Unintended Acceleration Issue

J

jhwilson

New member
There has been some discussion of this issue in other threads and some of the problem vehicles are those we use to tow our boats. The current edition of Car and Driver Magazine had an interesting and relevant article concerning the unintended acceleration issue. They tested a V-6 Camry (subject to the recall), a G37 Infiniti convertable, and a Roush Stage Three Mustang with 540 horsepower. The three vehicles were put through a series of tests where the throttle was closed and then forced full open.

The first test was to see if the brakes could stop the vehicle from 70 mph and then at 100 mph. The difference in braking distance was recorded with the throttle closed and then full open. In each case the brakes were able to bring the car to a stop in a relatively little more distance than with the throttle closed. The one exception to this was that the high power Mustang did take a much longer distance to stop from 100 mph with the throttle full open.

They also tested each vehicle to see how it would respond to being shifted into neutral at speed with the throttle full open. This did not apply to the Mustang since it had a manual transmission. With the other two there was no hesitancy for the car be shifted into neutral and brought to a quick stop.

Further they tested the three vehicles to determine if the engine could be turned off at the two speeds and what effect it would have. The cars with the push button took a few seconds of holding the button in to stop the engine but they did, in fact, cut power.

The entire article and accompaning charts is worth reading. You can access it at:
http://www.caranddriver.com/features/09 ... -tech_dept

Harper
 
With all the recent media attention and speculation I've wondered more than a few times why it would be so difficult to stop a vehicle should the accelerator become "stuck". :? As you mentioned, by simply shifting into "N" (on an auto) or pressing the clutch (manual), and then braking as usual ANYONE should be able to stop ANY vehicle. If they can't do THAT, perhaps the shouldn't own a vehicle or drive. Shutting off the engine would worsen the situation since you'd lose power steering and possibly lock the steering wheel. It's very common sense IMO.

I can only assume that those involved in such incidents with negative results cannot handle the situation, become overly stressed and go "condition black"; unable to analyze the situation, plan a course of action and then react accordingly.
 
Mark,

That's what I have always thought too. The one event that brings a question to that theory is that one of the most publicized accidents was when a California Highway Patrolman with 19 years of LE experience was at the wheel of a Lexus when it crashed after several miles of apparent uncontroled speed and killed all aboard.

It's somehow hard to believe that a veteran police officer wouldn't have tried everything.

Harper
 
In one of the other threads, I believe someone explained the issue...

These cars don't just have fly by wire accelerators, they are completely fly by wire, including the transmissions and ignitions.

I thought the same thing as Mark, just put it into neutral and slam on the brakes, which is what the test described above claims to do. The key here though is that that only works when the car is functioning as designed, but what happens when it doesn't work as designed. What happens when the system finds a software bug and behaves erratically? The manual overrides don't seem to exist!

I was watching CNBC when they were interviewing a Toyota tech who said that they have updated the software in the system to always allow the brake system to override the accelerator. Does that mean that the braking system is also fly by wire? Maybe not entirely, but why else would you need to program that into the car's computer if the systems were independent of one another?

Steve Wozniak claimed to have a software issue with his 2010 Prius. I didn't give it much thought until now that I realize that the entire car is computer controlled. These aren't the same cars that were built 20 years ago.
 
I watched a show on it and the biggest thing they emphasized was to not pump the brake at all. You only had 2 shots at breaking the car they were testing. I guess a lot of the models do not build break pressure while the car is accelerating, but have a small reserve of pressure. If you pumped the breaks 3 times on the car they were testing you lost all break pressure and could no longer break and it won't build pressure anymore.
 
jhwilson":2a8eyn00 said:
Mark,

That's what I have always thought too. The one event that brings a question to that theory is that one of the most publicized accidents was when a California Highway Patrolman with 19 years of LE experience was at the wheel of a Lexus when it crashed after several miles of apparent uncontroled speed and killed all aboard.

It's somehow hard to believe that a veteran police officer wouldn't have tried everything.

Harper
Click to expand...

I have only two names for you, Bsimarck Dinius and the most highly esteemed officer Russell Perdock.
 
The brake booster is powered by engine vacuum and if the throttle is wide open there is no vacuum being generated. That means you have only the assistance stored in the vacuum reservoir, if you use it up pumping the pedal you have no assistance stopping the car.

Regarding shifting into neutral during a runaway, the lady who testified before Congress today said that she moved the shifter into neutral as well as to the lower forward gears to no avail. Her car reached a speed of over 100 mph!
 
I have twin Mercury Verados on my boat. They are completely fly by wire. There is no cable connecting the throttle control to the transmission, everything is done electrically. There is no "clunk" into gear that I had with the old cable system.

I'm laying odds that these newer cars operate in the same way. There is very likely NO physical, mechanical connection between the lever you move inside the cabin of your car and the movement of the transmission. It is probably just a series of electronic commands.

Unfortunately, that means that if something goes wrong with the system, and you slam the transmission lever into reverse or park, all you are doing is moving the lever and not physically forcing anything to happen in the transmission. :crook
 
Llloyds,

It won't work. They did a segment on that on Mythbusters and the transmission wouldn't go into reverse or park when engaged at speed.

Nick
"Valkyrie"
 
lloyds":3v6739op said:
I bet if you crammed that puppy into park or reverse it would stop shortly.
Click to expand...

You are assuming that moving the shifter does more than move a potentiometer to send a signal to the transmission computer.
 
While I was SOOooooo worried about my new Tundra possibly experiencing unintended acceleration that I drove it as FAST as I possibly could over to the dealer just to get it fixed. After many near accidents on the way there, I put it in the hands of the nice Toyota staff. Problem solved now. So if you see a maroon Tundra with a high top canopy headed directly at you at a high and increasing rate of speed, rest assured that what's happening is intended acceleration. :wink:
 
In spacecraft, computers are know to have a Single Event Upset (SEU) due to the radiation and high energy particles out there. Different SEUs have different effects, depending if it's memory or the cpu or a control register. If an SEU hits in the right place, the computer crashes, and who knows what happens. So spacecraft have ways of guarding against this. The simplest (and slowest,) is a keep alive signal. If the computer doesn't reset that signal every so often, the computer is restarted using read only memory. Another protection is having three computers all running the same program and voting. 2 out of 3 wins. This is used for fast real time events, such as boost phase.

Autos, since they went with computer controlled fuel injection have a fail safe fuel injection mode to get you home. In some conditions. If the right part dies, you're towed home.

Looks like Toyota has discovered, here on Earth, the effects of a SEU in crashing a on-board computer. Yeah, the computer completely runs the auto/truck and I'll bet there's some fault in there that allows a SEU to do some of the wonderful things people have experienced.

And the best thing is that when the car is finally stopped and turned off, starting it again resets the computer and the dealer says "why that car is perfect (you dummy.)" What I'm not sure is why Toyota is the primary source of these events. Sounds like just bad software design for a real time system. That means somewhere there's a software designer saying " that software is perfect, you just show me where there's any error."

By the way, when I was young and someone else paid the bills, I'd jam the auto gearshift into low, reverse, etc. just for fun. A hydraulic doohickey in the trans would hold off the shift until the car slowed down. I'll bet that's in the Toyota software.

Boris
 
"Welcome to XXXX Airlines, this is your captain speaking. We have the pleasure today to welcome you on board the first aiplane to be flown completely by computer. Please be assured that all systems have been verified by bona fide government contractors and the software was written overseas, so nothing can go wrong....go wrong...go wrong......"


:twisted:

Merv
 
All very interesting. I had not seen nor heard any specifics about today's testimony in front of Congress, so I plead not guilty on that. :mrgreen: As far as the fly-by-wire, I'm not educated enough to make any suppositions as to exactly what's occurring, but obviously, something is wrong; I'll leave the fix to the engineers.

On the positive, I think I'll drive my 45 year old VWs more...you can't get any more "lo-tech".... :wink:
 
Then again, if you don't tighten your gas cap your 'check engine' light may go on. I knew a guy that had his car towed from Connecticut to his dealer in NJ when it went on. :disgust
 
We have a Mercedes with fly-by-wire throttle and brakes. So far so good. I know our Pilot also has a fly-by-wire throttle, and I'm sure some of our other cars do as well.

I am curious though as to how the transmission mechanism works on modern cars. Certainly, some cars have no mechanical link between the shifter and the transmission. Many new Mercedes have a little stubby gear shifter on the steering column. The Prius has something similar. But what about other cars? Any easy way to look this up?
 
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