Finite Element Analysis Method for the Overall Strength of an Automatic Tensioner

Abstract

A finite element analysis method for the overall strength of an automatic tensioner includes the following steps: (1) In the early stage of the development of the automatic tensioner, establish a three-dimensional digital model of the tensioner; (2) Analyze the interaction between the internal parts of the tensioner and simplify the digital model; (3) Analyze the force relationships of each part after simplification and introduce the calculation method of the force magnitude. (4) Establish a finite element model of the tensioner, submit it for operation, obtain the stress nephogram, and further obtain the safety factor. According to the design structure of the tensioner components, the present invention simplifies the parts. Through the finite element method, the overall strength of the tensioner can be quickly obtained, the design of the tensioner can be predicted whether it meets the strength requirements, it can be judged whether the tensioner design is balanced, the risk of possible fracture of the product can be informed in advance, the number of tests can be reduced, the early development work of the tensioner can be promoted, the efficiency is greatly improved, and at the same time, it provides strong guidance for the optimal design of the accessory gear train.

Description

Technical Field

[0001] The present invention relates to the field of engine front-end accessory drive systems, and particularly to a finite element analysis method for the overall strength of an automatic tensioner. Background Art

[0002] A mechanical automatic tensioner is composed of a tensioning arm, a housing, a core shaft, a bushing, a damping mechanism, and a spring, and is an important component of the front-end accessory system of an automobile engine. Among many domestic tensioner R & D enterprises at present, there is basically no ability to analyze the overall strength of the tensioner using finite element software, which has many defects. For example, it is not known whether the product strength meets the requirements, the design defects of the product are not understood, the product structure cannot be improved, and it is irresponsible to customers. It brings unnecessary troubles to the company's reputation and income. Only simply increasing the product material violates the requirements of lightweight design and increases additional investment.

[0003] The domestic R & D of tensioners is in a relatively late starting stage. In the actual development of tensioner products, at present, it is mainly determined by the experience of R & D engineers whether the tensioner meets the strength requirements, and it is mainly modified by referring to mature foreign products without performing CAE analysis, and it is difficult to grasp whether the structural strength of the product meets the requirements. Therefore, it is of great significance to perform strength analysis on the tensioner in the product design stage, and the analysis results can guide the structural and safety verification of the tensioner. Correspondingly, when the strength of the tensioner meets the requirements, the material can be reduced and the cost can be lowered.

[0004] Patent CN109214079A, "A Finite Element Calculation Method for the Wear Amount of an Automatic Tensioner Damping Part", provides a calculation method for the wear of the tensioner damping mechanism. Compared with the previous experimental method, it achieves the purpose of reducing the R & D cycle and cost, but it cannot analyze the overall strength of the tensioner. Summary of the Invention

[0005] Considering the interaction between the internal parts of the tensioner, the structure is appropriately simplified during the analysis. The simplified structure is the tensioning arm, the housing, the bushing, and the core shaft. The main technical problem to be solved by the present invention is to provide a finite element analysis method for the overall strength of an automatic tensioner, which can guide the structural and safety verification of the tensioner, greatly shorten the R & D cycle, and reduce the cost.

[0006] In order to achieve the object of the present invention, a finite element analysis method for the overall strength of an automatic tensioner provided by the present invention includes the following steps:

[0007] Establish a three-dimensional model of the tensioner and obtain the parameters of the tensioner;

[0008] Simplify the three-dimensional model of the tensioner. The simplified tensioner includes a tensioning arm, a housing, a bushing, and a core shaft;

[0009] Analyze the force relationships of each part after simplification and calculate the load force;

[0010] Determine the acting area of the spring external support force according to the contact relationships among the damping mechanism, the tensioning arm, and the housing;

[0011] Import the 3D models of the parts included in the simplified structure into the software for drawing meshes, perform mesh division, and obtain the mesh models of the parts;

[0012] Obtain the tensioner mesh model after assembly, i.e., the tensioner finite element model, based on the mesh models of the parts;

[0013] Submit the calculation, obtain the stress nephogram, acquire the maximum stress value from the stress nephogram, and obtain the safety factor used to evaluate the overall strength of the tensioner according to the maximum stress value.

[0014] Furthermore, when establishing the 3D model of the tensioner, chamfers less than 1 mm are removed.

[0015] Furthermore, when establishing the 3D model of the tensioner, the fitting method is modified from interference fit to clearance fit, and the size of the clearance is 0.02 - 0.05 mm.

[0016] Furthermore, the parameters of the tensioner include the swing angle at the nominal position of the tensioner, the hub loads of each wheel, the output torque, the length of the tensioning arm, and the geometric position angle of the tensioning arm.

[0017] Furthermore, the calculation method of the load force is as follows:

[0018] F s1 = F s2 = 2M t / D

[0019] F s3 = K p S

[0020] In the formula, F s1 represents the tangential force of the spring, F s2 represents the external support force of the spring, F s3 represents the axial force of the spring, M t represents the output torque, D is the mean diameter of the spring, S is the pre-compression height of the spring, and K p is the axial compression stiffness.

[0021] Furthermore, when importing the 3D models of the parts included in the simplified structure into the software for drawing meshes and performing mesh division, HYPERMESH software is used for mesh division.

[0022] Further, when importing the 3D models of the parts included in the simplified structure into the software for drawing meshes and performing mesh division, a volume mesh is obtained by first generating a surface mesh and then generating a solid mesh from the surface mesh. Among the generated surface meshes, the mesh angle is [15°, 145°].

[0023] Further, obtaining the assembled tensioner mesh model according to the mesh models of the parts includes:

[0024] After generating all the meshes, establish the material properties and cross-section properties;

[0025] Assign the material properties and cross-section properties to the corresponding volume meshes;

[0026] Export the volume meshes with the assigned material and cross-section properties into INP files respectively;

[0027] Import all the INP files into the finite element analysis software and assemble to generate the tensioner mesh model.

[0028] Further, in obtaining the safety factor used to evaluate the overall strength of the tensioner according to the maximum stress value, the safety factor is obtained by dividing the yield limit of the material by the obtained maximum stress value.

[0029] Further, after obtaining the stress nephogram, evaluate whether the tensioner design is balanced according to the stress nephogram of the bushing.

[0030] Compared with the existing methods, the beneficial effects of the present invention are at least as follows:

[0031] Use the finite element analysis software to quickly obtain whether the strength of the tensioner meets the requirements, so as to understand the design defects of the product, improve the product structure, promote the preliminary development work of the tensioner, and more importantly, reduce materials and costs. Description of the Drawings

[0032] Figure 1 is the explosion diagram of the tensioner;

[0033] Figure 2 is the schematic diagram of the finite element mesh models of the tensioning arm, housing, bushing, and core shaft;

[0034] Figure 3 is the schematic diagram of the constraint between the housing and the core shaft;

[0035] Figure 4 is the schematic diagram of the constraint between the bushing and the tensioning arm;

[0036] Figure 5 is the schematic diagram of the constraint between the core shaft and the bushing;

[0037] Figure 6 And 7 is the schematic diagram of the force loading;

[0038] Figure 8 It is a schematic diagram of boundary condition constraints;

[0039] Figure 9 It is a stress nephogram of the finite element calculation results;

[0040] Figure 10 It is the analysis flow chart of this finite element analysis method;

[0041] Figure 11 It is a schematic diagram of the structure of the engine front-end accessory drive system.

[0042] In the figure: 1 - housing; 2 - spring; 3 - damping mechanism; 4 - bushing; 5 - mandrel; 6 - tensioning arm; 7 - mandrel. Specific implementation mode

[0043] In the following description, the technical solutions are elaborated in combination with specific drawings so as to fully understand the present invention application. However, the present application can be implemented in many other ways different from those described herein. Similar extended embodiments made by those of ordinary skill in the art without creative efforts all fall within the scope of protection of the present invention.

[0044] The terms used in this specification are only for the purpose of describing specific embodiments and are not intended to limit this specification. The singular forms "a", "the" and "said" used in one or more embodiments of this specification and the appended claims are also intended to include the plural forms unless the context clearly indicates otherwise.

[0045] Figure 1 An exploded view of a mechanical automatic tensioner is given. Among them, the housing 1 is installed on the engine body. The housing 1 has an interference fit with the mandrel 5. The mandrel 5 has a clearance fit with the bushing 4. The bushing 4 has a clearance fit with the tensioning arm 6, applying a pre-tightening force to the spring 3. One end of the spring 3 acts on the housing 1, and the other end presses the damping mechanism 2 against the tensioning arm 6.

[0046] A finite element analysis method for the overall strength of an automatic tensioner provided by the present invention includes the following steps:

[0047] Step 1: In the early stage of the development of the automatic tensioner, establish a three-dimensional model of the tensioner and obtain the parameters of the tensioner.

[0048] Such as Figure 11As shown in the figure, it is a typical front-end accessory drive system of an engine. The system consists of a crankshaft pulley (CS) 1, an air-conditioning pulley (AC) 2, an alternator pulley (ALT) 3, a tensioner (TEN) 4, and a multi-wedge belt connecting the four pulleys. Among them, the positions of the crankshaft pulley, the air-conditioning pulley, and the alternator pulley are fixed after the engine design and cannot be changed. Perform a static layout on the front-end accessory drive system of the engine, that is, design the parameters, position of the tensioner, and the length of the multi-wedge belt. After the static layout is completed, the parameters, position of the tensioner, and the length of the multi-wedge belt can be obtained. Among them, the position of the tensioning arm after the static layout is completed is called the static balance position of the tensioner, also called the nominal position, and the multi-wedge belt already has a pre-tension force. At this time, the resultant force of the multi-wedge belt on the tensioning pulley is balanced with the spring torque, and the spring torque is not 0 here.

[0049] The parameters of the tensioner include the swing angle at the nominal position of the tensioner, the hub load (the resultant force of the multi-wedge belt on the tensioning pulley), and the output torque M t , the length of the tensioning arm, and the geometric position angle of the tensioning arm.

[0050] In one embodiment of the present invention, when establishing the three-dimensional model of the tensioner, the originally interference fit is changed to a clearance fit, and the size of the clearance is 0.02 - 0.05 mm; the smaller chamfer (chamfer less than 1 mm) is removed. Determine the mesh size to be 1 mm according to the overall size of the tensioner, the required result accuracy, and the computing power of the computer. If the chamfer is less than 1 mm, it will cause some mesh angles to be outside the range of [15°, 145°] when drawing the mesh.

[0051] Step 2: According to the obtained tensioner parameters, analyze the interaction between the internal parts of the tensioner, and appropriately simplify the structure of the tensioner: retain the tensioning arm, the housing, the bushing, and the core shaft, and remove the spring and the damping mechanism.

[0052] During the simplification of the three-dimensional model, the damping mechanism is removed, and the action of the damping mechanism on the housing and the tensioning arm is replaced by a uniform force during the implementation of the finite element method.

[0053] Step 3: In the finite element strength analysis, adding the load force requires knowing the magnitude of the load force. Calculate the load force by analyzing the force relationship of each part after simplification.

[0054] In one embodiment of the present invention, the hub load is converted into a spring loading force through moment balance. Analyze the force on the simplified structure:

[0055] The tensioning arm mainly bears the hub load F hb , the tangential force of the spring F s1 , the external support force of the spring F s2 , the axial force of the spring F s3 . According to the gear train report, when the tensioner is at the nominal position, the hub load F hbThe included angle α with the tension arm, and the hub load is the resultant force of the multi-wedge belt on the tension pulley.

[0056] The acting directions of the three spring forces are perpendicular to the acting surfaces, which are the contact positions between the springs and the parts respectively. The length of the tension arm is L. The housing mainly bears the tangential spring force F s1 , the external support spring force F s2 and the axial spring force F s3 . For the mandrel and the bushing, there is no external force acting on them in the overall finite element calculation of the tensioner strength after simplification, and there is only the interaction within the system.

[0057] The internal force acting relationship of the tensioner is as follows: The spring force acts on the damping mechanism, and the damping mechanism acts on the tension arm and the housing. The damping mechanism is in surface contact with the tension arm and the housing, that is, when the spring force is transmitted to the tension arm and the housing, it becomes the uniform force exerted by the damping mechanism on the tension arm and the housing. In the step of adding the load force in the finite element analysis, the magnitude of the added force comes from the spring force, so it is necessary to calculate the spring force.

[0058] Calculation of the spring force at the nominal position:

[0059] F s1 = F s2 = 2M t / D

[0060] In the formula: D is the mean diameter of the spring.

[0061] F s3 = K p S

[0062] In the formula: S is the pre-compression height of the spring, and K p is the axial compression stiffness.

[0063]

[0064]

[0065] In the formula: G is the shear modulus, E is the Young's modulus, v is the Poisson's ratio, d is the wire diameter of the spring, and n represents the number of turns of the helical spring. After calculation, the axial spring force F s3 can be obtained.

[0066] Step 4: Determine the acting area of the external support spring force according to the contact relationship between the damping mechanism and the tension arm and the housing.

[0067] In one embodiment of the present invention, the internal force acting relationship of the tensioner is as follows: the spring acts on the damping mechanism, and the damping mechanism acts on the tensioning arm and the housing. The damping mechanism is in surface contact with the tensioning arm and the housing, that is, when the external supporting force of the spring is transmitted to the tensioning arm and the housing, it becomes a uniform force exerted by the damping mechanism on the tensioning arm and the housing. And when adding a uniform force in the finite element strength analysis, the acting area of the force needs to be known. This step determines the acting point among the three elements of the force (magnitude, direction, acting point). The direction of the force is perpendicular to the acting surface.

[0068] Step 5: Import the 3D models of the respective parts included in the simplified structure into the software for drawing meshes, perform mesh division, and obtain a mesh model.

[0069] In one embodiment of the present invention, the software for drawing meshes is HYPERMESH. Of course, it can be understood that in other embodiments, other software for drawing meshes can be used.

[0070] In one embodiment of the present invention, Figure 2 it is a finite element model of a tensioner including a tensioning arm, a housing, a bushing, and a mandrel. In the process of dividing the mesh using HYPERMESH software, a method of first generating surface meshes and then generating solid meshes from the surface meshes is adopted to obtain volume meshes. Among them, generating surface meshes is a repetitive process. After each generation, the mesh quality needs to be checked, especially the mesh angle that affects the calculation convergence. Here, the angle cannot be too small, generally it should be above 15°, and the maximum angle cannot exceed 145°. After all meshes meet the conditions, volume meshes are generated.

[0071] In one embodiment of the present invention, in the finite element analysis of the overall strength of the tensioner, the main function of the mandrel is to restrain the tensioning arm and the housing. Simplify the mandrel and ignore the swaging feature and the relief groove.

[0072] Step 6: Obtain the assembled tensioner mesh model according to the mesh models of the respective parts.

[0073] Specifically, in one embodiment of the present invention, this step specifically includes:

[0074] Step 6.1: After generating all meshes in Step 5, establish material properties and cross-section properties. And assign the material properties and cross-section properties to the corresponding volume meshes. Then export the volume meshes with the assigned material and cross-section properties into INP files respectively;

[0075] Step 6.2: Import the above INP files into the finite element analysis software respectively, and assemble each part into a system in this software. As Figure 8 shown is the assembled tensioner mesh model, and a finite element model of the tensioner is obtained.

[0076] In one embodiment of the present invention, the finite element analysis software uses ABAQUS software, and the ASSEMNLY module in this software is used to assemble each part into a finite element model of the tensioner.

[0077] Step 7: Submit the operation to obtain a stress nephogram, obtain the maximum stress value in the stress nephogram, and obtain the safety factor used to evaluate the overall strength of the tensioner.

[0078] Specifically, in one embodiment of the present invention, this step specifically includes:

[0079] Step 7.1: Set up the analysis steps. Four analysis steps are established in this model, namely:

[0080] Step1: Establish preliminary contact to make the model more likely to converge;

[0081] Step2: Apply the average hub load;

[0082] Step3: Apply the maximum hub load;

[0083] Step4: Apply the minimum hub load.

[0084] Among them, in the contact setting, the definition of the master and slave surfaces follows the following rules: the mesh size of the master surface must be smaller than that of the slave surface; if the element types are the same, in order to avoid element penetration and non-convergence during the simulation analysis, the stiffness of the slave surface must be smaller than that of the master surface. The specific contact setting method is as follows: first define each contact surface, and then use the TIE constraint in the INTERACTION module to constrain each necessary contact pair according to the constraint principle, a total of three necessary constraint pairs. If other constraint methods are used for this bushing and the tensioning arm or the mandrel and the bushing, it will greatly increase the calculation time required and is likely to encounter non-convergence. Even if the result is calculated, it is basically no different from the result obtained by using the TIE constraint.

[0085] In one embodiment of the present invention, the constraint principle includes the constraint between the housing and the mandrel, the constraint between the bushing and the tensioning arm, and the constraint between the mandrel and the bushing. For details, please refer to Figure 3 、 Figure 4 and Figure 5 as shown.

[0086] Step 7.2: Establish reference points, action surfaces, coupling surfaces, and coordinate systems.

[0087] The action surface refers to the surface where the uniform load force acts, that is, the contact surface between the damping mechanism and the tensioning arm and the housing.

[0088] The coupling surface refers to: when adding boundary conditions, it is necessary to fix the bolt holes on the housing, find the center points of the bolt holes, then establish a coupling relationship between the hole surfaces and the center points, and then constrain the 6 degrees of freedom of this center point, that is, the 6 degrees of freedom of the entire hole surface are constrained.

[0089] The purpose of establishing the coordinate system is: when adding load forces, it is necessary to add hub loads. At this time, the direction of the force is given by establishing a spatial rectangular coordinate system, and the acting point (the magnitude of the force is already known). The direction is the X-axis direction of the coordinate system, and the acting point is the origin of the coordinate system.

[0090] Step 7.3: Set boundary conditions and apply force loading.

[0091] Figure 6 And Figure 7 The display is the application of force loading; the tensioning arm mainly bears the hub load F hb , the tangential force of the spring F s1 , the external support force of the spring F s2 , the axial force of the spring F s3 . According to the gear train report, when the tensioner is in the nominal position, the included angle of the load arm is α, and the hub load is F hb , and the output torque is M t . The acting directions of the three spring forces are perpendicular to the acting surface, and the acting surfaces are the contact positions between the spring and the parts respectively. The length of the tensioning arm is L. The housing mainly bears the tangential force of the spring F s1 , the external support force of the spring F s2 , the axial force of the spring F s3 . For the two parts of the mandrel and the bushing, there is no external force acting in the overall finite element calculation of the tensioner strength after simplification, and only the interaction within the system exists.

[0092] Figure 8 What is shown is the boundary condition constraint, and the 6 degrees of freedom of the housing bolt holes are completely fixed.

[0093] Step 7.4: Submit the operation to obtain the stress nephogram.

[0094] In one embodiment of the present invention, the stress nephograms of the tensioning arm, the housing, the bushing and the mandrel are obtained respectively, as Figure 9 shown.

[0095] Judge the position of the maximum stress and the dangerous position according to the stress nephogram in order to optimize the structure of the tensioner.

[0096] In one embodiment of the present invention, the yield limit of the material divided by the obtained maximum stress value is the safety factor. The larger the safety factor, the higher the overall strength of the tensioner and the better the reliability of the tensioner.

[0097] In one embodiment of the present invention, the tension arm and the housing are grouped using the same material, the mandrel is grouped using one material, and the bushing is grouped using one material. The maximum stress of each group of parts is used for calculation to obtain the safety factor of each group of parts, and the safety factor is compared with the empirical value of the corresponding material respectively.

[0098] In one embodiment of the present invention, it can be seen whether the tensioner design is balanced according to the stress nephogram of the bushing. Specifically as follows: if the change of the bushing nephogram is uniform, it indicates that the balance design in the tensioner design is better. On the contrary, if the stress change of the obtained bushing stress nephogram is uneven, it is determined that the tensioner design does not meet the balance requirement conditions, which is likely to form eccentric wear, accelerate the aging of the bushing, and cause serious consequences such as the tensioner getting stuck and breaking. Accordingly, the design of the tensioner can be improved according to the situation.

[0099] Through the method provided by the present invention, the overall strength of the tensioner can be quickly obtained, whether the design of the tensioner meets the strength requirements can be predicted, whether the tensioner design is balanced can be judged, the risk of whether the product may break can be informed in advance, the number of tests can be reduced, the preliminary development work of the tensioner can be promoted, the efficiency is greatly improved, and at the same time, it provides strong guidance for the optimal design of the accessory gear train.

[0100] The above embodiments are only examples for clearly illustrating the present invention, and are not intended to limit the embodiments of the present invention. Any other changes, modifications, substitutions, combinations, and simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A finite element analysis method for the overall strength of an automatic tensioner, characterized in that, it includes the following steps: Establish a three-dimensional model of the tensioner and obtain the parameters of the tensioner; Simplify the three-dimensional model of the tensioner. The simplified tensioner includes a tensioning arm, a housing, a bushing, and a mandrel; Analyze the force relationships of the simplified parts and calculate the load force; Determine the acting area of the spring external support force according to the contact relationships between the damping mechanism and the tensioning arm and the housing; Import the three-dimensional models of the parts included in the simplified tensioner into software for drawing meshes to perform mesh division and obtain the mesh models of the parts; Obtain the assembled tensioner mesh model based on the mesh models of the parts, i.e., the tensioner finite element model; Submit the operation to obtain a stress nephogram, obtain the maximum stress value in the stress nephogram, and obtain the safety factor used to evaluate the overall strength of the tensioner according to the maximum stress value; The calculation method of the load force is as follows: F s1 = F s2 = 2M t / D F s3 = K p S Where, F s1 represents the tangential force of the spring, F s2 represents the external supporting force of the spring, F s3 represents the axial force of the spring, M t represents the output torque, D is the mean diameter of the spring, S is the pre-compression height of the spring, K p is the axial compression stiffness; The obtaining of the assembled tensioner mesh model based on the mesh models of the parts includes: After generating all the meshes, establish the material properties and cross-section properties; Assign the material properties and cross-section properties to the corresponding volume meshes; Export the volume meshes with the assigned material and cross-section properties into INP files respectively; Import all the INP files into finite element analysis software to assemble and generate the tensioner mesh model.

2. A finite element analysis method for the overall strength of an automatic tensioner according to claim 1, characterized in that: When establishing the three-dimensional model of the tensioner, chamfers less than 1 mm are removed.

3. A finite element analysis method for the overall strength of an automatic tensioner according to claim 2, characterized in that: When establishing the three-dimensional model of the tensioner, the mating method is modified from interference fit to clearance fit, and the size of the clearance is 0.02 - 0.05 mm.

4. A finite element analysis method for the overall strength of an automatic tensioner according to claim 1, characterized in that: The parameters of the tensioner include the swing angle at the nominal position of the tensioner, the hub loads of each wheel, the output torque, the length of the tensioning arm, and the geometric position angle of the tensioning arm.

5. A finite element analysis method for the overall strength of an automatic tensioner according to claim 1, characterized in that, When importing the three-dimensional models of the parts included in the simplified tensioner into software for drawing meshes to perform mesh division, HYPERMESH software is used for mesh division.

6. A finite element analysis method for the overall strength of an automatic tensioner according to claim 1, characterized in that, Import the 3D models of the parts included in the simplified tensioner into the software for drawing meshes. In the process of mesh generation, first generate surface meshes, and then obtain volume meshes by generating solid meshes from the surface meshes. Among the generated surface meshes, the mesh angle is [15°, 145°] 。 7. A finite element analysis method for the overall strength of an automatic tensioner according to any one of claims 1 - 6, characterized in that, In obtaining the safety factor used to evaluate the overall strength of the tensioner according to the maximum stress value, the yield limit of the material is divided by the obtained maximum stress value to be the safety factor.

8. A finite element analysis method for the overall strength of an automatic tensioner according to any one of claims 1 - 6, characterized in that, After obtaining the stress nephogram, evaluate whether the tensioner design is balanced according to the stress nephogram of the bushing.

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