DE102018203309B4 - Arrangement of an internal combustion engine with an exhaust tract, motor vehicle and method for controlling an exhaust gas flow - Google Patents

Abstract

Arrangement (1) of an internal combustion engine (2) with an exhaust tract (3) in which at least one first LNT (5), at least one particle filter (6) and at least one second LNT (7) are arranged in the downstream sequence, downstream of the particle filter (6) a fork (12) divides the exhaust tract (3) into a first exhaust line (31) and a second exhaust line (32) which terminates downstream of the fork (12) and upstream of the second LNT (7) at a junction point (14) converge again in the exhaust tract (3), with a heat exchange device (13) being arranged in the area of the exhaust tract (3), in which the second exhaust gas line (32) and at least one oil line (16) are arranged for heat exchange with one another, and wherein in the area of the opening point (14) a valve (15) is arranged.

Description

The invention relates to an arrangement of an internal combustion engine with an exhaust tract, a motor vehicle and a method for controlling an exhaust gas flow in order to control an exhaust gas temperature downstream of a particle filter arranged in the exhaust tract.

In order to remove particles from the exhaust gas, particularly from internal combustion engines operated with diesel, particle filters are arranged in the exhaust gas tract of the internal combustion engine. If the particle load on a filter becomes too high, the exhaust gas emissions are impeded and the filter has to be regenerated. A filter is regenerated by burning the stored particles. A certain temperature is required to start burning the accumulated particulates. The required temperature can be provided, for example, by post-injection of fuel into the internal combustion engine or the exhaust system. If the particles are ignited, the particles ideally burn off on their own until all the soot stored in the filter has been burned.

This means that the regeneration of a particle filter is an exothermic reaction. The resulting high temperatures can have a negative effect on exhaust aftertreatment devices located downstream of the particle filter in the exhaust tract, especially on nitrogen oxide storage catalytic converters.

Nitrogen oxide storage catalytic converters (also called NOx storage catalysts, lean NOx traps, LNT) are used for the temporary adsorption of nitrogen oxides from the exhaust gas of internal combustion engines. In addition, they fulfill tasks of the oxidative after-treatment of carbon monoxide (CO) and hydrocarbons (HC). Nitrogen oxides produced during lean operation of an internal combustion engine can be stored in an LNT; To do this, the LNT oxidizes the nitrogen monoxide (NO) contained in the lean exhaust gas to nitrogen dioxide (NO2) and then stores it in the form of nitrates. Examples of adsorbents used in the coating of the LNT are barium and/or other oxides.

If the storage capacity of the LNT is exhausted, the LNT must be regenerated. In a regeneration event (purge), rich, lean of stoichiometry exhaust gas conditions are provided, e.g., by operating the internal combustion engine with an appropriate fuel-air mixture; The stored nitrogen oxides are desorbed again and reduced to nitrogen on the catalytically active components of the LNT with the help of the components in the rich exhaust gas (CO, HC). In addition to a purge that is only effected for regeneration, the LNT is of course also regenerated if the exhaust gas becomes substoichiometric, e.g. due to a power requirement of the internal combustion engine.

The stored nitrates continue to react in the LNT with molecular hydrogen produced under rich exhaust conditions by incomplete combustion of the fuel and also by reactions in the LNT, which also produce ammonia during regeneration. This ammonia can be harnessed by storing it downstream in a selective catalytic reduction (SCR) catalyst. The stored ammonia is used in the SCR to reduce nitrogen oxides to nitrogen under lean exhaust conditions.

The storage capacity of an LNT is limited, among other things, by the temperature of the exhaust gas. Modern LNTs can store nitrogen oxides in a temperature range of approx. 250 - 550°C with different efficiencies. The temperature range that can be used for LNTs can be expanded by arranging two LNTs in sequence. The first LNT can be arranged spatially close to the internal combustion engine in order to quickly reach its operating temperature after a cold start and to remain in the usable temperature range at operating points with low loads. If the exhaust gas temperature in the first LNT, e.g. at high load, should become too high for efficient functioning, the second LNT is at an advantage, which remains in the usable temperature range downstream, since the exhaust gas cools down in the exhaust tract. There are also optimal temperature ranges for the function of SCR catalytic converters.

The exhaust gas temperatures are already very high at the start of the regeneration of the particle filter, so that the function of said first LNT, which is arranged upstream of the particle filter, is already restricted. If the exhaust gas temperature downstream of the particulate filter also becomes too high, the function of said second LNT is also limited. High temperatures are also generated during desulfurization of LNT, so that high temperatures are present in the area downstream of the first LNT during desulfurization.

Furthermore, fuel additionally injected into the internal combustion engine for starting a particle filter regeneration leads to the dilution of lubricating oil of the internal combustion engine. Since the oil temperature depends on the number of revolutions and the load of the internal combustion engine, the evaporation of the fuel from the oil is very dependent on the driving style. Short-distance journeys in particular have an unfavorable effect, because one for the Verduns When fuel is removed from the oil, the temperature is not sufficient. After a certain number of regenerations of the particle filter, the oil dilution can lead to fatal damage. The oil dilution can be counteracted at great expense by providing more oil in the internal combustion engine and/or reducing the maintenance intervals.

In the DE 10 2008 028 262 A1 describes a waste heat collection device that collects waste heat from exhaust gas of an internal combustion engine using a loop heat pipe. The waste heat collecting device uses the collected heat to heat a heating medium such as engine coolant and engine oil of the internal combustion engine.

In the DE 10 2010 025 733 A1 shows an automotive heat exchange system suitable for use in an exhaust gas recirculation (EGR) circuit having a split EGR heat exchanger arrangement wherein exhaust gas is used to heat engine oil by means of a first heat exchanger during initial phases of an engine operating cycle, while in later phases of the operating cycle the recirculated exhaust gases are diverted to flow through a second heat exchanger where they are cooled by the engine coolant.

The task is to optimize exhaust aftertreatment.

This object is achieved by an arrangement having the features of claim 1 and by a method having the features of claim 7. Further advantageous configurations of the invention result from the secondary and subclaims, the figures and the exemplary embodiments. The configurations described can be combined with one another in an advantageous manner.

A first aspect of the invention relates to an arrangement of an internal combustion engine with an exhaust tract in which at least one first LNT, at least one particle filter and at least one second LNT are arranged in the downstream sequence, with a fork dividing the exhaust tract downstream from the particle filter into a first exhaust line and a second exhaust line which, downstream of the fork and upstream of the second LNT, converge again into the exhaust tract, with a heat exchange device being arranged in the area of the exhaust tract, in which the second exhaust gas line and at least one oil line are arranged for heat exchange with one another, and wherein a valve is arranged in the area of the opening point.

The arrangement according to the invention is advantageous because the oil-cooled heat exchanger enables the exhaust gas to be cooled during particle regeneration, so that the catalysts arranged downstream of the particle filter, especially LNT, are not restricted in their function by excessively high exhaust gas temperatures. The same also applies to phases of a high load on the internal combustion engine, in which high exhaust gas temperatures occur, as well as for desulfurization of the LNT, in the sense of the method according to the invention, in particular the first LNT, with high exhaust gas temperatures also being provided, which are then also present downstream of the first LNT.

In the arrangement according to the invention, the oil line is particularly preferably designed for conducting engine oil from the internal combustion engine through the heat exchange device and back to the internal combustion engine. As a result, the heat of the exhaust gas can advantageously be used to heat the lubricating oil of the internal combustion engine in order to counteract an undesired dilution of the oil by fuel, which does not sufficiently evaporate when the oil temperature is too low. The terms engine oil, lubricating oil and oil are used here synonymously for oil that is provided in the internal combustion engine for lubrication.

Furthermore, it is preferred if the valve is designed in such a way that, in a first state of the valve, exhaust gas can be routed through the first exhaust gas line to the second LNT. In other words, in the first state the valve is adjusted so that exhaust gas is routed directly to the second LNT without being routed via the heat exchange device. The valve is advantageously a three-way valve, which is well suited for controlling the flow of exhaust gases in the area of three lines. Under operating conditions in which the exhaust gas has a temperature that corresponds to the operating temperature of an LNT, exhaust gas heat can advantageously be used in order to ensure the function of the second LNT.

Furthermore, it is preferred if the valve is designed in such a way that, in a second state of the valve, exhaust gas can be routed through the second exhaust gas line to the second LNT. In other words, in the second state the valve is set in such a way that the exhaust gas is routed indirectly to the second LNT and is routed via the heat exchanger device. In this way, the exhaust gas can advantageously be cooled under operating conditions in which the exhaust gas has a temperature that is too high for an efficient functioning of an LNT. If the exhaust gas heat is given off to the engine oil of the internal combustion engine, the engine oil can advantageously be heated, so that the evaporation of fuel from the engine oil is supported. in the second Under certain conditions, heat may also be transferred from the engine oil to the exhaust if the exhaust is too cold for the second LNT to function efficiently. Furthermore, the valve is preferably also designed to be adjusted in such a way that exhaust gas can be routed through both the first and second exhaust gas lines if this is necessary or advantageous under certain operating conditions.

In the arrangement according to the invention, the internal combustion engine is preferably a self-igniting internal combustion engine and the particle filter is a diesel particle filter.

A second aspect of the invention relates to a motor vehicle with an arrangement according to the invention.

• - Betreiben der Brennkraftmaschine,
• - Leiten von Abgas durch die erste Abgasleitung,
• - Leiten von Öl durch die Ölleitung,
• - Erhöhen der Abgastemperatur,
• - Leiten von Abgas durch die zweite Abgasleitung, wenn die Abgastemperatur stromabwärts des Partikelfilters einen bestimmten Schwellenwert überschreitet,
• - Leiten von Abgas durch die erste Abgasleitung, wenn der bestimmte Schwellenwert wieder unterschritten wird.

A third aspect of the invention relates to a method for controlling an exhaust gas flow in an arrangement according to the invention, with the steps:

• - operation of the internal combustion engine,
• - conducting exhaust gas through the first exhaust pipe,
• - conducting oil through the oil line,
• - increasing the exhaust gas temperature,
• - directing exhaust gas through the second exhaust line when the exhaust gas temperature downstream of the particulate filter exceeds a certain threshold,
• - Conducting exhaust gas through the first exhaust pipe when the certain threshold value is undershot again.

The advantages of the method according to the invention correspond to the advantages of the arrangement according to the invention.

In the method, the exhaust gas temperature is preferably increased by injecting an additional quantity of fuel into the internal combustion engine in order to increase the exhaust gas temperature at the start of a regeneration of the particle filter. An increased exhaust gas temperature can also be provided for desulfurization of the LNT, desulfurization of the first LNT being particularly relevant here in terms of the method.

The exhaust gas temperature is preferably determined by sensors downstream of the particle filter. For this purpose, at least one temperature sensor is advantageously arranged in the exhaust tract in the area between the particle filter and the second LNT.

Alternatively or in combination with the sensory determination, the exhaust gas temperature downstream of the particle filter can also be determined based on a model. It is clear to a person skilled in the art how changing certain parameters, e.g. injecting a certain amount of fuel into the internal combustion engine, affects the exhaust gas temperatures.

• 1 eine schematische Darstellung einer Anordnung einer Brennkraftmaschine mit einem Abgastrakt entsprechend dem Stand der Technik.
• 2 eine schematische Darstellung einer erfindungsgemäßen Anordnung in einem ersten Zustand.
• 3 die Anordnung gemäß 2 in einem zweiten Zustand.
• 4 ein Flussdiagramm einer Ausführungsform des erfindungsgemäßen Verfahrens.

The invention is explained in more detail with reference to the figures. Show it:

• 1 a schematic representation of an arrangement of an internal combustion engine with an exhaust system according to the prior art.
• 2 a schematic representation of an arrangement according to the invention in a first state.
• 3 the arrangement according to 2 in a second state.
• 4 a flowchart of an embodiment of the method according to the invention.

1 shows a conventional arrangement 1 of an internal combustion engine 2, as is found in particular in a motor vehicle. The internal combustion engine 2 is a self-igniting internal combustion engine. Alternatively, it can also be a spark-ignited internal combustion engine. The internal combustion engine 2 is supplied with charge air via an intake tract (not shown) and with fuel via injection devices in the intake tract or directly in the combustion chambers of the internal combustion engine. The internal combustion engine 2 is connected to an exhaust tract 3 in order to discharge the exhaust gas produced when fuel is burned. An oil reservoir 4 is provided for providing lubrication for the internal combustion engine, for example an oil pan for wet-sump lubrication or an oil tank for dry-sump lubrication.

Various devices for exhaust gas aftertreatment are arranged in the exhaust tract 3 . A first LNT 5 is arranged immediately downstream of the internal combustion engine 2 . Not shown, but conventionally often located, is an oxidation catalyst, which may be located upstream of the first LNT 5 or provided combined with it in one device. A diesel particulate filter 6 is arranged downstream of the first LNT 5 . Closely coupled or in combination with the diesel particulate filter 6 , a selective catalytic reduction catalyst may be located downstream of the first LNT 5 .

A second LNT 7 is arranged in the exhaust tract 3 downstream of the diesel particle filter 6 . A catalytic converter for selective catalytic reduction 8 is arranged in the exhaust tract 3 downstream of the second LNT 7 . The exhaust tract 3 ends with the exhaust area 9. A temperature sensor 10 is arranged downstream of the diesel particle filter 6 (see 2 ). Further temperature sensors, lambda probes, nitrogen oxide sensors and further measuring devices can be arranged at different points of the exhaust tract 5 . The temperature sensor 10 is connected to a control device 11 , as illustrated by the arrow pointing from the temperature sensor 10 to the control device 11 .

In one embodiment of the arrangement according to the invention as shown in FIG 2 the exhaust tract 3 has a fork 12 into a first exhaust line 31 and a second exhaust line 32 downstream of the diesel particle filter 6 . The first exhaust line 31 leads directly in the direction of the second LNT 7 . The second exhaust line 32 runs through a heat exchange device 13 arranged in the area of the exhaust tract 3 . The first and second exhaust gas lines 31, 32 converge again at a junction point 14 to form a common exhaust gas line, which corresponds to the exhaust tract 3. A three-way valve 15 for controlling the flow of exhaust gas through the first 31 and/or second exhaust pipe 32 is arranged in the area of the discharge point 14 . The three-way valve 15 is connected to the controller 11 as illustrated by the arrow pointing from the controller 11 to the three-way valve 15 .

An oil line 16 which is connected to the oil reservoir 4 runs in the heat exchange device 13 . At least one pump (not shown) is arranged in the oil line 16 and causes the oil to flow from the oil reservoir 4 to the heat exchange device 13 and back.

In the heat exchange device 13, the second exhaust pipe 32 and the oil pipe 14 are arranged with one another in such a way that they run parallel to one another over most of their course within the heat exchange device 13. The exact arrangement of said lines within the heat exchange device 13 is at the discretion of the person skilled in the art.

In 2 3-way valve 15 is shown in a first state in which exhaust gas flow is directed through first exhaust line 31 to second LNT 7 . In the illustrated first state of the three-way valve 15, the second exhaust gas line 32 is blocked for the exhaust gas flow. In 2 For example, the oil line 16 is represented by a broken line to indicate that no oil is pumped through the oil line 16 when the three-way valve 15 is in the first state.

3 basically shows the arrangement according to 2 with the difference that in 3 3-way valve 15 is shown in a second state in which exhaust flow is directed through first exhaust line 32 to second LNT 7 . In the illustrated first state of the three-way valve 15, the second exhaust gas line 32 is blocked for the exhaust gas flow.

Furthermore is in 3 the oil line 16 shown with a solid line. This makes it clear that in the second state of the valve 14 oil is routed from the internal combustion engine 2 through the oil line 16 in order to interact with the exhaust gas. Within the heat exchanger 12, heat can then be transferred from the exhaust gas in the second exhaust line 32 to the oil in the oil line 16, or from the oil to the exhaust gas. Of course, oil can also be conducted through the oil line 16 in the first state of the valve 14 .

The three-way valve 15 is not limited to switching between the first and second states, but may have various opening degrees in which exhaust gas is passed through the first exhaust pipe 31 and the second exhaust pipe 32 in corresponding amounts.

In one embodiment of the method according to 4 the internal combustion engine 2 is operated in a first step S1. Under normal load conditions of the internal combustion engine 2, the three-way valve 15 is switched to the first state; exhaust gas is conducted through the first exhaust pipe 31 in a second step S2. In a third step S3, oil is conducted through the oil line 16. Steps S1 - S3 can run in parallel, ie at the same time.

In a fourth step S4, the exhaust gas temperature is increased. This is done intentionally to control regeneration of the diesel particulate filter 6 to achieve an exhaust gas temperature sufficient to ignite particulates stored in the diesel particulate filter 6 . The exhaust gas temperature can be increased by injecting an additional amount of fuel into the internal combustion engine 2, for example. After the start of the regeneration of the diesel particle filter 6 , the burning of the embedded soot particles also causes very high temperatures downstream of the diesel particle filter 6 . The temperatures are recorded by the temperature sensor 10 and transmitted to the control device 11 . Alternatively, the temperatures can also be determined based on a model.

If the exhaust gas temperature downstream of the particle filter exceeds a certain threshold value, in a fifth step S5 the control device 11 sends a control signal to the Three-way valve 15 granted to switch from the first to the second state, whereupon the first exhaust pipe 31 blocked and the second exhaust pipe 32 is opened. The first threshold is set by the person skilled in the art and corresponds, for example, to a temperature that would be too high for the second LNT 7 to function efficiently. In the second state of the three-way valve 15 , exhaust gas is routed through the second exhaust pipe 32 . Heat is transferred from the exhaust gas in the second exhaust pipe 32 to the lubricating oil of the internal combustion engine 2 in the oil pipe 16.

If the exhaust gas temperature downstream of the particle filter falls below the specific threshold value again, in a sixth step S6 the control device 11 issues a control signal to the three-way valve 15 to switch from the second state to the first state, whereupon the second exhaust pipe 32 is blocked and the first exhaust pipe 31 is opened. With this, exhaust gas is routed through the first exhaust pipe to the second LNT 7 without giving off heat to the oil.

High exhaust gas temperatures are also intentionally provided in step S4 for desulfurizing an LNT, so that the method can also be used for desulfurizing the first LNT 5 and/or the second LNT 7 . The method can also be used in phases of high load, when high exhaust gas temperatures are present.

Reference List

1

arrangement

2

internal combustion engine

3

exhaust tract

31

first exhaust pipe

32

second exhaust line

4

oil reservoir

5

first LNT

6

diesel particulate filter

7

second LNT

8th

Catalyst for selective catalytic reduction

9

exhaust area

10

temperature sensor

11

control device

12

crotch

13

heat exchange device

14

muzzle point

15

three-way valve

16

oil line

Claims (10)

Arrangement (1) of an internal combustion engine (2) with an exhaust tract (3) in which at least one first LNT (5), at least one particle filter (6) and at least one second LNT (7) are arranged in the downstream sequence, with a fork (12) dividing the exhaust tract (3) into a first exhaust line (31) and a second exhaust line (32) downstream of the particle filter (6) and downstream of the fork (12) and upstream of the second LNT (7) converge again into the exhaust tract (3) at an outlet point (14), with a heat exchange device (13) being arranged in the area of the exhaust tract (3), in which the second exhaust gas line (32) and at least one oil line (16) are arranged for heat exchange with one another, and with a valve (15) being arranged in the area of the outlet point (14). Arrangement (1) according to claim 1 wherein the oil line (16) is designed to conduct engine oil from the internal combustion engine (2) through the heat exchange device (13) and back to the internal combustion engine (2). Arrangement (1) according to one of the preceding claims, in which in a first state of the valve (15) exhaust gas is routed through the first exhaust pipe (31) to the second LNT (7). Arrangement (1) according to one of the preceding claims, in which in a second state of the valve (15) exhaust gas is routed through the second exhaust pipe (32) to the second LNT (7). Arrangement (1) according to one of the preceding claims, in which the internal combustion engine (2) is a self-igniting internal combustion engine and the particle filter (6) is a diesel particle filter. Motor vehicle with an arrangement according to one of the preceding claims. Method for controlling an exhaust gas flow with an arrangement (1) according to one of Claims 1 - 5 , with the steps: - operating the internal combustion engine (2), - conducting exhaust gas through the first exhaust pipe (31), - conducting oil through the oil pipe (16), - increasing the exhaust gas temperature, - conducting exhaust gas through the second exhaust pipe (32) if the exhaust gas temperature downstream of the particle filter (6) exceeds a certain threshold value, - conducting exhaust gas through the first exhaust pipe (31) if the certain threshold value is undershot again. procedure after claim 7 , wherein the increase in the exhaust gas temperature is effected by injecting an additional amount of fuel into the internal combustion engine (2) in order to increase the exhaust gas temperature at the start of a regeneration of the particle filter (6). procedure after claim 7 or 8th , wherein the exhaust gas temperature downstream of the particle filter (6) is determined by sensors. Procedure according to one of Claims 7 - 9 , wherein the exhaust gas temperature downstream of the particle filter (6) is determined based on a model.

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