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warrenmzz
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Joined: March 12, 2012
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 Posted: Sun Nov 12, 2017 10:16 am Post subject: Re: Syncro “AWD” Capabilty |
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Got the Sport VC from Van Cafe. As mentioned by syncro Jael, it works great. I also have a decoupler. |
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IdahoDoug
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| Posted: Sun Nov 12, 2017 10:59 am Post subject: Re: Syncro “AWD” Capabilty |
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Orange,
That's an interesting post. I wondered the same - given the limitations of a VC for providing dry and wet road performance (can't spin the front shaft faster than the rear), why would they do that to their image-leading vehicle? I have to think there is something else in the system to overcome that shortcoming. For instance, my full time 4WD LandCruiser has a VC-like feature in high range but it does not suffer from the VC road issues because of the rest of the planetary center diff's design. I wonder of some of the folks discussing it got the system's actual design wrong?
The VC delivers benefits during significant rear wheelspin which is slippery road and offroad. For ordinary road or track conditions I'm not clear on why they did it.
Doug
_________________
1987 2WD Wolfsburg Vanagon Weekender "Mango", two fully locked 80 Series LandCruisers. 2017 Subaru Outback boxer. 1990 Audi 90 Quattro 20V with rear locking differential, 1990 burgundy parts Vanagon. 1984 Porsche 944, 1988 Toyota Supra 5 speed targa, 2002 BMW 325iX, 1982 Toyota Sunrader |
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gears
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Location: Tamarack, Bend, Kailua
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| Posted: Sun Nov 12, 2017 11:01 am Post subject: Re: Syncro “AWD” Capabilty |
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Thank you SO much for taking the time to research this, Orange. Since I'm a snow guy, most definitely Sport version for my unicorn ..
_________________
aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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OrangeZA
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Location: Scottish Highlands
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| Posted: Sun Nov 12, 2017 2:42 pm Post subject: Re: Syncro “AWD” Capabilty |
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Doug, I think much of the reason why Porsche went for the VC on the 993 and indeed the later water-cooled 996s and non-turbo 997s, is due to the rear engined design. With it’s advantages in terms of traction, what percentage of engine torque in a rear engined car needs to be transferred to the front end to improve roadholding and the highly subjective matter of “handling”? Will too much front drive torque not just upset the steering in a rear-engined car? Nose heavy Audis originally came with a centre diff that split the torque distribution 50/50%, front/rear, but for later models Audi modified the diff so that the split was 40/60%, front/rear, the change appears to be a popular one within the motoring press.
Porsche's first foray into producing a 4-wheel drive 911, the 964 Carrera 4 utilised a system called PDAS, Porsche Dynamic All-Wheel Drive System, it consisted of planetary-type centre diffferential which nominally divided the engine’s torque 31% to the front and 69% to the rear. According to Karl Ludvigsen’s book:
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| “This basic torque division could be overridden as necessary by a multiple-disc clutch that was integral with the differential and applied hydraulically according to signals from a computer. Its function was to add inter-axle friction in the drive line that could ensure the continued application of torque to one pair of wheels if the other was on a slippery surface. A similar hydraulic control of the rear differential was also provided. Inputs to the controlling computer were generated by the pickups at each wheel that fed data to the ABS braking system and also by a lateral-acceleration sensor” |
The system added 100kgs to the weight of the 964.
Sounds awesome doesn’t it? The result was a controversial Porsche 911. Again from Ludvigsen:
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Ulich Bez was among those who were disappointed by the [964] Carrera 4’s heavy understeering handling, which was not at all as “agile” as a Porsche should be, so a new approach was not long in coming.
“We’ve defined four-wheel drive differently” with the 993, said Horst Marchart. “With our four-wheel-drive concept traction was not given absolute priority, but rather first-class handling.” Gone was the cumbersome PDAS with its planetary gears and computer-controlled differentials. Instead the drive to the front was through a viscous coupling at the nose of the transaxle, then forward through a torque tube to a compact open differential driving the front wheels. No computer controls were needed. |
My guess is that the 993’s VC is softer acting than the T3 syncro’s, because the T3’s application was primarily to improve traction in slippery conditions. The Porsche literature gives a baseline figure of 5% drive to the front axle and this percentage of drive goes up to a nominal maximum of 40+6%. My guess is the 5% is generated through slip when torque is applied to the rear wheels.
I think there is actually a lot of consensus in this discussion. I imagine everyone will agree that the VC cannot send more than 50% of engine torque to the front axle (I’d say it was slightly less that 50% having looked at table 6.2 of the SAE paper). I think everyone would also agree that if the T3 syncro was coasting around a bend, with the driver’s foot off the accelerator pedal, a braking force would be applied to the front wheels as the rear wheels would be spinning slower than the front wheels. The only disagreement appears to be at which point on applying torque to the transmission does the VC send torque to the front axle.
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Ultra sport: ... (+85 nm) of break away torque.
Sport: (+55nm) of breakaway torque
Stock: shimmed to factory specs... 35 newton meters |
How valid are these break away (or shear) torque comparisons, if I pumped a VC full of tomato sauce instead of siloxane, could I not produce a break away torque too? Is there not a better way to test a VC and how is reacts to the torque applied to it, how it shears, how the temperature and pressure rises within it and how finally it clamps together again? (See fig 8.1 of the SAE paper) Waldi earlier mentioned the test bed at Viscowerkstatt-Kern, I wonder if this can produce more valuable comparison data? https://vw-kern.at/our-testrig#anc-testbed |
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gears
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Location: Tamarack, Bend, Kailua
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| Posted: Sun Nov 12, 2017 3:20 pm Post subject: Re: Syncro “AWD” Capabilty |
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| Quote: |
How valid are these break away (or shear) torque comparisons, if I pumped a VC full of tomato sauce instead of siloxane, could I not produce a break away torque too? Is there not a better way to test a VC and how is reacts to the torque applied to it, how it shears, how the temperature and pressure rises within it and how finally it clamps together again? |
I believe it's the unique expanding properties of the VC's fluid which causes drag between the plates (unlike a ZF LSD in which plates & discs are tightly preloaded together). I wouldn't expect much resistance when using another type of fluid, and certainly not the characteristic "hump" mode.
I agree that "shear breakaway" might be a better term to use when discussing the point a VC yields.
Not having rebuilt a VC myself, I'm FAR from knowledgeable on the subject .. I really need to get some hands-on experience (like I have with LSDs).
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aka Pablo, Geary
9.36 @ 146 in '86 Hot & Sticky
'90 Syncro Westy SVX
'87 Syncro GL 2.5
https://guardtransaxle.com |
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Waldi
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| Posted: Sun Nov 12, 2017 3:28 pm Post subject: Re: Syncro “AWD” Capabilty |
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The break away numbers say nothing about how a VC works on track.
It just shows, it always transfers a minimum of torque.
Calling a non bench tested VC "Sport VC" can be a selling plus, but it tells not much about the specs of the VC in use.
A so called Sport VC can have higher break away numbers but it will not incrase torque transfer on numbers like a tested or new VC.
Same otherwise.
It can achieve too late hump mode and overheat this way.
Kern has tested some of my VCs on his bench.
This are graphs with 30.000, 60.000 and 100.000 silikon oil.
And already 5 gramms more or less change the curve too.
It is not possible to self made a VC within the specs without a test bench.
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hellenic vanagon
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Location: ATHENS GREECE
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| Posted: Sun Nov 12, 2017 6:04 pm Post subject: Re: Syncro “AWD” Capabilty |
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The Syncro white paper, the English translation:
http://www.vwsyncro.eu/p/blog-page_21.html
(Unfortunately, the picture quality in the pdf is degraded by the google's drive).
From the very first moment, vw claims that a 5% of the torque is transmtited, permanently, through the vct on the dry pavement in a straight line.
This diagram here, gives, at least, a 4%, at any speed, with 0 inclination, for the specific, in the test, configuration, (from the above paper):
Last edited by hellenic vanagon on Sun Nov 12, 2017 6:46 pm; edited 1 time in total |
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hellenic vanagon
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Jon_slider
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| Posted: Sun Nov 12, 2017 9:46 pm Post subject: Re: Syncro “AWD” Capabilty |
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I admire your passion
Posted: Mon Jul 01, 2013 12:18 pm Post subject: SAE "WHITE PAPER" ABOUT SYNCRO!
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hellenic vanagon
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| Posted: Mon Nov 13, 2017 12:58 am Post subject: Re: Syncro “AWD” Capabilty |
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| Jon_slider wrote: |
I admire your passion
Posted: Mon Jul 01, 2013 12:18 pm Post subject: SAE "WHITE PAPER" ABOUT SYNCRO!
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Thank you.
Between, (many), other things, it saved, (at least twice), my life, when, f.ex., I was able to pass over a, sudden, very slippery curve, and the Opel Vectra, (1990 mod), which was trying to follow me, (at about 80 km/h), oversteered, crashed on a very fat, grid's, cement column, chopping it and hanging it, by the cables, over a small house.
The driver saved by me, sawing from my mirror the incidence, (as well as, the flying cement fragments towards my Syncro), bleeding from his head. A terrible moment.
It was the Syncro vct, which, passed the point with just a negligible shaking, make me waiting for the worst for my ignorant "competitor" , because if a t3 Syncro passes with a little shaking, the vast majority of the common cars are in a serious danger. |
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Waldi
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Location: Germany
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| Posted: Mon Nov 13, 2017 1:25 am Post subject: Re: Syncro “AWD” Capabilty |
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This can easy go the other way with a out of specs hard VC.
While the most cars are desighnt to understeer for comon drivers savety, i dont like it.
For me it feels better with exact turn-in behavior on the front exle, and a bit loose rear axel which helps with steering.
But i am an old scool rear wheel rally driver.
Never liked front driven cars.
I couple only on snow, and than the syncro is overtaking all the luxury 4wd 300hp cars, which are afraied to drive fast.
The conclusion is, if you want to drive coupled on pavement, you need a VC within specs.
The reality shows, that ppl waste more likely money on a stronger engine, bigger, heavy bumper, than on a new/tested VC.
They are more interested in holding up with the traffic on a straight uphill road, or how the van looks, than to drive save on a slipperly curvy road.
We all have our priorities. |
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hellenic vanagon
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Joined: December 28, 2007
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Location: ATHENS GREECE
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| Posted: Mon Nov 13, 2017 1:49 am Post subject: Re: Syncro “AWD” Capabilty |
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| Waldi wrote: |
This can easy go the other way with a out of specs hard VC.
While the most cars are desighnt to understeer for comon drivers savety, i dont like it.
For me it feels better with exact turn-in behavior on the front exle, and a bit loose rear axel which helps with steering.
But i am an old scool rear wheel rally driver.
Never liked front driven cars.
I couple only on snow, and than the syncro is overtaking all the luxury 4wd 300hp cars, which are afraied to drive fast.
The conclusion is, if you want to drive coupled on pavement, you need a VC within specs.
The reality shows, that ppl waste more likely money on a stronger engine, bigger, heavy bumper, than on a new/tested VC.
They are more interested in holding up with the traffic on a straight uphill road, or how the van looks, than to drive save on a slipperly curvy road.
We all have our priorities. |
When vw made it, was very "easy" to put a decoupler, as initially intended.
But, for the average driver, for the daily use, (the races are another field), they found that:
"This clutch, which performs the function of the differential compensation, the optimal torque distribution and the central lock...", and "...it poses a positive effect on the brakes...", (from the Syncro white paper),
which is what a nowdays car offers with the various, fragile, electronics.
So, this is applied science, (30 years ago).
But, still, the people may have opinions. That's not bad at all, (?). |
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Waldi
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Location: Germany
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| Posted: Mon Nov 13, 2017 2:02 am Post subject: Re: Syncro “AWD” Capabilty |
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I am with you Helenic,
i try just to explain, that the old or self made VCs dont work like they should.
And i think this makes driving coupled with a harder VC more unsafty than driving a 2wd van.
And it puts more wear on the boxes.
I recoment to use 25.000 silicon oil for the VCs.
As it is visible on my graphs, the 30.000 is a bit hard.
But the best is to order one from Kern.
I can arrange this. |
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hellenic vanagon
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Joined: December 28, 2007
Posts: 283
Location: ATHENS GREECE
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| Posted: Mon Nov 13, 2017 2:32 am Post subject: Re: Syncro “AWD” Capabilty |
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| Waldi wrote: |
I am with you Helenic,
i try just to explain, that the old or self made VCs dont work like they should.
And i think this makes driving coupled with a harder VC more unsafty than driving a 2wd van.
And it puts more wear on the boxes.
I recoment to use 25.000 silicon oil for the VCs.
As it is visible on my graphs, the 30.000 is a bit hard.
But the best is to order one from Kern.
I can arrange this. |
I am proposing the operation vw intended to offer.
I wish you to continue your success to this, extremely, interesting field. |
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OrangeZA
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Joined: January 04, 2016
Posts: 110
Location: Scottish Highlands
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| Posted: Mon Nov 13, 2017 5:45 am Post subject: Re: Syncro “AWD” Capabilty |
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Thanks for translating the syncro white paper Hellenic, I know it must have been a very tedious task, some of those German words are so long! Going to enjoy some lunchtime reading now  |
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hellenic vanagon
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Location: ATHENS GREECE
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| Posted: Mon Nov 13, 2017 9:07 am Post subject: Re: Syncro “AWD” Capabilty |
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| OrangeZA wrote: |
| Thanks for translating the syncro white paper Hellenic, I know it must have been a very tedious task, some of those German words are so long! Going to enjoy some lunchtime reading now |
You are welcome.
The truth is that I had some difficult moments, the last few days, in order to decide where to cut these train German words, since the Google translator was unable to translate, except if you cat them. But by cutting the meaning is absolutely different depended on imagination where to cut.
Anyway, as you 'll see, just one word remains untranslated, and together with other updates, (suggestions wanted), everything will be better, (hopefully), in my second edition.
(This paper is referred το various unexpected, and heretic, phenomena observed, when a Syncro permanent 4wd system is used... So it is good that they are in German with very difficult words etc. etc... (That's, just, a Syncro joke  )). |
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hellenic vanagon
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Location: ATHENS GREECE
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| Posted: Tue Nov 14, 2017 3:03 am Post subject: Re: Syncro “AWD” Capabilty |
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Deep are the roots...
#1
Link
"Quattro with viscous coupling in the Audi R8
The quattro permanent all-wheel drive on the Audi R8 high-performance sports car has a pronounced rear-wheel bias. The transmission mounted behind the longitudinal mid-engine is fitted with a power take-off for a propshaft. This channels the drive power down one side past the engine to the front axle, where a viscous clutch distributes the torque. The basic power split is 15:85. If the rear wheels start to spin, an additional 15 percent is directed to the front in an instant. In this way, quattro once again provides the trademark Audi qualities: outstanding traction, acceleration with virtually no slip, sharper handling dynamics, improved straight-line stability – and, of course, a generous extra dose of driving pleasure".
#2
Link
(Audi's r8 transmission is used).
#3 With the "SYNCRO" badge at the rear! Record du Monde!
Link
Link
The mother of all, (V.A.G.), declares a permanent torque transfer, to the front differential, starting from a 15%, in a straight, dry pavement, line.
Last edited by hellenic vanagon on Tue Nov 14, 2017 11:55 pm; edited 2 times in total |
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OrangeZA
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Location: Scottish Highlands
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| Posted: Tue Nov 14, 2017 4:57 am Post subject: Re: Syncro “AWD” Capabilty |
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That’s interesting Hellenic.
This is from Audi’s Technology Portal website: https://www.audi-technology-portal.de/en/drivetrain/quattro_en/viscous-coupling
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Viscous coupling
The Audi R8 high-performance sports car occupies a special position in the Audi model range – and this extends to its packaging and its drive system. The mid-mounted engine is arranged longitudinally at the rear of the car in front of the rear axle, with the gearbox right behind it. It also includes an auxiliary drive for a prop shaft running past the engine on the side and up to the front axle.
There a viscous coupling distributes the power between the front axle and the rear axle, which is equipped with a locking differential. Under normal driving conditions, the coupling sends only about 15 percent of the torque to the front axle – the R8 has the rear bias typical of a sports car. If the rear wheels slip, an additional 15 percent almost immediately flows to the front.
The primary component of the viscous coupling is a package of round clutch disks, each with different gearing. One of each is connected to the prop shaft via the housing; the other is connected via the output shaft to the front axle. The clutch plates rotate in a viscous fluid. If they rotate at greatly different speeds due to a loss of traction at the rear axle, the oil becomes more viscous as a result of its internal friction. By picking up the other clutch disk of each pair, a greater torque is transferred via the drive shaft to the front axle. |
I can see parallels with the Porsche 911. A high performance sports car with a rear axle weigh bias, it's 43/57%, front/rear for the Audi R8, 41/59% for the 993 Carrera 4 and 49.3/50.7% for the T3 Syncro.
Also interesting to note, when fitted with 18” wheels the R8’s rear tyres have a greater diameter than the fronts. There is no mention of differing axle ratios front and rear in the specification. http://www.fourtitude.com/resources/downloads/documents/r8_42_techdata.pdf |
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tencentlife
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Location: Abiquiu, NM, USA
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| Posted: Fri Nov 24, 2017 10:28 am Post subject: Re: Syncro “AWD” Capabilty |
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| Jon_slider wrote: |
Planetary Center Diff: one input, TWO outputs capable of different speeds from each other, and front diff can spin faster than rear diff.
http://www.awdwiki.com/en/subaru/
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Um, that's not a planetary center differential.
Oh, and by the way, a VC is an "un-differential", folks, it's function is the exact opposite of a differential, so comparing it to a center diff is misleading.
Oh and another thing: "hump mode" is an outlier phenomenon, Peshke's paper even highlights it as a self-limiting curiosity that occurs at unusually high temps, not as the normal reliable function of the VC. Under most all conditions a VC is a progressive "un-differential" (some call it a clutch, but I don't because it's a passive device), at any internal temp below that which causes humping pressure the PDMS (polydimethylsiloxane) fluid transmits torque in progressive but non-linear proportion to the ∆VC rpm, first viscously, and at a certain increased ∆VC by becoming semi-plastic, with similar but less abrupt self-limiting behavior as hump mode in the semi-plastic mode (i.e. ∆VC falling below the plastic stress reaction speed allows the fluid to return to viscous liquid behavior). Semi-plastic behavior can be induced at sufficient ∆VC rpm at any temp.
Because PDMS is a Newtonian fluid (its viscosity decreases with temp, albeit very little compared to many other fluids) even while having seemingly non-Newtonian behaviors, in viscous transfer mode the torque transferred at a given ∆VC decreases slightly with fluid temp.
Due to mechanical resistance of the moving components (especially seal stiction) there is a base static torque transmission even at zero ∆VC, typically in the range of 5-25ft.lb (what people are calling "breakaway torque"). That falls slightly as the seal stiction is overcome, but at any non-zero ∆VC the fluid increases the torque transferred by adding viscous transfer to the remaining mechanical drag. And given it requires a certain force to move a vehicle, in any AWD/4WD vehicle under any given conditions any amount of force transferred thru one axle assembly is force that is NOT borne by the other (basic 2nd Law question).
Some good observations being made here but in most of these Syncro discussions there's still some magical thinking about such a simple device as the VC. Read the Wikipedia entry on PDMS if you want to break thru the nonsense. If you don't understand the fluid properties you will never begin to grasp how the VC works.
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Waldi
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| Posted: Sat Nov 25, 2017 3:42 am Post subject: Re: Syncro “AWD” Capabilty |
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The break away torque is not seal matter. Atleast not relevant.
The hump mode is always temp related.
The hump mode can be set by the vicousity and quantity of the fluid.
Without the hump mode a VC would be much useless offroad.
The graphs above show exactly why and how the VC is working.
While street/pavement orientated common cars work fine with any kind of differentials, a offroad or sportscar will work better with a Syncro VC system.
Not speaking about electronic controled systems. |
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