Motor Assembly

The invention relates to electric motor construction and, in particular, to the manufacture of universal type electric motors.

Universal type electric motors are widely used for their characteristics of high power and small physical size. In the manufacture of this type of electric motor, a production bottle-neck has been experienced in the wiring, termination, or other connecting of the field winding and brush elements. The steps involved in connecting these various elements were often hindered by the ordinarily small and relatively fragile elements involved, and the restricted or obstructed areas in which such elements were situated.

Those who have sought solutions to these problems with attempts to simplify connections and automate assembly have generally designed motors with integrated housings so that terminals and/or brushes, as well as armature bearing supports, have been part of a housing or enclosure for the motor.

The invention provides a construction for a universal motor having a design adapted for use in a wide variety of appliances, machines, and the like. The disclosed motor design avoids reliance on an external housing for support of any of its individual components so that it can be used without modification or special tooling in diverse housing styles ranging from closefitting units to envelopes containing the motor and other hardware of like or greater bulk.

The disclosed motor is economical to produce as a result of its unique construction, which avoids tedious or difficult to automate steps of assembly, particularly in making circuit connections. Field and brush terminations are made with lay-in or plug-in connections easily accomplished without complex movements or positional tolerances.

The motor construction involves the independent make-up of stator core and armature subassemblies. The stator core and armature components are ultimately joined in a simple push-in procedure to essentially complete assembly of the motor. Since the stator core and armature components are separately constructed, the speed of assembly of one component need not hold up assembly of the other component. The subassembly components can thus be separately inventoried and stored to be used on demand.

According to the invention, all of the motor elements are loosely fitted together until a last step in assembly of the motor, when tension screws are tightened. This prefitting of the various elements allows them to favorably align to one another before they are locked finally together by the tension screws. At completion of their assembly, all of the motor components are supported directly or indirectly on the stator core. The manner in which the motor circuit elements are terminated allows the motor to be conveniently supplied to a customer with or without power leads. Assembly of such power leads is accomplished by a simple push-in step. This is of particular advantage because of the requirements found in the wide number of applications for which the disclosed motor assembly is suited. The power rating of the motor is readily modified by increasing or decreasing the length of the stator core lamination and armature without the necessity of changes in the remaining motor parts.

FIG. 1 is a perspective view of a stator core and a terminal harness in axially exploded relation;

FIG. 2 is an axially exploded, perspective view of the major parts of a motor assembly;

FIG. 2a is a perspective view of a brush box subassembly of the motor assembly;

FIG. 3 is an end view at the brush side of the motor assembly;

FIG. 4 is a side view of the motor assembly;

FIG. 5 is a fragmentary, side view of a portion of a shaft support and brush holder being positioned on the stator core and terminal harness;

FIG. 6 is a fragmentary, perspective view, illustrating details of a typical terminal of the terminal harness.

FIG. 7 is an axially exploded view of a shaft support depicting details of its assembly; and

FIGS. 8a and 8b illustrate further details of the shaft support assembly and a manner of attachment of a brush holder plate thereto.

In the drawings, there is disclosed an electric motor assembly 10 of the universal type. A stator core 11 is composed of a stack or lamination of annular stampings permanently held together by rivets 12 or welds in customary fashion. A field winding 13 comprises a pair of opposed coils 14 and 16 in associated slots 17 formed in the body of the stator core 11. Sheets 19 of paper-based material or other electrically insulating material are disposed in the slots 17 prior to winding of the magnet wire forming the coils 14, 16 to protect the wires from the edges of the stator core laminations. The insulator sheets 19 project a distance from end faces 20 of laminations 21 of the stator core 11. Similarly, parts of the coils 14, 16 free of the slots 17 are spaced from these end faces 20.

The stator core 11 includes a C-shaped harness 26 having a planar web 27 and terminal support stations 28 which are angularly disposed about an axis of the motor and extend axially away from the plane of the web 27. The harness 26 is formed of electrically insulating material, preferably by injection molding a suitable plastic such as Valox 420, an engineering thermoplastic polyester sold by General Electric Co. The material forming the harness 26 is somewhat resilient. At the free or open ends of the C configuration of the harness and at points on its midsection, the harness 26 includes protrusions or hooks 29, 30. As indicated most clearly in FIG. 2, the protrusions 29, 30 interengage with areas of the sheet insulators 19 of the field coils 14, 16, and provisionally hold the harness 26 in place on the stator core 11. The material forming the harness 26, being somewhat resilient, allows a central area 33 of the harness web 27 to act as a hinge and various other areas of the web to elastically deflect and allow the protrusions 29, 30 to snap over respective areas of the field insulators 19. The harness is dimensionally molded so that in a free state, its geometry is slightly less than that of gripped points of the coil insulators 19. Cooperating pairs of hooks, i.e., a hook 29 at a free end of the web 27 and the hook 30 closest to it at the web center area 33, grasp the inside corners of opposite coils 14, 16. The hooks 29, 30 are dimensioned to fit under the space between the free portions of the coils and the stator core lamination end face 20. The protrusions 29, 30 hook onto the corners of the insulator sheets at the base areas of the slots 17, i.e., where the individual loops of the coils 14, 16 are smallest. Intermediate cooperating pairs of hooks 29, 30, locating tabs 36 extend axially from the plane of the harness web 27 in a direction opposite the terminal supports 28. The tabs or lugs 36 are adapted to index against the outside circumferential surfaces of the stator core laminations 21. The operative surfaces of the locator tabs 36 are generally opposed to the operative surfaces of the adjacent hooks 29, 30.

With reference to FIG. 6, the terminal supports 28 include rectangular cavities 38 sectioned by cross slots 39. Each slot 39 is adapted to receive one end of the magnet wire of an associated coil 14 or 16. Wire laced in a cross slot 39 is terminated by a terminal or solderless connector 41 having slots 42 which align with the cavity cross slots 39. The terminal slots 42 are dimensioned and otherwise constructed to strip insulating material from the magnet wire and make a permanent electrical connection therewith. An example of a typical connector suitable for use is disclosed in U.S. Pat. No. 3,984,908. Barbs 43 retain their associated terminals 41 in the respective cavities 38.

The described stator core subassembly, principally comprising the laminations 21, field coils 14, 16, and harness 26, is in a condition for assembly with remaining parts of the motor. As can be appreciated, the stator core parts are provisionally joined with sufficient integrity to allow them to be inventoried or otherwise stored for later use where immediate consumption is not desired.

An armature 46 of motor assembly 10 is generally conventional in design, and includes a commutator 47 adjacent one end. For purposes of economy, the armature shaft 48 maintains a constant diameter over the major part of its length to avoid machining operations. Either end of the shaft 48 may have extensions with a flat or machine threads or some other means of connecting it to a load. At the commutator end, the shaft 48 has a pair of axially spaced grooves 49 for receiving C washers.

Armature shaft supports 51, 52 of similar construction are provided at each end of the motor assembly 10. Opposite the commutator end of the motor, the shaft support 51 has a stepped structure ideally formed as a subassembly of stamped steel parts. The larger of these parts 54 comprises an end strap integrally formed with a cylindrical bearing cavity or bell 55, axially oriented stand-off legs 56, radially oriented flanges 57, and locating tabs 58. The bell 55 has a central opening 59 for clearance with the armature shaft 48. Holes 63 in the radial flanges 57 are adapted to align with diametrally opposed holes 64 to the stator core laminations 21. The locating tabs 58 are spaced from one another a distance corresponding to the transverse dimension of the stator core laminations 21 adjacent the holes 64 so that the tabs are adapted to locate the bell 55 concentrically with the axis of the stator core 11. A bearing 66, for example, a bronze bushing, is assembled into the bell 55 and retained therein by another part of the shaft support 51 in the form of an apertured plate 67 riveted to the main end strap 54.

With reference to FIGS. 8a, 8b, the end strap 54 is preferably formed with integral rivets 68 stamped into its body at the time of its fabrication for use in fixing the plate 67 to the end strap. For this same purpose, the plate 67 has a pattern of holes 69 (FIG. 7) adapted to mate with rivets 68. FIG. 7 schematically illustrates a production fixture 70 advantageously employed to align individual plates 67 and shaft supports 52. The fixture relies on the illustrated substantially identical peripheral configuration of the end strap 54 and plate 67, as viewed endwise or axially of the motor, to align one to the other with a set of four pins 75. The configuration of the end strap 54 and plate 67 includes a circular central portion interrupted by diametrally extending branches, as indicated in phantom in FIG. 7, at 80. The pins 75 are critically spaced in tangency to the points of intersection of the phantom circle and branches. By positioning the end strap 54 and then the plate 67 in the fixture 70, these elements are accurately aligned to one another with minimal effort.

With a bearing 66 sandwiched between the end strap 54 and plate 67 and the rivets 68 extending through the holes 69, the rivets are upset by a suitable tool, as indicated in FIG. 8b, to capture the bearing and plate onto the end strap. It will be understood that both the plate 67 and the bearing support 52 are bilaterally symmetrical with respect to a line perpendicular to the diametral direction of their branches, which permits their loading into the fixture 70 without regard to which end or branch is associated with which pair of related pins 75.

The armature shaft support 52 at the commutator end of the motor differs from the opposite shaft support 51 by having relatively longer legs 56a to accommodate the length of the commutator 47. Various other elements of these shaft supports or brackets 51, 52 are essentially the same, and are designated by the same numerals.

A brush holder assembly 71 is supported between the support legs 56a. The brush holder 71 assembly principally comprises an electrically insulating plate 72 and a pair of opposed brush boxes 73. The plate 72 is preferably stamped or otherwise formed into a polygonal configuration from sheet stock, with its center blanked out to form a clearance aperture 74 for the commutator. The brush boxes 73 are preferably formed of brass or other electrically conducting metal and are radially disposed on opposite sides of the plate aperture 74. Each box 73 includes an elongated U-shaped channel 76 with tabs 77 along longitudinal edges. The tabs 77 are inserted into holes punched or otherwise formed in the brush holder plate 72 and are bent over to retain the boxes to the plate 72. One side of each brush box 73 has an integral tab or prong 78 which depends radially over and axially inward of the plane of the plate 72. Upstanding rivets 79 are assembled in holes adjacent a longitudinal slot 81 in one side of each box 73 for purposes of mounting a brush spring 82, as discussed hereinbelow.

The brush holder assembly 71 is joined to the shaft support 52 by snapping the plate 72 into interlocking relation with the support legs 56a. The plate 72 and legs 56a are formed with cooperating slots 83 and 84 respectively. The transverse width of a plate slot 83 is substantially the same in dimension as the residual width of a support leg 56a remaining between a pair of slots 84, while the width of the slots 84 in the axial direction of the motor is at least as great as the thickness of the plate 72. Each support leg 56a is provided with an integrally formed rib 85 protruding from its plane towards the opposite leg. The ribs 85 are shaped to facilitate assembly of the plate on the shaft support 52. With reference to FIG. 8b, a rib includes a cam or ramp surface 90, which, when forcibly engaged by an edge 91 of the plate 72 as the plate is pushed towards the end strap 54, causes the legs 56a to spread, allowing tabs 101 on the plate 72 to align with and then snap into slots 84 in the support legs 56a. Inclined surfaces 102 of the ribs 85 hold the plate 72 snugly in the slots 84. The support legs 56a are sufficiently resilient to permit their temporary spreading for reception of the relatively rigid plate 72. The width of the plate 72 as measured across its slots 83 is dimensioned with respect to the inside dimension between the support legs 56a so as to provide a permanent interference fit and assure that the plate is snugly held by the legs. The plate 72 ultimately rests in a plane perpendicular to the axis of the armature shaft 48.

After installing the brush holder, the armature is assembled on the shaft support 51. This is readily accomplished by first assembling a C-washer 86 in a respective shaft groove 49 and a thrust washer 87 on the shaft outward of the C-washer. Following this, the armature shaft 48 is slipped through the bearing 60 and a second thrust washer is assembled over the outer end of the shaft, followed by a second C-washer 89 in the outermost groove 49. The armature shaft 48 is thus axially locked to the shaft support 51 by the C-washers 86, 89.

It will be understood from the foregoing that the armature assembly 46, shaft support 52, and brush box assembly 71 are secured together at this stage with ease, there being no problems during their assembly of physical interference with the stator core 11. This armature, support, and brush box subassembly can be handled immediately for use or can be inventoried for later use as desired without association of the stator core 11.

The stator core 11 is assembled with the armature dressed with the shaft support 52 and brush holder assembly 71 by simply dropping the armature through the center of the stator core. As indicated in FIG. 5, the legs 56a lead the brush prongs 78 and are caused to enter the space between a pair of adjacent terminal supports 28. The spacing between edges 92 of the supports 28 in relation to the width of the radial flanges 57 of the support legs 56a is such that the prongs 78 are coarsely aligned with their associated cavities 38. In the view of FIG. 5, the illustrated support leg 56a and flange 57 are at the extreme left in the gap between supports 28, the clearance being indicated at 93 between one of the terminal supports 28 and this leg. It will be seen, even in this extreme case, engagement between inclined guiding surfaces 94 and 96 of the prong 78 and cavity 38 will cause the prong to center itself with the cavity in an angular or circumferential direction with respect to the stator core. This type of camming action would occur if the leg 56a and flange 57 were at the right and surfaces 97 and 98 of the prong and cavity were operative. Further axial movement of the armature 36 and support 52 causes the prongs or connectors 78 to enter and electrically connect with the respective terminals 41 in the terminal supports 28. Any differences between the diametral spacing between the brush prongs 78 and the diametral spacing between the associated rectangular cavities 38 is readily taken up by slight elastic distortion of the harness web 27, allowing the terminal supports 28 to flex radially inwardly or outwardly as necessary to accommodate the prongs 78. When the radial flanges 57 of the support legs 56a are abutted against the harness web 27, the shaft support 52 is fully installed. The opposite shaft support 51 is then slipped over the opposite end of the armature shaft 48 and abutted against the associated stator core end face 20. At this point, substantially all of the motor elements are loosely assembled together, and are capable of aligning themselves to positions which account for the various dimensional tolerances involved in their manufacture. In this manner, the armature shaft 48 can seat itself in the bearings 66 without binding or excessive strains in various parts of the motor. Tension screws 99 assembled through the bearing support holes 63 and stator holes 64 are then drawn tight with nuts 101 to substantially complete construction of the motor. The screws 99 can be provided with additional length to that illustrated for purposes of mounting the motor to a housing structure or other support. Electrical brushes 102 are most conveniently slipped into the brush boxes 73 after the armature 46 is assembled with the shaft support 52. The brushes 102 are retained in the boxes 73 and are biased against the commutator by the springs 82 assembled on the rivets or posts 79, as indicated in FIGS. 3 and 4. As shown, the springs 82 operate through the slots 81.

Lead wires, indicated in phantom at 106 in FIG. 6, are pushed into a pair of connectors 41 not associated with the brush prongs 78. Such lead wires 106 can be installed by the manufacturer of the motor or a customer of such manufacturer. This freedom to install lead wires 106 after assembly of the motor has otherwise been completed affords a high degree of versatility to the motor, since the lead wires can be custom fit at any time.

It will be understood from the foregoing explanation that the axial length of the stator core laminations 21 and armature assembly 46 can be changed to modify the power rating or performance characteristics of the motor without requiring a change in any of the other disclosed motor elements, with the exception of the tension screws 99. Where desired, the shorter armature shaft support 52 may be replaced by one like the longer support 52 to provide clearance for an internal cooling fan mounted on the intermediate length of an extended armature shaft. The disclosed motor assembly 10 can be mounted in a variety of appliances and machines without changes in its structure, since it is a self-contained unit. All of its various parts, and in particular the shaft supports 51 and 52, are supported directly or indirectly by the stack of stator core laminations 21.

It should be evident that this disclosure is by way of example and that various changes may be made by adding, modifying or eliminating details without departing from the fair scope of the teaching contained in this disclosure. The invention is therefore not limited to particular details of this disclosure except to the extent that the following claims are necessarily so limited.