CN114692335A - 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: preliminarily setting the number, the arrangement mode and related parameters of the connecting bolts according to the spatial arrangement of the exhaust system; establishing a finite element simulation model of the exhaust system; according to the gas temperature and the mass flow at the inlet of the exhaust system, obtaining the temperature of the inner wall surface and the heat exchange coefficient of the model, and then calculating the temperature field of the model; carrying out thermo-mechanical coupling analysis according to the temperature field to obtain the axial bearing reaction force of the connecting bolt, the transverse direction of the gasket and the maximum displacement of the flange plate, establishing a simplified finite element analysis model, and inputting the axial bearing reaction force of the connecting bolt, the transverse direction of the gasket and the maximum displacement of the flange plate 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 standard is reached. 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 prevents gas leakage. Because the exhaust system works in extremely severe high-temperature environment, high-temperature airflow impacts frequently, and cold and hot environments alternate, meanwhile, because the cylinder cover and the exhaust system are made of different materials and have large structural difference, the connecting bolt is easy to have the condition of assembly failure, wherein the failure is mainly shown as fracture.
In the prior art, the connecting bolts of the exhaust system and the cylinder cover are subjected to bolt type selection according to the distribution of the arrangement design bolts and the mode recommended by standards or industries. However, due to the fact that materials and structures of the cylinder cover and the exhaust system are diversified, risks of the same bolt in different cylinder covers and different 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 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, the arrangement mode and relevant parameters of the connecting bolts according to the spatial arrangement of the exhaust system;
s2, establishing a finite element simulation model of the exhaust system according to the 3D data of the exhaust system;
s3, calculating the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model under the working conditions of cold and hot according to the gas temperature and 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 thermo-mechanical coupling analysis according to the temperature field of the finite element simulation model to obtain the axial bearing reaction force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate under the cold and hot working conditions;
s6, establishing a simplified finite element analysis model of a single connecting bolt, and inputting the axial bearing reaction 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 analysis reaches the standard, if not, optimizing the relevant parameters of the connecting bolt until the parameters reach 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 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 stud, a nut, a gasket and an exhaust manifold;
relevant parameters of the connecting bolt include bolt material, bolt grade, bolt length, bolt thread length and shim thickness.
Preferably, in S3, specifically, the method includes: according to the highest gas temperature and mass flow and the lowest gas temperature and mass flow at the inlet of the cylinder cover and the exhaust system, calculating two inner wall surface temperatures and heat exchange coefficients of the finite element simulation model under cold and hot working conditions by adopting Computational Fluid Dynamics (CFD) software.
Preferably, when the engine is under a 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 of the inner wall surface and the heat exchange coefficient of the finite element simulation model when the gas is at the highest temperature and the mass flow are obtained;
when the engine is in an idling working condition, the gas at the inlet of the exhaust system has the lowest temperature and the lowest mass flow, the lowest temperature and the lowest mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model when the gas is at the lowest temperature and the mass flow are obtained.
Preferably, in S4, specifically, the method includes: respectively inputting the temperatures of the two inner wall surfaces 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;
inputting the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model obtained when the gas is at the highest temperature and the mass flow into finite element analysis software, and calculating to obtain a temperature field T1;
and 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.
Preferably, in S5, specifically, the method includes: inputting the two temperature fields of the finite element simulation model into finite element analysis software, and carrying out thermal engine coupling analysis to obtain the axial bearing reaction force of all the connecting bolts, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate under the working conditions of cold and heat.
Preferably, before the temperature field is input into the finite element analysis software, a pretightening force needs to be loaded on the connecting bolt in the finite element simulation model, 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, and after the cycle is carried out for at least three times, obtaining the axial bearing reaction force of all the connecting bolts, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate, and selecting one connecting bolt with the largest difference value between the maximum axial bearing reaction force and the minimum axial bearing reaction force under the cold and hot working conditions;
the transverse maximum displacement of the gasket is the maximum displacement of the gasket transversely 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;
the maximum axial bearing reaction force and the minimum axial bearing reaction force of the connecting bolt under the last cycle of hot working conditions and cold working conditions are used as input parameters of the axial bearing reaction force;
taking two maximum displacement amounts of the gasket connected with the connecting bolt in the transverse direction relative to the cylinder body under the last cycle of thermal working conditions and cold working conditions as input parameters of the maximum transverse displacement amount of the gasket;
and taking the two maximum displacement amounts of the flange plate connected with the connecting bolt relative to the cylinder body under 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 preload force applied to the connecting bolt is an assembling axial force obtained by calculation according to the size and the torque after preliminarily determining relevant parameters of the connecting bolt.
Preferably, in S6, specifically, the method includes: in the finite element analysis software, a simplified finite element analysis model of a single connecting bolt is established, then an input parameter of axial bearing reaction force of the connecting bolt, an input parameter of transverse maximum displacement of a gasket and an input parameter of maximum displacement of a flange are input into the simplified finite element analysis model, and the stress of the connecting bolt is obtained through calculation.
Preferably, in S7, specifically, the method includes: inputting the obtained stress of the connecting bolt into fatigue analysis software to carry out fatigue analysis, calculating the safety coefficient of the connecting bolt, judging whether the analysis reaches the standard, if the analysis reaches the standard, adopting the connecting bolt which is preliminarily set, if the analysis does not reach the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the bolt until the analysis reaches the standard, and optimizing the process, the cost and the spatial arrangement after the analysis reaches the standard.
The invention has the beneficial effects that:
according to the design method of the connecting bolt in the exhaust system, the number, the arrangement mode and the related parameters of the connecting bolt in the exhaust system are designed in advance, a finite element analysis model of the exhaust system is established by adopting finite element analysis software, the stress condition of the connecting bolt in the exhaust system when the fracture risk is maximum is analyzed and calculated by Computational Fluid Dynamics (CFD) software under the working condition of an engine, and then the related parameters of the connecting bolt are optimally designed, so that the problem of assembly failure of the connecting bolt in the exhaust system is effectively avoided, and meanwhile, the finite element simplified analysis model is used for analysis, so that the analysis time is greatly reduced, 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 structural diagram of a finite element simulation model of a non-integrated exhaust system according to embodiment 1;
FIG. 3 is a schematic structural diagram of a simplified finite element analysis model of a non-integrated exhaust system in example 1.
Wherein, 1-cylinder cover; 2-connecting bolts; 3-a gasket; 4-an exhaust manifold; 5-a supercharger; 6-three-way catalyst; 7-a scaffold; 8-a nut; 9-exhaust manifold.
Detailed Description
Other advantages and effects of the present invention will become apparent to those skilled in the art from the disclosure herein, wherein the embodiments of the present invention are described in detail with reference to the accompanying drawings and preferred embodiments. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be understood that the preferred embodiments are illustrative of the invention only and are not limiting upon the scope of the invention.
It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention, and the components related to the present invention are only shown in the drawings rather than drawn according to the number, shape and size of the components in actual implementation, and the type, quantity and proportion of the components in actual implementation may be changed freely, and the layout of the components may be more complicated.
Example 1
As shown in fig. 1, a method for designing a connection bolt in a non-integrated exhaust system includes the following steps:
s1, preliminarily setting the number, the arrangement mode and relevant parameters of the connecting bolts according to the spatial arrangement of the non-integrated exhaust system;
the relevant parameters of the connecting bolt comprise bolt material, bolt grade, bolt length, bolt thread length and gasket thickness;
s2, establishing a finite element simulation model of the non-integrated exhaust system according to the 3D data of the non-integrated exhaust system;
as shown in fig. 2, 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 of the inner wall surface and the heat exchange coefficient of the finite element simulation model under the working conditions of cold and hot according to the gas temperature and mass flow at the inlet of the non-integrated exhaust system;
the method specifically comprises the following steps: calculating the temperature and the heat exchange coefficient of two inner wall surfaces of a finite element simulation model under the cold and hot working conditions by adopting Computational Fluid Dynamics (CFD) software according to the highest gas temperature and mass flow, the lowest gas temperature and mass flow at the inlet of the non-integrated exhaust system;
when the engine is under a 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 and input into Computational Fluid Dynamics (CFD) software, and the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model when the gas is at the highest temperature and the mass flow are obtained;
when the engine is in an idling 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 of the inner wall surface and the heat exchange coefficient of the finite element simulation model when the gas is at the lowest temperature and the mass flow are obtained;
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 specifically comprises the following steps: respectively inputting the temperatures of the two inner wall surfaces 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;
inputting the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model obtained when the gas is at the highest temperature and the mass flow into finite element analysis software, and calculating to obtain a temperature field T1;
inputting the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model obtained when the gas is at the lowest temperature and mass flow into finite element analysis software, and calculating to obtain a temperature field T2;
s5, carrying out thermo-mechanical coupling analysis according to the temperature field of the finite element simulation model to obtain the axial bearing reaction force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate under the cold and hot working conditions;
the method specifically comprises the following steps: loading 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 6 min;
taking the applied temperature field T1 and the applied temperature field T2 as a heating and cooling cycle, and after the cycle is carried out for three times, obtaining the axial support reaction force of all the connecting bolts, the maximum displacement of the gasket transversely relative to the cylinder body and the maximum displacement of the flange plate relative to the cylinder body, and selecting one connecting bolt 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 bearing reaction force of the connecting bolt under the hot working condition of the third cycle working condition is F1, and the minimum axial bearing reaction force under the cold working condition is F2 as an input parameter of the axial bearing reaction force;
the maximum transverse displacement of the gasket connected with the connecting bolt relative to the cylinder body under the hot working condition and the cold working condition of the third circulation is respectively U1 and U2 and serves as input parameters of the maximum transverse displacement of the gasket;
the maximum displacement of the flange connected with the connecting bolt relative to the cylinder body under the hot working condition and the cold working condition of the third cycle is respectively U3 and U4 as the input parameters of the maximum displacement of the flange;
the method comprises the following steps that a pre-tightening force is loaded on a connecting bolt, and after relevant parameters of the connecting bolt are preliminarily determined, an assembling axial force is obtained through size calculation;
s6, establishing a simplified finite element analysis model of a single connecting bolt, and inputting the axial bearing reaction 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, and an exhaust manifold 10; the stud is one type of bolt, and generally, the stud is adopted due to the advantage of convenient assembly, so that the stud is used in a simplified model;
the method specifically comprises the following steps: in finite element analysis software, establishing a simplified finite element analysis model of a single connecting bolt, loading a pretightening force F1 on the connecting bolt, loading a transverse maximum displacement U1 on a gasket, loading a maximum displacement U3 on a flange plate, then loading a pretightening force F2 on the connecting bolt, loading a transverse maximum displacement U2 on the gasket, loading a maximum displacement U4 on the flange plate, and calculating to obtain the stress of the connecting bolt;
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 specifically comprises the following steps: inputting the obtained stress of the connecting bolt into fatigue analysis software to carry out fatigue analysis, calculating the safety coefficient of the connecting bolt, judging whether the analysis reaches the standard, if the analysis reaches the standard, adopting the connecting bolt which is preliminarily set, if the analysis does not reach the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the bolt until the analysis reaches the standard, and optimizing the process, the cost and the spatial arrangement after the analysis reaches the standard.
In the present embodiment, the standard of safety factor of the connecting bolt is 1.2.
In S2, the finite element simulation model is built in the finite element analysis software, and the mesh of the bolt needs to be refined to highlight the structural features.
At S3, the maximum temperature and mass flow rate of the gas at the inlet of the non-integrated exhaust system are constant at full speed and full load of the engine, and the minimum temperature and mass flow rate of the gas at the inlet of the non-integrated exhaust system are constant at idle.
The number, the arrangement mode and the related parameters of the connecting bolts of the non-integrated exhaust system are designed and analyzed in advance to determine the optimal design parameters of the connecting bolts, so that the problem of assembly failure of the connecting bolts in the exhaust system is effectively avoided, and meanwhile, a simplified finite element analysis model is used for analysis, so that the analysis time is greatly reduced, and the working efficiency is improved.
In the embodiment, by designing the 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 optimization time of relevant parameters of the connecting bolt is greatly shortened, and the rapid and accurate design and production can be carried out.
At S3, since the actual non-integrated exhaust system is mainly affected by thermal fatigue loads (i.e., cold and hot impacts), the temperature field of the finite element simulation model at the highest exhaust temperature must be calculated to determine the maximum risk of the connecting bolt breakage.
Example 2
As shown in fig. 1, a method for designing a connection bolt in an integrated exhaust system includes the following steps:
s1, preliminarily setting the number, the arrangement mode and relevant parameters of the connecting bolts according to the spatial arrangement of the integrated exhaust system;
the relevant parameters of the connecting bolt comprise bolt material, bolt grade, bolt length, bolt thread length and gasket thickness;
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 of the inner wall surface and the heat exchange coefficient of the finite element simulation model under the working conditions of cold and hot according to the gas temperature and mass flow at the inlet of the integrated exhaust system;
the method specifically comprises the following steps: calculating two inner wall surface temperatures and heat exchange coefficients of the 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 and the lowest gas temperature and mass flow at the inlet of the integrated exhaust system;
when the engine is under a 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 of the inner wall surface and the heat exchange coefficient of a finite element simulation model when the gas is at the highest temperature and the mass flow are obtained;
when the engine is in an idling working condition, the gas at the inlet of the integrated exhaust system has the lowest temperature and the lowest mass flow, the lowest temperature and the lowest mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model when the gas is at the lowest temperature and the mass flow are obtained;
s4, calculating a temperature field of the finite element simulation model under the working conditions of cold and heat according to the temperature of the inner wall surface and the heat exchange coefficient;
the method specifically comprises the following steps: respectively inputting the temperatures of the two inner wall surfaces and the heat exchange coefficients of the finite element simulation model into finite element analysis software, and calculating two temperature fields of the finite element simulation model under the cold and hot working conditions;
inputting the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model obtained when the gas is at the highest temperature and the mass flow into finite element analysis software, and calculating to obtain a temperature field T1;
inputting the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model obtained when the gas is at the lowest temperature and mass flow into finite element analysis software, and calculating to obtain a temperature field T2;
s5, carrying out thermal-mechanical coupling analysis according to the temperature field of the finite element simulation model to obtain the axial bearing reaction force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate under the working conditions of cold and hot;
the method specifically comprises the following steps: loading 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 6 min;
taking the applied temperature field T1 and the applied temperature field T2 as a heating and cooling cycle, and after the cycle is carried out for three times, obtaining the axial support reaction force of all the connecting bolts, the maximum displacement of the gasket transversely relative to the cylinder body and the maximum displacement of the flange plate relative to the cylinder body, and selecting one connecting bolt 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 bearing reaction force of the connecting bolt under the hot working condition of the third cycle working condition is f1, and the minimum axial bearing reaction force under the cold working condition is f2 as an input parameter of the axial bearing reaction force;
the maximum displacement of the gasket connected with the connecting bolt in the transverse direction relative to the cylinder body under the hot working condition and the cold working condition of the third cycle is respectively u1 and u2 which are used as input parameters of the maximum displacement of the gasket in the transverse direction;
the maximum displacement of the flange connected with the connecting bolt relative to the cylinder body under the hot working condition and the cold working condition of the third cycle is respectively u3 and u4 as the input parameters of the maximum displacement of the flange;
the method comprises the following steps that a pre-tightening force is loaded on a connecting bolt, and the pre-tightening force is an assembling axial force obtained by 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 support reaction 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 bolt stress;
the simplified finite element analysis model of the integrated exhaust system comprises a cylinder cover, a stud, a nut, a gasket and a supercharger;
the method specifically comprises the following steps: in finite element analysis software, establishing a simplified finite element analysis model of a single connecting bolt, loading a pretightening force f1 on the connecting bolt, loading a transverse maximum displacement u1 on a gasket, loading a maximum displacement u3 on a flange plate, then loading a pretightening force f2 on the connecting bolt, loading a transverse maximum displacement u2 on the gasket, loading a maximum displacement u4 on the flange plate, and calculating to obtain the stress of the connecting bolt;
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 analysis reaches the standard, if not, optimizing the relevant parameters of the connecting bolt until the parameters reach the standard;
the method specifically comprises the following steps: inputting the obtained stress of the connecting bolt into fatigue analysis software to carry out fatigue analysis, calculating the safety coefficient of the connecting bolt, judging whether the analysis reaches the standard, if the analysis reaches the standard, adopting the connecting bolt which is preliminarily set, if the analysis does not reach the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the bolt until the analysis reaches the standard, and optimizing the process, the cost and the spatial arrangement after the analysis reaches the standard.
In the present embodiment, the standard of safety factor of the connecting bolt is 1.2.
In S2, the finite element simulation model is built in the finite element analysis software, and the mesh of the bolt needs to be refined to highlight the structural features.
At S3, the maximum temperature and mass flow rate of the gas at the inlet of the integrated exhaust system are constant at full speed and full load of the engine, and the minimum temperature and mass flow rate of the gas at the inlet of the integrated exhaust system are constant at idle.
In S3, since the actual integrated exhaust system is mainly affected by thermal fatigue loads (i.e., cold-hot impact), the temperature field of the finite element simulation model at the highest exhaust temperature must be calculated to determine the maximum risk of the connecting bolt breakage.
According to the design method of the connecting bolt in the exhaust system, the number, the arrangement mode and the related parameters of the connecting bolt in the exhaust system are designed in advance, a finite element analysis model of the exhaust system is established by adopting finite element analysis software, the stress condition of the connecting bolt in the exhaust system when the fracture risk is maximum is analyzed and calculated by Computational Fluid Dynamics (CFD) software under the working condition of an engine, and then the related parameters of the connecting bolt are optimally designed, so that the problem of assembly failure of the connecting bolt in the exhaust system is effectively avoided, and meanwhile, the finite element simplified analysis model is used for analysis, so that the analysis time is greatly reduced, 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 illustrating the present invention, and the scope of the present invention is not limited thereto. The equivalent substitution or change made by the technical personnel in the technical field on the basis of the invention is all within the protection scope of the invention.
Claims (10)
1. A design method of a connecting bolt in an exhaust system is characterized by comprising the following steps:
s1, preliminarily setting the number, the arrangement mode and relevant parameters of the connecting bolts according to the spatial arrangement of the exhaust system;
s2, establishing a finite element simulation model of the exhaust system according to the 3D data of the exhaust system;
s3, calculating the temperature of the inner wall surface and the heat exchange coefficient 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 thermo-mechanical coupling analysis according to the temperature field of the finite element simulation model to obtain the axial bearing reaction force of the connecting bolt, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate under the cold and hot working conditions;
s6, establishing a simplified finite element analysis model of a single connecting bolt, and inputting the axial bearing reaction 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 analysis reaches the standard, if not, optimizing the relevant parameters of the connecting bolt until the parameters reach the standard.
2. The method of 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 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 stud, a nut, a gasket and an exhaust manifold;
relevant parameters of the connecting bolt include bolt material, bolt grade, bolt length, bolt thread length and shim thickness.
3. The method for designing a connecting bolt in an exhaust system according to claim 2, wherein in S3, specifically: according to the highest gas temperature and mass flow and the lowest gas temperature and mass flow at the inlet of the cylinder cover and the exhaust system, calculating two inner wall surface temperatures and heat exchange coefficients of the finite element simulation model under cold and hot working conditions by adopting Computational Fluid Dynamics (CFD) software.
4. The method for designing the connecting bolt in the exhaust system according to claim 3, wherein when the engine is under a 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 of the inner wall surface and the heat exchange coefficient of the finite element simulation model are obtained when the gas has the highest temperature and the mass flow;
when the engine is in an idling working condition, the gas at the inlet of the exhaust system has the lowest temperature and the lowest mass flow, the lowest temperature and the lowest mass flow of the gas are used as boundary parameters to be input into Computational Fluid Dynamics (CFD) software, and the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model when the gas is at the lowest temperature and the mass flow are obtained.
5. The method for designing a connecting bolt in an exhaust system according to claim 4, wherein in the step S4, specifically: respectively inputting the temperatures of the two inner wall surfaces 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;
inputting the temperature of the inner wall surface and the heat exchange coefficient of the finite element simulation model obtained when the gas is at the highest temperature and the mass flow into finite element analysis software, and calculating to obtain a temperature field T1;
and 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.
6. The method for designing a connecting bolt in an exhaust system according to claim 5, wherein in the step S5, specifically: inputting the two temperature fields of the finite element simulation model into finite element analysis software, and carrying out thermal engine coupling analysis to obtain the axial bearing reaction force of all the connecting bolts, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate under the working conditions of cold and heat.
7. The method for designing the connecting bolt in the exhaust system according to claim 6, wherein a pretightening force is required to be loaded on the connecting bolt in the finite element simulation model before the temperature field is input into the finite element analysis software, then the temperature field T1 is applied on the finite element simulation model for 5-8 min, and then the temperature field T2 is applied on 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, and after the cycle is carried out for at least three times, obtaining the axial bearing reaction force of all the connecting bolts, the transverse maximum displacement of the gasket and the maximum displacement of the flange plate, and selecting one connecting bolt with the largest difference value between the maximum axial bearing reaction force and the minimum axial bearing reaction force under the cold and hot working conditions;
the transverse maximum displacement of the gasket is the maximum displacement of the gasket transversely 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;
the maximum axial bearing reaction force and the minimum axial bearing reaction force of the connecting bolt under the last cycle of hot working conditions and cold working conditions are used as input parameters of the axial bearing reaction force;
taking two maximum displacement amounts of the gasket connected with the connecting bolt in the transverse direction relative to the cylinder body under the last cycle of thermal working conditions and cold working conditions as input parameters of the maximum transverse displacement amount of the gasket;
and taking the two maximum displacement amounts of the flange plate connected with the connecting bolt relative to the cylinder body under 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 coupling bolt in an exhaust system according to claim 7, wherein the preload applied to the coupling bolt is an assembling axial force calculated from a size and a torque after preliminarily determining relevant parameters of the coupling bolt.
9. The method for designing a connecting bolt in an exhaust system according to claim 7, wherein in S6, specifically: in the finite element analysis software, a simplified finite element analysis model of a single connecting bolt is established, then an input parameter of axial bearing reaction force of the connecting bolt, an input parameter of transverse maximum displacement of a gasket and an input parameter of maximum displacement of a flange are input into the simplified finite element analysis model, and the stress of the connecting bolt is obtained through calculation.
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 carry out fatigue analysis, calculating the safety coefficient of the connecting bolt, judging whether the analysis reaches the standard, if the analysis reaches the standard, adopting the connecting bolt which is preliminarily set, if the analysis does not reach the standard, optimizing the related parameters of the connecting bolt, calculating the safety coefficient of the bolt until the analysis reaches the standard, and optimizing the process, the cost and the spatial arrangement after the analysis reaches the standard.
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