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Two-stage vapor cycle compressor

Two-stage vapor cycle compressor description/claims

The present invention generally relates to vapor cycle compressors and, more particularly, to a low cost two-stage vapor cycle compressor and a method for operating an electrically driven two-stage vapor cycle compressor.

Vapor compression refrigeration is a refrigeration method that is widely used for air-conditioning spaces, for example, public spaces such as private and public buildings, automobiles, and aircraft cabins, or for domestic or commercial refrigerators and other commercial and industrial services. Vapor-compression refrigerant systems typically circulate a liquid refrigerant as a medium that absorbs and removes heat from the space to be cooled and subsequently rejects that heat elsewhere. Vapor-compression refrigerant systems typically include a compressor, a condenser, a throttle or expansion valve, and an evaporator. The circulating refrigerant enters the compressor in a thermodynamic state known as saturated vapor, which has a low pressure and a low temperature, and is compressed to a higher pressure, resulting in a higher temperature as well. The hot vapor is routed through a condenser where it is cooled and condensed into a liquid. The now liquid refrigerant is routed through the expansion valve to the evaporator. Here the refrigerant absorbs and removes heat from air circulating through the evaporator and goes over into the saturated vapor state. To complete the refrigeration cycle, the refrigerant in vapor form is routed back to the compressor. Consequently, the main purpose of the compressor is to boost the pressure of the refrigerant in vapor form so that the high pressure, high temperature refrigerant in vapor form can be used to do heat transfer. A typical two-stage vapor cycle compressor includes two impellers to realize two stages of compression.

Industries, and especially the aerospace industry, typically strive for vapor cycle compressors that have a high reliability and long life span, that have a compact size, are easy to assemble, and can be manufactured at a low cost while operating highly efficiently. U.S. Pat. No. 6,564,560, for example, utilizes ceramic roller element bearings to achieve an oil-free liquid chiller. Still the roller element bearings have to be actively lubricated by liquid refrigerant.

U.S. Pat. No. 5,857,348, for example, utilizes non-lubricated radial bearings, such as magnetic or foil gas bearings cooled with refrigerant in vapor form, as journal bearings. First and second stage impellers are mounted on opposite ends of a drive shaft driven by a high-speed brushless DC (continuous current) permanent magnet motor. This layout may not allow a compact design of the compressor. The arrangement of the compressor components on the drive shaft and the use of return channels and guide vanes may not enable the most efficient cooling method for the air bearings and the motor but may increase the number of parts used in the assembly of the compressor.

U.S. Pat. 6,997,686, for example, teaches a two-stage compressor including a first impeller and a second impeller connected in series by a transition pipe and using a low-pressure refrigerant, such as R134a. Foil air bearings are used in combination with an induction motor running at high speeds. An encoder disc is included to sense the rotational speed of the rotating assembly of the compressor. The compressor housing includes a separate cooling inlet and outlet for circulating liquid refrigerant in an inner cooling jacket. O-rings are used to seal the cooling jacket within the compressor housing.

As can be seen, there is a need for a two-stage vapor cycle compressor that has a simple design including a reduced number of parts and interfaces compared to prior art compressors and that can be manufactured at a relatively low cost by taking advantage of modern high volume production techniques. Furthermore, there is a need for a method that optimizes the flow cooling the bearings and the motor to increase the efficiency of the compressor compared to prior art compressors.

In one aspect of the present invention, a two-stage vapor cycle compressor comprises a first stage impeller, a second stage impeller situated adjacent to the first stage impeller, an electric motor running on a pair of foil bearings, a thrust disk including two foil bearings, and a compressor housing enclosing the first and second stage impeller and the electric motor. The electric motor drives the first stage and the second stage impeller. The thrust disk is positioned between the second stage impeller and the electric motor. The compressor housing forms an internal passageway. The first stage impeller and the second stage impeller compress a refrigerant vapor. The refrigerant vapor flows through the passageway and cools the electric motor and the foil bearings.

In another aspect of the present invention, a passageway of a two-stage vapor cycle compressor comprises a compression loop including a first stage impeller and a second stage impeller, a thrust bearing and forward journal bearing cooling loop, and a rotor bore and aft journal bearing cooling loop. The first stage impeller and the second stage impeller compress a refrigerant vapor. A first portion of the refrigerant vapor exits the compression loop proximate to an outlet of the second impeller and flows over the thrust bearings and the forward journal bearing. A second portion of the refrigerant vapor exits the compression loop proximate to an inlet of the second stage impeller and travels axially through the rotor bore and flows over the aft journal bearing. The thrust bearings, the forward journal bearing, and the aft journal bearing are foil bearings.

In a further aspect of the present invention, a method for operating an electrically driven two-stage vapor cycle compressor comprises the steps of: compressing a refrigerant vapor in a first stage and in a second stage, extracting a first portion of the refrigerant vapor from the inlet to the second stage, cooling a rotor bore of an electric motor and an aft journal bearing with the first portion of the refrigerant vapor, extracting a second portion of the refrigerant vapor from the discharge of the second stage, and cooling thrust bearings and an forward journal bearing with the second portion of the refrigerant vapor.

These and other features, aspects and advantages of the present invention will become better understood with reference to the following drawings, description and claims.

FIG. 1 is a simplified cross-sectional side view of a two-stage vapor cycle compressor according to an embodiment of the present invention;

FIG. 2 is a perspective cut-away view of a shrouded impeller according to an embodiment of the present invention;

FIG. 3 is a simplified block diagram of an internal passageway of a two-stage vapor cycle compressor according to an embodiment of the present invention; and

FIG. 4 is a flow chart representing a method for operating an electrically driven two-stage vapor cycle compressor according to an embodiment of the present invention.

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• Utility Patent

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