Abstract:
A fan has a plurality of blades that are each configured to induce radial-flow adjacent the trailing edge of the blade while also being configured to induce both radial-flow and axial-flow near the base end of the blade. This is achieved by splitting each of the blades into two sections and orienting the chord-line of the blades near the hub of the fan at angle relative to the axis of the hub while maintaining the chord-line of the blades parallel to the axis near the trailing edges of the blades. This results in an increased ability of the fan to draw air in axially as compared to conventional radial-flow fans. The fan of the preferred embodiment also makes use of an annular ring joining the trailing edges of the blades. The ring has axially opposite sides that taper toward one another as the ring extends radially inward and acts as a diverter to channel air to axially opposite sides of an annular obstruction in the flow path of air being exhausted from the fan, thereby further increasing the fan&#39;s efficiency.

Description:
BACKGROUND OF THE INVENTION 
     (1) Field of the Invention 
     This invention pertains to the field of fans of the type mounted on shafts of electric motors and other dynamoelectric devices for cooling such devices during operation. More particularly, this invention pertains to a radial or centrifugal fan wherein the outer portion of its blades are configured to induce radial-flow on air expelled by the fan, and wherein the central portion of the fan&#39;s blades are configured to induce partial axial-flow and partial radial-flow to improve the intake of air into the fan from one of the fan&#39;s axially opposite sides. Additionally, the fan of the preferred embodiment has an annular wedge shaped ring connecting the trailing edges of the fan&#39;s blades that acts as a diverter to channel air exiting the fan to opposite axial sides of an annular grill bar on a cover that encloses the fan. The configuration of the fan of the invention improves efficiency of the fan without increasing its size, thereby providing greater cooling capacity over conventional radial fans of the same size. 
     (2) Description of the Related Art 
     Many dynamoelectric devices such as appliance motors, hand tool motors, generators, and alternators utilize fans mounted on their rotor shafts to provide for air cooling of stator and rotor windings of the devices during their operation. Typically such fans are mounted at an axial end of the dynamoelectric devices immediately adjacent the device housing and are configured to pull or push air through the housing and between the rotor and stator. 
     The majority of dynamoelectric devices are generally cylindrical in shape and the fans are commonly configured to have nearly the same diameter. It is also common for such devices to have a cover enclosing the fan, or to place the fan within the housing of the devices, to prevent objects from contacting the fan blades. Additionally, it is generally desirable to configure cooling fans in a manner such that they take only a minimum of space, since such cooling fans must generally fit within a specific cylindrical space of minimal axial length. 
     Although some machines in which dynamoelectric devices operate allow for the use of axial-flow fans, the configurations of many machines in which dynamoelectric devices are used often necessitate the use of radial-flow fans which discharge air radially outward. Radial-flow fans are designed to obtain maximum air flow rates for a given configuration, unlike centrifugal compressors which are often designed to obtain large pressure differentials under low flow rate conditions. Other design considerations include costs and whether the fan must operate in opposite directions of rotation. 
     Perhaps the simplest radial-flow fan design is a straight blade fan. Straight blade fans utilize a plurality of blades extending radially from a central hub. Like other fan designs, the hub of a straight blade fan is typically a generally cylindrical body having a through-hole aligned with its center axis for mounting the fan to the shaft of a dynamoelectric device. It is also common for the through-hole to be keyed with the shaft to insure that the fan rotates with the shaft without slippage. The blades of a straight blade fan are typically flat rectangular members oriented parallel to the center axis of the hub such that air is forced through the fan purely by centrifugal force. Thus, straight blade fans are typically symmetric about a plane that is perpendicular to the center axis of the hub and act to draw air inward from both of the opposite axial sides of the fan in response to the fan blades pushing air radially outward from the center hub. 
     To reduce the amount of air drawn into a radial fan from the side of the fan that faces away from the dynamoelectric device to be cooled, such radial fans often have an imperforate disk shaped backing mounted for rotation with the fan on the side of the fan farthest from the housing of the dynamoelectric device. Such backings generally increase the amount of air drawn into the fan from the side of the fan facing the housing of the dynamoelectric device. However, such backings take up axial space and thereby reduce the axial width of the fan blades for a given total axial length of the fan, thereby decreasing the total output of the fans compared to non-backed fans of equal axial length. Additionally, backings also increase the amount of material required to manufacture such fans. 
     A preferred method of reducing the amount of air drawn into a radial fan from the side of the fan that faces away from the dynamoelectric device is to configure the cover which typically surrounds the fan with an imperforate disk shaped end that is positioned with an axial gap between it and the fan. Thus, the disk shaped end of the cover acts much as a backing does to increase the amount of air drawn into the fan from the side of the fan facing the housing of the dynamoelectric device, without reducing the axial width of the fan blades. 
     Straight blade radial fans have an advantage of operating equally well in either direction of rotation. For this reason, straight blade radial fans are often used to cool dynamoelectric devices whose shafts rotate in opposite directions during operation. However, for those devices whose shafts seldom or never rotate in opposite directions, straight blade fans need not be used and other configurations having blades that curve in a plane perpendicular to the center axis of the fan hub have been used. By curving the blades of a radial fan in a direction opposite that of the rotation (commonly called a backward curved radial fan), the fan exhausts air using both centrifugal force and force caused by the blade pushing the air in partially the radial direction. However, such curved blades may or may not increase the overall air output, since curving the blades also reduces the circumferential velocity of the air passing through the fan and thereby decreasess the centrifugal force component generated by the fan. Generally, straight blade radial fans produce a greater air flow rate than backward curved blade fans of the same size and are thus desirable for use with most dynamoelectric devices. 
     Although radial-flow fans have proven effective for cooling dynamoelectric devices, it remains advantageous to design fans having ever greater efficiency. Furthermore, it is desirable to increase the efficiency of such fans without increasing the size of the fans and without significantly increasing the cost or adding additional components to the dynamoelectric device assembly. 
     SUMMARY OF THE INVENTION 
     The radial fan of the present invention increases the flow rate of cooling air through a dynamoelectric device as compared to prior art straight blade radial fans of the same size. The increased airflow is a result of the configuration of the blades of the fan as well as the configuration of an annular ring joining the blades. 
     In general, the fan of the preferred embodiment of the invention is a fan configured for use with a dynamoelectric device whose rotor shaft rotates in only one direction. The fan of the preferred embodiment is made more efficient by configuring the blades to perform as a conventional radial fan near their trailing edges while also configuring the blades to perform as a mixed-flow fan nearer the shaft or inlet. This is achieved by splitting each of the blades into two sections and orienting the chord-line of the blades near the hub at an angle relative to the axis of the hub while maintaining the chord-line of the blades near the trailing edges of the blades parallel to the hub axis. By configuring the blades as a mixed-flow fan near the hub of the fan, the fan more efficiently draws air from its axial side facing the dynamoelectric device. This results in a corresponding higher radial air flow rate from the fan and greater cooling of the dynamoelectric device. 
     The annular ring of the preferred embodiment of the fan also increases the flow rate from the fan by channeling the air into exhaust openings of the cover that circumferentially surrounds the fan. The cover used with the preferred embodiment of the fan has an annular grill bar which surrounds the blades of the fan and axially separates pairs of openings in the cover to prevent objects and fingers from contacting the blades of the fan when the fan is rotating. Thus, the grill bar of the cover partially obstructs the flow of air from the fan and the air must pass on either axial sides of the grill bar as it is being exhausted. The ring of the preferred embodiment has axially opposite sides that taper toward each other as they extend radially inward. As air flows past the ring while being exhausted, the taper of the ring axially separates the flow in a streamline manner, which then allows the air to pass the grill bar of the shroud more efficiently. 
     Like the preferred embodiment of the fan, an alternative embodiment of the fan has blades configured such that the chord-line of the blades near the hub are at an angle relative to the axis of the hub while the chord-line of the blades near the trailing edges of the blades are parallel to the hub axis. However, the disclosed alternative embodiment of the fan achieves this by extending a portion of the each of the blades, near the hub, axially forward of the remainder of the blade and curving such portions so that the portions are rotationally in advance of the remainder of the blades. Additionally, the alternative embodiment of the fan utilizes a ring positioned at the root edge of each of the blades that acts similar to a backing but that is absent where the chord-line of each blade is oriented at an angle relative to the axis of the hub. This allows the fan to be manufactured using simple molding methods that would not be possible if the fan had a disked shaped backing rather than a ring. 
     While the principle advantages and features of the invention have been described above, a more complete and thorough understanding of the invention may be attained by referring to the drawings and the detailed description of the preferred embodiment, which follow. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is an isometric view of the fan of the preferred embodiment of the invention. 
     FIG. 2 is a plan view of the fan of the preferred embodiment of the invention as seen looking at the tip edges of the blades. 
     FIG. 3 is a plan view of the fan of the preferred embodiment of the invention as seen looking at the root edges of the blades. 
     FIG. 4 is a cross-section of one of the blades of the fan of the preferred embodiment of the invention taken at the line  4 — 4  of FIG.  2 . 
     FIG. 5 is a partial cross-section of the ring of the fan of the preferred embodiment of the invention taken at the line  5 — 5  of FIG.  2 . 
     FIG. 6 is an assembly view of an electric motor of the type with which the fan of the preferred embodiment of the invention is configured for use. 
     FIG. 7 is an exploded view of the assembly of FIG. 6 showing the placement of the fan of the preferred embodiment of the invention relative to the motor and the cover. 
     FIG. 8 is an isometric view of a fan of an alternative embodiment of the invention. 
     FIG. 9 is a plan view of the fan of the alternative embodiment of the invention as seen looking at the tip edges of the blades. 
     FIG. 10 is a plan view of the fan of the alternative embodiment of the invention as seen looking at the root edges of the blades. 
     FIG. 11 is a cross-section of one of the blades of the fan of the alternative embodiment of the invention taken at the line  11 — 11  of FIG.  9 . 
     FIG. 12 is a partial cross-section of the fan of the alternative embodiment of the invention taken at the line  12 — 12  of FIG.  9 . 
    
    
     References and characters in the written specification indicate corresponding parts throughout the several views of the drawings. 
     DETAILED DESCRIPTION OF THE INVENTION 
     The preferred embodiment of the fan  20  of the invention is shown in its entirety in FIGS. 1-3. The fan  20  preferably comprises a central hub  22 , a plurality of blades  24 , and an annular ring  26 . The fan  20  of the preferred embodiment is configured to cool an electric motor  28  of the type having a rotor that rotates in only one direction and is enclosed by a cover  30  once it is assembled on the motor as shown in FIGS. 6 and 7. Additionally, the fan  20  is preferably formed of a polymeric resin as a single monolithic part. 
     The hub  22  of the preferred embodiment of the fan  20  is a generally cylindrical body having an outer periphal surface  32  and a center bore or opening  34  that extends through the hub  22  along its axis. The opening  34  of the hub  22  preferably has opposite arcuate surfaces  36  configured to slidably engage with the rotor shaft  38  of the motor  28 , as shown in FIG.  7 . An opposite pair of flats  40  separate the arcuate surfaces  36  of the opening  34  and are configured to engage with a pair of opposite notches  42  formed in the end of the rotor shaft  38  of the motor  28  to provide an interlocking fit between the hub  22  and the rotor shaft that ensures that the fan  20  rotates with the rotor shaft. However, it should be understood that numerous methods of attaching fans to shafts are known in the art and alternative configurations of the hub and rotor shaft and alternative methods of attaching one to the other could also be used. 
     The blades  24  of the preferred embodiment of the fan  20  of the invention are evenly spaced circumferentially about the axis of the hub  22 . Each of the blades  24  has a base end  44  that is secured to the hub  22 , and each extends radially from the hub to an opposite trailing edge  46 . Additionally, each of the blades  24  has a first radial section  48  extending radially inward from its trailing edge  46  and each has a second section  50  extending radially outward from its base end  44 . 
     The axial width or blade height of each of the blades  24 , measured from the tip edge  52  of each of the blades to the root edge  54  of each of the blades, preferably remains constant between the blade&#39;s base end  44  and trailing edge  46 . At any given radius from the axis of the hub  22 , the first section  48  of each of the blades  24  has a cross-section that is generally rectangular with a chord-line  56 , defined as an imaginary line extending from the tip edge  52  to the root edge  54  of the blade as shown in FIG. 4, that is oriented parallel to the axis of the hub. 
     Unlike the first section  48  of each of the blades  24 , the second section  50  of each of the blades, at any given radius from the axis of the hub  22 , has a cross-section that has its chord-line  58  oriented at an angle relative to the axis of the hub  22  such that the tip edge  52  is rotationally in advance of the root edge  54  as the fan  20  revolves with the rotor shaft  38 . Additionally, the cross-section of the blade second section  50  consists of a first portion  60  having opposite straight parallel sides  62  that are oriented parallel to the axis of the hub  22  and a second portion  64 , also having straight parallel sides  66 , that intersects the first portion at an angle. As the second section  50  of each of the blades  24  extends radially outward from the axis of the hub  22 , the angle between the parallel sides  62 , 66  of the first and second portions  60 , 64  increases from zero degrees at the base end  44  of each of the blades. Stated another way, the angle of the parallel sides  66  of the second portion  64  relative to the hub axis is zero degrees where the second portion joins the hub and progressively increases as the second portion  64  extends radially from the hub  22 . 
     The first and second sections  48 , 50  of each of the blades  24  extend radially toward each other and terminate at a common point that lies between the base end  44  and the trailing edge  46  of each blade, causing an abrupt discontinuity in the tip edge  52  of each of the blades where the sections meet. However, the entire root edge  54  of each of the blades  24  extends radially straight. 
     The ring  26  of the preferred embodiment of the fan  20  connects the trailing edges  46  of the blades  24  to one another and extends completely around the axis of the hub  22 . As shown in FIG. 5, the ring  26  is positioned centrally between the tip and root edges  52 , 54  of the blades  24  and has a wedge shaped cross-section (the cross-section taken in a plane that includes the axis of the hub). The wedge shaped cross-section of the ring  26  is formed by axially opposite side surfaces  68  that taper toward each other as the as the ring extends radially inward. An outer surface  70  of the ring  26  lies flush with the edge of the trailing edges  46  of the blades  24 . 
     In the preferred embodiment of the fan  20 , only the ring  26  and hub  22  connect the blades  24  to one another, i.e. there is no backing attaching the blades. Thus, voids extend axially through the fan  20  between each adjacent pair of blades  24 . 
     The fan  20  is assembled on the rotor shaft  38  of the motor  28  in a manner such that the tip edges  52  of the blades  24  are closer to the end shield  72  of the motor  28  than the root edges  54  of the blades. The cover  30  is then attached to the motor  28  where it covers the fan  20 . The particular method used to secure the components together are not pertinent to this invention and any method known in the art for assembling components could be used. 
     The cover  30  is generally a cylindrical shell that is closed at one end by an imperforate flat disk shaped wall  74 , and is configured such that the disk shaped wall  74  is positioned close to the root edges  54  of the blades  24  of the fan  20 . The cover  30  also has a plurality of exhaust openings  76  circumferentially spaced about its cylindrical wall  78 . When the cover  30  is attached to the motor  28 , the exhaust openings  76  are axially aligned with the tip ends  46  of the blades  24  of the fan  20 . To prevent fingers and other objects from contacting the blades  24  of the fan  20  during its operation, the cover  30  also has a cylindrical grill bar  80  that axially separates adjacent pairs of the exhaust openings  76 . 
     As the fan  20  rotates with the rotor shaft  38  of the motor  28 , the first sections of the blades radially discharge air by creating a pressure differential caused by centrifugal force. This pressure differential also acts to draw air from either of the axial sides of the fan  20 , but the disk shaped wall  74  of the shroud  30  prevents air from being drawn into the fan from the side of the fan opposite the motor  28 . Thus, air is drawn into the fan  20  through the vent openings  82  on the end shield  72  of the motor. While this is similar to the way conventional radial cooling fans operate, the configuration of the preferred embodiment of the fan  20  of the invention provides increased efficiency over prior art radial fans for any given fan size. This is because the first section  48  and the first portion  60  of the second section  50  of each blade  24  lie in the same plane and act as a radial-flow portion of each blade while the second portion  64  of the second section  50  acts as an axial-flow portion of the blade. In other words, because the first section and the first portion  60  of the second section  50  of each blade are in a plane that is parallel to the center axis of the hub  22 , these parts of each blade  24  induce a radial pressure differential while the second portion  64  of the second section  50  induces an axial pressure differential. Thus, the second portions  64  of the second sections  50  of the blades  24  act partially as an axial-flow fan, thereby cutting into the air to draw air in from the side of the fan  20  facing the motor  28 . The efficiency of the fan  20  is thereby increased as compared to conventional radial fans that draw air in purely by the pressure differential created as a result of the centrifugal force of the air near the trailing edges  54  of the blades  24 . 
     Another advantage of the fan  20  lies in the presence and configuration of the ring  26 . As air is expelled from the fan  20 , it must pass through the exhaust openings  76  of the cover  30  and, normally, the grill bar  80  axially separating adjacent exhaust openings obstructs the flow of air being expelled from the fan. However, the ring  26  is positioned on the fan  20  where it is axially aligned with the grill bar  80  of the cover  30  when both are assembled on the motor  28 . Additionally, the outermost surface  70  of the ring  26  has an axial width such that if the side surfaces  68  were continued outwardly, they would line up with the edges of the grill bar  80  of the cover  30 . Thus, the tapered side surfaces  68  of the ring  26  act to axially separate and deflect the flow of the air being expelled from the fan  20  such that the air can pass more easily around the grill bar  80  of the cover  30 . 
     An alternative embodiment of the fan  100  of the invention is shown in FIGS. 8-12 and comprises a central hub  102 , a plurality of blades  104 , and an annular ring  106 . Like the fan  20  of the preferred embodiment, the fan  100  of the alternative embodiment is configured to cool an electric motor of the type having a rotor that rotates in only one direction and is preferably formed of a polymeric resin as a single monolithic part. However, the fan  100  of the alternative embodiment is preferably configured to be enclosed by the housing of a motor. 
     Like the hub  22  of the fan  20  of the preferred embodiment, the hub  102  of the fan  100  of the alternative embodiment is a generally cylindrical body having an outer peripheral surface  108  and a center bore or opening  110  that extends through the hub  102  along its axis. However, the opening  110  is cylindrical and has a plurality of axial slots  112  extending into an axial end of the hub  102  such that the fan  100  can be attached to a rotor shaft using a C-clip or spring clip placed around the end of the hub in which the slots are formed. Again, it should be understood that this method of attaching a fan to a shaft is known in the art and numerous other known methods of attaching fans to shafts could also be used. 
     Similar to the preferred embodiment, the blades  104  of the alternative embodiment of the fan  100  are evenly spaced circumferentially about the axis of the hub  22  and each of the blades  104  has a base end  114  that is secured to the hub  102 , and each extends radially from the hub to an opposite trailing edge  116 . Likewise, each of the blades  104  has a first radial section  118  extending radially inward from its trailing edge  116  and each has a second section  120  extending radially outward from its base end  114 . 
     At any given radius from the axis of the hub  102 , the first section  118  of each of the blades  104  has a cross-section that is generally rectangular, albeit the cross-section may be slightly non-rectangular to account for fabrication draft angle requirements. Each blade  104  as a tip edge  122  and root edge  124  and throughout the first section  118  of each blade  104 , the chord-line  126  of the cross sections of the blade are oriented parallel to the axis of the hub  102 . 
     Further like the preferred embodiment, the second section  120  of each of the blades  104  at any given radius from the axis of the hub  102 , has a cross-section that has its chord-line  128  oriented at an angle relative to the axis of the hub  102  and, as the second section  120  of each of the blades  104  extends radially outward from the axis of the hub  102 , the angle of the chord-line  128  relative to the axis of the hub  102  increases. The cross-section, at any given radial distance from the axis, throughout the second section  120  of each blade  104  consists of a first portion  130  and a second portion  134 . The first portion  130  has opposite straight, generally parallel sides  132  that are oriented substantially parallel to the axis of the hub  102  and the second portion  134  has curved parallel sides  136 , that intersect the first portion tangentially. 
     The first and second sections  118 , 120  of each of the blades  104  extend radially toward each other. However, unlike the preferred embodiment of the invention, the second portion  134  of the second section  120  of each blade  104  of the alternative embodiment extends axially forward of the first section  118  of each blade, i.e. in a direction away from the root edge  124  of each blade, as shown best in FIG.  12 . The root edge  124  of each of the blades  104  also jogs axially forward as it extends from the first section  118  to the second section  120  of each of the blades. 
     The ring  106  of the fan  100  of the alternative embodiment extends completely around the axis of the hub  22  and connects the root edges  124  of the blades  104  to one another. As shown in FIG. 12, the ring  106  is disk shaped and extends radially inward along substantially the entire first section  118  of each of the blades  104 . The ring  106  is essentially a partial backing attached to the blades  104  except that it does not extend in the radial region of the second sections  120  of blades. Thus, voids extend axially through the fan  100  between the second sections  120  of each adjacent pair of blades  104 . As can be appreciated by one skilled in the art, the absence of the ring  106  in the radial region of the second section  120  of the blades  104  allows the fan  100  to be formed as a monolithic piece of polymeric material using a convention two-piece molding die. 
     The fan  100  of the alternative embodiment is assembled to a motor in a manner similar to the fan  20  of the preferred embodiment except that the fan  100  is configured to be positioned between an axial end of the stator (not shown) and an end shield of the motor, within the housing of the motor. Unlike the motor used with the fan of the preferred embodiment, exhaust openings aligned with the trailing edges  116  of the blades  104  extend directly through the housing of the motor used with the fan  100  of the alternative embodiment. An annular baffle or shroud (not shown) is preferably positioned between the first section  118  of the blades  104  of the fan  100  and the stator of the motor. The shroud is preferably shaped to substantially fill the axial space that exists between the stator of the motor and the first sections  118  of the blades  104  due to the second sections  120  of the blades of the fan  100  being axially forward of the first sections of the blades. The end shield has an imperforate disk shaped wall or alternatively has a cylindrical attachment that is positioned close to the ring  106  of the fan  100  or is attached to the center of the fan, and functions similar to the disk shaped wall  74  of the cover  30  used in conjunction with the fan  20  of the preferred embodiment. However, unlike a cover, the end shield has a centrally positioned bearing (not shown) for supporting the rotor shaft of the motor. The bearing protrudes axially into the motor from the wall of the end shield and is accommodated by the fact that the fan  100  is configured, as described above, such that root edge  124  along the second section  120  of each of the blades  104  is axially forward of the root edge along first section  118  of each blade. 
     In operation, the fan  100  of the alternative embodiment functions similar to the fan  20  of the preferred embodiment. The first section  118  and the first portion  130  of the second section  120  of each blade  104  lie in the same plane and act as a radial-flow portion of each blade while the second portion  134  of the second section acts as an axial-flow portion of the blade. The efficiency of the fan  100  is thereby increased as compared to conventional radial fans that draw air in purely by the pressure differential created as a result of the centrifugal force of the air near the trailing edges  116  of the blades  104 . 
     While the present invention has been described by reference to a specific embodiment, it should be understood that modifications and variations of the invention may be constructed without departing from the scope of the invention defined by the following claims.