Conventionally, a compressor has been known, in which refrigerant is sequentially compressed in compression chambers at lower and higher stages. The compressor of this type includes a compressor in which, on a refrigerant circuit in which a refrigeration cycle is performed, an intermediate injection path for injecting intermediate-pressure refrigerant of the refrigeration cycle into a compression chamber at a higher stage.
For example, Japanese Patent Publication No. 2007-239666 discloses a compressor including two fluid machines. In such a compressor, two compression chambers are formed in each of the first and second fluid machines. In a two-stage compression operation for compressing refrigerant at two stages, a first compression chamber of the first fluid machine and a second compression chamber of the second fluid machine serve as compression chambers at a lower stage, and a third compression chamber of the first fluid machine and a fourth compression chamber of the second fluid machine serve as compression chambers at a higher stage. In the two-stage compression operation, intermediate-pressure refrigerant from an intermediate injection path is mixed with refrigerant compressed in the first and second compression chambers, and then is sent to the third and fourth compression chambers.
In addition, in each of the fluid machines of the compressor of Japanese Patent Publication No. 2007-239666, a cylinder serves a movable member, and a housing including a piston serves as a fixed member. In the fluid machine, the compression chambers are formed between end plate sections of the movable member and of the fixed member.
In the compressor including the end plate sections, when compressing refrigerant, refrigerant pressure in the compression chamber acts on a front surface of the end plate section of the movable member as separating force. Thus, the compressor including the end plate sections is configured such that, in order not to separate the movable member from the fixed member by the separating force, high-pressure refrigerant machine oil is injected into a back surface of the end plate section of the movable member, and then the high-pressure refrigerant machine oil presses the movable member against the fixed member.