TOD discussion

[mbeach]

My initial idea was option 1. I liked the fact that the display would be correct. However, once the vehicle were stopped, the TOD would be thrown into confusion. So I abandoned it.

Option 2 is the most elegant, yet it is not reversable (easily), removable, or easily installed. I'm going to try to veer from this, but we'll see. My goal is to have a correct dash display, and 5 modes of operation: Auto, 2wd, 15, 30, 4hi. All selectable with a knob. I think that by keeping it simple (5 modes, or outputs rather than infinite) I can make the display work as well.

I would need to:
a) turn off the AUTO display when the knob is switched to any other position.
b) turn on the appropriate lights with each mode.
c) default to AUTO mode whenever 4Lo is activated -or maybe not. 2Lo is an interesting option, if it's even possible.

I guess that I'm looking at option 2.5. I want to be "inside" the TOD computer for the display benefits, but I want it to be accessable and easy for a novice to hook up.

I pick up a better (portable) scope this week. This weekend I'm going to pull the harness(s) off of the TOD computer and make extensions (to minimize my crawling under the seat) that I can easily tap in to. I have the workshop CD, I'll be looking it over tonight. I think that I have a few spare connectors around the shop.

[VehiGAZ]

I really appreciate this conversation, guys!

I want only one thing - to have a switch to flip to go into 50%/50% (4WD Hi) mode, which would be best on snowy roads when going into 4WD Low is overkill, while leaving it in Auto ToD mode means it is CONSTNATLY (and annoyingly) engaging and disengaging the front wheels.

I figure I can use a light-up switch to indicate that it's in the forced 4WD Hi mode. That means I should go with option 3, but without the multi-position selector.

So circuit-wise, my switch would be put a dummy load on the output to the ToD, correct? Any advice on how exactly to wire it, and what to put on the "alternate" circuit?

Lastly, I may have that extra ToD ECU you are looking for, mbeach. I will PM you.

[VehiGAZ]

mbeach, your PM box is full. I sent you an e-mail to your yahoo address instead.

[mbeach]

I cleaned out my PM box, please re-send your message -I have been without home internet for a few months thanks to a bum antenna for my wireless provider. I can't check webmail at work -I could use my phone but it takes forever.

I sat down with schematics and diagrams from the workshop CD last night. After about an hour, I think that I may have worked out a fair solution. One that will settle my desires as well as be easily installed and removed by anyone with fingers. I'm also looking at a 4hi only option as well (VehiGaz).

Just for kicks I looked up the TOD patent, just to see if there was some additional information that would be helpful. Wow. This is one impressive piece of engineering. It's patent #4,989,686 dated 5 February 1991 for those who care. There's tons of info in there, also some diagrams which I would really like to see (logic flowcharts, schematics, graphs of various clutch command signals). The patent also confirms the suspicion of a PWM signal from TOD to clutch, as well as a feedback signal from clutch to TOD.
I could not view the drawings however. If anyone can figure out a way to view them (free), please snatch them and post them here -if it's legal.

[VehiGAZ]

One of our patent attys is on the case right now. I'll post the diagrams if he can get at them and its legal.

[VehiGAZ]

Sweet! I got it. And it's all nice-and-legal. Apparently, all anyone needs is to be set up for viewing .tff files to see the diagrams.

I have it in a 1.9 MB .pdf file, but I can't upload it for some reason. Is it too big? Is the site just having some difficulties? Anyone know?

[bobmumgaard]

Thanks for digging up that patent mbeach. It sure has alot of information about the logic and control systems of TOD. The techs at Borg-Warner put together quite a system here. And the price of the TOD ecu now seems somewhat reasonable. The amazing part is that they didn't put in any user control, it certainly would have been pretty simple compared to the amount of work they put into the system. (maybe it was a liability or marketing issue)

After looking through the patent it appears that the signal to the clutch is PWM and if we cut that wire we need a dummy load (to satisfy the feedback requirements of the TOD computer) Other than that there might be still be more than one way to skin this cat.

I think I am going to apply my modifications after the TOD ecu only, as I dont want to fry such an expensive component. After studying the wiring diagrams for awhile I think it might be relatively simple to alter the dash lights along with the TOD ecu-solenoid signal.

Heres my plan:
I want to control the sysem with a knob, probably 5 positions like mbeach stated earlier: Auto, 2wd, ~15%, ~30%, and 50/50

I want to create a pin-to-pin harness between the wiring harness of the vehicle and the TOD ecu (to minimize cutting stock wires), this would make the modification very reversable and easy to install for most anyone. (literally "plug and play")

I plan to cut the ecu-solenoid wire with a relay, so when the knob is in auto mode everything functions normally. Then when the knob is anywhere other than auto mode the ecu is connected to a dummy load and the solenoid receives the signal from a PWM controller.

The PWM controller will probably be a 555, or 556 timer set up to send a 50Hz signal. The controller will be voltage controlled, with the control voltage coming from the 5 position switch. (with the descreet voltages set up by finite resistances)

To accompilsh the correct display lighting I was thinking about interputing the stock wires for the auto, and 3 bar lights with transistors, wired so when the knob is in auto mode the lights are controlled by the TOD ecu normally, but when anywhere other than auto, the lights are disconnected from the ecu. (this darkens the auto light, and allows the 3 bar lights to be controlled by the knob position; see next paragraph)

Then another set of transistors would connect each individual bar light to the illumination wire depending on what position the knob is in. (this lights the 3 bar lights up correctly)

And the whole thing could be bipassed by a relay controlled by the 4low switch, so if you took the transfer case shifter out of Auto the TOD ecu would have all electrical control

I have a rough circuit diagram drawn up right now, and it seems to look like it should work. I plan on spending some time in the University's electrical engineering lab tonight or tommorrow setting up the circuit and performing tests. I also still need to look at a few things in the VX before I go too far.

[Ldub]

as well as be easily installed and removed by anyone with fingers.

I can tell that if this comes to fruition, It'll be a good mod for me...cuz I have fingers!!!
Good work you most admirable brainiacs, Ldub