# Patent

## Title
Washing machine having ball balancers

## Abstract

A washing machine having a ball balancer coupled to the drum to compensate for a dynamic imbalance during rotation of the drum, the ball balancer including a ring-shaped racer having a closed internal space in which a plurality of balls and viscous oil are accommodated, the ring-shaped racer including a first injection molded member and a second injection molded member joined to each other to form the closed internal space, the first injection molded member including a first side wall, a second side wall and a connecting wall between the first side wall and the second side wall, the first injection molded member having an open side opposite to the connecting wall, and the second injection molded member is adapted to cover the open side of the first injection molded member.

## Background
CROSS-REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. application Ser. No. 11/898,054, filed Sep. 7, 2007, which in turn claims the benefit of Korean Patent Application No. 2006-0111278, filed Nov. 10, 2006, in the Korean Intellectual Property Office, the disclosure of which is incorporated herein by reference.


BACKGROUND
1. Field
Embodiments relate to a ball balancer of a washing machine, and more particularly, to a relation between a gap, between a racer and balls, and viscous oil of a ball balancer of a washing machine.
2. Description of the Related Art
Generally, washing machines wash laundry by rotating a drum containing the laundry using a driving motor. The drum is rotated at a low speed in regular and opposite directions during a washing process, and is rotated at a high speed in a regular direction during a dehydrating (drying) process.
During the dehydrating (drying) process, the drum is rotated at a high speed under the condition that laundry is not equally disposed in all regions of the drum and is crowded at a specific region of the drum, or the laundry is pushed to one side of the drum due to the accelerated rotation of the drum at an initial state of the dehydrating (drying) process. As a result, the center of gravity of the drum does not coincide with the center of rotation of the drum, thus generating vibration and noise. When the above phenomenon is repeated, components of the washing machine, including a drum, a rotary shaft, and a driving motor, break down or have a shortened life span.
Particularly, a drum washing machine has a structure in which a drum accommodating laundry is disposed horizontally so that the drum is rotated at a high speed in a dehydrating (drying) operation under the condition that the laundry is gathered together on the bottom of the drum by gravity. Thus, the center of gravity of the drum does not coincide with the center of rotation of the drum. Therefore, the drum washing machine has a great possibility of generating vibration and noise.
Drum washing machines, in which a drum is disposed horizontally, and vertical axis washing machines, in which a drum is disposed vertically, are generally provided with balancers for maintaining the dynamic balance of the drum.
Korean Patent Laid-open Publication No. 10-1999-0038279 discloses an example of a washing machine having balancers. Each of the balancers of this washing machine includes a racer installed at the upper or lower part of a drum for maintaining the dynamic balance of the drum when the drum is rotated at a high speed. Balls made of steel and freely movably are disposed in the racer, and viscous oil fills the inside of the racer.
When the drum is rotated, the drum cannot maintain its dynamic balance due to the unbalanced eccentric structure of the drum and the partial distribution of laundry in the drum. Then, the steel balls compensate for the above unbalance, thus allowing the drum to maintain its dynamic balance.
Since the viscous oil of the balancer employed by the above conventional washing machine is sensitive to an outdoor temperature, in the case that a gap between the inner wall of the racer and the steel balls is small, the ball balancer has a considerably high deviation in vibration (time) to attain a correct position according to the outdoor temperature.
On the other hand, in the case that the gap between the inner wall of the racer and the steel balls is large, the ball balancer rapidly attains a correct position, and thus the vibration of the drum is decreased. However, in this case, when the viscosity of the viscous oil is low, the ball balancer generates a large amount of noise. Further, when the gap is expanded to a certain extent, it is difficult to control vibration and noise characteristics due to the manufacturing error of the racer.
SUMMARY
In an aspect of embodiments, there is provided a washing machine having ball balancers, which adjusts a relation between a gap between the inner wall of a racer of each of the ball balancers and balls, and the washing machine having viscous oil, thus reducing the of vibration and noise of the washing machine.
In another aspect of embodiments, there is provided a washing machine having at least one ball balancer, each of which comprises balls and viscous oil accommodated in a racer, wherein the viscosity of the viscous oil is varied in proportion to a gap between the racer and the balls.
In another aspect of embodiments, there is provided a washing machine having ball balancers, in which a dynamic balance of a drum is maintained using the ball balancers, each comprising balls and viscous oil accommodated in a racer, wherein the viscosity of the viscous oil is 100 ̃380 cSt, and a gap between the racer and the balls is 1.0 ̃2.0 mm.
In another aspect of embodiments, there is provided a washing machine having ball balancers, in which a dynamic balance of a drum is maintained using the ball balancers, each comprising balls and viscous oil accommodated in a racer, wherein the viscosity of the viscous oil is 1 ̃100 cSt, and a gap between the racer and the balls is 0.5 ̃1.0 mm.
In another aspect of embodiments, there is provided a washing machine having ball balancers, in which a dynamic balance of a drum is maintained using the ball balancers, each comprising balls and viscous oil accommodated in a racer, wherein the viscosity of the viscous oil is 380 ̃1,000 cSt, and a gap between the racer and the balls is 2.0 ̃3.0 mm.
In accordance with yet another aspect of embodiments, there is provided a balancer for installation in a drum washing machine having a rotating drum, wherein: the balancer includes a racer to be installed in the rotating drum, the racer including a viscous oil and a plurality of ball balancers movably installed in the racer, the balancer to maintain a dynamic balance of the rotating drum using the ball balancers to compensate for an imbalanced mass caused by laundry during rotation of the rotating drum, and the viscosity of the viscous oil is varied in proportion to a gap between the racer and the balls.
In accordance with yet another aspect of embodiments, there is provided a plurality of balancers for installation in a drum washing machine having a rotating drum, wherein: each balancer includes a racer to be installed in the rotating drum, the racer including a viscous oil and a plurality of ball balancers movably installed in the racer, the plurality of balancers maintain a dynamic balance of the rotating drum using the ball balancers to compensate for an imbalanced mass caused by laundry during rotation of the rotating drum, and the viscosity of the viscous oil is varied in proportion to a gap between the racer and the balls in each balancer.



BRIEF DESCRIPTION OF THE DRAWINGS
These and/or other aspects, features, and advantages of exemplary embodiments will become apparent and more readily appreciated from the following description of exemplary embodiments, taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic sectional view of a washing machine in accordance with an exemplary embodiment;
FIG. 2 is an exploded perspective view of a drum of the washing machine in accordance with an exemplary embodiment;
FIG. 3 is a perspective view of the drum of the washing machine in accordance with an exemplary embodiment in an assembled state;
FIG. 4 is a view illustrating a ball balancer installed on the drum of the washing machine in accordance with an exemplary embodiment;
FIGS. 5 and 6 are graphs respectively illustrating vibration and noise values according to the relation between a gap and viscous oil in a ball balancer of a washing machine in accordance with an exemplary embodiment;
FIGS. 7 and 8 are graphs respectively illustrating vibration and noise values according to the relation between a gap and viscous oil in a ball balancer of a washing machine in accordance with another exemplary embodiment; and
FIGS. 9 and 10 are graphs respectively illustrating vibration and noise values according to the relation between a gap and viscous oil in a ball balancer of a washing machine in accordance with yet another exemplary embodiment.



DETAILED DESCRIPTION OF EMBODIMENTS
Reference will now be made in detail to exemplary embodiments, an example of which is illustrated in the accompanying drawings, wherein like reference numerals refer to like elements throughout. Exemplary embodiments are described below by referring to the annexed drawings.
FIG. 1 is a schematic sectional view of a drum washing machine in accordance with an exemplary embodiment. As shown in FIG. 1, the drum washing machine includes a housing 1 forming the external appearance of the washing machine, a tub 2 installed in the housing 1 for containing washing water, a drum 10 rotatably disposed in the tub 2 such that laundry is put into the drum to be washed, and a door 4 hinged to the opened front surface of the housing 1.
Water supply pipes 5 and a detergent supply device 6 for supplying washing water and a detergent to the tub 2 are disposed above the tub 2, and a drain pipe 7 for discharging the washing water contained in the tub 2 to the outside of the housing 1, when the washing of the laundry is completed, is disposed below the tub 2.
A rotary shaft 8 is extended through the rear surface of the tub 2 and is disposed on the rear surface of the drum 10, and a driving motor 9, to which the rotary shaft 8 is connected, is installed at the outside of the rear surface of the tub 2. Accordingly, when the driving motor 9 is operated, the rotary shaft 8 is rotated, and thus the drum 10 is rotated together with the rotation of the rotary shaft 8.
A plurality of dehydration holes 10a is formed through the circumferential surface of the drum 10. The dehydration holes 10a allow the washing water contained in the tub 2 to flow into the drum 10 so as to wash the laundry using the washing water, in which the detergent dissolves, in a washing operation, and allow the washing water to be discharged to the outside of the housing 1 through the drain pipe 7 in a dehydrating operation.
A plurality of lifters 10b is disposed in the drum 10 in the longitudinal direction. As the drum 10 is rotated at a low speed in the washing operation, the lifters 10b lift laundry, soaked in the washing water, from the bottom of the drum 10, and then drop the laundry to the bottom of the drum 10, thus allowing the laundry to be effectively washed.
Therefore, in the washing operation, the rotary shaft 8 is rotated alternately in regular and opposite directions using the driving motor 9 and the drum 10 is rotated at a low speed, thus washing the laundry. Further, in the dehydrating operation, the rotary shaft 8 is rotated in one direction and the drum 10 is rotated at a high speed, thus dehydrating the laundry.
When the drum 10 is rotated at the high speed in the dehydrating operation, the center of gravity of the drum 10 does not coincide with the center of rotation of the drum 10, or the laundry is not uniformly disposed in the drum 10 but is crowded at a specific region of the drum 10. Then, the drum 10 cannot maintain its dynamic balance.
In order to prevent the above dynamic unbalance of the drum 10 so that the drum 10 can be rotated at a high speed under the condition that the center of gravity of the drum 10 coincides with the center of rotation of the drum 10, ball balancers 20 are respectively installed at front and rear ends of the drum 10.
FIG. 2 is an exploded perspective view of the drum of the washing machine of an exemplary embodiment, and FIG. 3 is a perspective view of the drum of the washing machine of an exemplary embodiment in an assembled state. As shown in FIGS. 2 and 3, the drum 10 includes a cylindrical main body 11 having opened front and rear end portions and provided with the dehydration holes 10a and the lifters 10b, a front member 12 connected to the opened front end portion of the main body 11 and provided with an opening 14 through which laundry is put into or taken out of the main body 11, and a rear member 13 to which the rotary shaft 8 (with reference to FIG. 1) for rotating the drum 10 is connected, wherein the rear member 13 is connected to the opened rear end portion of the main body 11.
A ring-shaped recess 15 having an approximately U-shaped section for accommodating the ball balancer 20 is formed in the edge of the front member 12, and a ring-shaped recess (not shown) having an approximately U-shaped section for accommodating the ball balancer 20 is formed in the edge of the rear member 13.
The front member 12 and the rear member 13, as shown in FIG. 3, are respectively inserted into the rims of the front and rear ends of the main body 11, and are connected to the main body 11 using screws or by other methods.
FIG. 4 illustrates the ball balancer installed on the drum of the washing machine of an exemplary embodiment. As shown in FIG. 4, the ball balancer 20 includes a ring-shaped racer 21/23 and forming a closed internal space by melting, a plurality of metal balls filling the internal space of the racer 21/23 to exhibit a balancing function, and viscous oil (not shown), which is a silicon-based synthetic lubricant, for adjusting the moving speed of the balls 22. Of course, the plurality of the balls 22 and the viscous oil fill the internal space of the racer 21/23 before both ends of the racer 21/23 are connected.
The above ring-shaped ball balancer 20 is configured to be attachable to the drum 10 with the viscous oil and the plurality of balls 22 already in the ring-shaped ball balancer 20. The ring-shaped ball balancer 20 is disposed in each of the ring-shaped recesses 15 provided in the front and rear members 12 and 13 of the drum 10, and is welded to each of the ring-shaped recesses 15 at several points, thus being simply and rapidly assembled with the ring-shaped recesses 15.
The ring-shaped ball balancer 20 includes a first injection molded 21 member and a second injection molded member 23 joined to each other to form the closed internal space, the first injection molded member including a first side wall 24, a second side wall 26 and a connecting wall 25 between the first side wall 24 and the second side wall 26. The first injection molded member 21 has an open side opposite to the connecting wall, and the second injection molded member 23 is adapted to cover the open side of the first injection molded member 21. The first injection molded member 21 has a cross section of an approximately U-shaped cross-section with a first rounded corner between the first side wall 24 and the connecting wall 25 and a second rounded corner between the second side wall 26 and the connecting wall 25.
In FIG. 4, the first side wall 24 is located most distant from a center of rotation of the annular-shaped race, and the second side wall 26 is located closest to the center of rotation of the annular-shaped race. Alternatively, the second side wall 26 may be located most distant from a center of rotation of the annular-shaped race, and the first side wall 24 may be located closest to the center of rotation of the annular-shaped race.
The first side wall 24 of the first injection molded member 21 includes a first engaging portion 42a to engage with a first portion 43a of the second injection molded member 23, and the second side wall 26 includes a second engaging portion to engage with a second portion of the second injection molded member 23. As shown in FIG. 4, the first side wall 24 and the second side wall 26 of the first injection molded member 21 include first and second fusion ridges 42a to engage with first portion 43a of the second injection molded member 23, and the second side wall 26. The second injection molded member 23, which is coupled to the first injection molded member 21 in order to form a closed internal space for holding a plurality of balls 22 and a viscous fluid, includes first and second fusion grooves 43a recessed along edges thereof so as to correspond to the first and second fusion ridges 42a, and also includes outer pocket flanges 43b. The outer pocket flanges 43b protrude to external rib portions 42b formed on an outer surface of the first injection molded member 21 outside of the first and second fusion grooves 43a so as to be spaced apart from the first and fusion ridges 42a of the first injection molded member 21 by a predetermined distance.
Thus, when the first and second fusion ridges 42a of the first injection molded member 21 are fitted into the first and second fusion grooves 43a of the second injection molded member 23 in order to fuse the first injection molded member 21 with the second injection molded member 23, as shown in FIG. 4, when heat is generated between the first and second fusion ridges 42a of the first injection molded member 21 and the first and second fusion grooves 43a of the second housing 43, the first and second fusion ridges 42a and the first and second fusion grooves 43a are firmly fused with each other.
In accordance with an exemplary embodiment, in order to operate the ball balancer 20 rapidly, a relation between a gap (L1+L2), between the racer 21/23 and the balls 22, and the viscous oil is very important. Preferably, the viscosity of the viscous oil is in proportion to the gap (L1+L2) between the racer 21/23 and the balls 22. For example, in the case that the gap is increased, the viscosity of the viscous oil should be high so as to exhibit excellent vibration and noise characteristics, and in the case that the gap is decreased, the viscosity of the viscous oil should be low so as to effectively move the balls 22 to maintain the dynamic balance of the drum 10 rapidly.
More specifically, FIGS. 5 to 10 are graphs respectively illustrating vibration and noise values according to the relation between a gap and viscous oil in ball balancers of washing machines in accordance with various exemplary embodiments.
First, FIGS. 5 and 6 are graphs respectively illustrating vibration and noise values according to the relation between a gap and viscous oil in a ball balancer of a washing machine in accordance with one exemplary embodiment. FIGS. 5 and 6 illustrate results of a test, in which viscous oils having viscosities of 100, 200, and 350 cSt, being on the market at present, are used under the condition that the gap (L1+L2) varies. In the case that the ball balancer uses viscous oil having a viscosity of 100 ̃380 cSt under the condition that the gap is less than 1 mm, the obtained vibration exceeded a value (the range of the vibration of the drum), which is usually required, i.e., 2 mm, and thus this ball balancer was improper. On the other hand, in the case that the ball balancer uses the viscous oil having a viscosity of 100 ̃380 cSt under the condition that the gap is more than 2 mm, the obtained vibration satisfied the value but the obtained noise exceeded a value (the noise generated from balls), which is usually required, i.e., 57 dB, and thus this ball balancer was improper.
FIGS. 7 and 8 illustrate results of a test, in which viscous oil having a viscosity of 100 cSt is used under the condition that the gap (L1+L2) varies. In the case that the ball balancer uses viscous oil having a viscosity of 1 ̃100 cSt under the condition that the gap is less than 0.5 mm, the obtained vibration exceeded the value (the range of the vibration of the drum), which is usually required, i.e., 2 mm, and thus this ball balancer was improper. On the other hand, in the case that the ball balancer uses the viscous oil having a viscosity of 1 ̃100 cSt under the condition that the gap is more than 1 mm, the obtained vibration satisfied the value but the obtained noise exceeded the value (the noise generated from balls), which is usually required, i.e., 57 dB, and thus this ball balancer was improper.
FIGS. 9 and 10 illustrate results of a test, in which viscous oils having viscosities 500 and 1,000 cSt are used under the condition that the gap (L1+L2) varies. In the case that the ball balancer uses viscous oil having a viscosity of 380 ̃1,000 cSt under the condition that the gap is less than 2 mm, the obtained vibration exceeded the value (the range of the vibration of the drum), which is usually required, i.e., 2 mm, and thus this ball balancer was improper. On the other hand, in the case that the ball balancer uses the viscous oil having a viscosity of 380 ̃1,000 cSt under the condition that the gap is more than 3 mm, the obtained vibration satisfied the value but the obtained noise exceeded the value (the noise generated from balls), which is usually required, i.e., 57 dB, and thus this ball balancer was improper.
In the case that the ball balancer uses viscous oil having a viscosity of 1,000 cSt or more, the gap may be more than 3 mm. However, when the gap exceeds 3 mm, the ball balancer cannot correctly control the vibration and noise values due to the piling upon of the balls each other and the tolerance between injection molded products for forming the racer 21/23. Further, in the case that the ball balancer uses viscous oil having a viscosity of 1 cSt, being close to water, the viscosity of the viscous oil cannot be uniformly controlled.
Consequently, when the viscosity of the viscous oil is 1 ̃100 cSt, the gap is set to 0.5 ̃1.0 mm, when the viscosity of the viscous oil is 100 ̃380 cSt, the gap is set to 1.0 ̃2.0 mm, and when the viscosity of the viscous oil is not more than 380 ̃1,000 cSt, the gap is set to 2.0 ̃3.0 mm. Thereby, the ball balancer effectively exhibits a balancing function.
As apparent from the above description, exemplary embodiments provide a washing machine having ball balancers, in which a relation between a gap between the inner wall of a racer of each of the ball balancers and the balls, and viscous oil is optimized, thus minimizing the vibration and noise of the washing machine.
Although a few exemplary embodiments have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these exemplary embodiments, the scope of which is defined in the claims and their equivalents.

## Claims

1. A drum type washing machine comprising:
a housing;
a drum to receive laundry to be washed, the drum including a front cover with an opening provided at a front side of a drum body to receive laundry and a rear cover provided at a rear side of the drum body, an annular recess formed in the front cover such that the annular recess is located immediately adjacent to a wall of the drum body; and
a ball balancer coupled to the drum to compensate for a dynamic imbalance during rotation of the drum, the ball balancer including an annular-shaped racer having a closed internal space in which a plurality of balls and viscous oil are accommodated, the annular-shaped racer including a first injection molded member and a second injection molded member joined to each other to form the closed internal space, the first injection molded member including a first side wall, a second side wall and a connecting wall between the first side wall and the second side wall, the first injection molded member having an open side opposite to the connecting wall, and the second injection molded member is adapted to cover the open side of the first injection molded member,
wherein the ball balancer is supported by the annular recess formed in the front cover of the drum, the ball balancer is configured to be attachable to the drum with the viscous oil and the plurality of balls already in the ball balancer.

2. The drum type washing machine of claim 1, wherein the first side wall, the second side wall and the connecting wall form a three-sided annular-shaped structure having the open side.

3. The drum type washing machine of claim 2, wherein the three-sided annular-shaped structure has a U-shaped cross-section with a first rounded corner between the first side wall and the connecting wall and a second rounded corner between the second side wall and the connecting wall.

4. The drum type washing machine of claim 1, wherein the first side wall includes a first engaging portion to engage with a first portion of the second injection molded member, and the second side wall includes a second engaging portion to engage with a second portion of the second injection molded member.

5. The drum type washing machine of claim 4, wherein the first engaging portion includes a first fusion ridge.

6. The drum type washing machine of claim 5, wherein the second injection molded member is provided with a first fusion groove adapted to receive the first fusion ridge.

7. The drum type washing machine of claim 6, wherein the second injection molded member includes an outer pocket flange protruding from an outer side of the first fusion groove.

8. The drum type washing machine of claim 7, wherein the first side wall includes an external rib portion provided at an outer surface thereof to engage with the outer pocket flange of the second injection molded member.

9. The drum type washing machine of claim 8, wherein the first side wall is located most distant from a center of rotation of the annular-shaped racer, and the second side wall is located closest to the center of rotation of the annular-shaped racer.

10. The drum type washing machine of claim 8, wherein the second side wall is located most distant from a center of rotation of the annular-shaped racer, and the first side wall is located closest to the center of rotation of the annular-shaped racer.

11. The drum type washing machine of claim 8, wherein the second engaging portion includes a second fusion ridge.

12. The drum type washing machine of claim 11, wherein the second injection molded member is provided with a second fusion groove adapted to receive the second fusion ridge.

13. The drum type washing machine of claim 1, wherein the wall of the drum body and a part of the front cover forming the recess form double wall layers to reinforce the drum body.

14. The drum type washing machine of claim 13, wherein a width between opposing inner surfaces of the first and second side walls defining the closed internal space of the racer is greater than a diameter of the balls such a combined gap (L1+L2) in a range of 1.0 ̃2.0 mm is formed between the balls and the opposing inner surfaces of the first and second side walls and a viscosity of the viscous oil is in a range of 100 ̃380 cSt.