Electronic shift control


Last update: 7/15/10

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Background:

After using the paddle shifter awhile I decided I really want to convert it to some sort of semi automatic up shifting. As it is now I initiate a shift with the paddle shifter and either use the clutch or let up and press the gas pedal very quickly. When the torque is reduced the gears in the transmission will shift up without damaging the motorcycle transmission.


Plan A:

I designed and tested an ignition interrupter, which did the lessening of the torque on the gears in about 10/1000 (ten thousandth) of a second. This circuit was based on a simple NE555 IC controlling a relay to cut power to the ignition coils.

After trying various delay times, I've found that for street driving, the ignition cutoff delay time required doesn't seem to be the same for different engine speeds, how much throttle you are applying at the time etc etc. For testing I was using my delay circuit plus my normal paddle shifter which most likely did not apply the same instantaneous timing and pressure that an air shifter does. When it worked it was fantastic, but most of the time it just wouldn't shift at all even though I could definitely feel the engine hesitate when the cut off was in affect. I shelved my first ignition interrupter since I can shift the car using the throttle more consistently and smoother than my test electronics could.


Plan B:

After reading advertisements on the web for professional shifters etc I now realize that the good ones monitor what gear the transmission is in at the time of the shift and use that and other information to control the engine kill time. The time the engine is not running will be in the ~20 mS to 200 mS range. But it will be a variable electronically controlled kill time.

I came up with the following design criteria for my up shift controller;
  1. For the first iteration of the controller I will use some sort of switch on the paddle shifter cable to initiate the shift. I will use the paddle shifter in the normal manner but the engine kill time will be determined by electronics.
  2. No shift will be initiated if the transmission is in neutral.
  3. The shift will only occur if the car is in 1st through 5th gear. (No use shifting if you are already in top gear.)
  4. My engine doesn't pull to well below 3000 rpm so the controller will only shift if the engine speed is above 4000 rpm.
  5. The controller will monitor the electrical Gear Position Sensor (GPS) on the transmission to know what gear is in use.
  6. The output of the controller will be a negative going pulse to the Megasquirt (MS) ECU to kill the engine until the transmission is in the next higher gear. At that time the MS will be allowed to inject fuel again.
  7. The controller will also output signals to a LED gear position indicator so I'll know what gear I'm in.
Sounds like a lot to do but all of these functions can easily be handled by an integrated circuit called a "PIC".  I have already written the firmware and programed a 16F876 PIC to do all those functions and it does control the Microsoft ECU through one of the unused input pins. The MS is programed to have a second fuel table with all zeros in it so the engine will not get any fuel during the shift sequence. Eventually I can mount the small shift controller PCB inside the MS case.

Future ideas:

Once I (hopefully) get this system working I may convert it to some form of pneumatic shifting using push buttons on the steering wheel. I have several different size small air cylinders that should have enough power to shift the gears. I'll leave the down shifting without using the clutch to the professionals (they have the money to repair the damage).

Finding neutral won't be easy for a shifter so I will probably just use the paddle shifter to do that. (Get to 2nd and then manually shift to neutral.)