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Chrysler 42RE Transmission Controller Brainstorming 
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LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Hi all, it's me again. Back with another personal project that is likely to get abandoned, but hey it's the thought that counts...

A friend of mine is going to run his Jeep Grand Cherokee 4.0 on Megasquirt (blasphemy!) because he is supercharging it. He was just planning on keeping his stock PCM to run the transmission and doing various things to fool it so it doesn't go into limp mode.

But I've been looking for some sort of automotive-related microprocessor project that solves a problem that hasn't been addressed by the DIY crowd. It turns out that the 42RE transmission doesn't have any DIY support so I'm going to take a crack at it.

This thread is simply a dumping-place for all of the information I have gathered online, and any helpful contributions are welcome. If I abandon the project, at least all of the information will be in one place for someone else.

This is the end of the first post, I will be adding a second very shortly.

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Keith MacDonald
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Tue Jul 17, 2012 4:52 am
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LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Stock I/O Configuration

On/Off Solenoids (25-40 Ohms)
  • 3-4 Upshift
  • Torque Convertor Lockup
  • Transmission Relay

PWM Solenoid (3-5 Ohms)
  • Governor Pressure (operates at 512 Hz)

Analog Sensors
  • Transmission Temperature (1000 Ohms @ 70 F)
  • Governor Pressure (0-5 Volts 0-125 PSIA)

Pulse Input
  • Output Shaft Speed (VR 3 Volts @ 30 mph)

Digital Inputs
  • Park/Neutral Safety Switch (Grounds to enable start)

External Inputs
  • Throttle Position (0-5 Volts)
  • Vehicle Speed (5 Volt Pulse from ABS)
  • Engine Speed (5 Volt Pulse from sensor)
  • OD Disable Button (Grounds to disable)

External Outputs
  • OD Disable (LED in cluster)

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Keith MacDonald
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Last edited by thebigmacd on Tue Jul 17, 2012 5:50 am, edited 3 times in total.



Tue Jul 17, 2012 5:06 am
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LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Transmission Specifications

Code:
Gear      Ratio
----------------
1         2.74
2         1.54
3         1.00
4 (OD)    0.69
R         2.21


Fluid: ATF+3

Governor Pressure, Solenoid PWM, Pressure Sensor Feedback

Code:
Speed (MPH)   Governor (PSI)   Sensor (V)   Solenoid (V)    Solenoid (PWM%)
---------------------------------------------------------------------------
0             0                0.66         8.3             40
10            10               0.9          8.6             38
20            20               1.1          9.45            32
30            30               1.45         9.8             29
40            40               1.8          10.3            25
50            50               2.15         10.8            22
60            60               2.95         13.8            0

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Keith MacDonald
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Last edited by thebigmacd on Tue Jul 17, 2012 12:19 pm, edited 1 time in total.



Tue Jul 17, 2012 5:14 am
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LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
3-4 Shift Solenoid

Controlled by on/off current drain.
25-40 Ohms resistance.

Engages at closed throttle at 25-28 mph.
Disengages at closed throttle below 25 mph.

Disabled when OD switch is off.
Disabled at wide open throttle.
Disabled when temp < 0.5 C (30 F)
Disabled when temp > 126 C (260 F)
Enabled when temp < 110 C (230 F)

Torque Converter Clutch Solenoid

Controlled by on/off current drain.
25-40 Ohms resistance.

Engages above 72 km/h (45 mph) in overdrive.
Engages above 56 km/h (35 mph) in 3rd (when OD locked out).

Disabled when temp < 10 C (50 F)

Transmission Relay

Powers transmission solenoids.
Disables power for limp-mode.

Governor Pressure Solenoid

Controlled by PWM current drain.
3-5 Ohms resistance.

Modulates governor pressure between 0 and 60 psi.
1 Amp current = 0 psi
0 Amp current = 60 psi

Normally maintains 1 psi / mph. Gears 1-3 are shifted hydraulically by governor pressure + throttle pressure valves.

There are 4 pressure-vs-speed curves maintained by the TCM:
Code:
Curve    Condition            Result
--------------------------------------------
1        TransTemp < 30 F     Earlier shifts
2        Transtemp > 30 F     Normal
3        Wide Open Throttle   ?
4        4WD Low              Earlier shifts

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Keith MacDonald
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Tue Jul 17, 2012 5:47 am
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thebigmacd wrote:
Hi all, it's me again. Back with another personal project that is likely to get abandoned, but hey it's the thought that counts...

LOL! Indeed it is :-)

Quote:
This thread is simply a dumping-place for all of the information I have gathered online, and any helpful contributions are welcome. If I abandon the project, at least all of the information will be in one place for someone else.

Great attitude! Thanks on behalf of auto 42RE owners everywhere :-)

A transmission controller should be pretty easy to do if you don't have to generalise, right? Propeller again? Or what?

Fred.

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Tue Jul 17, 2012 8:41 am
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LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Yep, Propeller again. When you don't have to worry about microsecond timing it can all be done in the interpreted language instead of assembly. Makes it pretty easy.

My downfall is I rarely get the hardware sorted enough to do some serious coding.

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Tue Jul 17, 2012 12:10 pm
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LQFP144 - On Top Of The Game

Joined: Tue Dec 27, 2011 5:37 am
Posts: 268
I'd probably run the solenoids off a VND14NV04, because I have some sitting around not doing anything. You might need an op amp or something similar to shift the voltage to something higher than 3.3V.

I never tried to use a PWM on the Propeller. You might consider something like a MCZ33800. It supports 3.3V MCUs, PWM, and it has some low side gate drivers.

For the analog inputs I'd use a MCP3208.

You could use a MAX9926 on the VR sensor, and sample it as a frequency on the MCP3208. Here's a link to a nice MAX9926 breakout board.

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Tue Jul 17, 2012 4:43 pm
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While it's not for 42RE there might be something useful in PDF manual and windows configuration software available on http://www.powertraincontrolsolutions.c ... ontrol.php. Software works in offline mode without PCS hardware and there's base calibration templates one can load and play around for some GM and Ford transmissions included.


Tue Jul 17, 2012 5:12 pm
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LQFP112 - Up with the play

Joined: Thu Apr 10, 2008 5:51 pm
Posts: 205
Peter wrote:
I'd probably run the solenoids off a VND14NV04, because I have some sitting around not doing anything. You might need an op amp or something similar to shift the voltage to something higher than 3.3V.

I never tried to use a PWM on the Propeller. You might consider something like a MCZ33800. It supports 3.3V MCUs, PWM, and it has some low side gate drivers.

For the analog inputs I'd use a MCP3208.

You could use a MAX9926 on the VR sensor, and sample it as a frequency on the MCP3208. Here's a link to a nice MAX9926 breakout board.


My prototyping is going to be all through-hole, because I still like that sort of thing :)

I have lots of spare MS stuff so for the solenoid drivers I am going to use IRLZ44N. They can be triggered from 3.3V, and are good for 47 amps current sink (I only need 1 amp out of them).

PWM is one of the easiest things to do ever on the Prop. One of the sample programs is an RC servo driver.

For ADC I am using MCP3202, since I only *need* two inputs and I already have the chips laying around. Switching to a 3204 or 3208 in firmware later is beyond trivial (I love SPI/I2C).

For VR I am using LM1815, because once again I have some and I have made them work just fine on a Subaru 6/7 car (probably the only one that actually works from what I can tell).

I have a PPDB for basic prototyping, it already has all of the basic I/O stuff I need (USB, keyboard, VGA, etc).

The best part about the Propeller is I can write an on-chip jimstim-style simulator that has video output and keyboard input, and not mess with the actual transmission code while I am at it. Multicore at its best :)

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Keith MacDonald
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Tue Jul 17, 2012 9:13 pm
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thebigmacd wrote:
Switching to a 3204 or 3208 in firmware later is beyond trivial (I love SPI/I2C).

Just to clarify, you mean easier than trivial, not harder than trivial, which is how it read to me, right?

Quote:
For VR I am using LM1815, because once again I have some and I have made them work just fine on a Subaru 6/7 car (probably the only one that actually works from what I can tell).

FYI, the MAX992X is the golden child of VR chips. It is better than LM1815 in virtually every way. The only down side is the SMD nature of it. Saying that only LM1815 ICs work on subby 6/7 is somewhat ridiculous.

Fred.

_________________
DIYEFI.org - where Open Source means Open Source, and Free means Freedom
FreeEMS.org - the open source engine management system
FreeEMS dev diary and its comments thread and my turbo truck!
n00bs, do NOT PM or email tech questions! Use the forum!
The ever growing list of FreeEMS success stories!


Tue Jul 17, 2012 9:41 pm
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