Washing machine with balancing device having fluid accommodation portion

A washing machine provided with a balancing device which may suppress variation in horizontal vibration of a spin basket without performing control operation. The balancing device includes a ring-shaped casing installed to be concentric with the spin basket, and a plurality of the balancing balls and a viscous fluid. A ring-shaped ball accommodation portion, a fluid accommodation portion provided at a lower inner side of the ball accommodation portion in a radial direction of the ball accommodation portion, and a communication channel are formed in the casing. The fluid accommodation portion is provided at a portion of the casing along a circumferential direction of the casing. A bottom surface of the ball accommodation portion is inclined downward such that the balancing balls gather at the opposite position facing the fluid accommodation portion when rotation of the spin basket is stopped.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of Japanese Patent Applications Nos. 2012-209179 and 2012-202282, both filed on Sep. 14, 2012 in the Japanese Patent Office, and Korean Patent Application No. 10-2013-0064893, filed on Jun. 5, 2013 in the Korean Intellectual Property Office, the disclosures of which are incorporated herein by reference.

BACKGROUND

Embodiments of the present disclosure relate to a washing machine having an outer tub, a spin basket rotatably installed in the outer tub, and a balancing device mounted to the spin basket.

2. Description of the Related Art

Conventionally, a washing machine having an outer tub and a spin basket rotatably installed in the outer tub to perform washing, rinsing and drying of laundry such as clothing accommodated in the spin basket has been known.

The conventional washing machine is subjected to vibration when the spin basket having laundry accommodated therein rotates to perform drying operation. This vibration mainly results from uneven distribution of the laundry accommodated in the spin basket. Accordingly, a ball balancer to damp the vibration is mounted to the spin basket.

Specifically, the ball balancer is formed in a ring shape, and is provided with a plurality of balancing balls accommodated in an accommodation chamber and viscous fluid. The balancing balls and viscous fluid are allowed to move in the accommodation chamber in the circumferential direction of the accommodation chamber. The balancing balls are submerged in the viscous fluid and thus movement thereof is limited to an extent. Thereby, self-excited vibration of the balancing balls revolving in the accommodation chamber may be restricted. During rotation of the spin basket, the balancing balls are moved in the accommodation chamber in the circumferential direction by centrifugal force and finally positioned at the side opposite to the maldistributed laundry. As a result, balanced rotation of the spin basket is maintained by the weight of the balancing balls.

In the case that the positioned balancing balls fail to perform balancing during stoppage of rotation of the spin basket before start of the drying operation, the maldistribution of the balancing balls causes variation in magnitude of horizontal vibration (rocking rotation) of the spin basket while the rate of rotation of the spin basket crosses a first resonance section. If the horizontal vibration of the spin basket is large, the outer tub may collide with the outer casing. In addition, when the outer tub collides with the outer casing, control is generally performed to force the drying operation to be terminated. This may waste energy and time.

In the case of the conventional washing machine, a recessed accommodation portion to accommodate the balancing balls is formed on the bottom surface of the accommodation chamber. Thereby, unbalanced positioning of the balancing balls before start of the drying operation of the washing machine is resolved. Accordingly, when the rate of rotation of the spin basket passes the first resonance section, variation of the horizontal vibration of the spin basket due to maldistribution of the balancing balls may be suppressed.

However, the conventional washing machine has a viscous fluid accommodated in the accommodation chamber. Thereby, movement of the balancing balls may be restricted by the viscous resistance of the viscous fluid, and thus it may be difficult to accommodate the balancing balls in the recessed accommodation portion.

In this regard, a control operation may be performed to decelerate or accelerate rotation of the spin basket to move the balancing balls to positions where weight balance is formed between the balancing balls and the viscous fluid.

However, this control may take energy and time.

SUMMARY

Therefore, it is an aspect of the present disclosure to provide a washing machine which may suppress variation of horizontal vibration of the spin basket caused by maldistribution of the balancing balls when the rate of rotation of the spin basket passes the first resonance section, even without moving the balancing balls to positions where weight balance is formed between the balancing balls and the viscous fluid.

According to the present disclosure, a ball accommodation portion has a bottom surface inclined such that, when rotation of a spin basket is stopped, balancing balls gather at a position opposite to the side of a fluid accommodation portion.

In accordance with one aspect of the present disclosure, a washing machine includes an outer tub, a spin basket rotatably installed in the outer tub, and a balancing device mounted to the spin basket.

The balancing device includes a ring-shaped casing installed to be concentric with the spin basket, and a plurality of balancing balls and a viscous fluid, the balancing balls and the viscous fluid being accommodated in the casing. A ring-shaped ball accommodation portion to accommodate the balancing balls, a fluid accommodation portion provided at a lower inner side of the ball accommodation portion in a radial direction of the ball accommodation portion to accommodate the viscous fluid, and a communication channel allowing the ball accommodation portion to communicate with the fluid accommodation portion are formed in the casing. The fluid accommodation portion is provided at a portion of the casing along a circumferential direction of the casing. A bottom surface of the ball accommodation portion is inclined downward as the bottom surface extends from a position of the fluid accommodation portion to an opposite position such that the balancing balls gather at the opposite position facing the fluid accommodation portion when rotation of the spin basket is stopped.

According to the above description, the bottom surface of the ball accommodation portion is inclined downward as the bottom surface extends from a position of the fluid accommodation portion to an opposite position such that the balancing balls gather at the opposite position facing the fluid accommodation portion when rotation of the spin basket is stopped. Thereby, when rotation of the spin basket is stopped, weight balance is automatically formed among the balancing balls and the viscous fluid in the ball accommodation portion and the viscous fluid in the fluid accommodation portion. As a result, variation in horizontal vibration of the spin basket due to maldistribution of the balancing balls may be suppressed when the rate of rotation of the spin basket passes the first resonance section, even without moving the balancing balls to a position at which weight balance is formed between the balancing balls and the viscous fluid.

A majority of the viscous fluid is accommodated in the fluid accommodation portion and a remaining portion of the viscous may be accommodated in the ball accommodation portion, when rotation of the spin basket is stopped, and the balancing device is configured such that weight balance is formed, when rotation of the spin basket is stopped, among the balancing balls having gathered at the opposite position to the fluid accommodation portion, the viscous fluid in the ball accommodation portion, and the viscous fluid in the fluid accommodation portion.

According to the above description, the balancing device is configured such that weight balance is formed, when rotation of the spin basket is stopped, among the balancing balls having gathered at the opposite position to the fluid accommodation portion, the viscous fluid in the ball accommodation portion, and the viscous fluid in the fluid accommodation portion. Thereby, when rotation of the spin basket is stopped, weight balance is automatically formed among the balancing balls, the viscous fluid in the ball accommodation portion, and the viscous fluid in the fluid accommodation portion. As a result, variation in horizontal vibration of the spin basket due to maldistribution of the balancing balls may be suppressed when the rate of rotation of the spin basket passes (crosses) the first resonance section, even without moving the balancing balls to a position at which weight balance is formed between the balancing balls and the viscous fluid.

The communication channel may be configured not to allow the balancing balls to move from the ball accommodation portion to the fluid accommodation portion, and the balancing device is configured such that when a rate of rotation of the spin basket is lower than a predetermined rate of rotation, the viscous fluid is accommodated in the fluid accommodation portion due to gravity, and when the rate of rotation of the spin basket is equal to or higher than the predetermined rate of rotation, the viscous fluid in the fluid accommodation portion is moved into the ball accommodation portion through the communication channel by centrifugal force.

According to the above description, the balancing device is configured such that when a rate of rotation of the spin basket is lower than a predetermined rate of rotation, the viscous fluid is accommodated in the fluid accommodation portion due to gravity, and when the rate of rotation of the spin basket is equal to or higher than the predetermined rate of rotation, the viscous fluid in the fluid accommodation portion is moved into the ball accommodation portion through the communication channel by centrifugal force. Thereby, the balancing balls are submerged in the viscous fluid and movement thereof is limited by the viscous resistance of the viscous fluid when the rate of rotation of the spin basket is equal to or higher than the predetermined rate of rotation. As a result, during rotation of the spin basket, self-excited vibration by the balancing balls may be attenuated.

The casing may include a casing body having an opening open upward, and a cover to cover the opening of the casing body, wherein a partition wall may be integrally formed on a lower surface of the cover to protrude downward from the lower surface to partition the communication channel.

According to the above description, partition wall may be integrally formed on a lower surface of a casing cap to protrude downward from the lower surface to partition the communication channel. Thereby, the casing cap may be used to form the communication channel.

The balancing device may include the ring-shaped casing installed to be concentric with the spin basket, and a plurality of balancing ball groups of the balancing balls, and a viscous fluid, the balancing balls and the viscous fluid being accommodated in the casing, and each of the balancing ball groups including balancing balls of the balancing balls having the same diameter, wherein a diameter of the balancing balls included in one of the balancing ball groups is different from a diameter of the balancing balls included in another one of the balancing ball groups, the ball accommodation portion to accommodate the balancing ball groups is formed in the casing, wherein the ball accommodation portion is provided with a plurality of ring-shaped concave portions having different radial widths and integrally stacked such that the radial width of one of the concave portions is smaller than the radial width of another one of the concave portions positioned below the one of the concave portions, the balancing balls in each of the balancing ball groups is accommodated in one of the concave portions having a radial width corresponding to the diameter of the balancing balls, a bottom surface of each of the concave portions is inclined in a circumferential direction such that, when rotation of the spin basket is stopped, the balancing balls included in each of the balancing ball groups move by rolling and gather at a lowest position on the bottom surface to cause a center of gravity of the balancing ball groups to coincide with an axis of rotation of the spin basket.

According to the above description, the ball accommodation portion in the casing is provided with a plurality of concave portions having different radial widths and integrally stacked in a vertical direction, and the radial width of the ball accommodation portion is reduced as it extends downward. In addition, a balancing ball group including balancing balls having a diameter corresponding to the radial width of a corresponding concave portion with a bottom surface inclined in a circumferential direction is accommodated in the corresponding concave portion. The balancing balls accommodated in the corresponding concave portion move by rolling on the bottom surface in a circumferential direction of the concave portion and gather when rotation of the spin basket is stopped, such that the center of gravity of the balancing ball groups coincides with the axis of rotation of the spin basket. Since the balancing balls roll on the bottom surfaces of the respective concave portions and gather at one place due to gravity, thereby automatically forming weight balance, special control is not needed as in conventional cases. Accordingly, waste of time and energy may be prevented.

In addition, the balancing device has a simple structure in which ring-shaped concave portions having different radial widths are vertically stacked, a ball accommodation portion has concave portions each of which has a bottom surface inclined in a circumferential direction, and a plurality of balancing balls is accommodated in the respective concave portions, manufacture may be facilitated and manufacturing cost may be lowered.

Each of the concave portions may be disposed radially outward when extending downward, and each of the concave portions is provided with inner and outer circumferential walls formed in a shape of an approximately vertical round pipe, and the bottom surface formed in a shape of a flange extending from a lower end of the inner circumferential wall in a radially outward direction, wherein each inner circumferential wall extends upward from a radially outer edge of the bottom connected thereto, and each outer wall is connected with the outer circumferential wall of the concave portion vertically adjoining the each outer wall, and each of the balancing ball groups is pushed against the outer circumferential wall by centrifugal force to move upward along the outer circumferential wall when a rate of rotation of the spin basket is equal to or higher than a predetermined rate of rotation.

According to the above description, the outer wall of each concave portion is inclined upward in a radially outward direction, and is connected to an outer wall of a concave portion vertically adjacent thereto, and accordingly, when the balancing balls accommodated in each concave portion is moved upward along the outer circumferential wall of the concave portion when the rate of rotation of the spin basket is equal to or higher than a predetermined rate of rotation. For example, when the predetermined rate of rotation is over the first resonance section, the balancing ball groups move in the casing along a circumferential direction, and thus weight balance of the spin basket may be formed. In addition, the inner circumferential wall of each concave portion is connected to the outer edge of the bottom surface of another concave portion positioned at the upper side of the concave portion. Therefore, when the rate of rotation of the spin basket is relatively low, the balls fall down. At this time, the large-diameter balancing balls are first stopped by a bottom surface. Then, the balancing balls roll along the slope of the bottom surfaces in a circumferential direction to form weight balance. As such, after rotation of the spin basket is stopped, the balancing balls may autonomously form the weight balance.

The bottom surface may be inclined downward in a radially outward direction.

That is, since the bottom surface of each concave portion is inclined downward in a radially outward direction, small-diameter balancing balls move by rolling on this bottom surface in a radially outward direction and fall on a concave portion below each concave portion. Accordingly, the small-diameter balancing balls may be prevented from staying on the bottom surface of each concave portion.

The ball accommodation portion may include two concave portions vertically stacked, and the balancing ball groups includes a first balancing ball group including first balancing balls and a second balancing ball group including second balancing balls having a diameter smaller than a diameter of the first balancing balls, wherein a ratio of the diameter of the second balancing balls to the diameter of the first balancing balls is between about 0.25 and about 0.9.

According to the above description, two kinds of ball balancing groups are used, and accordingly the ball accommodation portion has at least two steps. Therefore, a compact balancing device may be realized. In addition, since the ratio of the diameter of the small-diameter balancing balls to the diameter of the large-diameter balancing balls is between about 0.25 and about 0.9, the area of the portion of the large-diameter balancing ball stuck in the concave portion accommodating the small-diameter balancing balls decreases, and therefore, the large-diameter balancing balls may move easily in a circumferential direction.

DETAILED DESCRIPTION

Reference will now be made in detail to the embodiments of the present disclosure.

Hereinafter, embodiment of the present disclosure will be described in detail with reference to the accompanying drawings, wherein like reference numerals refer to like elements throughout. The embodiments are simply illustrative and are not intended to limit the present disclosure,

FIG. 1is a longitudinal cross-sectional view showing a bell-shaped electric washing machine (hereinafter, referred to as a washing machine). As shown inFIG. 1, the washing machine10includes an outer casing11, an outer tub12(also referred to as a water tub), a spin basket13(also referred to as a washing tub), and a balancing device20(also referred to as a ball balancer).

The outer casing11is formed in the shape of an approximately rectangular box having a bottom. The outer tub12is elastically supported through a suspension15in the outer casing11. That is, the suspension15connects the outer casing11to the outer tub12. In addition, the suspension15damps vibration of the outer tub12. Washing water is accommodated in the outer tub12. The outer tub12is formed in the shape of a cylinder having a bottom.

The spin basket13is rotatably installed in the outer tub12. Laundry is accommodated in the spin basket13. The spin basket13is formed in the shape of a cylinder having a bottom. A pulsator14is installed at the bottom of the spin basket13. The pulsator14produces rotating water streams in the spin basket13. A plurality of through holes (not shown) is formed in the wall of the spin basket13. The through holes allow the spin basket13to share washing water with the outer tub12.

A power transmission unit18is installed at the bottom of the outer tub12. The power transmission unit18is provided with a driving motor16and a shaft assembly17. The driving motor16is connected with the pulsator14. The power transmission unit18selectively rotates the spin basket13or the pulsator14in a forward or reverse direction according to a program of a control unit (not shown). Thereby, washing, rinsing and drying of the laundry in the spin basket13are sequentially performed.

The balancing device20is mounted to the upper inner surface of the spin basket13. The balancing device20serves to maintain balance of rotation of the spin basket13. The balancing device20is formed in a circular ring shape.

FIG. 2is a plan view showing a balancing device with the cover of a casing removed from the casing, andFIG. 3is a perspective cross-sectional view showing a balancer with a portion thereof cut away. As shown inFIGS. 1 to 3, the balancing device20includes a casing21, and a plurality of the balancing balls30and a viscous fluid31accommodated in the casing21. In this embodiment, sixteen balancing balls30are provided.

The casing21is installed to be concentric with the spin basket13. The casing21is formed in a circular ring shape. The casing21has a casing body22and a cover23. The casing body22has an opening open upward. The cover23covers the upper side of the opening of the casing body22. Formed in the casing21are a ball accommodation portion24(also referred to as a race), a fluid accommodation portion25(also referred to as a tank), and a communication channel26.

The balancing balls30are accommodated in the ball accommodation portion24. The ball accommodation portion24is formed in a circular ring shape. The outer lateral surface24aof the ball accommodation portion24facing in the radial direction is inclined upward throughout the whole circumference of the ball accommodation portion24as it extends outward.

The fluid accommodation portion25is provided under the inner side of the ball accommodation portion24in a radial direction. The viscous fluid31is accommodated in the fluid accommodation portion25. The fluid accommodation portion25is provided along a portion of the circumference of the casing21. In the illustrated embodiment, the fluid accommodation portion25is arranged along a half of the circumference of the casing21. That is, the fluid accommodation portion25has a semi-circular ring shape. The fluid accommodation portion25is set to have a volume allowing weight balance to be formed, when rotation of the spin basket13is stopped, among the balancing balls30collected at a position opposite to the fluid accommodation portion25, the viscous fluid31in the ball accommodation portion24, and the viscous fluid31in the fluid accommodation portion25.

The bottom surface24bof the ball accommodation portion24is inclined downward from the location of the fluid accommodation portion25to the opposite side, such that the balancing balls30gather at one place opposite to the fluid accommodation portion25when rotation of the spin basket13is stopped. Specifically, the bottom surface24bof the ball accommodation portion24has the highest vertical position at a portion corresponding to the center of the fluid accommodation portion25in the circumferential direction (the left end portion of the bottom surface24binFIGS. 2 and 3). From this portion, the bottom surface24bis gradually lowered as it extends to the opposite side of the fluid accommodation portion25. The bottom surface24bof the ball accommodation portion24has the lowest point at a portion of the bottom surface24bfacing the highest portion of the bottom surface24bin the radial direction (the right end portion of the bottom surface24binFIGS. 2 and 3). That is, the balancing balls30gather in a predetermined portion including the portion at the lowest position when rotation of the spin basket13is stopped.

The bottom surface24bof the ball accommodation portion24is set to have an inclination angle allowing the balancing balls30to gather at one place at the opposite side of the fluid accommodation portion25even if the laundry is maldistributed in the spin basket13when rotation of the spin basket13is stopped. Specifically, the inclination angle of the bottom surface24bof the ball accommodation portion24is greater than or equal to about 1°. More specifically, it may be equal to or greater than about 2.5°.

The communication channel26allows the ball accommodation portion24to communicate with the fluid accommodation portion25. The communication channel26does not allow the balancing balls30to move from the ball accommodation portion24to the fluid accommodation portion25. That is, the width of the casing of the communication channel26in a radial direction is less than the outer diameter of the balancing balls30. Thereby, while the balancing balls30remain accommodated in the ball accommodation portion24, the viscous fluid31is allowed to move between the ball accommodation portion24and the fluid accommodation portion25through the communication channel26. The width of the communication channel may be, for example, between about 2 mm to 8 mm. This range may save space.

The communication channel26is partitioned by an inner partition wall23aand an outer partition wall25a. The inner partition wall23ais integrated with the casing cap23to protrude downward from the lower surface of the casing cap23along the entire circumferential length. Thereby, the casing cap23may be used to form the communication channel26. The portion of the inner partition wall23acorresponding to the fluid accommodation portion25protrudes farther downward than the bottom surface24bof the ball accommodation portion24. The inner partition wall23ais formed in a circular ring shape. The outer partition wall25ais formed by the outer side wall of the fluid accommodation portion25in the radial direction.

The casing21is adapted to form weight balance for itself. Specifically, the casing21is provided with a weight at a predetermined position such that the weight balance is formed by itself.

The balancing balls30are formed of a metal such as aluminum or iron. The balancing balls30are set to cancel the expected maximum maldistribution of the laundry in the spin basket13. The balancing balls30designed as above may attenuate vibration against the expected maximum maldistribution of the laundry or a maldistribution of the laundry weaker than the expected maximum maldistribution. The outer diameter of the balancing balls30may be, for example, about 20 mm. The balancing balls30are rotated around the ball accommodation portion24in a circumferential direction by rotation of the spin basket13.

The viscous fluid31is formed of oil having a predetermined viscosity. The total weight of the viscous fluid31is greater than that of the balancing balls30. The viscous fluid31is mainly accommodated in the fluid accommodation portion25when rotation of the spin basket13is stopped or when the rate of rotation of the spin basket13is lower than a first predetermined rate of rotation below the first resonance section (seeFIG. 4). Herein, the first resonance section is a range of rate of rotation in which the horizontal vibration (rocking rotating) of the spin basket13is maximized at the initial stage of the drying operation. In this embodiment, about 80% to 90% of the viscous fluid31is accommodated in the fluid accommodation portion25. The remaining portion of the viscous fluid31is accommodated in the ball accommodation portion24. Specifically, the remaining portion of the viscous fluid31is accommodated in the half the circumferential length of the ball accommodation portion24positioned at the opposite to the fluid accommodation portion25. In addition, the viscous fluid31in the fluid accommodation portion25and the viscous fluid31in the ball accommodation portion24forms a continuous surface when rotation of the spin basket13is stopped.

Meanwhile, the viscous fluid31in the fluid accommodation portion25is moved into the ball accommodation portion24through the communication channel by centrifugal force according to rotation of the spin basket13. In addition, the optimum section of rates of rotation of the spin basket for movement of the viscous fluid31from the fluid accommodation portion25into the ball accommodation portion24is larger than the first resonance section and smaller than the second resonance section. Herein, the second resonance section is the range of rate of rotation in which the vertical vibration of the spin basket13is maximized. The section of rate of rotation in which self-excited vibration occurs is the range of rate of rotation above than the second resonance section. In addition, when rotation of the spin basket13is stopped, the surface of the viscous fluid31becomes higher than the portion of the bottom surface24bof the ball accommodation portion24corresponding to both ends of the fluid accommodation portion25in the circumferential direction such that the viscous fluid31moving from the fluid accommodation portion25into the ball accommodation portion24moves back to the fluid accommodation portion25through the communication channel26due to gravity.

Hereinafter, a description will be given of the drying operation of the washing machine10.

When rotation of the spin basket13is stopped prior to start of the drying operation of the washing machine10, the balancing balls30gather at one place at the opposite side facing the fluid accommodation portion25since the bottom surface24bof the ball accommodation portion24is inclined downward from the fluid accommodation portion25to the opposite side of the fluid accommodation portion25(seeFIG. 3). At this time, a majority of the viscous fluid31is accommodated in the fluid accommodation portion25and the remaining portion thereof is accommodated in the ball accommodation portion24. In addition, weight balance is formed among the balancing balls30collected at one place opposite to the fluid accommodation portion25, the viscous fluid31in the ball accommodation portion24, and the viscous fluid31in the fluid accommodation portion25(the viscous fluid31in an area surrounded by a double dashed line inFIG. 2). This weight balance is maintained while the rate of rotation of the spin basket13is lower than the first predetermined rate of rotation. As such, when rotation of the spin basket13is stopped, weight balance is automatically formed among the balancing balls30and the viscous fluid31in the ball accommodation portion24and the viscous fluid31in the fluid accommodation portion25. As a result, variation in horizontal vibration of the spin basket13due to maldistribution of the balancing balls30may be suppressed when the rate of rotation of the spin basket13passes (crosses) the first resonance section, even without moving the balancing balls to a position at which weight balance is formed between the balancing balls and the viscous fluid.

When the drying operation of the washing machine10begins, the spin basket13starts to rotate. At this time, the balancing device20mounted to the spin basket13also starts to integrally rotate.

When the rate of rotation of the spin basket13passes the first resonance section, the balancing balls30in the ball accommodation portion24is automatically moved to the position opposite to the maldistributed laundry. Thereby, balance of rotation of the spin basket13may be maintained.

At this time, the balancing balls30in the ball accommodation portion24are moved to the inner upper side of the ball accommodation portion along the outer lateral surface24ain the radial direction of the ball accommodation portion24by centrifugal force according to rotation of the spin basket13(see the balancing balls30denoted by a double dashed line inFIG. 3).

As shown inFIG. 4, when the rate of rotation of the spin basket13is lower than the first predetermined rate of rotation, the viscous fluid31in the fluid accommodation portion25remains in the fluid accommodation portion25due to gravity.

When the rate of rotation of the spin basket13is equal to or higher than the first predetermined rate of rotation, the viscous fluid31in the fluid accommodation portion25is moved into the ball accommodation portion24through the communication channel26by centrifugal force according to rotation of the spin basket13. When the rate of rotation of the spin basket13becomes a second predetermined rate of rotation higher than the first resonance section and lower than the second resonance section, all the viscous fluid31in the fluid accommodation portion25is moved into the ball accommodation portion24. Thereby, the balancing balls30are submerged in the viscous fluid31and movement thereof is limited by the viscous resistance of the viscous fluid31. As a result, during rotation of the spin basket13, self-excited vibration by the balancing balls30may be attenuated.

When the drying operation of the washing machine10is terminated and the rate of rotation of the spin basket13becomes lower than the first predetermined rate of rotation, the viscous fluid31moved from the fluid accommodation portion25to the ball accommodation portion24is recovered as it flows to the fluid accommodation portion25through the communication channel26due to gravity. Thereby, a majority of the viscous fluid31is accommodated in the fluid accommodation portion25and the remaining portion of the viscous fluid31is accommodated in the ball accommodation portion24. As a result, the viscous fluid31returns to its original state.

When rotation of the spin basket13is stopped, the balancing balls30gather at one place opposite to the fluid accommodation portion25since the bottom surface24bof the ball accommodation portion24is inclined downward from the location of the fluid accommodation portion25to the opposite side. Thereby, the balancing balls30returns to their original state.

FIG. 5is a graph illustrating a relationship between weight balance formed by the balancing balls and the viscous fluid and variation in horizontal vibration of the spin basket. InFIG. 5, the horizontal axis represents the number of balancing balls that do not form weight balance with the viscous fluid, and the vertical axis represents the maximum amplitude of vibration of the spin basket when the rate of rotation of the spin basket passes the first resonance section. The illustrated embodiment corresponds to the case of having no balancing balls failing to form weight balance with the viscous fluid. As shown inFIG. 5, as the number of the balancing balls that do not form weight balance with the viscous fluid increases, the maximum amplitude of vibration of the spin basket increases and thus variation in horizontal vibration of the spin basket also increases. In addition, as the maximum amplitude of vibration of the spin basket increases, the possibility of collision between the outer tub and the outer casing increases.

While the bottom surface24bof the ball accommodation portion24is illustrated as being inclined along the entire circumferential length, embodiments of the present disclosure are not limited thereto. A portion of the bottom surface24bof the ball accommodation portion24corresponding to the balancing balls30gathering at one place opposite to the fluid accommodation portion25may be formed to be a horizontal plane and the other portion may be formed to be an inclined plane.

In addition, while the fluid accommodation portion25is illustrated as being arranged along half the circumferential length of the casing21, the range in which the fluid accommodation portion25is arranged is not limited thereto so long as weight balance is formed between the balancing balls30and the viscous fluid31when rotation of the spin basket13is stopped. Herein, a narrower range of arrangement of the fluid accommodation portion25may save more space.

Further, in the illustrated embodiment, a majority of the viscous fluid31is accommodated in the fluid accommodation portion25when rotation of the spin basket13is stopped. However, embodiments of the present disclosure are not limited thereto. All the viscous fluid31may alternatively be accommodated in the fluid accommodation portion25when rotation of the spin basket13is stopped.

In addition, while the first predetermined rate of rotation is illustrated in the embodiment as being a rate of rotation below the first resonance section, embodiments of the present disclosure are not limited thereto. The first predetermined rate of rotation may alternatively be a rate of rotation above the first resonance section and below the second resonance section.

As shown inFIGS. 6 to 11, a balancing device120according to another embodiment of the present disclosure is formed in a circular ring shape and mounted to the upper inner surface of the spin basket13.FIG. 7is a lateral cross-sectional view showing a balancing device120with the spin basket13stopped, andFIG. 8a partially enlarged view showing the balancing device120ofFIG. 7. The balancing device120has a ring-shaped casing121installed to be concentric with the spin basket13. Accommodated in the casing121are a large-diameter balancing ball group122(a first balancing ball group) configured with a plurality of large-diameter balancing balls122a(first balancing balls) having the same diameter, a small-diameter balancing ball group123(a second balancing ball group) configured with a plurality of small-diameter balancing balls123a(second balancing balls) having the same diameter smaller than the diameter of the large-diameter balancing balls122a, and a viscous fluid124. The balancing balls122aand123aare all formed of a metal such as, for example, aluminum or iron. The total weight of the small-diameter balancing ball group123is balanced with the total weight of the large-diameter balancing ball group122. In addition, the ratio rS/rLof the radius rSof the small-diameter balancing ball123ato the radius rLof the large-diameter balancing ball122amay be between about 0.25 and about 0.9. The ratio rS/rLmay be between about 0.5 and about 0.7. Additionally,FIGS. 6 and 7show one large-diameter balancing ball122aand one small-diameter balancing ball123a.

The casing121is formed of, for example, a resin in a circular ring shape. The casing121has a casing body125provided with a concave portion having an opening open upward, and a cover126approximately formed in a disk shape. The cover126closes the opening to form a ball accommodation portion127(also referred to as a race) to accommodate the large-diameter balancing ball group122and the small-diameter balancing ball group123. In addition, the casing121is adapted to form weight balance. Specifically, the casing121is provided with a weight, which is not shown, mounted at a predetermined position.

The ball accommodation portion127includes an upper concave portion128formed in a circular ring shape to allow the large-diameter balancing ball group122to be accommodated therein to be movable in the circumferential direction of the ball accommodation portion127, and a lower concave portion129integrally formed at the lower side of the upper concave portion128to allow the small-diameter balancing ball group123to be accommodated therein to be movable in the circumferential direction of the ball accommodation portion127. The lower concave portion129formed at the lower side of the upper concave portion128extends from a radial position father from the outer end of the upper concave portion128than the center of the upper concave portion128in a radial direction to the outer end of the upper concave portion128. The radial width WLof the lower concave portion129is less than the radial width WUof the upper concave portion128. In addition, the radial width WLof the lower concave portion129is slightly greater than the diameter2rSof the small-diameter balancing ball123a, and less than the radial width WUof the upper concave portion128. The radial width WUof the upper concave portion128is slightly greater than the diameter2rLof the large-diameter balancing ball122a.

The lower concave portion129is formed by an approximately vertical lower inner circumferential wall129aformed in a round pipe shape, a flange-shaped lower bottom surface129bradially protruding outward from the lower end of the lower inner circumferential wall129a, and a round pipe-shaped lower outer circumferential wall129cextending upward from the radial outer end of the lower bottom surface129b. In addition, the upper concave portion128formed by an approximately vertical upper inner circumferential wall128aformed in a round pipe shape and disposed at the upper side of the lower inner circumferential wall129aand radially more inward than the lower inner circumferential wall129a, a flange-shaped upper bottom surface128bradially protruding outward from the lower end of the upper inner circumferential wall128aand connected, at the radial outer end thereof, to the upper end of the lower inner circumferential wall129a, and a round pipe-shaped upper outer circumferential wall128cextending upward from the upper end of the lower outer circumferential wall129c.

The lower bottom surface129band the upper bottom surface128bare inclined in the circumferential direction, and the lowest points129dand128dthereof, which indicate the lowest positions on the lower bottom surface129band the upper bottom surface128bare spaced 180° from each other in the circumferential direction to face each other when they are viewed in a vertical direction. That is, inFIG. 7, the lowest point129dof the lower bottom surface129bis positioned on the left side, and the lowest point128dof the upper bottom surface128bis positioned on the right side. As shown inFIG. 8, the upper bottom surface128bis inclined downward in a radially outward direction, and the inclination angle θ1thereof is equal to or greater than about 1° with respect to a horizontal plane. Further, the lower outer circumferential wall129cis inclined upward in a radially outward direction, and the inclination angle θ2thereof is equal to or greater than about 40° and less than about 90° with respect to a horizontal plane. By setting the inclination angle θ2to be relatively large, the radial width of the casing121may be restricted and thus the balancing device120may become compact. Meanwhile, the lower end of the upper outer circumferential wall128cis inclined upward in a radially outward direction. This inclined portion has the same inclination angle as that of the lower outer circumferential wall129c, and a vertical dimension thereof increases as it approaches the lowest point128dof the upper concave portion128.

In addition, as shown inFIG. 8, a portion of the lower end of the large-diameter balancing ball122ais inserted into the lower concave portion129. The volume of the inserted portion varies with the radius ratio rS/rLbetween the balancing balls122aand123a. When the volume is large, the area of contact between the large-diameter balancing ball122a, the upper bottom surface128band upper outer circumferential wall128cbecomes large, resulting in large friction. In this case, it is difficult for the large-diameter balancing ball122ato roll on the upper bottom surface128b.FIG. 9is a graph illustrating a relationship between the radius ratio rS/rLand mobility of the large-diameter balancing ball122a, in which the horizontal axis represents the radius ratio rS/rL, and the vertical axis represents mobility of the large-diameter balancing ball122aon the upper bottom surface128b. As shown inFIG. 9, when the radius ratio rS/rLis set to a value between about 0.25 and about 0.9, the large-diameter balancing ball122amay relatively easily move. In addition, in view of restriction of the size of the balancing device120, setting the radius ratio rS/rLto be equal to or greater than about 0.25 may be practically desirable.

The viscous fluid124is configured with oil having a predetermined viscosity, and is accommodated in the ball accommodation portion127to a level causing the large-diameter balancing ball group122to be submerged. For example, the viscous fluid124fills about 80% of the volume of the ball accommodation portion127.

Operation of Balancing Device

Hereinafter, operation of the balancing device120during the drying operation of the washing machine10will be described with reference toFIGS. 7,8and10.FIG. 10is a view illustrating the state of the spin basket13rotating at a high rate of rotation after passing the first resonance section during the drying operation, which corresponds toFIG. 7. Herein, the first resonance section is a range of rate of rotation in which the horizontal vibration (rocking rotating) of the spin basket13is maximized at the initial stage of the drying operation. Similar toFIGS. 6 and 7,FIG. 10shows one large-diameter balancing ball122aand one small-diameter balancing ball123a.

When rotation of the spin basket13is stopped prior to start of the drying operation, the large-diameter balancing ball122aaccommodated in the upper concave portion128moves in the circumferential direction by rolling on the slope of the upper bottom surface128band gathers at the lowest point128d, as shown inFIG. 7. Meanwhile, the small-diameter balancing balls123aaccommodated in the lower concave portion129move in the circumferential direction by rolling on the slope of the lower bottom surface129b, and gather at the lowest point129d. The lowest point129dis at the position opposite to the lowest point128dof the upper bottom surface128b, when viewed in a vertical direction. Accordingly, the total weight of the large-diameter balancing ball group122is balanced with the total weight of the small-diameter balancing ball group123as described above. Thereby, the center of gravity of the large-diameter and small-diameter balancing ball groups122and123is on the axis of rotation of the spin basket13. This weight balance is maintained until the rate of rotation of the spin basket13passes the first resonance section. Since the large-diameter and small-diameter balancing balls122aand123aare made to roll on the bottom surfaces128band129bof the upper concave portion128and lower concave portion129and gather at one place due to gravity, automatically forming weight balance, unlike conventional cases, control of rotation of the spin basket13is not needed. Therefore, more energy and time may be saved than in the conventional cases. In addition, when the rate of rotation of the spin basket13passes (crosses) the first resonance section, variation in horizontal vibration of the spin basket13caused by maldistribution of the balancing balls122aand123amay be suppressed.

When the drying operation begins, the spin basket13starts to rotate. At this time, the balancing device20mounted to the spin basket13also starts to rotate together with the spin basket13. By centrifugal force, the balancing balls122aand123aare moved in a radially outward direction and moved upward along the outer circumferential walls128cand129cwhile being pressed against the outer circumferential walls128cand129c. In addition, once the rate of rotation of the spin basket13passes the first resonance section, the balancing balls122aand123aare raised up to the upper end of the ball accommodation portion127, and automatically moved in the circumferential direction to a position opposite to the maldistributed laundry. Thereby, balance of rotation of the spin basket13may be maintained.

When the rate of rotation of the spin basket13is relatively low, on the other hand, the viscous fluid124is accommodated such that the surface124athereof is almost level by gravity. When the rate of rotation of the spin basket13exceeds the first resonance section, the viscous fluid124is moved in a radially outward direction by centrifugal force, as shown inFIG. 10. Movement of the large-diameter and small-diameter balancing balls122aand123ain a circumferential direction is restricted by the viscous resistance of the viscous fluid124moved in a radially outward direction. As a result, collision between the balancing balls122aand123aor self-excited vibration and noise resulting therefrom may be suppressed during rotation of the spin basket13.

When the drying operation of the washing machine10is terminated and thus the spin basket13rotates at a low rate, the viscous fluid124having been collected at a radially outer portion of the inside of the ball accommodation portion127flows downward by gravity. As a result, the viscous fluid124returns to its original state. When the rate of rotation of the spin basket13becomes equal to or lower than a predetermined rate of rotation in the section of low rate of rotation, the large and small balancing balls122aand123arespectively fall. At this time, the large-diameter balancing balls122aare held in the upper concave portion128by the upper bottom surface128bof the upper concave portion128. Meanwhile, the small-diameter balancing balls123apass through the upper concave portion128and fall to the lower concave portion129below the upper concave portion128since the diameter thereof is smaller than the radial width WL the lower concave portion129. At this time, a small-diameter balancing ball123amay fall on the upper bottom surface128bof the upper concave portion128. In this case, the small-diameter balancing ball123amoves along the radial slope of the upper bottom surface128bin a radially outward direction and falls to the lower concave portion129. Since the upper bottom surface128bis inclined, the small-diameter balancing balls123amay be prevented from staying on the upper bottom surface128b.

Finally, when rotation of the spin basket13is stopped, the large-diameter balancing balls122amove in the circumferential direction (the direction indicted by a white arrow inFIG. 7) by rolling on the upper bottom surface128band gather at the lowest point128dof the upper bottom surface128b. In addition, the small-diameter balancing balls123ain the circumferential direction (the direction indicted by a black arrow inFIG. 7) by rolling on the lower bottom surface129band gather at the lowest point129dat the opposite side of the lowest point128dof the upper bottom surface128c. Thereby, the large and small balancing balls122aand123areturn to the original state thereof. Accordingly, the center of gravity of the large-diameter and small-diameter balancing ball groups122and123may be positioned on the axis of rotation of the spin basket13to form weight balance of the balancing device120.

FIG. 11is a graph illustrating an example of the relationship between the state of weight balance between the balancing balls122aand123aand the viscous fluid124and variation in horizontal vibration of the spin basket13. InFIG. 11, the horizontal axis represents the number of balancing balls122aand123athat do not form weight balance, and the vertical axis represents the maxim amplitude of vibration of the spin basket13when the rate of rotation of the spin basket13passes the first resonance section. The illustrated embodiment corresponds to the case of having no balancing balls122aand123afailing to form weight balance. As shown inFIG. 11, as the number of balancing balls122aand123athat do not form weight balance increases, the maximum amplitude of vibration of the spin basket3increases and thus variation in horizontal vibration of the spin basket13also increases. Therefore, it may be desirable that the total weight of the large-diameter balancing ball group122is balanced with the total weight of the small-diameter balancing ball group123as in the illustrated embodiment.

Other Embodiments

In the previous embodiment, two types of the balancing balls122aand123aare used. However, embodiments of the present disclosure are not limited thereto. Three or more types of balancing balls may be used. If the number of types of balancing balls increases, however, the volume of the ball accommodation portion127may need to be increased. Accordingly, using two types of balancing balls may be most suitable in view of making the device compact.

As is apparent from the above description, the bottom surface of the ball accommodation portion is inclined downward as the bottom surface extends from a position of the fluid accommodation portion to an opposite position such that the balancing balls gather at the opposite position facing the fluid accommodation portion when rotation of the spin basket is stopped. Thereby, when rotation of the spin basket is stopped, weight balance is automatically formed among the balancing balls and the viscous fluid in the ball accommodation portion and the viscous fluid in the fluid accommodation portion. As a result, variation in horizontal vibration of the spin basket due to maldistribution of the balancing balls may be suppressed when the rate of rotation of the spin basket passes the first resonance section, even without moving the balancing balls to a position at which weight balance is formed between the balancing balls and the viscous fluid.

In addition, since the balancing balls roll on the bottom surfaces of the respective concave portions and gather at one place due to gravity, thereby automatically forming weight balance, special control is not needed as in conventional cases. Accordingly, waste of time and energy may be prevented.