Patent Publication Number: US-6907726-B2

Title: Exhaust system for a V-type engine

Description:
FIELD OF THE INVENTION 
   The present invention relates to an exhaust system for a V-type engine, and more particularly, to an exhaust system that is capable of improving exhaust gas flow uniformity characteristics by improving the structure of the coupling portion of front exhaust pipes that are disposed upstream of a main catalytic converter of the vehicle, and of maintaining a catalytic activating temperature of exhaust gas by additionally including a heat protector. 
   BACKGROUND OF THE INVENTION 
   Generally, an exhaust system of a vehicle is either a close-coupled catalytic converter (CCC) type or an under-floor catalytic converter (UCC) type according to disposition of a catalytic converter, considering engine compartment layout and the degree of exhaust gas reduction demand. In the CCC type, the catalytic converter is disposed close to each runner of an exhaust manifold, and in the UCC type, the catalytic converter is disposed relatively far from an exhaust manifold so that a demand for making exhaust gas flow uniform is relatively small. 
   There have been various directions in research and development for improving exhaust gas characteristics in such exhaust systems. Factors for improving exhaust gas characteristics can be summarized as follows: an improvement of flow uniformity upstream of a catalytic converter; a selection of a mounting position of an oxygen sensor; an improvement of a catalytic activating temperature during cold start; and a suppression of an increase of back pressure. 
   In the UCC exhaust system that is usually adopted for a V-type engine, first and second exhaust pipes are respectively coupled to exhaust manifolds through front catalytic converters. The first and second front exhaust pipes are joined together at a coupling portion. 
   However, in such a conventional exhaust system for a V-type engine, the first and second front exhaust pipes are typically perpendicularly coupled at the coupling portion, so flow of exhaust gas inside the coupling portion becomes irregularly turbulent. Furthermore, the sectional area of the exhaust line in the coupling portion substantially decreases so that a large pressure increase occurs in that portion, and this may cause an increase of back pressure, so that full load performance becomes deteriorated. Because the distance between the exhaust manifolds and the main catalytic converter  115  is large, exhaust gas temperature in the main catalytic converter may become lower than a catalyst activating temperature. 
   The information disclosed in this Background of the Invention section is only for enhancement of understanding of the background of the invention, and should not be taken as an acknowledgement or any form of suggestion that this information forms the prior art that is already known to a person skilled in the art. 
   SUMMARY OF THE INVENTION 
   Embodiments of the present invention provide an exhaust system for a V-type engine in which a coupling portion wherein first and second front exhaust pipes are joined together is improved, and a heat protector is used, to improve the flow uniformity characteristics of exhaust gas and full load performance and to maintain the exhaust gas temperature higher than a catalyst activating temperature. 
   In a preferred embodiment of the present invention, the exhaust system for a V-type engine comprises: first and second exhaust manifolds, first and second front exhaust pipes, a center exhaust pipe, and a rear exhaust pipe. The first and second front exhaust pipes are respectively connected to the first and second exhaust manifolds upstream thereof through first and second front catalytic converters, and the first and second front exhaust pipes are joined together at end portions thereof to form a coupling portion. The center exhaust pipe is connected downstream of the coupling portion, and a main catalytic converter is disposed in the center exhaust pipe. The rear exhaust pipe is connected downstream of the center exhaust pipe. The coupling portion is formed such that an angle between a center line of an end portion of the first front exhaust pipe and a center line of an end portion of the second front exhaust pipe is less than 20 degrees. 
   It is also preferable that the coupling portion is formed such that both an angle between a center line of the end portion of the first front exhaust pipe and a center line of the center exhaust pipe and an angle between a center line of the end portion of the second front exhaust pipe and a center line of the center exhaust pipe are less than 60 degrees. 
   Preferably, a slanted portion is formed at one end portion of the first and second front exhaust pipes, and a curved portion is formed at the other of the end portions, wherein the slanted portion and the curved portion are joined together to form the coupling portion. 
   It is further preferable that the coupling portion is positioned such that a distance between a vertical center line of the coupling portion and a vertical center line of the one of the first and second exhaust manifolds that is positioned farther from the main catalytic converter is more than 800 mm. 
   It is preferable that the exhaust system further comprises a main heat protector and an auxiliary heat protector. The main heat protector is disposed in the center exhaust pipe in the vicinity of the coupling portion, and the auxiliary heat protector is disposed in one of the first and second front exhaust pipes that is longer than the other. 
   In another preferred embodiment of the present invention, the exhaust system for a V-type engine comprises: first and second exhaust manifolds, first and second front exhaust pipes, a center exhaust pipe, and a rear exhaust pipe. The first and second front exhaust pipes are respectively connected to the first and second exhaust manifolds upstream thereof through first and second front catalytic converters, and the first and second front exhaust pipes are joined together at end portions thereof to form a coupling portion. The center exhaust pipe is connected downstream of the coupling portion, and a main catalytic converter is disposed in the center exhaust pipe. The rear exhaust pipe is connected downstream of the center exhaust pipe. The coupling portion is formed such that both an angle between a center line of the end portion of the first front exhaust pipe and a center line of the center exhaust pipe and an angle between a center line of the end portion of the second front exhaust pipe and a center line of the center exhaust pipe are less than 60 degrees. 

   
     BRIEF DESCRIPTION OF THE DRAWINGS 
     The accompanying drawings, which are incorporated in and constitute a part of the specification, illustrate an embodiment of the invention, and, together with the description, serve to explain the principles of the invention, where: 
       FIG. 1  is a perspective view of an exhaust system for a V-type engine according to a preferred embodiment of the present invention; 
       FIG. 2  is an enlarged view of a coupling portion of both front exhaust pipes of an exhaust system of  FIG. 1 ; 
       FIG. 3  illustrates back pressure characteristics of the exhaust system according to the preferred embodiment of the present invention; 
       FIG. 4  illustrates performance of an engine adopting the exhaust system according to the preferred embodiment of the present invention; and 
   

   DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
   Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings. 
   As shown in  FIG. 1 , an exhaust system for a V-type engine according to the preferred embodiment of the present invention includes left and right front exhaust pipes  9  and  11  that are respectively coupled to left and right exhaust manifolds  1  and  3 , which are respectively coupled to cylinder heads of a V-type engine, through front catalytic converters  5  and  7 . 
   The left and right front exhaust pipes  9  and  11  are joined together at a coupling portion  13 , and the coupling portion  13  is connected upstream of a center exhaust pipe  17  including a main catalytic converter  15 , a front muffler  25 , and a center muffler  27 . 
   Left and right rear exhaust pipes  29  and  31  are respectively coupled downstream of the center exhaust pipe  17 , and left and right main mufflers  33  and  35  are respectively disposed in the left and right rear exhaust pipes  29  and  31 . 
   As shown in  FIGS. 1 and 2 , a distance L between a vertical center line of the coupling portion  13  and a vertical center line of the left exhaust manifold  1  that is positioned farther from the center exhaust pipe  17  than the right exhaust manifold  3  is more than 800 mm. An angle a between a center line of an end portion of the left front exhaust pipe  9  and a center line of an end portion of the right front exhaust pipe  11  is less than 20 degrees. 
   Further, both an angle b between a center line of an end portion of the left front exhaust pipe  9  and a center line of the center exhaust pipe  17  and an angle c between a center line of an end portion of the right front exhaust pipe  11  and a center line of the center line of the center exhaust pipe  17  are less than 60 degrees. For this connection, the right front exhaust pipe  11  has a curved portion P 1 . 
   That is, in the exhaust system according to this embodiment, the left front exhaust pipe  9  is provided with a slanted portion P 2  at an end portion thereof. An angle between a center line of the slanted portion P 2  and the center line of the center exhaust pipe  17  is approximately 40 degrees (angle b). The right front exhaust pipe  11  is coupled to a front end of the center exhaust pipe  17  through the curved portion P 1 , and an angle between a center line of an end portion of the curved portion P 1  and the center line of the center exhaust pipe  17  is approximately 55 degrees (angle c). 
   A main heat protector  19  is disposed in the center exhaust pipe  17  in the vicinity of the coupling portion  13  of the left and right front exhaust pipes  9  and  11 , and an auxiliary heat protector  21  is disposed in the right front exhaust pipe  11  that is exposed to atmosphere more than the left front exhaust pipe  11  because of its longer length. 
   Each of the main heat protector  19  and the auxiliary heat protector  21  is a device to reduce transmission of heat of exhaust gas passing therethrough, and for example, it can be made of heatproof material. 
   Therefore, according to the exhaust system as stated above, because the coupling portion  13  of the left and right front exhaust pipes  9  and  11 , which is positioned in front of the main catalytic converter  15 , is positioned such that a distance L between a vertical center line of the coupling portion  13  and a vertical center line of the left exhaust manifold  1  is more than 800 mm, the angle between the center line of the slanted portion P 2  of the left front exhaust pipe  9  and the center line of the end portion of the curved portion P 1  of the right front exhaust pipe  11  is less than 20 degrees, and simultaneously the angle between the center line of the slanted portion P 2  and the center line of the center exhaust pipe  17  and the angle between the center line of the end portion of the curved portion P 1  and the center line of the center exhaust pipe  17  are respectively less than 60 degrees, uniformity of the flow of exhaust gas can be improved by minimizing interference between the flows of the exhaust gas, and full load performance can be improved by reducing the back pressure. 
   Referring to  FIG. 3 , the solid line indicates back pressure upstream of the left or right front exhaust pipe  9  and  11  (downstream of one of the exhaust manifolds  1  and  3 ) corresponding to a change of engine RPM, and the dotted line indicates back pressure in the coupling portion  13  of the left and right front exhaust pipes  9  and  11  corresponding to a change of engine RPM. A back pressure difference between these two positions can be a measure of engine performance. That is, the lesser the difference, the higher the engine performance. As shown in  FIG. 3 , the difference in the back pressure is relatively small in the exhaust system according to the embodiment of the present invention. Consequently, as shown in  FIG. 4 , engine torque of an engine using the exhaust system according to the embodiment of the present invention is greater by a maximum of 4% than an engine using the exhaust system according to the prior art, in a range of 2500-3000 RPM, and in particular, engine performance is improved in a low RPM range. 
   Furthermore, the main heat protector  19  disposed in the center exhaust pipe  17  and the auxiliary heat protector  21  disposed in the right front exhaust pipe  11  prevent exhaust gas from being excessively cooled by heat transmission to atmosphere, so that exhaust gas temperature in the main catalytic converter  15  can be maintained higher than a catalyst activating temperature, and consequently, purification efficiency of the catalytic converter can be increased. 
   Although preferred embodiments of the present invention have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic inventive concepts herein taught which may appear to those skilled in the present art will still fall within the spirit and scope of the present invention, as defined in the appended claims.