Washing machine

A drum type washing machine is provided. The washing machine includes a tub, a drum rotatably installed in the tub, and a shaft that penetrates the tub and is connected to the drum so as to transmit a drive force of a motor to the drum. A stator is fixed to a rear wall of the tub, and an outer rotor, including at least one magnet, an annular back yoke, and a rotor frame, is rotatably disposed at the outside of the stator. The rotor frame may be made of an aluminum material, and includes a side wall portion and a rear wall portion integrally formed with the side wall portion.

This application claims the benefit of the Korean Patent Application Nos. 10-2005-0115766, 10-2005-0115767, 10-2005-0115768 and 10-2005-0115769 filed on Nov. 30, 2005, which are hereby incorporated by reference as if fully set forth herein.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a washing machine, and more particularly, to an improvement in the structure of a drive unit included in a drum type washing machine.

2. Discussion of the Related Art

Generally, drum type washing machines are designed to perform a washing operation by use of a frictional force between a drum and laundry as the drum is rotated by a drive force of a motor transmitted thereto in a state wherein the laundry is received in the drum together with wash water and detergent. The above described washing operation manner has several effects of causing damage to laundry as little as possible while preventing entangling of laundry and also providing excellent washing effects by pounding and rubbing.

Now, the configuration of a conventional drum type washing machine will be described in brief with reference toFIG. 1.

Referring toFIG. 1illustrating the configuration of the conventional drum type washing machine in longitudinal sectional view, the conventional washing machine comprises a tub2installed in a cabinet1and a drum3rotatably installed in the center of the tub2.

The tub2is mounted, at a lower side thereof, with a motor5aand in turn, the motor5ais connected to a motor pulley18by means of a shaft.

The drum3is mounted, at a rear side thereof, with a drum shaft, and a drum pulley19is mounted on the drum shaft.

The drum pulley19mounted on the drum shaft and the motor pulley18connected to the motor5aare connected to each other by means of a belt20as a power transmission element.

The cabinet1is provided, at a front side thereof, with a door21, and a gasket22is provided between the door21and the tub2.

A hanging spring23is mounted between an inner ceiling surface of the cabinet1and an outer upper surface of the tub2and adapted to support the tub2. Also, a friction damper24is mounted between an inner bottom surface of the cabinet1and an outer lower surface of the tub2and adapted to alleviate vibration of the tub2caused during a dehydrating operation.

In the above described conventional washing machine, a drive force of the motor5ais transmitted to the drum3by way of the motor pulley18, the drum pulley19, and the belt20connecting the motor pulley18and the drum pulley19to each other. Such an indirect power transmission manner, however, has the following problems.

Firstly, since the drive force of the motor5ais transmitted to the drum3through the belt20wound on both the motor pulley18and the drum pulley19rather than being directly transmitted to the drum3, there is a high potential loss of energy in the transmission course of the drive force.

Secondly, in the course of transmitting the drive force of the motor5ato the drum3through the above described several elements, such as the motor pulley18, the drum pulley19, and the belt20, and the like, there inevitably exists a problem of severe noise as compared to the case where the drive force is directly transmitted to the drum3.

Thirdly, a necessity for a great number of elements for transmitting the drive force of the motor5ato the drum3, such as the motor pulley18, the drum pulley19, the belt20, and the like, consequently, causes a complicated product assembling operation.

Fourthly, the above described great number of elements for transmitting the drive force of the motor5ato the drum3may result in a proportional increase in the number of potential failure areas, and this has a problem of increasing the generation frequency of failures.

In conclusion, due to the above described power transmission manner in which the drive force of the motor5ais indirectly transmitted to the drum3only by way of the motor pulley18, the belt20, and the drum pulley19, the conventional drum type washing machine has problems of a high potentiality of failures and noise generation as well as excessive consumption of energy and seriously, may result in deterioration in washing performance thereof, etc.

To solve the above described problems, the applicant of the present invention has proposed to use a direct connection type motor in a drive unit of a drum type washing machine, as disclosed in Korean Patent Laid-open Publication No. 10-2001-0037607.

In the above published patent invention, there is provided a rotor frame, which is formed by pressing an iron plate and installed to transmit a rotating force of a rotor to a drum directly while performing itself the function of a back yoke having a magnetic path. It could be found that the disclosed rotor frame has a capability of solving the above described problems of the indirect power transmission manner while achieving a simplified structure.

However, forming the rotor frame by pressing the iron plate has a difficulty, due to characteristics of a press operation, to obtain a required accuracy, more particularly, concentricity, when the thickness of the iron plate exceeds a predetermined value. On the other hand, when the rotor frame is formed by use of an iron plate having a thickness less than the predetermined value, there is a problem in that the rotor frame cannot obtain a required strength and may fluctuate during rotation.

Furthermore, to provide a passage of magnetic flux, that is to say, a magnetic path for the flow of magnetic flux generated by electric current flowing through coils of a stator, it is essential to provide a back yoke, which is made of a magnetic material and has an appropriate thickness, behind a magnet. Here, it is noted that the thinner the thickness of the back yoke, the lower a saturation point of the magnetic flux. Accordingly, when the rotor frame serving as the back yoke has a small thickness, there is a limit to increase the output of a motor even if the amount of current is increased to obtain a strong output.

Consequently, the attempt to form the rotor frame having the function of the back yoke by use of the iron plate in views of diversification of products reaches a limit due to the above described thickness problem of the rotor frame.

Also, due to characteristics of the iron plate, there is a risk in that the rotor frame tends to gather rust on its surface easily. The rust may cause deterioration in the strength of the rotor frame and in the worst case, there is a risk in that rust powder that falls from the rotor frame is attached in an air gap between the magnet and the stator, thereby acting to restrict rotation of the rotor.

In addition, the rotor frame, made of the iron plate, has a difficulty in the implementation of any subsequent process for improving accuracy and other processes.

SUMMARY OF THE INVENTION

An object of the present invention is to provide a drum type washing machine in which a drive unit, more particularly, a rotor frame that is adapted to transmit a rotating force of a rotor to a shaft directly, has an improved structure suitable to transmit a drive force of a motor to a drum directly, thereby achieving the effects of reducing the generation potential of noise and failure as well as excessive consumption of energy and of increasing the durability and stability of the washing machine.

To achieve these objects and other advantages and in accordance with the purpose of the invention, as embodied and broadly described herein, a washing machine comprising: a tub for receiving wash water therein; a drum rotatably disposed in the tub and adapted to wash laundry received therein; a shaft penetrated through the tub to thereby be connected to the drum, the shaft being adapted to transmit a drive force of a motor to the drum; a stator coupled fixedly to a rear wall portion of the tub while being located on the rear wall portion; and an outer rotor including at least one magnet, an annular back yoke defining a magnetic path, and a rotor frame rotatably disposed at the outside of the stator, wherein the rotor frame of the outer rotor is made of an aluminum material, and comprises a side wall portion for supporting the magnet and the annular back yoke and a rear wall portion for transmitting a rotating force of the rotor to the shaft.

Preferably, the rotor frame is formed by die casting, and the side wall portion and the rear wall portion of the rotor frame are integrally formed with each other.

The back yoke may be press fitted and coupled fixedly inside the side wall portion of the rotor frame. For this, the rotor frame may further comprise a plurality of protrusions arranged inside the rotor frame to be spaced apart from one another by a regular distance in a circumferential direction of the rotor frame, the protrusions also being spaced apart in a radial inward direction from the side wall portion of the rotor frame by a predetermined distance. The protrusions may be integrally formed with the rotor frame.

To achieve a further increase in a coupling strength between the rotor frame and the back yoke, an adhesive may be applied to coupling surfaces of the rotor frame and the back yoke. Of course, the magnet may be attached to an inner surface of the back yoke by use of an adhesive, to be disposed in a circumferential direction of the back yoke.

In the present invention, the back yoke may be formed via a variety of methods. For example, the back yoke may be formed by rolling an iron plate, having a smaller thickness than a desired thickness of the back yoke, multiple times, to have a radially multilayered structure. Also, the back yoke may be formed by spirally winding an iron band, having substantially the same width as a desired thickness of the back yoke, from a lowermost layer to an uppermost layer, to have a vertically multilayered structure. Of course, it will be appreciated by those skilled in the art that, although the back yoke may be formed by stacking a plurality of annular iron bands one above another, this may result in excessive loss of material in association with the manufacture of the iron bands.

Meanwhile, the back yoke may be provided, at an outer surface thereof, with at least one radially-formed recess or protrusion, and the side wall portion of the rotor frame may be provided, at an inner surface thereof, with at least one protrusion or recess corresponding to the recess or protrusion of the back yoke, whereby the back yoke is coupled fixedly inside the side wall portion of the rotor frame via engagement between the protrusion and the recess.

For example, the back yoke may be provided, at an outer surface thereof, with at least one radially-formed recess, and the side wall portion of the rotor frame may be provided, at an inner surface thereof, with at least one protrusion corresponding to the recess of the back yoke, whereby the back yoke is coupled fixedly inside the side wall portion of the rotor frame via engagement between the protrusion and the recess.

Here, the protrusion of the rotor frame may have a smaller height than a height of the side wall portion of the rotor frame. Alternatively, the recess of the back yoke is replaced by a slot perforated in a lower end portion of the back yoke through a thickness of the back yoke so that the protrusion is inserted through the slot.

The back yoke may be provided, at an outer surface thereof, with at least one radially-formed protrusion, and the side wall portion of the rotor frame may be provided, at an inner surface thereof, with at least one recess corresponding to the protrusion of the back yoke, whereby the back yoke is coupled fixedly inside the side wall portion of the rotor frame via engagement between the protrusion and the recess.

Here, the protrusion of the back yoke may extend throughout a height of the back yoke.

The back yoke may be inserted into a mold of the rotor frame during die casting of the rotor frame, to thereby be coupled fixedly inside the side wall portion of the rotor frame.

The back yoke may be inserted into the mold after being previously coupled, at an inner surface thereof, with the magnet. In this case, the magnet as well as the back yoke can be coupled fixedly inside the rotor frame with an increased coupling force.

Preferably, the back yoke has at least one groove or protuberance formed at an outer surface thereof for increasing a coupling force between the back yoke and the rotor frame. Also, preferably, the groove or protuberance is formed at a middle height portion of the back yoke. This is because the groove or protuberance can prevent scattering of the back yoke, in addition to increase a coupling force between the back yoke and the rotor frame.

The side wall portion of the back yoke may have an upper end extended in a radial inward direction by a predetermined length to cover upper ends of the back yoke and the magnet.

The above described drum type washing machine according to the present invention has the following effects.

Firstly, the washing machine of the present invention has a direct connection motor and thus, has the effect of significantly reducing the generation of noise and failure as well as the loss of power. Also, with the use of a metallic bearing housing, the washing machine of the present invention is applicable to products having a high-temperature drying function, without the risk of thermal deformation.

Secondly, in the washing machine of the present invention, the rotor frame is made of an aluminum material and thus, has no risk of gathering rust thereon. This results in an increase in the durability of the motor. Furthermore, the rotor frame of the present invention has a magnet seating plane for achieving a highly efficient mounting operation of the magnet. Also, with the provision of vent holes having the function of moisture discharge and ventilation, it is possible to prevent overheating of the motor while protecting the motor from invasion of moisture. This consequently has the effect of increasing the reliability of the motor and extending the lifespan of the motor.

Thirdly, according to the present invention, the rotor frame is formed by die casting an aluminum material. Accordingly, the rotor frame can be manufactured with a simplified manner while guaranteeing an improved processability required for any subsequent process. Also, forming the rotor frame by use of a light-weight material is efficient to minimize the power loss of the motor due to the inertia force of the rotor frame. In addition, the aluminum rotor frame provides a flexibility to ensure free change in the thickness of the back yoke in views of diversification of products. This enables an increase in the overall thickness of the rotor frame and consequently, the rotor frame is free from unwanted fluctuation during rotation thereof, thus resulting in reduced noise and vibration.

Fourthly, according to the present invention, the back yoke can be secured easily and firmly to the rotor frame with a variety of methods, resulting in an improvement in the reliability and productivity of the washing machine.

DETAILED DESCRIPTION OF THE INVENTION

In the present invention, a motor, more particularly, a rotor frame constituting a rotor, is made of an aluminum material, and a back yoke for providing the rotor frame with a magnetic path may be coupled fixedly to the rotor frame with a variety of methods.

Now, a first embodiment of the present invention will be described in detail with reference toFIGS. 2 to 7.

FIG. 2is a longitudinal sectional view illustrating the configuration of a washing machine according to the present invention, andFIG. 3is an enlarged detailed view of the portion “A” ofFIG. 2, illustrating the configuration of a drive unit included in the washing machine according to the present invention.

FIG. 4is a partially cut-away perspective view illustrating a rotor shown inFIG. 3,FIG. 5is a perspective view illustrating a stator shown inFIG. 3,FIG. 6is a perspective view illustrating a connector shown inFIG. 3, andFIG. 7is a bottom perspective view ofFIG. 6.

As shown inFIGS. 2 and 3, the washing machine according to the present embodiment comprises a tub2installed in a cabinet1and used to receive wash water therein, a drum3rotatably provided in the tub2and adapted to wash laundry received therein as it is rotated, a shaft4penetrated through the tub2and connected to the drum3, the shaft4being adapted to transmit a drive force of a motor5to the drum3, a stator14having winding portions around which coils are wound, the stator14being coupled fixedly to a rear wall surface200of the tub2, and a rotor13at the outside of the stator14.

The outer rotor13includes magnets13c, an annular back yoke300defining a magnetic path, and a rotor frame.

The rotor frame has a side wall portion13band a rear wall portion13a. The side wall portion13bserves to support the magnets13cand the back yoke300, to allow the magnets13cand the back yoke300to rotate at the outside of the stator14. The rear wall portion13aserves to transmit a rotating force of the magnets13cand the back yoke300to the shaft4.

Preferably, both the side wall portion13band the rear wall portion13aare made of an aluminum material, more particularly, an aluminum alloy, and are integrally formed with each other.

It will be appreciated that the rotor frame is preferably formed by a die-casting method that is suitable for mass production.

Meanwhile, in the present embodiment, a supporter17may be interposed between the rear wall surface200of the tub2and the stator14. The supporter17serves to increase a coupling strength between the tub2and the stator14.

Also, in the present embodiment, it is preferable that a bearing housing7be provided at the rear wall surface200of the tub2and used to receive bearings therein for rotatably supporting the shaft4.

Here, the stator14may be coupled fixedly to the rear wall surface200of the tub2through the bearing housing7and the supporter17.

The bearing housing7is preferably made of a metallic material, and more preferably, made of an aluminum material such as an aluminum alloy. Also, preferably, the bearing housing7is integrally formed with the rear wall surface200of the tub2via insert injection molding when the tub2, which is made of a plastic material, is injection molded.

Here, the bearing housing7may be integrally formed with the supporter17, to perform the role of the supporter17additionally. In this case where the bearing housing7is integrally formed with the supporter17, the supporter17is formed via insert injection molding during the injection molding of the tub2. In this case, the supporter17may be configured in such a manner that only a portion thereof, that is to say, a coupling portion for the bearing housing7, may be exposed rearward out of the tub2.

Integrally forming the bearing housing7with the supporter17enables the omission of a coupling process of the bearing housing7or supporter17, which has been conventionally performed in an assembling line in the course of securing the stator14to the rear wall surface200of the tub2. This has the effect of reducing manufacturing costs of the washing machine.

Meanwhile, the metallic bearing housing7is formed, at different positions of an inner circumference thereof, with short-stepped portions8aand8b. The short-stepped portions8aand8bserve to support front and rear bearings6aand6b, respectively, installed on the inner circumference thereof, so as to prevent the respective bearings6aand6bfrom being separated from the bearing housing7.

In this case, of the short-stepped portions8aand8bformed along the inner circumference of the bearing housing7, the short-stepped portion8a, which is formed at a front position, has an “L”-shaped form suitable to support a rear end of the front bearing6athat is installed on the outer circumference of a front end of the shaft4. On the other hand, the short-stepped portion8b, which is formed at a rear position, has an “L”-shaped form suitable to support a front end of the rear bearing6bthat is installed on the outer circumference of a rear end of the shaft4.

The shaft4is partially located in the bearing housing7and adapted to transmit the drive force of the motor5to the drum3. The shaft4is formed, at front and rear positions on the outer circumference thereof, with positioning short-stepped portions9aand9bfor determining the installation positions of the front and rear bearings6aand6brelative to the shaft4.

The front end of the shaft4is coupled to a spider10that is provided at a rear wall portion of the drum3. Also, to prevent the shaft4from gathering rust thereon, a brass bushing11is press fitted around a portion of the shaft4extended between the spider10and the front bearing6aat the outside of the bearing housing7. Here, the bushing11is provided, around an outer circumference thereof, with a sealing member12for completely preventing permeation of moisture into the bearings6aand6b.

The rotor13, which constitutes a part of a direct connection motor5, is coaxially coupled to the rear end of the shaft4. The stator14is located inside the rotor13so as to constitute the direct connection motor5along with the rotor13. Here, the stator14is coupled fixedly to the rear wall surface200of the tub2.

In the present embodiment, the rotor frame is made of an aluminum material. As shown inFIGS. 3 and 4, the side wall portion13bof the rotor frame, which is extended forward from an edge of the rear wall portion13a, is preferably formed, along a circumferential direction thereof, with a ledge having a seating plane130for supporting the magnets13cthat are attached to an inner surface of the side wall portion13bover a front portion of the inner surface. Also, preferably, the rear wall portion13aof the rotor frame is centrally formed with a hub132. Here, the hub132has a center through-hole131for allowing a coupling member15b, such as a bolt, etc., to pass therethrough in order to couple the rotor13to the shaft4.

Of course, it will be appreciated that the magnets13care not essentially intended to be supported on the seating plane130, and in the case of small capacity magnets, they may be coupled to the inner surface of the side wall portion13bat a position spaced apart upward from the seating plane130by a predetermined height.

As shown inFIG. 4, the rotor frame is preferably configured in such a manner that the side wall portion13bis integrally formed with the rear wall portion13aand the rotor frame is formed by die casting an aluminum material.

Around the hub132of the rotor frame are radially formed a plurality of cooling fins133. The cooling fins133serve to blow air toward the stator14during rotation of the rotor13, so as to remove heat generated in the stator14. In this case, each of the cooling fins133is formed to have a predetermined length in a radial direction of the rotor frame.

Preferably, the cooling fins133are integrally formed with the rotor frame and extend radially from the hub132to the ledge to have a height difference between the hub132and the seating plane130of the ledge. On the basis of the height difference, the cooling fins133can be linearly formed or curved convexly or concavely. With this configuration, the cooling fins133can act to blow air concentratively to specific portions of the stator14having the highest cooling requirement.

AlthoughFIG. 4illustrates that the cooling fins133are configured to have the highest height at the side of the ledge130, it will be appreciated that, conversely, the cooling fins133may have the highest height at the side of the hub132. Also, it is possible that the cooling fins133are integrally formed with the side wall portion13band the rear wall portion13a, to serve as ribs continuously connecting the hub132to the ledge, for the sake of reinforcing the overall strength of the rotor frame.

In the present invention, the rear wall portion13aof the rotor frame has a plurality of vent holes134perforated in regions between the respective adjacent cooling fins133. The vent holes134have the roles of moisture discharge and ventilation.

With the provision of the cooling fins133and the hub132, the rotor frame of the present invention can achieve a reinforced rigidity. Also, it will be appreciated that the cooling fins133and the hub132can achieve the effect of simplifying the manufacture of the rotor13because they can be formed simultaneously with the forming of the rotor frame.

Around the center through-hole131, which is perforated in the hub132of the rotor13, are formed a plurality of coupling holes137and a plurality of positioning holes138by regular distances. The plurality of positioning holes138are located, respectively, between the respective adjacent coupling holes137. The coupling holes137are used to couple a connector16to the rotor13. Here, the connector16is serration-coupled onto the outer circumference of the rear end of the shaft4extended rearward from the rear bearing6bat the outside of the bearing housing7. The positioning holes138are used to determine the assembling position of the connector16.

The connector16is made of a resin material having a different vibration mode from that of the aluminum rotor frame. Preferably, the connector16may be made of an insulating material and integrally formed with the rotor frame via insert molding. In this case, the coupling holes137and the positioning holes138perform the role of passage holes for allowing a part of the connector16to passage therethrough, in order to increase a coupling force between the connector16and the rotor frame.

Meanwhile, the connector16, as shown inFIGS. 2,6, and7, has coupling holes162perforated in an edge region thereof to be distributed along a circumferential direction, to correspond to the coupling holes137formed in the hub132of the rotor13. The connector16also has positioning bosses160integrally formed at positions between the respective adjacent coupling holes162. As the positioning bosses160are inserted into the positioning holes138of the rotor13, the coupling holes137of the rotor13are automatically aligned with the coupling holes162of the connector16.

In addition, the connector16has a center hub163, a serration164formed at an inner circumference of the hub163to be engaged with a serration400formed on the rear end of the shaft4, and reinforcing ribs161formed at an outer circumference of the hub163of the connector16for reinforcing the strength of the hub163.

Here, the serration164of the connector16may be formed by insert molding a member, which is made of a metallic material having a high strength and has a serration formed on an inner circumference thereof, during the forming of the connector16.

Meanwhile, as shown inFIGS. 3 and 5, the stator14, which constitutes the motor5along with the rotor13, includes a ring-shaped insulator140, and coils142wound on winding portions141arranged at the outside of the insulator140. In addition, coupling ribs143are integrally formed with the insulator140to be arranged inside the insulator140. The coupling ribs143serve to secure the stator14to the bearing housing7.

The stator14further includes a stator core, which consists of the winding portions141around which the coils142are wound, and an annular body portion having a magnetic path. Here, the insulator140serves to insulate the stator core and the coils142from each other. The plurality of winding portions are spaced apart from one another by a predetermined distance in a circumferential direction of the body portion to protrude radially from the body portion.

Here, the stator core may be an annular spiral core having a multilayered structure, which is obtained by spirally winding an iron plate, consisting of the winding portions141and the body portion, from the lowermost layer to the uppermost layer. In this case, differently from that shown inFIG. 5, the coupling ribs143for coupling the stator14to the tub2may be formed only at the insulator140. In this case, the insulator140has to be configured to guarantee an appropriate strength thereof. The stator14may be coupled to the tub2through coupling holes144formed in the respective ribs143.

Alternatively, the stator core may take the form of an annular sectional core, which is obtained by coupling a plurality of arched stator core sections, each consisting of a plurality of arched stator core pieces stacked one above another in multiple layers, with one another.

In the present invention, preferably, the stator14has thirty six poles and the rotor13has forty eight poles. The greater the number of the poles, the easier the positional detection and control of the stator14and the rotor13can be accomplished. Here, the forty eight poles of the rotor13alternately define a north pole and a south pole in such a manner that twelve permanent magnets, each having a total of four poles, are coupled inside the rotor frame.

Hereinafter, the coupling of the rotor frame and the back yoke included in the drum type washing machine according to the present invention will be described in detail.

First, in the present invention, the back yoke may be formed by stacking annular iron plates, preferably, annular silicon steel plates, which has substantially the same width as a desired radial thickness of the back yoke, one above another.

To reduce the loss of a material required for the manufacture of the back yoke, alternatively, the back yoke may be formed by spirally winding an iron plate band, which has substantially the same width as a desired thickness of the back yoke, from the lowermost layer to the uppermost layer, to have a multilayered annular structure. That is to say, the back yoke may be manufactured to have the same shape as the above described shape of the spiral core of the stator core.

Alternatively, the back yoke may be formed by rolling an iron plate, which has a thinner thickness than the desired radial thickness of the back yoke, multiple times, to have a multilayered structure in a radial direction. Even by the above described configuration, a reduction in the loss of a material can be expected.

When forming the back yoke by use of a predetermined thickness iron plate to have a multilayered structure as stated above, the back yoke of the present invention has the effect of minimizing the leakage of a magnetic flux and accordingly, is capable of performing the role of an efficient back yoke. This is because the multilayered back yoke can minimize the leakage of a magnetic flux in a direction perpendicular to the generation direction of a magnetic flux.

Meanwhile, the back yoke is made of an iron plate and thus, has a difficulty to be coupled to the aluminum rotor frame by welding. Accordingly, now, a desired method for coupling the iron back yoke to the aluminum rotor frame according to different preferred embodiments of the present invention will be described.

First, it should be noted that the back yoke and the rotor frame must have a coupling strength sufficient to prevent not only idling rotations of the rotor frame and the back yoke, in consideration of the fact that a rotating force of the back yoke and the magnets has to be transmitted to the shaft through the rotor frame, but also scattering and separation of the back yoke from the rotor frame. In conclusion, the back yoke and the rotor frame must have a highly reliable coupling strength therebetween.

In a first embodiment of the present invention, to provide the reliable coupling strength, the back yoke is press fitted inside and secured fixedly to the side wall portion of the rotor frame.

Specifically, the rotor frame, as shown inFIG. 8, may comprise a plurality of protrusions400, which are arranged inside the side wall portion13bto be circumferentially spaced apart from one another by a predetermined distance. The protrusions400are spaced apart in a radial inward direction from the inner circumference of the side wall portion13bto have a predetermined radial gap with the side wall portion13b. Thereby, the back yoke300is able to be press fitted and secured fixedly in the radial gap.

Preferably, the back yoke300is formed, at an inner circumference thereof, with recesses401corresponding to the protrusions400, to allow the protrusions400to be inserted into the recesses401. Thereby, the back yoke300can be inserted and coupled inside the side wall portion13bof the rotor frame. With the engagement of the protrusions400and the recesses401, consequently, it is possible to efficiently prevent the idling rotations of the rotor frame and the back yoke300during rotation of the rotor30.

Preferably, the protrusions400are integrally formed with the rotor frame. More preferably, the protrusions may be formed simultaneously with the die casting of the rotor frame. Also, preferably, the plurality of protrusions are spaced apart from one another by a predetermined distance along a circumferential direction of the rotor frame.

AlthoughFIG. 8illustrates that the protrusions400have the same height as that of the side wall portion13b, but the present invention is not limited thereto, and the protrusions400may have a smaller height than that of the side wall portion13b.

Meanwhile, to achieve a further increase in the coupling strength between the back yoke300and the rotor frame, it is preferable that an adhesive is applied to coupling surfaces of the rotor frame and the back yoke when the back yoke is inserted and coupled inside the side wall portion13bof the rotor frame. Of course, it will be appreciated that the magnets may be coupled to the inner circumference of the back yoke by use of an adhesive so that they are arranged in a circumferential direction of the back yoke.

Hereinafter, the assembling procedure and operation of the drive unit included in the washing machine according to the present invention will be described.

First, in the washing machine according to the present invention, the tub2is made of a plastic material having a superior heat resistance property. Injection molding the tub2by use of the light-weight material is advantageous to improve the productivity of the washing machine.

Also, the bearing housing7as bearing supporting means is made of a metallic material, such as an aluminum alloy, etc. This enables the present invention to be applied to washing machines having a high-temperature drying function, without the risk of thermal deformation.

In the present embodiment, the metallic bearing housing7is integrally formed with the tub2as it is insert molded into a hub201formed in the rear wall portion200of the tub2during the injection molding of the plastic tub2. Accordingly, there is no need for assembling the bearing housing7to the rear wall surface200of the tub2, and the overall assembling process of the tub2can be simplified.

Meanwhile, the rotor13is coupled to the center of the rear end of the shaft4and in turn, the stator14is located inside the rotor13, to constitute the direct connection motor5. The side wall portion13bof the rotor13, which is extended forward from the edge of the rear wall portion13a, is formed, in a circumferential direction thereof, with the ledge having the magnet seating plane130. Accordingly, when the magnets13care attached to an inner surface of the rotor13, they can be supported by the seating plane130of the ledge. This has the effect of facilitating the manufacture of the rotor13.

Here, the rotor frame is formed by die casting an aluminum material, resulting in a simplified manufacturing process. Also, since the rotor frame has a light-weight as well as an anti-rust function, it is possible to minimize the power loss of the motor due to the inertia force of the rotor frame and to achieve an improvement in processibility for any subsequent process. In addition, it is easy to provide the rotor frame with an additional rigidity reinforcement structure.

Also, by press fitting and coupling the annular back yoke, which is made of an iron plate, to the aluminum rotor frame, it is possible to achieve an increased coupling strength between the back yoke and the rotor frame. In this case, an adhesive may -be additionally used to achieve a further increase in the coupling strength.

Hereinafter, a drum type washing machine according to a second embodiment of the present invention will be described in detail with reference toFIG. 9. The present embodiment has approximately the same configuration as that of the above described first embodiment and thus, the description of the same configuration will be omitted.

A difference between the present embodiment and the above described first embodiment is a method for coupling the back yoke to the rotor frame. Specifically, in the present embodiment, the back yoke is press fitted and coupled fixedly inside the side wall portion of the rotor frame without the aid of any auxiliary means, but is not essentially intended to be press fitted to the rotor frame. That is to say, the back yoke may be coupled to the rotor frame as protrusions are inserted into their corresponding recesses, respectively.

For this, the rotor frame of the present embodiment, as shown inFIG. 9, has the recesses401formed at an outer surface of the back yoke in a radial direction and the protrusions400formed at an inner surface of the side wall portion of the rotor frame. As the protrusions400are engaged in the recesses401, the back yoke can be coupled fixedly inside the side wall portion of the rotor frame.

With the engagement of the protrusions and the recesses, it is possible to more efficiently prevent idling rotations of the rotor frame and the back yoke during rotation of the rotor.

Preferably, the protrusions400are integrally formed with the rotor frame to constitute a portion of the side wall portion13b. More preferably, the protrusions400may be formed simultaneously with the die casting of the rotor frame.

The plurality of protrusions400are preferably spaced apart from one another by a predetermined distance along a circumferential direction of the rotor frame.

AlthoughFIG. 9illustrates that the protrusions400have the same height as that of the side wall portion13b, but the present invention is not limited thereto, and the protrusions400may have a smaller height than that of the side wall portion13b.

Specifically, the protrusions400may be extended from a surface of the rear wall portion13aby a predetermined height smaller than the height of the side wall portion, or may be extended from a surface of the ledge having the seating plane130by a predetermined height smaller than the height of the side wall portion.

Alternatively, the recesses401of the back yoke may be replaced by slots perforated through the thickness of the back yoke. In this case, the protrusions400of the rotor frame are inserted through the slots.

In other words, the back yoke may be perforated, in a lower end portion thereof, with a plurality of slots in such a manner that the slots are spaced apart from one another by a regular distance in a circumferential direction of the back yoke, to allow the protrusions400to be inserted through the slots.

Preferably, the plurality of protrusions are spaced apart from one another by a predetermined distance in a circumferential direction of the rotor frame.

To guarantee an increased coupling strength between the back yoke and the rotor frame, it is preferable that an adhesive be applied to coupling surfaces of the rotor frame and the back yoke when the back yoke is inserted and coupled inside the side wall portion of the rotor frame. Of course, the magnets may be coupled to the back yoke by use of an adhesive so that they are arranged inside the back yoke in a circumferential direction.

Hereinafter, a drum type washing machine according to a third embodiment of the present invention will be described in detail with reference toFIG. 10. The present embodiment has approximately the same configuration as that of the above described second embodiment and thus, the description of the same configuration will be omitted.

A difference between the present embodiment and the above described second embodiment is in that the protrusions400are formed at the back yoke and the recesses401are formed at the rotor frame. Accordingly, the back yoke is coupled fixedly to the rotor frame via engagement between the protrusions400and the recesses401.

In conclusion, it will be appreciated by those skilled in the art that an important feature of the present invention is the provision of the protrusions400and the recesses401corresponding to each other. In other words, if the protrusions400are formed at the back yoke, the recesses may be formed at the rotor frame, and conversely, if the protrusions400are formed at the rotor frame, the recesses may be formed at the back yoke.

Hereinafter, a drum type washing machine according to a fourth embodiment of the present invention will be described. The present embodiment may be easily understood with reference toFIG. 4.

The present embodiment has a feature in that the annular back yoke is coupled fixedly inside the side wall portion of the rotor frame as it is inserted into a mold of the rotor frame during the die casting of the rotor frame.

This has the effect of increasing the coupling strength between the back yoke and the rotor frame as a molten metal is solidified similar to an insert injection molding method.

The implementation of the above described method is possible because a fusion point of the rotor frame is lower than that of the back yoke.

To achieve a further increase in the coupling strength, the back yoke may be formed, at the outer surface thereof, with grooves (not shown) or protuberances (not shown), to provide the back yoke with a stepped outer surface.

Specifically, a plurality of grooves or protuberances may be spaced apart from one another by a predetermined distance in a circumferential direction of the back yoke, and the height of the grooves or protuberances may be equal to the height of the side wall portion of the rotor frame.

Of course, the grooves or protuberances may have a height smaller than that of the side wall portion of the rotor frame, and may be positioned at approximately the middle height of the back yoke.

Forming the grooves or protuberances at a middle portion of the back yoke, furthermore, has the effect of completely preventing idling rotation as well as scattering of the back yoke.

Meanwhile, after coupling the back yoke with the magnets, the assembly of the back yoke and the magnets may be inserted into the mold of the rotor frame.

Also, the side wall portion of the rotor frame may be configured in such a manner that an upper end of the side wall portion is extended in a radial inward direction by a predetermined length sufficient to cover upper ends of the back yoke and the magnets. Although not shown inFIG. 4, specifically, the upper end of the side wall portion13bmay be configured to be bent in a radial inward direction to cover the back yoke300. Of course, preferably, the upper end of the side wall portion may be extended in a radial inward direction to cover even the magnets located inside the back yoke.

By providing the upper end of the side wall portion of the rotor frame with the above described configuration, it is possible to efficiently prevent the scattering of the back yoke and the magnets.

It will be apparent to those skilled in the art that various modifications and variations, related to the size, shape, and material of the constituent elements, can be made in the present invention without departing from the spirit or scope of the invention. Thus, it is intended that the present invention covers the modifications and variations of this invention provided they come within the scope of the appended claims and their equivalents.