Air compressor pneumatic noise testing method and system

Abstract

The application discloses an air compressor pneumatic noise testing method and system. The method comprises the following steps: obtaining sound pressures of multiple position points at an inlet or an outlet of an air compressor, wherein the sound pressure at each position point is formed by superposition of an incident wave and a reflected wave; and calculating a sound pressure level of the incident wave according to the obtained sound pressures of the multiple position points. The air compressor pneumatic noise testing method and system can realize pneumatic noise testing of the air compressor in a daily environment, improve testing efficiency, and reduce testing cost.

Description

Technical Field

[0001] This invention relates to the field of air compressor technology, and in particular to a method and system for testing aerodynamic noise of air compressors. Background Technology

[0002] A hydrogen fuel cell is a device that generates electricity by chemically reacting hydrogen with oxygen from air supplied by an air compressor. It boasts high conversion efficiency, and the only byproduct of the reaction is water, resulting in no pollutant emissions. It is a clean and environmentally friendly product and can be used in hydrogen fuel cell vehicles to supply electricity. With rising living standards, consumers have increasingly higher demands for vehicle comfort, and noise, as an important indicator of vehicle comfort, has become a crucial factor in vehicle selection. For hydrogen fuel cell systems, the air compressor is the primary noise source; therefore, testing and adjusting its aerodynamic noise to reduce noise during practical applications is of great significance.

[0003] Existing technologies typically require extremely low background noise for noise assessment, thus noise testing is usually only possible in a semi-anechoic chamber. However, most air compressor and hydrogen fuel cell manufacturers do not currently possess semi-anechoic chambers. Although some third-party testing centers are equipped with semi-anechoic chambers, a new test bench needs to be built specifically for the air compressor, increasing testing time and costs.

[0004] Therefore, it is necessary to propose a technical solution to overcome the shortcomings of existing technologies. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, this invention proposes a method and system for testing the aerodynamic noise of air compressors, which can realize the aerodynamic noise testing of air compressors in daily environments, improve testing efficiency, and reduce testing costs.

[0006] The present invention is achieved through the following technical solution: a method for testing the pneumatic noise of an air compressor, the method comprising the following steps: obtaining the sound pressure at multiple locations at the inlet or outlet of the air compressor, wherein the sound pressure at each location is formed by the superposition of incident wave and reflected wave; and calculating the sound pressure level of the incident wave based on the obtained sound pressure at the multiple locations.

[0007] As a further improvement to the present invention, the amplitude of the sound pressure at each location point is expressed by the following formula:

[0008]

[0009] Where, p + p is the amplitude of the incident wave. - denoted as the amplitude of the reflected wave, c as the speed of sound, m as the Mach number, f as the frequency, and x as the axial distance.

[0010] As a further improvement of the present invention, the plurality of position points includes at least three position points in the direction of air compressor drive airflow. The amplitude of the sound pressure at the three position points in the direction of airflow is expressed by the following formulas:

[0011]

[0012] p2 = p + +p - ;

[0013]

[0014] Where d1 is the distance between the first and second position points, and d2 is the distance between the second and third position points.

[0015] As a further improvement of the present invention, the sound pressure is obtained by Fourier transform of the time-domain signal P measured by the sound pressure sensor, that is: p = fft(P).

[0016] As a further improvement of the present invention, the incident wave time-domain effective value P + From the incident wave amplitude p + The result obtained by inverse Fourier transform is: P + =RMS(ifft(p + )).

[0017] As a further improvement of the present invention, the sound pressure level is calculated using the following formula:

[0018] Where P0 is the reference sound pressure, taken as 20 μPa.

[0019] As a further improvement of the present invention, the method further includes setting an intake silencer upstream of the air compressor inlet and an outlet silencer downstream of the air compressor outlet, wherein the plurality of locations are selected between the intake silencer and the air compressor inlet, or between the air compressor outlet and the outlet silencer.

[0020] As a further improvement of the present invention, the method includes changing one or more parameters of the air compressor's speed, pressure, and flow rate, and then repeating the above steps.

[0021] This invention is also achieved through the following technical solution: an air compressor pneumatic noise testing system, comprising an air compressor, an air inlet pipe for supplying air to the air compressor, and an air outlet pipe for discharging the compressed air from the air compressor, wherein the system includes:

[0022] The sound pressure detection device is configured to detect the sound pressure at multiple locations at the inlet and outlet of the air compressor, wherein the sound pressure at each location is formed by the superposition of incident and reflected waves; and

[0023] The sound pressure level calculation device is configured to calculate the sound pressure level of the incident wave at the inlet and outlet of the air compressor based on the sound pressure obtained at the plurality of location points.

[0024] As a further improvement of the present invention, the system includes an intake silencer located upstream of the air compressor inlet and an outlet silencer located downstream of the air compressor outlet. The plurality of location points are selected between the intake silencer and the air compressor inlet, and between the air compressor outlet and the outlet silencer.

[0025] As a further improvement of the present invention, the intake muffler and the exhaust muffler are reactive straight-through mufflers with a transmission loss of more than 20dB for sound waves of 500-4000Hz.

[0026] As a further improvement of the present invention, the sound pressure detection device includes a plurality of sound pressure sensors that are arranged one-to-one with the plurality of location points.

[0027] As a further improvement of the present invention, the diameter of the air intake pipe and the air outlet pipe is 40mm to 60mm.

[0028] As a further improvement of the present invention, the system further includes an air filter located upstream of the intake muffler, an intercooler located between the air compressor and the outlet muffler, and a throttle valve located between the intercooler and the outlet muffler.

[0029] The air compressor aerodynamic noise testing method and system provided by this invention obtains the sound pressure at multiple locations at the air compressor inlet or outlet. The sound pressure at each location is formed by the superposition of incident and reflected waves, and the sound pressure level of the incident wave is calculated based on the obtained sound pressure at the multiple locations. It can identify and eliminate the interference of reflected waves, enabling accurate testing of air compressor aerodynamic noise in everyday environments, improving testing efficiency and reducing testing costs. Attached Figure Description

[0030] Figure 1 This is a connection diagram of an embodiment of the air compressor pneumatic noise testing system of the present invention.

[0031] Figure 2 This is a schematic diagram of a silencer in one embodiment of the air compressor pneumatic noise testing system of the present invention.

[0032] Figure 3This is a diagram illustrating the noise reduction performance of a silencer in one embodiment of the air compressor pneumatic noise testing system of the present invention.

[0033] Figure 4 This is a schematic diagram of the location points where the sound pressure is measured in the air compressor aerodynamic noise testing method of the present invention.

[0034] Figure 5 This is an inlet noise diagram of an air compressor tested by the air compressor pneumatic noise testing system of the present invention.

[0035] Figure 6 This is an outlet noise diagram of an air compressor tested by the air compressor pneumatic noise testing system of the present invention.

[0036] The attached diagram is labeled as follows: 1-Air filter; 2-Flow sensor; 3-Intake muffler; 31-Intake port; 32-Outlet port; 4-Inlet sound pressure sensor; 5-Air compressor; 6-Outlet sound pressure sensor; 7-Intercooler; 8-Pressure sensor; 9-Temperature sensor; 10-Throttle valve; 11-Outlet muffler. Detailed Implementation

[0037] To provide a clearer understanding of the technical features, objectives, and effects of the present invention, specific embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0038] The technical solutions of the present invention will be clearly and completely described below with reference to the accompanying drawings of the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0039] Please see Figures 1 to 6 As shown, this invention provides a method and system for testing the aerodynamic noise of an air compressor. Please refer to the following sections first. Figure 1 As shown, the system involved in the test method of this invention is described. Figure 1As shown, in one embodiment, the air compressor pneumatic noise testing system includes an air filter 1, a flow sensor 2, an intake muffler 3, an inlet sound pressure sensor 4, an air compressor 5, an outlet sound pressure sensor 6, an intercooler 7, a pressure sensor 8, a temperature sensor 9, a throttle valve 10, and an outlet muffler 11. Atmospheric air is filtered by the air filter 1 and then enters the intake muffler 3 for noise reduction. After entering the air compressor 5, the air is compressed by the air compressor 5 and then discharged after passing through the intercooler 7, throttle valve 10, and outlet muffler 11 for further noise reduction. The air filter 1 is used to filter air to reduce the adverse effects of impurities in the air on the air compressor 5; the intake muffler 3 and the outlet muffler 11 can reduce noise interference from the external environment; the inlet sound pressure sensor 4 is used to detect the sound pressure at the inlet of the air compressor 5, and the outlet sound pressure sensor 6 is used to detect the sound pressure at the outlet of the air compressor 5; the throttle valve 10 is used to control the flow rate of the system by adjusting the opening size; the flow sensor 2, the pressure sensor 8, and the temperature sensor 9 are used to monitor the flow rate, pressure, and temperature parameters of the system to monitor the operating status of the system.

[0040] In one embodiment, the air compressor pneumatic noise testing method includes the following steps:

[0041] S1. Obtain the sound pressure at multiple locations at the inlet or outlet of the air compressor 5, wherein the sound pressure at each location is formed by the superposition of the incident wave and the reflected wave; and

[0042] S2. Calculate the sound pressure level of the incident wave based on the sound pressure at the multiple location points obtained.

[0043] The air compressor aerodynamic noise testing method provided by this invention can be performed outside of an anechoic chamber. Therefore, the obtained sound pressure is not simply the sound pressure of the incident wave, but is formed by the superposition of the incident wave and the reflected wave. This invention's testing method obtains the sound pressure at multiple locations and calculates the sound pressure of the incident wave and the reflected wave based on these locations, thereby eliminating interference from the reflected wave and obtaining the sound pressure of the incident wave, thus obtaining accurate aerodynamic noise parameters of the air compressor. Aerodynamic noise testing of an air compressor typically includes aerodynamic noise at the inlet and outlet of the air compressor 5. However, it should be noted that the application of this method at either the inlet or outlet of the air compressor 5 is within the scope of protection of this invention.

[0044] Please refer to the following: Figure 4 As shown, specifically, in one embodiment, the amplitude of the sound pressure at each location point is expressed by the following formula:

[0045]

[0046] Where, p + p is the amplitude of the incident wave. -Let be the amplitude of the reflected wave, c be the speed of sound, m be the Mach number, f be the frequency, x be the axial distance, and j be the imaginary part. In this embodiment, the axial distance represented by x is the distance along the direction of atmospheric flow.

[0047] In this embodiment, the plurality of location points includes at least three location points along the air compressor's airflow direction, and a sound pressure sensor is installed at each location point. For example... Figure 4 As shown, along the X-axis, the first dashed vertical line represents the first location point, i.e., the location of the first sound pressure sensor; the second dashed vertical line represents the second location point, i.e., the location of the second sound pressure sensor; and the third dashed vertical line represents the third location point, i.e., the location of the third sound pressure sensor. Substituting the X-value into the above formula, the amplitude of the sound pressure at the three location points along the airflow direction can be obtained as shown in the following formulas:

[0048]

[0049] p2 = p + +p - ;

[0050]

[0051] Where d1 is the distance between the first and second position points, and d2 is the distance between the second and third position points. Taking the second position point as the origin and the airflow direction as positive, d1 should be a negative value. Based on the obtained sound pressures p1, p2, and p3 at the three position points, and the determined d1, d2, c, and f, the incident wave amplitude p can be calculated. + and the amplitude of the reflected wave p - This allows us to eliminate the interference of reflected waves and obtain the sound pressure of the incident wave, thus obtaining accurate aerodynamic noise parameters of the air compressor.

[0052] Furthermore, the sound pressure is obtained by Fourier transforming the time-domain signal P measured by the sound pressure sensor, i.e., p = fft(P). The sound pressure sensor directly measures a time-domain signal, which is a signal matrix that reflects the waveform change of the sound wave over time. However, for complex waveforms, it is difficult to analyze the frequency and amplitude based on the time-domain signal alone; it is necessary to transform it into a frequency-domain signal for analysis. The transformation from the time domain to the frequency domain uses a Fourier transform. After the signal is transformed from the time domain to the frequency domain, its spectrum can be obtained. The spectrum can intuitively reflect the frequency f and amplitude p of the sound wave. The aforementioned Fourier transform can be performed by a sound wave analysis device connected to the sound pressure sensor.

[0053] The incident wave time-domain effective value P + From the incident wave amplitude p +The result obtained by inverse Fourier transform is: P + =RMS(ift(p + The incident wave's frequency domain signal is transformed into a time domain signal via inverse Fourier transform to obtain the effective value of the incident wave's time domain signal. This effective value is then substituted into the following sound pressure level calculation formula to calculate the sound pressure value. The sound pressure sensor's measurement of sound pressure, the Fourier transform from the time domain signal to the frequency domain signal, and the inverse Fourier transform from the frequency domain signal to the time domain signal are all well-known to those skilled in the art.

[0054] The sound pressure level is calculated using the following formula: Where P0 is the reference sound pressure, taken as 20 μPa.

[0055] In one embodiment, three location points are selected between the intake muffler 3 and the inlet of the air compressor 5, and three location points are selected between the outlet of the air compressor 5 and the outlet muffler 11. Please refer to [link / reference]. Figure 2 and Figure 3 As shown, in this embodiment, the intake muffler 3 and the exhaust muffler 11 are reactive straight-through mufflers with a transmission loss greater than 20dB for sound waves in the 500-4000Hz range. Figure 2 As shown, in one embodiment, the intake muffler 3 includes an inner tube and an outer tube. The inner tube has a silencing hole, and the inner tube and the outer tube are connected by several circular wing plates. One end of the inner tube is located outside the outer tube, forming an air inlet 31, and the other end of the inner tube is located inside the outer tube, forming an air outlet 32. The sound pressure sensor measures a one-dimensional plane wave inside the intake or exhaust pipe. Based on plane wave theory, the measurement cutoff frequency depends on the pipe diameter: f = 1.84c / 2πr. In one embodiment, the diameter of the inlet and outlet pipes is, for example, 50 mm, then the measurement cutoff frequency is 4000 Hz.

[0056] The above describes a test method using a defined airflow state as an example. Further, by changing one or more parameters of the air compressor 5, such as its speed, pressure, and flow rate, and repeating the steps of the above method, the aerodynamic noise of the air compressor 5 under different speeds, pressures, and flow rates can be obtained. Finally, inlet and outlet noise diagrams of the air compressor 5 can be plotted, as shown below. Figure 5 and Figure 6 As shown in the figure, by appropriately selecting the mass flow rate of the fuel cell system, the aerodynamic noise of the air compressor 5 can be reduced, thereby improving noise performance when applied to products such as vehicles.

[0057] Please refer to it again. Figure 1As shown, the present invention also provides an air compressor pneumatic noise testing system, including an air compressor 5, an air intake pipe for supplying air to the air compressor 5, and an air outlet pipe for discharging the compressed air from the air compressor 5. The system includes: a sound pressure detection device configured to detect the sound pressure at multiple locations at the air compressor inlet and outlet, wherein the sound pressure at each location is formed by the superposition of incident and reflected waves; and a sound pressure level calculation device configured to calculate the sound pressure level of the incident wave at the air compressor inlet and outlet based on the obtained sound pressure at the multiple locations. The sound pressure detection device includes multiple sound pressure sensors, each corresponding to one of the multiple locations, such as… Figure 1 The diagram shows three inlet sound pressure sensors 4 and three outlet sound pressure sensors 6. The sound pressure level calculation device is a device capable of calculating incident and reflected waves, specifically a processor such as an MCU.

[0058] In this embodiment, the system includes an intake muffler 3 located upstream of the inlet of the air compressor 5 and an outlet muffler 11 located downstream of the outlet of the air compressor 5. The plurality of locations are selected between the intake muffler 3 and the inlet of the air compressor 5, and between the outlet of the air compressor 5 and the outlet muffler 11. In one embodiment, the intake muffler 3 and the outlet muffler 11 are reactive straight-through mufflers with a transmission loss greater than 20dB for sound waves in the 500-4000Hz range. In this embodiment, the diameter of the intake and outlet pipes is 40mm to 60mm, specifically 45mm, 50mm, 55mm, etc. In this embodiment, the system also includes an air filter 1 located upstream of the intake muffler 3, an intercooler 7 located between the air compressor 5 and the outlet muffler 11, and a throttle valve 10 located between the intercooler 7 and the outlet muffler 11.

[0059] The air compressor aerodynamic noise testing system provided by this invention can be upgraded and modified on existing air compressor test benches by adding a silencer and sound pressure sensor, allowing for direct testing and avoiding the need for repeated bench construction. This system can assess the aerodynamic noise of an air compressor in everyday environments without requiring a third-party semi-anechoic chamber, effectively identifying incident and reflected sound waves and reducing development costs. By setting up the silencer and calculating based on sound pressure sensor measurement data, it can reduce other noise interference, such as structural noise and electromagnetic noise, enabling direct assessment of the air compressor's aerodynamic noise. The resulting air compressor noise map can be used for noise matching in hydrogen fuel cell systems, allowing for the identification of aerodynamic noise peaks before the fuel cell system is applied to vehicles and other products, facilitating timely adjustments.

[0060] When using the air compressor pneumatic noise testing system provided by this invention, the air compressor 5 is placed on the test bench, and the air filter 1, intake muffler 3, intake pipe, outlet pipe, intercooler 7, throttle valve 10, outlet muffler 11, inlet sound pressure sensor 4, and outlet sound pressure sensor 6 are connected. The air compressor is started, and parameters such as pressure and flow rate are adjusted to the state point. After the pressure and flow rate stabilize, the sound pressure measured by the sound pressure sensor is recorded. The sound pressure level at the inlet and outlet is calculated using the standing wave method. The noise map at the inlet and outlet is plotted based on the flow rate, pressure ratio, and noise.

[0061] As can be seen from the above description of specific embodiments, the air compressor pneumatic noise testing method and system provided by the present invention obtains the sound pressure at multiple locations at the inlet or outlet of the air compressor 5. The sound pressure at each location is formed by the superposition of incident and reflected waves, and the sound pressure level of the incident wave is calculated based on the obtained sound pressure at the multiple locations. It can identify and eliminate the interference of reflected waves, enabling accurate testing of air compressor pneumatic noise in everyday environments, improving testing efficiency and reducing testing costs.

[0062] This invention has been illustrated through several specific embodiments. Those skilled in the art will understand that various modifications and equivalent substitutions can be made to this invention without departing from its scope. Furthermore, various modifications can be made to this invention for specific situations or circumstances without departing from its scope. Therefore, this invention is not limited to the specific embodiments disclosed, but should include all embodiments falling within the scope of the claims.

Claims

1. A method for testing the aerodynamic noise of an air compressor, characterized in that, The method includes the following steps: The sound pressure at multiple locations at the inlet or outlet of an air compressor is obtained, wherein the sound pressure at each location is formed by the superposition of incident and reflected waves; and the sound pressure level of the incident wave is calculated based on the obtained sound pressure at the multiple locations. The air compressor is connected to an intake pipe that supplies air to the air compressor and an outlet pipe that discharges the compressed air from the air compressor. An intake silencer is installed upstream of the air compressor inlet, and an outlet silencer is installed downstream of the air compressor outlet. The plurality of locations are selected in the intake pipe between the intake silencer and the air compressor inlet or in the outlet pipe between the air compressor outlet and the outlet silencer.

2. The air compressor pneumatic noise testing method as described in claim 1, characterized in that, The amplitude of the sound pressure at each location point is expressed by the following formula: ; Where, p + p is the amplitude of the incident wave. - denoted as the amplitude of the reflected wave, c as the speed of sound, m as the Mach number, f as the frequency, and x as the axial distance.

3. The air compressor pneumatic noise testing method as described in claim 2, characterized in that, The plurality of location points includes at least three location points in the direction of airflow driven by the air compressor. The amplitude of the sound pressure at the three location points in the direction of airflow is expressed by the following formula: ;p2=p + +p - ; ; Where d1 is the distance between the first and second position points, and d2 is the distance between the second and third position points; Substituting the obtained p1, p2, p3, f, d1, and d2 into the above formula, we can solve for p. + .

4. The air compressor pneumatic noise testing method as described in claim 2, characterized in that, The sound pressure is obtained by Fourier transforming the time-domain signal P measured by the sound pressure sensor, i.e., p = fft(P), and the effective time-domain value P of the incident wave is... + From the incident wave amplitude p + The result obtained by inverse Fourier transform is: P + =RMS(ifft(p + )).

5. The air compressor pneumatic noise testing method as described in claim 4, characterized in that... The sound pressure level is calculated using the following formula: ; Where P0 is the reference sound pressure, taken as 20 μPa.

6. The air compressor pneumatic noise testing method as described in claim 1, characterized in that, The method involves changing one or more parameters of the air compressor, such as its speed, pressure, and flow rate, and then repeating the above steps.

7. An air compressor pneumatic noise testing system, comprising an air compressor, an air inlet pipe for supplying air to the air compressor, and an air outlet pipe for discharging compressed air from the air compressor, characterized in that, The system includes: The sound pressure detection device is configured to detect the sound pressure at multiple locations at the inlet and outlet of the air compressor, wherein the sound pressure at each location is formed by the superposition of incident and reflected waves; and A sound pressure level calculation device is configured to calculate the sound pressure level of the incident wave at the inlet and outlet of the air compressor based on the sound pressure at the obtained multiple location points; The system includes an intake silencer located upstream of the air compressor inlet and an outlet silencer located downstream of the air compressor outlet. The plurality of locations are selected in the intake pipeline between the intake silencer and the air compressor inlet or in the outlet pipeline between the air compressor outlet and the outlet silencer.

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