CN112329313A - Power battery pack fatigue life calculation method - Google Patents
Power battery pack fatigue life calculation method Download PDFInfo
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Abstract
The invention discloses a method for calculating the fatigue life of a power battery pack, which comprises two working conditions of multi-axis vibration fatigue analysis and torsional fatigue, wherein the load input of the two working conditions of vibration fatigue analysis and torsional fatigue is from experimental measured data, and the influence of welding spots and welding seams in a key area of the power battery pack on the fatigue life is considered.
Description
The technical field is as follows:
the invention relates to the technical field of new energy automobiles, in particular to a method for calculating the fatigue life of a power battery pack.
Background art:
the power battery pack is a core component of the new energy automobile, is the heart of the new energy automobile, and the performance of the power battery pack not only influences the driving comfort and reliability of the automobile, but also influences the safety of the new energy automobile. The structural mechanical properties of the power battery pack are the basis for reliability and safety. The fatigue life of the power battery pack is predicted through the simulation analysis technology, the optimization of the power battery pack is an important part of the structural design of the power battery pack, the mechanical property of the power battery pack can be improved through the simulation analysis technology, and the performance and the quality of the power battery pack are improved. Structural mechanics analysis of a conventional battery pack has modes of fixed frequency, frequency sweep, random vibration and the like, and the analysis methods mainly depend on relevant standards, such as GB/T31467 lithium ion power storage battery pack and system for electric vehicles, ISO 12405 test specifications of electric road vehicles-lithium ion traction battery packs and systems, SAE J2380 standard for vibration test of electric vehicles and the like, and the standards are not unified per se. Meanwhile, the standards only consider the vibration in the X, Y and Z directions, do not consider the complex vibration and are often deviated from the actual working condition. In addition, when the vehicle runs on an uneven road surface, the vehicle has a certain torsion angle and drives the power battery pack to twist, and the conventional analysis does not include the analysis of the torsion strength. Through failure fault analysis of a certain commercial vehicle battery pack, torsional fatigue failure is also one of the reasons for failure of the battery pack. Therefore, how to accurately calculate the fatigue life of the battery pack is a problem which needs to be solved at present.
The invention content is as follows:
the invention aims to provide a method for calculating the fatigue life of a power battery pack, which comprises the following steps:
a. acquiring an acceleration load: arranging 3 three-way acceleration sensors on a cross beam near the power battery pack, and collecting an acceleration load spectrum of the power battery pack on a typical road surface of a test field;
b. and (3) acceleration load processing: carrying out data rationality check on the measured acceleration load spectrum, selecting a relevant channel for filtering, and removing low-frequency and high-frequency parts with little influence on fatigue strength;
c. establishing a vibration fatigue finite element model: establishing a finite element model of a frame cut-off belt power battery pack, simulating welding spots and welding seams of a key area of the power battery pack by using a shell unit, carrying out constrained modal analysis, and judging whether the model meets the calculation requirement so as to apply an acceleration load spectrum;
d. calculating modal stress and modal coordinates: c, applying the acceleration load spectrum obtained by processing in the step b to the finite element model established in the step c, applying forced acceleration excitation at the position of the acceleration measuring point, and calculating modal stress and modal coordinates by adopting a modal stress recovery method;
e. transient method vibration fatigue analysis: d, substituting the modal stress and the modal coordinate file obtained in the step d into a fatigue analysis program, calculating the multi-axis vibration fatigue life of the shell, the welding spot and the welding line of each pavement power battery pack, and accumulating the fatigue damage values of each pavement to obtain the total fatigue damage value of all units of the power battery pack;
f. and (3) measuring the torsion angle of the vehicle frame: measuring the torsion angle of the frame of the vehicle under the limit torsion working condition;
g. establishing a torsional fatigue finite element model: establishing a finite element model of the frame assembly with the power battery pack, wherein the modeling method of the power battery pack is the same as that in the step c;
h. calculating unit load torsional stress: calculating the stress of the power battery pack under a unit torsion angle;
i. torsion fatigue analysis: substituting the torsional stress of the battery pack obtained in the step h into a fatigue analysis program, and calculating the torsional fatigue life of the shell of the power battery pack, the key welding points and the key welding lines;
j. and judging a result, and optimizing the structural design: optimizing the structure of the power battery pack according to the fatigue damage calculation results of the shell, the key welding points and the key welding lines of the power battery pack of e and i, so that the fatigue life of the power battery pack meets the requirement;
furthermore, two three-way acceleration sensors are arranged at the left and right positions of a front axle in front of the power battery pack in the step a, a three-way acceleration sensor is arranged in the middle of a frame cross beam behind the power battery pack, the sampling frequency of an acceleration load spectrum is 512Hz, and the arranged three-way acceleration sensors can truly reflect the actual vibration of the power battery pack, so that the simulation is more accurate compared with the traditional single-axle fixed frequency, frequency sweep and random vibration simulation.
Furthermore, the typical road surface in the step a includes belgium roads and short wave roads, and does not include a twisted road, and the twisted road surface is a low-frequency signal, and the error of the acceleration signal to the acquired low-frequency signal is large, and the distortion phenomenon is serious, so the twisted road surface is not used as the object for acquiring the acceleration signal.
Furthermore, the relevant channels in the step b are left front X and Z direction channels, the right front point is an X and Z direction channel, and the right middle point is a Y and Z direction channel.
Further, in the step b, the acceleration load spectrum is filtered, and frequency components of 0-5 Hz and above 35Hz in the signal are removed.
Further, the model in the step c meets the condition that the frequency value of the first-order mode of the frame truncation part under the constraint condition is not less than 40 Hz.
Furthermore, key areas of welding seams in the step c are four corners of the upper shell and the lower shell of the power battery pack, and key areas of welding spots are parts for connecting the longitudinal beam and the lower shell of the power battery pack.
And c, simulating the power battery pack core body in the finite element model in the step c by adopting a hexahedral unit, and connecting the power battery pack core body with the lower shell in a contact and gluing part by adopting TIE binding contact.
Furthermore, in the step c, the upper and lower metal plate welding cores of the welding spot in the finite element model are respectively composed of 12 quadrilateral shell units, the upper welding core and the lower welding core are connected by adopting a BAR beam unit, the length of the BAR beam unit is 0.5 times of the sum of the thicknesses of the welded pieces, and the elastic modulus of the inner welding core material is 8.4 multiplied by 106MPa, elastic modulus of the outer welding core material is 2.1 multiplied by 105MPa。
Furthermore, in the step c, nodes on one side of the quadrilateral units in the splicing welding of the power battery pack in the finite element model are necessarily on a welding line, the two sides of the welding line are the quadrilateral units, and the size of the quadrilateral units is 2-4 times of the thickness of the material.
Furthermore, in the step c, the power battery pack is connected with the frame through a rubber bushing, the rubber bushing is simulated by a CBUSH unit, the rigidity of the CBUSH in six directions is consistent with the design value, and the damping parameter of the CBUSH is set according to the following formula.
B, damping parameters;
λ -is the ratio of the dynamic stiffness to the static stiffness of the rubber bushing;
k is the stiffness of CBUSH in each direction;
omega-is the circular frequency, the value of which is equal to 2 pi f, f being the vibration frequency.
Further, the global structural damping coefficient G of the whole model in the finite element model in step c is set to 0.02.
Further, in the finite element model in the step d, the left front point constrains X, Z directional degrees of freedom, the right front point constrains X, Z directional degrees of freedom, and the rear midpoint constrains Y, Z directional degrees of freedom.
Furthermore, in the step e, the fatigue life of the welding spot, the welding seam and the structural part is calculated by considering the survival rate, the survival rate is set to be 99.9%, the higher the survival rate is, the larger the safety margin is, and the fatigue life of the welding spot is calculated by adopting a structural stress method.
Further, the total fatigue damage value D of all the units of the power battery pack in the step evComprises the following steps:
Dv＝C1D1+C2D2+…+CnDn
Dv: a total damage value on each cell of the power battery pack;
Cn: cycle number on n number of pavement;
Dn: and (3) fatigue damage value of the n-number road surface which is cycled once.
Furthermore, the limit torsion angle of the vehicle in the step f is measured under a quasi-static condition, the working condition is that the left front wheel is lifted by 150mm, the right rear wheel is lifted by 150mm, and the torsion angle of the front shaft and the rear shaft of the frame is measured to be theta.
Further, the finite element model in the step g comprises a frame, a front axle, a power battery pack and a dummy leaf spring.
Further, the working condition of the torsional fatigue life calculation in the step i is that the torsional angle of the front axle and the rear axle of the frame is-1.25 theta, and the cycle frequency is 15 ten thousand times.
Furthermore, the requirement on the fatigue life of the power battery pack in the step j is as follows:
Dvmax≤0.2,DTmax≤1.0；
Dvmax-maximum value of total fatigue life of each unit on the power battery pack under acceleration load excitation;
DTmaxthe maximum value of the fatigue life of each unit on the power battery pack under the torsion working condition.
Compared with the prior art, the invention has the beneficial effects that:
1. the method for calculating the fatigue life of the power battery pack not only comprises the test of the multi-axis vibration fatigue strength, but also comprises the torsional fatigue strength, and accurately and comprehensively considers the stress load of the power battery pack on various pavements, so that the method can quickly and effectively evaluate the performance of the power battery pack structure and help engineering technicians to carry out risk prediction on the power battery pack, thereby carrying out targeted optimization on the power battery pack and improving the performance of the power battery pack;
2. according to the method for calculating the fatigue life of the power battery pack, translation in three directions of X, Y, Z and rotation in the X, Y, Z space direction of the power battery pack are considered in multi-axis vibration fatigue analysis, load signals of the vibration are measured and converted through an acceleration sensor arranged on a real vehicle, actual vibration of the power battery pack is truly reflected, and compared with traditional single-axis fixed frequency, frequency sweep and random vibration simulation, the method is more accurate;
3. according to the method for calculating the fatigue life of the power battery pack, the power battery pack with the flexible connection structure is considered in vibration fatigue analysis, a rubber bushing modeling method is provided, the modeling precision is improved, and the simulation error is reduced;
4. according to the method for calculating the fatigue life of the power battery pack, welding points and welding lines of key parts are considered in multi-axis vibration fatigue analysis, a welding line modeling method is provided, and a gravity area is defined, so that the modeling efficiency of an engineer is improved, and the simulation precision is improved.
Description of the drawings:
FIG. 1 is a flow chart of a method for calculating fatigue life of a power battery pack according to the present invention;
FIG. 2 is a diagram illustrating the distribution of acceleration sensors in a multi-axis vibration fatigue analysis according to the present invention;
FIG. 3 is a diagram of a finite element model in a multi-axis vibration fatigue analysis according to the present invention;
FIG. 4 is a key weld on the upper shell of a power battery pack according to the present invention;
FIG. 5 is a key weld on a power cell pack lower housing according to the present invention;
FIG. 6 is a key weld point for connection of a stringer and a lower housing of a power battery pack according to the present invention;
FIG. 7 is a schematic view of a weld modeling according to the present invention;
FIG. 8 is a schematic modeling diagram of a splice weld joint according to the present invention;
FIG. 9 is a schematic diagram of a torsional fatigue analysis finite element model according to the present invention.
The specific implementation mode is as follows:
in order to make the objects, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. The examples, in which specific conditions are not specified, were conducted under conventional conditions or conditions recommended by the manufacturer. The reagents or instruments used are not indicated by the manufacturer, and are all conventional products available commercially.
Example 1: as shown in fig. 1, a method for calculating the fatigue life of a power battery pack includes the following steps:
a. acquiring an acceleration load: arranging 3 three-way acceleration sensors on a cross beam near the power battery pack, wherein the types of the acceleration sensors are as follows: the PCB 356A26 is used for collecting an acceleration load spectrum of the power battery pack on a typical road surface of a test field;
b. and (3) acceleration load processing: carrying out data rationality check on the measured acceleration load spectrum, selecting a relevant channel for filtering, and removing low-frequency and high-frequency parts with little influence on fatigue strength;
c. establishing a vibration fatigue finite element model: establishing a finite element model of a frame cut-off belt power battery pack, simulating welding spots and welding seams of a key area of the power battery pack by using a shell unit, carrying out constrained modal analysis, and judging whether the model meets the calculation requirement so as to apply an acceleration load spectrum;
d. calculating modal stress and modal coordinates: applying the acceleration load spectrum obtained by processing in the step b to the finite element model established in the step c, applying forced acceleration excitation at the position of an acceleration measuring point, applying an acceleration load consistent with the test at the position of the measuring point, and calculating modal stress and modal coordinates by adopting a modal stress recovery method;
e. transient method vibration fatigue analysis: d, substituting the modal stress file and the modal coordinate file obtained in the step d and SN curves of sheet metal materials, welding spots and welding seams into a fatigue analysis program (such as FEMFAT) to calculate the multi-axial vibration fatigue life of each pavement power battery pack shell, welding spot and welding seam, and accumulating the fatigue damage values of each pavement to obtain the vibration total fatigue damage value of all units of the power battery pack;
f. and (3) measuring the torsion angle of the vehicle frame: measuring the torsion angle of the frame of the vehicle under the limit torsion working condition;
g. establishing a torsional fatigue finite element model: establishing a finite element model of the frame assembly with the power battery pack, wherein the modeling method of the power battery pack is the same as that in the step c;
h. calculating unit load torsional stress: calculating the stress of the power battery pack under a unit torsion angle, simulating the working condition that the rear shaft is fixed and the front shaft is twisted by 1 degree around the X-axis of the vehicle, and calculating the stress of the power battery pack;
i. torsion fatigue analysis: b, substituting the torsional stress and the cycle number of the battery pack obtained in the step h and SN curves of the sheet metal materials, the welding spots and the welding seams into a fatigue analysis program (such as FEMFAT) to calculate the torsional fatigue life of the shell of the power battery pack, the key welding spots and the key welding seams;
j. and judging a result, and optimizing the structural design: optimizing the structure of the power battery pack according to the fatigue damage calculation results of the shell, the key welding points and the key welding lines of the power battery pack of e and i, so that the fatigue life of the power battery pack meets the requirement;
as shown in fig. 2, in the step a, two three-way acceleration sensors are arranged at left and right positions of a front axle in front of a power battery pack, one three-way acceleration sensor is arranged in the middle of a frame cross beam behind the power battery pack, the sampling frequency of an acceleration load spectrum is 512Hz, the multi-axis vibration fatigue frequency range researched by the power battery pack is 5-35 Hz, the set sampling frequency is higher than the research frequency range of 10 times, the sampling frequency is higher than 350Hz, the signal research frequency with the sampling frequency higher than 10 times does not cause obvious amplitude distortion, and the higher the sampling frequency is, the closer the acquired digital signal is to a real signal.
The typical road surface in the step a comprises a Belgium road and a short wave road, and does not comprise a twisted road, and the twisted road surface is a low-frequency signal, so that the error of the acceleration signal to the acquired low-frequency signal is large, and the distortion phenomenon is serious, so that the twisted road surface is not used as an object for acquiring the acceleration signal.
In the step b, the relevant channels are left front X and Z direction channels, the right front point is an X direction channel and a Z direction channel, the right middle point is a Y direction channel and a Z direction channel, the selection of the number of the channels ensures that the frame truncation in the finite element model cannot be over-constrained, and the simulated frame truncation has 6-direction degrees of freedom, namely translation in X, Y, Z three directions and rotation in X, Y, Z three directions.
And in the step b, filtering the acceleration load spectrum, eliminating frequency components of 0-5 Hz and above 35Hz in the signals, wherein the frequency components of 0-5 Hz are frequency signals, adopting acceleration signals to directly input the signals inaccurately, neglecting the influence of low-frequency signals on fatigue strength, and neglecting the influence of high-frequency signals above 35Hz on the fatigue of the power battery pack structure.
The model in the step C meets the condition that the frequency value of the first-order mode of the frame truncation part under the constraint condition is not less than 40Hz, the finite element model established in the step C is shown in figure 3, the frame truncation comprises the acceleration measuring points A, B and C in the step a, X, Y translational freedom degrees of the positions A and B are constrained, Y freedom degrees and Z freedom degrees of the positions C are constrained, the frequency value of the first-order mode of the frame truncation is calculated to be 48.3Hz, and the requirement that the frequency value of the first-order mode is not less than 40Hz is met, namely the frame truncation can only generate 3 translational freedom degrees and 3 rotational freedom degrees, and the frame is a rigid body relative to the power battery pack.
As shown in fig. 4, 5 and 6, in the step c, key areas of welding seams are four corners of the upper and lower shells of the power battery pack, and key areas of welding spots are parts for connecting the longitudinal beams and the lower shell of the power battery pack.
And c, simulating the power battery pack core body in the finite element model by adopting a hexahedral unit, connecting the power battery pack core body with the lower shell in a contact and gluing mode by adopting TIE binding contact, namely rigidly connecting the power battery pack core body with the lower shell in a contact plane of the gluing part, and preventing the binding area from generating relative motion and deformation.
As shown in fig. 7, in the finite element model in step c, the upper and lower metal plate nuggets of the welding spot are each composed of 12 quadrilateral shell units, the upper and lower nuggets are connected by BAR beam units, the upper nugget is a nugget of the welded article 1, the lower nugget is a nugget of the welded article 2, the length of the BAR beam unit is 0.5 times the sum of the thicknesses of the welded articles, and the elastic modulus of the inner nugget material is 8.4 × 106MPa, elastic modulus of the outer welding core material is 2.1 multiplied by 105MPa。
As shown in fig. 8, in the splicing welding of the power battery pack in the finite element model in step c, a node on one side of the quadrilateral unit is necessarily on a weld line, two sides of the weld line are the quadrilateral units, the size of the quadrilateral unit is 2-4 times of the material thickness, the thickness of the upper and lower shells of the power battery pack is 1mm, and the size of the quadrilateral units on two sides of the weld line is 4 mm.
In the step c, the power battery pack is connected with the frame through a rubber bushing, the rubber bushing is simulated by a CBUSH unit, the rigidity in six directions of the CBUSH is consistent with the design value, the damping parameter of the CBUSH is set according to the following formula, the CBUSH is a connecting unit and is a universal six-direction spring-damper unit, and the rigidity and the damping in up to 6 directions (three translation and three rotation) can be defined.
B, damping parameters;
lambda is the ratio of the dynamic stiffness to the static stiffness of the rubber bushing, and the selected value is 1.025;
k is the stiffness of CBUSH in each direction;
omega-is the circular frequency, the value of which is equal to 2 pi f, f being the vibration frequency.
And c, setting the global structural damping coefficient G of the whole model in the finite element model to be 0.02.
In the step d, the left front point in the finite element model restrains X, Z directional freedom degree, the right front point restrains X, Z directional freedom degree, and the rear middle point restrains Y, Z directional freedom degree, so that the frame stage in the finite element model cannot be over-restrained, and the simulation frame is ensured to cut off X, Y, Z translational motion in three directions and rotate 6 directional freedom degrees.
In the step e, the fatigue life of the welding spot, the welding seam and the structural part is calculated by considering the survival rate, the survival rate is set to be 99.9%, the fatigue life of the welding spot is calculated by adopting a structural stress method, the grid of the welding spot is fine by adopting the structural stress method, the calculation result precision is high, the post-processing judgment of which platinum of the welding spot fails is convenient, the higher the survival rate is set, the larger the safety margin is, the relationship between the stress borne by the battery pack and the time can be represented by the product of the modal stress and the modal coordinate, the larger the stress amplitude is, the moreTotal damage value DvThe larger the size, the more easily the battery pack is damaged.
E, the total fatigue damage value D of all the units of the power battery packvComprises the following steps:
Dv＝C1D1+C2D2+…+CnDn
Dv: a total damage value on each cell of the power battery pack;
Cn: cycle number on n number of pavement;
Dn: and (3) fatigue damage value of the n-number road surface which is cycled once.
Example 1: the loss value of 1 time of circulation of the node number 403826 on the welding seam of the power battery pack on the road surface at Belgium No. 1 is 1.6e-5And the loss value of 1 cycle on No. 2 short wave road surface is 2.2e-6Then the node number 403826 total damage value is:
Dv＝C1D1+C2D2；
Dv: a total damage value on each cell of the power battery pack;
C1: number of cycles on Belgium road No. 1, C1＝20440；
C2: number of cycles on short wave road surface No. 2, C2＝4088；
Dv＝20440×1.6e-5+4088×2.2e-60.33 > 0.2 does not meet the requirements.
Example 2: the loss value of the power battery pack weld joint node number 1905295 circulating on the road surface for 1 time at Belgium No. 1 is 2.81e-6And the loss value of 1 cycle on No. 2 short wave pavement is 1.05e-6Then the node number 1905295 total damage value is:
Dv＝C1D1+C2D2；
Dv: a total damage value on each cell of the power battery pack;
C1: number of cycles on Belgium road No. 1, C1＝20440；
C2: number of cycles on short wave road surface No. 2, C2＝4088；
Dv＝20440×2.81e-6+4088×1.05e-6The requirement is satisfied when the value is 0.062 < 0.2.
And f, measuring the limit torsion angle of the vehicle under a quasi-static condition, wherein the working condition is that the left front wheel is lifted by 150mm, the right rear wheel is lifted by 150mm, and measuring to obtain the torsion angle theta of the front shaft and the rear shaft of the frame, which is equal to 0.8 deg.
As shown in fig. 9, the finite element model in step g includes a frame, a front axle, a power battery pack, and a dummy leaf spring.
And (5) calculating the torsional fatigue life in the step i under the working condition that the torsional angle of the front axle and the rear axle of the frame is-1 DEG, and the cycle frequency is 15 ten thousand times.
The requirement of the fatigue life of the power battery pack in the step j is as follows:
Dvmax≤0.2,DTmax≤1.0；
Dvmax-maximum value of total fatigue life of each unit on the power battery pack under acceleration load excitation;
DTmaxthe maximum value of the fatigue life of each unit on the power battery pack under the torsion working condition.
It will be evident to those skilled in the art that the invention is not limited to the details of the foregoing illustrative embodiments, and that the present invention may be embodied in other specific forms without departing from the spirit or essential attributes thereof. The present embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein, and any reference signs in the claims are not intended to be construed as limiting the claim concerned.
Furthermore, it should be understood that although the present description refers to embodiments, not every embodiment may contain only a single embodiment, and such description is for clarity only, and those skilled in the art should integrate the description, and the embodiments may be combined as appropriate to form other embodiments understood by those skilled in the art.
Claims (19)
1. A power battery pack fatigue life calculation method is characterized by comprising the following steps:
a. acquiring an acceleration load: arranging 3 three-way acceleration sensors on a cross beam near the power battery pack, and collecting an acceleration load spectrum of the power battery pack on a typical road surface of a test field;
b. and (3) acceleration load processing: carrying out data rationality check on the measured acceleration load spectrum, selecting a relevant channel for filtering, and removing low-frequency and high-frequency parts with little influence on fatigue strength;
c. establishing a vibration fatigue finite element model: establishing a finite element model of a frame cut-off belt power battery pack, simulating welding spots and welding seams of a key area of the power battery pack by using a shell unit, carrying out constrained modal analysis, and judging whether the model meets the calculation requirement so as to apply an acceleration load spectrum;
d. calculating modal stress and modal coordinates: c, applying the acceleration load spectrum obtained by processing in the step b to the finite element model established in the step c, applying forced acceleration excitation at the position of the acceleration measuring point, and calculating modal stress and modal coordinates by adopting a modal stress recovery method;
e. transient method vibration fatigue analysis: d, substituting the modal stress and the modal coordinate file obtained in the step d into a fatigue analysis program, calculating the multi-axis vibration fatigue life of the shell, the welding spot and the welding line of each pavement power battery pack, and accumulating the fatigue damage values of each pavement to obtain the total fatigue damage value of all units of the power battery pack;
f. and (3) measuring the torsion angle of the vehicle frame: measuring the torsion angle of the frame of the vehicle under the limit torsion working condition;
g. establishing a torsional fatigue finite element model: establishing a finite element model of the frame assembly with the power battery pack, wherein the modeling method of the power battery pack is the same as that in the step c;
h. calculating unit load torsional stress: calculating the stress of the power battery pack under a unit torsion angle;
i. torsion fatigue analysis: substituting the torsional stress of the battery pack obtained in the step h into a fatigue analysis program, and calculating the torsional fatigue life of the shell of the power battery pack, the key welding points and the key welding lines;
j. and judging a result, and optimizing the structural design: and e, optimizing the structure of the power battery pack according to the fatigue damage calculation results of the shell, the key welding points and the key welding lines of the power battery pack of the e and the i, so that the fatigue life of the power battery pack can meet the requirement.
2. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein in the step a, two three-way acceleration sensors are arranged at left and right positions of a front axle in front of the power battery pack, a three-way acceleration sensor is arranged in the middle of a frame cross beam behind the power battery pack, and the sampling frequency of an acceleration load spectrum is 512 Hz.
3. The method for calculating the fatigue life of the power battery pack according to claim 1 or 2, wherein the typical road surface in the step a comprises a Belgium road and a short wave road.
4. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein the relevant channels in the step b are X-direction and Z-direction channels at a left front point, X-direction and Z-direction channels at a right front point, and Y-direction and Z-direction channels at a rear middle point.
5. The method for calculating the fatigue life of the power battery pack according to claim 1 or 4, wherein in the step b, the acceleration load spectrum is filtered, and frequency components of 0-5 Hz and above 35Hz in the signal are removed.
6. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein the model in the step c meets the condition that the frequency value of the first-order mode frequency of the frame truncation part under the constraint condition is not less than 40 Hz.
7. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein key areas of welding seams in the step c are four corners of the upper and lower shells of the power battery pack, and key areas of welding spots are parts where a longitudinal beam and the lower shell of the power battery pack are connected.
8. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein in the finite element model in the step c, the power battery pack core body is simulated by using hexahedral units, and the contact and adhesive parts of the power battery pack core body and the lower shell are connected by using binding contact pairs.
9. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein in the step c, the upper and lower metal plate welding cores of the welding point in the finite element model are respectively composed of 12 quadrilateral shell units, the upper welding core and the lower welding core are connected by a BAR beam unit, the length of the beam unit is 0.5 times of the sum of the thicknesses of the welded parts, and the elastic modulus of the material of the inner welding core is 8.4 x 106MPa, elastic modulus of the outer welding core material is 2.1 multiplied by 105MPa。
10. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein in the step c, the nodes on one side of the quadrilateral elements in the splicing welding of the power battery pack in the finite element model are necessarily on the weld line, the quadrilateral elements are arranged on two sides of the weld line, and the size of the quadrilateral elements is 2-4 times of the thickness of the material.
11. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein the power battery pack and the frame in the step c are connected through rubber bushings, the rubber bushings are simulated by CBUSH units, the six-direction rigidity of the CBUSH is consistent with a design value, and damping parameters of the CBUSH are set according to the following formula.
B, damping parameters;
λ -is the ratio of the dynamic stiffness to the static stiffness of the rubber bushing;
k is the stiffness of CBUSH in each direction;
omega-is the circular frequency, the value of which is equal to 2 pi f, f being the vibration frequency.
12. A power battery pack fatigue life calculation method according to any one of claims 1, 6, 7, 8, 9, 10, and 11, wherein the global structural damping coefficient G of the whole model in the finite element model in step c is set to 0.02.
13. The method for calculating the fatigue life of the power battery pack as claimed in claim 1, wherein in the finite element model in the step d, the left front point constrains X, Z directional degrees of freedom, the right front point constrains X, Z directional degrees of freedom, and the rear midpoint constrains Y, Z directional degrees of freedom.
14. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein the fatigue life of the welding spot, the welding seam and the structural member in the step e is calculated by taking the survival rate into consideration, the survival rate is set to be 99.9%, and the fatigue life of the welding spot is calculated by adopting a structural stress method.
15. The method for calculating the fatigue life of the power battery pack according to claim 1 or 14, wherein the total fatigue damage value D of all the units of the power battery pack in the step e isvComprises the following steps:
Dv＝C1D1+C2D2+…+CnDn；
Dv: a total damage value on each cell of the power battery pack;
Cn: n-type road surfaceThe number of cycles above;
Dn: and (3) fatigue damage value of the n-number road surface which is cycled once.
16. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein the limit torsion angle of the vehicle in the step f is measured under a quasi-static condition, the working condition is that the left front wheel is lifted by 150mm, the right rear wheel is lifted by 150mm, and the torsion angle of the front axle and the rear axle of the frame is measured to be theta.
17. The method as claimed in claim 1, wherein the finite element model in the step g includes a frame, a front axle, a power battery pack and a dummy plate spring.
18. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein the working condition of the torsional fatigue life calculation in the step i is that the torsional angle of the front axle and the rear axle of the frame is-1.25 theta, and the cycle number is 15 ten thousand times.
19. The method for calculating the fatigue life of the power battery pack according to claim 1, wherein the requirement on the fatigue life of the power battery pack in the step j is as follows:
Dv max≤0.2,DT max≤1.0；
Dv max-maximum value of total fatigue life of each unit on the power battery pack under acceleration load excitation;
DT maxthe maximum value of the fatigue life of each unit on the power battery pack under the torsion working condition.
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Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113792376A (en) * | 2021-08-20 | 2021-12-14 | 合众新能源汽车有限公司 | Battery pack vibration fatigue analysis method and device |
| CN116538989A (en) * | 2023-07-07 | 2023-08-04 | 宁德时代新能源科技股份有限公司 | Battery torsion detection method, related device, battery, equipment and storage medium |
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2020
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Cited By (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| CN113792376A (en) * | 2021-08-20 | 2021-12-14 | 合众新能源汽车有限公司 | Battery pack vibration fatigue analysis method and device |
| CN116538989A (en) * | 2023-07-07 | 2023-08-04 | 宁德时代新能源科技股份有限公司 | Battery torsion detection method, related device, battery, equipment and storage medium |
| CN116538989B (en) * | 2023-07-07 | 2023-10-10 | 宁德时代新能源科技股份有限公司 | Battery torsion detection method, related device, battery, equipment and storage medium |
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