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Custom cruise control

Old 06-24-2008, 10:03 PM
bwilson4web's Avatar
Engineering first
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Join Date: Oct 2005
Location: Huntsville, AL
Posts: 5,613
Default Custom cruise control


On a recent trip from Huntsville to DC and back, I ran some informal experiments using mass airflow and engine rpm. It looks like these algorithms in a network of microprocessors could eliminate and minimize 'regenerative' energy flows except in necessary braking:
  • microprocessor controlled "B" when braking - this uses more of the engine to slow the car and avoids dumping too much current into the traction battery. It cuts the rate of battery heating from exothermic charging in half.
  • microprocessor controlled "N" when foot on floor - if no energy is needed to maintain a speed, just flip into "N" for an energy neutral coast. This needs to monitor the speed and if in "N" and the velocity increases through 42 mph, go to "D" for 2-3 seconds to get ICE going or decreasing through 42 mph, go to "D" for 2-3 seconds to get ICE stopped. Otherwise, use "N" for feet on floor.
  • cruise control needs to seek the target speed +/- 5 mph but within a narrow engine rpm range, 1,600-2,700 rpm. As the speed bleeds off, the upper rpm range is applied to preserve momentum as long as possible. As the speed increases, the lowest rpm range consistent with resuming the target speed is used.
  • upon hitting the lower speed range, increase rpm as needed to minimize speed loss going to maximum rpm at the limit but with a driver 'alarm.'
My manual attempts to follow these rules led to MPG screens with no or very little regenerative icons. Implemented by a suite of microprocessors, this would be a very handy way to do long distances efficiently.

For your amusement, I drove 1,400 miles at an average speed for each segment, including start and stop, of about 60 mph. Most cruising was at 65 mph. My MPG ran about 54 MPG except for the 10% ethanol I used on the DC to HSV leg.

At temperatures above 82F, I used the AC but just the upper vents gave me the relief needed. There was some rain on both legs and on the way back, I took a 5 hour nap ... so I would not wake up in an ambulance. The trip included 6 hours in the NHTSA meeting trying to fix the "Bell the Hybrid" act.

I have no regret about this good use of ~25 gallons of gas to attend that meeting nor the other logistics expenses. I prefer my trips to have a goal, a purpose.

Bob Wilson
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