Abstract:
A method of manufacturing a valve element adapted to be mounted into a selenoid valve to open and close a valve seat of the valve. The method comprising a step of preparing a leaf spring including an outer peripheral ring section and a hub section, a step of forming an outer peripheral seal by vulcanizing and molding an elastic material along the outer peripheral ring section, a step of preparing a valve disk to be fitted to one surface of the hub section, and a step of providing a valve seal to be held in contact with the valve seat. The method further compring a step of preparing a movable core having a flange section arranged on an opposite surface of the hub section, a step of preparing a holder ring and bonding the holder ring to the valve disk wherein the movable core is secured to the leaf spring.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. application Ser. No. 09/455,688 filed Dec. 7, 1999 is now U.S. Pat. No. 6,213,448, entitled Valve Element and Method of Manufacturing the Same. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method of manufacturing a valve element adapted to be used in a solenoid valve, such valve element having a disk-shaped leaf spring carrying a movable core fitted thereto. 
     Control valves for controlling the flow of fluid include flow rate control valves, direction control valves and pressure control valves. The flow rate control valve is designed to modify the flow rate of fluid by providing appropriate resistance to the flow by means of a valve element and the direction control valve is designed to allow or block a flow of fluid in a given direction to shift the direction of a flow of fluid also by means of a valve element, whereas the pressure control valve is adapted to regulate the pressure of the flow of fluid in a fluid circuit by means of a valve element. A solenoid valve is a kind of control valve having a valve element to be operated by means of a solenoid. 
     Known solenoid valves for controlling the flow rate of fluid flowing through a flow path include the one proposed in Japanese Patent Application Laid-Open No. 7-145873. The proposed solenoid valve comprises a valve housing having two ports and a valve element fitted to the valve housing, the valve element having a valve seal adapted to take an open position for opening a valve seat and allowing the two ports to communicate with each other or take a closed position for closing the valve seat and blocking the communication therebetween. 
     A solenoid coil is arranged in the valve housing in order to operate the valve element. A fixed core (fixed iron core) and a movable core (movable iron core) are arranged at the center of the coil so that the valve element may be opened and closed by means of the movable core. As valve elements capable of being operated by a movable core, there has been developed a valve element provided with such movable core fitted thereto. The valve element of this type typically comprises a disk-shaped leaf spring, an outer peripheral seal arranged at the outer periphery of the leaf spring, a valve seal arranged on one of the surfaces of the leaf spring in order to open and close the valve seat, and a movable core arranged on the other surface of the leaf spring. 
     The inventors of the present invention have studied valve bodies having a movable core fitted thereto as well as methods for manufacturing such a valve element. As a result of intensive research efforts, the inventors of the present invention invented a method of placing a leaf spring in a metal mold and molding fluorine rubber into an outer peripheral seal and a valve seal so that a movable core and a leaf spring can be held together by means of the valve seal. 
     However, the sealing effect of a valve element relative to a valve seat may be ensured when costly fluorine rubber is only used for the valve seal but the arrangement of rigidly holding the movable core in position by means of a fluorine rubber valve seal and preparing the valve seal and the outer peripheral seal simultaneously by molding requires the valve seal to have a large capacity. Then, such a valve seal can be prepared only by using a large volume of costly and heavy fluorine rubber to consequently raise the weight of the valve element and counter all the efforts for reducing the weight of the valve element. Additionally, any attempt for rigidly holding a movable core and a leaf spring together by means of fluorine rubber is accompanied by an insufficient holding strength. Then, the valve element would not be able to enjoy a long service life and the solenoid valve comprising such a valve element would lose reliability. 
     SUMMARY OF THE INVENTION 
     Therefore, an object of the present invention is to provide a method of manufacturing a highly reliable valve element that can be prepared with a reduced volume of costly fluorine rubber and hence at reduced cost. 
     Another object of the invention is to provide a method of manufacturing a lightweight valve element. 
     Still another object of the present invention is to provide a method of manufacturing a highly durable valve element wherein the leaf spring and the movable core are rigidly held together with an enhanced level of strength. 
     According to one aspect of the invention, the above objects and other objects are achieved by providing a method of manufacturing a valve element adapted to be arranged in a solenoid valve to open and close a valve seat, comprising a step of preparing a leaf spring including an outer peripheral ring section, a hub section having a central hole and one or more than one connection holes and a plurality of radial arm sections for connecting between said outer peripheral ring section and said hub section, a step of forming a ring-shaped outer peripheral seal by vulcanizing and molding an elastic material such as rubber along said outer peripheral ring section, a step of preparing a resin-made valve disk with a central anchoring hole to be fitted to one of the opposite surfaces of said hub section, a step of preparing a movable core having at an end thereof a flange section to be held in contact with the outer surface of said hub section and arranged on said opposite surface of said hub section, a step of preparing a resin-made holder ring to be fitted onto said movable core, a step of forming a valve seal including a main body section to be fitted to the front surface of said valve disk and a holder section to be fitted to the rear surface of said valve disk by vulcanizing and molding an elastic material such as rubber and a step of arranging said valve disk on one of the surfaces of said hub section and said flange section onto the other surface of said hub section to make them contact with each other and ultrasonically welding said valve disk and said holder ring while holding said holder ring in engagement with said movable core and in contact with said valve disk so that said movable core is fitted to said leaf spring by means of said valve disk and said holder ring to be made integral with said valve disk. 
     Said holder ring may be provided with one or more than one meltable projections held in contact with said valve disk by way of said one or more than one connection holes respectively. Alternatively, said valve disk may be provided with one or more than one meltable projections held in contrast with said holder ring by way of said one or more than one connection holes respectively. Said holder ring is provided with a stepped section into which said flange section is put. Said valve disk and said holder ring are made or resin with an average specific gravity of less than 1.9 and apt to be ultrasonically welded. Said movable core is molded from a thin steel plate. 
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS 
     FIG. 1 is a schematic plan view of an embodiment of valve element according to the invention. 
     FIG. 2 is a schematic cross sectional view of the embodiment of FIG. 1 taken along line A—A in FIG.  1 . 
     FIG. 3 is an exploded cross sectional view of the embodiment of FIG. 1, showing the components of FIG. 2 in a separated state. 
     FIG. 4 is a schematic pan view of the disk-shaped leaf spring of the embodiment of FIG. 1 provided with an outer peripheral seal. 
     FIG. 5 is a schematic cross sectional view of the leaf spring taken long line B—B in FIG.  4 . 
     FIG. 6 is a schematic plan view of the holder ring shown in FIG.  2 . 
     FIG. 7 is a schematic cross sectional view of the holder ring taken along line C—C in FIG.  6 . 
     FIG. 8 is a schematic plan view of a holder ring obtained by modifying the holder ring of FIG.  6 . 
     FIG. 9 is a schematic cross sectional view of the holder ring of FIG. 8 taken along line D—D in FIG.  8 . 
     FIG. 10 is a schematic plan view of another holder ring also obtained by modifying the holder ring of FIG.  6 . 
     FIG. 11 is a schematic cross sectional view of the holder ring of FIG. 10 taken along line E—E in FIG.  10 . 
     FIG. 12 is a schematic plan view of a known valve element shown for the purpose of comparison. 
     FIG. 13 is a schematic cross sectional view of the valve element of FIG. 12 taken along line F—F in FIG.  12 . 
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT 
     Referring to FIG. 1 showing a preferred embodiment of valve element according to the invention, the valve element  10  comprises a disk-shaped leaf spring  11  made from a thin steel plate, which includes a center hub section  11   a,  an outer peripheral ring section  11   b  and a plurality of radial arm sections  11   c  connected to the hub section  11   a  and the outer peripheral ring section  11   b,  and a total of three openings  11   d  are formed between the hub section  11   a  and the outer peripheral ring section  11   b  as shown in FIGS. 4 and 5. A central hole  11   e  is cut through the hub section  11   a  and a total of three arcuate connection holes  11   f  are arranged around the central hole  11   e.    
     An outer peripheral seal  12  having a substantially circular cross section is formed around the outer periphery of the leaf spring  11  by vulcanizing and molding an elastic material such as rubber and rigidly secured to the leaf spring  11 . More specifically, the outer peripheral seal  12  is made of acrylonitrile-butadiene rubber (NBR). The valve element  10  is securely fitted to the valve housing of a solenoid valve as its outer peripheral seal  12  is held by the valve housing. 
     A resin-made valve disk  13  having an engaging hole  13   a  for engagedly receiving a valve seal  14  is fitted to one of the surfaces of the hub section  11   a  of the leaf spring  11 . The valve seal  14  includes a main body section  14   a  to be fitted to one of the surfaces of the valve disk  13  and held in contact with the valve seat of the solenoid valve, a small diameter section  14   c  projecting to the back side of the main body section  14   a  and a large diameter holder section  14   b  connected to the main body section  14   a  by way of the small diameter section  14   c  and is adapted to be fitted to the valve disk  13  by vulcanization and molding. 
     The valve seal  14  is made of fluorine rubber, which is more expensive than NBR. However, for the purpose of the invention, the volume of expensive fluorine rubber necessary for molding is limited so that the valve element  10  can be manufactured at low cost because the valve seal  14  is fitted to the valve disk  13  and hence it is sufficient for the valve seal  14  to have a size large enough for sealing the valve seat. 
     A metal-made cylindrical movable core  15  is arranged on the other surface of the leaf spring  11 . The movable core  15  has a flange  15   a  arranged at an end thereof and a void chamber  15   b  in the inside for containing the spring therein when the valve element  10  is fitted to the solenoid valve. A resin-made holder ring  16  having a central insertion hole  16   a  is brought into engagement with the outer periphery of the movable core  15  at an end thereof in order to securely hold the movable core  15 , the leaf spring  11  and the valve disk  13  together. As seen from FIGS. 6 and 7, a total of three arcuate meltable projections  16   b  are projecting from an end face of the holder ring  16  at positions corresponding to the respective connection holes  11   f  of the leaf spring  11  and a stepped section  16   c  is arranged along the inner periphery of the holder ring  16  so that it may be held in contact with the flange section  15   a  of the movable core  15 . The meltable projections  16   b  have a height slightly greater than the thickness of the leaf spring  11 . 
     The meltable projections  16   b  may alternatively be arranged on the valve disk  13  instead of the holder ring  16 . 
     As the meltable projections  16   b  are held in contact with the valve disk  13  by way of the respective connection holes  11   f  under pressure, an ultrasonic vibration is applied to the valve disk  13  and the holder ring  16  by means of an ultrasonic welding machine. Then, as a result, the valve disk  13  and the holder ring  16  are bonded together to produce an integral unit by ultrasonic welding. Then, the movable core  15  is rigidly secured to the leaf spring  11  by means of the valve disk  13  and the holder ring  16  that are now integral with each other so that the valve element  10  can reliably operate for a prolonged period of life. 
     Materials that can be used for the valve disk  13  and the holder spring  16  include polyphenylenesulfide (PPS) having an average specific gravity of 1.3 and hence lighter than fluorine rubber having an average specific gravity of 1.9 and ABS resin having a specific gravity of 1.3. Thus, the valve element  10  can be made lightweight by using any of such materials. 
     The valve element  10  obtained in this way is a unitary assembly comprising a leaf spring  11  having an outer peripheral seal  12 , a valve disk  13  having a valve seal  14 , a movable core  15  and a holder ring  16  and hence can be handled as a single product. As a result, any defects that may be given rise to in the manufacturing process and/or during transportation can be addressed quickly. 
     Now, a method of manufacturing a valve element  10  according to the invention will be described by referring to FIGS. 1 through 7. 
     A leaf spring  11  including an outer peripheral ring section  11   b,  a hub section  11   a  having a central hole  11   e  and three connection holes  11   f  and three radial arm sections  11   c  connecting the outer peripheral section  11   b  and the hub section  11   a  is formed by press-molding using a press machine (not shown). Thus, the obtained leaf spring  11  shows a configuration as shown in FIGS. 1 through 7. 
     A cylindrical movable core  15  having a flange section  15   a  at an end thereof is formed by press-molding a thin steel plate by means of another press machine (not shown). Thus, the obtained movable  15  having a cup-like cross sectional view as shown in FIGS. 2 and 3. 
     A valve disk  13  having a central anchoring hole  13   a  is formed by injection molding or some other molding technique, using a resin modelling metal mold (not shown). Meanwhile, an holder ring  16  having a central insertion hole  16  and meltable projections  16   b  arranged at an end face thereof is also formed by means of an injection molding technique as in the valve disk  13 , using another resin molding metal mold (not shown). 
     An outer peripheral seal  12  is formed around the outer peripheral section of the leaf spring  11  by vulcanizing and molding an elastic material such as rubber, NBR for example using a rubber molding metal mold (not shown) arranged around the leaf spring  11 . As a result, the outer peripheral seal  12  is manufactured to be rigidly secured to the leaf spring  11 . 
     A valve seal  14  is formed on the opposite surfaces of the valve disk  13  in respective central areas thereof by vulcanizing and molding an elastic material such as rubber, fluorine rubber for example, in a rubber molding metal mold (not shown) arranged around the valve disk  13 . As a result, the obtained valve seal  14  has a main body section  14   a  arranged on the front surface of the valve disk  13  and a large diameter holder section  14   b  arranged on the rear surface of the valve disk  13  connected mutually by a small diameter section  14   c  to form an integral entity. 
     Then, the holder ring  16  is placed in position by means of a jig (not shown) and the movable core  15  is inserted into the central insertion hole  16   a  of the holder ring  16  in such a way that the flange section  15   a  of the movable core  15  is aligned with the stepped section  16   c  of the holder ring  16 . Then, the leaf spring  11  carrying the outer peripheral seal  12  is placed on the holder ring  16  in such a way that meltable projections  16   b  are put into the respective connection holes  11   f.  As a result, the three meltable projections  16   b  of the holder ring  16  come into contact with the lower surface of the valve disk  13  through the respective connection holes  11   f.  Under this condition, the three meltable projections  16   b  are welded to the rear surface of the valve disk  13  by means of an ultrasonic welding machine (not shown). Thus, the movable core  15  is secured to the leaf spring  11  by means of the valve disk  13  and the holder ring  16  integral with the valve disk  13 . 
     FIGS. 8 and 9 schematically show a holder ring  16  obtained by modifying the holder ring  16  of the above embodiment and having meltable projections  16   b  with a triangular cross section. 
     FIGS. 10 and 11 schematic show another holder ring  16  also obtained by modifying the holder ring  16  of the above embodiment and having meltable projections with a hemispherical cross section. The meltable projections  16   b  are divided into three groups, each including four meltable projections  16   b.    
     FIGS. 12 and 13 schematically illustrate a known valve element  20  shown for the purpose of comparison. In the course of inventing a valve element according to the invention, the inventor firstly looked into a technique of securing a movable core  22  to a leaf spring  11  having a configuration similar to the leaf spring  11  of the above embodiment by means of a valve seal  21  in this valve element  20 . 
     The movable core  22  has a flange  22   a  at an end and a cabinet  22   b  in the inside thereof and is prepared by cutting. The valve seal  21  has a main body section  21   a  and a holder section  21   b  to be arranged on the rear surface of the leaf spring  11  by way of the connection holes  11   f  of the leaf spring  11 . In the case of this valve element  20 , expensive fluorine rubber has to be used for the holder section  21   b  as well as for the valve seal  21  to increase the volume of expensive fluorine rubber to be consumed for a valve element. Additionally, it is difficult to improve the holding strength of the movable core  22  relative to the leaf spring  11  to which it is directly fitted. 
     To the contrary, in the case of a valve element  10  according to the invention, the movable core is fitted to the leaf spring by means of a holder ring integrally bonded to the resin-made valve disk by partly melting the holder ring to improve the holding strength of the movable core relative to the leaf spring and also the durability and the reliability of the solenoid valve. The valve seal made of expensive fluorine rubber is arranged on the valve disk to reduce its volume and hence the cost of manufacturing the valve element. 
     In a valve element according to the invention, a leaf spring, a valve disk, a movable core and a holder ring are prefabricated and assembled together at the time of assembling the valve element so that they may be handled as many parts. As a result, any defects and/or damages that may be given rise to in the manufacturing process and/or during transportation can be addressed quickly. 
     The valve disk and the holder ring are made of resin with an average specific gravity of 1.9 or less so that the valve element can be made lightweight. The movable core is formed by press molding and hence the number of steps and the cost of manufacturing the movable core can be reduced when compared with its counterpart of FIGS. 12 and 13 that is prepared by cutting. 
     While the present invention is described above by way of a preferred embodiment thereof, the present invention is by no means limited thereto and the illustrated embodiment may be modified in various different ways without departing from the scope of the invention. For example, the valve seal  14  is made of expensive fluorine rubber in the above embodiment but it may alternatively be made of some other rubber. Similarly, while the leaf spring  11  has three radially arranged arm sections  11   c  in the above embodiment, any appropriate number of arm sections  11   c  may be used for the purpose of the invention. Likewise, while the leaf spring  11  and the holder ring  16  respectively have three connection holes  11   f  and three meltable projections  16   b  in the above embodiment, the number of connection holes  11   f  and that of meltable projections  16   b  are not limited to three and any appropriate number of connection holes  11   f  and meltable projections may be used for the purpose of the invention. The meltable projections  16   b  may be formed on the valve disk  13  instead of forming them on the holder ring  16 .