Have you ever wanted to own an electric car? or have you ever wanted to drive a Porsche 911? I wanted both, so I decided to build one. This blog is here to document my journey as I convert a 2002 Porsche 911/996 Carrera 2 from a gas guzzler to a completely electric vehicle - not a hybrid!

Wednesday, September 12, 2012

Transmission refinement

During my first test drive, the transmission was running in "Emergency Mode" because it lacked many sensor inputs that it expected for normal operation.  I also found that if I rev'ed the motor too fast, the transmission would make a terrible grinding noise, so I started to look into how to get the transmission out of "Emergency Mode" and back into normal operation mode.  The car has two main computers the ECU for the engine and the TCU for the transmission.   The ECU pumps sensor data over a CAN bus to the TCU.  If the TCU sees all the right signals, it should use the full range of gears and stock shift table.  This particular TCU expects these inputs: Engine RPM, Wheel Speed from 4 wheels, Throttle Position Sensor, and Engine Load.  The Wheel Speed and Throttle Position Sensors are still intact. The Engine RPM and Engine Load need to be figured out.  I went back to the ICE (still in the garage on a pallet) and scoped out the existing RPM sensor arrangement and signal levels.  Its a 60 period, 58 pulse wheel.  The sensor has two outputs, a +/- 5V triangle wave on one output and an inverted version of the signal on the other(180 degrees out of phase).

To measure RPM on the DC motor, I have a mechanical ring with 2 set screws and an inductive sensor that outputs +5V pulses for every pulse, courtesy of RechargeCar.com.

So the task at hand is to create a digital circuit that can capture the incoming 2 pulses per revolution and convert that to 58 pulses per revolution on the 60 period time base, then use some op-amps to change the digital output to triangle waves.  I did this using an Arduino for the digital stuff, and two OP07 op amps setup as integrators to create the triangle waves.  To create a negative (-5V) power rail for the op-amps, I used a RS232 level shifter I had on hand.  Here are some pictures of the completed contraption before stuffing in a project box.
Along the way I was able to do some spot tests with the DC motor spinning--it took a few days to debug the circuit, but it now properly displays the RPM in the dashboard console.  Once I got this complete, I wanted to take the car for a drive, but it wouldn't start!  After a bit of poking around, I found the Soliton1 was protecting the battery pack by not turning on because the pack voltage was too low.  Apparently the driving I did on the batteries originally, plus the DC-DC converter drain while parked for a week was enough to bring the batteries down to a voltage too low to move the car.  This means I had to get the charger working ASAP!

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