Hippo
Lord Hippo
We do know how/why the vcu works. Look up the sheering effect.
read this > http://www.landyzone.co.uk/lz/3080984-post22.html
read this > http://www.landyzone.co.uk/lz/3080984-post22.html
GrumpyGel
Well-Known Member
I think you'll find that that's right...... but wrong.
I agree there's always resistance. I agree the sheering effect creates heat (instantaneously). I agree there's a sort of equilibrium once the VCU has got the rear prop spinning the same as the front, then cools which may result in the speed difference, so it heats again - although it will only cool a little and heating is instantaneous so its probably more constant.
However, the science behind it looks as though as the temperature rises (through sheer) the fluid actually becomes less viscous (GKN describe 'degressive locking characteristics'). However, as the temp rises the fluid expands. Once the fluid has expanded to completely fill the coupling, 'Hump mode' occurs, pressure increases and the plates are pushed together in alternate plate sequence and the coupling essentially 'locks up' (once again shown in GKN's Hump Mode graphic).
The 'equilibrium' is likely to be the bordering on Hump Mode.
See the 2 graphs in the first post on http://www.landyzone.co.uk/lz/f38/definitive-freelander-vcu-testing-thread-99163.html. The first one has a constant viscosity as temp rises until Hump Mode, the second (which is off a dyno) shows viscosity falling as temp rises until Hump Mode. Also see section 8 "Conclusions" in this comprehensive analysis of viscous couplings http://www.easy2design.de/stuff/visco_sae.pdf.
I agree there's always resistance. I agree the sheering effect creates heat (instantaneously). I agree there's a sort of equilibrium once the VCU has got the rear prop spinning the same as the front, then cools which may result in the speed difference, so it heats again - although it will only cool a little and heating is instantaneous so its probably more constant.
However, the science behind it looks as though as the temperature rises (through sheer) the fluid actually becomes less viscous (GKN describe 'degressive locking characteristics'). However, as the temp rises the fluid expands. Once the fluid has expanded to completely fill the coupling, 'Hump mode' occurs, pressure increases and the plates are pushed together in alternate plate sequence and the coupling essentially 'locks up' (once again shown in GKN's Hump Mode graphic).
The 'equilibrium' is likely to be the bordering on Hump Mode.
See the 2 graphs in the first post on http://www.landyzone.co.uk/lz/f38/definitive-freelander-vcu-testing-thread-99163.html. The first one has a constant viscosity as temp rises until Hump Mode, the second (which is off a dyno) shows viscosity falling as temp rises until Hump Mode. Also see section 8 "Conclusions" in this comprehensive analysis of viscous couplings http://www.easy2design.de/stuff/visco_sae.pdf.
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SnapBrokeIt
New Member
Greatly appreciated GrumpyGel thanks for the steer in the right direction...
More reading I think, but unsure why I'm torturing myself on this!
thx
More reading I think, but unsure why I'm torturing myself on this!
thx
Hippo
Lord Hippo
The only difference I see from what we knew before, is that it's now said the plates are pushed together. This is where the theory falls over as there's nothing pushing the plates together. How are they pushed together? When taking my vcu apart I can't see how this is done.
The vcu metal outer bits will have an average temp due to it being hotter inside than outside. The heat generated by the sheering effect isn't strong enough to force the case higher in temp than what it heats too. The change in temp from ambient to finishing driving the same route is the same, at the same speeds. The final temp is higher if the ambient temp is higher, by the same amount. So there's a pattern ere. But that's down to testing.
One thing all this info proves is yer can't recon a vcu in yer garden shed with a magic mix which makes it better than the original, even if you are a dwarf. The vcu is simple in theory, but complex when considering it's use as part of the vehicle. Like an emergency stop when the front end drops down to reduce front wheel radius. Like timing of increased resistance when compared to the tc kicking in. LR openly admit the balance of the vcu caused them a lot of problems. For some owners that's also the case when it gives them a kick in the wallet.
Nearly 500 posts on this fred alone and how many fekin owut results?
Whilst I enjoy discussion on ere I think we should have a rule that yer can't post on vcu freds without putting up yer own owut results.
You've probably guessed I've had a crap day.
The vcu metal outer bits will have an average temp due to it being hotter inside than outside. The heat generated by the sheering effect isn't strong enough to force the case higher in temp than what it heats too. The change in temp from ambient to finishing driving the same route is the same, at the same speeds. The final temp is higher if the ambient temp is higher, by the same amount. So there's a pattern ere. But that's down to testing.
One thing all this info proves is yer can't recon a vcu in yer garden shed with a magic mix which makes it better than the original, even if you are a dwarf. The vcu is simple in theory, but complex when considering it's use as part of the vehicle. Like an emergency stop when the front end drops down to reduce front wheel radius. Like timing of increased resistance when compared to the tc kicking in. LR openly admit the balance of the vcu caused them a lot of problems. For some owners that's also the case when it gives them a kick in the wallet.
Nearly 500 posts on this fred alone and how many fekin owut results?
Whilst I enjoy discussion on ere I think we should have a rule that yer can't post on vcu freds without putting up yer own owut results.
You've probably guessed I've had a crap day.
htr
Well-Known Member
I agree, the plates are not intended to touch but the evidence is that due to the silicone fluid becoming discoloured then there must indeed be some contact happening. We have no way of knowing how the fluid moves inside the VCU or how the air is distributed. Air bubbles between those plates may allow areas of compression or expansion thus contact...
As non-newtonion fluids do when force is applied they stiffen. In that 1980s article they talk about sausage-like rolls of fluid observed between the plates of a test jig and this could well be happening as well as the fluid being caught in the slots and holes in the plates themselves thus transferring power through the VCU.
I now have a question for those who have opened up a VCU. When the 'cap' is removed [ input end] and the plates are removed and the internal cavity cleaned up, is there a bearing or some sort or seal that runs on the input shaft in that cap. At the other end is there again some sort of bearing that the input shaft seats into and runs in? If there is, are they identifiable and thus able to be sourced from suppliers?
As non-newtonion fluids do when force is applied they stiffen. In that 1980s article they talk about sausage-like rolls of fluid observed between the plates of a test jig and this could well be happening as well as the fluid being caught in the slots and holes in the plates themselves thus transferring power through the VCU.
I now have a question for those who have opened up a VCU. When the 'cap' is removed [ input end] and the plates are removed and the internal cavity cleaned up, is there a bearing or some sort or seal that runs on the input shaft in that cap. At the other end is there again some sort of bearing that the input shaft seats into and runs in? If there is, are they identifiable and thus able to be sourced from suppliers?
jedi
Well-Known Member
My understanding of it all......
1. Externally applied heat to the fluid will NOT make it stiffen up. It will in fact make it more viscous(runny). Otherwise hippos living on the equater would be in serious trouble.
2. The fluid stiffens with the shearing action of the plates inside a vcu. Or by just pouring the fluid it will stiffen. This is a property of the fluid. The heat is generated by the shearing effect and NOTHING else.
3. Hump mode and the air gap/bubble are like full diff lock. As the fluid heats up due to the shear effect of the plates rubbing against it. (Caused by wheels slipping etc) the air in the gap/bubble begins to expand. This increases the pressure inside the vcu and in turn accelerates the way the viscous fluid works (ie. It stiffens up extra quick time to the point of "hump") I don't belive the plates actually touch when this happens as there will be viscous fluid between them all....those that have seen scorchio marks on the plates this could be explained by how hard the vcu has been used through its life...eg trying to tow a jumbo jet will no doubt stress the vcu beyond what it was designed for. And all sorts of magical wonders happen.
1. Externally applied heat to the fluid will NOT make it stiffen up. It will in fact make it more viscous(runny). Otherwise hippos living on the equater would be in serious trouble.
2. The fluid stiffens with the shearing action of the plates inside a vcu. Or by just pouring the fluid it will stiffen. This is a property of the fluid. The heat is generated by the shearing effect and NOTHING else.
3. Hump mode and the air gap/bubble are like full diff lock. As the fluid heats up due to the shear effect of the plates rubbing against it. (Caused by wheels slipping etc) the air in the gap/bubble begins to expand. This increases the pressure inside the vcu and in turn accelerates the way the viscous fluid works (ie. It stiffens up extra quick time to the point of "hump") I don't belive the plates actually touch when this happens as there will be viscous fluid between them all....those that have seen scorchio marks on the plates this could be explained by how hard the vcu has been used through its life...eg trying to tow a jumbo jet will no doubt stress the vcu beyond what it was designed for. And all sorts of magical wonders happen.
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Hippo
Lord Hippo
Air pressure inside the vcu... would this have an effect on the fluid? I always thought you couldn't compress a fluid. Hence why it's used in hydraulics?
The temperature concern with vcu's is related to one person saying 70 degree is too hot, stating the fluid is damaged by this temp.
The temperature concern with vcu's is related to one person saying 70 degree is too hot, stating the fluid is damaged by this temp.
htr
Well-Known Member
Well I've fitted a new VCU and Bearings last night. Went for a short and gentle test drive this morning. Then this afternoon I re-did my one wheel up test.
Used the same test jig as above.
FL1 K series 1.8 194,000km, original VCU. All transmission oils have now been replaced. This FL has had a s/h IRD fitted at some point in the past.
Weather: High partial cloud, light westerly wind temp' 9ºC
Cold test:
#1 - 18.86
#2 - 18.44
#3 - 18.59
#4 - 17.92
#5 - 18.32
Average = 18.43
'Warm' test - identical route as the last test.
#1 - 17.16
#2 - 16.23
#3 - 16,17
#4 - 15.27
#5 - 16.32
Average = 16.23
Alibro
Well-Known Member
This is mine before I cut it open.
This is it after I re-welded it but before cleaning up the weld
To be honest I didn't pay much attention to bearings, but the end I cut off has a seal or/and bearing. I can't remember what is at the other end but I think there must be a bearing as the shaft can turn independently. Don't forget half the disks have teeth on the outer edge which mesh with casing of the VCU and the other half have teeth on the inside edge and mesh with the shaft.
This might show what I mean.
If you look carefully you can see the difference between the disks.
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Just did the wheel up test on my recently acquired Freelander. I have no information on the VCUs history but it says GKN on it - it looks fairly fresh (no rust anywhere) - this on a 05 plate TD4 Auto with 126k miles on it.
Ambient 22degrees - car stood overnight - 1.2m alloy tube onto the 35mm socket - 8kg weight.
First run 18secs for 45 to horizontal
Ran 5 more and it gradually worked down to 12secs
Went for a 2 mile run - checked VCU - still at 23degrees
Repeated test 5 times - went from 15secs down to 11secs
Repeated 5 times with a 5kg weight - went from 30secs to 28secs
Drove 16 miles and stopped on a layby to check VCU temp - it was only very slightly warm and cooler than the props (forgot my infrared thermometer)
So - I think I should be happy with that - it's a little free-er than Hippo's test of this thread Sept 18th 2012 - and also HTR's test report on Jun 27th 2015 on a brand new setup which tested almost identical to Hippo's but at a lower ambient (9degrees)
Car feels quite free on lock forwards or back - but with Auto not so easy to judge - and went up a steep grassy slope I know without any trauma - bit of scrabbling at the front but went straight up.
Just my tuppence worth (in support of Hippo's call for data)
Ambient 22degrees - car stood overnight - 1.2m alloy tube onto the 35mm socket - 8kg weight.
First run 18secs for 45 to horizontal
Ran 5 more and it gradually worked down to 12secs
Went for a 2 mile run - checked VCU - still at 23degrees
Repeated test 5 times - went from 15secs down to 11secs
Repeated 5 times with a 5kg weight - went from 30secs to 28secs
Drove 16 miles and stopped on a layby to check VCU temp - it was only very slightly warm and cooler than the props (forgot my infrared thermometer)
So - I think I should be happy with that - it's a little free-er than Hippo's test of this thread Sept 18th 2012 - and also HTR's test report on Jun 27th 2015 on a brand new setup which tested almost identical to Hippo's but at a lower ambient (9degrees)
Car feels quite free on lock forwards or back - but with Auto not so easy to judge - and went up a steep grassy slope I know without any trauma - bit of scrabbling at the front but went straight up.
Just my tuppence worth (in support of Hippo's call for data)
Alibro
Well-Known Member
I think you should be very happy with that. Sounds like yours has been changed sometime recently. If I wasn't such a lazy sod I'd have done the test on mine after the VCU refurb but I was kinda wanting to wait for a while to make sure it still works.
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Just had the opportunity to do another wheel-up test with exactly the same set-up as my test on my own last month - my Daughter called by with her Freelander on which she changed the VCU for a brand new one - GKN original equipment - about 10K ago - here are the results:- Car had driven 20 miles then stood for Half an hour at an ambient of 20 DegC - 1.2M bar
8Kg load - five runs through 45degrees as before :- 12secs first run down to 11 secs on the last run
5 kg load - 25secs down to 24 secs on the last run of 5
Very consistent throughout - probably 'cos the thing was still slightly warm from driving down - and re-assuringly similar to my test on my own
8Kg load - five runs through 45degrees as before :- 12secs first run down to 11 secs on the last run
5 kg load - 25secs down to 24 secs on the last run of 5
Very consistent throughout - probably 'cos the thing was still slightly warm from driving down - and re-assuringly similar to my test on my own
Graham3748
Member
I have been reading through the thread with interest having purchased a freelander recently. I have also had a look at the GKN website who I believe are the manufacturers of the VCU fitted to the Freelander.On their site they say that the VCU is a system sealed for life requiring no maintenance. Then it says that the Silicone fluid is optimised with specific additives for lifetime performance. Now correct me if I'm wrong but if it's a lifetime performance, and the suggestion is they need replacing at around 70000 miles to prevent any damage to other drive parts,which for the average driver is about every 7 years,taking into account the average person is supposed to do about 10000 miles a year. How is the fluid optimised for life? May be GKN need to address the problem or refrase their technical features. Just a thought!
Alibro
Well-Known Member
Ok, finally got off me arse and measured the time taken for a 8kg weight on a 1.2m stick to fall from 45deg to horizontal.
I tested it several times and got between 6 and 10 seconds. This means I either cocked up the fix completely or got it perfect depending on how you look at it. In my mind it is exactly as I wanted it ie not as tight as a new VCU would be but tight enough to stop me spinning the wheels on slippy ground.
Me's a happy bunny.
I tested it several times and got between 6 and 10 seconds. This means I either cocked up the fix completely or got it perfect depending on how you look at it. In my mind it is exactly as I wanted it ie not as tight as a new VCU would be but tight enough to stop me spinning the wheels on slippy ground.
Me's a happy bunny.
Hippo
Lord Hippo
The life time of a product isn't necessarily the amount of time it's use for, or lasts for, or is owned for. Some car manufacturers quote this to be 7 or 10 years. Hence the sealed for life aspect doesn't really apply to us as our vehicles last longer. In general, vcu's are designed with a secrete fluid mix (re-conners don't know the exact spec, they have guessed) and this performs well in normal use on and oft road. After a period of use the fluid changes from the original spec, which causes the vcu to stiffen. When this happens it puts additional stress in the transmission, which may break something. Hence why we test our vcu's to see if they have stiffened and if so, replace them. The 70k miles thing became a popular interval on LZ, but not other forums. theory being to just change it as it's cheaper than the costs of something breaking. Not the perfect solution as vcu's can fail at a lower mileage than this too. There's plenty of discussion on this subject and re-conners are more than happy to quote 70k miles being a fact, backed up by their self imposed expert status. The fact is they have a vested interest as they make money out of vcu's. The best thing to do is test yer vcu. If in doubt remove it (and don't forget to tell yer insurance).
