Transmissions

Somebody wake me up. This cannot be. It just cannot be.

One of the reported problems with the BMW Mini-E is that apparently MOST of the vehicles have a problem with the transmission just magically kicking into NEUTRAL while going down the road – even while accelerating. A lot of the owners are returning the cars for service on this issue, and reports are that the technicians are not only not expressing surprise, but actually seem familiar with the problem and can fix it rather readily.

Hooray.

I’m still stuck on the NEUTRAL part. How does the transmission kick into NEUTRAL? Well I watched one users video. And I watched it again. And what I saw just floored me. PRND. You’ve GOT to be kidding me.

Do NOT tell me, (actually if anyone can confirm this, please DO tell me) that they coupled an AC induction motor to an AUTOMATIC TRANSMISSION????

It simply cannot be. But it DOES explain another problem reported by owners. Apparently, there is a significant delay when starting out between pressing the accelerator and actually departing. It is reported to be sufficiently significant to be both annoying and potentially dangerous. And the explanation I read questioned why they would program this into the controller. It doesn’t appear while you are going down the road, just when taking off.

It can’t be.

An automatic transmission operates on hydraulic pressure in the torque converter. This is not only quite inefficient, but it poses a real problem to us electric drive types. You see a gasoline engine idles at the stop light. ANd it turns sufficient RPM to maintain the hydraulic pressure in the torque converter. An electric car does NOT idle at the stoplight. It just sits there. The shaft is quite still.

So one explanation might be that they did actually use an automatic transmission . ANd made no provisions for an external pump to maintain pressure. Without one, the pressure falls, and when you do finally put on an accelerator pedal, there will be a DELAY while the torque converter spins up to pressure. This would be very annoying.

There are two solutions to this. One is to tap into the transmission and add on an external hydraulic pump that runs all the time. That’s not very eifficient, but it solves the problem.

The other is a litttle tricky, you have to modify the controller/inverter to spin the shaft at low rpm even with no accelerator input. This is quite wasteful, but really doesnt take much power. ANd it would keep the torque converter under pressure.

The obvious solution is not to deal with it at all. VERY FEW car conversions are done with automatic transmissions. People converting automatic transmission cars mostly pull the entire rig and try to drive the differential directly with an electric motor. The problem with this is you need a much more powerful motor to take off, and usually they wind up increasing the gear ratios in the differential to at least 5:1 to do this.

With the front wheel drive, this really isn’t an option on the Mini automatic transmission. But it begs the question WHO DRIVES AN AUTOMATIC MINI anyway. It goes against the entire ethos of the car. And they have one of the best six speeds in the world with the Getrag 6 transmission that normally comes in the mini anyway!

This transmission is just a work of art. It has THREE overdrive gears, yet remains very tight and close, shifts like a dream, and makes this little economy car drive like a Porsche. It is just SUPERB. I don’t see the point in a sub compact economy car with an automatic transmission, but you can get one strangely enough. But I almost refuse to believe they mated an AC induction motor to an automatic transmission.

If so, great news. If they can get 100 miles, we can get 110 with the Getrag 6.

We have actually removed the engine and transmission from the car. We sent the motor and transmission to VAC MOTORSPORTS in Philadelphia to be mated. This is actually a BMW racing shop with full CNC machine shop that is going to do several things for us. First, they are going to device a bell housing adapter to allow us to bolt the motor to the Getrag. Second, they are going to work some sort of shaft in to mate the female involuted spline shaft of this strange motor to the flywheel. Third, they are going to install a lightweight aluminum flywheel. And finally, they are going to install a Quaif automatic torque biasing differential in the transmission.

This should give us a SUPERB drivetrain. After driving the stock Getrag, and examining it on removal, I would rate this piece of equipment AN ENGINEERING MARVEL. By installing a lightweight aluminum flywheel and Quaif differential, we will have brought it up to full track specs.

With all this going for it, that BMW would put an AUTOMATIC in the MINI-E is just not believable. Somebody tell me I’m wrong. But it WOULD explain the delay on takeoff that users are experiencing. And I DID see PRND in the video.

Jack Rickard