A screw compressor is disclosed, which includes a male rotor and a female rotor and an oil separator. The oil separator includes an outer cylinder, an inner cylinder located inside the outer cylinder, and an introducing flow path. An upper end portion of the inner cylinder is held by the oil separator and an outer wall of the inner cylinder is held independently of the inner wall of the outer cylinder. A diameter of an inner wall of the outer cylinder is configured so that the diameter is gradually reduced along a swirl flow path. Moreover, refrigerant that flowed in swirls and goes down along the swirl flow path. The separated gas refrigerant flows from a lower end portion of the inner cylinder into the inner cylinder and goes up and the separated oil flowing down along the inner wall surface of the outer cylinder.

A screw compressor in which it is possible to achieve size reduction and reduce the oil rate and a chiller unit equipped with the screw compressor are provided. In the screw compressor, an oil separator includes: an outer cylinder; an inner cylinder positioned inside the outer cylinder; and an introducing flow path that lets refrigerant discharged from a compression working chamber flow in so that the refrigerant swirls to the circumferential direction on the inner wall surface of the outer cylinder. The upper end portion of the inner cylinder is held by the oil separator and the outer wall of the inner cylinder is thereby held independently of the inner wall of the outer cylinder. The diameter of the inner wall of the outer cylinder is so configured that the diameter is gradually reduced along the swirl flow path in which refrigerant that flowed in through the introducing flow path swirls. The refrigerant that flowed in through the introducing passage swirls and goes down along the swirl flow path which is the inner wall of the outer cylinder and is thereby separated into gas refrigerant and oil. Thereafter, the separated gas refrigerant flows from the lower end portion of the inner cylinder into the inner cylinder and goes up; and the separated oil flows down along the inner wall surface of the outer cylinder.

A secondary airflow path can be provided for a compressor of a compressor system. The secondary airflow path can provide pressurized air to a boost port in communication with a closed compression cell of the compressor.

A supercharged internal combustion engine is drivably connected to a variable displacement supercharger operable to continuously supply varying amounts of an air mass to the engine in response to the varying power requirements of the engine. The variable displacement capability eliminates blowdown losses of fixed displacement superchargers and substantially reduces the need for throttling of the intake air. The device also presents an air-motoring mode that can recover a portion of the engine throttling losses as positive power returned to the engine crankshaft when the engine intake manifold is below atmospheric pressure.