LOW-RESTRICTION EXHAUST TREATMENT APPARATUS

Abstract: A low-restriction exhaust treatment apparatus (10) having a hollow outer shell (12) into which a means for treating exhaust gas emitted from an internal combustion engine is disposed, end portions (20,22) sealingly attached to each end (14,16) of the outer shell (12), and end tubes (28,30) inserted into apertures (24,26) formed in the sealing end portions (20,22) for facilitating exhaust flow into and out of the apparatus (10). The end tubes (28,30) according to the invention each have a plurality of axially-extending, radially inwardly-angled serrations (34) formed about one end thereof to form a lead-in portion of a reduced diameter for ease of insertion of the tubes (28,30) into the respective apertures (24,26) of the end portions (20,22) without the creation of undesirable back-pressure within the exhaust system.

Description: The present invention relates to an end tube for an exhaust treatment apparatus, such as a catalytic converter or the like, as specified in the preamble of claim 1, for example as disclosed in US-A-4,209,495. Typical automotive vehicle exhaust systems incorporate a catalytic converter and at least one muffler or other noise attenuator. Many of these devices have similar external housings which have conical or truncated end portions, see Figure 5 of the accompanying drawings, that necessitate the insertion of end tubes 28a and 30a through apertures formed therein. The end tubes allow the devices to be easily assembled to the exhaust system of an automobile by axial sliding engagement therewith. In order to facilitate the insertion of the end tubes into the end portions of the converters or mufflers, the tubes 28a often have a taper 36a, see Figure 4 of the accompanying drawings, at the insertion end thereof. The taper 36a reduces the end diameter of the tube to provide a lead-in radius for guiding the tube into the end portion of the device 10a. Whilst the tapered end tubes, 28a and 30a greatly simplify assembly of the exhaust system, the end result is a marked increase in overall exhaust system back-pressure. The taper increases the severity of flow separation at the inlet to the shell and in the outlet tube itself, as shown in Figure 5 of the accompanying drawings, leading to a reduction in exhaust system efficiency. Such increases in system back-pressure are undesirable from the standpoint of system efficiency. An end tube according to the present invention, for use in an exhaust treatment apparatus of an exhaust system for an internal combustion engine, is characterised by the features specified in the characterising portion of claim 1. In accordance with a preferred embodiment of the present invention, a low-restriction exhaust treatment apparatus for use in the exhaust system of an internal combustion engine is disclosed. The apparatus comprises a hollow outer shell, into which exhaust treatment means are inserted, having end portions which sealingly close the ends of the shell. The end portions have apertures formed therein to facilitate the insertion of end tubes which are useful for attachment of the exhaust treatment apparatus to the exhaust system of the engine. To simplify insertion of the end tubes into the apertures formed in the end portions, each end tube has a plurality of serrations formed about the circumference of one end. The serrations extend axially inwards and are angled radially inwards with the tip portions of the serrations forming a lead-in portion having a reduced diameter. During assembly the lead-in portion acts in a manner similar to the tapered end portion typically used. However, in operation, the serrations provide greatly reduced flow restriction and an increase in flow uniformity. The result is an increase in exhaust system efficiency. The invention and how it may be performed are hereinafter particularly described with reference to the accompanying drawings, in which: Figure 1 is a side view, partially in section, of a low-restriction exhaust treatment apparatus embodying the present invention; Figure 2 is a perspective view of an exhaust treatment apparatus end tube embodying the present invention; Figure 3 is a schematic side view of a catalytic converter embodying the present invention, showing gas flow characteristics therein; Figure 4 is a perspective view of a prior-art exhaust apparatus end tube; and Figure 5 is a schematic side view of a prior-art catalytic converter showing gas flow characteristics therein. In Figures 1-3 there is shown an exhaust treatment apparatus, designated generally as 10, useful for treating exhaust gas generated by an internal combustion engine prior to the release of said exhaust gas to the atmosphere. The apparatus 10 has an axially-extending, cylindrical outer shell 12 having first and second ends 14 and 16, respectively. Additional outer shell configurations such as oval, square, rectangular, or other shapes are also applicable, and depend on the particular application of the apparatus 10. Outer shell 12 is constructed of stainless steel or other suitable material having a high degree of durability under varying operating conditions. Exhaust treatment means are disposed within the outer shell 12 and, depending on the particular application, act to modify various undesirable characteristics of the engine exhaust passing therethrough. For example, a monolithic catalyst substrate or a particulate trap (not shown) may be used to minimize undesirable exhaust emissions within the exhaust gas. Alternatively, a noise-attenuating apparatus such as a series of baffles (not shown) may be used for reduction or modification of undesirable exhaust system noise. Mounting of the exhaust treatment means within the outer shell 12 is by any suitable method known in the art. First and second end portions 20 and 22 are sealingly attached to the first and second ends 14 and 16 of outer shell 12, respectively. End portions 20 and 22 may be conical in shape, as shown in Figure 1, or may have any other suitable configuration dependent upon the particular application of the exhaust treatment apparatus 10, and are constructed of material similar to that of outer shell 12. Inlet and outlet apertures 24 and 26 are formed in first and second end portions 20 and 22 respectively to facilitate flow of exhaust gas into and out of the apparatus. In order to provide ease in assembly of the exhaust treatment apparatus 10 to the exhaust system of the engine, end tubes 28 and 30 are provided, which sealingly engage apertures 24 and 26, respectively. Both end tubes are similar in configuration and, therefore, only end tube 28 will be subsequently described. End tube 28 comprises an axially-extending hollow conduit 32, see Fig. 2, having a plurality of axially inwardly-extending serrations 34 disposed about the perimeter of one end thereof. The serrated portions 34 are angled radially inwards, see Figure 1, to form a lead-in portion having a reduced diameter at the end to simplify insertion of that end of the pipe 28 into the aperture 24 of the end portion 20. The serrated portions 34 act to encourage flow uniformity of the exhaust gas flowing through the end pipe 28 whilst minimizing increase in exhaust system back pressure produced by the lead-in portion. As illustrated in Figure 3, flow separation at both the entrance and exit of the exhaust treatment apparatus 10 is minimal with the use of end tubes 28 and 30, as compared to the prior-art exhaust treatment apparatus 10a, see Figure 5, in which conventional tapered end tubes 28a and 30a are used. The following test results exemplify the difference in operating characteristics of an exhaust treatment apparatus having end tubes embodying the present invention as compared with an exhaust treatment apparatus in which conventional tapered end tubes are used. Pressure was measured on a test stand on which the inlet tube is opened to atmospheric pressure and the outlet tube, having a straight pipe configuration, is attached to a suction source. Pressure was measured as the difference between atmospheric pressure and pressure at the outlet fitting in millimetres of water (inches of water). The flow through the apparatus was measured in cubic metres per minute (cubic feet per minute). Since the amount of exhaust system back-pressure caused by such an obstruction is a function of the percentage tube blockage, the present invention achieves its greatest effectiveness when applied to small diameter tubes. These types of tubes are typically those used in conjunction with small engines where efficiency is a key factor. The exhaust treatment apparatus of the present invention is an efficient solution to undesirable exhaust system back-pressure found with conventional tapered-end end tubes. It is simple in construction, easy to manufacture, and may be used with current exhaust systems. Furthermore, greater efficiency is achieved when applied to small diameter exhaust systems where efficiency and economy are important factors.

Claims: An end tube (28,30) comprising: an axially-extending, hollow conduit (32) having first and second open ends, said first end being formed into a lead-in portion having a reduced diameter relative to said hollow conduit (32) to facilitate the insertion of said end tube (28,30) into an aperture in an exhaust treatment apparatus (10) of an exhaust system for an internal combustion engine, characterised in that said lead-in portion is formed from a plurality of axially inwardly-extending serrations (34) disposed about the circumference of said first end, and said serrated portions (34) are angled radially inwards to form said reduced diameter lead-in portion. An end tube (28,30) according to claim 1, in an exhaust treatment apparatus (10) for use in the exhaust system of an internal combustion engine, said exhaust treatment apparatus (10) comprising: an outer shell (12) having first and second open ends (14,16) and a hollow central portion; exhaust treatment means disposed within said hollow central portion; and end portions (20,22) configured to sealingly connect with said first and second open ends (20,22), respectively, each of which end portions (20,22) has an aperture (24,26) formed therein to facilitate flow of exhaust gas into and out of said central portion, characterised in that the end tube (28,30) has a cross-section corresponding to a respective one of said apertures (24,26) and is sealingly engaged within said respective aperture. An end tube (28,30) in an exhaust treatment apparatus (10) according to claim 2, in which said exhaust treatment means comprises a monolithic catalyst substrate for the treatment of undesirable exhaust emissions within the exhaust gas. An end tube (28,30) in an exhaust treatment apparatus (10) according to claim 2, in which said exhaust treatment means comprises sound-attenuating means for reducing undesirable noise emissions. An end tube (28,30) in an exhaust treatment apparatus (10) according to claim 2, in which said exhaust treatment means comprises a particulate trap for minimization of undesirable exhaust emissions within the exhaust gas.

Inventors: CHRISTENSON, BARRY ODELL, MAYFIELD, ALBERT HUNTER
Applicants: GENERAL MOTORS CORPORATION
Application year: 1991
Main classification: F01N3
IPC codes: F01N3