Scroll compressor of two-stage compression type having an improved volumetric efficiency

A scroll compressor comprising:

• a first scroll having a flat plate and first and second spiral ridges provided on opposite faces of the flat plate, said first scroll being drivably mounted on a drive shaft connected to a motor;
• a second scroll having an end plate with a flat face and a spiral ridge provided on the flat face of the end plate, the second scroll being placed on one side of the first scroll so that the flat face of the end plate is opposed to one face of the flat plate of the first scroll and that the spiral ridge of the second scroll is meshed with the first spiral ridge of the first scroll;
• and
• a third scroll having an end plate with a flat face and a spiral ridge provided on the flat face of the end plate of the third scroll, the third scroll being placed on the other side of the first scroll so that the flat face of the end plate of the third scroll is opposed to the other face of the flat plate of the first scroll and that the spiral ridge of the third scroll is meshed with the second spiral ridge of the first scroll;
• and
• a casing accommodating the first, second and third scrolls and having an internal space therein;
• a suction passage for introducing a fluid to be compressed into the casing;
• and
• a discharge passage for discharging the fluid out of the casing after the fluid is compressed, characterized in that:
• a lower-stage compression part provided with a suction port and a discharge port is formed between the first and second scrolls, the suction port of the lower-stage compression part being formed in the vicinity of external end portions of the first spiral ridge of the first scroll and the spiral ridge of the second scroll and communicating with the suction passage;
• a higher-stage compression part provided with a suction port and a discharge port is formed between the first and third scrolls, the suction port of the higher-stage compression part being formed in the vicinity of the external portions of the second spiral ridge of the first scroll and the spiral ridge of the third scroll, the discharge port of the higher-stage compression part being formed in the vicinity of internal end portions of the second spiral ridge of the first scroll and the spiral ridge of the third scroll and communicating with the discharge passage;
• and
• a discharge port of the lower-stage compression part communicates with the suction port of the higher-stage compression part,
• whereby the fluid is first compressed to a predetermined intermediate pressure at the lower-stage compression part and then the fluid is further compressed to a higher pressure at the higher-stage compression part.