Axial flow fan with brushless direct current motor

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates, in general, to an axial flow fan with a motor for electronic appliances, such as office or domestic electronic appliances, and, more particularly, to an axial flow fan with a BLDC(Brushless Direct Current) motor, the axial flow fan being optimally designed in diameter ratio, the number of blades, camber ratio, pitch angle and sweep angle, thus being reduced in operational noise in addition to being increased in air volume.

2. Description of the Prior Art

FIGS. 1

a

and

1

b

are plan and side views of a conventional axial flow fan integrated with a motor.

FIG. 2

is a sectional view of the conventional axial flow fan taken along the line A—A of

FIG. 1

a

.

FIG. 3

is a sectional view of an electromagnetic induction-heating cooker provided with the conventional axial flow fan.

As shown in

FIGS. 1

a

to

2

, the typical size of a conventional axial flow fan is set to 92 mm(W)×92 mm (D)×25 mm(H). Such a conventional axial flow fan comprises a fan housing

7

, with a motor

1

being firmly set within the housing

7

. A hub

3

is firmly mounted to the rotating shaft

2

of the motor

1

, with a plurality of blades

5

regularly fixed around the hub

3

. The fan housing

7

covers the blades

5

so as to protect the blades

5

from external impact.

In such conventional axial flow fans, the motor

1

is typically selected from small-sized BLDC motors. The above axial flow fan also typically has seven blades

5

. In the conventional axial flow fan, the axial height of the blades

5

has been set to be lower than that of the fan housing

7

as best seen in

FIG. 2

, and so the surface of the blades

5

is positioned lower than the surface of the housing

7

.

The axial height of the fan housing

7

of a conventional axial flow fan is limited to 25 mm with the surface of the blades

5

being necessarily positioned lower than the surface of the fan housing

7

. The blades

5

of the conventional axial flow fan undesirably have a simple shape.

In a detailed description, the maximum camber position of each blade

5

of the conventional axial flow fan is set to 0.45, with the camber positions being uniformly distributed on each blade

5

from the blade hub to the blade tip so as to allow the maximum camber position to be positioned close to the blade leading edge. The maximum camber ratio of each blade

5

is 2.0% at the blade hub and 8.0% at the blade tip while accomplishing a linear distribution on the blade

5

. Each of the blades

5

is almost free from any sweep angle, while the pitch angle of each blade

5

is rapidly changed from 52° at the blade hub to 26° at the blade tip having a linear distribution.

Such axial flow fans have been preferably used in electromagnetic induction-heating cookers as shown in

FIG. 3

for driving and cooling the cookers.

As shown in

FIG. 3

, the cooker has an axial flow fan

20

on the bottom wall of its casing. When the axial flow fan

20

is started, atmospheric air is sucked into the casing of the cooker through an inlet grille

21

by the suction force of the axial flow fan

20

and flows under the guide of an air guide

22

, thus cooling both a heat dissipating fin

23

and a heating coil

24

prior to being discharged from the casing through an outlet grille

25

.

Such axial flow fans

20

may be preferably used in a variety of electronic appliances in addition to the above-mentioned cookers. Particularly, the axial flow fans

20

may be preferably used for cooling the power supply units, lamps and LCD modules of conventional LCD projectors.

The axial flow fans

20

, used in electronic appliances, such as LCD projectors and induction-heating cookers, are important elements since the fans

20

drive and cool the appliances. However, the conventional axial flow fans

20

are problematic in that they undesirably generate operational noise, disturbing those around the appliances. Particularly, the operational noise of a conventional axial flow fan

20

installed in an induction-heating cooker forms about

70

percent of the entire operational noise of the cooker. Such an operational noise of the fans

20

causes a serious defect of the electronic appliances using the fans.

That is, the operational performance and operational noise of the axial flow fans directly influence the operational performance and operational noise of appliances using the fans.

The axial height of the blades

5

of a conventional axial flow fan is designed to be lower than that of the fan housing

7

. In addition, the blades

5

undesirably have a flat and wide shape with a low camber ratio, a low pitch angle and a low sweep angle. Therefore, the conventional axial flow fan merely generates a reduced air volume while undesirably increasing operational noise.

In a detailed description, when the axial height of the blades

5

is lower than that of the fan housing

7

, the radially sucked air volume of the blades

5

is less than the axially sucked air volume of the blades

5

. The conventional axial flow fan thus merely generates a reduced air volume while undesirably increasing operational noise.

When the blades

5

have a low sweep angle, they undesirably increase operational noise. When the blades

5

have a low pitch angle, the width of each blade

5

is reduced, thus failing to suck a desired air volume. When the blades

5

have a low camber ratio, it is almost impossible to desirably increase the static pressure of air passing through the fan. This forces the rpm of the fan to be increased so as to accomplish a desired air volume, and finally deteriorates the blowing efficiency of the fan.

Therefore, it is necessary to optimally design the axial heights of both the blades

5

and the fan housing

7

, the sweep angle, pitch angle, and camber ratio of the blades

5

so as to accomplish a desired operational effect of electronic appliances using the axial flow fans while accomplishing a desired air volume of the fan in addition to a reduction in operational noise of the fan.

SUMMARY OF THE INVENTION

Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an axial flow fan with a BLDC motor for electronic appliances, which is optimally designed in axial height of both the blades and the fan housing, diameter ratio, the number of blades, camber ratio, pitch angle and sweep angle, thus being improved in blowing operational efficiency in addition to a reduction in operational noise.

In order to accomplish the above object, the primary embodiment of the present invention provides an axial flow fan, comprising a BLDC motor, a hub mounted to the rotating shaft of the motor, a plurality of blades mounted to the hub, and a fan housing covering the blades while holding the motor therein, wherein the blades have an axial height higher than that of the fan housing, with the leading surface of the blades being placed outside the surface of the fan housing at a position higher than the surface of the fan housing by a predetermined projection height, thus increasing an air volume of the fan.

In the primary embodiment, the number of the blades of the axial flow fan is eight, with a diameter ratio of the inner diameter to the outer diameter of the fan being 0.40˜0.45, thus reducing operational noise of the fan. In this embodiment, the blades are designed to have a high sweep angle, a high pitch angle and a high camber ratio.

In the second embodiment, the number of the blades of the axial flow fan is seven, with a diameter ratio of the inner diameter to the outer diameter of the fan being 0.40˜0.43, thus reducing operational noise of the fan. In this embodiment, the blades are designed to have a high sweep angle, a high pitch angle and a high camber ratio.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other objects, features and other advantages of the present invention will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings, in which:

FIGS. 1

a

and

1

b

are plan and side views of a conventional axial flow fan integrated with a motor;

FIG. 2

is a sectional view of the conventional axial flow fan taken along the line A—A of

FIG. 1

a;

FIG. 3

is a sectional view of an electromagnetic induction-heating cooker provided with the conventional axial flow fan;

FIGS. 4

a

and

4

b

are plan and side views of an axial flow fan with a BLDC motor in accordance with the primary embodiment of the present invention;

FIG. 5

is a sectional view taken along the line B—B of

FIG. 4

a

, showing the construction of the axial flow fan according to the primary embodiment of this invention;

FIGS. 6

a

and

6

b

are plan and side views, showing the shape of the blades included in the axial flow fan according to the primary embodiment of this invention;

FIGS. 7

a

and

7

b

are sectional views, showing the shape of a blade included in the axial flow fan according to the primary embodiment of this invention;

FIG. 8

is a graph showing operational noise of the axial flow fan according to the primary embodiment of this invention as a function of the diameter ratio of the axial flow fan;

FIG. 9

is a graph showing operational noise of the axial flow fan according to the primary embodiment of this invention as a function of the maximum camber ratio of the axial flow fan;

FIG. 10

is a graph showing operational noise of the axial flow fan according to the primary embodiment of this invention as a function of the pitch angle of the axial flow fan;

FIG. 11

is a graph showing operational noise of the axial flow fan according to the primary embodiment of this invention as a function of the sweep angle of the axial flow fan;

FIGS. 12

a

and

12

b

are plan and side views of an axial flow fan with a BLDC motor in accordance with the second embodiment of the present invention;

FIG. 13

is a sectional view taken along the line C—C of

FIG. 12

a

, showing the construction of the axial flow fan according to the second embodiment of this invention;

FIGS. 14

a

and

14

b

are plan and side views, showing the shape of the blades included in the axial flow fan according to the second embodiment of this invention;

FIGS. 15

a

and

15

b

are sectional views, showing the shape of a blade included in the axial flow fan according to the second embodiment of this invention;

FIG. 16

is a graph showing operational noise of the axial flow fan according to the second embodiment of this invention as a function of the diameter ratio of the axial flow fan;

FIG. 17

is a graph showing operational noise of the axial flow fan according to the second embodiment of this invention as a function of the maximum camber ratio of the axial flow fan;

FIG. 18

is a graph showing operational noise of the axial flow fan according to the second embodiment of this invention as a function of the pitch angle of the axial flow fan; and

FIG. 19

is a graph showing operational noise of the axial flow fan according to the second embodiment of this invention as a function of the sweep angle of the axial flow fan.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 4

a

and

4

b

are plan and side views of an axial flow fan with a BLDC motor in accordance with the primary embodiment of the present invention.

FIG. 5

is a sectional view taken along the line B—B of

FIG. 4

a

, showing the construction of the axial flow fan according to the primary embodiment of this invention.

FIGS. 6

a

and

6

b

are plan and side views, showing the shape of the blades included in the axial flow fan according to the primary embodiment of this invention.

FIGS. 7

a

and

7

b

are sectional views, showing the shape of a blade included in the axial flow fan according to the primary embodiment of this invention.

As shown in

FIGS. 4

a

to

7

b

, the axial flow fan according to the primary embodiment of this invention comprises a fan housing

57

, with a motor

51

being firmly set within the housing

57

. A hub

53

is firmly mounted to the rotating shaft

52

of the motor

51

, with a plurality of blades

55

regularly fixed around the hub

53

. The fan housing

57

covers the blades

55

so as to protect the blades

55

from external impact. The axial flow fan of this invention is optimally designed in the axial height of both the blades

55

and the fan housing

57

, the number of blades

55

, diameter ratio of the inner diameter ID of the fan to the outer diameter OD, camber ratio, pitch angle and sweep angle of the blades

55

, thus being reduced in operational noise in addition to being increased in air volume.

In the above axial flow fan the axial height of the blades

55

relative to a lower surface of the fan housing

57

is designed to be higher than the axial height of an upper surface of the fan housing

57

relative to the lower surface of the fan housing

57

as best seen in FIG.

5

. Therefore, the leading surface of the blades

55

is placed outside the upper surface of the fan housing

57

at a position higher than the upper surface of the fan housing

57

by a predetermined projection height P. Therefore, the radially sucked air volume of the blades

55

is increased by the projection height P of the blades

55

, and so the axial flow fan of this invention desirably increases its air volume.

It is preferable for the axial flow fan of this invention to have eight blades

55

since the eight blades

55

are capable of desirably reducing the operational noise in addition to having an increase in air volume. In the primary embodiment, the diameter ratio of the inner diameter ID of the axial flow fan to the outer diameter OD is preferably set to 0.40˜0.45, with the inner diameter ID being equal to the diameter of the hub

53

.

As shown in

FIGS. 5

,

6

a

to

7

b

, the axial height S of the fan housing

57

is 21.0±0.4 mm, while the inner diameter Q of the fan housing

57

is 88.5±0.2 mm. On the other hand, the projection a height P of the blades

55

from the upper surface of the fan housing

57

is 4.5±0.1 mm. Therefore, the total height of the axial flow fan according to the primary embodiment is 25.5±0.5 mm, calculated by an addition of the axial height S of the fan housing

57

to the projection height P of the blades

55

.

On the other hand, the outer diameter OD of the blades

55

is 86±0.5 mm, while the inner diameter ID of the blades

55

(the diameter of the hub

53

) is 35±0.5 mm. Therefore, the diameter ratio of the blades

55

(the ratio of the inner diameter ID to the outer diameter OD of the blades

55

) is 0.407. On the other hand, the front leading distance FD of the blades

55

is 14.0±0.4 mm, while the rear trailing distance RD of the blades

55

is 4.94±0.4 mm. In such a case, the front leading distance FD of the blades

55

forms a rotating axis extending from the center point (

0

,

0

,

0

) of a blade dater to the maximum blade leading edge RE, while the rear trailing distance RD of the blades

55

forms a rotating axis extending from the center point (

0

,

0

,

0

) of the blade dater to the maximum blade trailing edge TE. That is, the two distances ED and RD are commonly defined on the rotating axis (Z-axis) of the hub

53

.

The center point (

0

,

0

,

0

) of the blade dater is positioned in the hub

53

and means the center point of the blade tips BT.

In a detailed description, the maximum camber position CP of each blade

55

is set to 0.65˜0.7, with the camber positions being uniformly distributed on each blade

55

from the blade hub BH to the blade tip BT. The maximum camber ratio of each blade

55

is 3.7˜4.1% at the blade hub BH and 9.7˜10.1% at the blade tip BT while accomplishing a linear distribution on the blade

55

.

In such a case, the maximum camber position CP of each blade

55

is located at a point at which the edge of the blade

55

is spaced furthest from a straight line extending from the blade leading edge RE to the blade trailing edge TE. The distance between said straight line and said point on each blade

55

is the maximum camber C. The maximum camber ratio is a ratio of the maximum camber C to the cord length CL. The cord length CL is the length of the straight line extending from the blade leading edge RE to the blade trailing edge TE.

The pitch angle Ψ of each blade

55

is 39.0°˜40.0° at the blade hub BH and 26.0°˜27.0° at the blade tip BT while being linearly distributed on the blade

55

from the blade hub BH to the blade tip BT. The pitch angle Ψ of, each blade

55

is an angle formed between the X-axis and a straight line extending between the blade leading edge RE to the blade trailing edge TE. That is, the pitch angle Ψ of each blade

55

expresses the slope of the blade

55

relative to a plane perpendicular to the Z-axis.

The sweep angle θ of each blade

55

is 0.0° at the blade hub BH and 34.0° at the blade tip BT while being quadratic-parabolically distributed on the blade

55

from the blade hub BH to the blade tip BT. The above sweep angle θ of each blade

55

is an angle formed between the Y-axis and a straight line extending between the center of the blade hub BH and the blade tip BT, with the center of the blade hub BH being positioned on the Y-axis. That is, the sweep angle θ of each blade

55

expresses the tilt of the blade

55

in the rotating direction of the blades

55

.

When the axial height of the blades

55

is designed to be higher than that of the fan housing

57

so as to allow the surface of the blades

55

to be projected from the surface of the housing

57

as described above, the radially sucked air volume of the blades

55

is increased by the projection height of the blades

55

. The axial flow fan of this invention thus desirably increases its air volume and reduces its operational noise.

In addition, when the axial flow fan of this invention has a high sweep angle θ, a high patch angle Ψ and a high camber ratio, the fan desirably, reduces its operational noise and has a wide blade width BD capable of increasing the air volume. In addition, it is possible to desirably increase the static pressure of air passing through the fan, and so the desired air volume of the fan may be effectively accomplished with a low rpm of the fan.

On the other hand, the blade interval between the blades

55

is set to 2.5 mm at the position ε, 5.0 mm at the position ∉, 7.0 mm at the position ∠, and 17.0 mm at the position ∇ as shown in

FIG. 6

a

. When setting the position of the blade hub BH on each blade

55

to zero (0.00) and the position of the blade tip BT to 1.00, the blade interval is primarily set to 2.5±0.5 mm at a position around the blade hub BH. On the other hand, the blade interval within the first positional section of 0˜0.75 is quadratic-parabolically, increased from 2.5±0.5 mm to 5.0±0.5 mm. In addition, the blade interval within the second positional section of 0.75˜0.97 is quadratic-parabolically increased from 5.0±0.5 mm to 7.0±0.5 mm. Within the third positional section of 0.97˜1.00 including the blade tip BT, the blade interval is cubic-parabolically increased from 7.0±0.5 mm to 17.0±1.0 mm.

In a brief description, the blade intervals of 5.0 mm and 7.0 mm are located at the positions of 0.75 and 0.97 of the extent from the blade hub BH to the blade tip BT. In such a case, the differentially derived function at the boundary points of 0.75 and 0.97 between the three sections is zero, while the blade interval distribution within the three sections forms quadratic and cubic-parabolic distributions.

In the axial flow fan with a BLDC motor in accordance with the primary embodiment of this invention, it is most preferable to set the axial height S of the fan housing to 21.0 mm, the inner diameter Q of the fan housing to 88.5±0.2 mm, and the projection height P of the blades from the surface of the fan housing to 4.5±0.1 mm.

It is also most preferable to set the outer diameter OD of the blades to 86 mm, the inner diameter ID of the blades to 35 mm, the front leading distance FD of the blades to 14.0±0.4 mm, the rear trailing distance RD of the blades to 4.94±0.4 mm, and the number of blades to eight.

On the other hand, it is most preferable to set the maximum camber position CP of each blade to 0.67 while uniformly distributing the camber positions on each blade

55

from the blade hub BH to the blade tip BT. In addition, the maximum camber ratio of each blade

55

is most preferably set to 3.8% at the blade hub BH and 9.89% at the blade tip BT while accomplishing a linear distribution on the blade

55

.

The sweep angle θ of each blade

55

is most preferably set to 0.0° at the blade hub BH and 34.0° at the blade tip BT while accomplishing a quadratic-parabolic distribution on the blade

55

from the blade hub BH to the blade tip BT. On the other hand, the pitch angle Ψ of each blade

55

is most preferably set to 39.65° at the blade hub BH and to 26.65° at the blade tip BT while accomplishing linear distribution on the blade

55

from the blade hub BH to the blade tip BT.

The variation of operational noise of the axial flow fan according to the primary embodiment of this invention as a function of designing factors is shown in the graphs of

FIGS. 8

to

11

.

FIG. 8

is a graph showing the operational noise of the axial flow fan as a function of the diameter ratio (ID/OD) of the blades

55

. This graph shows that it is possible to accomplish a desired minimum operational noise of 22.4 dB±0.1 when the diameter ratio of the blades

55

is set to 0.4˜0.45.

FIG. 9

is a graph showing the operational noise of the axial flow fan as a function of the maximum camber ratio of the axial flow fan. This graph shows that it is possible to accomplish a desired low operational noise of 22.6 dB±0.1 when the maximum camber ratio of each blade

55

is set to 3.7˜4.1% at the blade hub BH and to 9.7˜10.1% at the blade tip BT while accomplishing a linear distribution on the blade

55

. Particularly, this graph shows that when the maximum camber ratio of each blade

55

is set to 4.0% at the blade hub BH and to 10.0% at the blade tip BT while accomplishing a linear distribution on the blade

55

, the desired minimum operational noise of 22.5 dB is accomplished.

FIG. 10

is a graph showing the operational noise of the axial flow fan as a function of the pitch angle Ψ of the blades

55

. This graph shows that it is possible to accomplish a desired minimum operational noise of 22.5 dB±0.1 when the pitch angle Ψ of each blade

55

is set to 39.0°˜40.0° at the blade hub BH and to 26.0°˜27.0° at the blade tip BT while accomplishing a linear distribution on the blade

55

from the blade hub BH to the blade tip BT.

FIG. 11

is a graph showing operational noise of the axial flow fan as a function of sweep angle θ of the blades

55

. This graph shows that it is possible to accomplish a desired minimum operational noise of 22.6 dB when the sweep angle θ of each blade

55

is set to 0.0° at the blade hub BH and to 34.0° at the blade tip BT while accomplishing a quadratic-parabolic distribution on the blade

55

from the blade hub BH to the blade tip BT.

The boundary data of the blades

55

included in the axial flow fan according to the primary embodiment of the present invention is given in Table 1. As expressed in Table 1, the axial flow fan effectively reduces its operational noise by at least 3 dB(A) in comparison with a conventional axial flow fan while providing the same air volume.

TABLE 1

Blade Width = 18.95 mm

X

Y

Z

5.526

16.605

−4.580

4.352

16.950

−3.810

3.172

17.210

−3.003

1.993

17.386

−2.164

0.821

17.481

−1.298

−0.339

17.497

0.409

−1.481

17.437

0.498

−2.599

17.306

1.422

−3.652

17.115

2.404

−4.628

16.877

3.457

−5.526

16.605

4.580

−6.003

19.130

4.863

−6.292

21.706

4.941

−6.384

24.326

4.808

−6.261

26.983

4.461

−5.903

29.668

3.907

−5.280

32.372

3.159

−4.219

35.097

2.146

−2.622

37.809

0.884

−0.463

40.447

−0.544

5.960

42.585

−6.394

7.397

42.359

−7.669

8.967

42.055

−8.651

10.602

41.673

−9.468

12.257

41.216

−10.200

13.902

40.691

−10.902

15.548

40.091

−11.542

17.190

39.415

−12.119

18.824

38.661

−12.634

20.446

37.828

−13.083

22.051

36.915

−13.466

23.278

33.080

−13.770

20.305

32.002

−13.074

17.511

30.708

−12.119

14.886

29.228

−10.947

12.479

27.556

−9.647

10.415

25.667

−8.369

8.695

23.599

−7.179

7.310

21.385

−6.126

6.255

19.049

−5.250

5.526

16.605

−4.580

FIGS. 12

a

and

12

b

are plan and side views of an axial flow fan with a BLDC motor in accordance with the second embodiment of the present invention.

FIG. 13

is a sectional view taken along the line C—C of

FIG. 12

a

, showing the construction of the axial flow fan according to the second embodiment of this invention.

FIGS. 14

a

and

14

b

are plan and side views, showing the shape of the blades included in the axial flow fan according to the second embodiment of this invention.

FIGS. 15

a

and

15

b

are sectional views, showing the shape of a blade included in the axial flow fan according to the second embodiment of this invention.

As shown in

FIGS. 14

a

to

15

, the axial flow fan according to the second embodiment of this invention comprises a fan housing

157

, with a motor

151

being firmly set within the housing

157

. A hub

153

is firmly mounted to the rotating shaft

152

of the motor

151

, with a plurality of blades

155

regularly fixed around the hub

153

. The fan housing

157

is connected to a duct

160

and covers the blades

155

so as to protect the blades

155

from external impact. The axial flow fan of this embodiment is optimally designed in the number of blades

155

, diameter ratio of the inner diameter of the fan to the outer diameter, camber ratio, pitch angle Ψ and sweep angle θ of the blades

155

, thus being reduced in operational noise in addition to being increased in air volume.

It is preferable for the axial flow fan of this embodiment to have seven blades

155

, with the diameter ratio of the inner diameter ID′ of the blades

155

to the outer diameter OD′ being preferably set to 0.40˜0.43.

As shown in

FIGS. 14

a

to

15

b

, the axial height S′ of the fan housing

157

is set to 25.0±0.5 mm, while the inner diameter Q′ of the fan housing

157

is set to 88.5±0.2 mm.

On the other hand, the outer diameter OD′ of the blades

155

is set to 86.5±0.5 mm, while the inner diameter ID′ of the blades

155

is set to 35±0.5 mm. In addition, the front leading distance FD′ of the blades

155

is set to 11.51±0.4 mm, while the rear trailing distance RD′ of the blades

155

is set to 6.53±0.4 mm. In such a case, the blade width BD′, defined by both the front leading distance FD′ and the rear trailing distance RD′ of the blades

155

, is 18.04±0.5 mm. On the other hand, the height T of the blades

155

is set to 23.5±0.5 mm.

The maximum camber position CP′ of each blade

155

is set to 0.66˜0.69, with the camber positions being uniformly distributed on each blade

155

from the blade hub BH′ to the blade tip BT′. The maximum camber ratio of each blade

155

is set to 5.3˜5.7% at the blade hub BH′ and to 11.3˜11.7% at the blade tip BT′ while accomplishing a linear distribution on the blade

55

from the blade hub BH′ to the blade tip BT′.

The pitch angle Ψ′ of each blade

155

is set to 37.0°˜39.0° at the blade hub BH′ and to 24.0°˜26.0° at the blade tip BT′ while being linearly distributed on the blade

155

from the blade hub BH′ to the blade tip BT′.

On the other hand, the sweep angle θ of each blade

155

is set to 0.0° at the blade hub BH′ and to 37.0° at the blade tip BT′ while accomplishing a quadratic-parabolic distribution on the blade

155

from the blade hub BH′ to the blade tip BT′.

When the axial flow fan of this embodiment is designed to have such a high sweep angle θ′, a high pitch angle Ψ′ and a high camber ratio, the fan desirably reduces its operational noise and has a wide blade width BD′ capable of increasing the air volume. In addition, it is possible to desirably increase the static pressure of air passing through the fan, and so the desired air volume of the fan may be effectively accomplished with a low rpm of the fan.

On the other hand, the blade interval between the blades

155

is set to 2.5 mm at the position ε, 5.0 mm at the position ∉, 5.5 mm at the position ∠, and 17.0 mm at the position ∇ as shown in

FIG. 14

a

. When setting the position of the blade hub BH′ on each blade

155

to zero (0.00) and the position of the blade tip BT′ to 1.00, the blade interval is set to 2.5±0.5 mm at a position around the blade hub BH′. On the other hand, the blade interval within the first positional section of 0˜0.8 is quadratic-parabolically increased from 2.5±0.5 mm to 5.0±0.5 mm. In addition, the blade interval within the second positional section of 0.8˜0.97 is quadratic-parabolically increased from 5.0±0.5 mm to 5.5±0.5 mm. Within the third positional section of 0.97˜1.00 including the blade tip BT′, the blade interval is cubic-parabolically increased from 5.5±0.5 mm to 17.0±1.0 mm.

In a brief description, the blade intervals of 5.0 mm and 5.5 mm are located at the positions of 0.8 and 0.97 of the extent from the blade hub BH′ to the blade tip BT′. In such a case, the differentially derived function at the boundary points of 0.8 and 0.97 between the three sections is zero, while the blade interval distribution within the three sections forms quadratic and cubic-parabolic distributions.

In the axial flow far, with a BLDC motor in accordance with the second embodiment of this invention, it is most preferable to set the size of the fan to 92 mm(W)×92 mm(D)×25 mm(H), the axial height S′ of the fan housing to 25.0 mm, and the inner diameter Q′ of the fan housing to 88.5 mm.

It is also most preferable to set the outer diameter OD′ of the blades to 86.5 mm, the inner diameter ID′ of the blades to 35 mm, and the diameter ratio (ID′/OD′) to 0.405.

It is also most preferable to set the height of the blades to 23.5 mm, the front leading distance FD′ of the blades to 11.51 mm, the rear trailing distance RD′ of the blades to 6.53 mm, the blade width BD′ to 18.04 mm, and the number of blades to seven.

On the other hand, it is most preferable to set the maximum camber position CP′ of each blade to 0.67 while uniformly distributing the camber positions on each blade

155

from the blade hub BH′ to the blade tip BT′. In addition, the maximum camber ratio of each blade

155

is most preferably set to 5.47% at the blade hub BH′ and 11.47% at the blade tip BT′ while accomplishing a linear distribution on the blade

55

from the blade hub BH′ to the blade tip BT′.

The sweep angle θ′ of each blade

155

is most preferably set to 0.0° at the blade hub BH′ and to 37.0°˜38.0° at the blade tip BT′ while accomplishing a quadratic-parabolic distribution on the blade

155

from the blade hub BH′ to the blade tip BT′. On the other hand, the pitch angle Ψ′ of each blade

155

is most preferably set to 37.74° at the blade hub BH′ and to 24.74° at the blade tip BT′ while accomplishing linear distribution on the blade

155

from the blade hub BH′ to the blade tip BT′.

The variation of operational noise of the axial flow fan according to the second embodiment of this invention as a function of designing factors is shown in the graphs of

FIGS. 16

to

19

.

FIG. 16

is a graph showing the operational noise of the axial flow fan as a function of the diameter ratio (ID′/OD′) of the blades

155

. This graph shows that it is possible to accomplish a desired minimum operational noise of 22.4 dB±0.1 when the diameter ratio of the blades

155

is set to 0.4˜0.45.

FIG. 17

is a graph showing the operational noise of the axial flow fan as a function of the maximum camber ratio of the axial flow fan. This graph shows that it is possible to accomplish a desired low operational noise of 22.4 dB when the maximum camber ratio of each blade

155

is set to 5.3˜5.7% at the blade hub BH′ and to 11.3˜11.7% at the blade tip BT′ while accomplishing a linear distribution on the blade

155

from the blade hub BH′ to the blade tip BT′.

FIG. 18

is a graph showing the operational noise of the axial flow fan as a function of the pitch angle Ψ′ of the blades

155

. This graph shows that it is possible to accomplish a desired minimum operational noise of 22.4 dB when the pitch angle Ψ′ of each blade

155

is set to 37.0°˜39.0° at the blade hub BH′ and to 24.0°˜26.0° at the blade tip BT′ while accomplishing a linear distribution on the blade

155

from the blade hub BH′ to the blade tip BT′.

FIG. 19

is a graph showing operational noise of the axial flow fan as a function of the sweep angle θ′ of the blades

155

. This graph shows that it is possible to accomplish a desired minimum operational noise of 22.5 dB±0.1 when the sweep angle θ′ of each blade

155

is set to 0.0° at the blade hub BH′ and to 37.0°˜38.0° at the blade tip BT′ while accomplishing a quadratic-parabolic distribution on each blade

155

from the blade hub BH′ to the blade tip BT′.

The boundary data of the blades

155

included in the axial flow fan according to the second embodiment of the present invention is given in Table 2. As expressed in Table 2, the axial flow fan effectively reduces its operational noise by at least 3 dB(A) in comparison with a conventional axial flow fan while providing the same air volume.

TABLE 2

Blade Width = 18.04 m

X

Y

Z

6.448

16.269

−4.991

4.900

16.800

−4.144

3.339

17.179

−3.223

1.780

17.409

−2.241

0.238

17.498

−1.209

−1.276

17.483

−0.134

−2.749

17.283

0.972

−4.129

17.006

2.164

−5.362

16.658

3.503

−6.448

16.269

4.991

−7.159

19.061

5.809

−7.570

21.954

6.326

−7.664

24.932

6.531

−7.410

27.980

6.425

−6.774

31.076

6.026

−5.715

34.192

5.370

−4.116

37.301

4.469

−1.868

40.346

3.377

5.734

42.868

−2.467

7.366

42.618

−5.253

9.738

42.140

−6.359

12.075

41.530

−7.459

14.448

40.765

−8.370

16.798

39.855

−9.200

19.128

38.790

−9.912

21.429

37.568

−10.495

23.687

36.187

−10.950

25.888

34.646

−11.273

26.628

30.368

−11.436

22.781

29.822

−10.981

19.222

28.849

−10.189

16.020

27.477

−9.191

13.248

25.735

−8.132

10.908

23.693

−7.109

8.998

21.408

−6.203

7.513

18.924

−5.480

6.448

16.269

−4.991

As described above, the present invention provides an axial flow fan with a BLDC motor for electronic appliances, such as office or domestic electronic appliances. The axial flow fan of this invention is optimally designed in axial height of both the blades and the fan housing, the number of blades, diameter ratio of the inner diameter to the outer diameter of the blades, camber ratio, pitch angle and sweep angle of the blades, thus being reduced in operational noise in addition to being increased in air volume.

Therefore, when the axial flow fan of this invention is used in electronic appliances, such as office or domestic electronic appliances, it is possible to reduce operational noise of the appliances in addition to accomplishing an increase in air volume.

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

Number	Name	Date	Kind
2583374	Hoffman	Jan 1952	A
4055113	Monroe	Oct 1977	A
5320493	Shih et al.	Jun 1994	A
5577888	Capdevila	Nov 1996	A
5879141	Yokozawa et al.	Mar 1999	A
5957661	Hunt et al.	Sep 1999	A
6129528	Bradbury et al.	Oct 2000	A
6132170	Horng	Oct 2000	A
6193478	Lin et al.	Feb 2001	B1

Axial flow fan with brushless direct current motor

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