Abstract:
An electronic expansion valve includes a valve component for adjusting the flow of fluid. The valve component includes a valve body, a valve seat provided in the valve body, a valve needle able to open and close the valve seat, an actuating mechanism driving the axial movement of the valve needle and a drive mechanism supplying the actuating mechanism with motive power. The actuating mechanism includes a spindle able to move axially. The electronic expansion valve further includes an electromagnetic retaining mechanism for retaining the spindle. The valve is constructed such that when electricity is supplied to the electromagnetic retaining mechanism, the spindle is retained in a first axial position where the valve needle can adjust the opening degree of the valve seat; when the electricity to the electromagnetic retaining mechanism is cut, the spindle is released into a second axial position where the valve needle closes the valve seat.

Description:
[0001]    This application claims priority from Chinese Patent Application No. 201210047737.X titled “ELECTRONIC EXPANSION VALVE” and filed with the Chinese State Intellectual Property Office on Feb. 28, 2012, and Chinese Patent Application No. 201220068553.7 titled “ELECTRONIC EXPANSION VALVE” and filed with the Chinese State Intellectual Property Office on Feb. 28, 2012. The entire disclosures of the Chinese Patent Applications are incorporated herein by reference. 
       TECHNICAL FIELD 
       [0002]    The application relates to an electronic expansion valve. 
       BACKGROUND 
       [0003]    An electronic expansion valve is an important component in a refrigerating/heating system, and is primarily used to regulate flow rate of refrigerant fluid. A conventional electronic expansion valve generally includes a drive mechanism (e.g. a step motor), an actuation mechanism (e.g. a threaded screw rod mechanism), a throttle mechanism (e.g. a valve needle and a valve seat) and related auxiliary mechanism. 
         [0004]    However, a conventional electronic expansion valve, after de-energized, cannot close automatically since a driving force applied to the threaded screw rod mechanism is eliminated. Hence, in order to break the fluid circuit securely, an independent electromagnetic switch valve (which is generally a normal close valve, switches on when being energized, and switches off when being de-energized) is generally connected in series at upstream or downstream of the electronic expansion valve. In this way, when the system is de-energized, the electromagnetic switch valve will switch off automatically to break the fluid circuit. 
         [0005]    However, if the above configuration is adopted, on the one hand, the total cost of the system is increased since an independent electromagnetic switch valve is additionally provided, and one the other hand, in order to connect in series the electromagnetic switch valve, two braze welding joints (i.e., at an inlet and an outlet of the electromagnetic switch valve) will be additionally provided in the pipeline, which not only increases the assembling cost of the system, but also increases the risk of leakage of the system. 
         [0006]    Another method for achieving automatic closing of an electronic expansion valve after de-energized is to provide the electronic expansion valve with a standby power supply, for example, to additionally provide a super-capacitor for storing electric energy or be equipped with a standby battery on a control board of the electronic expansion valve. However, this method also increases cost of the electronic expansion valve and requires a more complicated controller. 
         [0007]    Therefore, an electronic expansion valve which may close automatically after de-energized is desired. 
       SUMMARY 
       [0008]    One object of one or more embodiments of the present application is to provide an electronic expansion valve which may close automatically after de-energized. 
         [0009]    Another object of one or more embodiments of the present application is to provide an electronic expansion valve which can decrease the overall cost of a refrigerating/heating system. 
         [0010]    Still another object of one or more embodiments of the present application is to provide an electronic expansion valve which can increase the safety of a refrigerating/heating system. 
         [0011]    In order to achieve one or more of the above objects, an electronic expansion valve is provided according to one aspect of the present application. The electronic expansion valve includes a valve component for regulating flow rate of fluid flowing through the electronic expansion valve. The valve component includes a valve body, a valve seat arranged in the valve body, a valve needle configured to open and close the valve seat, an actuation mechanism for driving the valve needle to move axially, and a drive mechanism for providing the actuation mechanism with motive power. The actuation mechanism includes a spindle which is movable axially. The electronic expansion valve further includes an electromagnetic retaining mechanism for retaining the spindle. The electromagnetic retaining mechanism is configured to retain the spindle in a first axial position at which the valve needle is allowed to adjust the opening degree of the valve seat when the electromagnetic retaining mechanism is energized, and to release the spindle to a second axial position at which the valve needle closes the valve seat when the electromagnetic retaining mechanism is de-energized. 
         [0012]    Preferably, the electromagnetic retaining mechanism includes an electromagnetic coil, a fixed iron stationary relative to the coil, and a movable iron movable relative to the fixed iron. 
         [0013]    Preferably, the movable iron is connected to a first end of the spindle in such a manner that the movable iron is rotatable but cannot move axially. 
         [0014]    Preferably, a rolling bearing is provided between the movable iron and the first end of the spindle, and includes an inner race fitted with the first end of the spindle and an outer race fitted with the movable iron. 
         [0015]    Preferably, a nut member for limiting an axial movement of the inner race of the rolling bearing is provided on the first end of the spindle, and a nut member for limiting an axial movement of the outer race of the rolling bearing is provided at an end, fitted with the spindle, of the movable iron. 
         [0016]    Preferably, a retaining ring for limiting an axial movement of the inner race of the rolling bearing is provided on the first end of the spindle, and a retaining ring for limiting an axial movement of the outer race of the rolling bearing is provided in the inner cavity of the movable iron. 
         [0017]    Preferably, a retaining ring is provided on the first end of the spindle and is configured to limit an axial displacement of the inner race of the rolling bearing, and a nut member is provided at an end, fitted with the spindle, of the movable iron and is configured to limit an axial movement of the outer race of the rolling bearing. 
         [0018]    Alternatively, the movable iron is fixedly connected to the first end of the spindle. 
         [0019]    Preferably, a thrust bearing is provided on a portion of the spindle close to the first end thereof and is configured to limit the axial displacement of the spindle by abutting against a fixing component of the electronic expansion valve. 
         [0020]    Preferably, the thrust bearing is a one-way thrust ball bearing. 
         [0021]    Preferably, the longitudinal axis of the electromagnetic retaining mechanism is substantially coincident with the axis of rotation of the spindle. 
         [0022]    Preferably, the electromagnetic retaining mechanism is arranged at an upper side of the valve component. 
         [0023]    Alternatively, the longitudinal axis of the electromagnetic retaining mechanism is substantially perpendicular to the axis of rotation of the spindle. 
         [0024]    Preferably, the first end of the spindle is provided thereon with an annular stopper or groove, and one end of the movable iron is provided thereon with a matched component capable of being engaged with the stopper or groove. When the electromagnetic retaining mechanism is energized, the matched component protrudes to be engaged with the stopper or groove, so as to retain the spindle in the first axial position, and when the electromagnetic retaining mechanism is de-energized, the matched component retracts so as to release the spindle to the second axial position. 
         [0025]    Preferably, the distance between the first axial position and the second axial position is larger than or equal to the largest stroke of the valve needle in adjusting the opening degree of the valve seat. 
         [0026]    Preferably, the actuation mechanism further includes: a supporting seat fixed relative to the vale body, a through hole being formed in the supporting seat; and a nut sleeve which is slidable but cannot rotate in the through hole, a second end of the spindle being operatively connected to the valve needle via the nut sleeve. 
         [0027]    Preferably, the through hole has a non-circular inner circumference surface, and the nut sleeve has a non-circular outer circumferential surface matched with the non-circular inner circumferential surface of the through hole. 
         [0028]    Preferably, the through hole has a polygon inner circumferential surface, and the nut sleeve has a polygon outer circumferential surface matched with the polygon inner circumferential surface of the through hole. 
         [0029]    Preferably, the through hole has a circular inner circumferential surface, with a key slot or key being formed on the inner circumference surface, and the nut sleeve has a circular outer circumferential surface, with a key or key slot being formed on the outer circumferential surface and being matched with the key slot or key on the inner circumference surface. 
         [0030]    Preferably, the nut sleeve includes a first section having an internal screw thread and a second section having no screw thread. An external screw thread is formed at the second end of the spindle, and the second end of the spindle is engaged with the first section of the nut sleeve via the internal screw thread and the external screw thread. 
         [0031]    Preferably, an end of the valve needle is fitted in the second section of the nut sleeve. 
         [0032]    Preferably, a stepped portion is provided between the first section and the second section of the nut sleeve. A compression spring is provided between the stepped portion and the valve needle, and the valve needle is slidable in the second section of the nut sleeve. 
         [0033]    Preferably, a fixing ring for retaining the valve needle is provided at an end of the second section of the nut sleeve. 
         [0034]    Preferably, a stepped portion is formed on an outer side of an end, fitted with the valve needle, of the nut sleeve, and a compression spring is provided between the stepped portion and the supporting seat. 
         [0035]    Preferably, a sealing block is provided at an end of the valve needle fitted with the valve seat and is configured to be capable of abutting against an end face of the valve seat. 
         [0036]    Preferably, the drive mechanism includes a stator and a rotor rotatable in the stator, and the spindle is fitted with the rotor such as to rotate together. 
         [0037]    Preferably, the spindle is fixedly connected with the rotor. 
         [0038]    Preferably, the spindle is slidably fitted in the rotor. 
         [0039]    The advantageous of an electronic expansion valve according to one or more embodiments of the present application lie in as follows. 
         [0040]    In an electronic expansion valve according to an embodiment of the present application, the electromagnetic retaining mechanism for retaining the spindle of the valve component is provided, and the electromagnetic retaining mechanism is configured to retain the spindle in a first axial position at which the valve needle is allowed to adjust the opening degree of the valve seat when the electromagnetic retaining mechanism is energized, and to release the spindle to a second axial position at which the valve needle closes the valve seat when the electromagnetic retaining mechanism is de-energized. Hence, when the system or the electronic expansion valve is de-energized suddenly, though the actuation mechanism consisted by a threaded screw rod mechanism cannot move the valve needle to close the valve seat, the spindle as a part of the actuation mechanism is released by the electromagnetic retaining mechanism and then may fall off, for example, under its self-gravity or a biasing force of any other elastic component(s), to a position where the valve needle can close the valve seat, thereby closing reliably the electronic expansion valve. Therefore, the technical solution in the present application can close the electronic expansion valve automatically when the electronic expansion valve is de-energized. 
         [0041]    In addition, since the electronic expansion valve itself can close when it is de-energized, an independent electromagnetic switch valve or other valve components are not required to be additionally provided in a system in which the electronic expansion valve is used, thereby reducing the overall cost of the system. Furthermore, since an additional electromagnetic switch valve is omitted, the number of the joints (braze welding joints) for connecting the electromagnetic switch valve in pipeline of the system are also reduced, which, on the one hand, reduces the risk of leakage of the system, and on the other hand, reduces the assembly procedures of the system and saves labor costs. 
         [0042]    Furthermore, in the electronic expansion valve according to the present application, since an electromagnetic retaining mechanism is adopted, the spindle connected to a movable iron of the electromagnetic mechanism may reliably move to a position which allows the valve needle to close the valve seat when the electronic expansion valve is de-energized, thereby improving the safety of the electronic expansion valve and thus the system greatly. 
         [0043]    In a further embodiment of the present application, the movable iron is connected to a first end of the spindle in such a manner that the movable iron is rotatable but cannot move axially. For example, a rolling bearing may be provided between the movable iron and the first end of the spindle. In this way, when the spindle is driven to rotate by the drive mechanism (a motor), the movable iron does not rotate relative to the fixed iron of the electromagnetic retaining mechanism, thereby minimizing the gap between the movable iron and the fixed iron and achieving good attraction. 
         [0044]    In a further embodiment of the present application, the rotatable connection between the movable iron and the first end of the spindle may be implemented in any one of ways as follows: 1) providing a nut member on the first end of the spindle to limit the axial displacement of the inner race of the rolling bearing, and providing a nut member at an end of the movable iron fitted with the spindle to limit the axial displacement of the outer race of the rolling bearing; 2) providing a retaining ring on the first end of the spindle to limit the axial displacement of the inner race of the rolling bearing, and providing a retaining ring in the inner cavity of the movable iron to limit the axial displacement of the outer race of the rolling bearing; and 3) providing a retaining ring on the first end of the spindle to limit the axial displacement of the inner race of the rolling bearing, and providing a nut member at the end of the movable iron to limit the axial displacement of the outer race of the rolling bearing. In the ways, the spindle can be stably connected to the movable iron in such a manner to be rotatable but cannot move axially relative to each other, and a good assembibility may be achieved. 
         [0045]    In a further embodiment of the present application, the movable iron may be fixedly connected to the first end of the spindle, which further simplifies the assembly process of the electronic expansion valve. In addition, with such a configuration, a thrust bearing may be further provided on the spindle to reliably limit the upward displacement of the spindle. 
         [0046]    In a further embodiment of the present application, the longitudinal axis of the electromagnetic retaining mechanism may be substantially coincident with the axis of rotation of the spindle. For example, the electromagnetic retaining mechanism may be arranged at an upper side of the valve component. With such a structure, a compact arrangement may be achieved. 
         [0047]    In a further embodiment of the present application, the longitudinal axis of the electromagnetic retaining mechanism may be substantially perpendicular to the axis of rotation of the spindle. For example, it is possible to provide an annular stopper or groove at a first end of the spindle, and to provide a matched component engaged with the stopper or groove at an end of the movable iron. When the electromagnetic retaining mechanism is energized, the matched component protrudes to be engaged with the stopper or groove, thereby retaining the spindle in the first axial position, and when the electromagnetic retaining mechanism is de-energized, the matched component may retract under the action of the biasing component such as a spring, thereby releasing the spindle to the second axial position. In such a configuration, since the gravity of the spindle and components connected with the spindle such as the nut sleeve and the valve needle is largely borne by the matched component, and the electromagnetic coil mainly functions to retain the matched component in a protruded position, a small electromagnetic coil may be adopted to further reduce the costs. Furthermore, with such a configuration, the electromagnetic retaining mechanism can be arranged more flexibly relative to the valve component. 
         [0048]    In a further embodiment of the present application, the spindle is connected to the valve needle by a nut sleeve, and the nut sleeve is slidable in the supporting seat but cannot rotate relative to the supporting seat. Thus, the rotation driving force of the motor results in an axial movement of the nut sleeve via the screw thread pair of the spindle and the nut sleeve. In addition, since the load generated by the axial displacement of the spindle is largely exerted on the electromagnetic retaining mechanism, the rotor connected to the spindle is only subjected to the rotation load without the axial load, and this is extremely advantageous for the motor. 
         [0049]    In a further embodiment of the present application, the spindle may be fixedly connected to the rotor of the motor, or may also be slidably fitted in the rotor. Especially in the latter case, it may better ensure that the rotor may be free from the axial load, and may save the space required for the axial movement of the rotor along with the spindle. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         [0050]    Features and advantages of one or more embodiments of the present application may become apparent from the following description made with reference to the drawings in which: 
           [0051]      FIG. 1  is a sectional view of an electronic expansion valve according to a first embodiment of the present application; 
           [0052]      FIG. 2  is an exploded sectional view of the electronic expansion valve shown in  FIG. 1 ; 
           [0053]      FIG. 3  is a perspective view of a supporting seat in the electronic expansion valve shown in  FIG. 1 ; 
           [0054]      FIG. 4  is a perspective view of a nut sleeve in the electronic expansion valve shown in  FIG. 1 ; 
           [0055]      FIGS. 5A ,  5 B,  5 C and  5 D show operation process of the electronic expansion valve; 
           [0056]      FIG. 6  is a sectional view of an electronic expansion valve according to a second embodiment of the present application; and 
           [0057]      FIG. 7  is a sectional view of an electronic expansion valve according to a third embodiment of the present application. 
       
    
    
     DETAILED DESCRIPTION 
       [0058]    The following description of the preferred embodiments is only illustrative rather than a limitation to the present application and application or use thereof. 
         [0059]    The configuration of the electronic expansion valve according to a first embodiment of the present application will be described first with reference to  FIGS. 1 to 4 . 
         [0060]    The electronic expansion valve  1  according to the present application may include a valve component  10  for regulating flow rate of fluid flowing through the electronic expansion valve and an electromagnetic retaining mechanism  60  for retaining or releasing an actuation mechanism in the valve component  10 . 
         [0061]    Specifically, the valve component  10  may include a valve body  12 . The valve body  12  is provided therein with an inlet  12 - 1  connected with an inflow pipe  14  and an outlet  12 - 2  connected with an outflow pipe  16 . A valve seat  18  may be provided at the outlet  12 - 2  of the valve body  12 . The electronic expansion valve  1  may further include a valve needle  24  configured to open and close the valve seat  18 , the actuation mechanism for driving the valve needle  24  to move axially, and a drive mechanism for applying motive power to the actuation mechanism. Furthermore, a filter screen  34  in a substantially cylindrical shape may be provided in the valve cavity of the valve body  12  to filter out impurities in the fluid flowing through the electronic expansion valve. Furthermore, a sealing gasket  32  may be further provided between the valve seat  18  and the valve body  12  to realize sealing connection between the both. 
         [0062]    In the example illustrated, the drive mechanism may be a motor including a stator  40  and a rotor  42 . The rotor  42  is rotatable in the stator  40 . A sleeve  44  may be arranged between the stator  40  and the rotor  42  for the purpose of convenient assembling and easy sealing. A lower end of the sleeve  44  or the stator  40  is fixed to a supporting seat  20  which will be described hereinafter, and an upper end of the sleeve  44  or the stator  40  is provided with a stopper  46 . 
         [0063]    The actuation mechanism may include the supporting seat  20  fitted with an upper opening  12 - 3  of the valve body  12 , a nut sleeve  22  which is slidable but cannot rotate in the supporting seat  20 , and a spindle  50  connected threadedly to the nut sleeve  22 . A sealing ring  38  may be provided between the supporting seat  20  and the valve body  12  to provide a better sealing effect. The spindle  50  may be fixedly connected to the rotor  42  to rotate together. 
         [0064]    Specifically, a through hole  20 - 1  is formed in the supporting seat  20 , and the nut sleeve  22  is slidable but cannot rotate in the through hole  20 - 1 . Particularly, the through hole  20 - 1  may have a non-circular or polygon inner circumferential surface, for example, a substantially octagon configuration as shown in  FIG. 3 . The nut sleeve  22  may have a non-circular or polygon outer circumferential surface matched with the non-circular inner circumferential surface of the through hole  20 - 1 , for example, an octagon configuration as shown in  FIG. 4 . 
         [0065]    The configurations of the supporting seat  20  and the nut sleeve  22  are not limited to the illustrated example, instead, they may be any configurations which allow the supporting seat  20  and the nut sleeve  22  to slide but not rotate relative to each other. For example, the through hole  20 - 1  of the supporting seat  20  may have a circular inner circumferential surface with a key slot or a key being formed thereon. The nut sleeve may have a circular outer circumferential surface, and a key or key slot matched with the key slot or key on the supporting seat are formed on the outer circumferential surface of the nut sleeve. It is to be understood by the skilled in the art that, lots of configurations can achieve the above function, which will not be listed one by one herein. 
         [0066]    The nut sleeve  22  may include a first section  22 - 1  having an internal thread, and a second section  22 - 2  having no screw thread. An external screw thread is formed at a second end (a lower end)  50 - 2  of the spindle  50 . The second end  50 - 2  of the spindle  50  may be connected to the valve needle  24  via the nut sleeve  22 . Specifically, the external screw thread of the second end  50 - 2  of the spindle  50  may be engaged with the internal screw thread of the nut sleeve  22  to form a threaded screw rod mechanism, thereby transforming the rotation movement of the rotor  42  and the spindle  50  into an axial movement of the nut sleeve  22 . 
         [0067]    The valve needle  24  may have one end fitted in the second section  22 - 2  of the nut sleeve  22 , and the other end cooperating with the valve seat  18  to open or close the valve seat  18 . In addition, the opening degree of the electronic expansion valve may be adjusted by adjusting the distance between the valve needle  24  and the valve seat  18 , so as to achieve the accurate control to the flow rate of the fluid. The valve needle  24  may be fixedly fitted in the nut sleeve  22 . Alternatively, the valve needle  24  may be slidably fitted in the nut sleeve  22 , and is urged at one end thereof by a spring so as to achieve a better sealing. Specifically, the nut sleeve  22  is provided with a stepped portion  22 - 3  between the first section  22 - 1  and the second section  22 - 2 , and a compression spring  28  is provided between the stepped portion  22 - 3  and the valve needle  24 . Further, a fixing ring  36  for retaining the valve needle  24  is provided at an end of the second section  22 - 2  of the nut sleeve  22 . With the above arrangement, the valve needle  24  is axially movable along with the nut sleeve  22 . Further, when the nut sleeve  22  moves downwards and the valve needle  24  abuts against the valve seat  18 , the compression spring  28  will apply a spring force to an end of the valve needle  24  so as to enable a proper abutting force between the valve needle  24  and the valve seat  18 , which, on the one hand, protects the valve needle and the valve seat from being damaged, and on the other hand, provides a reliable sealing effect. 
         [0068]    To provide a better sealing effect, a sealing block  30  may be provided at the end of the valve needle  24  fitted with the valve seat  18  and can abut against an end face of the valve seat  18 . 
         [0069]    A stepped portion  22 - 4  is formed on an outer side of the end of the nut sleeve  22  fitted with the valve needle  24  (see  FIG. 4 ), and a compression spring  26  is provided between the stepped portion  22 - 4  and the supporting seat  20 . The compression spring  26  may provide a downward spring force to the nut sleeve  22 , so as to assist the nut sleeve  22 , the valve needle  24  and the spindle  50  to move to a position where the valve needle  24  closes the valve seat  18  when the electronic expansion valve is de-energized, as will be described below. It may be appreciated by the skilled in the art that, since such a downward force may arise from weights of the nut sleeve  22 , the valve needle  24  and the spindle  50  themselves, the compression spring  26  can be omitted. 
         [0070]    The electromagnetic retaining mechanism  60  may be arranged on the upper side of the valve component  10 , and the electromagnetic retaining mechanism  60  may be arranged such that its axial direction is substantially coincident with the axis of rotation of the spindle  50 . The electromagnetic mechanism  60  is configured to retain the spindle  50  of the actuation mechanism of the valve component  10 . Specifically, the electromagnetic retaining mechanism  60  may be configured to retain the spindle  50  at a first axial position at which the valve needle  24  is allowed to adjust the opening degree of the valve seat  18  when the electromagnetic retaining mechanism  60  is energized, and to release the spindle  50  to a second axial position at which the valve needle  24  closes the valve seat  18  when the electromagnetic retaining mechanism  60  is de-energized. 
         [0071]    According to one embodiment of the present application, the electromagnetic retaining mechanism  60  may include an electromagnetic coil  61  which generates a magnetic force when being energized, a fixed iron  62  which is fixed relative to the electromagnetic coil  61 , and a movable iron  64  which is movable relative to the fixed iron  62 . To facilitate the assembly, a substantially cylindrical sleeve  72  may be provided in the electromagnetic coil  61 . One end of the fixed iron  62  may be fixed in the sleeve  72 . The movable iron  64  is slidable in the sleeve  72 . In addition, a magnetic yoke  74  may be provided outside the electromagnetic coil  61 . The magnetic yoke  74  may, on the one hand, increase the magnet force of the electromagnetic retaining mechanism  60 , and on the other hand, be employed as a fixing holder of the electronic expansion valve  1 . 
         [0072]    In the embodiment shown in  FIG. 1 , the movable iron  64  is connected to a first end (an upper end)  50 - 1  of the spindle  50  in such a manner that the movable iron  64  is rotatable but cannot move axially. Specifically, a rolling bearing  70  is provided between the movable iron  64  and the first end  50 - 1  of the spindle  50 . An inner race of the rolling bearing  70  is fitted with the first end  50 - 1  of the spindle  50 , and an outer race of the rolling bearing  70  is fitted with the movable iron  64 . 
         [0073]    More specifically, a nut member  68  may be provided at the first end  50 - 1  of the spindle  50  so as to limit an axial displacement of the inner race of the rolling bearing  70 , and a nut member  66  may be provided at the end (the lower end) of the movable iron  64  fitted with the spindle  50  so as to limit an axial displacement of the outer race of the rolling bearing  70 . In this way, the spindle  50  is rotatable relative to the movable iron  64  (in other words, the movable iron  64  may not rotate, which facilitates attraction between the movable iron  64  and the fixed iron  62 ), and is movable axially along with the movable iron  64 . 
         [0074]    A through hole, through which the spindle  50  passes, is provided in the stopper  46 , and a sliding bearing  48  may be provided in the through hole. A part of the spindle  50  is supported by the sliding bearing  48  so as to enable smoother rotation and axial movement. 
         [0075]    The operation process of the electronic expansion valve  1  according to the first embodiment of the present application is described hereinafter with reference to  FIGS. 5A ,  5 B,  5 C and  5 D. In these features, the letter G represents a gap between the fixed iron  62  and the movable iron  64 , and the letter V represents a distance from the lower end of the nut sleeve  22  to a certain horizontal plane. 
         [0076]      FIG. 5A  shows various components of the electronic expansion valve  1  in an initial state. In such a state, G reaches a maximum value, and V reaches a minimum value (for example, zero). Starting from such a state, the stator  40  is energized first, and meanwhile the electromagnetic coil  61  is kept to be de-energized. As a result, the spindle  50  is driven to rotate by the rotor  42 . Since the lower end of the spindle  50  is threadedly fitted with the nut sleeve  22 , and the nut sleeve  22  cannot rotate, the spindle  50  will move upwards and axially while rotating. Meanwhile, since the movable iron  64  cannot move axially relative to the spindle  50 , the movable iron  64  may also move upwards till the movable iron  64  abuts against the fixed iron  62 . Then, various components of the electronic expansion valve will be in a state shown in  FIG. 5B . 
         [0077]    In a state shown in  FIG. 5B , (G reaches a minimum value, for example, zero, and V reaches a minimum value), the valve needle  24  still closes the valve seat  18 . Then, the electromagnetic coil  61  is energized, and generates a magnetic force to attract the movable iron  64 . In addition, the stator  40  is kept being energized, and the spindle  50  will keep rotating. However, since the spindle  50  cannot move upwards further, the nut sleeve  22  will be pulled upwards due to the thread pair of the spindle  50  and the nut sleeve  22 , thereby driving the valve needle  24  to move upwards so as to enable a certain opening degree of the electronic expansion valve  1 . Then, various components of the electronic expansion valve will be in a state shown in  FIG. 5C . 
         [0078]    In the state shown in  FIG. 5C  (G reaches a minimum value, for example, zero, and V may reach a value between the minimum value and the maximum value), the stroke of the valve needle  24  may be controlled by controlling the stator  40 . In such a state, the electromagnetic coil  61  is kept being energized, whereas the stator  40  may be energized or de-energized and rotated in a forward direction or in a reverse direction depending on control requirements. 
         [0079]    When the electronic expansion valve  1  is de-energized suddenly, various components of the electronic expansion valve will be in a state shown in  FIG. 5D  (G reaches a maximum value and V reaches a minimum value). In such a state, since the electromagnetic coil  61  is de-energized, the fixed iron  62  will not attract the movable iron  64 . Thus, the movable iron  64 , the spindle  50 , the nut sleeve  22  and the valve needle  24  will fall downwards together under gravity and spring force of the compression spring  26  so that the valve needle  24  closes the valve seat  18 . 
         [0080]    Then, before the electronic expansion valve  1  is powered on again for normal operation, the rotor  42  may be first driven to rotate forwardly or reversely by certain turns until the spindle  50  and the nut sleeve  22  reach the initial position as shown in  FIG. 5A , and then the normal operations as shown in  FIGS. 5A ,  5 B and  5 C may be performed. 
         [0081]    It is to be noted that, the position of the spindle  50  as shown in  FIGS. 5B and 5C  (G reaches a minimum value) corresponds to the first axial position as defined in the claims, and the position as shown in  FIGS. 5A and 5D  (G reaches a maximum value) corresponds to the second axial position as defined in the claims. Furthermore, the distance between the first axial position and the second axial position (i.e., G) may be set to be larger or equal to the maximum stroke (V reaches a maximum value) of the valve needle  24  in adjusting the opening degree of the valve seat  18 . 
         [0082]    A second embodiment according to the present application will be described hereinafter with reference to  FIG. 6 . In the second embodiment, the like reference signs are used to indicate the like elements as in the first embodiment and thus the description of the like elements will not be repeated. 
         [0083]    The second embodiment is different from the first embodiment in for the way of fixing the spindle  50  to the movable iron  64 . Specifically, in the second embodiment, a retaining ring  84  is provided on the first end  50 - 1  of the spindle  50  for limiting the axial displacement of the inner race of the rolling bearing  70 , and a retaining ring  86  is provided in the inner cavity  82  of the movable iron  64  for limiting the axial displacement of the outer race of the rolling bearing  70 . With such a configuration, the configuration of the electronic expansion valve may be further simplified and the costs may be saved. 
         [0084]    Furthermore, the first embodiment may further be combined with the second embodiment. For example, the retaining ring  84  may be provided on the first end  50 - 1  of the spindle  50  for limiting the axial displacement of the inner race of the rolling bearing  70 , and the nut member  66  may be provided at the end of the movable iron  64  fitted with the spindle  50  for limiting the axial displacement of the outer race of the rolling bearing  70 . With such a configuration, the assemblability of the electronic expansion valve may be improved while the cost is saved. 
         [0085]    A third embodiment according to the present application will be described hereinafter with reference to  FIG. 7 . In the third embodiment, the like reference signs are used to indicate the like elements as in the first embodiment and thus the description of the like elements will not be repeated. 
         [0086]    The third embodiment is different from the first embodiment in the way of fixing the spindle  50  to the movable iron  64 . Specifically, in the third embodiment, the movable iron  64  is fixedly connected to the first end  50 - 1  of the spindle  50 . Therefore, the configuration of the electronic expansion valve may be further simplified and the cost may be saved. 
         [0087]    In addition, a thrust bearing, which can abut against a fixing component such as the stopper  46  of the electronic expansion valve  1  so as to limit an axial displacement of the spindle  50 , may be provided on the portion of the spindle  50  close to the first end  50 - 1  thereof. Preferably, the thrust bearing is a one-way thrust ball bearing  90 . 
         [0088]    Various embodiments of the present application have been described above with reference to  FIGS. 1 to 7 . However, it should be appreciated for the skilled in the art that the present application is not limited to the embodiments shown in the drawings, and various variations may be made. For example, the longitudinal axis of the electromagnetic retaining mechanism  60  may be substantially perpendicular to the axis of rotation of the spindle  50 . In such a case, an annular stopper or groove may be provided at the first end of the spindle, and a matched component capable of being engaged with the stopper or groove may be provided at an end of the movable iron. In this way, when the electromagnetic retaining mechanism is energized, the matched component protrudes to be engaged with the stopper or groove as the movable iron moves, so as to retain the spindle at the first axial position, and when the electromagnetic retaining mechanism is de-energized, the matched component may retract, for example, under the action of a spring, so as to release the spindle to the second axial position. The above configuration may achieve the same technical effects as the above embodiment as well. 
         [0089]    Furthermore, in the above embodiment, the spindle  50  and the rotor  42  are fixedly connected. Alternatively, the spindle  50  may be slidably fitted in the rotor  42 . In this way, the spindle  50  may move along with the rotor  42 , however, will not apply axial load to the rotor  42 . On the other hand, an axial space required for achieving the rotor to move axially along with the spindle in the motor component may be saved as well. 
         [0090]    While various embodiments of the present application have been described in detail herein, it should be understood that the present application is not limited to the specific embodiments described and illustrated herein in detail, and that those skilled in the art can also make other variations and modifications without departing from the spirit and scope of the application. These variations and modifications should also be deemed to fall into the protective scope of the application. Furthermore, all the elements described herein can be replaced by other technically equivalent elements.