AWD Torque Split Control
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From: Gig Harbor, WA
AWD Torque Split Control
I'm looking into the idea of retrofitting a 997 front differential into my 996 Turbo. I understand the basics of how PTM makes decisions about torque split and the sensors involved. But what I haven't been able to find any information about is HOW the center differential is controlled by PTM. Is it a scaled 0-5v (or 0-12v) signal, or is the solenoid pulsed rapidly to create the desired torque split?
For those who will undoubted ask "why?" the answer is "because I can." The viscous AWD in the 996 is primarily designed for high speed stability, not traction. Also, the viscous coupling is known to wear out and leave the AWD essentially useless. I like the idea of having all wheel drive so I figure I might as well see if I can make this work. I'm hoping it's controlled via a scaled signal because then I can just have an on/off switch and **** to control the split. Otherwise, I might have to get extra nerdy with G sensors and an Arduino or something.
Thanks for any help.
For those who will undoubted ask "why?" the answer is "because I can." The viscous AWD in the 996 is primarily designed for high speed stability, not traction. Also, the viscous coupling is known to wear out and leave the AWD essentially useless. I like the idea of having all wheel drive so I figure I might as well see if I can make this work. I'm hoping it's controlled via a scaled signal because then I can just have an on/off switch and **** to control the split. Otherwise, I might have to get extra nerdy with G sensors and an Arduino or something.
Thanks for any help.
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From: Gig Harbor, WA
Well, I was hoping to get a definitive answer in here, but I guess not. For anyone who might find this in the future: based on some additional research it appears the center differential is controlled by a 0-12v scaled signal where 0v = no power sent to front and 12v = clutch fully engaged. I'm still not 100% confident in this answer though, but I guess I'll just go with it for now.
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Meant to reply to this the other day but was on mobile. Not surprised that you didn't get an answer. I doubt few people here have ever had the need to delve into that particular system.
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I figured with the semi-regular talk of people wanting to convert to RWD or have the ability to disable the front drive (other than the handbrake click) there would be more knowledge floating around about the electromagnetic differential...
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Interesting project. As far as I know it is a multi plate wet clutch and there would of course be an actuator somewhere pushing the plates together to engage FWD. Not that I'm planning to do any mods myself but would be nice to know if you figure it out.
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I'll update this thread with additional info as I come across should anyone in the future be looking for similar data.
After some more research on how electromagnetic clutches work, I believe the clutch is controlled via pulse width modulation (PWM) rather than a simple 0-12v regulated current. Subaru uses a similar clutch system on the WRX STi and I'm betting it's also how Porsche accomplished it.
After some more research on how electromagnetic clutches work, I believe the clutch is controlled via pulse width modulation (PWM) rather than a simple 0-12v regulated current. Subaru uses a similar clutch system on the WRX STi and I'm betting it's also how Porsche accomplished it.
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From: DFW
This is on my to do list to measure(sadly for a couple of years) Just got a small oscilloscope and will be adding a jumper to the front solenoid wiring. Definitely PWM, just the voltage range is in question. In the later cars there is a dash display, like on 991's , macan's etc. I could not find a channel on the durametric that reflected it, but it may live on the CAN bus.
One true finding, running in non-sport mode adds more front drive. It is noticeable in the steering effort and in the ability to accelerate off corners. Feels like about 25/75 F/R vs 5/95 in Sport mode. I used to spin the car much more frequently in sport mode.
One true finding, running in non-sport mode adds more front drive. It is noticeable in the steering effort and in the ability to accelerate off corners. Feels like about 25/75 F/R vs 5/95 in Sport mode. I used to spin the car much more frequently in sport mode.
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Let me know what you find, I pulled the trigger and purchased a .2 differential. Hopefully by the time I get around to installing it later this winter I'll know how to control it...
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Okay, I've figured out some useful info. It IS controlled via pulse-width modulation and the clutch is at 100% lock-up at 12v.
My next question for the class is: does anyone know at what temperature the "PTM Inactive. Too hot." warning message is triggered? There is a temp sensor for the diff controller oil. Since it's basically a lightweight differential oil in there, I'm assuming it's somewhere around 200-220 degrees? If Porsche found it important enough to put a temp sensor in the front diff, I'm guessing I should install a warning light on the dash for it.
My 997.2 diff arrived today:
My next question for the class is: does anyone know at what temperature the "PTM Inactive. Too hot." warning message is triggered? There is a temp sensor for the diff controller oil. Since it's basically a lightweight differential oil in there, I'm assuming it's somewhere around 200-220 degrees? If Porsche found it important enough to put a temp sensor in the front diff, I'm guessing I should install a warning light on the dash for it.
My 997.2 diff arrived today:
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I have a 997.1 with almost 99k miles. Used on road and track over 14 years regularly had the car well above 200mph and never had that warning light. Good to know its there but not sure this may be over kill..Ruf carried on using the 996 turbo awd in their 997 based models. 993/996 vc system was more progressive and rear bias. In slow corners with lots of lock the way power goes from rear to front can unsettle the car a tiny bit in 997.
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By the way if someone came up with an electronic switch that can switch awd off in 997 turbo by preventing the voltage higher than minimum setting I think it would sell very well. I'd buy. Best of both worlds as the awd system has saved me from some extreme slip angles over the years. In a GT2 or GT3 even with t/c I'd have been a goner without awd.
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There is no temp gauge on the viscous AWD units, only on the 997.2 units.
There is no way to turn off the viscous AWD on the 996/997.1, but you can effectively turn it off on the 997.2 by pulling up the ebrake one click. The signal from the ebrake switch is tied into PTM and when the ebrake is on, it cuts power to the differential.
There is no way to turn off the viscous AWD on the 996/997.1, but you can effectively turn it off on the 997.2 by pulling up the ebrake one click. The signal from the ebrake switch is tied into PTM and when the ebrake is on, it cuts power to the differential.