A method for analyzing and measuring leakage in ball-head-cone seals based on extrusion marks.

Abstract

This invention discloses a method for analyzing and measuring leakage in ball-head-conical surface seals based on indentation marks. Three seals are installed at three connection points in a 200-bar high-pressure fuel direct injection system. Each seal includes a ball head, an outer nut, and an inner conical surface connector. Tightening the outer nut forms an annular sealing band between the ball head and the inner conical surface. Based on the parameters of the annular sealing band obtained by measuring instruments, the annular sealing band is classified into three types of indentations: Type A, Type B, and Type C. For Type A indentations, the roundness of the ball head indentation or the conical surface indentation is adjusted to ensure that the roundness of the ball head and conical surface indentation positions is less than or equal to 0.02 mm. For Type B indentations, the alignment of the ball head, nut, or conical surface is adjusted. For Type C indentations, the roughness of the ball head or conical surface is adjusted to ensure that Rzmax does not exceed 6.3 μm. This invention can completely eliminate potential leakage problems in ball-head-conical surface seals, optimize product design reliability, and overcome the shortcomings of the commonly used method in the industry that relies on direct leakage detection for superficial judgment and analysis.

Description

Technical Field

[0001] This invention relates to ball-head and conical sealing structures for high-strength connections in the aerospace and automotive industries. Specifically, it discloses a method for analyzing and measuring leakage of ball-head-conical seals based on extrusion marks. The method uses visual inspection and measurement of extrusion marks (hereinafter referred to as indentations or sealing strips) to conduct in-depth analysis and optimization of the potential leakage risks of the sealing structure. Background Technology

[0002] A certain turbocharged engine uses a 200bar high-pressure direct fuel injection system. The fuel lines are shown in the attached diagram. Figure 1 The connection consists of three points: the first point connects the low-pressure fuel line to the high-pressure fuel pump inlet; the second point connects the high-pressure fuel pump outlet to the high-pressure fuel line; and the third point connects the high-pressure fuel line to the high-pressure fuel rail inlet. To facilitate disassembly and prevent fuel leakage caused by vibration loosening of traditional sealing ring joints, thus improving the safety and durability of the fuel line, all these interfaces use a ball-head conical surface connection.

[0003] The principle of ball-head-cone sealing is explained in the appendix. Figure 2 Before the outer nut 2 is tightened, the ball head 1 and the inner conical surface 3 are in line contact. When a torque is applied to the outer nut 2, the ball head and the conical surface will be tightened together and squeezed into contact, resulting in elastic-plastic deformation, which forms an annular sealing band (indentation) between the ball head and the conical surface.

[0004] Although the leakage appears to stop after tightening, molecular-level leakage channels still exist due to part shape errors and roughness. (See attached document.) Figure 3 If the strength allows, appropriately increasing the tightening torque can reduce leakage channels. However, excessive torque will cause large plastic deformation. Although it can ensure that there is no leakage at the time, it is easy to cause leakage later under the effect of rapid stress relaxation.

[0005] This ball-head-cone sealing connection method was initially used in the aerospace industry, but with the popularization of turbocharged engines, it has begun to be used in the automotive industry.

[0006] For this structure, domestic intellectual property rights are mostly focused on research into stress relaxation of both components and the design and manufacturing of the ball head. Industry verification of leakage is limited to direct visual inspection and analysis of product quality, such as after actual operation under ultraviolet light and leak testing with a leak meter, as well as product design optimization verification. Emphasis is placed on research into factors such as the alignment of the ball head, nut, and conical surface, surface roughness, and tightening torque. Research on the internal observation and measurement of the sealing strip (indentation) and related factors is completely lacking. Summary of the Invention

[0007] To address the shortcomings of existing technologies, this invention provides a method for analyzing and measuring leakage in ball-head-conical surface seals based on indentation marks. It focuses on the observation and measurement of the sealing band (indentation) and easily overlooked factors affecting the indentation, particularly the relationship between indentation depth and roundness tolerance, as well as the difference in hardness between the two. Through a number of leakage case studies, this invention reveals three defects in leaking ball-head-conical surface seals: broken indentation band, indentation eccentricity, and indentation roughness. Furthermore, it demonstrates that under a constant tightening torque, the indentation depth is affected by the hardness difference between the ball-head and conical surfaces, and the indentation depth plus the change in roundness at that location before and after tightening must be greater than or equal to the defined roundness value of the indentation location before tightening.

[0008] This invention discloses a method for analyzing and measuring leakage of ball-head-conical surface seals based on indentation marks. Three seals are installed at the connections of the low-pressure fuel line and the high-pressure fuel pump inlet, the high-pressure fuel pump outlet and the high-pressure fuel line, and the high-pressure fuel line and the high-pressure fuel rail inlet in a 200-bar high-pressure direct injection fuel system. Each seal includes a ball head, an outer nut, and an inner conical surface connector. Tightening the outer nut forms an annular sealing band between the ball head and the conical surface. The depth of the ball head indentation and the ball head's indentation depth are obtained using measuring instruments. The indentation width, conical indentation depth, conical indentation width, roundness of the ball indentation, and whether there is a break in the indentation are used to classify the annular sealing band into Class A, Class B, and Class C indentations. For Class A indentations, the roundness of the ball indentation or the conical indentation is corrected so that the roundness of the ball indentation and the conical indentation position is less than or equal to 0.02mm. For Class B indentations, the alignment of the ball, nut, or conical surface is corrected. For Class C indentations, the roughness of the ball or conical surface is corrected to ensure that Rzmax does not exceed 6.3um.

[0009] In a preferred embodiment of the present invention, the three ball-head conical surface connection structures of the 200bar high-pressure fuel direct injection system are assembled and tightened according to the normal production tightening process. After that, the engine is fueled and tested on an unloaded bench. The ball-head conical surfaces that leak after being removed from the production line are disassembled and measured for analysis using ultraviolet light.

[0010] In a preferred embodiment of the present invention, the tightening torque for tightening the ball head, nut, and conical joint at the connection between the low-pressure fuel line and the high-pressure fuel pump inlet is 21 NM; the tightening torque for tightening the ball head, nut, and conical joint at the connection between the high-pressure fuel pump outlet and the high-pressure fuel line is 32 NM; and the tightening torque for tightening the ball head, nut, and conical joint at the connection between the high-pressure fuel line and the high-pressure fuel rail inlet is 32 NM.

[0011] In a preferred embodiment of the present invention, the ball indentation depth, ball indentation width, cone indentation depth, cone indentation width, ball indentation roundness, and cone indentation roundness of the ball indentation are measured at three ball-and-cone surface connection structures of a 200-bar high-pressure fuel direct injection system using a profilometer and a roundness meter. These measurements are then compared with those of a normal, leak-free engine at the same location on the ball and cone surfaces after test operation.

[0012] In a preferred embodiment of the present invention, an indentation that cannot be closed in a complete circle and has a broken sealing strip is called a Class A indentation; an indentation that is uneven in width and depth (one side is deep and wide, while the other side is shallow and narrow) is judged as a Class B indentation; and an indentation that is closed in a complete circle and has uniform width and depth but is uneven in height is called a Class C indentation.

[0013] In a preferred embodiment of the present invention, the roundness, centering, roughness, and other values ​​of the parts required to prevent leakage are obtained by indentation measurement, and then compared with the product definition. If the product definition is unreasonable, the product design needs to be optimized, and if the definition is reasonable, the conformity of the parts needs to be rectified.

[0014] In a preferred embodiment of the present invention, after a Class A indentation that shows leakage is detected by testing, engine production is not continued by increasing the number of re-tightening cycles. Instead, a light transmission method is used to quickly select parts with qualified roundness for production.

[0015] In a preferred embodiment of the present invention, the indentation depth of the part with low hardness and deep indentation after tightening, plus the roundness deformation before and after tightening, should be greater than the roundness definition value of the indentation position of the part before tightening.

[0016] In a preferred embodiment of the present invention, the hardness difference between the ball head and the inner conical surface does not exceed 125 HV. Within this range, the greater the hardness difference between the two, the easier it is to obtain a satisfactory indentation depth and the stronger the tolerance for roundness error.

[0017] The beneficial effects of this invention are: This invention focuses on the observation and measurement of the sealing band (indentation) and the factors that are easily overlooked influencing the indentation, particularly the relationship between indentation depth and roundness tolerance, and the difference in hardness between the two. Through a number of leakage case studies, this invention concludes that leaking ball-head conical seals exhibit three defects: broken indentation band, indentation eccentricity, and indentation roughness. Furthermore, it concludes that under a constant tightening torque, the indentation depth is affected by the hardness difference of the ball-head conical surface, and the indentation depth plus the change in roundness at that position before and after tightening must be greater than or equal to the defined roundness value of the corresponding indentation position before tightening. Attached Figure Description

[0018] Figure 1This invention relates to a method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks in a turbocharged engine, showing the connection diagram of three ball-head-cone surface seals.

[0019] Figure 2 This is a diagram of the ball-head-cone seal structure of the ball-head-cone seal based on the method for analyzing and measuring leakage of ball-head-cone seals according to the present invention;

[0020] Figure 3 This invention relates to a method for analyzing and measuring leakage in ball-head-cone seals based on compression marks.

[0021] aisle;

[0022] Figure 4 This is a schematic diagram of a profilometer measuring the depth and width of the ball head indentation in a ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks according to the present invention.

[0023] Figure 5 This is a schematic diagram of a profilometer measuring the depth and width of the cone indentation on a ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks, according to the present invention.

[0024] Figure 6 This is a schematic diagram of a roundness meter measuring the roundness of the ball indentation, which is a method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to the present invention.

[0025] Figure 7 This is a schematic diagram of a roundness meter measuring the roundness of the conical indentation, which is a method for analyzing and measuring leakage of ball-head-conical surface seals based on extrusion marks according to the present invention.

[0026] Figure 8 This is a schematic diagram of Class A indentation in the ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks according to the present invention.

[0027] Figure 9 This is a schematic diagram of the detection results of Class A indentation under a roundness tester for a ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks according to the present invention.

[0028] Figure 10 This is a schematic diagram of type B indentation in the ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks according to the present invention.

[0029] Figure 11 This is a schematic diagram of a Class C indentation in a ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks according to the present invention.

[0030] Figure 12 This is a schematic diagram of the rapid selection of Class A indented ball heads using the light transmission method, which is part of the present invention's method for analyzing and measuring leakage in ball-head-cone surface seals based on extrusion marks.

[0031] Figure 13 This is a schematic diagram of three sections for the roundness detection of a type A indented ball head, based on the ball head-cone surface sealing leakage analysis and measurement method according to the present invention.

[0032] Figure 14 This is a connection CT image of a type B defect in the ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks according to the present invention.

[0033] Figure 15 This is a schematic diagram of the tightening nut and the pre-positioning hole diameter of the ball head for a type B defect in the ball-head-cone surface seal leakage analysis and measurement method based on extrusion marks according to the present invention.

[0034] Figure 16 This is a flowchart of a method for analyzing and measuring leakage of a ball-head-cone seal based on extrusion marks, according to the present invention. Detailed Implementation

[0035] The technical solutions (including preferred technical solutions) of the present invention will be further described in detail below with reference to the accompanying drawings and by way of listing some optional embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0036] This invention discloses a method for analyzing and measuring leakage in ball-head-cone seals based on indentation marks. The aim is to analyze the internal characteristics of the sealing band (indentation) in leakage failure cases of ball-head-cone seal structures by observing and measuring the indentation, and comparing it with the indentation of normal parts. This analysis identifies three defect modes: broken indentation band, indentation eccentricity, and indentation roughness. Further quantitative improvements are then made to completely eliminate potential faults, optimize product design reliability, and overcome the shortcomings of the commonly used method in the industry that relies on direct leakage detection for superficial judgment and analysis. The specific steps include:

[0037] S1. Tighten the attachment according to the normal production tightening process. Figure 1 The three ball-head conical surface connection structures were assembled and tightened. After that, the engine was fueled and tested on the test bench under no-load conditions. The ball-head conical surface that was leaking after being removed from the production line was disassembled and measured for analysis using a UV lamp.

[0038] S2. Measure the depth, width, and roundness of the indentation on the faulty ball head and cone surface using a profilometer and a roundness meter, respectively, and compare them with the indentation depth, width, and roundness of the same position on an engine that is normal and leak-free after test operation. If the indentation cannot close completely, indicating a broken seal, it is classified as a Class A defect. If the width and depth of the indentation are uneven (deep and wide on one side, shallow and narrow on the other), it is classified as a Class B defect. If the indentation closes completely and the depth and width are uniform, but the indentation is uneven, it is classified as a Class C defect.

[0039] S3. If it is a Class A defect, check the roundness of the ball head and the conical surface, and optimize and rectify any unreasonable roundness (in this example, the roundness of the low-pressure ball head is too large and the definition is unreasonable); if it is a Class B defect, rectify the parameters that affect the neutrality of the ball head, nut, and conical surface (in this example, the pre-positioning hole diameter of the tightening nut at the high-pressure oil rail inlet and the ball head is too large, causing tightening eccentricity); if it is a Class C defect, rectify the roughness of the ball head and the conical surface (in this example, the roughness of the low-pressure ball head is unqualified).

[0040] In step S1, after visually inspecting for leaks with a UV lamp, the oil stains at the leak point are cleaned with a cleaning agent, and after a second tightening, the leak stops. This conventional approach masks the defect. Especially for Class A defects, although the leak appears to stop after tightening, after loosening and disassembling, it is found that the indentations on both the ball head and the conical surface are not completely closed (a broken band exists). Under stress relaxation, the potential risk of leakage in the later stages is extremely high.

[0041] In step S2, for Class A indentation breakage defects, the risk of leakage is extremely high; the greater the roundness error, the greater the leakage. When the roundness is at a critical state, there are extremely slight signs of leakage. For Class B centering defects, it is necessary to check the coaxiality of the ball head sealing position relative to the ball head and the nut positioning end; the thread of the tightened nut and the coaxiality of the nut and the positioning hole of the ball head; the thread of the conical surface and the coaxiality of the conical surface; and the pre-positioning of the nut and the stress on the oil pipe during the tightening process. For Class C roughness defects, the probability of occurrence is relatively low; the roughness of the ball head sealing strip position before tightening is mainly measured.

[0042] In step S3, the roundness, centering, roughness, and other values ​​of the parts required to prevent leakage are obtained by indentation measurement. Then, they are compared with the product definition. If the product definition is unreasonable, the product design needs to be optimized. If the definition is reasonable, the conformity of the parts needs to be rectified.

[0043] In step S3, after a Class A defect of leakage is detected through testing, engine production cannot continue by increasing the number of re-tightening cycles. Instead, the light transmission method can be used to quickly select parts with qualified roundness for production.

[0044] In step S3, the indentation depth of the part with low hardness and deep indentation after tightening, plus the roundness deformation before and after tightening, should be greater than the roundness definition value of the indentation position of the part before tightening.

[0045] In step S3, in order to obtain a satisfactory indentation depth and a suitable part roundness definition, it is preferred to have a hardness difference of 125HV between the ball head and the conical surface. Within this range, the greater the hardness difference between the two, the easier it is to obtain a satisfactory indentation depth and the stronger the tolerance for roundness error.

[0046] Specifically, tighten the attachment according to the normal production tightening process. Figure 1 The three ball-head conical surface connection structures were assembled and tightened. After that, the engine was fueled and tested on an unloaded test bench. The ball-head conical surface that was leaking after being removed from the production line was visually inspected with an ultraviolet lamp.

[0047] Use a profilometer to measure the depth and width of the indentation on the ball head, see... Figure 4 The profilometer probe travels its measurement stroke perpendicular to the annular indentation, symmetrically distributed above and below the indentation, extending 1-2 mm beyond each indentation, to obtain the following results: Figure 4 The ABXCD curve shown has spherical segments AB and CD that are arcs. Point X is the deepest point of the indentation. The perpendicular distance from point X to the line connecting points B and C at the edge of the indentation is the depth of the indentation. The distance between points B and C is the width of the indentation at that point.

[0048] Use a profilometer to measure the depth and width of the indentation on the conical surface. See Figure 5 The profilometer probe travels its measurement stroke perpendicular to the annular indentation, symmetrically distributed on both sides of the indentation, and extends 1-2 mm beyond each indentation to obtain the following result: Figure 5 The EFYGH curve shown is a conical surface, with segments EF and GH being straight lines. Point Y is the deepest point of the indentation, and the perpendicular distance from point Y to the line connecting EFGH is the indentation depth of the conical surface. The distance between points F and G is the indentation width at that point.

[0049] Use a roundness tester to measure the roundness of the indentation on the ball head. See Figure 6 The roundness tester probe measures one revolution along the annular indentation to obtain the roundness value of the ball head indentation.

[0050] Use a roundness tester to measure the roundness of the conical indentation, see Figure 7 The roundness tester probe measures one revolution along the annular indentation to obtain the roundness value of the conical indentation.

[0051] Appendix Figure 1 The first low-pressure ball-head-cone seal leak in the engine was observed when the ball head was disassembled and the sealing strip of the ball head and cone surface was inspected. The indentation could not be closed around the circumference, and there was a 2mm wide uncompressed deformation area, which was called a broken sealing strip.

[0052] The above method measures the attached Figure 1The indentation depth at the non-broken band of the ball head of the defective part at the inlet connection of the oil pump is 0.015-0.018mm and the width is 1.5-1.7mm. The indentation depth at the non-broken band of the conical surface is 0.002-0.004mm and the width is 1.5-1.7mm.

[0053] Furthermore, the above method measures the attached... Figure 1 At the inlet connection of the oil pump, there is a defective part with a ball-head indentation where the indentation depth is 0mm. The material at the fracture zone shows varying degrees of indentation. The conical indentation also has an indentation depth of 0mm at the fracture zone. This type of indentation, which cannot close (due to the presence of a fracture zone), is classified as a Class A indentation. This defect is called a Class A defect. (See attached...) Figure 8 Schematic diagram of type A indentation.

[0054] The results of the above method for measuring the roundness defects of Class A indentations are shown in the appendix. Figure 9 The test results of Class A indentations under the roundness tester show that the roundness results confirm that there is a material indentation on the ball head. The indented part cannot be squeezed and deformed with the conical surface, resulting in the indentation break. The roundness of the ball head indentation of the leaking part is 0.018-0.057mm.

[0055] Appendix Figure 1 The third instance of high-pressure ball-head-cone seal leakage in the engine was observed when the ball head was disassembled and the sealing strip of the ball head and cone surface was inspected. The indentations were basically closed, but there was an eccentric phenomenon with one side being deeper and wider than the other side being shallower and narrower.

[0056] The profilometer detected deep conical indentations on the defective parts after tightening. The deeper side had an indentation depth of 0.06-0.12 mm and a width of 3.0-3.7 mm, while the shallower side had an indentation depth of 0.01-0.05 mm and a width of 1.0-2.0 mm. Although the indentation was completely closed, leakage still occurred due to the 200 bar high pressure.

[0057] When the profilometer detects a defective part after tightening, it will show a shallower ball head indentation. The deeper side has an indentation depth of 0.005-0.009mm and an indentation width of 3.0-3.7mm, while the shallower side has an indentation depth of 0.002-0.006mm and an indentation width of 1.0-2.0mm. The indentation is also closed around the entire circle.

[0058] The roundness of the ball head indentation after tightening of the defective part is 0.004-0.01mm, and the roundness of the corresponding conical surface indentation after tightening is 0.003-0.01mm.

[0059] This defect is completely different from the aforementioned Type A indentation fracture zone; it belongs to another type of Type B indentation. This defect is a Type B defect, see Appendix. Figure 10 .

[0060] The above-mentioned A and B fault cases are numerous. In addition, there is another type of fault with a lower occurrence rate, which is the one mentioned above. Figure 1 The second location shown is the connection between the high-pressure oil pump outlet and the high-pressure oil pipe. The leaking joint was disassembled, and the indentation was measured. It was found that the depth and width of the indentation around the entire circumference were consistent with normal parts, and there was no breakage. However, the indentation marks were uneven.

[0061] The color near the ball head seal was found to be darker than normal parts. Upon inspection of the leaking parts, the roughness of the indentation edge exceeded the requirement of Rzmax6.3, confirming that it was caused by the failure of the polishing process, i.e., the roughness of the ball head seal area was not up to standard.

[0062] Indentations with acceptable depth and width, and no broken bands, but with unacceptable surface roughness, are classified as Class C defects. (See attached document.) Figure 11 .

[0063] For Class A indentation breakage defects, the oil stains were cleaned with a cleaning agent. Then, the process torque was increased from 21 NM to 25 NM or the torque was kept the same but the number of tightening cycles was increased. After running and observing, the original leakage point no longer leaked. However, after disassembly and inspection, it was found that the indentation was still not closed, and the risk of leakage in the later stage was extremely high. These measures can only temporarily cover up this leakage defect and production cannot continue. It is necessary to select parts and systematically rectify the roundness defects of the parts.

[0064] Handling of inventory parts: Use the light transmission method to quickly select low-pressure ball joints with material dent defects, see attached. Figure 12 Cut the high-pressure oil pump interface 1 off the oil pump and attach it to a hollow, horn-shaped base bracket. Dim the light in the inspection space, press the ball head of the part to be inspected vertically onto the inner conical surface by hand, emit light from the base, and observe whether there are any light-transmitting points around the ball head and the conical surface. If there are, mark the ball head with a defective mark; otherwise, release it normally.

[0065] A portion of defective low-pressure ball heads were selected using the light transmission method and placed in a roundness tester for inspection. The results were consistent with the attached... Figure 9 Similarly, the reliability of the light transmission method was confirmed, and the indentation (roundness) of the ball head material at the sealing strip position was generally between 0.025-0.062mm (before tightening and squeezing).

[0066] Take three low-pressure oil pipes and use the light transmission method to select those with defects. Then, use a roundness tester to perform three-section analysis (see attached). Figure 13 Testing was conducted. Ball heads with indentations of 0.0571mm, 0.040mm, and 0.0251mm were selected and installed on engines according to normal procedures. After bench testing, the 0.0571mm ball head showed a large leak, the 0.040mm ball head showed a moderate leak, and the 0.0251mm ball head showed an extremely slight leak. Upon disassembly of the three engines, it was observed that the 0.0571mm and 0.040mm ball heads showed varying degrees of broken bands, while the 0.0251mm ball head showed barely closed indentations. The greater the roundness, the more severe the broken bands and the more severe the leaks (see Table 1).

[0067]

[0068] After removing these three low-pressure ball joints from the engine, the roundness of the corresponding three sections was measured again on the roundness meter. The results are shown in Table 1 above. Comparing the difference in roundness values ​​at the indentation before and after tightening, it was found that the roundness at the indentation position would decrease by 0.004-0.01mm after tightening and squeezing, with an average of 0.007mm.

[0069] Spot checks of low-pressure connectors in other engines at the same location during normal production showed no leakage. The indentation width was uniform and there were no broken bands. The ball head indentation depth was 0.015-0.018mm, the width was 1.5-1.7mm, and the roundness was 0.006-0.014mm.

[0070] The depth of the low-pressure conical indentation corresponding to normal production without leakage is 0.002-0.004mm, and the roundness is 0.003-0.01mm.

[0071] The relevant data from the above measurements and the definitions of related products are compiled into Table 2.

[0072] Considering that tightening will reduce the roundness of the indentation by 0.007mm, the roundness of the leaking ball head before tightening is (0.018~0.057)+0.007=0.025~0.062mm.

[0073] Considering that tightening will reduce the roundness of the indentation by 0.007mm, the roundness of the ball head before tightening without leakage is (0.006~0.014)+0.007=0.011~0.021mm.

[0074] For Class A indentations, the indentation depth at the non-broken section of the ball head must be greater than or equal to the ball head's roundness before tightening minus the change in roundness before and after tightening to ensure indentation closure. In this example, the ball head indentation depth (0.015~0.018) ≥ the roundness before tightening X - 0.007, then X ≤ 0.022~0.025mm.

[0075] Comparing the product images, it was found that the roundness definition of the low-pressure oil pipe ball head is 0.05. The hardness difference between the two is 35HV. The ball head with the relatively lower hardness has a relatively deeper indentation. If the hardness and torque remain unchanged, combined with the above A and B indentation measurement data, it can be concluded that the 0.05 roundness definition of the low-pressure ball head is unreasonable.

[0076] For leaking ball heads, the minimum roundness of the indentation before tightening is 0.025; for non-leaking ball heads, the maximum roundness of the indentation before tightening is 0.021. The indentation depth and the change in roundness before and after tightening must be less than or equal to 0.022 for the roundness before tightening. Considering the potential impact of overlapping roundness errors at the ball head and conical surface indentations, a maximum roundness of 0.02 for the ball head sealing strip is appropriate. The roundness definition for the ball head sealing strip position before tightening needs to be changed from 0.05 to 0.02.

[0077] Similarly, the roundness of the conical surface corresponding to the low-pressure ball head is currently undefined and needs to be defined by 0.02.

[0078] After analysis and rectification of the roundness defect of the Class A indentation ball head, mass production was carried out, and its roundness was controlled within 0.02. The engine was 100% leak-free after rolling off the production line. After disassembling and tightening the ball head, the sealing strip could be closed. The leakage problem caused by the roundness error of the ball head was completely solved.

[0079] Further testing of the ball head and cone surface of type B defects using the aforementioned light transmission method revealed no light transmission, further confirming that neither had a roundness depression. This indicates that the sealing strip of this type of defect is indeed closed and has no roundness issue.

[0080] The joint condition of the B-defect ball head and conical surface under tightened condition was detected using industrial CT. (See attached image) Figure 14 The large gap between the threads on the left and the small gap between the threads on the right indicate that the extrusion pressure on the left is less than that on the right. This confirms the phenomenon observed visually above, where one side has a shallow and narrow indentation while the other side has a deep and wide indentation. This confirms that the leak is caused by eccentric tightening.

[0081] The high-pressure ball head, nut, and oil rail inlet were inspected and found to be within acceptable parameters, including coaxiality, surface roughness, roundness, and thread type. However, upon tightening the nut, significant wobble was observed in the threaded locating hole when it mates with the ball head, indicating poor pre-positioning. (See attached document) Figure 15 The problem of eccentric tightening was solved after changing the pre-positioning hole diameter of the nut and ball head from 9.80±0.10 to 9.40±0.10.

[0082] The indentation depth of the high-pressure ball head cone surface that does not leak is 0.05-0.10mm. Considering the reduction in the roundness of the indentation before and after tightening, it is found that a roundness definition of 0.05 for the ball head before tightening is barely reasonable, while a roundness definition of 0.02 for the oil rail is more reasonable.

[0083] The relevant design parameters and inspection results of the ball head and conical surface of Class B defects are summarized in Table 2 and compared with those of Class A defects.

[0084] The hardness of the low-pressure ball head is less than that of the oil pump inlet cone surface, with a hardness difference of 345-310=35HV. The average depth of the indentation on the ball head with lower hardness is 0.015-0.018mm. The hardness of the high-pressure ball head is greater than that of the oil rail cone surface, with a hardness difference of 310-185=125HV. The depth of the indentation on the cone surface with lower hardness is 0.05-0.10mm.

[0085] Based on the observation and measurement of indentations for both types of defects (A and B) and the definition of parameters, it is concluded that, under the condition of constant tightening torque, the preferred design is one with a relatively large difference in hardness between the two materials, which can achieve a satisfactory indentation depth and better overcome leakage caused by roundness errors of the two materials.

[0086] For Class C indentations, as long as the indentation depth is greater than or equal to the roundness of the indentation position before tightening minus the decrease in roundness before and after tightening, it indicates that the roundness and tightening torque definitions are correct. If leakage still occurs, the only possibility is that the surface roughness is unqualified. In this case, it is necessary to observe and measure whether the indentation filling rate is incomplete due to poor surface roughness, resulting in unevenness of the indentation surface.

[0087] Similarly, under the condition that the torque and hardness remain unchanged, the roundness definition of the ball head and the conical surface needs to be verified and determined based on the indentation depth and the reduction in roundness before and after tightening when the indentation depth and width are uniform. It is recommended that the indentation depth after tightening be greater than or equal to the roundness definition before tightening minus the reduction in roundness at the indentation position before and after tightening.

[0088] In summary, by measuring indentations, three types of leakage defects were identified: Type A indentation fracture, Type B indentation eccentricity, and Type C indentation roughness. This measurement and analysis method avoids the drawbacks of directly detecting leakage on the surface, allowing for deeper analysis and improvement of leakage problems. Furthermore, the transmissive inspection method for Type A defects can quickly select parts with roundness defects, ensuring both quality and efficiency. The analysis and measurement methods of this invention are worthy of promotion within the industry.

[0089] It should be noted that the units of the above figures in this article (except for roughness, which is in μm) are all mm; at the same time, Class A defects are defects contained in Class A indentations, Class B defects are defects contained in Class B indentations, and Class C defects are defects contained in Class C indentations.

[0090] Table 2: Parameter Tables and Test Results Comparison of Two Ball-Head-Conical Surface Designs

[0091]

[0092] Those skilled in the art will readily understand that the above are merely preferred embodiments of the present invention and are not intended to limit the invention. Any modifications, combinations, substitutions, improvements, etc., made within the spirit and principles of the present invention are included within the scope of protection of the present invention.

Claims

1. A method for analyzing and measuring leakage in ball-head-cone seals based on extrusion marks, characterized in that: Three seals are installed at the connections of the low-pressure fuel line and the high-pressure fuel pump inlet, the high-pressure fuel pump outlet and the high-pressure fuel line, and the high-pressure fuel line and the high-pressure fuel rail inlet of the 200bar high-pressure direct fuel injection system. Each seal includes a ball head, an outer nut, and an inner conical joint. Tightening the outer nut forms an annular sealing band between the ball head and the conical joint. The depth of the ball head indentation, the width of the ball head indentation, the depth of the conical indentation, and the width of the conical indentation are obtained using measuring instruments. The roundness of the ball head indentation, the roundness of the conical indentation, and whether there are any breaks in the indentation are all checked. The annular sealing band is divided into Class A, Class B, and Class C indentations. For Class A indentations, the roundness of the ball head indentation or the conical indentation is corrected so that the roundness of the ball head and conical indentation positions is less than or equal to 0.02 mm. For Class B indentations, the alignment of the ball head, nut, or conical surface is corrected. For Class C indentations, the roughness of the ball head or conical surface is corrected to ensure that Rzmax does not exceed 6.3 μm.

2. The method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to claim 1, characterized in that: The three ball-head conical surface connection structures of the 200bar high-pressure fuel direct injection system were assembled and tightened according to the normal production tightening process. After that, the engine was fueled and tested on the bench under no-load conditions. The ball-head conical surfaces that were leaking after the test were removed and measured for analysis using ultraviolet light.

3. The method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to claim 2, characterized in that: The tightening torque for tightening the ball head, nut, and tapered joint at the connection between the low-pressure fuel line and the high-pressure fuel pump inlet is 21 NM; the tightening torque for tightening the ball head, nut, and tapered joint at the connection between the high-pressure fuel pump outlet and the high-pressure fuel line is 32 NM; and the tightening torque for tightening the ball head, nut, and tapered joint at the connection between the high-pressure fuel line and the high-pressure fuel rail inlet is 32 NM.

4. The method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to claim 1, characterized in that: Based on the measurements taken by a profilometer and a roundness meter at three ball-and-cone joints of a 200-bar high-pressure fuel direct injection system, the ball indentation depth, ball indentation width, conical indentation depth, conical indentation width, roundness of the ball indentation, and roundness of the conical indentation were measured. These measurements were then compared with those taken at the same locations on an engine that did not leak normally after test operation.

5. The method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to claim 4, characterized in that: If the indentation cannot be completely closed and there is a break in the sealing strip, it is called a Class A indentation; if the depth and width of the indentation are uneven, with one side of the indentation being deep and wide and the other side being shallow and narrow, it is judged as a Class B indentation; if the indentation is completely closed and the depth and width are uniform, but the indentation is uneven, it is called a Class C indentation.

6. The method for analyzing and measuring leakage of ball-head-cone seals based on extrusion marks according to claim 5, characterized in that: The roundness, alignment, and roughness of the parts required to prevent leakage are obtained by indentation measurement. Then, the values ​​are compared with the product definition. If the product definition is unreasonable, the product design needs to be optimized. If the definition is reasonable, the conformity of the parts needs to be rectified.

7. The method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to claim 1, characterized in that: After testing revealed Class A indentations that caused leakage, instead of increasing the number of re-tightening cycles to continue engine production, a light transmission method was used to quickly select parts with acceptable roundness for production.

8. The method for analyzing and measuring leakage of ball-head-cone seals based on extrusion marks according to claim 1, characterized in that: After tightening, the indentation depth of parts with low hardness and deep indentations, plus the roundness deformation before and after tightening, should be greater than or equal to the roundness definition value of the corresponding indentation position of the part before tightening.

9. The method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to claim 1, characterized in that: The hardness difference between the ball head and the inner conical surface shall not exceed 125 HV.

10. The method for analyzing and measuring leakage of ball-head-cone surface seals based on extrusion marks according to claim 1, characterized in that: When the hardness difference between the ball head and the inner conical surface does not exceed 125HV, the greater the hardness difference between the ball head and the inner conical surface, the easier it is to obtain a satisfactory indentation depth and the stronger the tolerance for roundness error.

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