JPH09195790A - Noise reducer for enclosed engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To stably absorb noise even in the case of a significant change in noise level by using no analog processing. SOLUTION: When reducing noise with an active noise control(ANC) for an engine generator shrouded by an acoustic insulating case, an automatic adjust 59 for altering reference voltage for an A/D converter 58 with respect to a significant change in noise level, multipliers 115, 116, 117 for multiplying a given multiplication value to digital filters 111, 112, 113 in the ANC controller 25, and a multiplication controller 118 are provided to alter a system gain by digital processing. This allows to eliminate an electric processing delay in an analog processing unit.

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 enclosed engine which reduces noise of an engine surrounded by an enclosure such as a soundproof case.

[0002]

2. Description of the Related Art Conventionally, as a technique for reducing noise in an engine and an exhaust duct, a passive method of providing a sound absorbing material and a vibration damping material has been proposed. On the other hand, in recent years, active noise control (active noise control, hereinafter referred to as ANC) that emits a canceling sound of the same amplitude and opposite phase to noise to reduce the noise by the interference effect of sound waves has been put to practical use. Has been actively researched in various fields. According to ANC, it is difficult to reduce with sound absorbing material near 100 Hz to 500.
Since it also has a reducing effect on low-frequency noise in the vicinity of Hz, it is used to reduce muffled noise in the passenger compartment, air-conditioning duct noise, etc. (Japanese Patent Laid-Open No. 2-503219, Japanese Patent Laid-Open No. 3-204354, JP-A-5-88685).

As an example of such an ANC noise reduction device, there is an electronic silencing system capable of automatically following a large change in the noise level in the air duct of an air conditioning duct.
No. 685. This electronic silencing system, as shown in FIG.
1, a reference noise microphone 132 arranged on the upstream side, a speaker 133 for generating a canceling sound, a residual noise microphone 134 arranged on the downstream side, and an ANC controller 135.
An input level adjusting circuit 136 for adjusting the level of the input signal from the reference noise microphone 132, and the residual noise microphone 1
An input level adjusting circuit 137 for adjusting the level of the input signal from the A.C. 34, an output level adjusting circuit 138 for adjusting the level of the drive signal output from the ANC controller 135 to the speaker 133, and a level control circuit 139.
The level adjusting circuits 136, 137 and 138 are automatically controlled by the level control circuit 139.

That is, the level control circuit 139 controls the input level adjusting circuits 136 and 137 so that the input signal to the ANC controller 135 becomes optimum on the basis of the input signal from the reference noise microphone 132, and at the same time, the input level adjusting circuit 139. The output level adjusting circuit 138 is controlled corresponding to the level adjustment at 136. With this method, the publication describes that even if the noise level in the air passage 131 changes significantly, the input level to the ANC controller 135 can be changed in an analog manner to obtain a predetermined noise reduction effect. .

[0005]

However, a surrounding type engine such as a surrounding type engine generator is disclosed in Japanese Patent Laid-Open No. 5-8.
If the device disclosed in Japanese Patent No. 8685 is applied as it is to cope with a change in noise level, the following problems occur. (1) As shown in Fig. 9, the noise of the enclosed engine is complicated by the fundamental frequency and its harmonics caused by the rotation speed of the crankshaft, cooling fan shaft, etc., the wind noise of the fan, the vibration of the enclosure, etc. It has a wide spectrum. Therefore, in order to increase the noise reduction level unlike the case where periodic noise is reduced, it is necessary to minimize the electrical processing delay of the reference noise microphone, the residual noise microphone, and the input / output analog filter of the speaker. In other words, unlike periodic noise, irregular noise that includes peak frequencies with high noise levels such as harmonics requires a high-order filter stage in order to generate sufficient canceling noise. Due to the electrical processing delay of the output analog filter,
The filter coefficient calculation speed of the adaptive filter cannot follow the actual change in noise, and as a result, sufficient noise reduction cannot be achieved.

In the conventional configuration shown in FIG. 10, since the electrical processing delay due to the input level adjusting circuits 136 and 137 and the output level adjusting circuit 138 which are analog processing sections is large, the ANC control adaptive filters 141, 142 and 143 are provided.
There is a problem that the calculation of cannot keep up with the actual change in noise. (2) Also, as the noise to be reduced becomes in the low frequency range,
The values of capacitors and resistors that must be used in the analog processing section become large, and it becomes difficult to realize an analog filter that satisfies the required performance. Further, since the filter characteristics of such an analog filter are easily affected by temperature, the temperature difference between the start-up and the operation (such as a temperature difference of 60 degrees) is similar to that of an enclosed engine.
ANC control is likely to become unstable in a device with a high temperature.

(3) In an enclosed engine, it is essential to generate cooling air to cool the inside of the enclosure, and the influence of the cooling air must be considered in addition to the vibration of the engine. In other words, it is necessary to select an engine layout configuration and a duct configuration that have a good flow of cooling air and can exert a sufficient noise reduction effect when the ANC system is applied. Further, there is an enclosed type engine in which the rotation speed of the ventilation fan is changed according to the load of the engine in order to suppress the temperature rise inside the enclosed body, and when ANC is applied to this type of enclosed engine, there is ventilation. Since the peak frequency resulting from the rotation speed of the fan changes as the rotation speed changes, it is necessary to devise a method to follow the sudden change in the noise level.

[0008]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems, and it is an object of the present invention to provide an enclosure type engine capable of sufficiently improving noise reduction even in the case of an enclosure type engine in which the noise changes drastically and the noise reduction by the ANC is difficult. An object is to provide a noise reduction device.

[0009]

According to another aspect of the present invention, there is provided a noise reduction device for an enclosed engine, wherein the engine is housed in an enclosure, at least an intake port and an exhaust port are provided at predetermined locations in the enclosure, and outside air is introduced from the intake port. In order to reduce the noise of the enclosed engine that is taken in and exhausted from the exhaust port, at least the exhaust side duct that communicates with the exhaust port is formed around the enclosure, and the reference noise detection microphone that detects noise near the exhaust port, and the exhaust Residual noise detection microphone that detects noise close to the duct mouth of the side duct, canceling sound generation means installed in the exhaust side duct, and canceling noise that cancels noise at the duct mouth based on the reference noise signal and the residual noise signal. A / C for converting at least an analog reference noise signal into a digital signal.
A reference for changing the reference voltage value of the A / D conversion unit in response to detecting the maximum value of the A / D conversion data of the D conversion unit and detecting that the maximum value is within a predetermined small range. The voltage variable means, the multiplication value setting means for setting the multiplication value for multiplying the filter coefficient of the adaptive digital filter in the ANC control means, and the multiplication value set by the multiplication value setting means for each adaptive filter coefficient in the ANC control means. And a multiplying means for digitally multiplying.

According to a second aspect of the present invention, there is provided a noise reduction device for an engine of the enclosed type, wherein A
/ D conversion data is judged to be an appropriate value with respect to the maximum conversion value, and in response to it being judged to be an appropriate value, multiplication by the multiplication value is performed to obtain an appropriate value. It is characterized in that the reference voltage value is changed so as to have an appropriate value in response to the determination that it is not. The noise reduction device for an enclosed engine according to claim 3, wherein the exhaust duct has a bag-shaped air guide plate having an exhaust port on the lower side so as to cover the exhaust port from the upper side, and a wall surface of the enclosure having the exhaust port. A rectangular bowl-shaped exhaust duct case having an opening in the upper wall provided to accommodate the baffle plate, and a horizontal duct that is partitioned from the exhaust duct case by the upper wall and communicates with the opening and extends in the horizontal direction And an exhaust air guide chamber in which the cooling air emitted from the exhaust port is surrounded by a baffle plate, an exhaust side upward air passage formed by the air guide plate and an exhaust duct case, and a horizontal air passage in a horizontal duct. It is characterized in that it is configured to be discharged from the duct opening via the.

According to a fourth aspect of the noise reducing device for an engine of the present invention, a rod-shaped supporting member is fixedly provided in parallel with the extending direction of the exhaust-side upward air passage in the exhaust-side duct, and the rod-shaped supporting member is provided on the exhaust port side. A noise microphone is attached, a residual noise microphone is attached to the duct opening side of the rod-shaped support member, and a canceling noise generating means is arranged at a predetermined position in the exhaust-side upward air passage. In the noise reduction device for an enclosed engine according to claim 5, the reference noise microphone is fixed to the lower end region of the wind guide plate facing the exhaust side upward air passage, the residual noise microphone is fixed near the duct opening of the horizontal duct, and the exhaust air is discharged. It is characterized in that a canceling sound generating means is provided at a predetermined position on the upper wall of the duct case.

[0012]

In the noise reduction device for an enclosed engine according to claim 1, the noise in the enclosure is detected by the reference noise detection microphone, and the residual noise reduced by the interference with the canceling sound from the canceling sound generating means is the residual noise. Detected by microphone.
Then, based on the reference noise signal from the reference noise microphone and the residual noise signal from the residual noise detecting microphone, the ANC control means generates a drive signal of the canceling sound generating means by a predetermined ANC algorithm to generate canceling sound, Reduce noise.

Here, the reference voltage varying means A / A for converting at least an analog reference noise signal into a digital signal.
The maximum value of the A / D converted data of the D conversion unit is detected, and the maximum value is within a predetermined small range (for example, 1/2, 1/4).
And the like), the reference voltage value of the A / D converter is changed. That is, when the amplitude of the reference noise signal is small, the reference voltage value is reduced, and when the amplitude is large, the reference voltage value is increased. Then, the multiplication value setting means sets a multiplication value by which the adaptive filter coefficient of the ANC control means is multiplied, and the multiplication means digitally applies the multiplication value set by the multiplication value setting means to each adaptive filter coefficient in the ANC control means. To multiply. As a result, the dynamic range of the A / D converter can be effectively utilized regardless of the amplitude of the signal input, and it is also optimal for noise signals whose signal amplitude becomes small after reducing the peak frequency such as ventilation fan sound. Noise reduction control can be performed, and noise reduction can be improved.

Further, it is possible to eliminate the S / N ratio deterioration of the A / D converter with respect to the input signal (reference noise signal, residual noise signal). Furthermore, unlike the conventional example shown in FIG.
Since the setting of the reference voltage value and the multiplication of the multiplication values are all performed digitally, it is possible to eliminate the electric processing delay unlike the analog amplification. According to the enclosed engine noise reduction device of claim 2, according to the set reference voltage value,
Since the A / D conversion data is configured to discriminate whether the conversion maximum value has an appropriate value and change the reference voltage value to have an appropriate value, the reference voltage is always kept at an appropriate value. A value can be set, and stable noise reduction can be realized even if there are some unstable factors.

In the noise reducing device for an enclosed engine according to claim 3, the exhaust duct has the above-mentioned configuration, whereby the cooling air that has exited the exhaust port bypasses the baffle plate from the lower side where the exhaust port is located. It will be discharged and will be discharged from the duct opening of the horizontal air passage through the exhaust side ascending air passage. Since the cooling air bypasses the baffle plate here, it forms an exhaust side upward air path that rises from the lower side to the upper side in the exhaust duct case, so that the heated cooling air does not stagnate well. It can be released to the outside. Further, since the muffling region duct can be taken up by the vertical length of the exhaust duct case, it is possible to secure a space that can cancel the sound in the low frequency region. Further, by providing a suction type ventilation fan inside the exhaust port of the enclosure, the flow of cooling air can be improved and the ventilation performance can be improved.

According to another aspect of the noise reduction device for an enclosed engine of the present invention, the rod-shaped support member is fixed to the rod-shaped support member in parallel with the extending direction of the duct air passage in the exhaust side duct. By fixing the reference noise detection microphone to the exhaust port side and the residual noise detection microphone to the duct port side of the rod-shaped support member, the characteristics of vibration transmitted to the exhaust side duct are the same for the reference noise detection microphone and the residual noise detection microphone. Therefore, it is possible to enhance the sound correlation between the reference noise detection microphone and the residual noise detection microphone. Although the strength and direction of the cooling air may vary depending on the position of the duct air passage, the rod-shaped support member is fixedly installed in parallel with the extending direction of the duct air passage to flow through the duct air passage. Since the rod-shaped support member is arranged in parallel with the direction of the cooling air, the effect of the cooling air is almost the same in the reference noise detection microphone and the residual noise detection microphone. It is possible to increase the correlation of the sounds between.

Although the detailed reason is not clear in the case of the noise reducing device for an enclosed engine according to claim 5, the exhaust side duct structure, the canceling sound generating means, the reference noise detecting microphone, and the residual noise detecting microphone are arranged. According to the fifth aspect, the coherence between the reference noise detecting microphone and the residual noise detecting microphone can be improved, and A
The noise reduction level due to NC can be improved.

[0018]

As described in the above operation, according to the invention of claim 1, the following unique effects are exhibited. (B) The dynamic range of the A / D converter can be effectively used regardless of the amplitude of the signal input, and it is also optimal for noise signals whose signal amplitude has decreased after reducing the peak frequency such as ventilation fan noise. Noise reduction control can be performed, and noise reduction can be improved. (B) It is possible to eliminate the S / N ratio deterioration of the A / D converter with respect to the input signal. (C) Since the setting of the reference voltage value and the multiplication of the multiplication value are all performed digitally, unlike analog amplification, electrical processing delay can be eliminated, and it is also sufficient for aperiodic noise. Can correspond to.

According to the second aspect of the present invention, it is possible to always set an appropriate reference voltage value, and it is possible to achieve stable noise reduction even if there is some instability factor. According to the third aspect of the present invention, in the exhaust duct, the cooling air that has become lighter due to the higher temperature can naturally rise in the exhaust-side ascending air passage and be discharged to the outside from the duct opening, and the exhaust duct case It has a unique effect that it can be a muffling duct for the vertical length and can secure a space that can cancel the sound in the low frequency region.

According to the invention of claim 4, it is possible to enhance the sound correlation between the reference noise detection microphone and the residual noise detection microphone, and to bring about a unique effect that the noise reduction of the noise reduction system can be improved. Play. According to the invention of claim 5, it is possible to reduce the total noise level, improve the coherence between the reference noise detection microphone and the residual noise detection microphone, and increase the noise reduction amount. Play.

[0021]

BEST MODE FOR CARRYING OUT THE INVENTION Next, an example of the configuration of an ANC controller applicable to the present invention will be described. FIG. 1 is a schematic block diagram of an ANC system of this noise reduction device for an enclosed engine. This ANC system includes a reference noise microphone 46 provided on the upstream side of an exhaust side upward air passage of an exhaust side duct, which will be described later, and an anti-aliasing filter 57.
(Hereinafter referred to as AAF), an A / D converter 58 for converting an analog reference signal into a digital signal, and an automatic adjuster 59 for automatically adjusting an analog reference voltage of the A / D converter 58.
And a residual noise microphone 48 provided on the downstream side of the exhaust side updraft described later, an AAF 60, an A / D converter 61 for converting an analog reference signal into a digital signal, and a reference voltage of the A / D converter 61. An automatic adjustment unit 62 for automatically adjusting
An ANC controller 25 that outputs a speaker drive signal that is a digital signal that minimizes the residual noise at the position of the residual noise microphone 48 based on the digital reference signal and the digital residual signal by a predetermined ANC algorithm, and the exhaust side upwind passage Exhaust side speaker 47 provided at a predetermined position of
And a D / A converter 63 that converts the digital speaker drive signal output from the ANC controller 25 into an analog signal
And a smoothing filter 64.

As shown in FIG. 1, the ANC controller 25 is roughly divided into an adder 110, a compensation digital filter 111, a compensation digital filter 112, an adaptive digital filter 113, an LMS control section 114, and three multipliers 115. , 116, 117, and a multiplication control unit 118 that causes the three multipliers 115, 116, 117 to perform multiplication in response to a command from the automatic adjustment unit 59. The ANC controller 25 and the three multipliers 11
5, 116 and 117 are configured by software on the same digital signal processor (DSP). In addition, the automatic adjustment units 59 and 62 include a CPU,
It is composed of a D / A converter that converts the reference voltage setting data from the CPU into an analog voltage, and the variable reference voltage is A /
It is input to the AVref terminals of the D conversion units 58 and 61.

In the ANC controller 25, A
The digital signal from the / D converter 58 is added to the adder 110. The adder 110 has a compensation digital filter 1
The output signal from 11 is added to the output through the multiplier 115, the adder 110 adds these input signals, and the added reference noise signal Xn is supplied to the compensation digital filter 112 and the adaptive digital filter 113. Output. Also, the output signal Y of the adaptive digital filter 113
n is output via the multiplier 117, and the exhaust side speaker 4
7 becomes a digital drive signal. On the other hand, the A / D converter 61
The digital residual signal from is input to the LMS control unit 114. The output signal that has passed through the compensating digital filter 112 is input to the LMS control unit 114 via the multiplier 116.

The compensating digital filter 111 is a filter for compensating the electroacoustic characteristic <B> between the exhaust side speaker 47 and the reference noise microphone 46, and the compensating digital filter 112 is the exhaust side speaker 47 and the residual noise microphone 4.
This is a filter for compensating the electroacoustic characteristics <C> between the eight.
The LMS control unit 114 minimizes the residual noise signal en based on the reference input signal Xn and the residual noise signal en so that the canceling sound emitted from the exhaust side speaker 47 reduces the noise of the surrounding engine. Thus, the filter coefficient of the adaptive digital filter 113 is updated. Residual noise signal en
As a method of setting the filter coefficient of the adaptive digital filter 113 to the optimum value so that
"Filtered-xLM proposed by Widrow et al.
The "S algorithm" is well known.

In this algorithm, the filter coefficient of the adaptive digital filter 120 is recursively updated by the following equation. W _{n + 1} = W _n +2 μe _n · X, where Wn: adaptive digital filter coefficient (W [0], W
[1], ..., W [L-1]) Xn: Reference noise signal (X [n], X [n-1], ..., X
[N−L]) en: residual noise signal n: discrete time μ: convergence coefficient L: filter order.

The operation of the ANC system having the above configuration will be described with reference to FIG. 2 mainly by the process of changing the reference voltage values of the A / D converters 58 and 61. FIG. 2 is a flowchart showing the outline of the processing of this ANC system. First, in step SP1 of FIG. 2, it is determined whether or not the filter coefficients of the digital filters 111 to 113 in the ANC control operation are stable. If it is determined that the filter coefficients are stable, the output digital of the A / D converter 58 is output in step SP2. The maximum value of the data is detected, and it is determined in step SP3 whether or not the maximum value of the conversion data of the A / D conversion unit 58 has become a predetermined smaller value than the conversion maximum value.
If it is determined that the value becomes a predetermined small value, step S
Go to P4. On the other hand, if it is determined in step SP1 that the filter coefficients of the digital filters 111 to 113 are not stable, and if it is determined in step SP3 that the filter coefficients have not reached a predetermined small value, the determination operation of step SP1 is performed. repeat.

When the value becomes a predetermined small value, the automatic adjustment unit 59 causes the D / A conversion unit 5 to operate in step SP4.
The reference voltage value of 1/2, 1/4, ... Of the original reference voltage value is output to 8, and the output value of the reference voltage value is stored in the memory in the automatic adjustment unit 59 in step SP5, and in step SP6. In accordance with the output value, it is determined whether the A / D conversion value is an appropriate value with respect to the conversion maximum value by a predetermined determination method, and the A / D conversion value is an appropriate value with respect to the conversion maximum value. If it is determined that it is, step S
In P7, the multiplication control unit 118 sets the multiplication value βn {βn = reference voltage value × an, where an is an adjustment coefficient}, and in step SP8, the compensation digital filter 111,
The process of multiplying each output of the compensation digital filter 112 and the adaptive digital filter 113 by each multiplication value βn is repeated.

If it is determined in step SP6 that the A / D conversion value is not an appropriate value with respect to the maximum conversion value, the reference voltage value is changed to an appropriate value in step SP9. Then, the process returns to step SP4 to output the changed reference voltage value. Further, the operation of this embodiment will be described. The state in which the filter coefficient is stable is selected in step SP1 of the above-mentioned flowchart in order to check the A / D conversion value in the state in which the ANC control is being performed well. Step S
In P3, the process of determining whether or not the maximum value of the conversion data of the A / D conversion unit 58 has become a predetermined smaller value than the conversion maximum value, for example, when the conversion maximum value is set to 1,
This is a process for starting the adjustment process after step SP4 when the A / D converted data becomes 1/2, 1/4, ..., 1 / n. In order to avoid a malfunction, the determination in step SP3 should be performed after confirming a state in which the maximum value of the conversion data is a predetermined smaller value than the conversion maximum value for a predetermined time. preferable.

In the processing of steps SP4 to SP6 and step SP9, the automatic adjustment unit 59 executes step SP4.
This is a process of investigating whether or not the A / D conversion data has an appropriate value with respect to the reference voltage value provisionally set in (1) and finely adjusting it. The multiplication value βn in step SP7 is the multiplication value β1 corresponding to the compensation digital filter 111, which is updated every discrete time n in the above equation, the multiplication value β2 corresponding to the compensation digital filter 112, and the adaptive digital filter 1.
The multiplication value β3 corresponding to 13 is set, the multiplication value β1 is multiplied by the multiplier 115, and the multiplication value β2 is multiplied by the multiplier 116.
Is multiplied, and the multiplier 117 digitally multiplies the multiplication value β3 to automatically adjust the gain. The adjustment coefficient an takes into consideration the noise characteristics of each enclosed engine,
It is provided to achieve the most stable silencing in practice, and an appropriate value is set by trial and error through experiments.

The reference voltage of the A / D converter 61 for converting the residual noise signal into a digital signal is also changed by the operation of the automatic adjustment unit 62 in cooperation with the automatic adjustment unit 59. FIG.
As conceptually shown in (A), in the initial stage of ANC control, the explosion sound of the engine and the wind noise of the ventilation fan appear as peak frequencies 95 to 98 of harmonics of the rotation frequency. Amplitude fluctuation width H1 of the reference noise signal in this case
Is increased due to the amplitude of the peak frequency of the harmonic. As the ANC control progresses, as shown in FIG. 3B, the peak frequencies 95 to 98 are reduced and the amplitude fluctuation width H2 is reduced.
Becomes smaller. Even in this case, by changing the reference voltage value of the A / D converter 58, a small amplitude fluctuation width H2 can be obtained.
Accordingly, the input range of the A / D converter 58 can be used over the entire range, and ANC control for further fine noise reduction can be performed from the state of FIG.

According to this embodiment, since the substantial amplification processing of the input signal can be performed completely digitally according to the change of the amplitude of the input signal, there is no electrical delay and
Sufficient followability can be ensured even for irregular and unstable noises such as an enclosed engine. Figure 4 above
It is a figure which shows the concrete structure of the surrounding type engine to which an NC system is applied, FIG. 4 (A) is a schematic longitudinal cross-sectional view showing the structure of the noise reduction device of a surrounding type engine generator, and FIG. Left side view with the wind duct case removed, Figure 4
FIG. 4C is a right side view with the exhaust duct case removed, and FIG. 4D is a cross-sectional view taken along the line D-D of FIG. 4A.

FIG. 5 (A) is a perspective view for explaining how to dispose the reference noise microphone and the residual noise microphone in the exhaust duct case, and FIG. 5 (B) is an enlarged view of the main part thereof. In this enclosed engine generator, as shown in FIG. 4, a diesel engine 3 is arranged on the right side of the soundproof case 2 composed of six rectangular parallelepiped soundproof walls in the figure,
An engine generator 4 is arranged on the left side in the figure. Further, the discharge port 10 is opened at a substantially central position of the right soundproof wall 2b, and the intake port 21 is opened at a lower position of the left soundproof wall 2c. In addition, the inner wall of the soundproof case 2 and the exhaust duct case 7 described later.
1. The inner wall of the horizontal duct 75 is provided with a sound deadening material on one surface thereof for preventing high frequency sound of 1 kHz or more from leaking to the outside. As such a sound deadening material, a known lightweight and cheap sound deadening material such as glass wool is used.

The radiator 6 is provided in the soundproof case 2 with a discharge port 1
The radiator 6 is provided with a suction type radiator fan 20 that is driven by a fan belt in conjunction with the crankshaft. An air cleaner 24 that communicates with the intake pipe and a muffler 42 that communicates with the exhaust pipe are provided above the engine 3, and an exhaust gas discharge pipe 77 is provided.
Is communicated with the external exhaust pipe 78 via.

A bag-shaped air guide plate 73 having an air outlet 72 is attached so as to cover the outlet 10 of the right soundproof wall 2b from above. The baffle plate 73 employs a curved surface portion 73a having an upper wall with a predetermined radius. Two exhaust side speakers 47, 47 are provided side by side on the upper side of the baffle plate 73. The soundproof case right wall 2b has a substantially rectangular bowl-shaped exhaust duct case 71 having an opening 74 of a predetermined size in an upper wall 71a.
Is attached, and a horizontal duct 75 is horizontally attached to the exhaust duct case upper wall 71a so as to cover the opening 74. Lower wall 71c and right wall 7 of the exhaust duct case
The corner portion connecting 1b and the corner portion connecting the upper wall 75a and the right wall 75b of the horizontal duct 75 are curved surface portions 71d and 75c having a smooth predetermined radius, respectively. At the duct outlet 35 of the horizontal duct 75, a wire net 76 for preventing foreign matter from entering is stretched.

The exhaust duct case 71 is attached to the soundproof case right wall 2
By attaching to b, the noise emitted from the exhaust port 72 of the exhaust air guide chamber 79 in the baffle plate 73 causes the exhaust side ascending air passage 81 composed of the baffle plate 73 and the exhaust duct case right wall 71b. After passing through the opening 74 and the horizontal air passage 82 in the horizontal duct 75, the wire mesh 76 is discharged to the outside from the duct outlet 35 stretched. The horizontal duct 75 has a curved surface portion 75d that is not perpendicular to the extending direction S of the exhaust side upflow passage 81.

A rod-shaped microphone support member 83 having an L-shaped cross section from the lower wall 71c of the exhaust duct case to the upper wall 71a is fixed in the exhaust-side upward air passage 81 in the vertical direction. As shown in FIG. 4 (A), the microphone support member 83 is attached from the lower side in order of the reference noise microphone 46 and the residual noise microphone 48, and the microphones 46 and 48 are attached to the microphone support member 8 respectively.
It is firmly fixed to the No. 3 through the shock absorbing material 84. Examples of the shock absorbing material 84 include various vibration-proof sponges. The reference noise microphone 46 is arranged at a position slightly above the lowermost position of the right wall of the wind guide plate 73, and at this position, the canceling sound generated from the speaker 47 is generated by the wind guide plate 73.
It is shielded by the curved surface portion 73a and does not directly enter.

The lower end of the microphone support member 83 is planted in the exhaust air tact case lower wall 71c, and the upper end of the microphone support member 83 is fixed to the exhaust air duct case upper wall 71a via a support plate 85. The arrangement position of the microphone support member 83 is shown in FIG.
As shown in (D), it is provided at the central position in the exhaust-side upward air passage 81, which is symmetrical to the left and right. ANC
The noise reduction device includes the reference noise microphone 46, the exhaust-side speaker 47, the residual noise microphone 48 provided at the lower position of the opening 74, and an ANC controller (not shown). The detailed configuration of the ANC controller is as described in FIG.

Further, since the engine 3 and the generator 4 are housed in the soundproof case 2 via a vibration-proof rubber 55 arranged at a predetermined position on the bottom wall 2d of the soundproof case 2, the engine 3
Also, the vibration of the generator 4 is reduced from being transmitted to the soundproof case 2. Further, a fuel tank 22 is provided at a position where the intake port 21 at the upper left portion of the soundproof case 2 is not closed, and fuel can be supplied from a fuel spout 56 provided on the soundproof case upper wall 2a. .

The operation of the engine generator noise reduction device configured as described above will be described. Engine generator engine 3
When the engine is operated and power generation is started, the radiator fan 20 interlocked with the crankshaft of the engine is driven. The outside air taken in from the duct inlet 41 by the drive of the radiator fan 20 is introduced into the soundproof case 2 through the intake side ascending air passage 61 in the air intake duct case 67, the intake air guide chamber 50, and the generator 4 and After cooling the engine 3, the exhaust air guide chamber 79 and the exhaust side updraft 81 in the exhaust duct case 71.
And is discharged from the duct outlet 35 through the opening 74 and the horizontal air passage 82 of the horizontal duct 75 (see arrow H in the figure).

When the operation of the engine 3 is started, the ANC controller detects the reference noise in the lower part of the exhaust side upwind passage 81 by the reference noise microphone 46, and based on the reference noise signal and the residual noise signal of the residual noise microphone 48. The speaker 47 is driven so that the noise at the duct outlet 35 is minimized, and the canceling sound is generated. In this embodiment of the ANC operation, the L-shaped steel, which is hard to deform, is used to support the two microphones 46 and 48, so that the individual microphones 4 are
6 and 48 do not vibrate independently, and the correlation coefficient of sound between the reference noise microphone 46 and the residual noise microphone 48 can be improved. Further, since it is fixed to the microphone support member 83 via the shock absorbing material 84, the vibration of the microphone support member 83 generated by the engine vibration and exhaust air can be directly transmitted to the reference noise microphone 46 and the residual noise microphone 48. Can be suppressed, and the sound correlation between the two microphones can be improved.

The microphone support member 83 is arranged along the direction S of the exhaust side upward air passage 81 through which the exhaust air flows, and is also provided in a symmetrical position in the exhaust side upward air passage 81. Therefore, it is possible to detect the noise characteristics flowing along with the exhaust wind in all regions without bias, and as a result, it is possible to improve the noise reduction performance. Also,
By providing the horizontal duct 75, it is possible to reduce the noise level as compared with the form in which the residual noise is emitted to the outside as it is from the opening 74 of the exhaust duct case 71.
This is because the horizontal duct 75 is connected to the extending direction S of the exhaust-side upward air passage 81 at an angle of about 90 °,
This is because the corner portion of 5 is a curved surface portion 75c having a predetermined radius, and thus it is possible to prevent a standing wave from being generated in the exhaust side upward air passage 81. Further, the noise reduced by the speaker 47 due to the curved surface portion 75c collides with the upper wall 75a of the horizontal duct 75, and again the exhaust side ascending air passage 81.
There is also an advantage that you can reduce the components that return to.

The structure of the horizontal duct 75 is not necessarily limited to the curved surface portion 75c having a predetermined radius, and a duct having a wall surface having an angle inclined with respect to the extending direction S of the exhaust side upward air passage 81 is provided. In this case, the generation of standing waves can be suppressed. The inclination angle of the wall surface has the effect of suppressing the generation of standing waves, and the exhaust side ascending air passage 81 upon collision with the inclined wall surface.
It may be set as appropriate depending on the balance with the amount of noise components returned to.

As the simplest structure, a structure having a surface having an inclination angle θ of 45 ° with respect to the extending direction S of the exhaust side upwind passage 81 can be exemplified. The inclination angle θ is not limited to 45 °, and a horizontal duct 75 that spreads the inclination angle θ in the range of 30 ° to 50 ° may be provided. In this specification, the horizontal duct 75 is not limited to the duct in which the axial direction of the upper wall 71a and the duct coincide.
Even if the duct is slightly tilted up and down, it is configured to extend in a substantially horizontal direction, and any duct that can reduce noise at the duct port 35 is included. Further, the extending direction of the horizontal duct 75 is not limited to the duct port 35 extending toward the soundproof case right wall 2b side, and may extend toward the opposite side of the soundproof case right wall 2b side with the microphone support member 83 interposed therebetween. Good.

FIG. 6A is a vertical sectional view showing the detailed construction of the reference noise microphone 46 and the residual noise microphone 48, and FIG. 6B is a transverse sectional view taken along the line BB of FIG. 6A. The microphone 94 used in the surrounding type engine reduction device is a rectangular parallelepiped outer case 87 made of plastic or metal.
A vibration-damping material 108 such as a vibration-proof rubber, which is installed inside the outer case 87, a shock-absorbing material 88 such as a hard sponge housed inside the vibration-damping material 108, and a high-frequency wave of 700 Hz or more around the periphery. The microphone unit 89 is covered with a sound absorbing material 107 that absorbs noise.

The outer case 87 is composed of a rectangular bowl-shaped housing case 90 and a lid of the housing case. The rear wall of the housing case is provided with a notch 93 through which the microphone cord 92 of the microphone unit 89 is inserted. There is. The front wall 90a and the side wall 90b of the housing case 90 have a predetermined thickness (about 1 mm), and these walls 90a and 90b are not provided with sound wave inlets at all. The microphone unit 89 includes a housing case 90.
The sound transmitted through the outer case side wall 90b in front of the position where the front wall 90a and the microphone unit 89 are accommodated is detected.

The thickness of the shock absorbing material 88 is set so as to receive the elastic force of pressure contact from the side surface when the lid is attached, and the elastic force holds the microphone unit 89 at a predetermined position. The noise reduction due to the ANC of this enclosed engine generator cannot be reduced by the sound absorbing material as described above.
Sounds in the low frequency range below 0Hz (comes like belly)
It is intended for. Therefore, from a low frequency sound of 500 Hz or less to a few kHz like a conventional general microphone.
It is not necessary to detect even the above high frequency sounds.

According to the microphone of this embodiment, by transmitting the platic surface or the metal surface, 1 kHz
The above sound is absorbed by the latch, and only the sound of 1 kHz or less can be detected by the microphone unit. Further, in the case of the conventional vibration-proof microphone having the sound wave inlet, the turbulence of the strong cooling fan wind flowing in the exhaust duct case 71 may adversely affect noise detection, for example, the occurrence of vibration due to the sound wave inlet may occur. Problems such as generation of resonance sound and adhesion of contaminants occur, but the microphone 9 of the present embodiment
If it is 4, the problem can be solved, and the signal S
/ N can be improved. Like this microphone 94
The noise correlation between the reference noise microphone 46 and the residual noise microphone 48 can be obtained by taking measures against the turbulence and the vibration of the microphone and setting the position of the microphone support member to the appropriate position described in the fourth embodiment. You can improve your sex.

FIG. 7A shows a case in which the microphone 94 provided with measures against turbulence according to the present embodiment is used, and the microphone support member 83 is arranged in parallel with the extending direction of the exhaust side upflow passage 81 and symmetrically. In FIG. 7B, the correlation coefficient of the two microphones 46 and 48 in FIG. 7 is plotted on the vertical axis and the frequency is plotted on the horizontal axis. In FIG. 7B, a microphone with a normal sound wave inlet is used and the microphone support member 83 is used. FIG. 6 is a diagram showing a relationship between a correlation coefficient and two frequencies of two microphones 46 and 48 when the exhaust side upwind passage 81 is inclined with respect to the extending direction thereof. In FIG. 7 (A) corresponding to the present embodiment, the correlation coefficient is a good value close to about 1.0 for noise of 500 Hz or less which is the target of reduction, while FIG. 7 (B) is In the conventional configuration shown in A
Even if the NC control is performed, the sound is actually hardly reduced, which is a bad value of about 0.5. In the experiment using the actual machine, the noise level on the exhaust port 10 side was 85 dB when no countermeasure was taken, and after the countermeasure was taken, the noise absorption on the inner wall and the ANC control were combined. It was confirmed that it could be reduced to 75 dB.

[0049]

[Embodiment 2] FIG. 8 is a view showing a second embodiment of the present invention, and FIG. 8 (A) is a schematic vertical sectional view showing the configuration of a noise reduction device for an enclosed engine generator, and FIG. 8 (B). Figure 5
(A) It is an equivalent figure. The difference between the second embodiment and the first embodiment is as follows. First of all, first, the microphone support member 83 is not provided in the exhaust duct case 71, the reference noise microphone 46 is provided at the lower end portion of the wind guide plate 73, and the residual noise microphone 48 is provided outside the duct outlet 35 of the horizontal duct 75. It is a point provided on the upper end. Residual noise microphone 4
When 8 is provided on the outer upper end portion, the microphone surface is set parallel to the extending direction of the horizontal duct 75 as shown in FIG. There is. With this configuration, the cooling air discharged from the duct outlet 35 can be prevented from hitting directly, and the vibration of the residual noise microphone 48 can be prevented to perform good noise detection.

Secondly, the position of the exhaust side speaker 47 is set on the upper wall 71a of the exhaust duct case 71, and the speaker surface of the speaker 47 is directed toward the curved surface portion 75c. In the configuration in which the residual noise microphone 48 is disposed outside the duct outlet 35 as shown in FIG. 8, the upper wall 71a is more than in the configuration in which the speaker 47 is disposed above the air guide plate 73 (see FIG. 4). It has been confirmed that the noise reduction performance of the ANC is enhanced when the speaker 47 is provided above. Further, the length L in the depth direction of the exhaust duct case 71 in which the reference noise microphone 46 and the residual noise microphone 48 are arranged, and the horizontal duct 75 are the same, and both are arranged in symmetrical positions. ing. This configuration is necessary to enhance the sound coherence of both microphones 46 and 48. According to the second embodiment, the noise level on the side of the exhaust port 10 can be similarly reduced from 85 dB to 75 dB in the experiment without providing the microphone supporting member 83 as in the first embodiment shown in FIG. It was confirmed.

[Brief description of the drawings]

FIG. 1 is a schematic block diagram showing an ANC system of a noise reduction device for an enclosed engine according to the present invention.

FIG. 2 is a flowchart for explaining a process of the noise reduction device for an enclosed engine according to the present invention.

FIG. 3 (A) is a diagram showing a noise level before the peak frequency is reduced, and FIG. 3 (B) is a diagram showing a noise level after the peak frequency is reduced.

FIG. 4 is a diagram showing a configuration of a noise reduction device for an enclosed engine generator as an embodiment of a noise reduction device for an enclosed engine generator according to the present invention, and FIG. FIG. 4 is a schematic vertical sectional view showing the configuration of the noise reduction device.
4B is a left side view with the air intake duct case removed, FIG. 4C is a right side view with the air exhaust duct case removed, and FIG. 4D is D- of FIG. 4A. It is a transverse cross-sectional view of the D line direction.

FIG. 5 (A) is a perspective view for explaining how to dispose a reference noise microphone and a residual noise microphone in an air exhaust duct case, and FIG. 5 (B) is an enlarged view of a main part thereof.

6A is a vertical cross-sectional view showing a detailed configuration of a reference noise microphone and a residual noise microphone, and FIG. 6B is a horizontal cross-sectional view taken along the line BB of FIG. 6A.

7A is a diagram showing a relationship between a correlation coefficient and a frequency in the first embodiment, and FIG. 7B is a diagram showing a relationship between a correlation coefficient and a frequency in a comparative example.

FIG. 8 is a view showing a second embodiment of the present invention, FIG. 8 (A) is a schematic vertical cross-sectional view showing the configuration of a noise reduction device for an enclosed engine generator, and FIG. 8 (B) is It is a principal part enlarged view for demonstrating the structure of an exhaust duct case and a horizontal duct.

FIG. 9 is a diagram showing an example of a noise spectrum characteristic of an enclosed engine.

FIG. 10 is a block diagram showing a configuration of a conventional ANC silencer.

[Explanation of symbols]

2 ... Soundproof case, 3 ... Engine, 10 ... Exhaust port, 21 ...
Intake port, 25 ... ANC controller, 35 ... Duct outlet, 46 ... Exhaust side reference noise microphone, 47 ... Exhaust side speaker, 48 ... Exhaust side residual noise microphone, 58 ... A / D conversion section, 59 ... Automatic adjustment section, 71 … Exhaust duct case, 71
a ... upper wall, 73 ... baffle plate, 74 ... opening, 75 ... horizontal duct, 79 ... exhaust air guide chamber, 81 ... exhaust side upflow passage, 82 ...
Horizontal air passage, 83 ... Microphone support member, 111, 112, 1
Reference numeral 13 ... Digital filter, 115, 116, 117 ... Multiplier, 118 ... Multiplication control section.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G10K 11/16 G

Claims (5)

[Claims] 1. An engine (3) is housed in an enclosure (2), and at least a suction port (2) is provided at a predetermined position of the enclosure (2).
1) and an exhaust port (10) are provided, and at least the exhaust port (10) is provided in order to reduce the noise of the enclosed engine that takes in the outside air from the intake port (21) and exhausts it from the exhaust port (10).
The exhaust side duct (71, 75) communicating with the enclosure (2)
A reference noise detection microphone (46) that is formed around and detects noise near the exhaust port (10), and an exhaust side duct (71,
75) residual noise detection microphone (48) for detecting noise close to the duct opening (35), and exhaust side ducts (71, 75)
A canceling sound generating means (47) disposed inside the canceling sound generating means (47) is driven so as to generate a canceling sound for canceling noise at the duct opening (35) based on the reference noise signal and the residual noise signal. And a maximum value of A / D conversion data of an A / D conversion unit (58) for converting an analog reference noise signal into a digital signal is detected, and the maximum value is predetermined. A reference voltage changing means (59) for changing the reference voltage value of the A / D conversion section (58) in response to the detection of being within the small range of AN;
Adaptive digital filter (11) in C control means (25)
1, 112, 113) and a multiplication value setting means (118) for setting a multiplication value for multiplying the filter coefficient, and each filter in the ANC control means (25) for the multiplication value set by the multiplication value setting means (118). A noise reduction device for an enclosed engine, comprising: a multiplication means (115, 116, 117) for digitally multiplying a coefficient. 2. The reference voltage value set by the reference voltage changing means (59) determines whether the A / D conversion data has an appropriate value with respect to the maximum conversion value, and the value is an appropriate value. In response to the fact that it is determined that the set value is multiplied, the reference voltage value is changed so that it becomes an appropriate value in response to the fact that it is not determined to be an appropriate value. The noise reduction device for an enclosed engine according to claim 1, wherein: 3. The exhaust duct (71, 75) comprises a bag-shaped air guide plate (73) having an exhaust port (72) on the lower side so as to cover the exhaust port (10) from the upper side, and the exhaust port (73). 10) A rectangular parallelepiped bowl-shaped exhaust duct having an opening (74) in an upper wall (71a) provided to accommodate a baffle plate (73) on a wall surface (2b) of an enclosure (2) The case (71) and the upper wall (71
The opening (7) is separated from the exhaust duct case (71) by a).
4) and a horizontal duct (75) which extends in the horizontal direction and communicates with the exhaust duct (73) in which the cooling air discharged from the exhaust port (10) is surrounded by the baffle plate (73). The air is discharged from the duct port (35) through the exhaust side rising air passage (81) formed by the wind plate (73) and the exhaust air duct case (71) and the horizontal air passage (82) in the horizontal duct (75). The noise reduction device for an enclosed engine according to claim 1, configured as described above. 4. A rod-shaped support member (8) parallel to the extending direction of the exhaust-side upward air passage (81) in the exhaust-side duct (71, 75).
3) is fixed, and the exhaust port (10) of the rod-shaped support member (83)
The reference noise microphone (46) is attached to the side, and the residual noise microphone (4) is attached to the duct opening (35) side of the rod-shaped support member (83).
The noise reducing device for an enclosed engine according to claim 3, wherein the canceling noise generating means (47) is provided at a predetermined position of the exhaust side ascending air passage (81). 5. A reference noise microphone (46) is fixed to the lower end region of the baffle plate (73) facing the exhaust side upward air passage (81),
A residual noise microphone (48) is fixed near the duct opening (35) of the horizontal duct (75), and a canceling noise generating means (47) is provided at a predetermined position on the upper wall (71a) of the air exhaust duct case (71). Item 3. A noise reduction device for an enclosed engine according to Item 3.