PATENT DOCUMENT

Publication Number: US-9765788-B2
Application Number: US-201414559672-A
Country: US
Kind Code: B2

Title: Shrouded fan impeller with reduced cover overlap

Abstract:
The described embodiments relate to improving efficiency of a low-profile cooling fan. In one embodiment, an impeller of the cooling fan includes a shroud which covers a central portion of the impeller, thereby allowing a central inlet portion of the blades to have an increased fan blade height when compared to a cooling fan constrained by minimum part tolerances between the fan blades and a portion of the fan housing. In some embodiments, the impeller includes splitter blades that can improve performance of the low-profile cooling fan.

Claims:
What is claimed is: 
     
       1. An impeller enclosed within a cover, the impeller comprising:
 a central hub; 
 a plurality of blades extending radially from the central hub; and 
 a ring shaped shroud attached to the plurality of blades separated from the cover by a radial gap configured to allow the ring shaped shroud to rotate with the plurality of blades without contacting the cover, wherein the ring shaped shroud is characterized by an outermost radial edge and an inner edge, wherein the ring shaped shroud is characterized by a first thickness at the inner edge and a second thickness at the outermost radial edge, and wherein the second thickness is greater than the first thickness. 
 
     
     
       2. The impeller of  claim 1 , wherein the ring shaped shroud increases in thickness along a gradient from an innermost edge to the outermost radial edge. 
     
     
       3. The impeller of  claim 1 , wherein the plurality of blades is integrally formed with the ring shaped shroud. 
     
     
       4. The impeller of  claim 1 , wherein the ring shaped shroud has a first side and an opposing second side, wherein the plurality of blades is positioned on the first side of the ring shaped shroud. 
     
     
       5. The impeller of  claim 4 , wherein each of the plurality of blades has a trailing edge and a leading edge, wherein the ring shaped shroud is positioned at a central portion between the leading edge and the trailing edge of each of the plurality of blades. 
     
     
       6. The impeller of  claim 4 , wherein the plurality of blades has trailing edges and leading edges, and wherein the ring shaped shroud has an outer edge defining an outer diameter and an inner edge defining an inner diameter, wherein the plurality of blades is circularly arranged such that the leading edges define a leading edge diameter and the trailing edges define a trailing edge diameter, wherein the plurality of blades are arranged with respect to the ring shaped shroud such that the trailing edge diameter is larger than the outer diameter of the ring shaped shroud. 
     
     
       7. The impeller of  claim 6 , wherein the leading edge diameter of the plurality of blades is smaller than the inner diameter of the ring shaped shroud. 
     
     
       8. The impeller of  claim 1 , wherein each of the plurality of blades has a curved geometry. 
     
     
       9. The impeller of  claim 1 , wherein the impeller includes a plurality of splitter blades, each of the plurality of splitter blades positioned between pairs of the plurality of blades, wherein a length of each of the plurality of splitter blades is less than a length of each of the plurality of blades. 
     
     
       10. The impeller of  claim 9 , wherein each of the plurality of splitter blades has a common length. 
     
     
       11. The impeller of  claim 9 , wherein the plurality of splitter blades is characterized as having at least two different lengths. 
     
     
       12. A fan assembly, comprising:
 a housing; 
 a cover that cooperates with the housing to define a fan assembly interior portion, the cover defining a fan inlet zone external to the fan assembly suitable for receiving an air flow in accordance with a pressure difference; and 
 an impeller arranged to rotate in a manner that creates the pressure difference to drive the air flow and disposed within the interior portion of the fan assembly, the impeller comprising a plurality of fan blades that are integrally formed with a shroud that extends toward leading edges of the plurality of fan blades, the shroud and cover defining a radial gap, wherein the shroud is characterized by an annular shape having an outermost radial edge and an inner edge, wherein the shroud is further characterized by a first thickness at the inner edge and a second thickness at the outermost radial edge, and wherein the second thickness is greater than the first thickness. 
 
     
     
       13. The fan assembly as recited in  claim 12 , wherein a surface of the shroud is configured to bias air flow away from the radial gap between the shroud and the cover. 
     
     
       14. The fan assembly as recited in  claim 12 , wherein an outer diameter of the shroud extends to an outer tip of each of the plurality of fan blades. 
     
     
       15. The fan assembly as recited in  claim 12 , wherein the plurality of fan blades and the shroud cooperate to reduce a magnitude of a pressure gradient proximate to the radial gap, and to increase an impedance to air flow leakage through the radial gap from the interior portion to the fan inlet zone. 
     
     
       16. The fan assembly as recited in  claim 12 , wherein a portion of an outer diameter of the shroud comprises a protrusion that extends radially past the radial gap between the shroud and the cover. 
     
     
       17. The fan assembly as recited in  claim 16 , wherein a portion of an outer diameter of the shroud comprises a protrusion that extends radially past the radial gap between the shroud and the cover to obscure the radial gap and discourage air from passing through the radial gap. 
     
     
       18. A fan for an electronic device, the fan comprising:
 a cover; 
 an impeller arranged to rotate around a center of rotation independent of the cover, the impeller including a ring shaped shroud that cooperates with the cover to define an interior portion of the fan, wherein the ring shaped shroud includes blades and splitter blades radially positioned around the center of rotation, each of the splitter blades having a length that is less than a length of each of the blades, wherein the ring shaped shroud is characterized by an outermost radial edge and an inner edge, wherein the ring shaped shroud is characterized by a first thickness at the inner edge and a second thickness at the outermost radial edge, and wherein the second thickness is greater than the first thickness. 
 
     
     
       19. The fan of  claim 18 , wherein the ring shaped shroud and cover define a radial gap between the ring shaped shroud and the cover, wherein blades and the ring shaped shroud cooperate to reduce a magnitude of a pressure gradient proximate to the radial gap. 
     
     
       20. The fan of  claim 18 , wherein the splitter blades are characterized as having at least two different lengths. 
     
     
       21. The fan of  claim 18 , wherein the impeller further comprises a support disc having a smaller diameter than a diameter of the ring shaped shroud, wherein the support disc is coupled with leading edges of the blades. 
     
     
       22. The fan of  claim 18 , wherein the shorter length of the splitter blades provides less impedance of air flow through an interior region of the impeller. 
     
     
       23. The fan of  claim 18 , wherein the impeller comprises a blade support disc that has a center that corresponds to a center of rotation of the impeller and that is coupled with leading edges of the blades. 
     
     
       24. The fan of  claim 23 , wherein the splitter blades have leading edges that define a diameter with respect to a center of rotation of the impeller, wherein the diameter of the leading edges of the splitter blades is larger than a diameter defined by an outer edge of the blade support disc.

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application claims priority to U.S. Provisional Application Ser. No. 61/911,931 filed Dec. 4, 2013 entitled “Shrouded Fan Impeller With Reduced Cover Overlap”, which is incorporated herein by reference in its entirety. 
    
    
     FIELD 
     The described embodiments relate generally to fan designs that allow for an overall reduction in height of a fan assembly. More particularly, the present embodiments relate to maintaining an effective blade height of the fan assembly by utilizing a shroud to cover part of a bottom portion of the fan assembly. 
     BACKGROUND 
     As computer systems are reduced in thickness, the thickness of the modules and components inside must also be correspondingly reduced. Although these modules and components must get thinner, reduced performance is generally not an acceptable consequence and, hence, new methods are sought to improve performance of these modules. One particular component module that continues to need a relatively substantial amount of vertical height is a fan assembly. Unfortunately, a reduction in height of the fan assembly generally corresponds to a reduced effective blade height of the fan assembly, thereby reducing an effective flow rate of the fan assembly. 
     Therefore, what is desired is a configuration that allows for a reduction in fan assembly height without reducing the effective flow rate of the reduced height fan assembly. 
     SUMMARY 
     This paper describes various embodiments that relate to designs for efficient low profile fan assemblies. 
     According to one embodiment, an impeller enclosed within a cover is described. The impeller includes a central hub and a number of blades extending radially from the central hub. The impeller also includes a ring shaped shroud attached to the blades separated from the cover by a radial gap that allows the ring shaped shroud to rotate with the plurality of blades without contacting the cover. The shroud extends towards the tip of each of the blades, allowing an increase in the effective height of the blades. 
     According to another embodiment, a fan assembly is disclosed. The fan assembly includes at least the following: a housing; a cover that cooperates with the housing to define a fan assembly interior portion, the cover defining a fan inlet zone external to the fan assembly suitable for receiving an air flow in accordance with a pressure difference; and an impeller arranged to rotate in a manner that creates the pressure difference to drive the air flow and disposed within the interior portion of the fan assembly, the impeller including a number of fan blades that are integrally formed with a shroud that extends toward leading edges of the fan blades to allow an increase in an effective height of the fan blades. The shroud and cover are separated by a radial gap. This gap is designed to be as small as possible to maximize the impedance to air flow through the radial gap from the relatively high pressure zone proximate to the blades to the relatively low pressure zone proximate to the fan inlet. 
     According to a further embodiment, a fan for an electronic device is described. The fan includes a cover. The fan also includes an impeller arranged to rotate around a center of rotation independent of the cover. The impeller includes a ring shaped shroud that cooperates with the cover to define an interior portion of the fan. The ring shaped shroud includes blades and splitter blades radially positioned around the center of rotation, each of the splitter blades having a length that is less than a length of each of the blades. At least one of splitter blades is radially positioned between every two blades. 
     Other aspects and advantages of the invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings which illustrate, by way of example, the principles of the described embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The disclosure will be readily understood by the following detailed description in conjunction with the accompanying drawings, wherein like reference numerals designate like structural elements, and in which: 
         FIG. 1  shows a perspective view of a conventional computer fan; 
         FIG. 2  shows a partial cross-sectional view of the conventional computer fan of  FIG. 1 ; 
         FIG. 3  shows a way of increasing a height of the fan blades without increasing an overall height of the fan; 
         FIG. 4  shows a figure defining the “pressure” and “suction” sides of a centrifugal impeller fan blade; 
         FIG. 5  shows a cross-sectional view of a fan and a flow pathlines associated with that fan; 
         FIG. 6  shows a partial cross-sectional view of another fan in which some blade-cover overlap is implemented; 
         FIG. 7  shows an isometric view of the impeller of  FIG. 6 ; 
         FIGS. 8A-8E  show alternative embodiments in which a shroud ring has a curved shroud surface that guides air flow away from recirculating through a shroud/cover radial gap; 
         FIG. 9  shows a graph depicting both air flow performance characteristics with and without a shrouded impeller; 
         FIGS. 10 and 11  show a front view of an impeller with shroud that includes splitter blades; 
         FIGS. 12 and 13  show isometric views of portions of the impeller of  FIGS. 10 and 11 ; and 
         FIGS. 14A-14D  illustrate how a divergence angle between blades and splitter blades can affect air flow. 
     
    
    
     DETAILED DESCRIPTION 
     Representative applications of methods and apparatus according to the present application are described in this section. These examples are being provided solely to add context and aid in the understanding of the described embodiments. It will thus be apparent to one skilled in the art that the described embodiments may be practiced without some or all of these specific details. In other instances, well known process steps have not been described in detail in order to avoid unnecessarily obscuring the described embodiments. Other applications are possible, such that the following examples should not be taken as limiting. 
     In the following detailed description, references are made to the accompanying drawings, which form a part of the description and in which are shown, by way of illustration, specific embodiments in accordance with the described embodiments. Although these embodiments are described in sufficient detail to enable one skilled in the art to practice the described embodiments, it is understood that these examples are not limiting; such that other embodiments may be used, and changes may be made without departing from the spirit and scope of the described embodiments. 
     As computer systems are reduced in thickness, the thickness of the modules and components inside the computer systems must also be correspondingly reduced. Although these modules and components must get thinner, reduced performance is generally not an acceptable consequence and, hence, new methods are sought to improve performance of these modules. Fan modules and assemblies, in particular, can be difficult to make thinner without dramatic loss in air throughput and cooling performance. 
     The fans and fan systems described herein include features that can provide a thin fan profile while providing high cooling efficiency. In some embodiments, the fans include impellers with shrouds that rotate independently from stationary covers of the fans. The shrouds cooperate with the stationary covers to define interior portions of the fans. The shrouds can include blades that are fixedly coupled to the shrouds or integrally formed with the shrouds. In some embodiments, the shrouds include splitter blades, which are generally shorter than the regular blades of the fans and which can increase efficiency of the fans. 
     These and other embodiments are discussed below with reference to  FIGS. 1-14 . However, those skilled in the art will readily appreciate that the detailed description given herein with respect to these Figures is for explanatory purposes only and should not be construed as limiting. 
       FIG. 1  shows a fan  100  for which such a method would be useful. Fan  100  can have many uses. For example, fan  100  can be used in portable computing device such as a laptop computer or other portable computing devices having limited internal volumes due to external size constraints. It should be noted that while a centrifugal fan is utilized for exemplary purposes, it should be understood that the described embodiments could be applied to both axial and mixed flow fans. Fan  100  can include exhaust opening  102  for expelling exhaust air flow  103  to an external environment and inlet opening  104  for receiving inlet air flow  105 . It should be noted that, in general, inlet air flow  105  and outlet air flow  103  are generally about the same. Also depicted are cover  106  and impeller  108 . Impeller  108  can be rotationally coupled to a bearing (not shown) within cover  106  that can impart a rotational force to impeller  108  causing blades  110  to rotate in such a way as to convert inlet air flow  105  into exhaust air flow  103 . 
       FIG. 2  shows a partial cross-sectional view of fan  100  (as indicated by section line A-A of  FIG. 1 ) that is installed within enclosure  201 . More specifically, impeller  108  is depicted bringing a stream of cooling air  202  through opening  104 . Fan blade  204  is depicted with dashed lines as only a portion  206  of fan blade  204  extending from impeller  108  is contained within the depicted cross-section. Each of fan blades  204  can have a curved geometry, as is depicted in  FIG. 1 . Inlet air flow  105  is constrained by enclosure  201 , which leads to a loss of flow rate of air through fan  100 . One way to attempt to increase the flow rate of air through fan  100  is to increase the height H of fan blades  204  within fan  100  without increasing the thickness l of fan  100 . A consequence of increasing the blade height H in this manner is a reduction in blade/cover clearance  208  as shown in  FIG. 2 . Unfortunately, this clearance reduction increases the risk of fan blades  204  interfering and/or causing rubbing noise between fan blades  204  and cover  106 . 
     It may also be desirable to improve a number of other performance parameters of fan  100 , especially when factors such as fan noise and thermal performance are important. Two such performance parameters include a volumetric flow rate of air through fan  100 , and an acoustic output (otherwise referred to as fan noise) of the fan  100  under operating conditions. In applications noted above where fan  100  is anticipated for use in a laptop computer environment, it can be of particular importance that fan  100  remove as much heat as possible with as little fan noise as possible in keeping with a desired computer user&#39;s experience. For example, if a thickness T of the computer system surrounding fan  100  and a thickness l of fan  100  are reduced in such a way that the ratio of fan thickness to computer system thickness (l/T) remains constant, the change in air flow performance of fan  100  can be calculated using known scaling equations, such as scaling equations found in Chadha, Raman (2005), Design of High Efficiency Blowers for Future Aerosol Applications, M.S. Thesis, Texas A&amp;M University, College Station, Tex., USA, which is incorporated herein by reference in its entirety. In particular, using scaling equation 36 of Chadha, Raman (2005), a fan having a thickness l of 6.0 mm would be expected to deliver 71.1% of the volumetric flow rate that of a fan having a thickness l of 8.0 mm. That is, the volumetric flow rate is significantly reduced by such thickness change. The static pressure is less sensitive to thickness changes. Specifically, a fan having a thickness l of 6.0 mm is calculated to produce 99.0% of the static pressure compared to a fan having a thickness l of 8.0 mm. 
     The fan and fan assemblies described herein are thin such that they can be positioned within small spaces such as enclosures of laptops and other portable computing devices, yet can deliver exceptional cooling needed for modern high performance computer systems. The fans include fan blades that are incorporated with or attached to a shroud. The shroud can function as a portion of the cover of the fan, thereby providing a configuration that allows for an increased fan blade area compared to conventional fans. To illustrate,  FIG. 3  shows a cross-sectional view of a fan  300  in accordance with some embodiments. Fan is positioned within enclosure  301 , which can correspond to an enclosure for a computer system or an enclosure of a subsystem that is further encased within one or more enclosures of a computer system. In this way, fan  300  and enclosure  301  form a fan assembly. Fan blade  304  is represented with dashed lines since the cross-section view of  FIG. 3  shows a portion of impeller  308  that does not include fan blade  304 . Fan blade  304  is one of multiple fan blades that are not depicted in  FIG. 3 . Fan blade  304  is coupled with shroud  302  such that shroud  302  can rotate with fan blade  304  and independent of cover  306 . Shroud  302  can be located proximate to and separated from cover  306  by shroud/cover radial gap  303 . Pathlines  310  indicate air flow between enclosure  301  and fan  300 , and toward interior portion  316  of fan  300 . Shroud  302  can function as a portion of cover  306  in that shroud can physically prevent ingress of air flow into an interior of fan  300  other than as depicted by pathlines  310 . 
     It should be noted that fan  300  shows a particular technique for increasing blade height H compared to fan  100  of  FIG. 2  without decreasing a blade/cover clearance. That is, incorporating shroud  302  with blade  304  allows blade  304  to be taller compared to a blade height that would be possible if a stationary cover is used, such as fan  100  of  FIG. 2 . This increases the effective height of blade  304 , which corresponds to the height of the blade  304  that is effective in moving air. In addition, this configuration eliminates the need for a clearance between fan blade  304  and the portion of the cover that makes up shroud  302 . The extra blade height H (corresponding to increased blade area) afforded by shroud  302  allows more momentum to be imparted to the incoming air, which can result in the development of higher static pressures and increased flow rates. The blade height inboard of shroud  302  can also be increased, resulting in additional useful blade surface. 
     In some embodiments it may be beneficial to avoid having shroud  302  extend all the way to the blade tips, as shown in  FIG. 3 . This is because this configuration could result in shroud/cover radial gap  303  being located at a region where the pressure difference between the inside and outside of the fan would be at its highest. In some configurations, shroud/cover radial gap  303  can be on the order of between about 0.3 mm and 0.5 mm wide. Alternatively, to ensure a properly functioning shrouded impeller, the ratio of shroud/inlet radial gap (g) to impeller blade tip diameter (D) should be less than 0.01. That is, g/D&lt;0.01. This is because the pressure can increase significantly with distance from a rotational axis of the impeller due to the action of the fan blade  304  being rotated through the air. This is illustrated with at  FIG. 4 , which shows an isometric view of impeller  400 . Impeller includes a central portion or central hub  412 , and fan blades that extend radially from central hub  412 . V represents the air velocity as experienced by fan blades  402 , r represents the distance from rotational axis  404  of the impeller  400  to tips  410  fan blades  402 , and ω represents the rotational speed of impeller  400 . The pressure increases significantly with distance r from the rotational axis due to the action of the fan blades  402  being rotated through air. Rotation of impeller causes higher static pressure to develop in “pressure side”  406  compared to “suction side”  408  of fan blades  402 . This results in creating different pressure gradients within a fan. 
       FIG. 5  shows a cross-section partial view of fan  500  positioned within enclosure  501  illustrating how different pressure differentials can be formed. Fan  500  includes impeller  502  and cover  504 . Impeller  502  includes blades  506  and shroud  508 , with shroud  508  extending to tips  510  of blades  506 . Air flow into fan  500  is represented by pathlines  512 . Fan inlet zone  518  corresponds to a region external to fan  500  where air enters the fan  500 . Air pressure gradually decreases as air flows from outer edge  514  to inner edge  516  of cover  504 . Then, air pressure gradually increases as air flows from fan inlet zone  518  to tips  510  of blades  506 . The region of blades  506  immediately proximal to shroud/cover radial gap  505  experiences the highest static pressure. In particular, region of blades  506  immediately proximal to shroud/cover radial gap  505  experiences much higher static pressure compared to fan inlet zone  518 . This significant difference in static pressure is separated by only shroud/cover radial gap  505 . 
     Providing some amount of radial overlap between fan blades  506  and cover  504  can reduce this pressure difference. The reduced pressure difference results in a lower likelihood of recirculating air from fan blades  506  back out into the fan inlet zone  518 . The compromise required by this solution is the need to maintain a blade-cover axial clearance outboard of shroud  508 , which results in less available blade area for moving air when compared to an impeller that has shroud  508  that extends to tips  510  of blades  506 . In some embodiments, shroud  508  can extend across a bottom surface of cover  504  in more traditional configurations. 
     An example of an impeller that is shrouded and yet maintains some blade-cover overlap is shown in  FIG. 6 , which shows a partial cross-section view of fan  600  within enclosure  603 . Fan  600  includes impeller  608  and cover  601 . Shroud/cover radial gap  612  separates cover  601  and shroud  610 . Pathlines  614  indicate air flow between enclosure  603  and fan  600 , and toward interior portion  616  of fan  600 . An isometric view of the impeller  608  is shown in  FIG. 7 . As shown in embodiments of  FIGS. 6 and 7 , shroud  610  can be positioned relative to fan blades  606  such that portions of fan blades  606  overlap with cover  601  (indicated by overlap  602 ), which reduces a likelihood of recirculating air from fan blades  606  into fan inlet zone  605 .  FIG. 7  shows how shroud  610  can have a ring or disc shape that can be characterized as having a first side  702  and opposing second side  704 . Fan blades  606  each have a leading edge  706  and trailing edge  708 . Fan blades  606  can be circularly arranged with respect to shroud  610  such that leading edges  706  define a leading edge diameter and the trailing edges  708  define a trailing edge diameter. Fan blades can be positioned on first side  702  positioned, while second side  704  can correspond to a surface of shroud  610  that cooperates with cover  601  to prevent ingress of air into an interior of the fan until it reaches the fan inlet opening. 
     In some embodiments, shroud  610  is positioned at a central portion of fan blades  606  corresponding to a portion of fan blades  606  between leading edges  702  and trailing edges  704 . For example, shroud  610  can be characterized as having outer edge  710  and inner edge  712 . Outer edge  710  can define an outer diameter of shroud  610 , and inner edge  712  can define an inner diameter of shroud  610  that acts as the fan inlet. Fan blades  606  can be arranged with respect to the shroud such that the trailing edge diameter (corresponding to trailing edges  708 ) is larger than the outer diameter of shroud  610  (corresponding to outer edge  710 ). In some embodiments, the leading edge diameter (corresponding to leading edges  706 ) is smaller than the inner diameter of shroud  610  (corresponding to inner edge  712 ). 
       FIGS. 8A-8E  show alternative embodiments in which a shroud and/or a cover are designed to prevent air flow within a shroud/cover radial gap, thereby improving the efficiency of the fan.  FIG. 8A  shows a cross section view of fan  800  positioned within enclosure  801 . Fan  800  includes cover  802  and impeller  804 . Impeller  804  includes blades  806  and shroud  808 . Pathlines  805  indicate air flow between enclosure  801  and fan  800 , and toward interior portion  807  of fan  800 . Shroud  808  is separated from cover  802  by shroud/cover radial gap  812 . Shroud  808  includes outlet surface  810  that is tapered to guide air flow (indicated by pathlines  805 ) away from shroud/cover radial gap  812  preventing recirculating of air through shroud/cover radial gap  812 . That is, shroud outlet surface  810  is angled to impart a vertical velocity component to the air flow near shroud/cover radial gap  812 , thereby biasing air flow away from shroud/cover radial gap  812 . For example, shroud outlet surface  810  can be arranged to direct air flow above and away from shroud/cover radial gap  812 . In some embodiments, this can be accomplished by increasing a thickness of shroud  808  when traveling from inner edge  814  to outer edge  816  of shroud  808 . Specifically, the thickness of shroud  808  increases from a first thickness  818  at inner edge  814  to a second thickness  819  at outer edge  816 . In some embodiments, shroud outlet surface  810  has a straight or linear shape while in other embodiments shroud outlet surface  810  is curved. In some embodiments, shroud outlet surface  810  includes one or more steps that provide a desired amount of taper. In some embodiments, shroud outlet surface  810  has a combination of linear segments, curved segments and/or stepped segments. 
       FIG. 8B  shows fan  820  having another alternative configuration in accordance with described embodiments. Fan  820  includes cover  822  and impeller  824 . Impeller  824  includes blades  826  and shroud  828 . Pathlines  825  indicate air flow between enclosure  821  and fan  820 , and toward interior portion  827  of fan  820 . Shroud  828  is separated from cover  822  by shroud/cover radial gap  832 . Shroud  828 , in addition to having a tapered shroud outlet surface  830 , also includes an overlapping feature  838  that overlaps with cover  822  proximate shroud/cover radial gap  832 . Overlapping feature  838  can force air out of shroud/cover radial gap  832  and back toward interior portion  827  of fan  820 . This can prevent undesirable leakage of air through radial gap  832 . Overlapping feature  838  can correspond to a ledge or lip positioned at inner edge  836  of shroud  828 . 
       FIG. 8C  shows fan  840  having another configuration in accordance with described embodiments. Fan  840  includes cover  842  and impeller  844 . Impeller  844  includes blades  846  and shroud  848 . Pathlines  845  indicate air flow between enclosure  841  and fan  840 , and toward interior portion  847  of fan  840 . Fan  840  is configured such that surfaces defining shroud/cover radial gap  852  are slanted in a way to prevent air flow into shroud/cover radial gap  852 . Specifically, outer edge  850  of shroud  848  and surface  851  of cover  842  define a shroud/cover radial gap  852  having a diagonal geometry that is slanted in a direction different than the air flow into the fan (represented by pathlines  845 ). This diagonal configuration forces air out of shroud/cover radial gap  852  and back toward interior portion  847  of fan  840 , which as in fan  820  of  FIG. 8B  reduces a likelihood of a parasitic flow path from being established through shroud/cover radial gap  852 . 
       FIG. 8D  shows fan  860  having another configuration in accordance with described embodiments. Fan  860  includes cover  862  and impeller  864 . Impeller  864  includes blades  866  and shroud  868 . Pathlines  865  indicate air flow between enclosure  861  and fan  860 , and toward interior portion  867  of fan  860 . Fan  860  shows a configuration in which outer edge  876  of shroud  868  extends past trailing edges  869  of fan blades  866 . This configuration prevents high pressure air exiting fan blades  866  and entering interior portion  867  from recirculating through shroud-/cover radial gap  872 . In some cases this configuration adds more length to shroud  868  compared to the shrouds shown in  FIGS. 8A-8C . 
       FIG. 8E  shows fan  880  having another alternative configuration in accordance with described embodiments. Fan  880  includes cover  882  and impeller  884 . Impeller  884  includes blades  886  and shroud  888 . Pathlines  885  indicate air flow between enclosure  881  and fan  880 , and toward interior portion  887  of fan  880 . Fan  880  shows a configuration in which shroud  888  has a tapered shroud interior surface  890  and a tapered shroud exterior surface  891 . One or both of tapered shroud interior surface  890  and a tapered shroud exterior surface  891  can have a linear shape, curved shape, stepped shape, or a combination of linear, curved and/or stepped segments. The tapered shroud exterior surface  891  directs air away from the shroud/cover radial gap  892  on one side of shroud  888 , and curved shroud interior surface  890  directs air that has a tendency to recirculate within interior portion  887  away from shroud/cover radial gap  892  on another side of shroud  888 . 
     Note that any suitable combination of the shroud and cover configurations described above with reference to  FIGS. 8A-8E  can be utilized. For example, the shrouds can have any suitable combination of the above-described varying thicknesses, tapered shroud outlet surfaces, tapered shroud inlet surfaces, slanted outer edges, overlapping features and outer edges that extend past trailing edge of the blades. 
       FIG. 9  shows a graph depicting both air flow performance of a fan using a shrouded impeller, such as the one shown in  FIG. 7  and performance of an unshrouded, or conventional, impeller such as the one used in the fan of prior art  FIG. 1 . The solid line shows the fan curve of a shrouded impeller with similar overall geometry and fan speed, but with a shroud. A large increase in the air flow delivered is observed for a significant portion of the fan operating range. The dotted line shows an example of a conventional impeller. As depicted, the shrouded impeller can have various effects on fan performance and can be beneficial for certain air flow rates and static pressures. 
     In some embodiments, the fan includes splitter blades that can be coupled to the shroud or other portions of the impeller in order to increase the efficiency of the fan.  FIG. 10  shows a front view of impeller  1000 , which includes a number of blades  1002  radially positioned around an axis of rotation of impeller  1000 . Central portion  1004  covers an impeller motor and bearing when impeller  1000  is assembled within a fan. Blades  1002  can have any suitable shape, including curved geometries that can be curved into the direction of rotation. Each of blades  1002  includes leading edges  1002   a  that are positioned more proximate to the center of rotation than trailing edges or tips  1002   b . In some embodiments, impeller  1000  includes blade support disc  1012  that is coupled with and supports leading edges  1002   a  of blades  1002 . The center of blade support disc  1012  can correspond to a center of rotation of impeller  1000 . 
     Impeller  1000  includes shroud ring  1006  that can constitute part of a cover and reduce the overall height of a fan, as described above. Shroud ring  1006  can be rigidly coupled with and support blades  1002 , or formed integrally with blades  1002 . In this way, shroud ring  1006  can rotate with blades  1002  during fan operation. In addition to blades  1002 , impeller  1000  includes splitter blades  1008 / 1010 , which are also radially positioned around an axis of rotation. In some embodiments, splitter blades  1008 / 1010  are coupled with shroud ring  1006 . Like blades  1002 , splitter blades  1008 / 1010  can guide air flow when impeller  1000  is rotated. However, splitter blades are generally shorter in length than blades  1002  and can thus be referred to as partial blades. The shorter length of splitter blades  1008 / 1010  allows for optimized flow guidance in the channels formed between adjacent blades  1002 . 
     To illustrate,  FIG. 11  shows a view of impeller  1000  with dashed lines representing portions of blades  1002  and splitter blades  1008 / 1010  that are not visible from a front view. Blades  1002  and splitter blades  1008 / 1010  each have trailing edges that are defined by fan blade diameter  1108 . However, splitter blades  1008 / 1010  have different lengths than blades  1002 . In particular, the leading edges of splitter blades  1010  are defined by a first diameter  1102 , the leading edges of splitter blades  1008  are defined by a second diameter  1104 , and the leading edges of blades  1002  are defined by a third diameter  1106 . The shorter lengths of splitter blades  1008 / 1010  keep them from impeding air flow entering from interior region  1110 . At the same time, the additional trailing edges or tips of splitter blades  1008 / 1010  being positioned along the fan blade circumference corresponding to diameter  1108  allows for improved guidance of air into the fan compared to blades  1002  alone. This can be important since the guidance provided by the tips of blades  1002  and splitter blades  1008 / 1010  are critical in determining the amount of air pressure produced by impeller  1000 . In some embodiments, the leading edges of one or both of splitter blades  1008  and splitter blades  1010  do not overlap with blade support disc  1012 . That is, one or both of diameters  1102  and  1104  can be larger than a diameter defined by an outer edge  1107  of blade support disc  1012 . 
       FIGS. 12 and 13  show isometric section views of a portion of impeller  1000  showing additional details of blades  1002  and splitter blades  1008 / 1010 . As shown, blades  1002  and splitter blades  1008 / 1010  are coupled with shroud ring  1006 . A top surface of shroud ring  1006  can correspond to a portion of a cover that impeller  1000  is assembled in. Blade support disc  1012  is positioned below shroud ring  1006  and is coupled with the leading edges of blades  1002 , which provides additional structural support for the longer length of blades  1002 . In some embodiments support disc  1012  has a tapered shape such that surface  1302  of support disc  1012  is substantially parallel or divergent with respect to surface  1304  of shroud ring  1006 . Splitter blades  1008 / 1010  are shorter than blades  1002  and circumferentially positioned between blades  1002 . The shorter length of splitter blades  1008 / 1010  provides improved flow guidance within interior region  1110  of impeller  1000 , thereby providing more efficient air flow through impeller  1000 . 
     Note that since shroud ring  1006  supports splitter blades  1008 / 1010 , splitter blades  1008 / 1010  do not need to extend from a location closer to the center of rotation, thereby allowing splitter blades  1008 / 1010  to be shorter and thus reduce impedance of air into the channel between consecutive blades  1002 . In embodiments that do not include shroud ring  1006 , splitter blades  1008 / 1010  can be coupled with support disc  1012 . In these embodiments, support disc  1012  can include gaps between splitter blades  1008 / 1010  to allow for low-impedance air flow within interior region  1110 . However, removal of shroud ring  1006  may mean losing some extra blade height afforded by the addition of shroud ring  1006 , as describe above with reference to  FIG. 3 . In addition, there can be some loss of blade area near support disc  1012 . 
     Impeller  1000  shown in  FIGS. 10-13  is configured such that two shorter splitter blades  1010  and one longer splitter blade  1008  are positioned between blades  1002  (i.e., short-long-short). It should be noted that this configuration is exemplary and other configurations can be used. For example, in some embodiments, an impeller can include splitter blades that each has one length, or the impeller can include splitter blades having more than two different lengths. In some embodiments, the splitter blades are arranged in other orders, such as long-short-long, short-short-long, long-long-short, long-medium-short, etc. In some embodiments, there is one splitter blade between each blade  1002 , while in other embodiments there are two, three, four, or more splitter blades between each blade  1002 . That is, the number and order of splitter blades can vary depending on design choice. Generally, the larger the fan blade diameter  1108  is, the more blades  1002  and splitter blades  1008 / 1010  can be positioned within the impeller to optimize air flow. The optimal number, order and shape of blades and splitter blades can be calculated for a given impeller by considering parameters such as the fan blade diameter and divergence angle between consecutive blades. 
       FIGS. 14A-14D  illustrate how a divergence angle between blades  1402  and  1404  can affect air flow.  FIG. 14A  shows reference circle  1408 , which is at a first radial distance from the center of rotation of the impeller.  FIG. 14B  shows reference lines  1412  and  1414 , which are tangential to reference circle  1408 . Angle  1416  corresponds to the angle between reference lines  1412  and  1414 , also referred to as a divergence angle. If divergence angle  1416  is too large, the air flow between blades  1402  and  1404  becomes inefficient. This is illustrated in  FIG. 14C , showing air flow pathlines  1418  and  1420  passing between blades  1402  and  1404 . Pathline  1418  shows that some air passes over and follows a surface of blade  1404 . However, pathline  1420  shows that some air does not follow the surface of blade  1404  but instead reverses direction, also known as flow separation. This flow separation can occur if the divergence angle  1416  between blades  1402  and  1404  is too large, which decreases the air flow efficiency of the fan. 
       FIG. 14D  shows insertion of splitter blade  1422 . Reference circle  1423  is at a second radial distance from the center of rotation, which is greater than the first radial distance of reference circle  1408 . Reference lines  1412  and  1414 , which are tangential to circle  1408  define divergence angle  1424 . As shown, divergence angle  1424  between blade  1404  and splitter blade  1422  is less than divergence angle  1416  without splitter blade  1404 . The reduced divergence angle  1424  reduces or eliminates any flow separation and improves the air flow efficiency of the fan. In general, the larger the divergence angle  1416  between blades  1402  and  1404 , the more splitter blades  1422  should be used. Another words, at each radial location there can be calculated an optimal number of blades. When that optimal number reaches an integer, another splitter blade can be added. 
     The foregoing description, for purposes of explanation, used specific nomenclature to provide a thorough understanding of the described embodiments. However, it will be apparent to one skilled in the art that the specific details are not required in order to practice the described embodiments. Thus, the foregoing descriptions of specific embodiments are presented for purposes of illustration and description. They are not intended to be exhaustive or to limit the described embodiments to the precise forms disclosed. It will be apparent to one of ordinary skill in the art that many modifications and variations are possible in view of the above teachings.

Metadata:
Filing Date: 20141203
Publication Date: 20170919
Grant Date: 20170919
Priority Date: 20131204
Inventors: DYBENKO JESSE T.
AIELLO ANTHONY JOSEPH
MANCINI NICHOLAS D.
NIGEN JAY S.
NAGHIB LAHOUTI ARASH
Assignee: APPLE INC
CPC Classifications: [{"code": "F04D29/4226", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D25/0613", "inventive": true, "first": true, "tree": "[]"}, {"code": "F04D29/162", "inventive": true, "first": false, "tree": "[]"}, {"code": "G06F1/20", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/4226", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/162", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D25/0613", "inventive": true, "first": true, "tree": "[]"}, {"code": "F04D25/0613", "inventive": true, "first": true, "tree": "[]"}, {"code": "F04D29/281", "inventive": true, "first": true, "tree": "[]"}, {"code": "F04D29/4226", "inventive": true, "first": false, "tree": "[]"}, {"code": "F04D29/162", "inventive": true, "first": false, "tree": "[]"}]
Family ID: 53264965