Patent ID: 8851869

Claim:
An internal gear pump comprising: an inner gear that has plural outer teeth on an outer peripheral surface of the inner gear; and an outer gear that is formed with a housing space that is capable of housing the inner gear and that includes plural inner teeth meshing with the outer teeth on an inner peripheral surface that forms the housing space, one of the inner teeth and the outer teeth having a shape based on a tooth form that is respectively formed by a generating curve of the other of the inner teeth and the outer teeth, a section of each of the inner teeth that protrudes in a direction toward the inner gear having a first arc shape, a section of each of the outer teeth that protrudes in a direction toward the outer gear having a curved shape, each of both end sections of the curved shape having a second arc shape, if a radius of the first arc shape is set as ro, a radius of the second arc shape is set as ri, a diameter of a pitch circle of the inner teeth is set as dp, and the number of the inner teeth is set as z, the inner gear and the outer gear each having a shape that satisfies a relationship established by following equations: 1.6>ro/(dp/z)>1.0; and ro/(dp/z)>ri/(dp/z)≧0.13, and each of the inner teeth being provided so that an intersecting point that is between one of arcs that follow the first arc shapes of the adjacent inner teeth and the pitch circle of the inner teeth and that is in proximity to the other arc is located outside of the other arc.