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Big gearbox design
Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great.
Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-). Chris |
Big gearbox design
On Tue, 15 Aug 2017 23:47:37 -0700 (PDT), Christopher Tidy
wrote: Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great. Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-). Chris These are pretty big: https://goo.gl/7dcoqC Regards, Boris Mohar Got Knock? - see: Viatrack Printed Circuit Designs (among other things) http://www.viatrack.ca void _-void-_ in the obvious place --- This email has been checked for viruses by Avast antivirus software. https://www.avast.com/antivirus |
Big gearbox design
On 16/08/17 07:47, Christopher Tidy wrote:
Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great. Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-). Chris I don't think the guy I know that used to work for David Brown would agree. While he is no longer full time he does get call upon to work on North Sea oil rig gearboxes from time to time and has worked on large ship gearbox installations in the past from what he has said. |
Big gearbox design
Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington:
I don't think the guy I know that used to work for David Brown would agree. While he is no longer full time he does get call upon to work on North Sea oil rig gearboxes from time to time and has worked on large ship gearbox installations in the past from what he has said. It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well. Chris |
Big gearbox design
"Christopher Tidy" wrote in message
... Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great. Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-). Chris ============================ From what I've read it seems the reasons are mismatches between the engine and load torque/speed requirements and problems keeping the shafts aligned in large, somewhat flexible structures like ships. http://www.navweaps.com/index_tech/tech-038.htm https://www.wartsila.com/docs/defaul...la-o-gears.pdf Gears worked better when the speed was relatively constant or the load demand could be controlled by varying propellor blade pitch as on large WW2 aircraft engines. http://www.newcomen.com/wp-content/u...r-13-White.pdf http://www.machinedesign.com/news/co...tary-gearboxes Usually lowest overall cost drives the choice. -jsw |
Big gearbox design
On Wed, 16 Aug 2017 04:43:06 -0700 (PDT), Christopher Tidy
wrote: Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington: I don't think the guy I know that used to work for David Brown would agree. While he is no longer full time he does get call upon to work on North Sea oil rig gearboxes from time to time and has worked on large ship gearbox installations in the past from what he has said. It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well. Chris It might be just that. Since the volume of metal increases by the square of the diameter of the gear they must reach a point where moving that volume of metal takes too much energy compared to the amount of energy transmitted. So the cost of the gearbox plus the cost of transmitting the energy just gets too expensive. Eric |
Big gearbox design
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Big gearbox design
The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling.
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Big gearbox design
On Wed, 16 Aug 2017 17:39:57 -0400, "Jim Wilkins"
wrote: "Ed Huntress" wrote in message .. . On Wed, 16 Aug 2017 08:24:01 -0700, wrote: On Wed, 16 Aug 2017 04:43:06 -0700 (PDT), Christopher Tidy wrote: Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington: I don't think the guy I know that used to work for David Brown would agree. While he is no longer full time he does get call upon to work on North Sea oil rig gearboxes from time to time and has worked on large ship gearbox installations in the past from what he has said. It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well. Chris It might be just that. Since the volume of metal increases by the square of the diameter of the gear they must reach a point where moving that volume of metal takes too much energy compared to the amount of energy transmitted. So the cost of the gearbox plus the cost of transmitting the energy just gets too expensive. Eric This may or may not be an issue, but when gears get really large, they can become more expensive than the simple size proportion would indicate. It has to do with heat treatment and the relative risk (and cost) of failure. Big ones are often case-hardened, teeth only. As you go smaller, the tendency is toward flame hardening of teeth, and then through-hardening for the still smaller ones. We're talking about heavy-duty industrial gears here. I've watched this being done on 36-inch Curvics or spiral-bevels (I forget which) at Gleason Works, 30 years ago, and the really big ones go through a lot of steps. They're spotted with rouge and lapped after hardening in the biggest sizes. Lapping each gear can take a whole day. -- Ed Huntress https://www.geartechnology.com/issue...nstruction.pdf Yeah, for cast and fabricated mill gears. Notice the size range: 125 in. diameter and up. Those that Gleason was making started as steel forgings. -- Ed Huntress |
Big gearbox design
"Ed Huntress" wrote in message
... On Wed, 16 Aug 2017 17:39:57 -0400, "Jim Wilkins" wrote: "Ed Huntress" wrote in message . .. On Wed, 16 Aug 2017 08:24:01 -0700, wrote: On Wed, 16 Aug 2017 04:43:06 -0700 (PDT), Christopher Tidy wrote: Am Mittwoch, 16. August 2017 13:32:32 UTC+2 schrieb David Billington: I don't think the guy I know that used to work for David Brown would agree. While he is no longer full time he does get call upon to work on North Sea oil rig gearboxes from time to time and has worked on large ship gearbox installations in the past from what he has said. It might just be that big gearboxes cost dramatically more than smaller ones, and so other solutions become economic. Could be that simple. I'm just interested to know if there are technical reasons about gearbox scaling which affect the choice as well. Chris It might be just that. Since the volume of metal increases by the square of the diameter of the gear they must reach a point where moving that volume of metal takes too much energy compared to the amount of energy transmitted. So the cost of the gearbox plus the cost of transmitting the energy just gets too expensive. Eric This may or may not be an issue, but when gears get really large, they can become more expensive than the simple size proportion would indicate. It has to do with heat treatment and the relative risk (and cost) of failure. Big ones are often case-hardened, teeth only. As you go smaller, the tendency is toward flame hardening of teeth, and then through-hardening for the still smaller ones. We're talking about heavy-duty industrial gears here. I've watched this being done on 36-inch Curvics or spiral-bevels (I forget which) at Gleason Works, 30 years ago, and the really big ones go through a lot of steps. They're spotted with rouge and lapped after hardening in the biggest sizes. Lapping each gear can take a whole day. -- Ed Huntress https://www.geartechnology.com/issue...nstruction.pdf Yeah, for cast and fabricated mill gears. Notice the size range: 125 in. diameter and up. Those that Gleason was making started as steel forgings. -- Ed Huntress http://www.ronsongears.com.au/the-wo...-ingenuity.php |
Big gearbox design
Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb :
The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling. Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now. Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief. Nice thought, Randall. Chris |
Big gearbox design
"Christopher Tidy" wrote in message
... Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb : The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling. Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now. Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief. Nice thought, Randall. Chris =========== http://www.railway-technical.com/tra...l-locomotives/ |
Big gearbox design
On Thu, 17 Aug 2017 19:52:19 -0700 (PDT), Christopher Tidy
wrote: Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb : The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling. Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now. Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief. Nice thought, Randall. Chris A Loco doesn't use a clutch. The generator is directly coupled to the diesel. The traction motor is directly geared to the wheels. No clutch, just feild controls on the generator and motor to control voltage and current, and switching gear for reversing and braking. |
Big gearbox design
Not "clutch".
There were "diesel-hydraulic" locos in Britain. "Hymek" and "Warship Class" (???). Were they British "licences" of German designs? Seems a very German example of precision engineering - not easily replicated elsewhere. Advantage is said to be that hydraulic-mechanical transmission weighed less than electric transmission, so could pack more punch if the loco had to be small and light due to track / axle-load, etc. Check the real facts if interested. |
Big gearbox design
On Thu, 17 Aug 2017 19:52:19 -0700 (PDT), Christopher Tidy
wrote: Am Mittwoch, 16. August 2017 22:52:01 UTC+2 schrieb : The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling. Interesting comment. I can see this being a key problem. Just thinking about it, how do diesel engines scale? I mean, the bell housing on a small car engine has a diameter of what? 30 cm? And on a locomotive engine maybe 100 cm? So you can have something like a 25 cm diameter clutch in a car and a 85 cm diameter clutch in a locomotive? Let's assume it's a single plate clutch for now. There is no clutch on the usual a diesel-electric drive. Just an rheostat to control the electricity going to the motor(s). A diesel-electric vehicle often has a number of motors. Taking this a bit further, if you have maximum engine torque and 0 rpm at the wheels, how much power are you briefly sinking into the clutch? Maybe 50 kW in the car and 1500 kW in the locomotive? Which means you have 11 times the clutch area and 30 times the power. Following this logic, I can see how clutch scaling is going to max out at about the size of a large truck, and on top of that, trains accelerate quite slowly. The heating might not be so brief. The motor torque is normally applied directly to the driven wheel. Nice thought, Randall. Chris |
Big gearbox design
On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith
wrote: Not "clutch". There were "diesel-hydraulic" locos in Britain. "Hymek" and "Warship Class" (???). Were they British "licences" of German designs? Seems a very German example of precision engineering - not easily replicated elsewhere. Advantage is said to be that hydraulic-mechanical transmission weighed less than electric transmission, so could pack more punch if the loco had to be small and light due to track / axle-load, etc. Check the real facts if interested. Used primarily on narrow guage?? |
Big gearbox design
writes:
On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith wrote: Not "clutch". There were "diesel-hydraulic" locos in Britain. "Hymek" and "Warship Class" (???). Were they British "licences" of German designs? Seems a very German example of precision engineering - not easily replicated elsewhere. Advantage is said to be that hydraulic-mechanical transmission weighed less than electric transmission, so could pack more punch if the loco had to be small and light due to track / axle-load, etc. Check the real facts if interested. Used primarily on narrow guage?? Mainline - Standard gauge - Western region of UK. Hilly routes. https://en.wikipedia.org/wiki/British_Rail_Class_35 https://en.wikipedia.org/wiki/British_Rail_Class_42 |
Big gearbox design
"Richard Smith" wrote in message
... writes: On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith wrote: Not "clutch". There were "diesel-hydraulic" locos in Britain. "Hymek" and "Warship Class" (???). Were they British "licences" of German designs? Seems a very German example of precision engineering - not easily replicated elsewhere. Advantage is said to be that hydraulic-mechanical transmission weighed less than electric transmission, so could pack more punch if the loco had to be small and light due to track / axle-load, etc. Check the real facts if interested. Used primarily on narrow guage?? Mainline - Standard gauge - Western region of UK. Hilly routes. https://en.wikipedia.org/wiki/British_Rail_Class_35 https://en.wikipedia.org/wiki/British_Rail_Class_42 Underpowered locos on hilly routes were dangerous: https://en.wikipedia.org/wiki/Armagh_rail_disaster It's a good example of a chain of small problems compounding into a deadly disaster. |
Big gearbox design
On Fri, 18 Aug 2017 15:24:15 +0100, Richard Smith
wrote: writes: On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith wrote: Not "clutch". There were "diesel-hydraulic" locos in Britain. "Hymek" and "Warship Class" (???). Were they British "licences" of German designs? Seems a very German example of precision engineering - not easily replicated elsewhere. Advantage is said to be that hydraulic-mechanical transmission weighed less than electric transmission, so could pack more punch if the loco had to be small and light due to track / axle-load, etc. Check the real facts if interested. Used primarily on narrow guage?? Mainline - Standard gauge - Western region of UK. Hilly routes. https://en.wikipedia.org/wiki/British_Rail_Class_35 https://en.wikipedia.org/wiki/British_Rail_Class_42 Be a royal bitch if it sprung an oil leak!!! They were also "multi speed" geared transmissions - running on the short lines in the UK I guess they stood up OK,but I doubt they would have lasted long on our transcontinrntals and hauling freight through the North American Rockies, or even the appalachians with trains several miles long. |
Big gearbox design
On Wednesday, August 16, 2017 at 4:52:01 PM UTC-4, wrote:
The reason locomotives are diesel-electric is that the electric motors can deliver torque at 0 RPM - no need to slip a clutch until the huge mass got rolling. The engine block always need antifreeze. |
Big gearbox design
Am Freitag, 18. August 2017 05:43:55 UTC+2 schrieb Cla
A Loco doesn't use a clutch. I know. It was hypothetical. I was trying to work out why not. |
Big gearbox design
"Christopher Tidy" wrote in message
... Am Freitag, 18. August 2017 05:43:55 UTC+2 schrieb Cla A Loco doesn't use a clutch. I know. It was hypothetical. I was trying to work out why not. The history of locomotive engineering is interesting in that the demands of being such a heavy and powerful moving vehicle made the simplest-seeming things like following a curve or wheel balance very difficult. https://en.wikipedia.org/wiki/Hammer_blow One consequence was the gradual weakening of cast-iron bridge components: https://en.wikipedia.org/wiki/Tay_Bridge_disaster "A joiner who had worked on the bridge from May to October 1879 also spoke of a lateral shaking, which was more alarming than the up-and-down motion, and greatest at the southern junction between the high girders and the low girders. He was unwilling to quantify the amplitude of motion, but when pressed he offered 2 to 3 inches (50 to 75 mm). When pressed further he would only say that it was distinct, large, and visible." In addition to hammer blow the necessary 90 degree piston offset between the two sides to avoid being stuck on top-dead-center makes the loco wiggle (yaw) sideways. -jsw |
Big gearbox design
Christopher Tidy wrote:
Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great. On locomotives you need some means to connect an engine doing and requiring a couple of hundreds revs/min to wheels doing zero revs/min with some hundreds of kilonewtons drawbar power when taking off. -- "I'm a doctor, not a mechanic." Dr Leonard McCoy "I'm a mechanic, not a doctor." Volker Borchert |
Big gearbox design
writes:
On Fri, 18 Aug 2017 15:24:15 +0100, Richard Smith wrote: writes: On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith wrote: Not "clutch". There were "diesel-hydraulic" locos in Britain. "Hymek" and "Warship Class" (???). Were they British "licences" of German designs? Seems a very German example of precision engineering - not easily replicated elsewhere. Advantage is said to be that hydraulic-mechanical transmission weighed less than electric transmission, so could pack more punch if the loco had to be small and light due to track / axle-load, etc. Check the real facts if interested. Used primarily on narrow guage?? Mainline - Standard gauge - Western region of UK. Hilly routes. https://en.wikipedia.org/wiki/British_Rail_Class_35 https://en.wikipedia.org/wiki/British_Rail_Class_42 Be a royal bitch if it sprung an oil leak!!! They were also "multi speed" geared transmissions - running on the short lines in the UK I guess they stood up OK,but I doubt they would have lasted long on our transcontinrntals and hauling freight through the North American Rockies, or even the appalachians with trains several miles long. On huge transcontinental railways you are not limited for loco size - so you would not use the hydro-mechanical design to pack a lot of punch in a small light loco. |
Big gearbox design
"Richard Smith" wrote in message
... writes: On Fri, 18 Aug 2017 15:24:15 +0100, Richard Smith wrote: writes: On Fri, 18 Aug 2017 08:05:27 +0100, Richard Smith wrote: Not "clutch". There were "diesel-hydraulic" locos in Britain. "Hymek" and "Warship Class" (???). Were they British "licences" of German designs? Seems a very German example of precision engineering - not easily replicated elsewhere. Advantage is said to be that hydraulic-mechanical transmission weighed less than electric transmission, so could pack more punch if the loco had to be small and light due to track / axle-load, etc. Check the real facts if interested. Used primarily on narrow guage?? Mainline - Standard gauge - Western region of UK. Hilly routes. https://en.wikipedia.org/wiki/British_Rail_Class_35 https://en.wikipedia.org/wiki/British_Rail_Class_42 Be a royal bitch if it sprung an oil leak!!! They were also "multi speed" geared transmissions - running on the short lines in the UK I guess they stood up OK,but I doubt they would have lasted long on our transcontinrntals and hauling freight through the North American Rockies, or even the appalachians with trains several miles long. On huge transcontinental railways you are not limited for loco size - so you would not use the hydro-mechanical design to pack a lot of punch in a small light loco. http://www.victorianweb.org/technology/railways/23.html The different conditions here affected engineering practice, for example we didn't have an abundance of skilled labor while the frontier was open, so Americans built locos with exposed plumbing and outside cylinders that were easier to maintain. -jsw |
Big gearbox design
Ships of all sizes use them, Oil services use them some gears are so
large that they have to be on 80' heavy duty trailers mounted on an angle so the width would fit in 1 or 2 lanes and still under mandatory overpasses. Lufkin Industries here in town before being bought out by GE used to move some rather large gears to be used world wide. They had a gear box group that still works here - 'black magic' you don't mess with in the works. Large industrial air handlers and mills.... the gear boxes have to be designed right considering many parameters that are often ignored until the box blows up. Martin On 8/16/2017 1:47 AM, Christopher Tidy wrote: Any gearbox experts here? Just puzzling over why really big gearboxes are commonly avoided. Locomotives mostly use electric transmission and the reliability of gearboxes in things like wind turbines isn't great. Is there some reason to do with scaling the geometry, like if you double the size of every dimension, the shaft can transmit more torque than the teeth? At a quick glance, it doesn't seem that simple. Or is there more slip between the teeth and more wear? I can't figure out a concrete reason and it's bugging me :-). Chris |
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