Cooling fan module and system

A cooling fan module includes a frame, and a fan impeller having a plurality of fan impeller blades is located in an opening of the frame. The fan impeller blades are connected to a base portion of an outer fan ring. A lip portion of the outer fan ring extends from the base portion radially outward, and a leading end of the lip portion is turned in direction to the downstream side of the frame. A recirculating flow guiding device includes a plurality of guide vanes located on an upstream side of the frame and around the opening of the frame. An air gap is provided between the outer fan ring and the frame. A recirculating flow travels from downstream side of the cooling fan module through the air gap, and is turned by the leading end of the lip portion into the recirculating flow guiding device.

FIELD OF THE INVENTION

The present invention relates to a cooling fan module, in particular in the automotive field, e.g., for a motor vehicle, and a system comprising a cooling fan module and a radiator and/or condenser.

TECHNICAL BACKGROUND

Cooling fan modules are used to cool the engine in motor vehicles. In this connection, it is the aim to improve the cooling performance for the engine, transmission and the comfort of the vehicle occupants, especially with regard to increasing fan efficiency and minimising the noise generated by the cooling fan module.

Generally a cooling fan module consists of a fan impeller, a motor located at the centre of the fan to drive the fan impeller, and a frame or shroud which comprises assembly struts for fixing the motor. Further, the fan impeller of a cooling fan module is designed to produce an air flow with which the heat generated by the engine is removed.

In an engine cooling fan module, pressure downstream of or after the fan is higher than pressure upstream of or in front of the fan for the effective fan operating range. This pressure difference drives airflow from downstream of the fan back to upstream of it forming undesired recirculating flow through the running clearance between the frame orifice or shroud orifice and the fan ring of the fan impeller. Due to the rotation of the fan, there is a swirling motion in downstream of the fan, this swirling motion is carried to front of the fan by this recirculating flow, friction force from the rotating fan ring also contributes to this swirling motion in the recirculating flow. This recirculating flow then is drawn back into the fan again in fan blade tip region. As a result, in the tip region of the fan blade there is a large variation of tangential airflow velocity, and the blade is at varying angles of attack different from that of the main flow, which leads to airflow separation in blade tip region, this portion of blade becomes low in efficiency, noisy and inconsistent with the rest of the fan blade. At the largest radius, the tip region of the fan blade has the largest working potential and biggest influence on the performance of the entire fan. This reduced performance at the blade tip region decreases efficiency of the fan module significantly.

SUMMARY OF THE INVENTION

Against this background, an objective of the present invention is to provide an improved cooling fan module for a motor vehicle.

This objective is achieved according to the invention by a cooling fan module having the features in claim1.

A cooling fan module, in particular for a motor vehicle, comprising:

a frame, wherein the frame is provided with an opening;

a fan impeller located in the opening of the frame, wherein the fan impeller comprises a plurality of fan impeller blades, wherein the fan impeller blades are connected to one another at an outer end via an outer fan ring, wherein the fan ring comprises a base portion and a lip portion, wherein the fan impeller blades are connected to the base portion, wherein the lip portion extends from the base portion radially outward and wherein a leading end of the lip portion is turned in direction to the downstream side of the frame;

a recirculating flow guiding device located on the upstream side of the frame and around the opening of the frame,

wherein an air gap is provided between the fan ring and the frame, a recirculating flow from downstream side of the cooling fan module flowing through said air gap, and

is turned by the leading end of the lip portion into the recirculating flow guiding device to remove swirl motion from the recirculating flow.

The concept underlying the invention entails guiding airflow, so that the airflow flowing through the air gap can go straight outwards radially into the recirculating flow guiding device without been severely blocked or forced to turn axial immediately. Since the recirculating airflow can be effectively directed into the recirculating airflow guiding device instead of bypassing it swirl motion from the airflow can be removed by the recirculating flow guiding device. As a result performance of the tip region of the fan blades is improved which leads to a more efficient fan module and lower noise.

Advantageous embodiments and developments of the invention emerge from the additional subordinate claims and from the description with reference to the drawing figures.

According to an embodiment of the invention at least a downstream side of the lip section is turned in direction to the downstream side of the frame, wherein an upstream side of the lip section is also turned in direction to the downstream side of the frame or extends at least partially straight to the base section of the fan ring. This lip design force reverse airflow going radially outwards with velocity component toward downstream of the fan to more effectively directing airflow into guiding vanes and prevent airflow bypassing them. In an embodiment of the invention the leading end of the lip section is curved or folded to turn the leading end in direction to the downstream side of the frame, wherein the leading end is folded forming a sharp folding edge as shown below inFIG. 6or a rounded folding edge as shown by the dotted line below inFIG. 6.

In a further embodiment of the invention at least one of a leading edge or a trailing edge of the leading end is rounded or forms a sharp edge as shown below inFIGS. 5 and 7. A sharp edge is a little more effective in directing airflow direction, and a rounded edge has a slightly lower noise.

According to an embodiment of the invention the recirculating flow guiding device is located between the frame and the fan impeller on the upstream side of the frame. Since the swirl motion is removed by the recirculating flow guiding device, the airflow goes back into the fan impeller again with the same tangential relative velocity to the fan impeller as the normal incoming airflow. Thus, fan efficiency is enhanced.

In an embodiment of the invention, the recirculating flow guiding device comprises guide vanes which are arranged around the opening of the frame and the circumference of the fan impeller, wherein the guide vanes are oriented preferably in the radial direction of the fan impeller. Thus, the airflow flowing through the air gap can go straight outwards radially and can be further directed into the guide vanes to remove swirl motion.

In a further embodiment of the invention, at least two of the guide vanes comprise the same length or are different in length. Guide vanes of different length can be provided in case of geometry limitation as shown inFIGS. 22 and 25, or in case the distance between two long guide vanes is too small to fit in an additional long guide vane in between in the molding tooling as shown below inFIG. 20. Further, when radius increases, distance between guide vanes also increases and a partial guide vane or shorter guide can be fit in between the two longer or long guide vanes. Moreover, the more guiding vanes the better, as airflow will be less likely to separate and better follows curvature of the vanes.

In another embodiment of the invention at least two of the guide vanes comprise at least one curved portion and/or at least one straight portion. The leading edge of the curved portion of the guide vanes is aligned with incoming recirculating airflow direction. The curved guide vanes remove swirl motion by gradually change the direction of the recirculating airflow to reduce airflow separation, airflow loss and noise. When design is right, curved or a portion is curved guiding vanes will align its leading edge with incoming reverse airflow, so there is no separation, and guiding vanes is more effective and fan module is more efficient with less noise.

According to an embodiment of the invention at least two of the guide vanes extend to an outer edge of the frame or terminate at the outer edge of the frame as shown below inFIG. 25. Such guiding vanes can remove even more swirl motion as reverse flow stay longer within these vanes.

In an embodiment of the invention at least an outer portion of the guide vanes comprises a height, so that the outer portion of the guide vane extends beyond the upstream side of the fan ring, terminates at the upstream side of the fan ring or terminates before the lip section of the fan ring. Guide vanes which extend beyond the upstream side of the fan ring reduce airflow bypassing these guide vanes.

In a further embodiment of the invention the guide vanes are equally and/or unequally spaced around the circumference of the fan impeller. An angular spacing between two neighbouring guide vanes is for example in a range between 1° degree to 5° degrees. Tonal noise can be minimized when guide vanes are unequally spaced.

According to the preferred embodiment of the invention the clearance between the guide vanes and the fan ring is as tight as possible to reduce overall recirculating flow rate and reduce airflow bypassing these guide vanes. For a 400 mm to 500 mm diameter fan impeller the clearance is, e.g., in a range between 4 mm to 6 mm in radial direction and in a range between 5 mm to 7 mm in axial direction of the fan impeller.

In the preferred embodiment of the invention the frame is configured so that an airflow passing through an exit of an airflow passage formed by the air gap can go straight or essentially straight outwards radially without been blocked by a wall of the frame as shown below inFIG. 9. Thus, airflow flowing through the air gap and going straight outwards radially is not blocked and can be directed to the guide vanes to remove swirl motion.

In another embodiment of the invention the thickness of at least one guide vane is in a range of, e.g., 1 mm to 3 mm.

According to a further embodiment of the invention a system comprising a cooling fan module and further a heat exchanger. The heat exchanger can be arranged on the upstream side and/or the downstream side of the fan module dependent on the intended function or use.

The accompanying drawings should convey further understanding of the embodiments of the invention. They illustrate embodiments of the invention and clarify the principles and concepts behind the invention in conjunction with the description. Other embodiments and many of the described advantages are apparent with respect to the drawings. The elements of the drawings are not necessarily illustrated true to scale in relation to each other.

In the figures in the drawing, the same elements, features and components, or those serving the same function and having the same effect, are provided with the same reference numerals in each case—unless otherwise specified.

DESCRIPTION OF EMBODIMENTS

FIG. 1shows a perspective front view of a fan module1, in particular a cooling fan module for a vehicle, according to a first embodiment of the invention. Further,FIG. 2shows a perspective view of a section of the fan module1according toFIG. 1. Moreover,FIG. 3shows a perspective view of a section of the fan ring2ofFIGS. 1 and 2.

The cooling fan module1comprises a shroud or frame3provided with an opening4or orifice on which a fan or fan impeller5is located. In the following the term frame is used, but the term shroud can be used instead. The fan impeller5is fixed to a motor shaft, and the motor (not shown inFIG. 1) is located inside the fan hub8and fixed to the frame3by assembly means, e.g. struts etc., not shown inFIG. 1. The fan can rotate around the center line of the opening4perpendicular to the frame3by means of the motor shaft rotating inside the motor. The center point29of the opening of the frame3which lies of the center line is indicated inFIG. 1and further inFIGS. 21 and 22below.

Further, the fan impeller5, in particular an axial fan impeller, comprises a plurality of fan impeller blades6. The fan impeller blades6are attached at their lower end or inner end to a fan hub8and are further connected to one another at their upper end or outer end7via an outer fan ring2. The fan ring2is located between the fan impeller5and the frame3as shown inFIGS. 1 and 2. An air gap10(shown inFIGS. 9 and 11) is provided between the fan ring2and frame3, the recirculating airflow of the cooling fan module1flows through said air gap10.

Further, the inventive fan module1comprises an additional recirculating flow guiding device11comprising a plurality of guide vanes12located on an upstream side or front side of the frame3surrounding the opening or orifice4for the fan impeller5as shown in the embodiment inFIGS. 1 and 2. In the embodiment as shown inFIGS. 1 and 2, the guide vanes12are curved and are further oriented or essentially oriented in the radial direction of the fan impeller5. InFIG. 1the guiding vane12is curved with leading edge aligned with incoming recirculating flow, but the overall orientation of the curved guide vane12is still in radial direction. Furthermore, in the embodiment as shown inFIGS. 1 and 2, the guide vanes12have for example the same length and are evenly arranged or evenly spaced around the opening4of the frame3and the circumference of the fan impeller5. However, according to further embodiments of the invention, the length of the guide vanes12can be varied. In an embodiment of the inventive fan module between two longer guide vanes a shorter guide vane can be arranged (as shown inFIG. 20). However, the invention is not limited to this arrangement of guide vanes.

The guide vanes12shown in the embodiment inFIGS. 1 and 2are curved. The guide vanes12can be at least partially curved or completely curved as it is the case in the embodiment shown inFIGS. 1 and 2. Furthermore, the guide vanes12can be also at least partially straight, flat or unbent as shown in subsequentFIGS. 25 and 26or the guide vanes can be completely straight, flat or unbent as illustrated e.g. in subsequentFIG. 22. The provision of at least one guide vane12which comprises at least one portion which is curved and/or at least one portion which is straight applies to all embodiments of the inventive fan module1. Furthermore, in the embodiment as shown inFIG. 1, the guide vanes12have the same length and are arranged to form a ring around the opening4of the frame3and the fan impeller5. Further, the guide vanes12inFIG. 1terminate before an outer edge15of the frame3. In other embodiments as shown, e.g., in followingFIG. 22, the guide vanes can also extend to the outer edge of the frame.

As shown inFIGS. 2 and 3, the fan ring2comprises a base section13and a lip section14. The base section13extends, e.g., in an axial or essentially axial direction of the fan impeller5. Further, the fan impeller blades6are attached with their upper end or outer end7to the base section13of the fan ring2. The lip section14extends from the base section13upward or outward in direction to the outer edge of the frame3. In the embodiment as shown inFIGS. 1, 2 and 3the lip section14extends from the base section13upward in a radial direction or essentially radial direction of the fan impeller5. According to the invention the leading end16of the lip section14is formed to direct recirculating airflow into the guide vanes12.

According to the invention and as shown inFIGS. 1 to 3the leading end16of the lip section14is turned in direction to the rear side or downstream side of the frame3. This applies to all embodiment of the inventive fan module1.

In the first embodiment as shown inFIGS. 1-3, the leading end16of the lip section14is curved outwards in direction to the rear side or downstream side of the frame3as shown inFIG. 5. In an alternative embodiment as shown in subsequentFIG. 6, the leading end of the lip section is turned by bending the leading end of the lip section, e.g., in the axial direction of the fan impeller in direction to the rear side or downstream side of the frame.

InFIG. 4a cross-section of a conventional fan ring200is shown. The fan ring200comprises a base section130and a lip section140. The base section140extends in an axial direction of a fan impeller not shown. Further, the lip section140and its leading end160extend normally or straight to the base section130. The leading end160of the lip section140is not further turned in direction to the rear side or downstream side of the corresponding frame.

In the embodiment of the invention as illustrated inFIG. 5, the fan ring2comprises a base section13and a lip section14. The base section13extends in an axial direction of a fan impeller not shown. Further, as shown inFIG. 5the leading end16of the lip section14is turned, in direction to the rear side or downstream side of the frame3and forms a radius. According to the embodiment illustrated inFIG. 5, a front side or downstream side17and a back side or upstream side18of the lip section14are both turned, e.g., curved, in direction to the rear side or downstream side of the frame3. The front or downstream side17and the back side or upstream side18are two surfaces on both side of lip section14of fan ring2, they can be e.g. curved surfaces.

The radius formed by the downstream side17of lip section14in the embodiment shownFIG. 5is, e.g., 7.5 mm. However, the invention is not limited to a radius of 7.5 mm. The radius formed by the downstream side17of lip section14can be larger or smaller than 7.5 mm. In particular, the lip section14and its2side17and18can comprise any curvature or radius which is suitable to direct recirculating airflow into the guide vanes of the respective fan module. In the embodiment as shown inFIG. 5a leading edge19of the leading end16is rounded. Further a trailing edge20of the leading end16forms, e.g., a blunt angle. The radius at the leading edge19is really small, e.g. 0.5 mm, it can be sharp, too, as shown inFIG. 7. The purpose of this small radius is to reduce stress concentration and further to reduce the possibility of cut of hand when worker handling it. Moreover, this small radius reduce noise in certain airflow condition, when at very low airflow rate, recirculating flow will “hug” fan ring2all the way from downstream side to upstream side. This small curvature at the leading edge19will prevent flow separation at the leading edge19and reduce noise.

InFIG. 6a further cross-section of an example of a fan ring2according to the invention is shown. The fan ring2comprises a base section13and a lip section14. The base section13extends in an axial direction of a fan impeller not shown. Further, the lip section14extends for example normally or perpendicular to the base section13.

In the example shown inFIG. 6and as described before, the leading end16of the lip section14is turned by bending the leading end16of the lip section14, e.g., in direction to the rear side or downstream side of the frame3. In this connection the leading end16of the lip section14can be bent, e.g., in the axial or substantially axial direction of the fan impeller5in direction to the rear side of the frame. Furthermore, as shown inFIG. 6the lip section14can be turned or bent such that the inner part or lower part of the lip section remains normally or straight to the base section13while the outer part or upper part of the lip section14extends in direction to the rear side of the frame and, e.g., parallel or essentially parallel to the base section13.

Furthermore, the leading end16of the lip section14can be bent or folded to form a sharp edge21as shown exemplary inFIG. 6or to form a rounded edge, as illustrated by the dotted line inFIG. 6. Further, in the embodiment as illustrated inFIG. 6a leading edge19and a trailing edge20each form a sharp edge. However, the leading edge19and/or the trailing edge20can be also rounded instead of form a sharp edge. This applies to all embodiments of the invention.

InFIG. 7another example of a fan ring2according to the invention is shown. The fan ring2comprises a base section13and a lip section14. The base section13extends, e.g., in an axial or essentially axial direction of a fan impeller not shown. Further, the lip section14extends for example normally or perpendicular to the base section13, and the downstream side17of the leading end16shown in the embodiment inFIG. 7is turned in direction to the rear side or downstream side of the frame while the upstream side18of the leading end16extends normally or straight to the base section13. Moreover, in the embodiment as illustrated inFIG. 7a leading edge19and a trailing edge20of the leading end16each form a sharp edge. However, at least one of the leading edge19or the trailing edge20can be rounded. This applies to all embodiments of the invention.

InFIG. 8a cross-section of a section of a conventional fan module100and inFIG. 9aa cross-section of a section of an inventive fan module1are shown.FIG. 9bshows a cross-section corresponding to the fan module inFIG. 9a, wherein the guide vane12inFIG. 9bis short. In particular,FIGS. 8 and 9a,9beach illustrate a recirculating airflow passage formed by the fan ring2,200and the frame3,300of the fan module. In this connection, the inventive fan module1as shown inFIG. 9ais further provided with an additional recirculating flow guiding device11comprising a plurality of guide vanes12located on an upstream side or front side of the frame3. InFIG. 9aan exemplary guide vane12is shown by a dashed line. Furthermore, inFIGS. 8 and 9a, b, velocity vectors illustrate airflow through the recirculation passage.

As can be derived from a comparison of the conventional fan module100and the inventive fan module1, the frame3of the inventive fan module1is configured so that after recirculating airflow passing through the gap between fan ring2and the opening4of the frame3, it can go straight outwards radially without been severely blocked or forced to turn axial immediately as in a conventional fan module. InFIG. 8, the frame300extends above or covers an exit220of the recirculating airflow passage and thus forces the airflow after passing the exit to turn axially. In contrast, the frame3of the embodiment of the inventive fan module1as shown inFIG. 9ais formed not to interfere with the exit22or blocks the exit22of the recirculating airflow passage. Furthermore, since the height of the guide vanes12inFIG. 9ais high enough so that the guide vanes12extend beyond the upstream side of the fan ring2, recirculating flow goes through the guide vanes and swirl motion is removed. In case the height of the guide vanes12is too short as illustrated inFIG. 9b, so that the height of the guide vanes is not high enough and the guide vanes terminate before the leading end of the lip portion, a portion of recirculating flow may bypass the guide vanes12and keeps its swirl motion.

InFIG. 10a perspective view of a section of a conventional fan module100is shown, comprising a fan ring200and a frame300as shown before inFIG. 8. The airflow is illustrated inFIG. 10by velocity vectors. The velocity vectors show the recirculation flow carrying swirl motion. As described before, pressure after or downstream the fan impeller is higher than pressure in front or upstream of the fan impeller. This pressure difference drives airflow from downstream of the fan impeller back to upstream of it forming recirculation flow. Due to the rotation of the fan impeller, there is a swirling motion in downstream of the fan impeller. This swirl motion is also carried to the front or upstream of the fan impeller by this recirculation flow. As a result, at tip region of the fan impeller blade, encircled with a dashed line inFIG. 10, see a drastic relative tangential velocity change, which results in airflow separation at blade tip region and the fan module is significantly less efficient and generates more noise. The rotating direction of the fan is indicated with an arrow inFIG. 10.

In contrast thereto,FIGS. 11 and 12show perspective views of sections of the fan module according to the first embodiment of the invention, as shown before inFIGS. 1, 2, 3, 5 and 9. InFIGS. 11 and 12the airflow is also illustrated by velocity vectors. Further, the rotating direction of the fan is indicated with an arrow inFIG. 12.

The fan impeller5as shown inFIGS. 11 and 12comprises fan impeller blades6which are attached to the fan hub8and are further connected to one another via the outer fan ring2. As illustrated inFIGS. 11 and 12, the fan ring2is located between the fan impeller5and the frame3, wherein the air gap10is provided between the fan ring2and frame3. The recirculating flow guiding device11comprising guide vanes12is located on the upstream side or front side of the frame3surrounding the opening4of the fan impeller5. In the embodiment as shown inFIGS. 11 and 12, the guide vanes12are, e.g., curved and are further oriented or essentially oriented in the radial direction of the fan impeller5. Moreover, in the embodiment as shown inFIGS. 11 and 12, the guide vanes12have, e.g., the same length and are for example evenly arranged or evenly spaced around the opening of the frame3and the circumference of the fan impeller5. InFIG. 11further the upstream side28and the downstream side30of the fan ring2are indicated which correspond to the upstream side or front side and to the downstream side or rear side of the frame3, respectively.

As shown inFIG. 11by the velocity vectors, the lip section14of the fan ring2which is turned, e.g. curved, in direction to the rear side or downstream side of the frame3directs recirculation flow into the guide vanes12of the recirculating flow guiding device11. Further, as illustrated inFIG. 12by the velocity vectors, the swirl motion of the recirculation flow is removed by the guide vanes12.

Due to the pressure difference, recirculation flow comes into the air gap10between fan ring2and the frame3from the rear side or downstream side of the fan impeller5, and carries swirl motion with it. The lip section14of the fan ring2forces this airflow to make a sudden turn and directs this recirculation flow into the guide vanes12as illustrated by the velocity vectors inFIG. 11. When the airflow goes through the guide vanes12and out radially away from the fan impeller5, swirling motion is removed and the airflow goes back into the fan impeller5again with the same tangential relative velocity to the fan impeller5as the normal incoming airflow.

The tip region23of the fan impeller blade6, encircled with a dashed line inFIG. 12, has the maximum velocity of the fan blade because it is at the largest radius of the fan. Therefore, the tip region23is most important section of the fan impeller5. The specially designed fan ring to frame configuration of this invention directs recirculating airflow to go through the guide vanes12, wherein swirl is removed from the airflow. Because recirculation flow primarily influences the tip region23, the inventive fan module1drastically improves working condition in the tip region23and makes the direction of incoming airflow in this region much more stable and consistent with the rest of the fan impeller blade6. As a result, flow separation in this region is eliminated, fan pressure rise and fan efficiency increase significantly.

InFIG. 13a diagram is shown, illustrating the fan performance curve of a conventional cooling fan module as shown exemplary, e.g. inFIGS. 8 and 10before and the fan performance curve of a cooling fan module according to the invention as shown exemplary, e.g. inFIGS. 9, 11 and 12before.

Both, the conventional fan module and the cooling fan module of the invention inFIG. 13and subsequentFIG. 14, comprise the same fan impeller blades6and the same fan ring to frame clearance of, e.g., 6 mm. However, the inventive fan module comprises in contrast to the conventional fan module a recirculating flow guiding device comprising a plurality of guide vanes as shown, e.g., inFIGS. 9, 11 and 12, and a fan ring with a lip portion which is turned in direction to the rear side of the frame of the fan module to direct a recirculating airflow into the guide vanes. According toFIG. 13the fan pressure rise DP is shown depending on the volume flow rate Q. DP means “Difference in Pressure” before and after the fan. It shows the ability of a fan module in pumping airflow from upstream to downstream (against pressure gradient).

In the diagram the solid line indicates the fan performance of the conventional fan and the dashed line the fan performance of the fan module according to the invention. From the diagram it can be derived, that the inventive fan module provides a better fan performance than the conventional fan, since a higher fan pressure rise DP can be achieved at the same volume flow rate Q.

Further, inFIG. 14a diagram is shown, illustrating a fan efficiency curve of the conventional cooling fan module and that of the inventive cooling fan module ofFIG. 13.

According toFIG. 14the fan efficiency is shown changing with the volume flow rate Q.

In the diagram the solid line indicates the fan efficiency of the conventional fan and the dashed line the fan efficiency of the fan module according to the invention. It can be derived from the diagram as shown inFIG. 14, that the inventive fan module provides significantly better fan efficiency at the same volume flow Q than the conventional fan over most of the fan operating range.

InFIG. 15a perspective view of a section of the fan module1according to, e.g.,FIGS. 11 and 12is shown. Further,FIG. 16shows a cross-section of the fan module1ofFIG. 15in a perspective view.

Each guide vane12in the embodiment as shown inFIGS. 15 and 16and before inFIGS. 11 and 12is curved, e.g., completely curved along its length. A leading end or leading edge27of guide vanes12aligns with incoming recirculating airflow to reduce flow separation near the vanes as will be further explained with respect toFIGS. 17, 18 and 19below.

Further, each guide vane12is basically an extruded2D profile and its cross-section profile is located in the r-O plane of cylindrical coordinate system based on the fan impeller axis, the orientation of the cross-section profile is largely in r direction, and guide vanes12are extruded largely in z direction.

To avoid blocking airflow, the guide vanes12are preferably thin and the spacing between neighboring guide vanes12is preferably far enough. The thickness of the guide vanes12is preferably between 1 mm to 3 mm, and the angular spacing between neighboring guide vanes12is preferably between 1° degree to 5° degree. If the angle is too large, there will be a large space in between the neighboring guide vanes12and airflow will not follow the curvature of the guide vanes12to turn anymore.

As shown inFIG. 15, the angular degree between neighboring guide vanes12is for example 1.25 degree. In followingFIG. 21the angular degree between neighboring guide vanes is, e.g., 4° degree.

The guide vanes12can be unequally spaced to minimize possible tonal noise. Alternatively the guide vanes12can be equally spaced as shown inFIGS. 15 and 16.

The clearance between the guide vanes12and the fan ring2is preferably as tight as possible to reduce the overall recirculating flow rate, and reduce airflow bypass of guide vanes12. Further, the clearance is varying with the size of the fan impeller5and is for a 400 mm to 500 mm diameter fan impeller5used in the design implementation shown inFIG. 16, e.g., preferably 4 mm to 6 mm in radial direction and 5 mm to 7 mm in axial direction. As shown inFIG. 16for the 485 mm diameter fan impeller5the clearance is, e.g., 6 mm in radial direction and 6 mm in axial direction.

The guide vanes12also are preferably high enough to extend beyond the upstream side28of the fan ring2to reduce airflow bypass these guide vanes. InFIG. 16, the guide vanes12have a height so that the guide vanes12extend preferably in a range of 0 mm to 20 mm, e.g., 10 mm as shown inFIG. 16, beyond the leading edge20of the guide vanes12on the upstream side28of the fan ring2.

In case of 0 mm, the guide vanes12terminate at the upstream side28of the fan ring2as indicated by a dotted line inFIG. 16. In other words, the guide vanes12extend 0 mm beyond the upstream side28of the fan ring.

In case the height of the guide vanes12is too high so that the guide vanes12extend too far beyond the upstream side28of the fan ring2, the guide vanes12may collide with a radiator in front of the fan. On the other hand, if the height if the guide vanes12is too short, so that the guide vanes12terminate before the leading edge19a portion of recirculating airflow will bypass vanes12and swirl motion cannot be removed effectively as shown inFIG. 9b.

InFIGS. 17 and 18a schematic view of a guide vane12of the invention is shown. The corresponding neighboring guide vane is not illustrated. The airflow is further illustrated by velocity vectors. As can be derived fromFIGS. 17 and 18, the leading edge27of each guide vane12is aligned with the incoming recirculating airflow. After the incoming recirculating airflow went through the guide vanes12all swirl component is removed as shown inFIGS. 17 and 18without flow separation.

In contrast inFIG. 19a schematic view of a guide vane12is shown, wherein the leading edge27of the guide vanes12is not aligned with the incoming recirculating airflow. The corresponding neighboring guide vane is not illustrated inFIG. 19. Since the leading edge27of the guide vanes12is not aligned with the incoming airflow, the airflow is separated in between the guide vanes12as shown by the velocity vectors illustrating the airflow. This results in efficiency loss and increased noise.

InFIG. 20a perspective view of a section of an alternative of the fan module1according toFIG. 15is shown. In this alternative, instead of guide vanes having the same length as it is the case in the embodiment shown inFIG. 15, longer and shorter guide vanes12can be arranged alternately as shown exemplary inFIG. 20. Different lengths of the guide vanes12inFIG. 20are due to distance between A and B is too small to fit in a full guide vane in between in the molding tooling as shown inFIG. 20. When radius increases, distance between guide vanes12also increases and a partial guide vane12or shorter guide vane12can be fit in between the two long or longer guide vanes12. Further, the more guiding vanes12the better, as airflow will be less likely to separate and better follows curvature of the guide vanes12. However, the long and short guide vanes12inFIG. 20can be also at least partially straight or completely straight instead of curved as shown in followingFIGS. 21 to 26.

InFIGS. 21 and 22perspective views of a fan module1according to a further embodiment of the invention are shown. In this connection,FIG. 21shows a perspective view of a section of the fan module1. In contrast to the embodiment as shown, e.g., inFIG. 1, the embodiment as shown inFIGS. 21 and 22comprises straight, e.g., completely straight or flat guide vanes12and further a fan ring2with a configuration as shown before, e.g., inFIG. 7and in followingFIGS. 22 to 24.

FIGS. 23 and 24show cross-sections of the fan module1ofFIG. 22in a perspective view.

Each guide vane12in the embodiment as shown inFIGS. 21 to 24is, e.g., straight or flat and arranged on the upstream side or front side of the frame3. Further, each guide vane12is located in the radial direction or in the θ=constant plane of cylindrical coordinate system based on the fan impeller axis.

To avoid blocking airflow, the guide vanes12are preferably thin and the spacing between neighboring guide vanes12is preferably far enough. The thickness of the guide vanes12is in a range of, e.g., 1 mm to 3 mm, and the angular spacing between neighboring guide vanes is preferably an angular range between 1° degree to 5° degree, e.g., 4° degrees as shown inFIG. 21. InFIGS. 21 and 22the center point29of the opening4of the frame3is indicated.

Further, an upper portion or outer portion31of the guide vanes12extends beyond the upstream side28of the fan ring2while lower portion or inner portion32of the guide vanes12is arranged in the gap between the frame3and the fan ring2and further terminates before the base section13of the fan ring2as shown inFIGS. 23 and 24.

Furthermore, some or all of the guide vanes12can be unequally spaced to minimize possible tonal noise. Alternatively some or all of the guide vanes12can be equally spaced as shown, e.g., inFIGS. 21 to 24. Further, as pointed out before, the guide vanes12can have the same length or can be varied in length. In an embodiment of the inventive fan module longer and shorter guide vanes can be arranged alternately depending on packaging constrain, as shown before in the example inFIG. 20.

InFIGS. 25 and 26a,26ba further embodiment of the inventive fan module1is shown.FIG. 25shows a perspective view of the fan module1andFIG. 26ashows a sectional view of a section of the fan module1ofFIG. 25. FurtherFIG. 26bshows two sections of the fan module in a perspective view.

The embodiment of the fan module1shown inFIGS. 25 and 26a,26bis essentially identical with the embodiment shown and described with respect toFIGS. 1-3 and 5. The description thereof will be therefore not repeated. However, the fan module1shown inFIGS. 25 and 26a,26bdiffers from the fan module ofFIGS. 1-3 and 5in that the frame3is not rectangular, e.g. square, but comprises for example curved areas26to receive a larger fan impeller5. Furthermore, the guide vanes12of the recirculating flow guiding device11of the embodiment illustrated inFIGS. 25 and 26a,26bvary in length and each guide vane12comprises a curved portion24and a straight or flat portion25in contrast to the completely curved guide vanes shown inFIGS. 1 and 2. InFIG. 26a, the upstream side28of the fan ring2is indicated.

In the embodiment as illustrated inFIGS. 25 and 26a,26bthe length of the guide vanes12is adapted according to the form or contour of the frame3, wherein the length of the guide vanes12is shorter in the curved areas26of the frame3to allow to mount a fan impeller5in an opening4of the frame3and to surround the complete circumference of the fan impeller5with guide vanes12. Due to packaging constrain, it is possible to only partially surround fan impeller5with guide vanes12in circumferential direction on upstream side of frame3to take partial advantage of this invention. Further, as can be derived fromFIGS. 25 and 26a,26bthe curved portion24of the guide vane12is arranged adjacent to the fan ring2. Furthermore, the curved portion24of each guide vane12is identical and its leading edge27aligns with incoming recirculating airflow. As guide vanes start at different radial location, the longer but narrower guide vanes are arranged in a staggered manner to shorter but wider guide vanes to ensure their leading edge always align with incoming recirculating flow as shown inFIG. 26b.

Although the present invention has been fully described above by means of preferred embodiments, it is not limited to the above, but may be modified in a number of ways.

According to the invention as described before with respect to the figures a set of guide vanes largely oriented in the radial direction is created on the upstream side of the frame surrounding frame opening as shown, e.g., inFIGS. 1 and 2before. When the reverse or recirculating flow goes through the guide vanes, the swirl motion is removed and fan performance is improved. On the fan ring side, a lip portion is added to the larger radius leading edge side of the fan ring, as shown e.g. inFIG. 3before, to effectively direct recirculating flow into these guide vanes. The concept of this invention can also be applied outside of motor vehicle to any configuration of shroud/fan with ring in particular in the automotive field.

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