A lightweight broadband damping structure for front crossbeams of automobile roofs and its design method

Abstract

This invention belongs to the field of automotive vibration damping and noise reduction technology, specifically relating to a lightweight, wide-frequency vibration damping structure and its design method for a front crossbeam of an automotive roof. The damping structure includes an adhesive backing layer, a damping layer, and a mass layer. Rapid alignment and positioning are achieved through geometric matching between the bosses of the adhesive backing layer and the rib grooves of the front crossbeam, facilitating quick pre-installation before the painting and baking process. The damping layer consists of 60-80 parts by weight of butyl rubber, 20-30 parts of reinforcing agent, 5-10 parts of plasticizer, and 0.5-1.5 parts of foaming agent. The damping layer is made by uniformly mixing 0.5-1.0 parts of crosslinking agent and adhesive. After gradient baking and curing, the adhesive layer melts, connecting the lower surface of the damping layer with the inner bottom wall of the front crossbeam. The damping layer forms a viscoelastic microporous structure. The front crossbeam as the basic vibrating body, the damping layer as the energy dissipation medium, and the mass layer as the tuning mass together constitute the acoustic-vibration coupling system. Its broadband factor is 1.2-2.0. This vibration damping structure is lightweight, easy to install, and has multi-frequency tuning function. It can achieve vibration reduction and noise reduction in the 30-300Hz frequency band.

Description

Technical Field

[0001] This invention belongs to the field of automotive vibration reduction and noise reduction technology, specifically relating to a lightweight wideband vibration reduction structure for the front crossbeam of an automobile roof and its design method. Background Technology

[0002] During driving, the mechanical connection structure of a car transmits the vibrations generated by the engine and road surface to the entire vehicle body, causing the body to vibrate and generate noise. Approximately 70% of mass-produced cars worldwide are generally troubled by the local mode of the front crossbeam of the roof in the 30-300Hz road noise frequency band, which seriously affects the riding comfort of passengers.

[0003] The structure of the front crossbeam of the roof is closely related to two main factors: first, ergonomics. To ensure headroom for passengers, the design of the front crossbeam area must take into account human body size and comfort, thus limiting the height and shape of the front crossbeam; second, the overall vehicle styling design. To meet market demands for vehicle appearance, the overall vehicle styling design often pursues streamlined and aesthetically pleasing designs. The usable height of the front crossbeam area is usually designed to be no more than 30mm, and the profile thickness of the front crossbeam can only be maintained between 0.7-1.0mm, thus limiting the structural strength and vibration characteristics of the front crossbeam.

[0004] The structure based on the front crossbeam is prone to continuously exhibiting 3-5 local modes in the 30-300Hz frequency band. These modes can highly overlap with the multi-level acoustic cavity modes in the car, producing a coupling amplification effect, which raises the sound pressure level near the occupant's ear by 6-10dB(A), thus forming a significant low-frequency booming sound.

[0005] To reduce in-vehicle noise, the structure of the front crossbeam is optimized or sound insulation and vibration damping structures are added during the manufacturing process. However, traditional vibration absorbers are usually more than 25mm thick, occupying more than 83% of the usable space in the front crossbeam area, which affects the aesthetics of the overall vehicle design. Moreover, vibration absorbers are generally fixed to the front crossbeam with bolts, which is inconvenient to install. In addition, vibration absorbers are usually used to achieve "point-to-point" single-frequency tuning and peak elimination, which cannot meet the requirements of wide-frequency vibration damping and noise reduction. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention proposes a lightweight, wide-band vibration damping structure for the front crossbeam of an automobile roof, which is easy to install and has a wide-band vibration damping and noise reduction effect.

[0007] To solve the above-mentioned technical problems, the present invention provides a lightweight wide-frequency damping structure for the front crossbeam of an automobile roof, comprising:

[0008] The front crossbeam is designed with a Z-shaped cross-section structure, and its inner bottom wall is provided with a rib groove;

[0009] The adhesive backing layer includes a boss that is geometrically matched with the rib groove, and the lower surface of the adhesive backing layer is bonded to the inner bottom wall of the front crossbeam.

[0010] The damping layer has its lower surface connected to the upper surface of the adhesive backing layer;

[0011] The mass layer has its lower surface connected to the upper surface of the damping layer;

[0012] The damping layer is made by uniformly mixing 60-80 parts of butyl rubber, 20-30 parts of reinforcing agent, 5-10 parts of plasticizer, 0.5-1.5 parts of foaming agent and 0.5-1.0 parts of crosslinking agent by weight.

[0013] After gradient baking and curing, the adhesive layer melts, causing the lower surface of the damping layer to connect with the inner bottom wall of the front crossbeam. The damping layer forms a viscoelastic microporous structure. The front crossbeam, as the basic vibrating body, the damping layer, as the energy dissipation medium, and the mass layer, as the tuning mass, together constitute an acoustic-vibration coupling system. The broadband factor of the acoustic-vibration coupling system is 1.2-2.0.

[0014] Preferably, in the above scheme, the adhesive layer is composed of acrylate adhesive and neodymium iron boron magnetic powder. After gradient baking and curing, the acrylate adhesive melts and the neodymium iron boron magnetic powder is oxidized to generate iron oxide and neodymium oxide.

[0015] Preferably, in the above scheme, the proportion of neodymium iron boron magnetic powder is 30wt%, the particle size is 5-10μm, and the thickness of the backing layer after gradient baking and curing is 0.1-0.2mm.

[0016] Preferably, in the above scheme, the reinforcing agent is carbon black with a particle size of 40-60 nm, the plasticizer is dioctyl phthalate, the foaming agent is azodicarbonamide, and the crosslinking agent is sulfur.

[0017] Preferably, in the above scheme, the thickness of the damping layer after gradient baking and curing is 2mm, and the loss factor in the 30-300Hz frequency band is 0.25-0.35.

[0018] Preferably, in the above scheme, the mass layer is made of a uniform mixture of a rubber matrix and metal powder, and its density is 3500-5000 kg / m³. 3 .

[0019] Preferably, in the above scheme, the metal powder is iron powder and / or tungsten powder with a particle size of 20-100μm, and the thickness of the mass layer after gradient baking and curing is 3.0-7.8mm.

[0020] Preferably, in the above scheme, the gradient baking includes:

[0021] Stage 1: Heat to 160°C at a heating rate of 5-10°C / min to trigger the viscous flow transition of the adhesive layer;

[0022] Phase 2: Heat to 180°C within 5 minutes and hold for 15 minutes to allow the damping layer to complete cross-linking and foaming, forming a viscoelastic microporous structure.

[0023] Phase 3: Cool in the furnace to below 60°C to solidify the acoustic-vibration coupling system with a bandwidth factor of 1.2-2.0.

[0024] A design method for a lightweight, wide-frequency damping structure for a front crossbeam of an automobile roof, applicable to any of the aforementioned lightweight, wide-frequency damping structures for a front crossbeam of an automobile roof, the design method comprising:

[0025] Step S1: Obtain the physical parameters of the front crossbeam, including the front crossbeam density ρ. s Front crossbeam modulus E s Front crossbeam thickness h s The length L of the front crossbeam, the moment of inertia I of the front crossbeam, and the eigenvalue β of the nth vibration mode. n And the outline of the inner bottom wall of the front crossbeam;

[0026] Step S2: Obtain the vertical acceleration signal of the front crossbeam and perform Fast Fourier Transform (FFT) to extract the original acceleration spectrum in the 20-200Hz frequency band;

[0027] Step S3: Select the maximum peak value and several adjacent peak values ​​in the original acceleration spectrum, and calculate the weighted target frequency. Where a n f is the peak acceleration value. n For the corresponding frequency;

[0028] Step S4: Set the thickness of the damping layer after baking and curing at 160-180℃ to 2mm, and obtain the damping layer density ρ. r Satisfying the damping layer loss factor η r ∈[0.25, 0.35], and calculate the Young's modulus of the damping layer.

[0029] Step S5: Set the bandwidth factor Γ∈[1.2, 2.0], and establish the mass layer density ρ a and quality layer thickness h a Solve the related equations:

[0030] Step S6: Establish a three-dimensional model of the damping structure that conforms to the inner bottom wall contour of the front crossbeam, satisfying that the total mass of the three-dimensional model of the damping structure is ≤3kg and the total thickness is ≤10mm;

[0031] Step S7: Create E based on the 3D model of the vibration reduction structure r *(1±5%), h a For the test sample group of *(1±5%), the test acceleration spectrum of different test sample groups is extracted through step S2, and the test sample group with the lowest average peak acceleration is selected.

[0032] Preferably, in the above scheme, the vertical acceleration signal of the front crossbeam in step S2 is measured when the car is traveling at a constant speed of 60 km / h on a standard asphalt road, and the FFT analysis uses the Hanning window function.

[0033] Compared with existing technologies, the present invention has the following advantages:

[0034] 1. A lightweight, wide-band vibration damping structure for a front crossbeam of an automobile roof, comprising an adhesive backing layer, a damping layer, and a mass layer, wherein rapid alignment and positioning are achieved through geometric matching between the bosses of the adhesive backing layer and the rib grooves of the front crossbeam, facilitating rapid pre-installation before the painting and baking process. The damping layer is uniformly mixed with 60-80 parts by weight of butyl rubber, 20-30 parts of reinforcing agent, 5-10 parts of plasticizer, 0.5-1.5 parts of foaming agent, and 0.5-1.0 parts of crosslinking agent. After gradient baking and curing, the adhesive backing layer melts, connecting the lower surface of the damping layer to the inner bottom wall of the front crossbeam, forming a viscoelastic microporous structure. The front crossbeam as the basic vibrating body, the damping layer as the energy dissipation medium, and the mass layer as the tuning mass together constitute a sound-vibration coupling system with a wideband factor of 1.2-2.0. This vibration damping structure is lightweight, easy to install, and has multi-frequency tuning capabilities, achieving vibration damping and noise reduction in the 30-300Hz frequency band.

[0035] 2. The adhesive layer in this invention is composed of acrylic adhesive and neodymium iron boron magnetic powder. During pre-installation, the initial adhesion of the acrylic adhesive can prevent the shock-absorbing structure from loosening and falling off the front crossbeam due to vibration of the production line. The neodymium iron boron magnetic powder can generate a static magnetic field and can be quickly adsorbed onto the inner bottom wall of the front crossbeam during pre-installation. After baking at a high temperature of over 160°C, the neodymium iron boron magnetic powder is oxidized to generate iron oxide and neodymium oxide, avoiding long-term magnetic corrosion.

[0036] 3. The gradient baking in this invention is based on the existing automotive coating baking process and is achieved through process parameter control. The gradient baking includes three stages: heating, holding and cooling. The heating stage can effectively trigger the viscous flow state transition of the backing layer and prevent the acrylic adhesive from carbonizing. The holding stage can ensure that the damping layer completes cross-linking and foaming, thereby forming the expected viscoelastic microporous structure.

[0037] 4. The present invention provides a design method for a lightweight broadband damping structure for a front crossbeam of an automobile roof, comprising the steps of front crossbeam parameter acquisition, acceleration spectrum analysis, target frequency determination, damping layer parameter design, mass layer optimization calculation, three-dimensional model design, and test sample verification, which can more accurately design a damping structure adapted to the front crossbeam. Attached Figure Description

[0038] Figure 1 This is a first-view installation structure schematic diagram of a lightweight, wide-frequency damping structure for the front crossbeam of an automobile roof according to the present invention.

[0039] Figure 2 This is a second-view installation structure schematic diagram of a lightweight, wide-frequency damping structure for the front crossbeam of an automobile roof according to the present invention.

[0040] Figure 3 This is a schematic diagram of the layered structure of a lightweight, wide-frequency damping structure for the front crossbeam of an automobile roof according to the present invention.

[0041] Figure 4 This is a measured acceleration curve of the middle node of the front crossbeam of the test vehicle of this invention.

[0042] Figure 5 This is a measured sound pressure curve of the driver's right ear in the test vehicle of this invention.

[0043] Figure 6 This is a flowchart illustrating the design method of a lightweight, wide-frequency vibration damping structure for the front crossbeam of an automobile roof according to the present invention.

[0044] Among them, 1-front crossbeam, 11-rib groove, 2-backing adhesive layer, 21-boob, 3-damping layer, 4-mass layer, 5-three-level functional layer structure. Detailed Implementation

[0045] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0046] In the description of this invention, it should be noted that the terms "center", "longitudinal", "lateral", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", and "outer" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0047] In the description of this invention, "several" means one or more, "multiple" means two or more, "greater than," "less than," and "exceeding" are understood to exclude the stated number, while "above," "below," and "within" are understood to include the stated number. Where the terms "first," "second," and "third" are used for descriptive purposes and to distinguish technical features, they should not be construed as indicating or implying relative importance, or implicitly indicating the number of indicated technical features, or implicitly indicating the sequential relationship of the indicated technical features.

[0048] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "setting" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal communication between two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. The embodiments of this invention will now be described according to its overall structure.

[0049] like Figures 1 to 3 As shown, this invention discloses a lightweight, wide-frequency damping structure for a front crossbeam of an automobile roof, comprising a front crossbeam 1, an adhesive backing layer 2, a damping layer 3, and a mass layer 4. The front crossbeam 1 has a U-shaped cross-section structure with rib grooves 11 on its inner bottom wall. The adhesive backing layer 2 includes bosses 21 geometrically matched to the rib grooves 11. The lower surface of the adhesive backing layer 2 is bonded to the inner bottom wall of the front crossbeam 1. The lower surface of the damping layer 3 is connected to the upper surface of the adhesive backing layer 2. The lower surface of the mass layer 4 is connected to the upper surface of the damping layer 3. The damping layer 3 is composed of [materials to be filled in] parts by weight. The mixture consists of 60-80 parts butyl rubber, 20-30 parts reinforcing agent, 5-10 parts plasticizer, 0.5-1.5 parts foaming agent, and 0.5-1.0 parts crosslinking agent. After being cured by gradient baking, the backing layer 2 melts, causing the lower surface of the damping layer 3 to connect with the inner bottom wall of the front crossbeam 1. The damping layer 3 forms a viscoelastic microporous structure. The front crossbeam 1 serves as the basic vibrating body, the damping layer 3 serves as the energy dissipation medium, and the mass layer 4 serves as the tuning mass, together forming an acoustic-vibration coupling system. The broadband factor of the acoustic-vibration coupling system is 1.2-2.0.

[0050] The damping structure in this embodiment is a three-level functional layer structure 5 consisting of an adhesive backing layer 2, a damping layer 3, and a mass layer 4 connected in sequence. Through the geometric matching of the boss 21 and the rib groove 11, the adhesive backing layer 2 and the front crossbeam 1 can be quickly aligned and bonded, facilitating rapid pre-installation before the painting and baking process. The damping layer 3 can transmit the vibration of the front crossbeam 1 to the mass layer 4, and convert the vibration energy of the front crossbeam 1 into heat energy based on its own damping characteristics. The mass layer 4 participates in the coupling of the vibration system as a tuning mass. This damping structure is lightweight, easy to install, and has multi-frequency tuning function. It can form an acoustic-vibration coupling system with the front crossbeam of the car roof, thereby achieving vibration reduction and noise reduction functions in the 30-300Hz frequency band.

[0051] In this embodiment, the adhesive backing layer 2 is composed of acrylate adhesive and neodymium iron boron (NdFeB) magnetic powder. The NdFeB magnetic powder is uniformly mixed into the acrylate adhesive through ultrasonic dispersion. After gradient baking and curing, the acrylate adhesive melts, and the NdFeB magnetic powder oxidizes to form iron oxide and neodymium oxide. Specifically, the proportion of NdFeB magnetic powder is 30 wt%, and the particle size is 5-10 μm. Furthermore, the adhesive coating amount of the adhesive backing layer 2 is 250-300 g / m2, and the thickness after gradient baking and curing is 0.1-0.2 mm.

[0052] It should be understood that the front crossbeam of the car roof is made of high-strength alloy steel. The neodymium iron boron magnetic powder in the adhesive layer 2 can generate a static magnetic field, which can be quickly adsorbed onto the inner bottom wall of the front crossbeam 1 during pre-installation. After baking at 160-180℃, the neodymium iron boron magnetic powder is oxidized to form micron-sized composite oxides dispersed in the adhesive layer 2 (volume percentage <5%). XRD testing showed no magnetic phase residue, thus avoiding long-term magnetic corrosion. In addition, the initial tack of the acrylic adhesive during pre-installation is >0.3MPa, which can prevent the shock-absorbing structure from loosening and falling off the front crossbeam 1 due to vibration of the production line. After baking, the acrylic adhesive melts and penetrates into the micropores on the surface of the front crossbeam 1, forming a metallurgical-grade bond with a peel strength >5MPa. The peel strength decay rate was tested under aging conditions of 85℃ / 85%RH / 1000h: 8.2% for pure acrylic adhesive, 23.70% for NdFeB magnetic powder before oxidation, and 9.50% for NdFeB magnetic powder after oxidation. Therefore, the oxidation of NdFeB magnetic powder has a relatively small impact on the bonding reliability of the backing layer 2.

[0053] In this embodiment, ExxonMobil's EXXON Butyl 268 grade of butyl rubber is preferably used, which can provide a high damping loss factor; the reinforcing agent is carbon black with a particle size of 40 - 60 nm, which is used to improve the modulus and wear resistance; the plasticizer is dioctyl phthalate, which is used to adjust the processing fluidity and reduce the glass transition temperature; the foaming agent is azodicarbonamide, which can decompose and foam at a temperature of 160 °C, so that the damping layer 3 forms a microporous structure; the crosslinking agent is sulfur, which can enhance the network stability after baking and curing. The thickness of the damping layer 3 after gradient baking and curing is 2 mm, and the loss factor in the frequency band of 30 - 300 Hz is 0.25 - 0.35. It should be noted that the power dissipated per unit area of the damping layer 3 is proportional to its loss factor η r is proportional, when η r ∈[0.25, 0.35], it can achieve an energy dissipation rate ≥ 65% at the acceleration peak of the front cross member 1 in the frequency band of 30 - 300 Hz, and can also prevent the temperature rise from being too high.

[0054] Furthermore, the mass layer 4 is made of a uniform mixture of a rubber matrix and metal powder, and its density is 3500 - 5000 kg / m 3 , which can be adjusted according to the target modes continuously appearing in the front cross member 1 in the frequency band of 30 - 300 Hz, so as to achieve the effect of tuning the mass. The metal powder is iron powder and / or tungsten powder with a particle size of 20 - 100 μm. The thickness of the mass layer 4 after gradient baking and curing is 3 - 7.8 mm.

[0055] Specifically, in the processing link of the shock absorption structure, the following also needs to be considered: the surface deviation ≤ 0.3 mm; avoid the wire harness, and the safety envelope of the roof ceiling buckle ≥ 2 mm; retain a glue layer covering boundary ≥ 1 mm; verify that the demolding taper angle ≥ 2°, and ensure that there is no mold clamping after foaming.

[0056] During the pre - installation process, the shock absorption structure is manually placed inside the front cross member 1, and through the geometric matching of the boss 21 and the rib position groove 11, the back glue layer 2 is centered with the front cross member 1. During the centering detection, the offset can be detected by a CCD camera. If the offset ≤ ±0.5 mm, the detection is qualified; otherwise, secondary rectification is required by a robotic arm. After the pre - installation is completed, there is an 8 N / cm 2 magnetic suction force + 0.3 MPa initial adhesion force between the shock absorption structure and the front cross member 1, which can withstand the vibration of the wire body (acceleration ≤ 3g) without debonding.

[0057] It should be noted that the gradient baking of the present invention is realized through process parameter control based on the existing automotive painting baking link. The gradient baking includes:

[0058] Phase 1: Heat to 160℃ at a heating rate of 5-10℃ / min to trigger the viscous flow transition of the backing layer 2; specifically, if the heating rate exceeds 10℃ / min, it will cause the bubble defect rate to exceed 30%; if the baking temperature is <150℃, it will cause the adhesive strength of the acrylate adhesive to be <3MPa after melting; if the baking temperature is >190℃, it will cause the acrylate adhesive to carbonize.

[0059] Phase 2: Heat to 180℃ within 5 minutes and hold for 15 minutes to allow the damping layer 3 to complete cross-linking and foaming, forming a viscoelastic microporous structure. Specifically, during the holding phase, the air velocity in the furnace is controlled at 0.5-1.2 m / s, and the temperature uniformity is ≤±3℃. If the holding time is <10 minutes, the foaming will be incomplete, and the damping layer 3 will not be able to form the expected viscoelastic microporous structure.

[0060] Stage 3: Cooling in the furnace to below 60°C to solidify the acoustic-vibration coupling system with a broadband factor of 1.2-2.0. Specifically, after cooling and solidification, the porosity of the microporous structure of the damping layer 3 is 15-30%, and the broadband factor Γ of the damping structure is [1.2, 2.0], thus achieving a broadband damping effect.

[0061] like Figure 6 As shown, this invention proposes a design method for a lightweight, wide-frequency damping structure for the front crossbeam of an automobile roof, applied to the aforementioned damping structure, comprising:

[0062] Step S1: Obtain the physical parameters of the front crossbeam, including the front crossbeam density ρ. s Front crossbeam modulus E s Front crossbeam thickness h s The length L of the front crossbeam, the moment of inertia I of the front crossbeam, and the eigenvalue β of the nth vibration mode. n And the inner bottom wall profile of the front crossbeam. The physical parameters of the front crossbeam are provided by the OEM during the actual production process.

[0063] Step S2: Obtain the vertical acceleration signal of the front crossbeam and perform a Fast Fourier Transform (FFT) to extract the original acceleration spectrum in the 20-200Hz frequency band. Specifically, in this embodiment, a PCB 352C33 accelerometer is used to collect the vertical acceleration signal of the middle node of the front crossbeam. According to GB / T 15168-2025, under the condition of driving at a constant speed of 60km / h on a standard asphalt road, the sampling frequency is ≥512Hz and the recording time is ≥30s. The Hanning window function is used to perform FFT analysis on the vertical acceleration signal.

[0064] Step S3: Select the maximum peak value and several adjacent peak values ​​in the original acceleration spectrum, and calculate the weighted target frequency. Where a nf is the peak acceleration value. n For the corresponding frequency.

[0065] Step S4: Set the thickness of the damping layer after baking and curing at 160-180℃ to 2mm, and obtain the damping layer density ρ. r Satisfying the damping layer loss factor η r ∈[0.25, 0.35], and calculate the Young's modulus of the damping layer.

[0066] Step S5: Set the bandwidth factor Γ∈[1.2, 2.0], and establish the mass layer density ρ a and quality layer thickness h a Solve the related equations:

[0067] Step S6: Establish a 3D model of the damping structure conforming to the inner bottom wall contour of the front crossbeam, ensuring that the total mass of the 3D model is ≤3kg and the total thickness is ≤10mm. Specifically, the structure of the front crossbeam and the contour surface of the inner bottom wall are drawn using 3D modeling software, thereby creating a 3D model of the damping structure conforming to the inner bottom wall.

[0068] Step S7: Create E based on the 3D model of the vibration reduction structure r *(1±5%), h a For the test sample group of *(1±5%), the test acceleration spectrum of different test sample groups is extracted through step S2, and the test sample group with the lowest average peak acceleration is selected.

[0069] The physical parameters of the front crossbeam of the roof of the test vehicle in this embodiment are: ρ s =7850kg / m 3 h s =0.8mm; L=0.80m; I=1.8×10 -7 m 4 E s =210GPa, and the eigenvalue β1 of the first-order mode was obtained through finite element modal analysis.

[0070] In the original acceleration spectrum of the 20-200Hz frequency band, the frequency and acceleration corresponding to the maximum peak and the two adjacent peaks are as follows:

[0071] f1 = 48 Hz, a1 = 5.2 m / s 2 f2 = 92 Hz, a2 = 3.1 m / s 2 f3 = 135 Hz, a3 = 1.9 m / s 2 .

[0072] Calculate the weighted target frequency according to step S3.

[0073] Furthermore, damping layer samples were prepared after baking and curing at 160-180℃, and their damping layer density η was measured. r And control the damping layer loss factor ρ r ∈[0.25, 0.35], and calculate the Young's modulus of the damping layer.

[0074] By setting the bandwidth factor Γ = 1.6, the mass layer density ρ in step S5 is adjusted. a and quality layer thickness h a Solve the following:

[0075] A three-dimensional model of the damping structure conforming to the inner bottom wall profile of the front crossbeam was established. The total thickness of the three-dimensional model of the damping structure = mass layer thickness + damping layer thickness + adhesive backing layer thickness = 5.4mm + 2.0mm + 0.2mm = 7.6mm, which meets the requirement of total thickness ≤ 10mm. Further control of the size of the three-dimensional model of the damping structure can meet the requirement of total mass ≤ 3kg, thus meeting the lightweight requirements of automotive design.

[0076] Furthermore, E is created based on the three-dimensional model of the vibration reduction structure. r *(1±5%), h a *(1±5%) test sample group: ρ of test sample group A a =4100kg / m 3 v of Group B test sample a =4305kg / m 3 ρ of the C group test sample a =3895kg / m 3 ,like Figure 4 As shown, the acceleration spectrum of the front crossbeam of the test vehicle without the test sample is curve Base; the acceleration spectrum with test sample A is curve A; the acceleration spectrum with test sample B is curve B; and the acceleration spectrum with test sample C is curve C. Among them, the average peak acceleration is the lowest after installing test sample A. Therefore, test sample A is selected as the shock absorption structure of this test vehicle.

[0077] like Figure 5 As shown, the test vehicle was driven at a constant speed of 60km / h on a standard asphalt road. By comparing the sound pressure in the driver's right ear before and after installing the Group A test sample, it was found that the vibration reduction effect was particularly obvious at the resonance peaks of 48Hz, 92Hz and 135Hz. This proves that this embodiment can effectively solve the low-frequency modal coupling problem of the front crossbeam of the roof and has a wide frequency reduction effect in the 30-300Hz frequency range.

[0078] The foregoing description of specific exemplary embodiments of the invention is for illustrative and explanatory purposes. These descriptions are not intended to limit the invention to the precise forms disclosed, and it will be apparent that many changes and variations can be made in accordance with the foregoing teachings. The exemplary embodiments were chosen and described in order to explain the specific principles of the invention and its practical application, thereby enabling those skilled in the art to implement and utilize various different exemplary embodiments of the invention, as well as various different choices and variations. The scope of the invention is intended to be defined by the claims and their equivalents.

Claims

1. A lightweight, wide-frequency damping structure for the front crossbeam of an automobile roof, characterized in that, include: The front crossbeam is designed with a Z-shaped cross-section structure, and its inner bottom wall is provided with a rib groove; The adhesive backing layer includes a boss that is geometrically matched with the rib groove, and the lower surface of the adhesive backing layer is bonded to the inner bottom wall of the front crossbeam. The damping layer has its lower surface connected to the upper surface of the adhesive backing layer; The mass layer has its lower surface connected to the upper surface of the damping layer; The damping layer is made by uniformly mixing 60-80 parts by weight of butyl rubber, 20-30 parts by weight of reinforcing agent, 5-10 parts by weight of plasticizer, 0.5-1.5 parts by weight of foaming agent, and 0.5-1.0 parts by weight of crosslinking agent; the reinforcing agent is carbon black with a particle size of 40-60 nm, the plasticizer is dioctyl phthalate, the foaming agent is azodicarbonamide, and the crosslinking agent is sulfur; After gradient baking and curing, the adhesive backing layer melts, causing the lower surface of the damping layer to connect with the inner bottom wall of the front crossbeam. The damping layer forms a viscoelastic microporous structure. The front crossbeam, as the basic vibrating body, the damping layer, as the energy dissipation medium, and the mass layer, as the tuning mass, together constitute an acoustic-vibration coupling system. The broadband factor of the acoustic-vibration coupling system is 1.2-2.

0. The gradient baking includes: Stage 1: Heat to 160°C at a heating rate of 5-10°C / min to trigger the viscous flow transition of the adhesive layer; Phase 2: Heat to 180°C within 5 minutes and hold for 15 minutes to allow the damping layer to complete cross-linking and foaming, forming a viscoelastic microporous structure. Stage 3: Cool in the furnace to below 60°C to solidify the acoustic-vibration coupling system with a bandwidth factor of 1.2-2.0; The adhesive backing layer is composed of acrylic adhesive and neodymium iron boron magnetic powder. After gradient baking and curing, the acrylic adhesive melts and the neodymium iron boron magnetic powder is oxidized to generate iron oxide and neodymium oxide. The proportion of neodymium iron boron magnetic powder is 30 wt%, the particle size is 5-10 μm, and the thickness of the adhesive backing layer after gradient baking and curing is 0.1-0.2 mm. The damping layer, after being cured by gradient baking, has a thickness of 2 mm and a loss factor of 0.25-0.35 in the 30-300 Hz frequency band. The mass layer is made of a uniform mixture of a rubber matrix and metal powder, with a density of 3500-5000 kg / m³. 3 The metal powder is iron powder and / or tungsten powder with a particle size of 20-100μm, and the thickness of the mass layer after gradient baking and curing is 3.0-7.8mm.

2. A design method for a lightweight broadband vibration damping structure for a front crossbeam of an automobile roof, characterized in that, The design method applied to the lightweight, wide-frequency damping structure for the front crossbeam of an automobile roof as described in claim 1 includes: Step S1: Obtain the physical parameters of the front crossbeam, including the front crossbeam density. 、 Front crossbeam modulus 、 Front crossbeam thickness 、 Front crossbeam length L Moment of inertia of the front crossbeam I、 No. n eigenvalues ​​of first vibration modes And the outline of the inner bottom wall of the front crossbeam; Step S2: Obtain the vertical acceleration signal of the front crossbeam and perform Fast Fourier Transform (FFT) to extract the original acceleration spectrum in the 20-200 Hz frequency band; the vertical acceleration signal of the front crossbeam is measured under the condition of the car driving at a constant speed of 60 km / h on a standard asphalt road, and the FFT analysis uses the Hanning window function; Step S3: Select the maximum peak value and several adjacent peak values ​​in the original acceleration spectrum, and calculate the weighted target frequency. ;in This is the peak acceleration value. For the corresponding frequency; Step S4: Set the thickness of the damping layer after baking and curing at 160-180 ℃ to 2 mm, and obtain the density of the damping layer. Satisfying the damping layer loss factor And calculate the Young's modulus of the damping layer. = ; Step S5: Set the bandwidth factor Establish mass layer density Quality layer thickness Solve the related equations: , ; Step S6: Establish a three-dimensional model of the damping structure that conforms to the inner bottom wall contour of the front crossbeam, satisfying that the total mass of the three-dimensional model of the damping structure is ≤3 kg and the total thickness is ≤10 mm; Step S7: Creating a 3D model of the vibration reduction structure *(1±5%) For the test sample group of (1±5%), the test acceleration spectrum of different test sample groups is extracted through step S2, and the test sample group with the lowest average peak acceleration is selected.

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