AW4 Shift solenoid current draw?

[ChicksDigWagons]

How has this project come along?

Just today I put together a working model of a sequential shift circuit for my XJ.

I'm completely cutting out the TCU however. I'm swapping in a 258 in place of the 4.0 that has long been missing from my engine bay (in preparation for a 360 also on the garage floor) So the TCU isn't going to do a whole lot of anything without any computer control inputs.

Thus the sequential push-button shifting.

But you could say I cheated. I used a Basic Stamp.

I was also wondering what the draw of the solenoids was. The Stamp can only handle ~25mA per output, or a ~50mA total output current. Most relays want >100mA on the coil. So I'm going to have to figure out something for that.

In the first draft of the software, I have it run sequentially through First, Second, Third, OD and then OD with the Torque Converter locked. I may add a stand alone switch for lockup as well as a crude fully automatic mode. The stamp is only useing 5 of its 15 I/O channels for this function, so I'm probably going to try to add some other perks as well.

 

[old_man]

OK you guys were talking about using SCR's to control the relays. I'm a EE/CS/ME with 35 years experience. I have one question, how were you going to turn off the SCR's? There are lots of ways to drive the solenoids, but SCR's won't work unless you use a capacitive back charge circuit.

I have the capability to lay out a pcb if you guys work out what you want.

 

[ChicksDigWagons]

I was considering using discrete components but I wanted it to do way too many functions. I'm going to drive a trio of relays with some npn transistors tied to three outputs on the basic board.

I did some testing and a PNP transistor is going to draw way too much current from the I/O to get the current for the solenoids. I have no idea how to implement an opamp either. (electronic hobbiest newbie here) I have yet to test an NPN, but I don't suspect I'll be able to get 2A out of it without far exceeding the I/O pins limits.

I also hooked up a 7-segment display. Its very nice seeing a numerical gear selection. I don't like the fact that one digit eats up 8 I/O lines. I'll either add a BCD display driver or just get a serial driver for my parallel 2x16 backlit LCD. That way I free up most of my I/O lines and have the ability to display meaningful data.

If I get a nicely working model I'll likely port it over to a cheap standalone PIC chip. I wonder if I can just get a PIC16C57C and program is with my Basic stamp board then use it separately...

 

[lugu50]

Dear Friend Ed:

As I can see maybe you are the only person who can help me. The case is that I need desperately a schematic for TCU installed on AW4 of my XJ Limited '88. Lot of trouble, had to change 2 transistors on TCU to correct reverse (which was not engaging on cold transmission, and now at last, 1-2 gear will not engage not in Drive lever position , nor in Lever 1-2 position. If I disconect TCU. 1-2 gear will engage.

Any help and or advices will be very apreciated.

Thanks,


Luis

FWIW,

I burned 1/2 Watt diodes isolating the current to the solenoids. I changed my installation to relays for physical isolation of the TCU and override current (no problems since).

When the diodes burned the TCU went into limp mode: 1st, 3rd, 4th and no TC lock. No 2nd (unless you drove through the shift override limit in the 1-2 position detent) and no TC lock in the default mode. The limp mode will get you home, but the unlocked TC generates considerable heat.

I like your project, although I'll defer the critique to the EEE's (BSME only here).

When you get to the TC lock/unlock control, and speed sensor logic for the relay for auto mode, can you make the unlock speed setpoint adjustable? This would be a great addition to keep the AW4 cool in 1st gear (a locked TC is not available in 1st with the TCU program). Maybe something for a future term project?

Happy Trails!

 

[kastein]

Since this thread has been awoken from the dead...

I find this subject very interesting, as yet another EE/CompEng type. I'd look into building something neat, but I have absolutely zero understanding of how the transmission control signals actually work and make the transmission shift. Anyone care to enlighten me, as a complete transmission n00b?

As for driving the relays, I would probably use IRF511 N-channel MOSFETs in a ground side switch configuration, as they are cheap and readily available. Remember to install properly rated back-EMF clamp diodes across the relay coils or you WILL lose the MOSFETs. If the relays require less coil current than I think they do, Supertex VN0300s might work, and they have the benefit of being small and cheap (in fact Supertex will send you ten samples for free if you ask them!)