Exhaust system of hybrid vehicle

Abstract

To provide an exhaust system of a hybrid vehicle, which can accommodate the expansion of a drive battery pack, suppress standing waves, and muffle noise across the entire frequency range.SOLUTION: An exhaust system of a hybrid vehicle is equipped with at least an exhaust emission control device, a sub-muffler, a main muffler, and a plurality of flow path members that connect them and communicate an exhaust gas. The final emission control device is interposed in front of a drive battery pack on a vehicle body, and the main muffler is interposed behind the drive battery pack, facing towards the side of the vehicle body. At least one resonance-type sub-muffler with multiple holes drilled in its inner pipe is interposed at a side position of the drive battery pack, and the most downstream flow path member is inserted into an end plate on the bypass side of the main muffler.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust system for a hybrid vehicle that has a drive battery pack mounted under the vehicle body floor. [Background technology]

[0002] Hybrid vehicles, which have an internal combustion engine and an electric motor and are powered by at least one of these, are becoming increasingly common. In such hybrid vehicles (HEVs), the internal combustion engine and an electric motor, such as a motor generator, are mounted at the front of the vehicle, and a drive battery pack is mounted in the center of the vehicle. To reduce fuel consumption, it is desirable for hybrid vehicles to have as wide a driving range as possible using the electric motor, so increased battery capacity is required, making larger drive battery packs inevitable. In particular, in plug-in hybrid vehicles (PHEVs), which have a wide driving range using only the electric motor, the drive battery pack occupies a large area of ​​the vehicle, stretching from the center to the rear.

[0003] These circumstances are affecting the installation location and space of the exhaust system, which previously extended to the installation location of the drive battery pack.Specifically, the question is where to place and how to connect the exhaust system's components, including the exhaust purification device, sub-muffler (auxiliary silencer), main muffler (main silencer), and the flow path components (exhaust pipe) that connect them and form the flow path for exhaust gas, so that they do not interfere with the drive battery pack and are not affected by heat.

[0004] For example, Japanese Patent Publication No. 2021-116758 proposes an exhaust system layout in which an L-shaped exhaust purification device (catalytic converter, etc.) is placed in front of the drive battery pack in the direction of travel, the flow path member is routed to the side, a side branch type sub-muffler is interposed to the side of the drive battery pack, and the main muffler is interposed behind the drive battery pack along the direction of travel. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2021-116758 Summary of the Invention [Problem to be solved by the invention]

[0006] However, while interference can be avoided by having the front half of the exhaust system bypass the drive battery pack, the layout behind (downstream of) the drive battery pack remains the same as before, so it does not address the rearward expansion of the drive battery pack, which is based on the limited front-to-rear dimensions of the vehicle (rear end).In addition, because it uses a side-branch sub-muffler that has one or two openings in the inner cylinder and uses the long gap between the inner cylinder and the outer cylinder as a resonance space, it is long and difficult to install on the side of the drive battery pack, and because it only silences specific frequencies, its silencing effect across the entire frequency range is limited.

[0007] In view of the above-mentioned problems, the present invention aims to provide an exhaust system for a hybrid vehicle that can realize a mounting layout that can accommodate an expansion of the drive battery pack, and that can attenuate standing waves and silence noise across the entire frequency range. [Means for solving the problem]

[0008] In order to solve the above problems, the present invention provides an exhaust system for a hybrid vehicle that extends to the rear end of the vehicle, bypassing a drive battery pack connected to an internal combustion engine and placed under the floor of the vehicle to the side of the vehicle, and includes at least an exhaust purification device, a sub-muffler, a main muffler, and a plurality of flow path members that are connected to these and form a flow path for exhaust gas to flow through, the final exhaust purification device is interposed in front of the drive battery pack on the vehicle body, and the main muffler is interposed behind it, facing towards the side of the vehicle body, at least one resonance-type sub-muffler with multiple holes drilled in its inner tube is interposed at a position to the side of the drive battery pack, and the most downstream flow path member is inserted into an end plate located on the bypass side of the main muffler. [Effects of the Invention]

[0009] According to the present invention, in the exhaust system of a hybrid vehicle, it is possible to improve the degree of freedom in the mounting position of the resonance-type sub-muffler while minimizing the detour length, thereby making it possible to accommodate an expansion of the drive battery pack and to attenuate standing waves and silence noise across the entire frequency range. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a top view of an exhaust system for a hybrid vehicle according to a first embodiment of the present invention. [Figure 2] 10 is a top view of an exhaust system for a hybrid vehicle according to a second embodiment of the present invention. [Figure 3] FIG. 1 is a cross-sectional view of one embodiment of a sub-muffler used in the exhaust system of the present invention. [Figure 4] FIG. 1 is an explanatory diagram schematically illustrating standing waves in a typical exhaust system. DETAILED DESCRIPTION OF THE INVENTION

[0011] A preferred embodiment of the present invention will be described below with reference to Figures 1 to 4. In this embodiment, the traveling direction of a hybrid vehicle is defined as the forward direction, the horizontal direction perpendicular to the traveling direction is defined as the side, and the vertical direction perpendicular to the traveling direction is defined as the upward direction.

[0012] (First embodiment) As shown in Fig. 1, a hybrid vehicle 1 includes an internal combustion engine 2, a traction motor (not shown) integrally combined with the internal combustion engine 2, a drive battery pack 3, a fuel tank 4, and an exhaust system 5. The exhaust system 5 according to the first embodiment of the present invention has the following configuration.

[0013] The internal combustion engine 2 and the traction motor are mounted at the front of the hybrid vehicle 1, and a connection flange 10 provided at the upstream end of the exhaust system 5 is connected to the internal combustion engine 2 directly or indirectly via an exhaust manifold, a supercharging device, or the like, and is fixed in communication so that exhaust gas can flow into the exhaust system 5. The exhaust system 5 extends to near the rear end 9 of the vehicle body, and an outlet pipe 84 of the main muffler 8, which is the most downstream part of the exhaust system 5, opens at the rear end 9 of the vehicle body. In other words, the exhaust gas is discharged outside the hybrid vehicle 1 at the downstream end of the outlet pipe 84.

[0014] The configuration of the exhaust system 5 will be described starting from the upstream side. A first flow path member 11 connects the most upstream connecting flange 10 and the exhaust purification device 6, a second flow path member 13 connects the exhaust purification device 6 and the sub-muffler 7, a third flow path member 15 connects the sub-muffler 7 and the fastening flange 17, and a fourth flow path member 18 connects the fastening flange 17 and the main muffler 8, and an outlet pipe 84 is connected (leads out) to the main muffler 8. A support member 16 for suspending the exhaust system 5 from the vehicle body is attached to the third flow path member 15. These components constitute the exhaust system 5. The exhaust system 5 is connected to the internal combustion engine 2 and extends to the rear end 9 of the vehicle body, bypassing the drive battery pack 3 arranged on the floor of the vehicle body of the hybrid vehicle 1 to the side of the vehicle body.

[0015] The exhaust purification device 6 incorporates one or more (in tandem) catalyst carriers or filter bodies for reforming exhaust gas emitted from the upstream internal combustion engine 2 or trapping specific components, and also includes a space (cavity). The external shape of the exhaust purification device 6 is not limited to a straight pipe type, but may be any shape such as an L-shape or an arc shape. A spray device for adding a reducing agent to the exhaust gas may also be combined. In this embodiment, only one exhaust purification device 6 is installed between the internal combustion engine 2 and the first bend portion 12, but one or more additional exhaust purification devices may be installed between the exhaust purification device 6 and the internal combustion engine 2 (upstream side). In such a configuration, the exhaust purification device 6 is the last (most downstream) exhaust purification device.

[0016] At a first bend 12 downstream of exhaust purification device 6, the final exhaust purification device, second flow path member 13 changes direction to the side of the vehicle body (to the right in the direction of travel), and then further downstream at a second bend 14, changes direction to the rear of the vehicle body. In other words, exhaust system 5 forms a flow path that detours around drive battery pack 3 in a crank shape to the right in the direction of travel. The structure and position of sub-muffler 7 interposed between second flow path member 13 and third flow path member 15 will be described later.

[0017] The third flow path member 15 and the fourth flow path member 18 are airtightly connected by a fastening flange 17, but they may also be integrated without being separated and fastened. The rear end of the fourth flow path member 18 is directed again toward the side of the vehicle body to form an inlet pipe 83. The portion of the inlet pipe 83 that is inserted into the main muffler 8 is an insertion portion 85.

[0018] The main muffler 8 is composed of a long, rectangular body (shell) 81 in a top view and a pair of end plates 82 that close both end openings of the cylindrical body 81, with an inlet pipe 83 and an outlet pipe 84 inserted and fixed to the end plate 82 located on the bypass side of the flow path (in this embodiment, the right side in the direction of travel). In this way, by mounting the long, large main muffler 8 transversely with its longitudinal direction directed toward the side of the hybrid vehicle 1 body, the distance between the vehicle rear end 9 and the fuel tank 4 can be shortened, and the rear end of the drive battery pack 3 can be extended toward the rear of the vehicle body, thereby increasing the battery capacity of the drive battery pack 3.

[0019] Furthermore, by mounting the main muffler 8 horizontally with its longitudinal direction facing the side of the vehicle body and inserting the inlet pipe 83 into the end plate 82 on the bypass side, the length of the fourth flow path member 18 can be minimized. This allows the length of the exhaust flow path after the drive battery pack 3 to be minimized, thereby suppressing pressure loss and increased exhaust pipe weight due to a longer exhaust flow path.

[0020] Next, the reduction of standing waves in this embodiment will be described. Generally, standing waves occur in an exhaust system due to operating conditions (engine speed, exhaust gas temperature, etc.). For example, as shown schematically in Fig. 4, if the flow path member (exhaust pipe) 20 connecting the exhaust purification device 6, which has a large internal volume, and the main muffler 8 is a single straight pipe, a primary standing wave 22 and a secondary standing wave 23 with a node at the middle point c tend to occur between the rear end a (open end) of the exhaust purification device 6 and the rear end b (open end) of the insertion portion 21.

[0021] In hybrid vehicles, especially PHEVs, where the internal combustion engine operates at a constant speed for long periods of time, standing waves are more likely to occur. When standing waves occur, pulsation disturbances are superimposed on the standing waves, causing abnormal noise and potentially impeding the downstream flow of exhaust gas, resulting in increased back pressure. Furthermore, the fluctuations in the flow velocity of exhaust pulsation can adversely affect the residence time of exhaust gas within the exhaust purification device, resulting in a deterioration in exhaust purification efficiency.

[0022] Therefore, when an internal combustion engine is operated at a specific rotational speed, it is necessary to reduce the level of standing waves generated in the exhaust system or to move the air column resonance frequency outside the normal rotational range of the internal combustion engine, and the exhaust system must be configured (tuned) to meet this requirement. The most effective method is to place the sub-muffler in the midpoint between the open ends of the flow passage (a and b in Figure 4). Note that the midpoint here does not refer to the midpoint in terms of coordinate distance, but rather to the midpoint in the length of the flow passage through which the exhaust gas flows (referred to as the midpoint flow passage position).

[0023] As described above, the exhaust system 5 of this embodiment can minimize the length of the fourth flow path member 18, thereby shortening the flow path length from the exhaust purification device 6 to the rear end of the insertion portion 85 of the main muffler 8, and since the intermediate flow path position can be set to a relatively straight pipe portion on the side of the driving battery pack 3, it becomes easier to adjust the installation position of the sub-muffler 7. Therefore, according to this embodiment, the sub-muffler can be installed so that part of it is located in the intermediate flow path position between the rear end of the exhaust purification device 6 and the downstream end of the most downstream flow path member (insertion portion 85), which is optimal for suppressing standing waves, and the occurrence of predetermined standing waves can be effectively suppressed.

[0024] Furthermore, as described above, the length of the fourth flow path member 18 can be minimized, and the flow path length from the exhaust purification device 6 to the rear end of the insertion portion 85 of the main muffler 8 can be minimized, but the length of the insertion portion 85 itself can be freely adjusted within the range of the long body (shell) 81.In other words, after minimizing the length of the upstream flow path, the generation mode of standing waves can be adjusted by adjusting the length of the insertion portion 85, i.e., the open end, and together with adjusting the position of the sub-muffler, it becomes possible to suppress standing waves even more effectively.

[0025] Next, the standing wave suppression function of the sub-muffler 7 itself will be described. As shown in the cross-sectional view of FIG. 3, the sub-muffler 7 in this embodiment has the general structure of a multi-hole resonance-type sub-muffler. An inner cylinder 31 is fitted and supported within an outer cylinder 30, with a gap formed within it, forming a so-called double-pipe structure. The upstream end 34 of the outer cylinder 30 is airtightly connected to the upstream second flow path member 13, and the downstream end 35 is airtightly connected to the downstream third flow path member 15. A metal fiber braid 32 is wound around the outer circumferential surface of the inner cylinder 31, and the outer gap is filled with a sound-absorbing member 33 made of heat-resistant fiber. A large number of small-diameter holes 36 are drilled over a certain range d of the inner cylinder 31. In other words, a resonance-type sub-muffler is configured that has a sound-absorbing effect across the entire low, medium, and high frequency ranges.

[0026] This type of resonance-type sub-muffler 7 is highly effective in suppressing standing waves when placed near the antinodes of the standing waves, and is capable of attenuating a wide frequency range, not just the specific frequency attenuation achieved by the side-branch sub-muffler described in Patent Document 1. Furthermore, the sound-absorbing member 33 suppresses heat transfer from the inner cylinder 31 to the outer cylinder 30, reducing heat radiation from the outer cylinder 30 and preventing thermal effects on the driving battery pack 3 located immediately adjacent to it.

[0027] (Second embodiment) Next, an exhaust system 40 according to a second embodiment of the present invention will be described. The exhaust system 40 differs from the exhaust system 5 according to the first embodiment in that a second sub-muffler 41 is also provided in the third flow path member 42. In this way, a resonance-type sub-muffler with an optimum capacity can be added in an optimum position according to the required silencing volume and standing wave characteristics of the exhaust system 40 as a whole.

[0028] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments, and even if there are modifications in the scope that deviate from the spirit of the present invention, they are still included in the present invention. [Explanation of symbols]

[0029] 1. Hybrid vehicles 2. Internal combustion engine 3. Drive battery pack 4 fuel tanks 5, 40 Exhaust system 6 Exhaust purification device 7 Sub-muffler 8 Main muffler 9 Rear end of vehicle body 10 Connection flange 11 First flow path member 12 1st bending part 13 Second flow path member 14 Second bending part 15, 42 Third flow path member 18 Fourth flow path member 20 Flow path member 21, 85 Insertion part 22 1st order standing wave 23 Secondary standing wave 41 Second sub-muffler 81 Torso 82 End plate 83 Inlet pipe 84 Outlet pipe

Claims

1. An exhaust system for a hybrid vehicle that is connected to an internal combustion engine and extends to the rear end of the vehicle body while bypassing a drive battery pack disposed under the vehicle body floor to the side of the vehicle body, The exhaust gas purifying device includes at least an exhaust gas purifying device, a sub-muffler, a main muffler, and a plurality of flow path members that connect these devices and form a flow path for communicating exhaust gas, the final exhaust purification device is mounted in front of the drive battery pack in the vehicle body, and the main muffler is mounted behind the drive battery pack and directed toward the side of the vehicle body; the sub-muffler includes at least one resonance-type sub-muffler having a multi-hole inner cylinder mounted on a side of the drive battery pack, An exhaust system for a hybrid vehicle, wherein the flow path member located most downstream of the flow path is inserted into an end plate located on the bypass side of the main muffler.

2. 2. The exhaust system for a hybrid vehicle according to claim 1, wherein a portion of said resonance-type sub-muffler is located at an intermediate flow path position between a rear end of said exhaust purification device and a downstream end of said flow path member at the most downstream position of said flow path.

3. 3. The exhaust system for a hybrid vehicle according to claim 1, wherein a sound absorbing material is filled between the inner and outer cylinders of said resonance type sub-muffler.

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