SE540266C2 - Method and system for adapting the supply of additives to an exhaust stream - Google Patents

Abstract

The present invention relates to a process for correcting the supply of a first additive for reducing at least one first substance (NO) present in an exhaust stream. The method comprises, in said correction: - initiating a first accumulation (N1) of a representation of said first substance (N0, said first accumulation (N1) of said first substance (NO representing an accumulated amount of said first substance (NO downstream of said supply). - determining whether a first work (W1) has been performed by said internal combustion engine (101) while accumulating said first substance (NO; - interrupting said first accumulation of said first substance (NOWhen said first work (W1) has been performed of said combustion engine (101); and correcting the supply of said first additive based on said first accumulation (N1) of said first substance (NO).

Description

FIELD OF THE INVENTION The present invention relates to an exhaust gas purification system, and in particular to a method for correcting the supply of additives to an exhaust stream. , as well as a computer program and a computer program product, which implement the method according to the invention.

Background of the invention Due to e.g. increased government interests regarding pollution and air quality in e.g. urban areas, emission standards and regulations have been developed in many jurisdictions.

Such emission standards often constitute sets of requirements which define acceptable limits for exhaust emissions in vehicles equipped with internal combustion engines. For example, levels of nitrogen oxides (NOx), hydrocarbons (HC), carbon monoxide (CO) and particulate emissions are often regulated for most types of vehicles in these standards.

Unwanted emissions can e.g. is reduced by reducing fuel consumption and / or by after-treatment (purification) of the exhaust gases caused by the combustion engine combustion.

Exhaust gases from an internal combustion engine can e.g. post-treated by using a so-called catalytic purification process. There are different types of catalysts, where different types may be required for different fuels and / or for the purification of different types of exhaust components, and for at least nitrogen oxides NOx (such as nitric oxide NO and nitrogen dioxide NO2), heavy vehicles often include a catalyst where an additive is added to the exhaust gas stream resulting from the combustion of the internal combustion engine to reduce nitrogen oxides NOX (mainly to nitrogen gas and water vapor).

A common type of catalyst where additives are added is SCR (Selective Catalyst Reduction) catalysts. SCR catalysts use ammonia (NH3), or a composition from which ammonia can be generated / formed, as an additive to reduce the amount of nitrogen oxides NOX.

The additive is injected into the exhaust gas stream resulting from the internal combustion engine upstream of the catalyst.

The additive fed to the catalyst is absorbed (stored) in the catalyst, whereby nitrogen oxides NOxi the exhaust gases react with the ammonia stored in the catalyst.

The ability of the catalyst to store additives usually varies greatly with the temperature prevailing in the catalyst. At lower temperatures, larger amounts of ammonia can be stored, while the storage capacity at higher temperatures is lower.

When adding additives, it is important that the amount of added additive does not become too large or too small. Thus, it is desirable that the amount of additive added correspond to an expected amount of additive.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for correcting the supply of additives to an exhaust gas stream. This object is achieved with a method according to claim 1.

The present invention relates to a method of correcting the supply of a first additive for treating an exhaust stream resulting from combustion in an internal combustion engine, said first additive being supplied to said exhaust stream and said first additive being used to reduce at least a first in said exhaust stream substance. The method comprises, in said correction: - starting a first accumulation of a representation of said first substance, said first accumulation of said representation of said first substance representing an accumulated amount of said first substance downstream of said supply of said first additive; determining whether a first work has been performed by said internal combustion engine during accumulation of said first substance; interrupting said first accumulation of said first substance when said first work has been done by said internal combustion engine; correcting the supply of said first additive based on said first accumulation of said first substance, - further comprising, before starting said first accumulation of said first substance: - reducing the supply of said first additive to said exhaust gas stream.

The presence of at least certain substances in an exhaust gas stream resulting from combustion can be reduced by adding additives to the exhaust gas stream, the additive reacting with one or more substances present in the exhaust gas stream to thereby form less dangerous substances.

For example. addition of additives is required to reduce the concentration of nitrogen oxides NOxi the exhaust gases from the internal combustion engine. However, it is important that the additive is added in the right proportions in relation to the substance (s) to be reduced. If too little additive is added in relation to the presence in the exhaust stream of the substance to be reduced, an undesirable excess of the substance will still prevail, and thus be released into the vehicle environment with the risk of exceeding permissible limit values.

Conversely, if an excessive amount of additive is added in relation to the presence of the substance to be reduced, there is instead a risk that other undesirable substances added via the additive are released into the environment.

The risk of unwanted emissions can be reduced by adapting the supply of additives, ie. determine whether the amount of additive actually corresponds to the expected amount of additive added and, if necessary, correct the supply of additives. As explained below, however, the supply of additives is normally reduced in the event of such adaptation, with increased emissions as a result, whereby the available adaptation time may be limited.

The present invention provides a method which efficiently utilizes available adaptation time and which, moreover, does not take longer than necessary. This is accomplished by accumulating said first substance during a period of time during which the internal combustion engine performs a first work, i.e. when a certain work has been performed during ongoing accumulation. This has the advantage that the entire adaptation time can be utilized, and by ensuring that a certain work is performed by the internal combustion engine, it can be ensured that a representative adaptation is obtained.

Said accumulation can be performed by utilizing signals emitted by a sensor arranged downstream of said supply of said first additive. When said first substance consists of nitrogen oxides N0X, said first sensor may consist of a ??? - sensor.

As will be appreciated, accumulation of said first substance according to the invention constitutes an accumulation of the amount of said first substance which passes with the exhaust gas stream at the position where accumulation is performed. The accumulation thus does not constitute a physical collection of said first substance.

Furthermore, said representation of said first substance constitutes an applicable representation of the presence of said first substance in the exhaust gas stream, such as an amount determined by means of sensor signals or an amount estimated by means of a calculation model.

Said first accumulation of said first substance may be arranged to be compared with a second amount, said second amount may represent an presence of said first substance in said exhaust gas stream upstream of said supply of said first additive. Supply of said first additive can then be corrected based on said comparison.

Said comparison can be performed by determining a ratio between said first accumulation and said second amount, and comparing said determined ratio with a first ratio. Supply of said first additive can then be corrected based on said comparison. This correction can e.g. consists of determining a correction factor that is applied to the supply of additives, where thus e.g. the injection to be performed is multiplied by the correction factor, whereby the amount injected can be increased or decreased depending on the size of the correction factor.

Said second quantity can e.g. be arranged to be determined by using an upstream said supply of said first additive arranged sensor, said second amount may constitute an accumulation of said first substance upstream of said supply of said additive, or by using a calculation model representing the expected occurrence of said first substance based on work performed by said internal combustion engine, whereby an accumulation can thus be performed by utilizing said calculation model.

According to one embodiment, the supply of said first additive to said exhaust gas stream can be reduced before accumulation of said first substance begins, e.g. to any applicable degree of conversion regarding reduction of said first substance, wherein accumulation of said first substance may begin a first time after said supply of said first additive has been reduced, or after any applicable work has been done by said internal combustion engine after reduction of said supply of said first additive was started. This has the advantage that it can be ensured that e.g. in a catalyst stored reactant, supplied by said additive, can be reduced before accumulation begins to thereby ensure that stored reactant does not incorrectly affect estimation according to the invention.

Said first additive may be arranged to be fed upstream of a first catalyst, such as e.g. an SCR catalyst, and wherein said accumulation of said first amount of said first substance is an accumulation of said first substance downstream of said first catalyst.

Additional features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments and the accompanying drawings.

Brief Description of the Drawings Fig. 1A shows a driveline in a vehicle in which the present invention can be used to advantage.

Fig. 1B shows a control unit in a vehicle control system.

Fig. 2 shows an example of a finishing system in a vehicle in which the present invention can be used to advantage.

Fig. 3 shows an example of the change in the degree of conversion with added additive when converting a substance.

Fig. 4 shows an example of how the degree of conversion can change with time when adapting the supply of additives.

Fig. 5 schematically shows an exemplary method according to an embodiment of the present invention.

Fig. 6 shows an example of the change in the degree of conversion with time for an adaptation according to the present invention.

Detailed Description of Preferred Embodiments The present invention will be exemplified in the following for a vehicle. However, the invention is also applicable to other types of means of transport, such as to aircraft and watercraft, respectively, as long as an additive is supplied with an exhaust gas stream resulting from combustion.

Furthermore, the term "substance" is used in the present description and appended claims, which at least in the present description and appended claims includes chemical compounds.

Fig. 1A schematically shows a driveline in a vehicle 100 according to an embodiment of the present invention. The vehicle 100 schematically shown in Fig. 1A comprises a driveline with an internal combustion engine 101, which is connected in a conventional manner, via a shaft outgoing on the internal combustion engine 101, usually via a flywheel 102, to a gearbox 103 via a clutch 106. The internal combustion engine 101 is controlled by the control system of the vehicle 100 via an engine control unit 115. Likewise, in the present example, clutch 106 and gearbox, respectively, are controlled by a control unit 116.

Furthermore, a shaft 107 emanating from the gearbox 103 drives drive wheels 113, 114 via an end gear 108, such as e.g. a conventional differential, as well as drive shafts 104, 105 connected to said final gear 108. Fig. 1A thus shows a driveline of a certain type, but the invention is applicable to all types of drivelines, and also to e.g. hybrid vehicles. The vehicle shown also includes a post-treatment system 130 for post-treatment (purification) of the exhaust gases resulting from combustion in the internal combustion engine.

The functions of the finishing system are controlled by a control unit 131.

The after-treatment system can be of different types, and according to the embodiment shown, the addition of additives to a catalytic exhaust gas purification process is carried out. An example of a post-treatment system to which the present invention can be applied is shown in more detail in Fig. 2, and in the exemplary embodiment shown, the post-treatment system includes a SCR (Selective Catalytic Reduction) catalyst 201.

The finishing system may also include additional components not shown, such as e.g. additional catalysts and / or particulate filters, which may be located up and / or downstream of the SCR catalyst 201.

As mentioned above, the addition of an additive is required to reduce the concentration of nitrogen oxides NOxi the exhaust gases from the internal combustion engine by using an SCR catalyst. This additive is often urea-based, and can e.g. consist of AdBlue, which in principle consists of urea mixed with water. Urea forms ammonia when heated. Alternatively, other applicable additives may be used.

Fig. 2 shows, in addition to said catalyst 201, a urea tank 202, which is connected to a urea dosing system (UDS) 203.

The exhaust metering system 203 includes or is controlled by a UDS control unit 204, which generates control signals for controlling the supply of additives so that the desired amount is injected into the exhaust stream 119 from the tank 202 resulting from the combustion in the cylinders of the internal combustion engine 101 by means of an injection nozzle 20 .

In general, urea dosing systems are well described in the prior art, and exactly how injection of additives takes place is therefore not described in more detail here, but the present invention relates to a method of adapting the supply of additives in order to ensure that the amount of additive added corresponds to an expected amount of additive. in particular, the present invention provides a method that makes better use of available adaptation time. An exemplary method 500 according to the present invention is shown in Fig. 5 and is described below, where the method according to the invention may be arranged to be performed by any applicable control unit.

In general, control systems in vehicles consist of a communication bus system consisting of one or more communication buses for interconnecting a number of electronic control units (ECUs), or controllers, and various components arranged on the vehicle 100. Such a control system can thus comprise a large number of control units, and the responsibility for a specific function can be divided into more than one control unit.

For the sake of simplicity, in addition to the control unit 204 shown in Fig. 2, only three further electronic control units 115, 116, 131 are shown in Fig. 1A. such as e.g. The UDS control unit 204 or the control unit 131 which is generally responsible for the function of the finishing system 130, or alternatively be divided into several control units present at the vehicle 100.

Control units of the type shown are normally arranged to receive sensor signals from different parts of the vehicle, e.g. from gearbox, engine, clutch and / or other control units or components on the vehicle. The control unit generated control signals are normally dependent on both signals from other control units and signals from components. For example. the control of the control unit 204 of the supply of additives to the exhaust gas stream 119 will e.g. depend on information such as received from one or more additional controllers. For example. the control can be at least partly based on information from the control unit 115 which is responsible for the function of the internal combustion engine 101.

The control units can furthermore be arranged to emit control signals to different parts and components of the vehicle, such as e.g. means for controlling the injection nozzle 205. The present invention can thus be implemented in any of the above control units, or in any other applicable control unit in the control system of the vehicle.

Furthermore, the control units' control of various functions is often controlled by programmed instructions. These programmed instructions typically consist of a computer program, which when executed in the control unit causes the control unit to perform the desired control, such as for controlling the various functions present in the vehicle, and also for performing method steps according to the present invention.

The computer program usually forms part of a computer program product, wherein the computer program product comprises an applicable storage medium 121 (see Fig. 1B) with the computer program stored on said storage medium 121.

The computer program may be non-volatile stored on said storage medium. Said digital storage medium 121 may e.g. consists of any of the group: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash memory, EEPROM (Electrically Erasable PROM), a hard disk drive, etc., and be arranged in or in connection to the control unit, the computer program being executed by the control unit. By changing the instructions of the computer program, the behavior of the vehicle in a specific situation can thus be adapted.

An exemplary control unit (UDS control unit 204) is shown schematically in Fig. 1B, the control unit in turn may comprise a calculation unit 120, which may be constituted by e.g. any suitable type of processor or microcomputer, e.g. a Digital Signal Processor (DSP), or an Application Specific Integrated Circuit (ASIC). The computing unit 120 is connected to a memory unit 121, which provides the computing unit 120 e.g. the stored program code and / or the stored data calculation unit 120 need to be able to perform calculations, e.g. to determine whether an error code should be activated. The calculation unit 120 is also arranged to store partial or final results of calculations in the memory unit 121.

Furthermore, the control unit is provided with devices 122, 123, 124, 125 for receiving and transmitting input and output signals, respectively. These input and output signals may contain waveforms, pulses, or other attributes, which of the devices 122, 125 for receiving input signals may be detected as information for processing the calculation unit 120. The devices 123, 124 for transmitting output signals are arranged to convert calculation results from the calculation unit. 120 to output signals for transmission to other parts of the vehicle control system and / or the component (s) for which the signals are intended. Each of the connections to the devices for receiving and transmitting input and output signals, respectively, may consist of one or more of: a cable; a data bus, such as a CAN bus (Controller Area Network bus), a MOST bus (Media Oriented Systems Transport), or any other bus configuration; or a wireless connection.

As mentioned above, the SCR catalyst 201 for its function depends on the availability of the applicable substance with which the desired reduction can be carried out, such as e.g. ammonia NH3, which as above can be added by adding the appropriate additive. When reducing nitrogen oxides NOxi SCR catalyst, it is important that nitric oxide NOx and ammonia NH3 respectively are supplied in the right proportions in relation to each other. If too little ammonia NH3 is added to the SCR catalyst in relation to the presence of nitrogen oxides N0X in the exhaust gas stream, a surplus of nitrogen oxides N0Xatt will prevail after the SCR catalyst 201. Nitric oxide emissions are, as mentioned, regulated in laws where limit values may not be exceeded. An excessively small amount of available ammonia NH3 thus entails a risk that nitrogen oxides NOx will not be reduced to the desired extent, whereby limit values with regard to nitrogen oxides NOx may be exceeded.

Conversely, if an excessive amount of ammonia NH3i is added in relation to the amount of nitrogen oxides NOxi the exhaust gas stream, an excess of ammonia will prevail after the SCR catalyst and thus also be released into the environment of the vehicle 100. Ammonia NH3 consists of a strong-smelling and also harmful substance, which is also often regulated by law with regard to emissions, which is why excess ammonia is not desirable either.

It is thus desirable that the supply of ammonia NH3 be regulated in such a way that as little as possible presence of nitric oxide NOx and / or ammonia NH3 prevails when the exhaust gas stream is discharged into the vicinity of the vehicle 100. For this reason, adaptations are made to the supply of additives to ensure that an expected amount of additives is also actually supplied to the exhaust gas stream.

In this adaptation, and also for the general determination of the presence of nitrogen oxides in the exhaust gas stream downstream of the SCR catalyst, a NOx sensor 208 (down Fig. 2) arranged downstream of the SCR catalyst 201 can be used. However, the NOx sensor 208 is usually cross-sensitive to ammonia NH3, which means that emitted sensor signals represent the total presence of nitrogen oxides NOx and ammonia NH3, respectively. This means that in cases where the NOx sensor 208 detects an elevated value, it is not possible to determine based on the signals given alone whether the reason for the elevated value is that the dosage of ammonia is too high, whereby the proportion of ammonia downstream of the SCR catalyst 201 is too high, or whether the dosage of ammonia is too low and the proportion of residual nitrogen oxides NOx downstream of the SCR catalyst 201 is thus too high.

Therefore, in order to avoid such uncertainty, adaptation usually involves a process in which the NOx conversion is reduced, i.e. the supply of additives is reduced to a level where it can be ensured that complete NOx conversion will not prevail, and that an excess of nitrogen oxides NOxi the exhaust gas flow will thus certainly prevail.

This is illustrated in Fig. 3, where a curve 305 of the NOx conversion as a function of added additive is shown. The X-axis shows the ammonia-nitrogen oxide ratio (ANR), which consists of Image available on "Original document" ie. the amount (content) of ammonia NH3 divided by "crude NOx". "crude NOx" is the untreated amount (content) of nitric oxide NOx upstream of the SCR catalyst 201. The amount / content of crude NOx can be determined with an upstream SCR catalyst 201, and preferably upstream of the position at which additives are supplied to said aftertreatment system, arranged. generally one mole of ammonia NH 3 is required to reduce one mole of nitrogen oxides NOx, so complete (100%) conversion, ie. complete reduction of nitrogen oxides NOx, ideally obtained at a ratio ANR = 1, as also shown in the figure. During the reduction, ammonia and nitrogen oxides react with each other to mainly form nitrogen gas and water vapor. Thus, ideally the same amount of ammonia is added as the amount of nitrogen oxides NOxi the exhaust gas stream. Thus, to the left of ANR = 1 in Fig. 3 there is a deficit of ammonia, while an excess of ammonia prevails to the right of ANR = 1.

In Fig. 3, the y-axis represents the degree of conversion in percent, which e.g. can be expressed, in percent, as: Image available on "Original document" where tpNOx represents "tailpipe" -NOx, ie. the presence of nitric oxide when the exhaust gas stream is released into the vehicle environment, determined by the NOx sensor 208.

As can be seen in Fig. 3, the same degree of conversion, using the NOx sensors 207, 208, can be obtained for two different actual conditions depending on the cross-sensitivity of the NOx sensors to ammonia NH3. This is exemplified in Fig. 3 for approx. 90% conversion rate with points 301 and 302, respectively. The closer the conversion is to maximum (100%) conversion, the closer these points will be, and if the conversion rate is high, it can be difficult to know for sure if the dosage is actually at point 301, whereby an increase in the amount of additive added should be performed, or if the conversion is in practice at point 302 with the consequence that the amount of additive added should instead be reduced.

For this reason, upon adaptation, the degree of conversion can be reduced to a degree of conversion where there is certainly, or with a very high probability, a deficit of ammonia NH3. This is illustrated by point 303, which in this example represents approx. 80% conversion rate. If in such a situation it is established that the expected conversion rate in practice is less than (or exceeds) the expected conversion rate, e.g. by the estimated conversion rate being at point 304 instead of expected point 303, the supply of additives can be adjusted (in this case increased) so that expected conversion is obtained by forcing the conversion to follow curve 305 instead of 306.

By proceeding in this way, it is thus possible to adapt the supply of additives without, or at least with a reduced, risk that excess ammonia will affect the result. However, such adaptation has the disadvantage that the reduction in the degree of conversion inevitably leads to increased emissions of nitrogen oxides NOx. This in turn means that adaptation due to the increased emissions cannot be carried out as often as desired, and the adaptation possibilities can also be regulated by the authorities.

As is known, vehicles are usually driven under very varying conditions, with the result that the internal combustion engine operates transiently and non-stationary. This in turn causes difficulties in adaptation as large variations in the estimated degree of conversion will occur. Fig. 4 shows an example of how the estimated conversion can vary with the time t when the internal combustion engine 101 operates transiently. Line 401 represents the desired setpoint 80% at the time of adaptation, solid line 402 represents estimated setpoints and dashed line 403 represents the mean of the estimation, thus constituting point 304 in Fig. 3.

Since the power of the internal combustion engine 101 can vary widely during adaptation, it can be difficult to obtain reliable values. For example. it may be desirable that the output of the internal combustion engine 101 be at least to some applicable value, whereby only parts of the estimation shown in Fig. 4 can be considered representative and thus applicable for actual use in the adaptation. This means that the adaptation can take a very long time, e.g. in cases where longer periods of low internal combustion engine load occur during the adaptation and which are therefore not taken into account.

The present invention provides a method that makes better use of available adaptation time, and as above, Fig. 5 shows an exemplary method 500 according to the present invention. The process begins in step 501 where it is determined whether adaptation should be performed. When this is the case, the procedure proceeds to step 502. The adaptation can e.g. be arranged to be performed at applicable intervals, or when the NOx sensor 208 outputs values indicating that adaptation should be performed, or for any other appropriate reason.

In step 502, the conversion rate is reduced to a first conversion rate OMV1, which may be any applicable conversion rate, such as e.g. 80% according to the above example, or other applicable conversion rate. The process then proceeds to step 503, where it is determined whether conversion to said first conversion degree OMV1 has been performed. In general, there is a certain inertia in the system, e.g. due to stored ammonia NH3i SCR catalyst 201. It may therefore take some time before stored / stored ammonia NH3 has been consumed and the degree of conversion has thus actually been reduced. This reduction can be assumed to take a certain time, but according to the present embodiment it is instead determined whether a work W2 has been performed by the internal combustion engine 101 since reduction of the degree of conversion to said first degree of conversion was requested. For example. this work can be a work that is expected to reduce the stored ammonia NH3i to the desired extent.

This is illustrated in Figure 6, where the adaptation method of the present example is shown. Until time T1, the vehicle 100 is driven with any applicable expected degree of conversion, such as e.g. 95%. In the case of adaptation, a decrease in the setpoint for the nitrogen oxide conversion to OMV1 (such as to 80%) then begins at time T1. Starting from the time T1, a "swing-in time" is thus applied in order to e.g. ammonia stored in the SCR catalyst 201 must be reduced to the desired extent, and where this swing-in time thus according to an embodiment consists of a work performed by the combustion engine 101. The actual time taken by the oscillation process, the time up to the time T2 in Fig. 6, can thus vary from time to time depending on the load of the internal combustion engine 101 and thus the amount of nitrogen oxides generated per unit time.

Thus, in step 503, it is determined whether a desired work W2 has been performed by the internal combustion engine 101, and as long as this is not the case, the process remains in step 503, while the process proceeds to step 504 when desired work W2 has been performed at time T2 in Fig. 6. work W2 can be estimated in any applicable manner, and usually in the vehicle 100 control system there are well-functioning functions for estimating the work performed by the internal combustion engine 101.

The work can e.g. represented by a work expressed in kilowatt hours (kWh) or other applicable unit alternatively e.g. is represented by a quantity of fuel supplied to the internal combustion engine 101, such as e.g. a certain volume and / or weight, or a calculated energy content for added fuel. According to one embodiment, a swing-in time is applied instead, which consists of some applicable time which thus does not have to be controlled by the work of the internal combustion engine.

In step 504, the adaptation itself, which is performed during the time T2-T3 in Fig. 6, is then started by setting a first N1 and a second N2 variable to zero, respectively, where these variables N1 and N2 respectively represent accumulated nitric oxide amounts after and before the SCR catalyst 201, i.e. tpNOx ack, respectively rawNOx ac, k. Likewise, a variable representing generated internal combustion engine work can be set to zero. The NOx sensors 207, 208 emit a NOx content present in the exhaust gas flow, and by utilizing this NOx content together with the flow of the exhaust gas stream, which can be determined in an appropriate manner such as e.g. by means of a flow meter, the actual amount of nitric oxide NOx can be determined. Said amounts of nitric oxide N1 and N2, respectively, accumulate continuously as long as it is determined in step 505 that a work W1, which e.g. can consist of a larger work compared to the work W2 above, has not yet been performed by the internal combustion engine 101 of the vehicle 100 since the accumulation of nitrogen oxides NOx was started. Thus, as long as the desired work W1 has not been performed since the accumulation began, the amount of nitrogen oxides NOx accumulates before and after the SCR catalyst 201, respectively.

When then the desired work W1 during ongoing accumulation has been performed, the accumulation of nitric oxide is stopped and the process proceeds to step 506, where the NOx conversion is estimated, which e.g. can be performed according to eq. 1 above or by using a corresponding equation. For example. the conversion rate can be written as (in this example not expressed as a percentage): Image available on "Original document" In step 507 it is then determined whether correction of the supply of additives is to be performed and if not, e.g. so that the estimated degree of conversion corresponds to the desired degree of conversion, the process is terminated in step 509 while otherwise the supply of additives is corrected in step 508 before the process is terminated in step 509. This correction can e.g. determined as a correction factor, which e.g. can be written as Image available on "Original document" ie. the setpoint for the conversion rate divided by the conversion rate estimated at the time of adaptation. When the accumulation of nitric oxide NOx has been completed at time T3 in Fig. 6, the setpoint for reducing nitrogen oxides NOx can be reset, e.g. in any applicable of steps 506-509, to the pre-adaptation setpoint, or other applicable setpoint.

The present invention has the advantage that the adaptation can take place continuously, and by performing the estimation for a certain work, the adaptation can take place continuously regardless of whether the internal combustion engine 101 currently emits a high or low power. The time the adaptation takes, the time between T2-T3 in Fig. 6, will thus vary from time to time, where adaptation under low internal combustion engine load will take a longer time because it will take a longer time before the desired amount of nitrogen oxides has accumulated.

During the adaptation, the estimated degree of conversion will vary, e.g. according to curve 601 in Fig. 6, and as can be seen, the estimation of the degree of conversion will not be constant at desired e.g. 80% but can vary markedly for different times. According to the present invention, however, a fair mean value is obtained since the work of the internal combustion engine is taken into account. According to known technology, however, there is a risk that e.g. measurement at points such as e.g. 602 or 603 in Fig. 6 has a large impact on the estimated conversion ratio, with a high risk that an incorrect degree of conversion is determined and thus incorrect adjustment of the supply of additives is performed because the work of the internal combustion engine can vary greatly with the result that e.g. conversion rate at low load has an unjustifiably large impact. This is avoided according to the present invention.

The present invention thus provides a process which allows a good adaptation of the supply of additives, whereby also the desired conversion of nitrogen oxides NOx with greater probability can be obtained. The invention thus provides a significantly improved accuracy in adaptation compared to previously known solutions. According to the present invention, a method is also obtained where available adaptation time is utilized optimally because it is constantly utilized and the adaptation can be interrupted as soon as the desired work has been performed.

The present invention has been described above in connection with the reduction of nitric oxide NOx, but as will be appreciated by those skilled in the art, the invention is equally applicable to the reduction of any substance where conversion takes place by using an added additive. The supply of additives generally follows an applicable curve, where this curve can be measured in an engine sample cell with very accurate sensors, and where the amount of added additive is controlled e.g. based on the amount of nitrogen oxides NOx indicated by the NOx sensor arranged upstream of the SCR catalyst. Thus, the present invention provides a compensation factor for compensating for deviations from this curve.

Furthermore, the setpoint according to the method according to the invention can be arranged to be varied during ongoing adaptation.

The reason for this can e.g. be that the ability of the SCR catalyst to convert nitric oxide NOx may vary with different conditions. For example. a low catalyst temperature causes a smaller amount of nitrogen oxides NOxcan to be reduced, while conversely a high catalyst temperature causes a larger amount of nitrogen oxides NOxcan to be reduced. The flow of the exhaust stream also affects the size of the catalyst experienced by the exhaust stream.

When calculating the conversion factor during adaptation, an accumulation of nitrogen oxides NOx upstream of the catalyst is applied above. According to one embodiment, this accumulation can be replaced by a calculated amount, where the amount can be calculated based on any applicable model of the internal combustion engine and e.g. the amount of fuel supplied to the internal combustion engine. Thus, according to this embodiment, the ??? sensor 207 shown in Fig. 2 is not required.

The present invention has been exemplified above in connection with vehicles. However, the invention is also applicable to arbitrary means of transport such as aircraft or watercraft and also to industrial installations where a control system is used to control existing functions, and where parameters concerning physical conditions of the unit controlled by the control system can be determined.

Further embodiments of the method and system according to the invention are found in the appended claims. It should also be noted that the system may be modified according to various embodiments of the method according to the invention (and vice versa) and that the present invention is thus in no way limited to the above-described embodiments of the method according to the invention, but relates to and includes all embodiments within the appended independent the scope of protection of the requirements.

For example. For example, the present invention is applicable to the adaptation of all currently known and also future additives which are supplied to the exhaust gas stream to reduce any substance present in the exhaust gas stream. Likewise, the invention as above is equally applicable regardless of which substance in the exhaust gas stream is reduced. The invention is thus in no way limited to the reduction of nitrogen oxides, or additives from which ammonia is formed.

Claims (18)

Patent claims A method of correcting the supply of a first additive for treating an exhaust stream resulting from combustion in an internal combustion engine (101), said first additive being supplied to said exhaust stream and said first additive being used to reduce at least one first substance present in said exhaust stream. (NOx), characterized in that the method comprises, in said correction: - starting a first accumulation (N1) of a representation of said first substance (NOx), said first accumulation (N1) of said representation of said first substance (NOx) ) represents an accumulated amount of said first substance (NOx) downstream of said supply of said first additive; - determining whether a first work (W1) has been performed by said internal combustion engine (101) during accumulation of said first substance (NOx); interrupting said first accumulation of said first substance (NOx) when said first work (W1) has been performed by said internal combustion engine (101); correcting the supply of said first additive based on said first accumulation (N1) of said first substance (NOx), - further comprising, before starting said first accumulation of said first substance (NOx): - reducing the supply of said first additive to said exhaust gas. The method of claim 1, further comprising: - utilizing signals emitted by a first sensor arranged downstream of said first additive of said first additive in said first accumulation (N1) of said first substance (NOX). A method according to claim 1 or 2, wherein said first accumulation (N1) of said first substance (NOX) constitutes an accumulation of the amount of said first substance (NOX) passing with said exhaust gas stream. A method according to any one of claims 1-3, further comprising: - comparing said first accumulation (N1) of said first substance (NOx) with a second amount (N2), and - correcting supply of said first additive based on said comparison . The method of claim 4, wherein said second amount (N2) represents a second accumulation of said first substance (NOx) in said exhaust stream upstream of said supply of said first additive. A method according to claim 4 or 5, wherein said second amount (N2) is determined by using an upstream said supply of said first additive arranged sensor (207). A method according to any one of claims 4-6, further comprising: - determining a ratio between said first amount (N1) and said second amount (N2), respectively, - comparing said determined ratio with a first ratio, and - correcting supply of said first additive based on said comparison. A method according to any one of the preceding claims, further comprising reducing said supply of said first additive to a first degree of conversion with respect to reduction of said first substance (NOX). A method according to claim 7 or 8, further comprising: - starting said first accumulation (N1) of said first substance (NOX) a first time (T2-T1) after said supply of said first additive has been reduced. A method according to any one of claims 7-9, further comprising: - determining whether a second work (W2) has been performed by said internal combustion engine (101) since reduction of said supply of said first additive was started, and - starting said first accumulation ( N1) of said first substance (NOx) when said second work (W2) has been performed by said internal combustion engine (101). A method according to claim 1 or 10, wherein said first and / or second work consists of a work corresponding to a first number of kilowatt hours (kWh) or a first amount of fuel supplied to said internal combustion engine (101). A method according to any one of the preceding claims, further comprising determining a correction factor for correcting the supply of said first additive. A process according to any one of the preceding claims, wherein said first additive is fed upstream of a first catalyst (201), and wherein said first accumulation (N1) of said first substance (NOx) is an accumulation of a representation of said first substance (NOx). ) downstream of said first catalyst (201). The process of claim 13, wherein said first catalyst is an SCR catalyst (201). A computer program comprising program code, which when said program code is executed in a computer causes said computer to perform the method according to any one of claims 1-14. A computer program product comprising a computer readable medium and a computer program according to claim 15, wherein said computer program is included in said computer readable medium. A system for correcting the supply of a first additive for treating an exhaust stream resulting from combustion in an internal combustion engine (101), said first additive being supplied with said exhaust stream and said first additive being used to reduce at least one first substance present in said exhaust stream. (NOx), characterized in that the system comprises means adapted to, in said correction: - start a first accumulation (N1) of a representation of said first substance (NOx), said first accumulation (N1) of representation of said first substance ( NOx) represents an accumulated amount of said first substance (NOx) downstream of said supply of said first additive; - determining whether a first work (W1) has been performed by said internal combustion engine (101) during accumulation of said first substance (NOx); interrupting said first accumulation of said first substance (NOx) when said first work (W1) has been performed by said internal combustion engine (101); correcting the supply of said first additive based on said first accumulation (N1) of said first substance (NOx); and - reducing the supply of said first additive to said exhaust gas stream before starting said first accumulation of said first substance (NOX). Vehicle (100), characterized in that it comprises a system according to claim 17.