Cruise Control circuit breaker?

A state diagram makes it clearer but you've gotten the essential parts. It is a modal system and takes at least two previous state changes to reach RES/ACC. A simple ground of the control pin returns the system to OFF. A 'disabling' circuit breaker would normally be open and shorting to ground disables it. I believe that is how a classic, aviation magneto switch works.

Bob Wilson

 

That is correct about the magneto switch. If Toyota has to start adding circuit breakers to their cars for emergency use that will pose a major distraction to find and for many people would be hard to pull them open. I suggest dashboard toggle switches that accomplish the same--maybe with guards so they cannot be tripped accidentally? Next the Prius will need a driver training class that includes emergency situations and a bi-annual review that includes repeating the driving test.

 

...when the rich start flying around wearing 30 mile range jet packs requiring no license because they are under a certain weight limit?

 

ultra lights don't require a pilots license. When I learned to skydive they made me sign away that I knew I was an idiot and if I hurt myself it was my own fault. Running with the bulls and swimming with sharks did not require a similar signature, but both were outside of the legal limits of the US.

Seriously, I don't think a driving course would help with things like unintended acceleration that responds badly to braking, or abs brakes that reduce efforts infrequently. A short dealer instruction for new car purchases about adaptive cruise control seems like a no brainer though. They did point out the jump starting and towing quirks why not be able to tell woz how the cruise control works.

Its great that forum members informed me how to adjust the brake sensor to disable cruise control at a more normal braking pressure. It would have been nice if the dealer had been able to do it when requested. I would like hybrid technology to become more widespread. That requires continuous improvement on systems that don't follow conventions. Its a little insulting when legitimate problems are labeled something inherent about the hybrid. It is likely this attitude that makes some people question everything about the way the car is designed.

My vote is no circuit breaker, no special licensing requirements or training to drive a hybrid. Oh, and a rocket deployed parachute to slow down a lexus like there was on the last ultralight I flew.

 

Just a couple of comments.

First: Suppose that one has a malfunctioning cruise control switch. Take your pick: busted wires (an old CPO I had in the Navy said that 90% of your problems tended to be in the wires. I found him to be right, at least with aviation RADARs. ); broken switch contacts; mechanical failure.

Given time, thought, and some debouncing software, the software in the ECU should be capable of figuring out what died and to do something about it. Reject momentary contacts shorter than one pulse on the CPU cycling scheme, be suspicious of values changing too rapidly between different possible inputs (10 ms one value, 10 ms another value? The hardware can't move that fast!), and so on.

Think of the fun that might occur if a piece of metal breaks off in there and starts making contact with random bits of conductive metal.

My experience with this kind of thing is that some writing good debouncing software is not a trivial matter. It can be done, but testing it and verifying that it works requires not just good simulation capability, but a mind like Bruce Schiner's (that guy from BT) that can dream up fault scenarios as easily as normal people breathe.

Second point. I concur with comments made earlier: With the ECU and the cruise control integrated, there's no way to turn off the cruise control. It's not like my wife's Sienna where the cruise control is hooked up to a box with a spring-loaded cable coming out of it. Turn off the box, and the Box Is Off. As in depowered. Turn the CC on or off in current Toyotas and it is the software turning the dash LEDs on and off. Whether the CC actually works as advertised or not is strictly up to the black box software.

You don't know what that software is doing; I don't know what that software is doing. We have Toyota's assurance that Everything is Fine. Yep, and current software engineering practices and what happens when people write code does not make me feel all warm and fuzzy.

So, from an engineering/troubleshooting point of view, there's nothing to rule out software problems.

Hey, it can get worse. Suppose that there are rarely-entered software checking routines that, when a hardware fault occurs, instead of doing the expected thing, dive off into left field and command Full Speed Ahead?

Having duplicated processors doesn't necessarily guard against these kinds of faults because, well, both processors may be running the same faulty code. So they agree with each other! (Yes, and I have troubleshot problems like this. Usually, during the development cycle, but sometimes when there's gear in the field. Fun. Not.)

Look: I'm not saying that we need to abandon the Prius, or any other Toyota. I listened to that Webinar from Toyota. It sounds like they've got good people and outside engineering teams at least beginning to stare at the cars in question, and I hope like crazy that all the right people have access to the source code (which, by the by, you and I will never see the light of day on) so they can at least narrow things down.

I am going to leave you gentlemen with a couple more thoughts.

1. Ms. Smith said that the cruise control light came on when the incident occurred.
2. After she turned the car off and was out of the car, her husband shifted gears. That should not have happened.
3. When her husband shifted gears, the car started. Without a key in the cabin.

I don't know about you, but those three points SCREAM screwed up ECU to me. It's not just the CC software state machine fouled, it's major, "I'm not working right today and I'm giving you the Bronx Cheer" from the car. It's a gimme that the Toyota techie and the guy from the NHTSA didn't find any error codes - heck, with everything else that had gone beserk, what's one failure to write to SEEPROM?

OK, here's a question for you Prius junkies out there. When the car is Off, is power (real, live 12V DC) removed from the ECU? Or is that another software indicator and the CPU is alive, but on some form of standby?

Hmph. I wonder if somebody disconnected the 12V battery during the troubleshooting. If it was a full software bug, then the ECU would do a restart-from-power-off, and the buggie is gone.

KBeck.

 

Very interesting post. Anyone cares to reply? :rockon: