and hydraulic pressure is already there.

The LSD used by Haldex 4.0 is also not the mechanical limited-slip differential of old. They swapped the old system LSD for an electronic unit. The eLSD works in much the same way as the LSC, a feeder pump and pressure relief valve are used to control hydraulic pressure on the differential clutch pack. This allows for complete control of the rear differential lock-up without the need to wait for wheel slippage to occur. The system has its own control unit contained in the LSC. This control unit communicates between the vehicle systems to get sensor input for data such as wheel speed, rpms, throttle position, steering wheel input, etc. It also works with anti-lock brake and traction control systems.

The XWD system can transmit 100 percent of available torque to either the front or rear wheels. However, for those conditions to occur one end of the vehicle would have to lose all traction, like driving on ice for instance. During a standing start the rear wheels are put to use, without the need for any slip to occur. Then under straight-line cruising conditions, to conserve fuel and driveline wear, the torque split to the rear wheels is reduced to a level between 5 and 10 percent. Also up to 85 percent of torque can be transferred by the eLSD between to any single rear wheel if necessary. The system can adjust torque splits based on calculated conditions, such as those that indicate an aggressive lane change manoeuvre, to effectively reduce oversteer or understeer without any wheel slip occurring. In the event that some wheel slip does actually get to occur, the system can react more timely and efficiently than in the past. ^[6]

Thanks to this technology, the Saab 9-3 Turbo-X, with only 280 bhp (210 kW) can run a slalom faster than many high performance sports cars, beating German and Japanese rivals. Saab has an agreement with Haldex for exclusive first year access to the technology, and use of the "XWD" trademark. Haldex is currently developing a similar AWD system forHyundai Applications.^[7]"

If you dab the brakes in the Yeti then expect the power to be cut altogether.

Shouldn't do as long as you stay on the revs / gas

You have to use both feet

I didn't realise the Discovery3 doesn't have a locking diff, I presumed it would have done!

They are eDiffs, i.e. electronically controlled by the Terrain Response system. Centre eDiff as standard with an optional rear eDiff.

Can be open, fully locked, partly locked, primed for immediate locking or locked open. Depending on which Terrain Response setting you have selected and what the myriad of sensors are detecting. Clever stuff

And handily as the suspension is also controlled by the Terrain Response system to adjust wheel articulation etc... it does know when a wheel or wheels are off the ground or the vehicle is bellied out (will raise the suspension into Extended mode). Even so, it can get confused sometimes and the the trick mentioned above can help it make it mind up what it should be doing

Obviously the Haldex system in the Yeti is different and not as complex as the Land Rover one... but the trick may well work in a situation as described above... can't hurt to try it

Edited 17 April, 201016 yr by simonharper

Shouldn't do as long as you stay on the revs / gas

Power being cut when left foot braking is a well documented characteristic of VAG cars, as the DBW system acts upon the last input. We have developed maps that remove this "feature" as it can be detrimental to performance in certain situation such as track days and response driving.

WoW, never knew that.

They are eDiffs, i.e. electronically controlled by the Terrain Response system. Centre eDiff as standard with an optional rear eDiff.

Can be open, fully locked, partly locked, primed for immediate locking or locked open. Depending on which Terrain Response setting you have selected and what the myriad of sensors are detecting. Clever stuff

And handily as the suspension is also controlled by the Terrain Response system to adjust wheel articulation etc... it does know when a wheel or wheels are off the ground or the vehicle is bellied out (will raise the suspension into Extended mode). Even so, it can get confused sometimes and the the trick mentioned above can help it make it mind up what it should be doing

Obviously the Haldex system in the Yeti is different and not as complex as the Land Rover one... but the trick may well work in a situation as described above... can't hurt to try it

Simon, you had me confused then for a moment talking about adjustable suspension. I was sure the Yeti didn't have that until you mentioned Land Rover and I read the bit you were quoting mentioning Disco3 - then it all made sense. Of course they have clever stuff like that.

Edited 19 April, 201016 yr by Guest

At the last British Motor show at ExCeL in London I went on the Land Rover Experience. The LR man pointed out that on the central screen there is a white dash line under each wheel and that shows the wheel is touching the ground. The moment we went over something and a wheel left the ground the dash disappeared! Neat.

It is also interesting to see these Land Rovers in action over these obsticles as they have very long suspension travel to keep the wheels touching the ground. It amazes me when I see a Yeti off road video as to how little travel there seeminly is and how quickly the wheels are in the air!

vs:

But then the one is a soft-roader and the other a proper 4x4.

...In the Yeti brochure it says:

EDL off-road

• Maintains permanent traction of the car

• Can work diagonally across axles

• Brakes the slipping wheel(s)

• Helps maintain driver control and vehicle stability

And in the glossary for EDL it states:

EDL:

the Electronic Differential Lock continually compares the rpm of the drive wheels, and if it identifies a difference between them which could lead to an individual wheel spinning, for example if the two wheels are on different types of surface or accelerating on wet leaves, the system brakes the wheel affected until uniform rpm of all drive wheels is restored.

...

So it seems to me that EDL + 2wd Yeti will give most people very good (and usually "good enough") traction in extreme weather conditions. Having had some amazingly good experiences with FWD and All Weather Tyres in wintry USA weather, am wondering if anyone has had good (or other) experiences of EDL on 2WD?

I think EDL (or whatever it might be called) is quite common in modern car as a part of the electronic stability programs. If the car has ABS then it's virtually free to program to break the wheel spinning faster.

Having said that I am mighty impressed of the performance of the 2wd petrol Yeti (on proper winter tires). We had quite a lot of snow last winter but I never had any problems going where I wanted to go. I live in an urban area so no fresh snow, but the plowed walls might prove quite challenging as well... The extra ride height does do wonders for winter driving, and unless you really need 4wd (very bad terrain, pulling heavy trailers etc) the 2wd will outperform most other 2wd cars.

LOVED the music.

AWESOME vid too :yes:

But then the one is a soft-roader and the other a proper 4x4.

True and most people only need a softroader.

Coming from 8 years of driving nothing but Land Rover Defenders, Discoveries and (full fat) Range Rovers nearly every owner just wants the pose value, the size for internal space or towing ability. Probably less than 5% of people who buy Land Rovers will ever use that fabulous wheel travel and offroad ability, so they are paying for something they don't need.

It's why the Yeti is so good. It has what most people need at a sensible price.

And the running costs make a Land Rover look shocking.

But you can't knock them if you really need one. Just most peope don't.

In

video of the Yeti at 5.38 and 5.53 you see one back wheel coming off the ground. Sometimes the wheel is stopped from spinning and in the other shot it keeps spinning...

So why did this wheel in the video keep spinning? Is there a difference in how the EDL works depending on if the OFF ROAD button is pressed or not?

It's dead simple! Watch the video again, and you'll see that when the wheel is stationery the car is going down hill - so the car is not under power (or the brakes are on), and when the wheel is turning, the car is going uphill - so it's under power. Nothing more sinister than that!

I've tried it with my SM 4x4 and that's exactly what happens.

Edited 5 June, 201115 yr by speedsport