FR2801342A1 - Cooling device for exhaust of e.g. direct injection diesel engine has two paths each of same axial length with different heat exchange properties and valve directing flow from one path to other path - Google Patents

Abstract

A cooling device for installing in a vehicle exhaust system has two paths each having conduit(s) with an external surface contacted by cooling air. Each path has the same axial length but different heat exchange characteristics. A valve switches the gas flow from one path to the other depending upon a thermal parameter of the exhaust system. Preferred Features: The first path may have tube(s) with a simple metallic surface and the second path has relatively smaller diameter tube(s) insulated by an air jacket between internal and external surfaces. A temperature sensor operates the valve located at the downstream end of the first path. The device is located upstream of a NOx filter

Description

The invention relates to an adjustable cooling device for the engine of a motor vehicle, at two levels cooling, interposed in the path of the exhaust gas in a vehicle exhaust line.

Motor vehicle exhaust systems may include gas treatment devices such as pollution control systems in which certain pollutants such as nitrogen oxides (NOx) contained in the engine exhaust are removed. of the vehicle.

The exhaust gas treatment for removing pollutants involves passing the exhaust gas through a treatment device into contact with an active element composed of a mixture of different metals selected for their ability to catalyze pollutant transformation reactions or to adsorb pollutants. The active element is deposited in the form of an impregnating layer on a porous ceramic support fixed inside a sheet metal casing of the depollution device. The porous ceramic support is itself covered with a porous alumina-based layer called "wash-coat" intended to considerably increase the area of contact between the gases and the active elements which are deposited in the wash-coat. The active element of the pollution control system and the wash-coat can withstand a certain exhaust temperature and, when in contact with the exhaust gas at an excessive temperature, undergo irreversible damage. ; so that they are no longer able to perform their pollution function.

For example, in the case of pollution control systems designed to eliminate oxides of nitrogen in the exhaust gases of direct injection engines, these pollution control systems being generally referred to as "NOx scavengers", the limiting temperature that the NOx trap elements in contact with the exhaust gases can support is of the order of 850 C at present. The output of a direct injection gasoline engine reaches a temperature of 950 to 1000 C, in the phases of ine load of the engine.

In order to maintain the temperature of the gases at a maximum temperature of 850 ° C, for a gasoline engine with a direct injection of two liters of displacement, it is necessary to evacuate a power of the order of 15 kN. It is necessary to design an exhaust system with a cooling device that allows this energy to be exhausted before the exhaust gases enter the NOx trap.

In addition, still in the case of a NOx trap, the maximum efficiency in the removal of pollutants is obtained in a temperature range of between 300 and 500 approximately, because of the chemical reactions implemented. It is therefore necessary to keep the gases entering the trap as much as possible in this temperature range.

This requirement must be respected in particular in operating conditions of the regulatory clean-up cycle. In the regulatory regulation cycle, the gases typically evolve in a temperature range of about 350 ° C. to 700 ° C.

To remain within the efficiency range of the NOx trap, in the case of the regulatory clean-up cycle, for an engine as defined above, it is only necessary to discharge thermal powers of the order of 2 kW.

Consequently, in the case of full load operation of the engine, it is necessary to evacuate at least 15 kW of thermal power while, under the operating conditions of the regulatory clean-up cycle, no more than 2 kW must be evacuated.

In general, in the case of many depollution systems, it is necessary, for reasons of temperature resistance of the pollution control system elements, to prevent it from receiving exhaust gases at too high a temperature.

It is necessary, in order to effectively clean up the exhaust gases, that the exhaust gases passing through the pollution control system have a temperature within a well-defined interval, both of which define the position of the pollution elements on the exhaust gas. the exhaust line, are often incompatible.

It is then necessary, in order to fulfill the two conditions relating to the temperature of the exhaust gases in the pollution control system, conditions which may be incompatible, to provide an exhaust gas cooling device which can operate in a selective manner. ive in a first and second cooling conditions.

It has been proposed; to solve this problem, a cooling device which comprises a first and a second exhaust gas passage tubes whose outer wall is in contact with cooling air, for example atmospheric air, during the operation of the vehicle engine. One of the tubes of great length allows to evacuate maximum energy while the second tube of very reduced length allows to evacuate a very small amount of thermal energy. A pilot valve allows the exhaust gases to pass either in one tube or the other, depending on the operating conditions of the engine or exhaust line. By adapting the lengths of the two tubes according to the desired operating conditions, the temperature of the exhaust gases is adjusted before entering the pollution control system, under all engine operating conditions.

However, this solution may require the use of very long tubes that can not be easily accommodated in the vehicle either in the engine block or in the subfloor.

The object of the invention is therefore to propose a device for cooling gas exhaust from the engine of a motor vehicle, interposed on the exhaust gas path in a vehicle exhaust line, comprising a first lane of circulation. exhaust gas constituted by at least a first conduit in contact with its external wall with cooling air, a second gas flow path constituted by at least a second conduit having an outer wall in contact with the cooling air and means for diverting exhaust gases to the first or second circulation lanes, controlled according to a thermal parameter of operation of the engine exhaust line, this adjustable cooling device can be easily implanted in the exhaust line, for example in the subfloor or in the engine compartment of the motor vehicle.

For this purpose, the ducts constituting the first and the second circulation ducts have substantially equal lengths in the axial direction of the exhaust line and side walls of heat exchange with cooling I ir having heat exchange characteristics sen sibly different.

In order to understand the invention, an embodiment of an adjustable cooling device according to the invention will be described by way of example with reference to the appended figures.

Figure 1 is a schematic perspective view of a portion of an exhaust line of a motor vehicle having an adjustable cooling device according to the invention.

FIGS. 2A and 2B are perspective views of the cooling device according to the invention in a phase of operation with a high energy loss and in a phase of operation with low energy loss, respectively.

FIG. 1 shows part of an exhaust line of a motor vehicle on which is inserted a cooling device according to the invention generally designated by the reference numeral 1.

The exhaust line generally designated by the reference comprises an upstream portion 2 'connected to the outlet pipes 3 of the exhaust gas of a motor 4 (shown conventionally in the form of a parallelepiped in phantom) . The upstream part 2 'of the exhaust line comprises in particular a first depollution unit 5 which is constituted by a catalyst having a three-way function, that is to say making it possible to eliminate in the exhaust gas carbon monoxide CO, unburnt hydrocarbons and oxides of nitrogen, the catalyst being disposed inside a metal casing connected to pipes of the first section 2 'of the exhaust line. The upstream part of the exhaust line also comprises a decoupler 6 which makes it possible to avoid the transmission of vibrations from the engine 4 to the part of the exhaust line situated downstream of the decoupler.

The exhaust line comprises a downstream portion 2 "on which is inserted a depollution device 7 made in the form of a pi ', that is to say a depollution device for eliminating the' nitrogen in the exhaust gas.

The adjustable cooling device 1 according to the invention comprises an inlet manifold 8, an outlet manifold 9, and two substantially straight gas circulation tubes 10 and 11 arranged parallel to one another and connected, at one of their ends, at the inlet manifold 8 and, at their second end, at the outlet manifold 9.

The inlet manifold 8 comprises an inlet duct connected to the upstream part 2 'of the exhaust line downstream of the decoupler 6 and two branches having outlet openings in which the tubes 10 and 11 are fixed.

The outlet manifold 9 comprises an outlet duct connected to the downstream 2 "of the exhaust line upstream of the NOx trap 7 and two inlet ports having apertures in which are fixed I second ends of the tubes 10 and 11.

As a result, the cooling device 1 of the exhaust gases interposed between the upstream part 2 'of the exhaust line and the e 1 <B> 1 </ B> 2 "and placed immediately upstream of the NOx trap 7 The tubes 1 11 ensuring the passage of the exhaust gas between the upstream portion 2 'and the downstream 2 "of the exhaust line are cooled in their dull surface by atmospheric air, so that the gases of Exhaust undergoes some cooling through the tubes 10 and 11 in the direction iale corresponding to the longitudinal direction of the exhaust line. The tubes 10 and 11 have lengths, in the axial direction, which are substantially equal, these lengths to allow to accommodate the tubes 10 and 11 without difficulty on the exhaust line, for example the interior of a subfloor of the motor vehicle.

The tubes 10 and 11, however, are different from each other, firstly with regard to their internal diameter of the gas flow, the inner diameter of the tube 11 being substantially smaller than the inside diameter of the tube 10 (see FIG. Figures 2A and 2B).

in addition, the walls of the tubes 10 and 11 have characteristics of heat exchange with the cooling air extremely different. The tube 10, which may be made for example of aluminized steel, has a very good heat exchange between the cooling air and the exhaust gas; so that the exhaust gases can be strongly cooled, with a large amount of heat energy, during their passage through the tube 10 in the axial direction. On the other hand, the tube 11 comprises a wall ensuring a low heat exchange between the cooling element and the exhaust gases. For this, the wall of the tube is made so as to provide a certain thermal insulation of the ratio to the cooling air in contact with the outer tube surface 11. The tube 1 may be constituted for example in the form of a tube with a blade air, that is to say a tube whose wall defines an air gap insulation between an inner wall member and an outer wall member.

The thermal insulation characteristics of the wall of the tube 11 can also be obtained by isolating the outer wall of the tube 11 of the ambient air, by a layer of insulation fibers, preferably fibers made of a refractory material.

The cooling device 1 comprises a valve 12 for closing the downstream end of the duct 10 connected to one of the inlet legs of the outlet manifold 9. The valve 12 is associated with an actuating motor 13 which enables placing the valve of the valve 12 in an open position or in a closed position of the conduit end 10.

the control motor 13 of the valve 12, which may be an electric motor or a pneumatic motor, depending on the possibility of supplying the motor 13 from an electrical source or from a depressed chamber and a vacuum pump. vacuum, is controlled by an electronic control unit 14 as a function of a temperature measurement performed by a temperature sensor 15 'or 15 "which can be placed for example in the upstream part 2' of the exhaust line in 6 of the decoupler 6 or on the engine exhaust pipes 3. Depending on the temperature indication of the probe, the control unit controls the motor 13 in the direction of opening or closing the valve 12.

The operation of the cooling device 1 according to the invention will be described with reference to FIGS. 2A and 2B, on which there is shown; in the same way as in FIG. 1, the elements of the cooling device and the circulation of the exhaust gases in the cooling device, by arrows.

In the case where the temperature measured by the probe 15 'or 15 "is greater than a set value, for example in the case of operation of the engine at high speed with an exhaust gas outlet at very high temperature, the actuating motor 13 of the valve is controlled by the control unit 14, in the direction of opening the valve, that is to say, as shown in FIG. 2A, so that the valve of the valve secured to the valve stem connected to the engine is remote the outlet opening of the conduit 10 inside the manifold Due to the difference of the internal passage section of the tubes 10 and 1 gas. exhaust entering the inlet manifold 8 are distributed between the tubes 10 and 11 by the manifold 8. such that the tube 1 high energy loss is traversed by a main stream 16 of the exhaust gas and the tube 11 by a residual flow 16 'The main flow 16 presents high flow rate while the flow 16 'has a very low flow rate, the flow rate of the stream 16 thus being only very slightly less than the total exhaust gas flow rate. As a result, the exhaust gas passing through the cooling device 1, mainly via the high energy loss tube, is strongly cooled. This mode of operation shown in FIG. 2A is maintained as long as the temperature of the gases remains above a limit which may be, for example, 850 C; in the case of a cooling device arranged upstream of a NOx trap as shown in FIG. 1.

In the case where the temperature measured by the temperature probe 15 'or 15 "is lower than the set value, the control unit 14 transmits to the control motor 13 of the valve 12 an order to close the exit of the conduit 10 to In this case, as shown in FIG. 2B, the exhaust gases entering the inlet reader neck 8 penetrate and circulate in their entirety inside the tube 11, in the form of a flow. corresponding to the total flow of the exhaust The circulation of the exhaust gases inside the tube 11 is performed with a low energy loss, that is to say a low-cooling gas, because the heat exchange through the insulated wall of the tube 11 are reduced.

In a cooling device 1 used upstream of a NOx trap, can thus adjust the temperature of the exhaust gas in a temperature range ensuring a satisfactory operation NOx trap, this range of temperatures can be understood by example between 300 and 500 C.

The cooling device according to the invention can therefore be automatically introduced to ensure either an intense cooling of the exhaust gases with a significant thermal power evacuation, or a low cooling with an evacuation of a low thermal power. It is thus possible, particularly in the case of a NOx trap, to effectively protect the NOx trap against any thermal degradation by exhaust gases having an excessive temperature and to operate the NOx trap in very good conditions. performance conditions, regardless of the operating speed of the engine.

In particular, the cooling device according to the invention makes it possible to prevent the over-enrichment of fuel which is necessary in the case of direct injection diesel engines comprising conventional exhaust lines, this over-enrichment being necessary for to protect the protection of the NOx trap. A significant gain in consumption is thus obtained in the case of using the device according to the invention. This advantage is particularly important, since the manufacturers of tomobiles seek, in the case of direct injection diesel engines, a consumption gain compared to the consumption of conventional type engines. Furthermore, the device according to the invention provides the following advantages - concerning the treatment of gases in the exhaust line; the device makes it possible to remain in the effi city range of the pollution control system upstream of which it is placed and to protect the components of the pollution control system against thermal degradations - which concerns the implantation of the device, the latter is compact and can be easily implanted in a subfloor of the automo bile icule; indeed, the device comprises only two lanes which are generally constituted by simple rectilinear tubes which have identical lengths and compatible with an implementation of the cooling device under the floor of the motor vehicle; with regard to the ease and reliability of the device, the usual technologies are used in the case of the mass production of components for an exhaust line: the tube with high energy loss can be formed in the form of a conventional tube of an exhaust device and the low energy loss tube by performing thermal insulation of the wall of a conventional tube or by a well known air knife tube; the inlet and outlet collectors of the cooling device can be made using conventional technology, from i-shells.

various elements of the cooling device according to the invention namely the tubes and the collectors can be made of any material that can easily be formed and assembled and having a good resistance to corrosion at high temperature by the exhaust gases and cooling air. Such materials may be for example aluminized steel, stainless steel or a nickel alloy containing chromium.

The invention is not limited strictly to the embodiment which has been described.

Thus, the first way of circulation of gas with high energy loss can be obtained from a simple tube whose wall has a low thermal inertia and a high heat exchange capacity, but still in the form of two or more tubes of the same length arranged in parallel; this makes it possible to increase the surface exchange between the outer wall of the first circulation lane and the cooling air.

The second flow path of the exhaust gases of the cooling device can be carried out in other forms than those which have been described, in such a way that the exchange wall between the exhaust pipes and the cooling air has certain properties' thermal insulation.

Likewise, the inlet and outlet collectors of the cooling device may have different shapes from those described and shown.

The device for routing the gases in a circulati duct in another, as a function of a thermal parameter such as the temperature of the exhaust gas upstream of the cooling device, may have a shape different from that which has been described. In the case of the use of a valve controlled by an electric motor or a pneumatic or hydraulic device, the valve flap may be provided to close any end portion of an inlet or outlet of a valve. traffic way. The switching device may also be constituted by a plurality of registers disposed in the inlet manifold or in the outlet manifold and for directing the exhaust gas to one or the other of the circulation channels.

It may also be useful to add at least one bellows to one of the two tubes 10 and 11 as a differential expansion compensator between the two tubes of different technologies.

Preferably, the cooling device according to the invention is disposed immediately upstream of an exhaust gas treatment device such as a pollution control system.

Of course, the invention is not limited to the cooling of the upstream gases of a NOx trap but can be used upstream of any pollution control device whose components may need to be protected against thermal shock or against a high temperature. or to adjust the operating conditions, within a precise exhaust gas temperature range.

The invention applies to any type of motor vehicle comprising an exhaust gas iteration device such as a pollution system.

Claims (1)

<U> CLAIMS </ U> .- A device for cooling engine exhaust gas (4) of an automobile icule, inserted in the path of the exhaust gases in an exhaust line (2) of the vehicle, comprising a first circulati path (10) of the exhaust gas constituted by at least first conduit (10) in contact with its external wall with cooling air, a second gas circulation path constituted by at least a second conduit (11) having an outer wall in contact with the cooling air and means for switching (12, 13) the exhaust gases to the first or second circulation lanes controlled according to the thermal parameter of operation of the exhaust line of the engine (4), characterized in that the ducts (10, 11) constituting the first and the second circulation lies have lengths substantially in the direction of the exhaust line and the side walls of exchange the with the cooling air having substantially different heat exchange characteristics. - Device according to claim 1, characterized in that it comprises a first flow path constituted by at least one straight pipe (10) having a single metal exchange wall with the cooling air and a second circulation lane formed by at least one tube (1 having a thermally insulated wall.) Device according to claim 2, characterized in that the tube (1 constituting the first flow path of the exhaust gas is an aluminized steel tube. any of revendicati 2 and 3, cicário "in that the tube constituting the second circulation lane is an air tube tube whose wall is insulated by a blade of air isposé be a element 5. A device according to any one of claims 2 to 4, characterized in that the tube (10) constituting the first circulating channel an inner diameter substantially greater than the inner diameter of the tube (11) constituting the second circulation lane. 6. A device according to any one of claims 2 to 5, characterized in that the switching means (12, 13) of the exhaust gas to the first or the second flow path (10, 11) are constituted by a valve (12) having a valve for opening or closing an end of one of the circulation paths of the cooling device whose displacement is ensured by a motor 3) controlled by the control unit ( 14) connected to a probe, 15 ") measuring the temperature of the exhaust gas at a point on the exhaust line 7.- Device according to claim 6, characterized in that the valve (12) arranged in a manner that the valve valve provides the outlet end closure of the first circulating channel (10) with a high thermal energy loss, and the device according to any one of claims 2 to 7, characterized by the fact that comprises an inlet manifold (8) comprising an inlet duct connected to an upstream part (2 ") of the exhaust line and two outlet branches each connected to an inlet end, a tube (10, 11) constituting a circulation lane and a collector ie (9) having an outlet duct connected to the downstream portion (2 ") of the exhaust line and two input branches each connected to an outlet end portion of a tube (10, 11) constituting an exhaust gas flow path. 9.- Device according to claim 8, characterized in that it is arranged on the exhaust line (2) of the motor vehicle, upstream of a pollution control system such as a NOx trap (7), in particular a trap to a direct injection diesel engine. - Device according to any one of claims 2 to 9; it is characterized by the fact that at least one bellows is attached to at least one of the tubes) as a differential expansion compensator between the needles (10,