Patent Publication Number: US-10333369-B2

Title: Motor driving assembly and torque transmission mechanism

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This non-provisional patent application claims priority under 35 U.S.C. § 119(a) from Patent Application No. 201510477361.X filed in The People&#39;s Republic of China on Aug. 6, 2015. 
     FIELD OF THE INVENTION 
     The present invention relates to motors, and in particular to a single phase motor assembly for starting and driving a large load. 
     BACKGROUND OF THE INVENTION 
     When the rotational inertia of a load is too large, startup of the motor may fail because the motor cannot provide sufficient rotation torque at the moment of startup, and the motor may also be damaged in such situation. 
     When the motor is a single phase motor which usually has a small output torque, the above situation can more easily occur. 
     SUMMARY OF THE INVENTION 
     Thus, there is a desire for a motor driving assembly which can drive a large load by using a single phase motor. 
     In one aspect, the present invention provides a motor driving assembly which includes a single phase motor and a torque transmission mechanism. The torque transmission mechanism includes a driving member for being driven by the motor, a driven member for driving a load to rotate along a predetermined direction, and a connecting device comprising a resilient member and a damping member. The resilient member includes one end connected to the driving member and the other end connected to the driven member. The damping member is coated on or attached over the resilient member, or filled in void of the resilient member, in order to reduce noise produced by the resilient member. 
     Preferably, the single phase motor is a single phase permanent magnet direct current brushless motor or a single phase permanent magnet synchronous motor. 
     Preferably, the driving member and the driven member cooperatively form a receiving space, and the resilient member is a spiral spring received in the receiving space. 
     Preferably, the motor comprises an output shaft, the driving member is connected to an output shaft of the motor for synchronous rotation therewith, the driving member defines a receiving slot, and the one end of the resilient member is received in the receiving slot. 
     Preferably, the driven member defines a receiving slot, and the one end of the resilient member is received in the receiving slot. 
     Preferably, the single phase motor further comprises a startup circuit. The stator includes a stator winding. The stator winding and an external AC power are connected in series between a first node and a second node. The driving circuit includes a bidirectional AC switch, an AC-DC conversion circuit connected between the first node and the second node in parallel with the bidirectional AC switch, a position sensor, and a switch control circuit. No electrical current flows through the AC-DC conversion circuit when the bidirectional AC switch is turned on because the first node and the second node are short-circuited. The switch control circuit is configured to control the bidirectional AC switch to switch between turn-on and turn-off states of a positive half wave or a negative half wave according to a predetermined manner according to rotor magnetic pole position information detected by the position sensor and polarity information of the external AC power, such that the stator winding drives the rotor to rotate only along a predetermined startup direction during a startup period of the motor. 
     Preferably, the rotor comprises a plurality of permanent magnetic poles, the stator comprises a stator core and a stator winding wound around the stator core, the stator core comprises a plurality of stator teeth, each of the stator teeth comprises a tooth surface facing the rotor permanent magnetic pole, the tooth surface comprises a first section which is coaxial with the rotor and a second section forming a positioning slot such that the rotor is capable of stopping at an initial position which deviates from a dead point. 
     Preferably, the rotor is of an outer rotor type and includes a plurality of permanent magnetic poles. The stator includes a stator core and a stator winding wound around the stator core. The stator core includes a plurality of stator tooth. Each of the stator teeth includes a tooth surface facing the rotor permanent magnetic pole. An uneven air gap is formed between the permanent magnetic poles and the stator tooth face, and the air gap at each of the magnetic poles is symmetrical about a center line of the each of the magnetic poles. 
     Preferably, the air gap at each of the magnetic poles has a radial width gradually increasing from a center to two ends of the each of the magnetic poles. 
     In another aspect, a torque transmission mechanism is provided which includes a driving member for being driven by an external force, a driven member for driving a load to rotate along a predetermined direction, and a connecting device including a resilient member and a damping member. The resilient member includes one end connected to the driving member and the other end connected to the driven member. The damping member is coated on or attached over the resilient member, or filled in void of the resilient member. 
     Preferably, the driving member and the driven member cooperatively form a receiving space, and the resilient member is a spiral spring received in the receiving space. 
     Preferably, the driving member forms a first receiving slot, the one end of the resilient member is received in the first receiving slot, the driven member forms a second receiving slot, and the other end of the resilient member is received in the second receiving slot. 
     The present invention further comprises an electric apparatus comprising a fluid generating device comprising a plurality of blades; and a driving assembly for driving the fluid generating device to rotate. 
     The torque transmission mechanism of the present invention can provide a buffering function at the phase of startup of the motor, thus avoiding startup failure of the motor, preventing the motor from being damaged, and effectively reducing the noise from the source. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a simplified view of a motor driving assembly according to one embodiment of the present invention. 
         FIG. 2  is a perspective view of a torque transmission mechanism utilized in the motor driving assembly of  FIG. 1 . 
         FIG. 3  is a perspective view of a driving member of the torque transmission mechanism of  FIG. 2 . 
         FIG. 4  is a perspective view of the driving member and a connecting device of the torque transmission mechanism of  FIG. 2 . 
         FIG. 5  is a perspective view of a driven member and the connecting device of the torque transmission mechanism of  FIG. 2 . 
         FIG. 6  illustrates an inner rotor permanent magnet brushless motor utilized in the above embodiment. 
         FIG. 7  is a block diagram showing a startup circuit of the motor of  FIG. 6 . 
         FIG. 8  illustrates an outer rotor permanent magnet brushless motor utilized in the above embodiment. 
         FIG. 9  illustrates an example of a fluid generating device driven by the motor driving assembly of  FIG. 1 . 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     Referring to  FIG. 1  to  FIG. 5 , a motor driving assembly in accordance with a first embodiment of the present invention includes a single phase motor  10  and a torque transmission mechanism  30 . 
     The single phase motor  10  is preferably a single phase permanent magnet direct current brushless motor or a single phase permanent magnet synchronous motor, which includes an output shaft  12 . 
     The torque transmission mechanism  30  includes a driving member  40  configured to be driven by the output shaft  12  of the motor, a driven member  50  for driving a load along a predetermined direction, and a connecting device  60 . The connecting device  60  includes a resilient member  62  and a damping member  64 . The resilient member  62  has one end  68  connected to the driving member  40  and the other end  69  connected to the driven member  50 . The damping member  64  is coated on or attached around the resilient member  62  or is filled in a gap of the resilient member  62  to reduce noise produced by the resilient member  62 . 
     In this embodiment, at least one of the driving member  40  and the driven member  50  is plate-shaped or disc-shaped with a flange, and the driving member  40  and the driven member  50  cooperatively form a receiving space there between. The resilient member  62  is a spiral spring with a plurality of rings received in the receiving space. Preferably, one or more elastic pads  66  is disposed between one of two axial sides of the spring  62  and one of contact surfaces of the driving member  40  and driven member  50  in order to reduce axial play of the spring  62  in the receiving space to thereby reduce noise. Understandably, elastic pad  66  may be disposed between both axial sides of the spring  62  and contact surfaces of the driving member  40  and driven member  50  respectively. 
     The damping member  64  may be a damping layer coated on an outer surface of the resilient member  62 , a damping mud or damping rubber filled in gaps/spaces formed between rings of the spring  62 , a damping sleeve directly attached over the resilient member  62 , or a damping wire or strip wound around the resilient member  62 . 
     The driving member  40  is connected to the output shaft  12  of the motor for synchronous rotation therewith. Specifically, the driving member  40  defines an axial hole  42 , and the output shaft  12  of the motor passes through the axial hole  42 . The output shaft  12  of the motor and the axial hole  42  may be connected by interference-fit/press fit or in another fixed connecting manner to transmit torque. A receiving slot  44  is formed in one side of the driving member  40  toward the driven member  50 . In this embodiment, the receiving slot  44  extends along a circumferential direction. The one end  68  of the resilient member  62  is received in the receiving slot  44 . 
     In this embodiment, an annular flange  52  is formed at an outer edge of the driven member  50 . The annular flange  52  surrounds a cavity for receiving the spring  62 . The flange  52  defines a receiving slot  54  in which the other end  69  of the spring  62  is received. The flange  52  of the driving member  50  defines a slot for reducing the material and therefore weight of the driven member  50 . 
     In operation of the motor  10 , one end  68  of the spring  62  and the driving member  40  rotate along with the output shaft  12  of the motor, which makes the spring  62  start storing energy. When the energy stored by the spring  62  reaches a predetermined amount, the other end  69  of the spring  62  drives the driven member  50  to rotate, thus driving the load  70  connected with the driven member  50  to rotate together. When the rotation speed of the load  70  is equal to the rotation speed of the output shaft  12  of the motor, the spring  62  maintains in a stable tension state. 
     When the motor drives a load with a larger moment of inertia, in order to address the startup failure problem due to the fact that the output torque of the motor is not large enough to drive the load at the beginning of the startup, the present invention allows the driving shaft  12  to slip relative to the load  70  at the beginning of the motor startup. Only when the output torque of the motor reaches a certain value, the motor drives the load  70  to rotate via the load connecting mechanism  30 , such that the motor can be successfully started and drive the load with larger moment of inertia. In addition, by utilizing the motor driving assembly and its torque transmission mechanism provided by the present invention, there is no need to increase the size of the motor, and the power loss caused by other startup manner is also reduced. Furthermore, because the spring  62  is coated or wrapped with the damping member, vibration of the spring  62  can be effectively absorbed and the noise produced by the spring can be effectively reduced. 
     In this embodiment, the load  70  can be a fluid generating device with a plurality of blades such as a fan of an electric apparatus such as a ventilation fan or a range hood, or an impeller of a pump such as a drain pump or a circulation pump used in a washing machine or dishwasher. The driven member  50  of the torque transmission mechanism  30  drives the fan or impeller to rotate. 
       FIG. 6  illustrates a single phase permanent magnet brushless motor  10  utilized in the above embodiment. The motor is of an inner rotor type. The motor  10  includes a stator  13  and a rotor  14 . The stator  13  includes a stator core such as a laminated stator core  15  and a winding  16  wound around the stator core  15 . The rotor  14  includes a rotary shaft  17  and permanent magnetic poles  18 . Outer surfaces of the permanent magnetic poles  18  confront the stator core  15  with an air gap formed there between to allow the rotor to rotate relative to the stator. Preferably, the air gap is a substantially even air gap, i.e. most part of the outer surfaces of the permanent magnetic poles  18  are coaxial with most part of an inner surface of the stator core  15 . The stator core  15  includes a yoke  152  and a plurality of stator teeth  154  extending inwardly from the yoke  152 . Each of the stator teeth  154  comprises a tooth surface facing the rotor permanent magnetic pole, the tooth surface comprises a first section which is coaxial with the rotor and a second section forming a positioning slot  19  such that the rotor is capable of stopping at an initial position which deviates from a dead point (i.e. a center line of the permanent magnetic pole deviates from a center line of a corresponding stator tooth by an angle) when the stator windings  16  are not energized. In this embodiment, ends of the stator teeth  154  away from the yoke  152  are connected together to form a ring  156 . The positioning slots  19  are formed in an inner surface of the ring  156 . Preferably, the number of the teeth and the number of the positioning slots  19  are directly proportional to the number of the rotor permanent magnetic poles, and the stator teeth and the ring are integrally formed and are wound with the stator winding before being assembled to the yoke of the stator core. The motor further includes a position sensor  20  ( FIG. 7 ) such as a Hall sensor or a photo sensor. The position sensor  20  is used to sense the position of the rotor. 
       FIG. 7  is a block diagram showing a driving circuit  80  of the single phase permanent magnet brushless motor of the present invention. In the driving circuit  80 , the stator windings  16  and an alternating current (AC) power  81  are connected in series between two nodes A and B. The AC power  81  is preferably a commercial AC power supply with a fixed frequency such as 50 Hz or 60 Hz and a supply voltage may be, for example, 110V, 220V or 230V. A controllable bidirectional AC switch  82  is connected between the nodes A and B, in parallel with the series-connected stator windings  16  and AC power  81 . The bidirectional AC switch  82  is preferably a triode AC switch (TRIAC) having two anodes connected to the two nodes A and B, respectively. It should be understood that the controllable bidirectional AC switch  82  may be two silicon control rectifiers reversely connected in parallel, and control circuits may be correspondingly configured to control the two silicon control rectifiers in a preset way. An AC-DC conversion circuit  83  is connected between the two nodes A and B, in parallel with the switch  81 . An AC voltage between the two nodes A and B is converted by the AC-DC conversion circuit  83  into a low voltage DC. The position sensor  20  may be powered by the low voltage DC power outputted from the AC-DC conversion circuit  83 , for detecting the position of the magnetic poles of the permanent magnet rotor  14  of the synchronous motor  10  and outputting corresponding signals. A switch control circuit  85  is connected with the AC-DC conversion circuit  83 , the position sensor  20  and the bidirectional AC switch  82 , and is configured to control the bidirectional switch  82  to switch between a switch-on state and a switch-off state in a predetermined way, based on the magnetic pole position of the permanent magnet rotor and the polarity of the AC power source, such that the stator winding  16  urges the rotor to rotate only in the above-mentioned fixed starting direction during a starting phase of the motor. In this embodiment, in a case that the controllable bidirectional AC switch  82  is switched on, the two nodes A and B are short-circuited, and the AC-DC conversion circuit  83  does not consume electric energy because there is no electrical current flows through the AC-DC conversion circuit  83 , hence, the utilization efficiency of electric energy can be improved significantly. 
       FIG. 8  illustrates another type of motor  10  utilized in the above embodiment. The motor  10  is of an outer rotor type, with the rotor  14  disposed surrounding the stator  13 . An uneven air gap is formed between the permanent magnetic poles of the rotor and the stator core. Preferably, the air gap at each of the permanent magnetic poles is symmetrical about a center line of the each of the permanent magnetic poles, and has a radial width gradually increasing from a center toward two ends of the each of the permanent magnetic poles. 
       FIG. 9  illustrates an example of the fluid generating device  70 . In this embodiment, the fluid generating device  70  is an axial fan with a plurality of blades  72  used for bathroom fan, range hood and so on. Alternatively, the fluid generating device  70  may be an impeller with a plurality of blades used for a pump such as drain pump, circulation pump of a washing machine or dish washer. 
     Although the invention is described with reference to one or more preferred embodiments, it should be appreciated by those skilled in the art that various modifications are possible. For example, the motor may be of an inner rotor type or an outer rotor type. The air gap between the stator and rotor may be even or uneven. The material of the permanent magnet may be rare earth material or another material such as ferrite magnet. When the inner rotor motor is used, the permanent magnetic poles may be directly fixed to the rotary shaft of the rotor. Alternatively, the rotor core may be fixed to the rotary shaft, and then the permanent magnetic poles are fixed to an outer surface of the rotor core (i.e. surface mounted permanent magnetic poles), or are inserted into the rotor core (i.e. embedded permanent magnetic poles). Therefore, the scope of the invention is to be determined by reference to the claims that follow.