Methods and Apparatus for Gear Pump Lubrication

This invention relates to methods and apparatus for gear pump lubrication and particularly to gear pumps having means for lubricating the shafts with low pressure inlet fluid.

The lubrication of the shafts of gear pumps has long been recognized as a problem. In general, such lubrication has historically been based upon the use of high pressure fluid by-passed from the outlet side of the pump through the bearing. Many patents have proposed various structures for accomplishing this. Unfortunately, these high pressure lubricating systems have several undesirable qualities which are inherent in them. First, the oil is hotter by 20.degree. F. to 25.degree. F. than suction oil. Second, the high pressure feed of oil results in a loss in volumetric and thus overall efficiency in the pump. Third pump generated metal particles can be introduced into the bearing means with the high pressure oil. Avoiding any or all of these is desirable. These undesirable qualities can all be eliminated by using low pressure or suction oil for lubricating the bearings. Low pressure fluid has also been proposed for lubrication but only to a limited extent and has generally not met with favor. Typically of the structures proposed in the past for low pressure lubrication are Teruyama Pat. No. 4,090,820, Joyner Pat. No. 3,490,382 and Hodges et al. Pat. No. 3,447,472. In Teruyama, an axial groove is extended in the bore of each bushing from the inner end contacting the gear to the outer end. One end of this groove is connected to a chamber at the root of the gear which acts as a suction chamber. The other end of the groove is in communication with a hole extending along the casing. On rotation, the fluid in each tooth space is partially forced into and through the groove. In the case of Hodges and Joyner, there is provided grooving in the bore of each bushing which communicates with a side face of the gear rotor in a zone where the spaces between the rotating teeth are increasing in volume, the suction thus created inducing liquid to flow through the grooves. The problem with the latter Hodges and Joyner patents is that at low speed there is insufficient flow of liquid to provide adequate lubrication. In the case of Teruyama, on the other hand, there is a loss of efficiency as a result of fluid being drawn out of each rotating tooth space at chamber 55.

We have invented a new gear pump structure utilizing low pressure fluid which eliminates all of these problems of prior art lubricating structures. It provides a gear pump lubricated with low pressure fluid which is operative at all pressure levels and pump speeds and without any loss in efficiency in operation.

We provide a gear pump comprising a housing having a pump chamber, a suction chamber and a high pressure discharge chamber communicating with said pump chamber on opposite sides, a pair of meshing gears mounted for rotation in said pump chamber between said suction and discharge chambers, two axially spaced trunnions on opposite sides of each gear, bearing means surrounding each trunnion, said bearing means mounted in said housing a generally right-angled main suction port in said housing delivering fluid to said suction chamber around a substantially right-angled turn, a passage in the housing from the apex of the bend in the suction port to the bearing means at the end of each trunnion remote from the meshing gears, open conduit means on the housing connecting the ends of the bearing means adjacent the meshing gears and opening to said gears at the point of maximum suction between the gear teeth. Preferably, the housings are provided with floating end wear plates adjacent the meshing gears which wear plates carry the open conduit means. Preferably, open conduit means is slot in the end plates between the ends of the housings adjacent the meshing gears. The gears and trunnions preferably have an axial passage communicating between the ends of the bearing means remote from the meshing gears at each end and carrying fluid therebetween. Preferably, a flow restricting means in the form of a small clearance piece on the floating end plates is provided between the suction chamber and the point of maximum suction between the gear teeth.

In the foregoing general description of this invention, we have set out certain objects, purposes and advantages of our invention. Other objects, purposes and advantages of this invention will be apparent from a consideration of the following description and the accompanying drawings in which:

FIG. 1 is a vertical section through a typical gear pump according to this invention;

FIG. 2 is a horizontal section on the line II--II of FIG. 1, showing the driven gear and trunnions in elevation;

FIG. 3 is an isometric view of the port end plate of the pump of FIGS. 1 and 2 partly cut away;

FIGS. 4A-4D are schematic views of the sequence of gear teeth motion during pumping of the pump of FIGS. 1 and 2; and

FIG. 5 is an exploded view of the pump of FIGS. 1 and 2.

Referring to the drawings, we have illustrated a gear pump having a housing made up of a gear body 10, a port end cover 11, a shaft end cover 12, end plates 13 at each end cover and seal rings 14 between each end cover 11, 12 and the gear body 10. The gear body is provided ith a pump chamber 20 carrying the meshing gears 21 and 22, suction chamber 23 and a discharge chamber 24. Each of gears 21 and 22 is provided with integral coaxial trunnions 25, 26, 27 and 28 mounted for rotation in bushings 29 or other bearing means in bearing carrier wells 30 in each of the end covers 11 and 12. One trunnion 27 is extended through a passage 31 and seal 32 in shaft end cover 12 and is provided with a splined drive shaft end 33. The housing assembly is held together by through bolts 34.

The port end cover 11 is provided with a right-angled (90.degree. ) suction port 40 on one side communicating with the suction chamber 23 and a right-angled discharge port 41 communicating with discharge chamber 24 on the opposite side. Suction port 40 communicates through a passage 42 with the ends of well 30 beyond bushings 29 in the port end cover 11 remote from gears 21 and 22. This passage delivers fluid into the well 30. Each of the trunnions 25, 26, 27 and 28 and integral gears 21 and 22 has an axial bore 43 extending from end to end to discharge into wells 30 in drive end cover 12. In the case of trunnion 27, this is accomplished by providing a transverse radial passage 44 at the end of the bearing on the trunnion, communicating between bore 43 and well 30.

Each end plate 13 is provided with a slot 45 extending between the ends of bushings 29 within the end plate 13 and opening to the area of maximum suction 50 between the separating gear teeth of gears 21 and 22 during pumping.

The operation of the pump of this invention is as follows. Suction port 40 is connected to a reservoir of fluid (not shown) in the usual manner. When splined shaft 33 is rotated by a prime mover (not shown), it drives gear 21, which in turn drives gear 22 by their intermeshing teeth. The separation of the teeth at suction chamber 23 creates a suction or void causing fluid at a higher pressure, e.g., atmospheric pressure, to enter suction port 40. The fluid entering port 40 makes a 90.degree. turn and passes into suction chamber 23 of the gear housing where it is picked up by the gear teeth and carried to the discharge chamber 24 and discharge port 41. The fluid entering port 40 is usually at atmospheric pressure, designated here as P.sub.A. The pressure in suction chamber 23, designates P.sub.B is less than P.sub.A because of the frictional losses and particularly the losses induced by the 90.degree. bend. The pressure, designated P.sub.C, at the curve of port 40 and downstream from P.sub.A is greater than either P.sub.A or P.sub.B because of the momentum of the fluid and the flow resistance at the bend. As a result, the pressure of fluid in passage 42 is higher than the pressure P.sub.B in suction chamber 23, as is the pressure, designated P.sub.D in well 30 As a consequence, fluid flows through axial bores 43 to the opposite end wells 30 in drive end cover 12. This provides a higher absolute pressure of fluid at the ends of the wells 30 remote from gears 21 and 22.

Referring to FIG. 4, it will be seen that as the gears come out of mesh on the suction side, there are created rapidly increasing voids in certain tooth spaces. These voids create a sharp decrease in the absolute pressure. This decrease in pressure is communicated by slot 45 to the bushing ends adjacent the gears creating a substantial pressure differential between the pressure P.sub.D and the void area 50 between the teeth. This differential in pressure causes a flow of fluid through the clearance between the bushings 29 and trunnions 25, 26, 27 and 28. The flow of fluid from the suction chamber 23 into area 50 is retarded by small clearance 51.

In the foregoing specification, we have set out certain preferred practices and embodiments of this invention; however, it will be understood that this invention may be otherwise embodied within the scope of the following claims.