FR3100278A1 - Method of controlling a heat engine for the detection of a freezing plug of a differential pressure sensor when the engine is stopped - Google Patents

Abstract

The present invention relates to a method for controlling a heat engine allowing the diagnosis of a differential pressure sensor of a pollution control member of a combustion gas exhaust line, in particular for the detection of a gel cap. The method comprises a step of measuring (21) at least a first value of back pressure of the pollution control unit at a first instant. According to the invention, the method consists in carrying out the back pressure measurement (21) in a condition of zero flow of exhaust gas passing through the pollution control member and in activating (24) a diagnostic signal representative of a state sensor abnormality when the first value is outside a predetermined value range around the zero pressure value. Figure for the abstract: figure 2

Description

Method for controlling a heat engine for detecting a frost plug in a differential pressure sensor when the engine is stopped

The field of the invention relates to a heat engine control method for detecting an operating anomaly of a differential pressure sensor of the combustion gas exhaust line.

As is well known, the exhaust lines of internal combustion internal combustion engines with spark ignition and self-ignition by compression are equipped with pollution control devices, such as particulate filters. To ensure the correct operation of a particulate filter, diagnostic sensors are used to carry out diagnostics required by regulations, for example OBD diagnostics, as well as safety diagnostics.

For example, we know the French patent document FR2979017A1 describing a sensor assembly fitted with a probe and a tapping to introduce the probe inside the exhaust line.

In addition, other types of sensors are essential for monitoring an exhaust line, such as the differential pressure sensor which measures the pressure of the exhaust line upstream and downstream of a particulate filter in the direction of exhaust gas flow. The differential pressure sensor makes it possible in particular to detect clogging of the particle filter. A differential pressure sensor comprises, upstream and downstream of the particle filter, a combustion gas bypass pipe which connects a tapping of the exhaust line to an inlet of the sensor so as to measure the differential pressure of the gases d 'exhaust.

In cold weather, a frost plug may form in one of the branch pipes. Indeed, the electronic module of the sensor is generally installed under the bonnet of the vehicle, in the front part at the level of the apron, and because of this position it is subjected to temperatures below zero degrees and to air flows which can cause water freezing in the branch pipe. The formation of a gel plug causes a false detection of a failure of the particle filter, possibly a detection of clogging. The customer is then likely to take his vehicle to the after-sales service for an intervention, or even an unnecessary replacement of the particle filter.

There is therefore a need to overcome the aforementioned problems and to reduce the number of false detections, in particular those caused by a gel plug in the branch pipes of a differential pressure sensor. An object of the invention is to propose a method for controlling the heat engine allowing the detection of a frost plug in one of the sensor branch pipes.

More specifically, the invention relates to a method for controlling a motor vehicle internal combustion heat engine for diagnosing a differential pressure sensor measuring the pressure upstream and downstream of a depollution device inside of the duct of the combustion gas exhaust line of the heat engine, comprising the following steps: measuring at least a first value of back pressure of the depollution device at a first instant. According to the invention, the method consists in carrying out the measurement under a condition of zero flow of exhaust gas passing through the depollution device and further comprises a step of activating a diagnostic signal representative of a state of sensor anomaly when the first value is outside a predetermined range of values around the zero pressure value.

According to a variant, the range of values is delimited by the values [−6mbar; +6mbar].

According to a variant, the method also comprises the measurement of a second backpressure value at a second instant, and the activation of the diagnostic signal is also a function of a difference between the first and second backpressure values.

According to a variant, the diagnostic signal is activated in the event of detection of a difference between the at least said first and second values which is greater than a predetermined threshold.

According to a variant, the predetermined threshold has a value greater than 6 mbar, and preferably between 6 mbar and 100 mbar.

According to a first case of triggering the measurement, the measurement is triggered between an instant of detection of an engine key contact and an instant of detection of an engine starting phase.

According to a second case of triggering of the measurement, the measurement is triggered between a moment of detection of an engine stop and a moment of stopping the supply of a heat engine control computer.

According to a first sequence of the method, a first measurement is triggered between a moment of detection of an engine key contact and a moment of detection of an engine starting phase and a second successive measurement between a moment of detection of a stop engine and a moment of stopping the power supply to the heat engine control computer.

According to a second sequence of the method, a first measurement is triggered between a moment of detection of an engine stoppage and a moment of stopping the supply of the heat engine control computer and a second successive measurement is triggered between a moment detection of an engine key contact and an instant of detection of an engine starting phase.

According to a variant of the method, the anomaly state is representative of the presence of a gel plug at the level of a sensor gas bypass pipe.

The invention also relates to a motor vehicle comprising an internal combustion heat engine controlled by a control computer, and a combustion gas exhaust line comprising a pollution control unit and a differential pressure sensor upstream and downstream of said unit. depollution. According to the invention, the control computer is configured to implement the control method according to any one of the preceding embodiments for the diagnosis of the differential pressure sensor.

The invention also provides a program-computer product comprising instructions which, when the program is executed by an engine control unit, lead the latter to implement any one of the embodiments of the control method for the diagnosis of the differential pressure sensor.

The invention makes it possible to reliably detect a frost plug forming in one of the combustion gas bypass pipes towards an inlet of the sensor resulting from the residual pressure during the formation of a plug. It also helps to avoid false detections that can result from a sensor's drift values. The invention makes it possible to detect false detections concerning an anomaly in the state of the particle filter.

Other characteristics and advantages of the present invention will appear more clearly on reading the following detailed description comprising embodiments of the invention given by way of non-limiting examples and illustrated by the appended drawings, in which:

schematically represents an exhaust line of an internal combustion engine comprising a depollution device provided with a differential pressure sensor.

represents an algorithm of the engine control method according to the invention automatically allowing the detection of an anomaly of the differential pressure sensor.

represents a driving sequence of a motor vehicle and the execution of the control method according to the invention during this sequence.

The control method according to the invention allows the automatic detection of an operating anomaly of a differential pressure sensor controlling a depollution device of an exhaust line of an internal combustion heat engine. The control method is executed by the thermal engine control unit and automatically executes backpressure measurements of said component throughout the life of the vehicle in order to avoid false detection of anomalies in the pollution control component. The invention will be described in this variant for a differential pressure sensor of an internal combustion engine particulate filter of the self-ignition by compression type, or piloted ignition. It is envisaged that the invention can also be applied to any type of exhaust line pollution control device provided with a differential pressure sensor, such as a catalyst or any type of particulate filter.

More precisely, in FIG. 1, a part of a combustion gas exhaust line of an internal combustion heat engine of a motor vehicle is schematically represented. A depollution unit 1 is mounted in the exhaust line and in which the combustion gases circulate from upstream to downstream according to the arrow shown inside the combustion gas circulation duct. The depollution device 1 comprises a metal casing in which two depollution sub-devices are installed next to each other, first of all a catalyst 3 then a particulate filter 2 according to the direction of circulation of the gases burning. This side-by-side arrangement of the catalyst and the particulate filter is in no way limiting and other arrangements are possible and in no way affect the scope of the invention. In particular, the exhaust line can be fitted with other pollution control devices, for example a second catalyst upstream of catalyst 3.

In addition, a differential pressure sensor 4 is mounted in the vehicle, in the area under the bonnet generally close to the heat engine computer, and is capable of measuring the pressure of the combustion gases upstream and downstream of the particulate filter. For this purpose, the sensor is provided with a first bypass pipe 5 of the gases connected to a first tapping 9 of the exhaust line upstream of the particulate filter 2, and with a second bypass pipe 6 of the gases connected to a second tapping 8 downstream of the particle filter 2. It is recalled that a tapping is in the form of a ring allowing access for a probe or a pipe inside the metal casing in the exhaust gas circulation area. In the case of the differential pressure sensor, a tapping allows the derivation of the gases towards an inlet of the sensor.

The sensor 4 works out a measurement called counter-pressure measurement, calculating the difference between the downstream pressure P2 and the upstream pressure P1 and supplies a voltage proportional to the counter-pressure measurement. A backpressure measurement is equal to the following relationship: Delta P = P1-P2, or Delta P = P2-P1. Ideally, when a back pressure measurement corresponds to a value of 0 bar, this means that the engine is stopped and the flow of combustion gases is zero. When the back pressure value reaches approximately 0.9 bar, this value is indicative of clogging of the particle filter.

Furthermore, at zero flow, when a backpressure measurement indicates a non-zero value, this situation is likely to be caused by the presence of a gel plug 7 in one of the branch pipes, upstream and/or downstream. In fact, when the engine is running, the bypass pipes 5 and 6 are subjected to the pressure of the exhaust line at the level of the connections 9 and 8. When a blockage forms, the column of gases which is between the plug 7 and sensor 4 remains at a pressure equal to that which existed when plug 7 was formed. When the engine stops, the residual pressure between plug 7 and sensor 4 remains higher or lower than the value of 0 bar. The control method according to the invention aims to specifically detect this situation.

Figure 2 shows the process for controlling the heat engine making it possible to detect the formation of a frost plug in one of the gas bypass pipes towards the sensor. The process is implemented by the heat engine control unit, which is equipped with an integrated circuit computer and electronic memories. The computer and the memories are configured to execute the control method. But this is not mandatory. Indeed, the computer could be external to the heat engine control unit, while being coupled to the latter. In the latter case, it can itself be arranged in the form of a dedicated computer comprising a possible dedicated program, for example. Consequently, the control unit, according to the invention, can be produced in the form of software (or computer (or even “software”)) modules, or else of electronic circuits (or “hardware”), or even of a combination of electronic circuits and software modules.

The control method can be executed according to several embodiments to detect and signal a freeze plug in one of the branch pipes. The control method is activated when temperatures below zero degrees Celsius are detected during vehicle start-up, vehicle shutdown, or at any time between vehicle startup and shutdown.

More precisely, the method comprises a step 20 of detecting a condition for triggering the measurement at zero gas flow, then the control of a measurement step 21 of a backpressure value. Several situations are possible to trigger the measurement of a back pressure value when the engine is stopped.

A first trigger condition consists in detecting, in step 20, a parameter representative of a key contact when starting the engine, then in the event of detection of a key contact to be controlled, in step 21, the measurement of back pressure. The key contact is detected for example when a parameter specific to key detection changes value, in a state of "no contact" to a "key contact" state. The measurement of the back pressure is recorded, in a step 22, in the memory of the heat engine control unit. It will be noted that the measurement 21 is carried out after an instant of detection of an engine key contact and before an instant of triggering of an engine start-up phase to ensure zero gas flow in the exhaust line .

A second triggering condition consists in detecting, in step 20, a parameter representative of a moment when the heat engine is stopped, then in the event of detection, in step 21, controlling the counter-pressure measurement. The engine stop instant is detected for example from an engine state signal, "rotating state", "non-rotating state", the value of the engine shaft speed, or any type of signal or combination of signals to detect engine stoppage. The measurement of the back pressure is recorded, in a step 22, in the memory of the heat engine control unit. Measurement 21 is then carried out between a moment of detection of engine stoppage and a moment of stopping the power supply to the heat engine control computer. For the latter case, the ECU Power Latch logic signal can be monitored.

For the latter case, measurement 21 is authorized when a signal representative of the engine state indicates an engine state stopped and after the expiry of a predetermined time, for example five seconds, so as to ensure that the flow rate of the gas is effectively zero. The detections are carried out using information circulating on a data communication bus of the control unit of the heat engine, such as a CAN bus.

When the memory of the control unit contains a single M1 back pressure value and this value is different from 0 bar, this situation is likely to indicate the presence of a gel plug. A diagnostic signal can then be activated to signal this anomaly from the first measurement.

However, it happens that a differential pressure sensor indicates at zero flow a bypass value, due to a production dispersion of the sensor, of +/- 4 mbar as a 3 sigma value of the total production, this value being able to increase with aging and extreme temperatures in hot and cold. The bypass value can possibly reach 6 mbar at zero gas flow, instead of a normal value of 0 bar.

To this end, the control unit checks in a step 23 whether this first measurement M1 is outside the range of values delimited by the values [-6mbar; +6mbar], or greater than a predetermined threshold in absolute value, of a value of approximately 6mbar, or less than -6mbar, so as to rule out the situation of a sensor derivation value. In such a case, the method activates in a step 24 a diagnostic signal in a first state which is representative of an anomaly state of the sensor indicating the formation of a gel plug.

However, if the value of the first backpressure measurement M1 is within the range of values delimited by the values [-6mbar; +6mbar], compatible with both a freeze plug and a bypass value, the process is configured not to activate the diagnostic signal and to renew the backpressure measurement. Deactivated, the diagnostic signal is then driven into a second state which is representative of a correct operating state of the sensor. The cause of a back pressure value in the value range [-6mbar; +6mbar] not being certain, the control unit is advantageously configured to renew the measurement at a later time.

It is understood that the value range can be adapted, that is to say restricted or widened around the zero pressure value according to the sensor technology used and according to the derivation values that can be expected at zero gas flow. burning.

Then, the method again executes the control steps 20 to 24 in a loop. The method returns to step 20. If, at a later time, one of the two triggering conditions representative of engine stopping is detected, the method, in step 21, measures a second backpressure value M2. Between the two instants of the measurements of the values M1 and M2, the vehicle will have traveled (between a starting instant and a stopping instant) or will have remained stationary (between a stopping instant and a starting instant ). In step 22, the method saves the second counter-pressure value M2 in the memory of the control unit.

In step 23, the method checks this time whether there is a difference in value between the first measurement M1 and the second measurement M2. If this difference between the first and the second measurement is greater than 6 mbar, the diagnostic signal is activated in step 24 to warn of the presence of a gel plug. The M1 value is considered to be the value at zero flow, and therefore if this difference between M1 and M2 is greater than 6mbar then this is an indicator of the formation of a gel plug. By measuring from the second measurement cycle the difference between the values M1 and M2, the situation of detection of a sensor deviation value is ruled out. Otherwise, if the difference between M1 and M2 is less than 6mbar, the diagnostic signal is not activated.

As a variant, the method also verifies whether the measurement M2 is greater than the predetermined threshold in absolute value, with a value of approximately 6 mbar or more (or less than −6 mbar). If the M2 measurement is above the predetermined threshold of 6mbar and the M1 measurement is below the threshold, this situation indicates that a gel plug has formed between the instants of the M1 and M2 measurements. The control unit therefore activates the diagnostic signal at step 24 to alert of the presence of a gel plug. Otherwise, if the M2 measurement is within the value range [-6mbar; 6mbar] then the diagnostic signal is not activated.

Steps 20 through 24 are performed throughout the vehicle's life cycle. A number of N counter-pressure measurements are thus continuously recorded in the memory of the thermal engine control unit, where N can be equal to or greater than 1. At each instant of stopping of the engine for a duration of at least greater than 5 seconds, a measurement N is compared with measurement N-1, or it is checked whether the latter is positioned in the range of values [-6mbar;6mbar].

FIG. 3 represents an example of the sequence of the control method according to the invention. During a first phase, the control unit detects a starting phase of the vehicle and performs a first measurement M1 prior to starting the start. At time t1, the control unit detects a key contact, performs the very first measurement of the back pressure M1 at zero combustion gas flow, then triggers start-up at time t2. If the M1 measurement is greater than 6mbar, then a diagnostic signal is activated informing the formation of a gel plug. If the M1 measurement is between -6mbar and 6mbar then the diagnostic signal is not activated. In this case, the vehicle operates a trip TR1.

Then at time t3, the vehicle comes to a stop. At time t3, the control unit detects a stoppage of the heat engine. After a delay of approximately 5 seconds, the control unit performs a second back pressure M2 measurement, then performs a diagnostic check. If the M2 measurement, or if the difference between M2 and M1, is greater than 6 mbar, then a diagnostic signal is activated informing the formation of a gel plug that has taken place during the trip TR1. If the M2 measurement, or the difference between M2 and M1, is between -6mbar and 6mbar then the diagnostic signal is not activated. At time t4, the power to the control unit is turned off ("power Latch"). The vehicle is stationary during the rear phase.

Then, at time t5, the control unit detects a key contact. A third counter-pressure measurement M3 is taken then triggers start-up at time t6. A path TR2 is performed. If the M3 measurement, or if the difference between M3 and M2, is greater than 6 mbar, then a diagnostic signal is activated informing the formation of a frost plug having occurred during the AR stop. If the M3 measurement, or the difference between M3 and M2, is between -6mbar and 6mbar then the diagnostic signal is not activated. The control process repeats itself continuously throughout the vehicle's life cycle.

It is also specified that the control of the diagnostic signal representative of the state of the particle filter can be conditioned to the value of the diagnostic signal representative of the state of the sensor. This avoids the emission of false alerts when the sensor is faulty.

Claims (10)

Method for controlling a motor vehicle internal combustion heat engine for diagnosing a differential pressure sensor (4) measuring the pressure upstream and downstream of a depollution device (2) inside the duct of the exhaust line (1) of the combustion gases of the thermal engine, comprising a step of measuring (21) at least a first value (M1) of counter-pressure of the depollution unit at a first instant ( t1), characterized in that it consists in carrying out the measurement (21) in a condition of zero exhaust gas flow passing through the depollution device (2) and in that it further comprises an activation step (24) of a diagnostic signal representative of an abnormal state of the sensor when the first value (M1) is outside a range of predetermined values around the zero pressure value. Control method according to Claim 1, characterized in that the range of values is delimited by the values [-6mbar; +6mbar]. Control method according to Claim 1 or 2, characterized in that it further comprises the measurement of a second counter-pressure value (M2) at a second instant (t2), and in that the activation (24 ) of the diagnostic signal is also a function of a difference between the first and second backpressure values (M1, M2). Control method according to Claim 3, characterized in that the diagnostic signal is activated in the event of detection of a difference between the at least said first and second values (M1, M2) which is greater than a predetermined threshold. Control method according to Claim 4, characterized in that the predetermined threshold has a value greater than 6 mbar, and preferably between 6 mbar and 100 mbar. Control method according to any one of Claims 1 to 5, characterized in that the measurement (21) is triggered between an instant (t1) of detection of an engine key contact and an instant (t2) of detection of a engine starting phase. Control method according to any one of Claims 1 to 6, characterized in that the measurement (21) is triggered between a moment of detection (t3) of engine stopping and a moment (t4) of stopping the power supply to a heat engine control computer. Control method according to Claims 6 and 7, characterized in that a first measurement (M1) is triggered between an instant (t1) of detection of an engine key contact and an instant (t2) of detection of a starting of the engine and a second measurement (M2) successive between a moment (t3) of detection of an engine stop and a moment (t4) of stopping the supply of the heat engine control computer. Control method according to Claims 6 and 7, characterized in that a first measurement (M2) is triggered between an instant of detection of an engine stop (t3) and an instant (t4) of power supply of the thermal engine control computer and a second successive measurement (M3) is triggered between a time (t5) of detection of an engine key contact and a time (t6) of detection of an engine starting phase. Control method according to any one of Claims 1 to 9, characterized in that the anomaly state is representative of the presence of a gel plug at the level of a sensor gas bypass pipe.