JP7553626B2 - Internal combustion engine and related operating method - Google Patents

Description

The present invention relates to an internal combustion engine for a motor vehicle, in particular for a passenger vehicle, having the features set forth in the preamble of claim 1. The present invention further relates to a method for operating such an internal combustion engine.

An internal combustion engine of this kind is known from German Patent Application No. 69722260T2 and has an engine block with at least one cylinder bank with a number of combustion chambers. An exhaust system is connected to the cylinder bank for discharging the exhaust gas flow from the combustion chamber. Furthermore, the internal combustion engine is equipped with an exhaust gas turbocharger, the turbine of which is arranged in the exhaust gas system and through which the exhaust gas flow can flow. An oxidation catalyst is arranged downstream of the turbine in the exhaust gas system. Furthermore, the internal combustion engine is equipped with a secondary air inlet device for supplying secondary air to the exhaust gas flow, which is connected to the exhaust gas system upstream of the oxidation catalyst with respect to the exhaust gas flow via at least one inlet point. With a suitably configured engine control system, the internal combustion engine can be operated in such a way that a substoichiometric mixture is formed in the combustion chamber from fuel and primary air in order to heat the oxidation catalyst during cold start, the secondary air supply system feeding a large amount of secondary air into the exhaust gas flow in which a stoichiometric or superstoichiometric mixture is formed from unburned fuel and secondary air, the mixture finally being ignited in the exhaust gas flow. In the known internal combustion engine, ignition of the mixture takes place in the exhaust gas flow upstream of the turbine in order to make the enthalpy of the exhaust gas flow heated in the turbine available for increasing the power of the internal combustion engine. Ignition of the mixture in the exhaust gas flow is realized in the known internal combustion engine by autoignition, for which reason substoichiometric operation of the internal combustion engine must be carried out in such a way that high exhaust gas temperatures are generated. It should be noted that in the secondary air supply system, a sufficiently high temperature is then maintained in the mixture for autoignition.

According to Patent Document 2, for example, in order to heat the catalyst, a combustible mixture is ignited by an ignition device upstream of the turbine. In this case, hydrogen-containing reformed gas is supplied to the exhaust gas as fuel.

Further internal combustion engines in which the catalyst is heated are known from US Pat. No. 5,399,413, US Pat. No. 5,399,423, and US Pat. No. 5,399,423.

DE69722260T2 European Patent Application Publication No. 1637706 DE69520930T2 GB 2428465 GB 2280128

In the context of increasingly stringent emission legislation, it is necessary for internal combustion engines to be brought to the required operating temperature for exhaust gas aftertreatment as quickly as possible. This applies in particular to the cold start of an internal combustion engine, where the main components of the engine are within the ambient temperature range. Of particular importance in the context of exhaust gas aftertreatment are, in this case, oxidation catalysts for converting unburned or incompletely burned hydrocarbons. For correct operation, these need to be heated to their activation or start-up or light-off temperatures.

The present invention addresses the problem of showing an improvement or at least one alternative embodiment with respect to an internal combustion engine of the above-mentioned type or with respect to a method for operating such an internal combustion engine, characterized in particular by an increased efficiency.

This problem is solved according to the invention by the subject matter of the independent claims. Advantageous embodiments are the subject matter of the dependent claims.

The internal combustion engine according to the invention has an external ignition device for igniting a combustible mixture in the exhaust gas flow, which is arranged in the exhaust gas system downstream of each inlet point of the secondary air introduction device with respect to the exhaust gas flow. Moreover, the external ignition device, also referred to as the ignition device hereinafter, is arranged in the exhaust gas system downstream of the turbine. Furthermore, the ignition device is arranged in the exhaust gas system upstream of the oxidation catalyst. By using such an external ignition device downstream of the turbine, the mixture in the exhaust gas flow can be ignited between the turbine and the oxidation catalyst, so that in this case the released heat is provided to a large extent for heating the catalyst. When the mixture is ignited upstream of the turbine, part of the energy released in this case is absorbed by the turbine, while when it is ignited downstream of the turbine, almost all of the released energy is provided for heating the catalyst. Insofar as the heating of the catalyst can be carried out very quickly, this increases the heating efficiency. The sooner the oxidation catalyst reaches its start-up temperature, the less harmful emissions can reach the environment during operation of the internal combustion engine. Furthermore, by using an external ignition device, the internal combustion engine can be operated so that the exhaust gas temperature is reduced, thereby reducing harmful emissions.

For this purpose, the exhaust gas system can have a separate exhaust gas pipe for several or all combustion chambers of each cylinder bank, which guides the exhaust gas flow from each combustion chamber to an exhaust gas manifold arranged upstream of the turbine with respect to the exhaust gas flow. Such an exhaust gas manifold is often also called an exhaust gas manifold. Usually, all combustion chambers of each cylinder bank are connected to a common exhaust gas manifold. However, split embodiments are also known in which one half of the combustion chamber is connected to a first exhaust gas manifold and the other half is connected to a second exhaust gas manifold.

In accordance with the objective, according to one development, the secondary air introduction device can be provided with a separate inlet point for each combustion chamber of each cylinder bank, which is arranged in the exhaust gas pipe. This ensures that the secondary air is mixed circulatingly with the exhaust gas as quickly as possible, and thus intensively.

Alternatively, the secondary air introduction device can have a common inlet point for all combustion chambers of each cylinder bank, which is arranged downstream of the exhaust pipe in the exhaust manifold or between the exhaust manifold and the turbine. These measures simplify the structure of the secondary air introduction device.

Particularly advantageous is an embodiment in which the secondary air introduction device has a common inlet point for all combustion chambers of each cylinder bank, which is arranged downstream of the turbine of the exhaust gas system. This measure makes it possible to avoid a detrimental interaction of the secondary air introduction with the turbine. In particular, the secondary air introduction, if it takes place upstream of the turbine, can reduce the speed and/or temperature of the exhaust gas flow and thus its enthalpy, so that the power of the turbine is appropriately reduced.

Particularly advantageous is an embodiment in which the exhaust gas system has a mixture-formation chamber arranged between the turbine and the oxidation catalyst at the inlet and the ignition device. Thus, sufficient space is provided in the exhaust gas system for mixing the secondary air with the exhaust gas. The mixture-formation chamber can be formed in this case in the outlet region of the turbine and/or in the inlet region of the oxidation catalyst. It is also conceivable to form the mixture-formation chamber in a separate tube section arranged between the turbine and the oxidation catalyst. According to another advantageous embodiment, a mixer structure is arranged in the mixture-formation chamber, which brings about the mixing of the secondary air with the exhaust gas. Such a mixer structure can be formed, for example, by air flow directing elements or the like.

In another advantageous embodiment, the particulate filter can be arranged in the exhaust system downstream of the oxidation catalyst with respect to the exhaust gas flow. This makes it possible, in particular, to filter soot particles from the exhaust gas flow, which may be generated in the catalyst during the oxidation reaction.

In another embodiment, the internal combustion engine may be configured as an auto-ignition internal combustion engine. As fuel, then, preferably, diesel fuel is used. In diesel engines, the rapid heating of the oxidation catalyst is particularly significant, since efficient modern diesel engines have very little heat dissipation, so that the oxidation catalyst may require a lot of time to reach its activation temperature if no additional measures were taken.

The method according to the invention for operating a turbocharged internal combustion engine with an oxidation catalyst in the exhaust gas system presupposes that during a cold start of the internal combustion engine, the internal combustion engine is operated with a substoichiometric mixture in order to heat the oxidation catalyst. Furthermore, secondary air is supplied to the exhaust gas flow of the internal combustion engine generated during substoichiometric operation, such that a stoichiometric or superstoichiometric mixture is formed in the exhaust gas flow. Furthermore, this stoichiometric or superstoichiometric mixture in the exhaust gas flow is externally ignited downstream of the turbine of the exhaust gas turbocharger and upstream of the oxidation catalyst. By this measure, almost all of the heat generated during the exothermic conversion of the combustible mixture is used to heat the oxidation catalyst, so that the heating process can be carried out particularly quickly.

The secondary air introduction can in this case be carried out upstream of the turbine. The secondary air introduction can in this case be realized cylinder-selectively or collectively for all cylinders. Furthermore, the secondary air introduction can also be realized downstream of the turbine.

The internal combustion engine is usually designed as a piston engine, so that the combustion chamber is formed in a cylinder in which a piston is arranged with an adjustable stroke. In the case of a substoichiometric mixture, a fuel surplus prevails and the corresponding lambda value is less than 1, for example in the range from 0.6 to 0.9. Substoichiometric operation is also called rich operation or rich combustion. In the case of a stoichiometric mixture, the fuel and the air or the oxygen in the air are in a proportion sufficient to convert exactly the entire fuel, in which case all the oxygen is consumed. The associated lambda value is then equal to 1. In the case of a superstoichiometric mixture, there is an excess of air or oxygen. In the case of superstoichiometric operation, the entire fuel is converted, in which case the excess of air or the oxygen in the air remains. The associated lambda value can then be greater than 1, for example in the range from 1.1 to 1.5.

In one embodiment of the internal combustion engine as an in-line engine, the engine block has only one single cylinder bank in which all combustion chambers of the engine block are arranged. In one embodiment of the internal combustion engine as a V-engine, the engine block has two cylinder banks in which half of the combustion chambers are arranged in each case. In the case of two cylinder banks, two separate exhaust gas manifolds with two separate exhaust gas turbochargers are also provided. Purposefully, the exhaust gas manifolds can also be joined together upstream of a common turbocharger. It is clear that the invention can also be implemented appropriately in such an embodiment.

Further important features and advantages of the invention become apparent from the dependent claims, the drawings and the description of the drawings based on the drawings.

It will be appreciated that the features mentioned above and those to be discussed below may be used not only in the respective combinations specified, but also in other combinations or by themselves, without departing from the scope of the present invention. The components mentioned above and those to be discussed below of a higher-level unit, e.g. a separately shown facility, apparatus or arrangement, may form separate components or parts of such a unit, or may be an integrated region or part of such a unit, even if this is shown separately in the drawings.

Preferred embodiments of the present invention are illustrated in the drawings and detailed in the following description, where like reference numbers represent identical or similar or functionally identical components.

1A-1D are highly simplified illustrations of various embodiments of an internal combustion engine; 1A-1D are highly simplified illustrations of various embodiments of an internal combustion engine; 1A-1D are highly simplified illustrations of various embodiments of an internal combustion engine;

In accordance with FIGS. 1 to 3, an internal combustion engine 1 suitable for use in a motor vehicle, preferably a passenger car, has an engine block 2 with at least one cylinder bank 3 and has a number of combustion chambers 4. The combustion chambers 4 are usually formed in cylinders 5 in which pistons, not shown here, are arranged with adjustable strokes. The internal combustion engine 1 is further equipped with an exhaust system 6 which is connected to the cylinder bank 3 and which discharges exhaust gases or exhaust gas streams 7 from the combustion chambers 4. The exhaust gas streams 7 are indicated in this case by arrows. The internal combustion engine 1 is supercharged and for this purpose has an exhaust gas turbocharger 8, the turbine 9 of which is arranged in the exhaust system 6 and the compressor 10 of which is arranged in a fresh air system, not shown here. The turbine 9, in this case, is usually capable of being passed through by the exhaust gas stream 7 and thereby drives the compressor 10.

An oxidation catalyst 11 is arranged in the exhaust gas system 6, and is arranged so that the oxidation catalyst 11 is downstream of the turbine 9 with respect to the exhaust gas flow 7. Optionally, the exhaust gas system 6 can further be equipped with a particulate filter 12, which is arranged downstream of the oxidation catalyst 11 with respect to the exhaust gas flow 7.

Furthermore, the internal combustion engine 1 is equipped with a secondary air introduction device 13, which is here represented exclusively by a symbol representing the supply of secondary air 14 to the exhaust gas flow 7. It is clear that the secondary air introduction device 13 has a suitable conveying device for pushing the secondary air 14, such as a pump or a blower. The supply of the secondary air 14 to the exhaust gas flow 7 is in this case via at least one inlet point 15, via which the secondary air introduction device 13 is connected to the exhaust gas system 6 upstream of the oxidation catalyst 11. The relative positional designations "upstream" and "downstream" in the context of the present invention always relate to the exhaust gas flow and thus to the direction of the exhaust gas flow in the exhaust gas system 6.

The internal combustion engine 1 is further equipped here with an external ignition device 16 or an ignition device 16, which is represented by a lightning bolt in each of Figures 1 to 3. It can be seen that the ignition device 16 is arranged in this case in the exhaust gas system 6 downstream of the turbine 9 and upstream of the oxidation catalyst 11, such that the ignition device 16 can ignite a combustible mixture in the exhaust gas flow 7. The ignition device 16 can be a spark plug, a glow plug, etc.

The internal combustion engine 1 is further equipped with an engine control device 17, which is used to control the internal combustion engine 1 and is connected to the controllable components of the internal combustion engine 1 via control lines not shown here. In particular, the engine control device 17 is connected to the secondary air introduction device 13 and the ignition device 16. The secondary air introduction device 13 can in this case usually be equipped with a conveying device, not shown here, for example a pump or a blower, for pushing the secondary air 14.

The engine control device 17 is here configured to operate the internal combustion engine 1 in order to heat the oxidation catalyst 11 during a cold start of the internal combustion engine 1. For this purpose, the engine control device 17 controls the internal combustion engine 1 or its components in such a way that a substoichiometric mixture is formed and converted from fuel and primary air in the combustion chamber 4. The primary air is in this case air which is supplied to the combustion chamber by the fresh air device described further above. In the case of a substoichiometric mixture, this conversion or combustion takes place incompletely in the combustion chamber 4, so that the exhaust gas contains unburned fuel. By means of the secondary air introduction device 13, the exhaust gas flow 7 is supplied with a large amount of secondary air 14, so that a stoichiometric or rather a superstoichiometric mixture is formed in the exhaust gas flow 7. This mixture is therefore ignitable or combustible. The secondary air 14 can be branched off, in particular at a point suitable for the fresh air device described further above, preferably after the air filter.

The ignition device 16 ignites the ignitable mixture in the exhaust gas flow 7 downstream of the turbine 9 and upstream of the oxidation catalyst 11. This generates a large amount of heat directly at the inlet of the oxidation catalyst 11, which allows the oxidation catalyst 11 to reach its activation temperature quickly and realize its catalytic exhaust gas purification function.

In all the embodiments shown here, the exhaust system 6 has one individual exhaust pipe 18 and one exhaust manifold 19 for each combustion chamber 4 of the cylinder bank 3. The exhaust pipes 18 guide the exhaust gas flow 7 from each combustion chamber 4 to the exhaust manifold 9, which then guides the exhaust gas flow 7 to the turbine 9. The area of the exhaust manifold 19 connected to the exhaust pipes 18 is usually also called the exhaust manifold.

In the embodiment shown in FIG. 1, the secondary air introduction device 13 has one separate inlet point 15 for each combustion chamber 4 of the cylinder bank 3. The inlet points 15 are in this case each arranged at one end of one of the exhaust pipes 18, which is purposefully located away from the exhaust pipe 19.

In the embodiment shown in FIG. 2, the secondary air introduction device 13 has one common inlet point 15 for all combustion chambers 4 of the cylinder bank 3. This inlet point 15 is then arranged downstream of the exhaust pipe 18 of the exhaust manifold 19. If the turbine 9 is not arranged at the outlet end of the exhaust manifold 19, the inlet point 15 is at the outlet end of the exhaust manifold 19 or between the exhaust manifold 19 and the turbine 9. The part of the exhaust system 6 leading from the common inlet point 15 to the turbine 9 is used in this case as a mixing section for mixing the exhaust gases with the secondary air 14.

In the embodiment shown in FIG. 3, the secondary air introduction device 13 has one common inlet point 15 for all combustion chambers 4, as in FIG. 2, but unlike FIG. 2, it is arranged in the exhaust gas system 6 downstream of the turbine 9.

The exhaust gas system 6 may have a mixture-formation chamber 20 between the turbine 9 and the oxidation catalyst 11, in which the secondary air 14 is supplied and which is arranged in the ignition device 16. The mixture-formation chamber 20 may be formed by means of a separate pipe piece 21 connecting the turbine 9 to the oxidation catalyst 11. Alternatively, the mixture-formation chamber 20 may be arranged at the outlet of the turbine 9 and/or at the inlet of the oxidation catalyst 11.

The oxidation catalyst 11 has in this case an annular housing, not shown in detail, arranged in a flow-through catalytically active catalyst body. The particulate filter 12 has in this case an annular housing, not shown in detail, arranged in a flow-through particulate-retaining particulate filter body.

A mixer structure 22 may be arranged in the mixture formation chamber 20 to assist in mixing the secondary air 14 with the exhaust gas flow 7. The mixer structure 22 may have at least one air flow directing element.

In all embodiments, the internal combustion engine 1 may be configured as an externally ignited internal combustion engine 1, i.e. as a gasoline engine, or as a self-ignited internal combustion engine 1, i.e. as a diesel engine.

During normal operation of the internal combustion engine 1, which is usually operated lean or at least at a stoichiometric air-fuel ratio, the fuel supplied to the combustion chamber 4 is converted to a large extent. The remaining unconverted fuel residue is converted in the oxidation catalyst 11.

During a cold start of the internal combustion engine 1, the internal combustion engine 1 is operated with a substoichiometric mixture in order to heat the oxidation catalyst 11. In this case, the substoichiometric exhaust gases that are generated are then enriched with secondary air 14 so that a stoichiometric or rather superstoichiometric mixture is generated in the exhaust gas flow 7. This stoichiometric or rather superstoichiometric mixture in the exhaust gas flow 7 is ignited downstream of the turbine 9 and upstream of the oxidation catalyst 11 by means of an ignition device 16.

Claims (8)

An internal combustion engine (1) for a motor vehicle,
an engine block (2) having at least one cylinder bank (3) with a number of combustion chambers (4),
an exhaust gas system (6) connected to said cylinder bank (3) for extracting an exhaust gas flow (7) from said combustion chamber (4);
an exhaust gas turbocharger (8) whose turbine (9) is arranged in the exhaust gas system (6) and through which the exhaust gas flow (7) can flow,
an oxidation catalyst (11) arranged downstream of the turbine (9) in the exhaust gas system (6) with respect to the exhaust gas flow (7);
a secondary air intake device (13) connected to the exhaust gas system (6) upstream of the oxidation catalyst (11) with respect to the exhaust gas stream (7) via at least one inlet point (15) for supplying secondary air (14) to the exhaust gas stream (7);
an engine control device (17) for controlling the internal combustion engine (1), the engine control device (17) controlling the internal combustion engine (1) during a cold start of the internal combustion engine (1) to heat the oxidation catalyst (11),
--- so that a substoichiometric mixture is formed in the combustion chamber (4),
- by means of said secondary air introduction device (13) a quantity of secondary air (14) is supplied to said exhaust gas stream (7) such that a stoichiometric or superstoichiometric mixture is formed therein,
--- so that the mixture in the exhaust gas stream (7) is ignited,
and an engine control device (17) configured and/or programmed to control an internal combustion engine (1),
the internal combustion engine (1) comprises an external ignition device (16) for igniting a combustible mixture in the exhaust gas flow (7), the external ignition device (16) being arranged downstream of each inlet point (15) of the exhaust gas system (6) and downstream of a turbine (9) with respect to the exhaust gas flow (7) ;
the exhaust gas system (6) comprises a mixture preparation chamber (20) between the turbine (9) and the oxidation catalyst (11), in which the inlet point (15) and the ignition device (16) are arranged,
an internal combustion engine (1), characterized in that said mixture preparation chamber (20) is formed by one separate tube section (21) connecting said turbine (9) to said oxidation catalyst (11) . 2. The internal combustion engine (1) according to claim 1, characterized in that the exhaust system (6) comprises, for several or all of the combustion chambers (4) of the at least one cylinder bank (3), a respective individual exhaust pipe (18) which guides the exhaust gas flow (7) from each combustion chamber (4) to an exhaust gas collecting pipe (19) which is arranged upstream of the turbine (9) with respect to the exhaust gas flow (7). 3. The internal combustion engine (1) according to claim 2, characterized in that the secondary air introduction device (13) has a respective separate inlet point (15) arranged in each of the exhaust gas pipes (18) for each combustion chamber (4) of the at least one cylinder bank (3). 3. The internal combustion engine (1) according to claim 2, characterized in that the secondary air introduction device (13) has a common inlet point (15) for all combustion chambers (4) of the at least one cylinder bank (3) , which is arranged downstream of the exhaust pipe (18) of the exhaust gas collecting pipe (19) or between the exhaust gas collecting pipe (19) and the turbine (9) of the exhaust gas system (6). The internal combustion engine (1) according to claim 2, characterized in that the secondary air introduction device (13) has a common inlet point (15) for all combustion chambers (4) of each cylinder bank (3), which is arranged downstream of the turbine (9) of the exhaust gas system (6). 2. An internal combustion engine (1) according to claim 1 , characterized in that the mixture-forming chamber (20) comprises a mixer arrangement (22) for mixing the secondary air (14) with the exhaust gas. 7. An internal combustion engine (1) according to claim 1 , characterized in that a particulate filter (12) is arranged in the exhaust gas system (6) downstream of the oxidation catalyst (11) with respect to the exhaust gas flow (7). The internal combustion engine (1) according to claim 1, characterized in that the internal combustion engine (1) is configured as a self-ignition internal combustion engine (1).