Comparison of helical and skewed axis gerotor pumps

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The gerotor is a planar mechanism consisting of two surfaces whose relative motion can be described by the kinematics of orbiting pitch circles. Typically, gerotor surfaces are prismatic with the axes of rotation parallel to the ruled surfaces. For a given position, the generated cross section of the mechanism in the plane of motion is independent of the location of the section along the axis of rotation. In this work, a mathematical derivation for producing gerotors with non-prismatic surfaces is presented. The implementation results in two types of gerotors, mechanisms with conical surfaces relative to the rotor axis, and mechanisms with helical surfaces. These are relatively new inventions and this is the first publication of the mathematical model describing these mechanisms. The derivations of the mathematics associated with each mechanism are presented. Comparisons of the mechanisms are presented based on the displacement, compression ratio and surface area to volume ratio. © 1997 Elsevier Science Ltd.

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Mechanism and Machine Theory