Pipe for exhaust gas systems for internal combustion engines of motor vehicles and motorcycles

Abstract

 A pipe for gas-exhaust systems for internal combustion engines of motor vehicles and motor cycles, comprising at least one first tubular portion (8) of rectilinear longitudinal axis (X) and at least one second tubular portion (9) of curvilinear longitudinal axis (Y) integral with the first tubular portion (8), to adapt itself to the overall dimensions of the motor vehicles or motor cycles on which the exhaust system (1) is mounted. The first tubular portion (8) of rectilinear longitudinal axis (X) has a wall thickness (s1) smaller than the wall thickness (s2) of the second tubular portion (9) of curvilinear longitudinal axis (Y).

Description

[0001] The present invention relates to a pipe for gas-exhaust systems for internal combustion engines of motor vehicles and motor cycles.

[0002] It is known that reciprocating internal combustion engines equipping cars, motor cycles, lorries, etc. are provided with exhaust systems for emission of the gases resulting from combustion. A gas-exhaust system usually consists of a plurality of pipes that, starting from the engine, extend towards the rear portion of the motor vehicle or motor cycle.

[0003] The system further comprises at least one silencer, also known as muffler, which is located along the pipe extension so as to intercept the burnt gases. The muffler has the function of reducing the noise generated by gas ejection into the surrounding atmosphere and often devices for reduction of the polluting emissions are contained therein.

[0004] The pipes run under the respective vehicle and are fastened to the vehicle body at several points. In order to keep themselves away from the other devices belonging to the vehicle body such as the axle placed at the rear wheels, pipes must be suitably shaped.

[0005] Shaped pipes consisting of rectilinear sections and curved sections are known which are formed of a single tubular body made of steel, obtained by drawing for example, which is subsequently bent following known bending processes, herein not described.

[0006] To enable the tubular body to be bent in a precise manner, without being submitted to damages and in such a manner that a quality product is obtained, the wall thickness of said tubular body must reach at least one preestablished minimum value which is a function of the bending radius. In particular, the smaller is the bending radius given to a pipe, the larger the thickness of the pipe wall must be.

[0007] Pipes of the known art are made of austenitic stainless steel that, being malleable, is bent with greater ease and with qualitatively better results than ferritic steel.

[0008] The known-art pipes briefly described above, are therefore formed of a great amount of steel, which results in high weight of the whole system and high production costs, due to the necessary amount of raw material.

[0009] In addition, due to the high value of the thermal expansion coefficient of the austenitic steel, the known-art pipes are subjected to important elongations due to the temperatures of the exhaust gases.

[0010] Under this situation, the technical task underlying the present invention is to devise a pipe for gas-exhaust systems for internal combustion engines of motor vehicles and motor cycles capable of obviating the mentioned drawbacks.

[0011] In particular, it is an aim of the present invention to devise a pipe for gas-exhaust systems enabling the overall weight of the system on which the pipe is mounted, to be reduced.

[0012] It is a further aim of the present invention to provide a pipe for gas-exhaust systems to be manufactured at lower costs than the pipes of the known art presently in use.

[0013] Finally, it is an aim of the present invention to make a pipe for gas-exhaust systems enabling the overall elongations of the systems due to the high temperatures of the exhaust gases, to be reduced.

[0014] The technical task mentioned and the aims specified are achieved by a pipe for gas-exhaust systems for internal combustion engines of motor vehicles and motor cycles having the features set out in one or more of the appended claims.

[0015] A preferred, but not exclusive embodiment of a pipe for gas-exhaust systems for internal combustion engines of motor vehicles and motor cycles in accordance with the invention is now described by way of non-limiting example with the aid of the accompanying drawings, in which:

• Fig. 1 is a plan view of a gas-exhaust system comprising a pipe in accordance with the present invention;
• Fig. 2 shows an enlarged portion partly in section of the pipe in Fig. 1;
• Fig. 3 shows a detail to an enlarged view of the pipe in Fig. 2.

[0016] With reference to the drawings, the gas-exhaust system for internal combustion engines of motor vehicles and motor cycles in accordance with the present invention is identified by reference numeral 1.

[0017] System 1 comprises a plurality of pipes 2, preferably of stainless steel, connected to each other so as to form a path of travel 3 for exit of the burnt gases from an internal combustion engine 4 to the surrounding atmosphere.

[0018] Usually, the path runs from the front portion of the motor vehicle where the engine 4 is placed, to the rear axle.

[0019] System 1 further has at least one silencer or muffler 5 disposed between two pipes, i.e. an inlet pipe and an outlet or tail pipe, of the plurality of pipes 2, to intercept the gases along path 3 and damp the pressure waves responsible for the noise made by the vehicle's exhaust.

[0020] In the embodiment shown, the plurality of pipes 2 of the exhaust system 1 has four manifolds 2a directly beginning from the head of engine 4 and gathering into two front pipes 2b only. In turn, the two front pipes 2b lead to a single front pipe 2c connected to an auxiliary silencer 5a. The auxiliary silencer 5a is in fluid communication, by an intermediate shaped pipe 6, with a main silencer 5b from which a rectilinear end pipe 7 emerges.

[0021] Advantageously, at least one of the pipes of system 1 comprises at least one first tubular portion 8 of a rectilinear longitudinal axis X and at least one second tubular portion 9 of a curvilinear longitudinal axis Y, integrally abutting, preferably by welding, onto the first tubular portion 8.

[0022] The bending degree of the second portions 9, the number of the first straight portions 8 and said curved second portions 9, as well as the respective lengths, are calculated so as to adapt pipe 2 to the overall dimensions of the motor vehicle or motor cycle on which the exhaust system 1 is to be mounted.

[0023] In the embodiment shown in Fig. 1, the intermediate shaped pipe 6 has an alternate succession of first tubular portions 8 of a rectilinear longitudinal axis X and second portions 9 of a curvilinear longitudinal axis Y, connected to each other by respective welding beads 10 (more clearly shown in Fig. 3).

[0024] As clearly viewed from Figs. 2 and 3, the first tubular portions 8, of rectilinear longitudinal axis X, have a first wall thickness s1 and the second tubular portions 9, of curvilinear longitudinal axis Y, have a second wall thickness s2. Advantageously, the first wall thickness s1 is smaller than the second wall thickness s2.

[0025] Preferably, the wall thickness s1 of the first tubular portions 8 is at least as large as 0.7 mm, whereas the wall thickness s2 of the second tubular portions 9 is at least as large as 1.2 mm.

[0026] More specifically, the minimum thicknesses of the second tubular portions 9 are linked to requirements connected with the bending process to which the tubular portions are submitted: the smaller the bending radius of the pipe is, the larger the wall thickness of same must be.

[0027] According to a preferred embodiment shown in the accompanying figures, the first tubular portions 8 have an inner diameter d1 which is the same as the inner diameter d2 of the second tubular portions 9 and a smaller outer diameter. In addition, the first portions 8 and second portions 9 are coaxially in abutment against each other so as to obtain, along each pipe 2, a constant inner section for passage of the exhaust gases.

[0028] According to an alternative embodiment not shown, the second portions 9 being part of a single pipe 2 have wall thicknesses s2 that are in inverse proportion to their bending radius.

[0029] In detail, second portions 9 with a smaller bending radius have a wall thickness s2 larger than the wall thickness s2 of second portions 9 with a greater bending radius.

[0030] Advantageously, in addition, each of the first tubular portions 8 of rectilinear longitudinal axis is made of ferritic stainless steel and each of the second tubular portions 9 of curvilinear longitudinal axis Y is made of austenitic stainless steel.

[0031] This choice is dictated by the fact that ferritic steel advantageously has a thermal-expansion coefficient lower than austenitic steel, so that elongation of the straight tubular portions 8, due to the high temperatures of the exhausted gases (in the order of 600-700°C), and of the whole system 1 keeps limited. Austenitic steel is of easy workability and consequently is more adapted for being submitted to the bending process.

[0032] After describing the invention from a structural point of view, a process for manufacturing pipes for gas-exhaust systems for internal combustion engines of motor vehicles and motor cycles will be exposed hereinafter.

[0033] First of all a first and a second tubular body of rectilinear longitudinal axis with different wall thicknesses and the same inner diameter are made. Then, the first and second tubular bodies are cut to size, to form the plurality of first tubular portions 8 having the first wall thickness s1 of smaller value, and of second tubular portions 9 having the second wall thickness s2 of greater value than the first one s1.

[0034] Subsequently, the second tubular portions 9 are submitted to a bending process, known by itself and not described in detail, based on the shape to be given to system 1.

[0035] Finally, each of the first tubular portions 8 is coaxially abutted on a second curved tubular portion 9 and joined thereto by welding, so as to obtain a single pipe 6 having straight and curved sections and differentiated thicknesses.

[0036] The invention achieves important advantages.

[0037] It should be noted first of all that the pipe for gas-exhaust systems for internal combustion engines according to the present invention enables the amount of steel used in the exhaust-system construction to be reduced, which will bring about a reduction in the production costs of same up to values in the order of 30%.

[0038] In addition, the pipe for gas-exhaust systems in accordance with the present invention allows an important weight reduction as compared with the known-art pipes, due to the possibility of differentiating the tubular-portion thicknesses based on the features to be owned by the individual pipe portions.

[0039] Finally, use of ferritic steel for the straight portions, which steel is less malleable but also subjected to less important thermal expansions, enables reduction in the pipe elongation due to the high temperatures of the exhaust gases.

Claims

1. A pipe for gas-exhaust systems for internal combustion engines of motor vehicles and motor cycles, comprising:

- at least one first tubular portion (8) of rectilinear longitudinal axis (X) having a first wall thickness (s1);

- at least one second tubular portion (9) of curvilinear longitudinal axis (Y) integral with the first portion (8) and having a second wall thickness (s2);

characterized in that the first wall thickness (s1) of said at least one first tubular portion (8) of rectilinear longitudinal axis (X) is smaller than the second wall thickness (s2) of said at least one second tubular portion (9) of curvilinear longitudinal axis (Y).

2. A pipe for gas-exhaust systems as claimed in claim 1, characterized in that said at least one first tubular portion (8) is coaxially in abutment onto said at least one second tubular portion (9).

3. A pipe for gas-exhaust systems as claimed in claim 1 or 2, characterized in that it further comprises at least one welding bead (10) operatively active between said at least one first tubular portion (8) and said at least one second tubular portion (9).

4. A pipe for gas-exhaust systems as claimed in anyone of the preceding claims, characterized in that said at least one first tubular portion (8) has the same inner diameter (d1) as the inner diameter (d2) of said at least one second tubular portion (9).

5. A pipe for gas-exhaust systems as claimed in anyone of the preceding claims, characterized in that said at least one first tubular portion (8) has a wall thickness (s1) at least as large as 0.7 mm.

6. A pipe for gas-exhaust systems as claimed in anyone of the preceding claims, characterized in that said at least one second tubular portion (9) has a wall thickness (s2) at least as large as 1.2 mm.

7. A pipe for gas-exhaust systems as claimed in anyone of the preceding claims, characterized in that said at least one first tubular portion (8) is made of ferritic stainless steel.

8. A pipe for gas-exhaust systems as claimed in anyone of the preceding claims, characterized in that said at least one second tubular portion (9) is made of austenitic stainless steel.

9. A pipe for gas-exhaust systems as claimed in anyone of the preceding claims, characterized in that it has an alternate succession of first portions (8) of rectilinear longitudinal axis (X) and second portions (9) of curvilinear longitudinal axis (Y).

10. A gas-exhaust system for internal combustion engines of motor vehicles and motor cycles, comprising:

- a plurality of pipes (2) connected with each other to form a path of travel (3) for exit of the burnt gases from an internal combustion engine (4) towards the surrounding atmosphere;

- at least one silencer or muffler (5) disposed between at least two of said plurality of pipes (2) for gas interception along the exit or exhaust path (3);

characterized in that said plurality of pipes (2) has at least one pipe (6) according to one or more of claims 1 to 9.

11. A process for manufacture of a pipe as claimed in one or more of claims 1 to 9, characterized in that it comprises the following steps:

- making a first tubular body of rectilinear longitudinal axis having a first wall thickness (s1);

- making a second tubular body of rectilinear longitudinal axis having a second wall thickness (s2) larger than the first wall thickness (s1);

- cutting to size the first tubular body to form a plurality of first tubular portions (8);

- cutting to size the second tubular body to form a plurality of second tubular portions (9);

- bending the second tubular portions (9);

- abutting each of the first tubular portions (8) onto at least one second tubular portion of curved conformation (9) ;

- welding each of the first tubular portions (8) to said at least one second curved tubular portion (9).

Drawing