EP3411938A1

EP3411938A1 - Interior permanent-magnet rotor of a brushless motor

Info

Publication number: EP3411938A1
Application number: EP16703527.8A
Authority: EP
Inventors: Asuman Firat; Emin Gultekin SONMEZ; Pevrul Sarikaya; Gokhan ERGIN
Original assignee: Arcelik AS
Current assignee: Arcelik AS
Priority date: 2016-02-05
Filing date: 2016-02-05
Publication date: 2018-12-12
Also published as: WO2017133784A1; TR201701600A2

Abstract

The present invention relates to a brushless electric motor (1) for a water conducting household appliance. The brushless electric motor (1) comprises an outer stator; a shaft (2) and an inner magnet-rotor (3) without a core. In the brushless electric motor (1) of the present invention, the inner magnet-rotor (3) includes a cylindrical permanent magnet (4) having an axial hole (5) for receiving the shaft (2) with a clearance (6), wherein the shaft (2) has a ridged surface (7) inside the axial hole (5); attachment grooves (8) formed into the upper face (9) and the lower face (10) of the cylindrical permanent magnet (4) and an overmolded plastic retainer (11) formed exclusively onto the upper face (9) and the lower face (10) and into the axial hole (5) so as to inseparably join the cylindrical permanent magnet (4) with the shaft (2) and integrally fill the attachment grooves (8) and the clearance (6).

Description

[Title established by the ISA under Rule 37.2] INTERIOR PERMANENT-MAGNET ROTOR OF A BRUSHLESS MOTOR

The present invention relates to a brushless electric motor of an electrical household appliance, in particular a water-conducting household appliance such as a laundry washer or a dishwasher. The present invention more particularly relates to the inner magnet-rotor of the brushless electric motor.
Water conducting household appliances such laundry washers and dishwashers are commonly known in the art. A water conducting household appliance generally comprises a pump which has a brushless electric motor. The brushless electric motor generally comprises an outer stator, a shaft and an inner magnet-rotor. The inner magnet-rotor comprises a core and arc shaped permanent magnets which are disposed around the core. The inner magnet-rotor may be alternatively provided without a core.
US 7,911,109 B2 discloses a washing machine.
A common problem with the aforementioned prior art brushless electric motor is that the thermal stress resulting from the thermal fluctuations of the water can develop fractures in the arc shaped permanent magnets and even cause the arc shaped permanent magnets to break up and block the brushless electric motor.
An objective of the present invention is to provide a brushless electric motor for use in a water conducting household appliance which solves the aforementioned problems of the prior art in a cost effective way and which enables an improved production and a safe operation.
This objective has been achieved by the brushless electric motor as defined in claim 1 and the water conducting household appliance as defined in claim 4. Further achievements have been attained by the subject-matters respectively defined in the dependent claims.
In the brushless electric motor of the present invention the inner magnet-rotor includes: a cylindrical permanent magnet; an axial hole which is formed into the cylindrical permanent magnet and adapted to receive the shaft with a clearance, wherein the shaft has a ridged surface which is located inside the axial hole; a plurality of attachment grooves which are formed into the upper face and the lower face of the cylindrical permanent magnet and an overmolded plastic retainer which is exclusively formed onto the upper face, the lower face and into the axial hole around the shaft so as to inseparably join the cylindrical permanent magnet with the shaft, wherein the overmolded plastic retainer integrally fills the attachment grooves and the clearance.
A major advantageous effect of the present invention is that cylindrical permanent magnet and the shaft can be inseparably joined by means of the overmolded plastic retainer and thus the risk of disintegration and blockage can be eliminated or reduced as much as possible during the operation. Thereby, the breakage safety of the brushless electric motor has been improved and thus the brushless electric motor can be safely operated. Another major advantageous effect of the present invention is that the cylindrical permanent magnet and the shaft can be inseparably joined by means of the overmolded plastic retainer and thus the risk of slipping and relative motion of the cylindrical permanent magnet and the shaft can be eliminated. Thereby, the brushless electric motor can be reliably operated. Another major advantageous effect of the present invention is that the performance of the brushless electric motor can be increased as the overmolded plastic retainer doesnot cover the circumferential surface of the cylindrical permanent magnet and the gap between the outer stator and the inner magnet-rotor can be reduced. Another major advantageous effect of the present invention is that the cylindrical permanent magnet, including the axial hole and the attachment grooves can be simultaneously produced by sintering the raw material into a mold and the production costs can be reduced both in terms of labor and material. Another major advantageous effect of the present invention is that the overmolded plastic retainer can be easily formed by plastic injection molding without the need for using any auxiliary retainers for preassembling the cylindrical permanent magnet and the shaft and the production costs can be reduced both in terms of labor and material. Another major advantageous effect of the present invention is that the need for using any adhesive so as to secure the cylindrical permanent magnet to the shaft has been obviated by virtue of the overmolded plastic retainer and the ridged surface. Thereby, the production line can be protected from getting soiled through the adhesive and the production costs can be further reduced. Another major advantageous effect of the present invention is that the brushless electric motor can be more safely operated event at comparatively higher ambient temperatures and rotational speeds by virtue of the overmolded plastic retainer.
In an embodiment, the attachment grooves are arc shaped and concentrically arranged around the axial hole. This embodiment is particularly advantageous as the overmolded plastic retainer meshes into the attachment grooves and securely prevents disintegration of the cylindrical permanent magnet even in case of fractures that are caused through the thermal and mechanical stresses. This embodiment is also particularly advantageous as the overmolded plastic retainer meshes into attachment grooves and the ridged surface and securely prevents relative movement of the cylindrical permanent magnet with respect to the shaft during the operation.
In other alternative embodiments, the overmolded plastic retainer has a gearwheel which is formed onto the upper face or the lower face. These embodiments are particularly advantageous as the overmolded plastic retainer can be immediately connected to the rotating parts of the pump unit of the water conducting household appliance.
In another embodiment, the cylindrical permanent magnet is produced by sintering the raw material into a mold so as to simultaneously form the attachment grooves and the axial hole. The cylindrical permanent magnet is magnetized so as to have a predetermined number of circumferentially arranged poles. This embodiment is particularly advantageous as the cylindrical permanent magnet can be easily produced and thus the costs can be reduced both in terms of labor and material.
In other alternative embodiments, the cylindrical permanent magnet is made from a ferrite magnet or an NdFeB magnet. These embodiments are particularly advantageous as the cylindrical permanent magnet can have a relatively strong magnetic field.
In other alternative embodiments, the cylindrical permanent magnet and the shaft are placed into an injection mold so as to form the overmolded plastic retainer by plastic injection molding. This embodiment is particularly advantageous as the attachment grooves and the clearance can be integrally filled with plastic material and thus the shaft and the cylindrical permanent magnet can be inseparably joined.
In other alternative embodiments, a ridged surface is formed onto the shaft in a casting operation and/or machining operation. This embodiment is particularly advantageous as the ridged surface increases the grip to the overmolded plastic retainer.
Additional features and additional advantageous effects of the brushless electric motor of the present invention will become more apparent with the detailed description of the embodiments with reference to the accompanying drawings in which:
Figure 1 - is a schematic partial perspective view of a brushless electric motor which has an inner magnet-rotor according to an embodiment of the present invention, wherein the outer stator has been omitted for ease of illustration;
Figure 2 - is a schematic sectional view of the brushless electric motor of Fig. 1;
Figure 3 - is a schematic partial perspective view of the brushless electric motor according to an embodiment of the present invention, prior to forming the overmolded plastic retainer;
Figure 4 - is a schematic perspective view of the cylindrical permanent magnet in Fig. 1;
Figure 5 - is a schematic perspective view of the shaft in Fig. 1.
The reference signs appearing on the drawings relate to the following technical features.

Brushless electric motor
Shaft
Inner magnet-rotor
Cylindrical permanent magnet
Axial hole
Clearance
Ridged surface
Attachment grooves
Upper face
Lower face
Overmolded plastic retainer
Gearwheel

The brushless electric motor (1) is suitable to use in a water conducting household appliance (not shown).
The brushless electric motor (1) comprises an outer stator (not shown); a shaft (2) and an inner magnet-rotor (3) without a core (Fig. 1).
In the brushless electric motor (1) of the present invention, the inner magnet-rotor (3) includes: a cylindrical permanent magnet (4); an axial hole (5) which is formed into the cylindrical permanent magnet (4) and adapted to receive the shaft (2) with a clearance (6), wherein the shaft (2) has a ridged surface (7) which is located inside the axial hole (5); a plurality of attachment grooves (8) which are formed into the upper face (9) and the lower face (10) of the cylindrical permanent magnet (4) and an overmolded plastic retainer (11) which is exclusively formed onto the upper face (9), the lower face (10) and into the axial hole (5) around the shaft (2) so as to inseparably join the cylindrical permanent magnet (4) with the shaft (2), wherein the overmolded plastic retainer (11) integrally fills the attachment grooves (8) and the clearance (6) (Fig. 2 to Fig. 5).
The water conducting household appliance comprises the brushless electric motor (1).
In an embodiment, the attachment grooves (8) are arc shaped and concentrically arranged around the axial hole (5) (Fig. 4).
In another embodiment, the overmolded plastic retainer (11) includes a gearwheel (12) which is formed onto the upper face (9) or the lower face (10) (Fig. 1).
In the subsequent description, a method of producing the brushless electric motor (1) will be briefly explained by way of example. First, the shaft (2), including the ridge surface (7) is provided (Fig. 5). Next, the cylindrical permanent magnet (4), including the axial hole (5) and the attachment grooves (8) is provided (Fig. 4). The cylindrical permanent magnet (4) may be provided by sintering the raw material into a mold (not shown). The cylindrical permanent magnet (4) may be produced as a ferrite magnet or a NdFeB magnet. The axial hole (5) and attachment grooves (8) are simultaneously formed during the sintering step. Next, the cylindrical permanent magnet (4) is magnetized so as to have a predetermined number of circumferentially arranged poles (Fig. 4). Next, the shaft (2) is inserted into the axial hole (5) of the cylindrical permanent magnet (4) with a clearance (6) (Fig. 3). Next, the shaft (2) and the cylindrical permanent magnet (4) are placed into the injection mold (not shown). Next, the overmolded plastic retainer (11) is formed by injecting plastic onto the upper face (9), the lower face (10) and into the axial hole (5) around the shaft (2) so as to integrally fill the attachment grooves (8) and the clearance (6) (Fig.2). Thereby, the shaft (2) and the cylindrical permanent magnet (4) are inseparably joined.
A major advantageous effect of the present invention is that cylindrical permanent magnet (4) and the shaft (2) can be inseparably joined by means of the overmolded plastic retainer (11) and thus the risk of disintegration and blockage can be eliminated or reduced as much as possible during the operation. Thereby, the breakage safety of the brushless electric motor (1) has been improved and thus the brushless electric motor (1) can be safely operated. Another major advantageous effect of the present invention is that the cylindrical permanent magnet (4) and the shaft (2) can be inseparably joined by means of the overmolded plastic retainer (11) and thus the risk of slipping and relative motion of the cylindrical permanent magnet (4) and the shaft (2) can be eliminated. Thereby, the brushless electric motor (1) can be reliably operated. Other advantageous effects of the present invention can be taken from the above described embodiments.

Claims

A brushless electric motor (1) comprising an outer stator, a shaft (2) and an inner magnet-rotor (3) without a core, the brushless electric motor (1) being characterized in that the inner magnet-rotor (3) includes a cylindrical permanent magnet (4), an axial hole (5) which is formed into the cylindrical permanent magnet (4) and adapted to receive the shaft (2) with a clearance (6), wherein the shaft (2) has a ridged surface (7) which is located inside the axial hole (5), a plurality of attachment grooves (8) which are formed into the upper face (9) and the lower face (10) of the cylindrical permanent magnet (4) and an overmolded plastic retainer (11) which is exclusively formed onto the upper face (9), the lower face (10) and into the axial hole (5) around the shaft (2) so as to inseparably join the cylindrical permanent magnet (4) with the shaft (2), wherein the overmolded plastic retainer (11) integrally fills the attachment grooves (8) and the clearance (6).
The brushless electric motor (1) according to claim 1, characterized in that the attachment grooves (8) are arc shaped and concentrically arranged around the axial hole (5).
The brushless electric motor (1) according to claim 1 or 2, characterized in that the overmolded plastic retainer (11) includes a gearwheel (12) which is formed onto the upper face (9) or the lower face (10).
The water conducting household appliance characterized in that the brushless electric motor (1) as defined in any one of claims 1 to 3.