A method for calculating pressure and deformation relationship curve of wet clutch

Abstract

The application discloses a kind of wet clutch pressure and deformation relationship curve calculation method, according to the friction plate pressure-deformation relationship curve obtained from clutch friction plate compression performance test, based on the friction plate geometric parameter deduces the nominal stress-strain relationship curve of friction lining material, and it is separately endowed with friction lining structure;Steel sheet, friction lining, duplicate steel sheet are respectively endowed with the material mechanics attribute of itself, it can be applied to the case that the number proportion and volume proportion of arbitrary steel sheet, friction lining, duplicate steel sheet change;Friction lining is divided into different regions, define different material compression performance, the compression performance of friction lining material is corrected using finite element method, and the obtained material compression performance is more consistent with the actual;The compression performance parameters of friction lining material are obtained by adjusting Poisson's ratio using finite element technology, which is fast and accurate, can effectively shorten the compression performance test of substitute material, and further save the test cost.

Description

Technical Field

[0001] This invention belongs to the field of finite element analysis technology for clutches, specifically relating to a method for calculating the pressure-deformation relationship curve of a wet clutch. Background Technology

[0002] Wet clutches use worm gears and worm shafts as the transmission mechanism, with a motor as the drive unit to achieve the engagement and disengagement of the friction plates. The transmission mechanism has a large speed ratio; even a small axial deformation of the clutch requires a large motor rotation angle to meet the friction plate engagement pressure requirements. With a constant clutch response time, the motor speed needs to be significantly adjusted. Therefore, accurately predicting and controlling the clutch axial deformation is crucial for developing motor speed performance and designing the stiffness of clutch components.

[0003] In wet clutches, the friction linings are paper-based composite materials composed of fibers, friction modifiers, fillers, and resins, resulting in complex compositions and difficult-to-determine material constitutive models. Typically, a linear elastic constitutive model is used, where the elastic modulus and Poisson's ratio of the friction lining material are directly given to achieve satisfactory simulation accuracy in finite element analysis of clutch friction, wear, stress, and temperature fields. For example, the paper "Study on Engagement Characteristics of Wet Multi-Plate Clutches" uses an elastic modulus of 4000 MPa and a Poisson's ratio of 0.16 to study the stress and temperature fields of the friction pair during the engagement process of a wet multi-plate clutch; the paper "Simulation and Experiment of Warpage Characteristics of Wet Multi-Plate Clutches" uses an elastic modulus of 270 MPa and a Poisson's ratio of 0.12 to simulate the thermomechanical coupling stress of a wet multi-plate clutch. The paper "Study on Thermal Failure and Friction Characteristics of Wet Multi-Plate Clutch" simulated the contact pressure of the friction lining of a wet multi-plate clutch with a material elastic modulus of 2300 MPa and a Poisson's ratio of 0.25. The paper "Analysis of Heat Transfer Characteristics in the Joining Process of High Energy Density Friction Plates" analyzed the heat transfer characteristics in the joining process of high energy density friction plates with a material elastic modulus of 4000 MPa and a Poisson's ratio of 0.16. The paper "Simulation Analysis and Experimental Study on Thermo-Structure Coupling of Wet Clutch" analyzed the stress distribution and temperature field distribution of the clutch friction pair with a material elastic modulus of 7550 MPa and a Poisson's ratio of 0.12. However, when using the linear elastic constitutive model for simulation calculations related to the axial deformation of the clutch, different elastic moduli have a significant impact on the simulation results. For example, the paper "Study on the slip friction characteristics and thermal load characteristics of wet clutches" studied the influence of different elastic moduli on the slip friction work of the clutch, and the paper "Study on several working characteristics of wet clutches" studied the influence of different elastic moduli on the clutch torque response time and oil film thickness. These studies show that the simulation accuracy of the linear elastic constitutive model is poor. The reason for this is that the friction lining is a composite material, and there is a strong nonlinear relationship between the material stress and strain. The method of directly giving the elastic modulus and Poisson's ratio is no longer applicable. A nonlinear constitutive model should be adopted according to the actual situation.

[0004] CN202111078710.2 discloses a method for obtaining clutch pressure characteristic curves. This method simplifies the multiple steel plates, friction linings, and mating steel plates in a friction plate assembly into a single material. A nonlinear constitutive model is used to describe the overall mechanical properties of the friction plate assembly. This method is applicable when the relative volume ratio of the steel plates, friction linings, and mating steel plates remains constant, such as by simultaneously increasing or decreasing their quantities proportionally. In this case, the relationship between clutch axial pressure and deformation can be predicted quickly and effectively. However, when the relative volume ratio of the steel plates, friction linings, and mating steel plates changes, this method is no longer applicable because it fails to differentiate between the steel and composite materials in the friction plate assembly and assign them corresponding material mechanical properties. Summary of the Invention

[0005] To address the aforementioned problems in existing technologies, this invention provides a method for calculating the pressure-deformation relationship curve of a wet clutch. Based on the pressure-deformation relationship curve of the friction plate obtained from the clutch friction plate compression performance test, the nominal stress-strain relationship curve of the friction lining material is derived based on the geometric parameters of the friction plate and assigned separately to the friction lining structure. This achieves accurate definition of the material mechanical properties of the friction lining finite element model. This invention is applicable to situations where the quantity and volume ratio of any steel sheet, friction lining, and paired steel sheet changes, and can effectively guide clutch development.

[0006] The objective of this invention is achieved through the following technical solution:

[0007] A method for calculating the pressure-deformation relationship curve of a wet clutch includes the following steps:

[0008] S1. Mechanical property test of clutch friction lining material:

[0009] The friction plate of a single clutch is composed of a steel plate and friction linings bonded together. A certain number of friction linings are evenly arranged on one side of the steel plate, and the friction linings are symmetrically distributed about the circumference and thickness of the steel plate. The nominal stress-strain data of the friction lining material are derived by using clutch friction plate compression performance test.

[0010] S2. Select the hyperelastic constitutive model for the friction liner material;

[0011] S3, Correction of the compressibility of friction liner material:

[0012] S31. Establish a finite element simulation model consistent with the friction plate compression performance test in step S1:

[0013] Mesh generation was performed on the steel sheet, friction lining, and clamps: the friction lining was meshed with hexahedral meshes, ignoring the tiny oil guide grooves on the friction surface, and the element type was selected as force-displacement hybrid integral element; the steel sheet, the first clamp, and the second clamp were all meshed with hexahedral meshes; the bonding effect between the friction lining and the steel sheet was simulated using the common node method, that is, assuming that there is no relative displacement between them; the first clamp and the second clamp were defined as non-deformable rigid bodies;

[0014] The friction lining and steel sheet are each arranged with two or more layers of mesh units in the thickness direction;

[0015] Ignoring the tiny oil guide grooves on the friction surface of the friction lining, each friction lining is divided into two regions and gridded, namely the first region and the second region. The grid of the first region is located on the outside of the friction lining, and the grid of the second region is located on the inside of the friction lining. The purpose of this grid division is to define different material compression properties for different regions, thereby improving the accuracy of the correction of the material compression properties of the friction lining.

[0016] The load is transferred between the mutually aligned friction pads, and between the friction pads and the steel sheet, the first clamp, and the second clamp through defined contact relationships;

[0017] To facilitate the application of boundary conditions and loads, two rigid body elements need to be established: the first rigid body element RBE2 is established with the geometric center of the first clamp as the master point and the element nodes on the side of the first clamp where no contact relationship is defined as slave points; the second rigid body element RBE2 is established with the geometric center of the second clamp as the master point and the element nodes on the side of the second clamp where no contact relationship is defined as slave points.

[0018] S32. Define the materials for the finite element model:

[0019] The mechanical properties of the friction liner material are defined based on the strain energy function determined in step S2, including the nominal stress-strain data and Poisson's ratio μ in step S1.

[0020] The material mechanical properties of the steel sheet and its counterpart include the elastic modulus E and Poisson's ratio μ;

[0021] S33. Apply boundary conditions to the finite element model:

[0022] First, constrain all degrees of freedom of the principal point of the first rigid body element RBE2 defined in S31; second, constrain the degrees of freedom of the principal point of the second rigid body element RBE2 defined in S31 other than the degrees of freedom along the centerline of the steel sheet.

[0023] S34, Apply load 1:

[0024] Load 1 is a pressure, which is applied to the principal point of the second rigid body element RBE2, and the direction is along the center line of the steel sheet, so that the friction lining bears the pressure.

[0025] S35. Define the calculation conditions:

[0026] The calculation case consists of the boundary conditions in S33 and load 1 in S34;

[0027] S36. Perform finite element analysis:

[0028] According to the calculation conditions defined in S35, the pressure-deformation relationship curve of the friction plate is calculated considering geometric nonlinearity;

[0029] S37, Correction of compressibility properties of friction liner material:

[0030] Compare the friction plate pressure-deformation relationship curve calculated in step S36 with the friction plate pressure-deformation relationship curve tested in step S1. If the two curves deviate significantly, the Poisson's ratio μ of the friction lining material needs to be adjusted. The Poisson's ratio of the first region mesh finite element model of the friction lining should not be higher than that of the second region mesh finite element model. Then repeat steps S32 to S37 until the two curves show a basically consistent trend and the maximum error is less than 5% within the pressure range required for clutch torque transmission.

[0031] S4. Establish the finite element model of the clutch system assembly:

[0032] Based on the clutch torque transmission, heat capacity and design space requirements, determine the number of clutch friction plates. Then, divide the support shaft, baffle, thrust bearing, ball, worm gear, pressure plate, friction lining, steel plate, mating steel plate, clutch seat, clutch housing, sprocket, needle roller bearing and oil pump housing into a grid. Assemble them together by defining the contact relationship between the contacting parts.

[0033] The meshing method for friction linings and steel sheets is the same as in step S3;

[0034] To facilitate the application of boundary conditions and loads, two rigid body elements need to be established: a third rigid body element RBE2 is established with a point on the geometric center line of the support shaft as the master point and the element node of the baffle 1 that has no defined contact relationship and is close to the inner diameter as the slave point; a fourth rigid body element RBE2 is established with other points on the geometric center line of the support shaft as the master point and the element node of the end face of the oil pump housing away from the clutch friction plate as the slave point.

[0035] S5. Apply boundary conditions to the finite element model of the clutch system assembly:

[0036] First, constrain the degrees of freedom of the principal point of the third rigid body element RBE2 defined in step S4, except for the axial degree of freedom along the support axis; second, constrain all degrees of freedom of the principal point of the fourth rigid body element RBE2 defined in step S4.

[0037] S6. Apply load 2 to the finite element model of the clutch system assembly:

[0038] Load 2 is a pressure, which is applied to the principal point of the third rigid body element RBE2 in the direction along the center line of the support shaft, so that the friction plate bears the pressure;

[0039] S7. Define the calculation conditions for the finite element model of the clutch system assembly:

[0040] The calculation condition consists of the boundary conditions in step S5 and load 2 in step S6;

[0041] S8. Perform finite element analysis of the clutch system assembly:

[0042] According to the calculation conditions defined in step S7, the pressure-deformation relationship curve of the clutch system is calculated considering geometric nonlinearity. Based on the obtained curve, performance parameters such as motor speed can be determined in the early stage of product development without samples, effectively realizing the engagement and disengagement control of the clutch friction plates.

[0043] Preferably, in step S1, the step of deriving the nominal stress-strain data of the friction lining material using a clutch friction plate compression performance test includes:

[0044] ① A certain number of friction plates are stacked together and mounted on the testing machine, with the friction linings of each friction plate aligned with each other;

[0045] ② Perform multiple slow pressure tests and record the pressure-deformation curve of the friction plate in real time. Stop when the pressure-deformation curves of the previous two tests are relatively consistent.

[0046] ③ Take the friction plate pressure-deformation curve obtained from the last test, and calculate the nominal stress-strain data of the friction lining material based on the initial contact area and initial thickness of the steel plate and friction lining.

[0047] Preferably, the formula for calculating the nominal stress-strain data of the friction lining material based on the initial contact area and initial thickness of the steel sheet and friction lining is as follows:

[0048]

[0049]

[0050]

[0051] In the formula: σ is the nominal stress of the friction lining material; F is the pressure borne by the friction lining; i is the number of friction linings arranged on one side of the steel sheet; A is the contact area of ​​a single friction lining; ε is the nominal strain of the friction lining material; j is the number of friction linings; L is the total deformation of j friction linings under the action of F; L gH represents the total deformation of the steel plates in friction disc j; m E is the thickness of a single friction pad; E is the elastic modulus of the steel sheet material; H g This refers to the thickness of a single steel sheet.

[0052] Preferably, in step S2, the Marlow function is selected to characterize the nominal stress-strain relationship of the friction liner material, and the expression of the Marlow function is:

[0053]

[0054]

[0055]

[0056] J el =(V / V o ) / (1+ε th ) 3 (7)

[0057] In the formula: U is the strain energy, U dev For shape-changing specific energy, U vol For volume change specific energy, ε i For nominal principal strain, ε th V represents the linear thermal expansion strain, V is the current volume, and V0 is the initial volume.

[0058] Preferably, in step S31, the friction lining and steel sheet are meshed using a symmetrical modeling method. First, a local model is cut and removed from the friction lining and steel sheet using a symmetrical plane to perform finite element meshing. Then, the finite element mesh of the entire friction lining and steel sheet is obtained through a symmetrical approach, thereby improving the symmetry and simulation accuracy of the finite element simulation results.

[0059] Preferably, in step S31, the friction lining is divided into two regions as follows: first, the friction lining is projected onto the contact surface of the friction lining along the center line of the steel sheet to obtain a projected boundary line; then, the boundary line is reduced to a copy line with the geometric center of the boundary line as the origin, and the reduction ratio is 0.8; finally, the friction lining is cut along the center line of the steel sheet using the copy line to obtain two regions, the region between the boundary line and the copy line is the first region, and the remaining region is the second region.

[0060] Preferably, in step S32, the initial Poisson's ratio of the materials in the first and second region mesh finite element models of the friction lining is 0.5, meaning that the friction lining material is considered to be completely incompressible.

[0061] Preferably, in step S37, when adjusting the Poisson's ratio of the friction lining material, the adjustment is first performed with the Poisson's ratio of the first region mesh finite element model and the second region mesh finite element model of the friction lining being the same. This adjustment continues until the calculated curve of the friction lining pressure-deformation relationship is basically consistent with the trend of the experimental curve. Then, the Poisson's ratio of one region mesh finite element model is kept unchanged, and the Poisson's ratio of the other region mesh finite element model is finely adjusted until the error between the calculated curve and the experimental curve is less than 5%.

[0062] Preferably, in steps S33 and S5, the boundary conditions of the finite element model further include applying symmetric constraints on all steel sheets, and the symmetric constraints are applied by the following method:

[0063] Establish a rectangular coordinate system on the geometric center line of the steel sheet. The geometric center line of the steel sheet coincides with one of the coordinate axes of the rectangular coordinate system. The center line and the other two coordinate axes of the rectangular coordinate system form two planes. The two planes intersect the steel sheet. Constrain the degrees of freedom of the two rows of nodes at the intersection position of the first plane and the outer diameter side of the steel sheet, which are perpendicular to the first plane. Constrain the degrees of freedom of the two rows of nodes at the intersection position of the second plane and the outer diameter side of the steel sheet, which are perpendicular to the second plane.

[0064] Preferably, in step S4, the number of clutch friction plates is determined using formulas (8) to (9):

[0065] T = Fr m fz (8)

[0066]

[0067] In the formula: T is the torque transmitted by the clutch, F is the pressure borne by the friction plate, f is the coefficient of friction, z is the number of friction surfaces, and r m Let r be the average friction radius. o Let r be the outer radius of the friction surface. i Let be the inner radius of the friction surface.

[0068] The present invention has the following beneficial effects:

[0069] ① Based on the pressure-deformation relationship curve of the friction plate obtained from the clutch friction plate compression performance test, this invention derives the nominal stress-strain relationship curve of the friction lining material based on the geometric parameters of the friction plate, and assigns it separately to the friction lining structure, thereby realizing the accurate definition of the material mechanical properties of the friction lining finite element model.

[0070] ② This invention assigns each of the steel sheet, friction lining, and mating steel sheet its own material mechanical properties, which can be applied to situations where the quantity ratio and volume ratio of any steel sheet, friction lining, and mating steel sheet change, and can effectively guide clutch development.

[0071] ③ This invention divides the friction lining into different regions, defines different material compression properties, and uses the finite element method to correct the compression properties of the friction lining material. The resulting material compression properties are more consistent with reality, which can effectively improve the calculation accuracy of the pressure-deformation relationship curve of the clutch system and guide clutch development in the early stage of product development when there are no samples.

[0072] ④ This invention uses finite element method to obtain the compression performance parameters of friction lining material by adjusting Poisson's ratio. This method is fast and accurate, and can effectively shorten the compression performance test of alternative materials, thereby saving test costs. Attached Figure Description

[0073] The present invention will now be described in further detail with reference to the accompanying drawings and specific embodiments.

[0074] Figure 1 This is a schematic diagram of a single friction plate structure;

[0075] Figure 2 This is a schematic diagram of the compression performance test of 5 friction plates;

[0076] Figure 3 These are test curves showing the relationship between pressure and deformation of five friction plates;

[0077] Figure 4 yes Figure 2 Enlarged view of a portion of point A in the middle;

[0078] Figure 5 It is the nominal stress-strain relationship curve of the friction lining material;

[0079] Figure 6 It involves fitting the nominal stress-strain relationship curve of the friction plate material using different strain energy functions;

[0080] Figure 7 This is a schematic diagram of a finite element model of a single friction plate;

[0081] Figure 8 This is a schematic diagram of the finite element model of the compressibility of 5 friction plates;

[0082] Figure 9 This is a comparison between the calculated and experimental curves of the pressure-deformation relationship of five friction plates when Poisson's ratio is 0.5;

[0083] Figure 10 It is a process for correcting the compressibility of friction lining materials;

[0084] Figure 11 This is a schematic diagram of the finite element model of the clutch system assembly;

[0085] Figure 12 It is the calculated curve of the pressure-deformation relationship of the clutch system. Detailed Implementation

[0086] 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.

[0087] This embodiment provides a method for calculating the pressure-deformation relationship curve of a wet clutch, including the following steps.

[0088] S1. Mechanical property test of clutch friction lining material:

[0089] like Figure 1 As shown, the single-plate clutch friction plate 1 is composed of one steel plate 1001 and 32 friction lining plates 1002 bonded together. Sixteen friction lining plates are evenly arranged on one side of the steel plate 1001, and the friction lining plates 1002 are symmetrically distributed about the circumference and thickness of the steel plate 1001. The main steps for deriving the nominal stress-strain data of the friction lining plate 1001 material using clutch friction plate compression performance testing are as follows:

[0090] ①For example Figure 2 As shown, five friction plates 1 are stacked together and clamped on the testing machine, with the friction linings of each friction plate aligned with each other. The bottom first clamp 2001 is fixed, and a pressure load F is applied to the top second clamp 2002.

[0091] ②For example Figure 3 As shown, after four slow pressurization tests and real-time recording of the friction plate pressure-deformation curves, it was found that the curve of the fourth test was consistent with that of the third test. Therefore, no further tests were conducted after the fourth pressurization test.

[0092] ③ Take the friction plate pressure-deformation curve of the 4th test, and calculate the nominal stress-strain data of the friction lining 1002 based on the initial contact area and thickness of the steel plate 1001 and the friction lining 1002. The specific calculation method is shown in formula (1) to (3).

[0093]

[0094]

[0095]

[0096] In the formula: σ is the nominal stress of the friction lining material; F is the pressure borne by the friction lining; i is the number of friction linings arranged on one side of the steel sheet; A is the contact surface area of ​​a single friction lining; ε is the nominal strain of the friction lining material; j is the number of friction linings; L is the total deformation of j friction linings under the action of F; L g H represents the total deformation of the steel plates in friction disc j; mE represents the initial thickness of a single friction pad; E is the elastic modulus of the steel sheet material; H represents the initial thickness of the friction pad. g This represents the initial thickness of a single steel sheet.

[0097] like Figure 1 , Figure 4 As shown, the friction plate parameters in the embodiment are as follows: i = 16, A = 316.4 mm. 2 j = 5, H m =0.4mm, E=2.1e5Mpa, H g =0.9mm, based on the friction plate parameters and Figure 3 The nominal stress-strain data of the friction lining material were calculated from the pressure-deformation curve of the fourth test, as shown in the figure. Figure 5 As shown, due to Figure 3 Small fluctuations in the pressure-deformation curve of the friction lining within a relatively low pressure range can cause inconsistencies in the monotonicity of the calculated nominal stress-strain relationship curve. Therefore, in order to overcome this problem and meet the data requirements of simulation software, Figure 5 The stress-strain curves were smoothed.

[0098] S2. Selection of hyperelastic constitutive model for friction liner material:

[0099] Abaqus software provides a variety of nonlinear constitutive models, among which the hyperelastic constitutive model has a good ability to describe nonlinear mechanical properties and can be used to characterize the stress-strain relationship of friction lining materials. Specifically, it uses strain energy functions for characterization. There are various strain energy functions, such as first-order Polynomial, second-order Polynomial, Van_der_walls, Neo_Hooke, Marlow, Ogden, etc. Combining them with the least squares method can fit the material's mechanical property curves. Based on the fitting results, the strain energy function with a good fit and stable fitting data is selected as the constitutive relationship of the friction lining material.

[0100] Figure 6 The stress-strain curves obtained from the experiment were plotted. Figure 4 The fitting curves obtained by applying different strain energy functions are shown. It can be seen from the fitting results that the data fitting degree of the first-order Polynomial and Neo_Hooke functions is poor, and the stability of the data fitting of the second-order Polynomial, Ogden (N=3) and Yeoh functions is poor. Only the Marlow function performs well in terms of both the data fitting degree and the stability of the fitted data. Therefore, the Marlow function will be used to characterize the nominal stress-strain relationship of the friction lining material. The expression of the Marlow function is shown in formulas (4) to (7).

[0101]

[0102]

[0103]

[0104] J el =(V / V o ) / (1+ε th ) 3 (7)

[0105] In the formula: U is the strain energy, U dev For shape-changing specific energy, U vol For volume change specific energy, ε i For nominal principal strain, ε th V represents the linear thermal expansion strain, V is the current volume, and V0 is the initial volume.

[0106] S3, Correction of the compressibility of friction liner material:

[0107] Step S3 is further subdivided into steps S31 to S37;

[0108] S31. Establish a finite element simulation model consistent with the friction plate compression performance test in step S1:

[0109] right Figure 4 All steel sheets 1001, all friction linings 1002, the first clamp 2001, and the second clamp 2002 are meshed. Friction linings 1002 are meshed using hexahedral meshes, ignoring the tiny oil guide grooves on the friction surface, and the element type is selected as force-displacement hybrid integral element C3D8H. Steel sheets 1001, the first clamp 2001, and the second clamp 2002 are all meshed using hexahedral meshes, and the element type is selected as C3D8I. The bonding effect between friction linings 1002 and steel sheets 1001 is simulated using the common node method, that is, assuming that there is no relative displacement between them. The first clamp 2001 and the second clamp 2002 are defined as non-deformable rigid bodies.

[0110] The friction lining 1002 and the steel sheet 1001 are each arranged with two layers of mesh elements in the thickness direction to improve the calculation accuracy;

[0111] Friction lining 1002 and steel sheet 1001 are meshed using a symmetrical modeling method. First, a local model is cut and removed from the friction lining and steel sheet using a symmetrical plane to perform finite element meshing. Then, the finite element mesh of the entire friction lining and steel sheet is obtained through a symmetrical method, thereby improving the symmetry and simulation accuracy of the finite element simulation results.

[0112] Ignoring the tiny oil guide grooves on the friction surface of the friction lining, each friction lining is divided into two regions by meshing: a first region and a second region. The first region's mesh is located on the outside of the friction lining, and the second region's mesh is located on the inside. This meshing aims to define different material compressibility properties for different regions, thereby improving the accuracy of the correction for the friction lining material's compressibility properties. The friction lining is divided into two regions as follows, using one friction lining (10021) as an example for illustration: Figure 7 As shown, firstly, the friction lining 10021 is projected onto the contact surface of the friction lining 10021 along the center line 10011 of the steel sheet to obtain the projected boundary line 100211. Then, the boundary line 100211 is reduced to a copy line 100213 with the geometric center 100212 of the boundary line 100211 as the origin. The reduction ratio is 0.8. Finally, the friction lining 10021 is cut along the direction of the center line 10011 of the steel sheet using the copy line 100213 to obtain two regions. The region between the boundary line 100211 and the copy line 100213 is the first region 100214, and the remaining region is the second region 100215.

[0113] The load is transferred between the mutually aligned friction pads, and between the friction pads and the steel sheet, the first clamp, and the second clamp through defined contact relationships;

[0114] To facilitate the application of boundary conditions and loads, two rigid body elements need to be created: such as Figure 8 As shown, a first rigid body element 20012 is established with the geometric center 20011 of the first clamp 2001 as the master point and the unit nodes on the side of the first clamp 2001 where no contact relationship is defined as slave points; a second rigid body element 20022 is established with the geometric center 20021 of the second clamp 2002 as the master point and the unit nodes on the side of the second clamp where no contact relationship is defined as slave points.

[0115] S32. Define the materials for the finite element model:

[0116] The mechanical properties of the friction lining material are defined based on the Marlow function determined in S2. These mechanical properties include the nominal stress-strain number and Poisson's ratio μ from step S1. Figure 7 Taking the friction lining 10021 as an example, the material Poisson's ratio is defined by region. The initial value of the material Poisson's ratio of the first region 100214 mesh finite element model and the second region 100215 mesh finite element model of the friction lining 10021 is μ = 0.5, that is, the friction lining material is considered to be completely incompressible.

[0117] The steel sheet material has an elastic modulus E = 2.1e5 MPa and a Poisson's ratio μ = 0.3.

[0118] S33. Apply boundary conditions to the finite element model:

[0119] First, constrain all degrees of freedom of the principal point of the first rigid body element 20012 defined in S31; second, constrain the principal point of the second rigid body element 20022 defined in S31 along the centerline 10011 of the steel sheet. Figure 7 Degrees of freedom other than directional degrees of freedom;

[0120] The boundary conditions for the finite element model also include applying symmetric constraints on all steel sheets to ensure improved convergence speed without affecting computational accuracy; Figure 7 Taking the friction plate as an example, the method of applying symmetrical constraints is explained. A rectangular coordinate system 10012 is established on the geometric center line 10011 of the steel plate. The coordinate axis Z of the geometric center line 10011 of the steel plate coincides with that of the rectangular coordinate system 10012. The plane XOZ and the plane YOZ intersect the steel plate 1001 respectively. The Y degree of freedom of the two rows of nodes 10013 at the intersection position of the plane XOZ and the outer diameter side of the steel plate is constrained, which is perpendicular to the plane XOZ. The X degree of freedom of the two rows of nodes 10014 at the intersection position of the plane YOZ and the outer diameter side of the steel plate is constrained, which is perpendicular to the plane YOZ.

[0121] S34, Apply load 1:

[0122] Load 1 is a pressure, which is applied to the principal point of the second rigid body element 20022, and the direction is along the center line of the steel sheet, so that the friction lining bears the pressure.

[0123] S35. Define the calculation conditions:

[0124] The calculation condition consists of the boundary conditions in step S33 and load 1 in step S34;

[0125] S36. Perform finite element analysis:

[0126] According to the calculation conditions defined in S35, the pressure-deformation relationship curve of the friction plate, considering geometric nonlinearity calculations, is as follows: Figure 9 As shown;

[0127] S37, Correction of compressibility properties of friction liner material:

[0128] like Figure 9 As shown, the calculated pressure-deformation relationship curve of the friction pad in S36 is compared with the experimental curve in step S1. It can be seen from the figure that the two curves deviate significantly. At this point, it is necessary to adjust the Poisson's ratio μ of the friction pad material. The process of adjusting the Poisson's ratio in the example is as follows: Figure 10 As shown, according to the first area 100214 of the friction lining ( Figure 7The Poisson's ratio of the first region 100214 mesh finite element model and the second region 100215 mesh finite element model is adjusted to be the same. When the Poisson's ratio μ = 0.12, the calculated curve of the friction plate pressure-deformation relationship is basically consistent with the experimental curve, and the maximum error is less than 5% within the pressure range that meets the torque transmission requirements of the clutch, thus meeting the accuracy requirements. Therefore, the Poisson's ratio of both the first region 100214 mesh finite element model and the second region 100215 mesh finite element model of the friction lining is taken as μ = 0.12. In this case, it is not necessary to adjust the two regions to have different Poisson's ratios.

[0129] S4. Establish the finite element model of the clutch system assembly:

[0130] like Figure 11 As shown, based on the clutch torque transmission, heat capacity and design space requirements, the number of clutch friction plates was determined to be 10 using formulas (8) to (9). Then, the support shaft 3, first baffle 4001, first thrust bearing 5001, second baffle 4002, ball 6, worm gear 7, second thrust bearing 5002, pressure plate 8, friction plate 9001, mating steel plate 10001, clutch seat 11, third baffle 4003, clutch housing 12, fourth baffle 4004, sprocket 13, needle roller bearing 14, third thrust bearing 5003, fifth baffle 4005, and oil pump housing 15 were divided into grids. Then, they were assembled together by defining the contact relationship between the contacting parts.

[0131] T = Fr m fz (8)

[0132]

[0133] In the formula: T is the torque transmitted by the clutch, F is the pressure borne by the friction plate, f is the coefficient of friction, z is the number of friction surfaces, and r m Let r be the average friction radius. o Let r be the outer radius of the friction surface. i Let be the inner radius of the friction surface;

[0134] The mesh division method for the friction lining and steel sheet in friction plate 9001 is the same as in step S3;

[0135] The friction lining in friction plate 9001 is divided into two regions and meshed according to the same proportion as in step S3;

[0136] To facilitate the application of boundary conditions and loads, two rigid body elements need to be created: such as Figure 11As shown, a third rigid body element 40011 is established with point 3002 on the geometric center line 3001 of the support shaft 3 as the main point and the element node on the inner diameter side of the baffle 4001 with no defined contact relationship as the slave point; a fourth rigid body element 15001 is established with other points 3003 on the geometric center line 3001 of the support shaft 3 as the main point and the element node on the end face of the oil pump housing 15 away from the clutch friction plate 9001 as the slave point.

[0137] S5. Apply boundary conditions to the finite element model of the clutch system assembly:

[0138] First, constrain the degrees of freedom of the principal point of the third rigid body element 40011 defined in step S4, except for the axial degree of freedom along the support axis; second, constrain all degrees of freedom of the principal point of the fourth rigid body element 15001 defined in step S4.

[0139] The boundary conditions of the finite element model also include applying symmetric constraints on all steel sheets to ensure that the convergence speed is improved without affecting the calculation accuracy. The application method is the same as in step S3.

[0140] S6. Apply load 2 to the finite element model of the clutch system assembly:

[0141] Load 2 is a compressive force, applied to the principal point of the third rigid body element 40011, in the direction along the centerline of the support shaft 3, causing... Figure 11 The friction plate 9001 in the middle bears the pressure;

[0142] S7. Define the calculation conditions for the finite element model of the clutch system assembly:

[0143] The calculation condition consists of the boundary conditions in step S5 and load 2 in step S6;

[0144] S8. Perform finite element analysis of the clutch system assembly:

[0145] According to the calculation conditions defined in step S7, the pressure-deformation relationship curve of the clutch system considering geometric nonlinear calculation is as follows: Figure 12 As shown, the obtained curves can be used to determine performance parameters such as motor speed in the early stages of product development without samples, effectively realizing the engagement and disengagement control of the clutch friction plates.

[0146] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A wet clutch pressure versus distortion relationship curve calculation method characterized by, Comprising the following steps, S1, clutch friction lining material mechanical property test: Single piece clutch friction plate is composed of steel sheet and friction lining, a certain number of friction linings are uniformly arranged on one side of the steel sheet, and the friction linings are symmetrically distributed about the circumferential direction and thickness direction of the steel sheet; The nominal stress-strain data of the friction lining material is derived by using the compression performance test of the clutch friction plate; In step S1, the step of deriving the nominal stress-strain data of the friction lining material by using the compression performance test of the clutch friction plate includes: ① A certain number of friction plates are stacked together and clamped on the testing machine, and the friction linings of each friction plate are aligned with each other; ② Multiple slow pressure tests are performed and the pressure-deformation curve of the friction plate is recorded in real time, and the test is stopped when the current and previous two pressure-deformation curves are consistent; ③ Take the friction plate pressure-deformation curve obtained by the last test, and calculate the material nominal stress-strain data of the friction lining according to the initial contact area and initial thickness of the steel sheet and the friction lining; S2, select the hyperelastic constitutive model of the friction lining material; S3, correction of compression performance of friction lining material: S31, establish a finite element simulation model consistent with the friction plate compression performance test in step S1: Mesh the steel sheet, friction lining, and fixture: the friction lining is meshed with hexahedral elements, ignoring the small oil guide grooves on the friction surface, and the element type is selected as force-displacement mixed integral element; The steel sheet, the first fixture and the second fixture are meshed with hexahedral elements; The bonding effect between the friction lining and the steel sheet is simulated by the common node method, that is, it is assumed that there is no relative displacement between them; The first fixture and the second fixture are defined as non-deformable rigid bodies; The friction lining and the steel sheet are arranged with more than 2 layers of grid elements in the thickness direction respectively; After ignoring the small oil guide grooves on the friction surface of the friction lining, each friction lining is divided into two regions for meshing, namely the first region and the second region, the first region mesh is located outside the friction lining, and the second region mesh is located inside the friction lining. The purpose of this meshing is to define different material compression performance for different regions, thereby improving the accuracy of the compression performance correction of the friction lining material; The friction linings are aligned with each other, and the friction linings and the steel sheet, the first fixture, and the second fixture are in contact with each other to transfer the load; In order to apply boundary conditions and loads conveniently, two rigid body elements need to be established: the first rigid body element RBE2 is established with the geometric center of the first fixture as the master point and the element nodes on the side of the first fixture without defined contact relationship as the slave points; The second rigid body element RBE2 is established with the geometric center of the second fixture as the master point and the element nodes on the side of the second fixture without defined contact relationship as the slave points; S32, define the material of the finite element model: Based on the strain energy function determined in step S2, the mechanical properties of the friction lining material are defined, including the nominal stress-strain data in step S1, the Poisson's ratio μ; The material mechanical properties of the steel sheet and the counter steel sheet include the elastic modulus E and the Poisson's ratio μ; S33, apply boundary conditions to the finite element model: One is to constrain all degrees of freedom of the first rigid element RBE2 master point defined in S31, and the other is to constrain the degrees of freedom of the second rigid element RBE2 master point defined in S31 except the degrees of freedom along the center line direction of the steel sheet; S34, apply load 1: Load 1 is a pressure applied to the master point of the second rigid element RBE2, and the direction is along the center line of the steel sheet, so that the friction pad bears pressure; S35, define the calculation condition: The calculation condition is composed of the boundary condition in S33 and the load 1 in S34; S36, perform finite element analysis: According to the calculation condition defined in S35, the pressure-deformation relationship curve of the friction plate is calculated considering geometric nonlinearity; S37, modify the compression performance of the friction pad material: Compare the pressure-deformation relationship curve of the friction plate calculated in step S36 with the pressure-deformation relationship curve of the friction plate tested in step S1. If the deviation between the two curves is large, the Poisson's ratio μ of the friction pad material needs to be adjusted, wherein the Poisson's ratio of the first area grid finite element model of the friction pad is not higher than and the Poisson's ratio of the second area grid finite element model, and then steps S32 to S37 are repeatedly executed until the change trend of the two curves is basically consistent and the maximum error is less than 5% within the pressure range required by the clutch torque; S4, establish a clutch system assembly finite element model: According to the clutch torque, heat capacity and design space requirements, determine the number of clutch friction plates, then divide the grids of support shaft, baffle, thrust bearing, ball, worm, pressure plate, friction pad, steel sheet, dual steel sheet, clutch seat, clutch housing, sprocket, needle bearing, oil pump housing, and assemble them together by defining the contact relationship between the contacting components; The grid division method of the friction pad and the steel sheet is the same as in step S3; For the convenience of applying boundary conditions and loads, two rigid elements need to be established: a third rigid element RBE2 is established with a point on the geometric center line of the support shaft as the master point and the element node of the baffle 1 close to the inner diameter side without defining the contact relationship as the slave point; a fourth rigid element RBE2 is established with other points on the geometric center line of the support shaft as the master point and the element node of the oil pump housing far from the end surface of the clutch friction plate as the slave point; S5, apply the boundary conditions of the clutch system assembly finite element model: One is to constrain the degrees of freedom of the third rigid element RBE2 master point defined in step S4 except the axial degrees of freedom of the support shaft, and the other is to constrain all degrees of freedom of the fourth rigid element RBE2 master point defined in step S4; S6, apply load 2 to the clutch system assembly finite element model: Load 2 is a pressure applied to the master point of the third rigid element RBE2, and the direction is along the center line direction of the support shaft, so that the friction plate bears pressure; S7, define the calculation condition of the clutch system assembly finite element model: The calculation condition is composed of the boundary condition in step S5 and the load 2 in step S6; S8, perform finite element analysis of the clutch system assembly According to the calculation condition defined in step S7, the pressure-deformation relationship curve of the clutch system is calculated considering geometric nonlinearity, and according to the obtained curve, the performance parameters such as motor speed can be determined in the sample-free state in the early stage of product development, so as to effectively realize the combination and separation control of the clutch friction plate.

2. The method of claim 1, wherein, The calculation formula for calculating the nominal stress-strain data of the friction lining plate according to the initial contact area and initial thickness of the steel sheet and the friction lining plate is: where σ is the nominal stress of the friction lining material; F is the pressure taken by the friction plate; i is the number of friction linings arranged on one side of the steel plate; A is the contact area of a single friction lining; ε is the nominal strain of the friction lining material; j is the number of friction plates; L is the total deformation of j friction plates under the action of F; L g is the total deformation of the steel plate in j friction plates; H m is the thickness of a single friction lining; E is the elastic modulus of the steel plate material; H g is the thickness of a single steel plate.

3. The method of claim 1, wherein In step S2, the Marlow function is selected to represent the nominal stress-strain relationship of the friction lining plate material, and the expression of the Marlow function is: J el = (V / V o ) / (1+ε th ) 3 (7) where: U is the strain energy, U dev is the shape change specific energy, U vol is the volume change specific energy, ε i is the nominal principal strain, ε th is the linear thermal expansion strain, V is the current volume, and V0 is the initial volume.

4. The method of claim 1, wherein, In step S31, the friction lining plate and the steel sheet are meshed by using a symmetric modeling method, first, a local model is cut from the friction lining plate and the steel sheet by using a symmetric plane, and then the finite element mesh of the entire friction lining plate and the steel sheet is obtained by symmetrically dividing the local model, so as to improve the symmetry and simulation accuracy of the finite element simulation results.

5. The method of claim 1, wherein In step S31, the friction lining plate is divided into two regions by the following method, first, the projection boundary line is obtained by projecting the friction lining plate along the center line of the steel sheet on the contact surface of the friction lining plate, then the copy line of the boundary line is obtained by taking the geometric center of the boundary line as the origin and reducing the boundary line, the reduction ratio is 0.8, finally, the two regions are obtained by cutting the friction lining plate along the center line of the steel sheet using the copy line, the region between the boundary line and the copy line is the first region, and the remaining region is the second region.

6. A method of calculating a pressure versus deformation relationship curve for a wet clutch as set forth in claim 1, characterized by, In step S32, the initial value of the material Poisson's ratio of the first region grid finite element model and the second region grid finite element model of the friction lining plate is 0.5, that is, the friction lining plate material is considered to be completely incompressible.

7. A method of calculating a pressure versus deformation relationship curve for a wet clutch as set forth in claim 1, characterized by, In step S37, when adjusting the Poisson's ratio of the friction lining plate, first, adjust the Poisson's ratio of the first region grid finite element model and the second region grid finite element model of the friction lining plate to be the same, and continue to adjust until the trend of the calculated pressure-deformation relationship curve of the friction plate is basically consistent with the test curve, then keep the Poisson's ratio of one region grid finite element model unchanged, continue to fine-tune the Poisson's ratio of the other region grid finite element model, and terminate when the error between the calculation and the test curve is less than 5%.

8. The method of claim 1, wherein, In steps S33 and S5, the boundary conditions of the finite element model further include applying symmetric constraints on all steel sheets, and the symmetric constraints are applied by the following method: A rectangular coordinate system is established on the geometric center line of the steel sheet, the geometric center line of the steel sheet coincides with a coordinate axis of the rectangular coordinate system, the center line and the other two coordinate axes of the rectangular coordinate system form two planes, the two planes intersect with the steel sheet, the freedom perpendicular to the first plane of the two rows of nodes intersecting with the first plane on the outer diameter side of the steel sheet is constrained, and the freedom perpendicular to the second plane of the two rows of nodes intersecting with the second plane on the outer diameter side of the steel sheet is constrained.

9. A method of calculating a pressure versus deformation relationship curve for a wet clutch as set forth in claim 1, characterized by, In step S4, the number of clutch friction plates is determined by using formulas (8) and (9): In step S4, the number of clutch friction plates is determined by using formulas (8) and (9): T = Fr m fz (8) where: T is the torque transmitted by the clutch, F is the pressure on the friction plate, f is the friction coefficient, z is the number of friction surfaces, r m is the average friction radius, r o is the outer radius of the friction surface, r i is the inner radius of the friction surface.

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