How do the differential lock work? - Duster Mechanical - Dacia Forum

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How do the differential lock work?


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#1
magnuken

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Does anybody know how the 4x4 lock mode works in Duster? I think it is only a central differential lock between the front and rear axles and this is not even a nearly 100% diff.lock!

 

I think this, because I have had a couple of situations in Lapland of northern Finland when the Duster have been stuck on a very slippery fjeld road. Only sometimes one front wheel and one rear wheel spinned, mostly only one wheel revolved! Of course I have on the Duster studded tyres!



#2
ColdDacia

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Yea i think the diffs are open and it uses the Traction control to help. have to turn of the stability control for it to work properly if i understood the manual right.. if you have the ESP that is:P



#3
Tozci

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This the system that is fitted to the Nissan X-TRAIL, the DUSTER has exactly the same system fitted.

 

 

Attached File  ADVANCED ELECTRONICALLY CONTROLLED ALL MODE 4x4..pdf   716.24KB   3744 downloads


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4x4 drivers have an extra knob!!!!!     :P  

 

 

 

Laureate 1.5 dCi 4x4 with ASC/ESR - LHD - Basalt Grey (colour not available in UK)


#4
magnuken

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Ok, thanks for the links and explanation.

 

But, I don´t believe in those Nissan descriptions, the differential lock between the axles in the Romanian Duster can´t be 100% according to my experiences. Or then I have a faulty Duster or the Dacia application of the Nissan concept is different!



#5
ColdDacia

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Yea manual just says it puts power on both back and front not that its 100%. and what i've read its not a 50/50 system... but i guess its about how you read it.

 

"“4WD Lock” mode distributes the 

engine torque between the front and 
rear axles in order to optimise the performance capacity of the vehicle in offroad situations. This mode should only 
be used in extreme driving conditions" from 2.12


#6
Unicoder

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I think it will work as described, but with different front rear torque settings , depends on the weight distribution of the duster front to rear.

But the main thing to remember is that the lock mode ie 53/47 torque split will only work upto 18mph, over this speed it switches back to auto mode.
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#7
christhomas

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Magnuken - Does your car have ESC/ASR?  And, if so, did you have it switched off when this problem occurred?  I've seen a few videos of similar problems and have been speculating that the drivers had failed to switch ESC/ASR off (as instructed in the manual, I believe).

 

I also get the impression that (in the standing still / not enough traction to get going situation) the system requires a bit of welly to operate effectively (as distinct from the gently-gently approach which usually works best in 2WD or, "Proper" (mechanical) 4WD systems.  Can anyone confirm that?

 

Chris


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#8
Unicoder

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I don't think giving it welly will do much other than spin the wheels, if you have a basic duster with no traction control, then it will be better to be gentle on the gas. The 4x4 system will do its best to get traction but, it's not a proper off roader , a real diff lock and mechanical 4x4 would do much better, how do I know, I had an ASX Mitsubishi 4x4 with the same AWD system, it worked ok, but it was rather toy like when compared to real 4x4.
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#9
mattlong

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I think there is a bit of a misunderstanding as to what a locking centre differential does and slight confusion over differentials. Without meaning to state the obvious to those who know, but here's a quick lesson for those too scared to ask:

Firstly, a typical 4x4 system has three differentials. One on the front axle between the wheels, one on the rear axle between the wheels and one situated on the prop shaft that joins the front and rear axles (located where the drive leaves the gearbox)

The axle differentials between the wheels allow the wheels on that axle to turn at different speeds. This allows the vehice to turn around a corner as the wheel on the outside of the turn needs to travel further than the wheel on the inside of the turn. The differential allows the wheel that is easiest to turn (the one on the outside of the turn) to receive the majority, if not all, the engine power as the vehicle turns. This has the unwanted affect in slippery conditions of diverting all the engine power to the wheel that's spinning, rather than the one which has traction.

In a 4x4 system not only do the wheels on each axle need to turn at different speeds to go around corners but in fact the front and rear axles need to turn at different speeds too (when going around the corner the rear wheels turn a tighter circle than the fronts. Each wheel on the car is turning different radius turns from each other) In order for the front and rear axles to turn at different speeds we need to add a centre differential. This differential (located just after the gearbox) will send power to whichever axle (front or back) is easiest to turn, in the same way the axle differentials favour whichever wheel is easist to turn. Again, the downside is the centre differential will send the majority of the power to an axle that has spinning wheels rather than an axle that has grip.

Still following the plot?

In effect what will happen is that in a normal 4x4 system the differentials will favour the easiest wheels to turn, resulting in occasions where only one wheel is in fact being powered. This could even be the wheel that is not able to grip whilst the other three are able to grip! A nasty demonstration of this is in Land Rovers where you have a transmission handbrake. If you jack up one wheel without chocking the others the differentials will favour the lifted wheel (as it's easier to turn) and result in the other 3 wheels losing their connection to the gearbox brake. Result, the car rolls away!

So here we come onto locking diffs. I know there are variations and differents degrees of open and closed, but this is just a "basic" description of the concept.

The idea of a locking differential is to take away the differential's ability to divert all power to a single axle/wheel. Instead it sends equal, or as near to equal as required, power to each side of the differential. In most 4x4 systems (like the one in the Duster) only the centre differential has the ability to be "locked" allowing power to be sent to both front and rear axles, regardless of which is easier to turn. However the axle differentials in these systems are not lockable so they still favour the easiest wheel on each axle. This results in only one wheel on each axle getting power in slippery conditions (as described in one of the posts above) Whilst this is not ideal, it is still an improvement on only 1 out of 4 wheels getting power without the locking differential! The reason the system in the Duster shuts off at speed is because to constantly drive with the centre differential locked, therefore sending equal power to front and rear axles, will cause "wind up" in the transmission that can destroy components and will also make the vehicle's turning circle larger and cause uneven tyre wear (besides from the fact the vehicle wouldn't corner particularly well!)

Some more competent 4x4's also have locking axle differentials which allow both wheels on the axle to get power. These differentials should only be used in slippery, low speed conditions as the vehicle would be virtually impossible to turn due to all the wheels being forced to turn at the same speed.

So, in the case of the Duster, the only lockable differential is the centre, therefore allowing at best only 2 wheels to remain powered under slippery conditions. In "auto" mode the centre differential favours sending the power to the front axle with the ability to send that power to the rear axle when required. The axle differentials on a Duster do not lock, therefore only one wheel on each axle will receive power in slippery conditions. This is not a failing of the Duster's system, but instead is characteristic of all 4x4 systems with only a lockable centre differential.

I hope this has been of use to anyone who wanted to know a little more about the subject.


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#10
Unicoder

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So which version of the center diff does the duster have ?

Clutch plates ?

Viscous coupling ?

It also has a sudo LSD by virtue of the ABS system , so I've read somewhere !!
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#11
mattlong

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The variation on the duster and nissan xtrail is that the centre differential is not mechanical in the traditional sense (as on the axles). It is located just ahead of the rear axle instead of behind the gearbox. This means that the prop shaft is constantly spinning. The differential itself is an electrically operated clutch that engages/disengages the rear axle. One advantage of this system is that the front axle always gets power, with the rear axle only being used when needed or "locked" in place.
There is something like a LSD system using the abs. Apparently the abs applies braking force to a spinning wheel when in lock mode to prevent the axle differential favouring that wheel over the one with grip.

#12
christhomas

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I think there is a bit of a misunderstanding as to what a locking centre differential does and slight confusion over differentials. Without meaning to state the obvious to those who know, but here's a quick lesson for those too scared to ask:

Firstly, a typical 4x4 system has three differentials. One on the front axle between the wheels, one on the rear axle between the wheels and one situated on the prop shaft that joins the front and rear axles (located where the drive leaves the gearbox)

The axle differentials between the wheels allow the wheels on that axle to turn at different speeds. This allows the vehice to turn around a corner as the wheel on the outside of the turn needs to travel further than the wheel on the inside of the turn. The differential allows the wheel that is easiest to turn (the one on the outside of the turn) to receive the majority, if not all, the engine power as the vehicle turns. This has the unwanted affect in slippery conditions of diverting all the engine power to the wheel that's spinning, rather than the one which has traction.

In a 4x4 system not only do the wheels on each axle need to turn at different speeds to go around corners but in fact the front and rear axles need to turn at different speeds too (when going around the corner the rear wheels turn a tighter circle than the fronts. Each wheel on the car is turning different radius turns from each other) In order for the front and rear axles to turn at different speeds we need to add a centre differential. This differential (located just after the gearbox) will send power to whichever axle (front or back) is easiest to turn, in the same way the axle differentials favour whichever wheel is easist to turn. Again, the downside is the centre differential will send the majority of the power to an axle that has spinning wheels rather than an axle that has grip.

Still following the plot?

In effect what will happen is that in a normal 4x4 system the differentials will favour the easiest wheels to turn, resulting in occasions where only one wheel is in fact being powered. This could even be the wheel that is not able to grip whilst the other three are able to grip! A nasty demonstration of this is in Land Rovers where you have a transmission handbrake. If you jack up one wheel without chocking the others the differentials will favour the lifted wheel (as it's easier to turn) and result in the other 3 wheels losing their connection to the gearbox brake. Result, the car rolls away!

So here we come onto locking diffs. I know there are variations and differents degrees of open and closed, but this is just a "basic" description of the concept.

The idea of a locking differential is to take away the differential's ability to divert all power to a single axle/wheel. Instead it sends equal, or as near to equal as required, power to each side of the differential. In most 4x4 systems (like the one in the Duster) only the centre differential has the ability to be "locked" allowing power to be sent to both front and rear axles, regardless of which is easier to turn. However the axle differentials in these systems are not lockable so they still favour the easiest wheel on each axle. This results in only one wheel on each axle getting power in slippery conditions (as described in one of the posts above) Whilst this is not ideal, it is still an improvement on only 1 out of 4 wheels getting power without the locking differential! The reason the system in the Duster shuts off at speed is because to constantly drive with the centre differential locked, therefore sending equal power to front and rear axles, will cause "wind up" in the transmission that can destroy components and will also make the vehicle's turning circle larger and cause uneven tyre wear (besides from the fact the vehicle wouldn't corner particularly well!)

Some more competent 4x4's also have locking axle differentials which allow both wheels on the axle to get power. These differentials should only be used in slippery, low speed conditions as the vehicle would be virtually impossible to turn due to all the wheels being forced to turn at the same speed.

So, in the case of the Duster, the only lockable differential is the centre, therefore allowing at best only 2 wheels to remain powered under slippery conditions. In "auto" mode the centre differential favours sending the power to the front axle with the ability to send that power to the rear axle when required. The axle differentials on a Duster do not lock, therefore only one wheel on each axle will receive power in slippery conditions. This is not a failing of the Duster's system, but instead is characteristic of all 4x4 systems with only a lockable centre differential.

I hope this has been of use to anyone who wanted to know a little more about the subject.

 

 

The variation on the duster and nissan xtrail is that the centre differential is not mechanical in the traditional sense (as on the axles). It is located just ahead of the rear axle instead of behind the gearbox. This means that the prop shaft is constantly spinning. The differential itself is an electrically operated clutch that engages/disengages the rear axle. One advantage of this system is that the front axle always gets power, with the rear axle only being used when needed or "locked" in place.
There is something like a LSD system using the abs. Apparently the abs applies braking force to a spinning wheel when in lock mode to prevent the axle differential favouring that wheel over the one with grip.

An excellent description, Mattlong.  Thanks.

 

Picking-up on the use of the ABS to mimic (to an extent) the effect of  locking differentials - According to the manual, the ABS has an, "Off-road", mode which becomes active when 4WD Lock is engaged.  The manual also recommends that ESP (=ESC/ASR?) should be switched off in, "Sand, mud, deep snow", conditions.  I assume this is to avoid conflict between the ABS (in it's off-road mode) and ESP systems.

 

So - In summary (if I understand correctly).  If you can't get enough traction to start moving - Select 4WD Lock and switch ESP off.

 

I'm still unsure about whether the, "Off-road", mode of the ABS requires a little bit of welly (and therefore significant rotational speed in the spinning wheel) before it cuts-in, brakes the spinning wheel and therefore transfers torque to the other wheel on that axle.

 

Chris


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#13
Unicoder

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So this system must use an hydraulic pump driven by the propshaft and one driven by the back wheels with the resultant difference in pressure to electronically operate the rear diff clutch.

The pressure difference depends on which set of wheels are loosing grip. With all wheels gripping, there's no difference in pressures, so no torque to the rear wheels, unless in lock mode and under 18mph.
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#14
mattlong

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So this system must use an hydraulic pump driven by the propshaft and one driven by the back wheels with the resultant difference in pressure to electronically operate the rear diff clutch.

The pressure difference depends on which set of wheels are loosing grip. With all wheels gripping, there's no difference in pressures, so no torque to the rear wheels, unless in lock mode and under 18mph.

From my understanding of the system it relies purely on electrical signals from a wide range of sensors including ABS, steering wheel angle, speed, etc. The signal is sent from the 4wd system's ecu and an electromagnet inside the differential pushes the clutch together to connect the rear axle.



#15
Unicoder

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Here's a nice link describing all available AWD systems, a quick look at the dacia duster in the list says it has an LSD , but doesn't say which country, region that has it.

The link takes you to the Nissan AWD system

http://www.awdwiki.com/en/nissan/
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#16
Bex

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Hi Mattlong, being female and very thick does that mean that the Duster would be better in Auto mode on snow and ice than 4x4?
Many thanks

I think there is a bit of a misunderstanding as to what a locking centre differential does and slight confusion over differentials. Without meaning to state the obvious to those who know, but here's a quick lesson for those too scared to ask:
Firstly, a typical 4x4 system has three differentials. One on the front axle between the wheels, one on the rear axle between the wheels and one situated on the prop shaft that joins the front and rear axles (located where the drive leaves the gearbox)
The axle differentials between the wheels allow the wheels on that axle to turn at different speeds. This allows the vehice to turn around a corner as the wheel on the outside of the turn needs to travel further than the wheel on the inside of the turn. The differential allows the wheel that is easiest to turn (the one on the outside of the turn) to receive the majority, if not all, the engine power as the vehicle turns. This has the unwanted affect in slippery conditions of diverting all the engine power to the wheel that's spinning, rather than the one which has traction.
In a 4x4 system not only do the wheels on each axle need to turn at different speeds to go around corners but in fact the front and rear axles need to turn at different speeds too (when going around the corner the rear wheels turn a tighter circle than the fronts. Each wheel on the car is turning different radius turns from each other) In order for the front and rear axles to turn at different speeds we need to add a centre differential. This differential (located just after the gearbox) will send power to whichever axle (front or back) is easiest to turn, in the same way the axle differentials favour whichever wheel is easist to turn. Again, the downside is the centre differential will send the majority of the power to an axle that has spinning wheels rather than an axle that has grip.
Still following the plot?
In effect what will happen is that in a normal 4x4 system the differentials will favour the easiest wheels to turn, resulting in occasions where only one wheel is in fact being powered. This could even be the wheel that is not able to grip whilst the other three are able to grip! A nasty demonstration of this is in Land Rovers where you have a transmission handbrake. If you jack up one wheel without chocking the others the differentials will favour the lifted wheel (as it's easier to turn) and result in the other 3 wheels losing their connection to the gearbox brake. Result, the car rolls away!
So here we come onto locking diffs. I know there are variations and differents degrees of open and closed, but this is just a "basic" description of the concept.
The idea of a locking differential is to take away the differential's ability to divert all power to a single axle/wheel. Instead it sends equal, or as near to equal as required, power to each side of the differential. In most 4x4 systems (like the one in the Duster) only the centre differential has the ability to be "locked" allowing power to be sent to both front and rear axles, regardless of which is easier to turn. However the axle differentials in these systems are not lockable so they still favour the easiest wheel on each axle. This results in only one wheel on each axle getting power in slippery conditions (as described in one of the posts above) Whilst this is not ideal, it is still an improvement on only 1 out of 4 wheels getting power without the locking differential! The reason the system in the Duster shuts off at speed is because to constantly drive with the centre differential locked, therefore sending equal power to front and rear axles, will cause "wind up" in the transmission that can destroy components and will also make the vehicle's turning circle larger and cause uneven tyre wear (besides from the fact the vehicle wouldn't corner particularly well!)
Some more competent 4x4's also have locking axle differentials which allow both wheels on the axle to get power. These differentials should only be used in slippery, low speed conditions as the vehicle would be virtually impossible to turn due to all the wheels being forced to turn at the same speed.
So, in the case of the Duster, the only lockable differential is the centre, therefore allowing at best only 2 wheels to remain powered under slippery conditions. In "auto" mode the centre differential favours sending the power to the front axle with the ability to send that power to the rear axle when required. The axle differentials on a Duster do not lock, therefore only one wheel on each axle will receive power in slippery conditions. This is not a failing of the Duster's system, but instead is characteristic of all 4x4 systems with only a lockable centre differential.
I hope this has been of use to anyone who wanted to know a little more about the subject.


<p>Duster, Mariana Blue, Ambience 4x4 with Esc, Protection pack. Ordered 9th March.
Expected June

#17
mattlong

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Hi Mattlong, being female and very thick does that mean that the Duster would be better in Auto mode on snow and ice than 4x4?Many thanks

Hi Bex! In ice and snow on the roads using auto probably a better idea as the system will just engage the rear axle when needed. If driven slow and steady the Duster should cope fine in snow and ice in this mode. Using "lock" may have the adverse affect that with the rear axle being powered all the time the risk of oversteer (sliding the rear end out on corners) would be increased.
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#18
Bex

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Thanks very much for the explanation on that Mattlong. Very helpfull. :ph34r:  :)

Hi Bex! In ice and snow on the roads using auto probably a better idea as the system will just engage the rear axle when needed. If driven slow and steady the Duster should cope fine in snow and ice in this mode. Using "lock" may have the adverse affect that with the rear axle being powered all the time the risk of oversteer (sliding the rear end out on corners) would be increased.


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<p>Duster, Mariana Blue, Ambience 4x4 with Esc, Protection pack. Ordered 9th March.
Expected June

#19
mattlong

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Thanks very much for the explanation on that Mattlong. Very helpfull. :ph34r:  :)


No problem. Hope it's been of some use.

#20
Micknand

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Welcome to the forum mattlong

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