Abstract:
A rotor for a brushless motor is resistant to degradation in alternative fuels and has desirable magnetic properties. A stator for a brushless DC motor includes coils wound both clockwise and counterclockwise around teeth of a back iron. Pairs of the coils are electrically connected in parallel.

Description:
BACKGROUND 
       [0001]    1. Field of the Invention 
         [0002]    The invention relates to brushless motor systems for vehicle fuel pumps. 
         [0003]    2. Discussion 
         [0004]    In a conventional DC motor, stationary brushes contact a set of electrical terminals on a rotating commutator. This contact forms an electrical circuit between a DC electrical source and armature coil-windings. The brushes and commutator form a set of electrical switches, each firing in sequence. Electrical power flows through the armature coil closest to the stator. 
         [0005]    Conventional fuel pumps for E-85 fuel, i.e., a mixture of up to 85% fuel ethanol and gasoline by volume, include brushed DC motors. Brushes of these motors are susceptible to electrochemical deposition of ions when operating in E-85 fuel. This electrochemical deposition increases the resistance of the motor, which may slow the armature speed, resulting in a reduction of the flow rate of the pump. 
         [0006]    A brushless DC motor is an AC synchronous electric motor. Permanent magnets of a rotor rotate relative to a wound stator. An electronic controller distributes power via a solid-state circuit. As power passes through the windings, the induced magnetic field in the windings reacts with the field in the rotor to create mechanical rotation. This mechanical rotation is harnessed via an impeller and pumping chamber in a fuel pump to create desired hydraulic pressure and flow. 
         [0007]    Conventional neodymium compression bonded ring magnets used in brushless DC motors soften and come apart when submerged in E-85 fuel. This may result in a locked rotor condition of the motor. 
         [0008]    Slot fill is a measure of the percentage of open space of a cross section of a lamination which is filled with copper windings. Conventional winding techniques require thicker wires to achieve desired stator resistance. These thicker wires limit achievable slot fill because the wires bow out from the lamination during winding. 
       SUMMARY 
       [0009]    An automotive fuel pump includes a motor. The motor includes a magnet. The magnet is resistant to material degradation when exposed to alternative fuels. The magnet also exhibits desirable magnetic properties. 
         [0010]    While exemplary embodiments in accordance with the invention are illustrated and disclosed, such disclosure should not be construed to limit the claims. It is anticipated that various modifications and alternative designs may be made without departing from the scope of the invention. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is an exploded perspective view of an exemplary brushless DC electric motor. 
           [0012]      FIG. 2  is an exemplary plot of crush strength versus soak time for a high functionality epoxy resin binder. 
           [0013]      FIG. 3  is a perspective view of a portion of the back iron and end cap of  FIG. 1 . 
           [0014]      FIG. 4  is an enlarged perspective view, in cross-section, of the back iron and end cap of  FIG. 3  taken along line  4 - 4  of  FIG. 3 . 
           [0015]      FIG. 5  is a plan view, in cross-section, of the stator of  FIG. 1  taken along line  5 - 5  of  FIG. 1 . 
           [0016]      FIG. 6  is a schematic representation of the windings of  FIG. 1 . 
           [0017]      FIG. 7  is an exemplary plot of efficiency versus torque for the motor of  FIG. 1 . 
           [0018]      FIG. 8  is an exemplary plot of speed and current versus torque for the motor of  FIG. 1 . 
           [0019]      FIG. 9  is an exploded perspective view of the adaptor ring and terminals of  FIG. 1 . 
           [0020]      FIG. 10  is a side view, in cross-section, of a portion of the stator of  FIG. 1  taken along line  10 - 10  of  FIG. 1 . 
           [0021]      FIG. 11  is a schematic representation of windings of a leg of an exemplary stator. 
           [0022]      FIG. 12  is another schematic representation of windings of a leg of an exemplary stator. 
           [0023]      FIG. 13  is a flow chart of a method of forming a ring magnet for a rotor of a brushless motor. 
           [0024]      FIG. 14  is a flow chart of a method for manufacturing a stator having a plurality of teeth. 
       
    
    
     DETAILED DESCRIPTION 
       [0025]      FIG. 1  is an exploded perspective view of an exemplary brushless electric motor  8 . The motor  8  includes a rotor  10  and a stator  12 . The rotor  10  rotates relative to the stator  12  to convert electrical power to mechanical power. 
         [0026]    The rotor  10  includes a shaft  14 , core  16  and ring magnet  18 . In the example of  FIG. 1 , the shaft  14  is made of stainless steel and the core  16  is made from powered iron. The ring magnet  18  is made from a magnetic powder, preferably a rare-earth magnet powder, compression bonded with a high functionality thermoset resin formulation utilized as a binder. As an example, neodymium-iron-boride may be compression bonded with an epoxy novalac resin formulation. As another example, neodymium-iron-boride may be compression bonded with a phenol-formaldehyde resin formulation. Other configurations and materials may also be used. The ring magnet  18  of  FIG. 1  has a residual flux density, Br, in the range of 0.68-0.72 Tesla. Residual flux densities may range from 0.59 to above 0.72 Tesla. 
         [0027]    Functionality defines the number of reactive sites available for formation of chemical bonds (or cross-links) between, for example, the epoxy resin molecules during the curing or thermosetting process. The formation of a three dimensional chemical structure by chemical cross-linking imparts the physical, chemical, and mechanical properties to the cured resin formulation. The higher cross-link densities provided by high functionality thermoset resins, such as epoxy resins, typically provide greater chemical resistance, higher mechanical stiffness, and higher thermal stability in the cured resin formulation. 
         [0028]    The functionality of an epoxy resin is typically reported as epoxide equivalent weight (EEW) which is defined as the number of grams of material containing one gram equivalent of reactive epoxide group. Resins with smaller values for EEW contain higher epoxide levels and are of higher functionality. Individual high functionality resins typically possess an EEW of less than 200. High functionality, as used herein, refers to an EEW of less than 200. 
         [0029]    Unlike conventional rotors coated with organic, inorganic or metallic coatings to protect them from corrosion, the rotor  10  is uncoated. Compression bonding the magnetic powder with the thermoset resin effectively surrounds the particles of the magnetic powder and protects them from corrosion due to exposure to aggressive fuels, such as E-85 ethanol. 
         [0030]      FIG. 2  is an exemplary plot of material crush strength versus soak time for the high functionality thermoset resin of the ring magnet  18 . The retained material crush strength of the high functionality thermoset resin of the ring magnet  18 , i.e., the material crush strength after 1,500 hours of soak time in E-85 ethanol at 60 degrees Celsius, is about 95%. In performing this testing of the retained material crush strength, a compression tester applies a compressive load to a 14 Millimeter×15 Millimeter×4 Millimeter sample. The compressive load is increased until the top and bottom of the tester heads measurably displace relative to one another, i.e., until the sample crushes. This process is repeated three times. Further samples are soaked in E-85 ethanol at 60 degrees Celsius. Every 500 hours, samples are removed and tested as described above. Initially, the high functionality thermoset epoxy resin of the ring magnet  18  crushed at about 80,000 Newtons. After 1,500 hours, the high functionality thermoset epoxy resin of the ring magnet  18  crushed at about 76,000 Newtons. 
         [0031]    Referring to  FIG. 1 , the stator  12  includes a back iron  20 , end caps  22 , coils  24   a - 24   f , adaptor ring  26 , and terminals  28   a - 28   c.    
         [0032]      FIG. 3  is a perspective view of a portion of the back iron  20  and end cap  22 . The back iron  20  includes teeth  30 . Coils  24   a - 24   f  (not shown) are formed around teeth  30 . 
         [0033]      FIG. 4  is an enlarged perspective view, in cross-section, of the back iron  20  and end cap  22  taken along line  4 - 4  of  FIG. 3 . The back iron  20  of  FIG. 4  is made from a series of stamped sections bonded together via interlock lamination. The end cap  22  of  FIG. 4  is insert molded with the back iron  20  using, for example, a high temperature nylon plastic. In alternative embodiments, the back iron  20  and end cap  22  may be manufactured in any desired fashion. For example, the back iron  20  may be cast in several pieces and assembled. Each of the teeth  30  include an anti-cogging notch  32  to reduce the tendency of the rotor  10  to cog while rotating relative to the stator  12 . 
         [0034]      FIG. 5  is a plan view, in cross-section, of the motor  8  taken along line  5 - 5  of  FIG. 1 . Each of the coils  24   a - 24   f  is wrapped around a respective tooth  30  of the back iron  20 . In the embodiment of  FIG. 5 , some of the coils  24   a - 24   f  are wrapped clockwise (as indicated by arrow looking radially outward from the center of the motor  8 ), while other of the coils  24   a - 24   f  are wrapped counterclockwise (again, as indicated by arrow looking radially outward from the center of the motor  8 ). 
         [0035]      FIG. 6  is a schematic representation of the coils  24   a - 24   f . The coils  24   a - 24   f  are shown in a wye configuration. Delta configurations are also possible. Coils  24   a  and  24   d  are electrically connected in parallel and electrically connected with the terminal  28   b . Coils  24   b  and  24   e  are electrically connected in parallel and electrically connected with the terminal  28   c . Coils  24   c  and  24   f  are electrically connected in parallel and electrically connected with the terminal  28   a . Coils  24   a ,  24   b  and  24   f  are wound clockwise. Coils  24   c ,  24   d  and  24   e  are wound counterclockwise. This electrical configuration permits the use of higher gauge wires and an increased number of windings to achieve desired motor performance. As a result, this electrical configuration allows for increased slot fill. 
         [0036]    In the embodiment of  FIG. 6 , coils  24   a  and  24   d  are formed from a continuous wire, coils  24   b  and  24   e  are formed from another continuous wire, and coils  24   c  and  24   f  are formed from yet another continuous wire. This continuous wire configuration reduces the number of free ends  35   a - 35   f  associated with the coils  24   a - 24   f . Therefore, relatively few connections are necessary. In alternative embodiments, the coils  24   a - 24   f  may be formed from individual wires. This individual wire configuration would increase, e.g., double, the number of free ends associated with the coils  24   a - 24   f.    
         [0037]    Each of the wires has a respective interpole section  33   a - 33   c . Coils  24   a - 24   f  are electrically connected at crimp  34  (see  FIG. 1 ). 
         [0038]      FIG. 7  is an exemplary plot of efficiency versus torque, at  12  volts, for the motor  8 . In the example of  FIG. 7 , the stator  12  has 22 turns at  20 . 5  American Wire Gauge. In alternative embodiments, other turns and gauges may be used, e.g., 20 turns at  20  American Wire Gauge, 30 turns at  22  American Wire Gauge, etc. The plot of  FIG. 7  shows efficiencies between 60 and 75 percent for a range of torques from 0.02 to 0.08 Newton-Meters. Efficiency peaks around 0.06 Newton-Meters. 
         [0039]      FIG. 8  is an exemplary plot of speed and current versus torque, at 12 Volts, for the motor  8 . In the example of  FIG. 8 , the stator  12  has 20 turns at  20  American Wire Gauge. In alternative embodiments, other turns and gauges may be used, e.g., 22 turns at  20 . 5  American Wire Gauge. The plot of  FIG. 8  shows speeds between 11,000 and 9,000 revolutions per minute and currents between 3 and 9 Amps for a range of torques from 0.02 to 0.08 Newton-Meters. 
         [0040]      FIG. 9  is an exploded perspective view of the adaptor ring  26  and terminals  28   a - 28   c . Terminals  28   a - 28   c  set within a tower portion  36  of the adaptor ring  26 . Terminals  28   a - 28   c  each include a respective slot portion  38   a - 38   c  which receives and retains the free ends  35   a - 35   f  ( FIG. 6 ) of the coils  24   a - 24   f.    
         [0041]      FIG. 10  is a side view, in cross-section, of a portion of the stator  12  taken along line  10 - 10  of  FIG. 1 . Free ends  35   a  and  35   d  associated with coils  24   a  and  24   d  electrically connect with the terminal  28   b , preferably through a solderless connection using an insulation-displacement terminal  28   b . Similar connections are made for free ends  35   b  and  35   e  and the terminal  28   c  and free ends  35   c  and  35   f  and the terminal  28   a.    
         [0042]      FIG. 11  is a schematic representation of coils  124   a - 124   n  of a leg of a stator. Numbered elements differing by 100 have similar, although not necessarily identical, descriptions. This leg may be used in a wye or delta winding pattern. Coils  124   a - 124   n  may be formed from a continuous wire. At least one of the coils may have a wind direction opposite the others. For example, for 3 coils, coils  124   a  and  124   c  may be wound clockwise. The coil  124   b  may be wound counterclockwise. Other winding configurations are also possible. Some or all of the coils  124   a - 124   n  may be formed from individual wires. Some or all of the coils  124   a - 124   n  may have the same wind direction. For example, for 3 coils, the coils  124   a - 124   c  may be wound counterclockwise. Other winding configurations are also possible. 
         [0043]      FIG. 12  is a schematic representation of coils  224   a - 224   n  of a leg of a stator. This leg may be used in a wye or delta winding pattern. Coils  224   a - 224   n  may be formed from a continuous wire. At least one of the coils may have a wind direction opposite the others. For example, for 4 coils, coils  224   a  and  224   c  may be wound clockwise. Coils  224   b  and  224   d  may be wound counterclockwise. Other winding configurations are also possible. Some of the coils  224   a - 224   n  may be formed from individual wires. Some or all of the coils  224   a - 224   n  may have the same wind direction. For example, for 4 coils, coils  224   a  and  224   c  may be wound counterclockwise. Coils  224   b  and  224   d  may be wound clockwise. Other winding configurations are also possible. 
         [0044]      FIG. 13  is a flow chart of a method of forming a ring magnet for a rotor of a brushless motor. At  40 , a high functionality thermoset binder, e.g., epoxy resin, is provided. At  42 , the high functionality thermoset binder is mixed with a rare earth magnet powder, e.g., a neodymium-iron-boride powder. At  44 , the mixture is compression bonded to form a ring magnet for a brushless motor. 
         [0045]      FIG. 14  is a flow chart of a method for manufacturing a stator having a plurality of teeth. At  46 , a first wire is wound clockwise around a first tooth. At  48 , the first wire is wound counterclockwise around a second tooth. At  50 , a second wire is wound clockwise around a third tooth. At  52 , the second wire is wound counterclockwise around a fourth tooth. At  54 , a third wire is wound clockwise around a fifth tooth. At  56 , the third wire is wound counterclockwise around a sixth tooth. At  58 , the windings are electrically connected in parallel at the overlap of interpole sections of the first, second and third wires. 
         [0046]    While embodiments of the invention have been illustrated and described, it is not intended that these embodiments illustrate and describe all possible forms of the invention. Rather, the words used in the specification are words of description rather than limitation, and it is understood that various changes may be made without departing from the spirit and scope of the invention.