GB2302141A

GB2302141A - Axial flow fan for microwave oven

Info

Publication number: GB2302141A
Application number: GB9600102A
Authority: GB
Inventors: Mu-Yong Choi
Original assignee: LG Electronics Inc
Current assignee: LG Electronics Inc
Priority date: 1995-06-13
Filing date: 1996-01-04
Publication date: 1997-01-08
Anticipated expiration: 2016-01-04
Also published as: CN1143730A; CN1089142C; GB9600102D0; GB2302141B

Abstract

An axial flow fan for a microwave oven capable of more effectively cooling a magnetron and a high voltage transformer of the same and more effectively circulating air in the interior of the same, so that an improved microwave oven having a higher efficiency and a lower noise can be achieved, includes five blades 52 spaced-apart at a regular interval and formed at the outer circumferential surface of a cylindrical hub 51. The blades 52 have a ratio "fan hub diameter/fan outer diameter" in the range of 0.28 0.35. Preferred blade pitch and sweep angle ranges, and dimensions are also disclosed.

Description

AXIAL FLOW FAN FOR MICROWAVE OVEN The present invention relates to an axial flow fan for a microwave oven, and particularly to an improved axial flow fan for a microwave oven capable of more effectively cooling a magnetron and a high voltage transformer of the same and more effectively circulating air in the interior of the same, so that an improved microwave oven having a high efficiency and a low noise can be achieved.

Fig. 1 shows a conventional microwave oven, which includes a cooking chamber 2 formed in a body 1 for receiving food to be cooked therein. A turntable 3 is rotatably disposed at the bottom of the cooking chamber 2. A door 4 is pivotally hinged to a predetermined portion of the body 1.

In addition, a magnetron 5 and a high voltage transformer 6, as shown in Fig. 2, are provided in the interior of the body 1.

A duct 7 is disposed at one side of the rnagnetron 5 for guiding microwaves generated by the magnetron 5 to the cooking chamber 2 and an inner air discharging port 8 is disposed at a periphery of the magnetron 5.

In addition, an axial flow fan 9 connected to a fan motor 10 is rotatably disposed behind the magnetron 5 and the high voltage transformer 6.

In addition, an air suction port 12 is formed at the back surface of the microwave oven and behind the axial flow fan 9.

In addition, a suction guide 11 is disposed in front of the axial flow fan 9 for guiding air discharged by the rotation force of the axial flow fan 9 toward the magnetron 5 and the high voltage transformer 6, and an external air discharging port 13 is formed at a predetermined portion of the lower surface of the microwave oven.

The operation of the conventional microwave oven equipped with an axial flav will now be explained with reference to the accompanying drawings.

To begin with, when electric power is applied to the conventional microwave oven, the turntable 3 of the cooking chamber 2 is rotated, and at the same time, the magnetron 5 and the high voltage transformer 6 is operated, so that microwave is generated by the magnetron 5.

The microwave wave is directed to cooking food on the turntable 3 which is rotated in the cooking chamber 2.

At this time, the high voltage transformer 4 supplies a high voltage of 4000V to the magnetron 3.

Therefore, the magnetron 5 and the high voltage transformer 6 generates a high temperature beat In order to prevent other elements of the microwave oven from the heat, the temperature therewithin should be decreased.

Therefore, the axial flow fan 9 is driven so as to supply air from the outside of the system into the cooking chamber through the air suction port 12.

The thus sucked air is guided by the suction guide I toward the magnetron 3 and the high voltage transformer 4 and serves to cool the magnetron 5 and the high voltage transformer 6, and to discharge food smell to the outside of the system.

The conventional axial flow fan 9, as shown in Figs. 3 and 4, includes spacedapart four blades at the circumferential surface of a cylindrical hub 21.

An axis fixing port 23 is formed at the central portion of the hub 21.

The axial flow fan 9 is formed of a poly ethylene material, and has a fan tip diameter A of 108mm, and a fan hub diameter B of 30mm, and a width C of 27.5rum.

In addition, the maximum camber position is about 0.5 when the leading edge is zero (0) and the trailing edge is one (1), and the maximum camber position is evenly distributed at a certain cross-section of the blade from the hub 21 to the tip 22c.

In addition, the sweep angle e is below 10.

In the drawings, reference character G denotes the width of the hub 21, H denotes the length of the hub 21, I denotes the length of the front portion of the fan, and J denotes the length of the back portion of the fan.

In addition, Fig. 5A shows an air flowing state measured in the direction "A" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM, and Fig. SB shows an air flowing state measured in the direction "B" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM, and Fig. SC shows an air flowing state measured in the direction "C" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM, and Fig.SD shows an air flowing state measured in the direction "D" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM, and Fig. 6A shows an air flowing state measured in the direction "A" of Fig. 1 within a range of 0 through 20 Khz at 3020 RPM, and Fig. 6B shows an air flowing state measured in the direction "B" of Fig. 1 within a range of 0 through 20 Khz at 3020 RPM, and Fig. 6C shows an air flowing state measured in the direction "C" of Fig. 1 within a range of 0 through 20 Khz at 3020 RPM, and Fig. 6D shows an air flowing state measured in the direction "D"of Fig. 1 within a range of 0 through 20 Khz at 3020 RPM, and Fig. 7A shows a cooking noise state measured in the direction "A" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM, and Fig. 7B shows a cooking noise state measured in the direction "B" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM, and Fig. 7C shows a cooking noise state measured in the direction "C" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM, and Fig. 7D shows a cooking noise state measured in the direction "D" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM.

However, since the axial flow fan of the conventional microwave oven includes the maximum camber of 0.5 and the sweep angle of below 10 , when the cooling flow is formed, the flowing direction of the cooling air is axially fonned, the corresponding elements such as the magnetron and the high voltage transformer can not be effectively cooled.

In addition, since the conventional axial flow fan is driven at 3020 RPM (revolutions per rninute), the audible noise level is increased as shown in Figs. 5 through 7.

Accordingly, it is an object of certain embodiments of the present invention to provide an axial flow fan for a microwave oven, which overcomes or reduces the problems encountered in a conventional axial flow fan for a microwave oven.

It is another object of certain embodiments of the present invention to provide an improved axial flow fan for a microwave oven capable of more effectively cooling a magnetron and a high voltage transformer of the same and more effectively circulating air in the interior of the same, so that an improved microwave oven having a higher efficiency and a lower noise may be achieved.

I n accordance with one aspect of the present invention, there is provided an axial flow fan for a microwave oven, which includes fifth blades spaced-apart at a regular interval and formed at the outer circurnferential surface of a cylindrical hub; and a ratio "fan hub diameter/fan outer diameter" of the blades having a range of 0.28~0.35.

In accordance with another aspect of the present invention, there is provided an axial flow fan for a microwave oven, which includes fifth blades spaced-apart at a regular interval and formed at the outer circumferential surface of a cylindrical hub; and a ratio "fan hub diameter/fan outer diameter" of the blades having a range of 0.28~0.3.

For a better understanding of the present invention and as to how the same may be carried into effect, reference will now be made by way of example to the accompanying drawings in which: Fig. 1 is a perspective view showing a conventional microwave oven.

Fig. 2 is a side cross-sectional view showing a rnicrowave oven so as to show a construction of a cooping air flow path of a microwave oven equipped with a conventional axial flow fan.

Fig. 3 is a front view of an axial flow fan for a conventional microwave oven.

Fig. 4 is an enlarged view of Fig. 3.

Fig. 5A is a graph of an air flowing state measured in the direction "A" of Fig.

1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. SB is a graph of an air flowing state measured in the direction "B" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. 5C is a graph of an air flowing state measured in the direction "C" of Fig. 1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. SD is a graph of an air flowing state measured in the direction "D" of Fig.

1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. 6A is a graph of an air flowing state measured in the direction "A" of Fig.

1 within a range of 0 through 20 Khz at 3020 RPM.

Fig. 6B is a graph of an air flowing state measured in the direction "B" of Fig. 1 within a range of 0 through 20 Khz at 3020 RPM.

Fig. 6C is a graph of an air flowing state measured in the direction "C" of Fig. 1 within a range of 0 through 20 Khz at 3020 RPM.

Fig. 6D is a graph of an air flowing state measured in the direction "D" of Fig.

1 within a range of 0 through 20 Khz at 3020 RPM.

Fig. 7A is a graph of a cooking noise state measured in the direction "A" of Fig.

1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. 7B is a graph of a cooking noise state measured in the direction "B" of Fig.

1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. 7C is a graph of a cooking noise state measured in the direction "C" of Fig.

1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. 7D is a graph of a cooking noise state measured in the direction "D" of Fig.

1 within a range of 0 through 2 Khz at 3020 RPM.

Fig. 8 is a front view of an axial flow fan for a microwave oven of a first embodiment according to the present invention Fig. 9 is an enlarged view of Fig. 8.

Fig. 10 is a plan view shown in the direction of an axis X-Z of Fig. 9 so as to show the maximum camber of an axial flow fan of a first embodiment according to the present invention.

Fig. 11 is a plan view shown in the direction of an axis X-Z of Fig. 9 so as to show a pitch angle of an axial flow fan of a first embodiment according to the present invention.

Fig. 12 is a table showing a result of a noise performance test of an axial flow fan between a first embodiment of the present invention and the prior art.

Fig. 13 a view showing a construction for performing the noise test of Fig. 12 embodying the present invention.

Fig. 14A is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 3020 RPM in the direction "A" of Fig. 1.

Fig. 14B is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 3020 RPM in the direction "B" of Fig. 1.

Fig. 14C is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 3020 RPM in the direction "C" of Fig. 1.

Fig. 14D is a graph of a coolcing noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 3020 RPM in the direction "D" of Fig. 1.

Fig. 1 SA is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2400 RPM in the direction "A" of Fig. 1.

Fig. lSB is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2400 RPM in the direction "B" of Fig. 1.

Fig. 15C is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2400 RPM in the direction "C" of Fig. 1.

Fig. 15D is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2400 RPM in the direction "D" of Fig. 1.

Fig. 16A is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2350 RPM in the direction "A" of Fig. 1.

Fig. 1 6B is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2350 RPM in the direction "B" of Fig. 1.

Fig. 1 6C is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2350 RPM in the direction "C" of Fig. 1.

Fig. 16D is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2350 RPM in the direction "D" of Fig. 1.

Fig. 17A is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2145 RPM in the direction "A" of Fig. 1.

Fig. 17B is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2145 RPM in the direction "B" of Fig. 1.

Fig. 17C is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2145 RPM in the direction "C" of Fig. 1.

Fig. 17D is a graph of a cooking noise of a microwave oven equipped with an axial flow fan of a first embodiment according to the present invention, which is measured at 2145 RPM in the direction "D" of Fig. 1.

Fig. 18 is a table of a fan boundary data of an axial fan of a first embodiment according to the present invention.

Fig. 19 is a front view of a blade of an axial flow fan for a microwave oven embodying the present invention.

Fig. 20A is a plan view of an axial flow fan of a second embodiment according to the present invention.

Fig. 20B is a side view of an axial flow fan of a second embodiment according to the present invention.

Fig. 21A is a cross-sectional view of a fan blade showing the maximum camber of an axial flow fan of a second embodiment according to the present invention.

Fig. 21B is a cross-sectional view of a fan blade showing a pitch angle of an axial flow fan of a second embodiment according to the present invention.

Fig. 22A is a graph of a cooking noise measured in the direction "A" of Fig. 1 of a microwave oven in a range of 0 through 2 at 2460 RPM of a second embodiment according to the present invention.

Fig. 22B is a graph of a cooking noise measured in the direction "B" of Fig. 1 of a microwave oven in a range of 0 through 2 at 2460 RPM of a second embodiment according to the present invention.

Fig. 22C is a graph of a cooking noise measured in the direction "C" of Fig. 1 of a microwave oven in a range of 0 through 2 at 2460 RPM of a second embodiment according to the present invention.

Fig. 22D is a graph of a cooking noise measured in the direction "D" of Fig. 1 of a microwave oven in a range of 0 through 2 at 2460 RPM of a second embodiment according to the present invention.

Fig. 23A is a graph of a cooking noise measured in the direction "A" of Fig. 1 of a microwave oven in a range of 0 through 20 at 2460 RPM of a second embodiment according to the present invention.

Fig. 23B is a graph of a cooking noise measured in the direction "B" of Fig. 1 of a microwave oven in a range of 0 through 20 at 2460 RPM of a second embodiment according to the present invention.

Fig. 23C is a graph of a cooking noise measured in the direction "C" of Fig. 1 of a microwave oven in a range of 0 through 20 at 2460 RPM of a second embodiment according to the present invention.

Fig. 23D is a graph of a cooking noise measured in the direction "D" of Fig. 1 of a microwave oven in a range of 0 through 20 at 2460 RPM of a second embodiment according to the present invention.

Fig. 24A is a graph of a cooking noise measured in the direction "A" of Fig. 1 of a microwave oven in a range of 0 through 2 at 3020 RPM of a second embodiment according to the present invention.

Fig. 24B is a graph of a cooking noise measured in the direction "B" of Fig. 1 of a microwave oven in a range of 0 through 2 at 3020 RPM of a second embodiment according to the present invention.

Fig. 24C is a graph of a cooking noise measured in the direction "C" of Fig. 1 of a microwave oven in a range of 0 through 2 at 3020 RPM of a second embodiment according to the present invention.

Fig. 24D is a graph of a cooking noise measured in the direction "D" of Fig. 1 of a microwave oven in a range of 0 through 2 at 3020 RPM of a second embodiment according to the present invention Fig. 25 is a table of an axial fan boundary data of an axial fan of a second embodiment according to the present invention.

Fig. 26 is a front view of a blade of Fig. 25 embodying the present invention.

Fig. 8 shows an axial flow fan for a microwave oven of a first embodiment according to the present, which includes spaced-apart five blades 52 disposed at the outer circumferential surface of a cylindrical hub 51.

The ratio of the fan hub diameter B/fan outer diameter A of the blades 52 is a range of 0.28 through 0.35.

In addition, as shown in Fig. 9, the fan front portion length I from the fan data central portion "0, 0, 0" to the maximum leading edge 52a is 15.14+0.5mrn on the rotation axis (Z-axis).

In addition, the fan rear portion length J from the fan data central point "0, 0, 0" to.the maximum trailing edge 52b is 15.14+0.5mm on the rotation axis (Z-axis).

In addition, the ratio of the fan hub diameter B/fan outer diameter A of the blade 52 is preferably 0.33.

The fan outer diameter A is 108+ imam, and the fan hub diameter B is 35.6t lmm.

The sweep angle 6 is (0-25 )il from the hub to the tip, that is, it is characterized to have a lineal parabola, and as shown in Fig. 11, the pitch angle (p is (43.99-30.99)+1 and has a lineal distribution.

As shown in Fig. 10, the maximum camber position L is 0.45~0.5 and has an even distribution from the hub 51 to the tip F.

Here, the maximum camber ratio "(maximum camber M/code length)x100" is (5.01~11.01%)#0.05% from the hub 51 to the tip 52c and has a lineal distribution.

In addition, the thickness of the blade 52 at the tip 52c is "Tt=0.75Th" (where, Th denotes the maximum thickness) and has a lineal distribution, and the thickness distribution between the leading edge 52a and the trailing edge 52b is formed in a duplicated elliptical curbed line expression.

The distance " a~b~c~d" between the blades 52 is "6.2-10.4-8.0-21.6" as shown in Fig. 8.

That is, when the hub 51 is 0, and the tip 52 is 1, the distance from the hub 51 is 6.2+0.5mum, and the interval of 0'0.75 is a lineal parabola of which an interval from 6.2+0.5mum to l0.4j0.Srnm is increased, and the interval of 0.75~0.95 is a lineal parabola of which an interval from 10.4+0.5mum to 8.0+0.5rum is decreased, and the interval of 0.95-1.0 at the tip portion is a cubic parabola, of which an interval from 8.0+0.5mum to 21.6 0.5mm is sharply increased.The differential function at a boundary of 0.75 and 0.95 within each interval is 0 (zero), it is formed using lineal and cubic parabolas.

With the above-mentioned embodiment of the present invention, in order to test the noise reduction effect of an axial flow fan, the cooling performance comparison of the number of the fan revolution is compared between the conventional axial flow fan at 3020 rpm and the axial flow fan embodying the present invention at 2400 rpm and between the conventional axial flow fan at 2350 and an axial flow fan embodying the present invention at 2145 rpm, and the results are shown in Fig. 12.

As shown therein, the average noise value of the conventional axial flow fan (3020 rpm) adopted to the conventional microwave oven is 46.06 db(A), as compared to the average noise value of 41.88 db(A) of the axial flow fan (2400 rpm) embodying the present invention. In addi.tion, the average noise value of the conventional axial flow fan (2350 rpm) adopted to the microwave oven embodying the present invention is 43.24 db(A), and the average noise value of the axial flow fan (2145 rpm) embodying the present invention is 39.47 db(A). As a result, the axial flow fan embodying the present invention has achieved about 3.8t of noise reduction, as compared to the prior art.

Fig. 13 shows a construction of the test of Fig. 12 embodying the present invention. In Fig. 13, reference numeral 71 denotes a magnetron, 72 denotes a control unit, 73 denotes a louver position, 75 denotes a cooling portion of the magnetron HVT, 76 denotes an MWO fan, 77 denotes a suction louver, 78 denotes a cooking chamber;79 denotes a suction louver of the cooking chamber, 79a denotes a discharging louver, 80 denotes a door of the cooking chamber.

In addition, Fig. 14A shows a cooking noise of a microwave oven equipped with an axial flow fan of the Mrst todinnt according to the present invention, which is measured at 3020 RPM in the direction "A" of Fig. 1, and Fig. 14B shows a cooking noise of a microwave oven equipped with an axial flow fan fthefirst embodiment according to the present invention, which is measured at 3020 RPM in the direction"B" of Fig. 1, and Fig. 14C shows a cooking noise of a microwave oven equipped with an axial flow fan ofthefirst embodiment according to the present invention, which is measured at 3020 RPM in the direction "C" of Fig. 1, and Fig. 14D shows a cooking noise of a microwave oven equipped with an axial flow fan of first embodiment according to the present invention, which is measured at 3020 RPM in the direction "D" of Fig. 1, and Fig. lSA shows a cooking noise of a microwave oven equipped with an axial flow fan of first embodiment according to the present invention, which is measured at 2400 RPM in the direction "A" of Fig. 1, and Fig. lSB shows a cooking noise of a microwave oven equipped with an axial flow fan of thirst embodiment according to the present invention, which is measured at 2400 RPM in the direction "B" of Fig. 1, and Fig. lSC shows a cooking noise of a microwave oven equipped with an axial flow fan of thefirst embodiment according to the present invention, which is measured at 2400 RPM in the direction "C" of Fig. 1, and Fig. lSD shows a cooking noise of a microwave oven equipped with an axial flow fan ofthefirst embodiment according to the present invention, which is measured at 2400 RPM in the direction "D" of Fig. 1, and Fig. 16A shows a cooking noise of a microwave oven equipped with an axial flow fan of thirst embodiment according to the present invention, which is measured at 2350 RPM in the direction "A" of Fig. 1, and Fig. l6B shows a cooking noise of a microwave oven equipped with an axial flow fan of thirst embodiment according to the present invention, which is measured at 2350 RPM in the direction "B" of Fig. 1, and Fig. 16C shows a cooking noise of a microwave oven equipped with an axial flow fan of dIrst embodiment according to the present invention, which is measured at 2350 RPM in the direction "C" of Fig. 1, and Fig. 16D shows a cooking noise of a microwave oven equipped with an axial flow fan ofts first embodiment according to the present invention, which is measured at 2350 RPM in the direction "D" of Fig. 1, and Fig. 17A shows a cooking noise of a microwave oven equipped with an axial flow fan of thirst embodiment according to the present invention, which is measured at 2145 RPM in the direction "An of Fig. 1, and Fig. 17B shows a cooking noise of a microwave oven equipped with an axial flow fan oftfirst embodiment according to the present invention, which is measured at 2145 RPM in the direction "B" of Fig. 1, and Fig. 17C shows a cooking noise of a microwave oven equipped with an axial flow fan of first embodiment according to the present invention, which is measured at 2145 RPM in the direction "C" of Fig. 1, and Fig. 17D shows a cooking noise of a microwave oven equipped with an axial flow fan of first embodiment according to the present invention, which is measured at 2145 RPM in the direction "D" of Fig. 1.

In addition, Fig. -18 shows a fan boundary data of an axial fan of thirst embodiment according to the present invention, and Fig. 19 shows a blade of an axial flow fan for a microwave oven embodying the present invention.

In Fig. 19, reference numerals 1, 41, 81, 121, and 161 denote points of a coordinate.

Meanwhile, Figs. 20A and 2B show an axial flow fan of a second embodiment according to the present invention, which includes a hub 62 having a rotary shaft (not shown) inserted into the central portion of the axial fan 60, and five blades 64 formed at the outer circumferential surface of the hub 62.

The axial flow fan 60 of the second embodiment according to the present invention has a ratio 0.28 ~ 0.3 between the hub diameter DH and the fan outer diameter DT.

At this time, the fan diameter Dt is preferably 10B h lmm, and the hub diameter DH is preferably 30.2#1mm.

Meanwhile, the pitch angle OP as shown in fig. 21B has a lineal distribution of value "(41.96 -28.96 ) | 1 from the hub 62 to the tip 63, and the sweep angle OS is a lineal parabola of value "(0 -30 )i2 from the hub 62 to the tip 63.

In addition, as shown in Fig. 21A, the maximum camber position CMP has an even distribution of a range "0.6-0.65" from the hub 62 to the tip 63, and the maximum cam ratio(maximum camber/code length(CL)x100) is a lineal value "(3.46-9.46)#0.05% from the hub 62 to the tip 63.

As shown in Fig. 21B, the distance from the center "0" to the maximum leading edge 64a on the rotation axis (Z-axis) is a front portion distance VL, and as shown in Fig.

20B, the distance from the center "0" to the maximum trailing edge 64b is the rear portion distance RL on the rotation axis (Z-axis).

The front portion distance VL is 19.420.5mm and the rear portion distance RL is 11.53 +0.5mm in this embodiment.

When the maximum thickness of the blade 64 is "Th", the thickness Tt at the tip 63 of the blade is "0.75Th. In addition, the thickness of the blade between the hub 62 and the tip 63 has a linearly varying value, and the thickness distribution between the leading edge 64a and the trailing edge 64b is a duplicated elliptical curve.

When the interval CB between the blades 64 is increased to have a lineal parabola wherein when the position of the hub 62 is "0", and the position of the tip is "1", the interval CB between the hub 62 and the blade 64 is 6.7iO.5mm, and in a range of "O ~ 0.75, the interval is 6.7i0.Srnm and 11.2+0.5rnm. In addition, in a range of 0.75 ~ 0.95, the interval has a range between 11.2+0.5mum and 9.00.5mm to have a lineal parabola, and in a range of 0.95 - 1, the interval has a range between 9.0+0.5mum ~ 23.0j0.Smm to have a cubic parabola, and at the boundary of 0.75 and 0.95 which is a boundary of each interval, when the differential function value is "0", the spaces CB between the blades 64 is performed using lineal and cubic parabolas.

In it the drawings, character reference HL denotes a hub path, and HW denotes the width of the blade hub.

The effects of the second embodirnent according to the present invention are well known in Figs. 22 through 24.

That is, Fig. 22A shows a cooking noise measured in the direction "A" of Fig. 1 of a microwave oven in a range of 0 through 2 at 2460 RPM of the second eobdizt according to the present invention, and Fig. 22B shows a cooking noise measured in the direction "B" of Fig. 1 of a microwave oven in a range of 0 through 2 at 2460 RPM of second embodiment according to the present invention, and Fig. 22C shows a cooking noise measured in the direction "C" of Fig. 1 of a microwave oven in a range of O through 2 at 2460 RPM ofthaiecond embodiment according to the present invention, and Fig. 22D shows a cooking noise measured in the direction "D" of Fig. 1 of a microwave oven in a range of 0 through 2 at 2460 RPM ofbhesecond embodiment according to the present invention, and Fig. 23A shows a cooking noise measured in the direction "A" of Fig. 1 of a microwave oven in a range of 0 through 20 at 2460 RPM ofthe second embodiment according to the present invention, and Fig. 23B a cooking noise measured in the direction "B" of Fig. 1 of a microwave oven in a range of 0 through 20 at 2460 ti of the secmd embodiment according to the present invention, and Fig. 23C a cooking noise measured in the direction "C" of Fig. 1 of a microwave oven in a range of O through 20 at 2460 RPM ofthdiecond embodiment according to the present invention, Fig.

23D shows a cooking noise measured in the direction "D" of Fig. 1 of a microwave oven in a range of 0 through 20 at 2460 RPM ofthgecond embodiment according to the present invention, and Fig. 24A shows a cooking noise measured in the direction "A" of Fig. 1 of a microwave oven in a range of 0 through 2 at 3020 RPM of the secondembodiment according to the present invention, and Fig. 24B shows a cooking noise measured in the direction "B" of Fig. 1 of a microwave oven in a range of 0 through 2 at 3020 RPM of second embodiment according to the present invention, and Fig. 24C shows a cooking noise measured in the direction "C" of Fig. 1 of a microwave oven in a range of O through 2 at 3020 RPM of the secaldembodiment according to the present invention, and Fig. 24D shows a cooking noise measured in the direction "D" of Fig. 1 of a microwave oven in a range of 0 through 2 at 3020 RPM of the secmdembodiment according to the present invention.

As shown in Figs. 22 through 24, embodiments of the present invention are directed to reducing a discrete noise, as compared to the conventional fan, and the sound of the broad band noise is decreased.

In addition, in the cooking state, the discrete noise is increased. That is, the axial flow fan for a microwave oven is directed to reducing the noise level by about 4.8 db(A) in an air flowing state, and to reducing the noise level by about 4.8 db(A) in a cooking state.

Meanwhile, the temperature increasing test of the microwave oven of the second embodiment according to the present invention is performed.

To begin with, the cooking chamber is provided a container with water of 2000ml, and the test is performed for two hours. In this state, the temperature of the heating unit is not changed, and the temperature in a saturated state is checked..

At this time, the temperature is performed with respect to the magnetron anode and the upper surface of the high voltage transformer using a hybrid recorder HR2500E (Yokogaya), and a K-type thermocouple is used.

As a result of the above-mentioned test, the following results are obtained.

[Table I) Temperature increasing test for microwave oven

Fan type Tested portions Number of fan T ("C) rotation Fan of prior art Magnetron 148.2 HVT 3020 96.8 Fan of present Magnetron invention 2460 147.4 HVT 100.4 In the above table, HVT denotes a high voltage transformer.

As seen in the above table, it is noted that with less rotation of the fan, it is possible to reach the conventional temperature.

In addition, the noise test was performed with respect to the microwave oven.

To begin with, the noise test of the cooking state was performed in a condition that a contained with 1200ml water is provided in the cooking chamber and heated for 30 minutes. During the above-mentioned operation, the noise was reduced. In case of the noise test with respect to the air flowing, only the fan is operation. The result is as follows.

table U] Noise test of microwave oven

FT NR TS noise level A A B C D FA 3020 flowing 42.13 45.74 44.99 51.36 46.06 cooking 42.21 45.31 44.71 50.96 45.80 FP flowing 36.80 40.75 38.88 44.75 40.30 2460 cooking 37.67 40.80 40.24 45.16 40.97 In the above table, Ft denotes fan type, and Nr denotes the number of fan rotation, and AV denotes average value, FA denotes a fan of prior art, and FP denotes a fan embodying the present invention. In addition, A, B, C, and D denote that viewing directions of Fig. 13.

As shown in the above table II, the fan embodying the present invention produces less noise, as compared to the prior art.

Meanwhile, Fig. 25 shows an axial fan boundary data of an axial fan of a second embodiment according to the present invention, and Fig. 26 shows a blade of Fig. 25 embodying the present invention.

In Fig. 26, reference numerals 1, 41, 81, 121, and 161 denote points of a point coordinate of Fig. 25.

As described above, the axial flow fan for a microwave oven bodying the present invention is directed to more effectively cooling a magnetron and a high voltage transformer of the same and more effectively circulating air in the interior of the same by differing the number of the blades and by improving sweep angle, pitch angle, the maximum camber and the maximum camber position, and the distance of blades, so that an improved microwave oven having a high efficiency and a low noise can be achieved.

Although the preferred embodiments of the present invention have been disclosed for illustmtive purposes, those skilled in the art will appreciate that various modifications, additions and substitutions are possible, without departing from the scope of the invention as described in the accompanying claims.

Claims

What is claimed is:

1. An axial flow fan for a microwave oven, comprising: five blades spaced-apart at a regular interval and formed at the outer circumferential surface of a cylindrical hub; and a ratio "fan hub diameter/fan outer diameter" of said blades having a range of 0.280.35.

2. The fan of claim 1, wherein said fan outer diameter is 108+ lrnm, and said fan hub diameter is 35.6jlmm.

3. The fan of claim 1 or 2, wherein said sweep angle is directed.to have a range of (0~250)+10 from the hub of to the tip of the blade, said sweep angle being formed with a lineal parabola.

4. The fan of claim 1, 2 or 3, wherein said pitch angle is directed to have a range of (43.99"30.990)10 from the hub to the tip of the blade, said pitch angle being formed with a lineal distribution formation.

5. The fan of any one of the preceding claims, wherein said maximum camber position is evenly formed from the hub to the tip of the blade with a range of 0.45"0.5, and said maximum camber ratio (maximum camber/code length x 100) is linearly formed from the hub to the tip of the blade with a range of (5.01-11.01a) + 0.05 .

6. The fan of any one of the preceding claims, wherein the thickness of said blade is formed to have a lineal distribution with a thickness of Tt=0.75Th (where, Tt denotes the thickness of blade, and Th denotes the maximum thickness at the hub), and the thickness distribution between a leading edge and a trailing edge is distributed to have a duplicated and elliptical curve.

7. The fan of any one of the preceding, claims, wherein when the hub is o, and the tip is 1, the distance from the hub is 6.2+0.5mm, and the interval of 0-0.75 is a lineal parabola of which an interval from 6.2iO.Smm to l0.4j0.Srnm is increased, and the interval of 0.75~0.95 is a lineal parabola of which an interval from 10.4+0.5mm to 8.0j0.5mm is decreased, and the interval of 0.951.0 at the tip portion is a cubic parabola, of which an interval from 8.0 # 0.5mm to 21.6 t0.Smm is sharply increased, and a differential function at a boundary of 0.75 and 0.95 within each interval is O (zero), and it is formed using lineal and cubic parabolas.

8. The fan of any one of the preceding clai.ms, wherein said axial fan includes a front portion length of 5.14#0.5mm and a rear portion length of 15.14+0.5mm.

9. An axial flow fan for a microwave oven, comprising: five blades spaced-apart at a regular interval and formed at the outer circumferential surface of a cylindrical hub; and a ratio "fan hub diameter/fan outer diameter" of said blades having a range of 0.28-0.3.

10. The fan of claim 9, wherein said fan outer diameter is 108i imam, and said fan hub diameter is 30.2 j lrnm.

11. The fan of claim 9 or 10, wherein said sweep angle is directed to have a range of (0~30 )+2 from the hub to the tip of the blade, said sweep angle being formed with a lineal parabola.

12. The fan of claim 9, 10 or 11, wherein said pitch angle is directed to have a range of (41.96-28.96 )+1 from the hub to the tip of the blade, said pitch angle being forrned with a lineal distribution formation.

13. The fan of any one of claims 9 to 12, wherein said maximum camber position is evenly formed from the hub to the tip of the blade with a range of 0.6-0.65, and said maximum camber ratio (maximum camber/code length x 100) is linearly formed from the hub to the tip of the blade with a range of (3.46-9.46%) # 0.05%.

14. The fan of any one of claims 9 to 13, wherein the thickness of said blade is formed to have a lineal distribution with a thickness of Tt=0.75Th (where, Tt denotes the thickness of blade, and Th denotes the maximum thickness at the hub), and the thickness distribution between a leading edge and a trailing edge is distributed to have a duplicated and elliptical curve.

15. The fan of any one of claims 9 to 14, wherein when the hub is 0, and the tip is 1, the distance from the hub is 6.7j0.5mm, and the interval of 0'0.75 is a lineal parabola of which an interval from 6.7iO.5rnm to 11.2iO.Smm is increased, and the interval of 0.7S-O.9S is a lineal parabola of which an interval from 11.2iO.5mm to 9.0iO.5mm is decreased, and the interval of 0.95 1.0 at the tip portion is a cubic parabola, of which an interval from 9.0i0.5rnm to 23.00.5mm is sharply increased, and a differential function at a boundary of 0.75 and 0.95 within each interval is O (zero), and it is formed using lineal and cubic parabolas.

16. The fan of any one of claims 9 to 15, wherein said axial fan includes a front portion length of 19.42+0.5mm and a rear portion length of 11.53r0.5mm.

17. A fan substantially as hereinbefore described with reference to Figures 8 to 19 or Figures 20 to 26.