1. Field of the Invention
The present invention relates to a pilot operated electromagnetic valve.
2. Description of the Related Art
An automotive air conditioner is generally configured such that it includes a compressor, a condenser, an evaporator, and so forth arranged in a refrigerant circulation passage. Various types of control valves are provided for the purpose of, for example, switching the refrigerant circulation passages according to the operation state in such a refrigeration cycle and regulating the flow rate of refrigerant. A pilot operated electromagnetic valve capable of controlling the opening and closing of a large valve section using a relatively small electric power may be used as such the control valve (see Reference (1) in the following Related Art List, for instance).
Such an electromagnetic valve drives a small pilot valve element by a solenoid so as to open and close a pilot valve and then drives a large main valve element by a pressure difference regulated thereby so as to open and close a main valve. A piston is formed integrally with the main valve element, and a back pressure chamber is formed by this piston as a separated space inside a body. A leak passage, through which to introduce the refrigerant into the back pressure chamber and a pilot passage, through which the refrigerant is led out from the back pressure chamber, are formed in the main valve element. And the opening and closing of the pilot valve opens and blocks the pilot passage, respectively. With this structure, the opening and closing of the main valve is controlled by varying the pressure of the back pressure chamber. The pressure of the back pressure chamber is regulated through a balance between the flow rate of refrigerant introduced into the back pressure chamber and the flow rate of refrigerant led out from the back pressure chamber.