DE102018216531A1 - Method and device for operating an internal combustion engine with an exhaust tract having a particle filter - Google Patents

Abstract

The present invention relates to a method for operating an internal combustion engine with an exhaust tract having a particle filter, critical material vibrations of the particle filter being prevented, in which it is provided in particular that on the basis of at least one predeterminable, maximum permissible differential pressure in the particle filter at least one of the operating state of the The engine torque-dependent limit value curve of the engine torque is determined (210) and that the internal combustion engine is operated with a maximum engine torque that is limited within the limit value curve.

Description

The invention relates to a method for operating an internal combustion engine, in particular a motor vehicle, with an exhaust tract having a particle filter, according to the preamble of claim 1. The present invention also relates to a computer program, a machine-readable data carrier for storing the computer program and an electronic control device by means of which the the inventive method is feasible.

State of the art

Due to the increasingly strict exhaust gas regulations in the field of exhaust gas emission, the installation of particle filters is not only being considered for self-igniting internal combustion engines (diesel engines) but also for spark-ignited internal combustion engines (petrol engines) with direct fuel injection. Such a particle filter collects and stores particles, in particular soot particles, which are formed during combustion in a manner known per se.

In the case of diesel engines, as soon as a certain amount of soot particles is present in the particle filter, certain engine parameters, e.g. the ignition timing, adjusted so that the exhaust gas is heated to a temperature of about 600 ° C. As soon as this temperature is reached, the control unit changes the air / fuel ratio to a lambda value greater than 1, so that an excess of oxygen is generated in the exhaust gas. This excess of oxygen, in combination with the high exhaust gas temperatures, leads to an oxidation of the soot particles, by means of which the soot particles are converted into carbon dioxide. This oxidation process is called "regeneration". After the particulate filter has been completely freed from soot particles, the lambda value and the exhaust gas heating are reset to a normal operating state.

In the case of gasoline engines, on the other hand, a distinction is made between active and passive regeneration, since there is already a higher exhaust gas temperature level. The so-called “active regeneration” described in the previous section is only carried out if no regeneration can take place using a passive procedure based on pure oxygenation.

Due to the exhaust gas mass flow present during operation of the internal combustion engine, a pressure drop is generated via the particle filter. Since the loading condition of the particle filter also changes during operation, the amount of pressure drop changes accordingly. In addition, the particle filter is also regenerated, particularly when the internal combustion engine is in operation, and the load state of the filter is thereby significantly changed or reduced. In addition, an active regeneration of the particle filter is carried out when a maximum loading of the particle filter is reached and this could not be reduced by passive regeneration.

Disclosure of the invention

The invention is based on the idea of providing a protective function in order to avoid damage to an internal combustion engine or of components in its exhaust tract by excessively high exhaust gas back pressure or pressure pulsations. In particular for a particle filter of an internal combustion engine affected here, the aim is to prevent high differential pressures occurring within the particle filter with such a protective function. The protective function is intended to effectively protect the particle filter from mechanical destruction.

The protective function is also intended to prevent, at the same time, that excessively high exhaust gas back pressures lead to undesired opening of exhaust valves of the internal combustion engine.

The proposed method for operating an internal combustion engine with an exhaust tract having a particle filter, whereby critical material vibrations of the particle filter are prevented, provides in particular that, based on at least one predeterminable, maximum permissible differential pressure in the particle filter, at least one limit value curve of the engine torque that is dependent on the operating state of the internal combustion engine is determined and that the internal combustion engine is operated with a maximum engine torque that is limited within the limit value curve.

It should be noted here that this torque limitation can preferably be implemented by appropriately suitable limitation or limitation of the filling of cylinders (so-called “cylinder filling”) of the internal combustion engine.

It should also be noted that a particle filter affected here according to the prior art is only protected by a temperature protection function. A possible mechanical destruction due to excessive pressure differences and pressure pulsations in the exhaust tract of the internal combustion engine is not taken into account.

In the case of the proposed method, it is also advantageous that the corresponding method steps can be carried out by internal engine measures which already exist in an internal combustion engine concerned here.

In addition, by incorporating pressure difference information along the particle filter made available according to the proposed method, it is possible to react to manufacturing tolerances and different loading conditions of the filter. A pressure limitation carried out according to the proposed method can simply be canceled again after regeneration of the particle filter.

It should be noted here that the pressure difference information or the pressure values on which it is based can be measured or modeled, the pressure difference being assumed as a function of the exhaust gas mass flow or exhaust gas volume flow, the soot loading and the ash loading (as the degree of aging) of the particle filter.

In the proposed method it can be provided that a maximum permissible exhaust gas mass flow or exhaust gas volumetric flow is calculated at a predetermined, maximum permissible differential pressure, as described below, and the limit curve of the engine torque, which is dependent on the operating state of the internal combustion engine, is determined therefrom.

It should first be noted here that in the internal combustion engines affected here, a continuously calculated exhaust gas mass flow is already available as a central variable in their control unit and thus only has to be referenced by the proposed protective function. In order to be able to take into account the temperature curve on the particle filter required for the protective function as a continuous, variable variable in the exhaust gas mass flow, a conversion or conversion of the exhaust gas mass flow into a corresponding volume flow, and vice versa, is required.

This conversion is carried out using the general gas equation p * V = m * R * T, from which the relationship m = (V * p) / (R * T) results from the transformation.

wobei die Größe vfLimnEgp_saved dem limitierten Volumenstrom für die Berechnung der Füllungsbegrenzung, msfabr_fild dem gefilterten Massenstrom, der durch die Auslassventile aus dem jeweiligen Brennraum der Brennkraftmaschine fließt, pDifGpf dem aktuell ermittelten Differenzdruck über den Partikelfilter, pDifGpf_Crit dem maximal zulässigen Differenzdruck über den Partikelfilter, t_CritPDif dem Zeitpunkt, an dem die Drucküberschreitung pDifGpf > pDifGpf_Crit erfolgt, R die Gaskonstante, p_ExhCat dem Abgasdruck vor dem Partikelfilter, T_ExhCat die Abgastemperatur vor dem Partikelfilter, und die Größe msfabr_LimnTCor dem maximal zulässigen Abgasmassenstrom, welcher anhand der Abgastemperatur vor Partikelfilter bereits korrigiert wurde, entsprechen.In the course of the protective function, if the permissible differential pressure is exceeded, a volume flow is calculated based on the currently existing exhaust gas mass flow and preferably temporarily stored, for which the following relationship according to equation 1 applies: $${\text{vfLimnEgp}}_{\text{saved}}\left(\text{t}={\text{t}}_{\text{CritPDif}}\right)=\left({\text{msfabr}}_{\text{fild}}\left(\text{t}={\text{t}}_{\text{CritPDif}}\right)*\text{R}*{\text{T}}_{\text{ExhCat}}\right)/{\text{p}}_{\text{ExhCat}}$$

whereby the variable vfLimnEgp _saved the limited volume flow for the calculation of the charge _limit , msfabr _fild the filtered mass flow that flows through the exhaust valves from the respective combustion chamber of the internal combustion engine, pDifGpf the currently determined differential pressure via the particle filter, pDifGpf _Crit the maximum permissible differential pressure via the particle filter , t _CritPDif the time at which the pressure is exceeded pDifGpf> pDifGpf _Crit , R the gas constant, p _ExhCat the exhaust gas _pressure upstream of the particle filter, T _ExhCat the exhaust gas temperature _{upstream of} the particle filter, and the size msfabr _LimnTCor the maximum permissible exhaust gas mass flow, which is based on the exhaust gas temperature before the particle filter has already been corrected.

The critical point in time t _CritPDif thus exists when the condition is met that pDifGpf> pDifGpf _Crit .

On the basis of the volume flow vfLimnEgp _saved , the correction can be made in real time via the temperature response at the particle filter, which can then be converted into a corrected mass flow according to the following equation 2: $${\text{msfabr}}_{\text{LimnTCor}}=\left({\text{vfLimnEgp}}_{\text{saved}}*{\text{p}}_{\text{ExhCat}}\right)/\left(\text{R}*{\text{T}}_{\text{ExhCat}}\right).$$

in der die Größe ratChrgRednPfilDifP die maximal zulässige Füllung in Abhängigkeit vom Differenzdruck über den Partikelfilter, msfabr_LimnTCor den maximal zulässigen Abgasmassenstrom, und zwar bereits anhand der Abgastemperatur vor dem Partikelfilter korrigiert, und umsrln einen Umrechnungsfaktor zur Umrechnung der Füllung in einen Massenstrom, mit umsrln = Motordrehzahl * Brennraumvolumen * Konstante, bedeuten.In the case of the proposed method, it can further be provided that, based on the calculated, maximum permissible exhaust gas mass flow from an instantaneous engine speed and from an existing combustion chamber volume of the internal combustion engine in accordance with the following relationship according to equation 3, a maximum cylinder charge corresponding to the maximum permissible exhaust gas mass flow and / or corresponding maximum engine torque is calculated: $$\text{ratChrgRednPfilDifP}={\text{msfabr}}_{\text{LimnTCor}}/\text{umrln},$$

in which the size ratChrgRednPfilDifP the maximum permissible filling depending on the differential pressure across the particle filter, msfabr _LimnTCor the maximum permissible exhaust gas mass flow, already corrected on the basis of the exhaust gas temperature upstream of the particle filter, and umrln a conversion factor for converting the filling into a mass flow, with umrln = Engine speed * combustion chamber volume * constant, mean.

In the proposed method, it can further be provided that a determined value of the differential pressure is compared with a predetermined value of the maximum permissible differential pressure, and that when the maximum permissible differential pressure is reached during operation of the internal combustion engine, the corresponding, currently available value of the exhaust gas mass flow or exhaust gas volume flow is stored and that the stored value of the exhaust gas volume flow is used as a basis when calculating the maximum cylinder charge and / or the corresponding maximum engine torque.

It can also be provided in the proposed method that an upper limit for the respective desired value of the cylinder charge is calculated by forming a minimum of a current value of the calculated exhaust gas volume flow and the maximum permissible exhaust gas volume flow.

In the proposed method, it can also be provided that the runtime of the exhaust gas in the exhaust tract is taken into account when determining the maximum permissible differential pressure.

In the proposed method, it can also be provided that, depending on the measured or modeled, operating point-dependent pressure behavior or pressure curve in the exhaust tract, an additional lowering of the cylinder charge and / or the corresponding maximum engine torque can take place in order to press open exhaust valves of the internal combustion engine to prevent.

In the proposed method, it can finally be provided that the degree of loading of the particle filter is learned in order to control a regeneration process of the particle filter.

The invention can be used both in spark-ignited internal combustion engines (gasoline engines) and in self-igniting internal combustion engines (diesel engines), since the fuel is also introduced or injected directly into the combustion chamber in diesel engines.

The computer program according to the invention is set up to carry out each step of the method, in particular if it runs on a computing device or a control device. It enables the method according to the invention to be implemented on an electronic control unit without having to make structural changes to it. For this purpose, the machine-readable data carrier is provided, on which the computer program according to the invention is stored. By loading the computer program according to the invention on an electronic control device, the electronic control device according to the invention is obtained, which is set up to control the operation of an internal combustion engine having a particle filter affected here by means of the method according to the invention.

Further advantages and refinements of the invention result from the description and the accompanying drawings.

It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or on their own without departing from the scope of the present invention.

Figure list

• 1 zeigt typische Verläufe des Motormomentes über der Motordrehzahl für verschiedene Abgasmassenströme.
• 2a - c zeigen drei Prozessroutinen gemäß Ausführungsbeispielen des erfindungsgemäßen Verfahrens, und zwar anhand von einzelnen Flussdiagrammen.

Embodiments of the invention are shown in the drawings and are explained in more detail in the following description.

• 1 shows typical curves of engine torque versus engine speed for various exhaust gas mass flows.
• 2a - c show three process routines according to exemplary embodiments of the method according to the invention, specifically using individual flow diagrams.

Embodiments of the invention

The following description of exemplary embodiments is based on the knowledge that pressure changes, in particular pulsed pressure vibrations, of the exhaust gas mass flow in the exhaust tract of an internal combustion engine affected here lead to material vibrations of the filter within a particle filter affected here. In addition, a relatively large differential pressure in the filter also leads to such material vibrations. These vibrations can mechanically destroy the particle filter. Therefore, a maximum permissible differential pressure in the particle filter must not be exceeded.

It is also based on the knowledge that the pressure drop and thus also the differential pressure across the particle filter are dependent on the exhaust gas mass flow through the filter. This is in the 1 illustrates in the typical curves of the engine torque M in the unit [Nm] above the engine speed n in the unit [s ^-1 ] for different exhaust gas mass flows are shown.

The in the 1 shown family of curves 100 , 105 , 110 , 115 , 120 represents curves of the same exhaust gas mass flow or corresponding pressure difference across the particle filter. The curve 115 corresponds to a limit value curve of the engine torque M calculated according to the method according to the invention, specifically to prevent said material vibrations. As can be seen, the course of the limit value of the engine torque M depends on the engine speed n and thus the respectively permissible engine torque depends on the operating state of the internal combustion engine or can be varied accordingly with it.

According to the in 2a The first process routine shown in accordance with an exemplary embodiment of the method described here is changed to a corresponding one to that shown in FIG 1 shown family of curves according to the curve 115 Predeterminable, maximum permissible differential pressure pDifGpf _Crit via the particle filter (see equation 1 above) calculates a maximum permissible exhaust gas mass flow msfabr _LimnTCor 200. A value for the maximum permissible differential pressure pDifGpf _Crit , at which critical material vibrations of a particle filter can be reliably avoided, can, for example can be obtained by simulation calculations.

It should be noted that a value of the maximum permissible exhaust gas mass flow msfabr _{LimnTCor can} also be derived or derived from a specification regarding the new condition of the respective internal combustion engine.

On the basis of equation 1, on the basis of the 200 maximum permissible exhaust gas mass flow msfabr _LimnTCor calculated in this way, a maximum corresponding to the maximum permissible exhaust gas mass flow msfabr _LimnTCor corresponding to the maximum permissible exhaust gas mass flow msfabr LimnTCor is _obtained from an actual engine speed and the predetermined combustion chamber _volume (or displacement of the internal combustion engine) Cylinder filling or a corresponding maximum engine torque Mmax calculates 205.

It should be noted here that the protective function described here calculates the torque limitation to Mmax on the basis of a target cylinder charge, on the basis of which a specific engine torque is established. The protective function can also be used directly when calculating the motor torque. Using the maximum engine torque Mmax calculated in this way, a limit value for the target value of the cylinder charge or, as in the present exemplary embodiment, a corresponding limit value for a current target value of the engine torque M target _{(limit) is} calculated 210. This calculation is also carried out on the basis of a current driver's desired torque M _FW 215.

The limitation of the engine torque Mmax to the value _{Mset (limit)} , which depends in particular on the engine speed, ensures that the maximum permissible exhaust gas mass flow msfabr _LimnTCor and thus also the corresponding maximum permissible differential pressure pDifGpf _{Crit are} not exceeded.

In addition or in parallel to the process steps just described 200 - 215 can according to the in 2 B shown second process routine, a currently determined value of the (actually) existing differential pressure Δp is _determined 220 with a named, empirically predeterminable value of the maximum differential pressure pDifGpf _Crit 225 which can be compared via the particle filter 230. The comparison results 230 That the maximum permissible differential pressure pDifGpf _Crit 225 is actually reached during operation of the internal combustion engine, then the corresponding, currently available value of the permissible exhaust gas mass flow msfabr _LimnTCor or exhaust gas volume flow vfLimnEgp can be saved 235 and in the step described 200 the in 2a first process routine shown are used as a basis. Otherwise, it jumps back 240 to the beginning of the second process routine.

in der die Größe vfLimnEgp_saved den limitierten Volumenstrom für die Berechnung der Füllungsbegrenzung, vfLimnEgpRef den Referenzvolumenstrom über die Auslassventile aus der Zylinderkammer (gemäß der Spezifikation eines fabrikneuen Partikelfilters) und vfEgp den Volumenstrom, berechnet auf der Grundlage von Abgasgegendruck und Massenstrom, bedeuten.Alternatively or additionally, according to the in 2c shown third process routine, by forming a minimum value 240 from a currently available value of the calculated exhaust gas volume flow 245 and the maximum permissible exhaust gas volume flow 250 (back-calculated or converted into an exhaust gas mass flow), based on the described conversion of the engine speed into a corresponding cylinder charge, an upper limit for the respective target value of the cylinder charge is calculated using equations 2 and 3 above 255, the size vfLimnEgp _saved ( t = t _CritPDif ) is calculated by forming the minimum according to the following equation 4: $${\text{vfLimnEgp}}_{\text{saved}}\left(\text{t}={\text{t}}_{\text{CritPDif}}\right)=\text{MIN}\left[\text{vfLimnEgpRef},\text{vfEgp}\right],$$

in which the size vfLimnEgp _{saved means} the limited volume flow for the calculation of the filling limitation, vfLimnEgpRef the reference volume flow via the exhaust valves from the cylinder chamber (according to the specification of a brand new particle filter) and vfEgp the volume flow, calculated on the basis of exhaust gas back pressure and mass flow.

It should also be noted that when the installation location is not close to the engine, the runtime of the exhaust gas in the exhaust tract can also be taken into account when calculating the exhaust gas mass flow through the particle filter or when calculating a corresponding differential pressure. This allows manufacturing-related tolerances of the particle filter to be included in the calculation described. This also allows an increase in the loading of the particle filter due to driving operation to be taken into account, since loading with particles or soot also changes the physical relationship between the exhaust gas mass flow or exhaust gas volume flow and the differential pressure.

If there is a previously learned first threshold value for the exhaust gas mass flow or exhaust gas volume flow, a current differential pressure can be compared with an empirically predeterminable limit value of the differential pressure for the particle filter. If it emerges from this comparison that the current differential pressure lies within an also empirically predeterminable second threshold value below the permissible differential pressure in the particle filter, then an existing filling or torque limitation can be canceled again or released again. In addition, this limitation can be removed with a time delay and / or can be carried out in a filtered manner in order to prevent sudden torque jumps of the internal combustion engine which are disadvantageous for driving comfort.

$$\text{pDifPfil}<{\text{pDifPfil}}_{\text{Crit},}$$

in denen die Größe flgChrgLimnEgpRel die Bedingung angibt, unter welcher eine bestehende Füllungsbegrenzung durch einen geeigneten Abgasgegendruck aufgehoben werden kann, vfEgp den Volumenstrom berechnet auf der Grundlage von Abgasgegendruck und Massenstrom, vfLimnEgp_saved den limitierten Volumenstrom für die Berechnung der Füllungsbegrenzung, der angegebene Summand „Toleranz“ einen empirisch vorgebbaren Toleranzwert für den limitierten Volumenstrom vfLimnEgp_saved, pDifPfil den aktuell ermittelten Differenzdruck über den Partikelfilter und pDifPfil_Crit den maximal zulässigen Differenzdruck über den Partikelfilter bedeuten.The two relationships according to the following equations 5 and 6 apply as a condition for the release of any existing limitation: $$\text{flgChrgLimnEgpRel}=\left(\text{vfEgp}>\left({\text{vfLimnEgp}}_{\text{saved}}-\text{tolerance}\right)\right)\text{and}$$

$$\text{pDifPfil}<{\text{pDifPfil}}_{\text{Crit},}$$

in which the size flgChrgLimnEgpRel indicates the condition under which an existing filling limitation can be canceled by a suitable exhaust gas back pressure, vfEgp calculates the volume flow on the basis of exhaust gas back pressure and mass flow, vfLimnEgp _saved the limited volume flow for the calculation of the filling limitation, the specified summand “tolerance “An empirically predeterminable tolerance value for the limited volume flow vfLimnEgp _saved , pDifPfil means the currently determined differential pressure across the particle filter and pDifPfil _Crit the maximum permissible differential pressure across the particle filter.

The variable vfLimnEgpRef (not shown here) can also be used as a reference volume flow via the exhaust valves from the cylinder chamber (according to a brand-new particle filter).

After the torque limitation has been released again, the respectively saved volume flow vfLimnEgp _{saved is increased} to a value vfLimnEgpRef, preferably by means of an empirically predeterminable change dynamic, or increased accordingly.

The described method can be implemented in the form of a control program for an electronic control unit for controlling an internal combustion engine or in the form of one or more corresponding electronic control units (ECUs).

Claims (10)

Method for operating an internal combustion engine with an exhaust tract having a particle filter, characterized in that on the basis of at least one predeterminable, maximum permissible differential pressure in the particle filter, at least one limit value curve of the engine torque, which is dependent on the operating state of the internal combustion engine, is determined (210) and that the internal combustion engine with a maximum engine torque is operated within the limit value curve. Procedure according to Claim 1 , characterized in that if the maximum permissible differential pressure in the particle filter is exceeded, a volume flow is calculated on the basis of a currently existing exhaust gas mass flow (200). Procedure according to Claim 2 , characterized in that on the basis of a calculated (200), maximum permissible exhaust gas mass flow from a current engine speed and from an existing combustion chamber volume of the internal combustion engine, a maximum cylinder charge corresponding to the maximum permissible exhaust gas mass flow or a corresponding maximum engine torque is calculated (205): Procedure according to Claim 3 , characterized in that a measured value of the differential pressure (220) is compared (230) with a predetermined value of the maximum permissible differential pressure (225), that when the maximum permissible differential pressure (225) is reached during operation of the internal combustion engine, the corresponding, currently available value of the exhaust gas mass flow or exhaust gas volume flow is stored (235) and that the stored (235) value of the exhaust gas mass flow or exhaust gas volume flow is used as a basis when calculating the maximum cylinder charge and / or the corresponding maximum engine torque. Procedure according to Claim 3 or 4th , characterized in that an upper limit for the respective desired value of the cylinder charge is calculated (255) by forming a minimum of a current value of the calculated exhaust gas mass flow or exhaust gas volume flow (245) and the maximum permissible exhaust gas mass flow or exhaust gas volume flow (250). Procedure according to one of the Claims 2 to 5 , characterized in that, depending on a pressure behavior dependent on the operating state of the internal combustion engine, an additional lowering of the cylinder charge and / or the corresponding maximum engine torque is carried out in the exhaust tract of the internal combustion engine in order to prevent the exhaust valves of the internal combustion engine from being pressed open. Method according to one of the preceding claims, characterized in that the runtime of the exhaust gas in the exhaust tract is taken into account when calculating the maximum permissible differential pressure. Computer program which is set up each step of a method according to one of the Claims 1 to 7 perform. Machine-readable data carrier on which a computer program according to Claim 8 is saved. Electronic control device, which is set up, an internal combustion engine with an exhaust tract having a particle filter by means of a method according to one of the Claims 1 to 7 to operate.

Images