A gerotor is a positive displacement pump . The name gerotor is derived from “generated rotor “. A gerotors unit consists of an inner and outer rotor. The inner rotor has n teeth, while the outer rotor has n +1 teeth; With n defined as a natural number greater than or equal to 2 . The axis of the inner rotor is offset from the axis of the outer rotor and both rotors rotate on their respective axes. The geometry of two rotors divides the volume between them into n Various dynamically changing volumes. During the rotation cycle of the assembly, each of these volumes changes continuously, so any volume first increases, and then decreases. Growth creates a vacuum . This vacuum creates suction , and therefore, this part of the cycle is where the inlet is located. As the volume decreases, compression occurs. During this compression period, liquids may be pumped, or, if they are gaseous liquids, may be compressed.
Gerotors pumps are generally designed using a trichoidal inner rotor and an outer rotor, with circular arcs formed by a coil. 
A gerotor can also function as a pistonless rotary engine . High pressure gas enters the intake and pushes against the inner and outer rotors, causing both to rotate as the volume increases between the inner and outer rotors. During the compression period, the exhaust is pumped out.
At the most basic level, a GE-rotor is essentially one that is moved by means of fluid power. Originally this fluid was water, today there is widespread use in hydraulic equipment. Myron F. Hill, who can be called the father of the G-rotor, in his pamphlet “Kinematics of G-rotors”, listed efforts by Galloway in 1787, by Nash and Tilden in 1879, by Cooley in 1900, by Professor Lilly. Is. of the University of Dublin in 1915, and by Furheard in 1918. These were all working to complete an internal gear mechanism by a one-tooth gap to provide displacement .
Myron Hill made his first attempt in 1906, then, in 1921, devoted his entire time to developing the GE-rotor. He developed many of the geometric principles underlying these rotors, coined the term GE-rotor (meaning “generated rotor”), and obtained a basic patent on the GE-rotor.
GE-rotors are widely used throughout industry today, and are produced in a variety of shapes and sizes in many different ways.
- oil pump
- fuel pump
- high speed gas compressor
- hydraulic motors
- power steering units
- limited-slip differential