Patent Publication Number: US-2022213975-A1

Title: Water inlet solenoid valve capable of improving electromagnetic attraction and implementing method therefor

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a continuation application of U.S. patent application Ser. No. 17/762,580 filed Mar. 22, 2022 which is a U.S. National Stage Application of PCT/CN2020/112858 assigned the international filing date of Sep. 1, 2020 and claiming the benefit of priority from C.N. patent application 201910898273.5 filed Sep. 23, 2019, the disclosure of these applications is herein incorporated by reference. 
    
    
     TECHNICAL FIELD 
     The present invention relates to the technical field of manufacture of solenoid valve for water, and in particular to a stator assembly with water-isolating sleeve applied to solenoid valve for water and implementation method thereof. 
     BACKGROUND ART 
     A solenoid valve for water (or water inlet valve) functions to control supply or cut off of water source. Since water has a certain pressure during operation, it can be designed as a packless pilot-operated solenoid valve for water.  FIG. 1  shows the structure of a solenoid valve for water that is currently more commonly used, including a plastic-sealed layer  116  for plastic-sealing a coil winding, a magnetic yoke  111  mounted on the outside of the plastic sealed layer, a plug  107 , a water inlet  215  and a water outlet  216 . 
       FIG. 1  shows a solenoid valve for water consisting essentially of two parts, a pilot valve and a primary valve. When a winding  109  is not energized, a movable iron core  201  falls due to the self-weight and the reaction force of the return spring, and closes a flow-through hole  210  of a primary valve plug  203 , so that the water entering the upper cavity of the valve plug from a balanced hole  213  cannot leak out, and due to the difference in effective bearing areas on and below the valve diaphragm, a pressure difference is formed, so that the valve plug diaphragm is pressed against the primary valve seat, and the valve is closed. When the winding  109  is energized, the magnetic attraction draws the movable iron core  201  up, and the water in the upper cavity  211  of the valve plug is discharged to an outlet of the valve through the flow-through hole  210 . Since the flow capacity of the flow-through hole is designed to be much greater than the flow capacity of the balanced hole  213 , a sufficient pressure loss is generated on the balanced hole  213  by the water flow, the pressure in the upper cavity  211  of the valve plug sharply decreases, while the pressure in the lower cavity  212  of the valve plug maintains the same as the pressure of the inlet, so that the pressure difference between the upper and lower sides of the valve plug diaphragm causes the valve plug diaphragm to bulge upwards, the valve is opened. 
     The major problem of the solenoid valve for water shown in  FIG. 1  is that a water-isolating sleeve  117  needs to be separately manufactured, and the manufactured water-isolating sleeve is inserted into the magnetic conductive inner sleeve by means of assembly, so the water-isolating sleeve  117  installed in a middle hole of a coil rack  104  needs to have a certain thickness in order to withstand the pressure impact when the valve is closed and the possible structural damage during mechanical assembly, resulting in that the non-working air gap of the existing solenoid valve for water is greater than 1.5 mm, thus requiring more electromagnetic force to make the movable iron core act; in addition, manufacturing the water-isolating sleeve separately increases the manufacturing cost. 
     In addition, since the yoke  111  is mounted to the outside of the plastic-sealed layer  116  of the plastic-sealed coil winding, the yoke  111  must be welded together with the magnetic conductive inner sleeve in order to fix the yoke to the coil rack via the magnetic conductive inner sleeve, which the welding process and manufacturing cost are increased. 
     The winding enameled wires of the solenoid valves for waters in the market all use copper wires, with a total amount of about 26.5-28 g. Reducing the amount of copper wire is the most straightforward way to reduce cost. However, reducing the amount of copper wires will inevitably affect the performance of the solenoid valves for waters. By improving the magnetic circuit structure, the usage of copper wire can be reduced under the condition of maintaining or even improving the performance level of the water inlet valve, and the balance between performance and cost can be achieved, which is the problem to be solved by the invention. 
     SUMMARY OF THE INVENTION 
     It is an object of the present invention to provide a stator assembly with water-isolating sleeve applied to solenoid valve for water and implementation method thereof for enhancing an electromagnetic force acting on a movable iron core and simplifying a production process for manufacturing the solenoid valve for water and reducing a production cost. 
     According to a first aspect of the present invention, an implementation method of stator assembly with water-isolating sleeve applied to solenoid valve for water, comprising:
         forming a coil assembly with a cavity by installing an element including an insert on a coil rack wound with a coil winding;   forming a stator assembly by installing an upper magnetic conductive inner sleeve and a lower magnetic conductive inner sleeve at both sides in a hole in the coil rack of the coil assembly, and fixing the yoke connecting the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve outside the coil assembly;   injecting plastic on the stator assembly to form the stator assembly with water-isolating sleeve.       

     Preferably, the step of injecting plastic on the stator assembly to form the stator assembly with water-isolating sleeve comprises:
         by injecting plastic on the stator assembly, covering the coil winding and the yoke with plastic, exposing the insert and the hole in the coil rack, thereby manufacturing a primary plastic-sealed stator assembly;   by injecting plastic into the primary plastic -sealed stator assembly, forming the water-isolating sleeve in the hole of the coil rack with the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve, thereby manufacturing the stator assembly with water-isolating sleeve.       

     Preferably, the hole of the coil rack has a magnetic conductive inner sleeve positioning ring for positioning the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve so as to keep the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve at a predetermined distance in the hole of the coil rack. 
     Preferably, at the same time of injecting plastic into the primary plastic -sealed stator assembly, the water-isolating base located at the lower end of the water-isolating sleeve is formed, which is used for connecting and fixing the valve body assembly of the solenoid valve for water. 
     According to a second aspect of the present invention, an implementation method of stator assembly with water-isolating sleeve applied to solenoid valve for water, comprising:
         forming a water-isolating sleeve assembly with a magnetic conductive sleeve by injecting plastic into a upper magnetic conductive inner sleeve, a stopper and a lower magnetic conductive inner sleeve to form water-isolating sleeve;   forming a coil assembly by installing an element including an insert on a coil rack wound with a coil winding, and fixing the yoke connecting the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve outside the coil assembly;   inserting the water-isolating sleeve assembly with the magnetic conductive sleeve into the hole of the coil rack of the coil assembly to form a stator assembly;   manufacturing the stator assembly with water-isolating sleeve by injecting plastic into the stator assembly to cover the coil winding and yoke on the stator assembly.       

     Preferably, the water-isolating sleeve assembly comprises:
         an upper magnetic conductive inner sleeve, a stopper and a lower magnetic conductive inner sleeve which are fixed together by injecting plastic;   a water-isolating sleeve formed on the inner surfaces of the upper magnetic conductive inner sleeve, the stopper and the lower magnetic conductive inner sleeve by injecting plastic;   a water-isolating sleeve base located at the lower end of the water-isolating sleeve and integrally formed therewith.       

     Preferably, the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve are a cylinder respectively, and the cylinder walls are provided with radial through holes which glue flows. 
     Preferably, the inner surfaces of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve are provided with axial grooves which communicate with the radial through holes. 
     Preferably, the inner surfaces of the upper and lower magnetic conductive inner sleeves are provided with circumferential grooves which communicate with the axial grooves. 
     Preferably, by injecting plastic, the water-isolating sleeve and the water-isolating sleeve base are formed on the inner surfaces of the upper magnetic inner sleeve and the lower magnetic inner sleeve ; during injecting plastic, the hot-melt plastic flows into the radial through hole of the magnetic conductive inner sleeve along the axial grooves of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve, forming the root for fixing the injection water jacket. 
     According to a third aspect of the present invention, a stator assembly with water-isolating sleeve applied to a solenoid valve for water, comprising:
         the coil assembly comprising a coil rack, a coil winding wound on the coil rack and an insert arranged on the coil rack, wherein a hole of coil rack is formed in the middle of the coil rack;   an upper magnetic conductive inner sleeve, a lower magnetic conductive inner sleeve and a water-isolating sleeve which are arranged in the hole of the coil rack, wherein the water-isolating sleeve is formed by injecting plastic on the inner surfaces of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve;   a yoke located outside the coil assembly, wherein upper end and lower end of the yoke are closely connected with the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve respectively;   a plastic sealing layer covering the coil assembly formed by injecting plastic, wherein the plastic sealing layer does not cover the part of the insert electrically connected with the external power supply.       

     Preferably, the lower end of the water-isolating sleeve is provided with a water-isolating sleeve base integrally formed by injecting plastic, and the water-isolating sleeve base is not covered by the plastic sealing layer so as to be connected and fixed with the valve body of the water inlet solenoid valve. 
     Preferably, a yoke positioning groove of the yoke clamps the yoke positioning bosses provided on the upper and lower end faces of the coil rack, so that the yoke is positioned on the coil rack on the one hand and connected with the upper magnetic conductive inner sleeve on the other hand. 
     Preferably, the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve are cylindrical, and both of them are provided with water-isolating sleeve fixing structures for attaching the water-isolating sleeve to the inner surfaces of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve. 
     Preferably, the water-isolating sleeve fixing structure comprises a radial through hole which glue flows. 
     Preferably, the water-isolating sleeve fixing structure further comprises grooves provided on the inner surfaces of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve. 
     Preferably, the groove comprises an axial groove communicating with the radial through hole. 
     Preferably, the groove comprises a circumferential groove communicating with the axial groove. 
     According to a fourth aspect of the present invention, a solenoid valve for water, comprising a valve body assembly and above-mentioned the stator assembly with water-isolating sleeve, wherein the stator assembly with water-isolating sleeve is assembled with the valve body assembly to form the solenoid valve for water. 
     With respect to the prior art, it is an advantageous technical effect of the present invention that the improvement of the magnetic circuit structure enhances the end surface suction force generated by the main magnetic flux, so that the total electromagnetic suction force is greater when the valve is activated and the low pressure activation performance is better. 
     In addition, by forming a water-isolating sleeve on the inner surfaces of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve by injecting plastic, the thickness of the water-isolating sleeve can be greatly reduced, thereby enhancing the electromagnetic force acting on the movable iron core. 
     On the other hand, by fixing the yoke and the coil assembly together by injecting plastic, the production process for manufacturing the solenoid valve for water can be simplified, the production cost can be reduced, and the product quality can be improved. 
     The present invention will be described in detail below with reference to the accompanying drawings and embodiments, so as to further understand the content, features and technical effects of the present invention. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  is a schematic view showing a structure of a conventional solenoid valve for water; 
         FIG. 2  is a diagram illustrating a load reaction force of a movable iron core with respect to a stroke of the movable iron core; 
         FIG. 3  is a sectional view of a solenoid valve for water of the present invention; 
         FIG. 4  is a sectional view of a plastic-sealed stator assembly of the solenoid valve for water of the present invention; 
         FIG. 5  is an exploded view of the stator assembly of the solenoid valve for water of the present invention; 
         FIG. 6  is a perspective view of a stator assembly of the solenoid valve for water of the present invention; 
         FIG. 7  is a perspective view of a primary plastic-sealed stator assembly formed by firstly injecting plastic on the stator assembly of the solenoid valve for water of the present invention; 
         FIG. 8  is a cross-sectional view of a primary plastic-sealed stator assembly of the solenoid valve for water of the present invention; 
         FIG. 9 a    is a front view of a first embodiment of an upper magnetic conductive inner sleeve of the solenoid valve for water of the present invention; 
         FIG. 9 b    is a sectional view A-A of  FIG. 9 a    of the present invention; 
         FIG. 9 c    is a sectional view B-B of  FIG. 9 a    of the present invention; 
         FIG. 9 d    is a perspective view of a first embodiment of an upper magnetic conductive inner sleeve of the solenoid valve for water of the present invention; 
         FIG. 10  is a perspective view of a stator assembly with a water-isolating sleeve formed by a primary plastic-sealed stator assembly of the solenoid valve for water which has been subjected to a secondary plastics-packing of the present invention; 
         FIG. 11  is a cross-sectional view of a stator assembly with a water-isolating sleeve of the solenoid valve for water of the present invention; 
         FIGS. 12-14  are schematic views of another embodiment of the present invention for forming a water-isolating sleeve, wherein  FIG. 12  shows the positional relationship of an upper magnetic conductive inner sleeve, a lower magnetic conductive inner sleeve and a stopper as an insert,  FIG. 13  is a perspective view of a water-isolating sleeve assembly formed by injecting plastic on the upper magnetic conductive inner sleeve, the lower magnetic conductive inner sleeve and the stopper as a inserts, and  FIG. 14  is a sectional view of the water-isolating sleeve assembly. 
     
    
    
     Description of reference numerals: stator assembly with a water-isolating sleeve— 100 ; 
     primary plastic-sealed stator assembly— 101 ; stator assembly  102 ; coil assembly— 103 ; coil rack— 104 ; yoke positioning boss— 105 ; magnetic conductive inner sleeve positioning ring— 106 ; insert— 107 ; electronic components— 108 ; coil winding— 109 ; yoke— 111 ; yoke positioning groove— 112 ; upper magnetic conductive inner sleeve— 113 ; lower magnetic conductive inner sleeve— 114 ; magnetic conductive inner sleeve glue passing hole— 115 ; plastic—sealed layer— 116 ; water-isolating sleeve— 117 ; water-isolating sleeve base— 118 ; inner cavity of water-isolating sleeve— 119 ; magnetic conductive seat— 121 ; magnetic conductive inner sleeve axial inner groove— 122 ; magnetic conductive inner sleeve joint seam— 123 ; return spring— 200 ; movable iron core— 201 ; flow-through hole plug rubber— 202 ; valve plug— 203 ; valve plug rubber— 204 ; valve body  205 ; mounting rack— 206 ; pressure relief ring— 207 ; rubber gasket— 208 ; filter screen assembly— 209 ; flow-through hole— 210 ; valve plug upper cavity— 211 ; valve plug lower cavity— 212 ; balanced hole— 213 ; water inlet— 215 ; water outlet— 216 . 
     DETAILED DESCRIPTION OF THE INVENTION 
     The present invention starts from the structure of a coil rack, a magnetic conductive inner sleeve, a water-isolating sleeve, a movable iron core and a magnetic conductive base, and enhance the electromagnetic suction force when a water inlet valve is started by improving a magnetic circuit structure, the wire consumption is reduced and the cost is reduced under the condition of meeting the minimum starting voltage requirement. 
     The magnetic circuit of the solenoid valve for water of the present invention is composed of a yoke, a magnetic conductive seat, an upper magnetic conductive inner sleeve, a movable iron core and a lower magnetic conductive inner sleeve. 
       FIG. 2  shows the relationship between load reaction force of the movable iron core and the stroke of the movable iron core, and the load reaction force characteristic acting on the movable iron core in operation is shown as curve  1  in  FIG. 2 . In the F-S coordinate system, F is a load reaction force acting on the movable iron core, and S is a suction stroke of the movable iron core. The load reaction force is mainly composed of the force F 1  of water acting on the movable iron core, the self-weight G of the movable iron core and the elastic force F 2  of the spring, wherein F 1  and F 2  are significant and varied. When the movable iron core closes the flow-through hole, F 1  is equal to the product of the water source pressure and the cross-sectional area of the flow-through hole, and point A in the figure corresponds to the closed valve state; at the initial stage of the movable iron core rising after the power-on, since the valve plug diaphragm also rises, the flow-through hole fails to be unblocked, the pressure of the upper cavity of the valve plug still has a downward action force on the movable iron core, but has been continuously reduced; the spring is then compressed and the spring force is intensified. Since F 1  decreases faster than F 2  increases, the first half of curve  1  decreases slowly. At point B, the valve plug diaphragm fully rises, the flow-through hole is unblocked, F 1  completely disappears, and the load reaction force rapidly drops to the lowest point; thereafter, the movable iron core rises against F 2 , and the slope of the inclined line segment after point B is the elastic coefficient of the spring. 
     In order to adapt to the load reaction force characteristic, the electromagnetic suction force characteristic acting on the movable iron core is as shown in  FIG. 2 . The relative positions of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve and the movable iron core plays an important role in the specific effect of electromagnetic suction force. A working air gap exists between the movable iron core and the upper magnetic conductive inner sleeve, and a main non-working air gap is formed between the movable iron core and the lower magnetic conductive inner sleeve. Before the movable iron core is not sucked into the upper magnetic conductive inner sleeve, the magnetic potential mainly falls in the working air gap; the electromagnetic suction force includes the electromagnetic force generated by the leakage flux on the side surface of the movable iron core and the end surface suction force generated by the main magnetic flux; when the upper end surface of the movable iron core is close to the lower edge of the upper magnetic conductive inner sleeve, the effect of the end surface suction force is greater; the closer the upper end surface is to the lower edge of the upper magnetic inner sleeve, the greater the total electromagnetic suction force, and the maximum value is reached when the movable iron core is about to enter the upper magnetic conductive inner sleeve. After the movable iron core is sucked into the upper magnetic conductive inner sleeve, the length of the working air gap does not change, and the area of the air gap increases with the depth of the movable iron core, the working air gap magnetic quickly increases to a degree that can be compared with the non-working air gap magnetic conductance, so that the working air gap magnetic pressure drop decreases proportionally and the electromagnetic suction force thus decreases. The descending section of the electromagnetic suction force characteristic curve and the ascending section of the load reaction characteristic curve intersect at point C, the movable iron core is completed, and the solenoid valve for water is also conducted. 
     In view of the fact that the movable iron core must have a certain suction stroke, magnetic leakage exists in the gap between the upper magnetic inner sleeve and the lower magnetic inner sleeve, and the magnetic seat is installed in the upper magnetic inner sleeve, the present invention improves the magnetic circuit structure as follows: 
     1. the upper end face of the movable iron core at the initial position (equivalent to the position where the movable iron core is located before power-on) is not lower than the upper edge of the lower magnetic conductive inner sleeve, and is not higher than ¼ of the distance between the upper edge of the lower magnetic conductive inner sleeve and the lower edge of the upper magnetic conductive inner sleeve, so that the upper end face of the movable iron core at the initial position is slightly higher than the upper edge of the lower magnetic conductive inner sleeve, such that the magnetic leakage of the gap between the upper edge of the lower magnetic conductive inner sleeve and the lower edge of the upper magnetic conductive inner sleeve fully acts on the movable iron core at the initial position, and ensures that the movable iron core has a reliable suction stroke, thereby improving the reliability of suction. 
     2. the socket length between the movable iron core at the initial position and the lower magnetic conductive inner sleeve (equivalent to the length of the movable iron core at the initial position in the lower magnetic conductive inner sleeve) is not less than ¼ of a sum of the heights of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve, i.e., the length of the movable iron core can be less than the length of the lower magnetic conductive inner sleeve, but is greater than or equal to ½ of the length of the lower magnetic conductive inner sleeve, so as to ensure that the magnetic conduction of the non-operating air gap is not too small, the iron core being saturated, and improve the ability of the solenoid valve for water to bear a large impulse current impact. 
     The specific numerical values are set as follows: 
     a gap between the upper magnetic conductive inner sleeve and lower magnetic conductive inner sleeve is 2 to 5 mm; 
     the weight of magnetic conductive seat shall not be less than 60% of movable iron core; 
     the diameter of the movable iron core is reduced from 6 mm to 5±0.1 mm; 
     the inner diameter of the water-isolating sleeve is 5.5±0.1 mm, the wall thickness is 0.5 mm, and the outer diameter is 6.5±0.1 mm; 
     the inner diameter of the magnetic conductive inner sleeve is 6.5±0.1 mm, the wall thickness is 1 mm, and the outer diameter is 8.5±0.1 mm; 
     the aperture of the hole in the coil rack is about 8.7 mm; and 
     the coil rack wall thickness is reduced from 1 mm to 0.4 mm. 
     As a result of the reduced diameter of the moving iron core, the noise generated by the attractive collision between the magnetized magnetic conductive seat and the moving iron core is also reduced when the coil winding is energized. The apertures of the water-isolating sleeve, the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve and the coil rack are reduced to accommodate the reduction of the diameter of the movable iron core. When the aperture of the coil rack is reduced, the copper wire consumption is reduced, the winding resistance is reduced and the current is increased under the condition that the number of winding turns and the wire diameter are unchanged, which improves the solenoid attraction and low voltage starting performance. 
     The present invention provides an implementation method of a solenoid valve for water capable of improving a electromagnetic suction force, which comprises: 
     obtaining a plastic-sealed stator assembly by injecting plastic on a stator assembly; 
     assembling the plastic-sealed stator assembly and a valve body assembly comprising a movable iron core  201  together to form the solenoid valve for water; 
     as shown in  FIG. 3 , the plastic-sealed stator assembly of the present invention comprises: a coil assembly  103  having a coil rack  104 , a coil winding  109  wound on the coil rack  104 , an insert  107  and an electronic component  108  mounted on the coil rack  104  (see  FIG. 5 ); an upper magnetic conductive inner sleeve  113  and a lower magnetic conductive inner sleeve  114  mounted in the hole of the coil assembly; a water-isolating sleeve  117  located inside the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114 ; a yoke  111  located outside the coil assembly and connecting the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114 ; a magnetic conductive seat  121  mounted inside the upper water-isolating sleeve  117 ; and a plastic-sealed layer  116  covering the coil assembly and the yoke  111 . 
     according to the present invention, the upper end face of the movable iron core  201  at the initial position is set as not lower than the upper edge of the lower magnetic conductive inner sleeve  114  and not higher than ¼ of the distance from the upper edge of lower magnetic conductive inner sleeve  114  to the lower edge of upper magnetic conductive inner sleeve  113 , so as to increasing the electromagnetic suction force of the solenoid valve for water. 
     Referring to  FIG. 3 , the valve body assembly of the solenoid valve for water of the present invention includes: a return spring  200  and a movable iron core  201  which are received in a water-isolating sleeve; a flow-through hole valve plug rubber  202 ; a valve plug  203 ; a valve plug rubber  204 ; a valve body  205 , a mounting rack  206 , a pressure relief ring  207 , a rubber gasket  208 , and a filter screen assembly  209 , etc. Since these components of the valve body assembly of the solenoid valve for water are all components of an existing solenoid valve for water, and the connection relationship thereof is also substantially the same as that in the prior art, it falls within the prior art. For the sake of brevity, a detailed description of what is considered to be prior art is omitted. 
     According to the present invention, by setting the length of the movable iron core in the lower magnetic conductive inner sleeve in the initial position to be not less than ¼ of a sum of the heights of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve, so as to ensure that the magnetic conduction of the non-operating air gap is not too small, avoiding magnetic saturation of the iron core, and improving the ability of the solenoid valve for water to withstand a large impulse current impact. 
     Specific parameters of the present invention for achieving the above-mentioned improvement of the magnetic circuit structure include: the gap between the upper and lower magnetic conductive inner sleeves is between 2 mm and 5 mm; the diameter of the movable iron core is reduced from 6 mm to 5±0.1 mm; the inner diameter of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve is 6.5±0.1 mm, the wall thickness is 1 mm, and the outer diameter is 8.5±0.1 mm; the inner diameter of water-isolating sleeve is 5.5±0.1 mm, and the outer diameter is 6.5±0.1 mm; and the weight of the magnetic conductive seat is not less than 60% of the weight of the movable iron core, so as to appropriately increase the magnetic conductive seat, increase the electromagnetic suction force, and enhance the reliability of valve suction. 
     Referring to  FIG. 4 , the present invention can form a water-isolating sleeve inside the upper and lower magnetic conductive inner sleeves  113  and  114  by injecting plastic inside the upper and lower magnetic conductive inner sleeves  113  and  114  mounted in the coil assembly. 
       FIG. 5  to  FIG. 11  show a specific process of forming a water-isolating sleeve inside the upper and lower magnetic conductive inner sleeves  113  and  114  according to the present invention. 
     As shown in  FIG. 5 , an upper magnetic conductive inner sleeve  113  and a lower magnetic conductive inner sleeve  114  are mounted on a cavity on the coil assembly, and a magnetic conductive inner sleeve positioning ring  106  (see  FIG. 4 ) in a hole in the coil rack  104  defines the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114  at a position capable of contacting the magnetic yoke  111 ; then, the yoke positioning grooves  112  of the yoke  111  are engaged with the yoke positioning bosses  105  of the upper and lower end faces of the coil rack  104 , so that the yoke  111  is positioned on the coil rack  104  on the one hand and closely contacted and coupled with the upper and lower magnetic conductive inner sleeves  113  and  114  on the other hand, thereby forming the stator assembly  102  shown in  FIG. 6 . 
     Compared with the prior art, the present invention can reduce the welding process of welding the yoke  111  to the upper and lower magnetic conductive inner sleeves, and can reduce one yoke. However, in the prior art, it is necessary to weld the upper magnetic conductive inner sleeve with one yoke, weld the lower magnetic conductive inner sleeve with the other yoke, and then butt-join the two yokes (there might be a quality problem that the butt joint cannot be achieved). Thus, according to the present invention, the steps can be reduced, the cost can be reduced, and the product quality can be improved. 
     In the present invention, the stator assembly  102  is used as a base or an insert, and plastic is injected on the stator assembly  100  with a water-isolating sleeve, comprising: 
     by putting the stator assembly  102  shown in  FIG. 6  into the mold and injecting plastic for the first time, the coil winding  109 , the yoke  111  and the electronic component  108  are wrapped with plastic, but the insert  107  and the hole in the coil rack  125  with the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114  are exposed, thus forming the primary plastic-sealed assembly  101  shown in  FIGS. 7 and 8 ; 
     By putting the primary plastic-sealed assembly  101  into another mold and injecting plastic for the second time, the water-isolating sleeve  117  is formed on the hole in the coil rack  125  with the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114 , so as to manufacture the integrated stator assembly  100  with water-isolating sleeve as shown in  FIGS. 10 and 11 . 
       FIG. 11  shows the structure of the integrated stator assembly  100  having a water-isolating sleeve. The yoke  111  is tightly fixed to the coil assembly  103  by a plastic-sealed layer  116 , and the water-isolating sleeve  117  is injection molded on the inner walls of the upper and lower magnetic conductive inner sleeves  113  and  114 , so that the water-isolating sleeve  117  having a thickness of about 0.5 mm is formed in the hole of the coil rack, that is, the present invention reduces the thickness of the water-isolating sleeve  117  by the injection-plastic process. The present invention can greatly reduce the gap between the movable iron core  201  and the magnetic conductive inner sleeve, and increase the electromagnetic force acting on the movable iron core  201 , with respect to the water-isolating sleeve of 1.7 mm thick in the prior art. 
     In addition, in the second injection plastic, the base  118  of the water-isolating sleeve having external threads is also injection molded so that the integrated stator assembly  100  having a water-isolating sleeve can be screwed onto the valve body  205  having internal threads when assembling the solenoid valve for water, see  FIG. 11 . 
     The magnetic conductive seat  121  is then mounted within the upper magnetic conductive inner sleeve  113  to form the plastic-sealed stator assembly shown in  FIG. 4 . 
       FIGS. 9 a -9 d    show the structure of the upper and lower magnetic conductive inner sleeves of the present invention. The upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114  of the present invention are cylindrical, and its wall is provided with a radial through-hole  115  for glue passing, and the inner surface of the cylinder wall is provided with an magnetic conductive inner sleeve axial groove  122  (for facilitating the flow of hot melt plastic during injection-plastic), and the magnetic conductive inner sleeve axial groove  122  communicates with the radial through-hole  115 . By injecting plastic oin the hole of the coil rack having the upper and lower magnetic conductive inner sleeves, the injected plastic used to form the water-isolating sleeve flows along the upper and lower magnetic conductive inner sleeve axial grooves  122  into the magnetic conductive inner sleeve through hole  115 , forming a root for positioning the water-isolating sleeve  117 , such that the water-isolating sleeve  117  is firmly secured to the upper and lower magnetic conductive inner sleeves  113 ,  114  that have been positioned by the magnetic conductive inner sleeve positioning ring  106 . 
     In addition, the present invention may further provide a plurality of circumferential grooves (not shown) on the inner surfaces of the upper and lower magnetic conductive inner sleeves  113  and  114  for further fixing the water-isolating sleeve using the radial grooves when the water-isolating sleeve is plastic sealed. 
       FIGS. 12-14  illustrate another embodiment of the present invention for forming a water-isolating sleeve. First, the upper magnetic inner sleeve  113 , the stopper  106  and the lower magnetic inner sleeve  114  are placed together (as shown in  FIG. 12 ). 
     Second, the upper magnetic inner sleeve  113 , the stopper  106  and the lower magnetic inner sleeve  114 , which are placed together, are used as inserts for injecting plastic, so as to manufacture a water-isolating sleeve assembly including the water-isolating sleeve formed inside the upper magnetic inner sleeve and the lower magnetic inner sleeve (see  FIGS. 13 and 14 ). Then, the water-isolating sleeve assembly is installed into the hole in the coil assembly and plastic is injected, thus forming the plastic-sealed stator assembly as shown in  FIG. 4 . 
     Compared with a technology of “injection molding the upper and lower magnetic conductive inner sleeves as inserts together with the water jacket and the bobbin”, the realization method of the water inlet solenoid valve of the present invention can greatly reduce the working air gap, because the water-isolating sleeve of the present invention is formed by injecting plastic in the hole of the coil rack, and a very thin water isolating sleeve can be formed. The technology of “injection molding the upper and lower magnetic inner sleeves as inserts together with the water jacket and the bobbin” is that “the magnetic inner sleeve, the water jacket and the coil rack are injection molded into an integrated part”, so it is necessary to manufacture separate water jacket, coil rack and magnetic inner sleeve; Considering factors such as manufacturing process and strength, the water jacket must have a certain thickness, so that its thickness is greater than that of the water-isolating sleeve of the present invention which plastic is injected in the hole of the coil rack. In addition, the technology of “injection molding the upper and lower magnetic inner sleeves as inserts together with the water jacket and the bobbin” cannot package the yoke, the coil winding, the insert, the coil rack, the magnetic inner sleeve and the water-isolating sleeve together to form an integrated stator assembly. 
     The present invention also provides a solenoid valve for water with increasing electromagnetic suction force, made according to the above method, which comprises: 
     a plastic-sealed stator assembly; 
     a valve body assembly comprising a movable iron core for assembling with the plastic-sealed stator assembly to form the solenoid valve for water; 
     as shown in  FIG. 3 , the plastic-sealed stator assembly of the present invention comprises: a coil assembly having a coil rack  104 , a coil winding  109  wound on the coil rack  104 , an insert  107  and an electronic component  108  mounted on the coil rack  104  (see  FIG. 5 ); an upper magnetic conductive inner sleeve  113  and a lower magnetic conductive inner sleeve  114  mounted in the hole of the coil assembly; a water-isolating sleeve  117  located inside the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114 ; a yoke  111  located outside the coil assembly and connecting the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114 ; a magnetic conductive seat  121  mounted inside the upper water-isolating sleeve  117 ; and a plastic-sealed layer  116  covering the coil assembly and the yoke  111 . 
     according to the present invention, the upper end face of the movable iron core  201  at the initial position is set as not lower than the upper edge of the lower magnetic conductive inner sleeve  114  and not higher than ¼ of the distance from the upper edge of lower magnetic conductive inner sleeve  114  to the lower edge of upper magnetic conductive inner sleeve  113 , so as to increasing the electromagnetic suction force of the solenoid valve for water. 
     Referring to  FIG. 3 , the valve body assembly of the solenoid valve for water of the present invention includes: a return spring  200  and a movable iron core  201  which are received in a water-isolating sleeve; a flow-through hole valve plug rubber  202 ; a valve plug  203 ; a valve plug rubber  204 ; a valve body  205 , a mounting rack  206 , a pressure relief ring  207 , a rubber gasket  208 , and a filter screen assembly  209 , etc. 
     According to the present invention, the upper end face of the movable iron core at the initial position is set as not lower than the upper edge of lower magnetic conductive inner sleeve and not higher than ¼ of the distance from the upper edge of lower magnetic conductive inner sleeve to the lower edge of upper magnetic conductive inner sleeve, so as to enhance the electromagnetic suction force of the solenoid valve for water. 
     According to the present invention, by setting the length of the movable iron core in the lower magnetic conductive inner sleeve in the initial position to be not less than ¼ of a sum of the heights of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve, so as to ensure that the magnetic conduction of the non-operating air gap is not too small, avoiding magnetic saturation of the iron core, and improving the ability of the solenoid valve for water to withstand a large impulse current impact. 
     Specific parameters of the present invention for achieving the above-mentioned improvement of the magnetic circuit structure include: the gap between the upper and lower magnetic conductive inner sleeves is between 2 mm and 5 mm; the diameter of the movable iron core is reduced from 6 mm to 5±0.1 mm; the inner diameter of the upper magnetic conductive inner sleeve and the lower magnetic conductive inner sleeve is 6.5±0.1 mm, the wall thickness is 1 mm, and the outer diameter is 8.5±0.1 mm; the inner diameter of water-isolating sleeve is 5.5±0.1 mm, and the outer diameter is 6.5±0.1 mm; and the weight of the magnetic conductive seat is not less than 60% of the weight of the movable iron core, so as to appropriately increase the magnetic conductive seat, increase the electromagnetic suction force, and enhance the reliability of valve suction. 
     Moreover, according to the present invention, the water-isolating sleeve inside the upper and lower magnetic conductive inner sleeves is formed by injecting plastic on the inner surfaces of the upper and lower magnetic conductive inner sleeves. 
     Alternatively, the invention can also place the upper magnetic inner sleeve, the stopper and the lower magnetic inner sleeve together as an insert, and perform injection molding on them to form the water-isolating sleeve assembly which is installed in the hole of the coil assembly and includes water-isolating sleeve formed by injection molding on the inner surfaces of the upper magnetic inner sleeve and the lower magnetic inner sleeve. 
     On the other hand, the upper magnetic conductive inner sleeve  113  and the lower magnetic conductive inner sleeve  114  of the present invention are cylindrical, and its wall is provided with a radial through-hole  115  for glue passing. the inner surface of its wall is provided with an magnetic conductive inner sleeve axial groove  122 , and the magnetic conductive inner sleeve axial groove  122  communicates with the radial through-hole  115 . By injecting plastic in the hole of the coil rack having the upper and lower magnetic conductive inner sleeves, the injected plastic used to form the water-isolating sleeve flows along the upper and lower magnetic conductive inner sleeve axial grooves  122  into the magnetic conductive inner sleeve through hole  115 , forming a root for positioning the injection molded water-isolating sleeve  117 . 
     According to the experimental study of the inventor, the magnetic circuit structure of the solenoid valve for water is designed in such a size that, while not affecting the low-pressure starting performance of the valve, the consumables can be reduced and the cost can be reduced. The diameter of the movable iron core is reduced from 6 mm to 5±0.1 mm; the inner diameter of the water-isolating sleeve is 5.5±0.1 mm, the wall thickness is 0.5 mm, and the outer diameter is 6.5±0.1 mm; the inner diameter of the upper and lower magnetic conductive inner sleeves is 6.5±0.1 mm, the wall thickness is 1 mm, and the outer diameter is 8.5±0.1 mm; the aperture in the hole in the coil rack is about 8.7 mm. 
     Since the water-isolating sleeve vibrates due to the action of the movable iron core during the operation of the valve, the coil rack needs to meet certain rigidity requirements to prevent damage. According to the provisions of GB14536.1-2008 “Electrical automatic controllers for household and similar purposes” and GB 4706.1-2005 “Safety of electrical appliances for household and similar purposes”, the magnetic yoke of water inlet valve is exposed and accessible to human hands. In order to meet the requirements for insulation, the skeleton wall thickness must be greater than 0.7 mm. The magnetic yoke of the water inlet valve of the present invention is plastic-sealed, which can&#39;t be touched by human hands, and the skeleton has no thickness requirement, and only needs to ensure the strength so as not to be deformed when winding, so that the thickness of the skeleton can be minimized. 
     Since the invention adopts the manufacturing process of water-isolating sleeve injection molding, the water-isolating sleeve is formed by injecting plastic on the stator assembly and is integrated with the coil rack, and the wall thickness of the coil rack is not limited by the national standard, the wall thickness of the hole in the coil rack is reduced from 1 mm to 0.4 mm, so that the coil diameter is further reduced, and the amount of copper wire is further reduced under the condition that the number of winding turns and the wire diameter are unchanged. 
     Moreover, as the movable iron core becomes smaller and lighter, when the coil winding  109  is energized, the noise generated by the attraction between the magnetized magnetic seat  121  and the movable iron core  201  also decreases. 
     It should be noted that the injection-molding process of the water-isolating sleeve used in the solenoid valve for water of the present embodiment is merely illustrative of the manufacturing process of the solenoid valve for water, and does not limit the magnetic circuit structure. The magnetic circuit structure improvement method of the present invention is effective for all solenoid valve for waters in enhancing the solenoid attraction force at start-up, reducing the wire consumption and reducing the noise generated by moving iron core suction under the condition of meeting the minimum start-up voltage requirements. 
     Although the present invention has been described in detail above, the present invention is not limited thereto, and various modifications can be made by a person skilled in the art according to the principles of the present invention. Thus, modifications made in accordance with the principles of the present invention should be understood to fall within the scope of the invention.