Jeroen_M625
Samba Member
Joined: September 23, 2015
Posts: 74
Location: Breda (NL)
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 Posted: Thu Nov 30, 2017 1:12 pm Post subject: Re: Syncro “AWD” Capabilty |
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| Waldi wrote: |
The pinion turns faster, but on both axels.
What you feel if you missmatch front and rear 6,16 and 4,85 ist exactly the 26% difference btw fron and rear. So how can you feel the 26% if you use same ratio on front and rear ? |
FTR, I alway talk about same R&P on front and rear. The 26% is the difference driveshaft speed between both drivetrains.
That 26% will result in a larger amount of absolute difference in RPM between front and rear in driveshaft for the 6.17 R&P.
i.e 4.86 has 10% difference between front and rear due to steering or wheel spin, then at 500rpm driveshaft speed, the absolute difference is 50rpm,
for 6.17 it will then be 63rpm. For each deltaRPM, the graph will show how much toque is generated by VC and the difference between those two is what can be noticed. |
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Waldi
Samba Member
Joined: February 28, 2014
Posts: 1752
Location: Germany
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| Posted: Thu Nov 30, 2017 2:34 pm Post subject: Re: Syncro “AWD” Capabilty |
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| Jeroen_M625 wrote: |
| Waldi wrote: |
Maybe this helps.
Lets take a u-turn of 10m.
10x3,14:2=15,7
2m tire circle, lets say the rear wheel makes 7,85 revs and the front 9,1.
6,16 Rear pinion makes 48,36 revs and front 56,06. Difference 7,7
4,85 rear pinion makes 38,87 revs and front 44, 14. Difference 5,3
So the difference in a u-turn is 2,4 revs between front and rear pinion.
The VC would not get significant harder from this.
Edit:
Ah, and dont forget, if there are realy 16% in a u-turn, there will be less in praxis, as rear and front tires slip. |
Slip on both front and rear axle will not cancel relative speed difference, it just increases total speed of the axles.
You are totally correct that the VC will not harden by turning. A VC can be turned into infinity as long as the speed is low enough so energy dissipation is lower than heat tranfsfer.
From the graph: 10rpm-->80Nm => that gives 0.08kW for a VC to warm up, while 75rpm-->190Nm => 1.5kW. It is indeed ridiculous to asume that one would donut a syncro, but in sanddunes this could be an issue.
But you forget the essence of the VC: difference in speed. otherwise said: deltaRPM.
Without speed there is no torque transfer, see the test graph.
I will take your calculation as starting point:
So 4.86 diff makes 5.3 revolutions.
Lets say it takes a whole minute to make that U-turn. Then delta RPM is 5.3rpm in graph that means a transfer of 50Nm.
Lets speed up a bit: twice as fast so this would mean 30s U-turn -> 5.3rev/0.5min=10.5rpm, 80Nm
Again dubble the speed: 15s U-turn->21rpm, 110Nm
And again: a U-turn in 7.5s, (15,7m in 7.5s= 7.5km/h)-->42rpm, 155Nm of torque is generated by the VC. Wich translates into 753Nm at front wheels.
Same for 6.17 diff, wich makes 7.7 in that same U-turn
1 min (thats about Unimog speed  )->7.7rpm, 50+Nm
30sec-> 15.4rpm
15sec->30.8rpm, 140Nm (alsmost same as other diff with half the speed)
7.5sec ->61.6rpm, 180Nm of torque is generated by the VC. Which translates into 1110Nm at the front wheels.
Like I said before, it is about the speed, the difference in rpm; the silicon molecules don't wait for a period or count down a certain amount of revolutions to go in (re)action. |
In a turn the rears slip contrary the fronts due to the binding of the VC.
So the difference between front and rear will be less than uncoupled.
I do not forget how the VC is working.
As i do not forget, that there is never same revs on front and rear on any driving conditions. So the VS transfers always torque.
You can see on the graph that the torque transfer starts at about 20-50nm. That means the rear tire slip is always less than on a 2-wd rear wheel drive. As more difference there is, as more the rear tire slip as more goes to the front.
Driving 65mph coupled the difference will never reach (didnt measure it, but you are wellcome) 3%. (Difference as sayed would be 0,8 from 4,85-6,16) The only difference between 6,16 and 4,85 will be, the VC goes into hump a bit earlier, which you wont feel. As harder the VC gets, as less differance there is between front and rear. No matter what ratio.
If you have a worn out VC outside the specs which gets harder on lower different revs, you may feel the 6,16 to 4,85 change, but on a VC within the specs it is how i sayed, splitting hairs. |
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