Alternator for vehicle

Abstract: In an alternator, a brush holder (15) holds a pair of brushes (16) which abut slip rings (18) perpendicularly. The brush holder (15) is disposed within an inner periphery of a cooling fan (8) so that the brush holder (15) overlaps with the cooling fan (8) in the axial direction by approximately a width of one of thea brushes (16). The brush holder (15) is secured to the rear housing (2) and disposed to face an air intake window (HIa). As a result, the axial length of the alternator is reduced without sacrificing cooling capacity for the brushes (16).

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an alternator for a vehicle according to the preamble of claim 1. 2. Description of the Related Art Document JP-A-56086052 (= EP-A-0300063) discloses an alternator according to the preamble of claim 1. This alternator is shown in Fig. 4. The alternator has a front housing 31 and a rear housing 32, which are connected together by stud bolts 44 and nuts 45. In the front housing 31, a stator core 35 with a stator winding 34 wound thereon is secured and a pair of claw pole cores 36 with a field winding 37 disposed therebetween are carried by a rotary shaft 38 which is driven by a pulley 33. The rotary shaft 38 is rotatably carried by a front bearing 41 and a rear bearing 42. The pulley 33 is secured to the rotary shaft 38 by a pulley lock nut 43. Cooling fans 39 and 40 are secured to opposite ends of the pole cores 36 to intake and discharge cooling air as indicated by arrows W. A rectifying unit is disposed outside the rear housing 32 and is provided with a minus-pole heat sink 47, plus-pole heat sink 48, and diodes 49 and 50. A brush holder 46 and the rectifying unit are covered by a rear cover plate 52. A voltage regulator 51 is held between the rear housing 32 and the cover plate 52 and juts out from the cover plate 52. Slip rings 54 are disposed at the rear side of the rotary shaft 38 and brushes 53 are held in the brush holder 46 to abut the slip rings 54. Another example of an alternator is disclosed in the document US-A-3 184 625, in which a brush is held in parallel with a rotary shaft and another brush is held perpendicular to the rotary shaft. A further example of an alternator is disclosed in the document US-A-3 198 972, in which brushes held in a relatively long brush holder at the rear side of the alternator are disposed perpendicular to a rotary shaft. Recently, an accommodation space for accessories in a vehicle engine compartment has become narrower as the the sixe of the vehicle engine compartment has been decreasing. Reduction in size and weight of the alternator is also required for saving fuel consumption. In order to attain the reduction in size and weight of the alternator for a vehicle, it is generally required to reduce the diameter and the axial dimension thereof. However, in the alternator disclosed in the above document JP-A-5 6086052, sizes of the field coil, the brush holder and the slip rings account for a significant part of the axial length of the alternator and are an obstacle to reduction of the alternator size. Further, since the brush holder is disposed outside the counter pulley-side rear bearing, cooling air generated by the counter pulley-side fan may not flow around the brush holder sufficiently. Further, in the alternator disclosed in the document US-A-3 184 625, since the radius of the slip ring which corresponds to the brush disposed in parallel with the rotary shaft is greater than the radius of the slip ring which corresponds to the other brush, the former brush is subject to a higher slip speed than the latter brush and wears out sooner than the latter brush. Thus a longer brush holder to accommodate a longer brush is necessary. Still further, in the alternator disclosed in the document US-A-3 198 972, since relatively long brushes are disposed at a rear side of the cooling fan blades, the axial length of the rear portion increases, thereby increasing the axial length of the alternator. SUMMARY OF THE INVENTION The object of the present invention is to provide an improved alternator for a vehicle, the axial dimension and the size of which are reduced without sacrificing heat dissipation of the brush holder. This object is achieved by means of the combination of the features defined in claim 1. Preferable embodiments of the invention are set forth in the subclaims. In the following the invention is further illustrated by an example with reference to the appended drawings. In the drawings: Fig. 1 is a cross-sectional view illustrating an overall structure of an embodiment according to the present invention; Fig. 2 is an enlarged partial view illustrating a portion around a brush holder shown in Fig. 1; Fig. 3 is a plan view illustrating the brush holder being installed in a rear housing shown in Fig. 1; and Fig. 4 is a cross-sectional view illustrating the overall structure of a prior art device. In Fig. 1, an outer periphery member of the alternator consists of aluminum die-cast front housing 1 and rear housing 2, which are connected by a plurality of stud bolts 13 and nuts 14. An air intake window HIb, an air outlet window HOc and the like are formed in the front housing 1. An air intake window HIa and air outlet windows HOa and HOb are formed in the rear housing 2. In order to carry a rotary shaft 9, a front bearing 10 is secured to the front housing 1 and a rear bearing 11 is secured to the rear housing 2 respectively at their boss portion la and 2a by way of press-fitting and squeezing. The shaft 9 is press-fitted to a pair of claw pole cores (field core) 6 in which a field coil 7 is disposed and to slip rings 18 to form a rotor. A stator core (armature core) 5 is secured inside the front housing 1 around the pole core 6 and forms a stator 32 with a stator coil 4 of 2π/3 short pitch multi-phase windings wound in slots of the stator core 5. There are a brush means 15, a rectifying unit 19, voltage regulator (not shown) and other electrical parts disposed in the rear housing 2. The brush means 15 is disposed radially inside the cooling fan 8. The rectifying unit 19 has a plurality of diodes 25 secured respectively on a plus pole heat radiation fin and a minus pole heat radiation fin. The rotary shaft 9 is respectively press-fitted to inner members of the front and rear bearings 10 and 11, and the front bearing 10 of the rotary shaft 9 is press-fitted and secured to the inside of the boss portion la which extends forward from the front housing 1. The rotary shaft 9 also carries the pulley 3 which has a recess to receive the boss portion la therein. The recess is formed to have a distance between its bottom and a loading center of the pulley which is about 2 mm to 8 mm shorter than a distance between the end of the front bearing 10 and a loaded center of the front bearing 10. The pulley 3 is tightly secured to the rotary shaft 9 by a pulley lock nut 12 in such a manner that a bottom of the pulley's recess abuts an end of the inner member of the front bearing 10. The cooling fan 8 has a plurality of fan blades welded to the rear side (counter pulley side) of the rotor 6. The slip rings 18 are molded into a unit with the cooling fan 8. As shown in Figs. 2 and 3, the brush means 15 has a brush case (brush holder) 23 made of resinous material, a pair of brushes 16 and springs 17. The brushes 16 are held in the brush case 23 to extend perpendicular to the rotary shaft 9 and biassed by the springs 17 against the slip rings 18. The brush means 15 is positioned within an area having a diameter C which is slightly smaller than the diameter of the inner periphery of the fan and its front-side brush is located within a zone having width A of the fan blades of the cooling fan 8. That is, the brush means 15 and the cooling fan 8 overlap axially with each other in the zone B by approximately one brush width. As shown in Fig. 3, the brush means 15 is secured to rib members 24 between the air intake windows HIa inside the rear housing 2 by a metal holder 22 and screws 21. The brush case 23 is positioned to face the air intake windows HIa to receive a sufficient amount of cooling air. The rectifying unit 19 rectifies output current generated in the stator coil 4. In the alternator of the embodiment described above, cooling air is introduced into the rear housing through the air intake window HIa to flow around the brush holder and the brushes, along the shaft and is discharged from the air outlet windows HOa and HOb. Therefore, sufficient cooling air is supplied to the brush means and brushes. In particular, the front side brush, where temperature rise is otherwise significant, receives a sufficient amount of cooling air to dissipate generated heat, thereby reducing the axial size of the brushes and brush means. The front housing 1 and the rear housing 2 may be replaced by press-formed material like iron plate or laser-cut iron block instead of the die-cast aluminum. In the alternator according to the invention, the brush holder (15) holds a pair of brushes 16 which abut slip rings 18 perpendicularly. The brush means 15 is disposed within the inner periphery of the cooling fan 8 so that the brush means 15 overlaps with the cooling fan 8 in the axial direction by approximately a width of one of thea brushes 16. The brush means 15 is secured to the rear housing 2 and disposed to face the air intake window HIa. As a result, the axial length of the alternator is reduced without sacrificing cooling capacity for the brushes 16.

Claims: An alternator for a vehicle comprising: a housing (1, 2) having a stator core (5) with an armature coil (4); a rotor having claw pole cores (6), a magnetic-field coil (7), a pulley (3) to be driven by an engine, a cooling fan (8) secured to said rotor at an end opposite said pulley (3) and having a plurality of fan blades (8), and a slip ring member (18); a brush means (15; 16, 17, 18, 23) secured to said housing (2) and having a brush case (23) and a front and a rear brush (16) abutting against said slip ring member (18), characterized in that said brush means (15; 16, 17, 18, 23) is disposed to face an air intake window (HIa), whereby cooling air is introduced through the air intake window to flow around the brush case (23) and brushes (16); and said brush case (23) is disposed within the inner periphery of said fan blades (8) in a zone where said brush case (23) overlaps with said fan blades (8) in the axial direction. An alternator according to claim 1, characterized in that said housing comprises a front housing (1) having a front bearing (10) and a rear housing (2) having a rear bearing (11), wherein said rotor has a pulley (3) carried by a shaft (9) press-fitted into said claw pole cores (6) and carried by said front and rear bearings (10, 11). An alternator according to claim 2, characterized in that said brush means (15, 16, 17, 23) overlaps with said fan blades (8) by approximately a width of said front brush (16). An alternator according to claim 2 or 3, characterized in that said armature coil (4) comprises 2π/3 short pitch multi-phase windings. An alternator according to one of claims 2 to 4, characterized in that said pulley (3) has a recess with its bottom abutting against said front bearing (10) so that the distance between said bottom and a loading center of said pulley is 4 mm to 8 mm shorter than the distance between said bottom and a loaded center of said front bearing (10). An alternator according to one of claims 1 to 5, characterized in that said slip ring member (18) comprises a pair of slip rings molded into a unit with resinous material. An alternator according to one of claims 2 to 6, characterized in that said housing (1, 2) has further cooling air windows (HIa) and a rib member (24) formed between said windows (HIa); and said brush case (23) is secured to said rib member (24). An alternator according to claim 7, characterized in that said cooling air windows (HIa) are formed in said rear housing (2). An alternator according to one of claims 1 to 8, characterized in that said brush case (23) overlaps with said fan blades (8) by approximately a width of one of said brushes (16). An alternator according to one of claims 1 to 9, characterized in that a radially-outer end of said brush case (23) is disposed close to the inner periphery of said fan blades (8).

Inventors: ISHIDA HIROSHI, MUKAI TAKUZOU, ISHIDA, HIROSHI, MUKAI, TAKUZOU
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1995
Main classification: H02K9
IPC codes: H02K9, H02K13, H02K19, H02K5, H01L25