Explicit dynamics-based underpinning simulation method for power battery pack of electric vehicle

Abstract

The invention relates to an explicit dynamics-based underpinning simulation method for a power battery pack of an electric vehicle. The method comprises the following steps of: defining a working condition as an underpinning working condition; modeling an obstacle model; modeling a power battery pack model; modeling a tire model; a road surface model is of a rigid body structure, a whole vehicle dynamic model comprises a front suspension, a rear suspension, a power battery pack, tires, a vehicle body and other structures, the mass of parts such as a power assembly system and a steering system is equivalent to the vehicle body model, and it is guaranteed that the whole vehicle mass and the rotational inertia are consistent with design values before and after the whole vehicle mass and the rotational inertia are equivalent; a contact relation is established, after modeling is completed, model debugging is conducted on the whole vehicle model, and simulation calculation is started after model debugging is completed; and carrying out post-processing result analysis. According to the method, a detailed constitutive model of the power battery pack is established through underpinning simulation of the power battery pack of the whole-vehicle-level electric vehicle, the impact load between the battery pack and an obstacle is predicted, and the safety of the battery pack is evaluated in combination with the deformation response of the battery pack.

Description

Technical Field

[0001] The present invention belongs to the technical field of new energy vehicles, and in particular relates to a method for simulating the bottoming of a power battery pack of an electric vehicle based on explicit dynamics. Background Art

[0002] In recent years, with the growth of new energy vehicle ownership, the safety issue of vehicle spontaneous combustion caused by power battery packs has attracted much attention. Such accidents are mostly caused by collisions with foreign objects on the road or other mechanical loads, which cause the power battery pack to be impacted and squeezed, and the battery shell is deformed, resulting in short circuits or thermal runaway fires in electrical components such as module cells and high-voltage wiring harnesses. Therefore, the bottom collision safety of the power battery pack is extremely important.

[0003] At present, the simulation analysis of foreign object collision at the bottom of the power battery pack is mainly about the mechanical response of a single power battery pack under the impact of foreign objects, while the establishment of a vehicle system-level model and comparative analysis with experiments are still relatively rare. Simulation analysis of the impact of the power battery pack in the vertical direction (bottoming condition) is relatively rare. Summary of the invention

[0004] The purpose of the present invention is to provide an electric vehicle power battery pack bottoming simulation method based on explicit dynamics to solve the problem of vehicle-level electric vehicle power battery pack bottoming simulation.

[0005] The objective of the present invention is achieved through the following technical solutions:

[0006] A method for simulating the bottoming of a power battery pack of an electric vehicle based on explicit dynamics comprises the following steps:

[0007] A. The working condition is defined as the bottoming condition, that is, when the vehicle goes down the stepped road, the raised obstacles on the road surface impact the bottom of the vehicle vertically;

[0008] B. Obstacle model building:

[0009] The obstacle model is a combination of a hemisphere with a radius R of 90 mm and a cylinder. A three-axis force sensor is installed inside the sphere. The total height of the obstacle is expressed by formula (1):

[0010] H＝h+Δh (1)

[0011] Where: h is the ground clearance of the battery pack; Δh is the overlap between the battery pack and the obstacle;

[0012] C. Modeling of power battery pack:

[0013] Number the modules in sequence along the x-direction of the vehicle coordinate system, perform fine modeling on the collision module, connect the various parts of the module, and use rigid units to connect the bolt holes on both sides of the end plate to the battery frame to fix the module on the battery pack frame. Simplify the various parts of the module into a solid rectangular structure, and use rigid units to connect the module to the battery pack frame.

[0014] D. Tire model building: According to the tire size information, a tire cross-section model is built, and then a rotational sweep is performed to build a complete finite element model of the tire, such as Figure 5 The tire finite element model includes the rim, rim flange, bead cover, sidewall, inner tread, upper tread, and lower tread. The material properties of each part of the tire are shown in Table 1. The bead cover, upper tread, and lower tread are all made of rubber. The Mooney-Rivlin hyperelastic material model is used, which assumes that the material is in an ideal incompressible state and the Poisson's ratio is 0.5.

[0015] E. Vehicle-road simulation model building:

[0016] The road surface model consists of a stepped structure consisting of two road surfaces. The upper road surface is a horizontal straight road surface. The lower road surface includes a horizontal straight road surface and an obstacle. The lateral position of the obstacle from the center of the vehicle is consistent with the test, and the longitudinal position is determined according to the position of the collision module. The vehicle dynamics model includes the front suspension, rear suspension, power battery pack, tires and body structure. The mass of components such as the powertrain system and steering system is equivalent to the body model, and the equivalent front and rear vehicle mass and moment of inertia are guaranteed to be consistent with the design values.

[0017] F. Establishing contact relationships, including contact between the tire and the road surface, contact between the obstacle and the power battery pack, and self-contact within the power battery pack;

[0018] G. Model debugging: After the modeling is completed, the vehicle model is debugged to ensure that the suspension spring preload and the ground clearance of the power battery pack are consistent with the design values ​​during static balance;

[0019] H. After the model debugging is completed, simulation calculation begins;

[0020] I. Post-processing result analysis.

[0021] Further, in step B, a plurality of gaskets are arranged under the hemisphere, and the sampling frequency of the three-way sensor is 300 Hz, so as to collect the impact load when the power battery pack collides with an obstacle.

[0022] Furthermore, in step C, the parts are connected by gluing, welding or contacting.

[0023] Furthermore, in step D, the road surface model is a rigid structure, and its material properties are set to MAT_RIGI D (20).

[0024] Further, in step E, the upper road surface is 10 mm away from the lowest point of the wheel, and the two road surfaces of the lower road surface are vertically separated by 100 mm.

[0025] Furthermore, in step E, except for the rear suspension trailing arm which is a two-dimensional shell element, the control arms and subframes of the front and rear suspensions are simplified to rigid structures, and their material properties are set to MAT_RIGID(20); the stiffness properties of the elastic elements such as bushings, springs, shock absorbers, and limit blocks are retained, and their material properties are set to MAT_NONLINEAR_ELASTIC_DISCRETE_BEAM(67), MAT_SPRING_NONLINEAR_ELASTIC(S04), MAT_DAMPER_NONLINEAR_VISCOUS(S05), and MAT_SPING_NONLINEAR_ELASTIC(S04), respectively.

[0026] Furthermore, step F specifically includes the following steps:

[0027] F1, tire and road contact type: ONE_WAY_SURFACE_TO_SURFACE;

[0028] F2, contact type between obstacle and power battery pack: AUTOMATIC_SURFACE_TO_SUR FACE;

[0029] F3. Self-contact type inside the power battery pack: SINGLE_SURFACE.

[0030] Further, step G is specifically:

[0031] G1. The road surface is replaced with a horizontal straight road surface, excluding obstacles and steps, and the gap between the road surface and the tire is maintained at 10mm;

[0032] G2, constrain the road surface in 6 directions;

[0033] G3, perform free fall simulation of the whole vehicle, the duration is 0.5s, and the vehicle reaches a stable state;

[0034] G4, post-processing reads the contact force between the tire and the road surface and checks whether it is consistent with the design value;

[0035] G5. Post-processing reads the minimum gap between the power battery pack and the road surface, repeatedly adjusts the spring preload, and repeats the simulation until the ground clearance of the power battery pack is consistent with the design value.

[0036] Further, step H specifically includes the following steps:

[0037] H1. The initial state of the vehicle is set to be horizontal, and a gap of 10 mm is maintained between the upper road surface and the lowest point of the tire;

[0038] H2, release the longitudinal degree of freedom of the upper road surface, constrain the remaining 5 degrees of freedom; constrain the 6 degrees of freedom of the lower road surface;

[0039] H3. Use the BOUNDARY_PRESCRIBE_MOTION_RIGID function to apply a speed of 100 m / s to the upper road surface in the opposite direction of the vehicle's forward direction. The speed is 0 in the first 0.5s. The vehicle falls freely and reaches a balanced state. After 0.5-1s, the speed increases to the target speed. The vehicle falls freely again and collides with an obstacle.

[0040] H4. Use CONTROL_TERMINATION to set the simulation time to 3.5s, and use CONTROL_TIMESTEP to control the simulation step size, where TSSFAC = 0.9, DT2MS = -1e-007;

[0041] H5. Execute simulation calculations.

[0042] Furthermore, step I specifically includes the following steps:

[0043] I1. Read the file named binout000;

[0044] I2. Read the contact force between the obstacle and the power battery pack, which is mainly vertical force;

[0045] I3. Read the plastic deformation of the battery pack;

[0046] I4. Evaluate the safety of the battery pack according to relevant standards.

[0047] Compared with the prior art, the present invention has the following beneficial effects:

[0048] The electric vehicle power battery pack bottoming simulation method of the present invention is based on explicit dynamics. Through the whole vehicle-level electric vehicle power battery pack bottoming simulation, a detailed power battery pack constitutive model is established to predict the impact load between the battery pack and obstacles. Combined with the deformation response of the battery pack, the safety of the battery pack is evaluated. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0050] Figure 1 Working condition diagram;

[0051] Figure 2 Spherical obstacle model;

[0052] Figure 3 Schematic diagram of power battery pack;

[0053] Figure 4 Module finite element model, where Figure 4a To refine the model, Figure 4b To simplify the model;

[0054] Figure 5 Tire finite element model;

[0055] Figure 6 Complete vehicle model;

[0056] Figure 7 Modeling flowchart;

[0057] Figure 8 A flow chart of the steps of the electric vehicle power battery pack bottoming simulation method based on explicit dynamics of the present invention. DETAILED DESCRIPTION

[0058] The present invention will be further described below in conjunction with embodiments:

[0059] The electric vehicle power battery pack bottoming simulation method based on explicit dynamics of the present invention comprises the following steps:

[0060] 1. Working condition definition

[0061] like Figure 1 As shown, the present invention adopts a bottoming condition, which specifically refers to the vertical impact of a raised obstacle on the bottom of the vehicle when the vehicle goes down a stepped road.

[0062] 2. Obstacle modeling:

[0063] The important boundary conditions of the bottom support condition are the shape, size and height of the obstacle. The test obstacle is a hemisphere with a radius of 90 mm. Different numbers of pads under the hemisphere can adjust the height. A three-axis force sensor is installed inside the hemisphere with a sampling frequency of 300 Hz to collect the impact load when the power battery pack collides with the obstacle. The obstacle model is considered to be a rigid structure, such as Figure 2 As shown in the figure, it is obtained by combining a hemisphere with a radius R of 90 mm and a cylinder. The total height of the obstacle is expressed by formula (1):

[0064] H＝h+Δh (1)

[0065] Where: h is the ground clearance of the battery pack; Δh is the overlap between the battery pack and the obstacle.

[0066] 3. Power battery pack modeling: The power battery pack model is as follows Figure 3 As shown, in order to be consistent with the test conditions and the battery pack is a bilaterally symmetrical structure, only the battery pack is considered to collide on one side, and the modules are numbered in sequence along the x-direction (longitudinal) of the vehicle coordinate system. When the bottom of the battery pack collides with foreign objects, the stiffness of the battery module has a certain influence on the impact load. Therefore, the collision module must be modeled in a refined manner. The detailed structure of the module is shown in Figure 4a As shown in the figure, the various parts of the module are connected by gluing, welding, contact, etc., and the bolt holes on both sides of the end plate are connected to the battery frame by rigid units to fix the module on the battery pack frame. In order to balance the calculation accuracy and efficiency, the connection relationship between the internal parts of the module is ignored to ensure that the shape and quality of the module remain unchanged. The various parts of the module are simplified into a solid rectangular structure, as shown in Figure 4b As shown, the connection between the module and the battery pack frame adopts a rigid unit.

[0067] 4. Tire model building: According to the tire size information, build a tire cross-section model, and then perform a rotational sweep to build a complete finite element model of the tire, such as Figure 5 The tire finite element model includes the rim, rim flange, bead cover, sidewall, inner tread, upper tread, and lower tread. The material properties of each part of the tire are shown in Table 1. The bead cover, upper tread, and lower tread are all made of rubber. The Mooney-Rivlin hyperelastic material model is used, which assumes that the material is in an ideal incompressible state and the Poisson's ratio is 0.5.

[0068] 5. Vehicle-road simulation model building: based on Figure 1 , Figure 2 The whole vehicle-road simulation model is established by using the schematic diagram of Figure 6As shown. The road surface model is considered as a rigid structure, and its material property is set to MAT_RIGI D (20). It consists of two road surfaces forming a step structure. The upper road surface is a horizontal straight road surface, which is about 10 mm away from the lowest point of the wheel; the two lower road surfaces are 100 mm apart vertically, including a horizontal straight road surface and an obstacle. The lateral position of the obstacle from the center of the vehicle is consistent with the test, and the longitudinal position is determined according to the position of the collision module. The vehicle dynamics model includes structures such as the front suspension, rear suspension, power battery pack, tires and body. Except for the rear suspension trailing arm, which is a two-dimensional shell element, the control arms and subframes of the front and rear suspensions are simplified to rigid structures, and their material properties are set to MAT_RIGID(20); the stiffness properties of the bushings, springs, shock absorbers, and limit blocks are retained, and their material properties are set to MAT_NONLINEAR_ELASTIC_DISCRETE_BEAM(67), MAT_SPRING_NONLINEAR_ELASTIC(S04), MAT_DAMPER_NONLINEAR_VISCOUS(S05), and MAT_SPRING_NONLINEAR_ELASTIC(S04), respectively, so that the dynamic characteristics of the vehicle when colliding with obstacles are realistic and reliable. In addition, in order to improve the calculation efficiency, the mass of the powertrain system, steering system and other components is equivalent to the body model, and the equivalent front and rear vehicle mass and moment of inertia are guaranteed to be consistent with the design values.

[0069] 6. Contact relationship establishment: The contact relationship includes the contact between the tire and the road, the contact between the obstacle and the power battery pack, and the self-contact inside the power battery pack.

[0070] 61. Tire-road contact type: ONE_WAY_SURFACE_TO_SURFACE;

[0071] 62. Contact type between obstacle and power battery pack: AUTOMATIC_SURFACE_TO_SUR FACE;

[0072] 63. Self-contact type inside the power battery pack: SINGLE_SURFACE;

[0073] 7. Model debugging: After modeling is completed, the vehicle model must be debugged to ensure that the suspension spring preload and the ground clearance of the power battery pack are consistent with the design values ​​during static balance. The method is as follows:

[0074] 71. The road surface is replaced with a horizontal straight road surface, excluding obstacles and steps, and a 10mm gap is maintained between the road surface and the tire;

[0075] 72. Constrain the road surface in six directions;

[0076] 73. Perform free fall simulation of the whole vehicle, and the duration is 0.5s for the vehicle to reach a stable state;

[0077] 74. Post-processing reads the contact force between the tire and the road surface and checks whether it is consistent with the design value;

[0078] 75. Post-processing reads the minimum gap between the power battery pack and the road surface, repeatedly adjusts the spring preload, and repeats the simulation until the ground clearance of the power battery pack is consistent with the design value.

[0079] 8. After the model debugging is completed, the simulation calculation begins. The specific process is as follows:

[0080] 81. The initial state of the vehicle is set to be horizontal, and a gap of 10 mm is maintained between the upper road surface and the lowest point of the tire;

[0081] 82. Release the longitudinal degree of freedom of the upper road surface and constrain the remaining five degrees of freedom; constrain the six directions (full constraint) of the lower road surface;

[0082] 83. Use the BOUNDARY_PRESCRIBE_MOTION_RIGID function to apply a speed of 100m / s (infinite) to the upper road surface in the opposite direction of the vehicle's forward direction. The speed is 0 for the first 0.5s. The vehicle falls freely and reaches a balanced state. After 0.5-1s, the speed increases to the target speed. The vehicle falls freely again and collides with an obstacle.

[0083] 84. Use CONTROL_TERMINATION to set the simulation time to 3.5s. Use CONTROL_TIMESTEP to control the simulation step size, where TSSFAC = 0.9, DT2MS = -1e-007;

[0084] 85. Perform simulation calculations.

[0085] 9. Post-processing result analysis:

[0086] 91. Read the file named binout000;

[0087] 92. Read the contact force between the obstacle and the power battery pack, which is mainly vertical force;

[0088] 93. Read the plastic deformation of the battery pack;

[0089] 94. Evaluate the safety of battery packs according to relevant standards.

[0090] Note that the above are only preferred embodiments of the present invention and the technical principles used. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and that various obvious changes, readjustments and substitutions can be made by those skilled in the art without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in more detail through the above embodiments, the present invention is not limited to the above embodiments, and may include more other equivalent embodiments without departing from the concept of the present invention, and the scope of the present invention is determined by the scope of the appended claims.

Claims

1. A simulation method for the bottoming of an electric vehicle power battery pack based on explicit dynamics, characterized in that: The following steps are involved: A. The working condition is defined as the bottoming condition, that is, when the vehicle goes down the stepped road, the raised obstacles on the road surface impact the bottom of the vehicle vertically; B. Obstacle model building: The obstacle model is a combination of a hemisphere with a radius R of 90 mm and a cylinder. A three-axis force sensor is installed inside the sphere. The total height of the obstacle is expressed by formula (1): H=h+Δh (1) Where: h is the ground clearance of the battery pack; Δh is the overlap between the battery pack and the obstacle; C. Modeling of power battery pack: Number the modules in sequence along the x-direction of the vehicle coordinate system, perform fine modeling on the collision module, connect the various parts of the module, and use rigid units to connect the bolt holes on both sides of the end plate to the battery frame to fix the module on the battery pack frame. Simplify the various parts of the module into a solid rectangular structure, and use rigid units to connect the module to the battery pack frame. D. Tire model building: According to the tire size information, a tire cross-section model is established, and then a rotational sweep is performed to establish a complete finite element model of the tire, as shown in Figure 5. The tire finite element model includes the rim, rim flange, bead cover, sidewall, inner tread, upper tread, and lower tread. The material properties of each part of the tire are shown in Table 1. The bead cover, upper tread, and lower tread are all made of rubber. The Mooney-Rivlin hyperelastic material model is used, which assumes that the material is in an ideal incompressible state and the Poisson's ratio is 0.

5. E. Vehicle-road simulation model building: The road surface model consists of a stepped structure consisting of two road surfaces. The upper road surface is a horizontal straight road surface. The lower road surface includes a horizontal straight road surface and an obstacle. The lateral position of the obstacle from the center of the vehicle is consistent with the test, and the longitudinal position is determined according to the position of the collision module. The vehicle dynamics model includes the front suspension, rear suspension, power battery pack, tires and body structure. The mass of components such as the powertrain system and steering system is equivalent to the body model, and the equivalent front and rear vehicle mass and moment of inertia are guaranteed to be consistent with the design values. F. Establishing contact relationships, including contact between the tire and the road surface, contact between the obstacle and the power battery pack, and self-contact within the power battery pack; G. Model debugging: After the modeling is completed, the vehicle model is debugged to ensure that the suspension spring preload and the ground clearance of the power battery pack are consistent with the design values ​​during static balance; H. After the model debugging is completed, simulation calculation begins; I. Post-processing result analysis.

2. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: Step B: multiple gaskets are arranged under the hemisphere, and the sampling frequency of the three-way sensor is 300 Hz, so as to collect the impact load when the power battery pack collides with an obstacle.

3. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: Step C: the parts are connected by gluing, welding or contacting.

4. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: In step D, the pavement model is a rigid structure, and its material properties are set to MAT_RIGID(20).

5. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: In step E, the upper pavement is 10 mm away from the lowest point of the wheel, and the two pavements of the lower pavement are 100 mm apart vertically.

6. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: Step E: Except for the rear suspension trailing arm which is a two-dimensional shell element, the control arms and subframes of the front and rear suspensions are simplified to rigid structures, and their material properties are set to MAT_RIGID(20); the stiffness properties of the elastic elements such as bushings, springs, shock absorbers, and limit blocks are retained, and their material properties are set to MAT_NONLINEAR_ELASTIC_DISCRETE_BEAM(67), MAT_SPRING_NONLINEAR_ELASTIC(S04), MAT_DAMPER_NONLINEAR_VISCOUS(S05), and MAT_SPRING_NONLINEAR_ELASTIC(S04), respectively.

7. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: Step F specifically comprises the following steps: F1, tire and road contact type: ONE_WAY_SURFACE_TO_SURFACE; F2, contact type between obstacle and power battery pack: AUTOMATIC_SURFACE_TO_SUR FACE; F3. Self-contact type inside the power battery pack: SINGLE_SURFACE.

8. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: Step G is specifically: G1. The road surface is replaced with a horizontal straight road surface, excluding obstacles and steps, and the gap between the road surface and the tire is maintained at 10mm; G2, constrain the road surface in 6 directions; G3, perform free fall simulation of the whole vehicle, the duration is 0.5s, and the vehicle reaches a stable state; G4, post-processing reads the contact force between the tire and the road surface and checks whether it is consistent with the design value; G5. Post-processing reads the minimum gap between the power battery pack and the road surface, repeatedly adjusts the spring preload, and repeats the simulation until the ground clearance of the power battery pack is consistent with the design value.

9. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: Step H specifically comprises the following steps: H1. The initial state of the vehicle is set to be horizontal, and a gap of 10 mm is maintained between the upper road surface and the lowest point of the tire; H2, release the longitudinal degree of freedom of the upper road surface, constrain the remaining 5 degrees of freedom; constrain the 6 degrees of freedom of the lower road surface; H3. Use the BOUNDARY_PRESCRIBE_MOTION_RIGID function to apply a speed of 100 m / s to the upper road surface in the opposite direction of the vehicle's forward direction. The speed is 0 in the first 0.5s. The vehicle falls freely and reaches a balanced state. After 0.5-1s, the speed increases to the target speed. The vehicle falls freely again and collides with an obstacle. H4. Use CONTROL_TERMINATION to set the simulation time to 3.5s, and use CONTROL_TIMESTEP to control the simulation step size, where TSSFAC = 0.9, DT2MS = -1e-007; H5. Execute simulation calculations.

10. The electric vehicle power battery pack bottoming simulation method based on explicit dynamics according to claim 1, characterized in that: Step I specifically includes the following steps: I1. Read the file named binout000; I2. Read the contact force between the obstacle and the power battery pack, which is mainly vertical force; I3. Read the plastic deformation of the battery pack; I4. Evaluate the safety of the battery pack according to relevant standards.

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