An electric motor

Abstract: An electric drive motor, for example, for a disc storage drive, comprises a shaft (5) on which a mounting flange (8) is journalled. The mounting flange (8) supports a stator (15) surrounded by a rotor (21) fixed to the shaft (5) for rotation therewith. A hub (11) for supporting information disks is supported on the shaft (5) by way of bearings (6, 7). The hub (11) includes a cover disk (41) for sealing an extremity of the bearings (6, 7) and an inverted cup-shaped rotor (33) provides magnetic shielding. The flange (8) is provided with a mounting rim (45) substantially aligned with the base surface of the cup-shaped rotor. The facing rotor (33) and flange (8) readily enable sealing of the lower bearings (6, 7).

Description: The present invention relates to an electric motor. There is a continuing demand for compactness in electric motors for directly driving rotary loads, such as information storage disks. This demand has been satisfied by providing drive motors of the external rotor type, which can be axially relatively short. US-A-4760298 describes an electric drive motor comprising a shaft defining a central axis, a stator carrying a winding arranged substantially coaxially relative to said central axis, and a rotor arranged substantially coaxially relative to said central axis and to be external relative to, and to substantially surround, said stator winding wherein a mounting flange for supporting said motor is arranged substantially coaxially relative to said central axis, said stator and said mounting flange together forming a stationary part of said motor, said mounting flange having an axially extending recess surrounded by a mounting rim, and wherein said rotor comprises a cup-shaped rotor of magnetic material which projects into said recess. However, is it now required that the information storage disks have ever diminishing diameters so that the apparatuses which hold them can also be more compact. At the same time, the motor must still supply adequate torque, and have a certain minimum angular momentum and smooth-running operation. Furthermore, it is necessary to inhibit the passage of dirt particles from motor bearings and torque-generating regions towards a "clean room" region, all without increasing the overall axial dimension of the motor. According to the present invention an electric drive motor as defined above is characterised in that said shaft is arranged to support a hub for rotation by said motor, said hub and said rotor forming a movable part of said motor, in that said hub comprises a disk-bearing element having a substantially radially extending lower surface, in that said cup-shaped rotor has a substantially radially extending, substantially planar base with which said lower surface of said hub is engaged, and in that the diameter of a cylindrical air gap defined between the stator and the rotor is greater than the external diameter of said hub. In an embodiment, the mounting flange has an axially-deepened tank form which facilitates an offset mounting rim thereon. This rim amy be aligned substantially in the back plane of the rotor, thereby avoiding axial lengthening of the motor. The offset mounting rim together with the rotor may be arranged to provide an approximation of an outer labyrinth seal for dust particles from the motor and provide superior magnetic shielding. Preferably, the motor has a stationary shaft enabling axial separation of ball bearings and a central annulus of the flange. This may lead to a corresponding reduction in the diameter of the motor. An embodiment of the present invention will hereinafter be described, by way of example, with reference to the accompanying drawing, in which the sole Figure shows a section of half of a drive motor of the invention. In Figure 1 there is shown in section a drive unit 1, which serves for example as a hard disk storage drive. This drive unit 1 incorporates a drive motor 30 having a substantially cup-shaped or bell-shaped rotor 33. The rotor 33 is preferably deep-drawn out of soft iron sheet and surrounds a generally annular permanent magnetic rotor magnet 21 which serves as the magnetic return path in a simultaneously provided outer rotor housing. The permanent magnetic rotor magnet 21 is fastened to the inner surface of a substantially cylindrical wall of the rotor 33. One end surface of the rotor magnet 21 terminates approximately at the edge of the cylindrical wall at the open end of the rotor 33. The opposite end surface of the rotor magnet 21 is spaced from the inner surface of the base of the rotor 33, but alternatively, may be connected thereto, for example, by a hard and tough plastics layer, for example, of a hot-setting adhesive. The drive motor 30 has a shaft 5 which is substantially centrally mounted and fixed to a mounting flange 8. The shaft 5 is supported in axially spaced ball bearings 6, 7, the inner rings of which are rigidly mounted on the shaft 5. The outer rings of the ball bearings 6, 7 are mounted at a predetermined spacing on the inner wall 34 of the central bore of a hub 11. The hub 11 is arranged to be rotatable relative to the shaft 5 which is stationary. Preferably the hub 11 is a one-piece part made of aluminium. The hub 11 has a first projection 35 extending centrally into the base of the bell-shaped rotor 33 and is rigidly connected thereto, for example, circumferentially by sputtering or gluing. A second projection 36 of the hub 11 extends into an annular groove 37 of an annular part 38. A U-shaped gap defined between the projection 36 and the annular groove 37 acts as a labyrinth packing. The centrla bore of the annular part 38 is fixed rigidly to a hub-like projection 39 of the mounting flange 8. Stator laminations 19, preferably in the form of a grooved stack of sheets, are fixed with the winding to the radial outer side of the annular part 38. Hot-setting adhesive or a different plastics is inserted into the gap 17 between the flange-sided winding head 16 and the inner wall of a recess 12 of the flange 8. A cover disk 41 sealing the mounting of the motor from the "clean room" environment is arranged on the upper ball bearing 7. Instead of hot-setting adhesive, other plastics can be used for the connection of motor parts as, for example, easy to work casting resins. The mounting flange 8 comprises a cup-shaped flange having an axially extending recess defined therein into which the cup-shaped rotor 33 projects. The flange 8 has a substantially annular, axially projecting rim 81 having a substantially radially extending outer surface which extends substantially in the same plane as that containing the outer surface 32 of the base of the cup-shaped rotor 33. The stationary shaft 5 is arranged substantially centrally of the floor of the recess of the flange 8 and is rigidly inserted within the central bore of the projection 39 of the mounting flange 8. The base surface of the cup-shaped rotor 33 extends radially inwardly towards the shaft 5, preferably to extend over or beyond the windings 19. In this manner, the base surface of the rotor 33 provides magnetic shielding for the disk chamber adjacent the hub 11, where magnetic information disks, and reading and recording heads are housed. The drive unit illustrated, which has a stationary shaft, has a very compact arrangement. A cover disk 41 is arranged to rotate with the hub 11, and in the illustrated embodiment forms the upper axial termination of the hub 11. The cover disk 41, which extends over the ball bearing 7, is bonded to the hub 11. In this manner, a flawless separation or seal of the upper ball bearing 7 from the "clean room" disk chamber is provided. Under the lower ball bearing 6 and also within the rotor bell-shape, the labyrinth seal 23, 36, 37, 38 is provided. This seal or packing extends into the stator side of the flange 8. These stator-side labyrinth elements 23, 38, engage or extend around a rotor-side, ridge-like projection 36 and are supported on the hub-like projection 39 of the flange or on the flange base. Alternatively, the stator could be directly fixed to the mounting flange 8, for example, to its projection 39. In this case, a seal or packing is not required. In the illustrated embodiment, the central stationary shaft 5 is held in the projection 39, and the one piece hub 11 extends, by way of at least the ridge-like projection 36, downwardly into the annular groove formed by the walls of elements 23 and 38. The hub 11 is arranged to carry at least one disk (not shown) on its outer cylindrical surface 24. Preferably, the one or the first disk is supported also on a generally flat shoulder 25 of the hub 11. The cup-shaped rotor 33 is held on the shoulder 35 of the hub from below, and the hub also supports the cover disk 41 that rotates with it over the upper bearing 7. The hub has at least one axially extending projection 36, which rotates in the stator-side labyrinth seal projections, and extends below the lower ball bearing 6. Between the labyrinth seal and the cover disk 41 the two ball bearings 6 and 7 are axially arranged. The hub-like projection 39 centrally arranged of the flange 8, which holds the, for example, press-fit stationary shaft, supports the stator 19. The stator is set over the annular part 23 (including the axial groove) to which it is fastened, for example, by means of glue. This mounting can also be accomplished by injecting the entire stator block (laminated core grooved winding) together with at least the recessed part of the flange 8. Outer winding extremities 75, 76 of the stator winding may be overlaid with a casting resin seal so that there is no risk that dirt particles will move out of the stator winding region 75, 76 into the "clean room". To achieve this casting resin is injected in the crucial places well and compactly. The mounting flange 8 is provided at its extreme outer edge with a radial projection or rim 45 which is utilised to fasten the motor 30 into disk information storage apparatus. In general, this projection 45 will be connected to a lower wall defining the "clean room", for example, by screws or a screw-connection. The axial integration of a direct drive, external rotor, motor (with cylindrical air gap) makes possible the full use in the hub of an in-hub-motor of the radially intermediate space between the preferable stationary shaft and the output-bearing cylindrical hub wall for the storage arrangement, which can also occupy the entire available axial space reaching to the adjacent motor region. The outer diameter of the cylindrical air gap is not dependent upon the hub diameter. This enables the stator to be more annular, because the inner stator is, so-to-speak, shifted radially away from the shaft axis. The axial projections from both the rotor and stator sides which are axially annularly interdigitated among one another for rotary motion (which could also be a larger number of ridge-like projections) are arranged radially between the stator and the shaft. This near-shaft region also receives the cover which covers the bearing space to separate it from the "clean room", as well as any arrangements for separating or sealing the inner motor space from the "clean room". This radially extending, intermediate space between the central shaft and its support and the inner surface of the stator annulus is available because there is no need to provide a radially wider electromagnetic field with a large air gap diameter for the stator annulus, that is, for the laminated stator magnetic stock. Embodiments of the invention have the advantage that an increased momentum requirement is producible (achievable because the air gap can be kept large, and in any case is not dependent upon hub diameter) which is dependent upon the standardization requirements for information storage disks. Since the tendency is towards ever-smaller disks, output drive diameter also tending to be smaller, so the power requirements for a drive motor placed in the hub is set at pre-existing limits. In a drive unit as described, the diametrical moment arm of the air gap of an outer rotor motor may be increased as desired, practically at will, through radial enlargement of the axially deepened flange configuration. The deepening of the flange configuration in itself permits an axial compactness because the bearings 6, 7 and axial projection 39 are axially, rather than radially aligned. The iron cup or rotor 33 in the motor housing provides relatively good magnetic shielding because it also acts as the magnetic return path. Generally, the cup 33 is therefore thicker than would be needed for magnetic shielding. In this way, all of the space between the outer surface of the stationary shaft and the inner wall of the hub for the output system is put to good use. If the outer hub diameter must become smaller, because of the ever-diminishing diameter of the information storage disks, and therewith also a diminishing size above a minimum size of a central hole must be set, there is virtually no alternative to the one-piece hub 11 as described above, to be made out of low-remanence magnetic material. A circuit board 43 is supported on the base of the recess of the flange 8. The circuit board 43 has a printed circuit thereon, and may form part of the connection of the stator-side casting resin seal. The motor thus provided, which boasts a large ratio or air gap diametrical dimension to axial length, is, for example, a brushless outer rotor motor with three strings provided for a three-or-six pulse drive, or for a two- or one-pulse drive provided, such as that described in the following patent documents DE-O5 22 25 442; (offenlagungschaft) and DE-PS 23 46 380 and/or DE-PS 23 14 259. The invention is especially suitable for motors whose diameter D is large compared to the overall axial length L, that is, D/L amounts to at least 2. It will be appreciated that modifications and variations to the invention as described and illustrated can be made within the scope of the appended claims.

Claims: An electric drive motor (30) comprising a shaft (5) defining a central axis, a stator (19) carrying a winding (75, 76) arranged substantially coaxially relative to said central axis, and a rotor (33) arranged substantially coaxially relative to said central axis and to be external relative to, and to substantially surround, said stator winding (75, 76), wherein a mounting flange (8) for supporting said motor (30) is arranged substantially coaxially relative to said central axis, said stator (19) and said mounting flange (8) together forming a stationary part of said motor, said mounting flange (8) having an axially extending recess surrounded by a mounting rim (45), and wherein rotor (33) comprises a cup-shaped rotor of magnetic material which projects into said recess, characterised in that said shaft (5) is arranged to support a hub (11) for rotation by said motor, said hub (11) and said rotor (33) together forming a movable part of said motor, in that said hub (11) comprises a disk-bearing element having a substantially radially extending lower surface, in that said cup-shaped rotor (33) has a substantially radially extending, substantially planar base (32) with which said lower surface of said hub is engaged, and in that the diameter of a cylindrical air gap defined between the stator (19) and rotor (33) is greater than the external diameter of said hub (11). An electric motor as claimed in Claim 1, wherein part of said mounting flange (8) is substantially radially aligned with said substantially planar base (32) of said rotor (33). An electric drive motor as claimed in Claim 1 or Claim 2, wherein said mounting flange (8) has an axially deepened tank form and said mounting rim (45) of said mounting flange (8) is axially offset relative to said recess and, together with said rotor (33), provides an approximation to an outer labyrinth seal. An electric drive motor as claimed in any preceding claim, wherein said shaft (5) is stationary and extends beyond said stator (19), and wherein bearing means (6, 7) are arranged on said shaft (5) on which said hub (11) is supported. An electric drive motor as claimed in any preceding claim, wherein said stator (19) is supported within said recess in the mounting flange (8) within the limits of said rotor (33). An electric drive motor as claimed in any preceding claim, wherein said cup-shaped rotor (33) is deep-drawn, of soft magnetic material, and carries permanent magnetic elements (21), said cup-shaped magnetic material and said permanent magnet elements effectively covering the stator (19). An electric drive motor as claimed in any preceding claim, wherein said hub (11) comprises support means for information storage disks, and a cover plate (41) rotatable with the hub, and wherein said cup-shaped rotor (33) is positioned to form magnetic shielding means for shielding the stator (19) from said support means. An electric drive motor as claimed in any preceding claim, wherein movable and stationary parts of said motor are interdigitated, and said interdigitated movable and stationary parts (36, 37, 38) define seal means arranged between the hub (11) and the stator, and radially within the stator and axially offset relative to bearing means (6, 7) for said hub toward the flange. An electric drive motor as claimed in any preceding claim, wherein said shaft (5) is stationary, a first part of the shaft being mounted in the recess of said mounting flange (8), and a second part of the shaft carrying bearing means (6, 7) for said hub (11), wherein the axial length of said bearing means (6, 7) approaches that of said second part of the shaft (5), and wherein the axial length of said first and second parts of the shaft is substantially the same. An electric drive motor as claimed in any preceding claim, wherein a conductor plate and/or a shielding ring (43) is located between said mounting flange (8) and the winding of the stator (19), and for example, is or are partially or entirely cast or moulded with plastics on both sides. An electric drive motor as claimed in any preceding claim, wherein parts of the cup-shaped rotor (33) are connected to each other by a plastics layer, wherein the layer is applied point-like, annularly, radially, or sheetlike. An electric drive motor as claimed in any preceding claim, wherein the rotor surface (33) is connected to a rotor magnet (21) by way of a plastics layer. An electric drive motor as claimed in any preceding claim, wherein the hub (11) is a one-piece part made of aluminium.

Inventors: CAP HEINRICH, ELSAESSER DIETER, KOLETZKI ULRICH, PAPST GEORG FRIEDRICH, CAP, HEINRICH, ELSAESSER, DIETER, KOLETZKI, ULRICH, PAPST, GEORG FRIEDRICH, Elsässer, Dieter
Applicants: PAPST MOTOREN GMBH & CO KG, PAPST LICENSING GMBH
Application year: 1990
Main classification: H02K7
IPC codes: H02K7, H02K5, H02K21, H02K29