FR3096736A1 - PROCEDURE FOR DIAGNOSING A CONNECTION STATE OF A DIFFERENTIAL PRESSURE SENSOR - Google Patents

Abstract

The invention relates to a method for diagnosing a connection state of a differential pressure sensor (6) connected upstream and downstream of a particulate filter (4) of a heat engine (1) respectively by the 'intermediary of an upstream branch (6a) and a downstream branch (6b), comprising a step of acquiring the differential pressure measurement signal returned by the sensor (6), characterized in that it comprises a step determining the frequency of this measurement signal, a step of comparing this frequency with the frequency of passage of all the pistons at TDC, a step in which it is diagnosed that the downstream nozzle of the sensor (6) is either correctly connected if the frequency of the measurement signal is double the frequency of passage of all pistons at TDC, or disconnected if the frequency of the measurement signal is equal to this passage frequency. Figure 1

Description

METHOD FOR DIAGNOSING A CONNECTION STATE OF A DIFFERENTIAL PRESSURE SENSOR

The present invention The present invention lies in the field of depollution of the exhaust gases of a combustion engine. More specifically, the invention relates to a method for diagnosing a connection state of a downstream tapping 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-membrane differential pressure sensor, which is less expensive than a double membrane 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 can be emitted. These particles typically have a size between a few nanometers and one micrometer. To trap them, particulate filters can advantageously be provided, usually consisting of a mineral matrix, of the 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 sealed 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 fitted with a differential pressure measurement sensor to measure the pressure difference between an upstream tapping and a downstream tapping of the particulate filter from which it is possible to deduce a mass of accumulated soot.

Regeneration of the particulate filter is controlled when the latter is sufficiently loaded with particles. To do this, the temperature in the exhaust line is increased, which leads to the combustion of soot in the particulate filter. At the end of regeneration, the particle filter is freed from the soot it contained and a new charging cycle begins.

In particular, two types of differential pressure sensors for particulate filters are known, namely conventional single-membrane differential pressure sensors and latest-generation double-membrane differential pressure sensors. Double-membrane sensors have the advantage of being able to meet CARB (California Air Resources Board) or equivalent regulations requiring the ability to detect a disconnection of a tapping downstream of the sensor. However, the double membrane sensor is more expensive than the single membrane sensor.

The document FR3021355A1 describes a method for detecting the disconnection of the downstream tapping of a differential pressure sensor by comparing the temporal pressure gradient of the real signal with a predicted temporal gradient. However, this method is sensitive to measurement disturbances, to sensor drifts and to the calibration of the model which serves as a reference for the comparison of the gradient.

There is therefore a need to be able to reliably detect the connection fault of the downstream tapping with in particular a conventional single-membrane sensor in order to comply with the new regulations.

The invention aims to effectively meet this need by proposing a method for diagnosing a connection state of a differential pressure sensor connected upstream and downstream of a particulate filter of a heat engine respectively via an upstream tapping and a downstream tapping, the heat engine comprising cylinders in each of which a piston slides between a Top Dead Center and a Bottom Dead Center, comprising a step for acquiring the differential pressure measurement signal returned by the differential pressure sensor, characterized in that it comprises:
-a step of determining the frequency of this measurement signal,
-a step of comparing this frequency with the frequency of passage of all the pistons at Top Dead Center,
-a step in which it is diagnosed that the downstream tapping of the sensor is either:
- correctly connected if the frequency of the measurement signal is twice the frequency at which all the pistons pass through Top Dead Center,
- disconnected if the frequency of the measurement signal is equal to the frequency at which all the pistons pass through Top Dead Center.

The technical effect is to obtain a reliable diagnosis of a disconnection of the downstream tapping of the differential pressure sensor.

Various additional features may be provided, alone or in combination:

According to one embodiment, the method comprises a step of detecting authorization conditions for implementing the diagnosis.

According to one embodiment, the method comprises a step of detecting operating stability conditions of the heat engine.

According to one embodiment, the operating stability conditions of the heat engine are detected when the speed of the heat engine and the torque of the heat engine are within a predetermined range calibrated around their current value at least for a predetermined duration.

According to one embodiment, the step of determining the frequency of the differential pressure signal includes a step of filtering pressure peaks of amplitude lower than a determined pressure threshold.

According to one embodiment, the pressure threshold is determined as the average value of the differential pressure measurement signal returned by the differential pressure sensor.

According to one embodiment, a safety margin of between 5 and 15% of the mean value of the differential pressure measurement signal is added to the mean value of the differential pressure measurement signal.

According to one embodiment, the diagnosis of disconnection of the downstream tapping of the sensor is confirmed if several consecutive results of comparisons have shown that the frequency of the measurement signal is equal to the frequency of passage of all the pistons at Top Dead Center.

The invention also relates to an electronic computer, characterized in that it comprises the means for acquisition, processing by software instructions stored in a memory as well as the control means required for implementing a method according to one previously described variants.

The invention also relates to a vehicle equipped with a heat engine connected to an exhaust line comprising a particle filter instrumented with a differential pressure sensor, characterized in that it comprises such a computer.

Figure 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. 2 presents the phenomenon observed on the basis of the method of the invention.

Figure 3 is a representation of the steps of the method of the invention.

FIG. 1 represents a heat engine 1 in particular intended to equip a motor vehicle. The heat engine 1 is connected to an exhaust line 2 for the evacuation of the burnt gases produced by the operation of the heat engine 1.

Conventionally, the heat engine 1 comprises several cylinders 1a in line, here three in FIG. 1. The heat engine 1 can however have a different number of cylinders. In each of the cylinders 1a slides a piston, not shown. During operation of the heat engine 1, each of these pistons slides alternately between Top Dead Center, the highest point of its travel in its cylinder and a Bottom Dead Center, the lowest point of its travel in cylinder 1a.

The exhaust line 2 comprises a gaseous pollutant pollution control unit 3, for example an oxidation catalyst or a three-way catalyst. The three-way catalyst 3 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 2 further comprises a particulate filter 4 for filtering soot particles in the exhaust gases of the thermal engine 1. The particulate filter 4 is suitable for filtering soot particles originating from the combustion of the fuel.

In the particulate filter 4, 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 comprises a blocked end, so that the exhaust gases flowing in the particulate filter 4 pass from channel to channel, crossing the walls of the different channels to exit the particulate filter 4. The particulate filter 16 may be based on a porous ceramic matrix, for example cordierite, mullite, aluminum titanate or silicon carbide. If necessary, the depollution device 3 and the particle filter 4 can be installed inside the same envelope 5.

The exhaust line 2 is also provided with a sensor 6 for measuring the differential pressure between the upstream and downstream of the particulate filter 4 from which it is possible to deduce a mass of accumulated soot. Upstream and downstream are here defined relative to the direction of gas flow in the exhaust line 2. For this purpose, the sensor 18 is connected upstream and downstream of the particulate filter 16 respectively via an upstream branch 6a and a downstream branch 6b.

An electronic computer 7, for example the engine computer or a dedicated computer, makes it possible to carry out a diagnosis of the operation of the sensor 6 of differential pressure. To this end, the computer 7 comprises the means of acquisition, of processing by software instructions stored in a memory as well as the control means required to implement the diagnostic method of the invention.

The method of the invention allows the detection of a disconnection of the tapping 6b downstream of the differential pressure sensor 6 of the particulate filter 4 via the monitoring of the behavior of the high frequency pressure signal, which has substantially the form of a sinusoid, thus being able to distinguish its behavior when the downstream tapping 6b is not connected.

Figure 2 presents the phenomenon observed at the basis of the method of the invention. In FIG. 2, the dotted curve 20 illustrates a measurement of the pressure upstream of the particulate filter 4, at the level of the upstream tapping 6a. A signal is observed with a main frequency amplitude which is equal to the frequency at which all the pistons pass through Top Dead Center (arrow F1). This is explained by the fact that each time you go to TDC, a gas pulse is emitted at the output of the heat engine, which is found in the exhaust line. We can distinguish the presence of disturbances with an amplitude lower than that of the main signal and which appear between two PMH peaks. These disturbances come from the tubes of sensor 6 and are originally caused by the presence of pressure waves which form inside the tubes and which propagate along them.

Still in FIG. 2, the dotted curve 21 illustrates a measurement of the pressure downstream of the particulate filter 4, at the level of the downstream tapping 6b. There is still a signal with a main frequency amplitude which is equal to the frequency at which all the pistons pass through Top Dead Center. We also observe disturbances of amplitude lower than the main one which are located between the two main amplitude peaks.

The solid line curve 22 now represents the measurement of the differential pressure (upstream pressure - downstream pressure). It can be observed that the phase shift between the two signals 20 and 21 results in the amplification F3 of the disturbances between two TDCs. This therefore gives a differential pressure signal in which the disturbances have the same amplitude as the main signal. At first sight, the frequency of the differential pressure signal is 2 times greater than the frequency of passage of all the pistons at Top Dead Center.

Curve 23 in dotted lines represents the mean value of the differential pressure signal.

Thus if the sensor 6 is correctly connected upstream 6a and downstream 6b, the computer 7 will observe a differential pressure measurement signal 22 whose frequency is twice the frequency of passage of all the pistons at Top Dead Center. And if the differential pressure sensor 6 is disconnected downstream, the sensor 6 therefore measures the pressure upstream of the filter only, the frequency of which is the frequency of passage of all the pistons at Top Dead Center. Lower amplitude peaks are not counted in the calculation of the differential pressure signal frequency.

Figure 3 shows an embodiment of the method of the invention. The computer 7 receives a flow of information at the input of the diagnostic function, in particular the differential pressure measurement signal Dp returned by the sensor 6. The computer 7 preferably uses the raw signal from the sensor 6, without any filtering or processing. . The signal from sensor 6 is sampled at a high frequency to correctly follow the dynamics of the signal, preferably at least 1 kHz (for a sampling period equal to or less than 1 ms).

The computer 7 also receives as input the speed N of the heat engine, the torque C of the heat engine, which is a quantity representative of the load of the engine, the combustion mode M of the heat engine, the outside temperature Text.

The diagnostic function of computer 7 can generate Diag information on the connection status of the tapping downstream of sensor 6, as explained in more detail below.

The computer 7 verifies, in a step 30, that the diagnostic implementation authorization conditions are fulfilled.

In particular, the engine operating point which is a function of the speed N, and of the torque C must be within a range of calibratable values for which the method of the invention is deemed to be robust. These calibratable values can vary according to parameters such as the type of engine, the configuration of the exhaust line, the length of the tubes of the sensor 6. In the context of heat engines normally used on the automotive market for private vehicles , an example of implementation is a speed range N between 2000 and 3500 rpm an engine torque up to 75% of its maximum. Combustion mode M is preferably nominal, insofar as specific modes can falsify the measurement of sensor 6.

The outside temperature Text must be within a range of predetermined values that can be calibrated. For example, it is avoided to carry out the diagnosis in very cold conditions because frost is likely to form in the tappings 6a, 6b of the sensor 6, which can falsify the pressure difference measurement. According to an example implementation, the outdoor temperature Text must be at least greater than -7°C.

The computer 7 detects in a step 31 that stability conditions in terms of speed N and load of the heat engine are fulfilled. Under these conditions, the back pressure of the filter 16 also stabilizes, which makes it possible to establish a robust diagnosis on its measurement.

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

Similarly, a range of calibratable values is defined around a value of torque C. If torque C of heat engine 10 remains within this range of values for at least a calibratable duration of several seconds, then torque C is considered as being stable. The range of torque values C is for example defined by plus or minus 10% relative to the current torque C.

The stability conditions are detected if the speed N and the torque C of the heat engine are both considered to be stable.

If the authorization and stability conditions are met, the engine computer 7 then performs, in a step 32, the calculation of the frequency of the differential pressure measurement signal returned by the differential pressure sensor 6. To this end, this step 32 uses the differential pressure measurement signal Dp returned by the differential pressure sensor 6 and acquired by the computer 7 at the frequency of 1 kHz. The computer 7 can also calculate an average value of the differential pressure measurement signal Dp, Dpmay.

In order not to take into account the disturbances of pressures of amplitude lower than the main one which are located between the two main amplitude peaks in the calculation of the frequency, it is possible to plan to take into account only the higher pressure peaks to a calibratable pressure threshold for the frequency calculation of the differential pressure measurement signal returned by the differential pressure sensor 6.

This pressure threshold can be determined as being the average value of the differential pressure measurement signal, Dpmay, to which can also be added a safety margin of between 5 and 15%, for example approximately 10% of the average value Dmoy.

Then, in the next step 33, a comparison is made between the calculated frequency of the differential pressure measurement signal returned by the differential pressure sensor 6 and the frequency of passage of all the pistons at Top Dead Center, F _TDC .

The next step 34, either it is diagnosed that the downstream tapping of sensor 6 is correctly connected if the frequency of the measurement signal is twice the frequency of passage of all the pistons at Top Dead Center, F _PMH , or diagnoses that the downstream tapping of sensor 6 is disconnected if the frequency of the measurement signal is equal to the frequency of passage of all the pistons at Top Dead Center. The Diag connection state output information takes on a value accordingly to the result of this comparison.

Step 34 can include a confirmation step, in which it is ensured to have several consecutive comparison results for which the frequency of the measurement signal is equal to the frequency of passage of all the pistons at Top Dead Center to confirm that the downstream tapping of sensor 6 is disconnected. This number of consecutive results can be at least three consecutive results. This step improves the reliability of the diagnosis.

Claims (10)

Method for diagnosing a state of connection of a differential pressure sensor (6) connected upstream and downstream of a particulate filter (4) of a heat engine (1) respectively via a upstream tapping (6a) and a downstream tapping (6b), the thermal engine (1) comprising cylinders (1a) in each of which a piston slides between a Top Dead Center and a Bottom Dead Center comprising a step for acquiring the differential pressure measurement signal returned by the differential pressure sensor (6), characterized in that it comprises:
-a step (32) for determining the frequency of this measurement signal,
-a step (33) for comparing this frequency with the frequency at which all the pistons pass through Top Dead Center,
-a step (34) in which it is diagnosed (Diag) that the downstream tapping of the sensor (6) is either:
- correctly connected if the frequency of the measurement signal is twice the frequency at which all the pistons pass through Top Dead Center,
- disconnected if the frequency of the measurement signal is equal to the frequency at which all the pistons pass through Top Dead Center (F _PMH ). Method according to Claim 1, characterized in that it comprises a step (30) of detecting conditions for authorizing implementation of the diagnosis. Method according to claim 1 or claim 2, characterized in that it comprises a step (31) of detecting operating stability conditions of the heat engine (1). Method according to claim 3, characterized in that the operating stability conditions of the heat engine (1) are detected when the speed (N) of the heat engine (1) and the torque (C) of the heat engine (1) are in a predetermined range calibrated around their current value at least for a predetermined duration. Method according to any one of the preceding claims, characterized in that the step (32) of determining the frequency of the differential pressure signal comprises a step of filtering pressure peaks with an amplitude lower than a determined pressure threshold. Method according to the preceding claim, characterized in that the pressure threshold is determined as the average value (Dpmay) of the differential pressure measurement signal returned by the differential pressure sensor (6). Method according to the preceding claim, characterized in that a safety margin of between 5 and 15% of the average value (Dpmay) of the differential pressure measurement signal is added. Method according to any one of the preceding claims, characterized in that the diagnosis of disconnection of the tapping downstream of the sensor (6) is confirmed if several consecutive results of comparisons have shown that the frequency of the measurement signal is equal to the frequency of passage of all the pistons at Top Dead Center (F _PMH ). Electronic computer (7), characterized in that it comprises the means for acquisition, processing by software instructions stored in a memory as well as the control means required to implement a method according to one of the preceding claims . Vehicle equipped with a combustion engine (1) connected to an exhaust line (2) comprising a particle filter (4) instrumented with a differential pressure sensor (6), characterized in that it comprises a computer ( 7) according to the preceding claim.