Prediction Method for Duration and Equivalent Aperture of Positive Pressure Leakage Process of Automotive Fuel System

Abstract

The present invention provides a method for predicting the duration and equivalent pore diameter of a positive-pressure leakage process in an automobile fuel system. The method includes calculating the dimensionless time corresponding to the system's detection pressure differential during the positive-pressure leakage process, obtaining an estimated leakage duration through calibration testing, and calculating and obtaining a flow coefficient from the calibration test. Finally, the calibrated flow coefficient is used to detect the actual pressure decay process and calculate the equivalent pore diameter of the leak hole. The present invention has the following advantages: it eliminates the need for extensive test calibration for diagnostic models, reduces R&D costs, establishes a standard for detection duration, and can detect information about the leak hole diameter, thus providing wide applicability.

Description

Technical Field

[0001] The present invention relates to the technical field of automobile detection, and in particular to a method for predicting the duration and equivalent pore diameter of a positive pressure leakage process of an automobile fuel system. Background Art

[0002] With the increase in the number of cars on the road, the environmental pollution and increased carbon emissions caused by the leakage of HC emissions from fuel vapor generated in the fuel evaporation system of motor vehicles cannot be ignored. The country has also formulated relevant regulations and put forward requirements for online diagnostic testing of leakage in the fuel evaporation system of motor vehicles, promoting the continuous improvement of monitoring technology and controlling the pollution of HC emissions to the environment.

[0003] Existing technologies, such as patent CN109113897B, propose a vehicle fuel evaporation leak diagnostic device and method. These devices utilize multiple devices to address leak diagnosis issues in turbocharged engines and dual-fuel vehicles. The diagnostic criterion is the detected pressure decay rate curve: the diagnostic result is obtained by comparing the detected pressure decay rate curve with a preset curve. This diagnostic method uses different preset pressure curves for different vehicle models and fuels, and the preset pressure values, preset times, and preset temperatures required to be obtained through extensive testing. Targeted research on diagnostic models for specific vehicle models using a specific fuel requires significant experimental effort, and the resulting diagnostic models are not universally applicable.

[0004] Numerous researchers have proposed methods for diagnosing fuel evaporation system leaks, but existing diagnostic models are mostly based on extensive testing. Model parameters are not universally applicable, requiring significant human and material resources to determine diagnostic parameters for specific vehicle models, placing a heavy burden on companies. The diagnostic time set in diagnostic methods is also based on testing, lacking a unified basis or standard, and some methods have long detection times. Furthermore, existing diagnostic methods are mostly targeted at leaks within a specific aperture and are unable to obtain information about equivalent apertures.

[0005] To solve the above problems, the present application provides a leakage hole prediction method for the positive pressure leakage process of the automobile fuel system, which solves or improves the problems in the existing technology that the diagnostic model parameters need to be calibrated with a large number of tests, the R&D cost is high, and the detection time has no clear standard. It can also detect the pore size information and has a wide applicability. Summary of the Invention

[0006] In order to solve the above technical problems, the present invention discloses a method for predicting the duration and equivalent pore diameter of the positive pressure leakage process of an automobile fuel system. The technical solution of the present invention is implemented as follows:

[0007] A method for predicting the duration of a positive pressure leakage process in an automobile fuel system comprises the following steps:

[0008] S1. Calculate the dimensionless time of the system detection pressure difference corresponding to the positive pressure leakage process;

[0009] S2. Conduct calibration test and predict test detection time;

[0010] Wherein, the S1 step includes

[0011] S1.1. Detect the ambient atmospheric pressure p;

[0012] S1.2. Determine the system detection pressure difference Δp;

[0013] S1.3. Determine the initial system pressure p C,0 ;

[0014] S1.3.1. Based on the detected ambient atmospheric pressure p and the system detection pressure difference Δp, and according to the preset pressure difference Δp0 of the gas source in the diagnostic device, the initial pressure of the system is obtained. The calculation formula is:

[0015] p C,0 =p+Δp0;

[0016] S1.4. Calculate the dimensionless time of the positive pressure leakage process using the following formula:

[0017]

[0018] The S2 step includes:

[0019] S2.1. Obtaining the gas volume V of the container c ;

[0020] S2.2. Get the ambient temperature T C ;

[0021] S2.3. Determine the leakage aperture d of the leakage point;

[0022] S2.4. Estimate the flow coefficient C' in the calibration test d ;

[0023] S2.5. Obtain the estimated time for the system initial pressure to decay to the system detection pressure difference. The calculation formula is as follows:

[0024]

[0025] Preferably, step S1.4 includes S1.4.1, when the preset pressure difference of the gas source is twice the system detection pressure difference Δp0=2Δp, the calculation formula of the dimensionless time is as follows:

[0026]

[0027] Preferably, the step S1.4 further includes S1.4.2, when the system detects that the pressure difference is 0, the calculation formula of the dimensionless time is as follows:

[0028]

[0029] A method for predicting an equivalent aperture during a positive pressure leakage process of an automobile fuel system is characterized by comprising the following steps:

[0030] S1. Perform a calibration test to obtain the leakage hole flow coefficient;

[0031] S2. Use the calibrated flow coefficient to detect the actual pressure decay process and calculate the equivalent aperture of the leak hole;

[0032] The S1 step includes:

[0033] S1.1. Perform the calibration test to detect the initial pressure change process of the corresponding system and obtain a pressure decay curve;

[0034] S1.2. Calculate the flow coefficient C of the system's initial pressure decay process during the calibration test d , the calculation formula is as follows,

[0035]

[0036] S1.2.1. The time required for the pressure to decay to the system detection pressure difference t C ;

[0037] The step S2 includes:

[0038] S2.1. Obtain the actual gas volume V in the system;

[0039] S2.2. Obtain the actual gas temperature T in the system;

[0040] S2.3. Detect the time t required for the system initial pressure to decay to the system detection pressure difference;

[0041] S2.4. Calculate the constant B determined by the leak hole;

[0042] S2.5. Compare the obtained constants with those obtained in the calibration test. The basic range of pore size can be determined as

[0043] S2.6. Calculate the discharge coefficient using interpolation based on the basic range of apertures;

[0044] S2.7. Obtain the equivalent aperture of the system leakage hole based on the obtained flow coefficient

[0045] Preferably, the calculation formula of step S2.4 is as follows,

[0046]

[0047] Preferably, the calculation formula of step S2.6 is as follows,

[0048]

[0049] Preferably, the calculation formula of step 2.7 is as follows:

[0050]

[0051] Preferably, the equivalent pore size The definition is: refers to the equivalence in flow rate, that is, the leakage of the system is equivalent to the leakage under a specific circular hole diameter.

[0052] The implementation of the technical solution of the present invention can solve the technical problems in the prior art that a large number of test calibrations are required for diagnostic model parameters, the R&D cost is high, and there is no clear standard for detection time. The implementation of the technical solution of the present invention calculates the dimensionless time corresponding to the detection pressure difference in the positive pressure leakage process, and obtains the estimated leakage time through calibration tests. At the same time, through the calibration test, the flow coefficient of the calibration test is calculated and obtained. Finally, the calibrated flow coefficient is used for the actual pressure decay process detection, and the equivalent aperture of the leakage hole is calculated and obtained, which can achieve the technical effects of reducing R&D costs, reducing test calibration, establishing clear time detection standards, being able to detect aperture information, and wide applicability. BRIEF DESCRIPTION OF THE DRAWINGS

[0053] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are merely embodiments of the present invention applicable to certain test conditions. For ordinary technicians in this field, other drawings can be obtained based on these drawings without any creative work.

[0054] Figure 1 It is a workflow diagram of the present invention;

[0055] Figure 2 This is the pressure decay process diagram under the equivalent leakage aperture of 0.5mm;

[0056] Figure 3 This is the pressure decay process diagram under the equivalent leakage aperture of 1.0mm. DETAILED DESCRIPTION

[0057] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0058] Example 1

[0059] In a specific embodiment 1, Figure 1 As shown in , a method for predicting the duration of the positive pressure leakage process of the automobile fuel system is Figure 1 As shown, the steps include:

[0060] S1. Calculate the dimensionless time corresponding to the detection pressure difference during the positive pressure leakage process;

[0061] S2. Conduct calibration test and predict test detection time;

[0062] Among them, step S1 includes:

[0063] S1.1. Obtain the atmospheric pressure p of the testing environment based on the ambient temperature and altitude at the time of testing;

[0064] S1.2. A constant gas source is provided in the device using the positive pressure decay method to determine the system detection pressure difference Δp;

[0065] S1.3. Determine the initial system pressure P C ;

[0066] S1.3.1. Based on the detected ambient atmospheric pressure p and the system detection pressure difference Δp, and the preset pressure difference Δp0 of the gas source in the diagnostic device, the system initial pressure is obtained. The specific calculation formula is:

[0067] p C,0 =p+Δp0;

[0068] S1.4. Calculate the dimensionless time of the positive pressure leakage process using the following formula:

[0069]

[0070] The units of the dimensionless time calculation formula are expressed as follows:

[0071] τ — dimensionless time;

[0072] p C,0 ——Initial pressure of the container, in kPa;

[0073] Δp——detection pressure difference, unit is kPa;

[0074] p——ambient atmospheric pressure, in kPa;

[0075] Step S2 includes:

[0076] S2.1. Obtaining the gas volume V of the container c ;

[0077] S2.2. Get the ambient temperature T C ;

[0078] S2.3. Determine the leakage aperture d of the leakage point;

[0079] S2.4. Estimation of the flow coefficient C' during the test d In the process of estimating the flow coefficient, the flow coefficient corresponding to the leakage hole is estimated based on the test or empirical formula. For example, for a thin-walled circular hole, the flow coefficient is generally 0.6-0.62. When the flow coefficient is 1, the leakage speed reaches the maximum and the leakage time is the shortest.

[0080] S2.5. Obtain the estimated time for the system initial pressure to decay to the system detection pressure difference. The calculation formula is as follows:

[0081]

[0082] in

[0083] t′——estimated detection time, in seconds;

[0084] V C ——Volume of gas in container, in m 3 ;

[0085] C d ——Small hole flow coefficient, for thin-walled circular holes, take 0.60-0.62;

[0086] d——diameter of the small hole, in m;

[0087] R is the gas constant of dry air, which is 287 J / (kg·K);

[0088] T C ——Ambient temperature, in K.

[0089] In this embodiment, when the initial pressure of the container is determined, the dimensionless leakage time during the positive pressure leakage process when the pressure drops to a certain value is obtained. The implementation of this method solves the problem of long detection time of the diagnostic methods of some companies in the existing technology, and provides a unified standard and basis for the diagnostic time, without spending a lot of costs on a large number of experiments.

[0090] In a preferred embodiment, to ensure the accuracy of the detection device and the rationality of the range of pressure difference variation, step S1.4 includes S1.4.1. Generally, half of the preset gas source pressure difference is taken, that is, the preset gas source pressure difference is twice the system detection pressure difference. In this case, the expression is Δp0 = 2Δp. Substituting this expression into the calculation formula of the initial system pressure at this time and the calculation formula of the dimensionless time of the positive pressure leakage process, the dimensionless time at this time is calculated. After simplification, the calculation formula of the dimensionless time at this time is obtained:

[0091]

[0092] In a preferred embodiment, step S1.4 further includes S1.4.2. When the system detected pressure difference is 0, that is, the system initial pressure decays to atmospheric pressure, the expression is substituted into the calculation formula of the system initial pressure at this time and the calculation formula of the dimensionless time of the positive pressure leakage process to calculate the dimensionless time at this time. After simplification, the calculation formula of the dimensionless time at this time is obtained:

[0093]

[0094] Example 2

[0095] In a specific embodiment 2, a method for predicting the equivalent aperture of a positive pressure leakage process of an automobile fuel system is provided. Figure 1 As shown, the steps include the following:

[0096] S1. Perform a calibration test to obtain the leakage hole flow coefficient;

[0097] S2. Use the calibrated flow coefficient to detect the actual pressure decay process and calculate the equivalent aperture of the leak hole;

[0098] The S1 step includes:

[0099] S1.1. Conduct a calibration test to detect the pressure change process in the corresponding system and obtain the pressure decay curve;

[0100] S1.2. Calculate the flow coefficient C during the pressure decay process during the calibration test d , through the flow coefficient and the time t required for the pressure to decay to the detection pressure difference C The relationship between the two is converted to obtain the flow coefficient calculation formula of the pressure decay process in the calibration test.

[0101]

[0102] t C ——The time required for the initial pressure of the system to decay to the detection pressure difference during the calibration test, in seconds;

[0103] S1.2.1. Detect the time t required for the system initial pressure to decay to the system detection pressure difference C ;

[0104] Step S2 includes,

[0105] S2.1. Obtain the actual gas volume V in the system. If the vehicle's fuel tank contains some fuel, the actual gas volume is the tank volume minus the volume occupied by the fuel.

[0106] S2.2. Obtain the actual gas temperature T in the system;

[0107] S2.3. Detect the time t required for the system initial pressure to decay to the system detection pressure difference;

[0108] S2.4. Calculate the constant B determined by the leak hole;

[0109] S2.5. Compare the obtained constants with those obtained in the calibration test. The basic range of pore size can be determined as

[0110] S2.6. Use interpolation method to calculate the flow coefficient based on the basic range of aperture to reduce errors;

[0111] S2.7. Obtain the equivalent aperture of the system leakage hole based on the obtained flow coefficient

[0112] At this time, for a given system detection pressure difference, the system pressure can be monitored to obtain information on the equivalent aperture of the leak hole, which can provide a method for high-precision monitoring of automobile system leaks.

[0113] In this embodiment, the calibrated flow coefficient can be used to diagnose the equivalent leakage hole diameter in actual detection, providing higher-precision data for automobile online monitoring. At the same time, in this specific implementation method, this part is the actual detection application part. After the detection parameter calibration is completed, the actual gas volume and ambient temperature are obtained, and the time required for the actual leakage to the detection pressure difference is detected. Finally, the equivalent hole diameter of the leakage hole is obtained. Compared with the parameter model of traditional technology, which is not universal and requires a lot of manpower and material costs to determine the diagnostic parameters for specific vehicle models, this method does not require a large number of calibration tests and is low-cost, reducing the burden on enterprises. In response to the country's call to reduce the leakage of HC emissions in fuel vapor generated in the fuel system of motor vehicles, advanced monitoring technology is proposed to achieve the purpose of controlling the pollution of HC emissions to the environment.

[0114] In a preferred embodiment, the calculation formula of step S2.4 is as follows:

[0115]

[0116] in

[0117] t——The time required for the pressure to decay to the detection pressure difference during detection, in seconds;

[0118] V——gas volume in the system, in m 3 ;

[0119] T——gas temperature, in K;

[0120] When using this calculation formula, the constant can be obtained by only detecting the gas volume V in the system, the gas temperature T, and the time t required for the initial pressure of the system to decay to the detection pressure difference.

[0121] In a preferred embodiment, the calculation formula of step S2.6 is as follows:

[0122]

[0123] in

[0124] d1——small aperture, in m;

[0125] d2——large aperture, in m;

[0126] C d,1 ——the small hole flow coefficient when the aperture is d1;

[0127] C d,2 ——The macropore flow coefficient when the pore diameter is d2;

[0128] ——Leakage hole flow coefficient.

[0129] In a preferred embodiment, the calculation formula of step 2.7 is as follows:

[0130]

[0131] Among them ——Equivalent aperture of leakage hole, in m.

[0132] In a preferred embodiment, the equivalent pore size The definition is: it refers to the equivalence in flow rate, that is, the leakage of the system is equivalent to the leakage under a specific circular hole diameter. During the actual operation of the system, there is no need to measure the actual circular hole. It is only necessary to detect the current flow coefficient and enter it into the calculation formula to obtain the information of the leakage hole diameter, and the data provided is also very accurate.

[0133] Application Examples

[0134] Taking the positive pressure leakage process of a certain automobile fuel system as an example, the pressure decay process and the time required to decay to the system detection pressure difference under different leak hole diameters are predicted. The steps are as follows:

[0135] S1.1. Based on the ambient temperature and altitude at the time of testing, the atmospheric pressure of the testing environment is 101 kPa;

[0136] S1.2. The system's detection pressure difference is 0kPa;

[0137] S1.3. It can be determined that the initial system pressure is 105 kPa;

[0138] S1.4. The dimensionless time of the positive pressure leakage process calculated using the method given in the present invention is 0.395.

[0139] S2.1. The gas volume of the container is 60L;

[0140] S2.2, obtain the ambient temperature as 20°C;

[0141] S2.3. Determine the leak points with leak apertures of 0.5 mm and 1.0 mm respectively;

[0142] S2.4. The flow coefficients corresponding to 0.5 mm and 1.0 mm obtained from the calibration experiment are 0.84 and 0.87 respectively.

[0143] S2.5. The estimated time for the system initial pressure to decay to the system detection pressure difference is 350.4s and 84.6s respectively.

[0144] S2.6: If the test is performed at half the preset pressure difference, the estimated time for the system initial pressure to decay to half the original gauge pressure (the difference between the internal pressure of the container and the ambient pressure) is 102.8s and 24.8s respectively. Compared with the test time in S2.5, the test efficiency can be increased by 2 times.

[0145] Analyze and calculate the pressure decay process under the equivalent leakage aperture of 0.5mm as follows Figure 2 As shown, the pressure decay process under the equivalent leakage aperture of 1.0 mm is as follows Figure 3 shown. Figure 2 and Figure 3 In the figure, the horizontal axis is the detection time, and the vertical axis represents the change process of the gauge pressure in the container from the initial leakage to the complete leakage and the consistency with the ambient pressure. The dotted line represents the attenuation process of the container gauge pressure when the flow coefficient is not corrected, and the solid line is the attenuation process of the container gauge pressure calculated based on the leakage coefficient of the existing standard parts. Figure 2 and Figure 3It can be seen that the decay process slows down after considering the flow coefficient. The application example further illustrates that the larger the leak diameter, the faster the internal gauge pressure decays. Furthermore, if only the case where the internal pressure decays to half of the original gauge pressure is considered, the detection time can be further shortened to 30% of the original full leak process.

[0146] The beneficial effects of the present invention are:

[0147] 1. The present invention uses calibrated leak holes and pressure differential data to diagnose the equivalent leak hole diameter present during the system's initial pressure decay. Given a fixed initial pressure in the container, the dimensionless leakage time required for the pressure to drop to a certain value during a positive pressure leak can be calculated using a formula. Calibration testing can then be performed to determine the flow coefficient of the corresponding leak hole. Finally, the calibrated flow coefficient is used to diagnose the equivalent leak hole diameter during actual testing, providing higher-precision data for online vehicle monitoring.

[0148] 2. The detection indicators given in the present invention are only time and pressure value at the corresponding time. There is no need to monitor the pressure for a long time and perform data analysis in the method of using parameter change rate for diagnosis. This plays an important role in simplifying the detection device and saving detection costs.

[0149] It should be pointed out that the above are only preferred embodiments of the present invention and are not intended to limit the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for predicting the duration of a positive pressure leakage process in an automobile fuel system, characterized in that: The steps are as follows: S1. Calculate the dimensionless time of the system detection pressure difference corresponding to the positive pressure leakage process; S2. Conduct a calibration test and predict the detection time of the calibration test; Wherein, the step S1 includes S1.

1. Detect ambient atmospheric pressure p; S1.

2. Determine the system detection pressure difference Δp; S1.

3. Determine the initial system pressure p C,0 ; S1.3.

1. Based on the detected ambient atmospheric pressure p and the system detection pressure difference Δp, and according to the preset pressure difference Δp0 of the gas source in the diagnostic device, the initial pressure of the system is obtained. The calculation formula is: p C,0 =p+Δp0; S1.

4. Calculate the dimensionless time of the positive pressure leakage process using the following formula: The step S2 includes: S2.

1. Obtaining the gas volume V in the container c ; S2.

2. Get the ambient temperature T C ; S2.

3. Determine the leakage aperture d of the leakage point; S2.

4. Estimation of the flow coefficient C' during the test d ; S2.

5. Obtain the estimated time for the initial system pressure to decay to the system detection pressure difference, using the following calculation formula:

2. The method for predicting the duration of a positive pressure leakage process in an automobile fuel system according to claim 1, characterized in that: The step S1.4 includes S1.4.1, when the preset pressure difference of the gas source is twice the system detection pressure difference Δp0=2Δp, the calculation formula of the dimensionless time is as follows:

3. The method for predicting the duration of a positive pressure leakage process in an automobile fuel system according to claim 2, characterized in that: The step S1.4 also includes S1.4.2, when the system detects that the pressure difference is 0, the calculation formula of the dimensionless time is as follows:

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