BRIEF DESCRIPTION OF THE DRAWINGS
The various features and advantages of this invention will become apparent to those skilled in the art from the following detailed description of the currently preferred embodiment. The drawings that accompany the detailed description can be briefly described as follows.
FIG. 1 illustrates an axial cross-sectional view of an example gerotor pump.
FIG. 2 illustrates a radial cross-sectional view of the gear sets of the gerotor pump depicted in FIG. 1.
FIG. 3 illustrates an example gerotor pump system having multiple gerotor pumps in parallel.
FIG. 4 illustrates example output fluid flow curves of the gerotor pump system of FIG. 3.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
FIGS. 1 and 2 illustrate simplified schematic views of selected portions of an example gerotor pump 20 for efficiently pumping a fluid and avoiding maintenance problems such as seizure. In this example, the gerotor pump 20 includes a housing 22 having a pocket 24 that contains an inner rotor 28 having lobes 29 that extend outward, and an outer rotor 30 (i.e., gear sets). In this example, the outer rotor 30 is a ring gear having lobes 31 that extend inwards. A selected number, N, of planetary gears 32 are received between the inner rotor 28 and the outer rotor 30 for revolution about the inner rotor 28 and simultaneous revolution within the outer rotor 30.
In this example, a cover 34 retains the rotors 28, 30 and planetary gears 32 within the pocket 24. The cover 34 is secured to the housing 22 in a known manner to provide a sealed chamber in which the rotors 28, 30 and planetary gears 32 operate.
The housing 22 includes an inlet port 44 and an outlet port 46. Each of the inlet port 44 and the outlet port 46 includes a first slot 48a and a second slot 48b that is parallel to and radially inward of the first slot 48a. This “split slot” configuration provides the advantage of providing an unrestrictive flow path while preventing the planetary gears 32 from falling into the ports 44 and 46 as they revolve next to the ports 44 and 46. Alternatively, the inlet port 44, the outlet port 46, or both are ported through the cover 34 instead of the housing 22 (as seen in phantom at 44′ and 46′), depending on the particular needs of a design.
The inner rotor 28 is operatively coupled with a drive shaft 47 along an axis A1. The outer rotor 30 rotates about a central axis A2 that is eccentric relative to the inner rotor 28 rotational axis A1, and the planetary gears 32 revolve about a central axis A3. In the disclosed example, the axes A1, A2, and A3 align collinearly along a line L (FIG. 2) and are offset from each other. In this example, the axis A1 is offset a magnitude, e1, from axis A3, and the axis A2 is offset an equal magnitude e1 from axis A3. In one example, the offset value e1 is used to model the profile shape of the lobes 29 and 31. In a further example, the profile shapes of the lobes 29 and 31 are modeled from the offset value e1 using a known modeling technique, such as SAE 99P-464 entitled “Modeling and Simulation of Gerotor Gearing in Lubricating Oil Pumps.”
In the illustrated example, the gerotor pump 20 includes five planetary gears 32 (i.e., N=5); however, it is to be understood that the benefits described in this description will also be applicable to pumps having different numbers of planetary gears 32. The number of planetary gears may be selected during a design stage of the gerotor pump 20 and determines the configuration of the rotors 26. In one example, for N planetary gears 32, the inner rotor 28 has N−1 lobes 29 and the outer rotor 30 has N+1 lobes 31. Thus, in the illustrated example, there are four lobes 29 of the inner rotor 28 and six lobes 31 of the outer rotor 30.
The planetary gears 32 each include teeth 50a. The teeth 50a intermesh with corresponding teeth 50b and 50c on the inner rotor 28 and the outer rotor 30, respectively.
Similar to the relationship between the number of planetary gears 32 and the number of lobes 29 and 31, a number X of teeth 50a on the planetary gears 32 determines the number of teeth 50b and 50c on the inner rotor 28 and outer rotor 30, respectively. In one example, for X teeth 50a and N planetary gears 32, the inner rotor has X·(N−1) teeth 50b and the outer rotor 30 has X·(N+1) teeth 50c. The relationship between the number N of planetary gears 32 and its number X of teeth 50a and the number of lobes 29 and 31 and number of teeth 50b and 50c of the inner rotor 28 and the outer rotor 30, respectively, provides the benefit of forming a tight seal between the planetary gears 32 and the rotors 28, 30 to increase the pumping efficiency.
The relationship between the number N of planetary gears 32 and its number X of teeth 50a and the number of lobes 29 and 31 and number of teeth 50b and 50c of the inner rotor 28 and the outer rotor 30, respectively, in the disclosed example also provides a desirable rotational speed relationship. For X teeth 50a and N planetary gears 32 that rotate about the axis A3 with a speed Z, the inner rotor 28 rotates at a speed of Z·N/(N−1) and the outer rotor rotates at a speed of Z·N/(N+1). In this example, each of the planetary gears 32 travels over one of the lobes 29 of the inner rotor 28 and one of the lobes 31 of the outer rotor 30 with each revolution about the axis A3.
In operation, the drive shaft 47 rotates the inner rotor 28. This in turn drives the planetary gears 32 to revolve along a path 60 about central axis A3 and rotates the outer rotor 30 about its axis A2. In the illustrated configuration, the planetary gears 32 accelerate from a “short side” (i.e., the bottom in FIG. 2) to a “long side” (i.e., the top in FIG. 2) and decelerate from the “long side” to the “short side.” As the planetary gears 32 revolve, fluid enters through the inlet port 44 into compression chambers 62 between the planetary gears 32. The planetary gears 32 reduce the size of the compression chamber 62 along the path 60 between the inlet port 44 and the outlet port 46 to compress the fluid. The compressed fluid is then discharged through the outlet port 46.
The correspondence between the number of planetary gears 32 and the number of lobes 29 and 31, and the correspondence between the number of teeth 50a on the planetary gears 32 and the number of teeth 50b and 50c on the inner rotor 28 and the outer rotor 30 provides the benefit of maintaining a desired operational relationship between the planetary gears 32, the inner rotor 28, and the outer rotor 30. As seen in FIG. 2, the planetary gears 32 maintain a tangential relationship with the inner rotor 28 and the outer rotor 30 along the path 60. Each of the planetary gears 32 maintains a first tangent point P1 between each of the planetary gears 32 and the inner rotor 28 and a second tangent point P2 between each of the planetary gears 32 and the outer rotor 30 such that the tangent points P1 and P2 are collinear (designated with lines 64) with a central axis A4 of each of the planetary gears 32 entirely along the path 60. The lines 64 intersect at point C, also known as the pitch circle contact point. Maintaining this tangential relationship provides the benefit of directing radial forces from the inner rotor 28 to the outer rotor 30 through the centers of the planetary gears 32 to prevent sliding and maintain a tight seal between the interlocking teeth 50a, 50b, and 50c. This in turn prevents fluid escape from the compression chambers 62 to provide efficient pumping, which is a drawback with some prior gerotor pumps.
FIG. 3 illustrates a simplified schematic view of an embodiment having a gerotor pump system 21 comprising multiple gerotor pumps 201, 202, and 203 arranged in parallel. In the illustrated example, the gerotor pumps 201, 202, and 223 are similar to the gerotor pump 20 described in the above example. In this example, the gerotor pumps 201, 202, and 203 have progressively offset planetary gear 32 sets. That is, the planetary gears 32 of the gerotor pump 202 are offset by an angle relative to the planetary gear sets 32 of the gerotor pumps 201 and 203. Likewise, the planetary gears 32 of the gerotor 201 are offset from the planetary gears 32 of the gerotor pump 203. The drive shaft 47′ drives all three of the gerotor pumps 201, 202, and 203 in this example. Fluid enters into each inlet port 44 of the gerotor pumps 201, 202, and 203 from a common inlet manifold 66 and is discharged from each outlet port 46 into a common outlet manifold 68.
Generally, a single gerotor pump 20 produces fluid flow ripples as the chambers 62 discharge the fluid through the outlet port 46. In some instances, it is desirable to reduce the magnitude of the ripples (i.e., a difference between a maximum fluid flow and a minimum fluid flow through the outlet port 46) to, for example, promote quieter operation.
In the disclosed example, each gerotor pump 20 within the gerotor pump system 21 has the same number N planetary gears 32. This provides the benefit of minimizing fluid flow ripple issuing from a gerotor pump system 21.
In one example demonstrated by FIG. 4, the gerotor system 21 includes an odd number M of gerotor pumps 201 through 20M. The gerotor pumps 201 through 20M have progressively offset planetary gear 32 sets. In the disclosed example, the offset is an angle with respect to the direction of rotation of the drive shaft 47′ and is a function of the number M of gerotor pumps 20 in the gerotor pump system 21 and the number N of planetary gears 32 in each gerotor pump 20. In a further example, the offset angle equals 2·360°/(M·N).
In this example, M=3 and N=5 whereby the desired progressive offset angle is 2·360°/(3·5)=48° such that the planetary gears 32 of the gerotor pumps 201, 202, and 203 are oriented 48° out of phase from each other. For example, if the direction of rotation of the drive shaft 47′ is clockwise, the planetary gears of the second gerotor pump 202 are oriented 48° in a clockwise direction from the first gerotor pump 201, and the planetary gears of the third gerotor pump 203 are oriented 48° in a clockwise direction from the second gerotor pump 202. Thus as will be apparent from an inspection of FIG. 4 below, the out of phase orientation provides the benefit of offsetting the fluid flow ripples produced by each of the gerotor pumps 201, 202, and 203 to reduce the magnitude of the resulting output fluid flow ripple.
The example illustrated in FIG. 4 shows a graph of relative volume of fluid flow versus radians (relative to rotation of the inner rotors 28) for the three gerotor pumps 201, 202, and 203. The curves near the bottom of the graph represent the relative volume of fluid flow curves of the compression chambers 62 of a single gerotor pump 20 as the compression chamber 62 receives, compresses, and discharges fluid. The three curves near the top represent the total relative volume flow (which is proportional to fluid flow) of the respective gerotor pumps 201, 202, and 203. The three curves are offset by 48° in this example because of the 48° offset angle between the planetary gears 32 of the gerotor pumps 201, 202, and 203. As can be appreciated, the individual curves near the bottom of the graph depict the fact that in each of the gerotor pumps 20 there is finite asymmetry in fluid flow from each of the compression chambers 62. Thus, it will be appreciated that progressively offsetting each of the M gerotor pumps 201 through 20M at an angle of 2·360°/(M·N) rather than by an angle of 360°/(M·N) results in dispersing sets of three absolute minimum fluid flow cusps 70 (i.e., in this case at 2·360°/(M·N)=48° rather than sets of three in succession at 360°/(M·N)=24° followed by sets of three reduced magnitude cusps 72). In any case, it can be observed that the difference D1 in magnitude between the peaks and valleys of the three fluid flow curves is significantly smaller than the difference D2 between the peaks and valleys of any single curve. Thus, using multiple gerotor pumps 201, 202, and 203 provides the benefit of reducing the magnitude of output fluid flow ripple. It is to be understood that although the example illustrates use of three gerotor pumps 201, 202, and 203, in general, fewer pumps or additional pumps may be used as desired.
Although a preferred embodiment of this invention has been disclosed, a worker of ordinary skill in this art would recognize that certain modifications would come within the scope of this invention. For that reason, the following claims should be studied to determine the true scope and content of this invention.
Patent Application
20080031760
