TOD discussion

[Child's Play]

Man, this sounds sweet. I'm in the same boat as VehiGaz. If I could just have 4-High constantly at the turn on a knob or push button, that would be enough for me. Anyway, I'm completely lost in the post, but I did see this on E-Bay and thought it may help you guys out. Thought I would try to help out in some way, since I don't have clue one about what you guys are talking about. Here's the link:

http://cgi.ebay.com/ebaymotors/2000-...QQcmdZViewItem

[mbeach]

I am marlon506 and I am high bidder.
If I don't win, I hope that SOMEONE here does get it.

So instead of 2hi, 4hi, auto and manual modes, we can do an AUTO, MANUAL, 4HI.
That sounds reasonable, and the manual mode can be controlled via potentiometer (by modifying the control voltage to the timer circuit).
We can use Bob's transistor arrangement to control the dash lights.

The only catch is:
We can only vary the torque to the front axle as long as it is GREATER than what is actually required.
If the speed diferential between front and rear axles is too great, then expect the mechanical 'clutch' to engage the front axle. So no donuts or dynos in 15% mode.
I can live with that.

[bobmumgaard]

http://cgi.ebay.com/ebaymotors/2000...Qc mdZViewItem

Anyone know if this is includded in Tone's Cd? If not, (or even if so) is anybody going to snap this up and maybe scan it for others to use? It would be a great addition to overall knowledge about the VX in addition to the specific issue we are discussing.

If not I'll start bidding, and post it when if I win it.

[bobmumgaard]

mbeach, you beat me to the punch, its all yours

[mbeach]

Bob,
As an ME, do you think that my assessment of our situation (no 2wd) is correct?

Oh, and I've already bid on the book. Believe me, it's knowledge will flow forth like water...

[blacksambo]

If it's any help there is a 1999 version of this booklet offered on a consistent basis on:www.books4cars.com for $40.00. It seems likely that 1999 technology would be the same as 2000 VX's.

[bobmumgaard]

Tone-
Your axle breaking could shed alot of light on this whole subject. I did a search but couldn’t come up with anything. What exactly happened? I assume it was on a dyno pull. So it was probably in third gear and strapped down with no power to the TOD ecu. Where did the axle break? What rpm? (and thus speed of rear wheels, and speed differential between front and rear) What did the break point look like? Was the break plane smooth, jagged, notched in a pattern, did it look like it snapped or did it deform ductilly? I have a few theories about how it could have happened but they depend on the exact situation, and I could be absolutely wrong on them.

[mbeach]

I know where you're going with that thought. I considered it as well. It would be extremely difficult to do a failure analysis at this point, with no photographic or video evidence of the break. I also would like to see the fracture, measure the diameter and wall thickness of the driveshaft, and see if I could come up with a torque value that could have produced the failure.

I can guarantee that it was more than 15% of 230 lb/ft for sure.

[VehiGAZ]

So I've been wondering (as I've been learning)...

The normal operation of the ToD system on a slippery road will transfer torque up front to keep the front wheels spinning about the same as the back wheels, right?

Then it backs off of that torque bias when you come to a stop - partially because you don't need it when stopped, but also (and I am speculating here) to protect itself if you make a sharp turn from that complete stop - in that case, the full 50/50 bias setting may not allow enough rotational speed differential between the sets of wheels and you'd get wheel spin from an axle unwinding, you'd slip the transfer case differential clutch (if you were on dry, grippy pavement that didn't allow for any wheel spin). It makes sense that you wouldn't want any torque transfer to the front while turning at very low speeds (i.e., when starting from a stop).

Well, if we come up with a switch & circuit that will tell the transfer case differential clutch to keep applying a full 50/50 torque split all the time, won't we be asking for trouble in those types of situations? On a snowy road, an axle can unwind pretty easily by letting a tire slip, but if you were turning onto a clear road, wouldn't that stress on the transfer case differential still be there? And wouldn't that be not-so-good?

I freely admit to speaking in total ignorance on this subject (as I said, I've just started learning about how differentials and transfer cases work) - I'm just trying to follow along with the other discussions.

I have come to one conclusion, though - the Trooper ToD conversion in the first post is not as easy to implement for the VX.

Any thoughts?

[bobmumgaard]

I've spent a few hours studying the patent and look at the maintenance manual and I think I have a pretty good idea about how this thing is assembled and how it operates. Though I would love to get one on the bench to take apart and examine.

About torque:
mbeach is correct that you can only transmit as much torque as something (say a wheel) can hold. This means that if the wheel was on ice, you could send torque to the wheel until traction faltered and then the wheel would just spin, So if you are sending torque to the rears and they are spinning, trying to send more torque causes the wheel to spin faster, nothing more. Now if the wheel is locked, say the VX is strapped down on a dyno and you send alittle torque to the front, nothing will probably happen. If you send more and more torque eventually the wheel will either start slipping against the ground, the straps will snap or you will break something in the drivetrain, say an axle.

Construction of the transfer case:
It seems to me that the clutch works very much like a Cusco or Kaaz limited slip differential. This means that they do allow a difference in rotational speed front to rear. And this makes sense because otherwise it would be the equivalent to a true mechanical lock. If the front and rear HAD to spin at the same speed it would be like driving in 4Low all the time, lots of scrub.

The transfer case appears to take the output from the engine and transmits it to the rear wheels through a shaft, much like there is just a driveshaft and no transfer case. This means the rear is powered all the time, no matter what and always spins at the same rate as the transmission output. (unless we activate the planetary gearset for 4low) On this shaft is a sprocket, this sprocket is connected by a chain to another sprocket on the front driveshaft. Inside the first sprocket (the one on the mainshaft) is the clutch. The clutch appears to consist of 13 friction disks. 6 of these are attached to the mainshaft, (and thus spin at the speed of the rear wheels) and 7 are attached to the sprocket (and thus spin at the speed of the front wheels) These disks alternate, one for the rear next to one for the front next to one for the rear and so on..

There is then an inductive coil that creates a magnetic field when we send current through it. This coil squeezes all the friction disks together. So when we power this coil up the squeezing action increases the friction between the front and rear shafts, this means we take some of the torque we were sending to the rear and send it to the front. Now the front might not move, if the wheels were in a tough spot then the clutch would just slip. Squeeze harder and you get more friction=more torque. Keep squeezing and eventually the front wheels will either move, something will break or you will be squeezing your hardest and the friction disks in the clutch will still just slip. However, in normal situations, if you squeeze the front will start to spin at same rate as the rear, and if it doesn’t, the TOD ecu just squeezes harder until they spin at the same speed (or the ecu is happy with the speed difference)

The system is the same in a clutch type limited slip differential like Cusco or Kaaz, we just modulate the squeezing electronically; they do it with elaborate shims. And the same principle as the multidisk clutches you see on high torque cars.

In fact, this is almost the same system we see on any car’s clutch. In that case, your foot controls the squeezing, and the clutch slips, it is still transmitting some torque even though it’s slipping. Hopefully the clutch eventually stops slipping and is then transmitting 100% of the engine’s torque to the wheels.

The ball ramp system appears to be there to make sure that the clutch doesn’t self activate. (Imagine if it did at 75 mph, dangerous liability there) and it doesn’t appear to be able to transmit very much torque, atleast not enough to break a driveshaft. Though I am still looking the whole ramp thing over, but this is my initial assessment, though I could be wrong. In addition to its small size, I don’t think that the ball ramp system is involved with any automatic torque transfer because if it was the clutch would be a VERY expensive redundancy.

So… the moment we are waiting for….can we get true 100% 2wd? In my opinion not 100%, but maybe 95%

Because the friction disks are always in some contact, and there are so many of them they will always create some friction, even when there is no squeezing from the solenoid. How much friction (and thus torque) probably depends on how fast everything is spinning.
This means that if you take off the front driveshaft, the front output of the transfer case will still turn. Also, if you break a CV joint and have the TOD disconnected everything will still spin due to this residual friction. An interesting experiment would be to disconnect the front driveshaft and connected the transfer case output to a brake (like an engine brake used my manufacturers to dyno engines) and measure this torque.

A more practical experiment would be to put the TOD control we are talking about in a VX (I think we are on the right track with electronic systems discussed above). And take the VX to a brake based dyno. In fact, dynopack is the most common brake based system. This dyno attaches a large brake to each hub of a 4wd car and applies a variable resistance to the wheel. This resistance measures the torque each wheel is putting out. (most dynos are inertia based (use rollers) and measure power and then infer torque, the opposite strategy as a load (brake) based system)

If someone really wants to find out the exact characteristics of the TOD system, find a dynopack system. They are used for rally cars most often, so the best bet is to find a place that works on STi’s and Evos. Unfortunately for me I’ve never located a dynopack system within a few states of Nebraska.

Load based dyno info:
http://www.mustangworld.com/ourpics/News/nowheel.htm
http://www.dynopack.co.nz/

Limited slip info:
http://auto.howstuffworks.com/differential8.htm

Normal car clutch info:
http://auto.howstuffworks.com/clutch.htm

About the mechanical lock
When we put the transfer case in 4Low it slides a mechanical lock between the front and rear axles. (actually the mainshaft and sprocket) In this situation the clutch is completely out of the loop. This means both axles rotate at the same speed no matter what. So if both front wheels where on the ground and the rears where not (imagine the VX hanging off a cliff, scary aint it?) then the car should be able to pull itself up (assuming enough traction and engine power) in this situation the fronts receive 100% of engine torque because of the mechanical lock (there can’t be any slipping) and because the rears cannot transmit any torque because they would be spinning against air at the same rate as the fronts pull against the ground.

Well alright, sorry this was so long, just trying to hash out the exact nature of the things we are working with here.

And again, I could be completely wrong on all this. What are your guy’s thoughts?

[bobmumgaard]

I'm still fairly certain about the ball/ramp's ability to transmit large amounts of torque to the front driveshaft. I thought the same thing about the redundancy of the e-clutch, but I believe that its primary purpose is to proportion/modulate the amount of torque to the front, rather than to simply link the two shafts together. mbeach

After further review, there is no indisputable conclusive evidence that my analysis of the ball ramp thing is right and the play stands as called on the field by mbeach

Afterall, the techs at Isuzu went through alot of trouble to put the ball-ramp mechanism in there. And SOMETHING had to cause Tone's broken axle. And I certainly don't think it was residual friction from a few ~5 inch disks.

I think someone should call Merlin and see about finding the supplier for those connectors, they would make this a fool-proof modification. Right now I am looking at tapping or modifying 9 different wires (though i am trying to reduce this #). I talked to a contact at Bosch but they weren't very helpful.

mbeach, I drew up my circuit diagram on SmartDraw and am looking it over. I think the next step is to find those PWM values for the solenoid, and Voltage values for the other important wires And while youre in there, some data on the real currents the solenoid is drawing might be helpful to us when it comes time to select timer components. If I had a portable scope I'd be in the VX confirming your numbers but right now I am using aTektronix TDS 210 that is chained to the lab.

VehiGAZ, glad to help, and I hope I got everything right on my analysis.

I'm an MEtech working in an EE's position. I think Bob's an ME as well. That's why we're overanalyzing everything

If only ME's built everything: We'd run out of titanium, parts would start at 1million dollars, everything would fix itself and the world would be bombproof.
Mechanical Engineering: the definition of 8 gallons in a 5 gallon bucket.