JP2926193B2 - Active cancel muffler - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to an active cancel muffler mounted on an internal combustion engine, and more particularly to an active cancel muffler provided with an adaptive digital filter.

[Prior art] As an active cancel muffler, for example,
As described in JP-A-63-118321, a speaker tube is provided at an outlet of an exhaust pipe serving as a noise outflow pipe with respect to an internal combustion engine as a noise source, a cancel speaker is connected to this speaker pipe, and a predetermined It is known that noise from an internal combustion engine, that is, a dense / dense pressure wave having a phase opposite to that of the exhaust sound is output from a cancel speaker in response to a control signal, and the sound is canceled by a canceling action of both pressure waves. The device described in the publication focuses on the directional characteristics of the pressure wave from the cancel speaker. As for the active cancel control means, various types of input information are subjected to arithmetic processing according to processing conditions predetermined by the CPU. It is only briefly explained.

By the way, recently, an input analog signal is converted into a digital amount, and after being appropriately processed by a digital signal processing circuit, converted into an analog signal again and output, and a predetermined amount is provided between the input analog signal and the output analog signal. Attention has been focused on digital filters having characteristics.

With this digital filter, it is possible to detect information that affects the control system and automatically change its own control characteristics according to the change to realize adaptive control that optimizes the state regardless of changes in load. This is called an adaptive digital filter (adaptive digital filter, ADF), and its use for various controls is being studied. Especially, in the acoustic field, in order to cancel an echo generated through an acoustic path between a speaker and a microphone, use of the acoustic echo canceller to generate and identify a pseudo echo signal substantially equal to the echo has attracted attention. I have. Adjusting the former transfer function such that the transfer function of the adaptive digital filter becomes equal to the transfer function of the unknown system and the prediction error becomes zero is referred to as "identifying the unknown system".

[Problems to be Solved by the Invention] In the active cancel muffler described above, the internal combustion engine is a source of exhaust noise, and the exhaust sound path of the exhaust manifold and the exhaust pipe can be called an acoustic path. May be applicable, but there are many problems in consistency with the problems specific to the internal combustion engine, and it is not immediately applicable. For example, when a noise detector is mounted near the exhaust manifold outlet of an internal combustion engine in accordance with a general arrangement to detect a pressure wave of a noise source, not only the temperature change of the external environment but also the high-temperature exhaust gas Since it is exposed, durability becomes a problem. In Japanese Utility Model Application Laid-Open No. 63-118321, the frequency of the pressure wave of the exhaust noise is increased in proportion to the rotation speed of the internal combustion engine, and the crank angle sensor detects the angular velocity of the crankshaft and indirectly detects the frequency. The frequency of the noise pressure wave is to be detected. However, this cannot be directly applied to the adaptive digital filter.

Further, as shown in FIG. 4, the exhaust noise of the internal combustion engine has a periodic waveform synchronized with the rotation of the engine. Therefore, using an adaptive digital filter for the active cancel muffler,
For example, when the control is performed in accordance with an impulse synchronized with the rotation of the internal combustion engine, if the number of taps of the adaptive digital filter is constant, a plurality of impulses are input to the adaptive digital filter when the internal combustion engine is rotating at a high speed. It becomes difficult to control the adaptive digital filter. On the other hand, if the number of taps is set so as to be suitable at the time of high rotation of the internal combustion engine, the noise reduction effect at low rotation becomes small.

Therefore, the present invention utilizes an adaptive digital filter,
An object of the present invention is to provide an active cancel muffler that can surely mute a sound without being affected by a change in the rotation speed of an internal combustion engine.

Means for Solving the Problems In order to achieve the above object, the present invention provides a pressure wave output unit that opens at an output port of an exhaust sound path including a range pipe of an internal combustion engine and outputs a sparse and dense pressure wave; A pressure wave detecting unit arranged near the output port of the sound path and outputting a signal corresponding to the output pressure wave, a rotation detecting unit outputting a rotation signal corresponding to the rotation of the internal combustion engine, and an output rotation of the rotation detecting unit Edge detection means for outputting an impulse synchronized with the rotation of the internal combustion engine based on the signal; and an adaptive digital filter. The number of taps of the adaptive digital filter is set according to the rotation of the internal combustion engine, and the pressure wave is set. The output signal of the detecting means is input, and the pressure is adjusted so that the transfer function of the adaptive digital filter is identified as the transfer function of the exhaust sound path according to the output impulse of the edge detecting means. Filter means for driving and controlling the wave detection means.

In the active cancel muffler, the filter unit includes a tap counter for counting the number of taps, and when there is an output impulse of the edge detection unit, the value of the tap counter is set to the number of taps.
It is preferable that the tap counter is incremented when there is no output impulse.

[Operation] When the internal combustion engine is started and rotated, an explosion sound generated in response to an explosion in each cylinder is transmitted through an exhaust sound path including an exhaust pipe to form an exhaust sound. Further, a rotation signal corresponding to the rotation of the internal combustion engine is output from the rotation detecting means to the edge detecting means. The rotation signal is converted into an impulse by the edge detecting means, and an impulse synchronized with the rotation of the internal combustion engine is output to the adaptive digital filter. On the other hand, a signal corresponding to the output pressure wave output from the exhaust sound path is detected by the pressure wave detecting means and output to the adaptive digital filter.

In the adaptive digital filter, the transfer function is set so as to be equal to the transfer function of the exhaust sound path based on the output signal of the pressure wave detecting means in response to the output impulse of the edge detecting means. , A drive signal is output. In response to this drive signal, the pressure wave output means outputs a compression pressure wave to the output port of the exhaust sound path, and the pressure wave of the exhaust sound output from the exhaust sound path is cancelled, so that the exhaust sound disappears. In this case,
Since the number of taps of the adaptive digital filter is set according to the rotation of the internal combustion engine, an optimal noise reduction effect is ensured in all the operating states of the internal combustion engine from low rotation to high rotation.

Hereinafter, a preferred embodiment of the active cancel muffler according to the present invention will be described with reference to the drawings.

FIG. 1 shows an embodiment of the present invention.
The exhaust pipe 3 is connected to the exhaust manifold 2. Therefore, an exhaust sound path is constituted by the exhaust manifold 2 and the exhaust pipe 3 for the internal combustion engine 1 which is an exhaust sound source. In the vicinity of the outlet of the exhaust pipe 3, a speaker pipe 4 is mounted coaxially with the exhaust pipe 3 so as to surround the outlet, and an actuator 5 composed of an electromagnetic or electrodynamic type speaker and outputting a coarse / dense pressure wave is provided. It is housed in a tube 4. The actuator 5 and the speaker tube 4 constitute a pressure wave output unit according to the present invention. The number of the actuators 5 may be one or more, and the invention is not limited to an electromagnetic speaker and the like, and the diaphragm may be hydraulically driven by an electromagnetic valve in order to secure high output.

A pressure sensor 6 that outputs a signal corresponding to the output pressure wave of the exhaust pipe 3 and the speaker pipe 4 is provided near the outlet of the exhaust pipe 3. The pressure sensor 6 constitutes the pressure wave detecting means according to the present invention, and may be in any form as long as it is means for converting a pressure signal into an electric signal such as a microphone.

On the other hand, the internal combustion engine 1 is provided with a rotation signal detector 7 that outputs a pulse signal synchronized with the rotation. The rotation signal detector 7 constitutes rotation detection means according to the present invention, and is provided, for example, opposite to a rotating plate (not shown) that rotates in synchronization with the internal combustion engine 1 and according to a change in magnetic flux density. It is a known detector such as an electromagnetic induction type pickup that outputs an electric signal, but is a known ignition signal generator (not shown).
May be used as a rotation signal. The rotation signal detector 7 is connected to an edge detector 8 as an edge detecting means according to the present invention, and outputs an impulse synchronized with the rotation of the internal combustion engine 1 based on the rotation signal input thereto.

The output impulse of the edge detector 8 is configured to be supplied to an adaptive digital filter 10. The output signal of the pressure sensor 6 is amplified through an input amplifier 11, converted into a digital signal by an A / D converter 12, and input to the adaptive digital filter 10. The digital signal output from the adaptive digital filter 10 is converted into an analog signal by the D / A converter 13, amplified through the power amplifier 14, and amplified.
Is supplied as a drive signal to the power supply.

The adaptive digital filter 10 is a digital filter 10f
And an adaptive algorithm 10a for sequentially controlling the multiplier coefficients constituting the adaptive filter 10a. The transfer function of the digital filter 10f is identified with respect to the transfer function of the exhaust sound path of the exhaust manifold 2 and the exhaust pipe 3. As such, each coefficient is set via the adaptive algorithm 10a.

The above-mentioned adaptive digital filter 10 can be realized by forming an integrated circuit using a multiplier, an adder, etc. In this embodiment, as shown in FIG. 2, a digital signal processor (DSP) 10p, a memory 10m, an oscillator 10s, etc. The filter function can be easily changed by changing the program. The oscillator 10s is used for sampling (sampling), and the memory 10m may be built in the digital signal processor 10p. Since these are well known, the description is omitted.

Further, the digital signal processor 10p has a tap counter 10 driven according to the output of the edge detector 8.
t is connected, and the number of taps of the digital filter 10f is set according to the value of the tap counter 10t. The tap counter 10t may be provided with a counter program in the program of the digital signal processor 10p.

Next, the operation of the active cancel muffler of this embodiment will be described. When the internal combustion engine 1 starts and rotates, an explosion sound generated in response to an explosion in each cylinder is transmitted through an exhaust sound path of the exhaust manifold 2 and the exhaust pipe 3 to form an exhaust sound. Therefore, the exhaust sound is mainly constituted by the sound of the exponent order component. Further, a rotation signal corresponding to the rotation of the internal combustion engine 1 is output from the rotation signal detector 7 to the edge detector 8. The edge detector 8 converts the impulse into a rotation signal impulse, and the impulse synchronized with the rotation of the internal combustion engine 1 is input to the digital signal processor 10p. In response to the impulse, the digital signal is processed in the digital signal processor 10p as described later and a digital signal is output. Then, the output digital signal is converted into an analog signal via the D / A converter 13 and then amplified by the power amplifier 14 to drive the actuator 5.

As a result, a coarse / dense pressure wave is formed in the speaker tube 4 and is output so as to surround the pressure wave of the exhaust sound. That is, both pressure waves are combined and output so as to cancel each other.
The output pressure wave is detected by the pressure sensor 6, amplified through an input amplifier 11, converted into a digital signal by an A / D converter 12, and then converted into a digital signal by a digital signal processor 10.
Input to p as an error signal. Then, the coefficient is marched by the adaptive algorithm 10a so that the transfer function of the digital filter 10f is identified as the transfer function of the exhaust sound path of the exhaust manifold 2 and the exhaust pipe 3.

The operation of the digital signal processor 10p during this time will be described with reference to FIG. First, step 100
As a result, the number of taps of the digital filter 10f is cleared as an initial condition, and the tap counter 10t is reset to zero. Next, in step 101, it is determined whether or not it is the conversion timing according to the sampling signal of the oscillator 10s.
Proceeding to 2, the presence or absence of an input from the edge detector 8 is determined. If there is an edge detection, that is, if there is an impulse input, the number of taps of the digital filter 10f is set to the value of the tap counter 10t in step 103, and then the process proceeds to step 104 where the tap counter 10t is reset to 0.
It is said. Then, in step 105, “1” is input to the digital filter 10f. If it is determined in step 102 that there is no edge detection, the process proceeds to step 106, where the tap counter 10t is incremented and 1 is added, and "0" is input to the digital filter 10f in step 107. Accordingly, a transfer function is calculated according to the former "1" signal, and a digital signal is output from the digital filter 10f in step 108. Note that this output digital signal is converted into an analog signal by the D / A converter 13, and the output
Is driven.

Further, in step 109, the output signal of the pressure sensor 6 is A / D converted and input as a digital signal to the digital filter 10f.
The coefficient of 0f is updated according to the adaptive algorithm 10a, the transfer function is set to be equal to the transfer function of the exhaust sound path, and the process returns to step 101. Thus, the above steps are repeated so that the output of the pressure sensor 6 is minimized.

As described above, since the exhaust noise of the internal combustion engine 1 is mainly composed of the sound of the order component of the explosion,
By inputting an impulse synchronized with the rotation of, the sound of higher order components can be silenced, and the order of the adaptive digital filter 10 is reduced, and the structure is simplified. In addition, the rotation speed of the internal combustion engine 1 is low and the edge detector 8
The longer the input interval of the impulse from the tap detector 10t, the larger the count value of the tap counter 10t becomes.
When the impulse from is input, the number of taps set in step 103 increases. Conversely, when the rotation speed of the internal combustion engine 1 is high and the input interval of the impulse from the edge detector 8 is short, the count value of the tap counter 10t becomes small. As described above, since the number of taps changes in accordance with the rotation speed of the internal combustion engine 1, it is possible to always perform the silencing operation in an optimum state from a low rotation speed to a high rotation speed without being affected by the change in the rotation speed of the internal combustion engine 1. Can be.

[Effects of the Invention] Since the present invention is configured as described above, the following effects can be obtained.

That is, according to the active cancel muffler of the present invention, the transfer function of the adaptive digital filter is controlled so as to be identified as the transfer function of the exhaust sound path with an impulse response synchronized with the rotation of the internal combustion engine. Sound can be reliably muted. In addition, since the number of taps of the adaptive digital filter is set according to the rotation of the internal combustion engine, it is possible to mute the sound in an optimum state from a low rotation to a high rotation of the internal combustion engine.

[Brief description of the drawings]

FIG. 1 is a block diagram of an active cancel muffler according to an embodiment of the present invention, FIG. 2 is a block diagram showing a configuration of an adaptive digital filter, and FIG. 3 is a flowchart showing a control operation of a digital signal processor. ,
FIG. 4 is a characteristic diagram of exhaust noise of the internal combustion engine. 1 ... internal combustion engine, 2 ... exhaust manifold (exhaust sound path), 3 ...
Exhaust pipe (exhaust sound path), 4 ... speaker pipe (pressure wave output means), 5 ... actuator (pressure wave output means), 6 ... pressure sensor (pressure wave detection means), 7 ... rotation signal detector (rotation detection means) ), 8 ... edge detector (edge detection means), 10 ... adaptive digital filter (filter means) 10p ... digital signal processor

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁶ , DB name) F01N 1/00

Claims (1)

(57) [Claims] 1. A pressure wave output means which is open at an output port of an exhaust sound path including an exhaust pipe of an internal combustion engine and outputs a compression / dense pressure wave, and is disposed near an output port of the exhaust sound path and responds to the output pressure wave. Pressure wave detecting means for outputting a signal, rotation detecting means for outputting a rotation signal according to the rotation of the internal combustion engine, and outputting an impulse synchronized with the rotation of the internal combustion engine based on the output rotation signal of the rotation detecting means Edge detection means, an adaptive digital filter, the number of taps of the adaptive digital filter is set according to the rotation of the internal combustion engine, an output signal of the pressure wave detection means is input, and an output impulse of the edge detection means is provided. Filter means for driving and controlling the pressure wave output means so that the transfer function of the adaptive digital filter is identified as the transfer function of the exhaust sound path in accordance with Active cancellation muffler which is characterized.