GB1584983A - Creación de Inventos y Patentes con Inteligencia Artificial

GB1584983A – Shaded pole motors
– Google Patents

GB1584983A – Shaded pole motors
– Google Patents
Shaded pole motors

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Publication number
GB1584983A

GB1584983A
GB2047377A
GB2047377A
GB1584983A
GB 1584983 A
GB1584983 A
GB 1584983A
GB 2047377 A
GB2047377 A
GB 2047377A
GB 2047377 A
GB2047377 A
GB 2047377A
GB 1584983 A
GB1584983 A
GB 1584983A
Authority
GB
United Kingdom
Prior art keywords
span
pole
motor
electrical degrees
shading coil
Prior art date
1976-05-20
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)

Expired

Application number
GB2047377A
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)

General Electric Co

Original Assignee
General Electric Co
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
1976-05-20
Filing date
1977-05-16
Publication date
1981-02-18

1976-05-20
Priority claimed from US05/688,251
external-priority
patent/US4131814A/en

1977-05-16
Application filed by General Electric Co
filed
Critical
General Electric Co

1981-02-18
Publication of GB1584983A
publication
Critical
patent/GB1584983A/en

Status
Expired
legal-status
Critical
Current

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Classifications

H—ELECTRICITY

H02—GENERATION; CONVERSION OR DISTRIBUTION OF ELECTRIC POWER

H02K—DYNAMO-ELECTRIC MACHINES

H02K17/00—Asynchronous induction motors; Asynchronous induction generators

H02K17/02—Asynchronous induction motors

H02K17/04—Asynchronous induction motors for single phase current

H02K17/10—Motors with auxiliary phase obtained by split-pole carrying short-circuited windings

Description

(54) SHADED POLE MOTORS
(71) We, GENERAL ELECTRIC COMPANY, a Company organised and existing under the laws of the State of New York, United States of America, of 1 River Road,
Schenectady 12305, State of New York, United States of America, do hereby declare the invention, for which we pray that a patent may be granted to us, and the method by which it is to be performed, to bye particularly described in and by the following statement:
This application is for a Patent of Addition to our British Patent 1,445,416. The invention relates to dynamoelectric machines and, more particularly, to salient-pole shaded pole motors having concentrated windings disposed around circumferentially spaced apart pole pieces that each have a leading pole tip separated by an air gap from the trailing pole tip of the pole piece adjacent thereto.
Shaded pole motors of the concentrated winding, salient-pole variety, are one of the less expensive types of motors to manufacture. Accordingly, this type of motor is usually selected for alternating voltage applications whenever the heretofore known operating characteristics (in terms of starting torque, maximum or break down torque, running torque, dip.torque, efficiency, etc.) of this type of motor will meet the needs of an intended application.
If one or more operating characteristics of this type of motor is’ not satisfactory for a given application. however, distributed wound motors will normally be used. Generally speaking.
distributed wound motors are more expensive to manufacture than shaded pole motors. In addition, mechanical duty distributed wound motors utilize approaches such as selectively energizeable auxiliary winding arrangements so’that desired operating characteristics can be achieved. For example, increased starting or locked rotor torque, efficiency. and so forth can be realized with these more expensive motors of similar overall physical size.
Shaded -pole motors of the concentrated winding salient-pole variety. when designed to be relatively efficient during operation (e.g.. those having efficiencies of 35% to 40% and greater) have relatively low starting torques. For example when motors of this type have an operatirigéfficiency in the neighborhood of 40% or more, the ratio of starting or locked rotor torque to maximum torque seems invariably to be about .33 or less. This is one of the primary reasons why the use of shaded pole motors has been generally limited to applications for driving fans and other fluid moving devices such as pumps. In many of these applications. the needed locked rotor torque is a relatively small fraction of the desired maximum torque or running torque (expressed as a percentage of maximum torque); although in some specific fan applications. the locked rotor torque may have to be in the neighborhood of one-half of the rated running torque.
In the more efficiently designed concentrated winding salient-pole shaded pole motors, pole pieces project radially from a magnetizeable yoke. In addition, the pole tips of adjacent ones of such pole pieces are spaced apart by air gaps (as shown. for example, in U.S.
Patent 3.313.965) and thus are not interconnected with magnetic material. With designs of this general type. changes that increase efficiency (for a given dip to maximum torque ratio) will decrease the ratio of locked rotor torque to maximum torque. On the other hand, for a given looked-rotor torque and maximum torque, any further improvement in efficiencies causes, expectedly. a decrease in dip torque (DT).
While a reduction in dip torque may be generally undesirable, it may become intolerable (because of loss of motor stability) in motors designed with tapped windings and intended for multi-speed-operation. For example, while a multispeed salient-pole shaded pole motor may be stable for high speed fan operation; when the motor is energized for low speed operation, it will not come up to speed if the dip torque is less than the amount of torque needed to accelerate the fan or other load past the speed associated with the dip torque of the motor. However, for a given locked rotor torque and maximum torque, any increase in stability associated with increased dip torque causes a reduction in operating efficiency with prior art approaches.
It therefore should now be understood that it would be advantageous and desirable to provide new and improved salient-pole shaded pole motors having winding coils concentrated about radially disposed pole pieces; such motors having characteristics that would not make it necessary (among other things) to sacrifice efficiency for increased locked rotor torque to maximum torque ratios for a given dip torque to maximum torque ratio. It would also be of importance to provide new and improved salient-pole shaded pole motors with characteristics that would permit the use of this type motor in so-called mechanical duty applications where the more expensive types of induction motors (with auxiliary starting devices) have been used heretofore. Two general examples of this type of application is the business machine field and electric motor driven gear reducer fields. It also would be desirable to provide a way to increase the efficiency of small fan motors.
In accordance with one aspect of the present invention there is provided a shaded pole motor including a stator assembly comprising a magnetizable yoke and a plurality of spaced apart pole pieces extending from the yoke towards a rotor receiving space with the leading pole tip of each pole piece magnetically separated from the. trailing pole tip of the adjacent pole piece, at least one of said pole pieces having a leading pole tip with either a step or with an equivalent chamfered or slotted construction providing a relatively high magnetic reluctance compared with the trailing pole tip of the same pole piece, first -and second shading coils disposed on the trailing pole tip of the same pole piece, the two shading coils having different spans which are both less than the span of the said step, the shading coil having the larger span having a span of between 50% and of the said step span; and a rotor assembly supported for rotation in said rotor receiving space.
In accordance with a further aspect of the present invention there is provided a.salient- pole shaded pole motor including a stator assembly and rotor assembly; the stator assembly comprising a magnetizable core having a magnetizable yoke and a plurality of magnetically spaced apart pole pieces each having a leading and trailing pole tip, with the leading tip of each pole piece magnetically spaced from the trailing pole tip of a pole piece next adjacent thereto; said stator assembly further including at least a first and a second electrically short circuited shading coil disposed on and thereby identifying each of the trailing pole tips, and a winding comprising at least one concentrated group of conductor turns accommodated closely adjacent to at least one of the pole pieces; said rotor assembly including a short circuited squirrel cage rotor spaced by an air gap from bore defining faces of the pole pieces, and the leading pole tip of each pole piece having either a step with a span of one-third of a pole pitch or a chamfered or slotted construction providing magnetic reluctance substantially equal to that produced by a step with a span of one third of a pole pitch; the first shading coil having a span of between 30 electrical degrees and 59 electrical degrees; and the second shading coil having a span less than the span of the first shading coil.
By way of example, the invention will be further described by references to the accompanying drawings in which:
Figure 1 is an end elevation of a salient-pole shaded pole motor, with parts removed and parts in section, embodying the invention in one form;
Figure 2 is a plan view of one of the stator laminations of the motor shown in Figure 1;
Figure 4 is an end elevation, with parts removed, broken away, and in section, of a prior art motor;
Figure 3 is a view, with parts in section, parts broken away, and parts removed, of another motor embodying improvements over the motor shown in Fig. 4 but not embodying the present invention.
Figure 5 is a plot of speed versus torque for motors of the general type described herein;
Figurs 6 through 9 are plots of various performance or operational characteristics for motors of the type described herein as prior art and for motors embodying the invention and of these:
Figure 6 is a plot of gross efficiency at 70%of maximum torque versus the ratio of locked rotor torque to maximum torque;
Figure 7 is a plot of watts input per watt output at 70% of maximum torque load versus the ratio of locked rotor torque to maximum torque (LRT/MT);
Figure 8 is a plot of main winding copper loss per watt output at 70% of maximum torque versus LRT/MT; and
Figure 9 is a plot of locked rotor input watts per watt output at 70% of maximum torque versus LRT/MT.
Referring now to the drawings, and particularly to Figure 1, there is illustrated a salientpole shaded pole motor 10 that includes a stator assembly, rotor assembly, and not shown bearing means as well as associated supporting structure.
The stator assembly includes a magnetic core formed of a plurality of magnetizeable laminations that define a magnetizeable yoke and a plurality of spaced apart pole pieces.
The stator assembly also includes a plurality of turns of conductor wire disposed about a portion 11 of each of a plurality of substantially identical pole pieces 12. The portions 11 extend generally radially from the geometric center of the stator core which, for the motor of Figure 1, also lies along the center of axis of rotation of the rotor.
The winding coils 14 about each pole piece are substantially identical in terms of conductor size and number of turns. These coils are interconnected in conventional manner so that when not shown external power leads (connected to the ends of the winding comprised of the coils 14) are connected to a suitable source of excitation voltage, the rotor 15 will turn in a direction indicated by the arrow A, i.e., from the leading pole tips 17 toward the lagging or trailing pole tips 18.
For simplicity of description and clarification of illustration, parts of the complete motor 10 have not been illustrated and will not be further described except to note that the motor 10 also includes stationary structure for supporting the stator core 20. There also is included one or more bearing supports by means of which one or more bearings are positioned to journal the shaft 16 for rotation. It is also noted that the motor 10 may be of either the unit bearing or dual bearing type.
The body of rotor assembly 15 may be formed in any conventional manner and, preferably, is comprised of a stack of laminations formed from the same type of magnetizeable low carbon iron or steel as the laminations of the stator core 20. All of the motors illustrated herein were constructed from laminations that were about 0.025 inches thick. The rotor laminations have slots formed therein for accomodating the bars of a short circuited squirrel cage winding. These bars and associated end rings may readily be formed of aluminum in a die casting process.
The leading pole tip 17 of each of the pole pieces 12 is chamfered so that the air gap flux density under the leading pole tips, as compared to the air gap flux density at the center of each of the pole pieces 12, is reduced. With the illustrated structure, the relatively less iron in the magnetic circuit in the vicinity of the leading pole tips, as compared with the amount of air, provides the desired differential air gap flux density. Other approaches may also be used to accomplish this result. For example, other approaches would be to provide a stepped bore, or reluctance slots in the leading pole tips so as to establish high reluctance leading pole tips.
Pairs of shading coils 21, 22 are accommodated on the trailing pole tip 18 of each pole piece 12. These coils 21, 22 are disposed in slots 23, 24 formed in each df the salient-pole pieces. The relationship, shape, and configuration of the slots 23 and 24 are most clearly revealed in Figure 2 which shows the core 20 with all windings and shading coils removed therefrom.
It will be noted that the slots 23 in the trailing pole tips 18 have been configured to accommodate a round shading coil whereas the slots 24 are formed to accommodate a rectangular shaped shading coil. The shapes of these coils have been selected on the basis of convenience and manufacturability. The actual cross-sectional area of the coils for slots 23, 24 are selected so that the shading coils will have an electrical resistance that is preselected for a given application. The material out of which the shading coils will be constructed may also be chosen on the basis of economics, ease of manufacture, and efficient utilization of the space available on a given core for accommodating the shading coils.
A four-pole salient-pole construction is illustrated by Figures 1 and 2. However, advantages of the present invention may also be realized with two-pole, six-pole and other multiple-pole constructions.
In the motors depicted by Figures 3 and 4, portions of each of these motors have been removed. broken away, or shown in section for purposes of description. It is to be understood however, that motors depicted by Figures 3 and 4 have been constructed and tested for purposes of comparison.
The prior art motor depicted by Figure 4 has been available commercially from the assignee of this application for more than a year prior to October 2, 1972. This motor, designated by reference numeral 31, includes a rotor assembly formed of a two inch stack of laminations. The rotor body was constructed with eighteen uniformly spaced apart die cast aluminum conductor bars and end rings. The fundamental calculated resistance of the rotor 30, referred or reflected to the main winding was about 4.75 ohms.
The stator core 32 was also a two inch stack of laminations that were held together by keys that were retained in keyways 33 formed in the magnetizeable yoke portion of the laminations.
The rotor 34 of motor 36 shown in Figure 3 was substantially identical to rotor 30 and core 37 of motor 36 was substantially identical to core 32 with the exception that two keyways and two winding pin accommodating holes in the magnetizeable yoke portion 35 of the stator laminations were omitted. Essentially, the only other structural difference between motors 31 and 36 were those differences observed when the trailing pole tips 55, 38 are compared in Figures 3 and 4.
Essentially all other construction details of motors 31 and 36 were the same. For example, available bearing supports and bearing structures of the same size and type were used to support the rotors 30, 34 for rotation relative to the respective stator cores 32 and 37. All of this is here pointed out so that the totally unexpected differences in performance and characteristic relationships that become apparent after testing motors 31 and 36 will be better appreciated.
Considering Figures 3 and 4 now in detail, and with initial reference to Figure 4, the leading pole tip 39 of each of the pole pieces 41-is chamfered at 40 for a span of 80 electrical degrees as illustrated. The radial depth of the chamfer was about 0.08 inches, measured on the centerline of wire admitting slots 42. This centerline is represented in Figure 4 by reference line 43.
Pole pieces 41 were also provided with slots or notches 44 in each of which a copper shading coil 46 was accommodated.
The center of opening 47 for shading coil slot 44 was 30 electrical degrees measured from reference line 43 and thus each coil 46 shaded 30 degrees of the total span of the magnetic pole established by ole piece 41. The size and position of slots 48 (and openings 49 in pole pieces 51 of core 37) relative to center reference line 52 were the same as the relations just discussed for core 32. Moreover, the two coils 46 and two coils 53 were all formed of uninsulated copper conductor that was .281 inches wide and .05 inches thick.
Disposed about each of the pole pieces 41 and 51 was a coil of winding turns. Each of the coils 54 and each of coils 56 comprised 125 turns of .0359 inch (conductor diameter) insulated copper wire. Substantially the only difference between the windings for motors 31 and 36 was that the winding resistance of motor 31 was about 1.6 ohms whereas the winding resistance of motor 36 was about 1.7 ohms. This however, was caused by the need to have slightly increased lengths of wire for those turns in the vicinity of pole tips 38 of motor-36 as compared to the lengths of wire in the turns adjacent to pole tips 55. of motor 31.
Since the chamfer 57 was substantially the same, both in span and depth, ‘as chamfer 40.
the only other difference between motors 31 and 36 was that motor 36 included additional shading coils 58, each of which were carried on an enlarged pole tip 38 in a slot pair 59. The coils 58 were formed of No.9AWG uninsulated copper conductor, the wire diameter being about .1144 inches. The tips 38 were enlarged (relative to tips 55 of motor 31) an amount sufficient to prevent magnetic saturation of the laminations under coils 58 due to the shading coil flux. The span of shading coils 58, i.e., the arcuate measure from reference line 52 to the center of opening 61 was 18 electrical degrees, it being noted that (as is wellknown) electrical degrees are equal to mechanical degrees for two-pole motors.
A motor 36 was then tested, and the test data was recorded and then compared with test data for motors like motor 31. The tests were performed with a reaction dynamometer while the shaft of the- motor being tested was coupled to the shaft of a direct current motor.
The speed of motor 36 was very precisely controlled by varying the speed of the d.c. motor which, in effect, acted as a fixed speed driven device. A tachometer on the d.c. motor provided a speed signal while strain gauges provided a signal that was indicative of test motor torque for various speeds. Sensors were also used to determine current (in amperes) gnd power (in watts) drawn or used by the test motor under various load conditions.
Three motors were constructed as exemplified by motor 36 and the average data for these three motors. after testing, is reported in column B of Table I, while column A reports data obtained by corresponding tests of a motor constructed as described for motor 31. In
Table I, the load condition and characteristic investigated is listed on the left-hand side of the table while recorded. observed. and calculated quantities appear in column A and B.
Table I
A B
Winding Resistance, ohms 1.552 1.674
Test Voltage, 60 Hz 115 115
Main Winding I2R (heating) loss, watts 41.64 43.13
No Load Condition
Speed, rpm 3516 3531
‘amps 5.18 5.08
watts 233 249
Max Torque Condition
Speed, rpm 2720 2793
(MT) Torque, oz-ft 8.25 8.47
Current, amps 7.20 6.71
Power Input, watts 534 540
.7 Max Torque Condition
(EFF) Gross Efficiency, % 41.8 43.5
Speed, rpm 3188 3234
(.7MT) Torque, oz-ft 5.78 5.93
Current, amps 5.80 5.47
Power Input, watts 391 391
Dip Torque Condition
(DIP) Minimum torque, oz-ft 3.66 3.47
Locked Rotor Condition
(LRT) Torque, oz-ft 2.52 3.38
Current, amps 9.68 8.92
Power Input, watts 667.5 669
Calculated Ratios
DIP/MT .444 .409
LRT/MT .305 .399
.7MT Eff., % 41.8 43.5
It is believed that much of the data in Table I is self-explanatory. However, Figure 5 of the drawings is a typical speed-torque curve for salient-pole shaded pole motors, and is presented as an aid to understanding the data of Table I. The subheading «No Load» refers to a test condition when the motor being tested was operating at no load or maximum speed conditions. «Max Torque» refers to the maximum torque (also referred to as breakdown torque) point on the curve of Figure 5; «Dip Torque» refers to the similarly labeled minimum torque region of the Figure 5 curve; «.7 Max Torque» would represent a condition where a load was applied to a test motor so that it operated at a speed between maximum speed and maximum torque speed and on a point on the Figure 5 curve corresponding to 70% of maximum torque. As a final point of explanation, «Gross Efficiency» as used herein is calculated or measured to include output power used to overcome bearing friction as part of the useful output power of the motor, and is defined as watts output per watts input x 100.
The data of Table I indicates that the motors 36 had several surprising and significantly improved operational characteristics as compared to the motors 31. For example, the no-load speed of motor 36 is higher than for motor 31. Even more significantly however.
the max. torque speed and max. torque were both increased while max. torque current decreased. The fact that max. torque power input was greater in column B than in column A indicates that the power factor of motors like motor 36 are closer to unity than was the case for’motor 31 — and this is also a desirable feature.
Of even more significance, although column B dip torque is about 5% less than that of column A. the starting or locked rotor torque recorded in column B is at least 1/3 or 33% greater than the torque recordedin column A.
A comparison of the calculated ratios in Table I even further emphasizes the significant and surprising differences between motors 31 and 36. Motors like motor 36 had an
LRT/MT (locked rotor torque to maximum torque) ratio above .33 while being 43.5% efficient and also while being relatively stable as evidenced by the calculated value of the ‘ration «DIP/MT».
Heretofore it has appeared that compromise must be made. in shaded pole motor designs, between any need for efficiencies greater than 35% and any need for LRT/MT ratios in excess of .33. For example. skeleton type motors (as shown for example in U.S.
patent 2.454.589) may be optimized (by using multiple shading coils and chamfered pole faces). to have LRT/MT ratios in excess of 1/3; but the efficiency of such motors would be
only about 35 % at best.
Motors as shown in Figure 4 herein on the other hand may be optimized in design to have efficiencies in the neighborhood of 50%, but only at the expense of ever reducing LRT/MT ratios from an upper limit of about 1/3.
Because of the improvement in performance of motors like motor 36, which was surprising to an unexpected degree, a quantity of other such motors were constructed and tested in the manner described above. All of these additional motors were of salient-pole shaded pole type. Moreover, to limit the number of variables, each had: a double shading coil trailing pole tip design; the same winding in terms of conductor size and number of turns; the same core stack height; a high reluctance leading pole tip that was stepped rather than chamfered; the same rotor stack height; the same rotor end ring; and the same basic stator core lamination design. The stator core laminations were varied, one from another, by providing variations in the: spans for the step in the leading pole tips; depths for the steps in the leading pole tips; span of the larger shading coils; span of the smaller shading coils; conductor size of the larger shading coils; and the conductor size of the smaller shading coils. In addition, the size of the rotor conductors (and therefore rotor resistance) was varied.
The data obtained from testing these motors was then used to establish a mathematical model and the model employed, in turn, to establish points for various curves which are presented in Figures 6, 7, 8 and 9. The data obtained from the motor actually constructed of course verified the solid line curves in these figures. Before describing the significance of these curves, it should be noted that further variations could be made in salient-pole, shaded pole motors that would result in motor efficiencies in the neighborhood of 50% or locked rotor torque to maximum torque ratios in excess of 0.6 with efficiencies of 40% or more, all as will be explained hereinafter. For example, salient-pole, shaded pole motors have now been constructed with an efficiency of 39% and an LRT/MT ratio of 0.6.
Turning now to Figures 6, 7, 8, and 9; the broken line curves represent characteristic relationships associated with prior art salient-pole shaded pole motors typified, for example, by motor 31 of Figure 4. The solid line curves in Figures 6-9 are plots that represent characteristic relationships associated with motors of the type shown in Fig. 3.
A brief review of these curves quickly indicates that motors of the type shown in Fig. 3 will have operating characteristics or properties that provide significant advantages. For example (refer to Figure 6), salient-pole shaded pole motors now can have LRT/MT ratios well in excess of 1/3 with efficiencies of 40% and more when providing 70% of maximum torque.
Figure 7, being a plot of watts input per watts output at 70% of maximum torque, is in effect in inverse plot of the curves of Figure 6 and emphasizes that, for a given DIP/MT ratio, an increase of locked rotor torque to maximum torque can be obtained with motors that will operate at 70% of maximum torque with reduced input to output power ratios.
The curves of Figures 8 and 9 have been presented to further emphasize the difference in other characteristic ratios of motors of the type shown in Fig. 3 as compared with motors of the type shown in Fig. 4 that might be argued to be the most closely related thereto. For example, Figure 8 shows that for applications requiring increased LRT/MT ratios (in excess of 1/3); Fig. 3 type motors will exhibit the desired relationships of decreasing amounts of power loss due to I2R losses in the stator winding at operating conditions.
Figure 9 on the other hand reveals that. for LRT/MT ratios greater than .33, Fig. 3 type motors will require relatively low amounts of power (expressed as a multiple of the power required for operation at 70% of maximum torque) under locked rotor conditions.
With reference once again to Figure 6, it should be noted that, in general, if the leading pole tips of salient-pole shaded pole motors of the type shown in Fig. 3 are not designed to reduce the air gap flux density along the leading pole tip. the motor efficiency at 70% MT would be expected to be about ten points less than that indicated in Figure 6.
Still having reference to Figure 6. it has been found that, for a given DIP/MT ratio. the ratio of LRT/MT (and therefore operating efficiency) for a given Fig. 3 motor design may be increased by decreasing the span of the shading coils along the trailing pole tips. However. it then also is desirable to reduce the span of any chamfer or step along the leading pole tip-and to make such chamfer or step deeper. so as to increase the reluctance along the leading pole tip (i.e.. further reduce the air gap flux density along the leading pole tip).
It may also be desired. given a motor having an LRT/MT ratio above 1/3, to increase the
DIP/MT ratio. To accomplish this change, one would increase the rotor resistance; reduce the small shading coil span relative to the large shading coil span; increase the conductor size of the larger shading coil; reduce the size of the smaller shading coil conductor; and change the reluctance characteristic of the leading pole tip. e.g.. by increasing the depth of the step or chamfer. It should also be recognized that. with larger motors (e.g. 1/6 or 1/4 hp). it will be relatively easier to manufacture optimized multi-shading coil designs as compared to 1/20 hp and smaller size motors. The reduced physical size of the smaller motors would make it more difficult to use more than two shading coils or to reduce the span of the smaller shading coils beyond practical manufacturable limits.
The preceding description has been directed primarily to the structures shown in Figures
3 and 4, but the described charges could apply equally to similar motors of other dimen
sions, and of other sizes, even though such changes may lead to less efficient motors. For
example, the outer diameter of the stator laminations for the motors 31 and 36 were about
3.7 inches, the bore thereof was about 1.5 inches (all as is clearly revealed in the drawings),
and the cores had a stack height of two inches. These motors had gross efficiencies of 41.8% and 43.5% as previously stated. As is well known, if motors were constructed to be gener
ally identical to motors 31 and 36 except that the core stack height was reduced to about 3/4 of an inch, the efficiency of each such motor would be reduced by about ten percentage
points.
Also, and as is well known, if a two-pole motor of a modest size and a given design (such
as shown, for example, in Figure 3) is optimized for efficiency; a four-pole motor that is otherwise substantially identical thereto would be ex
appears that utilization of the present invention in this same contemplated application could
result in an efficiency of about 20%.
When using a motor such as motor 10 of Figure 1 for the 1400 rpm fan application just
mentioned, it is preferred that the span for the large span shading coil be in the optimum
range of forty electrical degrees to fifty electrical degrees as shown, (it being noted that the
center of the opening of slots 24 as revealed in Figure 1 was about forty-four electrical
degrees and thus closely coincides with the intended optimum of forty-five electrical
degrees). As just mentioned, the span of the large shading coil may be varied within the
preferred range of about forty and fifty electrical degrees; and it should be noted that if the
span of the large span coil were one third pole pitch (i.e., sixty electrical degrees), then the
space phase displacement between the main and shading coil winding third harmonics
would be zero, with the result that no additional starting torque would be provided and dip
torque would be reduced. Optimum ranges for the span of the step or chamfer along the
leading pole tip have also now been determined and the values for these optimums are
fifty-nine to sixty-one electrical degrees for a step construction; and sixty-five to seventy
electrical degrees for a chamfer construction (although the chamfer might have as little as a
sixty degree span for some applications). In terms of relative relationships between the span
of the large span shading coil (measured from a reference line such as line 52 in Figure 3 to
the center of the large shading coil slot opening at the bore) to the span of the step (also
measured from the same reference line); it has now been determined that the span of the
step preferably is about twenty-five percent longer than the span of the large span shading
coil. This preference, however, may not be easily attained with small diameter motors and
in such cases the span of the step may be as little as eighteen percent more than the span of
the large span shading coil (thus, depending on size of the motor, the large span shading coil
span upper limit will be about 45″ EL to 49.2 EL or approximately 75% to 82% of the
span of the step). On the other hand, if the span of the large span shading coil is less than
50% of the span of the step (i.e., less than 30 EL for a sixty degree step); very objection
able dips would occur in the speed-torque curve of the motor. Based on the discussion just
presented, it should now be apparent that motors embodying the present invention and
constructed with a step (as opposed to a chamfer or slots) should have the span of the large
span coil selected to be in the range of from about 50% to about 82% of the span of the
step. Furthermore, the optimum range of the large shading coil span (from an efficiency
standpoint) would be from about 75% to about 82% of the span of the step with the step
span held close to sixty electrical degrees (i.e., 1/3 pole span).
While the above data concerns the most desirable «span» relationships between the large
shading coil and a step; similar relationships exist for constructions utilizing the chamfer or
internal reluctance slot approach. Persons of ordinary skill in the art can determine
mathematically the span and depth of a chamfer that yields a magnetic reluctance equival
ent to a specific step, and the same may also be done to identify the dimensions and
locations of one or more slots that would yield reluctance effects similar to a selected step.
In view of this, rather than presenting extensive mathematical analyses or empirical data,
reference will hereinafter be made to equivalent chamfered or slotted constructions which
provide a pole tip with a magnetic reluctance broadly equivalent to that provided by a single
step.
It is now again emphasized that preferred forms of the invention are embodied in motor
constructions wherein the spaced apart pole pieces have the leading pole tips thereof spaced
by an air gap from the trailing pole tip of the pole pieces adjacent thereto. Thus, in such a
construction, there will be substantially no magnetically permeable material forming bridge between such adjacent pole tips and thus, no substantial low reluctance magnetic path will
be provided such that magnetic flux could be dispersed or short circuited directly from one
pole tip to the tip of another pole. The flux leaving a given pole tip therefore will cross the
air gap and couple with the rotor rather than being dispersed around or along the air gap to
another pole.
It should be specifically understood that non-magnetic material (such as plastics, wood,
etc.) spacers or plugs could be disposed between and in contact with adjacent pole tips, in
this event the pole pieces would still be spaced apart magnetically. Accordingly, language
used herein concerning «pole pieces being spaced apart» so that tips of pole pieces are
«spaced from» tips of other pole pieces is intended to convey the meaning that adjacent
pole tips are «magnetically» spaced from one another.
WHAT WE CLAIM IS: l. A shaded pole motor including: a stator assembly comprising a magnetisable yoke
and a plurality of spaced apart pole pieces extending from the yoke towards a rotor receiv
ing space with the leading pole tip of each pole piece magnetically separated from the
trailing pole tip of the adjacent pole piece, at least one of said pole pieces having a leading
pole tip with either a step or with an equivalent chamfered or slotted construction providing
**WARNING** end of DESC field may overlap start of CLMS **.

Claims (11)

**WARNING** start of CLMS field may overlap end of DESC **.
appears that utilization of the present invention in this same contemplated application could
result in an efficiency of about 20%.
When using a motor such as motor 10 of Figure 1 for the 1400 rpm fan application just
mentioned, it is preferred that the span for the large span shading coil be in the optimum
range of forty electrical degrees to fifty electrical degrees as shown, (it being noted that the
center of the opening of slots 24 as revealed in Figure 1 was about forty-four electrical
degrees and thus closely coincides with the intended optimum of forty-five electrical
degrees). As just mentioned, the span of the large shading coil may be varied within the
preferred range of about forty and fifty electrical degrees; and it should be noted that if the
span of the large span coil were one third pole pitch (i.e., sixty electrical degrees), then the
space phase displacement between the main and shading coil winding third harmonics
would be zero, with the result that no additional starting torque would be provided and dip
torque would be reduced. Optimum ranges for the span of the step or chamfer along the
leading pole tip have also now been determined and the values for these optimums are
fifty-nine to sixty-one electrical degrees for a step construction; and sixty-five to seventy
electrical degrees for a chamfer construction (although the chamfer might have as little as a
sixty degree span for some applications). In terms of relative relationships between the span
of the large span shading coil (measured from a reference line such as line 52 in Figure 3 to
the center of the large shading coil slot opening at the bore) to the span of the step (also
measured from the same reference line); it has now been determined that the span of the
step preferably is about twenty-five percent longer than the span of the large span shading
coil. This preference, however, may not be easily attained with small diameter motors and
in such cases the span of the step may be as little as eighteen percent more than the span of
the large span shading coil (thus, depending on size of the motor, the large span shading coil
span upper limit will be about 45″ EL to 49.2 EL or approximately 75% to 82% of the
span of the step). On the other hand, if the span of the large span shading coil is less than
50% of the span of the step (i.e., less than 30 EL for a sixty degree step); very objection
able dips would occur in the speed-torque curve of the motor. Based on the discussion just
presented, it should now be apparent that motors embodying the present invention and
constructed with a step (as opposed to a chamfer or slots) should have the span of the large
span coil selected to be in the range of from about 50% to about 82% of the span of the
step. Furthermore, the optimum range of the large shading coil span (from an efficiency
standpoint) would be from about 75% to about 82% of the span of the step with the step
span held close to sixty electrical degrees (i.e., 1/3 pole span).
While the above data concerns the most desirable «span» relationships between the large
shading coil and a step; similar relationships exist for constructions utilizing the chamfer or
internal reluctance slot approach. Persons of ordinary skill in the art can determine
mathematically the span and depth of a chamfer that yields a magnetic reluctance equival
ent to a specific step, and the same may also be done to identify the dimensions and
locations of one or more slots that would yield reluctance effects similar to a selected step.
In view of this, rather than presenting extensive mathematical analyses or empirical data,
reference will hereinafter be made to equivalent chamfered or slotted constructions which
provide a pole tip with a magnetic reluctance broadly equivalent to that provided by a single
step.
It is now again emphasized that preferred forms of the invention are embodied in motor
constructions wherein the spaced apart pole pieces have the leading pole tips thereof spaced
by an air gap from the trailing pole tip of the pole pieces adjacent thereto. Thus, in such a
construction, there will be substantially no magnetically permeable material forming bridge between such adjacent pole tips and thus, no substantial low reluctance magnetic path will
be provided such that magnetic flux could be dispersed or short circuited directly from one
pole tip to the tip of another pole. The flux leaving a given pole tip therefore will cross the
air gap and couple with the rotor rather than being dispersed around or along the air gap to
another pole.
It should be specifically understood that non-magnetic material (such as plastics, wood,
etc.) spacers or plugs could be disposed between and in contact with adjacent pole tips, in
this event the pole pieces would still be spaced apart magnetically. Accordingly, language
used herein concerning «pole pieces being spaced apart» so that tips of pole pieces are
«spaced from» tips of other pole pieces is intended to convey the meaning that adjacent
pole tips are «magnetically» spaced from one another.
WHAT WE CLAIM IS: l. A shaded pole motor including: a stator assembly comprising a magnetisable yoke
and a plurality of spaced apart pole pieces extending from the yoke towards a rotor receiv
ing space with the leading pole tip of each pole piece magnetically separated from the
trailing pole tip of the adjacent pole piece, at least one of said pole pieces having a leading
pole tip with either a step or with an equivalent chamfered or slotted construction providing
a relatively high magnetic reluctance compared with the trailing pole tip of the same pole piece, first and second shading coils disposed on the trailing pole tip of the same pole piece, the two shading coils having different spans which are both less than the span of the said step, the shading coil having the larger span having a span of between 50% and 82% of the said step span; and a rotor assembly supported for rotation in said rotor receiving space.

2. A motor according to Claim 1 in which the step span lies in the range of 59 to 61 electrical degrees, and the span of the larger span shading coil is between 75% and 82% of the said step span.

3. A motor according to Claim 1 or Claim 2 in which the shading coil having the larger span has a span of between 30 electrical degrees and 59 electrical degrees.

4. A motor according to Claim 1 in which the said leading pole tip is chamfered with a span of between 65 and 70 electrical degrees, and the shading coil having the larger span has a span of between 40 and 50 electrical degrees.

5. A motor according to any one of the preceding claims having four pole pieces, the span of the shaded coil having the larger span being more than 30 electrical degrees but less than one third of the pole span.

6. A motor according to any one of the preceding claims further comprising a winding comprising at least one concentrated group of conductor turns accommodated closely adjacent to at least one of the pole pieces, the motor exhibiting, during excitation of the said winding by a given voltage, a locked rotor torque to maximum torque ratio of at least 33%.

7. A motor according to any one of the preceding claims in which the rotor assembly includes a short circuited squirrel cage rotor.

8. A salient-pole shaded pole motor including a stator assembly and rotor assembly; the stator assembly comprising a magnetizable core having a magnetizable yoke and a plurality of magnetically spaced apart pole pieces each having a leading and trailing pole tip, with the leading tip of each pole piece magnetically spaced from the trailing pole tip of a pole piece next adjacent thereto; said stator assembly further including at least a first and a second electrically short circuited shading coil disposed on the thereby identifying each of the trailing pole tips, and a winding comprising at least one concentrated group of conductor turns accommodated closely adjacent to at least one of the pole pieces; said rotor assembly including a short circuited squirrel cage rotor spaced by an air gap from bore defining faces of the pole pieces, and the leading pole tip of each pole piece having either a step with a span of one-third of a pole pitch or a chamfered or slotted construction providing a magnetic reluctance substantially equal to that produced by a step with a span of one third of a pole pitch; the first shading coil having a span of between 30 electrical degrees and 59 electrical degrees; and the second shading coil having a span less than the span of the first shading coil.

9. A motor according to Claim 8 in which the motor exhibits, during excitation of the winding by a given voltage, a locked rotor torque to maximum torque ratio of at least 0.33.

10. A motor according to Claim 9 in which the rotor assembly includes a plurality of conductors and a shaft, the pole pieces each include a portion extending generally radially outwardly from the shaft, and the magnetizable yoke substantially encompasses the pole pieces and the plurality of conductors.

11. A motor according to any one of the claims 8 – 10 in which each leading pole tip is chamfered with a span of between 65 and 70 electrical degrees, and in which the longest span shading coil is disposed in a slot having a span in the range of 40 to 50 electrical degrees. . r . s

GB2047377A
1976-05-20
1977-05-16
Shaded pole motors

Expired

GB1584983A
(en)

Applications Claiming Priority (1)

Application Number
Priority Date
Filing Date
Title

US05/688,251

US4131814A
(en)

1972-10-02
1976-05-20
Concentrated winding salient-pole shaded pole motors having multiple short circuited shading coils for each pole and methods of making same

Publications (1)

Publication Number
Publication Date

GB1584983A
true

GB1584983A
(en)

1981-02-18

Family
ID=24763718
Family Applications (1)

Application Number
Title
Priority Date
Filing Date

GB2047377A
Expired

GB1584983A
(en)

1976-05-20
1977-05-16
Shaded pole motors

Country Status (4)

Country
Link

JP
(1)

JPS52143423A
(en)

FR
(1)

FR2366734A2
(en)

GB
(1)

GB1584983A
(en)

IT
(1)

IT1115315B
(en)

Families Citing this family (2)

* Cited by examiner, † Cited by third party

Publication number
Priority date
Publication date
Assignee
Title

EP0043498B1
(en)

1980-06-25
1985-02-20
Robert Stahlschmidt
Electromotor

IT1129889B
(en)

1980-11-21
1986-06-11
Ceset Spa

SINGLE-PHASE INDUCTION ELECTRIC MOTOR

1977

1977-05-16
GB
GB2047377A
patent/GB1584983A/en
not_active
Expired

1977-05-18
FR
FR7715344A
patent/FR2366734A2/en
active
Granted

1977-05-19
IT
IT2375977A
patent/IT1115315B/en
active

1977-05-20
JP
JP5928077A
patent/JPS52143423A/en
active
Granted

Also Published As

Publication number
Publication date

JPH0118666B2
(en)

1989-04-06

IT1115315B
(en)

1986-02-03

FR2366734B2
(en)

1980-09-26

FR2366734A2
(en)

1978-04-28

JPS52143423A
(en)

1977-11-30

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