Slide bearing and pump device

Abstract

The present invention pertains to a slide bearing used for a rotary machine such as a pump and a turbine, and particularly to a slide bearing used in an extremely low temperature environment. The slide bearing is provided with: a sliding contact pad (1) having a shaft support surface (1a) for supporting the outer peripheral surface of a rotating shaft (100); a shell (2) disposed on the radially outer side of the sliding contact pad (1); and a pad pressing mechanism (3) for pressing the sliding contact pad (1) against a pad support surface (2a) of the shell (2) when the sliding contact pad (1) contracts.

Description

Plain bearings and pump equipment

[0001] The present invention relates to a plain bearing used in rotary machines such as pumps and turbines, and more particularly to a plain bearing used in cryogenic environments. The present invention also relates to a pump device equipped with such a plain bearing.

[0002] Rotating machines generally have bearings to support the rotating shaft. Rotating machines that handle fluids, such as pumps and turbines, sometimes use plain bearings. A plain bearing has a sliding pad that makes sliding contact with the rotating shaft and a metal shell placed on the outside of the sliding pad, with the sliding pad held in place by the shell. When the rotating machine is operating, the fluid comes into contact with the plain bearing and acts as a lubricant for the plain bearing.

[0003] The sliding pads are made of a resin material with a low coefficient of dynamic friction. However, when the fluid in contact with the sliding bearing is a cryogenic fluid such as liquid hydrogen, the sliding pads contract more than the shell due to the difference in linear expansion coefficient between the resin sliding pads and the metal shell and fixing members. As a result, the load pressing the sliding pads against the shell decreases. In the worst case scenario, the sliding pads may separate from the shell.

[0004] Japanese Patent Application Laid-Open No. 2022-188902

[0005] The present invention relates to a sliding bearing for use in rotating machinery such as pumps and turbines, and provides a sliding bearing that eliminates the effect of differences in the linear expansion coefficients between the sliding pad and the shell, enabling operation in extremely low temperature environments. The present invention also provides a pump device equipped with such a sliding bearing.

[0006] In one aspect, there is provided a sliding bearing for supporting a rotating shaft, the sliding bearing comprising: a sliding pad having a shaft support surface for supporting the outer peripheral surface of the rotating shaft; a shell arranged radially outward of the sliding pad; and a pad pressing mechanism for pressing the sliding pad against the pad support surface of the shell when the sliding pad contracts.

[0007] In one aspect, the pad pressing mechanism includes a biasing member that biases the sliding pad toward the shell. In one aspect, the pad pressing mechanism further includes a pad support member supported by the shell, the sliding pad is supported by the pad support member, and the biasing member biases the sliding pad and the pad support member toward the shell to press the sliding pad against the pad support surface of the shell.

[0008] In one aspect, the pad pressing mechanism includes a pad support member having a tapered shaft portion fixed to the shell and a tapered hole formed in the sliding pad, the sliding pad being supported by the tapered shaft portion and the tapered hole being in surface contact with the outer circumferential surface of the tapered shaft portion. In one aspect, the pad pressing mechanism includes a dovetail groove formed in the sliding pad and a pad holding rail connected to the pad support surface of the shell, the pad holding rail having an inverted triangular cross-sectional shape that fits into the dovetail groove. In one aspect, the dovetail groove and the pad holding rail extend in an axial direction parallel to the center line of the sliding bearing. In one aspect, the sliding bearing further includes a biasing member that presses the sliding pad in the axial direction.

[0009] In one aspect, a pump device is provided that includes a rotating shaft, an electric motor that rotates the rotating shaft, an impeller fixed to the rotating shaft, a pump casing that houses the impeller, and the sliding bearing that rotatably supports the rotating shaft.

[0010] The pad pressing mechanism is configured to press the sliding pad against the pad support surface of the shell when the sliding pad contracts due to contact with a cryogenic fluid (for example, a liquefied gas such as liquid hydrogen). As a result, the sliding pad is firmly held in the shell, allowing the sliding bearing to maintain stable operation even in a cryogenic environment.

[0011] FIG. 10 is a horizontal cross-sectional view showing an embodiment of a sliding bearing. FIG. 11 is a longitudinal cross-sectional view of the sliding bearing shown in FIG. 1. FIG. 12 is an enlarged cross-sectional view showing a sliding contact pad and a pad pressing mechanism. FIG. 13 is a view showing an example of a state in which the sliding contact pad is contracted. FIG. 14 is a horizontal cross-sectional view showing another embodiment of the sliding bearing. FIG. 14 is a view showing an example of a state in which the sliding contact pad is contracted. FIG. 15 is a horizontal cross-sectional view showing yet another embodiment of the sliding bearing. FIG. 16 is a perspective view showing an embodiment of the sliding contact pad. FIG. 17 is a perspective view showing a part of an embodiment of the shell. FIG. 18 is a view showing an example of a state in which the sliding contact pad is contracted. FIG. 19 is a longitudinal cross-sectional view of the embodiment of the sliding bearing shown in FIG. 16. FIG. 19 is a view showing an example of a state in which the sliding contact pad is contracted. FIG. 19 is a cross-sectional view showing an embodiment of a pump device provided with a sliding bearing.

[0012] Embodiments of the present invention will be described below with reference to the drawings. The sliding bearing embodiments described below are suitable for use in supporting the rotating shaft of a rotary machine (such as a liquid pump or turbine). In particular, the sliding bearings of the embodiments described below are suitable for use as bearings that support the rotating shaft of a rotary machine used to transport cryogenic liquefied gases such as liquefied ammonia, liquefied hydrogen, liquid nitrogen, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas.

[0013] Fig. 1 is a horizontal cross-sectional view showing one embodiment of a sliding bearing, and Fig. 2 is a vertical cross-sectional view of the sliding bearing shown in Fig. 1. The sliding bearing includes a plurality of sliding pads 1, each having a plurality of shaft support surfaces 1a for supporting the outer peripheral surface of a rotating shaft 100, and a shell 2 arranged radially outward of the plurality of sliding pads 1. The plurality of sliding pads 1 are arranged around the rotating shaft 100. In the embodiment shown in Fig. 1, six sliding pads 1 are arranged, but five or fewer or seven or more sliding pads 1 may also be arranged. In the following description, "radial direction" means the radial direction of the sliding bearing, and "axial direction" means the direction parallel to the center line CL of the sliding bearing and the rotating shaft 100.

[0014] The shell 2 in this embodiment is a single member that surrounds the plurality of sliding pads 1. In one embodiment, the shell 2 may be an assembly made up of a plurality of members. The shell 2 has a plurality of pad support surfaces 2a that respectively support the plurality of sliding pads 1. The pad support surfaces 2a may be flat or curved. The outer surfaces of the plurality of sliding pads 1 are in contact with the plurality of pad support surfaces 2a, respectively.

[0015] The sliding bearing further includes a plurality of pad pressing mechanisms 5 that press the plurality of sliding pads 1 against the plurality of pad support surfaces 2a of the shell 2, respectively. The plurality of pad pressing mechanisms 5 are provided corresponding to the plurality of sliding pads 1, respectively. Since each pad pressing mechanism 5 has the same configuration, the pad pressing mechanisms 5 will be described in detail below with reference to FIG. 3.

[0016] Fig. 3 is an enlarged cross-sectional view showing the sliding pad 1 and the pad pressing mechanism 5. As shown in Fig. 3, the pad pressing mechanism 5 includes a spring 7 as a biasing member that biases the sliding pad 1 toward the shell 2, and a bolt 8 as a pad support member supported by the shell 2. The sliding pad 1 is supported by the bolt 8. The bolt 8 is made of metal.

[0017] The bolt 8 extends in the radial direction of the sliding bearing and penetrates the sliding pad 1 and the shell 2 in the radial direction. More specifically, the sliding pad 1 has a through hole 11 through which the threaded portion 8a of the bolt 8 passes, and further has a recessed portion 12 in which the head 8b of the bolt 8 is accommodated. The head 8b of the bolt 8 is in contact with the bottom of the recessed portion 12. The recessed portion 12 is formed in the shaft support surface 1a of the sliding pad 1. The threaded portion 8a of the bolt 8 extends through a through hole 15 formed in the pad support surface 2a of the shell 2. A nut 17 is threaded onto the threaded portion 8a of the bolt 8. The nut 17 is located outside the shell 2.

[0018] In this embodiment, the spring 7 serving as the biasing member is an annular disc spring. Disc springs have the advantage of having a large spring constant and being able to be made compact. In one embodiment, the spring 7 may be a coil spring. The spring 7 is sandwiched between the outer surface of the shell 2 and a nut 17 on the bolt 8. The spring 7 biases the bolt (pad support member) 8 and the sliding pad 1 toward the shell 2, pressing the sliding pad 1 against the pad support surface 2 a of the shell 2.

[0019] The shell 2 has, on its inner surface, a plurality of guide walls 20 extending in the axial direction of the sliding bearing. These guide walls 20 are located on both sides of the pad support surface 2a and face both side surfaces of the sliding pad 1. When the rotating shaft 100 rotates, the shaft support surface 1a of the sliding pad 1 comes into sliding contact with the outer circumferential surface of the rotating shaft 100. Therefore, a frictional force acts on the sliding pad 1 in the rotational direction of the rotating shaft 100. The plurality of guide walls 20 on both sides of the sliding pad 1 and the bolt 8 serving as a pad support member located at the center of the sliding pad 1 function to maintain the posture of the sliding pad 1.

[0020] 2 and 3 , the bolt 8 serving as the pad support member is located at the center of the sliding contact pad 1. In one embodiment, a plurality of bolts (for example, two bolts) serving as the pad support member may be arranged along the center line CL of the rotating shaft 100. The plurality of bolts can further stabilize the posture of the sliding contact pad 1. In another embodiment, a plurality of bolts serving as the pad support member may be arranged along the circumferential direction of the rotating shaft 100.

[0021] The sliding pad 1 and the shell 2 are made of different materials. The linear expansion coefficient of the sliding pad 1 is greater than that of the shell 2. More specifically, the sliding pad 1 is made of a resin such as PTFE (polytetrafluoroethylene) or PEEK (polyether ether ketone), and the shell 2 is made of a metal such as stainless steel.

[0022] It is assumed that the sliding bearing of this embodiment will be used while immersed in a liquefied gas such as liquid hydrogen. Therefore, the sliding bearing is required to operate stably at extremely low temperatures. When the sliding pad 1 and the shell 2 are cooled by the liquefied gas, the sliding pad 1 and the shell 2 contract. As described above, the sliding pad 1, which is made of resin, has a higher coefficient of linear expansion than the shell 2, which is made of metal, and therefore the sliding pad 1 contracts more than the shell 2.

[0023] 4 is a diagram showing an example of a state in which the sliding pad 1 is contracted. When the sliding pad 1 contracts, the restoring force of the spring 7 pulls the bolt 8 radially outward, and the sliding pad 1 is pressed against the pad support surface 2 a of the shell 2 by the bolt 8. Therefore, the contracted sliding pad 1 is maintained in contact with the pad support surface 2 a of the shell 2. As described above, according to this embodiment, the pad pressing mechanism 5 is configured to further press the sliding pad 1 against the pad support surface 2 a of the shell 2 as the sliding pad 1 contracts due to contact with the cryogenic fluid (e.g., liquid hydrogen). As a result, the sliding pad 1 is firmly held by the shell 2, and the sliding bearing can maintain stable operation even in a cryogenic environment.

[0024] Next, another embodiment of the sliding bearing will be described with reference to Figure 5. The configuration and operation of this embodiment not specifically described are the same as those of the embodiment described with reference to Figures 1 to 4, and therefore redundant description will be omitted. As shown in Figure 5, the sliding bearing is equipped with a pad pressing mechanism 5 located at the center of the sliding pad. Although not shown, a plurality of sliding pads 1 are arranged around the rotating shaft 100, similar to the embodiment shown in Figure 1.

[0025] The pad pressing mechanism 5 includes a pad support member 32 having a tapered shaft portion 31, and a tapered hole 35 formed in the sliding contact pad 1. The tapered shaft portion 31 is located inside the shell 2. The pad support member 32 extends in the radial direction of the sliding bearing and penetrates the sliding contact pad 1 and the shell 2 in the radial direction. The sliding contact pad 1 is supported by the pad support member 32. More specifically, the sliding contact pad 1 is supported by the tapered shaft portion 31, and the tapered hole 35 is in surface contact with the outer circumferential surface 31 a of the tapered shaft portion 31.

[0026] The sliding pad 1 has a recess 37 that receives the end of the tapered shaft portion 31 of the pad support member 32. The recess 37 is formed in the shaft support surface 1a of the sliding pad 1. The pad support member 32 is fixed to the shell 2. More specifically, the pad support member 32 has a threaded portion 32a that passes through a through-hole 38 formed in the pad support surface 2a. Double nuts 41, 42 are threadedly engaged with the threaded portion 32a of the pad support member 32, fixing the radial position of the pad support member 32. The double nuts 41, 42 are located outside the shell 2. The mechanism for fixing the radial position of the pad support member 32 is not limited to a double nut. For example, a single nut may be threaded onto the threaded portion 32a of the pad support member 32, and the nut may be welded to the pad support member 32.

[0027] The pad support member 32 including the tapered shaft portion 31 is made of a material, such as metal, that has a smaller linear expansion coefficient than the sliding pad 1. The outer peripheral surface 31a of the tapered shaft portion 31 and the tapered hole 35 have a truncated cone shape whose diameter gradually decreases radially outward (toward the shell 2). The outer peripheral surface 31a of the tapered shaft portion 31 is fitted into the tapered hole 35.

[0028] 6 is a diagram showing an example of a contracted state of the sliding pad 1. When the sliding pad 1 contracts due to contact with an extremely low-temperature fluid such as liquefied gas, the tapered hole 35 of the sliding pad 1 is pressed more strongly against the outer circumferential surface 31a of the tapered shaft portion 31 than at room temperature. The tapered hole 35 of the sliding pad 1 slides on the outer circumferential surface 31a of the tapered shaft portion 31, and a force acts on the sliding pad 1 to move the sliding pad 1 radially outward. As a result, the sliding pad 1 is pressed against the pad support surface 2a of the shell 2. Therefore, the contracted sliding pad 1 is maintained in contact with the pad support surface 2a of the shell 2.

[0029] Thus, according to this embodiment, the pad pressing mechanism 5 is configured so that, as the sliding pad 1 contracts due to contact with the cryogenic fluid (e.g., liquid hydrogen), it further presses the sliding pad 1 against the pad support surface 2a of the shell 2. As a result, the sliding pad 1 is firmly held by the shell 2, and the sliding bearing can maintain stable operation even in a cryogenic environment.

[0030] Next, still another embodiment of the sliding bearing will be described with reference to Figure 7. The configuration and operation of this embodiment not specifically described are the same as those of the embodiment described with reference to Figures 1 to 4, and therefore redundant description will be omitted. As shown in Figure 7, the sliding bearing is provided with a pad pressing mechanism 5 extending in the axial direction. Although not shown, a plurality of sliding pads 1 are arranged around the rotating shaft 100, similar to the embodiment shown in Figure 1.

[0031] The pad pressing mechanism 5 includes a dovetail groove 50 formed in the sliding pad 1 and a pad holding rail 51 that fits into the dovetail groove 50. The dovetail groove 50 is formed on the outer surface of the sliding pad 1. The pad holding rail 51 has an inverted triangular cross-sectional shape that fits into the dovetail groove 50. The pad holding rail 51 is connected to the pad support surface 2a of the shell 2 and extends axially on the pad support surface 2a. Examples of how the pad holding rail 51 is connected to the pad support surface 2a include a mode in which the pad holding rail 51 is fixed to the pad support surface 2a with screws or the like, and a mode in which the pad holding rail 51 and the shell 2 are integrally formed. The sliding pad 1 is held by the pad holding rail 51. The dovetail groove 50 has a first tapered side surface 50a, and the pad holding rail 51 has a second tapered side surface 51a that comes into surface contact with the first tapered side surface 50a of the dovetail groove 50.

[0032] Fig. 8 is a perspective view showing one embodiment of the sliding pad 1, and Fig. 9 is a perspective view showing a portion of one embodiment of the shell 2. As shown in Figs. 8 and 9, the dovetail groove 50 and the pad holding rail 51 extend in an axial direction parallel to the center line CL (see Fig. 2) of the sliding bearing. The pad holding rail 51 is fixed to the shell 2 by screws (not shown). In one embodiment, the pad holding rail 51 and the shell 2 may be an integral structure.

[0033] 10 is a diagram showing an example of a contracted state of the sliding pad 1. When the sliding pad 1 contracts due to contact with an extremely low-temperature fluid such as liquefied gas, the first tapered side surface 50a of the dovetail groove 50 is pressed more strongly against the second tapered side surface 51a of the pad holding rail 51 than at room temperature. The first tapered side surface 50a of the sliding pad 1 slides on the second tapered side surface 51a of the pad holding rail 51, and a force acts on the sliding pad 1 to move the sliding pad 1 radially outward. As a result, the sliding pad 1 is pressed against the pad support surface 2a of the shell 2. Therefore, the contracted sliding pad 1 is maintained in contact with the pad support surface 2a of the shell 2.

[0034] The sliding pad 1 and the pad holding rail 51 are made of different materials. The linear expansion coefficient of the sliding pad 1 is greater than that of the pad holding rail 51. In particular, in this embodiment, it is preferable to use a combination of materials in which the linear expansion coefficient of the sliding pad 1 is greater than that of the pad holding rail 51 by 50% or more. For example, a resin material can be used for the sliding pad 1, and a metal such as stainless steel can be used for the pad holding rail 51.

[0035] As described above, according to this embodiment, the pad pressing mechanism 5 is configured to further press the sliding pad 1 against the pad support surface 2a of the shell 2 as the sliding pad 1 contracts due to contact with the cryogenic fluid (e.g., liquid hydrogen). As a result, the sliding pad 1 is firmly held to the shell 2, and the sliding bearing can maintain stable operation in a cryogenic environment. In particular, according to this embodiment, the shaft support surface 1a of the sliding pad 1 does not have holes or recesses for passing the pad support members 8, 32 therethrough, as in the previously described embodiments, and therefore the area of ​​the shaft support surface 1a can be increased. Therefore, the sliding pad 1 is less likely to wear, and the sliding bearing can stably support the rotating shaft 100.

[0036] Figure 11 is a vertical cross-sectional view of the embodiment of the sliding bearing shown in Figure 7. The sliding bearing is equipped with an upper leaf spring 55 and a lower leaf spring 56 as biasing members that press the sliding contact pad 1 in the axial direction. The upper leaf spring 55 and the lower leaf spring 56 are in contact with the upper end and the lower end of the sliding contact pad 1, respectively. The upper leaf spring 55 and the lower leaf spring 56 are fixed to the upper end and the lower end of the shell 2 by retainers 58. The retainers 58 are fixed to the upper end and the lower end of the shell 2 by screws 59.

[0037] The upper leaf spring 55 and the lower leaf spring 56 are annular and extend along the circumferential direction of the shell 2. The upper leaf spring 55 and the lower leaf spring 56 protrude radially inward from the shell 2 and contact the sliding contact pad 1. In one embodiment, each of the upper leaf spring 55 and the lower leaf spring 56 may not be annular, but may be composed of a plurality of leaf spring elements arranged along the circumferential direction of the shell 2.

[0038] The axial length L1 of the sliding contact pad 1 at room temperature is greater than the axial length L2 of the shell 2 at room temperature. Therefore, the sliding contact pad 1 is sandwiched between an upper leaf spring 55 and a lower leaf spring 56 fixed to the shell 2. The upper leaf spring 55 and the lower leaf spring 56 are configured to be able to bend elastically in the axial direction. With this configuration, the axial position of the sliding contact pad 1 is maintained by the upper leaf spring 55 and the lower leaf spring 56, while allowing for slight changes.

[0039] 12 is a diagram showing an example of a contracted state of the sliding pad 1. When the sliding pad 1 contracts due to contact with a cryogenic fluid such as liquefied gas, the axial length L1 of the sliding pad 1 approaches the axial length L2 of the shell 2, but the sliding pad 1 is positioned between the upper leaf spring 55 and the lower leaf spring 56. Therefore, the axial position of the sliding pad 1 is maintained by the upper leaf spring 55 and the lower leaf spring 56. In other words, the upper leaf spring 55 and the lower leaf spring 56 can absorb the expansion and contraction of the sliding pad 1 that occurs due to temperature changes of the sliding pad 1.

[0040] The sliding bearing of this embodiment can be assembled as follows. At room temperature, the dovetail groove 50 of the sliding pad 1 and the pad holding rail 51 of the shell 2 are a clearance fit. Therefore, first, at room temperature, the dovetail groove 50 of the sliding pad 1 is slid over the pad holding rail 51 of the shell 2 so that the dovetail groove 50 of the sliding pad 1 is fitted into the pad holding rail 51. Then, the upper leaf spring 55 and the lower leaf spring 56 are fixed to the shell 2 with the retainer 58 and the screw 59. The circumferential position of the sliding pad 1 is fixed by the engagement between the dovetail groove 50 and the pad holding rail 51, and the axial position of the sliding pad 1 is fixed by the upper leaf spring 55 and the lower leaf spring 56.

[0041] Next, a pump device equipped with the embodiment of the plain bearing described with reference to Figures 1 to 12 will be described. Figure 13 is a cross-sectional view showing one embodiment of a pump device equipped with a plain bearing. The pump device has a pump 200 for transporting a liquid and an electric motor 210 that drives the pump 200. Examples of liquids include cryogenic liquefied gases such as liquefied ammonia, liquid hydrogen, liquid nitrogen, liquefied natural gas, liquefied ethylene gas, and liquefied petroleum gas. The pump device of this embodiment described below is a centrifugal pump device used to pressurize liquid hydrogen.

[0042] As shown in Fig. 13, pump 200 includes rotating shaft 100, a plurality of impellers 201a to 201h fixed to rotating shaft 100, bearings 205, 206 and a plain bearing 208 that rotatably support rotating shaft 100, and a pump casing 207 that houses impellers 201a to 201h. Plain bearing 208 is any of the plain bearings of the embodiments described with reference to Figs. 1 to 12. In other words, the embodiments described with reference to Figs. 1 to 12 are applicable to plain bearing 208.

[0043] The rotating shaft 100 extends vertically, and multiple impellers 201a to 201h are fixed to the rotating shaft 100. A pump device having a rotating shaft 100 that extends vertically is also called a vertical pump device. The multiple impellers 201a to 201h face the same direction (facing downward in this embodiment) and are arranged in series along the rotating shaft 100. A plain bearing 208 supports the rotating shaft 100 at a position between impellers 201d and 201e. The number of impellers 201a to 201h is not limited to this embodiment.

[0044] The pump device further includes an electric motor 210 that rotates the rotary shaft 100. The electric motor 210 includes a motor rotor 210A fixed to the rotary shaft 100, a motor stator 210B that surrounds the motor rotor 210A, and a motor housing 210C that houses the motor stator 210B. The motor housing 210C is fixed to the pump casing 207.

[0045] The electric motor 210 is configured to be able to rotate the rotary shaft 100 and the impellers 201a-201h as a single unit. In this embodiment, the electric motor 210 is an immersed motor that can come into contact with liquid hydrogen. That is, while the pump device is in operation, the motor rotor 210A and the motor stator 210B are immersed in the liquid hydrogen and are cooled by the liquid hydrogen. In one embodiment, at least one of the motor rotor 210A and the motor stator 210B may have a sealed structure that does not allow liquid to enter.

[0046] The pump device is disposed in a suction vessel (not shown), which is filled with liquid hydrogen, so that the pump 200 and the electric motor 210 are operated while being entirely immersed in the liquid hydrogen.

[0047] Bearings 205 and 206 are disposed above and below electric motor 210. In this embodiment, bearings 205 and 206 are ball bearings capable of supporting both radial and axial loads. In one embodiment, either bearing 205 or 206 may be the plain bearing 208 according to any of the above-described embodiments. During operation of the pump device, bearings 205 and 206 and plain bearing 208 are immersed in liquid hydrogen and are lubricated and cooled by the liquid hydrogen.

[0048] Pump casing 207 has inlet 207a for liquid hydrogen. When electric motor 210 rotates impellers 201a to 201h, liquid hydrogen in the suction vessel flows into pump casing 207 through inlet 207a. The liquid hydrogen is pressurized inside pump casing 207 as impellers 201a to 201h rotate. The pressurized liquid hydrogen is discharged from the pump device through discharge passage 216 and outlet 217. Discharge passage 216 is formed inside pump casing 207 and motor housing 210C, and outlet 217 is formed in motor housing 210C. A portion of the pressurized liquid hydrogen comes into contact with bearings 205, 206, slide bearing 208, and electric motor 210.

[0049] The pump device further includes a first thrust balance mechanism 220 and a second thrust balance mechanism 240 that cancel out the weight of the rotor including at least the rotating shaft 100 and the plurality of impellers 201a-201h and the axial thrust acting on the plurality of impellers 201a-201h. The first thrust balance mechanism 220 is disposed on the discharge side of the plurality of impellers 201a-201h. More specifically, the first thrust balance mechanism 220 is disposed between the final-stage impeller 201h and the electric motor 210. A portion of the liquid hydrogen pressurized by the rotation of the plurality of impellers 201a-201h flows through the first thrust balance mechanism 220 and comes into contact with the bearings 205, 206 and the electric motor 210, thereby cooling the bearings 205, 206 and the electric motor 210. Liquid hydrogen is returned from the electric motor 210 through a communication line 221 to the low pressure side of the pump casing 207 .

[0050] One end of communication line 221 is connected to motor housing 210C of electric motor 210 and communicates with the interior of motor housing 210C. The other end of communication line 221 is connected to pump casing 207 and communicates with a low-pressure region within pump casing 207. More specifically, the other end of communication line 221 communicates with the interior of pump casing 207 at a position between first-stage impeller 201a and final-stage impeller 201h. Therefore, communication line 221 communicates with the discharge side of any one of impellers 201a to 201h.

[0051] The connection position of the communication line 221 and the pump casing 207 is determined appropriately based on factors such as the weight of the rotor (including the rotating shaft 100 and the impellers 201a to 201h). In this embodiment, if the multiple impellers 201a to 201h are divided into a low-pressure side group of impellers 201a to 201d including the first-stage impeller 201a and a high-pressure side group of impellers 201e to 201h including the final-stage impeller 201h, the communication line 221 communicates with the inside of the pump casing 207 at the position of the low-pressure side group.

[0052] The liquid hydrogen in the motor housing 210C is returned to the pump casing 207 through the communication line 221. Therefore, the pressure of the liquid hydrogen in the motor housing 210C is substantially the same as the pressure on the low-pressure side of the pump casing 207. In this embodiment, the communication line 221 communicates with the interior of the pump casing 207 at the position of the second-stage impeller 2b (i.e., communicates with the discharge side of the impeller 2b), but the communication line 221 may also communicate with the interior of the pump casing 207 at the position of another stage of impeller.

[0053] In one embodiment, communication line 221 may be connected to the inside of the suction vessel (i.e., the outside of pump 200) without being connected to pump casing 207. In this case, the pressure of liquid hydrogen in motor housing 210C is substantially the same as the pressure on the suction side of impeller 201a (i.e., the pressure before being increased by impellers 201a to 201h).

[0054] The second thrust balance mechanism 240 includes a wall structure 246 having a low-pressure chamber 243 and a high-pressure chamber 245 therein, and a partition wall 250 disposed within the wall structure 246 and between the low-pressure chamber 243 and the high-pressure chamber 245. The partition wall 250 is connected to the rotating shaft 100. The high-pressure chamber 245 is located below the low-pressure chamber 243. The names low-pressure chamber 243 and high-pressure chamber 245 mean that the pressure in the low-pressure chamber 243 is lower than the pressure in the high-pressure chamber 245, and do not mean that the pressure in the low-pressure chamber 243 is equal to or lower than a specific pressure, or that the pressure in the high-pressure chamber 245 is equal to or higher than a specific pressure.

[0055] One end of the intermediate communication line 241 is connected to the wall structure 246 and communicates with the high-pressure chamber 245. The other end of the intermediate communication line 241 is connected to the discharge side of one of the multiple impellers 201a to 201h. More specifically, the other end of the intermediate communication line 241 is connected to the pump casing 207 at a position on the discharge side of one of the multiple impellers 201a to 201h, and communicates with the interior of the pump casing 207. In this embodiment, the high-pressure chamber 245 is connected to the discharge side of the intermediate-stage impeller 201d through the intermediate communication line 241. That is, the other end of the intermediate communication line 241 is connected to the interior of the pump casing 207 at a position on the discharge side of the impeller 201d. In one embodiment, the other end of the intermediate communication line 241 may be connected to the discharge side of an impeller of another stage, such as the intermediate-stage impeller.

[0056] One end of return line 280 is connected to wall structure 246 and communicates with low-pressure chamber 243. The other end of return line 280 is connected to pump casing 207 at a position on the discharge side of first-stage impeller 201a, which is a suction-side impeller located upstream of intermediate-stage impeller 201d, and communicates with the interior of pump casing 207. Therefore, return line 280 communicates the discharge side of first-stage impeller 201a, which is a suction-side impeller, with low-pressure chamber 243. In one embodiment, the suction-side impeller may be an impeller other than first-stage impeller 201a (e.g., second-stage impeller 201b), as long as it is located upstream of intermediate-stage impeller 201d.

[0057] The partition wall 250 has a piston shape and is fixed to the lower end of the rotating shaft 100. The partition wall 250 rotates integrally with the rotating shaft 100 within the structure 246 and is capable of moving axially integrally with the rotating shaft 100. The wall structure 246 has an inner circumferential surface parallel to the axial direction of the rotating shaft 100, and the partition wall 250 has an outer circumferential surface parallel to the axial direction of the rotating shaft 100. The entire outer circumferential surface of the partition wall 250 is surrounded by the inner circumferential surface of the wall structure 246 via a gap. The partition wall 250 is capable of moving axially within the wall structure 246 in accordance with the axial movement of the rotating shaft 100.

[0058] There is a radial gap between the outer peripheral surface of the partition wall 250 and the inner peripheral surface of the wall structure 246. The size of this radial gap is constant regardless of the axial position of the rotating shaft 100. The second thrust balance mechanism 240 of this embodiment is a fixed gap type in which the size of the radial gap does not change regardless of the axial position of the rotating shaft 100. This type of fixed gap type is also called a fixed orifice type.

[0059] The liquid hydrogen filling the high-pressure chamber 245 moves to the low-pressure chamber 243 through a radial gap between the outer circumferential surface of the partition wall 250 and the inner circumferential surface of the wall structure 246. The liquid hydrogen flows from the low-pressure chamber 243 through a return line 280 into the interior of the pump casing 207. In order to control the flow rate of liquid hydrogen passing through the radial gap, grooves (axial grooves, spiral grooves, circumferential grooves, etc.) may be provided on at least one of the inner and outer circumferential surfaces.

[0060] The pressure in the low-pressure chamber 243 is substantially equal to the pressure on the discharge side of the impeller 201a. Therefore, the partition wall 250 receives an upward force equivalent to the difference between the pressure in the high-pressure chamber 245 and the pressure in the low-pressure chamber 243. This upward force is generated by the second thrust balance mechanism 240 and is a force that resists the weight of the rotating body (including at least the rotating shaft 100 and the impellers 201a to 201h) and the axial thrust acting on the impellers 201a to 201h. The upward force generated by the second thrust balance mechanism 240 is determined by the difference between the pressure in the high-pressure chamber 245 and the pressure in the low-pressure chamber 243, and does not change depending on the axial position of the rotating shaft 100.

[0061] The combination of the upward force generated by the first thrust balance mechanism 220 and the upward force generated by the second thrust balance mechanism 240 can cancel out the weight of the rotating body (including at least the rotating shaft 100 and the impellers 201a to 201h) and the axial thrust acting on the impellers 201a to 201h. Therefore, the axial thrust acting on the bearings 205, 206 becomes substantially zero, and the life of the bearings 205, 206 is extended.

[0062] The return line 280 connects the discharge side of the first-stage impeller 201a, which is the suction-side impeller, with the low-pressure chamber 243. Therefore, during operation of the pump device, the pressure in the low-pressure chamber 243 is substantially the same as that on the discharge side of the first-stage impeller 201a. That is, the pressure in the low-pressure chamber 243 is substantially the same as the pressure increased by the first-stage impeller 201a. When liquid hydrogen moves from the high-pressure chamber 245 through the radial gap to the low-pressure chamber 243, the pressure of the liquid hydrogen decreases. However, since the pressure in the low-pressure chamber 243 is substantially the same as the pressure increased by the first-stage impeller 201a, the liquid hydrogen is unlikely to vaporize. The liquid hydrogen returned from the low-pressure chamber 243 through the return line 280 to the pump casing 207 does not contain any air bubbles, allowing the pump device to perform its intended pumping performance and preventing vibrations caused by the intake of air bubbles.

[0063] When the liquid hydrogen filling the high-pressure chamber 245 moves through the radial gap to the low-pressure chamber 243, the liquid hydrogen forms a liquid film in the radial gap. This liquid film functions as a bearing supporting the rotor including the rotating shaft 100 and the multiple impellers 201a-201h, thereby contributing to improving the stability of the rotor. This bearing function of the second thrust balance mechanism 240 is particularly advantageous for a multi-stage pump device equipped with multiple impellers. That is, a multi-stage pump device equipped with multiple impellers has a long shaft length and an increased number of whirling elements, which can cause problems with the stability of the rotor including the multiple impellers. The liquid film formed in the radial gap can improve the stability of such a rotor.

[0064] The density of liquid hydrogen is approximately one-sixth the density of liquefied natural gas. When a pump device handles such liquid hydrogen, it is difficult for the first thrust balance mechanism 220 alone to generate a sufficient upward force to support the rotor. According to this embodiment, the first thrust balance mechanism 220 and the second thrust balance mechanism 240 can generate an upward force large enough to support the weight and axial thrust of the rotor. In particular, by appropriately setting the connection position between the intermediate communication line 241 and the pump casing 207, the second thrust balance mechanism 240 can generate an optimal upward force.

[0065] The second thrust balance mechanism 240 forms a liquid hydrogen loop that is completely independent of the first thrust balance mechanism 220. In other words, the pressure within the high-pressure chamber 245 of the second thrust balance mechanism 240 corresponds to the pressure on the discharge side of the intermediate-stage impeller among the multiple impellers 201a to 201h. The pressure within the high-pressure chamber 245 varies depending on the connection position between the intermediate communication line 241 and the pump casing 207. Therefore, the appropriate connection position between the intermediate communication line 241 and the pump casing 207 is determined based on the weight of the rotor and the upward force required to counteract the axial thrust acting on the impellers 201a to 201h.

[0066] As shown in Fig. 13, a plain bearing 255 may be provided above the second thrust balance mechanism 240. In the embodiment shown in Fig. 13, the plain bearing 255 is located above the second thrust balance mechanism 240 and below the impellers 201a to 201h.

[0067] The above-described embodiments have been described for the purpose of enabling a person of ordinary skill in the art to practice the present invention. Various modifications of the above-described embodiments would be obvious to a person skilled in the art, and the technical concept of the present invention may be applied to other embodiments. Therefore, the present invention is not limited to the described embodiments, but is to be interpreted in the broadest scope in accordance with the technical concept defined by the claims.

[0068] The present invention is applicable to plain bearings used in rotary machines such as pumps and turbines, and particularly to plain bearings used in cryogenic environments. The present invention is also applicable to pump devices equipped with such plain bearings.

[0069] DESCRIPTION OF SYMBOLS 1 Sliding pad 1a Shaft support surface 2 Shell 2a Pad support surface 5 Pad pressing mechanism 7 Spring 8 Bolt (pad support member) 8a Threaded portion 8b Head 11 Through hole 12 Recessed portion 15 Through hole 17 Nut 20 Guide wall 31 Tapered shaft portion 31a Outer circumferential surface 32 Pad support member 32a Threaded portion 35 Tapered hole 37 Recessed portion 38 Through hole 41, 42 Nut 50 Dovetail groove 50a First tapered side surface 51 Pad holding rail 51a Second tapered side surface 55 Upper leaf spring 56 Lower leaf spring 58 Retainer 59 Screw 100 Rotating shaft

Claims

1. A sliding bearing for supporting a rotating shaft, comprising: a sliding pad having a shaft support surface for supporting the outer peripheral surface of the rotating shaft; a shell arranged radially outside the sliding pad; and a pad pressing mechanism for pressing the sliding pad against the pad support surface of the shell when the sliding pad contracts.

2. The sliding bearing according to claim 1, wherein said pad pressing mechanism comprises an urging member that urges said sliding pad toward said shell.

3. A sliding bearing as claimed in claim 2, wherein the pad pressing mechanism further comprises a pad support member supported by the shell, the sliding pad is supported by the pad support member, and the biasing member biases the sliding pad and the pad support member towards the shell, thereby pressing the sliding pad against the pad support surface of the shell.

4. A sliding bearing as described in claim 1, wherein the pad pressing mechanism comprises: a pad support member having a tapered shaft portion fixed to the shell; and a tapered hole formed in the sliding pad, the sliding pad being supported by the tapered shaft portion, and the tapered hole being in surface contact with the outer circumferential surface of the tapered shaft portion.

5. A sliding bearing as claimed in claim 1, wherein the pad pressing mechanism comprises a dovetail groove formed in the sliding pad and a pad holding rail connected to the pad support surface of the shell, the pad holding rail having an inverted triangular cross-sectional shape that fits into the dovetail groove.

6. The plain bearing according to claim 5, wherein said dovetail groove and said pad retaining rail extend in an axial direction parallel to a centerline of said plain bearing.

7. The sliding bearing according to claim 6, further comprising a biasing member for urging said sliding pad in said axial direction.

8. A pump device comprising: a rotating shaft; an electric motor that rotates the rotating shaft; an impeller fixed to the rotating shaft; a pump casing that houses the impeller; and a plain bearing according to any one of claims 1 to 7 that rotatably supports the rotating shaft.

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