Method for determining repeated welding position of electric vehicle differential housing and driven gear

Abstract

The present invention discloses a method for determining the repeated welding position of a differential housing and a driven gear of an electric vehicle. The method puts forward in detail the steps for determining the repeated welding position of the differential housing and the driven gear from the aspects of finite element model construction, calculation condition selection and result analysis. By calculating the weld stress and damage under typical working conditions, the overall distribution of weld damage after linear superposition is obtained, from which the area with less weld fatigue damage can be intuitively analyzed and used as the preferred area of ​​the repeated welding position, which can effectively ensure the service life of the repeated welding position, improve the reliability of the weld, avoid the tediousness caused by repeated analysis and judgment of weld stress distribution under many typical working conditions, simplify the repeated welding position determination process, correct the problem of poor accuracy of directly determining the repeated welding position based on weld stress, and enable different engineers to objectively determine the repeated welding position, thereby providing effective guidance for the implementation of the welding process.

Description

Technical Field

[0001] The present invention belongs to the technical field of transmission systems, and in particular relates to a method for determining a repeated welding position of a differential housing and a driven gear of an electric vehicle. Background Art

[0002] In order to assist in the lightweight design of electric vehicle transmission systems and reduce the differential's rotational inertia and oil churning losses, the connection method between the differential housing and the supported driven gear has been improved from traditional bolt connection to laser welding connection. Laser welding eliminates the need for connecting bolts for fastening the differential housing and the driven gear, and avoids drilling holes in the differential housing and the driven gear. It has high production efficiency and simple process, and is the preferred connection method for two different materials.

[0003] The differential housing and driven gear are axisymmetric rotating parts. Under the large impact load of electric vehicles, the differential housing and driven gear are connected together using a laser welding process. A complete weld should be welded between the two, that is, the arc starting position and the arc ending position of the weld are just connected together, and there is no repeated welding, thereby effectively ensuring the connection strength and impact toughness of the weld.

[0004] However, in actual welding operations, intermittent welding or uncontrollable repeated welding often occurs at the arc starting and arc ending positions of the weld, resulting in unstable welding process and difficulty in meeting design requirements. There are two main problems with intermittent welding. First, there is a stress concentration coefficient area at each end of the weld, which is prone to cracking; second, when the differential rotates at high speed, the intermittent welding position is prone to dynamic imbalance due to lack of welding materials. Repeated welding can effectively avoid the problems of intermittent welding. It not only has fewer stress concentration areas and better dynamic balancing ability, but also has high process stability. However, repeated welding is secondary welding, which is easy to introduce further welding defects.

[0005] In order to effectively reduce the impact of welding defects caused by repeated welding and ensure the connection strength of welds in repeated welding areas, it is necessary to select the repeated welding position in the area with less weld fatigue damage during the product design stage, and predict whether the fatigue performance of the repeated welding position can meet the requirements.

[0006] CN112989665A "A fatigue life analysis method for the differential housing of an electric drive assembly" records the method and steps for fatigue life analysis of the differential housing, which fully considers the influence of the impact load and combines the actual load-bearing torque to improve the accuracy of the fatigue life analysis of the differential housing. It does not involve fatigue analysis of welds. The patent CN202110173895.9 "A laser sealing process suitable for different packaging surface structures of silicon-aluminum workpieces" records that by setting the welding starting and end positions of continuous sealing, the secondary impact on the silicon-aluminum workpiece to be welded during the sealing process is reduced; by setting continuous welding process parameters, the input energy in the linear gradient finishing process is reduced, the secondary heat input in the repeated welding area is reduced, and the cracking of the finishing point and the generation of welding thermal cracks are avoided. It does not give the process of selecting the repeated welding area.

[0007] CN201010224067.5 "Laser welding connection method for automobile drive axle differential housing and driven bevel gear" records the use of a CNC rotary table and a reflective focusing structure light guide system to transmit the focused laser beam to the welding area for welding the differential housing and the driven bevel gear. It does not analyze the stress state of the weld and perform welding based on it. In summary, none of the prior arts involve methods for determining repeated welding positions based on the stress state and fatigue damage of the weld, thereby providing support for improving weld reliability and providing guidance for the development of laser welding processes. Summary of the invention

[0008] In order to solve the problem that in the prior art, a differential housing and a driven gear are connected together by a laser welding process, and repeated welding is used at the arc starting and arc ending positions of the weld to ensure the integrity of the weld, but repeated welding will introduce secondary welding defects. The present invention provides a method for determining the repeated welding position of a differential housing and a driven gear of an electric vehicle. In the product design stage, the repeated welding position needs to be selected in an area with less weld fatigue damage, and it is predicted whether the fatigue performance of the repeated welding position can meet the requirements, so as to effectively reduce the influence of welding defects caused by repeated welding and ensure the connection strength of the weld in the repeated welding area.

[0009] The objective of the present invention is achieved through the following technical solutions:

[0010] A method for determining a repeated welding position of an electric vehicle differential housing and a driven gear comprises the following steps:

[0011] S1. Establish a finite element model of differential assembly: divide the differential case and driven gear into solid meshes respectively, and the mesh nodes of the contact parts of the two correspond one to one. Then, the differential case and the driven gear are assembled together by defining the contact relationship of the contact parts of the two. Extract the surface meshes of the differential case and the driven gear at the weld position, close them and generate a weld solid mesh model. The weld is directly connected to the differential case and the driven gear in a common node manner.

[0012] S2. Define the material properties of the finite element model: define the material elastic modulus E, Poisson's ratio μ, and thermal expansion coefficient α of the finite element model of each component;

[0013] S3. Apply boundary conditions of the finite element model. The boundary conditions include two types: one is to fix the surface of the differential case in contact with the inner diameter of the bearing inner ring, where the surface of one end of the differential case fixes the translational freedom in three directions, and the surface of the other end fixes the translational freedom in two directions except the axial translation, and the rotational freedom is not constrained at both ends; the other is to fix the rotational freedom of the surface of the shaft hole of the differential case where the pin is installed around the axis of the differential case;

[0014] S4. Define the initial temperature of the finite element model: apply the initial temperature to the differential housing, driven gear, and weld;

[0015] S5. Apply load 1: Load 1 is the centrifugal force of the differential case, the driven gear, and the weld. The centrifugal force is applied by defining the axis of the differential case as the rotation axis and the rotation speed around the rotation axis;

[0016] S6, apply load 2: Load 2 is a temperature load, that is, the same high temperature load is applied to the differential housing, the driven gear, and the weld;

[0017] S7, apply load 3: Load 3 is the meshing force of the driven gear when the differential assembly works in the forward gear; then it is applied to the pitch circle of the driven gear;

[0018] S8, apply load 4: Load 4 is the meshing force of the driven gear when the differential assembly works in reverse gear; then it is applied to the pitch circle of the driven gear;

[0019] S9. Define calculation conditions:

[0020] Calculation condition 1: including the boundary conditions in step S3, the initial temperature in step S4, the load 1 in step S5, the load 2 in step S6 and the load 3 in step S7;

[0021] Calculation condition 2: including the boundary conditions in step S3, the initial temperature in step S4, the load 1 in step S5, the load 2 in step S6 and the load 4 in step S8;

[0022] S10, perform finite element analysis: calculate the stress distribution of the weld in sequence according to the calculation condition 1 and the calculation condition 2 defined in step S9;

[0023] S11. Determine the repeated welding position:

[0024] Import the weld stress corresponding to the working condition 1 calculated in step S10 into the fatigue simulation software, define the weld position and weld type in the fatigue simulation software, and calculate the fatigue damage of the weld considering the mechanical properties of the weld material and the weld defects;

[0025] The weld stress corresponding to the calculation condition 2 in step S10 is imported into the fatigue simulation software, the weld position and weld type are defined in the fatigue simulation software, and the fatigue damage of the weld is calculated considering the mechanical properties of the weld material and the weld defects;

[0026] The fatigue damage of the weld corresponding to working condition 1 and working condition 2 is calculated by linear superposition to obtain the overall fatigue damage distribution of the weld, and the area with smaller damage is determined as the repeated welding position.

[0027] Furthermore, in step S1, the contact portion between the differential housing and the driven gear is defined as a zero-clearance fit.

[0028] Furthermore, in step S2, the elastic modulus E of the weld material is the larger elastic modulus of the differential housing and the driven gear, the Poisson's ratio μ is the Poisson's ratio of the material with the larger elastic modulus, and the thermal expansion coefficient α is the thermal expansion coefficient of the material with the larger elastic modulus.

[0029] Further, in the step S3, the surface of the differential case in contact with the inner diameter of the bearing inner ring is fixed by means of the RBE3 unit, and RBE3 units are established at both ends of the differential case respectively, the slave point of the RBE3 unit is defined at the intersection of the axis of the differential case and the normal line of the inner diameter surface of the bearing outer ring, the normal line of the inner diameter surface of the bearing outer ring is located in the middle position of the inner diameter surface of the bearing outer ring, and the RBE3 master point selects the surface of the contact between the differential case and the inner diameter of the bearing inner ring; the rotational freedom of the surface of the shaft hole for mounting the pin on the differential case is fixed by means of the RBE3 unit, the slave point of the RBE3 unit is defined at the intersection of the axis of the differential case and the axis of the pin, and the master point selects the surface of the shaft hole for mounting the pin.

[0030] Further, in step S5, the rotation speed is defined as 1.2 times the maximum design speed of the differential assembly, and the maximum design speed of the differential assembly includes the maximum design speed of the forward differential assembly and the maximum design speed of the reverse differential assembly.

[0031] Furthermore, in the steps S7 to S8, the driven gear meshing force is calculated using formula (1) and applied using a local cylindrical coordinate system defined on the axis of the differential case, wherein the Z axis of the coordinate system is along the axis of the driven gear, R is along the radial direction of the driven gear, and t is determined by Z and R according to the right-hand rule;

[0032]

[0033] In the formula, F t 、F r 、F a are the circumferential force, radial force and axial force of the gear respectively, M is the torque transmitted by the gear, d is the pitch diameter of the gear, a n is the normal pressure angle of the gear, and β is the helix angle at the gear pitch circle.

[0034] Furthermore, in the steps S7 to S8, the driven gear meshing force is applied to multiple nodes of the driven gear pitch circle, the gear nodes are evenly distributed, the driven gear meshing force is applied no less than 12 times, and the gear meshing force applied each time is equal in magnitude.

[0035] Furthermore, in the steps S7 to S8, the positions and times of applying the meshing force of the driven gears of the forward gear and the reverse gear are the same.

[0036] Furthermore, in step 11, fatigue damage is calculated using the linear Palmgren-Miner rule of formula (2):

[0037]

[0038] Where: D is the cumulative damage; n i is the number of cycles of the weld stress amplitude under a certain level of load; Ni is the fatigue life corresponding to the weld stress amplitude under a certain level of load.

[0039] Furthermore, the method further comprises step S12: based on the differential assembly finite element model established in step S1, redefine the rotation speed of the differential housing and the driven gear in step S5, the meshing force of the driven gear in steps S7 and S8, and the calculation condition in step S9 according to the differential load spectrum; and calculate the weld stress corresponding to each condition according to step S10; and then import them into fatigue simulation software respectively, define the weld position, weld type and repeated welding position determined in step S11 in the fatigue simulation software, calculate the weld fatigue damage considering the mechanical properties of the weld material and the influence of the weld defects, and calculate the fatigue damage using the linear Palmgren-Miner law of formula (2):

[0040]

[0041] Where: D is the cumulative damage; ni is the number of cycles of weld stress amplitude under a certain level of load; Ni is the fatigue life corresponding to the weld stress amplitude under a certain level of load;

[0042] If the fatigue damage of the weld at the repeated welding position is less than 1.0, it means that the determined repeated welding position is reasonable.

[0043] Compared with the prior art, the present invention has the following advantages:

[0044] ① The present invention proposes in detail the steps for determining the repeated welding position of the differential housing and the driven gear from the aspects of finite element model construction, calculation condition selection and result analysis. By calculating the weld stress and damage under typical working conditions, the overall distribution of weld damage after linear superposition is obtained, from which the area with less weld fatigue damage can be intuitively analyzed. Taking it as the preferred area of ​​the repeated welding position can effectively ensure the life of the repeated welding position, improve the reliability of the weld, avoid the tediousness caused by repeated analysis and judgment of the weld stress distribution under many typical working conditions, simplify the repeated welding position determination process, correct the problem of poor accuracy of directly determining the repeated welding position based on the weld stress, and achieve different engineers can objectively determine the repeated welding position, providing effective guidance for the implementation of the welding process.

[0045] ② When calculating the stress distribution of the weld between the differential case and the driven gear, the influence of the temperature of the differential case and the driven gear, as well as the influence of the centrifugal force, are considered. The calculation is highly consistent with the actual working state of the differential, the weld stress obtained is more consistent with the actual state, and the determined repeated welding position is more effective.

[0046] ③ When using weld fatigue damage to confirm the effect of repeated welding positions, based on the strong linear relationship between weld stress and torque, the weld stress corresponding to the minimum torque in the load spectrum is multiplied by the torque coefficient to directly obtain the weld stress corresponding to other torques. This avoids the finite element calculation of weld stress for other torques, saves simulation time, and shortens the product development cycle. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0048] Figure 1 1 is a schematic diagram of the structure of the differential assembly according to an embodiment of the present invention (angle 1);

[0049] Figure 2 2 is a schematic diagram of the structure of the differential assembly according to an embodiment of the present invention (angle 2);

[0050] Figure 3 is a cross section of the differential assembly according to an embodiment of the present invention;

[0051] Figure 4 is Figure 3 The cross section of the differential assembly at B is partially enlarged in the middle;

[0052] Figure 5 is a schematic diagram of the position of the meshing node of the driven gear according to an embodiment of the present invention;

[0053] Figure 6 is Figure 2 The schematic diagram of the RBE3 unit established at A in the middle is partially enlarged;

[0054] Figure 7 is Figure 5 The weld stress distribution calculated by the gear meshing force when the forward gear is applied sequentially at different driven gear meshing node positions;

[0055] Figure 8 is Figure 5 The weld stress distribution calculated by the gear meshing force when the reverse gear is applied sequentially at different driven gear meshing node positions;

[0056] Fig. 9 Schematic diagram of the position where fatigue damage of the weld is relatively small according to the embodiment of the present invention;

[0057] Fig.10 is a schematic diagram of repeated welding positions determined in an embodiment of the present invention;

[0058] Fig.11 It is the weld fatigue damage distribution calculated under the load spectrum conditions of the differential assembly described in the embodiment of the present invention. DETAILED DESCRIPTION

[0059] The present invention is described in detail below with reference to the accompanying drawings and specific embodiments.

[0060] This embodiment is a method for determining the repeated welding position of an electric vehicle differential housing and a driven gear, comprising the following steps:

[0061] S1. Establish the finite element model of differential assembly: The differential assembly is as follows: Figure 1 , Figure 2 As shown, it includes a differential case 1, a driven gear 2, a weld 3, a first bearing 4, a second bearing 5, a pin 6, a planetary gear 7, and a half-shaft gear 8. The differential case 1 and the driven gear 2 are divided into solid meshes, and the contact parts 121, 122, 123, and 124 (such as Figure 4 The grid nodes at the positions (as shown) correspond one to one, which can effectively improve the load transfer accuracy between the components. At the same time, the contact relationship is defined at the above-mentioned contact positions 121, 122, 123, and 124, and the differential housing 1 and the driven gear 2 are assembled together; Figure 3 , Figure 4As shown, the mesh of the surface 11 of the differential case and the mesh of the surface 21 of the driven gear at the position of the weld 3 are extracted, and the two surface meshes are closed by using the mesh of the surface 31 of the weld to generate the solid mesh of the weld 3. The solid mesh of the weld 3 is connected with the solid mesh of the differential case 1 and the solid mesh of the driven gear 2 at the common nodes;

[0062] When performing entity mesh division of the differential case 1, first divide its 1 / 2 entity mesh model, and then obtain the finite element model of the entire differential case through symmetry, so as to improve the symmetry and simulation accuracy of the finite element calculation results of the weld position on the differential case.

[0063] The contact parts 121 , 122 , 123 , and 124 between the differential housing 1 and the driven gear 2 are defined as zero-clearance fit. At this time, the stress on the weld is relatively severe, and the repeated welding positions determined thereby are more accurate and effective.

[0064] S2. Define the material properties of the finite element model: the material of the differential case 1 is QT600, with an elastic modulus of E = 175000 MPa, a Poisson's ratio of μ = 0.3, and an α of 0.0000118 / °C; the material of the driven gear 2 is FAS3420, with an elastic modulus of E = 210000 MPa, a Poisson's ratio of μ = 0.3, and an α of 0.0000127 / °C; the elastic modulus of the differential case material QT600 is lower than that of the driven gear material FAS3420. In order to improve the stress sensitivity of the weld and determine a more accurate overlapping welding position, the elastic modulus and Poisson's ratio of the weld material are consistent with those of FAS3420, that is, the elastic modulus E = 210000 MPa, the Poisson's ratio μ = 0.3, and the α of 0.0000127 / °C.

[0065] S3. Apply finite element model boundary conditions: Figure 3 As shown, the boundary conditions include two types. One is to fix the differential case surface 11 that contacts the inner diameter of the inner ring of the No. 1 bearing 4, and the differential case surface 12 that contacts the inner diameter of the inner ring of the No. 2 bearing 5, so as to simulate the supporting effect of the bearing on the differential case, wherein the differential case surface 11 needs to fix the three-direction translational degrees of freedom, and the differential case surface 12 needs to fix the two-direction translational degrees of freedom except the axial translation; the second is to fix the rotational degrees of freedom of the shaft hole surface 14 on which the pin 6 is installed on the differential case around the axis line 13 of the differential case, so as to simulate the reaction force of the half-axle on the differential assembly.

[0066] The first differential case surface 11 that is fixed at the contact position with the inner diameter of the inner ring of the first bearing 4 and the second differential case surface 12 that is fixed at the contact position with the inner diameter of the inner ring of the second bearing 5 both need to use the RBE3 unit. The method of establishing the RBE3 unit is explained by taking the differential case surface 12 as an example. The slave point of the RBE3 unit 121 is defined at the intersection 1211 of the differential case axis 13 and the normal line 51 of the outer ring inner diameter surface of the second bearing 5. The normal line 51 is the surface normal corresponding to the middle position of the width of the outer ring inner diameter surface of the second bearing 5. According to the slave point defined in this way, its support reaction torque is zero, which correctly reflects the force of the differential assembly finite element model established in the step S1, and avoids the tediousness of first arbitrarily determining a slave point to calculate the slave point support reaction force, and then manually applying the slave point support reaction torque and then performing finite element analysis. The RBE3 unit master point selects the node on the second differential case surface at the contact position between the differential case 1 and the inner diameter of the inner ring of the second bearing 5.

[0067] The rotational freedom of the shaft hole surface 14 for mounting the pin shaft 6 on the fixed differential housing 1 requires the aid of the RBE3 unit. The slave point of the RBE3 unit 141 is defined at the intersection 1411 of the differential housing axis 13 and the pin axis 61, and the master point is selected as the node on the shaft hole surface 14 for mounting the pin shaft 6.

[0068] S4. Define the initial temperature of the finite element model: apply initial temperature to the differential housing, driven gear, and weld, and the temperature value is equal to room temperature 25°C.

[0069] S5. Apply load 1: Load 1 is the centrifugal force of the differential case 1, the driven gear 2, and the weld 3. The centrifugal force is applied by defining the axis line 13 of the differential case as the rotation axis and the rotation speed around the rotation axis.

[0070] The rotation speed of the differential housing 1, the driven gear 2, and the weld 3 is defined as 1.2 times the maximum design speed of the differential assembly to ensure that the weld still has good reliability when the differential assembly rotates at an overspeed.

[0071] In the forward gear, with the shaft centerline 13 as the rotation axis, 1.2 times the maximum design speed of the forward gear differential is applied to the differential case 1, the driven gear 2, and the weld 3. At this time, the load is named load 11.

[0072] In reverse gear, with the axis line 13 as the rotation axis, 1.2 times of the maximum design speed of the reverse differential is applied to the differential housing 1, the driven gear 2, and the weld 3. At this time, the load is named load 12.

[0073] S6. Apply load 2: Load 2 is a temperature load, that is, the same temperature of 120°C is applied to the differential case 1, the driven gear 2, and the weld 3 to consider the weld stress caused by the inconsistent deformation of the differential case and the driven gear, and to improve the simulation accuracy of the weld stress.

[0074] S7. Apply load 3: Load 3 is the gear meshing force of the driven gear 2 when the differential assembly is working in the forward gear. The gear meshing force is obtained based on the torque M transmitted by the differential assembly, the gear meshing parameters and the gear load calculation formula (1), and then applied to the driven gear pitch circle. The gear meshing force application position and application times should be able to correctly reflect the weld stress during the rotation of the differential.

[0075] The torque M transmitted by the differential assembly is related to the power input and road adhesion of the electric vehicle. During structural design, the maximum design torque of the differential assembly should be higher than them. Considering the impact of the electric vehicle on the transmission system, when calculating the force on the forward gear weld 3, the torque M transmitted by the differential assembly is taken as 2.5 times the maximum design torque of the forward gear differential assembly.

[0076] The driven gear meshing force is applied to multiple nodes of the driven gear pitch circle 2, and the gear nodes 23 are evenly distributed, such as Figure 5 As shown, the driven gear meshing force is applied 12 times, and the gear meshing force applied each time is equal. The corresponding driven gear meshing forces are named load 31, load 32, load 33, load 34, load 35, load 36, load 37, load 38, load 39, load 310, load 311, and load 312 respectively.

[0077] The meshing force of the driven gear can be decomposed into circumferential force, radial force and axial force, which are calculated using formula (1) and applied with the help of the local cylindrical coordinate system 9 defined on the axis of the differential housing. The Z axis of the coordinate system is along the axis of the driven gear, and R is along the radial direction of the driven gear. t is determined by Z and R according to the right-hand rule.

[0078]

[0079] In the formula, F t 、F r 、F a are the circumferential force, radial force and axial force of the gear respectively, M is the torque transmitted by the gear, d is the pitch diameter of the gear, a n is the normal pressure angle of the gear, β is the helix angle at the pitch circle of the gear;

[0080] like Figure 6As shown, taking any node in the gear node 23 as an example, the gear meshing force application process is explained, and the gear meshing force application process on other nodes is the same; the gear meshing force is applied with the help of the RBE3 unit, the slave point 241 of the RBE3 unit 24 selects the gear meshing node, and the main point of the RBE3 unit 24 selects the unit node on the tooth surface 242 and the tooth surface 243 near the gear meshing node; the number of RBE3 units is the same as the number of times the gear meshing force is applied, that is, 12 RBE3 units need to be established, and their slave points are evenly distributed on the gear pitch circle.

[0081] S8, apply load 4: Load 4 is the driven gear meshing force when the differential assembly works in reverse gear. The driven gear meshing force is obtained according to the torque M transmitted by the differential assembly, the gear meshing parameters and the gear load calculation formula (1), and then applied to the driven gear pitch circle. The gear meshing force application position and application times are consistent with the forward gear in step S7. The corresponding driven gear meshing forces are named load 41, load 42, load 43, load 44, load 45, load 46, load 47, load 48, load 49, load 410, load 411 and load 412 respectively.

[0082] S9. Define calculation conditions

[0083] The boundary conditions in step S3, the initial temperature in step S4, the load 1 in step S5, and the load 2 in step S6 are used in each calculation condition and are named as common load conditions;

[0084] Calculation condition 1: including common load conditions and load 31 in step S7;

[0085] Calculation condition 2: including common load conditions and load 32 in step S7;

[0086] Calculation condition 3: including common load conditions and load 33 in step S7;

[0087] Calculation condition 4: including common load conditions and load 34 in step S7;

[0088] Calculation condition 5: including common load conditions and load 35 in step S7;

[0089] Calculation condition 6: including the common load condition and the load 36 in step S7;

[0090] Calculation condition 7: including the common load condition and the load 37 in step S7;

[0091] Calculation condition 8: including the common load condition and the load 38 in step S7;

[0092] Calculation condition 9: including the common load condition and the load 39 in step S7;

[0093] Calculation condition 10: including the common load condition and the load 310 in step S7;

[0094] Calculation condition 11: including the common load condition and the load 311 in step S7;

[0095] Calculation condition 12: including common load conditions and load 312 in step S7;

[0096] Calculation condition 13: including the common load condition and the load 41 in step S7;

[0097] Calculation condition 14: including the common load condition and the load 42 in step S7;

[0098] Calculation condition 18: including the common load condition and the load 43 in step S7;

[0099] Calculation condition 16: including the common load condition and the load 44 in step S7;

[0100] Calculation condition 17: including the common load condition and the load 45 in step S7;

[0101] Calculation condition 18: including the common load condition and the load 46 in step S7;

[0102] Calculation condition 19: including the common load condition and the load 47 in step S7;

[0103] Calculation condition 20: including common load conditions and load 48 in step S7;

[0104] Calculation condition 21: including common load conditions and load 49 in step S7;

[0105] Calculation condition 22: including common load conditions and load 410 in step S7;

[0106] Calculation condition 23: including the common load condition and the load 411 in step S7;

[0107] Calculation condition 24: includes common load conditions and load 412 in step S7.

[0108] S10, perform finite element analysis: calculate the stress distribution of the weld in the order of calculation condition 1, calculation condition 2, ..., calculation condition 24 defined in step S9, and the corresponding maximum principal stress distribution is as follows: Figures 7-8 shown.

[0109] S11. Determine the repeated welding position:

[0110] The weld stresses corresponding to the calculation conditions 1 to 12 in step S10 are sequentially imported into the fatigue simulation software, the weld position and weld type are defined in the fatigue simulation software, and the fatigue damage of the weld is calculated considering the mechanical properties of the weld material and the weld defects. The fatigue damage is calculated using the linear Palmgren-Miner law of formula (2);

[0111]

[0112] Where: D is the cumulative damage; n i is the number of cycles of the weld stress amplitude under a certain level of load; Ni is the fatigue life corresponding to the weld stress amplitude under a certain level of load.

[0113] The weld stress corresponding to the calculation conditions 13 to 24 in step S10 is imported into the fatigue simulation software, the weld position and weld type are defined in the fatigue simulation software, and the fatigue damage of the weld is calculated considering the mechanical properties of the weld material and the weld defects. The fatigue damage is calculated using the linear Palmgren-Miner law of formula (2);

[0114] The weld fatigue damage calculated by calculation conditions 1 to 12 and the weld fatigue damage calculated by calculation conditions 13 to 24 are linearly superimposed to obtain the overall fatigue damage distribution of the weld, such as Fig. 9 As shown, the fatigue damage of the C area and the D area is relatively small, and both areas can be used as repeated welding positions. In the embodiment, the C area is determined as the repeated welding position, and the specific method is as follows: Fig.10 Repeat welding position 32 in.

[0115] S12. Calculation of weld fatigue damage:

[0116] On the basis of the differential assembly finite element model established in step S1, the rotation speed of the differential housing and the driven gear in step S5, the meshing force of the driven gear in steps S7 and S8, and the calculation working condition in step S9 are redefined according to the differential load spectrum (Table 1), and the weld stress corresponding to each working condition is calculated according to step S10; in order to save simulation time and shorten the product development cycle, the following method is adopted in the embodiment to obtain the weld stress corresponding to each working condition, firstly calculate the weld stress σ1 corresponding to the minimum torque 302Nm in the forward gear of the load spectrum, according to the strong linear relationship between the weld stress and the torque, the weld stress corresponding to other torques is directly obtained by multiplying σ1 by the torque ratio, for example, the weld stress σ4 corresponding to the torque 1030Nm of the fourth level load spectrum in the forward gear is σ1×(1030÷302);

[0117] Table 1 Differential load spectrum

[0118]

[0119] The 12 calculation conditions corresponding to each torque are respectively imported into the FEMFAT fatigue simulation software. The weld position, weld type and repeated welding position 32 determined in step S11 are defined in the fatigue simulation software. The weld fatigue damage is calculated considering the mechanical properties of the weld material and the influence of weld defects. The fatigue damage is calculated using the linear Palmgren-Miner law given by formula (2), as follows: Fig.11 As shown, the maximum fatigue damage of repeated welding position 32 is 9.87e-5, which is much smaller than 1.0, indicating that the determined repeated welding position is reasonable.

Claims

1. A method for determining the repeated welding position of an electric vehicle differential housing and a driven gear, characterized in that: The following steps are involved: S1. Establish a finite element model of differential assembly: divide the differential case and driven gear into solid meshes respectively, and the mesh nodes of the contact parts of the two correspond one to one. Then, the differential case and the driven gear are assembled together by defining the contact relationship of the contact parts of the two. Extract the surface meshes of the differential case and the driven gear at the weld position, close them and generate a weld solid mesh model. The weld is directly connected to the differential case and the driven gear in a common node manner. S2. Define the material properties of the finite element model: define the material elastic modulus E, Poisson's ratio μ, and thermal expansion coefficient α of the finite element model of each component; S3. Apply boundary conditions of the finite element model. The boundary conditions include two types: one is to fix the surface of the differential case in contact with the inner diameter of the bearing inner ring, where the surface of one end of the differential case fixes the translational freedom in three directions, and the surface of the other end fixes the translational freedom in two directions except the axial translation, and the rotational freedom is not constrained at both ends; the other is to fix the rotational freedom of the surface of the shaft hole of the differential case where the pin is installed around the axis of the differential case; S4. Define the initial temperature of the finite element model: apply initial temperature to the differential housing, driven gear, and weld; S5. Apply load 1: Load 1 is the centrifugal force of the differential case, the driven gear, and the weld. The centrifugal force is applied by defining the axis of the differential case as the rotation axis and the rotation speed around the rotation axis; S6. Apply load 2: Load 2 is a temperature load, that is, the same high temperature load is applied to the differential housing, the driven gear, and the weld; S7, apply load 3: Load 3 is the meshing force of the driven gear when the differential assembly works in the forward gear; Then it is applied to the pitch circle of the driven gear; S8, apply load 4: Load 4 is the meshing force of the driven gear when the differential assembly works in reverse gear; Then it is applied to the pitch circle of the driven gear; S9. Define calculation conditions: Calculation condition 1: including the boundary conditions in step S3, the initial temperature in step S4, the load 1 in step S5, the load 2 in step S6 and the load 3 in step S7; Calculation condition 2: including the boundary conditions in step S3, the initial temperature in step S4, the load 1 in step S5, the load 2 in step S6 and the load 4 in step S8; S10, perform finite element analysis: calculate the stress distribution of the weld in sequence according to the calculation condition 1 and the calculation condition 2 defined in step S9; S11. Determine the repeated welding position: Import the weld stress corresponding to the working condition 1 calculated in step S10 into the fatigue simulation software, define the weld position and weld type in the fatigue simulation software, and calculate the fatigue damage of the weld considering the mechanical properties of the weld material and the weld defects; The weld stress corresponding to the calculation condition 2 in step S10 is imported into the fatigue simulation software, the weld position and weld type are defined in the fatigue simulation software, and the fatigue damage of the weld is calculated considering the mechanical properties of the weld material and the weld defects; The fatigue damage of the weld corresponding to working condition 1 and working condition 2 is calculated by linear superposition to obtain the overall fatigue damage distribution of the weld, and the area with the smallest damage is determined as the repeated welding position.

2. A method for determining repeated welding positions of an electric vehicle differential housing and a driven gear according to claim 1, characterized in that: In the step S1, the contact portion between the differential housing and the driven gear is defined as a zero-clearance fit.

3. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 1, characterized in that: In step S2, the elastic modulus E of the weld material is the largest elastic modulus of the differential case and the driven gear, the Poisson's ratio μ is the Poisson's ratio of the material with the largest elastic modulus, and the thermal expansion coefficient α is the thermal expansion coefficient of the material with the largest elastic modulus.

4. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 1, characterized in that: In the step S3, the surface of the differential case in contact with the inner diameter of the bearing inner ring is fixed by means of the RBE3 unit, and the RBE3 units are respectively established at both ends of the differential case, the slave point of the RBE3 unit is defined at the intersection of the axis of the differential case and the normal line of the inner diameter surface of the bearing outer ring, the normal line of the inner diameter surface of the bearing outer ring is located in the middle position of the inner diameter surface of the bearing outer ring, and the RBE3 master point selects the surface of the contact between the differential case and the inner diameter of the bearing inner ring; the rotational freedom of the surface of the shaft hole for mounting the pin on the differential case is fixed by means of the RBE3 unit, the slave point of the RBE3 unit is defined at the intersection of the axis of the differential case and the axis of the pin, and the master point selects the surface of the shaft hole for mounting the pin.

5. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 1, characterized in that: In the step S5, the rotation speed is defined as 1.2 times the maximum design speed of the differential assembly, and the maximum design speed of the differential assembly includes the maximum design speed of the forward gear differential assembly and the maximum design speed of the reverse gear differential assembly.

6. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 1, characterized in that: In the steps S7 to S8, the driven gear meshing force is calculated using formula (1) and applied using a local cylindrical coordinate system defined on the axis of the differential case, where the Z axis of the coordinate system is along the axis of the driven gear, R is along the radial direction of the driven gear, and t is determined by Z and R according to the right-hand rule; In the formula, F t 、F r 、F a are the circumferential force, radial force and axial force of the gear respectively, M is the torque transmitted by the gear, d is the pitch diameter of the gear, a n is the normal pressure angle of the gear, and β is the helix angle at the gear pitch circle.

7. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 6, characterized in that: In the steps S7 to S8, the driven gear meshing force is applied to multiple nodes of the driven gear pitch circle, the gear nodes are evenly distributed, the driven gear meshing force is applied no less than 12 times, and the gear meshing force applied each time is equal in magnitude.

8. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 1, characterized in that: In the steps S7 to S8, the driven gear meshing force application position and application times of the forward gear and the reverse gear are the same.

9. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 1, characterized in that: In step 11, fatigue damage is calculated using the linear Palmgren-Miner rule of formula (2): Where: D is the cumulative damage; n i N is the number of cycles of weld stress amplitude under a certain level of load; i It is the fatigue life corresponding to the stress amplitude of the weld under a certain level of load.

10. The method for determining the repeated welding position of the electric vehicle differential housing and the driven gear according to claim 1, characterized in that: The step S12 is further included: based on the differential assembly finite element model established in step S1, redefining the rotation speeds of the differential case and the driven gear in step S5, the meshing forces of the driven gear in steps S7 and S8, and the calculation conditions in step S9 according to the differential load spectrum; And calculate the weld stress corresponding to each working condition according to step S10; then import them into fatigue simulation software respectively, define the weld position, weld type and repeated welding position determined in step S11 in the fatigue simulation software, and calculate the weld fatigue damage considering the mechanical properties of weld material and the influence of weld defects. The fatigue damage is calculated using the linear Palmgren-Miner law of formula (2): Where: D is the cumulative damage; n i N is the number of cycles of weld stress amplitude under a certain level of load; i is the fatigue life corresponding to the stress amplitude of the weld under a certain level of load; If the fatigue damage of the weld at the repeated welding position is less than 1.0, it means that the determined repeated welding position is reasonable.

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