BACKGROUND OF THE INVENTION 
     1. Technical Field 
     The present invention relates to a commutator motor provided with a commutator. 
     2. Background of Art 
     FIG. 9 is a sectional view of a conventionally used commutator motor. In FIG. 9, the commutator motor  10  is mainly comprised of a rotary shaft  1 , an armature  2 , a commutator  3 , a brush holder  4 , a brush  41 , a brush casing  42 , a magnet  5 , a yoke  6 , a bearing  7 , and a housing  8 . Further, the commutator  3  has a conductive section  32  mounted on the rotary shaft  1  through an insulating section  31  disposed between the conductive section  32  and the rotary shaft  1 , the rotary shaft  1  is pressed into and held in the hole in the center of the insulating section  31 , and the conductive section  32  is brought into contact with the brush  41 . 
     In the structure of the commutator motor  10  constituted as above, when rotating the armature  2 , vibration is generated in the contact portion between the brush  41  and the commutator  3 . A hard material of a high mechanical strength, for example, thermosetting resin like thermoset phenolic resin, forms the insulating section  31  of the commutator  3 . Thus, the insulating section  31  can securely hold the rotary shaft that is pressed into the insulating section  31 . Since the commutator  3  behaves, due to the mentioned structure, as a rigid body as a whole, the vibration described above is directly transmitted to the rotary shaft  1  without attenuation in the commutator  3 . The vibration is then transmitted to the bearing  7  incorporated in the rotary shaft  1  and further to the yoke  6 . Such transmission of vibration is one of the causes of vibration and noise generated in the commutator motor  10 . Furthermore, the torque of the commutator motor  10  is transmitted from the armature  2  to the output side and the torque thus transmitted in the commutator motor  10  gives rise to a torsional strain in the direction of rotation along the rotary shaft  1 . This torsional strain brings about positional displacement in the direction of rotation between the commutator  3  and an armature core  21 , and consequently the armature coil  22  is subjected to tensile stress. This stress is one of the causes responsible for coil breakage due to fatigue fracture. 
     The Japanese Utility Model Publication (examined) No. 21085/1995 has disclosed a technique of giving a floating support to a brush holder forming a part of a housing by using rubber bushes for end-brackets, for the purpose of absorbing vibration in radial and axial directions due rotation of an armature in a commutator motor. This known technique is, however, not always sufficient to prevent the mentioned vibration and noise of a commutator motor. 
     SUMMARY OF THE INVENTION 
     In view of the above-discussed problems incidental to the conventional commutator motor, it is an object of the present invention to reduce vibration and noise generated in commutator motor, and to improve durability against breakage of armature coil. 
     (1) A commutator motor according to the invention comprises: a commutator having a conductive section mounted on a rotary shaft through an insulating section between the conductive section and the rotary shaft; and a vibration-isolating member disposed between the conductive section and the rotary shaft. 
     (2) In the commutator motor according to the mentioned paragraph (1), the vibration-isolating member is formed on an inner surface of the insulating section, the inner surface facing the rotary shaft, by adhesion to or integral formation with the insulating section. 
     (3) In the commutator motor according to the mentioned paragraph (1), the vibration-isolating member is formed between the conductive section and the insulating section by adhesion to or integral formation with these two sections. 
     Accordingly, vibration developed in the contact portion between a brush and the commutator due to rotation of the armature, is absorbed by the vibration-isolating member prepared in various forms as described above, whereby the commutator motor is prevented from occurrence of vibration and noise generated. Furthermore, due to the absorption of vibration by the vibration-isolating member, the mentioned torsional strain does not occur, and consequently the problem associated with fatigue fracture of armature coil can be solved. 
     (4) In the commutator motor according to any of the above-mentioned paragraphs (1) to (3), the vibration-isolating member has protrusions embedded in the insulating section in a radial direction of the rotary shaft. Accordingly, the protrusions exhibit an advantage of preventing positional displacement of the vibration-isolating member in an axial direction with respect to the insulating section. 
     (5) In the commutator motor according to the mentioned paragraph (1), the commutator motor further comprises a brush holder section for holding a brush coming in contact with the commutator, and in which another vibration-isolating member supports the bush holder section. Accordingly, in addition to isolation of vibration by the vibration-isolating member disposed between the conductive section and the rotary shaft as described above, another way of preventing vibration is provided by another vibration-isolating member. As a result, the commutator motor is more securely prevented from occurrence of vibration and noise. Furthermore, any torsional strain along the rotary shaft does not occurs, whereby the problem associated with fatigue fracture of the armature coil is solved. 
     (6) In the commutator motor according to the mentioned paragraphs (1) or (5), the vibration-isolating member is made of rubber. Accordingly, excellent elasticity of rubber can provide a great vibration-isolating effect. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a sectional view of a commutator motor according to Embodiment 1 of the present invention, with a part thereof omitted; 
     FIG. 2 is a radial sectional view of a commutator  3  used in FIG. 1; 
     FIG. 3 is a radial sectional view of a commutator used in a commutator motor according to Embodiment 3 of the invention; 
     FIG. 4 is a radial sectional view of a commutator used in a commutator motor according to Embodiment 5 of the invention; 
     FIG. 5 is a sectional view taken along the line V—V in FIG. 4; 
     FIG. 6 is a partially enlarged sectional view of a commutator motor according to Embodiment 7 of the invention; 
     FIG. 7 is a plan view of a brush holder used in Embodiment 7; 
     FIG. 8 is a plan view showing a state after removing the brush holder and other parts from FIG. 7; and 
     FIG. 9 is a sectional view of a commutator motor according to the prior art. 
    
    
     DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     In the Embodiments 1 to 4 described below, the same reference numerals are designated to the same or like parts and further description thereof are omitted herein. 
     EMBODIMENT 1 
     FIGS. 1 and 2 explain a commutator motor according to Embodiment 1 of the present invention. FIG. 1 is a partially cut out sectional view of the commutator motor  10 , and FIG. 2 is a radially sectional view of the commutator  3  in FIG.  1 . In FIGS. 1 and 2, reference numeral  33  shows a vibration-isolating member. FIG. 1 is different from FIG. 9 in the aspect that the vibration-isolating member  33  is added in FIG. 1, and constitution of the other elements in FIG. 1 is the same as that in FIG.  9 . The vibration-isolating member  33  is adhered with an adhesive (not shown) to the inner surface facing the rotary shaft  1  of the insulating section  31  in the commutator  3 . Thus, the commutator  3  in this Embodiment 1 has a structure having the vibration-isolating member  33  in innermost part, on which the insulating section  31  and the conductive section  32  are disposed in order. The vibration-isolating member  33  absorbs vibration developed in the contact portion between the brush  41  and the commutator  3  due to rotation of the armature  2 . As a result, the commutator motor is prevented from occurrence of vibration and noise. 
     Furthermore, the above-mentioned vibration absorption by the vibration-isolating member  33  is also effective for reducing the amount of torsional strain in the rotary shaft  1 . As a result, a great advantage is exhibited such that the problem associated with fatigue fracture of the armature coil  22  is solved, whereby the commutator motor  10  is improved in durability. 
     In the commutator motor  10  in this Embodiment 1, the commutator  3  of three-layer structure shown in FIGS. 1 and 2 is employed instead of the commutator  3  shown in FIG. 9, and it is possible to assemble the commutator motor by pressing the rotary shaft  1  in the hole provided in the center of the commutator  3 , i.e., center hole of the vibration-isolating member  33 . 
     There is no restriction in selecting constituent materials of the vibration-isolating member  33  as long as they can absorb vibration generated in the contact portion between the brush  41  and the commutator  3 . In general, it is preferable to employ elastic materials such as rubber. Among many types of rubber, the followings are preferred: ethylene-propylene copolymer rubber (EPM), ethylene-propylene-diene ternary copolymer rubber (EPDM), ethylene-vinyl acetate copolymer rubber, isoprene rubber, acrylonitrile-butadiene rubber, styrene butadiene rubber, chloroprene rubber, butyl-rubber, epichlorohydrin rubber, silicon rubber, fluorine rubber, and cross-linking-based polymer including cross-linking rubber like natural rubber, or various types of thermoplastic elastomer. 
     When the insulating section  31  is formed of a thermosetting resin like thermosetting phenol resin, such insulating section  31  and the vibration-isolating member  33  made of the above-mentioned rubber can be adhered to each other with an adhesive such as elastomer-metamorphic-epoxy adhesive or a rubber cement prepared by dissolving petroleum resin like rosin and not-yet-cross-linked rubber in an organic solvent. In the case that a rubber of low polarity such as EPM or EPDM is used, it is preferable to apply a primer or a surface treatment to the adhered face of the vibration-isolating member  33  for improving adhesion properties before application of the adhesive. 
     EMBODIMENT 2 
     In this Embodiment 2, the vibration-isolating member is integrally formed with the insulating section and disposed in position. This Embodiment 2 is different from the foregoing Embodiment 1 only in this respect, and the constitution of the other elements is the same as that in the foregoing Embodiment 1. The commutator whose vibration-isolating member and insulating section are integrally formed can be manufactured, for example, by the steps of heating the conductive element forming an conductive section  32 , not-yet-set thermosetting resin, and not-yet-cross-linked rubber inside a mold under pressure, and causing the thermosetting resin to set and the rubber to cross-link. 
     EMBODIMENT 3 
     FIG. 3 is a radially sectional view of a commutator  3  to explain a commutator motor according to Embodiment 3 of the invention. The commutator  3  in this Embodiment 3 is different from that in FIG. 2 in the aspect that the vibration-isolating member  33  is located between the insulating section  31  and the conductive section  32  and is adhered to both sections with an adhesive (not shown), and the remaining constitution is the same as that in the foregoing Embodiment 1. 
     EMBODIMENT 4 
     In this Embodiment 4, the vibration-isolating member located between the conductive section and the insulating section is integrally formed with both sections. Accordingly, this Embodiment 4 is different from the foregoing Embodiment 3 only in this respect and the remaining constitution is the same as that in the foregoing Embodiment 3. 
     EMBODIMENT 5 
     FIGS. 4 and 5 are to explain a commutator motor according to Embodiment 5 of the invention. FIG. 4 is a radially sectional view of a commutator  3  and FIG. 5 is a sectional view taken along the line V—V in FIG.  4 . The commutator  3  in this Embodiment 5 is different from that shown in FIG. 2 in the aspect that the vibration-isolating member  33  has protrusions  33   a  and the remaining constitution the same as that in the foregoing Embodiment 1. The protrusions  33   a  are laid inside the insulating section  31  in a radial direction of the rotary shaft (not shown), whereby it is possible to prevent positional displacement of the vibration-isolating member in an axial direction with respect to the insulating section. 
     EMBODIMENT 6 
     In this Embodiment 6, the vibration-isolating member located between the conductive section and the insulating section is integrally formed with both sections. Accordingly, this Embodiment 6 is different from the foregoing Embodiment 5 only in this respect and the remaining constitution is the same as that in the foregoing Embodiment 5. 
     EMBODIMENT 7 
     FIGS. 6 to  8  are to explain a commutator motor  10  according to Embodiment 7 of the invention. The reference numbers used in FIGS. 6 to  8  that are common to FIG. 1 designate the same elements as FIG.  1 . Thus, the description of these elements is not repeated here. FIG. 6 is a partially enlarged sectional view of the commutator motor  10 , FIG. 7 is a plan view of a brush holder  4 , and FIG. 8 is a plan view of a state after removing the brush holder and other parts from FIG.  7 . In FIGS. 6 to  8 , numeral  41  is a brush, numeral  42  is a brush casing, numeral  44  is a screw, numeral  45  is a rubber bush, and numeral  46  is a rubber sheet. The rubber bush  45  and rubber sheet  46  are another example of vibration-isolating member that is different from that employed in the foregoing Embodiments 1 to 6. 
     The brush holder  4  is secured with the screw  44  to a housing  8  through the rubber bush  45  between the bush holder  4  and the housing  8 . The rubber sheet  46  (indicated by many horizontal lines in FIG. 8) is secured onto the surface of the brush holder  4  facing to the housing  8 , thus the brush holder  4  is in contact with the housing  8  holding the rubber sheet  46  between them. 
     In this Embodiment 7, the commutator  3  has the vibration-isolating member  33  innermost in the same manner as in the foregoing Embodiment 1. Therefore, in addition to the isolation of vibration rendered by the vibration-isolation element  33 , a further isolation of vibration is applied by the rubber bush  45  and rubber sheet  46 . As a result, the commutator motor  10  can be prevented more effectively from occurrence of vibration and noise, and the rotary shaft  1  can be also prevented from torsional strain. As for the material constituting the rubber bush  45  and the rubber sheet  46 , it is preferred to employ the aforementioned rubber and other materials suitable for the vibration-isolating member  33 .
The invention provides a commutator motor capable of reducing vibration and noise generated in commutator motor and improving durability against breakage of armature. A commutator 3 having a conductive section 32 mounted on a rotary shaft 1 through an insulating section 31 is provided with a vibration-isolating member 33 made of rubber by adhesion or integral formation at the location between the conductive section 32 and the rotary shaft 1, for example, between the insulating section 31 and the rotary shaft 1 or between the conductive section 32 and the insulating section 31. In one aspect of the invention, another vibration-isolating member supports a brush holder 4 for holding a brush 41 coming in contact with the commutator 3.