Plane sealing reliability acceleration test method

Abstract

The invention provides a plane sealing reliability acceleration test method, which comprises the following steps of: analyzing a plane sealing failure mechanism, determining a stress type of a sealing part, establishing a leakage characterization model, and performing durability simulation analysis on the sealing part; determining an acceleration factor of the sealing failure according to a plane sealing failure mechanism analysis result; a wear degradation model and an acceleration model are established and solved, and predicted values are obtained; a plane sealing reliability acceleration test is carried out, stress is applied in a graded mode in the test, and test data are obtained; and comparing the test data with the predicted value, and judging whether the plane sealing reliability acceleration test is effective or not. The plane sealing reliability acceleration test method is short in time consumption and high in verification efficiency.

Description

Technical Field

[0001] The invention relates to the field of testing methods, in particular to the field of plane sealing testing methods. Background Art

[0002] In the high-pressure common rail system, its key components are constantly subjected to high-frequency pulsating oil pressure. After long-term operation, micro-wear occurs between the sealing surfaces of precision parts, leading to seal failure. Therefore, it is necessary to conduct a plane seal reliability test.

[0003] Traditional flat seal reliability tests are time-consuming and have low verification efficiency. It is necessary to propose a rapid testing method that is shorter, less expensive, and has higher verification efficiency. Summary of the invention

[0004] An object of the present invention is to provide a planar seal reliability accelerated test method which is time-saving and has high verification efficiency.

[0005] The planar seal reliability accelerated test method for achieving the above-mentioned purpose includes the following steps: performing a planar seal failure mechanism analysis, determining the stress type of the sealing parts, establishing a leakage characterization model, and performing a durability simulation analysis of the sealing parts to obtain the sealing surface stress parameters; determining the acceleration factor of the seal failure according to the planar seal failure mechanism analysis results; establishing a wear degradation model and an acceleration model and solving them to obtain a predicted value; performing a planar seal reliability accelerated test, applying stress in different levels during the test to obtain test data; comparing the test data with the predicted value to determine whether the planar seal reliability accelerated test is effective.

[0006] In one or more embodiments, the sealing surface adopts liquid sealing, and the leakage characterization model is: Among them, Q is the volume flow rate of fluid leakage; h is the gap between the two rough surfaces; η is the dynamic viscosity; r2 is the outer radius of the sealing interface; r1 is the inner radius of the sealing interface; p1 is the internal fluid pressure; and p2 is the external environmental pressure.

[0007] In one or more embodiments, the degradation model is a Gamma model, and a probability density function of the degradation amount is established.

[0008] In one or more embodiments, the acceleration model is an inverse power law model

[0009] LqCy k =a+blnS 1k +clnS 2k , where K is the degradation rate, a, b, c are constant coefficients, k is the stress level number, and S is the stress.

[0010] In one or more embodiments, small sample test data are used to determine model parameters in the degradation model and the acceleration model, and failure probability analysis is performed to determine wear degradation data prediction values.

[0011] In one or more embodiments, when performing a flat seal reliability accelerated test, different fuel pressure stress levels are loaded using different pulse waveforms.

[0012] In one or more embodiments, the test data includes the amount of end face wear under different stresses, and the predicted value includes a wear degradation prediction value; the end face wear amount and the wear degradation prediction value are respectively plotted into degradation curves; by comparing the overlap of the two degradation curves, it is determined whether the test data is valid, and then whether the accelerated test of planar seal reliability is valid.

[0013] In one or more embodiments, the contact surface flatness, roughness, residual deformation of the sealing plane, and leakage are recorded before the test; the fluid leakage and sealing surface wear are recorded during the test; and the flatness, roughness, residual deformation of the sealing plane, surface scratches, and leakage are recorded after the test.

[0014] In one or more embodiments, the sealing surface stress parameters include an average contact stress, a maximum contact stress, and a minimum contact stress of the sealing contact surface under different sensitive stresses.

[0015] In one or more embodiments, fuel pressure and sealing surface flatness are selected as acceleration factors.

[0016] The above-mentioned accelerated test method for flat seal reliability applies different stress levels during the test stage. Compared with the traditional method of applying constant force and long-term wear, it can achieve rapid testing, and by comparing the test data with the predicted values ​​obtained by the wear degradation model and the acceleration model, the effectiveness of the accelerated test for flat seal reliability under the stress can be judged. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The above and other features, properties and advantages of the present invention will become more apparent through the following description in conjunction with the accompanying drawings and embodiments, in which:

[0018] Figure 1 It is a flow chart of the accelerated test method for flat seal reliability;

[0019] Figure 2 It is a logic diagram of the accelerated test method for flat seal reliability. DETAILED DESCRIPTION

[0020] The present invention is further described below in conjunction with specific embodiments and drawings. More details are elaborated in the following description to facilitate a full understanding of the present invention. However, the present invention can obviously be implemented in a variety of other ways different from the description herein. Those skilled in the art can make similar generalizations and deductions based on actual application situations without violating the connotation of the present invention. Therefore, the protection scope of the present invention should not be limited by the content of this specific embodiment.

[0021] It should be noted that these and other subsequent drawings are only examples and are not drawn to scale, and should not be used to limit the actual scope of protection required by the present invention.

[0022] The high-pressure common rail system is the core subsystem of the internal combustion engine, and its reliability level is crucial to the long-term durability of the engine. During the operation of the high-pressure common rail system, key parts such as the electronically controlled fuel injector components will wear out after a long period of operation, resulting in seal failure. For example, if the seal on the high-pressure oil channel end face of the injector body fails, the high-pressure fuel entering the injector body will overflow along the cracks, and some serious failure parts may even have fractures and peeling on the edge of the seal end face.

[0023] The occasional failure of the above-mentioned parts is random and usually occurs during the long-term operation of the matching engine. If the parts are replaced, the machine state will change, the test time and cost will increase. In addition, the verification of new processes also faces problems such as small number of test samples, short verification cycle, and difficulty in obtaining comparative results.

[0024] Generally, a reliability test process is required to verify the life of components. Reliability refers to the probability that a component will maintain normal operation under specified conditions and time. However, conventional reliability tests are no longer applicable to the above-mentioned new process verification and occasional component failure scenarios. Therefore, it is necessary to provide a more time-consuming, low-cost, and more efficient accelerated test method for the reliability of flat seals for precision parts.

[0025] like Figure 1 As shown in the figure, the accelerated test method for plane seal reliability mainly includes the following processes:

[0026] Analyze the failure mechanism of flat seals, determine the stress type of sealing parts, establish a leakage characterization model, and perform durability simulation analysis of sealing parts to obtain sealing surface stress parameters;

[0027] Determine the acceleration factor of seal failure based on the analysis results of the plane seal failure mechanism;

[0028] Establish and solve the wear degradation model and acceleration model to obtain the predicted value;

[0029] Conducting accelerated tests on the reliability of flat seals, during which stress is applied in several levels in sequence to obtain test data;

[0030] The test data is compared with the predicted value to determine whether the accelerated test of plane seal reliability is effective.

[0031] The specific process of this method is introduced below.

[0032] First, based on the working principle of planar sealing components, load analysis, mechanism analysis and durability simulation analysis are carried out to determine whether the components and the planar seal meet the characteristics of accelerated life tests.

[0033] When performing load analysis, determine one or more stress types that are most likely to cause component failure under normal use conditions, i.e., sensitive stresses. Mechanical components generally include working stresses and environmental stresses. It is necessary to determine the number and type of stresses they have based on the characteristics of different plane seals, and determine the failure type based on the working principle of sealing components. For example, if the failure type is cumulative damage, the sensitive stress is pressure.

[0034] Taking a plane sealing structure of a high-pressure common rail system as an example, its composition type, working principle and working characteristics are analyzed according to the structural characteristics of the object. Load analysis is carried out in combination with the stress load spectrum of the operation process to determine the working stress and environmental stress type of related parts during the operation cycle.

[0035] When conducting mechanism analysis, aiming at the failure mechanism of wear, a mathematical function model based on the relationship between the physics of wear failure and materials, structure, stress, etc. is established to obtain a leakage characterization model.

[0036] In some embodiments, the sealing principle of the planar sealing structure is adopted, and considering that the seal between the two sealing surfaces is an annular surface contact seal, which conforms to the traditional leakage model, the leakage is characterized by the volume flow rate of the fluid leakage.

[0037] Specifically, due to the pressure difference, the volume flow rate of the fluid flowing from the inner radius to the outer radius through the gap can be expressed as Where Q is the volume flow rate of fluid leakage, and the unit is m 3 / s; h is the gap between the two rough surfaces, in m; η is the dynamic viscosity, in Pa·s; r2 is the outer radius of the sealing interface, in m; r1 is the inner radius of the sealing interface, in m; p1 is the internal fluid pressure, in Pa; p2 is the external environment pressure, in Pa. When the plane seal is good, the fluid leakage volume flow rate is 0, and the higher the fluid leakage volume flow rate, the worse the sealing effect.

[0038] Based on the principles of generalized stress-strength and cumulative damage, a part simulation model is established to perform durability simulation analysis on flat sealing parts. The basic value of fuel pressure is obtained by calculating the average contact stress and the maximum and minimum contact stresses of the sealing contact surface under different sensitive stresses. Different surface quality parameters can be selected, such as the flatness of different sealing planes, to calculate and analyze the sealing surface stress levels under different schemes. The contact stress of the sealing contact surface is output, and the calculation data of the sealing surface stress parameters such as the average contact stress, maximum contact stress, and minimum contact stress are output as input values ​​for the subsequent design of the sealing reliability accelerated test.

[0039] Under the condition that the failure mechanism and failure process of the flat seal are consistent, a leakage characterization model is established. When a flat seal fails, the gap h between the two rough surfaces of the sealing end face will change with the failure process. The leakage flow Q is related to the gap h between the two end faces and the pressure difference Δp. Therefore, the medium pressure p and the gap h between the two end faces are used as accelerating stress and sensitive stress, and the end face wear degradation process of the mechanical seal is experimentally studied.

[0040] Then the durability simulation analysis is carried out.

[0041] The acceleration factor of seal failure is determined based on the results of the planar seal failure mechanism analysis. In some embodiments, in the high-pressure common rail planar seal structure of the fuel system, the fuel pressure and the sealing surface flatness are selected as acceleration factors. The acceleration factor refers to the ratio of the life characteristic value under the accelerated stress to the life characteristic value under the normal stress, which is a dimensionless number.

[0042] After determining the acceleration factor, a wear degradation model is established according to the wear mechanism of mechanical parts. Based on the failure mode of the planar sealing structure, considering that wear is a loss-type mechanism and has degradation characteristics, in some embodiments, the degradation model Gamma process is selected to describe the end face wear degradation process of the precision parts seal.

[0043] The assumption for establishing the degradation model is that under the same test environment, the impact of random factors in the test process on the test samples tends to be consistent.

[0044] Assuming that a certain degradation quantity X(t) conforms to the Gamma process with shape parameter v (v>0) and scale parameter u (u>0), its probability density function can be expressed as:

[0045] in, is the Gamma function, x ≥ 0. Gamma distribution is an important process in random process theory, which can be used to describe monotonically increasing change processes; its shape parameter determines the shape of the distribution. For example, when v is less than 1, the gamma distribution presents a right-skewed shape, the tail of the distribution extends to the right, and the center is more concentrated than the tail; the scale parameter determines the amplitude of the distribution.

[0046] Considering that the characteristic life of products subjected to mechanical stress satisfies the inverse power law relationship, and that there are multiple sensitive stresses for the failure of the flat seal, a double stress inverse power law model is established as an acceleration model to evaluate the failure mode. The acceleration model can describe the relationship between medium pressure, end face flatness and degradation rate, and is used to analyze and predict the wear reliability and product life of mechanical seals.

[0047] From the basic inverse power law model, we can know that the linearized double stress inverse power law model can be expressed as lnK k =a+blnS 1k +clnS 2k , where: a=ln A, A>0, S represents stress, for example, S specifically represents mechanical stress, K is the degradation rate, a, b, c are constant coefficients, and k is the stress level number.

[0048] In the above formula, the degradation rate K is unknown, so the shape parameter v is used to describe the effect of the accelerated stress on the degradation process, and the relationship between the Gamma process and the double stress inverse power law model is established. The above acceleration model can be converted into lnv k =a+blnS 1k +clnS 2k .

[0049] The failure probability function of the pseudo-life of the sample is established based on the degradation probability density function to obtain the reliability function. The model parameters in the degradation model and the acceleration model are determined using small sample test data other than the accelerated test of the flat seal reliability. For example, the coefficient estimates a', b', c' in the acceleration model are obtained, and then the shape parameter v' and scale parameter u' of the degradation model under stress S are extrapolated. The Monte Carlo method is used to perform multiple random sampling of the degradation model and take the average value to perform failure probability analysis and obtain the wear degradation data prediction values ​​under different levels of stress.

[0050] When conducting the accelerated test of the reliability of the flat seal, stress is applied in different levels. The test selects the flatness h and the fuel pressure p as the accelerated stress, and conducts the test research on the end face wear degradation process of the mechanical seal.

[0051] In some embodiments, a dedicated reliability test bench with multiple pressure pulse waveforms is used to conduct the test. The fuel pressure used in the accelerated test is set, and the fuel pressure stress level is loaded by selecting different pulse waveforms. For example, the pulse waveform can be set to a sine wave, and the sine wave mean and amplitude range are set at the same time; the stress can be set to several levels and applied in sequence. The flatness stress level is achieved by selecting samples with different flatness schemes.

[0052] After obtaining the data of end face wear, working time, etc., the test value and the predicted value are verified. The end face wear and the wear degradation prediction value are plotted into degradation curves respectively; by comparing the coincidence of the two degradation curves, it is judged whether the test data is valid, and then whether the accelerated test of flat seal reliability is valid. When the overall change trend of the wear simulation data is basically consistent with that of the test data, it is considered that the calculation method of the above acceleration model is correct, and it can be judged that the acceleration method is effective.

[0053] The above-mentioned accelerated test method is specifically described below by taking the high-pressure common rail system injector body-guide body as a specific plane sealing structure.

[0054] First, the failure mechanism of the plane seal is analyzed. Combined with the seal structure of the injector body-guide body seal surface of the high-pressure common rail system, due to the high-pressure oil inside the injector body, the installation preload and vibration in two directions exist at the outer end. Therefore, the main stresses borne by the end face of the injector body include high-pressure fuel pressure, end face clamping force, thread preload, working medium temperature, etc.

[0055] Taking the injector body seal plane structure of the electronic fuel injector as an example, there are three types of plane contact between the injector body and the guide body end face: high-pressure oil channel, low-pressure oil channel and support boss. Based on the calculation formula of the fluid leakage volume flow rate Q, it can be concluded that the high-pressure oil channel is more prone to leakage than the low-pressure oil channel. Therefore, the subsequent simulation calculation and experimental method design focus on the sealing leakage of the high-pressure oil channel.

[0056] Durability simulation analysis is performed. Taking the high-pressure common rail flat seal structure of the fuel system as an example, the unit type of the high-pressure sealing ring of the injector body-guide body is set to Trias triangular secondary unit, and the mesh unit type is C3D10M. The number of meshes in the entire calculation model is about 500,000. Multi-scheme modeling and simulation are carried out for different injector body flatnesses. The flatness setting can be 0.001um, 0.002um, 0.003um and other schemes. After assigning values ​​to the material properties of the injector body and the guide body, the contact surface and contact equivalent contact relationship are defined, and the load is divided into several analysis steps for sequential application. The contact stress of the injector body-guide body sealing contact surface is calculated, and the stress data such as the average contact stress, maximum contact stress, and minimum contact stress are output. This data is used to guide the definition of the accelerated stress level value of the subsequent test link.

[0057] In the process of durability simulation analysis, since 1.2 or 1.5 times the fuel pressure is often used as the critical contact stress when the sealing surface leaks in engineering, the relationship between the two critical contact stresses of 1.2 or 1.5 times and the basic value is compared. The critical stress value is generally larger than the basic value, and the sealing reliability is verified. By setting different schemes to calculate model parameters, it is compared whether the sealing surface under different contact stress values ​​forms a sealing ring, that is, whether there is a leakage channel between the high-pressure oil channel and the outside world, so as to determine the sealing state. By analyzing whether there is a sealing state, it is determined whether it has failed. If it is in a non-sealed state, it means failure.

[0058] In the high-pressure common rail flat seal structure of the fuel system, fuel pressure and sealing surface flatness are selected as acceleration factors, and the Gamma degradation model and acceleration model based on the end face wear are constructed.

[0059] Carry out the accelerated test and select the test equipment to apply the load. The test equipment is a pressure pulse test bench (PN283 model), which provides square wave and sine wave waveforms; the pulse frequency range is 1 to 15Hz; the rail pressure measurement range is 0 to 400MPa.

[0060] In the accelerated test of the reliability of the flat seal of the high-pressure common rail fuel system, the combination of the fuel pressure mean value P0, amplitude A0 and flatness h0 is selected as the conventional stress level S0, and the remaining stress level combinations S1, S2, and S3 are used as accelerated stresses. The stress levels are shown in Table 1.

[0061] Table 1 Test stress levels

[0062]

[0063] It should be noted that the test samples under the same stress level are grouped together, and the number of samples in a group is not less than 4. The above fuel pressure can be determined by referring to 3 to 4 groups of stresses between the conventional stress level S0 and the material limit Smax.

[0064] For example, the first group of stresses S1 = 90% × (Smax-10% × Smax), the second group of stresses S2 = 90% × S1, the third group of stresses S3 = 85% × S2, and the fourth group of stresses S4 = 80% * S3. During the test, stresses are applied in sequence according to the above-mentioned levels.

[0065] For the injector body sealing plane, the inspection items before the test are the morphological parameters, surface condition and performance parameters, including flatness, roughness, residual deformation of the sealing plane, leakage amount / rate, and high-pressure sealing under pressure P0.

[0066] During the test, observe whether the test samples in each test group have fuel leakage; if there is no leakage, after the same test time T0, take the same 4 positions along the circumference of the sealing plane as measurement points. Measure the change in the height of the sealing surface of different test samples, take the average value of the wear amount at the 4 measurement positions as the wear degradation data, obtain the end face wear amount under each stress, and draw the degradation curve.

[0067] After the test, the surface state of the morphological parameters, such as flatness, roughness, residual deformation of the sealing plane, and surface scratches (Rz) need to be obtained; at the same time, the detection performance parameters, such as leakage volume / rate, 200MPa high-pressure sealing and other parameters need to be obtained.

[0068] Finally, the test results and failure data under the above stress limit are used for analysis. The test data are compared with the predicted data to determine the reliability of the test.

[0069] In addition, reliable life prediction can also be performed. Ensure that the main failure modes of the tests of the above stress values ​​are the same, and draw the failure distribution curve found in the previous step in Weibull coordinates and determine the characteristic life of the test sample. Based on the established acceleration model, the number of cycles / failure time of the (failure) data points in the wear failure distribution curve under different stress levels is converted to the number of cycles / failure time under the expected normal stress. According to the reliability curve, the relationship between time and component reliability is obtained.

[0070] The above method applies different stress levels during the test phase. Compared with the traditional constant force and long-term wear method, it can achieve rapid testing, and by comparing the test data with the predicted values ​​obtained by the wear degradation model and the acceleration model, the effectiveness of the accelerated test of the reliability of the flat seal under this stress can be judged.

[0071] The present application uses specific words to describe the embodiments of the present application. For example, "one embodiment", "an embodiment", and / or "some embodiments" refer to a certain feature, structure or characteristic related to at least one embodiment of the present application. Therefore, it should be emphasized and noted that "one embodiment" or "an embodiment" or "an alternative embodiment" mentioned twice or multiple times in different positions in this specification does not necessarily refer to the same embodiment. In addition, some features, structures or characteristics in one or more embodiments of the present application can be appropriately combined.

[0072] Although the present invention is disclosed as above with preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art may make possible changes and modifications without departing from the spirit and scope of the present invention. Therefore, any modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall fall within the protection scope defined by the claims of the present invention.

Claims

1. Plane seal reliability accelerated test method, characterized in that: The steps include: Analyze the failure mechanism of planar seals, determine the stress type of sealing parts, establish leakage characterization models, and perform durability simulation analysis of sealing parts; Determine the acceleration factor of seal failure based on the analysis results of the plane seal failure mechanism; Establish and solve the wear degradation model and acceleration model to obtain the predicted value; Conducting accelerated tests on the reliability of flat seals, applying stress in different levels during the tests to obtain test data; The test data is compared with the predicted value to determine whether the accelerated test of plane seal reliability is effective.

2. The method according to claim 1, characterized in that The sealing surface adopts liquid sealing, and the leakage characterization model is Among them, Q is the volume flow rate of fluid leakage; h is the gap between the two rough surfaces; η is the dynamic viscosity; r2 is the outer radius of the sealing interface; r1 is the inner radius of the sealing interface; p1 is the internal fluid pressure; and p2 is the external environmental pressure.

3. The method according to claim 1, characterized in that The degradation model is a Gamma model, and a probability density function of the degradation amount is established.

4. The method according to claim 3, characterized in that The acceleration model is an inverse power law model lnK k =a+blnS 1k +clnS 2k , where K is the degradation rate, a, b, c are constant coefficients, k is the stress level number, and S is the stress.

5. The method according to claim 4, characterized in that The model parameters in the degradation model and the acceleration model are determined using small sample test data, and failure probability analysis is performed to determine the predicted value of wear degradation data.

6. The method according to claim 1, characterized in that When conducting accelerated tests on the reliability of flat seals, different fuel pressure stress levels are loaded using different pulse waveforms.

7. The method according to claim 6, characterized in that The test data includes the end surface wear amount under different stresses, and the predicted value includes the wear degradation prediction value; Plotting the end face wear amount and the wear degradation prediction value into degradation curves respectively; By comparing the overlap of the two degradation curves, it is determined whether the test data is valid, and further whether the accelerated test of plane sealing reliability is valid.

8. The method according to claim 1, characterized in that Before the test, the flatness, roughness, residual deformation of the sealing plane and the leakage of the contact surface are recorded; during the test, the fluid leakage and the wear of the sealing surface are recorded; after the test, the flatness, roughness, residual deformation of the sealing plane, surface scratches and leakage are recorded.

9. The method according to claim 1, characterized in that The sealing surface stress parameters include the average contact stress, the maximum contact stress and the minimum contact stress of the sealing contact surface under different sensitive stresses.

10. The method according to claim 1, characterized in that Fuel pressure and sealing surface flatness were selected as acceleration factors.

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