SE535748C2 - Apparatus and method for detecting a state of a NOx sensor of a motor vehicle - Google Patents

Abstract

SUMMARY The invention relates to a method for determining a state of at least one sensor (240; 270) of a motor vehicle (100; 112) including an engine (230) and an exhaust system with a catalyst (260). The method comprises the steps of: - changing a concentration of NOX gas downstream of the engine (230) by controlling operation of the engine (230) in a predetermined manner; - determining a difference of a first concentration of NOX gas upstream of said catalyst (260); - determining a difference of a second concentration of NOX gas downstream of said catalyst; and - determining a state of said at least one sensor (240; 270) on the basis of said difference of the first concentration of NOX gas and said difference of the second concentration of NOX gas. The invention also relates to a computer program product comprising program code (P) for a computer (200; 210) for implementing a method according to the invention. The invention also relates to a device for determining a state of a sensor of a motor vehicle and a motor vehicle equipped with the device. Figure 2 for publication

Description

535 'M8 In an imaginary type of diagnosis of sensors to detect NO, in the emissions, it may therefore be necessary to turn off the supply of urea to the exhaust gases, which has negative effects from an environmental perspective because too much nitrogen oxides are emitted from the vehicle. Shutting down the supply of urea to the exhaust gases also has negative effects from a fuel economy perspective, as the time that the urea dosing is switched off is weighted in emission cycles of the vehicle's control system.

In another type of diagnosis of sensors to detect NOX gas in the emissions, stored emission models can be used. However, this type of diagnosis is associated with excessive margins of error because the estimated concentrations of NOX gas are not sufficiently reliable.

It is known that a certain amount of ammonia is stored in SCR catalysts during operation of the vehicle. Thus, during operation of the vehicle, more ammonia is stored in the catalyst than is actually needed to react with the amount of temperature dependence added, where a smaller amount of ammonia may be stored in NO gas. The amount of ammonia stored is the catalyst at high temperatures and a larger amount of ammonia may be stored in the catalyst at low temperatures.

WO 2008/120649 describes a system which can determine whether a catalyst of a vehicle is saturated with absorbed ammonia or not as the fuel supply to an engine of the vehicle is limited by propulsion at low speeds.

JP 2008/133780 describes a method for diagnosing a NOX sensor downstream of a catalyst of a vehicle. The diagnosis is made under a condition when the supply of reducing agents is stopped to avoid the influence of the catalyst. There is a need to provide a method for diagnosing and determining a possible failure of one or more sensors to detect concentrations of NOx gas in emissions of a motor vehicle without minimizing urea supply during this process.

SUMMARY OF THE INVENTION An object of the present invention is to provide a new and advantageous method for determining a state of a sensor of an exhaust system of a motor vehicle. In particular, it is an object of the present invention to provide a new and advantageous method for determining a state of a NOx sensor of an exhaust system of a motor vehicle.

Another object of the invention is to provide a new and advantageous device and a new and advantageous computer program for determining a state of a sensor of an exhaust system of a motor vehicle. In particular, it is an object of the present invention to provide a new and advantageous device and a new and advantageous computer program for determining a state of a NOx sensor of an exhaust system of a motor vehicle.

A further object of the invention is to provide a method, an apparatus and a computer program for effecting a more robust determination of a condition of a sensor of a motor vehicle.

A further object of the invention is to provide a method, an apparatus and a computer program for effecting a more accurate determination of a condition of a sensor of a motor vehicle.

An object of the invention is to provide an alternative method for determining a state of a NOx sensor a motor vehicle. These objects are achieved by a method for determining a condition of at least one sensor of a motor vehicle according to claim 1.

According to one aspect of the invention, there is provided a method of determining a state of at least one NOX sensor of a motor vehicle including an engine and an exhaust system with a catalyst. The method comprises the steps of: - changing a concentration of NOx gas downstream of the engine by controlling operation of the engine in a predetermined manner; - determining a difference corresponding to said changed concentration of NO, - gas of a first concentration of NOx gas upstream of said catalyst; determining a difference corresponding to said changed concentration of NOx gas of a second concentration of NOX gas downstream of said catalyst, at least one of said determinations taking place based on measurement; and - determining a state of said at least one NOK sensor, which was used to measure the concentration of NOx gas, on the basis of said difference of the first concentration of NOX gas and said difference of the second concentration of NOx gas.

According to one aspect of the invention, it is possible to diagnose and adapt at least one NOx sensor by gradually increasing the concentrations of NO, upstream and downstream of the catalyst. Stepwise control of the concentrations of NO, in an exhaust system of the vehicle can be achieved by changing the injection angle of at least one cylinder of the vehicle's engine. By locking urea dosage to the SCR catalyst in all variables except mass fate, considerable ammonia in the catalyst can be consumed by taking at least one NOK step. The urea dosage will not be corrected. By subsequently performing additional NOx steps and comparing determined emission parameters of a first sensor arranged upstream of the catalyst with emission parameters of a second sensor arranged 535 748 downstream of the catalyst, any Gain and Off-set errors of the NO sensor can be determined.

The procedure is easy to implement in existing motor vehicles. Software for determining a state of at least one NOx sensor of a motor vehicle according to the invention can be installed in a control unit of the vehicle in the manufacture thereof. A buyer of the vehicle can thus be given the opportunity to choose the function of the procedure as an option. Alternatively, software including program code for performing the innovative method of determining a condition of at least one sensor of a motor vehicle may be installed in a control unit of the vehicle when upgrading at a service station. In this case, the software can be loaded into a memory in the control unit. Implementation of the innovative method is thus cost-effective, especially since no more advanced sensors for detecting concentrations of NOX gas in an exhaust system of the vehicle are required. The required hardware is already present in the vehicle today. The invention thus provides a cost-effective solution to the above problems. It is also likely that fewer workshop visits for the vehicle will be required as an automatic adaptation of misleading sensors can be performed according to the innovative procedure.

Software that includes program code for determining the condition of at least one NOX sensor of a motor vehicle can be easily updated or replaced. Furthermore, different parts of the software comprising program code for determining a state of at least one sensor of a motor vehicle can be replaced independently of each other. This modular configuration is advantageous from a maintenance perspective.

The method may further comprise the step of: - before initiating said control of the operation of the engine, determining whether a desired flow condition exists in said exhaust system. In this desirable state of fate, there is essentially no additional ammonia stored in the catalyst. 535 748 This makes it advantageously possible to carry out the innovative process at relatively low temperatures in the catalyst, where rather high storage of ammonia can normally be present during operation of the vehicle.

The method may further comprise the step of: - before initiating said control of the operation of the motor, setting a value representing a desired degree of stoichiometry.

The method may further comprise the steps of: - determining a first parameter associated with said difference of the first concentration of NOK gas; - determining a first parameter associated with said difference of the second concentration of NOx gas; and - determining whether the at least one NOK sensor has a Gain error based on the first two parameters.

The method may further comprise the steps of: - determining a second parameter associated with said difference of the first concentration of NOX gas; determining a second parameter associated with said difference of the second concentration of NOX gas; and determining whether the at least one NOx sensor has an Off-set error based on the other two parameters.

The method may further comprise the step of: - controlling injection of urea into the exhaust system on the basis of the determined condition of the at least one sensor.

The method may further comprise the step of: - controlling operation of the engine in a manner which causes a concentration of NOx gas downstream of the engine to be increased in one or more substantially discrete steps. The increase of said step may be within a range defined by [50, 3000] ppm. The increase of said step may be within a range defined by [500, 1000] ppm.

The operation of the engine can be controlled by influencing an injection angle of at least one cylinder of the engine.

According to one aspect of the invention, there is provided an apparatus for determining a condition of at least one sensor of a motor vehicle according to claim 9.

According to one aspect of the invention, there is provided an apparatus for determining a state of at least one NOx sensor of a motor vehicle including an engine and an exhaust system with a catalyst. The device comprises - means for changing a concentration of NOx gas downstream of the engine by controlling operation of the engine in a predetermined manner; means for determining a difference corresponding to said changed concentration of NOx gas of a first concentration of NOX gas upstream of said catalyst; means for determining a difference corresponding to said changed concentration of NOX gas of a second concentration of NOx gas downstream of said catalyst, at least one of said determinations taking place based on measurement; and - means for determining a state of said at least one NOX sensor, which is used to measure the concentration of NOK gas, on the basis of said difference of the first concentration of NOx gas and said difference of the second concentration of NOX gas. gas.

The device may further comprise means for determining, before said control of the operation of the engine, whether a desirable state of destiny prevails in said exhaust system. The device may further comprise means for setting, before said control of the operation of the motor is set, a value representing a desired degree of stoichiometry. The device may further comprise means for determining a first parameter associated with said difference of the first concentration of NOx gas; means for determining a first parameter associated with said difference of the second concentration of NOx gas; and - means for determining whether said at least one NOx sensor has a Gain error based on the first two parameters.

The device may further comprise means for determining a second parameter associated with said difference of the first concentration of NOx gas; means for determining a second parameter associated with said difference of the second concentration of NOX gas; and - means for determining whether said at least one NOx sensor has an Off-set error on the basis of the other two parameters.

The device may further comprise means for controlling injection of urea into the exhaust system on the basis of the determined condition of the at least one sensor.

The device may further comprise means for controlling operation of the engine in a manner which causes a concentration of NOX gas downstream of the engine to be increased in one or more substantially discrete steps. The increase of said steps may be within a range which they are fi denied by [50, 3000] ppm. The increase of said step may be within a range defined by [500, 1000] ppm.

The above objects are also achieved with a motor vehicle comprising the features of the device for determining a state of at least one NO, - 535 748 sensor of a motor vehicle. The motor vehicle can be a truck, bus or car.

Alternatively, the invention can be applied to other vehicles or platforms having an internal combustion engine. Examples of platforms other than ground vehicles are e.g. watercraft, such as a boat or a ship equipped with an engine that emits emissions, or an arbitrary stand-alone generator, such as e.g. a diesel-powered electric generator.

According to one aspect of the invention, there is provided a computer program for determining a state of at least one NOX sensor of a motor vehicle, said computer program comprising program code stored on a computer readable medium for causing an electronic control unit or another computer connected to the electronic control unit to perform the steps according to any one of claims 1-8.

According to one aspect of the invention, there is provided a computer program product comprising a program code stored on a computer readable medium for performing the method steps of any of claims 1-8, when said computer program is run on an electronic control unit or another computer connected to the electronic control unit. .

Additional objects, advantages, and novel features of the present invention will become apparent to those skilled in the art from the following details, as well as through the practice of the invention. While the invention is described below, it should be understood that the invention is not limited to the specific details described. Those skilled in the art having access to the teachings herein will recognize additional applications, modifications, and incorporations in other fields, which are within the scope of the invention. 535 748 SUMMARY DESCRIPTION OF THE DRAWINGS For a more complete understanding of the present invention and further objects and advantages thereof, reference is now made to the following detailed description which is to be read in conjunction with the accompanying drawings, in which like reference numerals refer to like parts throughout the various forms. Figure 1 schematically illustrates a vehicle, according to an embodiment of the invention; Figure 2 schematically illustrates a subsystem of the vehicle shown in Figure 1, according to an embodiment of the invention; Figure 3a schematically illustrates a diagram in which NOX concentration upstream of a catalyst of the vehicle is indicated as a function of time; Figure 3b schematically illustrates a diagram where NOX concentration upstream of a catalyst of the vehicle is indicated as a function of time; Figure 4a schematically illustrates a fate diagram of a method, according to an embodiment of the invention; Figure 4b schematically illustrates in further detail a flow chart of a method, according to an embodiment of the invention; and Figure 5 schematically illustrates a computer, according to an embodiment of the invention.

DETAILED DESCRIPTION OF THE FIGURES Referring to Figure 1, a side view of a vehicle 100 is shown. The exemplary vehicle 100 consists of a tractor 110 and a trailer 112.

The vehicle can be a heavy vehicle, such as a truck or a bus. The vehicle can alternatively be a car.

Here, the term "link" refers to a communication link which may be a physical line, such as an optoelectronic communication line, or a non-physical line, such as a wireless connection, for example a radio or microwave link.

Here, the terms "gain" and "gain error" generally refer to a sensitivity and a proportional error in the sensitivity of a sensor of the vehicle, respectively. In particular, the terms "gain" and "gain error" refer to a sensitivity and a proportional error in sensitivity of a NOx sensor of the vehicle, respectively.

The gain error of a NOx sensor can be determined by determining a characterizing constant associated with a change in a concentration of NOx gas upstream or downstream of a catalyst of the vehicle and comparing this value with a reference value.

Here, the terms "off-set" and "off-set error" generally refer to a systematic shift of a detected value and an error associated with the systematic shift of a detected value of a sensor of the vehicle, respectively. In particular, the terms "off-set" and "off-set error" refer to a systematic shift of a detected value and an error associated with the systematic shift of the detected value of a NOx sensor of the vehicle, respectively. of a NOx sensor can be determined by determining a characteristic constant associated with a change in a concentration of NOx gas upstream or downstream of a catalyst of the vehicle and comparing this value with a reference value.

Here, the term “stoichiometry” refers to a relationship between an existing concentration of NO, and an existing concentration of ammonia (NH3).

A ratio 1 between NH3 and NOx (NH3 / NOx) means a theoretical complete reduction of NOx as the amount of NH3 is exactly as much as required. A degree of stoichiometry does not reduce all NOx. A degree of stoichiometry 0.9 reduces 90% NOx in an ideal catalyst and exhaust gas mass de.

Referring to Figure 2, there is schematically shown a subsystem 299 of the vehicle 100. The subsystem 299 is arranged in the tractor 110. The subsystem 299 consists of an engine 230 which is arranged to drive the vehicle 100. The engine 230 is an internal combustion engine. The engine 230 can be a diesel engine with any number of cylinders, such as e.g. 4, 5 or 6 cylinders.

The exhaust gases generated by the engine during operation of the vehicle are arranged to be led in a first pipe 235 to a catalyst 260. According to this exemplary embodiment, the catalyst 260 is a so-called SCR catalyst. The catalyst 260 is connected to a second pipe 265 which is arranged to discharge the exhaust gases from the vehicle 100 to an environment thereof. It will be apparent to one skilled in the art that subsystem 299 may include additional components, particle filters. These other components have been omitted to clarify the invention. such as e.g.

A first sensor 240 is arranged upstream of the catalyst 260 at the first tube 235. The first sensor 240 is arranged to measure a gas concentration of the exhaust gases in the first tube 235. In particular, the first sensor 240 is arranged to measure a concentration of NOX gas in the exhaust gases in the first tube 235. The first sensor 240 is arranged to continuously detect a concentration of NOx gas in the first tube 235. The first sensor 240 is arranged to detect in real time a concentration of NOX gas in the first tube 235. The first sensor 240 is arranged for communication with an emission control unit 220 via a link 241. The first sensor 240 is arranged to continuously send signals including information about a prevailing concentration of NOx gas in the first tube 235 to the emission control unit 220.

The emission controller 220 is arranged to receive the signals transmitted from the first sensor 240.

Similarly, a second sensor 270 is arranged downstream of the catalyst 260 at the second tube 265. The second sensor 270 is arranged to measure a gas concentration of the exhaust gases in the second tube 265. In particular, the second sensor 270 is arranged to measure a concentration of NOx gas in the exhaust gases in the second tube 265. The second sensor 270 is arranged to continuously detect a concentration of NOx gas in the second tube 265. The second sensor 270 is arranged to detect in real time a concentration of NOX gas in the second tube 265. The second sensor 270 is arranged for communication with the emission control unit 220 via a link 271.

The second sensor 270 is arranged to continuously send signals including information about a prevailing concentration of NOX gas in the second tube 265 to the emission control unit 220. The emission control unit 220 is arranged to receive the signals transmitted from the second sensor 270.

The emission control unit 220 is arranged for communication with an injector 250 via a link 251. The fluid injector 250 is presently arranged at the first tube 235. The emission control unit 220 is arranged to control the link 251.

The fluid injector 250 is arranged to inject a fluid into the first tube 235 of the fluid injector 250 by means of control signals transmitted via depending on the received control signals.

According to this embodiment, the liquid injector is arranged to inject a liquid solution comprising urea into the first tube 235. An example of a liquid solution is AdBIue. A container (not shown) is provided to hold the liquid solution. The container is fl fitted to the injector via a passage arranged to direct the liquid solution to the injector 250 to be injected into the first tube 235 in a suitable manner.

By injecting e.g. AdB | ue, or other suitable liquid solution, enables a catalytic process in the catalyst 260 where NO 2 gas reacts with ammonia (NHS), whereby nitrogen gas (Ng) and water (H 2 O) can be formed.

It will be apparent to one skilled in the art that the first sensor 240, the second sensor 270 and the fluid injector 250 may be of a suitable type and that they may be configured in a suitable manner in the subsystem 299. A motor control unit 200 is according to one embodiment arranged for communication with the emission control unit 220 via a link 221. The motor control unit 200 is also referred to as a first control unit 200. The first control unit 200 is arranged to control the emission control unit 220 by continuously sending control signals thereto. In the first control unit 220, an emission model may be stored in a memory. The first control unit 200 can, with the aid of the stored emission model, estimate a prevailing concentration of NOX gas in the first pipe 235. The first control unit can, with the aid of the stored emission model, also estimate a prevailing concentration of NOX gas in the second pipe 265. According to an embodiment of the invention, the first control unit 200 is arranged to estimate a first concentration level of NOx gas in the first tube 235 which should be present at a given operating case 100. first concentration level of NOx gas in the first tube 235 may constitute a reference level for an actual prevailing concentration level of NOX gas in the first tube 235. Similarly, the first control unit 200 is arranged to estimate a second concentration level of NOx gas in the second tube 265 which should be present at a given operating case of the vehicle 100. This estimated second concentration level of NOK gas in the second tube 265 may be one of the vehicle This estimated reference level for an actual prevailing NOX gas concentration level in the second tube 265.

According to one example, the first controller 200 may be a Master and the emission controller may be a Slave.

The first control unit 200 is arranged to determine whether a substantially stationary flow state of the catalyst 260 is present. According to an example, the first control unit 200 is arranged to determine the substantially stationary flow state on the basis of a prevailing temperature of the catalyst 260, alternatively how the prevailing temperature of the catalyst 260 varies over time. According to an example, the first control unit 200 is arranged to determine the substantially stationary flow state on the basis of 535 748 how the prevailing fate of the catalyst 260 varies over time. The first control unit 200 is arranged to, after it has been determined that a substantially stationary flow state exists, select a value which represents a desired degree of stoichiometry. The first control unit 200 is arranged to lock the dosage of urea with respect to all variables except gas mass fl in the exhaust system. The first control unit 200 is arranged to provide a NOx step for gradually emptying the catalyst 260 of additional stored ammonia. The first control unit 200 is arranged to check whether additional stored ammonia is present in the catalyst 260. This can take place with a number of temporary increases in the concentration of NOx gas in the first tube 235.

It should be noted that the first control unit 200 is generally arranged to control the injection of urea into the first tube 235 according to stored drivers.

The urea dose will not be corrected for changes in NO gas during the innovative procedure. The first control unit 200 is arranged to change a concentration of NOx gas downstream of the engine 230 by controlling operation of the engine 230 in a predetermined manner. In this way, discrete NOX steps can be performed. The first control unit 200 is further arranged to determine a difference of a first concentration of NOx gas upstream of said catalyst 260 and to determine a difference of a second concentration of NOx gas downstream of said catalyst. The first control unit 200 is arranged to determine a state of at least one of the NOx sensors 240 and 270 on the basis of said difference of the first concentration of NOx gas and said difference of the second concentration of NOx gas.

A second control unit 210 is arranged for communication with the first control unit 200 via a link 211. The second control unit 210 may be detachably connected to the first control unit 200. The second control unit 210 may be a control unit external to the vehicle 100. The second control unit 210 may be arranged to perform the innovative process steps according to the invention. The second control unit 210 can be used to upload software to the first control unit 200, in particular software for performing the innovative method. The second control unit 210 may alternatively be arranged for communication with the first control unit 200 via an internal network in the vehicle. The second control unit 210 may be arranged to perform substantially similar functions as the first control unit 200, such as e.g. determining a state of at least one of the first sensor 240 and the second sensor 270.

According to the embodiment described with reference to Figure 2, the first sensor 240, the second sensor 270 and the injector 250 are signal connected to the emission control unit 220. It should be pointed out that other configurations can be realized. For example. the first sensor 240, the second sensor 270 and the injector 250 could be signal connected to the first control unit 200 and / or the second control unit 210. A person skilled in the art will realize that different variants are possible to realize. Parts of the innovative method can be executed by means of embedded software in the first control unit 200, the second control unit 210 and the emission control unit 220, or in a combination thereof.

Figure 3a schematically illustrates a diagram in which the concentration of NOX gas C [ppm] upstream of the catalyst 260 of the vehicle 100 is given as a function of the time T given in seconds.

Before time T1a, a certain concentration L0a of NOX gas is present in the first tube 235. According to an example, this level L0a is 1000 ppm. Before increasing the concentration of NO, gas C upstream of the catalyst 260, a substantially stationary flow state must be reached, with an equilibrium state in the catalyst 260 prevailing. The substantially steady state of fate can be determined according to an example on the basis of a prevailing temperature of the catalyst 260, or alternatively how the prevailing temperature of the catalyst 260 varies over time. After a substantially steady state has been determined, a value is represented which represents a desired degree of stoichiometry. According to an alternative, a value is chosen which represents a desired degree of stoichiometry, which value corresponds to a prevailing stoichiometry, i.e. a current stoichiometry is frozen. According to another alternative, a predetermined value is selected for the stoichiometry, such as e.g. 0.9 or 1.0. The selected value that represents a desired degree of stoichiometry is then set in e.g. the first control unit 200, the second control unit 210 and / or the emission control unit 220 as parameters in drivers stored therein. In this case, the dosage of urea is also locked with regard to all variables except gas mass fl fate in the exhaust system. This means, according to an example, that the amount of urea supplied to the first pipe 235 for a certain time is regulated on the basis of a prevailing gas mass flow in the first pipe 235.

At a first time T1a, after it has been determined that a substantially stationary flow condition exists in the exhaust system of the vehicle, that a value representing a desired degree of stoichiometry has been selected and that the dosage of urea has been read, the concentration of NOx gas downstream of 230 changes in the first tube 235 in a predetermined manner. According to this example, the NOX gas concentration is increased to a first predetermined level L1a corresponding to 1200 ppm.

At a second time T2a, the concentration of NOx gas downstream of the engine 230 in the first tube 235 is changed in such a way that a temporary increase of the NOX gas concentration to a second predetermined level L2a is achieved.

Thereafter, the concentration of NOX gas is changed so that it again reaches the first predetermined level L1a. This procedure is repeated according to this example three times at predetermined times. Then a second phase starts, given that an equilibrium state in the catalyst prevails. This equilibrium state includes a state where no additional ammonia is stored in the catalyst 260. This equilibrium state can be determined on the basis of at least two consecutive responses of the NOX concentration downstream of the catalyst in said temporary elevations of NO, upstream of the catalyst 260, described in further detail with reference to Figure 3b below.

At a predetermined time T3a, the concentration of NOX gas downstream of the engine 230 in the first tube 235 changes in such a way that an arbitrary increase in the concentration is achieved. In this case, the level is raised from the first level L1a to the second level L2a.

At a predetermined time T4a, the concentration of NOX gas downstream of the engine 230 in the first tube 235 changes in such a way that an arbitrary increase in the concentration is achieved. In this case, the level is raised from the second level L2a to a third level L3a. At a predetermined time T5a, the concentration of NOx gas downstream of the motor 230 in the first tube 235 changes back to the original level L0a, or other desired level.

According to this exemplary embodiment, the first level L1a corresponds to 1200 ppm N0. According to this exemplary embodiment, the second level L2a corresponds to 1300 ppm NOX. According to this exemplary embodiment, the third level L3a corresponds to 1400 ppm NOx.

The predetermined steps performed during the first and second phases may correspond to a change in NOX gas C concentration within a range [50, 3000] ppm.

Figure 3b schematically illustrates a diagram in which the concentration of NOx gas C [ppm] downstream of the catalyst 260 of the vehicle 100 is given as a function of the time T given in seconds.

Before a time T1b there is a certain concentration LOb of NOX gas in the second tube 265. According to an example, this level LOb is 100 ppm. At the first time T1b, the concentration C of NOX downstream of the catalyst in the second tube 265 changes depending on the engine control performed at time T1a as described above. According to this example, the NOX gas concentration is gradually increased to a first level L1b as ammonia stored in the catalyst 260 is consumed. The first level L1b in this example corresponds to 300 ppm. The times T1a and T1b are naturally shifted in time in such a way that the time T1b is later in time than T1a. The same relative displacement prevails between the times T2a and T2b, etc. for the times indicated in Figures 3a and 3b.

At a second time T2b, the concentration of NOx gas downstream of the catalyst 260 in the second tube 265 changes in such a way that a temporary increase in the NOX gas concentration is achieved. According to this example, the response to the first concentration increase at time T1a downstream of the catalyst 260 is not complete, because excess ammonia is still stored in the catalyst.

However, the response to the two remaining concentration increases during the first phase is complete and temporary increases in NOx gas concentration levels downstream of the catalyst are achieved. The two temporary increases in the concentration of NOx gas go from a first level L1b to a level L2b.

After at least two temporary increases in the concentration C of NOx gas are substantially equal downstream of the catalyst, given that the corresponding temporary increases in the concentration C of NOx gas upstream of the catalyst are substantially equal, it can be determined that an equilibrium state in the catalyst prevails.

It should be noted that said equilibrium state in the catalyst 260 can be determined in various ways. Here, a method is exemplified, namely that stated above. At a time T3b, the concentration of NOx gas downstream of the catalyst 265 in the second tube 265 changes due to the increase in the concentration of NOX gas upstream of the catalyst 260 at the time T3a. In this case, the level is raised from the first level L1b to the second level L2b.

At a time T4b, the concentration of NOx gas downstream of the catalyst 260 in the second tube 265 changes due to the increase in the concentration of NOx gas upstream of the catalyst 260 at time T4a. In this fail, the level is raised from the second level L2b to a third level L3b. At a time T5a, the concentration of NOx gas downstream of the motor 230 in the first tube 235 changes back to the initial level L0b, or other desired level, depending on the decrease in the concentration of NOx gas at time T5a. According to this exemplary embodiment, the first level L1 corresponds to 300 ppm NOX gas. According to this exemplary embodiment, the second level L2 corresponds to 400 ppm NOx gas. According to this exemplary embodiment, the third level L3 corresponds to 500 ppm NOx gas.

According to one aspect of the invention, a straight line equation y1 = k1x + m1 is determined for the step increases of NOX gas concentrations upstream of the catalyst 260 and a corresponding straight line equation y2 = k2x + m2 for the step increases of NOX gas concentrations downstream of catalyst 260 according to which is schematically shown according to Figure 3a and Figure 3b.

According to one aspect of the invention, the constants k1 and k; are compared with each other to determine a possible gain error of the first sensor 240 and / or the second sensor 270 on the basis thereof. If the difference between the values of the constants k1 and kg is greater than a predetermined limit value, it can be determined that a Gain error exists. The absolute amount of the difference between the values of the constants k1 and k; indicates the magnitude of the Gain error between the first sensor 240 and the second sensor 270.

According to one aspect of the invention, the constants k1 and k; is compared with a constant ka derived from an emission model that estimates the NO 2 concentration upstream of the SCR catalyst to determine a possible Gain error of the first sensor 240 and / or the second sensor 270 on the basis thereof.

According to one aspect of the invention, the constants m1 and m2 can be compared with each other, or with a predetermined reference value, such as e.g. a constant, for example zero (0) to determine a possible off-set error of the first sensor 240 and / or the second sensor 270 on the basis thereof. If the difference between the values of the constants m1 and m2 is greater than a predetermined limit value, it can be determined that an Off-set error exists. The absolute amount of the difference between the values of the constants m1 and m2 indicates the magnitude of the Off-set error between the first sensor 240 and the second sensor 270.

Alternatively, an off-set error can be determined by comparing the respective constants m1 and m2 with the predetermined value to determine the magnitude of the off-set error.

Figure 4a schematically illustrates a fate diagram of a method for determining a state of at least one sensor of a motor vehicle including an engine and an exhaust system with a catalyst, according to an embodiment of the invention. The method comprises a first method step s401. Step s401 includes the steps of: - changing a concentration of NOX gas downstream of the engine by controlling operation of the engine in a predetermined manner; determining a difference of a first concentration of NOx gas upstream of said catalyst; - determining a difference of a second concentration of NOx gas downstream of said catalyst; and determining a state of said at least one sensor based on said difference of the first concentration of NOx gas and said difference of the second concentration of NOx gas. After step s401, the process is terminated.

Figure 4b schematically illustrates a flow chart of a method for determining a state of a NOX sensor of a motor vehicle including an engine and an exhaust system with an SCR catalyst, according to an embodiment of the invention.

The method includes a first method step s410. Method step s410 includes the step of determining a flow condition in the exhaust system of the vehicle 100. The flow condition can be determined in a manner described in further detail with reference to the description of Phase 1 in Figures 3a and 3b. After the process step s410, a subsequent process step s420 is performed.

Method step s420 includes the step of determining whether the determined flow state is a substantially stationary flow state. According to an example, the substantially stationary state of fate can be determined on the basis of a prevailing temperature of the catalyst 260, alternatively how the prevailing temperature of the catalyst 260 varies over time. If a substantially stationary fl fate condition exists, a subsequent procedure step s430 is performed. If a substantially stationary flow condition does not exist, process step s410 is performed again.

The method step s430 includes the step of selecting a value representing a desired degree of stoichiometry. According to an alternative, a value is chosen which represents a desired degree of stoichiometry, which value corresponds to a prevailing stoichiometry, i.e. a current stoichiometry is frozen during the execution of the remaining process steps. According to another alternative, a predetermined value is selected which represents a desired degree of stoichiometry, such as e.g. 0.9 or 1.0. The selected value which represents a desired degree of stoichiometry is then set in e.g. the first control unit 200, the second control unit 210 and / or the emission control unit 220 as parameters in drivers stored therein. In the event that a value other than the value representing a prevailing degree of stoichiometry is selected, a new static flow condition should be awaited before the procedure proceeds. In other words, in this case, the concentration of NOx gas downstream of the catalyst 260 must swing to a certain substantially constant level before the process proceeds.

Process step s430 also includes the step of locking the dosage of urea with respect to all variables except gas mass fl fate in the exhaust system.

According to an example, this means that the amount of urea supplied to the first tube 235 for a certain time is regulated on the basis of a prevailing gas mass fl in the first tube 235. After the process step s430, a subsequent process step s435 is performed.

Process step s435 includes the step of actuating the catalyst 260.

Process step s435 includes the step of effecting a stepwise increase in the concentration of NO, in the first tube 235 from a level L0a to a level L1a, as illustrated in Figure 3a. In this case, the catalyst is actuated in such a way that extra ammonia stored therein is gradually consumed.

The process step s435 also includes the step of determining whether a desirable fl state of fate in said exhaust system actually exists. The desired flow state is a state where substantially no additional amount of ammonia is stored in the catalyst 260. The desired state of fate may be a state where an equilibrium state considering NO, and ammonia prevails.

According to one example, this desirable flow condition can be determined by providing an arbitrary number of temporary increases in the concentration of NOX in the first tube 235. With a certain delay, corresponding temporary increases in the concentration of NO in the second tube 265 can be detected. In the case where two successive temporary increases in the concentration of NO in the second pipe 265 are substantially equal, it can be determined that a desired flow state prevails in said exhaust system. This concludes Phase 1, which is described in more detail with reference to Figure 3a and Figure 3b. After the process step s435, a subsequent process step s440 is performed.

The step step s440 includes the step of taking an action. More specifically, a measure is taken to increase the concentration of NO in at least one discrete step, upstream of the catalyst 260. This can e.g. is achieved by controlling the injection angle α of at least one cylinder of the engine 230 of the vehicle 100. With a certain delay, a corresponding increase in the concentration of NO, downstream of the catalyst 260 will be achieved. After the process step s440, a subsequent process step s450 is performed.

Process step s450 includes the step of determining emission parameters associated with the concentration increases of NOX gas upstream and downstream of the catalyst, respectively. This is described in further detail with reference to, for example, Figures 3a and 3b. The emission parameters are the established constants k1, kg, m1 and m2. Method step s450 also includes the step of determining a possible Gain error of at least one of the NOX sensors 240 and 270. A possible Gain error of the at least one NO1 sensor 240 and 270 can be determined on the basis of the determined constants k1 and kg . A possible off-set error can be determined on the basis of the determined parameters m1 and / or m2. In a mutual comparison of the constants k1 and k; any sensor of the first sensor 240 or the second sensor 270 may be a reference. In a mutual comparison of the constants m1 and m2, an arbitrary sensor of the first sensor 240 or the second sensor 270 can constitute a reference. After the process step s450, a subsequent process step s460 is performed.

The process step s460 includes the step of, where applicable, adapting urea dosage for a possible Gain error and / or a possible Off-set error. The adaptation is intended to correct for automated direct 535 748 or indirect urea dosing of the subsystem 299. After the process step s460, the process is terminated. The stoichiometry is then regulated according to stored drivers and the subsystem 299 resumes normal operation of the SCR catalyst.

Referring to Figure 5, there is shown a diagram of an embodiment of a device 500. The controllers 200, 210 and 220 described with reference to Figure 2 may in one embodiment include the device 500. 500 includes a non-volatile 520, a data processing unit 510 and a read / write memory 550. The non-volatile memory 520 has a first memory portion 530 in which a computer program, such as a device memory operating system, is stored to control the operation of the device 200. Further, the device 500 includes a bus controller, a serial communication port, I / O means, an A / D converter, a time and date input and transfer unit, an event counter and an interrupt controller (not shown). The non-volatile memory 520 also has a second memory portion 540.

A computer program P is provided which comprises routines for determining the condition of at least one sensor of a motor vehicle according to the innovative method. Program P includes routines for determining emission parameters associated with the concentration increases of NOX upstream and downstream of the catalyst, respectively. Program P includes procedures for, on the basis of the established emission parameters, where applicable, adapting any Gain fault identified and / or any offset set fault, in accordance with the innovative procedure. The program P can be stored in an executable manner or in a compressed manner in a memory 560 and / or in a read / write memory 550.

When it is described that the data processing unit 510 performs a certain function, it is to be understood that the data processing unit 510 performs a certain part of the program which is stored in the memory 560, or a certain part of the program which is stored in the read / write memory 550. 535 748 26 The data processing device 510 can communicate with a data port 599 via a data bus 515. The useless memory 520 is intended for communication with the data processing unit 510 via a data bus 512. The separate memory 560 is intended to communicate with the data processing unit 510 via a data bus 511. The read / write memory 550 is arranged to communicate with the data processing unit 510 via a data bus 514. To the data port 599, e.g. the links 211, 221, 251 and 271 are connected (see Figure 2).

When data is received on the data port 599, it is temporarily stored in the second memory portion 540. After the received input data is temporarily stored, the data processing unit 510 is arranged to perform code execution in a manner described above. According to one embodiment, signals received at the data port 599 include information about a current concentration of NOx gas in the first tube 235. According to one embodiment, signals received at the data port 599 include information about a current concentration of NOx gas in the second tube 265. The received the signals on the data port 599 may be used by the device 500 to determine a state of at least one of the first sensor 240 and the second sensor 270. This state includes a state associated with a possible Gain error and / or a possible determined Off-set fault of at least one NOx sensor of the vehicle 100.

Parts of the methods described herein may be performed by the device 500 by means of the data processing unit 510 running the program stored in the memory 560 or the read / write memory 550. When the device 500 runs the program, the methods described herein are executed.

The foregoing description of the preferred embodiments of the present invention has been provided for the purpose of illustrating and describing the invention. It is not intended to be exhaustive or to limit the scope to the variants described. Obviously, many modifications and variations will occur to those skilled in the art. The embodiments were selected and described to best explain the principles of the invention and its practical applications, thereby enabling those skilled in the art to understand the invention for various embodiments and with the various modifications appropriate to the intended use.

Claims (21)

10 15 20 25 30 535 748 28 PATENT REQUIREMENTS A method of determining a state of at least one NOx sensor (240; 270) of a motor vehicle (100; 112) including an engine (230) and an exhaust system with a catalyst (260), each of said at least a NOx sensor is arranged in said exhaust system downstream or upstream of said catalyst, characterized by the steps of: - changing a concentration of NOX gas downstream of the engine (230) by controlling operation of the engine (230) in a predetermined manner; - determining a difference corresponding to said changed concentration of NOx gas of a first concentration of NOx gas upstream of said catalyst (260); determining a difference corresponding to said changed concentration of NOx gas of a second concentration of NOx gas downstream of said catalyst, wherein at least one of said determinations takes place based on measurement; and - determining a state of said at least one NOx sensor (240; 270), which is used to measure the concentration of NOx gas, on the basis of said difference of the first concentration of NOx gas and said difference of the second concentration of NOx gas. NOx gas. The method of claim 1, further comprising the step of: - before initiating said control of the operation of the engine, determining (s435) whether a desired flow condition exists in said exhaust system. The method of claim 1 or 2, further comprising the step of: - before initiating said control of the operation of the motor (230), setting (s430) a value representing a desired degree of stoichiometry. A method according to any one of the preceding claims, further comprising the steps of: - determining a first parameter (k1) associated with said difference of the first concentration of NOx gas; - determining a first parameter (kg) associated with said difference of the second concentration of NOX gas; and - determining whether the at least one NOx sensor (240; 270) has a Gain error based on the first two parameters (k1, kg). A method according to any one of the preceding claims, further comprising the steps of: - determining a second parameter (m1) associated with said difference of the first concentration of NOX gas; - determining a second parameter (m2) associated with said difference of the second concentration of NOK gas; and - determining whether the at least one NOx sensor (240; 270) has an Off-set error based on the other two parameters (m1, m2). A method according to any one of the preceding claims, further comprising the step of: - controlling operation of the engine (230) in a manner which causes a concentration of NOx gas downstream of the engine (230) to be increased in one or more substantially discrete steps. The method of claim 6, wherein the increase of said step is within a range defined by [50, 3000] ppm. 8A. A method according to any one of the preceding claims, wherein the operation of the engine (230) is controlled by influencing an injection angle (a) of at least one cylinder of the engine (230). An apparatus for determining a state of at least one NOX sensor (240; 270) of a motor vehicle (100; 112) including an engine (230) and an exhaust system with a catalyst (260), each of said 10 At least one NOx sensor is arranged in said exhaust system downstream or upstream of said catalyst, characterized by: means (230) for changing a concentration of NOX gas downstream of the engine (230) by controlling operation of the motor (230) in a predetermined manner; means (240; 220; 200; 210) for determining a difference corresponding to said changed concentration of NOx gas of a first concentration of NOx gas upstream of said catalyst (260); means (270; 220; 200; 210) for determining a difference corresponding to said changed concentration of NOx gas of a second concentration of NOx gas downstream of said catalyst (260), at least one of said determinations taking place based on measurement ; and - means (220; 200; 210) for determining a state of said at least one NOx sensor (240; 270), which is used to measure the concentration of NOx gas, on the basis of said difference of the first concentration of NOx gas and said difference of the second concentration of NOx gas. The apparatus of claim 9, further comprising: - means (220; 200; 210) for determining, before initiating said control of the operation of the engine (230), whether a desired flow condition exists in said exhaust system. The apparatus of claim 9 or 10, further comprising: - means (200; 210) for, before initiating said control of the operation of the motor (230), setting a value representing a desired degree of stoichiometry. Apparatus according to any one of claims 9 to 11, further comprising: - means (200; 210) for determining a first parameter (kt) associated with said difference of the first concentration of NOx gas; means (200; 210) for determining a first parameter (kg) associated with said difference of the second concentration of NOx gas; and means (200; 210) for determining whether said at least one NO 1 sensor (240; 270) has a Gain error based on the first two parameters (k1, kg). An apparatus according to any one of claims 9 to 12, further comprising: - means (200; 210) for determining a second parameter (m1) associated with said difference of the first concentration of NOX gas; means (200; 210) for determining a second parameter (m2) associated with said difference of the second concentration of NOx gas; and - means (200; 210) for determining whether the at least one NO, - sensor (240; 270) has an Off-set error on the basis of the two other parameters (m1, m2). The device of any of claims 9-13, further comprising: - means (200; 210; 220) for controlling injection of urea into the exhaust system based on the determined condition of said at least one sensor (240; 270). The apparatus of any of claims 9-14, further comprising: - means (200; 210) for controlling operation of the engine (230) in a manner that causes a concentration of NOx gas downstream of the engine (230) to be increased in a or several substantially discrete steps. The device of claim 15, wherein the increase of said steps is within a range of which they are fi. 3000] ppm. Device according to any one of claims 9-16, wherein the operation of the engine (230) is controlled by influencing an injection angle (a) of at least one cylinder of the engine (230). Motor vehicle (100; 110) comprising a device according to any one of claims 9-17. 10 15 535 748 32 A motor vehicle (100; 110) according to claim 18, wherein the motor vehicle is something of a truck, bus or passenger car. A computer program (P) for determining a state of a sensor of a motor vehicle, said computer program (P) comprising program code for causing an electronic control unit (200; 500) or another computer (210; 500) connected to the electronic the control unit (200; 500) to perform the steps according to any one of claims 1-8. A computer program product comprising a program code stored on a computer readable medium for performing the method steps of any of claims 1-8, when said computer program is run on an electronic control unit (200; 500) or another computer (210; 500) connected to the electronic control unit (200; 500).