Abstract:
An impeller and at least a portion of a cooperating peripheral volute may be integrated are integrally injection molded with, concentric outer rotor and inner stator assemblies, respectively, to achieve a low profile precision impeller mechanism based on an improved brushless D.C. motor with low length to diameter ratio and suitable for use in a variety of other applications. A rotating cap has an inner circumference which is molded about an outer ferromagnetic back ring that in turn supports a rotor magnet having a number of poles of alternating polarity and separated by a relatively small cylindrical air gap from a fixed stator assembly. The fixed stator assembly is integrally molded into a base housing having a bearing support that extends upwardly through the center of the stator assembly and that is rotatably coupled to a rotating shaft that extends downwardly from the center of the rotating cap.

Description:
CROSS RELATED APPLICATION 
       [0001]    This application is a continuation of U.S. application Ser. No. 11/362,198 filed Feb. 27, 2006, which is a continuation of and claims priority to U.S. application Ser. Nos. 10/795,207 filed on Mar. 5, 2004 and 60/453,038 filed on Mar. 7, 2003 each of which is incorporated herein by reference in its entirety. 
     
    
     BACKGROUND OF THE INVENTION 
       [0002]    The present invention relates generally to d.c. motors and more particularly to an improved d.c. brushless motor having a low length to diameter ratio and suitable for use with a low profile impeller mechanism. 
       BRIEF SUMMARY OF THE INVENTION 
       [0003]    In accordance with a first aspect, an impeller and at least a portion of a cooperating peripheral volute are formed on, and preferably are integrally injection molded with, respective concentric outer rotor and inner stator assemblies, to achieve a low profile precision impeller mechanism based on an improved brushless d.c. motor with low length (L) to diameter (D) ratio. 
         [0004]    In accordance with a second aspect, an improved low profile brushless d.c. motor suitable for use in a variety of different applications includes an injection molded rotating cap which has an inner circumference which is molded about an outer ferromagnetic back ring that in turn supports a permanently magnetized ring shaped rotor magnet having a number of poles of alternating polarity defined about its inner circumference and separated by a relatively small cylindrical air gap from the outwardly radially projecting selectively magnetized teeth of a fixed stator assembly. In one exemplary embodiment the rotor may have 8 poles and the stator may have 9 radial slots defining 9 respective teeth. The fixed stator assembly is preferably integrally molded into a base housing that also includes a precision fixed bearing support that extends upwardly through the center of the stator assembly and that is rotatably coupled to a rotating shaft that extends downwardly from (and preferably is integral with) the center of the rotating cap. A coaxial pair of preloaded ball bearings is preferably supported between an inner cylindrical surface of the fixed bearing support and an outer cylindrical surface of the rotating shaft, to thereby permit the rotor to rotate precisely about the stator with minimal variation in the cylindrical air gap therebetween. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0005]    Hereinafter, some exemplary embodiments of the present invention will be described in reference to the attached drawings, which are not necessarily to scale and which include reference labels to indicate various features thereof, like labels referring to like features throughout both the drawings and the written description. A description of one or more preferred or otherwise exemplary embodiments is not to be taken in a limiting sense, but is made merely for the purpose of describing the general principles of the invention. Additional embodiments, features and/or advantages of the invention will become apparent from the ensuing description or may be learned by the practice of the invention. 
           [0006]      FIG. 1  is a first exploded perspective view of an exemplary d.c. brushless motor in accordance with the present invention. 
           [0007]      FIG. 2  is a second exploded perspective view of the d.c. brushless motor of  FIG. 1 . 
           [0008]      FIG. 3  is a bottom perspective view of an exemplary integrally molded motor housing base portion suitable for use in the d.c. brushless motor of  FIG. 1 . 
           [0009]      FIG. 4  is a top perspective view of the motor housing base portion of  FIG. 3 . 
           [0010]      FIG. 5  is a top perspective view of a partially assembled d.c. brushless motor of  FIG. 1 . 
           [0011]      FIG. 6  is a bottom perspective view of the partially assembled d.c. brushless motor of  FIG. 5 . 
           [0012]      FIG. 7  is a cross-sectional view of a second exemplary d.c. brushless motor corresponding generally to section lines  7 - 7  of  FIG. 5 . 
           [0013]      FIG. 8  is a cross-sectional view of an exemplary stator corresponding generally to section lines  8 - 8  of  FIG. 1  and associated rotor and back-iron ring. 
       
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
       [0014]    As shown in  FIG. 1 , which is a first exploded perspective view of an exemplary d.c. brushless motor in accordance with the present invention and as shown in more detail in the second exploded perspective view of  FIG. 2 , the top perspective view of  FIG. 3 , the bottom perspective view of  FIG. 4 , and the cross-sectional view of  FIG. 7 , a preferred embodiment of the present invention may include a generally ring-shaped stator assembly  12  for a d.c. brushless motor  10  is injection molded as an integral part of a motor base housing  14  having the lower portion of an exit volute  16  about its outer periphery  18 . The mating upper portion of the assembly, or cover  40 , may contain certain completing features of the volute as it does in this exemplary d.c. brushless motor, or it may be a simple cover with an inlet hole. 
         [0015]    The exemplary stator assembly  12  (see also  FIG. 8 ) includes a plurality of radially extending slots collectively defining a like number of rotor teeth  20  about an outer circumference  22  of the stator assembly, and a respective low profile layer electrical winding  24  wound about an intermediate portion of each of the teeth  20  between two adjacent slots for selectively magnetizing a respective tooth of the stator assembly  12 . Such a stator assembly may be constructed, for example, from M19 silicon steel laminations, low viscosity adhesive such as Loctite® (ethyl cyanoacrylate), copper magnet wire windings, and 3M® Scotchcoat® electrical resin. The entire stator assembly  12  is preferably integrally molded into the base housing  14  by embedding it in the same injection moldable engineered thermoplastic material such as polycarbonate (which may be loaded with glass fibers or other materials for added strength or thermal conduction purposes) from which the base housing  14  is formed. In accordance with another embodiment of the present invention, the laminated stack which defines the individual arms  20  and associated stator slots and stator teeth, and which provides the flux-carrying medium within the stator assembly  12  between two adjacent teeth, may be replaced with a powdered metal stack (not shown). 
         [0016]    In one practical embodiment as shown in  FIG. 8 , the d.c. brushless motor may utilize a unitary rotor  28  with eight poles and a slotted stator  12  with nine teeth. However, alternative pole/slot combinations may be employed. 
         [0017]    As shown in  FIG. 3  and  FIG. 4 , a generally tubular precision bearing carrier  32 , which may be made, for example, from 303 stainless steel, a plurality of electrical terminals  34 , and a plurality of optional Hall sensor pockets  36  are preferably also embedded as integral parts of the injection molded base housing  14  by properly positioning them in the base housing mold (not shown) at the same time as the stator assembly  12 . This injection molding of the base housing  14  with an embedded stator assembly  12  and embedded precision bearing carrier  32  not only reduces motor assembly time, but maintains the static and rotating components in the proper radial and angular spatial relationships during final assembly and operation. In other embodiments, the bearing carrier  32  may be made from the same engineered plastic material as the housing base  14  either as a separate component or as an integral part of the base housing. Those skilled in the art will recognize that the stator  12  and any other separately fabricated components of the integrally molded assembly may be accurately positioned within the mold by means of suitable fixtures or protrusion in the mold corresponding to housing apertures  38  in the finished base. 
         [0018]    The depicted embodiment of the d.c. brushless motor  10  of the present invention also includes a motor cover  40  with an upper volute portion  42  that is adapted to attach or snap into place over the motor base housing  14  to thereby define a complete peripheral volute which functions as the exit of the rotating impeller assembly  44 . A generally ring-shaped shroud  46 , which may contain a contour that mirrors that of the lower volute and thereby forms part of a flow cutoff feature, is preferably coupled between the motor cover  40  and the impeller  44  to form an annular entrance  48  to the rotating impeller assembly. The shroud  46  may be made, for example, from 6061-T6 aluminum or molded from thermoplastic material. The motor cover  40  and base housing  14  may be molded from Noryl® which is modified polyphenylene oxide and polyphenylene ether with good heat resistance, extremely low water absorption (0.07%), and long term dimensional stability. 
         [0019]    As depicted in  FIG. 5  and  FIG. 6 , the exemplary motor  10  may also include a printed circuit board (PCB) driver assembly  50  which is preferably coupled to the bottom portion of the motor housing and which may include a commutation circuit board  52 , or for sensorless configurations this board may be simplified by eliminating Hall sensors and their associated pockets. As depicted the commutation circuit board includes a power connector  54  and is adapted to fit within a recess  56  ( FIG. 3 ) on the bottom portion of the motor housing  14 . The recess includes the molded-in electrical terminals  34  which operatively couple the commutation circuit board  52  to the integrated stator assembly  12 , and which, in one exemplary preferred embodiment of the present invention, are precisely positioned in both angular position and radial alignment with angular position being defined relative to the coils  20 , while radial alignment may be defined relative to the rotational axis. The PCB driver assembly  50  is preferably designed with this “in the mold” terminal-locating (preset “tuning” of the Hall sensors) technique to ensure that the combination of PCB driver  50  and molded stator  12  assemblies yields the desired positional relationship of integral Hall sensors to coils, with the integral Hall sensors  58  preferably disposed in the Hall sensor pockets  36 . 
         [0020]    As best seen in  FIG. 7  and  FIG. 8 , the motor  10  also includes a generally cup-shaped rotor assembly  28  comprising a generally ring-shaped rotor magnet  60  having a number (for example, eight) of radially oriented poles which is preferably incorporated into an integral generally cup-shaped impeller  44  together with a generally ring-shaped rotor hub back-iron ring  64  of magnetic steel (or other suitable ferromagnetic material) to thereby provide a magnetic return path between two adjacent poles of the rotor magnet, as shown by the dashed lines in  FIG. 8 . A person skilled in the art would readily recognize that the aforementioned preset tuning is advantageous in terms of (a) eliminating labor (tuning process), and (b) assuring consistency of performance among all assemblies. In particular, the individual Hall sensors  58  will be optimally located radially relative to rotor magnet  60  to detect the approach of the next rotor pole  62  at a known angular position relative to a given stator tooth  20  and thereby provide an accurate positional feedback signal to the commutation circuit board  52 . The impeller  44  has a circular base rim  66  adapted to accommodate the rotor magnet  62  and is operatively coupled to the motor housing, as generally illustrated in  FIG. 5 . The rotor magnet  60  may be formed of a suitable permanent magnetic material such as ceramic or high energy rare earth materials, for example a high energy ferromagnetic boron ally such as NdFeB, and is slightly smaller in diameter than the diameter of the rotor hub which, in turn, is made slightly smaller than the inner diameter of the impeller base rim. Specifically, in this example, the back-iron ring  64  is preferably embedded in the inner surface  68  of the base rim  66  of the impeller  44  (as best seen in the cross-section of  FIG. 7 ), and the rotor magnet  60  (which could be damaged during the molding process) is preferably adapted to be subsequently adhesively secured within the back ring  64 . However, in other embodiments constructed of other materials and/or fabricated using other molding techniques, both the back ring  64  and the magnetic rotor could be adhesively secured to the impeller or integrally molded therewith. In any event, a two-plane balance is preferably performed on the integral impeller assembly after the back ring and magnetic rotor have been installed, for example by removal of material from the exemplary locations  70 A, 70 B. 
         [0021]    In accordance with an exemplary embodiment of the present invention, the impeller  44  may be molded from a suitable thermoplastic; the rotor magnet  62  may be a bonded ferrite magnet, while the rotor hub  28  may be constructed from 416 stainless steel. In another exemplary embodiment, the impeller  44  may be constructed from 6061-T6 aluminum. The impeller includes a front side having vanes  47  for moving air flow through the impeller. The impeller has a back side  49  with a recess  51  that extends into the interior of the impeller. The bearing carrier  32  and stator assembly  12  extend into recess on the back side of the impeller. The back side  49  of the impeller includes an outer edge  53 . 
         [0022]    As best seen in  FIG. 7 , the motor  10  includes a generally cylindrical motor shaft  72  adapted to rotate on front and rear bearings  74 , 76  which are within the precision bearing carrier and preloaded via a compression spring  78 . Similar to the bearing carrier  32  in the housing base, the shaft  72  is preferably embedded as an integral part of the injection molded motor cover  40  during the injection molding process. As best seen in  FIG. 1 , a generally ring-shaped shim  80  may be coupled between the compression preload spring  78  and the front bearing  74 . On the opposite side, a housing snap ring  82  may be coupled between the rear bearing  76  and the compression preload spring  78 . A shaft snap ring  84  may be used between the precision bearing carrier  32  and the stator assembly  12 . By thus providing a precision bearing assembly about the rotational axis  86  defined by the bearing carrier  32  and the motor shaft  72 , and by integrally molding the bearing carrier  32  with the stator assembly  12  and by integrally molding the motor shaft  72  and the back ring  64  (which supports the rotor magnet  60 ) with the rotor assembly  28 , it is possible to maintain a relatively small air gap  88  between the inner circumference  90  of the ring-shaped rotor magnet  60  and the ends  92  of the radial stator arms  20  which define the outer circumference  22  of the stator assembly  12 . 
         [0023]    In accordance with an exemplary embodiment of the present invention, the front and rear bearings  74 , 76  may be made from chrome alloy steel, the shim  80  may be made from 300 stainless steel, the housing snap ring  82  may be made from carbon steel, the shaft snap ring  84  may be made from beryllium-copper alloy, and the compression preload spring  78  may be made from spring steel. 
         [0024]    The resultant motor has relatively low motor length (L) to overall motor diameter (D) ratio and may be used in a variety of applications. In accordance with one exemplary embodiment of the present invention, an L/D ratio of about ¼ was achieved using a motor length of about 1.25 inch, and an overall motor diameter (including peripheral volute) of about 5 inch. Other L/D ratios may be utilized depending on specific rotary pump applications. For example, the (low L/D ratio) motor of the present invention may be used as a CPAP (continuous positive airway pressure) device for OSA (obstructive sleep apnea) patients. 
         [0025]    It should be noted that practicing the invention is not limited to the applications described hereinabove. Many other applications and/or alterations may be utilized provided such other applications and/or alterations do not depart from the intended purpose and scope of the present invention. For example, the disclosed motor may be used to drive other rotating mechanisms such as a mechanical gyroscope or an optical scanner. 
         [0026]    It should also be appreciated that features illustrated or described as part of one embodiment can be used in another embodiment to provide yet another embodiment such that the features are not limited to the specific embodiments described above. Thus, it is intended that the present invention cover all such modifications, embodiments and variations as long as they come within the scope of the present invention. 
         [0027]    While the invention has been described in connection with what is presently considered to be the most practical and preferred embodiment, it is to be understood that the invention is not to be limited to the disclosed embodiment, but on the contrary, is intended to cover various modifications and equivalent arrangements included within the spirit and scope of the appended claims.