ELECTRIC MOTOR, PARTICULARLY FOR LAUNDRY WASHING MACHINES

Abstract: An electric motor for laundry washing machines, compris­ ing a hollow stator made of a ferromagnetic material and pro­ vided with a wire winding, and a rotor keyed onto a shaft for ro­ tation within said stator, to which it is connected by means of two supports press-fitted into interior rim portions of the stator at opposite ends thereof and carrying respective bearings. The bearings are retained in position of the shaft by the hub sleeves of respective blower wheels keyed onto the shaft. The motor according to the invention is composed of a reduced number of structural components without the use of additional connecting and fastening elements for the func­ tional components.

Description: Description The present invention relates to an electric induction motor adapted to be employed in particular for rotating the drum of a laundry washing machine with the intermediate of a belt transmission. Electric motors employed for this purpose usually have a hollow stator formed of a stack of laminations of a ferromagnetic material and provided with a copper wire winding, and a rotor, likewise made of a ferromagnetic material, fixedly secured to a shaft mounted by means of suitable bearings for rotation in a pair of electrically insulated end plates secured to a housing enclosing the stator. The mounting of the end plates, and thus in fact the final assembly of the motor is accomplished by means of tension bolts, by welting the rim of the housing over the peripheral edges of the end plates, or by welding along the outer periphery of the stator. A motor of this type requires adequate cooling for dissipating the#heat developed in operation, to which purpose it is provided with at least one blower wheel mounted on the rotor shaft. Motors of conventional type are usually provided with two such blower wheels disposed one at each end of the motor inwards of the rotor bearings, the latter being located outwards of the stator winding. These motors suffer from various shortcomings in that they are composed of numerous components requiring complicated and thus costly processing while resulting in excessive axial dimensions, whereby the mounting of such a motor in the confined space of a laundry washing machine is rendered difficult. In addition, the disposition of the various components in the axial direction calls for a relatively long shaft which has to have a relatively large diameter for avoiding the occurrence of bending during its rotation: this again requires the bearings to be overdimensioned. Also to be noted are the problems encountered with regard to the centering of the end plates relative to the housing for ensuring a uniform and constant gap between the stator and the rotor, on which the noise level of the motor depends. An improvement proposed for eliminating at least part of the noted shortcomings provides the mounting of the two shaft supports on the inner rim portions of the stator, and the mounting of the two cooling blower wheels on the end portions of the shaft outwards of the shaft supports (Italian Patent 869,350). This solution results in certain advantages, such as in the reduction of the shaft diameter (because the shaft supports are closer to one another) and thus of the bearing dimensions, and in an improvement of the ventilation, as the blower wheels may be disposed closer to the stator winding. This solution does not, however, really solve the problem of the overall axial dimensions of the motor, and does on the other-hand result in an even more complicated construction of the motor. As a matter of fact, the mounting of the bearing supports in or on the stator requires the employ of bolts extending at right angles to the axis of the motor. This necessitates the formation of holes in the stator with the resultant reduction of the amount of iron therein, and the employ of additional elements (bolts and nuts) which render the centering of the rotor for maintaining a uniform gap between it and the stator even more difficult. It would thus be desirable, and is an object of the present invention, to reduce the structural components of a motor of this type to a minimum, and to eliminate the necessity of employing any additional connecting or fastening elements for the essential functional components of the motor. This would permit an extremely compact construct ion of the motor, and a drastic reduction (by about 50%) of the length of the shaft and of the total weight of the motor, with the resultant advantages regarding the construction and operation of the motor and the mounting of the motor in a laundry washing machine. This object has been found to be attainable by the construction of an electric motor according to the invention without the employ of end plates, a housing, and the mentioned tension bolts, a motor of this type having been found in practical experiments to show all of the performance characteristics of a comparable conventional motor. The solution proposed herein has additionally been found to be extremely suitable for completely automatized assembly of the motor so as to ensure constant quality and reliability of the product. According to the invention, an electric motor comprises a hollow stator formed of a stack of laminations of a ferromagnetic material and provided with a copper wire winding, and a rotor, likewise of a ferromagnetic material, mounted for rotation within the stator and keyed to a shaft carrying two cooling blower wheels and a pulley for the engagement of a belt connecting it to the shaft of the drum of a laundry washing machine. This motor is characterized in that the shaft is mounted for roation in bearings fixedly secured to respective supports clampingly retained by inner edge portions of the stator at opposite sides thereof, and in that the bearings are retained in position on the shaft by a hub sleeve of one blower wheel and by a hub sleeve of the pulley, respectively, said pulley hub sleeve carrying the second blower wheel, both said hub sleeves being keyed onto the shaft so as to abut the inner race of the respective bearing. The bearing supports may be integrally formed with hoods or shrouds for the protection of the stator winding. The advantages and characteristics of the invention will become more clearly evident from the following description, given by way of example with reference to the accompanying drawings, wherein: fig. 1 shows a partially sectioned elevational view of a motor according to the invention,, with a partic ular detail shown on an enlarged scale, and fig. 2 shows a partially sectioned elevational view of a modified embodiment of the motor of fig. 1, with a specific detail shown on an enlarged scale. As shown in the drawings, the electric motor according to the invention comprises a hollow stator 11 formed of a stack 12 of laminations of a ferromagnetic material and provided with a winding 13 of suitably insulated copper wire, and a rotor 14 likewise of a ferromagnetic material and mounted for rotation in the hollow interior of stator 11. Rotor 14 is keyed onto a shaft 16 provided with a fluted surface portion 17 for this purpose. Mounted on shaft 16 at both Srldes of rotor stack 14 are bearings 18 retained in disk-shaped bearing supports 20, each of which is formed with a circumferentially extending arrangement of lightening and ventilation holes 22. Each bearing support with its respective bearing forms a unitary structural element which may be preassembled to facilitate final assembly of the motor. The outer peripheral rim portion 23 of bearing supports 20 is conveniently formed with a stepped profile, permitting the bearing support to be clampingly retained in a press fit by the corresponding inner rim portion 24 of the stator lamination stack 12.For accommodating this press fit mounting, the rotor has its outer peripheral edge 21 likewise formed as a stepped profile. In a preferred embodiment of the motor according to the in vention as shown in fig. 1, each support 20 is integrally formed with a hood 25 for the protection of the stator winding 13. Mounted on shaft 16 axially outwards of each bearingsupport subassembly are two blower wheels 26 each having a hub sleeve 27 keyed onto a respective fluted portion 28 of the shaft in a press fit. The inner end of each hub sleeve 27 is in abutment with the inner race of the respective bearing 18, so as to retain it in position on shaft 16. As shown in fig. 1, a pulley 29 for engagement with a transmission belt connecting it to a pulley on the shaft of the drum of the laundry washing machine (not shown) is integrally connected as by compression welding to the hub sleeve 27 of the respective blower wheel 26. In an alternative embodiment of the invention shown in fig. 2, each blower wheel 26 is integrally formed with a hood or shroud 30 for the protection of the stator winding 13. The hoods 30 thus perform the same function as the hoods or shrouds 25 shown in fig. 1. The descriebd motor has been found to be perfectly suitable for a completely automatized assembly operation. In a first step of such assembly operation, the stator is aligned in an assembly station. Subsequently one of the bearing supports with the respective bearing mounted therein is applied to the stator so as to seat on the inner peripheral edge thereof. This is followed by the insertion of the shaft with the rotor already mounted thereon, and by slipping the second support with its bearing onto the shaft so as to seat on the respective inner rim portion of the stator. Subsequently the hub sleeves with the respective blower wheels mounted thereon and with the pulley mounted on one of them are slipped onto the end portions of the shaft, whereupon the assembly operation is finished by the exertion of an axial compressive force on the various structural components. It is readily seen that all of these operations can be carried out by automatized equipment operating at a preestablished sequence, the assembly being carried out with an extremely reduced number of preassembled components and without the need for any supplementary fastener elements. The thus constructed motor has drastically reduced axial dimensions, because the supports of the shaft are located at the smallest possible distance from one another. This construction also results in a reduction of the weight of the motor, as there is no need for a housing, end plates, and tension bolts, whereby to ensure an improved centering and equilibration of the rotor. These characteristics result in further advantages with regard to the magnetic noise generation, to the performance of the motor, and to its mounting in a laundry washing machine.

Claims: Electric Motor, Particularly for Laundry Washing Machines Patent Claims 1. An electric motor, particularly for laundry washing machines, comprising a hollow stator formed of a stack of laminations of a ferromagnetic material and provided with a copper wire winding, and a rotor, likewise of a ferromagnetic material, mounted for rotation within said stator and keyed to a shaft carrying two cooling blower wheels and a pulley for the engagement of a belt connecting it to the shaft of the drum of the laundry washing machine, said motor being characterized in that said shaft (16) is mounted for rotation in bearings (18) fixedly secured to respective supports (20) clampingly retained by inner edge portions of said stator (11) at opposite sides thereof, and in that said bearings (18) are retained in position on said shaft (16) by a hub sleeve (27) of one blower wheel (26) and by a hub sleeve (27) of said pulley (29), respectively, said pulley hub sleeve carrying the second blower wheel (26), both said hub sleeves (27) being keyed onto said shaft (16) so as to abut the inner race of the respective bearing (18). 2. An electric motor according to claim 1, characterized in that the outer peripheral rim (23) of each bearing support (20) and the corresponding outer rim (21) of said rotor (14) are formed with stepped surfaces. 3. An electric motor according to claim 1, characterized in that said bearing supports (20) are formed with lightening and ventilating bores (22), and that a protecting hood (25) for the stator winding (13) is integrally formed with each bearing support (20). 4. An electric motor according to claim 1, characterized in that a protection hood (30) for the stator winding (13) is integrally formed with each blower wheel (26). 5. An electric motor according to claim 1, characterized in that each blower wheel (26) is formed integrally with its respective hub sleeve (27), and that said pulley (29) is likewise integrally formed integrally with the respective hub sleeve (27). 6. An electric motor according to claim 1, characterized in that said shaft (16) is formed with fluted surfaces at the locations (17, 28) whereat said rotor (14) and said hub sleeves (27) of said blower wheels (26) are keyed thereonto.

Inventors: ROSSI, LUIGI
Applicants: SOLE S.P.A.
Application year: 1985
Main classification: H02K5
IPC codes: H02K9, H02K5, H02K7