Centrifugal fan

A centrifugal blower impeller includes a central hub and a plurality of impeller blades. The central hub includes a conical section and an outer edge. The conical section is centered with respect to a center axis and extends from the center axis towards the outer edge. The plurality of impeller blades includes first and second ends. The conical section is coupled to the first ends of the impeller blades which extend axially upward from the first ends towards the second ends. The centrifugal blower impeller also includes a rim which has a generally circular shape and is connected to the second ends of the impeller blades.

FIELD OF THE INVENTION

The present invention relates generally to centrifugal blowers, and more specifically, to a centrifugal blower having improved performance and lower noise.

BACKGROUND OF THE INVENTION

The most familiar air moving mechanism is the simple axial fan, which is the stationary equivalent of an airplane propeller. Whether used for residential cooling or automotive radiator cooling, it simply pulls air axially straight through it. Less familiar is the so called centrifugal blower, which finds common usage in vehicle HVAC systems. A centrifugal blower has a generally cylindrical impeller or fan rotating in one direction that pulls air in along its central axis as it rotates, but then forces it radially outwardly, turning it ninety degrees, in effect. A scroll shaped blower housing surrounding the impeller collects and confines the expelled air and sends it through a tangential outlet to the rest of the HVAC system.

The basic cylindrical impeller includes a central hub, often dome shaped, through which a motor drive shaft is attached, and a flat, annular outer rim. Extending upwardly from the hub rim are an evenly spaced series of identical blades, which are parallel to the central axis.

Plastic centrifugal fans for HVAC applications have traditionally had outer rims that are either external to the blade (external rims) or above part of the blade (split louver rims). Both external rims and split louver rims have high stress areas between the blades as the fan is spun to its operating speed, known as hoop stress. Hoop stress requires the use of higher strength materials, which generally have higher mass, and are more costly.

In attempting to minimize hoop stress, prior art designs have used external rim designs with a long axial length or a split louver design with a parabolic shaped rim of constant thickness. Both of these designs, add axial length and reduce noise, however, they do not add strength to the overall design and require strong, plastic materials with fillers that increase mass, cost, and variation in as-molded balance.

The present invention is aimed at one or more of the problems identified above.

SUMMARY OF THE INVENTION AND ADVANTAGES

In one aspect of the present invention, a centrifugal blower impeller is provided. The centrifugal blower impeller includes a central hub, a plurality of impeller blades, and a rim. The central hub includes a conical section and an outer edge. The central hub is centered with respect to a center axis and extends from the center axis towards the outer edge. The impeller blades have first and second ends. The conical section of the central hub intersects the first ends of the impeller blades. The impeller blades extend axially upward from the first ends towards the second ends. The rim has a generally circular shape and is connected to the second ends of the impeller blades.

In another aspect of the present invention, a centrifugal blower impeller is provided. The centrifugal blower impeller includes a central hub, a plurality of impeller blades, and a rim. The central hub includes a conical section and an outer edge. The central hub is centered with respect to a center axis and extends from the center axis towards the outer edge. The impeller blades have first and second ends. The conical section of the central hub is coupled to the first ends of the impeller blades. The impeller blades extend axially upward from the first ends towards the second ends. The rim has a generally circular shape and is connected to the second ends of the impeller blades. The rim has a first portion and a second portion. The first portion is generally parallel to the center axis and the second portion is generally perpendicular to the center axis. The first and second portions having a generally L-shaped cross-section.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

With reference toFIG. 1, a centrifugal blower is indicated generally at10. The blower10includes a scroll shaped housing12, with a central, axial air inlet defined by a downturned cylindrical lip14and a tangential output16. A central motor driven shaft18lies on the center axis of inlet lip14, to which is secured a centrifugal blower impeller20. The centrifugal blower impeller20is driven through rotation of the motor driven shaft18. As the centrifugal blower impeller20spins, counterclockwise from the perspective ofFIG. 1, outside air is drawn axially in through the inlet lip14. Indrawn air is then pushed radially outwardly, swirling around counterclockwise between the centrifugal blower impeller20and the wall of housing12until it exits tangentially through outlet16.

With reference toFIGS. 2A and 2B, a diagrammatic illustration of a prior art impeller blade assembly22is shown. The prior art impeller blade assembly22includes a hub24, a plurality of blades26, and a locking ring28. An annular rim30is integral with the hub and extends generally perpendicular to a center axis of the impeller blade22. One end of each of the blades26is connected to an upper surface of the annular rim30. The blades26extend upward from the annular rim30. The opposite ends of the blades are coupled to the locking ring28.

With reference toFIGS. 2C and 2D, diagrammatic illustrations of two prior art locking rings28,28′ are shown. With specific reference toFIG. 2C, the locking ring28ofFIGS. 2A and 2Bis shown. The locking ring28is a circular band that encircles an outer edge of the blades26. As shown, the cross section of the locking ring28is generally rectangular. A portion of the locking ring28may extend past the end of the blades26. With specific reference toFIG. 2D, the locking ring28′ has a curved cross section and a portion of the locking ring28′ may extend past the end of the blades.

As discussed more fully below, the features of the centrifugal blower impeller20of the present invention improve the performance of the centrifugal blower10, in terms of reduced noise level and increased efficiency. Further, the design of the centrifugal blower impeller20minimizes the stress points along the centrifugal blower impeller20, allowing use of non-filled plastic materials with lower strength, thereby reducing cost, mass, and as-molded balance.

With reference toFIGS. 3 and 4, the centrifugal blower impeller20of the present invention includes a central hub32. The central hub32includes a conical section34and an outer edge36. The conical section34is centered along a center axis38and extends from the center axis38towards the outer edge36. The centrifugal blower impeller20includes a plurality of impeller blades40having first and second ends42,44.

The conical section34of the central hub32is coupled to the first ends of the impeller blades40. The impeller blades40extend axially upward (in the drawing) from the first ends42towards the second ends44, as shown.

The centrifugal blower impeller20also includes a rim46which has a generally circular shape and is connected to the second ends44of the impeller blades40.

In one aspect of the present invention, the central hub32intersects the first ends42of the impeller blades40. In one embodiment, the central hub32intersects the plurality of impeller blades40at an angle with respect to the center axis.

In one embodiment, the central hub32includes a central portion48formed at an end of the central hub32opposite the outer edge36. The central portion includes an interface aperture50. In one embodiment, the interface aperture is50a D-shaft interface aperture. The central motor driven shaft18is likewise shaped to fit the D-shaft interface aperture50. In another embodiment, the shaft18is a splined shaft. In still another embodiment, the shaft18is a smooth shaft.

In one embodiment, the central hub32is generally shaped as a right circular cone as shown. In another embodiment, the central hub32is concave. In still another embodiment, the central hub32is convex.

The impeller blades40have a blade length, identified as “C” onFIG. 5A(see below). The central hub32intersects the plurality of impeller blades40through a portion of the blade length C. In one embodiment, the portion of the blade length intersected by the central hub32is less than fifty percent of the total blade length. In another embodiment, the portion of the blade length intersected by the central hub32is greater then fifty percent of the total blade length. In still another embodiment, the portion of the blade length intersected by the central hub32is approximately one hundred percent of the total blade length.

In one embodiment, the centrifugal blower impeller is integrally molded from a plastic such as polypropylene. The blades40are radially wide enough, and flat enough, such that they would, without external support at the second ends42, flex and bend excessively in operation. As best seen inFIGS. 3 and 4, each blade40is forwardly inclined and curved, i.e., slopes in the direction of rotation.

With particular reference toFIG. 5A, in another aspect of the present invention, the rim46includes a first portion52and a second portion54.

In one embodiment, the first portion52is generally parallel to the center axis38and the second portion54is generally perpendicular to the center axis38. As shown, the first and second portions52,54having a generally L-shaped cross-section.

The first portion52of the rim46has a first edge56. In one embodiment, the first edge56is in a common plane with edges of the second ends44of the impeller blades40(as shown in FIG.5A). In another embodiment, the first edge56of the rim46extends past the second ends44of the blades40(as shown in dotted lines). In another embodiment, the second ends44of the blades40extend past the first edge56of the rim46.

The second portion54of the rim46has a rim outer edge58. Each impeller blade40has a blade outer edge60. In one embodiment, the rim outer edge58and the blade outer edges60are generally equidistance from the center axis38as shown. In another embodiment, the rim outer edge58may extend beyond the blade outer edges60. In still another embodiment, the blade outer edges60extend beyond the rim outer edge58.

With reference toFIGS. 5A and 5B, the following dimensions are defined:

R1: inside radius of rim46,

R2: outside radius of rim46,

R3: inside radius of fan blades40relative to the center axis38,

R4: outside radius of fan blades40relative to the center axis38,

A: radial length of the rim46,

B: axial length of the rim46into blade40,

C: length of blades40(R4−R3),

E: total axial length of rim46.

Although the first and second portions52,54are generally perpendicular, due to manufacturing limitations, the edges of the rim46may not meet at right angles. As shown in the illustration ofFIG. 5B, inner edges62A,62B are joined by an arc64. The arc64has a radius (defined by the dashed circle) of R1. Likewise outer edges66A,66B are joined by an arc68. The arc68has a radius (defined by the dashed circle) of R2.

In one aspect of the present invention, the inside radius (R1) of the rim46is minimized, i.e., less than a predetermined value. Minimizing the inside radius, R1, of the rim46reduces stress levels within the centrifugal blower impeller20and particularly, the rim46. Lower rim stress allows the use of lower strength, non-filled materials, such as polypropylenes which result in more consistent balance levels, lower mass and thus lower cost. In addition, the stronger centrifugal blower impeller allows for better dimensional stability.

With reference toFIG. 9A, finite element analysis (FEA) shows the relative maximum Von Mises stress of prior art rims28,28′ (as shown inFIGS. 2C and 2D, respectively) and the current design rim46, all made of the same material at a constant speed with the same air loading. As shown, the maximum Von Mises stress of the first prior art rim design28was 11.28 mega Pascal and the maximum Von Mises stress of the second prior art rim design28′ was 6.2 mega Pascal. In contrast, the maximum Von Mises stress of the current rim design46was 5.96 mega Pascal.

With reference toFIG. 9B, the specific sound power level of the two prior art rims28,28′ and the rim46of the present invention are shown, at the same speed (RPM), and same air restriction. As shown, the current design has a much lower specific sound power level than the two prior art designs.

In a first embodiment, 0≦R1≦0.5 millimeters.

In a second embodiment, 0≦R1≦1.0 millimeters.

In a third embodiment, 0≦R1≦2.0 millimeters.

In a fourth embodiment, 0≦R1≦4.0 millimeters.

In a fifth embodiment, 0≦R1≦8.0 millimeters.

In another aspect of the present invention, the outer radius of the rim46is minimized, i.e., less than a predetermined value. Minimizing the outer radius, R2, of the rim46reduces stress levels within the centrifugal blower impeller20.

In a first embodiment, 0≦R2≦0.5 millimeters.

In a second embodiment, 0≦R2≦1.0 millimeters.

In a third embodiment, 0≦R2≦2.0 millimeters.

In a fourth embodiment, 0≦R2≦4.0 millimeters.

In a fifth embodiment, 0≦R2≦8.0 millimeters.

In a sixth embodiment, R2is equal to 0.25 millimeters.

The rim46is designed to allow for maximum attachment to the blades40in both the vertical direction (along the first portion52) and the horizontal direction (along the second portion54). The second portion54of the rim46provides the strength in the centrifugal blower impeller20to reduce stress at the blade attachment to the rim46. By maximizing the blade40to rim46attachment area, the stress levels and deflection of the blades40are minimized. The second portion54also reduces the cantilever stress. For example, maximum stress with the centrifugal blower impeller20may be reduced up to fifty percent over prior art impeller designs of the type represented byFIGS. 2A-2D.

In one aspect of the present invention, the ratio of the radial length, A, of the rim46to the radial length, C, of the blades40is minimized to allow for maximum attachment between the rim46and the blade40.

In a first embodiment, 0.1≦(A/C)≦1.0.

In a second embodiment, 0.2≦(A/C)≦1.0.

In a third embodiment, 0.3≦(A/C)≦1.0.

In a fourth embodiment, 0.4≦(A/C)≦1.0.

In a fifth embodiment, 0.5≦(A/C)≦1.0.

In a sixth embodiment, A/C=0.4.

In a seventh embodiment, A/C=0.5.

In another aspect of the present invention, the ratio of the axial length of the rim into the blade, B, to the blade height, D, is between predetermined values.

In a first embodiment, 0.05≦(B/D)≦0.4.

In a second embodiment, 0.1≦(B/D)≦0.4.

In a third embodiment, B/D=0.23.

With reference toFIG. 6, the centrifugal blower impeller20of the present invention has been tested and proven to increase the efficiency of the centrifugal blower10. As shown, the efficiency of a centrifugal blower with a blade assembly having the locking ring28(ofFIG. 2C) is shown at70, the efficiency of a centrifugal blower with a blade assembly having the locking ring28′ (ofFIG. 2D) is shown at72, and the efficiency of the centrifugal blower10with the centrifugal blower impeller20of the present invention is shown at74.

Furthermore, the conical shape of the central hub32beneficially affects the airflow through the centrifugal blower10. Efficiency can be gained by a more uniform airflow through the blades40. The airflow through a prior art impeller blade is shown in FIG.7. First, the light blue coloring on the left and right sides of the graph (corresponding to the blades) show a concentration of airflow through a middle portion of the blades. Also on the left side of the graph, airflow is reduced significantly near the bottom of the blades.

In contrast, the graph ofFIG. 8, illustrates a more uniform flow of air through the centrifugal blower impeller20of the present invention which results in a higher efficiency.

Obviously, many modifications and variations of the present invention are possible in light of the above teachings. The invention may be practiced otherwise than as specifically described within the scope of the appended claims.