Field of the invention

The present invention relates to a combustion engine system and in particular to a method for diagnosis of 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 urisdictions.

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 (N0 _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

diagnosis of 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 diagnosis of a combustion engine whereby a post-treatment system comprising at least one particle filter is provided to post-treat an exhaust flow arising from combustion in said engine, which method 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 in said exhaust flow arising from said engine, and

- using said first particle content determined to determine whether said engine is malfunctioning.

Determining a particle content at a location upstream of said particle filter and then using this particle content as a basis for determining whether the engine, e.g. a combustion engine pertaining to a vehicle, is malfunctioning makes it possible to detect malfunctions at a very early stage and to take appropriate forms of remedial action. It is thus

possible to detect faults which otherwise might perhaps only be detected at a substantially later time, e.g. on the

occasion of a workshop visit.

The fault may be of such a kind that a vehicle' s particle emissions, despite a raised content due to malfunctioning of its engine, may continue to meet applicable legal requirements as above, since the particle filter may effectively capture the particles. However, the higher particle content will more quickly fill the particle filter, leading to 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, e.g. in the case of a vehicle, take place only when the vehicle visits a workshop/undergoes servicing. Applying the present invention to detect the fault at an early stage makes it possible to ensure that the vehicle can quickly be rectified as necessary.

The present invention makes diagnosis of the engine possible in that, unlike customary practice, the PM sensor is situated upstream of the particle filter, since the particle filter acts like a buffer and makes it difficult or impossible to detect the actual particle content leaving the engine.

It may for example be determined that the engine is

malfunctioning when said first particle content differs from, e.g. exceeds, a second particle content by more than a first value .

In one embodiment, a plurality of determinations of the particle content of the exhaust flow arising from the engine are made, and said determination of whether said engine is malfunctioning is based on said plurality of particle content determinations . Sensor location upstream of the particle filter affords the further advantage that the sensor' s actual reliability can be verified in a straightforward way. The higher particle content of the exhaust flow upstream of the particle filter will cause the PM sensor to deliver frequently and more or less regularly a signal indicating the presence of

soot/particles in the exhaust flow, which will thus also be easy to diagnose.

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 P 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 conducting engine diagnosis according to the present

invention .

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.

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 particles formed during combustion in, for example, a diesel engine consist largely of hydrocarbons, carbon (soot) and inorganic substances such as sulphur and ash. Soot particles may inter alia be formed when the fuel/air ratio during combustion in the engine's

combustion chambers becomes too great, i.e. when there is a so-called "rich" fuel mixture with too high a proportion of fuel relative to that of air, and particles may for example also be formed by oil splash from the engine's lubrication which enters the combustion chamber, or metal fragments from wear and/or manufacture of the engine. A further example is the vehicle's fuel, which may itself be more or less clean.

The soot particles are captured by the particle filter 202 and a very large proportion of those occurring 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 providing 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 makes it possible to determine whether the vehicle's emissions after the particle filter are below prescribed levels.

The present invention does however use a PM sensor location upstream of a particle filter, e.g. the sensor 222, not primarily to verify that emission requirements are complied with, but to diagnose the engine in order to be able to detect whether it is malfunctioning, and using the PM sensor makes such determination possible substantially earlier than has previously been the case, and especially when the vehicle is still in motion rather than only on the occasion of a workshop visit .

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 detecting malfunction of the vehicle's engine 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. Step 302 determines whether signals are being received from the PM sensor 202. The method stays at step 202 until sensor signals are received but not beyond the time when a timer ti reaches a time ΊΊ. If no sensor signals are received before the counter reaches T _lf which may for example be part of a second or a suitable number of seconds, the method can move on to a step 303 for diagnosis of the sensor, see below. If, on the contrary, sensor signals are received within time Ti, the method moves on to step 304 for determination of a particle content of the exhaust flow.

Step 304 determines a first particle content Pi on the basis of the signals delivered by the PM sensor 222. As the

determination is by means of a PM sensor situated upstream of the particle filter 202, a continuous flow of particles will be continually passing the sensor when the engine is in operation, and the measurements provided by the sensor

according to the present invention will result in the delivery of a substantially continuous signal which is representative of the actually prevailing conditions as compared for example with measurements downstream of a particle filter which itself acts like a buffer so that actual emissions after the filter will at least partly depend on its fullness etc.

PM sensor location according to the present invention thus makes it possible for changes in the exhaust flow' s particle content to be determined quickly and with great accuracy in that the sensor will also certainly deliver a signal, since the smallest amount of particles required for it to indicate their presence will assuredly be reached. The larger amount of particles compared with measurement after a particle filter also makes both size determination and diagnosis easier.

As well as the PM sensor 222 being situated in an environment where the exhaust flow has a higher particle content, its location upstream of the particle filter affords the further advantage of allowing it to be in a well-mixed and homogenous exhaust flow, thus ensuring that measurements are made in a representative part of the exhaust flow. In the embodiment depicted, the P sensor is situated upstream of both DPF 202 and DOC 205, but as exemplified below it might be at any of a number of different locations (but always upstream of the particle filter 202).

When a first particle content Pi has been determined at step 304 on the basis of the signals delivered by the PM sensor, the method moves on to step 305 in which a second particle content P ₂ is determined before being compared at step 306 with said first particle content Pi as below.

Said second particle content P ₂ is an expected particle content in prevailing conditions and may for example be a calculated or previously measured content for prevailing conditions. In other words, the second particle content P ₂ is an expected particle content in the conditions prevailing at the time with regard for example to engine speed, injection angle, amount of fuel injected, vehicle speed etc.

In cases where said second particle content P ₂ is calculated, this may be done by means of a suitable calculation model, possibly using for example different calculation models to represent different operating conditions in order to achieve as good a representation as possible. In cases where the particle content is a previously measured content 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 etc. Instead of tabulating previously measured values it is also possible to use values calculated in a suitable theoretical way. When said second particle content P ₂ has been determined, the method moves on to step 306 in which the first and second particle contents are compared. If it is determined that said first particle content Pi does not exceed said second particle content P ₂ , the method reverts to step 301 for fresh

determination/comparison .

If on the contrary it is determined that said first particle content Pi exceeds said second particle content P ₂ , e.g. by more than some suitable value and/or according to any of the criteria mentioned below, the method moves on to step 307 for determination of suitable remedial action, e.g. activation of a service indicator and/or engine fault indicator to make the vehicle' s driver aware that the engine is malfunctioning and needs servicing, whereupon the method moves on to step 308 for such activation before it ends or reverts to step 301 for continued particle content determination.

Alternatively, a diagnostic method as below may be commenced, in which case the method moves on to step 309 for diagnosis.

It may also be advantageous not to base determination on a single value but to determine that the engine is

malfunctioning if said first particle content P _x exceeds said second particle content P ₂ over a certain number of consecutive determinations, or at least over 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.

In one embodiment, either alternatively to, or in combination with, the foregoing, said first particle content Pi is

determined and is compared with a respective corresponding second particle content P ₂ as above (i.e. a second particle content which corresponds to the conditions at the respective measuring time) at a plurality of times at any suitable interval, e.g. any of the above periods, and said engine will be deemed to be malfunctioning when a combined value for said plurality of times fulfils a first condition, e.g. that the first particle content Pi exceeds the second particle content P2 in a certain number of determinations, or that the first particle content Pi exceeds the second particle content P2 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 raised levels persist after a

plurality of determinations, e.g. according to the above criteria, the method may move on to step 308 or step 309 as below.

The method may also comprise determining for the first

particle content Pi a variation which may be compared with an expected variation of it. On the basis of the comparison it is possible to determine whether the engine is malfunctioning. The variation may for example be arranged such as to be actively affected by altering operating parameters of the engine to cause expected changes.

The present invention thus affords the advantage that faults which may occur on the vehicle but are normally perhaps not detected for a considerable time or only on the occasion of a workshop visit can be determined substantially earlier and be brought to the driver' s attention so that suitable remedial action can be taken.

As well as detecting that the engine is malfunctioning, the present invention may also be used to determine actual causes, step 309. This may for example be achieved by particle content comparison for different running situations and/or by altering engine control parameters while at the same time determining their effect upon the particle content of the exhaust flow.

A number of malfunction causes which may result in raised particle content of the exhaust flow are exemplified below, and at least one of them is an example of how the reason for the engine malfunctioning may be determined on the basis of particle content determinations.

The air filter for the combustion air intake may for example be partly obstructed. Similarly, any charge air cooler fitted may be partly obstructed. In such situations the actual amount of air reaching the combustion chamber relative to the desired amount will be less than expected, and the greater the amount of air supposed to reach the combustion chamber, the greater will be the deviation in the actual amount of air, i.e. the more the air which should be supplied for the

combustion, the less air relative to the desired amount will actually reach the combustion chamber. This will in its turn result in the particle content of the exhaust flow increasing with increased need for air flow, since an ever smaller proportion of the desired air flow will reach the engine's cylinders, leading to undesirably rich fuel/air mixture.

By particle content comparison according to the present invention for different operating conditions with different air flow requirements it is thus possible to determine whether air filters and/or charge air coolers are obstructed, in which case it is for example possible for a service indicator and/or air filter change indicator to be activated and for the vehicle's driver to be made aware of the need for servicing.

Another possible cause of the particle content becoming undesirably high is when 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 which may for example be due to leakage or to EGR regulating faults. Such faults may for example be

determined by actively influencing the EGR regulation while at the same time variations in the particle content are

determined .

Another possible cause of malfunction is obstructed nozzle holes, which may for example lead to incorrect fuel dosing and/or incorrect injection patterns. The magnitude of the fault and the resulting particle content in 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. If it is determined that obstruction of nozzle holes is likely, remedial action may be taken to try to resolve the obstruction, e.g. by increasing the injection pressure in an attempt to blow the holes clean. Alternatively, or if the remedial action does not achieve the desired effect, an appropriate indicator may be activated to make the driver aware of the probable need for servicing action. A further possible cause of undesirably high particle contents is faults with regard to injection time/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 time/the angle a while at the same time the particle content variations are

determined as above.

As well as injection time, faults may also occur in amount 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. It may also be that the injection pressure is itself

incorrect. Too high an injection pressure may cause

undesirable wall impact or spray collision. Here again, pressure alteration may be employed to determine faults.

A further malfunction cause which may be more difficult to determine is the use of fuel which is not clean or not

approved by the vehicle's manufacturer. This may be difficult to distinguish from other causes, but in cases where for example the particle content increases suddenly after a refuelling operation the fuel may be suspected of being the cause, particularly if the particle contents later revert to normal levels after a subsequent refuelling.

A further possible malfunction cause is uneven cylinder balancing, i.e. the engine's cylinders not working equally hard. A particle content which exceeds a desired level as above, or is very uneven and is determined as recurring pulses at half the engine speed (in a four-stroke engine) , may indicate uneven cylinder balancing. If the sensor is rapid and is for example situated high up in a manifold, i.e. close to the engine's cylinders, it may even be possible to determine which one or more of the cylinders present deviating values. This fault may be determined by adjusting valve times and/or injection into the cylinder/cylinders suspected of causing high particle content, thereby also potentially achieving better cylinder function.

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 determined, making it also possible to take suitable remedial action immediately.

Various of the above faults will also cause the vehicle' s fuel consumption to be undesirably high, so the present invention affords the further advantage that problems of raised fuel consumption can be determined at an early stage.

In the diagnosis at step 309, the above possible malfunction causes may thus be evaluated, e.g. sequentially and according to any suitable probability ranking, in order to determine whether one or more of the above possibilities may be the actual cause of the engine malfunctioning.

The diagnosis may involve suitable indications in the

vehicle's control system to simplify a subsequent workshop visit, leading to shorter service time/reduced service cost.

It is also possible to combine the diagnostic process with simultaneous regulation of prevailing operating parameters so that the vehicle is as far as possible run in the most

economic way with regard to a particular aspect, e.g. fuel or emissions. This is described in detail in the parallel

Swedish patent application entitled "METHOD AND SYSTEM FOR REGULATION OF A COMBUSTION ENGINE" ("FORFARANDE OCH SYSTEM FOR REGLERING AV EN FORBRANNINGSMOTOR" , application number

1151075-7), with the same inventor, filing date and applicant as the present application. Said application describes a method whereby a signal delivered by a first sensor serves as a basis for determining whether said engine is malfunctioning, and at least one form of remedial action is taken to rectify the malfunction. A PM sensor situated upstream of a particle filter is then used to determine a particle content of the exhaust flow arising from the engine, and the particle content determined is used to determine whether said first remedial action has reduced the fault detected.

Locating the PM sensor upstream 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, the sensor may be assumed to be 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 engine may for example be intentionally set to operating points which are expected to result in substantially more particle emissions. By simultaneously observing the signals delivered by the sensor it is possible to determine whether they actually reflect the expected increase in the particle content of the exhaust flow. So long as expected changes in the sensor signal take place, the sensor may also be regarded as working properly. If on the contrary the signals do not increase despite increased particle emissions in the running situation, the sensor may be regarded as malfunctioning. The sensor may for example be of a type which delivers for example a voltage or current or presents a capacitance, inductance or resistance which varies with the presence of particles, in which case the control unit 208 may then use appropriate mathematical relationships or a table to convert measured values received to corresponding particle contents. The sensor may however also be of a type with its own control logic, in which case this internal control logic will

calculate a content which is then conveyed to the control unit, e.g. via the vehicle network or a dedicated cable.

As previously mentioned, locating the PM sensor 222 upstream of the particle filter affords also the advantage that it can with greater certainty be so situated as to cause its signals to be representative of the exhaust flow produced by the engine. The sensor 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 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.

Vehicles of the kind referred to above are often also provided with communication with, for example, a transport management system for the vehicle fleet to which they belong, such as Scania' s "Scania Fleet Management", e.g. via suitable

telecommunication systems. In addition or alternatively to activation of an indicator as above, the vehicle (the control system) may be arranged to send data to the transport

management system about malfunctions determined, which data can then be used to take appropriate remedial action, e.g. to call the vehicle in to a workshop.

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.