Method and Apparatus to Reduce Operating Noise of Dynamo Electric Machines, Particularly Vehicular Three-Phase Alternators

German Patent Application No. P 32 08 893.0 (DE-OS No. 32 08 893; U.S. Ser. No. 470,266 --filing date: Feb. 28, 1983), now U.S. Pat. No. 4,540,709, Hagenlocher et al.

The present invention relates to dynamo electric machinery, and more particularly to dynamo electric machines suitable for vehicular use, especically automotive-type three-phase alternators.

Dynamo electric machines, and especially alternators of the automotive type, in operation, cause noise which may be due to chatter or hum of laminations which vibrate with respect to each other. In automotive apparatus, which operates at highly variable speeds, the pitch of the generated noise changes with speed of the engine driving the alternator. It is particularly annoying at various speeds, where resonance effects may occur.

Alternators, especially of the vehicular type, usually have two end shields or end disks or end bells between which a stator package is clamped. The stator package customarily is formed of a plurality of essentially ring-like stator laminations, stacked together to form the stator magnetic circuit. The end bells form supports for accessory equipment, as well as for the bearings for a rotor, rotating within the stator.

It is an object to reduce the noise generated during operation of the machine, and especially to reduce noise of variable pitch which arises upon operation of an automotive-type alternator, at different speeds, and subjected to different loading.

Briefly, the operating noise is reduced by providing means to counteract varying magnetic forces which arise in operation of the machine and to stabilize the laminations of the stator stack against each other with respect to such forces. The laminations can be effectively stabilized by passing at least one welding seam or track, circumferentially and preferably also diagonally around the circular surfaces of the stack of laminations, thereby connecting edge portions of the laminations together.

In a preferred form of the invention, diagonal cross tracks may be formed, preferably extending at the outer circumference of the stator stack.

The arrangement has the advantage that noise reduction is effectively obtained with a minimum of additional operating steps during manufacture of the dynamo electric machine, and does not require additional components or structural elements, for example to shield noise which has already been generated.

Deformation of the stator laminations or the stack of laminations is effectively reduced. The present invention is based on the discovery that a substantial component of noise, resulting from operation in the machine, is caused by continuously changing magnetic forces which tend to radially and axially deform the stator of the generator, and, acting on the laminations, tend to continuously change the relative positions of the laminations with respect to each other. The stator stack may go into oscillation with frequencies which are determined by the operating speed of the alternator, and may, frequently, be a multiple of the respective speed in rpm. The magnetic forces, which cause radial as well as axial deformation of the stack of the stator laminations, cause noise; in accordance with the invention, the forces acting on the laminations are effectively countered so that the resulting noise is prevented from occurring.

In accordance with a preferred feature of the invention, a welding bead or welding seam is formed by a laser welding apparatus which connects the edges of the laminations. The resulting welding seam or welding bead extends, preferably, in zig-zag form, about the circumference of the stator stack, and in accordance with a preferred feature, around the outer circumference of the stator stack. Selecting the outer circumference has the advantage of simplicity of manufacture. More than one zig-zag seam may be provided, with the seams intersecting each other to form an open-mesh arrangement.

In accordance with a feature of the invention, the seams can be applied after the stator stack has been assembled, for example when, in the manufacture of the stator assembly and during winding of the stator with wire, the stator stack is rotated in a jig. The zig-zag seam can be applied at the same time. Alternatively, the stator stack can be held in a fixed position, and a laser passed thereabout, or a laser beam generated which is suitably deflected by mirrors, providing for impingement of the laser beam on the stator stack in accordance with deflection of the mirror .

FIG. 1 is a schematic longitudinal sectional view through an automotive-type claw-pole alternator of standard construction, and illustrating the basic structure, to which the present invention is applied;

FIG. 2a is a perspective schematic illustration of a stator lamination stack, illustrating magnetic forces acting thereon, and showing the welding seams or beads applied to reduce noise; and

FIG. 2b is a view similar to FIG. 2a, showing another arrangement of welding seams.

The vehicular, typically automotive-type three-phase alternator shown in FIG. 1 will be described only in general terms since the alternator may be of any well known structure.

Two end bells or bearings 1 and 5 have placed thereon, respectively, hubs 2, 6, to receive bearings for the shaft 4 of a rotor. The end bells or end shields 1, 5 are axially extended to form, essentially cylindrical cup or pot-shaped extensions 9, 10. A stator stack 12, having a stator winding 13 therein, is received in suitable stator receiving grooves or rings 14, 14', respectively, formed in the cylindrical extensions 9, 10 of the end shields or elements 1, 5. The axis of the stator stack extends lengthwise of the machine.

The rotor has a rotor shaft 4, on which two claw-pole halves 7, 8 are attached, and further including an iron core on which a field winding 16 is wound. The structure of the alternator described so far is entirely conventional.

During operation, that is, rotation of the rotor, magnetic forces will continually act on the stator of the generator due to the mutual magnetic induction effect and the change in magnetic force lines occurring due to the passage of the claw poles upon energization of the field winding 16. Referring to FIG. 2a, the stator laminations 12' are shown, omitting winding slots and the like, in highly schematic form. Magnetic forces shown by the heavy black arrows A and B tend to deform the stator laminations into the undulating form shown. Of course, the deformation is illustrated highly exaggerated, for purposes of better understanding and illustration. In a rotating field, the forces likewise will rotate and, as can readily be seen, the individual laminations of the stator stack 12' will be continuously subjected to the magnetic forces. The magnetic forces have a definite axial component, resulting in the deformations shown in FIG. 2a.

The magnetic forces tend to shift the stator laminations with respect to each other. In order to prevent this relative shift, welding beads or seams 8 are placed, in accordance with the present invention, endlessly around the circumference of the stator stack. In accordance with a preferred feature, the welding seams or beads are located externally, that is, about the outer circumference of the stator stack. Similar beads or seams may also be located at the inner circumference, as shown at 8aand both outer and inner seams or beads 8, 8a may be used in dependence on the forces to be overcome. The seams 8, 8a or, as shown in FIG. 2b, the seams 8', 8" and 8a', 8a" extend in approximate zig-zag or undulating form from one axial end of the stack to the other axial end about the circumference of the stator stack, as schematically shown in the drawings. Crossing weld seam arrangements, as shown schematically in FIG. 2b, are likewise possible. The zig-zag shape of the welding beams is particularly desirable since the respective stator stacks are all connected thereby and interconnected along the welding seams into a unitary hole. The welding seams or beads thus form a carrier or support structure for all of the stator laminations which, otherwise, are only adhered together. As can readily be seen, the welding seams or beads counteract axial and radial deformations and form quasi-stiff support struts or support trusses for the individual thin stator laminations, resulting in surrounding and complete stabilization of the structure of the stator stack formed by the individual stator laminations. The arrangement effectively prevents oscillations from occurring. The oscillations may be based on any external forces, the most usual external forces being counteracted, however, being the magnetic forces which tend to deform respectively adjacent laminations. Consequently, the noise generated in operation, due to occurring vibrations or slight shifting of the laminae with respect to each other is effectively avoided.

In accordance with a feature of the invention, the beads or seams are applied by laser beams which are directed, in well known and customary manner, against the respective circumferential surface of the laminations of the stack. Conventional laser welding arrangements may be used which are applied during the manufacture and/or the winding operations to form a complete wound dynamo electric stator 12, with winding 13 (FIG. 1). The welding step can be carried out either before or after the laminations are wound.

Various changes and modifications may be made, and features described in connection with any one of the embodiments may be used with any of the others within the scope of the inventive concept.