AXIAL FAN WITH SELF-COOLED MOTOR

Abstract: A fan (10) and electric motor (12) combination which provides improved cooling for the motor, using a centrifugal impeller including rotating impeller blades (24). The impeller blades span between an impeller inlet and an impeller outlet, and they rotate to assist cooling for the motor. Cooling airflow is also assisted by the position of the impeller in that the impeller outlet is positioned upstream of the intersection of the impeller fan blade trailing edge (92) and the hub (20).

Description: AXIAL FAN WITH SELF-COOLED MOTOR Field of the Invention This invention is in the general field of electric motor-driven axial fans, particularly fans used in automotive engine cooling applications. Background of the Invention Internal motor temperature has a critical effect on the performance and durability of electric motors. The internal temperature of an electric motor is greater than the ambient temperature due to the heat generated by the motor. In automotive engine cooling applications where the electric motor is under the hood of the vehicle the problem is made more severe by the high ambient temperatures produced by the vehicle's engine. Certain features may operate to reduce motor temperature rise over ambient temperature rise. McLane-Goetz et al . U.S. 5,180,279 disclose a fan which includes a scoop downstream of an axial fan to divert some of the axial fan airflow across the rear of the motor. DeFilippis U.S. 5,217,353 discloses a centrifugal blower motor having a stationary motor casing with holes for taking in air from the outside and for ventilating the interior of the motor; the motor also has a rotary part with holes which act as outlet ducts for the internal motor ventilation. Ribs of the fan driven by the motor which are primarily structural can have the additional benefit of cooling the motor. Summary of the Invention One aspect of the invention features a fan and electric motor combination (or a fan adapted to be used in such a combination) which provides improved cooling for the motor. This aspect of the invention generally features a centrifugal impeller comprising an inlet, an outlet, and rotating blades. The inlet is positioned to receive the motor-cooling airflow. The rotating blades cause the pressure at the impeller outlet to be greater than at the inlet. The pressure of the motor-cooling airflow is further increased by positioning the impeller outlet upstream of an intersection of the fan blade trailing edge and the hub (here upstream is interpreted in terms of the general, bulk airflow regardless of local anomalies) . Therefore, at least some (preferably all) of the pressure rise across the axial fan is added to the pressure rise of the impeller. If the impeller outlet is positioned still further upstream, e.g., upstream of an intersection of the fan blade leading edge and the hub, then the pressure rise of the impeller is increased by all or nearly all of the pressure rise across the axial fan. The resulting pressure rise overcomes the pressure losses of the motor-cooling flow path, and results in greater motor-cooling airflow. In referring to axial flow fans, we recognize that the general flow of air through axial fans may be entirely axial or the flow may be mixed, in which case there may be a significant component of radial flow. Typically, but not inevitably, the motor will include an outer casing. The invention provides some advantage for motors having a sealed outer casing, in that the impeller generates motor-cooling airflow along the outside of the motor casing. The invention is particularly advantageous for motors having a casing with at least one casing inlet and at least one casing outlet positioned near the impeller inlet, so that rotation of the impeller assists motor-cooling airflow through the inside of the motor -- i.e., through the casing inlet, into the inside of motor casing, and through the casing outlet to the impeller inlet. In one embodiment, the impeller blades are positioned between a forwardly-facing central region of the hub and a bottom plate spaced axially in front of the forwardly-facing central hub region. The central hub region serves as a top plate of the centrifugal impeller. Alternatively, there can be a top plate separate from the hub and the bottom plate. In other embodiments, the fan hub comprises a rearwardly-facing, concave, central region, constructed to serve as a bottom plate and a top plate spaced axially rearward of the central hub region. The impeller blades are positioned between the rearwardly- facing region and the top plate. Typically, the impeller blades are connected to the fan hub, so that hub rotation drives the impeller blades. Alternatively, the motor casing may serve as the top plate or a portion of the top plate. In this embodiment, the motor casing may include a flange constructed to serve at least part of the top plate of the centrifugal impeller. For motors in which at least part of the motor casing rotates with the fan hub, the impeller blades may be attached to the motor casing. For motors in which the motor casing is stationary, the assembly may include a seal (e.g., an extension from the hub toward the casing, or an extension from the casing toward the hub, or both) to reduce a gap between the casing and the hub. A rotatable motor driveplate may be connected to the motor, and at least at portion of the impeller blades may be attached to that driveplate, so that the motor drives the impeller blades. The driveplate may serve as either the top plate or the bottom plate. The driveplate may include a seal. The impeller blades and the driveplate may be made of metal to improve heat transfer from the motor to the cooling airflow. The fan and impeller blades may be formed of injection-molded plastic material. In some cases, the fan and impeller blades are molded as a single unit. The fan, impeller blades and either the top plate, the bottom plate, or both, can be molded as a single unit. In another case, the impeller blades and either the top plate, the bottom plate, or both, can be molded as a single unit. The above-described fan and motor combinations may be used to move air through an adjacent heat exchanger in a vehicle. The above-described fan/motor combinations may be assembled by attaching the motor to the fan. Other features and advantages will be apparent from the following description and from the claims. Brief Description of the Drawings Figs. 1A and IB are diagrammatic representations of an axial cooling fan for an electric motor. Fig. 1C is an exploded view of the fan of Figs. 1A and IB, showing the bottom plate and impeller blades separated from the rest of the assembly for illustration purposes . Fig. ID is an enlarged view of the motor casing and hub of Fig. 1A. Fig. IE is a diagrammatic representation of an axial cooling fan for an electric motor for pushing air through a heat exchanger. Fig. IF is a diagrammatic view of a sealed motor casing. Fig. 2 is a diagrammatic view of an axial cooling fan having the impeller blades integrally connected with the hub of the axial fan. Figs. 3A and 3B are diagrammatic views of an axial cooling fan with impeller blades having an outer radius greater than the radius of the bottom plate. Fig. 4 is a diagrammatic view of an axial cooling fan having a motor casing with a flange serving as the top plate. Fig. 5 is a diagrammatic view of an axial cooling fan with a rotating motor case. Figs. 6A and 6B are diagrammatic views of an axial cooling fan having the impeller blades integral with the fan/motor driveplate attachment . Fig. 6C is a diagrammatic view of a fan/motor combination in which a driveplate serves as a bottom plate . Figs. 7A and 7B are diagrammatic views of an axial cooling fan having the impeller blades positioned in a cavity formed in the rear of the fan hub. Figs. 8A and 8B is a diagrammatic view of an axial cooling fan in which impeller outlets are located downstream of the leading edges of the fan blades. Fig. 9 is a diagrammatic view of a fan/motor combination where the motor casing has cooling apertures positioned so that cooling air exits radially. Description of the Preferred Embodiments In Figs. 1A and IB, an axial fan 10 is used to "pull" air through a heat exchanger 11 upstream (from the point of view of mainstream airflow) of the fan. Fan 10 is driven by a motor 12 enclosed in a motor casing 14. Fan 10 includes a series of blades 16 integrally connected to a rotating band 18 and a hub 20 that is structurally reinforced with ribs 21. Blades 16, each having a leading edge 90 and a trailing edge 92, extend in a plane generally perpendicular to axis 22 of the fan and motor. Each blade 16 has a low-pressure surface 13 facing in the general direction of the upstream side of fan 10 and a high pressure surface (not shown) facing generally towards the downstream side of fan 10. To cool motor 12, multiple (for example, at least 5) impeller blades 24 are attached to bottom plate 25, and they extend between bottom plate 25 and hub 20. Blades 24 extend generally perpendicularly to axis 22. The combination of hub 20, plate 25, and blades 24 define the flow path of a centrifugal blower, with an inlet radially inward from its outlet. In a preferred embodiment, blades 24 and bottom plate 25 are molded as one piece as shown in Fig. 1C (parts are shown in an exploded view with blades 24 separated from hub 20 for purposes of clarity) , and fan 10 is molded as another unit . Hub 20 is attached to drive plate arms (for example, at least 3) , of which only arm 26 is shown for sake of clarity, which are integrally connected with shaft 28. In use, motor casing 14 remains stationary and motor 12 causes shaft 28 to rotate such that all the other above stated connected elements rotate about axis 22 as a single unit. Shown in Fig. ID is the airflow pattern induced by the fan/blower unit. As fan 10 rotates about axis 22, blades 16 draw air from the general upstream region (U) of fan 10 and they move the air through fan 10 to a general downstream region (D) as indicated by arrows 30 (as also shown in Fig. IB) . The induced airflow through fan 10 experiences a pressure increase ΔP 2 . The air is pulled from region (D) through inlet apertures 31 into motor casing 14 as shown by flow arrows 32. The air flows through the interior of motor 12, thereby cooling it, and is expelled through cooling apertures 33 as indicated by flow arrows 34. The airflow is then turned from a generally axial and tangential direction to a generally radial and tangential direction as it moves from cooling apertures 33 through the inlet (I) of impeller blades 24 to the outlet (O) of the blades as shown by flow arrows 35. As the air moves through impeller blades 24 of the centrifugal blower, it experiences a pressure rise ΔP X . The pressure increase άP 1 through impeller blades 24 and ΔP 2 through fan 10 is balanced by a pressure drop ΔP 3 that occurs as the airflow moves through motor 12, entering through apertures 31 and exiting through apertures 33, as shown by the relation ΔP, + ΔP 2 = ΔP 3 When the fan/motor is in operation, the airflow pattern just described continuously cools the interior of motor 12. To provide more heat rejection for the internal parts of motor 12, and to improve motor performance and durability, a sealing device 40 is employed to ensure that the airflow goes through the interior of the motor casing and not along the outside of the casing. Sealing device 40 is an extension of hub 20 extending axially towards motor casing top 38, defining a clearance gap 42 determined by manu acturing tolerances and design considerations. The inner radius, from axis 22, of sealing device 40 is slightly larger than the outermost edges of cooling apertures 33 so as not to interfere with the airflow exiting cooling apertures 33. Referring to Fig. IE, a motor/fan combination is arranged to "push" air, in the direction indicated by arrows 49, through heat exchanger 11 downstream (from the point of view of mainstream airflow) of the fan. Motor cooling air exits motor casing 14 and enters inlet (I) of impeller blades 24, as shown by arrow 34, and then flows through the impeller, exiting at the outlet (0) . From the outlet (O) , the cooling airflow enters into the mainstream airflow as indicated by arrow 35. All other identified elements are the same as those described above with reference to Fig. IB. Referring to Fig. IF, a sealed motor casing 300 is shown. In this embodiment, the motor cooling air flows along the outside of motor casing 300 in the general direction of arrow 301. The airflow enters inlet (I) of the impeller and flows through impeller blades 24, as indicated by arrow 304. Upon exiting the outlet (O) of the impeller, the airflow, indicated by arrow 306, enters the mainstream airflow, flowing in the general direction of arrow 308. Other embodiments of the invention will now be described. The same element numbers used in Figs. 1A through ID will be used to identify similar elements in Figs . 2 through 8. In Fig. 2, bottom plate 25 is a separately formed piece and impeller blades 24 are connected integrally with top of fan hub 20 such that impeller blades 24 and fan 10 are molded as a single unit. By having impeller blades 24 molded together with fan 10, impeller blades 24 provide additional structural support to hub 20. Bottom plate 25 is shown separated from impeller blades 24 for illustration purposes; in operation, bottom plate 25 would be centered relative to hub 20 by a groove 23 and connected to impeller blades 24, for example, by a heat- welding process. In other embodiments, bottom plate 25 could be snapped onto hub 20. The operation of the fan/motor shown in Fig. 2 is generally the same as that described in reference to Figs. 1A through ID, except that the airflow, upon exiting cooling apertures 33, flows through hub holes 53 disposed near the inlet (I) of impeller blades 24 prior to moving through the blades to the outlet (0) region of the impeller blades. With reference to Fig. 3, an illustration of an embodiment is shown in which bottom plate 25 is attached to a set of impeller blades 24 integrally molded with fan 10, where bottom plate 25 does not extend out to the outer radii of impeller blades 24. In addition, top plate 50 formed by hub 20 does not extend inward to the inner radii of impeller blades 24 thereby leaving an annular gap 52 breached only by impeller blades 24. This enables fan 10, impeller blades 24, and bottom plate 25 to be molded as a single unit. In another embodiment, as shown in Fig. 4, a flange 19 connected to motor casing 14 and extending outwardly towards hub 20 serves as a top plate. Alternatively, the motor casing may not have a flange in which the motor casing diameter is large enough so that at least a portion of the motor casing serves as the top plate. When the fan/motor is in operation, air flows through motor casing 14 in the direction indicated by arrows 34 through the cooling apertures 33. The airflow turns and flows through a series of flow paths formed by the combination of flange 19, impeller blades 24 and bottom plate 25, bottom plate 25 being attached to driveplate 27 integrally connected to shaft 28. A sealing device is formed by minimizing the gap 41 between flange 19 and hub 20. Referring to Fig. 5, an embodiment of the fan/motor is shown in which fan 10, impeller blades 24 and bottom plate 25 can be connected together to form a single piece that is attached, for example, with screw 62, to a rotatable outer motor casing 15. When the fan/motor is in use, fan 10, impeller blades 24, bottom plate 25 and outer motor casing 15 rotate about axis 22 while inner motor casing 17 remains stationary. Air flows in the general direction of arrow 60 into the interior of motor 12 through inlet apertures 31 and exits outer motor casing 15 through cooling apertures 33 and finally moves in a radial and tangential direction through impeller blades 24. Similar to that described in a previous embodiment (Fig. 1C) , sealing device 64 prevents the airflow from flowing across the outside of motor casing 15 and ensures that the flow is directed through the interior of motor 12, although, unlike that shown in Fig. 1C, hub 20 may be in contact with outer motor casing 15. Alternatively, outer motor casing 15 can be integrally connected to impeller blades 24, in which bottom plate 25, integral with fan hub 20, is attached to outer motor casing 15 with screw 62. In another arrangement (not shown) , the fan/hub/impeller combinations shown in Figs. IB, 2, and 7 (to be described below) , each showing a motor with stationary casing 14, can be used in combination with a motor having the rotatable outer motor casing 15. In the embodiment shown in Figs. 6A and 6B, impeller blades 24 are integral with a fan/motor driveplate attachment 72 so that driveplate/impeller blades unit serves as a top plate. Bottom plate 25 is attached to driveplate attachment 72 by a threaded bolt (not shown) placed through hole 70 and securely engaged with a threaded portion 74 of the driveplate attachment. A portion of driveplate attachment 72 extends axially towards housing 14 thereby defining a gap 71. By minimizing this gap, a sealing device is formed. In use, air flows out cooling apertures 33 of motor casing 14 through the flow paths formed by impeller blades 24, bottom plate 25 and driveplate attachment 72 and out through slots 76, as indicated by arrow 35. Referring to Fig. 6C, a fan/motor combination is shown in which a driveplate 400 is integral with impeller blades 24 such that the driveplate/impeller blades unit serves as a bottom plate. The airflow moves through motor casing 14 and impeller blades 24 as indicated by arrow 34. After exiting the impeller, the airflow then turns and enters the mainstream airflow as shown by arrow 35. In another arrangement, impeller blades 24 and fan/motor driveplate attachment 72 can be made of metal . The metal components act as a heat exchanger drawing heat from the motor armature through the shaft and rejecting heat from the motor blades to the induced cooling air. In the embodiment shown in Figs. 7A and 7B, impeller blades 24 are molded integrally to the underside of hub 20 such that hub 20 serves as a bottom plate. A separate annular shaped top plate 82 is attached to the bottom of impeller blades 24 to form a series of flow paths, each flow path having two adjacent impeller blades on each side and having hub 20 and top plate 82 as the bottom and top sides, respectively. This arrangement enables the airflow, having exited the motor casing, to move through the defined flow paths and exit through slots 80 disposed around the periphery of hub 20. The location of slots 80 can be indexed such that each is positioned near the low pressure surface 13 of a blade 16. The clearance 84 defined by the spacing between the region near the inner radius of top plate 82 and motor casing 14 is minimized to form a seal to ensure that the airflow moves through the interior of the motor and not around the outside of the motor casing. Shown in Figs. 8A and 8B is a motor/fan combination where cooling air, flowing in the direction of arrow 93, exits motor casing 14, flows through impeller blades 24, and exits through impeller outlet (O) , where the outlet (O) is located downstream of the leading edges 90 and upstream of the trailing edges 92 of fan blades 16. The other identified elements are similar to those described above. Referring to Fig. 9, motor casing 14 includes cooling apertures 33 located on the side of motor casing 14 and near the inlet (I) of impeller blades 24. With this configuration, motor cooling air exits motor casing 14 through cooling apertures 33 in a generally radial, as indicated by arrows 34, and tangential direction. The cooling airflow moves through impeller blades 24 and exits the impeller at the outlet (0) of the impeller blades. As indicated by arrow 35, the cooling airflow moves from the outlet and enters the mainstream airflow moving in the general direction of arrows 200. This embodiment may have the additional benefit of reducing the overall package depth by moving the impeller blades to a position more generally along the side of the motor casing. Other embodiments may incorporate one or more of the features described in reference to Figs. 1 through 9 and are within the scope of the following claims.

Claims: What is claimed is : 1. An axial flow fan and motor combination comprising a) a fan hub connected to outwardly extending fan blades, the hub and fan blades being rotatable to produce an airflow from a region upstream of a fan blade leading edge, to a region downstream of a fan blade trailing edge , and b) an electric motor connected to rotate the fan hub, the fan and motor combination further comprising: c) a centrifugal impeller comprising rotating impeller blades, an impeller inlet, and an impeller outlet, said impeller outlet being positioned upstream of an intersection of the fan blade trailing edge and the hub. 2. The combination of claim 1 wherein said motor comprises an outer casing. 3. The combination of claim 2 in which said motor casing comprises at least one casing inlet and at least one casing outlet, the casing outlet being positioned near the impeller inlet, whereby rotation of the impeller assists motor-cooling air flows through said casing inlet, into the inside of said motor casing, and through said casing outlet to said impeller. 4. The combination of claim 1 in which the impeller blades are connected to the fan hub, whereby hub rotation drives the impeller blades. 5. The combination of claim 1 in which said impeller outlet is positioned upstream of said fan blade leading edge. 6. The combination of claim 1 further comprising a top plate and a bottom plate, the bottom plate being spaced apart from the top plate, the flow path being formed by a space between the top and the bottom plate, impeller blades being positioned between the top plate and the bottom plate. 7. The combination of claim 1 in which the hub comprises a forwardly-facing central region, constructed to serve as a top plate, and a bottom plate spaced axially in front of said central hub region, said impeller blades being positioned in a space between said forwardly-facing central region and said bottom plate. 8. The combination of claim 1 in which the hub comprises a rearwardly-facing, concave, central region, constructed to serve as a bottom plate, and a top plate spaced axially rearward of said central hub region, said impeller blades being positioned in a space between said rearwardly-facing central region and said top plate. 9. The combination of claim 2 in which the motor casing is stationary. 10. The combination of claim 9 including a seal between the rotating hub and the stationary casing. 11. The combination of claim 10 in which the seal is an extension from the hub toward the casing, or an extension from the casing toward the hub, or both, said extension reducing a gap between the casing and the hub. 12. The combination of claim 2 in which at least part of the motor casing is configured to rotate with the impeller blades and the fan hub. 13. The combination of claim 12 wherein said impeller blades are integrally connected to said motor casing. 14. The combination of claim 2 in which the motor comprises a sealed outer casing, and the impeller generates motor-cooling airflow along the outside of the motor casing. 15. The combination of claim 2 wherein at least a portion of the motor casing serves as a top plate. 16. The combination of claim 15 in which said motor casing includes a flange, said flange being constructed to serve as the top plate of said impeller. 17. The combination of claim 1 including a rotatable motor driveplate connected to said motor. 18. The combination of claim 17 wherein said motor comprises a stationary outer casing, the combination further comprising a seal between said driveplate and said casing. 19. The combination of claim 17 wherein said driveplate serves as either a top plate or a bottom plate. 20. The combination of claim 17 wherein at least a portion of said impeller blades are attached to said driveplate, whereby motor driveplate rotation drives the impeller blades. 21. The combination of claim 20 wherein said impeller blades and said driveplate are made of metal. 22. The combination of claim 1 wherein at least said fan and said impeller blades are of injection molded plastic material. 23. The combination of claim 22 wherein said fan and at least said impeller blades are molded as a single unit . 24. The combination of claim 6, 7, or 8 wherein said fan, said impeller blades and either said top plate, said bottom plate, or both, are molded as a single unit. 25. The combination of claim 6, 7, or 8 wherein said impeller blades and either said top plate, said bottom plate, or both, are molded as a single unit. 26. A combination of an injection-molded plastic, axial flow fan and an electric motor for use in moving air through an adjacent heat exchanger, the combination comprising, a) a fan hub connected to outwardly extending fan blades, the hub and fan blades being rotatable to produce an airflow from a region upstream of a fan blade leading edge, to a region downstream of a fan blade trailing edge, b) a centrifugal impeller comprising rotating impeller blades, an impeller inlet, and an impeller outlet , c) a top plate and a bottom plate, the bottom plate being spaced apart from and positioned upstream of the top plate, said impeller blades being positioned between the top plate and the bottom plate, and d) an electric motor connected to rotate the fan hub, the motor comprising an external casing surrounding internal motor parts, the casing comprising at least one air inlet, and at least one air outlet, the casing outlet being positioned near the impeller inlet, the impeller outlet being upstream of an intersection of the fan blade trailing edge and the hub, whereby the fan and impeller generate motor- cooling airflow through the inside of the motor casing. 27. A method of moving air through a heat exchanger in a vehicle by operating the fan/motor combination of claim 1 adjacent the heat exchanger to move air through the heat exchanger. 28. A method of assembling the fan/motor combination of claim 3 by attaching the motor to the fan.

Inventors: BOOTH JEFF D, VAN HOUTEN ROBERT J, BOOTH, JEFF, D., VAN HOUTEN, ROBERT, J.
Applicants: BOOTH JEFF D, BOSCH AUTOMOTIVE SYSTEMS CORP, HOUTEN ROBERT J VAN, BOOTH, JEFF, D., BOSCH AUTOMOTIVE SYSTEMS CORPORATION, VAN HOUTEN, ROBERT, J.
Application year: 1998
Main classification: F04B39
IPC codes: F04D25, F04D29, H02K9