Rectifying unit for AC generator

Abstract: A rectifying unit B for an alternator is composed of AC input terminal and cooling fins (41-44) connected to output ends (including a neutral point) of a multi-phase stator coil, a negative-poled cooling fin (3) which is grounded and fixed to a rear cover of the alternator, diodes (51-54) whose anodes are soldered to the AC input fins (41-44) and whose cathodes are welded to a positive output terminal, and diodes (61-64) whose anodes are soldered to a negative-poled fin (3) and whose cathodes are welded to the AC input fins (41-44).

Description: The present invention relates to a rectifying unit to be mounted to an AC generator for a vehicle. As shown in Figs. 8 to 10, a conventional rectifying unit mounted to an AC generator has AC input terminals 101~103 connected to output ends of a Y-connected stator coil, a neutral point terminal 104 connected to a neutral point of the stator coil, a negative poled cooling fin 106 fixed to a rear cover 105 of the alternator, rectifying devices 107∼110 having anodes connected to the negative poled cathode output fin 106 and cathodes respectively connected to the AC input terminals 101~ 103 and the neutral point terminal 104, and rectifying elements 112∼115 having anodes respectively connected to the AC input terminals 101∼103 and the neutral point terminal 104 and cathodes connected to a positive-poled fin 111. The positive-poled fin 111 is connected electrically to a terminal bolt, and the negative-poled fin 106 is grounded to a generator housing. In JP-Y2-41-8169, JP-U-58-59363, JP-A-56-29441 and JP-U-56-54871 disclose a rectifying unit which has electrode fins serving as AC input terminals and an electrode fin serving as a neutral point terminal, rectifying elements connected to the electrode fins, a negative-poled terminal for connection of anodes of the rectifying elements with one another, and a positive-poled terminal for connection of cathodes of the rectifying elements with one another. However, in the above rectifying units, a pair of rectifying elements (e.g. rectifying elements 110 and 115 in Fig. 9) connected to the output fin and electrode fins are arranged different in polarity from each other. Consequently, in the case where the rectifying elements are potted diodes, it is necessary to provide two kinds of diodes (one whose anode is a container and the other whose anode is a terminal) and dispose the correct one at a predetermined place at the time of mounting. In the case where the rectifying elements are silicon chips, it is necessary to first discriminate the polarity and thereafter install them into the unit in the same direction or in the opposite direction. Thus, no matter whether the installation is made by an automatic machine or manually, the above installation process deteriorate the productivity markedly. Further, heat radiation from the rectifying elements is effected by the four electrode fins which are floated electrically from the generator housing. Therefore, the size of each electrode fin cannot be made so small because the size corresponds to the heat radiating property. Moreover, once a conduction path is formed between the positive-poled fin 111 and the generator housing by an inspection tool, a tester bar, or the like while maintenance or inspection (engine stop) is being carried out, short-circuit current may flow to cause troubles on the wire and the battery. Document DE-A-2 640 081 discloses a rectifying unit for an AC generator used in a vehicle, for example. The rectifying unit comprises six identical diodes, of which three are mounted on the housing serving as a negative terminal and also as a cooling fin. The remaining three diodes at the positive side of the rectifying unit are each mounted on separate support members with cooling fins integrally formed therewith. Thus, the rectifying unit according to this document requires one large cooling fin and three additional cooling fins. Furthermore, also document DE-A-2 640 081 discloses a rectifying unit for an AC generator in which semiconductor diodes are arranged such that diodes of the same type can be used. Moreover, also this rectifying unit comprises one large cooling fin serving as a negative terminal and three smaller cooling fins serving as AC input terminals. It is an object of the present invention to provide a new and improved rectifying unit for a vehicular AC generator which has rectifying elements of equal polarity with an improved productivity. According to the invention, this object is achieved by a rectifying unit as set out in claim 1. Further advantageous developments of the present invention are set out in the dependent claims. Therefore, the fist and second rectifying elements have the same polarity direction and, consequently, all the rectifying elements of the same structure can be mounted in the same direction, thus facilitating the assembling work and improving the productivity. Besides, it is not necessary to produce and manage two kinds of rectifying elements. Since plural rectifying elements are mounted on a single cooling fin, it is possible to reduce the volume occupied by the rectifying unit (the reduction in size of the AC generator can be attained) and high vibration resistance is obtained. This construction is particularly suitable for the case where the rectifying elements are thin and light-weight, for example in the form of silicon chips. Other objects, features and characteristics of the present invention as well as the functions of related parts of the present invention will become clear from a study of the following detailed description, the appended claims and the drawings. In the drawings: Fig. 1 is a partially cross-sectional view showing an alternator with a rectifying unit according to a first explanatory example mounted thereto; Fig. 2 is a plan view showing the rectifying unit of the first explanatory example; Fig. 3 is a partially cross-sectional view taken on line III-III in Fig. 2; Fig. 4 is a circuit diagram of the rectifying unit according to the first explanatory example; Fig. 5 is a partially cross-sectional view showing a main part of a rectifying unit according to an embodiment of the present invention; Fig. 6 is a partially cross-sectional view showing a main part of a rectifying unit according to a second explanatory example; Fig. 7 is a circuit diagram of the rectifying unit according to the second explanatory example; Fig. 8 is a plan view showing a conventional rectifying unit; Fig. 9 is a partially cross-sectional view taken on line IX-IX in Fig. 8; and Fig. 10 is a circuit diagram of the conventional rectifying unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The following description is now provided about a first explanatory example not forming part of the present invention with reference to Figs. 1 to 4. A rectifying unit B mounted to an alternator A , both shown in Fig. 1, has a negative-poled fin 3, AC input fins 41, 42, 43 and 44, potted diodes 51, 52, 53 and 54 as first rectifying elements, and potted diodes 61, 62, 63 and 64 as second rectifying elements. The alternator A , which has a rotor 71, a stator 72 and a housing 73, is driven by an engine to generate electric power and charge a vehicular battery for the supply of electric power to an electrical load. The rotor 71, which supplies a magnetic field, rotates integrally with a shaft 74. The rotor 71 has a Lundell type pole core 711, a field coil 712 and slip rings 713. A V-ribbed pulley 741 for transfer of the rotating power of the engine is mounted to the front end of the shaft 74. The V-ribbed pulley 741 is connected to a pulley which is mounted to an output shaft of the engine through a belt. The pole core 711 accommodates the field coil 712 therein and has cooling fans 714 and 715 respectively in front and in the rear thereof. The slip rings 713 are formed on a rear end of the shaft 74 on which brushes are slidably disposed. The stator 72 is composed of a stator core 721 disposed around the outer periphery of the pole core 711 and a three-phase Y-connected stator coil 722 wound in the stator core 721. The stator core 721 is a laminate of plural sheets formed of a magnetic material, which is press-fitted in the inner periphery of a front housing 731. Magnetic flux from the pole core 711 intersects the stator coil 722 to induce electromotive force. Three-phase alternating current is supplied from the output ends and neutral points of the Y-connected stator coil 722 which are respectively connected to AC input terminals 411, 421, 431 and 441 of the AC input fins 41, 42, 43 and 44. The housing 73 has a front housing 731, a rear housing 732, both formed by die casting of aluminum, and a rear cover 733 fixed to the rear housing 732. The front housing 731 and the rear housing 732 are clamped together by a plurality of stud bolts 734 and nuts 735. A pair of bearings 736 and 737 are disposed in the front portion of the front housing 731 and in the rear portion of the rear housing 732 respectively to support the shaft 74 rotatably. The negative-poled fin 3, which is formed of a highly heat-conductive metal such as copper for example, assumes a generally horseshoe shape and is grounded and fixed to the rear cover 733. The negative-poled fin 3 has concave portions 31 for mounting the potted diode 62 as shown in Fig. 3 and also diodes 61, 63 and 64. The AC input fins 41∼44, which are formed of a highly heat-conductive metal such as copper for example, assume a generally sectorial shape and are arranged spacedly in a radial plane in opposed relation to the negative-poled fin 3 through an insulating member 400 which will be described later. Since the AC input fins 41∼44 are electrically insulated from the rear cover 733, the radiation of heat to the rear cover by the heat conduction cannot be so much expected. For this reason those fins are arranged so as to be effectively exposed to the cooling air created by the cooling fan 715. As shown in Fig. 3, the AC input fin 42 (and fins 41, 43 and 44 as shown in Fig. 2) has a concave portion 420 for mounting of the potted diode 52 ( and also potted diodes 51, 53 and 54). Further, the AC input fins 41∼44 are provided with AC input terminals 411, 421, 431 and 441 for connection of the output ends and the neutral point of the stator coil 722. The potted diode 52 (and also diodes 51, 53 and 54) has a container 521 formed of a highly heat-conductive metal such as copper for example and a rectifying device sealed hermetically within the container using silicon rubber. The container 521 serves as an anode, while a lead electrode 522 serves as a cathode. The container bottom 521 of the potted diode 52 (51, 53, 54) is soldered to the concave portion 420, and each lead electrode 522 is welded to a terminal strip 401 which is connected electrically to a positive-poled bolt 501. The insulating member 400 for insulation between the AC input fins 41∼44 and the negative-poled fin 3, and a terminal block 402 for insulating and supporting the terminal strip 401 are fixed to the negative-poled fin 3 with pipe rivets 403 extending from the terminal block 402 into the fin 3. The negative poled fine is larger in size and thicker than any one of the AC input fins 41∼44. The potted diode 62 (and also the potted diodes 61, 63 and 64), like the potted diodes 51∼54, has a container 621 formed of a highly heat-conductive metal such as copper for example and a rectifying device sealed hermetically within the container using silicon rubber. The container 621 serves as an anode, while a lead electrode 622 serves as a cathode. The container bottom of the potted diode 62 (and also diodes 61, 63, 64) is soldered to a concave portion 31 of the negative-poled fin 3, while the lead electrode 622 is welded to the AC input fin 42. In summary, the container bottom (anode side) of the potted diode 52 (51, 53, 54) is soldered to the AC input fin 42 (41, 43, 44), the lead electrode 522 is welded to the terminal strip 401, the container bottom (anode) of the potted diode 62 (61, 63, 64) is soldered to the negative-poled fin 3, and the lead electrode 622 is welded to the AC input fin 42. Accordingly, all the potted diodes of the same structure can be mounted in the same direction. The container bottoms (anode) of the potted diodes 61∼64 are soldered to the negative-poled fin 3 which is grounded and fixed to the rear cover 733 to radiate heat from the potted diodes 61∼64. Further, the radiation of heat from the potted diodes 51∼54 is effected by the four AC input fins 41∼44 which are exposed effectively to the cooling air driven by the cooling fan 715. Accordingly, the AC input fins 41∼44 can be reduced in size and dead space can be utilized effectively. If a conduction path is formed between the AC input fins 41∼44 and a housing member such as the rear cover 733 by an inspecting tool, a tester bar, or the like, the flow of a short-circuit current is prevented by the presence of the potted diodes 51∼54. An embodiment of the present invention will be described below with reference to Fig. 5. As shown in Fig. 5, a rectifying unit C has a cooling fin 91, a negative terminal 93 and four AC input electrodes 94 formed on the cooling fin 91 through an insulating layer 92, four silicon chips each anode of which is soldered to one of the four AC input electrodes 94, respectively, and all cathodes of which are wire-bonded to a metallic positive terminal piece 95, and four silicon chips 97 all anodes of which are soldered to the negative terminal 93 and each cathode of which is connected electrically to one of the four AC input electrodes 94. The cooling fin 91 is a metallic plate formed of a highly heat-conductive metal such as copper for example and is grounded and fixed to a housing member of an AC generator. The insulating layer 92 is formed by a thin epoxy resin or ceramic vapor-deposited film superior in thermal conductivity. The negative terminal 93 and the AC input electrodes 94 are formed of a material superior in electrical conductivity such as copper plate, copper vapor-deposited film, or copper foil. The metallic positive terminal piece 95 is molded into an insulating terminal block 751 which is fixed to the cooling fin 91 with pipe rivet. The silicon chips 96 and 97 and the wire-bonded portions are sealed with silicone rubber 98. Although in this embodiment the metallic positive terminal piece 95 is molded into the insulating terminal block 751 which is fixed to the cooling fin 91 with pipe rivet, a positive output electrode corresponding to the metallic positive terminal piece 95 may be formed on the insulating layer 92 like the negative terminal 93 and the AC input electrodes 94. Also, the positive output electrode may be formed on the insulating layer 92, and the metallic negative terminal piece may be molded into the insulating terminal block 751. Since the rectifying elements are silicon chips which are thin and light-weight, the silicon chips 96 and 97 can be attached by soldering onto the negative terminal 93 and the four AC input electrodes 94 both formed on the cooling fin 91 through the insulating layer 92. Only one cooling fin is necessary in this embodiment, thereby decreasing the volume around the silicon chips and increasing resistance to vibration. Description is now directed to a second explanatory example with reference to Figs. 6 and 7. As shown in Figs. 6 and 7, a rectifying unit D is composed of a negative-poled fin 81, AC input fins 821~824, four insulating terminal blocks 831 for insulation and arrangement of gate terminals g1~g8 and a metallic positive terminal piece 860, the gate terminals g1~g8 being each connected to a gate circuit, four insulating members 832 for insulation of the AC input fins 821~824 and the negative-poled fin 81 from each other, SiC-MOSFETs 841~844 which constitute first rectifying elements, and SiC-MOSFETS 851~854a second rectifying elements. The insulating members 832 for insulation between the AC input fins 821~824 and the negative-poled fin 81, and the terminal block 831 for insulating and supporting the terminal piece 860, are each fixed to the negative-poled fin 81 with pipe rivet extending from the terminal block 831 into the fin 81. In the SiC-MOSFETs, their sources (bottoms) are soldered to concave portions of the AC input fins 821~824, their drains are connected to the metallic positive terminal piece 860 electrically by wire bonding, and their gates are connected electrically to the gate terminals g1~g4. In the SiC-MOSFETs 851~854, their sources (bottoms) are each soldered to a recess of the negative-poled fin 81, their drains are connected to AC input terminals k1~k4 electrically by wire bonding, and their gates are connected to the gate terminals g5~g8 electrically by wire bonding. In this example reversed source-drain relation may be also applicable. That is, each drain (bottom) is soldered onto the positive-poled fin and AC input fin, and the negative-poled terminal is disposed on the insulating terminal block. The SiC-MOSFETs 841~844, 851~854, and the wire bonding portions are sealed with a sealing material such as silicone rubber for example. A resin superior in adherence such as an epoxy resin for example can be used in place of the silicone rubber. Since the SiC-MOSFET is low in its on-resistance, the amount of heat generated is small. Consequently, the negative-poled fin 81 and the AC input fins 821~824 may be small in size. In the foregoing description of the present invention, the invention has been disclosed with reference to specific embodiments thereof. It will, however, be evident that various modifications and changes may be made to the specific embodiments of the present invention without departing from the scope of the invention as set forth in the appended claims. Accordingly, the description of the present invention in this document is to be regarded in an illustrative, rather than restrictive, sense.

Claims: A rectifying unit for an AC generator ( A ) having a stator coil ( 722 ) comprising: a plurality of AC input terminals ( 94 ) respectively connected to output ends of said stator coil ( 722 ); a positive output terminal ( 95 ); a negative output terminal ( 93 ); a plurality of first rectifying elements ( 96 ) respectively mounted on said AC input terminals ( 94 ) and each having an input electrode connected to said AC input terminals ( 94 ) and an output electrode connected to said positive output terminal ( 95 ); and a plurality of second rectifying elements ( 97 ) mounted on said negative output terminal ( 93 ) and each having an input electrode connected to said common negative output terminal ( 93 ) and an output electrode connected to one of said AC input terminals ( 94 ); characterised in that said AC input terminals ( 94 ) and said negative output terminal ( 93 ) are disposed on a single cooling fin ( 91 ) through an insulating member ( 92 ); each of said first rectifying elements ( 96 ) is mounted on one of said AC input terminals ( 94 ); and each of said second rectifying elements ( 97 ) is mounted on said negative output terminal ( 93 ). A rectifying unit according to any one of the previous claims, wherein each of said first and second rectifying elements comprises a semiconductor switching element. A rectifying unit according to claim 3, wherein each of said first and second rectifying elements comprises a SiC-MOS-FET.

Inventors: OOIWA TOORU, OOIWA,TOORU
Applicants: DENSO CORP, DENSO CORPORATION
Application year: 1996
Main classification: H02K11
IPC codes: H02K19, H02K11