JPH04342813A - Noise silencing device for internal combustion engine - Google Patents

Abstract

PURPOSE:To silence a noise component having a frequency corresponding to the rotational speed of an engine and a noise component having random frequencies in a wide range by amplifying outlet sounds from a plurality of speakers attached to an exhaust pipe in accordance with differences in outputs from a plurality of microphones which pick up noise in the exhaust gas pipe, in order to silence the noise in the exhaust pipe. CONSTITUTION:A sensor 1 for detecting an operational cycle period of an internal combustion engine 11 delivers its output to a program control circuit 10. Simultaneously, noise in an exhaust pipe is picked up by a first microphone 2 which delivers an electrical signal to the control circuit 10. Meanwhile, the control circuit 10 controls a first amplifying control circuit 4 in accordance with the delivered signals so as to amplify and control the output of a first speaker 3 in order to suppress sound in the exhaust pipe 12. In this case, first and second microphones 5, 6 which are successively attached to the downstream side of the exhaust pipe 12 pick up noises and delivers noise signals to a differential amplifier 6 so as to compute a difference between the noise signals. Further, the control circuit 10 controls a second amplifying control circuit 9 in accordance with this difference.

Description

[Detailed description of the invention]

0001

FIELD OF INDUSTRIAL APPLICATION The present invention is utilized as a device for reducing exhaust noise of an internal combustion engine. The present invention relates to a device that cancels the exhaust sound of an internal combustion engine by collecting the exhaust sound of an internal combustion engine with a microphone, calculating the output of the microphone, and generating a sound having the opposite phase and same sound pressure as the exhaust sound.

0002

BACKGROUND OF THE INVENTION Conventionally, this type of silencer has been disclosed in Japanese Patent Application Laid-open No. 58-214613 and Japanese Patent Application Laid-open No. 62-168.
There is one disclosed in Publication No. 914. In addition, the specific structure for implementing the device can be found in the "Automotive Technology Handbook" Basic/Theory Edition 328 published by the Society of Automotive Engineers of Japan.
It is described on pages 330 to 330.

As shown in FIG. 3, these silencers include a sensor 1 that detects the operating cycle of an internal combustion engine 11, a microphone 22 that collects sounds from the internal combustion engine 11 in the exhaust pipe 12, and a an amplification control circuit 24 that takes in the outputs of the sensor 1 and the microphone 22 and performs amplification control so as to cancel out the sound in the exhaust pipe 12; and a program control circuit 20 that controls the amplification control circuit 24. and will be provided.

[0004] The conventional silencer configured as described above has the following features:
The microphone 22 collects the noise generated by the internal combustion engine 11 and sent into the exhaust pipe 12, and the program control circuit 20 outputs a control signal based on the operating cycle of the internal combustion engine 11 detected by the sensor 1 to the amplification control circuit 24. The noise is then amplified and output to the speaker 23 so as to have a phase opposite to that of the exhaust sound, thereby canceling out the exhaust sound generated as rotation periodic sound.

Another device is a first microphone 32 disposed inside the exhaust pipe 12, as shown in FIG.
and a second microphone 33 arranged downstream thereof,
First microphone 32 and second microphone 33
a differential amplifier 34 that calculates the difference between the output of the first microphone 32 and the output of the second microphone 33;
an amplification control circuit 35 that amplifies the output of the second microphone 33 and supplies it to the speaker 23 so that the output of the second microphone 33 is minimized; and a program control circuit 30 that receives the output of the differential amplifier 34 and controls the amplification control circuit 35. I have something prepared.

In the case of this device, the noise generated in the internal combustion engine 11 and sent to the exhaust pipe 12 is transmitted to the first microphone 3.
2 and a second microphone 33, the differential amplifier 34 calculates the difference between the respective outputs and outputs it to the program control circuit 30, which controls the differential amplifier 34 based on the output. The output given to the speaker 23 is minimized, and wideband random sounds are muted.

[0007]

[Problems to be Solved by the Invention] In the above-mentioned example of a device intended for muffling periodic sounds, as shown in Fig. 5, the peak level of sound pressure after muffling is reduced, but broadband random sounds are completely muffled. There is a problem in that the overall sound pressure level cannot be lowered because the sound pressure level is not lowered.Furthermore, in an example of a device aimed at silencing broadband random sounds, the overall sound pressure level is lowered as shown in Fig. 6. There is a problem in that noise cannot be effectively muted because components of the rotation periodic sound of objects remain.

[0008] The present invention solves these problems and aims to provide a device that can mute both the rotation periodic sound and the broadband random sound components.

[0009]

[Means for Solving the Problems] The present invention includes a sensor that detects the operating cycle of an internal combustion engine, a first microphone that collects sounds from the exhaust pipe of the internal combustion engine, and a first microphone that is attached to the exhaust pipe. A silencer for an internal combustion engine, comprising: a speaker; and a first circuit means for amplifying and controlling the output sound of the speaker so as to cancel the sound in the exhaust pipe according to the output of the sensor; a second microphone located further downstream of the exhaust pipe; a third microphone located further downstream than the second microphone; a second speaker attached to the exhaust pipe; a differential amplifier that calculates the difference between the output of the second microphone and the output of the third microphone; The present invention is characterized by comprising a program control circuit that calculates the output of the second speaker so as to minimize the output.

0010

[Operation] The noise in the exhaust pipe is collected by the first microphone, its output is amplified, and is supplied to the first speaker.The output sound from the first speaker is also output according to the detected output of the operating cycle of the internal combustion engine. The rotation periodic sound is muted by canceling the rotation periodic sound. At the same time, the difference between the output from the second microphone and the output of the noise sampled from the third microphone is calculated, and the broadband random sound is muted so that the output to the second speaker is minimized.

[0011] Thereby, the rotation periodic sound component and the broadband random sound component can be simultaneously targeted for muffling, and the muffling effect can be further enhanced.

0012

Embodiments Next, embodiments of the present invention will be explained based on the drawings. FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

The embodiment of the present invention includes a sensor 1 for detecting the operating cycle of an internal combustion engine 11, and an exhaust pipe 12 of the internal combustion engine 11.
A first microphone 2 that collects sound, a first speaker 3 attached to the exhaust pipe 12, and the output sound of the first speaker 3 cancels the sound inside the exhaust pipe 12 according to the output of the sensor 1. A first amplification control circuit 4 that performs amplification control as shown in FIG.
a second microphone 5 disposed further downstream of the exhaust pipe 12; a third microphone 6 disposed further downstream than the second microphone 5; and a second microphone 5 and a third microphone 6. a second speaker 7 attached to an exhaust pipe 12 between the speakers, a differential amplifier 8 that calculates the difference between the output of the second microphone 5 and the output of the third microphone 6, and the first and second amplifiers. A program control circuit 10 that controls the control circuits 4 and 9 is provided.

Next, the operation of the embodiment of the present invention constructed as described above will be explained.

The sensor 1 detects the operating cycle of the internal combustion engine 11 and sends the detected output to the program control circuit 10. At the same time, the first microphone 2 captures the noise inside the exhaust pipe 12 and outputs it to the program control circuit 10 as an electrical signal. The program control circuit 10 controls the first amplification control circuit 4 based on these output signals, and outputs sound so as to cancel out the noise in the exhaust pipe 12. Through such an operation, it is possible to muffle the rotational periodic sound component generated by the operating period of the internal combustion engine 11.

On the other hand, a second microphone 5 provided on the downstream side of the exhaust pipe 12 and a third microphone 6 provided further downstream take in noise and output it to the differential amplifier 8 as an electrical signal. The differential amplifier 8 calculates the difference between these two outputs and outputs it to the program control circuit 10. The program control circuit 10 outputs a control signal to the second amplification control circuit 9 based on the calculation result.

FIG. 2 shows the relationship between frequency and sound pressure level before and after muffling. When the sound pressure level before muffling, shown by the solid line, is muffled by the device of this embodiment, the sound pressure level changes as shown by the broken line. It can be seen that both rotational periodic sounds and broadband random sounds are muted over the entire frequency range.

[0018]

As explained above, according to the present invention, the exhaust sound of an internal combustion engine is collected by a microphone, and its output is amplified to generate a sound having a phase opposite to that of the exhaust sound. Both the component and the broadband random sound component can be targeted for silencing, and the silencing effect can be further improved.

[Brief explanation of drawings]

FIG. 1 is a block diagram showing the configuration of an embodiment of the present invention.

FIG. 2 is a diagram showing the relationship between frequency and sound pressure level before muting and after muting by the device according to the embodiment of the present invention.

FIG. 3 is a block diagram showing the configuration of a conventional device that targets rotational periodic noise.

FIG. 4 is a block diagram showing the configuration of a conventional device that targets broadband random sounds.

FIG. 5 is a diagram showing the relationship between frequency and sound pressure level before and after muffling of a device that targets rotational periodic sound.

FIG. 6 is a diagram showing the relationship between frequency and sound pressure level before and after muting in a device that targets broadband random sounds.

[Explanation of symbols]

1 Sensors 2, 32 First microphone 3 First speaker 4 First amplification control circuit 5, 33 Second microphone 6 Third microphone 7 Second speaker 8, 34 Differential amplifier 9 Second amplification control Circuits 10, 20, 30 Program control circuit 11
Internal combustion engine 12 Exhaust pipe 22 Microphone 23 Speakers 24, 35 Amplification control circuit

Claims (1)

[Claims] 1. A sensor that detects the operating cycle of an internal combustion engine, a first microphone that collects sounds from an exhaust pipe of the internal combustion engine, a first speaker attached to the exhaust pipe, and an output of the sensor. and a first circuit means for amplifying and controlling the output sound of the speaker so as to cancel the sound in the exhaust pipe according to a third microphone located further downstream than the second microphone; and a third microphone mounted on the exhaust pipe between the second microphone and the third microphone. a differential amplifier that calculates the difference between the output of the second microphone and the output of the third microphone; 1. A silencer for an internal combustion engine, comprising a program control circuit that calculates the output of two speakers.