JP2721051B2 - Engine noise reduction device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a noise reduction device for an engine in which a soundproof box covering the engine is provided with a ventilation opening.

[0002]

2. Description of the Related Art Such a soundproof box covers an engine so that noise emitted from the engine does not leak to the outside as much as possible. However, an opening for ventilation is required for cooling the engine, and an opening area is required so that the engine does not overheat at the maximum load.

[0003]

For this reason, a sufficient noise reduction effect cannot be obtained, and it has been desired to further reduce the noise leaking from the opening to the outside. The present invention has been made in view of such circumstances, and has as its object to reduce the amount of noise emitted from an engine leaking from an opening of a box.

[0004]

According to a first aspect of the present invention, there is provided a sound reducing device for an engine, wherein a soundproof box covering the engine is provided with an opening for ventilation. In the configuration, a speaker is provided between the engine and the opening, and a microphone is provided in the opening,
Output and the vibration detection means for directly or indirectly detecting the vibration of the engine, the antiphase sound and at the same frequency as the fundamental frequency component of the noise from the engine based on the detection information of the vibration detection means from the speaker and control means provided <br/> et been that, the control means detects information of the microphone
Based on the detection sound of this microphone is reduced
So that the sound pressure or phase of the sound output from the speaker
The point is that it is configured to automatically adjust .

[0005] A second characteristic configuration is that the control means includes:
Based on the microphone detection information, the speaker
Change the sound pressure or phase of the sound output from the
The sound pressure or position of the sound so that the sound detected by the phone is low
In that it is configured to determine the phase .

[0006] For example, a piezoelectric element can be used as vibration detecting means for directly detecting vibration of the engine, and a microphone can be used as vibration detecting means for indirectly detecting vibration.

[0007]

According to the first feature, the control means obtains the fundamental frequency component of the noise from the engine vibration detected directly or indirectly by the vibration detection means ,
Sound and opposite phase at the same frequency as the fundamental frequency component, en
Microphone provided in the ventilation opening on the side of the box that covers the gin
Sound (for example, average sound pressure, etc.)
Sound pressure or to adjust automatically the phase while, engine and the through
The signal is output from a speaker provided between the battery and the opening. One
In short, the microphone is the noise from the engine and the speaker
Sound from the opening with the sound from the
I am feedback. Adjust both sound pressure and phase.
First, the position is set so that the detected sound pressure is minimized.
After adjusting the phase, adjust the sound pressure to further reduce the detected sound pressure.
It will be cheap. The fundamental frequency component is
Not limited to a single frequency component, it may be a composite wave of a plurality of frequency components. The opposite phase is a phase relationship in the opening, that is, a phase relationship in which noise from the engine and sound from the speaker weaken each other, and the sound leaking from the opening to the outside is reduced.

Accordingly, for example, a voltage signal detected by a piezoelectric element as a vibration detecting means is converted into a voltage waveform of substantially only a fundamental frequency component by a filter or the like, a phase is delayed by a predetermined amount through a delay circuit, and then a low-frequency amplification is performed. Output. As a result, of the many frequency components that make up the noise, the fundamental frequency component is weakened by the opposite-phase sound output from the speaker.

According to a second feature configuration, the control means includes:
Change the sound pressure or phase of the sound output from the speaker to
The sound pressure or phase that reduces the detected sound of the crophone
The sound pressure or phase of the sound output from the speaker.
Automatically adjust to the desired sound pressure or phase.

[0010]

Effect of the Invention] Thus, according to claim 1, of the noise emanating from the engine, while effectively Dim I by the reducing the fundamental frequency component is the largest component, open
By performing feedback control with detected sound information at the mouth
For example, if the frequency conditions of the noise
In such cases, take appropriate measures to reduce the
The sound effect can be maintained, and the noise leaking from the opening of the box can be surely reduced. Further
In the first aspect, a filter based on sound information detected at the opening is provided.
Feedback control with a simple configuration
it can. According to the second aspect, the sound pressure or the phase is changed.
The sound pressure or phase to reduce the noise.
Even if the noise frequency conditions fluctuate,
The sound reduction effect can be exhibited.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which the present invention is applied to a power generator will be described below with reference to the drawings. In FIG. 1 showing a schematic structure of the power generation device, 1 is a diesel engine, 2 is a generator,
Reference numeral 3 denotes a control device, and reference numeral 4 denotes a soundproof box covering these.
Air is taken in from the air inlet 5 provided on the side of the box 4,
The exhaust gas of the engine 1 passes through an exhaust pipe 6 and a silencer 7
Through the exhaust port 8.

A radiator 9 for cooling the engine and a radiator fan 10 are provided, and the air that has cooled the radiator 9 is provided with an air outlet 11 as an opening for ventilation provided in the box 4.
It is exhausted from. A shielding plate 12 is provided in an exhaust path from the engine 1 to the exhaust port 11, and functions to reduce noise leaking from the exhaust port 11 to the outside by reflecting noise from the engine 1.

A speaker 13 is mounted on the shield plate 12 with its vibration surface substantially facing the engine 1. By outputting a sound having the same frequency as the fundamental frequency component of the noise from the engine 1 and an opposite phase from the speaker 13, the fundamental frequency component, which is the largest component among many frequency components constituting the noise, is weakened. ,
Noise that leaks from the air outlet 11 to the outside is reduced. The sound emitted from the back of the speaker 13 is substantially absorbed by the structure of the box 4 and the sound absorbing material.

The configuration for outputting from the speaker 13 a sound having the same frequency as the fundamental frequency component of the noise from the engine 1 and having the opposite phase is as follows. First, a piezoelectric element 14 as vibration detection means for detecting (directly) vibration of the engine 1 is attached to a side surface of the engine 1 or an oil pan, and a voltage signal as detection information is input to the control means 15. .

Although various noises are generated from the engine 1 due to vibrations and impacts of various parts, all of them eventually become vibrations of the engine surface, and oscillate the air to generate noise. Therefore, the control means 15 can obtain a signal waveform having substantially the same frequency and phase as the noise by processing the voltage signal from the piezoelectric element 14. Further, as shown in FIG. 2, the high frequency band component and the low frequency band component are removed through the band pass filter 15a. The band to be passed is set to a band including a main component of noise (fundamental frequency component) whose approximate frequency band is known in advance.

The thus obtained signal having substantially only the fundamental frequency component is delayed through the delay circuit 15b.
The delay amount is determined so that the fundamental frequency component of the noise from the engine 1 and the sound output from the speaker 13 have a phase difference (opposite phase) in which the sound is weakened, and is automatically adjusted as described later.

Finally, this signal is amplified by the low frequency amplifier 15c and output from the speaker 13. The amplification factor of the low frequency amplifier 15c is also automatically adjusted. That is, as shown in FIG. 2, a microphone 16 is provided in the exhaust port 11, and the control unit 15 controls the delay circuit 15b based on the detection information.
And the gain of the low-frequency amplifier 15c are automatically adjusted. Accordingly, the phase and sound pressure of the sound output from the speaker 13 are automatically adjusted so that the noise emitted from the air outlet 11 is minimized.

In addition, as shown in FIG. 2, the arithmetic processing unit 15d of the control means 15 obtains the effective value of the voltage signal, which is the detection information of the microphone 16, and sets the delay circuit so that the effective value becomes minimum. The delay amount 15b and the amplification factor of the low frequency amplifier 15c are adjusted. The adjustment process is realized by a program of a microcomputer constituting the arithmetic processing unit 15d.

This adjustment processing program is executed at predetermined time intervals or when the effective value of the voltage signal of the microphone 16 (hereinafter referred to as detected sound pressure) fluctuates (increases) by a set value or more. And a program for automatically updating and setting the amplification factor of the low-frequency amplifier 15c.

When this processing routine is started, first,
After the delay amount of the delay circuit 15b is changed by a unit amount in one direction, a change in the detected sound pressure is checked. If the detected sound pressure is falling, the delay amount is further changed by the unit amount in the same direction. If the detected sound pressure rises or does not change, the delay amount is changed by a unit amount in the reverse direction. The amount of delay after repeating this process for a predetermined time is the updated amount of delay. Next, the amplification factor of the low-frequency amplifier 15c is similarly updated and set.

Hereinafter, other embodiments will be listed. A plurality of piezoelectric elements may be attached to different places such as an engine side surface or an oil pan, and the fundamental frequency components obtained separately from each piezoelectric element may be combined, amplified, and output from a speaker. However, in this case, it is difficult to adjust the delay amount (phase) and the amplification factor for each basic frequency component.

In the vibration detecting means of the above embodiment, the piezoelectric element mounted on the engine surface detects the acceleration due to the vibration of the engine. For example, a microphone is provided close to the engine surface to indirectly detect the vibration of the engine. May be configured to be detected.

The present invention is not limited to the power generating device as in the above-described embodiment, but can be applied to industrial machines, such as agricultural tractors, on which an engine is widely mounted.

In the claims, reference numerals are provided for convenience of comparison with the drawings, but the present invention is not limited to the configuration shown in the attached drawings.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a schematic structure of a power generator according to an embodiment of the present invention.

FIG. 2 is a block diagram of an engine sound reduction device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 4 Box 11 Opening 13 Speaker 14 Vibration detecting means 15 Control means 16 Microphone

Claims (2)

(57) [Claims] 1. An engine noise reduction device in which a soundproof box (4) covering an engine (1) is provided with a ventilation opening (11), wherein the engine (1) is provided. A speaker (13) is provided between the opening (11) and the opening (11).
Rofon (16) is provided, the engine (1) directly or indirectly detect the vibration detecting means vibrations (14) and, the vibration detecting means the engine based on the detected information (14) (1) noise control means for outputting a sound of the fundamental frequency component as and opposite phase at the same frequency from the speaker (13) (15) are provided, et al are of from, the control means (15), said microphone (16)
Of the microphone (16) based on the detection information of
From the speaker (13), the detected sound is reduced.
It is configured to automatically adjust the sound pressure or phase of the output sound.
Sound reduction device is to have engine. 2. The control means (15) , based on detection information of the microphone (16),
Changes the sound pressure or phase of the sound output from the speaker (13).
Further, the detection sound of the microphone (16) is low.
Configured to determine the sound pressure or phase of the sound so that
Sound reduction system for an engine according to claim 1, wherein that.