US2937803A - Air flow cooling apparatus and drive therefor - Google Patents

Description

AIR FLOW COOLING APPARATUS AND DRIVE THEREFOR Filed June 5, 1957 May 24, 1960 E. F. CUNNINGHAM 2 Sheets-Sheet 1 m mm m NN w c M R w m May 24, 1960 E. F. CUNNINGHAM 3 AIR FLOW COOLING APPARATUS AND DRIVE THEREFOR Filed June 5, 1957 2 Sheets-Sheet 2 INVENTOR. EDWARD I. CUNNINGHAM flTTORNEY United States Patent This inventionrelates to cooling devices, and more particularly to impelling means for, air and other gases.

In some-situations it is necessary, or at least desirable, to move substantiallyconstant mass of air through a cooling deviceor across a heated unit regardless of the varying density of the .air. One such instance is in con.- nection with cooling electronic or'other aircraft equipment by a moving column of air in. which the. density of the air to be impelled may vary from that at about sea level density to. more rarefied air atheight s in the order of 60,000 feet. Such rarefied air does not have the same cooling effect penunitfof volume. as the denser air.

' It' is an objectfof this invention to provide means whereby ,air or other gas to be propelled over a given space andoveijobjeetsgtliereinis so propelled that a substantially constantmass (as distinguished from volume) of gas is'automatically,impelledper'unit of time, thereby maintaining the cooling effect of the air substantially constant. i i I r This is accomplished according tothe present invention by providing an air impeller capable at a predetermined r.p.m. of movingthe desired mass of air of least density to be encountered, and a constant torque motor capable of driving the impeller at said predetermined rpm. and by connecting the motor and impeller with a magnetic coupling of the hysteresis type, the hysteresis characteristic ofwhich is such that the degree of slip between the driving and driven elements varies over a wide range with the density of the air in which the device is operating, to give an impeller speed which varies inversely with such density in the desired proportion for substantially constant mass air delivery.

It has been discovered that with the use of a magnetic coupling having a-permanent'multi-pole magnet as the driving element and a coaxial annular member of appropriate magnetic structure and high hysteresis as the driven element and scparatedfrom the driving element by a suitable air gap, thenthe torque exerted on the driven memher by the driving member will be substantially constant so that when the load. on the.dri ven membertends to increase in airof greater density, such, as accompanies a shift from-higher altitudes tolower altitudes, the slip between the driven member and the-d riving' member in remains substantially constant. H t

, Thus at sea level, even.though.t he motor is operating at creases but'the torque transmitted'to the drivenmember I constan'tapredetermined,r.plm.,' thei pfiller will be operating at a substantially lower speed but, due to the density of the air, Willbe propelling the optimum mass of air across the radiator or'unit being cooled by it.

A As the aircraft rises into more rarefied air, the load on the impeller, tends to decrease, but as this tendencyoccurs the slip between the driving member and the driven member of the coupling decreases with the result that, the r.p,m. oftheimpeller increases and the latter tends to move a greater volume of air perunit of time to give the same mass of air moved. I f

This would continue until the air became so rarefied wall of the motor casing 11 at the front or inner end,

that little if any slip occurs between the driving member and the driven member of the coupling and the impeller and the motor would move at substantially synchonous speeds. The height at which this occurs may be determined by the characteristics of the motor and impeller and coupling, and the torque may be varied within limits by adjusting the air gap between the driving and driven members of the coupling to meet the desired load requirements within the load capacity of the motor or to match the optimum torque of the impeller and motor.

According to the present invention, one element of the magnetic coupling is permanently magnetized so as to have a plurality of arcuately spaced poles while the other element is permanently magnetized to form within itself a closed magnetic circuit and these elements are juxtaposed so that the second-named element forms a high hysteresis magnetic path for the flux emanating from the other element. 7

Either element of the pair of cooperating magnetic elements may be driven by the driving means.

Another object of this invention is to provide a compact and efficient unit comprising driving means including an electric motor, means to be driven thereby and a magnetic coupling of the hysteresis type between the motor and the driven means. v

Other features and advantages will hereinafter appear. In the accompanying drawings Fig. l is a longitudinal section of an air impelling'unit Fig. 5 is a transverse section taken on the line 5-5 of Fi 4; i ig. -6 is a transverse action taken on the line 6-6 0 Fig. 4. a I a Fig. 7 is a schematic view showing the unit of the present invention when used in a cooling system. Referring first to the form-of the invention'shown in Figs. 1, 2 and 3 the air impelling unit of the present invention comprises a constant speed electric motor 10 mounted in a casing 11 and an air impeller or fan 12 mounted in a housing 13. The housing 13 has radial webs or struts 14 attached to a ring 15 and to the housing 13, as by Welding or casting for example, for mounting the motor casing 11 on the impeller housing 13.

The front end of the motor casing 11 has a fiange 16 and a sleeve 17 which receives a bearing sleeve 18 having a radial flange 19 located inwardly of the flange 16. Bolts 20 passing through aligned holes in the mounting ring 15 and the flange 16 and entering tapped holes in the flange 19 secure the motor casing '11 to the impeller housing 13.

The motor 10 has ribs 21 spacing it from the inner while a cover plate 22 secured to the casing 11 by bolts 23 and to the motor 10 by bolts 24 supports the outer end of the motor and spaces it from the casing. thereby providing around the motor 10 an annular passage 25 for air which may enter through holes 26 in the cover plate 22, and pass out through passages 46 and 45 for cooling the motor and the magnetic coupling.

The impeller 12 is carried by a shaft 27 which is supported in bearing 28 mounted in the bearing sleeve 18 so as tobe axially aligned with the motor shaft 29.

According to the present invention the impeller shaft 27 and motor shaft 29 are operatively connected by a magnetic coupling of the hysteresis type having two juxtaposed elements, one element 30 being permanently magnetized to have a plurality of fixed poles and the other element 31 being circularly magnetized. One element is connected to the shaft 27 and another element connected to the shaft 29 and so constructed and arranged that, due to the hysteresis characteristic of one of the elements, a substantially constant torque is transmitted from one element to the other while permitting variable rotational slip over a wide range between the elements, with the result that when the load on the impeller 12 tends to vary with increasing or decreasing density of the air, the speed, i.e. r.p.m. of the impeller 12, automatically varies inversely approximately with the square root of the density of the air, and in such proportion that the mass of the air moved by the impeller will remain substantially constant regardless of the density of the air. There is a slight deviation from this ideal arrangement, by changes in impeller efiiciency and bearing friction with increasing speeds, particularly at higher speeds, but such deviation is minor over a wide operating range from sea level tohigh altitude for example.

It has been found that either of the elements 30- or 31 may be connected to themotor shaft while the other is connected to the impeller shaft. Both arrangements are illustrated herein. in the form of the invention shown in Figs. 1, 2 and 3 the polarized magnet 30 is carried by the impeller shaft 27 and the circular magnet 31 is carried by the motor shaft 29, while in Figs. 4, 5 and 6 the arrangement is reversed and the polarized magnet 30a is carried by the motor shaft 29a and the circular magnet 31a is carried by the impeller-shaft 27a. There is no apparent difierence in the principle of operation of the couplings between the different arrangements.

Reverting to the form of theinvention shown in Figs. 1, 2 and 3, which is the form at present preferred for manufacturing reasons, the polarized permanent magnet 30 is in the form of a disk 32, made of high magneticretentive material such as an aluminum-nickel-cobalt alloy, the disk having on its face a plurality of laterally extending integral segmental pole pieces 33 separated by radial slots 34 and a central recess 35. The disk 32 has a central aperture to receive the threaded inner end 36 of the impeller shaft 27 and is secured to the latter by a nut 37.

The circularly magnetized element 31 is a plain annulus, likewise made of high magnetic-retentive material such as an aluminum-nickel-cobalt alloy, and is mounted so as to rotate with and be concentric to the motor shaft 29. As shown in Figs. 1, 2 and 3 the annulus is carried by a circularbody 38 of non-magnetic material, preferably of light weight and high thermal conductivity such as aluminum, which has a hub portion 39 provided with an aperture to receive the threaded inner end 40 of the motor shaft 29, and is secured thereto by a nut 4-1 and key 41. The annulus 31 is seated in a recess in the face of the body 38 so as to be directly opposite but spaced from the poles 33 of the element 30. The annulus 31 may be mounted in the body 33 in any suitable manner, for instance by being pressfitted therein.

Thecircularly magnetized element 31 is in magnetic relation with the polarized element 30 and therefore is magnetically coupled therewith for synchronous rotation under conditions of no load or low load near no load on the driven member such as the shaft 27, and for a synchronous rotation with progressively varying slip over a wide range while providing substantially constant torque as the load on the shaft 27 tends to vary under substantial load conditions. As the shaft 27 rotates with the impeller mounted on it, the work performed by the impeller in moving the air, which the blades encounter, places a load on the shaft. Any substantial load, tending to exceed the maximum torque of synchronous rotation, reduces the rpm. of shaft 27, and causes the coupling element 30 to lag behind the element 31, with the result that the magnetic'field pattern created in the element 31 by the magnetizing force exerted by the element 30 constantly shifts in position, i.e. rotates with respect to the element 31, but remains at substantially constant strength, and against the strong coercive force of its magnetic structure provides a substantially constant torque obtained between the element 31 and element 30. This effect, it is believed, is due to the hysteresis of the circu larly magnetized element 31 in the shifting or reorientation of its magnetic structure with the slip, which provides a substantial constant torque, over a wide range of difference in r.p.m.'of the driving and driven elements, the elements 31 and 30 respectively, in the device shown in Figs. 1, 2 and 3.

Nevertheless, it has been found that using an impeller capable of moving the desired mass of air at a predetermined r.p.m., a constant speed motor capable of delivering the torque required to operate the impeller to move the desired mass of air and coupling the motor with the impeller by a hysteresis drive of two cooperating permanent magnet type elements, one being polarized and the other having a closed magnetic circuit, a substantially constant torque will be transmitted from the motor to the impeller regardless of the speed which the impeller must attain to maintain substantially constant the mass of air moved per unit of time.

It will be understood, of course, that to'maintain constant the mass of air being moved, the r.p.m. of the impeller must vary inversely in a determinate proportion to the density of the air, which approximates an inverse square root relation. I

As an example, it has been found that with a 9.5 inch impeller, such as shown in Fig. 1, and a motor of A -I-I.P. having a constant speed of 11,500 r.p.m. at 'rated load, the speed of the impeller varies with the density of the air, reckoned in altitudes as follows, the figures being approximate:

- 1 (Approximately synchronous with the motor.)

The above figures are taken from constant temperature altitude chamber tests.

In designing the unit of the present invention for a particular purpose, as for instance the cooling of aircraft equipment, having determined the mass of air required to be moved over a radiator or other object to be cooled or from which a constantrate of heat is to be extracted to maintain a substantially constant and operating temperature, the impeller is designed to deliver such mass of air at a speed substantially synchronous with the speed of the motor in air of least density to be encountered, i.e. at the highest altitude to be reached by the aircraft, and the motor is designed to produce the required torque and power to so drive the impeller, as well as to drive the impeller at its reduced speed through the magnetic coupling at the maximum air density as at sea level for example. Withthe components so selected, the hysteresis coupling is so constructed and arranged to transmit a substantially constant torque from the constant speed motor to the impeller regardless of the-speed of the impeller over the operating range, so that at any height from miximum altitude to sea level, where the density of the air is greatest, even though the r.-p.m. of the impeller decreases, the same mass of air will be moved per unit of time so required.

The torque transmitted by the hysteresis coupling depends on its size and the strength of the magnetic field of the polarized elementand the size and hysteresis characteristics of the cooperating element as well as the air gap between the two elements. Since some variations from standards may occur in the manufacture of the components including the motor and motor casing, etc., the present invention provides convenient means for varying the air gap between the adjacent faces of the two elements of the coupling to adjust for the desired torque. As shown in Fig; lthisjisaccomplished byinserting shims 42 between-the outer end of the motor and'the cover plate '22 which has the effect of moving the element 31 closer to the element 30 to increase the torque for example. If

it is required to open 'the air gap, shims may be placed between the cover plate 22 and the motor casing 11 since this haslthe effect ofmoving the element 31 away from the element 30.

It should be understood that while the objective is to deliver to the equipment to be cooled a substantially constant mass of air, some tolerance may be permitted so long as a suflicient air mass for the purpose is maintained and it is customary to provide some modest margin of capacity. However, the present invention, with its automatic adjustment of impeller speed to air density load makes it possible to provide such small margin of capacity, in contrast with the manifold increase of power that would be required to drive the impeller atconstant speed by a,

positive connection at the maximum speed required at the highest altitude for example without the invention. Any such direct drive would re sult in moving a greatly excessive massof air at lower altitudes with the attendant enormous waste of power and greatly increased weight and cost because of requiring a larger motor and other components, all objectionable in aircraft.

Theresult of'the present invention therefore is the automatic provision of adequate and appropriate air cooling at all altitudes reached with relatively negligible loss of power and avoiding unnecessaryweight and cost.

The slip, i.e. relative rotation, between the elements 30 and 31, resulting in constant shifting of the flux patternin the element 31, causes heat to be generated in the latter. -To avoid the element 31 becoming excessively hot and thus changing its magnetic properties, the body 38 which carries. the annulus 31 is so made as to also serve the function of an air impeller, so that outside air will be drawn into the body to cool the annulus. Accordingly I the body 38, which advantageously may be made by diecasting, is provided with more or less radial fins 43 betweenfthe annulus 31 and the inner wall 44 forming passages 45 which at thehub 39 meet passages 46 opening into the motor casing 11. When the body 38 rotates, air is drawn in through the apertures 26 in the cover plate 22 through the air space 25-.in the motor casing 11, passage 46 and into passage 45 from which theair is expelledby centrifugal force through opening 47 in the motor casing 11 and into the air stream created by the impeller 12, the suction effect of which augments the action of the fins 43. The body 38 may preferably be made of aluminum for example for light weight and for good heat conduction.

The air thus circulated cools the annulus 31 not only by convection by passing over its exposed surface but also by conduction by cooling the entire body 38 which carries it.

The edges of the struts 14 may be beveled at 14' for improved air flow.

Many of the features of the present invention described and claimed herein may advantageously be employed in driving units including hysteresis couplings where it is desired to maintain substantially constant torque using a constant speed motor to drive means having a variable speed but a substantially constant load.

The form of the invention illustrated in Figs. 4 to 6, which is a prototype of that shown in Figs. 1 to 3, has

substantially the same principle of operation, differing only inconstruction.

In the form shown in Figs. 4 to 6 the polarized magnetized element 30a of the coupling is mounted in a non-magnetic body 50 being secured thereto by a nut 51 on threaded hub 50'. The body 50 is mounted on the shaft 29a of a motor 10a and secured thereto by a nut 52 and key 57. The motor 10a is secured in a motor housing 11a so as to leave an airspace 25a between it and the motor housing. The element 30a (see Fig. 5) has radial slots 34a forming pole pieces 30:: on its face.

, The element 31a is, like the element 31 of Fig. 1, an annulus which is circularly magnetized (havingsubstantially no polar orientation). It is set in a body 38a of nonmagnetic material which is secured to the shaft 27a on which the impeller 12a is mounted. The impeller shaft 27a is supported in bearings in a sleeve 18a mounted in the closed front end 16a of the motor casing 11a. The impeller housing 13a has radial webs 14a secured to a ring 15a which is fastened to the end 16a of the motor casing by bolts 20a.

The motor shaft 290 and the impeller shaft 27a are coaxial and the elements 30a and 31a are concentric and are spaced from each other to-provide an air gap between them.

The motor10a is spacers 58. 4

The principle of operationof the unit shown in Figs. 4, 5 and 6 is the same as that shown in Figs. 1, 2 and 3 even though the polarized magnetized element 30a is driven by the motor 10a while the circularly magnetized element 31a is connected to the impeller and drives the latter.

To dissipate the heat generated in the element 31a, the body 18a carrying it is provided with a plurality of radially inclined fins 53 andthe closed end of the motor casing 11a is .provided with air passages 46:: so that as the body 38a is rotated to drive the impeller, air is drawn in through the rear end of the motor casing through the air space 25a and is expelled through the air passages 46a. The air thus passing through the unit cools the body 38a and byconduction and convection the magnetic element 31a is kept from becoming overheated. The body 38a may be of aluminum for example.

The small impeller elements 53 in the form of Figs. 456 and the small centrifugal impeller elements 43 in the form of Figs. 1-23 serve to cool the motor as well as the hysteresis elements.

It will be noted that two forms of assembly of the coupling elements to .the shafts have been illustrated in Figs. 1-3 and Figs. 4 6, as examples of different forms which may be employed.

The unit of the present invention may be employed invarious ways, one typical example being shown in Fig. 7 wherein the unit is secured to a radiator structure including an air transmission piece 54 to which the unit is secured by ears 55 thereon and a radiator unit 56 at the other end of the piece 54.

Variations and modifications may be made within the scope of the claims, and portions of the improvements may be used without others.

I claim: i I

1. An air circulating unit comprising a mounting frame spaced from the housing 11a by the having an impeller housing and a motor casing, an im- I peller located in said housing, a constant speed motor mounted in said casing, a driving shaft for said motor, a driven shaft for said impeller, and a magnetic coupling of the hysteresis type in said motor casing between said impeller and said motor, said coupling comprising twocoaxial elements spaced to provide a determinate air gap between them, one of said elements being secured to the driving shaft of the motor and the other of said elements being secured to the driven shaft for the impeller, one of said elements being permanently magnetized to provide a plurality of oriented poles thereon and the other of said ass /30s elements being an annulus and being permanently circularly magnetized to be nonpolar,'the hysteresis characteristics of said magnetized elements permitting variable slip between said elements while transmitting a constant torque to compensate for varying loads per revolution on the impeller.

2. An air circulating unit as defined in claim 1, in which the motor is movably mounted in the motor casing to vary the air gap between said elements.

3. In a power transmitting unit of the character described, a casing, a constant speed motor within the casing and having a driving shaft, a driven shaft mounted in the casing coaxial with the driving shaft, two coaxial rotary magnetic elements within said casing and having juxtaposed faces axially spaced to provide a determinate air gap between them, one of said elements being secured to the driving shaft and the other element being secured to the driven shaft, one of said elements being permanently magnetized to provide a plurality of oriented poles thereon and the other of said elements being an annulus and being permanently circularly magnetized to be nonpolarized, said elements coupled magnetically across said faces and having a hysteresis characteristic attendant upon the shifting of the magnetic field in the circularly magnetized element upon rotary slip between said elements to transmit a constant torque at widely variable slip, whereby a determinate slip occurs between the drivingelement and the driven element in response to increased load per revolution applied to ;the driven ele ment.

4. The unit as described in claim 3 in which the circularly magnetized element is supported by a non-magnetic body secured to its shaft.

5. The unit as described in claim 3 in which means are provided for dissipating heat generated in the circularly magnetized element resulting from the shifting of the magnetic field in the circularly magnetized'element.

6. The unit as described in claim 3 in which means carrying the circularly magnetized element is provided with means for dissipating heat generated therein and resulting from the shifting of the magnetic field in the circularly magnetized element.

7. The unit as defined in claim 3, in which the polarized element is mounted on the driving shaft.

8. The unit as defined in claim 3, in which the polarized element is mounted on the driven shaft.

9. The unit as defined in claim 3, in which means are provided for varying the air gap between the two coaxial elements.

.10. The unit'as defined in claim 3, in which means are provided for axially adjusting the position of the motor in the motor casing to vary the air gap between said elements.

11. In a constant torque transmission device comprising driving means including power input means, driven meansincluding power take-off means, and a magnetic coupling of the hysteresis type between the driving means and the driven means, said coupling including two coaxial permanently magnetized elements mounted in axially spaced magnetic relation and having cooperating radial faces, one of said elements being mechanically driven by said driving means and the other of said elements mechanically driving said driven means, one of said elements t having oriented poles in its face in a circle about the common axis and the other of said elements being in ring form and circularly magnetized about the common axis and devoid of inherent oriented poles.

12. A constant torque transmission device comprising driving means including power input means, driven means including power take-off means, and a magnetic coupling of the hysteresis type between the driving means and the driven means, said coupling including two coaxial magnetized elements mounted in spaced magnetic relation, one of said elements being mechanically driven by said driving means and the other of said elements mechanically driving said driven means, one of said ele' ments liaving oriented poles and the other of said elements being a hysteresis element circularly magnetized and-devoid of inherent oriented poles, in which each element is mounted on a rotatable body, the body for one of the elements including air circulating means for cooling the hysteresis element and said driving means by im pellingjair thereby as said body rotates.

13. In a cooling system employing air flow for dissipating heat from craft subject to widely varying air density between high density in sea-level conditions and low density in high altitude conditions, the combination of an air impeller having a constant torque requirement for imp'elling 'aconstant mass of air per unit timejby varying its speed inversely substantially as the square root of the density of air, a substantially constant speedmotor for driving said impeller at substantially synchronous maximum speed for low density air at a determined substantially maximumaltitude, a permanent magnetic rotor element having at least one face'and magnetized to provide a plurality of pairs of poles arcuately arranged on saidone face, a second rotor element including'a ring of permanent magnet material coaxial with the first said permanentmagnet rotor element and magnetized generally only in a circular manner with respect to the axis to avoid poles on saidring and arranged to cooperate with the magnetized poles in said face of the-first said rotor element with a very small constant air gap to be magnetically coupled thereto for controlled constant torque transmission with variable slip between said rotor elements by hysteresis action in said ring, one of said rotor elements being driven by said motor at its constant speed and the other rotor element being mechanically coupled to said air impeller to provide such constant torque to so rotate said impeller at such varying speed automatically in response to such variation in air density, whereby constant mass air cooling will be provided over such wide range of air densities.

14. A constant air mass air impelling apparatusifor circulating air'at a variable speed inversely depending upon thedensity of air comprising, a constant speed motor having a driving shaft, an impeller adapted for moving air and having a driven shaft, a variable slip magnetic hysteresis coupling assembly for coupling the driving and driven shafts, said magnetic coupling including at least two cooperating magnetic elements having an air gap between them and being coaxially positioned withrespect to each other and to both the driving and driven shafts, at least oneof said elements being-permanently magnetized to provide a plurality of magnetic poles ona surface thereof, and the other of said elements including a ring of high hysteresis magnetic material having a. surface closely juxtaposed to the magnetically polarized surface of the said one cooperating element,

said ring being inherently devoid of oriented poles, said elements being present in position with respect to each other to provide a constant air gap between the magnetically cooperating surfaces to provide a constant torque to said impeller over a wide range of impeller speeds with variable rotational slip between said elements as the air density varies so that said impeller speed will vary inversely substantially as the square root of the air density to impel a substantially constant mass of air per unit of time with widely varying air density.

15. A constant air mass air impelling apparatus for circulating air at a variable speed inversely depending upon the density of air comprising, a constant speed motor having a driving shaft, an impeller adapted for moving air and having a driven shaft, a variable slip magnetic hysteresis coupling assembly for coupling the driving and driven shaft, said magnetic coupling including at least two cooperating magnetic elements having ain air gap between them and being coaxially positioned with respect to each other and to both the driving and driven shafts, at least one of said elements being permanently magnetized to provide a plurality of magnetic poles on a surface thereof, and the other of said elements including a ring of high hysteresis magnetic material having a surface closely juxtaposed to the magnetically polarized surface of the said one cooperating element, said ring being inherently devoid of oriented poles, two non-magnetic metal heat conducting members one of which is coupled to the driving shaft and the other coupled to the driven shaft, one of said magnetic elements being mounted directly on one of said heat conducting members and the other of said magnetic elements being directly mounted on the other of said-heat conducting members for retation therewith to cool at least said hysteresis element and its associated heat conducting member, said magnetic elements being preset in position with respect to each other to provide a constant air gap between their magnetically cooperating surfaces to provide a constant torque to said impeller over a wide range of impeller speeds with variable rotational slip between said elements as the air density varies so that said impeller speed will vary inversely substantially as the square root of the air density to impel a substantially constant mass of air per unit of time with widely varying air density while also providing cooling of the hysteresis element to remove the heat generated as a result of said rotational slip.

References Cited in the file of this patent UNITED STATES PATENTS 2,386,505 Puchy Oct. 9', 1945 2,556,004 Sachse et al. June 5, 1951 2,571,762 Rich et al. Oct. 16, 1951 2,594,931 Jaeschke Apr. 29, 1952

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