Cruise Control Less Efficient?

Hobbit (another PC member) has researched optimal driving methods extensively, and among his many conclusions is that cruise control is way too aggressive for maximum fuel economy. Here is one of his papers, with links to others:

http://www.techno-fandom.org/~hobbit/cars/sweet/

It's pretty technical, and he has a lot of added instrumentation in his car, but the take-home lesson for the average Prius driver seems clear enough: During mid-range or high speed cruising or acceleration maintain instantaneous FE between 35 and 75 MPG as much as possible. Below that range, you're obviously accelerating more aggressively and pushing the ICE to operate less efficiently. Above that range is also inefficient as the engine "loafs." In the latter case, you might as well apply a technique instead called "warp stealth" -- a method of gliding with no fuel consumption and minimal electricity use. (One of the paper's links describes this technique.) The problem with CC is that in its effort to maintain constant speed it routinely (and unnecessarily, in my view) pushes the ICE well beyond this range in both directions.

I used CC routinely when I first bought the car; now it's rare. I've added a ScanGauge to my car to, among other things, monitor a variety of additional engine performance parameters. The most valuable one to me is RPM. (It's a shame the car doesn't have a tach!) Applying Hobbit's findings, I use the RPM to maintain the engine efficiency sweet spot.

 

<div class='quotetop'>QUOTE(efusco @ Jan 25 2007, 05:12 AM) [snapback]380537[/snapback]</div>

Hmm. Missouri. I see why you could to 30 min. without any variation. To drive across town, or anywhere around here, I can't go more than a few miles without a change in elevation of at least 100 ft. I have that much in getting from home to a little more than a mile away where I work.

Dave M.

 

Well now I have to try this. I use my CC set to the speed limit every time I get on the interstate. During my daily 30-mile round trip to work, half the trip is interstate. The other half is a 45 mph road where I never use CC (and get much better FE).

I'm getting 45 mpg using CC (down from 51 when it was warmer out). I'll post whether or not it makes any difference.

 

<div class='quotetop'>QUOTE(efusco @ Jan 25 2007, 07:08 AM) [snapback]380567[/snapback]</div>

Elevation changes are still fairly large on I-90 around here. I know there's a significant drop in elevation going from Cheney to Moses Lake (90 mile west of here). I get much better mileage going in that direction than coming back. It's not uncommon to see mpg vary from 99.9 down to 20 along that stretch just going up and down relativetly "mild" hills. I wish the Nav system had elevation (or angle of incline) included though.

I haven't driven through MO since I got my Prius. And most of that was just between Kansas City and Columbia.

It still would be interesting to see what affect lowering speed in cruise control on the up hill would have on mileage. With so many other variables, it would probably difficult to get meaningful results. Everytime I travel any distance along I-90, weather conditions are different.

Dave M.

 

<div class='quotetop'>QUOTE(Tideland Prius @ Jan 25 2007, 01:52 AM) [snapback]380515[/snapback]</div>

Oh to dream of a day when there is a "fuel economy agressiveness control" where you could change your vehicle's behavior to be more fuel efficent, or more responsive. It needs to be more than a two position switch...

 

<_< I must agree that the Cruise Control programming is overly-AGRESSIVE and that, IMO, leads to a loss of fuel efficiency, particularly in rolling terrain.

If you take a highly technical approach, a trip in rolling terrain with, say, EQUAL up and down hills will not 'cancel out' due to the efficiency loss in recharging the traction battery when coasting. For over two years [2+ years in my 2004, 2 months in my 2007], I have tried both WITH C/C and WITHOUT C/C and cannot notice enough difference to be significant.

My conclusion: I drive my Prius in a way most comfortable to me in given circumstances.

 

I use cruise control mainly because when I don't, I become so obsessed with mileage that I start holding up traffic whenever there's any sort of hill. I might lose a tenth or two by using CC on my commute, but it's better for the world at large that I do so.

 

<div class='quotetop'>QUOTE(Zzyzx @ Jan 25 2007, 01:57 PM) [snapback]380658[/snapback]</div>

I hear that Zzyzx! It is better just to set the cruise. Less wear and tear on the car. From acceleration and deceleration. Just set the cruise and relax. You MIGHT lose 1-2 MPG.

 

<div class='quotetop'>QUOTE(Bobby @ Apr 20 2007, 11:23 AM) [snapback]426735[/snapback]</div>

How is there less wear and tear?

My experience suggests a loss of more than 1-2 MPG. Probably the best comparison for me is from trips on I-95 between Richmond, VA and Washington. Using CC I got numbers in the low 50s. Using techniques described in Hobbit's article (linked in a previous post of mine in this thread), I've pushed it into the high 50s or, in warm weather, even above 60.

 

<div class='quotetop'>QUOTE(Charles Suitt @ Jan 25 2007, 12:52 PM) [snapback]380654[/snapback]</div>

I find that in rolling terrain, I can slingshot from one hill to the next greatly increasing economy. The CC can't predict the next hill and will kick the ICE on more often. For flat terrain I can't do better than the CC.

 

hate to admit it but definitely doing better without using the CC!!!!

 

I find zero difference in my flat land driving. We have a local paper here called the Flatlander, if that tells ou anything! I can drive for about 40miles without an elevation change of more than 50 feet.. Anyway, in that situation I maintain speed about the same way the CC does - by leaving my foot in one position. I've tried it both ways, and at a steady 60mph, there simply isn't any significant difference one way or another. With hills I can see how there could be!

Edit: And now that I've finally gotten around to reading Hobbit's bit on this, I will no longer keep my foot still! Thanks for the awesome info, H! Man. The more I learn the more I realize I don't know. Do you guys have ANY idea how much easier it is to drive an EV?! None of these games come into play - you simply get what you pay for in the throttle department. There is no real "sweet spot" as about 90% of the throttle range is sweet!

 

The CC in this car is just like any other car's - It only has one goal: to maintain a constant speed.

If you were to put a scope on the CC modulator output you would see that it is constantly hunting (speeding up / slowing down) in attempt to keep the speed perfectly on target. This oscillation is extremely minute and can't be felt by the driver - however, the car in a sense is still accelerating / decelerating ever so slightly on a continuous basis.

A couple of conclusions arise from this:

1- On very flat land, the hunting effect is minimized and the differences between cruise and no cruise is small.

2- The cruise is always going to be less fuel efficient than a person that can hold the throttle perfectly still.

In addition to the above, the cruise does not anticipate or take advantage of hills.

As an additional enhancement, it would be very nice to have adaptive cruise control. It has been discussed, but never been built. There are two elements of this concept:

1- Setting 1: would be as current - Maintain Speed.

2- Setting 2: Would be more sloppy on maintaining speed - in an effort to optimize fuel consumption... As an example, it could target maintaining constant RPM instead of speed. Another example is that on uphills, it would allow the car to slow down by as much as 5 MPH and on downhills it would allow it to go 5 MPH over target.

In addition to the above, it has also been mentioned to tie the cruise control to the Navigation system, with elevations of road built into the data base. Therefore, the Cruise Control could take advantage of upcoming elevation changes.

 

<div class='quotetop'>QUOTE(Bobby @ Apr 20 2007, 11:23 AM) [snapback]426735[/snapback]</div>

I'll restate my earlier question: How is there less wear and tear? Bobby, you out there?

 

You probably still have a *little* bit of a hit at the top end in an
EV because of the Peukert effect if you draw heavy currents to maintain
a speed up a hill, but yeah, I could see it all being much more linear.
Trouble is, gassers aren't very linear, and we learn to adapt.
.
_H*

 

<div class='quotetop'>QUOTE(JimboK @ Jan 25 2007, 08:52 AM) [snapback]380533[/snapback]</div>

WOW ! ! That was quite a read! Costaltech needs to put that kind of data into a simple add on device, and into production. Hypermile'ing geekdom will never be the same.