Patent Publication Number: US-2002006328-A1

Title: Fan guide

Description:
BACKGROUND OF THE INVENTION  
       [0001] 1. Field of the Invention  
       [0002] The present invention relates to a fan guide, and, more particularly, to a fan guide for fixing and supporting a fan and a driving motor adapted to drive the fan at an intake part of the fan.  
       [0003] 2. Description of the Conventional Art  
       [0004] In general, a fan guide is used to support a fan and a driving motor, which are used in a cooling device or a ventilator of electronic products to produce an air flow.  
       [0005] In such a cooling device or ventilator, an air flow passing through the driving motor by a rotation of the fan generates a noise mainly by the fan. In an interrelation between the fan and the fan guide, it is known that the degree of the noise may vary greatly depending on the shape of the fan guide. No matter what any kind of the fan is used, the cooling device or the ventilator having the above mentioned fan guide structure produces a blade passing frequency, thus generating noise.  
       [0006] As shown in FIG. 1, a conventional microwave oven has a casing  1  defined with a cooking chamber  2  therein. A magnetron  3  producing a microwave is attached to an outer wall portion of the cooking chamber  2 . A waveguide  4  guiding the microwave is coupled between the magnetron  3  and the cooking chamber  2 . A cooling fan assembly  10  is attached to an inner wall portion of the casing  1  to cool the magnetron  3  along with a power supply unit  5 .  
       [0007] As shown in FIG. 2, the cooling fan assembly  10  comprises a fan guide  11  fixed to the inner wall portion of the casing  1 , a driving motor  12  arranged in front of the fan guide  11 , that is, upstream of the fan guide  11 , when viewed in a flow direction of air, and attached to the fan guide  11 , and a fan  13  connected to a driving shaft of the driving motor  12  and adapted to suck and discharge air.  
       [0008] Referring to FIG. 3, the fan guide  11  is more specifically described. The fan guide  11  comprises a guide body  11   a  and eight frames  11   b.  The frames  11   b  are arranged in pair around the center of the guide body  11   a  in the form of a lattice in such a fashion that those of each frame pair are connected together while defining a right angle there between. The drive motor  12  is fixedly mounted to the fan guide  11  at a joint between the frames  11   b  of each frame pair.  
       [0009] In FIG. 2, the reference numeral  11   c  denotes a motor fixture arranged at the joint between the frames  11   b  of each frame pair.  
       [0010] In the microwave oven having the above mentioned conventional fan guide  11 , the operating procedure of the microwave oven and the procedure of sucking air are carried out as follows.  
       [0011] Once electric power is supplied to the power supply unit  5 , a microwave is generated from the magnetron  3 , and supplied to the cooking chamber  2  through the wave guide  4 . By the supplied microwave, food in the cooking chamber  2  is heated and cooked. The electric power is also supplied to the driving motor  12  simultaneously with the application thereof to the power supply unit  5 , so that the driving motor  12  rotates. As a result, the fan  13  connected to the driving shaft of the driving motor  12  is rotated, thereby sucking outside air. Accordingly, the magnetron  3  and the power supply unit  5  are cooled by the sucked air.  
       [0012] At this time, the air, which is sucked by the fan  13 , flows toward the fan  12  after passing through spaces defined among the frames  11   b  arranged at the front surface of the fan guide  11 . During this sucking procedure, flow noise and flow loss may be generated due to the geometrical characteristics of the frames  11   b  coupled to the fan guide  11 .  
       [0013] This problem will now be described in detail.  
       [0014] In the conventional fan guide in which frames are arranged in pair around the center of the guide body in the form of a lattice in such a fashion that those of each frame pair are connected together while defining an angle α there between, the blade passing frequency generated by the fan is reinforced when the geometrical structure of those frames is more regular and uniform. The reinforced blade passing frequency results in a generation of flow noise. The air passing the frames generates a vortex shedding phenomenon, so that it interferes with the blades of the fan. Due to such an interference, there are problems of an increase in noise and an occurrence of flow loss.  
       SUMMARY OF THE INVENTION  
       [0015] Accordingly, an object of the present invention is to provide a fan guide having an asymmetric arrangement of frames capable of decreasing the degree of noise resulting from a blade passing frequency while destroying the regularity of a vortex shedding formed at each frame to reduce the interaction between a vortex flow and fan blades, thereby achieving a reduction in noise and flow loss.  
       [0016] In accordance with the present invention, this object is accomplished by providing a fan guide comprising: a rectangular guide body located at a suction part of a fan; a central frame positioned at a central portion of the guide body; motor fixtures provided at an outer circumferential surface of the central frame; and at least two frames for connecting the guide body and the central frame to each other while supporting the fan and a driving motor adapted to drive the fan, the frames being arranged around the central frame while being circumferentially spaced apart from one another by different angles, respectively. 
     
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
     [0017]FIG. 1 is a partially-broken schematic view of a conventional microwave oven.  
     [0018]FIG. 2 is an exploded perspective view of a fan guide according to the conventional microwave oven.  
     [0019]FIG. 3 is a front view of the conventional fan guide.  
     [0020]FIG. 4 is an exploded perspective view of a fan guide according to the present invention.  
     [0021]FIG. 5 is a front view of a fan guide of the present invention.  
     [0022]FIG. 6 is a front view of an another fan guide modified from the fan guide of FIG. 5.  
     [0023]FIG. 7 is a graph representing a comparative analysis of rear noise characteristics exhibited in a microwave oven, to which the fan guide of the present invention is applied, as compared to the case in which a conventional fan guide is applied. 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT  
     [0024] The above and other objects, characteristics, and advantages of the present invention will become apparent from the following description along with the accompanying drawings, in which the same elements as those in the related art will be designated by the same reference numerals.  
     [0025] As shown in FIG. 4, a cooling fan assembly  100  of a microwave oven having a fan guide of the present invention includes a fan guide  110  attached to an inner wall portion of a casing  1 , a driving motor  120  arranged in front of the fan guide  110 , and a fan  130  connected to a motor shaft of the driving motor  120  and located in rear of the fan guide  110 , that is, downstream of the fan guide  110 , and adapted to suck air from the front end of the fan guide  110  and to discharge the sucked air toward a magnetron  3  located in rear of the fan  130 .  
     [0026] As shown in FIG. 5, the fan guide  110  includes a guide body  111  receiving the fan  130 , three straight frames  112   a,    112   b,  and  112   c,  and a central frame  113 . Each of the straight frames  112   a,    112   b,  and  112   c  is integral, at the outer end thereof, with the front surface of the guide body  111  while being integral, at the inner end thereof, with the central frame  113 .  
     [0027] The straight frames  112   a,    112   b,  and  112   c  are arranged around the central frame  113  to extend in a direction similar to a radial direction while being circumferentially spaced apart from one another by different angles β 1 , β 2 , and β 3 , respectively.  
     [0028] Further, the arrangement of the straight frames  112   a,    112   b,  and  112   c  are set so that intersections P 1 , P 2 , and P 3  among lines extending inwardly along the straight frames  112   a,    112   b,  and  112   c  beyond the central frame  113 , respectively, discord from one another.  
     [0029] An another embodiment of the straight frames  112   a ,  112   b , and  112   c  is shown in FIG. 6. In accordance with this embodiment, curved frames  212   a,    212   b,  and  212   c  are provided.  
     [0030] The reference numeral  114  in FIG. 4 denotes a motor fixture.  
     [0031] Even in the microwave oven equipped with the fan guide of the present invention, the above mentioned blade passing frequency and vortex shedding may be generated when air is sucked. However, since the straight frames  112   a,    112   b,  and  112   c  or curved frames  212   a,    212   b,  and  212   c  are asymmetrically arranged, the degree of noise generated by the blade passing frequency is reduced as air passes through those frames. The regularity of the vortex shedding formed at each frame is also destroyed, thereby reducing the interaction between a vortex flow generated at each frame and the fan. Accordingly, a reduction in flow noise and flow loss is achieved.  
     [0032] Where the fan guide of the present invention is applied to a microwave oven, it is possible to considerably reduce the flow noise generated during the operation of the fan while considerably reducing the level of noise outwardly emitted from the oven, as compared to the cases using conventional fan guides. This is apparent from FIG. 7. As shown in FIG. 7, the fan guide of the present invention provides an effect of reducing the ventilation noise generated during the operation of the fan by an average of about 2.3 dB(A) when detected outside the casing.  
     [0033] While there have been illustrated and described what are considered to be preferred specific embodiments of the present invention, it will be understood by those skilled in the art that the present invention is not limited to the specific embodiments thereof, and various changes and modifications and equivalents may be substituted for elements thereof without departing from the true scope of the present invention.