In air conditioning/heating t-stats used in residential homes and commercial applications their is a temp. differential adjustment. This determines how far from the set point it will alow the temp to vary before turning the unit on. In other words if you don't mind the temp variance, one can vary the differential from 1,2 or more deg. away from the set point so the temp can vary away from what you have adjusted the set point to be.

Using the cruise control I have noticed when going up a slight grade the auto. transmission will down shift and the throttle will modulate in order to maintain a constant speed (or at least very close) . Driving the car without using the cruise, one can allow the car to slow down a little while going up a slight grade without downshifting and thus saving on fuel.

What I would like to know (see happen) is how can the cruise control speed differential be adjusted to allow the speed to vary more before forcing the trans to shift and opening the throttle.
Of course this would be something in the electronics that would have to be accessed and points changed. I dont know if it is possible but it seems like it could save fuel.

Anybody know about how to go about finding out about this idea?
Thanks

 

You’re referring to what some people have termed “load-based cruise” or “throttle position-based cruise”. And it would work exactly as you describe. The cruise speed would be based not on the actual speed of the car, but the load or TPS (throttle position sensor) reading at the time you set the cruise. It would work by setting the your desired speed on a flat surface, but unlike normal speed-based cruise control, the speed could, and would, fluctuate with grade changes.

This would be a huge plus in the fuel efficiency of all cars, and has probably been looked at by the OEMs, but I see a few potential problems/hazards. First, while overall speed wouldn’t be an issue on uphill portions of road, it could be a potential hazard on downhill portions, especially long downhill sections. If unregulated, the cruise would continue to push the car faster on downhill sections while trying to maintain a certain engine load or TPS reading. This could obviously lead to some major speed and subsequent speeding tickets and/or accidents. I’m convinced this is the number one reason why the OEMs haven’t already installed the system in current vehicles. The technology is already there, so it’s a freebie cost wise. Educating the general public on how this different type of cruise control system works would take a while and a form of governor would have to be hard coded into the computer to set a maximum speed above the set cruise speed that results from a certain load/TPS reading at the time of the user setting the cruise. Still, I don’t think it would pass legislative muster given the fact that you are giving the user a system that could force them to unwillingly break the law with regards to speed. Nevertheless, I would love to see such a system.

 

your car knows what's best for itself more than you know what;s best for it. if you floor the gas pedal to go up a hill, that is putting a lot of load on teh engine. if you had a scangauge, you'd see that. also, flooring the pedal makes the MPG drop nearly to 0

 

Crazy thought...what about implementing some sort of acceleromator(spelling?) sort of like a Wii Remote? I am definitely not an engineer and will not pretend to know much about how those work(though I am an IT guy), but it seems to it could be feasible. If the car is accelerating at a certain rate and the sensors detect a certain grade / slope, automatically adjust the cruise up or down...

Yeah I know. It's crazy and probably wouldn't work, but anything to divert my attention away from work after a rough morning...

 

This may not be a correct response to your question, but I know that if you do wish to keep it in 5th gear on the highway and are in cruise and have a sport, simply leave it in manual mode, with paddles engaged and put it in cruise, the only thing it will do is unlock the torque converter for some hills. I have heard though that engine RPMs aren't half as important as throttle position and since CC is designed to be the most economical, this could be a reason they engineered it this way. It's not a throttle position based CC at all, it's based on speed solely, believe me I live in CA, LOTS of hills and it does great on them! Just don't be afraid to let it rev your engine, it's a Honda

 

I was hoping to just see a possible adjustment in the programming that would allow the speed to vary more than it does stock. Instead of trying to maintain a speed +/- 1-2 mph, allow the speed to drop a little more (3-5mph) before the cruise would force the speed back to set point.
This is like the way I drive without using cc.
Loosen up the allowable variance from set point.
Possibly have a selector switch that would allow the user to chose between maintaining speed as first priority, or ECO mode which would allow more "slack" in the program so to speak, (less aggressive mode.)

 

Since the Fit is drive by wire, I'm pretty sure that the cruise settings are programmed into the ECU, so if you know somebody that can tune the Fit's ECU you could probably adjust the settings in there to do just what you are thinking of.

 

Right! I wish I knew that person!
I dont know where to start looking other than here?

 

I travel on I-80 between Kearney, NE and Omaha, NE twice a month. It about a 174 mi trip. And it has some signifcant hills (for the Fit, anyway)

My Fit does exactly what you describe, and it is particularly annoying to me because I have a heavy foot. When on the interstate, I set the cruise at about 85-90. At these speeds, engine runs 3300-3500 RPMS. When going up a hill, it goes down to fourth, resulting in RPMS of 4500-5500.

After a while, it gets really annoying! So I put it in S mode and lock it into 5th. Speed only varies 5-6 MPH!

 

What kind of gas mileage are you getting with cruise at 85-90?

 

As surprising as it may be, about 33-35 mpg. The Fit usually uses about 1/3 of a tank to make that trip (give or take a gallon or two). Again, its about 175 miles. However, weather is a major factor.

Once I made the trip from Omaha to Kearney with a tailwind of about 30mph. That trip took only 1/4 of a tank. I was really happy!

Funny, but unrelated story. I was filling up in Kearney, before going home. The gas station I went to had abnormally cheap gas. I found out why. After I finished filling up, I noticed a sign on the pump that was literally the size of a postage stamp that read "This gasoline contains 25% ethanol. For use in flex fuel cars only."

My heart sank. I just knew I was gonna have to endure the cost of new a new engine. I went inside and yelled at the gas station owner and and called my Honda dealer in Omaha. The service tech I talked to said that it was safe to drive. And that he owned a 07 Fit and he ran it on E85 cuz its so cheap. And the he's done so since he owned it, over a year ago. No mods.

Anyway, through that tank of gas the Fit was extremely peppy (more than normal). However, when I got to Omaha, the gas light was on. Needless to say, I won't be going back to that gas station ever again.

 

Back in the day when you could buy an aftermarket CC it was tunable. You could make it less aggressive. That is doable if you could modify the ECU program.

I'm a controls engineer and if I could design one from a white sheet it would have a 2nd Eco mode. In this more when you changed the "set point" it would be setting the desired manifold pressure. It would be the best way to do what you want.

It's all academic because the Honda ECU in a black box and no that I know has any way to modify it even a little bit like taking the Gain and Reset in the CC loop.

other options to consider....
I have not looked at mine yet but there is a servo that controls the throttle and may be a separate one for the CC. If there is you may be able to restrict the vacuum if thats the power to move the throttle or use a capacitor filter to slow it's response. Theres a good chance because it's FBW throttle that the servos is the same for normal throttle. If it's like that you can mess with it at all.

if this helps hit my rep.