Abstract:
A vacuum cleaner includes a housing adapted for movement on a subjacent surface and a nozzle defined in the housing, the nozzle having an opening. A brushroll tube, having first and second ends and a longitudinal axis, is rotatably mounted to the housing adjacent the nozzle opening. At least one cleaning element protrudes from the brushroll tube. A shaft is located in the brushroll tube and extends along the longitudinal axis thereof. A stator is rigidly mounted on the shaft. A cylinder surrounds the shaft and the stator and is spaced therefrom. The cylinder is rigidly connected to the brushroll tube. A permanent magnet rotor is fixedly mounted to an interior surface of the cylinder. The permanent magnet rotor overlies and is coaxial with the stator and is spaced therefrom. The rotor and stator form a motor for rotating the brushroll tube wherein the rotor is driven by changes in induced magnetic fields in the stator.

Description:
BACKGROUND OF THE INVENTION  
         [0001]    The present invention relates to the art of electric motors. The invention finds particular application in rotating a brush device in a vacuum cleaning apparatus. It is to be appreciated however, that the present invention may find further application in other environments where it is advantageous to controllably rotate cleaning devices or other parts.  
           [0002]    Typically, upright vacuum cleaners use a belt driven brushroll or agitator which rotates and urges dust, dirt, and the like up from the floor or other surface meant to be cleaned. In general, these devices use a relatively high speed motor that drives the brushroll by means of a rubberized flat belt, cogged belt or round cross section belt. In many embodiments, the motor shaft is relatively small in diameter, while the diameter of the brushroll tube is significantly larger. This results in a speed reduction of several fold.  
           [0003]    Historically, these belts have had a finite life and begin to slip and finally fail after a certain period of use. Operators must thus keep a supply of replacement belts on hand, and have the mechanical ability to replace these belts. If either the replacement belts or mechanical ability are lacking, there is some cost and inconvenience associated with the failure of these devices.  
           [0004]    The present invention contemplates an improved brushroll which overcomes the above-referenced problems and others.  
         SUMMARY OF THE INVENTION  
         [0005]    In accordance with one aspect of the invention, a combination brushroll and motor assembly is provided for cleaning device. More particularly in accordance with this aspect of the invention, the combination comprises a dowel having first and second ends along a longitudinal axis and a housing to which the dowel is rotatably mounted. At least one cleaning element protrudes from the dowel. A first shaft is connected to a first end of the dowel and extends along the longitudinal axis. A housing is secured to the first end of dowel and then circles at least a portion of the first shaft. The housing defines an interior volume. A motor assembly is supported within the interior volume and then circles at least a portion of the first shaft.  
           [0006]    In accordance with another aspect of the invention, a vacuum cleaner is provided. More particularly in accordance with this aspect of the invention, the vacuum cleaner comprises a nozzle and a brushroll positioned adjacent to the nozzle, the brushroll comprising first and second ends and longitudinal axis. A stationary shaft is connected to the brushroll at the first end and extends along the longitudinal axis. An interior volume is defined by the brushroll tube and a magnetic assembly is supported within the interior volume by the stationary shaft. The magnetic assembly selectively magnetically interacts with a wall of the interior volume to induce rotation of the brushroll.  
           [0007]    In accordance with still another aspect of the invention, a vacuum cleaner is provided. More particularly in accordance with this aspect of the invention, the vacuum cleaner comprises a housing adapted for movement on subjacent surface and a nozzle defined in the housing, the nozzle having an opening. A brushroll is rotatably mounted to the housing adjacent to the nozzle opening. The brushroll comprises a brushroll tube having first and second ends and a longitudinal axis and an interior volume defined in the brushroll tube. A magnet is rotatably mounted in the interior volume. An armature is rigidly mounted in the interior volume and spaced from the magnet.  
           [0008]    In accordance with yet another aspect of the invention, a vacuum cleaner is provided. More particularly in accordance with this aspect of the invention, the vacuum cleaner comprises a housing adapted for movement on a subjacent surface, a nozzle defined in the housing with the nozzle having an opening and a brushroll tube having first and second ends and a longitudinal axis. The brushroll tube is rotatably mounted to the housing adjacent the nozzle opening. At least one cleaning element protrudes from the brushroll tube. A shaft is mounted in the brushroll tube and extends along the longitudinal axis thereof. A stator is rigidly mounted on the shaft. A cylinder surrounds the shaft and the stator. The cylinder being rigidly connected to the brushroll tube. A permanent magnet rotor is fixedly mounted to an interior surface of the cylinder. The permanent magnet rotor overlies and is coaxial with the stator. The rotor and stator form a motor for rotating the dowel wherein the rotor is driven by changes in induced magnetic fields in the stator.  
           [0009]    In accordance with another aspect of the invention, a method of rotating a surface working apparatus in a vacuum cleaner comprises applying an electrical signal to a motor within the surface working apparatus. Responsive to the applied electrical signal, an electromagnetic field is generated which interacts with a permanent-magnetic field associated with an interior wall of the surface working apparatus, inducing rotation in the surface working apparatus. Rotational information concerning the surface working apparatus is computed, and the applied electrical signal to the motor is altered based on the computed rotational information. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]    The invention may take physical form in certain parts and arrangements of parts and in various steps and arrangements of steps. The drawings are only for purposes of illustrating the preferred embodiments and are not to be construed as limiting the invention.  
         [0011]    [0011]FIG. 1 is a front elevational view of the brushroll according to an embodiment of the present invention, shown in partial cross section;  
         [0012]    [0012]FIG. 2 is an enlarged end elevational view of an exemplary armature core of the motor of FIG. 1;  
         [0013]    [0013]FIG. 3 is an exploded perspective view of another motor assembly which suitably practices the present invention;  
         [0014]    [0014]FIG. 4 is a functional block diagram of a speed regulating mechanism suitable to practice the present invention;  
         [0015]    [0015]FIG. 5 is a functional block diagram of a speed regulating mechanism suitable to practice an alternate embodiment of the present invention; and,  
         [0016]    [0016]FIG. 6 is a perspective view of an upright vacuum cleaner together with an exploded perspective view of various components of an internally driven agitator employed therein;  
         [0017]    [0017]FIG. 7 is a perspective view of a carpet extractor together with an exploded perspective view of an internally driven brushroll employed therein;  
         [0018]    [0018]FIG. 8 is a perspective view of a carpet extractor together with an exploded perspective view of an internally driven agitator employed therein;  
         [0019]    [0019]FIG. 9 is a perspective view of a hand held portable vacuum cleaner together with an exploded perspective view of an internally driven agitator adapted for use therein;  
         [0020]    [0020]FIG. 10 is an exploded perspective view of an internally driven brushroll according to another embodiment of the present invention;  
         [0021]    [0021]FIG. 11 is a see through perspective view of the internally driven brushroll according to FIG. 10;  
         [0022]    [0022]FIG. 12 is a sectional view at the center of the internally driven brushroll according to FIG. 11;  
         [0023]    [0023]FIG. 13 is a see through perspective view of another internally driven brushroll according to still another embodiment of the present invention;  
         [0024]    [0024]FIG. 14 is a cross sectional view at the center of the internally driven brushroll according to FIG. 13;  
         [0025]    [0025]FIG. 15 is an exploded perspective view of an internally driven brushroll according to yet another embodiment of the present invention;  
         [0026]    [0026]FIG. 16 is a perspective view of the internally driven brushroll according to FIG. 15;  
         [0027]    [0027]FIG. 17 is a cross sectional view of the internally driven brushroll according to FIG. 15; and  
         [0028]    [0028]FIG. 18 is a cross sectional view at the center of the internally driven brushroll according to FIG. 15. 
     
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS  
       [0029]    With reference to FIG. 1, an internally driven brushroll A according to the present invention includes a dowel section  10  which optimally is formed from a continuous, solid piece of rigid material such as wood, hard plastic, or the like. Embedded in one end of the dowel  10  is a shaft  12  fixed within a closely shaped recess formed in the dowel. The shaft  12  is supported in an end cap  14 , by a bearing assembly  16 . This arrangement permits the shaft  12  and dowel  10  to rotate within the bearing  16  while the end cap  14  remains stationary. Attached to the dowel  10  is at least one agitating element  18 , illustrated as a tuft of brush material.  
         [0030]    At an opposite end, a rigid cylindrical housing  20  is partially pressed and fixed over a portion of the dowel  10 . The housing  20  comprises a magnetic steel tube having an outside diameter matching the outside diameter of the dowel  10 . The housing  20  defines an interior volume or cavity  22  sized to accommodate a motor M.  
         [0031]    In the illustrated embodiment, the motor M is a brushless type motor with a stationary armature and a rotating magnet. The stationary armature is supported in volume  22  by a stationary shaft  26 . Bearing assemblies  30 ,  32  support stationary shaft  26  on opposing ends, permitting rotational movement of the dowel  10  and housing  20  around stationary shaft  26 . In the illustrated embodiment, bearing  30  is snugly fit into a bearing insert  38  which is fixed to, and rotates with, dowel  10 . Similarly, bearing  32  is positioned in insert  40  which is fixed to housing  20 . Electrical leads  42  connect with the motor M through a channel (not illustrated) in shaft  26 . The leads extend out through a second end cap  44 .  
         [0032]    Motor M, as illustrated, includes a cylindrical permanent magnet sleeve  50  fixed in place on the interior wall of magnetic steel housing  20 . The magnet sleeve, which serves as the rotor of the electric motor M, can be an extruded magnet made from what to is referred to in the industry as “bonded” magnet material. Typically, the magnet is extruded in long pieces and cut to length. Such magnets may be magnetized either before or after assembly into the housing  20 . These types of tubular magnets  50  can be magnetized with various numbers of discrete poles. Alternately, if the magnet sleeve  50  is a molded sintered magnet, then the magnet is not extruded but molded and ground to size after sintering and then magnetized. In yet another alternative, individual magnets can be spaced around the inside periphery of the housing  20  with alternating north, south polarity. The basic magnetic materials are ferrite magnets both bonded and sintered, and bonded neodymium magnets, however any conceivable magnetic material could be used without loss of functionality.  
         [0033]    One means for preventing the metal tube  20  from spinning on the dowel  10  would be to provide tabs (not illustrated) locking the tube to the dowel.  
         [0034]    With continued reference to FIG. 2, motor M also includes a stator assembly  52 . The stator assembly includes an armature  54  which can be manufactured from a stack of armature laminations or as a single piece of advanced particulate material. Regardless of the core selected, a number of wire slots  56  consistent with the number of magnetic poles on sleeve  50  and torque requirements of the motor are incorporated. In general, the number of slots  56  is in the range of about 6-20. The slots  56 , positioned on the outside periphery of the core, permit armature windings  58  (FIG. 1) to be inserted into the armature. The armature windings  58  comprise a three-phase winding in either a wye connection or a delta connection. The winding is fed a phase-sequenced current from a properly commuted power source and a controller (more fully discussed below).  
         [0035]    The motor magnet, in general, will be multi-pole and usually will have on the order of 6-20 magnetized poles. Although the design could use individual magnets spaced around the inside periphery of the magnet yoke or housing  20  (which is a high permeability magnetic steel tube) with alternating north/south polarity, the current design employs a tubular magnet construction made by the extrusion process or the molding process so that the entire magnet is a one piece component that fits snugly into the inside diameter of the housing  20  so that the magnet flux can be efficiently transferred to the housing or magnet yoke and back again without requiring high magnet NMF. If the magnet tube is individual magnets, they would be cemented into place with fixturing directly to the housing or magnet yoke. However the more probable design would employ a single piece magnet sleeve cemented into place in the housing  20 .  
         [0036]    The motor armature is made from a stack of armature laminations in most cases. However it would be possible to utilize new advanced particulate materials that demonstrate low eddy current loss. If the armature core is made of the new advanced particulate materials, the armature can be one piece with no requirement for individual laminations. However at the moment low cost laminations are still the most practical approach. These laminations or the one piece core would have a given number of wire slots incorporated into them consistent with the number of magnet poles in the magnet and consistent with the torque requirement and manufacturing considerations. In general, the number of slots that would probably be used would be in the range of 6-20. The slots would be positioned on the outside periphery of the lamination and after insulating the slots, the armature winding would be inserted from the outer diameter.  
         [0037]    There are no limits in terms of the driving voltage necessary for driving the motor of the present invention. Thus, the voltage could be 9 or 24 volt DC, 110 volt AC, or 220 volt AC. In addition, the placement of the motor can be varied. While in the embodiments illustrated the motor is placed on the right hand end of the dowel, the placement could be anywhere in the dowel. For that matter a smaller motor could be placed at each end of the dowel if so desired. The motor may be placed in the middle of the dowel if the shaft bearing arrangement provides definite armature support that will maintain a uniform air gap between the armature  54  and the sleeve  50 . The length of the motor is in direct ratio to the torque of the motor (assuming the same diameter). Thus, a longer motor would be employed if more torque was desired and a shorter motor could be used if less torque were desired. For example, in the motor design illustrated in FIGS. 1 and 6, approximately 40-ounce inches of torque would be developed. It has been determined that a smaller diameter, longer motor is advantageous from the standpoint of providing more surface area through which to dissipate heat losses inside the motor. In that connection, the metal shell is useful for heat dissipation. It should also be recognized that there is a required minimum thickness of the metal sleeve to carry the necessary flux. It would be disadvantageous to have a shell thin enough that the shell would not carry all of the magnetic flux. With that type of design, the shell or housing  20  would also pick up magnetized or magnetizable metal objects such as paper clips or the like on the subjacent surface being cleaned.  
         [0038]    One supplier for the magnet sleeve is Seiko-Epson Company of Japan. The material is sold by Seiko-Epson under the code name NEODEX-10. The stator assembly can be made from laminations or can be a solid pressed metal part made from coated particulates.  
         [0039]    The use of the magnetic material discussed above allows a rather high power density for a reasonable cost. It is made from a rare earth magnet.  
         [0040]    With reference now to FIG. 3, another embodiment of a motor M according to the present invention includes a stationary shaft  126  illustrated with a square tip or end  160 . The square end  160  is received in a plastic insert cap  140 . The cap can be fitted with a complementary shaped insert  142  having a suitably shaped aperture  144  that accommodates the tip  160 . Also provided is a standard ball bearing  132  through which one end of the shaft  126  passes. Mounted on the shaft is an armature  154 . Rotating about the stationary armature  154  is a sleeve  150  which is mounted in a housing  120 . Preferably the sleeve is made from a multi-pole bonded NdFeB magnet. The sleeve  120  can be made from a steel material. Located on the other end of the sleeve  120  is a second standard ball bearing  130 . Positioned adjacent the second ball bearing  130  is an end cap  138 . Another end  162  of the shaft  126  extends through a central opening  139  in the end cap  138 .  
         [0041]    Those skilled in the art will recognize that the permanent magnet brushless DC motor type illustrated, while the presently preferred embodiment, is not the only type of motor which can provide the functionality disclosed herein. For example, so-called switch reluctance type motors can also be suitably adapted as the motor M. Typically, these motors do not use magnets, only simple windings in the armature and notched rotors with lobes that are sequentially attracted to the next armature lobe or pole when the proper coils are energized. As above, an inside-out version, in which the coils and armature are stationary and the rotor has shallow lobes that rotate with the brushroll, could also achieve the functionality disclosed above.  
         [0042]    Additionally, motor M could alternately be configured as an induction motor. Those skilled in the art will appreciate that this type of motor has an armature and winding similar to that discussed above. The rotor, however is different and employs what is commonly referred to as a “squirrel-cage” induction rotor usually with copper or aluminum bars extending from one end of the rotor to the other and shorted out end rings or cast connections. When the stator or armature is excited, induced current flows in the induction rotor causing torque in the motor. Again, an inside-out geometry is used with the squirrel-cage being positioned on the inner diameter of the motor tube and rotating along with the brushroll.  
         [0043]    Control schemes for the above-described motors are all somewhat varied, but in general the motors typically use three-phase power or a commuted three-phase power source. Alternately, a stand alone system operating from one phase power sources, such as batteries and the like, can also be employed with suitable electronic controllers designed to provide appropriate power signals, no matter what style of motor is used. Those skilled in the art will appreciate that electronic control circuits are widespread for the various described motors, and are relatively straightforward to implement.  
         [0044]    With reference now to FIG. 4, electrical signals to the stator assembly  52  can be provided from a power source  70  through a speed adjusting circuit  72 . Alternately, with reference to FIG. 5, a sensor assembly  74 , can be provided within the volume  22  (FIG. 1), for calculating a position of the housing  20  relative to the stator  52 . This position information is forwarded to the speed adjusting circuit  72  which permits selection of the proper commutated signal to be sent along leads  42  to the stator  52 . The sensor assembly  74  may include a magnetic field detector which detects the magnetic polarity of a determined portion of the magnet sleeve  50 . Alternately, the sensor assembly could include an optical type sensor configured to detect rotations of the housing. While the speed adjusting circuit  72  is illustrated as being located outside of the motor M, the circuitry could alternately be placed with the motor M inside the interior volume  22 .  
         [0045]    Moreover, the speed adjusting circuit or device  72  incorporates various functional capabilities such as constant brushroll speed maintenance; overload protection stopping brushroll rotation; reverse brushroll operation easing, for example, backward vacuum movement; and variable brushroll rotation depending on floor surface, e.g. no rotation on tile, wood and delicate floor coverings, and fast rotation for heavy duty carpeting or especially dirty environments.  
         [0046]    With reference now to FIG. 6, a vacuum cleaner  80  is illustrated with an exploded view of an internally driven agitator A′ according to the present invention. The vacuum cleaner is illustrated as being of an upright design. It has a suction nozzle located on the floor. Positioned in the nozzle or adjacent thereto is the agitator according to the present invention. In the current design, the agitator A′ rotates on its bearings  16 ,  30 , and  32  while the shaft  26  remains stationary. Thus, the stator assembly  52  remains stationary and the magnet sleeve  50  rotates along with the housing (which is not illustrated in FIG. 6).  
         [0047]    This illustration shows that the motor is a separate entity from the roller and is indeed much shorter. This permits the use of short shafts and bearings enabling less expensive and more accurate manufacture of the motor components. Indeed, with shorter shafts, it is much easier to maintain an accurate air gap between the rotor and the stator thus avoiding rubbing and other undesirable operations. Additionally, motors can be assembled in incremental lengths where a magnet of a unit length and an armature stack of unit length comprise the smallest motor. When two magnets and two armatures are joined, a motor of roughly double the power and torque is provided, simplifying the manufacturing process for a variety of applications.  
         [0048]    With reference now to FIG. 7, an alternate embodiment includes a motorized brushroll A″ in a carpet extractor  86 . In this embodiment, dowel  10 ″ is configured with agitator elements  18 ″ disposed in a predetermined pattern around the exterior surface of the dowel formed from a plurality of discreet bristle groups.  
         [0049]    With reference now to FIG. 8, carpet extractor  86 ′ is configured with an internally driven agitator A′″ having grooves  88  disposed along the exterior surface of the dowel  10 ′″ as a sponge-like cleaning element  87 . In this embodiment, the grooves  88  are especially suited to assist in the extraction of water or other fluid on the floor surface. This type of motor is instantly reversible which is advantageous in a carpet extractor environment.  
         [0050]    With reference now to FIG. 9, a hand-held vacuum cleaner  90  includes the internally driven agitator A″″ having a continuous agitating element or fin  92  formed of rubber or the like.  
         [0051]    Thus the present invention pertains to an inside out brushless motor having a stationary armature or “stator” and a rotating magnet sleeve or “rotor.” This is just the opposite of a traditional electric motor. With the motor of the present invention, one can sense and control the speed of the rotating brushroll of the vacuum cleaner. In addition, this design eliminates the driving belt for the agitator or brushroll since the belt, as discussed above, is prone to failure.  
         [0052]    With reference now to FIG. 10, a brushroll B includes a brushroll tube  200  which rotates while a shaft  202  remains stationary. Thus, the stator assembly (not shown) of a custom motor N (as described above) remains stationary and a magnetic housing  204  rotates, having slotted tabs  205  fixedly mounted to the motor housing at each end, thus rotating with the magnetic housing  204 . The brushroll tube  200  can be formed from a continuous piece of extruded rigid material such as aluminum, steel, or the like. Attached to the brushroll tube  200  is at least one agitating element  206 , illustrated as bristles suitable for press-fitting into a plurality of holes  208  in the brushroll tube  200 . Fitted within the brushroll tube  200  is the motor N, with motor supports  210  and bearing assemblies  212  fitted within each end of the brushroll tube  200 . The motor supports  210  have cylindrically shaped outer ends  214  that extend through the bearings  212 , partially protruding beyond the ends of the brushroll tube  200 , and are fitted into cylindrical recesses  216  in stationary end caps  218  for support. The motor supports  210  have inner ends  220  that are configured to fit over respective ends of the motor shaft  202 . As illustrated, each end of the motor shaft  202  is configured with a D shape so that the shaft  202  and the motor supports  210  are keyed together for rotation. Further, each of the motor supports  210  is formed with a slot  222  that fits over a tab  224  on the respective end cap. Since the end caps  218  are mounted in a manner to prevent rotation, the motor supports  210  and the motor shaft  202  are, likewise, prevented from rotating. While each end of the motor shaft  202  are illustrated as having a D shape, other shapes, square for example, can be employed with equal efficacy. Similarly, other suitable structures may be employed to interlock or key the motor shaft  202 , motor support  210  and end cap  218  arrangement together so that they remain stationary while the brushroll tube  200  and the housing  204  are free to rotate in unison.  
         [0053]    With reference now to FIG. 11, it illustrates how motor N is cooled. Each end cap  218  is formed with an opening  226  permitting air to pass through. One of the openings  226  serves as an air intake while the opening of the remaining end cap  218  serves as an air outlet. Air flows in one of the openings  226 , past the respective motor support  210 , through a gap between the motor N and the brushroll tube  200  (as shown in FIG. 12), past the remaining motor support  210  and out of the remaining opening  226 . The gap between the stator and the magnet sleeve is not shown in this embodiment.  
         [0054]    [0054]FIG. 13 illustrates another brushroll B′ having a motor N′. In this embodiment, four openings  276  are provided in each end cap  268 . These are partitioned by a heat sink  280  into an intake half  282  and an exhaust half  284 . In this embodiment, no gap exists between the motor N′ and a brushroll tube  250 . Air thus enters the intake  282 , passing over the heat sink  280  to a respective end of the motor N′, thus cooling the respective end of the motor N′, and exits through the respective exhaust  284 , passing under heat sink  280 , thus transferring heat from the motor N′ and the heat sinks  280  to the environment. FIG. 14 illustrates a section at the center of brushroll B′, showing that no gap exists between the brushroll tube  250  and the motor N′. The gap between the stator and the magnet sleeve is not shown in this embodiment.  
         [0055]    With reference now to FIG. 15, another motorized brushroll B″ is illustrated according to the present invention. As with the previously described brushroll B′, a brushroll tube  300  rotates while a shaft  302  remains stationary. Brushroll B″ includes a motor N″, preferably employing a single piece magnet sleeve  304 , cemented, or fixed by other means, into place in a housing  306 , similar in concept to the magnet sleeve  50  and magnetic steel housing  20  of the embodiment described with respect to FIG. 1. Also included in the brushroll B″ are two motor bearings  308 , respective bearing insulators  310 , support cones  312 , brush bearings  314  and end caps  316 .  
         [0056]    The support cones  312  are supported at their outer ends by the respective end caps  316  and are each prevented from rotating by a tab  318  on the adjacent end cap  316  that interlocks with a slot  320  on the support cones  312 . Also shown are agitating elements  322  in the form of bristles (see FIG. 16) and a drive fastener  324  for fixing the housing  306  inside the brushroll tube  300 . The brushroll tube  300  has a plurality of mounting holes  326  suitable for press-fitting of agitating elements  322 . The tube  300  accommodates the end caps  316  and the drive fastener  324 . Cooling holes  328  are provided in the brushroll tube  300  and are described in further detail below. Each support cone  312  includes a plurality of ribs  332  separated by slots  336 .  
         [0057]    With reference now to FIG. 17, the motor shaft  302  is fixedly mounted, rotation wise, into the inner ends of the support cones  312  so that a stator assembly  330  of the motor N″ remains stationary while the magnet sleeve  304  and the housing  306  rotate with the brushroll tube  300 . The motor shaft  302  is supported at its ends by respective bearings  308  which are in turn supported by bearing insulators  310  supported by the housing  306 . The drive fastener  324  is shown locking the housing  306  to the brushroll tube  300 .  
         [0058]    Also illustrated in FIG. 17 is a means of removing heat from the motor N″. Heat generated by the motor travels by conduction, shown by arrows  340 , and travels along the motor shaft  302  towards the ends of the shaft. From the ends of the motor shaft, heat is transferred by conduction to the support cones  312  and is conducted along the ribs  332  forming the center portion of the support cones, as shown by arrows  342 . Air enters the brushroll tube  300  through openings  334  in the end caps  316  and flows, as shown by arrows  344 , through ventilation openings or slots  336 , between the support cone ribs  332 , thus removing heat from the support cones and carrying it away through cooling holes  328  in the brushroll tube  300 . Air flow may be facilitated by the vacuum present in the vicinity of the cooling holes  328 .  
         [0059]    [0059]FIG. 18 illustrates the motor shaft  302 , the stator  330 , the magnet sleeve  304 , the magnetic steel housing  306 , the brushroll tube  300  and the agitator elements  322 . A small gap  350 , as previously described, is maintained between the stator  330  and the magnet sleeve  304  to allow relative rotation therebetween.  
         [0060]    Exemplary dimensions for the embodiment of FIG. 17 are as follows:  
         [0061]    Magnetic steel housing  306  OD . . . 1.125″ 
         [0062]    Magnetic steel housing  306  ID . . . &gt;1.055″ 
         [0063]    Magnet sleeve  304  OD . . . &lt;1.055″ 
         [0064]    Magnet sleeve  304  ID . . . 0.90″ 
         [0065]    Stator assembly  330  stack length . . . 3.50″ 
         [0066]    Number of magnet sleeve  304  poles . . . 8  
         [0067]    Number of stator assembly  330  wire slots . . . 6  
         [0068]    The invention has been described with reference to the preferred embodiments. Modifications and alterations will occur to others upon a reading and understanding of the preceding detailed description. It is intended that the invention be construed as including all such modifications and alterations insofar as they come within the scope of the appended claims or the equivalents thereof.