Patent Publication Number: US-6666660-B2

Title: Motor-fan assembly for a floor cleaning machine

Description:
FIELD OF THE INVENTION 
     The present invention relates generally to a motor-fan assembly for a floor cleaning appliance. More particularly, the present invention relates to a motor-fan assembly for a floor cleaning appliance having an improved working air fan, fan chamber, and motor cooling fan housing cover design. 
     BACKGROUND OF THE INVENTION 
     In the floor care appliance art, a motor-fan assembly is typically used in what are known as “dirty air” systems as a vacuum source for drawing dirt laden air and/or dirty cleaning solution (both hereinafter referred to as dirty working air) through a nozzle and the fan chamber itself before directing it to a filter bag and/or a receptacle for collection and later disposal. A motor-fan assembly may also be used in what are known as “clean air” systems as a vacuum source for creating a suction in the receptacle for drawing the dirt laden air into the receptacle. The floor care appliances referred to include vacuum cleaners of the upright or canister type for vacuuming dirt particles from the floor surface and the extractor type cleaners for scrubbing floors and carpets. Known motor-fan assemblies, therefore, have a working air fan or impeller (hereinafter referred to as working air fan, fan, or impeller) driven by a motor that draws the dirty working air into the fan chamber and expels it through a fan chamber outlet into a receptacle. 
     In order to meet consumer demand for increased performance in floor care appliances, designers of motor-fan assemblies for such appliances have sought to improve the performance of one or more aspects of the motor-fan assembly. One such aspect is the performance of the working air fan in generating the vacuum source for drawing the dirty air. One other aspect sought to be improved is reducing the noise generated by the working air fan or other parts of the motor-fan assembly. Another aspect sought to be improved is the cooling performance of the motor-fan assembly. 
     Impellers and fans for use with motor-fan assemblies and the like are well known in the art. There are patents for fans attempting to improve fan performance and reduce noise, fans having spiral blades, and fans less susceptible to impact damage from debris. For example, in U.S. Pat. No. 5,755,555 issued to Swift a rotating fan assembly is provided for use in single stage and multi-stage applications. The fan assembly includes a fan member having a tapered disk member, a flat annular ring member and a plurality of spiral shaped blade members interposed between the disk and the ring. U.S. Pat. No. 5,573,369 issued to Du provides a fan for a vacuum cleaner having a fan housing, a motor and an impeller. The impeller has a hub and multiple blades. The blades have a leading edge that is tapered upward, a top edge that is tapered downward, and a trailing edge that is tapered downward. 
     However, no patents were found that improve the performance of aforementioned aspects of the motor-fan assembly such as the working air fan, reducing the noise generated by the working air fan or other parts of the motor-fan assembly, or improving the cooling performance of the motor-fan assembly in the manner of the present invention. 
     Accordingly, an object of the present invention is to improve the performance of a motor-fan assembly for a floor care appliance. 
     Another object of the present invention is to provide a motor-fan assembly for a floor care appliance with an improved working air fan design. 
     Yet still another object of the present invention is to provide a motor-fan assembly for a floor care appliance with an improved working air fan that improves debris passage. 
     Another object of the present invention is to provide a motor-fan assembly for a floor care appliance that reduces working air fan noise. 
     Yet another object of the present invention is to provide a motor-fan assembly for a floor care appliance with an improved working air fan design that is resistant to impact damage. 
     These and other objects will be readily apparent to one of skill in the art upon reviewing the following description and accompanying drawings. 
     SUMMARY OF THE INVENTION 
     The present invention provides an improved motor-fan assembly for a floor cleaning appliance such as a vacuum cleaner or extractor. In one disclosed embodiment, the motor-fan assembly includes a motor housing having a working air inlet, a working air outlet, a working air fan, and a housing cover for the working air fan cavity having a plurality of spiral shaped grooves on the inner surface for reducing noise. The motor-fan assembly further includes a cooling air inlet, a motor cooling air fan, a housing cover for the motor cooling air fan cavity having a plurality of vent openings of a novel design for improved cooling performance. A motor is supported inside the motor housing. A working air fan is positioned between the working air inlet and the working air outlet and is coupled to the shaft of the motor. The working fan draws working air into the motor housing through the working air inlet and blows the working air out of the motor housing through the working air outlet. The plurality of spiral shaped grooves formed on the inner surface of the housing cover covering the working air fan cavity are for reducing the noise generated in the cavity. 
     In another form of the present invention, a cooling air fan is positioned adjacent the motor and is coupled to the motor shaft. The cooling fan draws cooling air into the motor housing through the cooling air inlet to cool the motor. The cooling air is exhausted to the atmosphere through the plurality of vent openings located in the motor cooling fan housing cover covering the motor cooling air fan cavity. The plurality of vent openings are slot shaped and are spaced circumferentially about the hub of the motor cooling air fan housing cover. 
     In still another form of the present invention, the working air is generated by a working air fan having a greater number of fan blades compared to conventional fans having five to seven blades. The top edge of the fan blades are parallel to the inner surface of the working air fan cover to improve the passage of debris over the top of the working air fan. The increased number of closely spaced blades also helps prevent debris from getting stuck between the blades. 
     In an alternate embodiment of the present invention, the motor cooling air fan housing cover has a plurality of vent openings spaced circumferentially about the hub of the housing cover wherein adjacent vent openings are separated by a planar shaped vane. The airstream cooling the motor-fan assembly exits the motor housing through the plurality of vent openings past the planar shaped vanes. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     For a complete understanding of the objects, techniques and structure of the invention, reference should be made to the following detailed description and accompanying drawings wherein: 
     FIG. 1 is a perspective view of motor-fan unit according to the preferred embodiment of the present invention; 
     FIG. 2 is an exploded perspective view of the motor-fan assembly shown in FIG. 1; 
     FIG. 3A is front view of a fan chamber for use with a motor-fan assembly such as the one shown in FIG. 1; 
     FIG. 3B is rear view of the fan chamber shown in FIG. 3A showing the spiral grooves formed on the inner surface thereof; 
     FIG. 3C is a slightly elevated side view of the fan chamber shown in FIG. 3A; 
     FIG. 3D is a slightly elevated side view of the opposite side thereof of the fan chamber shown in FIG. 3A showing the details of the working air fan cavity; 
     FIG. 4A is a side view of a preferred embodiment of a motor cooling fan housing cover having a plurality of vent openings for use with a motor-fan assembly such as the one shown in FIG. 1; 
     FIG. 4B is a front view of the motor cooling fan housing cover shown in FIG. 4A showing the angular relationship φ between the plane of the longitudinal axis A of a vent opening and the radial axis Qr of the motor cooling fan housing cover; 
     FIG. 4C is an exploded view of a portion of the motor cooling fan housing cover shown in FIG. 4B; 
     FIG. 4D is a rear view of the motor cooling fan housing cover shown in FIG. 4A; 
     FIG. 4E is a partial cutaway view of a motor-fan assembly such as the one shown in FIG. 1 showing the major axes of the motor-cooling fan housing cover shown in FIG.  4 A and the individual directional components of the cooling airstream flowing through the plurality of vent openings in the direction of the major axes; 
     FIG. 4F is an exploded view of a portion of the motor cooling fan housing cover shown in FIG. 4E showing the detail of the individual directional components of the cooling airstream flowing through one of the plurality of vent openings in the direction of the major axes; 
     FIG. 5A is a top view of a working air fan for use in a motor-fan assembly such as the one shown in FIG. 1; 
     FIG. 5B is a side view of the working air fan shown in FIG. 5A; 
     FIG. 5C is a cross-sectional view of the working air fan shown in FIG. 5A taken along line  5 C— 5 C of FIG. 5A; 
     FIG. 5D is a cross-sectional view of the working air fan shown in FIG. 5A taken along line  5 D— 5 D of FIG. 5A; 
     FIG. 6 is a partial cutaway side view of a motor-fan assembly such as the one shown in FIG. 1 with a partial cutaway view of the fan chamber and the motor housing showing the details of the working air fan, fan cavity and the passage of debris over the working air fan to the exhaust conduit; 
     FIG. 7 is an exploded perspective view of an alternate preferred embodiment of a motor-fan assembly; 
     FIG. 8A is a front view of an alternate preferred embodiment of a motor cooling fan housing cover for use with a motor-fan assembly such as the one shown in FIG. 7; and 
     FIG. 8B is a cross-sectional view of the motor cooling fan housing shown in FIG. 8A taken along line  8 B— 8 B of FIG. 8A showing the resultant direction of the cooling airstream relative to the plane of the vane separating adjacent vent openings. 
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Referring now to the drawings and more particularly to FIG. 1, a motor-fan assembly  10  is shown for use in floor cleaning appliances such as upright and canister vacuum cleaners and extractors. Whatever floor cleaning appliance motor-fan assembly  10  is installed in, it is used as a vacuum source for drawing dirt laden air or dirty cleaning solution through a nozzle and directing it into a filter and/or receptacle for collection and later disposal. Motor-fan assembly  10  can be used in what is known as “dirty air” systems wherein the dirt and/or dirty cleaning solution (hereinafter dirty air) comes into direct contact with the working air fan (or impeller) before being directed to a filter and/or receptacle. Motor-fan assembly  10  can also be used in “clean air” systems wherein the dirty air is drawn into the receptacle by a vacuum created by motor-fan assembly  10  on the opposite side of the receptacle. The dirty air never comes into contact with the working air fan. For the purposes of disclosure, motor-fan assembly  10  is described for installation in a “dirty air” type floor cleaning appliance only. The actual shape and design of the motor housing  60  shown in FIG. 1 is of very little consequence to the present invention. The details of the novel portions of the present invention, namely the motor cooling fan housing cover  50 , working air fan  30  (not shown), and fan chamber  20  are described fully hereinbelow. 
     Referring now to FIG. 2, shown is an exploded perspective view of motor-fan assembly  10 . Motor-fan assembly  10  is comprised generally of a motor housing  60 , a rotor-cooling fan assembly  40 , a motor support  70 , a working air fan or impeller  30 , a motor-cooling fan housing cover or cap  50 , and a fan chamber or working air fan cover  20 . Motor-cooling fan housing cover  50  has a plurality of slot shaped vent openings  53  formed in a hemi-spherically shaped plate portion  52  spaced circumferentially around a central hub  55 . Hub  55  has an aperture  56  formed in the center for allowing the motor shaft  41  to pass therethrough. Motor-cooling fan housing cover  50  fits into an aperture  62  formed in one end of motor housing  60  such that vent openings  53  extend slightly beyond the plane of the end wall of motor housing  60 . The opposite side of motor-cooling fan housing cover  5 O has a cooling fan cavity  58  (FIG. 4A) for receiving cooling fan  42  of rotor-fan assembly  40 . Two or more lips  51  extend from the periphery of the plate portion  52  for securing motor-cooling fan housing cover  50  to the end wall of motor housing  60 . Apertures  54  in lip  51  of motor-cooling fan housing cover  50  are aligned with apertures  61  in the end wall of motor housing  60  to secure motor-cooling fan housing cover  50  and motor housing  60  together. Rivets or screws or the like may be used in apertures  54  and  61 . Alternately, motor-cooling fan housing cover  50  may be integrally formed on the end of motor housing  50  eliminating the need for attaching it separately. Of course, vent openings  53  would also have to be formed integrally therein. A plurality of cooling air inlet openings  63  are formed on the sidewall of motor housing  60  to allow the cooling air to be introduced into motor housing  60 . 
     As discussed, rotor-fan assembly  40  is inserted into cavity  58  (FIG. 4A) of motor-cooling fan housing cover  50  such that cooling fan  42  is free to rotate therein. Motor shaft  41  of rotor-fan assembly  40  is inserted into aperture  56  in hub  55  of motor-cooling fan housing cover  50  wherein hub  55  acts as a bearing for motor-shaft  41 . Motor shaft  41  extends from rotor  44  containing the field windings. Rotor  44  is surrounded by stator  43  also containing windings for generating the electromotive forces to drive motor-shaft  41 . Extending from an opposite end of rotor  44  is another section of motor-shaft  41  having a threaded section  41   a  on the end. Threaded section  41   a  of motor-shaft  41  is inserted into an aperture  73  in motor support  70 . A plurality of arms  71  extend sidewardly from a base portion  72  of motor support  70 . Arms  71  define a cradle for receiving and holding rotor-fan assembly  40 . A U-shaped channel portion  74  extends outwardly from base portion  72  for the purpose described in more detail further hereinbelow. Motor-shaft  41  extends further past base portion  72  of motor support  70  to receive working air fan  30 . Working air fan  30  is bolted to motor-shaft  41  via bolt  31  and threaded section  41   a  of motor shaft  41 . Fan chamber  20  is then attached by screws  21  or the equivalent over working air fan  30  to seal motor housing  60  with working air fan  30  being received by a working air cavity or working air chamber  29  formed in fan chamber  20 . A plurality of bosses  64  with apertures formed therein (not shown) are formed around the outer periphery of motor housing  60  for receiving screws  21 . The attachment of fan chamber  20  to motor housing  60  sandwiches motor support  70  between fan chamber  20  and rotor-fan assembly  40 . Rotor-fan assembly  40  is also thereby secured in an inner chamber  65  of motor housing  60 . When fan chamber  20  is attached to motor housing  60 , working air cavity  29  is sealed by motor support  70  creating a working air cavity  29  wherein the suction is created for the working airstream. A U-shaped channel portion  24  extends sidewardly from fan chamber  20  which mates with the U-shaped channel portion  74  of motor support  70  to form a rectangular shaped exhaust conduit or channel  75  for the working airstream to exhaust from within working air cavity  29  of fan chamber  20 . An inlet aperture  23  is in the center of the annular main body portion of fan chamber  20  which is generally connected to the nozzle (not shown) of the floor cleaning appliance to draw the dirty airstream into working air cavity  29 . 
     Referring now to FIGS. 3A to  3 D, shown is more detail of fan chamber  20 . FIG. 3A is a front view of fan chamber  20  showing the detail of the exterior surface  25  of fan chamber  20 . Inlet aperture  23  is shown in the center and a U-shaped channel portion  24  extends sidewardly to the left from fan chamber  20 . A plurality of eyelets  22   a  are formed around the outer periphery of fan chamber  20  having an aperture  22   b  formed therein for allowing screws  21  (FIG. 2) to pass therethrough for attaching fan chamber  20  to motor housing  60 . FIG. 3B shows the inner surface  27  of fan chamber  20  which is bordered by a sidewall  28  which surrounds the majority of the inner surface  27  of fan chamber  20  except for the portion leading into the U-shaped channel portion  24 . Sidewall  28  transitions into the opposing sidewalls of U-shaped channel portion  24  to direct the dirty airstream out of working air cavity  29 . A plurality of spiral shaped grooves  26  extend from inlet aperture  23  to sidewall  28  for creating a disturbance in the airflow near inner surface  27 . The airflow generated by the working air fan  30  (not shown) rotates in the direction of arrow  85 , which is opposite to the direction of spiral of the plurality of spiral grooves  26 . Grooves  26  are spaced equi-distant from each other circumferentially about inlet aperture  23 . The original re-circulation patterns of the generated airstream are broken into smaller re-circulation patterns that reduce the noise produced near the motor fundamental frequency, and its first few harmonics (between 300 and 1600 Hz). The shape and depth of the grooves  26  affect the noise and the air performance as well. In the preferred embodiment, the shape of the grooves are 0.04 inch deep by 0.08 inch wide with an outward spiral which is opposite to the fan rotational direction. 
     Additional views of fan chamber  20  can be seen in FIGS. 3C and 3D. FIG. 3D shows the orientation of sidewall  28  and inner surface  27  relative to each other and to the remaining portions of fan chamber  20 . Sidewall  28  is straight and is perpendicular to the plane intersecting the outer perimeter of inner surface  27 . The inner surface  27  extends in the radial direction from the plane intersecting the outer perimeter of inlet aperture  23  to sidewall  28 . Inner surface  27  is linear in the radial direction and in the preferred embodiment is angled at 35° C. off of the plane intersecting the outer perimeter of inner surface  27 . The importance of these relationships is discussed hereinbelow. FIG. 3D shows the detail of working air cavity  29  which receives working air fan  30  and the plurality of spiral grooves  26  formed on inner surface  27 . 
     Referring now to FIGS. 4A-4F, shown is motor cooling fan housing cover  50  and the plurality of slot shaped vent openings  53  spaced circumferentially about hub  55 . Specifically, FIG. 4A shows a side view of motor cooling fan housing cover  50 , which is comprised of a truncated semi-hemispherical shaped top plate  52 , an annular shaped hub  55  integrally molded on the geometric center of the truncated region of top plate  52 , a lip  51  surrounding the periphery of top plate  52 , and an annular ring  57  attached to the side of top plate  52  and lip  51  opposite hub  55 . The truncated hemispherical shape of top plate  52  gives the outer periphery a rounded appearance and a portion having a finite width extending beyond the plane of lip  51 . Motor cooling fan  42  (not shown) is received into a cavity  58  on the side of lip  51  opposite top plate  52 . As discussed, when motor cooling fan housing cover  50  is inserted into the aperture  61  (FIG. 2) of motor housing  60  (FIG.  2 ), the portion of top plate  52  having finite width extends beyond the plane of the end wall of motor housing  60  (FIG.  2 ). FIG. 4B shows a front view of motor cooling fan housing cover  50  and the plurality of vent openings  53  formed in top plate  52  and spaced circumferentially around hub  55 . Also seen is hub aperture  56  in the center of hub  55  and top plate  52  for receiving motor shaft  41  (not shown). Motor cooling fan  42  (not shown) and motor shaft  41  (not shown) rotate counter-clockwise in the direction of arrow  90 . In the preferred embodiment of the invention, there are 13 vent openings  53  formed in top plate  52  in the arrangement shown. In an alternate embodiment of the present invention, there are seventeen vent openings  53  in top plate  52 . However, the number of vent openings  53  in top plate  52  in either the preferred embodiment or the alternate embodiment is not limiting in that any number of vent openings  53  can be selected as a matter of design choice. 
     Each of said vent openings  53  are an elongated slot shape having parallel sides that terminate at one end at the outer periphery of top plate  52 . The opposite end of each of the plurality of vent openings  53  is rounded and is defined by a circle  53   a  (FIG. 4C) having a center. The center of the circle  53   a  of each of said plurality of vent openings is equidistant from the geometric center of top plate  52 . The plurality of vent openings  53  each have a longitudinal axis A parallel to the opposing parallel sides of the aforesaid vent openings  53 . Each of the plurality of vent openings  53  are oriented in this fashion so that the direction of the cooling airstream exiting inner chamber  65  of motor housing  60  through said plurality of vents openings  53  is parallel to or approximately parallel to the plane of the longitudinal axis A of each of the plurality of vent openings  53 . The direction and speed of the cooling airstream flowing through the plurality of vent openings  53  is the vector V which is the vector sum of the individual components of the airstream Va, Vr and Vt and illustrated in FIG.  4 E. Generally, motor cooling fan housing cover  50  has three major axes which define the directions of the individual components of the airstream. The axial direction of the cooling airstream is defined by the axis Qa, the radial direction by Qr, and the tangential direction by Qt shown in FIG.  4 E. The axial component of the airstream is represented in FIG. 4E (and in exploded view FIG. 4F) by Va, the radial component by Vr, and the tangential component by Vt. The vector sum of Va, Vr, and Vt is represented by V which is in the resultant direction of the airstream from motor-cooling fan  42 . The direction of the rotation of motor-cooling fan  42  is in the direction of arrow  90 . The direction of the plane of the longitudinal axis A of each of the vent openings  53  is desired to be parallel or approximately parallel to V. This direction can be described by the angle between the plane of the longitudinal axis A of each of the vent openings  53  and the radial axis Qr of motor cooling air housing cover  50  which is defined by a radial line passing through the geometric center of top plate  52  and the center of the circle  53   a  defining each of the rounded ends of the plurality of vent openings  53 . This relationship is illustrated in FIGS. 4B and 4C wherein φ represents the angle between the plane of the longitudinal axis A of each of the vent openings  53  and the radial axis Qr of motor cooling air housing cover  50 . Since the direction of the cooling airstream exiting through vent openings  53  is parallel or approximately parallel to the plane of the longitudinal axis A of each of vent openings  53 , the drag created by the moving airstream through vent openings  53  is minimized thus improving cooling efficiency. A reduction in noise is also obtained since the airstream is disturbed less as it exits through each of the vent openings  53 . In the preferred embodiment of the present invention, the angle φ between the plane of the longitudinal axis of each vent opening  53  and the radial axis Qr intersecting the geometric center of said top plate  52  and the center of the circle defining the rounded end of the vent opening  53  is 60°. The angle φ stated herein is non-limiting in that the angle chosen is a matter of design choice based upon the direction of the airstream exiting through vent openings  53  which could vary based upon such factors as the speed of fan  42 , size of motor housing  60 , and other factors. The angle φ could vary in the range of 0° to 75°. FIG. 4D shows further detail of the rear side of motor cooling fan housing cover  50  including cavity  57  for receiving cooling fan  42 . 
     Referring now to FIGS. 5A-5D, shown is fan  30  used for generating the working airstream inside working air cavity  29  of fan chamber  20 . Working air fan  30  is generally annular in shape having a plurality of blades  32  and  33  of two different radial lengths. Blades  32  and  33  are placed in an alternating arrangement and integrally molded on the upper surface of an annular shaped disc  31 . Working air fan blades  32  and  33  are of a curvilinear shaped design being forward swept at the trailing edges to increase blade loading and reduce noise as fan  30  is rotated in a clockwise direction as shown by arrow  95  in FIG.  5 A. The longer length fan blades  33  are spaced circumferentially about a hub portion  34  located in the geometric center of disc  31 . The longer length fan blades  33  extend from the outer periphery of hub portion  34  to the outer periphery of disc  31 . The working air fan blades  33  are backswept at the hub portion  34 . Formed in the center of hub portion  34  is a hexagonal shaped cavity  36  for receiving and holding fast nut  31  (FIG.  2 ). Thus, fan  30  can be bolted to the threaded end  41   a  (FIG. 2) of motor shaft  41  (FIG.  2 ). The shorter length fan blades  32  are also arranged circumferentially around hub portion  34  wherein one of the shorter length fan blades  32  is located in between adjacent longer length fan blades  33 . The shorter length fan blades  32  extend from the outer periphery of disc  31  a distance less than the full distance from the outer periphery of disc  31  to the outer periphery of hub portion  34 . The length of fan blades  32  was selected based upon empirical testing such there was enough space for efficient airflow between each of fan blades  32  and adjacent fan blades  33  but not so much space that debris could enter the space and become lodged therein between fan blades  32  and  33 . The leading edges  32   l  of fan blades  32  are linear or may be slightly arcuate extending from the upper surface of disc  31  to the top edges  32   t  of fan blades  32 . The leading edge  32   l  of fan blades  32  are sloped in the radial direction to promote efficient airflow and to guide debris that may attempt to enter the space just forward of fan blades  32  out of the space and over the top edge  32   t  of fan blades  32 . Conventional fan blades for use in floor care appliances use a much less number of blades to allow debris to pass between adjacent blades. Although accepted practice, large debris can become lodged between adjacent fan blades in conventional fan blades and over time cause failure of the fan blades from the numerous debris impacts. The fan  30  of the present prevents the debris from passing between adjacent blades  32  and  33  to improve the passage of debris through working air fan cavity  29  by preventing the possibility of debris from becoming lodged in the space between adjacent fan blades  32  and  33 . FIG. 5B shows a side view of fan  30  showing the detail of fan blades  32  and  33  formed on the upper surface of disc  31 . 
     FIG. 5C shows a cross-sectional side view of fan  30  taken along line  5 C— 5 C of FIG.  5 A through the center point of disc  31  and aperture  35  and cutting through a pair of fan blades  32  located directly opposite each other on opposite sides of hub portion  34 . This view shows the details of fan blades  32  wherein the leading edge  32   l  of fan blade  32  extends from the upper surface of disc  31  to the top edge  32   t  of fan blade  32 . Fan blade  32  slopes upwardly in a radially outward direction as it extends from the upper surface of disc  31  to the top edge  32   t  of blade  32 . The leading edge  32   l  of blade  32  may be linear or slightly arcuate. As discussed, this sloping leading edge  32   l  guides debris out of the space just forward of fan blade  32  over the top edge  32   t  of fan blade  32  so that the debris is passed to the exhaust outlet (FIG. 6) of fan chamber  20  (FIG.  6 ). The top edge  32   t  of fan blade  32  extends in the radially outward direction from a point between hub portion  34  and the outer periphery of disc  31  to the outer periphery of disc  31 . Fan blade  32  is at its maximum height at this point and at its minimum height at the outer periphery of disc  31 . Thus, the top edge  32   t  of fan blade  32  slopes downwardly in the radially outward direction. The slope of fan blades  32  is an angle ∝ as measured from the plane designated as plane B represented as a dashed line in FIG.  5 C. Plane B is the plane parallel to the upper surface of hub  34 . The angle ∝ is a matter of design choice but in the preferred embodiment ∝ is 35°. The top edge  32   t  of fan blades  32  is linear or may be slightly arcuate. Fan blades  32  project orthogonally upward from disc  31 , or in other words, perpendicularly from the plane of disc  31 . The trailing edge  32   s  of fan blades  32  is linear only and perpendicular to the plane of disc  31  and plane B. 
     FIG. 5D shows a cross-sectional side view of fan  30  taken along line  5 D— 5 D of FIG.  5 A. The top edge  33   t  of fan blades  33  can be seen extending in the radially outward direction from hub portion  34  to the outer periphery of disc  31 . Fan blades  33  are at their maximum height at the point where fan blades  33  meet the upper surface of hub portion  34 . Fan blades  33  are at their minimum height at the trailing edge  33   s  on the outer periphery of disc  31 . Fan blades  33  slope downwardly in the radially outward direction from their maximum height at hub portion  34  to their minimum height at the periphery of disc  31 . The slope of fan blades  33  is an angle ∝ as measured from plane B. The angle ∝ is a matter of design choice but in the preferred embodiment ∝ is 35°. The top edges of fan blades  33  are linear or may be slightly arcuate. Fan blades  33  project orthogonally upward from disc  31 , or in other words, perpendicular from the plane of disc  31 . The trailing edges of fan blades  33  are linear only and are perpendicular to the plane of disc  31  and plane B. 
     FIG. 6 shows a partially cutaway side view of fan chamber  20  installed on a partially cutaway portion of motor housing  60 . A portion of fan  30  inside working air fan cavity  29  can be seen through the cutaway. Arrow  80  shows the path that debris entering inlet aperture  23  of fan chamber  20  must take through working air fan cavity  29  to get to exhaust channel  75 . The dual length design of the fan blades  32  and  33  and the close spacing between adjacent fan blades prevents large debris from traveling in the space between the fan blades. The gap between the top edges  32   t ,  33   t  of fan blades  32  and  34  and inner surface  27  of fan chamber  20  is wider than in conventional motor-fan assemblies so that large objects and debris can pass over the top of fan  30  to exhaust channel  75 . The slope of the sidewall  20 A of fan chamber  20  in the region surrounding fan  30  as measured relative to plane B, and represented by the angle ⊖, is equal to the downward slope of the top edges  32   t ,  33   t  of fan blade  32  and  33  as measured relative to plane B, and represented by the angle ∝ in FIGS. 5C and 5D, so that the gap between the top edges  32   t ,  33   t  of fan blades  32  and  33  and the sidewall  20 A of fan chamber  20  is uniform along the entire length of the top edges  32   t ,  33   t  of fan blades  32  and  33 . The sidewall  20 A of fan chamber  20  in this region slopes downwardly in the radial direction. The sidewall  20 A of fan chamber  20  is straight in the radial direction or may be slightly arcuate. If the sidewall  20 A of fan chamber  20  is arcuate, the top edges  32   t ,  33   t  of fan blades  32  and  33  are likewise arcuate. Regardless of whether the top edges  32   t ,  33   t  of fan blades  32  and  33  and the sidewall  20 A of fan chamber  20  in the radial direction is straight or arcuate, the gap between the top edges  32   t ,  33   t  of fan blades  32  and  33  and the sidewall  20 A of fan chamber  20  in the radial direction remains uniform. Hence, the top edges  32   t ,  33   t  of fan blades  32  and  33  and the sidewall  2 OA of fan chamber 20  in the radial direction are parallel so that there is a clear passage for debris to flow to exhaust channel  75 . Sidewall  28  of fan chamber  20  extends downwardly from the outer periphery of fan cover  20  on the side of fan cover  20  opposite inlet aperture  23 . Sidewall  28  extends downwardly from the outer periphery of fan chamber  20  perpendicular to plane B and the plane cutting through the outer periphery of fan chamber  20 . Thus, the trailing edges  32   s ,  33   s  of fan blades  32  and  33  are parallel along their entire length to sidewall  28  on the outer periphery of fan chamber  20 . 
     Referring now to FIG. 7, shown is an alternate preferred embodiment of motor-fan assembly  110 . Motor-fan assembly  110  is similar to motor-fan assembly  10  in FIGS. 1-6. However, motor cooling fan housing cover  150  has been substituted for motor cooling fan housing cover  50 . Motor-fan assembly  110  may include a working air fan such as working air fan  30  or some other working air fan designated hereafter as working air fan  130 . Motor-fan assembly  110  may include a fan chamber such as fan chamber  20  or some arrangement of working air fan chamber or working air fan housing cover designated hereinafter as fan chamber  120 . Motor cooling fan housing cover  150  is installed in a motor housing  160  in the same manner as in the preferred embodiment. The remainder of motor-fan assembly  110  is typical of motor fan assemblies so the remainder of the disclosure will focus on the structure of motor cooling fan housing cover  150  only in FIGS. 8A and 8B. 
     FIG. 8A is a front view of motor cooling fan housing cover  150  comprised of a hub portion  152  and an aperture  156  in the center of hub portion  152 . A plurality of vanes  154  are connected and spaced angularly about hub portion  152  and connected to hub portion  152  on their most radially inward end. The plurality of vanes  154  are connected at the opposite end to a cylindrical main body portion  155 . A vent opening  153  is located between adjacent vanes  154 . A lip portion  151  surrounds main body portion  155  for connecting motor cooling fan housing cover  150  to motor housing  160 . A plurality of apertures  157  are formed in lip  151  for receiving screws or rivets or the like for attaching motor cooling fan housing cover  150  to motor housing  160 . The plurality of vanes  154  are planar in shape and have a plane that is oriented parallel or approximately parallel to the cooling airstream flowing past the vanes  154  to minimize drag and improve cooling efficiency. This is best demonstrated in FIG. 8B wherein a cross-sectional view of motor cooling fan housing cover  150  and one of the vanes  154  is shown. The plane D cuts through vane  154  and is offset by an angle μ relative to the axial direction Ta of the motor cooling fan housing cover  150 . It is desirable to have plane D parallel to the resultant direction of the airstream generated by motor cooling fan  142  which is in the direction of arrow  200 . This may occur when the angle μ between plane D and the axial direction Ta of the motor cooling fan housing cover  150  is greater than 0° but less than 90°. It has been found that when angle μ is 45° the orientation of the airstream is nearly parallel to plane D and the drag created by the cooling airstream flowing past the plurality of vanes  145  is minimized. However, this is in no way meant to be limiting in that the angle μ is a matter of design choice and could vary based upon factors such as the motor cooling fan speed and size, motor cooling fan blade angle, and other factors. 
     Thus it can be seen that at least one or more of the objects of the invention have been satisfied by the structure presented hereinabove. While in accordance with the patent statutes, the best mode of the invention has been presented and described in detail, the invention is not limited thereto or thereby. Accordingly, for an appreciation of the true scope and breadth of the invention, reference should be made to the following claims.