OIL PUMP

Abstract: A variable output gerotor oil pump of the kind having a common rotor (16) with n teeth meshed with two axially juxtaposed internally lobed annuli (14) with n + 1 teeth has the annuli individually located in eccentrics (12) formed with gear teeth to be turned in opposite directions by a gear drive. The teeth are straight cut, not bevel, and the drive includes an intermediate pinion (29) so that a single shaft turns (27) the eccentrics (12) in opposite directions.

Description: This invention relates to gerotor oil pumps of the kind in which a lobed rotor turns in and with an internally lobed annulus having a larger number of lobes, and the annulus is divided into two axially juxtaposed portions each in a corresponding eccentric having an external bevel gear set driven from a common bevel pinion so that the eccentrics can be simultaneously turned in opposite directions. This varies the displacement of the pump because of the shift in location of the chambers, defined between the inner and outer rotating parts, and the ports which form inlet and outlet passages respectively. Such an oil pump is to be found in E.P. 0076033A. However, the version illustrated in the said E.P. is found unsatisfactory because of the loading applied to the eccentrics which makes them difficult to rotate. In E.P. 0174734A, the difficulty in turning is overcome by using needle rollers between the eccentrics and the pump body in which they are to turn. But that pump has been found difficult to manufacture economically. Moreover, the bevel teeth occupy a certain axial dimension on each eccentric, which means that the construction can only be used where a particular axial rotor length is exceeded. This happens to exclude many of the possible output ratings for which such pumps would otherwise be useful. The objects of the invention is to solve these problems. According to the invention, an oil pump of the kind referred to is characterised by the provision of straight spur pinions provided on said eccentrics, a drive pinion rotatable about an axis parallel to that of said rotor meshed with one of said spur pinions, and an intermediate pinion also rotatable about a parallel axis effective between the other of said spur pinions and the drive to the intermediate pinion. This has the advantage of enabling a smaller part of the axial thickness of the eccentric to be used for drive transmission and a larger part for the bearing. This is because the height of the gear tooth is located radially, and can be accommodated without any difficulty in the thickness of the eccentric even at its minimum radial dimension, instead of being located axially. It thus extends the range of usefulness of such pumps. In practice it also means that caged rollers can be used, which are far simpler to assemble. One possibility for the drive gear arrangement is for the drive pinion to mesh directly with one eccentric spur pinion and also with the intermediate pinion which is itself meshed with the other eccentric spur pinion, in order to bring about the movement of the two eccentrics in opposite directions. In another possibility, a shaft carries a pair of drive pinions which are axially spaced, one of which meshes directly with one eccentric and the other of which meshes with an intermediate pinion to drive the other eccentric. In the prior art (the mentioned European Patents) a single pinion was inserted between two facing sets of gear teeth on the respective eccentrics and meshed with both so as to drive them in opposite directions. This necessitated bevel teethin order to get good meshing, which in turn made it difficult to journal the drive pinion against load. Also the volume taken up by the drive pinion both radially of the rotor axis and also parallel to the rotor axis restricted space available for the needle bearings in the arrangement of the E.P. 0174734A. These are only two of the design constraints resulting from the use of the single drive pinion and it is now found that both of these and others, are avoided by the present invention as will be better understood after consideration of the following description of presently preferred embodiments, wherein:- Figure 1 is a somewhat diagrammatic elevation of a first embodiment; Figure 2 is a sectional plan on the line 2-2 of Figure 1; Figure 3 is a view similar to Figure 1 of the second embodiment; Figure 4 is a sectional plan on the line 4-4 of Figure 3; Figure 5 is a sectional elevation on the line 5-5 of Figure 3. Turning now to the drawings and particularly Figures 1 and 2 thereof, the part 10 forms a casing for the pump and houses the eccentrics 12 which in turn receive the internally toothed annuli 14 surrounding the rotor 16. The rotor 16 has n teeth and the annulus 14 has n + 1 teeth. However other numbers are possible. The rotor is driven by shaft 18. The rotor 16 is a single component but the annulus 14 is a pair of components located axially end to end, and each annulus is located in a corresponding eccentric. As best seen in Figure 2, the eccentrics are each provided with straight cut spur pinion teeth 20, 22, and between the pinion teeth, is located two axially extending end-to-end independently caged sets of rollers 26, 28. The needle roller bearings are effective between the two eccentric components 12 and the casing 10. The location of the needle rollers and the teeth is diagrammatically indicated in Figure 1 by the reference 20/24. The drive arrangements are best seen in Figure 2. Drive shaft 27 is pinned to straight cut pinion 29 meshed with the gear ring 22. It is also keyed at 30 to a further such pinion 32 which is in turn meshed with pinion 34 journalled on shaft 36 and meshed with gear ring 20. It will be appreciated that when the shaft 27 turns, pinions 29 and 34 turn in opposite directions and likewise for the gear rings 20, 22 and hence the two eccentrics 12. A clock spring 38 or another torsion spring is provided and connected to the shaft 27 for example to return the same to a position in which the eccentricity is at a maximum. In the arrangement shown in Figure 3, from which the eccentrics, annuli and rotor are omitted for clarity, the casing 50 is provided with the outlet and inlet ports 52, 54 and in this case drive shaft 56 (Figure 5) is connected to the return spring by the slot 58 at one end, and carries pinion 60 meshed with gear ring 62 on the eccentric sheave 64 (only shown in Figure 5) and the same pinion 60 also meshes with a second pinion 66 (Figure 4) on a parallel shaft and that second pinion in turn meshes with a gear ring 68 on the second annuli 70 (Figure 5). In this case the spaces 72, 74 accommodate completely separate caged needle sets to journal the two annuli 64, 70.

Claims: 1. A variable output gerotor oil pump having a common rotor 16 with n teeth meshed with two axially juxtaposed internally lobed annuli 14 having n + x lobes, having the annuli individually located in eccentrics 12 formed with gear teeth 20 and with a drive system for turning the eccentrics in opposite directions, characterised in that the eccentrics have straight cut teeth 20, 22, one of the eccentrics being meshed with a direct drive pinion 29 or 60 and the other with an intermediate drive pinion 34 or 66. 2. A variable output pump as claimed in Claim 1 characterised in that said intermediate pinion 66 is also meshed with the drive pinion 60. 3. A variable output pump as claimed in Claim 1 characterised in that said direct drive pinion 29 is driven by a shaft 27 which drives the intermediate pinion 34. 4. A variable output pump as claimed in any preceding claim wherein the eccentrics are journalled by individual caged needle roller sets.

Inventors: CHILD, ROBIN EDWARD
Applicants: CONCENTRIC PUMPS LIMITED
Application year: 1987
Main classification: F04C2
IPC codes: F04C14, F04C2