EP0846868A2

EP0846868A2 - Centrifugal blower assembly

Info

Publication number: EP0846868A2
Application number: EP97203477A
Authority: EP
Inventors: Mark Joseph Parisi; Stephan Michael Vetter
Original assignee: Motors Liquidation Co
Current assignee: Motors Liquidation Co
Priority date: 1996-12-05
Filing date: 1997-11-10
Publication date: 1998-06-10
Also published as: JPH10176696A; EP0846868A3

Abstract

A centrifugal blower assembly (10) includes a volute housing (12) of the axially asymmetrically expanding type, with an upper end wall (24) flattened off for ease of installation and a spiraling lower end wall (26) and tangential outlet (34) that are consequently both downwardly axially displaced relative to the flat end wall (24) and the cylindrical air inlet (28) into the housing (12). To counteract the flow inefficiency that normally results from the axial displacement of inlet (28) relative to outlet (34), the blower (12) is formed with a curved tip ring (44) and correspondingly curved, axially opposed base rim (42) that shift axially downwardly from an air entrance (36) that is shifted axially above the flat end wall (24) and cylindrical inlet (28). Air drawn in through the entrance (36) by the blower (14) is thereby given a significant axially downward velocity component, which causes it to approach and better conform to the axially displaced end wall (26).

Description

TECHNICAL FIELD

This invention relates to centrifugal blower assemblies of the type used in automotive applications.

BACKGROUND OF THE INVENTION

Centrifugal blowers (often called impellers) have been used extensively in automotive heating and air conditioning systems for some time. In general, a centrifugal blower consists of a series of radially disposed, axially extending blades that are rotated about a central motor drive shaft axis. The blower sits within and is surrounded by a so called volute housing. The blades force air radially outwardly, thereby pulling outside air in one axial direction down the center of the blower through an air entrance into the housing, or sometimes through in both directions through two air entrances. The drawn-in air is forced radially outwardly and is captured between four walls of the volute housing that surround the blower and define a spiral air flow space. These four walls typically include a cylindrical inner wall and a radially opposed outer wall that spirals around the inner wall, moving progressively radially farther away therefrom in the direction of blower rotation. The inner and outer walls are typically bounded by two substantially flat axially opposed end (or side) walls, which are generally axially spaced apart by the same amount at every point. Air leaving the blower enters the spiral air space through a cylindrical inlet opening cut through the inner wall, usually subtending a full 360 degrees. The spiral air space also has a tangential outlet formed by the terminal edges of the four housing walls, and the outlet is generally axially aligned with the housing inlet opening. Air passing through the inlet swirls around in the direction of blower rotation, finally exiting the tangential outlet. The blower is mounted within and surrounded by the housing inner wall, so that the blower blades are axially aligned with the housing inlet opening. As a consequence, air exiting the blower blades has a radially outward velocity, but no deliberate or distinct axial velocity component in either axial direction. However, it has been noted in the prior art that the air entering the volute housing can rebound axially from the end walls, causing vortices which, while they are damped out and indistinguishable by the time the tangential outlet is reached, tend to decrease efficiency.

A variation on the standard volute housing has the two axially opposed end walls moving progressively apart, as the radially opposed peripheral walls do, in the direction of blower rotation. Examples may be seen in USPN 3,246,834 issued April 19, 1966 to Swenson (end walls 8, referred to as "side walls") and USPN 3,407,995 issued October 29, 1968 to Kinsworthy (end walls 35, also referred to as "side" walls). Volutes with both radial and axial expansion have been known for several decades, and rather complex formulae have been proposed for governing the degree of end wall axial expansion. This type of housing has proved particularly useful with a centrifugal blower of the type having rearwardly inclined blades. With rearwardly inclined blades, a higher static pressure is achieved, but a more radially expansive and radially wider volute is generally needed to provide sufficient air space expansion for efficient flow. Allowing for a degree of simultaneous axial expansion allows a radially narrower, and more radially compact volute to be used. One consequence of the end (side) walls moving progressively farther apart is that the axial width of the tangential outlet becomes significantly greater than the volute's inlet opening, although it is still axially symmetrical relative to the inlet opening, since the end walls expand axially symmetrically. Another consequence is that neither end wall is flat. Instead, both have a general corkscrew shape. This can be a disadvantage when mounting the volute housing to a flat panel, which is often necessary. An axially symmetrically expanding volute lacks a large, 360 degree flat surface area anywhere, which is preferred for secure, stable mounting.

Therefore, it has been proposed to hold a first end wall flat, while building all the axial expansion into the opposed end wall. The overall axial expansion between the end walls can be the same, but the flatness of the first end wall makes the volute housing much easier to mount a flat surface. A good example may be seen in USPN 5,156,524, issued October 20, 1992 to Forni particularly in Figure 1b thereof. As can be clearly seen there, the inlet opening and the axially wider outlet opening are no longer axially symmetrical to one another. Instead, the axially wider tangential outlet, especially the non flat second end wall thereof, is displaced in one axial direction relative to the narrower inlet opening. The blower, though not well illustrated, apparently still sits within the inner peripheral wall of the volute housing, presumably axially aligned with the volute housing inlet opening cut through the volute's inner peripheral wall (which is also not well illustrated). The 5,156,524 patent proposes an extremely complex formula for the volute shape, supposedly to improve the air flow efficiency, but does not describe specifically the axial asymmetry that the housing inlet opening (and blower, presumably) has relative to the tangential outlet, nor any negative effect on air flow due to that asymmetry.

Patents describing various designs for the volute housing often say little about the design of the centrifugal blower itself, although it is sometimes indicated whether the blades are forwardly or rearwardly inclined (sometimes referred to as forwardly or rearwardly curved.) Some patents describe very specific angles for the lead and trailing edges of the blower blades. However, less attention is typically paid to the rest of the blower, that is, to the structural elements that actually physically support the blades in the blower. Still, a pattern is evident across the various patents that describe different volute housing designs, and which also show some detail for the blower. In a typical centrifugal blower, the blades, whether forwardly or rearwardly curved, are radially disposed, like spokes of a wheel, and are axially captured between an upper tip ring and a lower base rim. The tip ring is basically an annulus, although it may be concave, like a section of a bowl. The base rim is also basically an annulus, and while it may be integral to a bowl shaped central dome, it is generally flat itself. The dome is designed to clear the upper end of the motor that spins the drive shaft, and the drive shaft is fixed to the center of the dome. The reason for the axially downward and radially outward curvature in the tip ring is to create a substantially constant air flow area between the tip ring and the base rim, as air moves radially outward through the blower blades and axially between the tip ring and base rim. There is no reason for the base rim to be anything but flat, however. A good example of this basic blower design may be seen in Figure 1 of USPN 4,946348 issued August 7, 1990 to Yapp, which has radially disposed blades, a concave upper tip ring, and flat lower base rim integral to a dome shaped hub. Two other common characteristics of centrifugal blowers relative to the blower housing is also evident, although the housing is not a volute housing there. First, the blower is located well down inside the blower housing, and does not extend very far, if at all, above the upper end wall of the housing. Consequently, the housing air entrance, which is just above the inner edge of the blower tip ring, also does not extend very far above the upper end wall of the housing. Second, the blower is generally substantially axially aligned with the cylindrical housing inlet opening. That is, the outer circular edges of the blower tip ring and base rim are both concentric to, and near, the respective upper and lower edges of the housing inlet opening. Being flat, the entire base rim is axially aligned with the lower axial edge of the housing inlet opening. As noted above, air pumped radially outwardly and out through the housing inlet opening by such a blower has no defined axial component. In the design shown in the Yapp patent, it is desired to turn that air flow and send it axially down through an annular envelope surrounding the motor housing. This must be done with a separate spiral airfoil vane around the motor housing.

SUMMARY OF THE INVENTION

A centrifugal blower assembly in accordance with the present invention is characterised by the features specified in claim 1.

In the preferred embodiment disclosed, the blower assembly includes a volute housing that has several structural features common to a typical axially expanding, but axially asymmetrical volute housing of the typed described above. That is, it has a flat upper end wall and a lower end wall that spirals steeply axially away from the upper end wall. The housing inlet is axially displaced above the tangential outlet, with an upper circular edge that is near the flat upper end wall, and a lower circular edge that sits axially well above the lower end wall. Unlike conventional axially asymmetrical volute housings, however, the circular air entrance to the housing is displaced axially well above the flat upper end wall and above the upper edge of the housing inlet opening, rather than being nearly flush to the flat upper end wall. More generally stated, the circular air entrance is displaced relative to the cylindrical housing inlet opening in the axial direction opposite to the direction in which the lower end wall is displaced relative to the housing inlet opening.

The centrifugal blower assembly also has a centrifugal blower with some structural features common to a typical centrifugal blower. It has radially disposed blades held between a generally annular tip ring and base rim, which is integral to a bowl shaped central dome. However, the tip ring curves radially outwardly and axially downwardly more steeply than is conventional. The base rim, rather than being flat, curves in the same direction as the tip ring, though not as steeply. Within the blower housing, after the dome has been fixed to the motor shaft, the inner circular edge of the tip ring is located concentric to and near the circular air entrance of the housing and, therefore, axially well above the upper edge of the housing air inlet. The tip ring slopes steeply down to an outer edge located concentric and near to the inlet opening upper edge. The base rim, since it is not flat, is not completely axially aligned with the lower edge of the housing inlet opening. Instead, the base rim begins at an inner circular edge that is between the two edges of the housing inlet opening, and slopes axially downwardly and radially outwardly to an outer circular edge, which is concentric to and axially aligned with the lower edge of the housing inlet opening. While the base rim is not sloped as steeply as the tip ring, the general trend of the cylindrical space between the tip ring and base rim ( as measured moving progressively radially outwardly) is a gradual decrease in height coupled with a gradual axial downward shift of the space per se, that is, down toward the lower edge of the inlet opening.

The unique shape of the space between the more highly sloped tip ring and the curved base rim, and the axially upward shifting (relative to the housing inlet) of both the upper edge of the blower and the housing air entrance creates a different air flow. The air that is drawn in through the entrance by the rotating blower and sent radially outwardly through the blades and into the cylindrical housing inlet is given a significant axially downward component of velocity, by virtue of being simultaneously forced axially downwardly between the tip ring and base rim, as it passes radially through the blades. As a consequence, the air is forced axially downwardly and toward the axially displaced housing end wall, and flows through the entire spiral air space of the volute housing more efficiently.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 is a perspective view of a preferred embodiment of the blower assembly of the invention, with approximately a quarter section of the assembly cut away;

Figure 2 is a cross section through the volute housing and the centrifugal blower, which together constitute the two main components of the blower assembly of the invention, shown disassembled;

Figure 3 is a perspective view of just the centrifugal blower, with approximately a quarter section cut away; and

Figure 4 is a cross section through the assembled centrifugal blower assembly of the invention, indicating the direction and pattern of air flow.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Referring first to Figures 1 and 2, a centrifugal blower assembly according to the invention, has a preferred embodiment of which is indicated generally at 10, has two main components, and a volute housing, indicated generally at 12, and a centrifugal blower, indicated generally at 14, both of which are made up of molded plastic parts. Blower 14 is rotated counterclockwise, by a motor drive shaft 16, about a central axis indicated at A. Shaft 16 is part of a conventional electric motor 18. As best seen in Figure 1, volute housing 12 is the axially expanding, but axially asymmetrical type. As such, a spiral air space is formed around the central axis A, defined by four walls. These include two radially opposed peripheral walls, an inner, generally cylindrical wall 20 and an outer wall 22 that spirals continuously farther away from inner wall 20, moving in the direction of rotation. Thus, the three successive radial dimensions shown, R1 through R3, are progressively greater, and are determined according to conventional and well established formulae. The other two walls defining the spiral air space are a first, upper end wall 24, which is flat, and a second, spiraling lower end wall 26. Upper and lower are understood to be terms of convenient reference related to the orientation of the drawing on the page, and are not intended to be limiting as to the orientation of the blower assembly 10 per se. The two end walls 24 and 26 move axially progressively away from one another, moving in the direction of rotation. Therefore, three successive axial spacings of the end walls 24 and 26 from one another, Z1 through Z3, are progressively larger, also determined by well established formulae. Air leaving the blower 14 enters the spiral air flow space so defined through a generally cylindrical inlet opening in the inner wall 20, indicated at 28 in Figure 2. Inlet opening 28 removes a good deal of the area of inner wall 20, and is defined by an upper circular edge 30 and lower circular edge 32, which have a constant axial separation. The upper circular edge 30 is actually a corner molded into (and axially flush with) the flat upper end wall 24, 360 degrees around, while the lower circular edge 32 is a narrow radial shelf. Air ultimately leaves the spiral air space through a generally rectangular tangential outlet 34, formed by the terminal edges of the four walls 20-26. Outlet 34 is axially displaced downwardly relative to the inlet opening 28, since the terminal edge of the spiraling end wall 26 is axially spaced away from the flat upper end wall 24 to the greatest degree, Z3, at the outlet 34. This axial displacement of the outlet away from inlet is typical of axially expanding volute housings with one fiat end wall. What is different here is that the outside air entrance to the housing 12 (not to be confused with the housing inlet opening 28 to the spiral air flow space) is defined by a circular lip 36, in conjunction with a coaming 38. Lip 36 sits atop coaming 38, axially well above the flat upper end wall 24, by a distance indicated at H, rather than being almost flush therewith. Lip 36 is riveted separately to coaming 38, which surrounds the inlet upper edge 30 and is molded integrally to the upper end wall 24.

Referring next to Figures 2 and 3, details of the centrifugal blower 14 are illustrated. Like almost any blower, blower 14 has radially disposed, axially extending blades 40, which may be, as illustrated, rearwardly inclined (rearwardly curved). An axially expanding volute housing like 12 is particularly suited for that type of blower, although the invention is not so limited. For purposes of structural integrity, as with a typical blower, the blades 40 are held and confined axially between a lower base rim, indicated generally at 42, and an upper tip ring, indicated generally at 44. Typically, the lower ends of the blades 40 are a molded integral extension of the base rim 42, while tip ring 44 is added to the upper ends of the blades by sonic welding, adhesive, riveting, or any desired fastening process. Base rim 42 may itself be, as in the embodiment disclosed, an integrally molded extension from the outer edge of a semi spherical dome 46. A dome like 46 is a convenient means for joining the entire blower 14 to shaft 16. Still, base rim 42 could be a visually distinct part, rotatably fixed to shaft 16 by some other means, or, dome 46 could be relieved by openings large enough to reduce it to little more than a series of spokes. In any event, base rim 42 may be conceptualized as having an inner circular edge 48 and an outer circular edge 50. A conventional base rim would be flat, with axially aligned inner and outer edges, as indicated by the dotted line in Figure 2. By contrast, base rim 42 slopes axially downwardly and radially outwardly from inner edge 48 to outer edge 50. Tip ring 44 has a shape generally like conventional tip rings, which curve radially outwardly and axially downwardly, from an inner circular edge 52 to an outer circular edge 54. The basic purpose for this is to create an air flow area between the tip ring 44 and base rim 42 that is progressively axially shorter as it grows in radius, so as to hold a substantially constant flow volume. An analogy would be a circular wave moving out from a point disturbance. If the wave grew progressively shorter by the inverse of the increase in radius squared, then it's volume would remain constant. The tip ring 44 here does that as well, but in addition, unlike a conventional tip ring, it also shifts axially downwardly linearly, a downward shift that is in addition to the downward curvature just described. This downward shift is illustrated by the series of double headed arrows in Figure 2 marked X1-X5. These represent the axial height of a cylindrical area confined between the axially opposed inner surfaces of the tip ring 44 and the base rim 42, at progressively increasing radii. Not only does the height of that area shorten, it shifts axially downwardly linearly, in step with the downwardly and outwardly sloping base rim 42. By contrast, a conventional blower would have a nearly flat base rim, as shown by the dotted lines, and the area between the tip ring and base rim would progressively axially shorten, but not shift axially downwardly as well.

The purpose for the unique shapes of the tip ring 44 and base rim 42, as well as for the upward shift of the housing lip 36, may be understood by referring to Figure 4. To assemble the blower assembly 10, blower 14 is fixed to shaft 16, and the lip 36 is riveted to the flat upper edge of coaming 38. This orients the tip ring inner edge 52 near, and basically concentric to the lip 36. The shape of the coaming 38 closely matches and is slightly spaced from the blower tip ring 44, so as to present the smallest possible pressurized air leak path. The lip 36 also axially overlaps the tip ring inner edge 52 slightly, to further block any air leakage. The two outer circular edges of blower 14, the tip ring outer edge 54 and base rim outer edge 50, are both located proximate to and substantially concentric to the respective upper 30 and lower 32 edges of the housing inlet opening 28. Since the base rim 42 is curved, however, its inner edge 48 is not axially aligned with the housing inlet lower edge 32, as would be the case with a conventional flat base rim. Instead, it is intermediate the inlet's two edges 30 and 32, although closer to the lower edge 32. This orientation of the various edges of blower 14 relative to the lip 36 and the housing inlet edges 30 and 32 creates a unique air flow pattern, indicated by the arrows in Figure 4. As the blower 14 is rotated, outside air is drawn axially downwardly through the circular air entrance provided by the lip 36 and into the center of blower 14. Air cannot pass through the dome 46, but instead is forced radially outwardly through the blades 40. Concurrently, since the radially outwardly flowing air is confined in the axially downwardly shifting space defined between the blower tip ring 44 and curved base rim 42, it is forced axially downwardly, that is, toward the housing air inlet opening 28. Since the blower outer edges 54 and 50 sit near the respective housing air inlet edges 30 and 32, air passes through the inlet opening 28 with minimal leakage, and into the volute spiral air flow spaced defined by the four walls 20 - 26. The air flow carries, at this point, a substantial axial velocity component in addition to the radial. This is indicated by the dotted lines R and Z, which represent a resolution of the air flow into radial and axial components respectively. The air flow is actually three dimensional, of course, and is also concurrently spiraling counterclockwise around the axis A. However, its axial velocity component is the feature most relevant to the invention. Because of that axial velocity component, the spiraling air flow will tend to flow around and down, approaching and conforming to the axially displaced lower end wall 26 more closely than it otherwise would. The air flow will also be less likely to rebound axially downwardly from the upper end wall 24, with the resultant flow vortices and reduction in flow efficiency. As a consequence, the flow exiting the axially displaced tangential outlet 34 will also be more regular and efficient, and its axial profile will be more uniform and even. It bears repeating, at this point, that "upper" and "lower" are arbitrary directions. In general, taking the first flattened end wall 24 as a standard reference frame, the second, non flattened end wall 26 is axially displaced in one direction, be that up, down or right, left. Therefore, the tangential housing outlet 34 is displaced relative to the cylindrical inlet opening 28 in the same direction. The fresh air entrance provided by the lip 36 is axially displaced relative to the flattened end wall 24 in the opposite axial direction. And the air flow is given a significant axial component in the direction of axial displacement, so as to mitigate the flow inefficiencies that would otherwise result from that axial displacement and asymmetry.

Variations in the disclosed embodiment could be made. As noted above, the blower hub configured as a semi spherical dome 46 is not new per se, and its particular shape has historically been seen simply as a necessity to clear the end of the motor 18. Nor has a dome shaped hub been continuous, in every design, but is often relieved with very large openings in order to pass cooling air to the motor. In designs where the motor did not intrude up as far, the blower hub has been flat or nearly so, nearly coplanar with the flat base rim. And, as noted, even when the hub has been dome shaped, the base rim has been nearly flat, since there was apparently no perceived reason for it to be anything but flat. Here, however, it can be seen that the curved shape of the dome 46 almost blends into the curvature of the base rim 42. As such, the dome 46 in fact cooperates with and assists the axially opposed base rim 42 and tip ring 44 in imparting the desired axial velocity component to the air flow. In the past, any such axial component imparted to the air flow by the dome 46 was essentially lost when the air hit the flat base rim 42 and was turned back into a radially outward flow. Still, the basic shape of the tip ring 44 and base rim 42 would work if the base rim 42 were integral to a basically flat hub, such as would exist with a motor that did not intrude axially as far upwardly as motor 18. Therefore, it will be understood that it is not intended to limit the invention to just the embodiment disclosed.

Claims

A centrifugal blower assembly (10) having a drive shaft (16) that rotates about a central axis and a volute housing (12) formed by a generally cylindrical inner peripheral wall (20) defined about said central axis an outer peripheral wall (22) that is spaced progressively radially farther away from said inner peripheral wall (20) moving in the direction of rotation, a generally flat first end wall (24), and a second end wall (26) that that is spaced progressively axially farther away from said first end wall (24) in one axial direction moving in the direction of rotation, and in which said housing inner peripheral wall (20) has a generally cylindrical housing inlet opening (28) therethrough with a first circular edge (30) near said flat first end wall (24) and a second circular edge (32) axially spaced from said first circular edge (30), said housing (12) also having a tangential outlet (34), and in which said housing second end wall (26) is displaced in said one axial direction relative to said housing inlet second circular edge (32), characterised in that:
said housing (12) further includes a generally circular air entrance (36) defined about said central axis that is substantially axially displaced to the other axial direction relative to said housing inlet (28), and,
said assembly (10) includes a centrifugal blower (14) fixed to said drive shaft (16), said blower (14) having radially disposed, axially extending impeller blades (40) axially captured between a tip ring (44) and a base rim (42), said tip ring (44) having an inner circular edge (52) that is concentric to and proximate to said circular air entrance (36) and being curved radially outwardly and in said one axial direction to an outer circular edge (54) that is concentric to and proximate to said housing inlet first circular edge (30), said base rim (42) having an inner circular edge (48) that is axially intermediate to said housing inlet circular edges (30,32), said base rim (44) curving radially outwardly and in said one axial direction to an outer circular edge (50) that is concentric to and proximate to said housing inlet second circular edge (32),
whereby, air that is drawn in through said air entrance (36) by said rotating blower (14) is forced radially outwardly and also in said one axial direction between said curved tip ring (44) and curved base rim (42), thereby entering said housing inlet (28) with a significant component of velocity in said one axial direction, thereby moving with increased efficiency along said axially displaced housing second end wall (26).
The centrifugal blower assembly as defined in claim 1, further characterised in that:
said base rim (42) is integral with a substantially semispherical dome (46).
The centrifugal blower assembly as defined in claim 1, further characterised in that:
said air entrance (36) is axially displaced by a coaming (38) surrounding said air inlet first circular edge (30), said coaming (38) further having a shape that closely matches said tip ring (44).