JPH0234421A - Noise reduction device of air conditioner - Google Patents

Abstract

PURPOSE:To reduce noise quickly and over a wide frequency range by extracting signal at a specified frequency on the basis of electric signal for sensing noise, delaying and inverting this signal, and generating sound in the opposite phase to the noise. CONSTITUTION:The phase characteristic of noise is controlled by a control circuit 17 on the basis of electric signals from a microphone 15 as a noise sensing and converting means, and sounds in the opposite phase to the noise from a speaker 16 as a sound generating means is generated to achieve reduction of the noise. The control circuit 17 is in series connected with a preamplifier 18 in connection with the microphone 15, analog filters 19, 23, 27 as extracting means, delay circuits 20, 24, 28 as signal delay means, phase inverter circuits 21, 25 as signal inverting means, and power amplifiers 22, 26, 29. Thereby signal processing by control circuit 17 is performed in a short time, and noise reduction is made over a wide frequency range.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an air conditioner with a short noise propagation path, for example,
This invention relates to a noise reduction device for an automobile air conditioner.

[Prior Art] An active noise reduction device detects noise with a microphone placed near the noise source, reproduces antiphase sound in a control circuit, and outputs it through a speaker installed downstream of the noise propagation path. Active silencer) is known. In this noise reduction device, since it has been developed for large-scale air conditioners for buildings, the distance between the microphone 1 and the speaker 2 can be long as shown in FIG. Therefore, the time required for signal processing within the control circuit 3 may be long.

[Problems to be Solved by the Invention] However, when this noise reduction device is applied to an automobile air conditioner, since the automobile air conditioner is small, the frequency and phase relationship shown in FIG. There is a large difference in the slope of the noise phase characteristic line L1 shown by the solid line in the figure and the slope of the canceling sound phase characteristic line L2 shown by the broken line.

Therefore, in phase control using only the delay time, the frequency range in which the phase is within 180±60', which is the noise reduction range, is Δf1. Δ
f2. It becomes extremely narrow as shown by Δf3. the result,
Evaluation based on overall values does not significantly reduce noise.

An object of the present invention is to provide a noise reduction device for an air conditioner, which can perform signal processing of a control circuit in a short time in a small air conditioner such as an automobile air conditioner, and can reduce noise over a wide frequency band. It is about providing.

[Means for Solving the Problems] The present invention includes a sound generating means provided on a noise propagation path of an air conditioner, and a sound generating means provided upstream of the sound generating means on the noise propagation path to detect the noise. and a noise extraction conversion means for converting the noise into an electrical signal and outputting the same, and controlling the phase characteristics of the electrical signal from the noise extraction conversion means to generate the sound having the opposite phase to the noise. A noise reduction device for an air conditioner that reduces noise by generating noise from the noise conversion means, comprising: an extraction means for inputting an electrical signal from the noise extraction conversion means and extracting a signal in a predetermined frequency band; and the extraction means. a signal delay processing means connected in series to the extraction means, inputting an electric signal from the extraction means and delaying the signal by a predetermined amount; and a signal delay processing means connected in series to the extraction means, inputting an electric signal from the extraction means and delaying the signal The gist of the invention is a noise reduction device for an air conditioner, which is provided with a signal inversion processing means for inverting the signal.

[Operation] The electric signal from the noise extraction conversion means is extracted by the extraction means in a predetermined frequency band, and is processed through the signal delay processing means for avoiding a predetermined amount of delay and the signal inversion processing means for inverting the signal. A signal that is a sound having a phase opposite to that of the noise is sent to the sound generating means. At this time, the inversion operation by the signal inversion processing means is quickly performed.

[Example] Hereinafter, an example in which the present invention is applied to a noise reduction device for an automobile air conditioner will be described with reference to the drawings.

As shown in FIG. 2, the automotive air conditioner of this example is as follows:
A blower 10 serving as a noise source sucks outside air or inside air and sends it into an air passage 11 serving as a noise transmission path. An evaporator 12, a damper 13, and a heater core 14 are arranged in this order in the air passage 11 downstream of the blower 10. Based on the opening degree adjustment of the damper 13, the air taken in by the blower 10 undergoes heat exchange in the evaporator 12 or the heater core 14, and is supplied into the vehicle interior as cooling/heating air. The frequency characteristics of the noise output from this air blower 1110 are as shown by the solid line in FIG.
~460H71550~700Hz, 880~980H
There are steep changes at three points in z.

A microphone 15 as a noise extraction conversion means is installed in the air passage 11 near the blower 10, and the microphone 15 converts the imaging pressure (sound pressure) of the air into an electrical signal. Further, a speaker 16 as a sound generating means is arranged in the air passage 11 near the installation position of the damper 13, and a control circuit 17 is connected to the speaker 16 and the microphone 15.
In addition to inputting the noise conversion signal (electrical signal) from 5, a control signal is output to the speaker 16 so that the air blower generates a sound wave having the same amplitude as the noise emitted by 10 but 180° different in phase.

To explain this control circuit 17 in detail, as shown in FIG. 1, a preamplifier 18 is connected to the microphone 15, and the electrical signal from the microphone 15 is amplified by the preamplifier 18. An analog filter 19 as an extraction means, a delay circuit 20 as a signal delay processing means, a phase inversion circuit 21 as a signal inversion processing means, and a power amplifier 22 are connected in series to the output side of the preamplifier 18. It is connected to the speaker 16. Similarly, for the series circuits 19 to 22, a series circuit of an analog filter 23 as an extraction means, a delay circuit 24 as a signal delay processing means, a phase inversion circuit 25 as a signal inversion processing means, a power amplifier 26, and an analog A series circuit of a filter 27, a delay circuit 28, and a power amplifier 29 are connected in parallel. Each analog filter 19.
23° 27 is composed of a low-pass filter F1 and a bypass filter F2, and limits the frequency band Δf of the sound to be muted.
~4601-(Z, 550~ at analog filter 23
700H2, 880-980 with analog filter 27
H2 is extracted.

The delay circuits 20 and 24 are 180°x2- with respect to the phase of the sound propagating from the blower 10 at the location where the speaker 16 is installed
The delay time τ1. Set τ2. However, the delay times τ1 and τ2 are set so that n is minimized. That is, as shown in FIG. 4, the signal SG2, which is delayed by time τ1 and τ2N with respect to the signal SG1 at the α point on the entrance side of the delay circuit 20.24, is outputted to the β point on the exit side.

As shown in FIG. 5, the phase inversion circuits 21 and 25 have a resistor R1 connected to the inverting input terminal of the operational amplifier OPI, and a resistor R2 connected in a feedback circuit to the inverting input terminal. As shown in FIG. 4, this phase inversion circuit 21.25 outputs an inverted signal SG3 at one point on the output side of the circuit 21.25, that is, there is no delay and the phase is shifted by 180 degrees.

Note that the delay circuit 28 performs a delay of time τ3, but since the output signal has a phase difference within 180° with respect to the electrical signal at the installation position of the speaker 16, only the delay processing by the delay circuit 28 and no inversion processing is performed. There is no such thing.

The power amplifiers 22, 26, and 29 set the amplitude to be approximately the same as the amplitude at the location where the speaker 16 is installed, and output the signal to the speaker 16.

Next, the operation of the noise reduction device for an automobile air conditioner constructed as described above will be explained.

Noise generated by the blower 10 propagates within the air passage 11. Microphone 15 is sent J! Since the speaker 16 is located on the downstream side of the tI 110, the sound wave propagates through the air until it reaches the speaker 16 from the microphone 15, that is, L/C (L; between the microphone 15 and the speaker 16). The control circuit 17 electrically controls the amplitude and phase at a distance of , C: speed of sound) to create an opposite phase sound and muffle the sound.

At this time, in the control circuit 17, the electric signal that has passed through the preamplifier 18 is transmitted to the analog filters 19, 23.27, and each analog filter 19. 70
0H2, 880 to 980H2) are separated and output. At this time, a phase difference occurs between the input and output of each analog filter 19, 23, 27. That is, it is the same as having a unique delay circuit, and the phase changes with respect to frequency.

The output signal of the analog filter 19.23 is sent to the delay circuit 20.
．． Since the phase difference between the electrical signal SGI and the electrical signal at the installation position of the speaker 16 is 180° or more and within 360°, the delay circuit 20.24 transmits the electrical signal to the electrical signal at the installation position of the speaker 16. The delay time τ1゜τ2 is set so that the phase is the same as that of the signal SG2 (fourth
In the figure, SG1→SG2>. Further, the output signal of the analog filter 27 is sent to a delay circuit 28 to set a delay time τ3.

The output signal of the delay circuit 20.24 is sent to the phase inversion circuit 21.2.
5, and the electrical signal is inverted (in Figure 4, SG
2→5G3). And power amplifier 22, 26.29
The sound is amplified by the speaker 16, and a sound having an opposite phase is output from the speaker 16, thereby canceling out the noise from the transmitter 10, as shown by the broken line in FIG.

In this way, the phase inversion circuit 21.25 quickly performs the inversion processing operation, and the processing time in the control circuit 17 is shortened, so that the microphone 15 and the speaker 16 are substantially separated (the distance between the two is 15.16). This is the same as increasing the That is, as shown in FIG.
In the relationship between frequency and phase, the slope of the noise phase characteristic line L1 shown by the solid line in the figure and the slope of the canceling sound phase characteristic line L2 shown by the broken line (change in phase with respect to frequency) are shown in FIG. It can be brought closer. In other words, the frequency range (noise reduction range) in which the phase is within 180±60' can be widened.

In this example, the noise is caused by the microphone 1.
5, the signal is detected and converted as an electrical signal, a predetermined frequency band is extracted by an analog filter 19.23, and the signal is passed through a delay circuit 20.24 that delays the signal by a predetermined amount and a phase inversion circuit 21.25 that inverts the signal. A signal with a phase opposite to that of the noise is sent to the speaker 16. At this time, the phase inversion circuit 21
．． The reversing operation by 25 is performed quickly. Therefore,
This means that a phase difference of 180° can be provided over a wide frequency range. Therefore, in a small air conditioner such as an automobile air conditioner, signal processing of the control circuit 17 can be performed in a short time, and noise can be reduced over a wide frequency band.

It should be noted that this invention is not limited to the above embodiments, but may be implemented as shown below.

(1) Although an analog filter was used in the above embodiment, a digital filter may also be used.

(2) The number of series circuits of the filter circuits 19 and 23, the delay circuits 20 and 24, and the phase inversion circuits 21 and 25 in the control circuit 17 is not limited to two, and an appropriate number may be prepared.

[Effects of the Invention] As detailed above, according to the present invention, signal processing of a control circuit can be performed in a short time in a small air conditioner such as an automobile air conditioner, and noise can be reduced over a wide frequency band. It shows the excellent effect that can be achieved.

[Brief explanation of the drawing]

1 to 6 are diagrams for explaining a noise reduction device for an automobile air conditioner embodying the present invention, and FIG. 1 is an electric circuit diagram of the noise reduction device for an automobile air conditioner, and FIG. 2
The figure is a cross-sectional view of a noise reduction device for an automotive air conditioner, Figure 3 is a diagram showing frequency characteristics, Figure 4 is a time chart showing waveforms, Figure 5 is an electric circuit diagram of a phase inversion circuit, and Figure 6 is a diagram showing frequency characteristics. Figures 7 to 9 are diagrams showing the relationship between frequency and phase, and Figures 7 to 9 are diagrams for explaining the conventional technology. FIG. 9 is a diagram showing the relationship with phase, and FIG. 9 is a diagram showing frequency characteristics. 10 is a blower as a noise source, 11 is an air passage as a propagation path, 15 is a microphone as a noise conversion means, and 16 is W'! A speaker as a generating means, 19 an analog filter as an extraction means, 20 a delay circuit as a signal delay processing means, 21 a phase inversion circuit as a signal inversion processing means, 23 an analog filter as an extraction means, 24 a signal Delay circuit as delay processing means, 25
is a phase inversion circuit as a signal inversion processing means. Patent applicant Nippondenso Co., Ltd. Agent Patent attorney On 1) Shisenpachi 21.25

Claims (1)

[Claims] 1. A sound generating means provided on the noise propagation path of the air conditioner; and a sound generating means provided upstream of the sound generating means on the noise propagation path, detecting noise, converting the noise into an electrical signal, and outputting the same. noise detection conversion means, the air conditioner is configured to reduce noise by controlling the phase characteristics of the electric signal from the noise extraction conversion means to generate sound having an opposite phase to the noise from the sound generation means. In the noise reduction device, an extraction means for inputting an electric signal from the noise detection conversion means and extracting a signal in a predetermined frequency band; and an extraction means connected in series to the extraction means, for inputting an electric signal from the extraction means. signal delay processing means for delaying the signal by a predetermined amount; and signal inversion processing means connected in series to the extraction means and inputting an electrical signal from the extraction means and inverting the signal. A noise reduction device for air conditioners.