GB2349749A

GB2349749A - Stator core for car AC generator and process for prodcing said core

Info

Publication number: GB2349749A
Application number: GB0017136A
Authority: GB
Inventors: Yoshihito Asao; Toshiaki Kashihara; Kyoko Higashino; Atsushi Ohashi; Katsumi Adachi
Original assignee: Mitsubishi Electric Corp
Current assignee: Mitsubishi Electric Corp
Priority date: 1999-03-19
Filing date: 1999-09-17
Publication date: 2000-11-08
Anticipated expiration: 2019-09-17
Also published as: GB2349749B; GB0017136D0

Abstract

The stator core 7 is of cylindrical form and comprises superposed metal sheet layers, with welded portions 74 for fixing the layers. There are a plurality of groups 740 of welded portions 74, each group being formed on the exterior (or the interior) from the lower end to the upper end. All the groups 740 extend in the same direction diagonal to the lamination direction. In each group 740 the welded portions 74 are parallel to the lamination direction and at different locations in the circumferential direction and the axial direction.

Description

STATOR CORE FOR CAR AC GENERATOR AND PROCESS FOR PRODUCING STATOR CORE FOR CAR AC GENERATOR The present invention relates to a stator core for an AC generator to be mounted on a vehicle and a production process therefor.

Fig. 5 is a sectional view of a car AC generator of the prior art. Tri-s AC generator comprises a case 3 formed by connecting an aluminum front bracket 1 and an aluminum rear bracket 2 by a bolt 3B, a shaft 5 provided in the case 3 and fitted with a pulley 4 for receiving the torque of an engine transmitted from a belt at one end, a randol type rotor 6 fixed to the shaft 5, fans 6F fixed to both side of the rotor 6, a stator 7A fixed on the inner wall of the case 3, slip rings 8, fixed to the other end of the shaft 5, for supplying a current to the rotor 6, a pair of brushes 9 and 9 which slide in contact with the slip rings 8, a brush holder 10 for storing the brushes 9 and 9, a rectifier 11, electrically connecte to the stator 7A, for rectifying an AC generated in the stator 7A into a DC, beet sink 12 attached to the brush holder 10, and a regulator 13, attache to the heat sink 12, for regulating an au voltage generated in the stator 7A. Denoted by 14a and 14b are bearings, and 15 rackets for connecting the AC generator to the engine.

The above rotor 6 comprises a rotor coil 6A forgenerating a magnetic flux with a current supplie and a pole core 6B for covering the rotor coil 6A and forming a magnetic pole with the magnetic flux. The pole core 6B consists of a pair of pole core unit 6x and a pole core unit 6y which engage with each other.

The pole core units 6x and 6y are made from iron and have claw-like magnetic poles 62 and 62, respectively.

The stator 7A comprises a stator core 17A and a stator coil 17B formed of a conductor wound round the stator core 17A.

An AC is generated in the stator coil 17B by the rotation of the rotor 6 according to changes in the magnetic flux from the rotor coil 6A.

In the car AC generator constituted above, a current is supplie to the rotor coi 5S ~~cm a battery (unshown) through the brushes 9 and 9 and the slip rings 8 to generate a magnetic flux. Meanwhile, the pulley 4 is driven by the engine and the rotor 6 is turned by the shaft 5, thereby giving a rotating field to the stator coil 17B to generate electromotive force in the stator coil 17B. This AC electromotive force is rectifie into a DC by the diodes 16 and 16 of the rectifier 11, the DC is regulated by the regulator 13, and the regulated DC is charged into the battery.

Fig. 6 is a sectional view of a car brushless AC generator of the prior art. The same or corresponding elements as those of Fig. 5 are given the same reference symbols and their descriptions are omitted. In the case of this car brushless AC generator, when the engine is started, an excitation current is supplie from the battery to an excitation coil incorporated in an excitation core 19 through a regulator 13A and the pole core units 6x and 6y of the rotor 6 are turned by the rotation of the shaft 5, whereby electromotive force is generated in the stator coil 17B of the stator 7A. This AC electromotive force is reçtified into a DC by the diodes 16 and 16 of the rectifier 11, the DC is regulated by the regulator 13A, and thé reguiated DC is charged into the battery.

Fig. 7 is a schematic perspective view showing an example of stator core 17A used in the car AC generator of the prior art shown in Fig. 5 and Fig. 6. The stator core 17A having a predetermined thickness S in a lamination direction is constructed by winding a single long iron metal sheet 17a which is punched as shown in Fig. g spirally in such a manner that the metal sheet layer are placed one upon another to form a cylinder and welding the cylinder at several locations on the peripheral side of the cylinder in the lamination direction.

The metal sheet 17a has recesses 17b for forming slots 20 and recesses 17c for forming bolt shelter grooves 21 after lamination. Fig. 9 is a schematic plan view of the stator core 17A.

In Fig. 7, four welding spots are provided on the peripheral side at inceLvdls of about 90 on the basis of the center of the cylinder. Generally speaking, four welding spots are provided from the view point of the strength of the core assembly. Welding is carried out linearly from the upper end to the lower end of the peripheral side of the cylinder with a jig movable in the lamination direction of the cylinder after the cylinder is sandwiche between chucks to bring the layers of the metal sheet 17a into close contact with one another.

A first-phasecoil, asecond-phasecoil and a third-phase coil are inserted into the respective slots 20 of the stator core 17A shown in Fig. 7 to construct the stator 7A shown in Fig. 10 for inducing a three-phase AC. The coil of each phase is inserted into every three slots. Conductors 17e forming the coil are fixed in each slot 20 with varnish 22 as shown in Fig.

11 and the opening side of the slot 20 is sealed with a resin 23.

By winding the long metal sheet 17a punched as shown in Fig. 8 spirally in such a matter that the metal sheet layers are placed one upon another, a plurality of bolt shelter grooves 21 are formed linearly on the peripheral side of the stator core 17A so that they are continuos in a vertical direction and parallel to the lamination direction of the metal sheet 17a.

The bolt shelter grooves 21 are formed at intervals of 10 , for example, on the basis of the center of the stator core 17A.

Besides the above method, the stator core having a predetermined thickness may be constructed by placing a plurality of ring-shaped metal sheets one upon another to form a cylinder and welding the peripheral side of the cylinder at several locations in the same manner as described above.

According to the above-described stator core 17A of the prior art, the peripheral side of the cylinder is welded linearly (parallel to the above bolt shelter grooves 21) in the lamination direction of the metal sheet continuously from the upper end to the lower end of the cylinder. Therefore, when suction force between the rotor 6 and the stator 7A Zc applied to the stator core 17A, there arises such a problem that the stator 7A qenerates a vibration mode in a radial direction as

a whole with a linear welcied portion serving as a joint as shown in Fig. 12.

Japanese Utility Patent Application No. 53-141410 discloses a stator core 30 in which a non-welded portion 31 is partly formed as shown in Fig. 13. Welded portions which are continuos in a vertical direction are formed at sevrai welding spots on the peripheral side of the stator core 30 having a predetermined thickness S. However, in this stator core 30, welded portions 32 continuos in a vertical direction are concentratedly formedat each welding spot and it cannot be said that the welded portions 32 are scattered in the peripheral direction and vertical direction of the stator core. Therefore, the welded portions 32 serve as joints and a vibration mode is still generated with some joints because the joints do not disappear and a variety of elements are existent in a car generator having a wide range of revolution speed.

As shown in Fig. 14, Japanese Laid-open Patent Application No. 54-124845 discloses a stator core 4u wnich s produced by forming oblique welded portions 41 on the peripheral side in a zigzag manner. Even in this case, since the upper and lower ends of the welded portion 41 are close to each other, the rigidities of the upper and lower ends of the welded portion 41 are high and joints cannot be eliminated completely.

Therefore, a vibration mode is still generated.

It is an object of the present inventionwhich has been made to solve the above problem of the prior art, to provide a stator core which hardly generates the joint of vibration in a radial direction and can suppress a vibration mode.

According to a first aspect of the present invention ; There is provided a stator core for an AC generator, the stator core being of cylindrical form, comprising superpose metal sheet layers, and shaving welded portions for fixing the metal sheet layers, wherein there are a plurality of groups of welded portions, each group being formed on the exterior or interior from the upper end to the lower end, all the groups on the exterior or interior extending in the same direction diagonal to the lamination direction, each group comprising welded portions parallel to the lamination direction at different locations in the circumferential direction and the axial direction.

Optional features are set forth in claims 2 and 3.

The invention also provides a process for producing a stator core as set forth in claim 4.

The preferred features and avantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings, in which : Fig. 1 is a schematic perspective view of a core structure forming a stator core not according to the present invention ; Fig. 2 is a diagram showing the effect of the stator core of Fig. 1 ; Fig. 3 is a diagram showing the effect of the stator core of Fig. 1 ; Fig. 4 is a schematic perspective view of a stator core according to the present invention ; Fig. 5 is a sectional view of a car AC generator of the prior art ; Fig. 6 is a sectional view of a car brush AC generator of the prior art ; Fig. 7 is a schematic perspective view showing an example of a stator core of the prior art ; Fig. 8 is a diagram showing a metal sheet forming the stator core of the prior art ; Fig. 9 is a schematic plan view of the stator core of the prior art ; Fig. 10 is a perspective view showing another example of stator core of the prior art ; Fig. 11 is a partial sectional view showing the relationship between a coil conductor and a slot ; Fig. 12 is a diagram for explaining the problem of the prior art ; Fig. 13 is a side view showing another example of a stator core of the prior art ; and Fig. 14 is a perspective view showing still another example of a stator core of the prior art.

The stator core 7 shown in Fig. 1, which is not in accordance with the invention, has a plurality of welded portions formed on the peripheral side of a cylinder frrim the upper and to the lower end of the cylinder in the same direction diagonal to the lamination direction of a metal sheet 17a. The same or corresponding elements as those of the prior art of Fig. 9 are given the same reference symbols.

Since the upper ends 72t of the welded portions 72 are spaced apart from one another at intervals of 45 on the basis of the center of the cylinder, eight welded portions are formed on the peripheral side of the cylinder in the same direction diagonal to the lamination direction of the metal sheet 17a. The upper end 72t and the lower end 72u of adjacent welded portions 72 are aligned with each other in a peripheral direction.

Welding may be carried out with a welding jig movable in the lamination direction of the cylinder while the cylinder is rotated after the cylinder is sandwiche between chucks so that the metal sheet layers 17a are brought into close contact with one another.

When the electromagnetic noise of a generator comprising the stator core 7 is measured and compare with the electromagnetic noise of a generator comprising the stator core 17A of the prior art the peak value of an unpleasant high-frequency element lowers. Thus, the effect of reducing the electromagnetic noise is obtained. Since a characteristic frequency with which the stator itself resonates mainly consists of 30 elements or 36 elements, the effect of the stator core 7 for each of the elements is shown in Fig. 2 and Fig. 3.

Fig. 2 shows the comparison result of a 304ment frequency. AsolidlineX indicatesthelevelofthe30-element electromagnetic noise of the generator comprising the stator core 7 of Figure 1 and a broken line Y indicates the level of the 30-element electromagnetic noise of theR generatcr comprising the stator core 17A of the prior art. It is seen from Fig. 2 that the level (dB) of the 30-element electromagnetic noise (3400 (ta) x 1/60 x 30 (Hz)) when the rotor turns about 3, 400 times or the level of the 30-element electromagnetic noise when the rotor turns about 7, 600 times is markedly lower than that of the prior art.

Fig. 3 is the comparison result of 36-element electromagnetic noise. A solid line X indicates the levez of the 36-element electromagnetic noise of the generator comprising the stator core 7 of

. 1 and a broken line Y indicates the level of the 36-element electromagnetic noise of the generator comprising the stator core 7A of the prior art.

It is seen from Fig. 3 that the level of the 36-element electromagnetic noise is almost totally lower than that of the prior art. It is also understood that the level of the 36element electromagnetic noise when the rotor turns about 4, 000 times is markedly lower than that of the prior art.

Therefore, according to the stator core 7, it s seen that the joint of vibration in a radial direction is hardly generated and that a vibrationmodecanbesuppressed.

According to the stator corse 7 of 9*iS-1, as welded portions having high rigidity are scattered at random in a lamination direction (the vertical direction of Fig. 1 or a shaft direction when the stator core is installe in the generator) and a peripheral direction, a stator core 7 which hardly generates the joint of vibration in a radial direction and can suppress a vibration mode can be obtained.

In the above-described core, welding is carried out obliquely and continuously. Welding may be carried out a plurality of times on part of the peripheral side of the cylinder from the upper end to the lower end of the cylinder in a direction parallel to the lamination direction of the metal sheet at different locations in a peripheral direction and a vertical direction. A set of these welding works may be carried out a plurality of times on the peripheral side of the cylinder in the same direction.

An embodiment according to the present invention will now be described with reference to Fig. 4.

Eight groups 740 of welded portions 74 formed from tapie upper end to the lower end of the cylinder are formed on the peripheral side of the cylinder at intervals of about 45 on the basis of the center of the cylinder. Each group 740 consists of welded portions 74 formed in parallel to the lamination direction of the metal sheet 17a at different locations in a peripheral direction and a vertical direction. The group 740 can be formed by carrying out the above welding work eight times in the same direction diagonal to the lamination direction of the metal sheet. As a result, the stator core 7 has eight groups 74 of welded portions 74 formed on the peripheral side of the cylinder in the same direction, the welded portions 74 of each group formed on part of the peripheral side of the cylinder from the unper end to the lower end of the, cylinder in parallel to the lamination direction of the metal sheet 17a at different locations in a peripheral direction and a vertical direction. The groups 740 are formed such that they do not overlap with one another in the lamination direction. The upper end and the lower end of adjacent welded portions 74 are slightly overlapped with each. other in a peripheral direction.

In this stator core and production process, welded portions having high rigidity are scattered substantially at random in a lamination direction and a peripheral direction.

It is desired that the groups 740 should not overlap with one another in a lamination direction but the upper end and the lower end of adjacent welded groups 740 may be aligned with each other in a peripheral direction.

In the above embodiment, the welded portions 74 and the groups 740 are formed in parallel to one another at equal intervals. However, they do not need to be formed in parallel to one another at equal intervals but may be formed in the same direction.

The number of the welded portions 74 and the number of groups 740 are generally three to four.

Welding may be carried out on the interior side of the cylinder.

In the above embodiment, the long metal sheet 17a is wound spirally so that the metal sheet layers are placed one upon another to form the cylinder. It is needless to say that the present invention can be applied to the case'where a plurality of ring-shaped metal sheets are placed one upon another to form the cylinder.

As described above, according to the present invention, there can be obtained a stator core which hardly generates the joint of vibration in a radial direction and can suppress a vibration mode.

Claims

Claims :1. A stator core for an AC generator, the stator core being of cylindrical form, comprising superpose metal sheet layers, and having welded portions for fixing the metal sheet layers, wherein there are a plurality of groups of welded portions, each group being formed on the exterior or interior from the upper end to the lower end, all the groups on the exterior or interior extending in the same direction diagonal to the lamination direction, each group comprising welded portions parallel to the lamination direction at different locations in the circumferential directicn and the avial direction.
2. A stator core as claimed in claim 1, wherein there is space in the circumferential direction between the upper end of each group of welded portions and the lower end of the adjacent group of welded portions.
3. A stator core as claimed in claim 2, wherein a plurality of bolt shelter grooves are formed on the peripheral side of the stator core and distributed in a circumferential direction and the said space is set to the circumferential width of one or more of the bolt shelter grooves.
4. A process for producing a stator core for an AC generator, comprising superposing metal sheet layers and welding the layers together at the exterior or interior of the cylinder, wherein a plurality of groups of welded portions are formed on the exterior or the interior, each group extending from the upper end to the lower end, all the groups on the exterior or interior extending in the same direction diagonal to the lamination direction, each group comprising welded portions parallel to the lamination direction at different locations in the circumferential direction and the axial direction.
5. A stator core substantially as described with reference to, and as shown in, Figure 4 of the accompanying drawings.
6. A process for producing a stator core, substantially as described with reference to Figure 4 of the accompanying drawings.