KR20150103439A - Outer rotor type motor, cooling air circulation using the same and refrigerator using the same - Google Patents

Outer rotor type motor, cooling air circulation using the same and refrigerator using the same Download PDF

Info

Publication number
KR20150103439A
KR20150103439A KR1020140024911A KR20140024911A KR20150103439A KR 20150103439 A KR20150103439 A KR 20150103439A KR 1020140024911 A KR1020140024911 A KR 1020140024911A KR 20140024911 A KR20140024911 A KR 20140024911A KR 20150103439 A KR20150103439 A KR 20150103439A
Authority
KR
South Korea
Prior art keywords
rotor case
rotor
magnet
type motor
outer rotor
Prior art date
Application number
KR1020140024911A
Other languages
Korean (ko)
Other versions
KR101622020B1 (en
Inventor
박관훈
정중희
정세정
오덕영
Original Assignee
주식회사 에스 씨디
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 주식회사 에스 씨디 filed Critical 주식회사 에스 씨디
Priority to KR1020140024911A priority Critical patent/KR101622020B1/en
Priority to PCT/KR2015/002029 priority patent/WO2015133787A1/en
Publication of KR20150103439A publication Critical patent/KR20150103439A/en
Application granted granted Critical
Publication of KR101622020B1 publication Critical patent/KR101622020B1/en

Links

Images

Landscapes

  • Connection Of Motors, Electrical Generators, Mechanical Devices, And The Like (AREA)
  • Motor Or Generator Cooling System (AREA)

Abstract

The present invention relates to an outer rotor type motor, comprising: a bearing holder in which a bearing is housed; A rotating shaft supported by the bearing holder; A stator coupled to the bearing holder; A rotor case disposed on the outside of the stator and integrally coupled to the rotating shaft by insert injection; And a magnet integrally coupled to the rotor case by insert injection.

Description

[0001] The present invention relates to an outer rotor type motor, a cold air circulation fan using the same, and a refrigerator using the same,

The present invention relates to a motor, and more particularly, to an outer rotor type motor, a cool air circulation fan using the same, and a refrigerator using the same.

In general, a motor is a device that converts electrical energy into mechanical energy such as rotational force. The motor is used in various devices requiring a rotational force such as a cold air circulating fan of a refrigerator, a blowing fan of an air conditioner, a compressor and an automobile.

The motor can be classified into an outer rotor type motor and an inner rotor type motor depending on whether or not the rotor is disposed outside the stator. The outer rotor type motor is advantageous in that it can be made compact in the radial direction and the axial direction as compared with the inner rotor type motor. For this reason, the outer rotor type motor has a tendency to be used in the circulation fan of the refrigerator because it can reduce the installation space of the motor and increase the internal space of the refrigerator.

Korean Patent Laid-Open Publication No. 10-2010-0029619 discloses an example of a conventional outer rotor type motor used for a cool air circulating fan of a refrigerator.

Hereinafter, a conventional outer rotor type motor used for a circulation fan of a refrigerator will be described with reference to the drawings.

1 is a cross-sectional view showing a conventional outer rotor type motor.

1, a conventional outer rotor type motor 1 includes a lower bearing 4, a stator 3 coupled to the lower bearing 4, an upper bearing 2 coupled to the stator 3, A rotor 6 coupled to a rotary shaft 5 rotatably supported by the upper bearing 2 and the lower bearing 4 and a blade assembly 7 installed on the outer peripheral surface of the rotor 6. [ The rotor 6 includes a rotor case 8 formed with a galvanized steel plate disposed to be spaced apart from the outer circumferential surface of the stator 3 and a magnet 9 attached to the inner circumferential surface of the rotor case 8, One end of the rotary shaft 5 is coupled to the center portion.

On the other hand, the rotor case 8 and the rotary shaft 5 are coupled by a press-fitting method.

Incidentally, when the rotary shaft 5 is press-fitted to the rotor case 8, inconsistency occurs between the axial center of the rotary shaft 5 and the center of gravity of the rotor 6 due to the pressure input. Therefore, when the rotor 6 rotates, there arises a problem that the rotor 6 vibrates. Furthermore, vibration and noise of the outer rotor type motor occur.

KR Patent Publication No. 10-2010-0029619 (Mar. 17, 2010)

SUMMARY OF THE INVENTION Accordingly, the present invention has been made to solve the above-mentioned problems occurring in the prior art, and an object of the present invention is to provide an outer rotor type motor for preventing vibration of a rotor by coupling a rotary shaft and a rotor case, And a refrigerator using the same.

According to an aspect of the present invention, there is provided an outer rotor type motor comprising: a bearing holder for receiving a bearing; A rotating shaft supported by the bearing holder; A stator coupled to the bearing holder; A rotor case disposed on the outside of the stator and integrally coupled to the rotating shaft by insert injection; And a magnet integrally coupled to the rotor case by insert injection.

Here, the rotation shaft may include a rotor case engaging portion to which the rotor case is engaged, and the rotor case engaging portion may include diamond knurling.

The rotor case engagement portion includes a rotor case separation preventing groove that prevents the rotor case from moving in the axial direction of the rotation shaft, And the rotor case slip prevention groove for preventing the slip of the rotor case. The rotor case slip prevention groove is formed around the rotation axis by a predetermined depth along the axial direction of the rotation axis, and the rotor case slip prevention groove is formed at a predetermined depth around the rotation axis, .

Further, the material of the rotor case may be plastic.

Further, the magnet may include a magnet departure prevention protrusion, and the rotor case may include a magnet release prevention groove into which the magnet departure prevention protrusion is fitted.

Further, the magnet may be a polar anisotropic plastic magnet.

According to another aspect of the present invention, there is provided a cooling fan using an outer rotor type motor, the cooling fan including an outer rotor type motor according to any one of the above aspects, The blade assembly is coupled.

According to another aspect of the present invention, there is provided a refrigerator using a cool air circulation fan using an outer rotor type motor, comprising a cool air circulation fan using the outer rotor type motor, The cool air circulation fan using the rotor type motor is installed in the cool air duct.

According to the embodiment of the present invention as described above, the rotary shaft and the rotor case are coupled by the insert injection method, so that the shaft center of the rotary shaft coincides with the center of gravity of the rotor case.

1 is a view showing a conventional outer rotor type motor.
2 is an exploded perspective view illustrating a circulation fan using an outer rotor type motor according to an embodiment of the present invention.
3 is a longitudinal sectional view illustrating a cooling fan using an outer rotor type motor according to an embodiment of the present invention.
FIG. 4 is an enlarged view of FIG. 2 A. FIG.
5 and 6 are views showing a coupling relationship between a rotary shaft and a rotor of an outer rotor type motor according to another embodiment of the present invention.
7 is a view illustrating a refrigerator using a cool air circulation fan using an outer rotor type motor according to an embodiment of the present invention.

The present invention is capable of various modifications and various embodiments, and specific embodiments are illustrated and described in the drawings. It should be understood, however, that the invention is not to be limited to the specific embodiments, but includes all modifications, equivalents, and alternatives falling within the scope of the invention.

Hereinafter, embodiments will be described in detail with reference to the accompanying drawings, wherein like or corresponding elements are denoted by the same reference numerals, and redundant description thereof will be omitted. Also, it is to be understood that the terms used in the following description, such as the up and down, left and right, front and rear, and the like, are terms based on the accompanying drawings.

Hereinafter, an outer rotor type motor and a cool air circulation fan using the outer rotor type motor according to an embodiment of the present invention will be described with reference to a cool air fan using an outer rotor type motor according to an embodiment of the present invention.

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a cooling fan for a cooling fan using an outer rotor type motor, and more particularly to a cooling fan using an outer rotor type motor according to an embodiment of the present invention. FIG. 4 is an enlarged view of FIG. 2, and FIG. 5 and FIG. 6 are views showing a coupling relationship between a rotary shaft and a rotor of an outer rotor type motor according to another embodiment of the present invention.

2 to 6, a cool air circulation fan 100 (hereinafter, referred to as a cool air circulation fan) using an outer rotor type motor according to an embodiment of the present invention is installed in a cool air duct of a refrigerator, And an outer rotor type motor 300 (hereinafter, referred to as a motor) for rotating the blade assembly 200 and the blade assembly 200.

The blade assembly 200 includes a hub 210 coupled to the rotation axis 360 of the motor 300, a blade support plate 220 extending in the centrifugal direction from the outer circumferential surface of the hub 210, The blades 230 of the first embodiment shown in FIG. The blade assembly 200 is rotated by the motor 300 to forcibly circulate the cold air of the refrigerator. That is, the blade assembly 200 sucks in the cold air of the refrigerator and exhausts it to the cold air duct of the refrigerator, or sucks the cold air of the cold air duct of the refrigerator, and exhausts it into the interior of the refrigerator.

The motor 300 includes a base plate 320 to which a circuit board 310 on which a drive circuit is formed is coupled, a bearing holder 330 coupled to the base plate 320 and receiving the bearings 340, a bearing holder 330, A rotor 360 rotatably coupled to the bearing 340 and a rotor 360 disposed on the outer side of the stator 350 and integrally coupled to the rotation shaft 360 370).

The base plate 320 may be formed in a variety of shapes depending on the shape of the place where the circulation fan 100 is installed. In the center of the base plate 320, a bearing holder coupling hole 321 is formed in which the bearing holder 330 is press-fitted. A circuit board 310 having a circuit for controlling a power source applied to a coil (not shown) of the stator 350 is coupled to the upper surface of the base plate 320.

The bearing holder 330 is formed in a cylindrical shape whose lower end is closed. A bearing receiving portion 331 is formed at an intermediate portion of the bearing holder 330, and a low-temperature portion 332 is formed at a lower portion thereof. When the rotary shaft 360 is rotated in the low oil part 332, the oil that reduces the frictional force between the bearing 340 and the rotary shaft 360 is stored.

The bearing receiving portion 331 may be formed as a cylindrical hole corresponding to the outer shape of the bearing 340 so that the bearing 340 can be received.

A slit washer 381 having a hole through which the rotating shaft 360 passes is seated at the bottom of the bearing receiving portion 331. The slit washer 381 is fixed to the bottom of the bearing accommodating portion 331 when the bearing 340 is received in the bearing accommodating portion 331. When the rotary shaft 360 moves in the axial direction of the rotary shaft 360, the rotary shaft detachment preventing portion 361 formed on the rotary shaft 360 is caught by the slit washer 381 so that the rotary shaft 360 is engaged with the bearing receiving portion 331 .

The low oil portion 332 is formed into a cylindrical shape having a diameter smaller than the diameter of the bearing accommodating portion 331 and the lower end closed. A thrust washer 380 may be seated on the bottom of the oil reservoir 332. The thrust washer 380 axially supports the rotary shaft 360 and disperses the force transmitted from the rotary shaft 360 to prevent the force from being concentrated at one point on the bottom surface of the low- Therefore, the thickness of the bottom surface of the low oil part 332 can be reduced.

The bearing 340 has a cylindrical rotary shaft hole 341 formed at the center thereof. The rotary shaft 360 is rotatably fitted in the rotary shaft hole 341. The bearing 340 may be embodied as an oilless bearing formed of oil-containing sintered metal. That is, it can be realized as a metal bearing in which oil is permeated into a porous copper alloy (brass system).

At the upper end of the bearing 340, an oil scattering-preventing washer 382 having a hole through which the rotary shaft 360 passes is seated. The oil splash proof washer 382 lowers the oil that has risen along the bearing 340 and the rotating shaft 360 downward to the bearing receiving portion 331 and prevents the oil from splashing to the outside of the bearing receiving portion 331 do.

The stator 350 includes a stator core 351 coupled to the outer circumferential surface of the bearing holder 330, a tooth 352 extending in a circumferential direction from the outer circumferential surface of the stator core 351, And may include a coil (not shown) wound around the insulator 353 and the insulator 353.

The stator core 351 and the teeth 352 may be formed by a plurality of divided cores and integrally combined with each other. The coil may be implemented as a three-phase connection that is divided into three. Here, the three-phase connection may be Y connection or? Connection (delta connection).

The stator 350 forms a rotor system when power is applied to the coil, and the rotor 370 is rotated by the rotor system thus formed.

The lower portion of the rotary shaft 360 is accommodated in the bearing receiving portion 331 and the rotor case engaging portion 362 is coupled to the rotor case 371 at an intermediate portion thereof. The blade assembly engaging portion 363 is formed.

In order to prevent the rotor case 371 from moving in the axial direction of the rotary shaft 360 and the rotor case 371 from sliding with respect to the rotary shaft 360, Likewise, it can include diamond knurling.

5 and 6, the rotor case engaging portion 362 includes a rotor case separation preventing groove 362-1 for preventing the rotor case 371 from moving in the axial direction of the rotating shaft 360, And a rotor case slip prevention groove 362-2 for preventing the rotor case 371 from sliding relative to the rotation shaft 360. [ That is, the rotor case separation preventing groove 362-1 is formed so as to be recessed at a predetermined depth toward the center of the rotation shaft 360 around the cross section of the rotation shaft 360. [ The rotor case separation preventing protrusion 371-1 formed in the rotor case 371 is fitted in the rotor case separation preventing groove 362-1. Therefore, when the rotor case 371 is moved in the axial direction of the rotating shaft 360, the rotor case separation preventing protrusion 371-1 is caught by the rotor case separation preventing groove 362-1 to rotate from the rotor case 371 to the rotating shaft 360 are prevented from being released. The rotor case slip prevention groove 362-2 is formed around the rotation axis 360 by a predetermined depth along the axis of the rotation axis 360. [ The rotor case slip prevention protrusion 371-2 formed in the rotor case 371 is fitted in the rotor case slip prevention groove 362-2. Therefore, when the rotor case 371 rotates, the rotor case slip prevention protrusion 371-2 is caught by the rotor case slip prevention groove 362-2 so that the rotor case 371 is prevented from sliding on the rotation axis 360 .

The blade assembly coupling portion 363 may also include a knurling for preventing the blade assembly 200 from slipping off.

The rotor 370 includes a rotor case 371 formed in a cylindrical shape with one end closed so that the stator 350 can be disposed therein and a magnet 372 formed into a cylindrical shape and coupled to the inner circumferential surface of the rotor case 371 .

The rotor case 371 is made of a plastic material. The plastic material is not limited to a specific plastic material but may be any material that can couple the rotation shaft 360 and the magnet 372 to the rotor case 371 by insert injection.

On the other hand, when the rotor case 371 is injection-molded, the rotation shaft 360 is inserted and formed integrally with the rotation shaft 360. Therefore, the center of gravity of the rotor case 371 and the shaft center of the rotation shaft 360 are easily aligned with each other, and the vibration of the rotor 370 is prevented when the rotor 370 rotates.

A magnet engagement portion 373 is formed on the lower inner circumferential surface of the rotor case 371 and a magnet departure prevention groove 374 is formed in the magnet engagement portion 373. [ A magnet separation preventing protrusion 372-1 is formed on the outer circumferential surface of the magnet 372. [ The magnet departure prevention protrusion 372-1 is fitted in the magnet departure prevention groove 374. [ Therefore, the magnet 372 is prevented from being detached from the magnet coupling portion 373.

The magnet 372 is implemented as a polar anisotropic plastic magnet having a ring shape. The polar anisotropic plastic magnet is injected into a ring-shaped magnet injection mold for mixing a ferrite magnet powder and a plastic mixture to melt and magnetize the magnetization magnetic field, and cooling the molten magnet powder so that the magnetization easy axis of the molten magnet powder is magnetized with a polar anisotropy . Therefore, a magnetic path is formed in the magnet 372 itself having a ring shape, so that the back yoke for forming the magnetic path can be eliminated.

Meanwhile, the magnet 372 may be integrally formed with the rotor case 371 when the rotor case 371 is injection-molded by the insert injection method. Therefore, unlike the conventional outer rotor type motor, the process of bonding or press-fitting the magnet to the rotor case is omitted, and manufacturing cost is reduced.

Hereinafter, a refrigerator using a cool air circulation fan using an outer rotor type motor according to another embodiment of the present invention will be described with reference to the drawings.

7 is a view illustrating a refrigerator using a cool air circulation fan using an outer rotor type motor according to an embodiment of the present invention.

Referring to FIG. 7, a refrigerator 400 (hereinafter, referred to as a refrigerator) using a cold air circulating fan using an outer rotor type motor according to an embodiment of the present invention includes an evaporator 40 for generating cold air, an evaporator 40, And a cool air duct 420 for guiding the cool air generated in the cool air chamber to the freezing chamber or the freezing chamber. A cool air circulation fan (100) is installed in the cool air duct (420). The cool air circulation fan 100 sucks the cool air of the inside of the room S and exhausts it to the cool air duct 420.

 Meanwhile, the cool air circulation fan 100 generates less vibration and noise as compared with the conventional cool air circulation fan 100. Accordingly, vibration and noise generated in the refrigerator 400 are also reduced. That is, the cool air circulation fan 100 using the outer rotor type motor 300 according to an embodiment of the present invention in which vibration and noise are reduced as compared with the conventional outer rotor type motor is used in the refrigerator 400, The vibration and the noise generated in the vehicle are reduced.

It will be apparent to those skilled in the art that various modifications and variations can be made in the present invention without departing from the spirit or scope of the present invention as defined by the following claims It can be understood that

100: cool air circulation fan 200: blade assembly
300: Outer rotor type motor 400: Refrigerator

Claims (9)

A bearing holder for receiving a bearing;
A rotating shaft supported by the bearing holder;
A stator coupled to the bearing holder;
A rotor case disposed on the outside of the stator and integrally coupled to the rotating shaft by insert injection; And
And a magnet integrally coupled to the rotor case by insert injection. The method according to claim 1,
Wherein the rotating shaft includes a rotor case engaging portion to which the rotor case is engaged,
Wherein the rotor case coupling portion includes diamond knurling. The method according to claim 1,
Wherein the rotating shaft includes a rotor case engaging portion to which the rotor case is engaged,
The rotor case coupling portion includes a rotor case separation preventing groove for preventing the rotor case from moving in the axial direction of the rotation shaft and a rotor case slip prevention groove for preventing the rotor case from sliding about the rotation axis. Outer rotor type motor. The method of claim 3,
The rotor case separation preventing groove is formed by being recessed at a predetermined depth around the rotation axis around the center of the rotation axis,
Wherein the rotor case slip prevention groove is formed to be recessed at a predetermined depth along an axial direction of the rotary shaft around the rotary shaft. The method according to claim 1,
Wherein the material of the rotor case is plastic. The method according to claim 1,
Wherein the magnet includes a magnet departure prevention protrusion,
Wherein the rotor case includes a magnet release preventing groove into which the magnet departure prevention protrusion is fitted. The method according to claim 1,
Wherein the magnet is a polar anisotropic plastic magnet. An outer rotor type motor according to any one of claims 1 to 7,
And a blade assembly for circulating cold air is coupled to the rotary shaft. A cold air circulating fan using an outer rotor type motor according to claim 8,
Wherein the cool air circulation fan using the outer rotor type motor is installed in the cool air duct.
KR1020140024911A 2014-03-03 2014-03-03 Outer rotor type motor, cooling air circulation using the same and refrigerator using the same KR101622020B1 (en)

Priority Applications (2)

Application Number Priority Date Filing Date Title
KR1020140024911A KR101622020B1 (en) 2014-03-03 2014-03-03 Outer rotor type motor, cooling air circulation using the same and refrigerator using the same
PCT/KR2015/002029 WO2015133787A1 (en) 2014-03-03 2015-03-03 Outer rotor type motor, cool air circulation fan using same, and refrigerator using same

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
KR1020140024911A KR101622020B1 (en) 2014-03-03 2014-03-03 Outer rotor type motor, cooling air circulation using the same and refrigerator using the same

Publications (2)

Publication Number Publication Date
KR20150103439A true KR20150103439A (en) 2015-09-11
KR101622020B1 KR101622020B1 (en) 2016-05-17

Family

ID=54243632

Family Applications (1)

Application Number Title Priority Date Filing Date
KR1020140024911A KR101622020B1 (en) 2014-03-03 2014-03-03 Outer rotor type motor, cooling air circulation using the same and refrigerator using the same

Country Status (1)

Country Link
KR (1) KR101622020B1 (en)

Cited By (7)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017213451A1 (en) * 2016-06-09 2017-12-14 엘지이노텍 주식회사 Drone motor and drone comprising same
KR20180013244A (en) * 2016-07-29 2018-02-07 산일테크(주) Fan motor
KR20180071986A (en) * 2016-12-20 2018-06-28 다이슨 테크놀러지 리미티드 A motor and a handheld product having a motor
KR101965512B1 (en) * 2017-11-23 2019-04-05 (주)타마스 Fan Motor
KR20190043831A (en) * 2017-10-19 2019-04-29 엘지이노텍 주식회사 Motor for drone and drone having the same
KR102041050B1 (en) * 2018-06-15 2019-11-27 뉴모텍(주) Fan motor having parts-integrated rotor
KR20220001812U (en) * 2021-01-15 2022-07-22 주식회사 에스 씨디 Fan motor with oil scattering prevention structure

Families Citing this family (2)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
KR20190061200A (en) 2017-11-27 2019-06-05 효성전기주식회사 Hole Structure of Rotor Case for Improving Cooling Efficiency
KR102613213B1 (en) * 2021-02-05 2023-12-15 주식회사 제이엠더블유 BLDC Motor rotor

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2017213451A1 (en) * 2016-06-09 2017-12-14 엘지이노텍 주식회사 Drone motor and drone comprising same
US11180247B2 (en) 2016-06-09 2021-11-23 Lg Innotek Co., Ltd. Drone motor and drone comprising same
KR20180013244A (en) * 2016-07-29 2018-02-07 산일테크(주) Fan motor
KR20180071986A (en) * 2016-12-20 2018-06-28 다이슨 테크놀러지 리미티드 A motor and a handheld product having a motor
KR20190043831A (en) * 2017-10-19 2019-04-29 엘지이노텍 주식회사 Motor for drone and drone having the same
KR101965512B1 (en) * 2017-11-23 2019-04-05 (주)타마스 Fan Motor
KR102041050B1 (en) * 2018-06-15 2019-11-27 뉴모텍(주) Fan motor having parts-integrated rotor
WO2019240363A1 (en) * 2018-06-15 2019-12-19 New Motech Co., Ltd. Fan motor having parts-integrated rotor
KR20220001812U (en) * 2021-01-15 2022-07-22 주식회사 에스 씨디 Fan motor with oil scattering prevention structure

Also Published As

Publication number Publication date
KR101622020B1 (en) 2016-05-17

Similar Documents

Publication Publication Date Title
KR101622020B1 (en) Outer rotor type motor, cooling air circulation using the same and refrigerator using the same
JP4835371B2 (en) Bearing unit and electric motor provided with the same
US20090184592A1 (en) Rotating electric machine
JP5217205B2 (en) motor
CN107044439B (en) Vacuum pump
JP2007037365A (en) Motor
US20110318200A1 (en) Blower fan and method of manufacturing the same
JP2009027821A (en) Motor, blower fan, and manufacturing method therefor
JP2011045156A (en) Electric motor and rotor
US11569713B2 (en) Axial flux motor including system for circulating coolant through air gap between stator and rotor
EP2080906B1 (en) Fan assembly
CN102025212B (en) Direct current brushless motor for heating ventilating and air conditioning system
JP2006121851A (en) Brushless motor and manufacturing method therefor
US8742638B1 (en) Hydrodynamic bearing assembly and spindle motor having the same
US10309458B2 (en) Brushless motor
US8836189B2 (en) Spindle motor having lubricant filled bearing clearance
JP2012095476A (en) Brushless motor
JP2010057300A (en) Motor and fan
US20190238030A1 (en) Stator-cooling structure and rotary electric machine
JP2007110795A (en) Rotating-electric machine and its manufacturing method
JP4992642B2 (en) Oil-impregnated bearing mechanism and brushless motor
JP2009303444A (en) Flat motor
JP2009180295A (en) Oil-leakage preventing cap
JP2019115225A (en) motor
US11808273B2 (en) Rotor assembly

Legal Events

Date Code Title Description
A201 Request for examination
E902 Notification of reason for refusal
E902 Notification of reason for refusal
E701 Decision to grant or registration of patent right
GRNT Written decision to grant
FPAY Annual fee payment

Payment date: 20190107

Year of fee payment: 4