Abstract:
A BLDC motor assembly and method for manufacturing same is disclosed. The motor has a housing, a shaft supported for rotation within the housing, a stator disposed within the housing for generating an electro-magnetic field, a rotor operatively coupled to the shaft and disposed for powered rotation within the stator in response to the electro-magnetic field, at least one temperature sensitive electronic device (TSED) disposed within the housing and electrically connected to the stator for controlling or measuring an aspect of the electro-magnetic field, and a fuel resistant and electrically insulated polymeric material encapsulating the TSED so that the TSED is protected from adverse temperature and chemical agents without the need for a separate internal container or a pre-potting operating. The TSED, which may be carried on a printed circuit board within the housing, is thus overmolded with polymeric material so that the polymeric material fills, or substantially fills, a space within the housing. Not only is the cost and weight associated with a prior art dedicated container for the electronics eliminated, but this invention allows greater design freedom in the location or placement of the various electrical devices within the housing for better motor efficiency and/or protection.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     The present application claims priority to U.S. provisional application entitled BLDC Motor and Pump Assembly with Encapsulated Circuit Board having Ser. No. 60/681,795 and filed on May 17, 2005. 
    
    
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The invention relates generally to a brushless direct current motor, and more particularly to a motor coupled to a fluid pump having electronic components and circuitry encapsulated in a polymeric material. 
     2. Related Art 
     With the introduction of electronic control systems for electric motors, the industry objectives of long life, efficiency, reliability and low EM interference have become achievable. This is in part due to the advent of brushless direct current (BLDC) motor technology. Not only are the problems once associated with the prior art permanent magnet direct current motors overcome, but advances in MOS-FET devices have led to further performance advantages. While prior art BLDC motor designs have achieved their intended purpose, problems still exist. For example, the addition of control circuitry within the motor has increased design and manufacturing complexity of the motor. More specifically, the control circuitry must be appropriately packaged to protect it from the fluid in which the motor is submerged. If the fluid contacts the control circuitry corrosion and malfunctioning of the circuit will occur. The control circuitry includes temperature sensitive components that may be damaged by excessive heat applied during either the manufacturing of the motor or operation of same. Furthermore, the control circuitry is susceptible to radiated emissions from surrounding electrical devices. 
     Therefore, a need exists to further reduce manufacturing costs of BLDC motors, as well as to protect the control circuitry from the surrounding fluid and radiated emissions. Further, the motor should be configured to protect temperature sensitive electronic devices from malfunction or damage due to overheating, both during the manufacturing process and during subsequent operation of the motor. 
     SUMMARY OF THE INVENTION AND ADVANTAGES 
     The subject invention provides further advances in the BLDC motor and pump assembly technology. According to one aspect of the invention, a BLDC motor assembly comprises a housing, a shaft supported for rotation within the housing, a stator disposed at least partially within the housing for generating an electro-magnetic field, a rotor operatively coupled to the shaft and disposed for powered rotation within the stator in response to the electro-magnetic field, at least one temperature sensitive electronic device (TSED) disposed within the housing and electrically connected to windings of the stator for controlling or measuring an aspect of the electro-magnetic field, and a fuel resistant and electrically insulated polymeric material introduced into the housing and in contact therewith while encapsulating the TSED so that the TSED is protected from adverse temperature and chemical agents without the need for a separate internal container or a pre-potting operating. The TSED, which may be carried on a printed circuit board within the housing, is thus overmolded with polymeric material so that the polymeric material fills, or substantially fills, a space within the housing. Not only is the cost and weight associated with a prior art dedicated container for the electronics eliminated, but this invention allows greater design freedom in the location or placement of the various electrical devices within the housing for better motor efficiency and/or protection. For example, a BLDC motor may typically include a Hall-effect sensor to monitor the position of the rotor. According to the invention, which obviates the need for a separate internal container for the electronics, the Hall-effect sensors can be optimally positioned to provide better responsiveness and in some cases even to eliminate the need for additional electromagnets mounted on the rotor. 
     According to another aspect of the invention, a BLDC motor assembly comprises a housing, a shaft supported for rotation within the housing, a stator disposed at least partially within the housing for generating an electro-magnetic field, a rotor operatively coupled to the shaft and disposed for powered rotation within the stator in response to the electro-magnetic field, at least one TSED disposed within the housing and electrically connected to windings of the stator for controlling an aspect of the electro-magnetic field, the TSED having a critical temperature above which device malfunction is possible, a fuel-resistant and electrically insulating polymeric material disposed in the housing and in contact therewith while encapsulating and in direct contact with the TSED, the polymeric material being introduced into the housing in a generally fluidic form at a temperature above the critical temperature of the TSED, and a production heat sink feature located proximate the TSED to rapidly draw heat away from the TSED as the polymeric material is introduced into the housing. The production heat sink feature can be either a permanent part of the motor and pump assembly which is capable of rapidly drawing heat away from the TSED, for example the housing, or the production heat sink feature can be a removable molding core or sacrificial heat absorbing element like polystyrene. In the case of a removable molding core, further enhanced cooling characteristics can be achieved if the molding core is chilled. Thus, the TSED is protected against damage during the encapsulation process by the strategic and intentional use of a production heat sink feature. 
     According to yet another aspect of the invention, a BLDC motor assembly comprises a housing, a shaft supported for rotation within the housing, a stator disposed at least partially within the housing for generating an electro-magnetic field, a rotor operatively coupled to the shaft and disposed for powered rotation within the stator in response to the electromagnetic field, at least one TSED disposed within the housing and electrically connected to windings of the stator for controlling an aspect of the electro-magnetic field, the TSED having a critical temperature above which device malfunction is possible; a fuel-resistant and electrically insulating polymeric material disposed in the housing and in contact therewith while encapsulating and in direct contact with the TSED, and a fluid flow passage extending through the housing and routing adjacent the TSED for convectively removing heat from the encapsulated TSED by the movement of fluid at a temperature below the critical temperature to prevent device malfunction. This aspect of the invention, which can be conveniently realized when incorporated with a fluid pumping device, such as a fuel pump, takes advantage of the natural convective effects of a moving stream of cool liquid to pull heat away from the TSED during operation, thereby helping to maintain its operating temperature below the critical temperature. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       These and other features and advantages of the present invention will become more readily appreciated as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings, wherein: 
         FIG. 1  is a partially exploded view showing a BLDC motor and an exemplary vane style pumping element; 
         FIG. 2  is a perspective view of the BLDC motor assembly highlighting the upper housing portion; 
         FIG. 3  is a perspective view of the BLDC motor assembly highlighting the lower housing portion; 
         FIGS. 4A and 4B  illustrate a vertical cross-section through the BLDC motor assembly taken in a plane intersecting the motor terminals; 
         FIGS. 5A and 5B  illustrate vertical cross-sections of the BLDC motor assembly taken in a plane off-set from that used in  FIGS. 4A and 4B ; 
         FIG. 6  is a partially sectioned view showing the BLDC motor assembly according to the subject invention; 
         FIG. 7  is an end view of the motor control circuit board with exemplary production molding cores super-imposed; 
         FIG. 8  is a perspective view of the upper housing after encapsulation of the motor control circuit; 
         FIG. 9  is a partially sectioned perspective view of the upper housing after encapsulation of the motor control circuit; 
         FIG. 10  is a view showing a MOS-FET device from two perspectives; and 
         FIG. 11  is a flowchart illustrating a method for manufacturing the fluid pump, in accordance with an embodiment of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to the Figures, wherein like numerals indicate like or corresponding parts throughout the several views, a brushless direct current (BLDC) motor assembly according to an embodiment of the present invention is generally shown at  10 . 
     In  FIG. 1 , the motor assembly  10  is illustrated in the application of a fuel pump. A fluid pump, generally shown at  12 , is coupled to the lower end of the motor assembly  10 . However, any other driven component or feature can of course be coupled to the motor assembly  10  instead of a fuel pump. The fluid pump  12  is shown here of the vane style, however, other pump types, such as other positive displacement styles, impeller styles, and the like, may be used with equal effect. 
     In  FIG. 1 , the fluid pump  12  is shown including an outlet port plate  14  which adjoins to the lower end of the motor assembly  10 . A cam ring  16  is held against the outlet port plate  14  and surrounds a rotor  18  and an away of captured rollers  20 . The rotor  18  is forcibly rotated by the motor assembly  10  and thus drives the rollers  20  in an orbit around the inner circumference of the cam ring  16 . Movement of the rollers  20  relative to pockets in the rotor  18  and cam ring  16  displaces a fluid, such as in this example fuel for an internal combustion engine. An inlet port plate  22  encloses the pumping chamber and a filter  24  screens the fluid as it is drawn in through an inlet port in the inlet port plate  22 . Thus, fluid drawn in through the filter  24  and inlet port plate  22  are forcibly discharged through an opening  13  in the outlet port plate  14  which directs the pumped media into the motor assembly  10  where it acts as a cooling medium before it is discharged through an outlet  15  in the upper portion of the motor assembly  10 . 
       FIGS. 2 and 3  show various perspective views of the motor assembly  10  and illustrate in particular the housing feature which is composed, preferably, of an upper housing portion  26  and a lower housing portion  28 . Stack laminations comprising part of a stator  30  are captured between the upper  26  and lower  28  housing portions. A shaft  32  is supported for rotation within the housing with an end portion thereof extending from the lower housing portion  28  in  FIG. 3 . This extending portion of the shaft  32  is coupled to the pump rotor  18  through an appropriate coupling device  34 . The opposite end of the shaft  32  is shown protruding from the upper housing portion  26  in  FIG. 2 . Bearings support the shaft  32 . One such bearing  17  is shown in the upper  26  housing portion in  FIG. 9 . The other bearing  19  may be located either in the lower housing portion  28  or in the pump assembly  12 , such as between the cam ring  16  and the inlet port plate  22 . Also protruding from the upper housing portion  26  are shown electrical terminals  36  for energizing the motor assembly  10  and transmitting the necessary control and feedback signals. If the terminals  36  do not align with mating connections, jumper straps  38  may be employed. 
     The stator  30  is better shown in  FIGS. 4A and 4B  as it is trapped between the upper  26  and lower  28  housing portions. The stator  30  includes the customary plate laminations and windings, and may be further powder coated for electrical insulation protection from the wires of the windings. The terminals  36  are electrically connected to the stator  30 . The terminals  36  are also mounted in, and electrically connected to, a circuit board  40 . When energized, the stator  30  creates an electro-magnetic field in the manner typical of direct current motors. 
     A rotor  42  is operatively coupled to the shaft  32  and disposed for powered rotation within the stator  30  in response to the electro-magnetic field generated by the stator  30 . The rotor  42  may be fabricated according to any of the known techniques, including a core which is subsequently overmolded or otherwise affixed with magnetic segments  44 . In the embodiment shown, four such magnet segments  44  are arrayed in equal arcuate increments about the exterior of the rotor  42 . These magnet segments  44  may be of the so-called neo-magnet type and can be charged either before or after bonding to the underlying rotor core  42 . 
     With continuing reference to  FIGS. 4   a  and  4   b , terminal seals  37  are shown in cross-section. Terminal seals  37  are disposed in an annular opening  39  in upper housing  26 . The terminal seals  37  are annular in shape and are made of a polymeric material. For example, seals  37  may be made of a material known as Hytrel, manufactured by Dupont of Delaware and sold under the product number 7246, or any comparable material. Further, seals  37  have an outside diameter dimensioned to have an interference fit with the inside diameter of annular opening  39  and an inside diameter dimensioned to have interference fit with the outside diameter of terminals  36 . As such, seals  37  prevent infiltration of fluid into opening  39  further enhancing the durability and reliability of motor assembly  10 . 
     Referring now to  FIGS. 5A ,  5 B and  6 , the circuit board  40  is shown supporting a plurality of electrical circuits, components and devices. Typically, these electronic devices will include one or more Hall-effect sensors responsive to the magnet segments  44  (or secondary magnets), and one or more MOS-FETS  46  associated with each of the Hall-effect sensors. Further, circuit board  40  includes a plurality of capacitors  45  for suppressing conducted emissions. Capacitors  45  are operatively connected to circuit board  40  and associated circuitry to filter out any conducted emissions. Advantageously, the inclusion of capacitors  45  on circuit board  40  eliminates the need for external filtration devices in the fluid pump wiring and/or connectors. The Hall-effect sensors (not shown in the drawings) are preferably located on the underside of the circuit board  40 , whereas the MOS-FETS  46  extend upwardly from the circuit board  40 . The MOS-FETS  46  may be temperature sensitive electronic devices (TSED) having a critical device junction temperature of approximately 150° C. If at any time the MOS-FETS  46  are subjected to temperatures in excess of the critical temperature, device damage and subsequent malfunction is possible. Therefore, it is important to protect not only the circuit board  40  and all of its electronics, but also to guard against overheating of the MOS-FETS  46  (or other TSED) during the fabrication process and during normal operation of the motor assembly  10 . 
     During the fabrication process, the circuit board  40  with all its pre-joined components, including the Hall-effect sensors and the MOS-FETS  46 , are deposited into a mold cavity, which is then filled with a fuel-resistant and electrically insulating polymeric material  47 , such as a resin. Preferably, this polymeric material  47  is injection molded under pressure and in a fluidic condition, to forcibly drive the polymeric material  47  into all interstitial spaces of the mold cavity and minimize the potential for air inclusions. Thus, the fuel-resistant and electrically insulating polymeric material  47  fully encapsulates and is in direct contact with the electrical components and the circuit board  40 . In this manner, the full complement of electronics are protected from adverse temperature swings, abrasions, vibrations, and chemical agents without the need for a separate internal container or a pre-potting operation as taught by the prior art. Furthermore, this in situ overmolding process allows greater design freedom to locate the various electrical components, including the Hall-effect sensors, in more strategic locations to improve performance and heat transfer, and to other advantage. For example, the prior art BLDC motor assemblies which enclosed the electrical components in a dedicated container within the housing may require additional magnets, i.e., in addition to the magnet segments  44  on the rotor  42 , to properly influence the Hall-effect sensors. Further, excess weight and unnecessary preassembly operations are avoided. As shown in  FIGS. 1 ,  2 ,  4 A,  4 B,  5 A,  5 B, and  6 - 9 , after final assembly, the polymeric body  47  encircles both a portion of the rotor  42  axially spaced from said plurality of magnets  44  and a portion of the stator  30 . Also, as shown in  FIGS. 1 ,  2 ,  4 A,  4 B,  5 A,  5 B, and  6 - 9 , the bearing  17  that supports a second end of the rotor  42  is supported by the polymeric body  47 . 
     A method  100  for forming upper housing  26  and overmolding circuit board  40  is illustrated in  FIG. 11 , in accordance with an embodiment of the present invention. In an initial step, circuit board  40  is placed in an empty mold cavity, as represented by block  102 . A fixture holds the circuit board  40  in a predetermined location within the mold. For example, the fixture clamps onto the terminals that are attached to circuit board  40 . In order to protect the TSEDs attached to the circuit board from exposure to excessive heat of the overmolding process production heat sinks, as described below, are held in place adjacent the TSEDs, as represented by block  104 . The production heat sinks may be actively cooled by passing a fluid over the heat sink, as represented by block  106 . At block  108 , a polymeric material is injected into the mold to form upper housing  26  and encapsulate circuit board  40  in the polymeric material  47 . The production heat sinks are then removed from the upper housing  26 , as represented by block  110 . The removal of the production heat sinks, in an embodiment of the present invention, form cavities  50  and passageways  54  shown in  FIG. 8 . Upper housing  26  with encapsulated circuit board  40  may also be formed directly on the stator  30  in a single operation. In an alternative method, the circuit board  40  with all its pre-joined components, including the Hall-effect sensors and the MOS-FETS  46 , are deposited into an empty shell upper housing, which is then filled with the fuel-resistant and electrically insulating polymeric material  47 , such as a resin. 
     Referring again to the temperature sensitivity issue inherent in some of the electrical components, such as for example with a MOS-FET  46 , various strategies can be employed to protect these temperature sensitive electrical devices (TSED). This is particularly important when the fuel resistant electrically insulating polymeric material  47  is introduced into the mold cavity or an empty shell housing at a temperature above the critical temperature of the TSED. For example, if the overmolding process requires the polymeric material  47  to be heated above 150° C., which is an exemplary critical temperature for the MOS-FET  46 , it is necessary to provide a production heat sink feature located proximate to the TSED that will rapidly draw heat away from the TSED as the hot polymeric material  47  is introduced into the housing  26 . Thus, the production heat sink feature is used during the production, or fabrication, process to prevent overheating damage to the TSED. 
     The production heat sink feature can take many forms. For example, if the upper housing portion  26  is made from a material having rapid heat transfer qualities such as is common with many metals, the TSEDs could be located in physical contact with or nearly proximate to the housing so that heat is pulled away and the temperature of the polymeric material  47  quickly reduced to the point of solidification and below the critical temperature. Another alternative for the production heat sink feature can take the form of a removable molding core.  FIG. 7  illustrates the possible location of several removable molding cores  48  disposed between the MOS-FETS  46  and the housing  26 . When removed, the molding cores  48  result in cavities  50  as shown in  FIG. 8  whose open quality will promote good heat transfer during subsequent operation. Alternatively, and referring again to  FIG. 7 , the removable molding core can be disposed radially inwardly from the MOS-FETS  46  such as represented by the removable core  52 . After the overmolding process and removal of the core  52 , fluid flow passages  54  remain as features in the upper housing portion  26 . As shown in  FIGS. 1 ,  2 ,  4 A,  4 W  5 A,  5 W and  6 - 9 , the passageway  54  is substantially axially centered with respect to said polymeric body  47 . As shown in  FIGS. 1 ,  2 ,  5 A,  5 B, and  6 - 9 , the passageway  54  substantially encircles the bearing  17 . As shown in  FIGS. 1 ,  2 ,  7  and  8 , at least a portion of the passageway  54  defines a multifid cross-section. As best shown in  FIGS. 7 and 8 , at the outlet  15 , the cross-section of the passageway  54  defines lobes  57 ,  59 ,  61 ,  63 . The lobes  57 ,  59 ,  61 ,  63  extend from a center axis of the passageway toward the sensors  46 . The plurality of cavities  50  are radially aligned with lobes  57 ,  59 ,  61 ,  63  of the multifid cross-section. Thus, the surface area for heat transfer between the polymeric body  47  and the fuel passing through the motor assembly  10  is enhanced. The removable cores  48 ,  52  can be forcibly cooled, such as with circulating water or other chilling operation, to further enhance the heat removing characteristics of the production heat sink feature. Of course, other variations and methods of removing heat from the TSED during the overmolding operation are entirely possible and within the scope of this invention. 
     While the foregoing description has been concerned primarily with the protection of the TSED during the production process, it is also important to protect the TSED from overheating during subsequent use of the motor assembly  10 . The subject invention advantageously addresses this problem by routing the fluid flow passage  54  through the housing  26  adjacent the TSED for convectively removing heat from the encapsulated TSED by the movement of fluid through the flow passage  54  at a temperature below the critical temperature of the TSED. Thus, by taking advantage of the movement of a fluid or gas through the flow passage  54  which is at a temperature lower than the critical temperature of the TSED, heat can be transferred by convection into the flowing fluid stream to help maintain a safe operating temperature for the TSED. As shown in the examples, wherein the MOS-FETS  46  have been, for purposes of discussion only, designated as the TSED components, they have been strategically located adjacent to the flow passage  54  to take advantage of the convective cooling phenomenon. 
     To further enhance these operational heat sinking characteristics, the TSED, i.e., the MOS-FET  46 , is provided with a cooling plate  56  which is either manufactured as part of the FET or affixed in a pre-assembly operation. The cooling plate  56 , which is perhaps best shown in  FIG. 10 , can be a metal or other heat conductive material adjoined to the MOS-FET  46  so as to draw heat away through conduction. One side of each cooling plate  56  is thus exposed to the fluid flowing through the passage  54  to enhance the cooling capabilities. Thus, as shown in  FIGS. 5A ,  5 B, and  8 - 10 , the cooling plate  56  physically contacts the sensor  46  and has a surface  55  open to the passageway  54 . The cooling plates  56  may also be particularly advantageous during the overmolding operation, wherein the removable molding cores  48  are in touching contact or close proximity to the cooling plates  56  to help maintain the TSED below its critical temperature. Moreover, the cooling plates  56  may have a variety of configurations to enhance heat transfer. For example, cooling plates  56  may include one or more cooling fins  58  which extend from a surface of the cooling plate into and towards a center axis of the passage  54  to increase the surface area of the cooling plate to be cooled by the fluid flowing through passage  54 . 
     The invention has been described in an illustrative manner, and it is to be understood that the terminology which has been used is intended to be in the nature of words of description rather than of limitation. Obviously, many modifications and variations of the present invention are possible in light of the above teachings. It is, therefore, to be understood that within the scope of the appended claims, the invention may be practiced otherwise than as specifically described. The invention is defined by the claims.