Patent Publication Number: US-6655918-B2

Title: Impeller of axial-flow blower

Description:
BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to an improvement of an impeller for an axial-flow blower used in various office automation equipment and the like. 
     2. Description of the Related Art 
     Office automation equipments, such as computers or copying machines, have many electronic parts enclosed in the housing thereof, generating excessive heat therefrom, which may destroy the parts. Accordingly, an axial-flow blower is mounted at a ventilation hole provided in the housing to release the interior heat to the outside therefrom. 
     This conventional type of blower, in this case an axial-flow blower driven by an outer rotor type motor, will be hereinafter described with reference to FIG.  10 . 
     As shown in the drawing, a shaft  4  is rotatably penetrated and supported in a cylindrical section  1   a  at the center of a casing  1  via bearings  2  and  3 . 
     The shaft  4  is mounted at the center of an impeller  5  (the center of a cup section  5   a ) including the cup section  5   a  and a plurality of impeller blades  5   b  at the outer periphery thereof. 
     The cup section  5   a  has a motor yoke  6   a  molded at the inner periphery thereof, to which a ring-shaped permanent magnet  6   b  is fixed. The permanent magnet  6   b  forms a principle structure of a rotor (an outer rotor)  6  together with the motor yoke  6   a.    
     The cylindrical section  1   a  has a stator  7  including a stator core  7   a  and windings  7   b  opposing the permanent magnet  6   b  fixed to the outside thereof. A printed circuit board  8  on which an electronic circuit is mounted for supplying a predetermined current to the stator windings  7   b  to operate the stator  7  and the rotor  6  as a stator and a rotor of a brushless DC motor is attached below the stator  7 . 
     The stator winding  7   b  is connected to the electronic circuit on the printed circuit board  8  with a pin  9 . The printed circuit board  8  is connected to a lead wire  10 . 
     In the blower thus constructed, when a power of a predetermined DC voltage is applied to the lead wire  10 , a current controlled by the electronic circuit on the printed circuit board  8  flows in the stator winding  7 . Accordingly, magnetic flux is generated from the stator core  7   a  to rotate the rotor  6  around the shaft  4  by the mutual magnetic action with magnetic flux from the permanent magnet  6   b , thereby rotating the impeller  5  integrated with the motor yoke  6   a  of the rotor  6  to blow air. 
     In this case, the impeller  5  is often made by synthetic resin molding. FIGS. 11 and 12 are a rear view and a partly cutaway left side view, respectively, showing the rotor section of the axial-flow blower including such an impeller  5 . In each drawing, same numerals are shown if same with or similar to parts indicated in FIG.  10 . 
     In the case where the impeller  5  of the axial-flow blower as shown in the drawings is formed by synthetic resin molding, an axial coupling type die is used. Accordingly, as shown in FIG. 11, one of the forming conditions is that when the impeller  5  is seen from the axial direction, adjacent impeller blades  5   b  and  5   b  among the impeller blades  5   b  arranged at the outer periphery of the cup section  5   a  at equal angles are set so as not to overlap each other. 
     In such an axial-flow blower, there is a case in which it is required that the adjacent impeller blades  5   b  and  5   b  overlap each other when looking at the impeller  5  from the axial direction for reasons such as increase of static pressure. 
     However, according to the conventional art, it is not easy to form such an impeller  5  by synthetic resin molding at low cost because of the above forming conditions, whereby improvements thereto have been required. 
     Also, in the case where the axial-flow blower is mounted in office automation equipments, which are located in a relatively quiet place, it has been strongly required to take measures to reduce noise generated during the rotation of the impeller (blower). 
     SUMMARY OF THE INVENTION 
     The present invention is made in light of the above problems. Accordingly, it is an object of the present invention to provide an impeller of an axial-flow blower having a structure in which adjacent impeller blades overlap each other when seen from the axial direction in an easy procedure and at a low cost even though by synthetic resin molding. In addition to the above, noise generated during rotation can be also reduced. 
     In order to attain the above object, according to the present invention, there is provided an impeller of an axial-flow blower driven by an outer rotor type motor and integrated with a rotatably supported shaft and a motor yoke, the impeller and the motor yoke rotating outside the stator around the shaft to blow air, wherein the impeller comprises a plurality of individual impeller sections each having a different number of impeller blades, the individual impeller sections being separately formed of a synthetic resin and arranged in series in the axial direction of the shaft. 
     In the present invention, preferably, among the plurality of individual impeller sections that are adjacent with each other at the front and rear sides in the axial direction of the shaft, the number of the impeller blades of the front section impeller is more than that of the rear section impeller. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a rear view of a rotor section of an axial-flow blower having an impeller according to an embodiment of the present invention; 
     FIG. 2 is a right side view of the rotor section in FIG. 1; 
     FIG. 3 is a rear view of a state prior to mounting a rear section impeller in the impeller in FIG. 1; 
     FIG. 4 is a right-side sectional view of an essential part in FIG. 3; 
     FIG. 5 is a view of the rear section impeller in FIG. 1; 
     FIG. 6 is a right side view of the rear section impeller in FIG. 5; 
     FIG. 7 is a sectional right side view of an essential part showing a state in which the rear section impeller in FIGS. 5 and 6 is mounted on the rotor section in FIGS. 3 and 4 (a completed state); 
     FIG. 8 is a graph of a result of measuring the noise generated daring the rotation of the impeller in the embodiment in FIG. 1; 
     FIG. 9 is a graph of a result of measuring the noise generated during the rotation of the impeller when the number of impeller blades of the front section impeller and that of the rear section impeller are the same; 
     FIG. 10 is a partly cut-away cross sectional view of a conventional blower; 
     FIG. 11 is a rear view of a rotor section of an axial-flow blower having an impeller formed by synthetic resin molding; and 
     FIG. 12 is a partially cut-away sectional right side view of the rotor section in FIG.  11 . 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENT 
     An embodiment of the present invention will be hereinafter described with reference to the drawings. 
     FIG. 1 is a rear view showing a rotor section of an axial-flow blower having an impeller according to an embodiment of the present invention. FIG. 2 is a right side view of the rotor section in FIG.  1 . 
     As shown in the drawing, an impeller  5  of the present invention is constructed in such a manner that a plurality of individual impeller sections, in this case, two stages of individual impeller sections  5 F and  5 R, are arranged in series in the axial direction of a shaft  4  (the horizontal direction in FIG.  2 ). 
     The front section impeller  5 F has, as shown in FIGS. 3 and 4, a plurality of impeller blades, in this case, nine impeller blades  5 Fb, arranged on a cylinder-shaped cup section  5 Fa having a bottom at equal angular spacing on the outer periphery of a cylinder section  5 Ft of the cup section  5 Fa. 
     In addition, the rear section impeller  5 R has, as shown in FIGS. 5 and 6, a different number of impeller blades from that of the front section impeller  5 F, in this case, seven impeller blades  5 Rb arranged at equal angular spacing on the outer periphery of a cylinder section  5 Ra. 
     The cylinder section  5 Ft of the cup section  5 Fa of the front section impeller  5 F and the cylinder section  5 Ra of the rear section impeller  5 R are set to have almost the same inner and outer diameter. Accordingly, as described later, when the individual impeller sections  5 F and  5 R are assembled as the impeller  5  of the present invention, the cylinder section  5 Ft of the cup section  5 Fa and the cylinder section  5 Ra are connected without a step forming one cylinder section with both the cylinders (refer to FIG.  7 ). 
     In addition, the individual impeller sections  5 F and  5 R are separately formed by synthetic resin molding. Here, the adjacent impeller blades  5 Fb and  5 Fb among the impeller blades  5 Fb of the individual impeller  5 F are set so as not to overlap each other when seen from the axial direction of the impeller  5 F (refer to FIG.  3 ). With respect to the impeller blades  5 Rb of the rear section impeller  5 R, the adjacent impeller blades  5 Rb and  5 Rb are also set so as not to overlap each other when seen from the axial direction of the impeller  5 R (refer to FIG.  5 ). Accordingly, the individual impeller sections  5 F and  5 R can be easily and cheaply formed by molding with an axial coupling type die. 
     The individual impeller sections  5 F and  5 R are assembled, for example, by the following procedure to construct the impeller  5  of the present invention. 
     First, as shown in FIG. 4, the front section impeller  5 F in which the shaft  4  is inserted and fixed at the center part of the inner surface of the bottom of the cup section  5 Fa is fixed to a front end portion of an almost cylindrical motor yoke  6   a . Here, the front end portion of the motor yoke  6   a  is press-fitted in an inner peripheral section of the cup section  5 Fa so that the front section impeller  5 F is fixed to the motor yoke  6   a.    
     Subsequently, as shown in FIG. 7, the cylinder section  5 Ra is press-fitted to the outer periphery on the rear side of the motor yoke  6   a  so that the rear section impeller  5 R is fixed to the motor yoke  6   a.    
     In this instance, the front end of the rear section impeller  5 R (the cylinder section  5 Ra) is brought into contact with the back end of the front section impeller  5 F (the cup section  5 Fa) so that the cylinder section  5 Ft of the cup section  5 Fa and the cylinder section  5 Ra are assembled to connect without a step so as to form one cylinder section. 
     In addition, in order to increase the static pressure or the like of the axial-flow blower, some or all of the impeller blades  5 Fb of the individual impeller  5 F are overlapped with some of the impeller blades  5 Rb of the individual impeller  5 R when the impeller  5  is seen from the axial direction. 
     Also, a ring-shaped permanent magnet  6   b  forming a principle structure of a rotor (an outer rotor)  6  together with the motor yoke  6   a  is fixed to an inner periphery of the motor yoke  6   a  (refer to FIGS. 1,  3 ,  4 , and  7 ). 
     FIG. 8 shows the results of measuring the noise generated during the rotation of the impeller in which the front section impeller  5 F having the nine impeller blades  5 Fb and the rear section impeller  5 R having the seven impeller blades  5 Rb are arranged in series as described above. Also, FIG. 9 shows the result of measuring the noise generated during the rotation of an impeller in which the front and rear section impeller sections  5 F and  5 R having the same number of impeller blades  5 Fb and  5 Rb, respectively, are arranged in series, which impeller is not shown. 
     As can be understood by comparing both the drawings, in the case where the numbers of the impeller blades of the front and rear section impeller sections  5 F and  5 R are the same (FIG.  9 ), a measurement result was obtained such that a prominent noise peak  91  is generated at a frequency of around 600 Hz. On the other hand, in the case where the number of the impeller blades of the front section impeller  5 F is nine and the number of the impeller blades of the rear section impeller  5 R is seven FIG.  8 ), the noise peak  91  disappeared. In addition, the average noise level generated during the rotation of the impeller was 54.4 dB in the example shown in FIG. 8 in which the number of the impeller blades of the front section impeller  5 F was more than that of the rear section impeller  5 R; on the other hand, the average noise level in the example shown in FIG. 9, in which the numbers of the impeller blades of the individual impeller sections  5 F and  5 R are the same, was 55.7 dB. That is, the impeller of the present invention in which the number of the impeller blades of the front section impeller  5 F is more than that of the rear section impeller  5 R generates a noise level, which is 1.3 dB lower than the impeller in which the numbers of impeller blades of the individual impeller sections  5 F and  5 R are the same, and also the average noise level decreased. 
     In the present invention, the impeller is formed individually and the individual impeller sections are arranged in series to construct the entire impeller, and the individual impeller sections are placed so that the adjacent impeller blades do not overlap each other when seen from the axial direction. Accordingly, the impeller can be formed by molding with an axial coupling type die. 
     Also, according to the present invention, in the process of arranging the molded individual impeller sections in series (the assembly process), by setting the angular positions of the impeller blades of the front and rear section impeller sections in the direction around the shaft, modifications of the entire impeller can be provided. 
     Consequently, according to the present invention, the impeller structure in which the adjacent impeller blades overlap each other when seen from the axial direction can be easily and cheaply realized even though formed by synthetic resin molding. 
     In addition, according to the present invention, since the numbers of the impeller blades of the plurality of individual impeller sections are different, and more particularly, the number of the impeller blades of the front section impeller is more than the number of the impeller blades of the rear section impeller, the noise generated during the rotation of the impeller can be reduced. 
     That is, when the numbers of the impeller blades of the front and rear section impeller sections are the same (FIG.  9 ), a noise peak is generated at a frequency of around 600 Hz; on the other hand, when the number of the impeller blades of the front section impeller is nine and the number of the impeller blades of the rear section impeller is seven (FIG.  8 ), the noise peak disappeared. Also, the average noise level generated during the rotation of the impeller was lower in the impeller of the present invention, in which the number of the impeller blades of the front section impeller is more than that of the rear section impeller  5 R, than that in the impeller in which the numbers of impeller blades of both the individual impeller sections are the same. The noise peak disappeared and also the noise generated during the rotation of the impeller was remarkably reduced; accordingly, generation of a harsh grating noise can be prevented.