Runaway Car

[lightplay22]

LOL, I've never had my prius over 90 but I think it would make 100 (with your feet still inside) and I think it was Al Gore's son who got a ticket for doing 105 in a prius some time back.

One thing for sure is, its got some VERY good brakes which probably has something to do with how little the car weighs.

I hope it never tries to run away and that they get to the bottom of the problem without anyone getting hurt or killed.

 

[Empath]

A fail-safe system of shutting down the gas feed when the brakes are applied, while significantly accelerated, should be a relatively simple system to include in manufacture. Cruise control already incorporates the feature.

 

[StarHalo]

A car's brakes will always work regardless of the throttle, gear, or key position, as will neutral gear.

Also, the top speed of a current Toyota Prius is a drag-limited 115 mph (meaning it can go faster depending on conditions); while its off-the-line power is underwhelming, the CVT transmission means when the throttle is floored, the engine is pinned at redline, providing surprising freeway/passing acceleration - it can reach its top speed in about the same amount of time as any other car.

 

[gswitter]

...which probably has something to do with how little the car (Prius) weighs.

Compared to what? The Prius is actually quite heavy for its size.

 

[Mjolnir]

I don't really understand why people can't deal with runaway acceleration. The brakes on a car are very strong; even if the car is accelerating they can bring it to a stop. With a manual transmission, brakes can easily stall a car, even one that is nearly floored. It won't be good for the car, but it will work. I would imagine that it would not be very hard for the brakes to stop the Prius's 76 HP engine (or 99 in the new model).

The Prius may have a CVT that optimizes the engine power during accleration, but you can't get away from the fact that it is still less than 100 HP. Acceleration from all speeds will be much slower than a 300+ horsepower car.

Oh, and apparently the M3 is more economical than the Prius... :nana:
http://www.youtube.com/watch?v=dKTOyiKLARk

 

[lightplay22]

I think I'll trade it on a bmw tomorrow! LOL.

As far a weight goes, I don't know if 3000lb is light or heavy for a car of its size, but it feels very light when driving it... especially if its windy!

It is much lighter than my 3500 Express van (4.6 tons) and feels much lighter than our old '96 lexus es300.

46/48 MPG is really nice when it comes time to fill up. My brother-in -law's BMW 745 only gets 6-7 MPG when he's playing and having fun.

I guess I can take comfort in knowing that if all those 76 horses go wild and try to run away, the brakes should win easily!

 

[turbodog]

...

I should also add that the brake will always overpower a runaway engine. Car&Driver did tests on this in the 1980s. If the accelerator pedal gets stuck, just stand on the brake. The car will stop, and in not much more distance than it would without the engine running (I was actually surprised by this).

Sorry. Not true.

From various sources:

"The ES 350 and most other modern vehicles are equipped with power-assisted brakes, which operate by drawing vacuum power from the engine. But when an engine opens to full throttle, the vacuum drops, and after one or two pumps of the brake pedal the power assist feature disappears.

As a result, a driver would have to apply enormous pressure to the brake pedal to stop the car, and if the throttle was wide open might not be able to stop it at all, safety experts say."


Also.... today's cars can be a LOT more powerful that those from the 80's. Accumulated speed combined with powerful engines equals boiling brake fluid and no brakes.

 

[SFG2Lman]

shoot a honda CRX from 1991 got 51MPG which is the same as the prius...i think the diesel volkswagens are getting 60+ now, and they don't hafta worry about their batteries being useless in a few years...but back to the subject at hand, even vacuum assisted brakes are capable of stopping a car, the huge fluid cylinder you press puts so much force into stopping, even without power assist...but i do agree that not being able to shut off your car, shift it out of drive, or brake efficiently makes for a very deadly combination thats what happens when we over-automate

 

[StarHalo]

shoot a honda CRX from 1991 got 51MPG which is the same as the prius...i think the diesel volkswagens are getting 60+ now

These are correct highway figures, the Prius gets 51 MPG city.

If you do the majority of your driving in city-cycle, you'll get the best MPG from a hybrid. If the majority is freeway, go diesel.

 

[jtr1962]

Sorry. Not true.

From various sources:

"The ES 350 and most other modern vehicles are equipped with power-assisted brakes, which operate by drawing vacuum power from the engine. But when an engine opens to full throttle, the vacuum drops, and after one or two pumps of the brake pedal the power assist feature disappears.

As a result, a driver would have to apply enormous pressure to the brake pedal to stop the car, and if the throttle was wide open might not be able to stop it at all, safety experts say."


Also.... today's cars can be a LOT more powerful that those from the 80's. Accumulated speed combined with powerful engines equals boiling brake fluid and no brakes.

If that's all true (and right now I don't have time to do the necessary research to say one way or another), then that's a fatal design flaw. Every car should have a braking system capable of bringing it to a complete stop from whatever speed it's capable of reaching, irrespective of whether the engine is at idle or full throttle, period. From what you're telling me, combined with what others have said about some of today's vehicles not having a fail-safe way to turn them off on account of not having a keyed ignition, this basically means a runaway car will continue on until some obstacle stops it. I for one can't believe engineers would overlook putting in some sort of failsafe to keep this sequence of events from occurring, if for no other reason than to protect themselves from liability.

And according to at least this article, it appears what you wrote is true:

"The Times reports that the combination of design features may have been so impossible for a driver that even a 19-year CHP veteran could not regain control of the Lexus, which had been lent to the family while Saylor's wife's Lexus was in for service at a dealership.

The brakes on the doomed Lexus near San Diego were reportedly on fire as he car hurtled up the freeway."

All I can say is :shakehead

I suspect we're about to see some new legislation regarding braking systems on account of this.

 

[StarHalo]

This subject was done to death on a car forum I frequent, and the final verdict was that the Lexus driver was either specifically trying to crash the car, or simply gave up too easily when/if the brakes alone would not hold the car.

Once you take into account the broad range of ways to get a car to stop over a long distance with plenty of warning, regardless of its mechanical state, there just isn't any excuse for arriving at a catastrophic crash.

 

[jtr1962]

This subject was done to death on a car forum I frequent, and the final verdict was that the Lexus driver was either specifically trying to crash the car, or simply gave up too easily when/if the brakes alone would not hold the car.

Once you take into account the broad range of ways to get a car to stop over a long distance with plenty of warning, regardless of its mechanical state, there just isn't any excuse for arriving at a catastrophic crash.

You may be correct here. I was just doing some math. The engine on the Lexus is rated at 272 HP according to the article. I won't even bother accounting for transmission efficiency, and will therefore assume that the full 272 HP is available at the wheels. As some may know, the equation for tractive force in pounds is F = 375*horsepower/speed in mph. So at 120 mph we have roughly 850 pounds of tractive force.

The car's brakes are capable of applying enough tractive force to cause the car to decelerate at maybe 0.75g, so for a 4000 pound (?) Lexus that would be at least 3000 pounds of braking. So the braking system can easily decelerate the car at 120 mph, even not accounting for the fact that just keeping the car moving at 120 mph requires a large percentage of that 850 pounds of tractive force. In fact, going by the numbers, the brakes should be able to overpower the engine down to at least 34 mph in theory, in practice much lower. After all, the transmission isn't 100% efficient. More importantly, as the car slows the engine will be out of it's peak power band, and will be making significantly less than 272 HP. And unless it's four wheel drive you'll only have two wheels driving but all four braking. You won't even be able to get enough tractive force on the road via the two driven wheels to overpower the other two braked wheels.

Yes, I now tend to believe they just gave up, perhaps because the brakes weren't as effective due to the combination of conditions. Nevertheless, this is still a dangerous problem meriting correction. If a 19 year CHP veteran has trouble controlling a vehicle, you can bet the average driver will be utterly helpless.

 

[LukeA]

And another reason I will only ever drive manuals...

Those are some lofty expectations coming from somebody without a license.

 

[John_Galt]

True, considering that less than 10% of cars are now sold with manual transmissions.


***Note: Statistic rings a bell from some old car mag... I'll have to check on that, though...

And I can drive proficiently... My uncle has a farm with a dirt/gravel road surrounding it. I've driven both automatic cars and manual trucks/SUV's dozens of times there, over the last year or two.

 

[Mjolnir]

I don't understand why the brakes of the Lexus would be "on fire." First of all, the disks themselves would not be "burning," since they are metal. Unless the brake fluid ignited, I don't see why there would be any combustion. I suppose that by "on fire" they could mean that the disks were glowing because they reached a high temperature, but that would mean that a significant amount of force was being applied to the brakes, which would definitely be able to stop the car, even if it was being "floored."
I'm not completely sure about this, but I think that the brake fluid is supposed to stay inside the brake lines, since if it was outside the brake lines, it wouldn't be much help for braking.
If the brakes are not functioning properly, then you have 2 issues: Whatever causes the "runaway acceleration" and an issue with the brake design.

 

[LuxLuthor]

I have a really dumb question, but if I had a "runaway car" couldn't you put it in neutral (or manual transmission out of gear)? Then it seems the brakes should stop it even if the engine is running to beat the band.

 

[flasherByNight]

I believe the solution here is like a locked up computer, push and hold the start button for several seconds to kill the engine.

Ctrl-Alt-Del

 

[notrefined]

Brake pads, Ignite!

 

[John_Galt]

I, too, have a dumb question... Why don/t they make the brakes on vehicles more like the air brakes on big rigs, as in, you release air pressure by stepping on the brakes, and the loss of air pressure causes the brakes to apply?

I do however, realize what a cost this would be to automobile manufacturers, with additional r+d manifested in higher prices, but then you couldn't have brake failure.

 

[LuxLuthor]

Ctrl-Alt-Del

Oh God, if Microsoft is involved in this car, we're all doomed.

Air brakes....probably the issues of the pressurized ballast tank, the noise they make, and cost.