IMPROVED BUSHING ASSEMBLY AND POSITIVE DISPLACEMENT ROTARY PUMP COMPRISING SAID BUSHING ASSEMBLY

Abstract

Improved bushing assembly (10) for supporting the shafts of the intermeshed rotors of a positive displacement rotary pump avoiding, jamming, said bushing assembly (10) comprising on a lateral surface (13) thereof at least one compensation tank (15; 16) facing a suction side of the pump and at least one bleed channel (14) which connects said compensation tank (15; 16) to the discharge side.

Claims

1-14. (canceled)

15. A bushing assembly for a positive displacement rotary pump, arranged to be inserted into an internal cavity of a positive displacement rotary pump, axially floating therewithin, and to support the ends of a pair of shafts bearing the rotors of said positive displacement rotary pump; said bushing assembly comprising an inner face, facing, while in use, the rotors; an opposed external face; wherein, while in use, the bushing assembly is free to axially slide within the internal cavity due to fluid pressures acting on the inner and external faces; the bushing assembly further comprising: a lateral surface which connects the two inner and outer faces, said lateral surface being arranged to be coupled within the inner chamber with a first portion facing a suction side and a second portion facing a discharge side; at least one compensation tank on the first portion of said lateral surface, in a position closer to the inner face than to the outer one; and at least one bleed channel which connects said compensation tank to the second portion of the lateral surface; wherein the at least one compensation tank is laterally closed on both sides, i.e. it does not open on the inner face nor on the external face of the bushing assembly.

16. The bushing assembly according to claim 15, shaped as two sleeve- shaped semigroups coupled to each other, said semigroups being made in one piece or separated from each other.

17. The bushing assembly according to claim 16, wherein said lateral surfaces comprise two cylindrical portions connected or juxtaposed in two coupling areas of the semigroups, on the discharge side and on the suction side respectively.

18. The bushing assembly according to claim 17, wherein said bleed channel connects, while in use, the coupling area on the discharge side with the at least one compensation tank; and wherein said bleed channel does not reach the coupling area on the suction side.

19. The bushing assembly according to claim 17, wherein said bleed channel takes the form of an external circumferential groove formed on at least one of the cylindrical portions of the lateral surface.

20. The bushing assembly according to claim 19, wherein said at least one compensation tank takes the form of a widening in the axial direction of the circumferential groove which defines the bleed channel.

21. The bushing assembly according to claim 20, wherein said at least one compensation tank extends axially towards the inner face with respect to the bleed channel.

22. The bushing assembly according to claim 20, wherein said at least one compensation tank has a substantially parallelepiped conformation.

23. The bushing assembly according to claim 20, wherein said compensation tank and said bleed channel have the same depth.

24. The bushing assembly according to claim 20, wherein said compensation tanks are at least two for each semigroup.

25. The bushing assembly according to claim 24, wherein the two compensation tanks of each semigroup are connected by the same bleed channel.

26. The bushing assembly according to claim 15, wherein the compensation tanks are at least one intermediate compensation tank which intercepts the extension of the bleed channel, and at least one terminal compensation tank, whereat the bleed channel ends.

27. The bushing assembly according to claim 15, comprising a bushing ring, monolithic or in two pieces, which can be associated with two inner bushings, the bleed channel and at the least one compensation tank being made on the bushing ring.

28. A positive displacement rotary pump comprising: a casing provided with an internal cavity with a discharge port opening on a discharge side and a suction port opening on an opposite suction side; a pair of shafts which bear, in their intermediate portion, as many intermeshing rotors rotating within the inner chamber for pumping a fluid from the discharge port to the suction port; two bushing assemblies according to claim 1, said bushing assemblies being arranged at the opposite ends of the rotors for supporting the shafts with the inner face facing the rotors and the lateral side coupled within the internal chamber; said compensation tank facing the suction side of the internal cavity; and said at least one bleed channel connecting said compensation tank to a portion of the lateral surface facing the discharge side, wherein, while in use, said compensation tank is filled with fluid under pressure defining a straightening torque on the respective bushing assembly.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0032] The enclosed FIGS. 1-12 show the following:

[0033] FIG. 1 shows a perspective view with exploded parts of a generic positive displacement rotary pump, in particular a gear pump, on which the main aspects of the present invention are not detailed;

[0034] FIG. 2, as previously discussed, shows a perspective view of an element of a bushing assembly according to the prior art;

[0035] FIG. 3, as previously discussed, shows a perspective view of another bushing assembly according to the prior art;

[0036] FIG. 4, as previously discussed, shows a first schematic representation of the distribution of forces within a positive displacement rotary pump of the prior art;

[0037] FIG. 5, as previously discussed, shows a second schematic representation of the distribution of forces within a positive displacement rotary pump of the prior art;

[0038] FIG. 5a, as previously discussed, shows the graphs of the load F, the moment T and the corresponding deformation D of the structure constituted by rotor and bushing assemblies in the pump represented in FIG. 5;

[0039] FIG. 6, as previously discussed, represents the lines of force that are generated within a two-dimensional model of the bushing assemblies—rotor group in the pump represented in FIG. 5;

[0040] FIG. 7 shows a perspective view of a bushing assembly of a positive displacement rotary pump according to the present invention;

[0041] FIG. 8 shows a perspective view, according to a different angle, of the bushing assembly of FIG. 7;

[0042] FIG. 9 still shows the perspective view of FIG. 7 highlighting an area of greater concentration of loads;

[0043] FIG. 10 shows a lateral view of the bushing assembly of FIG. 7;

[0044] FIG. 11 shows a schematic representation of the distribution of forces within a positive displacement rotary pump according to the present invention;

[0045] FIG. 11a shows the graphs of the load F, the moment T and the corresponding deformation D of the structure constituted by rotor and bushing assemblies in the pump represented in FIG. 11;

[0046] FIG. 12 represents the lines of force that are generated within a two-dimensional model of the bushing assemblies—rotor group in the pump represented in FIG. 11.

DETAILED DESCRIPTION

[0047] With reference to FIG. 1, reference number 1 globally and schematically indicates a positive displacement rotary pump made according to the present invention with gear cog wheels.

[0048] The positive displacement rotary pump 1 comprises a pair of rotors 2, in particular of toothed wheels, supported by respective shafts 5 and enclosed in a casing 3. A first driving toothed wheel is connected to a drive shaft with a protruding end with respect to the casing 3, and a second driven toothed wheel is rotated by the driving wheel. In a preferred embodiment of the present invention, the two rotors 2 are gear wheels with helical teeth.

[0049] The casing 3 is closed fore and aft by two covers or flanges that are not represented because of the known type. On one side the casing has a suction port for the fluid, which is not represented in the enclosed figure, and on the other one a discharge port 4. Furthermore, the casing defines an internal cavity, within which the rotors 2 and the bushing assemblies 10 are introduced, which has a suction side S at the suction mouth and an opposed discharge side at the discharge mouth D.

[0050] Within the casing 3, the shafts 5 of the rotors 2 are supported at the two ends by two bushing assemblies 10, only one of which is represented in FIG. 1. Each of the bushing assemblies 10 may be made in one piece, as represented in the figure, or in two separated and juxtaposed semigroups 10a, analogously to what is provided for in the prior art of FIG. 2. Preferably, each of the bushing assemblies 10 comprises a bushing ring and two bushings 19 mounted thereon.

[0051] It should be noted that FIG. 1 does not illustrate the peculiarities of the bushing assemblies 10 according to the present invention, which are instead visible in the subsequent FIGS. 7-10.

[0052] As it may be observed, each bushing assembly 10 has an inner face 11, arranged to contact the rotors 2, except for an oil film, and an external face 12 which is opposed to the first one and faces the side of the covers or flanges of the casing 3. The two faces are connected by a lateral surface 13 constituted by the two cylindrical surfaces 13a, connected to each other in a coupling area 17 on the discharge side D and in a coupling area 18 on the suction side S.

[0053] On the bushing assemblies 10 two bleed channels 14, made as circumferential grooves on the respective cylindrical surfaces 13a are provided. The bleed channels 14 extend from the coupling area 17 on the discharge side D until they reach two compensation tanks 15, 16 on the suction side S. The compensation tanks 15, 16 are advantageously arranged in a maximum stress H area of the bushing assembly 10, which is located on the suction side S in a close area with respect to the inner face 11.

[0054] As clearly visible in FIG. 10, an intermediate compensation tank 15 intercepting the bleed channel 14 and a subsequent terminal compensation tank 16, at which the bleed channel 14 interrupts, are provided.

[0055] The compensation tanks 15, 16 may be of a different shape; in the preferred embodiment herein illustrated, they are substantially parallelepiped, they have a depth that is substantially equal to that of the bleed channel 14 and extend towards the inner face 11 of the bushing assembly 10.

[0056] Starting from said preferred configuration, the position and conformation of the bleed channel 14 and of the compensation tanks 15, 16 may be identified by means of the following measures: [0057] Axial width of the bleed channel 14; [0058] Axial width of each compensation tank 15, 16 (preferably, but not necessarily, the same); [0059] Distance of the bleed channel 14 from the inner face 11 of the bushing assembly 10; [0060] Circumferential length of each compensation tank 15, 16 (preferably, but not necessarily, the terminal tank 16 has a length that is less than the intermediate tank 15); [0061] Circumferential distance between the two subsequent compensation tanks 15, 16 (preferably, but not necessarily, approximately equal to the circumferential length of the intermediate tank 15); [0062] Position of the tanks with respect to the axis of the bearing center.

[0063] The above measures may be identified through numerical modeling to obtain, depending on the size and intended use of the pump, the maximum redistribution of the load, i.e. the minimum surface pressure in the above area of maximum stress H.

[0064] The above described conformation of the bushing assemblies 10 favours, during the use of the pump, the bleeding of the fluid under pressure within the compensation tanks 15, 16. In this way, a realignment force Fr is obtained at the area of maximum stress of the bushing assembly 10, which generates a corresponding realignment moment Tr, helping to realign the bushing assembly 10 with the pump axis and to rebalance the loads acting thereon, thus eliminating or at least reducing the phenomenon of local abrasion and that of the consequent jamming in the operational transients.

[0065] FIG. 11 introduces the realignment force Fr and the realignment moment Tr determined by the compensation tanks 15, 16 in the diagram of FIG. 5. FIG. 11a shows graphs indicative of the load F, the moment T and the corresponding deformation D of the structure. There is a significant redistribution of the stresses along the bushing assembly 10, and a decrease in the constraint reactions at the edge with the inner face 11.

[0066] FIG. 12 shows the lines of force—calculated by a modeling software—that are generated within a two-dimensional model of the bushing rings—rotor group. By comparing with the model of the prior art in FIG. 6, it can be noted that, although the average pressure on the remaining surface portion remains constant, the effort is better distributed by widening the portion of the surface that most cooperates in supporting the bushing assembly 10.

[0067] By further calculations the maximum effort can be reduced by about 40% for the reason explained above.

[0068] Obviously, a skilled person can make several changes and variants to the above described invention, in order to meet contingent and specific needs, all of them by the way contained in the scope of protection of the invention as defined by the following claims.