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