A sound insulation optimization method based on polyurethane foam electro-driven acoustic package

Abstract

This invention relates to a sound insulation optimization method based on a polyurethane foam electro-driven acoustic package, comprising the following steps: S1, determining the sound insulation layer material. S2, optimizing the sound insulation performance in the mid-to-low frequency range. The chemical reaction ratio of polyether polyol and isocyanate is adjusted to change the internal skeletal structure of the polyurethane foam and control the Young's modulus of the polyurethane, thereby altering the natural frequency of the structure composed of "motor metal shell - polyurethane foam material - sound insulation layer material" and improving acoustic performance. S3, optimizing the sound insulation performance in the mid-to-high frequency range. For the polyurethane foam material, the optimal air permeability is determined using both sound absorption and sound insulation evaluation methods. Based on the principle of prioritizing sound insulation while considering sound absorption, the air permeability is determined. This serves as the basis for determining the foam stabilizer content in the formulation system, altering the elasticity of the pore walls during cell formation, thereby controlling the foam's density and achieving optimal air permeability, thus improving the mid-to-high frequency acoustic effect.

Description

Technical Field

[0001] This invention relates to a method for optimizing the acoustic performance of automotive acoustic packages, particularly for improving the sound insulation performance of acoustic packages in electric drive assemblies of new energy vehicles, and belongs to the field of automotive NVH performance development. Background Technology

[0002] In recent years, the number of new energy vehicles in the Chinese market has been continuously increasing, and automakers are constantly expanding new features in the research and development of vehicle performance to attract consumers. The NVH (Noise, Vibration, and Harshness) level of the entire vehicle remains one of the key areas of focus for both manufacturers and consumers. Compared with the engine of a gasoline vehicle, the most significant characteristic of the noise in the electric drive system of new energy vehicles is its more complex composition, higher order of noise, and wider frequency range. Furthermore, the exhilarating acceleration "sound" of traditional gasoline vehicle engines, which some consumers appreciate, is gone. Multiple factors contribute to the poor sound quality of the electric drive system, and installing acoustic packages for noise reduction is currently the main countermeasure taken by manufacturers.

[0003] Polyurethane foam, due to its unique pore structure, offers better formability compared to fibrous sound-absorbing cotton, making it a widely used porous sound-absorbing material in automotive interiors and exteriors. In traditional gasoline-powered vehicles, it is often combined with sound insulation layers and used in interior components such as the front fascia and carpets, generally to block airborne sound transmission and reduce cabin noise. However, as a typical noise source in new energy vehicles, the acoustic package is directly installed on the electric drive assembly. It generates noise from the vibration of the engine casing surface, the radiated noise from this vibration, and airborne noise. Therefore, the noise reduction requirements for the electric drive acoustic package are higher than those for traditional interior acoustic packages.

[0004] Polyurethane foam materials are produced through the chemical reaction of polyether polyols and isocyanates. However, the same polyurethane foam material requires significantly different performance characteristics in different industries, and this is also true from an acoustic perspective; different polyurethane foam materials will produce different acoustic effects. How to quickly improve acoustic performance by controlling the raw material formulation parameters is a crucial issue in optimizing the acoustic package of an electric drive assembly. Furthermore, with the trend towards lightweighting in automobiles, according to the sound insulation quality law, there is a certain conflict between the lightweighting of the acoustic package and the improvement of sound insulation performance.

[0005] Therefore, by adjusting the raw material formulation and changing the internal cell structure of polyurethane foam, the requirements for lightweighting and acoustic performance can be met with the lowest possible amount of sound insulation layer material, which is of great significance for optimizing the sound quality inside the vehicle. Summary of the Invention

[0006] One objective of this invention is to provide a rapid and effective method for evaluating and optimizing the acoustic performance of an electric drive assembly acoustic package composed of sound insulation layer material and polyurethane foam material, based on the acoustic performance requirements of the acoustic package material for different projects. This method solves the problem of simply relying on increasing the weight of the sound insulation layer to meet noise reduction requirements. It can minimize the weight and cost of materials while meeting performance requirements, and at the same time saves the time and cost required for testing, thereby improving R&D efficiency.

[0007] Specifically, this invention provides a sound insulation optimization method based on a polyurethane foam electro-driven acoustic package, comprising the following steps:

[0008] S1. Determination of Sound Insulation Layer Material: Based on the sound insulation law of single-layer materials, 2000Hz is set as the critical frequency band. The weight of the sound insulation layer material corresponding to the target sound insulation value of 5dB below the critical frequency band is found, and the sound insulation layer curve is determined accordingly. l 1 Then, the polyurethane foam material was optimized according to low-frequency and high-frequency, with low-frequency being 400-2000Hz and high-frequency being 2000-8000Hz.

[0009] S2. Optimization of sound insulation performance in the mid-to-low frequency range: The Young's modulus and damping factor of the initial state polyurethane foam material were measured, and the natural frequency of the initial state structure was determined. f 0 By processing the sound insulation layer curve of S1 through rotation and translation, the frequency difference of the translation is obtained. ∆f The Young's modulus of the polyurethane foam material to be optimized was determined. The final chemical reaction ratio of polyether polyol and isocyanate was obtained to alter the inherent frequency of the structure composed of "motor metal casing - polyurethane foam material - sound insulation layer material," thereby improving the mid-to-low frequency acoustic performance.

[0010] S3. Optimization of sound insulation performance in the mid-to-high frequency range: Based on the sound absorption characteristics and sound leakage law of polyurethane foam material in the mid-to-high frequency range, the air permeability of the two states is determined respectively. Taking sound insulation performance as the main factor and sound absorption performance as a secondary factor, the optimal air permeability is calculated according to relevant formulas. Based on this, the content of foaming stabilizer in the formulation system is determined, the fineness of the foam is controlled, and the sound insulation performance in the mid-to-high frequency range is improved.

[0011] Preferably, in step S1, the sound insulation performance of the electro-acoustic package in the low-to-mid frequency range is optimized by adjusting the chemical reaction ratio of the raw materials polyether polyol and isocyanate, while the sound insulation performance in the mid-to-high frequency range is mainly achieved by adjusting the content of foaming stabilizer in the formulation system.

[0012] Preferably, in step S2, the chemical reaction ratio of polyether polyol and isocyanate is determined based on the Young's modulus of the polyurethane foam material. The Young's modulus and damping factor used in the acoustic elasticity model of the polyurethane foam material can be obtained by the QMA quasi-static mechanical testing and analysis instrument.

[0013] Preferably, in step S2, the method for determining the Young's modulus to be optimized is as follows: The re-layering sound insulation curve obtained in step S1 is... l 1 The curve is obtained by rotating counterclockwise. l 2 ,satisfy l 2 and l 1 The ratio of the slopes is 3; then the curve l 2 Translate until the curve is reached. l 2 The sound insulation value in the 400Hz frequency band reached the set target value, and the frequency difference during translation was recorded. ∆f This allows us to determine the optimized structural resonance frequency, and from the resonance frequency calculation formula, we can deduce the Young's modulus to be optimized.

[0014] Preferably, in step S3, the sound insulation performance of the electro-acoustic package in the mid-to-high frequency range is achieved by adjusting the content of foaming stabilizer in the polyurethane formulation system; adjusting the amount of foam stabilizer can enable the pores to grow to a thickness suitable for opening, creating conditions for opening. Different types of foam require different types of stabilizers, and the sound insulation performance is improved by refining the cell structure.

[0015] Preferably, in step S3, the content of the foaming stabilizer is determined based on the air permeability of the polyurethane foam material, and the acoustic performance of the polyurethane foam material is improved from two directions in the mid-to-high frequency range:

[0016] S3-1. At a certain thickness, there is a suitable range of air permeability that allows the polyurethane foam material to achieve optimal sound absorption performance. Under this condition, when the radiated noise of the drive assembly is reflected back and forth between the housing and the outer sound insulation layer, the intermediate polyurethane foam material can fully absorb the sound energy.

[0017] S3-2. According to the law of sound insulation leakage, leakage will significantly reduce the high-frequency sound insulation performance; reduce the air permeability of polyurethane foam material, reduce the sound energy transmission rate, and thus improve the overall sound insulation performance.

[0018] Preferably, in step S3, based on the principle of prioritizing sound insulation performance while also considering sound absorption performance, the optimal air permeability of the polyurethane foam material is determined; specifically, the air permeability of the polyurethane foam material is calculated under two conditions: 1. When the average sound absorption coefficient reaches its maximum value, the obtained air permeability value is... R 1 2. The slope of the sound insulation curve is the same as that of the optimized mid-low frequency band, and the resulting air permeability value is... R 2 Compare the breathability values ​​under the two conditions, substitute them into the following formula, and calculate to obtain the optimal breathability value. R :

[0019] a.when ( R 2 - R 1 ) / R 2 When ≤20%, R =( R 1 +R 2 ) / 2;

[0020] b. When 20% < ( R 2 - R 1 ) / R 2 When <50%, R = nR 1 +(1-n) R 2 ， in n=E 1 / E 0 ;

[0021] c. When ( R 2 - R 1 ) / R 2 When ≥50%, R = R 2 .

[0022] Compared with the prior art, the present invention has the following beneficial effects:

[0023] This paper proposes a sound insulation optimization method based on polyurethane foam electro-driven acoustic packages. This method improves the molecular and pore structure of the lightweight polyurethane foam material within the acoustic package, overcoming the increased structural weight and cost associated with increasing the mass of the heavy-duty sound insulation layer to improve acoustic performance. This approach aligns with the trend towards lightweight components and can quickly and effectively address the acoustic performance requirements of OEMs in product development, avoiding the time, cost, and accuracy issues associated with experimental testing. It provides a superior solution for research on automotive acoustic materials, particularly the development and application of polyurethane acoustic packages. Attached Figure Description

[0024] Figure 1 This is a schematic diagram illustrating the sound insulation optimization of polyurethane composite materials.

[0025] Figure 2 Schematic diagram of improving sound insulation performance by changing vibration frequency;

[0026] Figure 3 A schematic diagram illustrating the method for determining the optimal air permeability of polyurethane.

[0027] Figure 4 Comparison of sound insulation performance before and after optimization of a certain acoustic package material. Detailed Implementation

[0028] The following detailed description of exemplary embodiments of the invention is taken with reference to the accompanying drawings, which form part of the description and illustrate exemplary embodiments in which the invention may be practiced. While these exemplary embodiments have been described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be implemented and various changes may be made to the invention without departing from the spirit and scope thereof. The more detailed description of embodiments of the invention below is not intended to limit the scope of the claimed invention, but is merely illustrative and not restrictive of the description of the features and characteristics of the invention, to suggest the best mode for carrying out the invention, and is sufficient to enable those skilled in the art to practice the invention. Therefore, the scope of the invention is defined only by the appended claims.

[0029] The difference between the noise of an electric drive system in a new energy vehicle and that of a gasoline engine lies in its wider frequency range (almost covering the entire range of hearing), more order components (mechanical noise, electromagnetic noise, switching frequency noise, etc.), and poorer sound quality. It also lacks the exhilarating acceleration "engine roar" that some consumers crave in gasoline vehicles. These characteristics of electric motor noise contradict the "comfortable driving experience" that is pursued in the performance development of new energy vehicles. Therefore, reducing the transmission of electric drive system noise to the ears of drivers and passengers is one of the key indicators for improving the overall NVH performance of a vehicle.

[0030] One effective way to deal with electric drive noise is to make effective acoustic packaging on the surface of the motor. Due to the complex surface structure of electric drive and the presence of many curved surfaces, as well as the harsh conditions such as high temperature, humidity, low temperature, impact from foreign objects, and oil corrosion, the requirements for the acoustic packaging of electric drive are higher than those for traditional interior parts. Polyurethane foam material, due to its good mechanical properties and conformability, is widely used in automotive interior and exterior parts when combined with sound insulation materials.

[0031] Unlike other interior and exterior trim components, the acoustic package, as a typical sound source, is directly attached to the surface of the electric drive. It not only needs to block airborne noise transmitted from the electric drive but also reduce vibration of the housing surface in contact with it, as well as the structural noise generated by that vibration. Therefore, from a material performance perspective, modifying relevant parameters to maximize the sound insulation performance of the electric drive acoustic package without increasing raw material and manufacturing costs, while also achieving lightweight design, is a crucial factor to consider in the development of acoustic package products.

[0032] Please see Figures 1-4 This invention provides a method for improving the full-frequency sound insulation performance of an electro-acoustic package with a polyurethane foam composite structure, comprising the following steps:

[0033] S1. Determine the sound insulation layer material

[0034] The acoustic target curve for materials, primarily focused on sound insulation performance, is a graph with 1 / 3 octave band as the horizontal axis and insertion loss (dB) as the vertical axis. Generally, the NVH targets for the entire vehicle are broken down into subsystems, and then further broken down into component targets, thus determining the acoustic targets for the materials.

[0035] After the acoustic objectives are determined, the total sound insulation frequency band is divided into two parts: based on the different influence factors of polyurethane foam material on sound insulation in different frequency bands, 2000Hz is set as the critical frequency band, and the acoustic performance of the low-to-mid frequency band (200-2000Hz) and the mid-to-high frequency band (2000-8000Hz) are optimized respectively.

[0036] The combination of the electric drive assembly and the acoustic package is regarded as a "mass-spring-mass" series system. Based on the structural resonance characteristics, the mid-to-low frequency sound insulation performance is improved by changing the Young's modulus. Then, based on the sound absorption characteristics of polyurethane foam material and the influence law of sound insulation leakage, the air permeability is used as a calculation parameter to optimize the mid-to-high frequency sound insulation performance.

[0037] The insertion loss value of the target curve in the critical frequency band is IL 0 Based on the sound insulation law of single-layer materials, the surface density of the sound insulation layer material is determined so that the sound insulation value of the sound insulation layer material in the critical frequency band is 5dB lower than the target value, and the sound insulation of the single-layer material is... STL The calculation formula is:

[0038]

[0039] in, M The surface density (kg / m^2) of the sound insulation layer material. f It is the center frequency of the 1 / 3 octave band.

[0040] Utilizing the self-adhesive properties of polyurethane foam, when sound insulation composite materials are combined with polyurethane foam, the following generally occurs: compared to a single sound insulation composite material, the performance of the composite in the mid-to-high frequency range is improved, while the performance in the mid-to-low frequency range is actually reduced. The different states of the polyurethane foam material are one of the important reasons for this phenomenon. To improve the sound insulation performance across the entire frequency range, different optimization methods are applied to different frequency bands.

[0041] S2. Optimization of acoustic performance in the mid-to-low frequency range

[0042] The electric drive assembly of new energy vehicles integrates equipment such as motors, reducers, and inverters. Under actual working conditions, it generates a wide range of noise frequencies. As a typical sound-absorbing material, polyurethane foam material has a significant impact on the overall sound insulation performance when combined with sound insulation layering materials in different states. In some frequency bands, it even acts as a transfer of sound energy and fails to play a sound insulation role.

[0043] The fundamental way to improve sound insulation performance in the mid-to-low frequency range is to change the natural frequency of the structure. Since the surface of the drive assembly housing is a metal layer, the polyurethane foam material within the acoustic enclosure is a viscoelastic material, and the outermost layer is a sound-insulating layer, the combination of these three components can be approximated as a "mass-spring-mass" vibration system in the mid-to-low frequency range. The inherent frequency f of the structure is:

[0044]

[0045] in, M 1 、M 2 These are the surface densities of the electric drive housing and the sound insulation layer material, respectively. E The Young's modulus of the intermediate viscoelastic material. d The thickness of the intermediate layer material.

[0046] According to vibration theory, a structure will resonate when subjected to external excitation close to its natural frequency, at which point the sound insulation of the acoustic package is at its lowest. Referring to the sound insulation characteristics of a single-layer panel, to improve sound insulation performance, the natural frequency of the structure needs to be lowered, meaning the curve will skew to the left overall. Furthermore, from the perspective of the "mass-spring-mass" system, lowering the natural frequency, while keeping the weight and spacing thickness of the electric drive housing and the sound insulation layer constant, can effectively reduce the Young's modulus of the viscoelastic material by decreasing the natural frequency of the structure. This can effectively reduce the transmission of vibration signals between the two mass units, thereby improving the overall sound insulation effect.

[0047] use QMA The Young's modulus of the polyurethane foam material in its initial state was measured using a quasi-static mechanical testing and analysis instrument. E 0 Substituting into the above formula, we obtain the natural frequency of the structure. f 0 .

[0048] Let the sound insulation layering curve in step S1 be... l 1 The slope is k 1 First, the curve l 1 The curve is obtained by rotating counterclockwise. l 2 The slope is k 2 ,satisfy k 2 and k 1 The ratio is 3, then... l 2 Shift to the left to obtain the curve. l 3 and satisfy l 3 Once the sound insulation value in the 400Hz frequency band reaches the target value, record the frequency difference after translation. ∆f The structural resonant frequency to be optimized f 1 =f 0 -∆f Then, based on the natural frequency formula, the optimized Young's modulus value of the polyurethane foam material is derived. E 1 .

[0049] The structure of the electric drive acoustic package is similar to the "double wall" theory in acoustics, but it differs from a typical "double wall" in that the excitation on the surface of a typical "double wall" sound insulation structure is mostly airborne noise. However, as one of the important noise sources of the entire vehicle, the acoustic package of the electric drive assembly is directly installed on its surface structure. In addition to isolating the air noise generated inside the motor, the acoustic package also suppresses the vibration of the motor surface and the structural noise generated by the vibration to the greatest extent.

[0050] Polyether polyols and isocyanates can produce complex reaction results depending on their ratio in a chemical reaction. By changing the ratio of polyether polyol to isocyanate to alter the Young's modulus of polyurethane foam, not only can the sound insulation performance of the composite structure be improved, but the damping loss factor of the material can also be increased. This allows the material to adhere to the surface of the motor, thereby increasing damping and reducing the vibration radiation energy of the motor surface.

[0051] Assume the ratio of polyether polyol to isocyanate in the initial chemical reaction of the polyurethane foam material. X 1 Foaming was performed in a closed mold in the laboratory, and adjustments were made. X 1 The value, under the condition that the total foaming mass (density) remains unchanged, is the reaction mass of the polyether polyol in the chemical reaction of the optimized polyurethane foam material, and the ratio of the amounts is: X 2 Based on this, the linear relationship between Young's modulus and formulation ratio can be determined, and the formulation ratio required for subsequent acoustic target adjustments can be predicted.

[0052] Therefore, by adjusting the degree of chemical reaction between the two components according to a given ratio, the Young's modulus of the resulting polyurethane foam material is kept within a controllable range. The advantage of this adjustment method is that, during production, the required adjustment ratio can be determined based on prior theoretical calculations. Relevant parameters can be directly changed on the foaming line, thereby quickly obtaining the desired polyurethane foam material to meet the needs of product performance optimization and enabling rapid product switching.

[0053] S3. Optimization of mid-to-high frequency acoustic performance

[0054] The electric motor drive assembly also generates complex noise in the mid-to-high frequency range, such as high-order electromagnetic radiation and umbrella-shaped order noise from the switching frequency. These noises are absent in the radiated noise of traditional internal combustion engine engines and need to be addressed. Performance optimization in the mid-to-high frequency range is based on the following approach:

[0055] The electric drive acoustic package is wrapped around the motor in the form of a "sound insulation layer + polyurethane foam material," primarily serving to isolate the motor's noise radiation. However, as a typical sound-absorbing material, the sound absorption capacity of polyurethane foam also contributes to the overall sound insulation effect of the acoustic package. Therefore, the optimization direction of the material is defined based on the following two perspectives:

[0056] (a) Sound absorption performance of polyurethane foam materials. According to the Allard & Champoux theory, for a given thickness, air permeability is an important parameter affecting the sound absorption performance of a material. There is a suitable range of air permeability that allows the material to achieve optimal sound absorption performance at a given thickness, while air permeability that is too high or too low is not conducive to the material's energy absorption.

[0057] (b) Sound insulation performance of composite components. Based on the sound leakage characteristics of single-layer sound insulation, the leakage area has a significant impact on sound insulation in the mid-to-high frequency range. In particular, high-frequency sound insulation performance will show a significant decrease. To improve the sound insulation performance of composite materials, the air permeability of the polyurethane foam should be reduced as much as possible.

[0058] The two optimization approaches described above may conflict to some extent: reducing the air permeability of the polyurethane foam material according to (b) may fall outside the appropriate range proposed in (a). Therefore, considering the overall effectiveness of the polyurethane foam material in the acoustic package, the optimal air permeability is determined through the following steps:

[0059] (1) Within the 2000-8000Hz range, with the goal of maximizing the average sum of the sound absorption coefficients of each frequency band in a 1 / 3 octave band, and using the adjustable range of the air permeability of the actual polyurethane foam material as a variable, the sound absorption coefficient is calculated in the acoustic calculation tool NOVA. The air permeability value of the polyurethane foam material corresponding to the maximum value of the average sound absorption coefficient is then determined. R 1 ;

[0060] (2) The curve obtained by S1 l 2 slope k 2 As the target slope to be achieved for the 2000-8000Hz sound insulation curve, the adjustable range of the air permeability of the actual polyurethane foam material is used as a variable. This is substituted into NOVA to calculate the insertion loss of the composite flat material of S1 sound insulation layer and polyurethane foam material, and recorded within the adjustable range of variables. The minimum air permeability value corresponding to achieving the target slope is... R 2 ;

[0061] (3) Comparison R 1 and R 2The final optimal breathability value is R Its determination method is (generally speaking) R 1 < R 2 ):

[0062] a.when ( R 2 - R 1 ) / R 2 When ≤20%, R =( R 1 +R 2 ) / 2;

[0063] b. When 20% < ( R 2 - R 1 ) / R 2 When <50%, R = nR 1 +(1-n)R 2 ， in n=E 1 / E 0 ;

[0064] c. When ( R 2 - R 1 ) / R 2 When ≥50%, R = R 2 .

[0065] The air permeability value is determined by considering the application scenarios of the acoustic materials. On the surface of the motor drive assembly, an acoustic package is used to block noise transmission to the ears of the occupants in the cockpit. The evaluation metric is the noise reduction before and after the installation of the acoustic package. Therefore, from the perspective of the material's acoustic performance, sound insulation is the primary focus, while sound absorption is also taken into account.

[0066] The optimal air permeability of polyurethane foam material is determined based on the above method. The foam cell structure is controlled by optimizing the foam stabilizer in the polyurethane foam material synthesis formula. Its main function is to disperse the large amount of polyurea compounds generated during the foaming process, improve the compatibility between the components, enable the pores to grow to a suitable thickness for opening, create conditions for opening, control the size and uniformity of the pores, and make the pore walls elastic, maintain tension balance, and prevent the collapse of the pores.

[0067] The dosage of foam stabilizer is determined using a linear interpolation method. This involves selecting any two foaming concentrations within the adjustable range of stabilizer content, choosing the corresponding air permeability for each concentration, and then determining the required foaming agent content based on the target air permeability. If the stabilizer content corresponding to the target air permeability exceeds the adjustable range, the lower or upper limit of the adjustable range is selected.

[0068] As an alternative example, a certain new energy electric drive acoustic package is composed of a sound insulation layer material, ethylene-vinyl acetate copolymer (EVA), and a polyurethane foam material. Using sound insulation performance as an evaluation index, this case illustrates an implementation example of optimizing the acoustic package of the electric drive assembly.

[0069] Determine the surface density of the sound insulation layer material. Following the step-by-step decomposition of the vehicle's NVH performance targets, for each set target, the lower limit of the insertion loss value for each frequency band from 400Hz to 8000Hz (1 / 3 octave band) is generally... P arrive Q And the slope is k 0 curve l 0 Following step S1, the EVA surface density is determined based on the sound insulation law of single-layer boards at a point 5 dB below the target value in the critical frequency band. M 1 And set the slope of the single-layer EVA sound insulation curve to be... k 1 .

[0070] The state of the polyurethane foam material to be optimized was determined. Following step S2, samples were first taken from the original drive assembly acoustic package, and the Young's modulus of the initial state of the polyurethane foam material was measured using a QMA quasi-static mechanical testing and analysis instrument. E 0 And the damping loss factor η, and then the structural theory of the vibration system composed of the drive assembly shell and the acoustic package, and the natural frequency of the original acoustic package structure calculated from the Young's modulus of the initial state polyurethane foam material. f 0 .

[0071] Determine the resonant frequency of the optimized structure. Following step S2, apply the sound insulation curve of the sound-insulating EVA layer obtained in step S1. l 1Using the sound insulation value of the critical frequency band as a fixed point, and rotating counterclockwise, the resulting curve is... l 2 The slope is k 2 ,satisfy k 2 : k 1 =3 , curve l 2 Then shift the position until the sound insulation value at 400Hz reaches the target value. P Let the curve at this time be... l 3 Simultaneously record the frequency deviation caused by translation. ∆f The resonant frequency of the structure to be optimized is obtained as follows: f 1 =f 0 -∆f And it introduces optimized Young's modulus values ​​for polyurethane foam materials. E 1 .

[0072] Based on the above method, the initial Young's modulus value of a certain new energy electric drive acoustic package is... E 0 At 140 kPa, the sound insulation effect of both the material and components after being combined with EVA was unsatisfactory. Based on the above structural frequency adjustment method, the Young's modulus value of the adjusted polyurethane foam material was determined to be 60 kPa. Simultaneously, the chemical reaction ratio of the two foaming raw materials was adjusted from the initial 1.67 to 2.23. The relationship between the Young's modulus of the polyurethane foam material and the reaction ratio in the formulation system of this acoustic package product can be determined as follows:

[0073]

[0074] According to step S3, for a certain new energy electric drive acoustic package, the thickness of the polyurethane foam material is distributed in the range of 10-20mm over 90% of the overall area. A thickness of 15mm is selected for analysis. First, using the Allard & Champoux sound absorption model, with the goal of maximizing the average value of the sum of the sound absorption coefficients of each 1 / 3 octave band within the 2000-8000Hz range, the optimal air permeability value at a pressure difference of 125Pa is calculated to be 61L / min. Second, the slope of the sound insulation curve from 2000-8000Hz is used to achieve... k 2 With the target value of 23 L / min, the air permeability was determined using the acoustic calculation software NOVA. Based on the final formula, the optimal air permeability value was found to be 23 L / min.

[0075] Based on the established ratio of polyether polyol to isocyanate, the adjustable range of foam stabilizer is 0.5%-2.1%. By selecting 3-5 of these ratios, corresponding polyurethane foam materials are prepared, their air permeability is measured, and the foam stabilizer content of this acoustic package is determined to be 1.80% using interpolation.

[0076] Based on the above analysis, the polyurethane foam material of a certain acoustic package can be adjusted from the original formula ratio of 1.67 and foaming stabilizer content of 1.27% to a formula ratio of 2.23 and stabilizer content of 1.80%. By adjusting the corresponding parameters of the production line accordingly, the acoustic target of the material can be achieved.

[0077] The present invention and its embodiments have been described above illustratively. This description is not restrictive, and the figures shown are only one embodiment of the present invention; the actual structure is not limited thereto. Therefore, if those skilled in the art are inspired by this description and design similar structures and embodiments without departing from the spirit of the present invention, such designs should fall within the protection scope of the present invention.

Claims

1. A method for sound insulation optimization based on polyurethane foam electro-driven acoustic package, characterized in that, Includes the following steps: S1. Determination of Sound Insulation Layer Material: Based on the sound insulation law of single-layer materials, 2000Hz is set as the critical frequency band. The weight of the sound insulation layer material corresponding to the target sound insulation value of 5dB below the critical frequency band is found, and the sound insulation layer curve is determined accordingly. l 1 Then, the polyurethane foam material was optimized according to low-frequency and high-frequency, with low-frequency being 400-2000Hz and high-frequency being 2000-8000Hz. S2. Optimization of sound insulation performance in the mid-to-low frequency range: The Young's modulus and damping factor of the initial state polyurethane foam material were measured, and the natural frequency of the initial state structure was determined. f 0 The sound insulation layering curve in step S1 is processed by rotation and translation. l 1 The frequency difference Δf of the translation is obtained, the Young's modulus of the polyurethane foam material to be optimized is determined, and the chemical reaction ratio of polyether polyol and isocyanate is finally obtained to change the natural frequency of the structure composed of "motor metal shell-polyurethane foam material-sound insulation layer material" and improve the mid-low frequency acoustic performance. S3. Optimization of Mid-to-High Frequency Sound Insulation Performance: Based on the sound absorption characteristics and sound leakage patterns of polyurethane foam materials in the mid-to-high frequency range, the air permeability of two states was determined. Prioritizing sound insulation performance while considering sound absorption performance, the optimal air permeability was calculated using relevant formulas. This was then used to determine the content of the foaming stabilizer in the formulation system, control the foam density, and improve mid-to-high frequency sound insulation performance. Specifically, based on the principle of prioritizing sound insulation performance while considering sound absorption performance, the optimal air permeability of the polyurethane foam material was determined. Specifically, the air permeability of the polyurethane foam material was calculated in two states:

1. When the average sound absorption coefficient reaches its maximum value, the obtained air permeability value is... R 1 ; 2. The slope of the sound insulation curve is the same as that of the optimized mid-low frequency band, and the resulting air permeability value is... R 2 Compare the breathability values ​​under the two conditions, substitute them into the following formula, and calculate to obtain the optimal breathability value. R : a.when ( R 2 - R 1 ) / R 2 When ≤20%, R =( R 1 +R 2 ) / 2; b. When 20% < ( R 2 - R 1 ) / R 2 When <50%, R = nR 1 +(1-n) R 2 ， in n=E 1 / E 0 ; c. When ( R 2 - R 1 ) / R 2 When ≥50%, R = R 2 .

2. The sound insulation optimization method based on polyurethane foam electro-driven acoustic package according to claim 1, characterized in that, In step S1, the sound insulation performance of the electro-acoustic package in the low-to-mid frequency range is optimized by adjusting the chemical reaction ratio of the raw materials polyether polyol and isocyanate, while the sound insulation performance in the mid-to-high frequency range is optimized by adjusting the content of foaming stabilizer in the formulation system.

3. The sound insulation optimization method based on polyurethane foam electro-driven acoustic package according to claim 1, characterized in that, In step S2, the chemical reaction ratio of polyether polyol and isocyanate is determined based on the Young's modulus of polyurethane foam material. The Young's modulus and damping factor used in the acoustic elasticity model of polyurethane foam material can be obtained by the QMA quasi-static mechanical testing and analysis instrument.

4. The sound insulation optimization method based on polyurethane foam electro-driven acoustic package according to claim 1, characterized in that, In step S2, the method for determining the Young's modulus to be optimized is as follows: The sound insulation layering curve obtained in step S1 is used as the basis for determining the Young's modulus. l 1 The curve is obtained by rotating counterclockwise. l 2 ,satisfy l 2 and l 1 The ratio of the slopes is 3; then the curve l 2 Translate until the curve is reached. l 2 The sound insulation value in the 400Hz frequency band reaches the set target value, and the frequency difference Δf of the translation is recorded. The optimized structural resonance frequency is determined from this, and the Young's modulus to be optimized is derived from the resonance frequency calculation formula.

5. The sound insulation optimization method based on polyurethane foam electro-driven acoustic package according to claim 1, characterized in that, In step S3, the sound insulation performance of the electro-acoustic package in the mid-to-high frequency range is achieved by adjusting the content of foaming stabilizer in the polyurethane formulation system. Adjusting the amount of foam stabilizer can allow the pores to grow to a thickness suitable for opening, creating conditions for opening. Different types of foam require different types of stabilizers, and the sound insulation performance is improved by refining the cell structure.

6. The sound insulation optimization method based on polyurethane foam electro-driven acoustic package according to claim 1, characterized in that, In step S3, the content of the foaming stabilizer is determined based on the air permeability of the polyurethane foam material, and the acoustic performance of the polyurethane foam material is improved from two directions in the mid-to-high frequency range: S3-1. Under a certain thickness, there is a suitable range of air permeability so that the sound absorption performance of polyurethane foam material reaches the optimal level. Under this condition, when the radiated noise of the drive assembly is reflected back and forth between the housing and the outer sound insulation layer, the middle layer of polyurethane foam material can fully absorb the sound energy. S3-2. According to the law of sound insulation leakage, leakage will significantly reduce the high-frequency sound insulation performance; reduce the air permeability of polyurethane foam material, reduce the sound energy transmission rate, and thus improve the overall sound insulation performance.

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