Improved bushing assembly and positive displacement rotary pump including the same

Abstract

An improved bushing assembly (10) for supporting the shaft of the intermeshing rotors of a positive displacement rotary pump in order to avoid jamming is disclosed, said bushing assembly (10) comprising on its side (13) at least one compensation box (15; 16) facing the suction side of the pump and at least one discharge channel (14) connecting said compensation box (15; 16) to the discharge side.

Description

Technical Field

[0001] The present invention relates to a bushing assembly and a corresponding positive displacement rotary pump (preferably a gear pump or a cam pump) comprising the bushing assembly.

[0002] Positive displacement rotary pumps can be usefully applied in various technical fields. In particular, the pump of the present invention is particularly suitable for high-pressure applications requiring a rotational speed that varies over time. Background Art

[0003] As mentioned above, the present invention is usefully applied to the technical field involving gear or cam positive displacement rotary pumps. This type of pump generally comprises two rotors, one of which (called the driving rotor) is connected to a drive shaft and rotates the other rotor (called the driven rotor).

[0004] The two rotors are carried by respective shafts supported by bushing assemblies, which are generally composed of bushing rings and the actual bushings. The bushing assembly is coupled in the inner cavity of the casing or pump body and floats axially therein, allowing the components to be enclosed due to the pressure acting on the relative planes of the assembly itself.

[0005] Currently used backing rings may have dimples on the flat surface facing the rotor or a gasket seat on the flat surface facing the closing flange of the housing. These dimples or seats can be used to facilitate the drainage of the oil lubricating the bushing and—as mentioned above—to compensate for the axial thrust caused by the pressurized fluid, i.e., to keep the surfaces of the rotor and bushing in direct contact, apart from the oil film. Other types of dimples allow the fluid trapped between the gear teeth to recirculate in the drainage area, thereby reducing pulsation and noise.

[0006] Various shapes and functions of the pits 100 are attached Figure 2 and attached Figure 3 As can be seen in the attached Figure 2 Shows a backing ring half element 10a according to the prior art, on the contrary, the attached Figure 3 A one-piece backing ring 10 according to the prior art is shown.

[0007] Hitherto, the design of the backing ring has always been aimed at obtaining its axial balance on the one hand and limiting the misalignment of the ring itself relative to the rotor axis on the other hand, thereby trying to control the center of pressure acting on the plane of the backing ring.

[0008] On the other hand, no intervention has ever been made on the cylindrical face of the ring to avoid friction and wear phenomena due to the distribution of the loads pressing on the rotor and released on the ring itself, which as previously described slides freely inside the bore of the pump casing.

[0009] The construction solutions employed hitherto, although substantially suitable for this purpose, have considerable disadvantages in the case of pumps subjected to heavy applications.

[0010] In fact, in these cases, the surface of the main body bore, into which the force of the liner is released, wears, and accordingly, the liner itself wears. Micro-slips between the two contacting surfaces cause degradation of the component's roughness, which triggers localized heating in areas subject to greater loads. The material then locally plasticizes and becomes less smooth: this causes the liner to seize during transients, with a corresponding deterioration in pump performance.

[0011] The above phenomenon is due to Figures 4 to 6 Explained and analyzed.

[0012] Figure 4 An example of a known type of gear pump is schematically shown. The pump is shown longitudinally sectioned along a plane perpendicular to the plane passing through the two rotor axes, with the suction side S in the lower section and the discharge side D in the upper section. In addition to the wall of the pump housing 3 on the suction side S, the drive rotor 2, the drive shaft 5, and two bushing assemblies 10 are also shown. Due to the overpressure that develops during pump operation, a distributed load F acts on both the bushing assemblies 10 and the rotor 2 from the discharge side D. The figure highlights the slight sliding area Z1 of the bushing ring 10 and the wear area Z2 where seizure occurs.

[0013] Figure 5 and Figure 5a A static analysis performed by the applicant is presented, which explains the above phenomenon. Figure 5 In FIG, the structure consisting of the backing ring 10 and the rotor 2 is modeled using four carriage constraints a, b, c, and d. Figure 5a A graph showing the load F, moment T, and corresponding deformation D of the structure is shown. It can be seen that the maximum restraint reaction force and maximum moment occur at points b and c, respectively, decreasing at points a and d. Therefore, by linearizing the reaction force along the entire backing ring, a trapezoidal distribution Sj is obtained. Consequently, the setup conditions are suboptimal, leading to the aforementioned problems.

[0014] Figure 6 Further analysis of this system is presented in Figure 2, which shows the force lines calculated by the modeling software and generated within a two-dimensional model of the liner-rotor assembly. As can be seen, the maximum stress concentration occurs at the inner edge of the liner, in the wear zone Z2 described above; this concentration decreases rapidly as one moves toward the outer edge.

[0015] Document US 4,087,216 discloses a rotary fluid pump according to the prior art, which uses needle roller bearings and does not use axial floating bushings.

[0016] Document FR 1,343,908 A discloses another rotary fluid pump according to the prior art.

[0017] In view of the above, the technical problem to be solved by the present invention is to conceive a bushing assembly and a corresponding positive displacement rotary pump, which at least partially solve the above-mentioned defects of the prior art and thus have improved performance and service life and lower transient response time. Summary of the Invention

[0018] The solution idea of the invention is to create pressurized boxes which are positioned below the part of the liner assembly that is in direct contact with the pump casing in use, ie at the inner edge of the suction side, in order to reduce the specific pressure in the more stressed areas.

[0019] In view of the idea of this solution, the above technical problem is solved by a volumetric rotary pump, which includes: a shell, which is provided with an inner cavity, which has a discharge port opening on the discharge side and a suction port opening on the opposite suction side; a pair of shafts, which carry a plurality of mutually meshing rotors rotating in the inner cavity at their middle part, and these rotors are used to pump the fluid from the discharge port to the suction port; two bushing assemblies, which are arranged at opposite ends of the rotor for supporting the shaft; the bushing assembly includes: an inner surface, which faces the rotor; an opposite outer surface; and a side surface, which connects the two inner surfaces and the outer surface, and the side surface is connected in the inner cavity; wherein the bushing assembly includes at least one compensation box on its side, which faces the suction side of the inner cavity at a position closer to the inner surface than to the outer surface; and at least one discharge channel, which connects the compensation box to the part of the side facing the discharge side.

[0020] In the case of a positive displacement rotary pump as a whole, the technical problem is also solved by a bushing assembly of the type described above.

[0021] The bushing assembly according to the invention may comprise a one-piece or two-piece bushing ring; in this case, the drain channel and at least one compensation box are made on the bushing ring, which is arranged to carry two inner bushings. On the other hand, it is not excluded that the bushing assembly may be made as a single element or as two juxtaposed elements, without the presence of a bushing ring distinct from the bushings it supports.

[0022] Due to the above structure, the compensation tank is filled with fluid under pressure from the discharge pump during use. The straightening torque on the corresponding bushing assembly is thus limited, which helps to relieve the maximum stress area that is prone to wear in pumps according to the prior art.

[0023] In other words, the structure according to the invention aims to drain the exhaust fluid and bring it into the aforementioned compensation tank in order to promote the support of the corresponding bushing assembly.

[0024] In a manner known per se, the bushing assembly is formed as two sleeve-shaped halves coupled to one another, the halves being made in one piece or separate from one another.

[0025] The side surface thus comprises two cylindrical parts which are connected or juxtaposed in any manner in two coupling regions of the half-group, respectively on the discharge side and on the suction side.

[0026] The discharge channel preferably connects the connection region on the discharge side to at least one compensation tank; it preferably interrupts before reaching the opposite connection region on the suction side.

[0027] Preferably, the discharge channel takes the form of a peripheral groove of limited depth, which is made in at least one, preferably both, cylindrical portions of the side surface.

[0028] In a preferred embodiment, the compensation box takes the form of an axial widening of a circumferential groove defining the discharge channel, for example having a substantially parallelepiped shape.

[0029] Preferably, the compensation tank extends axially relative to the discharge channel towards the inner surface.

[0030] Preferably, the compensating tank and the discharge channel have the same depth.

[0031] In a preferred embodiment, there are at least two compensating tanks for each half of each bushing assembly; these can be connected by the drainage channel itself. For example, the compensating tanks can include at least one intermediate compensating tank that intercepts the extension of the drainage channel and at least one terminal compensating tank at which the drainage channel terminates.

[0032] Features and advantages of the pump according to the invention will become apparent from the following description of an example of embodiment given by way of non-limiting example with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Attachment Figure 1 To the attached Figure 12 The following is shown:

[0034] Figure 1 An exploded perspective view of a conventional positive displacement rotary pump, in particular a gear pump, is shown, without detailing the main aspects of the present invention;

[0035] Figure 2 As described above, a perspective view of the elements of a bushing assembly according to the prior art is shown;

[0036] Figure 3 As described above, a perspective view of another bushing assembly according to the prior art is shown;

[0037] Figure 4 As described above, the first schematic diagram shows the force distribution within the prior art positive displacement rotary pump;

[0038] Figure 5 As described above, a second schematic diagram shows the force distribution within a prior art positive displacement rotary pump;

[0039] Figure 5a As described above, Figure 5 A graph showing the load F, moment T, and corresponding deformation D of the structure formed by the rotor and bushing assembly in the pump shown;

[0040] Figure 6 As mentioned above, Figure 5 The force lines generated within the 2D model of the bushing assembly-rotor group in the pump shown;

[0041] Figure 7 A perspective view of a bushing assembly of a positive displacement rotary pump according to the present invention is shown;

[0042] Figure 8 Shown Figure 7 The bushing assembly is shown in three-dimensional diagrams from different angles;

[0043] Figure 9 Still shows Figure 7 A perspective view of the , which highlights areas of greater load concentration;

[0044] Figure 10 Shown Figure 7 a side view of the bushing assembly;

[0045] Figure 11 A schematic diagram showing the force distribution within a positive displacement rotary pump according to the present invention;

[0046] Figure 11a Shown by Figure 11 a graph of load F, moment T, and corresponding deformation D of the structure formed by the rotor and bushing assembly in the pump shown; and

[0047] Figure 12 Indicates Figure 11 The force lines generated within a 2D model of the bushing assembly-rotor group in the pump shown. DETAILED DESCRIPTION

[0048] Reference Figure 1 , reference numeral 1 schematically and generally designates a positive displacement rotary pump with gears made according to the present invention.

[0049] The positive displacement rotary pump 1 comprises a pair of rotors 2, specifically gears, supported by respective shafts 5 and enclosed in a housing 3. A first driving gear is connected to a drive shaft having a protruding end relative to the housing 3, and a second driven gear is rotated by the driving gear. In a preferred embodiment of the present invention, the two rotors 2 are gears having helical teeth.

[0050] The housing 3 is closed at the front and rear by two covers or flanges, not shown, of a known type. The housing has a fluid intake opening (not shown in the drawings) on one side and a fluid discharge opening 4 on the other side. Furthermore, the housing defines an inner cavity into which the rotor 2 and the bushing assembly 10 are introduced, the inner cavity having a suction side S at the intake opening and an opposite discharge side at the discharge opening D.

[0051] Inside the housing 3, the shaft 5 of the rotor 2 is supported at both ends by two bushing assemblies 10. Figure 1 Each bushing assembly 10 can be made in one piece, as shown, or in two separate, juxtaposed halves 10a, similar to Figure 2 Preferably, each bushing assembly 10 comprises a bushing ring and two bushings 19 mounted thereon.

[0052] It should be noted that Figure 1 The unique features of the bushing assembly 10 according to the present invention are not described and will be discussed later. Figures 7 to 10 Visible in.

[0053] As can be seen, 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 housing 3. These two surfaces are connected by a side surface 13 consisting of two cylindrical faces 13a, which are 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.

[0054] Two drainage channels 14 are provided on the bushing assembly 10, which are formed as circumferential grooves on the respective cylindrical surfaces 13a. The drainage channels 14 extend from a connection area 17 on the discharge side D until they reach two compensation boxes 15, 16 on the suction side S. The compensation boxes 15, 16 are advantageously arranged in the area of maximum stress H of the bushing assembly 10, which is located on the suction side S in an area close to the inner surface 11.

[0055] As in Figure 10 As can be clearly seen in FIG, an intermediate compensation tank 15 is provided which intercepts the discharge channel 14 and a subsequent end compensation tank 16 at which the discharge channel 14 is interrupted.

[0056] The compensation boxes 15 , 16 may be of different shapes; in the preferred embodiment illustrated here, the compensation boxes are substantially parallelepipeds having a depth substantially equal to the depth of the discharge channel 14 and extending towards the inner surface 11 of the liner assembly 10 .

[0057] Starting from the preferred configuration described, the position and configuration of the discharge channel 14 and the compensation tanks 15, 16 can be determined with the aid of the following measurements:

[0058] - axial width of the discharge channel 14;

[0059] - the axial width of each compensation box 15, 16 (preferably but not necessarily the same);

[0060] - the distance between the drain channel 14 and the inner surface 11 of the bushing assembly 10;

[0061] - the circumferential length of each compensation box 15 , 16 (preferably, but not necessarily, the end box 16 has a length less than the intermediate box 15 );

[0062] - a circumferential distance between two subsequent compensating boxes 15 , 16 (preferably, but not necessarily, approximately equal to the circumferential length of the intermediate box 15 );

[0063] - The position of the box relative to the load-bearing central axis.

[0064] The above metrics can be determined by numerical modeling to obtain maximum load redistribution, ie minimum surface pressure in the above mentioned region of maximum stress H, depending on the size and intended use of the pump.

[0065] The above-described configuration of the bushing assembly 10 facilitates the discharge of pressurized fluid from the compensation tanks 15, 16 during use of the pump. Thus, a realignment force Fr is obtained in the maximum stress area of the bushing assembly 10, which generates a corresponding realignment moment Tr, thereby helping to realign the bushing assembly 10 with the pump shaft and rebalance the loads acting thereon, thereby eliminating or at least reducing localized wear and the resulting transient seizure during operation.

[0066] Figure 11 Introduced by Figure 5 The compensation boxes 15 and 16 in the figure determine the realignment force Fr and the realignment torque Tr. Figure 11a Graphs are shown indicating the load F, moment T and corresponding deformation D of the structure. There is a significant redistribution of stress along the bushing assembly 10 and a reduction in the restraint reaction forces at the edges and inner surface 11 .

[0067] Figure 12 Figure 2 shows the force lines calculated by the modeling software, which are generated within the 2D model of the liner-rotor assembly. Figure 6 By comparing the prior art model in FIG. 1 with FIG. 2 , it can be noted that by widening the surface portion that best engages the support bushing assembly 10 , the forces can be better distributed, although the average pressure on the remaining surface portion remains unchanged.

[0068] Due to the above reasons, through further calculation, the maximum force can be reduced by about 40%.

[0069] Obviously, those skilled in the art may make various changes and modifications to the above invention in order to meet possible and specific needs, and all these changes and modifications are included in the protection scope of the invention defined by the appended claims.

Claims

1. A bushing assembly (10) for a positive displacement rotary pump (1), the bushing assembly (10) being arranged to be inserted into an inner cavity (30) of the positive displacement rotary pump (1) and axially float in the inner cavity (30), and supporting the ends of a pair of shafts (5) carrying a rotor (2) of the positive displacement rotary pump (1); the bushing assembly (10) comprising: an inner surface (11), the inner surface (11) facing the rotor (2) when in use; an opposite outer surface (12); wherein, when in use, the bushing assembly (10) slides freely axially within the inner cavity (30) due to fluid pressure acting on the inner surface (11) and the outer surface (12); the bushing assembly (10) further comprising a side surface (13) connecting the two inner surfaces (11) and the outer surface (12), the side surface (13) being arranged to be coupled within the inner cavity (30) and having a first portion facing the suction side (S) and a second portion facing the discharge side (D); At least one compensation box (15; 16), at least one of said compensation boxes being located on said first portion of said side surface (13) and being closer to said inner surface (11) than to said outer surface (12); and at least one drainage channel (14), at least one of said drainage channels (14) connecting said compensation box (15; 16) to said second portion of said side surface (13); wherein at least one of said compensation boxes (15; 16) is laterally closed on both sides, i.e., at least one of said compensation boxes is not open on both said inner surface (11) and said outer surface (12) of said bushing assembly (10).

2. The bushing assembly (10) according to claim 1, wherein The bushing assembly (10) is formed into two sleeve-shaped half sets (10a) coupled to each other, and the half sets (10a) are made in one piece or separated from each other.

3. The bushing assembly (10) according to claim 2, wherein: The side surface (13) comprises two cylindrical portions (13a) which are connected or juxtaposed in two coupling areas (17; 18) of the half group (10a) on the discharge side (D) and the suction side (S), respectively.

4. The bushing assembly (10) according to claim 3, wherein: The discharge channel (14) connects the connection area (17) on the discharge side (D) to at least one compensation tank (15; 16) during use; and wherein the discharge channel (14) does not reach the connection area (18) on the suction side (S).

5. The bushing assembly (10) according to claim 3, wherein The discharge passage (14) is in the form of a peripheral groove formed on at least one of the cylindrical portions (13a) of the side surface (13).

6. The bushing assembly (10) according to claim 5, wherein At least one of the compensation boxes (15; 16) takes the form of an axial widening of a circumferential groove defining the discharge channel (14).

7. The bushing assembly (10) according to claim 6, wherein: At least one of the compensation boxes (15; 16) extends axially relative to the discharge channel (14) towards the inner surface (11).

8. The bushing assembly (10) according to claim 6 or 7, wherein: At least one of the compensating boxes (15; 16) has a substantially parallelepiped configuration.

9. The bushing assembly (10) according to claim 6 or 7, wherein: The compensation tank (15; 16) and the discharge channel (14) have the same depth.

10. The bushing assembly (10) according to claim 6 or 7, wherein: Each half group (10a) has at least two of the compensation boxes (15; 16).

11. The bushing assembly (10) according to claim 10, wherein: The two compensation tanks (15; 16) of each half group (10a) are connected via the same discharge channel (14).

12. The bushing assembly (10) according to claim 11, wherein The compensation tanks (15; 16) are at least one intermediate compensation tank (15) that intercepts the extension of the discharge channel (14) and at least one terminal compensation tank (16) where the discharge channel (14) ends.

13. The bushing assembly (10) according to any one of claims 1 to 7, comprising a bushing ring, which is integral or two-piece, capable of being associated with two inner bushings (19), the discharge channel (14) and at least one of the compensation boxes (15; 16) being made on the bushing ring.

14. A positive displacement rotary pump (1), comprising: A housing (3) provided with an inner cavity (30) having a discharge port (4) opening on a discharge side (D) and a suction port opening on an opposite suction side (S); a pair of shafts (5) carrying a plurality of mutually meshing rotors (2) rotating in the inner cavity (30) at their intermediate portions, the rotors (2) being used to pump a fluid from the discharge port (4) to the suction port; two bushing assemblies (10) according to any one of the preceding claims, the bushing assemblies (10) being arranged at opposite ends of the rotors (2) for supporting the shafts (5), wherein The inner surface (11) faces the rotor (2), and the side surface (13) is connected within the inner cavity (30); the compensation tank (15; 16), which faces the suction side (S) of the inner cavity (30); and at least one discharge channel (14), which connects the compensation tank (15; 16) to the portion of the side surface (13) facing the discharge side (D), wherein, in use, the compensation tank (15; 16) is filled with a fluid under pressure that defines a straightening torque on the corresponding bushing assembly (10).

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