TOD discussion

[Nazrat]

http://forum.australia4wd.com/lofive...php/t1153.html

-Tad

[bobmumgaard]

The guys on the link above and it's links have got the TOD system pinned down and solved.
If our system is the same as theirs (and it must be pretty close, same manufacturer, overal design, and basic operation) then the TOD brain sends a 50Hz PWM (pulse width modulation) signal to the transfer case solenoid with a duty cycle between 0% and 88%.

(0% being no torque to front and 88% being 50/50 split)

Aside for those not electrical engineering prone:
PWM sends a square wave to the load, this square wave has a peak voltage of about ~13.6V(in our case at least). By altering the width of the square wave you can change the effective voltage the load sees. So with an 88% duty cycle, the square wave occurs over 88% of the period and the average voltage to the load is about 12V. So if we wanted the load to see 7.2 V (this would be about 30% torque to the front) we would send a duty cycle of around 53%.
The advantages of PWM make it very common in automotive apllications, these advantages include a resistance to electrical noise, ablity to integrate digital and analoge components and a lower strain on electrical components (the current in PWM only flows for a fraction of an analoge only system). Infact many sensors, including most speed sensors use PWM.


Onward with the TOD side
This means we can alter the amount of transfer case lockup by altering the PWM signal the solenoid sees.

So heres a proposed idea:
If we want to have 4hi, 2hi, or anything in between (say 30% torque to the front) we could disconnect the TOD ecu from the solenoid (and connect the TOD ecu to a false load, say a 5? ohm resistor) and connect the solenoid to a PWM controler that we can vary. This PWM would be variable from 0% to 88%. (0V to 12V rms) this way we could dial in the amount of transfer case lock-up from 0 (2hi) to 50/50 (4hi).

The implications for those that want to full control over their TOD are huge. You could have a dial that selects the amount of torque to the front much like a rally car would. And the signal would be the same configuration the TOD auto mode sends, so no adverse affects. And if you wanted TOD auto mode you would reconnect the TOD ecu to the solenoid (with a relay) this would set the system up to operate as usual.

Modification could be made from there:
You could directly alter the TOD display lights with a series of relays in conjuction with the PWM controler so the display would display the front torgue correctly. You could aslo use a clever set of relays to set the sysem up so the TOD ecu automatically regains control over the transfer case in certain situations like 4 low or when the abs activates. Though i have not thought these all the way through yet they remain tantalyzing possiblities.

And, theorectically, the system could be done even simpler. The soleniod might not NEED to see a PWM signal to operate, you could simply alter the voltage it sees with a poteniometer instead of a PWM controller. Though this idea is alittle hairy because the potential for excessive wear and adverse affects because the signal the solenoid receives is not of the same form as it is design to use. I would have to do some extensive tests with the transfer case outside the vehicle to be sure how this could work.

So it looks like this winter I will be driving around in the snow with no passenger seat and a multimeter and oscillosope hooked to the TOD ecu to soleniod wire. Hopefully this research will confirm what the aussie and spanish Terracan drivers have discovered. From there it will be a matter of constructing the right circuit and we could have a viable torque split selector.


Anyway, if you read this and think I'm wrong, right or a moron, shoot back your ideas. With alittle brainstorming I think we could come up with a pretty nifty, inexpensive and reversible solution for those that want complete control over their transfer case.

[Joe_Black]

The Isuzu rally teams had an electronically selectable TOD ratio in their 5-speed VehiCROSSes, so it's basically knowing what/how to connect. From what I was able to read about the competition set-up indicated simplicity and plug-n-play reversibility to stock.

[Ldub]

Bob M,
YOU DA MAN...wish I had the tech. abilities reqd. to figure something this complex out in the first place. Seriuosly, your aside for the non elec. eng. prone was too deep for me.
However, if you get a handle on this thing & produce a few "plug & play" units (harness, controller, DETAILED instructions, etc.) You can count me in as your first customer.

Hope ya get it to work, Ldub

[mbeach]

I couldn't open the Terracan links, but I have been suspecting the same thing (PWM signal) for a couple of weeks.

I have plenty of snow for practice, what wire(s) should I monitor?
I think that a few inputs would be in order (front axle, rear axle, ABS, 4Lo) to the TOD ecu.
I'd definately monitor the TOD to clutch solenoid as well.

I figure that this weekend I could get started checking voltages and frequencies under various conditions. It will be difficult to catch a 70/30 or an 85/15 condition however. It seems that TOD is all-or-nothing on ice and snow.

I'll think about a nice spreadsheet for gathering all of this data.

If we get the right information together, I have an extensive inventory of tools and parts to make this happen.
Heck, if it works I might not sell the VX after all.

[mbeach]

I was discussing this with my lead tech (super genius).

We can make this happen, BUT:
I need a TOD computer. They pop up on eBay all the time, except for today. I will pay up to $100 for one, I cannot use of of mine right now (too much ice on the road still).

We were thinking about catching the signal INSIDE of the TOD computer, before it hits the amplifier section. This should eliminate the need for a dummy load. We can make a PWM generator with a timer (555?). By altering the control voltage into the timer, we should be able to modify the square wave output. This means a KNOB, with infinite variability or presets (whichever you want).

HELP ME FIND A COMPUTER!!!

[Thelgord]

I realize this is an old and probably dead thread, but did this ever work?

[ipd]

I'd also like to know. Although I realize that the odds are that even if someone who pulled it off still has his/her vx, they aren't apt to post on this forum anymore.

[Thelgord]

Yeah, but maybe someone knows someone who knows someone else? LOL!

[blacksambo]

Yeah, but maybe someone knows someone who knows someone else? LOL!

There is a physical ball ramp mechanism in the way of ever governing the TOD with merely electrical switching. Everybody who has tried didn't succeed. You can get a Trooper unit and install it easier. The VX was a deluxe Trooper , and a key selling point was it would always be instantly ready for whatever the terrain and weather threw at it.
If you have to turn it off and on manually it wouldn't be always ready to react.
Sorry.