To cruise, or not to cruise??
 

OK, here it goes.

Was doing some thinking, and some experimenting. This is basically what we've got.

In most "modern" vehicles, the cruise control module is vacuum driven. The basic function of cruise control is to maintain the set speed during driving conditions. With an auto tranny, this means that the CC will go to WOT at times, in order to downshift and maintain speed (especially on inclines). In a manual transmission, the CC will go to WOT, but is locked into whatever gear you put it in.

If you live in a flat area, (Kansas, OK, Northern TX, etc...) this is fine. No inclines = constant velocity = better MPG. If you don't live in the flatlands, using CC can hurt your MPG with the downshifting and what-not.

What about using a manual throttle control?? Something similar to a hand-throttle setup, except with the ability to lock it in place?? This would maintain throttle position, and therefore would provide most of the benefits of CC without the constant throttle changes (the cause of the bad MPG).


The only thing that has me concerned about using a hand throttle is the "what-if" situation. What if I need to panic-stop?? When using the CC, it is automagically dis-engaged when the brakes are applied. Any ideas on how to do this with a hand throttle??

I agree with you with using a manual trottle for better MPG. It is what I experimented lately. My hand lever trottle is locked in place by friction and therefore maintain trottle in any position from 0 to 85 engine load.

About security ? No need to panic here ! I got use to it quite fast and it is like not forgetting to take our right foot off the gas pedal. But I forgot a couple of time, and on applying the brakes, the car just stopped as usual, the brakes being much stronger at stopping the car than the little power of the engine trying to keep going. But on releasing the brake, the car accelerated slowly in a lower gear since the smart car has a sequential semi-auto gear change.

I think one of our members here has put a hand throttle in his Civic.

My father 1967 Fiat 850 Coupe had a hand throttle from the factory. It was to be used with the choke to set high idle when warming up the car. Fiat knew what folks would use it for so they integrated it into the throttle, clutch and brake. If you touched any of the pedals it would disengage. My father used it as a CC. They are even better than a CC because they fallow load driving principles.

psy

This was discussed at length in another thread.

I was thinking that if you already had a CC system and wanted to retrofit it as a fancy hand throttle, you could fake it out and change where it's getting it's speed feedback (halleffect device or optoisolator pulses?). The shutoff mechanisms and functions (clutch, brake pedal, emergency brake) would remain unchanged.

I'm not sure of the existing circuit design, but instead of getting the feedback from the driveline, inject pulses from a constant oscillator - a simple/cheap circuit you can DIY with a 555 timer. If this worked, you could even make it "dual mode" by switching between your oscillator pulse signal and the oem feedback source. You would want to make sure you disengage the CC before switching between modes (should be made failsafe as part of the switch).

If the CC control is part of the ECU, then I'm out of my lane here.

some cars have electronic CC so you would have to look in your car to find out which it has. but why not put your foot barely touching the pedal then disenguage cruise control (its one button..) when you see an incline up ahead. if you live where its constant hills then yea maybe some type of hand throttle would be better. you could get one of those lawnmower type throttle cables and run it to your throttle cable on the intake. or do what that one guy did and screw it to your gas pedal(wouldnt work in either of my cars, no space between pedal and tranny tunnel.) dont make somehting that would get caught on your foot if you had to make a panic stop....cant save gas if you cant drive a car...

While I can't say for sure, I think electric and vacuum operated cruise controls have a similar interface for the actuator itself: safety clutch, accelerate, decelerate. Thats how it seems to be on Honda/Acura vehicles anyway.
If that's the case with your car, you already have simple 12v+ signals to the actuator to increase or decrease the throttle opening... They could easily be wired to buttons. You could set up a pair of relays to operate the safety clutch in such a way that it would require no additional driver input in a panic-stop situation. The first relay is initially triggered by a momnetary push-button. The contacts supply power to the clutch and also back to it's coil so it latches on. The second relay, triggered by the brake light circuit, breaks the connection between the coil and contact of the first relay, cutting power to the safety clutch.

I will have to look into the wiring for my CC modules. I'm not the most comfortable with hacking into the wiring if I don't have to.....

I was looking more into something like this -- https://www.jeepforum.com/forum/showthread.php?t=311475 Not only will this allow me to maintain throttle position, but it will also allow me to control idle speeds in the case that I need to (i.e. running a winch, several lights on the job site, OBA, heavy use of pwr. inverter, jump starts, etc.....) Again, the only thing I'm slightly concerned about is the "oh sh*t" situation. Antoine, I'm not sure exactly how my Jeep will react to both brake and throttle. The 4L puts out one hell of a lot of HP and torque, especially on the low end of the power band.....But it may be something I have to deal with.

You won't stop in 4L, and you will slow down in 2HI and 4HI but if its is going heavy on the throttle you brakes aren't going to do much. In a panic situation you would might want to just leave the throttle alone and drop the tranny into neutral. It'll redline and sound like its going to blow up, but you will stop.

Most hand throttles, either RE or home made come with a cable lock to keep it in a single position.

Since the ECU used in later 4.0s are based off the Renix ECU I'm assuming that cruise control works the same. Meaning that it takes its reference signals off the VSS on the t-case's tail cone to figure out speed. It gets all directives from the ECU though, so I don't think it would be that easy to intercept the signal.

I'm going to have to disagree with you on this one. I've never seen a vehicle with good brakes where the engine could overcome brakes that were solidly applied. Your stopping distance would be greater but you will stop. I used to drive a semi many years ago and had the trailer brakes lock up while going down the freeway....brought me to a complete stop pretty quickly even with full throttle and the engine had close to a 1,000 ft/lbs of torque.

-- Scott

Usually, yes the brakes can stop the car, but atleast on my Jeep the brakes suck royally. I tried it once, engine wanted to stall, but it kept lurching forward.