US2976352A

US2976352A - Blower unit

Info

Publication number: US2976352A
Application number: US696537A
Authority: US
Inventors: Anwar A Atalla
Original assignee: Torrington Manufacturing Co
Current assignee: Madison Management Group Inc
Priority date: 1957-11-14
Filing date: 1957-11-14
Publication date: 1961-03-21
Anticipated expiration: 1978-03-21

Description

A. A. ATALLA 2,976,352

March 21, 1961 BLOWER UNIT 5 Shets-Sheet 1 24 FIG.4A zo j 14 Filed NOV. 14, 1957 INVENTOR.

ANWAR A. ATALLA BY Wi'mcM/M'a A TTORNEVS March 21, 1961 Filed Nov. 14, 1957 A. A. ATALLA 2,976,352

BLOWER UNIT 3 Sheets-Sheet 2 INVENTOR. ANWAR A. ATALLA BY TJZM 0M A TTORNEYS March 21, 1961 A. A. ATALLA BLOWER UNIT 3 Sheets-Sheet 3 Filed Nov. 14, 1957 AIR FLOW C.F.M.

INVENTOR. ANWAR A. ATALLA BY W 5' m a ATTORNEYS BLOWER UNIT Anwar A. Ataila, Torrington, Conn, assignor to The Torrington Manufacturing Company, Torrington, Conrn, a corporation of Connecticut Filed Nov. 14, 1957, Ser. No. 626,537

22 Claims. (Cl.-2391li7) The invention relates to a blower unit adapted for use with warm air furnaces and with air conditioning installations and otherwise, said unit being of the type that includes a housing having an air intake opening in one side wall and having a second wall parallel with said side wall and further having a discharge opening. The unit also includes a motor located with its shaft concentric with the intake opening and the unit has an air impeller located within the housing and driven by the motor and serving to draw air inwardly through the intake opening and to discharge said air through the discharge opening. As shown and as frequently preferred, the housing has two parallel side walls and has two opposite intake openings in said side walls. The motor is located within the housing and there are two impellers driven by the motor and serving to draw air inwardly and in opposite directions through said intake openings.

The general object of the invention is to provide a unit of the stated type that is simple and compact and inexpensive, and that has favorable power and performance characteristics through a wide range of operating conditions.

A more specific object of the invention is to provide a unit having a substantially flat power curve, the horsepower output of the motor and the speed of the motor varying to only small extents as the discharge pressure the constructions disclosed, and that the drawings and description are not to be construed as defining or limiting the scope of the invention, the claims forming a part of this specification being relied upon for that purpose. In each of the illustrated embodiments of the invention, there are two impellers at two opposite intake openings, but it will be understood that the invention in its broader aspects is not so limited.

Of the drawings:

Fig. l is a side view of a two-impeller blower unit embodying the invention, certain parts being broken away to more clearly show other parts.

Fig. 2 is a right end view of the blower unit with certain parts broken away and with other parts in vertical central section.

Fig. 3 is an enlarged fragmentary sectional view taken along the line 3-3 of Fig. l.

Fig. 4 is a side view of one impeller with parts broken away to show the details of construction, this propeller being that shown at the left in Fig. 2.

Fig. 4 is a fragmentary view similar to the upper left portion of Fig. 2 and showing an alternative embodiment of the invention.

Fig. 5 is an enlarged fragmentary schematic view showice?- ing the relationship of one'impeller blade to the axis of rotation and to the central partition and to other parts.

Fig. 6 is a fragmentary view similar to the upper por' tion of Fig. 2 and showing an alternative two-impeller unit embodying the invention.

Fig. 7 is a fragmentary side view showing a portion of one of the impellers shown in Fig. 6.

Fig. 8 is a fragmentary view similar to the upper portion of Fig. 2 and showing another alternative two-impeller unit embodying the invention; 7

Fig. 9 is an enlarged fragmentary view taken along the line 9-9 of Fig. l, but showing a detail of construction which is ordinarily used only with the alternative construction shown in Fig. 8. e

Fig. 10 is a chart showing representative performance characteristics of a blower unit embodying the invention. Referring to the drawings and more particularly to Figs. 1 to 5 thereof, the main housing of the blower unit is represented at '10, said housing preferably being formed of sheet metal. The shape of the housing can be \m'dely varied, but it is shown as being of the scroll or involute type. When the housing is of the last type, there is a longitudinal axis 12 and the housing has a peripheral wall 14'WhlCll conforms to a surface generated by moving a line approximately in an involute path about said axis 12. The housing is shown as having similar opposite parallel front and rear side walls'16 and 18. As shown, the peripheral wall 14 has opposite flanges 2t? and 22 which engage the peripheral portions of the

side walls

16 and 18 and which are suitably connected therewith, as for instance, by spot welding. When there are two

side walls

16 and 18, they are provided with similar large intake openings which openings are concentric with the axis 12. The housing has a relatively large peripheral discharge opening 24. The opening 24 is shown as being rectangular and it is defined in part by extended portions of the peripheral wall 14 and of the

side walls

16 and 18 and is further defined by a fourth wall 26 at the bottom thereof, said wall 26 being'suitably connected with said sid walls and said peripheral wall. t

When there are two side walls such as 16 and 18,'two generally

cylindrical shrouds

28 and 30 are fitted respectively within the intake openings in the side Walls, these.

shrouds being concentric with the axis 12. As shown in Figs. 1 to 5, the two side wall openings are of the same size and the two shrouds are of the same size. The major portions of the shrouds are cylindrical and said cylindrical portions are located to a major extent within the housing, but they may also extend outside of the housing.

Said shrouds are suitably connected with the side walls,

and when they are partly outside of the housing they may be connected by means of circular angle rings 32 and 34.

The outer portions of the shrouds 28 and 30may be bell-- mouthed as shown.

When there are two side walls such as 16 and 18 and two shrouds such as 28 and 30, a central panel or partition 36 is provided within the housing midway between and parallel with the side walls, this partition being formed of sheet metal and being suitably connected'with the peripheral wall 14, as for instance by means of a flange- Said partition 36 extends nearly to the discharge. opening 24, but preferably has its edge 40 spaced ininafter described motor and motor supportand the corre:

sponding one of said air impellers.

An electric motor 44 is provided with its drive shaft concentric with the central axis and with a portion of its shaft projecting toward at least one of the

side walls

16 and 18. When there are two chambers and a central partition 36, said partition has an opening 42 therein concentric with the axis 12 and the electric motor 44 is located at said opening. The motor includes a casing, preferably cylindrical, and it includes a drive shaft 46 having portions projecting at both ends of the casing. Means is provided for supporting said motor on said partition with its center of gravity at the central plane of the partition. The motor casing is symmetrically located in said partition opening 42 and the portions of said shaft 46 are concentric with said central axis 12, said shaft portions projecting toward the planes of the

housing side walls

16 and 18.

The supporting means for the motor preferably supports the motor resiliently, and it is shown as including a supporting ring or strap 48 located within said opening 42, but preferably not closely fitting said opening. When the supporting means supports the motor resiliently, the strap 48 is preferably connected with the partition 36 by means of a plurality of resilient connections 50. As shown, there are three such connections equally spaced circumaxially and one of said connections is illustrated in detail in Fig. 3.

In each said resilient connection a rubber grommet 52 is fitted within a hole in the partition 36, said grommet having a central bushing 54 therein. Preferably, in order to provide a larger bearing area for the grommet 52, a small plate 56 is welded or otherwise secured to the partition and has a hole for the grommet which has the same diameter as that in the partition. At one side of the grommet 52 is a clip 58 rigidly connected by welding or otherwise with the strap 48. At the opposite side of the grommet is a washer 60. A headed bolt 62 extends through said bushing 54 and through holes in the clip and washer, and a nut 64 on said bolt serves to firmly connect all of the last said parts with each other. By means of the three

connections

50, 50 the strap 48 is firmly but resiliently connected with the partition plate 36.

The casing of said motor 44 fits within the strap 48 so as to be held thereby in the stated relationship with the panel or partition 36 and with the housing. The supporting strap 48 is split and it has two spaced

ears

66, 66 as shown in Fig. l, the opening 42 having a notch 67 to receive said ears. Bolts 68 extend through holes in the said ears, and by means of said bolts the

ears

66, 66 can be drawn toward each other so as to firmly clamp the strap 48 against the periphery of the motor casing. Thus the strap firmly engages the motor 44 and serves to resiliently support said motor.

A conducting cable 70 for supplying current to the motor 44 extends upwardly through an insulating bushing in the lower portion of the peripheral housing wall 14 and then to themotor. As shown in Fig. 3, at least one electrical connecting wire 72 is engaged by the head of a corresponding one of the bolts 62 and said wire 72 is soldered or otherwise connected with the plate 56. This wire provides a grounding connection for the motor supporting strap 48 and for the casing of the motor 44.

It will be apparent that motors dilfering in exterior size from the disclosed motor 44 can be readily accommodated by merely substituting a strap similar to the strap 48 but differing in size to accommodate the selected motor. The strap 48 can be smaller than that shown, and the space between the strap 48 and the periphery of the opening 42 permits larger straps to be substituted without any necessary change in the partition.

Secured to at least one projecting end portion of the motor shaft is a rotary air impeller with the shroud at the corresponding intake opening. When there are two side walls and two intake openings, the projecting

end portions

46, 46 of the motor shaft carry two rotary air impellers respectively indicated at 74 and 76. The impellers are provided respectively with

blades

78, 80 and 82, 84 uniformly spaced circumaxially. The outer portions of the blades of the two impellers are respectively within the

shrouds

28 and 30, and said portions at their peripheral edges have reasonable running clearances with respect to the shrouds. Otherwise stated, the radii of said outer portions of the blades are only slightly less than the internal shroud radius. The two

impellers

74 and 76 are shown in Fig. 2 as being identical in size and shape except for opposite pitches of their said blades. The

impellers

74 and 76 rotate in the clockwise direction as viewed in Fig. l, and the

blades

78, 80 and 82, 84 have opposite pitches so that they draw air in opposite directions and inwardly through the corresponding shrouds and intake openings and toward the motor 44 and toward the panel or partition 36.

Preferably and as shown, the two

impellers

74 and 76 have the same number of blades and said blades of the two impellers are in circumaxially staggered relationship with each other as shown in Figs. 1 and 2. This staggered relationship substantially reduces noise.

The invention is not necessarily limited as to all of the details of impeller construction, but it is important that the total or aggregate width of all of the blades of each impeller be relatively large with a corresponding relatively large total or aggregate blade area. In order to provide the required total blade width each impeller preferably comprises two separate sheet metal blade members as illustrated in Fig. 4, the blade members for the front impeller 74 being shown. Said blade members have circular

central portions

86 and 88 and said central portions are in engagement. As shown, the central portion 86 of the blade member which is at the front has the blades 78 formed integrally therewith and the central portion 88 of the blade member which is at the rear has the blades 80 formed integrally therewith. Said

central portions

86 and 88 of the two blade members are suitably connected to a hub 90 and said blade members are so located on the hub 90 that said

blades

78 and 88 are in staggered circumaxial relationship with each other. By providing two separate blade members, the

blades

78, 78

and 80, 30 can be much wider than would be possible if there were only a single blade member. As shown, there are four blades 78 on one blade member and four blades 80 on the other blade member, but the invention is not limited as to the number of blades.

The hubs 90 of the two impellers are connected by set screws 92 to the corresponding motor shaft portions 46 so that portions of the impeller blades are within the shrouds as previously stated.

Each of said

blades

78, 78 and 80, 80 on the two blade members has an outer leading edge 96 and an inner trailing edge 98 and the two edges are preferably parallel with each other and with a radial line through the center of the blade. Said leading and trailing

edges

96 and 98 are relatively long so as to provide the main section thereof with a relatively large effective area, but, as shown, the bladeis so formed that the trailing edge 98 is somewhat shorter than the leading edge 96. Each blade is twisted at its root portion 94 to provide a suitable pitch angle as hereinafter more fully explained. Said root portion 94 of each blade is preferably located near the outer edge thereof, as clearly shown in Fig. 2, so that the main section of the blade projects or overhangs inwardly. The said main sections of the blades are suitably curved as also hereinafter more fully explained. After twisting, the leading edges 96 of all blades are approximately in a plane perpendicular to the central axis, and the trailing edges 98 of all blades are approximately in another plane perpendicular to the central axis. Said plane of the leading edges 96 is at least approximately coincident with the plane of the corresponding side wall, and said plane of the trailing edges 98 is near the panel or partition 36. As shown, all portions of the outer or peripheral edges of the aforesaid main sections of the blades are equidistant from the axis 12, but this is not always essential as will be hereinafter explained. Preferably, the

blades

78, 78 and 80, 80 are so related to their corresponding

central portions

86 and 88 that said blades have registering rotative paths. Figs. 1 and 2 of the drawings show a blower unit wherein the housing has two opposite intake openings and wherein a single motor supports and drives two impellers respectively adjacent said intake openings. However, the invention is not limited to a two-impeller unit and as to certain aspects it comprehends aunit having only one impeller. Fig. 4 shows a unit having only one impeller, this unit being identical in construction with the left portion of the two-impeller unit shown in Fig. 2. In view of the identityof construction no detailed separate description is necessary as to the alternative unit.

The presently preferred shape and pitch of each blade and the relationship of the blade to other parts are illustrated in Fig. 4 and in the schematic Fig. 5. Fig. 5 is applicable to the two-impeller unit as shown in Figs. 1 to 4 and is also applicable to the single-impeller unit as shown in Fig. 4

Each blade is transversely curved, preferably circularly, to provide a concave face at the leading or pressure side. of the curve thereof as represented by a in Fig. 5 is from to 20% of the length of the blade chord represented by b. The optimum camber a may be about of b.

The mean pitch angle of each blade with respect to a plane parallel to the axis as represented at c is within the range of 45 to 60, and the optimum mean pitch angle may be about 50. The blade curvature and the blade pitch angle are such that a tangent to the curvature at the trailing edge is approximately perpendicular to the panel 36 and approximately parallel with the axis 12.

As has been stated, it is important to provide a large aggregate blade width for each impeller and therefore a large aggregate blade area. With a large pitch angle such as above stated, the axially projected width of each blade is much less than the actual width measured along the curvature of the blade, but even so the axially projected width is large. The axially projected width of each impeller blade at or approximately at the periphery of the blade portion within the corresponding shroud is indicated at d in Fig. l. The aggregate of the axially projected widths of all of the blades at or approximately at the peripheries is 50% or more of the circumference of a circle including said peripheries. The required width and area of each blade are a function of the number of blades, and it will be obvious that, for any chosen aggregate blade width and area, the width. and area per blade would decrease proportionately to an increase in the number of blades.

When the pitch angle is within the range of 45 to 60 and when the aggregate of the axially projected blade Widths is 50% or more of the circumference of a corresponding circle as above stated, it will be evident that the aggregate of the actual widths measured along the curvature of the blades is on the order of 100% of the corresponding circle.

It is important that the blades of each impeller be properly located axially with respect to the corresponding shroud. In Fig. 5 the line e represents the plane of the inner edge of the shroud 28, the line f represents the plane of the outer edge of the cylindricalportion of the shroud, the line g represents the plane of the housing side wall, and the line It represents the plane of the inner edges of the impeller blades. The outer edges of the blades are shown as being at said line g representing the plane of the housing side wall. The dimension i between the lines g and h is the total laterally projected depth of the blades, that is, the depth projected in the direction of rotation or on a radial plane through the axis 12. Stated otherwise, the dimension i is the distance between'the plane of rotation of the leading edges of the blades and the plane of rotation of the trailing edges of the blades. The dimension j between the lines 2 and h is the laterally The blade is so curved that the depth or camber projected depth of the exposed or protruding portion of i the blades that extends axially inwardly beyond the end of the corresponding shroud at e. Said dimension i should be within the range of 60% to of said dimension i representing the total projected depth of the blades; The dimension k between the lines 1 and e is the total Said dimension I should be at least 30% of the dimension 1' which is the total laterally projected depth of the blades. The shroud may also project outwardly from the housing and the dimension k may therefore be larger than the dimension 1, but this is not essential.

The projected depth of the main section of each blade is such that the trailing portion of said main. section overlies the motor 44 to a substantial extent and moves around said motor, the trailing inner edges 98 of the blades being in a plane between the partition 36 and the end of the motor casing. This conserves space and makes it possible for the overall width of the unit to be substantially less than .would otherwise be necessary. Furthermore, the said location of the trailing portions 100 of the blades improves air circulation around the motor so that the motor is more effectively cooled. In order to further conserve space and to provide a minimum overall width of the blower unit, the portions 100 of the blades extend axially inwardly so that the trailing edges 98 of the blades are relatively close to the second wall or partition 36.

Referring again to Fig. 5, the line m represents the edge of the motor casing, and the dimension n represents the projection or overhang of the blades with respect to the motor. Said dimension it varies substantially with the length of the selected motor, but it is shown as being about 35% of the dimension i which is the total projected depth of the blades. The dimension 0 represents the width of the housing between the side wall 16 andthe second wall or partition 36. The dimension p' is the spacing between the plane of the inner or trailing edges 98 of the blades and the second wall or partition 36 and said dimension p should be as small as reasonably possible. Said dimension p is shown as being about 7% of the dimension 0.

It will be apparent from the drawings and from the foregoing description, that the air as moved by the blades of 'each impeller has three directional components of movement.

tangentially in the direction of impeller rotation. The portion of the projected blade depth which the air initially engages is located within the corresponding shroud as previously stated, and therefore the initial air movement has little or no radially outward component. In the portion of the projected blade depth that extends radially inwardly beyond the shroud, the air continues'to move axially, such movement being limited by the partition 36, and in the last said portion of the blade depth, the air also moves radially outwardly. The radially outward component of the air movement is the resultof centrifugal action and pressure is developed in the air as discharged from the tips of the blades. The space in each chamber within the housing and around the corresponding impeller is entirely unobstructed and said air under pressure is delivered into said surrounding space. The corresponding shroud projects into me chamber and,

therefore, the space in the outer portion of the chamber duplex, there being two chambers in the housing at oppo;

site sides of a central partition each of which chambers has an intake opening and a shroud, and there being'two Said air moves axially toward the partition 36, said air moves radially outwardly, and said air moves impellers respectively in the chambers and located respectively at the intake openings. While a duplex unit may ordinarily be preferred, it is to be understood that the invention, as to some aspects thereof, is not so limited.

Figs. 6 and 7 show an alternative construction which is or may be like that shown in Figs. 1 to 5, except that there are

different impellers

74 and 76 wherein the portions of the blades 78*, 80 82 and 84 that extend axially inwardly beyond the shrouds have projections 102 that extend radially outwardly beyond the radius of the shrouds. The blades at the projections 102 have a substantially greater radius, and this increases the effective areas of the blades.

To facilitate assembly of the unit as shown in Fig. 6, the

side walls

16 and 18 have openings therein large enough to receive the larger impellers. The circular angle rings 32 and 34 are larger and are of such size as to engage the side walls beyond said openings. Instead of being welded in place, the rings 32 and 34 may be fastened by screws 164. Thus the

shrouds

28 and 30 can be assembled and attached after the impellers are in place.

Figs. 8 and 9 show another alternative construction which is or may be similar to that shown in Figs. 1 to 5, except that there are

impellers

74 and 76 having different diameters with

shrouds

28 and 30 having correspondingly different diameters. As shown, the front impeller 7 thas a diameter substantially smaller than that of the rear impeller 76. The smaller impeller blades are represented at 78 80 and the larger impeller blades are represented at 82 84 In the construction shown in Figs. 8 and 9, the two impellers have different capacities, and the partition 36 need not be exactly midway between the side walls. This unit is particularly useful when there are two bodies of air which must be handled separately. In this case, two separate discharge ducts, not shown, would be connected to the discharge outlet at 24, the dividing wall between the ducts being extended to engage the partition 36 at the edge 40. When there are two separate bodies of air, they may be at different pressures and it may be desirable to prevent any flow through the central opening 42 in the partition 36. To this end a sealing ring 106 of flexible material, as shown in Fig. 9, may be attached to the motor supporting strap 4'5 and may be held in engagement with the partition 36. This ring is not attached to the partition and therefore does not affect the resilient mounting of the motor 44.

According to present practice, blower units for small domestic appliances and for such appliances as warm air furnaces and package air conditioners ordinarily comprise centrifugal blower wheels having forwardly curved blades. The performance of a blower unit of this type is graphically presented by the dotted curves of the chart in Fig. 10, it being assumed that the impellers are rotated at a constant speed of 1000 rpm. The curve A shows the relationship between the pressure developed by the blower unit and the volume of air that it can move or the air flow, and the curve B shows the relationship between the volume of air flow and the necessary brake horsepower. It will be understood that said curves A and B are inr tended to be merely illustrative and not to accurately represent any actual application.

It is normal practice to design the blower unit to provide a chosen air flow at a chosen pressure with the motor operating under normal conditions. in the illustrated example, the chosen air flow is about 260 c.f.m. and the chosen pressure is about .44 inch as represented by the point C on curve A. This point C corresponds to a brake horsepower output of about .037 as represented by the point D on curve B. The said brake horsepower is well within the normal operating range of the selected motor.

In many installations, as in a warm air furnace system for example, situations may arise by the opening of dampers or otherwise wherein the air flow is increased is no overloading.

far beyond the normal air flow for which the unit was designed. For instance, the air flow may be increased to that represented by the point E, that is, about 420 c.f.m. The said increase in air flow requires an increase in brake horsepower to that represented by the point F on curve B, or about .063 horsepower. This increase in brake horsepower greatly overloads the motor and may result in serious damage thereto if continued. Obviously, the degrees of motor overloading would be even more serious with a greater increase in air flow.

In a blower unit embodying the present invention, whether as shown in Figs. 1 to 5 or in Figs. 6 and 7 or in Figs. 8 and 9, the described shapes of the impeller blades and the relationship of the blades with other parts serve to eliminate, or to at least greatly reduce, the abovedescribed limitations inherent in blower units as heretofore provided. Assuming that the same motor is selected, the full line curves A and B correspond respectively to the previously described dotted line curves A and B. It should be particularly observed that curve B is almost fiat and varies only slighty from a straight line and that it represents only relatively small increases in brake horsepower for increases in air flow. It is assumed that the blower unit embodying the invention was designed for the same chosen air flow, and the point C is therefore common to curves A and A. The brake horsepower is that represented by the point D which is common to the curves B and B.

if the air flow is increased to the same extent as before, that is, to that represented by the point B on curve A, the increase in brake horsepower is only to that represented by the point P on the curve B, that is, about .045. The slightly increased brake horsepower is well within the normal operating range of the motor and there Even with an additional opening of dampers and with a much greater increase in air flow, there would be no abnormal increase in loading. As illustrated by curves A and B, the increase in horsepower is only about 55% when the air flow is increased from about 10G c.f.m. to about 500' c.f.m.

A blower unit embodying the invention eliminates overloading of the motor as above described. Furthermore, it is possible to use a unit for a variety of installations having widely different air-flow requirements. For example, the unit as above described could be used, without motor overloading, for various air flow requirements ranging from perhaps c.f.m. to perhaps 500 c.f.m. This greatly facilitates manufacture and sale as only a very few different sizes and designs of units would be needed for all requirements of customers. A blower unit embodying the invention has the further advantage that it is smaller and less expensive than prior units of comparable capacity.

The invention claimed is:

1. In a blower unit, the combination of a housing including a front side wall having a circular intake opening concentric with a central axis and including a second wall behind said front wall and parallel therewith, said housing having a peripheral discharge opening and having a chamber therein which is substantially closed except for said intake and discharge openings and which is unobstructed except for some of the hereinafter stated parts, a cylindrical shroud fitted within said intake opening, an electric motor including a drive shaft, means for supporting said motor with its drive shaft concentric with said central axis and with a portion of said shaft projecting toward the plane of said front wall, and an air impeller comprising a hub and a plurality of uniformly spaced blades connected with said hub and extending generally radially therefrom which hub is secured to the projecting portion of said motor shaft and is so located that the outer portions of its blades are within said shroud, said outer portions of the blades of the impeller having radii only slightly less than the internal shroud radius and said blades in their entireties being so pitched that said impeller amt-as V 9 r a r i 7 serves upon rotation by the motor to draw air inwardly through the shroud and intake opening and each blade of said impeller having a mean pitch angle with respect to a plane parallel to said axis which is within the range of 45 to 60 and each blade of said impeller having a portion of its laterally projected depth extending axially inwardly beyond the shroud to an extent Within the range of 60% to 70% of the total laterally projected depth.

2. A blower unit asset forth in claim 1, wherein each blade of the impeller is transversely curved to provide a concave face at the leading or pressure side and is so curved that the camber of its curve is within the range of 10% to of the length of the blade chord.

3. A blower unit as set forth in claim 1, wherein a portion of the shroud extends inwardly from the front side wall andtwherein the length of the last said portion of the shroud is at least of said total laterally projected depth of the blades of the impeller.

4. A blower unit as set forth in claim 1, wherein said electric motor includes a casing which is located at least partly within the housing chamber and wherein each blade of the impeller has a substantial portion of its laterally projected depth extending axially inwardly beyond the outer end of the motor casing and rotatable around the portion of said motor casing which is within the chamber.

5. In a blower unit, the combination of a housing including parallel side Walls respectively having circular intake openings concentric with a common central axis which housing has a peripheral discharge opening andis closed except for said intake and discharge openings, a thin partition in said housing parallel with and midway between said side walls and having a generally circular opening concentric with said axis, said partition providing two equal chambers within the housing which chambers are completely separated except for said partition opening and which chambers are unobstructed except for some of the hereinafter stated parts, two cylindrical shrouds respectively fitted within said intake openings, an electric motor including a casing and including a drive shaft having portions projecting at both ends of the casing, means'for supporting said motor on. said partition with the casing symmetrically located in said partition opening and with said shaft portions concentric with said central axis and projecting toward the planes of said side walls, and two air impellers each comprising a hub and a plurality of uniformly spaced blades connected with said hub and extending generally radially therefrom which hubs of the two impellers are secured respectively to the projecting portions of said motor shaft and are so located that the outer portions of the blades are within the corresponding shrouds, said outer portions of the blades of the two impellers having radii only slightly less than the internal radii of the shrouds and said blades of the two impellers in their entireties having opposite pitches so that each impeller serves upon rotation by the motor to draw air inwardly through the corresponding shroud and intake opening and each blade of each impeller having a mean pitch angle with respect to a plane parallel to said axis which is within the range of and and each blade of each impeller having a portion of its laterally projected depth extending axially inwardly beyond the corresponding shroud to an extent within the range of 60% to 70% of the total laterally projected depth.

6. A blower unit as set forth in claim 5, wherein the two impellers have the same number of blades, and wherein the uniformly spaced blades of the two impellers are in circumaxially staggered relationship with each other.

7. In a blower unit, the combination of a housing including a front side wall having a circular intake opening concentric with a central axis and including a second wall behind said front wall and parallel therewith, said housing having a peripheral discharge opening and having a chamber therein which is substantially closed except for said intake and discharge openings and which is un u 1G,,r obstructed exceptfor the hereinafter stated parts, a cylindrical shroud fitted within said intake opening, anlelectric motor including a drive shaft, means for supporting said motor'within its drive shaft concentric with said central axis and with a portion of said shaft projecting toward the plane of said front wall, and an airlimpeller comprising a hub and a plurality of generally radial uniformly spaced blades connected with said hub and extending generally radially therefrom which hub is secured to the projecting portion of said motor shaft and is so located that the outer portions of the blades are within said shroud, said outer portions of the blades of the impeller having radii only slightly less than the internal shroud radius and said blades in their entireties being so pitched that said impeller serves upon rotation by the motor to draw air inwardly through the shroud and intake opening and each blade of said impeller having a mean pitch angle with respect to a plane parallel to said axis which is within the range of 45 to 60 and the blades of said propeller being of such laterally projected depths and so located that their outer leading edges are approximately in the plane of said front wall and that their inner trailing edges are close to said second wall so that the width of the housing between saidrfront wall and said second wall is only slightly greater thanthe total laterally projected depths of the blades of the impeller.

8. In a blower unit, the. combination of a housing including parallel side walls respectively having circular intake openings concentric with a common central axis which housing has a peripheral discharge opening and is closedexcept for said intake and discharge openings, a thin partition in said housing parallel with and midway between said side walls and having a generally circular opening concentric with said axis, said partition providing two equal chambers withinthe housing, which chambers are completely separated except for said partition opening and which chambers are unobstructed except for the hereinafter stated parts, two cylindrical shrouds respectively fitted within said intake openings, an electric motor including a casing and including a drive shaft having portions projecting at both ends of the casing, means for supporting said motor on said partition with the casing symmetrically located in said partition opening and with said shaft portions concentric with said central axis and projecting toward the planes of said side walls, and two air impellers each comprising a hub and a plurality of uniformly spaced blades connected with said hub and extending generally radially therefrom which hubs of the two impellers are secured respectively to the projecting portions of said motor shaft and are so located that the outer portions of the blades are within the corresponding shrouds, said outer portions of the blades of the two impellers having radii only slightly less than the internal radii of the shrouds and said blades of the two impellers in their entireties having opposite pitches so that each impeller serves upon rotation bythe motor to draw air inwardly through the corresponding shroud and intake opening and each blade of each impeller having a mean pitch angle with respect to a plane parallel to said. axis which is vw'thin the range of 45 to 60 and the blades of each propeller being of such laterally projected depths and so located that their outer leading edges are approximately in the plane of the corresponding side wall and that their inner trailing edges are close to the central partition so that the total width of the housing is only, slightly greater than the, total of the laterally projected cylindrical shroud fitted within said intake opening, an electric motor including a drive shaft, means for supporting said motor with its drive shaft concentric with said central axis and with a portion of said shaft projecting toward the plane of said front wall, and an air impeller comprising a hub and a plurality of generally radial uniformly spaced blades connected with said hub and extending generally radially therefrom which hub is secured to the projecting portion of said motor shaft and is so located that the outer portions of the blades are within said shroud, said outer portions of the blades of the impeller having radii only slightly less than the internal shroud radius and said blades in their entireties being so pitched that said impeller serves upon rotation by the motor to draw air inwardly through the shroud and intake opening and each blade of said impeller having a mean pitch angle with respect to a plane parallel to said axis which is within the range of 45 to 60 and the aggregate of the axially projected widths of all of the blades of said impeller approximately at the periphery of the portion within the shroud being at least 50% of the circumference of a circle including said periphery.

10. A blower unit as set forth in claim 9, wherein each blade of the propeller has a portion extending radially inwardly beyond the shroud which last said portion has a laterally projected depth which is within the range of 60% to 70% of the total laterally projected depth.

11. A blower unit as set forth in claim 9, wherein the impeller includes two separate blade members each provided with one-half of the blades which members have central portions in engagement with each other and connected to the hub and are so relatively positioned that all of the blades are uniformly spaced circurnaxially.

12. A blower unit as set forth in claim 11, wherein said electric motor includes a casing which is located at least partly within the housing chamber, wherein each blade is connected with the central portions of the corresponding blade member by a narrow neck located near one side of the blade, and wherein said neck has been twisted relatively to said central portion to provide the required mean pitch angle and to position the trailing portion of the blade and the trailing edge thereof axially inwardly beyond the portion of said motor casing which is within the chamber,

13. A blower unit as set forth in claim 12, wherein the blades of the impeller are of such width and so located that their outer leading edges are approximately in the plane of the front side wall and that their inner trailing edges are close to the second wall so that the total width of the housing is only slightly greater than the total of the projected depths of the blades of the two impellers.

14. In a blower unit, the combination of a housing including parallel side walls respectively having circular intake openings concentric with a common central axis which housing has a peripheral discharge opening and is closed except for said intake and discharge openings, a thin partition in said housing parallel with and midway between said side walls and having a generally circular opening concentric with said axis, said partition providing two equal chambers within the housing which chambers are completely separated except for said partition opening and which chambers are unobstructed except for the hereinafter stated parts, two cylindrical shrouds respectively fitted within said intake openings, an electric motor including a casing and including a drive shaft having portions projecting at both ends of the casing, means for supporting said motor on said partition with the casing symmetrically located in said partition opening and with said shaft portions concentric with said central axis and projecting towardthe planes of said side walls, and two air impellers each comprising a hub and a plurality of uniformly spaced blades connected with said hub and extending generally radially therefrom which hubs of the two impellers are secured respectively to the projecting portions of said motor shaft and are so located that the outer portions of the blades are within the corresponding shrouds, said outer portions of the blades of the two impellers having radii only slightly less than the internal radii of the shrouds and said blades of the two impellers in their entireties having opposite pitches so that each impeller serves upon rotation by the motor to draw air inwardly through the corresponding shroud and intake opening and each blade of each impeller having a mean pitch angle with respect to a plane parallel to said axis which is within the range of to 60 and the aggregate of the axially projected widths of all of the blades of each impeller approximately at the peripheries of the portions within the shrouds being at least of the circumference of a circle including said peripheries.

15. A blower unit as set forth in claim 14, wherein each blade of each propeller has a portion extending axially inwardly beyond the corresponding shroud which last said portion is within the range of to of the total projected depth.

16. A blower unit as set forth in claim 14, wherein each impeller includes two separate blade members each provided with one-half of the blades which members have central portions in engagement with each other and connected to the corresponding hub and are so relatively positioned that all of the blades are uniformly spaced circumaxially, wherein each blade is connected with the central portions of the corresponding blade member by a narrow neck located near one side of the blade, wherein said neck has been twisted relatively to said central portion to provide the required mean pitch angle and to position the trailing portion of the blade and the trailing edge thereof axially inwardly beyond the corresponding outer end of the motor casing, and wherein the blades of each impeller are of such width and so located that their outer leading edges are approximately in the plane of the corresponding side Wall and that their inner trailing edges are close to the central partition so that the total width of the housing is only slightly greater than the total of the projected depths of the blades of the two impellers.

17. In a blower unit, the combination of a housing including parallel side Walls respectively having circular intake openings concentric with a common central axis which housing has a peripheral discharge opening and is closed except for said intake and discharge openings, a thin partition in said housing parallel with and midway between said side walls and having a generally circular opening concentric with said axis, said partition providing two equal chambers within the housing which chambers are completely separated except for said partition opening and which chambers are unobstructed except for the hereinafter stated parts, two cylindrical shrouds respectively fitted within said intake openings, an electric motor including a casing and including a drive shaft having portions projecting at both ends of the casing, means for supporting said motor on said partition with the casing symmetrically located in said partition opening and with said shaft portions concentric with said central axis and projecting toward the planes of said side walls, and two air impellers each comprising a hub-and a plurality of uniformly spaced blades connected with said hub and extending generally radially therefrom which hubs of the two impellers are secured respectively to the projecting portions of said motor shaft and are so located that the outer portions of the blades are within the corresponding shrouds, said outer portion of the blades of the two impellers having radii only slightly less than the internal radii of the shrouds and said blades of the two impellers in their entireties having opposite pitches so that each impeller serves upon rotation by the motor to draw air inwardly through the corresponding shroud and intake opening and each blade of each impeller having a mean pitch angle with respect to a plane parallel to said axis which is within the range of 45 to 60 and a substantial portion of the laterally projected depth of each blade of each 13 impeller extending axially inwardly beyond the corresponding shroud and having a radius substantially greater than that of the portion within the shroud.

18. A blower unit as set forth in claim 17, wherein the laterally projected depth of said inwardly extending portion of each blade is within the range of 60% to 70% of the total laterally projected depth of the blade.

19. A blower unit as set forth in claim 18, wherein each blade of each impeller has a substantial portion of its laterally projected depth extending axially inwardly beyond the corresponding outer end of the motor casing and rotatable around said casing.

20. In a blower unit, the combination of a housing including parallel side walls respectively having circular intake openings with different radii concentric with a common central axis which housing has a peripheral discharge opening and is closed except for said intake and discharge openings, a thin partition in said housing parallel with and between said side walls and having a generally circular opening concentric with said axis, said partition providing two chambers within the housing which chambers are completely separated except for said partition opening and which chambers are unobstructed except for the hereinafter stated parts, two cylindrical shrouds with different radii respectively fitted within said intake openings, an electric motor including a casing and including a drive shaft having portions projecting at both ends of the casing, means for supporting said motor on said partition with the casing symmetrically located in said partition opening and with said shaft portions concentric with said central axis and projecting toward the planes of said side walls, and two air impellers each comprising a hub and a plurality of uniformly spaced blades connected with said hub and extending generally radially therefrom and respectively having outer portions with diiferent radii conforming to the radii of the corresponding shrouds which hubs of the two impellers are secured respectively to the projecting portions of said motor shaft and are so i4 located that the said outer portions of the blades are within the corresponding shrouds, the blades of the two impellers having radii only slightly less than the internal inwardly through the corresponding intake opening and' each blade of each impeller having a pitch angle with respect to a plane parallel to said axis that is within the range of to 21. A blower unit as set forth in claim 20, wherein the laterally projected depth of said inwardly extending portion of each blade is within the range of 60% to of the total laterally projected depth of the blade.

22. A blower unit as set forth in claim 20, wherein each blade of each impeller has a substantial portion of its later-ally projected depth extending axially inwardly beyond the corresponding outer end of the motor casing and rotatable around said casing.

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