Abstract:
A motorized blower assembly ( 1 ) is provided for use in respiratory therapy applications. The active motor sub-assemblies ( 6, 7, 9 ) are encapsulated within an over-molded thermoplastic material ( 5 ) with selected vibration-dissipative and thermally-conductive properties. The resulting blower assembly operates at reduced sound levels of 1.0-3.0 dB, and with an increased efficiency of 3-9% over currently-marketed blowers of similar size and air flow capability.

Description:
FIELD OF THE INVENTION 
       [0001]    The present invention relates generally to: (a) improved motorized blower assemblies (e.g., for use in respiratory therapy for treating sleep apnea), (b) improved arrangements and assemblies of the various blower assembly components for precise alignment and retention when the blower assembly components are assembled, and (c) improved methods of manufacturing such blowers. 
       BACKGROUND OF THE INVENTION 
       [0002]    Sleep apnea machines contain specially-designed motors, motor controls, and impellers that move air into, and out of, a patient&#39;s respiratory system. 
         [0003]    Blowers for respiratory therapy are required to be quiet due to their proximity to the patient. Currently-marketed blowers have sound pressure levels of approximately 42 dB. Intrinsic structure-borne noise sources found in electric motors include torque disturbances, bearing displacements, and magnetostriction of ferromagnetic materials. Magnetic forces between the rotor and stator also interact with the motor structure. Similarly, the housing must have a sufficient stiffness to support the rotor. However, the housing transmits forces into the motor. The inherent acoustic sensitivity dictates the noise and vibration characteristics of the motor. In order to reduce noise to a minimum, potential sources of vibration between motor, rotor and stator should be reduced or eliminated whenever possible. 
         [0004]    A loud motor can result from intrinsically-small vibration sources coupled with poor motor housing structural acoustic sensitivity. Improving the acoustic sensitivity of the motor housing through the use of vibration-dissipative materials can reduce motor noise. 
         [0005]    One effective vibration control strategy accommodates large bearing displacements and results in low structural forces. One may achieve this using a resilient bearing foundation. Negative aspects of such a strategy include dynamic alignment, and durability issues. For example, the rotor and stator may rub under critical operating conditions, causing premature failure. Tolerance rings, elastomeric O-rings, cups, sleeves and various other constructions may be employed to provide the resilient mounting that damp vibrations. 
         [0006]    One relatively-recent innovation in the plastics molding industry is the ability to over-mold various motor components. Coils and stator assemblies have been encapsulated to protect them from the environment, for wash-down, down-hole, and other applications. Electric motor stator windings are also being encapsulated with materials having relatively high coefficients of thermal conductivity in order to improve motor performance. A wide range of thermoplastic elastomers (TPEs) with various fillers are being used in the over-molding process. 
         [0007]    Blower assemblies generally include an electric motor, a blower wheel or impeller, and a blower housing. These sub-assemblies are generally held in operative relation to one another by suitable mechanical means, such as screws or adhesives. The assembly time required to handle, align, and position these sub-assemblies, and then apply the mechanical retention, can add significant cost to the final blower assembly. 
         [0008]    Each of the aforementioned sub-assemblies has a dimensional tolerance. When the components are affixed in proper relationship to one another, the tolerances add together for a cumulative or aggregate tolerance, known as a tolerance stack-up. This tolerance stack-up has resulted in increased spacing between moving and stationary parts to prevent interference and seizing. However, an increased gap between the blower wheel or impeller and the housing results in reduced blower efficiency. Gaps in blowers of this type have typically been in the 0.030 inch ±0.018 inch range of clearance between moving and stationary blower parts. 
         [0009]    By molding the motor stator and bearing assemblies simultaneously in the blower housing, part of the tolerance stack-up between moving and stationary parts can be eliminated. The motor stator and the bearing assembly are located in the housing lower portion within molding die tolerances of about ±0.0005 inches. The housing upper portion locates off of the lower housing portion, and the impeller is located by the bearing assembly. The aggregate tolerance stack-up is reduced to about ±0.008 inches, allowing for a nominal clearance of about 0.020 inches. Testing confirms that a gap reduction of about 0.010 inches can produce a power savings of about 3% by reducing the impeller speed required to produce a particular flow. This reduced impeller speed can result in noise reduction, and in improved life and reliability of the blower assembly. The overall size of the blower assembly may also be reduced, and still achieve air-handling performance equivalent to that of a larger blower assembly. 
         [0010]    Electric motors that operate at higher efficiencies may run at cooler temperatures, and may have longer life and reliability characteristics than motors that run hotter. The motors in respiratory therapy blowers generally are insulated in a blanket of still air. Conducting heat away from the motor would allow it to run at a lower temperature with the benefits described. 
         [0011]    U.S. Pat. No. 7,154,200 B2 (Neal), which is incorporated by reference herein, describes forming the housing of a motor assembly while encapsulating multiple motor components with a molding material in a single step. The molding material may be selected such that it has a coefficient of thermal expansion similar to the coefficient of thermal expansion of the metal members of the assembly, is thermally conductive, has vibration-damping and shock-absorption properties, attenuates acoustic noise resulting from magnetostriction, and encapsulates electrical terminals. The process reduces tolerance stack-ups and assembly costs, and can include various types of inserts and various types of bearings. 
         [0012]    An improvement can be made over the single step of molding the motor housing while also over-molding the motor components. Molding a single material will require design compromises due to the molding requirement of keeping all wall sections roughly the same thickness. Molding the components into a preformed housing of a different material adds functionality and flexibility to the design. The preformed housing may have assembly-enhancing features, such as snap hooks, tabs for screws, and the like. The material for the housing may be selected such that it dissipates vibrations at frequencies other than those dissipated by the molding material. Thus, damping across a wider range of frequencies may be achieved. 
         [0013]    Most thermoplastic elastomers commonly used for over-molding have similar damping characteristics for vibrations in the 0-7 kHz frequency range. However, above 7 kHz, softer TPEs tend to damp vibrations more effectively. Fillers, such as glasses and ceramics, change the TPE damping characteristics and can be used to customize the TPE for damping particular frequency ranges. By using two TPEs with different damping characteristics, a broader and more effective vibration damping solution can be achieved. 
         [0014]    Additional details of known motor designs are shown and described in U.S. Pat. No. 6,058,593 A (Siess) and U.S. Pat. No. 7,012,346 B2 (Hoffman et al.), the aggregate disclosures of which are hereby incorporated by reference. 
       SUMMARY OF THE INVENTION 
       [0015]    Motorized blower assemblies have been invented that incorporate the best features of the current art of motor construction, and that yet improve upon those features. 
         [0016]    A first aspect of the invention is an improved motor with the stator sub-assembly and the bearing sub-assembly co-located within a matrix of thermoplastic material, which is molded into the housing lower portion. The housing lower portion also forms the lower portion of the blower air chamber. 
         [0017]    The thermoplastic material has vibration-damping properties, resulting in a quieter motor as compared with a motor constructed without such a material. 
         [0018]    In another aspect of the invention, an insert is over-molded into the housing lower portion, which receives the bearing sub-assembly in a subsequent assembly process step. 
         [0019]    In another aspect of the invention, the housing portions are made with features to enhance assembly of the upper blower housing portion or other component of the final assembly. The enhanced assembly features result in lower manufacturing costs, and the opportunity to utilize automated manufacturing methods for further cost reduction. 
         [0020]    In another aspect of the invention, the thermoplastic material also forms a gasket between the housing portions and/or between other components of the assembly. 
         [0021]    The molding material may be an injected-molded thermoplastic elastomer, a potting compound, or the like. It can be a filled or unfilled monomer or polymer. The material may be thermally conductive to achieve a higher power rating. 
         [0022]    In another aspect of the invention, affixing the sub-assemblies within the lower blower housing by means of the over-molded material results in a lower manufacturing cost and reduced tolerance stack-up as compared with other means of affixing the sub-assemblies. 
         [0023]    In another aspect of the invention, the housing lower portion forms an exit for the terminals of the stator assembly, and a pocket to receive an external connector. 
         [0024]    In still another aspect of the invention, the upper and lower housing portions, and the shaft, have features to enhance automated handling and assembly. With parenthetical reference to the corresponding parts, portions or surfaces of the disclosed embodiments, merely for purposes of illustration and not by way of limitation, the present invention broadly provides, in one aspect, an improved motorized blower assembly ( 1 ) for use in respiratory therapy. The improved blower assembly broadly includes: a housing ( 2 ,  3 ) having an air flow passageway extending between an inlet ( 11 ) and an outlet ( 12 ); a stator assembly ( 6 ) positioned within and secured to the housing; a bearing assembly ( 9 ) mounted on the housing in a predetermined position relative to the stator assembly; a rotor assembly having a shaft ( 8 ), an impeller ( 10 ) mounted on one marginal end portion of the shaft, and a magnet ( 7 ) mounted on an intermediate portion of the shaft; wherein another marginal end portion of the shaft is received in the bearing assembly; and an over-molded material ( 5 ) engaging said housing and encapsulating the motor stator assembly. 
         [0025]    The molding material may be a thermoplastic elastomer, or a potting compound which is applied via potting methods. 
         [0026]    The molding material may have a predetermined coefficient of thermal expansion and/or a predetermined coefficient of thermal conductivity. 
         [0027]    The molding material may be selected to have predetermined vibration-dissipative properties resulting in quieter blower operation. 
         [0028]    The components may have design features to enhance automated assembly and reduce assembly costs. 
         [0029]    The over-molded components and assemblies may have reduced tolerance stack-ups resulting in more efficient and quieter operation of the blower. 
         [0030]    A gasket may be molded onto one of the housings to create a seal between housings, resulting in more efficient and quieter operation of the blower. 
         [0031]    In another aspect, the invention provides an improved method of manufacturing a portion of a motorized blower assembly, comprising the steps of: providing a first die having complementary die halves ( 13 ,  14 ) defining a first housing part cavity therewithin; injecting a material into said first die cavity to form a first housing part ( 3 ); opening the first die by moving said first die halves apart; removing said first housing part ( 3 ) from such opened first die; providing a second die having complementary die halves ( 15 ,  16 ) defining a stator assembly cavity therewithin; opening the said second die by moving the second die halves away from one another; placing said first housing part ( 3 ) into the cavity of one ( 15 ) of said second die halves; providing a stator assembly ( 6 ) and a bearing assembly ( 9 ); placing the stator assembly and the bearing assembly in the other ( 16 ) of the second die halves; closing said second die by moving said second die halves toward one another to accurately position said housing first part, said stator assembly and said bearing assembly relative to one another, and to define a second mold cavity therebetween; injecting a thermoplastic material ( 5 ) into the second mold cavity to over-mold the stator assembly and the bearing assembly within said first housing part; opening said second die by moving said second mold halves away from one another; and removing said first housing part and said over-molded stator and bearing assemblies; thereby to manufacture a portion of a motorized blower assembly ( 1 ). 
         [0032]    Accordingly, the general object of the invention is to provide improved motorized blower assemblies. 
         [0033]    Another object is to provide improved methods and apparatae for arranging and assembling the various blower assembly components for precise alignment and retention when the blower assembly components are assembled together. 
         [0034]    Still another object is to provide an improved method of producing a low-cost, high performance, quiet motorized blower assembly. 
         [0035]    These and other objects and advantages will become apparent from the foregoing and ongoing written specification, the drawings, and the appended claims. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0036]      FIG. 1  is a fragmentary longitudinal vertical sectional view of a first form of an improved blower assembly. 
           [0037]      FIG. 2  is a top plan view of the blower assembly shown in  FIG. 1 , with a portion cutaway to illustrate details of the impeller. 
           [0038]      FIG. 3  is a schematic view of the housing lower portion molded within the first mold. 
           [0039]      FIG. 4  is schematic view, showing the first mold halves having been moved apart so that the molded housing lower portion can be removed. 
           [0040]      FIG. 5  is a schematic view of an opened second mold, this view showing the molded housing lower portion as having been positioned within the a second mold upper half, with the stator assembly and the bearing assembly being positioned on the second mold lower half. 
           [0041]      FIG. 6  is a schematic view similar to  FIG. 5 , but showing the second mold halves as having been moved together to close the second mold and to position the stator and bearing assemblies relative to the housing lower portion. 
           [0042]      FIG. 7  is a schematic view showing a thermoplastic elastomer as having been injected into the second mold cavity to over-mold the stator and bearing assemblies within the housing lower portion. 
           [0043]      FIG. 8  is a schematic view similar to  FIG. 7 , but showing the second mold halves as having been moved away from one another to open the second mold, and to allow the over-molded portion of the blower assembly to be removed from the second mold. 
           [0044]      FIG. 9  is an enlarged fragmentary longitudinal vertical sectional view showing the rotor assembly as having been inserted into the bearing assembly. 
           [0045]      FIG. 10  is a side elevation showing the housing upper portion as having been mounted on the housing lower portion, with a portion cutaway to show portions of the two housing portions in cross-section. 
           [0046]      FIG. 11  is an exploded side elevation of a second form of the improved motorized blower assembly. 
           [0047]      FIG. 12  is an enlarged fragmentary longitudinal vertical sectional view of a third form of the improved motorized blower assembly. 
       
    
    
     DESCRIPTION OF THE INVENTION 
       [0048]    At the outset, it should be clearly understood that like reference numerals are intended to identify the same structural elements, portions or surfaces consistently throughout the several drawing figures, as such elements, portions or surfaces may be further described or explained by the entire written specification, of which this detailed description is an integral part. Unless otherwise indicated, the drawings are intended to be read (e.g., cross-hatching, arrangement of parts, proportion, degree, etc.) together with the specification, and are to be considered a portion of the entire written description of this invention. As used in the following description, the terms “horizontal”, “vertical”, “left”, “right”, “up” and “down”, as well as adjectival and adverbial derivatives thereof (e.g., “horizontally”, “rightwardly”, “upwardly”, etc.), simply refer to the orientation of the illustrated structure as the particular drawing figure faces the reader. Similarly, the terms “inwardly” and “outwardly” generally refer to the orientation of a surface relative to its axis of elongation, or axis of rotation, as appropriate. 
         [0049]    Referring now to the drawings, and, more particularly, to  FIG. 1  thereof, a first embodiment of an improved motorized blower assembly according to the invention is designated generally indicated at  1 , and broadly includes a housing lower portion  3 , a housing upper portion  2 , a gasket  4  located between the two housing portions, a wound stator assembly  6 , a permanent magnet  7 , a shaft  8 , a bearing assembly  9 , an overmolded thermoplastic elastomeric material  5 , and an impeller  10 . 
         [0050]    The stator assembly  6  is first constructed using steel laminations, which are aligned and stacked to form a magnetically-inducible core having a plurality of poles, about which windings made up of insulated electrically-conductive wire are wound or placed. The art of forming poles and windings of various configurations to create magnetic poles is well known, and therefore need not be discussed further herein. 
         [0051]    The rotor sub-assembly is constructed by either over-molding the magnet  7  onto the shaft  8 , or by using adhesive to affix the magnet  7  onto the shaft  8 . The magnet  7  can be magnetized with any number of desired poles, either before or after assembly to the shaft. The impeller  10  is either molded onto the shaft  8 , or is molded separately and affixed to the shaft  8  by pressing on, by using an adhesive, or by some other suitable means. The assembly order is optional. 
         [0052]    In operation, the rotor sub-assembly consisting of the impeller  10 , the shaft  8 , and the magnet  7 , is caused to rotate due to tangential forces created between the stator  6  and the magnet  7  when electric current is caused to flow in the windings of the stator  6 . 
         [0053]    Referring now to  FIG. 2 , the rotating impeller  10  causes a pressure differential between the blower inlet  11  and the blower outlet  12 , which produces the desired air flow. 
         [0054]    Referring now to  FIG. 3 , the blower housing lower portion  3  is formed by means of injecting plastic into a cavity formed between mold die halves  13 ,  14 . In  FIG. 4 , the die is shown as having been opened, and the lower housing portion  3  is shown as being separated, prior to removal. 
         [0055]      FIG. 5  shows the housing lower portion  3  as having been placed into a separate upper die half  15 , which is like die half  14  but located in a different molding machine. Lower die half  16  is introduced, which has the stator assembly  6  and bearing assembly  9  pre-loaded and positively located in axial and radial relationship to each other. 
         [0056]    In  FIG. 6 , the die halves  15  and  16  are shown as having been closed, which positively locates the stator assembly  6  and bearing assembly  9  in axial and radial relationship with the lower housing portion  3  within die tolerances. The molding die has tolerances of about ±0.0002 inch on diameters and axial lengths. The lower housing portion locates within the die half within about ±0.003 inch. The axial and radial tolerance stack-up between bearing assembly and stator assembly is about ±0.0004 inch. The axial and radial tolerance stack-up between each of them and the housing is about ±0.0032 inch. 
         [0057]    In  FIG. 7 , the thermoplastic elastomer  5  is shown as having been injected into the mold, which locks the stator assembly  6  and bearing assembly  9  in place in the housing lower portion  3 . A potting material or epoxy may alternatively be used to fill the cavity in the mold. 
         [0058]    In  FIG. 8 , the two die halves  15 ,  16  are shown as having been separated, and the resulting assembly is shown as having been removed. 
         [0059]    In  FIG. 9 , the pre-assembled rotor assembly  17  is affixed to the molded assembly  18  by press fitting the shaft  8  into the bearing assembly  9 . Alternatively, the shaft  8  can be affixed to the bearing assembly  9  by a suitable adhesive or some other means. 
         [0060]      FIG. 10  shows the upper housing portion  2  as being affixed to the lower housing portion  3  by means of snaps, severally indicated at  20 . The pre-formed gasket  4  between the upper and lower housing portions  2 ,  3  prevents air leaks for higher blower efficiency, and results in quieter operation. Alternatively, the upper and lower housing portions  2 ,  3  can be held together by means of screws, clamps, an adhesive, or some other means. The three terminals  21  are secured by the molding material  5 , and are designed and located so as to receive a mating electrical connector. 
         [0061]    In  FIG. 1 , the motor design (i.e., the orientation of stator assembly  6  and magnet  7 ) has a radial orientation, with the rotor being within the stator member  6 . The invention can also be practiced with a motor design in an axial orientation. The invention can also be practiced with a motor design with radial orientation with the rotating member on the outside of the stationary member. 
         [0062]    In  FIG. 1 , the motor is a brushless DC motor. Such a motor may be run with feedback devices (e.g., Hall Effect devices, resolvers, encoders, or some other means), or it may be run without feedback in a sensorless drive scheme. The invention could also be practiced with other motor types, such as a brushless AC motor, a permanent magnet DC motor, an induction motor, a stepper motor, a switched reluctance motor, or some other motor type. 
         [0063]    In  FIG. 1 , a bearing assembly  9  is a type of cartridge with two rows of preloaded balls is molded into the housing lower portion  3 . The bearing pre-load is established in the construction of the bearing cartridge by the bearing vendor. The invention can also be practiced by mounting two separate bearings onto the shaft, either next to each other as a duplex pair, or, separated by some distance along the shaft. The invention can also be practiced as depicted in  FIG. 11  by mounting the bearing assemblies  9  onto the shaft  8  and pressing or bonding the bearing assemblies into a receiving sleeve  19  that has been molded into the lower housing assembly  3 . The invention may also be practiced by assembling the bearing cartridge between the magnet and the impeller thus reducing the over-hanging mass. The invention may also be practiced using a sleeve bearing, magnetic bearing, hydrodynamic bearing, or some other type of bearing system. 
         [0064]    In the preferred embodiment of  FIG. 1 , the molding material  5  may be selected so that it has a coefficient of linear thermal expansion similar to that of the plastic components or the metal components of the assembly such as the shaft  8 . The molding material  5  may also be selected so that it has an increased thermal conductivity, which may be isotropic or directional based on the needs of a particular application. The molding material  5  may also be selected for desired vibration damping properties that are tuned to specific frequencies or frequency ranges. The molding material  5  may be an injected molded thermoplastic elastomer, a potting compound, or the like. 
         [0065]    Referring to  FIGS. 4-5 , an alternate process to removing the housing lower portion  3  from die half  14  and replacing it with similar die half  15 , is to retain the housing lower portion  3  in die half  14  thereby requiring a two-shot molding operation. 
         [0066]    Referring to  FIG. 12 , an alternate construction is shown whereby the stator and bearing assemblies are replaced with a completed motor assembly  22  which has been over-molded into the lower blower housing  3 . With this embodiment of the invention, the impeller would be pressed onto the shaft  8  of the motor  22  after the overmolding process is completed. The improvements of the invention are not compromised by this alternate construction. 
         [0067]    Final assembly of the housing upper and lower portions may be accomplished by the use of screws, snaps, welding, bonding, or some other means, as commonly practiced. 
         [0068]    The invention thus far described has incorporated a single impeller to produce air movement in the motorized blower assembly. Other embodiments of the invention include fan and blower wheels, as well as multiple stages of the air mover. 
         [0069]    Therefore, the invention broadly provides: (a) improved motorized blower assemblies (e.g., for use in respiratory therapy for treating sleep apnea), (b) improved arrangements and assemblies of the various blower assembly components for precise alignment and retention when the blower assembly components are assembled, and (c) improved methods of manufacturing such blowers. 
       MODIFICATIONS 
       [0070]    The present invention contemplates that many changes and modifications may be made. 
         [0071]    For example, the housing may have different shapes, dimensions and/or proportions. The motor may be of different types, constructions and shapes. The assembly sequences may be changed or modified. The type of blower may also be changed. 
         [0072]    Therefore, while several preferred embodiments of the improved motorized blower assembly have been shown and described, and several modifications thereof discussed, persons skilled in this art will readily appreciate that various additional changes and modifications may be made without departing from the spirit of the invention, as defined and differentiated by the following claims.