GB2536951A

GB2536951A - Method and system of diagnosing efficiency of an aftertreatment system of an internal combustion engine

Info

Publication number: GB2536951A
Application number: GB1505713.6A
Authority: GB
Inventors: Cassani Stefano; Pio Sacco Nicola
Original assignee: GM Global Technology Operations LLC
Current assignee: GM Global Technology Operations LLC
Priority date: 2015-04-01
Filing date: 2015-04-01
Publication date: 2016-10-05
Anticipated expiration: 2035-04-01
Also published as: GB201505713D0; GB2536951B

Abstract

A method of diagnosing efficiency of an aftertreatment system 270 of an internal combustion engine 110, wherein the aftertreatment system comprises an exhaust duct 275, an oxidation catalyst 280 (e.g. a diesel oxidation catalyst - DOC) disposed in the exhaust duct, and a particulate filter 285 (e.g. a diesel particulate filter - DPF) disposed in the exhaust duct downstream of the oxidation catalyst. The method comprises the steps of: executing post injections of fuel into the engine to perform a regeneration process of the particulate filter; determining a value of an exhaust gas temperature in the exhaust duct between the oxidation catalyst and the particulate filter; adjusting a quantity of post injected fuel by means of a controller that receives as input a difference between the determined value of the exhaust gas temperature and a target value thereof; identifying a malfunctioning of the oxidation catalyst if, during the regeneration process, the value of exhaust gas temperature is below a predetermined threshold value, and contemporaneously a value of a parameter indicative of the post injected fuel quantity is above a predetermined threshold value.

Description

METHOD AND SYSTEM OF DIAGNOSING EFFICIENCY OF AN AFTERTREATMENT SYSTEM OF AN INTERNAL COMBUSTION ENGINE

TECHNICAL FIELD

The present disclosure relates to a method and a system for diagnosing efficiency of an aftertreatment system of an internal combustion engine, such as a Diesel engine of a motor vehicle.

BACKGROUND

It is known that an internal combustion engine of a motor vehicle is equipped with an aftertreatment system designed to change the composition of the exhaust gas in order to reduce the pollutant emissions.

Some aftertreatment systems may comprise a catalytic converter, for example a Diesel oxidation catalyst (DOC), followed by a particulate filter, for example a Diesel particulate filter (DPF).

A Diesel oxidation catalyst usually comprises a catalyst substrate (core), for example a ceramic monolith with a honeycomb structure, which supports a washcoat that carries catalytic materials, usually a mixture of precious metals, suitable for prompting the oxida-tion of unburned hydrocarbons (HC) and carbon monoxides (CO) into carbon dioxides (CO2) and water (H20).

A Diesel particulate filter is a device that comprises a ceramic body similar to the core of an oxidation catalyst but specifically designed to trap diesel particulate matter or soot contained in the exhaust gas.

Some diesel particulate filters may also comprise a washcoat containing a small quantity of precious metals, whose concentration is much lower than the concentration of precious metals in the oxidation catalyst (e.g. 10%) but still enough to promote oxidation re-actions at high temperatures.

When the accumulated particulate matter exceeds a predetermined threshold value, the diesel particulate filters are subjected to a regeneration process that empties the filter and restores its original efficiency.

This regeneration process is usually performed by increasing the temperature of the particulate filter up to a temperature (e.g. 630°C) that causes the accumulated particulate matter to burn off.

One of the most widely used strategies to increase the filter temperature is that of operating the fuel injectors of the internal combustion engine to execute so-called post injec10 tions.

The post injections are small quantities of fuel that are injected into the combustion chambers of the engine during the expansion stroke of the piston, when the exhaust valves are already open.

These small quantities of fuel exit unburnt from the combustion chamber and reach the 15 Diesel oxidation catalyst, where they are ignited and generate a stream of hot exhaust gas that flows towards the Diesel particulate filter located downstream, thereby increasing its temperature.

However, during the lifetime of the Diesel oxidation catalyst, the conversion efficiency of this component is not constant but decreases progressively due to ageing and/or poison-ing effects.

For this reason, it may happen that the conversion efficiency of the Diesel oxidation catalyst reaches a level which still allows this component to reduce the polluting emissions during the normal operation of the engine, but makes it unsuitable to efficiently oxidize the post injected fuel quantities during the regeneration process of the Diesel particulate filter.

As a consequence, these post injected fuel quantities may exit unburnt the Diesel oxidation catalyst and be ignited just inside the Diesel particulate filter, due to precious metals contained in its washcoat, thereby increasing the thermal stress of this component and of other neighbouring components of the motor vehicle, such as the vehicle underhood and underfloor.

In view of the above, an object of the present disclosure is that of identifying when an oxidation catalyst becomes unable to support the regeneration process of a particulate fil-ter, thereby allowing the adoption of countermeasures that can prevent the above mentioned side effects.

Another object is that of attaining this goal with a simple, rational and rather inexpensive solution.

These and other objects are achieved by the solution embodying the combination of features reported in the independent claim. The features reported in the dependent claims represents auxiliary aspect of the solution.

SUMMARY

An embodiment of the solution provides a method of diagnosing efficiency of an after-treatment system of an internal combustion engine, wherein the aftertreatment system comprises an exhaust duct, an oxidation catalyst disposed in the exhaust duct and a particulate filter disposed in the exhaust duct downstream of the oxidation catalyst, and wherein the method comprises the steps of: -executing post injections of fuel into the engine to perform a regeneration process of the particulate filter, -determining a value of an exhaust gas temperature in the exhaust duct between the oxidation catalyst and the particulate filter, -adjusting a quantity of post injected fuel by means of a controller that receives as input 20 a difference between the determined value of the exhaust gas temperature and a target value thereof, -identifying a malfunctioning of the oxidation catalyst, if during the regeneration process the value of exhaust gas temperature is below a predetermined threshold value thereof and contemporaneously a value of a parameter indicative of the post injected fuel quanti25 ty is above a predetermined threshold value thereof.

This method is based on the fact that, if the conversion efficiency of the oxidation catalyst is poor, during a regeneration process of the particulate filter, not all the post injected fuel quantities will burn inside such component, so that the temperature of the exhaust gas between the oxidation catalyst and the particulate filter will be lower than expected. At the same time, the controller will be striving to reach the target value of the exhaust gas temperature, thereby progressively increasing the post injected fuel quantity more than expected.

By looking at these two parameters, the proposed method represents a simple and reliable solution for identifying that the oxidation catalyst is unable to support the regeneration of the particulate filter.

According to an aspect of the solution, the determination of the value of the exhaust gas 5 temperature may be achieved through a measurement, for example by means of a temperature sensor disposed in the exhaust duct between the oxidation catalyst and the particulate filter.

In this way the determination of the temperature value becomes more reliable and the whole method more efficient.

According to another aspect of the solution, the parameter indicative of the post injected fuel quantity may be an overall output of the controller.

In this way the parameter represents a reliable indication of how much the controller is actually contributing to the post injected fuel quantity and thus of the actual behaviour of the oxidation catalyst.

An alternative aspect of the solution may provide that the parameter indicative of the post injected fuel quantity is a partial contribution to an overall output of the controller.

This solution allows to take into account specific and relevant aspects of the controller action and of the oxidation catalyst response.

By way of example, the partial contribution may be an integral contribution to the overall output of the controller.

The integral contribution is generally proportional to both the magnitude of the error received as input (i.e. the difference between the actual temperature value and the target value thereof) and the duration of the error.

In other words, the integral contribution of the controller is the sum of the instantaneous 25 error over time and gives the accumulated offset that should have been corrected previously.

As a consequence, it provides a reliable indication of how the oxidation catalyst has responded to the control actions.

According to an aspect of the solution, the threshold value of the exhaust gas tempera-30 ture may depend on engine speed and engine torque.

In this way the threshold value of the exhaust gas temperature can change allowing the diagnostic method to be efficiently performed also under transient operating conditions of the engine.

According to another aspect of the solution, the threshold value of the parameter indicative of the post injected fuel quantity may depend on engine speed and engine torque.

In this way the threshold value of the parameter can change allowing the diagnostic method to be efficiently performed also under transient operating conditions of the engine.

Another aspect of the solution may provide that the malfunctioning of the oxidation catalyst is identified (only) if the value of exhaust gas temperature is below the threshold value thereof and contemporaneously the value of a parameter is above the threshold value thereof for longer than a predetermined time period during the regeneration process. This aspect of the solution may reduce the probability of false identifications, thereby improving the reliability of the diagnostic method.

According to another aspect of the solution, the method may also comprise the step of inhibiting the regeneration process if the malfunctioning is identified.

This aspect makes it possible to prevent an excessive thermal stress of the particulate filter.

Another aspect of the solution may provide that the method comprises the step of limiting engine torque if the malfunctioning is identified.

Also this aspect has the effect of preventing an excessive thermal stress of the particu-late filter.

According to a further aspect of the solution, the method may comprise the step of generating a signal perceivable by a driver if the malfunctioning is identified.

In this way the driver may be informed of the malfunctioning of the oxidation catalyst and that a service intervention is needed.

The proposed solution may be carried out with the help of a computer program comprising a program-code for carrying out all the steps of the method described above, and in the form of a computer program product comprising the computer program. The method can be also embodied as an electromagnetic signal, said signal being modulated to carry a sequence of data bits which represent a computer program to carry out all steps of the method.

The present solution may be alternatively embodied as a system for diagnosing efficiency of an aftertreatment system of an internal combustion engine, wherein the aftertreat-ment system comprises an exhaust duct, an oxidation catalyst disposed in the exhaust dud and a particulate filter disposed in the exhaust duct downstream of the oxidation catalyst, and wherein the system comprises an electronic control unit configured to: -execute post injections of fuel into the engine to perform a regeneration process of the particulate filter, -determine a value of an exhaust gas temperature in the exhaust duct between the oxidation catalyst and the particulate filter, - adjust a quantity of post injected fuel by means of a controller that receives as input a difference between the determined value of the exhaust gas temperature and a target value thereof, - identify a malfunctioning of the oxidation catalyst, if during the regeneration process the value of exhaust gas temperature is below a predetermined threshold value thereof and contemporaneously a value of a parameter indicative of the post injected fuel quantity is above a predetermined threshold value thereof.

This embodiment achieves basically the same effects of the method described above, particularly that of providing a simple and reliable solution for detecting that the oxidation catalyst is unable to support the regeneration of the particulate filter.

According to an aspect of the solution, the electronic control unit may be configured to determinate the value of the exhaust gas temperature through a measurement, for ex-20 ample by means of a temperature sensor disposed In the exhaust duct between the oxidation catalyst and the particulate filter.

According to another aspect of the solution, the parameter indicative of the post injected 25 fuel quantity may be an overall output of the controller.

In other words, the integral contribution of the controller is the sum of the instantaneous error over time and gives the accumulated offset that should have been corrected previously.

As a consequence, it provides a reliable indication of how the oxidation catalyst has re-sponded to the control actions.

According to an aspect of the solution, the electronic control unit may be configured to determine the threshold value of the exhaust gas temperature on the basis of engine speed and engine torque.

In this way the threshold value of the exhaust gas temperature can change allowing the 15 diagnostic method to be efficiently performed also under transient operating conditions of the engine.

According to another aspect of the solution, the electronic control unit may be configured to determine the threshold value of the parameter indicative of the post injected fuel quantity on the basis of engine speed and engine torque.

Another aspect of the solution may provide that the electronic control unit is configured to identify the malfunctioning of the oxidation catalyst (only) if the value of exhaust gas temperature is below the threshold value thereof and contemporaneously the value of a parameter is above the threshold value thereof for longer than a predetermined time period during the regeneration process This aspect of the solution may reduce the probability of false identifications, thereby improving the reliability of the diagnostic method.

According to another aspect of the solution, the electronic control unit may be configured to inhibit the regeneration process if the malfunctioning is identified.

Another aspect of the solution may provide that the electronic control unit is configured to limit engine torque if the malfunctioning is identified.

According to a further aspect of the solution, the electronic control unit may be configured to generate a signal perceivable by a driver if the malfunctioning is identified. In this way the driver may be informed of the malfunctioning of the oxidation catalyst and that a service intervention is needed.

Another embodiment of the invention provides an automotive system comprising an internal combustion engine and an aftertreatment system, wherein the aftertreatment system comprises an exhaust duct, an oxidation catalyst disposed in the exhaust duct and a particulate filter disposed in the exhaust duct downstream of the oxidation catalyst, and wherein the automotive system further comprises: -first means for executing post injections of fuel into the engine to perform a regeneration process of the particulate filter, - second means for determining a value of an exhaust gas temperature in the exhaust duct between the oxidation catalyst and the particulate filter, - third means for adjusting a quantity of post injected fuel by means of a controller that 20 receives as input a difference between the determined value of the exhaust gas temperature and a target value thereof, - fourth means for identifying a malfunctioning of the oxidation catalyst, if during the regeneration process the value of exhaust gas temperature is below a predetermined threshold value thereof and contemporaneously a value of a parameter indicative of the 25 post injected fuel quantity is above a predetermined threshold value thereof.

According to an aspect of the solution, the second means may be configured to deter-30 mine the value of the exhaust gas temperature through a measurement, for example the second means may comprise a temperature sensor disposed in the exhaust duct between the oxidation catalyst and the particulate filter.

The integral contribution is generally proportional to both the magnitude of the error re-15 ceived as input (i.e. the difference between the actual temperature value and the target value thereof) and the duration of the error.

According to an aspect of the solution, the automotive system may comprise means for determining the threshold value of the exhaust gas temperature on the basis of engine speed and engine torque.

According to another aspect of the solution, the automotive system may comprise means for determining the threshold value of the parameter indicative of the post injected fuel 30 quantity on the basis of engine speed and engine torque.

In this way the threshold value of the parameter can change allowing the diagnostic method to be efficiently performed also under transient operating conditions of the en-gine.

Another aspect of the solution may provide that the fourth means are configured to identify the malfunctioning of the oxidation catalyst (only) if the value of exhaust gas temperature is below the threshold value thereof and contemporaneously the value of a parame-ter is above the threshold value thereof for longer than a predetermined time period during the regeneration process.

This aspect of the solution may reduce the probability of false identifications, thereby improving the reliability of the diagnostic method.

According to another aspect of the solution, the automotive system may comprise means for inhibiting the regeneration process if the malfunctioning is identified.

This aspect makes it possible to prevent an excessive thermal stress of the particulate fitter.

Another aspect of the solution may provide that the automotive system comprises means for limiting engine torque if the malfunctioning is identified.

Also this aspect has the effect of preventing an excessive thermal stress of the particulate filter.

According to a further aspect of the solution, the automotive system may comprise means for generating a signal perceivable by a driver if the malfunctioning is identified.

In this way the driver may be informed of the malfunctioning of the oxidation catalyst and 20 that a service intervention is needed.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, with reference to the accompanying drawings.

Figure 1 is a schematic representation of an automotive system according to an embodiment of the present solution.

Figure 2 is the section A-A of the internal combustion engine belonging to the automotive system of figure 1.

Figure 3 is a flowchart representing a strategy of controlling a post injected fuel quantity during a regeneration process of a particulate filter.

Figure 4 is a flowchart representing a strategy of diagnosing a malfunctioning of an oxidation catalyst.

DETAILED DESCRIPTION

Some embodiments may include an automotive system 100 (e.g. a motor vehicle), as shown in Figures 1 and 2, that includes an internal combustion engine (ICE) 110 having an engine block 120 defining at least one cylinder 125 having a piston 140 coupled to ro-tate a crankshaft 145. A cylinder head 130 cooperates with the piston 140 to define a combustion chamber 150. A fuel and air mixture (not shown) is disposed in the combustion chamber 150 and ignited, resulting in hot expanding exhaust gasses causing reciprocal movement of the piston 140. The fuel is provided by at least one fuel injector 160 and the air through at least one intake port 210. The fuel is provided at high pressure to the fuel injector 160 from a fuel rail 170 in fluid communication with a high pressure fuel pump 180 that increase the pressure of the fuel received from a fuel source 190. Each of the cylinders 125 has at least two valves 215, actuated by a camshaft 135 rotating in time with the crankshaft 145. The valves 215 selectively allow air into the combustion chamber 150 from the port 210 and alternately allow exhaust gases to exit through a port 220. In some examples, a cam phaser 155 may selectively vary the timing between the camshaft 135 and the crankshaft 145.

The air may be distributed to the air intake port(s) 210 through an intake manifold 200. An air intake duct 205 may provide air from the ambient environment to the intake manifold 200. In other embodiments, a throttle body 330 may be provided to regulate the flow of air into the manifold 200. In still other embodiments, a forced air system such as a turbocharger 230, having a compressor 240 rotationally coupled to a turbine 250, may be provided. Rotation of the compressor 240 increases the pressure and temperature of the air in the duct 205 and manifold 200. An intercooler 260 disposed in the duct 205 may reduce the temperature of the air. The turbine 250 rotates by receiving exhaust gases from an exhaust manifold 225 that directs exhaust gases from the exhaust ports 220 and through a series of vanes prior to expansion through the turbine 250. This example shows a variable geometry turbine (VGT) with a VGT actuator 290 arranged to move the vanes to alter the flow of the exhaust gases through the turbine 250. In other embodiments, the turbocharger 230 may be fixed geometry and/or include a waste gate.

The exhaust gases exit the turbine 250 and are directed into an aftertreatment system 270. The aftertreatment system 270 may include an exhaust duct 275 having one or more exhaust aftertreatment devices. The aftertreatment devices may be any device configured to change the composition of the exhaust gases. In the present example, the aftertreatment devices include a Diesel oxidation catalyst (DOC) 280 and a Diesel particulate filter (DPF) 285 located in the exhaust duct 275 downstream of the DOC 280.

Some embodiments may also include an exhaust gas recirculation (EGR) system 300 coupled between the exhaust manifold 225 and the intake manifold 200. The EGR system 300 may include an EGR cooler 310 to reduce the temperature of the exhaust gases in the EGR system 300. An EGR valve 320 regulates a flow of exhaust gases in the EGR system 300.

The automotive system 100 may further include an electronic control unit (ECU) 450 in communication with one or more sensors and/or devices associated with the ICE 110. The ECU 450 may receive input signals from various sensors configured to generate the signals in proportion to various physical parameters associated with the ICE 110. The sensors include, but are not limited to, a mass airflow and temperature sensor 340, a manifold pressure and temperature sensor 350, a combustion pressure sensor 360, coolant and oil temperature and level sensors 380, a fuel rail pressure sensor 400, a cam position sensor 410, a crank position sensor 420, a temperature sensors 430 located in the exhaust duct 275 between the DOC 280 and the DPF 285, an EGR temperature sensor 440, and an accelerator pedal position sensor 445. Furthermore, the ECU 450 may generate output signals to various control devices that are arranged to control the operation of the ICE 110, including, but not limited to, the fuel injectors 160, the throttle body 330, the EGR Valve 320, the VGT actuator 290, and the cam phaser 155. Note, dashed lines are used to indicate communication between the ECU 450 and the various sensors and devices, but some are omitted for clarity.

Turning now to the ECU 450, this apparatus may include a digital central processing unit (CPU) in communication with a memory system and an interface bus. The CPU is configured to execute instructions stored as a program in the memory system 460, and send and receive signals to/from the interface bus. The memory system 460 may include various storage types including optical storage, magnetic storage, solid state storage, and other non-volatile memory. The interface bus may be configured to send, receive, and modulate analog and/or digital signals to/from the various sensors and control devices. The program may embody the methods disclosed herein, allowing the CPU to carryout out the steps of such methods and control the ICE 110.

The program stored in the memory system 460 is transmitted from outside via a cable or in a wireless fashion. Outside the automotive system 100 it is normally visible as a computer program product, which is also called computer readable medium or machine readable medium in the art, and which should be understood to be a computer program code residing on a carrier, said carrier being transitory or non-transitory in nature with the consequence that the computer program product can be regarded to be transitory or non-transitory in nature.

An example of a transitory computer program product is a signal, e.g. an electromagnetic signal such as an optical signal, which is a transitory carrier for the computer program code. Carrying such computer program code can be achieved by modulating the signal by a conventional modulation technique such as QPSK for digital data, such that binary data representing said computer program code is impressed on the transitory electromagnetic signal. Such signals are e.g. made use of when transmitting computer program code in a wireless fashion via a WiFi connection to a laptop.

In case of a non-transitory computer program product the computer program code is embodied in a tangible storage medium. The storage medium is then the non-transitory carrier mentioned above, such that the computer program code is permanently or non-permanently stored in a retrievable way in or on this storage medium. The storage medium can be of conventional type known in computer technology such as a flash memory, an Asic, a CD or the like.

Instead of an ECU 450, the automotive system 100 may have a different type of processor to provide the electronic logic, e.g. an embedded controller, an onboard computer, or any processing module that might be deployed in the vehicle.

One of the tasks of the ECU 450 may be that of performing a regeneration process of the 25 DPF 285, when the amount of particulate matter accumulated therein exceeds a predetermined threshold value.

The regeneration process generally provides for the ECU 450 to increase the temperature of the DPF 450 up to a temperature (e.g. 630°C) that causes the accumulated particulate matter to bum off.

To achieve this temperature increase, the ECU 450 may be configured to command the fuel injectors 160 to operate so-called post injections, namely to inject small quantities of fuel into the combustion chambers 150 during the exhaust stroke of piston 140, when the exhaust ports 220 are already open.

In this way the post injected fuel quantities exit unburnt the combustion chambers 150 and reaches the DOC 280, where they are ignited and generate a stream of hot exhaust gas that is able to increase the temperature of the DPF 285 located downstream.

During the regeneration process, the quantity of fuel that is injected by means of the post injections may be adjusted using a feedback control strategy, an example of which is shown in figure 3.

This control strategy provides for the ECU 450 to determine an actual value T of the exhaust gas temperature in the exhaust gas dud 275 between the DOC 280 and the DPF 285 (block S100). For example, the actual value T may be measured by means of the temperature sensor 430. The value T is 'fed back" and used to calculate an error E, namely a difference between the value T and a target value Ttar of the exhaust gas temperature between the DOC 280 and the DPF 285 (block S105). The target value Tzar represents the temperature value above which the accumulated particulate matter burns off.

By way of example, the target value Ttar may be considered in a neighbourhood of 630°C. The error E is supplied as input to a controller (block S110) that yields as output an overall value A of a correction to be applied to the post injected fuel quantity, in order to minimize the error E. The overall value A of the controllers output may be the sum of more than one contribu-tion depending on the kind of controller involved.

For example, the controller S110 may be a Proportional-Integral-Derivative (PID) controller, whose overall output A is the sum of three partial contributions according to the following formula: A =P+I+D =K pE(t) 4-K E(t) dt K d-E (t) dt where P is a proportional contribution, I is an integral contribution, D is a derivative con-tribution, Kp is a proportional gain, K is an integral gain, Ku is a derivative gain and E is the error received as input.

In other embodiments, the controller S110 may be a Proportional-Integral (PI) controller or even a simple Proportional (P) controller and its mathematical formula may change 30 accordingly.

Irrespectively of that, the efficiency of the regeneration process of the DPF 285 depends on the conversion efficiency of the DOC 280, namely on the capability of the precious metals contained in the washcoat of the DOC 280 to prompt the ignition of the post injected fuel quantities.

For this reason, the ECU 450 may be further configured to execute a diagnostic strategy 5 aimed to identify whether the conversion efficiency of DOC 280 is high enough to support a regeneration process of the DPF 285.

This diagnostic strategy may be based on the fad that, if the conversion efficiency of the oxidation catalyst is poor, during a regeneration process of the particulate filter, not all the post injected fuel quantities will burn inside such component, so that the temperature of the exhaust gas between the oxidation catalyst and the particulate filter will be lower than expected. At the same time, the controller S110 will be striving to reach the target value Tsar of the exhaust gas temperature, thereby progressively increasing the post injected fuel quantity more than expected.

Based on this considerations, this diagnostic strategy provides that the ECU 450 oper15 ates the ICE 110 to perform a regeneration process of the DPF 285 according to the procedure that has been explained above (block S200).

While the regeneration process is underway, the diagnostic strategy provides for the ECU 450 to determine the value T of the exhaust gas temperature between the DOC 280 and the DPF 285 (block S205), and to determine a value Q of a parameter indicative of the post injected fuel quantity (block S210).

In particular, the temperature value T may be measured by means of the temperature sensor 430 as explained above, whereas the parameter indicative of the post injected fuel quantity may be the overall output of the controller S110, so that the value Q may coincide with the aforementioned overall value A. In other embodiments, the parameter indicative of the fuel injected quantity may be one of the partial contributions to the overall output of the controller S110, for example the integral contribution, so that the value Q may coincide with the aforementioned contributing value I. The value T of the exhaust gas temperature is compared to a threshold value Tin thereof 30 (block S215). The threshold value Tth may represent the temperature value above which the accumulated particulate matter burns off and thus may coincide with the target value Ttar involved in the closed-loop control strategy of the post injections. To a certain extent the threshold value Tth may be dependent on the engine operating conditions, namely on the engine speed and on the engine torque. For this reason, the ECU 450 may be configured to determine the current values of the engine speed and of the engine torque and to use them to determine a corresponding threshold value Tth of the exhaust gas temper-ature. By way of example, the threshold value Tth may be retrieved from a calibration map stored in the memory system 460.

At the same time, the value Q of the parameter is compared with a threshold value Qth thereof (block S220). The threshold value Qth may be indicative of the fact that the post injected fuel quantity, in particular the contribution provided by the controller S110, is too high. Also this threshold value Qth may be dependent on the engine operating conditions, namely on the engine speed and on the engine torque. For this reason, the ECU 450 may be configured to determine the current values of the engine speed and of the engine torque and to use them to determine a corresponding threshold value Qth of the parameter. By way of example, the threshold value Qth may be retrieved from a calibration map stored in the memory system 460.

If the value T of the exhaust gas temperature is smaller than the threshold value Tth and contemporaneously the value Q of the parameter is bigger than the threshold value QM (block S225), an anomalous condition is met that leads the ECU 450 to identify that a malfunctioning of the DOC 280 is occurred (block S230).

In particular, the malfunctioning of the DOC 280 may be identified provided that (i.e. only if) the aforesaid anomalous condition is met for longer than a predetermined time period, thereby reducing the possibilities of false identifications. This predetermined time period may be a calibration parameter and may be few seconds long.

Once a malfunctioning of the DOC 280 has been identified, the ECU 450 may be config- ured to perform one or more recovery actions (block S235). These recovery actions may include, but are not necessarily limited to, the inhibition of the regeneration process, the limitation of the engine torque and the generation of a signal perceivable by a driver, for example through the activation of a signaller (e.g. a light) disposed in a dashboard of the automotive system 100. Thanks to this last action, the driver may be informed of the mal-functioning of the DOC 280 and suggested to take some countermeasures, for example to go to the nearest car service center.

While at least one exemplary embodiment has been presented in the foregoing summary and detailed description, it should be appreciated that a vast number of variations exist. It should also be appreciated that the exemplary embodiment or exemplary embodiments are only examples, and are not intended to limit the scope, applicability, or configuration in any way. Rather, the foregoing summary and detailed description will provide those skilled in the art with a convenient road map for implementing at least one exemplary embodiment, it being understood that various changes may be made in the function and arrangement of elements described in an exemplary embodiment without departing from the scope as set forth in the appended claims and their legal equivalents.

REFERENCES

automotive system internal combustion engine engine block cylinder 130 cylinder head camshaft piston crankshaft combustion chamber 155 cam phaser fuel injector fuel rail fuel pump fuel source 200 intake manifold 205 air intake duct 210 intake port 215 valves 220 exhaust port 225 exhaust manifold 230 turbocharger 240 compressor 250 turbine 260 intercooler 270 aftertreatment system 275 exhaust dud 280 Diesel oxidation catalyst 285 Diesel particulate filter 290 VGT actuator 300 exhaust gas recirculation system 310 EGR cooler 320 EGR valve 330 throttle body 340 mass airflow and temperature sensor 350 manifold pressure and temperature sensor 360 combustion pressure sensor 380 coolant and oil temperature and level sensors 400 fuel rail pressure sensor 410 cam position sensor 420 crank position sensor 430 exhaust temperature sensor 440 EGR temperature sensor 445 accelerator pedal position sensor 450 ECU 460 memory system 5100 block S105 block S110 block S200 block S205 block S210 block S215 block S220 block S225 block S230 block S235 block

Claims

CLAIMS1. A method of diagnosing efficiency of an aftertreatment system (270) of an internal combustion engine (110), wherein the aftertreatment system comprises an exhaust duct (275), an oxidation catalyst (280) disposed in the exhaust duct and a particulate filter (285) disposed in the exhaust duct downstream of the oxidation catalyst, and wherein the method comprises the steps of: -executing post injections of fuel into the engine (110) to perform a regeneration process of the particulate filter (285), - determining a value of an exhaust gas temperature in the exhaust duct (275) between the oxidation catalyst (280) and the particulate filter (285), -adjusting a quantity of post injected fuel by means of a controller that receives as input 15 a difference between the determined value of the exhaust gas temperature and a target value thereof, - identifying a malfunctioning of the oxidation catalyst (280), if during the regeneration process the value of exhaust gas temperature is below a predetermined threshold value thereof and contemporaneously a value of a parameter indicative of the post injected fuel 20 quantity is above a predetermined threshold value thereof.
2. A method according to claim 1, wherein the determination of the value of the exhaust gas temperature is achieved through a measurement.
3. A method according to claim 1 or 2, wherein the parameter indicative of the post injected fuel quantity is an overall output of the controller.
4. A method according to claim 1 or 2, wherein the parameter indicative of the post injected fuel quantity is a partial contribution to an overall output of the controller.
5. A method according to claim 4, wherein the partial contribution is an integral contri-bution to the overall output of the controller.
6. A method according to any of the preceding claims, wherein the threshold value of the exhaust gas temperature is determined on the basis of engine speed and engine torque.
7. A method according to any of the preceding claims, wherein the threshold value of the parameter indicative of the post injected fuel quantity is determined on the basis of engine speed and engine torque.
8. A method according to any of the preceding claims, wherein the malfunctioning of the oxidation catalyst (280) is identified if the value of exhaust gas temperature is below the threshold value thereof and contemporaneously the value of a parameter is above the threshold value thereof for longer than a predetermined time period during the regeneration process.
9. A method according to any of the preceding claims, comprising the step of inhibit-ing the regeneration process if the malfunctioning is identified.
10. A method according to any of the preceding claims, comprising the step of limiting engine torque if the malfunctioning is identified.
11. A method according to any of the preceding claims, comprising the step of generating a signal perceivable by a driver if the malfunctioning is identified.
12. A system for diagnosing efficiency of an aftertreatment system (270) of an internal combustion engine (110), wherein the aftertreatment system comprises an exhaust duct (275), an oxidation catalyst (280) disposed in the exhaust duct and a particulate filter (285) disposed in the exhaust duct downstream of the oxidation catalyst, and wherein the system comprises an electronic control unit (450) configured to: - execute post injections of fuel into the engine to perform a regeneration process of the particulate filter (285), -determine a value of an exhaust gas temperature in the exhaust duct (275) between the oxidation catalyst (280) and the particulate filter (285), - adjust a quantity of post injected fuel by means of a controller that receives as input a difference between the determined value of the exhaust gas temperature and a target 25 value thereof, -identify a malfunctioning of the oxidation catalyst (280), if during the regeneration process the value of exhaust gas temperature is below a predetermined threshold value thereof and contemporaneously a value of a parameter indicative of the post injected fuel quantity is above a predetermined threshold value thereof.