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  #76  
Old 12-04-2007, 02:47 PM
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crazyhorse crazyhorse is offline
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For the transfer clutch to live any length of time, it must be an on/off proposition. Any less than that & it would lose effectiveness, any more would cause a VERY limited lifespan. When I mentioned "duty cycle on" or "duty cycle off" I mean the clutch engaged (on), or disengaged (off). By varying the pulse width of the Duty C the clutch would "mimic" slippage, while still delivering AWD.

The monkey wrench in my theory is, that, this would introduce a vibration, in extreme situations of high traction surfaces, and wheel slippage. Like in an auto-X, especially with sticky race compound tires. Unless the transfer clutch incorporates discs that would provide a slight viscous transfer, to aid the clutches themselves. This last part could be borne out by seeing the discs laid out of the transfer clutch. They would be slotted, and their spacing would be less than 1mm. This would create a "shear" effect. It would also do nothing, unless there was a speed difference.

This would also explain the use of an LSD in the rear. In this same situation, transferring power would result in wheelspin at the rear without it. This would cause the transfer clutch to have to slip, or stop transferring. SEVERELY upsetting the balance of the car as it transitioned from 50/50 to 90/10.

Wow! I really need to stop thinking out loud!
I'm not really equipped for that.
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  #77  
Old 12-04-2007, 05:20 PM
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Quote:
Originally Posted by Trevor View Post
It will be seen that much of the possible issue of clutch wear which has been suggested is negated.
Quote:
Originally Posted by Trevor View Post
...the clutch need not be applied at full pressure and a state of tension can exist between the plates but there will be no real slip.
These parts are where I see the explanation crack a bit. Partial clutch application not causing clutch wear?

Oh, and after being awake for a while and putting thought to the individual transmission designs, I did come up with an explanation which fits the information presented and still matches the technical documents I translated for the Japanese cars.

In the ACT-4 transmission, the drive gears point forward, meaning constant power will always be to the front differential regardless of situation. There will always be torque to the front because the front differential is what's connected to the drive gears. The MPT clutch engages off of the back of the drive gears, allowing up to half the torque (i.e. full engagement, dividing the torque in half) to go rearward. Thus if the fuse for Solenoid C (FWD fuse) is inserted, the solenoid goes to 95% duty and the clutch disengages fully. This means the drive gears only put power up front.

This also means that in any situation where solenoid C goes to 95% duty, 100% torque is at the front wheels. There is a very simple way to test this; have one of us with an ACT-4 transmission equipped SVX connect our select monitor to the car. Place the FWD fuse in. Monitor the Solenoid C duty cycle data (need not be driving the car). Now remove the fuse and go driving, while the computer records the stream of Solenoid C information. Go back and analyze the data, looking for code which matches the "FWD Fuse In" situation.

If there are matching points, this would suggest that during normal operation, the car does in fact use 100% front torque.

Now for the VTD-4WD transmission. In this transmission, the drive gears are pointed rearward, meaning torque will constantly be sent to the rear wheels. What I have not yet come to understand is the value of "30:70" in the documents I've seen. If torque is constantly rearward, then it should be possible to reach a 0:100 torque situation unless the clutch is always partially engaged, which as previously suggested would put undue stress on the friction surfaces. In this design, the MPT clutch is what connects to the front differential, so full engagement of the clutch still results in a 50:50 split like in the ACT-4 transmission. Since there is (for reasons stated above) no FWD fuse and instead there is a 4WD fuse which when inserted forces the clutch to full engagement (thus 50:50), then my explanation is that the VTD TCU has a reverse effect when given the "FWD Fuse" signal.

This would have to be confirmed by comparing the actual process code in the two TCUs. If the resultants are opposite (i.e. the ACT-4 has 95% duty, the VTD has 0% duty), then my theory here holds water. If the resultants are the same (i.e. ACT-4 has 95% duty, VTD has 95% duty) then I'm totally wrong about how the VTD operates and must start over.

Hopefully this was helpful. It does mean I'll have to figure out where the Solenoid C address is in the TCU and start streaming data from it. Thank god even my incomplete adapter can talk to the TCU!

So yeah, if anyone knows what address to query the TCU from to get the Solenoid C duty cycle, please let me know so I can run this experiment.
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  #78  
Old 12-04-2007, 05:50 PM
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Quote:
Originally Posted by Nomake Wan View Post
These parts are where I see the explanation crack a bit. Partial clutch application not causing clutch wear?

Oh, and after being awake for a while and putting thought to the individual transmission designs, I did come up with an explanation which fits the information presented and still matches the technical documents I translated for the Japanese cars.

In the ACT-4 transmission, the drive gears point forward, meaning constant power will always be to the front differential regardless of situation. There will always be torque to the front because the front differential is what's connected to the drive gears. The MPT clutch engages off of the back of the drive gears, allowing up to half the torque (i.e. full engagement, dividing the torque in half) to go rearward. Thus if the fuse for Solenoid C (FWD fuse) is inserted, the solenoid goes to 95% duty and the clutch disengages fully. This means the drive gears only put power up front.

This also means that in any situation where solenoid C goes to 95% duty, 100% torque is at the front wheels. There is a very simple way to test this; have one of us with an ACT-4 transmission equipped SVX connect our select monitor to the car. Place the FWD fuse in. Monitor the Solenoid C duty cycle data (need not be driving the car). Now remove the fuse and go driving, while the computer records the stream of Solenoid C information. Go back and analyze the data, looking for code which matches the "FWD Fuse In" situation.

If there are matching points, this would suggest that during normal operation, the car does in fact use 100% front torque.

Now for the VTD-4WD transmission. In this transmission, the drive gears are pointed rearward, meaning torque will constantly be sent to the rear wheels. What I have not yet come to understand is the value of "30:70" in the documents I've seen. If torque is constantly rearward, then it should be possible to reach a 0:100 torque situation unless the clutch is always partially engaged, which as previously suggested would put undue stress on the friction surfaces. In this design, the MPT clutch is what connects to the front differential, so full engagement of the clutch still results in a 50:50 split like in the ACT-4 transmission. Since there is (for reasons stated above) no FWD fuse and instead there is a 4WD fuse which when inserted forces the clutch to full engagement (thus 50:50), then my explanation is that the VTD TCU has a reverse effect when given the "FWD Fuse" signal.

This would have to be confirmed by comparing the actual process code in the two TCUs. If the resultants are opposite (i.e. the ACT-4 has 95% duty, the VTD has 0% duty), then my theory here holds water. If the resultants are the same (i.e. ACT-4 has 95% duty, VTD has 95% duty) then I'm totally wrong about how the VTD operates and must start over.

Hopefully this was helpful. It does mean I'll have to figure out where the Solenoid C address is in the TCU and start streaming data from it. Thank god even my incomplete adapter can talk to the TCU!

So yeah, if anyone knows what address to query the TCU from to get the Solenoid C duty cycle, please let me know so I can run this experiment.

Nomake, your thinking here that the AWD-VTD box works in the reverse way to the ACT-4 is erroneous. So far as I understand it the VTD box has a centre differential that splits torque, front to rear, and just like the diff in the back axle, it can send different proportions of power to the different ends.

The term VTD probably means Viscous Traction Differential. Basically this centre differential can vary power to the wheels between 65/35 R/F to 50/50 R/F, although Trevor has a more exact split based on the number of teeth in the gears.
I think Phil can read data from the TCU [b3lha], although I don't know if he knows which address is the C solenoid.

And I suspect the C solenoid probably addresses a slightly different function in the VTD box anyway.

Joe
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  #79  
Old 12-05-2007, 01:31 AM
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b3lha b3lha is offline
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All the answers are hidden in the assembler code for the TCU posted on my website. It just needs somebody to sit down and analyse it. I am currently about 20% through studying the ECU and I was planning to start the TCU afterwards. I will take a brief look and see if the address for solenoid C is obvious.

The TCU should be much easier to analyse than the ECU. It's only 16K of ROM and AFAIK it's all 8-bit data.

The most important question I want answered is: Why does the code in the 1994 TCU differ from that in the 1992 TCU. As far as I know the gearboxes are the same. Presumably they fixed some bugs in the code. I wonder if those bugs contribute to the premature failure of the 1992 gearboxes. If it looks plausible then I want to upgrade my 1992 TCU to the 1994 code.

I quite like the idea of modding the TCU software because nobody has tried that yet. The sort of thing I am thinking of is reprogramming the manual button to do something more useful. Or maybe changing the normal mode shift map to be a little more like the power mode map. (admittedly it's easier to just leave the power mode switch on). For the UK guys it should be possible to reprogram the econ mode switch as a power mode switch but I don't yet have a copy of the UK TCU code to look at.
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  #80  
Old 12-05-2007, 02:08 AM
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Quote:
Originally Posted by b3lha View Post
All the answers are hidden in the assembler code for the TCU posted on my website. It just needs somebody to sit down and analyse it. I am currently about 20% through studying the ECU and I was planning to start the TCU afterwards. I will take a brief look and see if the address for solenoid C is obvious.

The TCU should be much easier to analyse than the ECU. It's only 16K of ROM and AFAIK it's all 8-bit data.

The most important question I want answered is: Why does the code in the 1994 TCU differ from that in the 1992 TCU. As far as I know the gearboxes are the same. Presumably they fixed some bugs in the code. I wonder if those bugs contribute to the premature failure of the 1992 gearboxes. If it looks plausible then I want to upgrade my 1992 TCU to the 1994 code.

I quite like the idea of modding the TCU software because nobody has tried that yet. The sort of thing I am thinking of is reprogramming the manual button to do something more useful. Or maybe changing the normal mode shift map to be a little more like the power mode map. (admittedly it's easier to just leave the power mode switch on). For the UK guys it should be possible to reprogram the econ mode switch as a power mode switch but I don't yet have a copy of the UK TCU code to look at.
Well, I'm sure we could get you a copy of the UK code in that case.

You would be needing a loan of a UK TCU then? I'm sure somebody would have one of them.

Joe
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