A turbo chiller that has an oil-free configuration, which reduces the frequency of maintenance and maintenance-induced release of refrigerant, and can achieve a reduced environmental impact by utilizing the characteristics of the low-pressure refrigerant R1233zd(E) that reaches negative pressure at a saturation temperature of 18° C. or lower. The turbo chiller comprises a refrigeration cycle that includes a turbo compressor, a condenser, a decompression device, and an evaporator connected in sequence via piping and is filled with a refrigerant; wherein the refrigerant is a low-pressure refrigerant R1233zd(E) refrigerant with low global warming potential and low ozone depletion potential; the turbo compressor has a direct drive configuration in which a rotating shaft of impellers is directly joined to a motor; and the rotating shaft is supported by magnetic bearings.

A magnetic levitation bearing, a magnetic levitation rotor support assembly, and a compressor. The magnetic levitation bearing is used for supporting a rotor by interacting with a thrust disc on the rotor, and comprises: a radial stator core having an annular structure, which is disposed on a radial outer side of the thrust disc and corresponds to the thrust disc in an axial direction of the rotor, the radial stator core and the thrust disc being separated by a first radial gap X1; and a radial control coil, which is disposed on the radial stator core and can generate a radial electromagnetic force to the thrust disc in a radial direction of the rotor.

A magnetic levitation bearing, a magnetic levitation rotor support assembly, and a compressor. The magnetic levitation bearing is used for supporting a rotor by interacting with a thrust disc on the rotor, and comprises: a radial stator core having an annular structure, which is disposed on a radial outer side of the thrust disc and corresponds to the thrust disc in an axial direction of the rotor, the radial stator core and the thrust disc being separated by a first radial gap X1; and a radial control coil, which is disposed on the radial stator core and can generate a radial electromagnetic force to the thrust disc in a radial direction of the rotor.

A bearing structure includes a drive shaft that extends in a horizontal direction, a touchdown bearing, and a bearing housing. The drive shaft is supported by a magnetic bearing. The touchdown bearing includes a rolling member interposed between an outer ring and an inner ring. The bearing housing supports the touchdown bearing from an outer periphery. At least one of an outer peripheral surface of the drive shaft, an inner peripheral surface of the inner ring, an outer peripheral surface of the outer ring, and an inner peripheral surface of the bearing housing includes a recess in a region overlapping the rolling member in a bearing radial direction.

An expander and motor-compressor unit is disclosed. The unit includes a casing and an electric motor arranged in the casing. A compressor is arranged in the casing and drivingly coupled to the electric motor through a central shaft. Furthermore, a turbo-expander is arranged for rotation in the casing and is drivingly coupled to the electric motor and to the compressor through the central shaft.

An expander and motor-compressor unit is disclosed. The unit includes a casing and an electric motor arranged in the casing. A compressor is arranged in the casing and drivingly coupled to the electric motor through a central shaft. Furthermore, a turbo-expander is arranged for rotation in the casing and is drivingly coupled to the electric motor and to the compressor through the central shaft.

A thrust magnetic bearing includes a stator having a coil that produces a magnetic flux, and a rotor. The magnetic flux supports the rotor in a non-contact manner. The stator has main and auxiliary stator magnetic pole surfaces. The rotor has main and auxiliary rotor magnetic pole surfaces. The main and auxiliary rotor magnetic pole surfaces face the main and auxiliary stator magnetic pole surfaces. The auxiliary stator magnetic pole surface includes at least one first stator surface and at least one second stator surface, alternately arranged. The auxiliary rotor magnetic pole surface includes at least one first rotor surface, and at least one second rotor surface, alternately arranged. Nr≥1 and Nt≥2, with Nr representing a number of pairs of the first stator and rotor surfaces facing each other, and Nt representing a number of pairs of the second stator and rotor surfaces facing each other.

A thrust magnetic bearing includes a stator having a coil that produces a magnetic flux, and a rotor. The magnetic flux supports the rotor in a non-contact manner. The stator has main and auxiliary stator magnetic pole surfaces. The rotor has main and auxiliary rotor magnetic pole surfaces. The main and auxiliary rotor magnetic pole surfaces face the main and auxiliary stator magnetic pole surfaces. The auxiliary stator magnetic pole surface includes at least one first stator surface and at least one second stator surface, alternately arranged. The auxiliary rotor magnetic pole surface includes at least one first rotor surface, and at least one second rotor surface, alternately arranged. Nr≥1 and Nt≥2, with Nr representing a number of pairs of the first stator and rotor surfaces facing each other, and Nt representing a number of pairs of the second stator and rotor surfaces facing each other.

A magnetic bearing control apparatus and a vacuum pump which do not require a displacement sensor, which enable control with high accuracy, and which are small and low cost. A rate of change (di/dt) that is a time derivative of a current value I.sub.m flowing through an electromagnet varies in accordance with a magnitude of a displacement of a gap between a target member and the electromagnet. The rate of change (di/dt) can be obtained by detecting a voltage value V.sub.s that is generated at both ends of an inductive element. Therefore, by detecting the voltage value V.sub.s, the magnitude of the displacement of the gap can be estimated by calculation. Inductive elements are connected in series to electromagnets and the voltage V.sub.s between the inductive elements is detected by the differential input amplifier. A single period of switching of a PWM switching amplifier is constituted by a current control period of the electromagnet and a displacement detection period for detecting the rate of change (di/dt). In addition, the displacement detection period is further constituted by a current increase period and a current decrease period which are certain periods of time. The current increase period and the current decrease period are equal to each other.

A thrust magnetic bearing includes a stator having a coil that produces a magnetic flux, and a rotor. The magnetic flux supports the rotor in a non-contact manner. The stator has main and auxiliary stator magnetic pole surfaces. The rotor has main and auxiliary rotor magnetic pole surfaces. The main and auxiliary rotor magnetic pole surfaces face the main and auxiliary stator magnetic pole surfaces. The auxiliary stator magnetic pole surface includes at least one first stator surface and at least one second stator surface, alternately arranged. The auxiliary rotor magnetic pole surface includes at least one first rotor surface, and at least one second rotor surface, alternately arranged. Nr≥1 and Nt≥2, with Nr representing a number of pairs of the first stator and rotor surfaces facing each other, and Nt representing a number of pairs of the second stator and rotor surfaces facing each other.