FR3093134A1 - PROCESS FOR DIAGNOSING A STATE OF CONNECTION OF A DOWNSTREAM TIP OF A DIFFERENTIAL PRESSURE SENSOR - Google Patents

Abstract

The invention mainly relates to a method for diagnosing an operating state of a differential pressure sensor (18) connected upstream and downstream of a particulate filter (16) of a heat engine (10) respectively by the '' intermediary of an upstream tap-off (18.1) and a downstream tap-off (18.2), said method comprising: - a step of detecting authorization conditions for carrying out the diagnosis, - a step of detecting stability conditions operation of the heat engine (10), and - a diagnostic step of a connection state of the downstream tapping (18.2) of the differential pressure sensor (18) as a function of a maximum peak of a pressure measurement signal differential returned by the differential pressure sensor (18). Figure 1

Description

PROCESS FOR DIAGNOSING A CONNECTION STATE OF A DOWNSTREAM TIP OF A DIFFERENTIAL PRESSURE SENSOR

The present invention lies in the field of the pollution control of the exhaust gases of a heat engine. More specifically, the invention relates to a method for diagnosing a connection state of a downstream tap of a differential pressure sensor at the terminals of a particulate filter. The invention finds a particularly advantageous, but not exclusive, application with internal combustion engines (gasoline, diesel or hybrid), equipped with a particulate filter associated with a single diaphragm differential pressure sensor.

During the combustion of a mixture of air and fuel in a heat engine, solid or liquid particles consisting essentially of carbon-based soot and / or oil droplets may be emitted. These particles typically have a size between a few nanometers and one micrometer. To trap them, one can advantageously provide particle filters, usually made of a mineral matrix, of ceramic type, of honeycomb structure, defining channels arranged substantially parallel to the general direction of flow of the exhaust gases in the filter. , and alternately closed on the side of the gas inlet face of the filter and on the side of the gas outlet face of the filter, as described in document EP2426326.

The exhaust line is also provided with a differential pressure measurement sensor for measuring the pressure difference between an upstream nozzle and a downstream nozzle of the particulate filter from which it is possible to deduce a mass of accumulated soot. To this end, a map is used which establishes a correlation, as a function of the air flow admitted, between the pressure difference measurement and the mass of soot in the particulate filter.

The regeneration of the particle filter is controlled when the latter is sufficiently loaded with particles. For this purpose, the temperature in the exhaust line is increased, which causes the combustion of soot in the particulate filter. After regeneration, the particulate filter is freed of the soot it contained and a new charging cycle begins.

Two types of differential pressure sensors are known in particular for particle filters, namely conventional single-membrane differential pressure sensors as well as the latest generation double-membrane differential pressure sensors. Double membrane sensors have the advantage of being able to meet CARB (for "California Air Resources Board") or equivalent regulations requiring the ability to detect a disconnection of a downstream tapping of the sensor. The double membrane sensor is however more expensive than the single membrane sensor.

There is therefore a need to be able to detect the connection fault of the downstream branch with a conventional single membrane sensor in order to meet the new regulations.

The invention aims to effectively meet this need by proposing a method for diagnosing an operating state of a differential pressure sensor connected upstream and downstream of a diesel engine particulate filter respectively by means of an upstream branch and a downstream branch, said method comprising:
- a step of detecting authorization conditions for carrying out the diagnosis,
- a step of detecting conditions of stability of operation of the heat engine, and
- A diagnostic step of a connection state of the downstream branch of the differential pressure sensor as a function of a maximum peak of a differential pressure measurement signal returned by the differential pressure sensor.

According to one implementation, the authorization conditions for carrying out the diagnostic are met when the heat engine is operating at low load, the combustion mode is nominal, and an outside temperature and / or outside pressure are included. within a corresponding calibratable range of values.

According to one implementation, the conditions of stability of operation of the heat engine are detected when the speed of the heat engine and the filling of the heat engine are within a predetermined range calibrated around their current value at least for a predetermined period.

According to one implementation, the maximum measured peak used to carry out the diagnosis is the value of the differential pressure measurement signal for which a derivative of the measurement signal crosses a value 0 while passing from a positive value to a negative value, the value of the measurement signal must also be greater than a minimum threshold.

According to one implementation, the minimum threshold is calculated as a function of an average value of the pressure difference signal and of a standard deviation calculated for a current stabilized regime.

According to one implementation, the diagnostic step of connecting the downstream tap-off of the pressure sensor consists in performing a comparison between the maximum peak measured and a maximum calibratable peak threshold and in considering that there is a connection fault in the case where the maximum peak measured is greater than the maximum calibratable peak threshold.

According to one implementation, the maximum calibratable peak threshold depends on an operating point of the heat engine.

According to one implementation, the diagnosis is based on the use of a two-dimensional memory matrix comprising a plurality of boxes, each box of the matrix corresponding to a maximum peak of differential pressure which has been measured for an operating point. of the corresponding heat engine defined by a speed and a torque of the heat engine.

According to one implementation, in the case where, for a current box of the matrix for which the maximum peak of differential pressure is measured, this is the first time that this box is filled in, then the connection diagnostic of the downstream tapping of the sensor differential pressure is not engaged.

According to one implementation, if, for a current cell of the matrix, there is an old learning of the maximum peak of differential pressure which was carried out previously, then said method comprises:
- a step of calculating a ratio between a new learning of the maximum differential pressure peak divided by the old learning of the maximum peak, and
- if this ratio exceeds a maximum threshold, then it is considered that there is a connection fault on the downstream branch of the differential pressure sensor.

The subject of the invention is also a computer comprising a memory storing software instructions for implementing the method for diagnosing an operating state of a differential pressure sensor as defined above.

The invention will be better understood from reading the following description and examining the accompanying figures. These figures are given only by way of illustration but in no way limit the invention.

FIG. 1 is a schematic representation of an exhaust line of a heat engine comprising a particulate filter and a computer allowing the implementation of the method according to the invention;

FIG. 2a is an example of measurements of the amplitude of the differential pressure signal respectively with a sensor correctly connected and a sensor disconnected downstream of the particulate filter, as a function of filling the heat engine;

FIG. 2b is an example of measurements of the amplitude of the differential pressure signal respectively with a sensor correctly connected and a sensor disconnected downstream of the particulate filter, as a function of a speed of the heat engine;

FIG. 3 is a diagram of the steps of the method for diagnosing a connection state of a downstream tapping of a differential pressure sensor of a particulate filter;

FIG. 4 shows timing diagrams illustrating an implementation of the method according to the invention for diagnosing a connection state of a downstream tap of a differential pressure sensor.

FIG. 1 represents a heat engine 10 particularly intended to equip a motor vehicle. The heat engine 10 is connected to an exhaust line 12 for the evacuation of the burnt gases produced by the operation of the heat engine 10.

The exhaust line 12 comprises a member 14 for depolluting gaseous pollutants, for example an oxidation catalyst or a three-way catalyst. The three-way catalyst 14 makes it possible in particular to reduce the oxides of nitrogen to nitrogen and to carbon dioxide, to oxidize the carbon monoxides to carbon dioxide, and the unburnt hydrocarbons to carbon dioxide and water.

The exhaust line 12 further comprises a particulate filter 16 for filtering soot particles in the exhaust gases of the heat engine 10. The particulate filter 16 is suitable for filtering soot particles originating from the combustion of the engine. fuel.

In the particulate filter 16, the exhaust gases pass through the material making up the particulate filter. Thus, when the particulate filter 16 is formed of channels, each of these channels has a plugged end, so that the exhaust gases flowing in the particulate filter 16 pass from channels to channels, passing through the walls of the channels. different channels of the particle filter 16 to exit the particle filter 16. The particle filter 16 may be based on a porous ceramic matrix, for example cordierite, mullite, aluminum titanate or silicon carbide. If necessary, the depollution unit 14 and the particulate filter 16 may be located inside the same envelope 17.

The exhaust line 12 is also provided with a sensor 18 for measuring the differential pressure between the upstream and downstream side of the particulate filter 16 from which it is possible to deduce a mass of accumulated soot. For this purpose, the sensor 18 is connected upstream and downstream of the particulate filter 16 respectively by means of an upstream tapping 18.1 and a downstream tapping 18.2. In addition, a map makes it possible to establish a correlation, depending on the intake air flow, between the differential pressure measurement and the mass of soot in the particulate filter 16.

A computer 20, for example the engine computer or a dedicated computer, makes it possible to carry out an operating diagnosis of the differential pressure sensor 18. To this end, the computer 20 receives an information flow at the input of the diagnostic function, in particular the differential pressure measurement signal Dp returned by the sensor 18. The computer 20 preferably uses the raw signal from the sensor 18, without no filtering or processing.

The computer 20 also receives as input the speed W_mth of the heat engine, the torque C_mth of the heat engine, the combustion mode M_comb of the heat engine, the filling R_mth of the heat engine, the outside temperature T_ext, and the outside pressure P_ext.

The diagnostic function of the engine computer 20 may generate an output information flow containing in particular state variables F1, F2 for detecting a connection fault in the branching downstream of the sensor 18, as is explained in more detail below. after.

The calculation call frequency is at least 1kHz (for a sampling period equal to or less than 1 ms).

The following describes, with reference to FIG. 3, the operating diagnostic principle of the differential pressure sensor 18 of the particulate filter 16.

The computer 20 checks, in a step 100, that the diagnostic implementation authorization conditions are met. In particular, the speed W_mth and the filling R_mth of the heat engine must be within a range of calibratable values. According to an example of implementation, the W_mth speed range is between 1500 and 3000 revolutions / min and the R_mth filling range is between 0.1 and 0.5, because the diagnosis is more robust at low load. The combustion mode M_comb is preferably nominal, insofar as the specific modes can distort the measurement of the sensor 18.

The outside temperature T_ext and / or the outside pressure P_ext must be within ranges of predetermined values that can be calibrated. For example, we avoid performing the diagnosis in very cold conditions because frost is likely to form in the nozzles 18.1, 18.2 of the sensor 18, which can distort the pressure difference measurement. According to an example of implementation, the outside temperature T_ext must at least be greater than -7 ° C, while the atmospheric pressure must be at least of the order of 750 mbar.

The computer 20 detects in a step 101 that conditions of stability in terms of speed W_mth and load of the heat engine are met. Under these conditions, the back pressure of the filter 16 also stabilizes, which makes it possible to establish a robust diagnostic on its own.

Thus, a range of values that can be calibrated around a value of the current W_mth speed is defined. If the W_mth speed remains in this range for at least a calibratable period of several seconds, then the W_mth speed is considered to be stable. The range of W_mth speed values is for example defined by plus or minus 300 revolutions / min with respect to the current W_mth speed.

Similarly, a range of values that can be calibrated is defined around a value of the torque C_mth or a current filling value R_mth. If the filling R_mth of the heat engine 10 remains in this range of values for at least a calibratable period of several seconds, then the filling R_mth is considered to be stable. The range of R_mth padding values is for example defined by plus or minus 0.15 with respect to the current R_mth padding.

The stability conditions are detected if the speed W_mth and the filling R_mth of the heat engine are considered to be stable.

The engine computer 20 then performs, in a step 102, the operating diagnosis of the differential pressure sensor 18. The diagnostic criterion is based on the analysis of the evolution of the amplitude of the differential pressure signal Dp. This parameter is modified when the downstream connection 18.2 of the sensor 18 is disconnected. This variation is particularly visible at low load.

Thus, FIG. 2a shows that the measurements of the amplitude of the differential pressure signal obtained as a function of the filling of the engine R_mth with a sensor 18 disconnected downstream (represented by the crosses in the figure) are greater than those obtained for a sensor 18 correctly connected downstream of the particulate filter 16 (represented by the circles in the figure).

Figure 2b shows that the measurements of the amplitude Dp_max of the differential pressure signal obtained as a function of the engine speed W_mth with a sensor 18 disconnected downstream (represented by the crosses in the figure) are greater than those obtained for a sensor 18 correctly connected downstream of the particulate filter 16 (represented by the circles in the figure).

The first phase to carry out the diagnosis consists in measuring the maximum peak Dp_max of the differential pressure measurement signal Dp. To do this, two criteria are established:
- The first criterion is based on the fact that the derivative of the differential pressure signal Dp crosses the value 0 while passing from a positive value to a negative value.
- The second criterion is based on the fact that the value of the differential pressure signal Dp at the time of the detection of the above criterion of the "derivative" must be greater than a minimum threshold.

This minimum threshold is for example equal to the sum of the average of the differential pressure signal and of double the standard deviation. The mean value of the signal as well as the standard deviation are calculated in the current stabilized W_mth regime for a calibratable period. This calibratable duration is for example between 2s and 5s.

If the two aforementioned criteria are verified, the value of the maximum peak Dp_max is retained to carry out the diagnosis.

The second phase of the diagnosis consists in carrying out a comparison between the maximum peak Dp_max of differential pressure Dp retained with respect to a calibratable maximum peak threshold S_Dp. This maximum peak threshold S_Dp depends on the operating point of the heat engine defined by the engine speed W_mth and the engine torque C_mth.

In the case where the maximum peak Dp_max retained is greater than the threshold S_Dp, then a fault diagnosis of the connection of the downstream tap-off 18.2 of the differential pressure sensor 18 is established in a step 103.

In order to make the diagnosis more robust with respect to the dispersions of the heat engine 10 and of the differential pressure sensor 18, an alternative method is based on the same principle of measuring the amplitude of the differential pressure signal Dp.

In this case, over the life of the vehicle, each time a maximum differential pressure peak Dp_max is measured, it is recorded in a two-dimensional Mat_2D memory matrix (speed W_mth and torque C_mth of the heat engine) in a step 104. Each box of the Mat_2D matrix corresponds to a differential pressure peak Dp which was measured for a corresponding operating point (W_mth speed; C_mth torque).

The diagnosis is carried out as follows: for the current box (W_mth speed; C_mth torque) for which the maximum peak Dp_max of differential pressure Dp is measured, if this is the first time that this box is filled, the diagnosis n ' is not carried out.

If for the current box (speed W_mth; torque C_mth), there is already an old learning of the maximum peak Dp_max_a of differential pressure which was carried out previously, the ratio between the new learning of maximum peak Dp_max_n divided by the old learning of peak maximum Dp_max_a is calculated in a step 105.

If this ratio exceeds a maximum threshold which is a function of the operating point (speed W_mth; torque C_mth), then a fault diagnosis of the connection of the downstream tap-off 18.2 of the differential pressure sensor 18 is established in a step 106.

It will also be possible to verify that the old learning of Dp_max_a was carried out in a predetermined number of last kilometers traveled. This number could for example be between 50km and 15000km.

Figure 4 shows a diagram of temporal signals obtained during the implementation of the diagnostic method of a connection state of the downstream tap 18.2 of the differential pressure sensor 18 by comparison between the maximum peak Dp_max of the measurement signal Dp and a pressure threshold S_Dp.

The authorization conditions as well as the stability conditions being fulfilled with a substantially constant engine speed W_mth and a substantially constant filling R_mth, it is possible to implement the method.

Between times t0 and t1, the maximum peak Dp_max of the signal is lower than the threshold S_Dp, so that it is considered that there is no connection fault of the downstream tap 18.2 of the sensor 18.

At time t1, the maximum peak Dp_max of the signal becomes greater than the threshold S_Dp, so that it is considered that there is a connection fault of the downstream tap 18.2 of the sensor 18. A corresponding state variable ("flag "in English) F1 then changes to 1.

After a confirmation period Tc of the fault between times t1 and t2 during which the maximum peak Dp_max remains greater than the threshold S_Dp, a corresponding fault confirmation state variable F2 goes to state 1.

Claims (10)

Method for diagnosing an operating state of a differential pressure sensor (18) connected upstream and downstream of a particulate filter (16) of a heat engine (10) respectively via an upstream tapping (18.1) and a downstream tapping (18.2), characterized in that said method comprises:
- a step (100) of detecting authorization conditions for implementing the diagnostic,
- a step (101) of detecting conditions of operating stability of the heat engine (10), and
- a step (102) for diagnosing a connection state of the downstream tapping (18.2) of the differential pressure sensor (18) as a function of a maximum peak (Dp_max) of a differential pressure measurement signal (Dp) returned by the differential pressure sensor (18). Method according to Claim 1, characterized in that the authorization conditions for carrying out the diagnosis are fulfilled when the heat engine (10) is operating at low load, the combustion mode (M_comb) is nominal, and that a outdoor temperature (T_ext) and / or outdoor pressure (P_ext) are within a corresponding range of calibratable values. Method according to claim 1 or 2, characterized in that the conditions of operating stability of the heat engine (10) are detected when the speed (W_mth) of the heat engine (10) and the filling (R_mth) of the heat engine (10) lie within a predetermined range calibrated around their current value at least for a predetermined period. Method according to any one of Claims 1 to 3, characterized in that the maximum measured peak (Dp_max) used to carry out the diagnosis is the value of the differential pressure measurement signal (Dp) for which a derivative of the measurement signal ( Dp) crosses a value of 0 while passing from a positive value to a negative value, the value of the measurement signal (Dp) must also be greater than a minimum threshold. Method according to Claim 4, characterized in that the minimum threshold is calculated as a function of an average value of the pressure difference signal (Dp) and of a standard deviation calculated for a current stabilized regime. Method according to any one of claims 1 to 5, characterized in that the diagnostic step of connecting the downstream tapping (18.2) of the pressure sensor (18) consists in performing a comparison between the maximum peak (Dp_max) measured and a maximum calibratable peak threshold (S_Dp) and to consider that there is a connection fault if the maximum peak (Dp_max) measured is greater than the maximum calibratable peak threshold (S_Dp). Method according to Claim 6, characterized in that the calibratable maximum peak threshold (S_Dp) depends on an operating point of the heat engine. Method according to any one of Claims 1 to 5, characterized in that the diagnosis is based on the use of a two-dimensional memory matrix (Mat_2D) comprising a plurality of cells, each cell of the matrix (Mat_2D) corresponding at a maximum peak (Dp_max) of differential pressure which was measured for a corresponding operating point of the heat engine (10) defined by a speed and a torque (C_mth) of the heat engine. Method according to Claim 8, characterized in that in the case where, for a current box of the matrix (Mat_2D) for which the maximum peak (Dp_max) of differential pressure is measured, this is the first time that this box is filled in, then the connection diagnostic of the downstream connection (18.2) of the differential pressure sensor (18) is not activated. Method according to claim 8 or 9, characterized in that if, for a current cell of the matrix (Mat_2D), there is an old learning of the maximum peak (Dp_max_a) of differential pressure which was carried out previously, then said method comprises:
- a step of calculating a ratio between a new learning of the maximum peak (Dp_max_n) of differential pressure divided by the old learning of the maximum peak (Dp_max_a), and
- if this ratio exceeds a maximum threshold, then it is considered that there is a connection fault in the downstream tap-off (18.2) of the differential pressure sensor (18).