FR2983903A1 - Method for detection of stopper in liquid urea supply conduit of selective catalytic reduction device in exhaust line of car, involves comparing time interval, and detecting stopper when time interval is less than threshold time - Google Patents

Abstract

The method involves opening of an injector (54) during a predetermined time, and allowing detection of pressure (50) in a supply conduit in the injector by a pressure sensor. A determination is made if the pressure in the supply conduit exceeds a threshold pressure value. A time interval between openings of the injector is compared (66) with a threshold time to detect a threshold pressure value (48). A stopper is detected (68) when the time interval is less than the threshold time. A position of the stopper in the conduit is determined. The liquid urea is Adblue(RTM: Aqueous urea solution). Independent claims are also included for the following: (1) a method for removal of a stopper (2) a liquid urea supply system (3) a car.

Description

The present invention relates to a method of detecting and to a method of suppressing a plug in a liquid urea supply line. BACKGROUND OF THE INVENTION a device for selective catalytic reduction of an exhaust line of a motor vehicle. The invention also relates to a liquid urea supply system for a selective catalytic reduction device. The invention further relates to a motor vehicle comprising an exhaust line provided with a selective catalytic reduction device having such a liquid urea supply system. [0002] An internal combustion engine of a motor vehicle is associated with an exhaust line. The exhaust line may contain one or more treatment members. These treatment units are intended to reduce the polluting emissions produced during the combustion of the fuel in the internal combustion engine. These polluting emissions are mainly composed of hydrocarbons, carbon monoxide, particles and nitrogen oxides, which can also take the name of NOx. The invention relates to the field of motor vehicles with internal combustion engine, including diesel type, equipped with a NOx treatment member type selective catalytic reduction device, called SCR device. The NOx treatment is performed by injecting a reducer into the exhaust line. This reducer is routed to the injector through a supply line through a pump gauge module located for example in the trunk of the motor vehicle. This module also has the role of maintaining the liquid under pressure. The reducer can be in gaseous or liquid form depending on the technologies used. In liquid form, the reducing agent is generally liquid urea such as dilute liquid urea, in particular known under the trade name Adblue®. As illustrated in Figure 1, a conventional SCR device comprises a liquid urea reservoir 20 provided with a supply line 24 for placing in fluid communication the liquid urea reservoir 20 with the line exhaust system of the motor vehicle (not shown). The supply line 24 is provided with a pump 22, a pressure sensor 30 downstream of the pump 22, and an injector 26 downstream of the pressure sensor 30. The pump 22 allows the circulation liquid urea in the supply line 24. The pressure sensor 30 measures the pressure in the supply line 24. The injector 26 allows the injection of liquid urea into the exhaust line of the motor vehicle. When the external ambient temperature is low, the SCR reducer based on liquid urea can freeze in the feed pipe 24. To prevent the freezing of liquid urea, the supply pipe 24 is provided with a purge device. Nevertheless the purge of the supply pipe is never total. Liquid urea residues, once solidified due to a low ambient ambient temperature, become plugs capable of obstructing the supply line 24.

FIG. 2 illustrates the presence of a plug 28 in the supply line 24. The liquid urea is thus blocked in the supply line 24, in the portion upstream of the plug 28. [0006] Many devices propose detecting the presence of a plug in the supply line. In particular, it is known to detect the presence of a plug during the rolling phase of the vehicle at the time of need for liquid urea supply, that is to say when it is desired to inject the reducer in the line. exhaust. A major disadvantage of this known solution is that if the plug was not detected before, several vacuum injections could be performed. This can notably lead to a loss of SCR efficiency and / or damage to the injector, resulting in a fault diagnosis of the system. In addition, the detection of the plug during the driving phase at the time of a need for liquid urea feed causes a delay in the liquid urea supply of the exhaust line. A delay in the supply of liquid urea causes an increase in the amount of NOx escaping from the motor vehicle due to the lack of responsiveness of the system. [0007] EP 2 034 147 B1 proposes the detection of a clogging in the SCR system after the opening of the reducer injector of the system during a temporary shutdown of the pump of the system. Due to the opening of the injector and the stopping of the pump, a reduction of the pressure of the gearbox in the system must be observed. If this decrease in pressure is not sufficient, the presence of clogging is detected. The main disadvantage of this device is the necessary condition of a prior operation of the supply of liquid reductant line 24 before being able to perform the detection of a clogging. Thus, the detection of the presence of clogging is performed during a need for liquid urea feed, created a delay in the execution of the supply of liquid urea. [000s] There is therefore a need for a method of detecting a plug in a liquid urea supply line of a SCR device of an exhaust line of a motor vehicle does not have the aforementioned drawbacks. For this, the invention provides a method of detecting a plug in a liquid urea supply line of a selective catalytic reduction device of an exhaust line of a motor vehicle, the driving feeding device being provided with an injector, allowing the injection of liquid urea into the exhaust line, and a pressure sensor, adapted to measure the pressure in the supply line, the method comprising the steps consisting of: - opening the injector for a predetermined time; - the detection, by means of the pressure sensor, a pressure in the supply line greater than a threshold pressure value; the comparison of the time interval separating the opening of the injector from the detection of the pressure greater than the threshold pressure value with a threshold duration; detection of a plug when the time interval is less than the threshold duration. [0olo] According to one variant, the method is implemented at the start of the motor vehicle after parking the vehicle. Alternatively, the supply line is provided with a liquid urea circulation pump in the supply line for pressurizing the supply line. According to a variant, the method comprises a step consisting in: determining the position of the plug in the supply line from the comparison of the time interval separating the opening of the injector from the detection of the pressure higher than the threshold pressure value with the threshold duration. The invention further provides a method of removing a plug detected in a supply line, the plug being previously detected by the previous detection method. Alternatively, the supply line is provided with a heating device, the method comprising the step of: - heating the supply line by means of the heating device. Alternatively, the method further comprises the steps of: - closing the injector; - The successive start and stop of the pump. Alternatively, the supply line is provided with a purge device, the method comprising the step of: - purging the supply line by means of the purge device; the method further comprising, after purging, a new implementation of the steps of the detection method. The invention also proposes a liquid urea supply system of an exhaust line of a motor vehicle for selective catalytic reduction device, the system comprising a supply line, an injector, a sensor of pressure, the power system comprising a computer specially adapted to implement the above method. [Ools] The invention also proposes a motor vehicle comprising an internal combustion engine and an exhaust line of the engine gases, the exhaust line being provided with a selective catalytic reduction device having the fuel supply system. previous liquid urea. Other features and advantages of the invention will be apparent from the following detailed description of the embodiments of the invention, given by way of example only and with reference to the drawings which show: FIGS. 1 and 2, structural diagrams of a liquid urea reservoir and a supply duct respectively in the absence and in the presence of a stopper; FIG. 3, a chronogram of the various steps according to a proposed embodiment, in the presence of a plug and in the absence of a plug; - Figure 4, a graphical representation of the steps of a preferred embodiment of the method of detecting the presence of a plug in the supply line. The invention relates to a method for detecting a plug in a liquid urea supply line of an SCR device of an exhaust line of a motor vehicle. In the remainder of the description, reference is made to FIGS. 1 and 2 previously described for concretizing the reference to a liquid urea feed pipe 24 of an SCR device. As illustrated in Figure 2, the plug 28 to be detected may be a plug comprising frozen urea. Thus in the case of the use of liquid urea Adblue® type, the plug is a plug of Adblue®. However, the method is also applicable in the case of a plug of any other type. The method comprises in a first phase, the opening of the injector 26. Due to this prior step of opening the injector 26, in the case where the proposed method is implemented at the start of the vehicle , the air having purged the supply line 24 can be driven to make room for the reducer. In a second phase, the injector 26 is closed after a predetermined time. After the opening of the injector 26, the gearbox gradually taking place in the supply line 24, the pressure is likely to increase in the pipe. Indeed, the pressure increases due to the presence of a plug 28 and / or the fact that the injector has closed at the end of the predetermined time. The method then comprises the detection of a pressure by the pressure sensor 30 when the pressure in the supply line 24 becomes greater than a threshold pressure value. Preferably, the supply line 24 is provided with the pump 22 for circulating the liquid urea in the supply line 24 allowing the supply line 24 to be pressurized. [0025] The proposed method then comprises comparing the time interval separating the opening of the injector 26 from the detection of the pressure greater than the threshold pressure value with a threshold duration. This comparison can be performed using an on-board computer on the motor vehicle.

When the time interval is less than the threshold duration, the pressure in the supply line 24 has increased more rapidly than the nominal mode of operation without defect which allowed to predetermine the threshold duration. Consequently, the proposed method comprises the detection of a plug 28 when the time interval is less than the threshold duration 42. According to the proposed method, the time interval to be compared with a threshold duration has as its point starting the opening of the injector. Due to the prior step of opening the injector 26, the proposed method is likely to be implemented at the start of the vehicle, the opening of the injector for evacuating the purge air from the supply line 24, the purge having been carried out during the parking of the vehicle. The proposed method therefore advantageously makes it possible to solve the disadvantage of the previously known methods which can only be implemented during the running of the motor vehicle, at the moment of injection of the reducer into the exhaust line. Indeed, the proposed detection can be carried out preventively unlike EP 2 034 147 B1 forced to have a supply line 24 already full reducer before being able to implement the detection. In one embodiment, the proposed method is then implemented at the start of the motor vehicle after parking the motor vehicle. The method can also be implemented only at the start of the motor vehicle. The invention also relates to a liquid urea supply system of an exhaust line of a motor vehicle. The feed system is provided for a selective catalytic reduction device of the exhaust gases. The proposed supply system includes the supply line 24, the injector 26, and the pressure sensor 30 previously described. The power system further comprises the computer previously described, especially adapted to implement the above method. The invention further relates to a motor vehicle comprising an internal combustion engine and an exhaust line of the engine gases. In the proposed vehicle, the exhaust line is advantageously provided with the selective catalytic reduction device having the preceding feed system. Figure 3 shows a timing diagram of the various steps of the method, when a plug 28 is detected after the closure of the injector and when no detection of a plug. The timing diagram comprises a first marker, consisting of a first axis 45 defining the states of the injector 26 and a second axis 46 defining a time scale. The open and closed state of the injector 26 is represented by a first curve 32 in this first mark. The timing diagram further comprises a second marker composed of the second axis 46 and a third axis 47 defining a pressure scale in line 24. Second and third curves 34 and 36 represent, as a function of time, the evolution of the pressure in the supply line 24, respectively in the presence and in the absence of the plug 28. [0030] First and second time intervals 40 and 44 correspond to the time separating the opening of the injector 26 from the detection of a pressure greater than the threshold pressure value 38, respectively corresponding to the second and third curves 34 and 36. The first time interval 40 is less than the threshold time value 42, the presence of a plug 28 is thus detected. Conversely, the second time interval 44 is greater than the threshold time value 42. This illustrates the absence of the plug 28 in the supply line 24. According to an alternative case to that described with reference to FIG. 3, the pressure in the pipe may exceed the threshold pressure 42 while the injector is still open. In other words, the time interval separating the opening of the injector from the detection of the pressure greater than the threshold pressure value may be shorter than the predetermined time interval of opening of the injector. . This case occurs in particular when the position of the plug 28 in the pipe is very close to the pressure sensor 30 in the supply pipe 24. Indeed the time taken by the supply pipe 24 to reach the pressure value threshold 38 depends on the position of the plug 28 in the supply line 24 but also the length of the supply line 24 or the flow rate of the pump 22. The knowledge of these parameters allows to deduce the position of the plug 28 of the time taken by the supply line 24 to reach the threshold pressure value 38. [0032] Thus according to a preferred embodiment, the method can determine the position of the plug 28 in the supply line 24. The knowledge the position of the plug 28 is advantageous in that it facilitates the cap removal operations, the description of which preferred embodiments follows. [0033] FIG. 4 schematically represents the implementation by the computer of the detection method according to a preferred embodiment. A first operation 56 is performed to detect a rising edge on the first curve 32. A rising edge on the first curve 32 corresponds to an opening of the injector 26. A second operation 50 is performed to detect whether a first input 52, the pressure in the supply line 24, is greater than a first constant 48, the threshold pressure value 38. A third operation 58 makes it possible to calculate the time interval separating the detection of a rising edge on the first curve 32 of the detection of a higher value of the first input 52 relative to the first constant 48. A fourth operation 66 makes it possible to compare with a second constant 60 the time interval separating the detection of a rising edge on the first curve 32 of the detection of a higher value of the first input 52 relative to the first constant 48. The second constant 60 is the threshold duration 42 determined In the presence of a plug in the feed pipe 24, the fourth operation 66 for comparing the time interval calculated at 58 with the time constant 60 makes it possible to detect the presence of the plug 28 in the pipe. 24. A fifth operation 62 makes it possible to determine the position of the plug 28 as a function of the second constant 60, of a third constant 64, corresponding, for example, to the total length of the supply line 24, and the time interval determined by the third operation 58. [0034] The foregoing embodiments relate to detecting the presence of a plug. The invention also relates to a method of suppressing a detected plug. Such a suppression method first implements the proposed method of detecting the plug. When the plug 28 is detected, the deletion method provides for the removal thereof. According to the embodiments, the SCR device may comprise a heating device and / or a purge device respectively for heating and purging the supply line 24. When the cap 28 is detected, the heating device is switched on and the injector 26 is closed. Knowledge of the position of the plug may in particular allow the realization of a localized heating of the supply line 24 at the plug 28, 15 thus ensuring its more effective removal. Then, the pump 22 is successively turned on and off several times, to try to dislodge the cap 28, if necessary during the use of the heating device. Following these attempts, the purge device is turned on with the opening of the injector to again carry out the steps of the method of detecting the presence of the plug 28. If the presence of the plug 28 is still detected, the operations to remove the plug 28 are repeated. In a first embodiment of the purge device, a compressed air reservoir is associated with a purge line provided with a valve. The compressed air reservoir 25 and the valve are both open to purge the supply line 24. In a second embodiment, a switch is used to reverse the flow rate of the pump 22. The exhaust pipes are thus sucked and allow the purge of the supply pipe 24 to be purged. In a third embodiment of the purge device, a 4/2 way valve is arranged in the supply pipe 24 upstream of the pump 22. When a purge is performed, the 4/2 valve changes the flow direction in the supply line 24, thus allowing the exhaust gas to purge the supply line 24.

Claims (9)

REVENDICATIONS1. A method of detecting a plug (28) in a liquid urea supply line (24) of a selective catalytic reduction device of an exhaust line of a motor vehicle, the supply line (24) ) being provided with an injector (26), for injecting the liquid urea into the exhaust line, with a pressure sensor (30) adapted to measure the pressure in the supply line (24). ), and a pump (22) for circulating liquid urea in the supply line (24) for pressurizing the supply line (24), the method being characterized in that comprises the steps of: - opening the injector (26) for a predetermined time; - the detection, by means of the pressure sensor (30), a pressure in the supply line (24) greater than a threshold pressure value (38), the gearbox gradually taking place in the supply line; - comparing the time interval separating the opening of the injector (26) from the detection of the pressure greater than the threshold pressure value (38) with a threshold duration (42); - Detecting a plug (28) when the time interval is less than the threshold duration (42). 2. The detection method according to claim 1, characterized in that the method is implemented at the start of the motor vehicle after parking the vehicle. 3. Detection method according to one of claims 1 to 2, characterized in that it comprises a step consisting in: - determining the position of the plug (28) in the supply line (24) from comparing the time interval separating the opening of the injector (26) from the detection of the pressure greater than the threshold pressure value (38) with the threshold duration (42). 4. A method of removing a plug detected in a supply line, characterized in that the plug is previously detected by the detection method according to one of claims 1 to 3. 5. Suppression method according to claim 4, characterized in that the feed pipe (24) is provided with a heating device, the method comprising the step of: - heating the supply pipe (24) by means of the heating device. 6. Suppression method according to claim 4 or 5, characterized in that the method further comprises the steps of: - closing the injector (26); - The successive start and stop of the pump (22). 7. A method of removing a plug according to one of claims 4 to 6, characterized in that the supply line (24) is provided with a purge device, the method comprising the step of: - purging the supply line (24) by means of the purge device, the method further comprising, after purging, a new implementation of the steps of the detection method. 8. System for supplying liquid urea from an exhaust line of a motor vehicle for a selective catalytic reduction device, the system comprising a supply line (24), an injector (26), a pressure sensor (30), the feeding system being characterized in that it comprises a computer specially adapted to implement the method according to any one of the preceding claims. 9. A motor vehicle comprising an internal combustion engine and an exhaust line of the engine gases, the exhaust line being provided with a selective catalytic reduction device, the vehicle being characterized in that the selective catalytic reduction device a liquid urea feed system according to claim 8.