2hybrids said:
I suppose this really all depends on the layout of the terrain.
i'd counter that it depends on the layout of your brain.
my experience with using cruise controls is limited, and i've never designed one. in my estimation, however, cruise control is concerned with keeping RPM constant. it does whatever it takes to acheive that. after having driven the insight, i've come to believe that the "constant speed" is only the tip of the iceberg. clearly, the absolute bottom of the iceberg of fuel consumption is how much fuel one is consuming. i am not ready to assert science here, but i believe that to be the result of several factors combined, one of which is throttle position, another is the load the engine is under ( this is monitored by the O2 sensor?, or MAP, or some other devices where i don't know exactly which ). perhaps the engine load is the most important factor, as it would seem to denominate what throttle is required to achieve any specific constant RPM.
if one is concerned with keeping speed (ie, RPM) constant, one is paying regard only to the instantaneous requirement of that RPM under the conditions of the moment. there is no evaluation of the future.
if one is concerned with keeping fuel consumption to an overall constant minimum, one is willing to trade a short-term "over RPM bound" situation (eg, any situation where you keep constant throttle even though your RPM and thus MPH/KPH exceed what you would've set cruise control at) for a long term median of the same target RPM.
or, in other words, a human can control an average over an arbitrary interval of time, whereas the cruise control has a fixed or limited (likely short) average in which it has to work. it's not its fault, really, it's blind.
now that i'm thinking about it, the engine load might be a bit more "important" than the throttle... as an example, i'll pick a throttle position and then hit the upside of a hill - MPG seems to decrease more rapidly than MPH depending on the grade of the hill.
man, there's some fantastic math in all this that i would probably have a chance at tackling had i screwed up Calculus I three times due to being an ***.
