Cruise control and gas mileage

Andy K wrote in news:87740ea0-5844-4404-8bcf- snipped-for-privacy@googlegroups.com:

I bet the increase was due to the lower speed or your a inconsistent driver to begin with. cruse can`t antisipate a hill for exempale. KB

My cruise control had no problem with hills.

The speed was steady going up and down hills.

Andy

Does your ECU have "lean cruise mode", whereby it goes lean when the speed is constant over 40 MPH for a few minutes?

I do not think that it has that feature.

Andy

Andy K wrote in news: snipped-for-privacy@googlegroups.com:

I said your probably a incosistent driver, moving your gas pedal a small amount a lot. that will kill your mileage, you proabably dont even notice your doing it. KB

My truck will want to speed up downhill passing most others. I'm an advocate of wanting a cruise mode that tends to slow down uphill, without severe downshifting, and high rpms. It would be easy to have hill sensor. I'd call it the Eco mode.

Greg

Not at all.

Easy does it is how I drive.

The most economical way to drive is constant throttle, which means slowing down A LOT going uphill and speeding up when going down. It's a good way to go mad, especially if you are driving under the speed limit to limit engine wear. Trust me on this.

That's odd. In a friend's Mazda 2, there is a big fuel economy difference between manual throttle and cruise control take over. However, manual cont rol wins in hilly terrain.

Being "dumb," the cruise control revs up to maintain speed up hills. Often , it also has to downshift to get the requisite power. That's where fuel e conomy suffers. If we keep RPMs at 3000 or under when climbing a hill, the n coast downhill (respecting the speed limit), we get excellent fuel econom y.

It isn't always possible to do this, of course. Some hills are so steep th at you need the additional power of the 3000-4000 RPM range, or you'll get so slow that you're a hazard to traffic.

In a very flat place, I expect the cruise control would get better economy, as it is good at maintaining constant RPMs.

Even without a manual transmission, a tachometer can be helpful for increas ing fuel economy.

You raise an interesting point: how is the throttle going to be managed in self-driving cars? How is that handled in existing self-driving cars, such as Google's?

A variety of responses could be possible, perhaps selected at the driver's (passenger's?) discretion. In a hurry? Lock speed at the legal limit, reg ardless of throttle setting. Concerned about fuel economy? Let the car sl ow on hills, as long as it doesn't go X amount below the speed limit (where X depends on traffic conditions, and possibly local regulations). Somethi ng like that. It has to be thought about sooner or later.

Yep. I sort of understand my truck. I can't get good milage without going at least 50-60 mph where 4 cylinder mode kicks in and I'm going on fairly flat road. 21 mpg is about max. Down to 15 mpg 8 cylinder mode or less on grade. 99 coasting.

Greg