Patent Application
20150167692
Fans used in aviation systems include a case or housing and an impeller contained within the housing to create air flow. A fan is typically designed to meet specific design criteria, which may include alone or in combination any one of at least a particular air flow requirement, pressure rise, and/or rotational speed. When a new design criterion must be met, such as meeting a new air flow requirement, a new fan is designed. An existing fan can be redesigned to meet the new design criteria, such as by altering the impeller size, blade length, number of blades, etc. Often, redesigning the impeller also requires redesigning the fan housing. With any new fan design, costly new production tooling is also needed to then manufacture the fan.
A fan assembly includes a fan having an impeller comprising a hub with a diameter and plurality of blades extending radially from the hub, with a distance from the hub to a tip of the blade defining a working length of the blades, and a hub cap configured to mount to the hub. The hub cap includes an end wall having a diameter larger than the diameter of the hub, a peripheral side wall extending from the end wall, and a plurality of slots corresponding to the blades and formed in the side wall. The slots are sized to receive the blades, whereby, when the hub cap is mounted to the hub, the slots receive the blades to effectively shorten the working length of the blades.
The fan housing 22 is shown herein as having a generally cylindrical side wall 32, with an inlet end 34 and an outlet end 36, both of which are open to permit the flow of air through the fan housing 22. The impeller 16 is positioned at the inlet end 34 to draw air into the fan housing 22.
An opening 44 to the bore 28 is formed in the end wall 38. More specifically, as shown herein, the end wall 38 can have a recess 46 in which the opening 44 to the bore 28 is located. The recess 46 and opening 44 can be coaxially aligned along the rotational axis of the impeller 16.
The plurality of blades 20 extend radially outwardly from the side wall 40, from proximal ends 48 which join the side wall 40 to free distal ends 50. The number, spacing, geometry (including length, pitch, etc.) of the blades 20 can vary from the configuration shown herein.
A working length L of the blades 20 is generally defined by the length of the blades 20 exposed to air flow. Here, without the hub cap 14 (
An opening 58 is formed in the end wall 52. More specifically, as shown herein, the end wall 52 can have a recess 60 in which the opening 58 is located. The recess 46 and opening 44 can be coaxially aligned along the rotational axis of the impeller 16.
A plurality of slots 62 are formed in the side wall 54. The slots 62 can extend from the peripheral edge 56 toward the end wall 52. As shown herein, each slot 62 can include two opposing sides 64 which extend from an open end 66 at the peripheral edge 56 to a closed end 68. The number, spacing, geometry (including length, pitch, etc.) of the slots 62 can vary from the configuration shown herein.
The recess 60 of the hub cap 14 can be dimensioned to nest within the recess 46 of the hub 18, and the end walls 38, 52 and side walls 40, 54 of the hub cap 14 and hub 18 substantially align with each other so as to limit how far the hub cap 14 extends beyond the hub 18. By minimizing the dimensions of the hub cap 14 with respect to the dimensions of the hub 18, the hub cap 14 can be used with an existing fan 12 without modifying the fan housing 22.
The slots correspond in number and size to the blades, such that the slots receive the blades when the hub cap 14 is mounted to the impeller 16. The pitch and shape of the blades 20 may require the hub cap 14 to be rotated or twisted as the slots move over the changing shape of the blades 20 to the full seated position on the impeller shown in
As noted above, the working length L of the blades 20 is generally defined by the length of the blades 20 exposed to air flow. Here, with the hub cap 14 assembled with the impeller 16, the working length L of each blade 20 is the distance from the peripheral side wall 54 of the hub cap 14 to the distal end 50 of the blade 20. The hub cap 14 thereby shortens the effective length (or span) of each blade 20 and thus alters the performance characteristics of the fan 12. Conversely, the hub cap 14 also effectively enlarges the working hub of the fan 12.
Line A is the performance curve for the fan assembly 10 without the hub cap 14 which meets a first design point X of a particular combination of airflow rate and pressure rise. Under some circumstances, such as for another application of the fan assembly 10, a second or new design point Y of a different combination of airflow rate and pressure rise may be required. In some cases, the fan assembly 10 may be able to meet the new design point Y by adjusting the rotational speed of the impeller 16. However, in the illustrated case, lowering the rotational speed does not result in a performance curve that meets the new design point Y. Line B is the performance curve for the fan assembly 10 at approximately 90% of the rotational speed for Line A and Line C is the performance curve for the fan assembly 10 at approximately 75% of the rotational speed for Line A, neither of which passes through the new design point Y.
Line D is the performance curve for the fan assembly 10 with the hub cap 14 mounted on the impeller 16 as shown in
It is noted that while the first and second design points X, Y shown in
The above described embodiments provide for a variety of benefits, including that the hub cap can be added to an existing fan in order to effectively alter the impeller configuration so that the fan can meet other performance requirements in addition to those intended with the original design of the fan. Fans can be benefited by aspects of the invention discussed herein by allowing for performance changes without requiring a new impeller; in one example, a fan with a relatively small hub diameter and relatively long blades can be provided with the hub cap in order to create a fan with a larger hub diameter and shorter blades. The hub cap does not require any special attachment or assembly since it can be secured to the existing impeller drive shaft, using the existing fastener. Rather than custom-designing a new impeller, which would otherwise be required, this apparatus and method can save time and costs in only manufacturing a new hub cap for the fan.
This written description uses examples to disclose the invention, including the best mode, and also to enable any person skilled in the art to practice the invention, including making and using any devices or systems and performing any incorporated methods. The patentable scope of the invention is defined by the claims, and may include other examples that occur to those skilled in the art. Such other examples are intended to be within the scope of the claims if they have structural elements that do not differ from the literal language of the claims, or if they include equivalent structural elements with insubstantial differences from the literal languages of the claims.
