A prediction method for water flow noise in automobile heating core

Abstract

A method for predicting water flow sound of an automobile heater core. In the early stage of automobile development, a test bench is built to simulate the operation status of the whole vehicle to evaluate whether the automobile heater core has water flow sound. On the engine performance test bench, the cooling system and the air-conditioning heater core are connected to the engine according to the design coordinates to form a complete system; a water flow sound identification device is arranged in front of the heater core shell, the direction points to the heater core shell, and the rear end of the microphone is connected to the data acquisition device; the coolant is filled to the designed volume, and the air retained in the system is discharged to the atmosphere; after the coolant is filled, the engine is turned off and left to stand until the coolant temperature drops to the ambient temperature, so that the engine reaches a cold state; the water flow sound problem in normal working conditions and the water flow sound problem in the coolant post-boiling working condition are identified; the objective sound data collected above are processed to obtain the evaluation index of the cooling system and the air-conditioning heater core water flow sound, and the water flow sound performance in the whole vehicle is predicted based on the test bench results.

Description

Technical Field

[0001] The invention relates to a method for evaluating the water flow sound of the warm core of an automobile air-conditioning system and a cooling system. Background Art

[0002] With the continuous improvement of living standards, people have higher and higher requirements for the NVH (Noise, Vibration, Harshness) performance of automobiles. Automobile engines generate a lot of heat during operation, so the coolant needs to circulate to reduce the engine temperature. At the same time, the coolant temperature rises and can be used as a heat source to heat the passengers in the car. When the vehicle is running for a long time, the coolant temperature continues to rise, or when the vehicle stops suddenly after a long time of driving, the coolant cannot circulate and causes a sharp rise in temperature and boiling in the local area, which will produce a large number of bubbles; if the bubbles cannot be discharged into the atmosphere through the system in time after formation, when the vehicle is started again or accelerated suddenly, the bubbles flow at high speed with the coolant, impacting the wall of the air conditioning heater pipe, breaking and producing noise similar to water flow. Since the heater is located in the car close to the driver, the driver can clearly perceive and complain when the sound of water flow occurs. To address the above issues, currently the actual vehicle is manufactured after the prototype is developed, and then confirmed through actual vehicle driving evaluation to see if there is a problem. If there is water flowing sound, the actual vehicle needs to be tuned and the design needs to be changed for optimization, which not only increases the cost but also delays the development time of the prototype. Therefore, if the water flowing sound of the car warm core can be identified in advance in the early stage of automobile design and development to predict the subsequent water flowing sound performance of the actual vehicle, it can avoid problems after the prototype design is completed, avoid risks in advance and reduce development costs. Summary of the invention

[0003] In view of the shortcomings of the existing technology, the present invention proposes a method for predicting the water flow sound of the car heating core. By building a system bench in the early stage of automobile development and design, and connecting the entire cooling system and the air conditioning heating core system to the engine, the actual vehicle operation state is simulated, and through specific test conditions and methods, the water flow sound performance in the car during the process of car starting and rapid acceleration is identified in the early stage of automobile development, and the actual vehicle performance is predicted based on this result. If there is obvious water flow sound, the design needs to be changed for optimization to avoid problems after the prototype design is completed and avoid risks in advance.

[0004] To achieve the above object, the technical solution adopted by the present invention includes the following steps:

[0005] 1. Build the system bench

[0006] On the engine performance bench, the cooling system (expansion tank, intercooler) and air conditioning heater core are connected to the engine according to the design coordinates to form a complete system to ensure the normal operation of the engine. The air conditioning heater core is connected to an independent room outside through pipes.

[0007] 2. Connect the water flow sound recognition device

[0008] The water flow sound recognition device (sound collection sensor) is placed 10 cm in front of the heater shell, pointing towards the heater shell, and the rear end of the microphone is connected to the data collection device.

[0009] 3. Coolant filling

[0010] 3.1 Stand still and turn off the engine, and add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0011] 3.2 Start the engine and run it at idle speed for 5 minutes. As the engine runs, the air retained in the system will be discharged to the expansion tank along with the flow of coolant, and then enter the air; as the air is discharged, the coolant level will drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0012] 3.3 After the engine speed is accelerated to 2000rpm, it runs steadily for 15 minutes. At this time, the cooling system is turned on. As the air in the system is gradually discharged, the coolant level continues to drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0013] 3.4 After accelerating the engine speed to 3000rpm, run it stably for 5 minutes. The air inside the entire system is basically eliminated. At this time, observe the liquid level in the expansion water tank to confirm whether the liquid level is between the min line and the max line. If it is lower than the min line, continue to add coolant from the expansion water tank filling port until the coolant level stays between the min line and the max line of the expansion water tank;

[0014] 3.5 After completing the above four steps, the coolant is filled, turn off the engine and let it stand until the coolant temperature drops to the ambient temperature and the engine reaches a cold state.

[0015] The purpose of this process is to fill the coolant to the designed volume and expel the air retained in the system into the atmosphere, so as to avoid misjudgment caused by water flow sound caused by the air retained in the system during the bench construction process.

[0016] 4. Identification of water flow sound problems under normal working conditions

[0017] 4.1 The engine is in a cold, flameout and static state. Start the engine and wait until the engine stabilizes to the normal idle speed;

[0018] 4.2 Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, with an interval of 1 minute each time, and collect the sound data each time;

[0019] 5. Identification of water flow sound problems in the post-cooling boiling condition

[0020] 5.1 Accelerate the engine speed to 3000rpm and run it steadily. When the engine outlet water temperature reaches 110℃, continue to run for 10 seconds and then immediately stop the engine and turn off all the cooling fans on the test bench until the water temperature of the expansion tank reaches the ambient temperature.

[0021] 5.2 Start the engine at this time and wait until the engine stabilizes to normal idle speed;

[0022] 5.3 Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, with an interval of 1 minute each time, and collect the sound data each time;

[0023] 6. The objective sound data collected in steps 4 and 5 above are processed as follows:

[0024] 6.1 Perform Fourier time-frequency conversion on the collected sound data to convert it into frequency domain data (the window function is the Hanning window), and the frequency resolution is 1Hz;

[0025] 6.2 A large number of tests have shown that the frequency of subjective water flow sound is obviously in the range of 50-250Hz. Therefore, the data obtained in step 7.1 needs to be filtered through a Butterworth bandpass filter, retaining the data in the 50-250Hz frequency band, and calculating the effective mean of this frequency band to obtain the noise value of this frequency band;

[0026] 7. Subjective evaluation of water flow noise in the vehicle heating core;

[0027] Install the warm core that has collected the bench noise data on the vehicle and conduct a subjective evaluation of the corresponding working conditions;

[0028] 7.1 Coolant filling

[0029] 7.1.1 With the engine at rest and turned off, add coolant from the expansion tank filling port until the coolant level remains between the min and max lines of the expansion tank;

[0030] 7.1.2 Start the engine and run it at idle speed for 5 minutes. As the engine runs, the air retained in the system will be discharged to the expansion tank along with the flow of coolant, and then enter the air; as the air is discharged, the coolant level will drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0031] 7.1.3 After the engine speed is accelerated to 2000rpm, it is allowed to run steadily for 15 minutes. At this time, the cooling system is turned on. As the air in the system is gradually discharged, the coolant level continues to drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank.

[0032] 7.1.4 After accelerating the engine speed to 3000rpm, run it stably for 5 minutes. The air in the entire system is basically eliminated. At this time, observe the liquid level in the expansion water tank to confirm whether the liquid level is between the min line and the max line. If it is lower than the min line, continue to add coolant from the expansion water tank filling port until the coolant level stays between the min line and the max line of the expansion water tank;

[0033] 7.1.5 After completing the above four steps, the coolant is filled and the engine is turned off and left to stand until the coolant temperature drops to the ambient temperature and the engine reaches a cold state.

[0034] The purpose of this process is to fill the coolant to the designed volume and expel the air retained in the system into the atmosphere, so as to avoid misjudgment caused by water flowing sound caused by the air retained in the system during the replacement of the heater core.

[0035] 7.2 Identification of water flow sound problems under normal operating conditions

[0036] 7.2.1 The engine is cold and turned off. Start the engine and wait until the engine stabilizes to the normal idle speed.

[0037] 7.2.2 Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, and record the subjective score each time;

[0038] 7.3 Identification of water flow sound problems in the post-boiling condition of coolant

[0039] 7.3.1 Accelerate the engine speed to 3000rpm and run it steadily. When the engine outlet water temperature reaches 110℃, continue to run for 10 seconds and then immediately stop the engine and turn off all the cooling fans on the test bench until the water temperature of the expansion tank reaches the ambient temperature.

[0040] 7.3.2 Start the engine at this time and wait until the engine stabilizes to normal idle speed;

[0041] 7.3.3 Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, and record the subjective score each time;

[0042] 7.4 Select the lowest score from the subjective scores in the above steps as the subjective score of water flow sound of this system (cooling system, air conditioning heating core);

[0043] 8. Establish the subjective and objective correspondence module

[0044] For various types of heater cores, obtain the objective data of water flow noise on the test bench and the subjective score of water flow noise under the whole vehicle state, and determine the corresponding relationship between the objective index and the subjective score of each vehicle through a scatter plot;

[0045] 9. Determination of objective target value of water flow sound

[0046] It is used to find the objective indicator corresponding to the qualified score in the subjective score in the scatter plot, and determine the water flow sound target value according to the objective indicator corresponding to the qualified score.

[0047] Beneficial effects of the invention:

[0048] 1. The method for predicting water flow noise of automobile heating core of the present invention identifies problems in the early stage of automobile design, avoiding redesign after the subsequent actual car comes out, wasting development cycle and funds. By building a system bench in advance in the early stage of automobile design / prototype design stage, and connecting the entire cooling system and air conditioning heating core system to the engine, simulating the running state of the actual car, and through specific test conditions and methods, identifying the performance of water flow noise in the car during the process of automobile startup, rapid acceleration, etc. in the early stage of automobile development, confirming whether there is a water flow noise problem in the current design scheme, and predicting the subsequent water flow noise performance of the actual car based on the objective data results of this bench, avoiding risks in advance.

[0049] 2. The method for predicting water flow noise in the car warm core of the present invention aims to solve the problem of water flow noise caused by the circulation of coolant in the air-conditioning and cooling systems during cold start and rapid acceleration of the car. In the early stage of car development, a system bench is built to simulate the operating conditions of the whole vehicle system (the same as the driving evaluation conditions of the whole vehicle) to evaluate whether there is water flow noise, and the accuracy of identifying the problem is high. Based on the results of this bench, the performance of water flow noise in the whole vehicle is predicted, and whether there is a water flow noise problem can be identified in advance to avoid problems after the prototype car design is completed. Practice has verified that this method has high accuracy.

[0050] 3. The method for predicting water flow noise of automobile heater cores of the present invention has high repeatability and robustness. For various types of heater cores, the objective data of water flow noise on the test bench and the subjective scores of water flow noise under the whole vehicle state are obtained respectively, and the corresponding relationship between the objective index and the subjective score of each automobile is determined through a scatter plot; the objective index corresponding to the qualified score in the subjective score is searched in the scatter plot, and the target value of water flow noise is determined according to the objective index corresponding to the qualified score. BRIEF DESCRIPTION OF THE DRAWINGS

[0051] Figure 1 The figure shows a schematic diagram of a system bench for predicting the water flow noise of a car heating core;

[0052] Figure 2The figure shows the objective data of the bench - Fourier spectrum diagram;

[0053] Figure 3 The figure shows the Fourier spectrum of the objective data of the water flow sound on the test bench after filtering at -50 to 250 Hz;

[0054] Figure 4 Shown is a scatter plot of the correspondence between subjective scores and objective values;

[0055] Figure 5 The figure shows the objective data acquisition process of the bench;

[0056] Figure 6 The figure shows the process of bench data processing;

[0057] Figure 7 Shown is the subjective rating value of the water flow sound of the whole vehicle;

[0058] Figure 8 The figure shows the establishment of the corresponding module between the objective data of the test bench and the subjective rating of the whole vehicle;

[0059] Fig. 9 The objective data of water flow sound of A / B model warm core is shown. DETAILED DESCRIPTION

[0060] In order to make the technical concept and advantages of the invention more clearly understood, the technical solution of the invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the following embodiments are only used to explain and illustrate the preferred implementation methods of the invention and should not constitute a limitation on the scope of the patent protection required by the invention.

[0061] Example 1

[0062] The method for predicting water flow noise of automobile heating core of the present invention is to build a test bench to simulate the running state of the whole vehicle in the early stage of automobile development, evaluate whether there is water flow noise in the automobile heating core, and predict the performance of water flow noise in the whole vehicle based on the test bench result, and the steps include:

[0063] 1) Build the system bench

[0064] On the engine performance test bench, the cooling system (expansion tank, intercooler) and air-conditioning heater core are connected to the engine according to the design coordinates to form a complete system to ensure the normal operation of the engine; the air-conditioning heater core is connected to an independent room outside through pipes.

[0065] 2) Connect the water flow sound recognition device

[0066] Place the water flow sound recognition device (sound collection sensor) 10 cm in front of the heating core shell, pointing to the heating core shell, and connect the rear end of the microphone to the data collection device;

[0067] Alternatively, a stethoscope for abnormal sound is placed on the shell of the heating core and connected to the outside of the test stand through a high-fidelity headset. The engineer outside uses the headset to identify whether there is water flow sound and make a subjective evaluation.

[0068] System rack Figure 1 shown.

[0069] 3) Coolant filling

[0070] Fill the coolant to the designed volume and exhaust the air inside the system to the atmosphere; after the coolant is filled, turn off the engine and let it stand until the coolant temperature drops to the ambient temperature and the engine reaches a cold state;

[0071] 4) Identification of water flow sound problems under normal operating conditions

[0072] (1) Start the engine and wait until the engine stabilizes to normal idle speed, and monitor the water flow sound during this process;

[0073] (2) Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, with an interval of 1 minute each time, and collect the sound data each time;

[0074] 5) Identification of water flow sound problems during post-coolant boiling conditions

[0075] (1) Accelerate the engine speed to 3000 rpm and run it steadily. When the engine outlet water temperature reaches 110°C, continue running for 10 seconds and then immediately stop the engine and turn off all the cooling fans on the test bench until the water temperature in the expansion tank reaches the ambient temperature;

[0076] (2) Start the engine at this time, wait until the engine stabilizes to normal idle speed, and monitor the sound of water flow during this process;

[0077] (3) Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, with an interval of 1 minute each time, and collect the sound data each time;

[0078] 6) The objective sound data collected in the above steps 4) and 5) are processed as follows:

[0079] (1) Perform Fourier time-frequency conversion on the collected sound data to convert it into frequency domain data (where the window function is the Hanning window) and the frequency resolution is 1 Hz; Figure 2 The figure shows the objective data of the bench - Fourier spectrum diagram;

[0080] (2) The data with obvious water flow sound is filtered through a Butterworth bandpass filter, the data in the 50-250 Hz frequency band is retained, and the effective mean of this frequency band is calculated to obtain the noise value of this frequency band; Figure 3 As shown;

[0081] (3) Determine the water flow sound evaluation index of this system (cooling system, air conditioning heating core).

[0082] The above process can be seen in Figure 5 , Figure 6 .

[0083] Example 2

[0084] The method for predicting the water flow sound of the car heater core in this embodiment is different from that in Embodiment 1 in that: further, the specific process of adding coolant is disclosed:

[0085] Step 3, the coolant filling process includes:

[0086] 3.1 Stand still and turn off the engine, and add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0087] 3.2 Start the engine and run it at idle speed for 5 minutes. As the engine runs, the air retained in the system will be discharged to the expansion tank along with the flow of coolant, and then enter the air; as the air is discharged, the coolant level will drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0088] 3.3 After the engine speed is accelerated to 2000rpm, it runs steadily for 15 minutes. At this time, the cooling system is turned on. As the air in the system is gradually discharged, the coolant level continues to drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0089] 3.4 After accelerating the engine speed to 3000rpm, run it stably for 5 minutes. The air inside the entire system is basically eliminated. At this time, observe the liquid level in the expansion water tank to confirm whether the liquid level is between the min line and the max line. If it is lower than the min line, continue to add coolant from the expansion water tank filling port until the coolant level stays between the min line and the max line of the expansion water tank;

[0090] 3.5 After completing the above four steps, the coolant is filled, turn off the engine and let it stand until the coolant temperature drops to the ambient temperature and the engine reaches a cold state.

[0091] The purpose of this process is to fill the coolant to the designed volume and expel the air retained in the system into the atmosphere, so as to avoid misjudgment caused by water flow sound caused by the air retained in the system during the bench construction process.

[0092] Example 3

[0093] The method for predicting the water flow sound of the car heater core of this embodiment is different from that of Embodiment 1 and Embodiment 2 in that: it further comprises step 7: a subjective evaluation process of the water flow sound of the car heater core;

[0094] Install the warm core after collecting the bench noise data on the vehicle and conduct a subjective evaluation of the corresponding working conditions; Figure 7 , Figure 8 As shown, the process includes:

[0095] 7.1 Coolant filling

[0096] 7.1.1 With the engine at rest and turned off, add coolant from the expansion tank filling port until the coolant level remains between the min and max lines of the expansion tank;

[0097] 7.1.2 Start the engine and run it at idle speed for 5 minutes. As the engine runs, the air retained in the system will be discharged to the expansion tank along with the flow of coolant, and then enter the air; as the air is discharged, the coolant level will drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank;

[0098] 7.1.3 After the engine speed is accelerated to 2000rpm, it is allowed to run steadily for 15 minutes. At this time, the cooling system is turned on. As the air in the system is gradually discharged, the coolant level continues to drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank.

[0099] 7.1.4 After accelerating the engine speed to 3000rpm, run it stably for 5 minutes. The air in the entire system is basically eliminated. At this time, observe the liquid level in the expansion water tank to confirm whether the liquid level is between the min line and the max line. If it is lower than the min line, continue to add coolant from the expansion water tank filling port until the coolant level stays between the min line and the max line of the expansion water tank;

[0100] 7.1.5 After completing the above four steps, the coolant is filled and the engine is turned off and left to stand until the coolant temperature drops to the ambient temperature and the engine reaches a cold state.

[0101] The purpose of this process is to fill the coolant to the designed volume and expel the air retained in the system into the atmosphere, so as to avoid misjudgment caused by water flowing sound caused by the air retained in the system during the replacement of the heater core.

[0102] 7.2 Identification of water flow sound problems under normal operating conditions

[0103] 7.2.1 The engine is cold and turned off. Start the engine and wait until the engine stabilizes to the normal idle speed.

[0104] 7.2.2 Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, and record the subjective score each time;

[0105] 7.3 Identification of water flow sound problems in the post-boiling condition of coolant

[0106] 7.3.1 Accelerate the engine speed to 3000rpm and run it steadily. When the engine outlet water temperature reaches 110℃, continue to run for 10 seconds and then immediately stop the engine and turn off all the cooling fans on the test bench until the water temperature of the expansion tank reaches the ambient temperature;

[0107] 7.3.2 Start the engine at this time and wait until the engine stabilizes to normal idle speed;

[0108] 7.3.3 Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, and record the subjective score each time;

[0109] 7.4 Select the lowest score from the subjective scores in the above steps as the subjective score of water flow sound of this system (cooling system, air conditioning heating core);

[0110] The subjective scoring in this embodiment adopts a 10-point system. The lower the score, the more serious the water flow sound. Among them, 6 points in the subjective scoring is an acceptable state score, that is, 6 points are qualified points. If the subjective score is less than 6 points, the water flow sound is unacceptable and is judged as unqualified. If the subjective score is greater than or equal to 6 points, the water flow sound is acceptable and is judged as qualified. The subjective scoring standard is as follows:

[0111]

[0112] Example 4

[0113] The method for predicting water flow sound of a car heater core of the present embodiment is different from that of Embodiment 3 in that: further, by establishing a subjective and objective correspondence module, objective test bench water flow sound data and subjective water flow sound scores of a plurality of different types of heater cores are obtained respectively, and the correspondence between the objective index and the subjective score of each car is determined through a scatter plot; the objective index corresponding to the qualified score in the subjective score is searched in the scatter plot, and the water flow sound target value is determined according to the objective index corresponding to the qualified score, so as to determine the objective target value of the water flow sound.

[0114] The above description is only a preferred embodiment of the present invention and does not constitute a limitation of the present invention. Under the guidance of the prior art, those skilled in the art can make other modifications to the implementation of the present invention without creative work. Any modification made within the spirit and principle of the present invention or simple replacement or equivalent substitution using conventional technical means in the field should be included in the protection scope of the present invention.

[0115] Based on Example 4, through the following specific case analysis, it can be proved that the prediction method of the present invention can identify in advance whether there is a water flow sound problem, and the accuracy of identifying the problem is high.

[0116] Specific application cases

[0117] In this application case, water flow sound evaluation was performed on two air-conditioning heater cores (Type A and Type B) designed during automobile development to identify problems in advance.

[0118] 1. Press Figure 5 Build the scaffolding ( Figure 1 ), connect the heating core, collect objective data respectively, and press Figure 6 Process the objective data of A and B heating cores and get the following Fig. 9 The objective data of water flow sound of the A and B models of warm cores shown;

[0119] 2. Press Figure 7 Conduct subjective evaluation of the A / B heater cores and record the scores. As shown in the following table, the subjective score of the A heater core is 6.5, and the B heater core is 5.5 points;

[0120]

[0121]

[0122] 3. According to the above 1 / 2, we can get the objective data and subjective scores as shown in the following table. Figure 4 The scatter plot of the corresponding relationship between subjective scores and objective values ​​shows that the problematic warm core can be effectively distinguished and identified; and the bench and vehicle evaluation results are consistent, and the bench results can effectively predict the performance of the vehicle.

[0123] It can be seen that the method for predicting the water flow sound of the car heating core of the present invention, by building a system bench to simulate the operating conditions of the whole vehicle system, the bench simulates the installation and connection of the whole vehicle system, and the working conditions are the same as the whole vehicle driving evaluation conditions, and the accuracy of identifying problems is high. Predicting the performance of the water flow sound inside the whole vehicle based on the bench results can avoid problems that still exist after the design of the prototype vehicle is completed, and avoid the problem of redesign after the subsequent actual vehicle comes out, wasting development cycle and funds. And it has high repeatability and robustness.

Claims

1. A method for predicting water flow noise in a car heater core. In the early stage of car development, a test bench is built to simulate the running state of the whole vehicle, to evaluate whether there is water flow noise in the car heater core, and to predict the performance of water flow noise in the whole vehicle based on the test bench results. The method is characterized by: 1) Build the system bench On the engine performance test bench, the cooling system and air conditioning heater core are connected to the engine according to the design coordinates to form a complete system; 2) Connect the water flow sound recognition device The water flow sound recognition device is placed in front of the heating core housing, pointing to the heating core housing, and the rear end of the microphone is connected to the data acquisition device; 3) Coolant filling Fill the coolant to the designed volume and exhaust the air retained in the system into the atmosphere; After the coolant is filled, turn off the engine and leave it alone until the coolant temperature drops to the ambient temperature and the engine reaches a cold state; 4) Identification of water flow sound problems under normal operating conditions (1) Start the engine and wait until the engine stabilizes to normal idle speed, and monitor the sound of water flow during this process; (2) Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, with an interval of 1 minute each time, and collect the sound data each time; 5) Identification of water flow sound problems during post-coolant boiling conditions (1) Accelerate the engine speed to 3000 rpm and run it steadily. When the engine outlet water temperature reaches 110°C, continue running for 10 seconds and then immediately stop the engine and turn off all the cooling fans on the test bench until the water temperature in the expansion tank reaches the ambient temperature; (2) Start the engine at this time, wait until the engine stabilizes to normal idle speed, and monitor the sound of water flow during this process; (3) Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, with an interval of 1 minute each time, and collect the sound data each time; 6) The objective sound data collected in the above steps 4) and 5) are processed as follows: (1) Perform Fourier time-frequency conversion on the collected sound data to convert it into frequency domain data, with a frequency resolution of 1 Hz; (2) The data with obvious water flow sound is filtered through a Butterworth bandpass filter, the data in the 50-250 Hz frequency band is retained, and the effective mean of this frequency band is calculated to obtain the noise value of this frequency band; (3) Determine the evaluation index of water flow noise of cooling system and air conditioning heating core.

2. The method for predicting the water flow sound of a car heater core according to claim 1, characterized in that: Step 3) The process of adding coolant is as follows: (1) With the engine at rest and turned off, add coolant from the expansion tank filling port until the coolant level remains between the min and max lines of the expansion tank; (2) Start the engine and run it at idle speed for 5 minutes. As the engine runs, the air retained in the system will be discharged into the expansion tank along with the flow of coolant and then enter the air. As the air is discharged, the coolant level will drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank. (3) After the engine speed is accelerated to 2000 rpm, it is allowed to run steadily for 15 minutes. At this time, the cooling system is turned on. As the air in the system is gradually discharged, the coolant level continues to drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level remains between the min line and the max line of the expansion tank. (4) After accelerating the engine speed to 3000rpm, run it steadily for 5 minutes. The air inside the entire system is basically eliminated. At this time, observe the liquid level in the expansion water tank to confirm whether the liquid level is between the min line and the max line. If it is lower than the min line, continue to add coolant from the expansion water tank filling port until the coolant level stays between the min line and the max line of the expansion water tank; (5) After completing the above four steps, the coolant is filled. Turn off the engine and let it stand until the coolant temperature drops to the ambient temperature and the engine reaches a cold state.

3. The method for predicting the water flow noise of the vehicle heater core according to claim 1 or 2, characterized in that: it comprises step 7) a process of subjective evaluation of the water flow noise of the vehicle heater core; Install the warm core with collected bench noise data on the vehicle and conduct a subjective evaluation of the corresponding working conditions; the details are as follows: (1) Coolant filling 1.1) With the engine at rest and turned off, add coolant from the expansion tank filling port until the coolant level remains between the min and max lines of the expansion tank; 1.2) Start the engine and run it at idle speed for 5 minutes. As the engine runs, the air retained in the system will be discharged to the expansion tank along with the flow of coolant, and then enter the air; as the air is discharged, the coolant level will drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank; 1.3) After the engine speed is accelerated to 2000rpm, it is allowed to run steadily for 15 minutes. At this time, the cooling system is turned on. As the air in the system is gradually discharged, the coolant level continues to drop. At this time, continue to add coolant from the expansion tank filling port until the coolant level stays between the min line and the max line of the expansion tank. 1.4) After accelerating the engine speed to 3000rpm, run it stably for 5 minutes. The air in the entire system is basically eliminated. At this time, observe the liquid level in the expansion water tank to confirm whether the liquid level is between the min line and the max line. If it is lower than the min line, continue to add coolant from the expansion water tank filling port until the coolant level stays between the min line and the max line of the expansion water tank; 1.5) After completing the above four steps, the coolant is filled, and the engine is turned off and left to stand until the coolant temperature drops to the ambient temperature, so that the engine reaches a cold state; (2) Identification of water flow sound problems under normal operating conditions 2.1) The engine is in a cold, flameout and static state. Start the engine and wait until the engine stabilizes to the normal idle speed; 2.2) Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, and record the subjective score each time; (3) Identification of water flow sound problems during post-cooling boiling 3.1) Accelerate the engine speed to 3000rpm and run it steadily. When the engine outlet water temperature reaches 110℃, continue running for 10 seconds and then immediately stop the engine and turn off all the cooling fans on the test bench until the water temperature of the expansion tank reaches the ambient temperature; 2) Start the engine at this time and wait until the engine stabilizes to normal idle speed; 3.3) Accelerate the engine speed from the stable idle speed to the maximum speed at full throttle, repeat three times, and record the subjective score each time; (4) The lowest score among the subjective scores in the above steps is selected as the subjective score of the cooling system and air conditioning heater water flow sound.

4. The method for predicting the water flow sound of a car heater core according to claim 3, characterized in that: Including step 8) the process of establishing the subjective and objective correspondence modules: For various types of heater cores, obtain the objective data of water flow noise on the test bench and the subjective score of water flow noise under the whole vehicle state, and determine the corresponding relationship between the objective index and the subjective score of each vehicle through a scatter plot; And step 9) the process of determining the objective target value of water flow sound: It is used to find the objective indicator corresponding to the qualified score in the subjective score in the scatter plot, and determine the water flow sound target value according to the objective indicator corresponding to the qualified score.

5. The method for predicting the water flow sound of a car heater core according to claim 3, characterized in that: The subjective scoring adopts a 10-point system. The lower the score, the more serious the water flow sound. 6 points in the subjective scoring is an acceptable status score, that is, 6 points is a passing score. If the subjective score is less than 6 points, the water flow sound is unacceptable and is judged as unqualified. If the subjective score is greater than or equal to 6 points, the water flow sound is acceptable and is judged as qualified.

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