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AW4 trans control idea

R

R.DesJardin

NAXJA Forum User
Location
Clarkston, WA
OK, I had a vision, maybe a nightmare. But here goes,what if you connect the wires coming from your trans gear selector switch which is part of the XJ neutral safety switch to the AW4 solenoids. Since the TCM has to know what gear the floor shifter is in then it should be possible to use those wires to shift the trans. overiding the TCM, and if wired through a switch it would allow you to get overdrive by killing power to the solenoids aka 4th gear.
I'm sure it would work but not sure of the wiring since I sold my XJ to my son.
I'm sure there is someone out there that can figure this out. Of course this would require shifting the floor shifter for each gear.

Any thoughts?????????????
 
Lol. I was kinda thinking, "why are you asking us, didn't you invent the aw4"
 
DeftwillP said:
Lol. I was kinda thinking, "why are you asking us, didn't you invent the aw4"
Click to expand...
No I just perfected it!!!!!!!!!!!!!:laugh3:
I know everyone is always looking for a way around the TCM control, I think this is a way to do this on a low budget. It isn't the same as any of my control units and might not be as easy to wire or have all the cool features,

"BUT IT'S FREE"party1: just giving back a little.
For the 1-2 position it would be wired for 1st, D wired for 2nd, OD third, 4th would require a switch to kill the power to solenoids. Really how often do we need OD, really.
 
I don't see why you couldn't just operate the shift solenoids totally manually. I have not studied the AW4 shifting so I am not sure how it is wired but it would be like having two control modes that you can switch between automatic and manual. Lets say there are 4 solenoids to be switched, you use a switch that switches between two sets of 4 inputs each and has 4 outputs. So the normal solenoid outputs from the computer are hooked up to one set of inputs and the manual switches are hooked up to the other set of inputs. I don't know if the computer gets any kind of feedback from the solenoids though. Like I said, I have not studied this tranny , just thinking out loud :D
 
There are two different styles of NSS, the 96 down and 97 up. 96 down does not have continuity in D as noted, 97 up has a pin that has continuity in D iirc.

You could do this with a bank of relays or (what I'd do) some MOSFETs and a PAL/GAL/small PROM or ROM chip but it wouldn't be simply a matter of wiring things together. You *might* get away with using a 97 up NSS and diode switching but you'd be real close to or over the current limit on the NSS contacts, they aren't designed to switch high current loads like a ~12 ohm solenoid.

I considered doing this on my 96, but then I scrapped that heap of junk and put a 5-speed in the MJ, and my '98 is still too broken to try this on...
 
I looked into using a "smart" relay to do this. You could reprogram it for the shift points but... you would still need to add relays for the solenoids. It's a current supply issue like Kastein says a 12 Ohm solenoid draws a fair old bit of power. Then there is the cost of the electronics...

With solenoid control you need to use both Faraday's Law and Ampere's Law in the design as you need to consider not only the amperage needed to activate the solenoid, but how to discharge the induced EMF when it opens. The voltage has to go somewhere... Most of the solenoid driver circuits I have looked into provide a dropping resistor on the NC contacts of the driving relay to provide the discharge path to ground.

It would be nice though, to have complete control over the thing. What was Chrysler thinking...
 
I usually ignore Ampere's Law and simply throw a 1N400x series diode across the relay coil with the cathode connected to the positive side. Back-EMF gets shunted in a circle till it decays due to coil resistance, normal coil driving is blocked by the diode and therefore goes through the coil. Costs about 5 cents per relay to add it.

Ground-side-switch it with an N-channel enhancement mode MOSFET capable of handling the current and all you have to do is feed a couple nano-amps @ 5V into the gate of the MOSFET and the relay clicks shut, let the gate drop back to zero and the relay opens again.
 
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