Gerotor gear sets have been in commercial use for many years as hydraulic fluid pressure devices such as motors and pumps in which an inner rotor is eccentrically disposed within an outer rotor, each orbiting or rotating about its respective center or axis of rotation, with the interengagement of the teeth of the rotors defining expanding and contracting volume chambers. Motors of this type have been commercially successful, partially because the gerotor gear set is uniquely suited to provide a well-regulated output in a device which is both compact and relatively inexpensive.
Recently, gerotor pumps have been coupled with electric motors in fuel delivery systems for internal combustion engines. Such systems follow the precedent established in most gerotor applications in which one of the gears are directly mechanically driven. In typical prior art fuel pumps, a gerotor set is disposed in-line with the armature of a conventional brush-type fixed speed d.c. motor which mechanically drives the inner or star gear of the gerotor set to effect pumping action. Such configurations, although representing a distinct advantage over more conventional fuel pump designs, are typically large and difficult to package, particularly when integrated within an over-the-road vehicle. In addition to having a relatively high part count with attendant cost and multiple possible failure modes, the use of a brush-type motor can pose an explosion hazard from arcing inherent therein in the presence of a volatile fuel vapors.
The brush arcing problem has been somewhat mitigated in certain so-called wet motor gerotor fuel pump arrangements in which fuel passing through the pump also travels serially through passageways within the motor for purposes of cooling and flushing debris therefrom. This arrangement represents an improvement inasmuch as the cooling effect of the fuel flow permits a down sizing of the motor and enhanced compactness of the overall assembly. However, wet motor gerotor fuel pumps still suffer from a number of the infirmities of prior art devices described herein above.
Additional shortcomings of typical prior art pumps reside in their lack of speed control, and lack of reversibility. Finally, due to their mechanical complexity, they are particularly difficult to package in submersed applications.
It will become apparent from the subsequent description that the invention is equally adapted for use in any gear set comprising an internally-toothed member and an externally-toothed member disposed eccentrically within the internally-toothed member, in which at least one of the toothed members rotate about a fixed axis. However, the present invention is especially advantageous when applied to gerotor sets in which both of the toothed members rotate about offset fixed axes. It is also contemplated that the present invention could be employed with a Geroler.TM. gear set or similar arrangements wherein the axis of the externally-toothed member is not fixed, but rather orbits about the axis of the internally-toothed member. Furthermore, although described for use as a fuel pump, it should be apparent that the present invention could be easily adapted to any number of configurations and applications.