An adaptive silencer and its control method for a variable frequency oil-free screw air compressor

Abstract

This application provides an adaptive muffler and its control method for a variable frequency oil-free screw air compressor. The muffler includes a muffler body with an air inlet at one end and an exhaust port on the side wall. A linear drive mechanism is installed at the other end of the muffler body. A piston plate is installed inside the cavity of the muffler body, and the piston plate is rigidly connected to the output shaft of the linear drive mechanism. The linear drive mechanism is connected to a controller. When the controller detects a change in the operating frequency of the air compressor, it calculates the target position of the piston plate under the current operating condition based on the real-time collected air compressor operating frequency and exhaust temperature, combined with the transmission loss calculation formula. The controller then drives the piston plate to move to the target position through the linear drive mechanism, thereby automatically adjusting the muffler's silencing frequency band and achieving adaptive tracking and noise reduction of the air compressor's fundamental frequency. This adapts to the full operating conditions of the variable frequency air compressor.

Description

Technical Field

[0001] This invention relates to the field of air compressor technology, specifically to an adaptive silencer for a variable frequency oil-free screw air compressor, which is particularly suitable for noise reduction scenarios at the exhaust port of the final stage compressor of a variable frequency oil-free screw air compressor. It can adaptively adjust the silencer frequency range according to the operating speed of the air compressor. Background Technology

[0002] During operation, dry oil-free screw air compressors generate strong aerodynamic noise as the rotor teeth pass through the inlet and outlet ports, with the noise problem being particularly prominent at the exhaust port of the final stage compressor. After multiple stages of compression, the air pressure increases significantly, resulting in a substantial increase in airflow velocity and pressure difference at the exhaust port, directly causing the aerodynamic noise amplitude at this location to be much higher than at other ports. Therefore, the exhaust port of the final stage compressor in a dry oil-free screw air compressor must be equipped with a dedicated silencer.

[0003] The fundamental frequency of the exhaust noise of the final stage compressor of a dry oil-free screw compressor is the rotor tooth meshing frequency, specifically the product of the rotational speed of the male rotor per second and the number of teeth on the male rotor. Because there is no lubricating oil in the pressure chamber for noise reduction, aerodynamic noise becomes the dominant noise type. Currently, the commonly used silencing solutions in the industry are mostly a combination of resistive and reactive silencers. This type of solution has significant technical drawbacks: On the one hand, resistive silencers rely on their internal absorbing materials to reduce pressure pulsations through multiple reflections, but this structure causes a significant pressure drop in the pipeline, directly affecting the operating efficiency of the air compressor. On the other hand, the structure and dimensions of reactive silencers such as micro-perforated plate type and expansion type are fixed designs, covering a narrow silencing frequency range that cannot be adjusted.

[0004] In practical applications, the commonly used speed regulation range of variable frequency oil-free screw air compressors is 40%-100% of the rated speed. Its noise fundamental frequency will change synchronously with the change of operating speed. However, the above-mentioned traditional noise reduction solutions cannot adjust the noise reduction frequency range according to the change of air compressor speed. The noise reduction effect is greatly reduced under non-rated speed conditions, resulting in poor overall actual use effect. Summary of the Invention

[0005] In view of this, embodiments of the present invention provide an adaptive silencer for a variable frequency oil-free screw air compressor. This silencer adopts a resistive expansion chamber structure design, with no significant pressure drop, minimizing the impact on the operating efficiency of the air compressor. At the same time, it can automatically adjust the silencing frequency band according to the real-time operating speed of the air compressor, realizing adaptive tracking and noise reduction of the fundamental frequency of noise. It can effectively adapt to the actual operating conditions of the air compressor and solve the technical problems of traditional silencers having a fixed silencing frequency band and poor noise reduction effect at non-rated speeds.

[0006] This invention provides an adaptive muffler for a variable frequency oil-free screw air compressor, comprising a muffler body, an air inlet at one end of the muffler body, and an exhaust port on the side wall of the muffler body; a piston plate is provided inside the cavity of the muffler body, the piston plate is sealed to the inner side wall of the muffler body and can move along the length of the muffler body; a linear drive mechanism is installed at the other end of the muffler body, the output shaft of the linear drive mechanism is rigidly connected to the piston plate, and is used to drive the piston plate to perform linear reciprocating motion within the cavity of the muffler body; The linear drive mechanism is connected to a controller, which is configured to calculate the target position of the piston plate under the current operating conditions in real time based on the real-time collected air compressor operating frequency and exhaust temperature, combined with the transmission loss calculation formula, and control the linear drive mechanism to drive the piston plate to move to the target position.

[0007] Preferably, the distance from the centerline of the exhaust port to the piston plate is L2. The target position of the piston plate under the current operating condition is calculated in real time using the transmission loss calculation formula, including: The optimal target value of L2 under the current operating condition is calculated in real time by combining the transmission loss calculation formula, so that the transmission loss under the optimal target value reaches the maximum value.

[0008] Preferably, the cross-sectional area of ​​the air inlet is S1, the cavity cross-sectional area of ​​the muffler cylinder is S2, and the cross-sectional area of ​​the exhaust port is S3, where S1=S3=S, S2=εS, and ε is a constant greater than 1.

[0009] Preferably, the distance from the centerline of the exhaust port to the air inlet end face of the muffler cylinder is L1, and the wave number at a single frequency is k, where kL1=π / 2.

[0010] Preferably, when the piston plate is in the initial position, L2 = L1.

[0011] Preferably, the distance from the centerline of the exhaust port to the air inlet end face of the muffler cylinder is L1, and the wave number of the final stage main unit of the air compressor under rated speed is k1, where k1L1=π / 2.

[0012] Preferably, a top cover is fastened to the other end of the muffler cylinder, and the linear drive mechanism is fastened to the top cover.

[0013] Preferably, the top cover is provided with vent holes.

[0014] Accordingly, embodiments of the present invention also provide a control method for the adaptive muffler of the above-mentioned variable frequency oilless screw air compressor, including: When the air compressor is powered on, the linear drive mechanism performs an initialization and reset operation according to the controller's instructions, driving the piston plate to move to the preset initial position. After initialization is completed, the air compressor enters the standby state. When the air compressor receives the operation command and enters the loading operation mode, the controller calculates the target position of the piston plate under the current working condition in real time based on the real-time collected air compressor operating frequency and exhaust temperature, combined with the transmission loss calculation formula, and controls the linear drive mechanism to drive the piston plate to move to the target position.

[0015] The control method for the adaptive silencer of the aforementioned variable frequency oil-free screw air compressor also includes: When the controller detects the stop signal of the air compressor, it sends a reset command to the linear drive mechanism, which then drives the piston plate back to its initial position. After the reset is completed, the muffler stops along with the air compressor, waiting for the next operating command.

[0016] The embodiments of the present invention have the following beneficial effects: A piston plate is set in the cavity of the muffler cylinder and rigidly connected to the output shaft of the linear drive mechanism. When the controller detects a change in the operating frequency of the air compressor, it calculates the target position of the piston plate under the current operating condition in real time based on the real-time collected air compressor operating frequency and exhaust temperature, combined with the transmission loss calculation formula. The piston plate is then driven to move to the target position through the linear drive mechanism, thereby automatically adjusting the silencing frequency band of the muffler and realizing adaptive tracking and noise reduction of the air compressor's fundamental frequency. This can adapt to the full operating condition requirements of the air compressor's variable frequency operation. Attached Figure Description

[0017] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0018] Figure 1 This is a cross-sectional view of an embodiment of the present invention; Figure 2 This is a graph showing the variation of the noise reduction frequency band with L2 under the preferred parameters in this embodiment of the invention. Figure 3 This is a three-dimensional structural diagram of an embodiment of the present invention; Figure 4 This is a control flowchart of an embodiment of the present invention; The numbers in the diagram represent: 1. Muffler body; 11. Air inlet; 12. Exhaust outlet; 2. Piston plate; 3. Linear drive mechanism; 4. Top cover. Detailed Implementation

[0019] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] Please see Figure 1 As shown, an embodiment of the present invention provides an adaptive muffler for a variable frequency oil-free screw air compressor, including a muffler body 1. One end of the muffler body 1 has an air inlet 11, and the side wall of the muffler body 1 has an exhaust port 12. A piston plate 2 is disposed within the cavity of the muffler body 1. The piston plate 2 is sealed to the inner side wall of the muffler body 1 and can move along the length of the muffler body 1. A linear drive mechanism 3 is installed at the other end of the muffler body 1. The output shaft of the linear drive mechanism 3 is rigidly connected to the piston plate 2, and is used to drive the piston plate 2 to perform linear reciprocating motion within the cavity of the muffler body 1.

[0021] First, combined Figure 1 The core noise reduction principle of the embodiments of the present invention is introduced and the relevant formulas are derived.

[0022] The sound attenuation transmission loss calculation formula used in this embodiment of the invention is derived from the classical acoustic theory of single expansion chamber silencers and is a well-known sound attenuation performance calculation method for those skilled in the art. Its sound attenuation effect is expressed as the transmission loss L. TL (dB) characterization, L TL A higher dB value indicates a better noise reduction effect of the muffler. The core form of the formula for calculating transmission loss is as follows:

[0023] In the above formula, S1 is the cross-sectional area of ​​the muffler inlet 11, S2 is the cavity cross-sectional area of ​​the muffler cylinder 1, S3 is the cross-sectional area of ​​the muffler exhaust port 12, L1 is the distance from the centerline of the exhaust port 12 to the inlet end face of the muffler cylinder 1, and L2 is the distance from the centerline of the exhaust port 12 to the piston plate 2. k is the wave number at a single frequency. Since the gas at the outlet of the final stage of the air compressor is dry air, its pressure and temperature characteristics perfectly match the ideal gas law. Therefore, the wave number k can be calculated using the following formula:

[0024] Where f is the frequency, γ is the adiabatic index, R is the gas constant, and T is the fluid temperature.

[0025] To simplify calculations and better adapt to actual industrial applications, this embodiment of the invention preferably uses a design where the air inlet 11 and the exhaust outlet 12 have equal cross-sections, i.e., S1=S3=S. Simultaneously, the cross-sectional area of ​​the muffler cylinder 1 is set to S2=εS, where ε is the expansion ratio of the muffler, a constant greater than 1. Based on this preferred design, the above formula for calculating transmission loss can be simplified to:

[0026] To further simplify the formula and facilitate its application in engineering, this embodiment of the invention preferably uses the design condition kL1=π / 2. Under this preferred condition, the transmission loss calculation formula can be further simplified into a form that is easy to apply in engineering:

[0027] Under this preferred design condition, when L2=L1, the transmission loss L of the muffler is TL When the noise level reaches its maximum value (dB), the noise reduction effect is optimal, and L2 can be used as the initial position of piston plate 2.

[0028] The silencer parameter design in this embodiment of the invention is based on the rated speed operating condition of the final stage air compressor. Assuming the scavenging frequency at the rated speed of this stage air compressor is f1 and the long-term operating temperature is T1, the corresponding wavenumber k1 can be calculated. The silencer's structural parameters are designed and assigned values ​​based on the wavenumber k1 under this rated operating condition, ensuring that the silencer's transmission loss L under the rated air compressor condition is minimized. TL (dB) reaches its maximum, at which point the L1 design value of the muffler satisfies... .

[0029] Will Substituting the original transmission loss calculation formula into the original formula, we can obtain a transmission loss formula suitable for different operating conditions of the air compressor at different speeds:

[0030] To more intuitively illustrate the noise reduction characteristics of the muffler, this embodiment of the invention selects typical operating parameters from the industry as examples, preferably k1=10 and ε=3. Substituting these parameters into the above formula simplifies to:

[0031] For the wave number k corresponding to different speeds of the air compressor, L can be established. TL The (L2) equation states that, given a fixed target wavenumber k, an optimal L2 target value can always be found that minimizes the transmission loss L at that wavenumber. TL To reach the maximum value and achieve the optimal noise reduction effect under this working condition. Figure 2The paper clearly describes the overall downward shift of the silencing frequency range as L2 increases under the aforementioned optimized parameters. That is, under the premise of the above design, with L1 remaining constant, increasing L2 shifts the silencing frequency range of the muffler towards lower frequencies, while decreasing L2 shifts it towards higher frequencies. By adjusting the value of L2, the silencing frequency range of the muffler can be precisely matched to the scavenging frequency of the air compressor at different speeds, achieving targeted noise reduction.

[0032] Based on the above acoustic theory, and combined with the actual operating conditions of the product, the structure and working process of the silencer in the embodiment of the present invention will be described in detail.

[0033] This silencer is specifically installed on the outlet side of the final stage of the variable frequency oil-free screw air compressor, such as... Figure 3 As shown, compressed air enters the muffler cavity through the muffler inlet 11, and after being silenced, it is discharged through the muffler exhaust port 12. A top cover 4 is securely mounted on the end of the muffler cylinder 1 furthest from the inlet 11. A linear drive mechanism 3 is securely mounted on the top cover 4, and its output shaft is rigidly connected to the piston plate 2. Radial dynamic seal O-rings are installed on the side surface of the piston plate 2 to ensure the sealing performance between the piston plate 2 and the inner wall of the muffler cylinder 1, preventing compressed air leakage. The linear drive mechanism 3 requires a fast-response, precise-positioning design and is equipped with a braking device to resist displacement caused by gas pressure differential. The top cover 4 is securely mounted on the muffler cylinder 1, forming a closed cavity. The top cover 4 has a certain number of vent holes so that the pressure inside the cavity is not affected by the linear reciprocating motion of the piston plate 2. The linear drive mechanism 3 is connected to the controller, which can directly control the piston plate 2 to perform linear reciprocating motion in the cavity of the muffler cylinder 1, and can effectively stop at any position within the stroke range of the piston plate 2. By changing the position of the piston plate 2, the L2 value can be precisely adjusted.

[0034] The adaptive adjustment process of the muffler in this embodiment of the invention follows Figure 4 As shown in the control flow diagram, when the air compressor is powered on, the linear drive mechanism 3 of the muffler will perform an initialization and reset operation according to the controller's instructions, driving the piston plate 2 to move to the preset initial position, so that L2 reaches the initial set value. After initialization is completed, the air compressor enters the standby state. When the air compressor receives the operation command and starts up, it will enter the loading operation mode. Its pipeline pressure will directly affect the operating frequency of the air compressor. When the controller detects a change in the operating frequency of the air compressor, it will calculate the optimal target value of L2 (i.e., the target position of the piston plate 2) under the current operating conditions in real time based on the real-time collected air compressor operating frequency and exhaust temperature, combined with the above-mentioned transmission loss calculation formula. Then, under the controller's instructions, the linear drive mechanism 3 drives the piston plate 2 to move linearly, adjusting L2 to the calculated optimal target value.

[0035] Through the aforementioned real-time adjustment process, the silencer's silencing frequency band can be synchronously moved to follow the fundamental noise frequency of the air compressor, achieving an adaptive silencing effect for the air compressor's operating noise. When the controller detects the air compressor's shutdown signal, it sends a reset command to the linear drive mechanism 3. The linear drive mechanism 3 drives the piston plate 2 back to its initial position. After the reset is completed, the silencer stops along with the air compressor, awaiting the next operating command. The entire adjustment process requires no manual intervention, achieving fully automated adaptive tracking noise reduction, adapting to the full operating conditions of the air compressor's variable frequency operation.

[0036] The silencer of this invention focuses on the core operating conditions of the variable frequency oil-free screw air compressor at 70%-100% of its rated speed. In this speed range, the air compressor has a large exhaust flow rate and high velocity, which is the operating condition range where aerodynamic noise is most prominent. The silencer can maintain a high-efficiency noise reduction effect in this range. For the low-load operating conditions of 40%-70% of the rated speed, the aerodynamic noise sound pressure level will naturally and significantly decrease due to the reduced exhaust flow rate and velocity of the air compressor. Even if the noise reduction of the silencer is slightly reduced in this range, it can still meet the basic noise reduction requirements, taking into account both the core noise reduction requirements and the adaptability of the operating conditions in practical engineering applications.

[0037] This article uses specific examples to illustrate the principles and implementation methods of the present invention. The descriptions of the above embodiments are only for the purpose of helping to understand the technical solutions and core ideas of the present invention. Those skilled in the art should understand that they can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. These modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. An adaptive muffler for a variable frequency oil-free screw air compressor, characterized by: The device includes a muffler body, with an air inlet at one end and an exhaust outlet on the side wall of the muffler body. A piston plate is installed inside the cavity of the muffler body, the piston plate being sealed to the inner wall of the muffler body and capable of moving along the length of the muffler body. A linear drive mechanism is installed at the other end of the muffler body, the output shaft of which is rigidly connected to the piston plate, driving the piston plate to perform linear reciprocating motion within the cavity of the muffler body. The linear drive mechanism is connected to a controller, which is configured to calculate the target position of the piston plate under the current operating conditions in real time based on the real-time collected air compressor operating frequency and exhaust temperature, combined with the transmission loss calculation formula, and control the linear drive mechanism to drive the piston plate to move to the target position.

2. The adaptive silencer for a variable frequency oil-free screw air compressor according to claim 1, characterized in that: The distance from the centerline of the exhaust port to the piston plate is L2. Using the transmission loss calculation formula, the target position of the piston plate under the current operating condition is calculated in real time, including: The optimal target value of L2 under the current operating condition is calculated in real time by combining the transmission loss calculation formula, so that the transmission loss under the optimal target value reaches the maximum value.

3. The adaptive silencer for a variable frequency oil-free screw air compressor according to claim 2, characterized in that: The cross-sectional area of ​​the air inlet is S1, the cross-sectional area of ​​the muffler cylinder is S2, and the cross-sectional area of ​​the exhaust port is S3, where S1=S3=S, S2=εS, and ε is a constant greater than 1.

4. The adaptive silencer for a variable frequency oil-free screw air compressor according to claim 3, characterized in that: The distance from the centerline of the exhaust port to the air inlet end face of the muffler cylinder is L1, and the wave number at a single frequency is k, kL1=π / 2.

5. The adaptive silencer for a variable frequency oil-free screw air compressor according to claim 4, characterized in that: When the piston plate is in the initial position, L2 = L1.

6. The adaptive silencer for a variable frequency oil-free screw air compressor according to claim 3, characterized in that: The distance from the centerline of the exhaust port to the air inlet end face of the muffler cylinder is L1, and the wave number of the final stage main unit of the air compressor under rated speed is k1, where k1L1=π / 2.

7. The adaptive silencer for a variable frequency oil-free screw air compressor according to claim 1, characterized in that: A top cover is fastened to the other end of the muffler cylinder, and the linear drive mechanism is fastened to the top cover.

8. The adaptive silencer for a variable frequency oil-free screw air compressor according to claim 7, characterized in that: The top cover is provided with vent holes.

9. A control method for an adaptive silencer of a variable frequency oil-free screw air compressor according to any one of claims 1-8, characterized in that, include: When the air compressor is powered on, the linear drive mechanism performs an initialization and reset operation according to the controller's instructions, driving the piston plate to move to the preset initial position. After initialization is completed, the air compressor enters the standby state. When the air compressor receives the operation command and enters the loading operation mode, the controller calculates the target position of the piston plate under the current working condition in real time based on the real-time collected air compressor operating frequency and exhaust temperature, combined with the transmission loss calculation formula, and controls the linear drive mechanism to drive the piston plate to move to the target position.

10. The control method for an adaptive silencer of a variable frequency oil-free screw air compressor according to claim 9, characterized in that, Also includes: When the controller detects the stop signal of the air compressor, it sends a reset command to the linear drive mechanism, which then drives the piston plate back to its initial position. After the reset is completed, the muffler stops along with the air compressor, waiting for the next operating command.

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