Cruise control for constant throttle rather than speed?
 

It seems like there would be a way to do this, but I'm not sure how...

The only bump I've been able to get in the mileage on my '96 Suburu Legacy Wagon (auto tranny:mad: )has come from wedging my foot against the tranny hump and trying to keep a constant throttle and let the speed fluctuate between 40mph uphill and 65mph going downhill.

It seems the cruise control could be rigged to do this too, any ideas?

********Update and pics are at the bottom************

just a thought (might be stupid) if you are worried about throttle opening, why don't you do something to limit your play. you could put a restrictor plate behind the throttle body. or an even wilder idea is to put something behind the gas pedal to limit movement. I wouldn't recomend that because there may come a time when you need it.

you could rig up a stop that is on a pretty heavy spring to that you can go past that point if you want to but you will know when you hit it. I am speaking all mechanical that doesn't even touch the pedal until you depress it far enough to contact it. that way you know where that limit is but you can punch it if you need to.

*edit* not as good as the cruise idea but probably simpler to execute

The best way to do this would probably be low-tech, maybe a remote-operated clamp on the throttle cable or something...

A locking throttle cable? Motorcyclists have added these devices for decades. There is enough friction to prevent the return spring from closing the throttle plate, but not so much that a roll of the wrist can't overcome the friction of the grip when a flip of the release lever isn't quick enough.
But in a car there's no easy means of closing the throttle by pulling the pedal up

this may be way out there but you could set up a series of proximity sensors (maybe magnetic since the gas pedal is metal). you could rig up a series of LEDs that could tell you where your sweet spot is. you could monitor this so that it was in the same place (relatively) all the time. this way noting contacts the pedal or restricts your movement and you know where the pedal is and where it should be. it would take some time to rig up and set to the right throttle position though

sorry for overthinking this but it is an idea and I was talking about a completely stand alone system that is not hooked to the car in any way other than the battery.

I believe the Scangauge will display TPS voltage, you could use that as feedback to maintain a constant throttle setting manually.

Hmmm thinking of magnets... thinking a strong electromagnet close to the cable might lock it, then you could rig an on/off switch, with a light sensor override with the beam cutting across the tops of the pedals, so it would cut off immediately when your foot went for emergency acceleration or braking and broke the beam. Well, maybe you'd want to rig a set/reset pushbutton and latch it through electronics rather than a switch.

The easy way to do it is to disable the cruise control from opening and closing the vacuum servo that moves the throttle cable either by fixing the power that keeps them closed or open and yet still have the vacuum release on the brake / clutch pedal for safety. I think I will try this on mine once I get into the circuit a little since it will be easier to increase and decrease throttle if I have control of the valves that regulate the servo. I would also like to see when it is adding and removing vacuum to vary the throttle with a red/green led.

a friend of mine at work told me about the "old" cruise controls they had when he was younger (he is 61). He said they used a throttle cable hooked to the carburator that held the flap open a certain ammount and it had a thumb nut that held it into place. the problem (he said) was that it had no override so if you had to quickly slam on the breaks then you were fighting the engine with the breaks until you released the cable.

I think you could apply this to a throttle body but I would do it with caution. this sounds a little on the dangerous side and thus the reason they don't do it anymore.

hopefully the description above paints a descent picture. I haven't seen it, I am just going off of his description. he said himself that it wasn't verry safe.

The adjustable stop with a heavier spring sounds like the most straightforward idea to me.. Easy and cheap to implement and nothing really dangerous to go wrong like could possibly happen with clamping the throttle cable.

After reading all the posts I think I'm going to try a low tech variation of this.

Starting with a ball of playdough under the pedal to find out how much throttle I really use on commute, and then a length of screen door spring adjusted to that pedal position running from the pedal arm up to the lip of the dashboard.

Hopefully the spring will be just enough resistance to let me know when I'm "there"

if and when you do this, post some pics. another idea is to use multiple springs that aren't so high of tension so that you could vary the tension by adding more or taking some away.

The off roaders have been using something like you want.

jeep_throttle

custom-home-made-hand-throttle

You can always use an old T shifter and a friction base to hold the shifter in place.
Not too tight just enough to hold it in position. Push forward more throttle, pull back less throttle. If you have a console in the vehicle then you could align the T shifter so you can rest the shifter in your palm.

*****s U C C E S S ****
 

Ok, well, maybe it's not that exciting, but it was cheap and easy.

First I went to the hardware store, $14.95 for a screen door spring. That's not happening.

Then I went to that bastion of quality goods, The Dollar Store. Got one pack of PlayDough, (generic) and one pack of... bungee cords. Not the good multi strand ones, but the cheap, flat ribbon-like ones, with the plastic connectors rated for no more than, say, 3 lbs of pressure. Not what you want to hold your luggage on the roof for a long vacation, but for this, perfect.

https://www.fuelly.com/attachments/fo...d58651a778.jpg
Took the PlayDough straight out of the can and put the whole thing under the accelerator pedal. Gave just a bit of resistance, and after letting off would easily go back to that point and then more resistance as it squished. I gave it too much gas coming off the exit ramp and had to stop, reshape the silly putty and continue with a lighter throttle pressure. I was shooting for just enough throttle to get me up the hills at 40mph (the lower legal limit) and not use any more throttle than that.

When I got home it looked like this:
https://www.fuelly.com/attachments/fo...b831f7cf53.jpg

I put it back under the pedal and gently pushed down by hand to get an idea of how much travel I was using.
https://www.fuelly.com/attachments/fo...4de9e98ff7.jpg
It obligingly stuck to the pedal making the next step much easier, where I used the plastic hook on the bungee to go around the armature for the pedal. Then I hooked the other end onto some sturdy ductwork under the dash.
https://www.fuelly.com/attachments/fo...07d45d4fe9.jpg

Then I pressed down on the pedal until the PlayDough stopped it again, shortened the bungee to that length and tied the shortened end off with a half hitch.
https://www.fuelly.com/attachments/fo...e63ae0fcf6.jpg

Then I went for a ride. Sure enough, I could feel definite resistance when I got to the end of the slack in the bungee. But if I needed to floor it I could. When I drove my usual route to town with the pedal just at the bungee's engagement I was doing 68mph downhill (65mph limit) and about 37mph up the steepest hill, so I had to give it just a *little* juice to stay legal. (40mph minimum)

Average speed, surprisingly, was above 55mph. (not from a scangauge, just my observation), so I think my next area of improvement will be from aerodynamics. There is hope.

that is awesome. I figured it would take a lot to accomplish what you wanted to (originally). that solution is simple, effective, and still safe. oh yea and the most important COST EFFECTIVE (you know what I mean).

Now if I can just break 28mpg with it... then I'll be happy.

Good on ya'

Nice solution.

just curious, how much PM (preventative maintenance) have you done? you could change plugs, wires, fuel filter, air filter, and other wear items on your car. it would be hard to say how long it would take to see a return on your investment.

a grill block really helped me and so did the WAI (warm air intake) I have heard that the WAI doesn't work for everyone though.

my goals have changed since I started. I originally wanted 50mpg and then reality set in. then it was 35mpg and now my new goal is 40. it seems that my mpg is steady going up though. I figure I will plateau here pretty soon but that is OK too.

PM happens next week, as well as a check by the mechanic. Then comes the grill block, rear skirts, belly pan and then a mini kamm back.

Plugs and wires on this beast are EXPENSIVE (and I think you have to drop a wheel to get to one of them. Thanks Mr Engineer, for that kind design feature.)

I would like to get back in the 40's, but I think that's not likely in this car. I'd be pretty delighted to go from 21 to 35.

I got a nice little bump from changing the fuel filter. It was a lot easier than I thought and it was I think $6. I did change my plugs and wires but they were a little pricey and it will probably take a while for them to pay for themselves.

you may want to check into a WAI as well or at least read up on it. there are mixed opinions on it. I had a very positive experience with it. see if anyone else has a vehicle like yours here and see what they have done.

I went to the "garage" and searched for "cavalier" of course you wouldn't do that because you have something else but you see what I am talking about. it is always good to use other peoples trial and error to see what others have done.


if you have some free time, there is a member on here that has his own site www.metrompg.com and I know you don't have a metro but a lot of his info will work on any car and he has other good articles. it is a lot of info but it is good info.

This is a very interesting idea! I gave it a try today using my ScanGauge II to tell me the throttle position. It seemed to work quite well with the TPS at 13, which gives me a level cruise speed of 55. Up steep hills I had to add more, of course. Tempts me to look into an aftermarket cruise control...

The bungee cord is great, but I was thinking about what a more refined version of that idea would look like. Really, you need a snap action mechanism I think: puts up a lot of resistance right where you want to be, but then if you keep pushing, it eases off so driving at higher throttles doesn't get tiring. Here is a crude picture of one way this could be done (there are many possibilities, some probably much better; this one is good for illustrative purposes). The bottom piece is a cut strip of metal, with a sharp ramp and a shallower one. The small rectangle is the side view of a swinging arm that is spring loaded to bear against the other piece. You can imagine that to get the arm to climb the steep ramp against the force of the spring as you try and slide it sideways would be difficult, but once you'd cleared it it'd get easy (as would be the reverse direction, so it could slow down automatically). In theory you could have more than one position. I doubt it'd be worth doing in practice, but it made for some fun driving time speculation.

https://www.fuelly.com/attachments/fo...c0848f1dd6.jpg

Thinking more practically, for a single position you'd just need a disconnector. Picture two tubes, one inside the other. There'd be a spring loaded, spherical end pin in the inner pipe and a slot in the outer. When that pin comes up against the end of the slot it'll resist, but then once it is pushed in and retracts it won't resist any more. Since a pipe can push as well as pull, releasing the pedal would reset it. Now that's something that could actually be built reasonably. Still not worth it, most likely, but now the concept should leave me alone! :)

I've got one. I don't use it for cruise control per se, but on long rides, it lets you take your hand off the throttle and stretch out. It's a simple flick of the thumb to disarm it, but in a car I agree it'd be a lot harder...God forbid you get in an emergency situation, I hate to think what might happen if you couldn't get your throttle control...

Cruise control for constant throttle rather than speed
 

FamiliaGT had mentioned to me the last time we were working on cars that he heard that some of the cruise control parts from a different model I think it was an MX-6.... dont remember what gen were interchangeable. IF thats so, then it might be easier to find all the parts more quickly. My question to everyone else is, "what have you guys heard?" Can some parts from other models be used? Have any of you tried this?

Here is what I discovered with the Dakota;
With the speedometer needle touching the left side of the 65 MPH hash-mark, the truck got better gas mileage than if the speed was set so the needle touched the high side of the hash-mark. This was done for hundreds of thousands of miles and using the cruise control.
The point is, there seems to be a point in the computers algorithm where the optimum performance is. Find it with your vehicle and you'll get the best mileage.

Yup, Marvin has "sweet spots" like that, I think it's more due to intake and exhaust tuning.... because you can hear a slight difference.

His sweet spots are at 95kph, 105kph and 115kph when "in draft"

Wile-E is difficult, something is twitchy with him at the moment, you have to feel your way into it every time, which takes about half hour of driving so I can't hit them every day.

Since I'm too wimpy to risk my warranty installing an aftermarket cruise with custom electronics, I was thinking about how to actually build a practical snap action pedal stop. I can lathe the ramped cylinder in the center easily enough and the pin would be spring loaded (flat spring would be very easy, but I can't get that locally). As usual I've botched the scale, but the ends of the outer tube and inner rod would be fixed so pulling them apart would bring the pin into contact with the ramp, creating resistance which would then go away once the ramp was cleared and would only be in one direction. No need for a roller with such low speeds and cyclic rates, although I might want to round the end of the pin a bit. I could add more than one pin if I wanted several resistance positions for various speeds. I think this will work pretty well so now I need to examine how to actually mount it and what size it'd need to be. Getting the resistance right will require a bit of experimentation.

https://www.fuelly.com/attachments/fo...bba969ab12.jpg

I was thinking of better ways to design the snap action and while I came up with a few, I decided that I don't like the entire paradigm. Really I want a system I can lock anywhere and that, like a cruise control, sets the minimum throttle, allowing me to go higher than that without disengaging it to climb hills. I have a rough design in mind, but want to sleep on it a bit before drawing it up. While it could be manually operated, I think I prefer a solenoid lock so that various automatic disengagement systems could be used. I also like the idea of a safety kill switch just in case, which would be harder to do mechanically.

GM has done similar stuff on their throttle by wire cars. They put springs in there that get progressively much stiffer over the entire travel of the pedal.

There's also one manufacturer that experimented with (or produced?) a force feedback system that pushes the pedal back at you. Why it had to be an active system instead of a spring, I no longer remember...

If you're thinking of the one from Nissan, it's linked to a system that estimates optimal fuel usage based on the conditions.

That's the one. Good job finding it. :thumbup:

Well I have a rough outline of the mechanism. A pivoting arm will be held against the gas pedal arm by a very light spring. There's a solenoid operated brake on that arm to hold it in place and keep the gas pedal from retreating beyond that point.

Now I just need to figure out all the details. Only two big ones: how to mount it so it can be removed quickly (warranty) and how to implement the brake. I need a system that I can be very confident will never lock up. That would be bad.

I took a look and things are pretty tight under my dash around the gas pedal. I'm not feeling very confident I can come up with something that'd be easy to build and easily removable. I could fit a spring in, though, so maybe I'll try that simple system. I don't hold the pedal down for long periods anyway.

It probably is possible, but it is not the most efficient way to drive.

There is a difference.

Cruise Control.
Cruise control has always been meant to keep an assigned speed.
Cruise Control has worked off the speedometer or, now that everything is electronic, the computer.
Because the computer is in charge, the engine always runs optimally.
Once, it was inefficient MPG wise but now the computer is so good there is little difference between the MPG the vehicle gets by itself and the driver's foot.


Hand Throttle.
The hand throttle works by holding the throttle at one setting.
Vehicles started out with hand throttles so the driver could keep them running while using the choke while the engine was warming to operating temperature.
Hand throttles were useful to keep speed.
And also, in the case of utility vehicles like the Jeep, to ford deep water and keep the feet off the floor and from getting wet, also to run the PTO and drive pumps, saws, drill rigs and all the other tasks that could be dreamed up for them.
The drawback of the hand throttle is that the engine can run outside it's performance envelope in hilly country, racing and lugging, neither of which does any good at all.