Abstract:
A commutator ( 10, 40, 54, 60, 64, 70, 76, 78 ) for a brush motor includes a cylindrical insulating base ( 12 ), a plurality of segments ( 14 ) disposed on an outer surface ( 68 ) of the insulating base ( 12 ), circumferentially spaced from each other, and defining a plurality slots ( 42 ) between adjacent segments ( 14 ), and a plurality of insulating outgas elements ( 24 ) capable of releasing a gas having a lower conductivity than air and disposed on the outer surface ( 68 ) of the cylindrical insulating base ( 12 ). Each outgas element ( 24 ) is located between a corresponding pair of the plurality of segments ( 14 ), having a gas releasing surface ( 26 ) between the corresponding pair of segments ( 14 ) and lower than outer surfaces ( 28 ) of the corresponding pair of segments ( 14 ). A method for making a commutator is also provided.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional patent application claims priorities under 35 U.S.C. §119(a) from Patent Application No. 201210336520.0 filed in The People&#39;s Republic of China on 12 Sep. 2012 and Patent Application No. 201210336532.3 filed in The People&#39;s Republic of China on 12 Sep. 2012. 
     FIELD OF THE INVENTION 
     This invention relates to a commutator for brush motors and in particular, to a spark suppressing arrangement for the commutator. 
     BACKGROUND OF INVENTION 
     A brush motor typically includes a stator and a rotor. The rotor includes a shaft, a rotor core fixed on the shaft, a commutator fixed on the shaft adjacent the rotor core, and rotor windings wound about the teeth of the rotor core and electrically connected to the commutator. The stator includes stator magnetic poles, power terminals and at least a pair of brushes in sliding contact with segments of the commutator. External power is supplied to the rotor windings via the power terminals, the brushes and the commutator. When electrified, the rotor windings form rotor magnetic field which interacts with stator magnetic field to drive the rotor to rotate. 
     During commutation, when a brush leaves a segment of the commutator, the current passing through the corresponding rotor winding changes abruptly, thereby generating a large induced electromotive force and a strong electric field across an air gap between the brush and the segment. The air around the brush and the segment may be ionized under the strong electric field to form a discharge path and generate sparks. The spark may damage the slide contact between the brush and the commutator, which increases the worn of the brush and the commutator. Hence there is a desire for a commutator with diminished spark. 
     SUMMARY OF THE INVENTION 
     Accordingly, in one aspect thereof, the present invention provides a commutator for a brush motor includes a cylindrical insulating base, a plurality of segments disposed on an outer surface of the insulating base, circumferentially spaced from each other, and defining a plurality slots between adjacent segments, and a plurality of insulating outgas elements capable of releasing a gas having a lower conductivity than air and disposed on the outer surface of the cylindrical insulating base. Each outgas element is located between a corresponding pair of the plurality of segments, having a gas releasing surface between the corresponding pair of segments and lower than outer surfaces of the corresponding pair of segments. 
     Preferably, said plurality of outgas elements at least partly extend into the plurality of slots between adjacent segments. 
     Preferably, at least one of two opposite side surfaces of a pair of adjacent segments has a recess, and an outgas element of said plurality of outgas elements extends into the recess. 
     Preferably, the gas release surface of one of said plurality of outgas elements has a side surface defining a circumferential gap with one of two opposite side surfaces of a corresponding pair of adjacent segments. 
     Preferably, one of said plurality of outgas elements extends into a groove in the outer surface of said cylindrical insulating base and is radially confined by inner surfaces of a corresponding pair of adjacent segments. 
     Preferably, the gas releasing surface of one of said plurality of outgas elements is lower than or aligned with inner surfaces of a corresponding pair of adjacent segments. 
     Preferably, the gas releasing surface of one of said plurality of outgas elements includes an uneven surface. 
     Preferably, two opposite side surfaces of a pair of adjacent segments are inclined relative to a radial direction of said cylindrical insulating base, and a distance between the two opposite side surfaces gradually increases along the radial direction. 
     Preferably, said plurality of outgas elements and said cylindrical insulating base are formed as a monolithic member. 
     Preferably, said plurality of outgas elements and said cylindrical insulating base are detachably assembled together. 
     Preferably, said plurality of outgas elements are made of a same material as said cylindrical insulating base. 
     Preferably, said plurality of outgas elements and said cylindrical insulating base are made of different materials. 
     Preferably, said plurality of outgas elements are made of a thermal plastic material capable of spontaneously releasing a gas having a conductivity lower than air. 
     Preferably, said plurality of outgas elements are made of Polyamide 66. 
     Preferably, said cylindrical insulating base is made of a thermosetting material. 
     According to a second aspect, the present invention provides a method for making a commutator, comprising identifying an insulating base, disposing a plurality of segments circumferentially spaced on an outer surface of the insulating base, and disposing a plurality of insulating outgas elements capable of releasing a gas having a conductivity lower than that of air and spaced on the outer surface of the insulating base between corresponding pairs of adjacent segments with gas releasing surfaces lower than outer surfaces of the segments. 
     Preferably, disposing a plurality of insulating outgas elements further includes disposing an outgas element of the plurality of outgas elements at least partially in a slot between a corresponding pair of adjacent segments. 
     Preferably, disposing a plurality of segments includes disposing a plurality of segments at circumferential intervals, disposing a plurality of insulating outgas elements includes disposing an outgas element of the plurality of outgas elements at least partially in a slot between a corresponding pair of adjacent segments, and identifying an insulating base includes disposing an insulating base on the outgas elements and inner surfaces of the segments. 
     Preferably, identifying an insulating base further includes forming a plurality of grooves on the outer surface of the insulating base, disposing a plurality of segments further includes placing two adjacent segments on opposite sides of a groove of the plurality of grooves on the outer surface of the insulating base, and disposing a plurality of insulating outgas elements further includes disposing an outgas element of the plurality of outgas elements at least partially in a corresponding groove on the outer surface of the insulating base. 
     Preferably, disposing a plurality of segments includes providing a metal ring, identifying an insulating base includes disposing an insulating base on an inner surface of the metal ring, the insulating base having a plurality of grooves or holes on an outer periphery thereof, disposing a plurality of insulating outgas elements includes disposing the plurality outgas elements in the plurality of grooves or holes, and disposing a plurality of segments further includes forming a plurality of through slots in the metal ring to form the segments and expose the outgas elements. 
     Preferably, disposing a plurality of segments includes providing a metal ring, disposing a plurality of insulating outgas elements includes disposing the plurality outgas elements on an inner surface of the metal ring, identifying an insulating base includes disposing an insulating base on the outgas elements and an inner surface of the metal ring, and disposing a plurality of segments further includes forming a plurality of through slots in the metal ring to form the segments and expose the outgas elements. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Various embodiments of the invention are described, by way of example only, with reference to the drawings, in which identical or related structures, elements, or parts may be labeled with the same reference numerals throughout the figures. Dimensions of components and features shown in the figures are generally chosen for convenience and clarity of presentation and are not necessarily shown to scale. 
         FIG. 1  illustrates a commutator for a brush motor in accordance with an embodiment of the present invention; 
         FIG. 2  illustrates a planar view of the commutator shown in  FIG. 1 ; 
         FIG. 3  illustrates an insulating base of the commutator shown in  FIG. 1 ; 
         FIG. 4  illustrates a segment of the commutator shown in  FIG. 1 ; 
         FIG. 5  illustrates an outgas element on the commutator shown in  FIG. 1  in accordance with an embodiment of the present invention; 
         FIG. 6  illustrates a spark suppression process in accordance with an embodiment of the present invention; 
         FIG. 7  illustrates a planar view of a commutator in accordance with another embodiment of the present invention; 
         FIGS. 8 to 10  illustrate an exemplified method of forming the commutator shown in  FIG. 7 ; 
         FIG. 11  illustrates a planar view of a commutator in accordance with yet another embodiment of the present invention; 
         FIGS. 12 to 15  illustrates an exemplified method of forming the commutator shown in  FIG. 11 ; 
         FIGS. 16 to 18  illustrate an exemplified method of forming a commutator in accordance with another embodiment of the present invention; and 
         FIGS. 19 to 22  illustrate circumferential developed views of commutators in accordance with some additional embodiments of the present invention. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       FIG. 1  illustrates a commutator  10  for a brush motor in accordance with an embodiment of the present invention.  FIG. 2  illustrates a planar view of the commutator  10 .  FIGS. 3, 4, and 5  illustrate an insulating base  12 , a segment  14  and an outgas element  24 , respectively, of the commutator  10 . The commutator  10  includes a hollow insulating base  12  and a plurality of segments  14  disposed on the outer surface of the insulating base  12 . A ring  16  is tightly sleeved on the outer surfaces of the segments  14  for radially positioning the segments  14 . Every segment  14  has a terminal  18  at one end thereof for electrically connecting with a rotor winding  36  (shown in  FIG. 6 ) of the motor. 
     In accordance with an embodiment of the present invention, a plurality of axially extending grooves  20  are formed in the outer surface of the insulating base  12  at regular intervals in the circumferential direction. The segments  14  are arranged between adjacent grooves  20 . The circumferential distance between two opposite side surfaces  22  of two adjacent segments  14  is smaller than the circumferential width of the groove  20  so that the opposite side surfaces  22  of the adjacent segments  14  and the corresponding groove  20  define an inverted T-shaped slot. An inverted T-shaped insulating outgas element  24  is disposed in the inverted T-shaped slot. 
     Preferably, the outgas elements  24  and the insulating base  12  are made of different materials. In accordance with a preferred embodiment, the outgas elements  24  are made of a thermal plastic material such as, for example, Polyamide 66 that is sometimes also referred to as PA66, which is able to spontaneously release a gas with conductivity lower than air. The portion of the outer surface of an outgas element  24  between two corresponding adjacent segments  14  forms a gas releasing surface  26 . The gas releasing surface  26  is radially lower than the outer surfaces  28  of the segments  14 , so that the gas releasing surface  26  and the opposite side surfaces  22  of two adjacent segments  14  define a space  30  through which the gas released from the outgas element  24  spreads. The inverted T-shaped configuration makes the outgas elements  24  radially confined and prevents the outgas elements  24  from being thrown out during the high speed rotation of the commutator  10 . It also increases the size of the outgas elements  24 , thereby prolonging the usable life of the outgas elements  24  and/or increasing the gas released from the outgas elements  24 . 
       FIG. 6  illustrates a spark suppression process of the commutator  10 . During the operation of the motor, the outgas elements  24  in the commutator  10  spontaneously release gas  34  with conductivity lower than air via the gas releasing surface  26 . The gas  34  spreads between the adjacent segments  14  and between the commutator segments  14  and the brush  32  of the motor. When the rotor windings  36  of the motor generates large inductive electromotive force during commutation, the gas  34 , with its low conductivity, would reduce or diminish gas ionization (also referred to as arc discharge) generated between two adjacent segments  14  and between the segment  14  and the brush  32 . In other words, the electric arc in the air decreases, which reduces the brush  32  and the segments  14  from being worn. By configuring the gas releasing surface  26  to be radially lower than the outer surfaces of the segments  14 , friction between the outgas element  24  and the brush  32  is avoided, and no outgas element powder or solid particle is generated and attached to the outer surfaces  28  of the segments  14  to negatively influence the conductivity between the segments  14  and the brush  32 . 
     The commutator  10  may be formed by following an exemplified method described infra. The segments  14 , the ring  16 , the outgas elements  24  and the insulating base  12  with the grooves  20  are separately fabricated firstly. The outgas elements  24  are then inserted into the grooves  20  in the outer surface of the insulating base  12 . After that, the segments  14  are assembled on the outer surface of the insulating base  12  and between adjacent outgas elements  24 , and the ring  16  is sleeved on the outer surfaces of the segments  14  to radially confine the segments  14  on base  12 . 
     According to another exemplified method, the outgas elements  24  are inserted into the inverted T-shaped slots defined by the opposite side surfaces  22  of two adjacent segments  14  and corresponding groove  20  in the base  12  after the segments  14  are assembled on the outer surface of the insulating base  12 . 
     In the above described exemplified methods, the outgas elements  24  are independently formed and inserted into corresponding grooves  20  in the base  12  so that the outgas elements  24  and the insulating base  12  form pieces detachable from each other. According to another exemplified method, the outgas elements  24  are injection-molded in the grooves  20  in the insulating base  12 , before or after assembling the segments  14  to the insulating base  12 , so that the outgas elements  24  and the insulating base  12  form an inseparable or undetachable single piece. 
       FIG. 7  illustrates a commutator  40  in accordance with another embodiment of the present invention. The commutator  40  includes a hollow insulating base  12  and a plurality of segments  14  disposed on the outer surface of the insulating base  12  with a through slot  42  between adjacent segments  14 . A plurality of axially extending grooves  20  are formed in the outer surface of the insulating base  12  at regular intervals in the circumferential direction. Every groove  20  is connected with a corresponding through slot  42 . The outgas element  24  is entirely disposed in the groove  20 . The portion of the outer surface of the outgas element  24  between two adjacent segments  14  forms a gas releasing surface  26  that is radially lower than the inner surfaces  44  of the segments  14 . The gas releasing surface  26  and two opposite side surfaces  22  of two adjacent segments  14  define a space  30  through which the gas released from the outgas element  24  spreads. 
       FIGS. 8 to 10  illustrate an exemplified method of forming the commutator  40 . Firstly, a metal ring  46  (shown in  FIG. 8 ) and a plurality of outgas elements  24  (shown in  FIG. 9 ) are separately fabricated. The metal ring  46  has a plurality of radial projections  48  projected from the inner surface thereof. The outgas element  24  is an elongate member with circular cross section. Secondly, as shown in  FIG. 10  and in an overmolding process, the insulating base  12  is molded on the inner surface of the metal ring  46  with a plurality of holes  50  formed at the outer periphery of the insulating base  12  with the projections  48  embedded in the insulating base  12 . The holes  50  may be formed by unloading the insulating base  12  from a mould having a plurality of corresponding protrusions after the insulating base  12  is molded on the inner surface of the inner surface of the metal ring  46  and the projections on the mould. The projections  48  on the inner surface of the metal ring  46  intensifies the bonding between the insulating base  12  and the metal ring  46 . Alternatively, the holes  50  can be replaced by grooves in the outer surface of the insulating base  12 . It should be understood the insulating base  12  may be formed on the inner surface of the metal ring  46  by other known ways to form an inseparable or undetachable single piece with the metal ring  46 . Then, the outgas elements  24  are inserted into the holes  50  or the grooves in the insulating base  12 . Finally, through slots  42  are formed in the metal ring  46  to form segments  14  and expose the outgas elements  24 . Preferably, the through slots  42  are formed by cutting. 
     In the above described method, the through slots  42  are formed after the outgas elements  24  are inserted into the holes  50  or the grooves in the insulating base  12 . According to another exemplified method, the through slots  42  are formed to connect with the holes  50  or the grooves in the insulating base  12  before the outgas elements  24  are inserted into the holes  50  or the grooves. 
     In above described methods, the outgas elements  24  are independently formed and then inserted into corresponding holes  50  or grooves so that the outgas elements  24  and the insulating base  12  are detachable from each other. Alternatively, the outgas elements  24  are injection-molded in the holes  50  or the grooves in the insulating base  12  so that the outgas elements  24  and the insulating base  12  form an inseparable or undetachable single piece. 
       FIG. 11  illustrates a commutator  54  in accordance with yet another embodiment of the present invention. In this embodiment, the insulating base  12  of the commutator  54  is disposed on the outgas elements  24  and the inner side of the segments  14 . The opposite side surfaces  22  of two adjacent segments  14  and a corresponding groove  20  in the outer surface of the insulating base  12  define an inverted T-shaped slot. The outgas elements  24  are entirely disposed in the grooves  20 . The gas releasing surface  26  of the outgas element  24  between two adjacent segments  14  is radially higher than the inner surface but lower than the outer surfaces  28  of the segments  14 . The gas releasing surface  26  and the opposite side surfaces  22  of two adjacent segments  14  define a space  30  through which the gas released from the outgas element  24  spreads. 
       FIGS. 12 to 15  illustrate an exemplified method of forming the commutator  54 . Firstly, a metal ring  46  (shown in  FIG. 12 ) and a plurality of outgas elements  24  (shown in  FIG. 13 ) are separately fabricated. A plurality of position slots  56  and projections  48  are alternately formed on the inner surface of the metal ring  46 . The outgas element  24  is an elongate member with inverted T-shaped cross section as shown in  FIG. 13 . Secondly, as shown in  FIG. 14 , the narrow portions of the invented T-shaped outgas elements  24  are inserted into the position slots  56  in the metal ring  46 . Thirdly, the insulating base  12  is molded on the outgas elements  24  and the inner side of the metal ring  46  with the projections  48  embedded in the insulating base  12 . The projections  48  on the inner surface of the metal ring  46  intensifies the bonding between the insulating base  12  and the metal ring  46 . It should be understood the insulating base  12  and the metal ring  46  may form an undetachable single piece by other known ways. Then, through slots  42  are formed in the metal ring  46  to expose the outgas elements  24 . Preferably, the through slots  42  are formed by cutting. 
     In above described methods, the outgas elements  24  are independently formed and then inserted into the position slots  56 . In another exemplified method, the outgas elements  24  are directly injection-molded in the position slots  56 . 
       FIGS. 16 to 18  illustrate an exemplified method forming the commutator  60 . Firstly, a plurality of segments  14  as shown in  FIG. 16  and a plurality of outgas elements  24  as shown in  FIG. 5  are separately formed. The segment  14  has a projection  48  projected from the inner surface thereof. The outgas element  24  is an elongate member with inverted T-shaped cross section. Secondly, as shown in  FIG. 17 , the narrow portions of the invented T-shaped outgas elements  24  are sandwiched between adjacent segments  14  such that the segments  14  and the outgas elements  24  are alternately arranged to form an annular ring. As shown in  FIG. 18 , the insulating base  12  is then molded on the outgas elements  24  and the inner side of the segments  14  with the projections  48  embedded in the insulating base  12 . The projections  48  on the inner surfaces of the segment  14  intensifies the bonding between the insulating base  12  and the segments  14 . 
     According to another embodiment of the present invention, the outgas elements  24  are connected together by a connecting ring. After the insulating base  12  is molded on the outgas elements  24  and the segments  14 , the connecting ring can be kept or removed. 
       FIG. 19  illustrates a circumferential developed view of a commutator  64  in accordance with another embodiment of the present invention. In this embodiment, both of the opposite side surfaces  22  of two adjacent segments  14  on the outer surface  68  of the insulating base  12  have a recess  66 . The outgas element  24  is arranged between the adjacent segments  14  and extends into the recesses  66  so as to be prevented from being throwing out during the high speed rotation of the commutator  64 . The recesses  66  is able to receive a larger outgas element  24 . According to another embodiment, only one of the opposite side surfaces  22  of two adjacent segments  14  has the recess  66 . 
       FIG. 20  illustrates a circumferential developed view of a commutator  70  in accordance with another embodiment of the present invention. The outgas elements  24  are made of the same material as the insulating base  12  and extend into the through slots  42  between the adjacent segments  14  from the outer surface of the insulating base  12 . The gas releasing surface  26  of the outgas element  24  has two side surfaces  72  respectively facing two opposite side surfaces  22  of the adjacent segments  14  with a circumferential gap  74  defined between the side surface  72  of the gas releasing surface  26  and the side surface  22  of the segment  14  facing the side surface  72 . By this configuration, the area of the gas releasing surface  26  increases so that the amount of gas released from the gas releasing surface  26  also increases. It should be understood the gas releasing surface  26  may have only one side surface  72  to form the circumferential gap  74  with the side surface  22  of the segment  14  facing the side surface  72 . Also the gas releasing surface  26  may be an uneven surface to increase the area. 
       FIGS. 21 and 22  illustrate circumferential developed views of commutators  76  and  78  in accordance with two other embodiments of the present invention. In  FIG. 21 , the outgas element  24  of the commutator  76  is arranged in the groove  20  in the outer surface of the insulating base  12  with the gas releasing surface  26  being concaved relative to the inner surfaces  44  of the adjacent segments  14 . In  FIG. 22 , the outgas element  24  of the commutator  78  is arranged in the groove  20  in the outer surface of the insulating base  12  with the gas releasing surface  26  and the outer surface of the insulating base  12  located on the outer surface of a same imaginary cylinder. 
     The commutator in accordance with embodiments of the present invention is especially suitable for high power motor applications. Under this situation, the insulating base  12  may be made of a thermosetting material to provide stable support for the segments  14  in an environment with high temperature. The outgas elements  24  are preferably made of insulating material that can spontaneously release gas with lower conductivity than air under non-high temperature condition and release more such gas under high temperature condition. It should be understood that the commutator in accordance with embodiments of the present invention is also applicable to the low power motors. 
     In the description and claims of the present application, each of the verbs “comprise”, “include”, “contain” and “have”, and variations thereof, are used in an inclusive sense, to specify the presence of the stated item but not to exclude the presence of additional items. 
     Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. Therefore, the scope of the invention is to be determined by reference to the claims that follow. 
     For example, two opposite side surfaces  22  of the adjacent segments  14  may be inclined relative to the radial direction and the distance between the two side surfaces  22  gradually increases along the direction from the inner surface  44  to the outer surface  28  of the segments  14 . 
     For another example, the gas releasing surface  26  may be uneven so as to increase the surface area and amount of gas released.