WO2009144171A1

WO2009144171A1 - Improved electric motor

Info

Publication number: WO2009144171A1
Application number: PCT/EP2009/056221
Authority: WO
Inventors: Antonio Ranalli; Rosalino Usci; Michele Marcantoni
Original assignee: Ln 2 S.R.L. A Socio Unico
Priority date: 2008-05-30
Filing date: 2009-05-22
Publication date: 2009-12-03
Also published as: ITPD20080158A1

Abstract

An electric motor comprises a rotor assembly (2) fixed for rotation with a motor shaft(3), the shaft being supported by rotational support means(4, 5)arranged at axially opposite ends of the rotor, a stator assembly(6) including a first portion (6a) comprising ferromagnetic plates (7) and a second portion (6b) comprising windings (8) of electrically conductive wire, and an element (9) made of electrically insulating material interposed between the first and second portions (6a, 6b) of the stator assembly. The insulating material comprises a casing having respective seats (14, 15) for housing the rotational support means (4, 5) for the shaft for the consequent axial restraint of the motor shaft (3) and relative clamping of the stator assembly(6).

Description

Improved electric motor

Technical field

The present invention relates to an electric motor having the characteristics set out in the preamble to the main claim. Technological background

In the relevant technical field, the stator assembly of the motor is typically supported between a pair of opposed caps in which central seats are provided for housing rolling-contact bearings or bushings for supporting the shaft, onto which the rotor assembly of the motor is keyed. The above-mentioned stator assembly typically has a laminated structure formed by a plurality of superimposed plates that are typically ring-shaped with toothed appendages which project radially inwardly and on which the copper stator windings are mounted. An electrical insulator in the form of a cage or casing otherwise known by the term "cartridge" is conventionally provided between the plates and the copper windings. The function of this element is mainly to ensure adequate electrical insulation. The opposed caps which support the shaft are also held together axially by means of clamping screws which extend axially between them and have the function of fastening the stator plates as an assembly by clamping the caps to one another.

Description of the invention

A main object of the present invention is to provide an electric motor which has a simplified structure in comparison with the solutions of the prior art, facilitating assembly and reducing the number of components, in particular without the need for screws for clamping the caps, resulting in greater compactness and reduced production costs.

This and other objects which will become clearer from the following description are achieved by the invention by means of an electric motor formed in accordance with the appended claims. Brief description of the drawings

Further characteristics and advantages of the invention will become clearer from the following detailed description of some preferred embodiments thereof which are described, by way of non-limiting example, with reference to the appended drawings, in which : Figure 1 is a perspective view of an embodiment of the electric motor formed in accordance with the present invention, Figure 2 is an exploded, perspective view of the motor of Figure 1, Figure 3 is an axial section through the motor of the preceding drawings, Figure 4 is a perspective view of a detail of the motor of the preceding drawings,

Figure 4A is a view corresponding to that of Figure 1, of a second embodiment of a detail of the invention,

Figure 5 is a perspective view of the motor of the preceding drawings with a variant of the detail of Figure 4, Figure 6 is a perspective view of the variant of the detail of Figure 5,

Figures 7, 8 and 9 are partially sectioned schematic views of respective further variants of a detail of the motor of the preceding drawings, and Figures 10, 11 and 12 are views corresponding to that of Figure 9 of further alternative variants of details of the present invention. Preferred embodiments of the invention With reference to the drawings mentioned, an electric motor formed in accordance with the present invention is generally indicated 1 and comprises a rotor assembly 2 fixed for rotation with the motor shaft 3 the axis of which is indicated X. Moreover, the motor shaft 3 is supported for rotation about the axis X at axially opposite ends of the rotor assembly 2 by a pair of rotational support means indicated 4 and 5, respectively. A stator assembly of the motor, indicated 6, includes a first portion 6a comprising ferromagnetic plates 7 and a second portion 6b comprising windings 8 of electrically conductive wire. The plates 7 are shaped as rings having four teeth 7a which extend radially towards the axis X and are arranged at regular angular intervals, each corresponding winding 8 of the stator portion being wound around a respective tooth 7a. An element, generally indicated 9, made of electrically insulating material, is interposed between the first and second portions 6a, 6b of the stator assembly and is formed as a type of casing having structural characteristics in addition to the functional characteristics of an electrical insulator, as will be explained further in the following description. More particularly, the casing 9 comprises a ring 10 from which radial portions 11 extend towards the axis X, each portion having a central opening 12 which can house the corresponding tooth 7a of the respective plate connected thereto. The electrically conductive wire of the corresponding winding 8 is wound onto the outer lateral surface of each portion 11, thus ensuring electrical insulation between the stator portions 6a, 6b. According to a principal characteristic of the invention, the casing 9 comprises a pair of seats 14, 15 for housing respective rotational support means 4, 5 for the shaft, for the consequent axial restraint of the motor shaft 3 and relative clamping of the stator assembly 2, as will be explained in detail below.

A pair of appendages 16, 17, which are integral with the casing, extend at the free end of each portion 11 of the casing, on axially opposite sides of the corresponding opening 12. With reference to Figure 4, the group formed by the four appendages 16 defines the seat 14 for housing one of the support means and the group of four appendages 17 defines the seat 15 of the other support means. In particular, each appendage 16, 17 has a circular surface profile concentric with the axis X. It should also be noted that the appendages of each of the above-mentioned groups are arranged at regular angular intervals with respect to the axis X.

The surface profiles of each group of appendages 16, 17 define respective portions 16a, 17a of a respective cylindrical surface suitable for being engaged by a respective annular support element 18, 19 of the respective support means with a form fit between the surfaces that are in mutual engagement.

Each annular element 18, 19 comprises an outer cylindrical skirt 18a, 19a which can be housed and restrained in the respective seat 14, 15 and a respective cylindrical central cavity 18b, 19b, which is coaxial with the axis X and constitutes a seat for housing a corresponding bearing 20, 21. The respective annular support element 18, 19 is clamped axially and radially in the corresponding seat 14, 15 by a restrained coupling arrangement, preferably a releasable restrained coupling arrangement, which is constituted, for example, by an interference fit between respective coupled surfaces in which the elements 18, 19 are restrained axially and radially in their respective seats by virtue of the surface friction between the surfaces 16a, 17a and the corresponding cylindrical surfaces 18a, 19a which are in mutual contact. As an alternative to coupling purely by interference, restraining means with mechanical stop elements may be provided, for example, by the provision of respective projections or teeth 16b, 17b which extend from the corresponding appendages 16, 17 and have respective end edges that project radially so as to constitute axial abutments for the annular element 18, 19 when it is housed in the corresponding seat 14, 15. Figure 10 shows schematically an embodiment in which the tooth 16b, 17b is arranged for the axial restraint of the respective annular element 18, 19. Figure 11 shows a variant in which the teeth 16b, 17b are arranged for engaging respective seats 18c, 19c formed in the outer skirt of the annular element 18, 19. These seats, which are formed as blind cavities, can be engaged by the corresponding teeth by a snap-fit. The tooth or projection may also be formed as a projection from the outer skirt of the annular element 18, 19, with the corresponding engagement seat provided in the appendage 16, 17, for example, in accordance with the configuration shown in Figure 12.

As a further alternative, combinations of the above-described restraining systems are also possible, for example, the provision of stop teeth may be combined with an interference fit. Figure 4A shows a further embodiment of the invention in which each seat 14, 15 has a configuration with a polygonal profile, in particular, a quadrilateral profile, the sides of the seats being defined by portions 16a, 17a that are formed as flat surfaces. In this case, the outer skirt of the annular element 18, 19 has a corresponding polygonal profile in which flat surface portions are formed in the surfaces for coupling with the appendages 16, 17. The configuration with a polygonal rather than a circular profile of the seats 14, 15 can also act as a means for preventing rotation of the annular element 18, 19 relative to the respective housing seat 14, 15. In this case, the radial and axial restraint of the annular element in its respective seat is facilitated by the presence of the polygonal coupling surface profile. In a preferred embodiment of the motor, the rotational support means 4, 5 comprise respective rolling-contact bearings 20, 21 each of which is provided with a respective outer race 20a, 21a and a respective inner race 20b, 21b with corresponding rolling bodies 22 (balls or rollers) interposed between the inner and outer races.

In this application with rolling-contact bearings, the outer race of each bearing is arranged to be housed and restrained in the corresponding central seat 18b, 19b of the respective annular support element 18, 19, and the inner race is keyed onto the motor shaft.

Alternatively, sliding friction bearings may be provided, for example, in the form of sliding bushings housed and restrained in the central seats provided in the respective annular support elements. It should be noted in particular that the insulating casing 9 performs a load- bearing function in the motor since the seats 14, 15 for housing the supports of the motor by means of a restrained coupling arrangement such as to ensure relative clamping between the stator assembly and the motor shaft are formed in the casing itself and consequently without the need to provide other, auxiliary axial clamping means (for example, of the screw type as provided in solutions of the prior art). It should also be noted that the number of components required for the assembly of the motor is reduced, making its structure simpler and more compact. In a preferred embodiment of the invention in which rolling-contact bearings 20, 21, in particular bearings with balls or tapered rollers, are provided for supporting the motor, the two bearings 20, 21 are mounted with an "O"-shaped mounting configuration with the respective inner races of the bearings keyed with pressure onto the shaft, in which the centres of gravity are shown in Figure 3. With an "O"-shaped mounting configuration of this type, in contrast with the alternative, "X"-shaped configuration of known solutions, the motor shaft itself axially restrains and holds together the stator assembly 2, the pair of opposed annular support elements 18, 19, and the insulating housing 9. This configuration thus avoids the provision of axial clamping screws of the type provided in motors of conventional design, with the further advantage of reducing the weight of the parts of the motor as a whole.

According to another characteristic of the invention, the annular support elements 18, 19 comprise means for self-alignment with the axis X of the motor. With reference to Figure 7, the self-alignment means comprise, in a first embodiment, a ring 25 of resiliently yielding material, for example, elastomeric material, which can be interposed between the bearing 20, 21 and the corresponding annular support element 18, 19. With reference to Figure 8, in a variant, the self-alignment means comprise localized portions 26 of the annular support element which have different resilience characteristics in the axial and/or radial direction, in comparison with the rest of the support element.

With reference to Figure 9, in a further variant, the self-alignment means comprise a first, tapered profile 27 formed on the surfaces 16a, 17a of the appendages 16, 17 which define the respective seats 14, 15 of the corresponding annular support elements 18, 19 and a second, spherical profile 28 formed on the outer skirt of the annular element 18, 19. The tapered and spherical profiles are in mutual engagement with surface coupling when the annular support element 18, 19 is housed in its corresponding seat 14, 15 of the casing 9, permitting the self-alignment relative movement.

In a further embodiment of the invention, illustrated in Figures 5 and 6, the casing 9 comprises a plurality of pin-like elements 29 for the fixing of other accessories such as, for example, electronic control boards or other components to the motor unit, these attachment elements being produced integrally with the casing and projecting axially and/or radially from the ring 10.

Moreover, appendages, indicated 30, which project radially from the ring 10 of the casing 9, have seats 30a with open circular profiles for the mounting and restraint of vibration-damping elements, not shown. These appendages, of which there are preferably three, are produced integrally with the casing, as shown clearly in Figure 6. A preferred configuration provides for the formation of three appendages 30, spaced apart at angular intervals of 120° , and three pin-like elements all of which extend from the ring 20 in the same direction, parallel to the axis X, and are arranged in positions adjacent the corresponding appendages; these elements are consequently also arranged at regular angular intervals. The appendages 30 and the pin-shaped elements 29 may advantageously be produced integrally with the casing 9 by injection moulding of the casing 9. When, for reasons connected with the moulding process, the casing has to be produced in at least two separate and interconnectible parts, the appendages 30 and the elements 29 are produced integrally with one or other of the parts that form the casing. The invention thus achieves the objects proposed, affording the above- described advantages over known solutions.

Claims

1. An electric motor of the type comprising :

- a rotor assembly (2) fixed for rotation with a motor shaft (3), the shaft being supported by rotational support means (4, 5) arranged at axially opposite ends of the rotor,

- a stator assembly (6) including a first portion (6a) comprising ferromagnetic plates (7) and a second portion (6b) comprising windings (8) of electrically conductive wire,

- an element (9) made of electrically insulating material interposed between the first and second portions (6a, 6b) of the stator assembly, characterized in that the element (9) made of insulating material comprises a casing having respective seats (14, 15) for housing the rotational support means (4, 5) for the shaft (3) for the consequent axial restraint of the motor shaft and relative clamping of the stator assembly (6).

2. A motor according to Claim 1 in which the casing comprises, for each rotational support means (4, 5), a plurality of appendages (16, 17) which are spaced apart angularly with respect to the axis of the motor shaft (3) and between which the corresponding rotational support means (4, 5) for the shaft (3) can be housed and restrained.

3. A motor according to Claim 2 in which the appendages (16, 17) of the plurality extend radially in the region of respective radial teeth (7a) of the first stator portion (6a), around which teeth the windings (8) of conductive wire of the second stator portion (6b) are wound.

4. A motor according to any one of the preceding claims in which each of the appendages (16, 17) has a circular surface profile which is concentric with the motor axis and is capable of surface coupling with an outer cylindrical skirt (18a, 19a) of the rotational support means (4, 5) for the shaft (3).

5. A motor according to Claim 4 in which the appendages (16, 17) extend at the respective free ends of corresponding radial portions (11) of the casing extending in the region of the teeth (7a) of the plate portion of the stator assembly (6).

6. A motor according to any one of the preceding claims in which the coupling of the rotational support means (4, 5) with the seats (14, 15) is of the restrained type.

7. A motor according to Claim 6 in which the restrained coupling is of the releasable type.

8. A motor according to any one of the preceding claims in which each of the rotational support means (4, 5) comprises an annular element (18, 19) which can be housed and restrained in the corresponding seat (14, 15) of the casing, the element comprising a respective second central seat (18b, 19b) for housing a respective bearing (20, 21) for the rotational support of the shaft (3).

9. A motor according to Claim 8 in which the bearing (20, 21) is of the rolling-contact friction type with a pair of races comprising an outer race

(20a, 21a) and an inner race (20b, 21b) between which the rolling bodies (22) of the bearing (20, 21) are mounted, the outer race being capable of being housed and restrained in the corresponding seat (18b, 19b) of the annular element (18, 19) defined by the respective appendages (16, 17) of the casing.

10. A motor according to Claim 8 in which the bearing is of the sliding friction type with sliding bushing bodies which can be housed and restrained in the central seat (18b, 19b) of the annular element.

11. A motor according to Claim 9 or Claim 10 in which the annular element (18, 19) comprises an outer cylindrical skirt (18a, 19a) which can be housed in the corresponding seat of the casing, engaging the circular- profiled surfaces of the appendages (16, 17), for the restraint of the annular element relative to the casing.

12. A motor according to Claim 9 in which the pair of rolling-contact bearings (20, 21) which are provided at the opposite ends of the rotor are mounted on the motor shaft with an "O"-shaped mounting configuration, with the respective inner races (20b, 21b) of the bearings keyed with pressure onto the shaft so that, with the said mounting configuration of the bearings, the motor shaft restrains axially and holds together the stator assembly (6), the pair of annular elements (18, 19) of the support means, and the casing (9).

13. A motor according to any one of the preceding claims in which the annular elements (18, 19) which are interposed between the casing of the insulating element and the corresponding support bearing for the motor shaft comprise means for self-alignment with the motor shaft as a result of the mounting in the casing.

14. A motor according to Claim 13 in which the self-alignment means comprise a ring (25) of resiliently yielding material which can be interposed between the bearing (20, 21) and the annular element (18, 19) having the seat for housing the bearing.

15. A motor according to Claim 13 in which the self-alignment means comprise portions (26) of the annular element (18, 19) having different resilience characteristics in the radial and axial directions.

16. A motor according to Claim 13 in which the self-alignment means comprise a first, tapered profile (27) formed on the surface portions of the appendages (16, 17) of the casing defining the seat (14, 15) for housing the annular element (18, 19) and a second, spherical profile (28) formed on the outer skirt of the annular element (18, 19), the said profiles being capable of mutual engagement during the fitting of the annular element in the corresponding seat of the casing.

17. A motor according to one or more of the preceding claims in which one or more support elements (29) are provided for the motor, extending from the casing of the insulating element.

18. A motor according to Claim 17 in which the support elements (29) are formed integrally with the casing.

19. A motor according to one or more of the preceding claims in which one or more appendages (30) are provided, projecting from the casing (9) and having seats (30a) for the mounting and restraint of vibration-damping elements.

20. A motor according to Claim 19 in which the appendages (30) are produced integrally with the casing.