The present invention relates to a combustion engine system and in particular to a method for regulating a combustion engine according to the preamble of claim 1 . The invention relates also to a system and a vehicle, and to a computer programme and a computer programme product, which implement the method according to the invention.

Background to the invention

Growing official concern about pollution and air quality, especially in major urban areas, has led to the adoption of emission standards and requirements in many jurisdictions.

Such emission standards often set requirements which define acceptable limits for exhaust emissions from vehicles equipped with combustion engines. These standards often regulate, for example, levels for emissions of nitrogen oxides (NO _x ) , hydrocarbons (HC) and carbon monoxide (CO) . These emission requirements also usually cover, for at least certain kinds of vehicle, the presence of particles in exhaust emissions.

These regulations are often organised in such a way that increasingly stringent emission level requirements are

introduced at intervals of one or a few years. The endeavour to meet these requirements has therefore led to the

development of systems for post-treatment (cleaning) of the exhaust gases which are formed during combustion in combustion engines .

These post-treatment systems often comprise some form of catalytic cleaning process whereby one or more catalysts are used to clean the exhaust gases. Such post-treatment systems often comprise other components as alternatives to, or in combination with, the one or more catalysts, e.g. post- treatment systems on vehicles with diesel engines often comprise particle filters.

Soot particles are formed during combustion of fuel in the combustion chambers (e.g. cylinders) of a combustion engine. As above, these soot particles are likewise subject to

emission requirements and standards, which may entail using particle filters to intercept the soot particles. In such cases the exhaust flow is for example led through a filter structure whereby soot particles are captured from the passing exhaust flow in order to be stored in the particle filter.

There are various methods for reducing emissions from a combustion engine. As well as requirements concerning

emission levels, it is also becoming increasingly common for there to be statutory requirements for vehicles to have internal diagnostic systems, so-called OBD (on-board

diagnostics) systems to ensure that not only at for example the time of visits to workshops but also in day-to-day

operation vehicles actually meet established requirements concerning emissions. In the case of particle emissions this may for example be achieved by means of a particle sensor, referred to in the description and claims set out below as a PM (particulate matter, particulate mass) sensor, situated in the tailpipe of the exhaust system to measure the particle content of the exhaust flow before it is released into the vehicle's surroundings.

Post-treatment systems with particle filters can be very effective and the resulting particle content after the exhaust flow has passed through the vehicle's post-treatment system is often low when the system is fully functional. This also means that the signals which the sensor delivers will indicate low or no particle emission.

Summary of the invention An object of the invention is to propose a method for

regulating a combustion engine pertaining to a vehicle. This object is achieved with a method according to claim 1.

The present invention proposes a method for regulating a combustion engine such that a post-treatment system comprising at least one particle filter is provided to post-treat an exhaust flow arising from combustion in said engine. A signal delivered by a first sensor serves as a basis for determining whether a first function of said engine is deviating from desired function and for taking when it does so deviate at least one form of remedial action, e.g. regulating a parameter which can be used to affect the engine's function and thereby rectify said deviation.

The method further comprises using a PM sensor situated upstream of said particle filter to determine, at a location upstream of said particle filter, a first particle content of said exhaust flow arising from said engine, and using said first particle content determined to determine whether said first remedial action has had an effect upon said deviation. Using suitable sensors such as, but not limited to, said PM sensor, comprising also for example other sensors such as pressure, temperature or concentration sensors, to determine whether the engine's function is deviating from desired function, e.g. because a function pertaining to the engine is not working properly, followed by trying to rectify the deviation, does for example make it possible not only for malfunctions to be detected at a very early stage but also to take appropriate forms of remedial action immediately in order to minimise the effects of the deviation. By then using a PM sensor to determine the particle content of the exhaust flow arising from combustion in the engine it is also possible to evaluate the results of the remedial action immediately on the basis of changes in the particle content.

Changes in the particle content may also be used to determine whether continuing forms of remedial action should be taken. The results of remedial action taken may for example be optimised by altering for example one or more regulating parameters, such as increasing and/or decreasing a value set for some regulating parameter, e.g. VGT setting, EGR setting, fuel injection parameters such as injection pressure,

injection start, injection length, injection rate shaping, pilot injections, injection main configuration and injection post-configuration. The one or more regulating parameters may be altered until it is observable by means of the PM sensor that the particle content of the exhaust flow in prevailing conditions has been minimised and/or has reached desired level, e.g. an expected level for prevailing conditions.

The present invention makes it possible for deviating function such as a fault which might otherwise not be detected for a substantially longer time, e.g. not until a workshop visit in cases where the engine is fitted in a vehicle, to be detected substantially earlier than has previously been possible. The present invention also makes it possible, e.g. in the case of a vehicle, for the effects of the fault/deviation to be reduced or completely eliminated by suitable regulation with a view to reducing/eliminating its effects upon the running of the vehicle.

Moreover, vehicles equipped with particle filters often have such a high degree of cleaning due to post-treatment of exhaust gases that their particle emissions, despite a raised content due to engine function deviating from desired function and, for example, not working properly, may still meet applicable legal requirements with regard to particle

emissions. In such situations, prior art will not detect any fault and will therefore not prompt any remedial action.

However, an undesirably high particle content upstream of the particle filter will fill it more quickly, resulting in more frequent filter regeneration and consequently greater fuel consumption. Moreover, a malfunctioning engine does itself often cause increased fuel consumption which may continue until the fault is detected, which may take place only when the vehicle visits a workshop/undergoes servicing. Using the present invention to detect deviating function at an early stage and also taking remedial action early means that the effects of the fault, e.g. in terms of filter fullness and fuel consumption, can be markedly reduced or even eliminated. Where necessary, a signal may also be generated to indicate a need for servicing/workshop action so that faults which cannot be dealt with by remedial action within the vehicle can be rectified by workshop visit.

Engine function deviations may be determined in various different ways. In one embodiment, as previously mentioned, said first sensor may take the form of said PM sensor which may be used both to diagnose engine function deviating from desired function and to determine whether remedial action taken within the vehicle produces desired results. Engine diagnosis by means of the PM sensor is made possible by the sensor being situated upstream of the particle filter. PM sensors are usually situated downstream of the filter, but location according to the present invention means that the sensor is not affected by the filter acting like a buffer. The filter' s buffer function makes it difficult or impossible to detect downstream of it the actual particle content leaving the engine. In cases where said diagnosis is by means of the PM sensor, it may for example be determined that engine function is

deviating from desired function when a particle content determined by means of the sensor exceeds an expected level by more than a first value.

In one embodiment said first sensor takes the form of some other suitable sensor, e.g. a lambda sensor which can for example detect an undesirably low lambda value (the weight ratio in kg between the amounts of air and petrol supplied for the combustion) . A further example of a type of sensor usable for determining whether the engine's function is deviating from desired function is an NOx sensor measuring the

proportion of nitrous gases in the exhaust flow, which may vary greatly between different operating conditions and also because of errors in, for example, injection timing/amount of fuel injected for combustion in the engine's combustion chambers .

One embodiment determines whether said engine is

malfunctioning on the basis of signals from two or more sensors. Similarly, in one embodiment suitable remedial action may be determined on the basis of signals from two or more sensors.

In one embodiment a plurality of determinations are made by means of said first sensor, and said determination of whether said engine's function is deviating from desired function is based on said plurality of determinations.

As exemplified below, it is possible, depending on the type of sensor which detects the deviation and on the type of

deviation detected, for various forms of remedial action to be taken, and their results may then be analysed on the basis of signals from the PM sensor. Further characteristics of the present invention and

advantages thereof are indicated by the detailed description of embodiment examples set out below and the attached

drawings .

Brief description of drawings

Fig. la depicts schematically a vehicle on which the present invention may be employed.

Fig. lb depicts a control unit in the control system for the vehicle depicted in Fig. 1. Fig. 2 depicts the post-treatment system in more detail for the vehicle depicted in Fig. 1.

Fig. 3 depicts an example of a method according to the

present invention.

Detailed description of embodiments The expression "particle content" in the description and claims set out below comprises both content in the form of unit weight and content /concentration, i.e. the unit number of particles. Moreover, the unit may be any suitable unit and the content may be expressed as, for example, weight or number of particles per unit volume, per unit time, per work

performed or per distance travelled by the vehicle.

Fig. la depicts a power train of a vehicle 100 according to an embodiment of the present invention. The vehicle

schematically depicted in Fig. 1 has only one axle provided with tractive wheels 113, 114 but the invention is also applicable on vehicles in which more than one axle is provided with tractive wheels. The power train comprises a combustion engine 101 which is connected in a conventional way, via an output shaft of the engine, usually via a flywheel 102, to a gearbox 103 via a clutch 106. The engine is controlled by the vehicle's control system via a control unit 115. The clutch 106, which may for example take the form of an automatically controlled clutch, and the gearbox 103 are also controlled by the vehicle' s control system by means of one or more suitable control units (not depicted). The vehicle's power train may of course also be of some other kind, e.g. a type with

conventional automatic gearbox etc.

An output shaft 107 from the gearbox 103 then drives the tractive wheels 113, 114 via a final gear 108, e.g. a

conventional differential, and driveshafts 104, 105 which are connected to said final gear 108.

The vehicle 100 further comprises a post-treatment system (exhaust cleaning system) 200 for treatment (cleaning) of exhaust emissions arising from combustion in the engine' s combustion chambers (e.g. cylinders).

The post-treatment system is depicted in more detail in Fig. 2, showing the vehicle's engine 101 from which the exhaust gases (the exhaust flow) generated by the combustion are led through a turbo unit 220. In turbo engines the exhaust flow arising from the combustion often drives a turbo unit which itself compresses the incoming air for the combustion in the cylinders. Alternatively, the turbo unit may for example be of compound type. The function of various kinds of turbo unit is well-known and is therefore not described in more detail here. The exhaust flow is then led via a pipe 204 (indicated by arrows) to a particle filter (diesel particulate filter,

DPF) 202 via an oxidation catalyst (diesel oxidation catalyst, DOC) 205.

The oxidation catalyst DOC 205 has various functions and is normally used primarily to oxidise remaining hydrocarbons and carbon monoxide in the exhaust flow to carbon dioxide and water. The oxidation of hydrocarbons (i.e. oxidation of fuel) results also in the formation of heat which may be utilised to raise the temperature of the particle filter at the time of its emptying, its so-called regeneration. The oxidation catalyst may also be used to oxidise nitrogen monoxide (NO) to nitrogen dioxide (N0 ₂ ) which may be utilised in so-called passive regeneration.

Post-treatment systems of the type referred to may also comprise other components, e.g. a (single, in the present example) SCR (selective catalytic reduction) catalyst 201 situated downstream of the particle filter 202. SCR catalysts use ammonia (NH ₃ ) , or a compound from which ammonia can be generated/formed, as additive to reduce the amount of nitrogen oxides NO _x .

Moreover, the post-treatment system 200 may also comprise more components than as exemplified above or, conversely, fewer components. It may for example comprise an ASC (ammonia slip catalyst) (not depicted) in addition to, or instead of, said DOC 205 and/or SCR 201. In the embodiment depicted, DOC 205, DPF 202 and also the SCR catalyst 201 are integrated in a combined exhaust cleaning unit 203, but it should be noted that DOC 205 and DPF 202 need not be integrated in a single exhaust cleaning unit, as they may be arranged in some other way deemed appropriate.

According to the present invention, the post-treatment system 200 comprises a PM sensor 222 situated upstream of DPF 202. This PM sensor, like other sensors associated with the post- treatment system, e.g. a pressure sensor 209, may deliver signals to a control unit 208, or some other suitable control unit, which controls or monitors the function of the post- treatment system. For example, the determination of

appropriate times for regeneration of the particle filter may be done by the control unit 208 at least partly on the basis of signals from the pressure sensor 209 which measures the differential pressure across the filter. The fuller the filter becomes, the greater will be the pressure difference across it. The pressure sensor may for example also be used for diagnosis of DPF 202. According to the present invention, the PM sensor 222 may alternatively or additionally transmit signals to, for

example, the engine control unit 115 or some other suitable control unit which uses sensor signals received as a basis for determining whether a function of the engine is deviating from desired function and for taking remedial regulating action according to the present invention. As explained above and exemplified below, however, some other sensor than the PM sensor 222 may be used in determining whether a function of the engine is deviating from desired function.

Control systems in modern vehicles generally comprise a communication bus system consisting of one or more

communication buses for connecting together a number of electronic control units (ECUs) , e.g. the control units or controllers 115, 208, and various components located on the vehicle. Such a control system may comprise a large number of control units and the responsibility for a specific function may be shared by two or more of them.

For the sake of simplicity, only the control units 115, 208 appear in Fig. la. In the embodiment depicted, the present invention is

implemented in the control unit 208, which as above is

responsible in the embodiment depicted for other functions in the post-treatment system, e.g. regeneration (emptying) of the particle filter 202, although the invention may equally well be implemented in a control unit dedicated to it, or wholly or partly in one or more other control units with which the vehicle is already provided, e.g. the engine control unit 115. Particularly where a deviating functionality is determined by means of some other sensor than the P sensor 222, it may be advantageous for the present invention to be implemented wholly or partly in some other control unit than the control unit 208.

The function according to the present invention of the control unit 208 (or the control unit or units in which the present invention is implemented) will depend not only on signals from the PM sensor 222 but probably also on, for example,

information received from, for example, the control unit or units which control engine functions, i.e. in the present example the control unit 115.

Control units of the type depicted are normally adapted to receiving sensor signals from various parts of the vehicle. The control unit 208 may for example receive sensor signals as above and also from the engine control unit 115 and other control units. Such control units are also usually adapted to delivering control signals to various parts and components of the vehicle, e.g. the control unit 208 may for example deliver signals to the engine control unit 115.

The control is often governed by programmed instructions, typically in the form of a computer programme which, when executed in a computer or control unit, causes the

computer/control unit to effect desired forms of control action, e.g. method steps according to the present invention.

The computer programme usually forms part of a computer programme product which comprises a digital storage medium 121 (see Fig. lb) with the computer programme 109 stored on it. Said digital storage medium 121 may for example take the form of any from among ROM (read-only memory) , PROM (programmable read-only memory) , EPROM (erasable PROM) , flash memory, EEPROM (electrically erasable PROM), a hard disc unit etc., and be situated in or in communication with the control unit, in which case the computer programme is executed by the control unit. The vehicle's behaviour in a specific situation may thus be modified by altering the computer programme's

instructions.

An example of a control unit (the control unit 208) depicted schematically in Fig. lb may itself comprise a calculation unit 120 which may for example take the form of any suitable kind of processor or microcomputer, e.g. a circuit for digital signal processing (Digital Signal Processor, DSP) , or a circuit with a predetermined specific function (Application Specific Integrated Circuit, ASIC) . The calculation unit 120 is connected to a memory unit 121 which provides it with, for example, the stored programme code 109 and/or the stored data which the calculation unit needs for it to be able to perform calculations. The calculation unit is also arranged to store partial or final results of calculations in the memory unit 121.

The control unit is further provided with respective devices 122, 123, 124, 125 for receiving and sending input and output signals. These signals may comprise waveforms, pulses or other attributes which the input signal receiving devices 122, 125 can detect as information for processing by the

calculation unit 120. The output signal sending devices 123, 124 are arranged to convert calculation results from the calculation unit 120 to output signals for conveying to other parts of the vehicle's control system and/or the

component /components for which the signals are intended. Each of the connections to the respective devices for receiving and sending input and output signals may take the form of one or more from among a cable, a data bus, e.g. a CAN (Controller Area Network) bus, an MOST (Media Oriented Systems Transport) bus or some other bus configuration, or a wireless connection.

As mentioned above, the combustion in the combustion chambers of the engine 101 results in the formation of particles which should not and in many cases are not permitted to be released into the vehicle's surroundings. The soot particles are captured by the particle filter 202 and a very large

proportion of those present in the exhaust flow can usually be separated. The particle filter thus contributes substantially to compliance with direct requirements concerning emission levels. It is becoming increasingly common for there to be statutory requirements for vehicles to have their own systems, so-called OBD (on-board diagnostics) systems, making it possible to ensure that not only on the occasion for example of workshop visit checks but also in commercial operation the vehicle's particle emissions stay below prescribed levels.

This may be achieved in a relatively straightforward way by having a particle sensor (PM sensor) associated with the tailpipe of the post-treatment system, i.e. substantially at the location where the exhaust flow is released into the vehicle's surroundings (indicated by ref. 221 in Fig. 2) . By monitoring signals from the sensor 221, e.g. by means of a control unit corresponding to the control unit 208, it is possible to ensure that the particle content of the exhaust flow leaving the vehicle will also be below prescribed levels.

However, the sensor location described entails disadvantages which are described in detail in the parallel Swedish patent application entitled "METHOD AND SYSTEM PERTAINING TO EXHAUST CLEANING" ( "FORFARANDE OCH SYSTEM VID AVGASRENING" ,

application no. 1151073-2), with the same inventor, filing date and applicant as the present application. Said parallel application further describes how such problems can be reduced or completely eliminated by locating the PM sensor upstream of the particle filter, as in the case of the sensor 222 depicted in Fig. 2, instead of downstream. The method described in said application uses a PM sensor situated upstream of the particle filter to determine whether the vehicle's emissions after the filter are below prescribed levels.

The present invention does however use PM sensor location upstream of a particle filter, e.g. the sensor 222, not primarily to verify that emission requirement levels are complied with but, when the function of the vehicle's engine deviates from a desired function, to determine a particle content of the exhaust flow arising from the engine, making it possible to use the particle content determined to determine whether remedial action taken to rectify said deviation has also had an effect on said deviation.

Thus according to the present invention the PM sensor 222 need not necessarily be used for determining whether the vehicle's emissions after the particle filter are below prescribed levels, although simultaneous use both according to the present invention and according to said application entitled "METHOD AND SYSTEM PERTAINING TO EXHAUST CLEANING"

("FORFARANDE OCH SYSTEM VID AVGASRENING" ) may of course be advantageous .

A method 300 according to the present invention for regulating a combustion engine pertaining to a vehicle is illustrated in Fig. 3. In the embodiment depicted the method is implemented in the control unit 208 but might equally well be implemented in some other suitable control unit. It begins at step 301 by determining whether the vehicle's engine 101 has been started. If it has, the method moves on the step 302, otherwise it stays at step 301 or ends. At step 302, signals are received from one or more sensors for use in determining whether the function of the engine 101 is deviating from desired function. According to the present invention various types of sensors may be used to determine as below whether engine function is deviating from desired function. In one embodiment the PM sensor 222 described above and situated upstream of the particle filter 202 may be used in determining whether engine function is deviating from desired function and is for example not working properly. In another embodiment some other suitable sensor may instead be used in determining whether engine function is deviating from desired function, e.g. a lambda sensor 223 may be used. The lambda sensor can detect an undesirably low lambda value which may then serve as an indication that some function of the engine is deviating from desired function. Another example of a sensor usable in determination of deviating function is an NOx sensor 224 for determination of prevailing NOx content of the exhaust flow. In one embodiment, signals from two or more sensors may be used in determining whether engine function is deviating from desired function, e.g. signals from two or more of the sensors exemplified above may be used. Depending on which sensor or sensors are used in determination according to the present invention, the PM sensor 222 may for example be connected directly to the control unit 208, whereas the lambda sensor 223 and the NOx sensor 224 may for example be connected to the engine control unit 115, in which case the control unit 208 may receive signals from the lambda sensor, e.g. via the engine control unit.

After signals have thus been received from one or more sensors at step 302, the method moves on to step 303, which determines corresponding expected sensor signals in prevailing

conditions. For example, the sensor signals received usually represent a value such as a certain level or content, e.g. a particle content, a fuel/air ratio etc. Step 303 may

therefore determine corresponding expected signals such as a corresponding expected value which may, e.g. in the case of a value measured by the P sensor, be an expected particle content in prevailing conditions and may for example take the form of a calculated or previously measured content for prevailing conditions. The value calculated/measured at step 303 is an expected value in the conditions prevailing at the time, e.g. with regard to engine speed, injection angle, amount of fuel injected, vehicle speed etc.

In cases where said expected value is calculated, this may for example be done by means of a suitable computing model, e.g. different computing models may be used to represent different operating conditions with a view to as good a representation as possible. In cases where the expected value is a

previously measured value for prevailing conditions, it is for example possible to make a tabular compilation for storing previously measured particle contents at different engine speeds, amounts of fuel injected, vehicle speeds etec.

Previously measured sensor values may for example be stored, in which case a reference tabulation value as below may be compared directly with a measured value. Instead of

tabulating previously measured values it is also possible to use values calculated in a suitable theoretical way. It will be appreciated that the above is applicable irrespective of the type of sensor actually used when expected values

irrespective of sensor type may for example be determined as above .

The method then moves on to step 304 to determine whether said signals from said one or more sensors indicate that some function of the engine is deviating from desired function by comparing measured with expected signals. Sensor signals delivered may thus be compared with expected signals, e.g. by comparing corresponding magnitude values which the signals represent with previously measured and/or calculated magnitude values, e.g. a particle content, an NOx content, a fuel/air ratio etc. This determination may as above be for example based on a lambda value detected by the lambda sensor 223, a particle content determined by means of the P sensor 222, an NOx content determined by the NOx sensor 224 etc. It may for example be determined that some function is deviating from desired function when measured sensor signals deviate from expected sensor signals, e.g. by more than some appropriate value and/or according to any of the criteria mentioned below. So long as measured values do not indicate deviating function, the method will revert to step 301 for fresh determination.

If on the contrary the sensor signals do indicate deviating function, the method moves on to step 305 to take appropriate remedial regulating action.

With regard to sensor signals received it may be advantageous, rather than basing the determination on a single value, to determine whether a function of the engine is deviating from desired function on the basis of a plurality of values, such as measured sensor signals having for example to deviate from expected signals to some appropriate extent over a certain number of consecutive determinations, or over at least a first subset of an amount of determinations, or over a period of time such as Is, 5s, 10s, 30s, 1 min, 2 min etc. or, for example, any desired number of seconds/minutes within the range 0-60 minutes, or part of a period of time, e.g. x% of, for example, any of said periods of time.

The sensor signals may be compared with a respective

corresponding value at a plurality of times at some suitable interval, e.g. any of the above periods, and a function of said engine may be determined as deviating from desired function when a combined value for said times fulfils a first condition, e.g. that a lambda value or a particle content be below or above an expected lambda value/particle content in a certain number of the determinations, or that a measured lambda value/particle content be below or above the comparison value by a certain level in a certain number of

determinations .

In other words, the method illustrated in Fig. 3 may be repeated one or more times y, and a counter x will be

incremented by one each time the method moves to step 307. The method may for example be repeated after a timer t ₂ has counted to a time T ₂ , e.g. a suitable number of seconds. By this procedure it is possible to determine whether the raised particle content is only temporary before dropping back below a prescribed level. If after this plurality of determinations it is determined that the engine's function is deviating from desired function, the method may move on to step 305.

The present invention thus affords the advantage that any deviating functionality, e.g. due to faults which may occur on the vehicle and are perhaps normally detected only after a longer period of use or on the occasion of a workshop visit, may be detected substantially earlier than has previously been possible. However, the present invention not only determines whether engine function is deviating from desired function but also takes forms of remedial action to reduce and/or

completely eliminate the deviation.

Step 205 therefore determines appropriate remedial action to be taken when deviating function of the vehicle's engine has been found at step 304. In one embodiment, one or more forms of remedial action are taken according to a probability criterion so that on the basis for example of the statistical presence of different faults at the time of a workshop visit it is possible to take remedial action according to a

principle whereby the reason for deviating function is initially assumed to be that which experience suggests is the most likely. Another embodiment uses instead of, or in combination with, the probability criterion a method whereby remedial action is chosen on the basis of the type of

deviation and/or the type of sensor used in determining the deviation. The particular form of remedial action may for example be chosen on the basis of how great the deviation is and/or the kind of operating conditions in which the deviation is detected.

In one embodiment, when deviating function has been found, determination is by comparing sensor signals for various different operating conditions and, where necessary, further sensor signals may be received for different operating conditions pertaining to such determination, e.g. different operating points for the engine, these signals may be compared with corresponding expected signals, e.g. for different operating points, and appropriate remedial action may be determined on the basis of the results of comparisons for different operating points.

When appropriate remedial action has been determined at step 305, is is implemented at step 306. A number of reasons are exemplified below which may be possible causes of deviating function of the engine, with examples of forms of remedial action which may be employed according to the present

invention . When too low a lambda value is detected by a lambda sensor, there may be various different reasons. For example, the air filter for the combustion air intake may be partly obstructed. Any charge air cooler fitted may likewise be partly

obstructed. Such situations cause the actual amount of air reaching the combustion chamber, relative to the desired amount, to be less than expected, and the larger the amount of air supposed to reach the combustion chamber, the greater the deviation presented by the actual amount of air, i.e. the more the air to be supplied for the combustion, the less air relative to the desired amount will actually reach the

combustion chamber. When such faults are suspected, e.g. on the basis of lambda value comparisons for various different operating points, the lambda set-point value may for example be increased to increase the air supply, which the engine control may for example achieve by reducing EGR feedback and/or increasing the flow of intake air. It is thus possible to compensate for the impaired air flow so that the adverse effects of too little air supply can be wholly or partly eliminated during the vehicle's continuing journey. At the same time it is for example possible for a service

indicator/service flag to be set so that as soon as possible or on the next servicing occasion the vehicle can rectify the cause of the fault.

It is thus possible at step 306 to take remedial action as above, followed by possibly determining at step 307 whether further remedial action is required. As above, the remedial action may comprise somewhat altering a set-point value, e.g. a lambda set-point value, or some other set-point value such as any of those exemplified below, making it possible at step 307 to determine whether there is continuing deviation. The determination at step 307 is by comparing a value delivered by the P sensor 222 with an expected value pertaining to

prevailing conditions. So long as it is found at step 307 that the deviation is decreasing, the method may revert to step 306 for further alteration of the set-point value, in which case fresh determination takes place at step 307, and so on. The method may further be arranged to wait for an

appropriate amount of time between set-point value

alterations/determinations before a fresh sensor value

determination is undertaken.

When the deviation no longer decreases as a result of further set-point value alteration, the set-point value which has resulted in the least deviation is used as the new set-point value during continued operation of the vehicle, step 308.

Finally, the method may revert to step 301 for continued monitoring of engine function. It is for example possible that, despite the minimisation of the deviation which takes place at steps 306-307 on the basis of appropriate remedial action, sensor signals may still show deviating function detected by one or more sensors at step 304, albeit less so, in which case step 305 may determine whether further remedial action is required, e.g. adaptation of a further regulating parameter.

One embodiment combines signals from two or more sensors when determining appropriate remedial action. Signals from the lambda sensor 223 may for example be combined with signals from the PM sensor 222. The particle content of the exhaust flow increases with increased air flow requirement, since an ever smaller proportion of desired air flow will reach the engine's cylinders, resulting in undesirably rich fuel/air mixture. By comparison of particle content and lambda value for different operating points with different air flow requirements it is for example possible to determine with greater certainty whether air filters and/or charge air coolers are obstructed.

If on the other hand the lambda sensor indicates too low a value while the PM sensor indicates normal presence of

particles, step 304 or 305 may determine that no remedial action need be taken at all or that some other remedial action should be taken instead.

Another possible cause of, for example, undesirably high particle content found at step 304 may be that the EGR

content, i.e. how much of the exhaust gases arising from the combustion is led back for subsequent combustion, reaches for some reason an undesirably high level. Too high an EGR content results in increased particle content and may for example be due to leakage or to EGR regulating faults. Such faults may for example be detected by actively influencing the EGR regulation while at the same time variations in the particle content are detected. A suitable form of remedial action may thus be to actively influence the EGR regulating set-point value in order to provide EGR feedback which as far as possible results in desired levels of particle content in the exhaust flow.

A further possible cause of undesirably high particle contents is faults with regard to fuel injection timing/injection angle a, particularly in that too late injection, with late end-of- injection (EOI), may lead to raised particle contents. This fault may be determined by varying the timing/the angle a while at the same time the particle content variations are determined as above, and appropriate measures may be taken by regulating injection timing/in ection angle until

desired/minimised particle content of the exhaust flow is achieved . As well as injection timing, faults may also occur in amounts of fuel injected (delta), which may for example be due to too high an injection pressure and/or too long an injection time. By varying the injection pressure it is possible to determine the influence of the amount of fuel upon the particle content. Regulating the injection pressure set-point value will

automatically regulate the amount of fuel injected (increased pressure set-point value will shorten injection time) .

It may also be that the injection pressure is itself

incorrect. Too high injection pressure may cause undesirable wall impact or spray collision. Here again, pressure set- point value alteration may be employed to detect faults. The pressure set-point value may be increased or decreased as necessary by regulating it while at the same time monitoring the particle content of the exhaust flow. It may also be advantageous to regulate both alpha and delta simultaneously or sequentially until a combined minimum particle content or minimum deviation from expected particle content is achieved.

A further possible source of deviating function is obstructed nozzle holes, which may for example lead to incorrect fuel dosing and/or incorrect injection pattern. The magnitude of the fault and the resulting particle content of the exhaust flow will vary with the pressure at which injection takes place. Obstructed nozzle holes will cause an increasing error in fuel amount as a function of increased injection pressure. By varying the injection pressure while at the same time monitoring the particle content it is possible to determine whether obstructed nozzle holes are a probable cause of prevailing raised particle contents of the exhaust flow, and appropriate remedial action may be taken. An attempt may for example be made to blow the holes clean by raising the

injection pressure to a high level, possibly followed by fresh particle determination to ascertain the result of the attempt. If it does not achieve the desired effect, fresh attempts may be made and/or appropriate indicators may be activated to make the driver aware of the probable need for servicing action. Another possible cause of deviating function is use of fuel which is not clean or not approved. This may be difficult to distinguish from other causes, but in for example cases where particle content increases suddenly after a refuelling

operation incorrect fuel may be suspected, particularly if the particle contents later revert to normal levels after a subsequent refuelling. The adverse effects of incorrect fuel on the vehicle's running may be reduced by regulation of alpha/delta/injection pressure as above.

A further possible cause of deviating function may be uneven cylinder balancing, i.e. the engine's cylinders may not be working equally hard. A particle content which exceeds desired level as above, or is very uneven and is detected as recurring pulses at half the engine speed (in a four-stroke engine), may indicate uneven cylinder balancing. If for example the sensor is rapid and is for example situated high up in the manifold, i.e. close to the engine's cylinders, it may even be possible to detect which one or more of the cylinders present deviating values, in which case individual forms of remedial action may be employed for each cylinder. This does however also apply in the general case, i.e.

remedial action may be taken cylinder by cylinder in order thereby to minimise undesirable deviation. Deviations for a specific cylinder may also be detected by adjusting valve times and/or injection cylinder by cylinder, making it

possible to determine on the basis of the particle content which cylinder or cylinders are functioning less optimally. The present invention thus uses the PM sensor 222 to determine whether remedial action taken has affected the deviation, irrespective of the type of sensor by which the deviation is detected, and therefore at least in certain cases also to detect deviating function. Determination by means of a PM sensor 222 situated upstream of the particle filter 202 means that a continuous flow of particles will continually pass the sensor when the engine is in operation, and the sensor' s measurements according to the present invention will result in a substantially continuous signal which is representative of the actually prevailing conditions.

PM sensor location according to the present invention means that changes in the particle content of the exhaust flow can be detected quickly and with great accuracy, with the sensor also certainly delivering a signal, since the smallest amount of particles required for it to indicate their presence will assuredly be reached.

The present invention thus affords the advantage that various kinds of faults which may occur on a vehicle but are perhaps normally not detected for a considerable time or only on the occasion of a workshop visit can be detected and largely be subjected to remedial action immediately.

As various of the above faults will cause increased fuel consumption, the present invention also affords the advantage that problems of raised fuel consumption can at an early stage not only be detected but also be largely reduced.

The determination at step 305 of remedial action may thus include evaluation of the above possible malfunction causes, e.g. sequentially and in any appropriate order of probability, to determine whether one or more of them is the actual cause of the engine malfunctioning, enabling appropriate remedial action .

Locating the PM sensor upstream of the particle filter has also further advantages. Since the sensor is so situated that measurement signals will be continually delivered, its

function may be verified by observing the signal delivered by it over time. So long as it delivers substantially continuous signals, or delivers for similar operating situations

substantially the same signal, the sensor may be regarded as working properly. If on the contrary it suddenly indicates substantially lower emissions than normal for a given running situation, it may be assumed that the sensor is

malfunctioning, and a service flag may for example be

activated in the vehicle's control system to indicate a need for servicing. This also means that active testing of the sensor's function can be undertaken.

The PM sensor 222 may for example be situated, as in Fig. 2, after a turbo unit 220 from which the exhaust flow is usually delivered in a predictable way. It may for example also be situated downstream of DOC 205 but upstream of the particle filter 202. In the embodiment depicted, the SCR catalyst 203 is downstream of the particle filter, but in one embodiment it is instead upstream of DPF 202, in which case the sensor may be downstream or upstream of the catalyst. The vehicle may also be equipped with a so-called exhaust brake in which the sensor 222 may for example be upstream of. It may also be situated in the EGR feedback of part of the exhaust flow as is commonly the case in vehicles of the above kind, since this part of the exhaust flow is representative of the composition of the total exhaust flow. The sensor 222 may for example also be situated upstream of the turbo unit 220. The turbo unit may be of the type with fixed geometry (FGT) or of the type with variable geometry (VGT) and be provided with

turbines to feed power back to crankshafts (turbo compound) or to some other part of the power train. The vehicle may also be provided with a so-called ammonia slip catalyst (ASC) which the PM sensor may be upstream or downstream of. There are thus a large number of possible locations for the PM sensor upstream of the particle filter.

Moreover, the present invention is exemplified above in relation to vehicles. The invention is nevertheless also applicable to any other means of transport/processes in which particle filter systems as above are applicable, e.g.

watercraft or aircraft with combustion processes as above.

Further embodiments of the method and system according to the invention are referred to in the attached claims. It should also be noted that the system may be modified according to different embodiments of the method according to the invention (and vice versa) and that the present invention is in no way restricted to the embodiments described above of the method according to the invention, but relates to and comprises all embodiments within the protective scope of the attached independent claims .