JPH0311110A - Exhaust noise reduction device for car engine - Google Patents

Abstract

PURPOSE:To make it possible to regulate the resonance of an exhaust system at a low level always by arranging a resonance detecting sensor at the position of a body in relation to the resonance mode produced in each exhaust system and switching the exhaust system to a non-resonance side based on resonance detection. CONSTITUTION:An engine 1 is provided with the system from an exhaust manifold 3 to the main tail tube 10 at the head or a sub-tail tube 11. In addition, in the state that the switch valve 12 positioned on the sub-tail tube 11 is closed, exhaust air is discharged from only the main tail tube 10, and another exhaust depending on whether the switch valve 12 is constituted. At this point and at the position of the body in relation to the resonance mode produced in each exhaust system, a resonance detection sensor 15 comprising a resonance chamber 16 and a temperature sensor 18 is arranged. When the resonance sensor 15 detects the occurrence of resonance as the lowering of detected temperature, a control unit 14 drives the opening and closing of the switch valve 12 to switch the current exhaust system to the other system in non-resonance condition. Therefore, resonance can always be regulated at a lower level.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an exhaust noise reduction device for reducing exhaust noise of an automobile engine, particularly noise generated due to resonance of an exhaust system.

BACKGROUND OF THE INVENTION For example, when an automobile engine is suddenly accelerated when it is not very warm, a very loud metal-like noise may be temporarily generated during the acceleration. This abnormal noise is a high-frequency sound of about 1 to I Ok Hz, and although the mechanism by which it occurs has not been precisely elucidated, it is known that it occurs when resonance occurs in the exhaust system. It is being In addition, it is particularly likely to occur in exhaust systems with low back pressure suitable for high-output engines. However, depending on various conditions,
It may also occur when the engine is decelerating.

In order to reduce such transient exhaust noise, it is effective to suppress resonance within the exhaust system.

Incidentally, in recent years, exhaust systems for automobile engines and the like have been known that allow selective use of multiple exhaust systems with different pipe lengths (for example, the
39453, Utility Model Application Publication No. 62-57718, etc.)
.

Problems to be Solved by the Invention However, none of the above-mentioned publications focus on resonance in the exhaust system, but simply develop exhaust systems suitable for low speed or low load ranges and high speed or high load ranges. It simply switches to the flow path.

Therefore, it is not always possible to effectively suppress resonance, and it is not possible to sufficiently reduce the noise and the like during the transient state in the cold machine state mentioned above.

Means for Solving the Problems The present invention provides an automobile engine that can selectively use a plurality of exhaust systems having different resonance modes, in which a front pipe is installed at a position approximately at the antinode with respect to the resonance mode generated in each exhaust system. A resonance detection sensor consisting of a resonance chamber communicating with the exhaust system through the neck pipe and a temperature sensor for detecting the temperature inside the neck pipe is provided, and the exhaust system is configured to be switched to a non-resonance side based on the resonance detection. It is characterized by what it did.

Effect When resonance occurs in one of the exhaust systems selected, sound pressure fluctuations occur sharply near the antinode position of the resonance mode.

Therefore, a resonance effect occurs with the resonance chamber of the resonance detection sensor, and the gas particles in the neck tube move back and forth violently. Therefore, heat exchange between the gas in the resonance chamber, which has been kept at a relatively low temperature due to the cooling effect of the outside air, and the gas in the exhaust system is promoted, and the temperature detected by the temperature sensor is temporarily lowered. That is, in the resonance detection sensor, occurrence of resonance is detected in the form of a decrease in detected temperature.

If resonance is detected in a certain exhaust system like this,
The exhaust system is switched to another exhaust system, ie a non-resonant exhaust system.

EXAMPLE Hereinafter, an example of the present invention will be described in detail based on the drawings.

FIG. 1 is a configuration explanatory diagram showing an embodiment of an exhaust noise reduction device according to the present invention.

In the figure, l is an engine, 2 is a front tube connected to the exhaust manifold 3 of this engine l, 4 is a catalytic converter connected to the front tube 2 via a flexible tube 5, and 6 is a first center tube 7. A pre-muffler 8 is connected to the catalytic converter 4 via a main muffler 8, and a main muffler 8 is connected to the pre-muffler 6 via a second center tube 9. A subtail tube 11 having a short pipe length is connected. A switching valve 12 of a butterfly valve type, for example, for opening and closing the subtail tube 11 is interposed in one of the subtail tubes 11. The switching valve 12 is driven to open and close by an actuator 13 such as a solenoid based on a control signal from a control unit 14. That is, when the switching valve I2 is closed, the exhaust gas is discharged only from the main tail tube 10, and when the switching valve 12 is open, the exhaust gas is discharged from both the main tail tube IO and the sub tail tube 11. be done. Therefore, a different exhaust system will be configured in each state, and its resonance mode and resonance frequency will be different.

Further, a resonance detection sensor I5 using a Helmholtz type resonance element is mounted at an appropriate position in the second center tube 9. For details, see the resonance modes that occur in each exhaust system,
For the resonance modes of nodes 2 to 4, which are particularly problematic in terms of noise, the resonance detection sensor 15
is installed.

As shown in FIG. 2, the resonance detection sensor I5 has a substantially cylindrical resonance chamber! 6 is connected to the second center tube 9 via a front tube 17, and the front tube 16 opens in a manner connected to the side surface of the second center tube 9 at a substantially right angle, and connects the resonance chamber I6 and the second center tube 9. It communicates with the inside of the center tube 9 via the front tube 17. A temperature sensor 18 made of a thermocouple or the like is disposed in the front tube 17 to detect the temperature inside the front tube 17. The output signal of this temperature sensor 18 is input to the control unit I4 and processed as described later to form a trigger signal for exhaust system switching control. In FIG. 1, reference numeral 19 denotes an engine rotation speed sensor that detects the engine rotation speed, and this determines whether the engine speed is being accelerated or decelerated, that is, whether the rotation speed is increasing or decreasing.

The resonance element made up of the resonance chamber I6 and the front pipe 17 is tuned to have a resonance frequency (peak frequency) higher than the frequency of the exhaust system resonance mode to be detected. In other words, the strength of resonance in the resonant element has a characteristic as shown in Figure 3 with the peak at the resonance frequency f0, but the resonance action rapidly decreases at frequencies higher than that peak, so it can be adjusted as appropriate on the lower frequency side. It is recommended that the range (indicated by symbol A) be used. - As an example, the resonance frequency f0 is given to about I kHz, but in this case, the diameter of the resonance chamber 16 required is 25xx, and the length is 10JF.
JI, the diameter of the front tube 17 is 511II+, the length is 25aX
It can be configured very compactly.

Next, the operation of the above configuration will be explained.

First, resonance detection by the resonance detection sensor 15 will be explained using FIG. 4. (A) in the same figure shows an example of the sound pressure characteristics of a certain exhaust system, and as shown in the figure,
Assuming that resonance occurs in the exhaust system at a certain rotational speed R, when the rotational speed approaches that rotational speed, severe sound pressure fluctuations occur at or near the antinode of the resonance mode. Here, if the resonance chamber 16 etc. is tuned so that the resonance frequency of the exhaust system at that time is within the range A in Fig. 3, the resonance detection sensor I5 side connected near the antinode of the resonance mode will also resonate. occurs, causing the gas particles within the tube 17 to violently reciprocate. Therefore, the cold air inside the resonance chamber 16, which has been cooled by outside air, flows out and acts on the temperature sensor 18, as shown in FIG. 4(B).
As shown in , the detected temperature temporarily decreases. This would indicate the occurrence of resonance in the exhaust system.

The above-mentioned temperature signal is differentiated as shown in FIG. 5(C) by signal processing within the control unit 14, and then differentiated once again as shown in FIG. 4(D). Then, based on the fall of the twice differentiated signal T'',
A trigger signal for exhaust system switching control is issued. Specifically, during acceleration, that is, when the engine speed is rising, a trigger signal is generated by selecting the falling edge t on the low speed side, as shown in (E) in the same figure, and during deceleration, that is, when the engine speed is falling. In this figure, select the falling edge t on the high rotation side (
A trigger signal is issued as shown in F). That is, these trigger signals are output at the point in time when resonance starts during acceleration or deceleration.

Next, actual switching control of the switching valve 12 will be explained based on FIG. 5, taking the case of acceleration as an example.

(A) in FIG. 5 shows the characteristics of exhaust noise generated during acceleration in the exhaust system shown in FIG.
When the switching valve 12 is "open", the characteristic is as shown by the broken line A, and when the switching valve 12 is "open", the characteristic is as shown by the solid line. As is clear from this figure, resonance occurs at some rotational speeds in both exhaust systems, but the rotational speeds are different between the two exhaust systems.

If acceleration is started with the switching valve 12 in the "closed" state, resonance will be detected when the rotational speed reaches R8, and a trigger signal will be output as shown in FIG. 2(B). Based on this trigger signal, the switching valve 12 is immediately switched to the "open" state, and the exhaust system having the characteristics indicated by the broken line A is completely switched to the other exhaust system (B). At this time, the exhaust system (b) does not resonate due to the difference in resonance conditions. When the rotational speed further increases, resonance occurs on the exhaust system (b) side. In response to this resonance, a trigger signal is also output at the rotation speed R1, and the switching valve 12 becomes "closed" again. In this way, based on the trigger signal, the two exhaust systems (A)
, (b) are switched alternately.

Therefore, the exhaust system in which resonance does not occur is always selected, and the actual noise characteristics are as shown by the solid line C in FIG. As a result, resonance during acceleration is suppressed to a low level, and generation of abnormal noise due to resonance can be prevented.

Although not shown, during deceleration, a trigger signal is also issued before the resonance reaches its peak, as described above, and based on this, switching control of the exhaust system is similarly performed.

If the exhaust system, such as the main muffler 8, is relatively complex, resonance may occur in one exhaust system (in the illustrated example, the exhaust system indicated by the broken line A with the switching valve I2 closed), as shown in Figure 6. However, the noise level of the other exhaust system (the exhaust system with the solid line in the example shown) is higher than that of the other exhaust system. The range indicated by the symbol B) may be determined experimentally in advance, and the configuration may be configured to stop outputting the trigger signal within that range.In the illustrated example, the range indicated by the symbol B ), the output of the trigger signal is stopped and the exhaust system is not switched.As a result, noise characteristics as shown by the solid line C in FIG. 2C can be obtained.

Next, in the embodiment shown in FIG.
A resonance detection sensor 15 is separately attached to each of the subtail tube 11 and the subtail tube 11. These resonance detection sensors 15 are mounted at selected positions that are concentric with respect to a plurality of resonance modes occurring in each exhaust system.

In this configuration, in which the resonance detection sensor 15 is individually arranged for each exhaust system, especially in a part other than the common part where exhaust gas always flows, the resonance detection sensor 15 of the other exhaust system is installed while one exhaust system is in use. 15 is sufficiently cooled by outside air. Therefore, the next time the exhaust system is switched and resonance detection is performed, a larger temperature difference between the resonance chamber 16 and the inside of each tail tube 10, 11 can be ensured, which has the advantage of improving resonance detection sensitivity accordingly.

In addition, in each of the above embodiments, tail tubes 1 having different pipe lengths are used.
Although two exhaust systems are formed by switching 011, the present invention is not limited to this type, and as long as it is possible to selectively use multiple exhaust systems whose resonance mode is stomach. , can be applied to any format. FIG. 8 shows, as an example, an embodiment in which a movable throttling mechanism 21 is interposed at an appropriate position in the exhaust pipe, for example, at the main muffler 8L flow position. As shown in FIG. 9, the throttle mechanism 21 includes a cylindrical valve case 22 and a butterfly valve type valve body 23 that can be opened and closed. A hole 24 is formed.

In this configuration, the throttle ratio changes by opening and closing the valve body 23, and two exhaust systems having mutually different resonance modes are formed.

Effects of the Invention As is clear from the above explanation, the exhaust noise reduction device for an automobile engine according to the present invention actually detects the occurrence of resonance in one of the exhaust systems and detects the occurrence of resonance in other exhaust systems in a non-resonant state. Since the exhaust system can be switched to , the resonance of the exhaust system can always be suppressed to a low level. Therefore, it is possible to reliably prevent an increase in noise due to resonance that tends to occur during acceleration or deceleration. Further, by using a resonance detection sensor using a Helmholtz type resonance element, it is possible to perform resonance detection targeting a large number of resonance modes with about one or two sensors.

[Brief explanation of drawings]

FIG. 1 is a configuration explanatory diagram showing one embodiment of the exhaust noise reduction device according to the present invention, FIG. 2 is a sectional view of a resonance detection sensor, FIG. 3 is a characteristic diagram showing resonance characteristics of the resonance detection sensor itself, and FIG. Figure 4 is a characteristic diagram showing the detection signal etc. of the resonance detection sensor.
The figure is a characteristic diagram showing noise characteristics etc. during acceleration, Figure 6 is a characteristic diagram showing another example of noise characteristics etc. during acceleration, and Figure 7 is a characteristic diagram showing another example of noise characteristics etc. during acceleration.Figure 7 is a characteristic diagram showing the noise characteristics etc. during acceleration.Fig. FIG. 8 is an explanatory diagram showing the configuration of an embodiment in which a plurality of exhaust systems are formed by a diaphragm mechanism, and FIG. 9 is a sectional view of the diaphragm mechanism. DESCRIPTION OF SYMBOLS 10... Main tail tube, 11... Sub tail tube, 12... Switching valve, 14... Control unit, 15... Resonance detection sensor, 16... Resonance chamber, 17... Consent, ! 8...Temperature sensor. Figure 2 9 16----Da Prefecture! +7-----Royuki +8---Ichikudo Senza Figure 3 Dark Shinku (+-1z) pm rpm

Claims (1)

[Claims] (1) In an automobile engine that can selectively use multiple exhaust systems with different resonance modes, the system is connected to the exhaust system via a neck pipe at a position approximately at the antinode of the resonance mode generated in each exhaust system. A vehicle for use in an automobile, characterized in that a resonance detection sensor consisting of a resonance chamber and a temperature sensor for detecting the temperature inside the neck tube is provided, and the exhaust system is switched to a non-resonance side based on the resonance detection. Engine exhaust noise reduction device.