Why can't the vehicles brakes overpower the engine, in a worst case scenario?
Question about runaway acceleration...
- Thread starter cchase
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Well, something to consider from a theoretical point of view is that on a steady-state basis the brakes have to dissipate "as heat" the power generated at the wheels. So if you have for example 201 hp being produced at the wheel by a stuck throttle you have to dissipate 150 kW of heat as long as they are applied, plus some more to decelerate the car to a stop.
That's a lot and if you don't stay on the brakes to get the job done quickly they could fail.
That's a lot and if you don't stay on the brakes to get the job done quickly they could fail.
i dont understand whats so hard about simply moving the shifter up 1 notch to Neutral. thats what i did once when i was put in that situation. worked like a charm.
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I just think its pathetic that most people would not know to put the car in neutral or "N" if the pedal sticks. Don't get me wrong, I like that Toyota sees the problem and is trying to correct it because it could potentially be very dangerous, but the average driver wouldn't have a clue what to do if it actually happened.
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Originally Posted By: Jakegday
i dont understand whats so hard about simply moving the shifter up 1 notch to Neutral. thats what i did once when i was put in that situation. worked like a charm.
Because they "freak-out" and go brain-dead. Even though the engine could over-power the brakes, they would at least slow down the vehicle until the trans could be put in neutral.
I promise you, I could stand on those brakes hard enough to break off the pedal if necessary.
I would venture to say that the vast majority of reported "unintended" acceleration claims are really just the driver getting confused.
Remember, in the early 80s when Audi was "accused" of unintended acceleration? There was no evidence that Audi was at fault -- total driver fault.
i dont understand whats so hard about simply moving the shifter up 1 notch to Neutral. thats what i did once when i was put in that situation. worked like a charm.
Because they "freak-out" and go brain-dead. Even though the engine could over-power the brakes, they would at least slow down the vehicle until the trans could be put in neutral.
I promise you, I could stand on those brakes hard enough to break off the pedal if necessary.
I would venture to say that the vast majority of reported "unintended" acceleration claims are really just the driver getting confused.
Remember, in the early 80s when Audi was "accused" of unintended acceleration? There was no evidence that Audi was at fault -- total driver fault.
And I realize you would lose power steering and power brakes, but can't you still just shut off the key? That seems like a much better alternative than trying to guide a runaway train...
i guess i just dont understand the "freak-out" or the "mind freezing" thing. my thinking sped up like a mofo when it happened to me
When something out of the ordinary like a stuck throttle happens to the average person, I would say that confusion as to what to do next would be the normal response. Remember that if the throttle is stuck open, there is no additional manifold vacuum on most cars to keep the brake booster working, making the brake pedal almost impossible to operate for most people. It gets hard as a rock to push down once that boost is gone.
Just a thought as to why there's more to this story -
My guess is the real problem may be that these are not throttle sticking problems like getting caught in the carpet as toyota first suggested, it's their 'fly-by-wire' electronic throttle control. There also is no mechanical key to turn the engine off, but a push button start/stop. There may even be an electronic control to the transmission so bumping the lever to Neutral may not have direct mechanical control.
We're at the mercy of hardware and software, which adds more confusion.
My guess is the real problem may be that these are not throttle sticking problems like getting caught in the carpet as toyota first suggested, it's their 'fly-by-wire' electronic throttle control. There also is no mechanical key to turn the engine off, but a push button start/stop. There may even be an electronic control to the transmission so bumping the lever to Neutral may not have direct mechanical control.
We're at the mercy of hardware and software, which adds more confusion.
Originally Posted By: cchase
Why can't the vehicles brakes overpower the engine, in a worst case scenario?
It basically can but you have to press down hard once and continuously. What drivers were doing was riding, pumping and dilly-dallying with the brake pedal. This cause the brakes to overheat and fade and/or the vaccuum assist to be used up.
The solution is simple, select neutral and brake hard. Turning the ignition off would work but you would lose power steering (except maybe for electrical steering models). Some had a push button ignition and the drivers didn't know how to turn it off when the vehicle was in motion.
Why can't the vehicles brakes overpower the engine, in a worst case scenario?
It basically can but you have to press down hard once and continuously. What drivers were doing was riding, pumping and dilly-dallying with the brake pedal. This cause the brakes to overheat and fade and/or the vaccuum assist to be used up.
The solution is simple, select neutral and brake hard. Turning the ignition off would work but you would lose power steering (except maybe for electrical steering models). Some had a push button ignition and the drivers didn't know how to turn it off when the vehicle was in motion.
Well my question is this, why did TOYOTA forget to equip the car with an override software that cuts throttle when brakes are pressed... you dont need throttle when braking...
... not that hard to think of that is it, considering how much electronics control the car these days...
I guess they didnt want to take away the burnout option from their owners?!
On a second note why on earth are these owners using WOT to accelerate?
I have hit WOT maybe 2 times in my entire ownership of my car and it has around 200hp and 4000lbs of weight...
Could be the fact that their cars have small engines that are often not enough to get out of lousy situations.
... not that hard to think of that is it, considering how much electronics control the car these days...
I guess they didnt want to take away the burnout option from their owners?!
On a second note why on earth are these owners using WOT to accelerate?
I have hit WOT maybe 2 times in my entire ownership of my car and it has around 200hp and 4000lbs of weight...
Could be the fact that their cars have small engines that are often not enough to get out of lousy situations.
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Originally Posted By: Jakegday
i guess i just dont understand the "freak-out" or the "mind freezing" thing. my thinking sped up like a mofo when it happened to me
Yeah, well...you aren't 75 yrs old either. Older minds tend to get rattled easier. Happened to my mom, she drove through a store window. I still think she hit the gas instead of the brake.
i guess i just dont understand the "freak-out" or the "mind freezing" thing. my thinking sped up like a mofo when it happened to me
Yeah, well...you aren't 75 yrs old either. Older minds tend to get rattled easier. Happened to my mom, she drove through a store window. I still think she hit the gas instead of the brake.
Those are good questions. I don't personally like the brake deactivating the throttle but for most owners and for Toyotas I can't see why it doesn't by design. I don't know why the Toyotas seem to accelerate at full throttle. Maybe the car was going WOT on its own without having been previously floored?
Originally Posted By: cchase
Why can't the vehicles brakes overpower the engine, in a worst case scenario?
What mechanix said. They usually can overpower the engine... once. After that point, they overheat and fade.
Possible solutions:
1. Brake pads with better fade resistance. Fade resistance comes with a whole list of possible disadvantages (i.e. one or more of the following):
- More dust
- More noise
- Shorter lifespan
- Faster rotor wear
- Higher price
- Poor performance at low temps
2. Bigger brakes: rotors, pads, calipers, hydraulics, the whole deal. That would make them a lot more expensive. They would also be heavier unless they were made out of special alloys, in which case they would be MUCH more expensive.
Either way, the advantages would be lost on most people since they don't really drive too hard and unintended acceleration is so rare (i.e. most people, even in Toyotas, never experience it).
Why can't the vehicles brakes overpower the engine, in a worst case scenario?
What mechanix said. They usually can overpower the engine... once. After that point, they overheat and fade.
Possible solutions:
1. Brake pads with better fade resistance. Fade resistance comes with a whole list of possible disadvantages (i.e. one or more of the following):
- More dust
- More noise
- Shorter lifespan
- Faster rotor wear
- Higher price
- Poor performance at low temps
2. Bigger brakes: rotors, pads, calipers, hydraulics, the whole deal. That would make them a lot more expensive. They would also be heavier unless they were made out of special alloys, in which case they would be MUCH more expensive.
Either way, the advantages would be lost on most people since they don't really drive too hard and unintended acceleration is so rare (i.e. most people, even in Toyotas, never experience it).
You can't overcome stupid.
Interesting thoughts. I was trying to avoid the politics of the situation, but in my mind a brake should be able to stop an engine dead... that's why I asked.
Not only does the brakes have to overpower the WOT engine output, but remember a 100mph 3500 lbs vehicle has a LOT of kinetic energy which the brakes will have to also convert to heat. Put both together, it will likely overwhelm the brake pads and cause them to fade in no time.
Originally Posted By: ZGRider
Originally Posted By: Jakegday
i guess i just dont understand the "freak-out" or the "mind freezing" thing. my thinking sped up like a mofo when it happened to me
Yeah, well...you aren't 75 yrs old either. Older minds tend to get rattled easier. Happened to my mom, she drove through a store window. I still think she hit the gas instead of the brake.
this is the exact reason i wholeheartedly believe senior citizens should HAVE to take a drivers test EVERY year. the actual driving test, not just the written. in my opinion, her drivers license should have been permanently revoked after that incident
the seniors might not like my idea, and if they dont, its cuz they know they're not all that "on it" any more and they might fail. if you really are a good driver you have absolutely nothing to worry about
Originally Posted By: Jakegday
i guess i just dont understand the "freak-out" or the "mind freezing" thing. my thinking sped up like a mofo when it happened to me
Yeah, well...you aren't 75 yrs old either. Older minds tend to get rattled easier. Happened to my mom, she drove through a store window. I still think she hit the gas instead of the brake.
this is the exact reason i wholeheartedly believe senior citizens should HAVE to take a drivers test EVERY year. the actual driving test, not just the written. in my opinion, her drivers license should have been permanently revoked after that incident
the seniors might not like my idea, and if they dont, its cuz they know they're not all that "on it" any more and they might fail. if you really are a good driver you have absolutely nothing to worry about
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I have run into 3 or 4 cases of "Unintended acceleration" at the dealership. Two involved me.
The one I was in was a 3.8L Cougar RWD that got the aftermarket floor mat lodged up under the brake pedal, and over the accelerator. Cold day, stiff plastic mat, and everytime you stepped on the brake, it pressed on the gas. I shut it down quick and figured it out. Most cars have the plastic retainer hooks molded into the carpet and a hole in the mat to combat this, many Fords at least.
I have seen one vehicle (Ford Contour) with an intermittently bad TP sensor take off without touching the pedal. The TP sensor had a bad spot in it and would show WOT occasionally with no throttle opening. At any time except idle the IAC is commanded to 100%. I remember you could let off the throttle and coast to a light and all the sudden it would just downshift and go by itself.
One of our service writers took a Merkur XR4ti into the back of the dealer principle's (maximum leader/boss) office one morning because of an unintended acceleration problem.
Brakes are a problem in some cases of unintended acceleration. Vac operated brakes, with insufficient manifold vac don't work long before vac is lost. Figure also the pads overheat and fail miserably.
Main problem is drivers lose their head when things like that occur.
The one I was in was a 3.8L Cougar RWD that got the aftermarket floor mat lodged up under the brake pedal, and over the accelerator. Cold day, stiff plastic mat, and everytime you stepped on the brake, it pressed on the gas. I shut it down quick and figured it out. Most cars have the plastic retainer hooks molded into the carpet and a hole in the mat to combat this, many Fords at least.
I have seen one vehicle (Ford Contour) with an intermittently bad TP sensor take off without touching the pedal. The TP sensor had a bad spot in it and would show WOT occasionally with no throttle opening. At any time except idle the IAC is commanded to 100%. I remember you could let off the throttle and coast to a light and all the sudden it would just downshift and go by itself.
One of our service writers took a Merkur XR4ti into the back of the dealer principle's (maximum leader/boss) office one morning because of an unintended acceleration problem.
Brakes are a problem in some cases of unintended acceleration. Vac operated brakes, with insufficient manifold vac don't work long before vac is lost. Figure also the pads overheat and fail miserably.
Main problem is drivers lose their head when things like that occur.
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