JP5724668B2 - In-vehicle radio noise reduction system - Google Patents

Description

  The present invention relates to an in-vehicle radio noise reduction system, and in particular, when a switching drive is performed at a predetermined frequency in a power conversion device, a beat sound generated when a harmonic wave is mixed into a radio broadcast wave is in an audio band. The present invention relates to an in-vehicle radio noise reduction system suitable for suppressing output as radio noise.

  2. Description of the Related Art Conventionally, an in-vehicle radio noise reduction system that is mounted on a vehicle having a power conversion device that performs switching drive and that reduces radio noise superimposed on radio broadcast waves is known (see, for example, Patent Document 1). When switching driving at the predetermined frequency f0 is performed in the power converter, harmonics based on the frequency f0 may be mixed into the radio broadcast wave and interfere with the radio broadcast wave. When such interference occurs, the difference frequency between the harmonic and the radio broadcast wave is generated as a beat sound, and the beat sound is output as radio noise in the voice band. In the system described above, the resonance frequency of the switching drive is shifted by adjusting the resonance circuit. When the resonance frequency is shifted, interference between the harmonic and the radio broadcast wave is eliminated, so that radio noise is reduced.

JP 2010-119240 A

  However, in the system described above, in order to reduce radio noise, it is necessary to shift the resonance frequency on the power conversion device side, which complicates the configuration of the power conversion device.

  The present invention has been made in view of the above-described points, and is capable of reducing radio noise based on a beat sound generated when switching driving is performed at a predetermined frequency in a power conversion device with a simple configuration. An object is to provide a radio noise reduction system.

The above object is a radio noise reduction system mounted on a vehicle having a radio receiver that receives radio broadcast waves and a power conversion device that performs switching drive at a predetermined frequency, and is received by the radio receiver. A transforming means for Fourier transforming an audio signal extracted from a radio broadcast wave to a frequency domain ; and a frequency domain obtained by the transforming means having a strength higher than a predetermined threshold with respect to the strength of an adjacent frequency on the low frequency side. peak frequency has high strength above a predetermined threshold value and relative intensity of frequencies adjacent the high-frequency side has, or against the one of the intensity of adjacent frequency intensity or high frequency side of the adjacent frequency in the low frequency side A peak frequency detecting means for detecting a peak frequency having an intensity higher than a predetermined threshold, and a peak frequency detected by the peak frequency detecting means. An equalizer means for lowering the output intensity at the peak frequency are achieved by vehicle-mounted radio noise reduction system comprising: a.

  ADVANTAGE OF THE INVENTION According to this invention, the radio noise based on the beat sound generated when switching drive is performed with a predetermined frequency in a power converter device can be reduced with a simple configuration.

It is a block diagram of the in-vehicle radio noise reduction system which is one Example of this invention. It is a figure showing an example of the relationship between the PWM fundamental wave based on the voltage conversion by PWM control in a power converter device, the harmonic of the PWM fundamental wave, and the carrier wave of a radio broadcast wave. It is a figure showing an example of the relationship between the frequency and intensity | strength of the audio | voice signal with which noise is superimposed. It is a flowchart of an example of the control routine performed in the vehicle-mounted radio noise reduction system of a present Example. It is a figure for demonstrating the method to reduce the radio noise in the vehicle-mounted radio noise reduction system of a present Example.

  Hereinafter, specific embodiments of an in-vehicle radio noise reduction system according to the present invention will be described with reference to the drawings.

  FIG. 1 shows a configuration diagram of an in-vehicle radio noise reduction system 10 according to an embodiment of the present invention. The in-vehicle radio noise reduction system 10 according to the present embodiment is mounted on a vehicle such as a hybrid vehicle or an electric vehicle. This vehicle has a power conversion device 12 that performs switching drive of a switching element such as an IGBT. The power converter 12 includes, for example, a DC-DC converter or an inverter that performs voltage conversion between the in-vehicle battery and the drive motor, and performs PWM (Pulse Width Modulation) control when performing such voltage conversion. Do. Such voltage conversion by PWM control is performed at a predetermined frequency f0.

  The vehicle also includes a radio receiver 14 that receives radio broadcast waves (for example, AM radio broadcast waves having a medium wave band of 535 kHz to 1605 kHz). The radio receiver 14 has a demodulation circuit 18 that demodulates the received radio wave received by the reception antenna 16 in accordance with channel selection. The demodulation circuit 18 converts and extracts an audio signal from the radio broadcast wave by demodulating the received radio wave.

  The vehicle also has an audio amplifier 20 that is electrically connected to the radio receiver 14. The audio amplifier 20 includes an equalizer 22 to which an audio signal that is the output of the demodulation circuit 18 is input, and an amplifier circuit 24 to which the output of the equalizer 22 is input. The equalizer 22 is an acoustic device that changes the frequency characteristics of an input audio signal, and can output audio after enhancing or reducing an arbitrary frequency component. The amplifier circuit 24 amplifies and outputs the audio signal output from the equalizer 22. The amplifying circuit 24 is electrically connected to a vehicle-mounted speaker 26 that outputs sound toward the vehicle interior. The in-vehicle speaker 26 outputs sound according to the sound signal from the amplifier circuit 24.

  FIG. 2 shows a PWM fundamental wave (frequency is a predetermined frequency f0) based on voltage conversion by PWM control in the power converter 12 and a harmonic of the PWM fundamental wave (frequency is an integer multiple of f0). ) And a carrier wave of the radio broadcast wave (frequency is a predetermined frequency F0). FIG. 3 is a diagram showing an example of the relationship between the frequency and intensity of an audio signal in which noise is superimposed on the frequency Fn.

  In the present embodiment, as described above, voltage conversion by PWM control in the power conversion device 12 is performed at a predetermined frequency f0. In this case, a harmonic (frequency is an integer multiple of f0) based on the predetermined frequency f0 is generated. When this harmonic wave is mixed into the radio broadcast wave and interferes with the radio broadcast wave, for example, as shown in FIG. 2, a difference frequency ΔFn between the harmonic wave of frequency n · f0 and the radio broadcast wave of frequency F0 is generated as a beat sound. Thus, the beat sound may be output as radio noise in the voice band (audible band) (specifically, radio noise of frequency Fn in FIG. 3). Therefore, in this embodiment, radio noise based on PWM control in the power converter 12 is reduced as described below.

  Hereinafter, the characteristic configuration and operation of the in-vehicle radio noise reduction system 10 of this embodiment will be described. FIG. 4 shows a flowchart of an example of a control routine executed in the in-vehicle radio noise reduction system 10 of the present embodiment. FIG. 5 is a diagram for explaining a technique for reducing radio noise in the in-vehicle radio noise reduction system 10 of the present embodiment. 5A shows the frequency characteristics of the signal input to the receiving antenna 16 of the radio receiver 14, FIG. 5B shows the frequency characteristics of the equalizer 22 itself, and FIG. 5C shows the frequency characteristics. Indicates frequency characteristics of signals output from the vehicle-mounted speaker 26, respectively.

  In the in-vehicle radio noise reduction system 10 of this embodiment, the radio receiver 14 has a peak detection circuit 30 that is electrically connected to the demodulation circuit 18. The peak detection circuit 30 first expands the audio signal extracted by the demodulation circuit 18 in the frequency domain by Fourier transform, and performs sampling at a predetermined frequency (for example, the frequency is... F (n -2), F (n-1), F (n), F (n + 1), F (n + 2), F (n + 3), ... where n is a positive value indicating the frequency at which noise is superimposed. It ’s a number.) Then, the peak detection circuit 30 detects the difference frequency by comparing the reception intensity at each sampled frequency with the reception intensity at the adjacent frequency, and compares the detected difference frequencies with each other. The peak frequency with the maximum intensity is detected.

  The radio receiver 14 includes a communication IC 32 that is electrically connected to the peak detection circuit 30. The communication IC 32 also determines whether the intensity at the peak frequency detected by the peak detection circuit 30 is higher than a predetermined threshold value with respect to the intensity of the frequency adjacent to the peak frequency in the developed frequency region. The predetermined threshold is a minimum intensity at which it can be determined that a beat sound having a difference frequency between the harmonic and the radio broadcast wave can be output as radio noise.

  The audio amplifier 20 has a communication IC 34 that is electrically connected to the equalizer 22. The communication IC 32 and the communication IC 34 are communicatively connected to each other via an in-vehicle communication line 36 such as a LAN. The communication IC 32 communicates a command to lower the output intensity at the peak frequency by the equalizer 22 to the communication IC 34 via the in-vehicle communication line 36 when the intensity at the peak frequency is equal to or greater than a predetermined threshold with respect to the intensity of the adjacent frequency. To do. The communication IC 34 receives a command from the communication IC 32. When the communication IC 34 receives a command to lower the output intensity at the peak frequency from the communication IC 32, the communication IC 34 controls the equalizer 22 to lower the output intensity at the peak frequency. The equalizer 22 changes the frequency characteristic of the audio signal supplied from the demodulation circuit 18 in accordance with control by the communication IC 34.

  In this embodiment, the radio receiver 14 demodulates the received radio wave by the demodulation circuit 18 every predetermined time, and extracts an audio signal from the radio broadcast wave (step 100). The audio signal extracted by the demodulation circuit 18 is supplied to the peak detection circuit 30. The peak detection circuit 30 Fourier-transforms the audio signal extracted by the demodulation circuit 18 into the frequency domain (step 102). When this Fourier transform is performed, reception intensity is obtained for each of a plurality of predetermined frequencies. Then, the peak detection circuit 30 detects the difference frequency by comparing the reception intensity at each sampled frequency with the reception intensity at the adjacent frequency, and compares the detected difference frequencies with each other. The peak frequency with the maximum intensity is detected.

  The communication IC 32 determines whether or not the intensity at the peak frequency detected by the peak detection circuit 30 is higher than a predetermined threshold value with respect to the intensity of the frequency adjacent to the peak frequency in the developed frequency area. In step 104, it is determined whether or not there is a peak frequency having an intensity higher than a predetermined threshold with respect to the intensity of adjacent frequencies. As a result, if it is determined that such a peak frequency does not exist, a command for maintaining or changing the equalizer 22 in a reference state in which the output intensity is not changed from the audio signal by the demodulation circuit 18 in the entire frequency region is then issued. Processing for communicating with the communication IC 34 via 36 is performed (step 106).

  When receiving the above command from the communication IC 32, the communication IC 34 controls the equalizer 22 to maintain or change the reference state. In this case, the equalizer 22 supplies the audio signal supplied from the demodulation circuit 18 to the amplifier circuit 24 as it is without changing the frequency characteristic in accordance with the control by the communication IC 34. Therefore, in this case, the audio signal based on the radio broadcast wave received by the receiving antenna 16 is output as it is from the vehicle-mounted speaker 26 without changing its frequency characteristic.

  On the other hand, if the communication IC 32 determines in step 104 above that there is a peak frequency that is higher than a predetermined threshold by an intensity of the adjacent frequency in the frequency region developed as shown in FIG. Then, a process of communicating a command for changing the equalizer 22 to a state in which the output intensity is reduced at the peak frequency to the communication IC 34 via the in-vehicle communication line 36 is performed (step 108).

  When the communication IC 34 receives the above command from the communication IC 32, the communication IC 34 controls the equalizer 22 so that the output intensity is reduced at the peak frequency. In this case, the equalizer 22 reduces the output intensity at the peak frequency with respect to the frequency characteristics of the audio signal supplied from the demodulation circuit 18 as shown in FIG. Then, the audio signal is supplied to the amplifier circuit 24. Therefore, in this case, as shown in FIG. 5C, the audio signal based on the radio broadcast wave received by the receiving antenna 16 is output from the in-vehicle speaker 26 with the output intensity at the peak frequency reduced. It becomes.

  As described above, in the in-vehicle radio noise reduction system 10 according to the present embodiment, the audio signal received by the receiving antenna 16 and extracted by the demodulation circuit 18 is expanded in the frequency domain by Fourier transform, and the peak at which the reception intensity is maximized. Detect frequency. When the intensity at the peak frequency is less than a predetermined threshold with respect to the intensity of the frequency adjacent to the peak frequency in the developed frequency region, the audio signal based on the radio broadcast wave received by the receiving antenna 16 Can be output as it is from the in-vehicle speaker 26 without changing its frequency characteristics, and the intensity at the peak frequency is a predetermined threshold value relative to the intensity of the frequency adjacent to the peak frequency in the developed frequency region. When the frequency is higher than the above, the audio signal based on the radio broadcast wave received by the receiving antenna 16 can be output from the in-vehicle speaker 26 with the output intensity at the peak frequency reduced.

  For this reason, according to the present embodiment, the harmonic based on the PWM control in the power converter 12 is mixed into the radio broadcast wave and interferes with the radio broadcast wave, and the difference frequency ΔFn between the harmonic and the radio broadcast wave. Is generated as a beat sound, radio noise due to the beat sound can be prevented from being output from the vehicle-mounted speaker 26, and the radio noise based on PWM control in the power converter 12 can be reduced.

  In this embodiment, in order to reduce radio noise based on PWM control in the power converter 12, it is sufficient to adjust the audio output by changing the frequency characteristics with the equalizer 22 of the audio amplifier 20. Thus, it is not necessary to shift the resonance frequency on the power conversion device 12 side, and the configuration of the power conversion device 12 is prevented from becoming complicated. Therefore, according to the present embodiment, radio noise based on the PWM control in the power conversion device 12 can be reduced with a simple configuration.

  Furthermore, in this embodiment, even if the peak frequency at which the reception intensity is maximum fluctuates, the audio signal based on the radio broadcast wave received by the receiving antenna 16 is output at the peak frequency following the fluctuation. Strength can be reduced.

  In the above embodiment, the frequency detected by the peak detection circuit 30 is added to the “conversion means” described in the claims that the peak detection circuit 30 executes the process of step 102 in the routine shown in FIG. In the “peak frequency detection means” described in the claims, it is detected that the presence of a peak frequency having an intensity higher than a predetermined threshold by the intensity of an adjacent frequency in the region. Reducing the output intensity at the peak frequency with respect to the frequency characteristics of the supplied audio signal corresponds to “equalizer means” described in the claims.

  By the way, in the above-described embodiment, the intensity at the peak frequency in the frequency region where the audio signal extracted by the demodulation circuit 18 is expanded is a predetermined threshold value relative to the intensity of the frequency adjacent to the peak frequency in the expanded frequency region. When the frequency is higher than the above, the output intensity at the peak frequency of the audio signal based on the radio broadcast wave received by the receiving antenna 16 is reduced, but the level of decrease in the output intensity is adjacent to the intensity at the peak frequency and the peak frequency. It is good also as what changes according to the difference (specifically magnitude | size exceeding said predetermined threshold value) with the intensity | strength of the frequency to perform. In this case, the level of decrease in output intensity may be increased as the intensity difference increases.

  Further, in the above-described embodiment, the intensity at the peak frequency in the frequency region where the audio signal extracted by the demodulation circuit 18 is expanded is a predetermined threshold value relative to the intensity of the frequency adjacent to the peak frequency in the expanded frequency region. When the frequency is higher than the above, the output intensity at the peak frequency of the audio signal based on the radio broadcast wave received by the receiving antenna 16 is reduced. However, the intensity at the peak frequency is lower than the frequency adjacent to the peak frequency on the low frequency side. When the intensity is higher than a predetermined threshold value and higher than the predetermined threshold value with respect to the intensity of the frequency adjacent to the peak frequency on the high frequency side, the output intensity at the peak frequency may be reduced for the audio signal. In addition, when the intensity at the peak frequency is higher than a predetermined threshold value with respect to either the intensity of the frequency adjacent to the peak frequency on the low frequency side or the intensity of the frequency adjacent to the high frequency side, the peak for the audio signal is obtained. The output intensity at the frequency may be reduced.

DESCRIPTION OF SYMBOLS 10 In-vehicle radio noise reduction system 12 Power converter 14 Radio receiver 18 Demodulator circuit 20 Audio amplifier 22 Equalizer 26 In-vehicle speaker 30 Peak detection circuit 32, 34 Communication IC

Claims (1)

A radio noise reduction system mounted on a vehicle having a radio receiver for receiving radio broadcast waves and a power conversion device that performs switching drive at a predetermined frequency,
Transform means for Fourier transforming an audio signal extracted from a radio broadcast wave received by the radio receiver into a frequency domain;
In the frequency region obtained by the converting means, the intensity is higher by a predetermined threshold than the intensity of the adjacent frequency on the low frequency side, and is higher than the predetermined threshold by the intensity of the adjacent frequency on the high frequency side. peak frequency, or a peak frequency detection means for detecting a peak frequency having a high strength over a predetermined threshold value for the one of the intensity of adjacent frequency intensity of adjacent frequency or high-frequency side in the low frequency side,
Equalizer means for reducing output intensity at the peak frequency detected by the peak frequency detection means;
An in-vehicle radio noise reduction system comprising:

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