WO2003054363A1

WO2003054363A1 - Method and device for cooling a catalytic device

Info

Publication number: WO2003054363A1
Application number: PCT/EP2002/012412
Authority: WO
Inventors: Ekkehard Pott; Michael Zillmer
Original assignee: Volkswagen Aktiengesellschaft
Priority date: 2001-12-13
Filing date: 2002-11-07
Publication date: 2003-07-03
Also published as: DE50205720D1; EP1458959A1; EP1458959B1; DE10161398A1

Abstract

The invention relates to a method for cooling a catalytic device (18) in the exhaust gas system (14 20) of an internal combustion engine (12) of a motor vehicle (10) by connecting a passive exhaust gas cooling device (14, 20) upstream whose cooling capacity, which is dependent on the operating states of the vehicle, engine and of the exhaust gas system, cannot be influenced. Said exhaust gas cooling device consists of an exhaust gas cooler (20) and of an exhaust gas section (14), which is connected upstream and/or downstream and whose cooling capacity is correlated with the required power of the motor vehicle (10) for overcoming level road resistances and with the displacement of the internal combustion engine (12). The inventive method is particularly suited for cooling an NOx storage-type catalytic converter (18) connected downstream from a DI spark ignition engine that is shift operable and/or can run lean, since the DI spark ignition engine (12), in the event of a corresponding lowering of the catalytic converter temperature in broad operating ranges, can be operated in an economical lean operation while optimizing consumption. The invention also relates to an exhaust gas system (14 - 20) and to a vehicle (10) for carrying out this method.

Description

Method and device for cooling a catalyst device

The present invention relates to a method for cooling a catalyst device according to the preamble of claim 1 and an exhaust system and a motor vehicle for performing this method.

Catalytic converter devices usually have only a relatively limited optimal thermal working range to ensure proper exhaust gas purification, which for NO _x storage catalytic converters is, for example, between approximately 220 ° C. and 550 ° C. Below this range, they are not yet sufficiently catalytically active to be fully functional and to store the undesired pollutants contained in the exhaust gas as desired and / or to convert them into harmless substances. If higher catalyst temperatures occur, lean gasoline engines must be operated stoichiometrically at the corresponding higher exhaust gas temperatures, although the combustion process would still allow a more economical lean operation associated with low fuel consumption. In addition, as catalyst temperatures continue to rise, thermal aging sets in, which can lead to severe deactivation of the catalyst device or even to catalyst destruction due to overheating. Since the catalytic converter temperature is essentially determined by the temperature of the exhaust gas flowing through, the control, in particular the lowering or at least limitation, of the exhaust gas temperature by engine measures and / or a targeted one is for the proper operation of exhaust gas catalysts and for a consumption-optimized operating mode of the associated internal combustion engine Exhaust gas cooling of particular importance.

In practice, both active and passive exhaust gas coolers are used for exhaust gas or catalyst cooling, which are connected upstream of the catalyst device to be cooled. In the case of a NO _x storage catalyst system with a pre-catalyst device, the exhaust gas cooler is usually arranged downstream of the pre-catalyst device in order to be able to use it with temperature-increasing measures with a correspondingly higher temperature level for better exothermic conversion of exhaust gas pollutants. Active or switchable exhaust gas coolers have a cooling capacity that can be regulated as required within a wide range of cooling capacities that can be specified by design. On the one hand, they can be designed to be sufficiently powerful, without having to fear corresponding disadvantages, in order to reliably prevent any thermal damage to the associated catalytic device in full-load operation with correspondingly high exhaust gas and catalytic converter temperatures. On the other hand, on the other hand, their cooling capacity can usually be reduced to at least close to the level of a simple exhaust pipe, so that, as for example in the case of desulfurization, they also enable the effectiveness of the catalyst temperature-increasing measures required due to operating conditions.

Such a large cooling capacity range can be achieved, for example, by using an exhaust gas cooler with a powerful exhaust gas heat exchanger for the actual exhaust gas cooling and an associated bypass line, in which, depending on the cooling requirement, any proportion of an incoming exhaust gas mass flow by means of a suitable exhaust gas control device, e.g. an exhaust gas flap device for cooling as required through the exhaust gas heat exchanger or through the bypass line almost uncooled past it. However, differently designed controllable or switchable exhaust gas coolers are known, the cooling capacity of which, for example, by controlling the cooling air flow and / or the cooling air flow by means of suitable cooling air guiding devices, such as e.g. controllable air or louvre flaps and / or cooling air channels, is adjustable in wide ranges. To increase the cooling capacity, controllable exhaust gas coolers can optionally also comprise a combination of different cooling mechanisms or cooling devices, the use of special cooling media also being conceivable for better heat dissipation to the environment.

Active exhaust gas coolers, however, are often designed to be technically complex due to their control and regulating devices for setting the cooling output as required. Due to the desired high maximum cooling capacities, they are also of a correspondingly large size, so that they have a large space requirement and practical use is associated with a correspondingly high cost. Despite these disadvantages, they are used due to their high cooling capacities which can be reduced as required, in particular in conjunction with NO _x storage catalytic converter systems, in order to keep them in the widest possible operating ranges in a working temperature range required for proper exhaust gas purification. Passive, non-switchable exhaust gas coolers with their non-controllable (but dependent on the vehicle, engine and exhaust system operating state) cooling capacity, on the other hand, are usually not only technically much simpler but also noticeably more compact than active exhaust gas coolers, so that they require a significantly lower cost compared to them and need noticeably less space for installation. However, these major practical advantages are offset by the not inconsiderable disadvantage that their cooling capacity can in practice only be selected as a compromise between conflicting technical requirements. On the one hand, because of their cooling capacity, which cannot be actively reduced, they may only be designed to be significantly weaker than active exhaust gas coolers, so as not to reduce the effectiveness of catalytic converter temperature-increasing measures in light-off and de-sulfation by excessive exhaust gas cooling. For _NOx - storage catalyst systems they can not in particular be designed so powerful that under certain operating conditions unacceptably high in the associated primary catalytic converter or even catalyst-damaging exhaust and catalytic converter temperatures might be required to the _NOx - storage catalyst system with compensation of the high heat loss through the exhaust gas cooler to heat up as required. On the other hand, passive exhaust gas coolers, on the other hand, must also be designed to be as powerful as possible in order to keep the catalytic converter device to be cooled in an operating temperature range required for proper exhaust gas purification by sufficiently high heat dissipation in the widest possible operating ranges. In particular, however, they must at least be designed to such an extent that any thermal damage to the catalyst device in full-load operation with correspondingly high exhaust gas and catalyst temperatures is reliably prevented.

The object of the present invention is to provide an improved cooling method for a catalyst device by means of an upstream exhaust gas cooler, which on the one hand is as cost-effective and space-saving as possible, but on the other hand not only offers sufficiently high protection against impermissibly high catalyst temperatures but also a high effectiveness of measures which increase the catalyst temperature enables and thereby combines the advantages of passive or active exhaust gas cooling as well as possible. The method sought is intended in particular to be suitable for cooling a NO _x storage catalytic converter connected downstream of a Dl gasoline engine which is capable of shift operation and / or is lean-running, in order to ensure that the Dl gasoline engine is always sufficient to be able to operate high catalyst cooling in wide operating areas in an economical, lean operation. The task also consists in creating an exhaust system and a motor vehicle for carrying out this method.

This object is achieved according to the invention by connecting a passive exhaust gas cooling device, the cooling capacity of which is selected as a function of the required output of the assigned motor vehicle in order to overcome the driving resistance in the plane during stationary vehicle operation and the displacement of the internal combustion engine of this motor vehicle. With increasing demand and a higher displacement, an appropriately adapted, more powerful exhaust gas cooling device is used in order to compensate for the expected higher exhaust gas temperatures and to be able to cool the catalyst device as required. The exhaust gas cooling device here comprises a passive exhaust gas cooler and an upstream and / or downstream exhaust line. It encompasses all gas-carrying exhaust gas ducts of the exhaust system or exhaust system involved in the heat exchange. In the NO _x storage catalytic converter system described in more detail below, the exhaust gas cooling device thus includes, for example, the entire exhaust gas path between the preliminary and main catalytic converter devices.

The exhaust gas cooler is selected so that its cooling capacity PKWT100 in kW in conjunction with an upstream exhaust line connecting the exhaust gas cooler with a pre-catalytic converter during stationary vehicle operation in the plane with a constant driving speed of 100 km / h in the warm operating state of the internal combustion engine at an ambient temperature of 20 ° C, a relative humidity of 20 ... 80% and a wind speed of less than 3 m / s according to

PKWT100 = f • PBFZG100 • (1.6 / VH) ⁿ is correlated with the demand power PBFZG100 of the motor vehicle in kW given the operating conditions and the displacement VH in liters. A value between 0.3 and 0.8, but preferably between 0.35 and 0.55, is selected for the parameter n, while a value between 0.30 and 0.55, but preferably between 0, is selected for the parameter f. 32 and 0.38 is selected. In the case of an internal combustion engine with a displacement of 1.6 I, the cooling power PKWT100 of the associated exhaust gas cooler is therefore proportional to the demand power PBFZG100 of the motor vehicle for overcoming the driving resistance in the plane by a factor of f. The cooling capacity of the exhaust gas cooler or the exhaust gas cooling device is preferably limited by a minimum value and a maximum value so that on the one hand there is always a sufficiently high cooling capacity to avoid impermissibly high catalyst temperatures and on the other hand the effectiveness of measures to increase the catalyst temperature due to excessive heat dissipation is not too great to reduce. The minimum and maximum value as the lower or upper limit for the cooling capacity is selected in such a way that an incoming exhaust gas mass flow through the exhaust gas cooling device under the specified operating conditions by at least 75 K or by a temperature value corresponding to a cooling capacity of 2.5 kW or by 250 K or can be cooled or cooled by a temperature value corresponding to a cooling capacity of 8.5 kW.

The method according to the invention is preferably used for cooling a NO _x storage catalytic converter connected downstream of a stratified and / or lean running internal combustion engine, in order to be able to operate it in a lean mode in a manner that is optimized for consumption in wide operating ranges by correspondingly lowering the catalytic converter temperature.

An exhaust system for carrying out this method comprises a catalytic converter and an upstream passive exhaust gas cooling device with a cooling capacity which cannot be influenced by the vehicle, engine and exhaust system operating state and which has the required power of the associated motor vehicle to overcome the driving resistance in the plane in a stationary vehicle mode and the displacement of the internal combustion engine of this motor vehicle is correlated. The exhaust gas cooling device here comprises a passive exhaust gas cooler and an upstream and / or downstream exhaust line. It encompasses all gas-carrying exhaust gas ducts of the exhaust system or exhaust system involved in the heat exchange. In the case of the NO _x storage catalytic converter system described here, it thus includes, for example, the entire exhaust gas path between the upstream and the main catalytic converter device.

The cooling capacity PKWT100 of the exhaust gas cooling device in kW with stationary vehicle operation in the plane with a constant driving speed of 100 km / h in the warm operating state of the internal combustion engine at an ambient temperature of 20 ° C, a relative humidity of 20 ... 80% and a wind speed of less than 3 m / s is according to

PKWT100 = f »PBFZG100» (1.6 / VH) "with the demand power PBFZG100 of the motor vehicle given in kW to overcome the driving resistance in the plane under the specified operating conditions and the displacement VH of the internal combustion engine in liters, where n is a parameter between 0 , 3 and 0.8, but in particular between 0.35 and 0.55, while f is a parameter between 0.30 and 0.55, but in particular between 0.32 and 0.38.

The cooling capacity of the exhaust gas cooling device is preferably within a performance range limited by a minimum value and a maximum value, the minimum value being 2.5 kW under the above-mentioned operating conditions or corresponding to a cooling capacity at which an incoming exhaust gas mass flow can be cooled or cooled by 75 K while the Maximum value in the above-mentioned operating conditions is 8.5 kW or corresponds to a cooling capacity at which an incoming exhaust gas mass flow can be cooled down or cooled down by 250 K.

The catalyst device preferably comprises a NO _x storage catalytic converter connected downstream of the exhaust gas cooling device.

A motor vehicle for carrying out the method according to the invention comprises an internal combustion engine, in particular a Dl gasoline engine which is capable of shift operation and / or lean-burn operation, and a downstream exhaust gas system of the type described.

Further features and advantages of the method according to the invention and the device according to the invention for carrying out this method result not only from the associated claims - individually and / or in combination - but also from the following description of a preferred embodiment according to the invention in conjunction with the associated one

Fig. 1, which shows a schematic representation of a motor vehicle with an exhaust system according to the invention. The motor vehicle 10 shown in FIG. 1 comprises a conventional shift petrol engine 12 with a displacement of 1.6 l and an engine output of 81 kW. The demand power PBFZG100 of this motor vehicle 10 for overcoming the driving resistance in the plane is when driving at a constant speed of about 100 km / h in homogeneously lean operation in the warm operating state of the DI gasoline engine 12 at an ambient temperature of 20 ° C., a relative humidity from 20 - 80% and a wind speed of less than 3 m / s about 13.4 kW.

The DI gasoline engine 12 is followed by an exhaust system 14-20 designed according to the invention for catalytic exhaust gas aftertreatment of the exhaust gases emitted by it. The exhaust system 14 - 20 comprises an exhaust line 14 with a conventional catalytic converter 16, 18, which consists of a small-volume pre-catalytic converter 16 and a downstream NO _x storage catalytic converter 18 serving as the main catalytic converter. Between these two catalytic converters 16, 18 there is a passive exhaust gas cooling device 14, 20, which cannot be influenced in terms of its vehicle, engine and exhaust system operating state, for further cooling of the incoming exhaust gas mass flow, which includes a passive exhaust gas cooler 20 and the exhaust line 14. Their cooling capacity is about 4.7 kW at a driving speed of about 100 km / h in the plane.

Under the specified operating conditions, the exhaust gas temperature at a driving speed of approximately 100 km / h in the plane behind the pre-catalytic converter 16 is approximately 600 ° C. with an exhaust gas mass flow of approximately 105 kg / h. The exhaust gas cooling device 14, 20 cools the exhaust gas before it enters the NO _x storage catalytic converter 18 to a temperature of approximately 460 ° C., so that a desired catalytic converter temperature, ie the temperature in the middle of the NO _x storage catalytic converter 18, decreases from is less than about 480 ° C. In these operating conditions, the DI gasoline engine 12 can be operated lean, which is associated with a clear consumption advantage over a motor vehicle with an uncooled NO _x storage catalytic converter.

In the case of intermittent desulphation, the catalyst temperature is increased to a value of about 650 ° C., for example by a late ignition, in order to release the stored sulfur under rich operating conditions in homogeneous operation. This desulphation temperature is under the specified operating conditions at a Exhaust gas temperature before the pre-catalyst 16 of about 920 ° C reached. The temperature behind the pre-catalyst 16 is approximately 950 ° C.

If an exhaust gas cooling device 14, 20 with a cooling capacity of noticeably more than 4.7 kW were used under the specified operating conditions, then inadmissibly high pre-catalyst temperatures with thermal damage would have to be applied in order to compensate for the high heat dissipation to the environment in order to compensate for the high heat dissipation of the pre-catalyst 16 would not be excluded.

If, on the other hand, an exhaust gas cooling device 14, 20 with a noticeably lower cooling capacity were used, then the high catalyst temperatures that would result in no consumption-saving lean operation would be possible in wide operating ranges. If, for example, the exhaust gas cooler 20 were dimensioned weaker by approximately 1 kW than in the present exemplary embodiment, a significantly higher exhaust gas temperature would set in front of the NO _x storage catalytic converter than approximately 500 ° C., which would at least be at the upper temperature limit to ensure proper NO _x storage operation would and would be quickly exceeded at higher loads in dynamic driving.

In other motor vehicles 10 with a different driving resistance PBFZG100 in the plane and an internal combustion engine 12 with a different displacement VH, a specially adapted exhaust gas cooling device 14, 20 is used, the cooling capacity of which according to the PKWT100 given the operating conditions

PKWT100 = f • PBFZG100 • (1.6 / VH) ^π correlates with the driving resistance PBFZG100 and the displacement VH. For a motor vehicle 10 with a driving resistance PBFZG100 of 15 kW and a displacement VH of 2 I, for example, depending on the selection of the parameters n and f, a cooling capacity of 3.8-7.7 kW results. For preferred values of n (n = 0.5) and f (f = 0.35), the cooling output is 4.7 kW.

Claims

PATE NTAN SP RU CHE

1. Method for cooling a catalytic converter device (18) in the exhaust system (14 - 20) of an internal combustion engine (12) of a motor vehicle (10) by connecting a passive exhaust gas cooling device (14, 20 that cannot be influenced in its vehicle, engine and exhaust system operating state, depending on the cooling capacity) ), characterized in that an exhaust gas cooling device (14, 20) is used, the cooling capacity PKWT 00 in kW during stationary vehicle operation with a constant driving speed of 100 km / h in the warm operating state of the internal combustion engine (12) at an ambient temperature of 20 ° C , a relative humidity of 20 - 80% and a wind speed of less than 3 m / s according to

PKWT100 = f »PBFZG100» (1.6 / VH) ⁿ is correlated in liters with the demand power PBFZG100 of the motor vehicle (10) specified in kW for overcoming the driving resistance in the plane under the specified operating conditions and the displacement VH of the internal combustion engine (12) , where f and n are parameters with 0.30 <f <0.55 and 0.3 <n ≤ 0.8, respectively.

2. The method according to claim 1, characterized in that the exhaust gas cooling device (14, 20) comprises an exhaust gas cooler (20) and an upstream and / or downstream exhaust line (14).

3. The method according to claim 1 or 2, characterized in that a value between 0.32 and 0.38 is selected for f.

4. The method according to any one of the preceding claims, characterized in that a value between 0.35 and 0.55 is selected for n.

5. The method according to any one of the preceding claims, characterized in that an exhaust gas cooler (20) or an exhaust gas cooling device (14, 20) are used, the cooling capacity of which is within a power range limited by a minimum value and a maximum value.

6. The method according to claim 5, characterized in that the minimum value is selected such that an incoming exhaust gas mass flow can be cooled under the above-mentioned operating conditions via the exhaust gas cooling device (14, 20) by 75 K or by a temperature value corresponding to a cooling capacity of 2.5 kW or cooled.

7. The method according to claim 5, characterized in that the maximum value is selected such that an incoming exhaust gas mass flow under the above-mentioned operating conditions can be cooled by the exhaust gas cooling device (14, 20) by 250 K or by a temperature value corresponding to a cooling capacity of 8.5 kW or cooled.

8. The method according to any one of the preceding claims, characterized in that the exhaust gas is cooled upstream of a NO _x storage catalyst (18).

9. exhaust system (14 - 20) for the internal combustion engine (12) of a motor vehicle (10) with a catalyst device (18) and an upstream passive exhaust gas cooling device (14, 20) with a vehicle power, engine and exhaust system operating state-dependent cooling capacity, characterized that the cooling capacity PKWT100 of the exhaust gas cooling device (14, 20) in kW in a stationary vehicle operation with a constant driving speed of 100 km / h in the warm operating state of the internal combustion engine (12) at an ambient temperature of 20 ° C, a relative humidity of 20 - 80 % and a wind speed of less than 3 m / s PKWT100 = f • PBFZG100 • (1.6 / VH) "is correlated in liters with the demand power PBFZG100 of the motor vehicle (10) specified in kW for overcoming the driving resistance in the plane under the specified operating conditions and the displacement VH of the internal combustion engine (12) , where f and n are parameters with 0.30 <f <0.55 and 0.3 <n <0.8, respectively.

10. Exhaust system according to claim 9, characterized in that the exhaust gas cooling device (14, 20) comprises an exhaust gas cooler (20) and an upstream and / or downstream exhaust line (14).

11. Exhaust system according to claim 9 or 10, characterized in that f is between 0.32 and 0.38.

12. Exhaust system according to one of claims 9 - 11, characterized in that n is between 0.35 and 0.55.

13. Exhaust system according to one of claims 9 - 12, characterized in that the cooling capacity of the exhaust gas cooler (20) or the exhaust gas cooling device (14, 20) is within a power range limited by a minimum value and a maximum value.

14. Exhaust system according to claim 13, characterized in that the minimum value in the said operating conditions is 2.5 kW or corresponds to a cooling capacity in which an incoming exhaust gas mass flow can be cooled by 75 K or is cooled.

15. Exhaust system according to claim 13, characterized in that the maximum value is 8.5 kW under the specified operating conditions or corresponds to a cooling capacity at which an incoming exhaust gas mass flow can be cooled or cooled by 250 K.

16. Exhaust system according to one of claims 9 - 15, characterized in that the catalyst device (18) comprises a NO _x storage catalyst (18).

17. Motor vehicle (10) with an internal combustion engine (12) and a downstream exhaust system (14 - 20) according to one of claims 9 - 16.

18. Motor vehicle according to claim 17, characterized in that the internal combustion engine (12) is a shift-operable and / or lean-running DI gasoline engine.