When is off not off? The strange case of drive by wire.

[oldRoger]

Disclaimer: I am not an expert and have never played one on TV, or in congress.
I love mechanical things, even electro-mechanical things. Relay ladder logic is not a closed book to me.
In days of yore when you pushed down on the accelerator pedal a mechanical linkage transmitted the motion to the carburetor and opened butterfly valves causing the engine to go faster. Over the years this may have been complicated by cables and may have set in motion other events. Still one could look at the system and see most of what was happening.
An old fashioned relay is a grand thing; it is adjustable, points can be cleaned & set, etc.
Alas, relays are now solid state and increasingly the button, switch, lever, or pedal is not mechanically connected, it is nothing but a position sensor.

Now we come to "drive-by wire" (heads up Lexus drivers). When you push a button, press down a pedal, or turn a switch, chances are very good that you are only signaling a computer. Now the computer has to sort through thousands of lines of code to determine what you were trying to convey to it.
You waltz out of the house with something that looks roughly like a key which stays in your pocket, open the door which unlocks as you approach, set down, and push a button, or press a pedal and you are off.
As all of this happens said computer is sorting through code, signaling various servos to operate etc. A lot of fairly complex high level "stuff" is happening.

Now comes the hard part, suppose you find yourself unexpectedly traveling 100 mph on a CA highway and want it all to just STOP!
With great presence of mind, you press the on/off switch, holding it in for 3 seconds. The computer meantime is trying to decide what you are up to, decisions, decisions, and decisions. If it decides correctly it will start to shut down systems. Meantime you have traveled 450 feet. And if you only held down for 2.75 seconds??? Good Luck!
More and more people want to do things for me (think S&W IL) that I can do for myself.

Roger

 

[OKFC05]

It took the F16 drivers a long time to decide that electrons were as reliable as hydralic hoses, too, but they eventually did.

 

[oldRoger]

I hope the F 16 gets a lot better maintenance by people who understand it a lot better than the typical auto.
How many people do you know who drive with check engine lights on?

 

[OKFC05]

I hope the F 16 gets a lot better maintenance by people who understand it a lot better than the typical auto.
How many people do you know who drive with check engine lights on?

Having flown on aircraft that were smoking, leaking, or otherwise yellow-tagged, I make no claims about maintenance on either one.

 

[The Big D]

Absolutely WRONG regarding the time delay referenced. The braking action is instantaneous and, in fact, faster than a mechanical connection.

Be safe.

 

[2000Z-71]

Throttle by wire is getting to be more and more popular on vehicles now. I've had 3 with it, an 06 Pontiac GTO, and 05 Nissan XTerra and now a 10 Nissan XTerra. Really not that big of a deal and adds an extra parameter for the ECU to adjust engine tuning with. The only problems I've seen with it is when you start to get into hotrodding and modifying. It adds an extra step and expense when you go to add a larger throttle body on a motor or go to install a more modern engine in an older vehicle.

 

[venomballistics]

cars are high vibration and hostile environments.
I don't mind a computer handling some aspects of engine control. a computer can do a better job of determining the best ignition advance and fuel mixture than any mechanical means.
but I want my foot directly controlling that throttle body valve and the brake system as well.
when I stick my foot in the machine I have a reason for standing on the go peddle. When I use the brakes, again there is a reason. These things should be mechanical commands not a compupolitical situation where my actions amount to a vote.

 

[oldRoger]

I didn't mean to imply that the decision was slow. The computer is very fast. But there has to be a decision and it is based upon computer code and sensor input.
I am all for computer control of parameters where nothing else will do, VVT is an example, mechanical variable valve timing has proven to be a nightmare, the computer does it very effectively.

My reference here was to the Lexus accident in CA, four killed, the Operator could not get it shut-down.

I want a simple shut-off, a kill switch if you will, and I want control of the brakes and transmission overriding the computer.

Take my current computer, when it freezes, as it does, I have to reach around and pull the plug. I can't reach the battery ground cable from the driver's seat, and would probably be going too fast anyway.

 

[The Big D]

Two points...and maybe more...

There is not a vehicle produced whose brakes can't override the engine. Test it on your own vehicle if you don't believe it.

There is so little possibility of redundant brake circuits failing concurrently that those who blame it on their "brakes failing" are almost universally wrong.

If loss of control is threatened by some sort of malfunction or driver error, simply put the vehicle in neutral and/or shut the engine off. That's done the same way you start it...use the key. Don't turn the key to the ignition lock position, however.

Be safe.

 

[oldRoger]

I agree, and most over rides are done at relatively slow speeds, however this car was going 100 plus. Turning off the switch is fine if there is a switch. Evidently there was a brake booster issue here as well.

Many Toyota "keyless entry" vehicles, others also as far as I know, do not have ignition switches. There is no keyed switch you leave the "key" in your pocket. The "start" button is a sensor which signals the comp. to begin the start sequence.
Override shut down is accomplished by holding the same button in for three seconds.
It seems that the brake booster is designed to limit at high speeds, I suppose to prevent panic over-application?' It is also said that with the engine in full race, the pedal jammed down or drive by wire failed, even a strong man would have difficulty making a fast stop.
On reflection the only way to over ride all of this is to put the transmission into neutral provided that the transmission control does not go through the computer. I am not certain that the transmission control is a direct link; it is not in some Toyota models. Would the computer control of the trans. prevent shift-to-neutral at full revs?
If you could get the trans. into neutral the rev limiter should override the accelerator. You would then have a fighting chance to get the vehicle under control.

At this speed you will not have much time for consideration and probably have to fight the tendency to keep both hands on the wheel.

 

[therevjay]

It don't much matter how well the bloody thing works. (while it's working) If it quits working 43 miles outside of Dooferville Idaho, can you fix it? With a mech. linkige you most often can.

 

[m1gunner]

cars are high vibration and hostile environments.
I don't mind a computer handling some aspects of engine control. a computer can do a better job of determining the best ignition advance and fuel mixture than any mechanical means.
but I want my foot directly controlling that throttle body valve and the brake system as well.
when I stick my foot in the machine I have a reason for standing on the go peddle. When I use the brakes, again there is a reason. These things should be mechanical commands not a compupolitical situation where my actions amount to a vote.

Diesels do not have throttle valves, never have. For the last 15 years, the "gas pedal" has been nothing more than a position sensor.

Can a diesel run away? ABSOLUTELY! Blow out an oil seal on your turbo, and you have a runaway, and- no - the brakes will not be able to over ride the engine, too much torque.

As far as olde technology, ever hear of a 2 cycle diesel? Used in trucks like trash trucks, etc. If you mess up pulling away on a hill, the engine can run backward, uncontrolled as well. There is a mechanical intake shutoff for just such an occurance. (Pull handle on dash often labeled "Jesus")

 

[Nygma]

Take my current computer, when it freezes, as it does, I have to reach around and pull the plug.

Hold the on button down for 5 seconds next time.

 

[Lee in Quartzsite]

Toyota currently has a recall underway that addresses stuck accelerators Toyota says are caused by the floormat becoming wedged under the pedal. There have been a few people on the Toyota Forums reporting incidents of unexplained acceleration without any floormats in the vehicle. Toyota's recall is to replace the accelerator pedal with one that is shorter. The pedal in my Tundra is short enough all ready and I don't see how the floormat could be an issue with this problem. Some are blaming unexplained acceleration on the computer, not a stuck pedal.

Newsroom : Toyota/Lexus Consumer Safety Advisory: Potential Floor Mat Interference with Accelerator Pedal / Toyota

Newsroom : Toyota Announces Details of Remedy to Address Potential Accelerator Pedal Entrapment / Toyota

ABC News Questions Toyota's Floormat Recall - KickingTires

 

[m1gunner]

Some are blaming unexplained acceleration on the computer, not a stuck pedal.

Something to chew on:

The owner's manual on one of my vehicles says to not operate cell phones and other digital devices while the engine is running. It says these devices can interfere with the onboard computer.

Sure, this is a 9 year old vehicle, but just look at the explosion of devices in the last 10 years that emit EM radiation. Even TV signals have changed dramatically. Could this be having an impact on vehicle electronics? Do a search on electro magnetic radiation hardening and decide for yourself.

BTW, the military had some big problems a while back when some of their fly by wire aircraft got too close to some active transmission towers......hmmmm...

 

[ImprovedModel56Fan]

Interesting. I had a "stuck-throttle" incident about six months ago. AFAIK, it was caused by my wearing excessively large boots in a tiny Jap car (the one I drive every day). Needless to say, I no longer wear those boots in the car. But it was not a problem. Without even thinking, the car went into neutral and my foot somehow got towards the brake (without any panic - I was in a rather deserted area).

I vaguely remember that I may have had a genuine stuck throttle in the distant past. My main point is that mechanical devices malfunction, not just electronic ones. The real issue is whether there are reliable and effective solutions READILY available. Obviously, a manual transmission is one. Reliable and effective brakes are perhaps another.

I hope that ultimate safety devices on cars are still reliable when I buy my next one. I don't want to have to buy a really old used car, like I do S&W revolvers.

 

[CW Spook]

I've got fly-by-wire in my Aeronca Chief. The wires are steel cables that run through pulleys over my head and beneath my feet....

 

[blacksharkL82]

stopping problem

You sir, have just stated why it took me so long to get a newer car.
My last, before this one, was a 79 corvette, with a carb and a key.
My "new to me" car, is a 92 corvette.
I used to work on my 79. The only thing I can do to my 92, is check the oil.
Not even visibile spark plug wires.
So far, I'm trouble free. I do know how to handle panic situations. I don't want to, though. I still have a key. Yes, I trust it.
What I don't trust, is that 18 year old kid, at the dealership, making $10. per hour that the dealer charges us $85. an hour.
The wrench twisters, need more money, not the dealers.
That service writer, is a salesman ,not a mechanic.