FR3068779A1 - DETERMINING THE LEVEL OF A LIQUID IN A RESERVOIR - Google Patents

Abstract

The invention provides a method for determining the level of liquid additive in a liquid additive tank of a motor vehicle exhaust gas treatment system equipped with a liquid level measurement system. The method firstly relies on the determination that a set of conditions inherent to the operation of the vehicle and the gas treatment system are satisfied or not. And, secondly, to use these conditions to choose either the measured value or the simulated value as a value determined by the system for measuring the level of liquid in the reservoir.

Description

The present invention relates generally to exhaust gas treatment systems for motor vehicles. It relates more particularly to a method for determining the level of a liquid additive used in an exhaust gas treatment system of a motor vehicle, such as a treatment system by selective catalytic reduction.

The invention finds applications, in particular, in vehicles equipped with diesel engines, for example in light vehicles, vehicles of the utility type or in trucks (or heavy goods vehicles) comprising such an engine.

The exhaust gases generated by vehicles with compression-ignition engines (called diesel engines) or by vehicles with positive-ignition engines (called petrol engines), are in particular composed of gaseous air pollutants such as carbon oxides (COx for CO and CO ₂ ) and nitrogen oxides (NOx for NO and NO ₂ ). Diesel engines, in particular, are subject to regulations aimed at reducing the quantity of polluting gases they emit. The standards capping the levels of nitrogen oxides emitted are an example of this, they tend to be more and more restrictive.

In the particular case of vehicles equipped with a diesel engine, the depollution of the engine exhaust gases can be carried out by means of a gas treatment device implementing a depollution method such as the selective catalytic reduction method. ("SCR, Selective catalytic reduction" in Anglo-Saxon language). The SCR method uses a depolluting liquid additive in order to selectively reduce the nitrogen oxides (NOx) contained in the exhaust gases. By depolluting liquid additive is meant a depolluting product which can be injected into an exhaust gas treatment device of an engine in order to depollute the exhaust gases before they are released into the atmosphere.

The liquid additive commonly used in the SCR method is called “diesel exhaust fluid” or FED (“Diesel exhaust fluid”, or DEF, in English) which is a 32.5% aqueous urea solution ( by weight), also marketed under the brand AdBlue®. The aqueous urea solution is a precursor of ammonia (NH ₃ ), and this ammonia reacts with the nitrogen oxides (NOx) of the exhaust gases to give less polluting species, namely dinitrogen (N ₂ ) , water and carbon dioxide (CO ₂ ). Thus, the ammonia used in the SCR method is a reducing agent, supplied in the form of a liquid additive.

In vehicles, the liquid additive is stored in a dedicated tank, which is equipped with a dosing module also called a liquid additive distribution device. The liquid additive dispensing device is adapted to take the liquid additive, dose a determined quantity and inject it into the exhaust gas treatment device for the purpose of cleaning up said gases. For this, the device for dispensing liquid additive comprises a housing in which are arranged functional components such as in particular means for pumping the liquid additive and / or means for dosing the additive, means for measuring the quantity of liquid additive in the tank, and sensors.

The means for measuring the amount of liquid additive in the tank allow the vehicle user to be informed of the amount of FED present in the tank. Due to the strict regulations surrounding exhaust gas pollution control, the user of a diesel vehicle must be alerted, if necessary, that the tank will soon be empty in order to be able to refill accordingly. In addition, this type of vehicle may see its engine torque voluntarily reduced or may be forced to stop completely when the quantity of FED present in the tank is considered insufficient or when the tank is empty, in the interests of respecting the 'environment.

It is therefore desirable to be able to provide vehicle drivers, with satisfactory accuracy and frequency of updates, with information concerning the quantity of FED remaining in the tank.

An approach already known for measuring the level of liquid additive in the dedicated tank of a motor vehicle is based on the use of an ultrasonic sensor. In general, this type of sensor is located at the bottom of the tank. The sensor is either immersed in the liquid or is placed outside the tank by being coupled to the tank by means of a medium allowing the transmission of the ultrasonic waves emitted and reflected through the wall of the tank.

Typically, the sensor comprises a transmitting unit and a receiving unit which are functionally separate but which can, in certain embodiments, be structurally combined into a single transmitting / receiving unit. The transmitting unit emits an ultrasonic wave which propagates through the liquid. The receiving unit picks up the reflected wave from the surface of the liquid in the tank, which reflects the amount of liquid additive remaining in the tank. The level measurement is based on determining the propagation time of the ultrasonic wave in a liquid whose properties are known, and in a tank whose geometry and dimensions are also known. Knowledge of the properties of the liquid includes in particular knowledge of the speed of propagation of the wave in the liquid and therefore allows the conversion of a propagation time into a distance traveled by the ultrasonic wave in the liquid, hence the 'We finally obtain information relating to the level of liquid additive present in the tank.

However, the properties of the liquid are not always known a priori, and they are also subject to variations due to variations in temperature or concentration of the liquid, in particular. Therefore, the measurement of the liquid level may require calibration in order to determine the actual speed of propagation of the ultrasonic wave in the propagation medium for each measurement. This calibration can be based on the use of one or more reflectors for the ultrasonic wave, which are located at determined positions in the tank (being located at distances from the ultrasonic transmission / reception unit which are known). Thus, by exploiting the respectively measured propagation times for the reflections generated by these reflectors, it is possible to calibrate the level measurement by determining the actual propagation speed of the wave in the liquid at a given instant.

An approach for measuring the level of FED in the reservoir based on the use of an ultrasonic sensor and two reflectors for calibration has for example been proposed in document WO 2016/008832 A1. It includes the use of two reflectors located vertically above the ultrasonic transmitter: one is close to the bottom of the tank and the other is located at a greater height to allow the liquid level in the tank even in situations of low filling. Thus, the propagation time used to determine the propagation speed can be either the propagation time between the two reflectors (when the tank is relatively full), or the propagation time between the emitter and the first reflector (when the tank is relatively empty).

Another approach, proposed in document WO 2015/1997792 A1, includes the use of an even greater number of reflectors (four in this case). This allows the ultrasonic wave to follow a path in the liquid which has vertical portions and horizontal portions. The distances between the submerged reflectors can thus be relatively large and significant whatever the level of liquid, which allows greater precision in determining the speed of propagation of the ultrasonic wave in the liquid concerned.

In summary, for both of these approaches, as for all approaches based on the use of an ultrasonic sensor integrated into the reservoir, the principle of measurement requires the precise determination of propagation times in the liquid from a transmitter to one or more reflective surfaces, whether it is the surface of the liquid stagnating in the tank or the surface of reflectors.

However, with regard to the EDF contained in a dedicated tank of a motorized vehicle, the measurement may be subject to disturbances preventing the proper exploitation of the measurement results obtained. In particular, the EDF freezes at a temperature of -11 ° C and, in the event of liquid freezing, the measurement based on the propagation of the ultrasonic wave in this medium is distorted or even impossible to perform. In the same way, an ice cavity (ie liquid surrounded by ice) can form within the reservoir when the liquid is in the thaw phase thanks in particular to means for heating the liquid provided in the dosing module, and this can lead to a false level measurement.

In addition, other causes can also lead to the fact that the level measurement based on the use of the ultrasonic sensor will be falsified. For example, when the vehicle, and by association the FED tank, is subjected to significant movements, bubbles can form and the surface of the liquid can move so that the wave which propagates within it can be either attenuated, or deviated and thus distort the measurement or even make it impossible. In addition, this type of sensor has intrinsic limitations associated with so-called “gray areas” measurement zones for which any measurement is affected by a non-negligible uncertainty. Indeed, some levels simply cannot be measured as long as they correspond to a window (i.e. a level range) given in a gray measurement area of the sensor.

Thus, for all the above reasons, it appears that the use of a level measurement based on the use of a physical sensor of the type of an ultrasonic sensor is insufficient in certain situations. It then obliges the user, in the best of cases, to wait until the measurement can be carried out in good conditions. For example after the liquid has warmed up after prolonged parking in winter, or after the vehicle has stabilized following movements that have caused the liquid in the tank to oscillate. However, it does not guarantee the user that it will be obtained quickly and regularly over time, with a reliable value enabling the remaining quantity of FED in the dedicated tank to be known. For example, for certain heavy goods vehicles whose tank can reach up to 80 liters of liquid additive, the complete thawing of the liquid contained in the tank can take 3 to 4 hours.

The invention aims to eliminate, or at least mitigate, all or part of the disadvantages of the aforementioned prior art.

To this end, a first aspect of the invention proposes a method for determining the level of liquid additive in a liquid additive tank of a motor vehicle exhaust gas treatment system also having a measurement system. of liquid level in said tank which comprises a sensor and a digital processing unit, characterized in that said method comprises the following steps implemented in the liquid level measurement system from the start of the vehicle, for the determination by the digital processing unit of a value of level of liquid additive in the tank:

if • the values of the liquid additive level acquired by the liquid level measurement system using the sensor satisfy a determined validity criterion, then:

• the value of the level of liquid additive which is determined is a value of level of liquid acquired using the sensor;

otherwise, the value of the level of liquid additive which is determined is a value of level of liquid estimated by calculation from at least one value of level of liquid previously acquired using the sensor and stored in a memory of the processing unit, in relation to a quantity of liquid additive consumed since said previously acquired liquid level value has been acquired and stored.

Embodiments taken individually or in combination, further provide that:

• the validity criterion for the liquid additive level values acquired by the liquid level measurement system is satisfied if, and only if, any set of N conditions among the following eleven conditions, where N is an integer included between 1 and 11, is satisfied:

A. a self-diagnostic module of the liquid level measurement system determines that said system acquires valid liquid levels;

B. the level of liquid additive determined by the liquid level measurement system is not included in a first window or in a second window each corresponding to ranges of respective levels of liquid additive level;

C. the variation in the values of the liquid additive level obtained using at least two successive acquisitions made by the sensor of the liquid level measurement system is less than a determined threshold value;

D. a determined number of values of the level of liquid additive successively acquired in the same range of values using the sensor of the system for measuring the level of liquid is reached since an initialization of the system for measuring the level of liquid;

E. the cumulative running time of the engine, over one or more operating cycles close to the engine, since the start of said engine of the motorized vehicle is greater than a determined threshold;

F. the quantity of liquid additive that has been consumed since a full filling of the liquid additive tank is greater than a determined threshold;

G. the motorized vehicle is static or in driving conditions satisfying a determined stability criterion; and,

H. the value of the liquid additive level acquired using the sensor of the liquid level measurement system is above a determined threshold;

I. the temperature of the measured liquid additive is above a determined temperature threshold;

J. an ice cavity is not detected in the liquid additive tank; and,

K. a liquid additive heating source integrated in the liquid additive tank is not in use.

• the validity criterion for the values of the level of liquid additive acquired using the sensor of the level measurement system is satisfied, moreover, if at least one of the following conditions is satisfied:

L. a full filling of the liquid additive tank is detected; and,

M. the level of liquid additive determined using the sensor of the liquid level measurement system is higher than the last level of liquid additive measured, increased by a determined value.

• the liquid level measurement system sensor is an ultrasonic sensor:

- the acquisition by the liquid level measurement system includes:

• the acquisition, by the ultrasonic sensor, of measurement values corresponding to the propagation times of an ultrasonic wave in the liquid between its emission and the reception, by the sensor, of reflected ultrasonic waves, respectively, by at at least two reflectors located in the liquid at respective determined positions and by the surface of the liquid in the tank; and, • the processing by the digital processing unit of the measurement values acquired by the sensor, said processing comprising the calculation of liquid additive levels on the basis of the measurement values acquired by the sensor;

- the driving conditions which satisfy the stability criterion include at least one of the following conditions:

• the instantaneous speed of the vehicle is between two determined threshold values; and, • the vehicle engine rotation speed is between two determined threshold values; and, • the engine torque produced by the vehicle engine is between two determined threshold values;

- the detection of an ice cavity includes:

the detection of an ice cavity is positive if:

• the time course of the temperature of the measured liquid additive increases; or, • the time course of the measured level of liquid additive decreases; or, • the heating source is in use;

while the detection of an ice cavity is negative if:

• the difference between the level of liquid additive measured and the level of liquid additive estimated is less than a determined threshold value; or, • the time course of the measured level of liquid additive increases; or, • a full filling of the liquid additive tank is detected;

- The first and second windows of condition B also correspond to ranges of propagation time values acquired by the sensor;

- for condition D, a determined number of successive measurement values of the propagation times of the ultrasonic wave in the liquid, acquired in the same range of values, is reached for each of the following measurement values:

• the propagation time between the sensor and the first reflector; and, • the propagation time between the sensor and the second reflector; and, • the propagation time between the sensor and the surface;

- for condition C, the variation of the propagation time value obtained for at least two successive measurements is less than a value determined for each of the following measurements:

• the propagation time between the sensor and the first reflector; and, • the propagation time between the sensor and the second reflector; and, • the propagation time between the sensor and the surface;

- for condition F, the determined quantity of liquid additive consumed corresponds to two different determined values depending on whether the motorized vehicle is static or in motion since an initialization of the liquid level measurement system;

- the driving conditions which satisfy the stability criterion also include at least one of the following conditions:

• the temporal variation of the instantaneous speed of the vehicle is between two determined threshold values; and, • the time variation of the vehicle engine rotation speed is between two determined threshold values; and, • the time variation of the engine torque produced by the vehicle engine is between two determined threshold values;

- for condition E, the threshold to which the cumulative running time of the elapsed engine is compared is a function of the temperature (s) of the measured liquid additive (s).

According to the second aspect, the invention also relates to a system for measuring the level of liquid in a tank for liquid additive comprising means capable of carrying out all of the preceding steps of the process alone or in combination.

According to the third aspect, the invention also relates to a motor vehicle having an internal combustion engine, an exhaust gas treatment device and a reservoir for containing the liquid additive used by the device to depollute the exhaust gases. exhaust of said engine, said tank comprising a system for measuring the level of liquid in the tank according to the second aspect of the invention.

Other characteristics and advantages of the invention will become apparent on reading the description which follows. This is purely illustrative and should be read in conjunction with the accompanying drawings in which:

- Figure 1 is a block diagram of a motor vehicle engine with an exhaust gas treatment device for NOx reduction comprising a system for measuring the level of liquid additive in a tank;

- Figure 2 is a diagram illustrating the operation of an ultrasonic sensor according to the state of the art for measuring the level of a liquid in a tank;

- Figure 3 gives an illustration of the operation of an ultrasonic sensor of Figure 2;

- Figure 4 is a step diagram illustrating a context in which the method of measuring the level of a liquid in a tank can be implemented; and,

- Figure 5 is a diagram of steps illustrating an embodiment of the method.

In the description of embodiments which follows and in the figures of the appended drawings, the same or similar elements bear the same reference numbers.

Figure 1 schematically shows a motor vehicle 101 with an internal combustion engine 102, for example a diesel engine. The motor vehicle 101 is for example a passenger car, a utility vehicle, a truck or a coach. The motor vehicle 101 also includes a device 103 for treating exhaust gases with a module 104 for implementing the SCR depollution method. The vehicle 101 also comprises a reservoir 105 for the liquid additive, coupled to an injector 108 for introducing the liquid additive into the device 103 for treating gases, by means of a module 106 for dosing liquid additive.

The metering module 106, or device for dispensing liquid additive, comprises a housing in which are arranged, in particular, functional components for withdrawing the liquid additive and for delivering various information on the quantity and quality of the liquid additive present in the reservoir 105. Among the functional components arranged in the housing, there are for example: a pump for withdrawing liquid additive from the reservoir, conduits for conveying the liquid additive withdrawn by the pump towards the injector 108, at least one valve, various sensors such as level, pressure, temperature and / or flow sensors, an electronic control unit, filters, a heater, etc.

The housing of the metering module 106 is partially disposed in the interior space of the reservoir 105. The part of the housing disposed in the reservoir 105 provides a surface in contact with the liquid additive present in the reservoir. The housing also has another part which is in contact with the reservoir 105. These two parts can be made of aluminum for example. Thus, a heating device can be connected to these aluminum parts in order to transmit heat to the liquid additive by conduction, to heat the liquid in winter, for example. In addition, the additive reservoir and the housing of the dosing module advantageously form a compact assembly thus saving space in the motor vehicle. In the configuration as shown in Figure 1, for example, the housing does not protrude.

When the engine 102 is running, it produces exhaust gases, and these gases are directed to the exhaust gas treatment device 103. The exhaust gas treatment device 103 is supplied with liquid additive thanks to the distribution device liquid additive 106 and to the injector 108. The metering module 106 doses the quantity of liquid additive to be injected. Then, thanks to the conduit 107 to which the module 106 is connected, the liquid additive is sent to the injector 108. The injector 108 introduces the depolluting solution into the module 104 in order to allow the selective catalytic reduction of NOx according to the SCR method . The exhaust gas pollution control is thus operated.

The liquid additive extracted from the reservoir circulates via the channel 107 and is injected under the control of the metering module, only when necessary and only in the quantity required, into the enclosure of the depollution device 103 via an injector 108.

In parallel, the measurement of the level of liquid additive (FED) present in the reservoir is carried out, for example continuously (that is to say, in practice, at regular time intervals), by an ultrasonic sensor 109 , also located in the tank or coupled to the tank. This measurement allows you to know at all times the quantity of FED remaining in the tank. All the liquid level measurement and injection control operations are then, in the example corresponding to FIG. 1, controlled by a control unit 110 of the dosing module.

With reference to Figure 2, we will now explain the operation of the ultrasonic sensor 109 for measuring the level of FED in the reservoir 105 of Figure 1, in an example where this type of sensor is used for this purpose.

The reservoir 105 contains a metering module 106 integrated into its wall 201, which is adapted and used to extract the liquid additive in the quantities just necessary. The ultrasonic sensor 109 is integrated into the module 106, for example at the bottom of the tank. Its surface 202 is flush with the wall formed by the module 106. After having been emitted by the ultrasonic emission / reception unit of the sensor 109, the ultrasonic waves penetrate directly into the liquid (if necessary after having passed through a wall through which the wave propagation time is known and taken into account, or considered negligible).

In the particular case illustrated in Figure 2, the measurement is based on the determination of the propagation time in the liquid (round-trip flight time) of the ultrasonic wave emitted by the sensor to precise reflection points. , then reflected back to the sensor 109. In particular, as already explained with reference to the prior art described above, the method used in this example employs two reflectors 203 and 204. These reflectors are located at positions known with respect to the transmission / reception unit of the ultrasonic sensor 109 in order to calibrate the actual speed of propagation of the wave. Once the calibration has been carried out, the reflection on the surface 205 of the liquid in the tank (the additive in this case) is used to determine the level of FED present in the tank.

Figure 3 illustrates in a simplified manner the principle of measuring the level of liquid in the reservoir containing the EDF using the means of Figure 2. The propagation times in the liquid are determined from and until ultrasonic wave transmission / reception unit 301 of the ultrasonic sensor 109. It is indeed the back-and-forth times of the ultrasonic wave that are measured. We also speak of measuring the echoes associated with these different elements. Typically, the wave is produced by a piezoelectric system vibrating under the effect of an electrical signal oscillating at a given frequency. The receiver is located at the transmitter. The ultrasonic wave therefore propagates from the source of the ultrasonic wave to a reflective element producing a reflected ultrasonic wave, which propagates back to the transmitter / receiver of the unit 301.

In the case of the example illustrated in Figures 2 and 3, the propagation times are measured from the transmitter / receiver 301 to a first reflector 203 in the liquid and / or to a second reflector in the liquid 204 and / or to the surface of the liquid 205. These data are then used and processed digitally to deduce therefrom, by calculation, the level of the liquid present in the reservoir. For example, averages can be performed on several successive measurements, and / or digital filtering operations performed on these averages in order to obtain the most reliable values possible. The values measured in time of flight of the ultrasonic wave are converted into values of FED level in the reservoir using the speed of propagation of the wave in the liquid (which is estimated by the reflectors which make it possible to measure it and therefore calibrate the device), further based on the known shape (ie dimensions) of the tank.

The measurement windows 302, 303 and 304 correspond in turn to time windows in which a reflection signal is expected. The measurement can then be optimized by preferentially exploiting one or the other of the reflections depending on whether a signal is detected in one or the other of the measurement windows. For example, the calibration of the propagation speed can be obtained from the propagation time measured between the first reflector 203 and the second reflector 204 when a signal is detected in the window 304 when it can, as a variant, be derived from the propagation time between the transmitter 301 and the first reflector 203.

Figures 2 and 3 and their description above make it possible to understand some of the limitations inherent in the use of an ultrasonic sensor for measuring the level of liquid additive in the DEF tank. In particular, in the case where the tank 105 is subjected to significant movements, for example due to the chaos due to the imperfections of the road on which the vehicle is traveling, the reflection signal associated with one of the reflecting surfaces (reflector or surface liquid) can come out of the corresponding measurement time window, thereby distorting the measurement in progress. In addition, if the ultrasonic wave on its path crosses media with inhomogeneous properties (as is the case for example if part of the additive is in solid form due to the freezing of urea, for example, then that another part of the additive is in liquid form) the measured values can also come out of the expected value windows. In addition, the wave paths (represented by arrows in the diagram in Figure 3) are assumed to be straight and the ability to measure propagation times implies that the transmitted wave returns well to the transmitter. However, the possible presence of elements in suspension in the liquid, or the deposit of elements on the walls of the tank and / or on the reflecting surfaces which are liable to deflect the wave will necessarily lead to a false measurement or even the impossibility perform the measurement.

The invention is based on the use of a measurement device structurally similar to that described above. Such a liquid level measurement system is therefore also integrated into the reservoir which contains the liquid additive in order to be able to determine the level of EDF in the reservoir, but the physical measurements which it delivers are used on the basis of a particular strategy. overcoming the drawbacks of the prior art which were mentioned in the introduction.

For this purpose, the measurement system includes not only at least one sensor for physical measurement of the level of the liquid but also a digital processing unit. Physical propagation time measurements are made continuously (i.e. at regularly spaced time intervals). Then the measurements are processed digitally by a processing unit to obtain the level value determined by the system. The sensor can, for example be an ultrasonic sensor and the processing unit can integrate a processor to perform calculations, as well as a memory for storing information useful for carrying out these calculations (in particular values from previous measurements).

The step diagram of Figure 4 gives a schematic representation of the use case in which modes of implementing the method according to the invention can be implemented. This logic diagram illustrates different stages of the treatment carried out, which lead to the determination of the level of liquid in the reservoir.

The proposed method allows a continuous and precise determination of the level of additive in the tank, based on both direct measurement of the level and its estimation by a model. This, by exploiting at all times what is most relevant, depending on the circumstances, to determine the level as precisely as possible. The liquid level measurement system includes a physical sensor similar to those of the prior art, as described above with reference to Figures 2 and 3, as well as a digital processing unit which performs additional processing.

After the vehicle 401 has been put into service by the user, the measurement system is initialized, in step 402, and the ultrasonic sensor is calibrated as in the prior art described above. However, during this initialization step 402, the system validates or invalidates the calibration of the sensor. For this purpose, and on the basis of the values of the first measurements of the time of flight of the ultrasonic wave which are carried out with the sensor, the processing unit of the system determines whether the measurement of the time of flight of the ultrasonic wave in the propagation medium (ie, in the liquid additive) could be carried out correctly or not, so that the level measurements are considered as valid or not. For example, if the measurements fluctuate significantly (over several successive measurements) or have values outside normal measurement windows, this can be interpreted as meaning that the level of the liquid cannot be determined correctly on the basis of measurements made in using the sensor.

After initialization 402, and in case 403 it is determined that the liquid level can be validly measured with the sensor, the measurement system uses the result of the physical measurements to determine the level of additive in the tank. The determined value can be indicated to the user of the vehicle so that he can judge whether or not it is necessary to fill the tank. It may be an indication given to the user, in step 408, by visual information on the dashboard and / or by audio information, and / or by any other way of informing the user.

Otherwise 404, the system uses in step 405 an estimation model, based for example on measurements previously carried out, for example when the vehicle was last used, to estimate the level of the liquid additive in the tank. Here again, the value thus estimated can be indicated to the user of the vehicle, in step 408, instead of a value resulting from physical measurements.

The estimation of the liquid level can for example be carried out in step 405 by the digital processing unit of the system by performing one (or more) calculation (s) using in particular the last value (s) ( s) that have been produced by the measurement system. Such a previously measured value may, for example, have been stored for this purpose in a non-volatile memory of the processing unit. A simple estimation model consists for example in subtracting from the last known value of the level of liquid in the reservoir the quantity of liquid which has been injected into the catalysis system since this value has been obtained by one (or more) measurement (s) valid physical (s). For this purpose, the injector or the pump of the extraction unit are provided, for example, with means which measure the flow of liquid extracted from the tank and injected into the pollution control system, and communicate it to the digital processing system. .

In embodiments, the processing by the processing unit is iterative, that is to say that its steps are executed in a loop. With each estimate 405 of the liquid level is associated the implementation, in step 406, of a test consisting on the one hand in determining in real time, on the basis of measurements and / or calculations carried out by the system of measurement, the state of a set of criteria, and on the other hand to decide, according to the state of all these criteria, to use either the estimation model or the physically measured value to indicate to the user the liquid level in the tank. The determination and decision process for step 406 will be detailed later, with reference to the step diagram in Figure 5.

In summary, depending on whether a set of conditions are considered in step 406 as being satisfied or not, the value used to indicate to the user the level of liquid in the tank is the value measured from step 402 or the value estimated in step 405.

Thus, in case 407 where it is determined that the level value from the physical measurements is valid and can be used, the liquid level value determined by the system switches to the value thus measured. We say that we “synchronize” the estimate to express the fact that the value of the level of additive in the reservoir which is indicated to the user, in step 408, then corresponds to a value actually (physically) measured, and no longer at a value estimated as just before. Otherwise 409, the estimated value is chosen by the system to determine the level of liquid in the tank.

In both cases (407 and 409), once the level information of the liquid is indicated to the user, the method loops leading to the repetition 410 of the estimation operations 405 of the level and determination 406. In Indeed, the determination of the level is preferably carried out continuously, that is to say for example at regular time intervals. The liquid level value which is determined by the system can thus change dynamically and be alternately the estimated value or the measured value according to the result obtained at each iteration of the treatment according to the modes of implementation of the invention. For example, in a use case where the driving conditions of the vehicle change from time to time causing conditions giving a measurement which is considered in step 402 sometimes as valid and sometimes as invalid, the method will always allow use the most relevant (most precise) value to know the level in the tank.

The diagram in Figure 5 is a logic diagram illustrating an embodiment of the method according to the invention. A set of various logical values trigger, via Boolean logical operators 512 and 516, the carrying out of a given action. In this case, action 517 which is triggered or not according to the logical result (ie binary) of these combined conditions is the decision by the system for measuring the level of the additive liquid, of the values measured physically by the system for determining the level of FED in the dedicated tank of the motor vehicle.

The logical operator 512 of type ET receives as input a set of logical information, for example eleven pieces of information 501 to 511, respectively. If and only if all of this information 501 to 511 has the logical value "TRUE" (binary value 1) simultaneously, then the operator 512 outputs a positive result 513, that is to say logical information "TRUE" . Otherwise, this result 513 is negative, namely a logical value "FALSE" (binary value 0).

The operator 516 is an OR type operator which receives as input the result 513 coming from the logical operator 512, as well as two other logical pieces of information 514 and 515. As soon as at least one of the three logical pieces of input information is "TRUE", the result 517 at the output of the operator 516 is positive. In this case, it means using the value measured by the level measurement system to determine the level of FED remaining in the tank.

It will be noted that the logical information 501-511,514 and 515 are themselves each the logical result of respective logical conditions, which give logical information “TRUE” when they are satisfied (we also say validated), or logical information “FALSE” in the opposite case. In what follows, we refer without distinction to the logical information itself or to the logical condition which gives its logical value to said logical information.

Those skilled in the art will appreciate that the invention is not limited either by the number of logical information taken into account, or by the nature of the conditions which are tested to generate it. In addition, different combinatorial logic, for example more complex than that illustrated by the diagram in Figure 5, can be implemented according to the specificities of each application.

In summary, Figure 5 shows a nonlimiting example in which, since all the conditions (which will be detailed below) 501 to 511 are true at the same time or that one of the conditions 514 and 515 (also detailed below -after) is true, then the system uses the measured value to determine the level of liquid in the tank. Otherwise, the system uses the estimated value, using an estimation model, to determine the level of liquid in the tank.

The first condition 501 may consist in verifying that the measurement of the level carried out by the measurement system is valid. In one example, the system itself performs its self-diagnosis on the basis of given criteria and delivers logic information 501 confirming or invalidating the validity of the measurement. For example, this self-diagnostic can consist in examining a processor error signal, a sensor error signal and / or detecting the obtaining of aberrant liquid level values (taking into account the known dimensions of the reservoir) . As a variant or in addition, the system can also, thanks to other sensors present in the tank, recover values of the measured temperature of the liquid considered to be unsuitable for allowing the measurement. In all cases, a validity indicator is issued by the system.

The second condition 502 may consist in verifying that the level of liquid measured by the system is not included in either a first determined window or a second determined window. The term window here means ranges of values within which the measured value must not lie. In addition, when the physical sensor of the system is an ultrasonic sensor, as in the example given above, several measurements of the propagation time of the ultrasonic wave expressed in seconds are converted into level measurements, which are expressed in millimeters, for example. The windows, also called rejection windows, can for example specify time and / or distance limit values defining the upper and lower limits of ranges of values in which the measurement cannot be considered as reliable. For example, such a range can correspond, in the case of the use of an ultrasonic sensor and of several reflectors, to a reflection of the wave which it is difficult or impossible to decide if it took place on a reflector submerged or on the surface of the liquid.

The third condition 503 can consist in checking whether the successive acquisitions of the level measurement sensor are stable. In other words, the digital processing unit of the system controls the possible variation of the values of the successive acquisitions and ensures that it is below a determined threshold. This can be done, for example, by measuring the difference between the maximum value and the minimum value obtained on a certain number of acquisitions, or by generating a distribution of the values obtained and by calculating the standard deviation associated with this distribution. For example, such a distribution can be calculated approximately every 20 seconds so as to correspond to approximately 200 successive acquisitions of a propagation time relating to a path in the liquid.

In one embodiment, the measurement system comprises an ultrasonic sensor performing in parallel the measurement of three round-trip propagation times (called "runtimes") of the ultrasonic wave generated by its emitter and reflected, respectively, by a first reflector, by a second reflector and by the surface of the liquid. The propagation times measured relate to the reflections of the same ultrasonic wave emitted by the transmitter of the sensor and reflected at three different times by three respective reflecting surfaces. An acquisition for each of the three return journeys can be carried out in less than 100 ms. The satisfaction of condition 503 can be imposed for each of these three acquisitions carried out in parallel.

The fourth condition 504 may consist in verifying whether a minimum number of successive acquisitions in the same range of values has been carried out by the ultrasonic sensor of the measurement system. Indeed, as already mentioned, the digital processing unit of the system can, for example, use a large number of successive acquisitions of the sensor to make statistics, generate distributions and / or filter these results digitally in order to finally produce the value obtained by the measurement system. In this context, as long as a given number of acquisitions in the same range of values by the sensor has not been reached, condition 504 is not satisfied.

In addition, in the same way as for condition 503, the satisfaction of this condition 504 can be tested in parallel for several different acquisitions associated with several paths of the ultrasonic wave in the liquid.

The fifth condition 505 consists in checking whether the vehicle engine has been started for at least a minimum time, that is to say for a duration greater than a determined threshold. This delay guarantees, among other things, that the level measurement system has had the time to initialize correctly and to carry out the set of tests / measurements necessary for the implementation of the process. In addition, the definition of the timeout to wait can be subject to several criteria. For example, depending on the ambient temperature or that of the potentially measured liquid, depending on the engine rotation speed or depending on the state of a heating source potentially integrated in the tank, the minimum time to wait can be lengthened or decreased. In one embodiment, the counter used to measure this time can be temporarily stopped and restarted over several operating cycles close to the engine until the liquid in the tank thaws.

The sixth condition 506 may consist in verifying that a minimum quantity of FED (i.e. an amount greater than a threshold) has indeed been consumed since the engine was put into service. The amount of FED can be known, for example, by measuring the volume of liquid extracted by the extraction unit and subtracting it from the last known value of the level of FED in the tank. The volume extracted since the last measurement is obtained, for example, by reading the volume pumped by the pump of the extraction unit or by reading the volume injected into the catalysis system by the dedicated injector, or via a combination of the two.

Furthermore, in a given embodiment, the consumed EDF threshold to be reached may be a function of the conditions of use of the vehicle. In other words, the threshold takes on a different value depending on whether the vehicle remains stationary after the engine has started or is set in motion immediately.

The seventh condition 507 may consist in verifying that the vehicle in which the liquid additive tank is located is indeed static (i.e. at a standstill) or under stable driving conditions. By stable driving conditions is meant that by observing precise criteria, it is determined whether or not the vehicle is moving substantially at constant speed (therefore at zero or close to zero acceleration). For example, in one embodiment, the criteria used to determine these conditions are the vehicle speed, its acceleration and the engine rotation speed (expressed in number of revolutions per minute) which also provides information on the engine load. More precisely, according to the ranges of values in which these three criteria are included, the vehicle will be considered as stable or not. Indeed, these criteria give an idea of the driving conditions, which can be mild, dynamic, even sporting, with an impact on the stability of the vehicle and therefore on the relevance of the liquid level measurements in the DEF tank.

The eighth condition 508 may consist in checking whether the tank is empty, or almost empty. Indeed, below a predetermined threshold, the level measurement system returns a constant value. It is said that the measured level is thus locked (in English "latched") as soon as the output value of the system is substantially equal to this value. In other words, condition 508 makes it possible to verify that the level measured in the tank is not locked, in the sense above.

The ninth condition 509 may consist in checking whether the temperature of the FED in the tank is higher than a given value. One or more temperature sensors may be present in the tank and dynamically communicate the temperatures recorded to the liquid level measurement system. Thus, if the measured temperature is below a threshold value condition 509 is not satisfied. In addition, in a particular embodiment, the temperature threshold used by this condition is a function of the level estimated at each instant by the estimation model. In other words, depending on whether the estimated value of the level of liquid in the reservoir is greater or less, the temperature threshold to be reached for condition 509 to be satisfied changes.

The tenth condition 510 can consist in verifying that no ice cavity is detected in the reservoir. The presence or absence of such a cavity is detected by the measurement system on the basis of the level and temperature values obtained and on their evolution over time. In one example, a sudden drop in the measured level value may correspond to the presence of an ice cavity in the tank. In another example, a positive time gradient (with a given slope) of the measured temperature could also be considered as the signature of an ice cavity in the reservoir.

In an embodiment of the method according to the invention, the detection of a cavity is based on several criteria such as: a cavity is detected if the measured temperature increases (that is to say increases) suddenly, or if the measured liquid level decreases (i.e. decreases) suddenly, or if a heating source in the tank is in use. Conversely, no cavity is detected if the difference between the measured level and the estimated level is lower is small or if the measured level increases or if a filling of the tank has taken place.

The eleventh condition 511 may consist in verifying in which mode there is a heating source integrated in the tank. Indeed, one or more heating sources are present in the tank to contribute to the thawing of the liquid when all or part of it has frozen due to a very low outside temperature during a prolonged stop / parking of the vehicle. Depending on the needs at a given time, the heating source can be put in one mode or another. For example, depending on the level of cold or the amount of frozen additive, the power of the heating source and its evolution over time varies according to a determined curve. This development corresponds to a heating procedure (in English "heating strategy") which also determines whether or not condition 511 is considered to be satisfied.

Finally, in the example of implementation described here, the condition 513 of entry of the operator 516 of the OR type is therefore fulfilled if, and only if, all the previously cited conditions 501 to 511 are fulfilled simultaneously. In this case, action 517 consisting in using the value measured by the system to determine the level of liquid in the reservoir is carried out. Those skilled in the art will of course appreciate that other implementations may take into account only some of the conditions 501 to 511, or conversely take others into account which may be of specific interest in certain use cases .

In other words, condition 513 is fulfilled if, and only if, any set of N conditions among the eleven conditions 501 to 511, where N is an integer between 1 and 11, is satisfied.

In addition, other conditions such as conditions 514 and 515 make it possible to trigger action 517 without necessarily implying the validation of all the conditions 501 to 511. We speak in their regard of preponderant conditions ) in the sense that these make it possible to override the need to have all the conditions 501 to 511 satisfied simultaneously. So as soon as only one of these conditions is satisfied, the logical value 517 is TRUE, that is to say that the global condition is validated.

Condition 514 consists, for example, in checking whether the tank has been filled. In this way, as soon as a filling is detected, the system automatically uses the measured value to determine the level in the tank. In addition, this condition is validated regardless of the time of filling. If filling takes place when the vehicle engine is stopped, this is known as key refill and the filling will be detected at start-up. If the filling is carried out when the engine is started we speak of fast filling ("fast refill" in English) and the filling is detected immediately. These two cases constitute two versions of filling the tank which is the subject of condition 514.

Finally, condition 515 may consist in checking whether the liquid level obtained by the EDF level measurement system corresponds to a locked level. In other words, it is a question of checking whether the tank is empty or almost empty as defined earlier. Furthermore, in a particular embodiment, the condition linked to a locked level can be modified when the additive is frozen. For example, below a certain temperature, this condition can be ignored.

Finally, Figure 5 presents conditions which, alone or in combination, lead to choosing the value measured by the level measurement system in the tank as soon as they are satisfied. Conversely, and as has already been said, if these conditions are not satisfied, the value retained by the system to determine the level of additive in the tank remains the estimated value. Finally, and as shown in Figure 4, this process operates continuously, which implies that all these conditions are constantly checked and can possibly lead to flip-flops from using the estimated value to the measured value, and vice versa.

The present invention has been described and illustrated in the present detailed description and in the figures of the appended drawings. The present invention is not limited to the embodiments presented. Other variants and embodiments can be deduced and implemented by the person skilled in the art on reading this description and the drawings.

In the claims, the term "include" does not exclude other elements or steps. A single processor or several other processing units can be used to implement the invention. Likewise, several memories, possibly of different types, can be used to store information. The various features presented and / or claimed can be advantageously combined. Their presence in the description or in different dependent claims does not exclude this possibility. The reference signs should not be understood as limiting the scope of the invention.

Claims (15)

1. Method for determining the level of liquid additive in a tank (140) of liquid additive of a motor vehicle exhaust gas treatment system (100) also having a system for measuring the level of liquid in said tank which comprises a sensor and a digital processing unit, characterized in that said method comprises the following steps implemented in the liquid level measurement system as soon as the vehicle is started, for determination by the unit digital processing of a level of liquid additive level in the tank: if • the values of the liquid additive level acquired by the liquid level measurement system using the sensor satisfy a determined validity criterion, then: • the value of the level of liquid additive which is determined is a value of level of liquid acquired using the sensor; otherwise, the value of the level of liquid additive which is determined is a value of level of liquid estimated by calculation from at least one value of level of liquid previously acquired using the sensor and stored in a memory of the processing unit, in relation to a quantity of liquid additive consumed since said previously acquired liquid level value has been acquired and stored. 2. Method according to claim 1, in which the criterion of validity of the liquid additive level values acquired by the liquid level measurement system is satisfied if, and only if, any set of N conditions among the eleven conditions following, where N is an integer between 1 and 11, is satisfied: N. a self-diagnostic module of the liquid level measurement system determines that said system acquires valid liquid levels; O. the level of liquid additive determined by the liquid level measurement system is not included in a first window or in a second window each corresponding to ranges of respective values of level of liquid additive; P. the variation in the values of the liquid additive level obtained using at least two successive acquisitions made by the sensor of the liquid level measurement system is less than a determined threshold value; Q. a determined number of values of the level of liquid additive successively acquired in the same range of values using the sensor of the system for measuring the level of liquid is reached since an initialization of the system for measuring the level of liquid; R. the cumulative running time of the engine, on one or more operating cycles close to the engine, since the start of said engine of the motorized vehicle is greater than a determined threshold; S. the quantity of liquid additive that has been consumed since a full filling of the liquid additive tank is greater than a determined threshold; T. the motorized vehicle is static or in driving conditions satisfying a determined stability criterion; and, U. the level of liquid additive level acquired using the sensor of the liquid level measurement system is above a determined threshold; V. the temperature of the measured liquid additive is higher than a determined temperature threshold; W. an ice cavity is not detected in the liquid additive tank; and, X. a liquid additive heating source integrated in the liquid additive tank is not in use. 3. Method according to claim 1 or claim 2, in which the criterion of validity of the values of the level of liquid additive acquired using the sensor of the level measurement system is satisfied, moreover, if at least one of the following conditions are satisfied: Y. a full filling of the liquid additive tank is detected; and, Z. the level of liquid additive determined using the sensor of the liquid level measurement system is higher than the last level of liquid additive measured, increased by a determined value. 4. Method according to any one of claims 1 to 3, wherein the sensor of the liquid level measurement system is an ultrasonic sensor. 5. Method according to claim 4, in which the acquisition by the liquid level measurement system comprises: • the acquisition, by the ultrasonic sensor, of measurement values corresponding to the propagation times of an ultrasonic wave in the liquid between its emission and the reception, by the sensor, of reflected ultrasonic waves, respectively, by at at least two reflectors located in the liquid at respective determined positions and by the surface of the liquid in the tank; and, • the processing by the digital processing unit of the measurement values acquired by the sensor, said processing comprising the calculation of liquid additive levels on the basis of the measurement values acquired by the sensor. 6. Method according to any one of claims 2 to 5, in which the driving conditions which satisfy the stability criterion comprise at least one of the following conditions: • the instantaneous speed of the vehicle is between two determined threshold values; and, • the vehicle engine rotation speed is between two determined threshold values; and, • the engine torque produced by the vehicle engine is between two determined threshold values. 7. Method according to any one of claims 2 to 6, in which the detection of an ice cavity comprises: the detection of an ice cavity is positive if: • the time course of the temperature of the measured liquid additive increases; or, • the time course of the measured level of liquid additive decreases; or, • the heating source is in use; while the detection of an ice cavity is negative if: • the difference between the level of liquid additive measured and the level of liquid additive estimated is less than a determined threshold value; or, • the time course of the measured level of liquid additive increases; or, • a full filling of the liquid additive tank is detected. 8. The method of claim 5, wherein the first and second windows of condition B further correspond to ranges of propagation time values acquired by the sensor. 9. The method of claim 5, further comprising that, for condition D, a determined number of successive measurement values of the propagation times of the ultrasonic wave in the liquid, acquired in the same range of values, is reached for each of the following measurement values: • the propagation time between the sensor and the first reflector; and, • the propagation time between the sensor and the second reflector; and, • the propagation time between the sensor and the surface. 10. The method as claimed in claim 5, further comprising that, for condition C, the variation in the value of the propagation time obtained for at least two successive measurements is less than a value determined for each of the following measurements: • the propagation time between the sensor and the first reflector; and, • the propagation time between the sensor and the second reflector; and, • the propagation time between the sensor and the surface. 11. Method according to any one of the preceding claims, in which, for condition F, the determined quantity of liquid additive consumed corresponds to two different determined values depending on whether the motorized vehicle is static or in motion since an initialization of the liquid level measurement. 12. The method as claimed in claim 6, in which the driving conditions which satisfy the stability criterion further comprise at least one of the following conditions: • the temporal variation of the instantaneous speed of the vehicle is between two determined threshold values; and, • the time variation of the vehicle engine rotation speed is between two determined threshold values; and, • the time variation of the engine torque produced by the vehicle engine is between two determined threshold values. 13. Method according to any one of the preceding claims, in which, for condition E, the threshold to which the cumulative running time of the elapsed engine is compared is a function of the temperature (s) of the liquid additive measured. (s). 14. System for measuring the level of liquid in a tank for liquid additive comprising means capable of carrying out all the steps of the method according to any one of claims 1 to 13. 15. Motorized vehicle having an internal combustion engine (104), an exhaust gas treatment device (103) and a tank (105) to contain the liquid additive used by the device (103) to clean up the exhaust gases exhaust of said engine, said tank comprising a system for measuring the level of liquid in the tank according to claim 14. 1/5