JPH116172A - Silencer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a manifold type silencer that makes its length one-fourth in wavelength in response to noise characteristics that change in accordance with the rotation condition of an engine. SOLUTION: A manifold is provided on the side of an exhaust gas introduction pipe inserted into a muffler 2, and the length of the manifold is made variable by a cylinder 3. Engine revolutions detected by an engine revolution sensor 11 and exhaust gas temperature detected by a thermometer 2 inserted into the muffler 2 are detected, and a degree corresponding to the engine revolutions is set by a degree setting switch 61a. From these values, the length of the manifold necessary for suppressing the acoustic energy of maximum sound pressure is calculated, and the length of the manifold is changed so that it may be one-fourth of the acoustic frequency of the cylinder 3 in wavelength by its expansion and contract.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a silencer widely used in the fields of construction machines, automobiles, and industrial machines.

[0002]

2. Description of the Related Art There is known a silencer applied to a noise source whose noise characteristics change according to an engine operating condition. In particular, examples of a variable resonance silencer for silencing a predetermined frequency include those disclosed in Japanese Patent Publication No. 5-75553 and Japanese Utility Model Publication No. 5-13333.

Japanese Patent Publication No. 5-75553 discloses that a maximum sound pressure within a specific evaluation range of a preset frequency is actually measured by a sound pressure detector installed near an air inlet of an intake pipe. There is disclosed a silencer that silences by changing the volume of a resonance container provided in a part of an intake pipe using an actuator so as to have a resonance frequency equal to the frequency at which sound pressure is generated.

Japanese Utility Model Publication No. 5-13933 discloses that a duct through which intake air or exhaust gas flows and a resonance chamber communicate with each other via a plurality of tuning pipes having different lengths, and these pipes are opened and closed using an actuator. A silencer that silences by setting a resonance frequency according to the engine speed is disclosed.

[Problems to be solved by the invention]

[0005] However, a sound pressure detector and a frequency analyzer are indispensable for the variable volume resonance silencer disclosed in Japanese Patent Publication No. 5-7553, but these are very precise and expensive. However, even if it can be applied in a laboratory, it is difficult to commercialize it in consideration of the cost of mounting on a vehicle. Furthermore, this resonance silencer reduces the noise of the intake system, and if it is to be applied to the noise reduction of the exhaust system which is higher in temperature than the intake system, a sound pressure detector with high heat resistance is required. Such sound pressure detectors are expensive.

The resonance silencer disclosed in Japanese Utility Model Publication No. 5-13333 discloses a pipe having a predetermined length from among a plurality of tuning pipes having different lengths so as to have a resonance frequency corresponding to the engine speed. Is selected and applied, and the resonance frequency at which the sound can be silenced is limited to the type of the tuning pipe. If an attempt is made to provide a tuning pipe corresponding to all engine speeds, a large number of types of tuning pipes are required, and the structure thereof becomes complicated and large.

An object of the present invention is to provide an inexpensive and easy-to-use silencer corresponding to noise characteristics that change according to the engine rotation condition.

[0008]

FIG. 1 shows an embodiment of the present invention.
This will be described with reference to FIGS. (1) The invention according to claim 1 is applied to a silencer having a branch pipe 25 having one end closed in the middle of an exhaust pipe 21 or an intake pipe, and based on an engine speed, 1/1 of an acoustic frequency.
Wavelength calculating means 6 for calculating four wavelengths, and actuator 3 for adjusting the length LA of the branch pipe 25 based on the result of the wavelength calculating means 6 so as to be に な る wavelength of the acoustic frequency.
The above object is achieved by providing the following. (2) The order setting device 61 for setting the order of the engine speed in the muffler according to claim 1.
a, and the wavelength calculating means 6 calculates a quarter wavelength according to the order set by the order setting device. (3) According to a third aspect of the present invention, in the muffler of the first aspect, there is provided a thermometer 23 for detecting the temperature of the exhaust gas or the intake air, and the wavelength calculating means 6 has a quarter of the acoustic frequency according to the temperature of the exhaust air or the intake air. This is to calculate the wavelength. (4) The invention according to claim 4 is a mode selection means 7 for selecting any one of a plurality of operation modes, and an engine speed for adjusting the engine speed according to the mode selected by the mode selection means 7. The present invention is applied to a silencer used for a vehicle having setting means 1A and 6 and having a branch pipe 25 having one end closed in the middle of an exhaust pipe 21 or an intake pipe. A wavelength calculating means 6 for calculating a quarter wavelength of the acoustic frequency based on the order and the engine speed determined based on the operation mode selected by the mode selecting means 7, and a calculation result of the wavelength calculating means 6. The above object is achieved by providing the actuator 3 for adjusting the pipe length LA of the branch pipe 25 to be 1/4 of the acoustic frequency. (5) The invention according to claim 5 is the invention according to claim 4, wherein
A thermometer 23 for detecting an exhaust gas temperature or an intake air temperature;
The wavelength calculating means 6 calculates １ ／ wavelength of the acoustic frequency according to the detected exhaust gas temperature or intake air temperature.

In the section of the means for solving the above-mentioned problems, which explains the configuration of the present invention, the drawings of the embodiments are used to make the present invention easy to understand. However, the present invention is not limited to this.

[0010]

Embodiments of the present invention will be described below with reference to the drawings. -First Embodiment- Fig. 1 is a schematic diagram showing a relationship between a muffler according to a first embodiment of the present invention and peripheral devices thereof. In FIG. 1, an engine 1 provided to a construction machine, an industrial machine, an automobile, etc.
An exhaust pipe 21 is connected to the exhaust manifold, and the exhaust of the engine 1 is guided from the exhaust pipe 21 to the variable branch pipe type muffler 2 and discharged from the exhaust discharge pipe 22 to the outside. Engine 1
Is controlled by driving the governor 1A by the control circuit 6.

As shown in FIG. 2, the variable branch pipe type muffler 2
An opening 21a is opened on a side surface of the exhaust pipe 21 having a tip inserted into the outer shell 24 of the above, and a branch pipe 25 is connected thereto. One end of the branch pipe 25 is joined to the muffler shell 24,
An opening 24a is opened at the center of the joint.
A cylinder rod 3a of the cylinder 3 is inserted into the branch pipe 25 through the opening 24a, and a piston 3b slidable along the inner wall of the branch pipe 25 is provided at the tip of the cylinder rod 3a. ing.

The expansion and contraction of the cylinder 3 is controlled by an electromagnetic switching valve 4 as shown in FIG. That is, by controlling the electromagnetic switching valve 4 based on a signal from the control circuit 6, the hydraulic pressure from the hydraulic pressure source 5 is controlled to control the cylinder rod 3a.
Is controlled. The stroke of the cylinder rod 3a is detected by the position sensor 31, and the detected stroke signal λ is sent to the control circuit 6.

As shown in FIG. 2, the muffler 2 has an opening 24b opened in the muffler outer shell 24 and an exhaust introduction pipe 21.
A thermometer 23 is provided through an opening 21b which is opened at the center of the exhaust introduction pipe 21.
And the center line L2 of the branch pipe 25. As shown in FIG. 1, the temperature t detected by the thermometer 23 is also sent to the control circuit 6, and the order setting switch 61a outputs an order setting signal n for determining the order of the sound frequency to be silenced. 6 is sent. further,
The engine speed is detected by the engine speed sensor 11, and the engine speed signal ne is also input to the control circuit 6. The control circuit 6 includes an engine speed signal ne, an exhaust temperature signal t,
The target pipeline length λref is calculated based on the order setting signal n, and the output signal I is output so that the stroke signal λ detected by the position sensor 31 becomes the target pipeline length λref, thereby controlling the stroke of the cylinder 3. .

FIG. 3 is a diagram showing details of the control circuit 6. An order setting circuit 61 generates an order n for generating a maximum sound pressure corresponding to the engine speed in response to a signal from an order setting switch 61a.
Set. Using the temperature t detected by the temperature sensor 23 inserted into the exhaust gas introduction pipe 21, the sonic velocity calculation circuit 62 calculates the sonic velocity c by the following equation.

[Equation 1] c = 331.5 {(273 + t) / 273}

The target frequency calculation circuit 63 calculates a fundamental frequency fr as a function of fr = f (ne) based on the engine speed ne detected by the engine speed sensor 11, and the order setting circuit 61 The target frequency fref is calculated by multiplying the set order n. The target pipeline length calculation circuit 64 uses the sound speed c and the target frequency fref obtained by the sound speed calculation circuit 62 and the target frequency calculation circuit 63 to calculate a target corresponding to １ ／ wavelength of the maximum sound pressure generation by the following equation. The pipeline length λref is calculated.

[Equation 2] λref = c / 4fref

The servo control circuit 65 calculates a deviation e between the stroke λ detected by the position sensor 31 and the above-described target pipeline length λref by a PID control circuit. The output signal obtained by the PID operation is amplified via the amplifier 66, and the amplified output signal I is input to the electromagnetic switching valve 4. Based on the output signal I, the electromagnetic switching valve 4 determines the pipe length L.
The cylinder 3 is controlled so that A becomes the target pipe length.

Next, the operation of the first embodiment will be described with reference to FIGS. Exhaust gas from the engine 1 passes through the exhaust pipe 21 and flows into the muffler 2. The exhaust gas flowing into the muffler 2 causes reflection and interference of a sound wave of a specific wavelength corresponding to the length LA of the branch pipe in the branch pipe 25. The pipeline length LA is set to a target value by controlling the electromagnetic switching valve 4 based on the signal from the control circuit 6 to adjust the stroke of the cylinder 3 as described above, that is, the acoustic frequency at which the maximum sound pressure is generated. Is set to be equal to １ ／ wavelength of When the pipe length LA becomes equal to １ ／ wavelength of the acoustic frequency, the phases of the incident wave IW and the reflected wave RW are reversed by 180 ° as shown by the dotted line in FIG. 2, and the acoustic energy is attenuated and muted. The muffled exhaust flows out of the muffler via the expansion chamber 28 and the exhaust discharge pipe 22.

As described above, according to the first embodiment, the pipe length LA of the branch pipe 25 is made variable, and the target pipe of the branch pipe 25 is set by setting the exhaust gas temperature t, the engine speed ne and the engine speed n. Since the path length is determined, the maximum sound pressure is always silenced even when the exhaust gas temperature and the engine speed change, and the maximum silencing effect can be obtained.

-Second Embodiment- FIG. 4 is an explanatory diagram showing a configuration of a control circuit according to a second embodiment of the present invention. The same parts as those in FIG. 3 are denoted by the same reference numerals, and description thereof will be omitted. The second embodiment is different from the first embodiment in the method of order setting. In FIG. 4, the operation mode selection switch 7
Selects one of the high load mode P, the fuel efficiency mode E, and the low load mode L in the case of a hydraulic shovel, for example, and a signal indicating one of the modes is input to the governor drive circuit 67. The governor drive circuit 67 controls the governor 1A according to the input mode, whereby the engine speed becomes a value suitable for each mode. The order setting circuit 68 sets the order n based on the operation mode selected by the operation mode selection switch 7. The order n at which the maximum sound pressure is generated varies depending on the engine speed, but since the engine speed varies depending on the operation mode according to the working state, the relationship between the operation mode and the order n is grasped in advance by a unit test or the like. If this relationship is used, an appropriate order according to the operation mode selected by the operation mode selection switch 7 is automatically set by the order setting circuit 68 by using this relationship. In the second embodiment, the order of the high load mode P is first order, the fuel efficiency mode E is second order,
The low load mode L corresponds to the third order, respectively. Hereafter, the first
The sound energy is silenced by the same procedure as in the embodiment.

As described above, according to the second embodiment, the order setting is automatically performed, so that the order changeover switch 61a
Is unnecessary, and the operation of switching the order of the operator is omitted, and the workability is improved.

In the second embodiment, a signal from the engine speed sensor 11 is converted to a target frequency change operation circuit 63.
However, since the target frequency is determined based on the selected mode, the target frequency may be used instead of the actual rotation speed.

Although the silencer in the above embodiment is applied to an exhaust system, it may be applied to an intake system. Also,
Although a hydraulic cylinder is used as an actuator for changing the pipe length LA of the branch pipe 25, pneumatic pressure may be used. Furthermore, although the relationship between the operation mode and the order according to the engine speed was used, the relationship between the engine speed and the order was directly obtained, and this relationship was used to automatically obtain a predetermined order corresponding to the engine speed. Alternatively, it may be set in a specific manner.

Further, as shown in FIG. 5, a neck 8 may be provided at the intersection of the exhaust introduction pipe 21 and the branch pipe 25, and the branch pipe may be used as a variable displacement resonance vessel. in this case,
Engine speed sensor 11 and order setting switch 61
a based on the information of the mode selection switch 7 or FIG.
Alternatively, an acoustic frequency corresponding to the engine speed is calculated by the target frequency calculation circuit 63 of FIG. Then, the conduit length LA is set so that the resonance container has a resonance frequency equal to the acoustic frequency. As described above, when the variable resonance silencer is used, the calculation of the wavelength is unnecessary, and therefore, a thermometer is also unnecessary.

In the correspondence between the above embodiment and the claims, the control circuit 6 controls the wavelength calculating means, the cylinder 3 controls the actuator, the order setting switch 61a controls the order setting device, and the operation mode selecting switch 7 controls the mode selecting means. The governor 1A constitutes the engine speed setting means.

[0025]

【The invention's effect】

(1) According to the invention of claim 1, １ ／ wavelength of the acoustic frequency that changes according to the engine rotation condition is calculated, and the length of the branch pipe is set to １ ／ wavelength of the acoustic frequency. Therefore, even if the acoustic frequency at which the maximum sound pressure is generated fluctuates due to a change in the engine speed, the maximum sound pressure is always silenced, and the maximum silencing effect can be obtained. In addition, an expensive device such as a sound pressure detector or a complicated structure such as a tuning pipe is not required, and the noise reduction effect can be achieved by an inexpensive and easy structure. (2) According to the second aspect of the invention, the order of the engine speed to be silenced is input, and a quarter wavelength of the acoustic frequency is calculated according to this order. Even if the maximum sound pressure generation order changes, the maximum sound pressure can always be muted. (3) According to the invention of claim 4, when a certain operation mode is selected, the order is automatically set according to the operation mode, and a quarter wavelength of the acoustic frequency is calculated according to this order. This eliminates the need for the operator to set the order, thereby improving workability. (4) According to the third and fifth aspects of the present invention, since the above quarter wavelength is calculated in consideration of the exhaust gas temperature, the pipe length of the branch pipe can be accurately determined even if the sound speed changes according to the temperature. It can be set to １ ／ wavelength of the acoustic frequency.

[Brief description of the drawings]

FIG. 1 is a diagram showing a muffler according to a first embodiment and peripheral devices thereof.

FIG. 2 is a sectional view of a muffler of the muffler according to the first embodiment.

FIG. 3 is a detailed block diagram of a control circuit according to the first embodiment.

FIG. 4 is a detailed block diagram of a control circuit according to a second embodiment.

FIG. 5 shows a variable displacement resonance container according to a modification of the embodiment.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Engine 1A Governor 3 Cylinder 6 Control circuit 7 Operation mode selection switch 23 Thermometer 21 Exhaust pipe 25 Branch pipe 61a Order setting switch

Claims (5)

[Claims] 1. A silencer having a branch pipe having one end closed in the middle of an exhaust pipe or an intake pipe, a wavelength calculating means for calculating a quarter wavelength of an acoustic frequency based on an engine speed, And an actuator that adjusts the length of the branch pipe so as to be １ ／ wavelength of the acoustic frequency based on the result of the means. 2. The muffler according to claim 1, further comprising an order setting device for setting an order of the engine speed.
A muffler, wherein the wavelength calculating means calculates a quarter wavelength according to the order set by the order setting device. 3. The muffler according to claim 1, further comprising a thermometer for detecting the temperature of the exhaust gas or the intake air, wherein the wavelength calculating means calculates a quarter wavelength of the acoustic frequency according to the temperature of the exhaust air or the intake air. A silencer characterized by calculating. 4. A vehicle having mode selection means for selecting one of a plurality of operation modes, and engine speed setting means for adjusting the engine speed in accordance with the mode selected by the mode selection means. A muffler to be used, which has a branch pipe with one end closed in the middle of an exhaust pipe or an intake pipe, wherein an order and an engine speed determined based on an operation mode selected by the mode selection means are provided. Acoustic frequency 1 by number
Wavelength calculating means for calculating ４ wavelength; and an actuator for adjusting the length of the branch pipe so as to be １ ／ of the acoustic frequency based on the calculation result of the wavelength calculating means. Sound silencer. 5. The muffler according to claim 4, further comprising: a thermometer for detecting an exhaust gas temperature or an intake air temperature, wherein said wavelength calculating means is configured to output one of said acoustic frequencies according to said detected exhaust gas temperature or said intake air temperature. A silencer characterized by calculating / 4 wavelength.