Cruise Control (with MPG sensitive logic)

[oldbeaver]

Originally Posted by Cardinal Grammeter

This is a huge thread and I hope I'm not repeating the obvious...

I drove a Scion xb that had instantaneous mpg display.

Much to my shock, it became crystal clear that mpg was a simple function of Throttle Position. So if you wanted to drive at a constant 45 mpg, you would set your throttle position to get that mpg and simply hold it up and down hills.
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Regards,
Tom

Sorry, but it is not crystal and not clear to me that the instantaneous mpg of a car is a "simple" function of throttle position. At least, it must consider rpm and speed also. Obviously, if you push the throttle "ceteris paribus" you will see a change in consumption, but that do not mean it depends only on throttle.

Therefore, ask Scion makers and think it again.

Oldbeaver

[bheadrick]

Perhaps what you're looking for is more like an auto P&G? I've given some thought to this idea myself. You'd set your "target" speed the same way you set your cruise control speed. The problem is that this system would have to be able to disengage the engine and maybe even cut the engine as well as popping the clutch to restart if it needs to accelerate or if you tap the brake. This isn't something that would be possible on a manual transmission vehicle, but might be possible on a car with an automatic transmission.
I'm still doubtful that you could actually do something like that, but it's fun to think about.

On the more realistic side of the fence, maybe rather than trying to set it to stay at a fixed mpg, you set it to your speed like normal, but rather than trying to get to that speed as quickly as possible and stay there, it uses an optimal throttle to maximize the mpg to get there and stay within 5mph.

[briank]

Originally Posted by Cardinal Grammeter

This is a huge thread and I hope I'm not repeating the obvious...

I drove a Scion xb that had instantaneous mpg display.

Much to my shock, it became crystal clear that mpg was a simple function of Throttle Position. So if you wanted to drive at a constant 45 mpg, you would set your throttle position to get that mpg and simply hold it up and down hills.

So for constant mpg, a simple hand control would be the proper controller.

Regards,
Tom

I drive a 2008 2nd Gen xB automatic, and I see a similar behavior. Say I've got up to 42 mph and let the auto lock up in 4th. So at a given constant accelerator position where the instantaneous mpg reads 20 mpg, the car will accelerate moderately from 42 mph all the way to say 55 mph and the mpg will display about a constant 20 mpg for the duration of that 13 mph speed increase. I then ease off the gas pedal to maintain 55 mph. So when keeping the gas pedal constant the FI duty cycle and actual throttle must be opening as speed increases otherwise mpg would go up proportional to speed. So all I need is just to keep a steady foot going up hill such as not to cause a downshift or exit TC lock up.

[mjspiess]

I drive a '95 Geo Metro 3 cylinder 5 speed and decided to do this mod. I got everything hooked up tonight. It works, but not exactly how I pictured it. I think I might have to do some fine tuning with the DIP switches. It seems to over react and pulse & glide, rather than using small subtle changes in the throttle. I just tested it in town. From what I gathered on my short little run. It doesn't seem to know how to resume speed, or MPG in this case. It seemed to lock in 45 mpg pretty well, but that doesn't do me any good when my lifetime average MPG is over 51 mpg for the last 3 years. It couldn't lock in anything in the 50s or 60s without pulsing and gliding and losing speed all the while, but my foot may not have been steady when I set the MPG. I'll have to keep testing and see if there are any settings I can mess with to make it level out. I have the Rostra Global Cruise and it has 12 DIP switches. I currently have it set to:
Gain (Sesnativity): Extra Low - OFF OFF
Pulses/Mile: 8000 - ON ON OFF OFF
Engine/SetUp Timer: 8 Cylinder/Low - OFF OFF OFF
VSS Source: Square Wave Input - ON
Transmission: Manual - OFF
Control Switch: ON

I guess I'll start with the 8 Cylinder DIP switches and change it to 4 cylinder. I read on this thread to set your vehicle to 8 cylinder/high power to decrease the sensativity. Any other input? Why else would it be so jerky and unable to "lock" onto a certiain engine load/MPG?

[pete c]

Read only the first 3 pages of this marathon thread, so I am sure I'll cover points all ready discussed.

An instantaneous mpg based CC is a bad idea, IMO, for the simple reason that driving for mpg requires strategy. And strategy requires some morm of intelligence, which machines can't do. I suppose it could be done if GPS and detailed topographical maps were incorporated. This would allow the system to know what was ahead and know whether it was a good idea to coast or build speed.

I think there is a type of CC that could be used with automatic trannies. My idea is to incorporate P&G. The P&G mph range could be adjustable as a wider speed range could be set for higher efficiency or a smaller range set to keep other drivers from killing you. Perhaps that might even work with manual trannies if you tied it in with cylinder deactivation as is used in some engines already. But, in this case, all cylinders would deactivate.

Of course, all of this is available today. It's called driver involvement. Personally, I think more driver involvement is a good thing, as involved drivers are inherently safer than the typical zombie you find behind the wheel today. In fact, since I have been reading this forum, I have used aggressive hypermiling as a defense against what I believe is, by far, the number one driver safety issue, driver fatigue.

[mjspiess]

I got it! For whatever reason, the cruise simply could not stay steady when set to 8000 PPM. I tried 4000 PPM and still no luck. I tried 9650 PPM and it works almost flawlessly! Some things I've noticed:

You can set your MPG at any speed. For example, while leaving my apartment complex, it's 15 mph. I can set it for 45 mpg in 3rd gear & creep on out to the exit maintaining 45 mpg.

When setting your desired MPG, the car will go as fast as it is capable of doing so based on that specific engine load. For example, setting the MPG at 55 mpg, my speed fluctuated between 35 mph-56 mph based on the road elevations, wind, etc.

Speed varies a lot depending on the road you're driving on.

9650 PPM is prob. not pefect, because when setting the cruise, sometimes it still wants to over react, but I found if you just gently place your foot on the gas pedel to about the desired MPG/speed, the cruise levels out. There is an option for 6400 PPM I might try to see if that works any better.

This mod is probably only useful for people who do not encounter much traffic or drive back roads all the time, but you can always over ride what your cruise wants you to do. I haven't taken it on the highway yet.

Resume works now. It will remember the previous load you had set after hitting the brakes.

If I want to change from MAP to VSS, I'd have to devise a way to change PPM back to 4000 as well switch from MAP to VSS since my cruise control does not support tachometer only mode as far as I can tell. That is a bummer because it would be nice to be able to switch on the fly.

Here are some videos of MPG "locked" in. Instant MPG upper left, speed upper right, current MPG lower left, distance lower right. Sorry for the shakyness...some of the roads I was testing on were not very smooth.

http://www.youtube.com/watch?v=QirSq8mmkj8

http://www.youtube.com/watch?v=EnYAzloX9s4

http://www.youtube.com/watch?v=IcA2WGkfwnU

http://www.youtube.com/watch?v=nsVXEoNMTfI

[oldbeaver]

Spectacular !

Did you design and make it? Or where did you get it?

I want it too!

Wunderwar !

OldBeaver

[oldbeaver]

Dear Jomel,

Have you seen the last post of member mjspiess?

He is showing videos of a device that control speed on a mpg control logic. Is that yr device or is he developing a similar device?

I don´t see yr post noticing the Forum that you succeed on finishing yr arduino based Cruise control based on a mpg logic.

Looking forward to hearing from you,

OldBeaver

[Cardinal Grammeter]

OldBeaver and others,

RE: Scion MPG function of Throttle Position.

There was no "thinking" involved in this since it was a direct observation.

I drove the car for 4 hours over big hills and across deep valleys and the instantaneous MPG readout in the dash could literally be "set" by "adjusting" the throttle pedal.

If you wanted 50 mpg, just press the pedal 1/32 or an inch.

It did not matter if you were losing speed going up a hill or gain speed going down a hill. The mpg did not change if you did not change the pedal position.

So the "game" became, "What minimum pedal position (max MPG) will be necessary to crest this next hill at 30 mph?"

When I could see a valley where I would be going from one hilltop to another, I would "set" the MPG around 45 (very small pedal position) and let the car build up speed until it hit the bottom at 70-75 mph and then reach the next hilltop at my target 25-35 or so mph.

What was very useful about this information is that knowing that pedal position is your "MPG setting," you can do a pretty good job w/o any instrumentation.

Now keep in mind I'm driving 5th gear (top gear) and obviously engine revs never reach more than perhaps 2500 rpm.

I drove an HHR that instantaneous MPG dash readout and it was similar but not the precise relationship shown in the Scion. Of course the HHR was an automatic and no matter what throttle position, on the level it could only do a best of 35 mpg. The Scion could actually exceed 50 mpg on the level but the pedal position was too small to humanly maintain. It was probably equivalent to a 1/4 turn of an idle adjustment screw.
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The irony of all this is that a "smart" cruise control would be a fixed pedal position(!) So I was thinking a Hand Throttle would work.

The issue with design a Cruise Control would be knowing where the hilltop was.

One technique might be to allow speed to drop say 10 mph below the setting without changing throttle position. Once the drop was experienced, slowly increase throttle position until the set speed is achieved. There is nothing so infuriating when the Cruise bludgeons the gas pedal right at a crest.

[Cd]

Great thread ! Subscribed !