Abstract:
A motor assembly comprises a plurality of redundant bearings, a plurality of coaxial support elements, with at least one of the support elements rotatable about an axis of rotation, and an armature rotatably guided by the plurality of support elements to rotate about the axis of rotation. The bearings provide redundancy to continue armature rotation in the event one bearing fails.

Description:
BACKGROUND OF THE INVENTION  
       [0001]     1. Field of the Invention  
         [0002]     This invention relates to electric systems, and more particularly to motor assemblies.  
         [0003]     2. Description of the Related Art  
         [0004]     Electric motor driven fans have become an integral part of design for thermal management in electronics. These fans, typically used to cool heat generating components in computer servers, personal computers (PCs) and other electronics, play a critical role in system reliability and longevity. Typical fans have stator windings (“stators”), a single bearing sleeve and a shaft. The stators induce rotor magnets (“rotors”) on a blade assembly armature  130  to rotate, causing air movement through the fan. Various types of fans are used to cool heat generating components, including tube-axial, vane-axial, centrifugal, and blower fans. Regardless of the type of fan used, motor and bearing failures must be minimized to enhance reliability and longevity.  
         [0005]     One approach to reduce the impact of motor and bearing failures is described by D. Kim et al. in U.S. Pat. No. 5,920,264. Thermal conditions around the system&#39;s cooled parts are monitored to provide a warning should overheating develop. When the temperature around the monitored parts increases past a predetermined level, an alarm sounds from a speaker so that a user can stop the power supplied to the system. Another solution is presented by S. Wrycraft in U.S. Pat. No. 6,011,689 in which an array of fans arranged in parallel cool components in a computer system. Each fan includes an airflow closure member that closes upon failure of the fan. The closure prevents cool air from escaping through the failed fan prior to flowing over a component to be cooled. In this manner, a fan suffering from a failed motor or bearing will not adversely affect the performance of the other fans in the array.  
         [0006]     Another solution to reduce the impact of motor and bearing failures is to use multiple fans in series. Unfortunately, this arrangement produces undesirable turbulence noise and increased system impedance if one of the fans should fail. Fan redundancy, either with fans positioned in parallel or series, also reduces the space available for other components and increases system cost due to the increased parts count.  
         [0007]     A need continues to exist, therefore, for a motor assembly with increased reliability and longevity without increasing noise, system cost or reducing space available for other components.  
       SUMMARY  
       [0008]     A motor assembly is described, in one embodiment, comprising a plurality of redundant bearings, a plurality of coaxial support elements, with at least one of the support elements rotatable about an axis of rotation, and an armature rotatably guided by the plurality of support elements to rotate about the axis of rotation. The bearings provide redundancy to continue armature rotation in the event one bearing fails.  
         [0009]     Another embodiment is described that has a rotational shaft, an inner sleeve surrounding the rotational shaft, an outer sleeve surrounding the inner sleeve, a first bearing between the shaft and inner sleeve, and a second bearing between the inner and outer sleeves, so that the sleeve and bearing combinations provide redundancy for continued shaft rotation in case of failure of one of the bearings. 
     
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0010]     The components in the Figures are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. Moreover, in the Figures, ‘like’ reference numerals designate corresponding parts throughout the different views.  
         [0011]      FIG. 1  is a perspective view of one embodiment of the invention that uses multiple coaxial sleeves, redundant stators and an armature to guide the rotation of blades in a fan for use in a computer system.  
         [0012]      FIG. 1A  is a cross-section view of the embodiment of the invention shown in  FIG. 1  along the line  1 A- 1 A.  
         [0013]      FIG. 1B  is a cross-section view of the embodiment of the invention shown in  FIG. 1  along the line  1 B- 1 B.  
         [0014]      FIG. 2  is a cross-section view of one embodiment that has a single centripetal sleeve, a housing with races and redundant stators, without the use of a shaft, to guide blade rotation.  
     
    
     DETAILED DESCRIPTION  
       [0015]     Motor reliability and longevity are increased, particularly for fan motors used to drive fans in computer systems, by providing redundant bearings, support elements and motors. In one embodiment, inner and outer sleeves guide a coaxial shaft and provide redundancy for the shaft to rotate about its axis with respect to either one or both of the sleeves. The blades connect to the shaft and are rotated by a plurality of motors that provide redundancy in case of a failure of any one motor.  
         [0016]      FIG. 1  illustrates a personal computer (PC)  200 , in one embodiment of the invention, having a chassis  115  mounted on an inner housing  120 . The chassis  115  is designed to support various components, such as a processor motherboard and peripherals. The inner housing  120  is shown in its open position, pulled out from the interior of an outer housing  125  to allow user access to the chassis  115 . A fan  230  is either supported by the chassis  115  or attached to adjacent ventilation openings  133  in the outer housing  125 . The ventilation openings  133  either accept cool air from the exterior of the PC or allow component-heated air to escape, depending on the orientation of the fan  130 , when the inner housing  220  is closed. Blades  135  of the fan  130  are carried by a shaft  137  that is supported by an inner sleeve  140  and an outer sleeve  145  and rotates with respect to either the inner or outer sleeves ( 140 ,  145 ). Stators  147 , such as motor windings, are mounted to the outer sleeve  145  to induce the blades to rotate.  
         [0017]     Although a desktop computer is illustrated, the fan could be used to cool other components such as a server or laptop computer, or non-computer applications such as automobiles, buildings, or machines. The fan  130  would normally be positioned adjacent ventilation openings  133  to either push air into or pull air out of the enclosure.  
         [0018]     Referring now to  FIGS. 1A and 1B , a frame  150  supports a hub  155  that contains electronics (not shown) for electrical control of the fan  130 . The outer sleeve  245  is attached to the hub  155  to support the inner sleeve  140  and shaft  137  assembly, both of which are located coaxially with the outer sleeve  145 .  
         [0019]     A plurality of shaft races  157  are provided in the inner sleeve  140  circumferentially around the shaft  137 . As illustrated, each shaft race  157  is configured to accept inner bearings  160  to enable easy shaft rotation with respect to the sleeves ( 140 ,  145 ). As illustrated in  FIGS. 1A and 1B , the bearings can be ball or roller bearings  160  housed in shaft races  157  in the inner sleeve adjacent the shaft. Alternatively, the bearings could be implemented as air bearings or sleeve bearings. If designed for use with air bearings, the shaft races  157  would be replaced with an air-bearing pad extending circumferentially and longitudinally about the shaft  137  and would include orifice, porous-wall or compound compensation. The inner sleeve  140  has a plurality of first-inner races  165  on its face opposing the shaft  137  that are complementary to the shaft races  157 , as described above. The races ( 157 ,  165 ) and inner bearings  260  allow the shaft  137  to rotate freely with respect to the inner sleeve  140 .  
         [0020]     A plurality of second-inner races  170  are located on the opposite face of the inner sleeve  140  and, as described above for the first-inner races  165 , can accept ball bearings, roller bearings or are designed as sleeve or air bearings (ball bearings are illustrated in  FIGS. 1A and 1B ). The outer sleeve  145  has outer races  175  that are complementary to the second-inner races  170  to accept outer bearings  180  such as those described for the shaft and first-inner races ( 157 ,  165 ). Rotation of the outer bearings  180  between the outer and second-inner races ( 175 ,  170 ) allows the inner sleeve  140  to rotate freely with respect to the fixed outer sleeve  145 .  
         [0021]     The inner and outer sleeves ( 140 ,  145 ), used in combination with the races ( 157 ,  165 ,  170 ,  175 ) and bearings ( 160 ,  180 ), allow rotation of the shaft  137  even if either the inner or outer bearings ( 160 ,  180 ) fail. For example, if the inner bearings  160  fail, friction would increase between the shaft  137  and inner sleeve  140 , but the outer bearings  180  would allow the shaft  137  and inner sleeve  140  assembly to rotate freely. If the outer bearings  180  fail, friction would increase between the inner and outer sleeves ( 140 ,  145 ), but the inner bearings  160  would allow the shaft  137  to continue rotation. In either case, reliability and longevity of the bearings are improved.  
         [0022]     Although it is possible to design a fan  130  having only one fan blade, the shaft  137  is connected to, preferably, at least two fan blades  135 . The blades  135  connect to the shaft  137  through an armature  182  having a recess  185  for accepting the shaft  137  using a pressed friction fit, adhesive, fixed pin, or through a non-recess attachment point. If a non-recessed attachment point is used, the shaft  137  and armature  182  can be molded as one piece or connected together using methods similar to those described for the recess  185 . The stators  147  are mounted to the outer sleeve  145  opposite rotors  190 . The separate rotors  190  on the armature  182  may be combined into a single long rotor to facilitate manufacturing. Redundant mechanisms are used to produce the electric field for rotational movement of the blades  135  about an axis defined by the shaft  137 . Either the rotors  190  or the stators  147  can generate the required electric field. If the stators  147  provide the field, each stator has inputs  192  and outputs  194  to receive a current to produce the field, and at least one fan blade  135  has an opposing rotor  190 , such as a magnet or electromagnet.  
         [0023]     If either of the race pairs ( 157 / 165  and  170 / 175 ) accept ball bearings, that pair provides resistance to longitudinal motion of the assembly by the bearing seat in their generally cylindrical surfaces. If either of the race pairs is designed for an air bearing or sleeve-bearing configuration, the shaft  137  would receive a shaft-retaining ring  296  and/or an inner-sleeve ring  197  to mate with complementary shaft grooves  198  to resist longitudinal movement of the inner sleeve  140  and shaft  137 . Although the fan  130  has been described with only the shaft  137  rotating during normal operation, in an example, rotation would also be imparted on the inner sleeve  140  through friction between the inner bearing  160  and first inner race  165 . Also the number and type of races used in the inner and outer sleeves ( 140 ,  145 ) would be complementary to the type of bearings used.  
         [0024]      FIG. 2  illustrates an embodiment using redundant bearings and stators without the use of a concentric shaft. A plurality of housing races  200  are attached to an interior portion of a housing  205  and positioned opposed to, and in complementary fashion with, first-centripetal races  210  attached to a face of a centripetal sleeve  215 . The centripetal sleeve  215  is coaxial with the housing  205 . As described above for the races in  FIGS. 1A and 1B , the races accept either ball bearings, roller bearings or are designed for an air or sleeve-bearing configuration (collectively “housing bearings 220”). The races ( 200 ,  210 ) allow rotational movement of the centripetal sleeve along the interior portion of the fan housing  205  while limiting longitudinal movement.  
         [0025]     On the opposite face of the centripetal sleeve  215  are attached a plurality of second-centripetal races  225  positioned opposed to and in complementary fashion with blade races  230  attached to the distal end of each blade  235 . The second centripetal and blade races ( 225 ,  230 ) also accept ball bearings, roller bearings or are modified for an air or sleeve-bearing configuration (collectively “blade bearings 140”). Rotation of the blade bearings  240  allows the blades  335  to rotate with respect to the centripetal sleeve  215 .  
         [0026]     Motion is imparted to the blades  235  using redundant stators  245 , such as motor windings, connected to an interior portion  250  of the housing  205 . Each stator has inputs  252  and outputs  254  to receive a current to produce the field. The stators  245  provide an electromotive force to rotors  255 , which are either magnets or electromagnets, positioned opposite the stators  245  and connected to the blades  235 . The blades are connected together using an armature  260 . With this arrangement, a concentric shaft is not needed to guide the blades  235 . The housing  205  and centripetal sleeve  215 , used in combination with the races ( 200 ,  210 ,  225 ,  230 ) and bearings ( 220 ,  240 ), allow rotation of the blades even if one of either the housing or blade bearings fail ( 220 ,  240 ). For example, if the blade bearings  240  fail, the blades  235  and centripetal sleeve  215  would rotate with respect to the housing  205 . If the housing bearings  210  fail, only the blades  235  would rotate with respect to the housing  205 . In either case, reliability and longevity of the bearing action is improved.