Obtaining method of engine natural frequencies, detection method of engine abnormalities, and calculation unit, and program

Abstract

To provide an obtaining method of engine natural frequencies capable of solving the following problem that even when the natural frequency of an engine acquired when the engine is stopped is used, there is a possibility that it may deviate from the natural frequency when the engine is running; thus, it is desirable to acquire the natural frequencies of the engine while it is running.SOLUTION: The obtaining method of engine natural frequencies includes the following steps: acquiring first waveform data of an engine during steady operation; acquiring second waveform data of the engine during transient unsteady operation; acquiring information representing the vibration characteristics of the engine by comparing the first waveform data and the second waveform data; and acquiring the natural frequency of the engine during operation based on information showing vibration characteristics.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present disclosure relates to a method for acquiring a natural frequency of an engine, a method for detecting an abnormality in an engine, a computing device, and a program. [Background technology]

[0002] One example of an engine abnormality detection method is described in the following Patent Document 1. In Patent Document 1, a vibration sensor is attached to a gas engine, and a frequency band component near a frequency corresponding to the natural frequency of the gas engine is selectively extracted by a bandpass filter, and when the frequency band component has a signal level higher than normal, an abnormality determination circuit determines that a misfire abnormality has occurred. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2003-65142 A Summary of the Invention [Problem to be solved by the invention]

[0004] Although not described in the above Patent Document 1, the natural frequency of an engine is generally obtained by analyzing data obtained in a hammering test in which a test object (engine) is struck with a hammer to vibrate it, and the vibration (so-called impulse response) generated in the test object by the vibration is measured. The hammering test is performed when the engine is stopped. When the engine is running, the engine itself becomes a vibration source, so that even if the engine is vibrated with a hammer, it is not possible to measure a vibration waveform for obtaining the natural frequency.

[0005] However, the temperature distribution of the engine is significantly different when the engine is in operation and when it is stopped, and the natural frequency of the engine when it is in operation (high temperature) also changes from the natural frequency when the engine is stopped (low temperature). Therefore, in determining misfire abnormality as in the above-mentioned Patent Document 1, even if the natural frequency of the engine obtained when the engine is stopped is used, it may deviate from the natural frequency when the engine is in operation. Therefore, it is desirable to be able to obtain the natural frequency of the engine while it is in operation. In addition, in order to improve the accuracy of abnormality detection, it is desirable to be able to detect abnormalities in the engine while it is in operation without being affected by the deviation of the natural frequency of the engine between when the engine is stopped and when it is in operation.

[0006] The present disclosure is devised to solve the above-mentioned problems, and aims to provide an engine natural frequency acquisition method, a computing device, and a program that enable acquisition of the natural frequency of an engine while it is running, and an engine abnormality detection method that enables detection of an engine abnormality without being affected by the deviation in the engine natural frequency between when the engine is stopped and when it is running. [Means for solving the problem]

[0007] The method for acquiring the natural frequency of an engine according to the present disclosure includes the steps of acquiring first waveform data during steady operation of the engine, acquiring second waveform data during transient, non-steady operation of the engine, acquiring information indicative of vibration characteristics of the engine by comparing the first waveform data with the second waveform data, and acquiring the natural frequency of the engine during operation based on the information indicative of the vibration characteristics.

[0008] The engine abnormality detection method according to the present disclosure includes a step of acquiring first information indicating vibration characteristics of the engine during abnormal operation by comparing first waveform data during steady operation of the engine with second waveform data during transient abnormal operation of the engine, acquiring second information indicating vibration characteristics of the engine based on waveform data acquired sequentially during operation of the engine, and determining the presence or absence of an abnormality in the engine during operation based on a comparison between the acquired second information and the first information.

[0009] The calculation device of the present disclosure includes a data acquisition unit that acquires first waveform data during steady operation of an engine and second waveform data during transient, non-steady operation of the engine, a memory unit that stores the first waveform data and the second waveform data, and a control unit that acquires information indicating vibration characteristics of the engine by comparing the first waveform data with the second waveform data, and acquires the natural frequency of the engine during operation based on the information indicating the vibration characteristics.

[0010] The program of the present disclosure causes a computer to execute the steps of acquiring first waveform data during steady operation of an engine, acquiring second waveform data during transient, non-steady operation of the engine, acquiring information indicative of vibration characteristics of the engine by comparing the first waveform data with the second waveform data, and acquiring the natural frequency of the engine during operation based on the information indicative of the vibration characteristics. Effect of the Invention

[0011] According to the present disclosure, it is possible to provide an engine natural frequency acquisition method, a computing device, and a program that enable acquisition of the natural frequency of an engine while it is running, and an engine abnormality detection method that enables detection of an engine abnormality without being affected by the deviation in the engine natural frequency between when the engine is stopped and when it is running. [Brief description of the drawings]

[0012] [Figure 1]FIG. 1 is an explanatory diagram of a device configuration related to a method for acquiring the natural vibration frequency of an engine. [Diagram 2] FIG. 2 is a flowchart illustrating the method for acquiring the natural vibration frequency of the engine according to the first embodiment. [Diagram 3] FIG. 3 is a schematic diagram showing an example of the first waveform data. [Figure 4] FIG. 4 is a schematic diagram showing an example of the second waveform data. [Diagram 5] FIG. 5 is a schematic diagram showing an example of vibration input data and output vibration data. [Figure 6] FIG. 6 is a schematic diagram showing frequency spectra of the vibration input data and the output vibration data shown in FIG. [Figure 7] FIG. 7 is a schematic diagram showing an example of the transfer function data. [Figure 8] FIG. 8 is a flowchart illustrating the engine abnormality detection method according to the second embodiment. [Figure 9] FIG. 9 is a schematic diagram illustrating the abnormality determination process. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0013] Preferred embodiments of the present disclosure will be described in detail below with reference to the accompanying drawings. Note that the present disclosure is not limited to these embodiments, and when there are multiple embodiments, the present disclosure also includes combinations of the embodiments.

[0014] [First embodiment] 1 is an explanatory diagram of a device configuration related to a method for acquiring the natural vibration frequency of an engine according to the first embodiment. First, the engine whose natural vibration frequency is acquired will be described in detail.

[0015] <Engine configuration> The engine 10 that is the subject of the natural frequency acquisition method according to the first embodiment is particularly suitable for an engine that has no (or has little) load fluctuation and is operated in a steady operating state at a preset rotation speed. Such an engine is, for example, an engine for a generator. The type of engine 10 is not particularly limited, but is, for example, an internal combustion engine such as a reciprocating engine. In addition, the engine 10 is, for example, a gas engine that burns gaseous fuel (gas) and converts the generated thermal energy into mechanical energy. The engine 10 may be a gasoline engine that runs on liquid fuel.

[0016] An engine 10 shown in FIG. 1 includes a plurality of cylinders 11. FIG. 1 illustrates a V-type 16-cylinder engine 10. The engine 10 includes eight cylinders 11 in each of two rows, an L row and an R row. Each cylinder 11 includes a cylinder and a piston that reciprocates in the cylinder. The cylinder has a combustion chamber to which fuel gas is supplied. When a mixture of fuel gas and air supplied to the combustion chamber is ignited by an ignition plug, combustion occurs in the cylinder, and the piston is operated by the expansion of air in the cylinder due to the combustion. The piston is connected to a crankshaft via a connecting rod, and the reciprocating motion of the piston is converted into the rotational motion of the crankshaft. For example, in the case of a four-stroke engine, the engine 10 repeats four strokes, namely an intake stroke, a compression stroke, a combustion / expansion stroke, and an exhaust stroke, as one cycle. Note that FIG. 1 does not show the structure related to the intake and exhaust of the engine 10.

[0017] An output shaft of the engine 10 is connected to a generator 91. The generator 91 generates electricity as the output shaft of the engine 10 rotates. The engine 10 and the generator 91 are fixed side by side on a base plate 93. A cooler 92 is provided adjacent to the engine 10. The cooler 92 is fluidly connected to the engine 10 so as to circulate a refrigerant therethrough, and cools the engine 10 with the circulating refrigerant and releases heat absorbed by the refrigerant from the engine 10 to the outside of the cooler 92. The engine 10, the generator 91, and the cooler 92 constitute a part of a power generation facility GE.

[0018] The method for acquiring the natural frequency of an engine according to the first embodiment is for acquiring the natural frequency of the engine 10 while the engine 10 is in operation (that is, during cycle operation).

[0019] <Data acquisition and analysis configuration> In the first embodiment, as physical quantities measured from the engine 10 during operation, in-cylinder pressure waveform data 31 of the engine 10 and vibration waveform data 32 of the engine 10 are acquired. The in-cylinder pressure waveform data 31 is pressure data in the cylinders 11 of the engine 10. The in-cylinder pressure waveform data 31 is acquired over time by an in-cylinder pressure sensor 15 provided in the cylinders 11 of the engine 10. The in-cylinder pressure sensor 15 is provided separately for each cylinder 11 of the engine 10. The vibration waveform data 32 is data obtained by measuring the vibration state of the engine 10. The vibration waveform data 32 is acquired over time by an acceleration sensor 16 attached to the engine 10 or a structure (such as the generator 91, the base plate 93, the cooler 92, etc.) connected to the engine 10. The installation position of the acceleration sensor 16 in the engine 10 is not particularly limited, but the acceleration sensors 16 are installed in a plurality of distributed locations for the purpose of measuring the overall vibration state and various vibration modes of the engine 10. In FIG. 1, the acceleration sensors 16 are installed at multiple locations, such as each cylinder 11 of the engine 10, the main body of the engine 10 (cylinder block, crankcase, etc.), each corner of the generator 91, the base plate 93, and the bottom of the cooler 92.

[0020] The in-cylinder pressure waveform data 31 and the vibration waveform data 32 are subjected to analysis processing by the calculation device 20.

[0021] The arithmetic device 20 is, for example, a computer. The arithmetic device 20 has a control unit 21, an input unit 22, an output unit 23, a communication unit (data acquisition unit) 24, and a storage unit 25. The control unit 21 includes an arithmetic circuit such as a CPU (Central Processing Unit). The input unit 22 is a device that accepts user operations, and may be, for example, a mouse, a keyboard, or a touch panel. The output unit 23 is a device that outputs information, and may be, for example, a display that displays images. The communication unit 24 is a communication module that communicates with an external device of the arithmetic device 20. The communication method of the communication unit 24 may be either wired communication or wireless communication. The arithmetic device 20 acquires in-cylinder pressure waveform data 31 from the in-cylinder pressure sensor 15 and acquires vibration waveform data 32 from the acceleration sensor 16 through the communication unit 24. The storage unit 25 is a memory that stores various information such as the calculation contents and programs of the control unit 21. The storage unit 25 includes, for example, a main storage device such as a random access memory (RAM) and a read only memory (ROM), and an external storage device such as a hard disk drive (HDD).

[0022] The calculation device 20 may be configured as a stand-alone device, may be configured integrally with other devices, or may be configured as a system combining various devices such as a calculation device and a data server, and is not particularly limited.

[0023] <Details on how to obtain natural frequency> FIG. 2 is a flow chart for explaining the method for acquiring the natural frequency of the engine according to the first embodiment. FIG. 3 is a schematic diagram showing an example of the first waveform data, and FIG. 4 is a schematic diagram showing an example of the second waveform data. As shown in FIG. 2, the method for acquiring the natural frequency of the engine includes a step S1 for acquiring the first waveform data 41 (see FIG. 3) during steady operation of the engine 10, a step S2 for acquiring the second waveform data 42 (see FIG. 4) during transient non-steady operation of the engine 10, a step S3 for acquiring information (transfer function data) indicating the vibration characteristics of the engine 10 by comparing the first waveform data 41 and the second waveform data 42, and a step S4 for acquiring the natural frequency of the engine 10 during operation based on the information indicating the vibration characteristics. Each of these steps S1 to S4 is realized by the calculation device 20 (control unit 21) executing the engine natural frequency acquisition program stored in the storage unit 25.

[0024] The arithmetic device 20 acquires first waveform data 41 (see FIG. 3) during steady operation of the engine 10 through the communication unit 24 (step S1). Steady operation is an operating state in which no abnormality occurs in the engine 10, and the engine 10 is operated at a constant load and at a preset rotation speed. As shown in FIG. 3, the first waveform data 41 includes a set of in-cylinder pressure waveform data 31a and vibration waveform data 32a acquired during steady operation. The in-cylinder pressure waveform data 31a and the vibration waveform data 32a are data from the same measurement period (data at the same point in time). The arithmetic device 20 stores the acquired first waveform data 41 in the memory unit 25.

[0025] In the in-cylinder pressure waveform data 31a, the vertical axis indicates pressure value, and the horizontal axis indicates time. The in-cylinder pressure waveform data 31a in FIG. 3 indicates data measured in a predetermined one of the multiple cylinders 11 (for example, the first cylinder 11 in L row). In the in-cylinder pressure waveform data 31a, a peak where the pressure value increases instantaneously appears at the ignition timing for each cycle. In the in-cylinder pressure waveform data 31a, a pulse (rectangular wave) that appears at regular intervals is a convenient representation of a reference pulse (cam pulse) for one cycle. FIG. 3 exemplarily shows time series data for 25 cycles. In the vibration waveform data 32a, the vertical axis indicates acceleration, and the horizontal axis indicates time. The vibration waveform data 32a in FIG. 3 exemplifies data measured at one location selected from multiple measurement locations.

[0026] The arithmetic device 20 acquires the second waveform data 42 (see FIG. 4) during the transient non-steady operation of the engine 10 through the communication unit 24 (step S2). The transient non-steady operation is an operation state in which some event (an event not occurring in the first waveform data 41) occurs in the engine 10, causing the operation state of the engine 10 to deviate from the steady state, and the engine 10 returns to the steady state over time. In the first embodiment, the second waveform data 42 includes data on a state in which an instantaneous abnormality occurs in the engine 10 during operation. Specifically, the instantaneous abnormality in the engine 10 during operation includes the occurrence of a misfire in the engine 10. A misfire in the engine 10 refers to a failure to ignite the mixed gas in the cylinder 11, which is performed once per cycle during the operation of the engine 10.

[0027] In the method for acquiring the natural frequency of the engine according to the first embodiment, a misfire (momentary abnormality) of the engine 10 during operation can be reproduced experimentally by intentionally causing a misfire (not igniting) in any one cycle of the engine 10 during operation in the control of the engine 10. The second waveform data 42 is data obtained when a misfire of the engine 10 during operation is intentionally reproduced in this manner.

[0028] As shown in FIG. 4, the second waveform data 42 includes a set of in-cylinder pressure waveform data 31b and vibration waveform data 32b acquired during unsteady operation. The in-cylinder pressure waveform data 31b and the vibration waveform data 32b are data for the same measurement period (data at the same time point). The arithmetic device 20 stores the acquired second waveform data 42 in the storage unit 25. The second waveform data 42 shown in FIG. 4 is data acquired in a case where a misfire is intentionally caused in only one predetermined cycle during the measurement period for one cylinder 11 of the engine 10. The in-cylinder pressure waveform data 31b in FIG. 4 shows data measured in one predetermined cylinder 11 (the first in the L row), as in FIG. 3. It can be seen from the in-cylinder pressure waveform data 31b in FIG. 4 that the peak of the in-cylinder pressure is small in a predetermined cycle (the third cycle in FIG. 4). In the in-cylinder pressure waveform data 31b, the pulses (rectangular waves) appearing at regular intervals are illustrative of one cycle of a reference pulse (cam pulse). The vibration waveform data 32b in FIG. 4 shows data measured at the same measurement points as in FIG.

[0029] For the in-cylinder pressure waveform data 31b and the vibration waveform data 32b of the second waveform data 42, ignition is performed normally in cycles other than the specific cycle in which misfire occurred, and therefore waveforms similar to those of the first waveform data 41 are obtained. Note that for the vibration waveform data 32b, if the horizontal axis of the graph is enlarged to examine only the timing of misfire in detail, a difference in the acceleration waveform caused by misfire can be seen, but in the graph shown in Fig. 4, the difference between the vibration waveform data 32a and the vibration waveform data 32b is almost impossible to recognize visually.

[0030] The arithmetic device 20 acquires information indicating vibration characteristics of the engine 10 by comparing the first waveform data 41 (see FIG. 3) with the second waveform data 42 (see FIG. 4) (step S3). In the first embodiment, the step S3 of acquiring information indicating vibration characteristics of the engine 10 includes extracting an impulse-like vibration waveform caused by a momentary abnormality based on the difference between the first waveform data 41 and the second waveform data 42.

[0031] In step S3, the arithmetic device 20 acquires vibration input data 43 based on the difference between the in-cylinder pressure waveform data (31a, 31b) of the first waveform data 41 and the second waveform data 42 (step S3a), acquires output vibration data 44 based on the difference between the vibration waveform data (32a, 32b) of the first waveform data 41 and the second waveform data 42 (step S3b), and acquires transfer function data 45 (see FIG. 7) of the engine 10 based on the vibration input data 43 and the output vibration data 44 as information indicating the vibration characteristics of the engine 10 (step S3c). Each step will be described below. FIG. 5 is a schematic diagram showing an example of the vibration input data 43 and the output vibration data 44. The arithmetic device 20 acquires the vibration input data 43 based on the difference between the in-cylinder pressure waveform data (31a, 31b) of the first waveform data 41 and the second waveform data 42 (step S3a). In the examples shown in Figures 3 and 4, the first waveform data 41 and the second waveform data 42 differ only in "whether or not a misfire occurs in a predetermined cycle within the measurement period." Therefore, by calculating the difference between the in-cylinder pressure waveform data 31a (see Figure 3) of the first waveform data 41 and the in-cylinder pressure waveform data 31b (see Figure 4) of the second waveform data 42, the difference in the in-cylinder pressure change caused by the misfire is extracted. Therefore, the vibration input data 43 shown in Figure 5 includes an impulse-shaped peak reflecting the in-cylinder pressure change for one misfire.

[0032] The arithmetic device 20 also obtains output vibration data 44 by calculating the difference between the vibration waveform data (32a, 32b) of the first waveform data 41 and the second waveform data 42 (step S3b). The difference between the vibration waveform data 32a (see FIG. 3) of the first waveform data 41 and the vibration waveform data 32b (see FIG. 4) of the second waveform data 42 extracts vibration components that appear at each vibration measurement point of the engine 10 due to a change in the in-cylinder pressure caused by one misfire. In other words, the output vibration data 44 shown in FIG. 5 is data that extracts vibrations that occur in the engine 10 as a result of the impulse-like excitation force shown in the excitation input data 43 acting on the engine 10. Therefore, the output vibration data 44 includes an impulse-like vibration waveform that has a peak at the misfire timing and then attenuates.

[0033] In this way, in the first embodiment, impulse-like vibration input data 43, similar to that performed in a hammering test, and output vibration data 44, which is a vibration damping waveform when a vibration force is applied to the engine 10, are acquired during operation of the engine 10 by using the difference between the first waveform data 41 and the second waveform data 42. The output vibration data 44 can be acquired for one vibration input data 43 by the number of acceleration sensors 16 (the number of data), but only one data is illustrated in FIG.

[0034] Then, the arithmetic device 20 acquires transfer function data 45 (see FIG. 7) of the engine 10 based on the vibration input data 43 and the output vibration data 44 as information indicating the vibration characteristics of the engine 10 (step S3c). The arithmetic device 20 first acquires the frequency spectrum of each of the vibration input data 43 and the output vibration data 44. That is, the arithmetic device 20 converts the time domain data into frequency domain data. FIG. 6 shows a frequency spectrum 43S of the vibration input data 43 and a frequency spectrum 44S of the output vibration data 44. In the frequency spectrum 43S, the vertical axis indicates the intensity of the pressure value, and the horizontal axis indicates the frequency. In the frequency spectrum 44S, the vertical axis indicates the intensity of the acceleration, and the horizontal axis indicates the frequency.

[0035] The calculation device 20 obtains transfer function data 45 (see FIG. 7) by dividing the frequency spectrum 44S of each output vibration data 44 by the frequency spectrum 43S of the excitation input data 43. FIG. 7 is a schematic diagram showing an example of the transfer function data 45. The transfer function data 45 is obtained by determining the transfer function of the engine 10 by regarding the frequency spectrum 43S and the frequency spectrum 44S as an impulse input and an impulse response to the engine 10, respectively.

[0036] In the transfer function data 45 in FIG. 7, the vertical axis indicates the magnitude (strength) of the value of the transfer function, and the horizontal axis indicates the frequency. In the transfer function data 45 in FIG. 7, a plurality of transfer function waveforms acquired for each output vibration data 44 (acceleration sensor 16) are superimposed. The transfer function data 45 obtained by the impulse response has a peak Pk at the natural frequency (frequency) of the engine 10. The engine 10 usually has a plurality of vibration modes, and the vibration mode that is easily detected varies depending on the measurement position of the output vibration data 44. Therefore, as can be seen by comparing the curve L1 (solid line) and the curve L2 (dashed line), for example, the peak Pk of the transfer function data 45 appears with particularly high strength in one of the transfer function waveforms, or appears commonly in a plurality of transfer function waveforms. By calculating the transfer function for each of the output vibration data 44 acquired from the plurality of acceleration sensors 16, the vibration characteristics of various vibration modes of the engine 10 can be grasped.

[0037] 1, in the first embodiment, the vibrations of not only the main body of the engine 10 but also the corners of the generator 91 and the base plate 93 are acquired by the acceleration sensor 16. Therefore, not only the vibration characteristics of the engine 10 itself but also the influence of the installation state of the engine 10 on the vibration characteristics of the engine 10 can be grasped.

[0038] Thereafter, the arithmetic device 20 acquires the natural frequency of the engine 10 during operation based on the information indicating the vibration characteristics (transfer function data 45) (step S4).

[0039] The calculation device 20 acquires the frequency of the peak Pk included in the transfer function data 45 as the natural frequency of the engine 10 during operation. The calculation device 20 acquires the frequencies of the peaks Pk included in the transfer function data 45, for example, the first, second, ..., Nth order natural frequencies, and stores the values ​​of each natural frequency in the storage unit 25.

[0040] The above steps S1 to S4 are performed for any one of the cylinders 11. The excitation force (excitation input data 43) generated from one cylinder 11 may have a correlation with a specific vibration mode of the engine 10 depending on the position of the cylinder 11 in the engine 10. Therefore, when the engine 10 has a plurality of cylinders 11, it is desirable to obtain transfer function data 45 for a plurality of cylinders 11 selected from all the cylinders 11, or for all the cylinders 11. By considering the plurality of transfer function data 45 obtained for each cylinder 11, the natural frequency for each vibration mode of the engine 10 can be comprehensively obtained.

[0041] This completes the process of the engine natural frequency acquisition method according to the first embodiment.

[0042] [Second embodiment] FIG. 8 is a flow chart for explaining an engine abnormality detection method according to the second embodiment. FIG. 9 is a schematic diagram for explaining an abnormality determination process. In the first embodiment, the first waveform data 41 during steady operation of the engine 10 and the second waveform data 42 during transient non-steady operation are experimentally obtained to obtain the transfer function data 45 and natural frequency of the engine 10 during operation. In the second embodiment, an example is shown in which the transfer function data 45 during test operation of the engine 10 is obtained in advance, and the data during operation obtained from the engine 10 during power generation is compared with the previously obtained data to determine the presence or absence of an abnormality in the engine 10 during actual operation.

[0043] As shown in FIG. 8, the engine abnormality detection method of the second embodiment includes a step S11 of acquiring first information 51 (see FIG. 9) indicating the vibration characteristics of the engine 10 during abnormal operation by comparing first waveform data 41 during steady operation of the engine 10 with second waveform data 42 during transient abnormal operation of the engine 10, a step S12 of acquiring second information 52 (see FIG. 9) indicating the vibration characteristics of the engine 10 based on waveform data acquired sequentially during operation of the engine 10, and a step S13 of determining the presence or absence of an abnormality in the engine 10 during operation based on a comparison between the acquired second information 52 and the first information 51.

[0044] The arithmetic device 20 acquires the first information 51 stored in advance by reading it from the storage unit 25 (step S11). Here, the transient abnormal operation of the engine 10 is, for example, a misfire of the engine 10. The first information 51 indicating the vibration characteristics of the engine 10 is the transfer function data 45 (see FIG. 7). That is, during a test run of the engine 10, the transfer function data 45 in a case where a misfire occurs in the engine 10 is acquired by the same process as steps S1 to S3 of the first embodiment, and the acquired transfer function data 45 is stored in advance in the storage unit 25 as the first information 51. This first information 51 is acquired from the storage unit 25 by the arithmetic device 20 during actual operation of the engine 10.

[0045] The arithmetic device 20 sequentially acquires real-time waveform data over time during actual operation of the engine 10 (step S12). The waveform data sequentially acquired during operation of the engine 10 includes a set of in-cylinder pressure waveform data 31 of the engine 10 (see FIG. 1) and vibration waveform data 32 of the engine 10, as shown in FIG. 9. The arithmetic device 20 then acquires real-time transfer function data based on the acquired waveform data, and stores the acquired transfer function data in the storage unit 25 as second information 52.

[0046] As a method of acquiring the transfer function data, for example, there is a method of acquiring vibration input data of the in-cylinder pressure waveform and output vibration data of the vibration waveform from the difference between real-time waveform data and the first waveform data 41 acquired in advance in step S11, and acquiring the transfer function data (second information 52) by dividing these data. Alternatively, there is a method of acquiring vibration input data of the in-cylinder pressure waveform and output vibration data of the vibration waveform from the difference between data of a first measurement period and data of a second measurement period subsequent to the first measurement period, among the real-time waveform data, and acquiring the transfer function data (second information 52) by dividing these data.

[0047] Since misfires are not intentionally caused during operation of the engine 10, the two waveform data to be subtracted in step S12 should both be waveform data during steady operation. In that case, the two equivalent waveform data cancel each other out, so the obtained vibration input data and output vibration data are not significant. Therefore, the second information 52 obtained from the vibration input data and output vibration data usually has a spectrum that is completely different from that of the first information 51.

[0048] On the other hand, if misfire occurs in the engine 10 at a certain timing during operation of the engine 10, one of the two waveform data to be subtracted will be waveform data during normal operation, and the other will be waveform data during misfire (abnormal operation). In that case, the obtained vibration input data and output vibration data will have impulse-like vibration waveforms as in Fig. 5. Therefore, the second information 52 obtained from the vibration input data and output vibration data will be similar to the first information 51 obtained by intentionally causing a misfire.

[0049] Therefore, the arithmetic device 20 compares the second information 52 sequentially acquired in real time with the first information 51 stored in advance to determine whether or not there is an abnormality in the engine 10 during operation (step S13). For example, in step S13, the arithmetic device 20 acquires a similarity between the spectrum of the second information 52 and the spectrum of the first information 51 (step S13a), determines whether or not the obtained similarity is equal to or greater than a preset threshold (step S13b), and determines that there is an abnormality in the engine 10 during operation if the obtained similarity is equal to or greater than the preset threshold (step S13c), and determines that there is no abnormality in the engine 10 during operation if the obtained similarity is less than the threshold (step S13d). When it is determined that there is an abnormality in the engine 10 during operation, the arithmetic device 20 notifies the abnormality via the output unit 23, or transmits a notification of the abnormality to a preset destination via the communication unit 24.

[0050] In step S13a, the calculation device 20 performs template matching processing on the spectrum of the second information 52 using the spectrum of the first information 51 as a template, for example, to find a similarity. The calculation device 20 performs the above steps S11 to S13 every time waveform data is acquired over time, thereby making it possible to monitor in real time whether or not there is an abnormality in the engine 10 during operation.

[0051] This completes the process of the method for detecting an abnormality in the engine 10 during operation.

[0052] The arithmetic device 20 may perform the above steps S11 to S13 for each cylinder 11 of the engine 10. In this case, it is possible to determine whether or not a misfire (abnormality) has occurred in each cylinder 11 while the engine 10 is operating.

[0053] (effect) The method for acquiring the natural frequency of the engine 10 according to the first embodiment of the present disclosure includes a step S1 of acquiring first waveform data 41 during steady operation of the engine 10, a step S2 of acquiring second waveform data 42 during transient non-steady operation of the engine 10, a step S3 of acquiring information indicating vibration characteristics of the engine 10 by comparing the first waveform data 41 with the second waveform data 42, and a step S4 of acquiring the natural frequency of the engine 10 during operation based on the information indicating the vibration characteristics. According to the present disclosure, the difference between the steady operation state and the transient non-steady operation state can be extracted by comparing the first waveform data 41 with the second waveform data 42. That is, even while the engine 10 is operating, a change in the transient vibration state occurring in the engine 10 can be grasped. This change in the transient vibration state shows vibration characteristics similar to a vibration response (impulse response) in a hammering test performed when the engine 10 is stopped. As a result, the natural frequency of the engine 10 during operation can be acquired based on the obtained information indicating the vibration characteristics of the engine 10.

[0054] The method for acquiring the natural frequency of the engine 10 according to the second aspect of the present disclosure is the method for acquiring the natural frequency of the engine 10 according to the first aspect, in which the second waveform data 42 includes data of a state in which an instantaneous abnormality occurs in the engine 10 during operation, and the step S3 of acquiring information indicating the vibration characteristics of the engine 10 includes extracting an impulse-like vibration waveform caused by the instantaneous abnormality by the difference between the first waveform data 41 and the second waveform data 42. According to the present disclosure, the impulse-like vibration waveform caused by the instantaneous abnormality is extracted by the difference between the first waveform data 41 and the second waveform data 42, so that an impulse-like vibration waveform that is similar to a vibration response (impulse response) in a hammering test performed when the engine 10 is stopped can be obtained. Therefore, according to the present disclosure, the natural frequency of the engine 10 during operation can be acquired with high accuracy.

[0055] The method for acquiring the natural frequency of the engine 10 according to the third aspect of the present disclosure is the method for acquiring the natural frequency of the engine 10 according to the second aspect, and the momentary abnormality of the engine 10 during operation includes the occurrence of a misfire in the engine 10. According to the present disclosure, an impulse-like vibration waveform equivalent to a vibration response (impulse response) in a hammering test can be extracted using the second waveform data 42 when a misfire occurs in the engine 10. That is, by intentionally causing a cycle in which the engine 10 misfires among the engine cycles repeated in a very short time, the second waveform data 42 at the moment when the in-cylinder pressure does not rise can be obtained. When the difference between the second waveform data 42 and the first waveform data 41 is taken, the vibration during the period when no misfire occurs is canceled because it is almost common to both waveform data, and the difference at the moment when the misfire occurs is extracted, so that an impulse-like vibration waveform having sufficient equivalence to the impulse response by the hammering test can be easily obtained.

[0056] A method for acquiring the natural frequency of the engine 10 according to a fourth aspect of the present disclosure is the method for acquiring the natural frequency of the engine 10 according to any one of the first to third aspects, and the first waveform data 41 and the second waveform data 42 each include a set of the in-cylinder pressure waveform data 31 (31a, 31b) of the engine 10 and the vibration waveform data 32 (32a, 32b) of the engine 10. According to the present disclosure, the in-cylinder pressure waveform data 31 (31a, 31b) which is waveform data of the excitation force (pressure change in the cylinder 11) that vibrates the engine 10, and the vibration waveform data 32 (32a, 32b) observed in the engine 10 as the excitation force acts on the engine 10 are obtained. That is, the input waveform and the output waveform of the excitation force in the test subject, the engine 10, are obtained. Based on these input / output relationships, information indicating the vibration characteristics of the engine 10 can be acquired with high accuracy.

[0057] A method for acquiring the natural frequency of the engine 10 according to a fifth aspect of the present disclosure is the method for acquiring the natural frequency of the engine 10 according to the fourth aspect, and the step S3 of acquiring information indicating the vibration characteristics of the engine 10 includes a step S3a of acquiring vibration input data 43 based on the difference between the in-cylinder pressure waveform data (31a, 31b) of the first waveform data 41 and the second waveform data 42, a step S3b of acquiring output vibration data 44 based on the difference between the vibration waveform data (32a, 32b) of the first waveform data 41 and the second waveform data 42, and a step S3c of acquiring transfer function data 45 of the engine 10 based on the vibration input data 43 and the output vibration data 44 as information indicating the vibration characteristics of the engine 10. According to the present disclosure, a transfer function (transfer function data 45) of the engine 10 during operation is acquired from the input / output relationship between the vibration input data 43 and the output vibration data 44. Based on this transfer function data 45, the natural frequency of the engine 10 during operation can be easily obtained.

[0058] The method for detecting an abnormality in the engine 10 according to the sixth aspect of the present disclosure includes a step S11 of acquiring first information 51 (i.e., transfer function data 45) indicating the vibration characteristics of the engine 10 during abnormal operation by comparing the first waveform data 41 during normal operation of the engine 10 with the second waveform data 42 during transient abnormal operation of the engine 10, a step S12 of acquiring second information 52 indicating the vibration characteristics of the engine 10 based on waveform data acquired sequentially during operation of the engine 10, and a step S13 of determining the presence or absence of an abnormality in the engine 10 during operation based on a comparison between the acquired second information 52 and the first information 51. According to the present disclosure, the first waveform data 41 and the second waveform data 42 can be acquired in advance by a test run or the like, and the first information 51 indicating the vibration characteristics of the engine 10 when an abnormality occurs can be acquired in advance. Then, the second information 52 during normal operation is obtained by acquiring a plurality of waveform data sequentially during normal operation of the engine 10 and comparing the waveform data. Then, depending on whether the obtained second information 52 is similar to the previously acquired first information 51, it can be determined whether there is an abnormality in the engine 10. Since both the first information 51 and the second information 52 are based on waveform data of the engine 10 while it is running, not while it is stopped, it is possible to detect an abnormality in the engine 10 without being affected by the deviation in the natural frequency of the engine 10 between when the engine 10 is stopped and when it is running.

[0059] A calculation device according to a seventh aspect of the present disclosure includes a communication unit (data acquisition unit) 24 that acquires first waveform data 41 during steady operation of engine 10 and second waveform data 42 during transient unsteady operation of engine 10, a storage unit 25 that stores the first waveform data 41 and the second waveform data 42, and a control unit 21 that acquires information indicating vibration characteristics of engine 10 by comparing the first waveform data 41 with the second waveform data 42, and acquires the natural frequency of engine 10 during operation based on the information indicating the vibration characteristics. According to the present disclosure, the natural frequency of engine 10 during operation can be acquired.

[0060] A program according to an eighth aspect of the present disclosure causes a computer (arithmetic device 20) to execute a step S1 of acquiring first waveform data 41 during steady operation of engine 10, a step S2 of acquiring second waveform data 42 during transient unsteady operation of engine 10, a step S3 of acquiring information indicating vibration characteristics of engine 10 by comparing the first waveform data 41 with the second waveform data 42, and a step S4 of acquiring the natural frequency of engine 10 during operation based on the information indicating the vibration characteristics. According to the present disclosure, the natural frequency of engine 10 during operation can be acquired.

[0061] Although the embodiment of the present disclosure has been described above, the embodiment is not limited by the contents of this embodiment. In addition, the above-mentioned components include those that a person skilled in the art can easily imagine, those that are substantially the same, and those that are within the so-called equivalent range. Furthermore, the above-mentioned components can be appropriately combined. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the gist of the above-mentioned embodiment.

[0062] In particular, in the first and second embodiments, the second waveform data 42 is data of a state where the engine 10 misfires, but the present invention is not limited to the above-mentioned embodiments. It is sufficient to obtain waveform data of the engine 10 in a process where an operating state different from the steady state occurs temporarily and then returns to the steady state, and the data is not limited to a misfire of the engine 10. The shorter the period of time in which such an operating state different from the steady state ends, the more preferable the data obtained by comparing (taking a difference between) the first waveform data 41 and the second waveform data 42 is, since it approximates an impulse input (response). The second waveform data 42 may be data obtained when the ignition timing is intentionally shifted in any one cycle of the engine 10, for example.

[0063] In the above first and second embodiments, the information (first information, second information) indicating the vibration characteristics of the engine is transfer function data, but the information is not limited to the above-mentioned embodiments. The information (first information, second information) indicating the vibration characteristics of the engine may be, for example, a set of vibration input data 43 and output vibration data 44. [Explanation of symbols]

[0064] 10 Engine 20 Calculation device (computer) 21 Control section 24 Communication section (data acquisition section) 25 Memory section 31, 31a, 31b Cylinder pressure waveform data 32, 32a, 32b Vibration waveform data 41 First Waveform Data 42 Second Waveform Data 43 Vibration input data 44 Output vibration data 45 Transfer function data 51 1st information 52 Second information

Claims

1. acquiring first waveform data during steady-state operation of the engine; acquiring second waveform data during a transient, unsteady operation of the engine; obtaining information indicative of a vibration characteristic of the engine by comparing the first waveform data with the second waveform data; acquiring a natural frequency of the engine during operation based on information indicating the vibration characteristics; A method for acquiring the natural frequency of an engine comprising:

2. The second waveform data includes data of a state in which a momentary abnormality occurs in the engine during operation, The step of acquiring information indicating a vibration characteristic of the engine includes extracting an impulse-like vibration waveform caused by the momentary abnormality based on a difference between the first waveform data and the second waveform data. The method for acquiring a natural frequency of an engine according to claim 1 .

3. The momentary abnormality of the engine during operation includes the occurrence of a misfire in the engine. The method for acquiring the natural vibration frequency of an engine according to claim 2.

4. The first waveform data and the second waveform data each include a pair of in-cylinder pressure waveform data of the engine and vibration waveform data of the engine. The method for acquiring the natural frequency of an engine according to any one of claims 1 to 3.

5. The step of obtaining information indicative of a vibration characteristic of the engine includes: acquiring vibration input data based on a difference between the in-cylinder pressure waveform data of the first waveform data and the in-cylinder pressure waveform data of the second waveform data; obtaining output vibration data based on a difference between the vibration waveform data of the first waveform data and the vibration waveform data of the second waveform data; acquiring transfer function data of the engine based on the vibration input data and the output vibration data as information indicating vibration characteristics of the engine, The method for acquiring the natural vibration frequency of an engine according to claim 4.

6. acquiring first information indicating vibration characteristics of the engine during abnormal operation by comparing first waveform data during steady operation of the engine with second waveform data during transient abnormal operation of the engine; acquiring second information indicative of a vibration characteristic of the engine based on waveform data sequentially acquired during operation of the engine; determining whether or not an abnormality exists in the engine during operation based on a comparison between the acquired second information and the acquired first information; An engine abnormality detection method comprising:

7. a data acquisition unit that acquires first waveform data during steady operation of the engine and second waveform data during transient non-steady operation of the engine; a storage unit that stores the first waveform data and the second waveform data; a control unit that acquires information indicating a vibration characteristic of the engine by comparing the first waveform data with the second waveform data, and acquires a natural frequency of the engine during operation based on the information indicating the vibration characteristic; A computing device comprising:

8. acquiring first waveform data during steady-state operation of the engine; acquiring second waveform data during a transient, unsteady operation of the engine; obtaining information indicative of a vibration characteristic of the engine by comparing the first waveform data with the second waveform data; acquiring a natural frequency of the engine during operation based on information indicating the vibration characteristics; A program that causes a computer to execute the following.

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