Scroll-type compressor having injection passage part to establish communication between an external injection pipe and compression chamber, and relief mechanism to establish communication between compression chamber and back pressure chamber

A scroll-type compressor, comprising:

• a compression-chamber-forming member having a movable scroll and a fixed scroll cooperating to form a compression chamber;
• a shaft arranged to drive the movable scroll relative to the fixed scroll to compress refrigerant in the compression chamber;
• a housing forming a back pressure chamber, refrigerant for applying back pressure to the compression-chamber-forming member being accumulated in the back pressure chamber;
• an injection passage part formed in at least one of the compression-chamber-forming member and other surrounding members, and the injection passage part being linked to the compression chamber;
• and
• a relief mechanism provided to the compression-chamber-forming member, the relief mechanism being configured to establish a communication between the compression chamber and the back pressure chamber communicating when injection pressure, which is the pressure of the refrigerant flowing from the injection passage part into the compression chamber, is higher than the pressure in the back pressure chamber,
• the relief mechanism including
• a relief passage part formed radially through a peripheral wall of an outer edge part of the fixed scroll, the relief passage part being configured to establish a communication between the compression chamber and the back pressure chamber, and
• a check valve associated with the relief passage part, the check valve being opened when the pressure in the back pressure chamber is reduced and the pressure difference between the compression chamber and the back pressure chamber exceeds a prescribed pressure.