U.S. May Set Rule Requiring Brake Override System on Cars

[Turbineguy]

The Obama administration is considering requiring all automobiles to contain a brake override system intended to prevent sudden acceleration episodes like those that have led to the recall of millions of Toyotas, the Transportation secretary, Ray LaHood, said Tuesday.

http://www.nytimes.com/2010/03/03/business/global/03toyota.html

I suspect this idea would result in increased emissions as a result of sudden slowdown transients.

[ChairmanAgnostic]

1. do you know how much excess weight is caused by

seatbelts?

Imagine how much less oil would be burned if we removed all seatbelts from all vehicles! And Airbags! And bumpers! Get rid of them all and save emissions and oil!

[BeFree]

2. A shift to neutral would work

It might even save gas. I have an automatic that friggin winds up the motor as it downshifts. Got the brakes on and as it shifts down the damn engine speeds up. Stupid.

ETA; 'matic' to auto, and this: There needs to be an rpm controller. Even with cruise on, the engine revs up and down according to speed set. 'Twould be better if the rpm's were set... better fuel mileage.

[Xithras]

6. That doesn't increase fuel consumption in new cars.

Automatics have downshifted so that engine compression can help decelerate the car for many decades, but newer cars cut the fuel flow to the injectors so that it doesn't waste gas. If you shift to neutral, you're just wearing your brakes out faster without gaining any real fuel savings.

[BeFree]

7. Brakes are cheap

Fuel and engines are expensive. A steady revolution (rpm)is more fuel efficient.

On a stick shift, downshifting can slow a car, but with my automatic it actually speeds up the car. You can feel it surge as it shifts down.

An ICE uses gas according to rpms, speed has no bearing on fuel use.
Time running and rpms are the only two factors in fuel efficiency.

[NoNothing]

8. Neutral *wastes* gas

You used to be right, in the days of carburetion. But not now, with computer-controlled injectors.

When you are in idle, the engine must burn fuel to idle and provide power the car's systems. Including the brakes, which also create a power drain on the engine. This consumes fuel. On the other hand, if you use the engine compression to slow the car, the car's momentum is turning the engine. The fuel computer reduces fuel injection to nearly nothing, and the kinetic energy of the car powers the car's systems, energy that you are wasting as heat in the brakes.

A modern, computer-controlled ICE uses gas according to the minimum needs of the engine at any given time.

[BeFree]

9. when RPM's go up

The need of fuel goes up. If it starved the engine of fuel the engine would die.
The minimum needs of the engine are dictated by the rpm.

Brake assistance mostly work on air suction from the engine. Power brakes suck air and when the rpms go up it increases the air load needed to burn the fuel.

Have seen some newer cars that have an electric pump(?) on the brake assist system.

[Xithras]

11. Sorry, but that's not right.

When the engine is engaged to the drive-train, you can completely cut off all fuel and spark while decelerating without "killing" the engine. The momentum of the car will keep the engine turning via the drive-train, though you will slow down as power is no longer being applied. If you want to accelerate again, you merely need to begin supplying fuel and spark to the engine again, and it will start running without missing a beat.

It's the same concept that manual transmission users utilize when they "push start" a car with a dead battery, and it can be verified on any car with a manual transmission. At speed, turn the key to the off position (don't lock the wheel, obviously) without taking the car out of gear. The car will immediately begin to slow down, but your tachometer will still show engine RPM's. If you turn the key back to the "on" position (without hitting "start"), you should be able to just hit the gas pedal and speed up again.

The concept here is very similar. When decelerating in a modern computer controlled car, the computer cuts the fuel back to almost nothing until you either hit the gas pedal again, or slow enough that the computer has to place the engine into idle to keep it from dying. There is NO necessity to keep fuel up at high RPM's when decelerating, and cars haven't behaved that way since the days of carbueration.

[BeFree]

13. Those are nice theories.

Who wants a dead, no fuel engine at any time? Not anyone I know, not while moving. At anytime the rpm's are turning on a gas engine, it is burning that much fuel depending on load. When downshifting the load on the engine increases and rpms go up and more fuel is delivered.

VW tried an engine that shut down and fired up on gas pedal demand. It flopped.

[Xithras]

16. Which is why they don't cut the fuel COMPLETELY off.

My example was just an example. In practice, cutting the fuel off would lead to a bit of hesitation when you hit the gas again, which is why attempts to create fuel free deceleration have flopped. What they now do, instead, is provide only a very minimal amount of fuel to the engine. Far less than needed for idling.

As for the rest, I don't know what to tell you. I can't spend hours writing out posts explaining all of the details of how modern vehicles manage fuel mixtures (I know it, but I have better things to do than sit here and explain it), but I CAN tell you, very definitively, that your understanding of the process is way off. If you want to know how it really works, I suggest finding a good mechanic with lots of experience working on the fuel and computer systems of newer cars (mid 90's or newer) and discuss it over a beer or two. I suspect that you'd learn a lot. Your understanding was correct at one time, but is outdated by a couple of decades. You might even consider calling Click and Clack, as they haven't discussed the topic in quite a while and could do so in a fairly understandable fashion.

In the meantime, if you're shifting your car to neutral when slowing down, you're just wasting brakes and fuel. If your car was made in the last 15 years, there's no valid reason to go into neutral. By doing so, you're actually overriding the computers own fuel saving features.

[BeFree]

18. Sheesh

I fix my own brakes and do almost all the mechanic work on my cars.

Believe me when I tell you, that this new damned car actually surges when it downshifts. The rpms go up and the car surges ahead for a second until the rpm goes down to idle. Totally unlike a manual tranny. BTW, it is a Toyoda. Hmmmm.

Idle means barely sustainable engine speed. When it goes below idle the engine is dying. The idea that an rpm above idle means less fuel use than idle, is just dumb.

[Xithras]

10. That is completely incorrect.

An ICE uses gas according to rpms, speed has no bearing on fuel use. Time running and rpms are the only two factors in fuel efficiency

Modern computer controlled vehicles alter the amount of fuel injected into the engine based on air temp/density, engine temperature, throttle position, engine RPM's, and a couple of other factors. Throttle position vs. engine RPMs is the biggest factor, but it's only one of many. Air resistance, vehicle load, and even tire inflation can dramatically alter the fuel consumption on a modern vehicle, even when compared to itself traveling at the same speed with the same engine RPM's. This is why my car, at 6000RPM in 3rd gear at 50MPH, consumes far more fuel at 6000RPM in 5th at 120MPH. Same RPM's thanks to transmission gearing, but the increased air drag forces the computer to compensate by altering the mixture to add more fuel.

When your auto transmission downshifts during deceleration, your foot is off the gas. At that point, the computer is actually feeding the engine less fuel that it would at an idle. By shifting into neutral, the computer places the engine into idle, which actually increases consumption slightly. The difference is small, but it's real.

[BeFree]

12. eh?

My foot off the gas, the engine goes to idle @ 1,000 rpm and it uses more gas than when the engine is at 1,500 rpm? Yeah, sure.

Drag is a time factor, the faster you go is a time factor. Slower you go is a time factor. Load on the engine is a time factor.

A steady rpm properly computed is more fuel efficient than up and down rpm's.
There is no way around it except for time factors.

If you go one mile in one minute with the hammer down, versus one mile in two minutes at a steady rpm, you will burn more fuel with the hammer down.

[NoNothing]

17. idle @ 1,000 rpm and it uses more gas than when the engine is at 1,500 rpm?

Yes, that is completely correct. At 1,000 RPM, the engine must still provide sufficient horsepower to turn the engine and power the car's systems. During deceleration, the engine must provide 0 horsepower because energy can be harvested from the car's momentum. The car's computer knows this and almost completely cuts fuel flow during deceleration, to less than idle flow. The computer knows that the 1,500 RPM are being caused by momentum and not throttle activation, so it also knows it doesn't need to supply fuel.

Your confusion is arising because you are not making a distinction between RPM's and power. They are related but are not the same thing.

[BeFree]

19. No

When rpm goes up, fuel flow increases. The gas pedal not being down does starve the engine from the increasing rpms, so the rpms go down, but rarely below idle speed. If it does, it is for a micro second.

When rpms go up there is a temporary increase in fuel supply, but the engine (properly running) rarely ever (maybe a micro second) goes below the fuel needed for idle speed or it would shut off.

[NoNothing]

20. Not in a modern vehicle

First of all, the engine does not *need* fuel when decelerating. It is for all practical purposes "shut off" during that time. It continues to spin because the momentum of the car is pushing it, the same way the starter motor pushes it when it starts up. Only when there is no external force turning the engine is it necessary to consume fuel to keep it turning.

In other words, there are two things that can cause an engine to rotate: (1) it is generating power or (2) an external force is rotating it. That's all that RPM's measure: rotation. However, fuel is only needed under condition 1: when the engine needs to generate power. You seem to be under the impression that RPM's and power are directly correlated, but they are not. The engine can generate more power without changing RPM's (e.g. going up a hill at a constant speed; RPM's stay the same but more fuel is required because more work is done by the engine). Also, RPM's can change without the engine changing its power generation, as when you decelerate. Remember, RPM's ONLY measure rotation; that's it, while fuel consumption is a very close approximation of power generated.

Now, unless condition 2 above applies, some power is needed simply to keep the engine turning and the car's systems running even if the car is not moving. This uses fuel. However, if condition 2 above DOES apply, then no power is needed to keep the engine turning and the car's systems running. This uses no fuel.

[BeFree]

23. heh

"The engine can generate more power without changing RPM's (e.g. going up a hill at a constant speed; RPM's stay the same but more fuel is required because more work is done by the engine)."

yeah, it uses more gas going up hill because you push down the gas pedal. Try going up a hill without pushing on the gas pedal.

Y'know, you have a good theory on how a perpetual motion engine would work.
ICE's not.

The simple fact is that less rpms means less fuel consumption. If you are sitting there idling you less fuel than if you are sitting there revving the engine, right?

[NoNothing]

26. Define "revving the engine"

Do you mean using the throttle to increase engine power generation? That uses more fuel.

Or do you mean using the vehicle's momentum to rotate the engine? That uses less fuel.

Nothing perpetual about it - when the vehicle runs out of momentum then there is no more energy to rotate the engine without fuel, and fuel is used to idle the engine.

[Xithras]

22. One has nothing to do with the other.

Fuel flow is not controlled by engine speed. At all. That hasn't been true since the olden days of the 1970's when mechanical fuel pumps received their power from the crankshaft and higher RPM's meant higher pump speed.

Every car built since the early 80's has an electric fuel pump, which delivers constant fuel pressure irrespective of engine RPM. The two are not connected at all any more. The introduction of fuel injection to this system also meant that there was no longer any forced relationship between engine airflow and fuel consumption. The computer, via the injectors, can deliver large masses of fuel at low RPM, or no fuel at all at high RPM. The rate of fuel flow is entirely at the discretion of the programmer who wrote the software for your car.

Higher RPM's certainly suck more air through the engine, but they only increase fuel consumption if the computer tells it to. If your foot isn't on the gas, it shouldn't do so (though it IS a Toyota, so bad programming isn't beyond the realm of possibility).

As for the engine "shutting off", you have to remember that the drivetrain is fully capable of rotating the engine on its own without fuel. An engine, engaged to a drive train, will keep turning while the car is in motion even with no fuel or spark at all. As I said in my other post, resuming power at this point is simply a matter of the computer commanding the injectors to resume fuel delivery and the ignition module to apply spark at the appropriate moment. The pistons, valves, and everything else in the engine will keep moving even with the engine "off", if the transmission is engaged and the vehicle is moving.

When idling with the car out of gear, the computer has to apply enough fuel and air to overcome the engines internal friction and the resistance of the air compressing in the cylinders. That requires a certain amount of fuel. When the engine is engaged but decelerating, the motion from the drivetrain can overcome that friction and resistance itself, requiring no additional fuel. The only reason that ANY fuel is added during this process is to eliminate hesitation, and to ensure that any hydrocarbons in the expelled air are burned completely to reduce pollution. The amount of fuel required for this task IS lower than the amount of fuel required to idle.

I don't know what else to say. These are the facts, and you don't need to take our words for it. There's plenty of supporting information out there on the Internet. If it doesn't matter to you, and want to waste your gas and brakes, that's your decision.

[BeFree]

24. So, what is your point?

Are you still saying that higher rpms use less fuel than at lower rpms?

[NoNothing]

25. They can

Higher RPM's while decelerating use less fuel than lower RPM's at idle, because the engine is fully capable of being rotated by the tires without any fuel at all.

[Kolesar]

3. A circuit to disable cell phones when the car is in "drive" would save more lives than this

preachy me

[sailor65]

4. It's a good thing

our President doesn't design cars for a living.....

just sayin'

[Xithras]

5. And millions of bad drivers will scream in fury.

How many idiots drive with both feet, constantly riding the brake? An override system means that drivers trying this will simply find themselves at a full stop. You'll have to choose one or the other. It also means an end to the brakestand in newer musclecars.

I'm not saying this is a bad thing, but you know that a lot of people are going to complain anyway. Millions of people will have to completely relearn the pedal controls. My MIL is one of these. Right foot gas, left foot brake, and frequently both at once. I've chided her for years about it (especially now that she's old enough to need our financial help every time she needs a brake job), but she refuses to drive with one foot.

[Edweird]

14. Actually, I'm kind of surprised they didn't already have this on 'drive by wire' cars.

I think relying solely on software is a stupid stupid thing.

[FarCenter]

15. This only fixes one part -- other subsystems also need to be redundant

Otherwise, for example, if the throttle position motor is commanded to open the throttle, but the throttle position sensor doesn't show it opening, the engine control module will continue to command the throttle to open.

[ecstatic]

21. And then when another issue worse than acceleration turns up as a result of the tinkering...?

Let's let the engineers be engineers and the politicians be politicians... Right now the acceleration issue is mainly affecting Toyotas--and I suspect that their problem is due to someone tinkering around trying to improve (or fix) another issue. Let's not mess around and f*ck up all the cars!