Air intake duct for internal-combustion engine

Abstract

An air intake duct (1) used in an internal-combustion engine for an automobile includes: a main duct portion (2) extending in a substantially straight line; an air intake port (3) opened toward the side; and a curved section (4) smoothly connecting the air intake port (3) and the main duct portion (2). Over a length range including a part of the main duct portion (2) from an opening position of the air intake port (3) or directly below the opening position, a partition wall (11) is provided for partitioning a flow path in the duct (1) into a first flow path (12) and a second flow path (13). Since the passage lengths of the two flow paths (12, 13) are different, air column resonance occurs in each of the flow paths (12, 13), and a resonator effect is obtained for each frequency.

Description

Internal combustion engine intake duct

[0001] The present invention relates to an improvement in an intake duct for an internal combustion engine such as an automotive internal combustion engine, which has an intake port at its tip for taking in outside air.

[0002] An intake system for an internal combustion engine includes an air cleaner and a duct that guides outside air to the air cleaner, and the most upstream portion of the duct is configured as an intake duct with an intake port at its tip. In most cases, in an automotive internal combustion engine, the intake port opens toward the front of the vehicle, and the downstream end of the intake duct routed inside the engine compartment is connected to an air cleaner case.

[0003] In the intake system of such an internal combustion engine, the high-speed air flow generates so-called intake noise, which is known to be emitted to the outside from the intake port at the tip. For this reason, the intake duct of an internal combustion engine for a vehicle is often equipped with one or more resonators that use Helmholtz-type resonance elements to reduce specific frequencies.

[0004] This resonator requires a space with a volume corresponding to the frequency, which makes it difficult to install the intake duct in the engine room.

[0005] Patent Document 1 discloses an intake duct equipped with a straightening vane at a bend away from the intake port. This straightening vane is located far downstream from the intake port and is only provided locally at the bend, so it does not have the resonator effect of the present invention.

[0006] JP 2013-234614 A

[0007] This invention relates to an intake duct for an internal combustion engine, which includes a main duct portion extending in a substantially straight line, an intake port that opens toward the side of the main duct portion at the tip of the main duct portion, and a curved portion that smoothly connects the intake port and the main duct portion, and which is provided with a partition wall that divides the flow path within the duct into a first flow path that runs along the inner side of the curve of the curved portion and a second flow path that runs along the outer side, over a length range from the opening position of the intake port or just below it to including a part of the main duct portion.

[0008] In this configuration, the first flow path along the inner periphery of the curve is relatively short, while the second flow path along the outer periphery of the curve is relatively long, resulting in two flow paths with different passage lengths. The ends of each flow path open to the outside at the intake port. This causes air column resonance (air column vibration) at a resonant frequency determined by the passage length and diameter of each flow path, resulting in a resonator effect according to that frequency.

[0009] Fig. 3 is a diagram illustrating the configuration of an embodiment of an air intake duct according to the present invention; Fig. 4 is a diagram illustrating the action of a resonator; Fig. 5 is a diagram illustrating the frequency characteristics of intake noise measured at point P1 in Fig. 2; Fig. 6 is a diagram illustrating the frequency characteristics of intake noise measured at point P2 in Fig. 2; Fig. 7 is a diagram illustrating the frequency characteristics of intake noise measured at point P3 in Fig. 2;

[0010] An embodiment of the present invention will now be described in detail with reference to the accompanying drawings.

[0011] 1 shows an embodiment of an air intake duct 1 according to the present invention. The air intake duct 1 of this embodiment is applied to an internal combustion engine of an automobile, and is entirely formed in a tubular shape from a hard synthetic resin. For example, the duct may be divided into a plurality of sections, each molded from a hard synthetic resin material, and then integrated by welding, adhesive, or other means.

[0012] The air intake duct 1 includes a main duct portion 2 extending substantially linearly, an air intake port 3 at the tip of the main duct portion 2 that opens toward the side of the main duct portion 2, and a curved portion 4 that smoothly connects the air intake port 3 to the main duct portion 2. The main duct portion 2, which extends substantially linearly, is disposed at the front edge of the engine compartment of the automobile, for example, above the radiator, with the longitudinal direction of the main duct portion 2 aligned with the vehicle width direction. In this arrangement, the air intake port 3 at the tip of the main duct portion 2 opens toward the front of the vehicle. In other words, the main duct portion 2 and a short portion of the air intake port 3 form a substantially L-shaped duct. The other end 5 of the main duct portion 2 is connected to an air cleaner case (not shown). Note that FIG. 1 corresponds to a plan view of the engine compartment from above.

[0013] The main duct portion 2 has a flattened passage cross-sectional shape so that its dimension in the vehicle vertical direction is small. For example, it has a flattened oval or rectangular cross-sectional shape. Corresponding to the flattened passage cross-sectional shape of the main duct portion 2, the intake port 3 has a narrow, flat opening shape that is elongated along the longitudinal direction of the main duct portion 2, for example, a flattened oval or rectangular opening shape.

[0014] In one embodiment, the direction of the air intake 3 is 90° different from the longitudinal direction of the main duct portion 2. The curved portion 4 has curved outer and inner walls 4a and 4b, and smoothly connects the main duct portion 2 and the air intake 3, which are 90° different in direction.

[0015] The intake duct 1 further includes a partition wall 11 therein. In the plan view of the intake duct 1 shown in Figure 1, this partition wall 11 extends from the opening of the intake port 3 or immediately below it, through the curved portion 4, and over a length that includes part of the main duct portion 2, dividing the flow path within the intake duct 1 into a first flow path 12 that runs along the inner periphery of the curved portion 4 and a second flow path 13 that runs along the outer periphery. As shown in Figure 1, the partition wall 11 is disposed so as to vertically cross near the center of the flattened cross-sectional shape of the main duct portion 2, and the end portion on the intake port 3 side similarly vertically crosses near the center of the flattened opening shape.

[0016] The first flow path 12 and the second flow path 13 separated by the partition wall 11 are basically independent of each other at the intake port 3, and merge together at the middle of the main duct portion 2 in the longitudinal direction. As will be described later, the length of the partition wall 11 is set according to the noise frequency to be silenced. For example, a length of about several tens of centimeters is required.

[0017] The partition wall 11 is integrated with the outer wall portion of the intake duct 1 by an appropriate method such as welding, bonding, or integral molding, but it is desirable to configure it so that there is no leakage of intake air between the first flow path 12 and the second flow path 13.

[0018] Furthermore, the partition wall 11 is curved along the curved shape of the bending portion 4 so as to smoothly guide the flow of intake air in the bending portion 4. In other words, the partition wall 11 also functions as a flow straightening plate that smooths the flow in the bending portion 4.

[0019] In one embodiment, the position of the partition wall 11 is set so that the cross-sectional area of ​​the second flow path 13 along the outer periphery of the curved portion 4 is slightly smaller than the cross-sectional area of ​​the first flow path 12 along the inner periphery, taking into consideration that the passage resistance due to the bend is relatively larger in the first flow path 12 on the inner periphery.

[0020] Next, the resonator effect, a key feature of the present invention, will be described with reference to FIG. 2 . The first and second flow passages 12 and 13, partitioned by the partition wall 11, can each be considered a tube with both ends open. Air column resonance (air column vibration) occurs at a resonant frequency F determined by the passage length L and passage diameter d of each flow passage. The passage length L is the length of a line passing through the center of the passage cross section, and the passage diameter d is the equivalent diameter of the passage cross section. Because the partition wall 11 is provided over a length range that includes the curved portion 4, the passage length L1 of the first flow passage 12 and the passage length L2 of the second flow passage 13 are different from each other. Therefore, the first and second flow passages have different resonant frequencies, and the resonator effect is achieved at these resonant frequencies. In one embodiment, the intake duct 1 has a flattened cross section, and the distance between the outer peripheral wall 4a and the inner peripheral wall 4b of the curved portion 4 is large, so a large difference between the passage length L1 of the first flow passage 12 and the passage length L2 of the second flow passage 13 can be easily achieved.

[0021] The resonant frequency F of the air column resonance is determined by the following formula, where c is the speed of sound and n is the order.

[0022] F=n·c / 2(L+0.82·d / 2) For example, if the passage length L is about 430 mm and the passage diameter d is about 60 mm, resonance frequencies can be obtained around 380 Hz, 760 Hz, etc., depending on the order n.

[0023] For example, when resonance occurs in the second flow path 13 at a first-order resonant frequency F2 (e.g., 380 Hz), a standing wave is generated in the second flow path 13, with high sound pressure at the center 21 in the longitudinal direction and low sound pressure at both end portions 22, 23. The downstream end 23 is essentially the confluence with the first flow path 12, and the lower sound pressure in this portion reduces the overall sound pressure in the first flow path 12. Therefore, the sound pressure at the resonant frequency F2 in the sound emitted from the first flow path 12 decreases. Note that, for such a resonator effect to occur, the passage length L1 of the first flow path 12 (in other words, the resonance condition) must be sufficiently different from the passage length L2 of the second flow path 13.

[0024] The same applies when resonance of the first order resonant frequency F1 occurs in the first flow path 12, and as a result, a standing wave is generated in the first flow path 12, resulting in a decrease in sound pressure at the resonant frequency F1 in the sound emitted from the second flow path 13. Since the first flow path 12 is shorter than the second flow path 13, the resonant frequency F1 is basically higher than the resonant frequency F2 of the second flow path 13.

[0025] Since the sounds emitted from the first flow path 12 and the second flow path 13 are combined and reach an external listener, the listener perceives the intermediate frequency range between the resonance frequencies F1 and F2 of the two sounds as being attenuated. The same applies to air column resonances of second and higher orders. Therefore, the passage lengths L1 and L2 and the passage cross-sectional areas of the respective flow paths 12 and 13 are tuned so that the frequency F1 of the air column resonance in the first flow path 12 and the frequency F2 of the air column resonance in the second flow path 13 are located on either side of the target sound-attenuation frequency.

[0026] 3 to 5 show the frequency characteristics of intake noise in one specific example. Note that FIGS. 3 to 5 compare the characteristics of a comparative example not including the partition wall 11 with the characteristics of the example. These characteristics are those when a constant flow rate of air is flowing through the intake duct 1. FIG. 3 shows the frequency characteristics of intake noise measured at a position immediately before the center of the opening of the first flow path 12 in the intake port 3, i.e., point P1 in FIG. 2. As shown in FIG. 3, the sound pressure level drops significantly at two frequencies, f11 and f12, in front of the opening of the first flow path 12. These two frequencies correspond to the first and second order resonance frequencies in the second flow path 13.

[0027] 4 shows the frequency characteristics of the intake noise measured at a position immediately before the center of the opening of the second flow passage 13 in the intake port 3, i.e., at point P2 in FIG. 2. As shown in FIG. 4, the sound pressure levels at two frequencies, f21 and f22, decrease in front of the opening of the second flow passage 13. These two frequencies correspond to the first and second order resonance frequencies in the first flow passage 12.

[0028] Figure 5 shows the frequency characteristics of intake noise measured at a position just before the edge of the partition wall 11 at the intake port 3, i.e., at point P3 in Figure 2. As shown in Figure 5, in front of the partition wall 11, the sound whose frequency characteristics are shown in Figure 3 and the sound whose frequency characteristics are shown in Figure 4 are combined, so the sound pressure levels at two frequencies, f31 between f11 and f21, and f32 between f21 and f22, are reduced. In other words, the passage lengths L1 and L2 and the passage cross-sectional area are tuned so that these silencing frequencies f31 and f32 become desired frequencies. As mentioned above, the cross-sectional area of ​​the second flow passage 13 along the outer periphery of the curved portion 4 is set slightly smaller than the cross-sectional area of ​​the first flow passage 12 along the inner periphery. Therefore, the length of the partition wall 11 and other factors are set to achieve the desired silencing frequency, taking into account the difference in these cross-sectional areas. As shown in the comparative examples in Figures 3 to 5 , the intake noise generated by the basic shape and dimensions of the intake system, including the air cleaner case, has several frequency peaks. However, it is desirable to set the length of the partition wall 11 and other factors so that the resonator function of the intake duct 1 described above can be used to silence relatively low frequency peaks. Generally, a Helmholtz resonator is attached to the duct to reduce intake noise of a specific frequency. However, the lower the frequency of the Helmholtz resonator, the larger the size. Therefore, by utilizing the resonator function of the intake duct 1, a large Helmholtz resonator can be omitted. As a specific example, it is desirable to set the length of the partition wall 11 so that the frequency of the air column resonance in the relatively long second flow passage 13 is 500 Hz or less. This can be adequately achieved with a partition wall 11 having a length of about 40 cm. The intake duct 1 of the present invention can be used in combination with a Helmholtz resonator to reduce intake noise peaks other than the silencing frequencies caused by the air column resonance in the flow passages 12 and 13 described above.

[0029] Although one embodiment of the present invention has been described above, the present invention is not limited to the above embodiment and various modifications are possible. For example, although the intake duct 1 in the above embodiment has been described as having an end connected to the air cleaner case, another duct may be interposed between the intake duct and the air cleaner case. Furthermore, the duct is not limited to a duct with a flat cross section, and may have any cross section.

Claims

1. An intake duct for an internal combustion engine includes a main duct portion extending in a nearly straight line, an intake port opening laterally to the main duct portion at the tip of the main duct portion, and a curved portion smoothly connecting the intake port and the main duct portion, The duct is provided with a partition wall that divides the flow path within the duct into a first flow path along the inner circumference of the curve in the curved section and a second flow path along the outer circumference, extending from the opening position of the above-mentioned intake port or directly below it, over a length range including a part of the above-mentioned main duct section. The passage length and cross-sectional area of ​​each passage are tuned such that the frequency of the air column resonance in the first passage and the frequency of the air column resonance in the second passage lie on either side of the noise-canceling frequency to be silenced. Intake duct for an internal combustion engine.

2. The above-mentioned partition wall is curved along the curved section in order to smoothly guide the flow in the curved section. An intake duct for an internal combustion engine as described in claim 1.

3. The main duct portion described above has a flattened passage cross-sectional shape, and corresponding to this flattened passage cross-sectional shape, the air intake port has an elongated, flattened opening shape along the longitudinal direction of the main duct portion. The above-mentioned partition wall is provided so as to cross the area near the center of the above-mentioned flattened passage cross-sectional shape. An intake duct for an internal combustion engine as described in claim 1.

4. The cross-sectional area of ​​the second channel is smaller than the cross-sectional area of ​​the first channel. An intake duct for an internal combustion engine according to claim 2.

5. (delete)

6. The length of the partition wall is set such that the frequency of the air column resonance in the second flow path is 500 Hz or less. An intake duct for an internal combustion engine as described in claim 1.