Fan guard of blower unit and air conditioner

Details Fan guard of blower unit and air conditioner Fan guard of blower unit and air conditioner

2001-04-04

2003-01-07

Look, Edward K. (Department: 3745)

Fluid reaction surfaces (i.e., impellers)

Protective screen or guard

Water or marine propellers

C415S121200, C415S211200

Reexamination Certificate

active

06503060

ABSTRACT:

TECHNICAL FIELD
The present invention relates to a fan guard for an air blowing unit which does not make noise or a short-circuit while the fan is in operation (blowing air), and to an air-conditioning device provided with the fan guard.
BACKGROUND ART
One example of the air blowing unit is the outdoor unit of an air-conditioning system. As shown in
FIGS. 20 and 21
, an outdoor unit (
20
) of an air-conditioning system is composed of a heat exchanger (
21
) and a propeller fan (
22
) which are stored in a box-shaped casing. On the front side of the casing, an air outlet (
20
a
) is formed by a bell mouth (
23
), which is a fan guide. A grille-structured fan guard (
24
) for protecting the fan is arranged to cover the air outlet (
20
a
) of the casing.
Rotating the propeller fan (
22
) causes air to be taken into the casing through the opening for air intake (
20
b
) on the rear side. The air passes through the heat exchanger (
21
), the propeller fan (
22
), the bell mouth (
23
), the air outlet (
20
a
), and the fan guard (
24
) in this order so as to be blown toward the front of the outdoor unit (
20
) as indicated with the arrows.
The fan guard (
24
) has a grille structure where a plurality of protecting ribs (
25
,
25
. . . ) and a plurality of supporting ribs (
26
,
26
. . . ) form a fan-shaped lattice. The protecting ribs (
25
) are extended in the form of rings around the rotation axis of the propeller fan (
22
) and are made from a steel wire which is circular in cross section in consideration of the outward appearance. On the other hand, the supporting ribs (
26
) are extended in the radial direction at predetermined intervals orthogonal to the rotation axis (O-O′) of the propeller fan (
22
), and are made from a steel wire which is circular in cross section. The supporting ribs (
26
) are welded to the protecting ribs (
25
) so as to support them.
This structure of the outdoor unit (
20
) can protect the propeller fan (
22
) inside the outdoor unit (
20
), and also makes the fan (
22
) harder to be seen from outside, thereby enhancing the exterior of the entire casing and also offering a well-balanced structure in terms of design.
PROBLEM SOLUTIONS
However, the above-described prior art fan guard (
24
) made from a steel wire requires the welding of the supporting ribs (
26
) to the protecting ribs (
25
), which increases the cost.
In addition, when a current caused by the propeller fan (
22
) passes into the fan guard (
24
), it cannot smoothly follow the surfaces of the ribs (
25
,
26
) because the surfaces are circular in cross section. As a result, the current is split by the surfaces so as to develop vortexes, which leads to a pressure loss and makes noise.
It would be possible to reduce the pressure loss by forming the ribs (
25
,
26
) flat with respective predetermined widths. At the same time, it would be possible to lower the cost by integrally making the ribs (
25
,
26
) from a synthetic resin.
However, in that case, the current from the propeller fan (
22
) flowing into the fan guard (
24
) includes a speed component having a predetermined magnitude in the direction of rotation of the propeller fan (
22
). This makes the direction of the air flowing from the propeller fan (
22
) disagree with the angle at which the flat surfaces of the ribs (
25
,
26
) are set so that the current comes into collision with the flat surfaces, thereby developing vortexes. This leads to a pressure loss and makes noise.
The velocity of flow of air generated by the propeller fan (
22
) differs among different positions in the direction of the radius of the fan (
22
). As known from the measured data shown in
FIG. 13
, the current from the outer portions of the blades (
22
a
) of the propeller fan (
22
) a little closer to the hub (
22
b
) than the tips (
27
) of the blades (
22
a
) has a higher velocity than the current from the tips (
27
). The velocity distribution in the direction of the radius of the fan (
22
) indicates that the velocity of the current decreases from the outer portions of the blades (
22
a
) both towards the hub (
22
b
) side and towards the tips (
27
) side.
Inside the outer diameter of the hub (
22
b
), a difference in pressure causes a reverse current which goes from the downstream side of the propeller fan (
22
) to the hub (
22
b
) side. The reverse current interferes with the current flowing in the intended direction, thereby causing an issue of noise.
When the air blowing unit is applied to the outdoor unit of an air-conditioning system as described above, a short-circuit phenomenon occurs. That is, the air blown by the propeller fan (
22
) after passing through the heat exchanger (
21
) spreads outward in the direction of the radius of the fan (
22
) to be drawn towards the rear side, and again goes into the heat exchanger (
21
). This short-circuit phenomenon, which deteriorates the air conditioning performance, must be avoided as effectively as possible.
However, the current from the propeller fan (
22
) generally has a speed component in the centrifugal direction, and tends to spread outward in the direction of the radius of the fan (
22
). As a result, the air flown out through the fan guard (
24
) adheres to the front-side wall of the casing due to Coanda effect, and travels towards the heat exchanger (
21
), which may cause a short-circuit. This tendency is more conspicuous in a case where an oblique fan is used instead of the propeller fan.
DISCLOSURE OF THE INVENTION
Each invention of the present application has been contrived with the aim of solving the above-mentioned problems. In order to achieve the object, the inventions are provided with the following effective problem-solving means.
(1) First Invention
The first invention is provided with a frame (
4
a
) arranged around the perimeter of an air outlet (
2
a
) of a fan (
6
), and with a plurality of board-shaped ribs (
41
,
41
. . . ) extending radially from the vicinity of the center of the frame (
4
a
) outward in the direction of the radius of the fan (
6
).
The board-shaped ribs (
41
) are outward curved in the direction of rotation of the fan (
6
), and also inclined in the direction of air flowing from the fan (
6
).
In other words, the first invention comprises a frame (
4
a
) arranged around the perimeter of the air outlet (
2
a
) of the fan (
6
), and a plurality of board-shaped ribs (
41
,
41
. . . ) extending radially from the vicinity of the center of the frame (
4
a
) corresponding to the rotation axis (O-O′) of the fan (
6
) outward in the direction of the radius of the fan (
6
). The plurality of board-shaped ribs (
41
,
41
. . . ) are extended in the direction of rotation of the fan (
6
) and also inclined in the direction of air blowing from the fan (
6
).
As stated before, there is a case where the air blowing unit is applied to the outer unit of an air-conditioning system. In this case, the occurrence of a short-circuit must be prevented as much as possible because it decreases the air-conditioning performance. The air taken in through the opening for air intake on the back side of the casing passes through a heat exchanger and then is blown off through the air outlet (
2
a
) on the front side of the fan (
6
). It is necessary to avoid a phenomenon in which the blown air is again taken in through the opening for air intake and supplied to the heat exchanger. However, the current generated by the fan (
6
) arranged upstream of the fan guard (
4
) tends to flow outward in the direction of the radius of the fan (
6
). Consequently, if nothing is done, it is likely that the current from the fan guard (
4
) adheres to the surface of the front wall of the casing due to Coanda effect and travels towards the heat exchanger on the rear side, thereby causing a short circuit.
Therefore, in the first invention, the plurality of board-shaped ribs (
41
) are curved in the direction of rotation of the fan (
6
). As a result, the board-shaped ribs (
41
) makes a force (Fr) inward in the direction of the radius of the fan (
6
) apply on the current outwar

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