[Script Info]
Title: 
[Events]
Format: Layer, Start, End, Style, Name, MarginL, MarginR, MarginV, Effect, Text
Dialogue: 0,0:00:00.28,0:00:01.75,Default,,0000,0000,0000,,The planetary gear set,
Dialogue: 0,0:00:02.09,0:00:04.51,Default,,0000,0000,0000,,also known as the epicyclic gear train,
Dialogue: 0,0:00:04.58,0:00:07.93,Default,,0000,0000,0000,,is one of the most important and\Ninteresting inventions in engineering.
Dialogue: 0,0:00:08.79,0:00:10.90,Default,,0000,0000,0000,,They are great speed variation mechanisms
Dialogue: 0,0:00:11.10,0:00:15.48,Default,,0000,0000,0000,,and are often used in automobiles as \Na vital part of automatic transmissions.
Dialogue: 0,0:00:18.56,0:00:22.12,Default,,0000,0000,0000,,Let's explore the secrets of\Nthe planetary gear set in this video!
Dialogue: 0,0:00:25.15,0:00:27.90,Default,,0000,0000,0000,,A planetary gear set has four main parts:
Dialogue: 0,0:00:28.87,0:00:29.89,Default,,0000,0000,0000,,the sun,
Dialogue: 0,0:00:30.77,0:00:32.03,Default,,0000,0000,0000,,planet gears,
Dialogue: 0,0:00:32.87,0:00:34.14,Default,,0000,0000,0000,,ring gear,
Dialogue: 0,0:00:35.66,0:00:36.96,Default,,0000,0000,0000,,and carrier.
Dialogue: 0,0:00:37.64,0:00:40.31,Default,,0000,0000,0000,,You can see that it sometimes\Nrotates quickly,
Dialogue: 0,0:00:41.82,0:00:43.24,Default,,0000,0000,0000,,sometimes slowly,
Dialogue: 0,0:00:46.38,0:00:48.38,Default,,0000,0000,0000,,and sometimes even in reverse.
Dialogue: 0,0:00:50.20,0:00:52.31,Default,,0000,0000,0000,,But, how does this happen?
Dialogue: 0,0:00:52.67,0:00:55.81,Default,,0000,0000,0000,,You will be able to predict the motion\Nof this gear set completely,
Dialogue: 0,0:00:55.83,0:00:58.04,Default,,0000,0000,0000,,if you understand one simple fact!
Dialogue: 0,0:00:59.55,0:01:01.52,Default,,0000,0000,0000,,When two gears are moving as shown,
Dialogue: 0,0:01:01.77,0:01:04.68,Default,,0000,0000,0000,,they should have the same \Nspeed at the interface.
Dialogue: 0,0:01:05.28,0:01:08.28,Default,,0000,0000,0000,,This means, that the speed of \Ngear A should be the same
Dialogue: 0,0:01:08.28,0:01:10.54,Default,,0000,0000,0000,,as gear B at their mating point.
Dialogue: 0,0:01:17.56,0:01:19.42,Default,,0000,0000,0000,,The speed has to be the same,
Dialogue: 0,0:01:19.57,0:01:23.12,Default,,0000,0000,0000,,otherwise the gear teeth will\Npenetrate each other as shown.
Dialogue: 0,0:01:23.45,0:01:25.62,Default,,0000,0000,0000,,That is an impossible condition!
Dialogue: 0,0:01:27.15,0:01:29.70,Default,,0000,0000,0000,,Just apply this fact to planetary gear sets
Dialogue: 0,0:01:29.100,0:01:33.60,Default,,0000,0000,0000,,and you will be able to predict how\Nspeed variation is achieved.
Dialogue: 0,0:01:36.23,0:01:39.94,Default,,0000,0000,0000,,Assume that the ring gear is held \Nstationary and we rotate the sun gear.
Dialogue: 0,0:01:43.93,0:01:46.28,Default,,0000,0000,0000,,Think of what happens to the planet gears!
Dialogue: 0,0:01:48.39,0:01:51.65,Default,,0000,0000,0000,,At point A, the planet gear\Nshould have a certain speed.
Dialogue: 0,0:01:51.84,0:01:54.79,Default,,0000,0000,0000,,And at point B, the speed should be zero,
Dialogue: 0,0:01:54.79,0:01:56.73,Default,,0000,0000,0000,,as the ring gear is stationary.
Dialogue: 0,0:01:57.09,0:02:01.22,Default,,0000,0000,0000,,However, how are both of these conditions\Npossible at the same time?
Dialogue: 0,0:02:01.94,0:02:03.66,Default,,0000,0000,0000,,There is only one way!
Dialogue: 0,0:02:04.03,0:02:06.65,Default,,0000,0000,0000,,The planet gear should \Nspin as well as turn!
Dialogue: 0,0:02:07.91,0:02:10.78,Default,,0000,0000,0000,,The spinning will produce velocities \Nin opposite directions
Dialogue: 0,0:02:10.78,0:02:13.33,Default,,0000,0000,0000,,at the top and bottom points, as shown.
Dialogue: 0,0:02:13.98,0:02:17.61,Default,,0000,0000,0000,,Whereas the turning produces \Nunidirectional velocities.
Dialogue: 0,0:02:19.14,0:02:23.36,Default,,0000,0000,0000,,At the top, the spinning and turning\Nvelocities are in opposite directions,
Dialogue: 0,0:02:23.45,0:02:25.89,Default,,0000,0000,0000,,so the velocity of point B is zero.
Dialogue: 0,0:02:26.84,0:02:29.05,Default,,0000,0000,0000,,At the bottom, they get added up.
Dialogue: 0,0:02:30.15,0:02:33.08,Default,,0000,0000,0000,,In short, the planet gears \Nare forced to turn
Dialogue: 0,0:02:33.19,0:02:36.00,Default,,0000,0000,0000,,in order to satisfy \Nthe condition of velocity.
Dialogue: 0,0:02:36.33,0:02:38.97,Default,,0000,0000,0000,,As the carrier is attached \Nto the planet gear
Dialogue: 0,0:02:38.97,0:02:41.63,Default,,0000,0000,0000,,it will turn along with the planet gears.
Dialogue: 0,0:02:43.00,0:02:46.23,Default,,0000,0000,0000,,Now, let's see what happens when\Nthe sun gear is held stationary
Dialogue: 0,0:02:46.23,0:02:48.17,Default,,0000,0000,0000,,and the ring gear is rotated.
Dialogue: 0,0:02:50.34,0:02:53.27,Default,,0000,0000,0000,,This is the exact opposite \Nto the previous case.
Dialogue: 0,0:02:53.36,0:02:55.51,Default,,0000,0000,0000,,At the inner point of the planet gear,
Dialogue: 0,0:02:55.51,0:02:57.50,Default,,0000,0000,0000,,the velocity should be zero
Dialogue: 0,0:02:57.62,0:03:00.70,Default,,0000,0000,0000,,and the outer points should have\Nthe speed of the ring gear.
Dialogue: 0,0:03:00.98,0:03:02.02,Default,,0000,0000,0000,,In this case,
Dialogue: 0,0:03:02.16,0:03:06.62,Default,,0000,0000,0000,,the planetary spin will reverse in order\Nto satisfy the speed conditions.
Dialogue: 0,0:03:09.06,0:03:11.62,Default,,0000,0000,0000,,However, this case has\None more difference.
Dialogue: 0,0:03:12.35,0:03:14.49,Default,,0000,0000,0000,,The speed of point B, will be higher
Dialogue: 0,0:03:14.49,0:03:17.49,Default,,0000,0000,0000,,than the speed of point A \Nin the previous case.
Dialogue: 0,0:03:18.27,0:03:21.81,Default,,0000,0000,0000,,This is obvious, as the ring\Ngear radius is higher.
Dialogue: 0,0:03:26.23,0:03:29.98,Default,,0000,0000,0000,,This will make the planet gear spin\Nand turn at a higher speed.
Dialogue: 0,0:03:30.28,0:03:33.42,Default,,0000,0000,0000,,Thus, the carrier will turn\Nat a higher speed.
Dialogue: 0,0:03:36.60,0:03:40.28,Default,,0000,0000,0000,,Let's now explore this reverse \Nmechanism of planet gears.
Dialogue: 0,0:03:42.65,0:03:43.56,Default,,0000,0000,0000,,For this,
Dialogue: 0,0:03:43.56,0:03:46.68,Default,,0000,0000,0000,,what you have to do is just \Narrest the motion of the carrier.
Dialogue: 0,0:03:48.03,0:03:51.15,Default,,0000,0000,0000,,This means, that the planet gears\Nare not allowed to turn
Dialogue: 0,0:03:51.44,0:03:52.82,Default,,0000,0000,0000,,and can only spin.
Dialogue: 0,0:03:55.02,0:03:58.21,Default,,0000,0000,0000,,This spin will be opposite to\Nthe rotation of the sun gear.
Dialogue: 0,0:03:59.56,0:04:03.99,Default,,0000,0000,0000,,This spinning planet gear will make \Nthe ring gear rotate in the same direction.
Dialogue: 0,0:04:04.52,0:04:05.33,Default,,0000,0000,0000,,In short,
Dialogue: 0,0:04:05.33,0:04:09.26,Default,,0000,0000,0000,,the direction of rotation of the ring gear\Nwill be the opposite to the sun gear.
Dialogue: 0,0:04:09.48,0:04:11.70,Default,,0000,0000,0000,,Thus, we will get the reverse gear.
Dialogue: 0,0:04:15.37,0:04:18.65,Default,,0000,0000,0000,,Here, you can note, that in order\Nto achieve different speeds,
Dialogue: 0,0:04:18.68,0:04:22.48,Default,,0000,0000,0000,,the input must be given to different\Nparts of the planetary gear set.
Dialogue: 0,0:04:22.59,0:04:25.56,Default,,0000,0000,0000,,This is practically difficult \Nin an actual mechanism.
Dialogue: 0,0:04:26.37,0:04:28.92,Default,,0000,0000,0000,,In an automatic transmission,\Nto achieve this,
Dialogue: 0,0:04:28.92,0:04:32.35,Default,,0000,0000,0000,,three planetary gear sets\Nare connected in series
Dialogue: 0,0:04:32.35,0:04:34.70,Default,,0000,0000,0000,,as shown with coaxial shafts.
Dialogue: 0,0:04:35.71,0:04:39.46,Default,,0000,0000,0000,,To understand, how this arrangement\Neffectively transfers the input rotation
Dialogue: 0,0:04:39.46,0:04:41.91,Default,,0000,0000,0000,,to different parts of \Nthe planetary gear set,
Dialogue: 0,0:04:41.91,0:04:44.13,Default,,0000,0000,0000,,watch our video on automatic transmission.
Dialogue: 0,0:04:45.57,0:04:47.30,Default,,0000,0000,0000,,Your support on patreon.com
Dialogue: 0,0:04:47.30,0:04:50.78,Default,,0000,0000,0000,,is greatly appreciated to make our\Neducational service sustainable.
Dialogue: 0,0:04:50.78,0:04:51.73,Default,,0000,0000,0000,,Thank you.