An acceleration sensor-based method for testing the mass flow of an automobile airbag inflator

Abstract

The application discloses a kind of quality flow test methods of automobile safety air bag gas generator based on acceleration sensor, utilize rigid container, piston, acceleration sensor, refrigeration type infrared thermal imager, pressure sensor and data recording device;The linear motion process of piston is measured by acceleration sensor, and the volume of gas generated by gas generator is converted;Combining the measured gas pressure, temperature, the gas density is solved by ideal gas state equation;Gas volume and density are solved by gas mass flow and its dynamic change.By the application, the mass flow of mixed gas generated after ignition of air bag gas generator and the mass flow of single gas component can be measured, and a gas mass flow test method is provided for the research and production of actual air bag gas generator.

Description

Technical Field

[0001] This invention relates to automotive passive safety technology, specifically to a mass flow test method for automotive airbag gas generators based on an acceleration sensor. Background Technology

[0002] With the rapid development of the automotive industry in various countries, the number of car models and vehicles on the market is increasing. Based on road safety and consumers' growing emphasis on safety, the China New Car Assessment Program (C-NCAP) and the China Insurance Automotive Safety Index (C-IASI) have been adjusting the passive crash test conditions for automobiles year by year, raising the evaluation standards for crash performance. For example, in recent years, frontal 50% overlap vehicle-to-vehicle collision (MPDB), right-side 25% overlap small offset collision (SORB), and side pole impact have been added, improving the quality of the collision barrier and the collision speed. This has placed increasingly higher demands on the area protected by car airbags and their performance.

[0003] Automotive airbags mainly consist of a gas generator and an airbag. The gas generator, a core component of the airbag, primarily comprises an ignition agent, a gas-generating agent, and a metal filter. The igniter ignites the ignition agent, which releases heat. The gas-generating agent undergoes a violent chemical reaction, producing gases such as nitrogen. The metal filter filters out any remaining agent residue, and the gas enters the airbag through the inflation port. The gas generator largely determines whether the airbag performance meets the requirements for protecting occupants from hard contact with the vehicle structure after a collision. The mass flow of the airbag gas generator determines the airbag's inflation and deployment speed, pressure changes within the airbag, etc. Furthermore, the mass flow curve is a crucial parameter in airbag CAE (Computer-Aided Engineering) modeling, affecting the accuracy of airbag CAE simulation results. Therefore, testing the mass flow of the airbag gas generator is essential for the research, development, and production of airbag gas generators, as well as for airbag CAE modeling.

[0004] The commonly used method for obtaining the mass flow rate of gas generators in existing technologies is to conduct a closed combustion chamber test (Tank test) on the gas generator. This involves detonating the airbag gas generator within a sealed, rigid container, obtaining a pressure-time (pt) curve using a pressure sensor, and then using empirical algorithms to calculate the mass flow rate curves for each gas component. Alternatively, sophisticated instruments such as spectrometers and chromatographs are used to determine the gas components and their proportions, but it is difficult to accurately measure the mass flow rate curves of each gas component. Existing technologies still have certain limitations in addressing increasingly stringent automotive crash safety standards.

[0005] Patent application number 200520104200.8 provides a performance testing device for an airbag gas generator, capable of testing the pressure-time curve, temperature, composition and concentration of the gas produced after ignition, as well as the composition and content of solid residue after combustion. However, it cannot directly and accurately measure the mass flow curve of the airbag gas generator.

[0006] The patent application number 201610586401.9 provides a performance testing device for airbag gas generators, which can realize the rapid opening and closing of the canister lid of the testing device, improving the convenience of existing testing devices. However, it is still based on existing testing and evaluation methods and devices, and cannot directly and accurately measure the mass flow curve of the airbag gas generator.

[0007] The patent application number 202021296314.8 provides a test pressure device for airbag gas generators, which solves the problems of existing airbag gas generator test devices being unable to effectively fix the tested product and the inconvenience of moving the airbag gas generator test device; however, it only improves the operational convenience of the existing test device and cannot directly and accurately measure the mass flow curve of the airbag gas generator. Summary of the Invention

[0008] Purpose of the Invention: The purpose of this invention is to address the shortcomings of existing technologies and provide a method for testing the mass flow of an automotive airbag gas generator based on an accelerometer. This method measures the linear motion of the piston using an accelerometer, converting this motion into the volume of gas produced by the gas generator. Combined with the measured gas pressure and temperature, the gas density is calculated using the ideal gas law. The gas mass flow and its dynamic changes are then determined from the gas volume and density. This invention can measure the mass flow of the mixed gas and the mass flow of individual gas components generated after the airbag gas generator ignites, providing a gas mass flow testing method for the research and development and production of actual airbag gas generators.

[0009] Technical solution: The present invention provides a mass flow testing method for automotive airbag gas generators based on an acceleration sensor, comprising the following steps:

[0010] Step S1: Set up the test device; the test device includes a rigid container, a piston, an accelerometer, and a cooled infrared thermal imager; the rigid container is a transparent hollow cylinder, and an airbag gas generator is fixed at the bottom of the rigid container. The piston is located inside the rigid container, and the piston as a whole is a hemispherical shell with the opening facing downwards. A pressure sensor is set at the center of the top of the piston. The accelerometer and the cooled infrared thermal imager are respectively placed perpendicular to the central axis of the rigid container; a positioning cantilever is fixed above the rigid container, and a square positioning hole is placed on the cantilever at a position corresponding to the central axis of the rigid container. A positioning post is installed at the top of the piston, and the cross-section of the positioning post matches the shape and size of the positioning hole.

[0011] Step S2: Activate the ignition device inside the rigid container and simultaneously start the accelerometer, cooled infrared thermal imager, and data recording device; after ignition, the piston moves vertically linearly inside the rigid container; the accelerometer collects the piston's trajectory in the rigid container, the cooled infrared thermal imager collects the dynamic change of the gas temperature distribution cloud map inside the rigid container over time during the test, and the pressure sensor records the dynamic information of the gas pressure value per unit area.

[0012] Step S3: Based on the real-time data collected by the accelerometer, cooled infrared thermal imager, and pressure sensor, calculate the increase in volume formed by the piston and the rigid container during the piston's movement. This increased volume is the amount of gas produced by the violent combustion of the airbag gas generator. The pressure sensor measures the gas pressure value, and the gas density is solved using the ideal gas law. Then, using the gas volume and density, the mass flow rate M′ of the total mixed gas produced by the combustion of the airbag gas generator is calculated. G Its dynamic changes over time, and the solution of the mass flow M′ of a single gas in the gas generated by the combustion of the airbag gas generator. N and its dynamic changes over time;

[0013] Step S4: After the piston stops moving, turn off all equipment, and record all data and image information by the data recording device.

[0014] Furthermore, the mass flow M′ of the total mixed gas generated by the combustion of the airbag gas generator G The mass flow M′ of a single gas in the gas generated by the combustion of the gas in the airbag gas generator N The specific solution method is as follows:

[0015] (A) Solve for the mass M of the mixed gas according to formula (1) G :

[0016] M G =ρ T ·V G (1)

[0017] In equation (1), M G The unit is kg; ρ T Density of the gas mixture, in kg·m³ -3 V G Volume, unit m 3 ;

[0018] (A1), the density ρ of the mixed gas in equation (1) T The solution method is as follows: Based on the chemical ratio of the ignition agent and the gas-generating agent, the N gas components produced by the gas generator combustion can be obtained through agent experiments and by consulting relevant physicochemical handbooks. The molar ratio of the corresponding N gas components is denoted as: N1∶N2∶…N N ,

[0019] Where N1+N2+…N N =1; the molar mass of the corresponding N gases is denoted as M. G1 M G2 , ...M GN The unit is kg / mol;

[0020] From the ideal gas law: PV=nR(T+273.15) (2)

[0021] In equation (2), P is pressure, in Pa; V is volume, in m³. 3 n is the number of moles, in mol; R is the proportionality constant, taken as 8.31 J / (mol·K); T is the temperature in Celsius, in °C; 273.15 is the conversion factor for converting Celsius to absolute temperature in K.

[0022] Given n = m / M m Substituting ρ=m / V into equation (2), we get:

[0023] ρ = PM m / [R(T+273.15)] (3)

[0024] In the formula, m is the mass, in kg, M m ρ is the molar mass, in kg / mol, and ρ is the density, in kg·m³. -3 The remaining parameters are the same as in equation (2);

[0025] In equation (3), the mixed gas pressure is obtained by extracting the dynamic relationship between the gas pressure per unit area and time from the pressure sensor on the inner side of the piston top:

[0026] P T =J0+J1T 1 +J2T 2 +…J n T n (4)

[0027] In equation (4), P T The pressure of the mixed gas per unit area, in Pa, J0…J n Let T be an undetermined constant, and T be a time variable in milliseconds; n = 0, 1, 2, 3…n;

[0028] Based on the theory of partial pressures of gases, according to equation (4) and the molar ratio of N gas components N1:N2:…N… N Solve for the gas pressure of a single gas:

[0029] First gas: P1 = N1·(J0 + J1T) 1 +J2T 2 +…J n T n )

[0030] The second gas: P2 = N2·(J0 + J1T) 1 +J2T 2 +…J n T n )

[0031] And so on to the Nth gas: P N =N N ·(J0+J1T 1 +J2T 2 +…J n T n (5)

[0032] The sum of the partial pressures of N gases is the pressure of the mixed gas: P1 + P2 + ... + P N =P T ;

[0033] At high temperatures, gas molecules move violently, and the molar mass of a gas mixture is the weighted sum of the molar masses of the N gases:

[0034] M mol =M G1 N1+M G2 N2…+M GN N N (6)

[0035] In equation (6), M mol Molar mass of the gas mixture, in kg / mol;

[0036] Gas temperature acquisition method: A cooled infrared thermal imager was used to acquire the dynamic change of gas temperature distribution cloud map over time T throughout the entire test process, and the following data were extracted:

[0037] Time = nΔt; Temperature = T Gn

[0038] Time represents the moment the temperature distribution cloud map was acquired, in milliseconds (ms); Δt represents the sampling time interval, in milliseconds (ms); Temperature represents the temperature, in degrees Celsius (°C), or T. Gn The average gas temperature at time nΔt;

[0039] Based on the extracted data, the average gas temperature T is fitted. G The dynamic equation of change with time T is (7):

[0040] T G =E0+E1T 1 +E2T 2 +E3T 3 +…E n T n (7)

[0041] In equation (7), E0…E n For each variable, T is an undetermined constant; T is a time variable, in milliseconds (ms).

[0042] Substituting equations (4), (6), and (7) and R = 8.31 J / (mol·K) into equation (3), we can obtain the density ρ of the mixed gas produced by the combustion of the airbag gas generator. T Polynomial equations that vary with time:

[0043] ρ T =(J0+J1T) 1 +··J n T n (M) G1 N1+··M GN N N ) / [8.31(E0+E1T 1 ··E n T n +273.15)] (8)

[0044] (A2), Mixed gas volume V G The solution method is as follows: Read the acceleration sensor data on the outer side of the piston top and extract the dynamic equation of acceleration versus time:

[0045] a k =b0+b1T 1 +b2T 2 +b3T 3 +…b n T n (9)

[0046] In equation (9), n = 0, 1, 2, 3, 4…n, a k The linear acceleration of the piston is expressed in mm / ms²; b0…b nFor each variable, T is an undetermined constant; T is a time variable, in milliseconds (ms).

[0047] Integrating the time variable T of equation (9), we can solve the polynomial equation of the linear velocity of the piston versus time:

[0048]

[0049] In equation (10), v′ k This refers to the linear speed of the piston, in mm / ms; the other parameters are the same as in equation (9);

[0050] Equation (10) is integrated again with respect to the time variable T to solve the polynomial equation of the piston's linear motion displacement versus time:

[0051]

[0052] In equation (11), D′ k This refers to the linear displacement of the piston, in mm; the other parameters are the same as in equation (9).

[0053] Before testing, the volume of the airbag gas generator was measured to be V. f Unit: mm 3 Then, before the test, the initial gas volume V0 in the space formed by the piston and the hollow cylindrical rigid container is:

[0054] V0=(2 / 3πr 3 -V f )×10 -9 (12)

[0055] In equation (12), V0 refers to the initial gas volume of the system, in m³. 3 r is the inner radius of the piston hemispherical shell, in mm;

[0056] The gas volume within the ignition and combustion system of the airbag gas generator is the sum of the volumes of the sealed space formed by the piston and the rigid container, combined with equation (11) for the linear displacement D′ of the piston. k The gas volume V in the airbag gas generator ignition and combustion system is:

[0057] V=(2 / 3πr 3 +2πR 2 ·D′ k -V f )×10 -9

[0058]

[0059] In equation (13), V G Unit m 3 R is the inner radius of the rigid container, in mm; the other parameters are the same as in equation (11);

[0060] The gas production V of the airbag gas generator can be obtained from equations (12) and (13). G For, unit m 3 :

[0061]

[0062] Substituting equations (8) and (14) into equation (1), we obtain the mass M of the mixed gas produced by the combustion of the airbag gas generator. G The polynomial equation that varies with time represents the total mass flow of the gas mixture produced by the combustion of the airbag gas generator:

[0063]

[0064] (B) Differentiating the time variable T in equation (15), we can obtain the mass flow equation of the mixed gas produced by the combustion of the airbag gas generator:

[0065]

[0066] In equation (16), M′ G The mass flow rate of the mixed gas is expressed in kg / ms; other parameters are the same as in equation (15).

[0067] (C) For the mass flow of a single gas component, equations (5) and (7) and the molar mass M of the single gas are combined. GN Substituting R = 8.31 J / (mol·K) into equation (3), we can obtain the density ρ of the single gas produced by the gas generator in the airbag. N Polynomial equations that vary with time:

[0068] ρ N =N N ×M GN ·(J0+J1T 1 +…J n T n ) / [8.31(E0+E1T 1 ··E n T n +273.15)] (17)

[0069] In the formula, ρ N Density, unit: kg·m -3 N N M is the molar ratio of the gas components; GN The molar mass of a single gas is expressed in kg / mol; the other parameters are the same as in equation (3).

[0070] According to the theory of gas partial pressure, the volume of a single gas in the gas mixture is still the same as the volume of the gas mixture. Substituting equations (17) and (14) into equation (1), we obtain the mass M of the single gas in the gas mixture produced by the combustion of the gasbag gas generator. N The polynomial equation that varies with time represents the mass flow of a single gas produced by the combustion of the airbag gas generator:

[0071]

[0072] In equation (18), M N Unit: kg; other parameters are the same as in formula (15);

[0073] Differentiating equation (18) with respect to the time variable T yields the mass flow equation for the single gas produced by the combustion of the airbag gas generator:

[0074]

[0075] In equation (19), M′ N For the mass flow of a single gas, the unit is kg / ms; the other parameters are the same as in equation (18);

[0076] The mass flow rate M′ of the total mixed gas produced by the combustion of the airbag gas generator is calculated according to equation (16). G and its dynamic changes over time;

[0077] The mass flow rate M′ of a single gas in the gas generated by the combustion of the airbag gas generator is calculated according to equation (19). N And its dynamic changes over time.

[0078] Furthermore, the average gas temperature T is fitted. G The specific steps of the dynamic change equation (7) with time T are as follows:

[0079] T G =E0+E1T 1 +E2T 2 +E3T 3 +…E n T n (7)

[0080] In equation (7), E0…E n : Undetermined constant; T: Time variable, unit: ms;

[0081] The average gas temperature T at time nΔt above Gn The data extraction method is as follows, with Time = nΔt and Temperature = T Gn For example:

[0082] Step 1: Use image processing software to read the gas temperature distribution cloud map and high-speed camera image acquired by the infrared thermal imager at time nΔt;

[0083] Step 2: Read the piston movement distance L at time 3Δt using high-speed camera images;

[0084] Step 3: Based on the gas temperature distribution cloud map, divide the hollow cylindrical rigid container along the central axis from the filling hole to the piston position into regions according to different temperatures, and record the temperature and the length of the corresponding temperature region: t1, L1; t2, L2…t n L n ;

[0085] Step 4: Using the length ratio of different temperature regions as a weighting factor, calculate the weighted average gas temperature at time nΔt:

[0086] in Unit: °C;

[0087] Step 5: Similarly, extract data T G1 T G2 T G4 …T Gn Polynomial fitting was performed to obtain equation (7).

[0088] Furthermore, both the rigid container and the piston are made of a smooth, rigid material. The part where the piston contacts the rigid container is coated with a lubricating layer. The cross-section of the positioning post matches the shape and size of the positioning hole. During testing, the positioning post passes through the positioning hole and can slide freely within the positioning hole. The contact area between the positioning post and the positioning hole is coated with a lubricating coating.

[0089] Furthermore, a base is fixed to the bottom of the rigid container, and the gas generator is fixed to the base by bolts. The detonation harness of the gas generator passes through the harness hole on the base and is connected to the ignition device.

[0090] Furthermore, the outer wall of the rigid container is provided with vertical scale lines; when not ignited, the piston is located at the starting position of the scale line at the bottom of the rigid container, and the central axis of the pressure sensor coincides with the central axis of the hollow cylindrical rigid container; after the ignition device is activated, the igniter of the ignition device detonates the ignition agent, the ignition agent ignites the gas-producing agent, and a large amount of gas is rapidly released, which pushes the piston to move vertically inside the rigid container.

[0091] Beneficial effects: Compared with the prior art, the present invention has the following advantages:

[0092] (1) The rigid container of the present invention is made of transparent material, which makes it easy for the accelerometer to record the movement trajectory of the piston during the entire test process; the cross-section of the positioning column matches the shape and size of the positioning hole, which effectively restricts the rotation of the piston; the part of the piston that contacts the expanding gas is a hemispherical shell structure, which makes the transition between the contact position with the rigid container smooth, prevents stress concentration, makes the piston uniformly stressed, and makes the linear motion process more stable.

[0093] (2) The present invention can measure the linear motion process of the piston by an acceleration sensor and convert it into the volume of gas generated by the gas generator; combined with the measured gas pressure and temperature, the gas density is solved by the ideal gas law; and the gas mass flow and its dynamic changes are solved by the gas volume and density.

[0094] (3) This invention has a reliable theoretical basis, is easy to operate, and provides accurate measurement results. It can measure the mass flow of the mixed gas and the mass flow of a single gas component generated after the airbag gas generator is ignited, providing a gas mass flow testing method for the research and development and production of actual airbag gas generators. Attached Figure Description

[0095] Figure 1 This is a schematic diagram of the hollow cylindrical rigid container structure of the present invention;

[0096] Figure 2 This is a schematic diagram of the piston structure of the present invention;

[0097] Figure 3 This is a schematic diagram of the rigid container and piston assembly of the present invention;

[0098] Figure 4 This is a partial structural schematic diagram of the present invention. Detailed Implementation

[0099] The technical solution of the present invention will be described in detail below, but the scope of protection of the present invention is not limited to the embodiments described.

[0100] Example 1:

[0101] To accurately test under normal pressure, a vertically placed, hollow, transparent cylindrical rigid container was used. A piston, in contact with an airbag gas generator, was placed inside the rigid container, and its rotation was restricted by positioning pins and holes. An accelerometer recorded the vertical trajectory of the piston within the rigid container during the intense combustion process of the airbag gas generator. This trajectory was simplified into a physical model, and the increase in volume formed by the piston and the hollow cylindrical rigid container during the piston's movement was measured and calculated. This increased volume represents the amount of gas produced by the intense combustion of the airbag gas generator. A pressure sensor measured the gas pressure, and the gas density was calculated using the ideal gas law. Finally, using the gas volume and density, the gas mass flow and its dynamic change curve were calculated.

[0102] Its theoretical derivation is as follows:

[0103] In this embodiment, the rigid container is made of transparent material, and its outer wall is marked with equally spaced graduations. The inner diameter of the rigid container is 2R, and its wall thickness is h. The piston is a hemispherical shell with a mass m, an inner diameter of 2r, and a wall thickness of h. Both the rigid container and the piston are made of smooth, rigid material, and their contact parts are coated with a lubricating layer to minimize the influence of friction. The mass unit is kilogram (kg), and the dimension unit is millimeter (mm). A pressure sensor is installed at the center of the top of the piston hemispherical shell, and the central axis of the pressure sensor coincides with the central axis of the rigid container.

[0104] The aforementioned testing device, its connecting parts, and sealing locations can withstand a design pressure exceeding 500 kPa. The embodiment uses an accelerometer with a sampling frequency of 1000 Hz and a cooled infrared thermal imager with a sampling frequency of 240 Hz.

[0105] During testing, the detonation harness of the airbag gas generator is first passed through the base harness hole of the rigid container, and the base harness hole is sealed. The airbag gas generator 8 is fixed to the base 2 by base bolts. A pressure sensor 6 is installed at the center of the top of the piston 4 hemispherical shell. The piston 4 is placed inside the rigid container column 1, and the positioning pin 5 passes through the positioning hole 3. The contact part is coated with a lubricating coating. The piston 4 is placed at the starting position of the scale line on the outside of the rigid container column, and the base 2 is sealed to the rigid container column 1. The fixing bolt holes on the outer ring of the base are connected to the fixing base to fix the entire test system. The accelerometer 9 and the cooled infrared thermal imager 10 are placed perpendicular to the central axis of the rigid container 1. The detonation harness of the airbag gas generator is connected to the ignition device. The accelerometer 9, the cooled infrared thermal imager 10, and the pressure sensor 6 are connected to the data recording device. The ignition device is connected to the data recording device.

[0106] The ignition device, accelerometer 9, cooled infrared thermal imager 10, and data recording device (e.g., USB flash drive) are activated simultaneously. The igniter detonates the ignition agent, which ignites the gas-generating agent, rapidly releasing a large amount of gas. This gas propels piston 4 to move linearly within the rigid container cylinder 1. Accelerometer 9 collects the trajectory of piston 4, and cooled infrared thermal imager 10 captures the dynamic changes in gas temperature distribution cloud map over time throughout the test. Pressure sensor 6 on the inner side of the piston top records the dynamic information of gas pressure per unit area. After piston 4 stops, all equipment is shut down, and all data and image information are recorded by the data recording device.

[0107] Based on the above theoretical derivation, the linear motion process of the piston recorded by the accelerometer is converted into the volume of gas produced by the gas generator; combined with the measured gas pressure and temperature, the gas density is solved using the ideal gas law; and the gas mass flow and its dynamic changes are solved from the gas volume and density.

[0108] Example 2

[0109] Reference Figure 1 The rigid container, its base 2, and the cantilever are all made of transparent tempered glass with a tempering degree of 2-4 N / cm, capable of withstanding a stress of 95 MPa, and with a smooth surface and low coefficient of friction. The rigid container column 1 is 450 mm long, 26 mm in inner diameter, and 3 mm thick, and is designed to measure a gas capacity of approximately 200 liters; it has a scale line with a range of 400 mm, with adjacent scale values ​​of 1 mm; the base is detachably and sealed to the rigid container column, and the cantilever has a square positioning hole 3 with a side length of 1 mm at the position corresponding to the central axis of the rigid container column.

[0110] Reference Figure 2 The piston 4 has a hemispherical shell as its main body, with an outer diameter of 26 mm and a wall thickness of 2 mm. A positioning post 5, 460 mm long and with a square cross-section of 1 mm side length, is set on the outer side of the top of the piston 4 main body. A pressure sensor 6 is set at the center of the top of the hemispherical shell, and the pressure sensor is located on the inner surface of the hemispherical shell. The piston is made of dark tempered glass with a tempering degree of 2-4 N / cm, can withstand a stress of 95 MPa, and has a smooth surface and a low coefficient of friction.

[0111] Reference Figures 3 to 4 During testing, the detonation harness of the airbag gas generator is first passed through the base harness hole of the rigid container, and the base harness hole is sealed. The airbag gas generator 8 is fixed to the base 2 by base bolts. A pressure sensor 6 is installed at the center of the top of the piston 4 hemispherical shell. The piston 4 is placed inside the rigid container column 1, and the positioning pin 5 passes through the positioning hole 3. A lubricating coating is applied to the contact part. The piston 4 is placed at the starting position of the scale line on the outside of the rigid container column, and the base 2 is sealed to the rigid container column 1. The fixing bolt holes on the outer ring of the base are connected to the fixing base to fix the entire test system. The accelerometer 9 and the cooled infrared thermal imager 10 are placed perpendicular to the central axis of the rigid container 1. The detonation harness of the airbag gas generator is connected to the ignition device. The accelerometer 9, the cooled infrared thermal imager 10, and the pressure sensor 6 are connected to the data recording device. The ignition device is connected to the data recording device.

[0112] Example 3,

[0113] The testing apparatus and its connection in this embodiment are the same as those in Embodiments 1 and 2. The specific gas generator mass flow testing method is as follows:

[0114] Mass of mixed gas MG Solution:

[0115] M G =ρ T ·V G (1)

[0116] In equation (1), M G Units: kg; ρ T Density of mixed gas, unit: kg·m³ -3 V G Volume, unit m 3 .

[0117] Mixed gas density ρ T Solution: Based on the chemical ratio of the ignition and gas-generating agents, the N gas components produced by the gas generator during combustion can be obtained through agent testing or by consulting relevant physicochemical handbooks. The molar ratio of the corresponding N gas components is denoted as:

[0118] N1∶N2∶…N N Where N1+N2+…N N =1; the molar mass of the corresponding N gases is denoted as M. G1 M G2 , ...M GN Unit: kg / mol.

[0119] From the ideal gas law: PV=nR(T+273.15) (2)

[0120] In equation (2), P: pressure, unit Pa; V: volume, unit m³ 3 n: number of moles, in mol; R: proportionality constant, taken as 8.31 J / (mol·K); T: temperature in Celsius, in °C; 273.15 is the conversion factor for converting Celsius to absolute temperature in K.

[0121] Given n = m / M m Substituting ρ=m / V into equation (2), we get:

[0122] ρ = PM m / [R(T+273.15)] (3)

[0123] In the formula, m: mass, unit kg, M m Molar mass, in kg / mol; ρ: density, in kg·m³. -3 The remaining parameters are the same as in equation (2).

[0124] In equation (3), the mixed gas pressure is obtained by extracting the dynamic relationship between the gas pressure per unit area and time from the pressure sensor on the inner side of the piston top:

[0125] PT =J0+J1T 1 +J2T 2 +…J n T n (4)

[0126] In equation (4), P T Pressure of mixed gas per unit area, in Pa, J0…J n : Undetermined constant, T: Time variable, unit: ms.

[0127] Based on the theory of partial pressures of gases, according to equation (4) and the molar ratio of N gas components N1∶N2∶…N N Solve for the gas pressure of a single gas:

[0128] First gas: P1 = N1·(J0 + J1T) 1 +J2T 2 +…J n T n )

[0129] The second gas: P2 = N2·(J0 + J1T) 1 +J2T 2 +…J n T n )

[0130] And so on to the Nth gas: P N =N N ·(J0+J1T 1 +J2T 2 +…J n T n (5)

[0131] The sum of the partial pressures of N gases is the pressure of the mixed gas: P1 + P2 + ... + P N =P T .

[0132] At high temperatures, gas molecules move violently, and the molar mass of a gas mixture is the weighted sum of the molar masses of the N gases:

[0133] M mol =M G1 N1+M G2 N2…+M GN N N (6)

[0134] In equation (6), M mol Molar mass of the gas mixture, in kg / mol.

[0135] Gas temperature acquisition method: A cooled infrared thermal imager was used to acquire the dynamic change of gas temperature distribution cloud map over time T throughout the entire test process, and the following data were extracted:

[0136] Time = nΔt; Temperature = T Gn

[0137] Time: The moment the temperature distribution cloud map was acquired, in milliseconds (ms); Δt: The sampling time interval, in milliseconds (ms); Temperature: Temperature, in degrees Celsius (°C), T. Gn The average gas temperature at time nΔt. The average gas temperature T is fitted based on the extracted data. G The dynamic equation of change with time T is (7):

[0138] T G =E0+E1T 1 +E2T 2 +E3T 3 +…E n T n (7)

[0139] In equation (7), E0…E n : Undetermined constant; T: Time variable, unit: ms.

[0140] The average gas temperature T at time nΔt above Gn The data extraction method is as follows, with Time = 3Δt and Temperature = T G3 For example:

[0141] 1) Use image processing software to read the gas temperature distribution cloud map and high-speed camera image acquired by the infrared thermal imager at time 3Δt;

[0142] 2) Read the piston movement distance L at time 3Δt using high-speed camera images;

[0143] 3) Based on the gas temperature distribution cloud map, divide the hollow cylindrical rigid container into regions along the central axis from the filling hole to the piston position according to different temperatures, and record the temperature and the length of the corresponding temperature region: t1, L1; t2, L2…t n L n ;

[0144] 4) Using the length ratio of different temperature regions as a weighting factor, calculate the weighted average temperature of the gas at time 3Δt:

[0145] in Unit: °C.

[0146] 5) Similarly, extract data T G1T G2 T G4 …T Gn Polynomial fitting was performed to obtain equation (7).

[0147] Substituting equations (4), (6), and (7) and R = 8.31 J / (mol·K) into equation (3), we can obtain the density ρ of the mixed gas produced by the combustion of the airbag gas generator. T Polynomial equations that vary with time:

[0148] ρ T =(J0+J1T) 1 +··J n T n (M) G1 N1+··M GN N N ) / [8.31(E0+E1T 1 ··E n T n +273.15)] (8)

[0149] Mixed gas volume V G The solution method is as follows: Read the acceleration sensor data on the outer side of the piston top and extract the dynamic equation of acceleration versus time:

[0150] a k =b0+b1T 1 +b2T 2 +b3T 3 +…b n T n (9)

[0151] In equation (9), n = 0, 1, 2, 3, 4…n, a k The linear acceleration of the piston, in mm / ms. 2 b0…b n For each variable, T is an undetermined constant; T is a time variable, in milliseconds (ms).

[0152] Integrating the time variable T of equation (9), we can solve the polynomial equation of the linear velocity of the piston versus time:

[0153]

[0154] In equation (10), v′ k This refers to the linear speed of the piston, in mm / ms; the other parameters are the same as in equation (9).

[0155] Equation (10) is integrated again with respect to the time variable T to solve the polynomial equation of the piston's linear motion displacement versus time:

[0156]

[0157] In equation (11), D′ k This refers to the linear displacement of the piston, in mm; the other parameters are the same as in equation (9).

[0158] Before testing, the volume of the airbag gas generator was measured to be V. f Unit: mm 3 Then, before the test, the initial gas volume V0 in the space formed by the piston and the hollow cylindrical rigid container is:

[0159] V0=(2 / 3πr 3 -V f )×10 -9 (12)

[0160] In equation (12), V0 refers to the initial gas volume of the system, in m³. 3 r is the inner radius of the piston hemispherical shell, in mm.

[0161] The gas volume within the ignition and combustion system of the airbag gas generator is the sum of the volumes of the sealed space formed by the piston and the rigid container, combined with equation (11) for the linear displacement D′ of the piston. k The gas volume V in the airbag gas generator ignition and combustion system is:

[0162] V=(2 / 3πr 3 +2πR 2 ·D′ k -V f )×10 -9

[0163]

[0164] In equation (13), V G Unit m 3 R is the inner radius of the rigid container, in mm; the other parameters are the same as in equation (11).

[0165] The gas production V of the airbag gas generator can be obtained from equations (12) and (13). G For, unit m 3 :

[0166]

[0167] Substituting equations (8) and (14) into equation (1), we obtain the mass M of the mixed gas produced by the combustion of the airbag gas generator. G The polynomial equation that varies with time represents the total mass flow of the gas mixture produced by the combustion of the airbag gas generator:

[0168]

[0169] Differentiating the time variable T in equation (15), we can obtain the mass flow equation for the mixed gas produced by the combustion of the airbag gas generator:

[0170]

[0171] In equation (16), M′ G The mass flow rate of the mixed gas is expressed in kg / ms; the other parameters are the same as in equation (15).

[0172] For the mass flow of a single gas component, equations (5) and (7) and the molar mass M of the single gas are combined. GN Substituting R = 8.31 J / (mol·K) into equation (3), we can obtain the density ρ of the single gas produced by the gas generator in the airbag. N Polynomial equations that vary with time:

[0173] ρ N =N N ×M GN ·(J0+J1T 1 +…J n T n ) / [8.31(E0+E1T 1 ··E n T n +273.15)] (17)

[0174] In the formula, ρ N Density, unit: kg·m -3 N N M is the molar ratio of the gas components; GN The molar mass of a single gas is expressed in kg / mol; the other parameters are the same as in equation (3).

[0175] According to the theory of gas partial pressure, the volume of a single gas in the gas mixture is still the same as the volume of the gas mixture. Substituting equations (17) and (14) into equation (1), we obtain the mass M of the single gas in the gas mixture produced by the combustion of the gasbag gas generator. N The polynomial equation that varies with time represents the mass flow of a single gas produced by the combustion of the airbag gas generator:

[0176]

[0177] In equation (18), M N Unit: kg; other parameters are the same as in formula (15).

[0178] Differentiating equation (18) with respect to the time variable T yields the mass flow equation for the single gas produced by the combustion of the airbag gas generator:

[0179]

[0180] In equation (19), M′ N The mass flow rate is for a single gas, in kg / ms; the other parameters are the same as in equation (18).

[0181] The mass flow rate M′ of the total mixed gas produced by the combustion of the airbag gas generator is calculated according to equation (16). G and its dynamic changes over time;

[0182] The mass flow rate M′ of a single gas in the gas generated by the combustion of the airbag gas generator is calculated according to equation (19). N And its dynamic changes over time.

Claims

1. A method for testing the mass flow of an automotive airbag gas generator based on an accelerometer, characterized in that: Includes the following steps: Step S1: Set up the test device; the test device includes a rigid container, a piston, an accelerometer, and a cooled infrared thermal imager; the rigid container is a transparent hollow cylinder, and an airbag gas generator is fixed at the bottom of the rigid container. The piston is located inside the rigid container, and the piston as a whole is a hemispherical shell with the opening facing downwards. A pressure sensor and an accelerometer are set at the center of the top of the piston. The cooled infrared thermal imager is placed perpendicular to the central axis of the rigid container; a positioning cantilever is fixed above the rigid container, and a square positioning hole is placed on the cantilever at a position corresponding to the central axis of the rigid container. A positioning post is installed at the top of the piston, and the cross-section of the positioning post matches the shape and size of the positioning hole. Step S2: Activate the ignition device inside the rigid container and simultaneously start the accelerometer, cooled infrared thermal imager, and data recording device; after ignition, the piston moves vertically linearly inside the rigid container; the accelerometer records the dynamic acceleration information of the piston's linear motion, the cooled infrared thermal imager collects the dynamic change process of the gas temperature distribution cloud map inside the rigid container over time during the test, and the pressure sensor records the dynamic information of the gas pressure value per unit area; Step S3: Based on the real-time data collected by the accelerometer, cooled infrared thermal imager, and pressure sensor, calculate the increase in volume formed by the piston and the rigid container during the piston's movement. This increased volume is the amount of gas produced by the violent combustion of the airbag gas generator. The pressure sensor measures the gas pressure value, and the gas density is solved using the ideal gas law. Then, using the gas volume and density, the mass flow rate of the total mixed gas produced by the combustion of the airbag gas generator is calculated. Its dynamic changes over time, and the solution of the mass flow of a single gas in the gas generated by the combustion of the airbag gas generator. and its dynamic changes over time; Step S4: After the piston stops moving, turn off all equipment, and record all data and image information by the data recording device; the mass flow of the total mixed gas generated by the combustion of the airbag gas generator. The mass flow of a single gas in the gas generated by the combustion of the airbag gas generator The specific solution method is as follows: (A) According to formula (1) the mass of the mixed gas Solution: (1) In formula (1) The density of the mixed gas; This refers to the volume of the mixed gas; (A1), the density of the mixed gas in equation (1) The solution method is as follows: based on the combustion of the airbag gas generator... gas components, query to obtain The molar ratio of the gas components is denoted as: , in Then the corresponding The molar mass of a gas is denoted as ; From the ideal gas law: (2) In equation (2), refers to pressure volume; This refers to the number of moles. This refers to the proportionality constant. This refers to Celsius temperature; 273.15 is the conversion of Celsius to absolute temperature. Conversion factor; Known , Substituting into equation (2), we get: (3) In the formula, It refers to quality. This refers to molar mass. This refers to density; The pressure of the mixed gas in equation (3) The dynamic relationship between the gas pressure per unit area and time is obtained by extracting the pressure sensor on the inner side of the piston top: (4) In equation (4), This refers to the pressure of a mixed gas per unit area. For undetermined constants, It is a time variable; ; Based on the theory of gas partial pressure, according to equation (4) and ratio of molar amounts of the gas components Solve for the gas pressure of a single gas: The first gas: The second gas: And so on up to the 1st Gases: (5) The sum of the partial pressures of the gases is the pressure of the mixed gas: ; At high temperatures, gas molecules move violently, and the molar mass of the gas mixture is... Weighted sum of the molar masses of the gases: (6) In equation (6), This refers to the molar mass of the gas mixture; The gas temperature in equation (3) is obtained by using a cooled infrared thermal imager to collect the gas temperature distribution cloud map over time throughout the entire test process. The dynamic change process was observed, and the following data was extracted: Time= ; Temperature = Time refers to the moment when the temperature distribution cloud map was collected; The sampling time interval; Temperature refers to the temperature. It means The average gas temperature at that time; Based on the extracted data, the average gas temperature was fitted. Over time The dynamic change equation (7): (7) In equation (7), These are undetermined constants; Equations (4)(6)(7) and =8.31 Substituting into equation (3), the density of the mixed gas produced by the combustion of the airbag gas generator can be obtained. Polynomial equations that vary with time: (8) (A2) Volume of mixed gas The solution method is as follows: Read the acceleration sensor data on the outer side of the piston top and extract the dynamic equation of acceleration versus time: (9) In equation (9) , This refers to the linear acceleration of the piston. These are undetermined constants; It is a time variable; For the time variable in equation (9) Integrate and solve the polynomial equations for the linear velocity and time of the piston: (10) In equation (10), This refers to the linear speed of the piston. Equation (10) for time variables Integrate again to solve the polynomial equations for the linear motion of the piston versus time: (11) In equation (11), This refers to the linear displacement of the piston. The volume of the airbag gas generator was measured before the test. The initial gas volume within the space formed by the piston and the hollow cylindrical rigid container before the test is... for: (12) In equation (12), It is the inner radius of the piston hemispherical shell; The gas volume within the ignition and combustion system of the airbag gas generator is the sum of the volumes of the sealed space formed by the piston and the rigid container, combined with the linear displacement of the piston in equation (11). The gas volume within the airbag gas generator ignition and combustion system for: (13) In equation (13), The inner radius of the rigid container; The gas production of the airbag gas generator can be obtained from equations (12) and (13). for: (14) Substituting equations (8) and (14) into equation (1), we obtain the mass of the mixed gas produced by the combustion of the airbag gas generator. The polynomial equation that varies with time represents the total mass flow of the gas mixture produced by the combustion of the airbag gas generator: ； { }·[ ] (15) (B) Regarding the time variable in equation (15) Differentiation yields the mass flow equation for the gas mixture produced by the combustion of the airbag gas generator: (16) In equation (16), It is the mass flow of the mixed gas; (C) For the mass flow of a single gas component, combine equations (5) and (7) with the molar mass of the single gas. and =8.31 Substituting into equation (3), the density of a single gas produced by the airbag gas generator can be obtained. Polynomial equations that vary with time: (17) In the formula, Density; The molar ratio of gas components; The molar mass of a single gas; According to the theory of gas partial pressure, the volume of a single gas in the gas mixture is still the same as the volume of the gas mixture. Substituting equations (17) and (14) into equation (1), we can obtain the mass of a single gas in the gas mixture produced by the combustion of the gasbag gas generator. The polynomial equation that varies with time represents the mass flow of a single gas produced by the combustion of the airbag gas generator: Equation (18) applies to the time variable Differentiation yields the mass flow equation for the single gas produced by the combustion in the airbag gas generator: (19) In equation (19), It is a mass flow of a single gas; The mass flow rate of the total mixed gas produced by the combustion of the airbag gas generator is calculated according to equation (16). and its dynamic changes over time; The mass flow rate of a single gas in the gas generated by the combustion of the airbag gas generator can be calculated according to equation (19). And its dynamic changes over time.

2. The method for testing the mass flow of an automotive airbag gas generator based on an acceleration sensor according to claim 1, characterized in that: Fitted gas average temperature Over time The specific steps of the dynamic change equation (7) are as follows: (7) In equation (7), Undetermined constants; Time variable, unit ; The above The average gas temperature at time 10:00 The data extraction method is as follows, using Time= Temperature= For example: Step 1: Use image processing software to read the time of data acquisition by the infrared thermal imager. Gas temperature distribution cloud map and high-speed camera images; Step 2: Reading images from high-speed cameras The piston movement distance L at any given moment; Step 3: Based on the gas temperature distribution cloud map, divide the hollow cylindrical rigid container along the central axis from the filling hole to the piston position into regions according to different temperatures, and record the temperature and the length of the corresponding temperature region: ; Step 4: Calculate using the length ratio of different temperature regions as a weighting factor. The weighted average gas temperature at that time: , in =1; Step 5: Similarly, extract the data. , , Polynomial fitting was performed to obtain equation (7).

3. The method for testing the mass flow of an automotive airbag gas generator based on an acceleration sensor according to claim 1, characterized in that: Both the rigid container and the piston are made of smooth, rigid material. The part where the piston contacts the rigid container is coated with a lubricating layer. The cross-section of the positioning post matches the shape and size of the positioning hole. During testing, the positioning post passes through the positioning hole and can slide freely within the positioning hole. The contact part between the positioning post and the positioning hole is coated with a lubricating coating.

4. The method for testing the mass flow of an automotive airbag gas generator based on an acceleration sensor according to claim 1, characterized in that: The rigid container is fixed to a base at the bottom. The gas generator is fixed to the base by bolts. The detonation harness of the gas generator passes through the harness hole on the base and is connected to the ignition device.

5. The method for testing the mass flow of an automotive airbag gas generator based on an acceleration sensor according to claim 1, characterized in that: The rigid container has vertical scale lines on its outer wall. When not ignited, the piston is located at the starting position of the scale line at the bottom of the rigid container. The vertical central axis of the acceleration sensor and the central axis of the pressure sensor coincide with the central axis of the hollow cylindrical rigid container. After the ignition device is activated, the igniter of the ignition device detonates the ignition agent, which ignites the gas-producing agent and rapidly releases a large amount of gas. The gas pushes the piston to move vertically inside the rigid container.

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