Abstract:
A method of manufacturing a valve element for a solenoid valve to open and close a valve seat, comprising the steps of; preparing a leaf spring including an outer peripheral ring section and a hub section having a central hole, forming a ring-shaped outer peripheral seal along the peripheral ring section, and preparing a movable core having a cup-shaped cross section and including a cylindrical section and an end wall section. The method further comprising, forming a valve seal on the end wall section by placing the movable core and the leaf spring in a mold and aligning and holding the leaf spring and the stepped section in contact with each other, and aligning a holder ring along an outer periphery of the movable core, and bringing the holder ring into engagement with the movable core, wherein the leaf spring and the movable core are rigidly secured to each other.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 09/455,689 filed Dec. 7, 1999 which issued Sep. 18, 2001 as U.S. Pat. No. 6,290,205. 
    
    
     BACKGROUND OF THE INVENTION 
     The present invention relates to a method of manufacturing a valve element adapted to be used in a solenoid valve, the 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 method of manufacturing refers to a solenoid valve comprising 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 movable core with a cup-shaped cross section arranged in a central area of the leaf spring and a valve seal arranged at an end face of the movable core in order to open and close the valve seat. 
     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 inventor of the present invention invented a method of placing a leaf spring in a metal mold with a movable core held in engagement with the central hole of the leaf spring and forming a leaf spring holding section for rigidly holding the movable core and the leaf spring through vulcanization and molding at the time of forming a valve seal for an end wall section of the movable also through vulcanization and molding so that the leaf spring and the movable core may be rigidly held together by the leaf spring holding section formed integrally with 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 a leaf spring holding section made of expensive fluorine rubber is accompanied by an insufficient holding strength particularly when the leaf spring holding section is poorly contractible during the molding process. 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 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 another aspect of the invention, there is provided 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 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 movable core having a cup-shaped cross-section and including a cylindrical section and an end wall section, said end wall section being arranged at an end of the cylindrical section and having a central through hole, said cylindrical section having on its outer periphery a stepped section to be held in contact with said leaf spring and having a groove section, a step of forming a valve seal through vulcanization and molding at said end wall, said valve seal having a main body section disposed on an outer surface of said end wall section, a small diameter section disposed in said through hole, and an holding section located on an inner surface of said end wall section and connected to said main body section by way of the small diameter section, a step of placing said movable core and said leaf spring in a thermal caulking metal mold and aligning and holding said leaf spring and said stepped section in contact with each other, a step of aligning a holder ring along an outer periphery of said movable core and a step of bringing said holder ring into engagement with said groove by thermal caulking to that said leaf spring and said movable core are rigidly secured to each other by means of said holder ring. 
    
    
     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 a schematic pan view of the disk-shaped leaf spring of the embodiment of FIG. 1 provided with an outer peripheral seal. 
     FIG. 4 is a schematic cross sectional view of the leaf spring taken long line B—B in FIG.  4 . 
     FIG. 5 is a schematic plan view of the movable core shown in FIG.  2 . 
     FIG. 6 is a schematic cross sectional view of the movable core taken along line C—C in FIG.  5 . 
     FIG. 7 is a schematic cross sectional view of the movable core taken along line D—D in FIG.  5 . 
     FIG. 8 is a schematic cross sectional view of the movable core provided with a valve seal. 
     FIG. 9 is a schematic plan view of the movable core of FIG. 8 provided with a valve seal. 
     FIG. 10 is a schematic cross sectional view of a thermal caulking metal mold for rigidly securing the movable core to the leaf spring by means of a holder ring. 
     FIG. 11 is a schematic plan view of a known valve element shown for the purpose of comparison. 
     FIG. 12 is a schematic cross sectional view of the valve element of FIG. 11 taken along line E—E in FIG.  11 . 
    
    
     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 lid are formed between the hub section  11   a  and the outer peripheral ring section  11   b  as shown in FIGS. 3 and 4. A central hole  11   e  is cut through the hub section  11   a.    
     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. 
     As shown in FIG. 5, the movable core  13  includes a cylindrical section  13   a  and an end wall section  13   b  arranged at an end thereof and shows a cup-shaped cross section. A through hole  13   c  is cut through an central area of the end wall section  13   b  of the movable core  13  and an annular groove  13   d  is formed on the outer periphery of the cylindrical section  13   a . A stepped section  13   e  is formed in the groove  13   d  and used for aligning the leaf spring  11 . The movable core  13  had a cabinet  13   f  in the inside thereof for containing a spring therein when the valve element  10  is mounted into a solenoid valve. 
     A valve seal  14  is formed through vulcanization and molding and fitted to the end wall section  13   b . 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 only fitted to the end wall section  13   b  of the movable core  13  and hence it is sufficient for the valve seal  14  to have a size large enough for sealing the valve seat. The valve seal includes a main body section  14   a  arranged on the outer lateral surface of the end wall section  13   b , a small diameter section  14   b  held in engagement with the through hole  13   c  and a large diameter section  14   c  arranged on the inner surface of the end wall section  13   b  and is formed integrally by vulcanization and molding. The surface of the main body section  14   a  of the valve seal  14  may be coated with fluorine resin such as polytetrafluoroethylene (PTFE) in order to improve the friction resistance of the sealing surface. 
     A holder ring  15  made of thermal plastic resin is held in engagement with the groove  13   d  of the movable core  13  so that the leaf spring  11  is rigidly secured to the movable core  13  by the holder-ring  15 . 
     Now, a method of manufacturing a valve element  10  according to the invention will be described below. 
     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 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. 
     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 leaf spring  11  is manufactured to have the outer peripheral seal  12  rigidly secured thereto. 
     A movable core  13  is firstly formed by press molding, forging or casting to produce a cylindrical section  13   a  and an end wall section  13   b  and to show a cup-shaped cross section and subsequently machined to produce a groove  13   d  on the outer periphery of the cylindrical section  13   a.    
     Then, a valve seal  14  is formed on the end wall section  13   b  of the movable core  13  by vulcanizing and molding an elastic material such as rubber, fluorine rubber for example, in a rubber molding metal mold (not shown) in which the movable core  13  is placed in position. The main body section  14   a  of the valve seal  14  arranged on the outer surface side of the end wall section  13   b  and the large diameter holding section  14   c  of the valve seal  14  arranged on the inner surface side of the end wall section  13   b  are connected by a small diameter section  14   b , which sections are formed integrally through vulcanization and molding. 
     Now, the process of assembling the leaf spring  11  carrying the outer peripheral seal  12  and the movable core  13  carrying the valve seal  14  by means of a holder ring  15  will-be described by referring to FIG.  10 . 
     The thermal caulking metal mold  20  shown in FIG. 10 comprises a die  21  and a punch  22 , and the die  21  has a recess  21   a  for receiving a movable core  13  and an annular recess  21   b  for receiving an outer peripheral seal  12 . As seen from FIG. 10, the punch  22  can be moved toward and away from the die  21  by means of a pneumatically operated press machine (not shown) and is provided in the inside with a heater. The punch  22  has a recess  22   a  for receiving the end wall side of the movable core  13 , said recess  22   a  having a first slope  22   b  of a small angle of inclination arranged near the opening of the recess  22   a  and a second slope  22   c  of a large angle of inclination extending from the first slope  22   b.    
     The movable core  13  is placed in position in the recess  21   a  with its opening side facing downward, while the portion of the leaf spring  11  carrying the outer peripheral seal  12  is placed in position in the recess  21   b . Thus, both the movable core  13  and the leaf spring  11  are placed in position in the die  21  of the metal mold  20 . 
     The holder ring  15  made of thermal plastic resin is preliminarily heated to make it easily deformed and then fitted to the outer periphery of the movable core  13  from the side of the end wall  13   b . As the punch  22  is moved toward the die  21  under this condition, the angular section of the upper surface of the holder ring  15  is pushed inwardly by the first slope  22   b  of the punch  22  and then further pushed inwardly by the second slope  22   c . Thus, when the punch  22  is completely moved to the position closest to the die  21 , the holder ring  15  is tightly held into engagement with the groove  13   d  of the movable coil  13  as shown in FIG.  2 . 
     When the lower surface of the punch  22  comes closest to the die  21 , any excessive part of the holder ring  15  is guided by the first slope  22   b  and moved outside of the groove. 
     Since the outer peripheral seal  12  is formed on the leaf spring  11  through vulcanization and molding, while the valve seal  14  is formed on the end wall section  13   b  of the movable core  13  also through vulcanization and molding, the outer peripheral seal  12  may be made of less expensive NBR, and the valve seal  14  may be made of expensive rubber such as fluorine rubber. 
     FIGS. 11 and 12 schematically illustrate a known valve element  30  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  32  to a leaf spring  11  having a configuration similar to the leaf spring  11  of the above embodiment by means of a valve seal  31  in this valve element  30 . 
     The movable core  32  has a large diameter section  32   a  and a small diameter section  32   b , and the leaf spring  11  is brought into contact with a stepped section  32   c  of the large diameter section  32   a . The valve seal  31  has a main body section  31   a  to be held in contact with a valve seat and a holder section  31   b  integral with the main body section  31   a  and adapted to entirely cover the small diameter section  32   b  of the movable core. In the case of this valve element  30 , expensive fluorine rubber has to be used for the holder section  31   b  as well as for the main body section  31   a  of the valve seal  31  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  32  relative to the leaf spring  11  to which it is directly fitted by means of rubber. 
     To the contrary, in the case of a valve element  10  according to the invention, the movable core  13  is fitted to the leaf spring  11  by means of a resin-made holder ring  15  to improve the holding strength of the movable core relative to the leaf spring. Additionally, since a rubber-made valve seal  14  is formed only on the end wall section  13   b  of the movable core  13  through vulcanization and molding, the volume of rubber to be used for the valve element can be reduced to manufacture the valve element  10  with lower cost even if expensive fluorine rubber is used for the valve seal  14 . 
     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 and 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.