Title of Invention	AUTOMOTIVE ALTERNATOR
Abstract	In an automotive alternator, mutually-different odd numbers of blades are formed on a pair of fans that are fixed to two axial end surfaces of a rotor, at least one fan in the pair of fans is formed so as to have an outside diameter that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as an outside diameter of the magnetic pole core, the magnetic pole core includes a gradually decreasing portion that is formed such that an outside diameter of a shoulder portion of the clawshaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape, and an outside diameter at the axial end surface of the magnetic pole core is approximately equal to the outside diameter of the fan.

Title of Invention

AUTOMOTIVE ALTERNATOR

Abstract

In an automotive alternator, mutually-different odd numbers of blades are formed on a pair of fans that are fixed to two axial end surfaces of a rotor, at least one fan in the pair of fans is formed so as to have an outside diameter that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as an outside diameter of the magnetic pole core, the magnetic pole core includes a gradually decreasing portion that is formed such that an outside diameter of a shoulder portion of the clawshaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape, and an outside diameter at the axial end surface of the magnetic pole core is approximately equal to the outside diameter of the fan.

Full Text	AUTOMOTIVE ALTERNATOR BACKGROUND OF THE INVENTION [0001] Field of the Invention The present invention relates to an automotive alternator in which a Lundell rotor is supported in a case by means of a bearing, and particularly relates to a fan construction that reduces wind noise of fans that are mounted to two ends of a magnetic pole core. Description of the Related Art [0002] Figures 18 and 19 are a longitudinal section and a front elevation, respectively, of a first conventional automotive alternator. [0003] In Figures 18 and 19, a stator 1 includes- a cylindrical stator core 2 in which a plurality of slots that extend axially are formed at a predetermined pitch circumferentially; and a stator coil 3 that is wound onto the stator core 2. A rotor 4 is constituted by- a field coil 5 that generates magnetic flux on passage of electric current; and front-end and rear-end magnetic pole cores 6 and 7 that are disposed so as to cover the field coil 5 and in which magnetic poles are formed by the magnetic flux that is generated by the field coil 5. The front-end and rear-end magnetic pole cores 6 and 7 are made of iron, and six front-end and rear-end claw-shaped magnetic poles 6a and 7a are respectively disposed on outer circumferential edge portions so as to project at a uniform angular pitch circumferentially. The magnetic pole cores 6 and 7 are disposed so as to face each other such that the claw-shaped magnetic poles 6a and 7a are alternately intermeshed circumferentially, and are fixed to a shaft 8 that is inserted through at a central axial position. In addition, front-end and rear-end centrifugal fans 30 and 31 are fixed to two axial end surfaces of the rotor 4, i.e., to end surfaces of the magnetic pole cores 6 and 7. [0004] A case 10 is constituted by: a front bracket 11 and a rear bracket 12 that are made of aluminum and that are each approximately bowl-shaped. A plurality of front-end air intake apertures 11a are formed on an axial end portion of the front bracket 11, and a plurality of front-end air discharge apertures lib are formed on an outer circumferential side portion of the front bracket 11. Similarly, a plurality of rear-end air intake apertures 12a are formed on an axial end portion of the rear bracket 12, and a plurality of rear-end air discharge apertures 12b are formed on an outer circumferential side portion of the rear bracket 12. [0005] The rotor 4 is housed inside the case 10 such that the shaft 8 is rotatably supported by means of bearings 13. The stator 1 is mounted to the case 10 so as to surround the rotor 4 such that two axial end surfaces of the stator core 2 are pressed and held from two axial ends between opening edge portions of the front bracket 11 and the rear bracket 12 by fastening force from a fastening bolt 14. [0006] A pulley 15 is fixed to an end portion of the shaft 8 that projects out through the front bracket 11. A pair of slip rings 16 that supply excitation current to the rotor 4 are fixed to a rear end of the shaft 8 by means of an insulating sleeve. A pair of brushes 17 are housed inside a brush holder 18 that is disposed radially outside the pair of slip rings 16, and are disposed so as to slide on the respective slip rings 16. A rectifier 19 is disposed at a rear end inside the case 10, and is electrically connected to the stator coil 3 so as to rectify an alternating-current voltage that is induced in the stator coil 3 and output a direct-current voltage. A voltage regulator 20 is mounted to the brush holder 18, and detects the output voltage from the rectifier 19 and controls the excitation current so as to adjust a terminal voltage to a predetermined value. [0007] In a first conventional automotive alternator that is configured in this manner, current is supplied from a battery (not shown) through the brushes 17 and the slip rings 16 to the field coil 5 of the rotor 4, generating a magnetic flux. The clawshaped magnetic poles 6a of the front-end magnetic pole core 6 are magnetized into North-seeking (N) poles by this magnetic flux, and the clawshaped magnetic poles 7a of the rear-end magnetic pole core 7 are magnetized into South-seeking (S) poles. At the same time, rotational torque from an engine (not shown) is transmitted from an output shaft of the engine to the shaft 8 by means of a belt and the pulley 15 such that the rotor 4 is rotated. [0008] Thus, a rotating magnetic field is applied to the stator coil 3 of the stator 1 such that an electromotive force is induced in the stator coil 3. This alternating-current electromotive force is rectified into direct-current power by the rectifier 19, charges the battery, and is supplied to an electric load. [0009] When the shaft 8 is rotated, the centrifugal fans 30 and 31 are also driven to rotate together with the rotor 4. Thus, as indicated by arrows A in Figure 18, a cooling airflow is sucked into the case 10 at a front end through the front-end air intake apertures 11a due to the rotation of the front-end centrifugal fan 30, is deflected centrifugally by the front-end centrifugal fan 30, cools a front-end coil end 3a of the stator coil 3, and is then discharged externally through the front-end air discharge apertures lib. As indicated by arrows B in Figure 18, a cooling airflow is also sucked into the case 10 at a rear end through the rear-end air intake apertures 12a due to the rotation of the rear-end centrifugal fan 31, cools the rectifier 19 and the voltage regulator 20, is deflected centrifugally by the rear-end centrifugal fan 31, cools a rear-end coil end 3b of the stator coil 3, and is then discharged externally through the rear-end air discharge apertures 12b. [0010] Figure 20 is a longitudinal section of a second conventional automotive alternator. In Figure 20, slip rings 16 are fixed to an end portion of a shaft 8 that projects out through a rear bracket 23. A brush holder 18 that houses brushes 17, a rectifier 19, and a voltage regulator 20 are disposed radially outside the slip rings 16 axially outside the rear bracket 23. In addition, a cover 24 is mounted to the rear bracket 23 so as to cover the brush holder 18, the rectifier 19, and the voltage regulator 20. A plurality of rear-end air intake apertures 23a are formed on an axial end portion of the rear bracket 23, and a plurality of rear-end air discharge apertures 23b are formed on an outer circumferential side portion of the rear bracket 23. In addition, a plurality of cover air intake apertures 24a are formed on an end portion of the cover 24. Moreover, the rest of the configuration is configured in a similar manner to that of the first conventional automotive alternator. [0011] At a rear end of a second conventional automotive alternator that is configured in this manner, as indicated by arrows C in Figure 20, cooling airflows are sucked into the cover 24 through the cover air intake apertures 24a due to the rotation of the rear-end centrifugal fan 31, and cool the rectifier 19 and the voltage regulator 20. The cooling airflows that have cooled the rectifier 19 and the voltage regulator 20 are sucked into the case 10 through the rear-end air intake apertures 23a, are deflected centrifugally by the rear-end centrifugal fan 31, cool the rear-end coil end 3b of the stator coil 3, and are then discharged externally through the rear-end air discharge apertures 23b. [0012] Next, conventional centrifugal fan constructions will be explained. Whereas the number of magnetic poles in the magnetic pole cores 6 and 7 is twelve poles, ten blades 30a are formed on the conventional front-end centrifugal fan 30 that is shown in Figure 19. Moreover, twelve front-end air intake apertures 11a are formed on the front bracket 11. [0013] Second conventional front-end and rear-end centrifugal fans 30A and 31A are shown in Figures 21 and 22. Whereas the number of magnetic poles in the magnetic pole cores 6 and 7 is twelve poles, twelve blades 30a are formed on the second conventional front-end centrifugal fan 30A, and reinforcing ribs 30b are formed by pressing. Ten blades 31a are formed on the second conventional rear-end centrifugal fan 31A. Protruding portions 31c for passage of connecting wires 9 of a field coil are formed on a rear surface of the rear-end centrifugal fan 31A. [0014] A third conventional front-end centrifugal fan 30B is shown in Figure 23. Whereas the number of magnetic poles in a magnetic pole core 6 and a magnetic pole core 7 that is not shown is sixteen poles, ten blades 30a are formed on the third conventional front-end centrifugal fan 30B. [0015] Thus, in conventional automotive alternators, whereas the number of magnetic poles is an even number (twelve or sixteen poles), the number of blades 30a in the front-end centrifugal fan 30, 30A, or 30B is also an even number (ten or twelve blades), and one problem has been that harmonic components of wind noise that result from the magnetic poles coincide with harmonic components of wind noise that result from the centrifugal fan, increasing wind noise. If the automotive alternator is a three-phase alternator and the number of slots is one slot per phase per pole, the number of slots in the stator core 2 will be 36 slots if the number of magnetic poles is twelve poles, and 48 slots if there are sixteen poles. Thus, another problem has been that harmonic components of wind noise coincide if the number of blades in the centrifugal fan is twelve blades, increasing wind noise. [0016] Now, in the conventional automotive alternators that are shown in Figures 18 and 20, clearance between outer circumferential surfaces of shoulder portions of the claw-shaped magnetic poles 6a and 7a of the magnetic pole cores 6 and 7 and the coil ends 3a and 3b of the stator coil 3 is small. Inner surfaces of the coil ends 3a and 3b are also irregular. Thus, another problem has been that irritating wind-splitting noise that results from interference between the inner surfaces of the coil ends 3a and 3b and the outer circumferential surfaces of the shoulder portions of the claw-shaped magnetic poles 6a and 7a occurs when the rotor 4 rotates. [0017] In order to solve this problem, a third conventional automotive alternator has been proposed in which outer circumferential surfaces of shoulder portions of claw-shaped magnetic poles 6a and 7a of magnetic pole cores 6 and 7 are formed so as to have inclined surfaces 25 in which clearance from the coil ends 3a and 3b gradually increases toward axial end surfaces, as shown in Figure 24. In the third conventional automotive alternator, the occurrence of noise that results from interference between the inner surfaces of the coil ends 3a and 3b and the outer circumferential surfaces of the shoulder portions of the claw-shaped magnetic poles 6a and 7a is suppressed by forming the outer circumferential surfaces of the shoulder portions of the clawshaped magnetic poles 6a and 7a so as to have inclined surfaces. However, because clearance between the centrifugal fans 30 and 31 and the coil ends 3a and 3b is made narrow in order to improve cooling efficiency in the coil ends 3a and 3b, wind-splitting noise that results from interference between the coil ends 3a and 3b and the centrifugal fans 30 and 31 still occurs when the rotor 4 rotates. SUMMARY OF THE INVENTION [0018] The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator that suppresses increases in wind noise that result from coincidence between harmonic components of wind noise that result from fans and harmonic components of wind noise that result from magnetic poles, and that reduces wind-splitting noise that results from interference between the fans and the magnetic poles. [0019] In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including^ a case; a rotor having: a shaft that is rotatably supported in the case by means of a bearing; a magnetic pole core that is fixed to the shaft such that a plurality of clawshaped magnetic poles that project on outer circumferential edge portions intermesh so as to alternate circumferentially, and that is disposed inside the case! and a field coil that is mounted to the magnetic pole core so as to be covered by the clawshaped magnetic poles; a pair of fans that are fixed to two axial end surfaces of the magnetic pole core! and a stator that is disposed in the case so as to surround the rotor. A cooling airflow ventilation channel is configured by disposing a plurality of air intake apertures on two axial end portions of the case and disposing a plurality of air discharge apertures on an outer circumferential side portion of the case such that a cooling airflow flows into the case through the air intake apertures, is deflected centrifugally by the fans, and is subsequently discharged outside the case through the air discharge apertures when the fans rotate together with rotation of the rotor. Mutually different odd numbers of blades are formed on the pair of fans and at least one fan in the pair of fans is formed so as to have an outside diameter that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as an outside diameter of the magnetic pole core. In addition, the magnetic pole core includes a gradually decreasing portion that is formed such that an outside diameter of a shoulder portion of the claw-shaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape, and an outside diameter at the axial end surface of the magnetic pole core is approximately equal to the outside diameter of the fan. [0020] According to the present invention, wind noise is reduced because harmonic components of wind noise that result from the front-end and rear-end fans do not coincide with harmonic components of wind noise that result from the magnetic poles, and in addition the harmonic components of wind noise that result from the front-end and rear-end fans also do not coincide with each other. Because the outside diameter of the fans is set to a size that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as the outside diameter of the magnetic pole core, noise from each of the fans is reduced, and wind-splitting noise that is generated by interference with coil ends when the fans rotate is also minimized. In addition, because a gradually decreasing portion that is formed such that an outside diameter of a shoulder portion of the clawshaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape is included, clearance between the shoulder portions and the coil ends of the clawshaped magnetic poles is enlarged, reducing wind-splitting noise that is generated by interference between the clawshaped magnetic poles and the coil ends. BRIEF DESCRIPTION OF THE DRAWINGS [0021] Figure 1 is a longitudinal section of an automotive alternator according to Embodiment 1 of the present invention? Figure 2 is a perspective of a rotor in the automotive alternator according to Embodiment 1 of the present invention! Figure 3 is a front elevation of a magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention; Figure 4 is a partial perspective of the magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention; Figure 5 is a front elevation of a front-end fan in the automotive alternator according to Embodiment 1 of the present invention; Figure 6 is a front elevation of a rear-end fan in the automotive alternator according to Embodiment 1 of the present invention! Figure 7 is a graph of measured results of wind noise in the automotive alternator according to Embodiment 1 of the present invention! Figure 8 is a graph of measured results of output in the automotive alternator according to Embodiment 1 of the present invention; Figure 9 is a cross section that shows relationships between a stator and the magnetic pole cores of the rotor in the automotive alternator according to Embodiment 1 of the present invention; Figure 10 is a graph of measured results of overall values of wind noise in the automotive alternator according to Embodiment 1 of the present invention?" Figure 11 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in an automotive alternator according to Embodiment 3 of the present invention; Figure 12 is a partial perspective of a magnetic pole core in the automotive alternator according to Embodiment 3 of the present invention! Figure 13 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in an automotive alternator according to Embodiment 4 of the present invention; Figure 14 is a partial perspective of a magnetic pole core in the automotive alternator according to Embodiment 4 of the present invention! Figure 15 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in an automotive alternator according to Embodiment 5 of the present invention! Figure 16 is a partial perspective of a magnetic pole core in the automotive alternator according to Embodiment 5 of the present invention; Figure 17 is a partial perspective of a second example of a magnetic pole core in the automotive alternator according to Embodiment 5 of the present invention; Figure 18 is a longitudinal section of a first conventional automotive alternator; Figure 19 is a front elevation of the first conventional automotive alternator; Figure 20 is a longitudinal section of a second conventional automotive alternator; Figure 21 is a front elevation of a second conventional front-end fan; Figure 22 is a front elevation of a second conventional rear-end fan; Figure 23 is a front elevation of a third conventional front-end fan! and Figure 24 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in a third conventional automotive alternator. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS [0022] Preferred embodiments of the present invention will now be explained with reference to the drawings. Embodiment 1 Figure 1 is a longitudinal section of an automotive alternator according to Embodiment 1 of the present invention, Figure 2 is a perspective of a rotor in the automotive alternator according to Embodiment 1 of the present invention, Figure 3 is a front elevation of a magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention, Figure 4 is a partial perspective of the magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention, Figure 5 is a front elevation of a front-end fan in the automotive alternator according to Embodiment 1 of the present invention, and Figure 6 is a front elevation of a rear-end fan in the automotive alternator according to Embodiment 1 of the present invention. Moreover, identical numbering will be given to portions identical to or corresponding to those in the conventional automotive alternators that are shown in Figures 18 through 24, and explanation thereof will be omitted. In Figures 1 through 6, a rotor 40 is constituted by: a field coil 5 that generates magnetic flux on passage of electric current; and front-end and rear-end magnetic pole cores 41 and 42 that are disposed so as to cover the field coil 5 and in which magnetic poles are formed by the magnetic flux that is generated by the field coil 5. The front-end and rear-end magnetic pole cores 41 and 42 are made of iron, and six front-end and rear-end clawshaped magnetic poles 41a and 42a are respectively disposed on outer circumferential edge portions so as to project at a uniform angular pitch circumferentially. The magnetic pole cores 41 and 42 are disposed so as to face each other such that the claw-shaped magnetic poles 41a and 42a are alternately intermeshed circumferentially and are fixed to a shaft 8 that is inserted through at a central axial position. [0024] A front-end centrifugal fan 44 is fixed to an axial end surface of the front-end magnetic pole core 41, and has eleven blades 44a that are formed by bending. A rear-end centrifugal fan 45 is fixed to an axial end surface of the rear-end magnetic pole core 42, and has thirteen blades 45a that are formed by bending. Reinforcing ribs 45b are formed on the rear-end centrifugal fan 45 by pressing, and protruding portions 45c for passage of connecting wires 9 to the field coil 5 are also formed thereon. The centrifugal fans 44 and 45 are formed so as to have an outside diameter that is 92 percent as large as the outside diameter at an outermost portion of the magnetic pole cores 41 and 42. [0025] Front-end and rear-end end plates 46 and 47 are formed so as to have ring shapes that have an outside diameter that is less than or equal to the outside diameter of the centrifugal fans 44 and 45, and are mounted to the centrifugal fans 44 and 45 by being fixed to end portions of the blades 44a and 45a. Gradually decreasing portions 43 are formed on shoulder portions of the claw-shaped magnetic poles 41a and 42a of the magnetic pole cores 41 and 42 so as to have inclined surface shapes in which outside diameters of the shoulder portions of the claw-shaped magnetic poles 41a and 42a of the magnetic pole cores 41 and 42 gradually decrease toward the axial end surfaces. Thus, outside diameters at the axial end surfaces of the magnetic pole cores 41 and 42 are approximately equal to the outside diameter of the centrifugal fans 44 and 45. [0026] In an automotive alternator that is configured in this manner, current is supplied from a battery (not shown) through brushes 17 and slip rings 16 to the field coil 5 of the rotor 40, generating a magnetic flux. The claw-shaped magnetic poles 41a of the front-end magnetic pole core 41 are magnetized into North-seeking (N) poles by this magnetic flux, and the claw-shaped magnetic poles 42a of the rear-end magnetic pole core 42 are magnetized into South-seeking (S) poles. At the same time, rotational torque from an engine (not shown) is transmitted from an output shaft of the engine to the shaft 8 by means of a belt and a pulley 15 such that the rotor 40 is rotated. Thus, a rotating magnetic field is applied to the stator coil 3 of the stator 1 such that an electromotive force is induced in the stator coil 3. This alternating-current electromotive force is rectified into direct-current power by a rectifier 19, charges the battery, and is supplied to an electric load. [0027] When the shaft 8 is rotated, the centrifugal fans 44 and 45 are also driven to rotate together with the rotor 40. Thus, as indicated by arrows A in Figure 1, a cooling airflow is sucked into a case 10 at a front end through front-end air intake apertures 11a due to the rotation of the front-end centrifugal fan 44, and is deflected centrifugally by the front-end centrifugal fan 44. A portion of the cooling airflow passes inside the front-end end plate 46, cools a front-end coil end 3a of the stator coil 3, and is then discharged externally through front-end air discharge apertures lib. The remainder of the cooling airflow passes through the magnetic pole cores 41 and 42, cools the field coil 5, and flows rearward. Here, the cooling airflow that is sucked in by the front-end centrifugal fan 44 flows around smoothly because of the presence of the front-end end plate 46. Thus, even though the outside diameter of the front-end centrifugal fan 44 is only 92 percent as large as the outside diameter of the outermost portion of the front-end magnetic pole core 41, the quantity of flow in the cooling airflow is not reduced, and the front-end coil end 3a and the field coil 5 are cooled efficiently. [0028] As indicated by arrows B in Figure 1, a cooling airflow is also sucked into the case 10 at a rear end through rear-end air intake apertures 12a due to the rotation of the rear-end centrifugal fan 45, cools the rectifier 19 and a voltage regulator 20, and is deflected centrifugally by the rear-end centrifugal fan 45. Then, the cooling airflow passes inside the rear-end end plate 47, merges with the cooling airflow that has flowed in from the front end, cools a rear-end coil end 3b of the stator coil 3, and is then discharged externally through rear-end air discharge apertures 12b. Here, the cooling airflow that is sucked in by the rear-end centrifugal fan 45 flows around smoothly because of the presence of the rear-end end plate 47. Thus, even though the outside diameter of the rear-end centrifugal fan 45 is only 92 percent as large as the outside diameter of the outermost portion of the rear-end magnetic pole core 42, the quantity of flow in the cooling airflow is not reduced, and the rear-end coil end 3b is cooled efficiently. Because the end plates 46 and 47 are mounted to the centrifugal fans 44 and 45 in this manner, the cooling airflows can be made to flow efficiently even though the outside diameter of the centrifugal fans 44 and 45 is reduced, enabling the coil ends 3a and 3b and the field coil 5 to be cooled efficiently. [0030] Because the centrifugal fans 44 and 45 and the end plates 46 and 47 are formed so as to have an outside diameter that is 92 percent as large as the outside diameter at the outermost portion of the magnetic pole cores 41 and 42, noise from the centrifugal fans 44 and 45 themselves can be reduced. The clearances between the centrifugal fans 44 and 45 and the coil ends 3a and 3b are also enlarged, enabling wind-splitting noise that is generated there to be reduced. [0031] Outer circumferential surfaces of the shoulder portions of the clawshaped magnetic poles 41a and 42a of the rotor 40 that face the coil ends 3a and 3b are given an inclined surface shape to form gradually decreasing portions 43 in each of which an outside diameter decreases gradually toward an axial end surface. Outside diameters at the axial end surfaces of the magnetic pole cores 41 and 42 are approximately equal to the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47. Thus, the clearances between the gradually decreasing portions 43 of the clawshaped magnetic poles 41a and 42a and the coil ends 3a and 3b are enlarged, enabling the above-mentioned wind-splitting noise to be further reduced. [0032] Now, measurements of wind noise and output in an automotive alternator according to Embodiment 1 are shown in Figures 7 and 8. Moreover, during measurement, the dimensions of the respective portions were set as indicated in Figure 9, the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 was set to a range from 100 percent to 80 percent as large as the outside diameter at the outermost portion of the magnetic pole cores 41 and 42 (100.2 mm), and each of the measured values was compared to when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 was 100 percent as large as the outside diameter of the magnetic pole cores 41 and 42 (i.e., when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 was 100.2 mm). Moreover, all dimensions in Figure 9 are in millimeters. [0033] From Figure 7, it can be seen that the overall value of wind noise gradually decreases after the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 becomes less than 96 percent as large as the outside diameter of the magnetic pole cores 41 and 42 (i.e., when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 is 96.192 mm). From Figure 8, it can also be seen that output does not change greatly while the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 is in a range of 100 percent to 85 percent as large as the outside diameter of the magnetic pole cores 41 and 42, but gradually decreases at less than 85 percent (i.e., when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 is 85.17 mm). From these results, it is desirable for the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 to be set to a range that is 96 percent to 85 percent as large as the outside diameter at the outermost portion of the magnetic pole cores 41 and 42 (i.e., a diameter of 96.192 mm to 85.17 mm). Moreover, in Figure 9, a right-angled step (having a height of approx. 0.75 mm along the diameter) is formed between the outside diameter at the outermost portion of the magnetic pole cores 41 and 42 (100.2 mm) and the outside diameter at a starting portion of the inclined surfaces of the gradually decreasing portions 43 (99.45 mm), and service life of cold forging metal molds for the clawshaped magnetic poles 41a and 42a can be extended by disposing this step compared to when there is no step. [0035] Now, measured results of overall values of wind noise in an automotive alternator in which respective portions were set to the dimensions that are shown in Figure 9 are indicated by a solid line in Figure 10. Similarly, measured results of overall values of wind noise in a comparative example that used magnetic pole cores on which gradually decreasing portions were not formed and centrifugal fans that had an outside diameter equal to the outside diameter at the outermost portion of the magnetic pole cores are indicated by a broken line in Figure 10. From Figure 10, it can be seen that wind noise can be reduced by adopting the configuration of the present automotive alternator. [0036] Next, reductions in wind noise due to the blades 44a and 45a of the centrifugal fans 44 and 45 will be explained. In Embodiment 1, eleven blades 44a are formed on the centrifugal fan 44 that is fixed to the axial end surface of the front-end magnetic pole core 41, and thirteen blades 45a are formed on the centrifugal fan 45 that is fixed to the axial end surface of the rear-end magnetic pole core 42. The number of magnetic poles in the rotor 40 is sixteen poles. [0037] Thus, the numbers of blades 44a and 45a in the front-end centrifugal fan 44 and the rear-end centrifugal fan 45 differ from each other at eleven blades and thirteen blades, respectively, and also differ from the number of magnetic poles in the rotor 40 (sixteen poles). Thus, wind noise is reduced because the harmonic components of wind noise that result from the centrifugal fans 44 and 45 do not coincide with each other, and the harmonic components of wind noise that result from the centrifugal fans 44 and 45 also do not coincide with the harmonic components of wind noise that result from the magnetic pole cores 41 and 42. [0038] Here, wind noise will also be reduced if the centrifugal fans 44 and 45 are applied to a rotor in which the number of magnetic poles is twelve poles because the harmonic components of wind noise that result from the centrifugal fans 44 and 45 do not coincide with each other, and the harmonic components of wind noise that result from the centrifugal fans 44 and 45 also do not coincide with the harmonic components of wind noise that result from the magnetic pole cores 41 and 42. In three-phase alternators, the number of slots in a stator core is a multiple of three, being expressed by 3 x P x n, where P is the number of poles, and n is the number of slots per phase per pole. In Embodiment 1, because the numbers of blades 44a and 45a are eleven blades and thirteen blades, wind noise is also reduced because the harmonic components of wind noise that result from the centrifugal fans 44 and 45 do not coincide with the harmonic components of wind noise that result from the slots. [0039] The numbers of blades in the centrifugal fans 44 and 45 will now be explained from the viewpoint of wind noise reduction. First, because the number of magnetic poles is an even number, coincidence between the harmonic components of wind noise that result from the centrifugal fans 44 and 45 and the harmonic components of wind noise that result from the magnetic pole cores 41 and 42 is eliminated by setting the numbers of blades in the centrifugal fans 44 and 45 to odd numbers that are different from each other, enabling wind noise to be reduced. [0040] In addition, it is also desirable from the viewpoint of wind noise reduction to ensure that the number of front-end blades 44a and the number of rear-end blades 45 are different from each other, and that the number of magnetic poles in the rotor 40 and the number of slots in the stator core 2 are not multiples of the number of blades 44a and 45a. Thus, it is desirable to make the numbers of blades in the centrifugal fans 44 and other. The harmonic components of wind noise that result from the centrifugal fans 44 and 45 can thereby be reliably prevented from coinciding with the harmonic components of wind noise that result from the magnetic pole cores 41 and 42 and the slots, enabling wind noise to be further reduced. [0041] Because the blades 44a and 45a are formed by cutting and raising from metal plates, it is more desirable for the numbers of blades in the centrifugal fans 44 and 45 to be prime numbers that are less than or equal to nineteen because workability is poor and blade area cannot be ensured if the number of blades exceeds twenty blades. In order to eliminate coincidence of harmonic components of wind noise and reduce wind noise, it is also preferable to ensure that the number of air intake apertures 11a in the front bracket 11 is not a multiple of the number of front-end blades 44a, and that the number of air intake apertures 12a in the rear bracket 12 is not a multiple of the number of rear-end blades 45a. [0042] Embodiment 2 In Embodiment 1 above, an automotive alternator has been explained in which end plates 46 and 47 were fixed to centrifugal fans 44 and 45, but in Embodiment 2, an automotive alternator is configured without the end plates 46 and 47. In Embodiment 2, increases in airflow rate due to the end plates 46 and 47 cannot be expected, but effects such as being able to reduce noise from each fan, and being able to reduce wind-splitting noise that arises between the centrifugal fans 44 and 45 and the coil ends 3a and 3b when the centrifugal fans 44 and 45 rotate can be achieved in a similar manner to Embodiment 1 above. [0043] Moreover, in Embodiment 2, both of the end plates 46 and 47 are omitted, but only one of the end plates 46 and 47 may also be omitted. In that case, the quantity of cooling airflow can be increased compared to Embodiment 2 above by an amount proportionate to the mounted end plate, enabling cooling to be improved. [0044] Embodiment 3 In Embodiment 1 above, gradually decreasing portions 43 that have an inclined surface shape were formed on the shoulder portions of the claw-shaped magnetic poles 41a and 42a of the magnetic pole cores 41 and 42, but in Embodiment 3, gradually decreasing portions 43A that have a curved surface shape are formed on shoulder portions of clawshaped magnetic poles 41a and 42a of magnetic pole cores 41 and 42, as shown in Figures 11 and 12. In Embodiment 3, clearance between the coil ends 3a and 3b and the shoulder portions of the clawshaped magnetic poles 41a and 42a is also enlarged by forming the gradually decreasing portions 43A, reducing wind-splitting noise that is generated there. [0045] Embodiment 4 In Embodiment 4, gradually decreasing portions 43B that are constituted by two inclined surface shapes that have steps are formed on shoulder portions of clawshaped magnetic poles 41a and 42a of magnetic pole cores 41 and 42, as shown in Figures 13 and 14. In Embodiment 4, clearance between the coil ends 3a and 3b and the shoulder portions of the clawshaped magnetic poles 41a and 42a is also enlarged by forming the gradually decreasing portions 43B, reducing wind-splitting noise that is generated there. In addition, because the steps of the gradually decreasing portions 43B make the magnetic flux less likely to be affected, decreases in output current are further reduced. [0046] Embodiment 5 In Embodiments 1 through 4 above, gradually decreasing portions 43, 43A, or 43B were formed over an entire circumferential width of the shoulder portions of the clawshaped magnetic poles 41a and 42a, but in Embodiment 5, gradually decreasing portions 43C are formed at a front end of a circumferential width of shoulder portions in a direction of rotation of clawshaped magnetic poles 41a and 42a, as shown in Figures 15 and 16. In Embodiment 5, because the gradually decreasing portions 43C are formed only at the front ends of the circumferential widths of the shoulder portions in the direction of rotation of the clawshaped magnetic poles 41a and 42a, reductions in the outside diameter of the rotor 40 are minimized, enabling decreases in output current to be prevented proportionately. Clearance between the coil ends 3a and 3b and the shoulder portions of the claw-shaped magnetic poles 41a and 42a is also enlarged in regions of formation of the gradually decreasing portions 43C, reducing wind-splitting noise that is generated there. [0047] Moreover, it is not necessary for the gradually decreasing portions 43C to be formed only at the front end of the circumferential widths of the shoulder portions in the direction of rotation of the claw-shaped magnetic poles 41a and 42a; the gradually decreasing portions 43C may also be formed at the front end and the rear end of the circumferential widths of the shoulder portions in the direction of rotation of the claw-shaped magnetic poles 41a and 42a. The cross-sectional shapes of the gradually decreasing portions 43C may also be any two inclined surface shapes that include an inclined surface shape similar to that of the gradually decreasing portions 43, a curved surface shape similar to that of the gradually decreasing portions 43A, or steps similar to those of the gradually decreasing portions 43B. WHAT IS CLAIMED IS: 1. An automotive alternator comprising: a case a rotor comprising: a shaft that is rotatably supported in said case by means of a bearing; a magnetic pole core that is fixed to said shaft such that a plurality of clawshaped magnetic poles that project on outer circumferential edge portions intermesh so as to alternate circumferentially, and that is disposed inside said case; and a field coil that is mounted to said magnetic pole core so as to be covered by said clawshaped magnetic poles; a pair of fans that are fixed to two axial end surfaces of said magnetic pole core; and a stator that is disposed in said case so as to surround said rotor, wherein a cooling airflow ventilation channel is configured by disposing a plurality of air intake apertures on two axial end portions of said case and disposing a plurality of air discharge apertures on an outer circumferential side portion of said case such that a cooling airflow flows into said case through said air intake apertures, is deflected centrifugally by said fans, and is subsequently discharged outside said case through said air discharge apertures when said fans rotate together with rotation of said rotor, characterized in that: mutually-different odd numbers of blades are formed on said pair of fans; at least one fan in said pair of fans is formed so as to have an outside diameter that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as an outside diameter of said magnetic pole core; and said magnetic pole core comprises a gradually decreasing portion that is formed such that an outside diameter of a shoulder portion of said clawshaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape, and an outside diameter at said axial end surface of said magnetic pole core is approximately equal to said outside diameter of said fan. 2. An automotive alternator according to Claim 1, wherein said fan that is formed so as to have an outside diameter that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as said outside diameter of said magnetic pole core has a ring-shaped end plate that is fixed to an end portion of said blades and that has an outside diameter that is equal to or less than said outside diameter of said fan. 3. An automotive alternator according to Claim 1, wherein the number of said air intake apertures is not a multiple of said numbers of said blades. 4. An automotive alternator according to any one of Claims 1 through 3, wherein the numbers of blades in said pair of fans are prime numbers that are greater than or equal to five.

Full Text

AUTOMOTIVE ALTERNATOR
BACKGROUND OF THE INVENTION
[0001] Field of the Invention
The present invention relates to an automotive alternator in which a Lundell rotor is supported in a case by means of a bearing, and particularly relates to a fan construction that reduces wind noise of fans that are mounted to two ends of a magnetic pole core. Description of the Related Art
[0002]
Figures 18 and 19 are a longitudinal section and a front elevation, respectively, of a first conventional automotive alternator.
[0003]
In Figures 18 and 19, a stator 1 includes- a cylindrical stator core 2 in which a plurality of slots that extend axially are formed at a predetermined pitch circumferentially; and a stator coil 3 that is wound onto the stator core 2. A rotor 4 is constituted by- a field coil 5 that generates magnetic flux on passage of electric current; and front-end and rear-end magnetic pole cores 6 and 7 that are disposed so as to cover the field coil 5 and in which magnetic poles are formed by the magnetic flux that is generated by the field coil 5. The front-end and rear-end magnetic pole cores 6 and 7 are made of iron, and six front-end and rear-end claw-shaped magnetic poles 6a and 7a are respectively disposed on outer circumferential edge portions so as to project at a uniform angular pitch circumferentially. The magnetic pole cores 6 and 7 are disposed so as to face each other such that the claw-shaped magnetic poles 6a and 7a are alternately intermeshed circumferentially, and are fixed to a shaft 8 that is inserted through at a central axial position. In addition, front-end and

rear-end centrifugal fans 30 and 31 are fixed to two axial end surfaces of the rotor 4, i.e., to end surfaces of the magnetic pole cores 6 and 7.
[0004]
A case 10 is constituted by: a front bracket 11 and a rear bracket 12 that are made of aluminum and that are each approximately bowl-shaped. A plurality of front-end air intake apertures 11a are formed on an axial end portion of the front bracket 11, and a plurality of front-end air discharge apertures lib are formed on an outer circumferential side portion of the front bracket 11. Similarly, a plurality of rear-end air intake apertures 12a are formed on an axial end portion of the rear bracket 12, and a plurality of rear-end air discharge apertures 12b are formed on an outer circumferential side portion of the rear bracket 12.
[0005]
The rotor 4 is housed inside the case 10 such that the shaft 8 is rotatably supported by means of bearings 13. The stator 1 is mounted to the case 10 so as to surround the rotor 4 such that two axial end surfaces of the stator core 2 are pressed and held from two axial ends between opening edge portions of the front bracket 11 and the rear bracket 12 by fastening force from a fastening bolt 14.
[0006]
A pulley 15 is fixed to an end portion of the shaft 8 that projects out through the front bracket 11. A pair of slip rings 16 that supply excitation current to the rotor 4 are fixed to a rear end of the shaft 8 by means of an insulating sleeve. A pair of brushes 17 are housed inside a brush holder 18 that is disposed radially outside the pair of slip rings 16, and are disposed so as to slide on the respective slip rings 16. A rectifier 19 is disposed at a rear end inside the case 10, and is electrically connected to the stator coil 3 so as to rectify an alternating-current voltage that is induced in the stator coil 3 and output a direct-current voltage. A voltage

regulator 20 is mounted to the brush holder 18, and detects the output voltage from the rectifier 19 and controls the excitation current so as to adjust a terminal voltage to a predetermined value.
[0007]
In a first conventional automotive alternator that is configured in this manner, current is supplied from a battery (not shown) through the brushes 17 and the slip rings 16 to the field coil 5 of the rotor 4, generating a magnetic flux. The clawshaped magnetic poles 6a of the front-end magnetic pole core 6 are magnetized into North-seeking (N) poles by this magnetic flux, and the clawshaped magnetic poles 7a of the rear-end magnetic pole core 7 are magnetized into South-seeking (S) poles. At the same time, rotational torque from an engine (not shown) is transmitted from an output shaft of the engine to the shaft 8 by means of a belt and the pulley 15 such that the rotor 4 is rotated.
[0008]
Thus, a rotating magnetic field is applied to the stator coil 3 of the stator 1 such that an electromotive force is induced in the stator coil 3. This alternating-current electromotive force is rectified into direct-current power by the rectifier 19, charges the battery, and is supplied to an electric load.
[0009]
When the shaft 8 is rotated, the centrifugal fans 30 and 31 are also driven to rotate together with the rotor 4. Thus, as indicated by arrows A in Figure 18, a cooling airflow is sucked into the case 10 at a front end through the front-end air intake apertures 11a due to the rotation of the front-end centrifugal fan 30, is deflected centrifugally by the front-end centrifugal fan 30, cools a front-end coil end 3a of the stator coil 3, and is then discharged externally through the front-end air discharge apertures lib. As indicated by arrows B in Figure 18, a cooling airflow is also

sucked into the case 10 at a rear end through the rear-end air intake apertures 12a due to the rotation of the rear-end centrifugal fan 31, cools the rectifier 19 and the voltage regulator 20, is deflected centrifugally by the rear-end centrifugal fan 31, cools a rear-end coil end 3b of the stator coil 3, and is then discharged externally through the rear-end air discharge apertures 12b.
[0010]
Figure 20 is a longitudinal section of a second conventional automotive alternator.
In Figure 20, slip rings 16 are fixed to an end portion of a shaft 8 that projects out through a rear bracket 23. A brush holder 18 that houses brushes 17, a rectifier 19, and a voltage regulator 20 are disposed radially outside the slip rings 16 axially outside the rear bracket 23. In addition, a cover 24 is mounted to the rear bracket 23 so as to cover the brush holder 18, the rectifier 19, and the voltage regulator 20. A plurality of rear-end air intake apertures 23a are formed on an axial end portion of the rear bracket 23, and a plurality of rear-end air discharge apertures 23b are formed on an outer circumferential side portion of the rear bracket 23. In addition, a plurality of cover air intake apertures 24a are formed on an end portion of the cover 24. Moreover, the rest of the configuration is configured in a similar manner to that of the first conventional automotive alternator.
[0011]
At a rear end of a second conventional automotive alternator that is configured in this manner, as indicated by arrows C in Figure 20, cooling airflows are sucked into the cover 24 through the cover air intake apertures 24a due to the rotation of the rear-end centrifugal fan 31, and cool the rectifier 19 and the voltage regulator 20. The cooling airflows that have cooled the rectifier 19 and the voltage regulator 20 are sucked into the case

10 through the rear-end air intake apertures 23a, are deflected centrifugally by the rear-end centrifugal fan 31, cool the rear-end coil end 3b of the stator coil 3, and are then discharged externally through the rear-end air discharge apertures 23b.
[0012]
Next, conventional centrifugal fan constructions will be explained.
Whereas the number of magnetic poles in the magnetic pole cores 6 and 7 is twelve poles, ten blades 30a are formed on the conventional front-end centrifugal fan 30 that is shown in Figure 19. Moreover, twelve front-end air intake apertures 11a are formed on the front bracket 11.
[0013]
Second conventional front-end and rear-end centrifugal fans 30A and 31A are shown in Figures 21 and 22. Whereas the number of magnetic poles in the magnetic pole cores 6 and 7 is twelve poles, twelve blades 30a are formed on the second conventional front-end centrifugal fan 30A, and reinforcing ribs 30b are formed by pressing. Ten blades 31a are formed on the second conventional rear-end centrifugal fan 31A. Protruding portions 31c for passage of connecting wires 9 of a field coil are formed on a rear surface of the rear-end centrifugal fan 31A.
[0014]
A third conventional front-end centrifugal fan 30B is shown in Figure 23. Whereas the number of magnetic poles in a magnetic pole core 6 and a magnetic pole core 7 that is not shown is sixteen poles, ten blades 30a are formed on the third conventional front-end centrifugal fan 30B.
[0015]
Thus, in conventional automotive alternators, whereas the number of magnetic poles is an even number (twelve or sixteen poles), the number of blades 30a in the front-end centrifugal fan 30, 30A, or 30B is also an even number (ten or twelve blades), and one problem has been that

harmonic components of wind noise that result from the magnetic poles coincide with harmonic components of wind noise that result from the centrifugal fan, increasing wind noise.
If the automotive alternator is a three-phase alternator and the number of slots is one slot per phase per pole, the number of slots in the stator core 2 will be 36 slots if the number of magnetic poles is twelve poles, and 48 slots if there are sixteen poles. Thus, another problem has been that harmonic components of wind noise coincide if the number of blades in the centrifugal fan is twelve blades, increasing wind noise.
[0016]
Now, in the conventional automotive alternators that are shown in Figures 18 and 20, clearance between outer circumferential surfaces of shoulder portions of the claw-shaped magnetic poles 6a and 7a of the magnetic pole cores 6 and 7 and the coil ends 3a and 3b of the stator coil 3 is small. Inner surfaces of the coil ends 3a and 3b are also irregular. Thus, another problem has been that irritating wind-splitting noise that results from interference between the inner surfaces of the coil ends 3a and 3b and the outer circumferential surfaces of the shoulder portions of the claw-shaped magnetic poles 6a and 7a occurs when the rotor 4 rotates.
[0017]
In order to solve this problem, a third conventional automotive alternator has been proposed in which outer circumferential surfaces of shoulder portions of claw-shaped magnetic poles 6a and 7a of magnetic pole cores 6 and 7 are formed so as to have inclined surfaces 25 in which clearance from the coil ends 3a and 3b gradually increases toward axial end surfaces, as shown in Figure 24. In the third conventional automotive alternator, the occurrence of noise that results from interference between the inner surfaces of the coil ends 3a and 3b and the outer circumferential surfaces of the shoulder portions of the claw-shaped magnetic poles 6a and

7a is suppressed by forming the outer circumferential surfaces of the shoulder portions of the clawshaped magnetic poles 6a and 7a so as to have inclined surfaces. However, because clearance between the centrifugal fans 30 and 31 and the coil ends 3a and 3b is made narrow in order to improve cooling efficiency in the coil ends 3a and 3b, wind-splitting noise that results from interference between the coil ends 3a and 3b and the centrifugal fans 30 and 31 still occurs when the rotor 4 rotates.
SUMMARY OF THE INVENTION
[0018]
The present invention aims to solve the above problems and an object of the present invention is to provide an automotive alternator that suppresses increases in wind noise that result from coincidence between harmonic components of wind noise that result from fans and harmonic components of wind noise that result from magnetic poles, and that reduces wind-splitting noise that results from interference between the fans and the magnetic poles.
[0019]
In order to achieve the above object, according to one aspect of the present invention, there is provided an automotive alternator including^ a case; a rotor having: a shaft that is rotatably supported in the case by means of a bearing; a magnetic pole core that is fixed to the shaft such that a plurality of clawshaped magnetic poles that project on outer circumferential edge portions intermesh so as to alternate circumferentially, and that is disposed inside the case! and a field coil that is mounted to the magnetic pole core so as to be covered by the clawshaped magnetic poles; a pair of fans that are fixed to two axial end surfaces of the magnetic pole core! and a stator that is disposed in the case so as to surround the rotor. A cooling airflow ventilation channel is configured by disposing a plurality

of air intake apertures on two axial end portions of the case and disposing a plurality of air discharge apertures on an outer circumferential side portion of the case such that a cooling airflow flows into the case through the air intake apertures, is deflected centrifugally by the fans, and is subsequently discharged outside the case through the air discharge apertures when the fans rotate together with rotation of the rotor. Mutually different odd numbers of blades are formed on the pair of fans and at least one fan in the pair of fans is formed so as to have an outside diameter that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as an outside diameter of the magnetic pole core. In addition, the magnetic pole core includes a gradually decreasing portion that is formed such that an outside diameter of a shoulder portion of the claw-shaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape, and an outside diameter at the axial end surface of the magnetic pole core is approximately equal to the outside diameter of the fan.
[0020]
According to the present invention, wind noise is reduced because harmonic components of wind noise that result from the front-end and rear-end fans do not coincide with harmonic components of wind noise that result from the magnetic poles, and in addition the harmonic components of wind noise that result from the front-end and rear-end fans also do not coincide with each other.
Because the outside diameter of the fans is set to a size that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as the outside diameter of the magnetic pole core, noise from each of the fans is reduced, and wind-splitting noise that is generated by interference with coil ends when the fans rotate is also minimized.
In addition, because a gradually decreasing portion that is formed

such that an outside diameter of a shoulder portion of the clawshaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape is included, clearance between the shoulder portions and the coil ends of the clawshaped magnetic poles is enlarged, reducing wind-splitting noise that is generated by interference between the clawshaped magnetic poles and the coil ends.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021]
Figure 1 is a longitudinal section of an automotive alternator according to Embodiment 1 of the present invention?
Figure 2 is a perspective of a rotor in the automotive alternator according to Embodiment 1 of the present invention!
Figure 3 is a front elevation of a magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention;
Figure 4 is a partial perspective of the magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention;
Figure 5 is a front elevation of a front-end fan in the automotive alternator according to Embodiment 1 of the present invention;
Figure 6 is a front elevation of a rear-end fan in the automotive alternator according to Embodiment 1 of the present invention!
Figure 7 is a graph of measured results of wind noise in the automotive alternator according to Embodiment 1 of the present invention!
Figure 8 is a graph of measured results of output in the automotive alternator according to Embodiment 1 of the present invention;
Figure 9 is a cross section that shows relationships between a

stator and the magnetic pole cores of the rotor in the automotive alternator according to Embodiment 1 of the present invention;
Figure 10 is a graph of measured results of overall values of wind noise in the automotive alternator according to Embodiment 1 of the present invention?"
Figure 11 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in an automotive alternator according to Embodiment 3 of the present invention;
Figure 12 is a partial perspective of a magnetic pole core in the automotive alternator according to Embodiment 3 of the present invention!
Figure 13 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in an automotive alternator according to Embodiment 4 of the present invention;
Figure 14 is a partial perspective of a magnetic pole core in the automotive alternator according to Embodiment 4 of the present invention!
Figure 15 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in an automotive alternator according to Embodiment 5 of the present invention!
Figure 16 is a partial perspective of a magnetic pole core in the automotive alternator according to Embodiment 5 of the present invention;
Figure 17 is a partial perspective of a second example of a magnetic pole core in the automotive alternator according to Embodiment 5 of the present invention;
Figure 18 is a longitudinal section of a first conventional automotive alternator;
Figure 19 is a front elevation of the first conventional automotive alternator;
Figure 20 is a longitudinal section of a second conventional automotive alternator;

Figure 21 is a front elevation of a second conventional front-end fan;
Figure 22 is a front elevation of a second conventional rear-end fan;
Figure 23 is a front elevation of a third conventional front-end fan! and
Figure 24 is a cross section that shows relationships between a stator and magnetic pole cores of a rotor in a third conventional automotive alternator.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0022]
Preferred embodiments of the present invention will now be explained with reference to the drawings. Embodiment 1
Figure 1 is a longitudinal section of an automotive alternator according to Embodiment 1 of the present invention, Figure 2 is a perspective of a rotor in the automotive alternator according to Embodiment 1 of the present invention, Figure 3 is a front elevation of a magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention, Figure 4 is a partial perspective of the magnetic pole core of the rotor in the automotive alternator according to Embodiment 1 of the present invention, Figure 5 is a front elevation of a front-end fan in the automotive alternator according to Embodiment 1 of the present invention, and Figure 6 is a front elevation of a rear-end fan in the automotive alternator according to Embodiment 1 of the present invention. Moreover, identical numbering will be given to portions identical to or corresponding to those in the conventional automotive alternators that are shown in Figures 18 through 24, and explanation thereof will be omitted.

In Figures 1 through 6, a rotor 40 is constituted by: a field coil 5 that generates magnetic flux on passage of electric current; and front-end and rear-end magnetic pole cores 41 and 42 that are disposed so as to cover the field coil 5 and in which magnetic poles are formed by the magnetic flux that is generated by the field coil 5. The front-end and rear-end magnetic pole cores 41 and 42 are made of iron, and six front-end and rear-end clawshaped magnetic poles 41a and 42a are respectively disposed on outer circumferential edge portions so as to project at a uniform angular pitch circumferentially. The magnetic pole cores 41 and 42 are disposed so as to face each other such that the claw-shaped magnetic poles 41a and 42a are alternately intermeshed circumferentially and are fixed to a shaft 8 that is inserted through at a central axial position.
[0024]
A front-end centrifugal fan 44 is fixed to an axial end surface of the front-end magnetic pole core 41, and has eleven blades 44a that are formed by bending. A rear-end centrifugal fan 45 is fixed to an axial end surface of the rear-end magnetic pole core 42, and has thirteen blades 45a that are formed by bending. Reinforcing ribs 45b are formed on the rear-end centrifugal fan 45 by pressing, and protruding portions 45c for passage of connecting wires 9 to the field coil 5 are also formed thereon. The centrifugal fans 44 and 45 are formed so as to have an outside diameter that is 92 percent as large as the outside diameter at an outermost portion of the magnetic pole cores 41 and 42.
[0025]
Front-end and rear-end end plates 46 and 47 are formed so as to have ring shapes that have an outside diameter that is less than or equal to the outside diameter of the centrifugal fans 44 and 45, and are mounted to the centrifugal fans 44 and 45 by being fixed to end portions of the

blades 44a and 45a.
Gradually decreasing portions 43 are formed on shoulder portions of the claw-shaped magnetic poles 41a and 42a of the magnetic pole cores 41 and 42 so as to have inclined surface shapes in which outside diameters of the shoulder portions of the claw-shaped magnetic poles 41a and 42a of the magnetic pole cores 41 and 42 gradually decrease toward the axial end surfaces. Thus, outside diameters at the axial end surfaces of the magnetic pole cores 41 and 42 are approximately equal to the outside diameter of the centrifugal fans 44 and 45.
[0026]
In an automotive alternator that is configured in this manner, current is supplied from a battery (not shown) through brushes 17 and slip rings 16 to the field coil 5 of the rotor 40, generating a magnetic flux. The claw-shaped magnetic poles 41a of the front-end magnetic pole core 41 are magnetized into North-seeking (N) poles by this magnetic flux, and the claw-shaped magnetic poles 42a of the rear-end magnetic pole core 42 are magnetized into South-seeking (S) poles. At the same time, rotational torque from an engine (not shown) is transmitted from an output shaft of the engine to the shaft 8 by means of a belt and a pulley 15 such that the rotor 40 is rotated.
Thus, a rotating magnetic field is applied to the stator coil 3 of the stator 1 such that an electromotive force is induced in the stator coil 3. This alternating-current electromotive force is rectified into direct-current power by a rectifier 19, charges the battery, and is supplied to an electric load.
[0027]
When the shaft 8 is rotated, the centrifugal fans 44 and 45 are also driven to rotate together with the rotor 40. Thus, as indicated by arrows A in Figure 1, a cooling airflow is sucked into a case 10 at a front end through

front-end air intake apertures 11a due to the rotation of the front-end centrifugal fan 44, and is deflected centrifugally by the front-end centrifugal fan 44. A portion of the cooling airflow passes inside the front-end end plate 46, cools a front-end coil end 3a of the stator coil 3, and is then discharged externally through front-end air discharge apertures lib. The remainder of the cooling airflow passes through the magnetic pole cores 41 and 42, cools the field coil 5, and flows rearward. Here, the cooling airflow that is sucked in by the front-end centrifugal fan 44 flows around smoothly because of the presence of the front-end end plate 46. Thus, even though the outside diameter of the front-end centrifugal fan 44 is only 92 percent as large as the outside diameter of the outermost portion of the front-end magnetic pole core 41, the quantity of flow in the cooling airflow is not reduced, and the front-end coil end 3a and the field coil 5 are cooled efficiently.
[0028]
As indicated by arrows B in Figure 1, a cooling airflow is also sucked into the case 10 at a rear end through rear-end air intake apertures 12a due to the rotation of the rear-end centrifugal fan 45, cools the rectifier 19 and a voltage regulator 20, and is deflected centrifugally by the rear-end centrifugal fan 45. Then, the cooling airflow passes inside the rear-end end plate 47, merges with the cooling airflow that has flowed in from the front end, cools a rear-end coil end 3b of the stator coil 3, and is then discharged externally through rear-end air discharge apertures 12b. Here, the cooling airflow that is sucked in by the rear-end centrifugal fan 45 flows around smoothly because of the presence of the rear-end end plate 47. Thus, even though the outside diameter of the rear-end centrifugal fan 45 is only 92 percent as large as the outside diameter of the outermost portion of the rear-end magnetic pole core 42, the quantity of flow in the cooling airflow is not reduced, and the rear-end coil end 3b is cooled efficiently.

Because the end plates 46 and 47 are mounted to the centrifugal fans 44 and 45 in this manner, the cooling airflows can be made to flow efficiently even though the outside diameter of the centrifugal fans 44 and
45 is reduced, enabling the coil ends 3a and 3b and the field coil 5 to be
cooled efficiently.
[0030]
Because the centrifugal fans 44 and 45 and the end plates 46 and 47 are formed so as to have an outside diameter that is 92 percent as large as the outside diameter at the outermost portion of the magnetic pole cores 41 and 42, noise from the centrifugal fans 44 and 45 themselves can be reduced. The clearances between the centrifugal fans 44 and 45 and the coil ends 3a and 3b are also enlarged, enabling wind-splitting noise that is generated there to be reduced.
[0031]
Outer circumferential surfaces of the shoulder portions of the clawshaped magnetic poles 41a and 42a of the rotor 40 that face the coil ends 3a and 3b are given an inclined surface shape to form gradually decreasing portions 43 in each of which an outside diameter decreases gradually toward an axial end surface. Outside diameters at the axial end surfaces of the magnetic pole cores 41 and 42 are approximately equal to the outside diameter of the centrifugal fans 44 and 45 and the end plates
46 and 47. Thus, the clearances between the gradually decreasing
portions 43 of the clawshaped magnetic poles 41a and 42a and the coil
ends 3a and 3b are enlarged, enabling the above-mentioned wind-splitting
noise to be further reduced.
[0032]
Now, measurements of wind noise and output in an automotive alternator according to Embodiment 1 are shown in Figures 7 and 8.

Moreover, during measurement, the dimensions of the respective portions were set as indicated in Figure 9, the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 was set to a range from 100 percent to 80 percent as large as the outside diameter at the outermost portion of the magnetic pole cores 41 and 42 (100.2 mm), and each of the measured values was compared to when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 was 100 percent as large as the outside diameter of the magnetic pole cores 41 and 42 (i.e., when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 was 100.2 mm). Moreover, all dimensions in Figure 9 are in millimeters.
[0033]
From Figure 7, it can be seen that the overall value of wind noise gradually decreases after the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 becomes less than 96 percent as large as the outside diameter of the magnetic pole cores 41 and 42 (i.e., when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 is 96.192 mm). From Figure 8, it can also be seen that output does not change greatly while the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 is in a range of 100 percent to 85 percent as large as the outside diameter of the magnetic pole cores 41 and 42, but gradually decreases at less than 85 percent (i.e., when the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 is 85.17 mm). From these results, it is desirable for the outside diameter of the centrifugal fans 44 and 45 and the end plates 46 and 47 to be set to a range that is 96 percent to 85 percent as large as the outside diameter at the outermost portion of the magnetic pole cores 41 and 42 (i.e., a diameter of 96.192 mm to 85.17 mm).

Moreover, in Figure 9, a right-angled step (having a height of approx. 0.75 mm along the diameter) is formed between the outside diameter at the outermost portion of the magnetic pole cores 41 and 42 (100.2 mm) and the outside diameter at a starting portion of the inclined surfaces of the gradually decreasing portions 43 (99.45 mm), and service life of cold forging metal molds for the clawshaped magnetic poles 41a and 42a can be extended by disposing this step compared to when there is no step.
[0035]
Now, measured results of overall values of wind noise in an automotive alternator in which respective portions were set to the dimensions that are shown in Figure 9 are indicated by a solid line in Figure 10. Similarly, measured results of overall values of wind noise in a comparative example that used magnetic pole cores on which gradually decreasing portions were not formed and centrifugal fans that had an outside diameter equal to the outside diameter at the outermost portion of the magnetic pole cores are indicated by a broken line in Figure 10.
From Figure 10, it can be seen that wind noise can be reduced by adopting the configuration of the present automotive alternator.
[0036]
Next, reductions in wind noise due to the blades 44a and 45a of the centrifugal fans 44 and 45 will be explained.
In Embodiment 1, eleven blades 44a are formed on the centrifugal fan 44 that is fixed to the axial end surface of the front-end magnetic pole core 41, and thirteen blades 45a are formed on the centrifugal fan 45 that is fixed to the axial end surface of the rear-end magnetic pole core 42. The number of magnetic poles in the rotor 40 is sixteen poles.
[0037]
Thus, the numbers of blades 44a and 45a in the front-end

centrifugal fan 44 and the rear-end centrifugal fan 45 differ from each other at eleven blades and thirteen blades, respectively, and also differ from the number of magnetic poles in the rotor 40 (sixteen poles). Thus, wind noise is reduced because the harmonic components of wind noise that result from the centrifugal fans 44 and 45 do not coincide with each other, and the harmonic components of wind noise that result from the centrifugal fans 44 and 45 also do not coincide with the harmonic components of wind noise that result from the magnetic pole cores 41 and 42.
[0038]
Here, wind noise will also be reduced if the centrifugal fans 44 and 45 are applied to a rotor in which the number of magnetic poles is twelve poles because the harmonic components of wind noise that result from the centrifugal fans 44 and 45 do not coincide with each other, and the harmonic components of wind noise that result from the centrifugal fans 44 and 45 also do not coincide with the harmonic components of wind noise that result from the magnetic pole cores 41 and 42.
In three-phase alternators, the number of slots in a stator core is a multiple of three, being expressed by 3 x P x n, where P is the number of poles, and n is the number of slots per phase per pole. In Embodiment 1, because the numbers of blades 44a and 45a are eleven blades and thirteen blades, wind noise is also reduced because the harmonic components of wind noise that result from the centrifugal fans 44 and 45 do not coincide with the harmonic components of wind noise that result from the slots.
[0039]
The numbers of blades in the centrifugal fans 44 and 45 will now be explained from the viewpoint of wind noise reduction.
First, because the number of magnetic poles is an even number, coincidence between the harmonic components of wind noise that result

from the centrifugal fans 44 and 45 and the harmonic components of wind noise that result from the magnetic pole cores 41 and 42 is eliminated by setting the numbers of blades in the centrifugal fans 44 and 45 to odd numbers that are different from each other, enabling wind noise to be reduced.
[0040]
In addition, it is also desirable from the viewpoint of wind noise reduction to ensure that the number of front-end blades 44a and the number of rear-end blades 45 are different from each other, and that the number of magnetic poles in the rotor 40 and the number of slots in the stator core 2 are not multiples of the number of blades 44a and 45a. Thus, it is desirable to make the numbers of blades in the centrifugal fans 44 and
other. The harmonic components of wind noise that result from the centrifugal fans 44 and 45 can thereby be reliably prevented from coinciding with the harmonic components of wind noise that result from the magnetic pole cores 41 and 42 and the slots, enabling wind noise to be further reduced.
[0041]
Because the blades 44a and 45a are formed by cutting and raising from metal plates, it is more desirable for the numbers of blades in the centrifugal fans 44 and 45 to be prime numbers that are less than or equal to nineteen because workability is poor and blade area cannot be ensured if the number of blades exceeds twenty blades.
In order to eliminate coincidence of harmonic components of wind noise and reduce wind noise, it is also preferable to ensure that the number of air intake apertures 11a in the front bracket 11 is not a multiple of the number of front-end blades 44a, and that the number of air intake apertures 12a in the rear bracket 12 is not a multiple of the number of

rear-end blades 45a.
[0042] Embodiment 2
In Embodiment 1 above, an automotive alternator has been explained in which end plates 46 and 47 were fixed to centrifugal fans 44 and 45, but in Embodiment 2, an automotive alternator is configured without the end plates 46 and 47.
In Embodiment 2, increases in airflow rate due to the end plates 46 and 47 cannot be expected, but effects such as being able to reduce noise from each fan, and being able to reduce wind-splitting noise that arises between the centrifugal fans 44 and 45 and the coil ends 3a and 3b when the centrifugal fans 44 and 45 rotate can be achieved in a similar manner to Embodiment 1 above.
[0043]
Moreover, in Embodiment 2, both of the end plates 46 and 47 are omitted, but only one of the end plates 46 and 47 may also be omitted. In that case, the quantity of cooling airflow can be increased compared to Embodiment 2 above by an amount proportionate to the mounted end plate, enabling cooling to be improved.
[0044] Embodiment 3
In Embodiment 1 above, gradually decreasing portions 43 that have an inclined surface shape were formed on the shoulder portions of the claw-shaped magnetic poles 41a and 42a of the magnetic pole cores 41 and 42, but in Embodiment 3, gradually decreasing portions 43A that have a curved surface shape are formed on shoulder portions of clawshaped magnetic poles 41a and 42a of magnetic pole cores 41 and 42, as shown in Figures 11 and 12.
In Embodiment 3, clearance between the coil ends 3a and 3b and

the shoulder portions of the clawshaped magnetic poles 41a and 42a is also enlarged by forming the gradually decreasing portions 43A, reducing wind-splitting noise that is generated there.
[0045] Embodiment 4
In Embodiment 4, gradually decreasing portions 43B that are constituted by two inclined surface shapes that have steps are formed on shoulder portions of clawshaped magnetic poles 41a and 42a of magnetic pole cores 41 and 42, as shown in Figures 13 and 14.
In Embodiment 4, clearance between the coil ends 3a and 3b and the shoulder portions of the clawshaped magnetic poles 41a and 42a is also enlarged by forming the gradually decreasing portions 43B, reducing wind-splitting noise that is generated there. In addition, because the steps of the gradually decreasing portions 43B make the magnetic flux less likely to be affected, decreases in output current are further reduced.
[0046] Embodiment 5
In Embodiments 1 through 4 above, gradually decreasing portions 43, 43A, or 43B were formed over an entire circumferential width of the shoulder portions of the clawshaped magnetic poles 41a and 42a, but in Embodiment 5, gradually decreasing portions 43C are formed at a front end of a circumferential width of shoulder portions in a direction of rotation of clawshaped magnetic poles 41a and 42a, as shown in Figures 15 and 16.
In Embodiment 5, because the gradually decreasing portions 43C are formed only at the front ends of the circumferential widths of the shoulder portions in the direction of rotation of the clawshaped magnetic poles 41a and 42a, reductions in the outside diameter of the rotor 40 are minimized, enabling decreases in output current to be prevented proportionately. Clearance between the coil ends 3a and 3b and the

shoulder portions of the claw-shaped magnetic poles 41a and 42a is also enlarged in regions of formation of the gradually decreasing portions 43C, reducing wind-splitting noise that is generated there.
[0047]
Moreover, it is not necessary for the gradually decreasing portions 43C to be formed only at the front end of the circumferential widths of the shoulder portions in the direction of rotation of the claw-shaped magnetic poles 41a and 42a; the gradually decreasing portions 43C may also be formed at the front end and the rear end of the circumferential widths of the shoulder portions in the direction of rotation of the claw-shaped magnetic poles 41a and 42a.
The cross-sectional shapes of the gradually decreasing portions 43C may also be any two inclined surface shapes that include an inclined surface shape similar to that of the gradually decreasing portions 43, a curved surface shape similar to that of the gradually decreasing portions 43A, or steps similar to those of the gradually decreasing portions 43B.

WHAT IS CLAIMED IS:
1. An automotive alternator comprising:
a case a rotor comprising:
a shaft that is rotatably supported in said case by means of a bearing;
a magnetic pole core that is fixed to said shaft such that a plurality of clawshaped magnetic poles that project on outer circumferential edge portions intermesh so as to alternate circumferentially, and that is disposed inside said case; and
a field coil that is mounted to said magnetic pole core so as to be covered by said clawshaped magnetic poles; a pair of fans that are fixed to two axial end surfaces of said magnetic pole core; and
a stator that is disposed in said case so as to surround said rotor, wherein a cooling airflow ventilation channel is configured by disposing a plurality of air intake apertures on two axial end portions of said case and disposing a plurality of air discharge apertures on an outer circumferential side portion of said case such that a cooling airflow flows into said case through said air intake apertures, is deflected centrifugally by said fans, and is subsequently discharged outside said case through said air discharge apertures when said fans rotate together with rotation of said rotor,
characterized in that:
mutually-different odd numbers of blades are formed on said pair of fans;
at least one fan in said pair of fans is formed so as to have an outside diameter that is in a range of greater than or equal to 85 percent and less than or equal to 96 percent as large as an outside diameter of said

magnetic pole core; and
said magnetic pole core comprises a gradually decreasing portion that is formed such that an outside diameter of a shoulder portion of said clawshaped magnetic poles decreases gradually toward an axial end surface in an inclined surface shape, a curved surface shape, or a stepped shape, and an outside diameter at said axial end surface of said magnetic pole core is approximately equal to said outside diameter of said fan.
2. An automotive alternator according to Claim 1, wherein said fan
that is formed so as to have an outside diameter that is in a range of
greater than or equal to 85 percent and less than or equal to 96 percent as
large as said outside diameter of said magnetic pole core has a ring-shaped
end plate that is fixed to an end portion of said blades and that has an
outside diameter that is equal to or less than said outside diameter of said
fan.
3. An automotive alternator according to Claim 1, wherein the
number of said air intake apertures is not a multiple of said numbers of
said blades.
4. An automotive alternator according to any one of Claims 1 through
3, wherein the numbers of blades in said pair of fans are prime numbers
that are greater than or equal to five.

Documents:

929-che-2007 amanded claims 12-04-2010.pdf

929-che-2007 amended claims 02-07-2010.pdf

929-che-2007 correspondence others 02-07-2010.pdf

929-CHE-2007 CORRESPONDENCE OTHERS 12-04-2010.pdf

929-CHE-2007 AMANDED CLAIMS 10-12-2009.pdf

929-CHE-2007 EXAMINATION REPORT REPLY RECEIVED 10-12-2009.pdf

929-CHE-2007 POWER OF ATTORNEY 10-12-2009.pdf

929-che-2007-abstract.pdf

929-che-2007-claims.pdf

929-che-2007-correspondnece-others.pdf

929-che-2007-description(complete).pdf

929-che-2007-drawings.pdf

929-che-2007-form 1.pdf

929-che-2007-form 18.pdf

929-che-2007-form 3.pdf

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Patent Number

242090

Indian Patent Application Number

929/CHE/2007

PG Journal Number

33/2010

Publication Date

13-Aug-2010

Grant Date

10-Aug-2010

Date of Filing

01-May-2007

Name of Patentee

MITSUBISHI ELECTRIC CORPORATION

Applicant Address

7-3, MARUNOUCHI 2-CHOME, CHIYODA, TOKYO 100-8310, JAPAN

Inventors:

#	Inventor's Name	Inventor's Address
1	KASHIHARA, TOSHIAKI	C/O MITSUBISHI ELECTRIC CORPORATION, 7-3, MARUNOUCHI 2-CHOME, CHIYODA, TOKYO 100-8310, JAPAN

PCT International Classification Number

H02K 19/22

PCT International Application Number

N/A

PCT International Filing date

PCT Conventions:

#	PCT Application Number	Date of Convention	Priority Country
1			NA