Acoustics – Sound-modifying means – Muffler – fluid conducting type
Reexamination Certificate
2002-03-18
2004-03-09
Nappi, Robert (Department: 2837)
Acoustics
Sound-modifying means
Muffler, fluid conducting type
C181S212000, C181S228000, C181S238000, C060S272000, C060S323000
Reexamination Certificate
active
06702062
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust system for an internal combustion engine that is equipped in an automotive vehicle, and, more particular, to an engine exhaust system that has a plurality of discrete exhaust pipes branching off from an exhaust pipe and connected to a cylinder head and an exhaust pipe.
2. Description of Related Art
Typically, a catalytic converter, that is disposed in an engine exhaust line, is desirably activated in a short period of time after a start of an engine in order to improve a catalytic conversion efficiency. In recent years, for quick activation of the catalytic converter, there has been proposed a heat insulated exhaust manifold operative to hold a temperature of an exhaust gas discharged from the engine as high as possible and then to direct the exhaust gas to the catalytic converter. Such heat insulated exhaust manifolds are known from, for example, Japanese Unexamined Patent Publication No. 11-303630 and Japanese Unexamined Utility Model Publication No. 63-54816.
The prior art heat insulated exhaust manifold disclosed in Japanese Unexamined Patent Publication No. 11-303630 comprises four double-walled discrete exhaust pipes connected at upstream ends to a cylinder head and joined at downstream ends to a double-walled chamber for collecting exhaust gases passing through the discrete exhaust pipes. This double-walled structure is somewhat troublesome to manufacture the heat insulated exhaust manifold and exerts various restraints on the configuration of the heat insulated exhaust manifold. Specifically, a bent portion of the heat insulated exhaust manifold must be large in bending radius and long in length. In other words, due to layout requirements of the engine in an engine compartment, a straight portion of the double-walled heat insulated exhaust manifold must be short in length. As a result, the double-walled heat insulated exhaust manifold provides an exhaust gas with a high resistance, so as to have an adverse influence on the output property of the engine.
The prior art heat insulated exhaust manifold disclosed in Japanese Unexamined Utility Model No. 63-54816 comprises single wall discrete exhaust pipes and a double-walled chamber for collecting exhaust gases passing through the discrete exhaust pipes. This heat insulated exhaust manifold having the double-walled chamber is focused only on lowering noises of an exhaust gas flow passing therethrough and preventing pulsations of the exhaust gas from propagating into exhaust pipes before and after the double-walled chamber.
While the heat insulated exhaust manifold is advantageous to protecting parts around the exhaust manifold from heat damage and activating quickly a catalytic converter in an exhaust line, the heat insulated exhaust manifold is apt to be heated by a hot exhaust gas passing therethrough and therefore to be filled with heat. Accordingly, the heat insulated exhaust manifold is necessary to have a heat releasing mechanism. If releasing heat through a fitting flange of the heat insulated exhaust manifold through which the heat insulated exhaust manifold is fitted to the cylinder head, a rubber gasket (a sealing member) between the cylinder head and the cylinder cover and supplementary devices around the engine are apt to encounter heat deterioration.
There has been proposed in Japanese Unexamined Utility Model 4-91224 an exhaust manifold having a generally U-shaped fitting bracket. Specifically, the exhaust manifold for an in-line four cylinder engine comprises four discrete exhaust pipes made of steel pipes that are connected to a cylinder block through a fitting flange and a collective chambered pipe made of a casting pipe, that are divided by a casting partition into two collective chambers and connected to downstream ends of the discrete exhaust pipes so that exhaust gas streams passing through the discrete exhaust pipes merge together in the collective chambered pipe. The exhaust manifold is fitted to the engine by securing the U-shaped fitting bracket bolted to the collective chambered pipe to a fitting boss of a cylinder head of the engine. As the partition is also made of a casting as well as the collective chambered pipe and is thick, it does not make noises resulting from engine vibrations.
When using a steel pipe in place of the casting pipe for the collective chambered pipe in order to reduce the weight of the collective chambered pipe, the partition makes vibrations resulting from engine vibrations, so as to make noises. In addition, as the U-shaped fitting bracket is fitted to the collective chambered pipe by fastening bolts into bolt holes formed in bosses of the collective chambered pipe and also to the boss of the cylinder block, it is hard to absorb thermal expansion of the exhaust manifold due to a hot exhaust gas.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide an exhaust system having a heat insulated exhaust manifold that can provide an engine with an improved output characteristic and gain improved heat insulation effectiveness.
It is another object of the present invention to provide an exhaust system having a heat insulated exhaust manifold is adapted to radiate heat from a space formed between a fitting flange of an exhaust manifold and a cylinder head and has a heat guide member operative to conduct heat toward far from the engine so as thereby to prevent a sealing member disposed between a cylinder head and a cylinder cover and supplementary devices around the engine from encountering heat deterioration.
It is still another object of the present invention to provide an exhaust system having an exhaust manifold that is improved in structural rigidity by securing a partition of the collective chambered pipe to a welded joint structure of high rigidity through which a plurality of discrete exhaust pipes are joined to a collective chambered pipe.
It is still a further object of the present invention to provide an exhaust system having an exhaust manifold that is further improved in structural rigidity by supporting the exhaust manifold to the engine through a supporting bracket that is attached at or in close proximity to a welded joint structure between discrete exhaust pipes and a collective chambered pipe.
The exhaust manifold according to an embodiment of the present invention comprises a plurality of single-shell discrete exhaust pipes connected to exhaust ports formed in the cylinder head, respectively, a collective chambered pipe joined to the single-shell discrete exhaust pipes that is made up of an internal pipe shell into which exhaust gas streams passing through the single-shell discrete exhaust pipes are introduced and merge together and an external pipe shell surrounding the internal pipe shell, and spherical joint means connecting the collective chambered pipe to the exhaust pipe disposed downstream the collective chambered pipe and supported to the vehicle body. Each of the single-shell discrete exhaust pipes has a bent portion and a straight portion continuously extending from the bent portion to the collective chambered pipe. The bent portions of the single-shell discrete exhaust pipes are oriented toward a center of a straight row of cylinders so as to lay the straight portions of the single-shell discrete exhaust pipes nearly parallel to one another, and the single-shell discrete exhaust pipes and the collective exhaust pipe are joined to each other at least partly at a height of a plane including the interface between the cylinder block and the cylinder head.
The exhaust manifold thus structured can be provided with a long straight path of exhaust gas by the straight portions of the single-shell discrete exhaust pipes and the collective chambered pipe that is straight, so as thereby to reduce the resistance of exhaust gas. This results in helping the engine to raise output. In addition, the collective chambered pipe can be provided with high heat insulation effectiveness by having a length as long as possible. This results in quick activatio
Kusabiraki Yoshiharu
Nishida Ryotaro
Wakasa Akinori
Mazda Motor Corporation
McCloud Renata
Nappi Robert
Nixon & Peabody LLP
Studebaker Donald R.
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