The present invention pertains to combustion engines, and in particular to a method for the control of a combustion engine according to the preamble of claim 1. The invention also relates to a system and a vehicle, as well as a computer program and a computer program product, which implement the method according to the invention.

Background of the invention

The background description below constitutes a background description for the invention, and thus need not necessarily constitute prior art technology.

In connection with increased government interests concerning pollution and air quality, emission standards and regulations regarding emissions from combustion engines have been drafted in many jurisdictions.

Such emission regulations often consist of requirements defining acceptable limits for exhaust emissions in vehicles equipped, with combustion engines. For example, levels of nitrogen oxides (N0 _X ) , hydrocarbons (HC) and carbon monoxide (CO) are often regulated. These emission regulations may also handle the occurrence of particles in exhaust emissions.

In an effort to comply with these emission regulations, the exhausts caused by the combustion of the combustion engine are treated (purified) , By way of example, a so-called catalytic purification process may be used, so that exhaust treatment systems in e.g. vehicles and other vessels usually comprise one or more catalysts and/or other components. For example, the exhaust treatment systems in vehicles with a diesel engine often comprise particulate filters. The occurrence of unwanted compounds in the exhaust flow, resulting from the combustion engine, is to a large extent caused by the combustion process in the combustion engine's combustion chamber, at least partly depending- on the amount of fuel consumed in the combustion. For this reason, and due to that a very large part of the operating economy of primarily heavy goods vehicles is controlled by the amount of fuel consumed, great efforts are also made to make the combustion engine's combustion more efficient in an effort to reduce emissions and fuel consumption,

SuHsmary of the invention

One objective of the present invention is to provide a method to control a combustion engine. This objective is achieved with a method according- to claim 1. The present invention pertains to a method for the control of a combustion engine, where said combustion engine comprises at least one combustion chamber and elements for the supply of fuel to said, combustion engine, wherein the combustion in said combustion chamber occurs in combustion cycles. The method is characterised in that:

- during a first part of a first combustion cycle, a first measure of nitrogen oxides NO _x resulting from, combustion during said first combustion cycle is estimated, and

- based on said first measure, the combustion during a

subsequent part, of said combustion cycle is controlled.

As mentioned above, the efficiency of the combustion engine has a great impact on a. vehicle's total economy, in particular with respect to heavy goods vehicles. For this reason, it is often desirable that the combustion is controlled in a manner that entails as efficient a combustion as possible. Combustion may also be controlled with respect to desired exhaust features. For example, the timing of injection and/or the amount of injected fuel may be controlled in order to impact the course of the combustion and thus the temperature and/or composition of the exhaust stream. For example, in certain cases a higher exhaust temperature may be desirable at the expense of the efficiency of the combustion engine, in order for a desired function for one or several components in the after-treatment system to be obtained. It. may also be the case that the total efficiency, including the exhaust after- treatment, may be improved even in the event of a

deter'iorati on of the combustion engine ' s efficiency, because of e.g. reduced consumption of reducing agent, such as urea supply for the reduction of nitrogen oxides NO _x , i.e. nitrogen monoxide NO and nitrogen dioxide NO ₂ , respectively, which are generally comprised in the generic term nitrogen oxides NO _z , in the exhaust stream. In certain situations, a deterioration of the total efficiency may also be acceptable, e.g. to achieve a desired condition in the after-treatment system.

The present invention pertains to controlling the combustion process where an ongoing combustion cycle's progress may be controlled during the ongoing combustion to achieve a desired result of the combustion. Specifically, the combustion's progress is controlled with respect to a resulting nitrogen oxide content during the combustion.

Control according to the present invention may be achieved by, during a first part of a first combustion cycle, predicting- a first measure of nitrogen oxides NO _x by estimation such as a content and/or quantity/mass for the resulting nitrogen monoxide (NO) and/or nitrogen dioxide (NO ₂ ) , resulting from the combustion during- said first combustion cycle, and - based on said first measure, by controlling the combustion during a subsequent part of said first combustion cycle with the objective to impact, during the ongoing combustion cycle, the resulting- nitrogen oxides NO _x during said first combustion cycle .

A first parameter value representing a physical quantity relating to combustion in said combustion chamber may be determined, during said first part of said combustion cycle, and based on said first parameter value said first measure may be estimated. Said first parameter value thus constitutes a representation of an actually prevailing condition for said physical quantity at a point in time/crank angle position when said first combustion cycle has been initiated. Said first parameter value may be determined through the use of sensor elements such as pressure sensor elements.

By proceeding in this manner, the nitrogen oxides NO _x resulting during combustion may be controlled, so that the desired control, e.g. minimisation of nitrogen oxides NO _z , may to a great extent be obtained during combustion. For example, it may be desirable for the total amount, of nitrogen oxides NO _x , at a maximum, to equal a certain applicable amount. For example, the nitrogen oxide emissions may be controlled, with the objective of being as proximate to the legislation as possible as regards nitrogen oxide emissions, with a positive impact on the fuel consumption as a consequence.

Alternatively, it may be desirable to attempt to

reduce/minimise the nitrogen oxides NO _x resulting at combustion to the greatest extent possible. According to the invention, the nitrogen oxides NO _x usually resulting but unwanted at combustion, may usually be controlled already during the combustion process, e.g. in order to reduce the load on the after-treatment system, and e.g. in order to reduce the use of reducing (additive) agents such as urea-containing additives.

Control according to the present invention may thus be

achieved, by, during a first part of the combustion cycle, i.e. when the combustion cycle has been started, determining a parameter value representing a physical quantity during combustion, e.g. a pressure prevailing in the combustion chamber. Based on this parameter value, e.g. a pressure prevailing in a combustion chamber, the resulting nitrogen oxides ΝΟχ may be estimated during the combustion cycle, not only for the already lapsed part of the combustion cycle but also for the future part of the said combustion cycle, , so that the combustion during the subsequent part of the

combustion cycle may then be controlled with respect to resulting nitrogen oxides NO _z , where e.g. the combustion during the subsequent part, of said combustion cycle may be controlled with the objective of, compared with the estimated resulting nitrogen oxides NO _x , reducing the resulting nitrogen oxides NO _x so that the nitrogen oxides NO _x actually resulting during the combustion cycle may e.g. be reduced in relation to the estimated nitrogen oxides NO _x . The parameter value may be arranged to be determined when the combustion of fuel has been started during said first combustion cycle.

During the control of combustion, the combustion may be arranged to be controlled with respect to any applicable physical quantity, e.g. pressure and/or temperature in the combustion chamber, where the resulting- nitrogen oxides NO _x may be controlled by controlling said quantity, e.g. pressure and/or temperature, where the control is carried out based on a correlation between the pressure and/or temperature during combustion and the resulting nitrogen oxides NO _x . The control may e.g. be arranged to be regulated based on the temperature and/or pressure change which the combustion process undergoes during the combustion cycle, i.e. the control may be carried out based on how the combustion temperature varies during the combustion, where the combustion e.g. to the extent possible may be made to track some applicable pressure/ temperature curve, where this pressure/temperature curve is controlled by impacting the combustion during an ongoing combustion cycle, so that a desired variation is obtained during the combustion. The control may e.g. be arranged to be controlled toward an empirically or otherwise determined pressure/temperature curve (track), alternatively e.g. toward a limitation of the maximum temperature and/or the maximum pressure which arises during the combustion.

The method according to the invention may comprise to

determine a parameter value, corresponding to said first parameter value, at. several points in time/crank angle

positions during said first combustion cycle, and to estimate a respective measure of nitrogen oxides resulting at

combustion during said first combustion cycle for said several parameter ^' values. Following the determination of the

respective parameter value, the combustion may then be

controlled during a subsequent part of said first combustion cycle based on a respective estimated measure of nitrogen oxides. Said parameter value corresponding to said first parameter value may be determined at a number of points in time/crank angle positions after the combustion of fuel has been initiated during said first combustion cycle.

The regulation of the combustion may also be arranged to be carried out individually for each cylinder, and it is also possible to control a combustion during a subsequent

combustion cycle, based on information from one or several previ ous combustion processes . This type of control has the advantage that e.g. differences between different cylinders may be detected and compensated with the help of individual adjustment of parameters for a specific cylinder, such as the opening time for the injection nozzle, etc. However, it may also be the case that differing control of different cylinders may be desirable, e.g. in order to control certain cylinders toward the fulfilment of some criterion, and other cylinders toward some other applicable criterion, which may also be achieved according to the

invention. Further, only one or some of the cylinders may be arranged to be controlled according to the invention, while combustion in the remaining cylinders may be carried out in a customary or other applicable manner.

According to one embodiment, an injection schedule is

determined which results in at least half of the requested work being achieved, in order to ensure that the work, achieved may not be regulated to a level which is too low when

generated nitrogen oxides NO _x are regulated.

The method, according to the present, invention may e.g. be implemented with the help of one or several FPGA (Field- Programmable Gate Array) circuits, and/or one or several ASIC (application-specific integrated circuit) circuits, or other types of circuits which, may handle the desired calculation speed .

Further characteristics of the present invention and

advantages thereof will be described in the detailed

description of example embodiments set out below and in the enclosed drawings .

Fig. 1A snows schematically a vehicle in which the present invention may be used. Fig. IB shows a control device in the control system for the vehicle shown in Fig. 1A.

Fig. 2 shows the combustion engine in the vehicle shown in

Fig. 1A in more detail.

Fig. 3 shows an example embodiment according to the present invention .

Fig. 4 shows an example of an estimated temperature track in a combustion.

Figs. 5A-B show an example of regulation in situations with more than three injections.

Fig, 6 shows an example of MFC.

Fig. 7 illustrates an alternative method for estimation of pressure changes during a combustion process.

Detailed description of enihodiniesits

Fig. 1A shows schematically a driveline in a vehicle 100 according to an embodiment of the present invention. The driveline comprises one combustion engine 101, which in a customary manner, via an output shaft on the combustion engine 101, usually via a flywheel 102, is connected to a gearbox 103 via a clutch 106.

The combustion engine 101 is controlled by the engine's control system via a control device 115. Likewise, the clutch 106, which may consist of e.g. an automatically controlled clutch, as well as the gearbox 103 are controlled by the vehicle's control system, with the help of one or more

applicable control devices (not shown} . Naturally, the

vehicle's driveline may also be of another type, such as a type with a conventional automatic gearbox, or a type with a manual gearbox, etc. An output shaft 107 from the gearbox 103 operates the driving wheels 113, 114 in a customary manner via the end gear and driving shafts 104, 105. Fig. 1A shows only one shaft with driving wheels 113, 114, but in a customary manner the vehicle may comprise more than one shaft equipped with driving wheels, or one or more extra shafts, such as one or more support shafts . The vehicle 100 also comprises an exhaust system with an after-treatment system 200 for customary treatment

(purification) of exhaust, emissions resulting from combustion in the combustion chamber (e.g. cylinders} of the combustion engine 101.

The after-treatment system often comprises some form, of catalytic purification process, where one or several catalysts are used to purify the exhausts. Vehicles with diesel engines often also comprise a diesel particulate filter (DPF) in order to catch soot particles formed during combustion of fuel in the combustion engine's combustion chamber. Further, after- treatment systems in vehicles of the type shown may comprise an oxidation catalyst (Diesel Oxidation Catalyst, DOC) . The oxidation catalyst DOC has several functions, and is normally used primarily in the after-treatment to oxidise remaining hydrocarbons and carbon monoxide in the exhaust stream into carbon dioxide and water. The oxidation catalyst may also e.g. oxidise nitrogen monoxide (NO) into nitrogen dioxide (N0 ₂ ) . Also, an after-treatment system may comprise more components than as exemplified above, as well as fewer components. For example, the after-treatment system 200 may comprise an SCR (Selective Catalytic Reduction) catalyst arranged downstream of the particulate filter. SCR. catalysts use ammoniac (NH.3) , or a composition from which ammoniac may be generated/formed, as an additive to reduce the amount of nitrogen oxides NO _x in the exhaust stream. Further, combustion engines in vehicles of the type shown in Fig. 1A are often equipped with controllable injectors, in order to supply the desired amount of fuel at the desired point in time in the combustion cycle, such as at a specific piston position (crank angle degree} in the case of a piston engine, to the combustion engine's combustion chamber.

Fig. 2 shows schematically an example of a fuel injection system for the combustion engine 101 exemplified in Fig. 1A. The fuel injection system consists of a so-called Common Rail system, but the invention is equally applicable in other types of injection systems. Fig. 2 shows only one

cylinder/combustion chamber 201 with a piston 203 active in the cylinder, but the combustion engine 101 consists, in the present example, of a six-cylinder combustion engine, and may generally consist, of an engine with any number of

cylinders/combustion chambers, e.g. any number of

cylinders/combustion chambers in the range 1-20 or even more. The combustion engine also comprises at least one respective injector 202 for each combustion chamber (cylinder) 201. Each respective injector is thus used for injection/supply of fuel in a respective combustion chamber 201. Alternatively, two or more injectors per combustion chamber may be used. The

injectors 202 are individually controlled by respective actuators (not shown) arranged at the respective injectors, which, based on received control signals, e.g. from the control device 115, control the opening/closing of the

injectors 202.

The control signals for the control of the actuators'

opening/closing of the injectors 202 may be generated by some applicable control device, such as, in this example, by the engine control device 115. The engine control device 115 thus determines the amount of fuel which actually is to be injected at any given time, e.g. based on prevailing operating- conditions in the vehicle 100.

The injection system shown in Fig. 2 thus consists of a so- called Common Rail system, which means that all injectors (and therefore all combustion chambers) are supplied with fuel from a common fuel conduit 204 (Common Rail) , which, with the use of a fuel pump 205, is filled with fuel from, a fuel tank (not. shown) at the same time as the fuel in the conduit 204, also with the help of the fuel pump 205, is pressurised to a certain pressure. The highly pressurised fuel in the common conduit 204 i s then injected into t.he combustion engine ' s 101 combustion chamber 201 when the respective injector 202 is opened. Several openings/closings of a specific injector may be carried out during one and the same combustion cycle, whereby several injections may thus be carried out during the combustion of one combustion cycle. Further, each combustion chamber is equipped with a respective pressure sensor 206, for sending of signals regarding a prevailing- pressure in the combustion chamber to e.g. the control device 115. The

pressure sensor may e.g. be piezo-based and should be fast enough to be able to send crank angle resolved pressure signals, e.g. at every 10th, every 5th or every crank angle degree or with another suitable interval, e.g. more

frequently.

With the help of a system of the type shown in Fig. 2, the combustion during a combustion cycle in a combustion chamber- may to a large extent be controlled, e.g. with the use of multiple injections, where the times and/or duration of the injections may be controlled, and where data from e.g. the pressure sensors 206 may be taken into consideration in connection with this control. According to the present

invention, e.g. injection timings and/or the duration of the respective injections and/or the injected fuel amount, is adapted during an ongoing combustion, based on data from the ongoing combustion, with the objective of controlling the combustion with respect to the nitrogen oxides NO _x generated at combustion. Fig. 3 shows an example method 300, according to the present invention, where the method according to the present example is arranged to be carried out by the engine control device 115 shown in Figs, 1A-B.

In general, control systems in modern vehicles consist of a communication bus system consisting of one or more

communications buses to connect, a number of electronic control devices (ECUs) , such as the control device, or controller, 115, and various components arranged on the vehicle. According to prior art, such a control system may comprise a large number of control devices, and the responsibility for a specific function may be distributed among more than one control device.

For the sake of simplicity, Figs. 1A-B show only the control device 115, in which the present invention is implemented in the embodiment displayed. The invention may, however, also be implemented in a control device dedicated to the present invention, or wholly or partly in one or several other control devices already existing in the vehicle. Considering the speed at which calculations according to the present invention are carried out, the invention may be arranged to be implemented in a control device which is especially adapted for real time calculations of the type described below. The implementation of the present invention has shown that e.g. ASIC and FPGA solutions are suitable for and cope well with calculations according to the present invention.

The function of the control device 115 (or the control

device (s) at which the present invention is implemented), according to the present invention, may, apart from depending on sensor signals from the pressure sensor 202, e.g. depend on signals from other control devices or sensors. Generally, control devices of the type displayed are normally arranged to receive sensor signals from different parts of the vehicle, as well as from different control devices arranged on the

vehicle .

The control is often controlled by programmed instructions. These programmed instructions typically consist of a computer program, which, when it is executed in a computer or control device, causes the computer/control device to carry out the desired control action, as a method step in the process according to the present invention.

The computer program usually consists of a computer program product, where the computer program product comprises an applicable storage medium 121 (see Fig. IB), with the computer program stored on said storage medium 121. Said digital storage medium 121 may e.g. consist of any from the following- group: ROM (Read-Only Memory), PROM (Programmable Read-Only Memory), EPROM (Erasable PROM), Flash, EEPROM (Electrically Erasable PROM), a hard disk unit, etc., and may be set up in or in combination with the control device, where the computer program is executed by the control device. By changing the computer program's instructions, the vehicle's behaviour may thus be adjusted in a specific situation.

An example control device (control device 115) is shown schematically in Fig, IB, and the control device in turn may comprise a calculation unit 120, which may consist of e.g. a suitable type of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP) , one or several FPGA (Field-Programmable Gate Array) circuits or one or several circuits with a predetermined specific function (Application Specific Integrated Circuit, ASIC) , The calculation unit 120 is connected to a memory unit 121, which provides the calculation unit 120 with e.g. the stored program code and/or the stored data which the calculation unit 120 needs in order to be able to carry out calculations. The calculation unit 120 is also set up to store interim or final results of calculations in the memory unit 121.

Further, the control device is equipped with devices 122, 123, 124, 125 for receipt and sending of input and output signals. These input and output signals may contain waveforms, pulses, or other attributes which may be detected as information for processing by the calculation unit 120 by the devices 122, 125 for the receipt of input signals. The devices 123, 124 for sending output signals are arranged to convert the calculation result from the calculation unit 120 into output signals for transfer to other parts of the vehicle's control system and/or the component (s) for which the signals are intended. Each one of the connections to the devices for receipt and sending of input and output signals may consist of one or several of the following; a cable, a data bus, such as a CAN (Controller Area Network) bus, a MOST (Media Oriented Systems Transport.} bus, or any other bus configuration; or of a wireless

connection .

Reverting to the method 300 shown in Fig, 3, the method begins at step 301, where it is determined whether the control according to the invention of the combustion process should be carried out. The control according to the invention may e.g. be arranged to be carried out. continuously as soon as the combustion engine 101 is started. Alternatively, the control action may be arranged to be carried out e.g. as long as the combustion engine's combustion is not to be controlled

according to some other criterion. For example, there may be situations where it is desirable that, control action is carried out based on factors other than, primarily, the nitrogen oxides NO _x generated at combustion. According to one embodiment, simultaneous control of the combustion is carried out with respect to the resulting nitrogen oxides NO _x and. at least one additional control parameter. For example, a

weighing up may be carried out, where the control parameters' prioritisation on fulfilment of a desired control result may e.g. be arranged to be controlled according to some suitable cost function.

The method, according to the present, invention thus consists of a method for the control of the combustion engine 101, while the combustion takes place in said combustion chamber 201 in combustion cycles. According to prior art, the term combustion cycle is defined as the steps comprised in a combustion in a combustion engine, e.g. a two-stroke engine's two strokes and a four-stroke engine's four strokes. The term also includes cycles where no fuel is actually injected, but where the combustion engine is still operated with a certain engine speed, such as with the vehicle's driving wheels via the driveline in e.g. dragging. That is to say, even if no

injection of fuel is carried out, a combustion cycle is still completed for e.g. every two revolutions (for four-stroke engines), or e.g. every revolution (two-stroke engines), which the combustion engine's output shaft rotates. The same applies to other types of combustion engines.

In step 302, it is determined whether a combustion cycle has been or will be started, and where this is the case, the method continues to step 303 while a parameter i representing an injection number is set equal to one. In step 303, an injection schedule is determined, e.g. in an entirely conventional manner based on e.g. a desired achieved work. Alternatively, an injection schedule may be determined, which is expected to result in a wanted generation of nitrogen oxides NO;„ _: during the combustion, e.g. an injection schedule which is expected to result in maximally a certain amount of nitrogen oxides NO _x , or generally in a minimisation of

generated nitrogen oxides NO _x during the combustion cycle's combustion .

Generally, the supply of fuel, both with respect to quantity and manner of supply, i.e. the one or several fuel injections that are to be carried out during the combustion cycle, is normally defined in advance, e.g. depending on the work

(torque) which the combustion engine must carry out during the combustion cycle, since no change of the determined injection schedule is carried out during an ongoing combustion cycle according to prior art. Predetermined injection schedules may e.g. exist in tables in the vehicle's control system for a large number of operating modes, such as different engine speeds, different, requested work, different combustion air pressures, etc., where tabulated data may e.g. be prepared by ^¬ way of applicable tests/measurements during e.g. the

development of the combustion engine and/or vehicle, so that the applicable injection schedule may be selected based on prevailing conditions.

According to one embodiment, the injection schedules may be prepared, e.g. through applicable - such as empirical - tests/measurements, where several injection schedules may be defined for a specific operating condition and in order to result in a certain achieved work, but where different injection schedules may be prepared in order to fulfil different additional criteria, e.g. a criterion for the nitrogen oxides NO _x resulting during the combustion and/or other parameters. NO _x emissions may thus have been measured for different injection schedules and then fed into the vehicle's control system, where one injection schedule may initially be determined, by table lookup or in another applicable manner, based on e.g. a reference value for NO _x emissions. Thus, nitrogen oxide determinations may be carried out in advance for a large number of operating- modes, where these

determinations may be used in the selection of an injection schedule .

According to one embodiment, however, initially an injection schedule is thus applied which is determined based on e.g.

only requested work.

These injection schedules may consist of the number of

injections and respective characteristics in the form of e.g. timing (crank angle position) at the start of injection, the duration of the injection , the inject ion pressure and/or amount, etc., and thus may be stored for a large number of operating modes in the vehicle's control system, and e.g. be calculated/measured with the objective of fulfilling some criterion, such as a certain achieved work, a certain

resulting exhaust temperature or another applicable criterion.

According to one embodiment of the invention, the injection schedule may also be arranged to be determined before the combustion starts, i.e. already before a first fuel injection is carried out, by way of applicable calculations, e.g. as set out be1 ow, where e.g. different inj ection schedu1es defined in advance may be compared with each other in order to determine a most preferred injection schedule, and where e.g. a desired achieved work and/or desired emissions (e.g. a high/low fraction of nitrogen oxides NO _x ) may constitute parameters in the calculations.

According to the present embodiment. , in step 303 such a predetermined injection schedule is applied, where this predetermined injection schedule is selected based on some applicable manner as set out above, e.g. by way of table lookup, where, according to the above, different injection schedules may - but need not - be defined where different amounts of nitrogen oxides NO _x are expected at combustion at the same time as e.g. the same work on the combustion engine's output shaft is carried out, but where the injection schedule thus may also be arranged to e.g. only consider a desired achieved work, where control of generated nitrogen oxides NO _x may be arranged to be carried out only after a first

injection, or a first, part of an injection, has been effected.

Since specific assumed conditions probably result in the same preferred injection schedule every time, it. may be

advantageous to select an injection schedule by some type of lookup before a combustion cycle, and thus to reduce the calculation load, where a calculation, e.g. as set out below, may thus be carried out only after the injection has been started. In addition to the example below of how the injection schedule may be determined, other models with a similar function may alternatively be applied. The amount of nitrogen oxides NO _x desired, or desired at a maximum, during combustion may be determined in some

applicable manner, e.g. by an overall function that requests some applicable level for NO _x emissions. This level may e.g. be represented by a request for minimised NO _x emissions, but also by a request for higher NO _x emissions, e.g. if this is

considered, for some reason, desirable for subsequent rea.cti.ons in the after-treatment system, or e.g. a level corresponding to statutory levels for nitrogen oxide

emissions .

Fuel injection is thus normally carried out according to an injection schedule, where several injections may be arranged to be carried out during one and the same combustion cycle. This entails that the injections may be relatively short. For example, there are injection systems with 5-10 fuel

injections/combustion, but the number of fuel injections during a combustion cycle may also be significantly greater, e.g. in the range of 100 fuel injections. The number of possible injections is controlled generally by the speed of the elements with which injection is carried out, i.e. in the case of a Common Rail system how fast the injectors may be opened and closed.

According to the present example, at least three fuel

injections insp _x are carried out during one and the same combustion cycle, but as mentioned and as set out below, a greater number of injections may be arranged to be carried out, as well as only one.

A first injection inspi is carried out, and in step 304 it is determined whether said first injection inspi has been carried out, and if so, the method, continues to step 305, where it is determined whether all injections i have been carried out. Since this is not yet the case in the present example, the method continues to step 306 while i is incremented by one for the next injection. In step 306, the prevailing pressure in the combustion chamber is determined with, the use of the pressure sensor 206. Further, with the use of the pressure sensor 206, the prevailing pressure in the combustion chamber may be determined substantially continuously, such as with applicable intervals, e.g. every 0,1-10 crank angle degrees.

The combustion process may generally be described with the pressure change in the combustion chamber, which the

combustion gives rise to. The pressure change during a

combustion cycle may be represented by a pressure track, i.e. a representation of how the pressure in the combustion chamber varies during the combustion. As long as the combustion continues as expected, the pressure in the combustion chamber will be equal to the initially expected or estimated pressure. As soon as the combustion deviates from the expected

combustion however, the pressure will deviate from the

estimated pressure. Additionally, the combustion during the subsequent part of the combustion cycle and thus the

temperature development will be impacted.

In step 306, the pressure p _f(p i is determined in said combustion chamber 201 for a. prevailing crank angle degree cpi after said, first injection has been carried out, with the help of said pressure sensor 206, and in step 307 the injection schedule is evaluated and changed if needed by estimating expected

generated nitrogen oxides NO _x during the combustion cycle, which may be carried out with the help of applicable

calculations, where one way of carrying out the calculation is exemplified below. Alternatively, other models with similar functions may be applied.

Generally, nitrogen oxides NO _x at a combustion process are mainly formed for three different reasons. The fuel may comprise nitrogen, and nitrogen will be released during combustion and at least form nitrogen N9 and nitrogen oxides ΝΟχ. This type of NO _x formation may in some types of

combustion, and depending on the type of fuel, account for a large part of the total amount of nitrogen oxides NO _x which is generated at combustion. As explained below, this type of NO _x formation may, however, be disregarded during normal

combustion according to e.g. the diesel cycle. Another source of ΝΟχ formation consists of so-called prompt NO _x formation, but this may generally be disregarded since the impact is small in relation to other sources. A third source, which during normal combustion also constitutes the primary cause of ΝΟχ formation during combustion at high combustion

temperatures, consists of thermal formation of NO _x , which may account for in the range of 90-95% or even more of the NO _x formation during the combustion cycle. It is also primarily this type of NO _x formation which may be impacted by impacting the combustion, which is why NO _x control may be carried out with good results by only taking thermal NO _x formation into consideration, as carried out below.

The NOx formation is thus heavily dependent on the combustion temperature, and the formation itself of thermal NO _x may in a prior art manner be described e.g. according to three main reactions (the expanded Zeldovich mechanism) :

, where thus the reaction speed is heavily temperature

dependent, and where also the temperature dependency as such is known, where the amount of nitrogen oxides NO _x formed may be estimated through knowledge about the (substance) amount of the substances comprised and the temperature.

According to the present invention, NO _x formation is estimated with the use of the above chemical compounds, equation (1) , and with the use of an estimation of additional combustion data. The calculation thus also requires knowledge about the available amount of nitrogen N ₂ and oxygen 0 ₂ as well as knowledge about access to hydrogen H, These may be obtained from the combustion's combustion chemistry, which is known to a. person skilled in the art, and for which the supplied amount of fuel and combustion air, respectively, as well as any exhaust recirculation is known, where, in combination with the fact that the fuel composition is normally known, the amounts of the substances comprised in equation (1) may be calculated.

Also, an estimation of the combustion's temperature is

required for the amount, of nitrogen oxides NO _x generated to be estimated, since the reaction speed is temperature dependent. Likewise, an estimation of pressure and/or temperature in the combustion chamber is required in order to, through the combustion chemistry, be able to estimate released nitrogen and oxygen, respectively, during the combustion.

The combustion may, as is known to a person skilled in the art, be modelled according to equation (2):

, where K is used to calibrate the model. consists

of a constant which is usually in the range of 0-1, but may also be arranged to assume other values, and which is

determined individually, cylinder by cylinder, or for a certain engine or engine type, and depends in particular on the design of the injectors' nozzles (spreaders) . dQ may also be modelled in another suitable manner, e.g. by also including other parameters, e.g. turbulence at fuel supply, where this may be modelled in an applicable manner. Q _fuP , constitutes the energy value for the injected fuel amount , and Q consists of the amount of energy burned. The combustion dQ is thus proportionate to the injected fuel amount, minus the hitherto consumed fuel amount. The combustion dQ may, alternatively, be modelled with the use of another applicable model, where e.g. regard may be had also to other parameters. For example, the combustion may also constitute a function which depends on a model of turbulence at the supply of air/fuel, which may impact the combustion to different

extents, depending on the amount of air/ fuel supplied.

Regarding the fuel injections, these may e.g. be modelled as a sum of step functions:

The fuel flow measured in supplied mass m at an injection k, i.e. how the fuel enters the combustion chamber during the time window u when the injection is carried out, expressed as the time lapsed during the crank angle degree φ interval during which the injector is open, may be modelled for a specific injection k as: where m constitutes the injected fuel amount, and f (m) e.g. depends on the injection pressure, etc. f (m) may e.g. be measured or estimated in advance in a prior art manner .

The energy value for the fuel, such as diesel or petrol,

is generally specified, so that such a general specification may be used. The energy value may also be specifically provided, by e.g. the fuel manufacturer,, or be approximated for e.g. a country or a region. The energy value may also be arranged to be estimated by the vehicle's control system. With the energy value, the equation (2} may be resolved, and the heat release may be determined as the combustion progresses. Thus, the heat release for a future part of the combustion cycle may also be estimated by carrying out the calculations for expected future injections.

Further, through the use of a predictive heat release- equation, the pressure change in the combustion chamber may be est imated as e.g.:

, where φ constitutes a crank angle degree, i.e. the pressure change is expressed in crank angle degrees, which entails an elimination of the combustion engine speed dependency in the calculations, γ constitutes a parameter estimated in advance, or is set at a fixed value, γ constitutes the heat capacity ratio, i.e. C„ and/or C _v are prepared and tabulated for

different molecules, and since the combustion chemistry is known, these tabulated values may be used jointly with the combustion chemistry in order thus to calculate each

molecule's (e.g. water, nitrogen, oxygen, etc.) impact on e.g. the total C value, so that this may be determined for the calculations above with a good accuracy. Alternatively, C _D and/or C _v may be approximated in a suitable manner.

Integration of equation (5) entails the following result:

constitutes an initial pressure, which prior to the

beginning of the compression may e.g. constitute the ambient pressure for combustion engines without a turbo, or a

prevailing combustion air pressure for an engine with a turbo. When an. estimation is carried out at a later point in time during the combustion cycle, Ρ„ _ήήα ι may consist of the then prevailing pressure, determined with the use of pressure sensor 206, as the pressure p _f(pl at crank angle degree cpi as set out above. Thus the pressure in the combustion chamber may be estimated for the entire combustion, where the estimation after each inj ect. ion, or the next. est. imat. ion after a cert.ain time has lapsed, will result in an increasingly high accuracy in the estimation, since the actual pressure change during an increasing part of the combustion cycle will be known. The pressure may be estimated with some applicable resolution, such as crank angle degree or a tenth, hundredth or thousandth of a crank angle degree, etc..

At the estimation of the amount, of nitrogen oxides NO _x formed., knowledge about the combustion temperature itself is required. The temperature is higher in the part of the combustion chamber where the combustion is ongoing-, and the combustion chamber may be considered to consist of two zones, where combustion takes place in one zone, with a high temperature in this zone as a consequence, while no combustion, with a lower resulting temperature, takes place in the other zone.

The pressure change p as a function of crank angle degree φ in a cylinder (combustion chamber) for a. combustion cycle may be estimated according to equation (6) above. Further, with the use of an estimated pressure, the temperature for the part of the combustion chamber where no combustion occurs may be estimated with the help of an estimated pressure and with the use of equation (7), where the temperature for the part of the combustion chamber where no combustion takes place is

expressed as:

, where may constitute corresponding combustion air

temperature at the point in time/crank angle position where p is determined above, and

, where n, n+l, etc. constitute consecutive points in time or crank angle positions.

, where and/or and thus K , may be determined according

to what is set out above.

With the use of equation (7) the temperature for the part of the combustion chamber where no combustion takes place may be determined, where this temperature, however, is impacted by ongoing combustion through the action of the heat release on the pressure, which in turn impacts the temperature according to equation (7) . When a combustion then does take place, the neat release will give rise to a temperature increase in the part (s) of the combustion chamber where combustion is taking place. Such temperature increase, which is added to the temperature determined according to equation (7) in order to obtain the combustion temperature, may be calculated based on the connection :

, where constitutes heat release, which may be determined as above . m consists of burned mass (i.e. fuel + air + EGR comprised in the combustion) , which is also determined as set out above,

C _p , i.e. specific heat capacity, which may also be calculated as set out above. dT constitutes the temperature increase obtained from the combustion with a given burned mass and with a given C ₀ value.

By using equation (8), dT and therefore ΔΤ may thus be determined., so that, the increase generated by the combustion at each point in time/crank angle position may be added to the unburned zone's temperature, provided by equation (7), to obtain the combustion temperature. One example of the

variation of the combustion temperature for a combustion cycle is shown in Fig. 4.

When an estimation is carried out at a later point in time during the combustion, e.g. after a first fuel injection has been carried out, p _→ may be set as the pressure obtained through the pressure sensor 206, so that an estimation of a subsequent injection may be carried out with a starting pressure that takes into account the actual development of the previous combustion, so that a more accurate estimation for the subsequent combustion may be done. The estimated

temperature track for the combustion may thus have the

appearance e.g. of the temperature track in Fig-. 4. Obviously, the temperature track may, however, assume basically any appearance depending on the amount of fuel injected and the timing of the injection.

When the combustion temperature has been estimated,

concentrations and/or absolute amounts of primarily N ^' ₂ and O ₂ may thus be calculated with the use of the combustion

chemistry, so that, later, with the use of equation (1) and its combustion temperature dependency, generated nitrogen oxides NO _x may be estimated for the entire combustion cycle, i.e. also for the part which is subsequent to crank angle position cpl . The first injection will thus give rise to a combustion, and thus a neat release and a pressure increase. If the combustion had progressed exactly as estimated, the temperature development would be equal to the one initially expected.. The actual combustion temperature track will, however, very probably deviate from the predicted temperature track during the course of the combustion because of heat losses, deviations from the modelled combustion, etc. Thus the nitrogen oxides NO _x actually generated will differ from the expected, amount of nitrogen oxides NO _x (as set out above, no such estimation needs to have been carried out before the first injection), and the greater the temperature deviation becomes, the greater the difference between the estimated and the actually generated amounts of nitrogen oxides NO _x will probably be.

Since the pressure/temperature in the combustion chamber, after the first injection inspi has been carried out, may differ from the conditions expected according to the selected injection schedule, such as at crank angle position (pi in Fig. 4, the conditions in the combustion chamber at the point in time for the subsequent injection insp ₂ will also very probably differ from the predicted conditions, which is why the subsequent combustion will also very probably differ from the predicted combustion if the previously determined injection schedule were still used.

Thus, it is not at all certain that the desired nitrogen oxide levels will be achieved during the combustion cycle by the fuel injection according to prior art. Therefore it is also not certain that the originally determined injection schedule constitutes the most preferred injection schedule in an effort to achieve desired nitrogen oxide levels. It is for this reason that the control of the combustion according to the invention is carried out, and according to the present invention, the amount of nitrogen oxides NO _x which will be generated during a subsequent, part of the combustion cycle may be impacted after the first injection inspi has been carried out.

In step 307, therefore, an injection schedule is again

determined, with the objective of controlling the generation of nitrogen oxides NO _x , e.g. with the goal of minimising the nitrogen oxides NO _x generated during- the combustion cycle, or during the remaining part of the combustion cycle.

At the determination of an injection schedule, the above calculations may be carried out for several injection

schedules, so that subsequently an injection schedule is selected which is expected to result in generated nitrogen oxides NO _x fulfilling a desired condition.

At the calculations, several injection schedules determined in advance may be compared with each other, or calculations may be carried out for different injections where injection parameters, such as the injection time/duration, are gradually changed. At the evaluation of different injection schedules, it may also be advantageous to carry out control with the constraint that achieved work on the combustion engine's output shaft is maintained, since otherwise there is a large probability that only a small part of or no work at all will be achieved, to the extent that, only the generated nitrogen oxides NO _x are minimised, so that the efficiency relating to the generation of nitrogen oxides NO _x is optimised at the expense of low output. According to one embodiment, the control may thus be viewed as a minimisation problem, that consists of finding a control resulting in as small an amount of nitrogen oxides NO _x as possible being generated for a certain work achieved by the combustion engine.

Control of the combustion temperature in the combustion chamber may thus e.g. be carried out. by controlling- the fuel injection, and by, in step 307, carrying out an estimation of generated nitrogen oxides NO _x for a number of different injection schedules with varying injection times/injection durations /numbers of injections, an injection schedule may thus be determined which, to an applicable or as great an extent as possible, minimises heat losses during the

combustion .

Thus, in step 307, an injection schedule may be determined, such as one injection schedule among several defined injection schedules, which best minimises generated nitrogen oxides NO _x or fulfils another criterion with, respect to nitrogen oxides ΝΟχ, where such injection schedule may also be determined individually, cylinder by cylinder, e.g. based on sensor signals from at least one pressure sensor in the respective combustion chamber ,

When an injection schedule has been selected in step 307, the method, thus reverts to step 304 in order to carry out the next injection, so that this also gives .rise to a combustion, and thus a heat release and temperature track, which with great probability will deviate from the one just estimated in step 307, This also means that the combustion, also at subsequent injections, will probably be impacted by prevailing conditions in the combustion chamber when the injection is started.

The control action is then repeated during the ongoing

combustion cycle, in order to change the injection schedule where needed during an ongoing combustion, if the conditions actually prevailing in the combustion chamber differ from the predicted conditions. By continuously determining the pressure in the combustion chamber with the use of the pressure

transmitter 206, the actual pressure development may be compared continuously with the estimated pressure development, so that the method may also comprise initiating a

determination of a new injection schedule during an ongoing injection, when needed.

Thus, in step 307, after a subsequent injection has been carried out, another injection strategy for the remaining injections may be calculated, and the method then reverts to step 304 in order to carry out the subsequent fuel injection a.ccord.ing to the new injection strategy prepared -in step 307 , while still taking the work to be achieved during the

combustion into consideration, which is normally controlled by some superior process, e.g. in response to a request for a certain driving force from the vehicle's driver or another function in the vehicle's control system, e.g. a cruise control function. The control may thus be arranged to be carried out after each injection i, and when all subsequent injections i have been carried out, the method reverts from step 305 to step 301 to control a subsequent combustion cycle. At the above calculations, after each injection i, the current pressure determination p _ipi is used by using the pressure sensor 206 in the way described above, in order to estimate again

the temperature change during the combustion during the estimation of the amount of nitrogen oxides NO _x generated, in order to determine a new injection schedule based on the now prevailing conditions in the combustion chamber, but now with data obtained a little further into the combustion. That is to say, p _φ 1 after the first combustion and similarly determined ρ _φ1 for subsequent injections, where thus p„_ ₀ changes at

calculations during the combustion cycle, and where the fuel injection is adapted according to prevailing conditions after each injection, and with the consequence that, the injection schedule may change after each injection. At the same time, the hitherto accumulated nitrogen oxides NO _x generated may be estimated with good accuracy by using- the continuously

obtained pressure signals from, the pressure sensor 206, and thus the actual pressure track, instead of the estimated one during the part of the combustion cycle which has already lapsed, so that the hitherto generated, amount may also

constitute a parameter at. the selection of an injection schedule. If e.g. only a small amount of nitrogen oxides NO _x has been formed hitherto, e.g. a larger expected amount for subsequent parts of the combustion may, at least in certain situations, be accepted.

Hitherto, the entire injection schedule for the remaining combustion has been evaluated, but the evaluation may also be arranged to be carried out only for the future injection after a previous injection, so that subsequent injections may be handled gradually with a new injection every time the method reaches step 307, The injection schedule selected at. step 307 may thus consist of only the next, injection. The present invention thus provides a method that, adapts the combustion as the combustion proceeds, and generally

comprises, based on a first parameter value which is

determined after a first part of the combustion has be carried out, controlling the subsequent, part of the combustion during one and the same combustion cycle , so that the combustion is controlled with respect to the nitrogen oxides NO _x generated during the combustion process.

According to the present invention, the combustion is thus adapted during ongoing combustion, based on differences from the predicted combustion, and according to one embodiment each time an injection inspi has been completed, as long as

additional injections will be carried out.

According to the above described method, the injection

schedule at the combustion cycle's start has been determined based on tabulated values, but according to one embodiment the injection strategy may already before the fuel injection starts be determined in the manner described above, so that also the first injection is thus carried out according to an injection schedule determined as set out above.

Further, the method may be arranged to be interrupted when the temperature in the combustion chamber has reached the maximum temperature during the combustion, as substantially all nitrogen oxide generation will have taken place up to this point in time, so that subsequent control actions may instead e.g. be carried out according to the selected injection schedule, or may be carried out based on some other applicable criterion .

Further, the control has hitherto been described in a manner where the characteristics for a subsequent injection are determined based on prevailing conditions in the combustion chamber after the previous injection. The control may, however, also be arranged to be carried out continuously, where pressure determinations may be carried out with the help of the pressure sensor also during ongoing injection, and where the injection schedule may be calculated and corrected all the way, until the next injection is initiated.

Alternatively even the ongoing injection may be impacted by calculated changes in the injection schedule, also in the cases where several shorter injections are carried out. The injection may also consist of one single, longer injection, where changes to the ongoing injection may be made

continuously, e.g. by way of so-called rate shaping, e.g. by changing the opening area of the injection nozzle and/or the pressure with which the fuel is injected, based on estimations and measured pressure values during the injection. Further, the fuel supply during the combustion may comprise only two fuel injections, where e.g. only the second or both injections are controlled e.g. with the help of rate shaping. Rate shaping may also be applied in the event three or more

injections are carried out.

As the number of fuel injections carried out during a

combustion cycle increases, the number of parameters that may change also increases, while the achieved work must be

maintained.. In the event, of a large number of injections the control may therefore become relatively complex, since a large number of parameters may be varied and would thus need to be evaluated. For example, a very great, number of injections may be arranged to be carried out. during one and the same

combustion cycle, such as ten, or even hundred or so

injections.

In such situations, there may be several equivalent injection strategies, which thus result in substantially the same amount of generated nitrogen oxides NO _x . This introduces an unwanted complexity in the calculations.

According to one embodiment, a control action is applied where the injection nearest in time is treated as a separate

injection, and subsequently following fuel injections are treated as one single additional "virtual" injection. This is exemplified in Fig, 5A, where the injection 501 corresponds to inspi, as set out above, the injection 502 corresponds to insp?, as set out above, and where the remaining injections 503-505 are treated as one single virtual injection 506, i.e. the injection 506 is treated as one injection with a fuel amount substantially corresponding to the total fuel amount for the injections 503-505, and where a distribution may be made between the injection 502 and the virtual injection 506. By proceeding in this manner, a fuel shifting between insp2 and. subsequent injections, e.g. in order to bring forward or postpone a calculated amount of fuel (the total amount of fuel to be injected may be substantially constant, however, but where needed with consideration for efficiency changes, so that desired, work is still achieved) which does not need to be distributed specifically between the injections 503-505 _f but. instead distribution at this stage is made between the

injection 502 and the "virtual" injection 506, respectively.

When the injection 502 has been carried out, the method is repeated as above, with a. new determination of an. injection schedule, in order to control the nitrogen oxides NO _x

generated, but with the injection 503 as a separate injection, see Fig. 5B, and the injections 504, 505 jointly constitute one virtual injection with a distribution as set out above.

In Fig. 5A the virtual injection 506 is constituted by three injections, but as is obvious, the virtual injection 506 may comprise, from the beginning, more than three injections, such as tens of injections or hundreds of injections , depending on now many injections that are planned to be carried out during the combustion cycle, so that the method is repeated until all the injections have been completed.

According to one embodiment, e.g. MPC (Model Predictive

Control) is used in the control according to the invention. One example of MPC is shown in Fig, 6, where the reference curve 603 corresponds to the expected development for the generation of nitrogen oxides NO _x during the combustion cycle. The curve 603 thus represents the development for the

accumulated nitrogen oxides NO _x generated, which are sought during the combustion cycle. This curve may e.g. consist of a level, which is realistically achievable during- the combustion cycle (e.g. the lowest or any other desired level} for the generated nitrogen oxides NO _x with the current load and

prevailing engine speed, and may advantageously be determined in advance, e.g. with applicable calculations and/or

measurements on the engine type, so that such data may be stored in the control system's memory as a function of e.g. engine speed and load. This also entails that the combustion does not need to be controlled only toward a generation of nitrogen oxides NO _x prevailing at each time, but may also be arranged to be controlled toward an expected total development for the amount of nitrogen oxides NO _x generated, e.g. the curve 603 in Fig. 6, so that each injection may have as its

objective to result in a hitherto accumulated amount of nitrogen oxides NO _x which at any given point, in time amounts to the corresponding point on the curve 603. The curve 603 may in one embodiment consist of a curve representing expected nitrogen oxides NO _x generated at each point, i.e. not an accumulated amount of nitrogen oxides NO _x , so that the generated amount of nitrogen oxides NO _x may be controlled toward this reference curve instead.

The solid curve 602 up to the time k represents the actually generated amount of nitrogen oxides NO _x up to the time 7c and which has been calculated as set out above with the help of actual data from the crank angle resolved pressure

transmitter. The curve 601 represents the predicted

development for the nitrogen oxides NO _x generated, based on the selected injection profile, and thus constitutes the

development for the generation of nitrogen oxides NO _x which is expected. Dashed injections 605, 606, 607 represent the predicted control signal, i.e. the injection profile which is expected to be applied, and 608, 609 represent already

completed injections, The predicted injection profile is updated with applicable intervals, e.g. after each completed injection or during an ongoing injection, in order to reach the final value sought, and which is given by the reference curve 603, and where the next injection is determined based on prevailing conditions in relation to the estimated generation of nitrogen oxides NO _x .

The invention has been exemplified above in a manner where a pressure sensor 206 is used to determine a pressure in the combustion chamber, and with the help of which the temperature and nitrogen oxide generation, as set. out. above, may be estimated. One alternative to using pressure sensors may instead consist of the use of one (or several) other sensors, e.g. high-resolution ion current sensors, knock sensors or strain gauges, where the pressure in the combustion chamber may be modelled with the use of sensor signals from such sensors. It is also possible to combine different types of sensors, e.g. in order to obtain a more reliable estimation of the pressure in the combustion chamber, and/or to use other- applicable sensors, where the sensor signals are converted into corresponding pressures for use in control, as set out above . Control according to the invention may also comprise, in addition to carrying out an estimation of several possible control alternatives based only on generated nitrogen oxides ΝΟχ, evaluating control alternatives based on other criteria. For example, control may be carried out based on a cost function for different contro1 parameters .

For example, in cases where several injection

schedules/control alternatives fulfil applicable conditions, other parameters may be used to select which of these are to be used. There may also be other reasons for simultaneously effecting control also based on other parameters. For example, injection schedules may also be partly selected based on one or several of the perspectives pressure change rate, heat loss, exhaust, temperature, work, achieved in the combustion chamber, or pressure amplitude at combustion as an additional criterion, in addition to being selected based on generated nitrogen oxides NO _Xf where such determination may be carried out according to any of the parallel patent applications specified be1ow . Speci fica.1.1y, the para .11e.1 app1 ication

"METHOD AND SYSTEM FOR CONTROL OF A COMBUSTION ENGINE I"

(Swedish patent application, application number: 1350506-0) shows a method to, based on an estimated maximum pressure change rate, control subsequent, combustion.

Additionally, the parallel application "METHOD AND SYSTEM FOR CONTROL OF A COMBUSTION ENGINE II" (Swedish patent

application, application number: 1350507-8) shows a method to, during a first combustion cycle, control a subsequent part of combustion during said first combustion cycle, with respect to a temperature resulting in said subsequent combustion.

Further the parallel application "METHOD AND SYSTEM FOR

CONTROL OF A COMBUSTION ENGINE III" (Swedish patent

application, application number: 1350509-4) shows a method to, during a first combustion cycle, control the combustion during a subsequent part, of said first combustion cycle with respect, to work achieved during the combustion.

Further, the parallel application "METHOD AND SYSTEM FOR THE CONTROL OF A COMBUSTION ENGINE IV" (Swedish patent

application, application number: 1350510-2) shows a method to, during a first combustion cycle, control combustion during a subsequent part of said first combustion cycle with respect to a representation of a heat loss resulting during said

combustion.

Further, the parallel application "METHOD AND SYSTEM FOR THE CONTROL OF A COMBUSTION ENGINE V" (Swedish patent application, application number: 1350508-6) shows a method for controlling subsequent combustion, based on an estimated maximum pressure amplitude.

Further, in the above description an example method to

estimate temperature change during the combustion cycle has been applied. Obviously, applicable methods to estimate pressure and/or temperature and/or generated nitrogen oxides ΝΟχ other than those exemplified in the present description may be applied..

Further, in the above description only fuel injection is adjusted.. Instead of controlling the amount of fuel supplied, the combustion may be arranged to be controlled with the help of e.g. exhaust valves, so that injection may be carried out according to a predetermined schedule, but where the exhaust valves are used to control the pressure in the combustion chamber and thus also the temperature.

Further, control may be carried out with some applicable type of regulator, or e.g. with the help of state models and state feedback (e.g. linear programming, the LQG method or similar).

The method according to the invention for the control of the combustion engine may also be combined with sensor signals from other sensor systems where the resolution of the crank angle level is not available, e.g. another pressure

transmitter, NO _x sensors, N¾ sensors, PM sensors, oxygen sensors and/or temperature transmitters, etc., the input signals of which may e.g. be used as input parameters in the estimation of e.g. expected pressure/temperature with the complete or partial use of computer-driven models, instead of models of the type described above.

Additionally, the present invention has been exemplified above in relation to vehicles. The invention is, however, also applicable to any vessels/processes where nitrogen oxide control as set out above is applicable, e.g. watercrafts or aircrafts with combustion processes as per the above.

Tt 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 in no way limited to the above described embodiments of the method according to the invention, but pertains to and

comprises all embodiments in the scope of the enclosed

independent claims .