Abstract:
A method and device for detecting presence of an exhaust gas treatment system in an exhaust line of an internal combustion engine. The method determines the derivative of the temperature upstream of the treatment system, determines the derivative of the temperature downstream of the treatment system, and compares the downstream temperature derivative with a threshold value for detecting absence of the treatment system using a pre-determined upstream temperature derivative level.

Description:
BACKGROUND 
     The present invention relates to the field of the treatment of the exhaust gases of a motor vehicle internal combustion engine, and more particularly, a method and a device for detecting the presence of an exhaust gas treatment system in an exhaust line of a motor vehicle. 
     The invention applies to all types of treatment systems: particulate filter type, nitrogen oxide trap, catalytic or oxidizing converter, etc. 
     Some current regulations require that on-board diagnostic systems, which check that exhaust gas treatment devices are operating correctly, be responsible moreover for detecting the presence of such a system. 
     Various types of technique are currently used to detect the presence or the absence of an exhaust gas treatment system in an exhaust line. 
     Thus, detecting the presence of a particulate filter in an exhaust line of an internal combustion engine using a determination of the differential pressure at the boundaries of the filter is known, the absence of the particulate filter being shown by a change in behavior of the differential pressure. 
     However, this technique requires working at high volume flow rates. Moreover, the signals supplied are not very reliable, because the differential pressure is usually worked out from very noisy measurements. 
     Detecting the presence of a nitrogen oxide trap is also known using signals supplied by an exhaust gas mixture sensor placed downstream of the filter, such as a binary mixture sensor, or a proportional mixture sensor, the mixture composition detected making it possible to determine the absence or the presence of the nitrogen oxide trap in the exhaust line. 
     This technique also has a certain number of disadvantages relating in particular to the fact that the signals supplied by the sensor are not very reliable, because the aging of the sensor causes a shift in the measurements provided, and relating to the cost of the sensor. Moreover, the mixture composition measured by the sensor must be processed in relation to the mixture composition of the exhaust gases upstream of the nitrogen oxide trap. Now, with regard to diesel engines, it is difficult to check the mixture composition of the exhaust gases upstream of the nitrogen oxide trap, so that this technique is relatively difficult to employ reliably. 
     BRIEF SUMMARY 
     In view of the above, the object of the invention is to overcome the disadvantages of the prior art and enable the detection of the presence of an exhaust gas treatment system in an exhaust line of a motor vehicle internal combustion engine, reliably, simply and inexpensively. 
     The subject of the invention is therefore, according to a first aspect, a method for detecting the presence of an exhaust gas treatment system in an exhaust line of a motor vehicle internal combustion engine, comprising the following stages:
         determination of the derivative of the temperature upstream of the treatment system;   determination of the derivative of the temperature downstream of the treatment system; and   comparison of the derivative of the temperature downstream of the treatment system with a threshold value for detecting the absence of the treatment system, using a preset level of the derivative of the temperature upstream of the treatment system.       

     According to one embodiment, a counter is incremented each time the threshold value is exceeded and it is concluded that the treatment system is absent when the count level of the counter exceeds a second preset threshold value. 
     Advantageously, the derivative of the temperature downstream of the system is also compared with the threshold value when the derivative of the temperature upstream of the system exceeds a third threshold value. 
     According to another feature of the invention, the upstream and downstream temperature variations are divided into classes of preset values of temperature variations and a detection of the absence of the treatment system is carried out on a set of preset temperature variation value classes. 
     In that case, advantageously, each class of values being associated with a probability of occurrence of a corresponding temperature variation, said detection is carried out for classes of values higher than a class of values above which the probability of obtaining a corresponding temperature variation for an exhaust line provided with a designated treatment system is zero, and lower than a class of values above which the probability of obtaining an increase in temperature variations is zero. 
     It is then concluded that the treatment system is absent when the probability of obtaining a temperature variation downstream of the treatment system higher than a preset threshold value is lower than a probability of obtaining said variation for an exhaust line not provided with a treatment system, and higher than a minimum probability. 
     According to another aspect, the subject of the invention is a device for detecting the presence of an exhaust gas treatment system in an exhaust line of an internal combustion engine, comprising determination means for calculating the derivative of the temperature upstream and downstream of the system and a central processing unit comprising comparison means for comparing the calculated value of the derivative of the temperature downstream of the treatment system with a threshold value for detecting the absence of the treatment system. 
     According to another feature of this treatment system, it includes moreover a counter controlled by the output of the comparison means and which is incremented each time the threshold value is exceeded, and second comparison means for comparing the count level with a second threshold value above which it is concluded that the treatment system is absent. 
     According to a particular embodiment, the detection device includes moreover third comparison means for comparing the calculated value of the derivative of the temperature upstream of the treatment system with a third threshold value, the derivative of the temperature downstream of the treatment system being compared with the first threshold value when the derivative of the temperature upstream of the treatment system exceeds the third threshold value. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Other aims, features and advantages of the invention, given only as non-limiting examples, will emerge on reading the following description written with reference to the attached drawings, in which: 
         FIG. 1  is a schematic drawing of an internal combustion engine fitted with an exhaust line provided with a device for detecting the presence of an exhaust gas treatment system according to the invention; 
         FIG. 2  is a schematic drawing illustrating the general layout of a device for detecting the presence of an exhaust gas treatment system; 
         FIG. 3  shows curves illustrating the derivative of thermal signals upstream and downstream of an exhaust gas treatment system; 
         FIG. 4  shows curves illustrating the variation of probability of obtaining rates of temperature increase for various exhaust line configurations; and 
         FIG. 5  shows curves illustrating the variation of probability of obtaining rates of temperature increase upstream and downstream of an exhaust gas treatment system, illustrating the principle on which the invention is based. 
     
    
    
     DETAILED DESCRIPTION 
       FIG. 1  illustrates schematically the general layout of an internal combustion engine of a motor vehicle, designated by the general reference number  10 . 
     In the embodiment being considered, the engine  10  is provided with four cylinders  12  in line. 
     The cylinders  12  are fed with air via an intake manifold  14 , itself fed by a pipe  16  provided with an air filter (not illustrated) and a turbocharger  18  for boosting the air feed to the engine. 
     An exhaust manifold  20  collects the exhaust gases generated by the combustion and discharges them toward the outside, through the compressor  18  and an exhaust line  22 . 
     An exhaust gas recirculation circuit collects a portion of the exhaust gases from the intake manifold  18 , so as to limit the quantity of nitrogen oxides produced by the combustion while avoiding the formation of smoke in the exhaust gases. 
     As seen in  FIG. 1 , the recirculation circuit essentially includes a valve to regulate the flow of recirculated exhaust gases, designated by the reference number  24 . 
     With regard to the exhaust line  22 , this essentially includes an exhaust gas treatment system  28  composed of, for example, a particulate filter, a nitrogen oxide trap, or any conventional type of catalytic converter or oxidizing converter. 
     Finally, the engine  10  is associated with a central processing unit  30  which checks the operation of the engine  10 , in particular the adjustment of its operating parameters, as well as checking the operation of the treatment system  28 , and analyzing its operating condition. 
     Moreover, the central processing unit  30  is duly programmed to detect the presence of the treatment system  28  in order, for example, to emit an alarm signal if the treatment system is removed. 
     To carry out the check on the operation of the engine  10 , it is provided with a turbocharging pressure sensor  32  and an air intake temperature sensor  33  in the intake manifold  14 , as well as a flow sensor  34  fitted to the feed pipe  16 . These sensors, as well as the main functional components of the engine and its air feed circuit, are connected to the central processing unit  30 . 
     With regard to the detection of the presence of a treatment system  28 , the exhaust line  22  is provided, on either side of the treatment system  28 , with a first temperature sensor  38  designed to measure the temperature upstream of the treatment system  28 , and a second temperature sensor  40  designed to measure the temperature downstream of the treatment system  28 . 
     As will be described in detail hereinafter, the temperature values upstream and downstream of the treatment system  28  are processed by the central processing unit  30 , so as, in particular, to calculate the derivative of the temperatures upstream and downstream of the treatment system  28  and compare the derivative of the temperature downstream of the treatment system with a threshold value for detecting the absence of the treatment system. This comparison is only made for set values of temperature variations upstream of the treatment system. 
     Thus, as illustrated in  FIG. 2 , the central processing unit  30  includes a first comparator  42  which provides a comparison between the derivative of the temperature dTdownstream downstream of the treatment system  28  and a first threshold  1  value. A comparator  44 , controlled by the output of the comparator  42 , is incremented when the derivative of the downstream temperature T exceeds the threshold  1  value. A second comparator  46  makes a comparison between the count level of the counter  44  and a second threshold  2  value to take a decision D when the count level exceeds the threshold  2  value. 
     Thus, when the derivative of the temperature downstream of the treatment system  28  exceeds the threshold  1  value, it is considered that the exhaust line  22  is not provided with a system  28 . However, it is actually concluded that the exhaust line is not provided with its treatment system only when it is observed that the threshold  1  value is exceeded a preset number of times fixed by the threshold  2  value. 
     Moreover, in addition to the counter  44  and the comparators  42  and  46 , the central processing unit  30  is provided with a third comparator  48  which makes a comparison between the derivative of the temperature dTupstream, and a third threshold  3  value, in order to authorize the detection of the presence of the treatment system  28  only when the derivative of the temperature dTupstream upstream of the treatment system  28  exceeds the threshold  3  value. Thus, such an analysis is only carried out for variations with time of the temperature upstream of the treatment system  28 , which are large enough to be able to observe differences in behavior between an exhaust line equipped with a treatment system and an exhaust line not provided with a treatment system. 
     Now will be described, with reference to  FIGS. 3 to 5 , the principle for detecting the presence of the treatment system according to the invention. 
     Reference will first be made to  FIG. 3 , which illustrates the derivative of temperature measurements supplied by the sensors  38  and  40 , upstream of the system  28  (curve  1 ), downstream of the system  28 , for a system of which the filtering material is composed of “cordierite” (curve  2 ), downstream of a treatment system  28  of which the filtering material is composed of silicon carbide (curve  3 ), and the derivative of the temperature measurement supplied by one of the temperature sensors  38  or  40 , in the absence of a treatment system  28  (curve  4 ). 
     For example, these signals are obtained during a cold New European Driving Cycle (NEDC). 
     As seen in this  FIG. 3 , for a given input signal composed of the derivative of the temperature upstream of the system  28 , the output signal, namely the dTdownstream signal, is attenuated and out of phase. It is noted that the attenuation and the phase difference depend on the thermal inertia of the emission control component used. Thus, the greater its inertia, the greater the attenuation and the phase difference. Such is the case in particular of a treatment system based on silicon carbide SiC, which produces a large attenuation and a large phase difference. On the contrary, in the absence of a treatment system  28 , the phase difference and the attenuation are relatively small. 
     With reference to  FIG. 4 , the temperature variations upstream and downstream of the system  28  are divided into classes of preset values of temperature variations. It will be noted however that the size of these classes is configurable. Such sampling makes it possible to determine the number of values of derivatives of temperature upstream and downstream of the system  28 , for various types of treatment systems, and also in the absence of treatment systems, for each of these classes, during a given configurable observation period which corresponds, in the embodiment considered, to a cold NEDC. 
     It can be seen in this  FIG. 4 , that the probability of occurrence, during a cycle, of a variation of the derivative of the upstream temperature of between 1° C./s and 1.5°/s is 0.13 (curve  5 ). For this type of driving, the probability of obtaining a dTdownstream response of between 1° C./s and 1.5° C./s is 0.13 in the absence of a treatment system (curve  6 ), 0.06 for a component with low thermal inertia (curve  7 ) and 0 for a component with high thermal inertia, in this case a silicon carbide-based system (curve  8 ). 
     It is therefore observed that, depending on the emission control component used, the probabilities of obtaining the dTdownstream signal by classes of value are different, and that for the same type of driving. 
     A threshold value of the dTdownstream derivative also occurs above which the probability of obtaining a higher value of the dTdownstream derivative is zero. This threshold value depends on the thermal inertia of the emission control component used. 
     In particular, for a silicon carbide-based treatment system  28 , the threshold value is 1° C./s, while the threshold value is 1.5° C./s for a cordierite-based treatment system. 
     It is also noted that for the class of temperature variation values between 0.5° C./s and 1° C./s, it is impossible to distinguish an exhaust line provided with a high thermal inertia treatment system from an exhaust line not provided with a treatment system. Thus, as seen in  FIG. 5 , the detection of the presence of the treatment system  28  is only carried out for upstream temperature derivatives dTupstream higher than the threshold value S 3 . In the example considered, this threshold value is fixed at 1° C./s. 
     This detection range P is limited, at its upper value, by a threshold S 4  which corresponds to the classes of temperature variations above which the probability of obtaining an increase in temperature variation is zero. 
     As shown previously with reference to  FIG. 2 , to carry out the detection of the presence of the treatment system  28 , the derivative of the temperature dTdownstream worked out from the signals supplied by the sensor  40  is compared with the calibrated threshold value S 1 , then the number of times this value is exceeded is counted and listed with a view to taking a decision D. 
     In other words, it is considered that the treatment system  28  is absent when the temperature derivatives worked out from the signals supplied by the downstream sensor  40  are located in an area S 5  defined by the threshold S 1 , the curve  6  corresponding to the variation of downstream temperature derivatives, in the absence of a treatment system  28 , and a minimum threshold S 6 , so as to eliminate the values which correspond to a probability which is too small.