Ulllted States Patent [19]
`Trago et al.
`
`US005806169A
`[11] Patent Number:
`[45] Date of Patent:
`
`5,806,169
`Sep. 15, 1998
`
`4,841,190
`4,922,604
`5,008,572
`
`,
`
`,
`
`5,331,237
`
`6/1989 Matsushita et al. .................. .. 310/257
`5/1990 Marshall et al.
`29/598
`4/1991 Marshall et al.
`310/45
`gakagi
`............................. .. 313/9429);
`7/1994 Ichimura
`310/44
`8 1994 Y'
`t
`l. .............................. .. 385 484
`/
`1p 6 a
`/
`FOREIGN PATENT DOCUMENTS
`0553811
`8/1993 European Pat. Off. .
`0562146 2/1959 Italy .................................. .. 264/2722
`56-094952 7/1981 Japan .
`59-105864 6/1984 Japan .
`59220051 12/1984 Japan .
`31120
`1/1995 Japan .
`W0 91 09441
`6 1991 WIPO .
`/
`/
`Primary Examiner—Carl E. Hall
`Attorney, Agent, or Firm—Leydig, Voit & Mayer
`[57]
`ABSTRACT
`
`[54] METHOD OF FABRICATING AN INJECTEI)
`MOLDED MOTOR ASSEMBLY
`
`[76] Inventors: Bradley A_ Trago, 922 Cerasus Dr”
`ggillifezrdl’llélvsggging‘gagg'
`’
`.
`"
`,
`’
`Carpentersville, Ill. 60110; Grl?' D.
`Neal, 2600 N. Southport Ave., Unit 31,
`Chlcago’ In‘ 60614
`
`_
`
`[21] APPI- NO-I 415,639
`.
`_
`[22] Flled-
`
`AP“ 3’ 1995
`
`[51] Int. Cl.6 ................................................... .. H02K 15/04
`[52] US. Cl. ......................... .. 29/596; 264/2722; 310/42,
`310/43; 310/90
`[58] Field of Search ...................... .. 29/596, 598; 310/42,
`310/43, 90, 71; 264/2722, 272.19
`
`[56]
`
`References Cited
`
`U.S. PATENT DOCUMENTS
`
`370467604
`
`Macks ..................................... ..
`7/1962 Gr‘fhan} et al' '
`19min“ et a1‘
`31O/9O
`""" "
`3/1969
`3’433’986
`29/596
`3/1977 Tanaka et
`4’015’154
`31O/49
`6/1977 Chai et aL
`4ZO29Z977
`310/90
`4/1980 Binns er a1, __
`4,200,344
`. . . . .. 310/90
`5/1983 Isaacson . . . . . . . .
`4,382,199
`8/1985 Kawada et al
`4,538,084
`310/217
`- 310/43 X
`4,549,105 10/1985 Yamamoto et a1-
`4,626,725 12/1986 Kawada et al. ......................... .. 310/89
`""""""""""""""""""" " 29/5519
`4,713,570 12/1987 Mastromattei
`310/154
`4,763,034
`8/1988 Gamble ....... ..
`310/181
`4,781,610 11/1988 Mercer ..
`.... .. 310/71
`
`41
`
`umi e a .
`
`............................. ..
`
`5,333,957
`
`An electrical motor and the process for forming that motor
`utilizes in'ection moldin techni ues to unitiZe the stator
`J
`g
`_ q
`_
`_
`assembly. The stator assembly includes a stator lamination
`Stack and preferably a metal front end Cap
`is Secured
`to the lamination stack after the lamination stack is insulated
`and Wound. The Windings are terminated at a plurality of
`conductive pins fusion Welded to the terminating ends of the
`Windings. The stator assembly With front end cap in place is
`positioned in an injection'molding die. Pressure is applied to
`the die, and molten plastic is 1n]ected under pressure to ?ll
`voids in the stator assembly, and also to form a plastic mass
`Which Will serve as the rear end cap. The rear end cap is also
`molded With a connector portion Which ?xes the conductive
`pins in place as a part of the Connecton Abore formed in the
`stator assembly provides mounting surfaces for bearings on
`a rotor assembly‘
`
`28 Claims, 10 Drawing Sheets
`
`BMW-1009
`Page 1 of 21
`
`

`

`U.S. Patent
`US. Patent
`
`Sep. 15,1998
`Sep. 15,1998
`
`Sheet 1 0f 10
`Sheet 1 0f 10
`
`5,806,169
`5,806,169
`
`
`
`BMW-1009
`
`Page 2 of 21
`
`BMW-1009
`Page 2 of 21
`
`

`

`U.S. Patent
`
`Sep. 15, 1998
`
`J,
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`BMW-1009
`Page 3 of 21
`
`

`

`U.S. Patent
`US. Patent
`
`Sep. 15,1998
`Sep. 15,1998
`
`Sheet 3 0f 10
`Sheet 3 0f 10
`
`5,806,169
`5,806,169
`
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`BMW-1009
`
`Page 4 of 21
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`BMW-1009
`Page 4 of 21
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`

`

`U.S. Patent
`
`Sep. 15,1998
`
`Sheet 4 0f 10
`
`5,806,169
`
`27a
`
`69a
`66a
`
`BMW-1009
`Page 5 of 21
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`

`

`U.S. Patent
`US. Patent
`
`Sep. 15,1998
`Sep. 15,1998
`
`Sheet 5 0f 10
`Sheet 5 0f 10
`
`5,806,169
`5,806,169
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`BMW-1009
`
`Page 6 of 21
`
`BMW-1009
`Page 6 of 21
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`

`

`U.S. Patent
`US. Patent
`
`Sep. 15,1998
`Sep. 15, 1998
`
`Sheet 6 0f 10
`Sheet 6 0f 10
`
`5,806,169
`5,806,169
`
`
`
`BMW-1009
`
`P g
`
`7 f21
`
`BMW-1009
`Page 7 of 21
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`

`

`U.S. Patent
`US. Patent
`
`Sep. 15,1998
`Sep. 15, 1998
`
`Sheet 7 0f 10
`Sheet 7 0f 10
`
`5,806,169
`5,806,169
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`
`BMW-1009
`Page 8 of 21
`
`

`

`U.S. Patent
`
`Sep. 15,1998
`
`Sheet 8 0f 10
`
`5,806,169
`
`107
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`
`BMW-1009
`Page 9 of 21
`
`

`

`U.S. Patent
`US. Patent
`
`Sep. 15,1998
`Sep. 15,1998
`
`Sheet 9 0f 10
`Sheet 9 0f 10
`
`5,806,169
`5,806,169
`
`104
`
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`
`
`
`BMW-1009
`
`Page 10 on1
`
`BMW-1009
`Page 10 of 21
`
`

`

`U.S. Patent
`
`Sep. 15,1998
`
`Sheet 10 0f 10
`
`5,806,169
`
`156
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`BMW-1009
`Page 11 of 21
`
`

`

`1
`METHOD OF FABRICATING AN INJECTED
`MOLDED MOTOR ASSEMBLY
`
`BACKGROUND OF THE INVENTION
`
`1. Field of the Art
`The present invention relates to electric motors, and more
`particularly to a fabrication method and related assembly of
`potted electrical motors.
`2. Discussion of the Related Art
`US. Pat. Nos. 4,922,604 to Marshall et al. and 5,008,572
`to Marshall et al., both assigned to an assignee of the present
`invention and hereby incorporated by reference, describe an
`electrical motor and fabrication method for achieving pre
`cise bearing registration of an internally disposed rotor
`assembly. As described more fully in the aforementioned
`references, an electrical motor comprising stator and rotor
`assemblies is fabricated by utiliZing a potting compound to
`both unitiZe the stator assembly and provide improved
`thermal characteristics.
`More particularly, the stator assembly is formed from a
`stack of stator laminations having inWardly projecting poles
`that de?ne the Walls of an un?nished internal chamber for
`housing a rotor assembly. Through-bolts attach front and
`rear aluminum end caps to the lamination stack, and this
`entire stator assembly is potted to unitiZe the lamination
`stack and ?ll voids betWeen the stator poles With potting
`compound. The internal chamber is then ?nished by machin
`ing a continuous, cylindrical bore substantially coincident
`With the sideWalls de?ned by the inWardly projecting stator
`poles. Precision registration of the rotor assembly is
`achieved by aligning end bearings on the rotor shaft With
`internal receiving surfaces machined in the stator end caps;
`the receiving surfaces being part of the cylindrical bore.
`While the motor and fabrication method described in the
`’604 and ’572 references achieve substantial advances over
`the prior art, further improvements are still desired. In this
`regard, various features of the assembly and method
`described in the ’604 and ’572 references Were identi?ed for
`improvement.
`One area sought to be improved relates to the potting of
`the stator assembly. Speci?cally, it has been determined
`empirically that a double cure cycle is desired for the potting
`compound; the second cure cycle improves the rigidity of
`the stator assembly, thereby yielding more ef?cient opera
`tion over the life of the motor. When only a single cure cycle
`is employed it has been found that, after a period of use, the
`rotor assembly occasionally locks Within the stator
`assembly, thereby limiting the useful life of the motor.
`Adding a second cure cycle, hoWever, undesirably increases
`manufacturing costs.
`A related aspect sought to be improved is the removal of
`air pockets formed Within the potting compound. As dis
`cussed in the ’572 and ’604 references, air is a poor thermal
`conductor. Filling the otherWise open space betWeen the
`stator poles With potting compound, improves thermal con
`ductivity and, accordingly, improves dissipation of the heat
`developed Within the motor. The process used in potting the
`stator assembly, hoWever, is knoWn to leave an air pocket
`under the rear end cap. This impedes the How of heat from
`the rear end cap. Therefore, further improvements in the
`thermal characteristics of the motor assembly are sought by
`eliminating the air pocket.
`Another area sought to be further improved relates to
`providing external electrical connections to the stator Wind
`ings Within the motor assembly. As described in the ’572 and
`
`10
`
`15
`
`20
`
`25
`
`30
`
`35
`
`40
`
`45
`
`55
`
`60
`
`65
`
`5,806,169
`
`2
`’604 references, an insulator having connectors is seated
`against the rear end of the stator lamination stack. The
`terminating ends of the stator Windings are brought out to the
`connectors, and a printed circuit board is con?gured to plug
`into connectors, establishing electrical continuity betWeen
`the stator Windings and conductive traces on the printed
`circuit. A second connector having conductive pins electri
`cally connected to the conductive traces on the printed
`circuit, is provided in conjunction With the printed circuit
`board to accommodate remote access to the stator Windings
`by Way of a complementary external connector. In this Way,
`external signals are readily connected to the stator Windings
`for controlling the motor operation.
`This second connector is nested Within the rear stator end
`cap. As previously described, both end caps are attached to
`the lamination stack by means of several through bolts,
`before the potting compound is applied. To prevent any
`potting compound from leaking betWeen the rear end cap
`and the second connector, a sealing means is provided
`around the second connector. Although the aforementioned
`structure provides an effective means for connecting exter
`nal motor drive signals to the stator Windings, a simpler and
`therefore more cost-effective solution is desired.
`In short, improvements are sought Which Will more ef?
`ciently address the aspects described above, While maintain
`ing the bene?ts and advantages in the motor assembly and
`method as described in the ’572 and ’604 references.
`
`SUMMARY OF THE INVENTION
`
`In vieW of the foregoing, it is a primary aim of the present
`invention to simplify and, thereby, achieve a loWer cost
`motor assembly and fabrication method, than that presently
`knoWn.
`Another object of the present invention is to provide an
`electrical motor assembly having improved thermal charac
`teristics.
`In more detail, it is an object of the present invention to
`eliminate the small air gap betWeen the potted Windings and
`the metal of the aluminum end cap. In even greater detail, an
`object of the present invention is to provide high dielectric
`paths of good thermal conductivity betWeen the electrical
`conductor and pole structure and the exterior of the motor,
`in order to increase the capacity of the motor to dissipate
`heat.
`Another object of the present invention is to provide an
`electrical motor fabrication method that simpli?es the
`method previously knoWn and used by eliminating the cost
`and time demanded by a second potting compound cure
`cycle, While maintaining the structural integrity of the ?nal
`motor assembly.
`Still another object of the present invention is to provide
`an electrical motor assembly having a simpli?ed and thus
`improved electrical connection betWeen the internal stator
`Windings and an external connector.
`Additional objects, advantages and other novel features of
`the invention Will be set forth in part in the description that
`folloWs and in part Will become apparent to those skilled in
`the art upon examination of the folloWing or may be learned
`With the practice of the invention. The objects and advan
`tages of the invention may be realiZed and obtained by
`means of the instrumentalities and combinations particularly
`pointed out in the appended claims.
`To achieve the foregoing and other objects, one aspect of
`the present invention is directed to a method of producing an
`electrical motor, Wherein an intermediate or un?nished
`
`BMW-1009
`Page 12 of 21
`
`

`

`3
`stator assembly is formed by compiling a stack of stator
`laminations and stator Windings. The intermediate stator
`assembly is then placed into a mold, and molten plastic is
`injected under pressure into the mold, Whereby the molten
`plastic is forced into and ?lls interior voids betWeen poles of
`the intermediate stator assembly. The molten plastic also
`forms a rear end cap for the stator assembly. The plastic used
`in this invention may be any thermoplastically processible
`resin, or blends of such resins. The resin may optionally
`include additives such as ?ame retardants, reinforcements,
`colored pigments, ?llers, plasticiZers, heat or light stabiliZ
`ers. Next, a continuous bore is machined through the center
`of the molded stator assembly to produce a concentric bore
`for housing a rotor assembly; the bore also providing
`mounting surfaces for receiving rotor assembly bearings.
`Finally, the rotor assembly is mounted into the stator assem
`bly by inserting the rotor assembly into the continuous bore
`and engaging the rotor bearings With the mounting surfaces.
`Arelated aspect of the present invention is directed to the
`injection molded electrical motor assembly, Which includes
`a rotor assembly having a central rotor portion on a rotor
`shaft, and a rotor bearing disposed near each end of the rotor
`shaft. Aunitary stator assembly includes a stator lamination
`stack Which forms stator poles that carry stator Windings,
`and front and rear end caps. The stator poles and Windings
`are substantially encapsulated by an injection molded plastic
`mass, Which ?lls the space betWeen the stator poles. The
`molded plastic also integrally forms the rear end cap. A
`continuous bore formed in the stator assembly through the
`front end cap, the stator lamination stack, and the rear end
`cap, forms mounting surfaces in the end caps for receiving
`the rotor bearings; the rotor assembly being carried Within
`the bore by an engagement betWeen the rotor bearings and
`the mounting surfaces in the end caps.
`Having summariZed the present invention above, the
`discussion Will noW be directed to a preferred embodiment
`of the invention. As an intermediate step of the fabrication
`process of a preferred embodiment, a matrix of conductive
`pins is fusion Welded to the stator Windings. The rear end cap
`is formed by the injection molded molten plastic to surround
`the matrix of pins and form a connector housing about the
`conductive pins. In this Way, the motor assembly provides a
`connector that is readily adapted for electrical connection to
`an external or remote source for controlling the motor. The
`injection molded end cap is an extension of the injection
`molded mass in the stator, and thus provides an ef?cient
`continuous path for dissipation of heat generated in the
`Windings.
`BRIEF DESCRIPTION OF THE DRAWINGS
`The accompanying draWings incorporated in and forming
`a part of the speci?cation, illustrate several aspects of the
`present invention, and together With the description serve to
`explain the principles of the invention. In the draWings:
`FIG. 1 is a perspective vieW illustrating a completely
`assembled motor constructed in accordance With one
`embodiment of the present invention;
`FIG. 2 is a partially exploded vieW shoWing a motor
`according to the invention With the rotor assembly removed
`from the stator assembly;
`FIG. 3 is a process How chart illustrating the steps of
`constructing a motor in accordance With the preferred
`embodiment of the present invention;
`FIG. 4 is an elevational vieW illustrating a partially
`assembled rotor, including a partial cut-aWay vieW;
`FIG. 5 is an elevational vieW illustrating a rotor assembly
`With bearings and bushing in place and ready for insertion
`into a stator assembly;
`
`4
`FIG. 6 is an elevational vieW of an individual stator
`lamination, illustrating the inWardly directed stator poles
`and pole teeth;
`FIG. 7 is a perspective vieW shoWing an assembled stator
`lamination stack made up of individual laminations as
`illustrated in FIG. 6;
`FIG. 8 is a perspective vieW of the front end of the stator
`lamination stack of FIG. 7 With insulators and stator Wind
`ings in place;
`FIG. 9 is the cut-aWay vieW as illustrated by arroWs in
`FIG. 6, illustrating a Wound stator assembly Within the caps
`and connector in place;
`FIG. 10 is a perspective vieW of the rear end of the
`un?nished stator assembly, shoWing the insulators, stator
`Windings, and matrix of connector pins in place;
`FIG. 11 is a partial vieW illustrating the matrix of con
`nector pins as disposed in relation to the stator lamination
`stack;
`FIG. 12 is a partial vieW illustrating the partially com
`pleted stator assembly of FIG. 9 after injection molding;
`FIG. 13 is a vieW similar to FIG. 12 illustrating the
`injection molded assembly after it has been machined and is
`thus ready for insertion of the rotor assembly;
`FIG. 14 is a side elevational vieW shoWing a mold ?xture
`used in fabricating the motor assembly of the present
`invention;
`FIG. 15 is a perspective vieW With a partial cut-aWay of
`the mold ?xture shoWn in FIG. 14;
`FIG. 16 is a partly broken aWay side vieW, and FIG. 17 is
`an axial section taken along the line 17—17 of FIG. 16,
`respectively, shoWing an alternative construction of motor
`adapted for practice of the present invention;
`FIG. 18 is an elevational vieW of a rotor assembly for the
`motor of FIGS. 16 and 17; and
`FIGS. 19 and 20 are an elevational cross section and an
`axial cross section taken along the line 20—20 at FIG. 19,
`respectively, shoWing a permanent magnet motor adapted
`for practice of the present invention.
`Reference Will noW be made in detail to various presently
`preferred embodiments of the invention, examples of Which
`are illustrated in the accompanying draWings.
`
`DETAILED DESCRIPTION OF THE
`PREFERRED EMBODIMENTS
`
`Turning noW to the draWings, FIG. 1 shoWs a perspective
`vieW of a hybrid permanent magnet stepping motor, and
`FIG. 2 a partly exploded vieW shoWing the rotor and rotor
`retaining elements removed from the stator assembly. It Will
`be noted at the outset, hoWever, that While the invention Will
`be described in connection With a hybrid stepping motor, it
`is also applicable to other motor types. For example, the
`invention is applicable to brushless variable reluctance step
`ping motors, permanent magnet brushless motor designs,
`sWitched reluctance motors, enhanced variable reluctance
`motors, as Well as enhanced and unenhanced stepping
`motors of the hybrid stepping type. Finally, induction motors
`could also utiliZe the present invention as could other motor
`types as Will be apparent to those skilled in the art upon
`reading the folloWing detailed description.
`Referring to FIGS. 1 and 2, there is shoWn a hybrid
`stepping motor generally designated by reference numeral
`20 comprised of a stator assembly 21 and a rotor assembly
`22. The rotor assembly is ?tted With bearings 23, 24 Which
`in turn mount in end caps 25, 26 that support the rotor
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`assembly 22 for rotation in the stator assembly 21. The end
`caps 25, 26, sandwich a central stator lamination stack 27
`that forms stator poles Which carry stator Windings (not
`shoWn in FIGS. 1 and 2). In the presently preferred
`embodiment, the stator laminations are aligned in registry
`and initially secured by Weld joints 70 (See FIG. 7) along the
`corners of the lamination stack. As Will be described in
`greater detail beloW, the lamination stack is further secured
`by means of a high-strength injection molded plastic Which
`completely encapsulates the interior of the lamination stack
`and preferably projects partly into a central bore 30 after
`molding. The bore 30 is then machined as by honing to form
`bearing surfaces 31, 32 (See FIG. 9) in the end caps 25, 26
`and also to form a smooth bore 30 through the lamination
`stack 27, contiguous With the bearing surfaces 31, 32.
`In the illustrated embodiment of FIG. 2, retaining rings 36
`secure the rotor assembly 22 in the stator assembly 21. In
`another embodiment, the rotor assembly 22 is retained in the
`stator assembly by a press-?t engagement betWeen bearings
`23, 24 and receiving surfaces 31, 32. The front end cap 26
`has a ?ange 37 Which in turn has a machined surface 38 With
`a mounting boss 39 to locate the motor in a mounting
`bracket. Mounting holes 40 provide means for mounting the
`motor to its bracket (not shoWn). The rear end cap 25
`includes an integral electrical connector 41 for supplying
`poWer to the stator Windings.
`As shoWn in FIG. 2, the rotor assembly 22 includes a rotor
`shaft 50 Which supports a rotor section 51, (i.e., the portion
`of the rotor Which is magnetically active) and outboard
`bearings 23, 24. In the illustrated embodiment, the rotor
`comprises toothed lamination sections 52, 53 separated by a
`permanent magnet 54. The magnet is positioned to provide
`the lamination sections 52, 53 With opposite magnetic
`polarities making, for example, lamination section 52 a
`north pole and lamination section 53 a south pole. In one
`embodiment, the laminations are formed With external teeth,
`of the same pitch as the teeth associated With the stator poles
`of the stator assembly. Other ratios of stator/rotor pitch can
`also be used such as 52/50 or 48/50. As is knoWn in the art,
`the teeth of section 53 are offset by about one half pitch With
`respect to the teeth of the section 52 in order to form a hybrid
`permanent magnet rotor. Thus, When the stator Windings are
`energiZed by a drive current coupled through the pins of
`connector 41, the rotating magnetic ?eld Which is produced
`in the stator tends to successively align the teeth of rotor
`lamination sections 52, 53, With the ?eld of the stator teeth,
`causing the motor to step in sequence. Control of the
`rotational rate and direction of the stator ?eld thus alloWs
`control of the rate and direction of rotor rotation.
`Turning noW to FIG. 3, there is illustrated the process for
`fabricating a motor in accordance With the present invention.
`Concentrating ?rst on the rotor assembly, it is seen that the
`primary raW materials Which go to make up the rotor are
`brought together at process step 100, and include rotor
`shafts, rotor laminations (or prestacks) and magnets. Those
`items are assembled at a step 101 and the assembled rotor
`Which results is best illustrated in FIG. 4. There is shoWn a
`rotor shaft 50 having a pair of lamination stacks 52, 53
`disposed thereon, With a permanent magnet 54 interposed
`betWeen the lamination stacks forming a rotor section 51
`intended to be driven by the rotating magnetic ?eld pro
`duced by the stator. In a hybrid permanent magnet stepping
`motor, the rotor laminations 52 and 53 have alternate teeth
`and valleys of a given pitch related to (as described above)
`the pitch of the teeth on the stator poles. Moreover, the teeth
`in the sections 52 and 53 are offset With respect to each other
`by one-half pitch. The magnet 54 serves to magnetically
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`polariZe the stacks 52, 53 With, for example, the stack 52
`being a north pole and the stack 53 being a south pole.
`The shaft 50 has a pair of machined sections 60, 61
`adapted to receive the inner race of bearings 23, 24 (FIG. 5)
`for support of the rotor Within the stator assembly. The shaft
`50 can have its output end keyed as illustrated, unkeyed if
`desired, or With any other adaptor con?guration. The motor
`can also be con?gured With an output shaft on the rear end
`to form a double-ended motor. Such constructional details
`form no part of the present invention and Will not be
`emphasiZed herein.
`Having assembled the rotor 22 in step 101 (FIG. 3), the
`rotor is then passed to a grinding station Where step 102 is
`performed to grind the rotor outer diameter. Such grinding
`tends to produce teeth in the lamination stacks 52, 53 Which
`have relatively sharp corners. In addition, the grinding step
`produces a rotor Which is substantially concentric and there
`fore can operate in a carefully machined stator bore With a
`relatively small air gap.
`Having thus con?gured the rotor magnetic section 51, and
`after machining debris is cleaned from the rotor, a step 103
`is then performed in Which bearings 22, 23 are assembled
`onto the bearing support surfaces 60, 61 of the rotor. In the
`exemplary embodiment, spacer bushings 62, 63 are inter
`posed betWeen the bearings 23, 24 and the lamination stacks
`52, 53 respectively. The bushings ride betWeen the lamina
`tion stack and the inner race of the bearings to form a spacer
`element to properly locate the bearings on the shaft. The
`bearings are press ?t on the shaft, preferably in an appro
`priate ?xture, in the step 103.
`Referring to FIG. 5, there is shoWn the rotor assembly
`including bearings 23, 24 and the spacing bushings 62, 63,
`providing a rotor assembly Which is ready for insertion into
`a stator assembly. FIG. 5 illustrates, in someWhat exagger
`ated fashion, the fact that the outer diameter of the bearings
`23, 24 is slightly greater than the outer diameter of the rotor
`section 51. It Was previously noted that the stator bore is a
`continuous straight through bore formed in a single opera
`tion after assembly of the stator. Thus, providing the bear
`ings 23, 24 With a slightly greater outer diameter than the
`rotor section 51 alloWs the entire rotor assembly to be
`inserted into the bore, With the outer race of the bearing 23,
`24 seating in the bearing surfaces of the end caps While the
`rotor section 51 has a suf?cient, although a very small,
`clearance for rotation. The precision thereby achieved
`alloWs the motor to be con?gured With a relatively small air
`gap, thus providing higher torque and ef?cient operation.
`As illustrated in FIG. 3, the initial raW material compo
`nent for the stator assembly procedure is individual stator
`laminations Which are assembled in a step 105. An indi
`vidual lamination 27a is illustrated in FIG. 6. it is seen that
`each lamination, Which can be formed by stamping, has a
`series of poles 66a With a plurality of teeth 67a formed on
`each of the poles. The poles 66a are separated by gaps 68a
`Which provide an area for receiving the stator Windings. The
`laminations also have punched clearance holes 69a through
`Which alignment bolts can pass for initially registering the
`stator assembly. Preferably a clearance hole 69a is associ
`ated With each pole 66a such that the stator laminations are
`symmetrical and can be installed in any of eight orientations.
`Thus, it is possible in assembly to turn the stator laminations
`With respect to each other such that the grain of the steel
`from Which the laminations are made is not in a single
`direction, alloWing the magnetic properties of the lamination
`stack due to grain to be averaged.
`As illustrated in FIG. 7, the step 105 (FIG. 3) is imple
`mented by assembling a stack of laminations of a predeter
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`mined height and af?xing the laminations together, in the
`illustrated embodiment by means of Welds 70. Alternatively,
`prestacks (i.e., groups of laminations joined by stamped
`dimples formed during the laminations stamping operation)
`may be used. Using the Welding technique, preferably a
`stack of laminations is placed under pressure, and automatic
`machinery gauges that the laminations stack is of the appro
`priate height before the Welds are made. If it is not lamina
`tions are either added or removed until the desired height is
`obtained at Which point automatic Welding equipment pref
`erably applies four Welds 70 at corners of the lamination
`stack displaced 90 degrees from each other. As seen in FIG.
`7, the assembled lamination stack thereupon provides a pole
`structure 66 separated by inter-pole Winding gaps 68, each
`pole structure having axially disposed teeth 67 of a prede
`termined pitch. It is also seen that the anchor holes 69 are
`aligned such that an alignment bolt or injection molding
`needle can pass through the lamination stack at the appro
`priate point in the assembly process.
`After the lamination stack is assembled, and in the
`optional case Where an “enhanced” motor is to be produced,
`in a step 105 elongate magnetic strips 85 are inserted in each
`gap betWeen stator teeth 67 (See FIG. 12). As Will be
`described beloW, the magnets Which are inserted betWeen
`stator teeth tend to enhance the magnetic properties of
`certain classes of motor. The magnetic strips have suf?cient
`frictional engagement With and magnetic attraction for the
`gaps into Which they are inserted to temporarily maintain the
`strips in place during subsequent manufacturing steps until
`they are ?rmly secured in their gaps by means of injection
`molded plastic material.
`FolloWing the magnet insertion step 105 if performed, or
`the simple Welding of the lamination stack 105 for a non
`enhanced motor, as shoWn in FIG. 3 subsequent operations
`are performed on the assembled lamination stack to associ
`ate the stator electrical components With the stack and to
`magnetiZe the stator poles. In this regard, the stack is
`insulated, Wound, and the Windings are terminated. In FIG.
`3 the insulation step is indicated at 106. Preferably, discrete
`insulators are supplied along With the Welded stator lami
`nation stack in order to provide appropriate insulation
`betWeen the stator Windings and the lamination stack. Turn
`ing brie?y to FIG. 8, one end of the insulator assembly is
`illustrated at 71 and is shoWn to completely line the slot 68
`as Well as to cover the face 72 of each pole 66. Upstanding
`insulator sections 71‘ help retain the stator Windings, and
`Will interface With the end cap When they are juxtaposed.
`Bolt protectors 71“ insulate the fasteners 28 and prevent
`contact betWeen the fasteners and the Windings. A mating
`end for the insulator is illustrated in FIG. 10 at 90. It is seen
`that the insulator 90 is similar to the insulator 71 in that it
`provides a face 92 for insulating the end of the pole,
`channels 93 Which completely line the inter-pole slots, and
`upstanding projections 90‘ for retaining the stator Windings.
`FIG. 10 illustrates bolt protectors 90“ on the rear facing
`insulator section. Since the rear end cap 25 is formed from
`molded plastic and bolts are not used to secure it to the
`lamination stack 27, it should be apprec