Abstract:
A device for diagnosing a particle filter attached onto a main exhaust line of an internal combustion engine, wherein the diagnosis device includes, downstream from the first particle filter, a detection filter and a sensor for measuring an output parameter of the detection filter. The detection filter is arranged in a secondary exhaust line through which a first portion of the gases from the particle filter passes, wherein a second portion of the gases from the particle filter follows the main exhaust line. The device can be used for diagnosing particle filters for an automobile having a combustion engine.

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
       [0001]    The present application is a U.S. National Stage filing of International Application No. PCT/EP2010/063455, filed on Sep. 14, 2010, titled “Device For Diagnosing a Particle Filter”, which claims priority to FR Patent Application No. 0956326, filed Sep. 15, 2009, and EP Patent Application 10164347.6, filed May 28, 2010, the entire disclosures of which are incorporated herein by reference. 
     
    
     BACKGROUND 
       [0002]    A diagnostic device for a fixed particle filter on the main exhaust system of an internal combustion engine is provided, and includes a standard diagnostic device fitted after the first particle filter and consisting of a detection filter and a means of measuring the output setting from the detection filter. 
         [0003]    In order to reduce pollution from automotive vehicles with combustion engines, it is common practice to fit the main gas exhaust line from the engine with a particle filter that is designed to reduce the quantity of particles in the exhaust gases to a value below that of the tolerated threshold. 
         [0004]    The particle filters most commonly used consist of a set of channels with filtering walls and outlets alternately at the input or output points ( FIG. 1 ). The exhaust gases thus enter one channel and exit through another after have passed through at least one filtering wall. In silicon carbonate, (SiC) filters, these channels are grouped into segments connected by a joint that makes it possible to compensate for the considerable expansion of the silicon carbonate as hot gases pass through it. 
         [0005]    The particle filters installed on almost all of the automotive vehicles in Europe are very efficient and make it possible to reduce particle emissions to less than 5 mg per km covered, the maximum level tolerated by the Euro 5 standard that will come into force in 2010, measured according to the NEUDC standardized driving cycle. Standards for diesel applications or more generally vehicles using a thermal engine (trucks, agricultural machinery, construction vehicles) in Europe as well as in other countries, such as the United States and Japan, impose similar limits. 
         [0006]    Even if particle filters are known to be robust and to perform their function acceptably throughout the lifespan of the vehicles in which they are installed, certain filters may be defective, due to a manufacturing defect for example, or they may become defective as a result of extreme operating conditions. The best known failures manifest in the cracking of a filter wall, the failure of a joint connecting several segments and/or a blockage closing one or more channels. These failures translate into particle emission that is higher than the threshold tolerated by the legislation. 
         [0007]    The current OBD (On Board Diagnostic) standard requires the introduction of means of detection when a component fails (especially a particle filter) that is liable to result in a higher level of pollutant emission than the threshold fixed by legislation. These means of detection are needed to send a signal visible to the driver of the vehicle to indicate the need to have the pollutant emissions system checked. 
         [0008]    Several types of means of detection are currently being assessed or developed, such as resistance detectors having a metal plate positioned in the particle filter outlet and that shows an increase in resistance when particles stick to it. The mechanisms for depositing soot on the resistant element are very complex as they depend on settings that are hard to control. Furthermore, low-intensity electrical signals require complex electronic processing. An electrical discharge sensors may include two electrodes placed in the gases discharged from the particle filter and, when a predefined high voltage is applied between these electrodes, there is an electrical discharge if the quantity of particles in the gases discharged is higher than a certain threshold value. These sensors nevertheless require the use of complex electronic devices if they are to create sufficient current to produce an electrical discharge. An optical sensor includes an optical signal passing through the gas expelled from the filter makes it possible to determine the quantity of particles present in the outflow. These sensors are hard to maintain in good working order, however, in a difficult environment such as that of exhaust fumes. 
         [0009]    Another technique, considered in document DI (KR20070062309), consists in inserting a detection filter subsequent to the particle filter and detecting the difference in pressure between the entry and exit of the detection filter. A difference in pressure that is close to zero indicates that the detection filter is not stopping any particles, i.e. the particles present in the exhaust gases discharged from the engine have been correctly filtered through the particle filter. Conversely, an increasing difference in pressure indicates that the detection filter is being obstructed by particles that have not been filtered by the particle filter, i.e. that the particle filter is defective. The main disadvantage of the solution offered in D1 is that, in normal operation, the detection filter will produce a significant counter-pressure in the exhaust pipe, especially when the engine points are working hard and there is a high exhaust output. Counter-pressure of this kind will result in excessive fuel consumption and poorer engine performance. Furthermore, if the particle filter fails, the detection filter will become blocked with particles and will soon plug the exhaust system, in which case the vehicle should be immobilized immediately or the engine will be damaged. 
         [0010]    WO 03/091553 describes a default detection device for a particle filter. The device takes the form of a chamber installed on the engine&#39;s exhaust pipe, placed after the particle filter. The chamber consists of a filtering wall, facing the flow of exhaust gases, as well as an orifice in the facing wall through which the gases emerge. The device uses two oxygen sensors, one inside the chamber and the other inside the pipe. 
       SUMMARY 
       [0011]    The present disclosure proposes a new diagnostic device that does not have the disadvantages of the earlier devices described above. 
         [0012]    More specifically, the disclosure proposes a diagnostic device consisting of a fixed particle filter on the main exhaust line of an internal combustion engine, the diagnostic device consisting, prior to the first particle filter, of a detection filter and a device for measuring the output from the detection niter that indicates how well the particle niter is functioning. In the disclosure, the throughput of the detection filter consists of a first part of the gases emitted by the particle filter, the second part of the gases emitted by the particle filter following the main exhaust line. 
         [0013]    Furthermore, should the particle filter fail and the detection filter become blocked, the exhaust gases can continue to flow without obstruction through the main exhaust line. It will thus be possible to continue to use the vehicle. 
         [0014]    The proportion of gases passing through the detection filter should be small in relation to the total amount of gases output from the particle filter, consisting, for example, of between 0.1 at 70%. In order to minimize the effect of the detection filter on the functioning of the exhaust line, the amount of gases passing through the detection filter should be limited to an amount necessary and sufficient to enable measurement of the output settings of the detection filter with the desired level of accuracy. Thus, the proportion of gases passing through the detection filter should be restricted to 0.1 at 15% of the total amount of gases output from the particle filter, and they should preferably be between 0.1 at 10%, and even 0.1 at 5%. With such a low proportion of exhaust gases, it would be possible to use a small detection filter. This would take up less room, while still enabling accurate measurement. 
         [0015]    The detection filter would be installed on a secondary exhaust line dividing the flow from the main line, subsequent to the particle filter, and extending to outside the main line (at least partially). In order for this to happen, the secondary line may consist of an exhaust input linked to the main exhaust line at a point subsequent to the particle filter. Various possibilities exist for creating a connection to the secondary exhaust line output; it could be connected further down the line, in the open air, or attached to the engine&#39;s air intake. 
         [0016]    The use of a secondary line separate from the main line (and external to it) is especially advantageous when working on the basis of temperature variations produced when the detection filter becomes clogged, because this prevents overheating through the main exhaust line. The secondary line could, of course, consist of an entry section placed on the main line to divert part of the gases and, where appropriate, an exit section could be positioned on the main line. 
         [0017]    The means of measuring an output setting on the detection filter could consist of a sensor placed in that part of the secondary line that is outside the main line and it could be used alone or in combination with a sensor installed before it, as discussed above. 
         [0018]    The detection filter could be placed in the secondary line (outside the main line) or in the input section of the secondary line in the main line. This last configuration is advantageous in regenerating the detection filter via reheating caused by regeneration of the particle filter. 
         [0019]    Also, according to the variations, the means of measurement could be a sensor measuring temperature, throughput, speed of flow or oxygen concentration of the gases, positioned at the detection filter outlet, or a differential measurement device capable of establishing a difference (gradient) between the input and output from the detection filter. It could be means of measuring the pressure differential or temperature differential, consisting of an initial pressure sensor, and respectively a pressure sensor, before the detection filter, with a second pressure sensor, respectively for the temperature, after the detection filter and a comparison device capable of determining a difference in pressure, respectively of the temperature, between the input and the output (the difference before and after) of the detection filter. 
         [0020]    Thus, the present disclosure will make it possible to use known measurement sensors that are simple and robust. 
         [0021]    The diagnostic device can also include a warning that would produce an alarm signal if the output from the detection filter were to be different from a reference profile. 
         [0022]    The device is of particular interest for fitting on automotive vehicles such as automobiles, tracks, tractors, etc. But it can also be used more generally as a diagnostic tool for any particle filter associated with a thermal engine, such as for example motors on fixed motors or engines on fixed installations, ships&#39; engines, lifting gear, etc. 
         [0023]    Other features and advantages of the present disclosure will be readily appreciated, as the same becomes better understood after reading the subsequent description taken in conjunction with the accompanying drawings. 
     
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS  
         [0024]      FIG. 1  is a perspective view of a diagnostic device. 
           [0025]      FIGS. 2 through 5 ,  11 , and  12  illustrate variations of the diagnostic device of FIG  1 . 
           [0026]      FIG. 6  is a graph illustrating the speed of exhaust gases related to the condition of the particle filter. 
           [0027]      FIGS. 7 ,  8 , and  10  are graphs illustrating signals measured by sensors that can be operated by the engine&#39;s electronic controller. 
           [0028]      FIG. 9  is a graph illustrating the calibration and detection operation of the present device. 
       
    
    
     DETAILED DESCRIPTION  
       [0029]      FIG. 1  represents a known particle filter  10  consisting of an input  11  designed to be linked to the exhaust outlet of a thermal engine. The outlet  12  of the particle filter  10  is linked to a main exhaust line  13  in which the exhaust gas has a total output of Qt when the thermal engine is operating normally. In a given section of the exhaust line, total pressure Ptotal is shown by the ratio: Ptotal=Pstatic+Pdynamic. The dynamic pressure is a function of the speed V of the movement of the gases: Pdynamic−1/2*rho*V*V, rho being the mass by volume of the exhaust gases. 
         [0030]    The diagnostic device is subsequent to the particle filter  10 , detection filter  14  and a measuring device  15 . The detection filter  14  is positioned in such a way as to receive only part of the gas output from the particle filter, and the means of detection  15  is preferably attached to the detection filter outlet (below it, after it). It is also possible to consider using two sensors, one placed in front of (prior to) the detection filter and the out at the outlet (after it), which would make it possible to measure a difference in temperature or a difference in pressure as will be seen below (the terms “input” and “before”, as well as “outlet” and “after”, are used here as synonyms for each other). 
         [0031]    The detection filter would preferably have filtering properties similar to those of a particle filter. The most commonly used particle filters currently are those employing silica carbonate or cordierite but possessing different filtration properties such as porosity, size of the pores and the number of channels per section through which the exhaust passes. The detection filter may be designed so as to permit a very low loss of load when the detection filter is not heavy with soon so that it can then unclog itself quickly, even at very low soot emissions. 
         [0032]    Other filters, such as metallic foam or woven metal can be used as long as their filtering behavior is the same. In an initial variation, the detection filter  14  is placed in a branch pipe or secondary exhaust line  16 . The dimensions of the secondary line are such (section, shape, etc.) that only 0.1 to 70% of the total exhaust gases are diverted to the secondary line and the detection filter. The section may be reduced so that only 0.1 at 15%, 0.1 at 10% or 0.1 at 5%, of the total exhaust gases will be diverted to the secondary line and the defection filter, to limit the repercussions on the functioning of the engine if the detection filter  14  becomes blocked when the particle filter  10  fails. 
         [0033]    An input  17  from the secondary line is connected to the main line  13  below the particle filter  10  so that the said input  17  is subjected to the total pressure=Ptotal of the gases. According to a variation, an output from the secondary line is linked to the main exhaust line in such a way that when the gases emerge from the secondary line, it is only subjected to static pressure. 
         [0034]    An output is created from the secondary line so that when the gases exit from the secondary line, they are subjected to a pressure that is lower than or equal to the static pressure Pstatic. Thus, the difference in pressure between the input and output of the secondary line is greater than or equal to the dynamic pressure and a fraction of the gases is naturally drawn toward the secondary line and the detection filter. According to a variation, the exit from the secondary line is linked to the main line, and the gases are thus subjected, as they emerge, to the static pressure and the difference in pressure between the input and the output of the secondary line equals Pdynamic=Ptotal−Pstatic. According to another variation, the secondary line vents to the outside air, so that the gas output is subject solely to atmospheric pressure (which is lower than the static pressure) and the difference in pressure between the input and output of the secondary line will be greater than the dynamic pressure. 
         [0035]    The flow of gas along the secondary line depends on factors such as the difference in pressure between the input and output of the secondary line losses of load in the secondary line, due to the detection filter and the secondary line (shape, cross-section, length, rough texture of the walls, etc.) 
         [0036]    The shape and dimensions of the secondary line and its connection to the main line should thus be dimensioned so that the secondary flow of gases is sufficient to enable detection of a setting for the gases through the means of detection  14 . If necessary, several solutions could be considered to increase the secondary flow. 
         [0037]    The secondary exhaust line thus diverts a proportion of the exhaust gases and constitutes a separate line from that of the main pipe extending out of it. To connect it to the main line, it could be attached to the main pipe or consist of an input section (or primer) inside the main line to facilitate the diversion of the gases. The input section may be parallel to the gas flow. 
         [0038]    It is possible to locally reduce the cross-section of the main line close to (in front of or behind) the entry of the secondary line  FIG. 2 , by narrowing it  19 . Thus the speed of the gases and consequently the dynamic pressure, will increase locally. The secondary flow, a function of the dynamic pressure, will increase accordingly. Alternatively, a restriction may be placed inside the main line between the input  17  and the output  18  of the secondary line  16  in such a way as to force part of the flow to pass through the detection filter  14 . Such a restriction should be limited to the minimum necessary for ensuring a sufficient flow of gases to the detection filter in order to ensure that the measurement is accurate ( FIG. 2   b ). The restriction could take the form of a grid ( 19   a ) placed around the input section  17  of the secondary line or a simple restriction ( 19   b ) or any other device that would make it possible to increase the loss of load in the main exhaust line behind the input section  17 . 
         [0039]    A valve may be placed on the main line close to the entry of the secondary line (instead of the narrowing  19 —not shown in the figure), that would make it possible to adjust the secondary flow as desired. 
         [0040]    In an example of a main line containing a series of a particle filters  10  and an additional element (such as a muffler  20  or resonator), a secondary line input may be positioned between the output of the particle filter  10  and the input of the additional element. The secondary line would thus be an offshoot the main line. Since the loss of the load in the main line is increased by the presence of the additional element, the flow of gases in the secondary line parallel to the main line is increased. 
         [0041]    The outlet  18  on the secondary line can be left open ( FIG. 1 ), in such a way that the exhaust gases are evacuated to the open air, in the same way as the gases circulating in the main line. The outlet  18  can also be linked to the main line below the inlet  17  ( FIGS. 2 ,  3 ). The outlet  18  can also be linked to the main line below the additional element, if any ( FIG. 4 ). It can also be linked at any point to the exhaust line or where air enters the engine (not shown) that could present a sufficient difference of pressure to ensure a diverted flow at an appropriate rate. In this context, the outlet  18  could be connected to the line that provides air to the engine, especially a low-pressure section (for example between the throttle and the compressor, as appropriate). 
         [0042]    The secondary line  16  can be installed inside a muffler  20  as a space-saving measure ( FIG. 5 ). 
         [0043]    The detection filter  14  has filtering properties similar to those of a particle filter. For example, if the particle filter  10  functions normally, the detection filter will allow through all the particles that the panicle filter has allowed through (i.e. the smallest panicles or soot and a very small residual quantity thereof); the detection filter is thus virtually transparent as to the flow of gases passing through it. If the particle filter  10  is defective, the detection filter will block all the particles that the particle filter ought to have caught had it been operating correctly. Since the detection filter has detection capacities (in terms of volume and numbers of particles that it is capable of absorbing), the detection filter will gradually become clogged up until it is almost incapable of allowing gases to pass through it. 
         [0044]    If the particle filter  10  is working correctly, the parameters of gas flow at the outlet of the detection filter will evolve similarly over time to those of flow of gas discharged from the particle filter ( FIG. 6 , the dotted lines). At one operating point of the engine the flow to the detection filter will remain stable over time (FIG.  7 —without soot escaping). 
         [0045]    If the particle filter  10  is defective, it will let through a certain amount of soot that will be as significant as the importance of the failure. This leakage of soot will gradually clog the detection filter  14  thus increasing its resistance to the flow of gases. The variations over time of the gas flow at the outlet of the detection filter  14  will thus not follow the variations of the corresponding parameters of the flow at the outlet of the particle filter and the flow will gradually decrease to zero ( FIG. 6 , the unbroken line curves). 
         [0046]    This reduction in the flow of gases to the detection filter will occur with varying rapidity depending on the quantity of soot allowed to escape from the defective main filter (FIG.  7 —slight and significant escapes of soot). In fact, the detection filter will clog up more quickly the greater the escape of soot, and this will result in a quick reduction in the gases diverted. The change in the flow of gases diverted can be measured by using known sensors such as temperature or pressure sensors or any other type of sensor.  FIG. 8  shows an example of the change in the flow of diverted gases monitored with the help of a temperature sensor placed at the outlet of the detection filter. 
         [0047]    When it is operated on a vehicle or an engine it is sufficient to note the changes to the measurement parameter at the outlet or tire input/output gradient of the detection filter based on the level of soot escaping from the particle filter and the distance covered or operating time ( FIG. 9 ). This data will be considered as a specific reference to the application. Additionally, in an example, the level of soot may be defined so as not to exceed 10 mg/km in the example in  FIG. 9  which will also determine the distance covered (or the operating time) during which the discharge settings or the input/output gradient of the detection filter will have reached a certain value—the intersection of the horizontal line with line 10 mg/km on  FIG. 9 . This value of the parameter could be considered as a threshold to be associated with 1 Omg/km of soot escape. 
         [0048]    While the vehicle is in use, the reading of the output parameter from the detection filter is above this threshold, before the distance indicated on the graph of  FIG. 9  has been covered (stored in the controller and based on the calibrated data) it could be considered that the critical level of soot has been exceeded and an alarm signal should be sent. 
         [0049]    The quantity of soot escaping from the main filter can be determined by measuring the gas temperature gradient between the input and the output from the detection filter. In fact, when the flow of diverted gases to the detection filter is reduced due the filter clogging, the loss of temperature through the detection filter will tend to increase, as shown in  FIG. 10 . Whereas, if there is no escape of soot from the main filter, the temperature gradient between the input and the output of the detection filter remains constant. The increase in temperature gradient is directly linked to the level of escaping soot. It is therefore sufficient to characterize the temperature gradient through the detection filter over time as being dependent on the flow of diverted gases and the level of soot emission, and to store this reference data in the engine&#39;s control unit so as to be able to use it subsequently when the vehicle or the engine are in operation to produce an alarm signal as soon as a temperature gradient corresponding to the maximum tolerable level of soot has been reached or exceeded. 
         [0050]    The same methodology could also be used but by employing different sensors such as gas flow sensors, pressure sensors or others. 
         [0051]    The way the flow parameters to the detection filter will change will depend, of course, on the nature and size of element  14 . For certain applications it might be advantageous to reduce its size to ensure low resistance to the flow and thus increase the flow of diverted gases. But by reducing its size it would then be possible that the change in the temperature after the detection filter, as it gradually clogged up, would not be sufficiently significant and this would reduce the accuracy of detection of the level of soot escaping from the main filter  10 . To overcome this problem, one solution consists in placing a dispersing element  14  behind the detection filter  14  that would show a small loss of load but a significant capacity to absorb or exchange the heat with the ambient air,  FIG. 11 . This would make it possible to observe any change in the existing temperature by using the large detection filter though without the disadvantage of a serious loss of load. 
         [0052]    The detection filter could be created using the same principle and the same materials as the particle filter, although any other type of filter could be used, as long as it possessed the properties explained above. 
         [0053]    It should be recalled that when the particle filter is functioning normally, the parameters of the flow of gases at the particle filter outlet vary enormously in amount, depending on the way the engine works, the type of engine, etc. 
         [0054]    This can be checked by the parameters of the flow of gases such as temperature, pressure, flow, speed of discharge, concentration of oxygen, etc. placed at an outlet or/and at the detection filter input. It would thus be possible to use a single sensor as the measurement device at the outlet of the detection niter ( FIGS. 1 ,  2 ,  4 ,  5 ) such as temperature or pressure sensor, a flow meter, an anemometer, an oxygen probe, etc. 
         [0055]    All of these sensors are widely known, they have the advantage of being robust and efficient, even in a difficult environment such as that of exhaust gases and they do not require complex electronic controls. It would also be possible to use differential measurement, such as differential pressure or temperature (see  FIG. 3 ), consisting of an initial pressure sensor (resp. temperature)  24  prior to the detection filter  14 , a second pressure sensor (resp. temperature)  25  after the detection filter and a comparator  26  capable of detecting a difference in pressure (resp. temperature) before and after the detection filter. 
         [0056]    For it to work efficiently, the particle filter will be regenerated regularly when the thermal engine is in operation. To regenerate the particle filter, the temperature of the exhaust gases is increased considerably to burn off the soot absorbed by the particle filter. Since part of the exhaust gases discharged from the particle filter pass through the detection filter, this filter can be automatically regenerated each time the particle filter is regenerated. 
         [0057]    In certain cases, the particle filter is regenerated from time to time even if it is defective. In this case, the detection filter should be of such a size as to clog rapidly if the particle filter fails, in order to make it possible to detect this failure before the particle filter regenerates. In this case, a small size detection filter should be used. 
         [0058]    It is also possible to improve the regeneration of the detection filter by placing it in the input section of the secondary line, i.e. the part of the diversion surrounded by the main flow from the particle filter,  FIG. 12 . This will make it possible to benefit from all the power available in the flow of gases in order to regenerate the filter. 
         [0059]    Alternatively, regeneration could be performed with the help of electric power using the vehicle&#39;s own electrical circuitry (not shown in the figure). This solution is less recommended, however, in view of the fact that it would require additional fuel consumption. 
         [0060]    The present diagnostic device also has the advantage of including an alarm (not shown), to monitor the variations in the parameter measured by the means of measurement which will produce an alarm signal if the profile of the signal measured is different from a reference profile. 
         [0061]    When implemented, the alarm is a comparator, comparing the amplitude of the outlet parameter to a reference threshold and producing an alarm signal when the amplitude of the outlet parameter is lower than the reference threshold. 
         [0062]    In a different mode, the alarm will contain a memory and a comparator. The memory will contain a reference profile corresponding to the change detected in the parameter over time when the particle filter is functioning normally. The reference profile is obtained, for example, by testing the vehicle in which the diagnostic device is installed before it is sold in the market. When the thermal engine is working, the comparator will continuously compare the signal produced by the measurement tool with the reference profile and it will produce an alarm signal when the signal measured shows more than an X % difference from the reference profile. X is a percentage, the value of which can be adjusted depending on the properties desired for the diagnostic device (speed of detection of a failure of the particle filter, guarantee that an alarm will indeed represent a failure in the particle filter, etc.). 
         [0063]    Many modifications and variations of the present disclosure are possible in light of the above teachings. Therefore, within the scope of the appended claim, the present disclosure may be practiced other than as specifically described.