A method for predicting working tension of a connecting bolt of a new energy vehicle transmission housing

Abstract

The present application belongs to the field of automobile technology, and in particular to a method for predicting the working tension of a connecting bolt of a new energy vehicle transmission housing. The method comprises the following steps: 1) building a finite element model of the new energy vehicle transmission assembly; 2) defining the material properties of the finite element model; 3) defining the stiffness of each spring unit in step 1; 4) defining the boundary conditions of the finite element model; 5) defining the initial temperature of the finite element model; 6) defining the load of the finite element model; 7) defining the calculation condition; 8) performing finite element analysis; and 9) extracting the working pressure of the bolt. The calculated working tension of the bolt is more consistent with the actual value, and the precision is high, which effectively supports the selection of the bolt and effectively ensures the strength of the bolt and the connection rigidity and tightness of the transmission housing.

Description

Technical Field

[0001] This invention belongs to the field of automotive technology, specifically a method for predicting the working tensile force of connecting bolts in the transmission housing of a new energy vehicle. Background Technology

[0002] Bolted connections are a type of detachable connection characterized by their simple structure, ease of disassembly, reliable connection, high production efficiency, and low cost, making them widely used in various industries such as automotive, shipbuilding, and aerospace. The total tensile force on a bolt equals the sum of its working tensile force and its residual preload. When the working tensile force is too high, the following problems can occur: firstly, the increased total tensile force on the bolt can lead to insufficient bolt strength and breakage; secondly, a significant reduction in the residual preload can cause gaps between the connected parts, resulting in sealing failure. To effectively prevent these problems, it is essential to: 1) select bolts of appropriate performance grades to ensure sufficient strength; and 2) design a suitable initial bolt preload, ensuring it is sufficiently large relative to the working tensile force to guarantee the reliability of the bolted connection. In new energy vehicles, the frequency of rapid acceleration, deceleration, and repeated energy recovery is significantly higher than in traditional fuel vehicles. This results in a wider range of working tensile forces on the bolts securing the transmission housing. Therefore, it is crucial to accurately predict the bolt working tensile force to correctly select the bolt performance grade and set the initial bolt preload.

[0003] Currently, there are two main methods for obtaining the working tensile force of a bolt:

[0004] One method is to use sensor testing for prediction. High-precision displacement sensors are installed at the flange connection to collect and correct the relative displacement data of the flange. The bolt working tensile force is then calculated based on the displacement data. This method directly calculates the bolt working tensile force through displacement sensor test data. Its advantages are that the test data is accurate and can be monitored and warned online in real time. Its disadvantages are that the bolt working tensile force test can only be used for the later stage of product verification, not for the early stage of product development and design. In addition, the cost of use is high and the installation conditions are limited, making it unsuitable for applications such as the numerous connecting bolts in the transmission of new energy vehicles.

[0005] The second method is to directly estimate the bolt working force using a formula. This method calculates the engine's maximum working load based on the engine's maximum burst pressure and then roughly estimates the working tensile force of a single bolt based on the number of bolts fastening the cylinder head. Finally, based on a predetermined safety factor determined by axial force attenuation, the preload of a single bolt required for cylinder head sealing is determined from the bolt working tensile force. The advantage of this method is that it is quick to obtain the bolt working tensile force. The disadvantage is that it does not consider the influence of the structural rigidity of the cylinder head, gaskets, etc., resulting in poor accuracy in calculating the bolt working tensile force and bolt preload. Summary of the Invention

[0006] This invention provides a method for predicting the working tensile force of connecting bolts in the transmission housing of new energy vehicles. The calculated working tensile force of the bolts is more consistent with the actual value, with high accuracy, effectively supporting bolt selection, and effectively ensuring the strength of the bolts and the connection rigidity and tightness of the transmission housing. It solves the above-mentioned problems existing in the methods for predicting the working tensile force of bolts.

[0007] The technical solution of this invention is described below in conjunction with the accompanying drawings:

[0008] A method for predicting the working tensile force of connecting bolts in the transmission housing of a new energy vehicle includes the following steps:

[0009] Step 1: Build a finite element model of the new energy vehicle transmission assembly;

[0010] Step 2: Define the material properties of the finite element model;

[0011] Step 3: Define the stiffness of each spring unit in Step 1;

[0012] Step 4: Define the boundary conditions for the finite element model;

[0013] Step 5: Define the initial temperature of the finite element model;

[0014] Step 6: Define the loads in the finite element model;

[0015] Step 7: Define the calculation conditions;

[0016] Step 8: Perform finite element analysis;

[0017] Step 9: Extract the working pressure of the bolt.

[0018] Furthermore, in step one,

[0019] The finite element model of the new energy vehicle transmission assembly includes the transmission housing, mounts, bolts, bearings, gears, gear shafts, and differential housing. The transmission housing, mount outer sleeve, mount inner sleeve, bolts, bearings, gears, gear shafts, and differential housing are modeled using solid meshes. Bolts are modeled using a hybrid of solid elements, beam elements, and RBE2 elements. The meshes at contact points on the components are finely divided, while the meshes at other non-contact points are coarsely divided. Then, the components are assembled together by defining contact relationships between the contacting parts.

[0020] The suspended rubber structure is simulated using spring elements. The first RBE2 element is established with the geometric center of the outer sleeve as the master point and the nodes on the inner surface of the outer sleeve as slave points. The second RBE2 element is established with the geometric center of the inner sleeve as the master point and the nodes on the outer surface of the inner sleeve as slave points. Then, the spring element is established using the master point of the first RBE2 element and the master point of the first RBE2 element.

[0021] The inner sleeve of the suspension is connected to the transmission housing through an established RBE2 unit. There are two specific cases: First, for suspensions that directly support the transmission housing, the principal point of the established RBE2 unit is located at the geometric center of the inner diameter sidewall of the inner sleeve. Nodes on the inner diameter sidewall of the inner sleeve and the bolt hole wall of the transmission housing at the suspension's location are selected from this point. Second, for suspensions that do not directly support the transmission housing, the principal point of the established RBE2 unit is selected from the center of mass of the powertrain. Nodes on the inner diameter sidewall of the inner sleeve and the inner wall of the bolt hole on the transmission torque input end face are selected from this point. The powertrain includes the motor, controller, transmission housing, and gear shaft, gears, bearings, bolts, and lubricating oil supported by the suspension.

[0022] The bolt ends are divided into solid meshes, and the middle part is divided into beam elements. The solid meshes at both ends and the beam elements are connected together by RBE2 elements. The principal point of the RBE2 element is located on the bolt centerline in the middle of the solid meshes at both ends, and serves as the node of the beam element. The RBE2 element selects the node on the end face of the solid mesh from the point. The cross section of the beam element is circular, and the diameter is equal to the nominal diameter of the bolt thread.

[0023] The beam element is located near the bolt head.

[0024] Furthermore, in step two,

[0025] Define the elastic modulus of the materials in the finite element model of each component. Poisson's ratio Coefficient of thermal expansion .

[0026] Furthermore, in step three,

[0027] The stiffness of the spring element is defined in a local rectangular coordinate system, with the origin of the rectangular coordinate system at... Choose a point on the geometric center line of the suspended inner sleeve. The axis is perpendicular to the ground and points upwards, intersecting the geometric center line of the suspended inner sleeve. The axis is along the geometric center line of the suspended inner sleeve. Shaft shaft and The axis is determined according to the right-hand rule; the stiffness of each spring element consists of 6 parts, which are along the local index coordinate system. Shaft stiffness ,along Shaft stiffness ,along Shaft stiffness , around Shaft stiffness , around Shaft stiffness and around Shaft stiffness ;

[0028] , , Defined using a force-displacement relationship curve. , , It is defined by the relationship curve between torque and rotation angle.

[0029] Furthermore, in step four,

[0030] First boundary condition: Constrain the outer surface nodes of each suspended outer sleeve;

[0031] Second boundary condition: Constrain the rotational degrees of freedom of each gear shaft and differential housing about their respective centerlines;

[0032] The rotational degrees of freedom of the gear shaft and differential housing are constrained by the RBE3 element. The RBE3 element is defined from the point on the rotation centerline. The principal point is selected as a node on a cross section of the gear shaft or differential housing, which is located between the bearing and the gear. Then, the rotational degrees of freedom of the RBE3 element from the point about the centerline are constrained.

[0033] An RBE3 element needs to be established between each gear and bearing, and the rotational degrees of freedom of the RBE3 element from the point about the center line of the gear shaft or the center line of the differential housing should be constrained respectively.

[0034] Furthermore, in step five,

[0035] Apply initial temperature to the transmission housing, mountings, bolts, bearings, gears, gear shafts, and differential housing;

[0036] The initial temperature is defined as room temperature.

[0037] Furthermore, in step six,

[0038] First load: The first load is a temperature load, which means applying a high temperature load to the transmission housing, mounting, bolts, bearings, gears, gear shafts and differential housing;

[0039] Second load: The second load is the gear meshing force when the transmission is in any forward gear. The gear meshing force is applied to the gear through which the forward gear torque is experienced.

[0040] The third load is the gear meshing force when the transmission is in reverse gear. The gear meshing force is applied to the gear through which the reverse torque is experienced.

[0041] Fourth load: The fourth load is the impact load on the powertrain, which acts on the center of mass of the powertrain;

[0042] The same temperature is applied to the transmission housing, mounts, bolts, bearings, gears, gear shafts, and differential housing, and the temperature value is greater than the normal operating temperature value of the transmission.

[0043] Take the gear with the highest gear ratio when driving forward, and take the gear with the highest gear ratio when driving backward;

[0044] The torque transmitted by the gear shaft on which the second and third loads are based is equal to 2.5 times the rated torque of the motor multiplied by the gearbox ratio;

[0045] The gear meshing force is decomposed into circumferential force, radial force, and axial force, and calculated using the following formula. This is achieved using a local cylindrical coordinate system defined on the center lines of each gear shaft. The shaft is along the centerline of the gear shaft. Along the radial direction of the gear shaft, Depend on , Determined according to the right-hand rule;

[0046] (1)

[0047] In the formula, , , These are the circumferential force, radial force, and axial force of the gear, respectively. The torque transmitted by the gears; The pitch circle diameter of the gear; The normal pressure angle of the gear; The helix angle at the pitch circle of the gear;

[0048] Gear circumferential force radial force and axial force The RBE3 element is applied to the gear meshing node. The slave point of the RBE3 element selects the gear meshing node, and the master point of the RBE3 element selects the tooth surface element node with at least 2 teeth near the gear meshing node.

[0049] The fourth load is the downward vertical impact load on the powertrain, which is equal to 7 times the weight of the powertrain.

[0050] Furthermore, in step seven,

[0051] The first calculation case includes the first and second boundary conditions in step four, the initial temperature in step five, and the first, second, and fourth loads in step six.

[0052] The second calculation condition includes the first and second boundary conditions in step four, the initial temperature in step five, and the first, third, and fourth loads in step six.

[0053] Furthermore, in step eight,

[0054] According to the first and second calculation conditions defined in step seven, the quasi-static finite element method is used to perform finite element analysis of the bolt working load in sequence, taking into account geometric nonlinearity.

[0055] Furthermore, in step nine,

[0056] Extract the axial loads of the beam elements in step one under the first and second calculation conditions respectively. An axial load greater than zero indicates that the bolt working load is tensile, an axial load equal to zero indicates that the bolt does not bear a working load, and an axial load less than zero indicates that the bolt working load is compressive. The axial load greater than zero is the bolt working tensile force, and the maximum value should not exceed 1 times the bolt preload. If it exceeds this value, increase the bolt diameter and performance grade in step one, and repeat steps one to nine until the maximum bolt working tensile force meets the requirements.

[0057] The bolt preload is calculated using the following formula;

[0058] (2)

[0059] In the formula, This refers to the preload of the bolts. This refers to the bolt tightening torque. This is the bolt tightening torque coefficient; The diameter is the bolt diameter.

[0060] Based on the maximum tensile force of the beam element calculated in the first and second calculation conditions, all selected bolts have the same specifications and performance level.

[0061] The beneficial effects of this invention are as follows:

[0062] 1) This invention establishes a finite element model of the new energy vehicle transmission assembly, considering the influence of the stiffness of components such as the transmission housing, bearings, and gear shafts, as well as the effects of transmission temperature, forward gear torque, reverse gear torque, and powertrain inertial impact load. The calculated bolt working tensile force is more consistent with the actual value, exhibiting high accuracy and effectively supporting bolt selection.

[0063] 2) The bolts of this invention adopt a hybrid modeling method of solid elements and beam elements, which not only provides real connection stiffness for the transmission housing connection, but also makes it easy to obtain the working tensile force of each bolt according to the axial load of the beam element, which is suitable for any number of bolts.

[0064] 3) This invention selects applicable bolts based on the fact that the maximum working tensile force of the bolts in the bolt group does not exceed the bolt preload, which effectively ensures the strength of the bolts and the connection rigidity and tightness of the transmission housing. Attached Figure Description

[0065] To more clearly illustrate the technical solutions of the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. It should be understood that the following drawings only show some embodiments of the present invention and should not be regarded as a limitation on the scope. For those skilled in the art, other related drawings can be obtained based on these drawings without creative effort.

[0066] Figure 1 This is a schematic diagram of the transmission assembly structure;

[0067] Figure 2 A schematic diagram of the gear transmission mechanism inside the gearbox;

[0068] Figure 3 A schematic diagram of the RBE2 unit built on the suspended outer sleeve;

[0069] Figure 4 A schematic diagram of the spring unit and the RBE2 unit built on the inner sleeve of the suspension.

[0070] Figure 5 A schematic diagram of the RBE2 unit established on the inner sleeve of the suspension when the first type of suspension is connected to the transmission housing;

[0071] Figure 6 for Figure 5 A schematic diagram showing the location of the RBE2 unit on the transmission housing from a point;

[0072] Figure 7 A schematic diagram of the RBE2 unit established when the second type of mounting is connected to the transmission housing;

[0073] Figure 8 This is a schematic diagram of the finite element model of the bolt;

[0074] Figure 9 A schematic diagram defining the stiffness of a spring element;

[0075] Figure 10 A schematic diagram of the RBE3 unit built on the differential housing;

[0076] Figure 11 This is a schematic diagram of the cross-section where the RBE3 unit is located on the differential housing;

[0077] Figure 12 This is a schematic diagram of all the bolts on the transmission housing;

[0078] Figure 13This is a flowchart of the present invention. Detailed Implementation

[0079] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0080] It should be noted that similar reference numerals and letters in the following figures indicate similar items; therefore, once an item is defined in one figure, it does not need to be further defined and explained in subsequent figures. Furthermore, in the description of this invention, terms such as "first," "second," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0081] like Figure 13 As shown, a method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing includes the following steps:

[0082] Step 1: Building a finite element model of the new energy vehicle transmission assembly

[0083] like Figure 1 , Figure 2 As shown, the finite element model of the new energy vehicle transmission assembly includes a first transmission housing 101, a second transmission housing 102, a first mount 201, a second mount 202, a third mount 203, a bolt 301, a first bearing 401, a second bearing 402, a third bearing 403, a gear 501, a gear shaft 601, and a differential housing 701. The first transmission housing 101, the second transmission housing 102, the outer sleeve of the first mount 201, the inner sleeve of the first mount 201, the bolt 301, the first bearing 401, the gear 501, the gear shaft 601, and the differential housing 701 are meshed using solid meshes. The bolt 301 is modeled using a hybrid of solid elements, beam elements, and RBE2 elements. The meshes at the contact points of the components need to be finely meshed, while the meshes at other non-contact points are coarsely meshed to reduce the computational scale and improve the model's computational speed without affecting the force transmission accuracy. Then, the components are assembled together by defining the contact relationship between the contacting parts.

[0084] The rubber structures of the first suspension 201, the second suspension 202, and the third suspension 203 are simulated using spring units, such as... Figure 3 As shown, the first RBE2 element 207 is established with the first geometric center 205 of the first suspended outer sleeve 204 as the master point and the nodes on the inner surface 206 of the first suspended outer sleeve 204 as slave points; as Figure 4As shown, the second geometric center 209 of the first suspended inner sleeve 208 is the master point, and the nodes on the outer surface 210 of the first suspended inner sleeve 208 are the slave points to establish the second RBE2 unit 211. Then, the master point of the first RBE2 unit 207 and the master point of the first RBE2 unit 211 are used to establish the spring unit 212.

[0085] The inner sleeves of the first mount 201, the second mount 202, and the third mount 203 are connected to the transmission housing through the established RBE2 unit. Specifically, there are two cases. The first case concerns the first mount 201 and the second mount 202, which directly support the transmission housing. Taking the first mount 201 as an example... Figure 5 , Figure 6 As shown, the principal point of the RBE2 unit 213 established at this time is located at the third geometric center 215 of the inner diameter side wall 214 of the inner sleeve 208 of the first suspension. The nodes on the inner diameter side wall 214 of the inner sleeve 208 of the first suspension and the nodes on the bolt hole wall 103 of the second transmission housing 102 where the suspension is located are selected from this point. The second type is for the third suspension 203 that does not directly support the transmission housing, such as... Figure 7 As shown, the principal point of the RBE2 unit 216 established at this time is the centroid 217 of the powertrain, and the nodes on the inner diameter side wall 219 of the inner sleeve 218 of the third suspension 203 and the nodes on the inner wall of the bolt holes on the end face 220 of the transmission torque input end are selected from the points; as shown Figure 1 As shown, the powertrain includes a motor 801, a controller 802, a first transmission housing 101, a second transmission housing 102, and a gear shaft, gears, bearings, bolts, and lubricating oil supported by the first transmission housing 201, the second transmission housing 202, and the third transmission housing 203;

[0086] like Figure 8 As shown, each bolt 301 is divided into solid meshes at both ends and beam elements 302 in the middle. The solid meshes at both ends and the beam elements are connected together by RBE2 elements. The beam elements 302 are close to the bolt head. Taking RBE2 element 303 as an example, the main point 304 of RBE2 element 303 is located on the bolt centerline 305 in the middle of the solid meshes at both ends, and serves as a node of beam element 302. RBE2 element 303 selects the node on the end face 306 of the bolt solid mesh from the point. The cross section of beam element 302 is circular, and its diameter is equal to the nominal diameter of the bolt thread, which is 8mm in this embodiment.

[0087] Step 2: Define the material properties of the finite element model;

[0088] Define the elastic modulus of the materials in the finite element model of each component. Poisson's ratio Coefficient of thermal expansion ;

[0089] The first transmission housing 101 and the second transmission housing 102 are made of aluminum alloy AlSi9Cu3, with an elastic modulus of [missing value]. Poisson's ratio , The differential housing 701 is made of ductile iron QT600. Poisson's ratio , The others are iron alloys. Poisson's ratio , .

[0090] Step 3: Define the stiffness of each spring unit in Step 1;

[0091] like Figure 9 As shown, taking the spring element 212 as an example, its stiffness is defined in the local rectangular coordinate system 221, with the origin of the rectangular coordinate system at... Choose a point on the geometric center line of the suspended inner sleeve. The axis is perpendicular to the ground and points upwards, intersecting the geometric center line of the suspended inner sleeve. The shaft is along the geometric center line 222 of the inner sleeve 208. Shaft shaft and The axis is determined according to the right-hand rule; the stiffness of each spring element must include 6 parts, namely along the local index coordinate system. Shaft stiffness ,along Shaft stiffness ,along Shaft stiffness , around Shaft stiffness , around Shaft stiffness and around Shaft stiffness ;

[0092] When the stiffness of the rubber structure in the suspension is nonlinear, , , It can be defined using a force-displacement relationship curve. , , It can be defined using the torque-angle relationship curve; taking spring unit 212 as an example, by giving the rubber structure of suspension 201 in... Force and displacement data in the axial direction define stiffness See Table 1 for details. It equals the tangent value at each point on the force-displacement curve, for example, the value corresponding to number 1. The calculation process is as follows: (-4.52E+4-(-1.34E+05)) / (-7.75-(-8.03))=3.21E+05N / mm;

[0093] Table 1

[0094]

[0095] Step 4: Define the boundary conditions for the finite element model;

[0096] First boundary condition: Constrain the nodes on the outer surface of each suspension sleeve. Taking the first suspension 201 as an example, constrain the nodes on the outer surface 223 of the outer sleeve 204, such as... Figure 3 As shown;

[0097] Second boundary condition: Constrain the rotational degrees of freedom of the gear shaft 601 and the differential housing 701 about their respective centerlines. Applying this constraint requires the use of RBE3 elements. Taking the constraint of the rotational degree of freedom of the differential housing 701 as an example... Figure 10 and Figure 11 As shown, RBE3 element 702 is defined from point 703 on the rotation centerline 704. The principal point is selected as a node on the differential housing section 705, which is located between the bearing 403 and the gear 501 supported by the differential. Then, the rotational degree of freedom of RBE3 element from point 703 about the centerline 704 is constrained. An RBE3 element needs to be established between each gear and bearing, and the rotational degree of freedom of RBE3 element from point 703 about the gear shaft centerline or the differential housing centerline is constrained respectively.

[0098] Step 5: Define the initial temperature of the finite element model;

[0099] An initial temperature equal to room temperature (25°C) is applied to the transmission housing, mountings, bolts, bearings, gears, gear shafts, and differential housing.

[0100] Step 6: Define the loads in the finite element model;

[0101] First load: The first load is a temperature load, that is, the same temperature is applied to the transmission housing, suspension, bolts, bearings, gears, gear shafts and differential housing, with a value equal to 120°C, which is greater than the normal operating temperature of the transmission by 80°C;

[0102] Second load: The second load is the gear meshing force when the transmission is in any forward gear. In this embodiment, only the gear with the largest speed ratio is used for calculation. The gear meshing force is obtained based on the torque transmitted by the gear shaft, the gear meshing parameters, and the gear load calculation formula. Then it is applied to all gears through which the torque of the gear with the largest speed ratio in the forward gears passes. The torque transmitted by the gear shaft is equal to 2.5 times the rated torque of the motor multiplied by the maximum speed ratio of the transmission in the forward gears.

[0103] Gear meshing force can be decomposed into circumferential force, radial force, and axial force, which are calculated using formula (1) and applied using a local cylindrical coordinate system defined on the center line of each gear shaft. The shaft is along the centerline of the gear shaft. Along the radial direction of the gear shaft, Depend on , Determined according to the right-hand rule;

[0104] (1)

[0105] In the formula, , , These are the circumferential force, radial force, and axial force of the gear, respectively. The torque transmitted by the gears; The pitch circle diameter of the gear; The normal pressure angle of the gear; The helix angle at the pitch circle of the gear;

[0106] Gear circumferential force radial force and axial force The RBE3 element is applied to the gear meshing node. The slave point of the RBE3 element selects the gear meshing node, and the master point of the RBE3 element selects the tooth surface element node with at least 2 teeth near the gear meshing node.

[0107] The third load is the gear meshing force when the transmission is in reverse gear. In this embodiment, only the gear with the largest speed ratio is used for calculation. The gear meshing force is obtained based on the torque transmitted by the gear shaft, the gear meshing parameters and the gear load calculation formula (1), and then applied to the gear through which the torque of the gear with the largest speed ratio in reverse gear is experienced. The torque transmitted by the gear shaft is equal to 2.5 times the rated torque of the motor multiplied by the maximum speed ratio of the transmission in reverse gear.

[0108] Fourth load: The fourth load is as follows Figure 1 The powertrain shown is subjected to a downward vertical impact load, which acts on, as... Figure 7 The center of gravity of the powertrain shown is 217, and its size is equal to 7 times the weight of the powertrain.

[0109] Step 7: Define the calculation conditions;

[0110] The first calculation case includes the first and second boundary conditions in step four, the initial temperature in step five, and the first, second, and fourth loads in step six.

[0111] The second calculation condition includes the first and second boundary conditions in step four, the initial temperature in step five, and the first, third, and fourth loads in step six.

[0112] Step 8: Perform finite element analysis;

[0113] According to the first and second calculation conditions defined in step seven, the quasi-static finite element method is used to perform finite element analysis of the bolt working load in sequence, taking into account geometric nonlinearity.

[0114] Step 9: Extract the working tensile force of the bolt.

[0115] Extract the axial loads of the beam elements in step one under the first and second calculation conditions respectively. An axial load greater than zero indicates that the bolt working load is tensile, an axial load equal to zero indicates that the bolt does not bear a working load, and an axial load less than zero indicates that the bolt working load is compressive. The axial load greater than zero is the bolt working tensile force, and its maximum value should not exceed 1 times the bolt preload. If it exceeds this value, the diameter and performance grade of the bolt in step S1 need to be increased. Repeat steps one to nine until the maximum value of the bolt working tensile force meets the requirements.

[0116] For ease of description, Figure 12 The beam units are classified according to the bolts to which they belong. The calculated axial load of the beam unit, i.e. the bolt working load, is shown in Table 2. The maximum value in the table is 20225N. Considering the cost of bolts and the processing cost of the gearbox housing, 8.8 grade M8 bolts are selected. At this time, in formula (2) , , The calculated bolt preload is 20312N. The maximum value of the beam element in Table 2 does not exceed 1 times the bolt preload of 20312N, so the M8 bolt meets the design requirements.

[0117] The bolt preload is calculated using formula (2):

[0118] (2)

[0119] In the formula, This refers to the preload of the bolts. This refers to the bolt tightening torque. This is the bolt tightening torque coefficient; This refers to the bolt diameter.

[0120] Table 2 Bolt Working Load

[0121]

[0122] In summary, the calculated bolt working tensile force is more consistent with the actual value, has high accuracy, effectively supports bolt selection, and effectively ensures the strength of the bolt and the connection rigidity and tightness of the transmission housing.

[0123] Although embodiments of the present invention have been disclosed above, they are not limited to the applications listed in the specification and embodiments. It can be applied to various fields suitable for the invention. Further modifications can be readily made by those skilled in the art. Therefore, without departing from the general concept defined by the claims and their equivalents, the invention is not limited to the specific details and illustrations shown and described herein.

Claims

1. A method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing, characterized in that, Includes the following steps: Step 1: Build a finite element model of the new energy vehicle transmission assembly; Step 2: Define the material properties of the finite element model; Step 3: Define the stiffness of each spring unit in Step 1; Step 4: Define the boundary conditions for the finite element model; Step 5: Define the initial temperature of the finite element model; Step 6: Define the loads in the finite element model; Step 7: Define the calculation conditions; Step 8: Perform finite element analysis; Step 9: Extract the working pressure of the bolt; Among them, step one, The finite element model of the new energy vehicle transmission assembly includes the transmission housing, mounts, bolts, bearings, gears, gear shafts, and differential housing. The transmission housing, mount outer sleeve, mount inner sleeve, bolts, bearings, gears, gear shafts, and differential housing are modeled using solid meshes. Bolts are modeled using a hybrid of solid elements, beam elements, and RBE2 elements. The meshes at contact points on the components are finely divided, while the meshes at other non-contact points are coarsely divided. Then, the components are assembled together by defining contact relationships between the contacting parts. The suspended rubber structure is simulated using spring elements. The first RBE2 element is established with the geometric center of the outer sleeve as the master point and the nodes on the inner surface of the outer sleeve as slave points. The second RBE2 element is established with the geometric center of the inner sleeve as the master point and the nodes on the outer surface of the inner sleeve as slave points. Then, the master point of the first RBE2 element and the master point of the first RBE2 element are used to establish the spring element. The inner sleeve of the suspension is connected to the transmission housing through an established RBE2 unit. There are two specific cases: First, for suspensions that directly support the transmission housing, the principal point of the established RBE2 unit is located at the geometric center of the inner diameter sidewall of the inner sleeve. Nodes on the inner diameter sidewall of the inner sleeve and the bolt hole wall of the transmission housing at the suspension's location are selected from this point. Second, for suspensions that do not directly support the transmission housing, the principal point of the established RBE2 unit is selected from the center of mass of the powertrain. Nodes on the inner diameter sidewall of the inner sleeve and the inner wall of the bolt hole on the transmission torque input end face are selected from this point. The powertrain includes the motor, controller, transmission housing, and gear shaft, gears, bearings, bolts, and lubricating oil supported by the suspension. The bolt ends are divided into solid meshes, and the middle part is divided into beam elements. The solid meshes at both ends and the beam elements are connected together by RBE2 elements. The principal point of the RBE2 element is located on the bolt centerline in the middle of the solid meshes at both ends, and serves as the node of the beam element. The RBE2 element selects the node on the end face of the solid mesh from the point. The cross section of the beam element is circular, and the diameter is equal to the nominal diameter of the bolt thread. The beam element is located near the bolt head.

2. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 1, characterized in that, Step two, Define the elastic modulus of the materials in the finite element model of each component. Poisson's ratio Coefficient of thermal expansion .

3. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 1, characterized in that, Step three The stiffness of the spring element is defined in a local rectangular coordinate system, with the origin of the rectangular coordinate system at... Choose a point on the geometric center line of the suspended inner sleeve. The axis is perpendicular to the ground and points upwards, intersecting the geometric center line of the suspended inner sleeve. The axis is along the geometric center line of the suspended inner sleeve. Shaft shaft and The axis is determined according to the right-hand rule; the stiffness of each spring element consists of 6 parts, which are along the local index coordinate system. Shaft stiffness ,along Shaft stiffness ,along Shaft stiffness , around Shaft stiffness , around Shaft stiffness and around Shaft stiffness ; , , Defined using a force-displacement relationship curve. , , It is defined by the relationship curve between torque and rotation angle.

4. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 1, characterized in that, Step four, First boundary condition: Constrain the outer surface nodes of each suspended outer sleeve; Second boundary condition: Constrain the rotational degrees of freedom of each gear shaft and differential housing about their respective centerlines; The rotational degrees of freedom of the gear shaft and differential housing are constrained by the RBE3 element. The RBE3 element is defined from the point on the rotation centerline. The principal point is selected as a node on a cross section of the gear shaft or differential housing, which is located between the bearing and the gear. Then, the rotational degrees of freedom of the RBE3 element from the point about the centerline are constrained. An RBE3 element needs to be established between each gear and bearing, and the rotational degrees of freedom of the RBE3 element from the point about the center line of the gear shaft or the center line of the differential housing should be constrained respectively.

5. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 1, characterized in that, Step five, Apply initial temperature to the transmission housing, mountings, bolts, bearings, gears, gear shafts, and differential housing; The initial temperature is defined as room temperature.

6. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 1, characterized in that, Step six, First load: The first load is a temperature load, which means applying a high temperature load to the transmission housing, mounting, bolts, bearings, gears, gear shafts and differential housing; Second load: The second load is the gear meshing force when the transmission is in any forward gear. The gear meshing force is applied to the gear through which the forward gear torque is experienced. The third load is the gear meshing force when the transmission is in reverse gear. The gear meshing force is applied to the gear through which the reverse torque is experienced. Fourth load: The fourth load is the impact load on the powertrain, which acts on the center of mass of the powertrain; The same temperature is applied to the transmission housing, mounts, bolts, bearings, gears, gear shafts, and differential housing, and the temperature value is greater than the normal operating temperature value of the transmission. Take the gear with the highest gear ratio when driving forward, and take the gear with the highest gear ratio when driving backward; The torque transmitted by the gear shaft on which the second and third loads are based is equal to 2.5 times the rated torque of the motor multiplied by the gearbox ratio; The gear meshing force is decomposed into circumferential force, radial force, and axial force, and calculated using the following formula. This is achieved using a local cylindrical coordinate system defined on the center lines of each gear shaft. The shaft is along the centerline of the gear shaft. Along the radial direction of the gear shaft, Depend on , Determined according to the right-hand rule; （1） In the formula, , , These are the circumferential force, radial force, and axial force of the gear, respectively. The torque transmitted by the gears; The pitch circle diameter of the gear; The normal pressure angle of the gear; The helix angle at the pitch circle of the gear; Gear circumferential force radial force and axial force The RBE3 element is applied to the gear meshing node. The slave point of the RBE3 element selects the gear meshing node, and the master point of the RBE3 element selects the tooth surface element node with at least 2 teeth near the gear meshing node. The fourth load is the downward vertical impact load on the powertrain, which is equal to 7 times the weight of the powertrain.

7. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 6, characterized in that, Step seven, The first calculation case includes the first and second boundary conditions in step four, the initial temperature in step five, and the first, second, and fourth loads in step six. The second calculation condition includes the first and second boundary conditions in step four, the initial temperature in step five, and the first, third, and fourth loads in step six.

8. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 7, characterized in that, Step eight, According to the first and second calculation conditions defined in step seven, the quasi-static finite element method is used to perform finite element analysis of the bolt working load in sequence, taking into account geometric nonlinearity.

9. The method for predicting the working tensile force of connecting bolts in a new energy vehicle transmission housing according to claim 1, characterized in that, Step nine, Extract the axial loads of the beam elements in step one under the first and second calculation conditions respectively. An axial load greater than zero indicates that the bolt working load is tensile, an axial load equal to zero indicates that the bolt does not bear a working load, and an axial load less than zero indicates that the bolt working load is compressive. The axial load greater than zero is the bolt working tensile force, and the maximum value should not exceed 1 times the bolt preload. If it exceeds this value, increase the bolt diameter and performance grade in step one, and repeat steps one to nine until the maximum bolt working tensile force meets the requirements. The bolt preload is calculated using the following formula; （2） In the formula, This refers to the preload of the bolts. This refers to the bolt tightening torque; This is the bolt tightening torque coefficient; The diameter of the bolt; Based on the maximum tensile force of the beam element calculated in the first and second calculation conditions, all selected bolts have the same specifications and performance level.

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