FR2878895A1 - Exhaust line for motor vehicle, has exhaust gas cooling unit disposed between outlet of catalytic converter and outlet towards atmosphere, and comprising longitudinal or helical blades disposed on exhaust gas circulation conduit - Google Patents

Abstract

The line (50) has an exhaust gas cooling unit (60) disposed between an outlet of a catalytic converter (14) and an outlet (17) towards atmosphere. The cooling unit has longitudinal or helical blades that are disposed on an exhaust gas circulation conduit (40). The converter treats the exhaust gas that is provided from an exhaust manifold (13) by a blow-off pipe (20), where the manifold collects the exhaust gas issued from combustion. An independent claim is also included for a motor vehicle comprising an exhaust line.

Description

TECHNICAL FIELD TO WHICH THE INVENTION REFERS

  The present invention relates to an exhaust system for a motor vehicle equipped with an internal combustion engine.

  It relates more particularly to an exhaust line comprising an exhaust gas flow pipe which extends from the outlet of a catalytic converter to an outlet to the atmosphere and at least one volume crossed by said circulation pipe, and adapted to attenuate the pressure pulsations of the exhaust gas.

BACKGROUND

  Nowadays, in order to reduce the noise pollution due to the pressure pulsations of the exhaust gases in the exhaust line of a motor vehicle with an internal combustion engine, it is known to set up a line architecture of exhaust having volumes, such as mufflers or expansion pots, and lengths of tubes. This architecture makes it possible to reduce the amplitude of the pressure pulsations and to modify the resonance frequencies of these pressure waves at the exhaust.

  When the internal combustion engine of the vehicle is a very important source of noise, the volumes constituting the exhaust line, such as the expansion pot and the silencer, must be of large sizes.

  The size of these volumes poses a problem of boarding the exhaust line on the vehicle, as well as an extra cost of manufacturing an exhaust line. In addition, the large size of the volumes poses a major back-pressure problem in the exhaust line which penalizes the performance of the engine. It is then a question of making a compromise between the desired performances of the engine and the noise of the exhaust mouth.

  OBJECT OF THE INVENTION In order to overcome the aforementioned drawbacks of the state of the art, the present invention proposes an exhaust line in which the noise level is effectively lowered directly at the source, as close as possible to the output of the converter. catalytic, without penalizing the performance of this converter, as well as the performance of the engine.

  For this purpose, it is proposed according to the invention an exhaust line as defined in the introduction wherein there is provided exhaust gas cooling means disposed between the output of the catalytic converter and the outlet to the atmosphere.

  Thus, thanks to the cooling means according to the invention, the pressure pulsations of the exhaust gases are substantially reduced just after the output of the catalytic converter. The architecture of the exhaust line according to the invention which reduces noise pollution, is simplified by having smaller volumes.

  According to a first embodiment of the exhaust line according to the invention, the cooling means are located between the output of the catalytic converter and the inlet of the first volume.

  Thus, improved cooling of this first zone makes it possible to lower the level of exhaust port noise and to improve engine performance.

  According to a second embodiment of the exhaust line according to the invention, the cooling means are located between the inlet of the first volume and the outlet to the atmosphere.

  Thus, an improved cooling of this second zone makes it possible to effectively reduce the level of residual exhaust mouth noise at the outlet.

  Other non-limiting and advantageous features of the exhaust line according to the invention are the following: the cooling means comprise fins disposed on the exhaust gas circulation pipe. These fins make it possible to increase heat exchange by increasing the exchange surface.

  said fins may be axial fins.

  said fins may be spiral fins.

  the cooling means comprise aerodynamic air deflector type profiles distributed along the exhaust line. These profiles maximize the flow of ambient air along said exhaust line.

  the cooling means comprise a heat exchanger equipping the volume (s). Cooling takes place within the volume (s).

  The invention also relates to a motor vehicle with an internal combustion engine which comprises an exhaust line as described above.

  DETAILED DESCRIPTION OF AN EXEMPLARY EMBODIMENT

  The following description with reference to the accompanying drawings given as non-limiting examples, will make it clear what the invention is and how it can be achieved.

  In the accompanying drawings: FIG. 1 is a schematic diagram of a supercharged engine and an exhaust line according to the invention; FIG. 2 is a schematic diagram of an atmospheric engine and an exhaust line according to the invention; FIG. 3A is a perspective view of an exhaust gas flow line of a first embodiment of the exhaust line according to the invention; Figure 3B is a front view of the exhaust gas flow line of Figure 3A; - Figure 3C is a side view of the exhaust gas flow line of a second embodiment of the exhaust line according to the invention; FIG. 4 is a block diagram illustrating a third embodiment of the exhaust line according to the invention; - Figure 5 is a schematic perspective view of a fourth embodiment of the exhaust line according to the invention; FIG. 6 is a graph showing the exhaust pressure as a function of the crankshaft angle of a motor vehicle with an internal combustion engine equipped or not with an exhaust line according to the invention; FIG. 7 is a set of four graphs showing the noise at the exhaust and the harmonics of this noise as a function of the speed of the internal combustion engine of a motor vehicle equipped or not with an exhaust line according to FIG. invention; FIG 8 is a set of three graphs showing the performance of the combustion engine of a motor vehicle with or without an exhaust line according to the invention, depending on the speed of the engine; Preliminarily, it will be noted that from one figure to another, the identical or similar elements of the different embodiments of the invention will, as far as possible, be referenced by the same reference signs and will not be described at each time. times.

  FIGS. 1 and 2 show schematically the general structure of an internal combustion engine 10, 10 'and the exhaust line 50 of a motor vehicle 1.

  This engine comprises a combustion chamber 11 provided here with four cylinders 11A. The cylinders 11A of the combustion chamber 11 are supplied with fresh air by an intake distributor 12 itself supplied with fresh air by an intake duct 18.

  In the case of a supercharged engine 10 (see FIG. 1), the intake pipe 18 passes through a turbocharger-type supercharging device 30.

  An exhaust manifold 13 recovers the exhaust gases from the combustion.

  At the outlet of the exhaust manifold 13 is a discharge pipe 20 which sends the exhaust gas to a catalytic converter 14.

  In the case of a supercharged engine 10 (see FIG. 1), the exhaust pipe 20 also passes through the turbocharger-type supercharging device 30.

  The exhaust gases are then treated by the catalytic converter 14.

  Indeed these exhaust gases contain pollutants, such as nitrogen oxides (NOx), unburned hydrocarbons (HC), carbon monoxide (CO), it is necessary to treat before evacuating them in the atmosphere.

  The catalytic converter 14 makes it possible to oxidize the reducing molecules that are carbon monoxide (CO) and unburned hydrocarbons (HC).

  Then, there is provided an exhaust line 50 which extends between the output of the catalytic converter 14 and the outlet to the atmosphere 17.

  This exhaust line 50 comprises an exhaust gas circulation pipe 40 and at least one volume through which said exhaust gas circulation pipe.

  Here, as shown in Figures 1 and 2, there are provided in the exhaust line 50 two volumes 15 and 16 successive.

  The first volume is an expansion pot 15 and the second volume is a muffler 16.

  The expansion vessel 15 processes the amplitudes of the pressure of the exhaust gases, while the muffler mainly processes the frequencies of these pressure pulsations, that is to say the sounds of exhaust mouth.

  This exhaust line 50 thus comprises two zones, the first zone 51 is between the output of the catalytic converter 14 and the inlet of the expansion vessel 15 and the second zone 52 is between the inlet of the expansion vessel 15 and the exit 17. This second zone also incorporates the muffler 16.

  Advantageously, according to the invention, the exhaust line 50 is equipped with cooling means 60.

  According to a first embodiment shown in FIGS. 3A and 3B, these cooling means 60 may be longitudinal fins 61 or, as shown in FIG. 3C, helical fins 62 arranged on the exhaust gas circulation line 40. of the exhaust line.

  These fins make it possible to increase the heat exchange, between the exhaust gas and the outside air around the said circulation pipe, by increasing the exchange surface.

  It can be provided according to the invention that only the exhaust gas flow line 40 of the first zone 51 or the second zone 52 is equipped with said fins 61; 62. It may also be envisaged that the exhaust gas flow line 40 of the two zones 51, 52 is provided with said fins 61;

  FIG. 4 shows another embodiment of the cooling means 60 according to which they comprise aerodynamic profiles 63 distributed along the exhaust line 50 situated under the floor 3 of the vehicle 1, between the front and rear wheels 2.

  The aerodynamic profiles 63 are for example air deflectors that maximize the flow of ambient air along said exhaust line 50.

  FIG. 5 shows another embodiment of the cooling means 60 in which a heat exchanger 64 is provided for a volume 15, 16 of the exhaust line 50. This heat exchanger 64 may be of the heat exchanger type. heat. In this case, the cooling takes place within said volume 15; 16, the outside ambient air 70 being forced to pass into the latter.

  FIG. 6 represents the curves of the instantaneous exhaust pressure at the outlet of a supercharged engine, as a function of the engine crankshaft angle whose exhaust line is equipped or not with cooling means in the first zone. of said exhaust line.

  As can be seen in this figure, in the absence of cooling means of the first zone, the temperature of the exhaust line is of the order of 600 C. At the engine output, the solid curve shows that the amplitudes or instantaneous pressure variations can reach important values of the order of 600 mbar with instantaneous pressure values close to 1500 mbar.

  The pressure pulsations of the exhaust gases at the output of the engine have a high amplitude. This amplitude decreases throughout the exhaust line and more particularly to the passage of the catalytic converter and each volume of the exhaust line. The first volume through which the exhaust gases exit the exhaust manifold of the engine is the catalytic converter located upstream of the exhaust line.

  When, in accordance with the invention, cooling means 60 are installed in the first zone 51 of the exhaust line 50 making it possible to obtain a cooling of 100 ° C., the dashed curve of FIG. the pressure pulsations of the exhaust gases at the output of the engine 10, 10 'decrease by 150 mbar.

  In the first graph of FIG. 7, curves of variation of the exhaust mouth noise of a supercharged engine whose first zone of the exhaust line is equipped with or without cooling means are shown, as a function of regime of this engine.

  Thus, it can be seen from this graph that, thanks to the invention, a cooling improvement of 100 C in the first zone 51 of the exhaust line 50 makes it possible (as shown by the dashed line of the first graph of FIG. 7) to lower the exhaust noise level at the outlet 17. This decrease in the exhaust noise level is the consequence of a decrease in the amplitude of the exhaust pressure variations. The noise loss at the exit of exhaust line obtained is about 3 to 5 dB, a decrease of 3 dB corresponding to a pressure pulse amplitude reduced by half.

  This decrease in the exhaust noise level is confirmed on the last three graphs of Figure 7 representing three harmonics of this noise according to engine speed. The superposition of all the harmonics constitutes the noise. It is therefore consistent to observe a decrease in the value of these harmonics as illustrated by the dashed lines.

  FIG. 8 shows the engine torque, the fresh gas filling of the cylinders and the proportion of the residual burnt gases, as a function of the speed of a supercharged engine whose first zone of the exhaust line is equipped with no cooling means.

  FIG. 8 shows that, thanks to the cooling means according to the invention, a cooling improvement of 100 C in the first zone 51 makes it possible (as shown by the dotted curves) to increase the torque and to have a rate filling cylinders with more fresh gas while the proportion of residual burnt gases compared to those evacuated decreases.

  Thus, according to the invention, the cooling means 60 of the first zone of the exhaust line 50 allow a better emptying of the combustion chamber 11 and thus gains of the order of 3 Nm at an engine speed of 3000 rev / min.

  The performance of the supercharged engine 10, which is a function of the torque, the filling ratio and the proportion of residual flue gases, are thus improved.

  These gains are generally greater on supercharged engine 10 than on atmospheric engine 10 '. Indeed, the turbine of the turbocharger 30 allows a significant relaxation ratio. This important relaxation ratio increases the performance of said engine.

  In order to further reduce the amplitude of the variations in the pressure of the exhaust gases after passing through the catalytic converter and the first zone of the exhaust line 50, an expansion valve 15 is used at the inlet of the second zone 52 of the exhaust line 50.

  Beyond the expansion chamber 15, the pressure variations are no longer sufficient to have a significant role on the performance of the engine 10; 10 '. They only generate noise that is processed in the second zone 52 of the exhaust line 50.

  According to the invention, the cooling means 60 of the second zone 52 of the exhaust line 50 then make it possible to further reduce the amplitudes of the pressure pulsations coming from the first zone 51.

  Thus, the sound level, at the outlet of said exhaust line to the atmosphere, resulting from the pressure waves treated according to the invention, is effectively reduced so as to comply with the regulations put in place.

  The present invention is not limited to the embodiments described and shown, but the skilled person will be able to make any variant within his mind.

Claims (9)

  An exhaust line (50) of a motor vehicle (1) having an internal combustion engine (10; 10 ') comprising an exhaust gas flow line (40) extending from the outlet from a catalytic converter (14) to an outlet (17) to the atmosphere and at least one volume (15; 16) traversed by said circulation pipe, and adapted to attenuate the pressure pulsations of the exhaust gases , characterized in that it comprises cooling means (60) of the exhaust gas disposed between the output of the catalytic converter (14) and said outlet to the atmosphere (17).   2. Exhaust line (50) according to claim 1, characterized in that the cooling means (60) are located between the catalytic converter output (14) and the inlet of said volume (15; 16).   3. Exhaust line (50) according to claim 1, characterized in that the cooling means (60) are located between the inlet of said volume (15 15; 16) and said outlet to the atmosphere (17). 4. Exhaust line (50) according to one of claims 1 to 3, characterized in that the cooling means (60) comprise fins (61; 62) arranged on the exhaust gas circulation pipe ( 40).   5. Exhaust line (50) according to claim 4, characterized in that said fins disposed on said circulation pipe are axial fins (61).   6. Exhaust line (50) according to claim 4, characterized in that said fins disposed on said circulation pipe are spiral fins (62).   7. Exhaust line (50) according to one of claims 1 to 6, characterized in that the cooling means (60) comprise aerodynamic profiles (63) of air deflectors type distributed along the line d exhaust (50).   8. Exhaust line (50) according to one of claims 1 to 7, characterized in that the cooling means (60) comprise a heat exchanger (64) equipping said volume (15; 16). 9 _.z   9. A motor vehicle (1) with an internal combustion engine (10; 10 ') which comprises an exhaust line (50) according to any one of claims 1 to 8.