The effects of the generating pin size and placement on the curvature and displacement of epitrochoidal gerotors

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Gerotors do not have auxiliary gears in general, therefore the motion of one lobed gear relative to the other lobed gear is produced by the forces between the two contacting lobes. The contact forces, however, result in wear in one or both lobed gears which, in turn, reduces the life of the mechanism. As a gerotor cannot be adjusted to compensate for the wear, it is important that the contact forces be kept to a minimum. It is well known that the wear rate can be reduced by decreasing the curvature (or increasing the radius of curvature) of the lobes. The curvature is a function of the size and the placement of the pins which generate the lobe shape. In this paper, relationships are derived which show the influence of the trochoid ratio, the pin size ratio, and the radius of the generating pin on the curvature of the epitrochoidal gerotor. The relationships provide geometric insight into the design of gerotors which can save time and effort in the manufacturing process. In addition, the results are combined with previously published formulate for the pocket displacement to obtain design charts. These charts can be easily used by the designer to predict the effect of the geometry on the performance of a gerotor. An example is presented, which shows how a commercially available gerotor can be modified to give a 48.7% increase in the minimum radius of curvature with only a 3.2% decrease in the displacement and no change in the overall size of the gerotor. © 1992.

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Mechanism and Machine Theory