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.

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
       [0001]    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 
       [0002]    1. Field 
         [0003]    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. 
         [0004]    2. Description of the Related Art 
         [0005]    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. 
         [0006]    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. 
         [0007]    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. 
         [0008]    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. 
         [0009]    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. 
         [0010]    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. 
         [0011]    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. 
         [0012]    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 
       [0013]    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. 
         [0014]    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. 
         [0015]    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. 
         [0016]    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. 
         [0017]    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. 
         [0018]    In accordance with yet another aspect of embodiments, the present invention provides 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. 
         [0019]    In accordance with yet another aspect of embodiments, the present invention provides 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 
         [0020]    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: 
           [0021]      FIG. 1  is a schematic sectional view of a washing machine in accordance with an exemplary embodiment; 
           [0022]      FIG. 2  is an exploded perspective view of a drum of the washing machine in accordance with an exemplary embodiment; 
           [0023]      FIG. 3  is a perspective view of the drum of the washing machine in accordance with an exemplary embodiment in an assembled state; 
           [0024]      FIG. 4  is a view illustrating a ball balancer installed on the drum of the washing machine in accordance with an exemplary embodiment; 
           [0025]      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; 
           [0026]      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 
           [0027]      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 
       [0028]    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. 
         [0029]      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 . 
         [0030]    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 . 
         [0031]    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 . 
         [0032]    A plurality of dehydration holes  10   a  is formed through the circumferential surface of the drum  10 . The dehydration holes  10   a  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. 
         [0033]    A plurality of lifters  10   b  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  10   b  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. 
         [0034]    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. 
         [0035]    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. 
         [0036]    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 . 
         [0037]      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  10   a  and the lifters  10   b,  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 . 
         [0038]    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 . 
         [0039]    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. 
         [0040]      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  and forming a closed internal space by melting, a plurality of metal balls filling the internal space of the racer  21  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  before both ends of the racer  21  are connected. 
         [0041]    The above 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 . 
         [0042]    In accordance with an exemplary embodiment, in order to operate the ball balancer  20  rapidly, a relation between a gap (L 1 +L 2 ), between the racer  21  and the balls  22 , and the viscous oil is very important. Preferably, the viscosity of the viscous oil is in proportion to the gap (L 1 +L 2 ) between the racer  21  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. 
         [0043]    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. 
         [0044]    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 (L 1 +L 2 ) 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. 
         [0045]      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 (L 1 +L 2 ) 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. 
         [0046]      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 (L 1 +L 2 ) 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. 
         [0047]    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  31 . 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. 
         [0048]    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. 
         [0049]    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. 
         [0050]    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.