Cruise Control (with MPG sensitive logic)

[oldbeaver]

Originally Posted by 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.

....

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.
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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.

....

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.

Cardinal Grammeter,

mpg yield on a car depends, among other things, on the following:

- quality of pavement
- slope of the road
- speed of the wind
- direction of the wind
- density of the air, (temp, humidity)
- weight of the car
- gear of the transmission
- traffic
- quality of tires
- hardness of tires
- altitude
- temp of the engine
- speed of the car (resistance of air is proportional to the square of speed)
- rpm of the engine
- power of the engine
- (I may be missing some more)

On turboed or compressed cars, the yield depends if turbo is active or not also, which depends on a combination of factors, such as rpm, gear, slope, computer map (transition or final), etc.

There are variable geometry turbos also, where even intervention of turbo and its effect on yield is variable along a wide range of rpm.

This is easily demonstrated just by looking a computer or instrument that shows you mpg of yr car in every moment. If you had gotten one of these, you would have seen that even over a "flat" pavement (that looks like), keeping all other conditions "equal"(that seem like), mpg varies a lot depending on little variations of slope, wind, or any other of the above.

Moreover, even setting the computer to show MEAN mpg of the trip, it variates a lot over time, depending on the conditions I mentioned above.

Am I missing something or you are talking about something of yr imagination?
How can you keep all these conditions fixed with yr throttle pedal?
I think that you can keep only one thing fixed by fixing yr throttle pedal: yr throttle pedal itself.

Please, explain how you control all of the car, engine, climate, topography and surroundings with yr foot.

OldBeaver

[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?

[Cardinal Grammeter]

NOTE: Someone needs to dig up some PW formulas for Velocity and Mass systems if they want the answer to this. If fly by wire, the pedal could control just about anything the engineer chooses.

[mjspiess]

What you are seeing in my videos is just an MPGuino indicating constant MPG and speed fluctuating based on elevation changes, wind, etc. With the Ford MAP sensor in place, the cruise control is getting feedback from the MAP sensor instead of the VSS, so it "locks" in the load of the engine and tries its very best to maintain that specific load just as it would if it was hooked up to the VSS.

Today was the first true test as I went to work and it's 95% highway. Minimum speed limit is 55 mph & PSL is 70 mph. I typically set my cruise at 57 mph. During the longest steepest hill, my speed would drop to 55 mph & instant mpg would drop to 34 mpg.

So once I got up to 57 mph, I steadied the throttle and hit set at 53 mpg. To my surprise, my car actually slowly sped up to 62 mph and pretty much held 62 mph at 53 mpg. MPG fluctuated between 52-55 mpg and speed fluctuated between 59-62 mph. During the longest steepest hill, my speed only dropped to 56 mph and mpg only dropped to 48 mpg. Max speed was 71 mph heading down hill.

As I exited the highway, my trip MPG was just over 52 mpg. I had to go to a different school this morning for work, so I had more city driving than usual. It ended up being 51.51 mpg for the trip. Not excellent, nor bad.

The question is...What would have been my trip average had I just used normal cruise and set the speed at 57 mph like I usually do? During usual cruise, my MPG would get as low as 34 mpg on the longest steepest hill and well into the 100s on the down side of the hills with stretches in the 40s, mainly in the 50s, some in the 60s and on rare occasions some in the 70s. It seems to me, it prob. all averages out.

I think the cruise must take RPM into consideration because it held my speed way better than I had imagined.

Also, while cruising, if I hit Accel/Resume my speed MPG locks in a few MPG low and when I hit Set, MPG locks in a few mpg higher, very similar to speed when normally hooked up. That is pretty cool when you're trying to figure the slowest speed/highest MPG allowable for the current road conditions. For my current route at 55 mph limited speed limit, it looks like 53-55 mpg is prob. going to be the optimal setting without having to "over ride" the cruise on the hills.

On my way home tonight I had 15-25 mph head wind. I was able to set the cruise at 49 mpg. It fluctuated between 47-51 mpg and I maintained about 56 mph with drops down to 53 mph and peaked at 71 mph. Trip average was 48.84 mpg.

Despite the head wind, the cruise still managed to do quite well.

[bnmorgan]

Sounds like what we need is a constant throttle position based cruise instead of constant speed, or at least a constant speed with max tps. maybe some hysteresis based on how much throttle for maintaining speed on "level" so that it doesn't surge to high throttle for uphill or high speed on downhill, like a plain constant throttle position or throttle lock (on my motorcycle for instance) will do. I live in a very hilly area, and often when i hit a hill i kick off the cruise and just rest my foot against the "hump" at the throttle position that was keeping me at speed, and let the car drag down to whatever speed that will maintain on the hills.....which can be 60 down to 40 at times.

[oldbeaver]

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?

Dear Tom,

This outcome looks very strange to me.

Fuel yield in (miles/gallon) is calculated as the coeficcient of:

speed (miles/hour) / consumption (galons/hour) = miles/galon

If you keep the throttle fixed, you may get a rather constant consumption in galons/hour. However, the miles you travel per hour will variate a lot depending on speed which depends mainly on slope.

Anyway, from another source of info, consumption of a diesel engine (probably any engine) depends "ceteris paribus" on two variables: throttle position and rpm. This is because the injector pump graph of cubic mm injected per rpm is convex if you look it from above, concave to the X axis, for a determined throttle position.

You have a family of harmonic curves where each represents a load, meaning a throttle position.

I got this information from BOSCH which is the maker of the injection pump.

However, as Diogenes said, "movement is proved moving", then I will check the same excercise you did with my car, before come to a definitive opinion.

Then we can compare results.

Until then,

Oldbeaver

[Cardinal Grammeter]

OldBeaver, the diesel stuff is very interesting.

I was trying to remember everything I could from that 4 hour MPG drive.

While the MPG = f(TPS) lets reference the Throttle Position Sensor, I'm thinking there was some "2nd order" fluctuation.

In other words, for fixed TPS, the MPG would vary a "few" MPG. maybe 5%

Since this is neglible when compared to changing gears or TPS, I did not specifically mention it.

Another compensating relationship:

• Lower load => Higher Vacuum => Higher Flow past Throttle Plate => HIGHER IPW per revolution. (where IPW = Injector Pulse Width)
• Lower load => Leaner Mixture => LOWER IPW per revolution
• So there is some cancellation. (Opposite true going up hill.)

As far as controlling the cruise control, MPG = f(IPW). IPW determines the amount of fuel leaving the fuel tank per revolution.



Could this Intelligent Cruise Control be used to maintain a specific IPW and hence MPG?


Tom

[oldbeaver]

Originally Posted by Cardinal Grammeter

OldBeaver, the diesel stuff is very interesting.

I was trying to remember everything I could from that 4 hour MPG drive.

While the MPG = f(TPS) lets reference the Throttle Position Sensor, I'm thinking there was some "2nd order" fluctuation.

In other words, for fixed TPS, the MPG would vary a "few" MPG. maybe 5%

Since this is neglible when compared to changing gears or TPS, I did not specifically mention it.

Another compensating relationship:

• Lower load => Higher Vacuum => Higher Flow past Throttle Plate => HIGHER IPW per revolution.
• Lower load => Leaner Mixture => LOWER IPW per revolution
• So there is some cancellation. (Opposite true going up hill.)

As far as controlling the cruise control, MPG = f(IPW). IPW determines the amount of fuel leaving the fuel tank per revolution.

Could this Intelligent Cruise Control be used to maintain a specific IPW and hence MPG?

Tom

Sorry Tom,

What do you mean with IPW?

OldBeaver

[mjspiess]

I managed to set the cruise at 60 mpg today on my way to work. It fluctuated between 57-61 mpg and maintained 57 mph pretty well. Top speed was 66 mph & slowest speed was 47 mph. I had to over ride the cruise more often, but my trip mpg was 56.26 mpg. I had a 10-15 mph head wind.

The cruise definitely takes RPM into consideration. Once I was off the highway, I got up to 30 mph & hit resume & it locked into 60 mpg at 30 mph.

The instruction booklet claims the cruise must have VSS hooked up in order to operate. I might try leaving it unhooked and see what happens. If it operates with just the RPM wire, I might be able to switch from MPG sensative cruise to RPM/speed cruise on the fly by putting the VSS wire on a switch. I will keep testing.

I set the cruise at 60 mpg on my way home and averaged 56.42 mpg. I had 5-10 mph tail wind. I didn't have to over ride the cruise as much with the tail wind and also, there is not as much traffic at night on my way home. I filled up before I left and drove 479.9 miles on 8.754 gallons for a tank average of 54.8 mpg. Top speed was 72 mph & average moving speed was 44 mph. That is up 1.32 mpg from my last tank. I was pretty surprised by this because I drove over 40 miles just testing the cruise control, all urban/city driving with idling, stopping & restarting.

Another interesting observation I made is since you can resume your previous MPG, once I get into town I can hit resume and keep my instant MPG higher than my current trip, so my MPG continues to climb until I get home. Of course, this is assuming I don't experience many stop lights.

[oldbeaver]

Originally Posted by mjspiess

I managed to set the cruise at 60 mpg today on my way to work.....
....

The cruise definitely takes RPM into consideration. Once I was off the highway, I got up to 30 mph & hit resume & it locked into 60 mpg at 30 mph.

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I set the cruise at 60 mpg on my way home ....

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Question:

What instrument you have to set the cruise at 60 mpg? I think you can slow down until getting to 60 mpg but this will last for a fraction of a second !

Please, explain.

OldBeaver