Abstract:
A direct-action-type electrically-operated valve comprises a valve base provided with a valve cavity, a motor disposed on the upper end the valve base, and a screw rod. The screw rod is fitted and connected to a nut by means of threads. The nut is connected to a spool. Axial positions of a rotor of the motor and the valve base are relatively fixed. The upper end of the screw rod is fixedly connected to the rotor. Driven by the nut, the spool moves along the axial direction of the valve cavity to open or close a valve opening disposed on the valve base. The spool is a tubular structure provided with a balancing channel, and a seal piece for dividing the valve cavity into two independent cavities is disposed on the periphery of the spool.

Description:
[0001]    This application claims the benefit of priorities to Chinese Patent Application No. 201410026132.1 titled “DIRECT-ACTING ELECTRIC VALVE”, filed with the Chinese State Intellectual Property Office on Jan. 20, 2014, and Chinese Patent Application No. 201410025331.0 titled “DIRECT-ACTING ELECTRIC VALVE AND ASSEMBLY METHOD THEREFOR”, filed with the Chinese State Intellectual Property Office on Jan. 20, 2014, the entire disclosures of which are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The present application relates to the technical field of fluid control components, and particularly to a direct-acting electric valve. In addition, the present application further relates to an assembly method for assembling the direct-acting electric valve. 
       BACKGROUND 
       [0003]    In commercial air conditioners, such as multi-air conditioner or modular air conditioners, one outdoor unit system is connected with multiple indoor unit systems, and a flow control valve is required to be mounted in a refrigerant loop of each indoor unit for cutting off refrigerant or adjusting the flow. The flow control valve is required to be capable of being adjusted to any opening degree and acting stably. Further, since the refrigerant loop of each indoor unit needs one flow control valve, the flow control valve is required to meet the requirement of minimization and large-capacity. 
         [0004]    Currently, the flow control valve is generally a pilot control valve, and a valve core of the pilot valve is powered by a motor, and a main valve port is opened or closed by a main valve core and a valve core of the pilot valve cooperatively. However, when the pilot control valve opens the main valve port, the opening area is increased sharply, thus the flow changes sharply. That is to say, the pilot control valve cannot adjust the flow precisely. 
         [0005]    For precisely adjusting the flow of the refrigerant, a direct-acting control valve may be employed. In a conventional direct-acting control valve, a screw rod is connected to and driven by an output shaft of a motor via a gear system, and the screw rod is cooperated with a nut by screw threads. The nut is connected with a valve core and is limited in position to allow the nut to be slidable along an axial direction of the screw rod but unable to be rotated in a circumferential direction of the screw rod. In operation, the motor starts, and an output shaft of the motor rotates, and the rotation is transmitted to the screw rod via the gear system, and with the rotation of the screw rod, the nut slides in the axial direction, which allows the valve core to slide in the axial direction, and further achieves the purpose of adjusting an opening degree of the valve port. 
         [0006]    Since in the commercial air-conditioners such as multi-air conditioner or modular air conditioners, the area of the valve port of the flow control valve is required to be large, thus requiring a large driving force, and if the direct-acting control valve is adopted, a large size motor must be used for acquiring the large driving force, thus, the size of the control valve is excessively large, thus, not only the cost is increased, but also mounting and detaching are inconvenient. 
         [0007]    In another kind of conventional direct-acting control valve, a screw rod is fixed to a rotor of a motor, and is cooperated with a nut by screw threads, and a lower end of the screw rod is directly cooperated with a valve core, and the nut is fixed to a valve seat. In operation, the screw rod is rotated by the rotor of the motor, and since the screw rod is cooperated with the nut by screw threads and the nut is fixed, the screw rod may further be moved axially by the rotor, thus further allowing a valve core to open or close the valve port. However, when this kind of direct-acting control valve operates, the position of the rotor changes with respect to an axial center of the coil component due to an axial motion of the rotor, thus the rotor cannot be kept at the axial center of the coil component, which further reduces the driving force, and also. The size of the motor is also required to be increased for opening and closing a valve port with a large diameter. 
         [0008]    In view of this, a technical issue to be addressed by those skilled in the art presently is to improve a direct-acting control valve, through which a valve port with a large diameter can be opened and closed by a small-sized motor. 
       SUMMARY 
       [0009]    An object of the present application is to provide a direct-acting electric valve, through which a valve port with a large diameter can be opened and closed by a small-sized motor, thereby meeting the requirement of minimization and large capacity. 
         [0010]    For addressing the technical issues, a direct-acting electric valve is provided according to the present application, which includes a valve seat provided with a valve cavity, a motor arranged at an upper end of the valve seat, and a screw rod. The screw rod is cooperated with and connected to a nut by means of screw threads, and the nut is connected to a valve core. Axial positions of a rotor of the motor and the valve seat are fixed with respect to each other, and an upper end of the screw rod is fixedly connected to the rotor, and the valve core is movable axially in the valve cavity as the nut moves, so as to open or close the valve port arranged on the valve seat. The valve core is a column structure with an balancing passage, and a sealing member, which separates the valve cavity into two independent cavities, is provided outside a circumferential surface of the valve core. 
         [0011]    As designed above, in operation, the rotor is rotated by the coil component of the motor. Since the axial positions of the rotor and the valve seat are fixed and the screw rod is fixedly connected to the rotor, only the screw rod is rotated by the rotor. The nut cooperated with the screw rod by screw threads converts the rotation of the screw rod to the axial movement, thus moving the valve core axially, so as to open or close the valve port. The above structure dispenses the gear system, reduces unnecessary transmission, thereby reducing the power loss, and giving a direct, reliable and sensitive response. Further, the axial positions of the rotor and the valve seat are fixed with respect to each other, i.e., the relative position between the rotor and the coil component in operation is fixed, thus, the driving force provided by the motor will not change along with the axial moving of the valve core. In addition, the valve core has an balancing passage. When opening the valve, the valve core suffers a small resistance. Apparently, for the valve port with a same size, the size of the motor in this solution is smaller than the size of the motor in the conventional technology, which meets the requirement of minimization and large capacity to the valve body. 
         [0012]    The axial positions of the rotor of the motor and the upper valve seat are fixed with respect to each other, and the screw rod is fixedly connected to the rotor, thus, in operation, the screw rod is rotated by the motor directly, and the nut cooperated with the screw rod by screw threads converts the rotation of the screw rod into an axial movement, thereby moving the valve core axially, so as to open or close the valve port, which dispenses the gear system, and reduces unnecessary transmission, and has a small power loss, and a direct and reliable response. 
         [0013]    The axial positions of the rotor of the motor and the upper valve seat are fixed with respect to each other, such that the relative position between the rotor and the coil component of the motor is fixed, thus, in operation, a driving moment of the motor will not change along with an axial movement of the valve core, which, in conjunction with the above description, can effectively reduce the size of the motor. 
         [0014]    Preferably, the screw rod is fixed to the rotor via an annular connecting sheet by welding; and a peripheral edge of a through hole of the annular connecting sheet extends axially to form a protrusion. 
         [0015]    Preferably, the rotor is a permanent magnet rotor, and the ratio of an outer diameter of the rotor to the diameter of the valve port ranges from 0.8 to 1.8. 
         [0016]    Preferably, the nut includes a small diameter portion cooperated with the screw rod by screw threads and a large diameter portion, and 
         [0017]    an upper end of the valve core is provided with a receiving cavity for receiving the large diameter portion of the nut, and an upper end of an inner wall of the receiving cavity is provided with an annular step having a stepped surface facing to the screw rod, and a nut cover plate is provided on the annular step, which restricts the relative position between the nut and the valve core in an axial direction. 
         [0018]    Preferably, the balancing passage of the valve core includes the receiving cavity, an axial through hole in communication with the receiving cavity, and a vent groove arranged in a circumferential wall of the nut. 
         [0019]    Preferably, a lower end of an inner wall of the axial through hole is provided with an annular groove, and a sieve is provided in the annular groove. 
         [0020]    Preferably, a bottom end of the valve core is provided with an axial protrusion, and a sealing ring is riveted onto the axial protrusion, and in the case that the valve core is in a fully closed state, a lower end surface of the sealing ring fits against an end surface of the valve port to form a seal. 
         [0021]    Preferably, an axial central line of the rotor is coincident with an axial central line of the coil component of the motor. 
         [0022]    An assembly method for a direct-acting electric valve includes the following steps: 
         [0023]    mounting an assembled valve core assembly to an assembled lower valve seat assembly; 
         [0024]    screwing a screw rod of an assembled upper valve seat assembly into a nut of the valve core assembly, and fixing an upper valve seat of the upper valve seat assembly to a lower valve seat of the lower valve seat assembly by welding; and 
         [0025]    mounting a housing and a fixing rest by pressing, and assembling a coil component of a motor. 
         [0026]    The direct-acting electric valve according to the present application employs the above assembling method for the direct-acting electric valve, since the direct-acting electric valve has the above technical effects, the assembling method for assembling the direct-acting electric valve should also have the corresponding technical effects. 
         [0027]    Preferably, the assembling of the upper valve seat assembly includes the following steps: 
         [0028]    mounting a screw rod, a bearing and an upper valve seat by pressing; 
         [0029]    mounting a spacer to an upper end of the bearing, and riveting or welding the spacer to the upper valve seat; 
         [0030]    clamping a bush between the screw rod and the spacer, which allows the bush to abut against an upper end of the bearing and be fixed to the screw rod by welding; and 
         [0031]    sleeving a rotor of a motor on an upper end of the upper valve seat, and fixedly connecting the rotor of the motor to the screw rod. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0032]      FIG. 1  is a sectional view of an embodiment of a direct-acting electric valve according to the present application, which shows a valve core is in a fully opened state; 
           [0033]      FIG. 2  is a sectional view of the embodiment of the direct-acting electric valve according to the present application, which shows the valve core is in a fully closed state; 
           [0034]      FIG. 3  shows the structure of an balancing passage of a valve core assembly in the case that the valve core is in a fully closed state; 
           [0035]      FIG. 4  is a schematic view showing the structure of an upper valve seat assembly in  FIG. 1 ; 
           [0036]      FIG. 5  is a sectional schematic view showing the upper valve seat assembly in  FIG. 1 ; 
           [0037]      FIG. 6  is a top view of  FIG. 5 ; 
           [0038]      FIG. 7  is a schematic view showing the structure of a valve core assembly in  FIG. 1 ; 
           [0039]      FIG. 8  is a sectional schematic view of the valve core assembly in  FIG. 1 ; 
           [0040]      FIG. 9  is a top view of  FIG. 8 ; 
           [0041]      FIG. 10  is a schematic view showing the structure of a valve seat core in  FIG. 1 ; 
           [0042]      FIG. 11  is a schematic view showing the structure of a lower valve seat in  FIG. 1 ; 
           [0043]      FIG. 12  is an enlarged schematic view showing an upper cavity of an upper valve seat; 
           [0044]      FIG. 13  is a schematic view showing the structure of the upper valve seat; 
           [0045]      FIG. 14  is a schematic view showing the structure of a retainer ring; 
           [0046]      FIG. 15  shows a schematic flow chart of assembling a direct-acting electric valve; 
           [0047]      FIG. 16  shows a schematic flow chart of assembling an upper valve seat assembly; and 
           [0048]      FIG. 17  shows a schematic flow chart of assembling a valve core assembly. 
       
    
    
     DETAILED DESCRIPTION 
       [0049]    An object of the present application is to provide a direct-acting electric valve, through which a valve port with a large diameter can be opened and closed by a small-sized motor, thus meeting the requirement of minimization and large capacity. 
         [0050]    For those skilled in the art to better understand the solutions of the present application, the present application is further described in detail with reference to drawings and embodiments. 
         [0051]    It is noted that, the orientation terms referred herein are defined by the positions of the components in  FIGS. 1 to 11  and the position relationship between the components, which is only for clarity and ease of description of the technical solutions. It should be appreciated that, the orientation terms used herein should not limit the protection scope of the present application. 
         [0052]    Reference is made to  FIGS. 1 and 2 .  FIG. 1  is a sectional view of an embodiment of a direct-acting electric valve according to the present application, which shows the structure of a valve core is in a fully opened state.  FIG. 2  is a sectional view of the embodiment of the direct-acting electric valve according to the present application, which shows the structure of the valve core is in a fully closed state. 
         [0053]    In the embodiment, a direct-acting electric valve includes a valve seat  30  with a valve cavity therein, a housing  20  connected to the valve seat  30 , a motor  10  arranged at an upper end of the valve seat  30 , and a screw rod  312 . The screw rod  312  is connected to a nut  41  by means of screw threads, and the nut  41  is connected to a valve core  42 . A rotor  12  of the motor  10  is arranged in the housing  20  and fixed in an axial direction of the valve seat  30 . A coil component  11  is sleeved on the housing  20 , and an upper end of the screw rod  312  is fixedly connected to the rotor  12 , and the valve core  42  is movable in the axial direction of the valve cavity as t the nut  41  moves, so as to open or close a valve port  30   a  arranged on the valve seat  30 . The valve core  42  is a cylindrical structure with an balancing passage, and a sealing member, which separates the valve cavity into two independent cavities, is provided outside the circumferential surface of the valve core  42 . 
         [0054]    The direct-acting electric valve includes a valve core assembly  400  and a lower valve seat assembly  302 . The lower valve seat assembly  302  includes a lower valve seat  32  and a valve seat core  321  arranged in an inner cavity of the lower valve seat  32 . The valve core assembly  400  includes a nut  41  and a valve core  42  connected to the nut  41 . The direct-acting electric valve further includes an upper valve seat assembly  301 , which includes an upper valve seat  31 , a screw rod  312  and a rotor  12  of a motor  10 . The upper valve seat  31  is fixedly connected to the lower valve seat  32 , and the inner cavities of the upper valve seat  31  and the lower valve seat  32  are communicated with each other. The rotor  12  is sleeved on an upper end of the upper valve seat  31  and fixed in an axial direction of the upper valve seat  31 . An upper end of the screw rod  312  passes through the upper valve seat  31  and is fixedly connected to the rotor  12 , and a lower end of the screw rod  312  is cooperated with the nut  41  by screw threads. The valve core  42  is movable in an axial direction of a core cavity of the valve seat core  321  as the nut  41  moves, so as to open or close a valve port  32   a  arranged on the lower valve seat  32 . 
         [0055]    The direct-acting electric valve has following technical effects. 
         [0056]    The axial positions of the rotor  12  of the motor  10  and the upper valve seat  31  are fixed with respect to each other, and the screw rod  312  is fixedly connected to the rotor  12 , thus, in operation, the screw rod  312  is rotated by the motor  10  directly, and the nut  41  cooperated with the screw rod  312  by screw threads converts the rotation of the screw rod  312  into an axial movement, thereby allowing the valve core  42  to move axially and further opening or closing the valve port  32   a , which dispenses the gear system, and reduces unnecessary transmission, and has a small power loss and a more direct and reliable response. 
         [0057]    The axial positions of the rotor  12  of the motor  10  and the upper valve seat  31  are fixed with respect to each other, thus the relative position between the rotor  12  and the coil component  11  of the motor  10  is fixed, thus, in operation, a driving moment of the motor  10  will not change along with the axial movement of the valve core  42 , which, in conjunction with the above description, can effectively reduce the size of the motor  10 . 
         [0058]    The housing  20  is sleeved on the upper valve seat  31 , the coil component  11  of the motor  10  is sleeved on the housing  20 , and is supported by a fixing rest  21  sleeved on the housing  20 . 
         [0059]    As designed above, in operation, the rotor  12  is rotated by the coil component  11  of the motor  10 . Since the axial positions of the rotor  12  and the valve seat  30  are fixed, and the screw rod  312  is fixedly connected to the rotor  12 , only the screw rod  312  is rotated by the rotor  12 . The nut  41  cooperated with the screw rod  312  by screw threads converts the rotation of the screw rod  312  to the axial movement, thus allowing the valve core  42  to move axially and further opening or closing the valve port  30   a . The above structure dispenses the gear system, reduces unnecessary transmission, thereby reducing the power loss, and has a direct, reliable and sensitive response. Further, the axial positions of the rotor  12  and the valve seat  30  are fixed with respect to each other, i.e., in operation, the relative position between the rotor  12  and the coil component  11  is fixed, thus, the driving force provided by the motor  10  will not change along with the axial moving of the valve core  42 . Apparently, for the valve ports  30   a  with the same size, the size of the motor in this solution is smaller than the size of the motor in the conventional technology, which meets the requirement of minimization and large capacity of the valve body. 
         [0060]    In a preferred solution, an axial central line of the rotor  12  is coincident with an axial central line of the coil component  11 . In another preferred solution, axial central lines of the coil component  11 , a bearing  311  and the rotor  12  are coincident with each other, thus allowing the driving force provided by the motor  10  to be maximized. 
         [0061]    In this embodiment, the valve seat  30  includes the upper valve seat  31  and the lower valve seat  32  which are fixedly connected. The valve port  30   a  is arranged in the lower valve seat  32 . 
         [0062]    Reference is made to  FIGS. 4 to 6 .  FIG. 4  is a schematic view showing the structure of an upper valve seat assembly in  FIG. 1 .  FIG. 5  is a sectional schematic view showing the upper valve seat assembly in  FIG. 1 .  FIG. 6  is a top view of  FIG. 5 . 
         [0063]    As shown in the drawings, the upper valve seat  31  includes a small diameter segment inserted into the rotor  12  and a large diameter segment, and the screw rod  312  passes through the inner cavity of the upper valve seat  31  and is fixedly connected to the rotor  12 . 
         [0064]    In a specific solution, the screw rod  312  is fixed to the rotor  12  via an annular connecting sheet  315  by welding; and the annular connecting sheet  315  is in an annular shape with a middle through hole, and may be sleeved on the screw rod  312 . An outer side of the annular connecting strip  312  is fixed to the rotor  12  by welding, which ensures the connecting strength of the screw rod  312  and the rotor  12 . 
         [0065]    Further, a peripheral edge of the through hole of the annular connecting sheet  315  extends axially to form a protrusion. Thus, the protrusion is sleeved on the screw rod  312 , which may increase the contact area of the annular connecting sheet  315  and the screw rod  312 , thereby increasing the connecting strength between the screw rod  312  and the rotor  12 , and ensuring the screw rod  312  to be rotated by the rotor  12 . 
         [0066]    In the specific solution, the annular connecting sheet  315  and the rotor  12  may be an integral structure for facilitating the assembling. 
         [0067]    The inner cavity of the upper valve seat  31  is separated by an annular plate into an upper cavity and a lower cavity, and the annular plate and the upper valve seat  31  may be integrated. A bearing  311  is provided in the upper cavity, and an inner ring of the bearing  311  fits against an outer circumferential surface of the screw rod  312 , and an outer ring of the bearing  311  fits against an inner wall of the upper cavity. In this way, the axial positions of the screw rod  312  and the upper valve seat  31  are fixed with respect to each other via the bearing  311 , thus the axial positions of the rotor  12  and the upper valve seat  31  are fixed with respect to each other, i.e., the relative position between the bearing  311 , the screw rod  312  and the rotor  12  is fixed in the above described structure of the upper valve seat  31 . 
         [0068]    A circumferential wall of the upper valve seat  31  may further be provided with an balancing hole  31   d , and the balancing hole  31   d  may be provided in the small diameter segment of the upper valve seat  31  for balancing the pressure and reducing the rotational resistance of the screw rod  312 . 
         [0069]    Further, an upper end of the bearing  311  is further provided with a bush  313 , and the bush  313  is sleeved on the screw rod  312 , and is fixed to the screw rod  312  by welding, which may prevent the inner ring of the bearing  311  from being disengaged from the outer ring of the bearing  311  due to an axial force. A spacer  314  may further be sleeved on the bush  313 , and the spacer  314  may be welded to the upper end of the upper valve seat  31 , which may further prevent the disengagement of the inner ring and the outer ring of the bearing  311  from each other. 
         [0070]    The upper valve seat  31 , the bearing  311 , the screw rod  312  and the rotor  12  may be defined as the upper valve seat assembly. 
         [0071]    It is to be noted that, the above description provides a way for axially positioning the rotor  12  and the valve seat  30  only as an example, and in practical, the axial positions of the rotor  12  and the valve seat  30  may also be fixed by other manners. 
         [0072]    As shown in  FIG. 12 , an upper end of the annular plate of the upper valve seat  31  is provided with an annular step  31   f  with a stepped surface facing to the bearing  311 , which may prevent the inner ring of the bearing  311  from directly rubbing against the annular plate during the rotation. 
         [0073]    A threaded segment of the screw rod  312  is located at a lower cavity of the upper valve seat  31 , and the lower cavity includes a small diameter cavity  31   a  and a large diameter cavity  31   b . The small diameter cavity  31   a  is configured to guide the nut  41  connected to the screw rod  312  by screw threads, and the large diameter cavity  31   b  is configured to cooperate with the inner cavity of the lower valve seat  32  so as to form the valve cavity. That is to say, the lower cavity of the upper valve seat  31  provides a space for the valve core assembly  400  consisting of the nut  41  and the valve core  42  to move axially. The structural arrangement of the upper valve seat  31  allows the axial size of the valve body to be reduced, and facilitates the minimization of the valve body. 
         [0074]    Reference is made to  FIGS. 7 to 9 .  FIG. 7  is a schematic view showing the structure of the valve core assembly in  FIG. 1 .  FIG. 8  is a sectional schematic view of the valve core assembly in  FIG. 1 .  FIG. 9  is a top view of  FIG. 8 . 
         [0075]    The valve core assembly  400  includes the nut  41  and the valve core  42 . The nut  41  includes a small diameter portion  41   a  cooperated with the screw rod  312  by screw threads and a large diameter portion  41   b . An upper end of the valve core  42  has a receiving cavity for receiving the large diameter portion  41   b , and an upper end of an inner wall of the receiving cavity is provided with an annular step having a stepped surface facing to the rotor  12 , and a nut cover plate  411  is provided on the annular step, which limits the relative position between the nut  41  and the valve core  42  in the axial direction. 
         [0076]    When the rotor  12  rotates such that the screw rod  312  is rotated and the nut  41  is moved upward, the valve core  42  is move upward together with the nut  41  since an end portion of the large diameter portion  41   b  of the nut  41  interferes with the nut cover plate  411 , which prevents the nut  41  from being disengaged from the valve core  42 . 
         [0077]    When the rotor  12  rotates such that the screw rod  312  is rotated and the nut  41  is moved downward, the nut  41  may directly push the valve core  42  to move downward together, till the valve port  30   a  is closed. 
         [0078]    It is to be noted that, the rotor  12  of the motor  10  may be rotated clockwise or anticlockwise by the coil component  11 , thus the nut  41  is moved upward or downward. In practical arrangement, it may be configured as follows: when the rotor  12  is rotated clockwise, the nut  41  is moved upward, and when the rotor  12  is rotated anticlockwise, the nut  41  is moved downward. Apparently, it may also be configured as follows: when the rotor  12  is rotated clockwise, the nut  41  is moved downward, and when the rotor  12  is rotated anticlockwise, the nut  41  is moved upward. 
         [0079]    The small diameter portion  41   a  of the nut  41  protrudes into the small diameter cavity  31   a  of the lower cavity of the upper valve seat  31 . The screw rod  312  allows the small diameter portion  41   a  of the nut  41  to be moved axially in the small diameter cavity  31   a  and the small diameter cavity  31   a  may guide the axial movement of the nut  41 , thereby preventing the nut  41  from deviating in the axial movement, which adversely affects the sealing performance of the valve core  42  to the valve port  30   a.    
         [0080]    Apparently, for converting the rotation of the screw rod  312  to the axial movement and further move the valve core  42  axially via the nut  41 , a position-limiting member is further provided for restricting a circumferential rotation of the nut  41 . 
         [0081]    The position-limiting member may be in various forms, and specifically in this solution, the small diameter portion  41   a  of the nut  41  may have a column structure with a non-circular cross section, for example, a square column shown in  FIG. 7 . 
         [0082]    Correspondingly, the small diameter cavity  31   a  of the upper valve seat  31  matches with the square column. Apparently, in practical, the small diameter portion  41   a  of the nut  41  may also be as a column structure with other non-circular cross sections, for example, a pentagonal cross section, etc., and the small diameter cavity  31   a  matches with the small diameter portion  41   a . The inner wall of the small diameter cavity  31   a  may also be provided with a retainer ring, and an inner hole of the retainer ring may have a non-circular shape, and the small diameter portion  41   a  of the nut  41  may be a column with a non-circular cross section in cooperation with the retainer ring. In addition, a circumferential position-limiting groove may further be provided at the bottom of the receiving cavity, and the bottom of the large diameter portion  41   b  of the nut  41  is correspondingly provided with a circumferential position-limiting protrusion in cooperation with the circumferential position-limiting groove. The above described is only as several examples of position-limiting members for restricting the circumferential rotation of the nut  41 . 
         [0083]    As shown in  FIG. 13 , the small diameter cavity  31   a  of the upper valve seat  31  may have a circular cross section, and an annular groove is provided at a lower end of the cavity wall of the small diameter cavity  31   a . The annular groove is provided therein with a retainer ring  316 , and an inner hole of the retainer ring  316  is a non-circular hole.  FIG. 14  shows a structure in which the inner hole of the retainer ring  316  is a square hole, and the small diameter segment  41   a  of the nut  41  has a cross section matching with the inner hole of the retainer ring  316 , in this way, the circumferential rotation of the nut  41  is restricted. 
         [0084]    Reference is made to  FIGS. 10 to 11 .  FIG. 10  is a schematic view showing the structure of a valve seat core in  FIG. 1 .  FIG. 11  is a schematic view showing the structure of a lower valve seat in  FIG. 1 . 
         [0085]    The lower valve seat  32  is provided fixedly therein with a valve seat core  321 , and the valve seat core  321  is provided with a core cavity, and a circumferential wall of the valve seat core  321  is provided with at least one flow regulating groove  321   a . The valve seat core  321  separates the valve cavity into a first cavity and a second cavity surrounding the first cavity. Apparently, two cavities may be communicated with each other via the flow control valve  321   a . It may be appreciated that, the first cavity is just the core cavity of the valve seat core  321 , and the second cavity is in communication with a first connecting tube  322 , and the first cavity is in communication with a second connecting tube  323  via the valve port  30   a.    
         [0086]    For the valve seat core  321  suffering a steady force during the flow of the refrigerant being adjusted, multiple flow control valves  321   a  may be distributed uniformly along the circumferential wall of the valve seat core  321 . 
         [0087]    Further, the flow regulating groove  321   a  may have a structure in which the circumferential length is tapered downwards in the axial direction of the valve seat core  321 , as shown in  FIG. 10 . This structure allows the adjustment of the flow the refrigerant in a small flow range to be more precise. Apparently, in practical, the flow control valve  321   a  may be other structures, for example, a square structure, a circular structure, or an elliptical structure are also feasible, but the adjustment in a small flow range by these structures has a lower precision compared with the structure described above. 
         [0088]    The valve core  42  connected to the nut  41  is provided in the valve cavity, specifically, in the first cavity. When the valve core  42  is in a fully closed state and the valve port  30   a  is closed, the side wall of the valve core  42  can block the flow regulating groove  321   a , thus cutting off the communication of the first cavity and the second cavity. When the valve core  42  is moved upward by the nut  41 , the flow control valve  321   a  is opened gradually, and the circulation area of the flow regulating groove  321   a  is changed, thus allowing the first cavity and the second cavity to be communicated, and the flow rate of the refrigerant to be adjusted. Apparently, a seal is required to be formed between the valve core  42  and the valve seat core  321 . 
         [0089]    It may be understood by reference to  FIG. 3 , specifically, a core cavity of the valve seat core  321  may be a stepped hole, and the stepped hole forms a stepped surface facing to the upper valve seat  31 . An upper position-limiting sleeve  421  is inserted to an upper end of the valve seat core  321 , and an upper end of the upper position-limiting sleeve  421  is provided with an annular radial boss. The radial boss is rested against an upper end surface of the valve seat core  42  facing to the upper valve seat  31 . In this way, a lower end surface of the upper position-limiting sleeve  421 , i.e., the end surface facing to the valve port  30   a , the inner side wall of the valve seat core  12 , and the stepped surface of the valve seat core  321  form a mounting groove, and a sealing gasket  423  may be mounted in the mounting groove. 
         [0090]    Further, a lower position-limiting sleeve  422  may further be provided between the sealing gasket  423  and the stepped surface of the valve seat core  321 . Since the valve core  42  is generally a structure which is small on an upper side and large on a lower side, which ensures the sealing to the valve port  30   a . For meeting the assembling requirement of the valve core  42 , an assembling gap is presented between a small diameter through hole of the valve seat core  321  and the valve core  42 . The lower position-limiting sleeve  422  may prevent the sealing gasket  423  from being disengaged from the mounting groove in a reciprocating movement of the valve core due to the presence of the assembly gap. 
         [0091]    Further, an outer circumferential surface of the sealing gasket  423  is provided with a sliding assist member  423   a , and the sliding assist member  423   a  may be integrated with the sealing gasket  423 , i.e., the sliding assist member  423   a  is wrapped over the circumferential surface of the sealing gasket  423 , and may also be arranged independently. In the case that a pressure difference exists between the first cavity and the second cavity, the pressure squeezes the sealing gasket  423  to be deformed, and the sliding assist member  423   a , for being wrapped over the circumferential surface of the sealing gasket  423 , can conveniently suffer the squeezing force to the sealing gasket  423 , thereby fitting against the outer circumferential wall of the valve core  42 , which ensures the sealing, and at the same time, the sliding assist member  423   a  may further reduce the friction resistance of the valve core  42  when the valve core  42  moves axially. 
         [0092]    The upper position-limiting sleeve  421  may further be required to be fixed with respect to the valve seat core  321 . In this embodiment, an axial protrusion may be provided at the bottom of the large diameter segment of the upper valve seat  31 , thereby forming an annular stepped surface facing to the lower valve seat  32 . The upper valve seat  31  is inserted to the lower valve seat  32  via the axial protrusion, and an annular stepped surface of the upper valve seat  31  fits against an upper end surface of the lower valve seat  32 , and a lower end of the axial protrusion presses the upper position-limiting sleeve  421  against the upper end surface of the valve seat core  321  tightly. Further, such structure of the upper valve seat  31  may also easily ensures the coaxiality of the upper valve seat  31  and the lower valve seat  32 . Apparently, the upper position-limiting sleeve  421  and the valve seat core  321  may be fixed by other manners, for example by welding, or threaded connection. 
         [0093]    In the case that the valve core  42  is in the fully closed state, the sealing of the valve core  42  and the valve port  30   a  may also should be ensured. 
         [0094]    In this embodiment, a bottom end of the valve core  42  is provided with an axial protrusion, and a sealing ring  425  is riveted onto the axial protrusion. In the case that the valve core  42  is in the fully closed state, a lower end surface of the sealing ring  425  fits against the valve port  30   a  to form a seal. Apparently, the diameter at an outer end of the sealing ring  425  is larger than the diameter of the valve port  30   a.    
         [0095]    Further, the rotor  12  of the motor  10  of the direct-acting electric valve is a permanent magnet rotor, specifically, the rotor  12  may be made of a material of Neodymium-Iron-Boron (NdFeB) magnetic steel or anisotropic ferrite. In this way, when the valve core  42  is in the fully closed state, the motor  10  is de-energized, and since the rotor  12  is the permanent magnet rotor, the motor  10  has a positioning torque in a de-energized state, which can hold a relative position between the screw rod  312  and the nut  41 , preventing the screw rod  312  from sliding away the nut  41 . Thus, in the de-energized state of the motor  10 , the sealing between the valve core  42  and the valve port  30   a  is further ensured, and the inner leakage is avoided. 
         [0096]    The ratio of an outer diameter of the rotor  12  to the diameter of the valve port  30   a  preferably ranges from 0.8 to 1.8 in order to allow the motor  10  to have a certain positioning toque. 
         [0097]    Further, the valve core  42  has an axial through hole in communication with the receiving cavity, and a circumferential wall of the nut  41  is provided with a vent groove  41   c , i.e., the balancing passage of the valve core  42  includes the receiving cavity, the axial through hole in communication with the receiving cavity, and the vent groove  41   c  arranged in the circumferential wall of the nut  41 . In this way, in the case that the valve core  42  is in the fully closed state, the pressures at an upper end and a lower end of the valve core  42  are balanced, which can be understood by reference to  FIG. 3 .  FIG. 3  is a schematic view showing the structure in which the upper pressure and the lower pressure of the valve core assembly are balanced in the state that the valve port is in the fully closed state. As shown by the arrows in the drawing, the second connecting tube  323  is in communication with the axial through hole of the valve core  42  via the valve port  30   a , and is in communication with the large diameter cavity  31   b  of the upper valve seat  31  via the vent groove  41   c  of the nut  41 , and the pressure difference suffered by the valve core  42  is small. Only a small driving force is required when opening the valve port  30   a , i.e., a small motor  10  may power a large valve core  42 , thus further minimizing the direct-acting electric valve. 
         [0098]    Further, an annular groove is provided at a lower end of an inner wall of the axial through hole of the valve core  42 , and a sieve  424  is provided in the annular groove. The sieve  424  avoids the screw threads, through which the screw rod  312  and the nut  41  are cooperated, from being stuck due to a foreign substance brought into the axial through hole of the valve core  42  when the refrigerant flows. 
         [0099]    In addition, a stepped end surface  31   c  facing to the valve port  30   a  is formed at an area where the small diameter cavity  31   a  and the large diameter cavity  31   b  of the lower cavity of the upper valve seat  31  of the direct-acting electric valve are communicated, and the distance between the stepped end surface  31   c  and the valve port  30   a  restricts an axial moving distance of the valve core  42 . As shown in  FIG. 1 , in the case that the valve core  42  is in the fully opened state, the flow control valve  321   a  is fully opened, and the first connecting tube  322  is in communication with the second connecting tube  323  via the flow regulating groove  321   a , at this time, an upper end surface of the valve core  42  abuts against the stepped end surface  31   c . As shown in  FIG. 2 , in the case that the valve core  42  is in the fully closed state, the sealing ring  425  of the valve core  42  fits against the valve port  30   a  to form a seal, and the first connecting tube  322  and the second connecting tube  323  are not communicated, and the communication of the refrigerant is fully cut off. 
         [0100]    The direct-acting electric valve can achieve bi-directional flow, which can be understood by reference to  FIGS. 1 and 2 . Arrows in  FIGS. 1 and 2  represent the flow direction of the refrigerant. The solid arrow indicates that the refrigerant enters from the first connecting tube  322 , and flows out of the second connecting tube  323 , and the dotted arrow indicates that the refrigerant enters from the second connecting tube  323  and flows out of the first connecting tube  322 . 
         [0101]      FIG. 15  shows a schematic flow chart of assembling a direct-acting electric valve. The assembling method for the direct-acting electric valve includes the following steps: 
         [0102]    mounting an assembled valve core assembly  400  to an assembled lower valve seat assembly  302 ; 
         [0103]    screwing a screw rod  312  of an assembled upper valve seat assembly  301  into a nut  41  of the valve core assembly  400 , and fixing an upper valve seat  31  of the upper valve seat assembly  301  to a lower valve seat  32  of the lower valve seat assembly  302  by welding; and 
         [0104]    mounting a housing  20  and a fixing rest  21  by pressing, and assembling a coil component  11  of a motor  10 . 
         [0105]    Reference for the assembling flow chart of the upper valve seat assembly  301  is made to  FIG. 16 . The following steps are included: 
         [0106]    mounting a screw rod  312 , a bearing  311  and an upper valve seat  31  by pressing; 
         [0107]    mounting a spacer  314  to an upper end of the bearing  311 , and riveting or welding the spacer  314  to the upper valve seat  31 ; 
         [0108]    clamping a bush  313  between the screw rod  312  and the spacer  314 , which allows the bush  313  to abut against an upper end of the bearing  311  and be fixed to the screw rod  312  by welding; and 
         [0109]    sleeving a rotor  12  of a motor  10  on an upper end of the upper valve seat  31 , and fixedly connecting the rotor  12  of the motor  10  to the screw rod  312 . 
         [0110]    Reference for the assembling flow chart of the valve core assembly  400  is made to  FIG. 17 . The following steps are included: 
         [0111]    riveting a sealing ring  422  and a gasket  423  to an axial protrusion at a bottom end of the valve core  42 ; 
         [0112]    mounting a large diameter portion  41   b  of the nut  41  to a receiving cavity of the valve core  42  by pressing; 
         [0113]    fixing the nut cover plate  411  to the valve core  42  by welding; and 
         [0114]    assembling a sieve  424  and a sealing ring  425 . 
         [0115]    The direct-acting electric valve according to the present application employs the above assembling method for the direct-acting electric valve. Since the above direct-acting electric valve has the above technical effects, the assembling method for assembling the direct-acting electric valve should also have corresponding technical effects, which is not described here. 
         [0116]    The flow control valve according to the present application is described in detail hereinbefore. In the description, specific examples are used in the description of the principle and embodiments of the present application. It is noted that the examples and the embodiments are only for better understanding of the method and concept of the present application. It should be noted that, various improvements and modifications can be made by those skilled in the art without departing from the principle of the present application, which also fall within the scope of protection defined by the claims.