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Old 28-04-2017   #1
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Fiat Panda 4x4 system, "How does it work" ?

I can't find any information on how the system is working.
Is it 4x4 all the time, or only if you turn the nob on the centre console. ?
Does it get automatically 4x4 with certain slip of the front wheels. ?

Some info how it works would be great.
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Old 28-04-2017   #2
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Re: Fiat Panda 4x4 system, "How does it work" ?

From what I know it is in fact a full time 4x4, but power is predominately sent to the front wheels with very little to the rear under normal loads.

Drive is split with an electro hydraulic coupling, very similar to a Haldex clutch system.
(a haldex has alternate plates in fluid each locked to either the inner (front shaft) or outer shaft (rear shaft), heat it all up with by slipping it and it all grips together sending drive through it, very sinilar to a motorbike wet clutch).

Normally, torque is on demend, so as front wheels load up, the coupling starts to lock tighter and tighter, sending more and more power to the rear, until it's split 50/50.

This can be over ridden though as the electro hydraulic coupling can be pre activated to split power 50/50 from the off with the ELD button.

The ELD button also "mocks" a diff locking function.

Under normal circumstances, a spinning/slipping wheel on an axle would cause the open diff to not send power to the other wheel on that axle.
All the power runs to the slipping wheel, so no chance of the other wheel moving you, even if it had grip.

The ELD doesn't actually lock the diff, but uses the traction control system to detect a slipping wheel and brake it, this causes the power that would otherwise spin away to be sent to the other wheel on that axle that might stand a better chance.

Both ELD functions only work at limited speeds, something around the 30 kph mark I think.
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Old 28-04-2017   #3
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Re: Fiat Panda 4x4 system, "How does it work" ?

Quote Originally Posted by Goudrons View Post
From what I know it is in fact a full time 4x4, but power is predominately sent to the front wheels with very little to the rear under normal loads.

Drive is split with an electro hydraulic coupling, very similar to a Haldex clutch system.
(a haldex has alternate plates in fluid each locked to either the inner (front shaft) or outer shaft (rear shaft), heat it all up with by slipping it and it all grips together sending drive through it, very sinilar to a motorbike wet clutch).

Normally, torque is on demend, so as front wheels load up, the coupling starts to lock tighter and tighter, sending more and more power to the rear, until it's split 50/50.

This can be over ridden though as the electro hydraulic coupling can be pre activated to split power 50/50 from the off with the ELD button.

The ELD button also "mocks" a diff locking function.

Under normal circumstances, a spinning/slipping wheel on an axle would cause the open diff to not send power to the other wheel on that axle.
All the power runs to the slipping wheel, so no chance of the other wheel moving you, even if it had grip.

The ELD doesn't actually lock the diff, but uses the traction control system to detect a slipping wheel and brake it, this causes the power that would otherwise spin away to be sent to the other wheel on that axle that might stand a better chance.

Both ELD functions only work at limited speeds, something around the 30 kph mark I think.
I think Fiat must be ashamed of the system as they don't, won't and apparently can't tell you how it works. This is a great description though and describes it as I understand it after a whole pile of research. What I do know is it seems impossible to slip the wheels on my gravel drive and the car will climb up totally impossible looking slopes with arrogant ease so I don't know why they don't make a lot of what is clearly a first class bit of engineering. I suspect that most of the owners are actually interested.
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Old 28-04-2017   #4
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Re: Fiat Panda 4x4 system, "How does it work" ?

Quote Originally Posted by petercresswell View Post
I think Fiat must be ashamed of the system as they don't, won't and apparently can't tell you how it works...........

.............so I don't know why they don't make a lot of what is clearly a first class bit of engineering. I suspect that most of the owners are actually interested.
There's an obvious and easy answer to this, they probably don't fully understand it themselves and no one really sings and dances about other achievements!

I believe the system is by Magna-Steyr, not Fiat.
They just buy it in and nail it on!
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Old 28-04-2017   #5
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Re: Fiat Panda 4x4 system, "How does it work" ?

The speed-limit on the ELD can catch you out. Below the limit, when you attack a roundabout you can feel the rear end hunkering down, gripping and pushing you round, tightening the line as it does. But attack it too fast, and you're back in full-on FWD understeer-land.

Sometimes, less is more.
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Last edited by gar074; 28-04-2017 at 23:55.
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Old 29-04-2017   #6
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Re: Fiat Panda 4x4 system, "How does it work" ?

So, it will never be a 4x4 above 30 Km/h. ?
With other words when you drive, let's say 120 Km/h and the front wheels losing grip, the rear wheels will not come in play. ?
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Old 29-04-2017   #7
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Re: Fiat Panda 4x4 system, "How does it work" ?

No, it's always torque on demand and up to 50% of the power can be transmitted to the rear with the ELD off at any speed.
As the coupling slips, more and more power is diverted rearwards.

It's with the ELD function on, that is under speed limit.

Pressing the ELD button activates the electro part of the coupling, locking the coupling to power a split of 50/50 straight away.
There's no need for the coupling to slip before it starts diverting torque to the rear, it's already locked.

The ELD button also activates the mock diff lock function, which is why it's speed limited, you just can't really corner with diffs locked, at speed you'll just plow straight on.
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Last edited by Goudrons; 29-04-2017 at 12:18.
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Old 29-04-2017   #8
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Re: Fiat Panda 4x4 system, "How does it work" ?

Yes, i know.

Thanks for the info.
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Old 29-04-2017   #9
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Re: Fiat Panda 4x4 system, "How does it work" ?

Quote Originally Posted by gar074 View Post
The speed-limit on the ELD can catch you out. Below the limit, when you attack a roundabout you can feel the rear end hunkering down, gripping and pushing you round, tightening the line as it does. But attack it too fast, and you're back in full-on FWD understeer-land.
Quote Originally Posted by The Pretender View Post
So, it will never be a 4x4 above 30 Km/h. ?
With other words when you drive, let's say 120 Km/h and the front wheels losing grip, the rear wheels will not come in play. ?
Quote Originally Posted by Goudrons View Post
No, it's always torque on demand and up to 50% of the power can be transmitted to the rear with the ELD off at any speed. As the coupling slips, more and more power is diverted rearwards. It's with the ELD function on, that is under speed limit.
I stand corrected! I guess I'm just attacking those roundabouts too fast, then!
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Last edited by gar074; 29-04-2017 at 17:14.
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Old 30-04-2017   #10
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Re: Fiat Panda 4x4 system, "How does it work" ?

Something to note about the torque on demand system is that it's still a wet clutch pack system that mainly works when there's a difference in rotational speed between the two axles. So basically, if the front axle (and therefore centre diff input shaft) is spinning faster than the rear, the clutch packs swimming in hydraulic fluid begin to engage due to the shearing force created (similar to how a torque converter in an automatic transmission works), and fully engage when they are hydraulically pressed together. This means that under normal circumstances, when the front wheels don't have the traction to cope with the demand, engine torque will be sent to the rear axle once the fronts start slipping. The ELD button engages a solenoid in the centre diff, preloading the clutch packs and forcing constant 50/50 torque split. The other aspect is the aforementioned simulated differential lock that brakes wheels that are spinning faster than the rest.

There are, however, several limiting factors in the functioning of this system, some of which are common with 4wd applications. For example, a real differential lock means that both wheels on any given axle are forced to spin at the same speed. On high grip surfaces, this poses a problem when turning because the outside wheel has more difference to cover. That means the lateral torque from wheels that should be rotating at different speeds to cover different differences throughout the turn is all pushed through the axles and diff. Eventually, this can cause something called "binding", basically the torque mangles the axles, driveshafts, diffs. How serious this issue can be is also dependant on many factors, such as how much power is being sent through the axles, how much traction there is, how beefy the components are. The same is true for the brake based ELD system in that while the Panda doesn't really have the power to overload the system on its own, the brakes have the stopping power to clamp down enough to stop any spinning wheel. If one is spinning but the other isn't, anything in between can get seriously damaged. That's why mechanical limited slip, torsen, or even locking differentials can still work at higher speeds but electronic systems need finer tuning to work. This is part of why the ELD system doesn't work above 30mph/50kph, and explains the side to side involvement of the 4x4 system (with ELD enabled, disabled it's just an open diff and stability control does a limited amount of braking if pushed too hard).

The mysterious centre diff is also limited in this regard, and for a similar reason. In vehicles with a real locking centre diff, there is a miniscule amount of gearing that takes place in that diff which enables the front axle to turn slightly faster than the rear. It's not noticeable at low speeds or on low grip surfaces but high speed high and/or high grip surfaces cause the same binding effect, just front to back rather than side to side. Most drivetrains can cope with a certain amount of negative load in the driveshaft and centre diff, so they can withstand a bit of being pulled apart, but being pushed together mashing everything together puts directional load in parts and places they can't handle, not to mention the entire chassis essentially trying to withstand being squashed together like it's being crushed between two trucks. This is why locking centre diffs on serious off roaders can only be engaged at low speeds, on low grip surfaces. There are, of course, exceptions to the rule but then we're talking about Icelandic hillclimb trucks or rallycross vehicles costing well over half a million dollars to engineer and build. So how does this all pertain to the Panda? The hydraulic clutch pack in the centre diff locks the front and rear axles at 50/50 because it's a direct connection with no gearing. The small amount of slip allowed before the clutches engage is helpful in this regard, but when they do the clutches are engaged to put the rear axle in motion. When that happens, and if the speed differential between the two axles is too great, either the clutches manage to lock up but the driveshaft has to deal with all that force (it can't), or the clutches slip, wear, overheat, break, and cook the hydraulic fluid (which is supposed to be a lifetime fluid). Essentially, something would break. To avoid this, the ELD system disengages over a speed that could be this damaging. With ELD off, the front wheels spin for a moment before the centre diff is engaged but traction control kicks in if the front wheels spin too much, limiting power until everything is spinning at a speed it can cope with. The Panda also lacks the power to spin the front wheels in third gear unless it's driving on snow and ice, and then due to the higher gearing, the front wheels spin too fast for the clutches to engage without damaging them unless wheel spin increases very gradually. So essentially, the 4x4 system hardly ever engages above 50kph because it the circumstances hardly every call for it, and those circumstances are hardly ever met. Even in first and second and with ELD on, if the conditions are bad enough (like extremely icy conditions), you could row through the gears and get crazy wheelspin fast enough that even though you're not going anywhere, since the wheel speed sensors and gearbox speed sensor would say you passed 50 it would disengage the rear diff because everything is spinning faster than it should or faster than it can cope with. Even so, due to the hydraulic fluid in the centre diff and the shearing forces involved, around 5% of the total torque applied is always being sent to the rear axle, and the amount of engagement from the clutch packs determines how much more can be sent. Under most circumstances, if the front is slipping it tries to send as much to the rear as it can as soon as it can, so the clutches tend to lock up rather than slip. This makes the Panda rather good at a few things: chugging over obstacles at partial throttle because even if a wheel loses contact with the ground the rest are already getting torque applied, and climbing steep hills on open throttle because it's not faffing about with wheel speed sensors trying to calculate how much torque it should send to the back because the fronts aren't enough to pull it up (this is where Haldex diffs fall behind when they're trying to be all smart about it and only sending power as needed, which makes the "torque on demand" nomenclature a bit ironic). There are, however, two things that can trip up the 4x4 system here: surfaces with so little grip that everything exceeds their design speed, and rolling roads at inspection stations.

I learned that last part the hard (and expensive) way, and also how I got to poke around in it enough to figure it out.
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Last edited by oyumurtaci; 30-04-2017 at 23:27.
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Old 01-05-2017   #11
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Re: Fiat Panda 4x4 system, "How does it work" ?

Wow, that was a comprehensive explanation!!
My wife current car is a mk 4 panda 4x4, I can't get the keys off her that ofton
We also had a mk 2/3 Panda 4x4 climbing with the 'viscous coupling system' no ELD tho!!

It stood us in good stead for 9 years and was great across muddy fields & in the ice and snow we had over winters in earlier part of this decade!!
In v. icy conditions you had a fraction of a second delay whilst the rear caught up with the front!
Does this happen on mk 4
Is the current system the same or completely different??
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Old 01-05-2017   #12
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Re: Fiat Panda 4x4 system, "How does it work" ?

The current system is no longer a viscous coupling, but a set of clutches instead. That being said, the clutches are engaged hydraulically after the front wheels start slipping if ELD is not enabled, so there is that bit of delay under normal driving. The delay, however, can be eliminated by enabling the ELD system, which engaged the clutches with a solenoid in the centre diff.

The previous generation Panda's system, while slower to respond, had the advantage of being a relatively easily serviceable part. Add to that the fact that the Italian market really took to the 4x4 and that means there were (and still are) all sorts of aftermarket parts and modifications for the Panda "169". One of the few companies that makes well engineered spacers and strut lifts for the current Panda, for example (Prometeo Meccanica) also makes full mechanical limited slip and locking differentials (front, middle, and rear) for the previous Panda, along with stronger axles and driveshafts. Add to this the better approach, departure and breakover angles of the older Panda and well... Basically, the simplicity of the previous Panda makes it a great platform for making a surprisingly capable and serious off-roader.
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Old 01-05-2017   #13
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Re: Fiat Panda 4x4 system, "How does it work" ?

Wonder why Fiat didn't carry on with that system if it was that simple, prob some EU ruling!? I think later Panda Climbings and Mk 3 Cross had ELD tho so did they change it on latter previous models?!?
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Old 01-05-2017   #14
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Re: Fiat Panda 4x4 system, "How does it work" ?

While the viscous coupling allows for greater wheel speed difference between two axles, it's less efficient which was probably why it was ditched. The ELD system is basically some clever algorithms running with the ESP and ABS systems so it's probably tweaked but not significantly different.

Also, I'd like to say kudos to you for asking all the right questions as a new user. You're the sort of smart person we need in the enthusiastic car buying public to encourage manufacturers to innovate.
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Last edited by oyumurtaci; 01-05-2017 at 13:00.
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Old 01-05-2017   #15
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Re: Fiat Panda 4x4 system, "How does it work" ?

Quote Originally Posted by Alex4x4 View Post
Wonder why Fiat didn't carry on with that system if it was that simple, prob some EU ruling!? I think later Panda Climbings and Mk 3 Cross had ELD tho so did they change it on latter previous models?!?
Correct: the last of the 'old' model 4x4 and all of the previous model Cross saw the viscous coupling replaced by electromechanical engagement of the 4x4 system (from about 2010 onwards I think)
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