Abstract:
Provided is a starter that can ensure stable insulation and exhibits excellent leakage resistance. The starter includes: a starting motor realized with a dc motor that has a commutator, positive brushes which are disposed around the commutator to abut on the commutator and connected to an external power supply, negative brushes, which are opposed to the positive brushes, stored in a bracket bearing one end of a rotation shaft; and a starting switch that is mounted on the starting motor and electrically connects or disconnects the external power supply to or from the positive brushes. When an engine is started, the starting motor is driven with the external power supply via the starting switch, and the starting motor is mechanically coupled to the engine. Herein, the starting motor has an insulating member disposed only on the internal surface of the bracket neighboring the positive brushes.

Description:
BACKGROUND OF THE INVENTION 
       [0001]    1. Field of the Invention 
         [0002]    The present invention relates to a starter that starts an engine. 
         [0003]    2. Description of the Related Art 
         [0004]    Conventionally, for the above type of starter, a direct-current (dc) motor is adopted as a starting motor. There is a possibility that brush wear debris may be accumulated on the internal surface of a bracket and a leakage may occur between brush springs, which press respective positive brushes to a commutator or constrain the respective positive brushes to move toward the commutator, and the bracket. Therefore, a gap of a certain length or more has to be preserved between the brush springs and bracket. This imposes a limitation on a brush length and hinders durability. If the starting motor is continuously supplied with electricity for some reason, the commutator may be broken due to centrifugal force and a thermal effect. At this time, if the positive brushes, and the metallic brush springs and brush holders of the respective positive brushes are brought into contact with the internal surface of the bracket and short-circuited, there is a fear that a large current may flow upstream from the short-circuited point (for example, to a connector outside the starting motor) so as to bring about a terrible thermal damage. 
         [0005]    As one of countermeasures, it has been proposed as described in, for example, JP-A-10-191589 that an insulating plate is attached to the inner circumferential surface of a frame, which is opposed to a brush unit, in order to ensure an insulation resistance for the frame of a dc motor and brushes. 
         [0006]    However, the structure described in JP-A-10-191589 is such that a lead to be coupled to an external power supply is led out from the frame. The led part of the lead cannot be insulated. The aforesaid short-circuit fault cannot be therefore coped with. In addition, since an insulating plate is disposed on the internal surface of the frame so that it will be shaped like a letter C, the gap between the frame and brush springs decreases. The length of the brushes has to be decreased in consideration of assembling efficiency or the like. This degrades durability. 
       SUMMARY OF THE INVENTION 
       [0007]    The present invention addresses the foregoing problems. An object of the present invention is to provide a starter that can ensure stable insulation and exhibits excellent leakage resistance. 
         [0008]    A starter in accordance with the present invention includes: a starting motor that is realized with a dc motor having a commutator, positive brushes that are disposed around the commutator to abut on the commutator and are connected to an external power supply, and negative brushes, which are opposed to the positive brushes, stored in a bracket bearing one end of a rotation shaft; and a starting switch that is mounted outside the starting motor and electrically connects or disconnects the external power supply to or from the positive brushes. When an engine is started, the starting motor is driven with the external power supply via the starting switch, and the starting motor is mechanically coupled to the engine. The starting motor has an insulating member disposed only on the parts of the internal surface of the bracket neighboring the positive brushes. 
         [0009]    According to the starter to which the present invention is applied, a starter that can ensure stable insulation and exhibits excellent leakage resistance can be readily provided. 
         [0010]    The foregoing and other object, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0011]      FIG. 1  is a longitudinal sectional view showing the overall structure of a starter in accordance with an embodiment 1 of the present invention; 
           [0012]      FIG. 2  is a sectional view of a major part of the embodiment 1; 
           [0013]      FIG. 3  is a longitudinal sectional view of the major part along an A-A cutting-plane line shown in  FIG. 2 ; 
           [0014]      FIG. 4  is a plan view showing an example of an insulating tape employed in the embodiment 1; 
           [0015]      FIG. 5  is a plan view showing another example of the insulating tape employed in the embodiment 1; 
           [0016]      FIG. 6  is a schematic circuit diagram of the starter of the embodiment 1; 
           [0017]      FIG. 7  is a sectional view of a major part of an embodiment 2 of the present invention; 
           [0018]      FIG. 8  is a longitudinal sectional view of the major part along a B-B cutting-plane line shown in  FIG. 7 ; 
           [0019]      FIG. 9  is a longitudinal sectional view of a major part of an embodiment 3 of the present invention; and 
           [0020]      FIG. 10  is a longitudinal sectional view of a major part of an embodiment 4 of the present invention. 
       
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Embodiment 1 
       [0021]      FIG. 1  is a longitudinal view showing the overall structure of a starter in accordance with an embodiment 1 of the present invention.  FIG. 2  is a sectional view of a major part of the embodiment 1.  FIG. 3  is a longitudinal sectional view of the major part along an A-A cutting-plane line shown in  FIG. 2 . 
         [0022]    Referring to  FIG. 1 , the starter includes a starting motor  1  that generates a torque, a decelerating planetary gear drive  2  that decelerates the rotation of the starting motor  1  and outputs the torque, an overrun clutch  4  disposed on an output shaft  3  of the decelerating planetary gear drive  2 , and a pinion  5  disposed to be able to slide on the output shaft  3  as an integral part of the overrun clutch. The starter includes a starting switch  8  that supplies electricity to the starting motor  1  and constrains the pinion  5  to move to a ring gear  7  of an engine as the integral part of the overrun clutch  4  via a shift lever  6 . 
         [0023]    The starting switch  8  is located above the peripheries of the starting motor  1  and decelerating planetary gear drive  2 , and has the center axis thereof disposed substantially in parallel with the output shaft  3 . 
         [0024]    The starting motor  1  includes a stator  12  that is fixed to a frame  11  and has a field coil  12   a,  and a rotator  13  having a rotation shaft  14  thereof borne by the stator  12 . In a bracket  15  that bears the non-loaded side of the rotator  13 , a commutator  16  attached to the rotation shaft  14  and a brush unit  17  mounted with a gap preserved relative to the internal surface of the bracket  15  are stored. 
         [0025]    The brush unit  17  includes, as shown in  FIG. 2  and  FIG. 3 , a pair of positive brushes  18  disposed around the commutator  16  with an angle of 90° between them, and a pair of negative brushes  19 . The brushes  18  and  19  are each held in a metallic brush holder  22  placed on a metallic base  20  with a resin plate  21  between them, and thrust on the commutator  16  by a metallic brush spring  23  attached to part of the brush holder  22 . 
         [0026]    An insulating member  24  realized with, for example, a viscous insulating tape is bonded to the internal surface of the bracket  15 , which encloses the entire brush unit  17 , neighboring the respective positive brushes  18 . 
         [0027]    The range in which the insulating member  24  is disposed, in an axial direction thereof, is equal to or larger than the axial distance of the brush holder  22  (A in  FIG. 3 ), which supports the positive brush  18 , and has, in a width direction thereof, a distance equal to or larger than a width (B in  FIG. 2 ) between a point, at which an extension of a line linking the center of the commutator  16  and the periphery of a brush holding member of the brush holder  22  meets the internal surface of the bracket  15 , and a point at which an extension of a line linking the center of the commutator and the periphery of the brush spring  23  meets the internal surface of the bracket  15 . 
         [0028]    The insulating member  24  is realized with a glass cloth tape having glass fibers woven therein, and has two or more insulating tapes, that is, insulating tapes  24   a  and  24   b,  of which woven patterns are different from each other as shown in  FIG. 4 , or insulating tapes  24   c  and  24   d,  which have the weaving direction of the same woven pattern oriented differently from each other as shown in  FIG. 5 , superposed on each other and bonded to each other. 
         [0029]      FIG. 6  is a schematic circuit diagram of the starter. In  FIG. 6 , a key switch  31  is connected to a battery  30  that is the external power supply. By turning on or off the key switch  31 , a starting relay  32  is energized or de-energized. One terminal of the starting relay  32  is connected to the battery  30 , and the other terminal thereof is connected to the starting switch  8 . One terminal (terminal B) of the starting switch  8  is connected to the battery  30 , and the other terminal (terminal M) is connected to the positive brushes  18  of the starting motor  1  via the field coil  12   a.    
         [0030]    In the foregoing constitution, when the key switch  31  is turned on, the starting relay  32  and starting switch  8  are biased, and the end surface of the pinion  5  abuts on the end surface of the ring gear  7 . When the starting motor  1  is driven and the pinion  5  is rotated at a high speed, the engine is cranked via the ring gear  7 . 
         [0031]    In the foregoing actions, assuming that the starting motor  1  is continuously supplied with electric current for some reason, the commutator  16  maybe broken due to centrifugal force and a thermal effect. In this case, if the positive brushes  18  and the metallic brush springs  23  and brush holders  22  of the positive brushes are brought into contact with the internal surface of the bracket  15  and short-circuited, a large current may flow upstream from the short-circuit point (for example, to a connector outside the starting motor) so as to bring about a terrible thermal damage. In the present embodiment, since the insulating member  24  is disposed on the internal surface of the bracket  15  neighboring the positive brushes  18 , the starter having the short-circuit fault effectively prevented and exhibiting excellent leakage resistance can be provided. 
         [0032]    The range in which the insulating member  24  is disposed has, in the axial direction thereof the distance equal to or larger than the axial length (A in  FIG. 3 ) of the brush holder  22  supporting the positive brush  18 , and has, in the width direction, thereof the circumferential distance equal to or larger than the width (B in  FIG. 2 ) between the point, at which the extension of the line linking the center of the commutator  16  and the periphery of the brush holding member of the brush holder  22  meets the internal surface of the bracket  15 , and the point at which the extension of the line linking the center of the commutator  16  and the periphery of the brush spring  23  meets the internal surface of the bracket  15 . Therefore, once the insulating member  24  is disposed in the specified ranges, the short-circuit fault can be reliably prevented. 
         [0033]    Further, since the insulating member  24  has two or more viscous insulating tapes superposed on and bonded to each other, the insulating member  24  can be readily attached to a predetermined range on the internal surface of the bracket  15 . 
       Embodiment 2 
       [0034]      FIG. 7  and  FIG. 8  are a sectional view of a major part of the embodiment 2 of the present invention and a longitudinal sectional view of the major part thereof. Instead of bonding an insulating tape as the insulating member  24  in the same manner as in the embodiment 1, an insulating resin  24   e  is coated as an integral part of the bracket  15  over the parts of the internal surface of the bracket  15  neighboring the positive brushes  18 . 
         [0035]    According to the embodiment 2, similarly to the embodiment 1, the short-circuit fault can be readily avoided, and the thermal damage on the connector outside the motor can be prevented. 
       Embodiment 3 
       [0036]      FIG. 9  is a sectional view of a major part of the embodiment 3 of the present invention. A concave part  33  that serves as a positioning part to be used to set the insulating member  24  is formed to the internal surface of the bracket  15  which neighbor the positive brushes  18  and on which the insulating member  24  is disposed in the embodiment 1. Specifically, the concave part  33  for receiving the insulating member  24  is formed in the range, that is, corresponding to a range in which the insulating member  24  is disposed has, in the axial direction thereof the distance equal to or larger than the axial length of the brush holder  22  supporting the positive brush  18 , and has, in the width direction, thereof the circumferential distance equal to or larger than the width between the point, at which the extension of the line linking the center of the commutator and the periphery of the brush holding member of the brush holder  22  meets the internal surface of the bracket  15 , and the point at which the extension of the line linking the center of the commutator and the periphery of the brush spring meets the internal surface of the bracket  15 . 
         [0037]    According to the embodiment 3, the insulating member  24  can be accurately and readily disposed at the predetermined positions in the internal surface of the bracket  15  neighboring the positive brushes  18 . 
       Embodiment 4 
       [0038]      FIG. 10  is a longitudinal sectional view of a major part of the embodiment 4 of the present invention. In addition to the components of the embodiment 1, another insulating member  34  (made of, for example, a resin) is interposed between the end of the insulating member  24  disposed on the bracket  15  and a crossover  12   b  of the field coil  12   a  to which a pigtail  18   a  of a positive brush is spliced. 
         [0039]    According to the embodiment 4, similarly to the embodiment 1, a short-circuit fault can be avoided, and a thermal damage on a connector located outside the starting motor can be nullified. Further, there is the merit that stable insulation can be ensured. 
         [0040]    Various modifications and alterations of this invention will be apparent to those skilled in the art without departing from the scope and spirit of this invention, and it should be understood that this is not limited to the illustrative embodiments set forth herein.