Abstract:
A rotor assembly comprising: a rotor having an outer circumference and a longitudinal axis; and a plurality of magnet members secured to said outer circumference, each of said plurality of magnet members having a degree of curvature about said longitudinal axis, wherein a sum of said degrees of curvature is greater than 355.5 degrees.

Description:
BACKGROUND OF INVENTION  
         [0001]    This invention relates generally to permanent magnet motors and more particularly, to magnet arcs for magnet motors and a method of assembling the magnet arc to a rotor.  
           [0002]    Permanent magnet motors, also known as electronically commutated motors (ECM&#39;s), are used, or have potential for use, in a wide variety of applications, such as alternators, electronic throttle controls, electric power steering, fuel pumps, heater and air conditioner blower motors, and engine cooling fans. Typical permanent magnet motors have a plurality of arcuate-shaped magnets affixed about the core or circumference of a rotor. The rotor is positioned inside a closely-fitting housing which carries electromagnets for propelling the rotor shaft.  
           [0003]    These magnet arcs are affixed to the rotor core using an adhesive. Typically, three such magnet arcs are used, which have an inner curvature that circumscribes the outer circumference of the rotor core. It is desired to have a tight fit or bond between the inner face of the magnet arc and the rotor core to provide a durable and efficient motor. These magnet arcs have straight sides that are parallel to the longitudinal axis of the rotor. Prior magnet arcs have manufacturing tolerances that must be accounted for in assembling the arcs to the rotor core. To ensure that a tight fit between the inner face of the magnet arc and the outer circumference of the rotor core will be achieved, gaps occur between the magnet arcs. These gaps have a negative impact on the operation and performance of the permanent magnet motor, including resulting anomalies in the flux. Additionally, a gap formed between the magnet arcs, or a skewed line between the arcs, which passes by the teeth of the stator provides a blade pass component to the noise and torque of the motor. In prior motors, the total combined degree of curvature of the magnet arcs is less than 360 degrees.  
           [0004]    For example, based upon an industry tolerance of +/−1 degree of curvature in the manufacture of magnet arcs, three magnet arcs of 118.5 degrees can be used in the assembly of the magnet motor. Nominally, there will be gaps between the magnet arcs of 1.5 degrees each. With the maximum positive tolerance occurring during manufacturing, there will be gaps of 0.5 degrees between each magnet arc but with the maximum negative tolerance occurring during manufacturing, there will be gaps of 2.5 degrees between each magnet arc. The typical method of assembly uses application of a radial force each of the magnet arcs and attempts to evenly distribute the gaps between the magnet arcs.  
           [0005]    Accordingly, there is a need for a magnet motor with magnet arcs that address one or more of the aforementioned drawbacks and of the prior art. In addition, there is a need for a method of assembly of a permanent magnet motor that minimizes the gaps between the magnet arcs that are affixed to the rotor core.  
         SUMMARY OF INVENTION  
         [0006]    In one aspect, a rotor assembly is provided which comprises a rotor having an outer circumference and a longitudinal axis, and a plurality of magnet members secured to the outer circumference. Each of the plurality of magnet members has a degree of curvature about the longitudinal axis. The sum of the degrees of curvature is greater than 355.5 degrees.  
           [0007]    In another aspect, a rotor assembly is provided which comprises a rotor having an outer wall with a circumference, and a magnet separated into a plurality of members that are secured to the outer wall and circumscribe the circumference. Each of the plurality of members have a first end and a second end that opposes the first end. Each of the first ends is disposed adjacent to one of the second ends. At least one of the first ends is misaligned with one of the second ends along the circumference.  
           [0008]    In another aspect, a rotor assembly is provided which comprises a rotor having a longitudinal axis and an outer wall with a circumference, and a plurality of magnet members secured to the outer wall about the circumference. Each of the magnet members has opposing sides and a center axis. The center axis is parallel to the longitudinal axis. At least two of the plurality of magnet members has the opposing sides nonparallel along the center axis.  
           [0009]    In another aspect, a rotor assembly for a magnetic motor is provided which comprises a rotor having a longitudinal axis and a circumferential wall, and a magnet secured about the circumferential wall and separated into a plurality of members along separation lines. Each of the plurality of members are arcuate and have a center axis parallel to the longitudinal axis. Each of the plurality of members abuts another of the plurality of members. At least one of the separation lines is nonparallel to one of the center axes.  
           [0010]    In another aspect, a magnetic motor is provided which comprises a stator having an inner wall, a rotor operably connected to the stator and having a longitudinal axis and an outer wall, and a plurality of magnet members secured to either the inner wall of the stator or the outer wall of the rotor. Each of the plurality of magnet members have side walls that oppose each other. The plurality of magnet members circumscribes either the inner wall of the stator or the outer wall of the rotor. The pairs of side walls abut against each other. At least one of the pairs of side walls are nonparallel to the longitudinal axis of the rotor.  
           [0011]    In another aspect, a method of assembling a rotor is provided which comprises the steps of forming a plurality of magnet members; positioning the plurality of magnet members about a circumference of the rotor to circumscribe the circumference with the plurality of magnet members having at least one gap therebetween; and applying an axial force to each of the plurality of magnet members. The axial force causes the plurality of magnet members to slide together until the gap is eliminated.  
           [0012]    The above-described and other features and advantages of the present disclosure will be appreciated and understood by those skilled in the art from the following detailed description, drawings, and appended claims. 
       
    
    
     BRIEF DESCRIPTION OF DRAWINGS  
       [0013]    [0013]FIG. 1 is a top view of a prior art rotor configuration;  
         [0014]    [0014]FIG. 2 is a front view of a prior art magnet arc of the rotor configuration of FIG. 1;  
         [0015]    [0015]FIG. 3 is an exploded perspective view of an exemplary embodiment of a magnet motor with rotor assembly;  
         [0016]    [0016]FIG. 4 is a top view of the rotor assembly of FIG. 3;  
         [0017]    [0017]FIG. 5 is a perspective view of a magnet arc of the rotor assembly of FIG. 3;  
         [0018]    [0018]FIG. 6 is a front view of the magnet arc of FIG. 5;  
         [0019]    [0019]FIG. 7 is a top view of the magnet arc of FIG. 5;  
         [0020]    [0020]FIG. 8 is front view of the rotor assembly of FIG. 3; and  
         [0021]    [0021]FIG. 9 is a top view of another embodiment of a magnet motor. 
     
    
     DETAILED DESCRIPTION  
       [0022]    Referring now to the drawings, and in particular to FIGS. 1 and 2, the rotor configuration of a (prior art) conventional permanent magnet motor is shown and generally referred to by reference numeral  100 . Rotor configuration  100  has a rotor shaft  110  having a rotor core  120  with an outer wall  125 . The rotor configuration  100  also has three magnet arcs  150  having parallel side walls  160 ,  165 . The three magnet arcs  150  are affixed to outer wall  125  of the rotor core  120  by adhesive or other known methods. The assembly of rotor configuration  100  provides a tight fit between an inner face  155  of the magnet arcs  150  and the outer wall  125  of the rotor core  120 . However, the assembly of rotor configuration  100  results in the formation of gaps G between the side walls  160 ,  165  of each of the magnet arcs due to the manufacturing tolerances of the magnet arcs. The conventional method of assembly applies radial force R to each of the magnet arcs  150  for a tight bond between the magnet arcs and the radial core  120 , as well as to attempt to evenly distribute the gaps G between the magnet arcs.  
         [0023]    Referring to FIGS. 3 and 4, an exemplary embodiment of a magnet motor with a rotor assembly generally referred to by reference numerals  200 ,  300 , respectively, is illustrated. Rotor assembly  300  is for use with permanent magnet motor  200  and is positioned inside a closely-fitting housing  210  having a stator (not shown) for propelling the rotor assembly.  
         [0024]    Rotor assembly  300  has a rotor shaft  310 , a rotor core  320 , and a permanent magnet  400 . Permanent magnet  400  is separated into a plurality of magnet members or arcs  410 ,  420 ,  430  and  440 . Rotor core  320  has an outer circumference or circumferential wall  325 .  
         [0025]    In this exemplary embodiment, magnet  400  is separated into four magnet arcs  410 ,  420 ,  430  and  440  but can be separated into any number of magnet arcs.  
         [0026]    Referring to FIGS. 3 through 7, magnet arc  410  (as well as magnet arcs  420 ,  430  and  440 ) has a first end wall  460 , a second end wall  465 , a first side wall  470 , a second side wall  475 , a curved inner face  480  and a curved outer face  485 . Preferably, first and second end walls  460 ,  465  are parallel to each other and of different lengths. The different lengths of first and second end walls  460 ,  465  provides for different degrees of curvature along the curved inner face  480 . First and second side walls  470 ,  475  are nonparallel to both the longitudinal axis of rotor assembly  300  and a center axis of magnet arc  410  such that the first and second side walls are tapered, sloped or angled inwardly in the direction of first end wall  460 . The angled side walls  470 ,  475 , along with first and second end walls  460 ,  465 , provide a trapezoidal shape to magnet arc  410 . Preferably, first and second side walls  470 ,  475  are equally inwardly angled or have equal slopes. First and second side walls  470 ,  475  are preferably of equal length to form an isosceles trapezoidal shape.  
         [0027]    The inner face  480  of magnet arc  410  has a radius of curvature that is approximately equal to the radius of curvature of the outer wall  325  of the rotor core  320  to allow for a tight fit between the magnet arc and the rotor core  320 . Magnet arcs  410 ,  420 ,  430  and  440  are affixed to outer wall  325  of the rotor core  320  by adhesive or other known methods, in alternating orientations. By alternating the orientations of magnet arcs  410 ,  420 ,  430  and  440  along outer wall  325 , each first side wall  470  will abut against a corresponding first side wall, and each second side wall  475  will abut against a corresponding second side wall  475 , to form a hollow cylindrical magnet  400  circumscribing the outer wall of rotor core  320 . As shown in FIG. 8, the cylindrical magnet  400  has separation lines  405  formed by the abutment of the pairs of first side walls  470  and the pairs of second side walls  475 . Separation lines  405  are nonparallel with both the longitudinal axis of rotor assembly  300  and the center axis of magnet member  410 . The angle of first side walls  470  and second side walls  475  can be obtained through known methods, including machining, such as, for example, grinding, to achieve an equal angle or slope. For a trapezoidal shape of magnet arc  410 , a trapezoidal mold could be used with grinding being performed to achieve the smooth, precise surface.  
         [0028]    The assembly of rotor assembly  300  provides a tight fit between inner faces  480  of the magnet arcs  410 ,  420 ,  430  and  440  and the outer wall  325  of the rotor core  320  but eliminates any gap at separation lines  405  between adjacent first side walls  470  of each of the magnet arcs or between adjacent second side walls  475  of each of the magnet arcs. The gaps are eliminated even with the manufacturing tolerances that are incorporated into the degree of curvature of the magnet arcs  410 ,  420 ,  430  and  440 .  
         [0029]    Referring to FIGS. 3 through 8, to assemble rotor assembly  300 , axial forces A that are parallel to the longitudinal axis of the rotor assembly and radial forces R that are perpendicular to the longitudinal axis of the rotor assembly, are applied to each magnet arc  410 ,  420 ,  430  and  440 . As shown in FIG. 8, the axial forces A are applied to all of the second end walls  465  so that magnet arcs  410 ,  430 , and magnet arcs  420 ,  440 , which are oppositely orientated from each other, will receive an axial force in the opposite direction. However, alternatively, axial forces A could be applied to all of the first end walls  460 . Axial forces A cause magnet arcs  410 ,  420 ,  430  and  440  to slide together along second side walls  465  until any gap between the magnet arcs is eliminated. The radial forces R are applied to outer face  485  of each of the magnet arcs  410 ,  420 ,  430  and  440  to provide for a tight bond between the magnet arcs and rotor core  320 . Preferably, radial forces R are diametrically opposed along rotor assembly  300 .  
         [0030]    As shown in FIG. 8, the manufacturing tolerances in the degree of curvature that are incorporated into magnet arcs  410 ,  420 ,  430  and  440 , are accounted for along upper edge  500  and lower edge  600  of assembly  300 , where first and second end walls may not be completely aligned. This method of assembly using magnet arcs  410 ,  420 ,  430  and  440  with angled first and second side walls  460 ,  465  and alternating their orientation along outer wall  325  of rotor core  320 , effectively eliminates gaps between the magnet arcs.  
         [0031]    While the exemplary embodiment uses four magnet arcs  410 ,  420 ,  430  and  440  having the same size and shape, the present disclosure contemplates the use of any plurality of magnet arcs that use the together of tapered or angled first and second side walls  470 ,  475 . The first and second side walls  470 ,  475  can be disposed on each of the magnet arcs so that identical magnet arcs are used or can be distributed amongst the magnet arcs in combination with straight side walls. The use of magnet arcs  410 ,  420 ,  430  and  440  having the same size and shape is preferred because it is cost effective in manufacturing and assembly. Preferably, any even number of magnet arcs  410 ,  420 ,  430  and  440  can be used so that the magnet arcs are diametrically opposed along outer wall  325  of rotor core  320  and orientated in an alternating pattern along the outer wall.  
         [0032]    Additionally, the present disclosure contemplates the use of an odd number of magnet arcs  410 ,  420 ,  430  and  440  to form magnet  400 . In such a configuration, one (or more) of the magnet arcs could have straight side walls, while the remaining magnet arcs would have a straight side wall and an angled side wall (in opposing directions) so that the straight side walls could slide along each other while the angled side walls would slide along each other in opposing directions until any gaps were eliminated. The application of both radial forces R and axial forces A to the various configurations described-above, eliminates the gaps in magnet  400 . Rotor assembly  300  can have at least two nonparallel separation lines  405  in magnet  400  which will eliminate the gaps when axial forces A are applied causing movement along the separation lines.  
         [0033]    Referring to FIG. 9, another embodiment of a magnet motor generally referred to by reference numeral  700 , is illustrated. Magnet motor  700  has a rotor assembly  800  and a stator  900  operably connected to the rotor assembly. Rotor assembly  800  has a rotor shaft  810  and a rotor core  820 .  
         [0034]    Stator  900  has an inner wall or circumference  902  and a permanent magnet  904  secured thereto. Magnet  904  is separated into a plurality of magnet members or arcs  910 ,  920 ,  930  and  940  having outer faces  907 . In the embodiment of FIG. 9, magnet  904  remains stationary.  
         [0035]    The magnet members  910 ,  920 ,  930  and  940  abut against each other along separation lines  905 . The magnet members  910 ,  920 ,  930  and  940  have a size and shape that allows the outer face  907  of the magnet members to be secured to the inner wall  902  of the stator. Similar to the exemplary embodiment of FIGS. 3-8, the sizes and shapes of magnet members  910 ,  920 ,  930  and  940  eliminate any gap between the magnet members along the separation lines  905 .  
         [0036]    While the instant disclosure has been described with reference to one or more exemplary embodiments, it will be understood by those skilled in the art that various changes may be made and equivalents may be substituted for elements thereof without departing from the scope thereof. In addition, many modifications may be made to adapt a particular situation or material to the teachings of the disclosure without departing from the scope thereof. Therefore, it is intended that the disclosure not be limited to the particular embodiment(s) disclosed as the best mode contemplated for carrying out this invention, but that the invention will include all embodiments falling within the scope of the appended claims.