Method and device for selecting compression ratio adjusting shims of diesel engine

Abstract

The invention relates to the technical field of diesel engines, and particularly discloses a method and device for selecting a compression ratio adjusting gasket of a diesel engine. The selection method comprises the following steps that the first distance from the fire face of the air cylinder cover to the top face of the piston is obtained; before the cylinder cover is installed, measuring a second distance from the firepower surface of the cylinder cover to the connecting bottom surface of the cylinder cover; placing the piston to an upper dead center position, and obtaining a third distance from an adjusting gasket mounting surface of the cylinder sleeve to the top surface of the piston; and calculating the thickness of the adjusting shim based on the first distance, the second distance and the third distance. According to the method, measurement can be carried out before assembly, after calculation, the correct adjusting shim is selected and assembled, and then assembly is directly carried out, so that pre-assembly is avoided, and the assembly efficiency is improved.

Description

Technical Field

[0001] The invention relates to the technical field of diesel engines, and in particular to a method and a device for selecting a compression ratio adjusting gasket for a diesel engine. Background Art

[0002] Diesel engines are compression ignition engines. The ratio of the total cylinder volume to the combustion chamber volume is called the compression ratio, which indicates the degree to which the gas is compressed. When the compression stroke is near the end, the diesel injected into the cylinder burns by absorbing the heat of the compressed high-temperature, high-pressure air in the cylinder. In order to ensure the combustion quality of the diesel engine, the designed compression ratio must be guaranteed when assembling the diesel engine. The piston stroke of the diesel engine is fixed, and the volume of the combustion chamber within the piston stroke range remains unchanged. Adjusting the compression ratio is converted to adjusting the volume of the combustion chamber above the piston when the piston is at the top dead center, that is, excluding the volume of the combustion chamber within the piston stroke range. Since the cylinder diameter is fixed and the bottom area remains unchanged, adjusting the compression ratio is directly reflected in adjusting the distance from the top of the piston to the fire surface of the cylinder head. The distance from the fire surface of the cylinder head to the top of the piston can be achieved by setting adjustment gaskets of different thicknesses between the cylinder head and the cylinder body. These adjustment gaskets are generally made of metal and must have good high temperature and high pressure resistance to adapt to the harsh environment when the diesel engine is working. When the compression ratio needs to be precisely adjusted during the production, maintenance and modification of diesel engines, adjustment gaskets are used to ensure the performance of the diesel engine. When the thickness of the adjustment gasket increases, the volume of the combustion chamber increases, and the compression ratio of the diesel engine decreases; conversely, when the thickness of the adjustment gasket decreases, the volume of the combustion chamber decreases, and the compression ratio of the diesel engine increases.

[0003] At present, the lead pressing method is used to select the appropriate thickness of the adjustment gasket when assembling the diesel engine, that is, after assembly, the lead block is placed in the combustion chamber, and after cranking, the piston and the cylinder head press the lead block to deform, and after taking out the lead block, the distance between the two parallel surfaces of the lead block is measured, which is the distance from the piston top to the fire surface. The method mainly includes the following steps: S110, arbitrarily select a compression ratio gasket of a certain thickness; S120, pre-installed compression ratio gasket and cylinder head; S130, after assembly, extend the lead block from the injector mounting hole into the combustion chamber; S140, cranking the piston to make it pass the top dead center; S150, take out the lead block and measure the distance between the two parallel surfaces. This distance is the distance from the piston top to the cylinder head fire surface; S160, calculating the thickness of the diesel engine compression ratio adjustment gasket according to the difference between the distance and the required distance.

[0004] When the lead pressing method is used to select the appropriate thickness of the adjustment gasket, the distance from the piston top to the cylinder head fire surface is reflected after installation. It cannot be measured before installation and needs to be pre-installed. Therefore, the gasket cannot be selected before installation and needs to be pre-installed and measured, which is inefficient and affects the production rhythm.

[0005] Therefore, how to conveniently and efficiently select an adjustment gasket of appropriate thickness has become a technical problem to be solved urgently in the field of diesel engine technology. Summary of the invention

[0006] In view of the shortcomings of the prior art, the main purpose of the present invention is to provide a method and device for selecting a diesel engine compression ratio adjustment gasket. The method can measure before assembly, select the correct adjustment gasket after calculation, and then directly assemble, avoiding pre-assembly and improving assembly efficiency.

[0007] In order to solve at least one of the above technical problems, the present invention adopts the following technical solution: According to one aspect of the present invention, a method for selecting a compression ratio adjusting gasket for a diesel engine is provided, comprising the following steps: obtaining a first distance from a firing surface of a cylinder head to a top surface of a piston; before installing the cylinder head, measuring a second distance from the firing surface of the cylinder head to a connecting bottom surface of the cylinder head; moving the piston to a top dead center position, and obtaining a third distance from an adjusting gasket mounting surface of a cylinder liner to a top surface of the piston; and calculating a thickness of the adjusting gasket based on the first distance, the second distance, and the third distance.

[0008] According to another aspect of the present invention, a device for selecting a compression ratio adjusting gasket for a diesel engine is provided, comprising: a measuring frame, at least one end face of which is arranged against the adjusting gasket mounting surface of the cylinder liner during a measuring process; a moving rod mechanism, connected to the measuring frame and at least a portion of which is arranged against the top surface of the piston during a measuring process, wherein the moving rod mechanism is movable relative to the measuring frame along the stroke direction of the piston; and a measuring mechanism, connected to the measuring frame and arranged to measure the displacement of the moving rod mechanism relative to the measuring frame, so as to obtain the distance from the adjusting gasket mounting surface of the cylinder liner to the top surface of the piston when the piston disc is in the top dead center position.

[0009] According to one embodiment of the present invention, the measuring frame includes: a main body, which is arranged to radially span the cylinder liner; a first extension portion, which extends vertically downward from both ends of the main body, and during the measurement process, the first extension portion is arranged away from the end surface of the main body and abuts against the adjustment gasket mounting surface of the cylinder liner; and a second extension portion, which extends vertically upward from the middle part of the main body and is arranged to be connected to the moving rod mechanism and the measuring mechanism.

[0010] According to one embodiment of the present invention, the moving rod mechanism includes: a lever, mounted to the second extension portion and movable along the second extension portion; a measuring rod, connected to the middle portion of the lever and extending upward parallel to the second extension portion; and a measuring contact, connected to both ends of the lever and extending downward parallel to the second extension portion; wherein, through holes are provided at both ends of the main body portion to allow the measuring contact to pass through, and the measuring contact is arranged away from the end surface of the lever and against the top surface of the piston during the measuring process.

[0011] According to one embodiment of the present invention, a through hole is provided in the middle of the main body, and the second extension portion passes through the through hole and is welded and fixed to the main body; the second extension portion is provided with a cavity inside thereof along the axial direction to accommodate the measuring rod and allow it to move along the second extension portion; the second extension portion is provided with a radially through groove to allow the lever to pass through laterally.

[0012] According to an embodiment of the present invention, the measuring rod is pivotally connected to the lever via a first axis; and the measuring contact is pivotally connected to the lever via a second axis.

[0013] According to one embodiment of the present invention, the measuring mechanism includes: a dial base, fixedly connected to the second extension portion; an elastic sleeve, mounted on the dial base; and a dial indicator, detachably clamped and fixed by the elastic sleeve; wherein, in the installed state, the contact of the dial indicator passes through the dial base and the elastic sleeve and abuts against the top end of the measuring rod.

[0014] According to an embodiment of the present invention, the moving rod mechanism further includes: a spring, one end of which is connected to the measuring rod, and the other end of which is connected to the table base or the second extension portion.

[0015] According to an embodiment of the present invention, the measuring frame further comprises: a guide sleeve, which is circumferentially installed between the through hole of the main body and the measuring contact and limits the radial displacement of the measuring contact.

[0016] According to an embodiment of the present invention, the selection device further comprises: a plurality of process pads of different thicknesses, which are pressed against between the top surface of the piston and the moving rod mechanism during the measurement process.

[0017] By adopting the above technical solution, the present invention has at least one of the following advantages compared with the prior art: (1) According to the method of the present invention, measurement can be performed before assembly, and the correct adjustment gasket can be selected after calculation and then assembly can be performed directly; (2) The device according to the present invention is simple and convenient to operate, and can directly obtain the distance from the mounting surface of the adjusting gasket of the cylinder liner to the top surface of the piston; (3) The device according to the present invention can adapt to different compression ratios while ensuring the accuracy of measured data by using a plurality of process pads of different thicknesses. 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 This is a schematic diagram of the diesel engine cylinder head, adjusting gasket, piston and cylinder liner after installation; Figure 2 A flowchart of a method for selecting a diesel engine compression ratio adjusting gasket according to an embodiment of the present invention; Figure 3 A front view of a device for selecting a compression ratio adjusting gasket for a diesel engine according to an embodiment of the present invention; Figure 4 A top view of a device for selecting a compression ratio adjusting gasket for a diesel engine according to an embodiment of the present invention; Figure 5 A cross-sectional view of a device for selecting a compression ratio adjusting gasket for a diesel engine according to an embodiment of the present invention; Figure 6 A diagram showing the use status of a device for selecting a compression ratio adjusting gasket for a diesel engine according to an embodiment of the present invention; Figure 7 The present invention is a diagram showing the use status of a device for selecting a compression ratio adjusting gasket for a diesel engine according to another embodiment of the present invention.

[0020] In the accompanying drawings, 100, cylinder head, 110, fire surface, 120, connection bottom surface; 200, piston, 210, top surface; 300, cylinder sleeve, 310, upper end surface, 320, adjusting gasket mounting surface; 400, adjust the gasket; 500. Selection device, 510. Measuring frame, 511. Main body, 512. First extension part, 513. Second extension part, 514. Guide sleeve, 520. Moving rod mechanism, 521. Lever, 522. Measuring rod, 523. Measuring contact, 524. First axis, 525. Second axis, 526. Spring, 530. Measuring mechanism, 531. Table base, 532. Elastic sleeve, 533. Dial indicator, 540. Process pad. DETAILED DESCRIPTION

[0021] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the embodiments of the present invention are further described in detail below in combination with specific embodiments and with reference to the accompanying drawings.

[0022] It should be understood that the embodiments of the present invention shown in the exemplary embodiments are only illustrative. Although only a few embodiments are described in detail in the present invention, it is easy for those skilled in the art to appreciate that multiple modifications are feasible without actually departing from the teaching of the subject matter of the present invention. Accordingly, all such modifications should be included within the scope of the present invention. Without departing from the gist of the present invention, other replacements, modifications, changes and deletions may be made to the design, operating conditions and parameters of the following exemplary embodiments.

[0023] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by technicians in the technical field of the present invention; the terms used in this specification are only for the purpose of describing specific embodiments and are not intended to limit the present invention. For example, the directions or positions indicated by the terms "length", "width", "up", "down", "left", "right", "front", "back", "vertical", "horizontal", "top", "bottom", "inside", "outside", etc. are based on the directions or positions shown in the drawings, which are only for the convenience of description and should not be understood as limitations on the present technical solution.

[0024] It should be noted that all expressions using "first" and "second" in the embodiments of the present invention are for distinguishing two non-identical entities with the same name or non-identical parameters. It can be seen that "first" and "second" are only for the convenience of expression and should not be understood as limitations on the embodiments of the present invention. The subsequent embodiments will not explain this one by one.

[0025] See also Figure 1 The schematic diagram of the diesel engine cylinder head, adjustment gasket, piston, and cylinder liner after installation is shown. The first distance H from the fire surface 110 of the cylinder head 100 to the top surface 210 of the piston 200 can be achieved by arranging adjustment gaskets 400 of different thicknesses between the upper end surface 310 of the cylinder liner 300 and the connecting bottom surface 120 of the cylinder head 100. Based on one aspect of the present invention, a method for selecting a diesel engine compression ratio adjustment gasket is provided. Figure 2 As shown, the method generally comprises the following steps: S210: Acquire a first distance from the fire surface 110 of the cylinder head 100 to the top surface 210 of the piston 200; S220: Before installing the cylinder head, measuring a second distance from the fire surface 110 of the cylinder head 100 to the connection bottom surface 120 of the cylinder head 100; S230: Move the piston plate to the top dead center position, and obtain a third distance from the adjustment gasket installation surface 320 of the cylinder sleeve 300 to the top surface 210 of the piston 200; S240 : Calculating the thickness of the adjustment shim 400 based on the first distance, the second distance, and the third distance.

[0026] Continue to see Figure 1 , assuming that the distance from the top surface 210 of the piston 200 to the upper end surface 310 of the cylinder liner 300 is a, and the distance from the upper end surface 310 of the cylinder liner 300 to its adjusting gasket mounting surface 320 is b, then (ab) is equal to the third distance from the adjusting gasket mounting surface 320 of the cylinder liner 300 to the top surface 210 of the piston 200; the distance from the fire surface 110 of the cylinder head 100 to its connecting bottom surface 120 is c, which is the second distance, and the thickness of the adjusting gasket 400 is t, then according to the dimension chain, equation (1) can be obtained: H = c + t + (ab) (1) Based on equation (1), the thickness calculation formula (2) of the adjustment gasket 400 is derived: t = Hc-(ab)(2) Among them, the first distance H value is a dimension that can be calculated based on the designed compression ratio and is a known quantity; the second distance c can be measured before assembly; the third distance (ab) is the distance from the mounting surface of the adjustment gasket to the top surface of the piston when the piston disc is in the top dead center position, which can be measured before assembly, and the thickness of the adjustment gasket can be calculated before assembly.

[0027] According to the second aspect of the present invention, a diesel engine compression ratio adjustment gasket selection device 500 is provided, which is intended to measure the third distance (ab) from the adjustment gasket mounting surface to the piston top surface when the piston disc is at the top dead center position. Figure 3-5 As shown, the device 500 generally comprises: a measuring frame 510, a moving rod mechanism 520 and a measuring mechanism 530. Specifically, at least one end surface of the measuring frame 510 is arranged against the adjusting gasket mounting surface 320 of the cylinder liner 300 during the measuring process; the moving rod mechanism 520 is connected to the measuring frame 510 and at least a part thereof is arranged against the top surface 210 of the piston 200 during the measuring process, wherein the moving rod mechanism is movable relative to the measuring frame 510 along the stroke direction of the piston 200; the measuring mechanism 530 is connected to the measuring frame 510 and is arranged to measure the displacement of the moving rod mechanism relative to the measuring frame 510, so as to obtain the distance from the adjusting gasket mounting surface 320 of the cylinder liner 300 to the top surface 210 of the piston 200 when the piston disc is at the top dead center position.

[0028] Specific as Figure 5As shown, the measuring frame 510 may include: a main body 511 radially spanning the cylinder liner 300, a first extension 512 vertically extending downward from both ends of the main body 511, and a second extension 513 vertically extending upward from the middle of the main body 511. During the measurement process, the first extension 512 is arranged away from the end surface of the main body 511 against the adjustment gasket mounting surface 320 of the cylinder liner 300. The second extension 513 is arranged to be connected with the moving rod mechanism 520 and the measuring mechanism 530. The moving rod mechanism 520 includes: a lever 521, a measuring rod 522 and a measuring contact 523. Specifically, the lever 521 is mounted to the second extension 513 and is movable along the second extension 513; the measuring rod 522 is connected to the middle of the lever 521 and extends upward parallel to the second extension 513; the measuring contact 523 is connected to the lever 521 and extends downward parallel to the second extension 513. The main body 511 is provided with a through hole for allowing the measuring contact 523 to pass through, and the end surface of the measuring contact 523 away from the lever 521 is arranged against the top surface 210 of the piston 200 during the measurement process. Preferably, the moving rod mechanism 520 may also include a spring 526, one end of which is connected to the measuring rod 522, and the other end is connected to the second extension portion 513. Preferably, the spring 526 may be sleeved on the measuring rod 522, which can ensure the follow-up of the measuring rod 522 and the pair of measuring contacts 523 on the one hand; on the other hand, it can provide elastic pressure during the measurement process to ensure that the measuring contact 523 contacts the top surface 210 of the piston 200 at any time to avoid measurement errors caused by stagnation. Further preferably, the measuring frame 510 may also include a guide sleeve 514, which is circumferentially installed between the through hole of the main body 511 and the measuring contact 523 and limits the radial displacement of the measuring contact 523, while protecting the measuring contact 523. In an embodiment of the present invention, the guide sleeve 514 may be welded to the main body 511 of the measuring frame 510 as a whole.

[0029] In the embodiment of the present invention, a through hole is provided in the middle of the main body 511, and the second extension 513 passes through the through hole and is welded and fixed to the main body 511. On the one hand, the second extension 513 is provided with a cavity inside along the axial direction to accommodate the measuring rod 522 and allow it to move upward or downward; on the other hand, the second extension 513 is provided with a radially penetrating groove to allow the lever 521 to pass horizontally, which is convenient for assembly. The part of the lever 521 that passes horizontally through the second extension 513 is connected to the measuring rod 522, and a hole is provided at a portion of the second extension 513 corresponding to the connection to facilitate the connection operation. Preferably, the measuring rod 522 is pivotally connected to the lever 521 via a first axis 524, so that the lever 521 can rotate relative to the measuring rod 522 around the first axis 524; the measuring contact 523 is pivotally connected to the lever 521 via a second axis 525, so that the measuring contact 523 can rotate relative to the measuring rod 522 around the second axis 525 and move along the guide sleeve 514, so as to flexibly determine the positions of the measuring rod 522 and the measuring contact 523. In the embodiment of the present invention, a pair of measuring contacts 523 extend downward from both ends of the lever 521, respectively, and the two points follow the contact with the top surface 210 of the piston 200, which can effectively avoid the error of single-point measurement.

[0030] Reference Figure 5 Combination Figure 6-7 As shown, the measuring mechanism 530 includes: a gauge base 531 fixedly connected to the second extension 513, an elastic jacket 532 installed on the gauge base 531, and a dial indicator 533 detachably clamped and fixed by the elastic jacket 532. In an embodiment of the present invention, the gauge base 531 can be detachably fastened to the second extension 513 of the measuring frame 510 by, for example, a threaded connection, and then the gauge base 531 and the main body 511 are fixedly connected by welding the second extension 513 to the main body 511. In the installed state, the contact of the dial indicator 533 passes through the gauge base 531 and the elastic jacket 532 and abuts against the top end of the measuring rod 522, so as to facilitate the measurement of the distance from the adjusting gasket installation surface 320 of the cylinder sleeve 300 to the top surface 210 of the piston 200. In an embodiment of the present invention, one end of the spring 526 is connected to the measuring rod 522, and the other end is connected to the gauge base 531. The measuring rod 522 is connected to the base 531 via a spring 526 and can move up and down in the base 531, and at the same time, the measuring contact 523 moves along the guide sleeve 514. Therefore, when the dial indicator 533 is mounted on the base and its measuring head abuts against the top of the measuring rod 522, the movement of the measuring contact 523 can be transmitted to the measuring rod 522 through various mechanisms, and the movement of the measuring rod 522 can be measured by the dial indicator 533.

[0031] In order to make the measured data more accurate, a small measuring range is selected when manufacturing the selection device 500, that is, the measuring rod 522 is designed to have a small stroke as much as possible, for example, less than 5 mm. In the embodiment of the present invention, in order to make the selection device 500 adapt to diesel engines with different compression ratio requirements, a plurality of process pads 540 with different thicknesses are added. The process pad 540 abuts between the top surface 210 of the piston 200 and the moving rod mechanism 520 during the measurement process, and can adapt to different compression ratios while ensuring the accuracy of the measured data.

[0032] When the process pad 540 is used, the method for selecting a diesel engine compression ratio adjustment pad according to the present invention generally comprises the following steps: S310: Acquire a first distance from the fire surface 110 of the cylinder head 100 to the top surface 210 of the piston 200; S320: Before installing the cylinder head, measuring a second distance from the fire surface 110 of the cylinder head 100 to the connection bottom surface 120 of the cylinder head 100; S330: Move the piston plate to the top dead center position, and obtain a third distance from the adjustment gasket installation surface 320 of the cylinder sleeve 300 to the top surface of the process pad 540; S340 : calculating the thickness of the adjustment pad 400 based on the first distance, the second distance, the third distance, and the thickness of the process pad 540 .

[0033] Assuming the thickness of the process pad 540 is d, equation (3) can be obtained according to the dimension chain: H-d+(bA)=t+c(3) Based on equation (3), the thickness calculation formula (4) of the adjustment gasket 400 is derived: t = H - d + (bA) - c (4) The following is a description of the selection method according to the present invention in conjunction with a specific diesel engine selection process of the adjustment gasket 400. The process includes: S310: Query the design process parameters to obtain a first distance H from the fire surface 110 of the cylinder head 100 to the top surface 210 of the piston 200, which is 16 mm.

[0034] S320: Before installing the cylinder head, use the dial gauge 533 to measure the second distance c from the fire surface 110 of the cylinder head 100 to the connection bottom surface 120 of the cylinder head 100 to be 4.9 mm.

[0035] S330: Move the piston to the top dead center position, and obtain a third distance (bA) from the adjustment gasket installation surface 320 of the cylinder liner 300 to the top surface of the process pad 540 of 2.5 mm.

[0036] The specific acquisition process includes: S331: Install the dial indicator 533 to the elastic jacket 530, place the assembled device 500 on the platform, make the measuring head of the dial indicator 533 abut against the top end of the measuring rod 522, and then adjust to zero.

[0037] S332: First, place a process pad with a thickness of 12 mm on the piston 200, and then install the assembled device 500 on the cylinder with the piston plate at the top dead center position, ensuring that the end surface of the first extension 512 of the measuring frame 510 away from the main body 511 abuts against the adjustment pad installation surface 320 of the cylinder sleeve 300, and the end surface of the measuring contact 523 of the moving rod mechanism 520 away from the lever 521 abuts against the top surface of the process pad 540 during the measurement process, and record the measured value of the dial indicator 533. The measured value represents the displacement of the lever 521 along the second extension 513, that is, the third distance from the adjustment pad installation surface 320 of the cylinder sleeve 300 to the top surface of the process pad 540.

[0038] S340: Calculate the thickness of the adjustment pad 400 based on the first distance, the second distance, the third distance and the thickness of the process pad 540. For details, see formula (5): t=H-d+(bA)-c=16mm-12mm+2.5mm-4.9mm=1.6mm(5) By using the device and method of the present invention, measurement can be performed before assembly, and the correct adjustment gasket can be selected after calculation and then assembly can be performed directly, thereby avoiding pre-assembly and improving assembly efficiency.

[0039] The above description is only a preferred embodiment of the present invention and is not intended to limit the scope of implementation of the present invention. If the present invention is modified or replaced by equivalents without departing from the spirit and scope of the present invention, it should be included in the protection scope of the claims of the present invention.

[0040] A person skilled in the art should understand that the discussion of any of the above embodiments is only exemplary and is not intended to imply that the scope of the disclosure of the embodiments of the present invention is limited to these examples; under the idea of ​​the embodiments of the present invention, the technical features in the above embodiments or different embodiments can also be combined, and there are many other changes in different aspects of the embodiments of the present invention as described above, which are not provided in detail for the sake of simplicity. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the embodiments of the present invention should be included in the protection scope of the embodiments of the present invention.

Claims

1. A method for selecting a diesel engine compression ratio adjusting gasket, characterized in that: The following steps are involved: Obtaining a first distance from a fire surface (110) of a cylinder head (100) to a top surface (210) of a piston (200); Before the cylinder head is installed, measuring a second distance from a fire surface (110) of the cylinder head (100) to a connection bottom surface (120) of the cylinder head (100); Move the piston disc to the top dead center position, and obtain a third distance from the adjustment gasket mounting surface (320) of the cylinder sleeve (300) to the top surface (210) of the piston (200); The thickness of the adjustment gasket (400) is calculated based on the first distance, the second distance and the third distance.

2. A diesel engine compression ratio adjustment gasket selection device (500), characterized in that: include: A measuring frame (510), at least one end surface of which is disposed against an adjusting gasket mounting surface (320) of a cylinder sleeve (300) during a measuring process; a moving rod mechanism (520), connected to the measuring frame (510) and at least a portion of which is disposed against the top surface (210) of the piston (200) during the measuring process, wherein the moving rod mechanism is movable relative to the measuring frame (510) along the stroke direction of the piston (200); and A measuring mechanism (530) is connected to the measuring frame (510) and is configured to measure the displacement of the moving rod mechanism relative to the measuring frame (510) to obtain the distance from the adjusting gasket mounting surface (320) of the cylinder sleeve (300) to the top surface (210) of the piston (200) when the piston disc is at the top dead center position.

3. The selection device according to claim 2, characterized in that: The measuring frame (510) comprises: A main body (511) is arranged to radially span the cylinder sleeve (300); A first extension portion (512) vertically extends downward from both ends of the main body portion (511), and during the measurement process, the end surface of the first extension portion (512) away from the main body portion (511) is disposed against the adjustment gasket mounting surface (320) of the cylinder sleeve (300); and The second extension portion (513) extends vertically upward from the middle of the main body portion (511) and is configured to be connected to the moving rod mechanism (520) and the measuring mechanism (530).

4. The selection device according to claim 3, characterized in that: The moving rod mechanism (520) comprises: a lever (521) mounted on the second extension portion (513) and movable along the second extension portion (513); a measuring rod (522) connected to the middle portion of the lever (521) and extending upward parallel to the second extension portion (513); and A measuring contact (523), connected to both ends of the lever (521) and extending downwardly parallel to the second extension portion (513); Wherein, through holes are provided at both ends of the main body (511) to allow the measuring contact (523) to pass through, and the end surface of the measuring contact (523) away from the lever (521) is arranged against the top surface (210) of the piston (200) during the measurement process.

5. The selection device according to claim 4, characterized in that: A through hole is provided in the middle of the main body (511), and the second extension portion (513) passes through the through hole and is welded and fixed to the main body (511); The second extension portion (513) is provided with a cavity inside thereof along the axial direction so as to accommodate the measuring rod (522) and allow the measuring rod (522) to move along the second extension portion (513); The second extension portion (513) is provided with a radially through slot for the lever (521) to pass through laterally.

6. The selection device according to claim 4, characterized in that: The measuring rod (522) is pivotally connected to the lever (521) via a first shaft (524); The measuring contact (523) is pivotally connected to the lever (521) via a second shaft (525).

7. The selection device according to claim 6, characterized in that: The measuring mechanism (530) comprises: A watch base (531) fixedly connected to the second extension portion (513); An elastic jacket (532) mounted on the table base (531); and A dial indicator (533) is detachably clamped and fixed by the elastic clamping sleeve (532); Wherein, in the installed state, the contact of the dial indicator (533) passes through the dial base (531) and the elastic jacket (532) to abut against the top end of the measuring rod (522).

8. The selection device according to claim 7, characterized in that: The moving rod mechanism (520) further includes: A spring (526) has one end connected to the measuring rod (522) and the other end connected to the meter base (531) or the second extension portion (513).

9. The selection device according to claim 4, characterized in that: The measuring frame (510) further comprises: A guide sleeve (514) is circumferentially mounted between the through hole of the main body (511) and the measuring contact (523) and limits the radial displacement of the measuring contact (523).

10. The selection device according to claim 2, characterized in that: The selection device also includes: A plurality of process pads (540) of different thicknesses are pressed against between the top surface (210) of the piston (200) and the moving rod mechanism (520) during the measurement process.

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