Patent Application
20100300071
This application is claims benefit of Serial No. 10 2009 026 630.5, filed 2 Jun. 2009 in Germany and which application is incorporated herein by reference. To the extent appropriate, a claim of priority is made to the above disclosed application.
The invention relates to a method for controlling a regeneration process of an exhaust gas particle filter of an internal combustion engine, wherein the method comprises safeguards for protecting the exhaust gas particle filter from overheating and a gas flow of the gas flowing through the exhaust gas particle filter is reduced for limiting a reaction rate of an exothermal reaction taking place during the regeneration process. In addition the invention relates to a corresponding control device of an internal combustion engine, which is designed for carrying out such a method.
Internal combustion engines for motor vehicles, particularly diesel internal combustion engines, often have an exhaust gas particle filter for filtering out contaminated particles, particularly soot particles, from the exhaust gas produced by the internal combustion engine. Such exhaust particle filters are usually disposed in the exhaust gas tract of the internal combustion engine so that they have exhaust gas, which is discharged from the combustion chambers of the internal combustion engine, passing through them during the operation of said internal combustion engine. During the operation of the exhaust gas particle filter, pollutants filtered out of the exhaust gas are embedded in the form of soot in said exhaust gas particle filter. A regeneration process takes place from time to time during the operation of the exhaust gas particle filter, wherein soot situated in said exhaust gas particle filter is burned. In order to initiate the regeneration process, the internal combustion engine is normally operated such that the temperature of the exhaust gas flowing into the exhaust gas particle filter is so substantially raised that the soot embedded in said exhaust gas particle filter begins to burn off. Normally an exhaust gas temperature of approximately 600EC to 650EC is adjusted to perform said process. Because such high exhaust gas temperatures, particularly in diesel internal combustion engines, are at best achieved during normal operation in the full load range, the internal combustion engine is usually intentionally operated at an inefficient operating point, whereat said internal combustion engine has a relatively high heat output in comparison to its mechanical output.
For this purpose, a fuel injection system of the internal combustion engine can accordingly be operated. A main injection of fuel into the combustion chambers of the internal combustion engine can be temporally retarded, or an afterinjection, which temporally follows the main injection, can be provided. The afterinjection can be temporally defined, such that fuel injected into the combustion chambers during the afterinjection, still combusts within the combustion chambers. Provision can, however, also be made for the fuel injected by means of the afterinjection to first combust in the exhaust gas system of the internal combustion engine, particularly in an oxidation catalytic converter of the exhaust gas system. Suitable adjustment interventions in the air system of the internal combustion engine can be performed to raise the exhaust gas temperature. For example, a throttle valve disposed in an intake manifold of the internal combustion engine can at least partially be closed in order to reduce the gas flow through said internal combustion engine and therefore also the mass flow of the air flowing into said internal combustion engine so that a relatively small amount of the air has to be heated to the high temperatures per unit of time.
Because the combustion of the soot embedded in the exhaust gas particle filter relates to an exothermal reaction, the danger exists for the exhaust gas particle filter to overheat during the regeneration process and thermally critical filter materials within the exhaust gas particle filter to thereby be destroyed. The regeneration process must therefore be controlled such that a reaction rate of the exothermal reaction is limited. Measures for limiting the oxygen supply to the exhaust gas particle filter are thus provided. The oxygen supply can on the one hand be implemented by the corresponding control of the injections of fuel into the combustion chambers of the internal combustion engine and on the other hand by limiting a mass flow of the gas flowing into the exhaust gas particle filter.
A method for controlling a regeneration of an exhaust gas particle filter is known from the German patent publication DE 10 2006 010 095 A1, wherein adjustment interventions at the throttle valve and at a device for recirculating the exhaust gas are performed in order to protect the exhaust gas particle filter from damage to due to overheating.
Whereas the publication mentioned above shows a measure for reducing the reaction rate, a method for controlling an internal combustion engine is known from the European patent publication EP 1 364 110 B1, wherein a decision can be made whether measures for reducing the reaction rate have to be taken. According to this method, a parameter is ascertained, which characterizes a future intensity of the exothermal reaction. The stated measure is taken if this parameter exceeds a threshold value. Whether the measure for limiting the reaction rate is to be taken, is decided according to the invention before the beginning of the regeneration process with the aid of a prognosis. Because such a prognosis is subject to relatively large uncertainties, the threshold value must be chosen such that damage to or destruction of the exhaust gas particle filter as a result of it overheating can be eliminated in every conceivable case. As a result, the exothermal reaction during most of the regeneration processes takes place with a significantly smaller reaction rate than would be possible without overheating the exhaust gas particle filter and the regeneration process thereby lasts a relatively long time. This leads to a relatively high fuel consumption of the internal combustion engine because its inefficient operating point must be maintained quite long for the regeneration of the exhaust gas particle filter.
It is the aim of the present invention to provide a method, respectively a control unit, which allows for an efficient regeneration of an exhaust gas particle filter with little fuel consumption by the internal combustion engine, and nevertheless avoids damage to or the destruction of the exhaust gas particle filter as a result of it overheating. It is therefore the aim of the invention to improve a so-called regeneration efficiency of the regeneration process.
When implementing the method according to the invention, the instantaneous value for the current mass of soot situated in the exhaust gas particle filter is maintained and regularly updated at least during the regeneration process. This value is used to control the regeneration process. As a result, a reaction rate of the exothermal reaction can be ascertained at each point in time during the regeneration process, and the exothermal reaction can be controlled such that the temperature within the exhaust gas particle filter relatively markedly approaches a maximum admissible temperature within the exhaust gas particle filter without the danger existing of damage to or the destruction of the exhaust gas particle filter as a result of an overheating of said exhaust gas particle filter.
With the aid of the instantaneous value, a check can be made relatively accurately and reliably to determine whether the exhaust gas particle filter is even in a critical operating state, wherein the danger exists that it can be damaged or destroyed by the exothermal reaction. If this is not the case—if the exhaust gas particle filter is thus in an uncritical operating state—the safeguards are then suppressed. That means that they are not implemented even if they appear necessary due to other indicators as for example a high prognosis value ascertained before the beginning of the regeneration process. A quick regeneration of the exhaust gas particle filter hereby occurs at a on average comparatively high reaction rate. That means that a comparatively higher degree of regeneration efficiency is achieved by means of the method according to the invention.
It is particularly preferred for the uncritical operating state to be recognized in the event that the instantaneous value is smaller than a predetermined minimum value. It has in fact been shown that an inadmissibly high temperature of the exhaust gas particle filter can no longer be achieved if only a relatively small quantity of soot is embedded in the exhaust gas particle filter. In such a case, the safeguards can be eliminated without risk. In the case of small soot masses, a relatively fast regeneration is achieved by suppressing the safeguards. It is conceivable for the safeguards to be initially implemented at the beginning of the regeneration process and for said safeguards to be suppressed during the regeneration process as soon as the instantaneous value has dropped below the predetermined minimum value. That means the reaction rate is initially limited by decreasing the gas flow; and subsequently as soon as the uncritical operating state is achieved, the gas flow is no longer decreased so that the reaction rate is consequently no longer limited. In so doing, an efficient reaction is achieved toward the end of the regeneration process, whereby the degree of regeneration efficiency is increased.
As an alternative to or in addition to this, provision can be made for the uncritical operating state to be recognized in the event that a gas temperature of the gas flowing into the exhaust gas particle filter is lower than a predetermined first minimum temperature. This is the case because an overheating of the exhaust gas particle filter can at least substantially be ruled out if the gas temperature is relatively low even when the reaction rate is high. The safeguards are not required in such a case and also not desired because they would only unnecessarily prolong the duration of the regeneration process.
In addition to the check during the regeneration process to determine whether the critical or uncritical operating state is present, provision is made in a preferred embodiment of the invention for a check to be made already prior to the beginning of the regeneration process to determine whether the safeguards are required. Provision can particularly be made in this preferred embodiment for an initial value to be ascertained, which characterizes the mass of the soot situated in the exhaust gas particle filter prior to the beginning of the regeneration process. Secondly a check is made as a function of said initial value to determine whether the reaction rate during the regeneration process is anticipated to be too high. Finally said safeguards are only then carried out in the event that the check revealed that the reaction is anticipated to be too high.
The danger exists at a relatively low gas temperature that due to the gas flow the temperature of the exhaust gas particle filter is reduced to such an extent that the exothermal reaction at least largely comes to a standstill, i.e. the regeneration is discontinued before all of the soot deposits have been burned off in the exhaust gas particle filter. In order to avoid such a premature termination of the regeneration, provision can be made for the gas flow to be reduced to avoid a cooling of the exhaust gas particle filter in the event that the gas temperature is lower than a predetermined second minimum temperature. In so doing, it is ensured that each regeneration process is carried out reliably and completely. A high degree of average regeneration efficiency thus results.
It is particularly preferred for the gas flow to be manipulated by adjusting the actuating elements of an air and exhaust gas system of the internal combustion engine, preferably by adjusting a degree of opening of a throttle device and/or an exhaust gas recirculation valve. It is particularly preferred with regard to reducing the gas flow for the throttle device to be at least partially closed and the exhaust gas recirculation valve to be at least partially opened. As a result of these actions, at least a part of the gas flowing through the combustion chambers of the internal combustion engine is recirculated before reaching said combustion chambers via the exhaust gas recirculation valve disposed in the exhaust gas return channel. In so doing, the quantity of exhaust gas flowing through the exhaust gas particle filter is reduced.
Provision is made in the present invention for the instantaneous value, preferably model based, to be ascertained as a function of at least one state variable, which characterizes an operating state of the internal combustion engine—preferably as a function of an exhaust gas temperature, an oxygen concentration and/or a mass flow of the exhaust gas flowing into the exhaust gas particle filter. Relatively exact instantaneous values thus result across the entire regeneration process.
It is particularly preferred in this instance for the instantaneous value to be ascertained step-by-step by said instantaneous value being recalculated in regular intervals as a function of its current value and the at least one state variable. Said instantaneous value is therefore regularly updated according to a recursive calculation scheme during the regeneration process. At the beginning of said regeneration process, the initial value mentioned above, which characterizes the mass of the soot situated in the exhaust gas particle filter before the beginning of the regeneration process, can be used as the starting value for these calculations. The initial value can be ascertained in a suitable manner by means of calculations during the operation of the internal combustion engine before the beginning of the regeneration process, in particular using state variables of the internal combustion engine.
If the internal combustion engine is in the overrun mode, wherein no fuel is injected into the combustion chambers of the internal combustion engine, the gas flowing into the exhaust gas particle filter substantially corresponds to the ambient air and therefore has a comparatively high oxygen content of approximately 21 percent. Because the exothermal reaction relates to an oxidation, an especially large risk exists in the overrun mode for too high of a reaction rate. It is therefore preferred for the method to be executed while the internal combustion engine is being operated in said overrun mode. Moreover, the actuating elements of the internal combustion engine can be largely freely adjusted during the overrun mode because combustion processes in the combustion chambers of the internal combustion engine in this case do not have to be controlled in an open or closed loop. The method can therefore be easily applied in the overrun mode.
As a further solution to the inventive aim mentioned above, the invention is characterized by a control unit with the characteristics of claim 10. With the aid of a control unit of this type, the duration of the regeneration process can be reduced and said process can be reliably controlled. In this way, a high degree of regeneration efficiency results.
Particularly if the control unit is equipped for executing the inventive method, all of the advantages of said method can be realized. The control unit preferably has a computer, which is programmed for executing the inventive method and/or has a programmed storage for executing the inventive method.
Additional characteristics and advantages of the invention become apparent in the following description, wherein exemplary embodiments of the invention are explained in detail with the aid of the drawings. The following are thereby shown:
An internal combustion engine 11 schematically depicted in
An oxidation catalytic converter 39 of the air and exhaust gas system 17, which is followed by an exhaust gas particle filter 41 in the direction of flow, is disposed behind the turbine 33 in said direction of flow (depicted in
A first temperature sensor 43 for acquiring a temperature of the gas flowing into the oxidation catalytic converter 39 is disposed between the turbine 33 and the oxidation catalytic converter 39. A second temperature sensor 45 for acquiring a gas temperature of the gas 47 flowing into the exhaust gas particle filter 41 is situated between said oxidation catalytic converter 39 and said exhaust gas particle filter 41. In addition, a lambda probe 49 for acquiring an oxygen concentration 8 of the gas 47 flowing into said exhaust gas particle filter 41 is disposed between said oxidation catalytic converter 39 and said exhaust gas particle filter 41. The lambda probe 49 in the exemplary embodiment shown relates to a broadband lambda probe. Deviating from the exemplary embodiment shown, the oxidation catalytic converter 39 can also be omitted or be disposed at another location of the air and exhaust gas system 17. It is, however, preferred that the second temperature sensor 45 and the lambda probe 49 be disposed upstream of the exhaust gas particle filter 41 in the direction of flow (arrow 47). The first temperature sensor 43, the second temperature sensor 45 and the lambda probe 49 are connected to a control unit 51 of the internal combustion engine 11. The control unit 51 is furthermore connected to an actuating element of the throttle device 29 as well as to an actuating element of the exhaust gas recirculation valve assembly 37. The two actuating elements are configured as electromagnetic adjusting drives. In addition, said control unit 51 can activate the exhaust gas turbocharger 27 for manipulating a boost pressure of the gas situated in the channel 31. Provision can particularly be made for a closed-loop control of the boost pressure.
During the operation of the internal combustion engine 11, the compressor 25 compresses the air 21 drawn in via the intake manifold 19. The air travels into the air inlet of the engine block 13 via the channel 31 and from there to the individual combustion chambers 15 within said engine block 13. If the internal combustion engine 11 is not in the overrun mode, fuel is then injected into the combustion chambers 15 and is burned in said combustion chambers 15. The exhaust gas resulting from this combustion leaves the combustion chambers 15 and travels to the turbine 33 of the exhaust gas turbocharger 27 via the exhaust gas outlet of the engine block 25 and hereby drives the compressor 25 of said exhaust gas turbocharger 27. The gas flowing out of the turbine 33 is subsequently channeled through the oxidation catalytic converter 39 and after that through the exhaust gas particle filter 41 so that it finally leaves the exhaust gas particle filter 41 as exhaust gas 53 and as the case may be is released to the atmosphere after passing through additional components of the air and exhaust gas system 17.
The control unit 51 adjusts a degree of opening of the throttle device 29 by means of a first actuating signal s1 and a degree of opening of the exhaust gas recirculation assembly 37 by means of a second actuating signal s2. By predetermining certain values of the two actuating signals s1 and s2, the control unit 51 defines an exhaust gas recirculation rate, i.e. the mass flow mAGR of that gas, which flows out of the exhaust gas outlet of the engine block 13 and is directed back to the channel 31 via the exhaust gas recirculation channel 35. If the exhaust gas recirculation valve assembly 37 is not completely closed, an exhaust gas recirculation rate results that is different from zero so that a mass flow mk through the channel 31 is larger than a mass flow me of the air 21 flowing into the intake manifold 19 and a mass flow ma of the gas 47 flowing into the exhaust gas particle filter 41.
During the operation of the internal combustion engine 11, the control unit 51 controls the internal combustion engine 11 in a closed or open loop as a function of different operating variables of said internal combustion engine 11. For this purpose, the air mass flow sensor 23 generates an air mass flow signal m, which characterizes the mass flow mi of the air flowing into the intake manifold 19. The first temperature sensor 43 acquires a temperature signal, which characterizes a temperature To of the gas flowing into the oxidation catalytic converter 39. The second temperature sensor 45 correspondingly generates an additional temperature signal, which characterizes the temperature Tp of the gas flowing into the exhaust gas particle filter 41. Finally the lambda probe 49 generates a sensor signal, which characterizes an oxygen concentration 8 of the gas flowing into the exhaust gas particle filter 41. The control unit 51 acquires these sensor signals and ascertains actuating signals from them, like, for example, the two actuating signals s1 and s2 shown in
Soot particles form during the combustion processes within the combustion chambers 15 of the engine block 13, which are discharged out of the exhaust gas outlet of said engine block 13. If said soot particles do not then travel into the exhaust gas recirculation channel 35, they are directed through the oxidation catalytic converter 39 to the exhaust gas particle filter 41. The exhaust gas particle filter 41 retains the soot particles so that the gas discharging from said exhaust gas particle filter 41 is at least largely free of soot particles. With time the particles are deposited in the exhaust gas particle filter 41 in the form of soot.
In order to in turn remove these soot deposits, the control unit 51 carries out from time to time a regeneration process of the exhaust gas particle filter 41, in which the soot deposits situated in the exhaust gas particle filter 41 are burned off. In so doing, the control unit 51 adjusts to an operating state of the internal combustion engine 11, wherein a relatively high temperature Tp of the gas 47 flowing into the exhaust gas particle filter 41 arises. In the embodiment shown, a temperature Tp of approximately 600EC to 650EC is adjusted. The high temperature Tp of the gas 47 flowing into the exhaust gas particle filter 41 can, for example, be achieved by suitable after injections of fuel, which lead to additional combustions within the combustion chambers 15 or within the oxidation catalytic converter 39. At the same time, an inward flow of fresh air, which lowers the temperature Tp of the incoming gas 47, can be reduced by at least partially closing the throttle device 29.
Filter means of the exhaust gas particle filter 41 are heated up by the high temperature Tp of the inflowing gas 47 and an activation energy required for starting an exothermal reaction, wherein the soot deposits are burned off in the exhaust gas particle filter, is thereby provided. As soon as an exothermal reaction has been started, the control unit 51 controls the regeneration process, such that the reaction rate of this exothermal reaction remains so low that a maximally admissible temperature within the exhaust gas particle filter is not exceeded. If necessary the control unit 51 implements safeguards for protecting the exhaust gas particle filter 41 from overheating.
In the diagram shown in
A method 61 for controlling the regeneration process of the exhaust gas particle filter 41 is explained below in detail with the aid of
A check can additionally be made in branch 65 to determine whether the internal combustion engine 11 is operating in an overrun mode. If this is not the case (N), the branch 65 is repeated. With the exception of branch 65, the method 61 is therefore only then executed if said internal combustion engine 11 is operating in the overrun mode. In derogation from the embodiment shown, said branch 65 can also be omitted.
A check is subsequently made in an additional branch 67 to determine whether an uncritical operating state of the exhaust gas particle filter 41 is present. In order to check whether an uncritical operating state is present, an instantaneous value x(t), which characterizes the instantaneous mass x of the soot in the exhaust gas particle filter 41, is compared with a predetermined minimum value xmin. In addition the sensor signal Tp, which characterizes the temperature of the gas 47 flowing into the exhaust gas particle filter 41, is checked. If the instantaneous value xt is lower than the predetermined minimum value xmin, and the temperature Tp is lower than the predetermined first minimum temperature, then (Y) the uncritical operating state is recognized. In derogation from the embodiment shown, the check of the temperature Tp of the incoming gas can be omitted and the instantaneous value x(t) can merely be checked in branch 67.
In the event that the uncritical operating state is present, the method branches off to step 69, which opens the throttle device 29 in the overrun mode. The method branches off to step 71 only in the event of the critical operating state being present, wherein the safeguards for protecting the exhaust gas particle filter 41 from overheating are implemented. The safeguards 71 comprise two steps 71a and 71b. In step 71a the degree of opening of the throttle device 29 is decreased; and in step 71b following step 71a, the degree of opening of the exhaust gas recirculation valve assembly 37 is increased. In total the mass flow ma of the gas 47 flowing into the exhaust gas particle filter 41 is reduced by the two steps 71a and 71b of the safeguards 71. In derogation from the embodiment shown, steps 71a and 71b can also be executed in the reverse order, simultaneously or temporally overlapping.
A check is made in branch 73 following step 69 to determine whether the temperature of the incoming gas 47 is lower than a predetermined second minimum temperature Tmin2. If this is the case (Y), the throttle device 29 is then partially or completely closed in step 75 so that a cooling of the exhaust gas particle filter 41, which can cause the exothermal reaction to come to a standstill, is avoided. Otherwise (N) the method returns to step 69.
Branch 67 generally ensures that the safeguards 71 are suppressed and that steps 69, 73 are executed instead of said safeguards 71 if the exhaust gas particle filter 41 is in an uncritical operating state.
Provision can be made for a check to be performed in advance immediately prior to the beginning of the regeneration process to determine whether an overheating of the exhaust gas particle filter 41 can be ruled out with certainty. For this purpose, the sequence shown in
In one embodiment, wherein the sequence in
In total the present invention provides a method 61, with which on the one hand an unnecessary restriction of the reaction rate during regeneration of the exhaust gas particle filter 41 is avoided and in so doing a fast and more reliable regeneration is made possible, and on the other hand a cooling of said exhaust gas particle filter 41 is avoided during said regeneration process as a result of a relatively low temperature Tp of the gas 47 flowing into the exhaust gas particle filter 41. In this way, a considerable improvement of the regeneration efficiency is achieved and in so doing the fuel consumption of the internal combustion engine 11 is reduced.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10 2009 026 630.5 | Jun 2009 | DE | national |
