Noise analysis methods

Abstract

This invention provides a noise analysis method that reduces the computational load while performing electromagnetic field analysis using a wide range of components, including control units, at once. [Solution] The PU performs an electromagnetic field analysis on the ECU model alone (S14). Based on the results of the electromagnetic field analysis, the PU generates an equivalent model of the ECU by placing antennas in regions with high electric field strength and magnetic field strength (S28). The PU combines the equivalent model, the harness model, and the measurement environment model, and performs an electromagnetic field analysis on the whole (S32).

Description

Technical Field

[0001] The present invention relates to a noise analysis method.

Background Art

[0002] When electromagnetic waves from one electronic device mounted on a vehicle affect another electronic device, problems such as malfunction of the other electronic device may occur. For this reason, limits are imposed on the intensity of electromagnetic waves generated by each individual electronic device mounted on a vehicle. In order to meet these limits, when evaluating the electromagnetic waves generated by the electronic device by detecting the electromagnetic waves emitted when the electronic device mounted on the vehicle is driven using a measurement probe, a redesign is required each time an evaluation that the limit is not satisfied is made, which lengthens the vehicle development period.

[0003] Accordingly, for example, Patent Document 1 also proposes evaluating radiated electromagnetic waves by simulation. Specifically, in the technique described in this document, radiated electromagnetic waves are evaluated by electromagnetic field analysis using an ECU model, a harness model, and a measurement environment model.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] As described above, when electromagnetic field analysis is performed by combining an ECU model, a harness model, and the like, the computational load becomes excessive due to reasons such as an enormous number of meshes. For this reason, the model has to be simplified. However, simplifying the model may reduce accuracy due to oversight of specific phenomena.

Means for Solving the Problems

[0006] A noise analysis method that solves the above problems involves a computer performing a first analysis process, a generation process, a second analysis process, and an evaluation process. The first analysis process is a process that performs electromagnetic field analysis using a model of the control unit. The generation process is a process that generates an equivalent model in which noise sources are placed on the control unit based on the analysis results of the first analysis process. The second analysis process is a process that performs electromagnetic field analysis using the equivalent model, a harness model coupled to the control unit, and a measurement environment model. The evaluation process is a process that evaluates the noise radiation of the control unit based on the analysis results of the second analysis process. [Effects of the Invention]

[0007] This method allows for electromagnetic field analysis using a wide range of components, including control units, simultaneously, while reducing the computational load. Furthermore, it helps to suppress a decrease in accuracy. [Brief explanation of the drawing]

[0008] [Figure 1] This is a block diagram of a noise evaluation device. [Figure 2] Figure 1 is a flowchart showing the procedure of the processing performed by the evaluation device. [Figure 3] This is a plan view showing an example of an ECU model. [Figure 4] This diagram illustrates a method for generating equivalent models. [Modes for carrying out the invention]

[0009] The following describes one embodiment with reference to the drawings. "Configuration of a noise evaluation device" Figure 1 shows a noise evaluation device.

[0010] The evaluation device 10 is configured to evaluate electromagnetic radiation noise from an electronic control unit (hereinafter referred to as ECU) mounted on a vehicle. The evaluation device 10 includes a PU 12 and a storage device 14. The PU 12 is a processing unit that executes software processing such as a CPU or GPU. The storage device 14 may be an electrically unrewritable non-volatile memory. Alternatively, the storage device 14 may be an electrically rewritable non-volatile memory, or a storage medium such as a disk medium.

[0011] In particular, the storage device 14 may include multiple types of devices. The storage device 14 stores an evaluation program 14a. The evaluation program 14a defines commands for executing processing to evaluate electromagnetic radiation noise from the ECU. The storage device 14 also stores evaluation target data 14b.

[0012] The evaluation data 14b includes, as an example, 3D CAD data of the vehicle 20. The evaluation data 14b also includes 3D CAD data of the ECU 30, which is the target of evaluation for radiated noise according to this embodiment. The evaluation data 14b also includes, as an example, 3D CAD data of the harness 32 connected to the ECU 30. As data related to the ECU 30, the evaluation data 14b includes data related to the motor 40, which is the control target of the ECU 30, and the drive circuit 42 of the motor 40, as schematically shown at the bottom of Figure 1. In this embodiment, as an example, electromagnetic noise generated by driving the motor 40 is evaluated.

[0013] Furthermore, the evaluation data 14b also includes data related to the measurement probe used when electromagnetic noise is actually measured. This data defines the positional relationship between the measurement probe and the ECU 30, etc.

[0014] "Regarding the evaluation process of noise" Figure 2 shows the procedure for processing noise evaluation. The process shown in Figure 2 is achieved by the PU 12 executing the evaluation program 14a stored in the memory device 14. In the following, the step number of each process is represented by a number preceded by "S".

[0015] In the series of processes shown in Figure 2, the PU12 first sets the noise source (S10). In this embodiment, as an example, the drive circuit 42 of the motor 40 is set as the noise source. At this time, the PU12 also sets the switching pattern of the drive circuit 42. The process related to setting the switching pattern may be a process in which the PU12 reads out data that defines the switching pattern, which is pre-stored in the evaluation target data 14b.

[0016] Next, PU12 generates a model of ECU30 based on the data about ECU30 included in the evaluation data 14b (S12). Here, ECU30 may, for example, include a multilayer wiring board. In that case, PU12 may simplify the model to the extent of projecting the electronic components on the multilayer wiring board perpendicularly onto a single board surface. Figure 3 shows an example of a model of ECU30.

[0017] PU12 performs electromagnetic field analysis using the model of ECU30 generated by the processing in S12 (S14). One example of this electromagnetic field analysis method is the method of moments. In electromagnetic field analysis using the method of moments, PU12 may divide ECU30 into a mesh. The processing in S14 includes discrete Fourier transform processing to obtain the electric field strength spectrum and magnetic field strength spectrum for each region of ECU30.

[0018] The upper part of Figure 4 shows the electric field strength distribution at a given frequency. In the example shown in Figure 4, a higher density of dots indicates a stronger electric field. Returning to Figure 2, PU12 assigns "1" to both variables i and j (S16). Variable i is used to specify the frequency for the electric field strength and magnetic field strength. Variable j is used to specify the region of ECU30.

[0019] Next, the PU 12 sets an electric field strength threshold Seth(i,j) and a magnetic field strength threshold Smth(i,j) related to the frequency f(i) (S18). The electric field strength threshold Seth and the magnetic field strength threshold Smth can be set independently for each frequency f. Therefore, for example, the electric field strength threshold Seth(1,j) related to the first frequency f(1) and the electric field strength threshold Seth(2,j) related to the second frequency f(2) are different from each other. Here, the variable j indicating the region is the same. The electric field strength threshold Seth and the magnetic field strength threshold are set so as to satisfy required elements that may differ for each frequency.

[0020] The electric field strength threshold Seth and the magnetic field strength threshold Smth can be set independently for each region of the ECU 30. As an example, the PU 12 may set the electric field strength threshold Seth and the magnetic field strength threshold Smth such that a value in a region close to the connection point between the ECU 30 and the harness 32 is smaller than a value in a region far therefrom. This setting is made in consideration of the fact that the connection point with the harness 32 has a small electromagnetic shielding effect by the housing of the ECU 30.

[0021] The PU 12 executes a process of comparing the magnitude of the electric field strength Se and the electric field strength threshold Seth for the frequency f(i) in the region defined by the variable j (S20). Further, the PU 12 executes a process of comparing the magnitude of the magnetic field strength Sm and the magnetic field strength threshold Smth for the frequency f(i) in the region defined by the variable j (S20).

[0022] The PU 12 determines whether or not the logical AND of the fact that the variable i is a predetermined value N and the fact that the variable j is a predetermined value M is true (S22). The predetermined value N is the number of types of frequencies for which the electric field strength and the magnetic field strength are to be considered. The predetermined value M is the number of regions of the ECU 30.

[0023] When determining that the logical AND is false (S22: NO), the PU 12 updates the combination of the variables i and j to a combination that has not been adopted yet (S24), and returns to the process of S18.

[0024] On the other hand, if PU12 determines that the above logical AND is true (S22: YES), it extracts the region that exceeds the electric field strength threshold Seth and the region that exceeds the magnetic field strength threshold Smth (S26). Then PU12 generates an equivalent model of ECU30 based on the results of the processing in S14 (S28).

[0025] Here, PU12 places antennas in the region where the electric field strength threshold Seth and the magnetic field strength threshold Smth are exceeded within the region where ECU30 exists, as an example. The antennas are sources of electromagnetic waves. The antennas may be models of electric dipoles or antennas that generate loop currents. However, it is not essential to place a dedicated antenna model. For example, the conductor shape within the region of ECU30 may be partially extracted and used as an electromagnetic wave source. To make a partially extracted conductor an electromagnetic wave source, a simulation can be performed by applying a voltage or current to the partially extracted conductor. Note that this is also considered an antenna placement.

[0026] The equivalent model of ECU30 is a model in which antennas are placed as sources of electromagnetic waves in the region where ECU30 exists. PU12 should set the intensity of the electromagnetic waves generated by each antenna according to the electric field strength and magnetic field strength obtained by the processing in S14. Specifically, PU12 should, for example, configure the antennas to oscillate frequency noise of their electric field strength and magnetic field strength at frequencies exceeding a threshold. More precisely, PU12 should, for example, place antennas that have a frequency and generate a magnetic field of approximately Sm at frequencies where the magnetic field strength Sm exceeds the magnetic field strength threshold Smth.

[0027] The lower part of Figure 4 shows an example where antennas 50 and 52 are positioned according to the electric field strength distribution described in the upper part of Figure 4. The example shown in the lower part of Figure 4 is one in which two antennas are positioned because there are two regions where the threshold is exceeded.

[0028] Returning to Figure 2, PU12 generates a harness model that models the harness 32, and a measurement environment model that models the area around the ECU 30 and harness 32, including the ground plane and power supply (S30). Note that the process in S30 includes setting the placement location of the measurement probe by PU12.

[0029] Then, PU12 combines the ECU equivalent model with the harness model and the measurement environment model to perform electromagnetic field analysis (S32). Here, as an example, PU12 performs electromagnetic field analysis using the FDTD method.

[0030] Based on the results of the electromagnetic field analysis, PU12 determines whether the electric field strength and magnetic field strength at the measurement probe placement location exceed the threshold (S34). Here, the measurement probe placement location is the location where the intensity of the radiated noise from ECU30 is a concern. The electric field strength threshold is set independently for each frequency. Similarly, the magnetic field strength threshold is set independently for each frequency.

[0031] PU12 notifies (S36) if at least one of the electric field strength and magnetic field strength at at least one frequency exceeds a threshold (S34: NO). Furthermore, if PU12 makes a positive determination in processing S34, or if it completes processing S36, it will temporarily terminate the series of processes shown in Figure 2.

[0032] "The operation and effects of this embodiment" PU12 performs electromagnetic field analysis on the ECU30 model alone. Based on the results of the electromagnetic field analysis on the ECU30 alone, PU12 converts the ECU30 into an equivalent model of the ECU30 with noise sources placed on it. PU12 then performs electromagnetic field analysis on the entire equivalent model, harness model, and measurement environment model. This electromagnetic field analysis reduces the number of meshes compared to using the ECU30 model before conversion to the equivalent model. Therefore, it suppresses the increase in computational load, allowing electromagnetic field analysis to be performed without simplifying the harness model or measurement environment model. As a result, it is possible to analyze the noise radiation from the ECU30 and the propagation of noise in the harness, etc., with high accuracy.

[0033] According to the embodiment described above, the following effects and benefits can be obtained. (1) PU12 generates an equivalent model by placing noise sources in the region where the electric field strength Se is greater than or equal to the electric field strength threshold Seth and in the region where the magnetic field strength Sm is greater than or equal to the magnetic field strength threshold Smth. This makes it possible to generate an equivalent model suitable for evaluating whether the radiated noise of ECU30 meets the specifications.

[0034] (2) PU12 generates an equivalent model by placing noise sources in a region where the electric field strength Se is greater than or equal to the electric field strength threshold Seth and in a region where the magnetic field strength Sm is greater than or equal to the magnetic field strength threshold Smth for at least one frequency. This makes it possible to generate an equivalent model suitable for evaluating whether the radiated noise satisfies the requirements for each frequency.

[0035] (3) PU12 sets the electric field strength threshold Seth and the magnetic field strength threshold Smth to different values ​​for frequency f(1) and frequency f(2). This allows for accurate evaluation of whether the radiated noise falls within the acceptable range, even when the permissible upper limit of the radiated noise intensity differs with frequency.

[0036] (4) PU12 sets the electric field strength threshold Seth and magnetic field strength threshold Smth in the region near the harness connection point to smaller values ​​than in other regions. This allows for proper evaluation of radiated noise from regions where the electromagnetic shielding effect of ECU30 is weak.

[0037] <Other Embodiments> Furthermore, this embodiment can be implemented with the following modifications. This embodiment and the following modifications can be combined with each other to the extent that they do not contradict each other technically.

[0038] "Regarding the first analysis process (S14)" • It is not mandatory for the first analysis process to be an electromagnetic field analysis using the method of moments. The first analysis process may be an electromagnetic field analysis using, for example, the FDTD method. Alternatively, the first analysis process may be an electromagnetic field analysis using the FEM method.

[0039] • It is not essential to determine the electric field strength and magnetic field strength in the first analysis process. For example, depending on the requirements of the emission evaluation, the first analysis process may be limited to determining only the magnetic field strength.

[0040] "Regarding the second analysis process (S32)" • It is not mandatory for the second analysis process to be an electromagnetic field analysis using the FDTD method. The second analysis process may be an electromagnetic field analysis using, for example, the method of moments. Alternatively, the second analysis process may be an electromagnetic field analysis using the FEM method.

[0041] • It is not essential to determine the electric field strength and magnetic field strength through the second analysis process. For example, depending on the requirements of the emission evaluation, the second analysis process may be limited to determining only the magnetic field strength.

[0042] "Regarding the relationship between the first and second analysis processes" It is not necessary for the first and second analysis processes to be electromagnetic field analyses using different methods.

[0043] "Regarding the generation process (S16-S26)" It is not required that the threshold in the area near the connector be set to a lower value than the threshold in other areas.

[0044] The generation process does not necessarily have to include a process of placing noise sources in regions where the noise intensity is above a threshold. The generation process may, for example, include a process of placing noise sources in up to a predetermined number of regions, starting with the region with the highest noise intensity.

[0045] "Regarding the control unit (30)" • In the above embodiment, an example was shown in which the noise when a single drive circuit 42 is driven is the target of evaluation, but it is not limited to this. For example, the ECU 30 may be one device each for the steering system, drive system, etc., or it may be a device divided by area of ​​the vehicle, such as the front right, front left, rear right, and rear left of the vehicle. If the ECU 30 is such a device, it is a large device and has multiple drive circuits. In such cases, the computational load required for electromagnetic field analysis of the ECU 30 becomes large, making it even more difficult to perform electromagnetic field analysis using the ECU 30 model and harness model, etc., without generating an equivalent model. Therefore, the advantage of generating an equivalent model in the manner of the above embodiment is particularly great.

[0046] "About computers" The computer that evaluates noise is not limited to one that performs various processes using a PU. The computer may, for example, include a dedicated hardware circuit such as an ASIC that performs at least a part of the processes performed in the above embodiment. That is, the computer may include any of the following processing circuits (a) to (c): (a) A processing circuit comprising a processing unit that performs all of the above processes according to a program, and a program storage device such as a memory device that stores the program. (b) A processing circuit comprising a processing unit and a program storage device that perform a part of the above processes according to a program, and a dedicated hardware circuit that performs the remaining processes. (c) A processing circuit comprising a dedicated hardware circuit that performs all of the above processes. Here, there may be multiple software execution devices comprising processing units and program storage devices, or multiple dedicated hardware circuits.

[0047] <Summary of this embodiment> A noise analysis method comprising: a computer performing a first analysis process, a generation process, a second analysis process, and an evaluation process; the first analysis process being a process of performing electromagnetic field analysis using a model of a control unit; the generation process being a process of generating an equivalent model in which a noise source is placed on the control unit based on the analysis results of the first analysis process; the second analysis process being a process of performing electromagnetic field analysis using the equivalent model, a harness model coupled to the control unit, and a measurement environment model; and the evaluation process being a process of evaluating the noise radiation of the control unit based on the analysis results of the second analysis process.

[0048] In the above method, prior to performing electromagnetic field analysis using the control unit, the harness model connected to the control unit, and the environment model, an electromagnetic field analysis of the control unit is performed by a first analysis process. Then, an equivalent model is generated in which noise sources are placed on the control unit by a generation process. By using this equivalent model in the second analysis process, the number of meshes can be reduced in the second analysis process compared to using the control unit model used in the first analysis process. Therefore, the computational load can be reduced while performing electromagnetic field analysis using a wide range of components, including the control unit, at once.

[0049] The analysis results obtained by the first analysis process include the noise intensity distribution in the control unit, and the generation process is a noise analysis method that includes a process of placing noise sources in regions where the noise intensity is above a threshold.

[0050] In the method described above, the noise source is placed in the region where the noise intensity exceeds a threshold, and an electromagnetic field analysis combining the harness model and the circuit board model is performed. This allows for an appropriate evaluation of whether the radiated noise of the control unit meets the specified requirements.

[0051] The intensity distribution is a frequency-specific distribution, and the generation process includes a noise analysis method that places the noise source in a region where the noise intensity is greater than or equal to a threshold for at least one frequency.

[0052] The above method allows for a proper evaluation of whether the noise intensity at all frequencies meets the specified criteria by placing the noise source in a region where the noise intensity at at least one frequency is above a threshold.

[0053] A noise analysis method in which the threshold value is set such that the value for a first frequency and the value for a second frequency are different. Regulations regarding radiated noise from control units sometimes specify upper limits on noise intensity for each frequency. Therefore, the above method allows for accurate determination of whether the noise intensity meets the criteria by setting different threshold values ​​for the first frequency and the second frequency.

[0054] A noise analysis method in which the threshold value is a value in a first region of the control unit that is smaller than the value in a second region, and the first region is a region closer to the harness connection point than the second region.

[0055] In areas close to the aforementioned connection points, the magnetic shielding provided by the control unit's casing is ineffective, making it susceptible to external noise interference even at relatively low noise levels. Therefore, the above method allows for a more appropriate evaluation of the impact of radiated noise from the control unit by setting a smaller threshold value in the region close to the connection points. [Explanation of Symbols]

[0056] 10…Evaluation device

Claims

1. The computer performs the first analysis process, the generation process, the second analysis process, and the evaluation process. The first analysis process described above is a process that performs electromagnetic field analysis using a model of the control unit. The generation process is a process that generates an equivalent model in which a noise source is placed in the control unit based on the analysis results from the first analysis process. The second analysis process is a process that performs electromagnetic field analysis using the equivalent model, the harness model coupled to the control unit, and the measurement environment model. The evaluation process is a noise analysis method that evaluates the noise radiation of the control unit based on the analysis results of the second analysis process.

2. The analysis results obtained by the first analysis process include the noise intensity distribution in the control unit. The noise analysis method according to claim 1, wherein the generation process includes a process of placing a noise source in a region where the noise intensity is above a threshold.

3. The aforementioned intensity distribution is a distribution for each frequency, The noise analysis method according to claim 2, wherein the generation process includes a process of arranging the noise source in a region where the intensity of the noise is greater than or equal to a threshold for at least one frequency.

4. The noise analysis method according to claim 3, wherein the threshold value is set to different values ​​for a first frequency and a second frequency.

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