Throttle-Position Cruise Control

[rh77]

I've realized lately that constant throttle on hills has been a key element for me to gain FE.

I see the best results when the TPS sensor registers 19-20%, and I hold it there the best I can, but gravity usually takes hold and that number creeps up.

For long trips, would it be possible to design a throttle-position limiter, that can be actuated through the cruise control? My thoughts so far:

Since I have CC with a cable that runs parallel to the throttle cable.

* Is there a mechanical way to set the cruise, and limit the "tug" on the cable to that 20% mark? I haven't cracked-into the CC unit (out-of-town), so I'm not sure what's in there.

* Or, is there an electronic way perhaps to interrupt the speed sensor signal and produce the voltage it wants to pull the requested throttle input?

I've thought about putting a measured block of wood under the pedal and just romping on it, but with that, I can forsee disaster -- what if I need more throttle in an urgent situation?

RH77

[Matt Timion]

Of course the easiest solution is to have a cable that locks into place that is also attached to your throttle cable. I think that JC Whitney sells something like this, or perhaps it was another link someone posted a while ago.

Or perhaps you can have the gas pedal somehow rigged up to click and stay locked at a certain position. It could be moved still with a little pressure as well.

I think that both of these approaches are going to be MUCH easier than dabbing with the electronics.

[onegammyleg]

Almost all of the 70's Fiats and Alfa's (probably Lancias too) had hand throttles.
Usually placed down near the choke knob it was a similar cable to that used on chokes but instead it pulled on the throttle linkage.

Its not the sort of thing to use in the suburbs for obvious safety reasons , and I guess that why they always put the knobs in hard to reach places.

When I drove across Australia in a Fiat 125 Special we used it a lot and it was a great feature.
In a car that didnt have much power it would be a pain as it would slow at every grade , but the Fiat had tons of power , so it would go up hils and not loose much speed.

[rh77]

Originally Posted by onegammyleg

Almost all of the 70's Fiats and Alfa's (probably Lancias too) had hand throttles.

That sounds like a good solution as well -- providing there would be a way to cut the throttle in an emergency -- similar to cruise disengaging when the brake pedal is depressed.

I think both you and Matt have the right channel -- to mechanically go about it.

I assume that inside the CC control box, a servo rotates and draws the cable around a cog? If so, a clamp could be placed on the cable or stop-screw if a servo is involved -- that way the emergency throttle cut, using the brake, could be preserved.

Those hand-throttles sounded pretty cool. If you're cruising out in the middle of nowhere, it had to have been a huge convenience.

RH77

[zpiloto]

Maybe something as simple as a big spring, hard foam, bungee cord etc under the pedal so that when you get to the TPS of 20 it hits the spring and you known where it's at with out having to stare at the SG. Then of course if you need more you can easily push more. The object being that when you hit the resistance you know your at the TPS you want.

[rh77]

Well, I tried it on my trip today, and it needs some fine-tuning.

Basically, I opened the housing of the cruise-control servo assembly. Inside is essentially what looks like the throttle-body control attached to an electric servo. It has a metal stop on each end for zero cruise, and maximum cruise throttle. I found if you wedge a hex-wrench in there, then the arm rotates and stops depending on the size of the wrench. I got it to limit the cruise to 25% TPS, so I need a bigger wrench. It's very sensitive -- too big and it doesn't engage. Then, a couple of zip-ties and it's good to go (experimental only -- probably will clamp it in if it works.

RH77