Patent Publication Number: US-10767500-B2

Title: Fan blade pitch setting

Description:
I. TECHNICAL FIELD 
     The present invention relates generally to impellers. In particular, the present invention relates to approaches for optimizing the design and manufacture of fan impellers. 
     II. BACKGROUND 
     Impellers are fundamental to the operation of centrifugal pumps, turbines, and other fan-based applications. Impellers are typically used as a means of transmitting motion. In aerospace applications, for example, impellers can provide avionics cooling, cabin recirculation, and oil cooling, etc. When developing or manufacturing a new fan/impeller, fine-tuning of design is often needed, to meet a given airflow requirement. This process can be very time-consuming. Consequently, impellers often require longer lead times than other components during the manufacturing process. 
     Impellers for aerospace applications are typically formed of a single piece of cast metal. Additionally or alternatively, impellers can also be machine-cut from a billet. Often, when developing a new fan or impeller, multiple design iterations are used to test and verify that the fan/impeller meets a given airflow requirement. The design iterations typically include iterations of the impeller&#39;s blade setting angle (i.e., its pitch angle). As such, for a single-piece impeller, design iterations require re-making the entire impeller, and the manufacturing processes required to produce these conventional components can be costly and time intensive. 
     By way of example, the conventional manufacture of cast metal impellers is heavily dependent upon the manufacturing foundry&#39;s internal schedule. More than 20 weeks of lead time is not uncommon. In fact, one iteration of a single design can require more than 40 weeks altogether. 
     III. SUMMARY 
     The embodiments featured herein help mitigate the above-noted deficiencies as well as other issues known in the art. 
     In contrast to conventional impellers constructed of a single piece of material, the embodiments provide a modular impeller formed of several components. For example, one embodiment provides an impeller including a ring disposed in a hub of the impeller. The ring includes a recess shaped and positioned to impart a specified pitch angle to a blade extending outwardly from the ring through the hub. 
     Another embodiment provides an impeller including a blade having a portion shaped to mate with a recess of a ring disposed in a hub of the impeller. The recess provides a specified pitch angle for the blade. 
     Yet another embodiment provides an impeller assembly including a plurality of blades, a hub, and a pitch-setting ring disposed on an inner wall of the hub. The pitch-setting ring includes a plurality of recesses, where each recess is configured to mate with a portion of one blade to provide a specified pitch angle for the one blade. 
     Additional features, modes of operations, advantages, and other aspects of various embodiments are described below with reference to the accompanying drawings. It is noted that the present disclosure is not limited to the specific embodiments described herein. These embodiments are presented for illustrative purposes. Additional embodiments, or modifications of the embodiments disclosed, will be readily apparent to persons skilled in the relevant art(s) based on the teachings provided. 
    
    
     
       IV. BRIEF DESCRIPTION OF THE DRAWINGS 
       Illustrative embodiments may take form in various components and arrangements of components. Illustrative embodiments are shown in the accompanying drawings, throughout which like reference numerals may indicate corresponding or similar parts in the various drawings. The drawings are for purposes of illustrating the embodiments and are not to be construed as limiting the disclosure. Given the following enabling description of the drawings, the novel aspects of the present disclosure should become evident to a person of ordinary skill in the relevant art(s). 
         FIG. 1  illustrates an example of a conventional impeller. 
         FIG. 2  illustrates an example blade in accordance with various aspects described herein. 
         FIG. 3  illustrates an example cross-sectional view of an impeller in accordance with various aspects described herein. 
         FIG. 4  illustrates an example alternative cross-sectional view of an impeller in accordance with various aspects described herein. 
         FIG. 5  illustrates an example alternative view of the blade in accordance with various aspects described herein. 
         FIG. 6  illustrates an example impeller in accordance with various aspects described herein. 
         FIG. 7  illustrates an example blade performance graph in accordance with various aspects described herein. 
         FIG. 8  illustrates an example impeller in accordance with various aspects described herein. 
     
    
    
     V. DETAILED DESCRIPTION 
       FIG. 1  illustrates an example of a conventional impeller  100 . The conventional impeller  100  includes a set of blades  102  extending from a hub  104 , and a shaft bore  106  that is either machined, formed or otherwise fashioned in the center of hub  104 . The shaft bore  106  receives a shaft (not shown) around which the conventional impeller  100  can rotate. The conventional impeller  100  can be made from a single piece of material that can include an aluminum alloy. For instance, the aluminum alloy can be cast in a mold to make the conventional impeller  100 , and trimmed by a milling machine, with the shaft bore  106  being formed therein. 
     Tuning, adjusting or otherwise changing several parameters of the conventional impeller  100  will affect its air flow performance. For example, adjusting the pitch angle of the set of blades  102  can change the air flow performance of the conventional impeller  100 . Therefore, for a specified set of air flow requirements, the conventional impeller  100  has to be manufactured with the set of blades  102  having a specific pitch angle that meets the air flow requirements. 
     However, when the air flow requirements change, another conventional impeller having dimensions that meet the new requirements must be manufactured. Another conventional impeller is needed because the conventional impeller  100  is a single-piece component, and the pitch angle of its set of blades  102  cannot be independently altered. Therefore, because a new impeller is needed every time air flow requirements change, there can be significant delays and increased costs associated with maintenance of systems that utilize the conventional impeller  100 . 
     The embodiments described below solve the aforementioned issues by providing a modular assembly of a fan or impeller. The embodiments include a set of modular and detachable blades as well as a pitch-setting ring configured for insertion into a hub of the impeller. The pitch-setting ring includes a set of recesses shaped and positioned to impart a specified pitch angle to each blade. Specifically, the ring can be fitted with individual blades, and the recesses are angled in a manner to provide a specified pitch angle. The sub-assembly of the ring with the blades can be inserted in the hub and secured on an inner wall of the hub, thereby yielding the modular fan/impeller assembly. 
     As such, when air flow requirements change, in the embodiments, the blades and the hub do not need to be remade. Instead, only the ring is remade with new recesses that provide a different pitch angle, and the hub and the blades can be reused. That is, impellers with different pitch angles can be constructed at reduced costs and faster lead times. The embodiments thus provide significant savings in lead time, materials, inventory control, and overall cost. 
     Unlike the conventional impeller  100 , which is made with a single piece of material, the embodiments disclosed herein are modular and they include several components. For example, they include a set of blades (of which one is illustrated in  FIG. 2 ), and they include a hub and a pitch setting ring (which are illustrated in  FIG. 3 ). Specifically,  FIG. 2  illustrates an exemplary blade  200  that includes a first portion  202  and a second portion  204  that are joined by a rod  206 . The first portion  202 , i.e. the main section of the blade  200 , is configured to create a particular airflow pattern around it. The second portion  204  (i.e., tongue of the blade  200 ) and the rod  206  are dimensioned so as to interface with a hub  302  through a slot included in the body of the hub  302  (see  FIG. 3 ). 
     A set of blades  200  can be mounted on and secured on an exemplary impeller  300 , as shown in  FIG. 3 . Specifically, the set of blades  200  are mounted on the body of the hub  302 , with each blade  200  having its first portion  202  extending outwardly from the body of the hub  302 . Furthermore, in impeller  300 , the second portion  204  of the blade  200  engages with a recess from a set of a recesses  308  located in a pitch-setting ring  306 , and the rod  206  is sized appropriately to fit through a slot from a set of slots  304  in order to allow the first portion  202  of the blade  200  to extend outwardly from the body of the hub  302 . 
     The pitch setting ring  306  can be secured on the inner sidewall of the hub  302  using any appropriate fastener or fastening means. For example, pins or screws, or a combination thereof, can be used to attach the ring  306  to the inner wall of the hub  302 . Moreover, the set of slots  304  and the set of recesses  308  can be spaced equidistantly and respectively around the periphery of the hub  302  and the periphery of the pitch-setting ring  306 . Additionally or alternatively, however, any spacing can be employed, as long as a slot  304  is positioned in front of a recess  308  to allow a blade  200  to be secured onto the pitch-setting ring  306  secured on the inner sidewall of the hub  302 . 
     Furthermore, a recess  308  can be angled with respect to a vertical axis (e.g. with respect to one of the dashed lines in  FIG. 3 ) in a manner to provide a specified pitch angle to a blade  200  when the second portion  204  of the blade  200  is inserted into the recess  308 . For example, the recess  308  can be angled to provide a pitch angle of about 50 degrees when the second portion  204  of the blade  200  is inserted therein. Once assembled in impeller  300 , if another pitch angle is desired, the pitch-setting ring  306  can dismounted from the inner sidewall of the hub  302  and removed. A new ring can be made with recesses angled differently, thus providing a different pitch angle than the one achieved with the pitch setting ring  306 . As such, this modular impeller structure provides ease of manufacturing iteration for the impeller  300 , because only the pitch-setting-ring  306  to be remade, and the hub  302  and the set of blades  200  can be reused. 
     In one embodiment, all the recesses  308  of the pitch-setting ring  306  can be angled to provide the same pitch angle to each blade  200 . In other embodiments, however, at least two recesses  308  can be angled differently to provide a different pitch angle from one blade  200  to the next. In these latter embodiments, such an impeller can be used for reducing the noise created by impeller when it is rotating. 
       FIG. 4  illustrates an example alternative cross-sectional view of the impeller  300  in accordance with various aspects described herein. As previously discussed, the impeller  300  includes a set of blades  200  whose first portions  202  extend outwardly from the body of the hub  302 . The pitch-setting ring  306  is disposed on inside the hub  302  and secured on its inner sidewall. The recesses  308  (not shown in  FIG. 4 ) are shaped and disposed around the pitch-setting ring to confer a specified pitch angle to each one of the plurality of blades  200 . A blade  200  can be affixed to a particular recess  308  of the pitch-setting ring  306  by inserting its first portion  204  of into the particular recess  308  and through the slot  304  overlapping the particular recess  308 . 
       FIG. 5  illustrates an example alternative view  500  of the blade  200 , when mounted on the impeller  300 , as discussed above with respect to  FIG. 3  and  FIG. 4 . For ease of description, the blade  200  is shown together with a frame of reference given by a y-axis  502  and an x-axis  504 . 
       FIG. 5  illustrates a pitch angle  506  imparted to the blade  200  by a recess  308  (not shown in  FIG. 5 ) of pitch-setting ring  306  (not shown in  FIG. 5 ). The recess  308  is formed in the pitch-setting ring at an inclination given by line  508 . The impeller  300  can be reconfigured by changing the pitch angle  506 . To do so, one can construct a new pitch-setting that has a recess having a different inclination of line  508  than the inclination depicted in  FIG. 5 . 
       FIG. 6  is an illustration of a part of an impeller  300  according to various aspects described herein. As previously discussed, the impeller  300  includes a blade  200  mounted on the hub  302 . For ease of description, the pitch-setting ring  306  holding the blade  200  at the desired pitch angle is not shown. 
     During operation, an interface between the hub  302  and the blade  200  experiences a compressive stress. For example, when the impeller  300  is rotating, the surface  602  or the surface  604  may experience the compressive stress. Specifically, centrifugal forces created during rotation will translate into compressive stresses on the surfaces  602  and  604 . 
     As an example, in one implementation, the hub  302  and the blades  200  of the impeller  300  can be made of a cast aluminum alloy. Furthermore, the hub  302  can have a nominal diameter of 13 inches (in.) (i.e. twice the distance from the center of the hub  302  to a tip of the blade  200 ), and the diameter of the hub  302  can be nominally 6.5 in. In this example, the tongue surface area mating the inner wall (e.g. surface  602 ) is nominally 0.4 in 2 . Thus, at 8,000 revolutions per minute (rpm), the compressive stress exerted on surface  602  would be about 1,800 pounds per square inch (psi). As such, the compressive stresses exerted on the interface can be far below the yield strength of the cast aluminum alloy, which is typically about 30,000 psi. Under these conditions, material failures would not be expected to ensure based on the compressive stresses exerted on the interface. 
       FIG. 7  is a graph  700  plotting pressure rise against air flow rate for three different exemplary impellers. (The units are omitted for the sake of clarity.) All three impellers have the same hub and the same blades, but they each have a different pitch-setting ring, i.e. different pitch angles. Specifically, the first impeller includes a first pitch-setting ring whose recesses impart a first pitch angle to the blade, thus yielding a first performance curve labeled BASE. The second impeller uses a second pitch-setting ring to impart a second pitch angle to the blades, which yields a second performance curve labeled UP-PITCHED BLADES. Lastly, the third impeller uses a third pitch-setting ring to impart a third pitch angle to the blades, thus yielding a third performance curve labeled WITH DE-PITCHED BLADES. 
     As evidenced by graph  700 , the embodiments allow great flexibility in varying pitch angles by using different pitch-setting rings. As such, when impeller  300  is deployed in the field, if the pitch angle of its blades have to be changed because of new air flow performance requirements, its pitch-setting ring  306  can be removed and replaced with a new pitch-setting ring that meets the new requirements. Specifically, the removed pitch-setting ring can be replaced with another ring having recesses inclined to provide the pitch angle that meets the new requirements. Furthermore, the graph  700  shows that a large area of the flow-pressure domain can be covered with a single hub, as opposed to the conventional case, where operation is constrained to a single performance curve since the blades and the hub of the conventional impeller  100  makes one piece and are not modular. 
       FIG. 8  illustrates an embodiment where impeller  300  is fitted with a reinforcement ring  802  that optionally can be mounted on an outside wall of the hub  302 . The hub reinforcement ring  802  can prevent the hub  302  from expanding excessively during operation, when the impeller  100  is operated in high rpm regimes. The hub reinforcement ring  802  can be mounted on the outside wall of the hub using any suitable fastener, such as screws, pins, and the like. 
     Those skilled in the relevant art(s) will appreciate that various adaptations and modifications of the embodiments described above can be configured without departing from the scope and spirit of the disclosure. Therefore, it is to be understood that, within the scope of the appended claims, the disclosure may be practiced other than as specifically described herein.