WO2024132174A1

WO2024132174A1 - Machine for expanding or compressing compressible media

Info

Publication number: WO2024132174A1
Application number: PCT/EP2022/087620
Authority: WO
Inventors: Elvedin MUJIC; Klaus Feller; Roni LÖRCH; Ashraf AGHA
Original assignee: Bitzer Kühlmaschinenbau Gmbh
Priority date: 2022-12-22
Filing date: 2022-12-22
Publication date: 2024-06-27

Abstract

Machine for expanding or compressing compressible media, comprising a machine casing (10), at least one screw rotor (36,38) which is arranged in a screw rotor bore (32,34) in the machine casing and which extends between a low-pressure side (62) and a high-pressure side (64) of the screw rotor bore and which cooperates with the compressible medium, wherein by rotating about a screw rotor axis the at least one screw rotor (36,38) conveys the substantially gaseous medium either from the low-pressure side (62) to the high pressure side (64) by compressing it, or from the high-pressure side to the low pressure side by expanding it, wherein a motor generator unit (132) is coupled or couplable to the at least one screw rotor, wherein the at least one screw rotor is axially supported by a lubricant support film (210) provided between an end wall surface (126,128) of said screw rotor bore (32,34) and a high-pressure end face (122,124) of said at least one screw rotor (36,38) in order to prevent contact.

Description

MACHINE FOR. EXPANDING OR COMPRESSING COMPRESSIBLE MEDIA

The invention relates to a machine for expanding or compressing compressible media, said machine comprising a machine casing, at least one screw rotor which is arranged in a screw rotor bore in the machine casing and which extends between a low-pressure side and a high-pressure side of the screw rotor bore and which cooperates with the compressible medium, wherein by rotating about a screw rotor axis the at least one screw rotor conveys the substantially gaseous medium either from the low-pressure side to the high pressure side by compressing it, or from the high-pressure side to the low pressure side by expanding it, wherein said at least one screw rotor is mounted on both sides in the machine casing by means of a respective bearing set, wherein each bearing set has at least one radial acting bearing and at least one of the bearing sets has at least one axially acting bearing that supports the at least one screw rotor to counter an axial displacing movement of said screw rotor from its operating position in the direction of the low-pressure side, wherein a motor generator unit is coupled or couplable to the at least one screw rotor.

Such compressible media are for example substantially gaseous media.

Machines of this kind are known from the prior art. These machines have the problem that the axially acting bearings only support the screw rotors axially against displacement in the direction of the low-pressure side but not in the direction of the high-pressure side so that during a switch on or a switch off procedure or in the event of an interruption to operation or an incorrect direction of rotation the problem arises that the screw rotors can come into abutment with the machine casing on the high-pressure side and as a result can become damaged.

It is therefore the object of the invention to improve a machine of the type mentioned before such that these problems do not longer arise. According to the invention this object is achieved by the at least one screw rotor being axially supported by a lubricant support film provided between an end wall surface limiting said screw rotor bore and the high-pressure end face of said at least one screw rotor in order to prevent the high-pressure end face from making contact to the end wall surface and wherein the lubricant support film is maintained between said high-pressure end face and said wall surface by a lubricant supply unit.

Due to the maintenance of said lubricant support film between said end wall surface and the high-pressure end face contact of these faces due to the maintained axial support by the lubricant support film can be avoided.

In particular the invention makes it possible to act on the at least one screw rotor such that the axially acting bearing is constantly biased in the direction of the low-pressure side by the lubricant support film and thus as a whole a precise axial guiding of the at least one screw rotor is maintained.

In a simplified embodiment the lubricant support film is maintained permanently.

However, in a more sophisticated version it is also possible to maintain the lubricant support film at least in those phases of operation when there is a risk of contact of the faces.

In particular the lubricant support film is maintained by supplying lubricant to a support area which is arranged between said high-pressure end face of said respective screw rotor and said end wall surface and between an innermost diameter of the high-pressure end face and a radially outwardly arranged circular boarder line.

The advantage of this solution has to be seen in the fact that the outwardly arranged circular boarder line is a line having a continuous radius with respect to the screw rotor axes which helps maintaining the lubricant support film in the support area so that rotation of the screw rotors will not interrupt the lubricant support film as it would be the case if the radially outwardly arranged border line would deviate from a circular contour.

In particular it is of advantage if said circular border line is arranged radially outward from said innermost diameter of said high-pressure end face at maximum at a radially innermost root of the screw contour of said at least one screw rotor.

Further it is of advantage if said innermost diameter of said high-pressure end face is defined by an outer diameter of a pin section of said at least one screw rotor extending beyond said high-pressure end face.

It is in particular of advantage if said support area extends until said pin section of said at least one screw rotor on order to improve a sealing between said pin section and a bore in said end walls of said bearing casing by supplying lubricant thereto.

In connection with the explanation of the inventive concept concerning the lubricant support film it has not been defined in detail how said lubricant support film is to be maintained.

One advantageous solution provides that said lubricant support film within said support area is maintained by a supply of lubricant to said support area by at least one supply opening of said lubricant supply unit.

Such a supply opening can be arranged at different locations.

One advantageous solution provides that said at least one supply opening of said lubricant supply unit is arranged in the high-pressure end face of said at least one screw rotor. Alternatively, or additionally one advantageous solution provides that said at least one supply opening of said lubricant supply unit is arranged in the end wall surface of the machine casing.

This arrangement has the advantage that the at least one supply opening can be arranged stationary in a region with advantageous pressure relationship in the environment of said supply opening.

In particular in order to maintain a quite stable lubricant support film it is of advantage if said at least one supply opening is facing the support area so that the lubricant is directly supplied to the support area for distribution therein to the lubricant support film.

Another advantageous solution according to the present invention provides that said at least one supply opening extends to an area close to said circular border line.

This means that said supply opening will be arranged radially inside said circular border line.

However, it would be also possible that said at least one supply opening is arranged partially outside said support area adjacent to or overlapping with said circular border line so that the lubricant will enter the support area.

In the preceding embodiments the shape of the at least one supply opening has not been specified.

In general, the at least one supply opening can have any shape.

An advantageous embodiment provides that said at least one supply opening has a longitudinal shape in order to allow an equal distribution of lubricant within said support area. In particular the longitudinal shape extends transverse to said circular border line.

Another advantageous embodiment provides that the at least one supply opening extends between the circular border line and the innermost diameter, in particular starting and ending at a distance from the circular border line and the innermost diameter or even starting and/or ending adjacent the circular border line and/or the innermost diameter.

The lubricant for the lubricant supply film in principle could be supplied at a pressure which could be lower than the high-pressure at the high-pressure opening.

However, in order to provide a strong enough lubricant support film it is provided said lubricant is supplied to said lubricant support film in the support area at least at a pressure corresponding to the high-pressure at the high- pressure opening.

In order to enhance the supply of lubricant to the lubricant support film it is provided that the at least one supply opening is arranged in a region of said support area which is opposite to a high-pressure opening in said machine casing at said high-pressure side because the pressure of the gaseous medium surrounding the supply opening on this side is lower than the high-pressure close to said high-pressure opening so that a significant pressure gradient is available for the supply of lubricant to said support area.

In particular it is of advantage if said at least one supply opening is arranged in a region of said support area which is situated on a side of a screw rotor bore of said at least one screw rotor opposite to said high-pressure opening.

In particular it is of advantage if said at least one supply opening is arranged in a region of said support area on a side of the bearing pin section of said screw rotor or the screw rotor axis which region is opposite to said high-pressure opening because in this region of the support area the pressure in the surrounding of the supply opening is significantly lower than the high-pressure at said high-pressure opening, so that the pressure gradient for the supply of lubricant is close to the maximum available gradient in the support area.

In connection with the embodiments disclosed herein it has not been defined how said lubricant supply unit guides the lubricant to said at least supply opening.

One advantageous solution provides that said lubricant supply unit comprises a channel extending to said at least one supply opening.

In particular said channel can extend through said machine casing to the at least one supply opening arranged in said respective end wall surface.

Alternatively, it is provided that said channel extends through said at least one screw rotor to the supply opening arranged in said high-pressure end face of said at least one screw rotor.

In order to supply lubricant to said lubricant supply opening which is in a more or less condensed stage said lubricant supply unit comprises a lubricant reservoir comprising an accumulation of lubricant therein and wherein said lubricant accumulation being connected to said channel extending to said lubricant supply opening.

In order to impose pressure on said lubricant accumulation, one solution provides that said lubricant accumulation is exposed to the high-pressure of the gaseous medium at the high-pressure opening.

Another advantageous solution provides that the lubricant accumulation is arranged in a lubricant separator which can be arranged for example subsequent to said machine in a pipe for guiding the compressed gaseous medium. Another advantageous solution provides that said lubricant separator is arranged in said machine casing in particular integrated therein.

In order to provide a defined pressure for the supply of lubricant a version of the lubricant supply unit comprises a lubricant pump for feeding lubricant to the lubricant supply opening.

The inventive concept can be implemented alone or in combination with support units acting on the respective pin sections in directions away from the high- pressure side towards low-pressure side.

Further features and advantages of the invention form the subject matter of the description below and the representation in the drawings of some exemplary embodiments.

In particular, advantageous embodiments of the invention comprise the combination of features s defined by the following consecutively numbered embodiments.

1. A machine for expanding or compressing compressible media, comprising a machine casing (10), at least one screw rotor (36, 38), which is arranged in a screw rotor bore (32, 34) in the machine casing (10) and which extends between a low pressure side (62) and a high pressure side (64) of the screw rotor bore (32, 34) and which cooperates with the compressible medium, wherein by rotating about a screw rotor axis (52, 54), the at least one screw rotor (36, 38) conveys the substantially gaseous medium either from the low pressure side (62) to the high pressure side (64) by compressing it, or from the high pressure side (64) to the low pressure side (62) by expanding it, wherein said at least one screw rotor (36, 38) is mounted on both sides in the machine casing (10) by means of a respective bearing set (92, 94, 96, 98), wherein each bearing set (92, 94, 96, 98) has at least one radial acting bearing (102) and at least one of the bearing sets (96, 98) has at least one axially acting bearing (104) that supports the at least one screw rotor (36, 38) to counter an axial displacing movement of said screw rotor (36, 38) from its operating position in the direction (112, 114) of the low pressure side (62), wherein a motor/generator unit (132) is coupled or couplable to the at least one screw rotor (36, 38), characterized in that the at least one screw rotor (36, 38) is axially supported by a lubricant support film (210) provided between an end wall surface (126, 128) limiting said screw rotor bore (32, 34) and the high pressure end face (122, 124) of said at least one screw rotor (36, 38) in order to prevent the high pressure end face (122, 124) from making contact to the end wall surface (126, 128), and wherein the lubricant support film (210) is maintained between said high pressure end face (122, 124) and said end wall surface (126, 128) by a lubricant supply unit (222, 224).

2. Machine according to embodiment 1, wherein the lubricant support film (210) is maintained by supplying lubricant to a support area (232, 234) which is arranged between said high pressure end face (122, 124) of said respective screw rotor (36, 38) and said end wall surface (126, 128) and between an innermost diameter (242, 244) of the high pressure end face (122, 124) and a radially outwardly arranged circular border line (246, 248).

3. Machine according to embodiment 2, wherein said circular border line (246, 248) is arranged radially outward from said inner most diameter (242, 244) of said high pressure end face (122, 124) at maximum at a radially innermost root (252, 254) of the screw contour (42, 44) of at least one of said screw rotor (36, 38).

4. Machine according to embodiment 2 or 3, wherein said innermost diameter (242, 244) of said high pressure end face (122, 124) is defined by an outer diameter of a pin section (97, 99) of said at least one screw rotor (36, 38), extending beyond said high pressure end face (122, 124).

5. Machine according to one of the preceding embodiments, wherein said lubricant support film (210) within said support area (232, 234) is maintained by a supply of lubricant to said support area (232, 234) through at least one supply opening (262, 264) of said lubricant supply unit (222, 224). 6. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) of said lubricant supply unit (222, 224) is arranged in the high-pressure end face (122, 124) of said at least one screw rotor (36, 38).

7. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) of said lubricant supply unit (222, 224) is arranged in the end wall surface (126, 128).

8. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) is facing the support area (232, 234).

9. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) extends to an area close to said circular border line (246, 248).

10. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) is arranged partially outside said support area (232, 234) adjacent to or overlapping with said circular border line (246, 248).

11. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) has a longitudinal shape.

12. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) extends between said circular border line (246, 248) and said inner most diameter (242, 244).

13. Machine according to one of the preceding embodiments, wherein lubricant is supplied to said lubricant support film (210) in the support area (232, 234) at least at a pressure corresponding to the high-pressure at the high-pressure opening (80) 14. Machine according to one of the preceding embodiments, whereas said at least one supply opening (262, 264) is arranged in a region of said support area (232, 234) which is opposite to a high-pressure opening (80) in said machine casing (10) at said high-pressure side (64).

15. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) is arranged in a region of said support area (232, 234) which is situated on a side of a screw rotor bore (33, 34) of said at least one screw rotor (36, 38) opposite to said high-pressure opening.

16. Machine according to one of the preceding embodiments, wherein said at least one supply opening (262, 264) is arranged in a region of said support area (232, 234) on a side of the bearing pin section (97, 99) of said screw rotor (36, 38) or the screw rotor axis (52, 54) which region is opposite to said high- pressure opening (80).

17. Machine according to one of the preceding embodiments, wherein said lubricant supply unit (222, 224) comprises a channel (266, 268) extending to said at least one supply opening (262, 264).

18. Machine according to one of the preceding embodiments, wherein said channel (266, 268) extends through said machine casing (10) to the at least one supply opening (262, 264) arranged in said respective end wall surface (126, 128).

19. Machine according to one of the preceding embodiments, wherein said channel (269) extends through said at least one screw rotor (36, 38) to the supply opening (262, 264) arranged in said high pressure end face (122, 124) of said at least one screw rotor (36, 38).

20. Machine according to one of the preceding embodiments, wherein said lubricant supply unit (222, 224) comprises a lubricant reservoir (272, 274) comprising an accumulation of lubricant therein and wherein said lubricant accumulation being connected to said channel (266, 268) extending to said lubricant supply opening (262, 264).

21. Machine according to one of the preceding embodiments, wherein said lubricant accumulation (284) is exposed to the high pressure of the gaseous medium at the high-pressure opening (80).

22. Machine according to one of the preceding embodiments, wherein the lubricant accumulation (284) is arranged in a lubricant separator (282, 296).

23. Machine according to embodiment 22, wherein said lubricant separator (296) is arranged in said machine casing (10).

24. Machine according to one of the preceding embodiments, wherein said lubricant supply unit (222, 224) comprises a lubricant pump (312, 314).

25. Machine according to one of the preceding embodiments, wherein the screw rotors (36, 38) provided with support units (302, 304) acting on the respective pin sections (97, 99) in directions away from high-pressure side (64) towards low-pressure side (62).

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 shows a longitudinal section through a first exemplary embodiment of a machine according to the invention for depressurizing and/or compressing gaseous media;

Fig. 2 shows a section along the line 2-2 in Fig. 1;

Fig. 3 shows a schematic representation of a circuit using a machine according to the invention for depressurizing gaseous media;

Fig. 4 shows a schematic representation of a refrigerant circuit having a machine according to the invention for compressing gaseous media;

Fig. 5 shows an enlarged representation of a region A in Fig. 2; and

Fig. 6 shows a further enlarged section along the line 6-6 of the region illustrated in Fig. 5;

Fig. 7 shows a longitudinal section through a second exemplary embodiment of a machine according to the invention, similar to Fig. 1, for depressurizing and/or compressing gaseous media

Fig. 8 shows another embodiment corresponding to the embodiment in Fig. 2 provided in addition with support units;

Fig. 9 shows another embodiment corresponding to the embodiment in Fig. 4 provided in addition with a lubricant pump and

Fig. 10 shows another embodiment corresponding to the embodiment in Fig. 7 provided in addition with a lubricant pump. DETAILED DESCRIPTION OF THE INVENTION

A first exemplary embodiment of a machine according to the invention, in particular an expansion/compression machine, that is represented in Figs. 1 and 2 comprises a machine casing that is designated 10 as a whole and is formed by a screw rotor casing 12 adjoined on one side by a motor/generator casing 14, which is closed off by a casing cover 16 on an opposite side to the screw rotor casing 12.

On an opposite side to the motor/generator casing 14, the screw rotor casing 12 is adjoined by a bearing casing 18 that is closed off by a bearing casing cover 22 on the opposite side thereof to the screw rotor casing 12.

Provided in the screw rotor casing 12 are screw rotor bores 32, 34 in which there are arranged screw rotors 36, 38 that engage in one another by means of their screw contours 42, 44 and cooperate with wall faces 46, 48 of the screw rotor bores 32, 34 in order, during rotation about the respective screw rotor axes 52, 54, to form chambers 56 that are enclosed between the screw contours 42, 44 and the wall faces 46, 48, wherein these chambers 56 have the maximum possible volume at a point adjoining a low-pressure side 62 that adjoins the screw rotor bores, and the smallest volume at a point adjoining a high-pressure side 64.

Here, in the exemplary embodiment illustrated, the low-pressure side 62 lies on a side of the screw rotor casing 12 that faces the motor/generator casing 14, wherein the low-pressure side 62 is connected, by a gas path 72 passing through the motor/generator casing 14, to a low-pressure junction point 74 of the machine casing 10, and wherein the low-pressure junction point 74 is preferably arranged close to the casing cover 16 such that the gas path 72 running between the low-pressure junction point 74 and the low-pressure side 62 as far as possible passes through the motor/generator casing 14 over the entire length thereof. In the exemplary embodiment illustrated, the high-pressure side 64 lies on a side of the screw rotor casing 12 that faces the bearing casing 18, wherein the high-pressure side 64 is adjoined by a high-pressure opening 80 of rotor bores 32, 34 followed a high-pressure channel 82 that passes through the bearing casing 18 and the bearing casing cover 22 and leads to a high-pressure junction point 84 of the machine casing 10, which is arranged for example in the bearing casing cover 22.

As illustrated in Figs. 1 and 2, the screw rotors 36 and 38 are mounted to be rotatable about the respective screw axes 52 and 54 in the overall casing 10, wherein there is provided for each of the screw rotors 36, 38 a respective bearing set 92 and 94 on the low-pressure side, and for each of the screw rotors 36, 38 a bearing set 96, 98 on the high-pressure side.

Each of the bearing sets 92, 94, 96, 98 comprises at least one respective radial bearing 102, and in addition one of the bearing sets 92, 94, 96, 98 for each of the screw rotors 36, 38, for example the respective bearing set 96, 98 on the high-pressure side, also comprises at least one axially acting bearing 104.

The bearing sets 92, 94, 96, 98 are in particular each arranged on a bearing pin section 93, 95, 97, 99 of the respective screw rotor 36, 38.

Axially acting bearings 104 support the screw rotors 36, 38 to counter movement out of their operational position in direction of the low-pressure side 62, since the pressure difference between the high-pressure side 64 and the low-pressure side 62 acts on the screw rotors 36, 38 such that they tend to move in directions 112, 114 parallel to the screw axes 52, 54, away from the high-pressure side 64 and toward the low-pressure side 62, and thus to enlarge a sealing gap provided in the operational position between a respective end face 122, 124 of the respective screw rotor 36 and 38, in particular a closure at the end face 122, 124 of the screw rotors 36, 38 on the high-pressure side 64 and end wall surfaces 126, 128 formed by end walls 125, 127 of bearing casing 18 that close the screw rotor bores 32, 34 on the high-pressure side 64. Maintaining the operational position, and thus this sealing gap between the respective high pressure end face 122, 124 of the respective screw rotor 36 and 38 and the end wall surface 126, 128 respectively, which has a predetermined width and in conventional expanding or compressing machines is closed off by an lubricant film, is required in order to ensure optimal functioning of the machine, and therefore the operational position is predetermined by the action of the axially acting bearings 104 on the screw rotors 36, 38.

The screw rotors 36, 38, which rotate about their screw axes 52, 54, are coupled to an electrical motor/generator unit that is designated 132 as a whole, is provided in the motor/generator casing 14, and has a stator 134, which is arranged fixedly in the motor/generator casing 14, and a rotor 136, which is surrounded by the stator 134 and is seated on a common drive shaft 138 that passes through both the rotor 136 and the screw rotor 36 and is mounted on the bearing sets 92 and 102.

As illustrated in Figs. 1 and 2, the electrical motor/generator unit 132 is arranged such that the low-pressure channel 72 runs at least in certain regions along the stator 134 but, where appropriate, also runs through between the rotor 136 and the stator 134 in order to cool the electrical motor/generator unit 132 by means of the gas guided on the low-pressure side.

The screw rotor 36 that is coupled to the electrical motor/generator unit 132 is itself also coupled by way of the mutually engaging screw contours 42, 44 to the screw rotor 38, with the result that the chambers 56 that are formed migrate, depending on the direction of rotation of the screw rotors 36, 38, either from the high-pressure side 64 to the low-pressure side 62 and thus depressurize gas that is received on the high-pressure side 64, which is then present as expanded gas 62 on the low-pressure side 62, or from the low-pressure side 62 to the high-pressure side 64 and in so doing compress gas received on the low- pressure side 62, which is delivered on the high-pressure side 64. These two different operating modes are illustrated schematically in Fig. 3 and Fig. 4.

Fig. 3 illustrates a cycle, in particular a cycle that operates by a Rankine cycle, which is designated 140 as a whole and in which the working medium that is guided in a circuit 142 is compressed by a compressor 144 that is driven by a motor 146, then flows through a heat exchanger 148 and, as a result of a supply of heat from a heat stream 152, is evaporated, wherein the heat stream 152 is supplied to the heat exchanger 148 for example by means of a hot-water circuit and a hot-water pump 154 having a drive motor 156.

The working medium that is evaporated in the heat exchanger 148 as a result of the supply of the heat stream 152 is then supplied, downstream of the heat exchanger 148 in the circuit 142, to an expansion machine 160 that is formed in accordance with the expansion/compression machine illustrated in Figs. 1 and 2, wherein the motor/generator unit 132 operates as a generator.

According to Fig. 3, the working medium is supplied by way of the high-pressure junction point 84 to the machine 160 for expanding the working medium which arrives between the screw rotors 36, 38 on the high-pressure side 64, is received by the chambers 56 and is depressurized on the path of the chambers 56 to the low-pressure side 62, wherein - depending on the temperature and pressure -drops of liquid may also be formed.

The depressurized working medium is then supplied to a further heat exchanger 172 in which the working medium is condensed and a heat stream 174 is discharged, for example by a cold-water circuit in which a pump 176 driven by a motor 178 is likewise arranged.

However, it is also possible for the heat stream 174 to be discharged as a cooling air stream. In particular, as a result of the pump or the compressor 144 there is an increase of pressure of the working medium that is generated by the heat exchanger 172, and substantially isobaric evaporation of the subcooled system takes place in the heat exchanger 148 until the vapor-saturated state is reached, and in this state the working medium is then supplied to the expansion machine 160, as a result of which there is produced in the expansion machine 160 mechanical work that drives the motor/generator unit 132 and thus generates electrical energy.

Thereafter, there is isobaric, in particular completely isobaric, condensation of the working medium in the heat exchanger 172 as a result of discharging the heat stream 174, such that a liquid-saturated condensate can then once again be supplied to the compressor 144.

The expansion/compression machine that is described before and illustrated in Figs. 1 and 2 may, however, also be used according to Fig. 4 in a cycle 180 of a refrigerant circuit 182 in which the refrigerant is heated in a heat exchanger 184 by absorption of heat, for example provided by means of a fan 186, and then supplied to the low-pressure junction point 74, then compressed by the compression machine, which is driven by the motor/generator unit 132, on the path from the low-pressure side 62 to the high-pressure side 64, and supplied by way of the high-pressure junction point 84 to a heat exchanger 202 that cools the compressed refrigerant, for example by means of a fan 204, and then supplies it to an expansion member 206 for expansion, from which the expanded coolant is supplied to the exchanger 184 again.

In normal operation, in both the circuit 142 and the refrigerant circuit 182, in the expansion/compression machine the pressure on the low-pressure side 62 is always lower than the pressure on the high-pressure side 64, with the result that in these cases the screw rotors 36, 38 always strive to move their end faces 122, 124 away from the end wall surfaces 126, 128 in the directions 112, 114 and to maintain a sealing gap closed by a lubricant film that is predetermined by the axially acting bearings 104. However, during starting or stopping procedures, or in the event of aborted start or stop procedures or an incorrect direction of rotation of the motor/generator unit 132, it is possible for conditions to arise in which the forces acting on the screw rotors 36, 38 in the directions 112 and 114 are close to zero or in some cases are even negative.

In these cases, it is possible for the sealing gap to become narrowed and hence for the high pressure end faces 122, 124 of the screw rotor 36, 38 to come into contact with the end wall surfaces 126, 128, resulting in abrasion and heating, to a certain extent overheating, and consequently damage at the high pressure end faces 122, 124 and/or the end wall surfaces 126, 128 or the screw contours 42, 44 of the screw rotors 36, 38, since the axially acting bearings 104 are only active in the directions 112 and 114 but not in the directions opposed to the directions 112 and 114 (Fig. 5).

In order to avoid narrowing of the sealing gap and in particular to avoid contact of the end faces 122, 124 of the screw rotor 36, 38 with the end wall surfaces 126, 128 a lubricant support film 210 is provided between the end faces 122, 124 of screw rotors 36, 38 and end wall surfaces 126, 128 of machine casing 10 which lubricant support film 210 is maintained by lubricant supply units 222, 224 which supply lubricant to lubricant support film 210, in order to permanently supply lubricant at least in those operational phases of the machine in which there is a risk that the sealing gap could become narrowed (Fig. 5, 6).

According to a first embodiment of the inventive concept the lubricant support film 210 is primarily established in at least one of support areas 232, 234 of the screw rotors 36, 38 which are arranged in a radial distance from the respective screw rotor axes 52, 54 and which extend between an innermost diameter 242, 244 of the respective high pressure end face 122, 124 of the respective screw rotor 36, 38 and a radially outwardly arranged circular border line 246, 248 (Fig. 6). It could be sufficient to provide a lubricant support film 210 for the male screw rotor 36, which is the one connected to motor/generator unit 132.

However, a more advantageous design provides a lubricant support film 210 for both screw rotors 36, 38.

The innermost diameter 242, 244 is preferably defined by an outer diameter of the respective pin section 97, 99 extending beyond the high-pressure end face 122, 124 through bores 243, 245 in end walls 125, 127 and then into the respective bearing set 96, 98 for the respective screw rotor 36, 38 which bearing set 96, 98 is arranged in bearing casing 18.

According to an advantageous version of this design it is possible the allow the lubricant of lubricant support film 210 to enter into gaps between pin sections 97, 99 and the respective bores 243, 245 and to provide an improved sealing in these gaps as shown in Fig. 5.

The circular border line 246, 248 is radially outwardly arranged of the innermost diameter 242, 244 of the high-pressure end face 122, 124 and preferably at a radial distance from the respective screw axis 52, 54 which at maximum corresponds to the radial distance of an innermost root 252, 254 of the respective screw contour 42, 44 from the screw rotor axes 52, 54.

Therefore, the support area 232, 234 is a circumferentially closed area extending around the respective screw axis 52, 54 so that the lubricant support film 210 will not be circumferentially interrupted by the rotating screw rotor 36, 38 with portions of its screw contours 42, 44.

In order to supply lubricant to lubricant support film 210 lubricant supply units 222, 224 feed lubricant to at least one lubricant supply opening 262, 264 from which lubricant can enter the respective support area 232, 234. According to a first embodiment lubricant supply openings 262, 264 can be arranged to directly face the respective support area 232, 234 either by arranging the at least one lubricant supply opening 262, 264 in bearing casing 18 such that the respective lubricant supply opening 262, 264 is provided in the respective end wall surface 126, 128. In this case the respective lubricant supply unit 222, 224 is provided with a channel 266, 268, extending through bearing casing 18 to the respective lubricant supply opening 262, 264.

The channel 266, 268 is connected to a lubricant reservoir 272, 274 of the respective lubricant supply unit 222, 224 connected to the respective channel 266, 268.

Alternative lubricant supply openings 262, 264 can be arranged within the high- pressure end face 122, 124 of the respective screw rotor 36, 38 and in this case the respective channels 267, 269 have to extend through the respective screw rotor 36, 38 to receive lubricant from the respective lubricant reservoir 272, 274.

In general lubricant supply openings 262, 264 could be arranged radially somewhere between the inner most diameter 242, 244 of the high-pressure end face 122, 124 and the radially outwardly arranged circular border line 246, 248 and will be directly facing and supplying lubricant to the respective support area 232, 234.

Since lubricant within lubricant reservoir 272, 274 will be exposed to the high pressure of the gaseous medium which is expanded or compressed in the machine according to the present invention it is of advantage if the lubricant supply opening 262, 264 is arranged on a side of pin sections 97, 99 or screw axis 52, 54 opposite to said high-pressure opening 80 because the pressure of the gaseous medium in such a region of the respective support area 232, 234 is lower than in a region of the support area 232, 234 adjacent to high-pressure opening 80. In case the machine 10 is provided with two screw rotors 36, 38 as described before the two supply openings 262, 264 are arranged on a side of a plane 272 extending through both rotor screw axis 52, 54 because in these regions of the support area 232, 234 the pressure of the gaseous medium is below the high pressure of the gaseous medium in outlet opening 80.

An even more improved version provides arranging supply openings 262', 264' on sides of planes 274 and 276 extending through screw rotor axis 52, 54 but vertical to plane 272 which are directed towards the respective other rotor 38, 36 but also on a side of plane 272 which is opposite to outlet opening 80.

According to one advantageous version openings 262', 264' can be designed to have a longitudinal shape and to extend in a direction transverse to borderline 246, 248 and/or innermost diameter 242, 244.

An even further embodiment provides the arrangement of outlet openings 262" and 264" just adjacent to or radially overlapping with the radially outwardly arranged circular border line 246, 248 and starting at the circular border line 246, 248 or partially outside of support area 232, 234 and extending towards innermost diameter 224, 244 so that lubricant supplied through these openings 262", 264" will be fed into support area 232, 234 due to rotation of screw rotors 36, 38.

In all the aforementioned embodiments the lubricant reservoirs 272 or 274 is not further defined.

In one advantageous version according to the present invention as shown in Fig. 4 a lubricant separator 282 is provided in the refrigerant circuit 182, in particular following high-pressure junction point 84 and in particular between this high-pressure junction point 84 and heat exchanger 202.

In this lubricant separator 282 lubricant is collected and accumulated in a common lubricant reservoir 284 at the bottom thereof and representing lubricant reservoirs 272, 274 and subject to the high-pressure of the gaseous medium leaving high-pressure junction point 84.

From this lubricant reservoir 284 lubricant is supplied to the respective channels 222, 224 by pipe 286.

In a further embodiment, shown in Fig. 7 an additional casing 292 is arranged on the side of bearing casing 18, and in particular covering bearing casing 18, in which additional casing 292 a muffler 294 is arranged combined with a lubricant separator 296 so that a common lubricant reservoir 298 representing lubricant reservoirs 272, 274 is formed at a bottom of casing 292 so that lubricant accumulated in lubricant reservoir 298 can directly enter channels 266 and 268.

In a further embodiment shown in Fig. 8 the provision of the lubricant support film 210 can be combined with a support unit 302, 304 acting on pin sections 97 ,99 in direction 112 and 114 away from high-pressure side 64 and toward low- pressure side 62.

Examples of such support units 302, 304 are disclosed in WO 2020/160999 Al, US 2022/037229 Al, US 5,246,357 A and WO 2016/099746 Al.

According to a further embodiment shown in Fig. 9 which is based on the embodiment according to Fig. 4 and to which reference is made, a lubricant pump 312 is provided for in example in pipe 286 in order to supply lubricant with increased pressure to lubricant supply units 222, 224.

Another improved embodiment shown in Fig. 10, which is based on the embodiment according to Fig. 7 and to which reference is made, provides a lubricant pump 314 in association with lubricant reservoir 298 in order to be able to supply lubricant at a defined pressure by lubricant supply units 222, 224.

Claims

2. Machine according to claim 1, wherein the lubricant support film (210) is maintained by supplying lubricant to a support area (232, 234) which is arranged between said high pressure end face (122, 124) of said respective screw rotor (36, 38) and said end wall surface (126, 128) and between an innermost diameter (242, 244) of the high pressure end face (122, 124) and a radially outwardly arranged circular border line (246, 248).

3. Machine according to claim 2, wherein said circular border line (246, 248) is arranged radially outward from said inner most diameter (242, 244) of said high pressure end face (122, 124) at maximum at a radially innermost root (252, 254) of the screw contour (42, 44) of at least one of said screw rotor (36, 38).

4. Machine according to claim 2 or 3, wherein said innermost diameter (242, 244) of said high pressure end face (122, 124) is defined by an outer diameter of a pin section (97, 99) of said at least one screw rotor (36, 38), extending beyond said high pressure end face (122, 124).

5. Machine according to one of the preceding claims, wherein said lubricant support film (210) within said support area (232, 234) is maintained by a supply of lubricant to said support area (232, 234) through at least one supply opening (262, 264) of said lubricant supply unit (222, 224).

6. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) of said lubricant supply unit (222, 224) is arranged in the high-pressure end face (122, 124) of said at least one screw rotor (36, 38).

7. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) of said lubricant supply unit (222, 224) is arranged in the end wall surface (126, 128).

8. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) is facing the support area (232, 234).

9. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) extends to an area close to said circular border line (246, 248).

10. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) is arranged partially outside said support area (232, 234) adjacent to or overlapping with said circular border line (246, 248).

11. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) has a longitudinal shape.

12. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) extends between said circular border line (246, 248) and said inner most diameter (242, 244).

13. Machine according to one of the preceding claims, wherein lubricant is supplied to said lubricant support film (210) in the support area (232, 234) at least at a pressure corresponding to the high-pressure at the high-pressure opening (80).

14. Machine according to one of the preceding claims, whereas said at least one supply opening (262, 264) is arranged in a region of said support area (232, 234) which is opposite to a high-pressure opening (80) in said machine casing (10) at said high-pressure side (64).

15. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) is arranged in a region of said support area (232, 234) which is situated on a side of a screw rotor bore (33, 34) of said at least one screw rotor (36, 38) opposite to said high-pressure opening.

16. Machine according to one of the preceding claims, wherein said at least one supply opening (262, 264) is arranged in a region of said support area (232, 234) on a side of the bearing pin section (97, 99) of said screw rotor (36, 38) or the screw rotor axis (52, 54) which region is opposite to said high-pressure opening (80).

17. Machine according to one of the preceding claims, wherein said lubricant supply unit (222, 224) comprises a channel (266, 268) extending to said at least one supply opening (262, 264).

18. Machine according to one of the preceding claims, wherein said channel (266, 268) extends through said machine casing (10) to the at least one supply opening (262, 264) arranged in said respective end wall surface (126, 128).

19. Machine according to one of the preceding claims, wherein said channel (269) extends through said at least one screw rotor (36, 38) to the supply opening (262, 264) arranged in said high pressure end face (122, 124) of said at least one screw rotor (36, 38).

20. Machine according to one of the preceding claims, wherein said lubricant supply unit (222, 224) comprises a lubricant reservoir (272, 274) comprising an accumulation of lubricant therein and wherein said lubricant accumulation being connected to said channel (266, 268) extending to said lubricant supply opening (262, 264).

21. Machine according to one of the preceding claims, wherein said lubricant accumulation (284) is exposed to the high pressure of the gaseous medium at the high-pressure opening (80).

22. Machine according to one of the preceding claims, wherein the lubricant accumulation (284) is arranged in a lubricant separator (282, 296).

23. Machine according to claim 22, wherein said lubricant separator (296) is arranged in said machine casing (10).

24. Machine according to one of the preceding claims, wherein said lubricant supply unit (222, 224) comprises a lubricant pump (312, 314).

25. Machine according to one of the preceding claims, wherein the screw rotors (36, 38) provided with support units (302, 304) acting on the respective pin sections (97, 99) in directions away from high-pressure side (64) towards low-pressure side (62).