The engine revolutions have reached the upper limit of the engine’s tolerance - if you look on a rev counter, you’ll see a red section starting somewhere between 5,000 and 8,500 revolutions per minute (depending on the car).
That’s the redline - the rev limiter will kick in and briefly shut off the fuel pump if you go more than a few hundred revolutions into that range, in order to prevent the engine from spinning itself into pieces (actually, I think it’s most likely that the crankshaft would just snap, but I’m not sure about that). In any case, shifting gears while redlining the engine is not advisable.
The uncontrolled-acceleration problem apparently initiates maximum throttle, which will redline the engine rather quickly.
Small correction: The computer does not shut off the fuel pump to prevent over revving, it (briefly) shuts off the fuel injectors.
Likely engine damage from over revving is that the valves float, meaning they try to move so fast the valve springs have insufficient force to shut them. When this happens the valve will still be open when the piston comes up, piston hits valve and carnage ensues.
On large displacement engines you can also exceed the maximum piston speed where the inertia of the piston/rod overcomes the strength of the oil film on the rod bearings, leading to spun bearings. Again, carnage ensues.
The only way I know of to over rev a modern engine is if you have a manual transmission and manage to get it into a very low gear while going at speed, like shifting into 1st at 70 mph or so. Rare occurrence, but does happen.
Apparently, someone went on TV yesterday to give testimony (or some such) claiming that she shifted her runaway Lexus into every other gear (including reverse, which I really seriously don’t believe) with no effect: has there been any actual third-party verification that shifting to neutral does nothing?
I think that what she probably said was that she tried to shift into every other gear, and that it would not shift. Or that’s what actually happened, even if she doesn’t realize it.
That’s the problem that has been reported on the toyotas – that the computer won’t recognize the command to shift into neutral when this runaway acceleration is happening. And most cars have interlocks now that prevent you from shifting into reverse or lower gears when you are already traveling over x miles/hour, to prevent damage to the engine. But you should always be able to shift into neutral, with a mechanical shifter. The problem is with the electronic ‘drive-by-wire’ transmission controls.
I’ve noticed newer cars do not quite behave as older cars when it comes to shifting. My Honda, I am almost certain, will not let you start the car in neutral. However, I swore older cars would - specifically as a safety thing. Have the SDopers noticed this, too?
a) After hearing recent testimony by those who experienced “runaway Toyotas”, I wonder if they were using “cruise control” when this happened. b) I can bet the independent experts are right that the problem is electrical and/or software related. When the truth comes out that Toyota’s fix for floormats or sticky foot pedals wasn’t the answer, the Toyota name will only be found on mudflaps!
Modern computer controlled automatic transmissions will not engage reverse above a particular speed, say 3 mph for example. You can move the lever to R at 100 and it will just be in neutral.
So assuming you were on level ground and put the car in reverse at 100 you would still be at 100, so the driver’s statement would be true.
I can easily see how the engine screaming at redline, the car going faster than you have ever driven might just maybe rattle the driver just a tiny bit.
I haven’t read every word in this thread so excuse me if I am being redundant.
If the throttle pedal and the transmission controls are both ‘fly by wire’ (which they are on a lot of modern cars), and the brakes talk to the cars computer (which I’m sure they do on a Lexus) I can’t believe that someone in Toyota R and D didn’t put a routine into the cars ECU that cuts the throttle if the brakes are being applied and the throttle opening is high.
The software update will cause “the brake pedal to take precedence over the gas pedal if both were pressed” or “would cut power to the engine if both pedals were pressed.”
An interesting comment from SlashDot.org from someone who seems to know what they’re talking about:
About one time in 20, my Prius will ignore my first press of the park button. It’s kinda disturbing when you go to get out of the car and it starts moving:eek:
The first few times, I thought I was absent minded and forgot or something but it has happened a few times when I am totally paying attention. I’m guessing it has some kind of sensor to not allow it to go into park while the car is moving and that the sensor is mis-calibrated.
I actually prefer the staggered automatic gates to the push-button one (although my daily driver is a manual). It’s really not that confusing–the shift lever jumps into place very naturally and it just feels nicer than the push-button automatic (at least to me.)
