JP2579966B2 - Intake system noise reduction device - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an intake system noise reduction device for reducing intake system noise of an engine.

[Problems to be solved by conventional technology and invention]

In recent years, as the quality of vehicles has increased, the demand for lowering the noise of on-board engines has increased significantly. Above all, the intake system noise, in which low-frequency noise is a problem, is accompanied by the propagation of vibrations into the cabin, and the This is one of the reasons, and it is desired to reduce the noise.

In general, the noise of the intake system is a pulsating noise caused by the explosion of the engine, and is mainly a secondary component of the engine rotation. Conventionally, in order to reduce intake system noise, a method has been adopted in which a resonator called a resonator is provided in the middle of an intake system pipeline to attenuate sound waves equal to the resonance frequency. However, a resonator having a fixed capacity can reduce only a part of the sound wave of a certain frequency, and the intake system noise mainly composed of the sound of the secondary component of the engine rotation cannot be reduced over a wide rotation range of the engine.

An object of the present invention is to provide an apparatus that can actively reduce intake system noise of an engine over a wide rotation range of the engine in view of such circumstances.

[Means for solving the problem]

In view of the above, according to the present invention, a sound generating means provided on a propagation path of noise of an engine intake system and generating a sound which interferes with the noise, a rotational speed detecting means for detecting a rotational speed of the engine, Noise detecting means for detecting a signal related to the noise of the engine, and memory means for storing information of a delay time and an amplitude adjustment amount according to the number of revolutions of the engine, and the information stored in the memory means Noise control means for adjusting the delay time and amplitude of the detection signal detected by the noise detection means based on the engine speed detected by the rotation speed detection means; The sound generating means generates a sound having substantially the same amplitude and a substantially opposite phase as the noise of the intake system on the basis of the received signal.

[Action]

A signal relating to the noise of the intake system is detected by the noise detecting means and input to the noise control means as a detection signal. Further, the engine speed is detected by the speed detecting means and inputted to the noise control means. Therefore, the noise control means
The delay time and the amplitude of the detection signal are adjusted according to the detected engine speed. A delay time and an amplitude adjustment amount corresponding to the engine speed for adjusting the detection signal are stored in a memory unit included in the noise control unit. Thereby, the sound wave from the sound generating means generates a sound having substantially the same amplitude and a substantially opposite phase as the previous intake system noise,
Interference with intake system noise reduces intake system noise.

That is, even when the level and frequency characteristics of the intake system noise vary depending on the engine speed, the intake system noise can be actively reduced by the sound wave interference effect of the sound wave radiated from the sound generating means.

〔Example〕

An embodiment of the present invention will be described with reference to the following drawings.

FIG. 1 is an overall configuration diagram of an intake system noise reduction device of the present invention. The microphone 1 for noise detection is mounted in the intake system 11 of the engine 10, for example, near the gathering portion of the intake manifold. The microphone 1 detects noise in the intake pipe, converts the noise into an electric signal, and inputs the signal to a noise control circuit 2 including a microcomputer. The noise control circuit 2 detects the rotation speed based on a rotation signal from a rotation sensor 8 that detects the rotation speed of the engine, delays, amplifies, and filters the noise signal according to the rotation speed, and converts the signal to an air cleaner. The sound is output to a sound muffling speaker 3 mounted in the speaker 4. In addition, a microphone 6 provided near the suction port of the air cleaner 4 forms a noise reduction feedback circuit to enhance the noise reduction effect.

Next, the noise control circuit 2 will be described with reference to the block diagram of FIG.

The microphone signal from the microphone 1 input to the noise control circuit 2 is a filter 1, an AMP1, a delay controller,
The signal is guided to a silencer circuit 210 composed of AMP2, subjected to delay, amplification, and filtering, and then output to a muffling speaker 3. Incidentally, the optimum signal delay, amplification, and filtering process varies in an arbitrary intake system depending on the engine speed. So CPU220
Converts the rotation speed signal from the rotation sensor to interface 27
The control is performed by detecting the rotation speed by taking in through 0. Further, in the memory 230, information on the delay time and the amplification factor for each rotation speed experimentally obtained in the intake system and information on a filter frequency proportional to the rotation speed are written together with the rotation speed, and a CPU (central processing unit) 220 retrieves information necessary for control from the memory 230 via address lines and data lines.

A / D conversion circuit 240, D / A conversion circuit 250 and I / O (input / output) to perform various controls on the same line
A circuit 260 is connected, and inputs and outputs between the CPU 220 and the silencer circuit 210 and the feedback circuit 280. The signal from the feedback microphone 6 provided to enhance the noise reduction efficiency of the system is AMP
3, Filter 2, and taken into a feedback circuit composed of an RMS-DC-LOG converter, subjected to RMS-DC-LOG conversion described later, and then grasped as the current sound and used to enhance the reduction effect.

Next, the silencer circuit 210, which is a main part of the present invention, will be described with reference to the circuit diagram shown in FIG.

The signal from the microphone 1 measuring the intake system noise in the silencer circuit 210 is a terminal And passes through a two-stage high-pass filter (20 Hz) composed of an operational amplifier 211, a resistor, and a capacitor. Next, this signal also passes through a variable low-pass filter using an 8-bit programmable filter 212 (for example, DT208D made by NF circuit design block), and is narrowed down to only a signal of a predetermined frequency component. By the way, in general, the frequency component of the intake system noise is mainly the secondary component of the engine rotation, so the frequency component to be reduced is at most the fourth component of the engine rotation on the higher order side, and depends on the rotation speed. Since the frequencies are different, the programmable filter 212 is variably controlled by the CPU 22. So the terminal from CPU220 8-bit control signal through the programmable filter
Sent to 212.

By the way, preferably, the same time as the time required for the noise detected by the microphone 1 to reach the muffling speaker 3 via the noise control circuit 2 is equal to the time taken for the muffling speaker 3 to move from the installation position of the mike 1 to the installation position of the muffling speaker 3. It is necessary that the time required for propagation to be set uniformly. Therefore, in order to make this adjustment, the noise signal is delayed, and the solid-state delay element BBD that changes only the phase
(Bucket brigade device, for example, MN3007 manufactured by Matsushita Electric Industrial) 214 is used. Further, in order to control the delay time of the BBD 214, the clock frequency input thereto may be changed. Therefore, in order to delay according to the engine speed, a V / F converter 215 (for example, AD650 manufactured by Analog Devices) that can be controlled by the CPU 220 is used, The clock frequency is changed according to the signal from the
Control the delay time.

In addition, in order to control the input signal to the BBD 214, the resistors R ₅ and R ₆
Is provided, further controllable operational amplifier 216 of the amplification factor pin by T ₁ of the FET for controlling the output signal from the BBD It is connected to CPU220 through. If the sound pressure level of the sound emitted from the muffling speaker 3 and the sound pressure level of the intake sound propagating in the intake pipe near the muffling speaker 3 are the same level, the CPU 220 has the highest muffling efficiency. The amplification factor of the operational amplifier 216 is controlled by the engine speed to adjust the sound pressure level of the muffling speaker 3. Also,
If the phase of the sound emitted from the muffling speaker 3 is fundamentally opposite to the phase of the noise transmitted through the intake pipe, muffling will not be achieved, so the operational amplifier 218 and the resistors R ₈ and R ₉ invert the amplification factor 1. Amplification is in progress. Also, the operational amplifier 21
Coupling for impedance adjustment is also performed using 7.

Next, a feedback circuit 280 which forms a main part of the present invention together with the silencer circuit 210 will be described with reference to a circuit diagram shown in FIG.

As shown in FIG. 1, the signal from the feedback microphone 6 provided near the suction port of the air cleaner 4 is connected to a terminal. Is input to the feedback circuit 280, and is first amplified by the operational amplifier 281. Next, in order to accurately measure the muffling effect, it is necessary to apply a variable band-pass filter so as to be in the same range as the frequency range in which muffling is performed by the silencer circuit 210 described above. So the feedback circuit
Also in 280, a two-stage high-pass filter (20 Hz) composed of an operational amplifier 282, a resistor and a capacitor and a variable low-pass filter using an 8-bit programmable filter 283 are provided to narrow down the frequency component of the feedback signal according to the engine speed. . Also, the programmable filter 283 has a terminal so that the cutoff frequency is the same as that of the programmable filter 212. Is controlled by the CPU 220 via the.

In order to further calculate the sound pressure level of the feedback signal, the filtered signal is RMS (Root Mean Square).
e) -DC-LOG converter 284 (for example, AD536 manufactured by Analog Devices, Inc.)
It is converted to a value and output as a DC level representing a dB value.
The iC reference 285 (for example, AD580J manufactured by Analog Devices) supplies a reference voltage for converting a dB value. The feedback signal finally converted to a DC level is amplified to a predetermined multiple by an operational amplifier 286, The signal is output to the A / D converter 240 and is recognized by the CPU 220 as the exit sound of the air cleaner 4.

Next, the operation of the device having the above configuration will be described with reference to the waveform schematic diagram of FIG. 5 and the flowchart of FIG.

First, intake system noise is generated with the rotation of the engine. The noise level depends on the engine speed. Here, the intake system noise is detected by the microphone 1 attached near the gathering portion of the intake manifold, converted into an electric signal, and transmitted to the noise control circuit 2.

In the noise control circuit 2, the electric signal of the noise is narrowed down to a predetermined frequency corresponding to the engine speed by a variable band-pass filter including a programmable filter 212 and the like, and further reduced to the engine speed by a delay controller such as a BBD 214. Proper delay and amplification are provided.
At this time, the CPU 220 reads the information of the delay time, the amplification factor, and the filtering frequency corresponding to the engine speed derived from the engine speed signal from the memory 230, and outputs the signal for transmitting the clock frequency corresponding to the delay time to the V / F converter. 215, the amplification factor signal is output to the FETT ₁ connected to the operational amplifier 216, and the filtering frequency signal is output to the programmable filter 212 for control. The sound signal thus controlled is reproduced by the muffling speaker 3 mounted in the air cleaner 4, and interferes with the intake sound propagating in the intake pipe. As shown in the waveform schematic diagram of FIG. 5, the intake sound propagating in the intake pipe (FIG. 5A) and the sound emitted from the silencing speaker 3 (FIG. 5B) are the same sound, in other words, the same sound. Since the waveforms are in phase and opposite in phase, if the two waves interfere with each other, the sound waves cancel each other out, so that the noise cancellation is realized as shown in FIG. This silencing is realized by the control of the CPU 220 over the entire rotation range of the engine, and the intake system noise is reduced.

Further, in order to realize more efficient noise reduction, a microphone 6 attached near the air cleaner outlet is used.
A feedback loop is configured. This is to cope with the fact that the noise reduction effect changes depending on the environmental conditions at that time, such as temperature, so that the delay time is shifted back and forth, and the point at which the noise reduction efficiency is highest is evaluated by evaluating the air cleaner's exit sound. Operates by routine.

The flowchart of FIG. 6 shows a series of processes for the CPU 220 to execute silencing corresponding to the engine speed, and also includes the feedback routine. This processing is performed, for example, when the CPU 220 receives a trigger signal that is generated when the engine speed changes, and the processing in step G100 is performed.
More executed.

First, the engine speed (N) is measured and rounded to the nearest specified speed (G101). Next, information on the delay time (T), the amplification factor (M), and the low-pass filter upper limit frequency (F) according to the rotation speed is read from the memory 230 (G102), and the clock frequency to be sent to the delay element 214 is generated accordingly. The output voltage is output to the V / F converter 215, and the amplification factor of the output signal operational amplifier 216 and the filtering frequency of the programmable filters 212 and 283 are changed (G103 and G104). Also, in order to confirm the sound pressure after silencing, the sound pressure _PN is measured by the feedback microphone 6 attached near the air cleaner outlet (G10).
Five). Next, by controlling the clock frequency, the delay time is shifted back and forth by a predetermined time (Δt) from the delay time (T), and the air cleaner outlet sound pressure (P _S ,
P _L ) is also measured (G106 to G109).

The sound pressure (P _S , P _N ,
By comparing the magnitude of P _L ) (G110), a delay time with the best noise reduction efficiency is found. Specifically, three sound pressure data ((P _S , P _N ,
Magnitude relationship between the five types of cases of _{P L) (G111, G115,} G12
1, G122, G128) and discuss each. In addition, the classification of these cases is based on the fact that the sound pressure is the lowest at an appropriate delay time, and that the sound pressure gradually increases as the distance increases before and after that time, This considers where and how the preceding three sound pressure data are arranged on the parabola.

The flowchart for each case is described below.

(I) When P _S > P _N > P _L (G111 to G114) The optimum delay time is not included between the delay time (T−Δt) and (T + Δt), and the sound pressure data is delayed Since the longer the time, the longer the delay time, the delay time is further extended (Δt), the exit sound (P _LL ) is measured, and (T + 2Δ)
Prepare to check if the optimal delay time is not included by the time t). In step G114, each data is replaced, and the process returns to step G110 again.

(Ii) if P _S> P _N, while the _{P S> P L, P N} ≦ P L when (G115~G120) delay time (T) of the (T + Δt), are included optimum delay time And the delay time (T + 1 / 2Δ)
The exit sound (P _NL ) at the time of t) is measured, and three sound pressures (P _NL ) are again measured.
_N , P _NL , P _L ) are prepared. Step G1
At 20, each data is replaced and the process returns to step G110.

However, in the case of P _N = P _L for the delay time (T + 1 / 2Δt) is the optimum delay time, the routine ends (G132).

(Iii) for P _N <P _S = when P _L (G121) delay time (T) is the optimal delay time, and terminates the routine (G132).

(Iv) When P _L > P _N , P _L > P _S , P _N ≦ P _S (G122 to G126).

This is a case where the optimum delay time is included between the delay times (T−Δt) and (T), and the delay time (T−1 / 2Δ)
The outlet sound (P _NS ) at the time t) is measured, and the three sound pressures (P _NS ) are again measured.
_S , _PNS , _PN ) are prepared for the judgment. Step G1
At 27, each data is replaced and the process returns to step G110.

However, in the case of P _N = P _S a delay time (T-1 / 2Δt) is the optimum delay time, the routine ends (G132).

(V) when the _{P S <P N <P L} (G128~G131).

Since the optimal delay time is not included between the delay times (T−Δt) and (T + Δt), and the sound pressure data is lower as the delay time is shorter, the exit sound (P _SS ) Is measured and the delay time (T−Δt) is calculated from (T−Δt).
A preparation is made to check whether the optimum delay time is included during 2Δt). In step G131, each data is replaced, and the process returns to step G110 again.

The above flowchart is for a certain engine speed, but since the speed is constantly changing,
By continuously operating this routine in response to a trigger signal generated in response thereto, an optimal delay according to the engine speed can be realized, and highly efficient intake noise reduction can be achieved.

In the above embodiment, the noise detection signal from the microphone is performed in the order of delay, level adjustment, and phase inversion. However, these three processes may be performed in another order.

In the apparatus shown in FIG. 1, a general acoustic speaker 3 provided in an air cleaner 4 is used as sound producing means for silencing. Generally, the acoustic speaker 3 generates a sound by vibrating a cone by exciting vibration using a coil, but in order to produce a large-capacity output with low-frequency sound such as intake system noise. The coils and cones are larger, making them larger and heavier.

Therefore, as another example of the sound generating means for silencing, for example,
It is preferable to use a ceramic speaker using a PZT piezoelectric element. By using a ceramic speaker, an extremely thin, large-output, lightweight speaker can be realized. In addition, even when the air cleaner is provided in the air cleaner, it is possible to reduce the size of the air cleaner due to the built-in speaker.

7 (a) and 7 (b) show this ceramic speaker built-in type air cleaner, FIG. 7 (b) shows an internal plan view of the piezoelectric element side, and FIG. 7 (a) includes the case of FIG. FIG. 3 is a sectional view taken along line AA.

In the present invention, since a low-frequency sound of about 20 to 300 Hz, which is the most problematic in the intake system noise, needs to be reproduced by a ceramic speaker, as shown in FIG.
Is supported in a cantilever manner and extended in the longitudinal direction, thereby increasing the amplitude at the tip, and making the piezoelectric element itself extremely thin to facilitate vibration and facilitate reproduction of low-frequency sound.

In addition, the tip of each piezoelectric element 31 is bent at a right angle and fixed in the tangential direction of the reinforcing vibration ring 32 of the flat diaphragm 32 having a honeycomb structure, thereby increasing the number of elements and reducing the size. This is a major feature. As a result, a smaller diaphragm can be driven by more piezoelectric elements, so that high output can be obtained in a low frequency range. Reference numeral 34 denotes a fixing plate for the piezoelectric elements, 35 denotes a signal line for connecting the piezoelectric elements in parallel, and 36 denotes a signal connector.

Next, the operation of the ceramic speaker will be described with reference to FIGS. 7 and 8.

The sound signal for silencing generated by the noise control circuit 2 is amplified about 10 to 20 times by the booster circuit 5 and applied to the ceramic speaker 3. This signal causes the PZT bimorph piezoelectric element 31 to vibrate due to expansion and contraction, and this vibration propagates through the reinforcing vibration ring 32 to the planar vibration plate 33 to generate sound. Since the vibration is directly transmitted to the diaphragm 33 in this manner, a high output can be obtained with high efficiency.

Further, even if the piezoelectric element 31 and the vibration plate 33 are combined, the thickness is only about 10 mm, which is extremely thin, so that the mountability in the air cleaner 4 is high.

Further, as another embodiment of the noise detecting means, an intake pressure sensor using a PZT bimorph type piezoelectric element can be used instead of the microphone 7 for detecting the intake system noise as shown in FIG. . Large, ultra-thin, bimorph type PZ for the sensor diaphragm of the intake pressure sensor
By using a T piezoelectric element, a high output of 1 V or more can be obtained, so that an amplifier for signal amplification is not required, and a simple structure that only needs to be fixed around the periphery to be used as a diaphragm Is a major feature.

FIGS. 9 (a), (b) and (c) show this bimorph type PZ.
This shows an intake pressure sensor 7 using a T piezoelectric element 71,
(A) is an overall side view, (b) is a rear view and a sectional view taken along line AA, and (c) is a plan view of a bimorph type piezoelectric element and a sectional view taken along line BB. As shown in FIG. 9 (c), the intake pressure sensor 7 promotes pressure in a low frequency range of about 20 to 300 Hz, which is the most problematic in the intake system noise.
The piezoelectric element itself is easily vibrated by making the piezoelectric element 1a a relatively large direct-line and extremely thin bimorph type, and the periphery is fixed by the case 72, thereby providing a sharp and large output sensor. In addition, the case itself is an open type with a hole in the back cover 73, so that vibration in the low frequency range is easy to occur, and it is easy to install near the gathering part of the intake manifold with a tapered screw part. Has become. The output is via cable 74,
It is taken out from the connector 75.

Next, the operation of the intake pressure sensor 7 will be described. Air in the case communicating with the intake pipe system vibrates due to intake negative pressure vibration generated when the engine rotates, and this vibration causes the bimorph type PZT piezoelectric element 71 to vibrate. At this time, the piezoelectric element 71 generates a signal output according to the vibration by the piezoelectric effect. This signal output is a relatively large output in the present example, and therefore can be directly input to the noise control circuit 2 without requiring amplification by an amplifier.

〔The invention's effect〕

As described above, the intake system noise reduction device of the present invention detects the intake system noise of the engine and the number of revolutions of the engine, adjusts the delay time and amplitude of the noise signal according to the number of revolutions,
Since the sound generation means is driven to interfere with the intake system noise, the intake system noise can be efficiently reduced in a wide rotation range. Further, by obtaining and storing the delay time and the amplitude adjustment amount according to the rotational speed in advance by experiments or the like, it is possible to generate a sound having substantially the same amplitude as the noise of the intake system and a substantially opposite phase with good responsiveness.

Further, in the present invention, for example, if a ceramic speaker using a piezoelectric element is used as the sound generating means, the output becomes extremely thin with a high output, and the mountability to the intake system can be greatly improved.

[Brief description of the drawings]

1 is an overall configuration diagram showing one embodiment of the present invention, FIG. 2 is a configuration diagram of a noise control circuit in FIG. 1, FIG. 3 is an electric circuit diagram of a silencer circuit in FIG. The figure is an electric circuit diagram of the feedback circuit in FIG. 2, and FIG.
(B) and (c) are explanatory diagrams showing the principle of silencing, FIG. 6 is a flowchart showing a processing procedure in a central processing unit in FIG. 2, and FIGS. 7 (a) and (b) are sound generating means. FIG. 8 is a view showing the structure of a ceramic speaker incorporated in an air cleaner as another example, FIG. 8 is an apparatus configuration diagram when the ceramic speaker of FIG. 7 is used, and FIGS.
(B), (c) is a figure which shows the structure of the intake pressure sensor as another example of a noise detection means. 1 ... Microphone, 2 ... Noise control circuit, 3 ... Sound loudspeaker, 3 '... Ceramic speaker, 4 ... Air cleaner, 5 ... Boost circuit, 6 ... Feedback microphone, 7 ... Intake pressure sensor , 8 ... Rotation sensor, 10 ... Engine, 11 ... Intake system, 31,71 ... Bimorph piezoelectric element, 210
…… Silencer circuit, 212,283 …… Programmable filter, 214 …… BBD, 216 …… Op amp for level adjustment, 218
…… Inverting operational amplifier, 220 …… CPU, 230 …… Memory, 280
...... Feedback circuit.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Masanori Kato 14 Iwatani, Shimoba Kakucho, Nishio City, Aichi Prefecture Inside the Japan Automobile Parts Research Institute (72) Inventor Satoshi Kuwamon 14 Iwatani, Shimohakakucho, Nishio City, Aichi Prefecture Japan Inside the Automotive Parts Research Laboratory (72) Inventor Tokio Obama 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Inside Denso Corporation (72) Inventor Yoshitaka Nishio 1-1-1, Showa-cho, Kariya-shi, Aichi Japan Denso Corporation (56) References JP-A-57-6897 (JP, A) JP-A-62-48910 (JP, A) JP-A-62-168913 (JP, A) JP-A-62-168914 (JP, A)

Claims (6)

(57) [Claims] 1. A sound generating means provided on a propagation path of noise of an engine intake system and generating a sound that interferes with the noise, a rotational speed detecting means for detecting a rotational speed of the engine, Noise detection means for detecting a signal relating to noise; and memory means for storing information of a delay time and an amplitude adjustment amount according to the number of revolutions of the engine. The information stored in the memory means and the rotation Noise control means for adjusting the delay time and amplitude of the detection signal detected by the noise detection means based on the engine speed detected by the number detection means; An intake system noise reduction device, wherein the sound generating means generates a sound having substantially the same amplitude and a substantially opposite phase as the intake system noise based on the received signal. 2. The noise control means receives a signal from feedback noise detection means for measuring a noise level after silencing, which is provided on the side opposite to the engine of the sound generation means, and extends or shortens the delay time. 2. The intake system noise reduction device according to claim 1, further comprising a correction unit. 3. The noise control means includes filter means for filtering detection signals from the two noise detection means, and controls a pass frequency of the filter means in accordance with a rotation speed. 3. The intake system noise reduction device according to claim 2, wherein: 4. A plurality of long piezoelectric elements vibrated by an acoustic signal from the noise control means, some of which are cantilevered in a case, and vibrations from the piezoelectric elements. 2. A ceramic speaker according to claim 1, further comprising a diaphragm connected to the other end of the piezoelectric element so as to propagate the sound and amplifying the vibration to generate sound. System noise reduction device. 5. The intake system noise reduction device according to claim 1, wherein said sound generating means is built in an air cleaner of an engine. 6. An intake system according to claim 1, wherein said noise detecting means is an intake pressure sensor for fixing a peripheral portion of a piezoelectric element by a case and detecting a pressure in an intake pipe by a diaphragm method. Noise reduction device.