Patent Publication Number: US-2011066316-A1

Title: Method and device for recognizing combustion in a particle filter

Description:
The present invention claims the priority of French application 0853563 filed on May 30, 2008 the content of which (text, drawings and claims) is incorporated here by reference. 
     The invention relates to the field of pollution control of internal combustion engines, and more specifically the control of particle filters installed in the exhaust line of the engines, in order to trap the particles emitted by the combustion in the engine. 
     During its operation, an internal combustion engine produces exhaust gas originating from the combustion of fuel and containing a certain number of regulated pollutants. The pollutants emitted by the combustion of an engine can contain solid carbonaceous particles. Failing to calibrate the engine so that it emits only the permissible quantity of regulated pollutants, the exhaust gas must undergo a treatment in order to reduce these pollutants to a level lower than the normalized thresholds. 
     The gas treatment device is in general situated in the exhaust circuit of the engine. This is called post-treatment of gas. This treatment device can consist of one or more elements and can comprise in particular a particle filter. 
     An automotive particle filter eliminates by filtration the solid particles present in the exhaust gas of engines, generally diesel engines. Once trapped inside the filter, the particles must be eliminated periodically by raising the temperature inside the filter from 450° C. to 700° C. in order to cause their combustion. This operation is usually called “regeneration” of the particle filter. Traditionally, the energy necessary for regeneration is supplied by controlled increase of the exhaust gas temperature. 
     Traditionally during the regeneration phases, the energy surplus at the exhaust necessary to raise the temperature relative to the normal operation of the engine is supplied by post injections, in other words delayed fuel injections, after the high dead point of the cycle, or by degradation of the combustion yield, or by direct fuel injection in the exhaust line. 
     In case of post injection, the injection can burn completely or partially in the engine, generating an increase of the exhaust gas temperature, or if the injection is sufficiently delayed, induce an increase of the quantity of CO and HC at the exhaust, which oxidize when they arrive at the oxidizing catalyst in order to generate heat. It is this last phenomenon which also plays a role if fuel is introduced directly in spray or vapor form in the exhaust line of the engine. 
     However, the carbonaceous particles trapped by the filter are combustible material, and their combustion can be self supporting beyond a temperature of approximately 450° C. if the filter employs an additive to facilitate regeneration, and 600° C. if not, and from the time that an oxidizer is available in sufficient quantity. 
     Since oxygen is always present in the exhaust gas of engines, the combustion of soot particles can start if the filter is significantly loaded with soot particles, leading to a significant release of energy in the filter, which can cause damage to the filter (for instance cracking) or its destruction. 
     Significant soot loading of the filter can be observed when the automotive vehicle equipped with the filter operates mainly in so-called urban driving, in other words at low speed and with frequent stops. In these conditions, it is extremely difficult to regenerate a particle filter, because the exhaust gas is far away from the regeneration temperature of the filter, or it reaches only a temperature high enough to trigger regeneration during a time interval which is too short to complete this regeneration. Typically, the exhaust gas temperature of an automotive diesel engine supercharged with a turbo compressor, and measured at the outlet of the turbine of the turbo compressor, is in the order of magnitude of 150° C., and minimum 450° C. is required to start regeneration of a filter with additives. 
     In other respects, if after extreme soot loading of the particle filter, the engine is subjected to prolonged operation under heavy load, the temperature of the exhaust gas can trigger spontaneous combustion of soot in the filter. In certain circumstances, the combustion of soot which started prior to the shut-down of the engine can continue after its shut down, and even initiate shortly after the shut-down, if the exhaust circuit is particularly hot and the filter is no longer cooled by the exhaust gas flow. 
     These uncontrolled combustions of soot can damage the filter, if they occur at high temperature or if they provoke a too rapid increase of the temperature in the filter. Such damage is detrimental for more than one reason. On the one hand, the efficiency of the post treatment system becomes questionable, and on the other hand, according to actual regulations and for on board diagnostics (“OBD” function), it is necessary to guarantee the efficiency of post treatment systems for the lifetime (typically 160,000 km according to EURO 5 standards) or to alert the driver of the vehicle in case of failure of the post treatment system. 
     Patent FR2814498 of Renault S. A. discloses means for diagnosing the failure of a particle filter or for calculating its loading by observing the energy released during regeneration of the filter. Although it is known how to control the regeneration of a particle filter through various strategies, prior technology does not know a method aimed at controlling the occurrence of this type of spontaneous combustion of particles in the filter, and the filter failures that they can generate. 
     Furthermore, the effect of this type of uncontrolled combustion of particles on the soot loading of the filter is actually not taken into account in the models for determining the loading. 
     The goal of the present invention is to propose a method for recognizing a combustion, and specifically an uncontrolled combustion, in a particle filter installed in the exhaust line of a combustion engine. This recognition and characterization of the detected combustion allow to diagnose a failure of the filter or to take into account the effect of this combustion on the soot loading of the filter, and this during the whole operational phase of the engine. The invention allows to control the filter during all its utilization phases, and not only during its commanded regenerations as known in prior technology. 
     To this end, the proposed method comprises a step of measuring or estimating the representative parameters of a combustion in the filter and a step of processing these parameters in order to diagnose the occurrence of a combustion and to determine the intensity of it, a method in which these steps are implemented during the whole operational phase of the engine and in particular outside the commanded regeneration phases of the filter, and in one variant, also during a predetermined time following the shut-down of the engine. 
     By preference, the considered representative parameters are respectively the temperature at the inlet of the particle filter and the temperature at the outlet of the particle filter. 
     The estimation or measurement of these parameters and their processing have therefore as originality of being performed also outside the phases of commanded regeneration of the filter. Furthermore, estimating, measuring and processing of the considered parameters are continued after engine shut down. 
     With this kind of method, the conclusion can be made that an uncontrolled combustion of particles occurred in the particle filter ( 6 ) if the temperature at the outlet of the filter ( 6 ) exceeds the temperature at the inlet of the filter by a predetermined margin for a predetermined time, while the engine control module does not command a regeneration. 
     In a variant, the temperature gradient in filter ( 6 ) is estimated based on the evolution of the temperatures at the inlet and outlet of the filter, and the conclusion is made that a combustion of particles occurred in particle filter ( 6 ) if the estimated temperature gradient is greater than a predetermined maximum. 
     When the occurrence of a combustion in the filter is detected, the quantity of soot burned during this combustion can also be evaluated based on the evolution of inlet and outlet temperatures of the filter during this combustion and based on the duration of this combustion. 
     The proposed method can serve as failure diagnostic of a particle filter installed in the exhaust line of a combustion engine. Indeed, failure of the particle filter is detected if the temperature downstream of the filter exceeds the temperature upstream of the filter by a predetermined value during a predetermined time. 
     The conclusion is also made that failure of the filter occurred if the observed temperature gradient exceeds a predetermined limit. 
     In the framework of a vehicle with internal combustion engine equipped with an exhaust line comprising a particle filter, and also equipped with “on board diagnostics” (OBD) module, the particle filter failure information can be entered in the module if a failure of the particle filter is detected. 
     Furthermore, if the vehicle contains an illuminated warning device for anomaly of the particle filter, for instance inside the cabin, the illuminated device is activated if a failure of the particle filter is detected in order to alert the user of the failure. 
     The invention relates also to a device for implementing the described method. This device comprises an internal combustion engine equipped with an exhaust line comprising a particle filter, means for commanding the regeneration of the filter, means for estimating the representative parameters of a combustion inside the particle filter, means for processing these parameters in order to diagnose the occurrence of a combustion and for estimating its intensity, and is characterized in that said means is periodically activated during the whole operational time of the engine, and not only during the controlled regenerations of the filter as is the case in prior technology. 
     By preference, the device is equipped with means for estimating or means for measuring the temperature at the inlet of the particle filter, and a temperature probe at the outlet of the filter. 
    
    
     
       The invention is described in more detail here after and with reference to the unique figure representing schematically a device for implementing the method according to a preferred implementation mode. 
         FIG. 1  represents schematically the assembly consisting of an internal combustion engine and its main air loop, in other words its intake and exhaust circuit, and means for post treatment of the exhaust gas, and the devices necessary for implementing the diagnostics strategy of the particle filter according to the preferred implementation mode of the invention. 
     
    
    
     A diesel engine  1  is supercharged by means of turbo compressor  2 . The admission of air in the engine takes place via inlet line  3 . The exhaust of gas after the combustion takes place via exhaust line  4 . 
     In the example shown here, the post treatment of exhaust gas involves an oxidizing catalyst  5  and a particle filter  6 . 
     The engine control module  7  (here shown as an assembly, but can consist of several elements or can be divided in multiple boards or electronic boxes) controls the various command strategies of the engine, the fuel injection strategy, and controls the post treatment means, and in particular monitors the filling of the particle filter. Processor  7  also integrates the command means suitable for commanding the periodic regeneration of particle filter  6 . The engine control module  7  comprises also an OBD function (On Board Diagnostics)  8  which catalogs and records the main operational failures or anomalies of the engine and its peripheral equipment, and can trigger, for instance, a warning in case of dysfunction, in the form of an illuminated device  9  warning the operator of the engine or the driver of the vehicle equipped with it. 
     In the preferred implementation mode shown here, a temperature probe  10  is located in the exhaust line  4  between the oxidizing catalyst  5  and the particle filter  6 , at the entrance of the particle filter  6 . A temperature probe  11  is located in the exhaust line  4  at the exit of the particle filter  6 . 
     Note that the temperature probe  10  at the entrance of the filter can be replaced easily by a digital model for estimating the temperature upstream of the particle filter, which is stored in the engine control module. This variant offers a certain cost advantage, at the price of a reduced accuracy, but nevertheless remains compatible with traditional automotive practice. 
     Temperature probe  10  at the entrance of filter  6  and temperature probe  11  at the exit of filter  6  communicate with engine control module  7 , for instance through the intermediary of bus  12  and  13 , the control module integrates moreover the proposed process. Overall, the developed process consists in comparing the temperature upstream and the temperature downstream of the particle filter  6 , as well as the evolution of these temperatures, during the operation of engine  1  and during a predetermined time, for instance of one minute, after engine shut down. Therefore, the temperatures are not only compared during the regenerations of filter  6  triggered by the engine control module. 
     By monitoring these two temperatures and their evolution, the proposed diagnostics allows, on the one hand, recognition of spontaneous combustions in particle filter  6 , and on the other hand, diagnosis of the degradation of filter  6  due to too intense or too rapid release of energy. 
     Typically, if the temperature measured by the probe at the exit of the filter  11  exceeds the temperature of the probe at the entrance of filter  10  by a certain margin during a certain time, while the engine control module  7  does not command a regeneration (for instance by post injection of fuel), the strategy concludes that an uncontrolled combustion of soot is taking place in filter  6 . These temperature and time thresholds allow the discrimination between a combustion in filter  6  and a reduction of the load of engine  1 , which results in less hot exhaust gas, which in function of the thermal inertia of the filter can result temporarily in the temperature measured by probe  10  being below the temperature measured by probe  11 . It is easily understood that the temperature threshold and the time in question depend on the employed filter and engine and the operating points authorized by the engine control module. 
     In addition, the temperature gradient in the filter can be estimated by monitoring the temperatures at the entrance and the exit of filter  6 . A high temperature gradient is a good indicator of an uncontrolled combustion in filter  6 . 
     By detecting the uncontrolled combustion, and observing the temperatures upstream and downstream of the particle filter and their evolution during this spontaneous combustion, the estimated loading level in particle filter  6  can be corrected, taking into account the quantity of oxidized particles during the uncontrolled regeneration. 
     Besides, whether we are dealing with commanded or uncontrolled regeneration of the particle filter, by comparing temperatures upstream and downstream of filter  6  the conclusion can be made that filter degradation occurred. If the temperature measured by probe  11  exceeds the temperature of probe  10  by a certain value (potentially different from the threshold used for detection of an uncontrolled combustion) during a certain time (potentially different from the time used for the detection of a spontaneous combustion), the conclusion is then that a degradation of the filter took place. 
     Similarly, if the estimated temperature gradient in filter  6  is greater than a predetermined maximum, the conclusion is that a degradation of the filter took place. 
     If the strategy concludes that a degradation of the filter took place, the OBD module  8  of engine control module  7  is then warned. In accordance with existing and future regulations, the information can be entered in a memory of engine control module  7  or of OBD module  8 , and an illuminated failure device  9  warns the driver of the encountered anomaly. 
     In the framework of an automotive application and in conformance with actual and future regulations, which impose for instance monitoring of the effectiveness of the filtration of the filter over 160,000 km in the framework of European standard EURO 5, it becomes possible to alert the user that a critical regeneration of the particle filter, either controlled or uncontrolled and eventually spontaneously triggered by vehicle driving conditions, was detected and that its performance could be degraded.