A method for predicting strength performance of engine cylinder block based on bench test

Abstract

The present application belongs to the technical field of engine cylinder bench test, and particularly relates to a strength performance finite element prediction method based on engine cylinder bench test; finite element models of an engine cylinder, an engine main bearing cover and other structures are established, a connection relationship is established according to a real assembly relationship, an interference amount and a gap amount are defined in a load, bolt load application is defined, hydraulic oil pressure load is applied, a boundary constraint condition is applied, a finite element model is calculated and solved, and the engine cylinder is evaluated according to a solution result; the present application accurately reproduces the engine cylinder bench test through a finite element simulation method, can replace the cylinder bench test within a certain range to predict the strength and durability life of the engine cylinder, and can simultaneously perform the strength prediction of the engine cylinder bench test condition in the design stage, can be performed simultaneously with the design, can not only predict the passability of the cylinder in the bench test condition, but also can predict a weak design point.

Description

Technical Field

[0001] This invention belongs to the field of engine block bench testing technology, specifically relating to a finite element method for predicting the strength performance of engine block bench tests. Background Technology

[0002] As a crucial foundational component of the engine, the engine block serves as the base for mounting connecting rods, crankshafts, and other parts, and bears numerous loads, including gas combustion pressure, connecting rod and crankshaft rotation, and temperature. Therefore, the engine block design must ensure sufficient rigidity and strength, while also possessing good fatigue durability to maintain reliability throughout the engine's entire service life.

[0003] To ensure the durability of the engine block throughout the vehicle's service life, cylinder block bench fatigue testing is an indispensable technical means in engine development. However, because cylinder block bench testing must be conducted after the entire engine prototype is completed, it is in the later stages of research and development. This results in a long testing cycle, high manpower and material costs, and multiple rounds of verification and optimization that are time-consuming and labor-intensive. Furthermore, cylinder block fatigue testing is generally a pass / fail test and is difficult to reflect the stress conditions of the cylinder block structure.

[0004] Therefore, it is necessary to find a method that can accurately predict the strength performance of engine blocks under bench test conditions. This would allow for the prediction of stress distribution in the cylinder block under fatigue test conditions during the early design phase, thereby advancing the verification stage, reducing the number of test cycles, and shortening the time cycle to meet product development needs.

[0005] Currently, two technical methods can be used to evaluate the fatigue strength performance of cylinder blocks.

[0006] One method is engine block bench testing during the product development and verification cycle. Engine block bench testing is currently the primary method for verifying the strength and durability of engine blocks, mainly checking the strength and durability of the block skirt. Engine block bench testing generally involves applying hydraulic pressure to the cylinder or fixture using a cylinder block testing machine, which then transmits the pressure to the main bearing housing through components such as the piston, connecting rod, and crankshaft. By adjusting the hydraulic pressure, the load amplitude and frequency are determined, thereby verifying the strength and durability of the block. The problems with engine block bench testing include:

[0007] ① Located in the late stage of product development, it cannot effectively guide the forward development and design of the product. The testing methods are heavily dependent on the development status of the cylinder and fixture. Failure to pass verification often leads to repeated product design iterations, resulting in a significant waste of time and costs.

[0008] ② The testing cycle is long and the cost is high. The verification life cycle of the cylinder block bench test is more than 10 million cycles, and even if it fails, the cycle is often several million cycles. Combined with the loading frequency of the cylinder block bench test machine, the verification time for a single engine cylinder block can be more than ten days, or even several tens of days.

[0009] ③ Cylinder block bench tests are generally pass / fail tests. The test results often only show the final failure location and failure period. If the test does not fail, the weak points in the structure cannot be revealed.

[0010] ④ Even if strain gauges are attached during fatigue testing, only the stress of the local structure can be obtained. Furthermore, due to limitations in structural dimensions and operating space, the actual location of the strain gauges may not be the location of failure.

[0011] The second method is to use the finite element method to perform simulations in the early stages of design to calculate the strength of the cylinder block.

[0012] Most current cylinder block strength simulation methods are based on thermo-mechanical coupling analysis under actual engine operating conditions, which differs significantly from cylinder block bench tests. Generally, simulation analyses based on actual operating conditions do not consider the effects of the crankshaft and connecting rods, directly simplifying the load to the main bearing housing location and taking temperature into account. The problem is that both the structure and the applied boundary conditions differ from experimental results. While these methods can reflect the structural strength performance to some extent, they cannot accurately predict the cylinder block strength performance under experimental conditions. Summary of the Invention

[0013] To overcome the above problems, this invention provides a finite element method for predicting the strength performance of engine cylinder blocks based on engine cylinder block bench tests. By accurately reproducing the engine cylinder block bench test using finite element simulation, it can replace the engine cylinder block bench test for predicting engine cylinder block strength, durability, and life within a certain range. At the same time, this invention can advance the strength prediction of engine cylinder block bench test conditions to the design stage, allowing it to be carried out simultaneously with design improvement. It can not only predict the passability of the cylinder block under bench test conditions but also predict its weak design points.

[0014] A finite element method for predicting the strength performance of engine block bench tests includes the following:

[0015] (I) Establishment of Finite Element Analysis Model

[0016] S1. Establish the finite element model of the engine block;

[0017] S2. Establish the finite element model of the engine main bearing cover;

[0018] S3. Establish finite element models of other engine structures, including all engine component structures and fixtures involved in the engine block bench test;

[0019] S4. Establish the connection relationships between parts based on the actual assembly relationship. Except for bolt and threaded connections which use special contact relationship definitions, all others are general contact relationships.

[0020] S5. Define the materials of the finite element model, including the elastic modulus E and Poisson's ratio μ of the finite element model materials of each component.

[0021] (II) Application of load boundary conditions

[0022] S6. Define the interference and clearance in the load in the assembly relationship calculated by finite element method;

[0023] S7, Definition of Bolt Load Application

[0024] For ordinary bolts, which are tightened in the elastic zone, the bolt preload is calculated using the following formula, with the direction of action along the bolt's axial direction:

[0025]

[0026] In the formula, F is the bolt preload, T is the bolt tightening torque, k is the bolt tightening torque coefficient, and D is the bolt diameter;

[0027] The bolts of the engine cylinder head and main bearing cap are fastened by torque plus rotation angle, which is a yield fastening method. The bolt preload is calculated using the following formula, and the direction of action is along the axial direction of the bolt.

[0028]

[0029] In the formula, F1 is the bolt preload, σ y For the bolt yield point stress, A s d is the nominal stress cross-sectional area of ​​the bolt. A The equivalent diameter of the bolt's nominal stress cross-sectional area is μ, where p is the pitch and μ is the diameter of the bolt. s d2 is the thread friction coefficient, d2 is the thread pitch diameter, and α′ is the thread flank angle;

[0030] S8. Applying hydraulic oil pressure load: According to the test conditions, an oil cavity is formed between the test cylinder head and the test cylinder body, and a hydraulic oil pressure value is applied to the surface;

[0031] S9. Apply boundary constraints: Constrain all degrees of freedom of the cylinder upper surface and the fixture bracket fixing point according to different stages;

[0032] (III) Statics Solution and Evaluation

[0033] S10, Solve the finite element model

[0034] The nonlinear statics solution is performed using Newton's method to calculate the stress and deformation of each structure.

[0035] The load solving step in step S10 is set as follows:

[0036] 1) Assembly Condition 1: Assembly of cylinder block, main bearing cap, main bearing cap bolts, piston, connecting rod, crankshaft, and fixture;

[0037] 2) Assembly Condition 2: Cylinder head, cylinder gasket, and cylinder head bolt assembly;

[0038] 3) Load Condition 1: Simulation of maximum oil pressure under test fluctuation load;

[0039] 4) Load Condition 2: Simulation of minimum oil pressure under test fluctuation load;

[0040] S11. Based on the solution results of step S10, evaluate the engine block: evaluate the stress state of the block structure under assembly condition 1 + assembly condition 2 + load condition 1 and assembly condition 1 + assembly condition 2 + load condition 2 respectively.

[0041] In step S1, it is necessary to ensure that the contact boundaries between the engine block and other components are clear, especially to ensure that the grids of the main bearing cap, main bearing shell and cylinder block contact surfaces correspond one-to-one.

[0042] In step S1, it is necessary to ensure that the overall grid size of the cylinder block ventilation holes and stop positions is less than 2mm, and at the same time ensure that the number of grid parts in the circumferential direction of the rounded corners is more than 8, and the grid aspect ratio is not greater than 1.5.

[0043] In step S2, it is necessary to ensure that the grid division of the top rounded corner of the main bearing cover is more than 6 parts, and the aspect ratio of the grid is not greater than 1.5.

[0044] In step S3, other engine structures include cylinder head, cylinder head gasket, piston, connecting rod, crankshaft, bearing shell, and bolts; the cylinder head gasket is constructed using a single-layer solid mesh, and the pressure wave part is grouped separately; the bolts are divided using a hexahedral mesh, without showing thread characteristics; the main bearing shell is divided using a two-layer hexahedral mesh, showing oil hole characteristics, but without showing positioning characteristics; other components are divided using tetrahedral or hexahedral meshes according to their shapes.

[0045] In step S4, the connection of the threaded part is defined according to the bolt connection contact relationship. The parameters that need to be defined are bolt spacing, thread helix angle, and thread clearance.

[0046] In step S5, if a single tetrahedral simulation is used to simulate cylinder head and piston components that are not of interest, their elastic modulus is calculated as 70% of their material elastic modulus.

[0047] In step S6, the interference and clearance are defined according to the design requirements, and the average value of the interference and clearance is taken.

[0048] In step S9, when assembling the cylinder block and internal components, all degrees of freedom of the nodes on the upper surface of the cylinder block are constrained; when assembling the cylinder head and cylinder gasket and applying loads, all degrees of freedom of the fixture bracket fixing points are constrained.

[0049] In step S11, the maximum principal stress of the structure is required to not exceed the fatigue strength limit of the cylinder material.

[0050] In step S11, when the number of units exceeding the material fatigue limit is less than 1 / 3 or concentrated at unit nodes, it is considered stress concentration and the structure is not optimized.

[0051] In steps S1 to S9, the finite element preprocessing software Hypermesh is used for processing.

[0052] Steps S10 and S11 are processed using the finite element post-processing software Abaqus.

[0053] The beneficial effects of this invention are:

[0054] ① This invention accurately reproduces engine block bench tests using finite element simulation, and can replace engine block bench tests for predicting engine block strength, durability, and lifespan within a certain range. Simultaneously, this invention allows for the prediction of engine block strength under bench test conditions to be performed earlier in the design phase, simultaneously with design refinement. It can not only predict the passability of the cylinder block under bench test conditions but also predict its weak design points.

[0055] ②This invention fully utilizes the advantages of finite element analysis, such as short calculation cycle and accurate prediction, and uses the maximum principal stress of the structure as a prediction of the structure's strength performance.

[0056] ③ This invention provides a standardized and streamlined method for predicting the strength performance of cylinder blocks under bench test conditions. It standardizes the finite element operation process from all dimensions, including finite element modeling, assembly, calculation, and evaluation. This greatly reduces the problem of large dispersion of calculation results caused by the subjective judgment of engineers, unifies the judgment criteria, and improves simulation efficiency.

[0057] ③ The method for predicting the strength performance of cylinder blocks under test conditions provided in this invention has the same structure, boundary conditions, and material parameters as the cylinder block test. Therefore, it can be used in the early stages of product development to guide structural optimization design and improve structural strength performance, ensuring the product passes test verification on the first attempt. It can also be used in the later stages of product development to address cylinder block failure issues that occur during testing. Attached Figure Description

[0058] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments of the present invention will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the content of the embodiments of the present invention and these drawings without creative effort.

[0059] Figure 1 This is a flowchart of the present invention.

[0060] Figure 2 This is a schematic diagram of the finite element model of the cylinder block test bench of the present invention. Detailed Implementation

[0061] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and not intended to limit it. Furthermore, it should be noted that, for ease of description, the accompanying drawings show only the parts relevant to the present invention, and not all of the structures.

[0062] In the description of this invention, unless otherwise explicitly specified and limited, the terms "connected," "linked," and "fixed" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0063] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0064] In the description of this embodiment, the terms "upper," "lower," "left," and "right," etc., refer to the orientation or positional relationship shown in the accompanying drawings. They are used only for ease of description and simplification of operation, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the present invention. In addition, the terms "first" and "second" are used only for distinction in description and have no special meaning.

[0065] Example 1

[0066] A finite element method for predicting the strength performance of engine block bench tests, such as... Figure 1 The above includes the following:

[0067] (I) Establishment of Finite Element Analysis Model

[0068] S1. Establish the finite element model of the engine block.

[0069] The engine block model focuses on refining the area around the main bearing housing;

[0070] S2. Establish the finite element model of the engine main bearing cap.

[0071] The engine main bearing cover model focuses on refining the chamfer position at the top of the main bearing cover;

[0072] S3. Establish finite element models of other engine structures; including the structures and fixtures of all engine components involved in the engine block bench test; such as... Figure 2 As shown;

[0073] S4. Establish the connection relationships between components based on the actual assembly relationship; except for bolt and thread connections which use special contact relationship definitions, all others are general contact relationships;

[0074] S5. Define the materials for the finite element model.

[0075] Define the elastic modulus E and Poisson's ratio μ for the materials of each component in the finite element model; generally, E = 210 GPa and μ = 0.30 for steel, and E = 70 GPa and μ = 0.33 for aluminum alloy. It should be noted that since engine blocks are generally made of cast aluminum alloy or cast iron, the performance of the structural materials after casting often differs significantly from the material standard performance due to the influence of casting processes, etc. It is recommended to use test data from actual samples of similar cylinder blocks produced by the same manufacturer.

[0076] (II) Application of load boundary conditions

[0077] S6, Definition of Interference and Clearance Assembly Load Application

[0078] In finite element analysis, the interference and clearance in assembly relationships are defined under load; according to design requirements, the interference and clearance are defined, and their average values ​​are taken.

[0079] In step S6, if the interference and clearance amounts are not explicitly given, they can be calculated based on the dimensions indicated in the design drawings. The applied interference or clearance amount δ can be calculated using the following formula (1):

[0080]

[0081] S7, Definition of Bolt Load Application

[0082] For ordinary bolts, which are tightened in the elastic zone, the bolt preload is calculated using the following formula, with the direction of action along the bolt's axial direction:

[0083]

[0084] In the formula, F is the bolt preload, T is the bolt tightening torque, k is the bolt tightening torque coefficient, and D is the bolt diameter;

[0085] The bolts of the engine cylinder head and main bearing cap are fastened by torque plus rotation angle, which is a yield fastening method. The bolt preload is calculated using the following formula, and the direction of action is along the axial direction of the bolt.

[0086]

[0087] In the formula, F1 is the bolt preload, σ y For the bolt yield point stress, A s d is the nominal stress cross-sectional area of ​​the bolt. A The equivalent diameter of the bolt's nominal stress cross-sectional area is μ, where p is the pitch and μ is the diameter of the bolt. s d2 is the thread friction coefficient, d2 is the thread pitch diameter, and α′ is the thread flank angle;

[0088] S8, hydraulic oil pressure load application

[0089] According to the test conditions, an oil cavity is formed between the test cylinder head and the test cylinder block, and hydraulic oil pressure is applied to the surface;

[0090] S9. Applying boundary constraints

[0091] According to different stages, constrain all degrees of freedom of the upper surface of the cylinder block and the fixing point of the fixture bracket respectively;

[0092] (III) Statics Solution and Evaluation

[0093] S10, Solve the finite element model

[0094] The nonlinear statics solution is performed using Newton's method to calculate the stress and deformation of each structure.

[0095] The load solving step in step S10 is set as follows:

[0096] 1) Assembly Condition 1: Assembly of cylinder block, main bearing cap, main bearing cap bolts, piston, connecting rod, crankshaft, and fixture;

[0097] 2) Assembly Condition 2: Cylinder head, cylinder gasket, and cylinder head bolt assembly;

[0098] 3) Load Condition 1: Simulation of maximum oil pressure under test fluctuation load;

[0099] 4) Load Condition 2: Simulation of minimum oil pressure under test fluctuation load;

[0100] S11. Evaluate the engine block based on the solution results of step S10;

[0101] The stress state of the cylinder block structure was evaluated under assembly condition 1 + assembly condition 2 + load condition 1 and assembly condition 1 + assembly condition 2 + load condition 2, respectively.

[0102] In step S1, it is necessary to ensure that the contact boundaries between the engine block and other components are clear, especially to ensure that the grids of the main bearing cap, main bearing shell and cylinder block contact surfaces correspond one-to-one.

[0103] In step S1, it is necessary to ensure that the overall grid size of the cylinder block ventilation holes and stop positions is less than 2mm, and at the same time ensure that the number of grid parts in the circumferential direction of the rounded corners is more than 8, and the grid aspect ratio is not greater than 1.5.

[0104] In step S2, it is necessary to ensure that the grid division of the top rounded corner of the main bearing cover is more than 6 parts, and the aspect ratio of the grid is not greater than 1.5.

[0105] In step S3, other engine structures include cylinder head, cylinder head gasket, piston, connecting rod, crankshaft, bearing shell, and bolts; the cylinder head gasket is constructed using a single-layer solid mesh, and the pressure wave part is grouped separately; the bolts are divided using a hexahedral mesh, without showing thread characteristics; the main bearing shell is divided using a two-layer hexahedral mesh, showing oil hole characteristics, but without showing positioning characteristics; other components are divided using tetrahedral or hexahedral meshes according to their shapes.

[0106] In step S4, the connection of the threaded part is defined according to the bolt connection contact relationship. The parameters that need to be defined are bolt spacing, thread helix angle, and thread clearance (interference).

[0107] In step S5, if a single tetrahedral simulation is used to simulate cylinder head and piston components that are not of interest, their elastic modulus is calculated as 70% of their material elastic modulus.

[0108] In step S9, when assembling the cylinder block and internal components, all degrees of freedom of the nodes on the upper surface of the cylinder block are constrained; when assembling the cylinder head and cylinder gasket and applying loads, all degrees of freedom of the fixture bracket fixing points are constrained.

[0109] In step S11, the maximum principal stress of the structure is required to not exceed the fatigue strength limit of the cylinder material.

[0110] In step S11, when the number of units exceeding the material fatigue limit is less than 1 / 3 or concentrated at unit nodes, it is considered stress concentration and the structure is not optimized.

[0111] In steps S1 to S9, the finite element preprocessing software Hypermesh is used.

[0112] Steps S10 and S11 are performed using the finite element post-processing software Abaqus.

[0113] Example 2

[0114] A method for predicting the strength performance of a cylinder block under cylinder block bench test conditions, characterized by comprising the following steps.

[0115] S1. Establish the finite element model of the engine cylinder block.

[0116] S2. Establish the finite element model of the engine main bearing cover.

[0117] S3. Establish finite element models of other engine structures. This includes all engine component structures and fixtures involved in the engine block bench test, such as the cylinder head, cylinder head gasket, piston, connecting rod, crankshaft, bearings, and bolts.

[0118] S4. Establish the connection relationships between parts based on the actual assembly relationships.

[0119] S5. Define the materials for the finite element model: Define the elastic modulus E and Poisson's ratio μ for the materials of each component in the finite element model. Generally, for steel, E = 210 GPa and μ = 0.30; for aluminum alloy, E = 70 GPa and μ = 0.33. It should be noted that since engine blocks are generally made of cast aluminum alloy or cast iron, the performance of the cast structural materials often differs significantly from the standard material properties due to casting processes and other factors. It is recommended to use test data from actual samples of similar cylinder blocks produced by the same manufacturer.

[0120] S6. Definition of Interference and Clearance Assembly Loads. In finite element analysis, the interference and clearance amounts in the assembly relationship are defined during load application. The interference and clearance amounts are defined according to design requirements, and their average values ​​are taken.

[0121] In step S6, if the interference and clearance amounts are not explicitly given, they can be calculated based on the dimensions indicated in the design drawings. The applied interference or clearance amount δ can be calculated using the following formula (1):

[0122]

[0123] S7, Bolt load application definition.

[0124] S8. Apply boundary constraints.

[0125] S9, hydraulic oil pressure load applied.

[0126] S10. Solve the finite element model: Use Newton's method to perform nonlinear statics solution and calculate the stress, deformation, etc. of each structure.

[0127] S11. Evaluate the stress state of the cylinder block structure under assembly condition 1 + assembly condition 2 + load condition 1 and assembly condition 1 + assembly condition 2 + load condition 2 respectively.

[0128] In step S1, it is essential to ensure clear contact boundaries between the engine block and other components, particularly ensuring that the grids on the contact surfaces of the main bearing cap, main bearing shell, and cylinder block correspond one-to-one. For cylinder block ventilation holes and stop positions, the overall grid size should be less than 2mm, while ensuring that the number of grid segments in the circumferential direction of the rounded corners is at least 8, and the grid aspect ratio is no greater than 1.5.

[0129] In step S2, it is necessary to ensure that the grid division of the top rounded corner of the main bearing cover is more than 6 parts, and the aspect ratio of the grid is not greater than 1.5.

[0130] In step S3, the cylinder head gasket is constructed using a single-layer solid mesh, and the pressure wave part is grouped separately. The bolts are divided using a hexahedral mesh, which does not reflect thread characteristics. The main bearing is divided using a two-layer hexahedral mesh, which reflects oil hole characteristics, but does not reflect positioning characteristics.

[0131] In step S4, the bolt connection uses the contact relationship to define the connection of the threaded part. The parameters that need to be defined are bolt spacing, thread helix angle, and thread clearance (interference).

[0132] In step S5, if a single tetrahedral simulation is used to simulate components such as cylinder heads and pistons that are not of interest, their elastic modulus is calculated as 70% of their material elastic modulus.

[0133] In step S7, the application of bolt preload is divided into elastic zone tightening and yield tightening, wherein:

[0134] Ordinary bolts are tightened in the elastic zone. The bolt preload is calculated using formula (2) and the direction of action is along the axial direction of the bolt.

[0135]

[0136] In the formula, F is the bolt preload, T is the bolt tightening torque, k is the bolt tightening torque coefficient, and D is the bolt diameter.

[0137] The bolts of the engine cylinder head and main bearing cap are fastened by torque plus rotation angle, which is a yield fastening. The bolt preload is calculated by formula (3) and the direction of action is along the axial direction of the bolt.

[0138]

[0139] In the formula, F1 is the bolt preload, σ y For the bolt yield point stress, A s d is the nominal stress cross-sectional area of ​​the bolt. A The equivalent diameter of the bolt's nominal stress cross-sectional area is μ, where p is the pitch and μ is the diameter of the bolt. s d2 is the thread friction coefficient, d2 is the thread pitch diameter, and α′ is the thread flank angle.

[0140] In step S9, when assembling the cylinder block and internal components, all degrees of freedom of the nodes on the upper surface of the cylinder block are constrained. When assembling the cylinder head and cylinder gasket and applying loads, all degrees of freedom of the fixture bracket fixing points are constrained.

[0141] In step S10, the load solution step is set as follows:

[0142] ① Assembly Condition 1: Assembly of cylinder block, main bearing cap, main bearing cap bolts, piston, connecting rod, crankshaft, and fixture;

[0143] ② Assembly Condition 2: Cylinder head, cylinder gasket, and cylinder head bolt assembly;

[0144] ③Load Condition 1: Simulation of maximum oil pressure under test fluctuation load;

[0145] ④ Load condition 2: Simulation of minimum oil pressure under test fluctuation load.

[0146] In step S11, the maximum principal stress of the structure must not exceed the fatigue strength limit of the cylinder material. It should be noted that when the location exceeding the material fatigue limit is less than 1 / 3 of the element, or concentrated at the element node, it is considered stress concentration and the structure does not need to be optimized.

[0147] The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the scope of protection of the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, any person skilled in the art can make equivalent substitutions or changes based on the technical solution and inventive concept of the present invention within the scope of the technology disclosed in the present invention. These simple modifications are all within the scope of protection of the present invention.

[0148] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0149] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A finite element method for predicting the strength performance of an engine block based on a bench test, characterized in that, Includes the following: (I) Establishment of Finite Element Analysis Model S1. Establish the finite element model of the engine block; S2. Establish the finite element model of the engine main bearing cover; S3. Establish finite element models of other engine structures, including all engine component structures and fixtures involved in the engine block bench test; S4. Establish the connection relationship between parts based on the actual assembly relationship. Except for bolt and threaded connections which use special contact relationship definitions, all others are general contact relationships. S5. Define the materials of the finite element model, including the elastic modulus E and Poisson's ratio μ of the finite element model materials of each component. (II) Applying load boundary conditions S6. Define the interference and clearance in the load in the assembly relationship calculated by finite element method. S7, Definition of Bolt Load Application For ordinary bolts, which are tightened in the elastic zone, the bolt preload is calculated using the following formula, with the direction of action along the bolt's axial direction: In the formula, F is the bolt preload, T is the bolt tightening torque, k is the bolt tightening torque coefficient, and D is the bolt diameter; The bolts of the engine cylinder head and main bearing cap are fastened by torque plus rotation angle, which is a yield fastening method. The bolt preload is calculated using the following formula, and the direction of action is along the axial direction of the bolt. In the formula, F1 is the bolt preload, σ y For the bolt yield point stress, A s d is the nominal stress cross-sectional area of ​​the bolt. A The equivalent diameter of the bolt's nominal stress cross-sectional area is μ, where p is the pitch and μ is the diameter of the bolt. s d2 is the thread friction coefficient, d2 is the thread pitch diameter, and α′ is the thread flank angle; S8. Applying hydraulic oil pressure load: According to the test conditions, an oil cavity is formed between the test cylinder head and the test cylinder body, and a hydraulic oil pressure value is applied to the surface; S9. Apply boundary constraints: Constrain all degrees of freedom of the cylinder upper surface and the fixture bracket fixing point according to different stages; (III) Statics Solution and Evaluation S10, Solve the finite element model The Newton method is used to perform nonlinear statics solutions to calculate the stress and deformation of each structure. The load solving step in step S10 is set as follows: 1) Assembly Condition 1: Assembly of cylinder block, main bearing cap, main bearing cap bolts, piston, connecting rod, crankshaft, and fixture; 2) Assembly Condition 2: Cylinder head, cylinder gasket, and cylinder head bolt assembly; 3) Load Condition 1: Simulation of maximum oil pressure under test fluctuation load; 4) Load Condition 2: Simulation of minimum oil pressure under test fluctuation load; S11. Based on the solution results of step S10, evaluate the engine block: evaluate the stress state of the block structure under assembly condition 1 + assembly condition 2 + load condition 1 and assembly condition 1 + assembly condition 2 + load condition 2 respectively.

2. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S1, it is necessary to ensure that the contact boundaries between the engine block and other components are clear, especially to ensure that the grids of the main bearing cap, main bearing shell and cylinder block contact surfaces correspond one-to-one. In step S1, it is necessary to ensure that the overall grid size of the cylinder block ventilation holes and stop positions is less than 2mm, and at the same time ensure that the number of grid parts in the circumferential direction of the rounded corners is more than 8, and the grid aspect ratio is not greater than 1.

5.

3. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S2, it is necessary to ensure that the grid division of the top rounded corner of the main bearing cover is more than 6 parts, and the aspect ratio of the grid is not greater than 1.

5.

4. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S3, other engine structures include cylinder head, cylinder head gasket, piston, connecting rod, crankshaft, bearing shell, and bolts; the cylinder head gasket is constructed using a single-layer solid mesh, and the pressure wave part is grouped separately; the bolts are divided using a hexahedral mesh, without showing thread characteristics; the main bearing shell is divided using a two-layer hexahedral mesh, showing oil hole characteristics, but without showing positioning characteristics; other components are divided using tetrahedral or hexahedral meshes according to their shapes.

5. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S4, the connection of the threaded part is defined according to the bolt connection contact relationship. The parameters that need to be defined are bolt spacing, thread helix angle, and thread clearance.

6. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S5, if a single tetrahedral simulation is used to simulate cylinder head and piston components that are not of interest, their elastic modulus is calculated as 70% of their material elastic modulus.

7. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S6, the interference and clearance are defined according to the design requirements, and the average value of the interference and clearance is taken.

8. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S9, when assembling the cylinder block and internal components, all degrees of freedom of the nodes on the upper surface of the cylinder block are constrained; when assembling the cylinder head and cylinder gasket and applying loads, all degrees of freedom of the fixture bracket fixing points are constrained.

9. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In step S11, the maximum principal stress of the structure is required not to exceed the fatigue strength limit of the cylinder material. In step S11, when the number of units exceeding the material fatigue limit is less than 1 / 3 or concentrated at unit nodes, it is considered stress concentration and the structure is not optimized.

10. The finite element method for predicting strength performance based on engine block bench testing according to claim 1, characterized in that, In steps S1 to S9, the finite element preprocessing software Hypermesh is used for processing; Steps S10 and S11 are processed using the finite element post-processing software Abaqus.

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