Project Land Yacht (BMW 5-series EV conversion) - Page 4 - Fuel Economy, Hypermiling, EcoModding News and Forum

mechman600 · 02-05-2013, 04:06 PM

Got it.

Are you going to attempt to use the tach for motor speed at all or will it just always read 300 rpm?

jackbauer · 02-05-2013, 04:35 PM

Yes the tach will read motor speed above 300rpm. The motor will have a 2 pulse per rev signal being fed to the arduino. this will do the math to turn that into a 60-2 reluctor wheel signal and feed it to the ecu. When the actual motor revs drop below 300rpm the arduino will maintain a 300rev signal to the ecu. Then when the motor revs over 300rpm it will revert to actual. Hope that makes sense

bennelson · 02-05-2013, 08:38 PM

Wait a minute! You are designing an electric car that will pass the pollution inspections that the gas version of the car must pass?!!?

Brilliant!

jackbauer · 02-06-2013, 05:22 PM

Yeh pritty much Ben! My current ev failed its first test a few years ago cos they couldnt find a place to put the exhaust gas probe!

fb_bf · 02-07-2013, 09:35 PM

I'm glad to hear you're keeping the transmission. I think many converters think they can do without it, but your comment about limited RPM range is right on. I kept my clutch, and my car drives like a ICE version. It's interesting to hear you don't have issues with shifting without the clutch. I would have never thought that. For my car, my torque almost matches the peak torque of the ICE engine, so I didn't worry about burning out the clutch. I machined the the flywheel down to the outer diameter of the clutch to reduce the rotary inertia losses from the flywheel. Unless your torque is way over the clutch limit, which means your over the whole drive train limit, I still think maintaining a clutch is a good idea. I see these incredible builds where the people say they left the clutch out to make it easier to do. I keep thinking that after all that work, you didn't bother to keep the clutch? Good luck on this build, though I don't think you need luck, you already know what you're doing.

mechman600 · 02-08-2013, 12:27 AM

It depends on the motor size. My small 7" motor shifts exactly the same as if you pushed the clutch in (when it had an ICE) even though there is no clutch. A 9" or 11" motor will definitely roast synchros in no time.

My next build will definitely have a clutch.

jackbauer · 02-08-2013, 12:48 PM

The 5 series uses the exact same getrag 5 speed gearbox as I'm running in the 3 series which has just passed 20k ev miles without a clutch and an 11" motor. Two things help here : I would only do about 20% of the shifts in an ev as i would do in an ice and secondly the getrag has very good synchros.