Direct Drive Refrigerant Screw Compressor with Refrigerant Lubricated Rotors

This application is a divisional of U.S. application Ser. No. 18/524,682 filed Nov. 30, 2023 which is a divisional of U.S. application Ser. No. 16/973,724 filed Dec. 9, 2020, which is a 371 of PCT Application No. PCT/US2020/033585 filed May 19, 2020, and claims the benefit of U.S. Provisional Patent Application No. 62/850,296, filed on May 20, 2019, each of which is incorporated herein by reference in its entirety.

The disclosure relates generally to compressor systems and, more specifically, to a direct drive refrigerant screw compressor using refrigerant lubrication of one or more components thereof.

Refrigeration systems are utilized in many applications to condition an environment. The cooling or heating load of the environment may vary with ambient conditions, occupancy level, other changes in sensible and latent load demands, and with temperature and/or humidity changes.

Refrigeration systems typically include a compressor to deliver compressed refrigerant to a condenser. From the condenser, the refrigerant travels to an expansion valve and then to an evaporator. From the evaporator, the refrigerant returns to the compressor to be compressed.

A direct drive screw compressor in an HVAC chiller application has a driving (male) rotor and a driven (female) rotor. An electric motor drives the driving rotor to rotate. The driving rotor then drives the driven rotor by way of meshing. The meshing process requires direct contact of the rotors at contact locations. Lubrication is necessary to protect both rotors and decrease the friction during operation. In addition, the rotors in a screw compressor in HVAC chiller applications are supported by rolling element bearings. These bearings may be lubricated using oil because of a high viscosity requirement of bearing lubricant. After passing through the bearings, oil is mixed with refrigerant in the compression process to be carried out of the compressor.

Disclosed is a direct-drive refrigerant screw compressor, comprising: a housing; a compression chamber in the housing; a pair of rotors, each rotor of the pair of rotors being rotationally disposed in the compression chamber and including an outer surface with a screw-geared profile; a fluid being disposed in the compression chamber, the fluid consisting of a working fluid for providing lubrication to each rotor; a first port extending through the housing and configured for directing the fluid toward the compression chamber; and when the compressor is activated, each rotor rotates and the fluid is distributed about each rotor to lubricate each rotor.

In addition to one or more of the above features, or as an alternate, the first port includes a flow control orifice.

In addition to one or more of the above features, or as an alternate, the first port extends directly into the compression chamber.

In addition to one or more of the above features, or as an alternate, the first port is fluidly connected to a passage in one rotor of the pair of rotors that directs the fluid to the compression chamber.

In addition to one or more of the above features, or as an alternate, the passage extends between an axial aft port in the one rotor and the outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, the passage includes an axial segment forming a blind hole and a radial segment fluidly connected between the axial segment and a surface port on the outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, the passage includes a plurality of the radial segments fluidly connected to a respective plurality of the surface ports on the outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, the plurality of the surface ports are staggered at regular intervals along the outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, the plurality of the radial segments each include opposing radial portions extending to a respective plurality of the surface ports on the outer surface of the one rotor.

Further disclosed is a refrigerant system including: a condenser; a compressor having one or more of the above disclosed features; and a conduit fluidly connecting the condenser and the first port of the compressor, and configured to transport the fluid to the compressor to provide the working fluid to each rotor.

Further disclosed is a method of directing fluid in a direct drive screw compressor, comprising: receiving fluid at a first port of a housing of the compressor, wherein the fluid consists of a working fluid for providing lubrication to each rotor of a pair of rotors in the compressor; and directing the fluid from the first port to a compression chamber in the compressor; and when the compressor is activated, each rotor rotates and the fluid is distributed about each rotor to lubricate each rotor.

In addition to one or more of the above features, or as an alternate, the method includes controlling flow through the first port with a flow control orifice.

In addition to one or more of the above features, or as an alternate, directing the fluid to the compression chamber includes: injecting the fluid from the first port directly into the compression chamber.

In addition to one or more of the above features, or as an alternate, directing the fluid to the compression chamber includes: injecting the fluid from the first port, through a passage in one rotor of the pair of rotors, whereby the fluid is injected into the compression chamber.

In addition to one or more of the above features, or as an alternate, injecting the fluid through the passage includes: directing the fluid from the first port into an axial aft port in the passage and out an outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, directing the fluid through the passage further includes: directing the fluid through an axial segment forming a blind hole in the one rotor and a radial segment fluidly connected between the axial segment and a first surface port on the outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, directing the fluid through the passage further includes: directing the fluid though a plurality of the radial segments fluidly connected to a respective plurality of the surface ports on the outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, directing the fluid through the passage further includes: directing the fluid through opposing radial portions of each of the plurality of the radial segments, the opposing radial portions extending to a respective plurality of the surface ports on the outer surface of the one rotor.

In addition to one or more of the above features, or as an alternate, receiving the fluid at the first port from a condenser in a refrigerant system in which the compressor is integrated, to provide the working fluid to each rotor.

A detailed description of one or more embodiments of the disclosed apparatus and method are presented herein by way of exemplification and not limitation with reference to the Figures.

Described herein are systems and methods for lubricating components of a compressor in a refrigeration system.illustrates a refrigeration systemthat is an oil lubricated system. The systemincludes a condenserthat receives a high pressure gaseous form of the working fluid, ejects heat from the working fluid, for example to the environment, and outputs a high pressure liquid form of the working fluid. Downstream of the condenseris an expansion valvethat receives the high pressure liquid form of the working fluid and outputs a low pressure liquid form of the working fluid. Downstream of the expansion valveis an evaporatorthat receives the low pressure liquid form of the working fluid, transfers heat to the working fluid, thereby conditioning warm air, and outputs a low pressure gaseous form of the working fluid. Downstream of the evaporatoris a compressorthat receives the low pressure gaseous form of the working fluid and outputs a high pressure gaseous form of the working fluid.

The compressormay be a screw compressor that includes suction bearings, discharge bearings, and a set of rotorstherebetween. Both sets of bearings,and the rotorsrequire some form of lubrication. Lubricating oil is provided by an oil separator. The oil separatortransfers oil to an oil filter. The oil filtertransfers oil a first portion of oilto one orifice, e.g. in the compressor housing, fluidly connected to the suction bearings. A second portion of oilis distributed in parallel to one orifice, e.g., in the compressor housing, fluidly connected to the rotorsand another orifice, e.g., in the compressor housing, fluidly connected to the discharged bearings. The oil then mixes with the working fluid in the compressor.

Output from the compressoris directed to the oil separator. The oil separatorseparates the output from the compressor into a first portionthat is the working fluid directed the condenser. The second portionis the lubricant directed to the filter. Unless otherwise indicated herein, for each embodiment all flows between the system components that are separately referred to are fluidly transferred in respective conduit lines. It is to be appreciated that fluid branches that are branched upstream or downstream of the orifices,in the housing of the compressormay be branched in conduit exterior to the housing of the compressor.

Viscosity of oil lubricant may be reduced when mixed with the working fluid. Both bearing load carrying capacity and oil sealing characteristics are dependent upon the oil viscosity. As such, due to lower viscosity, moving components, such as bearings and rotors, in some systems may experience increased wear during operation. In addition, separating lubricating oil from refrigerant requires the use and maintenance of additional equipment such as the oil separator and related filter. In addition, because the oil separation process cannot completely remove the oil from refrigerant, excessive oil may decrease heat transfer efficiency in the system and lower the overall system capacity. Oil may be saturated with refrigerant in the separator. The separation process is often unable to adequately lower the refrigerant content in the oil.

In view of the above challengesdisclose embodiments in which an oil separator and oil filter may be avoided. More specifically, turning to, disclosed is a refrigerant system(a chiller) applicable to each of the embodiments disclosed herein. The systemincludes a condenser, an expansion valve, an evaporator, and a dual rotor refrigerant screw compressor(compressor), which is a direct drive compressor. The compressorincludes two screw rotors. The rotorsare configured in the compressorwith a suction sideand discharge side(illustrated schematically in). The compressorincludes bearing packsincluding a suction side bearing packand a discharge side bearing pack. The suction side bearing packmay be referred to herein as a forward bearing pack and the discharge side bearing packmay be referred to herein as an aft bearing pack.

The condenser feeds first portionof a working fluid to the expansion valveand, in parallel, a second portionof the working fluidto the compressor. The working fluid consists of refrigerant form a condenser conduitto the compressorfor providing lubrication to components of the compressoras described below.

The second portionof the working fluid is distributed in parallel to a first branchand a second branch. The first branchis distributed in parallel to a third branchand a fourth branch. The third branchdelivers the working fluid through one or more orifices, e.g. in the compressor housing, to the suction side bearing pack. The fourth branchdelivers the working fluid through another one or more orifices, e.g. in the compressor housing, to the rotors. The second branchdelivers the working fluid to a further one or more orifices, e.g. in the compressor housing, to the branch side bearing pack

From the suction side bearing pack, the working fluid flows directly into the rotorswith the working fluid from the evaporator. This may occur within the compressor housing. From the discharge side bearing packthe working fluid flows to the evaporatorto mix with fluid therein and then be redirected to the rotorsof the compressor. This may occur by the working fluid exiting the compressor housingfrom the discharged side bearingsand being directed thereafter to the evaporator. Unless otherwise indicated herein, for each embodiment all flows between the system components that are separately referred to are fluidly transferred in respective conduit lines. It is to be appreciated that fluid branches that are branched upstream or downstream of the orifices,,in the compressor housingmay be branched in conduit exterior to the compressor housing

The features of the compressor are illustrated more specifically, for example, in. Turning now to, the compressorincludes the housing. A compression chamberis disposed in the housing. The compression chamberhas a forward endand an aft endwhich are respective suction and discharge sides of the compression chamber. For simplicity, inlet and outlet ports in the housingfor fluidly communicating working fluidin the refrigeration systemare not illustrated in.

The compressorincludes the plurality of rotors generally referred to as, including the first rotorand the second rotor, rotationally disposed in the compression chamber. Each rotorincludes an outer surfacewith a screw-geared profile, for example, having an alternating plurality of peaksand plurality of troughs, for example, in cross sectional view. The plurality of rotorsintermesh and form compression volumes within the compression chamber. The first rotoris a driven rotor and the second rotoris a drive rotor, driven by a motor.

For each rotor, the compressorincludes the plurality of bearing packs generally referred to asincluding the forward bearing pack generally referred to asand the aft bearing pack generally referred to as. For each rotor, the plurality of bearing packsmay disposed within a respective plurality of bearing chambers generally referred to as. The bearing chambersmay be structural portions of the housingin or proximate the compression chamberconfigured to securely position the respective bearing packs. The bearing chambersmay including a forward bearing chamber generally referred to asand an aft bearing chamber generally referred to as. The bearing chambersmay be fluidly connected with each other through the compression chamber.

Turning now to, an embodiment of the refrigeration systemis illustrated. The embodiment ofincludes all of the features illustrated in the systemillustrated in. In, the fluidis disposed within the compression chamber. A first portextends through the housingfor directing fluid toward the compression chamber. The first portis connected by the condenser conduitto the condenser. According to an embodiment, the first portincludes a flow control orifice. This may be used to reduce a flow volume or rate from the condenseras may be needed.

In, the first portextends directly into the compression chamber. Within the compression chamber, the first portdelivers working fluidbetween the two rotorsso that the working fluidflows to meshing points between the two rotors. In one embodiment, the first portis proximate one rotor(the second rotor) of the compressorand distal the other rotor(the first rotor). Identifying the one rotoras the second rotorand the other rotoras the first rotorin the embodiment inis for example only and not intended on limiting the scope of the embodiments. Rotation of the rotorsdistributes the fluidabout the rotors.

Turning now to, an embodiment of the refrigeration systemis illustrated. The embodiment ofincludes all of the features illustrated in the systemillustrated in. In, the fluidis disposed within the compression chamber. A first port, configured differently than the first portin the embodiment of, extends through the housing. In, the first portfluidly connects with a passagewithin one rotor(the first rotor) for directing fluid toward the compression chamber. Identifying the one rotoras the first rotor, and thus the other rotoras the second rotor, in the embodiment inis for example only and not intended on limiting the scope of the embodiments. The first portis connected by the condenser conduitto the condenser. According to an embodiment, the passageincludes a flow control orifice, which may be the same as the above introduced flow control orifice. This may be used to reduce a flow volume or rate from the condenseras may be needed.

The passagemay be an internal passage in the one rotor. The passagemay be fluidly connected between an axial aft portin the one rotorand the outer surfaceof the one rotor. The aft portmay be in the respective aft bearing chamber, though this placement is not intended to be limiting.

The passagemay include an axial segmentforming a blind hole in the one rotorand a radial segment generally referred to asfluidly connected between the axial segmentand a surface port generally referred to ason the outer surfaceof the one rotor. In one embodiment, the passagemay include a plurality of the radial segmentsfluidly connected to a respective plurality of the surface portson the outer surfaceof the one rotor. This configuration may provide a greater distribution of the fluidabout each rotoras compared with, for example, a single fluidport.

In one embodiment, the plurality of the surface portsmay be staggered at regular intervals along the outer surface, for example, at or proximate the plurality of alternating peaksor troughs. This configuration may provide an even distribution of fluidaround the outer surfaceof the each rotor. In one embodiment the plurality of the radial segmentsmay each include a plurality of opposing radial portions,extending to a respective plurality of the radial ports,on the outer surfaceof the one rotor. This configuration may provide an ability to quickly distribute fluidaround the outer surfaceof the rotors.

Turning to, a method is disclosed of directing fluidin the compressorfor the embodiment illustrated in. The method includes blockof receiving the fluidat the first portof the housing. In an embodiment, blockfurther includes controlling flow in the first portthrough a flow control orifice(which may be the same as orificein). The method further includes blockof directing the fluidin the compressor, from the first port, to the compression chamber. According to an embodiment, blockfurther includes injecting the fluidfrom the first portdirectly into the compression chamberproximate one rotorand distal the other rotor. At blockthe compressor is activated to distribute the fluid about the rotors.

Turning to, a method is disclosed of directing fluidin the compressorfor the embodiment illustrated in. Similar to the method in, the method ofincludes blockof receiving the fluidat the first portof the housing. The method ofincludes blockof directing the fluid, from the first port, to the compression chamber. In an embodiment, blockfurther includes controlling flow in the passagethrough a flow control orifice. In an embodiment, blockfurther includes injecting the fluidthrough the first port, through a passagein one rotor, and into the compression chamber. Then, at blockthe compressor is activated to distribute the fluid about the rotors.

Thus, in the above disclosed embodiments, the working fluidis drawn from a chiller condenser and used to provide lubrication to the compressor and more specifically to the screw rotors. The liquid can be injected direct from port(s) on the housing close to the rotor meshing locations or through a passage inside the driving rotor. The liquid flow can be adjusted by using flow restriction devices, such as a flow control orifice. The embodiments enable the utilization of pure refrigerant as the working fluidin the components of the system, including the condenser, evaporator, etc.

Turning now toa further embodiment of a refrigerant systemis illustrated. The embodiment ofincludes all of the features illustrated in the systemillustrated in. In, the fluidis disposed within each of the plurality of bearing chambersfor providing lubrication to the plurality of bearing packs, thus providing pure refrigerant lubricated (PRL) bearings. A plurality of bearing lubrication ports generally referred to asextend through the housingand into each of the plurality of bearing chambers.

In addition, a suction side (upstream) lubrication portincludes a suction side (upstream) flow control orifice(which may be the same as orificein). A discharge side (downstream) lubrication portincludes a discharge side (downstream) flow control orifice(which may be the same as orificein).

The condenser conduitfluidly connects the condenserto the plurality of bearing lubrication ports. From this configuration, the plurality of bearing lubrication portsare configured for injecting the fluidinto each of the plurality of bearing chamberswhen the compressoris running, to thereby provide lubrication to the plurality of bearing packs. In one embodiment the plurality of bearing lubrication portsinclude a respective plurality flow control orificesto reduce a flow volume or rate from the condenseras may be needed.

In one embodiment, the condenser conduitincludes a forward branchand an aft branchfor injecting in parallel the fluidto each forward bearing chamberand each aft bearing chamberin the compressor. Each branch,includes a plurality of sub-branches generally referred to asfor injecting in parallel the fluid to the bearing chamberson each branch,. This configuration enables the condenserto feed the fluidto the compressorfrom the single condenser conduit.

As further illustrated in, for each rotorthe compressorincludes a lubricant drain port generally referred to asfluidly connected to the evaporator by an evaporator conduit. The lubricant drain portis for draining the fluidfrom the plurality of bearing chambersof the respective rotorwhen the compressoris running. In one embodiment, each lubricant drain portextends into the respective aft bearing chamberand is fluidly connected to the respective forward bearing chamberthrough the respective aft bearing chamber.