Transfercase Sensor Resistance vs. Voltage - JeepForum.com
 
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post #1 of 14 Old 12-12-2011, 08:50 PM Thread Starter
cmdrjim
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Transfercase Sensor Resistance vs. Voltage

Hopefully there are a few electrical engineers on here that can possibly solve this for me.
The Transfercase motor has some type of 3 wire pot used for a position sensor
The three wires are:

Grn = 5VDC supply
LV = T313 (Mode Sensor Signal)
Gry = K594 (Drivetrain Sensor Return)

I have read resistance between the three wires, see attached picture.
I am trying to figure out how Jeep is getting a 0 to 5vdc signal back from these wires to show position for Hi Loc, Hi, Neutral, Lo and Low Loc.

From the service manual:

TRANSFER CASE MODE SENSOR SIGNAL
The Transfer Case Mode Sensor Signal Input will provide the FDCM feedback about the position of the transfer
case. The mode sensor will be a linear analog position sensor with a 1.4K +/- 20% potentiometer and a 1 K +/- 20%
wiper resistor that converts the motor shaft position into a multiplexed voltage.

DESCRIPTION
The transfer case mode sensor (3) provides the Final
Drive Control Module (FDCM) feedback about the
position of the transfer case. The sensor consists of a
linear analog position sensor that converts the motor
output shaft position into a DC signal. The sensor may
rotate a full 360 degrees. The FDCM must supply
5VDC (+/- 0.5v) to the sensor whenever the FDCM is
not in sleep mode and monitors the shift motor position.
The sensor position is monitored when the ignition
is in the RUN position and for 10 seconds after
the ignition is shifted to the OFF position. The sensor
is mechanically linked to the shaft of the cam which
allows the transfer case to shift. The mode sensor will
draw less than 20 mA of current during operation

The following information describes the different mode sensor positions:
4LOCK TARGET REGION - The position shall be considered 4LOCK if the voltage is greater than or equal to
encoder_4LOCK_min Volts and it is also less than or equal to encoder_4LOCK_max Volts.
AWD TARGET REGION - The position shall be considered AWD if the voltage is greater than or equal to
encoder_AWD_min Volts and it is also less than or equal to encoder_AWD_max Volts.
AWD SHIFT LIMIT - During Phase 2 and Phase 3 shifting, shifts may become unidirectional when a voltage is
greater than or equal to encoder_AWD_min Volts has been reached.
The mode sensor position will be considered invalid by the FDCM if the voltage is greater than or equal to encoder-
_High_Range_Limit Volts or if it is less than or equal to encoder_Low_Range_Limit Volts.
If FDCM looses the encoder signal during a shift, the FDCM will respond with a shift back in the opposite direction
of travel to first attempt to find the encoder signal. If the signal is not found, the FDCM will drive motor in AWD
direction for 1 second.
Refer to MODE SENSOR VOLTAGES table for the mode sensor voltages.
MODE SENSOR VOLTAGES
Parameter Name Voltage
encoder_4LOW_Min 4.19
encoder_4LOW_Max 4.35
encoder_AWD_Min 0.45
encoder_AWD_Max 0.55
encoder_High_Range_Limit 4.51
encoder_Low_Range _Limit 0.20


All three wires come from and go to the Final Control Module which controls the shift position of the transfercase. Can anyone shed light as to how Jeep gets a 0 to 5vdc range out of this sensor?

Attached Thumbnails
Tcase Sensor Ohms.jpg  

06 Red Jeep Commander 3.7L V6 "Manual QT2", and many more upgrades
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post #2 of 14 Old 12-13-2011, 06:52 AM
meep
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It reads to me that the computer is sending 5V to the potentiometer. it's a little confusing saying there is both a 1.4k pot and a 1k wiper resistor... they both have the same function - variable resistance. would be nice to see a schematic of the sensor itself.

What I *think* is happening is this.

5v+ ---------/\/\/\/\/\/\/\/\/\/\/\/--------sensor return (gnd)
mode sense signal__/\

so what happens is that if the wiper is far to the left, it approaches 5V, and if it's far to the right, it sees something approaching 0. It's a "voltage divider resistor network".

I think you'd want to measure that 5V against the sensor return and see if that reads a 5V (4.5 to 5.5) and then ohm from sensor return to ground, just to validate power to the sensor being GRN and GRY.

Mike
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post #3 of 14 Old 12-13-2011, 02:19 PM Thread Starter
cmdrjim
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Meep, I think you are probably right, I'm making this more difficult than it needs to be. I am looking at using a PLC to "manually" controll the NV245. Maybe I don't need the full 0-5vdc to control it.
Check my calulations, total resistance is 3300 ohms, so current is at 1.5mA with a 5vdc supply.
So my range would be Hi Loc = 3.14vdc and at the other end 2.12vdc.
My PLC has 1024 steps for 0-10vdc or .010vdc per step.
Hi Loc = 314 steps
Hi = 296 steps
Neutral = 266 steps
Lo = 244 steps
Lo Loc = 212 steps
I think I can make that work, I was hoping for a greater use of the 0-5vdc to have better resolution per step.

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post #4 of 14 Old 12-15-2011, 08:41 AM
meep
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as for steps... i assume you are meaning the use of a servo/stepper motor to actuate?

I can confirm that yes, 1.5ma across the pot is legit. And I agree, the voltage range isn't much as you've measured, BUT the FSM uses almost the full range.... ~.5v to ~4.2V, whereas the math derived from the resistance measurements suggests the smaller sweep. something's amiss.

How about sending 5V into the sensor mechanism between green and gray and then measuring LV to grey for voltage. Then see if it outputs similar numbers to the FSM.

??

I love this project BTW...
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post #5 of 14 Old 12-15-2011, 02:32 PM Thread Starter
cmdrjim
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Quote:
Originally Posted by meep View Post
as for steps... i assume you are meaning the use of a servo/stepper motor to actuate?

I can confirm that yes, 1.5ma across the pot is legit. And I agree, the voltage range isn't much as you've measured, BUT the FSM uses almost the full range.... ~.5v to ~4.2V, whereas the math derived from the resistance measurements suggests the smaller sweep. something's amiss.

How about sending 5V into the sensor mechanism between green and gray and then measuring LV to grey for voltage. Then see if it outputs similar numbers to the FSM.

??

I love this project BTW...
Not looking at a servo motor, but just using a PLC to power the transfercase motor with 12vdc and then have the PLC watch the pot in the transfercase motor to stop at the correct position. There is a brake in that motor as well.

So what I would do is use a switch to input the desired transfercase position, hi, hi loc, neutral, lo and lo loc. The PLC would energize the motor brake (energized = brake off) and power the the motor in the correct direction for the position selected. Once the pot has the correct location, stop the motor and de-energize the brake (turn it on)
The voltage changes as the pot rotates, the PLC is set to read 0-10vdc. the PLC converts the 0-10vdc to 1024 steps, hense the steps posted earlier.

Meep, can you tell me if the FDCM gives the motor 12vdc for all moves?

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post #6 of 14 Old 12-15-2011, 06:04 PM
criket
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Whew, my head is spinning. Can not compute....

Good luck man. When it comes to electricity jargon, I get lost.

2005 | WK | Khaki | 3.7 | QT1 | OME HD Front Struts | Rusty's 2" lift in Rear w/ Monroe load levelers (F150 version) | 265/70 Nitto Terra Grapplers | 17" Moabs | 1.5" wheel spacers | Pinch weld mod Rear fender trim mod | 4xG Matrix w/ reciever hitch | 4xG Belly guard | SOLID Diff cover | Cobra CB radio | 4xG antenna mount | Rola roof
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post #7 of 14 Old 12-15-2011, 06:35 PM
DonBray2
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I checked on the dealer connect wiring diagrams for the actuator but it is not showing one for the 3.7 liter. Is this for your vehicle? I know my in laws 3.7 only has the selection for 4-low.
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post #8 of 14 Old 12-15-2011, 06:55 PM Thread Starter
cmdrjim
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Quote:
Originally Posted by DonBray2 View Post
I checked on the dealer connect wiring diagrams for the actuator but it is not showing one for the 3.7 liter. Is this for your vehicle? I know my in laws 3.7 only has the selection for 4-low.
It is for my in my Jeep but is not yet in my Jeep, at least till I figure out how to control it.
If your in law has the 3.7LV6 with 4-low "qt2", than he has one of the rarer optioned Jeep. Most all of the 3.7LV6 are equipped with the single speed qt1 transfercase.

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post #9 of 14 Old 12-16-2011, 05:49 AM
DonBray2
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Your PCM is not going to have the rationality to recognize the actuator, which you stated in your earlier posts. I now understand what you are trying to accomplish. I will look and see if Chrysler corp has a description and operation for the part on their website and post back.
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post #10 of 14 Old 12-16-2011, 06:56 AM
meep
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I'd suspect that motor wants 12V, as it would require too much current at 5 to be happily driven. if nervous you could run it through a PWM at 50-75% but since it's intermittent duty, it won't be long enough to overheat. One benfit to slowing it down, however, is it'd give your controller more time to respond.

Also, if you are counting steps, will you have a calibrate function after a battery replacement, etc?

Also, did you check the pot/position sensor as I suggested as a sanity check? I'm curious, and unless you build in adjustaility in your design (don't know if you're programming a card or bread-boarding the interface) you might avoid a headache...

Others- folks I think Jim is trying to install 4wd in a jeep that didn't come with it, hence how it's not showing up as correct data for his vehicle build.

M
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post #11 of 14 Old 12-16-2011, 07:23 AM
Mr. Boh
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Quote:
Originally Posted by meep View Post

Others- folks I think Jim is trying to install 4wd in a jeep that didn't come with it, hence how it's not showing up as correct data for his vehicle build.

M
He's got 4WD, he just want to swap from QT1 to QT2, i.e. add 4LO selectability.
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post #12 of 14 Old 12-16-2011, 09:02 AM
meep
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gotcha.
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post #13 of 14 Old 12-16-2011, 01:07 PM
DonBray2
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The shift motor runs a 5 volt pulse width modulated signal through a potentiometer. The FDCM looks for voltage (analog) from the signal wire to recognize posistion of the motor. I believe the only way that your going to be able to rectify your situation using electronics is a stepper motor with programmable ciucuitry.
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post #14 of 14 Old 12-16-2011, 08:20 PM Thread Starter
cmdrjim
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Hey guys, thanks for ringing in with help. Yes I have QT1 and I'm planning on replacing with a QT2. I have gone round and round with Jeep and Jeep dealers with no help, they can't or won't make drivetrain changes period.

I have the 3.7L V6 NV245 t-case on my bench w/ the t-case motor. I also have another t-case motor that was given to me. I have taken one of the motors apart and reassembled it. The motor is a simple brush type dc motor, w/ a spring loaded brake, w/ a planetary gear reducer, and a rotational position switch (potentiometer).

The position sensor uses 5vdc, from what I see in the service manual. But I am not sure of the voltage used to power the motor or release the brake, but have assumed 12vdc. It may need the full 12vdc to overcome the clutch pack to get to the Hi Loc and Low Loc positions.

I have connected two switches, one to the motor leads and the other switch to the brake leads. Both at 12vdc. When I run the t-case motor all the way to either of the Loc positions and turn off the motor, the clutch pack in the t-case is able to back drive the motor off the clutch pack and it almost drives it back to the fully unlock position (hi or Lo). If I do the same and but then I de-energize the brake solenoid (apply the brake) at the Loc positions, there is no back driving of the motor. I have also connecting my multimeter to the position sensor (potentiometer) to read the resistance and have tried to stop the motor at the Hi, Neutral, and Lo positions, but the motor is either too fast or the response time of my multimeter too slow to stop in time. My guess it my multimeter is too slow. Meep & DonBray2 I can see where your 5vdc or PWM could slow down the motor and help with sensing position. I need to get a 5vdc power source and test the t-case motor to see if it has enough torque to overcome the clutch packs. I have a feeling the FDCM is fast enough to respond to the sensor and stop the motor quick enough. The response time of the PLC should be just as fast as the FDCM.

How I see this working:
Under normal driving situations (on road), you would leave the PLC off (not powered).
When ready to use Hi Loc, Neutral, Lo or Lo Loc, you would place the transmission in Neutral and
you would use a selector switch to pick the t-case position desired.
The PLC would verify that you have the transmission in Neutral and would then shift the transfer case to the selected position. Once in the position you could shift the transmission into gear and off you go.
You could also turn off the PLC until you are ready to shift t-case positions again.
Think of it as manually controlling your t-case.

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