A method of forming ribs or grooves on a shaft for the air or gas bearings of a compressor.

Abstract

To form grooves or ribs for air or gas bearings on a rotor shaft quickly.SOLUTION: A shaft may rotate around a longitudinal axis of a centrifugal compressor. According to this method, all ribs or grooves (32, 24) are formed on workpiece portions of the shaft and an axial bearing of the shaft at one time. The formation is performed by moving the shaft (7) or a tool holder attached with a machining tool in a longitudinal machining direction from a start point to an end point of the work portion or a surface, and by the machining tool performing reciprocating motion to be in a machining position where the machining tool is in contact with the shaft or the axial bearing of the shaft and a position where the machining tool is not contact with these components. The reciprocating motion of the machining tool is synchronised with a sinusoidal program executed in a machining unit and a desired and programmed arrangement of the ribs or grooves to be produced.SELECTED DRAWING: Figure 3

Description

Technical Field

[0001] The present invention relates to a method of forming ribs or grooves on a shaft for an air or gas bearing of a high-speed centrifugal fluid compressor. This compressor is a two-stage compressor and includes a casing having an inlet for the fluid and an outlet for the compressed fluid, and surrounds a shaft rotatably mounted about a vertical axis (main shaft). A first compressor wheel and a second compressor wheel are attached back-to-back to the shaft, the first compressor wheel constituting a first compression stage and the second compressor wheel constituting a second compression stage. The centrifugal compressor further includes a motor, preferably a synchronous electric motor, disposed between the first compressor wheel and the second compressor wheel and configured to rotate the shaft. At least one air or gas axial bearing forms part of the shaft and is attached to one end of the shaft. Also, a front air or gas axial bearing can be attached to the first end of the shaft, and a rear air or gas axial bearing can be attached to the second end of the shaft.

Background Art

[0002] Fluid compressors are commonly referred to as turbo compressors or centrifugal compressors. These are composed of a stator and a rotor that form a permanent magnet synchronous motor (brushless motor). They can reach very high speeds such as 100,000 to 500,000 rpm. The motor drives the compressor wheel at high speed, and the compressor wheel compresses the fluid. The fluid can be air, gas, refrigerant, or other suitable fluids. By using two compressor wheels, the fluid is compressed twice.

[0003] These compressors can be used, for example, in mobile HVAC (heating, ventilation, air conditioning) systems that use refrigerant gas, such as electric vehicles, hybrid vehicles, and hydrogen vehicles. These compressors can also be used in fixed systems that use refrigerant gas, such as heat pumps.

[0004] These compressors typically include a first circuit for circulating the fluid to be compressed, and a second circuit for circulating a coolant used to cool the compressor, particularly the motor and the air or gas bearings supporting the motor shaft, and the electronic components. Cooling of the compressor components is necessary to prevent damage, especially since the motor heats up considerably when rotating at high speeds. These circuits are usually located inside the compressor itself, at least in terms of the cooling circuits. There are no regulations to facilitate the flow of cooling gas or air, particularly at high speeds, while the compressor is running, which presents a challenge. Furthermore, the air or gas bearings supporting the rotor shaft are not designed to support the rotor shaft without friction, resulting in significant heat generation when the rotor rotates at high speeds, which presents another challenge.

[0005] Furthermore, it is known that grooves or ribs are created in air or gas bearings due to the flow of air or gas, resulting in pressure and cooling. However, these grooves are created by laser processing without a specific arrangement, which presents the challenge of long processing times and high costs. [Overview of the Initiative] [Problems that the invention aims to solve]

[0006] One objective of the present invention is to solve the various problems described above by providing a method for rapidly forming grooves or ribs for air or gas bearings, including air or gas axial bearings that form part of the shaft, on the rotor shaft. The grooves or ribs on the shaft are configured to overcome gravity when the compressor shaft rotates at high speed within each bearing, and to hold the rotating rotor shaft so that it does not mechanically contact the air or gas flow in the radial bearing, and therefore virtually frictionless.

[0007] In this context, the present invention relates to a method for machining and forming ribs or grooves on a shaft intended to rotate around the longitudinal axis of a centrifugal compressor and / or on an air or gas axial bearing forming part of the shaft, having the features of independent claim 1.

[0008] Dependent claims 2 to 10 specify some specific steps of the method.

[0009] One advantage of this method for machining and forming ribs or grooves on the shaft of a compressor in a machining unit and / or on the axial bearing of a workpiece shaft is that all ribs or grooves on the workpiece portion of the shaft, which is rotationally driven, can be obtained in a single pass from the start to the end of the workpiece portion of the shaft by a reciprocating machining tool. To achieve this, the reciprocating motion of the machining tool is synchronized with a sinusoidal program set in the machining unit and with the desired configuration of the ribs or grooves to be formed on the shaft.

[0010] One advantage of this method of machining and forming ribs or grooves on the axial bearing of the compressor workpiece shaft in this processing unit is that all ribs or grooves are formed on one or two surfaces of the axial bearing disc of the rotatably driven shaft.

[0011] During machining of a shaft and / or an axial bearing of a shaft, the tool holder supporting the shaft or the machining tool is also displaced in the longitudinal machining direction while the machining tool is reciprocating.

[0012] The reciprocating motion of this machining tool is compared to a piezoelectric oscillator that can increase or decrease the speed of the reciprocating motion of the machining tool by varying the vibration frequency according to how the machining unit is programmed, thereby obtaining the desired rib or groove. During this reciprocating motion, the machining tool may be in a machining position where it is in contact with the shaft or the axial bearing of the shaft, or at other times it may be in a position where it is not in contact with the shaft or the axial bearing of the shaft.

[0013] The workpiece shaft is mounted to the rotor structure of an electric motor that rotates it, or to at least one air or gas axial bearing that forms part of the shaft and is positioned between the compressor wheel and the air or gas radial bearing at the first end of the shaft. Ribs or grooves can be formed on one or preferably both sides of the disc of the air or gas axial bearing by a specific tool for machining and forming ribs or grooves in the axial bearing. However, the same machining tool can be used to machine and form ribs or grooves on the portion of the shaft for the radial bearing and on one or both sides of the disc of the air or gas axial bearing.

[0014] One advantage of this machining unit for forming ribs or grooves is that ribs or grooves can be formed very quickly and accurately on each workpiece portion of a shaft for an air or gas radial bearing in less than a minute. The same applies to ribs or grooves formed on one or both sides of a disc for a rotatably driven air or gas axial bearing. The machining tool is harder than the shaft or the material of the air or gas bearing.

[0015] Therefore, thanks to the sinusoidal function, it becomes possible to achieve synchronization between the rotation of the shaft and the longitudinal motion of the workpiece or shaft. The frequency and amplitude of the sinusoidal function are selected according to the groove shape, the number of grooves, the rotational speed of the shaft, and the velocity of the longitudinal displacement.

[0016] As explained above, the machining unit can be programmed to rotate synchronously with the machining tool according to a sinusoidal program or function, thereby obtaining rib or groove configurations on the shafts of each air or gas radial bearing and on each workpiece portion of the air or gas axial bearing.

[0017] Such ribs or grooves are preferably machined in a V-shape, where the orientation of each rib or groove changes at the center of each machined portion on the shaft. Thanks to this machining, a high-speed rotating shaft can be held within the air or gas radial bearings in the compressor without mechanical contact. Thus, the shaft is held within each radial bearing substantially frictionlessly by the pressure of the air or gas passing through the grooves or ribs as a result of the shaft's high-speed rotation. From a low rotational speed of 6000 rpm, the air or gas pressure in each aerodynamic radial bearing is configured such that the shaft does not mechanically contact the static radial bearing, thus avoiding any mechanical friction. Naturally, as the rotational speed of the shaft increases, the air pressure within the radial bearings increases, and the air or gas friction automatically increases.

[0018] The grooves or ribs are machined and formed by a machining unit and machining tools such that, according to a sinusoidal program and a desired configuration of the grooves or ribs, the orientation of the grooves or ribs on the shaft is reversed in the inner half of each static radial bearing substantially positioned on the ribs. This generates an air or gas pressure that can be increased as the rotation speed of the shaft increases.

[0019] Such high-speed centrifugal fluid compressors can rotate at very high speeds without excessive heating, thanks to the formation of ribs or grooves on the air or gas radial bearings.

[0020] Furthermore, an axial bearing is provided between the first compressor wheel and the first radial bearing. Helical grooves or ribs are formed on the circumferential surface of the front and rear surfaces of the disc of the axial bearing. As the shaft rotates, the grooves create a thin layer of air to hold the shaft in a well-centered position in the longitudinal direction. [Brief explanation of the drawing]

[0021] By reading the following detailed description of one embodiment of the present invention while referring to the attached drawings, the object, advantages, and features of the present invention can be understood more clearly. This description is given as an example.

[0022] [Figure 1] This diagram shows a longitudinal cross-section along vertical axis AA of the high-speed centrifugal compressor according to the present invention. [Figure 2] Figure 2a shows a longitudinal cross-sectional view along longitudinal axis AA of a rotor structure according to the present invention, comprising a shaft with a compressor wheel, aerodynamic axial and radial bearings, and one or more permanent magnets. Figure 2b shows an orthogonal projection from the side of the first compressor wheel and axial bearing forming part of the shaft according to the present invention. [Figure 3] Figures 2a and 2b are three-dimensional views of the assembly according to the present invention, showing grooves or ribs in each static radial bearing shown on the shaft, and in the axial bearings that form part of the shaft. [Figure 4] The diagram shows a longitudinal cross-sectional view of a machining unit according to the present invention, which uses a first machining assembly to machine and form grooves or ribs in an air or gas axial bearing that forms part of the compressor shaft, and a second machining assembly to machine and form grooves or ribs in two parts of a shaft for radial bearings. [Figure 5]A longitudinal cross-sectional view of a processing unit for forming grooves or ribs in an air or gas axial bearing that forms part of a compressor shaft using a first processing assembly and for forming grooves or ribs in two portions of the shaft for a radial bearing using a second processing assembly according to the present invention is shown.

Embodiments for Carrying Out the Invention

[0023] In this specification, all components forming part of a centrifugal compressor well known in the prior art are only briefly described. This is because the present invention essentially relates to a method of forming ribs or grooves on two portions of a shaft so as to be respectively covered by two static air or gas radial bearings, or on an air or gas axial bearing forming part of the shaft.

[0024] FIG. 1 shows a cross-section along the longitudinal axis A-A of a high-speed centrifugal compressor 1. The centrifugal compressor 1 includes a shaft 7 made of tungsten carbide or ceramics, which is mounted in a casing 2 so as to rotate around the longitudinal axis A-A passing through the front face 2b and the rear face 2c, and a first centrifugal compressor wheel 8 and a second centrifugal compressor wheel 10 which are mounted back-to-back at each end of the shaft 7. The first compressor wheel 8 constitutes a first compression stage, and the second compressor wheel 10 constitutes a second compression stage. In particular, in this embodiment, the shaft 7 is hollow and surrounds a threaded rod 11, and one of the compressor wheels 8, 10 is screwed at each end of the shaft 7, enabling easy attachment and removal of the compressor wheel. Therefore, the two compressor wheels 8 and 10 are driven on the same shaft 7, thereby improving energy efficiency and eliminating the need for a gearbox. There is a labyrinth seal behind the compressor wheels 8 and 10 for controlling the pressure in the compressor and balancing the axial force.

[0025] The casing 2 further encloses an electric motor, which is preferably a synchronous motor, arranged between the first compressor wheel 8 and the second compressor wheel 10 and configured to rotate the shaft 7. The motor comprises a stator 14 and a rotor structure 16, which interact with each other to form at least one permanent magnet 16a and a synchronous electric motor (brushless motor). In particular, the stator 14 is formed by coils 14a and two ferrite elements 14b, which are attached so as to be fixed to the casing 2. The rotor structure 16 comprises one or more permanent magnets 16a integrated with the shaft 7, for example by bonding, and is coated by a titanium lining 16b. A titanium flange 16c is attached (for example by bonding) to the side ends of the lining to ensure that the rotor can withstand centrifugal forces at high speeds.

[0026] The shaft 7 is mounted rotatably within the casing 2 about the longitudinal axis A-A by means of at least one front radial bearing 18, one rear radial bearing 22, and one axial bearing 24, which form an integral part of the shaft 7. The centrifugal compressor 1 comprises a front radial bearing support 26 for carrying the front radial bearing 18 and a rear radial bearing support 28 for carrying the rear radial bearing 22, which are configured to be arranged around the shaft 7 at the front and rear sides of the motor, respectively. Also, at the rear side, a volute 29 is provided between the rear radial bearing support 28 and the rear cover 3c. The volute 29 has an orifice leading to the tangential fluid outlet 6 after compression. Also, an axial bearing support 30 is provided to carry the axial bearing 24, which is configured to be arranged around the shaft 7 between the first compressor wheel 8 and the front radial bearing support 26. It is clear that the axial bearing can be provided at the rear side of the motor.

[0027] These bearings are non-contact, aerodynamic bearings designed to minimize friction. Such bearings require no lubrication and minimal maintenance. In particular, referring to Figures 2a, 2b, 3, 4, and 5, the axial bearing 24 is an aerodynamic bearing. According to the present invention, the axial bearing 24 is made simultaneously with the shaft 7 and from the same base material, forming a part of the shaft 7 so as to form an integral part with the shaft 7 in the form of an integrated unit at the end of manufacturing.

[0028] The axial bearing is composed of a disc, the disc having a first groove 24a on at least one of its faces, the first groove 24a preferably spiral over an annular region in the circumferential part, and configured to generate a thin layer of air. Preferably, the axial bearing 24 has grooves or ribs 24a, preferably spiral, on the circumferential parts of the front and rear surfaces of the disc of the axial bearing 24, obtained by a machining process described below with reference to Figures 4 and 5. The orientation of the grooves or ribs 24a can be different or the same on the front and rear surfaces. The axial bearing 24 with grooves or ribs 24a keeps the rotating shaft 7 longitudinally centered by generating thin layers of air from the front and rear surfaces. The front radial bearing 18 and the rear radial bearing 22 are aerodynamic bearings, and the shaft 7 is configured to generate a thin layer of air or gas when the shaft 7 rotates within the air or gas radial bearings, and has a second groove or rib 32 facing the front radial bearing 18 and the rear radial bearing 22.

[0029] In Figures 2a and 2b, it can be seen that the first centrifugal compressor wheel 8 and the second centrifugal compressor wheel 10 are still mounted back-to-back at each end of the shaft 7. A rotor structure 16, comprising at least one permanent magnet 16a of an electric motor, is mounted or fastened, for example, around or within the central portion of the shaft 7, to drive the shaft so as to be rotatable around the longitudinal axis AA, and a portion of the shaft 7 is formed by an air or gas axial bearing. A front air or gas axial bearing can be mounted on the first end of the shaft, and a rear air or gas axial bearing can be mounted on the second end of the shaft.

[0030] As shown in Figure 3, at the two ends of the shaft 7, one end has a first portion of the machined rib or groove 32, and the other end has a second portion of the machined rib or groove 32. The rotor structure 16, which includes at least one permanent magnet 16a, is mounted on the shaft at the center of the electric motor.

[0031] Figure 3 shows a three-dimensional view of a shaft 7 and an axial bearing 24 at the first end of the shaft 7. At both ends of the shaft 7, a first portion of a rib or groove 32 can be seen, on which a first radial bearing 18 is shown, and a second portion of the rib or groove 32 can be seen, on which a second radial bearing 22 is shown. Ribs or grooves 24a are also shown on the surface of the disk of the air or gas axial bearing 24 that forms part of the shaft 7. Ribs or grooves 24a of a specific depth are formed in an annular region that starts from the periphery of the disk and extends toward the center of the disk. The ribs or grooves 24a and their configuration are programmed, in particular in a machining unit, to form all ribs or grooves in a single pass by operating the machining tool. That is, for example, by moving the tool holder or rotating disk in a single machining direction from the periphery of the disk to the bottom of the annular region of the rib or groove. For example, starting from the periphery of a single-sided disk, a groove is gradually formed by the reciprocating motion of a machining tool, synchronized with a machining unit that rotates the disk at a predetermined speed according to a sinusoidal program.

[0032] This program, combined with the controlled reciprocating motion of the cutting tool, achieves the initiation of each groove 24a through the rotation of the disk and the reciprocating motion of the cutting tool. This is continuously repeated for the next groove or rib section, from the first groove section to the end or bottom of the annular region. In this method of forming different ribs or grooves 24a on the disk 24, the machining time per grooved surface of the disk is less than one minute, which is significantly shorter than previous machining techniques using laser beams.

[0033] The machining unit is programmed to rotate the shaft 7 synchronously with the machining tool according to a sinusoidal program to obtain a predetermined configuration of ribs or grooves 32 on the first workpiece portion of the shaft 7 for the front air or gas radial bearing 18. For example, starting from the first workpiece portion of the shaft 7 which is on the same side as the first end and has only one machining direction, all ribs or grooves 32 are machined and formed in a single pass up to the end of the first portion of the first end of the shaft 7, thereby significantly reducing machining time.

[0034] Therefore, it can be determined that the sinusoidal function actually achieves synchronization between the rotation of the shaft 7 and the longitudinal displacement of the workpiece or the shaft 7. The frequency and amplitude of the sinusoidal function are selected according to the shape of the groove 32, the number of grooves 32, the rotational speed of the shaft, and the speed of the longitudinal displacement.

[0035] In the processing unit, a specific arrangement of ribs or grooves 32 formed on a first portion of the first end of the shaft 7 is programmed. In one preferred embodiment, each rib or groove 32 is V-shaped, meaning that its orientation changes essentially from the center of the first workpiece portion of the shaft 7. This allows the shaft, rotating at high speed within the compressor, to be held without mechanical contact with the air or gas radial bearings. From a low rotational speed of 6000 rpm, the air or gas pressure of each aerodynamic radial bearing is configured such that the shaft does not mechanically contact the static radial bearing, thus avoiding mechanical friction.

[0036] As a supplement to Figure 1, the compressor 1 comprises an aluminum casing 2, the top surface 2a of which is closed by an upper cover 3a, and the front surface 2b and rear surface 2c of which are closed by a front cover 3b and a rear cover 3c, respectively. The side surface 2d of the casing is joined at its base to form a back surface 2e with a U-shaped cross-section.

[0037] The upper cover 3a is located on the same side as the compressor's electronic components. Therefore, access to the electronic components mounted on the compressor is easy and is provided through the upper cover 3a. The front cover 3b and rear cover 3c are used to access the inside of the compressor (motor, rotor, bearings, etc.). A gasket is positioned between the top surface of the casing 2 and the upper cover 3a. This gasket protects the electronic components from dust and moisture.

[0038] The casing 2 has an inlet 5 for the fluid to be compressed, located on the front cover 3b, and a tangential outlet 6 for the fluid to be compressed, located on one of the sides of the casing 2.

[0039] In Figure 1, the casing 2 has an inner housing formed coaxially with respect to the longitudinal axis AA from end to end between the front surface 2b and the rear surface 2c of the casing 2. This inner housing receives the front radial bearing support 26 and the front radial bearing 18, and the motor and rotor structure 16 is attached to the shaft 7, the rear radial bearing support 28 and the rear radial bearing 22, the second compressor wheel 10, and the volute 29. On the front surface 2b side, the inner housing is closed by the front cover 3b, thereby integrating the first compressor wheel 8, the axial bearing support 30, and the axial bearing 24. On the rear surface 2c side, the inner housing is closed by the rear cover 3c.

[0040] Advantageously, at least one orifice, for example, indicated by reference numeral 57a, is formed, configured to allow the fluid to be compressed to circulate within the channel and into the motor and between the stator 14 and the rotor structure 16; and at least one orifice, for example, indicated by reference numeral 57b, is formed, configured to allow the fluid to be compressed to cool the motor, exit the motor, and rejoin the channel.

[0041] Similarly, advantageously, at least one orifice, for example, indicated by reference numeral 59a in Figure 1, is formed, configured to allow the fluid to be compressed to circulate within the channel 54 and circulate near the axial bearing 24, the front radial bearing 18, and the rear radial bearing 22, and at least one orifice, for example, indicated by reference numeral 57b, is formed, configured to allow the fluid to be compressed to rejoin the channel 54 after the axial bearing 24, the front radial bearing 18, and the rear radial bearing 22 have been cooled.

[0042] Therefore, after the compressible fluid enters the first compression stage through the inlet 5, it passes through the compressor section located along the longitudinal axis between the first and second compression stages within the channel 54 and rejoins the second compression stage. As a result, the compressible fluid cools the motor and recovers heat lost by the motor before entering the second compression stage as it passes between the inner wall 52 and the motor's ferrite element 14b, thereby increasing efficiency. Furthermore, the orifices 57a, 57b, and 59a slightly deflect the flow, allowing the compressible fluid to circulate between the stator 14 and rotor structure 16 and within the bearings, cooling these elements and recovering heat losses in the motor and heat losses caused by friction in the bearings.

[0043] The centrifugal compressor 1 is capable of reaching very high rotational speeds in the range of 100,000 rpm to 500,000 rpm. The centrifugal compressor 1 allows the fluid compressed in the first compression stage to substantially pass through the entire system, recovering waste heat, particularly from the motor, bearings, and electronic components, thereby increasing efficiency before entering the second compression stage (as the pressure of the fluid being compressed increases as its temperature rises). Furthermore, the compressor becomes very compact due to the use of only the fluid being compressed to cool the compressor without the use of additional cooling circuits, and the configuration of the electronic components in the compressor for electronic devices mounted in the casing. Thus, the compressor according to the present invention has a large rotational speed and a high compression ratio despite occupying only a small volume. For example, the compressor according to the present invention has a compression ratio greater than 3 and an output of the order of 4 kW, with dimensions on the order of 14 × 8 × 11 L × W × H (cm) and a weight of only 1.6 kg.

[0044] For example, the compressor according to the present invention can be used in conjunction with a fuel cell that obtains power from air or gas, or any other system that uses compressed air (such as an industrial compressor, a medical compressor, or a ship).

[0045] The compressor according to the present invention can be used together with a refrigerant gas in HVAC (heating, ventilation, and air conditioning) systems for mobile vehicles, such as those in electric, hybrid, or hydrogen-fueled vehicles.

[0046] Furthermore, centrifugal compressors can also be used in stationary systems with refrigerant gases, such as heat pumps.

[0047] Centrifugal compressors can also be used with natural gas.

[0048] Figure 4 shows a machining unit 100 for forming ribs or grooves on the first and second end portions of the shaft 7, and on the first surface of the disk of the axial bearing 24 that forms part of the shaft 7, or further, on the second surface of the disk of the axial bearing 24 that forms part of the shaft 7.

[0049] The machining unit 100 includes a lathe 130 having two spindles 140 for holding and rotating the shaft 7 at both ends when machining and forming ribs or grooves at a predetermined rotational speed ω. The first spindle 140 is located on a first vertical column or wall 102 of the machining unit 100, and the second spindle 140 is located on a second vertical column or wall 103 opposite to the first vertical column or wall 102. The two vertical walls 102 and 103 of the machining unit 100 are connected by a base 101, which is provided with means for guiding at least one tool holder 160 capable of holding at least one machining tool 120, or two machining tools 120, 121, or several other different machining tools. Means for guiding the tool holder 160 at the base 101 of the machining tool 100 include, for example, one or two guide rails (not shown) on the base 101 that can move in the longitudinal direction AA.

[0050] As already described, the tool holder 160 can be moved parallel to the shaft 7, preferably horizontally, to position the first machining tool 120 in the machining position in order to machine and form a rib or groove on the first front portion or the second rear portion of the shaft 7, which is located between the two spindles 140 and driven so as to be rotatable around the vertical axis AA. The first machining tool 120 is oriented perpendicular to the portion of the shaft 7 so as to be able to machine and form a rib or groove on one of the workpiece portions of the shaft 7. The tool holder 160 is then moved again parallel to the shaft 7 toward the second workpiece portion of the shaft 7.

[0051] In a first alternative embodiment of this machining unit 100, a second machining tool 121 can be mounted on the same tool holder 160 as the first machining tool 120, or mounted on another tool holder (not shown) oriented perpendicular to the direction of the first machining tool 120. This second machining tool 121 can be used to machine and form ribs or grooves on at least one surface of the disc of the axial bearing 24 that forms part of the shaft 7. To do this, the tool holder 160 is moved parallel to the shaft 7 to the position of the disc of the axial bearing 24. After being positioned near the disc, the second machining tool 121 is driven to machine and form ribs or grooves on at least one surface of the disc of the axial bearing 24.

[0052] In the first alternative embodiment of this machining unit, it is preferable to avoid the occurrence of cantilevered sections and the resulting deterioration of machining accuracy by using the same tool holder for two machining tools. By using the same tool holder 160, the machining errors generated by the two tool holders due to different settings do not accumulate.

[0053] In one alternative embodiment, the spindle 140 that rotatably holds the shaft 7 can be moved in the longitudinal machining direction to form ribs or grooves. As already mentioned, the shaft 7 is tubular so that it can be mounted and moved in the longitudinal direction. Because the shaft 7 is tubular, at both ends of the shaft 7, the two spindles 140 can partially insert their ends into the inside of the tube of the shaft 7, holding the shaft 7 in a locked state, and rotating the shaft 7 at a rotational speed ω set for machining. Naturally, during the machining operation, the two spindles 140 can move longitudinally together with the shaft 7 being machined.

[0054] In this alternative embodiment, the machining unit 100 further comprises at least one tool holder 160 connected to the structure of the lathe 130. Naturally, the dimensions of the machining unit 100 are depicted smaller than they actually are. The tool holder 160 carries a first machining tool 120, the machining head of which contacts a shaft to machine and form grooves or ribs and can reciprocate depending on how the machining unit is programmed. At least the end of the machining head of the machining tool 120 can be made of diamond to machine and form ribs or grooves on a shaft 7 made of tungsten carbide or ceramics. This is done by rotating the shaft 7 synchronously with the first machining tool 120 according to a sinusoidal program to obtain a predetermined configuration of ribs or grooves on the workpiece portion of the shaft 7 with respect to each front or rear air or gas radial bearing.

[0055] In one alternative embodiment, instead of moving the shaft 7, the tool holder 7 to which the first machining tool 120 is attached can be moved in the longitudinal machining direction in order to machine and form ribs or grooves on the shaft.

[0056] Depending on how the machining unit 100 is programmed, the frequency of the reciprocating motion of the first machining tool 120 can also be changed. In particular, the reciprocating motion of the machining tool is synchronized by a sinusoidal program performed in the machining unit and to a desired programmed configuration that forms ribs or grooves on a portion of the shaft 7 and / or the disk of the axial bearing 24 of the shaft 7.

[0057] The axial bearing 24 of the shaft 7 is integrally manufactured from the same material as the shaft 7. Therefore, the shaft 7 and the axial bearing 24 of the shaft 7 can be manufactured by a molding operation, depending on the material used, or, preferably, by using at least one machining tool in the tool holder of the machining unit 100, which is used to machine ribs or grooves on the front and rear portions of the shaft 7. In this case, the first machining tool 120 of the tool holder 160 can be used. The initial blank of the shaft 7, which may already be tubular, can initially have a diameter substantially corresponding to the final outer diameter of the axial bearing 24 to be manufactured. This blank is mounted on two spindles 140 of the machining unit 100 so that it can rotate around a longitudinal axis. The first machining tool 120, which needs to be made of a harder and more abrasive material than the material of the shaft 7 blank, moves from the first end of the rotating shaft to a first position on the shaft 7 corresponding to the position of the disc surface of the axial bearing 24 to be manufactured. This first machining operation involves the blank of the rotating shaft and the machining tool 120, which allows a first thin layer of material to be removed from the shaft blank. Subsequently, the machining tool 120 removes several other continuous thin layers from the rotating shaft by displacing the first end longitudinally to the first position of the axial bearing 24 until the desired shaft diameter is reached, thereby creating the axial bearing 24 on the shaft 7. If the continuation of the shaft starts from a second position of the axial bearing at the opposite end of the shaft, machining by removing the thin layers must also be performed on the opposite side of the shaft blank, which is done by changing the orientation of the tubular blank and mounting the shaft blank to two opposite spindles 140, and repeating the operation with the machining tool 120 mounted in the tool holder 160 as before.This makes it easier to change the orientation of the shaft blank between the spindles 140, rather than having to move the tool holder 160 from another position in the machining unit 100 using the machining tool 120.

[0058] Naturally, after creating the shaft 7 to have the desired diameter and manufacturing the axial bearing 24, ribs or grooves can be machined and formed on the front and rear portions of the shaft by a first tool machining operation 120 connected to a tool holder 160.

[0059] Typically, the shaft 7 to be machined is made of tungsten carbide or ceramics. Therefore, the machining tool 120 typically has a diamond cutting head. This allows all ribs or grooves on the first workpiece portion at the first end of the shaft 7 to be formed in a single pass, from the beginning to the end of the first portion, which is done by the reciprocating motion of the machining tool 120, by the longitudinal displacement of the rotating shaft 7 during machining, and by the longitudinal displacement of the first tool holder 160 or the first tool 120 in the tool holder 160, depending on how the machining unit 100 is programmed.

[0060] In the first embodiment of this machining unit 100, the second machining tool 121, mounted on the tool holder 160 perpendicular to the first machining tool 120, needs to be configured to form ribs or grooves on one or both surfaces of the disk of the axial bearing 24 by changing the orientation of the shaft 7 mounted between the two spindles 140.

[0061] Furthermore, the first machining tool 120 can sequentially machine and form ribs or grooves on the first front portion and the second rear portion of the shaft. Depending on how the machining unit is programmed, when the first and second half of the workpiece portion of the shaft 7 is completed, the orientation of the ribs or grooves can be changed to obtain a V-shaped groove over the length of the machined first and second portions. The purpose of this is to generate air or gas pressure in the front radial bearing located in the first portion or the rear radial bearing located in the second portion when the compressor is operating so that the shaft 7 is rotating above a speed limit, thereby eliminating mechanical contact between the shaft and one or more front and rear radial bearings.

[0062] To machine the axial bearing 24 in the form of a disc, only a second machining tool 121 is used, which can be mounted on a tool holder 160 that is displaceable longitudinally along axis AA. The ribs or grooves and their configuration are programmed in the machining unit 100 to operate the second machining tool 121 to form all ribs or grooves on the first surface of the disc in a single pass, and this formation is performed by moving the machining tool or rotating disc in a single machining direction, from the periphery of the disc to the bottom of the annular region of the rib or groove, or vice versa, depending on how the machining unit 100 is programmed, and by the reciprocating motion of the machining tool 121. Two surfaces of the disc of the axial bearing 24 can be machined and formed by the second machining tool by reversing the orientation of the shaft 7 between two spindles 140.

[0063] Helical ribs or grooves can be formed on one or two surfaces of the disc of the axial bearing 24, such that the two surfaces have the same orientation or the two surfaces have different orientations, for the purpose of generating a layer of air through the grooves when the shaft 7 rotates to maintain the axis in a well-centered position in the longitudinal direction during the operation of the centrifugal compressor.

[0064] Furthermore, both the first machining tool 120 and the second machining tool 121 can be moved in the tool holder 160 in a first direction or the opposite second direction so that the first machining tool 120, or each machining tool 120, 121, comes into contact with or separates from the workpiece portion of the shaft 7, as symbolically indicated by the arrows in the tool holder 160.

[0065] Figure 5 partially uses a portion of the machining unit 100 of Figure 4. However, in Figure 5, there is only one tool holder 160 and only one machining tool 120. The machining tool 120 is rotatably positioned or moves around the shaft 150 of the tool holder 160 so as to be in the illustrated position (1) for machining and forming ribs or grooves on the front and rear portions of the shaft 7, and in the illustrated position (2) for machining and forming ribs or grooves on one or preferably two surfaces of the disc of the axial bearing 24.

[0066] With respect to the tool holder 160 shown in Figure 4, this tool holder 160 can be moved vertically on one or more guide rails arranged, for example, on the base 101 of the machining unit 100.

[0067] The second embodiment of this machining center 100 appears easier to use than the first embodiment shown in Figure 4, but it is not necessarily faster to form ribs or grooves on portions of the shaft 7 and on the disc of the axial bearing 24. All elements shown in Figure 5 are identical to those described with reference to Figure 4, so their description will not be repeated. The tool holder 160 can be equipped with more than two machining tools, but only one machining tool operates to machine and form ribs or grooves on one or two portions of the shaft 7 or on one or two surfaces of the disc of the axial bearing 24.

[0068] Naturally, the present invention is not limited to the examples described, and various alternative forms and modifications are possible and can be made, which will be obvious to those skilled in the art. Naturally, other combinations known to be used with centrifugal compressors are also possible. For other workpieces not described above, ribs or grooves can be machined quickly and accurately using uniform machining elements. [Explanation of Symbols]

[0069] 1. Centrifugal compressor 2 Casing 5 Fluid inlet 6. Outlet of compressed fluid 7 shafts 8, 10 Compressor vehicles 16 Rotor Structure 16a Permanent Magnet 18, 22 Radial bearings 24 Axial bearings 24a, 32 Ribs or grooves 100 processing units 120, 121 Processing tools 160 Tool Holder

Claims

1. A method for forming ribs or grooves on a shaft (7) intended to rotate around the vertical axis (A-A) of a centrifugal compressor (1), and / or on an air or gas axial bearing (24) that forms part of the shaft (7), To drive the shaft rotatably, a rotor structure (16) comprising at least one permanent magnet (16a) of an electric motor is intended to be mounted around or within the shaft (7). The centrifugal compressor (1) further comprises a casing (2) having a fluid inlet (5) and a compressed fluid outlet (6), a first compressor wheel (8) and a second compressor wheel (10) intended to be attached to two ends of the shaft (7) in the casing (2), a front air or gas radial bearing (18) intended to be attached to the first end of the shaft (7), and / or a rear air or gas radial bearing (22) intended to be attached to the second end of the shaft (7), The above method is performed in a machining unit (100) in which the axial bearing (24) is configured to receive the shaft (7) of a workpiece, The processing unit (100) includes a tool holder (160) having processing tools (120, 121) for processing and forming ribs or grooves on at least one portion of the shaft (7) or the axial bearing (24) of the shaft (7), All of the ribs or grooves (24a, 32) are formed on the machined portion of the rotatably driven shaft and / or the disk of the axial bearing (24) of the shaft. This formation is performed by the machining tool (120, 121) reciprocating between a machining position in contact with the shaft (7) and / or the disc of the axial bearing (24) of the shaft (7), or the tool holder (160), while the shaft (7) undergoes a single displacement in the longitudinal machining direction from the start to the end of the machined portion, and a position in which it does not contact the shaft (7) and / or the disc of the axial bearing (24) of the shaft (7). The position of the machining tool (120, 121) in the reciprocating motion is controlled by the machining unit (100) according to a sinusoidal function, and the frequency and amplitude of the sinusoidal function are selected according to the shape of the ribs or grooves (24a, 32), the number of the ribs or grooves (24a, 32), the rotational speed of the shaft (7), and the speed of the longitudinal displacement of the tool holder (160) or the shaft (7). A method characterized by the following:

2. Before machining and forming the ribs or grooves (32) on the shaft (7), the air or gas axial bearing (24) is made on the shaft (7). The method according to feature 1.

3. The aforementioned air or gas axial bearing (24) is made by using a blank shaft (7) having a diameter equal to the desired diameter of the axial bearing (24) to be manufactured. The blank of the shaft (7) is rotated around the vertical axis (A-A) in the processing unit (100). A machining tool (120) made of an abrasive material is moved from one end of the rotating shaft (7) to a first position on the shaft (7) corresponding to the position of the disc-shaped surface of the disc of the axial bearing (24) to be manufactured, thereby removing a thin layer of material from the shaft (7). As the machining tool (120) is displaced longitudinally from the first end to the first position of the axial bearing (24) until the desired diameter of the shaft (7) is reached, a series of thin layers are removed by the machining tool (120) from the rotating shaft (7). The method according to feature 2.

4. The same processing operation to remove the thin layer is performed sequentially from the opposite end of the shaft (7) to the second position of the axial bearing (24) corresponding to the second surface of the axial bearing (24), the second surface being the surface of the axial bearing (24) opposite to the disc-shaped surface of the disk. The method according to feature 3.

5. The shaft (7) to be processed is made of tungsten carbide or ceramics. The head of the aforementioned machining tool (120) is made of diamond. The shaft (7) rotates around the vertical axis (A-A) during machining. During a single longitudinal displacement of the shaft (7), the machining tool (120) reciprocates, thereby forming all the ribs or grooves (32) on the first machined portion of the shaft (7) from the start of the first machined portion at the first end to the end of the first machined portion, and the machined portion includes the first machined portion. The method according to feature 1.

6. The shaft (7) to be processed is made of tungsten carbide or ceramics. The head of the aforementioned machining tool (120) is made of diamond. The shaft (7) rotates around the vertical axis (A-A) during machining. During a single longitudinal displacement of the tool holder (160), the machining tool (120) reciprocates, thereby forming all the ribs or grooves (32) on the second machining portion of the shaft (7) from the start of the second machining portion at the second end to the end of the second machining portion, and the machining portion includes the second machining portion. The method according to feature 1.

7. During the machining of the rib or groove (32), when half of the first machined portion at the first end of the shaft (7) and half of the second machined portion at the second end of the shaft (7) are completed, the orientation of the rib or groove is changed to obtain a V-shaped groove over the length of the machined first and second machined portions, thereby generating air or gas pressure in the front radial bearing (18) located in the first machined portion or the rear radial bearing (22) located in the second machined portion when the centrifugal compressor (1) is operating so that the shaft (7) is rotating above a speed limit, so as to eliminate mechanical contact between the shaft (7) and one or more front radial bearings (18) and rear radial bearings (22). The method according to specification 5.

8. The disk is integrally formed with a part of the shaft (7), The machining unit (100) operates the machining tools (120, 121) to form ribs or grooves on the disc-shaped first surface of the disk, and the ribs or grooves are formed in an annular region that starts from the periphery of the disk and extends toward the center of the disk. This formation is performed by moving the machining tool or the rotating disk once in a single machining direction, from the periphery of the disk to the end of the annular region or vice versa, and by the reciprocating motion of the machining tool (120, 121). The method according to feature 1.

9. By moving the machining tool or the rotating disk once in a single machining direction, from the periphery of the disk to the end of the annular region or vice versa, and by the reciprocating motion of the machining tool (120, 121), all ribs or grooves (24a) on the second surface of the disk are formed, wherein the second surface is the surface opposite to the first surface. The method according to feature 8.

10. All of the ribs or grooves (24a) on the first surface and all of the ribs or grooves (24a) on the second surface are formed in the same helical shape, or all of the ribs or grooves (24a) on the first surface and all of the ribs or grooves (24a) on the second surface are formed in the same helical shape, so as the shaft (7) rotates, a layer of air is generated through the grooves to hold the shaft in a longitudinally centered position during the operation of the centrifugal compressor (1). The method according to feature 9.

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