PATENT ABSTRACT
The present invention relates to a pulley for an alternator, and in particular, to a pulley applicable to an automotive alternator. The pulley effectively mitigates the problem that a belt and a tension pulley of an alternator vibrate because a rotation speed of a vehicle engine changes, thereby improving the overall operating efficiency of the alternator and the service life of the working belt and the tension pulley.

PATENT DESCRIPTION
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application claims the benefit of priority from Taiwan patent application TW 103 124 194, filed Jul. 14, 2014, the contents of which are herein incorporated by reference. 
     BACKGROUND OF THE INVENTION 
     The present invention relates to a pulley for an alternator, and in particular, to a pulley for an automotive alternator. 
     An alternator is a type of generator that can produce an alternating current by converting mechanical energy into electrical energy. An automotive alternator converts mechanical energy of an engine into electrical energy to charge a battery, so as to supply electrical power to other electrical appliances on the automobile, and start a motor to rotate the engine. 
     An alternator generally has an annular stator and a rotor received in the annular stator. A wire is wound on the stator, and the rotor rotates rapidly in the stator so that the wire moves relative to a magnetic field generated by the rotor, and an induced electromotive force (voltage) is generated in the wire. 
     An automotive alternator is usually utilized by an engine driving a belt. The belt is wound on a pulley, and the pulley is connected to a rotor so as to drive the rotor to rotate. However, in conventional alternator design, when an engine starts, or accelerates or decelerates quickly in an instant, a waveform changes significantly at the moment the generator charges a battery, and it cannot be stabilized. In addition, one side of the belt wound on the pulley is tight, and the other side thereof is slack. The tension of the slack-side belt is low, and therefore a tensioner is disposed thereon to adjust the tension of the belt. However, when a rotation speed at which the engine transmits power changes suddenly, because the pulley of the generator is locked by a nut and the belt is made of a flexible material and cannot reflect the rotation speed immediately, a slip is easily caused between the belt and the pulley. Moreover, the fluctuation of the rotation speed causes the belt to bear not only a repeated stress but also a centrifugal force that is applied on the belt when the pulley rotates. The value of the centrifugal force changes with the rotation speed, and therefore the belt is often affected by adverse factors of an internal micro tension, which pulls the belt, and external large-amplitude shaking. 
     SUMMARY 
     The present invention provides a pulley for an alternator, which includes an outer wheel, provided with an axle hole at the center; a clutch wheel, fixedly disposed in the axle hole of the outer wheel and having a pivot hole; a hollow connecting shaft, having a first end and a second end, where the first end is rotatably disposed in the pivot hole of the clutch wheel, so that the hollow connecting shaft maintains a co-rotational relationship with the outer wheel in a first relative rotation direction by means of the clutch wheel, while in a second relative rotation direction, the hollow connecting shaft is disassociated from the co-rotational relationship with the outer wheel, and presents an idling state; and the second end of the hollow connecting shaft is provided with a first protruding portion; a hollow core shaft, having a first end and a second end, where the hollow core shaft is rotatably received in the outer wheel, and the second end of the hollow core shaft is rotatably arranged at the second end of the hollow connecting shaft; the second end of the hollow core shaft is provided with a second protruding portion, and the second protruding portion corresponds to the first protruding portion; the number of one of the first protruding portion and the second protruding portion is at least one, and the number of the other of the first protruding portion and the second protruding portion is at least two; and an elastic element, disposed between the second end of the hollow connecting shaft and the second end of the hollow core shaft. 
     When an external force drives the outer wheel to rotate, the outer wheel rotates relative to the hollow connecting shaft in the first relative rotation direction, and drives, through the clutch wheel, the hollow connecting shaft to rotate synchronously; the second end of the hollow connecting shaft presses the elastic element, and while being pressed, the elastic element pushes the second end of the hollow core shaft, thereby driving the hollow core shaft to rotate; and if a rotation angle of the hollow connecting shaft relative to the hollow core shaft exceeds a predetermined value at this time, the first protruding portion of the hollow connecting shaft contacts the second protruding portion of the hollow core shaft, thereby stopping relative rotation between the hollow connecting shaft and the hollow core shaft, so as to prevent the elastic element from being pressed excessively, and to set the hollow connecting shaft and the hollow core shaft in a synchronous co-rotational relationship. When the external force decreases or stops driving the outer wheel to rotate, the hollow core shaft continues to rotate due to inertia, and stretches the elastic element, and while being stretched, the elastic element pulls the second end of the hollow connecting shaft, thereby driving the hollow connecting shaft to rotate relative to the outer wheel in the second relative rotation direction, so that the hollow connecting shaft is disassociated from the co-rotational relationship with the outer wheel, and idles in the clutch wheel; and if a rotation angle of the hollow connecting shaft relative to the hollow core shaft exceeds a predetermined value at this time, the first protruding portion of the hollow connecting shaft contacts the second protruding portion of the hollow core shaft, thereby stopping relative rotation between the hollow connecting shaft and the hollow core shaft, so as to prevent the elastic element from being stretched excessively, and to set the hollow connecting shaft and the hollow core shaft in a synchronous co-rotational relationship. 
     According to another preferred embodiment of the present invention, the hollow core shaft passes through the hollow connecting shaft, and the first end of the hollow core shaft protrudes from the first end of the hollow connecting shaft; a tight-fit component is sleeved over an outer circumferential wall surface of the first end of the hollow core shaft in a tight-fit manner, and the tight-fit component is also tightly fit with an end surface of the first end of the hollow connecting shaft; therefore, the hollow connecting shaft and the hollow core shaft are made to corotate coaxially under a friction between the tight-fit component and the hollow connecting shaft and a friction between the tight-fit component and the hollow core shaft, and when the external force decreases or stops driving the outer wheel to rotate, the hollow core shaft continues to rotate due to inertia, and drives, through the tight-fit component, the hollow connecting shaft to rotate relative to the outer wheel in the second relative rotation direction, so that the hollow connecting shaft is disassociated from the co-rotational relationship with the outer wheel and idles in the clutch wheel. 
     According to another preferred embodiment of the present invention, the tight-fit component is a C-shaped retaining ring. 
     According to another preferred embodiment of the present invention, a first ball bearing is sleeved over the first end of the hollow core shaft, a second ball bearing is sleeved over the second end of the hollow core shaft, and the first ball bearing and the second ball bearing are disposed between the hollow core shaft and the outer wheel, so that the hollow core shaft is rotatable relative to the outer wheel. 
     According to another preferred embodiment of the present invention, three grooves are provided in a concave manner on an inner circumferential wall surface of the outer wheel, and an anaerobic adhesive is coated in the grooves, so that the clutch wheel, the first ball bearing, and the second ball bearing are separately tightly fit in the grooves, and are fixedly glued in the outer wheel by using the anaerobic adhesive. 
     According to another preferred embodiment of the present invention, a positioning casing is further sleeved over the first ball bearing, and an axial position of the pulley on the alternator is limited by the positioning casing. 
     According to another preferred embodiment of the present invention, an outer circumferential wall surface of the outer wheel is provided with a belt groove, for a belt to be wound on. 
     According to another preferred embodiment of the present invention, the belt is connected to a mechanical energy generating source, and the mechanical energy generating source provides an external force to drive the belt, thereby driving the outer wheel to rotate. 
     According to another preferred embodiment of the present invention, the mechanical energy generating source is an engine. 
     According to another preferred embodiment of the present invention, an inner circumferential wall surface of the hollow core shaft is provided with a threaded surface, the threaded surface is screwed with a joint lever having corresponding threads, and the joint lever is connected to a rotor, so that the hollow core shaft and the rotor corotate synchronously. 
     According to another preferred embodiment of the present invention, an inner circumferential wall surface of the outer wheel is provided with a step portion, for the clutch wheel to abut against, thereby limiting an axial displacement of the clutch wheel. 
     According to another preferred embodiment of the present invention, one end of the clutch wheel is provided with a positioning member, to limit an axial position of the clutch wheel, and the positioning member is a C-shaped retaining ring. 
     According to another preferred embodiment of the present invention, the elastic element is a torque spring, and a wire profile of the torque spring is circular, elliptical, or rectangular. 
     According to another preferred embodiment of the present invention, when the wire profile of the torque spring is rectangular, two end surfaces of the torque spring are grinded, so as to enhance axial positioning of the torque spring and control a free length of the torque spring more precisely. 
     According to another preferred embodiment of the present invention, two sides of the clutch wheel are each provided with an oil seal element, so as to prevent liquid in the clutch wheel from flowing into the outer wheel. 
     According to another preferred embodiment of the present invention, one side of one of the oil seal elements is provided with a positioning member, and the positioning member is sleeved over an inner side wall surface of the outer wheel in a tight-fit manner, to limit axial positions of the oil seal elements. 
     According to another preferred embodiment of the present invention, the positioning member is a C-shaped retaining ring. 
     According to another preferred embodiment of the present invention, an end, corresponding to the second end of the hollow core shaft, of the outer wheel is arranged with a dust cover, so as to prevent external dust from entering the outer wheel. 
     The present invention further provides a pulley for an alternator, which includes an outer wheel, provided with an axle hole at the center; a clutch wheel, fixedly disposed in the axle hole of the outer wheel and having a pivot hole; a hollow connecting shaft, having a first end and a second end, where the first end is rotatably disposed in the pivot hole of the clutch wheel, so that the hollow connecting shaft maintains a co-rotational relationship with the outer wheel in a first relative rotation direction by means of the clutch wheel, while in a second relative rotation direction, the hollow connecting shaft is disassociated from the co-rotational relationship with the outer wheel, and presents an idling state; and the second end of the hollow connecting shaft is provided with a first protruding portion; a hollow core shaft, having a first end and a second end, where the hollow core shaft is rotatably received in the outer wheel, and the hollow core shaft passes through the hollow connecting shaft; the first end of the hollow core shaft protrudes from the first end of the hollow connecting shaft, and the second end of the hollow core shaft is rotatably arranged on the second end of the hollow connecting shaft; the second end of the hollow core shaft is provided with a second protruding portion, and the second protruding portion corresponds to the first protruding portion; the number of one of the first protruding portion and the second protruding portion is at least one, and the number of the other of the first protruding portion and the second protruding portion is at least two; an elastic element, disposed between the second end of the hollow connecting shaft and the second end of the hollow core shaft; and a tight-fit component, sleeved over an outer circumferential wall surface of the first end of the hollow core shaft in a tight-fit manner and tightly fit with an end surface of the first end of the hollow connecting shaft, so that the hollow connecting shaft and the hollow core shaft corotate coaxially under a friction between the tight-fit component and the hollow connecting shaft and a friction between the tight-fit component and the hollow core shaft. 
     When an external force drives the outer wheel to rotate, the outer wheel rotates relative to the hollow connecting shaft in the first relative rotation direction, and drives, through the clutch wheel, the hollow connecting shaft to rotate synchronously, and the hollow connecting shaft drives, through the tight-fit component, the hollow core shaft to rotate; if the friction provided by the tight-fit component is insufficient to drive the hollow core shaft to rotate at this time, the second end of the hollow connecting shaft presses the elastic element, and while being pressed, the elastic element pushes the second end of the hollow core shaft, thereby driving the hollow core shaft to rotate; and if a rotation angle of the hollow connecting shaft relative to the hollow core shaft exceeds a predetermined value at this time, the first protruding portion of the hollow connecting shaft contacts the second protruding portion of the hollow core shaft, thereby stopping relative rotation between the hollow connecting shaft and the hollow core shaft, so as to prevent the elastic element from being pressed excessively, and to set the hollow connecting shaft and the hollow core shaft in a synchronous co-rotational relationship. When the external force decreases or stops driving the outer wheel to rotate, the hollow core shaft continues to rotate due to inertia, and drives, through the tight-fit component, the hollow connecting shaft to rotate relative to the outer wheel in the second relative rotation direction; and if the friction provided by the tight-fit component is insufficient to drive the hollow connecting shaft to rotate at this time, the hollow core shaft rotates relative to the hollow connecting shaft until the first protruding portion of the hollow connecting shaft contacts the second protruding portion of the hollow core shaft, thereby stopping relative rotation between the hollow connecting shaft and the hollow core shaft, and setting the hollow connecting shaft and the hollow core shaft in a synchronous co-rotational relationship. 
     According to another preferred embodiment of the present invention, when the external force decreases or stops driving the outer wheel to rotate, the hollow core shaft continues to rotate due to inertia, and drives, through the tight-fit component, the hollow connecting shaft to rotate relative to the outer wheel in the second relative rotation direction; if the friction provided by the tight-fit component is insufficient to drive the hollow connecting shaft to rotate at this time, the hollow core shaft stretches the elastic element, and while being stretched, the elastic element pulls the second end of the hollow connecting shaft, thereby driving the hollow connecting shaft to rotate relative to the outer wheel in the second relative rotation direction, so that the hollow connecting shaft is disassociated from the co-rotational relationship with the outer wheel; and if a rotation angle of the hollow connecting shaft relative to the hollow core shaft exceeds a predetermined value, the protruding portion of the hollow connecting shaft contacts the protruding portion of the hollow core shaft, thereby stopping relative rotation between the hollow connecting shaft and the hollow core shaft, so as to prevent the elastic element from being stretched excessively, and to set the hollow connecting shaft and the hollow core shaft in a synchronous co-rotational relationship. 
     According to another preferred embodiment of the present invention, the tight-fit component is a C-shaped retaining ring. 
     According to another preferred embodiment of the present invention, a first ball bearing is sleeved over the first end of the hollow core shaft, a second ball bearing is sleeved over the second end of the hollow core shaft, and the first ball bearing and the second ball bearing are disposed between the hollow core shaft and the outer wheel, so that the hollow core shaft is rotatable relative to the outer wheel. 
     According to another preferred embodiment of the present invention, three grooves are provided in a concave manner on an inner circumferential wall surface of the outer wheel, and an anaerobic adhesive is coated in the grooves, so that the clutch wheel, the first ball bearing, and the second ball bearing are separately tightly fit in the grooves, and are fixedly glued in the outer wheel by using the anaerobic adhesive. 
     According to another preferred embodiment of the present invention, a positioning casing is further sleeved over the first ball bearing, and an axial position of the pulley on the alternator is limited by the positioning casing. 
     According to another preferred embodiment of the present invention, an outer circumferential wall surface of the outer wheel is provided with a belt groove, for a belt to be wound on. 
     According to another preferred embodiment of the present invention, the belt is connected to a mechanical energy generating source, and the mechanical energy generating source provides an external force to drive the belt, thereby driving the outer wheel to rotate. 
     According to another preferred embodiment of the present invention, the mechanical energy generating source is an engine. 
     According to another preferred embodiment of the present invention, an inner circumferential wall surface of the hollow core shaft is provided with a threaded surface, the threaded surface is screwed with a joint lever having corresponding threads, and the joint lever is connected to a rotor, so that the hollow core shaft and the rotor corotate synchronously. 
     According to another preferred embodiment of the present invention, an inner circumferential wall surface of the outer wheel is provided with a step portion, for the clutch wheel to abut against, thereby limiting an axial displacement of the clutch wheel. 
     According to another preferred embodiment of the present invention, one end of the clutch wheel is provided with a positioning member, to limit an axial position of the clutch wheel, and the positioning member is a C-shaped retaining ring. 
     According to another preferred embodiment of the present invention, the elastic element is a torque spring, and a wire profile of the torque spring is circular, elliptical, or rectangular. 
     According to another preferred embodiment of the present invention, when the wire profile of the torque spring is rectangular, two end surfaces of the torque spring are grinded, so as to enhance axial positioning of the torque spring and control a free length of the torque spring more precisely. 
     According to another preferred embodiment of the present invention, two sides of the clutch wheel are each provided with an oil seal element, so as to prevent liquid in the clutch wheel from flowing into the outer wheel. 
     According to another preferred embodiment of the present invention, one side of one of the oil seal elements is provided with a positioning member, and the positioning member is sleeved over an inner side wall surface of the outer wheel in a tight-fit manner, to limit axial positions of the oil seal elements. 
     According to another preferred embodiment of the present invention, the positioning member is a C-shaped retaining ring. 
     According to another preferred embodiment of the present invention, an end, corresponding to the second end of the hollow core shaft, of the outer wheel is arranged with a dust cover, so as to prevent external dust from entering the outer wheel. 
     The present invention further provides an alternator having the pulley according to the present invention. 
     According to another preferred embodiment of the present invention, the alternator is used on a vehicle. 
     For better understanding of the detailed description of the present invention, the features and technical advantages of the present invention are described generally above. The following describes the additional features and advantages of the present invention. Persons skilled in the art should be aware that the disclosed concept and specific implementation manner can be easily used as a basis for modifying or designing other structures for implementing objectives the same as the present invention. Persons skilled in the art should also be aware that such equivalent structures do not depart from the spirit and scope of the present invention which are claimed in the patent application scope. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       For a more thorough understanding of the present invention and advantages of the present invention, the following descriptions are provided with reference to the accompanying drawings, where: 
         FIG. 1  is a three-dimensional exploded view of a pulley for an alternator according to the present invention; 
         FIG. 2  is a sectional assembled view of a pulley for an alternator according to the present invention; 
         FIG. 3  is a schematic structural view of a hollow connecting shaft according to the present invention; 
         FIG. 4  is a schematic structural view of a hollow core shaft according to the present invention; and 
         FIG. 5  is a schematic view of a rotor of an alternator according to the present invention. 
     
    
    
     MEANING OF REFERENCE NUMERALS 
     
         
         
           
               10  Pulley 
               20  Joint lever 
               30  Rotor 
               110  Outer wheel 
               111  Axle hole 
               112  Belt groove 
               113  Step portion 
               120  Clutch wheel 
               121  Pivot hole 
               122  Housing 
               123  Rolling member 
               124  Elastic member 
               125  Cap 
               130  Hollow connecting shaft 
               131  First end of the hollow connecting shaft 
               132  Second end of the hollow connecting shaft 
               133  First protruding portion 
               134  Stop wall of the hollow connecting shaft 
               140  Hollow core shaft 
               141  First end of the hollow core shaft 
               142  Second end of the hollow core shaft 
               143  First ball bearing 
               144  Second ball bearing 
               145  Protruding ring of the hollow core shaft 
               146  Second protruding portion 
               147  Stop wall of the hollow core shaft 
               148  Threaded surface 
               150  Elastic element 
               160  Tight-fit component 
               161  Positioning gasket 
               162  C-shaped retaining ring 
               170  Positioning casing 
               171  Protruding ring of the positioning casing 
               181  Oil seal element 
               182  Oil seal element 
               183  Positioning member 
               184  Dust cover 
               185  Positioning member 
           
         
       
    
     DETAILED DESCRIPTION OF EXEMPLARY EMBODIMENTS 
     The following embodiments describe the present invention in further detail. The embodiments are merely used to describe the present invention and illustrate the advantages of specific embodiments of the present invention, but it does not mean that the present invention is limited to such implementations. 
       FIG. 1  and  FIG. 2  are respectively a three-dimensional exploded view and a sectional assembled view of a pulley for an alternator according to the present invention. As shown in  FIG. 1  and  FIG. 2 , a pulley  10  for an alternator according to the present invention mainly includes an outer wheel  110 , a clutch wheel  120 , a hollow connecting shaft  130 , a hollow core shaft  140 , an elastic element  150 , and a tight-fit component  160 . The outer wheel  110  is a wheel-shaped member provided with an axle hole  111  at the center, and is provided with a belt groove  112  on an outer circumferential wall surface thereof and a step portion  113  on an inner circumferential wall surface thereof. The clutch wheel  120  is annular, provided with a pivot hole  121  at the center, and fixedly disposed in the axle hole  111  of the outer wheel  110 . For example, a groove may be provided in a concave manner on the inner circumferential wall surface of the outer wheel  110 , and an anaerobic adhesive is coated in the groove so that the clutch wheel  120  can be fixedly connected to an inner circumferential wall surface of the axle hole  111  of the outer wheel  110  by means of tight fit and adhesion of the anaerobic adhesive. One end of the clutch wheel  120  abuts against the step portion  113  of the outer wheel  110  to limit an axial position of the clutch wheel  120  and to ensure that an end surface of the clutch wheel  120  is perpendicular to the hollow connecting shaft  130  and the hollow core shaft  140 , prevent axial displacement of the clutch wheel  120  during high-speed rotation, and moreover, provide an axial positioning reference during assembly of components in the outer wheel  110 , which facilitates positioning during the assembly. 
     The hollow connecting shaft  130  has a first end  131  and a second end  132 . The first end  131  is rotatably disposed in the clutch wheel  120  so that the hollow connecting shaft  130  can maintain a co-rotational relationship with the outer wheel  110  in a first relative rotation direction by means of the clutch wheel  120  (for example, the hollow connecting shaft  130  rotates anticlockwise relative to the outer wheel  110 ), and it is disassociated from the co-rotational relationship with the outer wheel  110  in a second relative rotation direction to enter an idling state (for example, the hollow connecting shaft  130  rotates clockwise relative to the outer wheel  110 ), and at this time, the hollow connecting shaft  130  rotates independently of the outer wheel  110 . The hollow connecting shaft  130  is provided with a first protruding portion  133  on the second end  132 , as shown in  FIG. 3 . 
     In a preferred embodiment of the present invention, the clutch wheel  120  has a housing  122 , a plurality of rolling members  123 , a plurality of elastic members  124 , and two caps  125 . The clutch wheel  120  is provided with a positioning member  185  on an end opposite to the end abutting against the step portion  113  to limit the axial position of the clutch wheel  120  and prevent the caps  125  of the clutch wheel  120  from falling off. The positioning member may be a C-shaped retaining ring. For the detailed structure and operating principle of the clutch wheel  120 , reference may be made to Taiwan Patent Application No. 098129945 filed by the applicant on Sep. 4, 2009. However, the clutch wheel of the present invention is not limited thereto, and any speed-difference clutch apparatus capable of implementing the functions of the clutch wheel  120  described in the present invention may be designed as the clutch wheel  120  of the present invention. Moreover, in the present invention, two ends of the clutch wheel  120  are each provided with an oil seal element  181 / 182  so as to prevent a liquid (for example, a lubricating oil) in the clutch wheel  120  from permeating and polluting the interior of the pulley  10 . Furthermore, a positioning member  183  may be sleeved over one side of the oil seal element  182 . The positioning member  183  may be a C-shaped retaining ring, and may be sleeved over an inner side wall surface of the outer wheel  110  in a tight-fit manner, to limit axial positions of the oil seal elements  181  and  182  and the clutch wheel  120 . 
     The hollow core shaft  140  is disposed in the outer wheel  110  and has a first end  141  and a second end  142 . A first ball bearing  143  is sleeved over the first end  141 , and a second ball bearing  144  is sleeved over the second end  142 . The first ball bearing  143  and the second ball bearing  144  are both fixedly connected to the inner circumferential wall surface of the outer wheel  110  (for example, the outer wheel  110  may be provided with two grooves on the inner circumferential wall surface in a concave manner, and an anaerobic adhesive is coated in the grooves so that the first ball bearing  143  and the second ball bearing  144  can be fixedly connected to the inner circumferential wall surface of the axle hole  111  of the outer wheel  110  by means of tight fit and adhesion of the anaerobic adhesive) so that the hollow core shaft  140  is rotatable relative to the outer wheel  110 . In addition, the hollow core shaft  140  passes through the hollow connecting shaft  130 , and the first end  141  of the hollow core shaft  140  protrudes from the first end  131  of the hollow connecting shaft  130 . A protruding ring  145  is annularly arranged at the second end  142  of the hollow core shaft  140 . The protruding ring  145  is rotatably arranged on the second end  132  of the hollow connecting shaft  130 . A second protruding portion  146  is provided in a protruding manner in a direction towards the hollow connecting shaft  130 , and the second protruding portion  146  corresponds to the first protruding portion  133  so that after the hollow connecting shaft  130  and the hollow core shaft  140  rotate by a particular degree relative to each other, the first protruding portion  133  of the hollow connecting shaft  130  contacts the second protruding portion  146  of the hollow core shaft  140 , thereby stopping relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140 . For example, when the hollow connecting shaft  130  is provided with two first protruding portions  133  at the second end  132 , and when the hollow core shaft  140  is provided with three second protruding portions  146  at the second end  142 , the hollow core shaft  140  can only rotate clockwise or anticlockwise by 120 degrees relative to the hollow connecting shaft  130  after being sleeved over the hollow connecting shaft  130  because relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  is stopped when the first protruding portions  133  contact the second protruding portions  146 . 
     The elastic element  150  is disposed between the second end  132  of the hollow connecting shaft  130  and the second end  142  of the hollow core shaft  140 . In a preferred embodiment of the present invention, the elastic element is a torque spring, and a wire profile of the torque spring may be circular, elliptical, or rectangular. When the wire profile of the torque spring is rectangular, two end surfaces of the torque spring may be grinded so as to enhance an axial positioning capability of the torque spring and control a free length of the spring more precisely. The hollow connecting shaft  130  is provided with a stop wall  134  in a concave manner on an inner circumferential wall surface of the second end  132  (as shown in  FIG. 3 ) so that one end of the elastic element  150  can abut against the stop wall  134 , and the elastic element  150  may also be fixedly connected to the stop wall  134 . In addition, The hollow core shaft  140  is also provided with a stop wall  147  on an inner side of the protruding ring  145  of the second end  142  (as shown in  FIG. 4 ) so that the other end of the elastic element  150  can abut against the stop wall  147 , and the elastic element  150  may also be fixedly connected to the stop wall  147 . When the two ends of the elastic element  150  are fixedly connected to the stop wall  134  of the hollow connecting shaft  130  and the stop wall  147  of the hollow core shaft  140 , relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  presses or stretches the elastic element  150 ; when the two ends of the elastic element  150  merely abut against but are not fixedly connected to the stop wall  134  of the hollow connecting shaft  130  or the stop wall  147  of the hollow core shaft  140 , relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  only presses the elastic element  150 . 
     The tight-fit component  160  is a C-shaped retaining ring; the C-shaped retaining ring is sleeved over the outer circumferential wall surface of the first end  141  of the hollow core shaft  140  in a tight-fit manner, and is tightly fit with a tail end surface of the first end  131  of the hollow connecting shaft  130 . Therefore, under a friction between the tight-fit component  160  and the end surface of the first end  131  of the hollow connecting shaft  130  and a friction between the tight-fit component  160  and the outer circumferential wall surface of the first end  141  of the hollow core shaft  140 , the hollow connecting shaft  130  and the hollow core shaft  140  drive each other and corotate coaxially, as shown in  FIG. 3 . 
     A positioning casing  170  is further sleeved over the first ball bearing  143 , and the positioning casing  170  is a hollow annular pipe provided with a protruding ring  171  at one end; therefore, the protruding ring  171  penetrates the first ball bearing  143  and provides an abutting and cushioning function when the pulley  10  is installed on an alternator, and an axial position of the pulley  10  on the alternator is limited by the positioning casing  170 . 
     The hollow core shaft  140  is provided with a threaded surface  148  on an inner circumferential wall surface thereof, the threaded surface  148  may be screwed with a joint lever  20  having corresponding threads, and the joint lever  20  is connected to a rotor  30  of the alternator so that the hollow core shaft  140  and the rotor  30  corotate synchronously (as shown in  FIG. 5 ). In addition, an end, corresponding to the second end  142  of the hollow core shaft  140 , of the outer wheel  110  is arranged with a dust cover  184  so as to prevent external dust from entering the outer wheel  110 . 
     With the structure described above, when a mechanical energy generating source provides an external force to drive the outer wheel  110  to rotate, the outer wheel  110  rotates relative to the hollow connecting shaft  130  in the first relative rotation direction and drives, through the clutch wheel  120 , the hollow connecting shaft  130  to rotate synchronously, and with the friction provided by the tight-fit component  160 , the hollow connecting shaft  130  drives the hollow core shaft  140  to rotate. At this time, if the friction provided by the tight-fit component  160  is insufficient to drive the hollow core shaft  140  to rotate, the hollow connecting shaft  130  rotates relative to the hollow core shaft  140 , which causes the stop wall  134  at the second end  132  of the hollow connecting shaft  130  to press the elastic element  150 , and while being pressed, the elastic element  150  pushes the stop wall  147  at the second end  142  of the hollow core shaft  140 , thereby driving the hollow core shaft  140  to rotate. At this time, if a relative rotation angle between the hollow connecting shaft  130  and the hollow core shaft  140  exceeds a predetermined value (for example, 120 degrees), the first protruding portion  133  of the hollow connecting shaft  130  contacts the second protruding portion  146  of the hollow core shaft  140 , thereby stopping relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  so as to avoid pressing the elastic element  150  excessively and damaging the structure thereof, and to set the hollow connecting shaft  130  and the hollow core shaft  140  in a synchronous co-rotational relationship; the hollow core shaft  140  also drives the rotor  30  to rotate so that the alternator generates an induced current. 
     In addition, if the outer wheel  110  is originally in a rotation state, when the mechanical energy generating source provides an external force to accelerate the rotation of the outer wheel  110 , an operating principle of the pulley  10  of the present invention is substantially the same as the aforementioned operating principle in the case of starting the outer wheel  110  to rotate, and therefore it is not repeated herein. 
     On the contrary, when the external force stops driving the outer wheel  110  to rotate, the hollow core shaft  140  continues to rotate due to inertia of the rotor  30 . At this time, the hollow core shaft  140  drives, by using the friction provided by the tight-fit component  160 , the hollow connecting shaft  130  to rotate relative to the outer wheel  110  in the second relative rotation direction so that the hollow connecting shaft  130  is disassociated from the co-rotational relationship with the outer wheel  110 . At this time, if the friction provided by the tight-fit component  160  is insufficient to drive the hollow connecting shaft  130  to rotate, the hollow core shaft  140  rotates relative to the hollow connecting shaft  130 ; if the elastic element  150  merely abuts against but is not fixedly connected to the hollow connecting shaft  130  and the hollow core shaft  140 , the hollow core shaft  140  keeps rotating relative to the hollow connecting shaft  130  until the second protruding portion  146  of the hollow core shaft  140  contacts the first protruding portion  133  of the hollow connecting shaft  130 , thereby stopping relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  and setting the hollow connecting shaft  130  and the hollow core shaft  140  in a synchronous co-rotational relationship so that the hollow connecting shaft  130  and the hollow core shaft  140  rotate relative to the outer wheel  110  in the second relative rotation direction. 
     If the elastic element  150  is fixedly connected to the hollow connecting shaft  130  and the hollow core shaft  140 , when the friction provided by the tight-fit component  160  is insufficient to drive the hollow connecting shaft  130  to rotate, the hollow core shaft  140  rotates relative to the hollow connecting shaft  130  and stretches the elastic element  150 , and while being stretched, the elastic element  150  pulls the second end  132  of the hollow connecting shaft  130 , thereby driving the hollow connecting shaft  130  to rotate relative to the outer wheel  110  in the second relative rotation direction so that the hollow connecting shaft  130  is disassociated from the co-rotational relationship with the outer wheel  110 . At this time, if rotation of the hollow connecting shaft  130  relative to the hollow core shaft  140  exceeds a predetermined value (for example, 120 degrees), the first protruding portion  133  of the hollow connecting shaft  130  contacts the second protruding portion  146  of the hollow core shaft  140 , thereby stopping relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  so as to avoid stretching the elastic element  150  excessively and damaging the structure thereof, and to set the hollow connecting shaft  130  and the hollow core shaft  140  in a synchronous co-rotational relationship so that the hollow connecting shaft  130  and the hollow core shaft  140  rotate relative to the outer wheel  110  in the second relative rotation direction. 
     In addition, if the external force driving the outer wheel  110  decreases, the operating principle of the pulley  10  of the present invention is substantially the same as the aforementioned operating principle in the case in which the outer wheel  110  stops rotating, and therefore it is not repeated herein. 
     In the pulley  10  of the present invention, a belt (not shown in the figure) may be wound on the belt groove  112  of the outer wheel  110  so that the mechanical energy generating source can provide an external force to drive the belt, thereby driving the outer wheel  110  to rotate. In addition, the pulley  10  of the present invention is applicable to an alternator system, such as a power generation system and an alternator system of a vehicle. The pulley of the present invention is especially suitable to be used as a stator structure of an automotive alternator. When the pulley of the present invention is applied to an automotive alternator, the mechanical energy generating source is an automobile engine. 
     In a preferred embodiment of the present invention, the tight-fit component  160  of the pulley  10  of the present invention may be omitted, and two ends of the elastic element  150  are fixedly connected to the stop wall  147  at the second end  142  of the hollow core shaft  140  and the stop wall  134  at the second end  132  of the hollow connecting shaft  130 . In this manner, when an external force drives the outer wheel  110  to rotate, the outer wheel  110  rotates relative to the hollow connecting shaft  130  in the first relative rotation direction and drives, through the clutch wheel  120 , the hollow connecting shaft  130  to rotate synchronously; the second end  132  of the hollow connecting shaft  130  presses the elastic element  150 , and while being pressed, the elastic element  150  pushes the stop wall  147  at the second end  142  of the hollow core shaft  140 , thereby driving the hollow core shaft  140  to rotate. At this time, if a rotation angle of the hollow connecting shaft  130  relative to the hollow core shaft  140  exceeds a predetermined value, the first protruding portion  133  of the hollow connecting shaft  130  contacts the second protruding portion  146  of the hollow core shaft  140 , thereby stopping relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  so as to prevent the elastic element  150  from being pressed excessively, setting the hollow connecting shaft  130  and the hollow core shaft  140  in a synchronous co-rotational relationship, and drive the rotor  30  to rotate. 
     On the contrary, when the external force decreases or stops driving the outer wheel  110  to rotate, the hollow core shaft  140  continues to rotate due to inertia of the rotor  30  and stretches the elastic element  150 , and while being stretched, the elastic element  150  pulls the second end  132  of the hollow connecting shaft  130 , thereby driving the hollow connecting shaft  130  to rotate relative to the outer wheel  110  in the second relative rotation direction so that the hollow connecting shaft  130  is disassociated from the co-rotational relationship with the outer wheel  110  and idles in the clutch wheel  120 . At this time, if a rotation angle of the hollow connecting shaft  130  relative to the hollow core shaft  140  exceeds a predetermined value, the first protruding portion  133  of the hollow connecting shaft  130  contacts the second protruding portion  146  of the hollow core shaft  140 , thereby stopping relative rotation between the hollow connecting shaft  130  and the hollow core shaft  140  so as to prevent the elastic element  150  from being stretched excessively, and to set the hollow connecting shaft  130  and the hollow core shaft  140  in a synchronous co-rotational relationship, in which the hollow connecting shaft  130  and the hollow core shaft  140  idle in the outer wheel  110 . In addition, in a preferred embodiment of the present invention, in the pulley  10  of the present invention, the first protruding portion  133  and the second protruding portion  146  may not be disposed, the protruding ring  145  at the second end  142  of the hollow core shaft  140  is directly sleeved over the second end  132  of the hollow connecting shaft  130 , and two ends of the elastic element  150  are fixedly connected to the stop wall  147  at the second end  142  of the hollow core shaft  140  and the stop wall  134  at the second end  132  of the hollow connecting shaft  130 . Therefore, when an external force drives the outer wheel  110  to rotate, the outer wheel  110  rotates relative to the hollow connecting shaft  130  in the first relative rotation direction and drives, through the clutch wheel  120 , the hollow connecting shaft  130  to rotate synchronously, and the hollow connecting shaft  130  drives, through the tight-fit component  160 , the hollow core shaft  140  to rotate. At this time, if the friction provided by the tight-fit component  160  is insufficient to drive the hollow core shaft  140  to rotate, the stop wall  134  at the second end  132  of the hollow connecting shaft  130  presses the elastic element  150 , and while being pressed, the elastic element  150  pushes the stop wall  147  at the second end  142  of the hollow core shaft  140 , thereby driving the hollow core shaft  140  to rotate, so as to drive the rotor  30  of the alternator to rotate. 
     On the contrary, when the external force decreases or stops driving the outer wheel  110  to rotate, the hollow core shaft  140  continues to rotate due to inertia of the rotor  30  and drives, through the tight-fit component  160 , the hollow connecting shaft  130  to rotate relative to the outer wheel  110  in the second relative rotation direction. At this time, if the friction provided by the tight-fit component  160  is insufficient to drive the hollow connecting shaft  130  to rotate, the hollow core shaft  140  stretches the elastic element  150 , and while being stretched, the elastic element  150  pulls the second end  132  of the hollow connecting shaft  130 , thereby driving the hollow connecting shaft  130  to rotate relative to the outer wheel  110  in the second relative rotation direction so that the hollow connecting shaft  130  is disassociated from the co-rotational relationship with the outer wheel  110  and idles in the clutch wheel  120 . 
     Further, in a preferred embodiment of the present invention, in the pulley  10  of the present invention, the tight-fit component  160 , the first protruding portion  133 , and the second protruding portion  146  may not be disposed; the protruding ring  145  at the second end  142  of the hollow core shaft  140  is directly sleeved over the second end  132  of the hollow connecting shaft  130 , and two ends of the elastic element  150  are fixedly connected to the stop wall  147  at the second end  142  of the hollow core shaft  140  and the stop wall  134  at the second end  132  of the hollow connecting shaft  130 . In this manner, when an external force drives the outer wheel  110  to rotate, the outer wheel  110  rotates relative to the hollow connecting shaft  130  in the first relative rotation direction and drives, through the clutch wheel  120 , the hollow connecting shaft  130  to rotate synchronously; the stop wall  134  at the second end  132  of the hollow connecting shaft  130  presses the elastic element  150 , and while being pressed, the elastic element  150  pushes the stop wall  147  at the second end  142  of the hollow core shaft  140 , thereby driving the hollow core shaft  140  to rotate. 
     On the contrary, when the external force decreases or stops driving the outer wheel  110  to rotate, the hollow core shaft  140  continues to rotate due to inertia of the rotor  30  and stretches the elastic element  150 , and while being stretched, the elastic element  150  pulls the second end  132  of the hollow connecting shaft  130 , thereby driving the hollow connecting shaft  130  to rotate relative to the outer wheel  110  in the second relative rotation direction so that the hollow connecting shaft  130  is disassociated from the co-rotational relationship with the outer wheel  110  and idles in the clutch wheel  120 . 
     Although the present invention and advantages thereof are described in detail above, it should be understood that variations, alternative solutions, and modifications can be made herein without departing from the spirit and scope of the present invention which are defined in the appended patent application scope. Moreover, the scope of the present invention is not limited to the specific implementations of the process, machine, product, material composition, means, method, and steps described in the specification. For example, persons skilled in the art can easily learn from the disclosure of the present invention that existing or to-be-developed processes, machines, products, material compositions, means, methods and steps that substantially implement the same function or substantially achieve the same result as the corresponding implementation manner described herein may be used. Correspondingly, the appended patent application scope is intended to cover such processes, machines, products, material compositions, means, methods or steps.