Abstract:
A brushless alternating current generator for vehicles comprises a stator, rotor, field winding, rectifier, housing, cover, and extension member. The rectifier has plural rectifying elements to rectify a voltage from the stator winding and output the rectified voltage and a radiating fin to which the rectifying elements are attached. The housing has a side wall and houses both the stator and the rotor and has an end face to which electric parts including the rectifier are attached. The side wall Is along the axial direction. The end face is along the radial direction. Both the side wall and the radiating fin are mutually adjacent to provide a gap in the radial direction. The cover encloses the end face of the housing and has plural air inlets that takes in cooling air. The extension member is secured to the cover and extends into the gap in the axial direction.

Description:
CROSS REFERENCES TO RELATED APPLICATIONS 
       [0001]    The present application relates to and incorporates by reference Japanese Patent Application No. 2007-166160 filed on Jun. 25, 2007. 
       BACKGROUND OF THE INVENTION 
       [0002]    1. Field of the Invention 
         [0003]    The present invention relates to a vehicular alternating current generator (i.e., alternator), and in particular, to a brushless type of alternating current generator mounted In motortrucks, construction machines, agricultural machines, and others. 
         [0004]    2. Description of the Related Art 
         [0005]    In recent years, manufactures for passenger automobiles and motortrucks have been improving the engines so as to comply emission standards. This improvement tends to increase the ambient temperature around the components mounted on an engine. Also, safety devices, additional power supplies, and other in-vehicle amenities have increased gradually, whereby electrical loads to an alternating current (AC) generator (alternator) In each vehicle are on the increase. 
         [0006]    The vehicular AC generator can be divided Into two types in terms of its brush structure. One type is an AC generator with brushes, which are mainly for passenger automobiles. The other type is known as a brushless type of AC generator, which is generally longer operating line. This generator is mainly for motortrucks which travel for a long time, and construction and agricultural machines obliged to work in adverse environments with dust. The brushless type of AC generator is disclosed by Japanese Patent Laid-open Publication No. 2002-95215. 
         [0007]    In the brushless type of AC generator disclosed by the publication, there is a housing which encloses various components. However, the housing has no cooling windows formed through its side walls, because the existence of the cooling windows may allow inhalation of foreign materials and liquid from the outside and also physical damage from the outside. This may result in short-circuited or damaged electrical parts. In addition, the electrical parts such as a rectifier are generally protected by the housing side walls. Cooling for such electrical parts is realized by external cooling fans screwed to the rotary shaft of the generator. 
         [0008]    Recent needs for the AC generator involve making it compact in size and raising its output. Such needs are met by enlarging the outer diameter of a stator mounted in the generator, elongating the stack thickness of the stator, and/or reducing the resistance of windings wound in the stator. However, there still remains a problem that the higher output causes the internal electric parts to have higher temperature. 
         [0009]    Of course, one known countermeasure is to increase the mount and/or speed of air blown by the cooling fans. However, the external fans provided in the brushless type of AC generator is impossible to increase their outer diameters, due to a limitation in fan size along the radial direction. 
         [0010]    Another countermeasure is to increase the number of fan blades and/or the axial area of the fan blades. However, this measure may decrease the strength of the fan blades, which therefore limits the increase in the number and/or area of fan blades. This makes it difficult to obtain a desired speed and/or amount of cooling air Still another countermeasure Is to narrow the gap between radiating fins of electric parts, such as the rectifier, and side walls of the housing so that the cooling air is allowed to sufficiently pass around the radiating fins and through the inside of the housing. However, this narrowed-gap technique tends to cause foreign matters to be accumulated In the gap, because of a reduction in the creeping distance (i.e., clearance or insulating gap) therebetween. The accumulated foreign matters may cause an electrical short circuit, reducing operational reliability of the generator 
       SUMMARY OF THE INVENTION 
       [0011]    The present Invention has been made In consideration of the above various difficult situations, and an object of the present Invention is to provide a brushless type of alternating current generator that Is able to improve cooling performance of electric parts, such as a rectifier, mounted therein and prevent the operational reliability from being lowered In terms of the clearance between the radiating fins of the electric parts and housing side walls. 
         [0012]    In order to realize the above object, the present invention provides, as its basic structure, a brushless alternating current generator for vehicles, comprising: a stator shaped to have an inner circumferential surface and provided with a stator winding; a rotor disposed in the inner bore of the stator so as to face the inner circumferential of the stator, the rotor having a rotary shaft providing an axial direction therealong; a field winding that generates magnetic flux to the rotor; a rectifier having a plurality of rectifying elements to rectify a voltage from the stator winding and output the rectified voltage and a radiating fin to which the rectifying elements are attached; a housing that has a side wall and houses both the stator and the rotor and has an end face to which electric parts including the rectifier are attached, the side wall being along the axial direction, the end face being along a radial direction perpendicular to the axial direction, and both the side wall and the radiating fin being mutually adjacent to provide a gap therebetween in the radial direction; a cover that encloses the end face of the housing and has a plurality of air inlets that takes cooling air into an inside of the cover; and an extension member that 15 secured to the cover and that extends into the gap in the axial direction. 
         [0013]    This allows the extension member to be present in the gap between the radiating fin of the rectifier and the side wall of the housing. Thus the extension member acts as a baffle member against the flow of cooling air passing the gap, so that the cooling air is forced to pass along and through the radiating fin more strongly, improving the cooling performance to the rectifier. 
         [0014]    It is preferred that, by way of example, the extenuation extends into the gap to provide a distance of 1.5 mm or less between the extenuation member and the radiating fin. Thus it is possible to reliably interfere with the flow of the cooling air through the gap, resulting in reliable cooling of the radiating fin. In addition, the distance of 1.5 mm or less makes It possible to prevent deterioration of work of assembling the cover. Such a design for deliberately (or positively) making the gap smaller speeds up the cooling air passing the gap, more effectively cooling the rectifier. 
     
    
     
       BRIEF DESCRIPTIONS OF THE DRAWINGS 
         [0015]    In the accompanying drawings: 
           [0016]      FIG. 1  is a partially sectioned side view showing the overall configuration of a brushless type of vehicular AC generator according to an embodiment of the present invention; 
           [0017]      FIG. 2  is a side view showing, with a rear cover removed, a rear side of the AC generator; 
           [0018]      FIG. 3  is a partial sectional view illustrating the passages of cooling air flowing through the AC generator; 
           [0019]      FIG. 4  is a partial sectional view illustrating the passages of cooling air flowing through a conventional brushless type of vehicular AC generator; 
           [0020]      FIG. 5  is a partial sectional view showing a desired positional relationship In a skirt portion of the AC generator shown in  FIG. 1 ; and 
           [0021]      FIG. 6  shows comparative measurement results of the temperature between a rectifier in the embodiment and a rectifier in the convention structure. 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0022]    Referring to the accompanying drawings, the brushless type of alternating current (AC) generator for vehicles, called an alternator, according to an embodiment of the present Invention will now be described. 
         [0023]      FIGS. 1 and 2  show a brushless type of AC generator  1  according to the embodiment, in which the AC generator (alternator)  1  is provided with a stator  2 , a rotor  3 , field windings  4 , a front housing  51 , a rear housing  52 , a rectifier  6 , a regular  7 , and a rear cover  8 . 
         [0024]    The stator  2 , which functions as an armature, comprises a stator core  21  and stator windings wound around the stator core  21 . The rotor  3 , which functions as a field generator, is located to face the inside circumferential surface of the stator  2 . This rotor  3  comprises a rotary shaft  31 , rotary yoke portions  32  and  33  rotatable with the rotary shaft  31 , an unguis-form (claw shaped) magnetic pole  34  integral with the rotary yoke portion  33 , and an unguis-form magnetic pole  36  integral with the unguis-form magnetic pole  34  by a ring-like support member  35 . The rotary shaft  31  has a rear end (the leftward end in  FIG. 1 ), on which a bearing  37  is arranged to rotatably support this rotary shaft  31 . 
         [0025]    The field winding  4 , which is wound about a stator yoke portion  41 , generates magnetic flux to be supplied to the rotor  3 . The stator yoke portion  41  is a cylindrical member and is fixed to the rear housing  52  by means of a bolt  42 . The stator yoke portion  41  constitutes a part of the magnetic field constituted by the rotor  3 . 
         [0026]    The front housing  51  and the rear housing  52  support the stator  2  and the rotor  3 . The bearing  37  is press fitted and fixed to the rear housing  52 . An end portion of the rotary shaft  31  is projected from the front housing  51 . A cooling fan  53  and a pulley (not shown) are clamped by a nut  54  for fixation to the projected rotary shaft  31 . The regulator  7  adjusts the output voltage of the AC generator  1  by interrupting the excitation current supplied to the field winding  4 . 
         [0027]    An explanation is given in detail hereinafter on the rectifier  6  and the rear cover  8 . The rectifier  6  includes a high-side (or positive-side) radiating fin (cooling fin)  62  and a low-side (or negative side) radiating fin (cooling fin)  63 , which are stacked face to face, being apart from each other In the axial direction with an interposition of a terminal base  61 . 
         [0028]    The high-side radiating fin  62  has six mounting holes passing therethrough, with six high-side rectifying elements  64  being press fitted and attached thereto. Similarly, the low-side radiating fin  63  has six mounting holes passing therethrough, with six low-side rectifying elements  65  being press fitted thereto. A set of three high-side rectifying elements  64  and three low-side rectifying elements  65  constitutes a three-phase full-wave rectifying circuit. The rectifier  6  of the present embodiment has two sets of such three-phase full-wave rectifying circuits to rectify the output voltage of the stator winding  22 , for externally outputting the output current through output terminals fixed to the radiating fin  62 . 
         [0029]    In the present embodiment, the low-side and high-side rectifying elements mean rectifying elements connected to the higher potential side and lower potential side of the power source, respectively. The low-side and high-side radiating fins mean radiating fins disposed at the low-side and high-side rectifying elements, respectively. 
         [0030]    In addition, the rectifier  6  has three auxiliary diodes  67  which rectify the voltage induced to the stator winding  22  to supply excitation current to the field winding  4 . The auxiliary diodes  67  are attached to the terminal base  61 . The radiating fin  62  has an outer peripheral portion which is provided with a plurality of auxiliary fins  62   a  each having a length larger than the thickness of the fixing portion of the rectifying elements  64 , along the axial direction of the rotor  3 , and axial vents (i.e., cooling air holes)  62   b  formed between these auxiliary fins  62   a.    
         [0031]    The rear cover  8  protects the electrical components consisting of the rectifier  6  and the regulator  7 , and has a plurality of suction holes  81  for introducing cooling air into the interior (the side of the electrical components), and a skirt portion  8   a,  an extended portion, made of a resin material, which is disposed between a side wall face  52   a  of the rear housing  52  and the radiating fin  62 . As shown in  FIG. 1 , the side wall face  52   a  of the rear housing  52  and the radiating fin  62  are adjacent to each other In the vertical direction with respect to the rotary shaft  31 , with the rear cover  8  being partially extended along the rotary shaft to form the skirt portion  8   a  between the side wall face  52   a  and the radiating fin  62 . The skirt portion  8   a  is inclined toward the side of the side wall face  52   a  in such a way that the radial thickness of the skirt portion  8   a  is reduced toward an end thereof. 
         [0032]      FIG. 3  is an explanatory view of vent paths for passing cooling air in the AC generator  1  of the present embodiment.  FIG. 4  is an explanatory view of vent paths for passing cooling air In an AC generator having a convention structure, without having a skirt portion. In these figures, the flow of the cooling air is indicated by the thick arrows. 
         [0033]    As shown in  FIG. 3 , in the AC generator  1  of the present embodiment, upon rotation of the cooling fan  53  with the rotary shaft  31 , cooling air is introduced into the Inner space of the rear cover  8  via the suction holes  81  formed in the rear cover  8 . The cooling air then passes through holes  63   a  formed in the radiating fin  63  of the rectifier  6  and the auxiliary fins  62   a  formed on the outer peripheral side of the radiating fin  62  to cool the radiating fins  63  and  62 . Thereafter, the cooling air passes through a suction port  52   b  of the rear housing  52  and is discharged from an exhaust port  51   a  of the front housing  51  via an inner space of the rear housing  52  (the space accommodating the stator  2  and the rotor  3 ). Since the AC generator  1  of the present embodiment is arranged with the skirt portion  8   a  between the auxiliary fins  62   a  of the radiating fin  62  and the side wall face  52   a  of the rear housing  52 , the gap on the outer peripheral side of the auxiliary fins  62   a  is narrowed. In this way, the relative proportion of the amount of the cooling air that flows through this gap without contributing to the cooling of the rectifier  6 , can be reduced. 
         [0034]    On the other hand, as shown in  FIG. 4 , the AC generator of the convention structure has a large gap on the outer peripheral side of the auxiliary fins  62   a.  Due to this structure, the relative proportion of the amount of the cooling air that flows through the gap without contributing to the cooling of the rectifier  6 , is increased. 
         [0035]    As described above, the AC generator  1  of the present embodiment permits the interposition of the skirt portion  8   a  of the rear cover  8  into the gap between the high-side radiating fin  62  of the rectifier  6  and the side wall face  52   a  of the rear housing  52 . Owing to this structure, the vent path for the cooling air passing through this gap can be ensured to pass along the radiating fin  62  or through the through hole  63   a  of the radiating fin  63 , to thereby enhance the cooling performance of the rectifier  6 . 
         [0036]    Also, by radially reducing the thickness of the skirt portion  8   a  toward the end thereof for the inclination of the skirt portion to the side of the side wall face  52   a,  the cooling air can be prevented from turbulently flowing at the end portion of the skirt portion  8   a.  Further, the gradual enlargement of the gap between the side wall face  52   a  and the auxiliary fins  62   a  toward the end portion of the skirt portion  8   a,  may hardly cause foreign matters to accumulate between the auxiliary fins  62   a  and the skirt portion  8   a.    
         [0037]      FIG. 5  is a partial sectional view showing a desired positional relationship in the vicinity of the skirt portion  8   a.  As shown in  FIG. 5 , the distance between the skirt portion  8   a  and the auxiliary fins  62   a  is set to 1.5 mm or less. Thus, the flow of the cooling air through the gap between the auxiliary fins  62   a  and the skirt portion  8   a  can be interfered or blocked to reliably cool the rectifier  6 . In addition, the gap of about 1.5 mm can prevent deterioration in the workability at the time when the rear cover  8  is assembled. The design for deliberately (or positively) making the gap smaller speeds up the cooling air passing the gap, more effectively cooling the rectifier. 
         [0038]    In the present embodiment, the positional relationship is set to satisfy an inequality expression L 2 ≧L 1 , where reference L 1  represents the distance between the side wall face  52   a  and the auxiliary fins  62   a  (e.g., 5 mm), which distance is required for ensuring the insulation properties, and reference L 2  represents the length of the projection of the skirt portion  8   a  from an end face of the auxiliary fins  62   a.  This positional relationship may ensure a creeping distance, which is sufficient for ensuring the insulation properties, between the auxiliary fins  62   a  and the side wall face  52   a  of the rear housing  52 . Thus, reliability can be prevented from being deteriorated, which reliability would otherwise be deteriorated by short circuiting, for example, between the auxiliary fins  62   a  and the side wall face  52   a  of the rear housing. This provides the rectifier with high resistance against water or liquid. 
         [0039]      FIG. 6  shows a comparative measurement results of the temperature between the rectifier in the embodiment and a rectifier in the convention structure. In  FIG. 6 , “A” represents the temperature of the rectifying elements of the rectifier  6  in the AC generator  1  according to the present embodiment (e.g., the temperature of the high-side rectifying elements  64 ), and “B” represents the temperature of the rectifying elements of the rectifier in an AC generator having the convention structure. As can be seen from  FIG. 6 , the cooling performance was enhanced by about 20° C. by Improving the vent paths for cooling with the aid of the skirt portion  8   a.    
         [0040]    The present invention is not limited to the embodiment described above, but various variations may be made within the spirit of the present Invention. For example, as in the embodiment described above, the skirt portion  8   a  may desirably be integrated into the rear cover  8  as a portion thereof to achieve smooth flow of cooling air. In this regard, large axial length of the skirt portion may tend to raise the cost of fabricating the mold. Thus, alternative to the present embodiment, the skirt portion  8   a  may be separately provided in order to reduce the cost of fabricating the mold, and then may be Integrated Into the main body cover having no skirt portion  8   a,  using such technique as welding, bonding or snap fitting. Alternatively, the same effect may be exerted by fixing the skirt portion  8   a  to the side wall face  52   a  of the rear housing  52 , using such technique as welding, bonding or snap fitting. 
         [0041]    The embodiment described above has been based on the case where the high-side radiating fin  62  having the auxiliary fins  62   a  is used. However, the present invention may be applied to the case where no auxiliary fins  62   a  are used. Further, in the embodiment described above, the through holes have been formed only in the low-side radiating fin  63 , but the through holes may also be formed in the high-side radiating fin  62 . 
         [0042]    The present invention may be embodied In several other forms without departing from the spirit thereof. The embodiments and modifications described so far are therefore Intended to be only illustrative and not restrictive, since the scope of the invention is defined by the appended claims rather than by the description preceding them. All changes that fall within the metes and bounds of the claims, or equivalents of such metes and bounds, are therefore intended to be embraced by the claims.