Patent Description:
Such fans are often manufactured in large volumes via a plastic injection molding process in which a mold of the fan <NUM> is injected with molten plastic in the vicinity of the hub-forming portion (<FIG>). From the injection point(s) <NUM>, the molten plastic (represented by arrows) flows within the mold cavity from the hub-forming portion, radially outward through the blade forming portions, and then circumferentially along the band-forming portion. When two flow-fronts meet within the band-forming portion, a knit-line <NUM> is formed in the resulting fan band <NUM>. Knit-lines <NUM> are formed in the band <NUM> approximately mid-way between each pair of adjacent fan blades <NUM>. Knit-lines <NUM> are typically weaker than other regions of the band <NUM> where there are no knit-lines <NUM>, and thus may be a point of failure initialization within the fan <NUM>.

The fan band knit line strength could be improved by simply uniformly increasing band thickness. But as thickness is added, the mass of the band increases and therefore the centrifugal stresses increase. Additionally, adding mass to an injection molded part far from the injection location is undesirable from a molding best-practices standpoint.

Provided is an axial fan according to claim <NUM>, which includes structurally reinforced knit-lines that improve the strength of band knit regions, thereby increasing overall the structural robustness of the fan.

To increase the stiffness and strength of the fan band between fan blades, where the band knit-line occurs, reinforcing ribs are provided on the hub-facing surface of the fan band cylindrical portion. Each rib protrudes inward toward the hub and extends circumferentially across (or "bridges") the knit-line. Each rib has a complex shape that minimizes air flow losses and unwanted noise, and is dimensioned to lower stress in the band while ensuring that the knit-line is bridged.

The fan includes a hub configured to be driven by motor to rotate about a fan rotational axis, and a band that surrounds the rotational axis and is concentric with the hub. The band includes a cylindrical portion that extends in parallel to the fan rotational axis, a lip portion that extends in a direction perpendicular to the fan rotational axis, and a curved intermediate portion that connects one end of the cylindrical portion to one end of the lip portion. The fan includes blades that protrude radially from the hub. Each blade has a root that is connected to the hub and a tip that is connected to a hub-facing surface of the cylindrical portion. The fan also includes a structurally-reinforcing rib that protrudes from the hub-facing surface of the cylindrical portion. The rib is disposed between respective tips of an adjacent pair of the blades. A circumferential dimension of the rib is at least <NUM> percent of a distance along the hub-facing surface between the respective tips of the blades of the adjacent pair of the blades.

In some embodiments, the reinforcing rib includes a leading end, a trailing end that is opposed to the leading end and is circumferentially spaced apart from the leading end, and opposed side surfaces that extend between the leading end and the trailing end. The circumferential dimension of the rib corresponds to a distance between the leading end and the trailing end. The circumferential dimension of the rib is greater than a thickness dimension of the rib, where the thickness dimension of the rib corresponds to a distance between the opposed side surfaces. In addition, the leading end and the trailing end are rounded.

In some embodiments, the circumferential dimension of the rib is at least ten times the thickness dimension.

In some embodiments, a radial dimension of the rib is non-uniform along the circumferential dimension of the rib.

In some embodiments, a radial dimension of the rib at the leading end and the trailing end is less than a radial dimension of the rib at a location that is midway between the leading end and the trailing end.

In some embodiments, a radial dimension of the rib is at most twenty percent of a blade span, the blade span corresponding to a distance between the root and the tip of one of the blades.

The rib comprises a plurality of ribs, each rib being disposed between a pair of adjacent blades such that a single rib is disposed between the blades of a given pair of adjacent blades. In some embodiments, the circumferential dimension of the rib is proportional to the spacing between the respective tips of the blades of the given pair of adjacent blades.

In some embodiments, number of ribs equals the number of blades.

In some embodiments, the rib is disposed mid-way between the tips of the blades of the adjacent pair of the blades.

In some embodiments, the rib is disposed closer to a tip of one of the blades of the adjacent pair of blades than to the other of the blades of the adjacent pair of blades.

According to the invention, the rib extends onto the intermediate portion.

To increase the stiffness and strength of the fan band between fan blades, where the band knit-line occurs, the band includes regions of increased radial thickness (referred to as "thickened regions") that are provided on the outward-facing surface of the fan band cylindrical portion. Each thickened region protrudes outward away from the hub and extends circumferentially across (or "bridges") the knit-line. Each thickened region is configured to have a smooth transition to other portions of the band outward-facing surface, and is dimensioned to lower stress in the band while ensuring that the knit-line is bridged and adequately reinforced.

By provided localized regions of increased thickness, the fan band knit line strength is improved while minimizing band mass increases, and thus also minimizing corresponding increases in the centrifugal stresses. In addition, the undesirable effects of added band thickness are minimized by limiting the band thickness addition to (<NUM>) the cylindrical portion of the band and (<NUM>) to regions of the band that are not radially aligned with the fan blades. This added thickness strategy adds strength to the weak band knit lines and does so efficiently by avoiding adding mass where it will not increase knit strength.

In some embodiments, the tip of each blade is joined to the cylindrical portion along a corresponding blade tip region. The cylindrical portion includes first regions of the line having a first radial dimension and second regions of the line having a second radial dimension. The second radial dimension is less than the first radial dimension. The first regions of the line are disposed between respective blade tip regions of tips of a pair of adjacent blades, and the second regions of the line are radially aligned with the respective blade tip regions.

In some embodiments, the first radial dimension is greater than an axial dimension of the lip portion.

In some embodiments, the first radial dimension is at least five percent greater than the second radial dimension.

In some embodiments, a dimension of the intermediate portion is non-uniform along a circumference of the band such that the dimension of the intermediate portion at locations radially aligned with the first regions of the line is greater than corresponding dimensions of the intermediate portion at locations radially aligned with the second regions of the line.

In some embodiments, the cylindrical portion includes third regions of the line having a tapered radial dimension. The third regions of the line provide a transition between the first regions of the line and the second regions of the line, wherein a circumferential dimension of each third region of the line is at least as long as a circumferential dimension of the first region of the line that it adjoins.

In some embodiments, the cylindrical portion includes third regions of the line having a tapered radial dimension. The third regions of the line provide a transition between the first regions of the line and the second regions of the line, wherein a sum of the circumferential dimensions of one of the first regions of the line and each adjoining third region of the line is at least fifty percent of a distance between tips of adjacent blades.

Referring to <FIG>, an axial flow fan <NUM>, which may be used for cooling heat exchange medium passing an inside of a heat exchanger such as a radiator of an automobile, is provided with a hub <NUM> that is coupled to a driving source (not shown) such as a motor. The fan <NUM> includes a plurality of blades <NUM> that protrude radially outward from the hub <NUM>. In addition, the fan <NUM> includes a band <NUM> that surrounds the hub and connects the tips <NUM> of each blade <NUM> so as to prevent the blades <NUM> from being deformed. The hub <NUM>, the blades <NUM> and the band <NUM> are formed as a single piece, for example in an injection molding process. The fan <NUM> is rotated by rotational force transferred from the motor to the hub <NUM>. In the illustrated embodiment, the fan <NUM> rotates about the fan rotational axis <NUM> in the clockwise direction with respect to the view shown in <FIG>, and the air flow direction, represented by the arrow A, is parallel to the fan rotational axis <NUM>. The band <NUM> includes structurally reinforced knit-lines that improve the strength of band knit regions, thereby increasing overall the structural robustness of the fan. The band <NUM> includes reinforcing ribs <NUM> that reduce band stress and increase the structural integrity of the band <NUM> in the vicinity of the knit-lines <NUM>. Additionally, the band <NUM> includes thickened regions <NUM> that reduce band stress and increase the structural integrity of the band <NUM> in the vicinity of the knit-lines <NUM>. The reinforcing ribs <NUM> and the thickened regions <NUM> are described in detail below.

The hub <NUM> is a hollow cylinder that is closed at one end by an end surface <NUM> that is perpendicular to the fan rotational axis <NUM>. An outer circumference <NUM> of the hub <NUM> faces the band <NUM>.

Each blade <NUM> includes a root <NUM> that is coupled to the band-facing surface <NUM> of the hub <NUM>, and a tip <NUM> that is spaced apart from the root <NUM>. Each tip <NUM> is coupled to a hub-facing surface <NUM> of the band <NUM>. The air-flow directing surfaces of each blade <NUM> have a complex, three-dimensional curvature that is determined by the requirements of the specific application. The blade configuration, including the number of blades <NUM> employed by the fan <NUM>, the shape of the blades <NUM>, the blade spacing, etc., are also determined by the requirements of the specific application.

The direction of the air flow that is discharged from the fan <NUM> is dependent at least in part on the blade curvature, and includes a substantial axial flow component. As used herein, the term "axial flow component" refers to a component of air flow that flows in a direction parallel to the fan rotational axis <NUM>.

The band <NUM> is a generally L-shaped circumferential ring that is concentric with hub <NUM> and is spaced radially outward from hub <NUM>. In particular, the band <NUM> includes a cylindrical portion <NUM> that corresponds to one leg of the L-shape and extends in parallel to the fan rotational axis <NUM>. The band <NUM> includes a lip portion <NUM> that corresponds to the other leg of the L-shape and extends at an angle to the fan rotational axis <NUM>. In the illustrated embodiment, the lip portion <NUM> is perpendicular to the cylindrical portion <NUM>, and provides the leading end <NUM> of the band <NUM> with respect to the direction A of air flow through the fan <NUM>. In addition the band <NUM> includes a curved intermediate portion <NUM> that connects one end of the cylindrical portion <NUM> to one end of the lip portion <NUM>. The cylindrical portion <NUM> encircles the hub <NUM>, and the lip portion <NUM> protrudes from the cylindrical portion <NUM> in a direction away from the hub <NUM>.

The band <NUM> has a first surface <NUM> that faces, and comes into contact with, air flowing through the fan <NUM>, and a second surface <NUM> that is opposed to the first surface. Accordingly, the hub-facing surface <NUM> of the cylindrical portion <NUM> provides a portion of the first surface <NUM>.

Each blade tip <NUM> is joined to the hub-facing surface <NUM> of the cylindrical portion <NUM> along a circumferentially-extending region referred to as the "blade-tip region" <NUM> of the cylindrical portion <NUM>.

The band <NUM> includes structurally-reinforcing ribs <NUM> that protrude from the hub-facing surface <NUM> of the cylindrical portion <NUM>. Each rib <NUM> includes a leading end <NUM>, and a trailing end <NUM> that is opposed to the leading end <NUM> and is spaced apart from the leading end <NUM> along a circumference of the band <NUM>. Each rib <NUM> includes opposed side surfaces <NUM>, <NUM> that extend between the leading end <NUM> and the trailing end <NUM>, and are spaced apart from each other in a direction parallel to the fan rotational axis <NUM>. In the illustrated embodiment, the opposed side surfaces <NUM>, <NUM> are generally linear and parallel to each other.

In some embodiments, the cross-sectional shape of the ribs <NUM> is "blade-like". As used herein, the term "blade-like" refers to having an aerodynamic shape, that is, a shape that reduces the drag from air moving past the rib <NUM>. For example, the ribs <NUM> are generally aligned with the direction of air flow along the hub-facing surface <NUM> of the band <NUM>, and include rounded leading and trailing ends <NUM>, <NUM>. By configuring the ribs <NUM> to have the shape of a blade, undesirable noise and undesirable aerodynamic losses are minimized.

Each rib <NUM> is elongated in that the circumferential dimension <NUM> of the rib <NUM> (e.g., a distance between the leading end <NUM> and the trailing end <NUM> along a circumference of the hub-facing surface <NUM>, <FIG>) is greater than a thickness dimension <NUM> of the rib <NUM> (e.g., a distance between the opposed side surfaces <NUM>, <NUM>, <FIG>). The circumferential dimension <NUM> of the rib <NUM> is at least ten times the thickness dimension <NUM>. For example, in the illustrated embodiment, the circumferential dimension <NUM> of the rib <NUM> is about twenty times the thickness dimension.

The band <NUM> includes a rib <NUM> disposed between each pair of adjacent blades <NUM> such that a single rib <NUM> is disposed between the blades <NUM> of a given pair of adjacent blades <NUM>. In addition, the circumferential dimension <NUM> of the rib <NUM> is proportional to the spacing between the respective tips <NUM> of the adjacent blades <NUM>. In the illustrated embodiment, the number of ribs <NUM> equals the number of blades <NUM>.

The ribs <NUM> are disposed between respective tips <NUM> of an adjacent pair of the blades <NUM>. In the illustrated embodiment the rib <NUM> is disposed mid-way between the respective tips <NUM> of the adjacent pair of blades <NUM> so as to extend across the corresponding knit-line <NUM>. However, in applications in which the knit-line <NUM> is not disposed mid-way between the respective tips <NUM>, such as might occur in fans having unequal blade spacing, it is understood that the rib <NUM> may be offset toward one blade of the adjacent pair of blades in order to bridge the knit-line <NUM>.

A circumferential dimension <NUM> of each rib <NUM> is at least <NUM> percent of the inter-blade arc length <NUM> (e.g., a distance along the hub-facing surface <NUM> between the respective tips <NUM>, or blade tip regions <NUM>, of adjacent blades <NUM>, <FIG>). Having such a large circumferential extent ensures that the band knit-line <NUM> will lie in the radial projection of the reinforcing rib <NUM>. This ensures that the ribs <NUM> properly reinforce the respective knit-lines <NUM> even when there are relatively large variations in the location of plastic injection during the manufacturing process. The ribs <NUM> extend circumferentially to an extent that the ribs <NUM> extend beyond the hub-facing surface <NUM> onto the curved intermediate portion <NUM> of the band <NUM>.

To further reduce drag, each rib <NUM> has a non-uniform radial dimension <NUM> along the circumferential dimension of the rib <NUM>, where the term "radial" is used with reference to the fan rotational axis <NUM>. For example, the leading end <NUM> and the trailing end <NUM> of each rib <NUM> may have a smaller radial dimension <NUM> than a midportion of each rib <NUM>. The ribs <NUM> have a low profile, in that the radial dimension <NUM> of the rib <NUM> is at most twenty percent of a blade span <NUM>, where the blade span <NUM> corresponding to the distance between the root <NUM> and the tip <NUM> of one of the blades <NUM>. This configuration reduces unwanted noise and aerodynamic issues such as air flow losses.

Referring to <FIG>, a fan <NUM>, which is not according to the invention, illustrates additional structural features that provide structural reinforcement of the knit lines <NUM>. Fan <NUM> is an axial flow fan that is similar to the axial flow fan <NUM> described above with respect to <FIG>, and common reference numbers are used to refer to common elements. The fan <NUM> of <FIG> differs from the previous embodiment in that the reinforcing ribs <NUM> are omitted, and the cylindrical portion <NUM> of the band <NUM> includes structurally-reinforcing thickened regions <NUM> that protrude from the second surface <NUM>. As used herein, references to the thickness of the band <NUM> refer to a distance between the first surface <NUM> and the second surface <NUM>. Within the cylindrical portion <NUM>, the thickness of the band <NUM> corresponds to the radial dimension of the band <NUM>, whereas within the lip portion <NUM>, the thickness of the band <NUM> corresponds to the axial dimension of the band <NUM>.

Since the fan <NUM> is injection molded, the fan <NUM> includes structures that facilitate the injection molding manufacturing process. For example, the hub <NUM> and band <NUM> may have a draft angle that allows the fan <NUM> to be removed from a mold. In another example, the surfaces of the hub <NUM> and band <NUM> that face each other may include shut offs that control flow of molten plastic within the mold in the vicinity of the parting line. Although the band <NUM> includes features such as draft and shutoffs that are required for manufacturing purposes and that affect the thickness of the band <NUM>, such manufacturing-related features do not reinforce the knit-lines <NUM> and are not considered to be part of the thickened regions <NUM>. Since the manufacturing-related features such as draft and shut-offs do not extend to a trailing end <NUM> of the band (e.g., the end of the band <NUM> that is most downstream with respect to the direction A of air flow through the fan <NUM>), the thickened region <NUM> may be defined with respect to a line <NUM> that extends about a circumference of the band, where the line <NUM> is disposed on the hub-facing surface <NUM> of the band <NUM> at the trailing end <NUM>, and is represented as a dot-dash line in <FIG>. In particular, the distance <NUM> between the fan rotational axis <NUM> and the hub-facing surface <NUM> of the band <NUM> is constant for every location along the line <NUM>, and the radial dimension of the band <NUM> is non-uniform along the line <NUM>. That is, the thickened region <NUM> corresponds to a protrusion from the band second surface <NUM>. It is understood that the thickened region <NUM> is not limited to the line <NUM> and extends axially between the lip portion <NUM> and the trailing end <NUM>.

Each thickened region <NUM> has a thickness t1 that is greater than the thickness t2 of the band cylindrical portion <NUM> at locations spaced apart from (e.g., between) the thickened regions <NUM>. In particular, the portions of the band cylindrical portion <NUM> that are radially aligned with the blade tip regions <NUM> are not provided with an increased thickness, and are referred to as non-thickened regions <NUM>. In the non-thickened regions <NUM>, the band cylindrical portion <NUM>, the band intermediate portion <NUM> and the band lip portion <NUM> each have the thickness t2. In the illustrated embodiment, the thickness t2 of non-thickened regions <NUM> is equal to the thickness tlip of the lip portion <NUM>. Although the thickened regions <NUM> may extend axially (e.g., in a direction parallel to the fan rotational axis <NUM>) into a portion of the curved intermediate portion <NUM>, the lip portion <NUM> of the band <NUM> is free of thickening and has a uniform thickness tlip about the circumference of the band <NUM>.

In some embodiments, the thickness t1 of the thickened regions <NUM> is at least five percent greater than the thickness t2 of the non-thickened regions <NUM>. In other embodiments, the thickness t1 of the thickened regions <NUM> is at least <NUM> percent, <NUM> percent, <NUM> percent, <NUM> percent, <NUM> percent or <NUM> percent greater than the thickness t2 of the non-thickened regions <NUM>. The thickness t1 of the thickened regions <NUM> is determined based on the requirements of the specific application, while improving knit line strength and minimizing band mass increases, and thus also minimizing corresponding increases in the centrifugal stresses.

The band <NUM> includes a thickened region <NUM> disposed between each pair of adjacent blades <NUM> such that a single thickened region <NUM> is disposed between each pair of adjacent blades <NUM>. In the illustrated embodiment, the number of thickened regions <NUM> equals the number of blades <NUM>.

The thickened regions <NUM> are disposed between respective tips <NUM> of an adjacent pair of the blades <NUM>. In the illustrated embodiment the thickened region <NUM> is disposed mid-way between the respective tips <NUM> of the adjacent pair of blades <NUM> so as to extend across the corresponding knit-line <NUM>. However, in applications in which the knit-line <NUM> is not disposed mid-way between the respective tips <NUM>, such as might occur in fans having unequal blade spacing, it is understood that the thickened region <NUM> may be offset toward one blade of the adjacent pair of blades in order to bridge the knit-line <NUM>.

Each thickened region <NUM> extends circumferentially. In some embodiments, a circumferential dimension c1 of each thickened region <NUM> is in a range of <NUM> percent to <NUM> percent of the inter-blade arc length c2, where the inter-blade arc length corresponds to a distance along the hub-facing surface <NUM> between the respective tips <NUM>, or blade tip regions <NUM>, of adjacent blades <NUM>.

The cylindrical portion <NUM> of the band <NUM> includes transition regions <NUM> that are disposed between each thickened region <NUM> and the adjacent blade tips <NUM>. In some embodiments, the sum of the circumferential dimension c1 of each thickened region <NUM> and the circumferential dimensions c3 of the adjoining transition regions <NUM> is in a range of <NUM> percent to <NUM> percent of the inter-blade arc length c2.

In the embodiment illustrated in <FIG>, the circumferential dimension c3 of each of the transition regions <NUM> adjoining the thickened region <NUM> is about the same as the circumferential dimension c1 of the thickened region <NUM>, each region <NUM>, <NUM>, <NUM> extending along approximately one-third of the inter-blade arc length c2. In other embodiments, the thickened region <NUM> may not extend circumferentially since the maximum thickness may occur at a single, substantially zero-width line (e.g., in this case, the circumferential dimension c1 of each thickened region <NUM> approaches zero), and the transition regions <NUM> may be relatively large so that the thickness change is very gradual across the inter-blade space.

Thus, the band cylindrical portion <NUM> has a non-uniform thickness along the circumference of the band <NUM> such that the thickness varies periodically along the circumference of the band. In addition, the cylindrical portion <NUM> has a maximum thickness at locations between adjacent blades <NUM>, and a minimum thickness at locations aligned with a blade <NUM>.

The thickened regions <NUM> have a low profile, in that the thickness t1 of the thickened region <NUM> is at most <NUM> percent of a blade span <NUM>, where the blade span <NUM> corresponding to the distance between the root <NUM> and the tip <NUM> of one of the blades <NUM>. This configuration minimizes fan diameter, improving packaging flexibility. In some applications such as engine cooling, an engine cooling fan may have a thickened region <NUM> in which the thickness t1 may be in a range of two to three percent of the blade span <NUM>. Since the thickened regions <NUM> have a relatively large circumferential extent, it is assured that each band knit-line <NUM> will lie in the radial projection of a thickened region <NUM>. In turn, this ensures that the thickened regions <NUM> properly reinforce the respective knit-lines <NUM> even when there are relatively large variations in the location of plastic injection during the manufacturing process.

By providing the thickened region <NUM> on the second surface <NUM> of the band <NUM>, flow losses as air passes through the fan <NUM> are minimized.

Referring to <FIG> and <FIG>, a fan <NUM> according to the invention includes structural features that provide structural reinforcement of the knit lines <NUM>. The fan <NUM> is an axial flow fan that is similar to the axial flow fans <NUM>, <NUM> described above with respect to <FIG>, and common reference numbers are used to refer to common elements. The fan <NUM> of <FIG> is a fan according to the invention and differs from the previous embodiments in that the fan <NUM> includes both the reinforcing ribs <NUM> that protrude toward the hub <NUM> from the band first surface <NUM> on the cylindrical portion <NUM> as described above with respect to <FIG>, and the thickened regions <NUM> that protrude from the band second surface <NUM> on the cylindrical portion <NUM> as described above with respect to <FIG>. Like the previous embodiments, in the fan <NUM>, the reinforcing ribs <NUM> and the thickened regions <NUM> are provided at each knit line <NUM>, and are configured to extend across the knit line <NUM> so as to structurally reinforce the knit line <NUM>. In some embodiments, each rib <NUM> is disposed between tips <NUM> of adjacent blades <NUM> such that a midpoint <NUM> of the rib <NUM> (e.g., the point mid way between the rib leading end <NUM> and the rib trailing end <NUM>) coincides with the knit line <NUM>. For a fan having evenly spaced blades <NUM>, this location is generally mid-way between the tips <NUM> of adjacent blades <NUM>. In addition, each thickened region <NUM> has a maximum value at locations corresponding to a corresponding (e.g., radially aligned) rib <NUM>. For example, in some embodiments, each thickened region <NUM> may be centered on a corresponding rib <NUM> such that the thickened regions <NUM> have a maximum value at locations corresponding to the midpoint <NUM> of each rib <NUM>.

Employment of reinforcing ribs <NUM> and/or thickened regions <NUM> on the band <NUM> is not limited to the fans <NUM>, <NUM>, <NUM> having a downstream-stator design, as shown in <FIG> and redrawn schematically in <FIG>, where the stator (not shown) supports a motor (not shown) which drives the fan <NUM> via the hub <NUM>. In the downstream-stator design, the stator is disposed downstream of the fan <NUM> with respect to the direction A of air flow through the fan <NUM>. In the downstream-stator design, the lip portion <NUM> provides a leading end <NUM> of the band <NUM>. The reinforcing ribs <NUM> and the thickened regions <NUM> can be employed to reinforce the band knit lines <NUM> in a fan <NUM> having an upstream-stator design, as shown in <FIG>. In an upstream-design, the stator is disposed upstream of the fan <NUM> with respect to the direction A of air flow through the fan <NUM>. In <FIG>, the lip portion <NUM> provides the leading end <NUM> of the band <NUM>. In an alternative fan <NUM> having an upstream-stator design (<FIG>), the lip portion <NUM> provides the trailing end <NUM> of the band <NUM>. Although the lip portion <NUM>, as shown in <FIG>, may extend in a direction perpendicular to the fan rotational axis <NUM>, the lip portion is not limited to this configuration. For example, in some embodiments not forming part of the current invention, the lip portion <NUM> may extend at an acute angle relative to the fan rotational axis <NUM>, as shown in the alternative band <NUM> of the upstream-stator design fan <NUM> illustrated in <FIG>, or in downstream-stator design fans (not shown).

Although the cooling fans illustrated in <FIG> are automotive cooling fans, the cooling fans described in <FIG> are not limited to automotive applications. For example, the cooling fans may be used in a computer to cool a hard drive, in a heating and ventilation unit to cool a compressor, etc. Moreover, the cooling fans illustrated in <FIG> are not limited to being used in cooling applications.

Claim 1:
An axial fan (<NUM>, <NUM>, <NUM>), comprising:
a hub (<NUM>) configured to be driven by motor to rotate about a fan rotational axis (<NUM>);
a band (<NUM>) that surrounds the rotational axis and is concentric with the hub, the band (<NUM>) including a cylindrical portion (<NUM>) that extends in parallel to the fan rotational axis (<NUM>), a lip portion (<NUM>) that extends in at an angle to the fan rotational axis (<NUM>), and a curved intermediate portion (<NUM>) that connects one end of the cylindrical portion (<NUM>) to one end of the lip portion (<NUM>);
blades (<NUM>) that protrude radially from the hub (<NUM>), each blade (<NUM>) comprising a root (<NUM>) that is connected to the hub (<NUM>) and a tip (<NUM>) that is connected to a hub-facing surface (<NUM>) of the cylindrical portion (<NUM>); and
a structurally-reinforcing rib (<NUM>) that protrudes from the hub-facing surface (<NUM>) of the cylindrical portion (<NUM>), the rib (<NUM>) disposed between respective tips (<NUM>) of an adjacent pair of the blades (<NUM>), wherein
a circumferential dimension (<NUM>) of the rib (<NUM>) is at least <NUM> percent of a distance along the hub-facing surface (<NUM>) between the respective tips (<NUM>) of the blades (<NUM>) of the adjacent pair of the blades (<NUM>),
wherein the hub (<NUM>), the blades (<NUM>) and the band (<NUM>) are formed as a single piece;
wherein the rib (<NUM>) comprises a plurality of ribs (<NUM>), each rib (<NUM>) being disposed between a pair of adjacent blades (<NUM>) such that a single rib (<NUM>) is disposed between the blades (<NUM>) of a given pair of adjacent blades (<NUM>),
wherein a distance (<NUM>) between the fan rotational axis (<NUM>) and the band (<NUM>) is constant for every location along a line (<NUM>) that extends about the circumferences of the band (<NUM>), where the line is disposed on the hub-facing surface (<NUM>) of the band (<NUM>) at the band trailing end (<NUM>), wherein the line (<NUM>) does not intersect with the rib (<NUM>),
characterized in that
the rib (<NUM>) extends onto the curved intermediate portion (<NUM>), and in that a radial dimension of the band (<NUM>) is non-uniform along the line (<NUM>),
wherein the radial dimension of the band (<NUM>) has a maximum value at locations corresponding to a rib (<NUM>).