Video: Driving with a Steady Speed, or a Steady Accelerator?
 

When I have my cruise control on (which by the way is a real crummy after-market cruise) the throttle enjoys accelerating to speed and then decelerating once the set speed is attained. This is noticeable on a ScanGauge as the MPGs fluctuate intermittently from around 40mpg to 100mpg and can get irritating.

Another option of driving technique is to hold a steady accelerator postition and letting the car's speed fluctuate as it goes up hills and down descents. The question is, what is the method for optimal fuel efficiency?

This video attempts to verify this:

[youtube]http://www.youtube.com/v/QYuZQhpuzfI[/youtube]

Feel free to discuss.

BTW, great to see you around, Peakster :)

Have you investigated a constant throttle version of CC? I haven't done any extensive testing on it, but I rigged-up my cruise to govern the throttle to about a 21 TPS.

-If I set the cruise for 65, it will hold the speed at 60-65 without a problem and reduces the throttle if the target speed has been exceeded.
-When a hill approaches, speed starts scrubbing-off as load builds. If winds and the hill are neither too extreme, then the lowest speed results in 50-55 mph. -Then after the crest of the hill, speed builds again.

It's a great "set it and forget it" feature for long highway trips, reducing fatigue. Of course, I need to test it more thoroughly -- i just have tank data to support some incremental improvement.

Usually, how long are your tests (distance-wise)?

RH77

Virtually all my tests I've captured on video have been on the same stretch of freeway in the city of Regina. Naturally, with a city population of around 200,000, the freeway segment I used is only about 7 kilometres in length. Most of it is pretty flat (other than the grades created by under/overpasses at each interchange).

Unfortunately I haven't tested the constant throttle version of cruise.

I would have to vote for the steady accelerator method also known as DWL.(Driving With Load) This seems to work best in the Prius on a long highway cruise. I recently went on a trip to visit my grandpa and monitored TPS and IGN on the SG2 and, when the terrain cooperated, was able to maintain 70-80+ mpg with occasional flashes to 90 for miles at a time. Speed varied from 55-45 mph. This works best on a 4-lane highway when you stay in the right lane.;)

Larry, correct me if I'm wrong, but my understanding of DWL is that it's not technically a steady throttle. Well, it would be if the road was flat...

But if you hit a hill while DWL, you may actually have to ease off as load increases and speed falls. If you hold the throttle steady on a long enough hill, FE will plummet.

Have I been reading it wrong?

PS - 70-80 mpg @ 55-45 mph? That's insanely nice. Wow.

Rick, that's cool. How did you do that?

I haven't engaged cruise on my car since the last time I ran an experiment! If it would do actual DWL, I might be tempted to use it again ... sometimes :D

The only problem is when terrain/traffic doesn't cooperate then the numbers drop like a lead balloon.:(

I think you are right. I've been up since 3:30 am(EST) and I'm getting things mixed up.:o I was thinking about how I try to pick a certain mpg number and hang onto it as long as possible. So, yes, you would have to ease off for a hill.

Picking a target MPG and holding on to it by playing the throttle (and speed) ... that's what I call DWL.

Maybe we need to start calling fixed throttle something more like "DWL-lite".

I rigged this up about a year ago...

First, I opened the housing of the cruise-control servo assembly. Inside is essentially what looks like the throttle-body arm attached to an electric servo. It has a metal stop on each end for zero throttle input, and maximum cruise throttle input.

I found if you wedge a hex-wrench in there, then the arm rotates and stops depending on the size of the wrench. With manual rotation and SG monitoring, I got it to limit the cruise to 21% TPS by trying a variety of wrench sizes. Then the whole works was clamped together.

For safety purposes, nothing restricts the 0-21% movement of the cog -- so it can still be de-activated by pressing the brake, etc.

It's great for longer highway trips that become tiresome.

BTW, great numbers Larry, and Welcome :thumbup: I had the pleasure of renting about 4 Priuses lately and I absolutely love them! I have to admit that actually they're fun to drive from the way they operate to handling, etc. I drove on some twisty mountain roads and found that the response and handling is surprising agile and forgiving -- more like a small sportscar, if I could be so bold. Great for those downhill charge-ups :D

RH77

Hello guys. I am a brand new member who has been lurking for a few days now.

I have a lot of interest in this as a mechanical engineer graduating in May and going on to graduate school in fluids and heat transfer for more efficient machine designs.

Anyways, I go to school in the mountains of Vermont and drive through the NH mountains for various reasons as well, since I live at the foot of them in southern NH. I am really interested in which is best for these types of situations. I don't often see flat roads to drive on...

This summer I will invest in some equipment to do real testing, but for now does anyone have some resources on handling these mountains best?

So, what are you driving? Automatic or 5-speed? By the "testing equipment" comment, I take it you don't have OEM fuel economy instrumentation or a ScanGauge?

I don't have any of that... yet. I drive a 2001 Ford focus, automatic. That will also be changing this summer because its a shared deal with my younger brother and he will be taking it permanently.

I find that most cruise controls only get you better fuel economy if your a "regular" driver or are on really flat hills. If it's got even low hills, it seems that more throttle is put on going up hills. CC is more of SC, or speed control, it puts on gas while going up hills so that your speed is constant, and lets off going down hill. If your a real ecomodder then you're probably good with your feet while driving and can hold a constant throttle without realizing it, whereas normal drivers fluctuate with the pedal. And it seems they also have trouble with their feet stop working while talking on a cell phone.

Cruise control IS a savior tho on road trips :thumbsup:

Cruise control on road trips down south is AMAZING. I can pull in really good mileage on the Focus. I'm not sure if I can do better simply because the distances are too great for me to have bothered trying, to be honest. However, in the mountains cruise control can drop me down to 26 MPG in a Focus, which is utter trash. Using my foot I can get back around 32 MPG but that's without any technique and driving way too quickly.

This sort of dedication to mileage is something I just never considered - maybe because I didn't think it would make sure a huge difference. Now I really want to start with the best habits that will boost me in the hills and work on physical modifications this summer on my own machine. CC isn't it for the mountains, though. I have a feeling peakster would have had some more interesting results on some good hills.

Man, you know what? I have precious little experience driving automatics and even less driving in really mountainous country. I don't think I'm qualified to give out a lot of advice on that combination except the obvious:

- At highway speeds, keep the torque converter locked if at all possible. (Can you even do that in the mountains? Does the car even have a lock-up converter?)

- Your best constant speed efficiency with an attentive right foot (and traffic conditions that give you enough lattitude) is going to be whatever speed you're at just after the highest gear / torque converter engages.

- Hills.... if it's a short, steep climb, that could mean DWL (driving with load): actually releasing the accelerator as the vehicle speed drops, to keep the car from downshifting. Regain speed gradually on the other side.

- Obviously the above doesn't apply if it's a long climb.

- On the descents, neutral is your friend, provided it doesn't cause you to get into situations where you have to brake, otherwise just leave it in gear.

Call me a noob, but wouldn't you stop quicker if you were in neutral in a sudden stop? or does it have to do with brakes and engine power?

I was thinking more from the perspective of gathering too much speed on a descent in N that it forces you to ride the brake, or brake repeatedly to keep things under control. In that situation, might as well just stay in drive.

Thanks for all the advice. Rt 89 is pretty barren when I travel it so I can vary my speed a lot assuming no statey latches onto me at the bottom of a big hill / small mountain. Super troopers may have been based off of VT cops but they aren't that bad in my experiences. I have always planned on making my next car a manual transmissions. And, I have no idea what a lock up converter is hehe.

Manual transmission is definitely the way to go if you're going to develop ecodriving/hypermiling techniques. The EPA ratings comparing an auto vs. manual transmission for the same car may not be that far apart, but in the hands of a determined hypermiler, they'll be miles apart.

http://auto.howstuffworks.com/torque-converter4.htm

A lock up torque converter makes a direct connection between the engine & transmission, typically in the highest gear, once engine & transmission speeds are close. It improves efficiency by eliminating slip between the 2 sides of the fluid coupling.

Gen, the simple way to maximize your FE in up and down terrain is to imagine you're having to pedal your car. You want to carry speed through the valleys to get you up the other side and try not to knock yourself out going up the hill by maintaining speed -- when you crest the summit, you'll want to have bled as much speed off as traffic conditions will permit.

Driving in cycling terms. Not sure why I never thought of it like this :D

I've been trying to apply a lot of the techniques I am learning to my daily driving. I haven't used a full tank of gas since I started and I don't have proper instrumentation so it is very hard for me to see anything. However, driving back to my university this Sunday, I will definitely see how well I can do. As well as block out some extra time since I won't be doing 80 mph the whole way :turtle:

We should all drive our cars like bicycles!

Bicyclists are the most insanely efficient travelers in the world.

I have always tried to time stop lights so I can roll through without hitting red.

Bicyclists also ride at a reasonable speed, either slow enough that wind resistance isn't a factor or that areomod if they are going really fast.

Cars could learn a lot from bikes.