4EAT Diff-Lock Switch and Handbrake Mod - "Torquemada Lite" - Page 5 - Subaru Impreza GC8 & RS Forum & Community: RS25.com
 
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4EAT Diff-Lock Switch and Handbrake Mod - "Torquemada Lite"
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Old 02-24-2009, 01:06 PM   #41
defcon5
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Very nice StartRestart! I like the inclusion of the formulas - classy!
A few observations:
On the "Duty Solenoid C" wire, you might want to note which end is going to the TCM plug and which is going to the actual solenoid. Without that info, it's possible to put the wrong end on the switch's "com" pin.
Also, on the "top" wire, I'm not sure you need the line that continues on to the resistor bank after the switch junction(connects on the right side). Basically, I'd let that line hook to the switch alone - no need to continue on to the ground side of the resistor bank as the solenoid provides a suitable ground on that end.
Also a reference to ground from the resistor bank would be helpful. Though I suppose the "unneeded" connection above could provide the ground via the solenoid eh? Dunno, doesn't seem right in my head.
Gee...can you guess who doesn't know how to read schematics?
I've sent my version of the schematic to obsolete, and he's going to give it the proper "EE" treatment, so we'll have that soon.

Update on further developments: I'm waiting on a big order of parts to keep building the basic diff lock kits at cost if anyones interested. Also in that order are the parts for my "variable torque" version. I hope to have it built in the next few weeks, and if it's sucessful, I'll be signing up for a vendor account and y'all can have some new toys to play with.
If all goes as I hope, they should be pretty cost effective. They should also have the handbrake mod sorted out and included.
The reason I haven't posted my current version is that once I was able to see a real-time map of the duty cycle response, I realized that my method worked for my car, but wasn't feasible for a wider range of cars and driving styles.

Long story short, my soldering iron and I are going to be busy for the next few weeks. Stay tuned...
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Old 02-24-2009, 04:26 PM   #42
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Awesome, can't wait to see what you come up with.
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Old 02-25-2009, 09:58 AM   #43
obsolete
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As requested by defcon, here's the schematic. The switch is shown in the "mod activated" position, so the TCU sees 17Ω to ground and input the Duty C Solenoid is floating (disconnected).



With all the info, pictures & schematics that have been posted so far, this mod should practically do itself

Last edited by obsolete; 02-25-2009 at 10:04 AM..
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Old 02-25-2009, 08:06 PM   #44
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Is it even possible to "dial in" the torque split on an AT? If the torque split is controlled by a clutch pack, then I don't think you can. A clutch pack is either engaged or not. If it is slipping, it will burn up the clutch discs pretty quickly I believe. Variable control might not be such a good idea after all, but I could be wrong. I think we r stuck with either full on or off.

Last edited by levis76; 03-01-2009 at 03:18 PM..
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Old 03-01-2009, 06:16 PM   #45
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RE: E-Brakes.. you ever thought about using a relay on the e-brake light to simply enable the FWD fuse? kinda crude i guess
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Old 03-01-2009, 09:59 PM   #46
obsolete
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Quote:
Originally Posted by levis76 View Post
Is it even possible to "dial in" the torque split on an AT? If the torque split is controlled by a clutch pack, then I don't think you can. A clutch pack is either engaged or not. If it is slipping, it will burn up the clutch discs pretty quickly I believe. Variable control might not be such a good idea after all, but I could be wrong. I think we r stuck with either full on or off.
I'm not so sure--how does Subaru get away with the 90/10 default split, then? The rear wheels are definitely engaged to some degree, but nowhere near fully, and the car is in this config. most of the time.

That said, I don't really see myself needing anything other than FWD (solenoid fully powered), 4WD (solenoid disconnected), and AWD (let the car handle it).
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Old 03-02-2009, 12:27 PM   #47
defcon5
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It's funny that this would come up now. The other day, I spent close to 2 hours with my meter hooked up to the TCU as I drove around town. I monitored voltage across the transfer solenoid under every conceivable acceleration/deceleration situation, and I can definitively say that the clutch is clearly designed to experience partial lockup for much of the time. In fact, far more time than it ever experiences full lock or unlock. Without boring anyone with all the various voltages, the highlights look something like this:

Vehicle stopped - 95% duty cycle (90/10 torque split?)
Cruising speeds from 25mph to 75mph - 68% - 73% duty cycle (~80/20?)
It also exposed a gigantic flaw in my current handbrake cutout - but that's another story...

In short, the solenoid is always partially engaged. Under normal driving, I never saw 0 or 100% duty cycle. which leads me to believe that the system is either designed to slip, or can achieve full lock or unlock at lower duty cycles. I won't know for sure until I physically pull the transfer clutch and see exactly how it's implemented. And that's not happening until the temperature in my shop gets back up above 20 degrees.

To address levis76's (and several others via PM) concerns: The idea behind my mod is to use it as necessary and disable it when not needed. It is NOT to be used full-time, and should not be considered as a replacement for the stock AWD system. If you want the exact "whys" and "how comes", feel free to PM me. But for now, lets just say that in 90% of driving conditions, the car knows best and you should just let it do it's job.
However, if you're driving on snow, or racing on mixed surfaces where the stock response time can be a hinderance - flip the switch (or hopefully soon - turn the knob), and you'll have a lot more control. When you're done - turn it off. It's not going to make any difference on a dry interstate anyway, so why risk the extra wear and tear?

Like obsolete, my needs don't go much beyond "on" (50/50) and "off" (AWD), but anything that's worth doing, is worth overdoing - so development of the variable version will continue.

---Late edit - Many thanks to obsolete for the above schematic (post 43). He turned my preschool level notes into a fine schematic that smart people (and even less-smart people like me) can understand. *round of applause*

Last edited by defcon5; 03-03-2009 at 08:12 AM.. Reason: recognition of obsoletes fantastic schematicz skillz
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Old 03-02-2009, 04:40 PM   #48
spdfreek0o
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Quote:
Originally Posted by defcon5 View Post
I won't know for sure until I physically pull the transfer clutch and see exactly how it's implemented. And that's not happening until the temperature in my shop gets back up above 20 degrees.
a write up on this might come in handy, btw
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Old 03-03-2009, 08:06 AM   #49
defcon5
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^^You know I will. I'm the master of turning a simple 5-step DIY into a two-day novel
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Old 03-03-2009, 01:08 PM   #50
obsolete
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Quote:
Originally Posted by defcon5 View Post
The other day, I spent close to 2 hours with my meter hooked up to the TCU as I drove around town. I monitored voltage across the transfer solenoid under every conceivable acceleration/deceleration situation, and I can definitively say that the clutch is clearly designed to experience partial lockup for much of the time.
So, you had a scope hooked up, or do you have a DMM that can measure duty cycle? Anyway, a live AWD torque split gauge would be a pretty sweet project too

Quote:
It also exposed a gigantic flaw in my current handbrake cutout - but that's another story...
What's the flaw? Does the solenoid disengage too slowly?

Thanks for your compliments on the schematic. Let me know if you need any more help with board layout/microcontroller stuff. I have not done any PWM programming though, so I might not be a lot of help with that, but I can try.
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