Patent Publication Number: US-6986271-B2

Title: Washing machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
   This application claims the benefit of Korean Patent Application No. 2002-8244 filed on Feb. 15, 2002, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference. 
   BACKGROUND OF THE INVENTION 
   1. Field of the Invention 
   The present invention relates to washing machines and, more particularly, to a washing machine having a wobbling device which causes a wobbling action of a washboard installed at an inner bottom surface of a spin-drying tub, so as to effectively wash clothes. 
   2. Description of the Related Art 
   Generally, washing machines are used to wash clothes by rotating a cylindrical rotary tub containing the clothes and wash water therein. Such washing machines have been typically classified into two types, that is, drum type washing machines and vertical shaft type washing machines. In the drum type washing machines, a rotary tub is horizontally set in a cabinet and is rotated around a horizontal axis of the cabinet in opposite directions. These actions repeatedly move the clothes seated on an inner lower surface of the rotary tub upward, and allow the clothes to be dropped from the top to the bottom inside of the rotary tub, due to gravity, to wash the clothes. The vertical shaft type washing machines are designed such that a rotary tub with a pulsator is vertically set in a cabinet, and is rotated around a vertical axis of the cabinet in opposite directions. The forced water currents generated by the pulsator wash the clothes placed inside the rotary tub of the vertical shaft type washing machines. 
   The present invention relates to vertical shaft type washing machines.  FIG. 1  shows the construction of a conventional vertical shaft type washing machine. The conventional vertical shaft type washing machine comprises a cabinet  1  which forms the external appearance of the washing machine. A tub assembly, consisting of two tubs, is set in the cabinet  1 . That is, a washing tub  2  is vertically set in the cabinet  1  and contains wash water therein, while a spin-drying tub  3  is rotatably and concentrically set in the washing tub  2 . The spin-drying tub  3  is perforated in its sidewall to have spin-drying perforations  3   c.  A pulsator  4  is installed on the bottom of the spin-drying tub  3 , and generates wash water currents inside the spin-drying tub  3 . The vertical shaft type washing machine also has a drive motor  5  and a power transmission unit  6 , which are installed in a space between the bottom of the washing tub  2  and the bottom of the cabinet  1 . The drive motor  5  is a reversible motor which generates a reversible rotating force. The power transmission unit  6  transmits the reversible rotating force from the drive motor  5  to the tub assembly, thus rotating the spin-drying tub  3  and the pulsator  4 . 
   The top of the cabinet  1  is open to allow a user to place or remove the clothes from the spin-drying tub  3 . A door  7  is hinged to an edge of the open top of the cabinet  1 . The user is thus allowed to open the top of the cabinet  1  to place or remove the clothes from the spin-drying tub  3 . A drain hose  8  extends from the bottom of the washing tub  2  to the outside of the cabinet  1 , and discharges the wash water from the washing tub  2  to the outside after a washing mode operation. 
   The spin-drying tub  3  comprises a bottom part  3   a,  with a spin-drying shaft holder  9  exteriorly mounted to the bottom part  3   a.  The power transmission unit  6  has two shafts  6   a  and  6   b.  That is, the spin-drying shaft  6   a  of the power transmission unit  6  is coupled to the bottom of the spin-drying tub  3  by the spin-drying shaft holder  9 , while the washing shaft  6   b  of the power transmission unit  6  passes through the interior of the spin-drying shaft  6   a  so as to be coupled to the pulsator  4 . The pulsator  4  is installed on the bottom of the spin-drying tub  3 . The washing shaft  6   b  rotates the pulsator  4  during the washing mode operation. 
   The above vertical shaft type washing machine with the pulsator  4  is operated as follows. When the washing machine is turned on, after placing clothes into the spin-drying tub  3 , water is primarily fed into the washing tub  2 . The reversible drive motor  5  is rotated to generate a rotating force, which is transmitted to the pulsator  4  through the washing shaft  6   b  of the power transmission unit  6 . Accordingly, the pulsator  4  is rotated in opposite directions. Such a reversible rotating action of the pulsator  4  generates forced wash water currents inside the spin-drying tub  3 , and the clothes are washed by being forcibly moved along with the forced wash water currents while coming into frictional contact with both an internal surface of the spin-drying tub  3  and with each other. 
   When such a washing mode operation is completed, after elapse of a predetermined period of time, the wash water is drained from the washing tub  2  to the outside of the washing machine through the drain hose  8  before a rinsing mode operation is started. After the rinsing mode operation, a high speed rotating force of the reversible drive motor  5  is transmitted to the spin-drying tub  3  through the spin-drying shaft  6   a  of the power transmission unit  6 , thus rotating the spin-drying tub  3  in a direction at a high speed to spin-dry the clothes. When a spin-drying mode operation is completed, the washing machine finishes the operation of washing the clothes. 
   In the washing mode operation of the conventional vertical shaft type washing machine, the pulsator  4  is alternately rotated in opposite directions to generate the forced wash water currents in the spin-drying tub  3 , thereby washing the clothes by the forced wash water currents. The clothes are thus forcibly moved in the opposite directions, and are twisted and tangled up to each other. Therefore, the conventional vertical shaft type washing machine abrades and damages the clothes during a washing operation, and forces a user to untwist and untangle the clothes after the washing operation. Accordingly, such a vertical shaft type washing machine is inconvenient to use and promotes rapid wear and tear of the clothes. 
   In addition, to generate the forced wash water currents, the pulsator  4  must be reversibly rotated in short time intervals during the washing mode operation. Thus, the reversible drive motor  5  consumes a lot of electric power while being repeatedly rotated in the opposite directions at such short time intervals. Such an alternating rotation of the reversible drive motor  5  also reduces the expected life span of the reversible drive motor  5 . 
   Furthermore, the conventional vertical shaft type washing machine with the pulsator  4  is designed such that a desired washing effect is enhanced by forcibly rotating the clothes in the opposite directions using the forced water currents. Accordingly, such a design requires an excessive amount of water in the washing tub  2  during the washing mode operation. A large volume of the water required for the washing operation, in turn, requires an additional use of detergent, inevitably causing a greater harm of the environment. Recent trends show that consumers are making a conscious decision to save water and restrict the use of household chemicals to preserve the environment. Therefore, there is a need to solve the above-mentioned problems experienced by the conventional vertical shaft type washing machines. 
   SUMMARY OF THE INVENTION 
   Accordingly, it is an object of the present invention to provide a washing machine having a wobbling device which causes an upward and downward wobbling action of a washboard without rotating the washboard during a washing mode operation, thus effectively washing the clothes. 
   Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention. 
   To achieve the above and other objects of the present invention, there is provided a washing machine comprising a washing tub for containing wash water therein, a spin-drying tub rotatably set in the washing tub for containing clothes therein, a spin-drying shaft which rotates the spin-drying tub, a washing shaft which axially passes through and projects from a top end of the spin-drying shaft, and a wobbling device which is coupled to a projected end of the washing shaft and causes the clothes to wobble upward and downward to wash the clothes. 
   The wobbling device comprises an inclined rotary shaft which is arranged in an axial direction of the washing shaft at an angle of inclination, a first rotary unit which rotates in response to torque of the washing shaft, having a first sloping surface which is inclined in a radial direction of the washing shaft at a set angle of inclination, a second rotary unit which is arranged to be rotated relative to the first rotary unit, having a second sloping surface which corresponds to the first sloping surface of the first rotary unit, and a hole which is axially formed in the second rotary unit and rotatably receives the inclined rotary shaft therein, an actuating pin which is installed to and rotates along with one of the washing shaft, the first rotary unit and the inclined rotary shaft, a wobbling pin and a leveling pin which are provided on the second rotary unit at spaced positions, and a washboard which is arranged at an inner lower portion of the spin-drying tub, and wobbles in response to rotating of the actuating pin in contact with the wobbling pin and being leveled in response to rotating of the actuating pin in contact with the leveling pin. 
   The inclined rotary shaft passes through the hole of the second rotary unit so as to be projected at an upper end thereof from an upper end of the second rotary unit. The actuating pin is transversely mounted to the upper end of the inclined rotary shaft, and the leveling and wobbling pins are arranged on an upper surface of the second rotary unit at positions angularly spaced apart from each other at an angle of, for example, about 180°. 
   The first inclined surface is formed at an upper end of the first rotary unit, and the second inclined surface is formed at a lower end of the second rotary unit. Accordingly, the upper surface of the secondary rotary unit is leveled to have the washboard in a leveled position in response to the actuating pin being rotated in a first direction while coming into contact with the leveling pin, wherein an upper part of the first sloping surface meets an upper part of the second sloping surface. On the other hand, the upper surface of the secondary rotary unit is inclined to have the washboard in a wobbling position in response to the actuating pin being rotated in a second direction while coming into contact with the wobbling pin, wherein a lower part of the first sloping surface meets the upper part of the second sloping surface. 
   The washing machine may further comprise a vertical rotary shaft which is arranged between the washing shaft and the first rotary unit, and transmits the torque of the washing shaft to the first rotary unit, wherein the vertical rotary shaft is coupled at a upper end thereof to a lower end of the first rotary unit, and coupled at a lower end thereof to an upper end of the washing shaft. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     These and other objects and advantages of the present invention will become apparent and more readily appreciated from the following description of the embodiments, taken in conjunction with the accompanying drawings of which: 
       FIG. 1  is a sectional view showing the construction of a conventional vertical shaft type washing machine with a pulsator; 
       FIGS. 2A and 2B  are sectional views showing the construction of a vertical shaft type washing machine having a wobbling device according to an embodiment of the present invention, in which  FIG. 2A  shows the washing machine with the wobbling device placed in its leveling position for performing a spin-drying mode operation, and  FIG. 2B  shows the washing machine with the wobbling device placed in its wobbling position for performing a washing mode operation; 
       FIG. 3  is an exploded perspective view showing the construction of the wobbling device shown in  FIGS. 2A and 2B ; 
       FIG. 4  is a sectional view of the wobbling device shown in  FIGS. 2A and 2B  in its leveling position; 
       FIG. 5  is a sectional view of the wobbling device taken along the line V—V of  FIG. 4 ; 
       FIG. 6  is a sectional view of the wobbling device shown in  FIGS. 2A and 2B  in its wobbling position; and 
       FIG. 7  is a sectional view of the wobbling device taken along the line VII—VII of FIG.  6 . 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Reference will now be made in detail to the embodiments of the present invention, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout. The embodiments are described below in order to explain the present invention by referring to the figures. 
     FIGS. 2A and 2B  show the construction of a vertical shaft type washing machine having a wobbling device according to an embodiment of the present invention. Specifically,  FIG. 2A  shows the wobbling device placed in its leveling position for performing a spin-drying mode operation, while  FIG. 2B  shows the wobbling device placed in its wobbling position for performing a washing mode operation. The technical term “wobbling position” is defined as a position where the wobbling device arranges a washboard in an inclined position so as to cause an upward and downward wobbling action of the washboard. The technical term “leveling position” is defined as a position where the wobbling device arranges the washboard in a horizontal position so as to hold the washboard without allowing such a wobbling action of the washboard. 
   As shown in  FIGS. 2A and 2B , the vertical shaft type washing machine (“washing machine”) of the present invention comprises a tub assembly having two tubs set in a cabinet  1 . That is, a washing tub  2  is vertically set in the cabinet  1  for containing wash water therein, while a spin-drying tub  3  is rotatably and concentrically set in the washing tub  2 . The spin-drying tub  3  is perforated on its sidewall to have a plurality of spin-drying perforations  3   c.  In addition, both a drive motor  5  and a power transmission unit  6  are installed in a space between the bottom of the washing tub  2  and the bottom of the cabinet  1 . The washing machine further comprises a wobbling device  20  installed on the bottom of the spin-drying tub  3 . 
   A spin-drying shaft holder  9  is mounted to an exterior portion of a bottom part  3   a  of the spin-drying tub  3 . The bottom part  3   a  couples a spin-drying shaft  6   a  of the power transmission unit  6  to the spin-drying tub  3 . The spin-drying shaft  6   a  rotates the spin-drying tub  3  during a spin-drying mode operation. A washing shaft  6   b  of the power transmission unit  6  passes through the interior of the spin-drying shaft  6   a,  and is projected upward from a top end of the spin-drying shaft  6   a  so as to be coupled to a wobbling device  20 . 
   The wobbling device  20  is provided inside the cabinet  1  at the bottom of the spin-drying tub  3 . During a washing mode operation of the washing machine, the wobbling device  20  is selectively placed at the wobbling position as shown in  FIG. 2B , so as to cause an upward and downward wobbling action of clothes to wash the clothes. During a spin-drying mode operation of the washing machine, the wobbling device  20  is placed at the leveling position as shown in  FIG. 2A , so as to be rotated along with the spin-drying tub  3  to spin-dry the clothes. 
     FIG. 3  shows an exploded perspective view of the wobbling device  20  of  FIGS. 2A and 2B . 
   As shown in  FIG. 3 , the wobbling device  20  comprises a vertical rotary shaft  21 , which is coupled to the washing shaft  6   b  of the power transmission unit  6 . An inclined rotary shaft  22  is arranged above the vertical rotary shaft  21  while being inclined relative to a vertical axis at a predetermined angle of inclination. The wobbling device  20  further comprises a first rotary unit  30  which is used to rotate the vertical and inclined rotary shafts  21  and  22  at the same time. A second rotary unit  40  rotatably receives the inclined rotary shaft  22 , and is laid at its lower surface on an upper surface of the first rotary unit  30 . An actuating unit  50  is arranged on an upper surface of the second rotary unit  40 , and selectively shifts the wobbling device  20  between the wobbling position and the leveling position. A washboard  60  is included in the wobbling device  20 . The washboard  60  is shifted between two positions, that is, the inclined position and the horizontal position, in accordance with the change in position of the wobbling device  20  between the wobbling position and the leveling position. 
   The vertical rotary shaft  21  is coupled at its lower end to the upper end of the washing shaft  6   b  of the power transmission unit  6  through a tubular boss  70 . The vertical rotary shaft  21  is coupled at its top end to a lower portion of the first rotary unit  30  by means of a first locking pin  32 , which transversely passes through both the first rotary unit  30  and the vertical rotary shaft  21 . The vertical rotary shaft  21  is thus rotated along with the first rotary unit  30  when the washing shaft  6   b  is rotated. 
   To couple the vertical rotary shaft  21  to the washing shaft  6   b  so as to transmit torque of the washing shaft  6   b  to the vertical rotary shaft  21  without failure, both the lower end of the vertical rotary shaft  21  and the upper end of the washing shaft  6   b  are machined at their external surfaces to have uniformly spaced spline ridges  21   a  and  6   c,  respectively. The tubular boss  70  is machined at its internal surface to have corresponding spline grooves  72 . Therefore, the splined lower end of the vertical rotary shaft  21  is fitted into and coupled to the splined upper end of the boss  70 . In the same manner, the splined upper end of the washing shaft  6   b  is fitted into and coupled to the splined lower end of the boss  70 . 
   As shown in  FIG. 4 , a step  71  is formed at an intermediate portion of the internal surface of the boss  70  so as to separate the two shafts  6   b  and  21  from each other. The vertical shaft  21  is rotatably supported by both a base  23  and a housing  24 , which are installed at the bottom part  3   a  of the spin-drying tub  3  of FIG.  2 A. The construction of the base  23  and the housing  24  is not shown in  FIG. 3 , but will be described in more detail later herein with reference to FIG.  4 . 
   Referring back to  FIG. 3 , an upper surface of the first rotary unit  30  forms a first sloping surface  31 , which is inclined in a radial direction of the washing shaft  6   b  at an angle of inclination. A lower surface of the second rotary unit  40 , laid on the upper surface of the first rotary unit  30 , forms a second sloping surface  41 , which is inclined in the radial direction of the washing shaft  6   b  at the same inclination angle as that of the first sloping surface  31 . The angle of inclination of the two sloping surfaces  31  and  41  determines the upward and downward wobbling angle of the washboard  60 . In the present invention, the inclination angle of the two sloping surfaces  31  and  41  is, for example, about 5°˜20°. 
   The positional change of the wobbling device  20  between the wobbling position, which causes an inclined position of the washboard  60  for performing a washing mode operation as shown in  FIG. 2B , and the leveling position, which causes a horizontal position of the washboard  60  for performing a spin-drying mode operation as shown in  FIG. 2A , is accomplished by varying an angular position of the second sloping surface  41  of the second rotary unit  40  relative to the first sloping surface  31  of the first rotary unit  30 . Such a positional change of the wobbling device  20  will be described in more detail later herein. 
   The inclined rotary shaft  22  is rotatably received by the second rotary unit  40  while being inclined relative to the vertical rotary shaft  21   a  at the same inclination angle as that of the first and second sloping surfaces  31  and  41 , as best seen in FIG.  4 . This inclined rotary shaft  22  is coupled at its lower end to the upper portion of the first rotary unit  30  by means of a second locking pin  33 , which transversely passes through both the first rotary unit  30  and the inclined rotary shaft  22 . The inclined rotary shaft  22  is thus rotated along with the first rotary unit  30 . That is, the first rotary unit  30  is coupled to both the vertical rotary shaft  21  at its lower end and the inclined rotary shaft  22  at its upper end. Both the first rotary unit  30  and the inclined rotary shaft  22  are thus rotated at the same time when the vertical shaft  21  is rotated. 
   In such a case, the inclined rotary shaft  22  passes through an inclined hole  44  of the second rotary unit  40  prior to being coupled at its lower end to the first rotary unit  30 . The inclined rotary shaft  22  and the hole  44  of the second rotary unit  40  are designed so as to have a small gap formed between the shaft  22  and the hole  44  to allow the shaft  22  to be rotated in the second rotary unit  40 . 
   A support unit  80  is fitted over the second rotary unit  40 , and rotatably supports the second rotary unit  40 . The support unit  80  also supports the washboard  60  so as to have the washboard  60  wobble upward and downward without being rotated during a washing mode operation. In order to rotatably support the second rotary unit  40  relative to the support unit  80 , a first bearing  42  is interposed between the second rotary unit  40  and the support unit  80 . Two oil seals  43  are respectively provided at upper and lower ends of the first bearing  42  to seal the first bearing  42 . 
   The upper surface of the second rotary unit  40  is a horizontal surface as compared to its inclined lower surface  41 . The actuating unit  50  is arranged on the horizontal upper surface of the second rotary unit  40 . 
   The actuating unit  50  comprises an actuating plate  51 , which is fastened to the upper surface of the second rotary unit  40  by a locking bolt  55 . Two spaced pins, that is, a leveling pin  52  and a wobbling pin  53 , extend upward from the upper surface of the actuating unit  50  at spaced positions to a predetermined height. An actuating pin  54  is transversely mounted to the upper portion of the inclined rotary shaft  22  so as to have the actuating pin  54  be selectively stopped by either of the two pins  52  and  53  in accordance with a rotating direction of the inclined rotary shaft  22 , thus rotating the second rotary unit  40  in a desired direction. The construction and operation of the actuating unit  50  will be described in more detail later herein. 
   The above actuating unit  50  is covered with a cap  85  so as to be isolated from the outside of the cap  85 . The cap  85  is fastened to an upper end of the support unit  80 . 
   The washboard  60  comprises a central boss part  61 , which is formed at a central portion of the washboard  60 . The central boss part  61  has a cylindrical shape and is fitted over an external surface of the support unit  80 . A circular blade part  62  is integrally formed around an outside edge of the central boss part  61 , and seats clothes thereon during a washing operation. The blade part  62  initially extends downward and outward from the outside edge of the boss part  61  to form a diffuser shape, and secondarily extends horizontally to form a horizontal circular shape. A plurality of perforations  64  are formed at the blade part  62  to allow an upward and downward circulation of wash water through the washboard  60 . 
   As shown in  FIGS. 2A and 2B , a covering plate  68  is arranged along a circular edge of the blade part  62  of the washboard  60  and covers a gap between the spin-drying tub  3  and the edge of the blade part  62 . The covering plate  68  prevents the clothes from dropping to a position under the washboard  60 . The covering plate  68  is made of a material which is more flexible than the material of the washboard  60 . The covering plate  68  is arranged such that a gap is less likely to be left between the covering plate  68  and the spin-drying tub  3 . 
   Referring back to  FIG. 3 , to fasten the washboard  60  to the support unit  80 , a plurality of vertical ribs  81  are regularly formed on an external surface of the support unit  80 . A plurality of vertical grooves  63  are regularly formed on an internal surface of the central boss part  61  of the washboard  60 , and engage with the vertical ribs  81  of the support unit  80 , respectively. 
   A covering cap  65  covers the upper end of the support unit  80  at the top of the central boss part  61  of the washboard  60 , thus isolating the support unit  80  from the clothes seated on the washboard  60  during the washing operation. The covering cap  65  is fastened to the support unit  80 , for example, through a screw type engagement. 
     FIG. 4  shows a sectional view of the wobbling device  20  in the leveling position.  FIG. 5  shows a sectional view taken along the line V—V of  FIG. 4  illustrating an operation of the actuating unit  50  where the wobbling device  20  is placed in the leveling position. 
   As shown in  FIGS. 4 and 5 , the vertical rotary shaft  21  is rotatably held by a second bearing  25  inside the housing  24 . Two oil seals  26  are respectively provided at upper and lower ends of the second bearing  25  to seal the second bearing  25  and prevent an undesired infiltration of external impurities into the second bearing  25 . The housing  24 , for example, is bolted to the upper surface of the base  23 . The base  23 , having a disc shape with several holes, is also bolted to an internal surface of the bottom part  3   a  of the spin-drying tub  3  as shown in  FIGS. 2A and 2B . The lower end of the vertical rotary shaft  21  and the upper end of the washing shaft  6   b  are coupled to the tubular boss  70  through a spline coupling method, and the vertical rotary shaft  21  is rotated by the torque of the washing shaft  6   b.    
   The inclined rotary shaft  22  passes through the inclined hole  44  of the second rotary unit  40  at a predetermined angle of inclination, so as to have the upper and lower ends of the inclined rotary shaft  22  project from both ends of the second rotary unit  40 . In such a case, a small gap is formed between the inclined rotary shaft  22  and the hole  44  of the second rotary unit  40  so as to allow the shaft  22  to be rotated relative to the second rotary unit  40 . 
   The upper end of the vertical rotary shaft  21  and the lower end of the inclined rotary shaft  22  are coupled to the first rotary unit  30  by the two locking pins  32  and  33 , respectively. Therefore, the two shafts  21  and  22  are rotated along with the first rotary unit  30 . 
   The second rotary unit  40  is rotatably held in the support unit  80  by the first bearing  42  having the oil seals  43 . The washboard  60  is assembled to an external surface of the support unit  80 . 
   The actuating plate  51  of the actuating unit  50  is fastened to the upper surface of the second rotary unit  40  by the locking bolt  55 . The two spaced pins, that is, the leveling pin  52  and the wobbling pin  53 , extend upward from the upper surface of the actuating unit  50  at two positions, which are angularly spaced apart from each other by, for example, an angle of about 180° as shown in FIG.  5 . The actuating pin  54  is transversely mounted to the upper portion of the inclined rotary shaft  22 . The actuating pin  54  of the inclined rotary shaft  22  is selectively stopped by either of the two pins  52  and  53  in accordance with a rotating direction of the inclined rotary shaft  22 , thus rotating the second rotary unit  40  assembled with the actuating plate  51 . 
   When the actuating pin  54  of the inclined rotary shaft  22  is rotated from a position shown by the two-dot chain line of  FIG. 5  to another position shown by the solid line in accordance with a clockwise rotating action of the inclined rotary shaft  22 , the actuating pin  54  is brought into contact with the leveling pin  52 . In such a case, an upper part  31   a  of the first sloping surface  31  of the first rotary unit  30  meets an upper part  41   a  of the second sloping surface  41  of the second rotary unit  40  as shown in FIG.  4 . In addition, a lower part  31   b  of the first sloping surface  31  of the first rotary unit  30  meets the lower part  41   b  of the second sloping surface  41  of the second rotary unit  40 . Therefore, the upper surfaces of both the second rotary unit  40  and the support unit  80  are horizontally positioned. This creates a horizontal positioning of the washboard  60 , which is assembled with the support unit  80 . That is, the wobbling device  20  of this invention is placed in its leveling position for performing a spin-drying mode operation. 
   The second rotary unit  40  is rotatably set in the support unit  80  by the first bearing  42 . Thus, it is necessary to stably hold the support unit  80  such that the support unit  80  is not rotated by a rotating action of the second rotary unit  40 . To accomplish the above and other objects, a flexible holder  86  is installed at a position between the housing  24  and the support unit  80 . The flexible holder  86  surrounds the first rotary unit  30  and a central portion of the housing  24 . The flexible holder  86  is designed so as to be flexible in a vertical direction in response to a wobbling action of the washboard  60 . Upper and lower ends of the flexible holder  86  are fastened to the support unit  80  and the housing  24  by, for example, fastening wires  87 , respectively. 
     FIGS. 6 and 7  show sectional views corresponding to  FIGS. 4 and 5 , respectively, where the wobbling device  20  is converted from the leveling position to the wobbling position. That is, the washboard  60  wobbles upward and downward to perform a washing mode operation.  FIG. 7  shows a sectional view of the wobbling device  20  taken along the line VII—VII of  FIG. 6  to illustrate an operation of the actuating unit  50  when the wobbling device  20  is placed in the wobbling position. 
   When the actuating pin  54  of the inclined rotary shaft  22  is rotated from the position shown by the two-dot chain line of  FIG. 7  to another position shown by the solid line in accordance with a counterclockwise rotating action of the inclined rotary shaft  22 , for performing a washing mode operation, the actuating pin  54  is brought into contact with the wobbling pin  53 . In such a case, the upper part  31   a  of the first sloping surface  31  of the first rotary unit  30  meets the lower part  41   b  of the second sloping surface  41  of the second rotary unit  40  as shown in FIG.  6 . In addition, the lower part  31   b  of the first sloping surface  31  of the first rotary unit  30  meets the upper part  41   a  of the second sloping surface  41  of the second rotary unit  40 . Therefore, the two sloping surfaces  31  and  41  are positioned almost horizontally, while the upper surfaces of both the second rotary unit  40  and the support unit  80  are inclinedly positioned. This creates an inclined position of the washboard  60 , which is assembled with the external surface of the support unit  80 . When both the inclined rotary shaft  22  and the second rotary unit  40  in the above state are rotated by the torque of the washing shaft  6   b,  the washboard  60  wobbles upward and downward at a predetermined amplitude in response to a rotating speed of the inclined rotary shaft  22 . 
   An operational effect of the vertical shaft type washing machine of the present invention having the wobbling device  20  will be described herein below. 
   When the washing machine is turned on after placing the clothes into the spin-drying tub  3 , water is primarily fed into the washing tub  2 . At the same time, the drive motor  5  is rotated to generate a rotating force, which is transmitted to the wobbling device  20  through the power transmission unit  6 , thus actuating the wobbling device  20 . 
   That is, while the water is fed into the washing tub  2 , both the washing shaft  6   b  and the vertical rotary shaft  21  are rotated, for example, clockwise by the drive motor  5  at a low speed to rotate the spin-drying tub  3  at a low speed, and cause the clothes to be wetted by water. The inclined rotary shaft  22 , coupled to the vertical rotary shaft  21  through the first rotary unit  30 , is also rotated along with the two shafts  6   b  and  21 . The inclined rotary shaft  22  is thus rotated clockwise at an angle of about 90° from the position shown by the two-dot chain line of  FIG. 5 , and so the actuating pin  54  of the inclined rotary shaft  22  is brought into contact with the leveling pin  52 . In such a case, the upper part  31   a  of the first sloping surface  31  of the first rotary unit  30  meets the upper part  41   a  of the second sloping surface  41  of the second rotary unit  40  as shown in FIG.  4 . Therefore, the upper surfaces of both the second rotary unit  40  and the support unit  80  are horizontally positioned, thus creating a horizontal positioning of the washboard  60 . That is, the wobbling device  20  of this invention is placed in its leveling position. 
   When the inclined rotary shaft  22  at such a leveling position is further rotated clockwise, the upper surface of the second rotary unit  40  is rotated along with the inclined rotary shaft  22  while maintaining the horizontal position of its upper surface. Both the support unit  80  and the washboard  60  maintain their horizontal positions without performing any wobbling action. In such a case, the spin-drying tub  3  is rotated at a low speed by the spin-drying shaft  6   a,  thus rotating the clothes laid on the washboard  60  and allowing the clothes to be uniformly wetted by the water fed into the washing tub  2 . 
   When the washing shaft  6   b  in the above state is rotated counterclockwise, with the spin-drying shaft  6   a  stopped, the vertical rotary shaft  21 , the first rotary unit  30  and the inclined rotary shaft  22  are simultaneously rotated counterclockwise. Therefore, the actuating pin  54  of the inclined rotary shaft  22  is rotated counterclockwise from the position of  FIG. 5  at an angle of about 180°, thus being brought into contact with the leveling pin  52  as shown in  FIG. 7   
   When the actuating unit  50  is shifted from the position of  FIG. 5  to the position of  FIG. 7 , the upper part  31   a  of the first sloping surface  31  of the first rotary unit  30  meets the lower part  41   b  of the second sloping surface  41  of the second rotary unit  40  as shown in FIG.  6 . Therefore, the upper surfaces of both the second rotary unit  40  and the support unit  80  are inclinedly positioned, thus creating an inclined position of the washboard  60 . That is, the wobbling device  20  of this invention is placed in its wobbling position. 
   When the inclined rotary shaft  22  at such a wobbling position is further rotated counterclockwise, the second rotary unit  40  is rotated along with the inclined rotary shaft  22 . In such a case, both the support unit  80  and the washboard  60  wobble upward and downward without being rotated. When both the support unit  80  and the washboard  60  wobble upward and downward without being rotated as described above, the washboard  60  imparts vertical impact energy to the clothes, and generates vertically directional water currents, thus washing the clothes. In such a case, the impact energy applied to both the clothes and the wash water is increased in proportion to the rotating speed of the washing shaft  6   b.  Therefore, it is possible to accomplish a desired washing effect by appropriately controlling both the amount of wash water and the rotating speed of the washing shaft in accordance with the amount of clothes to be washed. 
   When the washing mode operation is completed, after a predetermined length of time from a start of the washing operation, the wash water is drained from the washing tub  2  through the drain hose  8  prior to starting a rinsing mode operation which removes detergent from the clothes. After the rinsing mode operation, the spin-drying tub  3  is rotated at a high speed by the spin-drying shaft  6   a  to spin-dry the clothes. In such a case, the actuating pin  54  of the actuating unit  50  is rotated clockwise from the position of  FIG. 7  to the position of FIG.  5 . The wobbling device  20  is thus converted to its leveling position where the washboard  60  is positioned horizontally. In such a case, the washboard  60  is rotated along with the spin-drying shaft  6   a  without performing any wobbling action, and a desired spin-drying mode operation is performed. 
   In the washing mode operation, clothes are washed by the wobbling action of the washboard  60 . That is, during the wobbling action of the washboard  60 , the clothes are imparted with both mechanical impact energy acting in a vertical direction, and hydraulic impact energy caused by the wash water flowing through the perforations  64  of the washboard  60 . Thus, it is possible to accomplish a desired washing effect with a small amount of water contained in the washing tub  2  where the clothes laid on the washboard  60  are merely wetted by the water. Accordingly, the washing machine of the present invention reduces the amount of water required in a washing operation, as compared to a conventional washing machine having a pulsator. 
   As described above, the wobbling device  20  includes the vertical rotary shaft  21 , which is arranged between the washing shaft  6   b  and the first rotary unit  30 . However, it is understood that the wobbling device  20  of the present invention may be fabricated without the vertical rotary shaft  21 . That is, the washing shaft  6   b  may be directly coupled to the first rotary unit  30  in place of being indirectly coupled to the first rotary unit  30  through such a vertical rotary shaft  21 , without affecting the functionality of the present invention. 
   In addition, the leveling pin  52  and the wobbling pin  53  are provided at the upper surface the actuating unit  50 , which includes the actuating plate  51  assembled to the upper surface of the second rotary unit  40 . However, it is understood that the positions of the two pins  52  and  53  may be changed without affecting the functionality of the present invention. That is, the two pins  52  and  53  may be directly formed at the upper surface of the second rotary unit  40  in place of being formed at the actuating plate  51 . 
   Furthermore, the actuating pin  54  is transversely installed at the upper portion of the inclined rotary shaft  22 . However, it is understood that the position of the actuating pin  54  may be changed. That is, the actuating pin  54  may be provided on any one of the first rotary unit  30 , the vertical rotary shaft  21  and the washing shaft  6   b.  In such a case, both the leveling pin  52  and the wobbling pin  53  may be placed at appropriate positions of the second rotary unit  40  in accordance with the position of the actuating pin  54 . 
   As described above, the present invention provides a vertical shaft type washing machine having a wobbling device which causes an upward and downward wobbling action of a washboard without rotating the washboard during a washing mode operation. Therefore, the washing machine does not cause clothes to be twisted and tangled up during the washing operation, thereby preventing abrasion and damage to the clothes during the washing operation. In addition, the washing machine is convenient to use as a user need not untwist and untangle the clothes after the washing operation. 
   In the washing machine of this invention, a washing shaft is rotated in one direction during the washing operation. Therefore, it is possible to reduce the consumption of electric power of a drive motor. In addition, the expected life span of the drive motor is increased. 
   Additionally, it is possible to accomplish a desired washing effect with a small amount of water (a low water level) in a washing tub, where the clothes laid on a washboard are merely wetted by the water. The desired washing effect is, in part, effectively accomplished by an upward and downward wobbling action of the washboard. Thus, the washing machine of the present invention requires less water and detergent to carry out a washing operation than the conventional washing machine. Accordingly, the washing machine of the present invention also provides a marketing advantage in light of the recent trend toward saving water and limiting the use of materials that pollute the environment. 
   Although a few embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the appended claims and their equivalents.