Technical Field

[1] The present invention relates, in general, to exhaust pipe structures for turbo chargers and, more particularly, to an exhaust pipe structure for a turbo charger which includes a first exhaust pipe provided at a side of a turbine of the turbo charger and a second exhaust pipe coupled to the first exhaust pipe, and in which a reduced-diameter part is provided at a position adjacent to a junction between the first and second exhaust pipes, so that, even in a low-rpm range of an engine, compressed air is smoothly generated, thus preventing a response delay phenomenon from occurring, and increasing a fuel consumption ratio. Background Art

[2] Turbo chargers are widely used in diesel engines to increase output of power and improve fuel consumption ratios. Typically, in turbo chargers, a turbine is installed at a side of a manifold of a diesel engine, and a blower is coupled to the turbine through a rotating shaft. The turbine is operated using exhaust gas, so that the turbine rotates the blower, and an intercooler is operated in conjunction with the blower, thus supplying compressed air into the engine.

[3] FIG. 1 illustrates an exhaust pipe structure for such a conventional turbo charger.

As shown in FIG. 1, exhaust gas, which is generated during an exhaust stroke of an engine, is discharged to the outside through a first exhaust pipe 12, a second exhaust pipe 11, a catalytic converter 17 and a muffler 18. The first exhaust pipe 12 is integrated with a turbine housing 13. The second exhaust pipe 11 is coupled to an end of the first exhaust pipe 12 using flanges 16. FIG. 2 is an enlarged sectional view of a circled portion A of FIG. 1. As shown in FIG. 2, the first exhaust pipe 12 extends from the turbine housing 13, and the second exhaust pipe 11 is coupled to the first exhaust pipe 12 by a coupling method using the flanges 16. Furthermore, a turbine 14 and a waste gate valve 15 are provided in the turbine housing. Therefore, gas, which has been exhausted from the engine, is discharged to the outside through the turbine 14, the first exhaust pipe 12 and the second exhaust pipe 11. Not shown in the drawing, in the case that supercharged pressure is applied to the turbine, the waste gate valve 15 is opened such that exhaust gas is bypassed.

[4] However, in the low-rpm range of the engine, because the amount of gas exhausted from the engine is small, the exhaust gas cannot supply sufficient energy to the turbine, so that the rotating speed of the turbine is reduced. Thus, the rotating speed of the blower (not shown), which is coupled to the turbine, is also reduced. Thereby, a

sufficient amount of compressed air is not supplied to the engine, and, due to the low pressure of exhaust gas discharged through the first and second exhaust pipes, some exhaust gas remains in the pipes, but the exhaust gas is not completely discharged to the outside. As a result, a phenomenon in which residual exhaust gas may flow backwards, that is, towards a combustion chamber of the engine, is induced. This phenomenon causes incomplete combustion in the low-rpm range of the engine, thus reducing the fuel consumption ratio and decreasing output of the engine, thereby causing a response delay problem. These problems are induced because gas generated during an exhaust stroke of the engine is not smoothly discharged to the outside through the exhaust pipe, the catalytic converter and the muffler. In particular, as these problems are induced by some exhaust gas remaining in the exhaust pipe and flowing backwards, that is, towards the combustion chamber, without moving towards the catalytic converter and the muffler, if smooth discharge of gas around the exhaust pipe is ensured, the above-mentioned problems may be mitigated. Disclosure of Invention Technical Problem

[5] Accordingly, the present invention has been made keeping in mind the above problems occurring in the prior art, and an object of the present invention is to provide an exhaust pipe structure for a turbo charger in which a reduced-diameter part is provided at a position adjacent to a junction between a first exhaust pipe and a second exhaust pipe, which are coupled to each other, so that, even in a low-rpm range of an engine, exhaust gas is smoothly discharged, thus increasing rotating speed of a turbine so that smooth supply of compressed air into the engine is ensured, thereby increasing a fuel consumption ratio even in the low-rpm range, and preventing a response delay phenomenon from occurring, thus enhancing output of power of the engine. Technical Solution

[6] According to a first embodiment, the present invention provides an exhaust pipe structure for a turbo charger, including: a first exhaust pipe extending from an end of a turbine housing of the turbo charger; and a second exhaust pipe coupled to the first exhaust pipe using coupling means. The exhaust pipe structure further includes a reduced-diameter part radially depressed at a position adjacent a junction between the first and second exhaust pipes.

[7] In the exhaust pipe structure according to a second embodiment of the present invention, the reduced-diameter part of the first embodiment may be formed on the second exhaust pipe.

[8] In the exhaust pipe structure according to a third embodiment of the present invention, the reduced-diameter part of the second embodiment may be formed on the

first exhaust pipe. [9] In the exhaust pipe structure according to a fourth embodiment of the present invention, the cross-sectional area of the pipe at the reduced-diameter part of the first through third embodiments is smaller than the cross-sectional areas of each of portion of the pipe preceding and following the reduced-diameter part.

Advantageous Effects

[10] In the present invention, a reduced-diameter part is provided on an exhaust pipe at a position adjacent to a turbine, so that pressure gradient, speed gradient and enthalpy gradient are induced at portions of the pipe adjacent to the reduced-diameter part. Therefore, even in a low-rpm range of an engine, exhaust gas can be smoothly discharged, thus preventing some exhaust gas from remaining in the exhaust pipe or flowing backwards. Furthermore, rotating speed of the turbine is increased, so that a sufficient amount of compressed air can be supplied into the combustion chamber of an engine, thus preventing incomplete combustion. As a result, there is an advantage in that performance (related to fuel consumption ratio and responsiveness) of the engine in a low-rpm range is markedly enhanced. Brief Description of the Drawings

[11] FIG. 1 is a schematic view showing a conventional exhaust pipe structure for turbo charger systems;

[12] FIG. 2 is an enlarged sectional view of a circled portion A of FIG. 1;

[13] FIG. 3 is a schematic view showing an exhaust pipe structure for turbo chargers, according to a first embodiment of the present invention; and

[14] FIG. 4 is a schematic view showing an exhaust pipe structure for turbo chargers, according to a second embodiment of the present invention. Best Mode for Carrying Out the Invention

[15] Hereinafter, the present invention will be described in detail with reference to the attached drawings.

[16] FIG. 3 is a schematic view showing an exhaust pipe structure for turbo chargers, according to a first embodiment of the present invention. As shown in FIG. 3, the exhaust pipe structure includes a turbine 25, which is rotated by exhaust gas discharged from an engine, a waste gate valve 26, which bypasses exhaust gas when supercharged pressure is applied to the turbine, a first exhaust pipe 23, which extends from an end of a turbine housing 24, and a second exhaust pipe 21, which is coupled to an end of the first exhaust pipe 23 using a coupling means 28. It is preferable that the coupling means 28 be a flange coupling method using nuts and bolts.

[17] Here, the turbine 25, the waste gate valve 26, a blower (not shown) and an in- tercooler (not shown) are well-known components of the conventional turbo charger

and have been described above, therefore further explanation is deemed unnecessary.

[18] The first exhaust pipe 23 is a pipe-shaped member which extends from the end of the turbine housing 24. The second exhaust pipe 22 is a pipe-shaped member which is coupled at an end thereof to the end of the first exhaust pipe 23 using the coupling means and is coupled at the other end thereof to a catalytic converter (not shown). Here, the coupling means 28 has preferably a flange-coupling structure, in which flanges are provided on the respective contact ends of first and second exhaust pipes so that the flanges are coupled to each other using nuts and bolts. The second exhaust pipe 22 has a reduced-diameter part 22 at a position adjacent to the junction 28 between the pipes. The reduced-diameter part 22 is formed by radially depressing a part of the circumferential outer surface thereof to a predetermined depth. The depth to which the reduced-diameter part is depressed should be appropriately selected by those skilled in the art in consideration of the diameters of the first and second exhaust pipes and a distance by which the reduced-diameter part is spaced apart from the junction between the pipes.

[19] Meanwhile, as can be appreciated from the above explanation, engine degradation, such as a reduction in fuel consumption ratio and a response delay phenomenon, is affected by the amount of combustion gas to be exhausted and is induced by exhaust gas that remains in the exhaust pipe. Therefore, formation of the reduced-diameter part 22 at a position adjacent to the junction 28 between the pipes is based on the point that, if exhaust gas is smoothly exhausted at the end of the pipe adjacent to the engine, influence of the exhaust gas is minimized. As such, in the case that the reduced- diameter part is formed, a cross-sectional area of the pipe at the reduced-diameter part 22 is reduced compared to that of other portions of the pipe. Then, a smooth flow of exhaust gas is realized based on the following hydrodynamic and thermodynamic theories.

[20] (1) volume flow

[21] When fluid passes through a predetermined control volume, the flux is constant at an every position. This originates from the law of mass conservation.

[22]

Q= V* A

[23] Q: volume flow, A: cross-sectional area, V: current speed

[24] (2) Bernoulli's theorem

[25] Bernoulli's theorem is applied to an incompressible, steady and nonviscous flow, but, as with other flow states, the theorem may be useful as a general standard for analysis of flow. [26]

[27] P ,P : pressure, V ,V : speed, Z , Z : height,

T

: viscosity coefficient [28] (3) enthalpy

[29]

h = u + - ^P

T

[30] h: enthalpy, u: internal energy, p: pressure,

T

: viscosity coefficient

[31]

[32] When the position of the reduced-diameter part 22 of the second exhaust pipe is designated by the reference character 2s, and a predetermined position of the first exhaust pipe which precedes the reduced-diameter part is designated by the reference character Is, current speed of the fluid at the position Is is Vl, pressure is P , height is Z and cross-sectional area is A , and current speed of the fluid at the position 2s is V , pressure is P , height is Z and cross-sectional area is A . Here, if the first exhaust pipe and the second exhaust pipe are horizontal, Z and Z are equal to each other. Furthermore, because the cross-sectional area A of the reduced-diameter part is smaller than the cross-sectional area A , the current speed V becomes higher than the current speed V according to the equation of the volume flow, the pressure P becomes less than the pressure P according to Bernoulli's theorem, and the enthalpy h becomes less than the enthalpy hi. Therefore, pressure gradient, speed gradient and enthalpy gradient are caused between the positions Is and 2s. As a result, in a low-rpm range of the engine, combustion gas can be rapidly exhausted through the first and second exhaust pipes. Meanwhile, because the cross-sectional area of the portion following the reduced-diameter part is equal to the cross-sectional area A , even if an exhaust amount of combustion gas is increased while the engine, which has been in the low-rpm range, enters a high-rpm range, combustion gas is smoothly exhausted, thus preventing the combustion gas from remaining in the second exhaust pipe.

[33] FIG. 4 is a schematic view showing an exhaust pipe structure for turbo chargers according to a second embodiment of the present invention. The general structures of a turbine housing 214, a turbine 215, a waste gate valve 216, a first exhaust pipe 213 and a second exhaust pipe 211 are the same as those of the first embodiment. Unlike the first embodiment, in the second embodiment a reduced-diameter part 212 is formed on

the first exhaust pipe, but the detailed structure of the reduced-diameter part is the same as that of the first embodiment.

[34] As shown in FIGS. 1 through 4, the first exhaust pipe is integrally provided on an end of the turbine housing, and the second exhaust pipe is coupled to the first exhaust pipe through a coupling means 28. Therefore, forming the reduced-diameter part 212 on the first exhaust pipe 213, which is an exhaust pipeline nearest the engine, (see, FIG. 4) is preferable to forming it on the second exhaust pipe 21 (see, FIG. 3). However, because the first exhaust pipe is integrated with the turbine side, there is a difficulty in forming the reduced-diameter part on the first exhaust pipe. Hence, the reduced-diameter part 22 is typically formed on the second exhaust pipe, which can be easily replaced with a new one or allowed to be repaired by decoupling the flanges at the junction 28 between the pipes. In any case, the cross-sectional area of the pipe at the reduced-diameter part must be smaller than that of the portions of the pipe preceding and following the reduced-diameter part. Furthermore, it is preferable that the reduced-diameter part be formed on the exhaust pipe at a position adjacent to the engine. The reason for this is that a phenomenon in which combustion gas remains in or flows backwards in the exhaust pipe and which causes engine degradation occurs at a position adjacent to the engine.

[35] Although the preferred embodiments of the present invention have been disclosed for illustrative purposes, it must be appreciated that various modifications, additions and substitutions realizing the technical idea of the invention fall within the bounds of the present invention.