GB2353824A

GB2353824A - Seal arrangement for centrifugal fan

Info

Publication number: GB2353824A
Application number: GB0020642A
Authority: GB
Inventors: Ronald L Dupree
Original assignee: Caterpillar Inc
Current assignee: Caterpillar Inc
Priority date: 1999-08-23
Filing date: 2000-08-23
Publication date: 2001-03-07
Also published as: GB0020642D0

Abstract

A centrifugal fan comprises a housing 12, and a rotatable impeller comprising blades 22, supported by a rim 24, having a collar 48, defining the fan inlet 34, so that the inlet rotates with the rest of the impeller. A seal 46, is provided between an edge of the rim 34, and the housing, the seal comprising a U-shaped component having leg portions (60, fig. 3) which are located on opposite sides of the rim. The rim may be provided with a stepped portion (68 fig. 4).

Description

2353824

Description

IMPROVED SEALING SYSTEM FOR A CENTRIFUGAL FAN Technical Field

This invention relates generally to an improved seal assembly for a centrifugal fan and more particularly to a seal mounted to a fan housing for sealing a fan impeller rim to the housing.

Backqround Art Centrifugal fans draw air in centrally and discharge air radially. The fans can be used to provide a cooling flow for various machine systems, including a heat exchanger, for example. Centrifugal fans typically have a housing and an impeller with a plurality of rotating blades that are used to generate the centrifugal airflow. A fan inlet is used to direct air toward the center of the rotating blades.

In known centrifugal fans, the fan inlet is mounted to the housing and remains stationary as the impeller rotates. The performance of the fan is strongly impacted by the ability to seal the area between the impeller and the fan inlet. The impeller draws air through the f an inlet and adds energy to the airf low by accelerating the flow to a high velocity. Thus, the air inside the housing is at a higher pressure than the aii- in the inlet. The performance of the sealing arran4ement between the inlet and the impeller determines Lw much of the high-pressure discharge air will be drawn into the inlet. Leaks at the sealing area between the inlet and the impeller are detrimental because leakage reduces the output flow of the fan.

These known centrifugal fans depend upon the ability to maintain tight clearances between the inlet and the impeller to minimize leakage within the fan, which is difficult. This requires heavy components to prevent movement of the impeller relative to the inlet, which is undesirable. Also, with such tight clearances, fan components can come into contact with each other causing pre-mature component wear and component failure.

The present invention is directed to overcoming one or more of the problems as set forth above.

Disclosure of the Invention In one aspect of this invention, a fan assembly for a machine cooling system is disclosed. The fan includes a housing mounted to a machine structure and a shaft rotatably supported with respect to the housing. An impeller is fixed for rotation with the shaft and includes a plurality of rotating blades supported on a rim. A fan inlet extends from the rim and directs air toward the blades. A seal is used to seal the rim to the housing to prevent leakage as the rotating blades generate a centrifugal airflow for discharge through a fan outlet.

In another aspect of this invention, a method for sealing a rotating fan impeller including a plurality of rotating blades supported on a rim member to a stationary housing is disclosed. The method includes the steps of mounting the housing to a machine structure, rotatably supporting a shaft with respect to the housing, fixing the impeller for rotation with the shaft, and sealing the rim to the housing to prevent leakage as the rotating blades generate a centrifugal airflow for discharge through a fan outlet.

Brief Description of the Drawings

Various embodiments of the invention will now be described, by way of example only, having regard to the accompanying drawings in which: FIG. 1A is a perspective view of a centrifugal fan assembly with two (2) impellers, known in the prior art; 20 FIG. 1B is an exploded view, partially cutaway to show only one impeller, of the fan assembly shown in FIG. 1; FIG. 1C is a cross- sectional view of the fan assembly shown in FIG. 1; 25 FIG. 2 is a cross- sectional view of a centrifugal fan incorporating the inventive seal assembly; FIG. 3 is an enlarged cross-sectional, partially cut-away, view of the seal assembly shown in

FIG. 2; and 1 FIG. 4 is cross-sectional view, like FIG. 3, of an alternate embodiment of a seal assembly.

Referring now to the drawings, and initially to FIGS. 1A-1C, a known centrifugal fan assembly 10 for a machine cooling system is shown. As is known in the art, centrifugal fans draw air in centrally and discharge air radially. The fans can be used to provide a cooling flow for a machine cooling system, such as a heat exchanger (not shown), for example. The fan can also be used to generate a centrifugal airflow to separate debris particles from the air before the air enters a heat exchanger or other machine component.

The fan assembly includes a housing 12 that is mounted to a machine structure 14 such as a machine frame member, for example. A shaft 18 is rotatably supported with respect to the housing 12 and an impeller 20 is fixed for rotation with the shaft 18.

The impeller 20 includes a plurality of rotating blades 22 that are supported between a riT 24 and a backplate 16.

As shown in FIG. 1A, the housing 12 includes a central body or scroll portion 26 with a pair of side sheets 28. A pair of impellers 20 are mounted within the scroll portion 26 on the shaft 18. The impellers 20 are separated by a center plate 30.

The fan assembly 10 also includes a central diverter plate 32 that directs airflow. Air is drawn into the housing 12 via a fan inlet 34, shown in FIG.

1b. In known centrifugal fans, the fan inlet 34 is mounted to the fan housing 12 and the impeller 20 is rotatably supported on a bearing support 36, which has an inlet collar 38.

The air is directed toward the center of the rotating blades 22 via the inlet 34. The rotating blades 22 generate a centrifugal airflow and discharge air through a fan outlet 40. The fan outlet 40 is def ined by an outlet area 42 that must be large enough to provide sufficient cooling air for the machine system.

As shown in FIG. 1C, the fan inlet 34 is mounted to the housing 12 and remains stationary as the impeller 20 rotates. The performance of the fan 10 is strongly impacted by the ability to seal the area between the impeller 20 and the fan inlet 34. The impeller 20 draws air through the fan inlet 34 and adds energy to the airflow by accelerating the flow to a high velocity. Thus, the air inside the housing 12 is at a higher pressure than the air in the inlet 34.

The performance of the sealing arrangement between the inlet 34 and the impeller 20 determines how much of the high-pressure discharge air will be drawn into the inlet 34. Leaks at the sealing area between the fan inlet 34 and the impeller 20 are detrimental because leakage reduces the output flow of the fan 10. The leak path is shown at 44 in FIG. 1C.

These know centrifugal fans depend upon the ability to maintain I tight clearances between the inlet 34 and the impeller 120 to minimize leakage within the -G- fan, which is difficult. This requires heavy components to prevent movement of the impeller 20 relative to the inlet 34, which is undesirable. Also, as the fan operates, components can move with respect to each other. With such tight clearances, components can come into contact with each other causing premature component wear and component failure.

A solution to these problems is shown in FIGS. 2-4. A seal 46 is used to seal the rim 24 to the housing 12 to prevent leakage as the rotating blades 22 generate a centrifugal airflow for discharge through the fan outlet 40. The seal can be metallic, nonmetallic, or a combination of metallic and nonmetallic. The seal 46 can be formed as a single piece or can be made of multiple pieces. Preferably, the seal 46 is made from a flexible nonmetallic and/or metallic material to allow easy removal of the impeller 20. This will be discussed in greater detail below. 20 As shown in FIG. 2, the fan inlet 34 extends outwardly from the rim 24 and directs air toward the blades 22. Preferably, the fan inlet 34 is formed as one piece with the rim 24 and includes a collar portion 48 extending outwardly beyond an external 25 surface 50 of the housing 12. Thus, the fan inlet 34 becomes a rotating part that rotates with the impeller 20. The impeller 20 is typically fastened to a driving mechanism, such as a motor (not shown), located at the rear of the impeller 20. If the impeller is to be removed from the housing 12 for service or repair, the typical method of disassembly is to disconnect the impeller 20 from the driving mechanism and remove the impeller 20 through the an 5 opening in the housing 12.

The impeller 20 and seal 46 must be properly sized to allow removal of the impeller 20 for service and repair. The blades 22 are defined by a maximum blade diameter and the rim 24 is defined by a rim diameter. The rim diameter should be greater than the blade diameter to allow the impeller 20 to be easily removed from the housing 12. Thus, the seal 46, defined by a seal diameter, should be greater than the rim diameter. When service is required, the impeller 20 can be removed through the housing 12 via the opening defined by the seal diameter. The seal 46 flexes to allow easy removal of the impeller 20.

The seal 46 and rim 24 interface is shown in greater detail in FIG. 3. The rim 24 includes a first surface 52, a second surface 54 located opposite from the first surface 52, and an edge 56 that extends from the first surface 52 to the second surface 54. The seal 46 is preferably U-shaped and includes a base portion 58 with a pair of leg portions 60 located on the opposing sides 52, 54 of the rim 24. The base portion 58 of the seal 46 is spaced apart from the edge 56 to define a first clearance gap 62. One of the leg portions 60 is spaced apart from the first surface 52 to define''a second clearance gap 64. The other of the leg portions Go is spaced apart from the second surface 54 to define a third clearance gap 66.

Thus, the leg portions 60 are spaced apart from one another by a predetermined distance that is greater than the thickness of the rim 24.

The unique U-shaped seal 46 allows the fan inlet 34 to move vertically (FIG. 3) without changing the performance of the seal 46. Also, fan performance is not sensitive to the clearance between the edge 56 of the rim 24 and the seal 46, i.e., the first clearance gap 62. This gap 62 can be left large without sacrificing sealing performance. An important variable is the difference between the leg portions 60 and the thickness of the rim 24. For acceptable performance, this difference should be between.5 and 10.0 millimeters.

This seal configuration can be used on a rim sealing location, as shown in FIG. 3, or optionally can be used on a fan with the seal at a housing 12 and fan inlet 34 interface.

An alternate embodiment of a seal 46 and rim 24 interface is shown in FIG. 4. The rim 24 can include a stepped portion 68 extending outwardly from the rim 24 to define a flow surface 70. The flow surface 70 directs debris particles 72 that are carried in the airflow, past the third clearance gap 66 formed between the rim 24 and leg portion 60. Debris particles 72 that enter the area between the rim 24 and the seal can cause abrasive damage to the impeller 20 or the seal 46. The stepped portion 68 directs air along the external flow surface 70 of the rim and beyond the seal cavity. This stepped rim design is also preferred for rims 24 that have a thickness that is greater than 10 millimeters.

A method for sealing the rotating fan impeller 20 to a stationary housing 12 includes the following steps. Mounting the housing 12 to a machine structure 14, rotatably supporting the shaft 18 with respect to the housing 12, fixing the impeller 20 for rotation with the shaft 18, and sealing the rim 24 to the housing 12 to prevent leakage as the rotating blades 22 generate a centrifugal airflow for discharge through the fan outlet 40. Additional steps can include providing a fan inlet 34 extending outwardly from the rim 24 to direct the air toward the blades 22 where the inlet 34 and the rim 24 are f ormed as one piece.

As discussed above, the seal 46 is preferably formed with a base portion 58 and a pair of leg portions 60 and additional method steps include mounting the base portion 58 to the housing 12 and positioning the leg portions 60 on opposing sides 52, 54 of the rim 24. The leg portions 60 should be spaced apart from one another by a predetermined distance such that rim thickness is less than the predetermined distance to define a clearance gap between the seal 46 and the rim 24.

An optional step includes forming a flow surface 70 on the rim 24 to direct debris particles 72 past the seal 46.

Industrial Applicability

The inventive seal assembly for a centrifugal fan eliminates the need to maintain tight clearances between a fan inlet member and an impeller and allows lighter fan components to be used. The following description is only for the purposes of illustration and is not intended to limit the present invention as such. It will be recognizable, by those skilled in the art, that the present invention is suitable for a plurality of other applications.

The present invention uses a U-shaped seal mounted to a fan housing to seal the impeller rim to the housing. The seal can be used for rim mounting or fan inlet mounting to the housing. The seal also is allows easy removal of the impeller system from the fan housing for service or repair. The seal can be used with centrifugal fans that utilize one or more impellers mounted within the housing.

Other aspects, objects and advantages of this invention can be obtained from a study of the drawings, the disclosure and the appended claims.

-11 i

Claims

1. A fan assembly for a machine cooling system comprising:

a housing mounted to a machine structure; a shaft rotatably supported with respect to the housing; an impeller fixed for rotation with the shaft and including a plurality of rotating blades supported on a rim; a fan inlet extending from the rim for directing air toward the blades; and a seal for sealing the rim to the housing to prevent leakage as the rotating blades generate a is centrifugal airflow for discharge through a fan outlet.

2. The assembly of Claim 1, wherein the blades are defined by a maximum blade diameter and the rim is defined by a rim diameter, the rim diameter being greater than the blade diameter.

3. The assembly of Claim 2, wherein the seal is defined by a seal diameter that is greater than the rim diameter.

4. The assembly of any of Claims 1 to 3, wherein the fan inlet is formed as one piece with the rim.

5. The assembly of any of Claims 1 to 4, wherein the fan inlet includes a collar portion extending outwardly beyond an external surface of the housing. 5

6. The assembly of any of Claims 1 to 5, wherein the seal is comprised of a base portion with a pair of leg portions located on opposing sides of the rim.

7. The assembly of Claim 6, wherein the rim includes a first surface, a second surface located opposite from the first surface, and an edge that extends from the first surface to the second surface and wherein the base portion of the seal is spaced apart from the edge to define a first clearance gap, one of the leg portions is spaced apart from the first surface to define a second clearance gap, and the other of the leg portions is spaced apart from the second surface to define a third clearance gap.

8. The assembly of Claim 6 or Claim 7, wherein the leg portions are spaced apart from one another by a predetermined distance and wherein the rim has a predetermined thickness that is less than the predetermined distance to define a clearance gap between the seal and the rim.

9. The assembly of Claim 8, wherein the rim includes a stepped portion extending outwardly f rom. the rim to def ine a f low surf ace, the f low surface for directing debris particles past the clearance gap.

10. A method for sealing a rotating fan impeller including a plurality of rotating blades supported on a rim member to a stationary housing comprising the steps of:

mounting the housing to a machine structure; rotatably supporting a shaft with respect to the housing; fixing the impeller for rotation with the shaft; and sealing the rim to the housing to prevent leakage as the rotating blades generate a centrifugal airflow for discharge through a fan outlet.

11. The method of Claim 10, including the step of providing a fan inlet extending outwardly from the rim for directing air toward the blades.

12. The method of Claim 11, including the step of forming the inlet and the rim as one piece.

13. The method of any of Claims 10 to 12, including the steps of defining the blades by a maximum blade diameter and defining the rim by a rim diameter with the rim diameter being greater than the blade diameter.

14. The method of Claim 13, including the steps of providing a seal assembly to seal the rim to the housing and defining the seal by a seal diameter that is greater than the rim diameter.

15. The method of any of Claims 10 to 14, including the steps of providing the seal with a base portion and a pair of leg portions, mounting the base portion to the housing, and positioning the leg portions on opposing sides of the rim.

16. The method of Claim 15, including the step of spacing the leg portions apart from one another by a predetermined distance such that rim thickness is less than the predetermined distance to define a clearance gap between the seal and the rim.

17. The method of any of Claims 10 to 16, including the step of forming a flow surface on the rim to direct debris particles past the seal.

18. A fan assembly substantially as hereinbefore described with reference to and/or as shown in Figures 2 to 4 of the accompanying drawings.

19. A method for sealing a rotating fan impeller substantially as hereinbefore described with reference to and/or as shown in Figures 2 to 4 of the accompanying drawings.