AU2019329626A1

AU2019329626A1 - Washing machine

Info

Publication number: AU2019329626A1
Application number: AU2019329626A
Authority: AU
Inventors: Myunghun Im; Hwanjin JUNG; Jaehyun Kim; Kayeon Kim; Sunggyun KIM; Junghoon Lee; Kyungchul Woo
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 2018-08-30
Filing date: 2019-08-21
Publication date: 2021-05-06
Also published as: CN112654742A; EP3845696A1; WO2020045888A1; US20210355622A1; EP3845696A4; JP2021534897A

Abstract

The present invention relates to a washing machine formed such that a cylindrical drum formed by machining a metal sheet rotates around a horizontal shaft, wherein the washing machine includes a plurality of protruding parts extended to be long in a longitudinal direction on the inner peripheral surface of the drum and spaced apart in a circumferential direction, and the height at which the protruding part protrudes toward the inner side of the drum is 2.0-6.0% of the diameter of the drum.

Description

TITLE OF THE INVENTION WASHING MACHINE AND METHOD OF CONTROLLING THE SAME BACKGROUND OF THE INVENTION

1. Field of the invention

The present disclosure relates to a washing

machine having a drum rotated about a horizontal axis,

and more particularly, to a washing machine having a

height of protrusion structure, which is formed on an

inner circumferential surface of the drum, that is less

than 40 mm.

2. Description of the Related Art

A washing machine configured to have a drum, into

which laundry is loaded, that is rotated about a

horizontal axis is widely known. For example, in a

washing machine disclosed in Korean Patent Publication

No. 10-2011-0022359, a lifter disposed in an inner

circumferential surface of a drum lifts laundry when

the drum rotates.

In such a washing machine provided with the

lifter installed in the drum, laundry is lifted up to a

certain height by the physical force exerted by the

lifter and then falls, or a friction between the lifter

and the laundry is induced. Therefore, it is possible to secure a certain level of washing force, which is less affected by the amount of water filled in the drum, the amount of laundry (cloth amount), and the rotational speed (RPM) of the drum, in comparison with a structure having no lifter.

Meanwhile, in the case of a drum having no lifter,

the centrifugal force caused by the rotation of the

drum becomes the driving force for lifting the laundry.

In this case, when the rotational speed of the drum is

equal to or higher than a cloth adhering speed at which

the centrifugal force exerted on the laundry equals

gravity, the laundry is rotated while being adhered to

the inner circumferential surface of the drum.

Although there is a variation depending on the diameter

of the drum, the cloth adhering speed is 90 to 110 rpm.

Meanwhile, when the lifter is installed in the

drum, the force of lifting the laundry by the lifter is

more applied as well as the centrifugal force.

Therefore, even if the rotational speed of the drum is

lower than 90rpm, laundry can be rotated while being

adhered to the drum. In the conventional washing

machine, a lifter having a height of about 40 mm is

applied. In this case, when the rotation speed of the

drum reaches about 55 rpm, the laundry is rotated while

being adhered to the drum.

That is, such a conventional washing machine has

to limit the rotational speed of the drum to about 55

rpm or less so that the laundry is lifted up by the

lifter and dropped. However, there are various factors

that affect the washing force. For example, various

factors include the friction between the drum and the

laundry, the impact force exerted on the laundry by the

lifter, and the bending and stretching of the laundry

as well as the drop of laundry by the lifter. In

particular, since these factors are closely related to

the rotational speed of the drum, there is a need to

devise a method that can rotate the drum at a higher

speed than the conventional one while causing a drop of

laundry.

SUMMARY OF THE INVENTION

The present disclosure has been made in view of

the above problems, and provides a washing machine

which enhances an upper limit of drum rotation speed

that can induce a drop of laundry due to the rotation

of drum, and induce the flow of laundry in comparison

with the prior art.

The present disclosure further provides a washing

machine which forms a protrusion for lifting laundry on

an inner circumferential surface of drum, appropriately designs the height of the protrusions, so that the laundry can flow in the drum while not adhering to the drum even if the rotation speed of the drum is 60 rpm or more.

The present disclosure relates to a washing

machine configured to have a drum, into which cloth is

loaded, that is rotated around a horizontal axis. A

plurality of protrusions are provided on an inner

circumferential surface of the drum. The protrusion is

extended in a front and rear direction, and a plurality

of protrusions are spaced along a circumferential

direction.

The protrusion has a height protruding inwardly

into the drum is 2.0 to 6.0% of a diameter of the drum.

Alternatively, the protrusion protrudes inwardly into

the drum at a height of 10 to 30 mm.

A protrusion structure higher than any one of the

plurality of protrusions does not exist, between a pair

of adjacent protrusions arbitrarily selected from among

the plurality of protrusions, on the inner

circumferential surface of the drum.

The drum further includes a plurality of

embossing, on the inner circumferential surface, formed

to be lower than any of the plurality of protrusions,

and a protrusion structure does not exist excluding at least one of the plurality of embossings, between the pair of adjacent protrusions arbitrarily selected from among the plurality of protrusions, on the inner circumferential surface of the drum. A height of the embossing is 5mm or less.

Between a pair of adjacent protrusions

arbitrarily selected from the plurality of protrusions,

there is no protrusion structure on the inner

circumferential surface of the drum, or only at least

one of the plurality of embossings exists.

The protrusion includes: a first side surface

portion that forms a positive first angle with respect

to the inner circumferential surface at a first point

on the inner circumferential surface of the drum, when

viewed from a front; and a second side surface portion

that forms a negative second angle with respect to the

inner circumferential surface at a second point

circumferentially spaced from the first point on the

inner circumferential surface, when viewed from the

front. At least one of the first angle and the second

angle is 17.5 degrees or less.

A length from a front end to a rear end of the

protrusion is 50 to 100% of a length of the drum. The

drum has a front end band portion and a rear end band

portion that are flat and formed in a front end and a rear end, respectively, and the protrusion is disposed between the front end band portion and the rear end band portion.

The protrusion is formed integrally with the drum.

The drum is manufactured by processing a metal sheet of

stainless steel, and has a thickness of 0.4 to 0.6mm.

Alternatively, the protrusion is made of

synthetic resin and coupled with the drum.

A diameter of the drum may be 484mm, and the

height at which the protrusion protrudes toward the

inside of the drum may be 10.0 to 30.0mm.

A diameter of the drum may be 515mm, and the

height at which the protrusion protrudes toward the

inside of the drum may be 10.6 to 30.9mm.

A diameter of the drum may be 575mm, and the

height at which the protrusion protrudes toward the

inside of the drum may be 11.8 to 34.5mm.

A diameter of the drum may be 590mm, and the

height at which the protrusion protrudes toward the

inside of the drum may be 12.1 to 35.4mm.

A method of controlling a washing machine of the

present disclosure controls the drum to be continuously

rotated one or more revolutions in one direction at a

set speed between 60 to 90 rpm such that the cloth is

lifted to a certain height by the protrusion and then dropped at least once.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and

advantages of the present disclosure will be more

apparent from the following detailed description in

conjunction with the accompanying drawings, in which:

FIG. 1 is a side cross-sectional view of a

washing machine according to an embodiment of the

present disclosure;

FIG. 2 schematically illustrates a cross section

of a washing tub shown in FIG. 1;

FIG. 3 schematically illustrates a longitudinal

section of the washing tub shown in FIG. 1;

FIG. 4 is a cross-sectional view taken along a

line IV-IV of FIG. 3;

FIG. 5 is a graph showing a cloth adhering speed

according to a height of protrusion;

FIG. 6 is a diagram referred to explain the

correlation between a height of protrusion and a side

surface angle; and

FIG. 7 illustrates a flow of cloth according to a

rotational speed of drum.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Advantages and features of the present disclosure

and methods for achieving them will be made clear from

the embodiments described below in detail with

reference to the accompanying drawings. The present

disclosure may, however, be embodied in many different

forms and should not be construed as being limited to

the embodiments set forth herein. Rather, these

embodiments are provided so that this disclosure will

be thorough and complete, and will fully convey the

scope of the invention to those skilled in the art.

The present disclosure is defined only by the scope of

the claims. Like reference numerals refer to like

elements throughout the specification.

Referring to FIG. 1, a washing machine according

to an embodiment of the present disclosure may include

a casing 1 forming an outer shape, a water storage tank

3 which is disposed in the casing 1 and stores washing

water, a washing tub 4 which is rotatably installed in

the water storage tank 3 and into which laundry is

loaded, and a motor 9 which rotates the washing tub 4.

The washing tub 4 includes a front cover 41

having an opening for entering and exiting laundry, a

cylindrical drum 42 disposed substantially horizontally

so that a front end is coupled to the front cover 41,

and a rear cover 43 coupled to a rear end of the drum

42. The rotating shaft of the motor 9 may be connected

to the rear cover 43 by passing through the rear wall

of the water storage tank 3. A through hole 42h may be

formed in the drum 42 so that water may exchange

between the washing tub 4 and the water storage tank 3.

The washing tub 4 is rotated about a horizontal

axis. Here, "horizontal" does not mean a geometric

horizontal in a strict sense, and even when the washing

tub 4 is inclined at a certain angle with respect to

the horizontal as shown in FIG. 1, it is closer to

horizontal than vertical. Thus, it can be said that

the washing tub 4 is rotated about a horizontal axis.

In addition, the washing tub 4 includes a

plurality of protrusions 20 provided on an inner

circumferential surface of the drum 42. A plurality of

protrusions 20 are extended long in the front-rear

direction on the inner circumferential surface of the

drum 42, and these protrusions 20 are spaced apart

along the circumferential direction, and preferably,

disposed at a constant angle (equal angle) with respect

to the center 0 of the drum 42.

A protrusion structure higher than any one of the

plurality of protrusions 20 does not exist between a

pair of adjacent protrusions 20 selected arbitrarily

(or randomly) from among the plurality of protrusions

20.

In other words, no matter how the pair of

adjacent protrusions 20 are taken, a protrusion

structure protruding higher than the protrusion 20 does

not exist between them.

A plurality of embossings 425 may be provided on

the inner circumferential surface of the drum 42. The

embossing 425 has a protruding structure formed on the

inner circumferential surface, and the height

protruding into the drum 42 is lower than any of the

plurality of the protrusions 20.

On the inner circumferential surface of the drum

42, a protrusion structure except at least one of the

plurality of embossings 425 does not exist between a

pair of adjacent protrusions arbitrarily selected from

among the plurality of protrusions 20.

Embossing 425 may be formed integrally with drum

42, and the plurality of embossings 425 need not to be

constant in size and or height, and as shown in FIG. 3,

a plurality of embossings 425 having a size that

gradually increases or decreases in the longitudinal

direction of the drum 42 may be formed.

The height of the embossing 425 is 5 mm or less.

Meanwhile, the drum 42 is manufactured by

processing a metal sheet of stainless steel, and the thickness may be 0.4 to 0.6mm. A cylindrical drum 42 can be formed by rounding a rectangular metal sheet and joining (e.g. welding) both ends to each other. The metal sheet is preferably an STS430 series, but is not necessarily limited thereto.

A laundry loading port is formed in the front

surface of the casing 1, and a door 2 for opening and

closing the laundry loading port is rotatably provided

in the casing 1. Inside the casing 1, a water supply

valve 5, a water supply pipe 6, and a water supply hose

8 may be installed. When the water supply valve 5 is

opened to supply water, the washing water passing

through the water supply pipe 6 may be mixed with the

detergent in a dispenser 14, and then supplied to the

water storage tank 3 through the water supply hose 8.

An input port of a pump 11 is connected to the

water storage tank 3 by a discharge hose 10, and a

discharge port of the pump 11 is connected to a drain

pipe 12. Water discharged from the water storage tank

3 through the discharge hose 10 is pumped by the pump

11 and flows along the drain pipe 12, and then

discharged outside the washing machine.

FIG. 7 shows the flow of cloth according to the

rotational speed of the drum. Referring to FIG. 7, in

a process where the drum 42 is rotated, the forces acting on the cloth introduced into the drum 42 may be centrifugal force Fc caused by the rotation of the drum

42, gravity Fg, and lifting force Fn applied from the

protrusion 20.

As shown in FIG. 7A, since the centrifugal force

Fc is relatively small when the drum 42 is rotated at a

low speed, the cloth is raised to a certain height by

the protrusion 20, and then the cloth is separated from

the protrusion 20 and falls when the sum of the

centrifugal force Fc and the lifting force Fn is unable

to bear the gravity Fg. Such a flow of cloth is

defined as a rolling motion.

FIG. 7B shows a state in which the rotational

speed of the drum 42 is higher than that of FIG. 7A,

and shows that the cloth falls after rising to a higher

position. In particular, the position where the cloth

falls is equal to or greater than 90 degrees of

rotation angle from the lowest point of the drum, and

such a flow of cloth is defined as a tumbling motion.

If the rotational speed of the drum 42 further

increases, as shown in FIG. 7C, the cloth does not fall

even at the highest point of the drum 42 but is rotated

while being adhered to the drum 42. The lowest value

of the rotational speed of the drum 42, which can cause

the cloth adhering in a form like FIG. 7C, is defined as a cloth adhering speed Vf.

When the drum 42 does not have the protrusion 20,

the lifting force Fn is eliminated, and thus, only the

centrifugal force Fc and the gravity Fg remain as the

force acting on the cloth. In this case, the cloth

adhering speed vf can be obtained from an equilibrium

equation where centrifugal force equals gravity. Since

the mass of the cloth is canceled in both sides of the

equilibrium equation, the cloth adhering speed Vf

becomes a value which is dependent on the diameter of

the drum irrespective of the mass of the cloth, and is

a preset value that can be obtained by knowing the

diameter of the drum.

Meanwhile, when the protrusion 20 is formed in

the drum 42, the lifting force Fn acts further, and

thus, the cloth adhering speed Vf becomes low in

comparison with the case where the protrusion 20 is not

applied. At this time, the cloth adhering speed Vf

will vary depending on the structure of the protrusions

20. However, the cloth adhering speed Vf is about 55

rpm or less, in a conventional washing machine where

the drum 42 has a diameter of 24 to 27 inches and the

height of the lifter (protrusion) 40mm or more.

The washing force is determined by several

factors such as flexing, friction, and drop of the cloth. These factors are closely related to the rotational speed of the drum 42, and in particular, the drop of the cloth or the relative movement (or flow in the drum) with respect to the drum such as rolling or tumbling motion is induced, but at this time the higher rotational speed of the drum 42 is advantageous to enhance the washing force.

In this aspect, it is necessary to devise a

method to increase the cloth adhering speed Vf while

rotating the drum 42 at a higher speed than in the

related art, and the present disclosure lowers the

height h (i.e. the height protruded into the drum 42)

of the protrusion 20 in comparison with the related art

to reduce the lifting force Fn. The height h of the

protrusion 20 at this time is 2.0 to 6.0% of the

diameter D in comparison with the diameter D of the

drum 42, and is approximately 10 to 30 mm in absolute

value.

The control method of the washing machine

according to an embodiment of the present disclosure

can implement a rolling or tumbling motion while

rotating the drum 42 at a higher speed than in the

related art.

Specifically, when the protrusion height of the

protrusion 20 is 2.0 to 6.0% of the diameter of the drum 42, the drum 42 is continuously rotated one or more revolutions in one direction at a speed set between 60 and 90 rpm. Thus, it is possible to perform an operation that the cloth inside the drum 42 is lifted to a certain height by the protrusion 20 and then falls at least once.

The set speed may be a speed at which a rolling

motion is induced, and in this case, the cloth in the

drum 42 is lifted to an angle of 90 degrees or less in

the rotational direction of the drum 42 from the lowest

point of the drum 42 and then falls.

Alternatively, the set speed may be a speed that

induces tumbling motion. At this time, the cloth in

the drum 42 is lifted to an angle of 90 degrees or more

and 180 degrees or less in the rotational direction of

the drum 42 from the lowest point of the drum 42, and

then falls.

A controller (not shown) for controlling the

rotation of the motor 9 may be provided, and the drum

42 may be rotated by the speed control of the motor 9

by the controller.

FIG. 2 schematically illustrates a cross section

of a washing tub shown in FIG. 1, FIG. 3 schematically

illustrates a longitudinal section of the washing tub

shown in FIG. 1, and FIG. 4 is a cross-sectional view taken along a line IV-IV of FIG. 3. Hereinafter, it will be described with reference to FIGS. 2 to 4.

When viewed from the front of the drum 42, the

protrusion 20 is longer in the longitudinal direction

(or the front and rear direction) of the drum 42 than

the width of the drum 42 in the circumferential

direction. These protrusions 20 are disposed

symmetrically with respect to the center of the drum 42,

and in the embodiment, three protrusions 20 are

disposed at an isometric angle of 120 degrees with

respect to the center of the drum 42, but is not

necessarily limited thereto.

The protrusion 20 may be integrally formed with

the drum 42. For example, the protrusion 20 can be

formed by plastic working of the metal sheet. However,

the present disclosure is not limited thereto, and in

some embodiments, the protrusion 20 may be formed

separately from the drum 42, and then coupled to the

drum 42. In particular, in the latter case, the

protrusion 20 may be made of synthetic resin.

Meanwhile, in order to smoothly lift up the cloth

by expanding the contact area (or the area on which the

protrusion 20 exerts a lifting force Fn) between the

protrusion 20 and the cloth, the length of the

protrusion 20 should be appropriate, and in this aspect, the present disclosure suggests that the length Li from the front end to the rear end of the protrusion 20 is

50 to 100% of the length LO of drum L. In particular,

even when the length Li of the protrusion 20 is close

to 50% of the length LO of the drum 42, it is

preferable that the protrusion 20 is provided in such a

manner that the front end of the protrusion 20 is

located in a position spaced rearward from the front

end of the drum 42, so that the protrusion 20 can be

disposed to encompass the front and rear of the drum 42.

Specifically, the drum 42 has a front end band

portion 42a and a rear end band portion 42b which are

flat and formed at the front end and the rear end

respectively, and the protrusion 20 may be disposed

between the front end band 42a and the rear end band

42b.

Meanwhile, referring to FIG. 4, when viewed from

the front, the protrusion 20 may include a first side

surface portion 21 that forms a positive first angle +0

with respect to the inner circumferential surface at a

first point P1 on an inner circumferential surface of

the drum 42, and a second side surface portion 22 that

forms a negative second angle -E with respect to the

inner circumferential surface at a second point P2

circumferentially spaced from the first point P1 on the inner circumferential surface. Here, at least one of the first angle and the second angle is 17.5 degrees or less. Hereinafter, angle E is defined as a side surface angle.

In the embodiment, the first side surface portion

21 and the second side portion 22 are symmetrical, and

the first angle and the second angle have the same size,

but are not necessarily limited thereto.

FIG. 5 is a graph showing a cloth adhering speed

Vf according to a height of protrusion. FIG. 6 is a

diagram referred to explain the correlation between a

height of protrusion and a side surface angle. First,

as described above, FIG. 5 shows that as the height h

of the protrusion 20 becomes higher, the cloth adhering

speed Vf becomes lower. Meanwhile, when the height h

of the protrusion 20 is 5mm or less, the washing

performance seems to be good as the cloth adhering

speed Vf is high, but actually it is not.

When the height h of the protrusion 20 is 5 mm or

less, in a state of not reaching the cloth adhering

speed Vf of the drum 42 as the lifting force Fn of the

protrusion 20 is too small, when the cloth rolls almost

in place, or moves only up and down within a very small

angle of rotation section, and then suddenly starts to

adhere to the drum 42 when reaching the cloth adhering speed Vf. Such a type of flow of cloth is intensified as the cloth amount becomes small, and the drop or flexion of the cloth is not smoothly induced, such that the washing power is not good. For this reason, the height h of the protrusion 20 should be greater than at least 5 mm, preferably at least 10 mm or more.

The height h of the protrusion 20 is preferably

30 mm or less, and in this case, the cloth adhering

speed Vf becomes about 65 rpm or more, so that an

increase in the cloth adhering speed of about 18% can

be expected in comparison with 55 rpm when the

conventional height is 40 mm.

For each diameter D of the drum 42, preferred

values of the lower limit LSL and the upper limit USL

of the height h of the protrusion 20 are as follows.

Here, the diameter of the drum 42 may be any of an

inner diameter, an outer diameter, or an intermediate

value between the inner diameter and the outer diameter

of the drum 42.

[TABLE 1]

Drum Diameter(D(mm)) LSL(mm) USL(mm)

484 10.0 30.0

515 10.6 30.9

575 11.8 34.5

590 12.1 35.4

Meanwhile, referring to FIG. 6, it can be known

that the rolling or tumbling of the cloth is not

induced in the area A where the height h of the

protrusion 20 is smaller than 5 mm and the side surface

angle E is smaller than 17.5 degrees. Accordingly,

even when the height h of the protrusion 20 is 5 mm,

the side surface angle 0 is preferably at least 17.5 mm

so as to induce rolling or tumbling.

The area B shown in FIG. 6 indicates an area in

which the height h of the protrusion 20 is 5 mm or more

and the side surface angle 0 is 17.5 or more, and it is

possible to induce rolling or tumbling motion of the

cloth in this area. However, the height of the

protrusion 20 which can further enhance a washing

performance due to such a motion is preferably 10mm or

more.

Meanwhile, the curve shown by the dotted line in

FIG. 6 connects the threshold values of the side

surface angle 0 that can induce rolling or tumbling.

As described above, according to the washing

machine of the present disclosure, even if the drum is

rotated at a higher speed than in the related art, the cloth is not adhered to the drum, but can flow in the drum, thereby improving the washing force.

In particular, even if the rotational speed of

the drum is 60rpm or more, the laundry does not adhere

to the drum but flows in the drum, thereby increasing

the cloth adhering speed by approximately 18% in

comparison with the related art.

Further, since the cloth flows inside the drum

even while the drum is being rotated at a higher speed

than in the related art, the friction force between the

cloth and the drum is increased, thereby enhancing the

rubbing effect.

Meanwhile, a control method of a washing machine

according to an embodiment of the present disclosure

can also be embodied as processor readable code on a

processor-readable recording medium. The processor

readable recording medium includes all kinds of

recording apparatuses storing data that can be read by

a processor. Examples of the processor-readable

recording medium is ROM, RAM, CD-ROM, magnetic tapes,

floppy disks, optical data storage apparatuses, and,

including those that are implemented in the form of

carrier waves such as data transmission through the

Internet. In addition, the processor-readable

recording medium is dispersed in computer systems connected through a network, the code that is read by the processor can be stored and executed in a distributed fashion.

Although embodiments have been described with

reference to a number of illustrative embodiments

thereof, it should be understood that numerous other

modifications and embodiments can be devised by those

skilled in the art that will fall within the scope of

the principles of this disclosure. More particularly,

various variations and modifications are possible in

the component parts and/or arrangements of the subject

combination arrangement within the scope of the

disclosure, the drawings and the appended claims. In

addition to variations and modifications in the

component parts and/or arrangements, alternative uses

will also be apparent to those skilled in the art.

Claims

WHAT IS CLAIMED IS:

1. A washing machine configured to have a drum,

into which cloth is loaded, that is rotated around a

horizontal axis, the washing machine comprising:

a plurality of protrusions which are extended in

a front and rear direction on an inner circumferential

surface of the drum, and are spaced along a

circumferential direction,

wherein the protrusion has a height protruding

inwardly into the drum is 2.0 to 6.0% of a diameter of

the drum, and a protrusion structure higher than any

one of the plurality of protrusions does not exist,

between a pair of adjacent protrusions arbitrarily

selected from among the plurality of protrusions, on

the inner circumferential surface of the drum.

2. The washing machine of claim 1, wherein the

drum further comprises a plurality of embossing, on the

inner circumferential surface, formed to be lower than

any of the plurality of protrusions, and

wherein a protrusion structure does not exist

excluding at least one of the plurality of embossings,

between the pair of adjacent protrusions arbitrarily

selected from among the plurality of protrusions, on the inner circumferential surface of the drum.

3. The washing machine of claim 2, wherein a

height of the embossing is 5mm or less.

4. The washing machine of claim 1, wherein the

protrusion comprises:

a first side surface portion that forms a

positive first angle with respect to the inner

circumferential surface at a first point on the inner

circumferential surface of the drum, when viewed from a

front; and

a second side surface portion that forms a

negative second angle with respect to the inner

circumferential surface at a second point

circumferentially spaced from the first point on the

inner circumferential surface, when viewed from the

front,

wherein at least one of the first angle and the

second angle is 17.5 degrees or less.

5. The washing machine of claim 1, wherein a

length from a front end to a rear end of the protrusion

is 50 to 100% of a length of the drum.

6. The washing machine of claim 5, wherein the

drum has a front end band portion and a rear end band

portion that are flat and formed in a front end and a

rear end, respectively,

wherein the protrusion is disposed between the

front end band portion and the rear end band portion.

7. The washing machine of claim 1, wherein the

protrusion is formed integrally with the drum.

8. The washing machine of claim 7, wherein the

drum is manufactured by processing a metal sheet of

stainless steel, and has a thickness of 0.4 to 0.6mm.

9. The washing machine of claim 1, wherein the

drum is formed of stainless steel, and

the protrusion is made of synthetic resin and

coupled with the drum.

10. The washing machine of claim 1, wherein the

protrusion has a height of 10 to 30mm protruding

inwardly into the drum.

11. A method of controlling a washing machine

configured to have a drum, into which cloth is loaded, that is rotated around a horizontal axis, to have a plurality of protrusions which are extended in a front and rear direction on an inner circumferential surface of the drum, and are spaced along a circumferential direction, and the protrusion has a height protruding inwardly into the drum is 2.0 to 6.0% of a diameter of the drum, the method comprising controlling the drum to be continuously rotated one or more revolutions in one direction at a set speed between 60 to 90 rpm such that the cloth is lifted to a certain height by the protrusion and then dropped at least once.

12. The control method of claim 11, wherein the

set speed is set such that the cloth in the drum is

lifted to an angle of 90 degrees or less in a

rotational direction of the drum from a lowest point of

the drum and then dropped.

13. The control method of claim 11, wherein the

set speed is set such that the cloth in the drum is

lifted to an angle of 90 degrees or more and 180

degrees or less in a rotational direction of the drum

from a lowest point of the drum and then dropped.