SE537009C2 - Method and system for determining a sensor function of a PM sensor - Google Patents

Abstract

The present invention relates to a method for determining a sensor function for a PM sensor (213) intended to predetermine a particle content in an exhaust stream resulting from combustion at a single-combustion engine (101), wherein a post-treatment system (200) is provided for post-treatment of said exhaust stream, vehicles comprise means for supplying additives to said exhaust gas stream. The method comprises: - determining a change of a signal emitted by said PM sensor (213) in response to a change in the supply of additives, and - based on said change of said signal emitted by said PM sensor, whether said PM sensor (213) emits a signal representative of said exhaust current. The invention also relates to a system and a vehicle. Fig. 3

Description

537009 Aftertreatment system for vehicles with diesel engine often particulate filter.

When combustion of fuel in the combustion chamber (eg cylinders) of the internal combustion engine, soot particles are formed.

According to the above, emission regulations and standards also apply to these soot particles, and to comply with the regulations, particulate filters can be used to capture the soot particles. In this case, the exhaust gas flow is led e.g. through a filter structure where soot particles are captured from the passing exhaust stream for storage in the particulate filter.

Thus, there are several methods for reducing emissions from an internal combustion engine. In addition to regulations regarding emission levels, it is also becoming more common with statutory requirements for in-vehicle diagnostic systems, so-called On-Board Diagnostics (OBD) system to ensure that the vehicle is also in daily operation, and not only in e.g. workshop visits, in fact comply with established regulations regarding emissions.

Regarding particulate emissions, this can e.g. is achieved by means of a particle sensor arranged in the exhaust system or the after-treatment system, in the following description and claims called PM sensor (PM = Particulate Matter, Particulate Mass), which measures the particle content in the exhaust stream. The particle content can e.g. be arranged to be determined as a particle mass per unit volume or weight, or a certain number of particles of a certain size per unit volume, where several determinations of the number of particles of different sizes can be used in a determination of a particle emission.

Particulate filter after-treatment systems can be very effective, and the resulting particle content after the exhaust stream passes through the vehicle's after-treatment system is often low with a fully functioning after-treatment system. This 537 009 also means that the signals emitted by the sensor will indicate a low or no particle emission.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for determining a sensor function for a PM sensor intended for determining a particle content in an exhaust stream resulting from combustion at an internal combustion engine. This object is achieved with a method according to claim 1.

The present invention relates to a method for determining a sensor function for a PM sensor intended for determining a particle content in an exhaust stream resulting from combustion at an internal combustion engine, wherein a post-treatment system is provided for post-treatment of said exhaust stream, said vehicle comprising means for supply of additives to said exhaust gas stream.

The method comprises: - determining a representation of a change (APU) of said signal emitted by said PM sensor (213) in response to a change of the supply of additives, - comparing said representation of said change (APU) of said of said PM. PM sensor (213) output signal with a representation of an expected change (APæ @) of the signal output from said PM sensor (213), and - based on said comparison of said representation of said change (APU) of said by said PM sensor (213) with said representation of said expected change (AP @@) of the signal emitted by said PM sensor (213), determining whether said PM sensor (213) emits a signal representative of said exhaust current.

As mentioned above, PM sensors can be used to ensure that the presence of particles in the exhaust gas stream resulting from the internal combustion engine does not exceed the prescribed levels.

However, in order to ensure that the presence of particles in the exhaust stream falls below the prescribed levels, the PM sensor is required to emit a correct signal. A PM sensor can be arranged at different positions in the exhaust stream, and depending on the position, the PM sensor can be arranged so that the particle presence at the location of the PM sensor is very small.

This applies to e.g. a PM sensor arranged downstream of a particulate filter, where a properly functioning particulate filter is often capable of separating a very large part of the particles emitted from the combustion chamber of the internal combustion engine.

This in turn means that it can be difficult to distinguish a situation where the particle filter works correctly, but where the particle occurrence downstream of the particle filter is very small, from a situation where the PM sensor indicates a small occurrence that the PM sensor actually works incorrectly or off otherwise does not emit a representative signal.

The reason why a PM sensor does not emit a representative signal may be several, and not only that the sensor is malfunctioning and thus indicates a lower incidence than is actually the case. However, the PM sensor itself can emit a representative signal for the environment in which the PM sensor is located, but instead the PM sensor and / or the after-treatment system have been manipulated in such a way that the sensor no longer measures the presence of particles in a representative exhaust stream.

For example. the sensor may have been moved from the intended position in the exhaust stream to e.g. a position where it measures the presence of particles in the vicinity of the vehicle. In this case, the PM sensor will always emit a signal representing a very low or no particle occurrence regardless of the actual particle content of the exhaust stream.

Another way of manipulating the signal emitted by the PM sensor in order to reduce detected particle occurrence is to divert all or part of the exhaust current past the PM sensor so that it is no longer exposed to a representative exhaust current. Thus, even in this way, the PM sensor can thus be caused to emit signals representing a lower particle occurrence than is actually the case. Another way to manipulate the sensor signal is to block the sensor so that the exhaust current is not conducted through the sensor.

Thus, there are several ways to manipulate a PM sensor, and since the PM sensor as above can be positioned in such a way that only a very small particle presence is detected, it can be very difficult to determine whether the sensor is manipulated or not.

According to the present invention, there is provided a method for determining whether the PM sensor can be assumed to emit a representative signal so as to also be able to determine whether the sensor is malfunctioning or has been tampered with.

This is achieved according to the present invention by means of an insight that different types of PM sensors can be cross-sensitive to additives which are supplied to the exhaust gas stream. For example, a common type of catalyst in at least some after-treatment systems, and perhaps especially in heavy vehicles, is SCR (Selective Catalyst Reduction) catalysts.

SCR catalysts usually use ammonia (NH3), or a composition from which ammonia can be generated / formed, such as e.g. urea, as an additive to reduce the amount of nitrogen oxides NOX in the exhaust gas stream. This additive is injected into the exhaust gas stream resulting from the internal combustion engine upstream of the SCR catalyst, the additive supplied to the catalyst being adsorbed (stored) in the catalyst, and nitrogen oxides in the exhaust gases reacting with the additive stored in the catalyst.

It has thus been found that the signal emitted by at least some PM sensors, ie. the signal which normally constitutes a representation of the presence of particles in the exhaust stream is cross-sensitive to such additives. This cross-sensitivity means that the PM sensor reacts to the presence of additives in the exhaust stream and thus generates a signal that indicates a higher presence of particles than is actually the case.

This insight is utilized according to the present invention in such a way that a change of a signal emitted by said PM sensor in response to a change of the supply of additives is determined, and based on the change of the signal emitted by the PM sensor it is determined whether said PM sensor emits a signal representative of said exhaust current.

If the signal emitted by the PM sensor does not reflect an expected change, it can be assumed that the PM sensor does not perform measurements on a representative exhaust current, ie. an exhaust stream that correctly reflects the composition of the exhaust stream leaving the combustion chamber of the internal combustion engine, and thus malfunctions or has been tampered with.

Additional features of the present invention and advantages thereof will become apparent from the following detailed description of exemplary embodiments and the accompanying drawings. Brief Description of the Drawings Fig. 1a schematically shows a vehicle in which the present invention can be used.

Fig. 1b shows a control unit in the control system for the vehicle shown in Fig. 1.

Fig. 2 shows the finishing system in more detail for the vehicle shown in Fig. 1.

Fig. 3 shows an exemplary method according to the present invention.

Fig. 4 shows an alternative exemplary method according to the present invention.

Detailed description of embodiments In the following description and the following claims, the term particulate content includes both content in the form of mass per unit and content / concentration, ie. number of particles per unit.

Furthermore, the unit can consist of any applicable unit and the content is expressed as e.g. mass or number of particles per unit of volume, per unit of mass, per unit of time, per work performed, or per distance traveled by the vehicle.

Fig. 1A schematically shows a driveline in a vehicle 100 according to an embodiment of the present invention. The vehicle 100 schematically shown in Fig. 1A comprises only one axle with drive wheels 133, 144, but the invention is also applicable to vehicles where more than one axle is provided with drive wheels, as well as to vehicles with one or more additional axles, such as one or more several support axles. The driveline comprises an internal combustion engine 101, which is connected in a conventional manner, via a shaft outgoing on the internal combustion engine 110, usually via a flywheel 102, to a gearbox 103 via a clutch 106. 537009 The internal combustion engine 101 is controlled by the control system of the vehicle via a control unit 115. Likewise, the clutch 106, which e.g. may be an automatically controlled clutch, and the gearbox 103 of the vehicle control system by means of one or more applicable control units (not shown). Of course, the driveline of the vehicle can also be of another type such as of a type with conventional automatic transmission etc.

A shaft 107 emanating from the gearbox 103 drives the drive wheels 113, 114 via an end gear 108, such as e.g. a conventional differential, and drive shafts 104, 105 connected to said final gear 108.

The vehicle 100 further includes an exhaust system with an after-treatment system 200 for treating (purifying) exhaust emissions resulting from combustion in the combustion engine 101 combustion chamber (eg, cylinders).

An example of a post-treatment system 200 is shown in more detail in Fig. 2. The figure shows the internal combustion engine 101 of the vehicle 100, where the exhaust gases generated during combustion are led via a turbocharger 220. In turbocharged engines, the combustion exhaust gas often drives a turbocharger. in turn compresses the incoming air to the combustion of the cylinders. Alternatively, the turbocharger can e.g. be of compound type. The function for different types of turbochargers is well known, and is therefore not described in more detail here. The exhaust stream is then passed via a pipe 204 (indicated by arrows) to a Diesel Particulate Filter (DPF) 202 via an Oxidation Catalyst (DOC) 205.

The oxidation catalyst DOC 205 has several functions, and is normally used primarily to oxidize residual hydrocarbons and carbon monoxide in the exhaust stream to carbon dioxide and water during the post-treatment of the exhaust gas stream. During the oxidation of 537,009 hydrocarbons, heat is also formed, which can be used to raise the temperature of the particle filter at e.g. emptying (regeneration) of the particulate filter.

The oxidation catalyst 205 can also oxidize nitrogen monoxide (NO) to nitrogen dioxide (NO 2), which is used in e.g. N02-based regeneration. Additional reactions may also occur in the oxidation catalyst.

Furthermore, the finishing system may comprise more components than those exemplified above, as well as fewer components. For example. The after-treatment system as in the present example may comprise a SCR (Selective Catalytic Reduction) catalyst 201 arranged downstream of the particulate filter 202. As above, SCR catalysts use ammonia (NH NOX in the exhaust stream Supply of this additive can be used according to the present invention to determine whether the PM sensor emits a representative signal.

In the embodiment shown, the components DOC 205, DPF 202 and SCR catalyst 201 are integrated in one and the same exhaust gas cleaning unit 203. However, it should be understood that these components do not have to be integrated in one and the same exhaust gas cleaning unit, but the components can be arranged in other ways where as deemed appropriate, and one or more of said components may e.g. consist of separate units. Fig. 2 also shows temperature sensors 210-212 and a differential pressure sensor 209, respectively. The figure also shows a PM sensor 213, the function of which is determined according to the present invention, and which in the present example is shown downstream of the exhaust gas purification unit 203. However, the PM sensor can also be arranged upstream the exhaust gas purification unit 203, as well as upstream of the turbocharger 220. Likewise, the vehicle's 537009 exhaust system may include more than one PM sensor, which may be arranged at different positions, and the function of all PM sensors present in the vehicle may be evaluated.

The PM sensor 213 in the present invention is integrated or co-located with a concentration / fraction sensor 214, where the concentration / fraction sensor 214 is adapted to determine the concentration of any applicable substance normally present in the exhaust stream.

As has been mentioned, soot particles are formed during the combustion of the internal combustion engine 10, and in many cases these soot particles must not be released into the environment of the vehicle. The soot particles are captured by the particulate filter 202, which works in such a way that the exhaust stream is passed through a filter structure where soot particles are captured from the passing exhaust stream and then stored in the particulate filter 202. By means of the particulate filter 202 a very large proportion of the particles can be separated from the exhaust stream.

The PM sensor 213 can be used to check that the particle filter 202 works in the desired manner, but also to monitor e.g. the function of the internal combustion engine 10O at e.g. a PM sensor position upstream of the particulate filter. The PM sensor 213 can also be used for other purposes.

However, in order for the particle occurrences determined by means of PM sensor signals to be representative, it is required that the PM sensor 213 itself actually emits signals which are representative of the environment in which the PM sensor is intended to be installed.

The present invention increases the reliability of the PM sensor signals by evaluating the environment of the PM sensor. Fig. 3 shows an exemplary method 300 according to the present invention by means of which the PM sensor can be evaluated and erroneous sensor signals due to non-representative exhaust current can be detected. The method is carried out according to the present example of the control unit 208 shown in Figs. 1A-B and Fig. 2, respectively.

In general, control systems in modern vehicles consist of a communication bus system consisting of one or more communication buses for interconnecting a number of electronic control units (ECUs) such as the control units, or controllers, 115, 208, and various components arranged on the vehicle. Such a control system can comprise a large number of control units, and the responsibility for a specific function can be divided into more than one control unit.

For the sake of simplicity, in Figs. 1A-B only the control units 115, 208 are shown.

The present invention is thus in the embodiment shown implemented in the control unit 208, which in the embodiment shown can also be responsible for other functions in the finishing system 200, such as e.g. regeneration (emptying) of the particle filter 202, but the invention can thus also be implemented in a control unit dedicated to the present invention, or in whole or in part in one or more other control units already present in the vehicle, such as e.g. motor control unit 115.

The function of the control unit 208 (or the control unit (s) to which the present invention is implemented) according to the present invention will, in addition to relying on sensor signals from a sensor 210 for determining a concentration and / or fraction of a substance likely to e.g. depend on information such as received from a PM sensor and e.g. the control unit (s) that control motor functions, ie. in the present example the control unit 115.

Control units of the type shown are normally arranged to receive sensor signals from different parts of the vehicle. The control unit 11 537 009 208 can e.g. further receive sensor signals as above, as well as from control units other than the control unit 115. Such control units are furthermore usually arranged to emit control signals to various vehicle parts and components. For example. the control unit 208 can emit signals to e.g. motor control unit 115.

The control is often controlled by programmed instructions. These programmed instructions typically consist of a computer program, which when executed in a computer or controller causes the computer / controller to perform the desired control, such as method steps of the present invention.

The computer program is usually part of a computer program product, the computer program product comprising an applicable storage medium 121 (see Fig. 1B) with the computer program 109 stored on said storage medium 121.

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

An exemplary control unit (control unit 208) is shown schematically in Fig. 1B, wherein the control unit may in turn comprise a calculation unit 120, which may consist of e.g. any suitable type of processor or microcomputer, e.g. a Digital Signal Processor (DSP), or an Application Specific Integrated Circuit (ASIC). The computing unit 120 is connected to a memory unit 121, which provides the computing unit 120 e.g. the stored program code 109 and / or the stored data calculation unit 120 need to be able to perform calculations for 12 537 009. The calculation unit 120 is also arranged to store partial or final results of calculations in the memory unit 121.

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

According to the above, according to the present invention, the reliability of the PM sensor signals can be increased by evaluating the signal emitted by the PM sensor. Thus, Fig. 3 shows a first exemplary method 300 according to the present invention. The process begins in step 301, where it is determined whether the PM sensor 213 should be evaluated. If the PM sensor 213 is to be evaluated, the method proceeds to step 302. Transition from step 301 to step 302 can e.g. be arranged to be controlled by a past time since a previous evaluation of the PM sensor 213. The PM sensor 213 may also be arranged to be evaluated continuously, at applicable intervals, each time the vehicle is started or at other applicable times, 13 537 009 such as t. ex. if for any reason, e.g. based on emitted PM sensor signals, or signals from other sensors / devices, it may be suspected that the PM sensor does not emit representative signals.

In step 302, a change of the signal S1 emitted by the PM sensor 213 is determined, where the emitted signal Slallmänt represents a particle occurrence in the exhaust gas stream. This change can e.g. is represented by a frequency for an amplitude variation, i.e. the emitted signal S1 may have amplitude peaks of a certain frequency. This determination can e.g. determined by applicable signal processing. The change determined in step 302 may also consist of another applicable determination, such as e.g. determine an amplitude change that occurs and then, as shown below, compare it with an expected change.

When the change of the signal S1 emitted by the PM sensor 213 has been determined in step 302, the method proceeds to step 303.

In step 303, a corresponding change in the supply of additives to the exhaust stream is determined. This change can e.g. consists of a determination of the frequency with which additives are supplied to the exhaust gas stream.

The additive is normally dosed by using e.g. an injector arranged in the exhaust system, where injection takes place at any applicable injection length with any applicable frequency, such as e.g. a frequency in the range 0.1-110 Hz.

This information can e.g. obtained from the part of the control system which is responsible for dosing additives to the exhaust gas stream, which according to one embodiment can consist of the same control unit in which the present invention is implemented. The change of the supply of additives can also e.g. consists of a change in injection frequency, or consists of a change in the amount of additives injected, or any applicable combination of these changes. The change of added additive may be controlled by factors different from the present invention, the change being observed only, but the change may also be arranged to be controlled by the present invention by a separate step preceding step 303 in Fig. 3.

The process then proceeds to step 304, where the change in the signal emitted by the PM sensor is compared with the change in the supply of additives. For example. For example, the frequency of the amplitude peaks of the signal emitted by the PM sensor can be compared with the dosing frequency. If these frequencies correspond to each other to some applicable extent, it can be assumed that the PM sensor performs measurements on the exhaust gas stream to which additives are supplied, and thus is also very likely exposed to a representative exhaust gas flow. Likewise, e.g. an average amplitude change during any applicable time of the signal emitted by the PM sensor is compared with an expected amplitude change caused by the change in added amount of additive.

In step 305 it is determined whether the comparison indicates that the PM sensor 213 emits a representative signal, in which case the procedure returns to step 301. If the comparison, on the other hand, indicates that the PM sensor 213 does not emit a representative signal, the procedure proceeds to step 306, where a error signal is generated, such as e.g. an alarm signal and / or an error code, to indicate to the control system of the vehicle 100 that the PM sensor 213 cannot be considered to emit a representative signal as this is not considered to be exposed to a representative exhaust flow.

The generated signal can e.g. be used by the control system of the vehicle 100 to set the status of the vehicle 100 to a state where the vehicle 100 is in immediate need of service for action 537 009 of the PM sensor 213. The control system may further be arranged to limit the functionality of the vehicle 100, such as e.g. by limiting the maximum removable power from the internal combustion engine 101 of the vehicle 100 until the fault has been rectified.

The process is then terminated in step 307.

According to the embodiment shown in Fig. 3, active action specifically intended to change the supply of additives can, but does not, be performed, but the determination according to the present invention can be performed when the vehicle is driven in such a way that detectable change of the supply of additives still occurs. , e.g. caused by the pulsation normally applied to the administration of additives or how the amount of dosed additive changes.

Fig. 4 shows an exemplary method 400 according to the present invention, in which change of supply of additives is actively performed.

The process begins in step 401, and the transition to step 402 may be controlled as described above. In step 402, a first representation EQ of the particle content in the exhaust stream is determined by means of said PM sensor 213.

When the particle content Plhar is determined in step 402, the process proceeds to step 403. In step 403, a change in the supply of additives is performed. This change can be carried out in various ways and according to one embodiment comprises completely switching off the supply of additives to the exhaust gas stream, or changing the amount of additives supplied to the exhaust gas stream. According to one embodiment, the supply of additives can instead be switched off, or switched off in a step preceding step 403, whereby in step 403 the supply can instead be resumed. According to the above, e.g. 16 537 009 the frequency of injection or the amount of additive added changes.

According to one embodiment, however, no action is specifically intended to change the supply according to the invention, but in step 403 it is expected that the applicable change of added additive is carried out by another cause controlled by the vehicle control system, where this change may be any of the examples given herein. or other applicable change.

According to one embodiment, the process then proceeds to a step where the process waits for a first time t1 to compensate for any inertia in the system so that the effects of previously added additives can be completely reduced or at least reduced. Said first time can e.g. is controlled by the position of the additive injector in the exhaust system in relation to the PM sensor and the number / type of components arranged in between.

The time t1 can be short, and according to the embodiment shown, this waiting step is not applied.

The process proceeds from step 403 to step 405, where a second representation of the particle content in the exhaust gas stream is determined by means of said PM sensor 213, i.e. a particle content Pg is determined at the PM sensor 213 after said action to change the supply of additives has been performed.

In step 405, an expected PM sensor signal change APg @ is then determined at the position of the PM sensor 213 after the change in the supply of additives taken in step 403, wherein in step 406 the change APU between the first Ey and second of the PM sensor indicated 17 537 009 particle content P2 is compared with the expected change in particle content (the change in sensor signal) AP @@. Although specific particle contents P1, P2 can be determined, this is not a requirement, but in principle it is sufficient to determine applicable representations of particle levels Ph Ib, from which the particle content change AP ”can be determined (as will be appreciated, the particle contents themselves are not necessarily correct because at least one of the determined particle contents may be influenced by the cross-sensitivity of the additive and thus emit a higher or significantly higher indicated particle content than is actually the case).

Thus, it is sufficient to determine a signal difference between the different determinations, where this signal difference can be converted into a particle content difference or compared with an expected signal difference. The same applies to the expected particle content change AP @ w, ie. it is sufficient to determine an expected difference without specifically determining between which actual levels / particle levels the difference is expected to occur.

The expected particle content change Pæw can e.g. determined by table look-up, where the expected signal emitted by the PM sensor for different dosages can be specified, where this expected emitted signal can constitute the signal difference which the additive itself is expected to give rise to due to the cross-sensitivity, and which thus constitutes the difference signal caused by the additive.

In step 406, the actual particle content (sensor signal) change APu is then compared with the expected particle content change AP @@, whereby a deviation A between expected particle content change AP @@ and measured particle content change APU is determined. 18 537009 In step 407, it is then determined whether the deviation A between the expected particle content change ATEW and the measured particle content change AT ”is greater than any applicable limit value Note. The limit value Ahm can e.g. be set in such a way that an appropriately large deviation can be allowed so as not to unnecessarily give rise to alarms regarding the function of the PM sensor 213, since the particle content change the PM sensor signal will indicate due to the additive may be difficult to predict with the desired accuracy.

As long as this is not the case, ie. as long as the deviation A is below the limit value Note, the PM sensor 213 can be assumed to give representative measured values regarding the particle presence in the exhaust stream, since the PM sensor 213 can be assumed to be at a position where the PM signal varies in an expected manner and thus probably also at the intended position in the exhaust system and thus perform measurements on a representative exhaust stream. The method therefore returns to step 401 to, if necessary, perform a new determination of the function of the PM sensor 213 at the applicable time as above.

If, on the other hand, it is determined in step 408 that the deviation A is greater than the limit value Ahm, the procedure proceeds to step 408. In step 408, an error signal is generated as described above, the procedure then being terminated in step 409.

Thus, according to the present invention, there is provided a method which can be used to determine whether the PM sensor 213 emits a representative signal by determining whether it is exposed to a representative exhaust flow, which is determined by determining whether the signal emitted by the PM sensor 213 changes in an expected manner with altered supply of additives. Thus, by means of the present invention, attempts to manipulate the function of the PM sensor 213 by e.g. move the PM sensor to a position outside the exhaust flow, alternatively that e.g. directing the exhaust current past the PM sensor 213 is detected during operation of the vehicle 100, since the PM sensor in such manipulation will not show any or a change in the emitted signal compared to a correctly positioned PM sensor in the event of a change in added additive. The invention thus reduces the possibilities of inadvertently manipulating the finishing system.

Regarding the methods described above, a comparison has been made on one occasion. As will be appreciated, the particle content of the exhaust stream 200 may vary substantially depending on other factors as well, such as e.g. the prevailing operating parameters of the internal combustion engine, whereby a measured individual particle content change in unfavorable conditions can deviate from the expected particle content change by more than the mentioned deviation Note even though the PM sensor 213 is both correctly arranged in the exhaust stream and exposed to a representative exhaust stream.

For this reason, determination of a number of measured values as above can be performed. For example. either method may be arranged to be traversed some applicable number of times x, such as e.g. a relatively large number of times x, whereby x measured values are determined, and thus X deviations A, where a weighted deviation for these X deviations can be determined and compared with the deviation limit value Note, and where the weighted value is used to determine whether the PM sensor 213 can be assumed be exposed to a representative exhaust gas flow.

The deviation Ahm can furthermore be arranged to vary depending on the number of measured values X. The larger the number of measured values X used in 10 537009, the lower the permissible deviation Anm can be set because the weighted accuracy increases with the number of measured values x.

According to one embodiment, a number of determinations are performed instead, e.g. at regular or applicable intervals, comparing the PM sensor signal change over time with an expected PM sensor signal change. Even in this case, deviations for each measured value can be determined and compared with the expected value. The deviations can also be compared with each other, and as long as the deviations are substantially similar, the PM sensor can still be considered to be correctly positioned.

In this case, it can thus be determined not only that the PM sensor 213 is placed in an exhaust composition, but also that the PM sensor 213 is arranged in an exhaust flow whose composition varies with varying operating conditions in a representative manner.

The present invention also has the advantage that determination according to the present invention is performed regardless of the position of the PM sensor in the exhaust system, as long as the change of additive is performed upstream of the PM sensor.

According to one embodiment, a frequency analysis is applied in determining whether the PM sensor 213 emits a representative signal. This frequency analysis can be performed by means of any applicable transform, such as e.g. Fourier transform or FFT (Fast Fourier Transform). As mentioned above, injection of additives is usually carried out at a certain frequency, such as e.g. a frequency in the range 0.l-10 Hz. This means that the additive will be "pulsed" out into the exhaust stream, and there will be pulsating differences in the presence of additives in the flow of the exhaust stream over time. This also means that the pulsation will give rise to concentration variations with the same frequency of the additive, which has also been used above, but which can be used in a way that enables safer detection.

If the PM sensor signal is instead evaluated in the frequency domain, the injection pulsation can be clarified and used according to the present invention.

As mentioned above, the additive pulses will be seen as amplitude variations with a frequency equal to the injection frequency. In the frequency plane, a spike / peak may thus appear at said frequency (weaker shadow pulses at multiples of the frequency may also occur).

Thus, this frequency analysis can at least in some cases be used to improve the certainty in the diagnosis of the PM sensor, since if this pulsation can be identified, it can also be assumed that the PM sensor is exposed to a representative exhaust current. The frequency analysis can be used alone, or combined with a comparison with a limit value as above, where this limit value can be set either in the time domain or in the frequency domain. By performing the determination in the frequency domain, detection with smaller variations is possible, ie. a lower limit value Note can be used.

The variation in the frequency domain can also be used actively since the injection frequency according to the method according to the invention can be varied to give a more reliable diagnosis. If e.g.

If an injection frequency is violated, a waiting error can be set, whereby one or more additional diagnoses for additional injection frequencies can be performed before a malfunction is finally found. 22 10 537 009 In general, it applies to the frequency analysis that the closer the pulsation source the analysis is performed, the more reliable the analysis result will be obtained.

Thus, according to this embodiment, said frequency analysis constitutes a representation of a change of the signal emitted by said PM sensor 213.

Furthermore, there are different types of PM sensors, and the present invention is applicable to all types of PM sensors that exhibit cross-sensitivity to additives. There are e.g. s.k. IDE sensors where ceramic plates coated with conductive materials are used to determine a particle content of a passing exhaust stream. As an exhaust stream containing particles passes through the coated ceramic plates, particles will get stuck, which in turn means that the conductivity between two adjacent non-contacting plates will change. As particles (soot) stick to these plates, the conductivity will increase, which means that e.g. a resistance, current, voltage, conductivity or inductance or the like can be detected, and where changes in relevant magnitude indicate particle occurrence. By determining a gradient for a change over time, particle occurrence can be estimated by determining how fast e.g. a resistance, current or voltage etc. changes. This type of particle sensors thus involves a relatively slow detection of particle occurrence, whereby it can take a long time before malfunction is detected. According to the present invention, however, manipulation of this type of sensors can be detected at an early stage.

There are also other types of particle sensors, such as e.g. electrostatic particle sensors, where particles pass a first electrode to pick up a charge and then pass a second electrode arranged in the particle sensor where the charge is emitted. Depending on the particle presence, the number of electrons per unit time transferred between the electrodes will thus vary, whereby both the particle presence and also the number of particles can be determined with immediate and very high accuracy.

According to one embodiment, this type of particle sensor is used to determine the concentration and / or fraction of particles in the exhaust gas stream. Thanks to the speed of the sensor, very good present value measurements can be performed, ie. very good values representing instantaneous particle contents are obtained.

Furthermore, the method according to the invention can be combined with that in the parallel Swedish application no. 1250961-8 with the title "PROCEDURE AND SYSTEM FOR EXHAUST CLEANING" and the same inventor and filing date as the present application, described to determine a sensor function for a PM sensor. "EXHAUST CLEANING PROCEDURE AND SYSTEM" provides a method for determining whether a PM sensor emits a representative signal, wherein the sensor function of the PM sensor is determined based on a representation of a pressure prevailing at the PM sensor, where the pressure is determined using a wide PM sensor arranged pressure sensor.

Furthermore, the method according to the invention can be combined with that in the parallel Swedish application no. 1250963-4 with the same inventor and filing date as the present application, described to determine a sensor function for a PM sensor. According to said application, a method is provided for determining whether a PM sensor emits a representative signal in which a representation of a concentration prevailing at the PM sensor and / or a fraction of a substance present in the exhaust stream is determined. Based on the representation of a concentration and / or fraction of said first substance determined on 24 537 009, it is determined whether the PM sensor emits a representative signal.

Likewise, the method according to the invention can alternatively, or in addition, be combined with that in the parallel Swedish application no. 1250964-2 with the same inventor and filing date as the present application, described to determine a sensor function for a PM sensor. According to said application, a method is provided for determining whether a PM sensor emits a representative signal where the sensor function of the PM sensor is determined by means of means for determining a representation of a temperature at the PM sensor.

By combining the method according to the present invention with one or more of the methods described above, an even more reliable assessment of the function of the PM sensor can be performed.

The present invention has been described above in connection with specific additives. However, PM sensors can also be cross-sensitive to other types of additives, and the present invention is also applicable to such additives.

Furthermore, the present invention has been exemplified above in connection with vehicles. However, the invention is also applicable to arbitrary vessels / processes where particulate filter systems as above are applicable, such as e.g. water or aircraft with combustion processes as above.

Further embodiments of the method and system according to the invention are found in the appended claims.

It should also be noted that the system may be modified according to various embodiments of the method of the invention (and vice versa) and that the present invention is in no way limited to the above described embodiments of the method of the invention, but relates to and includes all embodiments within the appended claims. the scope of protection of the independent requirements. 26

Claims (1)

10 15 20 25 30 537 009 Patent claims A method for determining a sensor function for a PM sensor (213) intended for determining a particle content in an exhaust stream resulting from combustion at an internal combustion engine (101), wherein a post-treatment system (200) is provided for post-treatment of said exhaust stream, wherein said vehicle comprises means for supplying additives to said exhaust gas stream, and wherein the method is characterized by: - determining a representation of a change (APU) of said signal emitted by said PM sensor (213) in response to a change of the supply of adding, - comparing said representation of said change (APU) of said signal emitted by said PM sensor (213) with a representation of an expected change (AP @@) of the signal emitted by said PM sensor (213), and - based on said comparison of said representation of said change (APU) of said by said PM sensor (213) with said representation of said expected change (APæ @) of the signal emitted by said PM sensor (213), determining whether said PM sensor (213) emits a signal representative of said exhaust current. . The method of claim 1, further comprising making a plurality of consecutive changes to the supply of additives to said exhaust stream, and - based on the corresponding determined changes of said signal emitted by said PM sensor, determining whether said PM sensor (213) emits a signal representative of said exhaust current. 27 10 15 20 25 30 537 009. A method according to claim 1 or 2, wherein said change of supply of additives to said exhaust gas stream comprises an increase or decrease of the amount of added additive. . A method according to any one of claims 1-3, wherein said change of supply of additives to said exhaust gas stream comprises a change of a frequency for supply of additives to said exhaust gas stream. . A method according to any one of the preceding claims, wherein said change of supply of additives to said exhaust gas stream consists of a shut-off of the supply of additives, or a resumption of the supply after a shut-off of the supply of additives. A method according to any one of claims 1-5, wherein said PM sensor (213) consists of an electrostatic or resistive PM sensor. . The method of claims 1-6, further comprising determining, when said representation of said first change (APU) of said signal emitted by said PM sensor (213), - at a first time, determining a first representation of one of said PM sensor (213) emitted particle content (P fl, - at a second time, different from said first time, determining a second representation of a particle content (P2) emitted by said PM sensor (213), said change (APU) of said signal emitted by said PM sensor (213) consists of a difference between said first (P1) and second (Eg) representations of a particle content emitted by said PM sensor (213) 28 10 15 20 25 30 10. ll. A method according to any one of claims 1-7, further comprising determining a change (APU) of said signal emitted by said PM sensor (213) at a plurality of times, comparing the respective determined change (APU) of said one of said PMs. PM sensor (213) output signal with an equivalent expected change (AP @ @) of said signal emitted by said PM sensor (213), and - based on said plurality of comparisons, determining whether said PM sensor (213) emits a signal representative of said exhaust current. A method according to any one of claims 1-8, further comprising determining based on said determined change of said signal emitted by said PM sensor in response to said change of the supply of additives whether said finishing system (200) and / or PM sensor ( 213) can be assumed to have been manipulated. A method according to any one of claims 1-9, further comprising determining whether said PM sensor (213) emits a signal representative of said exhaust gas by, based on said change of said signal emitted by said PM sensor in response to said change of supply of additives to determine whether said PM sensor (213) can be assumed to be in said exhaust stream. A method according to any one of the preceding claims, further comprising: - determining said change of said signal emitted by said PM sensor by means of frequency analysis of the signal emitted by said PM sensor, wherein at said 29 10 15 20 25 30 12 13 14 15. 16 17 537 009 frequency analysis said frequency-analyzed PM signal is compared with an injection frequency for the supply of additives. The method of claim 11, further comprising performing said frequency analysis for a plurality of injection frequencies for supplying additives to said exhaust gas stream. A method according to claim 11 or 12, wherein in said frequency analysis a frequency for an amplitude peak in the frequency plane is compared with the injection frequency for supply of said additive. A method according to any one of the preceding claims, comprising generating a signal indicating a malfunction of said PM sensor (213) when said change of the signal emitted by said PM sensor does not correspond to an expected change. A method according to any one of the preceding claims, wherein said after-treatment system (200) comprises at least one particulate filter (202), and wherein the intended PM sensor position is upstream or downstream of said particulate filter (202) in said exhaust gas stream. A method according to any one of the preceding claims, wherein said internal combustion engine is an engine in a vehicle, and wherein extractable power from said internal combustion engine is limited by using a control system arranged in said vehicle if said PM sensor does not emit a signal representative of said exhaust current. A method according to any one of the preceding claims, further comprising that, when a change of the supply of said additive has been carried out, waiting for a first time (tl) before said change of the one of said PM sensor (213) output signal is determined. A method according to any one of the preceding claims, further comprising determining a representation of a first concentration prevailing at said PM sensor and / or fraction of a first substance (S1) present in said exhaust gas stream by using means arranged at said PM sensor for determining of a representation of a concentration and / or fraction of said first substance (S1), and - means for determining, based also on said determined representation of a concentration of said first substance (S1), whether said PM sensor emits a for said exhaust current representative signal. A method according to any one of the preceding claims, wherein the method further comprises: - determining a representation of a first pressure prevailing at said PM sensor by using a pressure sensor arranged at said PM sensor, and - determining whether said PM sensor emits a signal representative of said exhaust stream also based on said determined first pressure. A method according to any one of the preceding claims, wherein the method further comprises: - determining a first temperature prevailing at said PM sensor by using means arranged at said PM sensor to emit a representation of a at said PM sensor (213) prevailing temperature, and - determining whether said PM sensor emits a signal representative of said exhaust current also based on said determined first temperature. A method according to any one of the preceding claims, wherein said additive is urea or ammonia. Computer program comprising program code, which when said program code is executed in a computer causes said computer to perform the method according to any one of claims 1-21. A computer program product comprising a computer readable medium and a computer program according to claim 22, wherein said computer program is included in said computer readable medium. A system for determining a sensor function for a PM sensor (213) intended for determining a particle content in an exhaust stream resulting from combustion at an internal combustion engine (101), a post-treatment system (200) being provided for post-treatment of said exhaust stream, said vehicle comprises means for supplying additives to said exhaust gas stream, characterized in that the system comprises: - means for determining a representation of a change (APU) of said signal emitted by said PM sensor (213) in response to a change in the supply of additives means for comparing said representation of said change (APU) of said signal emitted by said PM sensor (213) with a representation of an expected change (APEW) of the signal emitted by said PM sensor (213), and means for based on said comparison of said representation of said change (APU) of said of said PM sensor (213) with said representation of 32 1 0 537 009 said expected change (AP @@) of the signal emitted by said PM sensor (213), determining whether said PM sensor (213) emits a signal representative of said exhaust current. System according to claim 24, characterized in that said internal combustion engine consists of one of the group: vehicle engine, marine engine, industrial engine, diesel engine, otto engine, GDI engine, gas engine. A system according to claim 24 or 25, wherein said means for supplying additives are arranged upstream of said PM-SGTISOI. Vehicle (100), characterized in that it comprises a system according to any one of claims 24-26. 33