EEVblog Electronics Community Forum
Products => Dodgy Technology => Topic started by: NiHaoMike on February 12, 2022, 02:56:04 am
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https://arstechnica.com/cars/2022/02/radio-station-snafu-in-seattle-bricks-some-mazda-infotainment-systems/
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Well, that's just crap coding at it's finest. ::)
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And what happens if something like this happens again after the car warranty runs out?
edit. I mean much later on. When nobody at mazda remembers how this stuff works.
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From there, the infotainment systems became trapped in a rebooting loop, never successfully completing the task. When afflicted owners took their cars to be checked at local Mazda dealers, they were told that the "connectivity master unit" was dead and needed to be replaced.
The snag? A new CMU costs $1,500—if you can find one, which you can't, because of supply chain problems
Vipre77 Ars Praefectus
jump to post
Dr Gitlin wrote:
show nested quotes
The screen on which the backup camera is trying to project images is broken. So it's obviously true.
I’m not so certain…. I had a 2016 Mazda CX-3 and my wife still has a 2016 CX-5. Both of our cars had failures exhibiting identical symptoms as described in the article. In fact, it happened twice on my CX-3, but the failure the second time seemed to a little different. There is a button combination you can press to force a reboot. Doesn’t help the problem. I tried disconnecting the battery for an hour and that didn’t work either. In all cases, in my experience, the rear view camera continued to work even while the computer was constantly rebooting. I believe the display itself may have two inputs, one for the camera and one for the head unit, and it switches between them when you put the car in reverse. Either that or the camera system is somehow operating a lower level than the rest of the infotainment system and runs Independently of it.
The second failure I had on my CX-3 was odd. FM radio continued to operate at all times, even during the reboot process, but I was unable to change stations, inputs, or even the volume (mute still worked). The screen would cycle through the usual animations during the boot process. Eventually, the FM radio stopped worked, and later still, the display quit showing the reboot animations. You’d still see a little flicker of the back light to tell when it was rebooting. Even in this state the rear-view camera display kept working as intended.
Both cars were still under original factory warranty at the time and all three CMU replacements were covered.
Someone asked earlier and I’ve read on the Mazda forums that Johnson Controls developed the Infotainment system in these. If true, then odds are good that they did both the hardware and software work here. The problem can’t simply be flashed away with a firmware update. My dealer tried for several hours and the system reboots before you can even access the menu to start the flash. There’s no safe mode from which you can run the flash process, nor will it boot from a USB or anything. You can only run the updates after the system successfully boots into the OS and you can access the normal config menus. From what I can see, you’d either need to access a JTAG header like they’d use in the factory or a way to physically replace the cache memory with the offending file to have any hope. Even reflashing via JTAG might not do it if it doesn’t wipe the cache.
How can they allow radio stations and broadcasts to interrupt their system at a firmware level.
I don't remember this ever happening with car radios or consoles whatever they are called.
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And what happens if something like this happens again after the car warranty runs out?
edit. I mean much later on. When nobody at mazda remembers how this stuff works.
I doubt anyone at Mazda knows how this stuff works, it'll be designed and manufactured by some third party like Matsushita or Samsung, or as it's North American market maybe Motorola or someone?
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I hate how cars have gone to all these fully integrated systems, my $20 Aliexpress MP3 playing DIN slot headunit does me just fine.
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And what happens if something like this happens again after the car warranty runs out?
edit. I mean much later on. When nobody at mazda remembers how this stuff works.
I doubt anyone at Mazda knows how this stuff works, it'll be designed and manufactured by some third party like Matsushita or Samsung, or as it's North American market maybe Motorola or someone?
Doesn't seem to matter who or where it comes from, automotive is just sloppy like that. I'm reminded of the Toyota "unintended acceleration" fiasco, when it came out that the ECU was full of spaghetti code and single random bit flips could make it pin the throttle, among other horrors. If Toyota was screwing up that badly I'd assume their generally lower quality (IMO) competition is worse.
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Doesn't seem to matter who or where it comes from, automotive is just sloppy like that. I'm reminded of the Toyota "unintended acceleration" fiasco, when it came out that the ECU was full of spaghetti code and single random bit flips could make it pin the throttle, among other horrors. If Toyota was screwing up that badly I'd assume their generally lower quality (IMO) competition is worse.
I remember that, they blamed driver error, floor mats and I read the authorities started to take more notice and investigate when some highway officer and his family got killed in one of them.
I last read they got fined for it.
https://www.latimes.com/archives/la-xpm-2010-mar-03-la-fi-toyota-saylor3-2010mar03-story.html (https://www.latimes.com/archives/la-xpm-2010-mar-03-la-fi-toyota-saylor3-2010mar03-story.html)
MARCH 3, 2010 12 AM PT
Off-duty CHP Officer John Saylor, his wife, daughter and brother-in-law died Aug. 28 when their 2009 Lexus ES350 took off at full throttle, reaching an estimated 120 mph in rush-hour traffic in suburban San Diego, before crashing and killing all four on board.
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The brother of Saylor’s wife placed a chilling 911 call from the vehicle. He told an emergency dispatcher that the accelerator pedal was stuck and that Saylor was unable to slow the car down.
“We’re in trouble. . . . There’s no brakes. End freeway half-mile,” Christopher Lastrella said during the recorded conversation.
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The brother of Saylor’s wife placed a chilling 911 call from the vehicle. He told an emergency dispatcher that the accelerator pedal was stuck and that Saylor was unable to slow the car down.
“We’re in trouble. . . . There’s no brakes. End freeway half-mile,” Christopher Lastrella said during the recorded conversation.
"pedal stuck" is not a software thing, still that should never ever be possible
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The brother of Saylor’s wife placed a chilling 911 call from the vehicle. He told an emergency dispatcher that the accelerator pedal was stuck and that Saylor was unable to slow the car down.
“We’re in trouble. . . . There’s no brakes. End freeway half-mile,” Christopher Lastrella said during the recorded conversation.
"pedal stuck" is not a software thing, still that should never ever be possible
I think the only people who have the sang-froid to be precise and say "The accelerator system has become unresponsive to control inputs" when in a vehicle heading at top speed down a road that ends in half a mile also normally have Martin-Baker ejector seats to get them out of trouble and a brand new necktie in their near future. For the rest of us I suspect screaming "The ******** pedal's stuck!" is the nearest we're going to get to terminological exactitude under those circumstances. So there's no reason to believe that the description does not fit a "software induced failure in the acceleration system" any less well than it describes a simple mechanical failure.
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If you've time to make a phone call (even as a passenger), I'm surprised there wasn't time to try things like force it into a lower gear, or reverse (you might break the gearbox, but at least you're no longer accelerating), or even just turn the engine off (without completely removing the keys obviously, don't know if that model is keyless though).
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Lexus has been keyless for a while, top end model range almost always are these days. Probably also locked out shifting down a gear to protect the gearbox, and thus the shift does nothing, as it is also just a set of logic inputs to the drivetrain controller, with no actual linkages any more. Might have reset if you held in start stop button for 30 seconds, but kind of hard to read the manual while being in a semi guided missile.
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Click it into neutral?
I guess panic had set in.
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Certainly at the time Toyota was under fire for unintended acceleration, there were significant usability issues with the keyless system.
I had a lexus at the time and given the fuss, I thought it would be sensible to check functionality so that I had a plan. So I found an empty road and drove at 10mph while I tested mitigation strategies.
Pressing the start/stop button was my first thought. This did nothing at all.
Repeatedly mashing the button also did nothing.
I had to hold the button for what was a very disconcerting period of time, even at 10mph, although it was probably only 5 seconds.
Pushing the transmission lever into neutral worked perfectly and this was the obvious best choice out of the solutions tested.
It was fortunate that I had done this, as about 1 year later the car suddenly accelerated uncontrollably as I pulled out of a junction. I popped it onto neutral and coasted to a stop with the engine bouncing off the limiter.
The cause in this case was easily identified. The pedal had become Mechanically caught by the floor mat, when I had floored it to make a quick getaway from the junction.
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Certainly at the time Toyota was under fire for unintended acceleration, there were significant usability issues with the keyless system.
I had a lexus at the time and given the fuss, I thought it would be sensible to check functionality so that I had a plan. So I found an empty road and drove at 10mph while I tested mitigation strategies.
Pressing the start/stop button was my first thought. This did nothing at all.
Repeatedly mashing the button also did nothing.
I had to hold the button for what was a very disconcerting period of time, even at 10mph, although it was probably only 5 seconds.
Pushing the transmission lever into neutral worked perfectly and this was the obvious best choice out of the solutions tested.
It was fortunate that I had done this, as about 1 year later the car suddenly accelerated uncontrollably as I pulled out of a junction. I popped it onto neutral and coasted to a stop with the engine bouncing off the limiter.
The cause in this case was easily identified. The pedal had become Mechanically caught by the floor mat, when I had floored it to make a quick getaway from the junction.
The floor mat in some cars (I've seen it in Fords) has a small hole that a hook engages (from the floor), to prevent the mat sliding forward. Should really be mandatory...
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Lexus has been keyless for a while, top end model range almost always are these days. Probably also locked out shifting down a gear to protect the gearbox, and thus the shift does nothing, as it is also just a set of logic inputs to the drivetrain controller, with no actual linkages any more. Might have reset if you held in start stop button for 30 seconds, but kind of hard to read the manual while being in a semi guided missile.
It's quite troubling to realise that, especially with the ubiquity of electronic controls over physical ones nowadays, manufacturers seem to be happy to ignore the concept of fail+safe.
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If you've time to make a phone call (even as a passenger), I'm surprised there wasn't time to try things like force it into a lower gear, or reverse (you might break the gearbox, but at least you're no longer accelerating), or even just turn the engine off (without completely removing the keys obviously, don't know if that model is keyless though).
For the record, the correct action is to stand on the brake pedal until the car stops. Assuming the brakes aren't half functioning worn out junk, this will stop the car.
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For the record, the correct action is to stand on the brake pedal until the car stops brakes overheat, fade and catch fire.
TFTFY
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It matters what kind of car the throttle sticks on... if it is a Toyota Corolla, the brakes can probably win over the engine. If it happens in your supercharged hot-rod, you may have a problem! :D
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Brakes are sized according to vehicle mass more than anything else. They are not, as I understand them, intended to stop a vehicle at wide open throttle, especially if you already have significant momentum.
If you find yourself on an empty stretch of road suitable for trying it, please, feel free. Myself, I value my brake components and would prefer not to ruin them testing this, when I can simply take the vehicle out of gear.
The cause in this case was easily identified. The pedal had become Mechanically caught by the floor mat, when I had floored it to make a quick getaway from the junction.
A classic case of 'driving like a twat'..
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The cause in this case was easily identified. The pedal had become Mechanically caught by the floor mat, when I had floored it to make a quick getaway from the junction.
A classic case of 'driving like a twat'..
As my mother would say: "Takes one to know one!".
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It matters what kind of car the throttle sticks on... if it is a Toyota Corolla, the brakes can probably win over the engine. If it happens in your supercharged hot-rod, you may have a problem! :D
Brakes are going to overcome the engine of pretty much any road going (combustion engine) car. Stalling a runaway diesel in 1st gear? no problem, and thats close to corner case worst possible situation.
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It matters what kind of car the throttle sticks on... if it is a Toyota Corolla, the brakes can probably win over the engine. If it happens in your supercharged hot-rod, you may have a problem! :D
Brakes are going to overcome the engine of pretty much any road going (combustion engine) car. Stalling a runaway diesel in 1st gear? no problem, and thats close to corner case worst possible situation.
Try it. You're in Aus, and if there is anywhere in the world you can find a long, straight, unoccupied road it's in Aus. You might be surprised. Full throttle remember, not idle.
Alternatively you can work it out mathematically. My car produces 174 Nm at the engine shaft, 559 Nm at the rear shaft in 5th gear, 2314 Nm in 1st. That's a lot of torque to overcome. The brake force calculations versus engine torque are left as an exercise for the student but I've just done them on the back of an envelope and it's surprising. The engine wins.
Also the 143 BHP (107 kW) my car's engine produces is a lot of heat to get rid of from the brake discs. A brake disc is cast iron and weighs 4.5kg or thereabouts each, they have a specific heat capacity of 460 j/kgK and a melting point of around 1150 C, so need 9.35 MJ to raise the temperature of 4 x 4.5 kg = 18 kg discs to melting point from 20 C, which is just 87 seconds at 107kW ignoring any cooling (which wouldn't be very much). Anyone who has done any racing will tell you how quickly brakes fade once they get too hot.
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If you've time to make a phone call (even as a passenger), I'm surprised there wasn't time to try things like force it into a lower gear, or reverse (you might break the gearbox, but at least you're no longer accelerating), or even just turn the engine off (without completely removing the keys obviously, don't know if that model is keyless though).
The Toyota Prius does not have a traditional transmission, it has a fixed planetary gear set between 2 motors and the IC engine. Reverse is accomplished by running the electric motors backward and the IC engine stopped.
Their drivetrain control had something like 46 tasks, and the LOWEST priority task was monitoring the BRAKE pedal! YIKES! When overloaded, the real time manager would drop lower priority tasks. Supposedly, holding the "power" button for 4 seconds provides a hardware shutdown of all electronics that can't be overridden by software, and would have caused the car to coast to a stop. The gear shift on the dash is obviously just a set of switches that are read by the drivetrain computer. The Prius has no "ignition key/ignition switch" it just has a "power" button. The key fob has to be somewhere near the dash for the immobilizer to detect it.
Jon
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It matters what kind of car the throttle sticks on... if it is a Toyota Corolla, the brakes can probably win over the engine. If it happens in your supercharged hot-rod, you may have a problem! :D
Brakes are going to overcome the engine of pretty much any road going (combustion engine) car. Stalling a runaway diesel in 1st gear? no problem, and thats close to corner case worst possible situation.
Try it. You're in Aus, and if there is anywhere in the world you can find a long, straight, unoccupied road it's in Aus. You might be surprised. Full throttle remember, not idle.
Alternatively you can work it out mathematically. My car produces 174 Nm at the engine shaft, 559 Nm at the rear shaft in 5th gear, 2314 Nm in 1st. That's a lot of torque to overcome. The brake force calculations versus engine torque are left as an exercise for the student but I've just done them on the back of an envelope and it's surprising. The engine wins.
Also the 143 BHP (107 kW) my car's engine produces is a lot of heat to get rid of from the brake discs. A brake disc is cast iron and weighs 4.5kg or thereabouts each, they have a specific heat capacity of 460 j/kgK and a melting point of around 1150 C, so need 9.35 MJ to raise the temperature of 4 x 4.5 kg = 18 kg discs to melting point from 20 C, which is just 87 seconds at 107kW ignoring any cooling (which wouldn't be very much). Anyone who has done any racing will tell you how quickly brakes fade once they get too hot.
I said runaway, not idle. So something in the order of 4000Nm at the wheels, in first gear, engine stopped no problem. You jump to maths to try and justify your imagined truth but there are some basics which immediately point to it being wrong:
Combustion engine cars decelerate faster than they can accelerate, even if you take a car that can freely spin the wheels under power, when stopping hard ABS pulls down peak stopping force on the brakes to maintain traction.
Cars dont have brake fade from a single pull to stop from cruising speed, its something thats actually physically tested for Australian design rules compliance (15 back to back partial declarations).
So these things have been tested, it might be that the brakes on my vehicles are wildly high performance but being stock from the factory I dont think they are anything special (they do have highly non-linear servo assist for emergency force, but that should be fairly commonplace, again its something tested by the ADR compliance). Depending on region in Australia you are looking at 0.4 to 0.6g as the minimum braking force to meet roadworthy testing, which is more than enough to arrest regular engines, [sa]oddly enough high power vehicles have higher performing braking systems...[/sa]
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It matters what kind of car the throttle sticks on... if it is a Toyota Corolla, the brakes can probably win over the engine. If it happens in your supercharged hot-rod, you may have a problem! :D
Brakes are going to overcome the engine of pretty much any road going (combustion engine) car. Stalling a runaway diesel in 1st gear? no problem, and thats close to corner case worst possible situation.
Try it. You're in Aus, and if there is anywhere in the world you can find a long, straight, unoccupied road it's in Aus. You might be surprised. Full throttle remember, not idle.
Alternatively you can work it out mathematically. My car produces 174 Nm at the engine shaft, 559 Nm at the rear shaft in 5th gear, 2314 Nm in 1st. That's a lot of torque to overcome. The brake force calculations versus engine torque are left as an exercise for the student but I've just done them on the back of an envelope and it's surprising. The engine wins.
Also the 143 BHP (107 kW) my car's engine produces is a lot of heat to get rid of from the brake discs. A brake disc is cast iron and weighs 4.5kg or thereabouts each, they have a specific heat capacity of 460 j/kgK and a melting point of around 1150 C, so need 9.35 MJ to raise the temperature of 4 x 4.5 kg = 18 kg discs to melting point from 20 C, which is just 87 seconds at 107kW ignoring any cooling (which wouldn't be very much). Anyone who has done any racing will tell you how quickly brakes fade once they get too hot.
I said runaway, not idle. So something in the order of 4000Nm at the wheels, in first gear, engine stopped no problem. You jump to maths to try and justify your imagined truth but there are some basics which immediately point to it being wrong:
Combustion engine cars decelerate faster than they can accelerate, even if you take a car that can freely spin the wheels under power, when stopping hard ABS pulls down peak stopping force on the brakes to maintain traction.
Cars dont have brake fade from a single pull to stop from cruising speed, its something thats actually physically tested for Australian design rules compliance (15 back to back partial declarations).
So these things have been tested, it might be that the brakes on my vehicles are wildly high performance but being stock from the factory I dont think they are anything special (they do have highly non-linear servo assist for emergency force, but that should be fairly commonplace, again its something tested by the ADR compliance). Depending on region in Australia you are looking at 0.4 to 0.6g as the minimum braking force to meet roadworthy testing, which is more than enough to arrest regular engines, [sa]oddly enough high power vehicles have higher performing braking systems...[/sa]
"You jump to maths to try and justify your imagined truth" - Well, put some cold hard numbers on what you're saying then. On an engineering forum numbers are facts, everything else is opinion or hot air.
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You jump to maths to try and justify your imagined truth
- Well, put some cold hard numbers on what you're saying then. On an engineering forum numbers are facts, everything else is opinion or hot air.
So you can throw up misleading and incomplete models and claim you are more correct? No. Especially when your claims are directly contradicted by actual testing. You think the engine wins, I have done that specific test (in close to worst case) and found the opposite.
You put up some maths for some tiny fraction of the problem, and couldnt be bothered to check real world figures/sources. But ask me to justify?... Oh wait, I did:
https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules (https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules)
Entirely yours to peruse, the mandatory testing that road going motor vehicles must meet to be registered in Australia. That proves brakes are capable of pulling up, repeatedly, without failure. Energy dissipation is not the problem, clamping force/friction is likely the limiting factor (if it wasn't then brakes would be ripped from their mountings in emergency braking), yet all realistic road going cars with combustion engines decelerate faster than they can accelerate, energy in vs energy out, such a simple physics principle. Therefore they can easily shed speed even if the engine is running full tilt.
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Certainly at the time Toyota was under fire for unintended acceleration, there were significant usability issues with the keyless system.
I had a lexus at the time and given the fuss, I thought it would be sensible to check functionality so that I had a plan. So I found an empty road and drove at 10mph while I tested mitigation strategies.
Pressing the start/stop button was my first thought. This did nothing at all.
Repeatedly mashing the button also did nothing.
I had to hold the button for what was a very disconcerting period of time, even at 10mph, although it was probably only 5 seconds.
Pushing the transmission lever into neutral worked perfectly and this was the obvious best choice out of the solutions tested.
It was fortunate that I had done this, as about 1 year later the car suddenly accelerated uncontrollably as I pulled out of a junction. I popped it onto neutral and coasted to a stop with the engine bouncing off the limiter.
The cause in this case was easily identified. The pedal had become Mechanically caught by the floor mat, when I had floored it to make a quick getaway from the junction.
Weird stuff happened, even prior to the widespread use of microprocessors in cars.
My 1983 Holden Camira (a "beefed up" version of GM's "J" series "world car") had a nasty little trick, in that, if you intended to accelerate briskly from a standstill, the car would, instead, trickle away at a "snails pace", so you could find yourself part-way across an intersection with a large truck bearing down on you.
At the beginning, it sometimes wouldn't do this, so when I "took it back", the verdict was NFF.
As we were moving to a country town for work, & it was only really a problem if you needed to "take off" relatively fast in a few traffic situations, we didn't have the time to chase Holden about it, so, perforce, we developed a technique for these situations, where you floored the pedal, let it up, then immediately pushed it again, when it would operate normally.
This was not often needed in the country town, as, if you were joining a main road, you could usually see the "ginormous" wheat truck coming a fair distance away, & decide your options.
As being carless in a Wheatbelt town while I was at work wasn't a preferred option for SWMBO, we went back to Perth, & picked up a old "roughie" for me to drive-------a V8 Leyland P76! :o
The tyres weren't the best, so another trip to Perth to equip the old beast became necessary.
All good, so far, until I was stationary at traffic lights.
The lights went green, & momentarily, I forgot which car I was driving, & floored the throttle.
The results were impressive, to say the least!
It was just as well that I was replacing the tyres, as the old "P seventy-thing" probably left most of the remaining rubber on the rear ones behind! :scared::scared:
Epilogue: I found out later that the Camira's "vacuum logic" "Engine Management Module" had two hoses transposed.
Connecting them correctly fixed the fault.
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You jump to maths to try and justify your imagined truth
- Well, put some cold hard numbers on what you're saying then. On an engineering forum numbers are facts, everything else is opinion or hot air.
So you can throw up misleading and incomplete models and claim you are more correct? No. Especially when your claims are directly contradicted by actual testing. You think the engine wins, I have done that specific test (in close to worst case) and found the opposite.
You put up some maths for some tiny fraction of the problem, and couldnt be bothered to check real world figures/sources. But ask me to justify?... Oh wait, I did:
https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules (https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules)
Entirely yours to peruse, the mandatory testing that road going motor vehicles must meet to be registered in Australia. That proves brakes are capable of pulling up, repeatedly, without failure. Energy dissipation is not the problem, clamping force/friction is likely the limiting factor (if it wasn't then brakes would be ripped from their mountings in emergency braking), yet all realistic road going cars with combustion engines decelerate faster than they can accelerate, energy in vs energy out, such a simple physics principle. Therefore they can easily shed speed even if the engine is running full tilt.
No, you haven't justified or proven anything, just engaged in handwaving and vaguely alluded to "testing it" without providing any details. Let me be clear, I'm happy to be proved wrong by someone that puts the work in, even tells a convincing anecdote of when it happened to them, or how they tested it, but someone who just gainsays, and insultingly at that isn't adding anything useful to the conversation.
If you want to cite what I expect is hundreds of pages of Australian Design Rules, you could at least quote the paragraph that proves your point, possibly with a little extra explanation if it doesn't directly prove your point, but you don't. Failure to do so smacks of rhetorical tactic rather than an attempt to impart actual information - "Here, here's a 500 page document that proves I'm right, read it. Then when you have you're fit to discuss this". No, thank you.
"That proves brakes are capable of pulling up, repeatedly, without failure." under normal conditions of repeated braking I'm sure they do and I'm sure the ADR makes sure they do. Braking continuously against an engine locked on full throttle isn't normal conditions. But I must assume you know that, yet you still cite it as "justification". Again, rhetoric, not a useful factual contribution. You''ll have to forgive me at this point if I come to the conclusion that that you're more interested in bolstering your opinion than arriving at some objective proof.
So, will a modern car's brakes stop it if the engine has run away at full throttle?
I'd like to see a complete, calculated example from someone who knows what they are talking about rather than all the opinions and conjecture. "someone" clearly can't provide it, I'm pretty certain I can't (the reason for leaving my back of the envelope calculations to one side is (1) there's one point I don't completely trust, (2) I was rather hoping someone better than me would stick their oar in).
So, instead of bluster, handwaving and insults would anyone care to try for a reasoned solution like grown up engineers?
For completeness here's the back of the envelope calculations I did earlier. I actually put them to one side to have a think later, then got interrupted by someone who thought that the route to wisdom is pathed with handwaving and gainsaying.
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My car will produce 174 Nm at the engine shaft, 559 Nm at the rear shaft in 5th gear, 2314 Nm in 1st. I have "10 inch" brake discs the pads are about 2" across so let's take off 1" to find the centre of the pad's contact area. That gives a radius of 102 mm. Calculating back, assuming perfect brake pads and discs with a coefficient of friction of 1, you need to provide 559Nm at 0.102 m = 5480 N force at the brake pad to overcome 5th gear, and 2314Nm at 0.102m = 22686 N to overcome 1st gear. That's crudely 559 kgf and 2314 kgf.
Can I produce forces between 559 kgf and 2314 kgf on the brake pedal? No. Can I do it with the help of a vacuum servo? The biggest vacuum servos normally fitted are 11" and those have a force multiplier of around 2.4. So the question becomes can I produce between 233 kgf and 964 kgf at the brake pedal? The answers are respectively "No" and "No.".
But, the brake pedal provides mechanical advantage. How much? If it was 2:1 you can halve those figures. So I might be able to beat the engine at full throttle in 5th, I wouldn't stand a chance in 1st. If it was 5:1 then in 1st I'm down to 192 kgf, a bit more than twice my body weight - I might just manage that to save my life. In 5th we're at 46 kgf, a bit more than standing from a squat, definitely doable. So, we're down to the questions (1) what mechanical advantage is available, (2) what gear is the car stuck in before we can get to a plausible answer.
Note that we have completely ignored the momentum of the vehicle, just the force required to overcome the engine. If we want to do momentum too we'll have to get into differential equations, and nobody wants that do they? And then there's brake fade, that assumed perfect coefficient of friction is (1) false, (2) will rapidly become less as the brakes heat up, which is a fair assumption in this scenario.
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My sticking point is that I'm uncertain how much to account for mechanical advantage at the brake pedal. That's simply because I couldn't find any figures, whereas oddly I could find figures for the effects of servo assist for different size servos (I assumed the biggest available, I wasn't going out in the rain to check). Go figure.
Now, if anyone sensible can find fault with that please do and correct it. Perhaps we can work towards facts rather than conjecture and opinion.
What I can say from anecdote, is that in olden days it was a reasonable test of a handbrake to see if the car stalled trying to pull away with the handbrake on. Much to my embarrassment, I have to confess to having driven off with the handbrake on in the car cited above and got up to 30-40 mph (turning right from traffic lights from a Sainsbury's car park onto the North Circular Road, the embarrassment is sufficient that I remember exactly where I was), wondering why the car wasn't pulling properly, before I realised that I still had the handbrake on. And no, that's with a fully operational and MoT tested set of brakes (which requires that each wheel produces at least 100 kgf braking force on a rolling road, so 200 kgf minimum at the tyre for the two rear wheels operated by the handbrake, 575 Nm minimum if converted to torque terms).
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You jump to maths to try and justify your imagined truth
- Well, put some cold hard numbers on what you're saying then. On an engineering forum numbers are facts, everything else is opinion or hot air.
So you can throw up misleading and incomplete models and claim you are more correct? No. Especially when your claims are directly contradicted by actual testing. You think the engine wins, I have done that specific test (in close to worst case) and found the opposite.
You put up some maths for some tiny fraction of the problem, and couldnt be bothered to check real world figures/sources. But ask me to justify?... Oh wait, I did:
https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules (https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules)
Entirely yours to peruse, the mandatory testing that road going motor vehicles must meet to be registered in Australia. That proves brakes are capable of pulling up, repeatedly, without failure. Energy dissipation is not the problem, clamping force/friction is likely the limiting factor (if it wasn't then brakes would be ripped from their mountings in emergency braking), yet all realistic road going cars with combustion engines decelerate faster than they can accelerate, energy in vs energy out, such a simple physics principle. Therefore they can easily shed speed even if the engine is running full tilt.
So, instead of bluster, handwaving and insults would anyone care to try for a reasoned solution like grown up engineers?
[more imaginary justification with made up numbers]
You really are a masochist arent you?
https://roads-waterways.transport.nsw.gov.au/documents/roads/registration/brake-assessment-manual.pdf (https://roads-waterways.transport.nsw.gov.au/documents/roads/registration/brake-assessment-manual.pdf)
Boring car, 8000N of stopping force at the wheel/road interface from the front wheels.... pedal force 547N. So you're still out by an order of magnitude. Regular cars are no challenge to stop with their braking system, modern disc brakes are astonishing in their power.
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I think this is more a matter of "how to brake". If you are apply too little force over a longer period, you will destroy the pads and discs due to overheating, the brakes will hardly brake any more (this is a common failure on the combination of heavy vehicle, mountain and inexperienced driver). If you instead floor the brakes, your vehicle *will* stop. Of course you should not try that for fun for safety reasons...
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You jump to maths to try and justify your imagined truth
- Well, put some cold hard numbers on what you're saying then. On an engineering forum numbers are facts, everything else is opinion or hot air.
So you can throw up misleading and incomplete models and claim you are more correct? No. Especially when your claims are directly contradicted by actual testing. You think the engine wins, I have done that specific test (in close to worst case) and found the opposite.
You put up some maths for some tiny fraction of the problem, and couldnt be bothered to check real world figures/sources. But ask me to justify?... Oh wait, I did:
https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules (https://www.infrastructure.gov.au/infrastructure-transport-vehicles/vehicles/vehicle-design-regulation/australian-design-rules)
Entirely yours to peruse, the mandatory testing that road going motor vehicles must meet to be registered in Australia. That proves brakes are capable of pulling up, repeatedly, without failure. Energy dissipation is not the problem, clamping force/friction is likely the limiting factor (if it wasn't then brakes would be ripped from their mountings in emergency braking), yet all realistic road going cars with combustion engines decelerate faster than they can accelerate, energy in vs energy out, such a simple physics principle. Therefore they can easily shed speed even if the engine is running full tilt.
So, instead of bluster, handwaving and insults would anyone care to try for a reasoned solution like grown up engineers?
[more imaginary justification with made up numbers]
You really are a masochist arent you?
https://roads-waterways.transport.nsw.gov.au/documents/roads/registration/brake-assessment-manual.pdf (https://roads-waterways.transport.nsw.gov.au/documents/roads/registration/brake-assessment-manual.pdf)
Boring car, 8000N of stopping force at the wheel/road interface from the front wheels.... pedal force 547N. So you're still out by an order of magnitude. Regular cars are no challenge to stop with their braking system, modern disc brakes are astonishing in their power.
Again, pointing at some document off in the distance is not making your case, it's just ducking having to prove it. Still if that's the way: The MOT Inspection Manual (https://assets.publishing.service.gov.uk/government/uploads/system/uploads/attachment_data/file/671818/mot-inspection-manual-for-classes-3-4-5-and-7-from-20-may-2018-draft.pdf).
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I know someone that experienced a stuck wide-open-throttle in a powerful V8 sports car on a downhill section of road. He stood on the brakes, which were just about able to slow the car enough to make the final crash merely "expensive" rather than "fatal"...
I lost control of a car myself once, flooring it in a turn... the throttle stuck and the car spun out at the exit of the turn, despite turning the key off very fast (I was young, with good reactions, which didn't make up for the poor decision making on this occasion!).
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Try it. You're in Aus, and if there is anywhere in the world you can find a long, straight, unoccupied road it's in Aus. You might be surprised. Full throttle remember, not idle.
Alternatively you can work it out mathematically. My car produces 174 Nm at the engine shaft, 559 Nm at the rear shaft in 5th gear, 2314 Nm in 1st. That's a lot of torque to overcome. The brake force calculations versus engine torque are left as an exercise for the student but I've just done them on the back of an envelope and it's surprising. The engine wins.
Also the 143 BHP (107 kW) my car's engine produces is a lot of heat to get rid of from the brake discs. A brake disc is cast iron and weighs 4.5kg or thereabouts each, they have a specific heat capacity of 460 j/kgK and a melting point of around 1150 C, so need 9.35 MJ to raise the temperature of 4 x 4.5 kg = 18 kg discs to melting point from 20 C, which is just 87 seconds at 107kW ignoring any cooling (which wouldn't be very much). Anyone who has done any racing will tell you how quickly brakes fade once they get too hot.
Curiosity got the better of me on the way home from work tonight so I gave it a go in a 1.6 litre supercharged R53, 168 BHP, 220 Nm, 6 speed manual. The power and torque figures are peaks, but it's apples to apples from your example. They're measured at 6k RPM and 4k RPM respectively for peak figures if you're interested, or so some website says.
I floored it and applied the brakes in third, then second gear, at 30 MPH. Engine speed was 2200 RPM in third and 3100 RPM in second at 30. In third I was surprised at how quickly the car slowed down and couldn't get to the clutch quick enough to stop stalling it as I was watching the revs and speed, and the road, so there I was in the middle of a clear road with nothing in front of me, no reason to have stopped, restarting the car...
I tried the same in second and only went down to about 15 MPH. It was noticeably more difficult to slow the car down but it at no point felt like it wasn't ever going to happen, or run away. It was still slowing down at a decent rate. I was of course left-foot braking which itself is a strange experience, coupled with flooring it as well it felt like there was quite a lot going on, especially judging how hard to press the brakes with my left foot as usually that's going straight to the floor.
I didn't try first gear as the roads weren't exactly deserted and I didn't want to look like a total nutcase, driving around slamming the brakes on for no reason other than to conduct stupid experiments.
In most cases I'd be driving around in 4th at 30 MPH, somewhere between 1500 and 2k RPM, coupled with the less advantageous torque multiplier from the gearbox and diff.
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I remain curious as to how this would go at motorway speeds in a two tonne American compensation-mobile which has begun to accelerate madly by itself.
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I remain curious as to how this would go at motorway speeds in a two tonne American compensation-mobile which has begun to accelerate madly by itself.
This experiment has been done by several car magazines, for example:
https://www.motortrend.com/features/unintended-acceleration-test/ (https://www.motortrend.com/features/unintended-acceleration-test/)
https://www.caranddriver.com/features/a16576573/how-to-deal-with-unintended-acceleration/ (https://www.caranddriver.com/features/a16576573/how-to-deal-with-unintended-acceleration/)
The results of these tests are that most cars stop almost as quickly as if the accelerator was not depressed. The only exception was a muscle car tested at 100 mph where stopping distance was extended by a couple of hundred meters.
There are, however, some problems with these tests - as they did not test the worst case (i.e. the maximal brake pedal effort achievable by a physically weak driver, rather than an average driver or an athletic driver), nor do they take account of the fact that brake assistance will be rapidly lost if the pedal is pumped. Without brake assistance, the results are likely to be significantly different.
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Given that the case in point was a serving police officer, it's unlikely he was unable to provide enough pedal effort. One wonders at this point just how much separation happens between the brake pedal and the braking system on this vehicle; I'm not specifically aware of any braking-by-wire systems, but of course that doesn't mean they don't exist.
If these cars have an "intelligent" cruise control system, ie one that can brake as well as accelerate, I wonder if the car had already been braking slightly to compensate for the engine gradually throttling up, and when the driver tried to apply full braking the brakes were already hot and didn't have enough retardation available?
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Caranddriver states an interesting fact: When going at high speed (that Lexus should be able to reach 120mph easily), the brakes were not enough to actually stop the car, just to slow it down to a lighter crash.
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It matters what kind of car the throttle sticks on... if it is a Toyota Corolla, the brakes can probably win over the engine. If it happens in your supercharged hot-rod, you may have a problem! :D
Brakes are going to overcome the engine of pretty much any road going (combustion engine) car. Stalling a runaway diesel in 1st gear? no problem, and thats close to corner case worst possible situation.
Try it. You're in Aus, and if there is anywhere in the world you can find a long, straight, unoccupied road it's in Aus. You might be surprised. Full throttle remember, not idle.
Alternatively you can work it out mathematically. My car produces 174 Nm at the engine shaft, 559 Nm at the rear shaft in 5th gear, 2314 Nm in 1st. That's a lot of torque to overcome. The brake force calculations versus engine torque are left as an exercise for the student but I've just done them on the back of an envelope and it's surprising. The engine wins.
Also the 143 BHP (107 kW) my car's engine produces is a lot of heat to get rid of from the brake discs. A brake disc is cast iron and weighs 4.5kg or thereabouts each, they have a specific heat capacity of 460 j/kgK and a melting point of around 1150 C, so need 9.35 MJ to raise the temperature of 4 x 4.5 kg = 18 kg discs to melting point from 20 C, which is just 87 seconds at 107kW ignoring any cooling (which wouldn't be very much). Anyone who has done any racing will tell you how quickly brakes fade once they get too hot.
559Nm is a trivial amount of torque for brakes to overcome, a hard stop even from low speed generates far more than that. The problem is if the car is already travelling at significant speed then there is already lot of energy for the brakes to absorb, and having the engine working against them at the same time could push them over the edge if they were marginally sized to start with.
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Given that the case in point was a serving police officer, it's unlikely he was unable to provide enough pedal effort. One wonders at this point just how much separation happens between the brake pedal and the braking system on this vehicle; I'm not specifically aware of any braking-by-wire systems, but of course that doesn't mean they don't exist.
If these cars have an "intelligent" cruise control system, ie one that can brake as well as accelerate, I wonder if the car had already been braking slightly to compensate for the engine gradually throttling up, and when the driver tried to apply full braking the brakes were already hot and didn't have enough retardation available?
I know Prius (at least gen 3) is brake by wire in the rear, it pumps them up for the parking brake (no pawl in the transmission), you have to put into a service mode to do any work on them. The fronts that do most of the work still have a direct hydraulic path for safety though.