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https://www.thedenverchannel.com/news/local-news/several-vehicles-on-fire-following-crash-on-eb-i-70-at-colorado-mills-parkway-bridge With no brakes, what are your options for slowing, stopping when out of control? Does engine braking only work if you have a Jake brake installed? caught on video https://www.youtube.com/watch?v=sS7uo9o8XyI possibly same truck before the crash https://kdvr.com/2019/04/26/video-shows-a-semitrailer-out-of-control-in-mountains-ahead-of-fiery-i-70-crash/
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Apr 27, 2019 04:28
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UnderToad posted:https://www.thedenverchannel.com/news/local-news/several-vehicles-on-fire-following-crash-on-eb-i-70-at-colorado-mills-parkway-bridge The options were engine brake earlier (once it痴 going to fast, recovering becomes much less likely or impossible - you need to be engine braking before it gets going too fast) or, once engine braking has failed, drive it into a runaway ramp. After that, it ends with this or driving it into an inanimate and immovable object, which is probably not a decision most (people, but especially) 23 year olds are equipped to make.
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Apr 27, 2019 05:40
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I thought diesels couldn't really engine brake without a Jake brake, due to the high compression and the wide open throttle nature? (they regulate power via how much fuel is injected, instead of a throttle body) I'm not exactly knowledgeable about them though, especially big ones. Also, a lot of big rig gearboxes need double clutching to downshift, and if you can't rev the engine high enough to match the next gear down, you won't be able to downshift. These engines have far lower redlines than what a car engine can handle, and the engine computers (or pre-computer, the engine governor) just won't let you rev it that high. In any event, the fact that he passed a runaway ramp hosed him hard, and will gently caress him even harder in court. Yeah, using one of them is often seen as a "you hosed up bad to get to the point that you had to use one of these, you just totaled the truck and load, go dust off your resume and find a job in another industry" move, but it's sure as gently caress better than what happened here. A lot of jurisdictions prohibit use of a Jake brake inside city limits, and he may have had that on his mind, but laws go out the window when you're trying to stop an up to 80,000 pound truck without brakes. But with him being so young (23), there's no way he had much experience, and I'm sure he was panicking, making GBS threads himself, pissing himself, and hoping for a painless death all at the same time. We can armchair quarterback this all day, and there's plenty of things he could have done to avoid this (or at least minimize damage and casualties), but without being in the truck when it happened, there's no way to know for sure. It does sound like he lost his brakes (especially with all the smoke after he blew past the Youtuber's car), but the KDVR article makes it sounds like he lost his brakes well before this happened. Modern vehicles (all of them) carry some variant of a black box. Trucks in particular log a ton of poo poo; I'm sure the various computers from the truck will reveal a lot, assuming any of them survived the fire (some trucks will upload live data, I think, so maybe the trucking company may know a bit). If Powershift sees this, I'm sure he can help us out. randomidiot fucked around with this message at 07:55 on Apr 27, 2019 |
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Apr 27, 2019 07:46
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Looks like the white semi that flew past was either stuck traveling at full noise or paying almost zero attention to what was happening in front but as STR said:STR posted:We can armchair quarterback this all day, and there's plenty of things he could have done to avoid this (or at least minimize damage and casualties), but without being in the truck when it happened, there's no way to know for sure. It does sound like he lost his brakes (especially with all the smoke after he blew past the Youtuber's car), but the KDVR article makes it sounds like he lost his brakes well before this happened. In theory if you have no wheel brakes because you've over heated them then the truck should still slow down when you stop applying fuel with the throttle and are still in gear (sort of engine braking that you'd get in a car). If there are Jake brakes or Exhaust brakes installed and are switched to the on position then they should activate whenever the sensors sense no throttle input, which has been my experience. Alternatively you manually engage the exhaust brakes with the switch. Side note: the Eaton Fuller, Road Ranger boxes can be either double clutched or floated (changed without the clutch) in both directions depending on your skill. https://www.youtube.com/watch?v=dd4s22TAER0&t=187s
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Apr 27, 2019 11:56
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Assuming he completely cooked the brakes in the mountains, -and- the throttle was somehow stuck, it sure looks like it was pretty flat leading up to where the accident occurred. You can always shut it off, pull the spring brakes (for whatever they'll do), and leave it in gear to get whatever engine braking you can. Obviously some other action than barreling ahead until inevitably running into heavy traffic.
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Apr 27, 2019 13:28
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Without a Jake or compression brake, engine braking is going to be minimally effective. You can use it to hold a speed down a grade, but it's not really going to slow you down. I always question what it means to "lose brakes". It doesn't just happen and go from no issues to no braking immediately. There are warning signs and redundancies built into the truck.
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Apr 27, 2019 15:38
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It's possible to overheat the brakes so badly that they aren't very effective. The air supply has a redundancy in the spring brakes, but that's still the same overheated shoes, just applied via spring pressure. I promise that you will get some engine braking too, it takes energy to drag all that rotating mass around. Maybe it's not the prettiest controlled stop but it's not hauling rear end and plowing into stopped cars.
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Apr 27, 2019 15:58
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If you've overheated your brakes to the point of them being effective, you didn't just lose them. That's my point. You've ignored the continued diminishing braking capacity and increasing pedal effort until catastrophic failure. The air system has its own redundancies. Primary, secondardy, and trailer brakes have separate supply tanks so that a failure in one circuit doesn't take out the system. You have primary and secondary tank pressure gauges with a low pressure visual alert. Trucks even have failed circuit stopping distance requirements.
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Apr 27, 2019 16:57
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 Edit - none of the alarms or redundant air systems mean jack poo poo if you cook the shoes. Inspecting the shoes/slack adjusters is part of your pre trip, because if that doesn't work the rest of it is pointless. angryrobots fucked around with this message at 17:52 on Apr 27, 2019 |
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Apr 27, 2019 17:46
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Whats the diff between engine (jake?) brake and exhaust brake?
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Apr 27, 2019 18:59
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wesleywillis posted:Whats the diff between engine (jake?) brake and exhaust brake? Exhaust braking (a device brand for which is Jake Brake) restricts the exhaust, which raises the effort required to pump air through the engine (and rotate it). The net effect of which is increased engine braking. I think (but am not sure) that diesels should engine brake without a Jake Brake, though I'm not sure how dramatic the effect is. In some (gas powered) cars, there is very little engine braking, in others, there is a ton. Certainly, Jake Brakes exist because a lot of braking effort is needed to slow down an 80,000lb vehicle. tl;dr: Engine braking is the mechanism which slows a vehicle, an exhaust brake is a edit: \/ Oh, I thought a Jake brake was an exhaust brake. So it's a different device which operates differently, but similarly increases engine braking, yeah? e2:  
Krakkles fucked around with this message at 19:16 on Apr 27, 2019 |
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Apr 27, 2019 19:08
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Jake brake = you get a compression stroke, exhaust valve pops open at TDC to dump cylinder pressure so you don't get a *de*compression stroke pushing the piston back down. Exhaust brake =sealing off the exhaust pipe, so you get compression stroke, decompression, and then a high-effort exhaust stroke as you try to pump into the mostly sealed chamber. They're just two different ways of increasing the ratio of decelerating forces to accelerating forces in the idling engine, ie ways of improving engine braking in a diesel. Fender Anarchist fucked around with this message at 19:13 on Apr 27, 2019 |
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Apr 27, 2019 19:11
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angryrobots posted:Inspecting the shoes/slack adjusters is part of your pre trip, because if that doesn't work the rest of it is pointless. I service bulk liquid tankers, my shop is attached to a busy terminal. You can rest assured that a proper pre-trip happens about 0% of the time 
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Apr 27, 2019 19:56
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With most diesel engines there is very little engine braking due mostly to, as STR mentioned, the lack of a throttle valve. On a gasser when you lift your engine works to pull a deep-ish vacuum in the intake manifold and that work (along with all the parasitic loads, to a small extent) uses up a bunch of the energy your car carries and you slow down. A diesel takes a full gulp of air every intake stroke, compresses it and if no fuel is injected that air just pushes the piston back down with only minutely less energy than was used up to compress it. yes there are a lot of parasitic loads in a 14-16l diesel engine but they're not enough to do a whole lot of braking when you're dealing with all the extra inertia of a loaded truck/trailer. A compression brake/Jake Brake (Jake being short for the same Jacobs as the drill chuck company) is a device which fucks with your valve timing. Say you've got a Cummins 855. Each cylinder has 3 cam lobes 3 pushrods, 3 rockers. One intake, one exhaust, one injector. Injector lobe is timed to start lifting just before TDC on the compression stroke, obvs. What a Jake brake does is instead of having the injector rocker press down on the injector tappet, it hydraulically redirects that force to the stem of the exhaust valve, thus farting that intake charge your piston just worked its rear end off to compress right out the exhaust before it had a chance to do anything. Then it spends the rest of the would-be combustion stroke pulling a vacuum in the cylinder until the actual exhaust stroke starts, further wasting energy and slowing your fatass down. Engines without camshaft-driven injectors might use an electric-over-hydraulic system or other methods to pop the exhaust valve open but the effect is the same. Exhaust brakes are much quieter but less reliable, simply restricting exhaust flow and perhaps using a VGT to further increase the inefficiency of the engine and thus the braking force. Usually seen more on medium duty stuff. Detroit (possibly others but I play with DD16s all day so that's what I know) has started using a throttle body, partly to assist with engine braking without extreme noise (and partially because EGR is a shitload easier to implement reliably when you can pull a vacuum). And yeah, the only failure modes of an FMVSS-121 braking system that leave you with no brakes are extreme brake fade (almost certainly the case here), extreme wear causing overcamming (modern air drums are actuated by an S-cam system and if your brakes are so worn that the camshaft can rotate 360 degrees without shoe contact, you're hosed- though modern extended life shoe geometry makes this situation very difficult to achieve), maybe a bad slack (but once again extremely unlikely to affect more than one brake) or outright drum failure which is rare to even see on a single axle and would still leave you with 9 brakes in a standard 6x4 tractor/tandem trailer configuration). Individual redundancies in the air system are irrelevant to this discussion, no matter what fails the default state of a 121 system is springs applying the equivalent of a not-all-the-way-to-the-floor-but-holy-gently caress-I'm-gonna-die brake application. Turbo Fondant fucked around with this message at 20:01 on Apr 27, 2019 |
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Apr 27, 2019 19:58
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angryrobots posted:Assuming he completely cooked the brakes in the mountains, -and- the throttle was somehow stuck, it sure looks like it was pretty flat leading up to where the accident occurred. You can always shut it off, pull the spring brakes (for whatever they'll do), and leave it in gear to get whatever engine braking you can. I posted this in the share the road thread: LloydDobler posted:I work about a mile from there and commute that freeway every morning. That section is the runoff after the final descent down the mountains with several miles of steep grades, up to 6%. Everyone gets to the "flat" part (which is still a very steep downhill) and thinks it's over so they let their brakes cool as they engine brake up to 80 mph. Trucks set their brakes on fire and burn down on a regular basis all along there. The last runaway ramp was a few miles back, but he probably didn't need it at the time. But again, even though it looks flat it's still very steep through there. vvv Oh poo poo, yeah if that's the same truck he hosed up bad. LloydDobler fucked around with this message at 20:25 on Apr 27, 2019 |
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Apr 27, 2019 20:01
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From the video posted earlier, it sure looks like he was already hosed up while in the steeper grade, wildly changing lanes and narrowly missing other vehicles. Of course, it's also possible that dude had some kind of psychotic episode or was upset with a life issue.
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Apr 27, 2019 20:19
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Training drivers costs money though and turnover is high enough you can just go "CDL? Nice here are the keys" and hope for the best. If there was in fact a mechanical problem though vehicular manslaughter charges are 100% bullshit.
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Apr 27, 2019 20:48
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There is no way you can be rolling down a mountain and not notice your brakes are fading toward gently caress town. It doesn't go from working great to holy gently caress not working good one slow down to the next. Before you are hitting 100 mph you should be hitting the loving guard rail.
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Apr 27, 2019 21:08
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Drum brakes on the big trucks stop braking at around 1300 degrees.The disc setups stay a little cooler but they'll fail as well. I haven't watched the video but I can tell you that a truck that has been checked and everything in working order will still run away and lose brakes if the driver starts out too quickly at the top of a hill. If the driver is unfamiliar with the road and starts out at 60mph at the top, and its a good long hill, he has maybe 1 or 2 chances to get his speed under control while his brakes are cold. If he drags his brakes down the hill some and then realises he's in poo poo and tries to slow down, the possibility of a runaway is very real. The strongest engine brakes out there on trucks are around 475 braking horsepower. A fully loaded truck, especially the heavier setups will blow through an engine brake. And if you're going too quickly, you wont be able to downshift as your rev limiter wont let you grab a lower gear as you have to rev match. You could actually toss it into neutral in a panic and then not be able to get it back into any gear at all. My point is, the driver could have done everything safely, the truck could have been properly maintained, but if the conditions are right, the hill is big, and the driver hadn't been on that stretch before, bad things can happen if he doesn't get his speed under control right away. Also, we need a new truckin thread.
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Aug 2, 2019 11:19
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jonathan posted:Also, we need a new truckin thread. So you wanna make one or you want me to bastard this into one?
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Aug 2, 2019 15:28
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Diesels without dedicated exhaust brakes do still have quite a lot of engine braking compared to a petrol engine of the same displacement, but the kind of loads you're talking about with a big heavy artic will romp straight past that. If anyone thinks the lack of a throttle plate means a diesel lacks resistance, try hand-cranking one without a decomp valve.
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Aug 2, 2019 16:55
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You still have to build the compression in the first place, but that energy is given right back to the crankshaft once it turns over past tdc. So the net braking is less than something with a closed throttle plate. Modern gas engines are going so far as to control power and rpm with valve timing and lift while keeping the throttle partially open to reduce pumping losses at light loads.
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Aug 2, 2019 17:26
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That's fine in theory, as is everyone's talk of how it's all about vacuum being pulled against a closed throttle plate. But it doesn't correlate to experience of driving manual transmission vehicles in petrol and diesel guises, of similar capacities. I've never encountered this lack of engine braking in a diesel. Can the people who have say what vehicles they've found that to be the case?
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Aug 2, 2019 20:46
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I regularly drive commercial diesel trucks/trailers for work, with a gross weight in the 30-50k range and they will absolutely engine brake. No doubt having an exhaust brake fitted would be better, but you can still control speed on downgrades with planning and gear selection. There are warning signs on grades for a reason - you need to adjust your speed before it's too late to do so.
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Aug 2, 2019 21:37
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I finally found something that towing mirrors were good for
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Aug 20, 2019 04:09
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Funny I was just randomly reading up on downspeeding. It seams they have done all they can with engine management and are now focusing on drivetrain and differentials. http://www.danacv.com/advantek40/pdf/Downspeeding_WhitePaper.pdf?fbclid=IwAR1KOROS7EC0i_NFuXpNVeTsa8oKCXfSY05aGnncQFYKcV0kDtwRrNKr2jI
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Aug 21, 2019 07:39
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Adiabatic posted:So you wanna make one or you want me to bastard this into one? I browse from the awful app which doesn't allow new thread creation. So go wild ! See if you can get a mod to change the thread title.
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Aug 23, 2019 16:46
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jonathan posted:I browse from the awful app which doesn't allow new thread creation. So go wild ! See if you can get a mod to change the thread title. https://www.youtube.com/watch?v=04cwo850t3o Wo ist unser Nutcup?
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Aug 24, 2019 00:10
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