Impeller assembly and method for mounting an impeller on a shaft of an electric motor

Abstract

Impeller assembly (40) and method for mounting an impeller (11) on a shaft (12) of an electric motor (13), wherein the shaft (12) comprises a terminal end (19). The assembly (40) comprises first coupling means (14s) integral with the shaft and which include a first truncated conical part (17) decreasing toward the terminal end (19). The assembly (40) also comprises second coupling means (14b) integral with the impeller (11), which include a central element (23) with a substantially tubular shape and provided with a central through hole (24) having a first conical flare (25) configured to contact the first truncated conical part (17) and a second conical flare (27) configured to cooperate with centering means (29).

Description

FIELD OF THE INVENTION

[0001] The present invention concerns an impeller assembly and a method for mounting an impeller on the shaft of an electric motor, for example, but not limited to, for axial fans for heat pumps, air conditioners, or ventilation systems.BACKGROUND OF THE INVENTION

[0002] Various devices and methods are known for mounting and attaching in a removable manner an impeller on a shaft of an electric motor, for example, but not limited to, for axial fans for heat pumps, air conditioners, or ventilation systems.

[0003] An impeller of the above type usually comprises a central hub and a plurality of blades, distributed angularly at equal distances, which are manufactured together by injection molding of at least one thermoplastic material, for example polypropylene (PP), fiberglass reinforced polyamide (PA), or fiberglass reinforced antistatic polyamide, in order to form, together with a metal element coaxially embedded in the central hub, a single piece configured to then be mounted on a shaft, also usually made of metal, of an electric motor. Usually, the weight of such an impeller is comprised between 350 g and 1,000 g and the mechanical torque transmitted to the impeller by the shaft of the electric motor is of the order of 2.3 Nm.

[0004] The same Applicant, simultaneously to the present patent application, has filed another patent application for industrial invention entitled "APPARATUS AND METHOD FOR PRODUCING IMPELLERS BY MOULDING OF PLASTIC MATERIAL".

[0005] In order to attach an impeller of the above type on a shaft of an electric motor it is known to use a mechanical coupling, by means of interference or keying, or to use screws or bolts.

[0006] A disadvantage of known devices and methods lies in the fact that, once the assembly is complete, the longitudinal axis of the impeller does not always coincide perfectly with the axis of rotation of the electric motor's shaft, so that during the drive of the electric motor anomalies and noises develop that significantly lower the quality of the product on which the impeller is mounted.

[0007] AU 2011 / 333514A1 discloses a fan comprising an impeller that is attached to a shaft by means of a clamping between a first and a second support element which are held by the shaft and forced axially toward each other, and have conical rest surfaces at the point where they meet the impeller. In this solution, the impeller is not attached to a terminal portion of the shaft, but along the shaft itself.

[0008] US 2,317,070 discloses a device for connecting a shaft to a hub of an impeller.

[0009] There is therefore the need to perfect an impeller assembly and develop the corresponding method for mounting an impeller on the shaft of an electric motor.

[0010] To do this, it is necessary to resolve the technical problem of transmitting an adequate mechanical torque while simultaneously achieving, in a simple and reliable manner, the perfect coaxiality and coincidence of the impeller's longitudinal axis with the axis of rotation of the shaft of an electric motor.

[0011] In particular, one purpose of the present invention is to provide an impeller assembly and develop a method for mounting an impeller on the shaft of an electric motor which allow to achieve a precise and secure coupling between the two members, that is, their perfect axiality, using simple and easy-to-use components.

[0012] Another purpose of the present invention is to provide an impeller assembly and develop a method for mounting an impeller on the shaft of an electric motor which allow to achieve both an easy mounting of the impeller on the shaft, guaranteeing the aforementioned axiality, and also an equally easy disassembly of the impeller from the shaft, so that even not particularly specialized personnel can be used for these operations.

[0013] Another purpose of the present invention is to provide an impeller assembly and develop a method for mounting an impeller on the shaft of an electric motor which allow to realize both the aforementioned mounting and also the aforementioned disassembly, even in an automated manner using robotic equipment or machines of a known type.

[0014] The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.SUMMARY OF THE INVENTION

[0015] The present invention is set forth and characterized in the independent claims. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

[0016] In accordance with the above purposes and to resolve the technical problem described above in a new and original way, also achieving considerable advantages compared to the state of the prior art, an impeller assembly according to the present invention comprises an impeller, a shaft of a motor having an axis of rotation and a terminal end, and a device configured to mount the impeller on the shaft; the assembly comprises first coupling means integral with the drive shaft and comprising at least a first truncated conical part having a first taper decreasing toward the terminal end and second coupling means integral with the impeller and comprising a central element with a substantially tubular shape provided with a central through hole coaxial to a longitudinal axis of the impeller and able to receive the terminal end with play, and also with a first conical flare created on a first end of the central through hole, and also with a second conical flare created on a second end of the central through hole, opposite the first end.

[0017] In accordance with the present invention, the device comprises centering means configured to be associated with the terminal end and to cooperate with the second conical flare of the central element to axially thrust the first conical flare against the first truncated conical part, in order to keep the impeller clamped on the shaft by means of a shape coupling, with the longitudinal axis coinciding with the axis of rotation.

[0018] In accordance with another aspect of the present invention, the centering means comprise a clamping element comprising, or consisting of, a washer provided with an axial cavity configured to accommodate the terminal end with play, and in particular without contact, and having a second truncated conical part configured to be coupled to the second conical flare by means of a shape coupling.

[0019] The washer is therefore abutting against the central element only, and remains spaced apart from, and not in contact with, the terminal end of the shaft in both the axial direction as well as the circumferential direction. In this way, it is possible to achieve an optimal alignment between the shaft and the impeller even if the washer has possible defects of misalignment relative to the shaft, for example due to errors in the creation of the threaded axial hole, which lead to an imperfect centering of the hole with respect to the shaft's axis of rotation, because - since there are no reciprocal contact points - these defects are not transferred to the shaft and therefore do not affect the axiality between the shaft and the impeller.

[0020] In accordance with one aspect of the present invention, the axial cavity has a diameter substantially corresponding to that of the central through hole and larger than the diameter of the terminal end.

[0021] In accordance with another aspect of the present invention, the washer comprises a first flat part disposed transverse with respect to the first longitudinal axis and having a through axial hole for the passage of a clamping screw configured to screw into a threaded axial hole of the terminal end.

[0022] In accordance with another aspect of the invention, the second truncated conical part extends beyond the first flat part, laterally delimiting the axial cavity, in such a way that the first flat part is spaced apart from the top surface of the terminal end when the second truncated conical part is in contact with the second conical flare.

[0023] According to one aspect of the invention, the washer is U-shaped in section, wherein the axial through hole is located on the bottom of the "U" shape and the ends of the arms of the "U" shape define the second truncated conical part.

[0024] In accordance with another aspect of the present invention, the first truncated conical part has a first taper forming a first angle with the axis of rotation and the first conical flare has a second taper forming a second angle with the longitudinal axis, which is the same as the first angle.

[0025] In accordance with another aspect of the present invention, the second conical flare has a third taper forming a third angle with the longitudinal axis and the second truncated conical part has a fourth taper forming a fourth angle with the longitudinal axis, which is the same as the third angle.

[0026] In accordance with another aspect of the present invention, the central through hole has a first internal diameter slightly larger, of the order of micrometers, or micron (µm), preferably between about 20 µm and about 60 µm, than the second external diameter so as not to come into contact, during use, with the terminal end.

[0027] In accordance with another aspect of the present invention, there is provided a method for mounting an impeller on a shaft of an electric motor, wherein the impeller has a longitudinal axis, and the shaft has an axis of rotation, wherein the method comprises a first manufacturing step in which: a) the shaft is made so that it comprises at least one terminal end and a first truncated conical part having a first taper decreasing toward the terminal end; and b) the impeller is made so that it comprises a central element with a substantially tubular shape and provided with a central through hole coaxial to the longitudinal axis, and also with a first conical flare created on a first end of the central through hole, and also with a second conical flare created on a second end of the central through hole, opposite the first end. Moreover, the method also comprises a second manufacturing step in which centering means are made, configured to be associated with the terminal end and cooperate with the second conical flare of the central element in order to axially thrust the first conical flare against the first truncated conical part, so as to keep the impeller clamped onto the shaft by means of a shape coupling, with the longitudinal axis coinciding with the axis of rotation.

[0028] In accordance with another aspect of the present invention, the method comprises a subsequent assembly step in which the impeller is coupled to the shaft by means of a first sub-step in which the impeller is displaced axially toward the body of the electric motor, keeping the longitudinal axis coinciding with the axis of rotation and ensuring that the terminal end is inserted into the central through hole of the central element with play, and a subsequent second sub-step in which the impeller is thrust further toward the body of the electric motor until the first conical flare of the central element is in contact with the first truncated conical part of the shaft, where a first shape coupling is realized.

[0029] In accordance with the present invention, the centering means comprise a clamping element comprising, or consisting of, a washer provided with an axial cavity configured to accommodate the terminal end with play and having a second truncated conical part configured to be coupled to the second conical flare by means of a shape coupling.

[0030] In accordance with one aspect of the present invention, the washer is abutting only against the central element and there are no contact points with the terminal end.

[0031] In accordance with another aspect of the present invention, during the first manufacturing step as above a threaded axial hole is made on the terminal end and, in addition, the centering means also comprise a clamping screw screwable into the threaded axial hole; moreover, the method also comprises a subsequent clamping step in which the washer is mounted on the terminal end of the second part and is clamped thereon by screwing the clamping screw into the threaded axial hole, until the second truncated conical part is in contact with the second conical flare of the central element, where a second shape coupling is realized.

[0032] In particular, the shaft is abutting on a first side of the central element by means of the first truncated conical part and the washer is abutting on the second side by means of its second truncated conical part, effectively without any contact with the shaft, and it is connected to the terminal portion only by means of the clamping screw.DESCRIPTION OF THE DRAWINGS

[0033] These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of an embodiment, given as a non-restrictive example with reference to the attached drawings wherein: fig. 1 is an exploded view of a device according to the present invention for mounting an impeller on the shaft of an electric motor; fig. 2 is a schematic front view of equipment that uses a device according to the present invention; fig. 3 is a section along a longitudinal axis of the device according to the present invention, in a condition in which the impeller is mounted on the shaft of the electric motor of fig. 1; fig. 4 is an enlargement of fig. 3; fig. 5 is a front view of a detail of the device of fig. 1; fig. 6 is a top view of the detail of fig. 5; fig. 7 is a section along the line VII-VII of fig. 6.

[0034] We must clarify that the phraseology and terminology used in the present description, as well as the figures in the attached drawings also in relation as to how described, have the sole function of better illustrating and explaining the present invention, their purpose being to provide a non-limiting example thereof, since the scope of protection is defined by the claims. We must also clarify that the drawings are not to scale.

[0035] To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings.DESCRIPTION OF AN EMBODIMENT OF THE PRESENT INVENTION

[0036] With reference to figs. 1, 3 and 4, an impeller assembly 40 according to the present invention is described below, comprising an impeller 11, a shaft 12 of an electric motor 13, and a device 10 configured to mount the impeller 11 on the shaft 12.

[0037] For example, the impeller 11 is configured to be used in axial fans for heat pumps, air conditioners, such as the one shown schematically in fig. 2 and indicated generically with reference number 100, or ventilation systems. As an indication, to better frame the present invention, the weight of the impeller 11 can be comprised between 350 g and 1,000 g, and the mechanical torque transmitted to the impeller 11 by the shaft 12 can be of the order of 2.3 Nm.

[0038] The assembly 40 comprises first coupling means 14a integral with the drive shaft 12 and second coupling means 14b integral with the impeller 11.

[0039] The shaft 12 has an axis of rotation X1 (figs. from 1 to 4).

[0040] According to some embodiments, the shaft 12 comprises both a first part 15 (figs. 3 and 4) proximal to the fixed body from the electric motor 13 (fig. 4), for example cylindrical, and also a second part 16 distal from the fixed body from the electric motor 13 and cantilevered with respect thereto, also for example cylindrical, both parts being coaxial to the axis of rotation X1.

[0041] The first cylindrical part 15 has a first external diameter D1 and the second cylindrical part 16 has a second external diameter D2, smaller than the first external diameter D1.

[0042] The first part 15 and / or the second part 16, instead of being cylindrical, can be of different shapes, for example with a polygonal section. In the latter case, the diameter of a circle inscribed in or circumscribed about the polygonal shape can be considered as the first or second external diameter D1, D2.

[0043] Hereafter, the description will refer to an embodiment in which the first and second parts are cylindrical.

[0044] In accordance with one aspect of the present invention, the shaft 12 comprises a first truncated conical part 17 disposed in an intermediate position between the first part 15 and the second part 16 and having a first taper decreasing from the first part 15 toward the second part 16. The first truncated conical part 17 forms a first angle α1, for example comprised between 10° and 30°, with the axis of rotation X1 and is configured to perform the function of shoulder with conical surface for the impeller 11, as will be described below.

[0045] The second part 16 has a terminal end 19, disposed on the opposite side with respect to the first truncated conical part 17 and provided with a threaded axial hole 20. For example, the first external diameter D1 is comprised between about 6 mm and about 30 mm, and the second external diameter D2 is comprised between about 10 mm and about 40 mm. In the embodiment disclosed here, the difference between the first and second diameter is between about 1 mm and 3 mm. By way of example, the first external diameter D1 can be between about 11 mm and 12 mm, and the second external diameter D2 between about 9 mm and 10 mm.

[0046] Some embodiments of the present invention can provide that the first truncated conical part 17 and the first and second parts 15 and 16 are made in a single body, for example by mechanical machining of a shaft 12 of a known type. Alternatively, the first truncated conical part 17 can consist of a separate truncated conical element, attached onto the shaft 12 so as to rotate together with it about the axis of rotation X1.

[0047] At least the second part 16 and the truncated conical part 17 can define the first coupling means 14a. These coupling means 14a can be made directly on the drive shaft 12, in a single body, suitably conforming it, or they can be made as a separate component that can be joined or connected to the shaft 12 so as to be integral therewith.

[0048] The impeller 11 is, for example, of type that comprises a central element 23 (figs. 1 and 3) and a plurality of blades 22, for example 3, such as the one shown in fig. 1, made in a single body by injection molding of a thermoplastic material, for example as described in the aforementioned patent application for industrial invention that the Applicant has filed at the same time as the present application.

[0049] The impeller 11 also comprises a central element 23 (figs. 1 and from 3 to 7), for example consisting of a metal insert substantially shaped as a cylindrical bushing and provided with a cylindrical central through hole 24 (figs. from 3 to 7) coaxial to its own longitudinal axis X2 which, during use, is coinciding with the axis of rotation X1 of the shaft 12.

[0050] This central element 23 defines the second coupling means 14b.

[0051] In accordance with one aspect of the present invention, the central through hole 24 has a first internal diameter D3 slightly larger, of the order of microns, for example between about 20 µm and about 60 µm, than the second external diameter D2 so as not to come into contact, during use, with the second part 16 of the shaft 12, as will be described below. For example, in the embodiment disclosed here, the first internal diameter D3 can be between about 10 mm and 11 mm.

[0052] The central through hole 24 preferably has a circular section, although it is possible to provide a polygonal section with sizes and shape correlated to those of the second part 16 of the shaft 12, so as to allow an insertion therein substantially without contact on the lateral walls.

[0053] In accordance with one aspect of the present invention, a first conical flare 25 is created on a first end 26 of the central through hole 24 (fig. 7) having a second taper that forms a second angle α2 with the longitudinal axis X1, for example comprised between 10° and 30°. Advantageously, the second angle α2 is the same as the first angle α1, as can be seen in figs. 4 and 7.

[0054] Moreover, a second conical flare 27 is created on a second end 28 (fig. 7) of the central through hole 24, opposite the first end 26, having a third taper that forms a third angle α3 with the longitudinal axis X1, for example comprised between 30° and 60°. The third angle α3 can be the same as, or different from, the first two angles α1 and α2. In the embodiment shown here, the third angle α3 is greater than the first two angles α1 and α2.

[0055] The first conical flare 25 has a third external diameter D4 which can be either substantially the same as the first external diameter D1 or different therefrom, for example larger than the latter by at least a few tenths of a millimeter, for example about 0.2 mm, and which in the embodiment disclosed here can be about 12 mm.

[0056] The second conical flare 27 has a fourth external diameter D5, which in the embodiment disclosed here is larger than the third external diameter D4 and can be for example about 15 mm.

[0057] Some embodiments of the present invention can provide that the third external diameter D4 and the fourth external diameter D5 are the same as each other, especially when the third angle α3 is the same as the second angle α2.

[0058] The device 10 comprises centering means 29 (figs. 1, 3 and 4) which comprise a clamping element 30 (fig. 7) configured to be coupled to the terminal end 19, for example removably by means of a clamping screw 31 which is screwable into the threaded axial hole 20 thereof.

[0059] In accordance with one aspect of the present invention, the clamping element 30 comprises or consists of a washer 32, shaped so as to have an axial cavity 33 configured to accommodate the terminal end 19 with play.

[0060] The washer 32 comprises a second truncated conical part 35 having a fourth taper forming a fourth angle α4 with the axis of rotation X1, for example comprised between 30° and 60°, and configured to cooperate, during use, with the second conical flare 27 of the central element 23 and thus realize a shape coupling, that is, a coupling by contact. Advantageously, the fourth angle α4 is the same as the third angle α3.

[0061] The axial cavity 33 has a second internal diameter D6 slightly larger, of the order of microns, for example between about 20 µm and about 60 µm, than the second external diameter D2 of the second part 16. For example, in the embodiment disclosed here, the second internal diameter D6 is the same as the first internal diameter D3 of the central through hole 24, therefore it is also between about 10 mm and 11 mm.

[0062] Furthermore, the axial cavity 33 has a depth such that it is configured to never come into contact with the terminal end 19 of the second part 16 of the shaft 12 when the washer 32 is mounted thereon, as described below.

[0063] The washer 32 is also provided with an axial through hole 36 configured to allow the passage of the shank of the clamping screw 31 with play.

[0064] In particular, the washer 32 can comprise a first flat part 34 in which the axial through hole 36 is made, and the second truncated conical part 35 extends beyond the thickness of the flat part 34 in such a way that, when the truncated conical part 35 is in contact with the second conical flare 27, the flat part 34 always remains spaced apart from the terminal end 19 of the second part 16.

[0065] The washer 32 is U-shaped in section, wherein the axial through hole 36 is located on the bottom of the "U" shape and the ends of the arms of the "U" shape define the second truncate conical part 35.

[0066] The second truncated conical part 35 has a fifth external diameter D7, which can be either substantially the same as the fourth external diameter D5 of the second conical flare 27, or different from it, for example smaller than it, by at least a few tenths of a millimeter, for example about 0.2 mm. In the embodiment described here, the fifth external diameter D7 can be about 15 mm.

[0067] The fifth external diameter D7 can be the same as or larger than the fourth external diameter D5. In other words, the diameter D7 of the washer 36 can even be the same as, or larger than, the diameter D5 of the second flare 27, rather than smaller, as shown in the drawings.

[0068] Therefore, some embodiments of the present invention provide that the second angle α2 of the first conical flare 25 is the same as the first angle α1 of the first truncated conical part 17, and that the third angle α3 of the second conical flare 27 is the same as the fourth angle α4 of the second truncated conical part 35 of the washer 32. For example, the first angle α1 and the second angle α2 can be 25°, while the third angle α3 and the fourth angle α4 can be 45°. Other embodiments of the present invention provide that the four angles α1, α2, α3 and α4 are the same as each other.

[0069] The present invention also concerns the method for mounting the impeller 11 on the shaft 12 using the device 10 described above, so as to form the impeller assembly 40, which method essentially comprises the following steps.

[0070] First of all, the following are made in a manufacturing step: the central element 23, so that it comprises the central through hole 24 and the two conical flares 25 and 27, as well as the first truncated conical part 17 and the second part 16 of the shaft 12, and also the washer 32, as described above.

[0071] The method also comprises an assembly step in which the impeller 11 is coupled to the shaft 12; in particular, first the impeller 11 is displaced axially toward the first part 15 of the shaft 12 (to the left in figs. 1, 3 and 4), keeping the longitudinal axis X2 coinciding with the axis of rotation X1 and ensuring that the second part 16 is inserted into the central through hole 24 of the central element 23; then the impeller 11 is thrust further toward the first part 15 until the first conical flare 25 of the central element 23 is in contact with the first truncated conical part 17 of the shaft 12, where a first shape coupling is realized.

[0072] We must clarify that, thanks to the difference between the second external diameter D2 of the second part 16 of the shaft 12 and the first internal diameter D3 of the central through hole 24, a first circumferential play of a few tenths of a millimeter is created between them, which in the example given here can be between about 0.2 mm and 0.3 mm, which means that the impeller 11 can slide freely in an axial direction along the axis of rotation X1 without coming into contact with the second part 16 of the shaft 12.

[0073] A clamping step then follows, in which the washer 32 is mounted on the terminal end 19 of the second part 16 and is clamped thereon by screwing the clamping screw 31 into the threaded axial hole 20, until the second truncated conical part 35 of the washer 32 is in contact with the second conical flare 27 of the central element 23, where a second shape coupling is realized.

[0074] By firmly tightening the clamping screw 31, the impeller 11 is clamped onto the shaft 12, keeping the longitudinal axis X2 perfectly coinciding with the axis of rotation X1, without the circular surface of the central through hole 24 touching the shaft 12 anywhere.

[0075] Furthermore, we must clarify that, thanks to the difference between the second internal diameter D6 of the axial cavity 33 and the second external diameter D2 of the second part 16 of the shaft 12, a second circumferential play of a few tenths of a millimeter is created between them, which in the example given here is 0.3 mm. This means that, after the washer 32 has been clamped against the central element 23 of the impeller 11, the only parts that contact the latter are the first truncated conical part 17 of the shaft 12, whose function is to transmit the driving torque exerted by the shaft 12 to the central element 23, and the second truncated conical part 35 of the washer 32, screwed onto shaft 12, whose function is to clamp the central element 23 onto the latter, which parts contact the first conical flare 25 and the second conical flare 27, respectively, as if the central element 23 were gripped only between two conical jaws (16 and 35) coaxial to the axis of rotation X1, this because, thanks to the suitable depth of the axial cavity 33 of the washer 32, the flat part 34 of the latter remains spaced apart from the terminal end 19 of the second part 16 of the shaft 12.

[0076] In other words, the cylindrical surfaces of the washer 32 and the shaft 12 are coupled with play, therefore these surfaces do not touch each other and any deformations or manufacturing errors of the washer, which could compromise the coaxiality of the coupling between the impeller 11 and the shaft 12, do not have any effect on the terminal end 19 of the latter.

[0077] The lateral surfaces of the central element 23 and of shaft 12, that is, the internal surface of the central through hole 24 and the external surface of the second part 16, are also coupled with play, whereby the shaft 12 does not transmit the rotational torque to the central element 23 through these surfaces, and any small deformations of the central element 23 do not come into contact with the shaft 12, and therefore do not compromise the coaxiality of the coupling of the shaft 12 to the central element 23, and therefore to the entire impeller 11.

[0078] It is clear that modifications and / or additions of parts and / or steps may be made to the impeller assembly 40 and to the method as described heretofore, without thereby departing from the field and scope of the present invention, as defined by the attached claims.

[0079] It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art will be able to achieve other equivalent forms of impeller assembly and methods for mounting an impeller on the shaft of an electric motor, having the characteristics as set forth in the claims and hence all within the field of protection defined thereby.

[0080] In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the claims.

Examples

Embodiment Construction

[0036]With reference to figs. 1, 3 and 4, an impeller assembly 40 according to the present invention is described below, comprising an impeller 11, a shaft 12 of an electric motor 13, and a device 10 configured to mount the impeller 11 on the shaft 12.

[0037]For example, the impeller 11 is configured to be used in axial fans for heat pumps, air conditioners, such as the one shown schematically in fig. 2 and indicated generically with reference number 100, or ventilation systems. As an indication, to better frame the present invention, the weight of the impeller 11 can be comprised between 350 g and 1,000 g, and the mechanical torque transmitted to the impeller 11 by the shaft 12 can be of the order of 2.3 Nm.

[0038]The assembly 40 comprises first coupling means 14a integral with the drive shaft 12 and second coupling means 14b integral with the impeller 11.

[0039]The shaft 12 has an axis of rotation X1 (figs. from 1 to 4).

[0040]According to some embodiments, the shaft 12 comprises both...

FIELD OF THE INVENTION

[0001] The present invention concerns an impeller assembly and a method for mounting an impeller on the shaft of an electric motor, for example, but not limited to, for axial fans for heat pumps, air conditioners, or ventilation systems.BACKGROUND OF THE INVENTION

[0002] Various devices and methods are known for mounting and attaching in a removable manner an impeller on a shaft of an electric motor, for example, but not limited to, for axial fans for heat pumps, air conditioners, or ventilation systems.

[0003] An impeller of the above type usually comprises a central hub and a plurality of blades, distributed angularly at equal distances, which are manufactured together by injection molding of at least one thermoplastic material, for example polypropylene (PP), fiberglass reinforced polyamide (PA), or fiberglass reinforced antistatic polyamide, in order to form, together with a metal element coaxially embedded in the central hub, a single piece configured to then be mounted on a shaft, also usually made of metal, of an electric motor. Usually, the weight of such an impeller is comprised between 350 g and 1,000 g and the mechanical torque transmitted to the impeller by the shaft of the electric motor is of the order of 2.3 Nm.

[0004] The same Applicant, simultaneously to the present patent application, has filed another patent application for industrial invention entitled "APPARATUS AND METHOD FOR PRODUCING IMPELLERS BY MOULDING OF PLASTIC MATERIAL".

[0005] In order to attach an impeller of the above type on a shaft of an electric motor it is known to use a mechanical coupling, by means of interference or keying, or to use screws or bolts.

[0006] A disadvantage of known devices and methods lies in the fact that, once the assembly is complete, the longitudinal axis of the impeller does not always coincide perfectly with the axis of rotation of the electric motor's shaft, so that during the drive of the electric motor anomalies and noises develop that significantly lower the quality of the product on which the impeller is mounted.

[0007] AU 2011 / 333514A1 discloses a fan comprising an impeller that is attached to a shaft by means of a clamping between a first and a second support element which are held by the shaft and forced axially toward each other, and have conical rest surfaces at the point where they meet the impeller. In this solution, the impeller is not attached to a terminal portion of the shaft, but along the shaft itself.

[0008] US 2,317,070 discloses a device for connecting a shaft to a hub of an impeller.

[0009] There is therefore the need to perfect an impeller assembly and develop the corresponding method for mounting an impeller on the shaft of an electric motor.

[0010] To do this, it is necessary to resolve the technical problem of transmitting an adequate mechanical torque while simultaneously achieving, in a simple and reliable manner, the perfect coaxiality and coincidence of the impeller's longitudinal axis with the axis of rotation of the shaft of an electric motor.

[0011] In particular, one purpose of the present invention is to provide an impeller assembly and develop a method for mounting an impeller on the shaft of an electric motor which allow to achieve a precise and secure coupling between the two members, that is, their perfect axiality, using simple and easy-to-use components.

[0012] Another purpose of the present invention is to provide an impeller assembly and develop a method for mounting an impeller on the shaft of an electric motor which allow to achieve both an easy mounting of the impeller on the shaft, guaranteeing the aforementioned axiality, and also an equally easy disassembly of the impeller from the shaft, so that even not particularly specialized personnel can be used for these operations.

[0013] Another purpose of the present invention is to provide an impeller assembly and develop a method for mounting an impeller on the shaft of an electric motor which allow to realize both the aforementioned mounting and also the aforementioned disassembly, even in an automated manner using robotic equipment or machines of a known type.

[0014] The Applicant has devised, tested and embodied the present invention to overcome the shortcomings of the state of the art and to obtain these and other purposes and advantages.SUMMARY OF THE INVENTION

[0015] The present invention is set forth and characterized in the independent claims. The dependent claims describe other characteristics of the present invention or variants to the main inventive idea.

[0016] In accordance with the above purposes and to resolve the technical problem described above in a new and original way, also achieving considerable advantages compared to the state of the prior art, an impeller assembly according to the present invention comprises an impeller, a shaft of a motor having an axis of rotation and a terminal end, and a device configured to mount the impeller on the shaft; the assembly comprises first coupling means integral with the drive shaft and comprising at least a first truncated conical part having a first taper decreasing toward the terminal end and second coupling means integral with the impeller and comprising a central element with a substantially tubular shape provided with a central through hole coaxial to a longitudinal axis of the impeller and able to receive the terminal end with play, and also with a first conical flare created on a first end of the central through hole, and also with a second conical flare created on a second end of the central through hole, opposite the first end.

[0017] In accordance with the present invention, the device comprises centering means configured to be associated with the terminal end and to cooperate with the second conical flare of the central element to axially thrust the first conical flare against the first truncated conical part, in order to keep the impeller clamped on the shaft by means of a shape coupling, with the longitudinal axis coinciding with the axis of rotation.

[0018] In accordance with another aspect of the present invention, the centering means comprise a clamping element comprising, or consisting of, a washer provided with an axial cavity configured to accommodate the terminal end with play, and in particular without contact, and having a second truncated conical part configured to be coupled to the second conical flare by means of a shape coupling.

[0019] The washer is therefore abutting against the central element only, and remains spaced apart from, and not in contact with, the terminal end of the shaft in both the axial direction as well as the circumferential direction. In this way, it is possible to achieve an optimal alignment between the shaft and the impeller even if the washer has possible defects of misalignment relative to the shaft, for example due to errors in the creation of the threaded axial hole, which lead to an imperfect centering of the hole with respect to the shaft's axis of rotation, because - since there are no reciprocal contact points - these defects are not transferred to the shaft and therefore do not affect the axiality between the shaft and the impeller.

[0020] In accordance with one aspect of the present invention, the axial cavity has a diameter substantially corresponding to that of the central through hole and larger than the diameter of the terminal end.

[0021] In accordance with another aspect of the present invention, the washer comprises a first flat part disposed transverse with respect to the first longitudinal axis and having a through axial hole for the passage of a clamping screw configured to screw into a threaded axial hole of the terminal end.

[0022] In accordance with another aspect of the invention, the second truncated conical part extends beyond the first flat part, laterally delimiting the axial cavity, in such a way that the first flat part is spaced apart from the top surface of the terminal end when the second truncated conical part is in contact with the second conical flare.

[0023] According to one aspect of the invention, the washer is U-shaped in section, wherein the axial through hole is located on the bottom of the "U" shape and the ends of the arms of the "U" shape define the second truncated conical part.

[0024] In accordance with another aspect of the present invention, the first truncated conical part has a first taper forming a first angle with the axis of rotation and the first conical flare has a second taper forming a second angle with the longitudinal axis, which is the same as the first angle.

[0025] In accordance with another aspect of the present invention, the second conical flare has a third taper forming a third angle with the longitudinal axis and the second truncated conical part has a fourth taper forming a fourth angle with the longitudinal axis, which is the same as the third angle.

[0026] In accordance with another aspect of the present invention, the central through hole has a first internal diameter slightly larger, of the order of micrometers, or micron (µm), preferably between about 20 µm and about 60 µm, than the second external diameter so as not to come into contact, during use, with the terminal end.

[0027] In accordance with another aspect of the present invention, there is provided a method for mounting an impeller on a shaft of an electric motor, wherein the impeller has a longitudinal axis, and the shaft has an axis of rotation, wherein the method comprises a first manufacturing step in which: a) the shaft is made so that it comprises at least one terminal end and a first truncated conical part having a first taper decreasing toward the terminal end; and b) the impeller is made so that it comprises a central element with a substantially tubular shape and provided with a central through hole coaxial to the longitudinal axis, and also with a first conical flare created on a first end of the central through hole, and also with a second conical flare created on a second end of the central through hole, opposite the first end. Moreover, the method also comprises a second manufacturing step in which centering means are made, configured to be associated with the terminal end and cooperate with the second conical flare of the central element in order to axially thrust the first conical flare against the first truncated conical part, so as to keep the impeller clamped onto the shaft by means of a shape coupling, with the longitudinal axis coinciding with the axis of rotation.

[0028] In accordance with another aspect of the present invention, the method comprises a subsequent assembly step in which the impeller is coupled to the shaft by means of a first sub-step in which the impeller is displaced axially toward the body of the electric motor, keeping the longitudinal axis coinciding with the axis of rotation and ensuring that the terminal end is inserted into the central through hole of the central element with play, and a subsequent second sub-step in which the impeller is thrust further toward the body of the electric motor until the first conical flare of the central element is in contact with the first truncated conical part of the shaft, where a first shape coupling is realized.

[0029] In accordance with the present invention, the centering means comprise a clamping element comprising, or consisting of, a washer provided with an axial cavity configured to accommodate the terminal end with play and having a second truncated conical part configured to be coupled to the second conical flare by means of a shape coupling.

[0030] In accordance with one aspect of the present invention, the washer is abutting only against the central element and there are no contact points with the terminal end.

[0031] In accordance with another aspect of the present invention, during the first manufacturing step as above a threaded axial hole is made on the terminal end and, in addition, the centering means also comprise a clamping screw screwable into the threaded axial hole; moreover, the method also comprises a subsequent clamping step in which the washer is mounted on the terminal end of the second part and is clamped thereon by screwing the clamping screw into the threaded axial hole, until the second truncated conical part is in contact with the second conical flare of the central element, where a second shape coupling is realized.

[0032] In particular, the shaft is abutting on a first side of the central element by means of the first truncated conical part and the washer is abutting on the second side by means of its second truncated conical part, effectively without any contact with the shaft, and it is connected to the terminal portion only by means of the clamping screw.DESCRIPTION OF THE DRAWINGS

[0033] These and other aspects, characteristics and advantages of the present invention will become apparent from the following description of an embodiment, given as a non-restrictive example with reference to the attached drawings wherein: fig. 1 is an exploded view of a device according to the present invention for mounting an impeller on the shaft of an electric motor; fig. 2 is a schematic front view of equipment that uses a device according to the present invention; fig. 3 is a section along a longitudinal axis of the device according to the present invention, in a condition in which the impeller is mounted on the shaft of the electric motor of fig. 1; fig. 4 is an enlargement of fig. 3; fig. 5 is a front view of a detail of the device of fig. 1; fig. 6 is a top view of the detail of fig. 5; fig. 7 is a section along the line VII-VII of fig. 6.

[0034] We must clarify that the phraseology and terminology used in the present description, as well as the figures in the attached drawings also in relation as to how described, have the sole function of better illustrating and explaining the present invention, their purpose being to provide a non-limiting example thereof, since the scope of protection is defined by the claims. We must also clarify that the drawings are not to scale.

[0035] To facilitate comprehension, the same reference numbers have been used, where possible, to identify identical common elements in the drawings.DESCRIPTION OF AN EMBODIMENT OF THE PRESENT INVENTION

[0036] With reference to figs. 1, 3 and 4, an impeller assembly 40 according to the present invention is described below, comprising an impeller 11, a shaft 12 of an electric motor 13, and a device 10 configured to mount the impeller 11 on the shaft 12.

[0037] For example, the impeller 11 is configured to be used in axial fans for heat pumps, air conditioners, such as the one shown schematically in fig. 2 and indicated generically with reference number 100, or ventilation systems. As an indication, to better frame the present invention, the weight of the impeller 11 can be comprised between 350 g and 1,000 g, and the mechanical torque transmitted to the impeller 11 by the shaft 12 can be of the order of 2.3 Nm.

[0038] The assembly 40 comprises first coupling means 14a integral with the drive shaft 12 and second coupling means 14b integral with the impeller 11.

[0039] The shaft 12 has an axis of rotation X1 (figs. from 1 to 4).

[0040] According to some embodiments, the shaft 12 comprises both a first part 15 (figs. 3 and 4) proximal to the fixed body from the electric motor 13 (fig. 4), for example cylindrical, and also a second part 16 distal from the fixed body from the electric motor 13 and cantilevered with respect thereto, also for example cylindrical, both parts being coaxial to the axis of rotation X1.

[0041] The first cylindrical part 15 has a first external diameter D1 and the second cylindrical part 16 has a second external diameter D2, smaller than the first external diameter D1.

[0042] The first part 15 and / or the second part 16, instead of being cylindrical, can be of different shapes, for example with a polygonal section. In the latter case, the diameter of a circle inscribed in or circumscribed about the polygonal shape can be considered as the first or second external diameter D1, D2.

[0043] Hereafter, the description will refer to an embodiment in which the first and second parts are cylindrical.

[0044] In accordance with one aspect of the present invention, the shaft 12 comprises a first truncated conical part 17 disposed in an intermediate position between the first part 15 and the second part 16 and having a first taper decreasing from the first part 15 toward the second part 16. The first truncated conical part 17 forms a first angle α1, for example comprised between 10° and 30°, with the axis of rotation X1 and is configured to perform the function of shoulder with conical surface for the impeller 11, as will be described below.

[0045] The second part 16 has a terminal end 19, disposed on the opposite side with respect to the first truncated conical part 17 and provided with a threaded axial hole 20. For example, the first external diameter D1 is comprised between about 6 mm and about 30 mm, and the second external diameter D2 is comprised between about 10 mm and about 40 mm. In the embodiment disclosed here, the difference between the first and second diameter is between about 1 mm and 3 mm. By way of example, the first external diameter D1 can be between about 11 mm and 12 mm, and the second external diameter D2 between about 9 mm and 10 mm.

[0046] Some embodiments of the present invention can provide that the first truncated conical part 17 and the first and second parts 15 and 16 are made in a single body, for example by mechanical machining of a shaft 12 of a known type. Alternatively, the first truncated conical part 17 can consist of a separate truncated conical element, attached onto the shaft 12 so as to rotate together with it about the axis of rotation X1.

[0047] At least the second part 16 and the truncated conical part 17 can define the first coupling means 14a. These coupling means 14a can be made directly on the drive shaft 12, in a single body, suitably conforming it, or they can be made as a separate component that can be joined or connected to the shaft 12 so as to be integral therewith.

[0048] The impeller 11 is, for example, of type that comprises a central element 23 (figs. 1 and 3) and a plurality of blades 22, for example 3, such as the one shown in fig. 1, made in a single body by injection molding of a thermoplastic material, for example as described in the aforementioned patent application for industrial invention that the Applicant has filed at the same time as the present application.

[0049] The impeller 11 also comprises a central element 23 (figs. 1 and from 3 to 7), for example consisting of a metal insert substantially shaped as a cylindrical bushing and provided with a cylindrical central through hole 24 (figs. from 3 to 7) coaxial to its own longitudinal axis X2 which, during use, is coinciding with the axis of rotation X1 of the shaft 12.

[0050] This central element 23 defines the second coupling means 14b.

[0051] In accordance with one aspect of the present invention, the central through hole 24 has a first internal diameter D3 slightly larger, of the order of microns, for example between about 20 µm and about 60 µm, than the second external diameter D2 so as not to come into contact, during use, with the second part 16 of the shaft 12, as will be described below. For example, in the embodiment disclosed here, the first internal diameter D3 can be between about 10 mm and 11 mm.

[0052] The central through hole 24 preferably has a circular section, although it is possible to provide a polygonal section with sizes and shape correlated to those of the second part 16 of the shaft 12, so as to allow an insertion therein substantially without contact on the lateral walls.

[0053] In accordance with one aspect of the present invention, a first conical flare 25 is created on a first end 26 of the central through hole 24 (fig. 7) having a second taper that forms a second angle α2 with the longitudinal axis X1, for example comprised between 10° and 30°. Advantageously, the second angle α2 is the same as the first angle α1, as can be seen in figs. 4 and 7.

[0054] Moreover, a second conical flare 27 is created on a second end 28 (fig. 7) of the central through hole 24, opposite the first end 26, having a third taper that forms a third angle α3 with the longitudinal axis X1, for example comprised between 30° and 60°. The third angle α3 can be the same as, or different from, the first two angles α1 and α2. In the embodiment shown here, the third angle α3 is greater than the first two angles α1 and α2.

[0055] The first conical flare 25 has a third external diameter D4 which can be either substantially the same as the first external diameter D1 or different therefrom, for example larger than the latter by at least a few tenths of a millimeter, for example about 0.2 mm, and which in the embodiment disclosed here can be about 12 mm.

[0056] The second conical flare 27 has a fourth external diameter D5, which in the embodiment disclosed here is larger than the third external diameter D4 and can be for example about 15 mm.

[0057] Some embodiments of the present invention can provide that the third external diameter D4 and the fourth external diameter D5 are the same as each other, especially when the third angle α3 is the same as the second angle α2.

[0058] The device 10 comprises centering means 29 (figs. 1, 3 and 4) which comprise a clamping element 30 (fig. 7) configured to be coupled to the terminal end 19, for example removably by means of a clamping screw 31 which is screwable into the threaded axial hole 20 thereof.

[0059] In accordance with one aspect of the present invention, the clamping element 30 comprises or consists of a washer 32, shaped so as to have an axial cavity 33 configured to accommodate the terminal end 19 with play.

[0060] The washer 32 comprises a second truncated conical part 35 having a fourth taper forming a fourth angle α4 with the axis of rotation X1, for example comprised between 30° and 60°, and configured to cooperate, during use, with the second conical flare 27 of the central element 23 and thus realize a shape coupling, that is, a coupling by contact. Advantageously, the fourth angle α4 is the same as the third angle α3.

[0061] The axial cavity 33 has a second internal diameter D6 slightly larger, of the order of microns, for example between about 20 µm and about 60 µm, than the second external diameter D2 of the second part 16. For example, in the embodiment disclosed here, the second internal diameter D6 is the same as the first internal diameter D3 of the central through hole 24, therefore it is also between about 10 mm and 11 mm.

[0062] Furthermore, the axial cavity 33 has a depth such that it is configured to never come into contact with the terminal end 19 of the second part 16 of the shaft 12 when the washer 32 is mounted thereon, as described below.

[0063] The washer 32 is also provided with an axial through hole 36 configured to allow the passage of the shank of the clamping screw 31 with play.

[0064] In particular, the washer 32 can comprise a first flat part 34 in which the axial through hole 36 is made, and the second truncated conical part 35 extends beyond the thickness of the flat part 34 in such a way that, when the truncated conical part 35 is in contact with the second conical flare 27, the flat part 34 always remains spaced apart from the terminal end 19 of the second part 16.

[0065] The washer 32 is U-shaped in section, wherein the axial through hole 36 is located on the bottom of the "U" shape and the ends of the arms of the "U" shape define the second truncate conical part 35.

[0066] The second truncated conical part 35 has a fifth external diameter D7, which can be either substantially the same as the fourth external diameter D5 of the second conical flare 27, or different from it, for example smaller than it, by at least a few tenths of a millimeter, for example about 0.2 mm. In the embodiment described here, the fifth external diameter D7 can be about 15 mm.

[0067] The fifth external diameter D7 can be the same as or larger than the fourth external diameter D5. In other words, the diameter D7 of the washer 36 can even be the same as, or larger than, the diameter D5 of the second flare 27, rather than smaller, as shown in the drawings.

[0068] Therefore, some embodiments of the present invention provide that the second angle α2 of the first conical flare 25 is the same as the first angle α1 of the first truncated conical part 17, and that the third angle α3 of the second conical flare 27 is the same as the fourth angle α4 of the second truncated conical part 35 of the washer 32. For example, the first angle α1 and the second angle α2 can be 25°, while the third angle α3 and the fourth angle α4 can be 45°. Other embodiments of the present invention provide that the four angles α1, α2, α3 and α4 are the same as each other.

[0069] The present invention also concerns the method for mounting the impeller 11 on the shaft 12 using the device 10 described above, so as to form the impeller assembly 40, which method essentially comprises the following steps.

[0070] First of all, the following are made in a manufacturing step: the central element 23, so that it comprises the central through hole 24 and the two conical flares 25 and 27, as well as the first truncated conical part 17 and the second part 16 of the shaft 12, and also the washer 32, as described above.

[0071] The method also comprises an assembly step in which the impeller 11 is coupled to the shaft 12; in particular, first the impeller 11 is displaced axially toward the first part 15 of the shaft 12 (to the left in figs. 1, 3 and 4), keeping the longitudinal axis X2 coinciding with the axis of rotation X1 and ensuring that the second part 16 is inserted into the central through hole 24 of the central element 23; then the impeller 11 is thrust further toward the first part 15 until the first conical flare 25 of the central element 23 is in contact with the first truncated conical part 17 of the shaft 12, where a first shape coupling is realized.

[0072] We must clarify that, thanks to the difference between the second external diameter D2 of the second part 16 of the shaft 12 and the first internal diameter D3 of the central through hole 24, a first circumferential play of a few tenths of a millimeter is created between them, which in the example given here can be between about 0.2 mm and 0.3 mm, which means that the impeller 11 can slide freely in an axial direction along the axis of rotation X1 without coming into contact with the second part 16 of the shaft 12.

[0073] A clamping step then follows, in which the washer 32 is mounted on the terminal end 19 of the second part 16 and is clamped thereon by screwing the clamping screw 31 into the threaded axial hole 20, until the second truncated conical part 35 of the washer 32 is in contact with the second conical flare 27 of the central element 23, where a second shape coupling is realized.

[0074] By firmly tightening the clamping screw 31, the impeller 11 is clamped onto the shaft 12, keeping the longitudinal axis X2 perfectly coinciding with the axis of rotation X1, without the circular surface of the central through hole 24 touching the shaft 12 anywhere.

[0075] Furthermore, we must clarify that, thanks to the difference between the second internal diameter D6 of the axial cavity 33 and the second external diameter D2 of the second part 16 of the shaft 12, a second circumferential play of a few tenths of a millimeter is created between them, which in the example given here is 0.3 mm. This means that, after the washer 32 has been clamped against the central element 23 of the impeller 11, the only parts that contact the latter are the first truncated conical part 17 of the shaft 12, whose function is to transmit the driving torque exerted by the shaft 12 to the central element 23, and the second truncated conical part 35 of the washer 32, screwed onto shaft 12, whose function is to clamp the central element 23 onto the latter, which parts contact the first conical flare 25 and the second conical flare 27, respectively, as if the central element 23 were gripped only between two conical jaws (16 and 35) coaxial to the axis of rotation X1, this because, thanks to the suitable depth of the axial cavity 33 of the washer 32, the flat part 34 of the latter remains spaced apart from the terminal end 19 of the second part 16 of the shaft 12.

[0076] In other words, the cylindrical surfaces of the washer 32 and the shaft 12 are coupled with play, therefore these surfaces do not touch each other and any deformations or manufacturing errors of the washer, which could compromise the coaxiality of the coupling between the impeller 11 and the shaft 12, do not have any effect on the terminal end 19 of the latter.

[0077] The lateral surfaces of the central element 23 and of shaft 12, that is, the internal surface of the central through hole 24 and the external surface of the second part 16, are also coupled with play, whereby the shaft 12 does not transmit the rotational torque to the central element 23 through these surfaces, and any small deformations of the central element 23 do not come into contact with the shaft 12, and therefore do not compromise the coaxiality of the coupling of the shaft 12 to the central element 23, and therefore to the entire impeller 11.

[0078] It is clear that modifications and / or additions of parts and / or steps may be made to the impeller assembly 40 and to the method as described heretofore, without thereby departing from the field and scope of the present invention, as defined by the attached claims.

[0079] It is also clear that, although the present invention has been described with reference to some specific examples, a person of skill in the art will be able to achieve other equivalent forms of impeller assembly and methods for mounting an impeller on the shaft of an electric motor, having the characteristics as set forth in the claims and hence all within the field of protection defined thereby.

[0080] In the following claims, the sole purpose of the references in brackets is to facilitate their reading and they must not be considered as restrictive factors with regard to the field of protection defined by the claims.

Examples

Embodiment Construction

[0036]With reference to figs. 1, 3 and 4, an impeller assembly 40 according to the present invention is described below, comprising an impeller 11, a shaft 12 of an electric motor 13, and a device 10 configured to mount the impeller 11 on the shaft 12.

[0037]For example, the impeller 11 is configured to be used in axial fans for heat pumps, air conditioners, such as the one shown schematically in fig. 2 and indicated generically with reference number 100, or ventilation systems. As an indication, to better frame the present invention, the weight of the impeller 11 can be comprised between 350 g and 1,000 g, and the mechanical torque transmitted to the impeller 11 by the shaft 12 can be of the order of 2.3 Nm.

[0038]The assembly 40 comprises first coupling means 14a integral with the drive shaft 12 and second coupling means 14b integral with the impeller 11.

[0039]The shaft 12 has an axis of rotation X1 (figs. from 1 to 4).

[0040]According to some embodiments, the shaft 12 comprises both...

Claims

1. Impeller assembly (40) comprising an impeller (11) having a longitudinal axis (X2), a shaft (12) of a motor (13) having an axis of rotation (X1) and a terminal end (19), and a device (10) for mounting said impeller (11) on said shaft (12), said impeller assembly (40) comprising first coupling means (14a) integral with said shaft (12) and comprising at least a first truncated conical part (17) having a first taper decreasing toward said terminal end (19) and second coupling means (14a) integral with said impeller (11) and comprising a central element (23) with a substantially tubular shape and provided with a central through hole (24) coaxial to said longitudinal axis (X2) and configured to receive said terminal end (19) with play, and also with a first conical flare (25) created on a first end (26) of said central through hole (24), and also with a second conical flare (27) created on a second end (28) of said central through hole (24), opposite said first end (26), characterized in that said device (10) comprises centering means (29) configured to be associated with said terminal end (19) and cooperate with said second conical flare (27) to axially thrust said first conical flare (25) against said first truncated conical part (17) in order to keep said impeller (11) clamped on said shaft (12) by means of a shape coupling, with said longitudinal axis (X2) coinciding with said axis of rotation (X1), wherein said centering means (29) comprise a clamping element (30) comprising, or consisting of, a washer (32) provided with an axial cavity (33) configured to accommodate said terminal end (19) with play and having a second truncated conical part (35) configured to be coupled to said second conical flare (27) by means of a shape coupling.

2. Impeller assembly (40) as in claim 1, characterized in that said washer (32) comprises a flat part (34) having a through axial hole (36) for the passage of a clamping screw (31) configured to screw into a threaded axial hole (20) of said terminal end (19), and said second truncated conical part (35) extends beyond said first flat part (34) laterally delimiting said axial cavity (33) in such a way that said first flat part (34) is spaced apart from said terminal end (19) when said second truncated conical part (35) is in contact with said second conical flare (27).

3. Impeller assembly (40) as in claim 2, characterized in that said washer (32) is U-shaped in section, wherein said axial through hole (36) is located on the bottom of the "U" shape and the ends of the arms of the "U" shape define said second truncated conical part (35).

4. Impeller assembly (40) as in one or the other of the previous claims, characterized in that said first truncated conical part (17) has a first taper forming a first angle (α1) with said axis of rotation (X1) and in that said first conical flare (25) has a second taper forming a second angle (α2), the same as said first angle (α1), with said longitudinal axis (X2).

5. Impeller assembly (40) as in claim 4, characterized in that said first and second angle (α1, α2) are comprised between 10° and 30°.

6. Impeller assembly (40) as in one or the other of the previous claims, characterized in that said second conical flare (27) has a third taper forming a third angle (α3) with said longitudinal axis (X2) and in that said second truncated conical part (35) has a fourth taper forming a fourth angle (α4), the same as said third angle (α3), with said longitudinal axis (X2).

7. Impeller assembly (40) as in claims 4 and 6 or 5 and 6, characterized in that said third angle (α3) is greater than said first and second angle (α1, α2).

8. Impeller assembly (40) as in claim 6 or 7, characterized in that said third angle (α3) is comprised between 30° and 60°.

9. Impeller assembly (40) as in any claim hereinbefore, characterized in that both said central through hole (24) and also said axial cavity (33) have a first internal diameter (D3) slightly larger than a second external diameter (D2) of said terminal end (19), of the order of micrometers, preferably between about 20 µm and about 60 µm, so as not to come into contact, during use, with the latter.

10. Method for mounting an impeller (11) on a shaft (12) of an electric motor (13), wherein said impeller (11) has a longitudinal axis (X2) and said shaft (12) has an axis of rotation (X1), and wherein said method comprises a first manufacturing step in which: a) said shaft (12) is made so that it comprises at least one terminal end (19) and a first truncated conical part (17) having a first taper decreasing toward said terminal end (19); and b) said impeller (11) is made so that it comprises a central element (23) with a substantially tubular shape and provided with a central through hole (24) coaxial to said longitudinal axis (X2), and also with a first conical flare (25) created on a first end (26) of said central through hole (24), and also with a second conical flare (27) created on a second end (28) of said central through hole (24), opposite said first end (26), and a second manufacturing step in which centering means (29) are made, configured to be associated with said terminal end (19) and cooperate with said second conical flare (27) of said central element (23), wherein said method provides to insert said terminal end (19) into said central through hole (24) with play, keeping said longitudinal axis (X2) coinciding with said axis of rotation (X1) until said first conical flare (25) of said central element (23) is in contact with said first truncated conical part (17) of said shaft (12), where a first shape coupling is realized, and subsequently to associate said centering means (29) with said terminal end (19) and to axially thrust said first conical flare (25) against said first truncated conical part (17) in order to keep said impeller (11) clamped onto said shaft (12) by means of a shape coupling, wherein said centering means (29) comprise a clamping element (30) comprising, or consisting of, a washer (32) provided with an axial cavity (33) configured to accommodate said terminal end (19) with play and having a second truncated conical part (35) configured to be coupled to said second conical flare (27) by means of a shape coupling.

11. Method as in claim 10, characterized in that said washer (32) is abutting only against said central element (23) and there are no contact points with said terminal end (19).

12. Method as in claim 10 or 11, characterized in that a threaded axial hole (20) is made on said terminal end (19), in that said centering means (29) also comprise a clamping screw (31) screwable into said threaded axial hole (20), and in that it comprises a clamping step in which said washer (32) is clamped on said terminal end (19) by screwing said clamping screw (31) into said threaded axial hole (20) until said second truncated conical part (35) is in contact with said second conical flare (27) of said central element (23), where a second shape coupling is realized.

13. Method as in claim 12, characterized in that said washer (32) comprises a flat part (34) having a through axial hole (36) for the passage of said clamping screw (31), and said second truncated conical part (35) extends beyond said first flat part (34) laterally delimiting said axial cavity (33) so that, when said second truncated conical part (35) is in contact with said second conical flare (27), said first flat part (34) is spaced apart from said terminal end (19).

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