Technical Correct function of Electronic controlled 4x4

[MalcolmK]

Hi
My understanding is that the 4x4 system is meant to be part time. The drive to the rear only occurs if the car senses a lack of grip at the front. After the snow last sunday I know the 4 wheel drive is working well,
Does anybody know how to check only the front are being driven when grip is good and no slipping?
Thanks
Malcolm

 

[MalcolmK]

should say this is type 169 2010 year model

Malcolm

 

[Goudrons]

They are full time 4x4.

The rear axle will have differing amounts of power to it at any time.

They do not completely slip or disengage the rear axle at any time.

The drive to the front is like any other FWD car, but this has another output on the gearbox to drive the shaft for the rear axle.

On the shaft to the rear is a electromagnetically operated coupling (Cross and later 312 4x4 models).

It's very similar to a viscous or Haldex coupling.

If left to it's self it'll transmit power through it depending on the amount of torque on the shaft (torque on demand), anything up to 50% can get shunted rearwards.

The more torque on the shaft, the more the fluid in the coupling heats and expands, so the plates in it slip against each other less, but there's always some drag on it that transmits a little power through it to the rear.

It doesn't really need to detect the fronts slipping, it just needs certain levels of torque on the coupling to start shifting more and more power rearwards.
Drop the clutch hard from the lights and it'll shove power to the rear long before the fronts start to spin.

The electromagnetic part of the system on the Cross and later 312 4x4's forces the system to engage a 50/50 split with a push of a button, so there's no need to wait until torque on the coupling is high enough to transmit the full 50/50 split.
It's basically preloading the system to prime it for slippy situations.

There may also be a mock diff lock function called ELD, this operates on the same button that preloads the coupling to the 50/50 split.

It doesn't actually lock any diffs, but utilises the traction control/ABS system to detect and brake a spinning/slipping wheel on an axle.

Due to the nature of open diff which will send all it's power to a slipping wheel and nothing to the other on that axle, the braking action will stop the slipping wheel thus sending the power to the other wheel on that axle which would otherwise be starved of power in a hope it has more grip.

These two functions are speed limited to protect the system from damage and you from crashing as at speed braking slipping wheels this way will cause a big accident.

The standard Climbing models don't have the electromagnetic and ELD systems, they just run the torque on demand, viscous coupling part that self regulate.

 

[MalcolmK]

Thanks for the comprehensive reply. Just to clarify though mine is a 2010 climbing, with 1.2 petrol engine and and I am pretty sure it’s electronically actuated not a viscous coupling. Does this change anything stated above

Cheers
Malcolm

 

[Goudrons]

If there's no way of activating the coupling from within the car, it is not an electromagnetic coupling, but just a straight viscous coupling.

I am pretty sure just the Panda Cross (pre 2012) got the electro coupling with some sort of terrain dial on the centre consul, the Climbing just a straight viscous coupling with no way of over riding it.

 

[koalar]

The question how do you test if its working as a front wheel drive only if there is plenty of grip.

Is a good question

Unfortunately I don't have any ideas.

 

[MalcolmK]

Thanks
It makes sense that it’s viscous, but when I compared photos of my diff with others on the forum and mine mine looked like the electrically actuated, and it has a electrical cable connection to it.
I thought there were some late model Climbing that were not viscous, and that viscous types were obvious because the coupling can be seen between the prop shaft and rear diff.
When I get a chance I will post a photo. Even if it is electrical do you still think it’s permanent driving the rear to varying extents depending on demand?

 

[MalcolmK]

A photo of my diff is lower down in my previous post, hope this link works

https://www.fiatforum.com/panda/453560-panda-169-4x4-service-manual-new-post.html

 

[Goudrons]

They all have the viscous plate pack type coupling on the diffs nose.
You can see it in your image (oily bit to the left with the drain highlighted).

It seems Fiat changed supplier in 2008, from a GKN coupling to a Magna Steyr one.
These Magna Steyr do all appear to have an electropneumatic coupling.

I stole this to explain
"The unit can be viewed as a hydraulic pump in which the housing and an annular piston are connected to one shaft and a piston actuator is connected to the other.

The two shafts are connected via the wet multi-plate clutch pack, normally unloaded and thus transferring no torque between the shafts.


When both shafts are rotating at the same speed, there is no pumping action. When a speed difference occurs, the pumping starts immediately to generate oil flow. It is a piston pump, so there is a virtually instant reaction with no low-speed pumping loss.


The oil flows to a clutch piston, compressing the clutch pack and braking the speed difference between the axles. The oil returns to the reservoir via a controllable valve, which adjusts the oil pressure and the force on the clutch package."


So instead of the pack of plates slipping in oil then gripping together (old GKN system).
The difference in shaft speed actuates a pump to use fluid to compress the plate pack together, the greater the difference, the harder it pumps, the greater the pressure on the pack, the more torque it allows through.


This way the action is more instant.


Now it appears there are addition functions to the Cross and later 312 model 4x4's.
They have the ability to over ride it's self and actuate the pump before it detects differing shaft speeds, so by selecting a setting in the cabin, it actuates the pump and sets the system to 50/50 from the off.

The Climbing manages it's self.

 

[MalcolmK]

Ok
You obviously have access to better data than I have seen before.
Must say I am most impressed with the performance on snow and off.
Thanks for your help which is much appreciated

Can you tell me the source of yr data

Regards
Malcolm