Abstract:
A motor assembly includes a single phase motor and a friction clutch. The single phase motor includes a stator and a rotor. The friction clutch includes a pressing member rotating with the rotor, and a connecting member to be connected to a load. wherein when the pressing member rotates, the pressing member generates an axial or radial movement to thereby exert a pressing force to the connecting member to cause the connecting member to rotate due to a frictional force generated between the pressing member and the connecting member. The present invention further provides a fluid driving device incorporating the motor assembly.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    This non-provisional patent application claims priority under 35 U.S.C. §119(a) from Patent Application No. 201510556394.3 filed in The People&#39;s Republic of China on 2 Sep. 2015, and Patent Application No. 201510856741.4 filed in The People&#39;s Republic of China on 27 Nov. 2015. 
       FIELD OF THE INVENTION 
       [0002]    The present invention relates to the field of fluid driving devices, and in particular to a motor assembly and a fluid driving device employing the motor assembly. 
       BACKGROUND OF THE INVENTION 
       [0003]    When a motor drives an impeller of a blower, water pump, or the like, to rotate, if the startup load of the blower or water pump is too large, the motor may experience startup failure or may be damaged at the moment of motor startup because the motor is not able to provide a sufficient rotational torque. 
         [0004]    When the motor is a single phase motor, the above problem may occur more easily. 
         [0005]    Therefore, an improved technical solution is urgently desired. 
       SUMMARY OF THE INVENTION 
       [0006]    Thus, there is a desire for a motor assembly which can avoid the startup failure. There is also a desire for a fluid driving device employing the motor assembly. 
         [0007]    In one aspect, a motor assembly is provided which includes a single phase motor and a friction clutch. The single phase motor includes a stator and a rotor. The friction clutch includes a pressing member rotating with the rotor, and a connecting member to be connected to a load. wherein when the pressing member rotates, the pressing member generates an axial or radial Smovement to thereby exert a pressing force to the connecting member to cause the connecting member to rotate due to a frictional force generated between the pressing member and the connecting member. 
         [0008]    Preferably, the stator comprises a stator core and a winding wound around the stator core, the stator and the rotor being radially spaced to define an air gap, the stator core comprising a plurality of teeth extending radially outwardly, with each two adjacent teeth defining a winding slot there between, a radial end face of the tooth facing toward the rotor forming a pole face, a circumferential distance between the pole faces of two adjacent teeth having a width less than five times of a minimum radial width of the air gap. 
         [0009]    Preferably, the circumferential distance between the pole faces of two adjacent teeth is between one to three times of the minimum radial width of the air gap, 
         [0010]    Preferably, the motor is an inner-rotor motor, the rotor comprises rotary shaft, a rotor core fixed to the rotary shaft, and a permanent magnet attached to the rotor core. 
         [0011]    Preferably, the motor is an outer-rotor motor, the rotor comprises a rotary shaft, a magnetic-conductive housing fixed to the rotary shaft, and a permanent magnet attached to the magnetic-conductive housing. 
         [0012]    Preferably, the friction clutch is a centrifugal friction clutch, and the pressing member is a centrifugal body. When the rotor rotates, the centrifugal body generates a radial displacement under a centrifugal force, thereby directly or indirectly exerting the pressing force to the connecting member. 
         [0013]    Preferably, the centrifugal body includes a sleeve ring fixed relative to the fixing member and a plurality of centrifugal plates disposed or formed on the sleeve ring. Distal ends of the centrifugal plates are free ends which flare radially outwardly and abut against the load connecting member, such that the load connecting member is driven to rotate by means of the frictional force. 
         [0014]    Preferably, the motor assembly further comprises a positioning member for axially positioning the load connecting member. 
         [0015]    Preferably, the motor assembly further comprises a positioning pressing block disposed within the centrifugal plates to support the centrifugal plates. 
         [0016]    Preferably, the plurality of centrifugal plates extends from a circumference of the sleeve ring in an axial direction of the motor. 
         [0017]    Preferably, a groove is formed at a radial inner side of a joint between the centrifugal plate and the sleeve ring for facilitating the centrifugal plate deforming and flaring outwardly. 
         [0018]    The present invention further provides a fluid driving device including a driving body and a motor assembly. The motor assembly is any one described above. The driving wheel is connected with the single phase motor through the friction clutch, and the driving body and the load connecting member are connected or formed into an integral structure. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0019]    In order to more clearly describe the technical solutions in the prior art or the embodiments of the present invention, the accompanying drawings to be used in the descriptions of the prior art or the embodiments are briefly introduced as follows. Obviously, the following accompanying drawings just illustrate some embodiments of the present invention, and people skilled in the art can obtain other drawings from these drawings without paying creative efforts. 
           [0020]      FIG. 1  illustrates a first implementation of a motor assembly according to one embodiment of the present invention. 
           [0021]      FIG. 2  is a sectional view of the first implementation of the motor assembly according to the embodiment of the present invention. 
           [0022]      FIG. 3  is an assembled view of a second stop plate and a centrifugal part of the embodiment of the present invention. 
           [0023]      FIG. 4  illustrates the centrifugal part of the embodiment of the present invention. 
           [0024]      FIG. 5  illustrates a blower according to one embodiment of the present invention. 
           [0025]      FIG. 6  illustrates a second implementation of a motor assembly according to one embodiment of the present invention. 
           [0026]      FIG. 7  illustrates a single phase motor used in the motor assembly according to one embodiment of the present invention. 
           [0027]      FIG. 8  is a sectional view of the single phase motor of  FIG. 7 , with the stator winding removed for clearer illustration of an interior construction. 
           [0028]      FIG. 9  is an enlarged view of a boxed portion of  FIG. 8 . 
       
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
       [0029]    The technical solutions of the embodiments of the present invention will be clearly and completely described as follows with reference to the accompanying drawings. Apparently, the embodiments as described below are merely part of, rather than all, embodiments of the present invention. Based on the embodiments of the present disclosure, any other embodiment obtained by a person skilled in the art without paying any creative effort shall fall within the protection scope of the present invention. 
         [0030]      FIG. 1  illustrates a first implementation of a motor assembly according to one embodiment of the present invention.  FIG. 2  is a sectional view of the first implementation of the motor assembly according to one embodiment of the present invention.  FIG. 3  is an assembled view of a second stop plate and a centrifugal part of one embodiment of the present invention.  FIG. 4  illustrates the centrifugal part of one embodiment of the present invention. 
         [0031]    A friction clutch in accordance with one embodiment of the present invention is a centrifugal friction clutch which includes a centrifugal part  24  and a loading wheel  26 . The centrifugal part  24  includes a sleeve ring  241  and a centrifugal plate  242 . The sleeve ring  241  is configured to be fixed to the rotary shaft  11 . The centrifugal plate  242  is disposed on the sleeve ring  241 . A distal end of the centrifugal plate  242  is a free end. As the rotary shaft  11  rotates, the centrifugal part  24  rotates along with the rotary shaft  11 . The centrifugal plate  242  tilts in a direction away from an axis of the sleeve ring  241  under a centrifugal force. The loading wheel  26  is attached around an outer side of the centrifugal part  24 . That is, the loading wheel  26  has an inner hole in which the centrifugal part  24  is received. When the centrifugal part  24  rotates with the rotary shaft  11 , the free end of the centrifugal plate  242  flares radially outwardly to abut against an inner wall of the loading wheel  26  and, as a result, the loading wheel  26  is driven to rotate by a frictional force. 
         [0032]    In the centrifugal friction clutch of the embodiment of the present invention, at startup of the motor  1 , the centrifugal part  24  rotates along with the rotary shaft  11 . When the rotational speed of the rotary shaft  11  is low, the free end of the centrifugal plate  242  flares radially outwardly to a small extent because the centrifugal plate  242  is subject to a small centrifugal force, such that a frictional force between the centrifugal plate  242  and the loading wheel  26  is small or even zero, and the centrifugal part  24  slides relative to the loading wheel  26 . As the rotational speed of the rotary shaft  11  increases, the centrifugal force applied to the centrifugal plate  242  increases, and the free end of the centrifugal plate  242  tilts in the direction away from the axis of the sleeve ring  241 . The centrifugal part  24  is received in the inner hole of the loading wheel  26 , and the tilted centrifugal plate  242  contacts a wall of the inner hole, such that the frictional force between the centrifugal part  24  and the loading wheel  26  increases accordingly. When the frictional is large enough, the centrifugal part  24  drives the loading wheel  26  to rotate synchronously. 
         [0033]    By means of the above configuration, the frictional force between the centrifugal part  24  and the loading wheel  26  is small or even no frictional force exists therebetween at startup of the motor  1  when the rotational speed of the rotary shaft  11  is low. Because the loading wheel  26  and the load are directly or indirectly connected, the load is stationary at the startup of the motor  1 , such that the centrifugal part  24  and the loading wheel  26  slide relative to each other to form a sliding friction pair at the startup of the motor  1 . As the rotational speed of the rotary shaft  11  of the motor  1  increases, the centrifugal force applied to the centrifugal plate  242  increases, and the frictional force between the centrifugal part  24  and the loading wheel  26  also increases. The amount of relative sliding movement between the centrifugal part  24  and the loading wheel  26  decreases until the centrifugal part  24  and the loading wheel  26  become stationary relative to each other so that the motor drives the loading wheel  26  to rotate synchronously through the centrifugal friction clutch. In the centrifugal friction clutch of the embodiment of the present invention, the frictional force between the centrifugal part  24  and the loading wheel  26  is proportional to a square of the rotational speed of the rotary shaft  11 . When at low speed (at startup of the motor  1 ), the centrifugal plate  242  and the loading wheel  26  slide relative to each other, which reduces the rotational inertia and startup load torque applied to the rotary shaft  11 , reduces the vibrational noises at startup of the motor  1 , and avoids the startup failure of the motor  1 . 
         [0034]    It should be understood that the distal end of the centrifugal plate  242  is one end of the centrifugal plate  242  that is not connected with the sleeve ring  241 . Preferably, one end of the centrifugal plate  242  is connected with one end of the sleeve ring  241 , and one end of the centrifugal plate  242  away from the sleeve ring  241  is the distal end of the centrifugal plate  242 . Alternatively, the centrifugal plate  242  may also be disposed on an outer surface of the sleeve ring  241 . 
         [0035]    The embodiment of the present invention further provides a positioning member  20  for axially positioning the loading wheel  26 . By providing the positioning member  20 , the loading wheel  26  can be axially positioned, which avoids wobble of the loading wheel  26 . 
         [0036]    Referring to  FIG. 1  and  FIG. 2 , in a first embodiment, the positioning member  20  includes a positioning shaft sleeve  22  fixed on the rotary shaft  11  and a first stop plate  21  fixedly connected with the positioning shaft sleeve  22 . By means of the above configuration, the first stop plate  21  and the positioning shaft sleeve  22  achieve the axial positioning to the loading wheel  26  and facilitate mounting of the positioning member. In assembly of the loading wheel  26  to the rotary shaft  11 , an end face of one side of the loading wheel  26  toward an assembling direction contacts the first stop plate  21 . 
         [0037]    In this embodiment, the inner hole of the loading wheel  26  is a circular cylindrical hole. In order to prevent the loading wheel  26  from moving in a direction opposite to the assembling direction, the positioning member  20  further includes a second stop plate  23  for being fixed on the rotary shaft  11 . The second stop plate  23  is disposed at one end of the loading wheel  26  away from the first stop plate  21 . The first stop plate  21  is disposed at one end of the loading wheel  26 , and the second stop plate  23  is disposed at the other end of the loading wheel  26 , such that the loading wheel  26  can be axially positioned. Preferably, an axial length of the inner hole of the loading wheel  26  is the same as an axial length of the centrifugal part  24 , such that the centrifugal part  24  can be axially positioned by means of the first stop plate  21  and the second stop plate  23 . 
         [0038]    The positioning member  20  further includes a positioning ring  27  fixedly connected with the second stop plate  23 . An outer surface of the positioning ring  27  contacts an inner surface of the centrifugal plate  242 . The positioning ring  27  supports the centrifugal plate  242  and prevents the centrifugal plate  242  from bending toward a center of the centrifugal part  24 . 
         [0039]    Preferably, the positioning ring  27  and the second stop plate  23  are formed into an integral structure. Through this configuration, only one of the positioning ring  27  and the second stop plate  23  needs to be fixed relative to the rotary shaft  11 . In addition, separate fabrication and mounting of the positioning ring  27  and the second stop plate  23  is voided, which facilitates assembly thereof. 
         [0040]    In this embodiment, the centrifugal part  24  is fixedly disposed on the positioning shaft sleeve  22 . By attaching the centrifugal part  24  around the positioning shaft sleeve  22 , the axial length and hence the overall length of the centrifugal friction clutch is reduced. Alternatively, the centrifugal part  24  can also be directly fixed on the rotary shaft  11 , which is not described herein in detail and falls within the scope of the present invention. 
         [0041]    Further, the positioning shaft sleeve  22  and the first stop plate  21  are formed into an integral structure. With the positioning shaft sleeve  22  and the first stop plate  21  formed into an integral structure, only one of the positioning shaft sleeve  22  and the first stop plate  21  needs to be fixed relative to the rotary shaft. In addition, this avoids separate fabrication and mounting of the positioning shaft sleeve  22  and the first stop plate and facilitates assembly thereof. 
         [0042]    As shown in  FIG. 5  and  FIG. 6 , in a second embodiment, the inner hole of the loading wheel  26  is a stepped hole having coaxially arranged large-diameter hole and small-diameter hole. The centrifugal part  24  is disposed within the large-diameter hole of the stepped hole. A step end face of the stepped hole contacts an end face of the centrifugal part  24  away from the first stop plate  21 . The small-diameter hole allows the rotary shaft  11  to pass therethrough. 
         [0043]    The positioning member  20  of this embodiment likewise includes the positioning shaft sleeve  22  for being fixed on the rotary shaft  11  and the first stop plate  21  fixedly connected with the positioning shaft sleeve  22 . 
         [0044]    In this embodiment, a positioning pressing block  25  is disposed inside the centrifugal plate  242  of the centrifugal part  24 . One end face of the positioning pressing block  25  contacts the step end face of the stepped hole, and the other end face of the positioning pressing block  25  contacts an end face of the sleeve ring  241  that connects with the centrifugal plate  242 . The positioning pressing block  25  supports the centrifugal plate  242  and prevents the centrifugal plate  242  from bending toward a center of the centrifugal part  24 . 
         [0045]    As shown in  FIG. 4 , an elastic groove  243  is formed at a connecting area between the centrifugal plate  242  and the sleeve ring  241 . By providing the elastic groove  243 , a thickness of the connecting area between the centrifugal plate  242  and the sleeve ring  241  is reduced, which more facilitates the tilting of the centrifugal plate  242  under the centrifugal force. 
         [0046]    In this embodiment, the elastic groove  243  is located at an inner side of the connecting area between the centrifugal plate  242  and the sleeve ring  241 . Alternatively, the elastic groove  243  may also be formed at an outer side of the connecting area between the centrifugal plate  242  and the sleeve ring  241 . 
         [0047]    Further, there is a plurality of the centrifugal plates  242  uniformly arranged on the sleeve ring  241 . Through this configuration, the distribution of the frictional force between the centrifugal part  24  and the loading wheel  26  is made more uniform. Alternatively, at least one centrifugal plate  242  is provided. 
         [0048]    One embodiment of the present invention further provides a motor assembly including a single phase motor  1  and a centrifugal friction clutch  2 . The centrifugal friction clutch  2  is any one of the above-described centrifugal friction clutches. Since the above-described centrifugal friction clutches achieve the above-described technical results, the motor assembly employing the above-described centrifugal friction clutch can also achieve the same technical results, which are not described further herein one by one. 
         [0049]    One embodiment of the present invention further provides a blower including an impeller  3  and a motor assembly. In order to facilitate the axial positioning of the impeller  3 , the blower in accordance with the embodiment of the present invention further includes a position-limiting member  12  disposed on the rotary shaft  11  of the motor  1  to limit axial movement of the impeller  3 . The position-limiting member  12  is disposed at one side of the centrifugal friction clutch  2  opposite from a main body of the motor  1 . 
         [0050]    As shown in  FIG. 2 , the position-limiting member  12  is configured to be a nut, and an end portion of the rotary shaft  11  is provided with threads for engaging with the nut. In an alternative embodiment, the position-limiting member  12  is positioned on the rotary shaft  11  with a fastening screw  13 . In still another embodiment, the position-limiting member  12  may be configured to be a clip spring, and the end portion of the rotary shaft  11  is provided with a latching groove for engaging with the clip spring. These embodiments all fall within the scope of the present invention, which are not described further herein one by one. 
         [0051]    Since the above-described motor assemblies achieve the above-described technical results, the blower employing the above-described motor assembly can also achieve the same technical results, which are not described further herein one by one. It should be noted that the motor assembly of the present invention is not only suitable for use in the blower, but it also suitable for use in other fluid driving devices such as a water pump. 
         [0052]    Referring to  FIG. 7  to  FIG. 9 , the single phase motor in one embodiment of the present invention is an outer-rotor motor which includes a stator  30  and a rotor  40  surrounding the stator  30 . In another embodiment, the single phase motor may also be an inner-rotor motor. 
         [0053]    In this embodiment, the stator  30  includes a stator core  31  made from a magnetic-conductive material, an insulating bracket  33  attached around the stator core  31 , and windings  35  wound around the insulating bracket  33 . 
         [0054]    The stator core  31  includes an annular portion  310  disposed at a center of the stator core  31 , and a plurality of teeth extending radially outwardly from the annular portion  310 . A winding slot is formed between each two adjacent teeth. Each tooth includes a tooth body  312  and a tooth tip  314  extending from a distal end of the tooth body  112  along a circumferential direction. Each two adjacent tooth tips  314  define therebetween a slot opening  315  of one corresponding winding slot. Preferably, each slot opening  315  has the same width in the circumferential direction. That is, the tooth tips are evenly arranged along the circumferential direction. Preferably, each tooth is symmetrical with respect to a radius of the motor that passes through a center of the tooth body of this tooth. 
         [0055]    Preferably, outer surfaces  317  of the tooth tips  314 , i.e. the surfaces opposite from the annular portion  310 , are arc surface which form a pole face of the stator  30 . Preferably, the outer surfaces  317  of the tooth tips  314  are located on a same cylindrical surface concentric with the rotary shaft  11 . Inner surfaces  318  of the tooth tips  314 , i.e. the surfaces facing toward the annular portion  310 , are generally plane surfaces. 
         [0056]    In some embodiments, slits  316  are formed in connecting corner areas between the tooth tip  314  and the tooth body  312 . The provision of the slits  116  prevents creases during the process of bending the tooth tip  314  of the stator core  31 . Specifically, two parts of the tooth tip  314  on opposite sides of the tooth body  312  extend radially outwardly in an initial state, such that the width of the insulating slot and slot opening  315  may be enlarged to facilitate winding of the windings  15 . After the winding is completed, the two parts of the tooth tip  314  are bent inwardly about the slits  316  to a final position using a tool. It should be understood that, in some embodiments, the slit  116  may be formed only in a connecting corner area between the tooth body  112  and the part of the tooth tip  112  at a single side of the tooth body  112 . 
         [0057]    The rotor  40  includes the rotary shaft  11  passing through the annular portion  310 , a rotor yoke  42  fixedly connected with the rotary shaft  11 , and multiple permanent magnetic poles  44  disposed on an inner wall surface of the rotor yoke  22 . Preferably, an inner surface  441  of the permanent magnetic pole  44  is a flat surface, such that fabrication of the permanent magnetic pole  44  can be simplified. It should be understood, however, that the inner surface of the permanent magnetic pole may also be an arc surface. Preferably, a pole-arc coefficient of the permanent magnetic pole  44 , i.e. a ratio of the actual angle of the permanent magnetic pole  44  along the circumferential direction to the quotient of 360 degrees divided by the number of the rotor poles, is greater than 0.75, which can improve the cogging torque characteristics and enhance the motor efficiency. 
         [0058]    The inner surface  441  of the permanent magnetic pole  44  is opposed to the outer surface  317  of the tooth tip  314 , with an air gap  319  formed therebetween. A radial width of the gap  319  varies along a circumferential direction of the permanent magnetic pole  44 , thus forming an uneven air gap. The radial width of the air gap  319  progressively increases from a circumferential center toward opposite circumferential ends of the inner surface of the permanent magnetic pole  44 . As such, a radial distance between a circumferential center point of the inner surface of the permanent magnetic pole  44  and a cylindrical surface in which the outer surface of the tooth tip  314  is located is referred to as the minimum radial width of the air gap  319 , and a radial distance between a circumferential end point of the inner surface of the permanent magnetic pole  44  and the cylindrical surface in which the outer surface of the tooth tip  314  is located is referred to as the maximum radial width of the air gap  319 . 
         [0059]    Preferably, a ratio of the maximum radial width to the minimum radial width of the air gap  119  is greater than 2, and a width (usually referring to the minimum width of the slot opening  315  in the circumferential direction) of the slot opening  315  is greater than or equal to zero, but less than or equal to five times of the minimum radial width of the air gap  319 . Preferably, the width of the slot opening  315  is equal to or greater than the minimum radial width of the air gap  319 , but less than or equal to three times of the minimum radial width of the air gap  319 . Because of the above relationship between the slot opening  315  and the air gap  319 , when the motor is not energized, the rotor  40  stops at the initial position shown in  FIG. 9 . This initial position is offset from a dead-point position, thereby avoiding the failure of starting the rotor when the motor is energized. In this embodiment, the rotor  40  stops at the initial position shown in  FIG. 9  when the motor is not energized or powered off. At this initial position, a center line of the tooth body  312  of the stator core is aligned with a center line of the area between two adjacent rotor magnetic poles  44 . This position deviates the furthest from the dead-point position, which can effectively avoid the failure of starting the rotor when the motor is energized. Due to other factors such as friction in practice, the center line of the tooth body  312  of the stator core may deviate from the center line of the area between two adjacent rotor magnetic poles  44  by an angle such as an angle of 0 to 30 degrees, but the stop position is still far away from the dead-point position. 
         [0060]    In the above embodiments of the present invention, the rotor can be positioned at the initial position deviating from the dead-point position by the magnetic field produced by the rotor magnetic pole  44  itself. The cogging torque of the single-phase motor configured as such can be effectively suppressed, such that the motor has enhanced efficiency and performance. Experiments show that a peak of the cogging torque of a single-phase outer-rotor brushless direct current motor configured as above (with a rated torque of 1 Nm, a rated rotation speed of 1000 rpm, and a stack height of the stator core of 30 mm) is less than 80 mNm. The motor of the present invention can be designed with bidirectional startup capability according to needs. For example, the bidirectional rotation can be achieved by using two position sensors such as Hall sensors and an associated controller. It may also be designed to start up in a single direction, in which case only one position sensor is needed. 
         [0061]    All embodiments in the specification are described in a progressive way, each embodiment mainly describes the differences from other embodiments, and the same and similar parts among the embodiments can be referenced mutually. 
         [0062]    Although the invention is described with reference to one or more embodiments, the above description of the embodiments is used only to enable people skilled in the art to practice or use the invention. It should be appreciated by those skilled in the art that various modifications are possible without departing from the spirit or scope of the present invention. The embodiments illustrated herein should not be interpreted as limits to the present invention, and the scope of the invention is to be determined by reference to the claims that follow.