Fan arrangement for a vehicular AC generator

Abstract: A vehicular A.C. generator comprises a magnetic pole core 7, 8 secured to a shaft 6 and excited by an excitation coil 9, the magnetic pole core having opposite end faces, a stationary core 3a and coil 3b surrounding the magnetio pole oore, and a front and a rear bracket 1, 2 supporting the stationary core and rotatably supporting the shaft. The front and rear brackets have ventilation openings, and a fan 31, 32 mounted to each of the opposite end faces of the magnetic pole core is provided for generating flows of cooling air through the ventilation openings 1a, 1b, 2a, 2b in the front and rear brackets. An inlet opening side end portion of a blade 31a - 31e of the fan 31 that overlaps the inlet opening 1a, 2a has a radial length dimension which is equal to or less than 50% of the radial length dimension of the inlet opening side end portion. The fan 32 may be arranged to include a straight blade 32d, 32e and a curved blade 32a, 32b, 32c which are arranged at different angular intervals, and the inner end of all the blades may be positioned at the same distance from the center of rotation.

Description: BACKGROUND OF THE INVENTION This invention relates to a vehicular AC generator for use with a vehicular engine such as an automobile. Fig. 1 illustrates a sectional view of a conventional vehicular AC generator, in which 1 indicates a front side bracket, 2 indicates a rear side bracket and 3 indicates a stator having a stationary core 3a and a stationary coil 3b wound thereon. 1a and 2a indicate air inlet openings disposed in the end faces of the both brackets 1 and 2, 1b and 2b are air outlet openings disposed in an outer circumferential portion of both brackets 1 and 2, and 20 indicates bolts for connecting open ends of the brackets 1 and 2 at the outer circumferential end portions of the stator core 3a to hold the core 3a therebetween. 6 indicates a shaft, which is rotatably supported by bearings 4 and 5 mounted to both the brackets 1 and 2. 7 and 8 indicate magnetic pole cores secured on the shaft 6 to position inside of the stator 3, 7a and 8a are pole pieces of the magnetic pole core, 9 indicates an excitation coil held between the inner circumferences of the magnetic pole cores 7 and 8, 30 and 40 indicate a pair of fans secured to the respective ends of the magnetic pole cores 7 and 8 for rotation with the shaft, 11 indicates a slip ring mounted to the shaft 6, and 12 indicates a rotor composed of the shaft 6, the magnetic pole cores 7 and 8, the excitation coil 9, the fans 30 and 40 and the slip ring 11. 13 indicates an electric collector assembly having inside thereof a brush 13a contacting to the slip ring 11, 14 indicates a rectifier which rectifies and converts an a.c. current, which is induced in the stator coil 3b when an excitation current is supplied to the excitation coil 9 from the brush 13a through the slip ring 11 and when the excitation coil 9 as well as the magnetic pole cores 7 and 8 are rotated by an unillustrated engine through a pulley 15, into a d.c. current, 14a indicates a heat sink for dissipating the heat generated in the rectifier 14, 16 indicates a voltage regulator for controlling the excitation current by detecting the generator voltage to regulate the terminal voltage, and 16a indicates a heat sink of the regulator 16. In the figures, L₀ indicates a radial length dimension of blades 30a ∼ 30e of the fan 30, L₁ indicates a radial length dimension of the overlapping portions betwee the blades 30a ∼ 30e and the inlet opening 1a. Also, Fig. 2 illustrates a side view of the AC generator showing the positional relationship between the inlet opening 1a of the front side bracket 1 and the fan 30. Fig. 3 illustrates a front view of the fan 30, in which 30a ∼ 30h are blades disposed at equal angular interval ϑ°, and in which the inner end of each of the blades is located at an equal distance from the center of rotation of the rotor 12. Fig. 4 illustrates a front view of another fan 31 different from the above fan 30, in which 31a ∼ 31e are blades disposed at uneven angular intervals ϑ₁ ∼ ϑ₅ at every 180 degrees, and in which each blade 31a ∼ 31e has a curved portion which is tilted in the circumferential direction opposite to the direction of rotation toward the outer diameter. The operation of the conventional AC generator will now be described. The rotation of the fans 30 and 40 causes a cooling air to flow through the inlet opening 1a of the front bracket 1 as shown by an arrow a , to cool the bearing 4, the magnetic pole core 7, the excitation coil 9, the stator core 3a and the stator coil 3b to be exhausted to the exterior through the outlet openings 1b. Similarly, the cooling air is also introduced from the inlet opening 2a in the rear bracket 2 as shown by an arrow b , cools the bearing 5, the voltage regulator 16, the rectifier 14, the magnetic pole core 8, the excitation coil 9, the stator core 3a and the stator coil 3b, and exhausted to the exterior through the outlet opening 2b. Since the conventional vehicular AC generator is constructed as above described, the radial length dimension L₁ of the overlapping portion between the blades 30a ∼ 30e of the fan 30 and the inlet opening 1a is equal to or more than about 80% of the radial length dimension L₀ of the blades as illustrated in Fig. 1, so that the portion of the radial length dimension L₁ periodically and intermittently crosses the inlet opening 1a as the fan 30 rotates, resulting in a significant sound pressure of an annoying wind noise of a frequency of a rotational frequency multiplied by the number of the blades and a frequency of the number of the inlet openings 1a multiplied by an even number, i. e., the noise of 10th and 12th order frequencies in Fig. 2, leading to a main cause of an increased overall sound pressure level. JP 58-120759 shows an arrangement which generally exhibits these features, and, therefore, suffers from the above-described disadvantages. When the number of the magnetic pole units 7a and the number of the blades of the fan 30 are equal as illustrated in Fig. 3 for example, the blades and the magnetic pole pieces mutually amplify when they rotate together, generating a wind noise of a frequency of a rotation frequency multiplied by the number of the blades and a rotation frequency multiplied by two times the number of the blades, that is, the wind noise of the frequencies of the 8th and the 16th harmonics becomes significant and annoying leading to a main cause of an increased overall sound pressure. On the other hand, the fan 31 illustrated in Fig. 4 is the one improved from the fan 30, the main improvements being that the blades are disposed at uneven angular intervals at every 180 degrees, each blade has a curved configuration which is tilted in the circumferential direction opposite to the direction of rotation toward the outer diameter, and that the number of the blades and the number of the magnetic pole pieces are made not equal to each other. By applying the above improvements, with the fan 31 shown in Fig. 4, the overall level of the sound pressure level of the wind noise at various rotational speeds is generally decreased, but the ratio of the sound pressure of the frequencies of the 8th order and the 16th order to the overall level was not significantly changed. The reason for this is that two blades 31b of the fan 31 become small for the structural reason, so that it is not possible to match to the diameter of the inner ends of the other blades, whereby the effect of two blades 31b becomes small and has substantially similar function as that with eight blades. Thus, it has been very difficult to manufacture a fan in which the sound pressure level of the frequency of the orders of a multiple of the number of the magnetic pole pieces is decreased. FR 2 602 925 shows an AC generator in which the fan blades are positioned such that the overlay between the blade edges and inlet apertures is less than 50%. This produces a significant reduction in the sound pressure level for certain frequencies of wind noise. However, the reduction is not as great as is desirable. SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a vehicular AC generator free from the above-discussed problems. Another object of the present invention is to provide a vehicular AC generator in which an overall sound pressure level of the wind noise can be decreased. Another object of the present invention is to provide a vehicular AC generator in which the sound pressure level of the frequency multiplied by the number of the fan blades and the frequency multiplied by the even number of the inlet openings can be decreased, thereby eliminating annoying feelings. Still another object of the present invention is to provide a fan arrangement for a vehicular AC generator in which the sound pressure level of the frequency of the order of the multiple of the number of the magnetic pole pieces therewithin is decreased. With the above objects in view, the vehicular AC generator according to the present invention comprises a vehicular A.C. generator comprising: a magnetic pole core secured to a shaft and excited by an excitation coil, said magnetic pole core having opposite end faces; a stationary core surrounding said magnetic pole core and having mounted thereon a stationary coil; supporting or enclosing means having ventilation openings defined therein; and a fan mounted to at least one end face of said magnetic pole core for generating a flow of cooling air through said ventilation openings in which, on the side of a blade of the fan adjacent an inlet opening, the end portion of the said side of the blade that overlaps said inlet opening has a radial length dimension which is equal to or less than 50% of the overall radial length dimension of said inlet opening side end portion; characterized in that on the said side of the blade, the blade has a radially inner corner with a radius not less than 30% of the said overall radial length dimension. Since the arrangement is as above, a significant reduction in sound pressure level of a frequency of a rotational frequency multiplied by the number of the blades and a frequency of the number of the inlet openings multiplied by an even number, i. e., the sound pressure level ;of the 10th and 12th order frequencies out of the frequencies of a wind noise can be advantageously reduced. According to a further aspect of the invention there is provided a fan arrangement for a dynamoelectric machine having blades arranged at different circumferential intervals, each blade having a radially inner and a radially outer edge, characterized in that the blade configuration of the fan includes a straight blade and a curved blade, and that the inner edges of all the blades are disposed at the same distance from the center of rotation. In this arrangement, the frequencies of wind noise generated by the rotation of the fan is dispersed, and the sound pressure level of various frequencies is suppressed so that the overall level can be advantageously reduced. BRIEF DESCRIPTION OF THE DRAWINGS The present invention will become more readily apparent from the following detailed description of the preferred embodiments of the present invention taken in conjunction with the accompanying drawings, in which: Fig. 1 is a sectional view of a conventional vehicular AC generator; Fig. 2 is a side view showing the positional relationship of the conventional bracket inlet openings and the fan; Fig. 3 is a front view of the conventional fan arrangement; Fig. 4 is a front view of another conventional fan arrangement; Fig. 5 is a sectional view of the vehicular AC generator of one embodiment of the present invention; Fig. 6 is a front view illustrating the positional relationship of the bracket inlet openings and the fan; and Fig. 7 is a front view of another embodiment of the fan of the dynamoelectric machine of the present invention. DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will now be described in conjunction with one embodiment of the present invention. Fig. 5 is a sectional view of the vehicular AC generator of the present invention, and Fig. 6 is a side view illustrating the relationship between the inlet openings of the front bracket and the fan. In Figs. 5 and 6, 31 indicates a fan that can be used in place of the conventional fan 30, and 31a ∼ 31e indicate blades of the fan 31. L₀ is a radial length dimension of the end portions on the side of the inlet opening 1a of the blades 31a ∼ 31e, L₁ is a radial length dimension of the blade end portions at which the blades 31a ∼ 31e and the inlet opening 1a overlap and face to each other, and r is a radius of curvature of the radially inner corner of the inlet opening side end portions of the blades. In order to make the above L₁ equal to or less than 50% of L₀, the outer diameter  D of the above inlet opening 1a is made small, or the inner diameter of the end portions on the inlet opening side of the blades 31a ∼ 31e is made larger than the inner diameter at the roots of the blades 31a ∼ 31e, and further, a radius r of a value equal to or more than 30% of the radial length dimension L₀ is provided at the inner side corners of the inlet opening side end portions of the blades. The bracket 1c includes circumferentially spaced radial ribs between groups of inlet openings 1a, as best seen in figure 6. In order to complement the area of the inlet openings 1a, a second inlet opening 1c is defined in each rib of the bracket 1 as illustrated in figure 6. In Figs. 5 and 6, other reference numerals are the same as those of the conventional example illustrated in Figs. 1 and 2, so that the same reference numerals are assigned and their explanations are omitted. As has been described, according to the present invention, the above L₁ is made equal to or less than 50% of L₀, so that a significant reduction in sound pressure level of a frequency of a rotational frequency multiplied by the number of the blades and a frequency of the number of the inlet openings multiplied by an even number, i. e., the sound pressure level of the 10th and 12th order frequencies out of the various frequencies of a wind noise can be advantageously reduced. Also, since a radius r of a value equal to or more than 30% of the radial length dimension L₀ is provided at the inner side corners of the inlet opening side end portions of the blades, the sound pressure level of the 10th and the 12th order frequencies can be further decreased. As has been described, according to the present invention, the radial length dimension of the inlet opening side end portion of the blade of the fan that overlaps the inlet opening is equal to or less than 50% of the radial length dimension of the inlet opening side end portion, so that the overall sound pressure level of the wind noise can be decreased, thereby providing a low-noise vehicular generator with a suppressed annoying sound. Fig. 7 is a front view of another fan arrangement of the dynamoelectric machine of the present invention, in which 32 indicates a fan in its entirety, and 32a ∼ 32e indicate blades of the fan 32, the number of the blades being 10 as compared to 8 of the number of the magnetic pole pieces 7a of the magnetic pole core 7. These blades 32a ∼ 32e are composed of four opposing blades 32d and 32e of the straight line configuration and six curved blades 32a, 32b and 32c curved to tilt in the direction opposite to the direction of rotation toward the radially outward direction. Also, these blades 32a ∼ 32e are arranged at different circumferential intervals within 180 degree, and the inner end of all the blades are disposed at the same distance from the center of rotation. According to the above arrangement, since the magnetic pole core 7 and the fan 32 rotate together, the frequency includes a frequency multiplied by the number of the magnetic pole pieces 7a, i.e., the 8th order frequency with respect to the rotation frequency, a sum of the numbers of the magnetic pole pieces 7a and the unillustrated magnetic pole pieces in pairs with the pole pieces 7a, i.e., the 16th order frequency, and a frequency multiplied by the number of the blades of the fan 32, i.e., the 10th order frequency, and also it is dispersed into the frequencies of the 12th order, the 20th order, the 24th order and the 48th order. Thus, the sound pressure of the frequency of the 8th order and the 16th order is dissipated into the 10th order, the 12th order, the 20th order and the like, so that the annoying wind noise is eliminated and the overall sound pressure level is decreased. As has been described, according to the above embodiment, the blade configuration includes a straight blade and a curved blade, that the blades are arranged at different circumferential intervals, and that the inner end of all the blades are disposed at the same distance from the center of rotation, the overall sound pressure level of the wind noise can be reduced, providing a fan arrangement for a dynamoelectric machine which is low in noise and suppressed in the annoying noise. The fan illustrated in figure 7 is for use in an A.C. generator or alternator, having a general construction similar to that shown in figures 1 to 4, or in figures 5 and 6. Preferably, the fan of figure 7 is incorporated in an alternator such as to present the features already described with reference to figures 5 and 6, namely that the radial extent of the overlap between the air inlet openings and the inlet sides of the blades is not more than 50% of the overall radial extent of the inlet side of the blades.

Claims: A vehicular A.C. generator comprising: a magnetic pole core (7, 8) secured to a shaft (6) and excited by an excitation coil (9), said magnetic pole core having opposite end faces; a stationary core (3a) surrounding said magnetic pole core and having mounted thereon a stationary coil (3b); supporting or enclosing means (1, 2) having ventilation openings (1a, 1b, 2a, 2b) defined therein; and a fan (31) mounted to at least one end face of said magnetic pole core for generating a flow of cooling air through said ventilation openings in which, on the side of a blade (31a - 31e) of the fan (31) adjacent an inlet opening (1a, 2a), the end portion of the said side of the blade that overlaps said inlet opening has a radial length dimension which is equal to or less than 50% of the overall radial length dimension of said inlet opening side end portion; characterized in that on the said side of the blade, the blade has a radially inner corner with a radius not less than 30% of the said overall radial length dimension. A fan arrangement for a dynamoelectric machine having blades arranged at different circumferential intervals, each blade having a radially inner and a radially outer edge, characterized in that the blade configuration of the fan (32) includes a straight blade (32d, 32e) and a curved blade (32a, 32b, 32c), and that the inner edges of all the blades are disposed at the same distance from the center of rotation. A vehicular A.C. generator as claimed in claim 1 in which the fan has at least one straight blade (32d, 32e) and at least one curved blade (32a, 32b, 32c), with the blades arranged at different circumferential intervals and the inner ends of all the blades disposed at the same distance from the axis of rotation. A generator as claimed in claim 1 or 3 in which the supporting or enclosing means comprise front (1) and rear (2) brackets supporting the stationary core and rotatably supporting the shaft. A generator as claimed in claim 4, in which a said bracket (1) has circumferentially spaced ribs between groups of the first mentioned inlet openings (1a) and further inlet openings (1c) in the ribs.

Inventors: KIMURA YUTAKA C O HIMEJI SEISA,  KIMURA, YUTAKA, C/O HIMEJI SEISAKUSHO, Kimura, Yutaka, C/o Himeji Seisakusho
Applicants: MITSUBISHI ELECTRIC CORP, MITSUBISHI DENKI KABUSHIKI KAISHA
Application year: 1990
Main classification: H02K9
IPC codes: H02K9