CA1285980C - Closed slot rotor construction - Google Patents

Abstract

CLOSED SLOT ROTOR CONSTRUCTION

ABSTRACT OF THE DISCLOSURE
A rotor lamination for use in a dynamo-electric machine of the kind having a stacked laminated rotor, is formed of a flat circular plate of ferromagnetic material having a number of equally circumferentially spaced closed slots. Each of the lots is substantially V shaped at an upper slot region near the circumference of the plate, and is symmetrical about a radial center line. Each leg of the V forms an angle of about 30 degrees with respect to a line drawn perpendicular to the radial center line of the slot.

Description

1~859~1) CLOSED SLOT ROTOR CONSTRUCTION

BACKGROUND OF THE INVENTION
FI LD OF THE INVENTION --- The present invention relates generally to closed ~lot rotor lamlnations or punchings for use in dynamo-electric machines, and more particularly to a laminati ~ J- ~h~,~e ~
in which the ~lots are rormed with generally~L-~ep ends.

DESCRIPTION OF THE R~OWN ART
Rotors rormed of a ~tack Or laminatlons having closed slots equally spaced ~rom one another about the periphery of each laminatlon are known rrom, ~or example, ` U.S. Patents 2,794,138 (May 28, 1957) and No. 3,401,280 (September 10, 1968), both having been assigned to the assignee of the present lnvention.
; ;Such rotors are ordlnarily used in inductive AC
otors, wherein conducting members which extend axially along the rotor through aligned slots o~ the stacked laminatlons lnter-ct w~th a rotatlng magnetlc field ; oreated ~n an air gap between the outer circumrerence o~
the rotor and the inner circum~erence o~ the machine tator. ~indlrgs embedded in lot~ between radially 128s98~) inwardly proJectlng teeth Or the ~tator, ad~acent the a$r ~ap, are connected to the AC mains, and the ~tator winding conductors pass through a certain order of the qtator slots so as to cause magnetlc rlux in the air gap to rotate in synchronism with the fre~uency Or the AC mains.
To obtain high efriciency during normal rotational speed conditions for the rotor, the conducti~e members or bar~ in the rotor slots should have minimal resistance.
Low rotor resiQtance, however, results in low starting torque with a high starting current and a low Rtarting power ~actor. One way to achie~e an erfectively high rotor resistance at motor ~tart-up, is to employ a so-called double -Qquirrel cage rotor bar arrangement in which two parallel conductive bars pass through each rotor ~lot with top bars (i.e., the bars closer to the rotor circumrerence) ha~ing smaller cross-sectional area and, hence, higher reslstance, than bottom bars set deeper in the slots, i.o. clo~er to the axis Or the rotor.
The top bars and the bottom bars are all shorted together ; at the axial ends Or the rotor.
~ By oonstricting the rotor slotg between the top and : the bottom barq in the radial direction to rorm a ~o-called neck portion Or the slot, the bottom bars will have , ~: .: . ....... . ,- -. . . . .
.~ , ~ - ,:
~ . . . , .. - . - , . .

128~9~

a much 8reater inductance in relation to the top barQ and, thus, relati~ely llttle current ls lnduced in the bottom bars at motor start-up when the alr gap ~lux rotates at greatest speed relative to the rotor bars. The efrecti~e rotor reslstance at start-up $Q then about eQual to that of the top barQ and, thus, sufficlent start-up torque may be obtained. ~hen the rotor approaches normal running ~peed, however, the air gap field interacts with the rotor bars at a much lower frequency 80 that the inductance Or the bottom bars becomes lesQ signiricant. The lower re~istance of the bottom bars then provides greater operat~ng e~ficiency, the actual rotor re~iQtarce approximating that of both the bottom and top bars in parallel.
Closed ~lot rotor~ Or the double cage ~ariety con~entionally ha~e the slots in the rotor laminations formed with a generally V -Qhaped edge at the top of the ~lot w~th the center Or the V creating a narrow bridge part between the top of the slot and the outer clrcumference of the lam$natlon. ~urther, the angle def~ned between each leg Or the V and a l~ne drawn perpendicular to the radial center line o~ the qlot con~entionally haQ been between about 40 to 45 degree~.

.,.. ~..: .... .. .. . .
::' , : .......................................... . .
~ . . .

1~598~

Such angles aQ 40 degrees and 45 degrees ror the V shaped edge and would requlre a narrower br$dge ln order t~
dell~er the same performance, and would thererore present diff~culties ln machinlng Or the closed slots at the peripheries Or the rotor laminatlons.

, ~ , . . . . .

12~3598-) SUMMARY _ THE INVENTION
An object of the invention is to provide a closed slot rotor lamination which can be manufactured without imposing costly production procedures.
Another object of the invention is to provide a closed ',~l' slot rotor lamination having V-shaped top wherein the angle of the V allows for optimum electromagnetic performance.
A further object of the invention is to provide a closed slot rotor lamination in which neck portions of the slots are located to optimize machine performance.
According to the invention, a lamination used to form a rotor in a dynamo-electric machine, includes a flat circular plate of ferromagnetic material having a number of equally circumferentially spaced closed slots extending radially near the outer periphery of the plate. As will be understood by persons skilled in the art, the 810ts are formed to contain conducting members which extend along the rotor when a number of the plates (also called punchings or laminations) are stacked together and corresponding 610ts are placed in com-munication with one another. Each slot is substantially V-shaped at an upper slot region and symmetrical about a ra-dial center line. The legs of the V diverge from one another towards the center of the plate, and each leg of the V forms an .. ,.~ ., , , ~ , .
~''," ~ '. . .

8 59~

angle of about 30 degrees with respect to a line drawn perpendicular to the radial center line Or the slot.
The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part Or the present disclosure. For a better understanding of the invention, lts operating advantages and speciric ob~ects attalned by its use, reference should be had to the accompanying drawing and descriptive matter in which there are illu~trated and described prererred embod~ments Or the invention.

.

.
.-~8598-) BRIEF DESCRIPTION OF THE DRAWING
In the drawlng:
Fig. 1 is a side view, partly in ~ection, o~ a dynamo-electric machine in which the present in~entlon may be embodied;
Fig. 2 lq a front end view of the machine ln Fig. 1;
Fig. 3 is a plan view Or a rotor lamination according to one embodlment of the present ln~ention;
Flg. 4 ls an enlarged ~iew Or a closed slot in the lamination Or Fig. 3;
Fig. 5 is an enlarged view Or an upper slot region Or the slot in Fig. 4;
Fig. 6 i~ a plan view a rotor lamination according to a second embodiment Or the in~ention; and Fig. 7 is an enlarged view o~ a ~lot in the lamination of Fig. 6.

. .

, ~

lZ8~981~

DETAILED DESCRIPTION OF THE Il~VENTION
Fig. 1 ~hows a ~lde vlew, ln ~ectlon, of a dynamo electrlc machlne 10, in which the present inventlon may be embodled. A rront vlew Or the machlne 10 is shown in Fig.
2.
Basically, the machlne 10 lncludes a generally cylindrical outer casing 12, and a generally cyllndrlcal stator 14 fixed coaxlally withln the outer casing 12 and having a coaxial stator bore 16. A rotor 18 18 ~upported by suitable bearings 20a, 20b at the rront and back Or caslng 12, to extend axially within the rotor bore t6 and ~r rotational movement about the bore axis. In the partlcular example ~hown a Qhaft part 22 Or the rotor 18 extends axially rrOm a front end shield 24 Or the machine 10, and has a key 26 pro~ecting radially outward from a rece~s cut axlally a certaln di~tance from the rront of the Qhart part 22. ~ey 26 serves to lock the sha~t part 22 into a corresponding key way cut in a load member (not ~hown) e.g. a ran, to which rotational motive power 18 to be supplied by the machlne 10.
A back end shield 28 (Fig. 1) together wlth the caslng 12 and the rront end ~hield 24 serve to contaln and protect the stator 14, rotor 18 and a~sociated conductive wlndings. In the example ~hown a machine cooling ~an 30 ls mounted on a rotor ~tub part 32 which extends outside the :: .. . ' ~, . . .

:-` lX8598-t ~9~ 03 GP 6073 back end ~hleld 28, and dlrects an a~r current M ow o~er the casing.
~ s shown ln Flg. 1, the ~hart part 22 Or the rotor 18 extends axlally through the mac~lne ca~ing 12 and haQ a stac~ Or rotor lamlnations 50 rlxed coaxlally on the Jhart 22 lntermedlate the rront and back bearings20a, 20b. Sets of conducti~e bars 52 pass through axlally extending slots rormed ln the rotor 18 near the outer per~phery Or each Or the laminations 50. The bar~ 52 are ~horted to one another at the axlal ends or the stack o~ lamlnations 50 by a set Or end rlngs 54a, 54b.
Fig. 3 ls a plan ~lew Or one Or the rotor laminations 50. The lamination ls rormed Or a flat clrcular plate Or ferromagnetic material. The plate lamination 50 has a number (e.g., 28) Or unif~rmly clrcumrerentially spaced closed slots 56 extendlng symmetrically about radial center llne~ ln a region near the outer perlphery Or the laminat$on 50. Slots 56 are ormed to contain conductl~e bar~ 52 (Flg. 1) whlch extend ~ubstantially parallel to the aXlQ Or the rotor lô when the laminations 50 are stacked face-to-face with the corresponding slots 56 aligned (i.e., in communication with one another.)Each of , . . .. .. . .
, ~ - ~ , . . . .

12~3598~

the ~lotq 56 is substantlally V-shaped at an upper ~lot region 58 as ~hown in Figs.4 and ~. A Y-shaped edge 60 torming the upper ~lot region 58 ls symmetrical about the radlal center line, with the legs Or the V diverging rrom one another in the directlon toward the center Or the lamination 50.

In one preferred form, as specifically shown in Fig. 5, each leg o~ the ~ derining the edge 60, rorms an angle o~ about 30 tegrees with respect to a line drawn perpendicular to the radial center llne Or the slot 56. Further, the center of the V Qhaped cdge 60 is curved at a rirst radiu~
Rt between the ~traight legs Or the edge 60. A bridge area 62 is thus rormed between the upper slot region 58 and the outer circumference Or the lamination 50.
~referably, the radial dimen-~lon Or a narrowest part Or the ~ridge area 62 at the center Or the V-shaped edge 60 1~ at lea t .25 mm., and may be ln the range rrom about .25 mm. to about .4 mm.
As ~een more clearly in Fig. 4, the edges Or each ~lot 56 conQtrict toward the rad~al center line Or the nlot wlth opposing edges curvcd cont$nuously at a Jecond radlu~ R2 between d~tal ends 64a, 64b Or the ~tralBht legs Or the Y-shaped edge 60 to a rlr~t set Or polnt~ 66a, - , . . . -, .

128598-) ~ 03 GP 6073 66b, where the slot edges have a common tangent T which is perpendicular to the radial center line.
From the tangent line T, the opposite edges of the slots are curved continuously at a third radius R3 to constrict toward the center line over an arc of 90 degrees to a second set of points 68a, 68b defining tops of nec~ portions 70 of the slots 56. The tops of the neck portions 70 of the slots 56 are located at points radially of the laminations 50 such as to optimize electromagnetic performance when the conductive bars 52 are inserted in upper and lower regions of the slot 56 of a lamination stack to form a double cage rotor as in Fig. 1. In some specific cases, the segments of the slot contour that joins or blends the radii R2, R3 may be extremely small, or approach a limit such that such segments are essentially non-measurable in terms of length.
Table 1, below shows preferred values for the first, second, and third radii Rl, R2, R3 with the V-shaped edge 60 forming the 30 degree angle represented in Fig. 5.

PUNCHED DIAMETER R R R

95 mm. .932 mm..813 mm. .7 mm.
122 mm. .892 mm..919 mm. .76 mm.
122 mm. .933 mm..715 mm. .76 mm.
150 mm. .934 mm.1.105 mm. .762 mm.

: - : . . .

1 2~598~) -12- 0~ GP 6073 Table 2, below, Qhows preferred locations o~ the topQ Or neck portions 70, l.e., the radial di-Qtance ~rom the center of the la~ination 50 (Point C in Fig. 3 or Fig. 6) to a line mer~endicular to the radial center line of the slot 56 which line intersects the second set of points 68a, 6~b in Fig. 4. AS shown, the locations of the to~s of the neck Portions 70 ~referablv vary according to the diameter of the lamination 50.

" .

DIAMETER _ NECK PORTION 70 TOP_ _ 95 mm. 43.462 mm 122 mm. 56.9 mm.
150 mm. 70. mm.

Figs. 6 and 7 shows a closed slot rotor lamination according to a ~econd embodlment o~ the ~nventlon. Parts corresponding to those shown in the embodiment Or Fig. 3-5, ha~e corresponding reference character~. AQ shown in Fig. 7, however, the edge Or the slot 56' in the upper . - .

~28598-) regions 58' which leads away from the distal ends of the straight legs of the V-shaped edge 60', is only partially curved at a second radius R2, until such edge is parallel to the slot center line and then extends parallel to the center line a certain distance L before curving towards the slot center line at the second radius R2, until becoming tangent to the line T'. For a diameter of 115 mm. for the lamination 50', the distance L is preferably about .531 mm. with a first radius Rl, of .932 mm., and second and third radii R2, R3, all of .76 mm. The top of the neck portion 70' is preferably at 52.5 mm. from the center of the circular lamination 50'.
Machines constructed with double cage rotors comprised of laminations according to the present invention exhibited superior performance over rotors having slots with V-shaped edges defining angles of about 45 degrees with respect to breakdown torque, locked rotor torque, full load speed and full load efficiency.
Providing the 30 degree angle according to the invention allows sufficient material at the bridge area 62 (or 62') to avoid costly machining or casting procedures to fabricate the laminations 50 (or 50'), and enables th~ top conductive bars in the upper slot regions 58 to present a lower bar resistance at normal running speed. Moreover, ,, i~85~

undesirable reactance effects for the conductive bars 52 have been found to be diminished in accordance with the slot con-struction of the present invention.
Reference is made herein to "punched diameter", and "diameter" in the context of the outer diameter of a lamina-tion. In this context, "punched diameter" means "as punched"
by a punch press and does not contemplate finishing operations for establishing air gap defining finished surfaces. Thus, it should be understood that reference to, for example, a "plate diameter of about 150 mm." would be inclusive of an as punched lamination having a nominal as punched diameter of lS0 mm., but also a lamination within a finished rotor having a nominal finished outer diameter somewhat less than 150 mm. (so that an appropriate air gap will be maintained between rotor and stator).
While the foregoing description represents preferred embodiments of the present invention, it will be obvious to those skilled in the art that various changes and modifica-tions may be made, without departing from the true spirit and scope of the present invention.

, ~28S98~

RE:LATIONSHIP TO OTHBR APPLICATIONS
This application has been filed on March 10, 1988 as well as commonly assigned Canadian Application Serial No. 561,117 - BASE ASSEMBLY FOR DYNAMOELECTRIC
5 MACHINE,in the name of Robert L. Sieber, filed March 10, 1988; Canadian Application Serial No. 561,730 -DYNAMOELECTRIC MACHINE LAMINATION CONSTRUCTION in the name of Thomas W. Neumann, filed March 17, 1988; and Canadian Application Serial No. 561,110 - LIP
10 STRUCTURE FOR A STATOR IN A DYNAMOELECTRIC MACHINE in the names of Deepakkumar J, Gandhi et al, filed March 10, 1988.

- ,:

Claims (20)

1. A lamination for use in a lamination stack forming a rotor in a dynamoelectric machine, comprising:
a flat circular plate of ferromagnetic material having a number of equally circumferentially spaced closed slots extending radially in a region near the outer periphery of said plate, said slots being formed to contain conducting members which extend axially along the rotor when like ones of said plates are stacked face-to-face with corresponding slots in communication with one another, each of said slots having an upper edge that is substantially in the shape of a V at an upper slot region adjacent the periphery of said plate and symmetrical about a radial center line, portions of said upper edge corresponding to legs of the V
diverging from one another in the direction towards the center of said plate, and each upper edge portion corresponding to a leg of said V forms an angle of about 30 degrees with respect to a line drawn perpendicular to the radial center line of the slot;
wherein said circular plate has bridge areas between said upper slot regions and the outer periphery of said plate, a center region of the upper edge of each slot is curved at a first radius between the edge portions corresponding to legs of said V to define a bridge area for each slot, and said slots are each formed to constrict toward the radial center line of the slot with opposing edges curved at a second radius between distal ends of the upper edge and a first set of points along which the opposing edges have a common tangent which is perpendicular to said radial center line;
wherein the center region of the upper edge of each slot forms a narrowest part of each bridge area, and the radial dimension of said narrowest part is in the range from about 0.25 mm. to about 0.4 mm.

2. A lamination according to claim 1, wherein opposing edges of said slots are curved continuously at a third radius to constrict toward said center line from said common tangent line and radially inward over an arc of 90 degrees to a second set of points defining tops of neck portions of said slots.

3. A lamination according to claim 2, wherein the tops of said neck portions are located at points radially of said plate such as to optimize electromagnetic performance.

4. A lamination according to claim 2, wherein said first radius is about 0.932 mm., said second radius is about 0.813 mm., and said third radius is about 0.7 mm.

5. A lamination according to claim 2, wherein said first radius is about 0.892 mm., said second radius is about 0.919 mm., and said third radius is about 0.76 mm.

6. A lamination according to claim 2, wherein said first radius is about 0.933 mm., said second radius is about 0.715 mm., and said third radius is about 0.76 mm.

7. A lamination according to claim 2, wherein said first radius is about 0.934 mm., said second radius is about 1.105 mm., and said third radius is about 0.762 mm.

8. A lamination according to claim 3, wherein said plate has a diameter of about 95 mm. and the tops of said neck portions are located at a radius of about 43.462 mm.

9. A lamination according to claim 3, wherein said plate has a diameter of about 122 mm. and the tops of said neck portions are located at a radius of about 56.9 mm.

10. A lamination according to claim 3, wherein said plate has a diameter of about 150 mm. and the tops of said neck portions are located at a radius of about 70 mm.

11. A dynamoelectric machine, comprising:
a generally cylindrical casing;
a stator fixed in said casing and comprised of a stack of plate laminations of ferromagnetic material, said stator having a cylindrical bore;
a stator winding embedded in stator slots which extend radially outward from the circumference of said bore;
a rotor comprised of a stack of rotor laminations of ferromagnetic material and supported by said casing in said bore for rotational movement about the bore axis, said rotor including conductive means for interacting with a magnetic field when said stator windings are energized by an outside electrical source;
wherein each of the rotor laminations comprises:
a flat circular plate of ferromagnetic material having a number of equally circumferentially spaced closed slots extending radially in a region near the outer periphery of said plate, Claim 11 continued:
said slots being formed to contain conducting members which extend axially along the rotor when like ones of said plates are stacked face-to-face with corresponding slots substantially aligned with one another, each of said slots having an upper edge that is substantially in the shape of a V at an upper slot region adjacent the periphery of said plate and symmetrical about a radial center line, portions of said upper edge corresponding to legs of the V
diverging from one another in the direction towards the center of said plate, and each upper edge portion corresponding to a leg of said V forms an angle of about 30 degrees with respect to a line drawn perpendicular to the radial center line of the slot;
wherein said circular plate has bridge areas between said upper slot regions and the outer periphery of said plate, a center region of the upper edge of each slot is curved at a first radius between the edge portions corresponding to legs of said V to define a bridge area for each slot, and said slots are each formed to constrict toward the radial center line of the slot with opposing edges curved at a second radius between distal ends of the upper edge and a first set of points along which the opposing edges have a common tangent which is perpendicular to said radial center line;
wherein the center region of the upper periphery of each slot forms a narrowest part of each bridge area, and the radial dimension of said narrowest part is in the range from about 0.25 mm. to about 0.4 mm.

12. A machine according to claim 11, wherein opposing edges of said slots are curved continuously at a third radius to constrict toward said center line from said common tangent and radially inward over an arc of 90 degrees to a second set of points defining tops of neck portions of said slots.

13. A machine according to claim 12, wherein the tops of said neck portions are located at points radially of said plate such as to optimize electromagnetic performance.

14. A machine according to claim 12, wherein said first radius is about 0.932 mm., said second radius is about 0.813 mm., and said third radius is about 0.7 mm.

15. A machine according to claim 12, wherein said first radius is about 0.892 mm., said second radius is about 0.919 mm., and said third radius is about 0.76 mm.

16. A machine according to claim 12, wherein said first radius is about 0.933 mm., said second radius is about 0.715 mm., and said third radius is about 0.76 mm.

17. A machine according to claim 12, wherein said first radius is about 0.934 mm., said second radius is about 1.105 mm., and said third radius is about 0.762 mm.

18. A machine according to claim 13, wherein said plate has a diameter of about 95 mm. and the tops of said neck portions are located at a radius of about 43.462 mm.

19. A machine according to claim 13, wherein said plate has a diameter of about 122 mm.
and the tops of said neck portions are located at a radius of about 56.9 mm.

20. A machine according to claim 13, wherein said plate has a diameter of about 150 mm. and the tops of said neck portions are located at a radius of about 70 mm.