BACKGROUND AND SUMMARY OF THE INVENTION

This invention relates to an in-line noise attenuation device for a gas conduit where the gas conduit conveys gas toward a noise source. The device functions to attenuate noise that propagates from the noise source through the conduit in the direction opposite the direction of gas flow without causing serious restriction of the gas flow.

In the air induction system of a naturally aspirated internal combustion engine, air is drawn into the engine by virtue of the manifold vacuum that is created in the intake manifold as the pistons reciprocate within the cylinders. In automotive vehicles powered by such engines, it is typical practice to draw fresh intake air from the atmosphere through a flow path leading from the engine to an intake that is located away from the engine. The action of the engine creates noise that can readily propagate back through the air induction system and escape. Too high a level of such noise can be deemed objectionable.

The present invention is directed to a device that can attenuate this noise without introducing serious restriction to the flow of air into the engine. In particular the device of the invention is adapted for in-line insertion into the air induction system. Moreover, the device of the invention can be fabricated in a very conv lent manner from only two plastic parts.

The foregoing, features, advantages, and benefits of the invention, along with additional ones, will be seen in the ensuing description and claims that are accompanied by the drawings. The drawings disclose a presently preferred embodiment of the invention in accordance with the best mode contemplated at the present time in carrying out the invention.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 illustrates schematically one manner of using the device of the invention.

Fig. 2 is an elevational view, partly in cross section, through a first embodiment of the device.

Fig. 3 is a cross sectional view through one of the parts of the device of Fig. 2 shown by itself.

Fig. 4 is a transverse cross sectional view taken in the direction of arrows 4-4 in Fig. 3.

Fig. 5 is a view similar to Fig. 2, but of a second embodiment.

Fig. 6 is a cross sectional view through one of the parts of the device of Fig. 5 shown by itself.

Fig. 7 is a transverse cross sectional view taken in the direction of arrows 7-7 in Fig. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Fig. 1 illustrates usage of an in-line noise attenuation device 10 in the air intake system 12 of an automotive internal combustion engine 14. Device 10 is

inserted in-line in intake system 12 so that air from the atmosphere that is drawn into engine 14 passes through the device without significant restriction of the airflow while the device attenuates noise that propagates back through the air intake system toward atmosphere. Details of device 10 are presented in Figs. 2-4.

The device comprises a two part assembly consisting of an outer tubular part 16 and an insert 18 that is coaxially disposed within part 16. Both parts can be advantageously fabricated from suitable plastic by conventional plastic fabrication procedures. Nylon is a good materi,- for high temperature usage, while polypropylene is a more economical material where high temperatures a*-e not encountered.

Part 16 comprises a straight circular inlet section 20 leading to a frusto-conically shaped sect ~: 22 of increasing taper. Section 22 in turn leads a short straight section 24. A frusto-conically shaped section 26 of decreasing taper extends from section 24 to a straight circular section 28 that forms the end of part 16 opposite inlet section 20. These sections 20, 22, 24, 26, and 28 are coaxial. The end sections of part 16 are shaped to provide for the connection of hoses (not shown) when the device is installed in the intake system.

Part 18 comprises an ogival-shaped section 30, an aperture section 32, and a venturi section 34. These sections are coaxial. Ogival-shaped section 30 is axially co-extensive with frusto-conically shap*. section 22; aperture section 32, with straight section 24; and venturi section 34, with sections 26 and 28.

Ogival-shaped section 30 points toward, and is coaxial with, inlet section 20. It is also hollow, comprising, an exterior wall surface 36, an interior wall surface 38, and a circular opening 40 at the end that is toward venturi section 34.

Aperture section 32 comprises three identical, spaced apart circumferentially extending openings 42 that are of uniform axial dimension. Openings 42 are separated from each other by bars 44 that serve to join section 30 with section 34.

Venturi section 34 comprises two in-line Venturis 46, 48. There is a short straight section 50 at the end of part 18. Venturi 46 comprises a circular ideal entrance 52, and this ideal entrance, as well as the two Venturis 46, 48, are coaxial with section 30. Entrance 52, opening 40, and the area of outlet ■ section 50 are substantially identical. For best noise attenuation, the area of opening 40 should be at least as large as the area of entrance 52. At the junction of venturi 48 and section 50, the outside of part 18 is provided with . a circumferentially continuous ridge 54, of triangular cross section, and ridge 54 fits into a complementary shaped groove 56 within part 16. This provides a snap-fit attachment of the two parts 16, 18.

Airflow enters device 10 as a column at inlet section 20. It then passes through the annular space 58 that is defined between the exterior surface 36 of ogival-shaped section 30 and the interior surface of frusto-conically shaped section 22. Sections 30 and 22 are designed such that the transverse cross sectional area of space 58 is substantially constant throughout its

length and substantially the same as the transverse cross sectional area of inlet section 20. This design provides minimum disruption and restriction of the airflow in this region.

Venturi section 34 has a very close fit within section 28 of part 16 so that flow between the two parts 16, 18 is not possible beyond aperture section 32. Accordingly, the flow from space 58 passes through apertures 42 and into entrance 52. The flow continues through the two Venturis 46, 48 to exit the device through the circular open end of section 50.

Aperture section 32 is designed such that for the particular type of gas flowing through the device, formation of the vena contracta caused by the flow separation takes place in a smooth fashion so as to maintain very low flow restriction. The ideal entrance is designed to also keep the flow restriction to a minimum.

The venturi section 34 is designed around the vena contracta, i.e. the natural minimum diameter, such that it is "invisible" to flow, but effective for noise attenuation. Noise that enters section 50 passes through the venturi section and is "choked" in the process. The noise is first choked by venturi 48. The choking has two purposes: first, to reduce the noise by reducing the cross sectional area thr Th which the sour ^• is travelling; and second, to "concentrate" the noise to the center. These effects are repeated as the noise passes through venturi 46.

As the noise leaves venturi 46 through airflow entrance 52, it propagates toward the interior of the

hollow ogival-shaped section 30 where it is reflected back through the venturi section 34 to the engine and/or creates a standing wave. In this way, the noise that exits the device through the airflow inlet section 20 is significantly attenuated from the level at which it emanates from the engine.

Although the illustrated device comprises two

Venturis in the venturi section, it is contemplated that the number may be other than two in certain designs. The size of the aperture section may vary from design to design, but in any event it will generally be a compromise between flow restriction and noise escape. Increasing the aperture size tends to reduce the airflow restriction, but at the expense of allowing more noise to escape, and vice versa. For usage in the air induction system of one engine, the device has been found effective in attenuating noise in the range of 0-500 hertz by 3-4.db. The device is also effective in attenuating noise peaks, and this is believed due to the effectiveness of the hollow interior of the ogival-shaped section.

Figs. 5-7 portray a second embodiment 60 of device in which corresponding parts of device 10 are identified by like reference numerals. Tube 16 of device 60 has a slightly different shape wherein a .curved section 62 that is axially coextensive with aperture section 32 leads to a straight section 64 that is axially coextensive with the venturi section 34 and the section 50. The venturi sections are also differently shaped from the shapes of device 10. A final difference is that the ogival-shaped section 30 contains a pattern of dimples 66 that promotes smoother flow over this section.

While a preferred embodiment of the invention has been disclosed, it will be appreciated that principles are applicable to other embodiments. The invention can also be used in other applications, such as the intake systems of turbines and ventilation systems.