Legacy Postal Wagon AWD F4-2.2L SOHC (1998)
Planetary Gears: Description and Operation
5. PLANETARY GEAR
Construction
The planetary gear train uses two sets of simple planetary gears (front planetary gear and rear planetary gear), four sets of multi-plate clutches (reverse
clutch, high clutch, forward clutch, and overrunning clutch), one brake band, one set of multi-plate brake, and two sets of one-way clutches (one-way
clutch 1-2 and one-way clutch 3-4) in order to allow shifting of four forward speeds and one reverse speed.
Two sets of simple planetary gears are used to allow gear shifting from 1st speed to 4th speed or to reverse. Both the front and rear planetary gear
carriers are made from pressed steel which is electron-beam welded to other structural members. The front planetary gear has three pinions while the
rear planetary gear has four pinions. Both are part of an integral unit, and disassembling is not allowed.
Function
The automatic transmission uses a planetary gear system instead of the parallel shaft (two shafts) gear system adopted in the manual transmission.
The advantage of the planetary gear system is that it is compact because it has only one center shaft. The gear ratio can be changed by simply locking
or releasing or rotating certain portions, unlike the manual transmission that requires changing gear engagement.
The construction of the planetary gear is shown on the previous page. The sun gear is located at the center, and each of the pinion gears revolves
around the sun gear while rotating on its axis. These gears are all enclosed in a large ring, called the internal gear. Each pinion gear is supported by a
planetary carrier, so that the pinion gears revolve an equal amount in the same direction. As mentioned above, the planetary gear consists of four
elements: the sun gear, pinion gears, internal gear, and planetary carrier. The gears are shifted by imposing certain conditions on two of the following
three elements: sun gear, internal gear, and planetary carrier.
The clutches and brakes are used to impose the conditions on the planetary gear set.
