Screw pump with connection assembly

Abstract

Connection assembly (11) for screw pump, having an unusually limited overall axial dimension, comprising: a drive screw; a first half-coupling (13) arranged to be keyed on a drive shaft; a second half-coupling (14) integral with said drive screw and arranged to couple with said first half-coupling (13); and an elastomeric insert (18) arranged to be interposed between said first half-coupling (13) and said second half-coupling (14) in the coupled configuration.

Description

Field of application

[0001] The present invention relates to a connection assembly for a volumetric screw pump comprising a pump drive screw and a respective joint for coupling to the drive shaft, and a screw pump comprising said connection assembly.

[0002] The invention therefore finds application in the various industrial sectors in which screw pumps, and in particular two- and three-screw pumps, are traditionally used.Prior art

[0003] It is known in the industrial art that volumetric screw pumps are used in order to move fluids or solids in a desired direction along the axis of the screws. In its simplest form, the pump is provided with a single screw and comprises a rotor represented by a metallic helical screw, which rotates inside a casing. The continuous rotation of the rotor makes the fluid advance in a series of cavities along the axis of the pump. Double-screw or three-screw rotary pumps are also used: in the latter case, one or two driven screws rotate in synchrony with a drive screw, contributing to the displacement of the fluid along the axis of the pump.

[0004] Screw pumps are therefore operating machines in which the fluid is captured by the volume of the screws and transported towards the opposite end with the aid of mechanical energy coming from a motor, typically an electric motor, which drives the rotation of the drive screw.

[0005] Rigid or semi-rigid type connections can be used to connect the pump drive screw to the shaft of the electric motor, wherein one end of the pump drive screw is directly connected, without the interposition of any elastic element, to the shaft of an electric motor. In this case, the end of the drive screw has a female coupling, into which the shaft end of the electric motor is inserted. The rotation movement is thus transmitted directly from the electric motor to the end of the pump drive screw.

[0006] This rigid type connection has the advantage of giving compactness to the group comprising volumetric pump and electric motor, but, as a drawback, the performance of the pump over time and its service life are significantly reduced.

[0007] This is particularly the case for pumps having more than one rotating screw, as the volumetric machine needs the drive screw to be free of outer radial forces to allow it to adapt during operation. In other words, the screws must not be forced to rotate to a given position, but must have the possibility to position themselves where the interaction between the driven screws and the drive screw and the interaction between the drive screw and the surrounding stator body requires the least energy. The presence of the ball bearings both on the shaft of the electric motor and on the shaft of the drive screw also creates an additional constraint, hindering the drive screw from reaching its optimal position: without reaching this position, the pump screws and the stator body wear out prematurely, leading to a deterioration in the efficiency of the machine, and increasing the mechanical and fluodynamic noise of the pump.

[0008] In order to avoid the above, in the case of rigid connections, the coupling is sized on the drive screw so as to allow a considerable clearance in the housing of the shaft of the electric motor. This technological expedient allows the drive and driven screws of the pump to be positioned in the lowest energy position, but introduces premature wear on the mechanical pump-electric motor connection, which reduces the range of application thereof by lowering the limits of transmissible mechanical torque, and therefore of operating pressure. In addition, the maximum attainable rotation speed is also drastically reduced with the adoption of the increased clearance on the coupling.

[0009] To overcome the drawbacks described above related to a rigid type connection, elastic type connections have been developed between the screw pump and the electric motor, which are based on the interposition of an elastic coupling between the shafts of the two machines.

[0010] An elastic coupling is a device capable of making the ends of two consecutive shafts integral with each other, so that the one can transmit a rotation movement to the other, provided with a flexible element interposed between the hubs. The flexible element isolates from vibrations, axial and radial loads and dampens torque peaks at start-up.

[0011] For the connection between the shaft of a rotary pump and the shaft of an electric motor, a pin coupling or three-piece coupling is preferably used: it is an elastic coupling consisting of two hubs or half-couplings, each mounted respectively on one end of each shaft to be coupled, and of an insert made of elastomer. The motion between the two shafts is transmitted because these hubs or half -couplings are provided with pins that interlock with each other, with the interposition of the insert.

[0012] A schematic view of this type of elastic connection is proposed in Figure 1 attached to this patent application. It shows in sequence the mechanical connecting elements between a screw pump 1 and an electric motor 2, whose function is to drive the continuous rotation of the drive screw 3 of the volumetric pump 1.

[0013] The elastic coupling 6 which couples the drive screw 3 to the drive shaft 5 of the electric motor 2 is shown in Figure 1 broken down into its three constituent components: a first half-joint 7, an elastomeric insert 8, a second half-coupling 9. The first half-coupling 7 is arranged for coupling by means of a key with the end of the shaft 5 of the electric motor 2, while the second half-coupling 9 is arranged for coupling with the shaft, again by means of a key 4, to one end of the dragging screw 3 which protrudes from the frontal flange of the screw pump 1.

[0014] The elastomeric insert 8, visible in detail in the accompanying Figures 5a and 5b, is a component manufactured by polyurethane cast and has a star structure with radial separators projecting outwards.

[0015] The connecting ring 8b allows the radial separators 8a to be held in place during operation at high rotation speeds. During the rotation of the elastic coupling, centrifugal forces are generated which push the elastic teeth 8a outwards, lowering the maximum attainable speed: the inner connection ring 8b has the function of holding the elastic teeth 8a in place by increasing the permitted range of rotation. The inner connecting ring 8b is therefore essential for a proper operation of the elastic coupling according to the prior art.

[0016] It should be noted that the use of the elastic connection, despite being the preferred embodiment in two- and three-screw pumps due to the advantages identified above, represents on the other hand a significant increase in the axial overall dimension of the device, which provides for an interconnection section with minimum dimensions determined by the length of the two keys 4 in succession and by the interposed elastomeric insert 8.

[0017] In embodiments of this type, it is also provided for the use, as a distinct and additional component with respect to a frontal flange of the pump, of a housing casing 10 of the elastic coupling 6, which serves precisely to cover the entire interconnection section and has an additional construction element to be applied at the time of coupling with the electric motor.

[0018] Devices according to the prior art are shown in documents US 2012 / 039734 A1 and DE 43 08 755 A1.

[0019] In the light of the state of the art described above, the Applicant has identified the need to make available to the rotary pump industry a mechanical connection between pump and electric motor, which retains all the advantages of the elastic type connection, while at the same time minimising the overall dimension of the interconnection elements, so as to ensure a high degree of compactness between the two machines, comparable to that of the rigid or semi-rigid type connections described above.Summary of the invention

[0020] The technical problem identified above is solved by a connection assembly for a screw pump, comprising: a drive screw or rotor; a first half-coupling arranged to be keyed on a drive shaft; a second half-coupling integral to said drive screw and arranged to be coupled to said first half-coupling; and an elastomeric insert arranged to be interposed between said first half-coupling and said second half-coupling in the coupled configuration.

[0021] In contrast to what happens in the prior art, therefore, the second half-coupling is made integrally to the drive screw, in a production phase of the pump, and not interconnected to it by reversible coupling when connecting the screw pump to the electric motor. In other words, the second half-coupling is made as one piece or otherwise permanently made over the rotor. This results in a monolithic rotor / half -coupling piece, which is introduced already mounted into the pump casing. In the prior art, on the contrary, the front flange is closed, leaving the traditional frontal coupling of the rotor overhanging, and the half-coupling is only cold shrink-fit at a later stage.

[0022] The realisation of the second half-coupling with the driven screw as one piece can be achieved, for example, by direct milling of the attachment end of the drive screw.

[0023] Alternatively, as mentioned above, the second half-coupling can be made separately and coupled to the rotor in a substantially irreversible manner, e.g. by heat shrink-fitting, gluing, welding or other suitable method.

[0024] The Applicant has found that, thanks to the solution described above, it is possible to achieve a type of compact mechanical interconnection and at the same time with elasticity characteristics, modifying one end of the rotor of the screw pump in an original way and also being able to employ an elastomeric insert with innovative configuration.

[0025] The elastomeric insert has an annular shape and comprise a plurality of radial separators made of elastomeric material spaced by radial cavities, said first half-coupling and said second half-coupling presenting respectively a first frontal toothing and a second frontal toothing, wherein in the coupled configuration the teeth of the first frontal toothing and the teeth of the second frontal toothing are facing each other and alternatively accommodated in the radial cavities of the elastomeric insert.

[0026] Innovatively, the elastomeric insert may comprise an outer ring that interconnects said radial separators between them, the inner ends of which are free and face a central cavity. In this way, the central cavity can house the end of the drive shaft, which has standardised axial dimensions by having to carry the key: an axial overlap of the constituent elements of the connection is therefore achieved that allows to effectively reduce the overall dimensions thereof.

[0027] In other words, the particular outer ring structure of connection of the elastomeric insert allows an end portion of the shaft of the electric motor to overlap (upon completion of the connection) the frontal toothing of the drive screw, without parts of the elastomeric insert standing in the way of this overlap, as would happen if elastic elements with conventional geometric configuration were used.

[0028] Preferably, said radial separators are tapered in the direction of the outer ring, so as to achieve a retaining action on the teeth of the first and second frontal toothing interposed between the successive radial separators. Thanks to this expedient, a possible extraction of the elastomeric insert due to the centrifugal forces at high rotation speeds of the drive screw is avoided.

[0029] Preferably, the teeth of the first and second frontal toothing are frontal pins with substantially isosceles trapezium cross-section, wherein the sides of said isosceles trapezium are concave to adapt to the tapering of the radial separators.

[0030] The first half-coupling, as previously mentioned, may have a central through hole to allow the complete crossing of the drive shaft, said second half-coupling and said elastomeric insert defining, in the mounted configuration, a central cavity in continuation of said through hole for housing the free end of said drive shaft.

[0031] Said central cavity can in particular be defined by the inner ends of the radial separators and by the teeth of the first and second frontal toothing in the coupled configuration.

[0032] It also preferably has a diameter greater than twice the radial overall dimension of the drive shaft including the engaged key, so as to avoid any interference or friction among the elements.

[0033] The technical problem identified above is also solved by a screw pump comprising a containment case, on which a suction port and a delivery port open in longitudinal succession, and a connection assembly with the characteristics identified above, wherein the drive screw turns within the containment case.

[0034] The containment case may comprise, in a per se known manner, a main casing body to which at least one front flange is directly associated; in the invention, said front flange may, however, be arranged to be joined directly to an electric motor comprising the drive shaft. Thus, the first half-flange, the elastomeric insert and at least part of the second half-flange are completely housed within the front flange, without the need for an additional housing coupling as in the prior art.

[0035] In a known manner, the containment case may further comprise a rear flange that closes the main casing body at the opposing end with respect to the front flange.

[0036] Preferably, the front flange has a bell shape and joins an attachment section of said containment case to an attachment section of said electric motor.

[0037] The second half-coupling comprises a hub from which the second frontal toothing develops; this hub may be totally or predominantly inserted into a through opening of said front flange, e.g. rotatably mounted within said through opening with the interposition of bearings. In this case, the pump mounted complete with front flange has only a portion - possibly represented by the toothing alone - protruding into the chamber that houses the rest of the elastic connection. A further limitation of the overall axial dimensions of the device is achieved.

[0038] Finally, it should be noted that the screw pump is preferably a two- or three-screw pump and comprises one or more driven screws dragged into rotation by the drive screw. In accordance with a preferred embodiment of the present invention, the volumetric pump that is connected to the electric motor is a three-screw pump, comprising two side screws and a central screw. Pumps of this type are primarily suited for moving viscous fluids, particularly with viscosity between 4 est and 5000 cst.

[0039] The method of production of the screw pump according to the invention provides a step of realizing the monolithic drive screw / second half-coupling assembly, by machining in one piece or irreversible coupling of the drive screw to the rotor, and a subsequent step of inserting the assembly into the main casing body. A subsequent step comprises closing the casing by mounting the front flange, leaving at least one end of the second half-coupling protruding therefrom.

[0040] The advantages and distinctive characteristics of the connection assembly and of the screw pump according to the present invention will be made clearer by the description of an example of its embodiment, made below with reference to the attached drawings given by way of nonlimiting example.Brief description of the drawings

[0041] Figure 1 represents a schematic perspective view of the elements that make up an elastic type connection according to the prior art between an electric motor and a screw pump; Figure 2 represents a schematic perspective view, according to a rear observation point, of a screw pump with connection assembly according to the present invention, wherein the end portion of the pump drive screw is highlighted; Figure 3 represents a schematic perspective view, according to a rear observation point, of a screw pump with connection assembly according to the present invention, wherein the elastic coupling and the end portion of the shaft of the electric motor are highlighted; Figure 4 represents a side view, partially sectioned according to the vertical plane passing through the axis of rotation of the drive screw, of a screw pump with connection assembly according to the present invention, wherein the electric motor, the elastic coupling and the screw pump are mounted in the operational configuration; Figure 5a represents a front view of an elastomeric insert used in the connection assembly according to prior art; Figure 5b represents a perspective view of the elastomeric insert used in the connection assembly according to prior art; Figure 5c represents a front view of an elastomeric insert used in the connection assembly according to the present invention; Figure 5d represents a perspective view of the elastomeric insert used in the connection assembly according to the present invention; Figure 6 represents a cross-sectional view of the connection assembly according to the present invention in the operational configuration, at the elastomeric insert. Detailed description of an embodiment

[0042] With reference to the aforesaid Figures 2 -4, a screw pump according to the present invention, coupled by means of a connection assembly 50 to an electric motor 12 known per se, is globally indicated with 11.

[0043] Said screw pump 11 comprises in a known manner a containment case 30, on which a suction port 31 and a delivery port 32 open in longitudinal succession, and within which at least one drive screw 15 turns. The containment case 30 comprises a main casing body 30a, a rear flange 30b, and a front flange 30c.

[0044] Depending on the type of pump, there may be provided one or two driven screws, not visible in the accompanying figures, which mesh with the drive screw 15.

[0045] The assembly for the connection 50 to the electric motor 12 comprises an elastic coupling, comprising in turn a first half-coupling 13, a second half-coupling 14, and an elastomeric insert 18 interposed between the two half-couplings 13, 14. According to the teachings of the present invention, the second half-coupling is substantially integrated into an end portion of the central screw 15 of the pump 11.

[0046] The first half-coupling 13 and the second half-coupling 14 respectively comprise a first hub 26, from which a first frontal toothing 16 develops; and a second hub 29, from which a second frontal toothing 19 develops.

[0047] The first hub 26 is embodied, in a preferred embodiment, in a cylindrical sleeve provided with a central through hole arranged for the insertion of a drive shaft 23 of the electric motor 12. On the inner surface of the central through hole there is provided a square-sectioned groove for housing a standardized tab 24 provided on the drive shaft 23 for coupling with the first half-coupling 13. It can be seen that, in the mounted configuration, the drive shaft 23 passes completely through the first hub, partially protruding therefrom; the end portion of the tab 24 also protrudes from the hub, so that only a prevailing portion of this tab achieves the engagement between the two components.

[0048] The second hub 29 is also a cylindrical element, preferably solid, which, as mentioned above, is integral with the end of the drive screw 15, providing an increased diameter than the latter. In a preferred embodiment illustrated in the accompanying figures, the second hub 29 is made as one piece with the rest of the drive screw 15; alternatively, it can be made over the drive screw with irreversible coupling, e.g. by heat shrink-fitting, gluing, welding.

[0049] The first and second frontal toothing 16, 19, mirroring each other, are pin-type toohtings, i.e. comprising a plurality of teeth with frontal overhang, projecting in the direction of the axis of rotation of the central screw 15, intended to interpenetrate, with the interposition of radial separators 20 defined by the elastomeric insert 18, to achieve a rotating integral coupling.

[0050] In the preferred embodiment illustrated in the accompanying figures, both frontal toothings 16, 19 comprise four teeth: obviously, a different number of teeth can be used depending on the design choices.

[0051] The teeth of the two frontal toothings 16, 19 are arranged along an outer circular crown of the opposing frontal faces of the two hubs 19, 29, and there is therefore, as will be explained below, a free cylindrical volume between them.

[0052] The teeth of the frontal toothings 16, 19 present an essentially isosceles trapezoid cross-sectional shape, wherein the two bases are shaped according to arcs of circumference to conform to the circular pattern of the hub 26, 29 and the sides have a concavity whose function is explained below.

[0053] As previously mentioned, the elastomeric insert 18 is inserted between the two frontal toothings 16, 19 and which innovatively has an outer ring 21 from which the plurality of radial separators 20 branch inwards. Naturally, the number of radial separators is double than that of the teeth of the individual frontal toothings 16, 19, which are inserted into U-shaped radial cavities 17 defined between adjacent radial separators 20.

[0054] Advantageously, the side walls of the individual radial separators 20 have a curvature, tapering towards the base of attachment to the outer ring 21, which matches the concavity of the teeth discussed above. The aforesaid lobed shape of the radial separators 20 defines a containment shape for the teeth inserted in the radial cavities 17, which contributes to holding the elastomeric insert 18 in place even when subjected to high rotation speeds and to the resulting centrifugal forces.

[0055] It can be noted that the elastomeric insert 18 is preferably made as one single piece, and can be made by known techniques using any suitable elastomeric material: for example, it can be made of polyurethane cast like the inserts of the prior art.

[0056] In an operational configuration, the two frontal toothings 16, 19 then cooperate with each other with the interposition of the elastomeric insert 18. The outer ring 21 surrounds the toothings 16, 19 in this case, while the radial separators 20 are introduced between each tooth. This structure defines a cylindrical central cavity 25, delimited by the inner faces of the teeth and of the radial separators 20. The end portion of the drive shaft 23, as well as the key 24 supported by it are introduced inside this central cavity. In order to avoid interferences and frictions, said central cavity 25 therefore has a diameter θ c greater than twice the overall radial dimension r a of the drive shaft 23 including the engaged key 24, as can be seen in Figure 6.

[0057] As previously described, the containment case 30 of the screw pump 11 comprises a main casing body 30a, a rear flange 30b and a front flange 30c.

[0058] While the main casing 30a and the rear flange 30b have a conventional structure, in the present invention the front flange 30c is suitably shaped to couple with the electric motor 12, housing within it all the components that make up the elastic coupling between drive shaft 23 and drive screw.

[0059] For this reason, the front flange 30c has a bell-shaped structure that joins a base 22, screwed to the main casing 30a, up to a head plate arranged to be bolted to the electric motor 12.

[0060] Inside the base 22 there is provided a through opening 28, which is crossed by the drive screw 15. In particular, the second hub 29 is rotatably constrained within the through opening 28 by the interposition of ball bearings 27. Consequently, the only portion of the second half-coupling 14 that develops with overhang from the base 22, i.e. from the bottom surface of the bell-shaped body of the front flange 30c, is constituted by the second frontal toothing 19. In this way, the end of the drive shaft 23, with a predetermined dimension due to the standardisation of the tab 24, can extend up to close the aforesaid bottom of the front flange 30c, achieving an axial compaction that is comparable to that of the pumps with rigid coupling of the prior art.

[0061] A first advantage of the screw pump according to the present invention is that it achieves the transport of energy from the source (electric motor) to the user (screw pump) in an elastic manner, while maintaining a high degree of compactness of the assembly constituted by pump and electric motor.

[0062] A further advantage of the connection assembly is that it allows the elimination of the housing case made in the prior art as a mechanical element distinct from the front flange: the result is a space-saving that favours the compactness of the overall structure.

[0063] A further advantage of the connection assembly in accordance with the present invention derives from the fact that it provides for the presence of an elastomeric insert with circular shape, capable of adapting mechanically so as to surround the toothing with pins projecting from the end of the shaft of the screw pump: therefore, all the advantages of an elastic type connection between volumetric machine and electric motor are maintained. The presence of such an elastomeric insert avoids the direct metallic contact among the rotating components, and therefore isolates from vibrations, axial and radial loads and dampens torque peaks at start-up.

[0064] The connection assembly and the screw pump described above in a preferred embodiment thereof are susceptible to variations and modifications, all within the reach of the person skilled in the art and, as such, falling within the scope of protection of the present invention defined by the following claims.

Examples

Embodiment Construction

[0042]With reference to the aforesaid Figures 2 -4, a screw pump according to the present invention, coupled by means of a connection assembly 50 to an electric motor 12 known per se, is globally indicated with 11.

[0043]Said screw pump 11 comprises in a known manner a containment case 30, on which a suction port 31 and a delivery port 32 open in longitudinal succession, and within which at least one drive screw 15 turns. The containment case 30 comprises a main casing body 30a, a rear flange 30b, and a front flange 30c.

[0044]Depending on the type of pump, there may be provided one or two driven screws, not visible in the accompanying figures, which mesh with the drive screw 15.

[0045]The assembly for the connection 50 to the electric motor 12 comprises an elastic coupling, comprising in turn a first half-coupling 13, a second half-coupling 14, and an elastomeric insert 18 interposed between the two half-couplings 13, 14. According to the teachings of the present invention, the second...

Field of application

[0001] The present invention relates to a connection assembly for a volumetric screw pump comprising a pump drive screw and a respective joint for coupling to the drive shaft, and a screw pump comprising said connection assembly.

[0002] The invention therefore finds application in the various industrial sectors in which screw pumps, and in particular two- and three-screw pumps, are traditionally used.Prior art

[0003] It is known in the industrial art that volumetric screw pumps are used in order to move fluids or solids in a desired direction along the axis of the screws. In its simplest form, the pump is provided with a single screw and comprises a rotor represented by a metallic helical screw, which rotates inside a casing. The continuous rotation of the rotor makes the fluid advance in a series of cavities along the axis of the pump. Double-screw or three-screw rotary pumps are also used: in the latter case, one or two driven screws rotate in synchrony with a drive screw, contributing to the displacement of the fluid along the axis of the pump.

[0004] Screw pumps are therefore operating machines in which the fluid is captured by the volume of the screws and transported towards the opposite end with the aid of mechanical energy coming from a motor, typically an electric motor, which drives the rotation of the drive screw.

[0005] Rigid or semi-rigid type connections can be used to connect the pump drive screw to the shaft of the electric motor, wherein one end of the pump drive screw is directly connected, without the interposition of any elastic element, to the shaft of an electric motor. In this case, the end of the drive screw has a female coupling, into which the shaft end of the electric motor is inserted. The rotation movement is thus transmitted directly from the electric motor to the end of the pump drive screw.

[0006] This rigid type connection has the advantage of giving compactness to the group comprising volumetric pump and electric motor, but, as a drawback, the performance of the pump over time and its service life are significantly reduced.

[0007] This is particularly the case for pumps having more than one rotating screw, as the volumetric machine needs the drive screw to be free of outer radial forces to allow it to adapt during operation. In other words, the screws must not be forced to rotate to a given position, but must have the possibility to position themselves where the interaction between the driven screws and the drive screw and the interaction between the drive screw and the surrounding stator body requires the least energy. The presence of the ball bearings both on the shaft of the electric motor and on the shaft of the drive screw also creates an additional constraint, hindering the drive screw from reaching its optimal position: without reaching this position, the pump screws and the stator body wear out prematurely, leading to a deterioration in the efficiency of the machine, and increasing the mechanical and fluodynamic noise of the pump.

[0008] In order to avoid the above, in the case of rigid connections, the coupling is sized on the drive screw so as to allow a considerable clearance in the housing of the shaft of the electric motor. This technological expedient allows the drive and driven screws of the pump to be positioned in the lowest energy position, but introduces premature wear on the mechanical pump-electric motor connection, which reduces the range of application thereof by lowering the limits of transmissible mechanical torque, and therefore of operating pressure. In addition, the maximum attainable rotation speed is also drastically reduced with the adoption of the increased clearance on the coupling.

[0009] To overcome the drawbacks described above related to a rigid type connection, elastic type connections have been developed between the screw pump and the electric motor, which are based on the interposition of an elastic coupling between the shafts of the two machines.

[0010] An elastic coupling is a device capable of making the ends of two consecutive shafts integral with each other, so that the one can transmit a rotation movement to the other, provided with a flexible element interposed between the hubs. The flexible element isolates from vibrations, axial and radial loads and dampens torque peaks at start-up.

[0011] For the connection between the shaft of a rotary pump and the shaft of an electric motor, a pin coupling or three-piece coupling is preferably used: it is an elastic coupling consisting of two hubs or half-couplings, each mounted respectively on one end of each shaft to be coupled, and of an insert made of elastomer. The motion between the two shafts is transmitted because these hubs or half -couplings are provided with pins that interlock with each other, with the interposition of the insert.

[0012] A schematic view of this type of elastic connection is proposed in Figure 1 attached to this patent application. It shows in sequence the mechanical connecting elements between a screw pump 1 and an electric motor 2, whose function is to drive the continuous rotation of the drive screw 3 of the volumetric pump 1.

[0013] The elastic coupling 6 which couples the drive screw 3 to the drive shaft 5 of the electric motor 2 is shown in Figure 1 broken down into its three constituent components: a first half-joint 7, an elastomeric insert 8, a second half-coupling 9. The first half-coupling 7 is arranged for coupling by means of a key with the end of the shaft 5 of the electric motor 2, while the second half-coupling 9 is arranged for coupling with the shaft, again by means of a key 4, to one end of the dragging screw 3 which protrudes from the frontal flange of the screw pump 1.

[0014] The elastomeric insert 8, visible in detail in the accompanying Figures 5a and 5b, is a component manufactured by polyurethane cast and has a star structure with radial separators projecting outwards.

[0015] The connecting ring 8b allows the radial separators 8a to be held in place during operation at high rotation speeds. During the rotation of the elastic coupling, centrifugal forces are generated which push the elastic teeth 8a outwards, lowering the maximum attainable speed: the inner connection ring 8b has the function of holding the elastic teeth 8a in place by increasing the permitted range of rotation. The inner connecting ring 8b is therefore essential for a proper operation of the elastic coupling according to the prior art.

[0016] It should be noted that the use of the elastic connection, despite being the preferred embodiment in two- and three-screw pumps due to the advantages identified above, represents on the other hand a significant increase in the axial overall dimension of the device, which provides for an interconnection section with minimum dimensions determined by the length of the two keys 4 in succession and by the interposed elastomeric insert 8.

[0017] In embodiments of this type, it is also provided for the use, as a distinct and additional component with respect to a frontal flange of the pump, of a housing casing 10 of the elastic coupling 6, which serves precisely to cover the entire interconnection section and has an additional construction element to be applied at the time of coupling with the electric motor.

[0018] Devices according to the prior art are shown in documents US 2012 / 039734 A1 and DE 43 08 755 A1.

[0019] In the light of the state of the art described above, the Applicant has identified the need to make available to the rotary pump industry a mechanical connection between pump and electric motor, which retains all the advantages of the elastic type connection, while at the same time minimising the overall dimension of the interconnection elements, so as to ensure a high degree of compactness between the two machines, comparable to that of the rigid or semi-rigid type connections described above.Summary of the invention

[0020] The technical problem identified above is solved by a connection assembly for a screw pump, comprising: a drive screw or rotor; a first half-coupling arranged to be keyed on a drive shaft; a second half-coupling integral to said drive screw and arranged to be coupled to said first half-coupling; and an elastomeric insert arranged to be interposed between said first half-coupling and said second half-coupling in the coupled configuration.

[0021] In contrast to what happens in the prior art, therefore, the second half-coupling is made integrally to the drive screw, in a production phase of the pump, and not interconnected to it by reversible coupling when connecting the screw pump to the electric motor. In other words, the second half-coupling is made as one piece or otherwise permanently made over the rotor. This results in a monolithic rotor / half -coupling piece, which is introduced already mounted into the pump casing. In the prior art, on the contrary, the front flange is closed, leaving the traditional frontal coupling of the rotor overhanging, and the half-coupling is only cold shrink-fit at a later stage.

[0022] The realisation of the second half-coupling with the driven screw as one piece can be achieved, for example, by direct milling of the attachment end of the drive screw.

[0023] Alternatively, as mentioned above, the second half-coupling can be made separately and coupled to the rotor in a substantially irreversible manner, e.g. by heat shrink-fitting, gluing, welding or other suitable method.

[0024] The Applicant has found that, thanks to the solution described above, it is possible to achieve a type of compact mechanical interconnection and at the same time with elasticity characteristics, modifying one end of the rotor of the screw pump in an original way and also being able to employ an elastomeric insert with innovative configuration.

[0025] The elastomeric insert has an annular shape and comprise a plurality of radial separators made of elastomeric material spaced by radial cavities, said first half-coupling and said second half-coupling presenting respectively a first frontal toothing and a second frontal toothing, wherein in the coupled configuration the teeth of the first frontal toothing and the teeth of the second frontal toothing are facing each other and alternatively accommodated in the radial cavities of the elastomeric insert.

[0026] Innovatively, the elastomeric insert may comprise an outer ring that interconnects said radial separators between them, the inner ends of which are free and face a central cavity. In this way, the central cavity can house the end of the drive shaft, which has standardised axial dimensions by having to carry the key: an axial overlap of the constituent elements of the connection is therefore achieved that allows to effectively reduce the overall dimensions thereof.

[0027] In other words, the particular outer ring structure of connection of the elastomeric insert allows an end portion of the shaft of the electric motor to overlap (upon completion of the connection) the frontal toothing of the drive screw, without parts of the elastomeric insert standing in the way of this overlap, as would happen if elastic elements with conventional geometric configuration were used.

[0028] Preferably, said radial separators are tapered in the direction of the outer ring, so as to achieve a retaining action on the teeth of the first and second frontal toothing interposed between the successive radial separators. Thanks to this expedient, a possible extraction of the elastomeric insert due to the centrifugal forces at high rotation speeds of the drive screw is avoided.

[0029] Preferably, the teeth of the first and second frontal toothing are frontal pins with substantially isosceles trapezium cross-section, wherein the sides of said isosceles trapezium are concave to adapt to the tapering of the radial separators.

[0030] The first half-coupling, as previously mentioned, may have a central through hole to allow the complete crossing of the drive shaft, said second half-coupling and said elastomeric insert defining, in the mounted configuration, a central cavity in continuation of said through hole for housing the free end of said drive shaft.

[0031] Said central cavity can in particular be defined by the inner ends of the radial separators and by the teeth of the first and second frontal toothing in the coupled configuration.

[0032] It also preferably has a diameter greater than twice the radial overall dimension of the drive shaft including the engaged key, so as to avoid any interference or friction among the elements.

[0033] The technical problem identified above is also solved by a screw pump comprising a containment case, on which a suction port and a delivery port open in longitudinal succession, and a connection assembly with the characteristics identified above, wherein the drive screw turns within the containment case.

[0034] The containment case may comprise, in a per se known manner, a main casing body to which at least one front flange is directly associated; in the invention, said front flange may, however, be arranged to be joined directly to an electric motor comprising the drive shaft. Thus, the first half-flange, the elastomeric insert and at least part of the second half-flange are completely housed within the front flange, without the need for an additional housing coupling as in the prior art.

[0035] In a known manner, the containment case may further comprise a rear flange that closes the main casing body at the opposing end with respect to the front flange.

[0036] Preferably, the front flange has a bell shape and joins an attachment section of said containment case to an attachment section of said electric motor.

[0037] The second half-coupling comprises a hub from which the second frontal toothing develops; this hub may be totally or predominantly inserted into a through opening of said front flange, e.g. rotatably mounted within said through opening with the interposition of bearings. In this case, the pump mounted complete with front flange has only a portion - possibly represented by the toothing alone - protruding into the chamber that houses the rest of the elastic connection. A further limitation of the overall axial dimensions of the device is achieved.

[0038] Finally, it should be noted that the screw pump is preferably a two- or three-screw pump and comprises one or more driven screws dragged into rotation by the drive screw. In accordance with a preferred embodiment of the present invention, the volumetric pump that is connected to the electric motor is a three-screw pump, comprising two side screws and a central screw. Pumps of this type are primarily suited for moving viscous fluids, particularly with viscosity between 4 est and 5000 cst.

[0039] The method of production of the screw pump according to the invention provides a step of realizing the monolithic drive screw / second half-coupling assembly, by machining in one piece or irreversible coupling of the drive screw to the rotor, and a subsequent step of inserting the assembly into the main casing body. A subsequent step comprises closing the casing by mounting the front flange, leaving at least one end of the second half-coupling protruding therefrom.

[0040] The advantages and distinctive characteristics of the connection assembly and of the screw pump according to the present invention will be made clearer by the description of an example of its embodiment, made below with reference to the attached drawings given by way of nonlimiting example.Brief description of the drawings

[0041] Figure 1 represents a schematic perspective view of the elements that make up an elastic type connection according to the prior art between an electric motor and a screw pump; Figure 2 represents a schematic perspective view, according to a rear observation point, of a screw pump with connection assembly according to the present invention, wherein the end portion of the pump drive screw is highlighted; Figure 3 represents a schematic perspective view, according to a rear observation point, of a screw pump with connection assembly according to the present invention, wherein the elastic coupling and the end portion of the shaft of the electric motor are highlighted; Figure 4 represents a side view, partially sectioned according to the vertical plane passing through the axis of rotation of the drive screw, of a screw pump with connection assembly according to the present invention, wherein the electric motor, the elastic coupling and the screw pump are mounted in the operational configuration; Figure 5a represents a front view of an elastomeric insert used in the connection assembly according to prior art; Figure 5b represents a perspective view of the elastomeric insert used in the connection assembly according to prior art; Figure 5c represents a front view of an elastomeric insert used in the connection assembly according to the present invention; Figure 5d represents a perspective view of the elastomeric insert used in the connection assembly according to the present invention; Figure 6 represents a cross-sectional view of the connection assembly according to the present invention in the operational configuration, at the elastomeric insert. Detailed description of an embodiment

[0042] With reference to the aforesaid Figures 2 -4, a screw pump according to the present invention, coupled by means of a connection assembly 50 to an electric motor 12 known per se, is globally indicated with 11.

[0043] Said screw pump 11 comprises in a known manner a containment case 30, on which a suction port 31 and a delivery port 32 open in longitudinal succession, and within which at least one drive screw 15 turns. The containment case 30 comprises a main casing body 30a, a rear flange 30b, and a front flange 30c.

[0044] Depending on the type of pump, there may be provided one or two driven screws, not visible in the accompanying figures, which mesh with the drive screw 15.

[0045] The assembly for the connection 50 to the electric motor 12 comprises an elastic coupling, comprising in turn a first half-coupling 13, a second half-coupling 14, and an elastomeric insert 18 interposed between the two half-couplings 13, 14. According to the teachings of the present invention, the second half-coupling is substantially integrated into an end portion of the central screw 15 of the pump 11.

[0046] The first half-coupling 13 and the second half-coupling 14 respectively comprise a first hub 26, from which a first frontal toothing 16 develops; and a second hub 29, from which a second frontal toothing 19 develops.

[0047] The first hub 26 is embodied, in a preferred embodiment, in a cylindrical sleeve provided with a central through hole arranged for the insertion of a drive shaft 23 of the electric motor 12. On the inner surface of the central through hole there is provided a square-sectioned groove for housing a standardized tab 24 provided on the drive shaft 23 for coupling with the first half-coupling 13. It can be seen that, in the mounted configuration, the drive shaft 23 passes completely through the first hub, partially protruding therefrom; the end portion of the tab 24 also protrudes from the hub, so that only a prevailing portion of this tab achieves the engagement between the two components.

[0048] The second hub 29 is also a cylindrical element, preferably solid, which, as mentioned above, is integral with the end of the drive screw 15, providing an increased diameter than the latter. In a preferred embodiment illustrated in the accompanying figures, the second hub 29 is made as one piece with the rest of the drive screw 15; alternatively, it can be made over the drive screw with irreversible coupling, e.g. by heat shrink-fitting, gluing, welding.

[0049] The first and second frontal toothing 16, 19, mirroring each other, are pin-type toohtings, i.e. comprising a plurality of teeth with frontal overhang, projecting in the direction of the axis of rotation of the central screw 15, intended to interpenetrate, with the interposition of radial separators 20 defined by the elastomeric insert 18, to achieve a rotating integral coupling.

[0050] In the preferred embodiment illustrated in the accompanying figures, both frontal toothings 16, 19 comprise four teeth: obviously, a different number of teeth can be used depending on the design choices.

[0051] The teeth of the two frontal toothings 16, 19 are arranged along an outer circular crown of the opposing frontal faces of the two hubs 19, 29, and there is therefore, as will be explained below, a free cylindrical volume between them.

[0052] The teeth of the frontal toothings 16, 19 present an essentially isosceles trapezoid cross-sectional shape, wherein the two bases are shaped according to arcs of circumference to conform to the circular pattern of the hub 26, 29 and the sides have a concavity whose function is explained below.

[0053] As previously mentioned, the elastomeric insert 18 is inserted between the two frontal toothings 16, 19 and which innovatively has an outer ring 21 from which the plurality of radial separators 20 branch inwards. Naturally, the number of radial separators is double than that of the teeth of the individual frontal toothings 16, 19, which are inserted into U-shaped radial cavities 17 defined between adjacent radial separators 20.

[0054] Advantageously, the side walls of the individual radial separators 20 have a curvature, tapering towards the base of attachment to the outer ring 21, which matches the concavity of the teeth discussed above. The aforesaid lobed shape of the radial separators 20 defines a containment shape for the teeth inserted in the radial cavities 17, which contributes to holding the elastomeric insert 18 in place even when subjected to high rotation speeds and to the resulting centrifugal forces.

[0055] It can be noted that the elastomeric insert 18 is preferably made as one single piece, and can be made by known techniques using any suitable elastomeric material: for example, it can be made of polyurethane cast like the inserts of the prior art.

[0056] In an operational configuration, the two frontal toothings 16, 19 then cooperate with each other with the interposition of the elastomeric insert 18. The outer ring 21 surrounds the toothings 16, 19 in this case, while the radial separators 20 are introduced between each tooth. This structure defines a cylindrical central cavity 25, delimited by the inner faces of the teeth and of the radial separators 20. The end portion of the drive shaft 23, as well as the key 24 supported by it are introduced inside this central cavity. In order to avoid interferences and frictions, said central cavity 25 therefore has a diameter θ c greater than twice the overall radial dimension r a of the drive shaft 23 including the engaged key 24, as can be seen in Figure 6.

[0057] As previously described, the containment case 30 of the screw pump 11 comprises a main casing body 30a, a rear flange 30b and a front flange 30c.

[0058] While the main casing 30a and the rear flange 30b have a conventional structure, in the present invention the front flange 30c is suitably shaped to couple with the electric motor 12, housing within it all the components that make up the elastic coupling between drive shaft 23 and drive screw.

[0059] For this reason, the front flange 30c has a bell-shaped structure that joins a base 22, screwed to the main casing 30a, up to a head plate arranged to be bolted to the electric motor 12.

[0060] Inside the base 22 there is provided a through opening 28, which is crossed by the drive screw 15. In particular, the second hub 29 is rotatably constrained within the through opening 28 by the interposition of ball bearings 27. Consequently, the only portion of the second half-coupling 14 that develops with overhang from the base 22, i.e. from the bottom surface of the bell-shaped body of the front flange 30c, is constituted by the second frontal toothing 19. In this way, the end of the drive shaft 23, with a predetermined dimension due to the standardisation of the tab 24, can extend up to close the aforesaid bottom of the front flange 30c, achieving an axial compaction that is comparable to that of the pumps with rigid coupling of the prior art.

[0061] A first advantage of the screw pump according to the present invention is that it achieves the transport of energy from the source (electric motor) to the user (screw pump) in an elastic manner, while maintaining a high degree of compactness of the assembly constituted by pump and electric motor.

[0062] A further advantage of the connection assembly is that it allows the elimination of the housing case made in the prior art as a mechanical element distinct from the front flange: the result is a space-saving that favours the compactness of the overall structure.

[0063] A further advantage of the connection assembly in accordance with the present invention derives from the fact that it provides for the presence of an elastomeric insert with circular shape, capable of adapting mechanically so as to surround the toothing with pins projecting from the end of the shaft of the screw pump: therefore, all the advantages of an elastic type connection between volumetric machine and electric motor are maintained. The presence of such an elastomeric insert avoids the direct metallic contact among the rotating components, and therefore isolates from vibrations, axial and radial loads and dampens torque peaks at start-up.

[0064] The connection assembly and the screw pump described above in a preferred embodiment thereof are susceptible to variations and modifications, all within the reach of the person skilled in the art and, as such, falling within the scope of protection of the present invention defined by the following claims.

Examples

Embodiment Construction

[0042]With reference to the aforesaid Figures 2 -4, a screw pump according to the present invention, coupled by means of a connection assembly 50 to an electric motor 12 known per se, is globally indicated with 11.

[0043]Said screw pump 11 comprises in a known manner a containment case 30, on which a suction port 31 and a delivery port 32 open in longitudinal succession, and within which at least one drive screw 15 turns. The containment case 30 comprises a main casing body 30a, a rear flange 30b, and a front flange 30c.

[0044]Depending on the type of pump, there may be provided one or two driven screws, not visible in the accompanying figures, which mesh with the drive screw 15.

[0045]The assembly for the connection 50 to the electric motor 12 comprises an elastic coupling, comprising in turn a first half-coupling 13, a second half-coupling 14, and an elastomeric insert 18 interposed between the two half-couplings 13, 14. According to the teachings of the present invention, the second...

Claims

1. Drive screw (15) and connection assembly (50) for screw pump (11), comprising: a drive screw (15); a first half-coupling (13) arranged to be keyed on a drive shaft (23); a second half-coupling (14) integral with said drive screw (15) and arranged to couple to said first half-coupling (13); and an elastomeric insert (18) arranged to be interposed between said first half-coupling (13) and said second half-coupling (14) in the coupled configuration, characterized in that said elastomeric insert (18) has an annular shape and comprises a plurality of radial separators (20) made of elastomeric material spaced by radial cavities (17), said first half-coupling (13) and said second half-coupling (14) presenting respectively a first frontal toothing (16) and a second frontal toothing (19), wherein in the coupled configuration the teeth of the first frontal toothing (16) and the teeth of the second frontal toothing (19) are facing each other and alternatively accommodated in the radial cavities (17) of the elastomeric insert (18).

2. Drive screw (15) and connection assembly (50) according to claim 1, wherein said elastomeric insert (18) comprises an outer ring (21) interconnecting said radial separators (20) between them.

3. Drive screw (15) and connection assembly (50) according to claim 2, wherein said radial separators (20) are tapered in the direction of the outer ring (21), so as to achieve a retaining action on the teeth of the first (16) and second frontal toothing (19) interposed between the successive radial separators (20).

4. Drive screw (15) and connection assembly (50) according to claim 3, wherein the teeth of the first (16) and second frontal toothing (19) are pins with substantially isosceles trapezium cross-section, wherein the sides of said isosceles trapezium are concave to adapt to the tapering of the radial separators (20).

5. Drive screw (15) and connection assembly (50) according to one of the preceding claims, wherein said first half-coupling (13) has a central through hole to allow the complete crossing by the drive shaft (23), said second half-coupling (19) and said elastomeric insert (18) defining, in the mounted configuration, a central cavity (25) in continuation of said through hole for housing the free end of said drive shaft (23).

6. Drive screw (15) and connection assembly (50) according to claim5, wherein said central cavity (25) is defined by the inner ends of the radial separators (20) and by the teeth of the first (16) and second frontal toothing (19) in the coupled configuration.

7. Drive screw (15) and connection assembly (50) according to one of claims 5 or 6, wherein said central cavity (25) has a diameter (θc) greater than twice the radial overall dimension (ra) of the drive shaft (23) including the engaged key (24).

8. Drive screw (15) and connection assembly (50) according to one of the preceding claims, wherein said second half-coupling (14) is made as one piece with the drive screw (15) or irreversibly coupled thereto.

9. Screw pump (11) comprising a containment case (30), on which a suction port (31) and a delivery port (32) open in longitudinal succession, and a drive screw (15) and connection assembly (50) according to one of the preceding claims, wherein said drive screw (15) turns within the containment case.

10. Screw pump (11) according to claim 9, wherein said containment case (30) comprises a main casing body (30a) to which at least one front flange (30c) is directly associated, said front flange (30c) being arranged to be joined directly to an electric motor (12) comprising said drive shaft (23), the first half-coupling (13), the elastomeric insert (18) and at least part of the second half-coupling (14) thus being completely housed within the front flange (30c).

11. Screw pump (11) according to claim 10 wherein said front flange (30c) has a bell shape and joins a section of said containment case (30) to an attachment section of said electric motor (12).

12. Screw pump (11) according to one of claims 10 or 11, wherein said second half-coupling (14) comprises a hub (29) from which the second frontal toothing (19) develops, said hub (29) being totally or predominantly inserted into a through opening (28) of said front flange (30c).

13. Screw pump (11) according to claim 12, wherein said hub (29) is rotatably mounted within said through opening (28) by means of bearings (27).

14. Screw pump (11) according to one of claims 9-13, wherein said pump is a pump with two or three screws and comprises one or more driven screws dragged into rotation by the drive screw (15).

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