Engine muffler

Abstract

The present invention provides a silencer that prevents the phenomenon of reflected waves generated inside the silencer flowing back into the exhaust system, thereby degrading scavenging performance. [Solution] The silencer has a muffler shell 1, an inlet pipe 2, and an outlet pipe 3. The inlet pipe 2 has a double structure consisting of a fixed outer inlet pipe 2a and a rotatable inner inlet pipe 2b. The outer inlet pipe 2a and the inner inlet pipe 2b have a group of through holes 16 to 21 that can be selectively connected by the rotation of the inner inlet pipe 2b. When either pair of through holes are connected, exhaust gas escapes, which has the same effect as changing the length of the inlet pipe 2, and the frequency of the positive pressure wave can be changed so that it does not tune with the reflected wave.

Description

[Technical Field]

[0001] The present invention relates to a silencer for engines, and particularly preferably targets silencers for engines of four-wheeled motor vehicles. [Background Art]

[0002] A silencer for an automobile engine is arranged at the rear end of an exhaust system, and silences exhaust noise by combining expansion and throttling. The silencer includes a hollow muffler shell (case, housing), an inlet pipe and an outlet pipe arranged inside the muffler shell, and an atmosphere discharge pipe protruding outward from the muffler shell. The atmosphere discharge pipe is sometimes formed by extending the outlet pipe, and is sometimes formed independently of the outlet pipe.

[0003] As mentioned above, an engine silencer attenuates and eliminates exhaust noise by utilizing the expansion and throttling of exhaust gas. However, since the inlet pipe opens to the downstream end plate of the muffler shell, there is a phenomenon in which exhaust gas collides with the downstream end plate to generate reflected waves. Since the downstream end plate has an inherent frequency (wavelength) depending on its shape, thickness and other factors, when the frequency of the reflected wave is tuned with the inherent frequency of the downstream end plate, the energy of the reflected wave also increases.

[0004] On the other hand, a four-stroke engine generally has an overlap range in which both the exhaust valve and the intake valve are open, and the pulsation frequency of the positive pressure wave of exhaust gas flowing through the exhaust pipe changes according to the overlap angle. In an engine where the opening and closing timing of the intake valve is adjusted by VVT, when the overlap angle increases in the rotation range where the intake valve is advanced (particularly the mid-rotation range), the frequency of the positive pressure wave is tuned with the frequency of the reflected wave. A phenomenon occurs where the reflected wave acts to push back the exhaust gas, reducing the scavenging effect. Then, exhaust gas remains in the cylinder, leading to problems such as reduced charging efficiency and excessive EGR, which deteriorates engine performance.

[0005] To address this problem, two methods have been proposed: one to prevent or suppress the generation of reflected waves inside the silencer, and another to prevent reflected waves from synchronizing with positive pressure waves even if they are generated. As a means of the former, the inventor of the present invention has proposed in Patent Document 1 that a guide portion for diffusing exhaust gas be provided on the downstream end plate. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2020-122453 [Overview of the project] [Problems that the invention aims to solve]

[0007] As described in Patent Document 1, providing a guide section on the downstream end plate is beneficial for suppressing reflected waves. However, since the pulsation frequency (wavelength) of the positive pressure wave changes with rotational speed (overlap angle between the intake valve and exhaust valve), preventing the synchronization of reflected waves in response to changes in the pulsation frequency of the positive pressure wave can more accurately prevent the exhaust gas back-pushing phenomenon and maintain high scavenging performance over a wide range of engine rotations.

[0008] The present invention was made from this perspective and aims to disclose a silencer having a scavenging function that is excellent in responding to changes in rotational speed. [Means for solving the problem]

[0009] The engine silencer of the present invention is A silencer in which a straight-tube inlet pipe is arranged inside the muffler shell with its outlet opening on the downstream end plate side of the muffler shell, The inlet pipe is composed of a fixed outer pipe and an inner pipe fitted into the outer pipe and rotated by an actuator. The outer pipe and the inner pipe have one pair or multiple pairs of through holes that communicate with each other, spaced apart in the longitudinal direction, and the rotation of the inner pipe allows for the selection of a pair of the through holes to communicate. This is the structure.

[0010] In the present invention, having multiple pairs of through holes is beneficial in improving responsiveness to changes in rotation (changes in overlap angle). An electric motor such as a servo motor (stepper motor) or a rotary solenoid can be used as the actuator to drive the inner pipe. Various shapes can be adopted for the through holes, such as square slits, circles, or ovals. Since the outer pipe rotates relative to the inner pipe, both pipes are perfectly circular. [Effects of the Invention]

[0011] In the present invention, the inlet pipe is a double-walled pipe, making it less prone to vibration compared to the conventional single-walled system. Therefore, the natural frequency of the inlet pipe can be set to a value that is less likely to resonate with the pulsation frequency of the positive pressure wave. In other words, the inlet pipe is in a state similar to having a weight attached, making it less likely to resonate with the positive pressure wave.

[0012] When a pair of through-holes are connected, exhaust gases escape from that pair of through-holes, producing the same effect as if the length of the inlet pipe had changed. This changes the natural frequency of the inlet pipe and consequently the frequency of the reflected waves. Therefore, even if reflected waves are generated due to the dynamic pressure of the exhaust gases, their frequency can be significantly deviated from the frequency of the positive pressure waves. As a result, the phenomenon of strong reflected waves flowing back into the exhaust system due to the reflected waves synchronizing with the positive pressure waves is prevented, thus maintaining high scavenging performance.

[0013] Providing a plurality of pairs of through-holes can increase variation in changes to the natural frequency of the inlet pipe, which has the advantage of excellent adaptability to changes in engine rotational speed. [BRIEF DESCRIPTION OF THE DRAWINGS]

[0014] [Figure 1] It is an exploded perspective view of the embodiment. [Figure 2] It is a longitudinal side view in a state where the first through-hole is communicated. [Figure 3] It is a longitudinal side view in a state where the second through-hole is communicated. [Figure 4] It is a longitudinal side view in a state where the third through-hole is communicated. [Figure 5] It is a longitudinal side view in a state where none of the through-holes are communicated. [Figure 6] (A) is a view showing a second embodiment, and (B) is a view showing a third embodiment. [Figure 7] It is a view showing the second embodiment. [Figure 8] It is a view showing a fourth embodiment. [Figure 9] It is a view showing a fifth embodiment. [Figure 10] It is a longitudinal side view showing another example of the arrangement position of an actuator. [MODE FOR CARRYING OUT THE INVENTION]

[0015] (1). Structure of the First Embodiment Next, embodiments of the present invention will be described with reference to the drawings. First, the first embodiment shown in FIG. 1 will be described. The silencer comprises a muffler shell (case) 1 having an oval cross-section and a hollow structure, an inlet pipe 2 and an outlet pipe 3 arranged inside the muffler shell 1, and an atmospheric discharge pipe 4 exposed to the outside of the muffler shell 1.

[0016] Hereinafter, the terms front-rear and up-down are used to specify directions, wherein the front-rear direction is the longitudinal direction of the inlet pipe 2, and the up-down direction is the vertical direction.

[0017] The muffler shell 1 is formed into a hollow structure by a vertically elongated body (cylinder) 5 having an oval cross-section, an upstream end plate 6 closing the upstream end of the body 5, and a downstream end plate 7 closing the downstream end of the body 5. Although not explicitly shown in the drawings, the end plates 6 and 7 are fitted into the body 5 from the inner side and fixed to the body 5 by welding or brazing.

[0018] The inlet pipe 2 has a straight pipe shape and has a double structure consisting of an outer inlet pipe 2a and an inner inlet pipe 2b. The outer inlet pipe 2a penetrates the upstream end plate 6, and the outlet thereof opens toward the downstream end plate 7. On the other hand, the inner inlet pipe 2b penetrates the downstream end plate 7 and is fitted into the outer inlet pipe 2a, and is rotatably held by a motor unit 8 fixed to the outer surface of the downstream end plate 7.

[0019] The outlet pipe 3 is disposed below the inlet pipe 2 and has a U-shape in side view, with an inlet 3a and an outlet 3b opening toward the downstream end plate 7. Inside the muffler shell 1, two front and rear vertical partition plates 9 and 10 are disposed with the outer inlet pipe 2a and the outlet pipe 3 penetrating therethrough, and further, a horizontal partition plate 11 is connected between a middle height position of the outlet pipe 3 in the downstream vertical partition plate 10 and the downstream end plate 7.

[0020] Accordingly, the interior of the muffler shell 1 is partitioned into a first space 12 located on the upstream side of the upstream vertical partition plate 9, a second space 13 located between the front and rear vertical partition plates 9 and 10, a third space 14 located above the horizontal partition plate 11, and a fourth space 15 located below the horizontal partition plate 11. The atmosphere discharge pipe 4 is connected to the downstream end plate 7, but the atmosphere discharge pipe 4 may also be configured by extending the outlet pipe 3, in which case the horizontal partition plate 11 is not required. The vertical partition plates 9, 10 and the horizontal partition plate 11 are each formed of a perforated plate having a large number of small holes.

[0021] As clearly shown in Figure 1, the outer inlet pipe 2a has a first fixed through hole 16 opening upward at the location of the first space 12, a second fixed through hole 17 opening upward at the location of the second space 13, and a third fixed through hole 18 opening upward at the location of the third space 14, all arranged in series in the front-to-back direction. Meanwhile, the inner inlet pipe 2b has a first movable through hole 19 that can communicate with the first fixed through hole 16, a second movable through hole 20 that can communicate with the second fixed through hole 17, and a third movable through hole 21 that can communicate with the third fixed through hole 18.

[0022] The first movable through-hole 19, the second movable through-hole 20, and the third movable through-hole 21 are offset from each other in the circumferential direction. Therefore, by rotating the inner inlet pipe 2b, any pair of through-holes 16, 17, 18, 19, 20, and 21 can be selected to connect. The spacing between adjacent through-holes 16, 17, 18, 19, 20, and 21 is set to be the same, but it is also possible to make the spacing different.

[0023] Since the outlet of the outer inlet pipe 2a is located in front of the downstream end plate 7, the base of the inner inlet pipe 2b is exposed to the third space 14, and an exhaust gas outlet hole 22 is formed in this exposed portion. When viewed from the axial direction, the outlet hole 22 extends to the opposite side from the group of movable through holes 19-21. Therefore, regardless of which of the movable through holes 19-21 is facing upward, the outlet hole 22 is set to face downward. A conical guide projection 23 is provided on the inner surface of the downstream end plate 7, extending in the axial direction of the inlet pipe 2.

[0024] (2) Summary of the first embodiment In the above configuration, by rotating the inner inlet pipe 2b, the inlet pipe 2 can be configured in one of four ways: a first configuration in which the first fixed through hole 16 and the first movable through hole 19 are in communication, as shown in Figure 2; a second configuration in which the second fixed through hole 17 and the second movable through hole 20 are in communication, as shown in Figure 3; a third configuration in which the third fixed through hole 18 and the third movable through hole 21 are in communication, as shown in Figure 4; and a fourth configuration in which none of the through holes 16 to 21 are in communication, as shown in Figure 5.

[0025] In all cases, the exhaust gas released in a straight line from the inner inlet pipe 2b is released into the third space 14 from the outlet hole 22 of the inner inlet pipe 2b, expands in the third space 14, flows into the outlet pipe 3 where it is constricted, is released from the outlet pipe 3 into the fourth space 15 where it expands again, and then flows into the atmospheric discharge pipe 4 in a constricted state and is released into the atmosphere.

[0026] Due to the effects of this expansion and throttling, the pulsation of the exhaust gas is eliminated and the exhaust noise is almost completely eliminated. Since the partition plates 9-11 have many small holes, some of the exhaust gas passes through the partition plates 9-11 and flows from the third space 14 to the fourth space 15 and the second space 13, and finally reaches the fourth space 15. However, as the exhaust gas passes through the small holes in the partition plates 9-11, it is subjected to the effects of throttling and expansion, which also attenuates the exhaust noise.

[0027] When exhaust gas is released from the inner inlet pipe 2b, it collides with the downstream end plate 7. However, because the exhaust gas has pulsations due to the opening and closing of the exhaust valve, it has a positive pressure wave, and a reflected wave is generated when the exhaust gas collides with the downstream end plate 7. The frequency of the positive pressure wave also changes depending on the rotational speed and overlap angle, but if the frequency of the reflected wave caused by the collision of the exhaust gas with the downstream end plate 7 matches the natural frequency of the downstream end plate 7, the reflected wave is amplified by resonance and flows back into the exhaust system, acting to push the exhaust gas back and worsening the scavenging performance.

[0028] On the other hand, since the inlet pipe 2 also vibrates, the frequency of the positive pressure wave is also affected by the length of the inlet pipe 2. However, in this embodiment, when either pair of through holes 16 to 21 are connected, some of the exhaust gas escapes into the muffler shell 1 through the connected pair of through holes, thus shortening the length of the inlet pipe 2 and making it less prone to vibration. As a result, even if reflected waves are generated, the resonance of the inlet pipe 2 can be suppressed and the frequency of the positive pressure wave can be changed.

[0029] In other words, in this embodiment, since four configurations (1st to 4th) of communication patterns for the through-holes can be selected, the inlet pipe 2 effectively has four selectable lengths, even though its actual length remains constant. As a result, the frequency of the positive pressure wave can be substantially changed.

[0030] Therefore, by controlling the communication configuration of the through holes 16-21 according to the rotation speed, it is possible to prevent the positive pressure wave and the reflected wave from synchronizing. Just as a recorder has many holes arranged in a longitudinal direction, and the pitch (frequency) of the sound changes when any of the holes are blocked, this embodiment is similar; by connecting any pair of through holes or blocking all of them, the frequency of the positive pressure wave can be adjusted to prevent it from synchronizing with the reflected wave.

[0031] Specifically, connecting the through-holes 16-21 allows exhaust gas to escape, producing the same effect as shortening the inlet pipe 2. In the fully closed state shown in Figure 5, the wavelength is longest. For example, assuming that the wavelength shortens in proportion to the rotational speed, the rotational speed range below 1000 rpm is set as the first rotational speed range, 1000 rpm to less than 1500 rpm as the second rotational speed range, 1500 rpm to less than 2000 rpm as the third rotational speed range, and 2000 rpm or more as the fourth rotational speed range. By controlling the system in this way, the first through-holes 16 and 19 are connected in the first rotational speed range, the second through-holes 17 and 20 are connected in the second rotational speed range, the third through-holes 18 and 21 are connected in the third rotational speed range, and the system is kept fully closed in the fourth rotational speed range, it is possible to prevent the inner inlet pipe 2b from resonating with the pulsating pressure waves of the exhaust gas.

[0032] If the engine speed and the exhaust gas pulsation wavelength have an inverse relationship, then the control should be reversed. In any case, the configuration of the fixed through holes 16-18 should be selected so that the natural frequency of the inner inlet pipe 2b does not resonate with the wavelength of the exhaust gas pressure wave.

[0033] Since the synchronization phenomenon of positive pressure waves with the exhaust gas is a problem related to the overlap state between the intake and exhaust valves, it is possible to divide the overlap angle into multiple sections and control the communication state of the through-holes corresponding to each section. In other words, it is also possible to associate the communication state of the through-holes with VVT.

[0034] (3) Other embodiments Figures 6 and 7 show the second and third embodiments. In these embodiments, as shown in Figure 6(A), the first to third fixed through holes 16, 17, and 18 are arranged in a straight line in the outer inlet pipe 2a, while the first to third first movable through holes 19, 20, and 21 are formed in the inner inlet pipe 2b with a circumferential offset. However, the circumferential width dimensions of the first to third fixed through holes 16, 17, and 18 are the same, while the circumferential width dimensions of the movable through holes 19, 20, and 21 are different.

[0035] In other words, the circumferential width dimension of the first movable through-hole 19 is the same as the width dimension of the fixed through-holes 16-18, the circumferential width dimension of the second movable through-hole 20 is approximately twice the width dimension of the fixed through-holes 16-18, and the width dimension of the third movable through-hole 21 is approximately three times the width dimension of the fixed through-holes 16-18. Furthermore, the second movable through-hole 20 is elevated from the first movable through-hole 19, and the third fixed through-hole 18 is elevated from the second movable through-hole 20. When the inner inlet pipe 2b is rotated in one direction, each of the movable through-holes 19-21 is sequentially connected to the fixed through-holes 16-18.

[0036] Specifically, as schematically shown in Figure 7, four patterns can be selected: a fourth mode (fully closed mode) in which each fixed through hole 16-18 does not communicate with any of the movable through holes 19-21; a third mode in which only the third fixed through hole 18 communicates with the third movable through hole 21 and the first fixed through hole 16 and the second fixed through hole 17 are closed; a second mode in which the first fixed through hole 16 is closed and the second fixed through hole 17 and the third fixed through hole 18 communicate with the movable through holes 20 and 21; and a first mode (fully open mode) in which all of the fixed through holes 16-18 communicate with the movable through holes 19-21.

[0037] Furthermore, since the natural wavelength, which is inversely related to the natural frequency of the inner inlet pipe 2b, becomes longer from the first embodiment to the fourth embodiment, the natural frequency of the inner inlet pipe 2b can be set to a frequency that does not resonate with the exhaust gas pressure wave caused by pulsation by selecting the communication configuration of the fixed through holes 16 to 18 according to the engine speed range, as described in the first embodiment.

[0038] As shown in Figure 6(B) as a third embodiment, it is also possible to align the movable through holes 19 to 21 of the inner inlet pipe 2b in a straight line with equal width, and set the fixed through holes 16 to 18 of the outer inlet pipe 2a to different widths. The effect is the same as in the previously described case. It is also possible to set the circumferential width to decrease from the first through holes 16, 19 to the third through holes 18, 21.

[0039] Figure 8 shows a fourth embodiment, which is a modification of the second embodiment. In this embodiment, the third movable through-hole 21 and the second movable through-hole 20 are formed with a width larger than that of the fixed through-holes 16-18, and are formed as a plurality of holes separated in the circumferential direction. By separating the plurality of movable through-holes 20, 21 in this way, the fixed through-holes 16-18 and the movable through-holes 19-21 communicate over an equal area in each communicating body configuration, and it is expected that the natural frequency (natural wavelength) can be accurately controlled.

[0040] The fifth embodiment shown in Figure 9 is a combination of the first and second embodiments. Specifically, the outer inlet pipe 2a has fixed through holes 16 to 18 of equal width arranged in a straight line, while the inner inlet pipe 2b has a group of equally-width movable through holes 19a to 21a that are the same width as the fixed through holes 16 to 18 but are sequentially offset in the circumferential direction on one side of the fixed through holes 16 to 18 when viewed from the axial direction, and a group of different-width movable through holes 19b to 21b that are different widths from the fixed through holes 16 to 18 when viewed from the axial direction.

[0041] In this embodiment, the width dimension of the first movable variable-width through-hole 19b is set to be the largest and the width dimension of the third movable variable-width through-hole 21b is set to be the smallest, but it is also possible to set the width dimension pattern to be the same as in the second embodiment.

[0042] In this embodiment, since it is possible to select between a fully closed state in which all fixed through holes 16 to 18 are closed, and a state in which each fixed through hole 16 to 18 is individually connected, and a state in which multiple fixed through holes 16 to 18 are simultaneously connected, fine-grained control can be selected. The state in which the third fixed through hole 18 is connected can be selected by rotating in either direction, but the connection state can be sequentially changed by rotating in either the right or left direction, which is advantageous in terms of control.

[0043] In this embodiment, the motor unit 8 is fixed to the outer surface of the downstream end plate 7, but as shown in Figure 10 as the sixth embodiment, it is also possible to fix the motor unit 8 to the outer surface of the body 5. In this example, the driven gear 24 is fixed to the base end of the inner inlet pipe 2b, while the motor unit 8 is provided with a bracket portion 25 that covers the driven gear 24, and the driving gear 26 built into the bracket portion 25 is meshed with the driven gear 24. In this example, the inner inlet pipe 2b opens toward the outer inlet pipe 2a. Therefore, a guide member 27 is fixed to the inner surface of the outer inlet pipe 2a so as not to deflect the exhaust gas downwards.

[0044] The embodiments of the present invention have been described above, but the present invention can be implemented in various other ways. For example, the cross-sectional shape of the muffler shell does not necessarily have to be oval; circular, elliptical, or rectangular shapes can also be used. It is also possible to arrange the inlet pipe and outlet pipe horizontally. The number of through holes is not limited to three pairs; one pair, two pairs, or three or more pairs can also be used. [Industrial applicability]

[0045] The present invention can be implemented in an engine silencer. Therefore, it has industrial merit. [Explanation of symbols]

[0046] 1 Muffler Shell 2 Inlet pipes 2a Outer inlet pipe 2b Inner Inlet Pipe 3 Outlet pipes 4. Atmospheric discharge pipe 5 Torso 6 Upstream end plate 7 Downstream end plate 8. Motor unit as an example of an actuator 9,10 Vertical partition plate 12~15 spaces 16~18 Fixed through hole 19~21 Movable through hole

Claims

[Claim 1] A silencer in which a straight-tube inlet pipe is arranged inside the muffler shell with its outlet opening on the downstream end plate side of the muffler shell, The inlet pipe comprises a fixed outer pipe and an inner pipe fitted into the outer pipe and rotated by an actuator. The outer pipe and the inner pipe have one pair or multiple pairs of through holes that communicate with each other, spaced apart in the longitudinal direction. By rotating the inner pipe, one pair of the through holes can be selected to communicate with each other. Engine muffler.

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