Cruise Control (with MPG sensitive logic)

[2005_rs]

I'll probably have time to poke under the dash today and get some data.

Step one: to make a signal generator to replace the vss signal.

Step two: link the new vss signal to the throttle position sensor so that when the accellerate button is pushed, the 'fake' vss signal will increase. This should fix the problem of the cruise pushing the throttle to wide open due to a lack of feedback. It also means I don't have to hack into the cruise control itself. Unfortuneately, the TPS signal is variable voltage, not variable pulse like the VSS.

As I write this, putting in a ford MAF sensor and linking to that like another poster did is starting to sound like a simpler solution.

[rjacob]

This page here (Vehicle Speed Sensor Questions: Questions About a Vehicle Speed Sensor | Suite101.com) suggests the output of the VSS is 0.5 volts AC.

[JasonG]

Having a steady throttle setpoint may not be so good of an idea.
Removing the feedback loop from an analog circuit often causes undesirable results.
The very little part throttle needed to cruise on level ground can cause the vehicle to slow severely up a hill. While this can be corrected by a bit of right pedal, what happens when the reverse is true?
The vehicle will continue to accelerate downhill, possibly to a dangerous level.
A control circuits logic needs 3 parameters, a setpoint, a reference input and an analog output.
When watched on a graph, they get real funny when the input doesn't respond to the output. The PID gets more aggressive trying to make them match.
Given a reference that "behaves", as with the Ford MAP sensor, they will modulate correctly and "settle in" as tests show.

Readers Digest version: Controllers need real feedback not a faked signal or thay doan work so good.

[2005_rs]

I don't think I'm going too far on a limb here. Many motorcycles have a throttle lock for highway cruising. Obviously, if going up or down a steep hill, adjustments have to be made. I wouldn't do this on my ford taurus because it has a lot of momentum carrying it down a hill. The echo; not so much.

My VSS reads 2.1 V AC and the Hz changes with speed (as I would have hoped) from 0 to 80 HZ

[oldertech]

I know this is an old thread, but I stumbled on it and it made me think of my grandfather tonight. Years ago he had a device that was sold commercially that hooked up to the throttle and held it at a constant position. A lever set the position to the desired speed and you could move the lever up or down to tweak the speed. There was one safety feature that would disengage the thing if you stepped on the brake. It had a solenoid that released the mechanism. My guess is that something like like this would accomplish what you are talking about. It would drive all the other motorists crazy, but then it's not much different than me staying in leanburn in traffic. My grandfather's device was chrome and kind of ugly and probably only made to work for cars in the 50s and 60s that had big dashboards, etc., but for it's time it was a ecomoder-type device. All I have left of that device today is the solenoid

[Hugh Jim Bissel]

Originally Posted by Zotz

Perhaps a little cross pollenation: jeepers use hand throttles a lot offroad and it's a simple mod, probably adaptable to most cars. Here's an installation.

Many simply get the parts from a bike shop. Goes unsaid that you have to be a bit careful using it.

Thank you for the inspiration. I made one of these for my car in preparation for an out of town highway trip and it worked great! Though it was more to give my right leg some relief than for mpgs. (Here's my build thread)

I did it kind of quick so it would be ready for my trip, and had improvements in mind to add later, but since it looks like I'll be upgrading to a car with cruise control in a month or two I put the improvements on hold, but my vehicle upgrade set me to thinking about stock cruise controls:

It seems to me that if the transmission were prevented from downshifting a cruise control provides a form of P&G. With the cruise set, when a hill is encountered, the speed drops and the throttle is increased to compensate. If the speed doesn't return to the setting the throttle will continue to increase. If at full throttle the ECU over-riches the air/fuel mix, than limiting the throttle travel might also be required.

On the downhill, when the speed returns to the set speed the throttle is released until the point the set speed is maintained. The main downside is that if the hill is steep enough to permit gravity alone to maintain the speed the engine will DFCO instead of neutral coasting, but a modified cruise could suffer from that same problem. (And perhaps a hand throttle or other mod could be used to keep the engine out of DFCO.)

I may be way off base, and haven't had a chance to compare techniques with any sort of documentation; this is just theory, (and perhaps flawed theory at that). Just thought I'd add my 10 cents (inflation is affecting everything ) to the conversation.