JPS58214613A - Device for reducing pulsating sound of exhaust from engine - Google Patents

Abstract

PURPOSE:To provide a small capacity silencer for realizing low exhaust pressure and saving energy by providing a sound pressure generator for generating sound pressure having approximately opposite phase to pulsating sound of exhaust in an exhaust pipe of an engine. CONSTITUTION:While a sound pressure generator 5 is operated by signals from a signal generating circuit, the operation it-self is similar to that of a general speaker. A coil 7 is excited by signals to vibrate a permanent magnet 8 and thereby a diaphragm 10 through a connecting rod 9. And air is vibrated by the vibration of the diaphragm 10 to generate sound. On the other hand, pulsating sound of exhaust is generated by opening and closing intermittently an exhaust valve of an engine. Thus the max. sound pressure is provided in the instant that the exhaust valve is opened and in a time lag relatively to ignition pulse.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a device for reducing engine exhaust pulsation noise.

As a conventional exhaust pulsation noise reduction device, for example, Fig. 1 (A
There are silencers shown in ) to (C).

The basic idea of these mufflers is to minimize pressure fluctuations, and absorb the fluctuations by storing 1-no-1 air in the air A11I. (△), 1 is a pure expansion type silencer, and ([3) is a porous resonance type silencer 1. Also (C)44 multi-stage resonance type/l! The i-convex muffler uses a partition inside the muffler as a dynamic vibration absorber to absorb pressure fluctuations that cause noise.This muffler is described in Kogo Publishing 01. ``Noise countermeasures and silencing design''.

However, when using such conventional silencers, in order to increase the silencing effect, it is basically necessary to increase the capacity of the silencer. Since the layout under the vehicle floor panel inevitably determines the maximum volume M, there is a limit to the sound deadening performance.

On the other hand, 1) Reducing the power loss in the 1-gas system means (1) In this age of fuel efficiency, it is a serious issue, ,
'i (11), and since there is a relationship in which the capacity of the muffler is large, 1) the pressure increases, there is a problem that the muffling effect and fuel efficiency are in a contradictory relationship. Ta.

The present invention focuses on these conventional problems, and makes it possible to effectively reduce exhaust pulsation noise without increasing the size of the device, thereby making it possible to freely layout the exhaust system under the floor. Another object of the present invention is to provide an exhaust pulsation noise reduction device that enables low exhaust pressure and does not impede the demands for low fuel consumption.

In order to achieve the above object, the present invention provides a sound pressure generator in the exhaust pipe of an engine that receives a signal related to the exhaust pulsation sound and generates a sound pressure having a phase substantially opposite to that of the exhaust pulsation sound. This reduces the sound pressure level of exhaust pulsation noise.

The present invention will be described below based on an embodiment not shown in FIGS. 2 to 4. However, the engine will be a 4 cylinder, 4 cycle.

In FIG. 2, 1 is an engine body, 2 is an exhaust manifold, 3 is an exhaust pipe, and 4 is a muffler.

Here, a sound pressure generator 5 that generates sound pressure inside the exhaust pipe 3 is installed in the middle of the exhaust pipe 3.

The sound pressure generator 5 has the same configuration as a general speaker,
As shown in FIG. 3, a metal diaphragm is provided with a coil 7 and a permanent magnet 8 excited by the coil 7 in the main body, and this permanent magnet 8 is installed by a connecting rod 9 to cover the opening of the main body 6. It is connected to Tsukasa O. Although a cone is used in the speaker, a metal diaphragm is used due to heat concerns.

Then, the flange II at the opening 11 of the main body 6 is joined to the flange 13 at the opening provided in the exhaust pipe 3 via the peripheral edge of the diaphragm 10 and the heat insulation 102, and fixed e) with the bolt 14 and nut 15. It is. In addition, the main body 6 is connected to the vehicle floor panel 7"C through the anti-vibration rubber I6.
It is supported by +.

The signal from the sound pressure generator 5 (controller 7) is generated by the signal generating circuit shown in FIG. 4. The signal generation circuit 8 is basically based on the ignition pulse LJ to the ignition τl, and the ignition pulse generation ηE
1iFl lI3 (ignition = 1il) 17, rl-pass filter] 8, waveform shaping circuit 1! J, phase conversion circuit (
(F-V converter) 20 and an amplifier 21.

The amplifier 21 also includes an engine suction negative pressure detector 22.
The signal from is input as an auxiliary input.

To explain the operation, the ignition pulse is shaped by the low-pass filter 18 into only a signal of approximately 200 Hz or less, and further shaped into a sine wave, that is, a single frequency, by the waveform shaping circuit 19. This sine wave signal is then transferred to a phase conversion circuit 2 having a preset phase conversion characteristic.
After being input to 0 and having its phase converted, it is input to an amplifier 2 which has preset amplification characteristics and is amplified.
It is applied from the amplifier 21 to the coil 7 of the sound pressure generator 5.

The sound pressure generator 5 operates in response to a signal from a signal generation circuit, but its operation itself is similar to that of a general speaker. That is, the coil 7 is excited by the signal, and the permanent magnet 8 vibrates in accordance with the excitation of the coil 7. This vibration causes the diaphragm 10 to vibrate via the connecting rod 9. The vibration of the diaphragm 10 causes the air to vibrate and generate sound.

On the other hand, the 1-no-1 air pulsation sound is caused by the intermittent opening and closing of the engine's air valve. Therefore, the maximum sound pressure occurs at the moment the exhaust valve opens, and there is a time delay in relation to the ignition pulse. There is.

That is, an ignition pulse is generated when the piston enters the explosion stroke (actually, a little before this), and after the explosion, when the piston enters the IJI stroke, an exhaust pulsation sound is generated. If this time rough is T, then the engine 2
Since it corresponds to rotation, when the engine rotation speed is Nrpm, i'' = 3(]/N (sec).

In addition, if the distance between the 1-no-1 atmosphere manifold (2 and the sound pressure generator 5 is ), the pulsating sound generated in the exhaust manifold 2 reaches the mounting part of the sound pressure generator 5 at an exhaust temperature of 4 degrees. Assuming that the temperature is 500°C, the speed of sound transmitted through the exhaust gas is about 63 axes/sec, so it will be after L/630 (sec).

Therefore, the exhaust pulsation noise reaches the first part of the sound pressure generator 5 30/Nl/630 (aec) after the ignition pulse is output. In other words, at this time, the sound pressure due to the exhaust pulsation sound at the mounting part reaches the maximum level (Po).
become.

At this time, when the diaphragm 10 of the sound pressure generator 5 moves upward in the figure to generate a sound pressure of -Po, the sound pressure P reaching the mounting portion becomes P-Po+ (Po) and becomes zero. That is, the exhaust pulsation noise disappears.

By setting the characteristics of the phase conversion circuit 20 and the amplifier 21 in the signal generation circuit in this manner, it is possible to reduce the exhaust pulsation noise to zero or to a considerably low level.

Here, the characteristics of the phase conversion circuit 20 are considered as follows.

When the engine speed changes between 600rpm and 6000rpm, the ignition pulse is
It changes from 2011z to 20011z. Assuming that the exhaust temperature is 500°C and the sound speed is approximately 630 m/sec, the wavelength will be approximately 31.5I11 to 3.15 m.

Considering the length of the exhaust pipe 3, even at 6000 rpm, it is about -wavelength, so as long as the sound pressure generator 5 is installed relatively upstream of the exhaust pipe 3, there will be almost no change in the phase depending on the frequency at the mounting part. It will be done.

Also, regarding the amplification characteristics of the amplifier 21, the υ1 air noise is proportional to approximately the 6th power of the engine speed, so the characteristics are set to match this characteristic, but the υ 1 air noise also varies depending on the engine load. Generally, () 1 aspirate is proportional to the load, so
The Iff width of the amplifier 21 should also be matched to the second and first characteristics. Therefore, the engine intake negative pressure is detected as i*11& and inputted to the amplifier 21.

In this example, an ignition pulse is used as the signal generation source, but this is due to the following II+ for l''ll.

The frequency 111 of the exhaust noise is generally as shown in FIG. 5 (four-cylinder engine). In Figure 5, 2Kllz
The noise that occurs below is the exhaust pulsation sound that is generated every time the exhaust is intermittently discharged from the engine.
The noise from the old 1z to 1- is airflow noise. Here, the exhaust pulsation sound is generated by the engine exploding, and the basic frequency is 4 cycles, so it is twice the engine rotation.

Therefore, an ignition pulse having the same frequency as the fundamental frequency of the exhaust pulsation sound is used to reduce the basic exhaust pulsation sound.

In addition, considering that the mounting part of the sound pressure generator 5 to the exhaust pipe 3 should be as close to the engine as possible in order to minimize the amount of noise muffling by the muffler, it is better to have the catalyzer as close as possible to the engine. It is also desirable to consider the effects of heat.

As explained above, according to the present invention, the exhaust pulsation sound is generated in the exhaust pipe and a sound with a phase opposite to that of the exhaust pulsation sound is silenced. can be reduced.

Furthermore, since the capacity of the muffler can be reduced, exhaust pressure can be reduced, resulting in energy savings. Considering this from the perspective of engine horsepower, it shows that if the horsepower is the same, it is possible to reduce the displacement. Additionally, the layout of the exhaust system under the floor panel becomes more flexible, increasing its aerodynamic contribution.

[Brief explanation of drawings]

FIGS. 1(A) to 1(C) are schematic diagrams showing typical mufflers used conventionally. FIGS. 2 to 4 show an embodiment of the present invention, and FIG. 2 shows sound pressure generation 11 to the engine exhaust system.
(Figures 1 and 3 are cross-sectional views of the sound pressure generator, Figure 4 is a block diagram of the signal generation circuit to the back pressure generator, and Figure 5 is a general exhaust FIG. 3 is a diagram showing the frequency weight of noise.

Claims (3)

[Claims] (1) An engine exhaust pulsation noise reduction device comprising a sound pressure generator installed in the engine exhaust pipe, which receives a signal related to the exhaust pulsation noise and generates a sound pressure in phase substantially opposite to the exhaust pulsation noise. (2) The engine exhaust pulsation noise reduction device according to claim 1, wherein the signal related to the exhaust pulsation noise is an engine ignition pulse. (3) The engine exhaust pulsation noise reduction device according to claim 1, wherein the sound pressure generator generates sound pressure by vibrating a diaphragm using a coil and a permanent magnet.