Improved Bushing Assembly and Positive Displacement Rotary Pump Comprising the Bushing Assembly

Abstract

An improved bushing assembly (10) for supporting the shafts of the meshed rotors of a positive displacement rotary pump to prevent jamming, the bushing assembly (10) having on its side (13) at least one compensation tank (15, 16) facing the suction side of the pump and at least one bleed channel (14) connecting the compensation tank (15, 16) to the discharge side.

Description

Technical Field

[0001] The present invention relates to a bushing assembly and a positive displacement rotary pump comprising said bushing assembly, preferably a gear pump or a lobe pump.

[0002] Positive displacement rotary pumps can find useful applications in various technical fields. In particular, the pumps of the present invention are particularly thought to be suitable for high-pressure applications where it is necessary to vary the rotational speed over time.

Background Art

[0003] As mentioned above, the present invention finds useful applications in the technical field related to positive displacement rotary pumps with gears or lobes. This type of pump generally comprises two rotors, one of which is called the driving rotor and is connected to the drive shaft, and rotates the other, called the driven rotor.

[0004] The two rotors are each supported by a respective shaft, which is generally supported by a bushing assembly composed of a bushing ring and an actual bushing. The bushing assembly is connected in the internal cavity of the casing or pump body and can float axially therein, enabling packing of the components due to the pressure acting on the opposing flat surfaces of the assembly itself.

[0005] The currently used bushing rings can have pockets on the flat surface facing the rotor or gasket sheets on the flat surface facing the closing flange of the casing. These pockets or sheets are useful for facilitating the discharge of the oil lubricating the bushing, and also, as mentioned above, for compensating the axial thrust caused by the fluid under pressure, i.e., for keeping the surfaces of the rotor and the bushing in direct contact except for the oil film. Other types of pockets are useful for reducing vibration and noise by allowing the fluid trapped between the gear teeth to recirculate in the discharge area.

[0006] In the attached FIG. 2 showing a partial element 10a of a prior art bushing ring and the attached FIG. 3 showing instead an integral prior art bushing ring 10, pockets 100 with various shapes and functions can be identified.

[0007] So far, the design of bushing rings has always aimed, on the one hand, at achieving axial balance adjustment in an attempt to control the center of the pressure acting on the flat surface, and on the other hand, at restricting the displacement of the ring itself with respect to the axis of the rotor.

[0008] On the other hand, no intervention on the cylindrical surface of the ring has been made so far to avoid the friction and wear phenomena due to the dispersion of the load applied to the rotor and released to the ring itself (which, as mentioned, slide freely within the holes of the pump casing).

[0009] The solutions regarding the structures adopted so far are substantially suitable for the purpose, but nevertheless have significant drawbacks in the case of pumps targeted for high-load applications.

[0010] In fact, in these cases, the force of the bushing ring is released to the surface of the body hole and accordingly to the bushing ring itself, causing wear on the surface of the body hole. Due to the micro-sliding between the two contact surfaces, the roughness deterioration of the piece occurs, and the phenomenon of local heating is induced in the area with a high specific load. Next, the material is locally plasticized and the smoothness decreases. This is accompanied by the jamming of the bushing ring during the transient event and the corresponding deterioration of the pump performance.

[0011] Using FIGS. 4 to 6, the above phenomenon is illustrated and analyzed.

[0012] FIG. 4 schematically shows an example of a known type of gear pump. This pump is shown in a longitudinally divided state by a plane perpendicular to the plane passing through the axes of the two rotors, with the suction side S in the lower part of the cross-section and the discharge side D in the upper part. In addition to the wall of the suction side S of the pump casing 3, the drive rotor 2, the drive shaft 5, and the two bushing assemblies 10 are shown. Due to the excess pressure generated during pump operation, the distributed load F acts on both the bearing ring 10 and the rotor 2 from the discharge side D. This figure highlights the micro-sliding area Z1 and the wear area Z2 of the bushing ring 10 where jamming occurs.

[0013] FIGS. 5 and 5a present a static analysis executed by the applicant showing the basis of the above phenomenon. In FIG. 5, the structure composed of the bushing ring 10 and the rotor 2 is modeled together with four carriage restraint points a, b, c, d. FIG. 5a shows a graph indicating the load F, moment T, and corresponding strain D of the structure. As can be confirmed, at points b and c, there are both the maximum restraint reaction and the maximum moment, which decrease at points a and d respectively. Therefore, by linearizing the reaction along the entire bushing ring, a trapezoidal distribution Sj is obtained. Therefore, this setup condition is not optimal and leads to the above problems.

[0014] In Figure 6, a further analysis of the system is presented, showing the lines of force generated in a two-dimensional model of the bushing ring - rotor assembly, calculated by the modeling software. As can be seen, the maximum stress concentration occurs at the inner edge of the bushing ring, in the aforementioned wear zone Z2. This concentration decreases rapidly as it moves towards the outer edge.

[0015] U.S. Patent Document No. 4,087,216 discloses a rotary fluid pump according to the prior art. This pump uses needle bearings and does not use an axially floating bushing.

[0016] French Patent Document No. 1343908 A discloses a further rotary fluid pump according to the prior art.

[0017] In view of the above, the technical problem underlying the present invention is to at least partially solve the above - mentioned deficiencies of the claimed prior art, and thus to devise a bushing assembly and a corresponding positive displacement rotary pump having improved performance and service life and a reduced response time in transient events.

Summary of the Invention

[0018] The solution underlying the present invention lies in creating a pressurized tank positioned below the part of the bushing assembly that is in direct contact with the pump casing during use, i.e., the part at the inner edge on the suction side, in order to reduce the specific pressure in the area of high stress.

[0019] In view of this solution, the technical problem identified above is solved by a positive displacement rotary pump, which comprises a casing provided with an internal cavity having a discharge port open on the discharge side and a suction port open on the opposite suction side, a pair of shafts supporting the same number of meshing rotors rotating in an inner chamber for pumping fluid from the discharge port to the suction port at an intermediate portion, and two bushing assemblies arranged at both ends of the rotors for supporting the shafts, the bushing assemblies having an inner surface facing the rotors, an opposite outer surface, and side surfaces connecting the two inner and outer surfaces, the side surfaces being connected in the inner chamber, the bushing assemblies having, on their side surfaces, at least one compensation tank located closer to the inner surface than the outer surface and facing the suction side of the internal cavity, and at least one bleed channel connecting the compensation tank to a part of the side surface facing the discharge side.

[0020] The technical problem is also solved by a bushing assembly of the type identified above in relation to the positive displacement rotary pump as a whole.

[0021] The bushing assembly according to the invention may comprise an integral or two-piece bushing ring, in which case the bleed channel and at least one compensation tank are made on the bushing ring arranged to support the two inner bushings. On the other hand, it is not excluded that there may be no bushing ring different from the supporting bushing and the bushing assembly may be made as a single element or as two juxtaposed elements.

[0022] Due to the above structure, the compensation tank is filled with fluid under pressure coming from the discharge pump during use. Thus, a corrective torque for each bushing assembly is defined, which helps to relieve the maximum stress areas that tend to wear in pumps according to the prior art.

[0023] In other words, the structure according to the invention aims to facilitate the support of each bushing assembly by bleeding off the discharge liquid and transporting it into the aforementioned compensation tank.

[0024] In an essentially known manner, the bushing assembly is shaped as two sleeve-shaped semi-groups connected to each other, and the semi-groups are made in one piece or separated from each other.

[0025] Thus, the side surface comprises two cylindrical parts connected or juxtaposed in any way in two connecting areas of the semi-groups, which are respectively on the discharge side and the suction side.

[0026] The bleed channel preferably connects the discharge-side connecting area to at least one compensation tank and is preferably blocked before reaching the opposite suction-side connecting area.

[0027] Preferably, the bleed channel takes the form of a circumferential groove of limited depth made in at least one, preferably both, of the cylindrical parts of the side surface.

[0028] In a preferred embodiment, the compensation tank takes the form of an axially extended form of the circumferential groove defining the bleed channel, for example, substantially parallelepiped-shaped.

[0029] Preferably, the compensation tank extends axially towards the inner surface with respect to the bleed channel.

[0030] Preferably, the compensation tank and the bleed channel have the same depth.

[0031] In a preferred embodiment, there are at least two such compensation tanks for each semi-group of each bushing assembly, which may be connected by the bleed channel itself. For example, the compensation tank may include at least one intermediate compensation tank intersecting an extension of the bleed channel and at least one end-side compensation tank at the location where the bleed channel ends.

[0032] The features and advantages of the pump according to the present invention will become apparent from the following description of the embodiments shown as non-limiting examples, together with reference to the accompanying drawings.

Brief Description of the Drawings

[0033] The attached FIGS. 1-12 show the following.

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 5a

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10

Figure 11

Figure 11a

Figure 12

Mode for Carrying Out the Invention

[0034] Referring to FIG. 1, reference numeral 1 shows the positive displacement rotary pump made according to the present invention together with the gears of the gears as a whole and schematically.

[0035] The positive displacement rotary pump 1 includes a pair of gears of the rotor 2, which are supported by respective shafts 5 and surrounded by a casing 3. The first drive gear is connected to the drive shaft at the end protruding from the casing 3, and the second driven gear is rotated by a driven wheel. In a preferred embodiment of the present invention, the two rotors 2 are gears having helical teeth.

[0036] The casing 3 is closed at the front and rear by two covers or flanges (not shown because they are of a known type). On one side of the casing there is a fluid suction port (not shown in the attached drawings), and on the other side there is a discharge port 4. Further, the casing defines an internal cavity into which the rotor 2 and the bushing assembly 10 are introduced, having a suction opening on the suction side S and a discharge opening D on the opposite discharge side.

[0037] Inside the casing 3, the shaft 5 of the rotor 2 is supported at its two ends by two bushing assemblies 10 (only one of which is shown in FIG. 1). Each of the bushing assemblies 10 may be made in one piece as shown, or may be made of two separately juxtaposed semi - groups 10a as presented in the prior art of FIG. 2. Preferably, each of the bushing assemblies 10 comprises a bushing ring and two bushings 19 mounted thereon.

[0038] Note that FIG. 1 does not illustrate the characteristics of the bushing assembly 10 according to the present invention, and those characteristics can instead be verified in FIGS. 7 - 10 that follow.

[0039] As can be verified, each bushing assembly 10 has an inner surface 11 arranged to contact the rotor 2 except for the oil film, and an outer surface 12 opposite the first surface and facing the side of the cover or flange of the casing 3. The two surfaces are connected by a side surface 13 which is composed of two cylindrical surfaces 13a connected to each other in the connection area 17 on the discharge side D and the connection area 18 on the suction side S.

[0040] The bushing assembly 10 is provided with two bleed channels 14 formed as circumferential grooves on respective cylindrical surfaces 13a. The bleed channels 14 extend from the connection area 17 on the discharge side D to reach the two compensation tanks 15, 16 on the suction side S. The compensation tanks 15, 16 are advantageously arranged in the maximum stress H area of the bushing assembly 10, which is located in an area close to the inner surface 11 on the suction side S.

[0041] As can be clearly confirmed in FIG. 10, an intermediate compensation tank 15 intersecting the bleed channel 14 and, subsequently, a terminal-side compensation tank 16 blocking the bleed channel 14 are provided.

[0042] The compensation tanks 15, 16 may have different shapes. In the preferred embodiment illustrated herein, they are substantially parallelepipeds, have a depth substantially equal to the depth of the bleed channel 14, and extend towards the inner surface 11 of the bushing assembly 10.

[0043] Starting from the said preferred configuration, the positions and forms of the bleed channel 14 and the compensation tanks 15, 16 can be specified by the following criteria: - The axial width of the bleed channel 14, - The axial width of each compensation tank 15, 16 (preferably the same, but not necessarily so), - The distance of the bleed channel 14 from the inner surface 11 of the bushing assembly 10, - The perimeter of each compensation tank 15, 16 (preferably, the terminal-side tank 16 has a smaller length than the intermediate tank 15, but not necessarily so), - The circumferential distance between two successive compensation tanks 16 (preferably approximately equal to the perimeter of the intermediate tank 15, but not necessarily so), - The position of the tank with respect to the axis at the center of the bearing.

[0044] The above criteria can be determined by numerical modeling, depending on the pump size and purpose of use, to obtain the maximum load redistribution, i.e., the minimum surface pressure in the area of the above maximum stress H.

[0045] The above-described form of the bushing assembly 10 is advantageous for bleeding the fluid under pressure in the compensation tanks 15, 16 during pump operation. In this way, a re-aligning force Fr is obtained in the area of the maximum stress of the bushing assembly 10, and a corresponding re-aligning moment Tr is generated, which serves to re-align the bushing assembly 10 with the pump shaft and balance the load acting thereon, thus eliminating or at least reducing the resulting jamming phenomenon in local wear and transient events during operation.

[0046] FIG. 11 presents the re-aligning force Fr and the re-aligning moment Tr determined by the compensation tanks 15, 16 in the diagram of FIG. 5. FIG. 11a shows a graph indicating the structural load F, moment T, and corresponding strain D. The stress is highly redistributed along the bushing assembly 10, and the restraint reaction with the inner surface 11 at the edge is reduced.

[0047] FIG. 12 shows the lines of force generated in a two-dimensional model of a group of bushing rings and rotors calculated by modeling software. Comparing with the prior art model of FIG. 6, it can be seen that the average pressure in the remaining surface part remains constant, but the power is more favorably distributed by expanding the part of the surface that most cooperates in supporting the bushing assembly 10.

[0048] For the reasons explained above, further calculations can reduce the maximum power by about 40%.

[0049] Of course, those skilled in the art can make several changes and modifications to the above invention in a way that all are included in the protection scope of the invention defined by the following claims to meet the conditions and specific needs. [Other possible items] [Item 1] A bushing assembly (10) of a positive displacement rotary pump (1), which is inserted into an internal cavity (30) of the positive displacement rotary pump (1) and floats axially therein, and is arranged to support end portions of a pair of shafts (5) that support the rotor (2) of the positive displacement rotary pump (1). The bushing assembly (10) is During use, an inner surface (11) facing the rotor (2), and an opposite outer surface (12). During use, the bushing assembly (10) slides freely axially within the internal cavity (30) due to fluid pressure acting on the inner and outer surfaces (11, 12). The bushing assembly (10) is A side surface (13) connecting the two of the inner surface (11) and the outer surface (12), which is arranged to be connected within the inner chamber (30) such that a first portion faces the suction side (S) and a second portion faces the discharge side (D). At least one compensation tank (15, 16) located closer to the inner surface (11) than the outer surface (12) at the first portion of the side surface (13), and at least one bleed channel (14) connecting the compensation tank (15, 16) to the second portion of the side surface (13). A bushing assembly, characterized by comprising the above. [Item 2] The at least one compensation tank (15, 16) is closed on both sides, that is, it does not open on either the inner surface (11) or the outer surface (12) of the bushing assembly (10) as described in Item 1. [Item 3] The bushing assembly (10) according to item 1 or 2, which is formed as two sleeve-shaped semigroups (10a) connected to each other, and the semigroups (10a) are made in one piece or separated from each other. [Item 4] The bushing assembly (10) according to item 3, wherein the side surfaces (13) have two cylindrical portions (13a) that are connected or juxtaposed in two connecting areas (17, 18) of the semigroup (10a), which are respectively on the discharge side (D) and the suction side (S). [Item 5] The bushing assembly (10) according to item 4, wherein during use, the bleed channel (14) connects the connecting area (17) on the discharge side (D) to the at least one compensation tank (15, 16), and the bleed channel (14) does not reach the connecting area (18) on the suction side (D). [Item 6] The bushing assembly (10) according to any one of items 4 or 5, wherein the bleed channel (14) takes the form of an outer circumferential groove formed in at least one of the cylindrical portions (13a) of the side surface (13). [Item 7] The bushing assembly (10) according to item 6, wherein the at least one compensation tank (15, 16) takes the form of extending axially in the axial direction of the circumferential groove that defines the bleed channel (14). [Item 8] The bushing assembly (10) according to item 7, wherein the at least one compensation tank (15, 16) extends axially towards the inner surface (11) with respect to the bleed channel (14). [Item 9] The bushing assembly (10) according to any one of items 7 or 8, wherein the at least one compensation tank (15, 16) has a substantially parallelepiped shape. [Item 10] The bushing assembly (10) according to any one of items 7 to 9, wherein the compensation tank (15, 16) and the bleed channel (14) have the same depth. [Item 11] The compensation tanks (15, 16) are at least two for each semi-group (10a) of the bushing assembly (10) according to any one of Items 7 to 10. [Item 12] The two compensation tanks (15, 16) of each semi-group (10a) are connected by the same bleed channel (14) of the bushing assembly (10) according to Item 11. [Item 13] The compensation tanks (15, 16) are at least one intermediate compensation tank (15) intersecting the extension of the bleed channel (14) and at least one end-side compensation tank (16) where the bleed channel ends (14) of the bushing assembly (10) according to Item 12. [Item 14] Comprising an integral or two-piece bushing ring which may be combined with two inner bushings (19), and the bleed channel (14) and the at least one compensation tank (15, 16) are formed on the bushing ring, the bushing assembly (10) according to any one of the preceding items. [Item 15] A positive displacement rotary pump (1), A casing (3) provided with an internal cavity (30) having a discharge port (4) open at the discharge side (D) and a suction port open at the opposite suction side (S), A pair of shafts (5) supporting the same number of meshing rotors (2) rotating in the inner chamber (30) for pumping fluid from the discharge port (4) to the suction port, Comprising two bushing assemblies (10) according to any one of the preceding items, The bushing assembly (10) is arranged at both ends of the rotor (2) to support the shaft (5), The inner surface (11) facing the rotor (2), The side surface (13) connected in the internal chamber (30), the compensation tanks (15, 16) facing the suction side (S) of the internal cavity (30); at least one bleed channel (14) connecting the compensation tanks (15, 16) to a part of the side surface (13) facing the discharge side (D); During use, the compensation tank (14) is filled with fluid under pressure defining a corrective torque for the respective bushing assembly (10), a positive displacement rotary pump.

Claims

1. A bushing assembly for a positive displacement rotary pump, inserted into the internal cavity of a positive displacement rotary pump and floating axially therein, and arranged to support the ends of a pair of shafts that support the rotor of the positive displacement rotary pump. The bushing assembly has an inner surface facing the rotor and an opposite outer surface during use. During use, the bushing assembly slides freely axially within the internal cavity due to the fluid pressure acting on the inner and outer surfaces. The bushing assembly has a side surface connecting the two of the inner and outer surfaces, and is arranged to be connected in the internal cavity such that a first portion faces the suction side and a second portion faces the discharge side. The side surface, at least one compensation tank located closer to the inner surface than the outer surface in the first portion of the side surface, and at least one bleed channel connecting the compensation tank to the second portion of the side surface. The at least one compensation tank is closed on both sides, that is, it is not open on either the inner surface or the outer surface of the bushing assembly, The bushing assembly is formed as two sleeve-shaped semi-groups connected to each other, and the semi-groups are made in one piece or separated from each other, The side surface has two cylindrical portions connected or juxtaposed in two connecting areas of the semi-groups, which are respectively on the discharge side and the suction side, The bleed channel connects the connecting area on the discharge side to the at least one compensation tank during use, and the bleed channel does not reach the connecting area on the suction side. A bushing assembly.

2. The bushing assembly according to claim 1, wherein the bleed channel takes the form of an outer circumferential groove formed in at least one of the cylindrical portions of the side surface.

3. The bushing assembly according to claim 2, wherein the at least one compensation tank takes the form of extending axially in the direction of the inner surface with respect to the bleed channel.

4. The bushing assembly according to claim 3, wherein the at least one compensation tank extends axially towards the inner surface with respect to the bleed channel.

5. The at least one compensation tank has a substantially parallelepiped shape, and the bushing assembly according to claim 3 or 4.

6. The compensation tank and the bleed channel have the same depth, and the bushing assembly according to any one of claims 3 to 5.

7. The compensation tank has at least two for each semi-group, and the bushing assembly according to any one of claims 3 to 6.

8. The two compensation tanks of each semi-group are connected by the same bleed channel, and the bushing assembly according to claim 7.

9. The compensation tank is at least one intermediate compensation tank intersecting the extension of the bleed channel and at least one end-side compensation tank where the bleed channel ends, and the bushing assembly according to claim 8.

10. An integral or two-piece bushing ring arranged to support two inner bushings inside, and the bleed channel and the at least one compensation tank are formed on the bushing ring, and the bushing assembly according to any one of claims 1 to 9.

11. A positive displacement rotary pump, comprising a casing provided with an internal cavity having a discharge port open on the discharge side and a suction port open on the opposite suction side, and a pair of shafts supporting the same number of meshing rotors rotating in the internal cavity for pumping fluid from the discharge port to the suction port, and two bushing assemblies according to any one of claims 1 to 10, the bushing assemblies being arranged at both ends of the rotor to support the shaft, the inner surface facing the rotor, the side surfaces connected in the internal cavity, the compensation tank facing the suction side of the internal cavity, and the at least one bleed channel connecting the compensation tank to a part of the side surface facing the discharge side, and in use, the compensation tank is filled with fluid under pressure defining a corrective torque for each respective bushing assembly.

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