EP3067457B1

EP3067457B1 - Washing machine with direct drive motor and method for its manufacturing

Info

Publication number: EP3067457B1
Application number: EP15158899.3A
Authority: EP
Inventors: Dusan Heldak; Crescenzo Iannicelli; Peter Mihalka; Vladimir Olejar; Vaclav Petracek; Pavol Vasko
Original assignee: Whirlpool Corp
Current assignee: Whirlpool Corp
Priority date: 2015-03-12
Filing date: 2015-03-12
Publication date: 2018-05-30
Anticipated expiration: 2035-03-12
Also published as: EP3067457A1; US20160265151A1

Description

The present invention relates to a washing machine with a direct drive motor system comprising a tub, a drum rotatably mounted inside the tub, and a shaft connected to the drum for transmitting a driving torque of said direct drive motor system, this latter comprising a rotor assembly fastened to the shaft and a stator fastened to the tub.
Such known solution has the problem of a high precision alignment between the stator and the rotor, such alignment being required for guaranteeing proper air gap between rotor magnets and stator coils. Since the rotor and the stator are fastened to different components and to different areas of the rear wall of the tub, proper centering is of paramount importance for a correct working of the direct drive motor system.
Existing solutions for solving the above centering problem comprise a stator centering (before final fastening) on plastic pins provided "ad hoc" on the tub like e.g. the driving apparatus for washing machines described in document WO2006083083 , a stator centering on a cylindrical reworked metal hub surface, or a stator centering on metal pins provided on the metal hub. All the above solutions require special features for guaranteeing a proper centering, which increase the overall cost of the appliance and the complexity of the assembly thereof.
EP 2626459 discloses a washing machine having a direct drive motor where the stator comprises fixing pins inserted into the rear wall of the tub. The use of pins and holes make the overall construction of the washing machine more complex.
EP 1580311 discloses a direct drive motor where the stator is centered by means of a cylindrical or conical protuberance which enters the bearing hole which is precisely machined in order to seat ball bearings. This known solution requires to reduce the axial distance of the ball bearings, with a direct impact on the rigidity of the drum shaft support, or to increase the axial dimension of the central portion of the bearing spider. Moreover the solution disclosed by EP 1580311 is not for washing machine having a plastic tub, since it is clearly fit for washing machines having a metal tub.
DE 10060940 discloses a washing machine which, similarly to EP 1580311 , uses a metal bearing spider which cooperates with an axial protrusion of the stator during reciprocal engagement. Metal surface of the bearing spider has to be precisely machined in order to properly centering the stator.
Document WO2008099551 discloses a motor unit for a washing machine with a body having a rotating shaft, a stator holding part to be mounted on the washing machine body, a stator and a rotor, wherein the stator and the rotor are assembled first, the rotor is then mounted on the rotating shaft and the stator is finally mounted on the stator holding part.
It is therefore an object of the present invention to provide a washing machine which does not present the above technical problems and which has a low cost and a simple assembly of its components, particularly of its direct drive motor system, without requiring pins, removable adapters or any machining of the coupling surfaces.
The above object is reached thanks to the features listed in the appended claims.
According to the invention, the plastic tub comprises a central axially protruding portion where a central opening of the stator is centered before its final fastening to the tub.
The applicant has discovered that by injecting plastic material of the tub in a central zone thereof, particularly in a central zone of the rear wall of the tub, such central zone can maintain very strict dimensional tolerances which allows a precise centering of the stator, without any need of auxiliary centering pins or reworking of coupling metal surfaces. Such solution is therefore very simple and allow to obtain a high precision in the centering process while, at the same time, maintain the use of a plastic tub with related advantages in terms of cost and productivity. The applicant believes that such high precision is mainly due to the molding condition of the central zone of the tub, with high pressure and temperature which overcome problems of defects and shrinkage. Such degree of precision of the central part of the molded drum is identical or similar to the precision of machined metal surfaces. Moreover such precision is maintained even if the tub is stored in environment where the metal machined surface could be affected by corrosion or the like.
Preferably the centering of the stator on the tub is made by using only specific centering surfaces of the stator provided on the edge of the central opening used for its assembly to the protruding portion of the tub.
According to the invention, the plastic tub presents a rear wall in which a metal reinforcing element is embedded, i.e. co-injected. This increases the overall rigidity of the tub. Such metal reinforcing element forms also the central metal hub for mounting the bearings.
Further advantages and features according to the present invention will be clear from the following detailed description, with reference to the attached drawings in which:

figure 1 is a cross longitudinal section of the rear wall of a tub of a washing machine according to the invention, in which the direct drive motor system is installed,
figure 2 is an enlarged detail of figure 1, and
figure 3 is a detail of a front view of the rear wall of the tub, where the rotor has been removed.

With reference to the drawings, a direct drive washing machine comprises a plastic tub 10 whose rear wall 10a presents a reinforcing star-shaped metal element 12 which forms also a central hub 12a for mounting ball bearings 14. Such bearings 14 are used supporting a shaft 16 supporting a drum 18.
According to the invention, the rear wall 10a of the plastic tub 10 presents an axial rear protrusion 20 having a first portion 20a slightly tapered and a second portion 20b which is cylindrical and whose diameter corresponds exactly to the diameter of a circumference defined by three centering curved surfaces 22 formed on an edge 22a of a central hole of a stator 24.
On one end 16a of the shaft 16 opposite the drum 18 a cup-shaped rotor 26 is mounted.
In order to mount the stator 24 in a correct angular position on the tub 10, the rear wall 10a of the tub presents, on its axial protrusion 20 a radial extension 28 (figure 3) which corresponds to a radial seat 30 of the stator 24.
When the direct drive motor is assembled to the tub 10, first step is to insert the stator 24 on the axial protrusion 20 of the tub, so that centering surfaces 22 slide first on the tapered portion 20a for a pre-centering operation and then it slides on a cylindrical smooth surface 21 of a portion 20b for a final centering operation, such movement ending when the stator 24 abuts the rear wall 10a of the tub 10. Then the stator 24, perfectly centered on the tub 10, is fixed in a known way by means of screws 32.
Next and final step is to install the rotor 26 on the end 16a of the shaft 16.
In order to allow a precise dimension of the axial protrusion 20 of the tub 10, particularly of the plastic portion A which covers the metal hub 12a, it is important that, whatever polymeric material is used in the injection molding process, the injection point or points is placed very close to A in order to get rid of any shrinkage effect or any surface defects.

Claims

A washing machine with a direct drive motor system comprising a plastic tub (10, 10a) with a rear wall (10a) comprising a reinforcing star-shaped metal element (12), a drum (18) rotatably mounted inside the tub (10, 10a) and a shaft (16) connected to the drum (18) for transmitting a driving torque of a direct drive motor, the star-shaped metal element (12) forming a central hub (12a) configured for mounting bearings (14) for the shaft (16), said motor comprising a rotor assembly (26) fastened to the shaft (16) and a stator assembly (24) fastened to the tub (10, 10a), characterized in that the plastic tub (10) comprises a central axial rear protruding portion (20) formed by an outer plastic shell co-injected onto at least the central hub (12a) of the reinforcing star-shaped metal element (12), said central axial rear protruding portion (20) being configured for centering a central opening of the stator assembly (24) with the tub by axially sliding the stator assembly (24) on the central axial rear portion (20) before fastening of the stator assembly (24) to the tub (10, 10a).
Washing machine according to claim 1, wherein said central protruding portion (20) of the tub (10, 10a) comprises a tapered part (20a) for pre-centering the stator assembly (24) and a cylindrical portion (20b) for centering the stator assembly (24).
Washing machine according to claim 1 or 2, wherein in the metal hub (12a) ball bearings (14) are mounted.
Washing machine according to any of the preceding claims, wherein the stator assembly (24) is fixed to the tub (10, 10a) by means of screws (32) parallel to the shaft (16).
Washing machine according to claim 4, wherein said screws (32) are fastened to the metal hub (12a).
Washing machine according to any of the preceding claims, wherein said central protruding portion (20) comprises at least one radial extension (28) configured to cooperate with a corresponding seat (30) obtained on the stator assembly (24) for assuring a predetermined angular position of the stator assembly (24) with reference to the tub (10, 10a).
Washing machine according to any of the preceding claims, wherein the central opening of the stator assembly (24) has a plurality of centering surfaces (22) configured to cooperate with an outer cylindrical surface (21) of the central protruding portion (20) of the tub (10, 10a).
Method for producing a washing machine with a direct drive motor system comprising a plastic tub (10, 10a) with a rear wall comprising a reinforcing star-shaped metal element (12), a drum (18) rotatably mounted inside the tub (10, 10a) and a shaft (16) connected to the drum (18) for transmitting a driving force of a direct drive motor, said star-shaped metal element (12) forming a central hub (12a) configured for mounting bearings for the shaft and said motor comprising a rotor assembly (26) fastened to the shaft (16) and a stator assembly (24) fastened to the tub (10, 10a), characterized in that said method comprises the steps of:
• co-injecting the plastic tub (10, 10a) on at least the central hub (12a) of the star-shaped metal element (12) so that a central protruding plastic portion (20) is created as a plastic layer (A) on said central hub(12a); and

• axially sliding the stator assembly (24) on said plastic layer (A) in order to center the stator assembly (24) on the tub (10, 10a).
Method according to claim 8, wherein said step of creating a central protruding plastic portion (20) is carried out by injecting plastic material near said one end of said hub (12a).