CN114969971B - Solution for low-frequency brake noise of floating caliper disc brake - Google Patents
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Abstract
The invention relates to a method for solving low-frequency brake noise of a floating caliper disc brake, which is characterized by comprising the following steps of: the method comprises the following steps: s1: establishing a finite element analysis model of the automobile disc brake assembly, solving a rigidity and mass matrix of the brake assembly under a braking working condition, and calculating an assembly mode of the brake assembly under the braking condition; s2: carrying out frequency comparison and vibration mode comparison, and correcting the finite element analysis model of the automobile disc brake assembly; s3: performing decoupling analysis on the calculated unstable mode; s4: calculating modal strain energy of two-order adjacent modes, improving a part with the highest ratio of strain energy, and pulling open a frequency difference value of the two-order adjacent modes; and carrying out finite element analysis on the finally determined optimization scheme until the unstable mode is eliminated or the modal damping ratio of the unstable mode is smaller than a preset threshold value, and then carrying out noise test verification until the noise meets the test requirement.
Description
Technical Field
The invention belongs to the field of automobile disc brake, and relates to a method for solving low-frequency brake noise of a floating caliper disc brake.
Background
Brake squeal caused by brake friction has an important influence on the riding comfort of the automobile, and is a key and difficult problem in the industry and academia. At present, more braking noise development depends on foreign friction material manufacturers to change the formula to optimize the noise. Or the positions of the grooves and the chamfers of the brake blocks are changed by trial and error to find the rule, the development direction of noise is blind, the development period is long, and the generation excitation of the brake noise is great.
Disclosure of Invention
The invention provides a solution for low-frequency brake noise of a floating caliper disc brake.
In order to achieve the purpose, the invention provides the following technical scheme:
a solution for low frequency braking noise for a floating caliper disc brake comprising the steps of:
s1: establishing a finite element analysis model of the automobile disc brake assembly, solving a rigidity and mass matrix of the brake assembly under a braking working condition, and calculating an assembly mode of the brake assembly under a braking condition by taking a calculation result as an input of mode analysis;
s2: carrying out frequency comparison and vibration mode comparison, and if the difference between the frequency and the vibration mode existing in the test exceeds a threshold value, correcting the finite element analysis model of the automobile disc brake assembly until the calculation result meets the requirement;
s3: decoupling analysis is carried out on the calculated unstable mode;
s4: after determining the coupling component of the unstable mode, calculating the mode strain energy of two-order adjacent modes, improving the part with the highest strain energy ratio, and pulling away the frequency difference value of the two-order adjacent modes; and carrying out finite element analysis on the finally determined optimization scheme until the unstable mode is eliminated or the modal damping ratio of the unstable mode is smaller than a preset threshold value, and then carrying out noise test verification until the noise meets the test requirement.
Further, the step S1 specifically includes:
establishing a finite element analysis model of the automobile disc brake assembly by using general finite element analysis software ANSYS;
introducing friction coupling of a brake disc and a brake block into a motion equation of a structure, enabling a rigidity matrix of the structure to be an asymmetric matrix, solving a characteristic value of the asymmetric matrix structure to be a complex characteristic value, wherein a real part of the complex characteristic value represents stability of the structure, an imaginary part represents frequency, and a mode of the real part and the complex characteristic value is a modal damping ratio;
the larger the modal damping ratio is, the more unstable the modal is, when the real part of the complex eigenvalue is a positive value, the unstable modal represents that the order modal is an unstable modal, the unstable modal is 1 order formed by coupling two adjacent orders of real modal under the action of frictional coupling, and the two orders of modal vibration forms interfere with each other to generate self-excited vibration in the vibration process;
the larger the real part value of the complex eigenvalue is, the more unstable the structure is, the amplitude of the structure can exponentially increase along with time in the vibration process.
Further, step S1 specifically includes the following steps:
s11: performing mathematical discrete processing on a 3D brake model by using general finite element analysis software ANSYS, wherein the 3D brake model comprises a brake caliper assembly, a steering knuckle assembly and a brake disc;
s12: the discrete units of each part are given material parameters: inputting Young modulus, poisson ratio and density of isotropic material; for the brake pad, the anisotropic material is processed according to the orthotropic material, and 12 elastic constants measured by the experiment are input:
the above formula is the relationship between the stress, strain and elastic constants of orthotropic materials, where C 11 ～C 66 Is an elastic constant, σ x 、σ y 、σ z Stress in the directions of the x-axis, y-axis and z-axis, τ xy Shear stress in the x-and y-directions, τ yz Shear stress in the directions of the y-axis and z-axis, τ zx Shear stress in the z-and x-directions, ε x 、ε y 、ε z Strain in the x, y and z directions, respectively, gamma xy Is the angular strain, gamma, in the direction of the x-axis and the y-axis yz Is the angular strain, gamma, in the direction of the y-axis and the z-axis zx Is the angular strain in the z-axis and x-axis directions;
s13: simulating the load transmission behavior between the parts by establishing a contact equation of a connection surface unit between the parts:
in the formula, fn represents a normal contact force, kn represents normal contact rigidity, un represents contact penetration, ft represents a tangential contact force, kt represents tangential contact rigidity, ut represents contact slip distance, un represents contact penetration, and u represents a friction coefficient;
s14: and (3) defining constraint at the joint of the steering knuckle and the vehicle body connecting surface: inputting constraint rigidity with six degrees of freedom, and applying bolt pretightening force simulation bolt tightening process to a bolt simplified beam unit in the structure to define a brake load according to NVH experiment working conditions;
s15: using ANSYS finite element software to solve a rigidity matrix and a mass matrix of a structure of a brake assembly under a braking condition, wherein the rigidity matrix is a relation between load and displacement received by each node, and a calculation result is used as input of modal analysis to calculate an assembly mode of the brake assembly under the braking condition, frictional coupling of a brake disc and a brake pad is introduced into a motion equation of the structure, so that the rigidity matrix of the structure is an asymmetric matrix, a characteristic value for solving the asymmetric matrix structure is possibly a complex characteristic value, a real part of the complex characteristic value represents the stability of the structure, an imaginary part represents frequency, a module of the real part and the complex characteristic value is a modal damping ratio, a characteristic value with a positive real part is an unstable mode, and vibration exponentially increases along with time:
where { F } is the force due to the frictional coupling of the braking surfaces:
{F}＝[K F ]{μ}
in the formula [ K F ]The frictional coupling stiffness matrix represents the relationship between { F } and the node displacement { mu } [ K ] F ]Is asymmetric, yielding:
in the formula [ K-K F ]The characteristic matrix of the system is also asymmetric, when the characteristic is solved by using an ANSYS finite element software asymmetric solver, the real part of a characteristic value is a positive value, and a characteristic vector is solved at the same time:
λ＝-ζω±jω d
if the real part of the eigenvalue, ζ ω, is positive, the system is unstable due to the exponential growth of the vibration according to the response equation:
x(t)＝Ae -ζωt sin(ω d t+φ)。
further, the frequency comparison in step S2 includes: comparing the noise frequency appearing in the noise test with the unstable mode obtained by analysis, and if the frequency difference is within a preset threshold value, determining that the frequency similarity meets the requirement;
the mode shape comparison comprises the following steps: arranging acceleration sensor measuring points on a brake assembly to measure displacement vectors of the measuring points in three directions (X, Y and Z) in a vibration process, carrying out vector operation on the displacement vectors and the displacement vectors of corresponding points in an unstable mode, and if a calculation result reaches a preset threshold value, considering that the similarity between a simulated calculated vibration mode and a test vibration mode meets requirements;
and when the frequency value and the vibration mode value are different from the test, correcting the material parameters and boundary conditions of the finite element analysis model of the automobile disc brake assembly:
in the formula: { R jk },{R lk Respectively representing a displacement vector obtained by simulation analysis and an actually measured displacement vector; if { R } jk },{R lk If linear correlation exists before, the value of the MAC is close to 1, namely the calculated mode shape is completely consistent with the actual mode shape; otherwise, if the two are linearly independent, the MAC value is close to 0; and evaluating the consistency of the simulation analysis mode shape and the actual shape through the MAC value.
Further, in step S3, calculating modal results of different working conditions, and determining which two adjacent real modes of the order of unstable mode are coupled to form the order of unstable mode; the unstable mode is formed by coupling two adjacent real modes into 1 order under the action of frictional coupling, the two orders of mode vibration forms interfere with each other to generate self-excited vibration in the vibration process, decoupling analysis is needed to determine the composition of the coupling mode, the friction coefficient is dispersed in the analysis process, and the two independent real modes before coupling are respectively analyzed and found; then, the frequency difference of the two real modes is pulled apart by adjusting the structure, and the larger the frequency difference is, the larger the difference of the two real modes is, the probability of coupling is reduced.
Further, step S4 includes:
W＝1/2k(ΔL)(ΔL)
wherein W is strain energy, k is structural stiffness, and Δ L is strain.
The invention has the beneficial effects that: the invention can greatly shorten the development period of the braking noise and save the cost.
Additional advantages, objects, and features of the invention will be set forth in part in the description which follows and in part will become apparent to those having ordinary skill in the art upon examination of the following or may be learned from practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and claims thereof.
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For the purposes of promoting a better understanding of the objects, aspects and advantages of the invention, reference will now be made to the following detailed description taken in conjunction with the accompanying drawings in which:
FIG. 1 is a schematic flow chart of the method for solving the low frequency braking noise of the floating caliper disc brake according to the present invention;
FIG. 2 is a finite element analysis model;
FIG. 3 is a constraint stiffness input table;
fig. 4 is a diagram of a modal coupling process.
Detailed Description
The embodiments of the present invention are described below with reference to specific embodiments, and other advantages and effects of the present invention will be easily understood by those skilled in the art from the disclosure of the present specification. The invention is capable of other and different embodiments and of being practiced or of being carried out in various ways, and its several details are capable of modification in various respects, all without departing from the spirit and scope of the present invention. It should be noted that the drawings provided in the following embodiments are only for illustrating the basic idea of the present invention in a schematic way, and the features in the following embodiments and examples may be combined with each other without conflict.
Wherein the showings are for the purpose of illustrating the invention only and not for the purpose of limiting the same, and in which there is shown by way of illustration only and not in the drawings in which there is no intention to limit the invention thereto; to better illustrate the embodiments of the present invention, some parts of the drawings may be omitted, enlarged or reduced, and do not represent the size of an actual product; it will be understood by those skilled in the art that certain well-known structures in the drawings and descriptions thereof may be omitted.
The same or similar reference numerals in the drawings of the embodiments of the present invention correspond to the same or similar components; in the description of the present invention, it should be understood that if there is an orientation or positional relationship indicated by terms such as "upper", "lower", "left", "right", "front", "rear", etc., based on the orientation or positional relationship shown in the drawings, it is only for convenience of description and simplification of description, but it is not an indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and therefore, the terms describing the positional relationship in the drawings are only used for illustrative purposes, and are not to be construed as limiting the present invention, and the specific meaning of the terms may be understood by those skilled in the art according to specific situations.
Referring to FIG. 1, the present invention provides a solution for low frequency brake noise (1000-5000 Hz) for a floating caliper disc brake.
S1: the method comprises the steps of establishing a finite element analysis model of the automobile disc brake assembly by using general finite element analysis software ANSYS, solving a rigidity and mass matrix of the brake assembly under the braking condition, and calculating an assembly mode of the brake assembly under the braking condition (the condition that noise occurs in a noise test) by taking a calculation result as input of modal analysis. When the real part of the complex characteristic value is a positive value, the mode of the order is an unstable mode, the unstable mode is a 1-order mode which is formed by coupling two adjacent real modes (natural modes) under the action of frictional coupling, and the two modes are interfered with each other in the vibration process to generate self-excited vibration. The larger the real part value is, the more unstable the structure is during vibration, the amplitude will grow exponentially with time.
S11: the 3D model of the brake (comprising a brake caliper assembly, a steering knuckle assembly and a brake disc) shown in the figure 2 is subjected to mathematical discrete processing (gridding) by using the ANSYS software, because the 3D model reserves the types of detail characteristic units such as the drawing gradient, the parting line and the like of a casting for approaching a real object, the high-grade tetrahedral unit with higher discrete precision and stronger adaptability is selected, and the high-grade hexahedral unit is adopted as the braking surface. Ensuring that the average torsion degree Skewness of the body grid is less than 0.4. The 1D beam element is used to simplify the bolts in the structure.
S12: the discrete units of each component are given material parameters: the main inputs (young's modulus, poisson's ratio, density) for isotropic materials are treated as orthogonal anisotropic materials for brake pads. The experimentally measured 12 elastic constants were input:
the above formula is the relationship between the stress, strain and elastic constants of orthotropic materials, wherein C 11 ～C 66 Is an elastic constant, σ x 、σ y 、σ z Stress in the directions of the x-axis, y-axis and z-axis, τ xy Shear stress in the x-and y-directions, τ yz Shear stress in the directions of the y-axis and z-axis, τ zx Shear stress in the z-and x-directions, ε x 、ε y 、ε z Strain in the x-axis, y-axis and z-axis directions, respectively, gamma xy Is the angular strain, gamma, in the direction of the x-axis and the y-axis yz Is the angular strain, gamma, in the direction of the y-axis and the z-axis zx Is the angular strain in the z-axis and x-axis directions.
S13: and (3) simulating the load transmission behavior between the parts by establishing a contact equation of a connection surface unit between the parts.
Wherein Fn represents a normal contact force; kn represents the normal contact stiffness; un represents the contact penetration; ft represents the tangential contact force; kt represents the tangential contact stiffness; ut represents the contact slip distance; un represents the contact penetration; u represents a friction coefficient;
s14: and (3) defining constraint at the joint of the steering knuckle and the vehicle body connecting surface: the constraint stiffness in six degrees of freedom as described in fig. 3 is input. And (3) adding bolt pre-tightening force to the bolt simplified beam unit in the structure to simulate the bolt tightening process (considering the influence of bolt pre-tightening force on rigidity), and defining the braking load (braking hydraulic pressure and brake disc rotating speed) according to the NVH experimental working condition.
S15: the method comprises the steps of solving a rigidity matrix and a mass matrix of a structure of the brake assembly under the braking working condition by using ANSYS finite element software, wherein the mass matrix can be obtained by inputting material density under the known condition, and the rigidity matrix is mainly solved, namely the relation between load and displacement of each node of the structure. And calculating the assembly mode of the brake assembly under the braking condition by taking the calculation result as the input of the mode analysis, wherein the structural rigidity matrix is an asymmetric matrix by introducing the frictional coupling of a brake disc and a brake block into a motion equation of the structure, the characteristic value for solving the asymmetric matrix structure can be a complex characteristic value, the real part of the complex characteristic value represents the stability of the structure, the imaginary part represents the frequency, the mode of the real part and the complex characteristic value is the mode damping ratio, the real part is a positive characteristic value and is an unstable mode, and the vibration exponentially increases along with the time.
Where { F } is the force due to the frictional coupling of the braking surfaces. { F } is a representation that can be deduced by the displacement of a node on the braking surface
{F}＝[K F ]{μ}
In the formula [ K F ]The frictional coupling stiffness matrix represents the relationship between { F } and the node displacement { mu } [ K ] F ]Is asymmetric. Can obtain
In the formula [ K-K F ]The characteristic matrix of the system is also asymmetric, the asymmetric rigidity matrix means that the characteristic matrix of the system is also asymmetric, when the characteristic is solved by using an ANSYS finite element software asymmetric solver, the real part of a characteristic value is a positive value, and a characteristic vector (vibration mode) is solved at the same time
λ＝-ζω±jω d
If the real part of the characteristic value-Zeta omega is a positive value, the system is unstable due to the exponential increase of the vibration according to the response equation
x(t)＝Ae -ζωt sin(ω d t+φ)
S2: comparing the noise frequency appearing in a noise test with an unstable mode obtained by analysis, if the frequency difference is within a specified value, considering that the frequency similarity meets the requirement, then carrying out vibration mode comparison, arranging displacement vectors of three directions (X, Y, Z) of acceleration sensor measuring points in the vibration process measured on a brake assembly, carrying out vector operation according to a certain calculation method by using the results and the displacement vectors of corresponding points in the unstable mode, and considering that the vibration mode and the test vibration mode similarity calculated in a simulation way meet the requirement if the calculated result is greater than the specified value, and if the frequency value and the vibration mode value are different from the test, correcting the analysis model material parameters, boundary conditions and the like until the calculated result meets the requirement:
in the formula: { R jk },{R lk And represents the displacement vector obtained by simulation analysis and the actually measured displacement vector respectively. If { R } jk },{R lk Before linear correlation exists, the value of MAC is close to 1, namely, the calculated mode shape is completely consistent with the actual mode shape. Whereas if the two are linearly independent, the MAC value is close to 0. And evaluating the mode shape of the simulation analysis to be consistent with the actual mode shape through MAC value calculation.
S3: and decoupling and analyzing the calculated unstable modes, calculating the mode results of different working conditions according to specifications, and determining which two adjacent real modes of the unstable mode are coupled to form the unstable mode. The unstable mode is formed by coupling two adjacent real modes into 1 order under the action of frictional coupling, the two orders of modal vibration modes interfere with each other to generate self-excited vibration in the vibration process, decoupling analysis is needed to determine the composition of the coupling mode, generally, the coupling process is related to the friction coefficient between the brake disc and the brake block, namely two natural frequencies are continuously close to final coupling along with the increase of the friction coefficient (see fig. 4), so that the friction coefficients need to be discretized into 0.05, 0.1, 0.15, 0.2, 0.25, 0.35, 0.4, 0.45, 0.5 and 0.55 in the analysis process, and the two independent real modes before coupling are respectively analyzed and found. And then, the frequency difference of the two real modes is pulled up by adjusting the structure, and the larger the frequency difference is, the larger the difference of the two modes is. The chance of coupling is reduced.
S4: after the coupling component of the unstable mode is determined, the mode strain energy of two-order adjacent modes is calculated, the part with the highest strain energy ratio is improved, and the frequency difference of the two-order adjacent modes is pulled open according to the standard requirement. And (3) carrying out finite element analysis on the finally determined optimization scheme in step S1 until the unstable mode is eliminated or the modal damping ratio of the unstable mode is smaller than a specified value, and then carrying out noise test verification until the noise meets the test requirement:
W＝1/2k(ΔL)(ΔL)
in the formula: w is strain energy, k is structural stiffness, and Δ L is strain.
Finally, the above embodiments are only intended to illustrate the technical solutions of the present invention and not to limit the present invention, and although the present invention has been described in detail with reference to the preferred embodiments, it will be understood by those skilled in the art that modifications or equivalent substitutions may be made on the technical solutions of the present invention without departing from the spirit and scope of the technical solutions, and all of them should be covered by the claims of the present invention.
Claims (6)
1. A method for solving low-frequency braking noise of a floating caliper disc brake is characterized by comprising the following steps: the method comprises the following steps:
s1: establishing a finite element analysis model of the automobile disc brake assembly, solving a rigidity and mass matrix of the brake assembly under a braking working condition, and calculating an assembly mode of the brake assembly under a braking condition by taking a calculation result as an input of mode analysis;
s2: carrying out frequency comparison and vibration mode comparison, and if the difference between the frequency and the vibration mode existing in the test exceeds a threshold value, correcting the finite element analysis model of the automobile disc brake assembly until the calculation result meets the requirement;
s3: decoupling analysis is carried out on the calculated unstable mode;
s4: after determining the coupling component of the unstable mode, calculating the mode strain energy of two-order adjacent modes, improving the part with the highest strain energy ratio, and pulling away the frequency difference value of the two-order adjacent modes; and carrying out finite element analysis on the finally determined optimization scheme until the unstable mode is eliminated or the modal damping ratio of the unstable mode is smaller than a preset threshold value, and then carrying out noise test verification until the noise meets the test requirement.
2. The solution for low frequency braking noise of a floating caliper disc brake according to claim 1, characterized in that: the step S1 specifically includes:
establishing a finite element analysis model of the automobile disc brake assembly by using general finite element analysis software ANSYS;
introducing friction coupling of a brake disc and a brake block into a motion equation of a structure, enabling a rigidity matrix of the structure to be an asymmetric matrix, solving a characteristic value of the asymmetric matrix structure to be a complex characteristic value, wherein a real part of the complex characteristic value represents stability of the structure, an imaginary part represents frequency, and a mode of the real part and the complex characteristic value is a modal damping ratio;
the larger the modal damping ratio is, the more unstable the mode is, when the real part of the complex characteristic value is a positive value, the assembly mode is represented as an unstable mode, the unstable mode is formed by coupling two adjacent real modes into 1 order under the action of frictional coupling, and the two modes are mutually interfered in the vibration process to generate self-excited vibration;
the larger the real part value of the complex eigenvalue is, the more unstable the structure is, the amplitude of the structure can exponentially increase along with time in the vibration process.
3. The solution for low frequency braking noise of a floating caliper disc brake according to claim 1, characterized in that: the step S1 specifically includes the following steps:
s11: performing mathematical discrete processing on a 3D brake model by using general finite element analysis software ANSYS, wherein the 3D brake model comprises a brake caliper assembly, a steering knuckle assembly and a brake disc;
s12: the discrete units of each component are given material parameters: inputting Young modulus, poisson ratio and density for isotropic materials; for the brake pad, the anisotropic material is processed according to the orthotropic material, and 12 elastic constants measured by the experiment are input:
the above formula is the relationship of stress, elastic constant and strain of orthotropic material, wherein C 11 ～C 66 Is an elastic constant, σ x 、σ y 、σ z Stress in the directions of the x-axis, y-axis and z-axis, τ xy Shear stress in the x-and y-directions, τ yz Shear stress in the directions of the y-axis and z-axis, τ zx Shear stress in the z-and x-directions, ε x 、ε y 、ε z Strain in the x, y and z directions, respectively, gamma xy Is the angular strain in the directions of the x-axis and the y-axis, gamma yz Is the angular strain, gamma, in the direction of the y-axis and the z-axis zx Is the angular strain in the z-axis and x-axis directions;
s13: simulating the load transmission behavior between the parts by establishing a contact equation of a connection surface unit between the parts:
in the formula, fn represents a normal contact force, kn represents normal contact rigidity, un represents contact penetration, ft represents a tangential contact force, kt represents tangential contact rigidity, ut represents contact slip distance, un represents contact penetration, and u represents a friction coefficient;
s14: and (3) defining constraint at the joint of the steering knuckle and the vehicle body connecting surface: inputting constraint rigidity with six degrees of freedom, and applying bolt pretightening force simulation bolt tightening process to a bolt simplified beam unit in the structure to define a brake load according to NVH experiment working conditions;
s15: using ANSYS finite element software to solve a rigidity matrix and a mass matrix of a structure of a brake assembly under a braking condition, wherein the rigidity matrix is a relation between load and displacement received by each node, calculating an assembly mode of the brake assembly under the braking condition by using a calculation result as input of mode analysis, introducing frictional coupling of a brake disc and a brake block into a motion equation of the structure to enable the rigidity matrix of the structure to be an asymmetric matrix, solving a characteristic value of the asymmetric matrix structure to be a complex characteristic value, wherein a real part of the complex characteristic value represents the stability of the structure, an imaginary part represents frequency, a mode of the real part and the complex characteristic value is a mode damping ratio, a characteristic value with a positive real part is an unstable mode, and vibration increases exponentially along with time:
where { F } is the force due to the frictional coupling of the braking surfaces:
{F}＝[K F ]{μ}
in the formula [ K F ]The frictional coupling stiffness matrix represents the relationship between { F } and the node displacement { mu } [ K ] F ]Is asymmetric, yielding:
in the formula [ K-K F ]The asymmetric rigidity matrix means that the characteristic matrix of the system is also asymmetric, when the characteristic is solved by using the ANSYS finite element software asymmetric solver, the real part of the characteristic value is a positive value, and a characteristic vector is solved at the same time:
λ＝-ζω±jω d
if the real part of the eigenvalue, ζ ω, is positive, the system is unstable due to the exponential increase of the vibration according to the response equation:
x(t)＝Ae -ζωt sin(ω d t+φ)。
4. the solution for low frequency braking noise of a floating caliper disc brake according to claim 1, characterized in that: the frequency comparison in step S2 includes: comparing the noise frequency appearing in the noise test with the unstable mode obtained by analysis, and if the frequency difference is within a preset threshold value, determining that the frequency similarity meets the requirement;
the mode shape comparison comprises the following steps: arranging displacement vectors of three directions (X, Y and Z) of a measuring point of an acceleration sensor on a brake assembly to measure the displacement vectors of the measuring point in the vibration process, carrying out vector operation on the displacement vectors and the displacement vectors of corresponding points in the unstable mode, and if the calculation result reaches a preset threshold value, considering that the similarity between the vibration mode calculated by simulation and the test vibration mode meets the requirement;
and when the frequency value and the vibration mode value are different from the test, correcting the material parameters and boundary conditions of the finite element analysis model of the automobile disc brake assembly:
in the formula: { R jk },{R lk Respectively representing a displacement vector obtained by simulation analysis and an actually measured displacement vector; if { R } jk },{R lk If linear correlation exists before, the value of the MAC is close to 1, namely the calculated mode shape is completely consistent with the actual mode shape; otherwise, if the two are linearly independent, the MAC value is close to 0; and evaluating the consistency of the simulation analysis mode shape and the actual shape through the MAC value.
5. The solution for low frequency braking noise of a floating caliper disc brake according to claim 1, characterized in that: step S3, calculating modal results of different working conditions, and determining which two adjacent real modes are coupled to form the unstable mode; the unstable mode is formed by coupling two adjacent real modes into 1 order under the action of frictional coupling, the two orders of mode vibration forms interfere with each other to generate self-excited vibration in the vibration process, decoupling analysis is needed to determine the composition of the coupling mode, the friction coefficient is dispersed in the analysis process and is respectively analyzed to find out the independent real modes of the two orders before coupling; then, the frequency difference of the two real modes is pulled apart by adjusting the structure, and the larger the frequency difference is, the larger the difference of the two real modes is, the probability of coupling is reduced.
6. The solution for low frequency braking noise of a floating caliper disc brake according to claim 1, characterized in that: the step S4 comprises the following steps:
W＝1/2k(ΔL)(ΔL)
wherein W is strain energy, k is structural stiffness, and Δ L is strain.
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