Background of the invention US7240515 discloses a twin centrifugal refrigeration compressor including notably:

- a hermetic housing,

- an electrical motor including a stator and a rotor shaft, the rotor shaft having a first axial end portion, a second axial end portion, and an intermediate portion configured to be driven in rotation by the stator,

- a first and a second centrifugal refrigeration compressor each including a first and a second compression stage configured to compress a refrigerant, the first and second compression stages of the first centrifugal refrigeration compressor including a first and a second impeller connected to the first axial end portion of the rotor shaft, the first and second compression stages of the second centrifugal refrigeration compressor including a first and a second impeller connected to the second axial end portion of the rotor shaft, and

- a radial magnetic bearing assembly configured for rotatably supporting the rotor shaft.

In order to limit the axial length of the each of the first and second centrifugal refrigeration compressors, the first and second impellers of each of the first and second centrifugal refrigeration compressors are arranged close to each other. However, the configuration of the electrical motor and of the radial magnetic bearing assembly prevents to further reduce the axial length of the centrifugal refrigeration compressor.

Furthermore, due to the configuration of the electrical motor, and particularly of the rotor shaft, the mass of the rotating parts is high, which complicates the balancing of the centrifugal refrigeration compressor, and which thus could harm the compressor reliability and performance. Summary of the invention

It is an object of the present invention to provide a centrifugal refrigeration compressor which can overcome the drawbacks encountered with conventional centrifugal refrigeration compressors.

Another object of the present invention is to provide a compact centrifugal refrigeration compressor which can be easily balanced.

According to the invention such a centrifugal refrigeration compressor includes:

- a hermetic housing,

- a drive shaft including a first axial end portion, a second axial end portion and an intermediate portion arranged between the first and second end axial portions, the drive shaft including a central axial bore extending along at least a portion of the length of the drive shaft,

- a first and a second compression stage configured to compress a refrigerant, the first and second compression stages respectively including a first and a second impeller, the first and second impellers being connected to the first axial end portion of the drive shaft,

- an electrical motor configured for driving in rotation the drive shaft about a rotation axis, the electrical motor including a stator and a rotor, the rotor being connected to the second axial end portion of the drive shaft,

- a fixed shaft element secured to the hermetic housing and extending at least partially into the central axial bore of the drive shaft, and

- a radial bearing arrangement configured for rotatably supporting the drive shaft, the radial bearing arrangement being configured to cooperate with an outer surface of the fixed shaft element.

The configuration of the drive shaft and the fixed shaft element reduces the mass of the rotating parts, which limits the vibration generated by the centrifugal refrigeration compressor, and eases the balancing of the latter.

Further, the configuration of the radial bearing arrangement between the fixed shaft element and the drive shaft, i.e. inside the drive shaft, allows to arrange the electrical motor closer to the first and second compression stages, and thus to reduce the total axial length of the centrifugal refrigeration compressor.

The centrifugal refrigeration compressor may also include one or more of the following features, taken alone or in combination. According to an embodiment of the invention, the radial bearing arrangement includes at least one radial bearing extending along at least a portion of an inner surface of the rotor.

According to an embodiment of the invention, the radial bearing arrangement includes at least one radial bearing extending along at least a portion of at least one of the first and second impellers.

According to an embodiment of the invention, the radial bearing arrangement includes at least one radial bearing extending along at least a portion of an inner surface of the rotor, along the drive shaft and along at least a portion of at least one of the first and second impellers.

According to an embodiment of the invention, the radial bearing arrangement is arranged between an outer surface of the fixed shaft element and an inner surface of the drive shaft.

According to an embodiment of the invention, the radial bearing arrangement includes at least one radial bearing arranged between the outer surface of the fixed shaft element and the inner surface of the drive shaft. The radial bearing may be a sleeve bearing.

According to an embodiment of the invention, the radial bearing extends along at least a portion of the second axial end portion and/or at least a portion of the intermediate portion of the drive shaft.

According to an embodiment of the invention, the radial bearing arrangement is arranged within the central axial bore of the drive shaft.

According to an embodiment of the invention, the radial bearing arrangement includes a plurality of radial bearings distributed along the axial length of the fixed shaft element.

According to an embodiment of the invention, the centrifugal refrigeration compressor further includes a thrust bearing arrangement configured to limit an axial movement of the drive shaft during operation, the thrust bearing arrangement including a thrust bearing member arranged on the outer surface of the intermediate portion of the drive shaft.

According to an embodiment of the invention, the thrust bearing arrangement is a fluid thrust bearing arrangement, and for example a gas thrust bearing arrangement. Therefore, a compressed fluid, such as a compressed gas, at intermediate or high pressure is delivered to a space provided between the corresponding adjacent bearing surfaces of the thrust bearing arrangement. Hereby, the use of lubricant oil and associated problems with oil supply, oil temperature or oil circulation in the refrigerant compression can be avoided.

According to an embodiment of the invention, the thrust bearing member extends radially outwardly with respect to the intermediate portion of the drive shaft.

According to an embodiment of the invention, the thrust bearing member is annular.

According to an embodiment of the invention, the thrust bearing member is integrally formed with the drive shaft.

According to an embodiment of the invention, the thrust bearing member has a first thrust bearing surface and a second thrust bearing surface opposite to the first thrust bearing surface.

According to an embodiment of the invention, the first thrust bearing surface of the thrust bearing member is configured to cooperate with a first thrust bearing surface defined by a first thrust bearing element connected to the hermetic housing, and the second thrust bearing surface of the thrust bearing member is configured to cooperate with a second thrust bearing surface defined by a second thrust bearing element connected to the hermetic housing.

According to an embodiment of the invention, the first and second thrust bearing elements are annular.

According to an embodiment of the invention, the thrust bearing member is located between the electric motor and the first compression stage.

According to an embodiment of the invention, the central axial bore of the drive shaft extends along the entire length of the drive shaft, and the rotor includes a central axial passage extending along the entire length of the rotor, the fixed shaft element extending into and along the central axial bore and the central axial passage and having a first end portion and a second end portion respectively connected to the hermetic housing.

According to an embodiment of the invention, the fixed shaft element is supported in a cantilevered manner with respect to the hermetic housing. According to an embodiment of the invention, the fixed shaft element is connected to the hermetic housing near the first axial end portion of the drive shaft. According to another embodiment of the invention, the fixed shaft element is connected to the hermetic housing near the second axial end portion of the drive shaft. According to an embodiment of the invention, the axial bore of the drive shaft extends along at least the first axial end portion and the intermediate portion of the drive shaft.

According to an embodiment of the invention, the axial bore of the drive shaft extends along at least the intermediate portion and the second axial end portion of the drive shaft. According to said embodiment of the invention, the rotor may also include a central axial passage extending along the entire length of the rotor.

According to an embodiment of the invention, the radial bearing arrangement is a fluid radial bearing arrangement, and for example a gas radial bearing arrangement. Thus, the use of lubricant oil for lubricating the radial bearing arrangement and associated problems with oil supply, oil temperature or oil circulation in the refrigerant compression can be avoided.

According to an embodiment of the invention, the centrifugal refrigeration compressor is configured so that at least a part of the refrigerant compressed in the first and second compression stages is used as lubricating fluid in the fluid radial bearing arrangement and/or the fluid thrust bearing arrangement. According to said embodiment of the invention, the centrifugal refrigeration compressor may be considered as a mono-fluid compressor. This configuration of the centrifugal refrigeration compressor avoids a separate supply of lubricating fluid and thus reduces costs.

According to an embodiment of the invention, the first and second impellers are arranged in a back-to-back configuration.

According to an embodiment of the invention, the first and second impellers are integrally formed with the drive shaft. According to another embodiment of the invention, the first and second impellers are provided on an impeller member secured to the first axial end portion of the drive shaft.

According to an embodiment of the invention, each of the first and second compression stages includes a front side equipped with a plurality of blades configured to accelerate, during rotation of the drive shaft, the refrigerant entering the respective compression stage and to deliver the accelerated refrigerant to a diffuser arranged at the radial outside edge of the respective impeller.

According to an embodiment of the invention, each of the first and second compression stages includes a fluid inlet and a fluid outlet, the fluid outlet of the first compression stage being fluidly connected to the fluid inlet of the second compression stage. According to an embodiment of the invention, the hermetic housing includes a low pressure chamber located upstream the first compression stage, and a high pressure chamber located downstream the second compression stage, the electrical motor being arranged in the low pressure chamber.

According to an embodiment of the invention, the radial and/or the thrust bearing arrangements are arranged in the low pressure chamber.

According to an embodiment of the invention, the hermetic housing further includes an intermediate pressure chamber provided between the fluid outlet of the first compression stage and the fluid inlet of the second compression stage.

According to an embodiment of the invention, the fixed shaft element is a stepped fixed shaft element, and has an external diameter which varies along the axial length of the fixed shaft element.

According to an embodiment of the invention, the fixed shaft element and/or the drive shaft are made of high strength steel, ceramics materials, or combinations thereof.

According to an embodiment of the invention, the fixed shaft element extends substantially parallely to the drive shaft.

According to an embodiment of the invention, the centrifugal refrigeration compressor further includes a connection sleeve configured to rotatably connect the rotor and the second axial end portion of the drive shaft.

According to an embodiment of the invention, the connection sleeve surrounds at least partially the rotor and at least partially the second axial end portion of the drive shaft. The connection sleeve may entirely surround the second axial end portion of the drive shaft, and may also surround at least partially the intermediate portion of the drive shaft.

According to an embodiment of the invention, the centrifugal refrigeration compressor further includes a spacer member located between the drive shaft and the rotor.

According to an embodiment of the invention, the connection sleeve includes an end located near the thrust bearing member, and for example abutting against the thrust bearing member.

According to an embodiment of the invention, the connection sleeve may be integrally formed with the drive shaft.

These and other advantages will become apparent upon reading the following description in view of the drawing attached hereto representing, as non- limiting examples, embodiments of the centrifugal refrigeration compressor according to the invention.

Brief description of the drawings

The following detailed description of several embodiments of the invention is better understood when read in conjunction with the appended drawings being understood, however, that the invention is not limited to the specific embodiment disclosed.

Figure 1 is a longitudinal sectional view of a centrifugal refrigeration compressor according to a first embodiment of the invention.

Figure 2 is a longitudinal sectional view of a centrifugal refrigeration compressor according to a second embodiment of the invention.

Figure 3 is a longitudinal sectional view of a centrifugal refrigeration compressor according to a third embodiment of the invention.

Figure 4 is a longitudinal sectional view of a centrifugal refrigeration compressor according to a fourth embodiment of the invention.

Figure 5 is a longitudinal sectional view of a centrifugal refrigeration compressor according to a fifth embodiment of the invention.

Figure 6 is a longitudinal sectional view of a centrifugal refrigeration compressor according to a sixth embodiment of the invention.

Figure 7 is a longitudinal sectional view of a centrifugal refrigeration compressor according to a seventh embodiment of the invention.

Figure 8 is a longitudinal sectional view of a centrifugal refrigeration compressor according to an eighth embodiment of the invention.

Detailed description of the invention

Figure 1 represents a centrifugal refrigeration compressor 2, and particularly a two-stage centrifugal refrigeration compressor.

The centrifugal refrigeration compressor 2 includes a hermetic housing 3, and a drive shaft 4 rotatably arranged within the hermetic housing 3 and extending along a longitudinal axis A. The drive shaft 4 includes a first axial end portion 5, a second axial end portion 6 opposite to the first axial end portion 5, and an intermediate portion 7 arranged between the first and second end axial portions 5, 6. The drive shaft 4 may be made of high strength steel, ceramics materials, or combinations thereof. According to the embodiment shown on figure 1, the drive shaft includes a central axial bore 8 extending along the entire length of the drive shaft 4.

The centrifugal refrigeration compressor 2 further includes a first compression stage 9 and a second compression stage 11 configured to compress a refrigerant. The first compression stage 9 includes a fluid inlet 12 and a fluid outlet 13, while the second compression stage 11 includes a fluid inlet 14 and a fluid outlet 15, the fluid outlet 13 of the first compression stage 9 being fluidly connected to the fluid inlet 14 of the second compression stage 11.

The hermetic housing 3 includes therefore a low pressure chamber located upstream the first compression stage 9, a high pressure chamber located downstream the second compression stage 11, and an intermediate pressure chamber provided between the fluid outlet 13 of the first compression stage 9 and the fluid inlet 14 of the second compression stage 11.

The first and second compression stages 9, 11 respectively include a first impeller 16 and a second impeller 17. The first and second impellers 16, 17 are connected to the first axial end portion 5 of the drive shaft 4. According to the embodiment shown on figure 1, the first and second impellers 16, 17 are provided on an impeller member 18 secured to the first axial end portion 5 of the drive shaft 4. However, according to another embodiment of the invention, the first and second impellers 16, 17 may be integrally formed with the drive shaft 4.

The first and second impellers 16, 17 are arranged in a back-to-back configuration, so that the directions of fluid flow at the flow inlet 12, 14 of the first and second compression stages 9, 11 are opposite to each other.

Each of the first and second impellers 16, 17 includes a front side equipped with a plurality of blades configured to accelerate, during rotation of the drive shaft 4, the refrigerant entering the respective one of the first and second compression stages 9, 11, and to deliver the accelerated refrigerant to a diffuser arranged at the radial outside edge of the respective one of the first and second impellers 16, 17.

The centrifugal refrigeration compressor 2 includes an electrical motor 19 configured for driving in rotation the drive shaft 4 about the longitudinal axis A of the drive shaft 4. The electrical motor 19 includes a stator 21 and a rotor 22. The electrical motor is arranged in the low pressure chamber defined by the hermetic housing 3. According to the embodiment shown on figure 1, the rotor 22 includes a central axial passage 23 extending along the entire length of the rotor 22. The rotor 22 is connected to the second axial end portion 6 of the drive shaft 4. To this end, the centrifugal refrigeration compressor 2 includes a connection sleeve 24 configured to rotatably connect the rotor 22 and the second axial end portion 6 of the drive shaft 4. The drive shaft 4 and the rotor 22 may for example be firmly fitted, such as press-fitted, within the connection sleeve 24. The connection sleeve 24 may also be heat shrink fitted to the drive shaft 4 and the rotor 22.

According to the embodiment shown on figure 1, the connection sleeve 24 entirely surrounds the rotor 22 and the second axial end portion 6 of the drive shaft 4. The connection sleeve 24 may also surround at least partially the intermediate portion 7 of the drive shaft 4.

The centrifugal refrigeration compressor 2 includes a fixed shaft element 26 secured to the hermetic housing 3, and extending coaxially to the drive shaft 4. The fixed shaft element 26 may be made of high strength steel, ceramics materials, or combinations thereof. The fixed shaft element 26 may be stepped, and have an external diameter which varies along the axial length of the fixed shaft element 26, or it may have a cross-section substantially constant along its entire length.

According to the embodiment shown on figure 1, the fixed shaft element 26 extends into and along the axial bore 8 of the drive shaft 4 and the axial passage 23 of the rotor 22, and has a first end portion 26a and a second end portion 26b respectively connected to the hermetic housing 3.

The centrifugal refrigeration compressor 2 includes a radial bearing arrangement configured for rotatably supporting the drive shaft 4. The radial bearing arrangement includes a radial bearing 27, such as a radial sleeve bearing, arranged within the axial bore 8 of the drive shaft 4 and between the outer surface of the fixed shaft element 26 and the inner surface of the drive shaft 4. The radial bearing 27 may be a fluid radial bearing, and for example a gas radial bearing. According to the embodiment shown on figure 1, the radial bearing 27 extends along the second axial end portion 6 and along a portion of the intermediate portion 7 of the drive shaft 4. It should nevertheless be noted that the radial bearing arrangement may include a plurality of radial bearings distributed along the axial length of the fixed shaft element 26.

The centrifugal refrigeration compressor 2 further includes a thrust bearing arrangement arranged in the low pressure chamber and configured to limit an axial movement of the drive shaft 4 during operation. The thrust bearing arrangement may be a fluid thrust bearing arrangement, and for example a gas thrust bearing arrangement. The thrust bearing arrangement includes an annular thrust bearing member 28 arranged on the outer surface of the intermediate portion 7 of the drive shaft 7, and located between the electric motor 19 and the first compression stage 9. The thrust bearing member 28 may be integrally formed with the drive shaft 4, or may be secured to the latter. It should be noted that an end portion of the connection sleeve 24 may be located near the thrust bearing member 28, and may for example abut against the thrust bearing member 28.

The thrust bearing member 28 extends radially outwardly with respect to the intermediate portion 7 of the drive shaft 4, and has a first thrust bearing surface 29 and a second thrust bearing surface 31 opposite to the first thrust bearing surface 29. The first thrust bearing surface 29 of the thrust bearing member 28 is configured to cooperate with a first thrust bearing surface defined by a first annular thrust bearing element 32 connected to the hermetic housing 3, while the second thrust bearing surface 31 of the thrust bearing member 28 is configured to cooperate with a second annular thrust bearing surface defined by a second thrust bearing element 33 connected to the hermetic housing 3.

According to an embodiment of the invention, the centrifugal refrigeration compressor 2 is configured so that a part of the refrigerant compressed by the first and second compression stages 9, 11 is used as lubricating fluid in the fluid radial bearing arrangement and the fluid thrust bearing arrangement.

Figure 2 represents a centrifugal refrigeration compressor 2 according to a second embodiment of the invention which differs from the first embodiment shown on figure 1 essentially in that the fixed shaft element 26 is supported in a cantilevered manner with respect to the hermetic housing 3 and the first end portion 26a of the fixed shaft element 26 is connected to the hermetic housing 3. According to said second embodiment, the rotor 26 is devoid of axial passage.

Figure 3 represents a centrifugal refrigeration compressor 2 according to a third embodiment of the invention which differs from the first embodiment shown on figure 1 essentially in that the fixed shaft element 26 is supported in a cantilevered manner with respect to the hermetic housing 3 and the second end portion 26b of the fixed shaft element 26 is connected to the hermetic housing 3.

Figure 4 represents a centrifugal refrigeration compressor 2 according to a fourth embodiment of the invention which differs from the first embodiment shown on figure 1 essentially in that the radial bearing arrangement includes a first radial bearing 27a extending along the first and second impellers 16, 17 and the first axial end portion 5 of the drive shaft 4, and a second radial bearing 27b extending along the inner surface of the rotor 22. According to said fourth embodiment of the invention, the impeller member 18 is connected to the drive shaft 4 by means of the radial bearing arrangement, and more particularly by means of the first radial bearing 27a. For example, the impeller member 18 and the drive shaft 4 may be firmly fitted to the first radial bearing 27a.

Figure 5 represents a centrifugal refrigeration compressor 2 according to a fifth embodiment of the invention which differs from the fourth embodiment shown on figure 4 essentially in that the radial bearing 27 extends along the first and second impellers 16, 17, and along the entire axial length of the drive shaft 4 and of the rotor 22.

Figure 6 represents a centrifugal refrigeration compressor 2 according to a sixth embodiment of the invention which differs from the third embodiment shown on figure 3 essentially in that the radial bearing 27 extends along the first impeller 16, and along the entire axial length of the drive shaft 4 and of the rotor 22.

Figure 7 represents a centrifugal refrigeration compressor 2 according to a seventh embodiment of the invention which differs from the sixth embodiment shown on figure 6 essentially in that the radial bearing arrangement includes a first radial bearing 27a extending along the first impeller 16 and the first axial end portion 5 of the drive shaft 4, and a second radial bearing 27b extending along the inner surface of the rotor 22.

Figure 8 represents a centrifugal refrigeration compressor 2 according to a eighth embodiment of the invention which differs from the second embodiment shown on figure 2 essentially in that the radial bearing 27 extends along the first and second impellers 16, 17, and along substantially the entire axial length of the drive shaft 4.

Of course, the invention is not restricted to the embodiments described above by way of non-limiting examples, but on the contrary it encompasses all embodiments thereof.