Abnormal Sound Analysis Method

Abstract

This invention provides a noise analysis method that can determine abnormal noises caused by cavitation in the main bearings of an engine. [Solution] The abnormal noise analysis method involves detecting abnormal noises from sound pressure levels corresponding to the sound frequencies of each cylinder of the engine, calculating a standard deviation from a histogram of the frequencies of the sound pressure levels of the abnormal noises, and determining that the cause of the abnormal noise is cavitation of the main bearing corresponding to the cylinder if the timing of the occurrence of the abnormal noise is after the arrival of the top dead center of compression of the cylinder within the combustion cycle of the engine, and the standard deviation is greater than or equal to a threshold.

Description

Technical Field

[0001] The present invention relates to a method for analyzing abnormal noise.

Background Art

[0002] Regarding the method for analyzing abnormal noise, for example, Patent Document 1 describes determining the presence or absence of abnormal noise from sound data measured while a predetermined driving condition of a vehicle is maintained.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] The axis center of the main bearing corresponding to each cylinder of the engine of a vehicle makes complex movements according to specific driving conditions. As a result, the lubricating oil of the main bearing locally causes cavitation (pressure reduction boiling), and bubbles burst to generate shock waves. The technique described in Patent Document 1 cannot determine this type of abnormal noise.

[0005] Therefore, the present invention has been made in view of the above problems, and an object thereof is to provide a method for analyzing abnormal noise that can determine abnormal noise caused by cavitation of the main bearing of an engine.

Means for Solving the Problems

[0006] The present invention provides a method for analyzing abnormal noises, which involves detecting abnormal noises from sound pressure levels corresponding to the sound frequencies of each cylinder of an engine, calculating a standard deviation from a histogram of the frequencies of the sound pressure levels of the abnormal noises, and determining that the cause of the abnormal noise is cavitation of the main bearing corresponding to the cylinder if the timing of the occurrence of the abnormal noise is after the arrival of the top dead center of compression of the cylinder within the combustion cycle of the engine, and the standard deviation is greater than or equal to a threshold. [Effects of the Invention]

[0007] According to the present invention, it is possible to determine abnormal noise caused by cavitation in the main bearing of an internal combustion engine. [Brief explanation of the drawing]

[0008] [Figure 1] Figure 1 is a diagram showing an example of a system for analyzing abnormal sounds. [Figure 2] Figure 2(a) shows an example of sound data, Figure 2(b) shows an example of a timing signal, Figure 2(c) shows an example of the time variation of the sound pressure level of an abnormal sound, and Figure 2(d) shows an example of a histogram summarizing the frequency of sound pressure levels. [Figure 3] Figure 3 is a flowchart showing an example of abnormal sound analysis processing. [Modes for carrying out the invention]

[0009] (Configuration of the abnormal sound analysis system) Figure 1 is a configuration diagram showing an example of an abnormal noise analysis system S. The abnormal noise analysis system S includes a terminal 1 such as a tablet or personal computer, an engine 2 such as a gasoline engine or diesel engine, and an ECU (Electronic Control Unit) 3. The terminal 1 is installed, for example, in a service center of a vehicle equipped with the engine 2, and analyzes abnormal noises generated from the engine 2 in response to user requests.

[0010] Engine 2 has multiple cylinders 21. Note that Figure 1 shows only one cylinder 21. A piston 22 is provided inside cylinder 21. The piston 22 and cylinder 21 define a combustion chamber r for burning a mixture of fuel and air. A spark plug 20 is provided at the top of the combustion chamber r. When the spark plug 20 ignites the mixture, the piston 22 moves in the vertical direction D due to the combustion of the mixture. The piston 22 is connected to the crankshaft 25 via a connecting rod 23. The connecting rod 23 is connected to the main bearing 24 of the crankshaft 25. Therefore, the crankshaft 25 rotates in conjunction with the vertical movement of the piston 22.

[0011] Furthermore, engine 2 is equipped with a crank angle sensor 26 that detects the rotation angle of the crankshaft 25. The crank angle sensor 26 outputs the detected value to the ECU 3.

[0012] The ECU3 controls, for example, the output torque of the engine 2. The ECU3 communicates with terminal 1 via a communication unit (not shown). The ECU3 calculates the timing at which the piston 22 reaches top dead center of compression based on the rotation angle of the crankshaft 25 and the ignition timing of the spark plug 20, and notifies terminal 1 of this timing.

[0013] Terminal 1 is an example of a computer and includes a CPU (Central Processing Unit) 10, memory 11 such as ROM (Read Only Memory) and RAM (Random Access Memory), and a microphone 12. The CPU 10 executes a series of processes in a predetermined sequence according to a program stored in memory 11.

[0014] The microphone 12 acquires sound generated from each cylinder 21 and outputs it to the CPU 10. As will be described later, the CPU 10 generates sound data from the sound from the microphone 12 to detect abnormal noises and determines whether or not the cause of the abnormal noise is cavitation of the main bearing 24.

[0015] The axis of the main bearing 24 corresponding to each cylinder 21 undergoes complex movements depending on specific operating conditions. This causes localized cavitation (boiling under reduced pressure) of the lubricating oil in the main bearing 24, resulting in the bursting of bubbles and the generation of shock waves. This cavitation-induced abnormal noise is characterized by occurring immediately after combustion of the air-fuel mixture in each cylinder 21 unit (Condition A), and by a greater variation in sound pressure level than other noises (Condition B). Therefore, the CPU 10 identifies the abnormal noise caused by cavitation based on the frequency distribution of the sound pressure level and the timing of its occurrence, as described below.

[0016] (Data for abnormal sound analysis) Figure 2(a) shows an example of sound data, and Figure 2(b) shows an example of a timing signal. The sound data shows the change in sound frequency and sound pressure level over time. Here, the thicker the line, the higher the sound pressure level. The timing signal shows the timing when the piston 22 reaches top dead center of compression.

[0017] The CPU 10 generates sound data over time by performing processes such as the Fast Fourier Transform on the sound acquired by the microphone 12. At the same time, the CPU 10 receives a timing signal from the ECU 3. At this time, the ECU 3 generates a timing signal from the rotation angle of the crankshaft 25 and the ignition timing of the spark plug 20.

[0018] The CPU 10 detects abnormal noises from the sound pressure level corresponding to the sound frequency of each cylinder. For example, the CPU 10 detects a region N in the sound data where the sound pressure level is above a certain level as an abnormal noise. The CPU 10 compares the timing Tn of region N with the timing signal and determines whether the timing Tn of region N is later than the timing signal within the combustion cycle period Tc of the engine 2. At this time, the CPU 10 calculates the combustion cycle period Tc based on the timing signal.

[0019] As a result, the CPU 10 determines whether or not the timing of the abnormal noise occurrence is after the arrival of the top dead center of compression of the cylinder 21 within the combustion cycle of the engine 2. When the timing of the abnormal noise occurrence is after the arrival of the top dead center of compression, the above condition A is satisfied.

[0020] Further, FIG. 2(c) is a diagram showing an example of the temporal change in the sound pressure level of the abnormal noise, and FIG. 2(d) is a diagram showing an example of a histogram in which the frequencies of the sound pressure levels are aggregated. In FIG. 2(d), the solid line is a histogram regarding the abnormal noise caused by cavitation, and the dotted line is a histogram regarding the abnormal noise caused by general factors other than cavitation. The histogram is generated by aggregating the peak-to-peak values every two rotations of the engine 2 from the sound pressure levels shown in, for example, FIG. 2(c).

[0021] The sound pressure level of the abnormal noise caused by cavitation has a greater degree of variation compared to the abnormal noise caused by general factors other than cavitation. Therefore, the standard deviation of the sound pressure level of the abnormal noise caused by cavitation is greater than the standard deviation of the sound pressure level of the general abnormal noise other than cavitation. Thus, the CPU 10 calculates the standard deviation from the histogram and uses it for determination. When the standard deviation is equal to or greater than a predetermined threshold value, the above condition B is satisfied. When conditions A and B are satisfied, the CPU 10 determines that the cause of the abnormal noise is cavitation of the main bearing 24.

[0022] (Abnormal noise analysis process) FIG. 3 is a flowchart showing an example of the abnormal noise analysis process. This process is an example of an abnormal noise analysis method and is executed, for example, when the user starts the application of the terminal 1.

[0023] First, the CPU 10 instructs the ECU 3 to start the engine 2 according to the user's operation on the terminal 1 (St1). At this time, the start instruction is appended with the operating conditions (such as the rotational speed and torque) of the engine 2 for reproducing the abnormal noise of the cylinder 21.

[0024] Next, the CPU 10 acquires sound data for each cylinder 21 using the microphone 12 (St2), and receives a timing signal of the compression top dead point of the piston 22 for each cylinder 21 from the ECU 3 (St3). Each of the processes of St2 and St3 is executed in parallel for only the period required for the abnormal sound analysis of the sound data.

[0025] Next, the CPU 10 detects an abnormal sound from the sound pressure level corresponding to the frequency of the sound in the sound data (St4). Next, the CPU 10 generates a histogram by aggregating the frequencies of the sound pressure levels of the abnormal sounds (St5), and calculates the standard deviation σ from the histogram (St6).

[0026] Next, the CPU 10 compares the standard deviation σ with the threshold TH (St7). The threshold TH is preset based on experimental results and simulation results regarding abnormal sounds due to cavitation. When σ < TH holds (No in St7), the CPU 10 determines that the cause of the abnormal sound is a factor other than cavitation (St10).

[0027] Also, when σ ≥ TH holds (Yes in St7), the CPU 10 determines whether or not the timing of the occurrence of the abnormal sound is after the arrival of the compression top dead point of the cylinder 21 within the combustion cycle of the engine 2 based on the timing signal (St8). At this time, the CPU 10 determines, for example, whether or not the timing of occurrence of the abnormal sound in a certain number or more of the timings of occurrence of the abnormal sound within the abnormal sound analysis target period is after the compression top dead point. When the timing of occurrence of the abnormal sound is before the arrival of the compression top dead point (No in St8), the CPU 10 determines that the cause of the abnormal sound is a factor other than cavitation (St10).

[0028] Furthermore, if the timing of the abnormal noise occurs after the arrival of top dead center (Yes in St8), the CPU 10 determines that the cause of the abnormal noise is cavitation (St9). In this way, according to this method, it is possible to determine abnormal noise caused by cavitation of the main bearing 24 of the engine 2. In this example, the CPU 10 determined the cause of the abnormal noise by analyzing the waveform of the sound pressure level, but the cause of the abnormal noise may be analyzed by analyzing the vibration waveform instead of the sound pressure level. In this case, the CPU 10 detects the magnitude of acceleration for each cylinder 21 using, for example, an acceleration sensor instead of the microphone 12.

[0029] The embodiments described above are preferred examples of the present invention. However, the invention is not limited thereto, and various modifications are possible without departing from the spirit of the invention. [Explanation of symbols]

[0030] 1 terminal, 2 engines, 3 ECUs, 10 CPUs, 21 cylinders, 24 main bearings

Claims

[Claim 1] Abnormal noises are detected from the sound pressure level corresponding to the sound frequency of each engine cylinder. The standard deviation is calculated from the histogram obtained by aggregating the frequency of the sound pressure levels of the aforementioned abnormal noises. If the timing of the occurrence of the abnormal noise is after the cylinder reaches top dead center during the combustion cycle of the engine, and the standard deviation is greater than or equal to a threshold, the cause of the abnormal noise is determined to be cavitation of the main bearing corresponding to the cylinder. Methods for analyzing abnormal sounds.

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