JP4456927B2 - Catalyst heating method and control device for controlling the catalyst heating method - Google Patents

Description

  The present invention relates to lean combustion chamber filling and rich combustion in at least one combustion chamber in the exhaust gas of an internal combustion engine working by direct injection of fuel into the air filling of at least one combustion chamber and spark ignition. The present invention relates to a method for heating an occlusion catalyst arranged behind a pre-catalyst by alternately generating a chamber filling.

  In addition, the present invention provides a combustion chamber fill and rich in lean exhaust gas in an internal combustion engine that operates by direct injection of fuel into the air filling of at least one combustion chamber and spark ignition. The present invention relates to a control device for controlling the heating of an occlusion catalyst disposed behind a front catalyst by alternately generating various combustion chamber fillings.

  Such a method and control device are known on the basis of WO 98/46868.

  The catalysts used generally work only in limited temperature intervals. This temperature interval differs between the pre-catalyst and the post-storage catalyst. Whereas ternary catalysts can reduce and oxidize toxic components over a wide temperature range, the operating temperature range of storage catalysts is generally more strongly limited. In general, the exhaust gas apparatus is designed so that both catalysts work in an allowable temperature range that is acceptable in the wide operating range of the internal combustion engine. If one of the catalysts is likely to deviate from the allowed temperature interval, a heating means is introduced. In this case, this heating means may only be necessary for one catalyst. Therefore, in particular, the NOx storage catalyst must be periodically desulfurized (sulfur desorption). For this purpose, the NOx storage catalyst must be heated to 650 ° C. during operation of the internal combustion engine. In this case, it is desirable to avoid overheating of the front catalyst.

  Two means are known per se for heating the storage catalyst located behind the front catalyst in the exhaust gas of an internal combustion engine.

  According to the first means, high-temperature engine exhaust gas is generated in the exhaust valve. In this case, there is a drawback that the high temperature engine exhaust gas first heats the front catalyst. This allows the precatalyst to be overheated.

  According to a second means, also known as chemical catalyst heating, not only oxygen but also unburned hydrocarbons are fed to one catalyst. Three alternative possibilities for this supply are known.

  The first possibility is based on a Y-shaped exhaust gas device. A Y-shaped exhaust gas device means that the exhaust gas from different cylinders or groups of cylinders is separated first after leaving the cylinder head and before it is thoroughly mixed with the exhaust gas of another cylinder or group of cylinders. Means an exhaust gas apparatus guided to Since different cylinders or groups of cylinders are operated with different fuel / air ratios (air / fuel ratios), one exhaust line guides exhaust gas consisting of rich combustion chamber fills while the other The exhaust gas line guides the exhaust gas consisting of a lean combustion chamber fill. If the storage catalyst is located behind the separated exhaust gas line in the common part of the exhaust system where sufficient mixing takes place, the storage catalyst is heated by a rich and lean exothermic reaction of the exhaust gas. Can do. Since the three-way pre-catalyst is usually arranged in a separated exhaust gas line in such an arrangement, the three-way pre-catalyst is passed only by rich or lean exhaust gas. Therefore, the exothermic reaction is performed only with the occlusion catalyst and not with the three-way catalyst. This configuration is predicated on a partially separated exhaust gas pipe, which is troublesome and expensive.

  Within the framework of the second configuration, the internal combustion engine is operated with a generally rich combustion chamber filling. In this case, air oxygen is supplied to the exhaust gas containing unburned hydrocarbons in front of the storage catalyst. Accordingly, the exothermic reaction is limited to the storage catalyst that is also arranged behind the three-way catalyst. This alternative configuration can certainly also be used in exhaust systems with a common line of exhaust gas from all cylinders or combustion chambers, but with the added advantage of supplying air oxygen to the storage catalyst. Equipment is required.

  Within the framework of the third configuration, the internal combustion engine generates rich exhaust gas and lean exhaust gas alternately. The storage catalyst usually has a higher oxygen storage capacity than the three-way pre-catalyst provided closer to the internal combustion engine, so the chemical provided by the alternating rich and lean operation of the internal combustion engine. A larger part of the energy can be supplied to the storage catalyst. This certainly does not avoid, but is limited to, the pre-catalyst heat load due to the heating required for the desulfurization of the storage catalyst.

  The method described in WO 98/46868 mentioned at the beginning works with this third configuration. The publication relates to an internal combustion engine that can be operated in lean burn mode. In connection with the operation of the internal combustion engine, the lean burn mode can be realized in different ways. Thus, the internal combustion engine can be operated with a homogeneous distribution of a lean air / fuel mixture (mixture) in the combustion chamber.

  Alternatively, an internal combustion engine specially designed for this purpose may be operated with a stratified distribution of fuel / air mixture. In particular, a spark ignition type and gasoline direct injection type internal combustion engine can be operated not only in so-called “stratified combustion operation” but also in so-called “homogeneous combustion operation” during appropriate control.

In stratified combustion operation, the engine is operated with stratified cylinder charge and high excess air to achieve the lowest possible fuel consumption rate. Stratified charge is achieved by slow fuel injection. This fuel injection, in the ideal case, divides the combustion chamber into two zones: the first zone has a flammable air / fuel / mixture cloud near the spark plug. This air / fuel / mixture cloud is surrounded by a second zone. This second zone consists of an isolation layer consisting of air and residual gas. The potential for optimization of consumption comes from the possibility of operating the engine almost without squeezing while avoiding load conversion losses. Stratified combustion operation is favored at relatively low loads.

  At higher loads, where power optimization is central, the engine is operated with homogeneous cylinder filling. This homogeneous cylinder filling is obtained from an early fuel injection during the intake stroke. As a result, more time is provided for mixture formation until combustion. The possibility of this mode of operation for power optimization comes from using the entire combustion chamber volume, for example, to fill with a combustible mixture.

  Further, in a gasoline direct injection engine, fuel may be properly injected into the cylinder after combustion of the engine in the expansion stroke when operating in an excess air condition, i.e., preferably in stratified combustion operation. Here, the post-injected fuel reacts with the excess air portion of the engine combustion in the catalyst. The heat released during the exothermic reaction heats the catalyst. This is known for heating a NOx storage catalyst without a three-way pre-catalyst, based on DE 100 03 366 A1. According to the publication, switching to stratified combustion operation with post injection is performed in order to generate a high heat flow. In this case, it is desirable that the air flow be throttled until the required heat flow is achieved at the required temperature. This throttling is effected by a controlled closing of the throttle valve to a predefined angle or to a predefined opening angle. According to the publication, it is desirable that the mixture composition is close to lambda = 1 for maximum heat release. According to the publication, it is desirable to avoid a temporary mixture concentration increase to a lambda value <1 (rich mixture) due to dynamic driving with varying torque demands. This is because this increase in mixture concentration can exacerbate exhaust emissions in an undesirable manner.

  In other words, according to the publication, for the heating of the individual catalysts, an exhaust gas containing continuously not only oxygen but also unburned hydrocarbons is provided.

  Thus, when the three-way pre-catalyst and the post-storage catalyst are connected in series, it is impossible to avoid that not only the storage catalyst but also the front catalyst is continuously chemically heated. Thus, this measure does not result in a sufficient separation of heating between the pre-catalyst and the post-storage catalyst that must be heated to a temperature above 650 ° C. for desulfurization.

  In an internal combustion engine that is at least temporarily operated with a stratified combustion chamber fill of fuel and air, the amount of fuel injected during the stratified combustion operation defines the torque produced by the combustion. Therefore, the modulation of the air / fuel ratio performed for heating purposes, as proposed in WO 98/46868, has an undesirable effect on torque. According to the publication, this resulting variation in torque is compensated by ignition interference and / or filling interference. If the amplitude of the modulation is limited to a value that still does not produce unacceptably strong torque fluctuations, for example, when there is a slight torque demand, the disadvantage of the oxygen storage capacity of the three-way catalyst and the downstream storage catalyst At a low ratio, the energy supply to the storage catalyst is always insufficient.

  Undesirable torque increases are caused by the portion of the additional fuel that wants to heat the storage catalyst, so that any additional fuel that is injected is directly directed within the storage catalyst by an exothermic chemical reaction. Not provided for proper heating. In other words, the heat released in the catalyst is less than the heat freed in the storage catalyst by a conversion of one hundred percent of the additionally injected fuel. Therefore, the modulation efficiency is not optimal.

In stratified combustion operation of an internal combustion engine, an undesired increase in torque can be strong, so a compensation reduction of the combustion chamber fill with air must be made. This is undesirable for a number of reasons. Therefore, the throttle interference acts initially delayed due to the intake pipe volume. Furthermore, since the effect of throttle interference is distributed over multiple intake strokes of the internal combustion engine, lean combustion chamber filling due to abrupt transition between rich combustion chamber filling and lean combustion chamber filling during throttle interference It is difficult to generate individual fillings with rich combustion chamber filling.
WO 98/46868 pamphlet German Patent Application Publication No. 10043366

  In view of this background, the object of the present invention is to improve a method for heating an occlusion catalyst arranged behind a three-way catalyst, and the method comprises occlusion with improved efficiency of the heating means. Even with the stratified charge combustion operation of a spark ignition type internal combustion engine, which has an increased heat supply to the catalyst, it can be carried out with reduced influence on the torque generation of the internal combustion engine. To allow a rapid transition between lean combustion chamber filling.

  In order to solve this problem, according to the method of the present invention, the internal combustion engine is operated with the stratified combustion chamber filling in the first operation mode, and is operated with the homogeneous combustion chamber filling in the second operation mode. A charge is generated each time in the first operating mode by injection of a first amount of fuel, and a lean combustion chamber charge is ignited each time by spark ignition, and when the selected combustion chamber is filled, Rich combustion chamber fills are generated each time by subsequent fuel injections after spark ignition, in which case the combustion chamber fills and subsequent fuel flows are mutually compared so that an overall oxygen deficiency occurs in the exhaust gas. I tried to harmonize.

  Furthermore, in order to solve this problem, in the control device of the present invention, the control device controls the method.

  The method according to the invention and the control device according to the invention allow the heating of the storage catalyst arranged behind the three-way catalyst by means of an increased heat supply of the heating means to the storage catalyst with improved efficiency. . Heating can be performed even in a stratified combustion operation of a spark ignition type internal combustion engine with a reduced influence on the torque generation of the internal combustion engine, and abruptly between the rich combustion chamber filling and the lean combustion chamber filling. Enable migration.

  According to German Patent Application No. 10043366, the post-injection of fuel into a combustion chamber fill burned under excess air produces a stoichiometric exhaust gas, thereby allowing continuous operation in stratified combustion operation. Compared to heating that generates a heat flow, the present invention has the advantage that the storage catalyst can be heated violently without overheating the pre-catalyst.

  This advantage results from the fact that the present invention takes into account the different oxygen storage capacities of a catalytic device comprising a pre-catalyst and a post-storage catalyst. By injecting the subsequent fuel quantity according to the present invention only at the time of filling the selected combustion chamber, both catalysts are first completely filled with oxygen by the excess oxygen in the exhaust gas formed without post-injection in stratified combustion operation. . Since the oxygen storage capacity of the downstream storage catalyst is generally significantly larger than the oxygen storage capacity of the three-way catalyst, the storage catalyst stores more oxygen.

  Then, according to the invention, unburned fuel is generated by post injection in connection with the lack of oxygen in the exhaust gas. A smaller first part of the unburned fuel reacts with the oxygen storage capacity of the pre-catalyst, whereas a larger part of the fuel additionally metered by post injection reaches the storage catalyst. There, it can react exothermically with the stored oxygen.

  In other words, during the continuous generation of air and unburned fuel in the exhaust gas with an overall stoichiometric exhaust gas composition, there is a risk that a larger portion of the reaction heat will be released in the pre-catalyst. In contrast, the present invention allows a free distribution of reaction heat corresponding to the different oxygen storage capacities of the catalysts involved.

  Due to the greater oxygen storage capacity of the downstream storage catalyst, a greater amount of heat is freed in the storage catalyst. Thereby, compared to German Patent Application No. 10043366, the present invention provides a separation of the amount of heat released in different catalysts arranged in a row.

  Advantageously, the first fuel quantity is set so that a desired torque is generated based on the combustion.

  This embodiment advantageously achieves a sufficient separation of the effects of the first and subsequent fuel quantities on the torque. Since the first fuel quantity is set so that the desired torque is produced, the subsequent fuel quantity provides little or no torque contribution, but instead almost completely of the catalyst. It can be injected late so that it can be used for chemical heating.

  If intense heating of the pre-catalyst is desired without heating of the storage catalyst, an additional metered fuel is sufficient for reaction with the amount of oxygen stored in the pre-catalyst. The post injection can be controlled. Thereby, the heating action can be distributed to both catalysts in a desired manner by controlling the oxygen excess stage in the stratified combustion operation without post injection and controlling the post injection. The heating of the pre-catalyst can be achieved with an overall stoichiometric exhaust gas composition, for example by continuous post-injection, whereas the more intense heating of the post-storage catalyst varies with post-injection. This is achieved with a (rich) exhaust lambda below the stoichiometric air-fuel ratio.

  Further, the lean and rich combustion chamber filling during the operation of the internal combustion engine in the second operation mode is performed before the spark ignition each time, and the third fuel amount and the fourth injection amount of different sizes are performed. In this case, it is advantageous if a lean combustion chamber filling is generated by injection of a third fuel quantity, in which case a rich combustion chamber filling is generated by injection of a fourth fuel quantity. . In this case, these injections are referred to as the third injection and the fourth injection in order to distinguish them from the first injection and the second injection. Thus, in the homogeneous combustion operation, four injections are not performed, but two different injections are performed. Of both injections, one injection is performed for each combustion.

  With this means, known from WO 98/46868 for lean burn mode, a heating action can be obtained even in homogeneous combustion operation. Therefore, heating can be continued even when the control of the internal combustion engine changes from stratified combustion operation to homogeneous combustion operation. This can be caused, for example, by an increased torque demand.

  Furthermore, it is advantageous if the spark ignition of the rich combustion chamber fill is delayed with respect to the spark ignition of the lean combustion chamber fill.

  This embodiment has the advantage that the modulation of the air / fuel ratio in homogeneous combustion operation does not affect the torque. The torque increase that can be expected during the conversion control from the third fuel amount to the fourth fuel amount is reduced by the late adjustment of ignition that decreases the torque.

  It is also advantageous to set the spark ignition delay to produce the same torque based on the combustion of the lean and rich combustion chamber fills.

  This advantageously provides complete compensation for the effects of mixture changes on torque transmission.

Further, conversion between the first operation mode and the second operation mode is performed, and in this case, a homogeneous rich combustion chamber that is ignited with delay at the time of transition from the first operation mode to the second operation mode. A rich combustion chamber that causes the charge to follow the stratified lean combustion chamber charge and ignites the stratified lean combustion chamber charge at a time of transition from the second operation mode to the first operation mode. It is advantageous to follow the filling.

  In this way, the transition between the two operation modes can be realized in a torque neutral manner and with the heating action maintained.

  Furthermore, it is advantageous to pre-control lean combustion chamber filling in the second mode of operation, thereby achieving the desired torque to be obtained based on combustion with optimal ignition when maximally lean combustion chamber filling.

  In this way, a maximally lean combustion chamber filling and thus a maximum oxygen supply can be achieved per exhaust stroke of the internal combustion engine. In addition, a wide delay adjustment range for ignition during the transition to rich combustion chamber filling is obtained.

  The present invention performs a rapid changeover from a first operation mode (stratified combustion operation) to a second combustion mode (homogeneous combustion operation) from a predetermined combustion to the next combustion. Since the switching from filling to rich combustion chamber filling takes place, a very late ignition can be carried out immediately. The maximum value of the ignition retard shift is located significantly later than the stoichiometric composition of the combustion chamber filling in the second mode of operation. Therefore, the internal combustion engine can be operated with larger combustion chamber filling than usual in the second operation mode with the same torque.

Based on this, it is possible to convert between the first operating mode with oxygen shortage and the second operating mode without any change in the combustion chamber filling each time.

  This advantageously avoids filling interference to keep the torque constant. Filling fit can be a drawback. This is because this adaptation is relatively slow and requires mechanical interference, eg adjustment of the throttle valve position.

Furthermore, it is advantageous to control the conversion between rich combustion chamber filling and lean combustion chamber filling so that the oxygen storage of the storage catalyst is not completely emptied in a stage with oxygen deficiency.

  In this way, exhaust gas deterioration, for example, generation of unburned hydrocarbons behind the storage catalyst is sufficiently avoided.

Conversion is performed between the first and second operating modes, in which case a homogeneous lean combustion chamber filling is post-injected during the transition from the first operating mode to the second operating mode. The stratified combustion chamber filling with post-injection is replaced with a homogeneous lean combustion chamber stuff at the time of transition from the second operation mode to the first operation mode. It is also advantageous to follow.

  This embodiment makes it possible to maximize the heat supply to the catalytic device, in particular with a larger combustion chamber filling.

  It is also advantageous for the control device to control at least one of the advantageous methods described above.

  Other advantages are apparent from the specification and the accompanying drawings.

  Of course, the features described above in more detail below can be used not only in the combinations described each time, but also in other combinations or individually without departing from the scope of the invention.

  In the following, the best mode for carrying out the present invention will be described in detail with reference to the drawings.

  In FIG. 1, an overall view of an internal combustion engine 12 having an exhaust gas device 14 is shown by reference numeral 10. The internal combustion engine 12 has at least one combustion chamber 16. The combustion chamber 16 is movably sealed by a piston 18. The exchange of the filling in the combustion chamber 16 is controlled via at least one intake valve 20 and at least one exhaust valve 22. The intake valve 20 is operated by an intake valve actuator 24, and the exhaust valve 22 is operated by an exhaust valve actuator 25. Not only the intake valve actuator 24 but also the exhaust valve actuator 25 may be realized by a camshaft as a mechanical actuator, or realized by an electric, electrohydraulic or electropneumatic actuator. May be.

  When the intake valve 20 is opened, the piston 18 sucks air from the intake pipe 28. During the intake stroke and / or the subsequent compression stroke, fuel is metered directly into the combustion chamber 16 via the injection valve 30. The combustible mixture produced in the combustion chamber 16 is ignited (spark ignition) by the spark plug 32.

  When the exhaust valve 22 is opened, the burned residual gas is exhausted from the combustion chamber 16 into the exhaust gas device 14. The exhaust gas device 14 has an exhaust gas pipe 34. In the exhaust gas pipe 34, a front catalyst 36 is disposed between the internal combustion engine 12 and the storage catalyst 38. The pre-catalyst 36 and the storage catalyst 38 have support structures 40 and 42. This support structure 40; 42 is distinguished by its catalyst coating layer. The support structure 40 of the pre-catalyst 36 is usually provided with a coating layer that causes the pre-catalyst 36 to act as a three-way catalyst during lambda = 1 closed loop control.

During lambda = 1 closed loop control, the internal combustion engine 12 is operated alternately with excess oxygen and insufficient oxygen. In this case, the cycle of rich and lean conversion is in the second range. In this case, the pre-catalyst 36 occludes oxygen and nitrogen oxides in the oxygen excess stage, and the oxygen and nitrogen oxides in the oxygen deficient stage, in this case the hydrocarbons and carbon monoxide contained in the exhaust gas and the catalyst React to form carbon dioxide, water and nitrogen. In contrast, when the internal combustion engine 12 is operated for a longer time with a lean mixture, that is, with an excess of oxygen, the nitrogen oxides that are increased and released in this case are retained in the storage structure 42 in the storage catalyst 38. It is received by the catalyst coating layer and occluded in the form of nitrate.

  This nitrate is reduced again by short-time operation of the internal combustion engine 12 with a rich mixture, as is the oxygen stored in the storage catalyst 38 in parallel. Unlike the lambda = 1 closed loop control, the lean stage and the rich stage in which the storage catalyst 38 is operated are not substantially symmetrical. The occlusion catalyst 38 occludes oxygen and nitrogen oxides for a period in the order of minutes, and releases this oxygen and nitrogen oxides again in a converted form in a period in the order of seconds. To do. This allows the engine to run comprehensively lean without a greater amount of nitrogen oxides being increased and released in lean operation being released to the environment.

  Control of the internal combustion engine 12 is performed by the control device 42. This control device 42 processes at least the signal of the air mass meter 44, the signal of the rotational speed sensor 46 cooperating with the transmitter wheel 47, and the signal of the driver intention transmitter 48. Further, the control device 42 includes another sensor (not shown) relating to the signal of the first exhaust gas sensor 50, the signal of the second exhaust gas sensor 51, and the pressure and / or temperature in the region of the internal combustion engine 12 or the exhaust gas device 14. Signal). From these input signals and possibly another input signal, the controller 42 forms a control signal that can operate the internal combustion engine 12 in response to the driver's intention and / or pre-programmed requirements.

  Therefore, for example, the filling of the combustion chamber 16 in the homogeneous combustion operation of the internal combustion engine can be adjusted via the position of the throttle valve 52 operated by the throttle valve actuator 53. In homogeneous combustion operation, the torque produced by the internal combustion engine 12 is primarily defined by the mass of the combustion chamber fill and the selected ignition timing. On the other hand, in the stratified combustion operation, the internal combustion engine 12 is not substantially throttled but operates with the opened throttle valve 52 and the maximum combustion chamber filling of the combustion chamber 16 with air. In this case, the torque generated by the internal combustion engine 12 is markedly defined by the amount of fuel injected and the ignition timing. FIG. 1 qualitatively shows the stratified combustion operation of the internal combustion engine 12. In this stratified combustion operation, a zone 54 having a combustible mixture is formed by injection of a fuel amount through the injection valve 30. This zone 54 is surrounded by air inside the combustion chamber 16 and is ignited by the spark plug 32.

The injection and ignition positions as controlled by the control device 42 to heat the storage catalyst 38 are shown in different operating modes in FIGS. In this case, the height of each hatched digit represents the fuel amount Q to be injected. The injection and ignition positions are each shown relative to the crankshaft angle α. Each line indicated by reference numeral 56 represents an angle at which the intake valve 20 opens. Each line indicated by reference numeral 58 characterizes the top dead center for load conversion . Correspondingly, the lines indicated by reference numeral 60 each characterize the point in time when the intake valve 20 is closed, and the lines indicated by reference numeral 62 indicate the top dead center of the piston 18, respectively. Ignition is performed near this top dead center (ignition top dead center).

  According to FIG. 2, in the stratified combustion operation of the internal combustion engine 12, the injection of the relatively small first injection amount 64 is performed in the compression stroke after the intake valve 20 is closed. This injection during the compression stroke assists in the formation of zone 54 with a combustible mixture. Next, the normal ignition 63 located before the top dead center is performed. The position of the ignition 63 is normally defined so that the combustion of the combustion chamber filling forms the maximum torque. The first injection 64 is set so that the filling of the combustion chamber 16 is lean as a whole.

  When it is desired to heat the storage catalyst 38 for desulfurization (sulfur desorption) in the stratified combustion operation, a subsequent injection 66 is additionally performed on the first injection 64. In this case, the position of this injection is prescribed in advance relative to the crankshaft angle α. In this case, the injection is performed for the first time around the end of the combustion, so that the part in the combustion chamber 16 is no longer combusted or only a small part is combusted. Further, the amount of the subsequent injection 66 is set so that oxygen shortage occurs in the total filling of the combustion chamber 16. This is illustrated in FIG.

  In order to heat the storage catalyst 38 in the stratified combustion operation, the control device 42 alternately controls injection and ignition in accordance with the patterns of FIGS. In this case, the pattern of FIG. 2 is maintained as long as the oxygen storage of the catalysts 36 and 38 is completely satisfied. Injection and ignition are then performed according to the pattern of FIG. This pattern is maintained as long as the oxygen storage of the storage catalyst 38 is almost completely emptied.

  This can be done both in open loop control and in closed loop control. For an open loop controlled implementation, the pattern shown in FIG. 3 is maintained for a pre-defined number of subsequent injections 66. This number of times is set as an expected value for the oxygen storage capacity of the storage catalyst. This expected value may be set to be constant, or may be formed by the control device 14 based on the operation amounts of the internal combustion engine 12 and the exhaust gas device 14. When the closed loop control is performed, the pattern shown in FIG. 3 is maintained as long as the signal of the oxygen sensor 51 disposed behind the storage catalyst 38 indicates that oxygen is insufficient in the exhaust gas. Of course, such a signal of the exhaust gas sensor 51 may be used to correct the expected value formed by the model for the oxygen storage capacity of the storage catalyst 38. This means that it is not necessary to wait for the passage of the storage catalyst 38 due to hydrocarbons and CO during each heating of the storage catalyst 38, thereby eliminating unnecessary HC emissions and CO emissions over a plurality of heating processes. It has the advantage of being reduced.

As already described in detail above, during this means, i.e., control of injection and ignition corresponding to the patterns of FIGS. 2 and 3, each time the pre-catalyst 36 is converted between the patterns of FIGS. It is completely filled with oxygen and the oxygen in the precatalyst 36 is emptied. Due to the larger oxygen storage capacity of the storage catalyst 38, a larger portion of oxygen and fuel supplied into the exhaust gas system 14 undergoes an exothermic reaction in the storage catalyst 38.

FIGS. 4 and 5 show injection / ignition patterns that can maintain the heating of the storage catalyst 38 even in the homogeneous combustion operation of the internal combustion engine 12. The heating process started in the single stratified combustion operation can be maintained even when switching to the homogeneous combustion operation, which can be caused by an increased torque demand, so that the heating process started once is operated in the operating mode. It can also be completely terminated when converting .

  According to the pattern of FIG. 4, a relatively small amount of fuel 68 is injected into the combustion chamber 16 before the intake valve is closed. Thus, the injected fuel amount stays in the combustion chamber 16 for a relatively long time until the ignition 63 and can therefore be distributed almost uniformly in the combustion chamber 16. In this case, the amount of fuel injected is set so that a lean mixture composition and thus oxygen excess is generated in the combustion chamber 16. The ignition 63 is performed when an optimum torque is formed.

  The pattern shown in FIG. 4 is maintained again as long as not only the pre-catalyst 36 but also the storage catalyst 38 is completely filled with oxygen. Next, the injection / ignition pattern shown in FIG. 5 is switched suddenly, that is, from predetermined combustion chamber filling to subsequent combustion chamber filling.

  According to FIG. 5, a larger fuel amount 70 is also injected when the intake valve 20 is opened. In this case, the fuel amount 70 is set so as to cause an oxygen shortage with respect to the combustion chamber filling. If this rich combustion chamber fill is ignited at the point of delivery of optimum torque, an undesirable torque jump can occur. In order to prevent this, a delayed ignition 65 is performed in the pattern of FIG. The position of this ignition 65 is predefined so that torque loss is compensated based on ignition retard shift, and torque benefits are compensated based on richer combustion chamber fill combustion.

  FIGS. 6 and 7 show patterns that allow switching between the stratified combustion operation mode and the homogeneous combustion operation mode during one heating process. The pattern of FIG. 6 corresponds to the pattern of FIG. 2, and thus corresponds to the stratified combustion operation with oxygen excess in the combustion chamber 16. The amount of fuel 64 injected in the pattern of FIG. 6 substantially corresponds to the amount of fuel 68 injected in the homogeneous combustion operation shown in the pattern of FIG. Further, the ignition 63 is performed in the pattern of FIG. 6 so that the same torque contribution is generated from the combustion of the fuel amounts 64 and 68, similar to the pattern of FIG.

  For this reason, the torque contribution of the fuel according to the pattern of FIG. 6 corresponds not only to the torque contribution according to the pattern of FIG. 4 but also to the torque contribution according to the pattern of FIG. The pattern of FIG. 5 is identical to the pattern of FIG. 7, and therefore, the stratified combustion operation with the injection and ignition pattern according to FIG. 6 and the injection pattern according to FIG. It is possible to switch between homogeneous combustion operation with

1 is a schematic view of a direct injection internal combustion engine having an exhaust gas device including a pre-catalyst and a storage catalyst disposed behind the pre-catalyst. FIG. It is a figure which shows qualitatively the position of the 1st injection and ignition in the stratified combustion operation of an internal-combustion engine. FIG. 3 is a diagram qualitatively showing the positions of first injection, ignition and subsequent injection in the stratified combustion operation of the internal combustion engine as controlled alternately with the pattern shown in FIG. 2. It is a figure which shows qualitatively the position of the 3rd injection and ignition in the homogeneous combustion operation of an internal-combustion engine. FIG. 5 is a diagram qualitatively showing the positions of fourth injection and ignition in the homogeneous combustion operation of the internal combustion engine as controlled alternately with the pattern shown in FIG. 4. It is a figure which shows qualitatively the position of the 1st injection and ignition in the stratified combustion operation before change of an operation mode or after change. As controlled alternating pattern shown in FIG. 6 is a diagram qualitatively showing the fourth injection and position of the ignition after or converted prior to conversion operation mode.

  10 General view, 12 Internal combustion engine, 14 Exhaust gas device, 16 Combustion chamber, 18 Piston, 20 Intake valve, 22 Exhaust valve, 24 Intake valve actuator, 25 Exhaust valve actuator, 28 Intake pipe, 30 Injection valve, 32 Spark plug, 34 Exhaust gas line, 36 Pre-catalyst, 38 Storage catalyst, 40 Carrying structure, 42 Carrying structure or control device, 44 Air mass meter, 46 Speed sensor, 47 Transmitter wheel, 48 Driver intention transmitter, 50, 51 Exhaust gas Sensor, 52 throttle valve, 53 throttle valve actuator, 54 zone, 56, 58, 60, 62 wire, 63 ignition, 64 injection, 65 ignition, 66 injection, 68 injection, 70 injection, Q fuel amount, α crankshaft angle

Claims (8)

A combustion chamber lean in at least one combustion chamber (16) in the exhaust gas of an internal combustion engine (12) working by direct injection of fuel into the air filling of at least one combustion chamber (16) and spark ignition In a method for heating a storage catalyst (38) disposed behind a front catalyst (36) by alternately generating a charge and a rich combustion chamber charge, the internal combustion engine (12) In the second operation mode, the operation is performed with the homogeneous combustion chamber filling, and in the second operation mode, the lean combustion chamber filling is operated with the first fuel amount (64 ) And a lean combustion chamber filling is ignited each time by spark ignition (63), and a rich combustion chamber filling is sparked each time in the first operating mode when filling the selected combustion chamber. 63) generated by the subsequent injection of the subsequent fuel quantity (66), in which case the combustion chamber filling and the subsequent fuel quantity are coordinated with each other so that an overall oxygen deficiency occurs in the exhaust gas, and a lean combustion chamber A third amount of fuel of a different magnitude is applied to the charge and the rich combustion chamber charge before each spark ignition (63; 65) when the internal combustion engine (12) is operated in the second operation mode. (68) and a fourth injection quantity (70) injection, in which case a lean combustion chamber charge is generated by a third fuel quantity (68) injection, in this case rich combustion chamber filling. The fuel is generated by injection of the fourth fuel amount (70) , the internal combustion engine (12) is operated in the first operation mode or the second operation mode, and the first operation mode and the second operation mode are Switching between And pre-controlling the lean combustion chamber filling in the second mode of operation, thereby achieving the desired torque desired to be acquired based on the combustion with the optimal ignition when the combustion chamber filling is maximally lean, A catalyst heating method, wherein conversion is performed between a first operation mode accompanied by a shortage and a second operation mode without change in filling of the combustion chamber each time .   The method according to claim 1, wherein the first fuel quantity (64) in the first operating mode is set to produce a desired torque based on the combustion.   The method of claim 1, wherein the spark ignition (65) of the rich combustion chamber fill in the second mode of operation is delayed relative to the spark ignition (63) of the lean combustion chamber fill.   The method of claim 3, wherein the spark ignition (65) delay is set to produce the same torque based on the combustion of the lean and rich combustion chamber fills.   Conversion between the first operating mode and the second operating mode, in this case, a homogeneous rich combustion chamber filling that is ignited with delay upon transition from the first operating mode to the second operating mode Is made to follow the stratified lean combustion chamber filling, and the stratified lean combustion chamber filling is delayed and ignited at the time of transition from the second operation mode to the first operation mode. The method according to claim 1, wherein the method follows. The conversion between the rich combustion chamber filled with lean combustion chamber filling, the oxygen storage of the storage catalyst (38) is controlled so as not completely emptied at the stage accompanied by lack of oxygen, claims 1 to 5, The method according to any one of the above.   Conversion is performed between the first and second operating modes, in which case a homogeneous lean combustion chamber filling is post-injected during the transition from the first operating mode to the second operating mode. The stratified combustion chamber filling with (66) is caused to follow the stratified combustion chamber filling with post-injection (66) during the transition from the second operating mode to the first operating mode. 5. A method as claimed in any one of claims 1 to 4, in which a lean combustion chamber fill is followed. A combustion chamber lean in at least one combustion chamber (16) in the exhaust gas of an internal combustion engine (12) working by direct injection of fuel into the air filling of at least one combustion chamber (16) and spark ignition In the control device (42) for controlling the heating of the occlusion catalyst (38) arranged behind the front catalyst (36) by alternately generating the filling and the rich combustion chamber filling, the control 8. A control device for controlling a catalyst heating method, characterized in that the device (42) is adapted to control the method according to any one of claims 1 to 7 .

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