Motor-driven blower and method of manufacturing impeller for motor-driven blower

Abstract: Reduction of air resistance which acts on the conventional motor-driven blower is limited because crushed protrusions are formed by staking on the surface of the plate of the impeller of the motor-driven blower, and the air resistance is a significant impediment to the increase of the operating speed of the motor-driven blower. An impeller (712) comprises a front plate (101) having a suction opening (801), a back plate (102) disposed opposite to the front plate (101), and a plurality of blades (103) disposed between the front plate (101) and the back plate (102). At least either the front plate (101) or the back plate (102) is formed integrally with the blades (103).

Description: The invention relates to a motor-driven blower for a vacuum cleaner according to the preamble of claim 1. An impeller included in a conventional motor-driven blower comprises a front plate provided in its central part with a suction opening, a back plate disposed opposite to the front plate, and blades disposed between the front and the back plate. Each of the blades is provided with projections to be deformed for staking, the projections are inserted in square holes formed in the front and the back plate, and parts of the projections projecting from the front and the back plate are crushed to fix the blades to the front and the back plate by staking. All of those components of the impeller are formed of an Al alloy. The impeller thus assembled is fastened to the rotating shaft of a motor with a screw, and a fan casing is disposed over the impeller to form the motor-driven blower. A motor-driven blower intended for use in a recent vacuum cleaner is designed so as to operate at an increased operating speed to produce an increased suction at an improved efficiency e.g. WO-A- 97 19 629. Since the impeller of the conventional motor-driven blower is constructed by crushing the parts of the projections projecting from the front and the back plate by staking as mentioned above, the crushed parts of the projections protrude from the outer surfaces of the front and the back plate. The resistance of air against the movement of the crushed parts of the impeller is significant when the impeller rotates at a high rotating speed and is an impediment to the increase of the operating speed of the motor-driven blower. A technique proposed in, for example, JP-A 1-310198 to solve such a problem rounds the corners of end parts of the projections to be crushed by staking to reduce air resistance against the movement of the crushed parts of the projections. Although the technique proposed in JP-A 1-310198 rounds the corners of end parts of the projections to be crushed by staking to reduce air resistance against the movement of the crushed parts of the projections, the crushed parts still remain on the outer surfaces of the front and the back plate. Therefore there is a limit to the reduction of air resistance and the crushed parts are an significant impediment to the increase of the operating speed of the motor-driven blower. Increase in the operating speed of the motor-driven blower entails increase in stress induced in the impeller. Therefore the rigidity of the impeller must be enhanced. Since the components of the conventional impeller are fastened together by staking and the strength of the joints of the components formed by staking is lower than those of the blades and the plates. Consequently, the rigidity of the impeller constructed by assembling the components by staking is not very high, and hence increase in the rotating speed of the impeller is limited. Increase in the operating speed of the motor-driven blower entails increase in load on the rotating shaft of the electric motor. Therefore, it is necessary to reduce the load on the rotating shaft of the electric motor by reducing the weight of the impeller formed of an Al alloy. Accordingly, it is an object of the present invention to solve the foregoing problems, and to provide a motor-driven blower provided with an impeller capable of reducing air resistance against the rotation thereof, having an enhanced rigidity, and capable of reducing load on the rotating shaft of an electric motor for driving the impeller for rotation and of operating at an increased operating speed, to provide a method of manufacturing an impeller for such a motor-driven blower. According to the present invention, a motor-driven blower comprises an electric motor covered with a housing, an impeller fixedly mounted on a rotating shaft included in the electric motor, stationary guide blades disposed on the downstream side of the impeller, and a fan casing covering the impeller and the stationary guide blades; wherein the impeller comprises a front plate having a suction opening, a back plate disposed opposite to the front plate, and a plurality of blades disposed between the front plate and the back plate, and at least either the front plate or the back plate is formed integrally with the blades and the other plate is connected to the blades by brazing of welding. Advantagely, a brazing metal layer is formed on a surface of the other plate not formed integrally with the blades, and the other plate is brazed to the blades by the brazing metal layer. The impeller designed according to the invention is formed in a monolithic structure and does not have any crushed projections formed by staking. Therefore, the impeller of the invention is not subject to air resistance that may act thereon if the impeller has crushed projections and does not generate any noise which may be generated if the impeller has crushed projections. A motor-driven blower provided with the impeller of the present invention is able to operate at an increased operating speed and to improve the efficiency of suction of a vacuum cleaner. BRIEF DESCRIPTION OF THE INVENTION These and other objects of the Invention will be seen by reference to the description, taken in connection with the accompanying drawing, in which: Fig. 1 is an exploded perspective view of an impeller according to the present invention; Fig. 2 is an enlarged, fragmentary sectional view of an impeller in a preferred embodiment according to the present invention; Fig. 3 is an enlarged, fragmentary sectional view of an impeller in a preferred embodiment according to the present invention; Fig. 4 is an enlarged, fragmentary sectional view of an impeller in a preferred embodiment according to the present invention; Fig. 5 is an exploded perspective view of an impeller according to the present invention; Fig. 6 is a perspective view of a vacuum cleaner according to the present invention; Fig. 7 is a longitudinal sectional view of a motor-driven blower according to the present invention; Fig. 8 is a perspective view of an impeller according to the present invention; Fig. 9 is a plan view of an impeller according to the present invention; Fig. 10 is a plan view of an impeller according to the present invention; Fig. 11 is a longitudinal sectional view of an impeller according to the present invention; Fig. 12 is an exploded perspective view of an impeller according to the present invention; Fig. 13 is a longitudinal sectional view of an impeller according to the present invention; Fig. 14 is a longitudinal sectional view of an impeller according to the present invention; Fig. 15 is an exploded perspective view of an impeller according to the present invention; Fig. 16 is an exploded perspective view of an impeller according to the present invention. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described with reference to the accompanying drawings. Fig. 6 shows a vacuum cleaner relating to a preferred embodiment of the present invention in a perspective view. Referring to Fig. 6, there are shown a cleaner unit 601 internally provided with built-in devices including a motor-driven blower, a hose 602 having one end connected to an suction opening formed in the cleaner unit 601, a hose handle 603, an extension wand 604 connected to the other end of the hose 602 (the hose handle 603), an suction opening 605 connected to the extension wand 604, a switch operating unit 606 attached to the hose handle 603, a first infrared emitting unit 607 attached to the hose handle 603, a second infrared light emitting unit 608 attached to the hose handle 603, an infrared light receiving unit 609 attached to an upper wall of the cleaner unit 601, and a ceiling 610. The operation of the vacuum cleaner relating to the preferred embodiment will be described with reference to Fig. 6. An operator pushes one of switch buttons arranged in the switch operating unit 606. Then, infrared signals representing codes corresponding to the operated switch button are transmitted by the first infrared light emitting unit 607 and the second infrared light emitting unit 608. The first infrared light emitting unit 607 is directed vertically upward in the usual state. Therefore, the infrared signal emitted by the first infrared light emitting unit 607 fall on the ceiling or an wall of the room, is reflected therefrom and fall on the infrared light receiving unit 609. The second infrared light emitting unit 608 is directed obliquely downward at an angle to a horizontal plane. Therefore, the infrared signal emitted by the second infrared light emitting unit 608 falls directly on the infrared light receiving unit 609. The infrared signals are received by infrared photoelectric devices, not shown, arranged on the cleaner unit 601, and a control circuit, not shown, controls the operation of the cleaner unit 601 according to the infrared signals. The construction of the motor-drive blower disposed inside the cleaner unit 601 will be described with reference to Fig. 7. A motor-driven blower 701 comprises an electric motor 717 and a blower 718. The electric motor 717 comprises a housing 702, a stator 703 fixed to the housing 702, rotor shaft 705 supported in bearings 704 and 719 held on the housing 702, a rotor 708 fixedly mounted on the rotator shaft 705, a commutator 707 fixedly mounted on the rotor shaft 705, a brush 708 electrically connected to the commutator 707, and a brush holder 709 for holding the brush 708, attached to the housing 702. The commutator 707 is provided in its circular circumference with commutator bars connected to coils wound on the rotor 706. The brush 708 is held in the brush holder 709 and is pressed against the commutator 707 so as to be in sliding contact with the commutator 707 by a spring 710. A lead wire 711 electrically connected to the brush connects the brush 708 electrically to an external electrode. The lead wire 711 is connected to a terminal, not shown, attached to the brush holder 709. An end bracket 720 is attached to the housing 702 to connect a blower 718 to the electric motor 717. The end bracket 720 is provided with an air inlet opening 716 through which air blown by the 718 flows toward the electric motor 717. The end bracket 720 is provided with stationary guide blades 714. An impeller 712 disposed on the upstream side of the stationary guide blades 714 is fastened to the rotor shaft 705 with a nut 713. A casing 715 is put forcibly on and fixed to the end bracket 720 and is provided in its central part with a suction opening 721. When the electric motor is actuated, the rotor 706 rotates, and the impeller 712 coaxial with the rotor 706 is rotated to suck air through the suction opening 721 of the fan casing 715. Air flows through the impeller 712 and the stationary guide blades 714 and is discharged through the air inlet opening 716 toward the electric motor 717. The construction of the impeller 712 will be described hereinafter with reference to Figs. 8 and 9. Figs. 8 and 9 are a perspective view and a plan view, respectively, of the impeller 712 relating to the embodiment of the present invention. Referring to Figs. 8 and 9, the impeller 712 comprises a front plate 101 provided with a suction opening 801, a back plate 102 disposed below and opposite to the front plate 101, and blades 103 sandwiched between the front plate 101 and the back plate 102. The blades 103 are curved as shown in Fig. 9. The front plate 101, the back plate 102 and the blades 103 define a plurality of air outlets 802. When the impeller 712 is rotated, air is sucked through the suction opening 801 into the impeller, is discharged through the air outlets 802 toward the electric motor to cool the electric motor, and is discharged through the discharge opening of the cleaner unit. The impeller 712 needs to be rotated at a high rotating speed to produce a high suction. The impeller 712 must be lightweight and air resistance that will acts on the impeller 712 must be reduced to rotate the impeller 712 at a high rotating speed. A structure effective in forming the impeller 712 in a lightweight construction and reducing air resistance that will act on the impeller 712 will be described with reference to Figs. 1 to 4. Fig. 1 is an exploded perspective view of the impeller 712 relating to the embodiment of the present invention. As shown in Fig. 1, the front plate 101 and the blades 103 are formed in a monolithic structure. The front plate 101 and the blades 103 are formed in a monolithic structure by an injection molding process. This injection molding process, similarly to an injection molding process for molding a resin, kneads and melts pellets of a light metal in an injection molding machine without using a melting furnace, and injects the molten light metal into a mold to form a molding. The front plate 101 and the blades 103 can be formed in a monolithic structure as shown in Fig. 1 by the injection molding process. In this embodiment, any crushed protrusions formed by staking are not formed on the outer surface of the front plate 101 because the blades 103 are formed integrally with the front plate 101 by molding. Therefore, only reduced air resistance acts on the outer surface of the front plate 101. In this embodiment, the monolithic structure of the front plate 101 and the blades 103 is formed of a Mg alloy of Grade AZ91D specified in the ASTM (American Society of Testing Materials) Standards, USA. The Mg alloy AZ91D contains 8.3 to 9.7% by weight Al, 0.35 to 1.0% by weight Zn and 0.15 to 0.50% by weight Mn, has high moldability and is a high-purity alloy suppressing Cu, Ni and Fe contents. In this embodiment, the monolithic structure of the front plate 101 and the blades 103 may be formed of a Mg alloy of Grade AM60B specified in the ASTM Standards, USA and containing 5.5 to 6.5% by weight Al, 0.22% by weight Zn and 0.24 to 0.6% by weight Mn, instead of by the Al alloy of Grade AZ91D. The Mg alloy has a specific gravity of about 1.8 g/cm 3 , which is about 2/3 of the specific gravity of 2.7 g/cm 3 of an Al alloy. A method of bonding the back plate 102 to the blades 103 formed integrally with the front plate 101 will be described with reference to Fig. 2. The back plate 102 is formed of an Al-Mg alloy of Grade A5052 specified in the JIS (Japanese Industrial Standards), i.e., an Al alloy. The inner surface of the back plate 102 is coated with a brazing metal layer 201. In this embodiment, a brazing metal forming the brazing metal layer 201 is Zn. This embodiment employs an electroplating process to form the brazing metal layer 201 on the inner surface of the back plate 102. The electroplating process comprises degreasing, rinsing, electroplating, rinsing and drying. The desired brazing metal layer 201 of Zn is formed on the back plate 102 by using an appropriate electrolytic solution of an appropriate temperature, supplying a current of an appropriate current density for an appropriate plating time. The front plate 101 integrally provided with the blades 103, and the back plate 102 are held contiguously and coaxially without applying any pressure thereto or with a pressure that will not deform the front plate 101, the back plate 102 and the blades 103 applied thereto, and the front plate 101, the back plate 102 and the blades 103 are heated at an appropriate temperature below the melting points of the front plate 101, the back plate 102 and the blades 103 for an appropriate time to bond the back plate 102 to the blades 103 by brazing. When heated at the appropriate temperature for the appropriate time, the brazing metal layer 201 melts and penetrates the back plate 102 and the blades 103 to form reaction parts 202 which bonds the back plate 102 firmly to the blades 103. In this embodiment, any crushed protrusions formed by staking are not formed on the outer surface of the back plate 102 because the back plate 102 is bonded to the blades 103 by brazing. Therefore, only reduced air resistance acts on the outer surface of the back plate 102. Although this embodiment uses the electroplating process to form the brazing metal layer 201 on the back plate 102, the brazing metal layer 201 may be formed by a physical vapor deposition process, a chemical vapor deposition process, an ion plating process, a spraying process or a combination of some of those processes. Although this embodiment uses the brazing metal layer of Zn, a metal having a low melting point, such as Sn or Pb, and an alloy of a low melting point containing such a metal as a principal component are possible brazing materials. Preferable alloys having a low melting point are Zn-Sn alloys, Zn-Pb alloys, Sn-Pb alloys, Zn-Mg alloys and Zn-Al alloys. Although this embodiment uses the Al alloy of Grade A5052, JIS for forming the back plate 102, Al-Mn alloys (System 3000, JIS), Al-Si alloys (System 4000, JIS), Al-Cu-Mgalloys (System 2000, JIS), Al-Mg-Si alloys (System 6000, JIS) and Al-Zn-Mg alloys (System 7000, JIS) are possible materials for forming the back plate 102. In this embodiment, the front plate 101 and the blades 103 of the impeller 712 are made of the Mg alloy, the back plate 102 of the impeller 712 is made of the Al alloy having a specific gravity greater than that of the Mg alloy, and the impeller 712 is mounted on the rotor shaft of the electric motor with the back plate 102 on the side of the electric motor. Therefore the whirling of the rotor shaft due to the unbalanced distribution of load thereon can be suppressed, noise can be reduced, the abrasion of the carbon brush can be reduced and the life of the motor-driven blower can be extended. Although this embodiment employs the back plate 102 of the Al alloy, the back plate 102 may be made of the same Mg alloy as that forming the front plate 101 and the blades 103. A second embodiment of the present invention will be described with reference to Fig. 2. Fig. 2 is an enlarged, fragmentary sectional view of an impeller 712 relating to the second embodiment of the present invention. The impeller 712, similar to the impeller 712 relating to the first embodiment, has a front plate 101 and the blades 103 formed of a Mg alloy in a monolithic structure. The Mg alloy employed in this embodiment is a Mg alloy of Grade AZ91D or AM60B specified in the ASTM Standards, USA. The front plate 101 and the blades 103 are formed in a monolithic structure by an injection molding process. A back plate 102 to be disposed opposite to the monolithic structure of the front plate 101 and the blades 103 is made, similarly to the monolithic structure, of the Mg alloy of Grade AZ91D, ASTM Standards. A brazing metal layer 201 of Zn is formed beforehand on the inner surface of the back plate 102. In this embodiment, the brazing metal layer 201 is formed on the back plate 102 by cladding the back plate 102 with the brazing metal layer 201 of the Mg alloy of Grade AZ91D by a hot rolling pressure bonding process. The hot rolling pressure bonding process heats the back plate 102 and a metal sheet (a Zn sheet) for forming the brazing metal layer 201 respectively at appropriate temperatures respectively lower than the melting points of the back plate 102 and the metal sheet, superposes the back plate 102 and the metal sheet, compresses the superposed back plate 102 and the metal sheet between a pair of rolling rollers to form the brazing metal layer 201 of a desired thickness on the back plate 102. The brazing metal layer 201 may be formed on the back plate 102 by another method which passes the superposed back plate 102 and the metal sheet between a pair of rolling rollers, supplies a current across the pair of rolling rollers to compress the back plate 102 and the metal sheet for forming the brazing metal layer 201 between the pair of rolling rollers and to heat the back plate 102 and the metal sheet at temperatures respectively lower than the melting points of the back plate 102 and the metal sheet. When this method is employed, the back plate 102 and the metal sheet need not be heated before subjecting the same to rolling between the pair of rolling rollers and heating by the current supplied across the pair of rolling rollers. The front plate 101 integrally provided with the blades 103, and the back plate 102 provided with the brazing metal layer 201 are held contiguously and coaxially without applying any pressure thereto or with a pressure that will not deform the front plate 101, the back plate 102 and the blades 103 applied thereto, and the front plate 101, the back plate 102 and the blades 103 are heated at an appropriate temperature below the melting points of the front plate 101, the back plate 102 and the blades 103 for an appropriate time to bond the back plate 102 to the blades 103 with the brazing metal layer 201 by brazing. When heated at the appropriate temperature for the appropriate time, the brazing metal layer 201 melts and penetrates the back plate 102 and the blades 103 to form reaction parts 202 which bonds the back plate 102 firmly to the blades 103. In this embodiment, any crushed protrusions formed by staking are not formed on the outer surface of the back plate 102 because the back plate 102 is bonded to the blades 103 by brazing. Therefore, only reduced air resistance acts on the outer surface of the back plate 102. Although this embodiment uses the brazing metal layer of Zn, a metal having a low melting point, such as Sn or Pb, and an alloy of a low melting point containing such a metal as a principal component are possible brazing materials. Preferable alloys having a low melting point are Zn-Sn alloys, Zn-Pb alloys, Sn-Pb alloys, Zn-Mg alloys and Zn-Al alloys. Although this embodiment uses the Mg alloy of Grade AZ91D, for forming the back plate 102, a Mg alloy of Grade AM31B, ASTM Standards, USA and containing about 2.8% by weight Al, about 0.87% by weight Zn and about 0.41% by weight Mn or a Mg Alloy of Grade AM60B, ASTM Standards may be used for forming the back plate 102. A third embodiment of the present invention will be described with reference to Fig. 3. Fig. 3 is an enlarged, fragmentary sectional view of an impeller 712 relating to the third embodiment of the present invention. The impeller 712, similar to the impellers 712 relating to the foregoing embodiments, has a front plate 101 and a blades 103 formed of a Mg alloy in a monolithic structure. The Mg alloy employed in this embodiment is a Mg alloy of Grade AZ91D or AM60B specified in the ASTM Standards, USA. The front plate 101 and the blades 103 are formed in a monolithic structure by an injection molding process. The blades 103 are provided with a plurality of fixing projections 301. A back plate 102 is formed of an Al-Mg alloy of Grade A5052, JIS. The back plate 102 is provided with a plurality of holes 302 to receive the fixing projections 301 at positions respectively corresponding to the projections 301 of the blades 103. Preferably, the height of the fixing projections 301 is equal to the thickness of the back plate 102. A method of fastening the back plate 102 to the monolithic structure of the front plate 101 and the blades 103 will be described hereinafter. The fixing projections 301 of the blades 103 formed integrally with the front plate 101 are inserted into the holes 302 of the back plate 102, reaction parts 303 are formed by subjecting the projections 301 inserted into the holes 302 to spot welding, i.e., an electric resistance welding, meeting desired conditions about welding current, welding time, quality of electrode, diameter of electrode and such to connect the back plate 102 firmly to the monolithic structure of the front plate 101 and the blades 103. Parts of the fixing projections and parts of the back plate 103 around the holes 302 melt during welding. A laser welding process, an electron beam welding process or a combination of a laser welding process and an electron beam welding process may be used instead of the spot welding process to connect the back plate 102 to the monolithic structure of the front plate 101 and the blades 103. Although this embodiment uses the Al alloy of Grade A5052, JIS for forming the back plate 102, Al-Mn alloys (System 3000, JIS), Al-Si alloys (System 4000, JIS), Al-Cu-Mg alloys (System 2000, JIS), Al-Mg-Si alloys (System 6000, JIS) and Al-Zn-Mg alloys (System 7000, JIS) are possible materials for forming the back plate 102. In this embodiment, the blades 103 and the back plate 102 are welded together and any crushed protrusions for fastening the back plate 102 to the blades 103 by staking are not formed on the outer surface of the back plate 102. Thus, only reduced air resistance acts on both the outer surfaces of the front plate 101 and the back plate 102. A fourth embodiment of the present invention will be described with reference to Fig. 4. Fig. 4 is an enlarged, fragmentary sectional view of an impeller 712 relating to the fourth embodiment of the present invention. The impeller 712, similar to the impellers 712 relating to the foregoing embodiments, has a front plate 101 and a blades 103 formed of a Mg alloy in a monolithic structure. The Mg alloy employed in this embodiment is a Mg alloy of Grade AZ91D or AM60B specified in the ASTM Standards, USA. The front plate 101 and the blades 103 are formed in a monolithic structure by an injection molding process. The blades 103 are provided with a plurality of fixing projections 301. A back plate 102 is formed of an Al-Mg alloy of Grade A5052, JIS. The back plate 102 is provided with a plurality of holes 302 to receive the fixing projections 301 at positions respectively corresponding to the projections 301 of the blades 103. A brazing metal layer 401 of Zn is formed on an inner surface of the back plate 102. This embodiment employs an electroplating process to form the brazing metal layer 401 on the inner surface of the back plate 102. The electroplating process comprises degreasing, rinsing, electroplating, rinsing and drying. The desired brazing metal layer 401 of Zn is formed on the back plate 102 by using an appropriate electrolytic solution of an appropriate temperature, supplying a current of an appropriate current density for an appropriate plating time. A method of fastening the back plate 102 to the monolithic structure of the front plate 101 and the blades 103 will be described hereinafter. The fixing projections 301 of the blades 103 formed integrally with the front plate 101 are inserted into the holes 302 of the back plate 102 from the side of the brazing metal layer 401. The monolithic structure and the back plate 102 are heated at a desired temperature lower than the melting points thereof for a desired heating time to bond the monolithic structure and the back plate 102 together by brazing using the brazing metal layer 401. The brazing metal layer 401 penetrates the monolithic structure and the back plate 102 to form reaction parts 402 when heated at the desired temperature for the desired time. Parts of the back plate 102 around the holes 302 into which the fixing projections 301 are inserted are melted by hot pressing of a desired temperature, pressure and heating time to form reaction parts 403 for bonding together the monolithic structure and the back plate 102. Parts of the back plate 102 around the holes 302 and parts of the fixing projections 301 melt when heated and a pressure is applied thereto. Although this embodiment bonds together the monolithic structure 804 and the back plate 102 by brazing and the subsequent hot pressing, hot pressing may be executed before brazing. Although this embodiment uses the electroplating process to form the brazing metal layer 401 on the back plate 102, the brazing metal layer 401 may be formed by a physical vapor deposition process, a chemical vapor deposition process, an ion plating process, a spraying process or a combination of some of those processes. Although this embodiment uses the brazing metal layer of Zn, a metal having a low melting point, such as Sn or Pb, and an alloy of a low melting point containing such a metal as a principal component are possible brazing materials. Preferable alloys having a low melting point are Zn-Sn alloys, Zn-Pb alloys, Sn-Pb alloys, Zn-Mg alloys and Zn-Al alloys. Although this embodiment employs hot pressing to bond together the monolithic structure of the front plate 101 and the blades 103, and the back plate 103, a laser welding process, an electron beam welding process, an electric resistance welding or a combination of some of those processes may be used. Although this embodiment uses the Al alloy of Grade A5052, JIS for forming the back plate 102, Al-Mn alloys (System 3000, JIS), Al-Si alloys (System 4000, JIS), Al-Cu-Mg alloys (System 2000, JIS), Al-Mg-Si alloys (System 6000, JIS) and Al-Zn-Mg alloys (System 7000, JIS) are possible materials for forming the back plate 102. Since this embodiment bonds together the blades 103 and the back plate 102 by welding, any crushed protrusions for fastening the back plate 102 to the blades 103 by staking are not formed on the outer surface of the back plate 102. Thus, only reduced air resistance acts on both the outer surfaces of the front plate 101 and the back plate 102. In the foregoing first to fourth embodiments, the front plate 101 and the blades 103 are formed in the monolithic structure. The blades 103 may be formed integrally with the back plate 102 as shown in Fig. 5, and the front plate may be connected to the blades 103 by any one of the connecting methods explained in connection with the first to the fourth embodiment. In the first to the fourth embodiment of the present invention, the impellers are lightweight, air resistance acting on the surfaces of the plates can be reduced, the impeller of the motor-driven blower can be rotated at a rotating speed in the range of 45,000 to 50,000 rpm at a power consumption of 1000 W to operate the vacuum cleaner at a suction power of 550 W or above. Then, referring to Figs. 10 and 11, an injection molding structure in the preferred embodiment will be described In the preferred embodiment, both inner diameter and outer diameter of a front plate 101 are coaxially machined by applying a press punching operation or a machine cutting operation so as to correct oscillation or bending or the like generated at the inner and outer diameter sections of the front plate 101 due to a molding strain and to improve an accuracy in coaxial relation. With such an arrangement as above, an amount of unbalance of the impeller 712 generated by the molding operation is reduced and a balancing accuracy is improved. In particular, in the case that the motor-driven blower 701 used in an electric cleaner is rotated at a high speed, it may not only provide an effect of reducing vibratory noise but also improve an accuracy in size at both inner and outer circumferences of the impeller 712, stabilize its combining size with respect to the fan casing 715 or the fixed stationary guide blades 714 and then reduce a disturbance in aerodynamic performance. In the preferred embodiment, a thin-film like gate 1002 is once formed through a molten metal opening 1001 at an inner circumferential side of a suction opening 801 so as to cause the molten metal to be flowed uniformly on the circumference toward the front plate 101. In addition, the outer circumference of it is provided with two molten metal reservoirs 1003 for preventing a lack of filling of molten metal. Although these reservoirs are required for stabilizing quality when they are injection molded, they are not required after a product is made, so that they should be removed after molding operation. In Fig.11, each of the inner and outer circumferences indicated by arrows is removed. In this preferred embodiment, the molten metal opening 1001 or the molten metal reservoirs 1003 preventing lack of filling are arranged the inner and outer circumferences of the front plate 101, thereby they can be removed concurrently when the aforesaid inner and outer diameters are post-machined, and the number of working steps is not increased. As another preferred embodiment, in Fig.12 is shown a perspective view for indicating a state in which the rear plate 102 and the blades 103 are integrally molded. In this case, not only a balancing accuracy or aerodynamic performance can be improved as described above, but also it can be formed into a structure as shown in Figs.13 and 14. That is, in Fig.13, the inner circumference part of the rear plate 102 having the weakest rigidity is made thick to enable its rigidity to be increased. In particular, it is effective for a high-speed rotating machine. In Fig.13, the section of the impeller 712 placed adjacent to an air flow passage at the suction port 801 is raised up to improve a flow at the inlet port and then aerodynamic performance is improved. Further, in Fig.14, the raised section is extended in an opposite direction of the rotating shaft 705 so as to form a fixing part for the rotating shaft 705, resulting in that another separate hub used for fixing the member in the prior art can be reduced. In Figs.15 and 16, a thickness of the blade 103 is changed to form a so-called vane shape. In Fig.15, there is shown an example in which fixing claws for the front plate 101 are arranged, and in Fig.16, there is shown an example in which a thick part of the blade 103 is reduced to make a mean thickness and improve a forming characteristic. Both examples become possible due to the fact that the blade 103 and a mating plate are integrally formed, wherein a degree of freedom in design is increased more than the case in which the blade and the plate were formed by a thin plate as found in the aforesaid prior art, an aerodynamic performance can be improved through a most adaptation for flow within the impeller 712. In the preferred embodiment above, the front plate 101 and the blade 103 integrally formed together are formed by magnesium alloy. This magnesium alloy is of ASTM AZ91D of U.S.A. This AZ91D alloy is an alloy including 8.3 to 9.7 wt% of aluminum, 0.35 to 1.0 wt% of zinc and 0.15 to 0.50 wt% of manganese, wherein its forming characteristic is superior and this is also a high purity product in which an amount of inclusion of copper, nickel and iron is restricted. In the preferred embodiment, although the integrated part of the front plate 101 and the blade 103 is made of AZ91D magnesium alloy, it is also preferable that it may be of AM60B magnesium of ASTM Standards of U.S.A including 5.5 to 6.5 wt% of aluminum, 0.22 wt% of zinc and 0.24 to 0.6 wt% of manganese. A specific weight of magnesium alloy (g/cm 3 ) is approximately 1.8 and then a light weight formation of about 2/3 in respect to a specific weight of 2.7 of aluminum alloy can be attained. In addition, in the preferred embodiment, although the rear plate 102 is of A5052 aluminum alloy of JIS Standards, it may also be applicable to select any one of Al-Mn alloy (system 3000), Al-Si alloy (system 4000), Al-Cu-Mg alloy (system 2000), Al-Mg-Si alloy (system 6000) and Al-Zn-Mg alloy (system 7000). As described above, in accordance with the present invention, employing of magnesium alloy in the impeller 712 enables a weight of the impeller 712 to be reduced and further enables such a load applied to the rotating shaft to be reduced. In addition, in accordance with the present invention, the impeller is integrally formed to eliminate the fastening protrusions, so that it is possible to reduce an air resistance and noise or the like caused by the fastening protrusions. Further, in accordance with the present invention, the inner and outer diameters of the front plate 101 are coaxially machined, after forming operation, by adding a press punching or a machine cutting operation or the like so as to correct a twisting and a bending generated at the inner and outer diameter section due to forming strain and then a coaxial accuracy is improved. With such an arrangement as above, an amount of unbalance of the impeller 712 generated by forming operation is reduced and an accuracy in balance is improved. In the case that the motor-driven blower 1 used in the electric cleaner or the like, in particular, is rotated at a high speed, although it may provide a high effect of reducing vibratory noise, the present invention may provide not only this effect, but also an accuracy in size of the inner and outer circumferences of the impeller 712 may also be improved, a combining size between a fan casing 715 and the stationary guide blades 714 is also stabled and a disturbance in aerodynamic performance is eliminated. Additionally, the forming molten metal opening required in case of molding operation or the molten metal reservoirs for preventing a lack of filling are arranged at the inner or outer circumferences of the front plate 101 to enable them to be removed in concurrent with the post-machining operation for the aforesaid inner and outer diameters and so the number of working steps may not be increased. It is further understood by those skilled in the art that the foregoing description is a preferred embodiment of the disclosed device and that various changes and modifications may be made in the invention without departing from the scope thereof.

Claims: A motor-driven blower comprising an electric motor (717) accommodated in a housing (702), an impeller (712) fixedly mounted on a rotating shaft (705) included in the electric motor, stationary guide blades (714) disposed on the downstream side of the impeller (712), and a fan casing (715) covering the impeller (712) and the stationary guide blades (714), the impeller having a front plate (101) having a suction opening (801), a back plate (102) disposed opposite to the front plate (101), and a plurality of blades (103) disposed between the front plate (101) and the back plate (102), characterized in that either the front plate (101) or the back plate (102) is integrally formed with the blades (103), and the other plate not integrally formed with the blades is connected to the blades (103) by brazing or welding. Motor-driven blower according to claim 1, characterized in that either the front plate (101) or the back plate (102) is integrally formed with the blades (103) by a Mg alloy. Motor-driven blower according to claim 1, characterized in that the blades (103) are formed integrally with the front plate (101) by a Mg alloy and the back plate (102) is formed by an Al alloy. Motor-driven blower according to claim 1, characterized in that the blades (103) are formed integrally with the front plate (101) by a Mg alloy and the back plate (102) is formed by a Mg alloy. Motor-driven blower according to one of the preceding claims, characterized in that the other plate (101; 102) not integrally formed with the blades (103) has a brazing metal layer (201) on a surface thereof, and the plate is connected to the blades (103) by brazing using the brazing metal layer (201) being applied as a brazing material. Motor-driven blower according to claim 1, characterized in that the front plate (101) is integrally formed with the blades (103) by a Mg alloy, the back plate (102) is formed by either the Al alloy or the Mg alloy, end portions of the blades (103) are provided with a plurality of projections (301), the back plate (102) has on a surface thereof holes (302) into which the projections (301) are inserted, and the projections formed at the blades are inserted into the holes formed at the back plate and welded there. Motor-driven blower according to claim 6, characterized in that the projections (301) formed at the blades are inserted into the holes (302) formed on the surface of the back plate (102) and the projections and the holes are melted, deformed and connected by either one of a spot welding, an electron beam welding and a laser welding. Motor-driven blower according to claim 1, characterized in that the front plate (101) is integrally formed with the blades (103) by a Mg alloy, the back plate (102) is formed by either an Al alloy or a Mg alloy, end portions of the blades are provided with a pluraltiy of projections (301), the surface of the back plate has on and in a surface thereof a brazing metal layer (201) and holes (302) into which the projections (301) are inserted, the projections of the blades are inserted into the holes formed at the blades, the blades are connected to the back plate by brazing using the brazing metal layer being applied as a brazing material.

Inventors: AONO YASUHISA ING, INAGAKI MASAHISA ING, JYORAKU FUMIO ING, NAKAMURA KIYOMI ING, OBANA TAKESHI ING, OKAMURA HISANORI ING, SUKA HISAO ING, AONO, YASUHISA, ING., INAGAKI, MASAHISA, ING., JYORAKU, FUMIO, ING., NAKAMURA, KIYOMI, ING., OBANA, TAKESHI, ING., OKAMURA, HISANORI, ING., SUKA, HISAO, ING.
Applicants: HITACHI LTD, HITACHI, LTD.
Application year: 1998
Main classification: F04D29
IPC codes: F04D29