Centrifugal compressor with balancing function

Abstract

The present invention relates to a centrifugal compressor with a balancing function, comprising a connecting component and a shell fixed to the connecting component, wherein a compressor rotor coaxially arranged with the shell is arranged in the shell, and a plurality of key groups are arranged between the connecting component and the shell along the circumferential direction of the shell, wherein each key group comprises at least one key, and the keys in the key group can limit the expansion or contraction direction of the shell to the radial direction of the shell and keep the central axis of the shell unchanged during the expansion or contraction process. In the present invention, the central axis of the shell remains basically unchanged, thereby making the concentricity of the compressor rotor and the shell always in a good state under the operating condition, thereby improving the safety of the unit operation, and at the same time being conducive to controlling the uniformity of the gap of the sealing part in the compressor, thereby improving the operating efficiency of the unit.

Description

Technical Field

[0001] The invention relates to a centrifugal compressor, in particular to a centrifugal compressor with a balancing function. Background Art

[0002] The casing (sometimes also called the volute) is an essential key component of the centrifugal compressor. It is mainly used to contain the working medium (gas) of the compressor and send it out of the compressor in a certain direction. Compared with rotating parts such as the impeller and the main shaft, the casing is always in a stationary state during operation and is one of the stator parts of the compressor. The compressor casing is usually installed on the compressor base or support frame by bolts. On some types of compressors, the casing is installed on the bearing seat or gear box by bolts.

[0003] Since centrifugal compressors are generally assembled for the first time in the factory and assembled on site after routine maintenance, their installation temperature is generally the ambient temperature, that is, within the range of -40℃ to +40℃. However, the operating conditions of the compressor vary greatly due to different unit parameters. Some medium gas temperatures are nearly 100 degrees Celsius and hundreds of degrees Celsius (or as low as hundreds of degrees Celsius below zero), so there is inevitably a certain temperature difference between the installation state and the use state. The compressor housing is in direct contact with the gas medium, and its temperature field is directly affected by the temperature of the working medium. If the expansion direction of the compressor housing is not limited, then when the housing undergoes thermal expansion (or low-temperature contraction) (especially some high-temperature and low-temperature units), the expansion of the housing is arbitrary, which will cause the center of the housing to shift, and then cause uncontrollable changes in the concentricity of the rotor components and the housing and the components installed on the housing. In mild cases, the sealing components will be worn or fail, and in severe cases, the moving and static parts will collide, causing safety accidents.

[0004] At present, the common practice is to design locating pins or circumferential stoppers between the shell and the connecting parts, but both methods have defects. The original intention of the locating pin design was to define the center of the shell by the tight fit between the pin and the pin hole. However, for some high-temperature or low-temperature units, the expansion of the shell is inevitable and cannot be completely restricted, so there have been accidents on site where the locating pins were cut off after the high-temperature unit expanded. There is a contradiction between setting the stoppers in the circumferential direction in design and practice. For high-temperature / low-temperature units, due to the large expansion difference, the gap of the stoppers needs to be relatively large, which loses control of the center of the shell. Therefore, the compressor will run well for the first time, but once it stops, the center cannot be reset and the concentricity will have a large deviation. Summary of the invention

[0005] In order to overcome the above-mentioned defects, the present invention provides a centrifugal compressor with a balancing function, which can limit the expansion direction of the shell so that the center of the shell remains basically unchanged, thereby maintaining the concentricity of the shell and the compressor rotor in a good state at all times, thereby improving the operating safety of the unit.

[0006] The technical solution adopted by the present invention to solve its technical problem is:

[0007] A centrifugal compressor with a balancing function comprises a connecting component and a shell fixed to the connecting component, wherein a compressor rotor coaxially arranged with the shell is arranged in the shell, and a plurality of key groups are arranged between the connecting component and the shell along the circumferential direction of the shell, each key group comprises at least one key, and the keys in the key group can limit the expansion or contraction direction of the shell to the radial direction of the shell and keep the central axis of the shell unchanged during the expansion or contraction process.

[0008] Preferably, a part of the key is fixed to the shell, a keyway matching the key is provided on the connecting component, and the other part of the key is tightly inserted in the keyway; or a part of the key is fixed to the connecting component, a keyway matching the key is provided on the shell, and the other part of the key is tightly inserted in the keyway, and the key is fastened to the shell or the connecting component by at least two locating pins or one screw.

[0009] Preferably, at least three key groups are provided on the shell, and the keys in the same key group are located in the same circumferential direction of the shell, while each key group is located in a different circumferential direction of the shell.

[0010] Preferably, the key is an ordinary flat key, which is vertically installed in the shell and the connecting component. The horizontal cross-section of the flat key is an oblong structure. The flat key has a first upper surface and a first lower surface parallel to each other, and a first front surface and a first rear surface parallel to each other. The first upper surface is arranged perpendicular to the first front surface. When installed, the first upper surface is attached to the shell, the first lower surface is attached to the connecting component, and the first front surface and the first rear surface are both attached to the shell and the connecting component at the same time, wherein the first front surface and the first rear surface are two corresponding working surfaces.

[0011] Preferably, the key is a special-shaped key, which includes an upper combining portion and a lower combining portion that are connected to each other and staggered, and the horizontal surface between the upper combining portion and the lower combining portion is called a combining surface, and the horizontal cross-sections of the upper combining portion and the lower combining portion are both oblong structures, the upper combining portion includes a second upper surface and a combining surface that are parallel to each other, a second front surface and a second rear surface that are parallel to each other, and the combining surface is arranged perpendicular to the second front surface, the lower combining portion includes a combining surface and a second lower surface that are parallel to each other, a third front surface and a third rear surface that are parallel to each other, and the combining surface is arranged perpendicular to the third front surface, when installed, the upper combining portion is vertically installed in the shell, and the lower combining portion is vertically installed in the connecting component, wherein the second front surface and the second rear surface are two opposite working surfaces, and the third front surface and the fourth front surface are two opposite working surfaces.

[0012] Preferably, the center lines between two opposite working surfaces of each key in the same key group and parallel to the working surfaces are on the same straight line, and the extension lines of the straight lines intersect with the central axis of the shell and are perpendicular to each other. The straight lines are called concentric lines, wherein the angles between the concentric lines in any key group and the concentric lines of another key group are 90° or 180°, and there are both angles of 90° and 180° between the concentric lines.

[0013] Preferably, the shell and the connecting component are fixedly connected by a plurality of fasteners, and the plurality of fasteners are evenly arranged along the circumferential direction of the shell. The connecting component is a compressor base, a compressor support frame, a bearing seat or a gear box.

[0014] Preferably, the connecting component is a gear box, which includes a lower box body and an upper box body, the upper box body is fixed to the upper part of the lower box body by fastening bolts, and the shell is fixed to one side of the lower box body by fastening bolts.

[0015] Preferably, three key groups are provided between the shell and the lower box, including a first key group, a second key group and a third key group, and the keys in the same key group are in the same circumferential direction of the shell, while the first key group, the second key group and the third key group are in different circumferential directions of the shell.

[0016] Preferably, the first key group, the second key group and the third key group are each equipped with a key, the keys in the first key group and the second key group are respectively located on horizontal planes on both sides of the central axis of the shell, the central axis of the shell and the center lines of the keys in the first key group and the second key group in the shell are both located in the horizontal plane, the key in the third key group is arranged on a vertical plane perpendicular to the horizontal plane and is located below the central axis of the shell, and the central axis of the shell and the center line of the key in the third key group in the shell are both located on the vertical plane.

[0017] The beneficial effects of the present invention are as follows: the present invention includes a connecting component and a shell fixed to the connecting component, and a plurality of key groups are designed at the connection between the shell and the connecting component, the keys in each key group are designed side by side, and the extension line of the line connecting the center points of each group of keys in the shell intersects with the central axis of the shell and is perpendicular to each other, so that when a compressor installed at normal temperature is operated at high or low temperature, its shell can only expand or contract along the radial direction of the shell, so the central axis of the shell remains basically unchanged, thereby making the concentricity of the compressor rotor and the shell always in a good state under the operating conditions, thereby improving the safety of the unit operation, and at the same time being conducive to controlling the uniformity of the gap of the sealing part in the compressor, improving the operating efficiency of the unit, and the deformation is reversible, which is of great significance to the safe and efficient operation of the unit. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 A simplified diagram of the present invention;

[0019] Figure 2 is a simplified diagram of the connecting components in the present invention;

[0020] Figure 3 It is a front view of the flat key in the present invention;

[0021] Figure 4 It is a left side view of the flat key in the present invention;

[0022] Figure 5 is a top view of the flat key in the present invention;

[0023] Figure 6 It is a front view of the special-shaped key in the present invention;

[0024] Figure 7 It is a left view of the special-shaped key in the present invention;

[0025] Figure 8 is a top view of the special-shaped key in the present invention;

[0026] In the figure: 10-shell, 11-center axis, 20-connecting part, 21-fastener, 22-keyway, 30-flat key, 31-first upper surface, 32-first lower surface, 33-first front surface, 34-first rear surface, 40-special-shaped key, 41-upper connecting part, 42-second upper surface, 43-connecting surface, 44-second front surface, 45-second rear surface, 46-lower connecting part, 47-third lower surface, 48-third front surface, 49-third rear surface. DETAILED DESCRIPTION

[0027] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0028] It should be noted that the terms "first", "second", etc. in the specification and claims of the present application and the above-mentioned drawings are used to distinguish similar objects, and are not necessarily used to describe a specific order or sequence. It should be understood that the data used in this way can be interchangeable where appropriate, so that the embodiments of the present application described herein can be implemented in an order other than those illustrated or described herein, for example. In addition, the terms "including" and "having" and any of their variations are intended to cover non-exclusive inclusions, for example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units that are clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices.

[0029] For ease of description, spatially relative terms such as "above", "above", "on the upper surface of", "above", etc. may be used here to describe the spatial positional relationship between a device or feature and other devices or features as shown in the figure. It should be understood that spatially relative terms are intended to include different orientations of the device in use or operation in addition to the orientation described in the figure. For example, if the device in the accompanying drawings is inverted, the device described as "above other devices or structures" or "above other devices or structures" will be positioned as "below other devices or structures" or "below other devices or structures". Thus, the exemplary term "above" can include both "above" and "below". The device can also be positioned in other different ways (rotated 90 degrees or in other orientations), and the spatially relative descriptions used here are interpreted accordingly.

[0030] Example: Figure 1-2As shown, a centrifugal compressor with a balancing function includes a connecting component 20 and a shell 10 fixed to the connecting component, wherein a compressor rotor coaxially arranged with the shell is arranged in the shell 10, and a plurality of key groups are arranged between the connecting component 20 and the shell 10 along the circumferential direction of the shell, each key group includes at least one key, and the keys in the key group can limit the expansion or contraction direction of the shell 10 to the radial direction of the shell and keep the central axis 11 of the shell unchanged during the expansion or contraction process. The present invention improves the traditional centrifugal compressor. Specifically, a plurality of key groups are designed at the connection between the shell 10 and the connecting component 20. The keys in each key group are designed side by side, and the extension line of the center point connection line of each group of keys intersects with the central axis of the shell and is perpendicular to each other, so that when the compressor installed at normal temperature is operated at high or low temperature, its shell 10 can only expand or contract along the radial direction of the shell, so the central axis 11 of the shell remains basically unchanged, thereby making the concentricity of the compressor rotor and the shell always in good condition under the operating conditions, thereby improving the safety of the unit operation, and at the same time being conducive to controlling the uniformity of the gap of the sealing part in the compressor, thereby improving the operating efficiency of the unit.

[0031] A part of the key is fixed to the housing 10, a keyway 22 matching the key is provided on the connecting part 20, and the other part of the key is inserted into the keyway; or a part of the key is fixed to the connecting part 20, a keyway 22 matching the key is provided on the housing 10, and the other part of the key is inserted into the keyway, and the key is fastened to the housing 10 or the connecting part 20 by at least two locating pins or one screw. The key is made of metal material, a part of the key is fixed to the housing 10 or the connecting part 20, and the other part is inserted into the keyway 22 of the connecting part 20 or the housing 10, so the key only limits the expansion direction of the housing 10, which is different from the locating pin installed in the traditional technology. The locating pin is to completely limit the expansion of the housing through the tight fit between the pin and the pin hole, and then limit the center of the housing. However, for some high-temperature or low-temperature units, the expansion of the housing is inevitable and cannot be completely limited, so the accident of the locating pin being cut off occurs. The present invention guides the disordered expansion of the shell into orderly expansion through the provided keys, that is, the shell expands only radially, but does not limit the expansion amount of the shell. Therefore, the present invention ingeniously ensures that the shell releases expansion energy without changing the position of the central axis of the shell.

[0032] At least three key groups are provided on the housing 10, and the keys in the same key group are located in the same circumferential direction of the housing, while each key group is located in a different circumferential direction of the housing. Furthermore, the keys in the same key group are located on the same radius of the housing, and the radius is perpendicular to the central axis of the housing.

[0033] like Figure 3-5As shown, the key is an ordinary flat key 30, which is vertically installed in the shell 10 and the connecting component 20. The horizontal cross-section of the flat key 30 is an oblong structure. The flat key 30 has a first upper surface 31 and a first lower surface 32 that are parallel to each other, and a first front surface 33 and a first rear surface 34 that are parallel to each other. The first upper surface 31 and the first front surface 33 are arranged vertically. During installation, the first upper surface 31 is attached to the shell 10, the first lower surface 32 is attached to the connecting component 20, and the first front surface 33 and the first rear surface 34 are both attached to the shell and the connecting component at the same time, wherein the first front surface 33 and the first rear surface 34 are two corresponding working surfaces. Before installation, the operator will preset the key slots 22 on the shell and the connecting component. If the two key slots 22 are aligned during installation, an ordinary flat key can be used; as shown in FIG. Figure 5 As shown, the distance between the first front surface 33 and the first rear surface 34 is defined as the key width B, and the width of the key slot 22 is slightly larger than the key width B to ensure that the key is tightly inserted into the key slot in the width direction. Generally, the width of the key slot 22 is 20-50 μm larger than the key width.

[0034] like Figure 6-8 As shown, the key is a special-shaped key 40, which includes an upper combining portion 41 and a lower combining portion 46 that are connected to each other and staggered, and the horizontal surface between the upper combining portion 41 and the lower combining portion 46 is called a combining surface 43. The horizontal cross-sections of the upper combining portion 41 and the lower combining portion 46 are both oblong structures. The upper combining portion 41 includes a second upper surface 42 and a combining surface 43 that are parallel to each other, a second front surface 44 and a second rear surface 45 that are parallel to each other, and the combining surface 43 is arranged perpendicular to the second front surface 44. The lower combining portion 46 includes a combining surface 43 and a second lower surface 47 that are parallel to each other, a third front surface 48 and a third rear surface 49 that are parallel to each other, and the combining surface 43 is arranged perpendicular to the third front surface 48. When installed, the upper combining portion 41 is vertically installed in the shell 10, and the lower combining portion 46 is vertically installed in the connecting component 20, wherein the second front surface 44 and the second rear surface 45 are two opposite working surfaces, and the third front surface 48 and the fourth front surface 49 are two opposite working surfaces. If the two keyways 22 are staggered during installation, a special-shaped key 40 is selected, such as Figure 7As shown, the distance between the second front surface 44 and the second rear surface 45 is defined as the key width B1, and the distance between the third front surface 48 and the third rear surface 49 is defined as the key width B2, B1 and B2 can be the same or different, wherein the distance between the second front surface 44 and the third front surface 48 depends on the offset distance of the two keyways; the upper connecting portion 41 and the lower connecting portion 46 in the special-shaped key partially overlap and the two have the same structure, the central axes are parallel to each other, and the four working surfaces are also parallel to each other, thereby ensuring that the shell is only deformed in the radial direction. The setting of the special-shaped key 40 cleverly solves the problem of compressor installation and is very practical.

[0035] The center lines between the two opposite working surfaces of each key in the same key group and parallel to the working surfaces are on the same straight line, and the extension of the straight line intersects with the central axis 11 of the shell and is perpendicular to each other. The straight line is called a concentric line, wherein the angle between the concentric line in any key group and the concentric line of another key group is 90° or 180°, and there are both 90° and 180° angles between the concentric lines. Arranging multiple key groups in the above manner further ensures that the shell is only deformed in the radial direction and the central axis after deformation remains unchanged. More preferably, four key groups are provided on the shell, and two of the key groups are respectively provided on the horizontal planes on the left and right sides of the central axis of the shell 10, and the other two key groups are respectively provided on the vertical planes on the upper and lower sides of the central axis of the shell 10. It is also possible to design two key groups in the horizontal direction and one key group in the vertical direction; or design one key group in the horizontal direction and two key groups in the vertical direction. Such a design facilitates the accurate positioning and installation of the key groups in actual operation; of course, structures forming other angles can also be used between the key groups.

[0036] The shell 10 and the connecting component 20 are fixedly connected by a plurality of fasteners 21, and the plurality of fasteners 21 are evenly arranged along the circumferential direction of the shell 10. The connecting component 20 is a compressor base, a compressor support frame, a bearing seat or a gear box, and the fasteners 21 are fastening bolts or clamps.

[0037] In this embodiment, the connecting component 20 is a gear box, which includes a lower box and an upper box, the upper box is fixed to the upper part of the lower box by fastening bolts, and the housing 10 is fixed to one side of the lower box by fastening bolts. Three key groups are arranged between the housing 10 and the lower box, including a first key group, a second key group and a third key group, and the keys in the same key group are in the same circumferential direction of the housing, while the first key group, the second key group and the third key group are in different circumferential directions of the housing.

[0038] The first key group, the second key group and the third key group are each provided with a key, and the keys in the first key group and the second key group are respectively located on the horizontal planes on both sides of the central axis of the shell, the central axis of the shell and the center lines of the keys in the first key group and the second key group in the shell are all located in the horizontal plane, and the keys in the third key group are arranged on a vertical plane perpendicular to the horizontal plane and below the central axis of the shell, and the central axis of the shell 10 and the center line of the keys in the third key group in the shell are all located on the vertical plane. This is a preferred embodiment of the present invention, in which the shell is fixed to the lower case of the gearbox, the upper case of the gearbox can be removed, and three key groups are arranged between the lower case of the gearbox and the shell. For ease of installation, the first and second key groups are arranged on the horizontal plane in the exact center of the gearbox, and the third key group is arranged on the vertical plane in the exact center of the gearbox, and the central axis of the gearbox is located at the intersection of the horizontal plane and the vertical plane.

[0039] Practical application of the present invention:

[0040] Case 1: The centrifugal compressor designed and manufactured by the inventor for a domestic coal chemical enterprise has a medium operating temperature of about 210°C and a working pressure of about 4.0 MP(G). The medium is mainly dangerous media such as carbon monoxide and hydrogen. The compressor housing is installed on the gearbox, and special-shaped keys are arranged between the gearbox and the housing. Two of the special-shaped keys are arranged in the horizontal direction, and one is arranged in the vertical direction. All are installed on the housing, and keyways are opened at the corresponding parts of the gearbox. The unit was assembled in a cold state in the inventor's factory and sent to the site after the test run. During the operation of the high-temperature process gas on site, all components operated well and have been running smoothly to this day. Equipment from other manufacturers in the same system often experience housing displacement and seal wear after hot operation shutdown due to the lack of the key to limit the expansion direction, which causes great psychological pressure on the operating personnel and increases the maintenance workload;

[0041] Case 2: The water vapor compressor designed and manufactured by the inventor for a domestic chemical enterprise has a medium operating temperature of up to 530°C. The unit housing is installed on the base support plate, and a special-shaped key is set between the housing and the support plate. During the unit startup process, the staff clearly observed that the housing expanded about 2mm toward the periphery along the key width direction of the special-shaped key during the heating process, and the original design intention of the present invention was realized.

[0042] It should be noted that, for those skilled in the art, several modifications and improvements can be made without departing from the concept of the present invention, and these modifications and improvements all belong to the protection scope of the present invention. Therefore, the protection scope of the patent of the present invention shall be subject to the attached claims.

Claims

1. A centrifugal compressor with balancing function, characterized in that: The invention comprises a connecting component (20) and a shell (10) fixed to the connecting component, wherein a compressor rotor coaxially arranged with the shell is arranged in the shell (10), and a plurality of key groups are arranged between the connecting component (20) and the shell (10) along the circumferential direction of the shell, wherein each key group comprises at least one key, and the keys in the key group can limit the expansion or contraction direction of the shell (10) to the radial direction of the shell and keep the central axis (11) of the shell unchanged during the expansion or contraction process, and the connecting component (20) is a compressor base, a compressor support frame, a bearing seat or a gear box; A portion of the key is fixed to the housing (10), a keyway (22) matching the key is provided on the connecting component (20), and another portion of the key is inserted tightly into the keyway; or a portion of the key is fixed to the connecting component (20), a keyway (22) matching the key is provided on the housing (10), and another portion of the key is inserted tightly into the keyway, and the key is fastened to the housing (10) or the connecting component (20) by at least two positioning pins or one screw; The housing (10) is provided with at least three key groups, and the keys in the same key group are located in the same circumferential direction of the housing, while each key group is located in a different circumferential direction of the housing; The key is a common flat key (30), which is vertically installed in the housing (10) and the connecting component (20). The horizontal cross section of the common flat key (30) is an oblong structure. The common flat key (30) has a first upper surface (31) and a first lower surface (32) which are parallel to each other, and a first front surface (33) and a first rear surface (34) which are parallel to each other. The first upper surface (31) and the first front surface (33) are arranged vertically. When installed, the first upper surface (31) is attached to the housing (10), the first lower surface (32) is attached to the connecting component (20), and the first front surface (33) and the first rear surface (34) are both attached to the housing and the connecting component at the same time, wherein the first front surface (33) and the first rear surface (34) are two corresponding working surfaces. Alternatively, the key is a special-shaped key (40), the special-shaped key (40) comprises an upper connecting portion (41) and a lower connecting portion (46) which are connected to each other and staggered, and the horizontal plane between the upper connecting portion (41) and the lower connecting portion (46) is called a connecting surface (43), the horizontal cross-sections of the upper connecting portion (41) and the lower connecting portion (46) are both oblong structures, the upper connecting portion (41) comprises a second upper surface (42) and a connecting surface (43) which are parallel to each other, a second front surface (44) and a second rear surface (45) which are parallel to each other, and the connecting surface (43) and the second front surface (44) are parallel to each other. The upper connecting portion (41) and the lower connecting portion (46) are arranged vertically, the lower connecting portion (46) comprises a connecting surface (43) and a second lower surface (47) which are parallel to each other, a third front surface (48) and a third rear surface (49) which are parallel to each other, and the connecting surface (43) and the third front surface (48) are arranged vertically. When installed, the upper connecting portion (41) is vertically installed in the housing (10), and the lower connecting portion (46) is vertically installed in the connecting component (20), wherein the second front surface (44) and the second rear surface (45) are two opposite working surfaces, and the third front surface (48) and the third rear surface (49) are two opposite working surfaces; The center lines between two opposite working surfaces of each key in the same key group and parallel to the working surfaces are on the same straight line, and the extension lines of the straight lines intersect with the central axis (11) of the shell and are perpendicular to each other. The straight lines are called concentric lines, wherein the angle between the concentric lines in any key group and the concentric lines of another key group is 90° or 180°, and there are both angles of 90° and 180° between the concentric lines.

2. The centrifugal compressor with balancing function according to claim 1, characterized in that: The housing (10) and the connecting component (20) are fixedly connected via a plurality of fasteners (21), and the plurality of fasteners (21) are evenly arranged along the circumferential direction of the housing (10).

3. The centrifugal compressor with balancing function according to claim 2, characterized in that: The connecting component (20) is a gear box, which comprises a lower box body and an upper box body, wherein the upper box body is fixed to the upper part of the lower box body by fastening bolts, and the housing (10) is fixed to one side of the lower box body by fastening bolts.

4. The centrifugal compressor with balancing function according to claim 3, characterized in that: Three key groups are arranged between the shell (10) and the lower box, including a first key group, a second key group and a third key group, and the keys in the same key group are located in the same circumferential direction of the shell, while the first key group, the second key group and the third key group are located in different circumferential directions of the shell.

5. The centrifugal compressor with balancing function according to claim 4, characterized in that: The first key group, the second key group and the third key group are each provided with a key, the keys in the first key group and the second key group are respectively located on horizontal planes on both sides of the central axis of the shell, the central axis of the shell and the center lines of the keys in the first key group and the second key group in the shell are both located in the horizontal plane, the key in the third key group is arranged on a vertical plane perpendicular to the horizontal plane and is located below the central axis of the shell, and the central axis of the shell (10) and the center line of the key in the third key group in the shell are both located on the vertical plane.

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