Automobile exhaust system impedance composite staged muffler system and full-frequency acoustic matching method
By using a three-stage impedance composite graded silencing system and a full-band acoustic matching method, the problems of insufficient low-frequency response and acoustic mismatch in automotive exhaust mufflers are solved, achieving efficient noise reduction across the entire frequency band and a compact muffler design suitable for rapid adaptation to different engines.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ZHONGXIANG MINGDONG MUFFLER
- Filing Date
- 2026-03-01
- Publication Date
- 2026-05-29
AI Technical Summary
Existing automotive exhaust mufflers have insufficient noise reduction capabilities in the low-frequency range, are prone to acoustic impedance mismatch in the mid-to-high-frequency range, and lack a systematic matching method in their design, resulting in uneven noise reduction performance and difficulty in meeting the adaptation requirements of different engines.
It adopts a three-stage series structure, including a pre-orifice injection stage, a middle resistive grading stage, and a post-resistive absorption stage. Combined with inter-stage coupling tubes, it achieves precise noise reduction across the entire frequency band through graded noise reduction and impedance coupling design, combined with multi-parameter optimization based on the sound source spectrum and acoustic impedance model.
It achieves precise noise reduction across the entire frequency band from 20 to 5000 Hz, improves the consistency of noise reduction performance, has a compact structure, strong adaptability, low airflow resistance loss, and improves R&D efficiency.
Smart Images
Figure CN122106728A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of automotive exhaust noise control technology, specifically relating to an impedance composite graded silencing system for automotive exhaust systems and a full-frequency acoustic matching method. Background Technology
[0002] With increasingly stringent vehicle emission standards and rising user demands for NVH performance, automotive exhaust mufflers need to achieve efficient noise reduction across a wide frequency range while maintaining airflow resistance characteristics and structural compactness. Existing automotive exhaust mufflers mostly employ a single-impedance composite structure, combining sound-absorbing materials with resistive structures such as expansion chambers and internal tubes to achieve noise reduction. However, this approach has significant technical shortcomings: firstly, insufficient noise reduction capability in the low-frequency range (20–200Hz), making it difficult to effectively suppress low-frequency engine exhaust noise; secondly, reflection interference due to acoustic impedance mismatch in the mid-to-high frequency range, leading to fluctuations in noise reduction performance; and thirdly, the design of noise reduction parameters lacks a systematic matching method, relying heavily on experience-based adjustments, making it difficult to achieve precise noise reduction across the entire frequency range.
[0003] The core of impedance composite mufflers lies in the synergistic work of reactive structures and resistive materials. The reactive structure achieves low-frequency noise reduction through sound wave reflection and interference, while the resistive material achieves mid-to-high-frequency noise reduction through energy absorption. In existing technologies, some solutions improve low-frequency performance by increasing the number of expansion chambers, but this easily leads to excessively large structural volumes. Other solutions use micro-perforated sound-absorbing interlayers to optimize mid-to-high-frequency performance, but lack impedance matching design with the low-frequency reactive structure. Furthermore, traditional muffler system design methods do not establish a direct correlation between the sound source spectrum and system parameters, making it difficult to achieve precise matching for engines of different displacements and operating conditions. This results in poor adaptability of the muffler performance to the vehicle, limiting its application in new energy hybrid vehicles and large-displacement gasoline vehicles.
[0004] Therefore, developing a compact and precisely graded impedance composite anechoic system, as well as a full-band acoustic matching method based on sound source characteristics, to solve the problems of uneven frequency band coverage, impedance mismatch, and low design efficiency in existing technologies, has significant engineering and market value. Summary of the Invention
[0005] This invention aims to solve the technical problems of existing automotive exhaust mufflers, such as insufficient low-frequency noise reduction, mid-to-high frequency acoustic mismatch, uneven noise reduction coverage across the entire frequency band, lack of systematic matching methods for muffler system parameter design, and poor adaptability. It provides a compact, graded, and efficient impedance composite graded muffler system, as well as a full-frequency acoustic matching method based on the sound source spectrum and acoustic impedance model, to achieve accurate noise reduction across the entire frequency band from 20 to 5000 Hz, while controlling airflow resistance loss and meeting the adaptation requirements of different engines.
[0006] This invention provides an impedance composite graded silencing system for automotive exhaust systems, which adopts a three-stage series structure of "front-mounted small-hole injection stage - mid-mounted resistive graded stage - rear-mounted resistive absorption stage". Through graded silencing and inter-stage impedance coupling design, it achieves precise noise reduction in different frequency bands. At the same time, it provides a corresponding full-band acoustic matching method, which achieves full-band acoustic impedance matching based on the sound source spectrum and acoustic impedance model through multi-parameter optimization and inter-stage calibration.
[0007] (I) Impedance-based graded muffler system for automotive exhaust systems
[0008] Overall Structure: The system comprises a front-mounted small-hole injection muffler, a centrally located reactive graded muffler, a rear-mounted resistive absorption muffler connected in series, as well as interstage coupling pipes connecting each muffler and an exhaust tailpipe at the end. The modular design of each muffler facilitates assembly and adaptation to different vehicle layouts.
[0009] Pre-amplified small-orifice injection silencer: Composed of an intake pipe, a small-orifice injection pipe, and a first expansion chamber. The intake pipe is connected to the engine exhaust manifold, and the small-orifice injection pipe is coaxially arranged at the end of the intake pipe, with injection holes arranged circumferentially, the hole diameter being 0.5–2 mm and the opening ratio 3%–8%. The injection holes introduce part of the sound waves into the first expansion chamber, enhancing the low-frequency (20–200 Hz) silencing performance through the injection interference effect, thus solving the problem of insufficient low-frequency silencing in traditional reactive structures.
[0010] The central reactive graded noise reduction stage comprises 2–3 cascaded expansion chambers with a chamber volume ratio of 1:(0.6–0.8):(0.4–0.6), adapting to the reflection and interference requirements of sound waves in different frequency bands. Multi-scale internal tube assemblies are installed within the chambers. The length of the main internal tube is 0.3–0.7 times the equivalent length of the corresponding chamber, arranged in a cross-shaped pattern. The insertion depth difference between internal tubes in adjacent chambers is 50–150 mm to prevent direct sound wave transmission. Branch internal tubes are connected to a Helmholtz resonator, which is a modular structure with a neck diameter of 8–16 mm and a length of 10–25 mm. The cavity volume is calculated based on the target noise reduction frequency, used for precise suppression of mid-frequency (200–1000 Hz) peak noise.
[0011] Post-resistive absorption silencer stage: Composed of a silencer shell, micro-perforated plate, sound-absorbing material interlayer, and exhaust tailpipe. The micro-perforated plate and the inner wall of the silencer shell form a sandwich structure, filled with high-temperature resistant glass wool or ceramic fiber wool, with a filling thickness of 20–50 mm and a density of [not specified]. The micro-perforated plate has a pore size of 0.8–1.5 mm and a perforation rate of 1%–3%. It works synergistically with sound-absorbing materials to efficiently absorb high-frequency noise (1000–5000 Hz) with a sound absorption coefficient ≥0.8.
[0012] Interstage coupling structure: The interstage coupling tube is equipped with impedance matching holes with a diameter of 5–12 mm and a quantity of 2–6 holes. By adjusting the diameter and quantity of holes, the acoustic impedance of adjacent noise reduction stages can be calibrated, eliminating interstage sound wave reflection interference and improving the uniformity of noise reduction across the entire frequency band.
[0013] (II) Full-band acoustic matching method
[0014] Sound source spectrum acquisition: Through engine bench testing, the exhaust noise spectrum of the target engine under all operating conditions of idling, low speed, medium speed and high speed is acquired using a microphone. The sampling frequency is ≥10kHz. The peak frequency, sound pressure level distribution and spectral characteristics in the 20-5000Hz frequency band are analyzed to establish a sound source spectrum database, which provides a basis for subsequent matching design.
[0015] Acoustic impedance model construction: Based on the one-dimensional acoustic transfer matrix method, transfer matrices are established for the air inlet pipe, small-hole injection port, expansion chamber, inner tube, Helmholtz resonant cavity, sound-absorbing interlayer, and tailpipe, respectively. The total transfer matrix of the silencing system is obtained by matrix multiplication. Based on the total transfer matrix, the acoustic impedance characteristics and transmission loss of the system are calculated, clarifying the contribution of each silencing level and structural parameters to the silencing performance in different frequency bands.
[0016] Target transmission loss curve development: Combining the vehicle's NVH development goals with the China VI emission standard requirements, and based on the sound source spectrum database, a full-frequency band target transmission loss curve was developed. Specifically, the target is ≥25dB for the low-frequency band (20–200Hz), ≥20dB for the mid-frequency band (200–1000Hz), and ≥18dB for the high-frequency band (1000–5000Hz), ensuring that noise levels across the entire frequency band meet regulatory and user requirements.
[0017] Multi-parameter optimization matching: The optimization variables include the chamber volume of the centrally located reactive grade, the length and diameter of the internal tube, the opening ratio of the pre-injection orifice, the parameters of the rear micro-perforated plate, and the parameters of the Helmholtz resonator. The optimization objectives are to maximize the average transmission loss across the entire frequency band and minimize the airflow drag loss. A particle swarm optimization algorithm is used for multi-objective optimization. The optimization constraint is airflow drag loss. The optimal parameter combination is obtained by setting the weight coefficients ω1=0.8 and ω2=0.2.
[0018] Interstage impedance coupling calibration: By adjusting the diameter and number of impedance matching holes in the interstage coupling tube, the acoustic impedance coupling characteristics of adjacent silencing stages are changed, eliminating the silencing troughs caused by interstage sound wave reflection, and ensuring stable silencing performance across the entire frequency band.
[0019] Verification and Iteration: The optimized muffler system was simulated and analyzed using acoustic simulation software such as Virtual.Lab to calculate transmission loss and airflow resistance loss. The acoustic performance and drag characteristics of the muffler system were measured through engine bench tests. If the simulation or test results did not meet the target transmission loss curve, the process returned to the multi-parameter optimization step, and the parameters were readjusted until the acoustic matching requirements of the entire frequency band were met.
[0020] Beneficial effects:
[0021] 1. High-efficiency noise reduction across the entire frequency band: Through a three-stage graded silencing structure and a full-frequency acoustic matching method, precise noise reduction is achieved across the entire frequency band from 20 to 5000 Hz, with a transmission loss improvement of ≥8dB across the entire frequency band. Among them, the noise reduction in the low-frequency band (20–200 Hz) is ≥15dB, effectively solving the problem of insufficient low-frequency silencing in traditional silencers.
[0022] 2. Precise acoustic impedance matching: Based on the impedance model of the sound source spectrum and transfer matrix method, through multi-parameter optimization and inter-stage calibration, the mid-to-high frequency acoustic mismatch is eliminated, the noise reduction performance fluctuation is ≤3dB, and the noise reduction consistency of the whole frequency band is improved.
[0023] 3. Compact structure and strong adaptability: The modular and hierarchical structure design reduces the volume by 15%–20% compared to traditional multi-cavity mufflers. The Helmholtz resonant cavity and sound-absorbing materials can be quickly replaced to adapt to different displacement engines and vehicle layout requirements.
[0024] 4. Excellent airflow resistance characteristics: By optimizing the chamber structure and internal tube arrangement, the airflow resistance loss is ≤2kPa, avoiding the increase of engine exhaust back pressure and ensuring engine power performance and fuel economy.
[0025] 5. Significantly improved design efficiency: The systematic acoustic matching method shortens the traditional experience-based debugging cycle from 2-3 months to 2-3 weeks, reducing R&D costs and accelerating product iteration. Attached Figure Description
[0026] Figure 1 This is a schematic diagram of the overall structure of the noise reduction system in this invention;
[0027] Figure 2 This is a schematic diagram of the front-mounted small-hole injection noise reduction stage structure in this invention;
[0028] Figure 3 This is a schematic diagram of the centrally located reactive graded noise reduction stage structure in this invention;
[0029] Figure 4 This is a schematic diagram of the post-resistive absorption noise reduction stage structure in this invention;
[0030] Figure 5 This is a comparison chart of the transmission loss curves in simulation and experiment of Example 1 of the present invention. Detailed Implementation
[0031] The technical solution of the present invention will be further described in detail below with reference to specific embodiments.
[0032] Example 1
[0033] This embodiment provides an impedance composite graded silencing system and a full-frequency acoustic matching method adapted to a 2.0T turbocharged gasoline engine.
[0034] (I) Parameter Design of the Silencing System
[0035] Pre-amplified small-hole injection silencer: intake pipe diameter 60mm, small-hole injection pipe diameter 50mm, injection hole diameter 1mm, opening rate 5%, first expansion chamber volume 2.0L.
[0036] The centrally located reactive graded anechoic chamber comprises two expansion chambers with volumes of 3.5L and 2.5L (volume ratio 1:0.71). The main internal cannula in the first chamber is 280mm long, and the main internal cannula in the second chamber is 200mm long, with an insertion depth difference of 80mm. The Helmholtz resonator has a neck tube diameter of 12mm and a length of 18mm, a chamber volume of 0.8L, and a target anechoic frequency of 400Hz.
[0037] Post-resistive absorption silencing stage: Silencing shell diameter 180mm, micro-perforated plate with 1.2mm pore diameter and 2% perforation rate; sound-absorbing material is high-temperature resistant glass wool with a filling thickness of 35mm and a density of... .
[0038] Interstage coupling tube: 55mm in diameter, 8mm in diameter impedance matching hole, 4 in number.
[0039] (II) Implementation of the full-band acoustic matching method
[0040] Sound source spectrum acquisition: On the engine test bench, the exhaust noise spectrum of the 2.0T engine under idling (750r / min), low speed (1500r / min), medium speed (2500r / min), and high speed (4000r / min) conditions was acquired, and the peak frequencies were determined to be 80Hz, 400Hz, and 1800Hz, with sound pressure levels of 115dB, 110dB, and 105dB, respectively.
[0041] Acoustic impedance model construction: Based on the transfer matrix method, the transfer matrices of each component are established, and the total system transfer matrix is obtained by matrix multiplication. The transfer losses of the original system in the 80Hz, 400Hz and 1800Hz frequency bands are calculated to be 12dB, 16dB and 15dB, respectively.
[0042] Target transmission loss curve formulation: Based on the vehicle NVH target, the target transmission loss is formulated as follows: 80Hz≥28dB, 400Hz≥22dB, 1800Hz≥20dB, and the average value across the entire frequency band≥18dB.
[0043] Multi-parameter optimization matching: Using the chamber volume, inner tube length, injection orifice opening ratio, and Helmholtz resonant cavity parameters as optimization variables, the particle swarm optimization algorithm was used to obtain the optimal parameters: injection orifice opening ratio 6%, Helmholtz resonant cavity neck tube length 16mm, chamber volume 0.9L, and first chamber main inner tube length 290mm.
[0044] Interstage impedance coupling calibration: Adjust the diameter of the impedance matching hole of the interstage coupling tube to 9mm, and the number of holes to 4. After calibration, the interstage reflection coefficient is ≤0.1.
[0045] Verification and Iteration: Simulation analysis shows that the optimized system has transmission losses of 30dB, 24dB, and 22dB in the 80Hz, 400Hz, and 1800Hz frequency bands, respectively, with an average transmission loss of 20dB across the entire frequency band and an airflow drag loss of 1.8kPa. The bench test results are consistent with the simulation and meet the requirements of the target transmission loss curve.
[0046] Example 2
[0047] This embodiment provides an impedance composite graded silencing system and a full-frequency acoustic matching method adapted to a 1.5L naturally aspirated gasoline engine, which differs from Embodiment 1 in that:
[0048] The central reactive graded anechoic chamber uses three expansion chambers with volumes of 2.0L, 1.5L, and 1.0L (volume ratio 1:0.75:0.5).
[0049] The target silencing frequency of the Helmholtz resonator is 300Hz, the neck diameter is 10mm, the length is 15mm, and the cavity volume is 0.6L.
[0050] The rear sound-absorbing material uses ceramic fiber cotton, with a filling thickness of 25mm and a density of .
[0051] Bench test results show that the system improves transmission loss by ≥8dB across the entire frequency band, reduces noise by ≥16dB in the low frequency band (20–200Hz), and reduces airflow resistance by 1.5kPa, meeting the exhaust noise reduction requirements of a 1.5L engine.
Claims
1. A composite graded noise reduction system for automotive exhaust systems, characterized in that, It includes a pre-positioned small-hole injection silencing stage, a mid-positioned resistive graded silencing stage, and a post-positioned resistive absorption silencing stage connected in series. The pre-positioned small-hole injection silencer includes an air inlet pipe and a small-hole injection pipe. The small-hole injection pipe is circumferentially arranged with injection holes of 0.5–2 mm in diameter and 3%–8% in opening ratio, and is connected to the first expansion chamber. The centrally located reactive graded anechoic stage includes at least two series-connected expansion chambers, each containing a multi-scale internal tube assembly. The internal tube assembly includes a main internal tube and branch internal tubes. The length of the main internal tube is 0.3–0.7 times the equivalent length of the corresponding chamber, and the branch internal tubes are connected to the Helmholtz resonator. The post-resistive absorption noise reduction stage includes a noise reduction shell, a micro-perforated plate, and a sound-absorbing material interlayer. The interlayer is composed of the micro-perforated plate and the inner wall of the noise reduction shell, and is filled with porous sound-absorbing material. The micro-perforated plate has a pore diameter of 0.8–1.5 mm and a perforation rate of 1%–3%. It also includes an interstage coupling pipe and an exhaust tailpipe. The interstage coupling pipe is provided with an impedance matching hole for adjusting the acoustic impedance coupling characteristics of adjacent silencer stages.
2. The system according to claim 1, characterized in that, The Helmholtz resonant cavity is a modular structure, including a cavity body and a neck tube. The neck tube has a diameter of 8–16 mm and a length of 10–25 mm. The cavity volume is calculated and determined according to the target silencing frequency f0 using the formula V=(c²S) / (4π²f0²Leff), where c is the speed of sound, S is the cross-sectional area of the neck tube, and Leff is the effective length of the neck tube.
3. The system according to claim 1, characterized in that, The porous sound-absorbing material is high-temperature resistant glass wool or ceramic fiber wool, with a filling thickness of 20–50 mm, a density of 30–80 kg / m³, and a sound absorption coefficient ≥0.8 in the 1000–5000 Hz frequency band.
4. The system according to claim 1, characterized in that, The centrally located reactive graded anechoic chamber has 2–3 expansion chambers with a chamber volume ratio of 1:(0.6–0.8):(0.4–0.6). The main internal tubes are arranged in a cross pattern, and the insertion depth difference between the internal tubes of adjacent chambers is 50–150 mm.
5. A full-band acoustic matching method based on the system described in any one of claims 1–4, characterized in that, Includes the following steps: S1. Exhaust noise source spectrum acquisition: Through engine bench testing, the exhaust noise spectrum of the target engine under all operating conditions is acquired to determine the peak frequency and sound pressure level distribution in the 20–5000Hz frequency band and establish a sound source spectrum database. S2. Acoustic impedance model construction: Based on the one-dimensional acoustic transfer matrix method, the acoustic impedance model of the anechoic system is constructed to clarify the impedance characteristics and transmission loss contribution of each anechoic stage and the inter-stage coupling structure. S3. Target Transmission Loss Curve Development: Based on the vehicle's NVH targets and emission standards, and combined with the sound source spectrum, develop a full-frequency target transmission loss curve, where the target for the low-frequency band (20–200Hz) is ≥25dB, the target for the mid-frequency band (200–1000Hz) is ≥20dB, and the target for the high-frequency band (1000–5000Hz) is ≥18dB. S4. Multi-parameter optimization and matching: Using the chamber volume, internal tube parameters, injection orifice opening ratio, micro-perforated plate parameters, and Helmholtz resonant cavity parameters as optimization variables, and the full-band transmission loss and airflow resistance loss as optimization objectives, the particle swarm optimization algorithm is used to perform multi-objective optimization to obtain the optimal parameter combination. S5. Interstage impedance coupling calibration: By adjusting the diameter and number of impedance matching holes in the interstage coupling tube, the acoustic impedance matching degree of adjacent silencer stages is calibrated to eliminate interstage acoustic wave reflection interference. S6. Verification and Iteration: Verify the noise reduction performance through acoustic simulation and bench testing. If the target transmission loss curve is not reached, return to step S4 to re-optimize the parameters until the full-band acoustic matching requirements are met.
6. The method according to claim 5, characterized in that, In step S4, the optimization constraint for the airflow resistance loss is ≤2kPa, and the optimization objective function is: F = ω1 × (1 / TL_avg) + ω2 × ΔP, Where TL_avg is the average transmission loss across the entire frequency band, ΔP is the airflow drag loss, ω1 and ω2 are weighting coefficients, and ω1+ω2=1.
7. The method according to claim 5, characterized in that, In step S2, the matrix unit of the acoustic transfer matrix method includes the transfer matrices of the air inlet pipe, injection hole, expansion chamber, inner tube, Helmholtz resonant cavity, sound-absorbing interlayer and tail pipe. The total transfer matrix of the system is obtained by matrix multiplication, and then the system transfer loss and acoustic impedance are calculated.