Engine exhaust structure

Abstract

In the present invention, an exhaust pipe (22) guides and discharges the exhaust of an engine (12) to the rear of a vehicle body. A center muffler (24) is provided in the exhaust pipe (22). The exhaust pipe (22) is bent in the vehicle width direction in order to dispose the center muffler (24) at a position that, in the exhaust path from the engine (12), corresponds to a peak of a waveform representing the excitation force of the engine (12) and does not overlap a fuel tank (26) when viewed from the vertical direction of the vehicle body.

Description

Engine exhaust structure

[0001] The present invention relates to an engine exhaust structure.

[0002] In the engine exhaust structure disclosed in Patent Document 1, the muffler is located further forward on the vehicle body than the fuel tank. The underside of the fuel tank is formed with a housing portion that is recessed upward and extends in the fore-and-aft direction of the vehicle body, and the exhaust pipe passes through this housing portion.

[0003] Japanese Patent Application Laid-Open No. 2020-186707

[0004] To reduce exhaust muffled noise, it is desirable to position the muffler at the peak of the waveform, which represents the engine's vibratory force. The fewer the number of cylinders an engine has, the longer the wavelength becomes, so if the muffler is positioned toward the rear of the vehicle body to match the peak of the waveform, it will interfere with the fuel tank. Enlarging the fuel tank's storage area to accommodate the muffler will sacrifice fuel tank capacity, and raising the fuel tank's position will sacrifice passenger compartment space. The objective of this invention is to reduce exhaust muffled noise without sacrificing fuel tank capacity or passenger compartment space.

[0005] According to one aspect of the present invention, an engine exhaust structure includes an exhaust pipe and a muffler. The exhaust pipe guides and discharges engine exhaust toward the rear of the vehicle body. The muffler is provided in the exhaust pipe. The exhaust pipe is bent in a stepped manner in the vehicle width direction so that the muffler is positioned at a peak of the waveform representing the engine's vibratory force in the exhaust path from the engine and at a position that does not overlap with the fuel tank when viewed from the top and bottom of the vehicle body.

[0006] According to the present invention, the exhaust path can be extended by bypassing the exhaust pipe. This allows the muffler to be positioned at the peak of the waveform that represents the engine's vibratory force, without overlapping with the fuel tank. Therefore, it is possible to reduce muffled exhaust noise without sacrificing the fuel tank capacity or the vehicle interior space.

[0007] The present invention relates to a vehicle, an engine, and a muffler arrangement for a three-cylinder engine.

[0008] Hereinafter, embodiments of the present invention will be described with reference to the drawings. Note that the drawings are schematic and may differ from the actual product. Furthermore, the following embodiments exemplify devices and methods for embodying the technical concept of the present invention, and are not intended to limit the configuration to those described below. In other words, the technical concept of the present invention can be modified in various ways within the technical scope described in the claims.

[0009] 1 is a diagram showing a schematic configuration of a vehicle 11. The vehicle 11 employs a series hybrid system and includes an engine 12, a generator 13, a battery 14, an inverter 15, a motor 16, and wheels 17. The engine 12 has three cylinders and drives the generator 13. The generator 13 supplies generated electric power to the battery 14 and the motor 16 via the inverter 15. The battery 14 is charged and discharged via the inverter 15. The motor 16 drives the wheels 17 using electric power from the battery 14 and the generator 13, and conversely, charges the battery 14 through regeneration. The engine 12 is dedicated to power generation and not for driving, and is therefore normally operated in a highly efficient rotational speed range during power generation. The highly efficient rotational speed range is, for example, about 2,000 rpm.

[0010] FIG. 2 is a diagram showing the engine exhaust structure 21. Here, the vehicle 11 is shown as viewed from below. The engine exhaust structure 21 includes an exhaust pipe 22, a catalytic converter 23, a center muffler 24 (first muffler), and a rear muffler 25 (second muffler). The exhaust pipe 22 guides and discharges exhaust from the engine 12 toward the rear of the vehicle. The exhaust pipe 22 is made up of multiple pipes connected together, but for convenience, it will be described here as a single pipe. The section of the exhaust pipe 22 from point P1 to point P11 is defined as the exhaust path. Point P1, which is the starting point, is connected to the exhaust manifold of the engine 12, and point P11, which is the end point, is the exhaust outlet.

[0011] The section from point P1 to point P2 extends in the fore-and-aft direction of the vehicle body at the center in the vehicle width direction, and the catalytic converter 23 is provided on this path. The section from point P2 to point P3 extends from the center in the vehicle width direction toward the outside. The section from point P3 to point P4 extends in the fore-and-aft direction of the vehicle body at a position more outside in the vehicle width direction than the section from point P1 to point P2, and the center muffler 24 is provided on this path. In other words, the section from point P3 to point P4 is bent outward in the vehicle width direction and is offset relative to the section from point P1 to point P2.

[0012] The section from point P4 to point P5 extends diagonally from the outer side toward the center in the vehicle width direction as it moves toward the rear of the vehicle. The section from point P5 to point P6 extends in the fore-and-aft direction of the vehicle body more inward in the vehicle width direction than the section from point P3 to point P4. In other words, the section from point P5 to point P6 is bent in a step more inward in the vehicle width direction than the section from point P3 to point P4 and is offset. The section from point P6 to point P7 extends diagonally from the center toward the outer side in the vehicle width direction as it moves toward the rear of the vehicle body.

[0013] The section from point P7 to point P8 extends in the fore-and-aft direction of the vehicle body and is more outboard in the vehicle width direction than the section from point P5 to point P6. In other words, the section from point P7 to point P8 is bent in a step more outboard in the vehicle width direction than the section from point P5 to point P6, and is offset. A rear muffler 25 is provided between point P8 and point P9. The section from point P9 to point P10 extends from the inside to the outside in the vehicle width direction. The section from point P10 to point P11 extends in the fore-and-aft direction of the vehicle body and is more outboard in the vehicle width direction than the rear muffler 25.

[0014] The catalytic converter 23 converts carbon monoxide, hydrocarbons, and nitrogen oxides into harmless components through a chemical reaction. The center muffler 24 reduces exhaust noise by expanding the high-pressure exhaust gas. The center of the internal path in the center muffler 24 is designated as point Pc. A fuel tank 26 is disposed on the underside of the vehicle 11 at the center in the vehicle width direction toward the rear of the vehicle body, and the center muffler 24 extends in the fore-and-aft direction of the vehicle body and is disposed outward in the vehicle width direction from the fuel tank 26 so as not to overlap with the fuel tank 26 when viewed from the top-bottom direction of the vehicle body. The rear muffler 25 reduces exhaust noise by expanding the high-pressure exhaust gas. The center of the internal path in the rear muffler 25 is designated as point Pr. The rear muffler 25 extends in the vehicle width direction and is disposed toward the rear end of the vehicle body.

[0015] Next, the placement of the muffler in the exhaust path will be described. FIG. 3 is a diagram showing a waveform representing the vibratory force of the engine 12. The x-axis represents the position in the exhaust path, and the y-axis represents the wave displacement. The wavelength λ of the waveform representing the vibratory force of the engine 12 varies depending on the number of cylinders; the fewer the number of cylinders, the longer the wavelength λ. A four-cylinder engine is shown with a thick dashed line, and a three-cylinder engine is shown with a thick solid line. In the case of a four-cylinder engine, if the speed of sound in air is 331 m / s and the frequency at 2,000 rpm is 67 Hz, then the wavelength λ4 is 4.9 m. Therefore, the peak position of the first crest is λ4 / 4, or 1.22 m. In the case of a three-cylinder engine, if the speed of sound in air is 331 m / s and the frequency at 2,000 rpm is 50 Hz, then the wavelength λ3 is 6.62 m. Therefore, the peak position of the first mountain is 1.7 m at λ3 / 4.

[0016] To reduce exhaust muffler noise, the center muffler 24 and rear muffler 25 are positioned at the peaks of the waveform representing the vibratory force of the engine 12. FIG. 4 is a diagram showing the arrangement of mufflers in a three-cylinder engine. The x-axis represents the position of the exhaust path, and the y-axis represents the wave displacement. In the waveform representing the vibratory force of the engine 12, the amplitude is Am and the effective value of Am is Ae. The effective value Ae is the value obtained by dividing the amplitude Am by the square root of 2 (= Am / √2). The center muffler 24 is positioned in a region R1 where the center point Pc of the internal path is greater than the effective value Ae at the first peak. The rear muffler 25 is positioned in a region R2 where the center point Pr of the internal path is greater than the absolute value of the effective value Ae at the second peak.

[0017] <<Functions and Effects>> Next, the main functions and effects of the embodiment will be described. (1) The engine exhaust structure 21 includes an exhaust pipe 22 and a center muffler 24 (or a rear muffler 25). The exhaust pipe 22 guides and discharges exhaust from the engine 12 rearward. The center muffler 24 (or a rear muffler 25) is provided in the exhaust pipe 22. The exhaust pipe 22 is bent in a stepped manner in the vehicle width direction in order to position the center muffler 24 (or a rear muffler 25) at the peak of the waveform representing the vibratory force of the engine 12 in the exhaust path from the engine 12, and in a position that does not overlap with the fuel tank 26 when viewed from the top-bottom direction of the vehicle. In this way, the exhaust path can be extended by bypassing the exhaust pipe 22. This allows the center muffler 24 (or a rear muffler 25) to be positioned at the peak of the waveform representing the vibratory force of the engine 12, and in a position that does not overlap with the fuel tank 26. Therefore, it is possible to reduce muffled exhaust noise without sacrificing the capacity of the fuel tank 26 or the vehicle interior space.

[0018] (2) The exhaust pipe 22 is bent in a stepped manner from the center to the outside in the vehicle width direction. By routing the exhaust pipe 22 from the center to the outside in this manner, the exhaust path can be extended. This allows the center muffler 24 (or rear muffler 25) to be positioned at the peak of the waveform representing the vibratory force of the engine 12, without overlapping with the fuel tank 26. (3) The center muffler 24 (or rear muffler 25) is positioned in region R1 (or region R2) of the waveform where the absolute value of the effective value Ae at amplitude Am is greater. This effectively reduces muffled exhaust noise. (4) The center of the internal path of the center muffler 24 (or rear muffler 25) is positioned in region R1 (or region R2) of the waveform where the absolute value of the effective value Ae at amplitude Am is greater. This effectively reduces muffled exhaust noise.

[0019] (5) The engine exhaust structure 21 includes a center muffler 24. The center muffler 24 is provided in the exhaust path. The center muffler 24 is located outside the fuel tank 26 in the vehicle width direction. This allows the space to be effectively utilized to the sides of the fuel tank 26, allowing the exhaust to be diverted to the exhaust pipe 22 and extending the exhaust path. Therefore, the center muffler 24 can be located at the peak of the waveform representing the vibratory force of the engine 12, and in a position that does not overlap with the fuel tank 26. (6) The engine exhaust structure 21 includes a rear muffler 25. The rear muffler 25 is located in the exhaust path downstream of the center muffler 24 and rearward of the fuel tank 26 on the vehicle body. The exhaust pipe 22 is bent inward in the vehicle width direction from the center muffler 24 to the rear muffler 25, and then bent outward in the vehicle width direction. This allows the space to be effectively utilized behind the fuel tank 26, allowing the exhaust to be diverted to the exhaust pipe 22 and extending the exhaust path. Therefore, the rear muffler 25 can be disposed at the peak of the waveform representing the vibratory force of the engine 12 .

[0020] (7) The engine 12 has three cylinders. This allows the muffler to be positioned at the peak of the waveform representing the vibratory force of the engine 12, even in vehicles with a long wavelength. (8) The engine 12 is mounted on a series hybrid vehicle 11 that is used for power generation rather than for driving. In a series hybrid vehicle, the engine 12 is dedicated to power generation rather than driving, and can therefore be operated in a highly efficient rotational speed range. This makes the peak of the waveform representing the vibratory force of the engine 12 approximately constant, effectively reducing exhaust muffled noise. (9) The wavelength λ of the waveform is calculated based on the engine speed during normal power generation. This allows exhaust muffled noise to be reduced during normal power generation, which is the most frequently repeated period.

[0021] Next, a comparative example will be described. To reduce the muffled exhaust noise, it is desirable to position the center muffler 24 at the peak of the waveform representing the vibratory force of the engine 12. Since the wavelength λ becomes longer as the number of cylinders in the engine 12 decreases, attempting to position the center muffler 24 toward the rear of the vehicle body to match the peak of the waveform would result in interference between the center muffler 24 and the fuel tank 26. Therefore, it is conceivable to form a housing portion on the underside of the fuel tank 26 that is recessed upward and extends in the fore-and-aft direction of the vehicle body, and to house the center muffler 24 therein. However, forming a housing portion in the fuel tank 26 large enough to house the center muffler 24 would sacrifice the capacity of the fuel tank 26. Conversely, making the housing portion smaller and raising the position of the fuel tank 26 would sacrifice cabin space.

[0022] <<Modifications>> In the embodiment, the section of the exhaust pipe 22 from point P1 to point P2 is disposed in the center of the vehicle width direction, but this is not limited thereto. That is, the section of the exhaust pipe 22 from point P1 to point P2 may be disposed on the outer side of the vehicle width direction. In this case, the exhaust path can be extended by bending the section from point P3 to point P4 inward in the vehicle width direction. In the embodiment, the center muffler 24 is disposed on the side of the fuel tank 26, but this is not limited thereto. That is, it is sufficient that the center muffler 24 be disposed at the peak of the waveform representing the vibratory force of the engine 12 in the exhaust path and in a position that does not overlap with the fuel tank 26 when viewed from the top and bottom of the vehicle body. If this condition is satisfied, the center muffler 24 may be disposed, for example, in the section from point P2 to point P3.

[0023] Although the embodiment has been described with reference to a three-cylinder engine 12, the present invention is not limited to this. For example, the present invention may be applied to a two-cylinder engine or an engine with four or more cylinders. Since the wavelength λ becomes shorter as the number of cylinders increases, in the case of an engine with four or more cylinders, the center muffler may be positioned at the second peak of the waveform instead of the first peak. Although the embodiment has been described with reference to a series hybrid vehicle 11, the present invention is not limited to this. In other words, the present invention may be applied to any vehicle equipped with an engine, and may also be applied to parallel or split hybrid vehicles, and further to ordinary vehicles that run on engine power alone.

[0024] Although the present invention has been described above with reference to a limited number of embodiments, the scope of the invention is not limited thereto, and modifications of the embodiments based on the above disclosure will be obvious to those skilled in the art.

[0025] 11...vehicle, 12...engine, 13...generator, 14...battery, 15...inverter, 16...motor, 17...wheel, 21...engine exhaust structure, 22...exhaust pipe, 23...catalytic converter, 24...center muffler, 25...rear muffler, 26...fuel tank

Claims

1. An engine exhaust structure comprising: an exhaust pipe that guides and discharges engine exhaust toward the rear of a vehicle body; and a muffler provided in said exhaust pipe, wherein said exhaust pipe is bent in steps in the vehicle width direction in order to position said muffler at the peak of a waveform that represents the engine's vibratory force in the exhaust path from said engine, and in a position that does not overlap with the fuel tank when viewed from the top and bottom of the vehicle body.

2. The engine exhaust structure according to claim 1, wherein the exhaust pipe is bent in steps from the center in the vehicle width direction to the outside.

3. An engine exhaust structure according to claim 1, wherein the muffler is disposed in a region of the waveform where the absolute value of the effective amplitude is greater than the absolute value of the effective amplitude.

4. An engine exhaust structure according to claim 1, characterized in that the center of the internal path of the muffler is positioned in a region of the waveform where the absolute value of the effective amplitude is greater than the absolute value of the effective amplitude.

5. The engine exhaust structure according to claim 1, characterized in that the muffler comprises a first muffler provided in the exhaust path, the first muffler being positioned on the outer side of the fuel tank in the vehicle width direction.

6. An engine exhaust structure as described in claim 5, characterized in that the muffler includes a second muffler provided on the exhaust path downstream of the first muffler, the second muffler is positioned rearward of the fuel tank on the vehicle body, and the exhaust pipe is bent inward in the vehicle width direction from the first muffler to the second muffler, and then bent outward in the vehicle width direction.

7. The engine exhaust structure according to claim 1, wherein the engine is a three-cylinder engine.

8. The engine exhaust structure according to claim 7, wherein the engine is mounted on a series hybrid vehicle that is used for generating electricity rather than for driving.

9. An engine exhaust structure according to claim 8, wherein the wavelength of the waveform is calculated according to the engine speed during normal power generation.

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