FR2843422A1 - Internal combustion engine exhaust gas temperature increase procedure for catalyst heating on starting uses multiple injection for hybrid charge operation depending on piston head temperature - Google Patents

Abstract

An internal combustion engine (10) exhaust (14) gas temperature increase procedure adjusts (24) the firing angle and uses multiple injection so that a first injection in the aspiration phase gives a uniform fuel distribution and the last injection is in the cylinder (12) compression phase to give a stratified fuel concentration around the spark plug and finishes at an injection angle equal to the uniform charge injection start angle and depending on the piston head temperature (22) or correlated parameter such as time or number of cycles since starting. An internal combustion engine (10) exhaust (14) gas temperature increase procedure adjusts (24) the firing angle and uses multiple injection so that a first injection in the aspiration phase gives a uniform fuel distribution and the last injection is in the cylinder (12) compression phase to give a stratified fuel concentration around the spark plug and finishes at an injection angle equal to the uniform charge injection start angle and depending on the piston head temperature (22) or correlated parameter such as time or number of cycles since starting. An Independent claim is also included for an air flow around a torsion axis perpendicular to the piston movement.

Description

DESCRIPTION

  The present invention relates to a method for raising at least intermittently an exhaust gas temperature of an internal combustion machine by at least one motive measure, the motive measure at least one of comprising an adjustment of the ignition angle and a multiple injection, and during the multiple injection in a time of aspiration and compression of a cylinder of an internal combustion machine, at least two fuel injections being carried out in the cylinder, and the later of these

  injections taking place during a compression time of the cylinder.

  An increase in the combustion temperature respectively of the exhaust gases of an internal combustion machine is desirable in certain operating situations, in particular after a cold start of the engine, when the catalysts connected downstream of the internal combustion have not yet reached their operating temperature. In order for them to be ready for operation, the catalysts must have heated up to reach a starting or ignition temperature specific to the catalysts. In doing so, the starting temperature designates a temperature where the catalyst has a degree of conversion of 50%. Before reaching the time after the cold start of the engine where the catalyst reaches its starting temperature, harmful substances from the exhaust gases enter the atmosphere, mainly unprocessed. Various strategies are known for raising the temperature of the exhaust gases and thus accelerating the heating of the catalyst. We know how to adjust an ignition angle, therefore a moment when the ignition of an air-fuel mixture occurs in a cylinder during heating in the "late" direction relative to an ignition angle to the degree of efficiency. The highest. By adjusting the ignition angle, the combustion efficiency is reduced and the temperature of the exhaust gases is increased at the same time. As a result of the hotter exhaust gases, the heating of the catalysts is accelerated. The late ignition process does not apply to ignition angles where an operating noise of the internal combustion machine increases unacceptably and where reliable ignition can no longer

be guaranteed.

  Another method for raising the exhaust gas temperature is revealed by what is called multiple injection (homogeneous mode) which was described a short time ago for internal combustion machines with direct injection. and positive ignition, for which the fuel is injected directly into the combustion chamber of a cylinder by means of injection valves 10 (WO 00/08328, EP 0 982 489 A2, WO 00/57045). In doing so, a total quantity of fuel to be admitted during an operating cycle of a cylinder is divided into two portions, and is brought into a combustion chamber of the cylinder by two injection processes. A first early injection (homogeneous partial injection) takes place during an aspiration time of the cylinder so that the quantity of fuel injected has an at least mainly homogeneous distribution in the combustion chamber at the time of the next ignition. A second late injection (stratified partial injection), on the other hand, is carried out before ignition during a compression time which follows directly, in particular during the second half of the compression time, and leads to what is called a stratified charge. o the cloud of injected fuel is concentrated mainly in the area which is around a spark plug of the cylinder. Thus, in the multiple injection operating mode of the internal combustion machine, there is a mixed operating mode with stratified charge and with homogeneous charge. The multiple injection mode of operation leads to the possibility of ignition much later than in the single injection mode of operation and thus to an increased exhaust gas temperature compared to the pure homogeneous mode. In addition to the increased temperature of the exhaust gases, another advantage of multiple injection is the reduction of direct emissions 3 o of nitrogen oxide NOx and of unburned HC hydrocarbons which leads to a decrease

  discharge of harmful substances during the heating phase.

  The objective of the invention is therefore based on the provision of a process which produces, in particular in the first 15 seconds after starting the engine, a significant reduction in direct emissions, in particular in emissions

direct from HC.

  This objective is achieved by a process with, in a multiple injection operating mode, the end of priming of an injection angle of the latest injection varies as a function of the temperature of the piston head.

  and / or a correlated substitution.

  In doing so, the invention is based on the following knowledge: in operating mode 10 with multiple injection, an end of priming of an injection angle of the late injection is adjusted at least intermittently between 80 and 10 before an ignition top dead center (TDC ignition) and / or an ignition angle is adjusted at least intermittently between 10 and 45 after TDC ignition. The zones of the injection angle and of the ignition angle are thus, in comparison with known methods, in extremely late phases of a cylinder operating cycle. In this way, exhaust gas temperatures can be produced which go well beyond the mentioned prior art methods. In particular, a faster heating up of at least one first catalyst mounted downstream is obtained in less than 15 s after the end of the start-up.

  2 o from the engine, and a reduction in emissions of harmful substances.

  In a preferred embodiment, the end of priming of the injection angle of the late injection as well as the ignition angle were adjusted at the same time in the mentioned areas of the crankshaft. In this way, particularly late injection and ignition points can be applied in these areas and maximum exhaust gas temperatures can be obtained. In a particularly advantageous embodiment of the method, the end of priming of the injection angle was adjusted between 45 and 25 before TDC ignition, in particular between 40 and 35 before TDC ignition. For the moment of ignition, angles between 20 and 45 after TDC of ignition, in particular between 25 and 35 after

  3 0 TDC ignition, were thus possible.

  The drawback is that in the case of this technique, neither the temperature of the combustion chamber (temperature of the piston head), nor the time elapsed since the engine started, nor another substitution value correlated with the temperature of the piston head are not taken into account. However, this is advisable since the layered injection is fed to the spark plug through the piston head. And with the descending splash of the cold piston head, we could get more fuel build up

  low and thus a reduction in direct HC emissions.

  According to the invention, the end of injection of a stratified partial injection in a multiple injection operating mode (homogeneous stratified mode) is carried out in a variable manner, in close relation with the temperature of the piston head and / or of a substitution value correlated with the temperature of the piston head, for example with the engine running time since starting, the number of ignition processes since engine starting, the cumulative fuel consumption since starting the engine, the temperature of the exhaust gases at the outlet of the engine, the temperature of the coolant, the temperature of the oil and / or the cumulative flow of

  air masses since engine start or the like.

  It has been found advantageous to move, opposite the similar operating point hot enough to operate, the end of injection of the partial injection stratified towards "early" according to a measure which can be predefined, that is that is to say towards larger values of crankshaft before TDC ignition. The process is then controlled so that this offset from the priming end decreases linearly, gradually or decreasing to zero with an increasing temperature of the piston head and / or with a substitution value. in correlation, whereby the setting of a favorable angle for late ignition is however maintained between 20 and 45 after TDC of ignition,

  in particular between 25 and 35 after TDC of ignition, for the moment of ignition.

  This means that in a multiple injection operating mode, the early homogeneous partial injection and / or the end of injection of a late stratified partial injection before TDC of ignition are confronted with a shift dependent on the operating temperature. . The repositioning of the offset with the method according to the invention can take place considerably faster than during a “conventional” homogeneous injection of the known state of the art, since the division carried out into a homogeneous partial injection and a stratified partial injection guarantees very rapid heating of the combustion chamber. Taking into account the temperature of the piston head and / or a correlated substitution value makes it possible to design the process in a way

  essentially even more effective.

  The predefined height of the offset is preferably chosen according to the invention so that, at the start of injection of the homogeneous partial injection, the angle of the crankshaft deviates by the same value from the upper dead center ( OT) of the piston as the angle at the end of injection of a late stratified partial injection before TDC of ignition. This means for example that if the start of injection of a homogeneous injection is at an angle of 280 before 15 TDC ignition (= 80 after TDC), then the angle of end of injection of a

  Late stratified injection is preferably 80 before TDC ignition.

  But you can also choose different values. According to the invention, the end of priming of a stratified partial injection is defined at the latest in a piston angle of 40 before TDC of ignition. In a preferred embodiment, the end of priming of the injection angle of the latest injection is set between and 40, preferably between 80 and 50 before ignition TDC. The values indicated refer to engine revolutions in the range of 600 to 1500 min '. Where appropriate, the angle deviation also varies according to the number of revolutions of the engine and / or of the injection pressure, whereby the deviation generally increases as the number of revolutions of the engine increases, and it decreases when the injection pressure increases. This achievement permanently guarantees a

  optimal time interval for preparing the mixture.

  It is further provided that the multiple injection preferably comprises two injections, a first early partial injection taking place essentially during an aspiration time, in particular during a first half of the aspiration time. Due to the large time difference between the injection time of the early injection and the ignition point, the fuel supplied in the early injection adopts an essentially homogeneous distribution in the combustion chamber of the cylinder at the time of ignition. On the other hand, the second late partial injection preferably takes place in the second half of the compression time and forms at the time of ignition a charge cloud which is essentially in the region of the spark plug of the combustion chamber. . The production of such a layered charge is known in principle to internal combustion machines capable of layered charge, whereby the formation and guidance of the cloud of layered charge can be assisted by suitable configurations of a piston head and / or by construction measures which influence the flow conditions in an air intake pipe, for example in the form of movement valves for loads. In doing so, in the first case, we speak of a stratified charge operation with wall guidance and in the last case, we speak of air-guided operation. Preferably, the present method is used for internal combustion machines in which the operation under stratified charge is maintained by a combination of guiding measures by wall and by air. In this way, it is possible to produce particularly well-defined charge clouds which are therefore suitable for ignition and combustibles. The method has proven itself particularly for internal combustion machines with a stratified charge which operate with an air flow in the combustion chamber which has a torsion axis stretching in particular transversely to the movement.

piston.

  As already explained in the introduction, a mixed fuel preparation of this type (homogeneous / layered) leads to an increase in the temperature of the exhaust gases, and at the same time, to a reduction in the direct emissions of hydrocarbons. unburnt and nitrogen oxides. In doing so, the fuel shares of the two injections are preferably chosen so that the first injection (homogeneous partial injection) leads to a very poor air-fuel mixture, the only non-flammable one, which can only be ignited and burned help from

  cloud of stratified charge of the second injection (stratified partial injection).

  In order to guarantee total combustion of the homogeneous charge, the quantity of fuel supplied into the homogeneous injection should not be below 20% of the total quantity of fuel supplied. Preferably, the proportion of fuel brought into the layered injection amounts to between 50 to 70%, in particular to at least 70%. Preferably, a slightly lean stoichiometric air-fuel mixture is furthermore set to a lambda value between 1 and 1.2. This takes advantage of the fact that a catalyst start-up temperature in a lean exhaust gas atmosphere is always lower than a

stoichiometric atmosphere.

  The process according to the invention for the reduction of direct emissions is to

  preferably used during the heating of at least one catalyst mounted downstream of an internal combustion machine, in particular after starting the engine.

  The method is preferably used to bring at least approximately the direct emissions to their low start-up temperature before the heating of a precatalyst close to the engine.

  The process has the important advantage that thanks to this, the precious metal content of the catalytic coating can be reduced. The precious metal content of the catalyst, in particular of a precatalyst, at least one in number, preferably all the catalysts used, thus amounts to at most 3.59 g / dm 3 of the volume of the catalyst ( 100 g / ft3), preferably at most 2.87 g / dm3 (80 g / ft3). Known catalyst systems of spark-ignition engines suitable for stratified charge and direct injection have considerably higher contents of special metals, namely 3.95 g / dm3 (110g / ftI3), typically at least 4.67 g / dm3 (130 g / ft3), in order to respect in the "NEFZ" 25 (Neuer Europiischer Fahrzyklus / New European driving cycle) HC emissions of less than 0.07 g / km and a NOx emission of less than 0.05 g / km with sulfur-free and non-thermally deteriorated catalysts, and with a stratified operating time share of at least 250 s. (In doing so, a catalyst is designated as being sulfur-free when it has a mass of stored sulfur of less than 0.2 g / dmn3 of the volume of the catalyst.) These high loads of precious metals according to the prior art act against high direct HC emissions to the cold engine compared to conventional injections by suction pipe. Thanks to the process according to the invention described above, the direct HC emissions during the ignition phase of the precatalyst can be reduced in such a way that even when using a catalyst system provided with a precatalyst with a reduced precious metal content according to the invention, which has been subjected to aging in an oven at 1100 ° C. for 4 hours in an atmosphere at 2% O2 and 10% H2O, and using the process according to Invention, HC emissions of 0.1 g / km and NOx emissions of 0.08 g / km are not exceeded in the "NEFZ". Thanks to the reduction in the precious metal content combined with the use of the process according to the invention, compliance with the legal limit values for exhaust gases can be

  thus carried out economically.

  The method according to the invention is also characterized in that the multiple injection comprises two injections, the first early injection taking place essentially during an aspiration time, in particular during a first half of the aspiration time, and the fuel brought into the early injection adopts at the time of ignition an essentially homogeneous distribution in the combustion chamber of the cylinder, and in that the second late injection takes place in the second half of the compression time, and the fuel supplied in late injection is mainly concentrated in the area of a spark plug in the cylinder combustion chamber at the time of ignition, - the multiple injection operating mode is set so that the angle of the piston at the start of injection of a homogeneous partial injection deviates by the same value from the top dead center of the piston as the angle at the end of initiation of the injection partial stratified later before (top dead center of ignition), - the end of priming of the latest injection moves in a maximum of 100 crankshaft turns from at least 20 from the crankshaft to "late", 3 0 - the ignition angle is set between 20 and 45 after the top ignition dead center, in particular between 25 and 35 after the top ignition dead center, the ignition angle is set between 50 and 90 of the crankshaft, preferably between and 80 of the crankshaft after the end of the stratified injection, - the end of priming of the late injection and the ignition angle depend on the temperature of the piston head and / or a correlated substitution value, preferably the engine running time since starting, the number of ignition processes since engine starting, the cumulative fuel consumption since engine starting, the temperature exhaust gases at the engine outlet, coolant temperature, oil temperature, and / or the cumulative flow of 10 air masses since the engine started, and with an increasing piston head temperature and / or with a value of substitution in correlation, decreases linearly, gradually or decreasing to zero, - the internal combustion machine can be ignited by command and operate by direct injection and / or is suitable for the stratified load, - an air flow in the combustion chamber of the internal combustion machine has a torsion axis extending in particular perpendicular to the movement of the piston, and in that - a part of the fuel injected in the late injection amounts to 20 to 90%, of

  preferably 50 to 70%, of a total quantity of fuel injected.

  The invention is explained below in more detail in exemplary embodiments with the aid of the corresponding drawings. Are shown: in Figure 1, schematically, an internal combustion machine with a catalyst system mounted downstream; in FIG. 2, the upper part represents the sequence of a homogeneous fuel injection and the lower part, the sequence of a fuel injection and ignition according to an advantageous configuration of the method according to the invention and in FIG. 3, injection moments over time represented under

form of characteristic curves.

  FIG. 1 shows an internal combustion machine 10 usable with a lean and spark-ignition mixture which comprises for example four

  cylinders 12. The internal combustion machine 10 has a direct injection system not shown by which a fuel injection takes place directly in the cylinders 12. An exhaust gas produced by the internal combustion machine 10 is guided through an exhaust channel 14 and the catalytic system 16, 18 which is arranged there. The catalytic system comprises a small volume precatalyst 16 disposed near the engine as well as a main catalyst 18, for example a NOx storage catalyst which is normally arranged below the body. Regulation of an air-fuel ratio which supplies the internal combustion machine 10 takes place by measuring an oxygen concentration of the exhaust gases using a lambda probe 20.

  A thermal sensor 22 which is arranged downstream of the precatalyst 16 in the exhaust channel 14 makes it possible to measure a temperature of the exhaust gases and thus to deduce therefrom the temperature of the precatalyst and / or of the main catalyst 16, 18. signals made available by the sensors 20, 22 as well as various operating parameters of the internal combustion machine 10 are transmitted to an engine control unit 24 where they are evaluated and processed according to algorithms and recorded characteristic fields. Control of the internal combustion machine 10 by the engine control unit 24 takes place in close relation with these signals, in particular with the air-fuel ratio.

  2 0 of an injection mode as well as ignition.

  When a temperature of the catalytic system, in particular of the precatalyst 16, is evaluated using the thermal sensor 22 as being below a start-up temperature necessary for sufficient conversion of the harmful substances, for example after a when the engine is cold started, the engine control unit 24 triggers various measures to raise the temperature of the exhaust gases. The operation of the internal combustion machine 10 goes in particular from single injection to multiple injection. In doing so, an early first fuel injection 30 takes place, preferably in the first half of a suction time of a cylinder 12, so that the fuel supplied to this injection 30 is present at a time ignition essentially in homogeneous distribution in the combustion chamber (homogeneous partial injection). A second late fuel injection 32 (stratified partial injection) takes place taking into account the determined temperature of the piston head and / or a substitution value correlated with the temperature of the piston head with an end of priming of the injection 32, 5 which is located at least intermittently at engine revolutions between 600 and 1500 min-, at the latest 40 before an ignition top dead center (TDC ignition). The heating of the catalyst is preferably controlled so that the start of injection of the homogeneous partial injection 30 deviates by the same amount of TDC of the piston as the end of the stratified partial injection 32 10 before TDC of ignition . At the same time, an ignition angle 34 in the multiple injection operating mode is adjusted at least intermittently to engine revolutions between 600 and 1500 min 'from 20 to 45, preferably 30, after TDC . The particular combustion processes of the multiple injection operating mode as well as the extremely late ignition result in a rise in the temperature of the exhaust gases and thus a

  accelerated heating of the catalytic system 16, 18.

  The upper part of FIG. 2 represents a position of the piston and a

  conventional homogeneous injection 36 at an ignition angle 38 of 12 after TDC of ignition which represents, according to the state of the art, the moment of ignition as late as possible for an operation poor in HC and without failure d 'ignition.

  An even later ignition time, for example 30 after TDC, is impracticable since poor ignition properties known to all occur with a more misfire rate.

  high and direct HC emissions.

  As can be seen from the lower part of FIG. 2, ignition angles according to the invention can be predetermined at very late ignition times. At a crankshaft angle of at the latest 40 before TDC of ignition is located the late stratified partial injection 32 of the internal combustion machine operating mode at the end (end of priming) of the partial injection 3 o stratified. At this moment, a cloud of charge already reaches the piston head located nearby, the temperature and / or a value of which is correlated with it.

  account for the determination of the end of the stratified partial injection 32, and is guided towards the spark plug. The end of priming is between 120 and 40, preferably between 80 and 30 before TDC ignition, depending on the temperature of the piston head and / or the value correlated with the temperature of the piston head . The ignition 34 can take place when the piston is already in downward movement, in particular in an ignition angle of 20 to 35 after TDC ignition, preferably 30 after TDC ignition. The ignition angle of the ignition 34 is preferably chosen so that it is located from 50 to 90, in particular 60 to 80 after the end of priming of the layered partial injection 32 32.

  In Figure 3 are shown characteristic curves of the injection moments over time. A characteristic curve 40 is drawn there for the end of priming of the laminated partial injection 32 between a moment tl and a moment t2. The end of priming is indicated here as the angle of the crankshaft before TDC _5 ignition over time. The moment t, here defines the beginning of what is called the heating of the catalyst while the moment t2 defines the end of the heating of the catalyst, for example after starting the engine. It is clear that the end of priming of the stratified partial injection 32 moves in time in the direction of the ignition TDC. While at time t1, the end of priming 20 is still within a crank angle of 80 before TDC ignition, it decreases until a time t3 to reach a value of 50 before TDC ignition. This crankshaft angle of 50 before TDC ignition remains constant over the entire time interval t3 to t2. It is also clear that the characteristic curve of the end of priming of the stratified partial injection 32 over time first decreases linearly until time t3, and then remains

  constant. According to additional embodiments not shown, the characteristic curve 40 can also descend non-linearly.

  Priming can take place here so that the end of priming of the late stratified partial injection 32 is shifted by at least 20 from the angle of 3 o crankshaft towards "late", c ' that is to say in the direction of the ignition TDC, in the space

  a maximum of 100 crankshaft turns.

  By way of comparison, a characteristic curve 42 is shown in FIG. 3 which explains the course of the start of injection of a homogeneous injection according to the state of the art with respect to the course of the end of priming of the injection partial laminate 32 according to the invention. The characteristic curve 42 shows that in the state of the art, a slow forward movement of the start of injection of the homogeneous injection takes place over time, therefore away from the ignition TDC. In comparison, the invention provides for a rapid return movement from the end of priming of the stratified partial injection 32 towards the ignition TDC. In this way, the desired reduction in the splashing of the piston head with fuel is obtained, so that a rapid rise in the temperature of the exhaust gas occurs and

  thus reducing emissions of harmful substances.

  Particularly late ignition times, and thus particularly high exhaust gas temperatures, can be obtained in the case of combustion processes where the formation and guidance of the stratified charge cloud takes place both by the special form piston head, that is to say by wall guidance, only by suitable air flows which are produced by appropriate configurations of the air intake channel (air guide). Air flows with a torsion axis, which preferably extends transversely to the piston movement, are particularly well suited in the context of the method according to the invention. In the case of the preparation of this mixture, a cloud of the flammable mixture remains for a long time in the area of the spark plug, so that particularly late ignition angles

are possible.

Claims (11)

  1. Method for at least intermittently raising an exhaust gas temperature of an internal combustion machine (10) by at least one motive measure, the motive measure at least one of comprising an adjustment of l angle of ignition and multiple injection, and during multiple injection in a time of aspiration and compression of a cylinder (12) of an internal combustion machine (10), at least two injections of fuel being carried out in the cylinder (12), and the later of these injections taking place during a compression time of the cylinder (12), characterized in that in a multiple injection operating mode, an end of priming of an injection angle of the latest injection varies depending on the temperature   of the piston head and / or of a correlated substitution value.   2. Method according to claim 1, characterized in that the multiple injection comprises two injections, the first early injection taking place essentially during an aspiration time, in particular during a first half of the aspiration time, and the fuel brought into the early injection adopts at the time of ignition an essentially homogeneous distribution in the combustion chamber of the cylinder (12), and in that the second late injection takes place in the second half of the compression time, and the fuel brought into the late injection is mainly concentrated in the area of a spark plug 20 of the combustion chamber of the cylinder (12) at the time of ignition. 3. Method according to claim 1 or 2, characterized in that the operating mode with multiple injection is adjusted so that the angle of the piston at the start of injection of a homogeneous partial injection deviates according to the same 25 value of the top dead center of the piston as the angle at the end of priming of   the stratified partial injection later before the ignition top dead center.   4. Method according to any one of the preceding claims,   characterized in that the end of priming of the angle of injection of the latest injection is set between 120 and 40 before the top dead center of ignition,   preferably between 80 and 50 before top dead center of ignition.   5. Method according to any one of the preceding claims,   characterized in that the end of priming of the latest injection moves 5 in a maximum of 100 crankshaft revolutions of at least 20 from the crankshaft towards "late".   6. Method according to any one of the preceding claims,   characterized in that the ignition angle is adjusted between 20 and 45 after the top ignition dead center, in particular between 25 and 35 after the top ignition dead center 10.   7. Method according to any one of the preceding claims,   characterized in that the ignition angle is adjusted between 50 and 90 of the crankshaft,   preferably between 60 and 80 of the crankshaft after the end of the stratified injection.   8. Method according to any one of the preceding claims, characterized in that the end of initiation of the late injection and the ignition angle   depend on the temperature of the piston head and / or a correlated substitution value, preferably the engine running time since starting, the number of ignition processes since starting the engine, the consumption of cumulative fuel since the engine was started, the 2 o temperature of the exhaust gases at the engine outlet, the coolant temperature, the oil temperature, and / or the cumulative mass flow of air since the engine started, and with an increasing piston head temperature and / or with a correlated substitution value,   decrease linearly, gradually or degressively to zero.   9. Method according to any one of the preceding claims,   characterized in that the internal combustion machine (10) can be ignited by   control and operate by direct injection and / or is suitable for stratified load.   10. Method according to any one of the preceding claims,   characterized in that an air flow in the combustion chamber of the internal combustion machine (10) has a torsion axis extending in   particular perpendicular to the movement of the piston.   11. Method according to any one of the preceding claims, characterized in that a part of the fuel injected in the late injection amounts to 20 to 90%, preferably 50 to 70%, of a total amount of fuel injected.