FIELD OF INVENTION
[0001] The present invention relates to an air intake box structure and more particularly to a method for improving acoustic performance of an air intake box of a two-wheeler.
BACKGROUND OF INVENTION
[0002] Air intake box (AIB) is one of the elements in the internal combustion engine (IC engine) induction system besides ducts, filtering element and fuel supply system. Recent studies on induction system has found that pressure pulses generated inside the induction system can cause undesirable noise during the cyclic operation of the IC engine and it has a significant contribution to the overall vehicle noise levels.
[0003] This undesired noise can be amplified due to the acoustic resonance inside the induction system and can excite the structural components like ducts, AIB of the induction system as well. Hence, for acoustic performance and protection of structural components like ducts, AIB of the induction system, an air intake box equipped with noise attenuating mechanism is required.
SUMMARY OF THE INVENTION
[0004] The structural components of an air intake box, when excited, further add to undesirable noise, which can be controlled and dampened with sufficient stiffening elements. Here, in the current invention, stiffener elements are being employed to

control the unwanted structural vibration in the air intake box and thereby attenuate the noise generated from it.
[0005] There are various stiffening elements proposed in this invention for attenuating the vibration of the AEB panels and thereby reducing the noise. Here, in the current invention, ribs, dimples and curvatures on the surface of the panel has been used. These ribs, dimples and curvatures can be used individually as well as in combination for vibration reduction.
[0006] In a four stroke engine, the engine is charged as per the operation of intake valve. The intake valve lets in the air and is closed during *4th of its operating cycle. This cyclic process of opening and closing can create a significant amount of pressure pulses inside the induction system which generates undesirable noise. Apart from that, acoustic resonance is governed by the geometrical properties of an induction system like length of the duct, volume of the air intake box etc. The acoustic resonance frequency of an open duct is given by,
f=nv/2L
Where n is the positive integer representing node, v is the speed of sound and L is the length of the duct.
[0007] Pressure waves inside the components of an induction system can get amplified which acts as an excitation for the components structurally which can cause them to get deflected, vibrate at certain frequency and generate un desired noise.

Therefore, AEB panels need to be stiff enough to suppress any kind of vibration induced by the pressure waves inside the induction system.
BRIEF DESCRIPTION OF DRAWINGS
Figure 1 Shows typical mounting of an Air Intake System in a motorcycle.
Figure 2 Air Intake System illustrating air inlet duct, location of Air Intake Box (AEB) and air outlet duct
Figure 3 AEB panel stiffened with curvature
Figure 4 AEB panel stiffened with curvature and dimples
Figure 5 AEB panel stiffened with curvature and ribs
Figure 6 AEB panel stiffened with different stiffening elements like curvature, dimples and ribs
Figure 7 Rib pattern to impart stiffness to reduce vibration and noise.
Table-I Showing the experimental results of vibration reduction using combinations of various stiffening elements.
DETAILED DESCRIPTION OF THE INVENTION
[0008] The panels of AEB tend to mimic the working of a loudspeaker especially when it is compliant and have a broad area. There are different methods to improve the

stiffness of the panel. Increasing the thickness and material hardening are some methods; however, it comes with additional cost. Adding ribs, curvatures in the surface, dimples or a combination of any of these are better methods to improve the stiffness of a panel/surface effectively. This can in turn help in reducing the noise contribution from the panels.
[0009] The efficacy of the stiffener to suppress the vibration can be calculated and compared using the responses obtained from a harmonic response simulation. The response against frequency of a single degree of system with a mass, m, and stiffness, k, is given as
X/F=l/(k-mwA2)
Where x is the response, F is the forcing function and w is the frequency. So an increase in stiffness can reduce the response. Therefore, different methods are used here to increase the stiffness of the panels of AIB and are illustrated and discussed with figures and the respective responses.
[00010] Figure 1 shows a typical mounting arrangement of an air intake box on a two-wheeler motorcycle. The air intake box (located below shaded portion 11), inducts atmospheric air via an intake opening 12. The air is filtered in the air intake box below shaded portion 11 and is sent to the carburetor 14. The filtered air through the carburetor enters the engine 13.

[00011] Figure 2 shows location of a typical air intake box 21 located below the shaded portion 11, with the air intake opening 12, line of maximum deflection 22, filtered air output 23. The inner construction of the air intake box has two compartments mainly the intake side and output side, both being separated by a filter that functions as to filter the air coming from the intake side and block all the dirt particles. The line of maximum deflection 22 is a profile on the air intake box 21 along which the air intake box 21 has maximum tendency of getting deflected under pressurized condition.
[00012] Figure 3 shows the AIB with curvature 31 on the panel. Here curvature is the stiffening element for the panel. When the response on the vibration, using this stiffening element is analyzed and is compared with the response without any stiffening element on the panel in Figure 3, the result as shown in Table-I shows that, the vibration gets reduced from 1750mm/s2 to 800mm/s2. Assuming that the frequency range of vibrations, in which a two-wheeler mostly operates, is 150 to 300Hz, it is clear from the response, that the magnitude is lesser for the panel which is stiffened using a curvature.
[00013] Figure 4 shows the AIB with curvature 31 and dimple 41 on the panel. Here curvature and the dimples are the stiffening elements for the panel. When the response on the vibration, using this combination of curvature and dimples as stiffening elements is analyzed and it is compared with the response without any stiffening element on the panel in Figure 4, the result as shown in Table-I shows that,

the vibration gets reduced from 1750mm/s2 to 1150mm/s2. It is clear from the response, that the magnitude is lesser for the panel, which is stiffened using a combination of curvature and dimples.
[00014] Figure 5 shows the AIB with curvature 31 and ribs 51 on the panel. Here curvature and the ribs are the stiffening elements for the panel. When the response on the vibration, using this combination of curvature and ribs as stiffening elements is analyzed and it is compared with the response without any stiffening element on the panel in Figure 5, the result as shown in Table-I shows that, the vibration is reduced from 1750mm/s2 to 900mm/s2. It is clear from the response, that the magnitude is lesser for the panel, which is stiffened using a combination of curvature and ribs.
[00015] Figure 6 shows the AEB with curvature 31, dimples 41 and ribs 51 on the panel. Here curvature dimples and the ribs are the stiffening elements for the panel. When the response on the vibration, using this combination of curvature, dimples and ribs as stiffening elements is analyzed and it is compared with the response without any stiffening element on the panel in Figure 6, the result as shown in Table-I shows that, the vibration gets reduced from 1750mm/s2 to 1300mm/s2. It is clear from the response, that the magnitude is lesser for the panel, which is stiffened using a curvature 31, dimples 41 and ribs 51.
[00016] Figure 7 shows a stiffening pattern using ribs to arrest the excess magnitude of the response. As shown in the figure, this pattern is formed inside surface of the enclosed AIB panel whereas the previous pattern shown in Figure 1 is

outside the panel. A significant reduction in vibration and noise levels are attained using this stiffening pattern.

We claim:
1. A surface profile for reducing noise and vibration in an air intake box (21),
comprising of:
atleast one curvature (31), the said curvature (31)being an irregularity of material surface formed on the outer side of the compartment in which the air is being stored, the said irregularity on the said material surface may consist of inclined and step-up surface along the line of deflection of the surface when air compartment is pressurized;
atleast one dimple (41), the said dimple (41) being a concave shaped deformity brought on the outer side of the compartment in which the air is being stored, the said dimple (41) resists any further deflection or deformity of the surface on which it has been formed;
atleast one rib 51, the said rib 51 being a perpendicular projection of material on the outer side of the compartment in which the air is being stored, the said rib 51 resists the deflection or deformity of the surface on which the said rib 51 is placed;
wherein atleast one of any combination of the said curvature (31), dimple (41), or the said rib (51) are positioned along atleast one line of deflection (22) on the said air intake box (21).
2. The surface profile for reducing noise and vibration in an air intake box (21) as
claimed in claim 1 may consist of any number of combinations of rib (51), dimple
(41) or curvature (31).

3. The surface profile for reducing noise and vibration in an air intake box (21) as claimed in claim 1, the profile being formed on the surface along the line of maximum deflection (22).
4. The surface profile for reducing noise and vibration in an air intake box (21) as claimed in claim 1 being formed on the inner surface of the AIB panel.
5. The surface profile for reducing noise and vibration in an air intake box (21) as claimed in claim 1 equipped with the said curvature (31), dimple (41), or the said rib (51) on the inner surface.
6. The surface profile for reducing noise and vibration in an air intake box (21) as claimed in claim 1 equipped with the said curvature (31), dimple (41), or the said rib (51) on the outer surface.