JPH0639896B2 - Active silencer - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an active noise canceling device, and more particularly to an active noise canceling device useful for noise prevention of a blower duct, an intake / exhaust pipe of a vehicle engine, and the like.

[Prior Art] An active muffling circuit has a sound source for silencing and outputs a sound having a phase opposite to the noise from the sound source to cancel and cancel the noise. Compared with the conventional resonance type silencer that is large in size in response to the long wavelength of low-frequency sound, the active silencer has no relation to the wavelength of noise. It is attracting attention as a vehicle-mounted silencer that can effectively mute high-frequency sound and makes it difficult to secure an installation space.

And, usually use a speaker as the sound source for muffling,
A microphone is used to detect the noise waveform.

[Problems to be Solved by the Invention] By the way, when the active silencer is provided in a pipeline having one end connected to an engine as a noise source and the other open, such as an intake and exhaust pipe of a vehicle engine, the inside of the pipeline is Even if a microphone is installed, it is difficult to accurately detect the noise waveform due to the noise reflection phenomenon at the open end of the pipeline.

In view of such problems, it is an object of the present invention to provide an active silencer that can be installed in an intake / exhaust pipe or the like that causes open-end reflection and that can effectively reduce noise.

[Means for Solving the Problems] In the silencer of the present invention, as shown in FIG. 1, a speaker serving as a sound wave generating means is provided on the side wall of the conduit so as to face the inside of the conduit, and on the other hand outside the conduit. Is equipped with a microphone that is a sound collecting unit that faces the opening of the conduit and detects noise. The distance between the speaker and the microphone is L. The output signal of the microphone is input to the phase advancing means, and the phase advancing means advances the phase of the output signal for a predetermined time and outputs it as a phase advancing signal. The phase advance signal is input to the drive means, the phase is inverted, and the phase advance signal is given to the speaker as a drive signal. The constant time τ is set by the following equation.

τ = L / C where C is the speed of sound.

[Operation and Effect] The phase advance signal obtained by advancing the output signal of the microphone for the above-mentioned fixed time matches the phase of the noise passing through the speaker installation portion of the pipeline. If the speaker is driven by the drive signal that is the inverted phase advance signal, the sound emitted from the speaker effectively cancels and eliminates the noise.

Thus, according to the muffler of the present invention, since the microphone is provided outside the pipeline, the noise waveform can be accurately detected without being affected by the noise reflection at the pipeline opening,
As a result, it is possible to effectively reduce the noise that is transmitted and dissipated in the pipeline.

[Embodiment] In FIG. 2, one end 11 of the intake pipe 1 is connected to the intake manifold E1 of the engine E, and the other end 12 of the intake pipe 1 is open. A pressure fluctuation occurs in the manifold E1 along with the operation of an intake valve (not shown) during engine operation, which propagates in the intake pipe 1 and a part of the open end 12
Is reflected by, and the others are emitted from the open end 12 as noise (N in the figure). The intake pipe 1 is provided with a speaker 2 on the midway wall thereof, and a microphone 3 is provided outside the intake pipe 1 near the open end 12 toward the speaker. And
The distance between the speaker 2 and the microphone 3 is L.

The electric circuit of the silencer includes a preamplifier 41 and a phase comparator 4
2, low pass filter (LPF) 43, voltage controlled oscillator (VCO) 44, band pass filter (BPF) 45,
BBD (Bucket-Brigade Device)
It is composed of an analog delay element 46 using e), a signal amplification amplifier 47, a voltage control amplifier (VCA) 48, a power amplifier 49 and a phase inverter 50.

Of these, the phase comparator 42, the LPF 43, the VCO 44,
The BPR 45 and the delay element 46 form a phase feedback circuit. That is, the comparator 42 inputs the output signal 41a of the preamplifier 41 and the output signal 46a of the delay element 46, and outputs the output signal 42a according to the phase difference between them.
In this embodiment, as shown in FIG. 3, the phase difference is −π / 2 to −π / 2.
While changing at π / 2, the voltage of the signal 42a is Δ
Only V changes. The VCO 44 receives the signal 42a from which noise has been removed by the LPF 43, and outputs an oscillation signal whose frequency changes according to the voltage change ΔV.

The oscillation signal passes through the BPF 45 and is given to the amplifier 47 as a backward phase advance signal 45a.
Enter in 6. The delay time τ of the delay element 46 is the time required for a sound wave to propagate through the distance L, and the sound velocity is C
Is expressed by the following equation.

τ = L / C Then, the signal 46a delayed by the time τ is input to the phase comparator 42 as described above. The phase feedback circuit controls the phase of the signal 46a so as to always match the phase of the signal 41a. Here, the phase advance signal 45a leads the signal 41a by the time τ. Therefore, this signal 45a is in phase with the noise waveform passing through the speaker 2 installation portion of the intake pipe 1.

Therefore, if the phase advance signal 45a is passed through the amplifiers 47 and 49 and the phase thereof is inverted by 180 degrees by the phase inverter 50 and given to the speaker 2 as the speaker drive signal 50a, the output sound of the speaker 2 causes the inside of the intake pipe 1 to move. The noise that passes through is canceled out.

By the way, the noise level detected by the microphone 3 is naturally 0 when the phase difference between the signals 41a and 46a is 0.
It becomes a minimum when it becomes. Therefore, in this embodiment, VCA
48 is provided, and the phase comparison output signal 42a is used as a gain control signal thereof. That is, VCA4
As shown in FIG. 4, the amplification gain characteristic of No. 8 becomes maximum when the phase difference becomes zero. As a result, the signal level of the speaker drive signal 50a is kept constant regardless of the output level of the microphone 3.

Although the above embodiment is intended for noise of a single frequency, the configuration of FIG. 5 can also cope with wideband noise. In the figure, the electric circuit surrounded by the broken line is
In addition to the circuits of the above embodiment, band pass filters (BPF) 51 and 52 for taking in only signals in a predetermined frequency range are provided. Then, a plurality of circuits in broken lines having BPFs 51 and 52 set in different frequency ranges are provided, and these output signals are mixed by a mixer (MIX) 53. The phase of the mixed signal is inverted to form the speaker drive signal 50a.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of the present invention, FIG. 2 is a block diagram showing a configuration of a silencer, FIG. 3 is a diagram showing an output characteristic of a phase comparator, and FIG. 4 is a gain characteristic of a voltage controlled amplifier. FIG. 5 is a block diagram showing another embodiment of the silencer. E ... Engine 1 ... Intake pipe (pipe) 11 ... Open end 2 ... Speaker (sound wave generation means) 3 ... Microphone (sound collection means) 42 ... Phase comparison circuit 44 ... Voltage controlled oscillation circuit 46 ...... Delay circuit 48 ...... Voltage control amplifier circuit 50 ...... Phase inversion circuit

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Satoshi Kuwamon 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Stock Company Japan Auto Parts Research Institute (72) Inventor Katsuyuki Tanaka 14 Iwatani, Shimohakaku-cho, Nishio-shi, Aichi Stock Association Company Japan Auto Parts Research Institute (72) Inventor Koji Ito 1-1, Showa-cho, Kariya city, Aichi Nihon Denso Co., Ltd.

Claims (3)

[Claims] 1. An active noise suppressor provided in a pipeline having one end reaching a noise source and the other end being open, and a sound wave generating means provided on a side wall of the pipeline facing the inside of the pipeline, and at the other end. Sound collecting means provided outside the nearby conduit for detecting noise radiated from the conduit opening, and the phase of the output signal of the sound collecting means is advanced for a fixed time determined by the distance between the sound wave generating means and the sound collecting means. Phase advancing means for outputting as a phase advancing signal, and driving means for inverting the phase of the phase advancing signal and outputting as a drive signal for the sound wave generating means, wherein the fixed time τ is the sound wave generating means. Let L be the distance between the sound collecting means and C be the speed of sound,
Active silencer with τ = L / C set. 2. The phase advancing means comprises a delay circuit having a delay time set to the constant time, a phase comparison circuit, and a voltage controlled oscillator circuit for outputting an oscillation signal having a frequency proportional to an input voltage, The oscillation signal is used as the phase advance signal and a part of the oscillation signal is input to the delay circuit, and the output signal of the delay circuit and the output signal of the sound collecting means are input to the phase comparison circuit to output the phase comparison output. The active silencer according to claim 1, wherein the voltage-controlled oscillator circuit is input. 3. The driving means has a voltage control amplifier circuit whose gain changes in response to a voltage input, and the amplifier circuit amplifies the phase advance signal input thereto by a gain corresponding to the phase comparison output. The active muffling apparatus according to claim 2, wherein the active muffling apparatus outputs the output to the phase inversion circuit of the next stage.