CN114692335B - Design method of connecting bolt in exhaust system - Google Patents
Design method of connecting bolt in exhaust system Download PDFInfo
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Abstract
The invention relates to a design method of a connecting bolt in an exhaust system. The method comprises the following steps: according to the space arrangement of an exhaust system, the number, arrangement mode and related parameters of the connecting bolts are preliminarily set; establishing a finite element simulation model of an exhaust system; obtaining the temperature of the inner wall surface and the heat exchange coefficient of the model according to the gas temperature and the mass flow rate at the inlet of the exhaust system, and then calculating the temperature field of the model; according to the temperature field, carrying out heat engine coupling analysis to obtain the axial support reaction force of the connecting bolt, the transverse direction of the gasket and the maximum displacement of the flange, establishing a simplified finite element analysis model, and then inputting the axial support reaction force of the connecting bolt, the transverse direction of the gasket and the maximum displacement of the flange into the simplified model to obtain the stress of the connecting bolt; and finally, carrying out fatigue analysis, calculating the safety coefficient of the connecting bolt, and analyzing whether the safety coefficient meets the standard. The invention solves the problem that the connecting bolt in the existing exhaust system is easy to have assembly failure.
Description
Technical Field
The invention relates to the technical field of automobile engines, in particular to a design method of a connecting bolt in an exhaust system.
Background
The connecting bolt of the exhaust system and the cylinder cover is mainly used for fixing the sealing gasket, so that the sealing gasket generates sealing pressure and gas leakage is prevented. Because the exhaust system works in extremely severe high-temperature environment, high-temperature airflow is frequently impacted, cold and hot environments alternate, and meanwhile, due to different materials used by the cylinder cover and the exhaust system and large structural difference, the connecting bolt is extremely easy to have the condition of assembly failure, wherein the failure is mainly represented as fracture.
In the prior art, the bolts for connecting the exhaust system and the cylinder cover are distributed according to arrangement design bolts, and bolt selection is carried out according to standard comparison or industry recommended modes. However, due to the diversified materials and structures of the cylinder cover and the exhaust system, the risks of the same bolt in different cylinder covers and exhaust systems are completely different. Meanwhile, the exhaust system comprises a plurality of parts such as an exhaust manifold, a supercharger, a three-way catalyst and the like, so that the difficulty of bolt design is increased.
Disclosure of Invention
The invention aims to provide a design method of a connecting bolt in an exhaust system, which aims to solve the problem that the connecting bolt in the existing exhaust system is easy to have assembly failure.
In order to achieve the above purpose, the technical scheme adopted by the invention is as follows:
a design method of a connecting bolt in an exhaust system comprises the following steps:
s1, preliminarily setting the number, arrangement mode and related parameters of the connecting bolts according to the spatial arrangement of an exhaust system;
s2, establishing a finite element simulation model of the exhaust system according to 3D data of the exhaust system;
s3, calculating the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model under the cold and hot working conditions according to the gas temperature and the mass flow at the inlet of the exhaust system;
s4, calculating a temperature field of the finite element simulation model under the cold and hot working conditions according to the temperature of the inner wall surface and the heat exchange coefficient;
s5, carrying out heat engine coupling analysis according to a temperature field of the finite element simulation model to obtain axial support reaction force of the connecting bolt, transverse maximum displacement of the gasket and maximum displacement of the flange plate under cold and hot working conditions;
s6, establishing a simplified finite element analysis model of a single connecting bolt, and inputting the axial supporting force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate into the simplified finite element analysis model to obtain the stress of the connecting bolt;
and S7, carrying out fatigue analysis according to the stress of the connecting bolt, calculating the safety coefficient of the connecting bolt, and analyzing whether the safety coefficient meets the standard or not, if not, optimizing the relevant parameters of the connecting bolt until the safety coefficient meets the standard.
Preferably, the exhaust system is an integrated exhaust system or a non-integrated exhaust system;
the finite element simulation model of the integrated exhaust system comprises a cylinder cover, a connecting bolt, a gasket, a supercharger, a three-way catalyst and a bracket;
the finite element simulation model of the non-integrated exhaust system comprises a cylinder cover, a connecting bolt, a gasket, an exhaust manifold, a supercharger, a three-way catalyst and a bracket;
the simplified finite element analysis model of the integrated exhaust system comprises a cylinder cover, a double-end stud, a nut, a gasket and a supercharger;
the simplified finite element analysis model of the non-integrated exhaust system comprises a cylinder cover, a double-end stud, a nut, a gasket and an exhaust manifold;
the relevant parameters of the connecting bolt comprise bolt material, bolt grade, bolt length, bolt thread length and gasket thickness.
Preferably, in S3, specifically: and calculating the temperature and heat exchange coefficient of two inner wall surfaces of the finite element simulation model under cold and hot working conditions by adopting Computational Fluid Dynamics (CFD) software according to the highest temperature and mass flow of gas at the inlet of the cylinder cover and the exhaust system and the lowest temperature and mass flow of gas.
Preferably, when the engine is under full-speed full-load working condition, the gas at the inlet of the exhaust system has the highest temperature and the mass flow, the highest temperature and the mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the gas is at the highest temperature and the mass flow;
when the engine is in an idle working condition, the gas at the inlet of the exhaust system has the lowest temperature and mass flow, the lowest temperature and mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature and heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the gas is in the lowest temperature and mass flow.
Preferably, in S4, specifically: respectively inputting the two inner wall surface temperatures and the heat exchange coefficient of the finite element simulation model into finite element analysis software to calculate two temperature fields of the finite element simulation model under cold and hot working conditions;
the method comprises the steps of inputting the temperature and heat exchange coefficient of the inner wall surface of a finite element simulation model obtained when the gas is at the highest temperature and the mass flow rate into finite element analysis software, and calculating to obtain a temperature field T1;
and when the gas is at the lowest temperature and mass flow, the obtained temperature and heat exchange coefficient of the inner wall surface of the finite element simulation model are input into finite element analysis software, and a temperature field T2 is obtained through calculation.
Preferably, in S5, specifically: and inputting two temperature fields of the finite element simulation model into finite element analysis software to perform heat engine coupling analysis to obtain axial support reaction forces of all connecting bolts, transverse maximum displacement of gaskets and maximum displacement of flanges under cold and hot working conditions.
Preferably, before the temperature field is input into the finite element analysis software, the connecting bolts in the finite element simulation model are loaded with pretightening force, then the temperature field T1 is applied to the finite element simulation model for 5-8 min, and then the temperature field T2 is applied to the finite element simulation model for 5-8 min;
taking the applied temperature field T1 and the applied temperature field T2 as a heating and cooling cycle, after at least three times of cycle, obtaining the axial supporting reaction force of all the connecting bolts, the transverse maximum displacement of the gaskets and the maximum displacement of the flanges, and selecting one of the connecting bolts with the largest difference value between the maximum axial supporting reaction force and the minimum axial supporting reaction force under the cold and hot working conditions;
the maximum displacement of the gasket in the transverse direction is the maximum displacement of the gasket in the transverse direction relative to the cylinder body, and the maximum displacement of the flange plate is the maximum displacement of the flange plate relative to the cylinder body;
taking the maximum axial branch counter force and the minimum axial branch counter force of the connecting bolt in the hot working condition and the cold working condition of the last cycle as input parameters of the axial branch counter force;
taking two maximum displacement amounts of the gasket connected with the connecting bolt, which are transversely opposite to the cylinder body, in the hot working condition and the cold working condition of the last cycle as input parameters of the transverse maximum displacement amount of the gasket;
and taking two maximum displacement amounts of the flange plate connected with the connecting bolt relative to the cylinder body in the hot working condition and the cold working condition of the last cycle as input parameters of the maximum displacement amount of the flange plate.
Preferably, the pre-tightening force applied to the connecting bolt is an assembly axial force obtained by calculating according to the size and the torque after the relevant parameters of the connecting bolt are preliminarily determined.
Preferably, in S6, specifically: in finite element analysis software, a simplified finite element analysis model of a single connecting bolt is established, then input parameters of axial supporting force of the connecting bolt, input parameters of transverse maximum displacement of a gasket and input parameters of maximum displacement of a flange plate are input into the simplified finite element analysis model, and stress of the connecting bolt is calculated.
Preferably, in S7, specifically: inputting the obtained stress of the connecting bolt into fatigue analysis software to perform fatigue analysis, calculating the safety coefficient of the connecting bolt, analyzing whether the connecting bolt meets the standard, if the connecting bolt meets the standard, adopting the preliminarily set connecting bolt, if the connecting bolt does not meet the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the connecting bolt again, and optimizing the process, the cost and the space arrangement after the connecting bolt meets the standard.
The invention has the beneficial effects that:
according to the design method of the connecting bolts in the exhaust system, the number, the arrangement mode and the related parameters of the connecting bolts of the exhaust system are designed in advance, the finite element analysis software is adopted to establish the finite element analysis model of the exhaust system, the stress condition of the connecting bolts in the exhaust system when the fracture risk is maximum under the working condition of an engine is analyzed and calculated through Computational Fluid Dynamics (CFD) software, and the related parameters of the connecting bolts are designed in an optimized mode, so that the problem that the connecting bolts are invalid in assembly in the exhaust system is effectively avoided, meanwhile, the analysis is carried out by adopting the simplified finite element analysis model, the analysis time is greatly shortened, the working efficiency is improved, and the design method has popularization and application values in the technical field of automobile engines.
Drawings
FIG. 1 is a flow chart of a design method of the present invention;
FIG. 2 is a schematic diagram of a finite element simulation model of a non-integrated exhaust system according to example 1;
fig. 3 is a schematic structural diagram of a simplified finite element analysis model of a non-integrated exhaust system in embodiment 1.
Wherein, 1-cylinder cover; 2-connecting bolts; 3-a gasket; 4-an exhaust manifold; 5-a supercharger; 6-three-way catalyst; 7-a bracket; 8-a nut; 9-exhaust manifold.
Detailed Description
Further advantages and effects of the present invention will become readily apparent to those skilled in the art from the disclosure herein, by referring to the accompanying drawings and the preferred embodiments. The invention may be practiced or carried out in other embodiments that depart from the specific details, and the details of the present description may be modified or varied from the spirit and scope of the present invention. It should be understood that the preferred embodiments are presented by way of illustration only and not by way of limitation.
It should be noted that the illustrations provided in the following embodiments merely illustrate the basic concept of the present invention by way of illustration, and only the components related to the present invention are shown in the drawings and are not drawn according to the number, shape and size of the components in actual implementation, and the form, number and proportion of the components in actual implementation may be arbitrarily changed, and the layout of the components may be more complicated.
Example 1
As shown in fig. 1, a design method of a connecting bolt in a non-integrated exhaust system includes the following steps:
s1, preliminarily setting the number, arrangement mode and related parameters of the connecting bolts according to the spatial arrangement of a non-integrated exhaust system;
the relevant parameters of the connecting bolt comprise bolt materials, bolt grades, bolt lengths, bolt thread lengths and gasket thicknesses;
s2, establishing a finite element simulation model of the non-integrated exhaust system according to 3D data of the non-integrated exhaust system;
as shown in fig. 2, wherein the finite element simulation model of the non-integrated exhaust system includes a cylinder head 1, a connecting bolt 2, a gasket 3, an exhaust manifold 4, a supercharger 5, a three-way catalyst 6 and a bracket 7;
s3, calculating the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model under the cold and hot working conditions according to the gas temperature and the mass flow at the inlet of the non-integrated exhaust system;
the method comprises the following steps: calculating two inner wall surface temperatures and heat exchange coefficients of a finite element simulation model under cold and hot working conditions by adopting Computational Fluid Dynamics (CFD) software according to the highest gas temperature and mass flow at the inlet of a non-integrated exhaust system and the lowest gas temperature and mass flow;
when the engine is under full-speed full-load working condition, the gas at the inlet of the non-integrated exhaust system has the highest temperature and the mass flow, the highest temperature and the mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the gas is at the highest temperature and the mass flow;
when the engine is in an idle working condition, the gas at the inlet of the non-integrated exhaust system has the lowest temperature and the mass flow, the lowest temperature and the mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the gas is at the lowest temperature and the mass flow;
s4, calculating a temperature field of the finite element simulation model under the cold and hot working conditions according to the temperature of the inner wall surface and the heat exchange coefficient;
the method comprises the following steps: respectively inputting the two inner wall surface temperatures and the heat exchange coefficient of the finite element simulation model into finite element analysis software, and calculating two temperature fields of the finite element simulation model under cold and hot working conditions;
the method comprises the steps of inputting the temperature and heat exchange coefficient of the inner wall surface of a finite element simulation model obtained when the gas is at the highest temperature and the mass flow rate into finite element analysis software, and calculating to obtain a temperature field T1;
inputting the temperature and the heat exchange coefficient of the inner wall surface of the obtained finite element simulation model into finite element analysis software when the gas is at the lowest temperature and the mass flow, and calculating to obtain a temperature field T2;
s5, carrying out heat engine coupling analysis according to a temperature field of the finite element simulation model to obtain axial support reaction force of the connecting bolt, transverse maximum displacement of the gasket and maximum displacement of the flange plate under cold and hot working conditions;
the method comprises the following steps: the method comprises the steps of loading a pretightening force on a connecting bolt in a finite element simulation model, then applying a temperature field T1 to the finite element simulation model for 6min, and then applying a temperature field T2 to the finite element simulation model for 6min;
the method comprises the steps of taking an applied temperature field T1 and an applied temperature field T2 as a heating and cooling cycle, after three times of circulation, obtaining the axial support reaction force of all connecting bolts, the maximum displacement of a gasket transversely relative to a cylinder body and the maximum displacement of a flange plate relative to the cylinder body, and selecting one of the connecting bolts with the largest difference value between the maximum axial support reaction force and the minimum axial support reaction force under the cold and hot working conditions;
the maximum axial branch counter force of the connecting bolt in the hot working condition of the third circulating working condition is F1, and the minimum axial branch counter force in the cold working condition is F2, which is taken as an input parameter of the axial branch counter force;
the maximum displacement of the gasket connected with the connecting bolt in the transverse direction relative to the cylinder body in the third cycle under the hot working condition and the cold working condition is U1 and U2 respectively as the input parameters of the maximum displacement of the gasket in the transverse direction;
the maximum displacement of the flange plate connected with the connecting bolt relative to the cylinder body in the third cycle of the hot working condition and the cold working condition is U3 and U4 respectively as input parameters of the maximum displacement of the flange plate;
the method comprises the steps of loading a pre-tightening force on a connecting bolt, and obtaining an assembly axial force according to size calculation after relevant parameters of the connecting bolt are preliminarily determined;
s6, establishing a simplified finite element analysis model of a single connecting bolt, and inputting the axial supporting force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate into the simplified finite element analysis model to obtain the stress of the connecting bolt;
as shown in fig. 3, the simplified finite element analysis model of the non-integrated exhaust system includes a cylinder head 1, a stud 2, a nut 8, a gasket 9, an exhaust manifold 10; because the stud is one type of bolt, the stud is usually adopted due to the advantage of convenient assembly, so the stud is used in a simplified model;
the method comprises the following steps: in finite element analysis software, a simplified finite element analysis model of a single connecting bolt is established, a pretightening force F1 is loaded on the connecting bolt, a transverse maximum displacement U1 is loaded on a gasket, a maximum displacement U3 is loaded on a flange plate, a pretightening force F2 is loaded on the connecting bolt, a transverse maximum displacement U2 is loaded on the gasket, a maximum displacement U4 is loaded on the flange plate, and the stress of the connecting bolt is calculated;
s7, carrying out fatigue analysis according to the stress of the connecting bolt, calculating the safety coefficient of the connecting bolt, and analyzing whether the safety coefficient meets the standard, if not, optimizing the relevant parameters of the connecting bolt until the safety coefficient meets the standard;
the method comprises the following steps: inputting the obtained stress of the connecting bolt into fatigue analysis software to perform fatigue analysis, calculating the safety coefficient of the connecting bolt, analyzing whether the connecting bolt meets the standard, if the connecting bolt meets the standard, adopting the preliminarily set connecting bolt, if the connecting bolt does not meet the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the connecting bolt again, and optimizing the process, the cost and the space arrangement after the connecting bolt meets the standard.
In this embodiment, the standard of the safety factor of the connecting bolt is 1.2.
In S2, the finite element simulation model is built in finite element analysis software, and the grid of the bolts needs to be refined during building so as to highlight the structural characteristics of the finite element simulation model.
In S3, the highest temperature and mass flow of gas at the inlet of the non-integrated exhaust system are constant when the engine is in full speed full load condition, and the lowest temperature and mass flow of gas at the inlet of the non-integrated exhaust system are constant when the engine is in idle condition.
Through carrying out design analysis in advance to the number, the arrangement mode and the relevant parameter of connecting bolt of non-integrated exhaust system to confirm the optimal design parameter of connecting bolt, effectively avoided appearing the connecting bolt assembly inefficacy problem in exhaust system, the application is simplified finite element analysis model and is carried out the analysis simultaneously, has reduced analysis time by a wide margin, has promoted work efficiency.
In the embodiment, by designing a simplified finite element analysis model of a single connecting bolt, the optimization analysis time can be shortened from 28 days to 0.5 day, so that the time for optimizing relevant parameters of the connecting bolt is greatly shortened, and rapid and accurate design and production can be performed.
In S3, since the actual non-integrated exhaust system is mainly affected by thermal fatigue load (i.e. cold and hot impact), the temperature field of the finite element simulation model under the highest exhaust temperature must be calculated to determine the maximum risk of fracture of the connecting bolt.
Example 2
As shown in fig. 1, a design method of a connecting bolt in an integrated exhaust system includes the following steps:
s1, preliminarily setting the number, arrangement mode and related parameters of the connecting bolts according to the spatial arrangement of an integrated exhaust system;
the relevant parameters of the connecting bolt comprise bolt materials, bolt grades, bolt lengths, bolt thread lengths and gasket thicknesses;
s2, establishing a finite element simulation model of the integrated exhaust system according to the 3D data of the integrated exhaust system;
the finite element simulation model of the integrated exhaust system comprises a cylinder cover, a connecting bolt, a gasket, a supercharger, a three-way catalyst and a bracket;
s3, calculating the temperature and heat exchange coefficient of the inner wall surface of the finite element simulation model under the cold and hot working conditions according to the gas temperature and the mass flow at the inlet of the integrated exhaust system;
the method comprises the following steps: according to the highest temperature and the mass flow of gas at the inlet of the integrated exhaust system and the lowest temperature and the mass flow of gas, calculating two inner wall surface temperatures and heat exchange coefficients of a finite element simulation model under cold and hot working conditions by adopting Computational Fluid Dynamics (CFD) software;
when the engine is under full-speed full-load working condition, the gas at the inlet of the integrated exhaust system has the highest temperature and the mass flow, the highest temperature and the mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the gas is at the highest temperature and the mass flow;
when the engine is in an idle working condition, the gas at the inlet of the integrated exhaust system has the lowest temperature and the mass flow, the lowest temperature and the mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the gas is in the lowest temperature and the mass flow;
s4, calculating a temperature field of the finite element simulation model under the cold and hot working conditions according to the temperature of the inner wall surface and the heat exchange coefficient;
the method comprises the following steps: respectively inputting the two inner wall surface temperatures and the heat exchange coefficient of the finite element simulation model into finite element analysis software to calculate two temperature fields of the finite element simulation model under cold and hot working conditions;
the method comprises the steps of inputting the temperature and heat exchange coefficient of the inner wall surface of a finite element simulation model obtained when the gas is at the highest temperature and the mass flow rate into finite element analysis software, and calculating to obtain a temperature field T1;
inputting the temperature and the heat exchange coefficient of the inner wall surface of the obtained finite element simulation model into finite element analysis software when the gas is at the lowest temperature and the mass flow, and calculating to obtain a temperature field T2;
s5, carrying out heat engine coupling analysis according to a temperature field of the finite element simulation model to obtain axial support reaction force of the connecting bolt, transverse maximum displacement of the gasket and maximum displacement of the flange plate under cold and hot working conditions;
the method comprises the following steps: loading a pretightening force on a connecting bolt in the finite element simulation model, then applying a temperature field T1 to the finite element simulation model for 6min, and then applying a temperature field T2 to the finite element simulation model for 6min;
the method comprises the steps of taking an applied temperature field T1 and an applied temperature field T2 as a heating and cooling cycle, after three times of circulation, obtaining the axial support reaction force of all connecting bolts, the maximum displacement of a gasket transversely relative to a cylinder body and the maximum displacement of a flange plate relative to the cylinder body, and selecting one of the connecting bolts with the largest difference value between the maximum axial support reaction force and the minimum axial support reaction force under the cold and hot working conditions;
the maximum axial branch counter force of the connecting bolt in the hot working condition of the third circulating working condition is f1, and the minimum axial branch counter force in the cold working condition is f2, which is taken as an input parameter of the axial branch counter force;
the maximum displacement amounts of the gasket connected with the connecting bolt in the transverse direction relative to the cylinder body in the hot working condition and the cold working condition of the third cycle are u1 and u2 respectively as input parameters of the maximum displacement amounts of the gasket in the transverse direction;
the maximum displacement of the flange plate connected with the connecting bolt relative to the cylinder body in the third cycle of the hot working condition and the cold working condition is u3 and u4 respectively as input parameters of the maximum displacement of the flange plate;
the method comprises the steps of loading a pre-tightening force on a connecting bolt, and obtaining an assembly axial force according to size calculation after relevant parameters of the connecting bolt are preliminarily determined;
s6, establishing a simplified finite element analysis model of a single connecting bolt, and inputting the axial supporting force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate into the simplified finite element analysis model to obtain the bolt stress;
the simplified finite element analysis model of the integrated exhaust system comprises a cylinder cover, a double-end stud, a nut, a gasket and a supercharger;
the method comprises the following steps: in finite element analysis software, a simplified finite element analysis model of a single connecting bolt is established, a pre-tightening force f1 is loaded on the connecting bolt, a transverse maximum displacement u1 is loaded on a gasket, a maximum displacement u3 is loaded on a flange plate, a pre-tightening force f2 is loaded on the connecting bolt, a transverse maximum displacement u2 is loaded on the gasket, a maximum displacement u4 is loaded on the flange plate, and the stress of the connecting bolt is calculated;
s7, carrying out fatigue analysis according to the stress of the connecting bolt, calculating the safety coefficient of the connecting bolt, and analyzing whether the safety coefficient meets the standard, if not, optimizing the relevant parameters of the connecting bolt until the safety coefficient meets the standard;
the method comprises the following steps: inputting the obtained stress of the connecting bolt into fatigue analysis software to perform fatigue analysis, calculating the safety coefficient of the connecting bolt, analyzing whether the connecting bolt meets the standard, if the connecting bolt meets the standard, adopting the preliminarily set connecting bolt, if the connecting bolt does not meet the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the connecting bolt again, and optimizing the process, the cost and the space arrangement after the connecting bolt meets the standard.
In this embodiment, the standard of the safety factor of the connecting bolt is 1.2.
In S2, the finite element simulation model is built in finite element analysis software, and the grid of the bolts needs to be refined during building so as to highlight the structural characteristics of the finite element simulation model.
In S3, the highest temperature and mass flow of gas at the inlet of the integrated exhaust system are constant when the engine is in full speed full load condition, and the lowest temperature and mass flow of gas at the inlet of the integrated exhaust system are constant when the engine is in idle condition.
In S3, since the actual integrated exhaust system is mainly affected by thermal fatigue load (i.e. cold and hot impact), the temperature field of the finite element simulation model under the highest exhaust temperature must be calculated to determine the maximum risk of fracture of the connecting bolt.
According to the design method of the connecting bolts in the exhaust system, the number, the arrangement mode and the related parameters of the connecting bolts of the exhaust system are designed in advance, the finite element analysis software is adopted to establish the finite element analysis model of the exhaust system, the stress condition of the connecting bolts in the exhaust system when the fracture risk is maximum under the working condition of an engine is analyzed and calculated through Computational Fluid Dynamics (CFD) software, and the related parameters of the connecting bolts are designed in an optimized mode, so that the problem that the connecting bolts are invalid in assembly in the exhaust system is effectively avoided, meanwhile, the analysis is carried out by adopting the simplified finite element analysis model, the analysis time is greatly shortened, the working efficiency is improved, and the design method has popularization and application values in the technical field of automobile engines.
The above embodiments are merely preferred embodiments for fully explaining the present invention, and the scope of the present invention is not limited thereto. Equivalent substitutions and modifications will occur to those skilled in the art based on the present invention, and are intended to be within the scope of the present invention.
Claims (10)
1. The design method of the connecting bolt in the exhaust system is characterized by comprising the following steps of:
s1, preliminarily setting the number, arrangement mode and related parameters of the connecting bolts according to the spatial arrangement of an exhaust system;
s2, establishing a finite element simulation model of the exhaust system according to 3D data of the exhaust system;
s3, calculating the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model under the cold and hot working conditions according to the gas temperature and the mass flow at the inlet of the exhaust system;
s4, calculating a temperature field of the finite element simulation model under the cold and hot working conditions according to the temperature of the inner wall surface and the heat exchange coefficient;
s5, carrying out heat engine coupling analysis according to a temperature field of the finite element simulation model to obtain axial support reaction force of the connecting bolt, transverse maximum displacement of the gasket and maximum displacement of the flange plate under cold and hot working conditions;
s6, establishing a simplified finite element analysis model of a single connecting bolt, and inputting the axial supporting force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate into the simplified finite element analysis model to obtain the stress of the connecting bolt;
and S7, carrying out fatigue analysis according to the stress of the connecting bolt, calculating the safety coefficient of the connecting bolt, and analyzing whether the safety coefficient meets the standard or not, if not, optimizing the relevant parameters of the connecting bolt until the safety coefficient meets the standard.
2. The method of designing a connecting bolt in an exhaust system according to claim 1, wherein the exhaust system is an integrated exhaust system or a non-integrated exhaust system;
the finite element simulation model of the integrated exhaust system comprises a cylinder cover, a connecting bolt, a gasket, a supercharger, a three-way catalyst and a bracket;
the finite element simulation model of the non-integrated exhaust system comprises a cylinder cover, a connecting bolt, a gasket, an exhaust manifold, a supercharger, a three-way catalyst and a bracket;
the simplified finite element analysis model of the integrated exhaust system comprises a cylinder cover, a double-end stud, a nut, a gasket and a supercharger;
the simplified finite element analysis model of the non-integrated exhaust system comprises a cylinder cover, a double-end stud, a nut, a gasket and an exhaust manifold;
the relevant parameters of the connecting bolt comprise bolt material, bolt grade, bolt length, bolt thread length and gasket thickness.
3. The method for designing a connecting bolt in an exhaust system according to claim 2, wherein in S3, specifically: and calculating the temperature and heat exchange coefficient of two inner wall surfaces of the finite element simulation model under cold and hot working conditions by adopting Computational Fluid Dynamics (CFD) software according to the highest temperature and mass flow of gas at the inlet of the cylinder cover and the exhaust system and the lowest temperature and mass flow of gas.
4. The method for designing a connecting bolt in an exhaust system according to claim 3, wherein when the engine is in a full-speed full-load working condition, the gas at the inlet of the exhaust system has a maximum temperature and a mass flow, the maximum temperature and the mass flow of the gas are used as boundary parameters and are input into Computational Fluid Dynamics (CFD) software, and the temperature and the heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the maximum temperature and the mass flow of the gas are;
when the engine is in an idle working condition, the gas at the inlet of the exhaust system has the lowest temperature and mass flow, the lowest temperature and mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature and heat exchange coefficient of the inner wall surface of the finite element simulation model are obtained when the gas is in the lowest temperature and mass flow.
5. The method for designing a connecting bolt in an exhaust system according to claim 4, wherein in S4, specifically: respectively inputting the two inner wall surface temperatures and the heat exchange coefficient of the finite element simulation model into finite element analysis software to calculate two temperature fields of the finite element simulation model under cold and hot working conditions;
the method comprises the steps of inputting the temperature and heat exchange coefficient of the inner wall surface of a finite element simulation model obtained when the gas is at the highest temperature and the mass flow rate into finite element analysis software, and calculating to obtain a temperature field T1;
and when the gas is at the lowest temperature and mass flow, the obtained temperature and heat exchange coefficient of the inner wall surface of the finite element simulation model are input into finite element analysis software, and a temperature field T2 is obtained through calculation.
6. The method for designing a connecting bolt in an exhaust system according to claim 5, wherein in S5, specifically: and inputting two temperature fields of the finite element simulation model into finite element analysis software to perform heat engine coupling analysis to obtain axial support reaction forces of all connecting bolts, transverse maximum displacement of gaskets and maximum displacement of flanges under cold and hot working conditions.
7. The method for designing a connecting bolt in an exhaust system according to claim 6, wherein the connecting bolt in the finite element simulation model is required to be loaded with a pretightening force before the temperature field is input into the finite element analysis software, then the temperature field T1 is applied to the finite element simulation model for 5 to 8 minutes, and then the temperature field T2 is applied to the finite element simulation model for 5 to 8 minutes;
taking the applied temperature field T1 and the applied temperature field T2 as a heating and cooling cycle, after at least three times of cycle, obtaining the axial supporting reaction force of all the connecting bolts, the transverse maximum displacement of the gaskets and the maximum displacement of the flanges, and selecting one of the connecting bolts with the largest difference value between the maximum axial supporting reaction force and the minimum axial supporting reaction force under the cold and hot working conditions;
the maximum displacement of the gasket in the transverse direction is the maximum displacement of the gasket in the transverse direction relative to the cylinder body, and the maximum displacement of the flange plate is the maximum displacement of the flange plate relative to the cylinder body;
taking the maximum axial branch counter force and the minimum axial branch counter force of the connecting bolt in the hot working condition and the cold working condition of the last cycle as input parameters of the axial branch counter force;
taking two maximum displacement amounts of the gasket connected with the connecting bolt, which are transversely opposite to the cylinder body, in the hot working condition and the cold working condition of the last cycle as input parameters of the transverse maximum displacement amount of the gasket;
and taking two maximum displacement amounts of the flange plate connected with the connecting bolt relative to the cylinder body in the hot working condition and the cold working condition of the last cycle as input parameters of the maximum displacement amount of the flange plate.
8. The method of designing a tie bolt in an exhaust system according to claim 7, wherein the preload applied to the tie bolt is an assembly axial force calculated from the dimensions and torque after preliminary determination of relevant parameters of the tie bolt.
9. The method for designing a connecting bolt in an exhaust system according to claim 7, wherein in S6, specifically: in finite element analysis software, a simplified finite element analysis model of a single connecting bolt is established, then input parameters of axial supporting force of the connecting bolt, input parameters of transverse maximum displacement of a gasket and input parameters of maximum displacement of a flange plate are input into the simplified finite element analysis model, and stress of the connecting bolt is calculated.
10. The method for designing a connecting bolt in an exhaust system according to claim 9, wherein in S7, specifically: inputting the obtained stress of the connecting bolt into fatigue analysis software to perform fatigue analysis, calculating the safety coefficient of the connecting bolt, analyzing whether the connecting bolt meets the standard, if the connecting bolt meets the standard, adopting the preliminarily set connecting bolt, if the connecting bolt does not meet the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the connecting bolt again, and optimizing the process, the cost and the space arrangement after the connecting bolt meets the standard.
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