Exploring the mysteries of the Ranger/Explorer electric t-case - Ranger-Forums - The Ultimate Ford Ranger Resource


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  #1  
Old 01-29-2008
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Exploring the mysteries of the Ranger/Explorer electric t-case

I've posted here I'm putting together a manual t-case control system to get around the logic failures of the factory system without crawling under the truck when I'm in 3 feet of water, lol.

To that end I thought I'd share what I learned so far with those who might have and interest in these things.

Background:

The Ranger Explorer Borg Warner electric tranfer case has a 4 bit digital encoder built into it. The encoder, as it turns out, uses a sort of modified "Gray Code". This is a code system where successive values in the order differ by only one binary bit. Here's a wiki on gray code if you're interested:

http://en.wikipedia.org/wiki/Gray_code

The code in this case is modified because only a few values are "unique" in the rotation. These mark the 2HI, 4HI, and 4LO positions. All transition values between 2HI and 4HI, and between 4HI and 4LO are marked by repeating alternating codes that provide "clocking" or movement speed info back to the controller to show that the system is still moving.

Refer to the attached image (if it hangs around, lol) below for the following discussion. Note that in the columns for the switches that only one bit changes between adjacent codes.

First, what you are looking at is the codes based on the wire colors (which change by model year and model sometimes) for the 4 bit encoder on the back of the t-case shifter motor drive.

In the left hand column is the "sequence" which is just to note that there are 13 distinct "states" in the systems rotation.

Next is the 4 columns representing switch information, then a column identifying a functional position, then a column which displays the binary number the switchs in the encoder represents in hexadecimal. Don't worry if you don't know hexadecimal --it's just a shorthand we can use to see the relationships better here.

Note that the 2HI position at the top uses a unique hex code "C" to identify the position. 4HI uses two unique codes of "6" and "7" and 4LO uses the unique code "9".

In between 2HI and 4HI the codes "E" and "A" alternate. In between the 4HI and 4LO positions (where there is a neutral position where no power goes to either output shaft) there is an alternation between codes "5" and "D".

With this coding the controller can always know where it is generally: at 2HI, between 2HI and 4HI, at 4HI, between 4HI and 4LO, at 4LO.

Note that there is no unique code or codes for the neutral position. It doesn't look like they ever intended to move to neutral as a unique position.

The reason many t-cases stop operating is that the code seen by the controller does not fit the gray code pattern. This can happen due to a bad encoder, wiring or connector damage, or a bad end stop cushion. The end stop cushion/bushing for the rotation has a tendency to dent and crack away over time.

I've just finished designing my manual control system using simple logic to exploit the encoder to set end limits and indicate position. The only "active" component used is 4 relays. There are some diodes, LED's and resistors and of course a switch and some fuses but that's it. After I get it drawn up better I will be posting it for consideration and comment.

Here's a link to an article about rebuilding your electric shift mechanism which has great pics of the inside of the t-case motor positioner if you're curious:

http://www.explorerforum.com/forums/...d.php?t=123542

Last edited by n3elz; 01-29-2008 at 09:30 AM.
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  #2  
Old 01-29-2008
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nice job John. I can't wait to see your shifter mechanism finished!
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  #3  
Old 01-29-2008
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Here is the basic schematic (attached below). Don't build from this yet as it's slightly incomplete in labeling and I need to check it over. I just put it in from my notes.

NOTE: the LED labeled "2LOW" should be labeled "2HIGH". Sorry.

I'll explain it though. Here's some features:

1. End travel limits: relays RL 3 and RL 4 work in an "OR" configuration through diodes to lock out the end travel when the motor hits the end of it's rotation. This helps prevent damage to the end stop and gearing.

2. An "override" switch allow re-enabling motor operation in the event of a failure in the signals from the position encoder on the drive assembly. In this mode there are no end limits, but with careful "bumping" you can hit any position you need to get the vehicle back to where you need it to be.

3. Losing the fuse going to the encoder results in both the 4LOW and 2HIGH LED's illuminating.

4. The t-case can only be operated in neutral. Shift on the fly is abandoned to keep the logic simple and reliable.

Here's an explanation of how some of it works:

LOCKOUTS: Basically if you refer to the diagram I posted before, you can see that at the 2HIGH end position a unique condition exists -- both the BR/W and OR/W wires are "dead" (switch open). Diode "OR" logic basically says that if either of those bits is "1" the t-case motor can be operated in reverse. As long as one of those switches is closed, RL 4 is energized allowing operation in that direction. Similarly, at the 4LOW end stop, another unique condition exists: the OR/W and W wires are dead. Diodes again allow the RL 3 to activate as long as either one of those wires switches are closed.

OVERRIDE: Basically, you feed a source of 12 volts into the override line and it turns on RL 3 and RL 4 allowing the motor to be run in the event of encoder or end-stop bushing failure.

NEUTRAL INTERLOCK: This wire goes to the neutral line from the transmission range switch and when it is grounded it turns on relay RL 1 allowing power to flow to the control switch.

2HIGH and 4LOW LED's: They are basically operated off of the end limit relays. If you're at the end of rotation in a certain direction, you're in one of those positions.

4HIGH LED: This one was tricky. Basically the pattern we are looking for is that both the BR/W and OR/W wires are "hot" (switches closed), but the BR/Y wire is dead (switch open). If you were writing some kind of computer code for this it might look like IF BR.W AND OR.W AND NOT BR.Y THEN LED.ON -- basically if the BR/Y wire is hot, both sides of the LED are at 12 volts and it doesn't light.

SWITCHES: Actually I'm using two switches in one housing. It's like a window up/down switch or in this case it's a sunroof switch from an Explorer. It has one wire coming in for hot, 2 for ground, and 2 to go to the motor. At "rest" the switch grounds both motor leads. When pressed one way, it sends 12 volts to one wire of the motor, but leaves the other grounded. Pressed the other way it reverses that arrangement. Switches with 2 grounds allow you to independently enable/disable each direction. You could also use two momentary SPDT switches. Pressing either one would move the t-case one direction or another. Pressing both would do nothing as BOTH wires to the motor would then be hot.

Anyway, I'll refine this more later. The fuses aren't labeled, but the main one from 12 volts is 15 amp, and the other two are 2 amps each. One fuse feeds 12 volts down to the drive encoder on the t-case (Y/W wire).

Edit: Modified schematic posted
Attached Thumbnails
Exploring the mysteries of the Ranger/Explorer electric t-case-tcasecontroller.jpg  

Last edited by n3elz; 02-01-2008 at 12:04 PM. Reason: Changed schematic
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Old 01-29-2008
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Old 01-29-2008
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PPBBBBBLLLLLTTTTTTHHHHHHH!!!!!

(that is the fart noise your post deserves, Mr. Winkler...)
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Old 01-29-2008
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Nice, John.

IMO, this is the feature that makes the whole exercise worth doing:
Quote:
Originally Posted by n3elz View Post
2. An "override" switch allow re-enabling motor operation in the event of a failure in the signals from the position encoder on the drive assembly. In this mode there are no end limits, but with careful "bumping" you can hit any position you need to get the vehicle back to where you need it to be.
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Old 01-29-2008
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Thanks, Bob. In fact, that's where the whole design began, but adding proper display of position and an end limit function seemed reasonable.
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  #8  
Old 01-29-2008
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Quote:
Originally Posted by winks View Post



x2
That having been said, I'm not a trained mechanic, which why I am on this forum. This one just happens to be beyond me.
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  #9  
Old 01-29-2008
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It's not for everyone, I know. But thanks for looking. I had to razz Winks though, lol.
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  #10  
Old 01-29-2008
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Why not just use a manual shifting mechanism?
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Old 01-29-2008
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Thats too easy lol
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Old 01-30-2008
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Quote:
Originally Posted by Gearhead61 View Post
Why not just use a manual shifting mechanism?
I haven't seen a fabricated manual shift adapter for an electric t-case that isn't basically a jury rig -- unless you buy a manual transfer case. I'm not investing the time and effort finding a good one with the linkage.

This scheme allows me to use the case I've got with less chance of difficulty. I've rebuilt and resealed the motor and housing of the shifter mechanism so I'm pretty confident of its "integrity".

If I had a good manual t-case and good linkage, I'd use it. But I already have all the parts for this scheme lying around. Dirt cheap for me to do and really not that much time to build either.
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Old 01-30-2008
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Originally Posted by 04blackedge View Post
Thats too easy lol
It's actually harder to go manual in a Ranger. Harder and more expensive to find a good manual t-case with all the parts. I got a decent electric one for almost nothing and as I stated above, I have all the parts to make a different control system.

The older manual t-cases have slip-yoke front shafts and I don't want that anyway.
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Old 01-30-2008
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Quote:
Originally Posted by n3elz View Post
PPBBBBBLLLLLTTTTTTHHHHHHH!!!!!

(that is the fart noise your post deserves, Mr. Winkler...)
I believe it also deserves a dunce cap.

Being that you are working with an electric t-case, are you going to try to incorporate a 4x4 switch and bezel from another Ranger, or do you plan on adding more switches to your console?
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  #15  
Old 01-30-2008
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Not changing the bezel. The control switch is too different from the latching type that you just move to a position and leave it there. It's an excuse to add another switch...

And point well taken on your other statement so:

PPBBBBBLLLLLTTTTTTHHHHHHH!!!!!
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Old 01-30-2008
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So I read, neutral? As in there is a neutral position in the tcase?
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Old 01-30-2008
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Yes there is. Between 4HI and 4LO. But the controller doesn't look for it.
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Old 01-30-2008
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Would that neutral be safe for flat tow? just curious.
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Old 01-30-2008
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Maybe, but you'd have to do it carefully, or set up some indicators (much more complex to properly decode) when you are "truly" in neutral.

The problem is: there is no unique code or codes that tell you you are in neutral. For instance, we alternate between code D and 5. Well the codes closest to the 4HI and 4LO positions are actually "transition" areas where you can be partially engaged. So it would be necessary to find the right spot. I don't recommend it really but that's up to you.

One other thing I don't know, but I will when I take my spare case apart: does the oil pump drive off the output shaft? If not, then it depends on whether the output shaft and gears are adequately lubed when the pump isn't in operation. If not, then neutral is useless for what you're thinking.
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Old 01-30-2008
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that last statement makes sense I dont know for sure but i would hate to find out!
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Old 01-30-2008
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Quote:
Originally Posted by n3elz View Post
does the oil pump drive off the output shaft?
The oil pump is driven by the RWD output shaft on both the manual and electronic 1354's. If there was some way to overcome the neutral indexing problem, it should be possible to flat tow an automatic Ranger indefinitely with the electronic case in neutral.
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Old 01-30-2008
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Great info, Bob, thanks.

It can be overcome with microprocessor controls. I'm not sure what the minimum "hard wire" style logic would be to find neutral from either direction accurately. I may play around a bit and see what I can come up with. If I can figure out a clever way without getting into heavier electronic overhead I'll post it. Maybe someone else will first, lol.

I was thinking before about using a PIC microcontroller chip to make a controller. I have 4 of them lying around that are the flash programmable kind and the assembler to program for them. I designed the digital fan controller that remains unpublished using those chips. I was making the design for a vendor but he bailed on me and soured me on the whole idea after spending all the money getting junk to make them. So I've got quite a few parts around.

But with this design I'm trying to stay away from high tech.
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Old 01-30-2008
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umm thats i asked if he would build me one because i dont understand this mumbo jumbo im so lost
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Old 01-30-2008
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Originally Posted by winks View Post


x3
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  #25  
Old 01-30-2008
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ARRRGGGGHHHH!!!
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