Fluid reaction surfaces (i.e. – impellers) – Specific blade structure – Integrally shaped or blended into hub
Reexamination Certificate
2001-01-11
2002-07-09
Look, Edward K. (Department: 3745)
Fluid reaction surfaces (i.e., impellers)
Specific blade structure
Integrally shaped or blended into hub
C416S243000, C416SDIG002, C416SDIG005
Reexamination Certificate
active
06416288
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an axial-flow fan, and more particularly to an axial-flow fan mounted to the electric unit of a microwave oven and adapted to cool the magnetron and high-voltage transformer of the microwave oven.
2. Description of the Conventional Art
Typically, an axial-flow fan includes a hub coupled to the rotating shaft of a motor fixedly mounted to the mounting section of a fan guide, and blades arranged around the hub and integral with the hub. The blades rotate along with the hub, thereby causing a fluid to flow axially.
Such an axial-flow fan have diverse design parameters depending on the appliance to which the axial-flow fan is applied. Where such design parameters are improperly determined, noises of an increased level are generated during an operation of the appliance to which the axial-flow fan is applied.
In particular, the axial-flow fan involves noises resulting from a blade vortex interaction(VBI) of the blades occurring during a rotation of those blades as a downstream one of the blades, which viewed in a rotation of the blades, is struck against a vortex stream created by an upstream one of the blades.
In the axial-flow fan, noises may also be generated due to the so-called blade passing frequency(BPF) of a fluid, passing the blades, exhibited when the fluid is struck against a fixed construction such as a guide fixedly mounted around the blades.
The blade passing frequency is expressed by an integer multiple of the product of the number of the blades by the revolutions per minute of the blades. Such a blade passing frequency is generated due to the striking of a fluid flow against the fixed construction around the blades occurring during the rotation of those blades. This blade passing frequency serves as a major frequency increasing the level of noises generated at the axial-flow fan.
Referring to
FIG. 1
, a microwave oven installed with a conventional axial-flow fan is illustrated. As shown in
FIG. 1
, the microwave oven includes a casing
1
defined with a cooking chamber
2
. A magnetron
3
and a high-voltage transformer
5
, which serve to generate microwaves, are mounted to the outer wall surface of the cooking chamber
2
at a desired portion of the cooking chamber
2
. A waveguide
4
is arranged between the cooking chamber
2
and the magnetron
3
in order to guide microwaves to the cooking chamber
2
. An axial-flow fan assembly
10
is fixedly mounted to the inner wall surface of the casing
1
at a desired portion of the casing
1
in order to cool the magnetron
3
and the high-voltage transformer
5
.
As shown in
FIG. 2
, the axial-flow fan assembly
10
includes a suction guide
11
fixedly mounted to the inner wall surface of the casing
1
and adapted to assist in stably sucking a fluid, a drive motor
12
arranged upstream from the suction guide
11
and adapted to generate a rotating force, and an axial-flow fan
13
coupled to a rotating shaft of the drive motor
12
to receive the rotating force and adapted to suck air and to discharge the sucked air toward the magnetron
2
and the high-voltage transformer
5
.
The axial-flow fan
13
is a fan axially sucking and discharging a fluid. This axial-flow fan
13
includes a hub
13
a
coupled to the rotating shaft of the drive motor
12
to receive a rotating force from the drive motor
12
, and a plurality of blades
13
b
arranged around the hub
13
a
and integral with the hub
13
a
and adapted to move a fluid while rotating.
A general operation of the microwave oven including the above mentioned conventional axial-flow fan will now be described.
When the magnetron
3
generates microwaves in response to the application of electric power from the high-voltage transformer
5
thereto, the generated microwaves are supplied to the cooking chamber
2
via the waveguide
4
, so that food disposed in the cooking chamber
2
is heated and cooked. Simultaneously, electric power is applied to the drive motor
12
adapted to drive the axial-flow fan
13
coupled to the rotating shaft of the drive motor
12
, so that the axial-flow fan
13
rotates. During the rotation, the axial-flow fan
13
sucks ambient air, and discharges the sucked air toward the magnetron
3
and the high-voltage transformer
5
, thereby preventing the magnetron
3
and the high-voltage transformer
5
from being overheated.
Now, design parameters for determining the structural shape of the axial-flow fan
13
will be described in detail.
As shown in
FIG. 3A
, the conventional axial-flow fan
13
has an outer fan diameter Df′ of 108 mm and a hub diameter Dh′ of 30 mm. The number of blades in the axial-flow fan
13
is four. Also, the axial-flow fan
13
has a sweep angle &agr;′ of 28°. The sweep angle is an angle defined between the line, which connects an intermediate point of the leading edge LE′ of each blade with an intermediate point of the trailing edge TE′ of the same blade between the outer peripheral surface of the hub and the tip of the blade, and a Y-axis perpendicular to a rotating axis of the blade, that is, a Z-axis.
The leading edge of each blade is positioned at a forward portion of the blade when viewed in the rotating direction of the fan, and the trailing edge of the blade is positioned at a rearward direction of the blade.
In
FIG. 3B
, “&ggr;′” represents a rake angle, that is, an angle of each blade forwardly or rearwardly inclined with respect to the flow direction of a fluid passing through the axial-flow fan
13
when viewed from the side of the axial-flow fan
13
, that is, along the X-axis. The flow direction of the fluid corresponds to ±Z-axis. The axial-flow fan
13
has a rake angle &ggr;′ of 0°.
In
FIG. 3C
, “&bgr;′” represents a pitch angle of each blade in the axial-flow fan
13
. The pitch angle is an angle defined between a phantom line, that is, a chord line C′, extending between opposite blade tips when viewed from the side of the axial-flow fan
12
, that is, along the X-direction, and the Y-axis perpendicular to the rotating axis of the blade, that is, the Z-axis. The axial-flow fan
13
has a pitch angle &bgr;′ of 21°±2° at the outer tip of each blade and 30°±2° at the inner tip of each blade.
The position of a camber line CB′ connecting intermediate points between the upper and lower surfaces of each blade is expressed by a polynomial equation for the distance between the camber line CB′ and the chord line C′. The position on the camber line CB′ spaced apart from the chord line C′ by a maximum straight distance is referred to as a “maximum camber position” MCP′. The maximum straight distance of the maximum camber position MCP′ is referred to as a “maximum camber” MC′.
The ratio of the maximum camber MC′ to the length of the chord line C′ is referred to as a “maximum camber ratio” MCR′. The conventional axial-flow fan
13
has a maximum camber ratio of 5.2% at the outer blade tip and 7.2% at the inner blade tip. The maximum camber position MCP′ is defined at a point spaced apart from both the leading edge LE′ and the trailing edge TE′ by a distance of 0.5±0.1 when the distance between the leading and trailing edges LE′ and TE′ is defined to be 1.
In the above mentioned axial-flow fan applied to microwave ovens, air sucked by the axial-flow fan exhibits the above mentioned “blade passing frequency” while passing by the suction guide arranged at the suction section of the axial-flow fan, thereby generating noises. The level of such noises is also increased due to a blade vortex interaction of the blades occurring during a rotation of those blades as a downstream one of the blades is struck against a vortex stream created by an upstream one of the blades.
SUMMARY OF THE INVENTION
Therefore, an object of the invention is to provide an axial-flow fan capable of reducing noises generated during a suction of air, in particular, noise
Birch & Stewart Kolasch & Birch, LLP
LG Electronics Inc.
Look Edward K.
Nguyen Ninh
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