DE10140502A1 - Exhaust system comprises exhaust gas purification device and temperature control device with heat exchanger formed as radiation cooler having external housing with feed and discharge hoppers - Google Patents

Abstract

An exhaust system comprises an exhaust gas purification device and a temperature control device arranged between the engine and the exhaust gas purification device. The temperature control device has a heat exchanger (16) formed as a radiation cooler having an external housing (24, 26) with feed and discharge hoppers and a radiation sheet (28) which radiates the energy towards the housing. Preferred Features: The housing is formed by two half shells connected together gas-tight and between which a radiation sheet is arranged. The sheet is held in the housing via connecting sites. Tubes are arranged in the housing as gas feeds with the radiation sheet arranged within the tubes.

Description

The invention relates to an exhaust system for internal combustion engines, in particular those in motor vehicles, according to the preamble of claim 1.

Such an exhaust system is shown, for example, in DE 197 42 762 C1. The Temperature control device for the exhaust gases consists of a first Ab gas line section, in which a controllable flap is arranged, and ei NEN arranged around this exhaust pipe section heat exchanger with a housing with external cooling fins and internal Thermal baffles from the pipe section to the housing. For quick opening heating a downstream catalyst is the controllable flap ge opens and the exhaust gas flows directly through the inner line section. Has the downstream catalyst reaches a defined temperature, then the flap closed and the exhaust gas now for cooling by the outside outer heat exchanger directed.

The object of the invention is a simpler exhaust gas in construction to create plant of the generic type.

This object is achieved with the characterizing features of claim 1 solved. Advantageous and expedient training The invention can be found in the further claims.

According to the invention it is thus proposed that the heat exchanger be used as Radiation cooler with an outer housing with inlet and outlet funnels and with internal radiation sheets radiating to the housing is formed. In contrast to the heat exchanger described above, the is designed according to the heat conduction principle and the convection principle,  the proposed heat exchanger mainly acts after the jet development principle.

The advantage of such a construction is that initially, due to the low heat capacity of the heat exchanger, preferably from thin-walled sheets, the downstream catalyst or adsorber quickly reaches its light-off temperature of e.g. B. is heated to 250 ° C, the heat exchanger exerts a relatively low cooling effect. With increasing temperature of the exhaust gases and the heat exchanger, the radiation sheets are heated up and increasingly emit radiation energy to the housing and from it to the environment. According to the formula for calculating the amount of heat emitted, the fourth power is used in the calculation. This results in a rapidly increasing cooling effect at high temperatures, with which it is possible to clean the downstream exhaust gas cleaning device, e.g. B. a DeNO _X catalyst or a three-way catalyst to quickly bring the light off temperature and possibly in a desired temperature range without overheating.

In a technically and structurally advantageous manner, the housing of the Heat exchanger from at least two sheet metal parts or half shells be set, e.g. B. by deep drawing. At least one radiation sheet can be easily held between connecting flanges in terms of production technology be molded onto the housing half-shells.

For reasons of strength and to reduce any noise that may occur The housing can emit radiation in the form of side by side Tubes are formed, which are also favorable as regards production technology Half shells can be made and connected. The pipes can either directly form the outer housing or it can also have a smooth surface, enclosing the pipes and in essential Ge does not come into heat-conducting contact with the pipes be provided. The latter version has when used in Motor vehicles have the advantage of low air resistance with laminar Flow around.

Preferably, the temperature control device for the exhaust gas treatment device or the downstream catalyst only by the heat exchanger or its self-regulating effect. This means that the  Controllable flap and a corresponding bypass line can be omitted.

Possibly. can, however, a flow control element in the housing of the exhaust gas cooler be arranged by means of which the flow cross-section of the exhaust gas ver is wrestable. This means that the cold internal combustion engine or cold exhaust gas part of the exhaust gas cooler can be shorted to one more faster heating of the downstream emission control device cause.

Several embodiments of the invention are set forth below with others Details explained in more detail. The schematic drawing shows in

Fig. 1 partially an exhaust system for an internal combustion engine in a motor vehicle, with a heat exchanger as a temperature control device and a downstream exhaust gas cleaning device with a DeNO _X catalyst;

FIG. 2 shows a plan view of the heat exchanger according to FIG. 1;

FIG. 3 shows a cross section along the line III-III of FIG. 2 through the heat exchanger;

Fig. 4 is a graph of the heat exchanger of Figures 1 to 3 showing the heat flow across the exhaust gas temperature. divided into the convective components and the radiation components;

Figure 5 is a plan view of a modified heat exchanger, the sen outer housing is formed by a plurality of tubes lined up.

Fig. 6 is a cross section along the line VI-VI of Fig. 5;

Fig. 7 to 10 versions of the connection areas between the half-shells housed side and the radiant panel, each on an enlarged scale;

Figure 11 is a to the underside of the heat exchanger to be fixed shield.

FIG. 12 shows a section XII-XII through the shielding plate according to FIG. 11; and

Fig. 13 is a section XIII-XIII of Fig. 5 by the in the Ge of the exhaust gas cooler housing integrated flow conducting bi-metal.

Fig. 1 shows schematically an internal combustion engine 10 for a motor vehicle with an exhaust system with an exhaust manifold 12 , an exhaust pipe 14 , with an intervening three-way pre-catalyst 18 , egg nem heat exchanger 16 as a temperature control device and an exhaust gas cleaning device connected via a line 17 a DeNO _X adsorber 20 . At the adsorber 20 , the further gas system from a line 22 . B. connected with a main silencer and an exhaust pipe.

The heat exchanger 16 (cf. FIGS. 2 and 3) has a housing 24 , 26 for gas routing, which is composed of two half-shells 24 , 26 deep-drawn from a steel sheet. The half-shells 24 , 26 are provided with umlau fenden connecting flanges 24 a, 26 a, between which a housing 24 , 26 in the exhaust gas flow direction dividing radiation plate 28 z. B. is held by electrical resistance welding (roller seam welding).

Half of the half-shells 24 , 26 each have inlet and outlet funnels 24 b, 26 b, via which the heat exchanger 16 is connected to the adjoining exhaust pipes 14 , 17 .

The housing 24 , 26 of the heat exchanger 16 is essentially rectangular in shape and has a smooth surface ( FIG. 3). Furthermore, the radiation plate 28 , which is also made of steel sheet, is designed in a zigzag shape to enlarge its radiation area transversely to the exhaust gas flow direction. On the radiation plate 28 , a support plate 30 could possibly be provided approximately centrally to avoid vibrations. Abge see from the welded joints and possibly the support plate 30 , the radiation plate 28 relative to the housing 24 , 26 as easily as he visibly air gap insulated.

The heat exchanger 16 described has a low heat capacity due to the relatively thin-walled steel sheets; that is, the hot gas is initially cooled little and thus enables rapid heating of the downstream exhaust gas purification device 20 .

By showing the graph in Fig. 4 the heat flow Q of the heat exchanger 16 via the exhaust gas temperature T. It is seen that in addition to the approximately linearly increasing convection cooling (line 32), the radiation cooling is initially low (curve 34). This favors the rapid heating of the exhaust gas purification device 20 .

With increasing exhaust gas temperature T and operating time of the internal combustion engine, the radiation plate 28 and the housing 24 , 26 of the heat exchanger 16 are further heated, the radiation cooling increasing disproportionately. This already follows from the common equation
Q = ε × σ × A × T ⁴ .

Without going into the equation, it can be deduced that the temperature T is in the fourth power. The radiation plate 28 is thermally coupled to the half-shells 24 , 26 with an increasing radiation component, as a result of which the surface area of the heat exchanger 16 available for the convective heat emission of the exhaust gas stream is increased.

This increasing exhaust gas cooling causes a self-regulating effect of the gas temperature with low heat emission when cold starting the internal combustion engine and a high cooling capacity at high exhaust gas temperatures, so that a bypass line and a shut-off valve controlling this can be omitted and the heat exchanger 16 serves solely as a temperature control device.

The modified heat exchanger 16 'according to FIGS. 5 and 6 has a multi-part housing which is also formed from sheet steel and which is composed of the inlet funnel 36 ', the outlet funnel 38 'and two intermediate half-shells 40 , 42 .

The half-shells 40 , 42 are formed by a plurality of semicircular pipe sections 40 a and 42 a, which are arranged parallel next to one another and are formed by connecting flanges 40 b and 42 b per half-shell 40 and 42 to form a construction unit.

The half-shells 40 , 42 or their external connecting flanges 40 b, 42 b are, for. B. gas-tight with each other by roller seam welding; the inlet funnel 36 'and the outlet funnel 38 ' are welded in a gas-tight manner to the end faces of the half-shells 40 , 42 , so that a gas-tight housing with gas-carrying pipes 40 a, 42 a in the exemplary embodiment 5 in the region between the inlet funnel 36 'and the outlet funnel 38 'is created.

Between the half-shells 40 , 42 a radiation plate 28 'is arranged, which is seen in cross section (see FIG. 6) in each case in the area of the connecting flanges 40 b, 42 b flat and in the area of the tubes 40 a, 42 a is formed in a zigzag shape to give an effective radiation of thermal energy to the pipes 40 a, 42 a.

The radiation plate 28 'b in the outer connection regions only at local connection points 44 (see FIG. FIG. 5 and FIG. 10) with the dungsflanschen Verbin 40, 42 b via correspondingly molded tabs 28 a ver welded. In the remaining edge areas it is reset to form an air gap s and provided with a bevel 28 b, which increases its inherent rigidity in the gas flow direction.

Further, the radiation plate 28 'b at a plurality of joints 46 with the internal connecting flanges 40, 42 b of the half shells 40, heat-insulating manner 42nd

Referring to FIG. 7, the local connecting points 46 are formed in that in the connecting flanges 40 b, 42 b circular or slot-like before cracks 48 are embossed 50, the respective recesses 52 pass through the radiation plate 28 'and are firmly connected, for. B. by welding or soldering. For this purpose, a projection 48 is provided with a drilling 54 through which the welding or soldering can be performed. The recesses 52 in the radiation plate 28 'are so large that air gaps s remain between the recesses 52 and the projections 48 , 50 . The same applies between the connecting flanges 40 b, 42 b and the radiation plate 28 '.

In Fig. 8 the connection points 46 are designed, in which in the connec tion flanges 40 b, 42 b recesses 56 , 58 are formed, in which mushroom-shaped buffers 62 are guided from egg nem wire mesh or a metal tile. The buffers 62 are inserted into recesses 60 of the radiation plate 28 '. In the remaining areas, the radiation plate 28 'is in turn air gap insulated from the connecting flanges 40 b, 42 b via air gaps s. The radiation plate 28 'is thus kept vibration and heat insulated via the connection points 46 .

Finally, in FIG. 9, the connection points 46 are formed with rivets 64 , which rivets pass through corresponding bores 66 , 68 in the connection flanges 40 b, 42 b. Between the connecting flanges 40 b and 42 b are also made of a wire mesh spacer 70 is clamped, which are held by an annular groove 72 in corresponding recesses 74 of the radiation plate 28 '. The recesses 72 are chosen so large that a relative movement between the spacers 70 and the radiation plate 28 'z. B. is given to compensate for thermal stresses. Air gaps s are again formed between the connecting flanges 40 b and 42 b and the radiation plate 28 '.

The connection points 44 , 46 shown and described in FIGS. 7 to 10 can be used alternatively or in combination. Possibly. The heat exchanger 16 'according to FIGS. 5 and 6 can also be designed in the region of the pipe guides 42 , 44 with a smooth, outer jacket as a wide res housing part.

Furthermore, a shielding plate 80 against water hammer can be arranged on the underside of the heat exchanger 16 or 16 '(see FIGS. 11 and 12). This consists of a base plate 82 with openings 84 , from which, for. B. are formed by punching lamellae 86 . The fins 86 are seen in the direction of travel of the motor vehicle directed obliquely to the rear, so that they in particular repel splashed water (see arrows 88 ), but do not hinder the radiation of the thermal energy of the heat exchanger 16 .

The shielding plate 80 can be connected to the heat exchanger at its edge regions and / or via the described connection points 44 , 46 .

The heat exchanger 16 described is also structurally and manufacturing technically simple, robust in operation and insensitive to contamination in the exhaust system. It goes without saying that, particularly for the radiation sheet 28 , but also for the surrounding housing, sheets are to be used which give good emission values s.

The radiation plate 28 or possibly a plurality of radiation plates can additionally be catalytically effectively coated like a three-way catalytic converter or preferably like the DeNO _X adsorber 20 . As a result, the NO _x storage effect of the adsorber 20 can be additionally increased; Furthermore, for example, the desulfurization of the adsorber 20 can be improved at relatively high temperatures (z. B. 700 ° C) by the chemical exotherm in the measures initiated (secondary air supply) is already partially implemented in the heat exchanger 16 (lower risk of overheating).

In the housing of the exhaust gas cooler 16 '(see. Fig. 5 and Fig. 13) or in the inlet funnel 36' a flow guide 90 in the form is an elongated bi-metal strip is arranged or on an edge portion 90 a welded that over extends the entire width of the exhaust gas cooler 16 '.

The flow guide 90 is designed such that it is at relatively low conditions such. B. <180 ° C takes the ge drawn in solid lines and reduces the flow cross-section of the exhaust gas cooler 16 'by about half the height over the entire width (flow cross-section approx. 50%).

As the temperature continues to increase, the flow guide element 90 deforms increasingly in the direction of the lower wall of the inlet funnel 36 'and finally releases the full flow cross-section (shown in dashed lines).

The flow guide 90 can be a bimetal element in a manner known per se or consist of memory material.

Claims (20)

1. Exhaust system for internal combustion engines, in particular in motor vehicles, with an exhaust gas cleaning device and a temperature control device with a heat exchanger arranged in the exhaust gas path between the internal combustion engine and exhaust gas cleaning device, characterized in that the heat exchanger ( 16 , 16 ') acts as a radiation cooler with an outer housing ( 24 , 26 ; 40 , 42 ) with inlet and outlet funnels ( 36 , 38 ) and with at least one inner radiation plate ( 28 , 28 ') radiating from the housing. 2. Exhaust system according to claim 1, characterized in that the Ge housing is formed by two gas-tightly connected half-shells ( 24 , 26 ; 40 , 42 ), between which the at least one radiation plate ( 28 ) is arranged. 3. Exhaust system according to claim 1 or 2, characterized in that the at least one radiation plate ( 28 ') is only via some local connec tion points ( 44 , 46 ) and otherwise air gap insulated in the housing ( 40 , 42 ). 4. Exhaust system according to one of claims 1 to 3, characterized in that within the housing (z. B. 24 , 26 ) pipes ( 40 , 42 ) are provided as gas guides and that within the pipes ( 40 , 42 ) jet tion plates ( 28 ') are arranged. 5. Exhaust system according to one of claims 1 to 4, characterized in that the housing ( 16 ') is formed by a plurality of tubes ( 40 , 42 ) lined up. 6. Exhaust system according to claim 5, characterized in that the tubes with intermediate connecting flanges ( 40 b, 42 b) are also designed as half-shells ( 40 , 42 ). 7. Exhaust system according to one of the preceding claims, characterized in that the radiation plate ( 28 , 28 ') is essentially air-gap-insulated between the half-shells ( 24 , 26 ; 40 , 42 ). 8. Exhaust system according to one of the preceding claims, characterized in that the at least one radiation plate ( 28 , 28 ') has a de ren radiation area increasing configuration. 9. Exhaust system according to claim 8, characterized in that the at least one radiation plate ( 28 , 28 ') is shaped transversely to the exhaust gas flow direction in an undulating or zigzag shape. 10. Exhaust system according to one of the preceding claims, characterized in that the at least one radiation plate (28 ') between the connecting flanges (40 b, b 42) and the edge flanges (40 b, 42 b) of the housing (40, 42) held is. 11. Exhaust system according to claim 10, characterized in that the connections ( 46 ) of the at least one radiation plate ( 28 ') with the housing ( 16 ') act at least partially as sliding guides. 12. Exhaust system according to claim 11, characterized in that the sliding guides are formed by buffers ( 60 ) and or spacers ( 70 ) arranged at the connection points ( 46 ), which in corresponding recesses ( 56 , 58 ) of the connecting flanges ( 40 b, 42 b) leads and the recesses ( 60 , 74 ) of the radiation plate ( 28 ') pass through. 13. Exhaust system according to claim 11, characterized in that the sliding guides are formed by slot-shaped recesses ( 52 ) in the radiation plate ( 28 ') through which projections ( 48 , 50 ) fixed to the housing are firmly connected to one another. 14. Exhaust system according to one or more of the preceding claims, characterized in that the temperature control device is formed only by the heat exchanger ( 16 , 16 '). 15. Exhaust system according to one or more of the preceding claims, characterized in that the at least one radiation plate ( 28 , 28 ') and / or the inner surface of the housing ( 24 , 26 ; 36 , 38 , 40 , 42 ) is coated catalytically effectively are. 16. Exhaust system according to one or more of the preceding claims, characterized in that at least on the underside of the heat exchanger ( 16 , 16 ') a shielding plate ( 80 ) with radiation-permeable openings ( 84 ) is arranged. 17. Exhaust system according to claim 16, characterized in that the radiation plate ( 80 ) is provided with downwardly projecting, splash-water-sending fins ( 86 ). 18. Exhaust system according to claim 16 or 17, characterized in that the fins ( 86 ) are formed out of the openings ( 84 ) and are oriented obliquely to the rear with respect to the direction of travel of the motor vehicle. 19. Exhaust system at least according to claim 1, characterized in that a flow-guiding element ( 90 ) reducing the flow cross-section of this exhaust gas cooler ( 16 ) in defined operating states of the internal combustion engine is arranged in the housing ( 36 '). 20. Exhaust system according to claim 19, characterized in that the flow guide element ( 90 ) in the housing ( 36 ') is fixed and made of Bi-Me tall or memory metal and is designed such that it is temperature-dependent from a position reducing the flow cross-section deforms with increasing temperature into a position which releases the full flow cross section.