Cruise Control (with MPG sensitive logic)

[CrazyLee]

I like the idea of MPG cruise.

Don't forget the tranny may shift down. For autos that may save gas as the engine revs go up the throttle can go lesser. Look to keep the engine in the fat part of the torque curve for most engine torque with lowest RPM.

My motor home (Check my garage below.) is my attempt at "hyper Mileing" Any time the tranny shifts down the engine speeds up and the MPG drops like a rock! It has a 454 Chevy engine and the big cubic inches need fuel to satisfy the 14.8 to 1 fuel ratio. I like coasting, 999 mpg.

I usually get instant MPG about 12, but that becomes tank 8.5 mpg average, allowing for acceleration up through the gears. Each time it shifts up I get better mileage.

I am using an MPGuino as a fuel monitor.
The MPGuino calibration is almost impossible to do.

Total fuel mileage is usually 10.5 mpg from calculated fill ups. (That is a tough one, the tank holds 75 gallons! Really really bad on the wallet too.)

It's great for vacations though. 700 miles between fill ups.

1993 Fleetwood Flair My Website
Details: The Beast - 1993 Fleetwood Flair includes kitchen sink Fuel Economy - EcoModder.com garage

[TEiN]

Originally Posted by dopplereffect98

"EcoCruise control saves vehicle energy by slowing down acceleration compared to standard cruise control. Your vehicle may temporarily lose speed when going uphill. It can be switched on or off in the information display"

The ECO cruise control in the 2012 Honda Civic works the same way. So far, it seems like the easiest/best way to accelerate is to tap the "Resume" button and let the ECU handle the acceleration. When encountering hills, speed will drop about 3 mph before it starts to increase load. A single click on the minus button for the cruise prevents it from increasing load further to maintain that speed and lets it drop a little more. Once the hill is crested, a few quick clicks on the + button and you're back up to speed. It's very easy.

My non-hyper-miling wife is having no trouble getting >40mpg in everyday driving, which includes lots of short trips, and steep hills.

[thomason2wheels]

Originally Posted by Cardinal Grammeter

Let me try this one more time.

This is based on observations of the Instant MPG Readout of a Scion w/Toyota engine.

Lets say you want 45 mpg.

Depress the pedal until you read 45 mpg in the dash display.

As long as you keep the pedal at that position, you will continue to get 45 mpg up hill and down hill no mattery what rpm the engine is turning (everything is in 5th gear from about 25-75 mph, mostly 30-60 mph, calm wind conditions)

Its was that simple.

If you disagree with what happened, you can talk to the Scion. I'm only reporting what I observed during 4 hours of driving.

Obviously with such a simple relationship, all the effort of this thread seems focused on the wrong parameters.

One relevant question might be, does Scion use fly by wire? This Scion is probably 2008-ish vintage.

Regards,
Tom

PS. As an exercise, let me quickly categorize your parameters of concern:

N=Negligible
C=Constant (non-varying)
C=Dependent Variable (function of another variable)
V=Varying (true variable)

N- quality of pavement
V- slope of the road
C,N- speed of the wind
C,N- direction of the wind
C- density of the air, (temp, humidity)
C- weight of the car
C- gear of the transmission
C,N- traffic
C- quality of tires
C- hardness of tires
C,N- altitude
C- temp of the engine
V- speed of the car (resistance of air is proportional to the square of speed)
D- rpm of the engine
V- power of the engine

So you are left with Speed, Slope, and Load.

Load = f(Speed, Slope)

QUESTION: What would happen if injector pulse width was a function of throttle position? (all other parameters constant of course)

ANSWER: MPG would remain constant no matter what speed engine/car is going.

QUESTION: Is this possible?

I only have one observation to make. Since all those parameters mentioned do impact actual fuel economy, it is obvious to me that the algorithm used by Scion is bogus. Anybody here that disagrees, please explain how my analysis is in error.

[Cardinal Grammeter]

What analysis?

Yes, most do affect mileage, but that is the particular mileage for a particular condition. Once you have that locked in, then mpg is a function of throttle position.

Whatever the Scion did, the mpg displayed and fuel consumption at fill up were consistent.

I'm trying to visualize a "carburetor" as a fixed orifice (fixed throttle position) where fuel is entrained as a function of Velocity (really V**2 but carbs are tricked out with secondary air bleeds and emulsion tubes to make them linear-ish).

Orifice discharge coefficients are not linear. At low flow they are failrly linearly however. So if you double the speed of the engine, you double the flow and V and double the fuel (assuming incompressible flow like a liquid). But you've also doubled the distance traveled too - per unit time(!)

Double fuel, double distance = same mpg.

So if the discharge coefficient is fairly linear, I guess it makes sense.
______________________

If someone sees a different explanation, please expound upon it.

Thanks
Tom

[tinduck]

Sorry Cardinal,

back to physics class, please...

fuel consumption is dependant on throttle position - on that count you are right - and RPM, unfortunately.

As MetroMPG once said, and I can support this fully: I have yet to see a car which uses less fuel when cruising at higher RPM. Internal engine friction and pumping losses wil see to that! Apart from uphill situations or when accelerating, less RPM always means less fuel consumption as long as the engine can still hold the speed without flooring the pedal. So early upshifting (in my case, my diesel never sees more than 1600 rpm in first to fifth gear, sixth gear is engaged from 70 km/h on) and long last gears are absolutely essential for economic driving.

Furthermore, double fuel consumption does not mean double speed (and therefore not double traveled distance per fuel unit) unless you are traveling in vacuum or talking about ridiculously low speeds. Air resistance rises as a quadratic function, so going from 50 mph to 100 mph, you will more or less quadruple your fuel consumption while only doubling your traveled distance per time.

so long,

tinduck

[pete c]

Originally Posted by tinduck

I have yet to see a car which uses less fuel when cruising at higher RPM. Internal engine friction and pumping losses wil see to that!

This is more or less true, but, there may be cases where you are getting down close to lugging with your foot into it, where going a gear lower results in getting the engine up into a more efficient rpm range. I believe this is particularly true with diesels where the pumping loss advantage of having a wide open throttle is not a factor, but having it floored results in a much richer mixture. I had this explained to me by an old OTR driver with a few million miles of driving diesel trucks over mountain passes.

[tinduck]

Originally Posted by tinduck

As MetroMPG once said, and I can support this fully: I have yet to see a car which uses less fuel when cruising at higher RPM. Internal engine friction and pumping losses wil see to that! Apart from uphill situations or when accelerating, less RPM always means less fuel consumption as long as the engine can still hold the speed without flooring the pedal.

pete_c,

please do not rip sentences out of their natural surroundings :-)

As you see above, I allowed for special situations in which downshifting can result in higher rpms AND lower fuel consumption. But this is never the case when cruising on flat road, you will always have the best fuel efficiency in the highest possible gear there. To get best results uphill, use DWL.

so long,

tinduck

[Xist]

"Furthermore, double fuel consumption does not mean double speed (and therefore not double traveled distance per fuel unit) unless you are traveling in vacuum or talking about ridiculously low speeds. Air resistance rises as a quadratic function, so going from 50 mph to 100 mph, you will more or less quadruple your fuel consumption while only doubling your traveled distance per time."

Tinduck, I am actually finishing up Physics 101.

You are entirely correct. As I understand it, wind resistance is exponential because when your vehicle displaces air, you need to accelerate the air as you displace it. The idea of momentum is pretty simple, mass x velocity, but we are dealing with kinetic energy, and the formula for that is 1/2 x mass x velocity [squared]. I just figured out this regarding wind resistance!

I just wanted to add that using the same formula, accelerating 0-100 MPH would require four times as much energy as 0-50, which definitely figures into fuel economy.

[mjspiess]

I'm still using the Ford MAP sensor with my Rostra cruise control & it's working great.

[CrazyLee]

Originally Posted by LostCause

I don't think you'll be able to maintain 40mpg going up any long, steeply graded hill...going slow works to a point.

If it is constant throttle you seek, why not just hook the throttle servo to a potentiometer.

I'd imagine using a cruise control based on MPG might pose some dangerous situations. A car will shift its speed greatly as it is loaded differently throughout a drive. I can't imagine that driving 65mph, slowing to 40mph, and speeding up again to 60mph would be particularly safe in any form of traffic. If you are completely isolated, then I suppose it might be useful, but not as a daily use item.

I'm interested in watching any developments, though.

- Lostcause

I drive a large 26 foot motor home . Look for the Beast in the garage.

I have installed a MPGuino and Jcar module to monitor the fuel usage.

I get about 10.5 mpg using E10 fuel. The fuel mileage has gone down over the 5 years I have lost it because of the E10 gas.

Now, how do I make good use of the MPGuino? I now use my right foot except on very long flat roads I use cruise control because it isn't a reason not to

During acceleration the RV mileage starts at about 1.25 mpg. Each time it shifts up the mpg gets better. I have a 454 Chevy with automatic trans w/overdrive and lockup clutch. I accelerate as quickly as necessary.

Once I am in high gear I level off the gas at 50 mph. If the fuel is good, I can tell that right away. Once I have leveled off, I will check the instant mpg and keep an eye on it and the road.

Most cars and RV's are Fuel Injected engines and run on several modes depending on speed and load. One mode is acceleration. This mode adds fuel for more power. So don't accelerate! At least not up hill.

The desired mode is Lean Burn. The lean burn mode is descriptive, the ECU tells the FI to lean out the fuel. The engine likes lean burn but won't stay in it for long. Any small rise in the road will cause it to go back to normal fuel burn.

If I slightly release and press back down on the throttle the lean burn mode will come back. This is a very small release. I see 1.5 to 2 mpg more.

Here is the neat thing about lean burn. The ECU sees throttle position, manifold vacuum, air temperature and many other signals. When I am going up a hill I have found that if I hold the throttle very steady the fuel mpg will hold as well. The mpg will slowly go down but not go out of lean burn. If I wiggle the throttle the mpg will drop. I quit holding the throttle at 40 mph and press down for more speed. Then the fuel mpg will drop to 3-4 mpg. I was holding 10-12 mpg going up the hill.

Having the MPGuino has allowed me to watch for the best speed to go. The engine torque power curve gets strong at 1000 rpm and peaks at 1400 but it is very flat. The horsepower curve starts at 1000 rpm and peaks at 3600.

This is right in my speed range, cruising at 50 is about 1600 rpm. At about 3000 rpm I run about 70 mph.

This tells me that if I go faster I could get better fuel mileage by driving faster. This is because the engine is "On the cam" and getting better efficiency. That is is true, showing 10-12 mpg at 62-65, on lean burn, but I am usually slowing down. A tail wind really helps! I now do a pulse and cruise in and out of lean burn.

If I see a large hill before me I slowly increase speed. On an expressway I can go up to 70 mph. Once I encounter the hill I hold the throttle steady and go up the hill. My fuel mileage will stay steady since I had gotten a "head start" going up. I like to see 10-12 mpg while going over a big hill!

By watching the traffic and the terrain I can chose when I pulse it faster or let it cruise.

Because E10, E15 fuel is so bad, I am going to pure-gas. Known as E0 fuel. There lots of stations supplying it. I find it on pure-gas.org. Since I can go about 700 miles on my RV per tank full, I can plan out my gas stops. I can route right to the fuel stop with my Delorme Street Atlas GPS map. My RV has a 75 gallon tank. No, my MPGuino still hasn't had a proper calibration YET! it's getting real close though.

Ever get water in your fuel? With E10 in the tank the ethanol is very hygroscopic, meaning it sucks water right out of the air! That's why I am going to get E0 gas. E0 = No ethanol in the fuel

On my trip to Florida I noticed that the engine would sometimes die while running on the road. I knew what it was so I put more StarTron fuel treatment in. I didn't know how much water was in the tank, but the StarTron wasn't powerful enough to remove all the water. My guess is I had at least a quart of water.

I got stuck in Atlanta's famous rush our traffic when the engine died while going slow. This time I couldn't restart, and used up all the ether starting fluid I had. Now the starter died as well as the nose gear wouldn't engage.

With a $565.00 tow truck ride to Marietta GA to Georgia RV service, I got it repaired. New starter, new fuel filter. I still had lots of water too. No way of getting it out.

Anyway I was able to go south and watch the Detroit Tigers win some ball games.

Now you know why I HATE E10 gas!

Lee