EP1596046A1 - Apparatus and method for the regeneration of a diesel particulate filter - Google Patents

Abstract

The apparatus has a primary exhaust gas moved in a direction (30) of a common exhaust (22) and arranged for all cylinders. Periodically, on instruction of a motor control, the fuel injected is increased and the hydrocarbon concentration in the exhaust gas increases. The cylinders are divided into two (12, 14) group of cylinders, and in direction of flow before the primary exhaust gas treatment mechanism a secondary exhaust treatment mechanism (20) is provided. The exhaust gases move from the first group of cylinders into the common exhaust. The exhaust gases from the second group of cylinders are moved from the secondary exhaust gas treatment mechanism and into the common exhaust way for all cylinders. In the common exhaust a supercharger is arranged for all cylinders. The secondary exhaust gas treatment mechanism is arranged in a forward direction of flow and the primary exhaust gas treatment mechanism is in flow direction behind the supercharger (32). An independent claim is included for a method.

Description

The present invention relates to an arrangement for treating the exhaust gases a multi-cylinder internal combustion engine according to the preamble of claim 1 and a corresponding method.

As efforts to improve fuel efficiency continue In particular, in diesel engines tends to observe that in novel Combustion modes the CO and HC emissions in the untreated exhaust increase, whereas the exhaust gas temperature at the cylinder outlet decreases. conventional Oxidation catalysts (eg three-way catalysts) must, as generally known - operated in a certain temperature range, so an efficient implementation of the exhaust pollutant components (such as HC or CO) can take place. These temperatures, however, are especially true when the oxidation catalyst in the exhaust gas flow direction behind an exhaust turbocharger is arranged, not easily reached, so that in this If optimal exhaust gas purification is no longer possible and the light-off behavior of the oxidation catalyst is deteriorated after engine start. An additional - z. B. electrical - heating of the oxidation catalyst is basically possible, but increases the design effort and deteriorates the total energy utilization. Another measure to improve catalyst efficiency is an arrangement of the oxidation catalyst closer to the cylinders. However, such a measure comes - especially in a diesel engine with turbocharger - for various reasons regularly out of the question, et al due to lack of space or the risk of overheating. Furthermore It is increasing in diesel engines due to stricter emission standards required, in addition a particulate filter (DPF, diesel particulate filter) in the exhaust path to arrange, for various reasons also not close to the Cylinder - certainly not in front of an exhaust gas turbocharger - can be arranged. Such a particulate filter is immediate in known exhaust treatment arrangements provided behind an oxidation catalyst. For a regular regeneration, d. H. Combustion of soot particles accumulated in the filter, initiate In known particle filter arrangements, the proportion of unburned hydrocarbons in the exhaust gas and thus the exhaust gas enthalpy by a post-injection increased by fuel in the cylinder. This then leads to the oxidation catalyst to an increased oxidation and thus to an exhaust gas temperature increase, the continues on the particle filter and initiates a regeneration there. All in all So it is usually not possible, the oxidation catalyst together with the particulate filter in close proximity to the cylinders - especially before an exhaust gas turbocharger - to order. With a cylinder remote arrangement can However, the necessary emission rates are not achieved in many cases.

The present invention is accordingly based on the object of efficiency to improve the emission control, but at the same time the regeneration a diesel particulate filter should not be affected.

The solution of the above object is achieved with an arrangement according to the Features of claim 1 and by a method with the features of claim 9.

Advantageous embodiments of the present invention are in the dependent Claims described.

The improved exhaust gas purification is achieved in that in addition to the preferably consisting of an oxidation catalyst and a diesel particulate filter Exhaust treatment device, hereinafter referred to as "primary exhaust treatment device" is designated, provided a second exhaust treatment device hereinafter referred to as "secondary exhaust treatment device" is and which is arranged closer to the Zylinderauslaßventilen. Especially the secondary offgas treatment device is preferably in the flow direction still arranged in front of an exhaust gas turbocharger. As a result, the secondary exhaust treatment device supplied hotter gases than this at the Primary exhaust treatment facility would be possible, resulting in more efficient emission control and a better starting behavior is achieved. However, one leads Such secondary exhaust treatment device becomes a problem in regeneration of a particulate filter: The increased hydrocarbon fractions desired in this case in the exhaust gas would already be from the secondary exhaust treatment device oxidized at high conversion rates, so that the erforderl i-che Temperature increase at Primäroxidationskatalysator remaining.

Against this background, it is provided in the invention that the engine having divided for different cylinders exhaust paths, and that only the exhaust gases a first cylinder group of an additional exhaust gas purification by the secondary exhaust treatment device be subjected to, whereas the exhaust gases a second cylinder group past the secondary exhaust gas treatment device become. This arrangement opens up the possibility, as part of the regeneration phase only one post-injection for the cylinders of the second cylinder group provided so that the corresponding exhaust gas with increased enthalpy is fed directly to the primary exhaust treatment device. A post-injection in the cylinder of the first cylinder group, however, is preferably avoided, since this is only an undesirable increase in temperature in the secondary exhaust gas treatment device would affect the fuel economy and damage to the secondary exhaust treatment device can lead. In normal operation - d. H. in the present case, the operation outside the regeneration phase - although only the exhaust gases of the first cylinder group additionally cleaned by the secondary exhaust gas treatment device; this However, in many cases already sufficient to exhaust purification in the required Measures to improve, since the primary exhaust treatment device then exhaust gases can be supplied, which in terms of their CO and HC content the Corresponding emission level with conventional combustion.

In an internal combustion engine with V-shaped cylinder arrangement, it offers structurally, the secondary exhaust gas treatment device in the exhaust manifold for to provide a row of cylinders, whereas in the exhaust manifold of the other row of cylinders no additional exhaust treatment device is provided. alternative Of course it is also possible to use any number of cylinders in to provide the first and second cylinder groups; especially it is conceivable that only the exhaust gases of a single cylinder at the secondary exhaust treatment device be guided past, with this single cylinder then used to generate the high-enthalpy exhaust gas for regeneration is, with the exhaust gases of the remaining cylinders are additionally cleaned can. For this purpose, it may also be provided that several, räu m-Lich Separate secondary exhaust gas treatment facilities used For example, two such devices for both rows of cylinders V-engine, in which case, for example, the exhaust gases of a single cylinder a series only behind the secondary exhaust treatment device in the exhaust manifold are fed so that the respective secondary exhaust treatment device for this cylinder is bypassed.

To irregularities in the engine running in the regeneration phase despite different Injection strategies for both cylinder groups must be avoided the middle pressures of all cylinders at least approximately synchronized or be compensated. For this purpose, sensors can be used which Allow conclusions on the combustion process. These can be integrated cylinder pressure sensors (Arrangement in, for example, the glow plug, the cylinder head gasket or individual) or acceleration sensors (e.g., knock sensors). The adjustments the individual injection quantities or injection curves for each cylinder bank can by means of a suitable (feedback) regulation by a Motor control can be achieved. However, it is still possible for the injections to control exclusively by means of control maps, as in various controls known in the art.

The invention will be explained in more detail by way of example with reference to the drawing.

The single FIGURE shows a schematic diagram of an exhaust treatment system according to the invention. The internal combustion engine shown schematically in the figure 10, which in the specific embodiment is a six-cylinder diesel engine has two rows of cylinders 12 and 14 in V configuration. The exhaust gases from the exhaust valves of the two rows of cylinders are first collected via two separate exhaust manifolds 24, 26, located in front of an exhaust gas turbocharger 32 merge to a common exhaust path 22 for all cylinders. The exhaust gas turbocharger 32 has a turbine located in the exhaust gas flow, on the rotation in a known manner, the intake air is additionally compressed (The inlet branch is not shown in the figure).

In the flow direction behind the exhaust gas turbocharger 32 is a total of 30th characterized primary exhaust gas treatment device provided which is an oxidation catalyst 16 (in this case, a conventional three-way catalyst) and a diesel particulate filter disposed immediately downstream of the flow direction 18 (DPI, diesel particulate filter) has. The diesel particulate filter 18 decreases the soot particles in the exhaust gas. To clog the particulate filter 18 and a related pressure loss to counteract is in a known in the art at regular intervals from a (not shown) electronic engine control a regeneration phase initiated, within which the accumulated soot particles are burned. The time of regeneration can be determined from measured values (eg. B. based on a pressure drop across the particulate filter) or engine operating parameters with regeneration being preferred only in certain, particularly suitable engine operating conditions is performed.

To initiate the regeneration, it is necessary that the temperature of the primary exhaust treatment device 30 is greatly increased. This happens - like out the prior art known in principle - characterized in that a post-injection is made of fuel into the cylinder, through which the primary exhaust gas treatment device 30 supplied exhaust gases an increased proportion of unoxidized Have hydrocarbons. These are then in the oxidation catalyst 16 oxidized. The released heat of combustion then heats up the diesel particulate filter 18 arranged directly downstream in the exhaust path and leads to combustion of soot deposits.

Because of their relatively large space requirements (and others, such as thermal Reasons), the primary exhaust gas treatment device 30 only after the exhaust gas turbocharger 32 can be located at low combustion modes Exhaust gas temperatures sufficient catalyst temperature and thus a sufficient exhaust gas purification by the oxidation catalyst 16 is not always ensured because the exhaust gases cool on the long exhaust path, this Effect is further enhanced by the interposed exhaust gas turbocharger 32. Therefore, partial flows of the exhaust gases to support the oxidation catalyst 16 by a - usually smaller dimensioned - additional oxidation catalyst 20, also known as pre-turbine catalytic converter (PTC, pre turbine catalist, PTC) is purified. This is in the illustrated embodiment only in the exhaust path 26 of the right cylinder bank 14, so that the exhaust gases of the left-hand cylinder bank 12 pass by the oxidation catalytic converter 20 become. Although the oxidation catalyst 20 only a part of the exhaust gases cleans, thereby already a significant improvement in the total exhaust gas purification be achieved on the exhaust pipe and the Anspringverhaltens.

For the regeneration of the diesel particulate filter 18 is from the engine control a Post-injection causes only in the cylinder of the left bank of cylinders 12, so that the resulting exhaust gases with an increased content unburned Hydrocarbons past the additional oxidation catalyst 20 be and as desired first in the oxidation catalyst 16 of the primary exhaust treatment device 30 are oxidized. Because the injection of the other Cylinder bank 14 as far as possible to remain unchanged, the combustion process in the cylinder bank 12, however, influenced by the post-injection is, is by the engine control a corresponding adjustment of the injection to compensate for irregularities in the engine run performed. there can the injection quantities and times for both cylinder rows 12, 14 adapted be, for. B. can the injection quantity in the main injection in the cylinder bank 12 be shortened slightly to the condition caused by the post-injection increased combustion energy (eg., Due to fuel residues, the remain in the cylinder after the discharge stroke). This adaptation can be either through fixed, stored in a table memory intervention done in the injection control. Alternatively, an unround engine can also for example, detected by a high-resolution crankshaft angle sensor and compensated under a feedback scheme.

Although in the embodiment described so far, the cylinders are whole Series 12 can not be additionally catalysed, the number of not addition Catalysed cylinders can also be reduced to the effect of additional To improve exhaust gas purification. For example, in a V-array engine by a further oxidation catalyst 28 (dashed line in the drawing shown), the exhaust gas flow from the two rear cylinders of the left Cylinder row 12 additionally cleaned so that only one cylinder for Carrying out the post-injection remains. It is in principle conceivable that in this cylinder in the regeneration phase by changing the valve timing a combustion is prevented, so that the entire unburned Mixture of the primary exhaust treatment device 30 are supplied can. Such deactivation of combustion is of course also for more than one cylinder possible as long as engine operation is properly maintained can be.

Although the present invention with reference to a diesel engine 10 with a Exhaust gas turbocharger 32 has been described, the inventive idea can also in Related to other emission control equipment, which is a regular Require regeneration, and in other engine types with or without turbocharger be used, for example, in engines with exhaust gas recirculation.

Claims (9)

Arrangement for treating the exhaust gases of a multi-cylinder internal combustion engine (10) in which a primary exhaust gas treatment device (30) is arranged in a common exhaust path (22) for all cylinders periodically at the request of an engine control by changing the fuel injection of a regeneration by increasing the hydrocarbon concentration in the Is subjected to exhaust gas or exhaust enthalpy,
characterized in that
the cylinders are subdivided into a first (14) and a second (12) cylinder group, that in the flow direction before the primary exhaust gas treatment device (30) at least one secondary exhaust gas treatment device (20) is provided, via which the exhaust gases from the first cylinder group (14) are guided and are then passed into the common exhaust path (22), and that the exhaust gases from the second cylinder group (12) are passed to the secondary exhaust gas treatment device (20) in the common exhaust path (22) for all cylinders. Arrangement according to claim 1,
characterized in that
in the common exhaust path (22) for all cylinders an exhaust gas turbocharger (32) is arranged, and in that the secondary exhaust gas treatment device (20) in the flow direction before and the primary exhaust gas treatment device (30) downstream of the exhaust gas turbocharger (32) is arranged. Arrangement according to claim 1 or 2,
characterized in that
the internal combustion engine (10) is designed as a diesel engine, and in that the primary exhaust gas treatment device (30) has an oxidation catalytic converter (16) and a particle filter (18) arranged directly behind it in the flow direction and regularly requiring regeneration for combustion of the soot particles. Arrangement according to at least one of claims 1 to 3,
characterized in that
the secondary exhaust aftertreatment device (20) is designed as an oxidation catalyst. Arrangement according to at least one of claims 2 to 4,
characterized in that
the cylinders of the internal combustion engine are arranged in V-shape in two rows of cylinders (12, 14) with separate exhaust manifolds (24, 26) for each row, which combine in the flow direction upstream of the exhaust gas turbocharger (32) to the common exhaust path (22) for all cylinders wherein the secondary exhaust gas treatment device (20) in the exhaust gas flow path of the exhaust manifold of a cylinder bank (26) is arranged in spatial proximity to the cylinders. Arrangement according to at least one of claims 1 to 5,
characterized in that
the engine control is designed such that a post-injection into the second cylinder group (12) is initiated to carry out a regeneration. Arrangement according to at least one of claims 1 to 6,
characterized in that
the engine control is designed such that during the regeneration process, the mean pressures in the combustion processes in both the cylinders of the first and the second cylinder group (12,14) are adapted to each other so that a smooth engine running is ensured. Arrangement according to claim 7,
characterized in that
individual or all cylinders pressure and / or knock sensors are assigned, and that the engine control is designed such that the injection quantities and / or the injection times are controlled based on the output signals of the sensors such that even in the regeneration mode, the mean pressure of all cylinders is substantially equal , Method for operating an exhaust gas treatment arrangement, which is designed according to at least one of claims 1 to 8,
characterized in that
for the regeneration of the primary exhaust gas treatment device (30) in the cylinders of the second cylinder group (12) a change in the injection takes place such that the hydrocarbon concentration or the enthalpy of the primary exhaust gas treatment device (30) supplied exhaust gas are increased during the injection into the cylinders of the first cylinder group (14) is merely adapted to avoid nonuniformity in engine running.

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