Strange cruise control behavior?

[Indy]

When I am using the cruise, and I tap the brake pedal, the first small increment of pedal movement causes the brakes to be engaged, but the cruise does not shut off. Then if I depress the brake further, the cruise drops out of its set speed.

This cannot be right, can it, since the brakes are "dragging" while the cruise speed is being maintained?

[Frank Hudon]

the first small amount of brake pedal movement just starts the regen, no brake application the next small movement activates the brake light circuit that dissengages the CC. If the pedal travel is more than I'd say 1 1/2" the brake light switch might need adjustment.

[xevious]

You might want to have your brake switch inspected. This could be a sign of misadjustment or impending failure.

Were you eligible for the brake switch recall? If so, did you have the switch replaced?

[KTPhil]

If it's an '04, have you done the brake switch recall?

[DanMan32]

Not all '04s get the brake switch recall. Looked last night, even though I bought the car in August, it was mfd in June.

[Indy]

It's an '05 and it has done this since I got it.

I will have them look at it when I take it in for its next service.

I have learned to pull the cruise switch toward me to fall out of a set speed, which should be more efficient if I am not planning on braking otherwise. I have also learned that on anything other then a very flat, straight stretch of road, I can do better with MPG than the cruise can. But, sometimes I use it anyway for convenience or to ease foot fatigue.

It is a concern if it is related to the brake light switch, as I depend on brake taps to warn tailgaters of impending stops.

[Brian K]

Hi Indy,

I've found the same thing re: cruise control. I can do better re: mpg than it can by my maintianing semi "constant throttle" than it can by maintaining constant speed.

No surprise there, pretty much any vehicle does better with constant throttle. A simple software upgrade should accomplish this for us all and save our throttle foot. Fuzzy logic would make the "constant throttle" liveable since true constant throttle would get one run over by a semi'.

Brian K

[Indy]

Brian,

I have given a lot of thought to a system or set of directions that would maximize mileage and have decided it cannot be done.

Only you know what you are planning to do, and only you can interpret the myriad cues and signals you get on the road. Only you can make those critical safety decisions, like whether a constant throttle would be dangerous on a particular stretch of road at a particular time.

The bottom line is that you must make those decisions all the time, and your throttle position is the way you control the machinery to best accomodate those decisions. I like the cruise control because I am lazy, but I can get better mileage with my own brain than any fuzzy logic could manage.

[Brian K]

Good for you, that you're so certain. I don't agree.

The reason criuse control doesn't get max efficiency is because of it's slavish desire to maintain a given speed regardless of cosequences. In this case gas mileage. Another gent called it "too agressive a control" I agree with that phrase.

We have computers on board and an LCD. It's just a matter of programming and a (maybe but doubt it) different cruise control to allow the user to select an acceptable speed/acceleration range for the CC to maintain. Assuming of course the computers can accept the additional lines of code. It might even allow user input to the minimum MPG that is acceptable. Re: speed; Minus and plus tolerances, nothing more. When calling for power it's OK to accept a lower speed/acceleration profile to maintain mpg efficiency. That's what I mean by an acceptable speed/acceleration range. The default is a zero value, the driver sets the deviation. Pretty simple really, everything else works the same.

It might even be as simple as accepting factory defaults in CC; speed maximization or MPG maximizing, that'd work too. Probably be less code too.

Control systems like this are everywhere in industry, so your agreement isn't really needed, they already exist.

Obviously driver input is still needed, that's a given, I never gave any hint that that wasn't the case, that came from elsewhere. You misunderstood what I meant, but then, I didn't give a full explanation, I just thought common sense would apply. I probably still haven't fully explained for some. Just understand I'm not talking AI, just cruise control, one still must drive ones vehicle. It works now, my version would work better. From a driver standpoint there would be no operational change to the CC other than setpoints of some sort. Toyota could just implement it and update the software in our vehicles and not pay me and that would work just fine (hint, hint).

I still love our Prius and don't mind having my foot on the throttle. I'm certainly not ready to have AI pilot my vehicle for me.

[DanMan32]

The purpose of any cruise control is to maintain speed. You are better off maintaining a speed rather than deviating back and forth from it.

Also, don't forget, you do not have direct control of the throttle. You tell the HV ECU what acceleration you desire, and it does the calculations of throttle (ICE power), MG1/MG2 involvement, and how much power to inject from the battery.