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Brake system complexity and safety

@David L, maybe the predominance of odd or even harmonics? I don’t know for sure. I’ve got to wonder how high up the price scale you’d have to go in equipment to fully experience a difference between digital or analog music. (It is hard to find good floor speakers these day, IMHO, too much cheap junk being offered) Or even how many people have the hearing capable of discriminating between them.

“I’ve had it explained to me by an electrical engineer that digital music (CD’s, mp3’s, transistor amps) has harmonics on the odd numbers, 1,3,5,7 and analog music (tube amps, vinyl records) have harmonics on the even numbers 2,4,6,8 giving a “warmer” more pleasing sound.”

Transistor amps (especially the earlier ones) add mostly odd distortion products, whereas distortion from tube amps is usually a mix of odd and even products, with the 2nd harmonic dominating.
Odd harmonics are more grating and high order harmonics are more intrusive.
One rule of thumb to judge the listener’s sensitivity to harmonic distortion is to take the reciprocal of the inverse square of the harmonic number.
Example: The ear is 4x more sensitive to 4th harmonic as 2nd. 2.25x more to 3rd vs 2nd.
It’s better to have lower levels of ALL harmonic distortion products, but other problems can crop up with circuits designed to lower total harmonic distortion to very low levels.

Wes, you have my sincere and humblest apology.

that s ok, I ve been called worse… :slight_smile:

To bring the discussion back to cars: the volume knob on my 2011 Edge is obviously digital, as it changes in increments (you can feel the “bumps” as you turn it). I always seem to want it a little louder or softer than I can adjust. Is there a way to change this?

Just had to comment on this:

If you don't trust modern technology, Don't get on a modern airliner. A Boeing 777 has multiple miles of wiring in it, along with complicated software to run it all.

The difference is that the 777 went through an incredible certification process with the FAA that cars did not have to go through. The 777’s software has been bug-checked much more extensively than the software in a car - and btw, cars tend to have more code in them than planes. A fun statistic I found out when I got my '07 Acura is that my car has more lines of code than the F-22 stealth fighter (and, yes, I have found a bug in it).

If cars had to go through the rigorous review process that commercial airliners have to go through, a Hyundai would probably start at around a hundred grand, but it would be the safest car ever made.

@shadowfax, “I have found a bug in it” The F-22 or your Acura? :slight_smile:

Several people have commented that if the software misbehaves, I still have the hydraulic system. I’m not so sure. I am not privy to the software code that controls my brake system, but the behavior of the anti-lock feature suggests that two things occur: (1) brake pressure on the locked-up wheel is reduced, and (2) engine power is reduced. It’s the first process that concerns me. I have read enough software code in my life (been doing it since 1961) to know that if there is code in there that can reduce brake pressure, it is possible to have a bug that will cause that code to be executed at an inappropriate time.

I think this really boils down to a matter of odds. I would guess that more lives have been saved by adding software to brake systems to enhance driver control of the vehicle than have been lost from software bugs that cause the driver to lose control.

Carrying this forward to self-controlling cars (autoautomobiles?) I predict that we will see fewer accidents, but when one occurs, it will be much more horrific. Basically, cars will be interconnected through wireless means (as opposed to mechanical means) to create large mass transit vehicles.

My father, who was born on a farm in Michigan in 1917, told me that when they heard a car coming, everyone ran out from their homes to see it. I recall doing that when a jet flew over when I was a kid. Modern life is considerably safer than hunting and gathering.

Sigh…

The National Highway Transportation Safety Administration broaches this question in a recently published technical report. http://www-nrd.nhtsa.dot.gov/Pubs/811182.PDF The conclusions reached in that report may suprise and disappoint some.

The main question addressed is essentially a cost-benefit analysis of anti-lock braking systems. With regard to fatal collisions, the study finds “The Long-Term overall effect of ABS on fatal crash involvements is close to zero.”

@rplantz‌ Both! :wink: The Acura has a bug where under very rare conditions that I haven’t completely figured out (I think it has something to do with wheel slip at a certain speed) it won’t shift out of 2nd gear until you stop the car and put it in park. The theory right now is that all 3rd gen TL’s have this bug, and most owners experience it somewhere between 0 and 1 times.

With regard to your Prius’s brakes, I agree that they’re very complex and that there are most likely some failure modes that could be triggered by buggy software. Not just with the ABS, but with the main hydraulic service brakes, because there is no direct connection between the pedal and the brakes in normal conditions. The master cylinder presses against a “stroke simulator” that both makes it feel like you’re using normal brakes, and sends a signal to the skid control ECU to tell it how hard you’re pressing the brake. The skid control computer then sends a signal to the accumulator, which opens and closes valves as necessary to brake without locking up wheels or swerving.

Fortunately, the failsafe for the Prius is that if any problems are detected in any of the systems, it switches off the computer-controlled braking system, and your pedal essentially becomes directly (hydraulically) connected to the brakes just like in a normal car.

The iffy bit is that this leaves us hoping that the car can properly detect when something goes wrong, however the lack of fatalities involving malfunctioning mid-2000’s Prius brakes seem to indicate that most likely it reliably can.

@shadowfax My design experience goes back to the horizon scanners on the Gemini capsule and the LEM. In addition to the automated guidance control on those craft, they had manual valves on the jets so the astronauts could open and close them by hand.

I’ve read countless lines of computer code, a couple of decades in industry and a couple of decades teaching the subject. It is simply impossible to create perfect software. All it takes is one bit out of the billions to be wrong. And it’s not just the applications code. I’ve done more than one work-around because the production tools I used had bugs. So the applications programmer may do a perfect job (very unlikely), and then the vendor provides a new version of the compiler, which creates a bug (more likely, a different bug) in the software. Previous testing is now mostly invalid.

Oh well, I’m quite sure that my Prius is orders of magnitude safer than the first car I owned – a 1940 Ford convertible.

@David L
To bring the discussion back to cars: the volume knob on my 2011 Edge is obviously digital, as it changes in increments (you can feel the “bumps” as you turn it). I always seem to want it a little louder or softer than I can adjust. Is there a way to change this?

That is the case with pretty much most new electronics. In the car, I will try and change balance from front to back and also play with the base/treble and see if it helps find the sweet spot.

Rplantz, the benefits of software as applied to brakes is a hotly debated issue, mainly because its value depends largely on the specific vehicle characteristics, the specific system(s), and the environment in which they’re operated.

I think the greatest benefit “carrying this forward” is going to come with the widespread use of proximity sensing systems overriding driver controls for the critical safety systems. These systems currently used on high-end Mercedes that maintain safe following distances, brake automatically, slow the vehicle automatically, etc., will when they become widespread have a significant impact on accident reduction… and will save lives. These systems don’t drink, don’t get drowsy, don’t get tired and nod off, don’t become complacent, and IMHO will greatly compensate for our most serious (and dangerous) weaknesses.

Current ABS systems are IMHO a poor example, as I believe their tradeoffs outweigh their benefits, traction control systems and stability systems I haven’t enough experience with to judge (although I have my doubts). These systems as they currently exist have soured me on systems that override the driver’s control, but the new proximity sensing systems have great promise and may cause me to change my mind about automated controls.

@the same mountainbike A friend bought two Mercedes in the early 2000s. He bragged about the many electronic gadgets - rain sensor to close the sunroof, etc., etc. These gadgets have been constant, and costly, headaches for him over the years. Mercedes fell very low on the annual Consumer Reports’ reliability surveys in those years. The story I heard is that they greatly improved the reliability of their cars by deleting many of the gadgets.

Referring again to Consumer Reports’ surveys, it seems that one of the biggest reliability problems in cars these days is with the infotainment systems. (IMHO “car” and “infotainment” should not be in the same sentence.)

So here I am, driving a Prius, one of the most electronic-dependent cars on the road. Even with over 9 years of almost no problems, I still get nervous at times.

BTW, my friend attended the Bob Bondurant High Performance Driving School some years ago. The way they taught him to stop a car as fast as possible is to slam on the brakes until the front wheels lock up and then crank the steering wheel all the way to one lock. Won’t work if you have ABS. I don’t think he has ever had occasion to try this technique on public roads.

Rplantz, your point is an excellent one. I’m operating under the assumption that once the systems flow down to Toyota, Honda, Hyundai and the like, these manufacturers will make reliable systems. Mercedes reliability has been terrible for a very long time. IMHO they tend to offer cutting edge technology without doing the reliability engineering (or perhaps the supplier quality engineering) necessary to create robust systems.

Re: ABS, I personally have experienced the folly that is ABS. Get it on ice and it’ll get you killed. ABS is largely responsible for my current aversion to systems that override the operator’s control over his/her critical systems. IMHO to say ABS is overrated is an understatement… IMHO in some driving environments it’s downright dangerous.

I know some here will immediately get defensive and begin to argue, but that’s my opinion, and lengthy previous debates have not altered it one bit… so those of you about to heatedly bang on your keyboards on this subject might as well save your energy. I’m stating this as opinion, not fact, so relax.

@galant: I’ve played with the bass/treble with not much improvement. The front/rear fader may help. Of course, doing it while you’re driving is a distracting hassle.

and then the vendor provides a new version of the compiler, which creates a bug (more likely, a different bug) in the software. Previous testing is now mostly invalid.

And the tool vendors still wonder why there is such an aversion to continual upgrades among the actual users! But it has our latest and greatest features… no thanks.

The shuttle software is claimed to be the most verified code package ever produced. They required 100% re-verification for any change to the loadable object.

@the same mountainbike “the folly that is ABS” I also wonder about some traction control systems. On my 1995 Ford Contour, they simulated a limited slip differential by applying the brake on the slipping wheel. It was nearly seamless. On my 2005 Prius, they cut all power to both drive wheels. It gives me a real thrill when, say, exiting a driveway into oncoming traffic and there is a little water in the gutter. Zoom – pause – zoom.

I recently ran across a collection of old car ads. They’ve been pushing ease and comfort from the very beginning of the automobile. It’s gotten to the point where many people don’t even seem to realize that they’re in control of more than a ton of metal, plastic, and dangerous fluids hurtling down the highway at high speed. If we got rid of automatic transmissions, power windows, and touch screens, I believe it would reduce car traffic by at least 50%. Than in itself would probably save more lives that all the electronic “safety” gadgets.

For the record, I’m saying this having spent my entire working life designing electronically controlled devices, both analog and digital. So I have a pretty good understanding of the potential for problems in these devices.

@TwinTurbo This is off topic, but it’s an example of how bugs can creep into our designs. In the summer of 1984 I worked for HP. One of my projects was writing a log function in (Motorola 68000) assembly language for their in-house library. To get the required accuracy, I used triple-precision arithmetic. It was used in their spectrum analyzers. The next semester I was lecturing about signed integers in the assembly language class I was teaching. In the middle of the lecture it suddenly occurred to me that perhaps I had not accounted for overflow in my log algorithm. As soon as I finished the class, I ran back to my office and checked my notes. Fortunately, I had designed the algorithm such that all the integers were always non-negative. Sure was a distraction during the rest of my lecture. :wink:

Keep the automatics,ditch the rest,having driven everything from huge trucks to heavy earthmovers-to economy cars-I can assure you automatics are safer and a real upgrade,being able to slip a clutch,lug an engine ,clash gears,doesnt a driver make-Kevin

I completely disagree with you. Automatics suck, IMHO. They “disconnect” the driver from truly controlling the car, allow the driver to “daydream” along without thinking about what they’re doing.