Safety feature? High pedal relay causes unsafe rollback.

July 24, 2007 by Rob.

One of EVAmerica’s design recommendations is to use a relay on the pot box that open whenever the driver gets off the gas.  This is a safety feature because the relay turns off the positive contactor which kills power to the controller.  The safety feature is supposed to provide an emergency kill for the motor & controller if the driver lets go of the gas.  Apparently, on risk with DC systems is that a controller failure results in a short sending 100% of the traction voltage to the motor.  The effect would be the same as a stuck gas pedal and could be dangerous.  Sounds great in theory.

Unfortunately, this feature fights with the controller’s hardwired high pedal lockout (HPL) safety feature.  HPL ensures that controller does not go from 0 to 100% instantly if the driver has pressed on the gas when they turn the ignition key.  Imagine that I’m in a rush and I step on the gas and then turn the key.  There is no cranking start up like an ICE: the EV can launch like a rocket from it’s parking place.  To prevent this the controller will not start if the pedal input is too high.  Wow, another great safety feature!

Now, imagine that I’m stopped on a light at a hill.  The light changes and I step on the gas pedal fast to keep from rolling backwards.  The pedal relay activates the contactor which powers up the controller which then reads the pot box and starts the motor turning.  Most of the time the car follows this script and the controller’s solid state electronics start *nearly* instantly while the two mechanical relays appear to click instantly; however, I’m pressing the gas pedal down pretty fast on a hill.  In that case, the delays are enough that the pedal is too high when the controller wakes up so it goes into HPL mode.  The car is effectively dead and rolling backwards!

Without known the cause, I’ve been using the hand brake for hill starts.  It also happens while moving if I want to accelerate quickly.  Once I put all the pieces together it was easier to avoid, but still annoying and unsafe.  I’m considering alternatives for fixing the problem including eliminating the relay on the positive contactor, adding an override switch, or using the clutch position as an override.  I can’t disable the HPL feature of the Curtis.  I’m open to suggestions - just comment to this post.

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