Axial cooling fan shroud

A fan shroud for a cooling fan assembly with a fan that is rotatable about an axis of rotation defines a downstream direction along the axis of rotation. The shroud includes a barrel for containing the fan. The barrel is concentric with the axis of rotation and further includes a base portion. A plenum includes a plenum body extending radially from the base portion. The plenum body defines at least one edge of length L1. A skirt extends proximate the at least one edge of length L1 and substantially parallel to the axis of rotation. An interface joins the at least one edge of length L1 and the skirt and has a length L1. The interface comprises an underside having a transition surface of a length less than length L1.

BACKGROUND

The present invention relates to cooling fan shrouds and more particularly to cooling fan shrouds for use in axial-flow fan assemblies to cool engines.

A typical cooling fan assembly for drawing air through one or more heat exchangers includes a fan, a motor for driving the fan, and a shroud. The shroud serves at least three purposes: a) supporting the motor and fan, b) attaching the assembly to the heat exchanger, and c) guiding the cooling air from the downstream face of the heat exchanger into the fan.

SUMMARY

Fan efficiency and fan noise production are greatly influenced by the quality of the airflow into the fan. Two factors affecting this quality are flow uniformity and flow orientation. A more uniform flow pattern is desirable because typical cooling fans for this type of application are designed for a single inflow condition. Any non-uniformities in flow differing from this condition result in fan operation away from the design point and consequent operational inefficiency. Inflow non-uniformities also result in unsteady blade loading, which creates noise. Axial flow into the fan is equally desirable in order to more closely correspond with typical fan design methods, which assume such a condition. Flow streams other than axial therefore represent further losses in efficiency. A fan shroud configured for optimal air guidance for improved fan efficiency and reduced noise should therefore promote uniform and axial flow from the downstream face of the heat exchanger into the fan.

The present invention provides for an improved airflow structure enabling a more uniform and axial flow stream from the heat exchanger into the fan inlet, therefore allowing for more efficient fan operation while minimizing fan noise.

In one embodiment of a fan shroud for a cooling fan assembly having a fan that is rotatable about an axis of rotation and that defines a downstream direction along the axis of rotation, the fan shroud includes a barrel for containing the fan. The barrel is concentric with the axis of rotation and further includes a base portion. A plenum includes a plenum body extending radially from the base portion. The plenum body defines at least one edge of length L1. A skirt extends proximate the at least one edge of length L1and substantially parallel to the axis of rotation. An interface joins the at least one edge of length L1and the skirt and has a length L1. The interface comprises an underside having a transition surface of a length less than length L1.

In another embodiment of a cooling fan assembly for facilitating the transfer of heat through a heat exchanger, the cooling fan assembly includes a fan rotatable about an axis of rotation and defining a downstream direction along the axis of rotation. The fan is positioned downstream of the heat exchanger and further includes a plurality of fan blades. A fan shroud includes a barrel concentric with the axis of rotation and encircling the plurality of fan blades. The barrel defines a barrel radius and has a base portion. A plenum includes a plenum body and at least one skirt. The plenum body is coupled to the barrel and has a substantially rectangular platform viewed in the upstream direction. The plenum body defines an effective surface monotonically increasing in upstream distance from the base portion. The at least one skirt extends substantially parallel to the axis of rotation and is coupled to the plenum body. The at least one skirt includes a substantially rectilinear upstream border having a first end and a second end. The plenum defines for the at least one skirt a cross section C through the axis of rotation and normal to the skirt, a distance D1between cross section C and the first end of the upstream border, a distance D2between cross section C and the second end of the upstream border, and a distance D3, wherein D3is equal to the lesser of D1and D2, or is equal to D1if D1equals D2. The plenum also defines a plane P1parallel to and offset from cross section C an offset distance DP1less than D3. The plenum also defines a plane P2parallel to and offset from cross section C on the opposite side of cross section C from plane P1an offset distance DP2less than D3. The plenum also defines a plane P3perpendicular to both cross section C and the axis of rotation and containing a point on the upstream border, a plane P4perpendicular to plane P3and cross section C and containing a point located on cross section C and on the plenum body, a plane P5parallel to and offset from cross section C an offset distance equal to D3, and a plane P6parallel to and offset from cross section C on the opposite side of cross section C from plane P5an offset distance equal to D3. A volume V1is defined as enclosed by planes P1, P2, P3, P4and the effective surface. A volume V2is defined as enclosed by planes P1, P3, P4, P5and the effective surface. A volume V3is defined as enclosed by planes P2, P3, P4, P6and the effective surface. An average cross sectional area A1is defined as V1/(DP1+DP2). An average cross sectional area A2is defined as (V2+V3)/((D3−DP1)+(D3−DP2). A1is less than A2.

DETAILED DESCRIPTION

Typically, cooling fan shrouds include a plenum having one or more edges for contact with the surface of a heat exchanger, and a downstream circular barrel joined to the plenum that houses a cooling fan for drawing air through the shroud. More specifically, cooling fan shrouds may be conventionally characterized as having either a constant cone angle configuration or a constant wall height configuration.

Referring toFIG. 1, a shroud with a conventional constant cone angle design includes a plenum with a top surface extending from the barrel with a somewhat conical configuration, which is generally defined by a cone angle formed between a line tangent to the top surface and a line perpendicular to the axis of rotation. This cone angle is substantially constant in the azimuthal direction. A constant cone angle design has an advantage in that an overall high-volume plenum can be created through use of a small cone angle. A higher plenum volume improves the ability of the fan to draw air through the heat exchanger. The underside of a conventional constant cone angle design is shown inFIG. 2.

Referring toFIG. 3, a shroud with a conventional constant wall height design includes a plenum with a top surface configured such that in regions where the barrel is close to the shroud perimeter, the plenum surface adjacent to the barrel is more steeply angled than the surrounding surface, creating a more axial and uniform flow into the fan. An underside of the conventional constant wall height design is shown inFIG. 4. An improvement may be made to either configuration or to any fan shroud generally to enhance the air flow into the fan, as hereinafter described.

FIG. 5illustrates an axial cooling fan assembly including a fan shroud100surrounding an axial fan110. The fan110has one or more fan blades112coupled to a hub114rotating about an axis of rotation116for drawing air through a heat exchanger (not shown). A downstream direction along the axis of rotation116is defined such that the fan110is located downstream of the heat exchanger. The fan shroud is preferably constructed of plastic, preferably as an injection molded plastic part.

The fan shroud100includes a barrel118and a plenum130. The barrel118generally encircles and contains the axial fan110and is concentric with the axis of rotation116. The barrel118includes a housing portion120downstream of a base portion122that is coupled to the plenum130. The housing portion120includes an inner surface121. Referring toFIGS. 5 and 7, the barrel also defines a barrel radius124extending from a barrel midpoint126coincident with the axis of rotation, to inner surface121of the housing portion120.

The plenum130includes a plenum body132radially extending from the base portion122. The plenum body132defines one or more edges134, each edge134including a first end136and a second end138. The edges134generally have a length L1, shown inFIG. 5, coinciding with the distance between the first end136and the second end138. The plenum body132extends generally perpendicular to the axis of rotation116. Alternatively, the plenum body132can be angled from the base portion122such that the edge134is positioned further upstream than base portion122. If so angled, it is not necessary that the plenum body132be angled from the base portion122at a substantially constant angle. A skirt140extends proximate an edge134and in a substantially parallel direction to the axis of rotation116.

The plenum130also includes an interface142joining a respective edge134with a respective skirt140. The interface142will preferably be of length L1in correspondence with an adjacent edge134. Referring toFIG. 6, the interface142includes an underside144. More specifically, the underside144includes a transition surface146. The transition surface146is distinguished from a first segment148of the underside144, located on one side of the transition surface146, and a second segment150of the underside144, located on the other side of the transition surface146. As shown, the first segment148and the second segment150provide a generally smooth surface between the skirt140and the edge134. The transition surface146has a length less than length L1of the interface142and preferably has a length between about 0.25 and about 1.5 of the barrel radius124. The transition surface146can be positioned anywhere within the interface142but a center149of the transition surface146is preferably located at the midpoint of interface142, or, alternatively, substantially aligned with barrel midpoint126. In the embodiment shown inFIGS. 6,6A, and6B, the transition surface146is in the form of a concavity146aand can be any of several radii. More specifically, a radius152of the concavity146ais greater than a corresponding radius of both the first segment148and the second segment150.

Other embodiments of the transition surface146are contemplated. For example, as shown inFIG. 6A, the transition surface146can be in the form of a linearity146bor a convexity146c(shown in phantom). In still other embodiments, as shown inFIG. 6B, the transition surface146can be in the form of a first linear surface146dforming a vertex160with a second linear surface146e(shown in phantom). The vertex160can be positioned toward or away from the axis of rotation116(seeFIG. 5). In still other embodiments, the transition surface146can also be in the form of a plurality of steps (not shown). In the illustrated embodiments, plenum130, which includes the plenum body132, the skirt140, and the interface142with a transition surface146, has a substantially uniform thickness regardless of the specific manufacturing method. Such an interface142, including the transition surface146, allows for smoother flow of incoming air moving adjacent to skirt140and into axial fan110, increasing fan efficiency and reducing fan noise as previously discussed.

Although this embodiment was illustrated and described inFIGS. 5-6in terms of a single transition surface146, no such limitation is to be implied and any or all interfaces142, skirts140, and edges134defined by the plenum body132may be so configured. In addition, a particular edge134may have a defined length of magnitude more or less than that of length L1. For example, one edge134may have a length L1and another edge134may have a length L2, where L2is a different length than L1. In all other respects the above description is applicable to such a configured fan shroud and one, some, or all of edges134with respective length L1, length, L2, etc., may include an interface142with an underside144having a transition surface146joining the edge134with a respective skirt140as herein described. For example, a second edge134with a length L1(or length L2) may be joined to a second skirt140that extends proximate the second edge134with a second interface142preferably of length L1(or length L2) having an underside144with a transition surface146, a first segment148located on one side of the transition surface146, and a second segment150located on the other side of the transition surface146. The transition surface146of each such underside144has a length less than length L1(or length L2) of the respective interface142. The transition surface146of each underside can have a length as previously specified. Further, the transition surface146of each underside144can be in the form of any embodiment previously specified.FIG. 9Ashows a configuration having transition surfaces146for all four skirts illustrated, three of which are depicted in phantom. As with the above description, the transition surface146can be positioned anywhere within the respective interface142but a center149of the transition surface146is preferably located at the midpoint of the respective interface142, or, alternatively, substantially aligned with barrel midpoint126.

The barrel118can be variously positioned with respect to the plenum body132, as shown inFIG. 7. In a configuration such as shown inFIG. 7, the barrel midpoint126coincident with the axis of rotation need not be equidistant to the midpoint of each plenum edge134. Moreover, the ratio between the barrel radius124and the distance of a line170proceeding from the barrel midpoint126perpendicular to the axis of rotation and to the outermost extent of skirt140as shown, for at least one plenum edge134, can preferably range from approximately 0.70 to 0.88.

The following description utilizes additional reference numbers to express various geometric relationships within the cooling fan assembly previously described and as shown inFIGS. 5-7. Referring toFIGS. 8,9A,9B, and9C, an axial cooling fan assembly includes a fan shroud200surrounding an axial fan210. Fan210has one or more fan blades212coupled to a hub214rotating about an axis of rotation216for drawing air through a heat exchanger, not shown. A downstream direction along the axis of rotation216is defined such that the fan210is located downstream of the heat exchanger.

The fan shroud200includes a barrel218and a plenum230. The barrel218generally encircles and contains the axial fan210and is concentric with the axis of rotation216. The barrel218includes a housing portion220downstream of a base portion222that is coupled to the plenum230. The housing portion220includes an inner surface221. The barrel also defines a barrel radius224extending from a barrel midpoint226coincident with the axis of rotation to inner surface221of the housing portion220.

The plenum230includes a plenum body232radially extending from the base portion222and having a substantially rectangular platform viewed from the upstream direction. The plenum body232can be angled from the base portion222such that at a further radius from the axis of rotation216, the plenum body232is positioned further upstream. The plenum230also includes at least one skirt240coupled to the plenum body232and extending in a direction substantially parallel to the axis of rotation216. The skirt240includes a substantially rectilinear upstream border242having a first end236and a second end238.

A cross section C is defined parallel to the axis of rotation216and passes through barrel midpoint226. Cross section C is also substantially normal to skirt240through which it passes. Cross section C is not otherwise limited to a particular orientation nor is it dependent upon the position of barrel218with respect to the plenum body232. A distance D1is defined between cross section C and first end236and a distance D2is defined between cross section C and second end238. A distance D3is defined as the lesser value of D1and D2, or if D1equals D2, D3is equal to either D1or D2. A plane P1is defined as parallel to and offset from cross section C. Preferably, plane P1is offset a distance DP1equal to between about 0.125 of barrel radius224and about 0.75 of barrel radius224, but less than the value of D3. A plane P2is defined as parallel to and offset from cross section C, on the opposite side of cross section C from plane P1. Preferably, plane P2is offset a distance DP2equal to between about 0.125 of barrel radius224and about 0.75 of barrel radius224, but less than the value of D3. The sum of DP1and DP2is preferably within a range having a lower limit of about 0.25 of barrel radius224and an upper limit of about 1.5 of barrel radius224. A plane P3is defined as perpendicular to cross section C and contains a point that is on upstream border242of skirt240. A plane P4is perpendicular to plane P3and perpendicular to cross section C and contains a point250on cross section C on the plenum body232. Point250is preferably located a distance from the axis of rotation216at least a multiple of 1.1 of barrel radius224. A plane P5is defined as parallel to and offset from cross section C. Preferably, plane P5is offset a distance equal to D3. A plane P6is defined as parallel to and offset from cross section C on the opposite side of cross section C from plane P5. Preferably, plane P6is offset a distance equal to D3.

Referring toFIGS. 10A and 10B, an upstream surface251is defined as the surface of the plenum230located on the upstream side of plenum body232and continuous with the surface of skirt240up to the upstream border242. Generally, the upstream surface251monotonically increases in distance in a direction upstream from base portion222. By monotonically increasing, the upstream surface251either increases or at least does not decrease in distance from base portion222in the upstream direction. Fan shroud200, however, may include one or more surface deviations252departing from the monotonically increasing upstream surface251. InFIG. 10C, an effective surface260is defined and shown as overlaid onto upstream surface251. Referring toFIG. 10C, the effective surface260represents a surface equal to upstream surface251in the absence of a surface deviation252, and equal to a monotonically increasing surface in the presence of a surface deviation252. Therefore, effective surface260accounts for any surface deviations present in the fan shroud200in order to preserve a monotonically increasing reference surface.

With the aforementioned geometry, a volume V1is defined as a volume enclosed by plane P1, plane P2, plane P3, plane P4, and effective surface260. A volume V2is defined as enclosed by plane P1, plane P3, plane P4, plane P5, and effective surface260. A volume V3is defined as enclosed by plane P2, plane P3, plane P4, plane P6, and effective surface260. An average cross sectional area A1is defined as volume V1divided by the sum of offset distance DP1and offset distance DP2, or V1/(DP1+DP2). An average cross sectional area A2is defined as volume V2plus volume V3divided by the sum of distance D3minus offset distance DP1plus the distance D3minus offset distance DP2, or (V2+V3)/((D3−DP1)+(D3−DP2)).

As a result of the configuration of the axial cooling fan assembly, and in particular the fan shroud200as previously described, the average cross sectional area A1will be less than the average cross sectional area A2. This is shown visually inFIGS. 11 and 11A, in which shaded volume270, defined as previously described, represents volume V1, shaded volume272represents volume V2, and shaded volume274represents volume V3. The average cross sectional area calculated and depicted as area276is of a lesser value than the average cross sectional area calculated and depicted as area278, as illustrated inFIG. 11A. The areas276,278, are representative of average areas and no significance should be placed on their precise position inFIG. 11. For comparison,FIGS. 12 and 12Ashow a corresponding illustration of such volumes and areas as described above for the conventional fan shroud ofFIG. 1, andFIGS. 13 and 13Bshow a corresponding illustration of these volumes and areas for the conventional fan shroud ofFIG. 3.FIGS. 12A and 13Ain particular illustrate that area A1is generally greater than area A2for the conventional fan shrouds.

Though this embodiment was illustrated and described inFIGS. 8-11in terms of a single cross section relative to a single skirt240, no such limitation is to be implied. For example, separate cross sections, planes, and other parameters described above may be similarly defined and positioned with respect to one, some, or all of skirts240of a fan shroud200, resulting in volumes and cross sectional areas as previously described for each skirt240. Also as previously described and as illustrated inFIG. 7, the barrel218can be variously positioned with respect to the plenum body232, in which case distance D1is not equal to distance D2, which will be consequently reflected in the application of distance D3. In addition, the preceding description is applicable to embodiments beyond those disclosed inFIGS. 6A-6B.

The above descriptions are equally applicable for axial cooling fan assemblies having multiple fans300,302, as shown inFIG. 14. In this configuration, a plenum body304transitions into two barrels306,308and defines two fan shroud sections310,312. Barrels306,308contain the fans300,302and are concentric with axes of rotation314,316about which fans300,302rotate, respectively. In such a circumstance, each fan shroud section310,312is analyzed separately as previously described. For example,FIGS. 14A and 14Bshow a plan view and side view, respectively, of a dual fan configuration with a cross section, planes, and other parameters similar toFIGS. 9A and 9Band as previously described. More than two fans and two fan shroud sections may also be contemplated and analyzed in this way.