Crazy EV Assist System Idea

[cobbhc]

So I have a base 2013 FWD only. I've had this pie-in-the-sky idea of converting the rear end (frame, knuckles, differential, other things I haven't thought of yet.) of a 4WD version, fabricating a cross-member for an electric motor, and running an electric motor to the rear differential. The system would operate completely independent of the ICE. I know this is not realistic, but I wanted to talk this idea out with people who own and work on their own vehicles.

Here's what I know everyone is going to say right away: "Why convert your rear end? Why not just buy a comparable mileage 4WD and start from there?" I don't really have an argument AGAINST that right now other than I know exactly the work that's been done to mine, but lets just assume I want to keep my vehicle and do the rear end work.

What parts would I need that are 4WD specific? What I can think of right now are:

The rear frame assembly for 4WD (DB5Z-5R003-A) and all the fasteners/spacers/insulators.
The rear knuckles for 4WD (DB5Z-5B758-A and DB5Z-5B759-A)
I think the Hub Assemblies and Linkages are the same?
The differential
The half-shafts

Then the electric system:

I would fabricate a cross member for an AC-50 or AC-51 electric motor, and run a custom driveshaft and yoke it to the differential. I would remove the rear two seats and fabricate a new false bottom over the spare with a place to install my battery pack and controller and build it with a pair of hydraulic struts that I could use to access the spare. I would probably run the system at 130-144 volts and shoot for 6kWh to 8kWh battery pack. Depending on the weight of the pack I might go to heavier springs on the back.

The electric motor would always run so the vehicle would run in AWD for all intents and purposes. The controller would be programmed to run at full percentages during high throttle demand and high charge and taper in low throttle demand and low charge states, but it would always run.The system would charge itself hybrid style on the move and would also be able to plug in. I would have to sit down and really math out the best charging algorithm on the move, and I'm a long way from that being an issue.

So my other question about this, is how would this affect the shift curve for the 6f50? It can be circumvented by running the vehicle in manual mode, but I just wonder if it would even be needed.

Also, before you ask "Why?" - I'm one of those people wants to do things to see if it can be done. I wonder how much performance can be tacked on to a base setup without actually doing anything to the ICE powertrain. What kind of performance gain? What kind of efficiency increase?

So...I'm nuts. Yes. I know that. I'm looking less for, "What's the point?" comments and more, "You're crazy, but if I were going to do this, here's what I would do." I'm mostly interested in what I would need to do to the rear end. Would the cost of converting the rear end be comparable to dropping 10-12k for 4WD base or XLT? The electric stuff I have a handle on. It's the mechanical I need help with at the moment. I'm not afraid of the work, just want an idea how to attack it.

 

[Comando.explorer]

Wow.... Oddly enough I thought of a very similar setup driving my new explorer today. I feel electronic assisted 4wd would be so much more efficient. You just very effectively explained something similar I too envisioned.

 

[allmyEXes]

Regen can be a bit of an issue and also there are alternate ways to mount the electric motor. One being coupled to the front end of the differential and move with it and another that I have pondered if the space exist to do it is stacking on top of the differential with triple groove pulleys on the motor and differential in a belt drive fashion. Battery weight is always an issue but who knows... maybe NASA will all of a sudden have a major breakthrough having to do with battery technology.

 

[cobbhc]

Regen can be a bit of an issue and also there are alternate ways to mount the electric motor. One being coupled to the front end of the differential and move with it and another that I have pondered if the space exist to do it is stacking on top of the differential with triple groove pulleys on the motor and differential in a belt drive fashion. Battery weight is always an issue but who knows... maybe NASA will all of a sudden have a major breakthrough having to do with battery technology.

Sorry I'm just now getting back to this. I agree tuning your regen curve has to be something that would need a lot of attention. I also question exactly how to keep the wheel speeds going the same from front to back. I think you would probably have to tap into your wheel speed sensors from your ABS and use the digital inputs on your controller to monitor that input, and then tune your controller to keep your wheel speeds in the back the same as the front. That may be a problem in search of a solution, but it would let you tune how much work you wanted the electric motor doing.

As to the batteries, for battery assist you don't really need more than a couple of kWh - as low as 2-4 - to get the job done. That, again, assumes you tune the regen curve to maximize battery life. They would also need to be climate controlled effectively. Depending on the batteries you're going to use, and the voltage you want to run, the whole setup, motor and all, could be done for 200-400 pounds. It really depends on the motor. AC-35? That's lighter. Calb batteries or Tesla batteries? All those things are weight considerations.

I'm with you, though. I'm pretty crazy.