Variable-capacity control for refrigerating cycle without using a large pressure control valve

A variable-capacity control system for use with a refrigeration cycle that uses carbon dioxide as a coolant, said system comprising:

• a variable-capacity compressor having an intake side and being operable to compress the coolant, said variable-capacity compressor comprising a cylinder block, a drive shaft provided inside said cylinder block, a drive swash plate, a plurality of cylinders provided within said cylinder block, a plurality of pistons slidably provided at said cylinders, compression spaces defined by said cylinders and said pistons, a crank case formed on a non-compression space side of said pistons, an intake chamber, an outlet chamber and a variable-capacity mechanism;
• a radiator operable to cool the compressed coolant;
• an expansion device operable to expand the cooled coolant and having an outlet side;
• an evaporator operable to evaporate the expanded coolant;
• a low pressure line extending from the outlet side of said expansion device to the intake side of said variable-capacity compressor;
• and
• a pressure sensor operable to detect pressure of coolant in said low pressure line,
• wherein said drive swash plate is operable to rotate together with said drive shaft and has a variable angle of inclination relative to said drive shaft,
• wherein each of said cylinders has an axis parallel to said drive shaft,
• wherein said pistons are operable to reciprocally move within said cylinders as said drive swash plate rotates,
• wherein said intake chamber is arranged to communicate with the compression spaces during an intake phase of said pistons,
• wherein said outlet chamber is arranged to communicate with the compression spaces during a compression phase of said pistons,
• wherein said variable-capacity mechanism comprises an electromagnetic coil operable to generate an electromagnetic force, a plunger operable to slidably insert into said electromagnetic coil as a result of the electromagnetic force, a valve element operable to move between a first position and a second position as a result of movement of said plunger, a spring operable to apply a force to said valve element along a direction opposite to a plunger moving direction, a pair of low pressure chambers located at two ends of said valve element to communicate with said intake chamber, a pressure adjustment chamber arranged to communicate with said crank case, a high pressure chamber arranged to communicate with said outlet chamber, a low pressure side communicating port provided between said pressure adjustment chamber and said low pressure chamber, and a high pressure side communicating port provided between said pressure adjustment chamber and said high pressure chamber,
• wherein said valve element comprises an opening/closing portion, a small diameter portion and a sliding portion,
• wherein said pressure adjustment chamber is formed around said opening/closing portion,
• wherein said high pressure chamber is formed around said small diameter portion,
• wherein said low pressure side communicating port is operable to close or open via one end of said opening/closing portion,
• wherein said high pressure side communicating port is operable to open or close via another end of said opening/closing portion,
• wherein when said valve element is in the first position, a fluid communication is established between said pressure adjustment chamber and said low pressure chamber and a fluid communication is not establish between said pressure adjustment chamber and said high pressure chamber,
• wherein when said valve element is in the second position, a fluid communication is not established between said pressure adjustment chamber and said low pressure chamber and a fluid communication is established between said pressure adjustment chamber and said high pressure chamber, and
• wherein said electromagnetic coil is operable to place said valve element in the first position when a coolant pressure detected by said pressure sensor is equal to or higher than a target pressure, and to place said valve element in the second position when a coolant pressure detected by said pressure sensor is lower than the target pressure.