Solenoid valve

Patent Abstract
A solenoid valve capable of handling a corrosive control fluid and developing an increased attraction force. The solenoid valve 1 is adapted such that a fixed core is located in a wound coil 29 and protruding through the lower surface of the coil, a plunger 16 holding a valve sheet 17 is supported by a plate spring 18 under the fixed core, the valve sheet 17 is normally retained in contact with a valve seat 13 by spring force of the plate spring 18, and the valve sheet 17 is separated from the valve seat against the spring force of the plate spring 18 when the coil 29 is energized. The fixed core comprises two parts vertically coupled, an upper one of which is a first fixed core 26 located in the coil 29 in non-contact with the control fluid, the first fixed core being made of a material having high magnetic permeability, and a lower one of which is a second fixed core 27 fitted, protruding downward, in the coil bobbin to cover the lower end of the coil bobbin, the second fixed core being made of a material having corrosion resistance to the high-corrosive control fluid.

2. The solenoid valve according to claim 1, wherein the first fixed core is made of electromagnetic soft iron.

3. The solenoid valve according to claim 1, wherein the second fixed core is made of ferritic stainless steel.

4. The solenoid valve according to claim 2, wherein the second fixed core is made of ferritic stainless steel.

Patent Description
TECHNICAL FIELD

[0001] The present invention relates to a solenoid valve for controlling the stroke of a valve element by balance between an attraction force of a fixed core and a restoring force of a plate spring and, more particularly, to a solenoid valve for use in a mass flow controller or the like for handling corrosive gases.

BACKGROUND ART

[0002] A conventional solenoid valve used in a mass flow controller or the like to control the stroke of a valve element by balance between an attraction force of a fixed core and a restoring force of a plate spring may include for example a solenoid valve 100 of a normal closed type shown in FIG. 2.

[0003] This solenoid valve 100 includes a body 101 formed with an inlet passage 102 and an outlet passage 104, and a valve seat 103 projecting upward at an upper opening of the inlet passage 102. A valve sheet 105 which can be brought into contact with or separated from the valve seat 103 is supported, together with a plunger 106, by a plate spring 107. The plate spring 107 is pressed by a retainer 108 of which the peripheral edge is engaged in the body 101. A bonnet 111 serving as a yoke is fitted on the retainer 108. In this bonnet 111, a fixed core 112 is centrally secured. This fixed core 112 is disposed in a coil bobbin 115 around which a coil 113 is wound so that the fixed core 112 protrudes downward from the coil bobbin 115 with a small clearance between the lower end surface of the fixed core 112 and the plunger 106.

[0004] This solenoid valve 100 is normally held in a valve-closed state where the valve sheet 105 is pressed against the valve seat 103 by the spring force of the plate spring 107. When current is supplied to the coil 113, the fixed core 112 is magnetized, attracting the plunger 106 upward against the spring force of the plate spring 107. Accordingly, the valve sheet 105 is separated from the valve seat 103 to provide communication between the inlet passage 102 and the outlet passage 104, allowing control fluid to flow therethrough.

[0005] When the amount of current to be applied to the coil 113 is changed, a magnetic attraction force will accordingly vary. Thus, the amount of stroke of the plunger 106 is changed to adjust the degree of valve opening between the valve seat 103 and the valve sheet 105. It is accordingly possible to control the flow rate of control fluid to be allowed to flow into a secondary side through the outlet passage 104.

[0006] [Patent Document 1] Jpn. unexamined patent publication No. 2002-357280

DISCLOSURE OF THE INVENTION

Problems to be Solved by the Invention

[0007] However, if the conventional solenoid valve 100 is to be operated to flow a large flow rate of fluid, the electromagnetic attraction force generated by energization of the coil 113 would be insufficient to attract the plunger 106 upward to the fixed core 112 side. It is therefore firstly conceivable that increasing the size of the solenoid valve 100 itself with an increase in the winding number of the coil 113 may be effective in producing a sufficient attraction force. However, such large-sized solenoid valve may have an undesirable influence on a semiconductor manufacturing device or the like into which the solenoid valve could be integrated. Further, it is also conceivable that the amount of current to be applied to the coil 113 is increased to raise a magnetomotive force (AT). However, this configuration adversely would increase a heating value.

[0008] The mass flow controller in which the solenoid valve 100 is used is arranged to handle high-corrosive control fluid. Accordingly, the fixed core 112 may generate a larger attraction force if made of a material having high magnetic permeability, but the fixed core 112 will come in contact with high-corrosive control fluid in view of structure. However there is no appropriate material capable of increasing the attraction force and having corrosive resistance.

DISCLOSURE OF INVENTION

[0009] The present invention has been made to solve the above problems and has a purpose to provide a solenoid valve capable of handling a corrosive control fluid and developing an increased attraction force.

[0010] The solenoid valve of the present invention is characterized in that a solenoid valve adapted such that a fixed core located in a wound coil and protruding downward from a wound coil, a plunger is supported under the fixed core by a plate spring and holds a valve sheet which is normally retained in contact with a valve seat by spring force of the plate spring, and the valve sheet is separated from the valve seat against the spring force of the plate spring when the coil is energized, wherein the fixed core comprises two parts vertically coupled, an upper one of which is a first fixed core located in a coil bobbin around which the coil is wound and in non-contact with a control fluid, the first fixed core being made of a material having high magnetic permeability, and a lower one of which is a second fixed core fitted, protruding downward, in the coil bobbin to cover a lower end of the coil bobbin, the second fixed core being made of a material having corrosion resistance to a high-corrosive control fluid.

[0011] Further, the solenoid valve of the present invention is characterized in that the first fixed core is made of magnetic soft iron.

[0012] Furthermore, the solenoid valve of the present invention is characterized in that the second fixed core is made of ferritic stainless steel.

[0013] The solenoid valve of the present invention having the above structure is normally held in a valve-closed state where the valve sheet is pressed against the valve seat by a restoring force (a spring force) of the plate spring. When current is applied to the coil, the first fixed core made of magnetic soft iron or the like is magnetized, attracting the plunger upward against the spring force of the plate spring. In the case where the second fixed core is made of a magnetic material such as ferritic stainless steel, the second fixed core can also be magnetized.

[0014] When the plunger is moved up and thus the valve sheet is separated from the valve seat, the inlet passage of the valve is brought into communication with the outlet passage to