Planetary Gear Set Operation

In order to understand planetary gear set operation, it is important to understand some basic rules of operation:

• It is assumed that engine rotation is clockwise when referring to power flow charts and diagrams.
• Planetary pinions will always rotate in the same direction as the internal ring gear.
• When the sun gear is driven clockwise and the planetary carrier is held stationary the internal ring gear will rotate counter clockwise (reverse gear).
• When two or more planetary members are locked together, the assembly will rotate together. The ratio from input to output is 1:1.
• When the sun gear is held stationary and the planetary carrier is driven clockwise, the ring gear will be driven clockwise in an overdrive ratio (.75:1)

When trying to understand power flow schematics, it is important to be able to draw a comparison between the actual planetary components and the schematic symbols. The diagram below outlines the relationship between these components and the power flow schematic. The schematic is a representation of a cross section of the transmission, but you only see the top half of the cross section. The transmission is shown as though it has been quartered lengthwise. See Fig 1.