IMPROVEMENTS RELATING TO GEROTOR PUMPS

Abstract: A gerotor pump set is shown in Figure 4 having passages 32 extending parallel to the axis of rotation through the female lobed annulus, and similar passages (not shown in the illustration) through the male lobed rotor. These, or either of them, enable flow from the inlet 38 to pass into the working chamber such as 42a either directly at the inlet end, or after flow through those passages and through the transfer passage 43 at the opposite axial end to the inlet, without requiring a transfer passage externally of the annulus. The result is better axial filling of the working chambers, in a particularly compact design.

Description: This invention relates to gerotor pumps which, as well known, comprise a male and multi-lobed rotor located in and rotatable both with, and with respect to, a female annulus which is also multi-lobed but with a greater number of lobes. Each of the male lobes contact the , annulus at one or more points so as to form a series' of chambers between the rotor and annulus. As the rotor turns in the annulus, those chambers increase and decrease in volume in the course of each revolution relative to a fixed point. Inlet and outlet ports are diametrically related in the pump body and exposed to the chambers so that as the chambers process past the inlet port they increase in size and hence suck fluid into the chambers, and as the chambers process past the outlet port they decrease in size and so expel fluid from the chambers. One example of a pump of this kind is to be found in EP-A-0107824. The output of such a pump depends upon a number of parameters including physical size and also speed of rotation. Size includes the length of the chambers, that is the axial length of both rotor and annulus. It is found that increasing length, or increasing speed or both, in the interests of increased output, sometimes lead to reduced pump output as compared to what is theoretically possible, and this is believed to be due to cavitation, as pinted out in the said prior Patent, which suggests modifying the profile of the inlet port as a solution. A more conventional solution to the problem of cavitation is to provide matched pairs of inlet and outlet ports, so that each end of each chamber is exposed to the ports. This enables each chamber to be filled or emptied from both ends. However this solution is impractical in certain circumstances where space is restricted because of the need to connect the two inlets together by a linking passageway extending outside the body of the pump, and similarly with the two outlets. For example if the pump is a lubricating oil circulated pump in an I.C. engine and is located in or on the crank case wall, there may be no space available for the additional passageways which are involved in having ports at both ends. The invention provides a new solution to the problem. According to the invention one or other or both of the rotor and annulus is provided with transfer passages extending through its lobes and opening at one end only to the inlet port, and at the other end to a transfer cavity. The latter may be similar in area and location to the port. By these means the working fluid can flow into the chambers from the inlet port and simultaneously flow through the said transfer passages and via the cavities to enter the chambers from the opposite end to that exposed to the port but without it being necessary to provide additional passageways extending externally of the body. Better chamber filling with avoidance of cavitation but whilst maintaining compact dimensions of the pump is the result. The invention is more particularly described with reference to the accompanying drawings wherein:- Figure 1 is a diagrammatic elevation showing the rotor and annulus set of a gerator pump with the position of the inlet and outlet ports shown in broken line; Figure 2 is a section taken on the line A-A of Figure 1 showing the gerotor set assembled in a pump body arranged to provide inlet ports connected to both ends of the chambers: Figures 1 and 2 both represent the prior art; Figure 3 shows the gerator set similar to that in Figure 1 but utilising the invention in a simple form; Figure 4 is a view similar to Figure 2 but showing the set of Figure 3 assembled in a body according to the invention; Figure 5 shows a modification; and Figure 6 shows a further modification which is the presently preferred version. Referring first to Figure 1, the gerotor set comprises a male four-lobed rotor 10 assembled in a female five-lobed rotor 12. The inlet and outlet ports are shown in broken line at 14 and 16 respectively. Turning now to Figure 2, aperture 18 is connected to the fluid supply and opens first to the manifold chamber 20 which is exposed to one axial end face of the gerotor set over the port area 14. Substantially the same port area 14 opens to the gerotor set at the opposite axial end of the set and the two ends are connected together from the manifold area 20 via the transfer passage 22 which extends externally of the body of the pump which provides the cylindrical cavity in which the annulus 12 is located. The outlet port 16 may be arranged similarly to the inlet port 14, but because cavitation is not a problem on the delivery side, a single outlet port may be sufficient, as shown in the Figure. Turning now to Figures 3 and 4, it will be seen that the rotor is here provided with a single axially extending passage 30 in each of its lobes. The annulus is similarly provided with transfer passages 32 extending through each of its lobes. Each of the transfer passages extends from one axial end face of the rotor or annulus to the opposite axial end face of the same. Figure 4 shows the aperture 38 (corresponding to the aperture 18) communicating to chamber 40 which opens via the port 14 to the chambers. Transfer cavity 43 is, like the chamber 40, of the same area as the port 14 but at the opposite end. There is no connection between chamber 40 and cavity 43 except through the chambers between rotor and annulus and through the passages 30, 32 which are aligned with said chamber 40 and cavity 43. The outlet arrangements are the same as the inlet arrangements including chamber 44 and transfer cavity 46 which are both of the same area as the outlet port 16. In the result, fluid flowing through the inlet aperture 38 via the chamber 40 can flow directly into the chambers such as 42 from the right hand end as seen in the Figures, and also through the transfer passages in the parts so as to reach the transfer cavity 43 and hence flow into the pump chambers from the left hand end as seen in Figure 4. Likewise, in the outlet position, fluid can flow out of the working chamber 42b to the right in Figure 4 directly into the chamber 44 and exhaust, or to the left in Figure 4 via the transfer cavity 46 and through the transfer passage 32b to reach the chamber 44 on its way to the outlet. In any one pump design for a specific purpose, it may be found desirable to provide either apertures 30 or apertures 32 or both sets of apertures 30, 32. Where even greater flow capacity is needful to avoid cavitation, Figure 5 shows a possibility; and for maximum effect, Figure 6 shows the preferred arrangements. Figure 5 shows a modification in which the annulus lobes are each provided with two transfer passages 50, 52. Figure 6 shows a further modification in which both the rotor and annulus are provided with transfer passages of possibly the maximum size which is possible, those in the rotor being indicated by the reference numeral 60 and those in the annulus by the reference numeral 62. Passages of such complex cross-section as illustrated, which are complementary in shape to these lobes as necessary in order to make them of maximum cross-sectional area may be made for example by making the components as powder metal compacts.

Claims: 1. A gerotor pump comprising a male multi-lobed rotor (10) located in and rotatable both with, and with respect to, a female multi-lobed annulus (12) having a greater number of lobes, forming a series of chambers therebetween, and inlet and outlet ports (14,16) which are diametrically related and characterised in that one or other or both of the rotor and annulus is provided with transfer passages (30,32) extending through its lobes, a transfer cavity (43) at the opposite axial end of the chambers of the inlet port, so that in the course of rotation each said passage opens at one end to the inlet (30) and at the same time to the transfer cavity at the other end to allow transfer of fluid from the inlet directly into the chambers at the same axial end of the chambers as the inlet and also allow transfer of said fluid from the inlet through the passages via the cavity and into the chambers at the opposite end. 2. A pump as claimed in Claim 1 wherein the transfer cavity (43) is similar in area and location to the inlet port (14). 3. A pump as claimed in Claim 1 wherein the passages (30,32) are of circular cross-section. 4. A pump as claimed in Claim 3 wherein a plurality of passages (50,52) are provided in each lobe. 5. A pump as claimed in Claim 1 wherein the passages (60,62) are of a cross-sectional shape complementary to that of the lobes.

Inventors: CHILD, ROBIN EDWARD
Applicants: CONCENTRIC PUMPS LIMITED
Application year: 1989
Main classification: F04C2
IPC codes: F04C2, F04C15