Friday, January 9, 2009

More Motor Notes

I stumbled across some data on the Jeep's original engine and its performance. The original gas engine was an "AMC 250 I4" - a 2.5L 4-cylinder engine. This curve shows its torque versus the various electric motors I have data on:

Here is its horsepower - immense at high RPM. However, nobody runs the engine at race-car speeds of 5000+ RPM. When we drove it around before, we typically kept it under around 3000 RPM because nobody liked riding in the Jeep with the engine / tranny screaming like a banshee:

Using the data on the gearing ratios of the AX-5 transmission and Dana 35 rear axle, here are the various shifting ranges. The solid lines are the AC55; the dashed lines are the original AMC 250 I4. I assumed that both gas and electric would not be run at more than about 3000 RPM to make this chart.

Again, this highlights why you want a transmission. Although you *could* just run around in 4th gear all the time, you'd be really slow off the line as you started. And running electric motors at low RPM is fairly inefficient.

It will be interesting to see if that comparatively low performance above 60 MPH will limit the vehicle usability in any way. I suspect not - it is an in-town vehicle. Even at 75 MPH it's only missing about 15% performance relative to the gas motor.

For future reference - I believe the gearing ratios of my Jeep are:

  • First gear: 3.93
  • Second gear: 2.33
  • Third gear: 1.45
  • Fourth gear: 1.00
  • Fifth gear: 0.85
The Dana 35 final axle ratio is 4.10, and I'm assuming I'm running 31-inch tires.

1 comment:

electric cylinders said...

thats a good ratio..i wonder whats the ratio of mine..