More on that runaway Prius...

[salty]

That's easy. It's called a MALFUNCTION.

That's easy. It's called a MALFUNCTION

[clare]

Just as I thought. You have NO understanding of how the system works - and therefore no INKLING of what infitesemely small chance there is of such a thing happening ONCE - much less dozens of times, as is alleged to have happened.

[salty]

Maybe you need to go look up the word MALFUNCTION. You seem to be a little fuzzy on what it means.

[clare]

I know exactly what malfunction means - but you need to understand the FUNCTION first.

[salty]

I no longer believe that you do not drink.

[trader4]

Once again, you are dead wrong here. First, you don't know the specifics of how the actual ABS system is designed or works in the Prius. Without that, you are already speculating. Any car with ABS has a computer controlling the hydraulic pressure that is going to each wheel. The computer is looking for a wheel starting to lock up, at which point it reduces the pressure to that wheel to get it spinning normally again. So, tell us why a malfunction in the ABS computer could not command 2 wheels, or all 4 wheels to minimum pressure continuously? Have you not seen your own PC hang in some endless program loop?

Now I also remember you telling us how manufacturers are now making cars with only two computers and some have only one. You claimed some cars have the ABS, climate control, and radio all run off of one central computer. I've showed you this is a crock, complete with multiple links. You've provided nada. However, let's go with your claim that the engine computer and ABS are commonly co-mingled into one computer. So, now you have the computer that has malfunctioned in control of both the throttle and to a significant extent, also the brakes. Note, I am not saying this is a high probability event or that it explains what has happened in these runaway cars. But it's impossible to rule out. If you can do so, tell us exactly how it's impossible for whatever computer is controlling the ABS to not cause a loss of at least some braking capability during a malfunction.

Note, I still say IMO, the latest incident with Sikes is a hoax because of many other factors.

[clare]

On Sun, 21 Mar 2010 06:20:52 -0700 (PDT), [e-mail] wrote:

I've seen PCs do that - but the ABS computer is a much simpler system with no GUI and only a single hard coded program which watches 4 incoming pulse trains and the brake light switch.and compares the frequency of those 4 pulse trains. If, with the brake light switch active, one excedes the frequency of any or all of the others, the circuit related to the signal with the lower frequency is activated, putting the ABS cuicuit for that wheel into effect. The ABS device shuts off the pressure from the master cyl to the accumulator for that brake circuit, and a motor winds the piston in that accumulator down to reduce the hydraulic pressure untill the wheel stops skidding (starts turning the same speed as the faster wheel) at which it reverses and puts the pressure back up till it reaches incipient lockup again - and continues to modulate the pressure untill the pedal is released. During this active phase, pushing harder on the brake cannot increase the hydraulic pressure on that circuit. If the pedal is released, when the accumulator piston comes back up the fluid returns to the master cyl wirhout pressurizing the brake circuit, the same as with non-abs brakes. If the pedal is released while the brake is in lockup, the fluid pressure is reduced and the accumulator returns to the full pressure position.. With any mechanical malfunction of the ABS causing one brake (or more) to not apply, the ABS warning light comes on and stays on until the vehicle is shut off. With any electrical or electronic failure causing an accumulator to stay in the low-pressure position, the ABS light is also turned on..

Nobody to this point has reported the brake warning light to be on. It would be a pretty complex failure mode that would affect all 4 wheels, not turn on the ABS warning light, and not be VERY evident when investigators check the vehicle. In other words, the chances of it happening and not being provable are EXTREMELY low.

So low as to be VIRTUALLY impossible.

Same with the regen braking control on a hybrid. When the grake pedal is depressed, without computer intervention the hydraulic brakes work normally. With the computer working and requesting regenerative braking the motor is switched to operate as a generator slowing the vehicle down, and if the pedal is pressed farther, they hydraulics come into effect.

From the way it has been described to me, there is NOTHING the computer can do to "shut off" the hydraulic braking system. And with the power control system calling for power, there is no way the regenerative braking system can also be engaged - impossible because of the way Hybryd Synergy Drive works. Using the same components for drive and braking, they cannot do both at once.

Impossible. And regenerative braking is initiated as soon as you lift your foot from the gas. Don't need to touch the brake at all. So the only viable scenario for reduced braking at WOT is improper emergency use of the brake. It MUST be applied FIRMLY AND STEADILY - WITHOUT RELEASE - otherwise vacuum boost is lost and brake pressure is reduced.. ANd on the Prius, because it can run without the gasoline engine running, there is a standby electric vacuum pump to give vacuum to the booster even with no engine vacuum - so on a hybrid that pump would ALSO need to fail in order to reduce the brake pressure.

I just explained how ABS works. Not impossible to lose SOME braking capability - but not without turning on a warning light and leaving evidence.

I'd say it is EXTREMELY unlikely the ABS has been involved in ANY way, in ANY of the reported ren-aways - Hybrid or otherwise. So small a possibility as to be statistically irellevent or virtually impossible.

[trader4]

Even simple computers can fail. Less likely yes, but that is different from saying it's just impossible. And how did it suddenly become so simple? You were telling us that the trend is that ALL the computing function is being centralized in one or two computers in cars today to save money. You specifically told us before that some cars have the same computer that is doing the ABS doing the climate control and the radio. So, how is it that now the ABS computer is just a simple computer looking at pulse streams? It should be monitoring the air temp, the outside air temp, sending the radio station identification to the radio display, responding to the driver turning the tuning knob, and God only knows what else. You said it was easy, practical and safe to develop cars that way. I said it was a crock.

I didn't see you make that qualification when you wanted to know how a computer could interfere with the braking, implying it was impossible. You've just answered your own question. A malfunctioning ABS computer could do it. Also, if the ABS computer is stuck in some unforeseen mode and not responding, what makes you think it's going to put the ABS light on?

I agree with that, but that is different from stating that it's impossible for the computer to compromise the braking, which is the argument I believe you were making.

That should give us all lots of confidence. Have you found that car where the ABS, climate control and radio all use one computer?

You just like going further and further out on a limb, don't you? I think you'd have a very hard time in court with a judge, where you have to separate what you know as a fact from here-say, opinion, and conjecture.

And you have such detailed knowledge of the design of the ABS computer, that you know it can't be stuck in some loop, not responding and also not setting the warning light? Somehow I doubt that.

I'd say it's extremely unlikely too. But then the runaway action is also only happening in a minuscule fraction of Toyota's millions of cars. But I'm content to wait for NHTSA to conduct a complete forensic investigation together with the car engineers, engineers from companies that made the subsystems, etc. That's how you get to the bottom of things.

[Levee]

Hmmm, very little front brake wear at 170,000 miles [on the original pads] might indicate a serious malfunction. I'd give those front brakes a very close inspection to make sure they even work.

(Yes, I'm replying to an old post.)

[trader4]

He's was talking about the rotors, not the pads.....

[Dave M.]

The post is more than 2 yrs. old. The OP is certainly long gone.

Dave M.

[Jon Danniken]

It's a Prius, they use regenerative braking:

Jon

[clare]

Not at all. The regen does better than 80% of the braking on a Prius, so extremely long brake life is not out of the ordinary at all, outside the rust belt.

[Levee]

Thanks, but that doesn't explain why the rear rotors needed to be replaced, does it? Does regen only apply to the front wheels?

[clare]

It only works on the front brakes. Any rear braking still needs to be performed by the friction brakes. Rear braking is something about

30% of the stopping power, more or less. With regen, the front friction brakes can be responsible for less than 10%, depending on driving style.