Tilting pad thrust bearing assembly for steam turbine with load balancing function

Abstract

The present invention discloses a tilting pad thrust bearing assembly for a steam turbine with a load balancing function, and relates to the technical field of tilting pad thrust bearings. This scheme integrates a thrust bearing and a tilting pad bearing into one, and utilizes the basic principle that the sum of the loads of a single tilting pad in the tilting pad is equal to the total load. Based on the principle of the tilting pad bearing, during the continuous circulation of the lubricating oil medium, a return box and a connecting sleeve are set for the circulation direction of the lubricating oil medium and the tilting direction of the tilting pad. The essence of this scheme is: for the oil discharge process of the lubricating oil, a two-way sensing method is used to detect the hydraulic size of the lubricating oil medium, and in this way, the load capacity of the tilting pad at the corresponding position is reversely detected, and the balancing capacity is judged by each load capacity, and then the load capacity at each tilting pad is balanced by limiting the movement data of the return oil component or the oil injection component.

Description

Technical Field

[0001] The invention relates to the technical field of tilting pad thrust bearings, and in particular to a tilting pad thrust bearing assembly for a steam turbine with a load force balancing function. Background Art

[0002] For the tilting pad thrust bearing used in the steam turbine, the inclination angle is automatically adjusted through a special structure based on the fluid lubrication system to adapt to the needs of different working conditions. Specifically, it includes tilting pads and thrust pads, and the lubricating oil penetrates through the gap between the corresponding pads and the shaft to form a fluid dynamic pressure oil film, which reduces friction and wear.

[0003] It should be noted that: it is very important to balance the load capacity between each pad, but for the steam turbine, it is a high-power equipment with a rotational speed of up to 3000 rpm. In the process of switching the rotational speed, the axial force (forward / reverse) will change. In particular, different loads have different effects on the change in oil film thickness. For example, the greater the load, the greater the change in oil film thickness; the smaller the load, the smaller the change in oil film thickness. It can be understood that: when the axial force changes, there are differences in the load forces on the multiple pads in the bearing, such as the problem of excessive pad load limit or overload of pad load limit, which directly affects the operating stability of the tilting pad thrust bearing. This application proposes a solution. Summary of the invention

[0004] The purpose of the present invention is to provide a tilting pad thrust bearing assembly for a steam turbine with a load balancing function. For the tilting pad thrust bearing used in the steam turbine, during the speed adjustment process to meet the high speed difference, there are differences in the loads on the pads in different positions, and then there is an excess of the pad load limit or an overload of the pad load limit, which will affect the stable operation of the tilting pad thrust bearing and aggravate the wear of the pads.

[0005] The object of the present invention can be achieved by the following technical scheme: a tilting pad thrust bearing assembly for a steam turbine with a load balancing function, comprising two sets of half-shaft bodies and an oil seal sleeve, wherein the half-shaft bodies are provided with thrust pads and tilting pads, wherein the thrust pads are provided at one end of the half-shaft bodies, wherein the tilting pads are provided in a circular shape with equal spacing along the center point of the half-shaft bodies, and wherein the oil seal sleeves are provided with return boxes and connecting sleeves at positions corresponding to the tilting pads;

[0006] An outer ring oil tank is arranged between the oil seal sleeve and the half-axle body, an inner ring oil tank is arranged between the half-axle body and the tilting pad, the reflux box and the connecting sleeve penetrate the half-axle body and are communicated with the interior of the inner ring oil tank, and the reflux box and the connecting sleeve are respectively connected with an oil return pipe and an oil inlet pipe, a partition is installed at the center position of the inner part of the oil return pipe, and a left oil tank and a right oil tank are arranged inside the oil return pipe through the partition, and pressure probes are arranged in the left oil tank and the right oil tank.

[0007] It is further configured as follows: a ball head connecting rod is connected to the inner wall position of the semi-axle body corresponding to the tilting pad, and the bottom end position of the ball head connecting rod is movably connected to the tilting pad.

[0008] It is further configured as follows: the setting position of the ball head connecting rod is close to the setting position of the reflux box, a connecting spring is installed in the inner position of the connecting sleeve, and the end position of the connecting spring is connected to the tilting pad.

[0009] It is further configured as follows: the width of the reflux box is equal to the inner width of the oil seal sleeve, and oil leakage gaps are opened on both sides of the reflux box, and an oil port is opened on the inner wall position of the reflux box corresponding to the outer ring oil tank.

[0010] It is further configured as follows: a gap is provided between the top of the partition and the top position inside the reflux box, the left oil tank is directly connected to the inner ring oil tank, and the right oil tank is indirectly connected to the inner ring oil tank through the left oil tank.

[0011] It is further configured as follows: the reflux box is arranged at the middle position of the adjacent tilting pads, and the reflux box is arranged close to the ball head connecting rod, and the left oil tank and the right oil tank are respectively located at the left and right positions of the partition.

[0012] It is further configured that: during use, the oil return pipe is connected to an oil return assembly, the oil inlet pipe is connected to an oil injection assembly, a circulation system is provided between the oil return assembly and the oil injection assembly, and the circulation system includes the following control actions during use:

[0013] Control action 1: The lubricating oil medium is circulated in a closed loop in the outer ring oil tank and the inner ring oil tank through the oil injection component and the oil return component, and the closed loop circulation direction of the lubricating oil medium in the outer ring oil tank is from the left oil tank to the right oil tank;

[0014] Control action two: Based on control action one, the hydraulic value is obtained through the pressure measuring probe located from the left oil tank to the right oil tank in the reflux box, and a load capacity model is established with the hydraulic value. The load capacity of the corresponding tilt pad position is obtained in the load capacity model, and the operating data of the oil injection component or the oil return component is reversely controlled with the load capacity of each tilt pad.

[0015] The present invention has the following beneficial effects:

[0016] 1. The overall structure is based on the operating principle of conventional thrust bearings and tilting pad bearings, integrating the two into one to form a bearing assembly. On this basis, the basic principle that the sum of the loads of a single tilting pad in a tilting pad bearing is equal to the total load is utilized, and the tilting pad in the bearing assembly is taken as the main body. In the process of continuous circulation of the lubricating oil medium, the setting position of the reflux box and the connecting sleeve is further restricted. A single reflux box is for one tilting pad, and two pressure measuring probes in the reflux box are used to adopt a two-way sensing detection method to specifically detect the hydraulic pressure size of the lubricating oil medium when it is in the oil return stage, and indirectly feedback the load capacity of the tilting pad;

[0017] 2. In combination with the above content, it is explained that: based on the technology of two-way sensing and detecting the lubricating oil medium, it is used to directly feedback the load capacity on each tilting pad, and the inside of each reflux box is in a state of interconnection and connection, which is specifically manifested as: for the hydraulic changes of the lubricating oil medium flowing from the inner ring oil tank to the outer ring oil tank, and the hydraulic changes due to the lubricating oil medium rebounding to the reflux box, the load force can be balanced by controlling the operating data in the oil injection component or the oil return component. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0019] Figure 1 A schematic structural diagram of a tilting pad thrust bearing assembly for a steam turbine with a load balancing function proposed by the present invention;

[0020] Figure 2 The invention provides a tilting pad thrust bearing assembly for a steam turbine with a load balancing function. Figure 1 Split diagram of ;

[0021] Figure 3 A partial structural schematic diagram of a tilting pad thrust bearing assembly for a steam turbine with a load balancing function proposed by the present invention;

[0022] Figure 4 A cross-sectional view of an oil seal sleeve in a tilting pad thrust bearing assembly for a steam turbine with a load balancing function proposed by the present invention;

[0023] Figure 5 This is a schematic structural diagram of a return box in a tilting pad thrust bearing assembly for a steam turbine with a load balancing function proposed by the present invention;

[0024] Figure 6 A cross-sectional view of an oil seal sleeve and a return box in a tilting pad thrust bearing assembly for a steam turbine with a load balancing function proposed by the present invention;

[0025] Figure 7 This is a schematic structural diagram of part A of the tilting pad thrust bearing assembly for a steam turbine with a load balancing function proposed by the present invention.

[0026] In the figure: 1. half-axle body; 2. oil seal sleeve; 201. outer ring oil bin; 202. inner ring oil bin; 3. reflux box; 301. oil leakage gap; 302. pressure probe; 303. left oil bin; 304. right oil bin; 305. partition; 4. oil return pipe; 5. oil inlet pipe; 6. connecting sleeve; 7. thrust bearing; 8. tilting bearing; 9. connecting spring; 10. ball head connecting rod. DETAILED DESCRIPTION

[0027] The technical solution of the present invention will be clearly and completely described below in conjunction with the embodiments. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0028] Embodiment 1

[0029] For the tilting pad thrust bearing used in steam turbines, in the process of speed adjustment to meet the high speed difference, the load on the pads in different positions is different, and then there is an excess or overload of the pad bearing limit, which will affect the stable operation of the tilting pad thrust bearing and aggravate the wear of the pads. The following technical solutions are proposed:

[0030] Reference Figures 1 to 7 The tilting pad thrust bearing assembly for a steam turbine with a load balancing function in this embodiment comprises two sets of half-shaft bodies 1 and an oil seal sleeve 2. The half-shaft body 1 is provided with a thrust pad 7 and a tilting pad 8. The thrust pad 7 is provided at one end of the half-shaft body 1. The tilting pad 8 is provided in a circular shape and is equidistant along the center point of the half-shaft body 1. A return box 3 and a connecting sleeve 6 are respectively installed at positions of the oil seal sleeve 2 corresponding to the tilting pad 8.

[0031] 1. An outer ring oil tank 201 is provided between the oil seal sleeve 2 and the half shaft body 1, an inner ring oil tank 202 is provided between the half shaft body 1 and the tilting pad 8, a return box 3 and a connecting sleeve 6 penetrate the half shaft body 1 and communicate with the inner ring oil tank 202, and an oil return pipe 4 and an oil inlet pipe 5 are connected to the return box 3 and the connecting sleeve 6 respectively, a partition 305 is installed at the center position of the inner part of the oil return pipe 4, and a left oil tank 302 is provided inside the oil return pipe 4 through the partition 305. 3 and the right oil tank 304, the left oil tank 303 and the right oil tank 304 are both provided with pressure measuring probes 302, the semi-axle body 1 is connected with a ball head connecting rod 10 at the inner wall position corresponding to the tilting pad 8, the bottom end position of the ball head connecting rod 10 and the tilting pad 8 are movably connected, the setting position of the ball head connecting rod 10 is close to the setting position of the reflux box 3, and a connecting spring 9 is installed in the internal position of the connecting sleeve 6, and the end position of the connecting spring 9 is connected to the tilting pad 8.

[0032] Basic principle: The overall device is based on conventional thrust bearings and tilting pad bearings. Specifically, the two are integrated into one to form a bearing assembly, which includes thrust pad 7 and tilting pad 8, but still takes tilting pad 8 as the main body. Its essence is based on the basic principle of tilting pad bearings. The sum of the loads at each tilting pad position in the conventional tilting pad is equal to the total load. This part is the basic principle of the present invention.

[0033] A plurality of return boxes 3 and connecting sleeves 6 are provided for the tilting pad 8 and the oil seal sleeve 2 to realize the continuous circulation process of the lubricating oil medium. Figure 4 Explanation: The lubricating oil medium completely fills the outer ring oil tank 201 and the inner ring oil tank 202, and an oil film is formed between the tilting pad 8 and the outer wall of the rotating shaft on the steam turbine. Specifically, the directional rotation of the tilting pad 8 is achieved by the ball head connecting rod 10 in cooperation with the connecting spring 9, which is mainly used to change the thickness of the oil film. For example, when the bearing pressure of the lubricating surface increases, the oil film is squeezed and becomes thinner; on the contrary, when the thickness of the oil film increases, it is used to indicate that the load caused by the outer wall of the rotating shaft of the steam turbine on the tilting pad 8 is reduced;

[0034] What needs to be explained in this embodiment is that when the load on each tilting pad 8 is in a relatively stable state, it can be said that the operation process of the overall bearing assembly is relatively stable; on the contrary, when the load of the tilting pad 8 at a certain position is significantly different from the load of the tilting pad 8 at other positions, poor lubrication may occur, aggravated wear or even direct jamming.

[0035] Embodiment 2

[0036] This embodiment is to explain the reflux box in the first embodiment:

[0037] The width of the reflux box 3 is equal to the internal width of the oil seal sleeve 2, and oil leakage gaps 301 are opened on both sides of the reflux box 3, and an oil port is opened on the inner wall position of the reflux box 3 corresponding to the outer ring oil bin 201. A gap is set between the top of the partition 305 and the top position inside the reflux box 3, and the left oil bin 303 is directly connected to the inner ring oil bin 202. The right oil bin 304 is indirectly connected to the inner ring oil bin 202 through the left oil bin 303. The reflux box 3 is set in the middle position of the adjacent tilting pad 8, and the setting position of the reflux box 3 is close to the ball head connecting rod 10. The left oil bin 303 and the right oil bin 304 are respectively located on the left and right sides of the partition 305.

[0038] Solution Description: Refer to Figure 2 It is explained that: the oil injection assembly is connected to the oil inlet pipe 5, and the oil return assembly is connected to the oil return pipe 4. The oil injection assembly and the oil return assembly jointly complete the continuous circulation process of the lubricating oil medium. However, it should be explained that: the position corresponding to the connecting sleeve 6 is used as the inlet of the lubricating oil medium, and the position corresponding to the reflux box 3 is used as the outlet of the lubricating oil medium. The single-piece tilting pad 8 is respectively provided with a group of connecting sleeves 6 and reflux boxes 3. In this way, the load force at the position of the single-piece tilting pad 8 is sensed, specifically, the hydraulic pressure of the lubricating oil medium is detected by the pressure measuring probe 302 in the reflux box 3, as shown below:

[0039] S1: Under ideal conditions, it can be said that the oil injection assembly and the oil return assembly continuously circulate the lubricating oil medium in a stable manner. In this process, the interference factors that may occur in the rotation process of the turbine shaft are not taken into account. Therefore, when the lubricating oil medium flows from the inner ring oil tank 202 into the return box 3, it first enters the left oil tank 303 and gradually enters the right oil tank 304. The lubricating oil medium located in the outer ring oil tank 201 will also be connected and circulated through the oil port in the return box 3. In this process, the hydraulic pressure values ​​detected by the two pressure probes 302 are in an equal and stable state;

[0040] S2: However, during the specific operation, the load borne by each tilting pad 8 changes due to the change in the rotation speed of the turbine shaft, which directly affects the oil film thickness. In this process, it indirectly affects the return of the lubricating oil medium to the reflux box 3. Specifically, if the oil film thickness decreases instantaneously, it means that the load increases, and the speed at which the lubricating oil medium flows into the reflux box 3 increases in a short period of time. In this process, the hydraulic pressure value detected by the pressure probe 302 corresponding to the left oil tank 303 increases;

[0041] S3: Combined with the content of S2, if Figure 6 and Figure 4As shown, it can be understood that: the lubricating oil medium circulates continuously in the clockwise direction, and when a "short-term load increase" occurs at the tilting pad 8 at a certain position, it will also indirectly affect the position of the tilting pad 8 at the next position, thereby possibly causing the problem of instantaneous backflow of the lubricating oil medium, thereby indirectly affecting the hydraulic value detected by the pressure measuring probe 302 in the right oil tank 304.

[0042] It should be noted that the oil leakage gap 301 is used to ensure that the lubricating oil medium completes a closed-loop circulation in the outer ring oil tank 201, and the oil port in the reflux box 3 is for further connecting and flowing the lubricating oil medium.

[0043] Embodiment 3

[0044] This embodiment combines the first embodiment and the second embodiment to propose the following solution description:

[0045] During use, the oil return pipe 4 is connected to an oil return assembly, the oil inlet pipe 5 is connected to an oil injection assembly, and a circulation system is provided between the oil return assembly and the oil injection assembly. The circulation system includes the following control actions during use:

[0046] Control action 1: The lubricating oil medium is circulated in a closed loop in the outer ring oil tank 201 and the inner ring oil tank 202 through the oil injection assembly and the oil return assembly, and the closed loop circulation direction of the lubricating oil medium in the outer ring oil tank 201 is from the left oil tank 303 to the right oil tank 304;

[0047] Control action two: On the basis of control action one, the hydraulic value is obtained through the pressure measuring probe 302 located from the left oil tank 303 to the right oil tank 304 in the reflux box 3, and a load capacity model is established with the hydraulic value. The load capacity corresponding to the position of the tilting pad 8 is obtained in the load capacity model, and the operating data of the oil injection component or the oil return component is reversely controlled with the load capacity of each tilting pad 8.

[0048] Solution description: During use, it is necessary to mark the number of the location where each group of pressure measuring probes 302 is set, such as Figure 4As shown, the tilting pad 8 located directly above the semi-axle body 1 is taken as the starting point, and the pressure probe 302 corresponding to the position is marked as 1. The number of tilting pads 8 in the bearing assembly of the present invention is 6, and then the pressure probes 302 are numbered 1, 2, 3, 4, 5, and 6 respectively. As shown in the content of Example 2, the values ​​detected by the pressure probes 302 corresponding to the left oil tank 303 and the right oil tank 304 are Qa and Qb respectively. During the continuous operation, Qa and Qb in each reflux box 3 are continuously obtained and a corresponding value is established. The corresponding load capacity model is mainly a load capacity model that converts the hydraulic value detected by the pressure probe 302 into the load of the tilting pad 8. It can be understood that: the load of the tilting pad 8 is directly represented by the hydraulic value. In the normal mode of the load capacity model, the speed of the turbine shaft is stable. In the load capacity model, Qa and Qb change in a relatively stable state, that is, the curves formed by Qa and Qb remain horizontal, so that it can be indicated that the load capacity of each tilting pad 8 in the overall bearing assembly is in a relatively balanced state.

[0049] On the contrary, when the speed of the turbine shaft changes, when the load at the tilting pad 8 at one position increases or decreases, Qa changes most directly, and Qb changes in coordination with Qa. For example, when Qa becomes larger, it means that the tilting pad 8 at the corresponding numbered position has an overload problem; on the contrary, when Qa decreases, it means that the tilting pad 8 at the corresponding numbered position has a load reduction problem.

[0050] In this regard, according to the position of the tilting pad 8 where load overload or load reduction occurs, the operating data of the oil injection assembly or the oil return assembly is further controlled. For example, when the tilting pad 8 with number 3 has a load overload problem, the oil inlet pressure of the oil injection assembly corresponding to number 3 needs to be increased, and the oil return assembly corresponding to number 3 needs to reduce the oil return pressure of the lubricating oil medium again; otherwise, the oil inlet pressure of the oil injection assembly corresponding to number 3 needs to be reduced and the oil return pressure of the lubricating oil medium needs to be increased.

[0051] In summary: the thrust bearing and the tilt pad bearing are integrated into one, and the basic principle that the sum of the loads of a single tilt pad in the tilt pad is equal to the total load is utilized. Based on the principle of the tilt pad bearing, during the continuous circulation of the lubricating oil medium, a return box and a connecting sleeve are set according to the circulation direction of the lubricating oil medium and the tilt direction of the tilt pad. Its essence is: for the lubricating oil outlet process, a two-way sensing method is used to detect the hydraulic size of the lubricating oil medium, so as to reversely detect the load capacity of the tilt pad at the corresponding position, and judge the balance capacity by each load capacity, and then limit the movement data of the return oil component or the oil injection component to meet the balance of the load capacity at each tilt pad.

[0052] The above contents are merely examples and explanations of the structure of the present invention. The technicians in this technical field may make various modifications or additions to the specific embodiments described or replace them in a similar manner. As long as they do not deviate from the structure of the invention or exceed the scope defined by the claims, they should all fall within the protection scope of the present invention.

[0053] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0054] The preferred embodiments of the present invention disclosed above are only used to help explain the present invention. The preferred embodiments do not describe all the details in detail, nor do they limit the invention to only specific implementation methods. Obviously, many modifications and changes can be made according to the content of this specification. This specification selects and specifically describes these embodiments in order to better explain the principles and practical applications of the present invention, so that those skilled in the art can understand and use the present invention well. The present invention is limited only by the claims and their full scope and equivalents.

Claims

1. A tilting pad thrust bearing assembly for a steam turbine with a load balancing function, characterized in that: The invention comprises two groups of semi-axle bodies (1) and oil seal sleeves (2), wherein the semi-axle bodies (1) are provided with thrust pads (7) and tilting pads (8), wherein the thrust pads (7) are arranged at one end of the semi-axle bodies (1), and the tilting pads (8) are arranged in a circular shape and at equal intervals along the center point of the semi-axle bodies (1), and the oil seal sleeves (2) are respectively provided with return boxes (3) and connecting sleeves (6) at positions corresponding to the tilting pads (8); An outer ring oil bin (201) is provided between the oil seal sleeve (2) and the semi-axle body (1), an inner ring oil bin (202) is provided between the semi-axle body (1) and the tilting pad (8), the return box (3) and the connecting sleeve (6) penetrate the semi-axle body (1) and are communicated with the interior of the inner ring oil bin (202), and the return box (3) and the connecting sleeve (6) are respectively connected to an oil return pipe (4) and an oil inlet pipe (5), a partition (305) is installed at the center position of the oil return pipe (4), and a left oil bin (303) and a right oil bin (304) are provided inside the oil return pipe (4) through the partition (305), and pressure measuring probes (302) are provided in both the left oil bin (303) and the right oil bin (304); During use, the oil return pipe (4) is connected to an oil return assembly, the oil inlet pipe (5) is connected to an oil injection assembly, and a circulation system is provided between the oil return assembly and the oil injection assembly. The circulation system includes the following control actions during use: Control action one: the lubricating oil medium is circulated in a closed loop in the outer ring oil bin (201) and the inner ring oil bin (202) through the oil injection assembly and the oil return assembly, and the closed loop circulation direction of the lubricating oil medium in the outer ring oil bin (201) is from the left oil bin (303) to the right oil bin (304); Control action 2: Based on control action 1, a hydraulic value is obtained through a pressure measuring probe (302) located from the left oil tank (303) to the right oil tank (304) in the reflux box (3), a load capacity model is established based on the hydraulic value, and the load capacity corresponding to the position of the tilting pad (8) is obtained in the load capacity model, and the operating data of the oil injection component or the oil return component is reversely controlled based on the load capacity of each tilting pad (8).

2. The tilting pad thrust bearing assembly for a steam turbine with a load balancing function according to claim 1, characterized in that: A ball head connecting rod (10) is connected to the inner wall position of the semi-axle body (1) corresponding to the tilting pad (8), and the bottom end position of the ball head connecting rod (10) is movably connected to the tilting pad (8).

3. The tilting pad thrust bearing assembly for a steam turbine with a load balancing function according to claim 2, characterized in that: The setting position of the ball head connecting rod (10) is close to the setting position of the return box (3), and a connecting spring (9) is installed in the internal position of the connecting sleeve (6), and the end position of the connecting spring (9) is connected to the tilting pad (8).

4. The tilting pad thrust bearing assembly for a steam turbine with a load balancing function according to claim 1, characterized in that: The width of the reflux box (3) is equal to the internal width of the oil seal sleeve (2), and oil leakage notches (301) are provided on both sides of the reflux box (3). An oil port is provided on the inner wall of the reflux box (3) corresponding to the outer ring oil bin (201).

5. The tilting pad thrust bearing assembly for a steam turbine with a load balancing function according to claim 1, characterized in that: A gap is provided between the top of the partition (305) and the top position inside the reflux box (3); the left oil bin (303) and the inner ring oil bin (202) are directly connected; and the right oil bin (304) and the inner ring oil bin (202) are indirectly connected via the left oil bin (303).

6. The tilting pad thrust bearing assembly for a steam turbine with load balancing function according to claim 5, characterized in that: The reflux box (3) is arranged at the middle position of the adjacent tilting pad (8), and the reflux box (3) is arranged close to the ball head connecting rod (10), and the left oil bin (303) and the right oil bin (304) are respectively located at the left side and the right side of the partition (305).

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