US2773998A - Armatures for induced current torque transmitting apparatus - Google Patents

Description

Dec. 11, 1956 H. s. JACOBS ErAL 2,773,998

ARMATURES FOR INDUCED CURRENT TORQUE TRANSMITTING APPARATUS 2 Sheets-Sheet 1 Filed March 1 1954 INVENTORS W%GMZL Mal/M AT TORNEY Dec. 11, 1956 H. s. JACOBS ETAL ARMATUREIS FOR INDUCED CURRENT TORQUE TRANSMITTING APPARATUS 2 Sheets-Sheet 2 Filed March 3 1954 5 m m T m 7 N O 3 E T W T o l A E E P s P 4 5 3 United States Patent ARMATURES FOR INDUCED CURRENT TORQUE TRANSMITTING APPARATUS Henry S. Jacobs, Shorewood, and Jeremiah M. Curtin,

Milwaukee, Wis., assignors to Hamischfeger Corporation, Milwaukee, Wis., a corporation of Wisconsin Application March 1, 1954, Serial No. 413,096

7 Claims. (Cl. 310-105 This invention relates to induced current torque transmitting apparatus and more specifically resides in an armature for such apparatus having a flux conducting drum of magnetic material that supports circumferentially spaced inductor bars of low resistance and reactance with cooling fins of resistance greater than that of the bars attached between the ends of the bars to form current paths extending between the bar ends that limit the inductor bar currents and impart to the torque transmitting apparatus enhanced speed-torque characteristics in which output torque is of a substantial value over a wide range of operating speed.

The torque of a Wound armature induced current torque transmitter, having an external resistance forming a part of the armature circuit, may be varied at will for any given slip-speed by a simple variation of the value of the external resistance. Also, through a variation of the resistance with changing slip-speed high torque output over a substantial speed range may be attained. Self-contained armature circuits, on the other hand, do not permit such flexibility of operation through control of an external secondary resistance. The self-contained circuit is usually of the so-called squirrel cage type in which the armature inductor bars are short circuited one to another at their ends by end ring connections. In some instances cooling fins are disposed between the ends of the inductor bars and the short circuiting end rings. Such cooling fins act as inductor bar extensions that are disposed outside the working flux field for enhancing the rate of dissipation of heat that is evolved in the armature circuit. Whether or not such fins are employed, the circuit characteristics are fixed in the self-contained circuit and there is no provision for the variation of resistance through an external variable control.

For operating in the low slip-speed ranges the higher output torque values are obtained by employing a low resistance in the armature circuit. Conversely, in the higher slip-speed ranges the higher output torques are attained through the insertion of substantially higher resistance values in the armature circuits. It has been a common practice to provide an armature, with a selfcontained circuit, that has the characteristic of a low resistance circuit at the low slip-speeds and of a high resistance circuit at the higher slip-speeds, by placing a double cage in the armature. Such double cage has two sets of inductor bars, one of which is deeply embedded in the magnetic drum to produce a high reactance at high slip-speeds that effectively precludes current flow in this set of bars at such speeds. In this manner dual resistance characteristics are provided to enhance the torque output over an extended speed range.

The use of a double cage introduces a high reactance in the armature circuit which sharply curtails the maximum attainable torque output. Further, the resistance in the rotor bars extending through the magnetic drum causes the bars to become principal sources of heat evolution. This is particularly pronounced at the higher slip-speeds. Such heat must be effectively dissipated in Tue order to enjoy a sustained high level of torque output. While the problem of heat dissipation may not be vital in motor applications, it becomes of paramount importance in the operation of induced current clutches and brakes.

Rapid heat dissipation is necessary to retain thermally induced dimensional changes at a minimum and to avoid disruptive internal forces that may occur upon undue temperature increase in the magnetic drum. It is particularly desirable to have the evolution of heat occur outside the magnetic drum and to this end, in the practice of this invention, the inductor bars are of large cross section with a substantial circumferential width and a relatively shallow depth. The inductor bars then present a minimum of resistance and reactance to the armature circuit. Cooling fins with large surface areas and of resistance substantially greater than that of the bars are then joined to the bar ends to act as bar extensions through which the induced currents flow. The resistance of the fins causes the major evolution of heat to occur primarily within the fins and outside the magnetic drum. The cooling air that is passed across the fin surfaces carries away and rapidly dissipates the evolved heat.

The use of low resistance, low reactance rotor bars for the entire intended range of operating slip-speeds dispenses with the use of a double cage rotor bar construction which has heretofore limited peak torque output. A desirable variation in resistance with change in slipspeeds is provided in this invention by providing the major current limiting resistance in the armature circuit in the cooling fins. The value of the resistance may be selected to develop a desired speed-torque characteristic and the fins may be comprised wholly, or in part, of magnetic material that effects a change in resistance with slip-speed. The resulting variation in resistance provides for uniformly high torque output over a substantially wide operating range of slip-speed.

It is an object of this invention to provide an armature for an induced current torque transmitter having cooling fins that impart a resistance to the armature circuit that varies in value with slip-speed to provide enhanced speed torque characteristics for the apparatus.

It is another object of this invention to provide an armature for an induced current torque transmitter in which the armature circuit resistance and reactance characteristics are dominated by that of cooling fins forming inductor bar extensions.

It is another object of this invention to provide an armature for an induced current torque transmitter with cooling fins connected to the ends of the inductor bars that are securely fastened in position to withstand severe rotational forces encountered upon abrupt accelerations and decelerations.

It is another object of this invention to provide an armature for an induced current torque transmitter of low inertia for obtaining rapid acceleration and deceleration.

It is another object of this invention to provide an armature for an induced current torque transmitter in which heat evolution that occurs in the secondary circuit is localized in current conducting cooling fins to the side of the magnetic drum carrying the inductor bars, which fins are advantageously disposed for rapid dissipation of the heat evolved.

It is another object of this invention to provide an induced current torque transmitter in which inductor bars. of relatively large cross section disposed near the surface of a magnetic flux conducting drum are employed to present a minimum of resistance and reactance. to the secondary circuit.

7 These and other objects and advantages of this in vention will appear in the description to follow. In the systems 3 description-reference is made to the accompanying "drawings which form a part hereof and in which there is shown, by way of illustration and not of limitation,

"specificforms in which this invention may'beernbodied.

In"'the drawings:

"Fig. 1 is an end view in section with parts broken away of an induced current torque transmitter in the form of a clutch and in which this invention is embodied viewed through the plane 1l shown in Fig. 2,

'Fig. 2 is a side view in section of the clutch viewed through the plane 2-2 shown in Fig. 1,

Fig. 3 is a fragmentary end view in elevation of the induced current member of the clutch,

"Fig; 4 is a fragmentary view insection of an alterna- "tive form of an inductor'bar end and a cooling fin attachedthereto viewed through'the plane 4 S shown "in'Fig. 2,

Fig. S-is' a fragmentary side view with parts broken away'and in section of the inductor bar end and cooling fin shown in Fig. 4, and

"Fig. 6 is a graph of speed-torque characteristic curves that-maybe obtained in the use of the clutch.

"Referring'now to the drawings, there is shown in Figs. '1 and 2 an induced current torque transmitter in the 'form'of'a clutch '1. The clutch 1 has'an input shaft 2 to which is keyed'a hub 3 that supports a circular shroud plate'4. On the inner face of the shroud plate 4 there "is'secured a cooling air deflecting battle 5 in the form 'of'a'circular band, and extending radially between the hub 3 and the inner face of the baffie 5 is a plurality of circumferentially spaced bracing webs 6 that reinforce material which supports on its inner circumferential face 'a plurality of uniformly spaced pole 'pieces 10. The

pole pieces 10 are individually secured to the'magnetic *frame 9 by means of boltsll and surrounding each 'pole'piecelfl is'a'field winding 12. Upon an energization o-f'the windings 12 through usual connections not shown, alternatenorth and south magnetic poles Wlll be formed at the inner 'polefaces of the pole'pieces 10,

from 'whichmagnetic flux will extend for interception by an armature to be described.

"An' output shaft 13 in the form of a quill surrounds the inputshaft 2, as is shown in Fig.2, and a pair of tapered bearing sets 14 inserted between the shafts 2 andlS-provide for both the support of and the independent rotation of the shaft 13. Carried by the" shaft 13 is an armature, or induced current member, generally designated by the numeral 15 that intercepts and conducts the-magnetic'fiuxextending from thepole pieces 10. The

armature 15 has a hub 16 keyed to the'output'shaft 13 andboltedto one'side face of the'hub-16is a bearing "retainerl'lfor axially-aligning the-bearing sets 14=w1th the armature assembly. -A pair of transverse diaphragm plates 18 encircle and are firmly secured to-"thecuter circumferential face of thearmature hub 16. Supported by the diaphragm plates 18 is a plurality of spoke plates 19' that extend axially and radially outwardly. The plates 19 are paired, with the plates of each pair being convergent outwardly to support a bolster 20 that has an *arcuate circumferentiallyextending outer 'face in supporting relation with a magnetic' drum'21. Thedrum "21 is formed of a' plurality of transversely extending stacked laminations 22 and is rigidly secured to the'bolsters 20, and hence the spoke plates'19, so that the torque reac tion of the apparatus may be transmitted to the'output shaft 13 without adverse effect. A material-"of low thermal conductivity, such as a stainless steel,-isjpreferabIy employed for the spoke plates 19 and bolsters -20 'to inhibit the" conduction "of heat, "which maybe evolved "in'thexdrum 21,to"retain"the hub 16 and-the supporting shaft 13 and bearings 14 relatively cool.

Embedded in slots that extend axially across the outer circumferential air gap surface of the magnetic drum 21 is a plurality of low resistance inductor bars 23. As shown in Fig. 3, theradially outer surface of each conductor bar 23 is flush withthe =air'gap surface of the drum "21. .Toretain :the bars 23 in position, a groove is cut in the side faces of each bar, with corresponding mating. grooves being'formed in the adjacent slot faces, and a key rod 24 is'inserted in'each set of mating grooves. The ro'ds24are driven in place for a tightfitto sectlrelyholdthebars 23 from loosening and shifting position. Each bar 23 is preferably given a substantial circumferential width and a relatively shallow depth so that the reactance will be small. Also, by placing the bars 23 flush with the air, gap surface of the drum. 21 a maximum of working fiux'will be intercepted and the leakage flux is correspondingly reduced. The ends '25 'of'the inductor bars 23 extend axially beyond and overhang the magnetic drum '21. A sleeve 26 of weldable'material is'fittedover each inductor bar end 25. The'sleeves 26 may be constructed from fiat stock which is turnedto form an enclosed loop with theresulting'searnfbeing welded, as is shown in Fig. 4

at 27,or maybe formed 'in'other' suitable manner. By brazing the sleeves '26 to the inductor bars 23, which normally are of'copper or similar low resistance conducting material, the sleeves will be firmly secured in position. The sleeves 26 then provide firm anchorages for the support of a plurality of cooling fins 28.

The radially extending cooling fins 28 are constructed with outer surfaces of weldable material and each is attachcdby Welding at its radiallyouter end to the inner face of a'sleeve 26. Each fin 28 terminates at its radially inner'end' in a welded connection with a hoop like end ring'29 thatis supported' by a plurality of axially extendingbrackets 30 that project from a diaphragm plate 13. like end ring assemblies are provided on each side of-the armature 1L3, andeach end ring 29 is formed of an inner-rim '31- of a highly conductive material, such as copper, and-an outer rim 32 of -a strength imparting weld- I transmitter are of'la'rge cross section area to present a very low resistance to'the armature circuit, and this permits the selection of cooling fins'28 that'will have'a substantially greater resistance, but in which the overall resistance ofthe armature circuit is small 'to provide .the wanted hi'gh'torque'output at low slip-speeds. By enabling the'fins 28' and, :if' desired, parts of. theend rings 29, to: comprise the eifective resistance in the'armaturc circuit evolutionof' heat will'occur principally within'the fins f2? and the-end rings29, rather than in the bars 23 embedded in the magnetic drum 21. I that for optimum operation, wherein thermalsexpansion It has been found and thermally. induced stresses in'the armature/drum 21 are not. excessive, that the ohmic, or-udirect current,:-re-

- sistance -of. the fins 28 compared toithat of the bars -shouldnot be less than the ratio. 10:1.

' For the high slip-speeds it is desirable to have substantial torqueoutput to :quickly bring the driven member up' to runningi'speed, in theiinstanceof a'clutch, .orto a standstill; in the instance of a brake. I It is necessary,-then, to employa substantially larger resistance in the-armature circuit, asic'ontraste'd' w-ith-that ofloufslipespeed operation, fobcieaitihg-dhe -necessary tUrque. The? high armature circuit resistarice-must be localized'outside madam-'21 and the low resistance bars 23. Excessive heat evolution within the drum 21 will then be avoided for high slipspeed operation as well as low slip-speed operation. In the present invention the larger circuit resistance for the higher slip-speeds may be attained by selecting a low resistance magnetic steel for the cooling fins 28 that will introduce a so-called skin effect into the armature circuit. During low slip-speed operation the current passing through the fins 28 will be distributed nearly uniformly throughout the fin cross sectional area. The fins 28 then present a minimum of resistance to current flow and torque will increase rapidly as slip is slightly increased from the zero value, as is shown by the curve 33 in Fig. 6.

As slip increases the frequency in the armature circuit correspondingly increases and the magnetic field of self induction will give rise to the skin effect phenomenon in the fins 28. Being of magnetic material which provides a low reluctance flux path for the self induced flux, the fins 28 will exhibit a marked crowding of the current passing therethrough toward the outer surface, or skin. This crowding of current pronouncedly increases as the frequency of the induced currents increases. The crowding leaves the center cross section areas nearly void of current and the effective resistance of the fins 28 is thereby substantially increased with increased slipspeed. The increasing resistance with increasing slip-speed causes a high level of output torque to be maintained, and as is shown by the curve 33 the output torque may be made nearly constant over an extended range of working speed by proper selection and proportioning of the fin material.

In some applications it is desirable to attain a torque speed characteristic presenting a somewhat reduced torque at the larger slip-speeds, which torque is, however, sulficient to cause a rapid change in speed of the output shaft without severe shock being imparted to the driven apparatus. The curve 34 in Fig. 6 is an example of such a torquespeed characteristic, and in Figs. 4 and 5 there is shown a cooling fin 28' that may be employed in attaining the curve 34. The fin 28 comprises a thin central lamina 35 of a low resistance material such as copper that is flanked by outer laminae 36 of strength imparting weldable material, such as a stainless steel. The outer laminae 36 are welded to the associated sleeve 26 and the outer rim 32 of the end ring 29, similarly as the fins 28 of low resistance magnetic steel.

The copper and steel laminae 35, 36 are proportioned to give a sufficiently low resistance for a substantial torque output at the low slip-speeds. The magnetic effects of a stainless steel will not be as marked as for the highly magnetic fins 28, and as slip-speed now increases the resistance will not increase as greatly as for the fins 28 producing the curve 33. The resistance, however, may be sufficiently high for attaining a desired level of torque output for the higher slip-speeds. The curve 34 is representative of a speed torque characteristic that may thus be attained. Apparatus having a characteristic curve like 34 finds use in instances where a device moving in one direction is to be rapidly reversed, but where reversal is to be accomplished without shock or severe stresses being transmitted to the driven device as the reversing torque is first applied. An excavator cab, for example, with a loaded extended dipper may be rotating in one direction and rapid reversal in the direction of rotation is to be accomplished without endangering the equipment. For optimum speed of reversal the initial reversing torque should be less than the peak torque, and the torque should gradually increase as deceleration of the cab occurs. If the highest slip-speeds of the curve 34 be those encountered upon applying reversing torque to the cab, then the lower torque values at these speeds will commence a deceleration of the cab without unwanted shock. As deceleration proceeds torque increases, and as the cab reaches standstill torque will be approaching a maximum. With the occurrence of acceleration in the reverse direction torque will be maintained at high levels.

A combination fin having a central lamina of low resistance copper flanked by reinforcing laminae composed of iron or steel may also be advantageously employed to reduce the weight of the fin construction, thereby reducing the inertia of the armature. Quicker reversal, or change in rate of rotation, is then made possible. Likewise, a similar weight reduction in the construction of the end rings will further enhance the armature inertia characteristic to provide for rapid accelerations and decelerations.

By altering the proportion of copper and stainless steel in the fin 28' the torque-speed characteristic may be altered. The curve 37 in Fig. 6, for example, is representative of an armature employing fins with a reduced proportion of copper. The resistance at low slip is higher than for the fins of curves 33 and 34, and as slip-speed increases the resistance remains high for increased torque output. Other output characteristics may be attained by employing fin materials of increased magnetic characteristics with a copper lamina, or by other alterations in the selection and proportioning of the fin materials which will occur to one proficient in the art without departing from the invention.

There is thus provided a torque transmitter having a low level of heat evolution in the magnetic armature drum, wherein the dominant resistance of the armature circuit is disposed outside the drum to cause the principal heat evolution to occur in cooling fins having a variable resistance with change in slip-speed to provide desirable high level torque output.

In the employment of induced current clutches and brakes under extremely severe load conditions wherein accelerations and decelerations are frequent and rapid as, for example, may be encountered in the rotation of an excavator cab or in the crowding and retracting of an excavator dipper, the armature must be capable of withstanding large rotational stresses. To furnish adequate strength a weldable material is employed for the cooling fins 28 that may be firmly secured to supporting members through the agency of high strength welds. Connections with the copper inductor bars include jacketing the inductor bar ends with the sleeves 26, which are likewise composed of a weldable material, and which will not part from the bar ends 26 under the most severe stresses. Similarly, the end rings 29 present a surface of weldable material for attachment of the inner ends of the fins 28, thereby providing an apparatus of enhanced strength capable of withstanding large rotationally induced stresses. It is to be understood that end rings employed in conjunction with the cooling fins are not limited to the form of a laminated construction. If desired end rings may be formed of a homogeneous ma terial and for high strength welds with the cooling fins it is preferable to have an end ring material like that presented by the cooling fins.

We claim:

1. In an armature for an induced current torque transmitter the combination of a drum of magnetic material having a circumferential face forming an air gap surface concentric with an axis of rotation, a plurality of circumferentially spaced inductor bars of low resistivity supported by said drum having axially extending ends projecting from said drum, a plurality of electrically conductive laminated cooling fins of a resistance substantially greater than that of one of said inductor bars each having a current conducting lamina of copper and a second current conducting lamina of strength imparting ferrous material adjacent and supporting said copper lamina, and connections joining said cooling fins between the ends of said inductor bars with each fin forming an extension of an associated bar to provide current paths .forr. the'ftlow ,of 1 inductor bartcurrents whichiare limited in value'by said cooling fins. Y

.2. .In-ian armatureforlan induced current'torqueitrans .rnitter. the combination of-a drum of magnetic material having a circumferential'face forming an air gap surface concentric with an axis of rotation, a plurality of circum'ferentially spaced inductor bars of low resistivity supported by saiddrum'having axially extending ends projecting from'said drum, a plurality of thin'laminated electrically conductive elongatedfins with relatively large cooling surface areas each formed of a conductive central lamina of a low resistivity comparable to that of said inductor bars and a flanking lamina on each side of the centrallamina .of acon'duc'tive magnetic material whereby each fin has an effective resistance that increases with increase in frequency of a currentpassing therethrough concentric with anaxis of rotation, a plurality of circumferentially spaced inductor bars of low resistivity supported by said drum having axially extending ends projecting from said drum, a plurality of tubular sleeves of weldable material each closely surrounding and securely fastened to a projecting inductor bar end, a plurality of thin electrically conductive cooling fins each of substantially greater resistance than that of one of said inductor "bars and having a face area of weldable material with one edge abutting a sleeve on an inductor bar end at a point radially inside the sleeve, the abutting edge of each fin being securelywelded to the associated sleeve 'with the fin extending from the abutting edge to an op positely disposed end'ring connected edge, and end ring connectionsj'oining the'end ring connected edges of the 'fins to one'another including'a ring of low resistance conducting material "and 'asecond ring of strength innparting weldable material attached to said low resistance ring with weldsjoining'said second ring and the end ring connected edges of saidfins.

4. 'In an armature for an induced current torque transmitter the combination of a drum of magnetic material having a circum'ferential'faceforming an air gap surface "concentric with an axis'of rotation, a plurality of circumfereritiallyspaced'in'ductor'bars of low resistivityembedded' in said drum having axially extendingends projecting from said drum, a-plurality' of tubular sleeves of weldable material each 'encircling'aprojecting end of an'inductor tar an securely brazed thereto, a plurality of electrically conductiveilarninafed' cooling'finsof a resistance substantially greater than that'of one ofzsaidvinductor bars each having a'cur'rent eonductinglamina ofcopper and a sec-- ond current conducting lamina 'of'strength imparting weldable material adjacent and supporting said copper lamina, each "fin having an edge abutting and securely welded to a' sleeve encircling an inductor bar and extend ing from'the'inductor bar'to an end ring connectingedge, and end ring connections comprising a ring of low resistance conducting material and a second ring of strength imparting weldable material reinforcing saidlow resistance ring With welds joining the reinforcing ring with the end ringrconnecting edgesrof said fins.

5. In an armature'for an induced current torque trans- 'initter the combination of a drum of magnetic material having a circumferential face forming an air gap surface concentric with an axis of'rotation, a plurality ofcircumferentially spaced inductor bars of low'resistivity supported bysaid drum having axially extending ends projecting from said drum, a plurality of tubular sleeves 'of weldable material eachclosely surrounding and securely fastened toa projectinginductor bar end, a plurality of thin electrically conductive cooling fins each of substantially greater resistance than that of one of said inductor bars and having a face area of weldable material with one edge abutting'a sleeve on aninductor bar end, the abutting .edge'of each fin being securely welded to the associated sleeve with the fin extending from the edge to an oppositely disposed end ring connected edge to form a current path extending from the associatedbar, and end ring connections joining the end ring connected edges of the fins to one another to form current paths between bar ends for the flow of inductor'barcurrents which-are limited by theresistance of said fins.

6. An armature for an induced current torque transmitterin accordance with claim 1 in which the ohrnic resistanceof-each cooling fin is not less than ten times that of the associated inductor bar.

7. Anarmature for an induced current torquetransmit- 'ter in accordance with-claim 1 in which an end of each inductor bar is capped with a weldable @material, the strength imparting laminaiof each fin is of Weldable material, and'the connections joining the cooling fins to inductor bar ends comprise Welds.

References Cited in the file of thispatent UNITED STATES PATENTS 862,776 Waters Aug. 6, I907 991,626 Lord May 9, 1911 1,156,364 McColluin Oct. 12,1915 1,851,155 Schmid-Burgk Mar. 29, 1932 2,188,398 Bernard Jan. 30, 1940

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