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"And then he said 'Full throttle power transfer shouldn't break your transmission'..." laughed the Chrysler powertrain engineer with his watercooler buddies.
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Mar 15, 2018 20:32
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Metal Geir Skogul posted:The figures are just fine, and transmissions have multiple coolers: radiated and air-cooled by the casing, and oil-water-air coolers in the front radiator on automatic and (many) manual transmissions. Add to that that the lowest ignition point for ATF is about 215*C in ideal conditions, and otherwise observable ignition temps in the 350-450*C range, it adds up pretty well. E: to add the quote.
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Mar 15, 2018 20:32
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The only time I've set a car on fire involved ATF hitting a cat.
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Mar 15, 2018 20:37
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Oh. OHHHH A catalytic converter. Wow. I had some crazy ideas going through my head there.
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Mar 15, 2018 20:39
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BlackMK4 posted:The only time I've set a car on fire involved ATF hitting a cat. Yeah, well, that cat shouldn't have been reloading and smoking next to its illegal still.
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Mar 15, 2018 20:40
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https://www.youtube.com/watch?v=jKQtqEA7MKY
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Mar 15, 2018 21:45
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Dave Inc. posted:Oh. 
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Mar 15, 2018 21:53
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ThirstyBuck posted:I've never filled the front differential on my wife's Subaru with ATF. And I definitely did not attempt to drive it down the street after having drained the tranny. This! I've never done this, and it never got stuck after rolling off the hoist.
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Mar 15, 2018 22:00
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Metal Geir Skogul posted:Let's throw some Fermi Estimation into the mix: That's an automatic, with massively higher powertrain losses. Also, I'm not sure where you got your specific heat of water; water's specific heat is 4.2ish kJ/kg-K - so 420,000 joules to raise 1kg of it by 100C. Here's mine. WRX, call it 250 horsepower, 636,000btu/hour. 95,400 btu in heat if 85% efficient so 26.5 btu/second. WRX trans has about 4 quarts of oil; about 7 pounds. Oil has a specific heat of 0.4 btu/lb-F, so 2.8btu/F for our 7 pounds of oil. So at 26.5btu/second in, a little less than 10 degrees F per second of WOT. Starting at an operating temperature of 150-200F, you get to oil breakdown really drat quick, and way too quick for heat transfer out to play a factor.
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Mar 15, 2018 22:09
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Well, slidebite is not wrong about gear efficiency numbers. So, what are you proposing? Honest question, because you just threw out a quip about "think about what that means," without an answer, like you expect them to pull the correct answer out of thin air. As for my number, I was maybe including calculations for phase change instead of using the standard sp formula. I got my oil numbers from: http://www.thermalfluidscentral.org/encyclopedia/index.php/Thermophysical_Properties:_Engine_Oil,_Unused
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Mar 15, 2018 22:48
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Sagebrush posted:Yep, I did this one once. Dumped about a quart of oil on the driveway as soon as I started up the engine. I left the cock open on my oil catch can once. I was trying to find the source of an oil leak and had just drained the catch can to be sure that wasn't it. The best part was that I brought it to the dealership for an unrelated oil leak and was pretty embarrassed when they told me "well your oil catch can is open." Luckily they were also smart enough to realize that my oil leak was the valve cover gaskets, and not just the catch can.
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Mar 15, 2018 23:08
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jamal posted:I recently got in an argument on a subaru forum with a guy who insisted that a turbocharger was just a "fan" and could not compress air. I knew a guy that thought Subaru was an Australian car company. He owned one.
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Mar 15, 2018 23:15
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tactlessbastard posted:I knew a guy that thought Subaru was an Australian car company. He owned one. https://www.youtube.com/watch?v=6z9qohzqq9g So it was an easy thing to end up believing. It wasn't until the WRX started showing up in my video games that I realized.
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Mar 15, 2018 23:26
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Metal Geir Skogul posted:Well, slidebite is not wrong about gear efficiency numbers. So, what are you proposing? Honest question, because you just threw out a quip about "think about what that means," without an answer, like you expect them to pull the correct answer out of thin air. This should be done in the name of science. \/ yes, I was originally talking drivetrain loss in general, not necessarily just the transmission slidebite fucked around with this message at 23:44 on Mar 15, 2018 |
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Mar 15, 2018 23:30
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Metal Geir Skogul posted:Well, slidebite is not wrong about gear efficiency numbers. So, what are you proposing? Honest question, because you just threw out a quip about "think about what that means," without an answer, like you expect them to pull the correct answer out of thin air. Part of the confusion is that slidebite threw in the differential as well, so all that heat is not being generated in the transmission. Roughly 90% efficiency (86-94% according to this) for the transmission itself is about right. Automatics are sophisticated enough these days that they're actually a little better than manuals in overall efficiency, primarily due to lock-up torque converters and electronic control. So your numbers are probably about right.
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Mar 15, 2018 23:37
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Fermented Tinal posted:So how do rocket engines work then? Comedy answer: they don’t.   The New York Times, Tuesday, January thirteenth, 1920 Platystemon fucked around with this message at 00:30 on Mar 16, 2018 |
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Mar 16, 2018 00:15
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I put a new carb on my DRZ then took it out for a shakedown cruise. Ten minutes in it died going down the road, I coasted up on to the sidewalk, swore a lot, then got to work on the bike. Twenty minutes of poking and prodding at the bike and nothing - hit the starter, it might sputter for a second then nothing. I was out of gas.
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Mar 16, 2018 00:17
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Platystemon posted:Comedy answer: they don’t. That's hilarious. Almost as good as anti-vaxers spouting half-understood science. Or flat-Earthers. "Nothing to react against." Like a rocket engine is a paddle wheel or something...
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Mar 16, 2018 00:26
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It's only hilarious because Goddard wasn't deterred nor were his financial backers. The Times didn't print a retraction until just before a giant leap for mankind.
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Mar 16, 2018 00:57
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mekilljoydammit posted:That's an automatic, with massively higher powertrain losses. Also, I'm not sure where you got your specific heat of water; water's specific heat is 4.2ish kJ/kg-K - so 420,000 joules to raise 1kg of it by 100C. Yeah but even at WOT it's not putting out 250 hp for the whole RPM range, and I'm pretty sure you're not spending the majority of your time at 5000rpm with the pedal to the floor. Anyway don't discount active cooling: A couple weeks ago at work I was monitoring the hydraulic oil temperature in an excavator, and I watched it drop from 60 C to 50 C in about ten seconds of idling. Not quite 10 degrees F per second but we're talking a 200L oil tank, plus probably another 100L or so in all the lines and cylinders. A better example of how fast heat can actually be dissipated is that I used to test towable generators, the largest being rated for 1200 amps at 208/120 3ph, driven by a diesel engine. Part of the testing involved load banking, ie hook it up to a box of resistors and set it to run at 90% of capacity, with the aim of burning out any carbon buildup that happens when they're run way under capacity. 560 horsepower just screaming for like an hour. I tried to measure the temperature of the turbocharger but the thermometer I have maxes out at like 500 degrees Celcius. And the thing was rated to run at this setting basically forever with no problems.
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Mar 16, 2018 07:41
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EKDS5k posted:A better example of how fast heat can actually be dissipated is that I used to test towable generators, the largest being rated for 1200 amps at 208/120 3ph, driven by a diesel engine. Part of the testing involved load banking, ie hook it up to a box of resistors and set it to run at 90% of capacity, with the aim of burning out any carbon buildup that happens when they're run way under capacity. 560 horsepower just screaming for like an hour. I tried to measure the temperature of the turbocharger but the thermometer I have maxes out at like 500 degrees Celcius. And the thing was rated to run at this setting basically forever with no problems. I was going to say “it’s a shame that energy can’t be put to productive use” like they do at some datacentres. During periods of peak demand, the power company will give a signal and the facility will go onto generator power. It’s a win/win because the generators have to be run regularly for testing and maintenance and now the utility doesn’t have to build more generation or transmission capacity that will only be used for a few hours per year and/or import power at usurious rates. But generators of the size you’re working with aren’t large in absolute terms. It’s only a potential of a few dozen dollars of electricity.
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Mar 16, 2018 08:04
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I didn't think that diesel exhaust fluid was a thing until reading about it on AI It sounds like it comes from the same store that blinker fluid, left handed screwdrivers, and elbow grease do
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Mar 16, 2018 08:05
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The Door Frame posted:I didn't think that diesel exhaust fluid was a thing until reading about it on AI It always makes me think of this stuff:  Which is, surprisingly, almost literally what it says. Heat some wood, condense the vapours in a chilled pipe, and put it in a bottle along with a few additives.
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Mar 16, 2018 08:21
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Platystemon posted:I was going to say “it’s a shame that energy can’t be put to productive use” like they do at some datacentres. No, I know they're not "large" generators, as far as generators go. United Rentals has a 1 MW generator that I've only ever seen from the street, it's the size of a semi trailer. The ones I worked on are for construction sites, and movie sets generally, not for entire buildings. I guess in theory we could have wired something into the building and used that for load banking, but up here all our shop lights are 600V, and I've never seen a towable generator that puts that out.
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Mar 16, 2018 08:23
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I distinctly remember a discussion with someone about the guibo in my old e46, they claimed they were a terrible idea because they sapped 5% of the power. It's about 1kg of rubber. I didn't do the maths but I'm sure the answer would have been "expanding cloud of rubber vapour" This is fun, Let's do it now, 150bhp engine, probable cruising power 25bhp? 18.64kw into the guibo 5% "sapped" allegedly 0.93kw absorbed by 1kg of rubber. Call it 1kw for easy maths NBR specific heat 1350J/Kg-K? Before disapation it's a 1.3 second per Kelvin rise if I understand what I remember and remember what I understand? I'd regularly have a 45 minute cruise to work, I think "guibo becomes liquid and coats underside of Bavarian beater" would happen before I got there. Did I get that right?
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Mar 16, 2018 10:06
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The Door Frame posted:I didn't think that diesel exhaust fluid was a thing until reading about it on AI We actually had a woman come into Jiffy Lube and completely un-ironically ask if we checked blinker fluid as part of the service. It took a second to realize she was serious. Kinda reminds me of being in high school, one of our buddies had just bought an old Mustang from one of those shady used-only dealers. He wanted to be a mechanic and thought he knew way more than he actually did, to the point that it started getting on our nerves. It took a while but we managed to get him to believe his piston return springs were about to poo poo out on him, and we only let him in on the joke when he was seriously about to take it back to the dealer and give them an earful for it.
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Mar 16, 2018 10:38
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Deteriorata posted:Part of the confusion is that slidebite threw in the differential as well, so all that heat is not being generated in the transmission. Roughly 90% efficiency (86-94% according to this) for the transmission itself is about right. Automatics are sophisticated enough these days that they're actually a little better than manuals in overall efficiency, primarily due to lock-up torque converters and electronic control. So, we're claiming that the transmission with more gears transmitting torque is more efficient than the one with fewer gears doing so. Got it. Keep in mind we're talking power input vs power output where no, automatics aren't going to be more efficient - yes, driving cycle efficiency can be better due to the number of gears and lockup torque converters and so on and so forth - but in terms of how much power gets turned into heat due to friction from gearing, you're saying that electronic control will make more gears have less friction than something with fewer gears? Should I point out figure 5.29 on that link where they're showing an efficiency band of about 95-97% for the full transmission for a dry clutch DCT at full torque load? cakesmith handyman posted:I distinctly remember a discussion with someone about the guibo in my old e46, they claimed they were a terrible idea because they sapped 5% of the power. It's about 1kg of rubber. I didn't do the maths but I'm sure the answer would have been "expanding cloud of rubber vapour" Funny thing is that if you feed them big torque pulses (we use them as dyno couplings at work) the loading and unloading does heat them up pretty well, but that's not what a transmission on an actual car does. mekilljoydammit fucked around with this message at 12:26 on Mar 16, 2018 |
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Mar 16, 2018 12:24
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You guys are really oversimplifying your heating calculations. The hotter something gets, the faster it dumps heat into the air around it. Especially for a transmission, assuming that you are loading an engine at WOT by driving, you are going to be moving pretty quickly, which means even more heat dumped, generally.
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Mar 16, 2018 14:54
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Darchangel posted:I was so ticked off I hurled that jack across the parking lot into an empty field. This is the fate of all scissor jacks. EKDS5k posted:Anyway don't discount active cooling: A couple weeks ago at work I was monitoring the hydraulic oil temperature in an excavator, and I watched it drop from 60 C to 50 C in about ten seconds of idling. Not quite 10 degrees F per second but we're talking a 200L oil tank, plus probably another 100L or so in all the lines and cylinders. Observed cooling like that depends a great deal on where the temperature probe is placed within the system. MrYenko fucked around with this message at 15:39 on Mar 16, 2018 |
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Mar 16, 2018 15:37
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EightBit posted:You guys are really oversimplifying your heating calculations. The hotter something gets, the faster it dumps heat into the air around it. Especially for a transmission, assuming that you are loading an engine at WOT by driving, you are going to be moving pretty quickly, which means even more heat dumped, generally. And on the other hand, the exhaust is 4 inches away from the transmission and it's out of direct air flow? Yes, heat transfer gets complicated, but there's not a lot of airflow around a transmission behind an engine, and it's a lot of heat to dissipate. Seriously, I'm doing engine development of little air cooled industrial engines for my day job.. they're forced fan cooled, covered in fins and dissipating far less than 95k BTU/hour worth of heat, but the outer temperature of stuff is in the 200C range, which gets really borderline. Gears transferring heat to the oil is fast - the oil is between the gear teeth and absorbing the heating in the first place. Oil transferring heat to the transmission case isn't very fast because it's basically sitting there with not great surface/volume. And if you're doing this after operating temperatures, the heat transfer between oil and a transmission case that's already stabilized at (say) 160F isn't particularly fast compared to the amount of heating going on in the oil if the transmission is only 85% efficient. Also, I'm doing back of the envelope calculations of stuff at stock power outputs - that 10F per second of WOT? Now say we double that, and do a dyno run where there's no airflow to speak of. Or put the car on a race track where it's at WOT for about half the time for half an hour. 85% efficiency doesn't pass a lot of basic sanity checks.
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Mar 16, 2018 15:53
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Runaway ski lift failure: https://www.youtube.com/watch?v=EcPTcQpkso4 No gore or death, but there were some "serious" broken bones from people getting ragdolled. My knowledge of the function of chair lifts is basically zero but I would have thought if there was a drive failure it'd completely seize up instead of freewheeling. xzzy fucked around with this message at 16:28 on Mar 16, 2018 |
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Mar 16, 2018 16:24
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If it doesn't pass sanity checks, then what are all of these articles and whitepapers about? http://www.machinedesign.com/archive/second-look-gearbox-efficiencies This paper (I think) states a manual, mechanical transmission can go from 94 to 84% efficiency based on gearing, with higher rotational speeds inducing higher losses (table 3): http://spiff.rit.edu/classes/phys216/workshops/w10c/car_engine/efficiency.pdf This paper goes from 94 to 82%: https://link.springer.com/article/10.3103/S1068798X11060050 (second page in the preview) Something's got to give on one or the other side of this argument.
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Mar 16, 2018 16:24
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xzzy posted:Runaway ski lift failure: The weight of everyone on the chair plays a role here.
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Mar 16, 2018 16:29
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xzzy posted:Runaway ski lift failure: Why the poo poo is it going backwards?
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Mar 16, 2018 16:31
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xzzy posted:Runaway ski lift failure: jesus CHRIST
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Mar 16, 2018 16:37
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wesleywillis posted:Why the poo poo is it going backwards? Because no one rides it down. Obviously for some reason both the drive system and brake system failed, leading to a free spinning situation where the weight difference on the "up" direction lead to the system going backwards, from then on out it's just momentum. While it's disappointing that systems can still fail in such a easily preventable way, at least people rallied to yell for people to jump off. Sad part is, I'd probably be one of the people not jumping, cause gently caress that noise. SEKCobra fucked around with this message at 16:42 on Mar 16, 2018 |
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Mar 16, 2018 16:39
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Metal Geir Skogul posted:If it doesn't pass sanity checks, then what are all of these articles and whitepapers about? A weakness in the methodology on that first paper is that they're not measuring how much heat goes into the tires and the drum on the dynamometer and instead trying to estimate it, but OK. Table 3 and 4, notice from 1000 to 4500rpm for both FWD and RWD drivelines, the total efficiency calculated is over 90% - so for the RWD car, the gears in the transmission (4th gear was a bad choice for that table but note from Figure 8 the efficiencies are similar in lower gears) and the hypoid gear in the diff. Look at the polynomial fit on 2nd gear - all over 92% for most of the powerband. *edit* I'm looking at 2nd gear especially because that's going to reduce the effects of heating everything else in the driveline from friction too, by the way. At higher speeds there's going to get to be all sorts of frictional losses that will get harder to account for. Anyway, that's a far cry from "95% efficiency per gear stage is generous".
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Mar 16, 2018 17:20
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BraveUlysses posted:jesus CHRIST Indeed. That's horrifying.
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Mar 16, 2018 17:37
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mekilljoydammit posted:A weakness in the methodology on that first paper is that they're not measuring how much heat goes into the tires and the drum on the dynamometer and instead trying to estimate it, but OK. Table 3 and 4, notice from 1000 to 4500rpm for both FWD and RWD drivelines, the total efficiency calculated is over 90% - so for the RWD car, the gears in the transmission (4th gear was a bad choice for that table but note from Figure 8 the efficiencies are similar in lower gears) and the hypoid gear in the diff. Look at the polynomial fit on 2nd gear - all over 92% for most of the powerband. 95% efficiency per gear stage is a reasonable figure from pretty much every resource I have. I don't do automotive transmissions in my day job, but I do size up and spec out engineered industrial gearboxes on an almost daily, certainly weekly basis, which are capable of absorbing 100% of spec'd power & supplying torque output 24/7 and potentially higher if the designed service factor will allow it. I think the thermal absorption and dispersion of the oil/housing/internals is a real wildcard here. I know enough to be dangerous for calculating it, but I also know enough that, well, I don't know enough, and it's out of my comfort zone so I won't even attempt it. I admit I'm utilizing my limited industrial gearing knowledge and basically transposing it to an automotive application, but I really don't think the efficiencies for an automotive hypoid or helical gear is going to be much different from a hypoid or helical gear in a Falk or SEW-Eurodrive gearbox. I can say that industrial gearboxes run cooler in my experience than automotive applications, but they are typically physically waaay larger as well because they are meant to run 24/7 and properly sized as such (also typically will have higher reductions as well). I genuinely think that running an automotive application at a full load, WOT, the transmission and oil would, absolutely, get hot as hell before too long, but I also think it would cool down pretty quickly once full load is removed. Totally just my hunch though. The only thing I can think of is that the ratios themselves in an automotive transmission aren't typically wild, so you should be on the highside of efficiencies as opposed to the low side, but 95% is pretty generous. What are you thinking is a reasonable # that they should be? 98%? 99.5%? I'm not entirely sure how the heat going to the tires or dyno drum (presumably the coefficient to the road surface?) is taking heat away from the inefficiencies of the gear train... which the torque needs to go through first to get there? Or am I misunderstanding you?
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Mar 16, 2018 17:58
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The existence of aftermarket transmission cooling solutions for most vehicles likely to tow a trailer and many sports cars is pretty solid support for the idea that many transmissions can not dissipate the heat from being run at a high load for an extended period of time. I believe this was one of the major reasons behind the SAE standardizing the Davis Dam test for big pickups, to basically act as a torture test for the vehicle's cooling system and shut down the situation that had previously existed where some trucks might need upgrades right off the line if you wanted to safely and reliably use them at their maximum rated load. The existence of "lifetime" transmission fluid in most non-performance applications paired with warranties that keep getting longer is pretty solid support for the idea that most vehicles don't come anywhere close to maxing out their heat dissipation capabilities.
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Mar 16, 2018 18:34
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