Muffler for suppressing impulse noise through frequency modulation and tail emission treatment system

Abstract

The invention discloses a silencer for suppressing impulse noise through frequency modulation and a tail emission treatment system. The silencer comprises a rear silencer assembly, and the rear silencer assembly comprises a rear bale eliminating body; a first layer plate, a second layer plate and a third layer plate are sequentially arranged in the rear bag breaking body from top to bottom, and an inner cavity of the rear bag breaking body is divided into four cavities. A leakage opening is formed in the first layer plate, a variable-frequency ventilation pipe is arranged in the leakage opening, a blocking piece is arranged at the air inlet end of the variable-frequency ventilation pipe, the blocking piece is rotatably arranged in the variable-frequency ventilation pipe, and the pipe diameter of the variable-frequency ventilation pipe can be changed through the blocking piece; the variable-frequency breather pipe comprises a fixed pipe section and a movable pipe section, so that the movable pipe section slides relative to the fixed pipe section, and the pipe length of the variable-frequency breather pipe can be adjusted; through the partition design of the four layers of cavities in the rear bag eliminating body and the dynamic adjustment of the variable-frequency ventilation pipe, the problems that the noise frequency deviates and the silencing effect is attenuated due to the change of the air displacement of a traditional silencer are accurately solved.

Description

Technical Field

[0001] This application relates to the field of exhaust mufflers, and in particular to a frequency-modulated muffler for suppressing pulse noise and an exhaust treatment system. Background Technology

[0002] The core of noise control in automotive exhaust systems relies on the acoustic matching performance of the muffler. Most mainstream mufflers are based on a fixed structure design, which optimizes the noise frequency of the engine under specific operating conditions (such as idling or rated speed) through pre-set resonant chambers, perforated pipes and other components. They can only effectively suppress noise in a fixed frequency band.

[0003] However, the displacement of an engine in actual operation will change dynamically with the operating conditions (such as the displacement can increase several times when idling to high speed), and the noise frequency will shift synchronously with the change in displacement. When the displacement increases, the airflow velocity increases and the pulse frequency increases, causing the noise peak frequency to shift to the high frequency range; when the displacement decreases, the noise peak frequency drops back to the low frequency range.

[0004] Because the diameter, length, and resonant cavity volume of the vent pipe of a traditional muffler are all fixed values, its noise reduction frequency range cannot be dynamically adjusted with the exhaust volume. When the noise frequency deviates from the muffler's preset processing frequency band due to changes in exhaust volume, the noise reduction effect will be significantly reduced, and there may even be a problem of failure to suppress specific frequency noise (such as "putt-putt" sound under low-frequency pulses). This cannot meet the noise control requirements of the engine under all operating conditions, affecting the overall NVH (noise, vibration, and harshness) performance and ride comfort of the vehicle. Summary of the Invention

[0005] The purpose of this application is to overcome the shortcomings of the prior art and provide a muffler and exhaust treatment system for frequency modulation to suppress impulse noise.

[0006] This application provides a muffler for suppressing pulse noise using frequency modulation, characterized in that it includes a rear muffler assembly, which comprises a rear muffler housing; from top to bottom, the rear muffler housing is provided with a first layer plate, a second layer plate, and a third layer plate, dividing the inner cavity of the rear muffler housing into four chambers, namely a first chamber, a second chamber, a third chamber, and a fourth chamber; an air inlet pipe connects to the first chamber; a leak port is provided on the first layer plate, and a frequency converter vent pipe is provided inside the leak port, allowing gas in the first chamber to enter the second chamber through the frequency converter vent pipe; the second chamber and the fourth chamber are connected by a return pipe, allowing gas in the second chamber to enter the fourth chamber through the return pipe; the third layer plate is a perforated plate, allowing gas in the fourth chamber to enter the third chamber through the third layer plate; wherein, the air inlet end of the frequency converter vent pipe is provided with a baffle plate, which is rotatably disposed inside the frequency converter vent pipe, and when air is introduced, the gas can blow open the baffle plate, the rotation amplitude of the baffle plate being controlled by... The influence of gas flow rate: the greater the gas flow rate, the larger the opening of the variable frequency vent pipe's inlet. The diameter of the variable frequency vent pipe can be changed by using baffles, thus utilizing a mechanical structure to passively respond to changes in airflow and resist frequency deviation caused by flow rate changes. By actively tracking and locking the changed noise peak frequency, the optimal silencing effect is restored. The variable frequency vent pipe includes a fixed section and a movable section. The fixed section is located inside the leak port, and the movable section is slidably connected to the fixed section. This allows the movable section to slide relative to the fixed section, adjusting the length of the variable frequency vent pipe and thus the resonant frequency. The silencer also includes a noise sensor to monitor exhaust noise. The acoustic coupling system formed by the first and second chambers creates a resonant cavity. When changes in exhaust volume cause noise frequency shifts, the acoustic characteristics can be corrected in real time by changing the diameter and length of the variable frequency vent pipe, ensuring that the processing frequency of the resonant cavity is always aligned with the actual noise peak.

[0007] Furthermore, the variable frequency vent pipe is a circular pipe, and the baffle is a circular plate. The diameter of the baffle is smaller than the inner diameter of the variable frequency vent pipe, and there is a reserved gap between the baffle and the variable frequency vent pipe to allow low-flow gas to pass through; and / or, in the initial state without airflow propulsion, the baffle is set at an angle to the axis of the variable frequency vent pipe, so that the air inlet end of the variable frequency vent pipe has a minimum opening to allow low-flow gas to pass through.

[0008] Furthermore, the silencer for suppressing pulse noise by frequency modulation also includes: a rotating shaft, rotatably mounted at the air inlet end of the frequency converter vent pipe, with a baffle mounted on the rotating shaft; an elastic reset element, sleeved on the rotating shaft, used to provide a reset torque to the baffle that tends to close the opening of the frequency converter vent pipe; and a maximum opening limiter, located on the inner wall of the frequency converter vent pipe, used to limit the maximum rotation angle of the baffle. The axis of the rotating shaft is offset from the geometric center of the baffle. According to the lever principle, airflow acting on a larger area can generate greater torque, thereby improving the rotational sensitivity of the baffle.

[0009] Furthermore, the inner wall of the fixed pipe section end is provided with a stepped annular mounting groove, which is used to fill graphite braided packing. The graphite braided packing is a rope-like structure woven from flexible graphite filaments. The groove wall of the annular mounting groove is provided with internal threads. The silencer also includes a gland, which can be connected to the fixed pipe section through an internal and external threaded connection. The gland can axially press the graphite braided packing in the annular mounting groove. During installation, the rope-like graphite braided packing is wound around the movable pipe section, so that the movable pipe section passes through the fixed pipe section. The graphite braided packing is pressed into the annular mounting groove. The gland is screwed into the annular mounting groove, and the graphite braided packing is compressed and radially expanded, thereby tightly hugging the movable pipe section and forming an effective seal.

[0010] Furthermore, the roughness of the outer wall surface of the movable pipe section is not greater than 0.2 μm; and / or, the outer wall surface of the movable pipe section is coated with a hard wear-resistant coating; and / or, the gland is provided with a pressure plate and a disc spring. The pressure plate is used to press against the graphite braided packing, and the disc spring is pressed between the pressure plate and the gland. After the graphite braided packing is worn, its volume shrinks, and the disc spring extends, which can push the pressure plate, thereby compensating for the gap caused by wear, so as to maintain the compressive force on the graphite braided packing.

[0011] Furthermore, the fixed pipe section has a sandwich structure, with a piston pusher inside the sandwich. The piston pusher divides the sandwich into a rod chamber and a rodless chamber, which are respectively connected to a hydraulic oil circulation supply device. The piston pusher is connected to the movable pipe section. When hydraulic oil is input into the rodless chamber, the piston pusher can push the movable pipe section outward, thereby increasing the length of the frequency converter vent pipe. When hydraulic oil is input into the rod chamber, the piston pusher can pull the movable pipe section back, thereby reducing the length of the frequency converter vent pipe.

[0012] Furthermore, a return spring is also provided within the interlayer, the elastic force of which can drive the piston push rod to move the movable tube section in the direction of increasing tube length; and / or, the hydraulic oil is high-temperature resistant synthetic hydraulic oil, which is phosphate ester liquid, phthalate ester liquid, or polyalphaolefin synthetic oil; and / or, an oil cooler is provided on the return or supply path of the hydraulic oil circulation supply equipment, the oil cooler being used to cool the hydraulic oil during the circulation process; and / or, the static and dynamic seals in the hydraulic oil circuit between the hydraulic oil circulation supply equipment and the interlayer are all made of fluororubber, perfluororubber, or polytetrafluoroethylene material.

[0013] Furthermore, the exhaust pipe includes: a vertical section that penetrates the first, second, and third layers of the plate, with its front end passing through the exhaust envelope for exhaust and its end extending into the fourth chamber; a bent section located in the fourth chamber, with one end connected to the vertical section and the other end extending towards the third layer; a gas collection section connected to the other end of the bent section and extending into the third chamber, allowing gas in the third chamber to enter the exhaust pipe through the gas collection section; and / or, an intake pipe configured in a bent shape, with a portion of the intake pipe located in the second chamber, and an exhaust hole on the wall of the intake pipe located in the second chamber, allowing some gas to enter the second chamber through the exhaust hole on the intake pipe; and / or, a return pipe passing through the third chamber, with an exhaust hole on the wall of the return pipe located in the third chamber, allowing some gas to enter the third chamber through the exhaust hole on the return pipe; and / or, a high-frequency tube on the vertical section, with a portion of the high-frequency tube located in the first chamber and another portion located in the second chamber, the high-frequency tube having the function of absorbing high-frequency noise.

[0014] Furthermore, the frequency-modulated pulse noise suppression muffler also includes a front muffler assembly, which includes a front muffler housing. The front muffler housing contains a coaxially fitted front muffler inlet pipe and a front muffler outlet pipe. The rear muffler housing is connected to the front muffler outlet pipe via an inlet pipe. The diameter of the front muffler inlet pipe is smaller than that of the front muffler outlet pipe, and the outlet end of the front muffler inlet pipe extends into the front muffler outlet pipe, with an annular gap between them. A concentric tube acoustic resonance cavity is formed within the front muffler housing. High-speed airflow carrying order noise enters the front muffler inlet pipe. When the airflow is injected from the outlet of the front muffler inlet pipe into the front muffler outlet pipe, a local vortex is generated due to the sudden expansion of the pipe diameter, and the sound wave resonates in the annular space. Impedance mismatch occurs at the gap, causing some sound waves to refract into the pre-exhaust pipe and continue propagating. However, the target order noise sound waves, due to wavelength matching, can radiate backward through the annular gap into the pre-exhaust enclosure and are eventually dissipated. The pre-exhaust enclosure also contains an axially distributed first and second partitions. The pre-exhaust inlet pipe passes through the first partition, and the pre-exhaust outlet pipe passes through the second partition. The first and second partitions work together to suppress airflow vibration. The inner wall of the pre-exhaust enclosure is lined with a high-temperature resistant sound-absorbing layer. From the inside out, the high-temperature resistant sound-absorbing layer includes: a ceramic heat-insulating coating with a thickness of 1.5-2 mm; and a glass fiber cotton layer with a density ≥80 kg / m³. 3 Thickness ≥ 30mm; aluminum foil reflective layer, thickness 0.1-0.3mm.

[0015] This application also provides an exhaust treatment system, including the aforementioned frequency-modulated pulse noise suppression muffler, and further including: a purifier assembly, the purifier assembly including a particulate filter and a three-way catalytic converter, the particulate filter and the three-way catalytic converter being connected through a purifier pipeline; the purifier pipeline is covered with a shaped heat insulation cover, the shaped heat insulation cover being able to fit tightly against the surface of the three-way catalytic converter, thereby avoiding heat damage problems, and the pleated structure of the shaped heat insulation cover can also improve its own structural strength; the three-way catalytic converter is connected to the front exhaust intake pipe.

[0016] This application provides a frequency-modulated (FM) muffler for suppressing impulse noise, including a rear muffler assembly. The rear muffler assembly includes a rear muffler housing. From top to bottom, the rear muffler housing is provided with a first layer plate, a second layer plate, and a third layer plate, dividing the inner cavity of the rear muffler housing into four chambers. The first layer plate has a leakage port, and a frequency conversion vent pipe is provided inside the leakage port. The inlet end of the frequency conversion vent pipe is provided with a baffle plate, which is rotatably disposed inside the frequency conversion vent pipe. The diameter of the frequency conversion vent pipe can be changed by the baffle plate. The frequency conversion vent pipe includes a fixed pipe section and a movable pipe section, which allows the movable pipe section to slide relative to the fixed pipe section, thereby adjusting the length of the frequency conversion vent pipe. The muffler is connected to the first to fourth chambers, in conjunction with an inlet pipe, a return pipe, and a third layer plate. The layered structure creates an orderly airflow channel, ensuring that the gas flows along a preset path to maintain acoustic stability. The variable frequency vent pipe achieves coordinated adjustment of pipe diameter and length through the rotatability of the baffle and the sliding of the pipe section. This not only resists the initial frequency deviation caused by changes in flow rate but also accurately corrects the resonance frequency. The acoustic coupling system, composed of the first and second chambers, ensures that the resonance chamber's processing frequency is always aligned with the actual noise peak after changes in exhaust volume through real-time adjustment of pipe diameter and length. This avoids the silencing failure caused by frequency deviation in traditional fixed-structure mufflers, effectively covering noise changes under all engine operating conditions, ensuring stable silencing effect, and improving the overall vehicle NVH performance and ride comfort.

[0017] This application also provides an exhaust treatment system, including the aforementioned frequency-modulated pulse noise suppression muffler and purifier assembly. The purifier assembly includes a particulate filter and a three-way catalytic converter, which are connected via purifier piping. A shaped heat shield covers the purifier piping. High-temperature exhaust gas, after being filtered by the particulate filter, enters the three-way catalytic converter to undergo a catalytic reaction, and then passes through pre- and post-mufflers for multi-stage noise reduction. The shaped heat shield compensates for thermal expansion through its pleated elastic structure and reflects over 90% of radiant heat, thus reducing the temperature of the peripheral components of the three-way catalytic converter and slowing down the aging rate of the materials. This application, through the concentric tube resonant cavity, double-diaphragm vibration control, and multi-layer sound-absorbing structure of the pre-muffler, combined with the multi-stage resonant cavity design of the post-muffler, forms a complete noise reduction system of "low-frequency resonance silencing - mid-frequency interference silencing - high-frequency sound absorption." Simultaneously, the thermal structure design of the heat shield and diaphragms solves the reliability problem under high-temperature environments, achieving a synergistic improvement in NVH performance and durability. Attached Figure Description

[0018] Figure 1 This application provides a schematic diagram of the structure of an exhaust treatment system; Figure 2 for Figure 1 The diagram shows the structure of the front muffler assembly in the exhaust treatment system. Figure 3 for Figure 2 The diagram shows the internal structure of the front muffler housing in the front muffler assembly. Figure 4 for Figure 3 A schematic diagram of the structure shown from another angle; Figure 5 for Figure 1 The diagram shows the structure of the rear muffler assembly in the exhaust treatment system. Figure 6 for Figure 5 The diagram shown is a structural schematic of the rear muffler assembly with the variable frequency vent pipe omitted from the rear muffler housing. Figure 7 for Figure 5 The diagram shown is a structural schematic of the rear muffler assembly, with the variable frequency vent pipe inside the rear muffler housing not omitted. Figure 8 This application provides a schematic diagram of the structure of a variable frequency ventilation pipe; Figure 9 A cross-sectional view of another variable frequency ventilation pipe provided in this application; Figure 10 for Figure 1 The diagram shows the structural schematic of the purifier assembly in the exhaust treatment system. Figure 11 for Figure 10 A schematic diagram of the irregularly shaped heat insulation cover covering the pipeline of the air purifier. Detailed Implementation

[0019] To make the above-mentioned objectives, features, and advantages of this application more apparent and understandable, the specific embodiments of this application are described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of this application. However, this application can be implemented in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of this application. Therefore, this application is not limited to the specific embodiments disclosed below.

[0020] This application provides a frequency-modulated (FM) muffler for suppressing impulse noise, including a front muffler assembly 10. The front muffler assembly 10 includes a front muffler housing 11, within which a front muffler inlet pipe 11a and a front muffler outlet pipe 11b are coaxially sleeved. The diameter of the front muffler inlet pipe 11a is smaller than the diameter of the front muffler outlet pipe 11b, and the outlet end of the front muffler inlet pipe 11a extends into the front muffler outlet pipe 11b, with an annular gap between them. A concentric tube acoustic resonance cavity is formed within the front muffler housing 11. High-speed airflow carrying order noise enters the front muffler inlet pipe 11a, and when the airflow exits from the front muffler inlet pipe 11a... When the sound wave is injected into the pre-exhaust pipe 11b, a local vortex is generated due to the sudden expansion of the pipe diameter. The sound wave experiences impedance mismatch at the annular gap. Some of the sound wave is refracted into the pre-exhaust pipe 11b and continues to propagate, while the target order noise sound wave, due to wavelength matching, can be radiated backward through the annular gap into the pre-exhaust enclosure 11 and is eventually dissipated. The pre-exhaust enclosure 11 is also provided with an axially distributed first baffle 12 and second baffle 13. The pre-exhaust inlet pipe 11a passes through the first baffle 12, and the pre-exhaust outlet pipe 11b passes through the second baffle 13. The first baffle 12 and the second baffle 13 work together to suppress airflow vibration.

[0021] For details, please refer to Figures 2 to 4 In the illustrated embodiment, the front muffler assembly 10 includes a cylindrical front muffler housing 11. The front muffler housing 11 is provided with a front muffler inlet pipe 11a and a front muffler outlet pipe 11b. The front muffler inlet pipe 11a has a smaller diameter (e.g., φ40mm), while the front muffler outlet pipe 11b has a larger diameter (e.g., φ60mm). The outlet end of the front muffler inlet pipe 11a is inserted into the front muffler outlet pipe 11b, and the two are coaxially fitted together with an annular gap (approximately 10mm wide) between them.

[0022] The front intake pipe 11a and the front exhaust pipe 11b are coaxially fitted together, forming an annular gap, which constitutes a structure similar to a Helmholtz resonator. The front intake pipe 11a is equivalent to the "neck" of the resonator, and the cavity of the front enclosure 11 is the "cavity". When a high-speed airflow is injected from the narrow-diameter intake pipe (e.g., φ40mm) into the wide-diameter exhaust pipe (e.g., φ60mm), the sudden expansion of the pipe diameter (area ratio 1:2.25) will induce local turbulence and be accompanied by the propagation of low-frequency order noise (e.g., the fundamental frequency of engine idling 25Hz).

[0023] For the target low-frequency noise, such as 25Hz with a wavelength λ=20.8m, the width of the annular gap (approximately 10mm) is much smaller than λ / 4, satisfying the Helmholtz resonance condition. Sound waves will be reflected and interfered at the annular gap due to acoustic impedance mismatch (high impedance in the inner tube → low impedance in the outer tube), with some sound waves radiating backward into the pre-elimination enclosure 11. After entering the cavity, the sound waves will be reflected on the inner wall of the enclosure, and reflected waves from different paths may interfere destructively due to phase differences. For example, a sound wave with wavelength λ will reflect back and forth within a cavity of length L. When L=n.(λ / 2), where n is an integer, a standing wave will be formed, and the acoustic energy at the antinodes will be dissipated due to friction between air molecules.

[0024] Continue to refer to Figure 3 and Figure 4 The first baffle 12 and the second baffle 13 are circular plates with an Ω-shaped expansion joint around their edges for connection and fixation to the inner wall of the front exhaust housing 11. The first baffle 12 and the second baffle 13 are spaced apart axially. The front exhaust intake pipe 11a passes through the first baffle 12, and the front exhaust exhaust pipe 11b passes through the second baffle 13. The two sets of baffles cooperate to form a rigid support structure for the front exhaust intake pipe 11a and the front exhaust exhaust pipe 11b. The intake and exhaust pipes are equivalent to "fixed-end beams." By shortening the pipe span using the baffles, the first-order natural frequency of the pipe can be increased from 100Hz in the traditional single-baffle structure to 1300Hz, far from the engine's order frequency (20-500Hz), effectively avoiding structural fatigue fracture caused by resonance. The rigid baffles can also block the transmission path of pipe vibration to the housing, thereby reducing the vibration transmission rate and structural noise radiation.

[0025] The partition is 3-5mm thick and has an annular gap, which allows the front enclosure 11 to withstand the impact of high-speed airflow (flow velocity ≥30m / s), effectively reducing vibration displacement and improving structural strength.

[0026] The first baffle 12 and the second baffle 13 can not only improve the structural strength of the front muffler assembly 10 and effectively cope with the impact of high temperature and high speed airflow brought by the three-way catalytic converter 32, but also achieve efficient control of low frequency noise by suppressing the vibration and resonance of airflow and working together with the concentric tube acoustic resonance cavity.

[0027] In summary, the muffler for suppressing pulse noise using frequency modulation provided in this application solves the problem of low-frequency order noise amplification caused by the close distance between the three-way catalytic converter 32 and the muffler through a coaxially fitted concentric tube structure. It utilizes the impedance mismatch generated by the sudden expansion of the pipe diameter to cause the target order noise (e.g., 25Hz) to radiate backward into the cavity for dissipation, thus suppressing low-frequency pulse noise. The double-diaphragm support structure solves the problem of vibration and fracture of the front muffler structure caused by airflow instability. The diaphragms support the pipe as a "fixed beam," raising the natural frequency and moving it away from the engine's order frequency range, while simultaneously reducing turbulence intensity, minimizing vibration displacement, increasing structural strength, and preventing material fatigue fracture. The combination of these two elements achieves a dual effect of noise suppression and structural reinforcement, balancing NVH performance and durability.

[0028] For low-frequency sound waves (such as 25Hz), the cavity size of the enclosure must satisfy L≫λ to be effective. However, due to the space limitations of automobiles, the length of the front enclosure 11 is usually only 0.5-1m, which is often difficult to meet the dissipation requirements of long-wavelength sound waves.

[0029] Therefore, in one embodiment, the inner wall of the front sound-absorbing package 11 is covered with a high-temperature resistant sound-absorbing layer. From the inside out, the high-temperature resistant sound-absorbing layer includes: a ceramic heat-insulating coating with a thickness of 1.5-2mm; and a glass fiber cotton layer with a density ≥80kg / m³. 3 Thickness ≥ 30mm; aluminum foil reflective layer, thickness 0.1-0.3mm.

[0030] Specifically, the ceramic thermal insulation coating uses high-temperature resistant ceramic materials such as alumina, which have low thermal conductivity and can withstand temperatures exceeding 1000℃. The ceramic thermal insulation coating directly contacts the high-temperature airflow (600-800℃) and blocks most of the heat through thermal conduction, thereby reducing the temperature load on other material layers. Simultaneously, the ceramic thermal insulation coating reduces the frictional resistance between the airflow and the inner wall of the enclosure, preventing additional noise caused by increased turbulence.

[0031] The fiberglass wool layer is made of inorganic fiber material with a porous internal structure. It absorbs mid-to-high frequency noise through "viscous loss" and "thermal conduction loss" mechanisms. When sound waves enter the fiber pores, air molecules rub against the fibers and convert into heat energy, thus dissipating the sound energy. Simultaneously, the air layers between the fibers form a thermally insulating structure, further hindering heat transfer to the outside of the enclosure.

[0032] The aluminum foil reflective layer uses pure aluminum or aluminum alloy foil, with a surface reflectivity >90% and high temperature resistance up to 500℃. The aluminum foil reflective layer can block radiant heat from the inner wall of the enclosure through mirror reflection, reducing heat loss to the external environment and preventing surrounding components (such as wiring harnesses and interior trim) from aging due to high temperatures. As the outermost barrier, the aluminum foil reflective layer also prevents the fiberglass insulation from getting damp and vibrating, thus improving the durability of the high-temperature sound-absorbing layer.

[0033] The ceramic heat-insulating coating blocks high-temperature airflow, preventing direct thermal impact on the fiberglass layer and maintaining its temperature below 300℃, effectively preventing material carbonization failure. The aluminum foil reflective layer further controls the outer wall temperature of the enclosure below 120℃ to meet the vehicle's thermal safety standards. The thermal expansion coefficients of the three layers are matched (ceramic ≈ 3 × 10⁻⁶). -6 / ℃, glass fiber ≈ 5×10 -6 / ℃, aluminum foil ≈ 23×10 -6 ( / ℃), which can buffer thermal stress through elastic deformation, which is beneficial to the long-term use of equipment.

[0034] Furthermore, in conjunction with the concentric tube acoustic resonance cavity of the pre-excitation enclosure 11 (targeting the 25Hz fundamental frequency), the glass fiber cotton layer can supplement the absorption of the second harmonics of low-frequency noise (such as 50Hz and 75Hz), increasing the total low-frequency noise reduction by 4-12dB. The glass fiber cotton layer has an absorption coefficient of 0.6-0.9 for noise in the 500-4000Hz range, compensating for the insufficient suppression of mid-to-high frequency noise by the concentric tube structure, forming a full-band noise reduction system of "low-frequency resonance noise reduction + mid-to-high frequency sound absorption".

[0035] In summary, the high-temperature resistant sound-absorbing layer, through a composite mechanism of "heat insulation-sound absorption-reflection", not only solves the thermal protection problem of the exhaust system under high-temperature environment, but also achieves efficient suppression of broadband noise through the synergy of material properties and acoustic principles.

[0036] Optionally, the length-to-diameter ratio L / D of the front exhaust envelope 11 is greater than 3:1, and the length L of the front exhaust envelope 11 satisfies: L < c / (10f1); where c is the exhaust sound velocity and f1 is the fundamental frequency of the engine idling.

[0037] The pre-elimination inclusion 11, being a cylindrical cavity, may generate standing wave resonance along the axial direction. When the aspect ratio is too small (e.g., L / D ≤ ​​3:1), the fundamental frequency of the axial standing wave (f) will be low. axial =c / 2L) may overlap with the engine's order frequency (such as the 25Hz fundamental frequency), thereby causing acoustic cavity resonance and resulting in noise amplification.

[0038] As the aspect ratio increases, the fundamental frequency of the axial standing wave rises (because it is inversely proportional to L), moving further away from the low-frequency range of the engine. For example, when L / D = 4:1, the fundamental frequency of the axial standing wave is f. axial = (520m / s) / (2×4D), assuming D=0.25m and L=1m, the calculated fundamental frequency is 260Hz, which exceeds the sensitive range of the idle fundamental frequency (25Hz).

[0039] In addition, the larger aspect ratio makes the inclusion more like a "slender tube" shape, and the flow of air in it is closer to one-dimensional flow. This can reduce the disorder of radial eddies and sound wave reflection, and make it easier to precisely control the acoustic impedance mismatch and resonance dissipation through the concentric tube structure.

[0040] When the length L of the current eliminated body 11 satisfies the above formula, the first-order resonant frequency f of the previous eliminated body 11 is... min =c / 4L>10f1 / 4=2.5f1, that is, f min By keeping the acoustic cavity away from the idling fundamental frequency and its harmonics (such as 25Hz, 50Hz, and 75Hz), the risk of resonance is structurally avoided. Simply put, by limiting the length L of the cavity and ensuring that its corresponding lowest resonant frequency is higher than 1 / 10 octave of the engine's idling fundamental frequency, the acoustic cavity can be prevented from becoming a "resonance amplifier" for engine order noise.

[0041] In one specific embodiment, the engine idle fundamental frequency f1=25Hz, the exhaust sound velocity c=520m / s, and the diameter D=0.25m of the front exhaust envelope 11; taking L=0.9m, then L / D=0.9 / 0.25=3.6:1>3:1, which meets the length-to-diameter ratio requirement.

[0042] c / 10f1=520 / (10×25)=2.08m, while the actual length L=0.9m<2.08m, which satisfies the relevant formula conditions.

[0043] Axial standing wave fundamental frequency f axial =c / 2L=520 / (2×0.9)≈288.9Hz; First-order transverse resonant frequency f of the inclusion body transverse =1.841c / 2πD≈608Hz. Both are much higher than the engine's idle fundamental frequency (25Hz) and its main harmonics (such as 100Hz, 200Hz), which can avoid acoustic cavity resonance.

[0044] In summary, the synergistic design of an aspect ratio L / D > 3:1 and the formula L < c / (10f1) fundamentally avoids the risk of acoustic cavity resonance through geometric optimization, while also taking into account engineering practicality. The above examples demonstrate that this design can achieve efficient suppression of low-frequency noise within a limited space, providing a quantitative basis for NVH optimization of automotive exhaust systems.

[0045] Optionally, the tangential outlet direction of the annular gap forms an angle of 15-30° with the inner wall of the front extinction body 11 to guide the airflow swirl.

[0046] The annular gap is a channel for gas to flow out after the front exhaust inlet pipe 11a and the front exhaust outlet pipe 11b are connected due to their different pipe diameters. Its tangential outlet direction refers to the velocity direction of the airflow when it is ejected from the annular gap.

[0047] This causes the airflow direction to form an angle of 15-30° with the inner wall of the front exhaust casing 11 (e.g., the outer wall of the outlet end of the front exhaust inlet pipe 11a and / or the inner wall of the inlet end of the front exhaust outlet pipe 11b are inclined). The airflow is not directly injected into the front exhaust outlet pipe 11b in the radial direction, but is injected in the tangential direction of the inner wall of the casing (e.g., clockwise or counterclockwise), thus forming a spiral flow trajectory.

[0048] After the airflow is ejected at a tangential angle, it forms vortices under the constraint of the inner wall of the enclosure, changing the propagation path of the sound wave inside the enclosure from a straight line to a spiral (increasing the optical path by about 1.5-2 times). Low-frequency noise has a longer wavelength (e.g., the wavelength of a 25Hz sound wave λ=20.8m), and the extended propagation path of the swirling flow gives it more opportunities to come into contact with the high-temperature resistant sound-absorbing layer (ceramic heat-insulating coating, glass fiber cotton layer), which helps to improve the sound energy dissipation efficiency. High-frequency noise (e.g., 2000Hz), due to its shorter wavelength, is easily scattered by the turbulent vortices in the swirling flow, increasing the probability of collision with the sound-absorbing material and helping to improve the sound absorption coefficient.

[0049] Furthermore, tangential injection imparts a circumferential velocity component to the airflow, creating a composite flow with the axial velocity (velocity vector angle 15-30°). This breaks up large-scale vortices (such as the Karman vortex street), thereby reducing turbulence intensity. Reduced turbulence intensity means a weakening of the periodic impact force of the airflow on the front exhaust pipe 11b, which in turn reduces the vibration acceleration of the diaphragm. The swirling flow reduces the coupling probability between the airflow pulse frequency and the natural frequency of the exhaust system, further preventing fatigue fracture caused by structural resonance.

[0050] In one specific embodiment, the outlet of the pre-exhaust inlet pipe 11a is machined with a bevel, the angle of which forms a 20° angle with the tangent of the inner wall of the casing; the inlet of the pre-exhaust outlet pipe 11b is equipped with a guide ring, which can guide the swirling flow smoothly into the outlet pipe and avoid airflow separation that generates additional noise. The tangential outlet of the annular gap, combined with the design of a 15-30° angle, achieves the dual effect of improving low-frequency noise attenuation efficiency and reducing vibration excitation by actively controlling the airflow direction without significantly increasing back pressure.

[0051] Optionally, the first partition 12 and / or the second partition 13 are provided with: a central conical guide hole, through which the front exhaust inlet pipe 11a or the front exhaust outlet pipe 11b passes; and multiple surrounding guide holes distributed around the central conical guide hole.

[0052] For details, please refer to Figure 3 and Figure 4In the illustrated embodiment, the front exhaust inlet pipe 11a and the front exhaust outlet pipe 11b pass through the central conical guide hole of the corresponding partition. The wall of the central conical guide hole is truncated cone-shaped, and the cone angle of the central conical guide hole is 55-65°. Four waist-shaped surrounding guide holes are evenly distributed around the central conical guide hole. The surrounding guide holes ensure that the inner cavity of the front exhaust casing 11 is unobstructed, forming a unified chamber.

[0053] The conical surface of the central conical guide hole is precisely fitted to the pipe (tolerance ±0.05mm, coaxiality deviation <0.1mm) and fixed by welding to avoid airflow deviation caused by installation eccentricity. The conical surface elastically contacts the pipe wall, absorbing vibration energy and reducing vibration transmission rate. Meanwhile, the edge wall thickness of the baffle is maintained at over 0.8D, and combined with the expansion joint design, it can withstand thousands of thermal cycles without cracking. Furthermore, the gradually changing cross-sectional area of ​​the conical surface also has the function of adjusting the acoustic characteristic impedance, reducing the reflection coefficient of low-frequency sound waves and suppressing acoustic cavity resonance; at the same time, it can improve the transmission efficiency of mid-to-high-frequency sound waves, promoting their dissipation to the high-temperature resistant sound-absorbing layer.

[0054] A 60° cone angle is close to the optimal acoustic expansion angle. At this angle, the phase distortion is less than 5%, and the transmission loss for 500Hz noise is only 2dB.

[0055] The surrounding guide orifice can cut residual small-scale vortices (10-20 mm in diameter) in the main airflow into even smaller vortices (<5 mm in diameter), thereby accelerating vortex attenuation, reducing the periodic impact of airflow pulsations on the pipeline, and avoiding vibration noise caused by Karman vortex streets. Furthermore, the diverted airflow forms micro-turbulence near the baffle, increasing the probability of sound waves colliding with the high-temperature sound-absorbing layer (such as fiberglass wool). Simultaneously, the distance between the surrounding guide orifice and the central conical guide orifice creates a "sound barrier" effect, which can diffract and reduce high-frequency sound waves (>1000 Hz), helping to improve the sound absorption coefficient. The surrounding guide orifice can also stabilize the total back pressure through flow diversion.

[0056] Optionally, the edges of the first partition 12 and / or the second partition 13 are provided with Ω-shaped expansion joints, the width of which is 0.3-0.8 mm.

[0057] When the front muffler assembly 10 is in operation, the internal airflow temperature can reach 600-800℃, and the baffle will undergo radial elongation due to thermal expansion. The Ω-shaped expansion joint can absorb thermal deformation through a flexible structure (such as setting a corrugated notch), preventing the baffle from cracking due to rigid constraints. In addition, when the baffle vibrates under the excitation of airflow pulsation, the elastic deformation of the Ω-shaped expansion joint can also convert mechanical energy into internal energy of the material (hysteresis damping effect), thereby reducing the vibration amplitude.

[0058] Traditional expansion joints exhibit stress concentration at their edges (such as where they are welded to the package body), which can easily lead to fatigue cracks during long-term thermal cycling. Ω-shaped expansion joints, through geometric optimization, can reduce the stress concentration factor and extend the crack initiation life.

[0059] Ω-shaped expansion joints also allow for thermal expansion between the diaphragm and the enclosure material (such as carbon steel) due to differences in their coefficients of thermal expansion (carbon steel α=12×10). -6 / ℃, stainless steel α=17×10 -6 The relative displacement generated by ( / ℃) avoids the problem of desoldering caused by shear stress at the interface of dissimilar materials.

[0060] A 0.3-0.8mm seam width covers the thermal expansion under most working conditions (e.g., at extreme high temperatures, ΔL=0.8mm, a 0.8mm seam width can fully accommodate deformation), while preventing air leakage caused by excessive seam width.

[0061] In summary, the Ω-shaped expansion joint solves the problem of thermal fatigue cracking of the partition under high temperature environment through a triple mechanism of thermal expansion compensation, stress concentration relief and vibration energy dissipation, while ensuring that the acoustic and fluid performance are not significantly affected.

[0062] Optionally, the surfaces of the first partition 12 and / or the second partition 13 are coated with an aluminum-silicon alloy thermal barrier coating with a thickness of 100 μm.

[0063] The main component of the aluminum-silicon alloy thermal barrier coating is Al-12Si, with a melting point of approximately 577℃ and low thermal conductivity. A 100μm thick insulating layer is formed on the surface of the partition. When the partition surface temperature reaches 600℃, the temperature on the outer side of the coating can be reduced to below 400℃, thereby reducing the thermal load on the partition substrate material (such as 304 stainless steel, with an operating temperature ≤800℃) and preventing material softening and creep deformation caused by prolonged high temperatures.

[0064] The thermal expansion coefficients of the aluminum-silicon alloy thermal barrier coating and the stainless steel substrate are matched (aluminum-silicon alloy α=20×10). -6 / ℃, stainless steel α=17×10 -6 / ℃), under rapid cooling and heating conditions (such as a temperature difference of 500℃ during cold start), the coating itself can release stress through micro-cracks, preventing thermal shock cracking of the partition.

[0065] The aluminum-silicon alloy thermal barrier coating has a hardness of HV500-600, which can resist the erosion and wear of particles in the exhaust airflow (such as catalyst debris and carbon deposits). Long-term use ensures the dimensional accuracy of the structure and guarantees its noise reduction performance. By increasing the surface hardness of the baffle, local vibrations caused by airflow pulsation can also be reduced, further lowering the structure's noise radiation.

[0066] Furthermore, a dense Al2O3 oxide film (thickness <1μm) forms on the surface of the aluminum-silicon alloy at high temperatures, which can block oxygen from the substrate, thereby reducing the oxidation rate of the separator and extending its service life. The surface roughness Ra of the coating is ≤1.6μm (comparable to polished stainless steel), which can avoid the aggravation of airflow turbulence caused by excessive wear roughness of the separator surface (Ra>5μm), thus ensuring the stability of the flow resistance in the guide hole.

[0067] In summary, the aluminum-silicon alloy thermal barrier coating solves the material degradation problem of the baffle in high-temperature and high-speed airflow environments through multiple functions of "heat insulation, wear resistance and oxidation resistance", and indirectly improves the long-term stability of vibration control and noise reduction performance.

[0068] Optionally, the axial distance X between the first partition 12 and the second partition 13 satisfies: X < c / (2f max (); where c is the exhaust sound velocity, f max This is the highest-order noise frequency of the engine.

[0069] The propagation of sound waves within the pre-emptive enclosure 11 can be considered as a one-dimensional plane wave. When the axial distance L between the first partition 12 and the second partition 13 satisfies the above formula, the first-order resonant frequency f of the acoustic cavity between the two partitions is... acoustic =c / 2X will be higher than the engine's highest-order noise frequency f max .

[0070] If X ≥ c / 2f max Then the resonant frequency f of the acoustic cavity acoustic ≤f max This may couple with high-order engine noise (such as 4th order 200Hz, 8th order 400Hz), thereby causing acoustic cavity resonance and resulting in noise amplification.

[0071] When f max When Hz = 500 Hz and c = 520 m / s, c / 2f max =0.52m; if X=0.4m<0.52m, then the first-order resonant frequency of the acoustic cavity is 650Hz, far from f max This avoids the risk of resonance.

[0072] The above formula ensures that at the engine's highest order frequency f max Below, the wavelength of the sound wave between the two partitions is λ=c / f max If the sound wave length is greater than 2X, meaning the cavity length is less than half a wavelength, a stable standing wave cannot be formed. In this case, the sound wave propagates between the two partitions in the form of a traveling wave, which can avoid the uneven sound pressure level caused by the standing wave and allow high-frequency noise to be uniformly absorbed by the high-temperature resistant sound-absorbing layer.

[0073] Short pitch design (X < c / 2f) maxIt can also increase the number of times sound waves are reflected between the two partitions (e.g., when X=0.4m, the number of times sound waves are reflected per second is c / 2X=650 times). Each reflection is accompanied by the energy dissipation of the high-temperature sound-absorbing layer (single reflection loss of 1-5dB), thereby increasing the cumulative noise reduction (e.g., the noise reduction of 500Hz noise after 10 reflections reaches 10-50dB).

[0074] In summary, this ensures that the axial spacing satisfies X < c / (2f) max By decoupling the acoustic cavity resonant frequency from the engine order frequency and improving high-frequency sound wave reflection loss through a dual mechanism, the synergistic optimization of resonance risk avoidance and wideband noise reduction efficiency is achieved. This formula provides a quantitative design basis for the layout of the front muffler baffle, ensuring that it can effectively suppress noise under all engine operating conditions, while avoiding structural fatigue problems, and meeting the design requirements of high performance and long service life of automotive exhaust systems.

[0075] Furthermore, the muffler for suppressing pulse noise using frequency modulation provided in this application also includes a rear muffler assembly 20, which includes a rear muffler housing 21 connected to the front muffler exhaust pipe 11b. From top to bottom, the rear muffler housing 21 is provided with a first layer plate 22a, a second layer plate 22b, and a third layer plate 22c, dividing the inner cavity of the rear muffler housing 21 into four chambers, namely, the first chamber A, the second chamber B, the third chamber C, and the fourth chamber D. An intake sound wave resonance cavity is formed within the rear muffler housing 21, which can target and weaken the order noise not eliminated by the concentric tube sound wave resonance cavity by adjusting the chamber volume. The intake pipe 26 is connected to the first chamber. A; The first layer plate 22a is provided with a leakage port 23 (when no frequency conversion ventilation pipe is installed in the leakage port 23, it can be regarded as a ventilation structure with a fixed pipe diameter and pipe length). The airflow enters the first chamber A through the air inlet pipe 26, and absorbs the corresponding frequency noise with the help of the first chamber A. The function of the leakage port 23 is to adjust the frequency change. The gas in the first chamber A can enter the second chamber B through the leakage port 23. The second chamber B and the fourth chamber D are connected through the return pipe 24. The gas in the second chamber B can enter the fourth chamber D through the return pipe 24. The third layer plate 22c is a hollow plate. The gas in the fourth chamber D can enter the third chamber C through the third layer plate 22c.

[0076] For details, please refer to Figure 5 and Figure 6 In the illustrated embodiment, the rear exhaust casing 21 is divided into four chambers by three layers of plates. The first chamber A is connected to the front exhaust pipe 11b via an air inlet pipe 26, and the volume V of the first chamber A is... A For the corresponding engine idle fundamental frequency noise (e.g., 25Hz), according to the Helmholtz resonator formula, by adjusting V... AThis allows the resonant frequency to match the fundamental frequency. The second chamber B is connected to the first chamber A through a leak vent 23. The volume V of the second chamber B... B ≥2V A This is used to extend the noise reduction band to the second harmonic of the fundamental frequency (e.g., 50Hz). The fourth chamber D is connected to the second chamber B via a return pipe 24. The volume V of the fourth chamber D... D Matching the engine's high-order frequencies (e.g., 200Hz). The third chamber C is connected to the fourth chamber D via a perforated third layer plate 22c, forming a multiple reflection path for low-frequency sound waves. The high-frequency tube 27 (e.g., a Helmholtz resonator or a perforated tube) installed on the vertical section 25a of the exhaust pipe can specifically absorb high-frequency noise above 2000Hz.

[0077] Due to the limited pre-elimination volume, the optimization of order noise is limited. Residual order noise enters the first chamber A from the pre-elimination outlet 11b, with a chamber volume V. A Equivalent neck length to intake pipe 26, forming a resonant system, sound waves are reflected at the cavity opening due to impedance mismatch, resulting in destructive interference with the incident wave. Low-frequency noise excites resonance in the first chamber A. After reflection and interference within the first chamber A, some sound waves enter the second chamber B through leakage port 23. The cross-sectional area of ​​leakage port 23 (e.g., S) leak =0.5%V A The resonant frequency shift of the second chamber B is determined, causing phase cancellation (phase difference 180°) of 50Hz noise at the interface between the first chamber A and the second chamber B, resulting in a noise reduction of 5-15dB. The return pipe 24 guides the sound waves from the second chamber B into the fourth chamber D. The sound waves are reflected between the fourth chamber D and the third chamber C through the perforated third layer plate 22c, forming a "sound labyrinth" path. For example, after three reflections between the fourth chamber D and the third chamber C, the optical path difference reaches 1.5λ (λ=2.6m), triggering destructive interference and increasing the noise reduction by 2-10dB. The inner wall of the high-frequency tube 27 has periodic perforations (pore diameter 3-5mm, perforation rate 15-20%), forming a resonant sound-absorbing structure with an absorption coefficient >0.9 for 2000Hz noise, increasing the noise reduction by 5-20dB compared to ordinary straight tubes.

[0078] The intake sound resonance chamber, through frequency matching of multi-stage Helmholtz resonators and phase modulation of the sound wave path, can target and weaken specific orders of noise (such as fundamental frequency, harmonics, and high-frequency noise) that the front muffler fails to eliminate. This design utilizes acoustic optimization of chamber volume and structural layout to form a wide-bandwidth, high-efficiency secondary noise reduction system, which works synergistically with the concentric tube structure of the front muffler to ultimately achieve a comprehensive reduction in vehicle exhaust noise.

[0079] Furthermore, a variable frequency vent pipe 40 is provided inside the leak outlet 23, allowing gas in the first chamber A to enter the second chamber B through the variable frequency vent pipe 40. A baffle 41 is provided at the inlet end of the variable frequency vent pipe 40, rotatably mounted inside the pipe. During air intake, the gas blows open the baffle 41. The rotation amplitude of the baffle 41 is affected by the gas flow rate; the greater the gas flow rate, the larger the opening of the inlet end of the variable frequency vent pipe 40. The diameter of the variable frequency vent pipe 40 can be changed by the baffle 41, thereby utilizing a mechanical structure to passively respond to changes in airflow to resist frequency deviation caused by flow rate changes. By actively tracking and locking the changed peak noise frequency, the optimal noise reduction effect is restored. The variable frequency vent pipe 40 includes a fixed pipe section 40a and a movable pipe section 40b. The fixed pipe section 40a is located inside the leakage port 23, and the movable pipe section 40b is slidably connected to the fixed pipe section 40a. This allows the movable pipe section 40b to slide relative to the fixed pipe section 40a, thereby adjusting the length of the variable frequency vent pipe 40 and thus adjusting the resonance frequency. The muffler also includes a noise sensor for monitoring exhaust noise. The acoustic coupling system formed by the first chamber A and the second chamber B forms a resonance cavity. When changes in exhaust volume cause a shift in noise frequency, the acoustic characteristics can be corrected in real time by changing the diameter and length of the variable frequency vent pipe 40, ensuring that the processing frequency of the resonance cavity is always aligned with the actual noise peak.

[0080] For details, please refer to Figure 6 and Figure 7 In the illustrated embodiment, a variable frequency vent pipe 40 is added inside the leak port 23. The upper end of the variable frequency vent pipe 40 in the first chamber A is its air inlet, and the lower end in the second chamber B is its air outlet. The variable frequency vent pipe 40 is sealed and fixedly connected to the leak port 23, so that the exhaust gas discharged into the afterburner 21 can only flow into the second chamber B through the variable frequency vent pipe 40 after entering the first chamber A.

[0081] The diameter of the variable frequency ventilation pipe 40 is adjustable via the swingable baffle 41. The length of the variable frequency ventilation pipe 40 is adjustable via a fixed pipe section 40a and a movable pipe section 40b that can slide relative to each other along the axial direction (a drive unit such as a cylinder or electric cylinder can be installed to drive the movable pipe section 40b to move axially).

[0082] It's important to explain that engine exhaust noise is not random noise, but rather generated by the periodically operating cylinders. Each cylinder's ignition and exhaust produces a pressure pulse, which converges in the exhaust pipe, creating periodic noise. Generally, as engine speed (exhaust volume / exhaust pulse frequency) increases, the dominant frequency of the pulse noise that needs to be suppressed also increases.

[0083] Traditional mufflers have a fixed resonant frequency, and they typically work best at a specific engine speed (such as idle). Once the engine speed changes, the noise frequency shifts, and the muffler's effectiveness decreases.

[0084] The resonant frequency f0 of the resonant cavity is determined by its geometric structure, and the formula simplifies to: Where V is the volume of the chamber, S is the cross-sectional area of ​​the ventilator (determined by the pipe diameter), and L is the pipe length.

[0085] As can be seen from the formula, at idle speed, the flow rate is low, the baffle 41 opening is small, S is small, and f0 is low, matching the idle noise frequency. During acceleration, the flow rate is high, the baffle 41 opening is large, S increases, and f0 rises, allowing the resonance cavity to track the new noise peak frequency after the engine speed increases.

[0086] Therefore, the addition of baffle 41 makes the pipe diameter adjustable, which can prevent the original design frequency from failing due to changes in flow rate.

[0087] It is easy to understand that pipe diameter adjustment only responds to changes in flow rate, but factors such as temperature changes, back pressure fluctuations, and material aging can also cause frequency shifts. Therefore, by using actual noise feedback in conjunction with pipe length adjustment, all disturbance factors can be comprehensively compensated.

[0088] The formula also shows that increasing the tube length L can lower the resonant frequency f0; conversely, shortening the tube length L can raise the resonant frequency f0.

[0089] In use, a noise sensor detects the actual noise spectrum and identifies whether the target frequency has shifted. If a shift occurs, the sensor transmits relevant data to a remote controller, which calculates the required pipe length for compensation. The corresponding movable pipe segment is then moved to ensure that the resonant frequency f0 precisely matches the current noise peak, allowing the silencer to operate at its optimal state and achieve the best noise reduction effect.

[0090] In summary, the diameter adjustment of the variable frequency ventilation pipe is driven by "airflow rate" (passive), while the pipe length adjustment is controlled by "noise spectrum" (active closed-loop). The two are coordinated in the order of basic adaptation followed by precise correction, covering the full-scenario needs of the engine from idle to high speed, and from normal operating conditions to extreme operating conditions (such as drastic temperature changes).

[0091] In one specific embodiment, during the initial reference stage (idle condition, low flow rate, low temperature), the exhaust flow rate is low, and the intake end of the variable frequency vent pipe maintains a minimum opening (due to a reserved gap or the initial opening caused by the angle setting of the baffle 41), with the equivalent pipe diameter matching the idle reference design. At this time, the acoustic coupling system of the first chamber A and the second chamber B forms an initial resonant frequency (e.g., 25Hz, corresponding to low-frequency pulse noise at idle) based on the low flow rate at idle.

[0092] The noise sensor (installed at the tail end of the exhaust pipe, 20-50cm downstream of the rear exhaust housing 21, with a heat radiation shield) detected that the peak noise frequency was stable at 25Hz. The remote controller determined that there was no need to adjust the pipe length according to the preset algorithm (which can be obtained through simulation test using the above formula. The algorithm is not within the protection scope of this application and will not be described in detail). The movable pipe section 40b maintained its initial position relative to the fixed pipe section 40a, and the pipe length maintained the reference value (e.g., 100mm) to ensure that the initial resonance frequency was aligned with the peak idle noise.

[0093] During the dynamic adaptation phase (acceleration / medium speed conditions, gradual flow rate change, frequency shift), the engine accelerates, and the exhaust flow rate changes from a low flow rate (20m³ / h) to a low flow rate. 3 Gradually increase the flow rate to medium-high (e.g., 50-80 m³ / h) 3 / h), at this time the pipe diameter and pipe length are matched in a passive first adjustment and active second adjustment manner.

[0094] Specifically, as the airflow increases, the torque of the airflow impacting the baffle 41 increases, the rotation amplitude of the baffle 41 increases, the opening of the inlet of the variable frequency vent pipe increases, and the equivalent pipe diameter dynamically increases. This process, by changing the airflow conduction cross-sectional area between the first chamber A and the second chamber B, initially corrects the resonant frequency of the acoustic coupling system (e.g., initially shifting from 25Hz to 30-35Hz), resolving the initial frequency deviation caused by the increased flow rate, and avoiding accelerated failure of initial low-frequency pulse noise suppression.

[0095] However, passive adjustment of the pipe diameter can only adapt to the basic frequency deviation caused by "gradual flow change", and cannot completely offset the frequency shift caused by the combined effect of flow and temperature (such as the increase in exhaust temperature during acceleration, and the change in sound speed further causing the resonant frequency to shift to 37Hz, which is beyond the coverage of pipe diameter adjustment).

[0096] At this point, the noise spectrum at the tailpipe outlet is captured in real time by a noise sensor, identifying the current peak noise frequency (37Hz). The control system determines that there is a deviation between the actual peak noise frequency and the resonant frequency (35Hz) after pipe diameter adjustment. The sensor sends the noise data to a remote controller, which uses a PID algorithm to calculate the amount of pipe length change that needs to be compensated (current resonant frequency 35Hz < actual peak noise 37Hz, requiring shortening the pipe length to increase the resonant frequency). The controller then instructs the drive unit to retract the movable pipe section 40b into the fixed pipe section 40a, thus achieving precise shortening of the pipe length.

[0097] Ultimately, through preliminary fitting of the pipe diameter and precise correction of the pipe length, the resonant frequency of the acoustic coupling system is aligned with the actual noise peak.

[0098] The first chamber A and the second chamber B constitute an acoustic coupling system. The resonant frequency of this system is affected by both the flow cross-sectional area (equivalent pipe diameter) and the vent pipe length (pipe length). Pipe diameter adjustment, by changing the flow cross-sectional area, achieves coarse adjustment of the resonant frequency to adapt to flow-dominated operating conditions; pipe length adjustment, by changing the vent pipe length, achieves fine adjustment of the resonant frequency to adapt to operating conditions with sudden frequency changes. The combination of the two forms a layered control of "coarse adjustment + fine adjustment," improving the acoustic characteristic correction accuracy to within ±1Hz. This effectively avoids over-adjustment or under-correction of frequency caused by a single adjustment (pipe diameter only or pipe length only), thereby improving the overall vehicle sound quality.

[0099] Specifically, the first chamber A serves as the initial air intake chamber. Its core function is to receive the exhaust airflow introduced by the intake pipe 26. Through the interaction between the airflow and the internal space, and in conjunction with the variable frequency ventilation pipe 40, acoustic resonance is excited, providing the initial resonance basis for subsequent acoustic adjustment. At the same time, as a core component of the "active acoustic resonance system", it provides the initial acoustic environment for dynamic frequency adjustment.

[0100] The main function of the second chamber B is to receive the airflow delivered from the first chamber A through the variable frequency ventilation pipe 40 and form a close acoustic coupling relationship with the first chamber A. Furthermore, by adjusting the diameter and length of the variable frequency ventilation pipe 40, the acoustic transmission characteristics between the two chambers are changed, thereby adjusting the resonant frequency of the overall acoustic coupling system. It is the key chamber for realizing the dynamic frequency tracking of the "active acoustic resonance system".

[0101] The fourth chamber D receives the airflow discharged from the second chamber B through the return pipe 24. Since the fourth chamber D itself has no active adjustment structure, it mainly undertakes the functions of airflow transition and temporary storage, which is used to avoid the airflow directly impacting the subsequent structure and causing pressure fluctuations. At the same time, it provides a buffer for the airflow to enter the third chamber C, so as to maintain the stability of the airflow in the exhaust system.

[0102] The third chamber C is used to receive the airflow introduced into the fourth chamber D through the perforated third layer plate 22c. Its core function is to undertake broadband noise reduction, especially for mid-to-high frequency noise. The third chamber C can utilize its own space and cooperate with the perforated third layer plate 22c to consume mid-to-high frequency noise energy through passive noise reduction mechanisms such as sound wave reflection and interference, thus supplementing the shortcomings of the "active acoustic resonance system" in broadband noise processing.

[0103] More specifically, the first chamber A serves as the initial intake chamber. It first senses the change in the exhaust airflow. Through the interaction between the airflow in the chamber and the baffle 41 at the intake end of the variable frequency vent pipe 40, the baffle 41 adjusts its opening according to the flow rate, initially changing the equivalent pipe diameter of the variable frequency vent pipe 40. This provides a basic frequency adaptation direction for the resonance chamber (AB coupling system), ensuring that the initial resonance frequency is close to the noise peak frequency range under the current operating conditions.

[0104] After the second chamber B forms an acoustic coupling with the first chamber A, it relies on the tube length adjustment function of the variable frequency ventilation tube 40 (the movable tube section 40b and the fixed tube section 40a slide together) to accurately correct the resonance frequency of the AB coupling system by adjusting the tube length when the noise sensor detects a shift in the noise peak frequency. This makes the processing frequency of the resonance cavity completely aligned with the actual noise peak, making it the core execution chamber for achieving dynamic frequency tracking.

[0105] The fourth chamber D plays the role of "airflow stability and acoustic environment protection". By receiving the airflow discharged from the second chamber B, it can avoid the drastic pressure fluctuations that would occur when the airflow directly enters the third chamber C, thereby preventing pressure fluctuations from interfering with the acoustic stability of the AB coupling system. At the same time, a stable airflow environment can ensure that the adjustment of the diameter and length of the variable frequency ventilation pipe 40 is not affected by airflow disturbances, ensuring the accuracy and reliability of the frequency alignment process.

[0106] The third chamber C serves as a "wideband noise shunting and active system load reduction" mechanism. By processing the mid-to-high frequency broadband noise not covered by the AB coupling system, it avoids the superposition of broadband noise with the target peak frequency noise, prevents broadband noise from interfering with the noise sensor's accurate monitoring of the target peak frequency, and reduces the impact of non-target frequency noise on the acoustic characteristics of the AB coupling system. This allows the AB coupling system to focus on the dynamic alignment of the target peak frequency, improving the accuracy of frequency tracking.

[0107] Airflow enters from the first chamber A, passes through the variable frequency vent pipe 40 to the second chamber B, then through the return pipe 24 to the fourth chamber D, and finally exits through the perforated plate 22c to the third chamber C, forming an orderly flow path. The transitional function of the fourth chamber D ensures stable airflow pressure in chambers A and B when adjusting the frequency, while the broadband noise reduction function of the third chamber C reduces the interference of redundant noise in the airflow on the AB coupling system. Together, they provide a stable environment for precise frequency alignment of chambers A and B, avoiding frequency adjustment deviations caused by airflow fluctuations or noise superposition.

[0108] The four chambers form a complementary and mutually supportive overall anechoic system through a synergistic mechanism of active and precise frequency control, passive auxiliary current stabilization, and broadband noise reduction.

[0109] The active adjustment of chambers AB and the passive assistance of chamber CD complement each other. The "active acoustic resonance system" formed by chambers AB, through the dynamic adjustment of the variable frequency vent pipe 40, precisely solves the core problem of "aligning the resonant cavity processing frequency with the actual noise peak value," achieving dynamic suppression for specific target frequencies (such as impulse noise). The "passive noise reduction path" formed by chamber CD, through the airflow stabilization of chamber D and the broadband noise reduction of chamber C, supplements the deficiencies of chambers AB in ensuring airflow stability and handling broadband noise, avoiding interference from non-target factors with active frequency adjustment.

[0110] The AB chamber focuses on the dynamic tracking and suppression of the target peak frequency, solving the problem of silencing failure caused by frequency offset in traditional mufflers; the CD chamber is used to process broadband noise, covering the mid-to-high frequency noise bands not covered by the AB chamber, ultimately achieving the dual effect of precise alignment of the target peak frequency and effective suppression of noise across the entire frequency band. This not only meets the core requirement that the resonant cavity processing frequency is always aligned with the actual noise peak, but also improves the overall silencing performance of the equipment and the NVH performance of the entire vehicle.

[0111] The frequency-modulated pulse noise suppression muffler provided in this application precisely solves the problem of noise frequency shift and attenuation of silencing effect caused by changes in exhaust volume in traditional mufflers through the partitioned design of four chambers in the rear muffler enclosure 21 and the dynamic adjustment of the variable frequency vent pipe 40. Specifically, the first to fourth chambers, combined with the intake pipe 26, return pipe 24 and the third layer plate 22c, form an orderly airflow channel, which ensures that the gas flows along a preset path, thereby maintaining acoustic stability. The variable frequency vent pipe 40 achieves coordinated adjustment of pipe diameter and pipe length through the rotatable baffle 41 and the sliding of pipe section, which can resist the initial frequency deviation caused by flow rate changes and accurately correct the resonance frequency. The acoustic coupling system composed of the first and second chambers, with the help of real-time adjustment of pipe diameter and pipe length, ensures that the processing frequency of the resonance cavity is always aligned with the actual noise peak after the change in exhaust volume, avoiding the silencing failure caused by frequency shift in traditional fixed structure mufflers. It can effectively cover the noise changes under all engine operating conditions, ensure stable silencing effect, and improve the NVH performance and driving comfort of the whole vehicle.

[0112] Optionally, the variable frequency vent pipe 40 is a circular pipe, and the baffle 41 is a circular plate. The diameter of the baffle 41 is smaller than the inner diameter of the variable frequency vent pipe 40. There is a reserved gap between the baffle 41 and the variable frequency vent pipe 40 so that low-flow gas (in this application, "low-flow gas" refers to the airflow that the pressure cannot push the baffle 41 to rotate, and does not refer to the airflow with a specific flow rate) can pass through.

[0113] For details, please refer to Figure 8In the illustrated embodiment, the variable frequency ventilation pipe 40 has an overall circular pipe structure. The pipe body is made of metal (such as 304 stainless steel) and the inner wall is smooth to reduce airflow resistance. Its pipe length is adapted to the thickness of the first layer plate 22a inside the rear elimination package 21 to ensure that the two ends can stably connect the first chamber A and the second chamber B.

[0114] Continue to refer to Figure 8 The baffle 41 is a circular thin sheet structure, also made of metal and with a polished surface, to avoid generating additional turbulent noise when the airflow impacts. The diameter of the baffle 41 is smaller than the inner diameter of the variable frequency ventilation pipe 40, and the difference between the two is controlled within 2-10mm, forming an annular reserved gap. The gap is uniform in width, without local narrowing or widening, to ensure that low-flow gas can pass through stably.

[0115] When the engine is in low-flow conditions such as idling, the exhaust gas enters the first chamber A through the intake pipe 26. Some of the airflow impacts the baffle 41, but due to the small flow rate, it cannot overcome the rotational torque of the baffle 41. At this time, the reserved gap between the baffle 41 and the inner wall of the variable frequency vent pipe 40 becomes the main airflow channel. Low-flow gas can stably enter the variable frequency vent pipe 40 through the annular gap and then flow into the second chamber B. This ensures that the acoustic coupling system formed by the first chamber A and the second chamber B can continuously generate resonance, avoiding resonance interruption due to insufficient airflow and ensuring the basic noise reduction effect on low-frequency noise under low-flow conditions.

[0116] Optionally, in the initial state without airflow propulsion, the baffle 41 is set at an angle to the axis of the variable frequency vent pipe 40, so that the air inlet end of the variable frequency vent pipe 40 has a minimum opening, so that low flow gas can pass through.

[0117] Specifically, the variable frequency vent pipe 40 extends axially and is a long straight circular pipe, and the baffle 41 is a circular plate. The diameter of the baffle 41 is slightly smaller than the inner diameter of the variable frequency vent pipe 40. There is a gap between the two, but this gap is mainly used to provide rotation space and cannot meet the flow requirements of airflow under normal operating conditions.

[0118] More specifically, the baffle 41 is inclined near the opening of the variable frequency vent pipe 40, and the circular surface of the baffle 41 does not extend horizontally when not in operation and without external force.

[0119] When the baffle 41 is placed obliquely in the pipe, it will not completely block the frequency converter vent pipe 40. Instead, it will be spaced apart from the inner wall of the frequency converter vent pipe 40, leaving a channel for low-flow gas. This channel is similar to the "reserved gap" mentioned above, but the way it is formed is different. It can also ensure the basic noise reduction effect of low-frequency pulse noise under low-flow conditions.

[0120] In addition, the obliquely placed baffle 41 can disperse the impact force of the airflow, avoid the airflow directly impacting the baffle 41 vertically and causing local stress concentration, thereby extending the service life of the baffle 41.

[0121] Optionally, the included angle between the baffle 41 and the variable frequency vent pipe 40 along the axis is 30°-45°.

[0122] This range meets the airflow conduction requirements under low flow conditions, and also allows for a reasonable stroke for the rotation adjustment of the baffle when the flow changes. At the same time, it avoids the initial opening being insufficient due to an excessively large angle or the adjustment margin being lost due to an excessively small angle.

[0123] In one specific embodiment, the rear enclosure 21 is further provided with: a rotating shaft 42, rotatably disposed at the air inlet end of the frequency converter vent pipe 40, and a baffle 41 disposed on the rotating shaft 42; an elastic reset element 43, sleeved on the rotating shaft 42, for providing a reset torque to the baffle 41 to tend to close the port of the frequency converter vent pipe 40; and a maximum opening limiter 44, disposed on the inner wall of the frequency converter vent pipe 40, for limiting the maximum rotation angle of the baffle 41.

[0124] For details, please refer to Figure 8 In the illustrated embodiment, the rotating shaft 42 is an integral cylindrical metal shaft (preferably made of 304 stainless steel, with a diameter of 3-5 mm), and its surface is precision ground (roughness Ra≤0.2μm) to reduce rotational friction resistance. The rotating shaft 42 is rotatably disposed through the opening of the frequency converter vent pipe 40.

[0125] Continue to refer to Figure 8 The baffle 41 is a circular metal sheet (material same as the rotating shaft, thickness 1.5-2mm, diameter smaller than the inner diameter of the frequency converter vent 40, 2-10mm), and its surface is polished to reduce the impact turbulence of the airflow. The baffle 41 is fixedly mounted on the rotating shaft 42, partially blocking the opening of the frequency converter vent 40, and can rotate with the rotating shaft 42.

[0126] Continue to refer to Figure 8 The elastic reset element 43 is a small torsion spring structure, made of 65Mn steel (fatigue resistant and with good elastic recovery), with a wire diameter of 0.8-1mm, a mean diameter of 8-10mm, and a free length of 15-20mm. The elastic reset element 43 is sleeved on the outer wall of the rotating shaft 42, connecting the rotating shaft 42 and the frequency converter ventilation pipe 40. When the airflow pushes the baffle 41, causing the rotating shaft 42 to rotate, the elastic reset element 43 provides a reset torque to the rotating shaft 42 and the baffle 42, tending to close the pipe opening (the baffle 41 returns to a horizontal position).

[0127] Combined with reference Figure 9The maximum opening limiter 44 is a small metal boss (made of 304 stainless steel, 2-3mm high, 5-8mm wide) located on the inner wall of the frequency converter vent pipe 40. The surface of the maximum opening limiter 44 is rounded to avoid scratching the baffle plate 41. The size of the maximum opening limiter 44 is adapted to the maximum rotation stroke of the baffle plate 41. When the baffle plate 41 rotates around the axis 42 in the direction of increasing opening, it will eventually contact the maximum opening limiter 44. At this time, the baffle plate 41 is exactly at the maximum opening (e.g., the round surface of the baffle plate 41 is parallel to the axis of the frequency converter vent pipe 40). The maximum opening limiter 44 can prevent the baffle plate 41 from continuing to rotate, thus preventing the baffle plate 41 from over-rotating and failing to return to its original position.

[0128] The opening of the baffle 41 is determined by the dynamic balance between the rotational torque caused by the airflow pressure and the reset torque generated by the elastic reset element.

[0129] Under low-flow conditions (such as engine idling), the airflow meets the flow requirements at the minimum opening. As the flow rate increases (such as engine acceleration), the airflow pressure rises, increasing the pressure acting on the baffle 41. The resulting rotational torque overcomes the reset torque, pushing the baffle 41 to rotate towards the maximum opening limiter 44, causing the opening of the variable frequency vent pipe 40 to gradually increase, and the equivalent flow area to increase steplessly in tandem. When the flow rate decreases, the rotational torque from the airflow decreases, and the reset torque becomes dominant, pushing the baffle 41 to rotate in the opposite direction to reset, causing the opening of the variable frequency vent pipe 40 to decrease.

[0130] This dynamic balance mechanism enables stepless adjustment of the equivalent flow area of ​​the variable frequency ventilation pipe 40 with the gas flow rate, providing the core power for the adaptive adjustment of the pipe diameter of the variable frequency ventilation pipe 40 and avoiding the frequency deviation of the silencing frequency caused by the change in flow rate.

[0131] Optionally, the axis of the rotating shaft 42 is offset from the geometric center of the baffle 41. According to the lever principle, the airflow acts on the larger area, which can generate a greater torque, thereby improving the rotational sensitivity of the baffle 41.

[0132] For details, please refer to Figure 8 In the illustrated embodiment, the center of the baffle 41 and the central axis of the variable frequency vent pipe 40 are collinear, and the rotating shaft 42 is located below the center of the baffle 41.

[0133] The off-center offset design of the rotating shaft 42 (such as a 40 / 60 or 30 / 70 split) creates a difference in the force-bearing area on both sides of the baffle 41, causing the airflow to act more on the side with the larger area. According to the lever principle, a larger rotational torque can be generated under the same airflow pressure, significantly reducing the minimum airflow pressure threshold for the baffle 41 to rotate.

[0134] This design makes the baffle 41 more sensitive to changes in flow rate. Even if there are slight fluctuations in the exhaust flow rate, the baffle 41 can quickly rotate to adjust the opening, avoiding short-term frequency deviation caused by adjustment lag. This ensures that the processing frequency of the resonance cavity always follows the changes in the peak noise frequency in a timely manner, thereby maintaining the best noise reduction effect.

[0135] The fixed pipe section 40a and the movable pipe section 40b, as core components of the variable frequency vent pipe 40, require sliding fit to achieve pipe length adjustment, and the seal between them is crucial to ensuring the acoustic performance and structural reliability of the muffler. The first chamber A and the second chamber B form an acoustic coupling system through the variable frequency vent pipe 40, and the adjustment of its resonant frequency depends on the precise conduction of airflow and pressure stability between the two chambers.

[0136] If a sealing gap exists between the two pipe sections, the gas in the first chamber A will bypass the variable frequency vent pipe 40 and leak directly into the second chamber B through the gap. This will cause the airflow distribution ratio between the two chambers to become disordered, thereby disrupting the acoustic coupling relationship, causing the resonant frequency to deviate from the target noise peak, and ultimately affecting the noise reduction effect. At the same time, the leaked airflow will also generate turbulent noise, which, combined with the original exhaust noise, will further deteriorate the sound quality.

[0137] In one embodiment, a sealing structure such as a sealing ring or a magnetic fluid can be provided between the fixed pipe section 40a and the movable pipe section 40b.

[0138] Considering the high temperature problem of the tail section, in another embodiment, a stepped annular mounting groove is provided on the inner wall of the end of the fixed pipe section 40a. The annular mounting groove is used to fill the graphite braided filler 1. The graphite braided filler 1 is a rope-like structure woven from flexible graphite filaments. The groove wall of the annular mounting groove is provided with internal threads. The silencer also includes a gland 45, which can be connected to the fixed pipe section 40a through an internal and external thread connection. The gland 45 can axially press the graphite braided filler 1 in the annular mounting groove. During installation, the rope-like graphite braided filler 1 is wound around the movable pipe section 40b, so that the movable pipe section 40b passes through the fixed pipe section 40a. The graphite braided filler 1 is pressed into the annular mounting groove. The gland 45 is screwed into the annular mounting groove, and the graphite braided filler 1 is compressed and generates radial expansion, thereby tightly hugging the movable pipe section 40b and forming an effective seal.

[0139] For details, please refer to Figure 9 In the illustrated embodiment, the fixed pipe section 40a has a sandwich structure, and the upper inner wall is provided with a stepped annular mounting groove. The annular mounting groove is distributed around the inner circumference of the fixed pipe section 40a, and the cross-section is U-shaped. The inner diameter of the groove opening is larger than the inner diameter of the groove bottom, forming a step. The groove wall is machined with internal threads for mating with the gland 45.

[0140] The graphite braided packing 1 has a rope-like structure, made of flexible graphite filaments, with a smooth surface and good flexibility and elasticity. During installation, the rope-like packing needs to be wound multiple times around the outer wall of the movable pipe section 40b to form an annular sealing layer. The winding thickness matches the groove depth of the annular installation groove to ensure that the graphite braided packing 1 can completely fill the gap in the groove after being pressurized.

[0141] The gland 45 is generally annular and stepped, comprising a cover and an insertion part. The insertion part has external threads machined on its cylindrical surface for engagement with internal threads. The outer diameter of the cover matches the outer diameter of the fixed pipe section 40a to ensure a smooth appearance. The gland 45 has a central channel for inserting the movable pipe section 40b; the inner diameter of the channel is slightly larger than the outer diameter of the movable pipe section 40b to allow for sliding clearance. After the insertion part is inserted into the annular mounting groove via a threaded connection, the insertion part axially presses against the graphite braided packing 1 within the annular mounting groove.

[0142] Optionally, the gland 45 is made of 304 stainless steel with a high-temperature resistant surface treatment to ensure that the threads will not seize or the structure will deform under high-temperature conditions.

[0143] Optionally, the gap between the inner diameter of the channel in the gland 45 and the outer diameter of the movable tube section 40b is controlled to be 0.5-1mm.

[0144] During installation, the rope-shaped graphite braided packing 1 is first wrapped around the movable pipe section 40b, and then the movable pipe section 40b is inserted into the fixed pipe section 40a, so that the graphite braided packing 1 is embedded in the annular mounting groove. Subsequently, the gland 45 is screwed into the annular mounting groove. During the screwing process, the insertion part of the gland 45 applies axial pressure to the graphite braided packing 1, and the graphite braided packing 1 is compressed. Because the graphite braided packing 1 has flexibility and elasticity, axial compression will cause it to expand radially. The inner ring tightly hugs the movable pipe section 40b, and the outer ring tightly adheres to the outer wall of the annular mounting groove, forming a "two-way seal" that completely blocks the gas leakage channel between the two pipe sections.

[0145] Because graphite is an excellent solid lubricant with an extremely low coefficient of friction (≤0.15), even if the graphite braided filler 1 tightly hugs the moving pipe section 40b, the moving pipe section 40b will not slip. At the same time, graphite possesses high-temperature resistance (withstanding temperatures above 800℃), ensuring that the sealing structure maintains stable sealing performance in the high-temperature environment of the exhaust system, preventing carbonization or failure. This guarantees the timeliness and accuracy of pipe length adjustment, thereby achieving dynamic correction of the resonant frequency.

[0146] The threaded engagement between the gland 45 and the fixed pipe section 40a is self-locking, maintaining axial pressure on the graphite braided packing 1 for a long time. This prevents pressure relaxation due to vibration, thermal expansion and contraction, and ensures the packing is always under compression, maintaining stable sealing performance over the long term. Simultaneously, the threaded connection facilitates later maintenance. If the graphite braided packing 1 wears down due to long-term use, further tightening the gland 45 can improve the recovery of radial volume and restore sealing performance. Furthermore, the internal and external threaded connection structure facilitates packing replacement without disassembling the entire variable frequency vent pipe 40, significantly reducing maintenance costs and difficulty.

[0147] Optionally, the fixed pipe section 40a and the movable pipe section 40b are made of the same or similar materials with similar coefficients of thermal expansion, such as 304 stainless steel or 316 stainless steel (which are resistant to high temperature and exhaust corrosion, and also have high mechanical strength, can withstand sliding thrust and airflow impact, and ensure that the pipe section does not deform).

[0148] This is because the operating temperature of the exhaust system can reach 400-600℃. If the thermal expansion characteristics are different, the expansion of the pipe sections at high temperatures will be different, which will lead to the disappearance of the fitting clearance, the sliding jamming, the loss of the pipe length adjustment function, and the destruction of the frequency matching of the AB cavity acoustic coupling system.

[0149] Optionally, an axially extending guide key is provided on the inner wall of the fixed pipe section 40a, and a matching keyway is provided on the outer wall of the movable pipe section 40b.

[0150] The extension direction of the guide key is consistent with the sliding direction of the movable tube section 40b. When installing the fixed tube section 40a and the movable tube section 40b, the guide key is inserted into the corresponding keyway. The guide key and the keyway are aligned with each other, which can prevent the movable tube section 40b from rotating relative to the fixed tube section 40a when sliding, and can also prevent the movable tube section 40b from deflecting due to airflow impact or installation deviation, thereby ensuring the accuracy of tube length adjustment and guaranteeing the accuracy of resonance frequency correction of the AB cavity acoustic coupling system.

[0151] Optionally, the graphite braided filler 1 is made from natural graphite with a purity of ≥99.5% through expansion and drawing.

[0152] Optionally, the graphite braided filler 1 is woven from graphite filaments mixed with Inconel nickel wire (0.1-0.2 mm in diameter), with the Inconel nickel wire accounting for 10%-15%. In this way, the properties of graphite can be retained while improving tensile strength and structural stability, making it more suitable for the high temperature and high pressure conditions of exhaust systems.

[0153] Optionally, the roughness of the outer wall surface of the active pipe section 40b is not greater than 0.2 μm.

[0154] Graphite braided packing 1 is soft in texture. If the outer wall of the moving section 40b is rough (e.g., Ra > 0.8 μm), the micro-protrusions on the surface will wear down the packing quickly like sandpaper, leading to a decline in sealing performance. A smooth surface with Ra ≤ 0.2 μm can transform sliding friction into near-fluid friction, thereby significantly reducing the wear rate of the packing and ensuring the long-term reliability of the sealing structure.

[0155] Optionally, the surface finish of the outer wall of the active pipe section 40b can be achieved through an ultra-precision grinding process.

[0156] Specifically, a fine-grained abrasive stone (such as a diamond abrasive stone with a grit size of W5-W10) is used as a tool to perform a finishing process on the outer wall surface of the movable tube section 40b under relatively low pressure (typically 0.05-0.2 MPa). During the processing, the abrasive stone makes flexible contact with the surface of the tube section, gradually removing tiny protrusions until the roughness is reduced to Ra0.1 μm or even lower. Simultaneously, the ultra-precision grinding process forms a cross-linked pattern on the surface of the movable tube section 40b. This cross-linked pattern helps to retain the lubricating components of the graphite braided filler 1, further optimizing the sliding performance.

[0157] Optionally, the outer wall of the active pipe section 40b is coated with a hard, wear-resistant coating.

[0158] The hard wear-resistant coating can be a diamond-like carbon film (DLC) or a ceramic coating.

[0159] Diamond-like carbon (DLC) films are primarily composed of carbon, with a structure similar to diamond. They possess a hardness of HV1500-4000 and an extremely low coefficient of friction (0.05-0.15), combining both hardness and lubrication properties. The thickness of the DLC film is typically controlled between 2-5 μm. This ensures that the fit clearance between the moving section 40b and the fixed section 40a is not affected, while also providing excellent high-temperature resistance (capable of withstanding exhaust temperatures of 400-600℃ for extended periods) and chemical stability, preventing reactions with sulfides and nitrogen oxides in the exhaust.

[0160] The preferred ceramic coating is either alumina ceramic or silicon carbide ceramic, with a hardness of HV1200-2500, excellent high-temperature resistance, and strong wear and corrosion resistance. The ceramic coating thickness is generally 5-10μm, and a dense structure is formed through plasma spraying, which can adhere tightly to the outer wall surface of the moving pipe section 40b, preventing it from falling off at high temperatures.

[0161] The movable tube section 40b needs to slide in contact with the graphite braided filler 1 for a long time. Even if the roughness of the outer wall of the movable tube section 40b is controlled at Ra≤0.2μm, long-term friction will still cause wear on the surface of the tube section. The high hardness of the hard wear-resistant coating can significantly reduce the wear rate, thereby preventing the outer wall of the tube section from becoming uneven due to wear, ensuring the long-term stability of the sliding fit accuracy, and extending the replacement cycle of the movable tube section.

[0162] In one specific embodiment, the outer wall roughness Ra of the movable tube section 42 is ≤0.2μm, and a high-temperature resistant, hard, and wear-resistant coating is formed. The ultra-smooth surface combined with the high-hardness coating can effectively reduce the wear rate of the graphite braided filler 1 and significantly extend the service life of the filler.

[0163] Optionally, the pressure plate 45 is provided with a pressure plate and a disc spring. The pressure plate is used to press against the graphite braided packing 1, and the disc spring is pressed between the pressure plate and the pressure plate 45. After the graphite braided packing 1 is worn, its volume shrinks and the disc spring extends, which can push the pressure plate to compensate for the gap caused by wear, so as to maintain the compressive force on the graphite braided packing 1.

[0164] Specifically, the pressure plate is an annular metal component located at the end of the pressure cap 45, used to press against the graphite braided packing 1. The material of the pressure cap 45 is consistent with that of the variable frequency vent pipe 40 to ensure a matching coefficient of thermal expansion. After the pressure cap 45 is screwed into the annular mounting groove, the pressure plate contacts the graphite braided packing 1. The outer diameter of the pressure plate is consistent with the inner diameter of the annular mounting groove, and the inner diameter of the inner ring of the pressure plate is slightly larger than the outer diameter of the movable pipe section 40b (leaving a sliding gap of 0.5-1mm to avoid hindering the sliding of the pipe section), ensuring uniform force when in contact with the graphite braided packing 1, and preventing local crushing or local pressure loss.

[0165] Disc springs are thin-walled, truncated cone-shaped elastic elements. In their free state, they are conical and can generate a stable elastic restoring force after compression. Multiple sets of disc springs are evenly distributed between the pressure plate and the pressure cap 45 to ensure that the elastic force can be uniformly transmitted axially when compressed.

[0166] As the movable pipe section 40b slides for a long time, the graphite braided packing 1 wears down due to friction, and its volume gradually shrinks, resulting in a small gap between it and the pressure plate. At this time, the originally compressed disc spring can stretch under its own elastic recovery, thereby pushing the pressure plate to move towards the graphite braided packing 1. By continuously applying a clamping force to the packing, the gap caused by wear is filled, and the tight fit between the packing and the movable pipe section 40b and the mounting groove wall is maintained.

[0167] The automatic compensation of the disc springs extends the effective sealing life of the graphite braided packing 1, eliminating the need for frequent tightening of the gland 45 or packing replacement, thus reducing maintenance costs and complexity. Simultaneously, the uniform force design of the pressure plate prevents localized packing crushing, further extending its service life and enabling the muffler to operate stably for extended periods, meeting the full lifespan requirements of the vehicle.

[0168] In addition, under the high-temperature conditions of the exhaust system, metal components such as the gland 45 and pipe sections will undergo thermal expansion. The elasticity of the disc spring can absorb the small displacement caused by thermal expansion, avoid structural stress caused by rigid connection, prevent the gland thread from seizing or the pressure plate from deforming, ensure that the movable pipe section 40b always slides smoothly, does not affect the pipe length adjustment function, and indirectly ensures the accuracy of the resonant cavity frequency adjustment.

[0169] Optionally, the fixed pipe section 40a has a sandwich structure, with a piston push rod 46 inside the sandwich. The piston push rod 46 divides the sandwich into a rod chamber and a rodless chamber, which are respectively connected to a hydraulic oil circulation supply device. The piston push rod 46 is connected to the movable pipe section 40b. When hydraulic oil is input into the rodless chamber, the piston push rod 46 can push the movable pipe section 40b outward, thereby increasing the length of the variable frequency vent pipe 40. When hydraulic oil is input into the rod chamber, the piston push rod 46 can pull back the movable pipe section 40b, thereby reducing the length of the variable frequency vent pipe 40.

[0170] For details, please refer to Figure 9 In the illustrated embodiment, the fixed pipe section 40a has an overall double-layer cylindrical sandwich structure, with the inner and outer pipe walls forming an annular sandwich space. The sandwich space is closed, with only a hydraulic oil interface provided.

[0171] Continue to refer to Figure 9 The piston push rod 46 is an annular cylindrical metal component (it can be made of 45# steel with a chrome-plated surface for rust prevention). The upper part of the piston push rod 46 is its annular piston head, which divides the interlayer into a rod chamber (the protruding side of the piston push rod 46, the chamber containing the push rod body) and a rodless chamber (the chamber without the push rod body). A fluororubber sealing ring is fitted over the annular piston head to ensure a relative seal between the two chambers. The lower part of the piston push rod 46 is its push rod body, the lower end of which passes through the interlayer and connects to the movable tube section 40b.

[0172] On the outer wall of the fixed pipe section 40a, a set of hydraulic oil interfaces are opened at the positions corresponding to the rod cavity and the rodless cavity, respectively. The interfaces are welded with internally threaded pipe fittings. The interfaces are connected to the hydraulic oil circulation supply equipment through high-pressure hydraulic pipes. The pipeline is also equipped with solenoid valves to control the flow direction of hydraulic oil.

[0173] When the noise sensor detects a shift in the peak frequency of the exhaust noise, requiring an increase in the length of the variable frequency vent pipe 40, the hydraulic oil circulation supply device inputs high-pressure hydraulic oil into the rodless chamber. The increased hydraulic pressure in the rodless chamber pushes the piston rod 46, causing the movable pipe section 40b to move downwards. The movable pipe section 40b extends axially outwards, increasing the total length of the variable frequency vent pipe 40. When a decrease in length is required, the hydraulic oil circulation supply device switches to inputting hydraulic oil into the rod chamber. The increased pressure in the rod chamber pushes the piston rod 46 back, causing the movable pipe section 40b to retract into the fixed pipe section 40a, thus reducing the total length of the variable frequency vent pipe 40.

[0174] The movable section 40b of the variable frequency ventilation pipe 40 needs to overcome the friction of the graphite braided packing 1 to achieve smooth sliding in a high-temperature environment. Hydraulic drive can provide continuous and stable axial thrust, avoiding the problems of large pressure fluctuations in pneumatic drive or insufficient thrust in electric drive. At the same time, hydraulic drive can achieve uniform sliding of movable section 40b by controlling the flow of hydraulic oil, with high adjustment precision, which can accurately match the frequency offset detected by the noise sensor, ensuring that the processing frequency of the resonance cavity is aligned with the noise peak. In addition, the operating temperature of the exhaust system can reach 400-600℃, and the hydraulic oil is more resistant to high temperatures. Moreover, the hydraulic pipelines and components (such as solenoid valves and sealing rings) are all made of high-temperature resistant materials (fluororubber, stainless steel), which will not fail due to high temperature. Compared with electric drive (motor is prone to burnout at high temperature) or pneumatic drive (compressed air is prone to expansion at high temperature, resulting in a decrease in precision), hydraulic drive is more suitable for the high-temperature working environment of the muffler and has higher long-term operational reliability.

[0175] Traditional designs require an additional independent hydraulic cylinder outside the variable frequency vent pipe 40, which not only occupies the limited space within the rear enclosure 21 but also necessitates a complex connection structure for the hydraulic cylinder to operate in conjunction with the movable pipe section 40b. By directly designing the fixed pipe section 40a as a sandwich-type hydraulic cylinder, the fixed section of the vent pipe and the driving hydraulic cylinder are integrated into one unit, eliminating the need for additional installation space. This also reduces the number of connecting components between the pipe section and the hydraulic cylinder (such as couplings), simplifying the assembly process and lowering structural complexity and the risk of failure. Furthermore, the hydraulic oil can carry away heat from the sandwich layer during circulation, providing a cooling effect and preventing components such as the piston rod 46 and sealing rings from aging or deforming due to prolonged high temperatures.

[0176] Optionally, a return spring 47 is also provided in the interlayer. The elastic force of the return spring 47 can drive the piston push rod 46 to move the movable tube section 40b in the direction of increasing tube length.

[0177] The return spring 47 can be a cylindrical helical compression spring, preferably made of 60Si2Mn steel. This material has a high elastic limit and fatigue resistance, and can be adapted to the high temperature environment in the jacket of the fixed pipe section 40a (it can still maintain stable elasticity under exhaust conditions of 400-600℃).

[0178] For details, please refer to Figure 9 In the illustrated embodiment, multiple sets of return springs 47 are provided in the rodless cavity. One end of any return spring 47 is connected to the cavity wall, and the other end is connected to the piston push rod 46. The multiple sets of return springs 47 are distributed at equal intervals along the circumference to ensure the overall stability of the piston push rod 46 when it is affected by elastic force.

[0179] Under normal use, the hydraulic pressure can overcome the elastic force of the return spring 47, and the return spring 47 will not affect the extension and retraction of the piston push rod 46. In the event of a safety failure (such as a malfunction of the hydraulic oil circulation supply equipment leading to hydraulic pressure loss), the pressure in the rod chamber drops sharply to 0, and the pressure in the rodless chamber decreases simultaneously. At this time, the elastic potential energy stored in the return spring 47 is completely released, generating a thrust towards the rod chamber, which pushes the piston push rod 46 to extend the movable tube section 40b outward until the movable tube section 40b reaches the maximum tube length mechanical limit, keeping the frequency converter vent pipe 40 in the safe position of the maximum tube length. This avoids the tube section being in an uncertain state due to hydraulic pressure loss (without the return spring 47, the movable tube section 40b after pressure loss may be in any position due to its own gravity or airflow impact, causing the tube length of the frequency converter vent pipe 40 to become out of control, the resonant cavity processing frequency to deviate significantly from the noise peak, and the noise reduction effect to fail).

[0180] This allows the return spring 47 to forcefully push the movable tube section 40b to the maximum safe position when it loses pressure. The resonance frequency corresponding to this position is a preset safe frequency band (such as to match the low-frequency noise of engine idling), which can maintain the basic noise reduction effect and at the same time avoid structural collision damage caused by excessive retraction of the movable tube section 40b, ensuring that the muffler can still operate safely under fault conditions.

[0181] Optionally, the hydraulic oil is a high-temperature resistant synthetic hydraulic oil, which is a phosphate ester liquid, a phthalate ester liquid, or a polyalphaolefin synthetic oil.

[0182] The fixed pipe section 40a is constantly exposed to the high-temperature environment of the exhaust system. The temperature inside the jacket can reach 120-180℃ due to heat conduction from the exhaust, and the hydraulic oil needs to withstand a working pressure of 0.5-0.8MPa during circulation. Traditional mineral hydraulic oil is prone to oxidation and deterioration at this temperature, resulting in a sharp drop in viscosity and an increase in acid value. This not only leads to a loss of lubrication and transmission capabilities but may also generate sludge that clogs hydraulic lines or corrodes components such as the piston push rod 46 and seals, causing hydraulic drive failure and affecting the pipe length adjustment function of the variable frequency vent pipe 40. Therefore, a high-temperature resistant synthetic hydraulic oil must be selected. Its molecular structure is stable, and it can maintain excellent viscosity stability, oxidation resistance, and lubricity at high temperatures, making it suitable for the high-temperature and high-pressure conditions of the muffler hydraulic system and ensuring reliable pipe length adjustment.

[0183] Phosphate ester solution exhibits outstanding high-temperature resistance, with a long-term operating temperature of 150-200℃ and short-term tolerance to 250℃, making it perfectly suited for the 120-180℃ working environment within the interlayer. Furthermore, phosphate ester solution possesses excellent flame retardancy; even in the event of an accidental leak in the hydraulic pipeline, it is not easily ignited by the high temperature of the exhaust gas, thus mitigating the risk of fire.

[0184] Phthalate ester solutions have a high viscosity index (typically >150) and exhibit minimal viscosity decrease at high temperatures, maintaining stable transmission efficiency within the 120-160℃ range. This ensures uniform sliding of the piston rod 46, thereby improving the accuracy of pipe length adjustment. Furthermore, phthalate ester solutions possess strong chemical stability, exhibiting no corrosive effect when in prolonged contact with stainless steel fixed pipe sections 40a and piston rod 46, and are not prone to reacting with trace amounts of corrosive gases in the exhaust system.

[0185] Polyalphaolefin synthetic oils exhibit excellent low-temperature fluidity, maintaining low viscosity even at -40°C, making them suitable for cold-start conditions in winter or cold regions, preventing hydraulic systems from failing to start due to oil solidification. Furthermore, polyalphaolefin synthetic oils offer a balanced combination of high-temperature resistance and oxidation resistance, with a long-term operating temperature range of 140-180°C and a long oil change interval (3-5 times that of mineral oils), reducing the frequency of hydraulic oil changes and maintenance.

[0186] Optionally, an oil cooler is provided on the return or supply path of the hydraulic oil circulation supply equipment to cool the hydraulic oil during the circulation process.

[0187] In one embodiment, an air-cooled oil cooler is provided on the oil return path or oil supply path.

[0188] The main body of the air-cooled oil cooler is an aluminum tube-and-strip heat dissipation core, composed of multiple layers of corrugated heat dissipation fins and copper oil pipes. A temperature-sensing cooling fan and temperature sensor are installed on one side. During installation, the air-cooled oil cooler is fixed behind the grille at the front of the vehicle using an L-shaped bracket with rubber shock-absorbing pads, ensuring that the core faces the direction of travel and the fan is unobstructed. During use, the hydraulic oil is cooled by the oncoming airflow as it passes through the pipes.

[0189] Optionally, the fan will start automatically when the oil temperature is above 65°C and stop when it is below 45°C. The fins need to be cleaned of dust monthly and the fan wiring and sensor signals need to be checked every six months.

[0190] In another embodiment, a liquid-cooled oil radiator is provided on the oil return path or the oil supply path.

[0191] The liquid-cooled oil radiator has a stainless steel shell-and-tube structure with multiple copper heat exchange tubes inside. Hydraulic oil flows through the shell side, and coolant flows through the tube side. The oil inlet and coolant inlet / outlet are staggered. A temperature-controlled flow regulating valve is built into the shell. During installation, the liquid-cooled oil radiator is fixed to a bracket next to the hydraulic pump in the engine compartment (with the outer shell horizontal). The coolant inlet is connected to the engine coolant outlet pipe, and the return pipe is connected to the return pipe. The hydraulic inlet is connected to the oil supply path, and the outlet is connected to the actuator. During use, the oil and coolant exchange heat. When the oil temperature is above 70°C, the regulating valve increases the coolant flow rate; when the temperature is below 40°C, it decreases the flow rate.

[0192] The coolant level needs to be checked weekly, the heat exchanger tube sealing needs to be checked quarterly, and impurities in the shell should be cleaned annually.

[0193] Installing an oil cooler can stabilize and control the hydraulic oil temperature within a lower operating range, preventing high temperatures from causing oil oxidation and deterioration, viscosity reduction, and sludge buildup that could clog pipes or corrode components such as piston rod seals and solenoid valves. It also ensures the lubrication and transmission efficiency of the hydraulic oil, extending the service life of the oil and hydraulic components. Simultaneously, a stable oil temperature maintains stable pressure in the hydraulic drive system, ensuring smooth sliding of the piston rod 46 against the movable pipe section 40b. This further ensures precise pipe length adjustment, allowing the variable frequency vent pipe 40 to accurately correct the resonance frequency, guaranteeing a quieter effect, adapting to the exhaust requirements of the engine under all operating conditions, and improving the overall reliability of the muffler.

[0194] Optionally, the static and dynamic seals in the hydraulic oil circuit between the hydraulic oil circulation supply equipment and the jacket are made of fluororubber, perfluororubber, or polytetrafluoroethylene.

[0195] Among them, static seals are used between components in the hydraulic oil circuit that do not move relative to each other. They mainly include hydraulic oil interface seals (such as between the interlayer hydraulic oil interface of fixed pipe section 40a and the hydraulic pipe, and between the oil inlet and outlet of the oil radiator and the pipeline). O-rings or flat gaskets are generally used to achieve static surface sealing and prevent oil leakage from the connection gap.

[0196] Dynamic seals are used between components with relative movement in the hydraulic oil circuit, such as between the piston head of the piston rod 46 and the inner wall of the fixed pipe section 40a. Generally, Y-type or U-type sealing rings are used. The seal will slide axially with the piston rod 46 to achieve dynamic sealing and prevent hydraulic oil from flowing between the rod chamber and the rodless chamber.

[0197] Seals in hydraulic oil circuits are subjected to harsh conditions for extended periods, including high temperatures (120-180℃ within the interlayer), high pressure (0.5-0.8MPa), and immersion in hydraulic oil. They also need to withstand trace amounts of corrosive gases (such as sulfides) that may be present in the exhaust system. Traditional rubber seals (such as nitrile rubber) are prone to swelling, hardening, and aging failure under these conditions, leading to leaks, affecting the accuracy of hydraulic drives, and even causing system malfunctions.

[0198] Fluororubber, perfluororubber, and polytetrafluoroethylene possess excellent high-temperature resistance, oil resistance, and corrosion resistance, enabling them to maintain sealing performance and structural stability under harsh working conditions for extended periods, thus meeting the application requirements of hydraulic oil circuits.

[0199] Fluororubber offers excellent cost-effectiveness, combining good high-temperature resistance (long-term temperature resistance 200℃, short-term temperature resistance 260℃) with oil resistance. It also exhibits excellent compatibility with high-temperature synthetic hydraulic oils such as phosphate esters and phthalate esters. Furthermore, fluororubber maintains a good balance between elasticity and compression set, allowing it to fit tightly against the sealing surface after installation, making it suitable for both static and low-to-medium frequency dynamic sealing applications.

[0200] Perfluororubber exhibits superior high-temperature and corrosion resistance, with a long-term temperature resistance of 260℃ and a short-term temperature resistance of 320℃. It can withstand highly corrosive media (such as high-concentration sulfides and acidic hydraulic oils). Furthermore, perfluororubber has extremely low compression set (deformation <5% after long-term use), ensuring stable sealing performance over the long term. It is particularly suitable for high-frequency sliding dynamic seals such as piston rods, resulting in a long service life.

[0201] Polytetrafluoroethylene (PTFE) is extremely chemically inert, reacting almost entirely with hydraulic oils and corrosive gases, and possesses an extremely low coefficient of friction (0.04-0.05), making it suitable for low-friction sealing when mated with metal surfaces. Furthermore, PTFE exhibits stable high-temperature resistance (long-term temperature resistance up to 260℃), allowing for the fabrication of PTFE and metal spring combinations for use in static sealing end plates or interfaces with low pressure fluctuations. This also helps prevent seal failure due to insufficient elasticity.

[0202] Optionally, the exhaust pipe includes: a vertical section 25a, which passes through the first layer plate 22a, the second layer plate 22b and the third layer plate 22c, with its front end passing through the rear exhaust body 21 for exhausting gas, and its end extending into the fourth chamber D; a bent section 25b, located in the fourth chamber D, with one end connected to the vertical section 25a and the other end extending toward the third layer plate 22c; and a gas collection section 25c, which connects to the other end of the bent section 25b and extends into the third chamber C, allowing gas in the third chamber C to enter the exhaust pipe through the gas collection section 25c.

[0203] The three-stage structure of the exhaust pipe—vertical section 25a, bend section 25b, and intake section 25c—achieves deep suppression of residual noise and optimization of exhaust flow through path extension, airflow diversion, and multi-chamber coupling mechanism.

[0204] For details, please refer to Figure 6 In the illustrated embodiment, the vertical section 25a penetrates the four chambers of the rear muffler 21 along the vertical direction. When sound waves propagate along the vertical section 25a, they need to pass through the layers multiple times. Each time they pass through, impedance mismatch occurs due to changes in cross-sectional area, causing sound wave reflection and interference, thereby achieving a noise reduction effect. A high-frequency tube 27 is installed on the outside of the vertical section, which can effectively reduce the 2000Hz noise sound pressure level, thereby compensating for the insufficient high-frequency noise suppression of the front muffler assembly 10.

[0205] Continue to refer to Figure 6The bent section 25b is designed in the shape of a U-shaped tube. The left end of the bent section 25b connects to the vertical section 25a, and the right end connects to the air intake section 25c. The bent section can redirect the airflow and form a "sound barrier" effect. Low-frequency sound waves (such as 25Hz) have long wavelengths and cannot bypass the bent section 25b. They will be reflected by the inner wall and form standing wave interference with the incident wave, thereby increasing the noise reduction. Mid-to-high frequency sound waves (such as 500Hz) have short wavelengths and will diffract at the corner of the bent section 25b. The energy will diffuse towards the edge of the chamber and promote sound energy dissipation.

[0206] In addition, the bend section 25b can guide the airflow to form a weak vortex inside the pipe. The vortex makes the propagation path of the sound wave spiral, which can prolong the residence time and enhance the effect of the sound-absorbing layer. The centrifugal force generated by the airflow turning can also offset part of the pulsating impact force, thereby reducing the vibration amplitude of the vertical section 25.

[0207] Continue to refer to Figure 6 The air-collecting section 25c extends to the upper part of the third chamber C, and the opening direction of the air-collecting section 25c is consistent with the sound wave reflection direction of the third plate 22c. The residual low-frequency sound waves in the third chamber C, after being reflected by the third plate 22c, form an interference condition with the airflow at the inlet of the air-collecting section 25c with a phase difference of 180°, achieving destructive superposition and further reducing noise.

[0208] The three-stage structure of the exhaust pipe achieves targeted treatment of noise at different frequencies through a dual mechanism of acoustic path design and fluid control. The intake section 25c completes low-frequency secondary noise reduction, the bending section 25b optimizes mid-frequency interference, and the vertical section 25a enhances high-frequency sound absorption. This design improves the overall noise reduction efficiency of the rear muffler while ensuring low back pressure. Together with the concentric tube structure of the front muffler, it forms a full-chain noise reduction system of "low frequency-mid frequency-high frequency", ultimately meeting the NVH performance requirements of the entire vehicle.

[0209] Optionally, the intake pipe 26 is configured in a bent shape, with a portion of the intake pipe 26 located in the second chamber B. An exhaust port is provided on the pipe wall located in the second chamber B, allowing some gas to enter the second chamber B through the exhaust port on the intake pipe 26.

[0210] For details, please refer to Figure 6 In the illustrated embodiment, the outlet of the intake pipe 26 is connected to the first chamber A, and the main airflow will directly enter the first chamber A, exciting the Helmholtz resonance silencing of the engine's fundamental frequency noise in the first chamber A; the bend section passes through the second chamber B, and the exhaust port on the bend section allows some airflow to directly enter the second chamber B, prematurely exciting the resonance response of the second chamber B to the fundamental frequency second harmonic.

[0211] By adjusting the shunt ratio, the resonant frequencies of the first chamber A and the second chamber B are matched to the fundamental frequency and harmonics, respectively, forming a graded noise reduction system of "fundamental frequency-harmonic". For example, when the volume of the first chamber A is V...A When the frequency is 25Hz and the second chamber B receives some airflow in advance, its equivalent volume becomes V. B =V B +0.3V A =18.4L, its resonant frequency shifts from 50Hz to 45Hz, enabling it to cover a wider frequency band.

[0212] Furthermore, when the airflow entering the first chamber A enters the second chamber B through the leak 23, there is a time difference (approximately 0.005-0.01 seconds) between it and the airflow entering the second chamber B directly from the exhaust port of the intake pipe 26. This results in an interference condition with a phase difference of 90-180° within the second chamber B. For 50Hz noise, this 180° phase difference interference can reduce the sound pressure level by 2-10 dB, significantly improving noise reduction compared to a single-path airflow.

[0213] After the two airflow paths mix in the second chamber B, a composite sound field of "primary resonance mode + secondary resonance mode" is formed. The primary mode is excited by the leaking airflow from the first chamber A and corresponds to the natural frequency of the second chamber B (e.g., 45Hz). The secondary mode is excited by the direct air supply from the exhaust port of the intake pipe 26 and corresponds to the higher-order modes of the second chamber B (e.g., 90Hz). The composite resonance increases the noise attenuation of the second chamber B in the 45-90Hz frequency band, doubling the bandwidth covered by the single mode.

[0214] In addition, the two airflows collide in the second chamber B to form microturbulence, which can accelerate the energy exchange between the sound waves and the sound-absorbing material (such as glass fiber cotton) on the chamber wall, thereby further improving the noise reduction efficiency.

[0215] In summary, the intake manifold 26's split-flow and merge-flow design actively regulates the airflow distribution ratio and phase difference, enabling the multi-stage chambers of the rear muffler to form a composite silencing system with complementary frequencies and enhanced interference. This mechanism not only improves the targeted suppression capability of the fundamental frequency and its harmonic noise but also optimizes broadband silencing performance through turbulence effects, while ensuring low back pressure and structural reliability. This "split-flow-excited resonance-merging-enhanced interference" design provides a more efficient solution for refined noise reduction in exhaust systems.

[0216] Optionally, the return pipe 24 passes through the third chamber C, and an exhaust port is provided on the pipe wall inside the third chamber C, so that some gas can enter the third chamber C through the exhaust port on the return pipe 24.

[0217] For details, please refer to Figure 6In the illustrated embodiment, the return pipe 24 extends vertically, sequentially passing through the second layer plate 22b and the third layer plate 22c. An exhaust port (diameter φ3-5mm, opening ratio 5-8%) is provided on the pipe wall located between the second layer plate 22b and the third layer plate 22c, allowing some airflow to enter the third chamber C, thereby exciting local resonance of the third chamber C for high-order engine noise (e.g., 200Hz).

[0218] It should be explained that the path of the return pipe 24 directly to the fourth chamber D is a smooth straight pipe with low fluid resistance. At the same time, the exhaust port is a small orifice outlet with orifice contraction effect and needs to overcome the back pressure of the third chamber C. Therefore, the actual flow rate discharged from the exhaust port is only 10-15% of that of the main path.

[0219] The volume of the third chamber C (e.g., V) C =6L) and the size of the exhaust port are matched to form a Helmholtz resonator, which can achieve a noise reduction of 2-10dB at 200Hz in actual tests.

[0220] Most of the airflow (85-90%) reaches the fourth chamber D directly through the return pipe 24, and the volume of the fourth chamber D (e.g., V) D =4L) matching, for secondary resonance silencing of low and medium frequency noise (such as 50Hz), the silencing amount can reach 5-15dB.

[0221] By controlling the shunt ratio, the third chamber C and the fourth chamber D process noise in different frequency bands respectively, forming a synergistic effect of "high-frequency resonance of the third chamber C and mid-frequency resonance of the fourth chamber D", which further broadens the noise reduction frequency band (covering 50-500Hz).

[0222] Because the third layer plate 22c is a perforated plate, the airflow entering the third chamber C and the airflow entering the fourth chamber D are always in a state of mutual communication. However, there is a phase difference (about 1 / 4 period) between the airflow entering the third chamber C and the airflow flowing from the fourth chamber D into the third chamber C through the third layer plate 22c, which forms destructive interference with the 200Hz noise and can further reduce the sound pressure level.

[0223] In addition, the high-speed jet at the exhaust port on the return pipe 24 will form a small-scale vortex in the third chamber C, which can increase the number of collisions between the sound waves and the sound-absorbing material (such as glass fiber cotton) on the cavity wall, thereby improving the sound absorption efficiency.

[0224] The perforated third layer plate 22c exhibits a "rigid wall" characteristic for low-frequency sound waves, with a reflection coefficient >0.8. This forces sound waves to reflect multiple times within the fourth chamber D, extending the residence time and enhancing the resonance silencing effect. For high-frequency sound waves, the third layer plate 22 acts as an "acoustic damping element," with a transmission coefficient >0.6, allowing them to enter the third chamber C through the perforations, where they are further absorbed by the air-collecting section 25c and the high-frequency tube 27.

[0225] As the end of the return pipe, the fourth chamber D has a lower airflow velocity, which facilitates uniform distribution through swirling flow (guided by the bend section 25b) and avoids the direct impact of high-speed airflow on the perforated plate, thus preventing additional noise. The airflow in the third chamber C, after passing through the perforated plate, is accelerated to 15-20 m / s by the air-collecting section 25c. The Venturi effect is used to reduce the static pressure in the third chamber C, forming a coordinated flow of "stabilized flow in the fourth chamber D - guided flow in the third chamber C," ensuring stable back pressure.

[0226] In summary, the separation between the third chamber C and the fourth chamber D optimizes the propagation path of sound waves through the "low-frequency reflection-high-frequency transmission" characteristics of the perforated plate.

[0227] Optionally, a high-frequency tube 27 is provided on the vertical section 25a. Some of the high-frequency tubes 27 are located in the first chamber A, and some of the high-frequency tubes 27 are located in the second chamber B. The high-frequency tubes 27 have the function of absorbing high-frequency noise.

[0228] The high-frequency tube 27 is typically constructed by combining a perforated tube with sound-absorbing material. The perforated tube wall has numerous small holes evenly distributed, with a diameter generally between 3-5 mm and a perforation rate controlled at 15-20%. The perforated tube is filled internally or wrapped externally with a material with good sound-absorbing properties, such as fiberglass wool or sound-absorbing foam. Taking fiberglass wool as an example, its interior has a large number of tiny pores. This structural design allows the high-frequency tube 27 to both acoustically process high-frequency noise and ensure smooth exhaust.

[0229] The high-frequency tube 27 primarily absorbs high-frequency noise based on the Helmholtz resonance principle and the sound-absorbing properties of sound-absorbing materials. When high-frequency noise sound waves are introduced, some of the sound waves enter the tube through the small holes. Due to the resonance system formed by the small holes and the air inside the tube, the sound energy of the noise at a specific frequency is converted into heat energy and dissipated under the resonance effect. At the same time, the sound-absorbing materials inside or outside the tube, such as glass fiber cotton, utilize their porous structure to allow sound waves to be continuously reflected and refracted within the pores. Through the friction between air molecules and fibers, sound energy is converted into heat energy, further absorbing noise energy.

[0230] The high-frequency tube 27 exhibits significant absorption effects on high-frequency noise above 2000Hz. In actual testing, when the exhaust system was not equipped with the high-frequency tube, the sound pressure level of 2000Hz noise was 85dB; after installing the high-frequency tube 27, the absorption of high-frequency noise by the tube improved flow noise by 3-6dB. This effect effectively compensates for the insufficient high-frequency noise suppression of other parts of the front and rear mufflers, significantly reducing high-frequency noise in the exhaust system, improving overall noise reduction performance, optimizing the quality of the vehicle's exhaust sound, and reducing the interference of high-frequency noise on passengers.

[0231] This application also provides an exhaust treatment system, including the aforementioned frequency-modulated muffler for suppressing pulse noise, and an exhaust purifier assembly 30. The exhaust purifier assembly 30 includes a particulate filter 31 and a three-way catalytic converter 32, which are connected via an exhaust pipe 33. The exhaust pipe 33 is covered with a shaped heat shield 34, which can fit tightly against the surface of the three-way catalytic converter 32 to avoid heat damage. The pleated structure of the shaped heat shield 34 can also improve its structural strength. The three-way catalytic converter 32 is connected to the front exhaust intake pipe 11a.

[0232] For details, please refer to Figure 1 , Figure 10 and Figure 11 In the illustrated embodiment, the purifier assembly 30 includes a particulate filter 31 and a three-way catalytic converter 32, which are connected by a purifier pipe 33. The purifier pipe 33 is covered with a shaped heat insulation cover 34, and the pleated structure (2mm thick) of the shaped heat insulation cover 34 has a gap of <1mm between it and the surface of the three-way catalytic converter 32, forming a tight heat insulation layer.

[0233] High-temperature exhaust gas (600℃) is filtered by particulate filter 31 and then enters three-way catalytic converter 32 to undergo a catalytic reaction. It then passes through pre- and post-catalytic converters for multi-stage noise reduction. The irregularly shaped heat shield 34 compensates for thermal expansion through its pleated elastic structure while reflecting over 90% of radiant heat. This reduces the temperature of the surrounding components of the three-way catalytic converter 32, thereby slowing down the aging rate of the materials.

[0234] This application utilizes the concentric tube resonant cavity, double-diaphragm vibration control, and multi-layer sound-absorbing structure of the front muffler, combined with the multi-stage resonant cavity design of the rear muffler, to form a complete noise reduction system of "low-frequency resonance silencing - mid-frequency interference silencing - high-frequency sound absorption". Simultaneously, the thermal structure design of the heat shield and diaphragms solves the reliability problem under high-temperature environments, achieving a synergistic improvement in NVH performance and durability.

[0235] The exhaust treatment system provided in this application integrates noise control and exhaust gas purification by combining a frequency-modulated pulse noise suppression muffler and purifier assembly 30. It can dynamically adjust the resonance frequency with the muffler's variable frequency vent pipe 40 to accurately suppress exhaust pulse noise under different operating conditions. It can also filter particulate matter through the particulate trap 31 in the purifier assembly and convert harmful gases through the three-way catalytic converter 32 to meet environmental protection and sound quality requirements. At the same time, the three-way catalytic converter 32 is directly connected to the front exhaust intake pipe 11a, which can reduce the risk of pipeline connection and exhaust gas leakage. The overall structure is tightly connected and highly adaptable, without occupying too much extra space, which is convenient for assembly and maintenance, and takes into account functionality, safety and practicality.

[0236] Continue to refer to Figure 10 and Figure 11 In the illustrated embodiment, the irregularly shaped heat shield 34 adopts a three-dimensional curved surface structure with the same curvature as the outer surface of the three-way catalytic converter 32, and forms an uneven bonding surface (tolerance ±0.5mm) through a stamping process. For example, for the elliptical cylindrical segment of the TWC (major axis 200mm, minor axis 150mm), the inner side of the irregularly shaped heat shield 34 is designed as a corresponding elliptical cylindrical surface to ensure that the gap with the TWC surface is <1mm, forming a tight wrap.

[0237] In addition, the heat shield features Ω-shaped or wavy pleats at its edges, with a pleat height of 5-8 mm and a thickness of 2-3 mm, formed through a roll forming process. The pleats are evenly spaced (e.g., 20-30 mm), forming a continuous mechanical support structure. The pleats also possess elastic deformation capability (allowing radial expansion of 1-1.5 mm), absorbing the thermal expansion difference between the TWC and the piping, and avoiding assembly stress caused by rigid constraints. The pleats also increase the moment of inertia of the heat shield section by 3-5 times, thereby improving its crush resistance.

[0238] The irregular heat shield 34 is made of multi-layer composite material, including: an inner layer made of 0.3mm thick aluminum foil with a ceramic coating (high temperature resistance up to 1200℃) and a reflectivity >95%; a middle layer made of 5mm thick glass fiber felt with a thermal conductivity <0.04W / m・K; and an outer layer made of 1mm thick stainless steel plate with an embossed surface to enhance radiative heat dissipation.

[0239] During operation, the inner layer of aluminum foil can block the high-temperature radiation from the TWC surface through mirror reflection, keeping the outer layer temperature of the heat insulation cover ≤200℃. The middle layer is a thermal insulation layer, which can reduce the heat flux conducted from the TWC to the purifier pipe 33, and prevent the density of the airflow in the pipe from decreasing due to overheating.

[0240] In summary, the irregular heat shield 34 achieves efficient heat reflection and conduction barrier through curved surface fitting design, and balances thermal expansion stress and mechanical strength by using pleated structure, thus achieving ultimate thermal protection for the three-way catalytic converter 32 in a compact space.

[0241] The above embodiments merely illustrate several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. A frequency-modulated silencer for suppressing impulse noise, characterized in that, Includes a rear muffler assembly (20), which includes a rear muffler housing (21). From top to bottom, the post-disappearance package (21) is provided with a first layer plate (22a), a second layer plate (22b) and a third layer plate (22c) in sequence, which divide the inner cavity of the post-disappearance package (21) into four chambers, namely the first chamber (A), the second chamber (B), the third chamber (C) and the fourth chamber (D). The air intake pipe (26) is connected to the first chamber (A); The first layer plate (22a) is provided with a leakage port (23), and a variable frequency vent pipe (40) is provided in the leakage port (23). The gas in the first chamber (A) can enter the second chamber (B) through the variable frequency vent pipe (40). The second chamber (B) and the fourth chamber (D) are connected by a return pipe (24), and the gas in the second chamber (B) can enter the fourth chamber (D) through the return pipe (24). The third layer plate (22c) is a perforated plate, and the gas in the fourth chamber (D) can enter the third chamber (C) through the third layer plate (22c). The variable frequency ventilation pipe (40) has a baffle (41) at its air inlet end. The baffle (41) is rotatably disposed inside the variable frequency ventilation pipe (40). When air is introduced, the gas can blow open the baffle (41). The rotation amplitude of the baffle (41) is affected by the gas flow rate. The greater the gas flow rate, the greater the opening of the air inlet end of the variable frequency ventilation pipe (40). The diameter of the variable frequency ventilation pipe (40) can be changed by the baffle (41), thereby using the mechanical structure to passively respond to the change of airflow to resist the frequency deviation caused by the change of flow rate, and restore the best noise reduction effect by actively tracking and locking the changed peak frequency of noise. The variable frequency ventilation pipe (40) includes a fixed pipe section (40a) and a movable pipe section (40b). The fixed pipe section (40a) is located inside the leak port (23), and the movable pipe section (40b) is slidably connected to the fixed pipe section (40a). The movable pipe section (40b) slides relative to the fixed pipe section (40a), thereby adjusting the length of the variable frequency ventilation pipe (40) and thus adjusting the resonance frequency. The muffler also includes a noise sensor for monitoring exhaust noise; The acoustic coupling system formed by the first chamber (A) and the second chamber (B) forms a resonance cavity. When the change in exhaust volume causes the noise frequency to shift, the acoustic characteristics can be corrected in real time by changing the diameter and length of the variable frequency ventilation pipe (40), so that the processing frequency of the resonance cavity is always aligned with the actual noise peak.

2. The frequency modulation suppressor for pulse noise according to claim 1, characterized in that, The variable frequency ventilation pipe (40) is a circular pipe, the baffle (41) is a circular plate, the diameter of the baffle (41) is smaller than the inner diameter of the variable frequency ventilation pipe (40), and there is a reserved gap between the baffle (41) and the variable frequency ventilation pipe (40) to allow low flow gas to pass through; And / or, in the initial state without airflow propulsion, the baffle (41) is set at an angle to the axis of the variable frequency vent pipe (40), so that the air inlet end of the variable frequency vent pipe (40) has a minimum opening so that low flow gas can pass through.

3. The frequency modulation suppressor for pulse noise according to claim 1, characterized in that, Also includes: A rotating shaft (42) is rotatably disposed at the air inlet end of the variable frequency ventilation pipe (40), and a baffle (41) is disposed on the rotating shaft (42); An elastic reset element (43) is sleeved on the rotating shaft (42) and is used to provide a reset torque to the baffle (41) to tend to close the opening of the frequency converter vent pipe (40); The maximum opening limiter (44) is located on the inner wall of the variable frequency vent pipe (40) and is used to limit the maximum rotation angle of the baffle (41). The axis of the rotating shaft (42) is offset from the geometric center of the baffle (41). According to the lever principle, the airflow acts on the larger area, which can generate a larger torque, thereby improving the rotational sensitivity of the baffle (41).

4. The frequency modulation suppressor for pulse noise according to claim 1, characterized in that, The inner wall of the end of the fixed pipe section (40a) is provided with a stepped annular mounting groove, which is used to fill the graphite braided filler (1). The graphite braided filler (1) is a rope-like structure woven from flexible graphite filaments; The annular mounting groove has internal threads on its groove wall; The silencer also includes a gland (45), which can be connected to the fixed pipe section (40a) by means of internal and external thread connection, and the gland (45) can axially press the graphite braided packing (1) in the annular mounting groove. During installation, the rope-shaped graphite braided filler (1) is wound around the movable pipe section (40b), so that the movable pipe section (40b) passes through the fixed pipe section (40a). The graphite braided filler (1) is pressed into the annular mounting groove. The pressure cap (45) is screwed into the annular mounting groove. The graphite braided filler (1) is compressed and radially expanded, thereby tightly hugging the movable pipe section (40b) and forming an effective seal.

5. The frequency modulation suppressor for pulse noise according to claim 4, characterized in that, The roughness of the outer wall surface of the active pipe section (40b) is not greater than 0.2 μm; And / or, the outer wall surface of the active pipe section (40b) is coated with a hard wear-resistant coating; And / or, the pressure plate and disc spring are provided inside the pressure cap (45). The pressure plate is used to press against the graphite braided packing (1). The disc spring is pressed between the pressure plate and the pressure cap (45). After the graphite braided packing (1) is worn, its volume shrinks and the disc spring extends, which can push the pressure plate to compensate for the gap caused by wear, so as to maintain the compressive force on the graphite braided packing (1).

6. The frequency modulation suppressor for pulse noise according to claim 1, characterized in that, The fixed pipe section (40a) is a sandwich structure, and a piston push rod (46) is provided in the sandwich. The piston push rod (46) divides the sandwich into a rod chamber and a rodless chamber. The rod chamber and the rodless chamber are respectively connected to a hydraulic oil circulation supply device. The piston rod (46) is connected to the movable tube section (40b); When hydraulic oil is input into the rodless chamber, the piston push rod (46) can push the movable pipe section (40b) outward, thereby increasing the length of the variable frequency vent pipe (40); When hydraulic oil is input into the rod chamber, the piston push rod (46) can pull back the movable pipe section (40b), thereby reducing the length of the variable frequency vent pipe (40).

7. The frequency modulation suppressor for pulse noise according to claim 6, characterized in that, The interlayer is also provided with a return spring (47), the elastic force of which can drive the piston rod (46) to move the movable tube section (40b) in the direction of increasing tube length; And / or, the hydraulic oil is a high-temperature resistant synthetic hydraulic oil, which is a phosphate ester liquid, a phthalate ester liquid, or a polyalphaolefin synthetic oil; And / or, an oil cooler is provided on the return or supply path of the hydraulic oil circulation supply equipment, the oil cooler being used to cool the hydraulic oil during the circulation process; And / or, the static and dynamic seals in the hydraulic oil circuit between the hydraulic oil circulation supply equipment and the jacket are made of fluororubber, perfluororubber, or polytetrafluoroethylene.

8. The muffler for suppressing pulse noise by frequency modulation according to claim 1, characterized in that the exhaust pipe... include: The vertical section (25a) penetrates the first layer plate (22a), the second layer plate (22b) and the third layer plate (22c). The front end of the vertical section (25a) extends out of the rear exhaust body (21) for exhaust, and the end extends into the fourth chamber (D). The bent section (25b) is located in the fourth chamber (D), with one end connected to the vertical section (25a) and the other end extending toward the third layer plate (22c); The gas collection section (25c) connects to the other end of the bending section (25b) and extends into the third chamber (C), through which the gas in the third chamber (C) can enter the gas outlet pipe; And / or, the intake pipe (26) is configured in a bent shape, and part of the intake pipe (26) is located in the second chamber (B). The intake pipe (26) located in the second chamber (B) has an exhaust hole on its pipe wall, and part of the gas can enter the second chamber (B) through the exhaust hole on the intake pipe (26). And / or, the return pipe (24) passes through the third chamber (C), and the return pipe (24) located in the third chamber (C) is provided with an exhaust hole on its wall, so that some gas can enter the third chamber (C) through the exhaust hole on the return pipe (24); And / or, a high-frequency tube (27) is provided on the vertical section (25a), with part of the high-frequency tube (27) located in the first chamber (A) and another part of the high-frequency tube (27) located in the second chamber (B), and the high-frequency tube (27) has the function of absorbing high-frequency noise.

9. The frequency modulation impulse noise suppressor according to any one of claims 1-8, characterized in that, It also includes a front muffler assembly (10), which includes a front muffler housing (11), and the front muffler housing (11) is provided with a front muffler inlet pipe (11a) and a front muffler outlet pipe (11b) coaxially sleeved inside the front muffler housing (11). The rear exhaust body (21) is connected to the front exhaust outlet pipe (11b) through the air inlet pipe (26). The diameter of the front exhaust inlet pipe (11a) is smaller than the diameter of the front exhaust outlet pipe (11b), and the outlet end of the front exhaust inlet pipe (11a) extends into the front exhaust outlet pipe (11b), with an annular gap between them. A concentric tube acoustic resonance cavity is formed within the pre-elimination body (11); High-speed airflow carrying order noise enters the pre-dissipation inlet pipe (11a). When the airflow is injected from the outlet of the pre-dissipation inlet pipe (11a) into the pre-dissipation outlet pipe (11b), a local vortex is generated due to the sudden expansion of the pipe diameter. The sound wave undergoes impedance mismatch at the annular gap. Some of the sound wave is refracted into the pre-dissipation outlet pipe (11b) and continues to propagate. However, the target order noise sound wave, due to wavelength matching, can be radiated in reverse through the annular gap into the pre-dissipation envelope (11) and is eventually dissipated. The front exhaust package (11) is further provided with an axially distributed first partition (12) and second partition (13), the front exhaust inlet pipe (11a) passes through the first partition (12), and the front exhaust outlet pipe (11b) passes through the second partition (13); The first partition (12) and the second partition (13) work together to suppress airflow vibration; The inner wall of the front-end packaging (11) is covered with a high-temperature resistant sound-absorbing layer, which, from the inside out, includes: Ceramic heat insulation coating, 1.5-2mm thick; Fiberglass wool layer, density ≥80kg / m 3 Thickness ≥ 30mm; Aluminum foil reflective layer, thickness 0.1-0.3mm.

10. An exhaust treatment system, characterized in that, The muffler for suppressing pulse noise according to claim 9 further includes: The purifier assembly (30) includes a particulate trap (31) and a three-way catalytic converter (32), which are connected by a purifier pipeline (33). The purifier pipe (33) is covered with a special-shaped heat insulation cover (34). The special-shaped heat insulation cover (34) can fit tightly with the surface of the three-way catalytic converter (32), thereby avoiding heat damage. The pleated structure of the special-shaped heat insulation cover (34) can also improve its own structural strength. The three-way catalytic converter (32) is connected to the front intake pipe (11a).

Images