ELECTRIC MOTOR AND METHOD

Field of Invention

The present invention relates to electric motors and , more particularly, to electric motors having armature wind¬ ing patterns or distributions that improve commutation and reduce brush sparking and the generation of electro¬ magnetic interference (EMI) during motor operation.

Typical wound-armature electric motors in common use in power tools and appliances utilize an armature having a plurality of wound coils that are serially connected to- gether to define an armature circuit with the ends of each coil connected to adjacent commutator bars. The winding patterns vary from the relatively elementary lap or wave winding patterns to far more complicated winding distri¬ butions . In operation, the armature rotates through the field with the coils successively undergoing commutation as their connected commutator bars pass through the neutral zone of the motor. Although the electro-dynamics of commutation are generally of a complex nature, the direction of current flow through an armature coil is in a first direction as the coil's commutator bars move toward a brush to effect commutation of the coil winding. As the adjacent com¬ mutator bars of an armature coil pass under a brush, the brush will span the bars and establish a "make" contact which effectively and momentarily short circuits the coil undergoing commutation. Shortly thereafter, this shunting or short circuit "breaks" and the current to the coil is - reversed. During the time that the coil is shorted, the

current through the coil undergoing commutation can vary a complex manner depending upon the inductive and cap— acitive reactances of the coil and the coil resistance as well as the current flow through the coil just prior to commutation. The breaking of the contact after commutati results in brush sparking or brush fire, the intensity of which is a function of the electro-dynamics of the motor described above. The brush sparking causes brush erosion and contributes to commutator wear. The process of coi- mutation, including the existence of the brush sparking, responsible for some, if not all, the electromagnetic and radio frequency radiation generated by the motor during i operation. This electromganetic interference is typicall conducted through the power cord of the motorized device and transferred to a portion ό ^' f the power distribution system with the EMI typically interferring with the oper¬ ation of EMI susceptable devices on the common power cir¬ cuit, these other devices typically including computers, televisions, radio receivers, and the like. Various national and trans-national standards have be developed to limit EMI sources wi h these standards limit ing the amplitude of the generated EMI to specific signal levels over a broad frequency range. An example of one such standard is "Limits and Methods of Measurement of Radio Frequency Characteristics of Household Electrical Appliances, Portable Tools, and Similar Electrical Ap¬ paratus" (Pub. 14, 1975) published by the Comite International Special Des Perturbations Radio-electriques (C. I. S .P . R. ) . This document establishes EMI radiation standards for motor-driven devices, including portable power tools, in a frequency range of 0.15 MHZ to 300 MHZ.

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Tradi ionally , EMI generated by motor-driven appliances and portable tools has been suppressed using various types of filter networks that include capacitive and/or inductive reactances which bypass or impede the EMI signal flow. Examples of EMI filters include capacitors placed across the power line terminals to provide a low-reactance shunt path for the undesirable higher frequencies as well as more sophisticated filters that include multiple T-section and Pl-section filter networks. While traditional filtering techniques have been effective to suppress EMI, the cost of the suppression devices increases the overall cost of the appliance including the cost of fabrication. In the case of portable power tools, the EMI suppression components may also add weight to the tool and tend to increase the ^" physi¬ cal dimensions of the tool since the designer must provide a tool housing that accomodates the suppression components.

Summary of the Invention

In view of the above, it is a broad overall object of the present invention, among others, to provide an electric motor suitable for use in a wide variety of motor-driven devices having greatly improved commutation characteris ics

It is another object of the present invention to pro¬ vide an electric motor suitable for use in a wide variety of motor-driven devices having greatly reduced EMI gener- ation characteristics over a wide frequency range.

It is another object of the present invention to pro¬ vide an electric motor suitable for use in a wide variety of motor driven devices including appliances and power tools having a winding distribution or pattern that greatly reduces elec romagnetic interference generated by the tool and thereby reduces or eliminates the need for and the costs of associated EMI suppression components.

-4- It is another object of the present invention to pro¬ vide an electric motor suitable for use in a wide variety of motor-driven devices having reduced brush sparking to thereby provide reduced brush erosion and extended brush and commutator life.

It is still another object of the present invention t provide an armature for an electric motor having a windin distribution that provides improved commutation to reduce brush sparking and electromagne ic interference generated during commutation of the armature.

It is a further object of the present invention to pr vide a method for winding an armature for an electric mot for improved commutation to reduce brush sparking and ele tromagnetic interference generated during commutation of the armature.

Towards the fulfillment of these objects and others, the present invention provides an electric motor having a armature wound with a plurality of armature coils which a interconnected to define an armature circuit. Each arm- ature coil is divided into coil sub-sections with the sub sections distributed about the armature so that an armatu coil, when undergoing commutation by one of the brushes, has a first coil sub-section that shares common slots wit and is coupled to at least one coil sub-section of anothe armature coil that has completed commutation by the other brush and a second coil sub-section that shares common slots with and is coupled to a coil sub—section of anothe armature coil about to undergo commutation by the other brush. This winding distribution permits electrical ener in the armature coil undergoing commutation by the first-mentioned brush to be coupled to the coil sub-secti of the armature coil having completed commutation and/or

the coil sub-section of the armature coil about to undergo commutation by the. other brush to improve commutation and reduce both brush sparking and the generation of EMI across a wide frequency range.

The winding distribution reduces brush sparking with the consequent advantage of limiting or controlling brush erosion to provide extended brush operating life. In ad¬ dition, the winding distribution reduces EMI generated during commutation to permit motor-driven appliances, in- 'cluding portable power tools, to meet or exceed EMI stan¬ dards with a minimum of additional EMI suppression com¬ ponents and circuits and allows many motor-driven devices to be fabricated at lower cost.

Brief Description of the Figures The above-description, as well as the object, features, and advantages of the present invention will be more fully appreciated by reference to the following detailed des¬ cription of a presently preferred but nonetheless illustra¬ tive embodiment in accordance with the present invention when taken in conjunction with the accompanying drawings wherein:

Figure 1 is a partial pictorial representation of an armature drum having three armature coils distributed about the armature drum in accordance with the present invention; Figure 2A is a schematic and elevational view of a

12-slot, 24-bar armature having three armature coils dis¬ tributed in accordance with the present invention;

Figure 2B is a schematic end elevational view of the 12-slot, 24-bar armature shown in Figure 2A with three other armature coils shown distributed in accordance with the present invention;

-6- Figure 3 is a conventional flat-developed view of th winding pattern shown in Figure 2A in accordance with the present invention;

Figure 4 is an end elevational view, in schematic for of a 12-slot, 24-bar, two coils per slot preferred embodi ment of an armature rotor in accordance with the present invention; and

Figure 5 is a comparative graphical representation of the EMI generated during the operation of a conventional electic motor having a lap winding (dashed line) and a motor of the same type having an armature wound in accor¬ dance with the present invention (solid line).

Decription of the Preferred ^• Embodiment

The present invention may be best conceptually under- stood by consideration of the pictorial illustration in

Figure 1 showing the end portion of a conventional stacke lamination, 12-slot, one coil per slot armature drum 10 (shown in partial broken line illustration) with the slot consecutively designated by the reference characters SI through S12 and also showing three exemplary armature coi or windings Wl , W2 , and W3 (shown in cross-hatched, stippled, and plain outline form, respectively) wound on the armature drum 10 and distributed in accordance with t present invention. For reasons of clarity, the slot insu ation, the end face insulation, and the shaft insulation have been omitted from Figure 1 and the armature shaft an armature drum have been shown in broken line illustration

Each of the armature coils, Wl , W2 , and W3 is divided int two coil sub-sections or coil halves: the first coil Wl i divided into coil havles Wl and Wl, ; the second coil a b

W2 is divided into coil halves W2 and W2 _t - ; and the third coil W3 is divided into coil havles W3 and W3 a D

The term "coil halves or half," as used herein, is not limited to or restricted to coil sub-sections that have one-half the total number of wire turns of the armature coil but is intended to include coil halves that include more or less than one-half the total number of turns in the entire coil winding.

As shown in Figure 1, the wire turns of each armature coil are distributed to define a "V" configuration, that is, the coil half Wl 3. i _{s WO} und between slots S2 and S7 while its associated coil half Wl _fe i _s wound between slots

S7 and S12; the coil half W2 i _s wound between slots S2 a and S7 and its associated coil half W2,b is wound between slots S2 and S9 ; and the coil half W3a is wound between slots S5 and S12 and its associated coil half W3, is b wound between slots S7 and S12. The coil halves are dis¬ tributed so that the coil sides of a coil half share common slots with the coil sides of another coil half so that, as explained more fully below, the coil halves of an armature coil that is undergoing commutation by one of the brushes are coupled, by virtue of the shared slots, to the coil half of an armature coil that has completed commutation and the coil half of another armature coil about to undergo commutation by the other brush. In the example of Figure 1, the coil sides of coil half Wl 3. share common slots S2 and S7 with the coil sides of coil half W2a and the coil sides of coil half Wl _b share common slots S7 and S12 with the coil sides of coil half W3. Thus, coil sides of coil half Wl are coupled, by virtue of the coil sides in the slots S2 and S7 , to the coil half W2 and the coil sides of the coil half Wl are coupled, by virtue of the

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coil sides in slots S7 and S12, to the coil half W3, . b

The ^' coupling that extends between the coil sides of the different coil havles in the common slots is both of an ductive nature and a capacitive nature. The coil windings, Wl , W2 , and W3 , are interconnec e with the commutator bars, as explained more fully below connection with figures 2A and 2B, so that when the arm¬ ature 10 is rotated in the direction of the arrow 12 in Figure 1, the armature coil Wl will undergo commutation one of the brushes just as the armature coil W2 is about undergo commutation by the other brush and just after th armature coil W3 has u.ndergone commutation by the other brush. Energy in the armature coil Wl undergoing commut tion by the one brush, when the commutating brush breaks the momentary short circuiting of the coil, is transferre by virtue of the coupling described above to the armature coil W2 just about to undergo commutation by the other brush and/or to the armature coil W3 just having complete commutation by the other brush. It has been found, as de cribed more fully below, that this winding distribution provides improved commutation and effectively reduces bot brush sparking and the electromagne ic interference (EMI) generated over a wide range of frequencies to reduce or partially eliminate the need for and the costs associated with EMI suppression components. In the case of an arm¬ ature having two or more coils per slot, as described mor fully below, energy transfer may also take place between the coil (or coils) undergoing commutation by a brush and the other coil or coils in the same slot set undergoing commutation by the same brush as well as between the arc- ature coil about to undergo commutation by the other of t brushes and the armature coil having just completed . commutation by the other of the brushes

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A greater appreciation of the interaction of the arm¬ ature coil winding distribution in accordance with the present invention and the actual function of the brushes during commutation may be had by considera ion of the 12-slot, 24-bar (two coils per slot) armature drum 14 shown in front elevational end view in Figures 2A and 2B with each of these figures illustrating the armature core 16, the associated commutator ring 18, and the brushes Bl and B2. In the case of a motor designed for bi-directional applications, the brushes Bl and B2 are aligned along the neutral axis and the lead throw of the armature coils is such to provide a so-called neutral armature. In the case of a motor ^' designed for uni-directional applications, the brushes Bl and B2 may be shifted to one side or the other of the neutral axis to assist commutation in the preferred direction of rotation, or as is also conventional in the art, the lead throw of the armature coils may be shifted from the neutral connection pattern to achieve the same direction-of-rotation effect. The winding distribution provides improved commutation for both directions of rota¬ tion for neutral bi-directional motors and improved commu¬ tation for the preferred direction of rotation for uni¬ directional motors. In Figures 2A and 2B, it is assumed that the armatures are rotating in the counter-clockwise direction as indicated by the arrows 20 and 20' and that the field poles (not specifically shown) are located on op¬ posite sides of the armature intermediate the brush posi¬ tions, as is conventional. Figure 2A illustrates only the armature coil that is undergoing commutation by brush Bl and the two associated armature coils that are coupled to that coil, and Figure 2B illustrates only the armature coil

that is undergoing commutation by the brush B2 and the tw associated armature coils that are coupled to this latter coil; it being understood that the commutation shown in Figures 2A and 2B is generally simultaneous in time. For reasons of clarity, the coils or windings shown in Figure 2A and 2B appear as single coils, although it is to be understood that the exemplary armature described below is of the type having two individual coils per slot. Commu¬ tation of the individual armature coils occurs in a se- quential manner as the commutator bars pass beneath a brush. In the case of an armature winding having two coi per slot, the commutation sequence is as follows: the fir coil in a slot set, the second coil in that slot set, the first coil in the next successive slot set, the second co • in the next successive slot set, etc. In the description of the commutation of the armature in Figure 2A and 2B (a two coil per slot armature), the commutation of the secon or last armature coil of a slot set is described in detai it being understood that the commutation of the first arm ature coil in that slot set having preceded the commutati of the second coil.

In Figure 2A, the armature coils in slot set 2-7-12 (cross hatched) are shown connected to the commutator bar 12 and 13, and 13 and 14, respectively; the armature coil in slot set 7-2-9 (plain outline) connected to the commu¬ tator bars 2 and 3, and 3 and 4, respectively; and the ar ature coils in slot set 5-12-7 (stippled) connected to th commutator bars 22 and 23, and 23 and 24, respectively, with the coil in slot set 2-7-12 connected to the com u- tator bars 13 and 14 shown as undergoing commutation at t brush Bl during the time period that the brush Bl spans t adjacent comπutator bars 13 and 14. The coil distributio

-11- of Figure 2A is also shown in Figure 3 in conventional flat development, it being understood that the illustrated con-' nections to the commutator bars are the loop sides of con¬ ventional continuous lead loops with the end of each loop connected to its associated commutator bar by soldering or welding the loop end to a post or to the interior walls of a wire-receiving slot. As can be appreciated from an in¬ spection of Figure 2A, the coil half 2-7 of the armature coil 2-7-12 undergoing commutation at the brush Bl shares coil sides in slots S2 and S7 with and is coupled to the coil half 7-2 of the armature coil 7-2-9 which is just about to undergo commutation by the brush B2 , and the coil half 7-12 of the armature coil 2-7-12 undergoing commu¬ tation at the brush Bl shares coil sides in slots S7 and S12 with the coil half 12-7 of the armature coil 5-12-7 which winding has just completed commutation by the brush B2. Just prior to commutation by the brush Bl with the cpmmutator rotating in the direction indicated by the arrow 20 in Figure 2A, the current flow through the armature coil 2-7-12 will be in a first direction until the brush Bl spans the insulation between the commutator bars 13 and 14, which position is shown in Figure 2A, at which time the coil winding 2-7-12 will be momentarily short circuited by the brush Bl. The current in the now short circuited arm- ature coil 2-7-12 will descrease in a generally non-linear manner as the magnetic field therabout collapses. The cur¬ rent flow and its change will depend, in part, upon the magnitude of initial current flow through the armature coil 2-7-12 just prior to commutation (which initial current level is, in part, a function of the load experienced by the motor during the commutation process), the resistance of the coil wire, the inductive and capacitive reactances, fU £4 ^WIp o \

the reluctance of the armature drum, and the position of the voltage cycle. With continued rotation of the arm¬ ature, the brush Bl disconnects or breaks the connection between the commutator bar 13 and 14 to effect full con- nection with the commutator bar 14 with the direction of the current flow through the coil 2-7-12 reversing from direction just prior to its commutation.

As is known in the art, brush fire or brush sparking will occur during the commutation process depending upon the energy changes in the armature coil undergoing commu tation. By arranging the coil half 2-7 and the coil hal 7-12 of the armature coil 2-7-12 undergoing commutation the brush Bl so that the coil sides of the coil half 2-7 shares slots S2 and S7 with the coil sides of the coil h 7-2 of the armature coil 7-2-9 (just about to undergo co mutation of the brush B2) and by arranging the coil half 7-12 of the armature coil winding 2-7-12 undergoing comm tation at brush Bl so that the coil sides of the coil ha 7-12 share slots S7 and S12 with the coil sides of the c 12-7 of the armature coil 5-12-7 (just having completed commutation at the brush B2), it is believed that a port of the energy in the armature coil 2-7-12 undergoing commutation at the brush Bl is transferred to the armatu coil 7-2-9 just prior to this coil undergoing commutatio at the brush B2 and/or to the armature coil 5-12-7 just after this latter coil has undergone commutation at the brush B2 with the result that less total energy is available in the armature coil 2-7-12 after undergoing c mutation at the brush Bl for the generation of undesirab brush sparking and the resultant EMI. In addition to th energy transferred between the armature coils as just de cribed, energy transfer may also occur, in the case of a

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atures having two or more coils per slot, between the arm¬ ature coil undergoing commutation by a brush and the other coil or coils in the same slot sets as the coil undergoing commutation by that brush. Substantially simultaneously with the commutation of the armature coil 2-7-12 at the brush Bl in Figure 2A, the brush B2 is also placing an armature coil under commutation as illustrated in Figure 2B. As shown therein, the arm¬ ature coils in slot set 6-1-8 (cross hatched) are connected to the commutator bars 24 and 1 and 1 and 2, respectively; the armature coils in the slot set 1-6-11 (stippled) are connected to the commutator bars 10 and 11 and 11 and 12, respectively; and the armature coils in the slot set 3-8-1 (plain outline) are connected to the commutator bars 14 and 15 and 15 and 16, respectively, with the armature coil in the slot set 6-1-8 connected to the commutator bars 1 and 2 undergoing commutation at the brush B2 as shown. The coil sides of the coil half 6-1 share slots S6 and SI with the coil sides of the coil half 1-6 of the armature coil 1-6-11 (stippled) and the coil sides of the coil half 1-8 of the armature coil 6-1-8 undergoing commutation at the brush B2 share slots SI and S8 with the coil sides of the coil half 8-1 of the armature coil 3-8-1 (plain outline) . The coil in slot set 1-6-11 connected to the commutator bars 11 and 12 just completes commutation' by brush Bl while the coil 1-8-3 connected to the commutator bars 14 and 15 is just about to undergo commutation by the brush Bl as the coil 6-1-8 connected to the commutator bars 1 and 2 undergoes commutation by the brush B2. As in the case of the ar - ature coils discussed above in co nection with Figure 2A, energy transfer is believed to take place between the coil winding 6-1-8 undergoing com utatio-i at the brush B2 and

the armature coil 1-8-3 about to undergo commutation by other brush Bl and/or the armature coil 1-6-11 having jus completed commutation by the other. brush Bl so that the energy level in the armature coil 6-1-8 is diminished wi a consequent diminishment of brush sparking and EMI. Ad ditionally, it is believed that energy transfer takes pla between the armature coil undergoing commutation in a slo set and the other coil or coils in that same slot set. I is believed that the energy transfer that takes place be tween the inter-distributed coils is through inductive and/or capacitive couplings therebetween.

The energy transfer that takes place between the inter-dis ributed armature coils can also be conceptualiz as follows: when an armature coil is undergoing commutati at one brush, that one brush momentarily short circuits o shunts the adjacent commutator bars for that armature coi Shortly thereafter, the shunt connection "breaks" and at least part of the energy in that commutator armature coil will be transferred across the armature drum to slots on the opposite side of the armature drum from that one brus This across-the-drum energy transfer is effected, in part by energy transferred from the coil sides of the armature coil undergoing commutation by that one brush which coil sides are located in slots on the opposite side of the drum. This energy is transferred to an armature coil abo to undergo commutation by the opposite brush and/or an ar ature coil having just completed commutation by the op¬ posite brush. Shortly after these events take place, the armature coil that was about to undergo commutation by th opposite brush does, in fact, undergo such commutation wi the energy in this armature coil now being transferred ba across the armature drum to slots on the same side of the

armature drum as the first-mentioned one brush. In effect, part of the energy in the armature coil windings can be visualized as being passed back and forth or exchanged in a reciprocating manner across the armature drum during ro¬ tation of the armature.

Example I

A preferred embodiment of an armature in accordance with the present invention is schematically represented in Figure 4 which illustrates a 12-slot, 24-bar, two coils per slot (24 coil) winding distribution in which the winding pitch (1/P) of the first coil half of each armature coil is 1/6 and the winding pitch for the second coil half of the coil is 1/8 (l/P+2). In Figure 4, the intermediate or cen¬ tral coil side of each armature coil is identified by an upper case letter while the coil sides of the first and second coil halves associated therewith have been identi¬ fied with the same letter in lower case and with the sub¬ scripts 1 and 2. The second armature coil in the same slots are identified by the same upper and lower case des- ignations as is the first armature coil in the slots but with a prime (' ) designation. Thus, the first armature coil winding A starts in slot 1 and is wound through slots 6 (that is with 1/6 pitch) to define coil half A-a.. and thereafter the coil half A-a ₂ i _s wound through slots 1 and 8 (that is, a 1/8 pitch). The second armature coil winding for those slots is then wound with the same slot distribution to define coil half A ¹ -a' between slots 1 and 6 and the coil half A ' -a ' between the slots 1 and 8. In the same manner, each of the remaining armature coils are wound to define the distribution shown in Figure 4. The winding distribution of the preferred embodiment

-16- illustrated in Figure 4 is further defined in Table 1 and Table 1A below with Table 1 listing slots Sl-12 on the left-hand side and the corresponding coil sides that occu those slots on the right-hand side and Table 1A listing t commutator bar assignment for each of the armature coils A-L and A'-L'. Six additional examples, II and VII, of armature embodiments in accordance with the present inven tion are listed below in Tables 2 and 2A, 3 and 3A, 4 and 4A, 5 and 5A, 6 and 6A, and 7 and 7A. Examples II throug VII define, respectively, a 12-slot, 12,-bar, one coil/slo armature; a 13-slot, 26-bar, two coils/slot armature; a 14-slot, 42-bar, three coils/slot armature; a 14-slot, 28-bar, two coils/slot armature; a 14-slot, 14-bar one coil/slot armature; and a 10-slot, 10-bar, one coil/slot armature. In the case of the fourth example, a double pr (") is used to designate the third coil in each slot. These embodiments are not intended to be limiting, but ar intended to merely demonstrate winding distributions on armature drums commonly used in domestic appliances and portable power tools.

Example I

TABLE 1 TABLE IB

Commutator Bar

Slot No, Coil ^■ Sides Coils (24) Assignment

A 1-2

A' 2-3

B; g ₂ ; i _χ ; B ¹ ; g' ₂ ; i^ B 3-4

B' 4-5

C 5-6

C* 6-7

D; i ₂ ; k ₁ ; D* ; i' ₂ ; ^ D 7-8

D' 8-9

E 9-10

E' 10-11

F ^• a ^■ k ^{• "} P ^{■ •} Ά ' ^• k ¹ F 11-12

F' 12-13

G; b. G 13-14

G' 14-15

H: H' H 15-16

H ¹ 16-17

I 17-18

I' 18-19

10 J; c ₂ ; e ₁ ; J ' ; c ' ₂ ; e ' _χ J 19-20

J' 20-21

11 ; K K 21-22

K' 22-23

12

^' 2' L' L 23-24

L' 24-1

-18-

Example II

TABLE 2 TABLE 2A

Commutator Ba

Slot No Coil Sides Coils (12) Assignme

A; £ ₂ ; h _χ 1-2

B; g ₂ ; i _χ 2-3

^C ' 2- 3-4

D; i ₂ ; _χ 4-5

; j ₂ ; l _χ 5-6

F; a _χ ; k ₂ 6-7

G b _χ ; ι ₂ 7-8

^{H; a} ₂ ; ^c ι 1-9

i; _{2; dl} 9-10

10 J; c _{2; βl} 10-11

11 K; d ₂ ; _fχ 11-12

12 ^{L; e} 2' ^§ 1 12-1

-19-

Example III

TABLE 3 TABLE 3

Commutator Bar

Slot No. Coil Sides Coils (26) Assignment

A; h. A' 1-2

A' 2-3

B 3-4

2 ι » 2 1 -' " 2

B ¹ 4-5

D; D'j ₂ » * i D 7-8

D' 8-9

E 9-10

E ¹ 10-11

F; 1 ; _m - F'l ₉ ; m* F 11-12

2' 1

F' 12-13

G ; m ^• ι ^■ G' m ^■ G 13-14

2 n 2' ^a 1

G' 14-15

H; ? > b, ; H n ^■ H 15-16

2' " 1

H' 16-17

2 9 2 ' I 17-18 ' 1

I ¹ 18-19

10 J 19-20 _.

J' 20-21

11 K; d ₂ ; e _χ ; K' ; d ' _∑ ; e^ K 21-22

K' 22-23

12 L; ^e 5 f ι ϊ !■ > ^e -i j f ι L 23-2^

L ¹ 24-25

13 M ^• -- ^> f 2- ' σ °1 '- M' '- f ' ? ^• ' s ' 1 M 25-26

M' 26-1

-g!TR ^ s. ^'■

Example IV

TABLE 4 TABLE 4A Commutator

Slot Bar (42)

No Coil Sides Coils Assignment

A; g. l- A"; g' A 1-2

A' 2-3

A" 3-4

B; h,

J 1 B"; h". B 4-5

B ' 5-6

B" 6-7

C; k". C 7-8

C 8-9

C" 9-10

D; j D 10-11

D' 11-12

D" 12-13 m E"; k" m

2' E 13-14

E' 14-15

E" 15-16

6 ^υ F*, l ^•L 2' • n ⁿ l'• F ' •' 1 ⁱ '2 •' n 'l •' T?" •' 1 "2 '• n "1' F 16-17

F' 17-18

F" 18-19

7 G; a 1 _; ' _m ^m 2 ^• G' ; a* 1 ; ^> m',2; G"; a", 1;' m"2 G 19-20

G- 20-21

G" 21-22

8 E; b _{ι ; n2 ; H} ' ; b^; n' ₂ ; H"; b'^; n". H 22-23

H' 23-24

H" 24-25 ^{^} ' ^<1 2 ^, 1' ^, 2' 1' ^, 2' 1 I 25-26

-21-

Example IV

TABLE 4 TABLE 4A

Slot Commutator

Bar (42)

No Coil Sides Coils Assignment

.0 J"; b". d"- J 28-29

J' 29-30

J" 30-31

11 K; K' "; K 31-32

K' 32-33

K" 33-34

12 L; d, L' L" ; d". f". L 34-35

2'

L' 35-36

L" 36-37 13 M; e ₂ ~ _γ ; M' ; e' ₂ ; ^ M" ; e" ₂ * g'^ M 37-38

M' 38-39

M" 39-40

14 N; f ₂ ; b _χ ; N' ; f ₂ ' h ^; N"; f" ₂ ' h'^ N 40-41

N' 41-42

N" 42-1

Example V

TABLE 5 TABLE 5B

C Dmmu tator Bar

Slot No. Coi 1 Sides Coils (28) Assignmen

1 A; ~2, ' ^£ li A' ; g' ₂ ; i 1 A 1-2 A' 2-3

2 B; B' ; h' ₂ ^h 2- Jι ^; ; j 1 B 3-4 B' 4-5

3 C; ^l Z- ^k li C ; i' ₂ ; k 1 C 5-6 C 6-7

4 D; J 9 ; h ^; D' ; j ' ₂ ; 1 1 D 7-8 D' 8-9

5 E; ^m l ^; E" ; K ₂ j m -10

1 E 9 E' 10-11

6 F; ^l 2>- tι _χ ; F' ; i' ₂ ; n 1 F 11-12 F' 12-13

7 G; ^a ι- ₂ > G' ; 13-14 ^a 'l' m 2 G G' 14-15

8 H; 15-16 ^b lϊ n ₂ ; H* ; ^b 'li n 2 H H' 16-17

9 I; ^a 2' ^c l' i' ; a' ₂ ; c 17-18

1 I I' 18-19

10 J; 19-20 ^d li J' ; b ' ₂ ; d 1 J

J' 20-21

O

Exampl e V

TABLE 5 TABLE 5B

Commutator Bar

Slot No Coil Sides Coils (28 ) Assignment

11 K; K' 9 2 '- ^~ _x K 21-22

K ¹ 22-23

12 L; d ₂ ; t ₁ - '; d' ₂ ; f ' _χ L 23-24

L' 24-25

13 M; 2- 8 '1 _L ' M' M 25-26

M ¹ 26-27

14 N; f ₂ ; h _{l 5} N' ; f ^» ₂ ; f ' _χ N 27-28

N' 28-1

^"''

Example VI

TABLE 6 TABLE 6A

Commutator Ba

Slot No Coil Sides Coils (14) Assignme

A; g ₂ ; i ₁ A 1-2

^{B; b} ₂ ; ii B 2-3

c; i _2J . _kl C 3-4

^{D ;} 2- ^l l D 4-5

E; k ₂ ; _m]L E 5-6

F; l _{ι ;} n-_ F 6-7

G; a _χ ; m ₂ G 7-8

K; b _χ ; n ₂ H 8-9

i; a _{2 ; Cl} 9-10

10 J; b _{2 ; d]} _ 10-11

11 ; c ₂ ; _&l K 11-12

13 ^e ₂ ; ^§ ι M 13-14

14 ^f ₂ ; ^i N 1

Example VII

TABLE 7 TABLE 7B

Commutator Bar

Slot No Coil Sides Coil s (24) Assignment

^A ; ^e ₂ ; ^§ 1 1-2

B; f ₂ ; h _j 2-3

^c; s ₂ ; i _λ 3-4

D; lι ₂ ; j _χ 4-5

^{E; a} l ^{> £} 2 5-6

F; _{ι ;} j ₂ 6-7

G ; a

2 ^{; c} l 7-8

H; b ₂ ; d _λ J-9

i; c ₂ ; e _χ 9-10 ^'

10 J; _{2 ;} f _χ 10-1

An appreciation of the EMI reduction aspect of an armature wound in accordance with the present invention may be had by consideration of the test results shown in Figure 5 in which the EMI signal levels generated by two test armatures are graphically illustrated, one of the armatures being wound in a conventional manner and the other being wound in accordance with the present invention. In the graph of Figure 5, the ordinate represents the EMI signal level in decibels (Db) and the abscissa represents fre- quency in Megahertz (Mhz) with the frequency plotted logar¬ ithmically from 0.1 Megahertz to 1000 Megahertz and with the test being conducted in accordance with the aforeme tioned C.I.S.P.R. Publication 14 "Limits and Methods of Measurement of Radio Interference Characteristics of Household Electrical Appliances, Portable Tools and Similar Electrical Apparatus" for motors drawing less than 700 watts.

The conventional motor tested was a 14-slot, 28-bar, two coils per slot universal motor (two pole) in which the coil windings were conventionally distributed to define a lap armature winding, which motor is commonly used in portable power tools in combination with standard EMI suppression components. The EMI performance of this motor is plotted in broken line illustration in Figure 5. The test armature was also a 14-slot, 28-bar, two coils per slot armature but wound in accordance with the present invention (in combination with the same standard suppression components as the conventional motor). The EMI performance of this test motor is shown in solid line illustration in Figure 5. As can be appreciated from an inspection of the graphical results, the test motor in accordance with the present

invention has an EMI output that is generally lower than the standard motor below two Megahertz with the difference between the two plots increasing up until 30 Megahertz at which point the EMI output for both motors rises somewhat until 100 Megahertz and thereafter drops. As can be appreciated, the armature winding in accordance with the present invention provides a substantial decrease in EMI output when compared to the prior, standard motor design. It has also been found that the winding distribution of the present invention provides practical advantages when designing so-called neutral armature motors for bi-directional applications, such as reversible portable power tools. In providing a motor for bi-directional applications, the conventional practice is to align the brushes along the neutral axis and connect the armature coil leads to their associated commutator bars to provide a so-called neutral armature. These types of motors .generate greater than normal brush sparking when compared to the motors that have a preferred direction of rotation in which the previously described brush shift has been effected. It has been the common practice in the industry to increase the field turns ratio for bi-directional motors in an attempt to reduce the brush sparking to an acceptable level. As a consequence, motors of this type have suffered from reduced power . output , and to some extent, larger frame size-. It. has been found that in bi-directional -motors having armatures wound in accordance with the present invention, the brush sparking is sufficiently reduced so that the practice of increasing the field turns ratio can be eliminated to provide a smaller, more powerful motor that is nonetheless ^• well suited for bi-directional motor applications.

OMPI \

The wire turns of the armature coils may be applied t the armature drum in either of two manners. For example, the first coil half of an armature coil may be wound and then thereafter the second half of that coil may be wound or, in the alternative, the wire turns of the armature co may be alternately wound between the slots that define th first and second coil halves. For example, the first wire-turn may be wound in those slots that define the fir coil half, a second wire-turn then wound in the slots tha define the second coil half, a third wire-turn then wound in the first coil half slots, etc. with this procedure fo lowed until the entire armature coil is in place.

When winding an armature stack using the so-called flying arm winding type machines in which a movable arm having a wire dispensing end is orbited about the stack t lay the wire into the various slots, an armature may be wound in accordance with the present invention by winding the first coil half, e.g., between slots 1 and 6 (in a 12-slot stack) and then indexing the armature to a new po ition in which the eighth slot occupies the position form erly occupied by the first slot, reversing the direction the flyer, and then winding the second coil half between slots 8 and 1. In those applications in which two coils are wound per slot, the armature can then be indexed back to its original position and any conventional lead con¬ nection procedure followed to connect the coil lead to it associated commutator bar. Then the winding procedure ca be sequentially followed to place the second armature coi in the same slot as the first armature coil, and the coil lead connection to its commutator bar again effected. Of

course, the same procedure set forth above may be used on winding machines having double flying arms, on winding ma- ^' chines which tumble the armature with or without indexing when winding the coil havles, as well as other types of winding machines.

In the armature embodiments described above, including the even slot embodiments of Examples I, II, and IV to VII and the odd slot embodiment of Example III, the pitch of the coil halves as measured in terms of slot pitches (that is, the number of slots that a coil half extends) conforms to the following relationship: Eq. (1)

Pitch (in slot pitches) = total number of slots —n

2 where n for armatures having an even number of slots is selected from the series 1,' 2, 3..., and where n for armatures having an odd number of slots is selected from the series 1/2, 3/2, 5/2, ... For example, the coil half pitch for the even, 14-'slot armature drums of the embodiments of Examples IV, V, and VI is 6- ^' slot pitches where n is selected a 1 ( 14/2-'l=6 ) . Thus, the coil half A- ^' a^ _^ for these embodiments extends 6-slot pitches between slots SI and S7 and the coil half A- ^" a„ extends 6- ^* slot pitches between slots SI and S9. Likewise, the coil half pitch for the odd , ^• 13- ^' slot embodi- ^' ent of Example III is 6- ^" slot pitches where n is selected as 1/2 (13/2-1/2=6). Thus, the coil half A- ^' a ₁ for this latter embodiment extends 6- ^' slot pitches between slots SI and S7 and the coil half A-a ₂ also extends 6-'slot pitches between slots SI and S8. While the present invention has

J ϊ.χ- A - IT

been disclosed in the context of armature drums having slots substan ially parallel to the armature axis of rota¬ tion, the invention is equally suited to armatures having skewed slo s.

As can be appreciated by those skilled in the art, var¬ ious changes and modifications may be made to the disclosed embodiments of the present invention without departing from the spirit and scope of the present invention as defined in the appended claims and their legal equivalent.

-^- ^E AJ