TABLE OF CONTENTS Planetary gear sets are widely used in automatic transmissions. A planetary gear set is also a device found in many hybrid vehicles to combine mechanical power from various (usually, two) power sources to various (usually, two) mechanical loads. In the typical configuration of a combined hybrid vehicle, a planetary gear set connects an engine, a motor, a generator, and the drive train.
A basic planetary gear has three main rotating parts (Fig. 4.44). The inner part is termed sun, the outer part is the ring. The intermediate part carries three rotating elements (planets) and is called carrier. More complex configurations are possible but they are not considered here. Each of the three parts can be connected to the input shaft, the output shaft, or can be held stationary. Choosing which piece plays which role determines the gear ratio for the gear set. Actually, common automatic transmissions use a compound planetary gear set which acts like two gear sets.
The causality representation of a planetary gear set in quasistatic simulations is sketched in Fig. 4.45. The input variables are the torque and speed at the load shafts, ? 3( t), ? 4( t), T 3( t), T 4( t). The output variables are the torque and speed at the power source shafts, ? 1
