Wednesday, May 21, 2008

Transmission Tinkering

Now we're getting somewhere!

The auto transaxle/gearbox in my Pulsar is a hydraulic gearbox, not an electronic one. Some engines have a computer sensor in the engine that tells the gearbox how fast it's going. The gearbox uses this information to select the correct gear, and to know when to change. Mine isn't that complicated, but it's still quite clever.

It has a governor. This is a funny looking stick with a cog at the bottom and two hinged arms at the top. The engine spins the cog, and centrifugal force pulls the hinged arms apart, just like a figure skater spinning on the spot. As the arms open, oil is pushed into the gearbox to make the gear changes. If the governor is spinning too fast for second gear, it won't downshift and blow the motor.

Here's a picture of the governor on a diesel locomotive engine. It's not exactly the same, but you get the idea.

Now the rub: the electric motor has a different torque curve to an Internal Combustion Engine. While an ICE takes a few seconds to really provide power, an electric motor supplies all the power immediately. If I hook up the WarP9 directly to the transmission, it would probably shift right into top gear as soon as I give it some throttle: clunk, clunk, clunk, clunk. Not optimal!

So what I need to do is figure out a way to modify the governor and delay the shift. I haven't found an EV out there that has solved this problem, so we might be in uncharted territory... That's exciting, even for this accountant!

Here are a couple of ideas I've had so far:
  • Use an oil pump and a computer sensor/controller. This would probably work, but it's expensive and complicated.
  • Shave some weight off the governor arms. This might work, but a uniform reduction isn't really what I'm after. I need something that will align a straight torque curve (WarP9) to the curved torque curve of the ICE.
  • Add springs to the arms to slow the expansion of the arms. This is what I'm leaning towards at the moment. There may be a formula somewhere to tell me what kind of spring to use, but trial and error may be my last resort.

So, to quote Sherlock Holmes: "The game's afoot!"

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