Abstract:
An alternator for vehicles, the alternator being provided with a rotary shaft, comprising slip rings fixed to a rotary shaft to be rotated with the rotary shaft, brushes being placed to be in slide contact with the slip rings a brush holder that accommodates the brushes to be held therein; connection terminals fixed to the brush holder, brush leads electrically connecting the brushes to the connection terminals respectively, and a slip ring cover that covers the slip rings in cooperation with the brush holder, wherein the brush holder comprises first chambers in which the bushes are fixedly accommodated second chambers in which the brush leads are accommodated, the second combers communicating with the first chambers, and first air holes formed to open outside of the housing and formed as inlet/exhaust passages communicating with the second chambers.

Description:
CROSS REFERENCES TO RELATED APPLICATION 
     The present application relates to and incorporates by reference Japanese Patent application No. 2008-016087 filed on Jan. 28, 2008. 
     BACKGROUND OF THE INVENTION 
     1. Field of the Invention 
     The present invention relates to a vehicle alternator (i.e., AC generator) mounted to vehicles such as automobiles and trucks. 
     2. Description of the Related Art 
     A typical vehicle alternator widely known comprises a stator, and a rotor that is disposed against the inner surface side of the stator, both of which are accommodated in a housing. The rotor is fixedly provided with a cooling fan that generates cooling air as the rotor rotates about a rotary shaft. The cooling air generated by the cooling fan is exhausted through an exhaust window provided to the housing. The rotary shaft is fixedly provided with slip rings that rotate with the rotary shaft. The vehicle alternator further comprises components such as a brush holder for accommodating brushes that are in sliding contact with the slip rings, and a rear cover for covering electric components accommodating the brushes. 
     The conventional vehicle alternator is required to have an airflow passage and to protect the brushes from getting wet, in order to prevent the brushes from wearing caused by the increased high temperature. A number of inventions have been proposed to pursue the same object. For example, Japanese unexamined utility model publication No. 58-51663 discloses a structure comprising mazy grooves that have a plurality of bending portions formed on an end face of a brush holder. Japanese examined patent publication No. 7-32571 discloses a construction that comprises a sealing member provided with cooling air passage between a brush holder and a rear cover. Japanese unexamined patent publication No. 5-199701 discloses a seal member having mazy cooling air passage formed by a plurality of bending portions. Further, Japanese unexamined patent publication No. 2000-139058 discloses a mazy structure constructed by a brush holder and a slip ring cover, a portion of the slip cover is inserted into a concave portion formed on the brush holder. also, Japanese unexamined patent publication No. 2006-340467 proposes a construction comprising a first air hole for connecting sliding portion of brush to the outside, and a second air hole for directly connecting chamber for brush to the outside, in order to inlet and exhaust the air around the sliding portion of the brush. 
     The aforementioned Japanese unexamined patent publication No. 2006-340467 is assumed effective to exhaust powder produced by sliding motion of the brushes. However, this construction has to supply the air into a very small gap formed between the brush and the chamber for brush. This decreases the amount of airflowing because of the increased resistance in the airflow, which requires an air inlet/exhaust apparatus to have a large bulk in order to supply sufficient airflow. Increasing the gap between the brush and the chamber for brush could decrease the resistance of the airflow. However, this proposal is unacceptable because such structure will increase rattling of the brush, thereby increasing wear and noise of the brush, during the slide movement of the brush. Further, the same Japanese unexamined patent publication introduces such a construction that the airflow is provided only to the chamber for brush at the rear side, leading to the chamber for the brush at the rear side to be cooled more than the other one at the front side. This causes the brush at the front side to have a shorter lifetime than the other one at the rear side. Consequently, this construction fails to allow the brushes to have the lifetime as long as it is initially expected. 
     SUMMARY OF THE INVENTION 
     The present invention has been invented in such a view, and it is therefore an object of the present invention to provide a vehicle alternator with increased amount of air for cooling a pair of brushes and for exhausting powders produced by sliding motion of the brushes. It is another object of the present invention to increase the lifetime of the pair of brushes and to improve the performance in exhausting the powder produced by sliding motion of the brushes, by individually providing a sufficient amount of air to each of the brushes. 
     An alternator for vehicles, the alternator being provided with a rotary shaft according to the present invention, which has been invented to overcome the above-mentioned problem, comprises slip rings fixed to a rotary shaft to be rotated with the rotary shaft, brushes being placed to be in slide contact with the slip rings a brush holder that accommodates the brushes to be held therein; connection terminals fixed to the brush holder, brush leads electrically connecting the brushes to the connection terminals respectively, and a slip ring cover that covers the slip rings in cooperation with the brush holder, wherein the brush holder comprises first chambers in which the bushes are fixedly accommodated second chambers in which the brush leads are accommodated, the second chambers communicating with the first chambers, and first air holes formed to open outside of the housing and formed as inlet/exhaust passages communicating with the second chambers. 
     Accordingly, the vehicle alternator is allowed to have a larger air passage compared to the conventional small gap formed between the brush and the first chamber, which can significantly increase the amount of air for cooling the sliding portions of the brushes and for removing the powder produced by sliding motion of the brushes. Further, the vehicle alternator allows the brush leads, which are electrically connected to the brushes, to be directly cooled, which prevents the temperature increase of both the brushes and the connection terminals. The prevention of the temperature increase of the connection terminals is able to prevent temperature increase of the brush holder to which the connection terminals are fixed. Consequently, such a construction can significantly decrease the temperature of the brushes, resulting in a long brush lifetime. 
     Preferably, the slip rings are composed of a pair of slip rings for electrical transmission, the brushes are composed of a pair of brushes each made to touch each of the slip rings, the brush leads are composed, brush by brush, of a pair of brushes, the first chambers are composed of a pair of first chambers in each of which each of the brushes is accommodated, the second chambers are composed of a pair of the second chambers in each of which each of the brush leads is accommodated, and first air holes are two in number, in which each of the first air holes are formed to directly communicate with each of the second chambers. 
     Further preferably, one of the first chambers is prepared for a positive electrode, and the other of the first chambers is prepared for a negative electrode; and one of the second chambers is prepared for the positive electrode, and the other of the second chambers is prepared for the negative electrode. Accordingly, the alternator is allowed to have a sufficient amount of air for cooling the brush at the front side as well as for the brush at the rear side, which can increase the lifetime of both brushes. 
     It is preferred that the first air holes have opening areas which are different from each other. Accordingly, the alternator can supply sufficient air to both the brush at the front side and the brush at the rear side, individually, based on the temperature difference between them caused by the positions of the brushes, by adjusting the opening area of each of the first air holes. This enables the lifetime of the brushes to be increased. 
     It is further preferred that the brush holder is provided with a second air hole, the second air hole is directly communicated with the sliding portions of the slip rings. It is also preferred that the alternator comprises a rear cover for covering electrical components accommodating the brushes, where the rear cover is provided at its end face with a cylinder in an axial direction, the cylinder is communicated with the first air hole. Further, It is preferred that the alternator comprises a rear cover for covering electrical components accommodating the brushes, the rear cover is provided at its end face with two cylinders both in an axial direction, one of the cylinders is communicated with the first air hole, and the other cylinder is communicated with the second air hole. 
     Accordingly, this construction having a simple structure allows air to be inlet and exhausted from/to the outside, which permits the lifetime of the brushes to be significantly increased, and the powder produced by sliding motion of the brushes to be sufficiently exhausted. 
     It is further preferred that the cylinder is connected to an inlet/exhaust apparatus disposed in the vehicle side via a connecting member. Accordingly, the inlet/exhaust apparatus is allowed to perform sufficient inletting and exhausting of the air, as well as the exhausting of powder produced by sliding motion of the brushes, which prevents the invasion of foreign objects and improves the mechanical environment of the vehicle alternator, even if the vehicle alternator operates under the over flooding condition. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       In the accompanying drawings: 
         FIG. 1  is a sectional view showing a vehicle alternator of a first preferred embodiment of the present invention; 
         FIG. 2  is an enlarged sectional view showing a substantial part of the vehicle alternator of the first embodiment; 
         FIG. 3  is a perspective view showing a brush apparatus having a brush holder and a slip ring cover combined together; 
         FIG. 4  is a perspective view showing a brush holder before brushes are mounted thereto; 
         FIG. 5  is a cross section at arrow Y-Y of  FIG. 4 ; 
         FIG. 6  is a perspective view showing the slip ring cover; 
         FIG. 7  is a perspective view showing a positional relation among seal members, the brush holder, and the slip ring cover; 
         FIG. 8  is a partial sectional view showing the vehicle alternator connected with an inlet/exhaust apparatus; 
         FIG. 9  is a perspective view showing a brush apparatus having a modified brush holder and the slip ring cover combined together; 
         FIG. 10  is a perspective view showing the modified brush holder before the brushes are mounted thereto; and 
         FIG. 11  shows an example deformation of a brush holder before the brushes are mounted thereto. 
     
    
    
     DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS 
     A vehicle alternator according to a preferred embodiment of the present invention will be described in detail referring to the drawings.  FIG. 1  is a sectional view of the vehicle alternator according to the embodiment.  FIG. 2  is an enlarged sectional view showing a substantial part of the vehicle alternator of the embodiment. 
     As illustrated in  FIG. 1 , the vehicle alternator  1  of the preferred embodiment comprises a stator  2  composed of a wire wound armature  23 . The vehicle alternator  1  also comprises a rotor  3 , which is composed of a field winding  31 , and which is disposed against the inner circumference side of the stator  2 . The vehicle alternator  1  further comprises cooling fans  35 ,  36 , which are fixed to axial end faces of the rotor  3 , and which function as a means for generating cooling air as the rotor  3  rotates. The vehicle alternator  1  also comprises a front-side housing  4   a  and a rear-side housing  4   b  that support the stator  2  and the rotor  3 , a brush apparatus  5  for providing power to the field winding  31 , a voltage control apparatus  6  for controlling output voltage to a predetermined value. The vehicle alternator further comprises a rear cover  7  that covers electrical components such as the brush apparatus  5  and the voltage control apparatus  6  to protect them from foreign objects, and a pulley  20  that transmits rotary driving force from an engine (not shown) to the rotor  3 . 
     The front-side housing  4   a  is provided at its side portion with a plurality of cooling air exhaust windows  42 . These cooling air exhaust windows  42  are provided to exhaust the cooling air to the outside of the front-side housing  4   a , which is generated by the rotation of the cooling fan  35  disposed at the side of the pulley  20 , and is flowing in the centrifugal direction. The rear-side housing  4   b  is provided at its side portion with a plurality of cooling air exhaust windows  42 . These cooling air exhaust windows  42  function to exhaust the cooling air to the outside of the rear-side housing  4   b , which is generated by the rotation of the cooling fan  36  disposed at the side of the rear cover  7 , and is flowing in the centrifugal direction. 
     A pair of slip rings  37 ,  38  are fixedly provided to a rotary shaft  33  of the rotor  3  at its one end, which rotate with the rotary shaft  33 . The brush apparatus  5  comprises a brush holder  53  that accommodates the slip rings  37 ,  38  and a pair of brushes  51  each of which is in slide contact with one of the slip rings  37 ,  38 . The brush apparatus  5  also comprises a slip ring cover  54  that covers the outer circumference of the slip rings  37 ,  38  in cooperation with the brush holder  53 . The brush apparatus further comprises a pair of seal members  55 ,  56  that are provided at the axial end of the brush holder  53  and the slip ring cover  54 . The seal members  55 ,  56  improve the sealing property of a space provided around the slip rings  37 ,  38 . The seal members  55 ,  56  are made of plate-shaped rubbers. 
     The rear cover  7  is mounted to cover such electrical components in order to protect them from foreign objects that accommodate the brushes  51 ,  52 , particularly the brush apparatus  5  and the voltage control apparatus  6  which are mounted outside the rear-side housing  4   b . The rear cover  7  is made of resin, and comprises a first cylinder  71  and a second cylinder  72  that inlet and exhaust the air to/from the inside of the brush apparatus  5 . In this embodiment, the first cylinder  71  is used to exhaust the air, while the second cylinder  72  is used to inlet the air. 
     The brush holder  53  and its circumference structure will be described in detail.  FIG. 3  is a perspective view showing the brush apparatus  5  in which the brush holder  53  and the slip ring cover  54  are combined together.  FIG. 4  is a perspective view showing the brush holder  53  before the brushes  51 ,  52  are mounted to.  FIG. 5  is a cross section at arrow Y-Y of  FIG. 4 .  FIG. 6  is a perspective view showing the slip ring cover  54 .  FIG. 7  is a perspective view showing a positional relation among the seal members  55 ,  56 , the brush holder  53 , and the slip ring cover  54 . 
     The brush holder  53  made of thermosetting resin comprises a box member  152  that is provided with first chambers for brushes  150 ,  150  used for accommodating the brushes  51 ,  52 , and second chambers  151 ,  151  used for accommodating brush leads  60 ,  60 . The box member  152  comprises a thick portion at the side of the slip rings  37 ,  38 , which has a concavely curved configuration along the outer circumference of the slip rings  37 ,  38 , enlarging the surface area of the box member  152 . The box member  152  of the brush holder  53  is provided at its both radial side surfaces  154 ,  154  with positive and negative connection terminals  155 ,  155  made of metal plates, each integrally molded to the box member  152  and projecting from the corresponding side surface  154 . A portion of each connection terminal  155  is exposed in the second chamber  151 , and is connected to the edge portion of the brush lead  60  by soldering. Each brush lead  60  electrically connects the brush  51  or  52  with the corresponding connection terminal  155 . The thick portion  153  having a concavely curved surface is provided at both of radial side portions with concave portions  156 ,  156 , each having a rectangular shape in section, along its entire axial length. The thick portion  153  is also provided at its both radial side surfaces with two convex portions  157 ,  157 , respectively. The box member  152  comprises a air hole  170  on the upper surface  159  thereof, which is communicated with the second chamber  151 . In this embodiment, two air holes  170  are provided; one directly communicating with the second chamber  151  used for accommodating the brush  52  at the rear side, and the other directly communicating with the second chamber  151  used for accommodating the brush  51  at the front side. The brush holder  53  exemplified in  FIG. 4  has the first air hole  170  above the middle portion of the second chamber  151 . The position of the air hole  170 , however, can be relocated. 
     The slip ring cover  54  functions to cover and protect the slip rings  37 ,  38  provided at one end of the rotary shaft  33 . The slip ring cover  54  has such a configuration that one-fourth of entire cylinder circumference is removed, remaining three-fourth of the cylinder circumference in section in the radial direction. The slip ring cover  54  made of resin (for example, nylon) is composed of a peripheral wall  160  having a roughly cylindrical shape formed by the three-fourth circumference of a circle. The peripheral wall  160  is provided at its both circumference sides with V-shaped convex portions  161 ,  161 , each is relatively thin and is extending in the axial direction, and is to be engaged with the corresponding concave portion  156  of the brush holder  53 . A hook-shaped projection  162  is formed at the outside of each of the V-shaped convexes  161 ,  161 , which is to be engaged with the corresponding convex portion  157  of the brush holder  53 . 
     The first cylinder  71  provided to the rear cover  7  is disposed at such a position that allows the interior space, which accommodates the sliding portions of the slip rings  37 ,  38  in slide contact with the brushes, to communicate with the outside. The second cylinder  72  is disposed at such a location that allows the second chamber  151  in the brush holder  53  to communicate with the outside of the rear cover  7  through the first air hole  170 . The second cylinder  72  is disposed against the first air hole  170  that is formed at the upper surface  159  of the box member  152  of the brush holder  53 . The second cylinder  72  in combination with the air hole  170  forms an inlet passage that connects the second chamber  151  with the outside. As shown in  FIG. 7 , the seal member  56  has an opening  561  at a location corresponding to the first cylinder  71 , and has another opening  562  at a location corresponding to the second cylinder  72 . The opening  561  is directly communicated with the sliding portions of the slip rings  37 ,  38  to function as a second air hole. 
       FIG. 8  is a drawing showing the vehicle alternator  1  according to this embodiment connected to an inlet/exhaust apparatus  100 . The first cylinder  71  and the second cylinder  72  are connected to the inlet/exhaust apparatus  100  mounted to a vehicle via a tubular connecting member  101  to forcefully inlet and exhaust the air, which allows the air to flow sufficiently as well as the evacuation of the powder produced by the sliding motion of the brushes  51 ,  52  to be sufficiently completed, led by the inlet/exhaust apparatus  100 . Accordingly, such construction prevents foreign objects from entering into the vehicle alternator  1  and improves the mechanical environment of the vehicle alternator even it is used under the overhead flooding condition. 
     As described above, the rear cover  7  of the vehicle alternator  1  according to the preferred embodiment comprises the second cylinder  72  that allows the second chamber  151  of the brush holder  53  to communicate with the outside. The rear cover  7  also comprises the first cylinder  71  that allows the sliding portions of the slip rings  37 ,  38  to communicate with the outside. Accordingly, the air is supplied to and exhausted from the interior space of the brush holder  53  by the first cylinder  71  and the second cylinder  72 . Consequently, this construction can completely prevent foreign objects from reaching the brushes  51 ,  52  and their adjacent surroundings even when the interior space of the vehicle alternator  1  is flooded. 
     The seal member  56  is disposed between the brush holder  53  and the rear cover  7  in order to seal the interior space surrounding the sliding portions of the brushes  51 ,  52 . The seal member  56  is provided with the openings  561 ,  562  at the positions opposing to the first cylinder  71  and the second cylinder  72 , respectively. The brush holder  53  is provided at its one face (the upper surface  159 ) with the air holes  170 ,  170  that communicate with the second chambers  151 ,  151 . Accordingly, such construction sufficiently seals between the brush holder  53  and the rear cover  7 , besides performing the sufficient prevention of foreign objects&#39; invasion and the improvement of the mechanical environment of the vehicle alternator. 
     The inlet of the air by the second cylinder  72  and the outlet of the air by the first cylinder  71  cause the sliding portions of the brushes  51 ,  52  to be directly cooled by air having relatively low temperature. This prevents the brushes  51 ,  52  from wearing, and eliminates the powder produced by the sliding motion of the brushes  51 ,  52  through the first cylinder  71 . 
     While the present invention has been disclosed in terms of the preferred embodiment in order to facilitate better understanding thereof, it should be appreciated that the invention can be embodied in various ways without departing from the principle of the invention.  FIG. 9  is a perspective view showing a modified brush apparatus  5 A in which a modified brush holder  53 A and the slip ring cover  54  are combined together.  FIG. 10  is a perspective view showing the modified brush holder  53 A before the brushes  51 ,  52  are mounted to it. 
     The modified brush holder  53 A shown in  FIGS. 8 and 9  is provided with a modified pair of air holes  170 A,  170 A having different opening spaces. In general, the brush  51  at the front side disposed closer to heat generating components such as the stator  2  and the rotor  3  has inferior cooling performance compared to the brush  52  at the rear side. Therefore, in this modified configuration, the first air hole  170 A communicating with the second chamber  151  that accommodates the brush  51  at the front side is provided with a large opening space compared to the other first air hole  170 A. Such construction allows the pair of brushes  51 ,  52  to be cooled evenly. 
       FIG. 11  shows an example deformation of a brush holder  53 B before the brushes are mounted thereto. In the example deformation, only one air hole  170 B is provided. In this case, the second chambers  151 ,  151  may be partially communicated.