5 ms·

Epicyclic Gearing

131 points by llambda 14y ago

bprater 14y ago
Quickly clicking thru the options on this webpage will give you an idea on how automatic transmissions work in automobiles -- using the planetary gearset. The core mechanic is the locking of different combinations of the gears. This is a completely different mechanic than in the standard 'stick shift' manual transmission, which uses traditional toothed gears meshing together.
- pkulak 14y ago
  I think you're thinking of an electronic CVT, like the Prius uses.
  - majormajor 14y ago
    Wikipedia tells me that there are some CVTs that use planetary gears, but a traditional automatic uses them too: http://auto.howstuffworks.com/automatic-transmission2.htm http://auto.howstuffworks.com/automatic-transmission2.htm
  - abthomson 14y ago
    Both "normal" automatic transmissions and the Prius use epicyclic gears. The main difference between the two would be that an automatic transmission in normal operation has one power input (the engine) and one output. As bprater alluded to, any variation in gearing is achieved through fixing different parts of the transmission. The Prius has two electric motors and a gas engine. It's not a CVT in the traditional sense though, this simulator does a good job of demonstrating how it works(implemented in Flash, not D3...) http://eahart.com/prius/psd/ http://eahart.com/prius/psd/
    - robgolding 14y ago
      That simulation is absolutely fascinating. I knew hybrid cars were packed with loads of advanced electronic tech, but the use of epicyclic gears as the PSD is pretty cool.
      - lloeki 14y ago
        Toyota's HSD system uses such a scheme, but mechanically, Honda's IMA replaces the flywheel with an electric generator/motor, the remainder of the drivetrain being your typical car (they use either a CVT or a manual stick, depending on models and regions). The key then is entirely in the logic driving the electric motor and the VTEC system. [0] http://www.blogcdn.com/www.autoblog.com/media/2010/06/2011cr-z008technical-copy.jpg http://www.blogcdn.com/www.autoblog.com/media/2010/06/2011cr...
  - hencq 14y ago
    No, he's not. A CVT doesn't have fixed gear ratios (that's where the continuous comes in). A traditional automatic transmission uses planetary gears to have a fixed number of gear ratios.
- bigiain 14y ago
  I (along with nearly everybody I knew) had a bicycle with that gearbox in it back in the '70s. http://sheldonbrown.com/internal-gears.html http://sheldonbrown.com/internal-gears.html (And I was _so_ jealous of the few kids with the "10 speed racers"!)
  - aidos 14y ago
    Oh, that's how they work! I hadn't looked into it but I have one sitting around at home waiting for a spare weekend so I can dissect it to figure it out.
raymondh 14y ago
Beautiful website. Fascinating display. Nice source code.
- mikepurvis 14y ago
  Agreed, very nice. I did some demos like this a few years ago, and it was definitely not as clean. Modern JS libs are marvelous things. (eg: http://sandbox.mikepurvis.com/design/engine.svg http://sandbox.mikepurvis.com/design/engine.svg)
samlittlewood 14y ago
This was how the Model T Ford transmission worked - the foot pedal fixed various parts to get low, high and reverse. Edit: http://www.modeltcentral.com/transmission_animation.html http://www.modeltcentral.com/transmission_animation.html
jakeonthemove 14y ago
That's also how chain hoists work - I'm still amazed at how much you can lift using one! I actually thought the article will be about Biopace bike chain rings: bikers are using them as an advantage in races (and it really makes sense!).
- Terretta 14y ago
  Supposedly, Biopace was shown to be counterproductive, while the newer Rotor Q-Rings are correctly designed. The new hotness: http://www.rotorbikeusa.com/science.html http://www.rotorbikeusa.com/science.html
jebblue 14y ago
Interesting but it uses 80% CPU time on my system, here is a Java applet showing the same thing - it takes a long time to load but uses less than 10%: http://www.zfm.ethz.ch/meca/applets/planeten/PG.html http://www.zfm.ethz.ch/meca/applets/planeten/PG.html
joe_bleau 14y ago
Another good one is the hypoid gearset (http://en.wikipedia.org/wiki/Hypoid http://en.wikipedia.org/wiki/Hypoid) , as used in automotive rear ends. For some reason I've always found them pretty. Cone drive sets and harmonic gearing (http://en.wikipedia.org/wiki/Harmonic_drive http://en.wikipedia.org/wiki/Harmonic_drive) are neat, too. And then there's the Torsen (http://www.youtube.com/watch?v=Z9iPqIQ_8iM http://www.youtube.com/watch?v=Z9iPqIQ_8iM), which I still don't really understand. From the service manuals I've seen, I think some of the smaller 4 cylinder cars, especially from Japan, use a mainshaft/countershaft arrangement (like a traditional manual transmission) in their automatics, rather than planetary gearing.
- HeyLaughingBoy 14y ago
  Because the machining is gorgeous I used to have the hypoid pinion I removed from my Toyota pickup truck rear end (when I changed the gear ratio to compensate for larger tires) as a paperweight on my desk. The flowing curves and polished steel gave it a really Art-Deco look. It was free, beautiful and weighing close to 10 lbs, very functional. Can't beat that :-)
  - joe_bleau 14y ago
    Speaking of gorgeous, if you're ever in a machine shop and get a chance to look inside the headstock of a top end 1940-1970s vintage engine lathe, do it. The quality and precision makes automotive stuff look like hammered pot metal.
    - HeyLaughingBoy 14y ago
      I hang out on a couple of online machinist fora and I agree. Even the outsides of something like, e.g., a Monarch 10EE are beautiful. Sculpted in a way that just doesn't seem to happen anymore. Two of my favorite machine porn photos are from WW2 - a woman at a beautiful Warner & Swasey turret lathe: http://www.shorpy.com/node/1809 http://www.shorpy.com/node/1809 There's another one on that site of a woman using a Heald Borematic that I can't find right now, but it's even more amazing. I need to find it so I can order a large print. Yeah, I love machine tools :-)

131 points by llambda 14y ago

Quickly clicking thru the options on this webpage will give you an idea on how automatic transmissions work in automobiles -- using the planetary gearset. The core mechanic is the locking of different combinations of the gears. This is a completely different mechanic than in the standard 'stick shift' manual transmission, which uses traditional toothed gears meshing together.

pkulak 14y ago
I think you're thinking of an electronic CVT, like the Prius uses.
- majormajor 14y ago
  Wikipedia tells me that there are some CVTs that use planetary gears, but a traditional automatic uses them too: http://auto.howstuffworks.com/automatic-transmission2.htm http://auto.howstuffworks.com/automatic-transmission2.htm
- abthomson 14y ago
  Both "normal" automatic transmissions and the Prius use epicyclic gears. The main difference between the two would be that an automatic transmission in normal operation has one power input (the engine) and one output. As bprater alluded to, any variation in gearing is achieved through fixing different parts of the transmission. The Prius has two electric motors and a gas engine. It's not a CVT in the traditional sense though, this simulator does a good job of demonstrating how it works(implemented in Flash, not D3...) http://eahart.com/prius/psd/ http://eahart.com/prius/psd/
  - robgolding 14y ago
    That simulation is absolutely fascinating. I knew hybrid cars were packed with loads of advanced electronic tech, but the use of epicyclic gears as the PSD is pretty cool.
    - lloeki 14y ago
      Toyota's HSD system uses such a scheme, but mechanically, Honda's IMA replaces the flywheel with an electric generator/motor, the remainder of the drivetrain being your typical car (they use either a CVT or a manual stick, depending on models and regions). The key then is entirely in the logic driving the electric motor and the VTEC system. [0] http://www.blogcdn.com/www.autoblog.com/media/2010/06/2011cr-z008technical-copy.jpg http://www.blogcdn.com/www.autoblog.com/media/2010/06/2011cr...
- hencq 14y ago
  No, he's not. A CVT doesn't have fixed gear ratios (that's where the continuous comes in). A traditional automatic transmission uses planetary gears to have a fixed number of gear ratios.
bigiain 14y ago
I (along with nearly everybody I knew) had a bicycle with that gearbox in it back in the '70s. http://sheldonbrown.com/internal-gears.html http://sheldonbrown.com/internal-gears.html (And I was _so_ jealous of the few kids with the "10 speed racers"!)
- aidos 14y ago
  Oh, that's how they work! I hadn't looked into it but I have one sitting around at home waiting for a spare weekend so I can dissect it to figure it out.

raymondh 14y ago

Beautiful website. Fascinating display. Nice source code.

mikepurvis 14y ago
Agreed, very nice. I did some demos like this a few years ago, and it was definitely not as clean. Modern JS libs are marvelous things. (eg: http://sandbox.mikepurvis.com/design/engine.svg http://sandbox.mikepurvis.com/design/engine.svg)

samlittlewood 14y ago

This was how the Model T Ford transmission worked - the foot pedal fixed various parts to get low, high and reverse. Edit: http://www.modeltcentral.com/transmission_animation.html http://www.modeltcentral.com/transmission_animation.html

jakeonthemove 14y ago

That's also how chain hoists work - I'm still amazed at how much you can lift using one! I actually thought the article will be about Biopace bike chain rings: bikers are using them as an advantage in races (and it really makes sense!).

Terretta 14y ago
Supposedly, Biopace was shown to be counterproductive, while the newer Rotor Q-Rings are correctly designed. The new hotness: http://www.rotorbikeusa.com/science.html http://www.rotorbikeusa.com/science.html

jebblue 14y ago

Interesting but it uses 80% CPU time on my system, here is a Java applet showing the same thing - it takes a long time to load but uses less than 10%: http://www.zfm.ethz.ch/meca/applets/planeten/PG.html http://www.zfm.ethz.ch/meca/applets/planeten/PG.html

joe_bleau 14y ago

Another good one is the hypoid gearset (http://en.wikipedia.org/wiki/Hypoid http://en.wikipedia.org/wiki/Hypoid) , as used in automotive rear ends. For some reason I've always found them pretty. Cone drive sets and harmonic gearing (http://en.wikipedia.org/wiki/Harmonic_drive http://en.wikipedia.org/wiki/Harmonic_drive) are neat, too. And then there's the Torsen (http://www.youtube.com/watch?v=Z9iPqIQ_8iM http://www.youtube.com/watch?v=Z9iPqIQ_8iM), which I still don't really understand. From the service manuals I've seen, I think some of the smaller 4 cylinder cars, especially from Japan, use a mainshaft/countershaft arrangement (like a traditional manual transmission) in their automatics, rather than planetary gearing.

HeyLaughingBoy 14y ago
Because the machining is gorgeous I used to have the hypoid pinion I removed from my Toyota pickup truck rear end (when I changed the gear ratio to compensate for larger tires) as a paperweight on my desk. The flowing curves and polished steel gave it a really Art-Deco look. It was free, beautiful and weighing close to 10 lbs, very functional. Can't beat that :-)
- joe_bleau 14y ago
  Speaking of gorgeous, if you're ever in a machine shop and get a chance to look inside the headstock of a top end 1940-1970s vintage engine lathe, do it. The quality and precision makes automotive stuff look like hammered pot metal.
  - HeyLaughingBoy 14y ago
    I hang out on a couple of online machinist fora and I agree. Even the outsides of something like, e.g., a Monarch 10EE are beautiful. Sculpted in a way that just doesn't seem to happen anymore. Two of my favorite machine porn photos are from WW2 - a woman at a beautiful Warner & Swasey turret lathe: http://www.shorpy.com/node/1809 http://www.shorpy.com/node/1809 There's another one on that site of a woman using a Heald Borematic that I can't find right now, but it's even more amazing. I need to find it so I can order a large print. Yeah, I love machine tools :-)