Purge phase control strategy for a selected catalytic reduction system   

Abstract: The method according to the invention is a method for controlling the purging of a sélective catalytic réduction System (1) for a vehicle. The sélective catalytic réduction System (1) has a pump (4) for reducing agent (3), at least one supply line (5) supplying reducing agent (3) to an exhaust line (10) of the vehicle, and a purge fluid suction device. The method is characterized in that it involves determining a purge duration as a fonction of a state of fill of the supply line (5) prior to activation of the purge phase, and in that the method forther comprises the updating of the purge duration during purging.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is the US National Stage under 35 U.S.C.§371 of International Application No. PCT/FR2011/050573, filed Mar. 21, 2011, and which claims priority to French Application No. 1052814 filed Apr. 13, 2010, the content (text, drawings and claims) of which is incorporated here by reference.

The present invention relates to a purge control method for a selective catalytic reduction system for a vehicle.

In the context of decontamination of the exhaust gases of a diesel engine, the selective catalytic reduction (or SCR) systems have the purpose of reducing the nitrogen oxides (NOx) contained in the exhaust gases. The SCR system uses a chemical reaction between said NO and a reducing agent. Conventionally, the reducing agent is ammonia (NH3). The ammonia is injected into the exhaust line for the gases. The injection of ammonia can be carried out through the intermediary of another chemical species such as urea.

The currently available decontamination systems require an SCR system that can bring the reducing agent to the injector under adequate injection conditions. An example of an SCR system is presented in FIG. 1. The SCR system 1 consists of one or more reservoirs 2 for storing the reducing agent 3, a pump 4, one or more lines 5, and an injector 6. The line 5 can be a heating line. The reservoirs 2 also have a level sensor 7, a temperature sensor 8, and at least one heating element 9. The line 5 makes it possible to bring the reducing agent 3 into the exhaust line 10 of the vehicle before the catalyst 11 of the SCR system 1. At the end of each run (operation of the vehicle), the lines 5, the injector 6 and/or the pump 4 (or a portion thereof) can be drained of their reducing agent 3. Thus, when these components are sensitive to cold, the purging of the reducing agent 3 makes it possible avoid damage in the case of a freeze when the vehicle is not in use. During the purge phase, the reducing agent 3 contained in these components is returned to the reservoir 2 and replaced with a purge fluid (air or exhaust gas). This purge method can be carried out, for example, by causing the pump 4 to rotate in the opposite direction, and by opening a suction device. The suction device can be the injector 6 in order to replace the reducing agent 3 with the exhaust gases.

In a vehicle, after being shut off by key, a phase of operation starts in which the computer of the engine and the actuators of the power train are kept supplied by the battery as long as needed to carry out the required recordings, updates and post-cooling phase. The purge phase is carried out during this phase of operation referred to as the power latch phase. This power latch phase can be as short as possible to avoid major short circuits.

The document FR-A-2 921 105 describes a purge procedure that includes the sequential activation and/or deactivation of the operation of the pump and of the suction device. However, the document does not describe a method that makes it possible to minimize the power latch phase.

Thus, there is a need for a method for controlling the purge phase that makes it possible to minimize the power latch phase.

SUMMARY

For this purpose, a purge control method for a selective catalytic reduction system for a vehicle is disclosed. The selective catalytic reduction system has a pump for a reducing agent, at least one line for supplying reducing agent to an exhaust line of the vehicle, and a device for suctioning purge fluid. The method includes determining a purge duration as a function of a filling state of the supply line before the activation of the purge, and in updating of the estimated purge duration during the purge.

According to a variant, the filling state of the supply line is determined by the percentage or the volume of reducing agent contained in the reducing agent supply line.

According to a variant, the updating of the purge duration is a function of the state of contact of the pump with the air and/or of the pressure at the outlet of the pump.

According to a variant, the state of contact of the pump with the air is determined by a measurement of the current consumed by the pump.

According to a variant, the method additionally includes:

determining the consistency between two of three pieces of data, the data being the purge duration, the measurement of the current consumed by the pump, and the measurement of the pressure at the outlet of the pump, and

performing a diagnosis on the state of operation of the elements of the selective catalytic reduction system.

According to a variant, the determination of the purge duration is also a function of the pressure at the device for suctioning purge fluid

According to a variant, the purge of the selective catalytic reduction system is activated as a function of at least one of the parameters selected from the group consisting of the temperature in the exhaust line of the vehicle, the filling level of a reducing agent reservoir, and combinations thereof.

According to a variant, the method additionally includes the calculation of the filling state of the supply line throughout the entire purge, and the recording of the filling state of the line when the purge is deactivated.

According to a variant, an activation of the purge includes the sequential activation of the pump and of the suction device.

According to a variant, a deactivation of the purge includes the sequential deactivation of the pump and of the suction device.

According to a variant, the activation or deactivation sequence of the pump and of the suction device is predetermined.

According to a variant, the suction device is a reducing agent injector or a valve.

A selective catalytic reduction (SCR) system for a vehicle is also disclosed that includes a reducing agent pump, at least one line for supplying reducing agent to an exhaust line of the vehicle, and a device for suctioning purge fluid, wherein the SCR system includes a controller which uses the above-described method.

In addition, a vehicle is disclosed that includes an exhaust line, wherein the vehicle includes the just-noted selective catalytic reduction system.

Other characteristics and advantages of the method will become apparent when reading the following detailed description of the embodiments, which are given only as examples and in reference to the drawings which show:

FIG. 1, already described, shows an example of an SCR system, and

FIG. 2 is an explanatory diagram of an example of a method according to the invention.

A purge control method for a selective catalytic reduction system 1 for a vehicle is provided. According to FIG. 1, the SCR system 1 has a pump 4 for a reducing agent 3, at least one line 5 for supplying reducing agent to an exhaust line 10 of the vehicle, and a device for suctioning purge fluid. The method of the invention includes the determination of a purge duration as a function of a filling state of the supply line 5 before the activation of the purge. The method further includes the updating of the purge duration during the purge.

As set forth below, the filling of the supply line 5 is the percentage or volume of reducing agent 3 contained inside the line 5. This can be determined as a function of the number of rotations of the pump or of its duration of operation. The suction device can be an injector 6 for reducing agent 3 in the exhaust line 10 of the vehicle. The purge fluid is then comprised of the exhaust gases of the vehicle. Alternatively, the suction device can be a valve which sucks in air as the purge fluid. The valve is supported, for example, by the injector 6.

The purge control method makes it possible to control the purge of an SCR system with highly precise management of voltage application to the computers and actuators required for this purge to take place. Thus, the method makes it possible to obtain a power latch phase duration which is as short as possible in order to avoid major short circuits and minimize the power consumption of the vehicle. The method allows a generic control of the safety of the supply lines, while avoiding the risks caused by an excessively long power latch duration.

The purge control method makes it possible to manage the purge of several types of SCR systems. The method can be used in the presence or absence of a pressure sensor at the outlet of the pump 4, at the outlet of the supply line 5, or at the injector 6 in the exhaust line 10 of the vehicle. The method is suitable for SCR systems 1 having different positions of the SCR catalyst 11 in the exhaust line 10. The method is suitable for an SCR system 1 which uses air or the exhaust gas as the purge fluid. The method is advantageously used in an SCR system which has no pressure sensor.

The steps of the method according to the invention will be better understood in reference to FIG. 2. The figure describes an example of the method which is used by a supervisor or controller of the SCR system 1, and in which the suction device is the injector 6. FIG. 2 has, on the three time axes, the respective states of the engine of the vehicle, of the controller of the SCR system 1, and of the actuators used during the purge.

During the operation of the vehicle, the engine turns, the controller maintains the SCR system under pressure. The pump 4 and the injector 6 for the reducing agent 3 are activated.

In step A, reference 14 indicates a stop in the application of a voltage to the engine, which implies a preactivated need for a purge. In other words, the stop of the engine (stop in the application of a voltage to the engine) indicates the need for a purge. If the contact key does not indicate a stop in the power supply to the vehicle (the contact key can be in the “accessories” position in one vehicle example), the purge authorization process is triggered after a prolonged engine stop (possibly based on the temperature at the exhaust). Alternatively, the purge authorization process can be triggered by shut off by key, that is to say a position of the key indicating a stop in the power supply to the vehicle. The shut-off by key then confirms the need for a purge, which is preactivated by the stopping of the engine. If the need for a purge is confirmed, the control method proceeds to the next step. A lack of heating can also preactivate a need for a purge.

In step B, the controller requests maintenance of the engine state in the power latch phase, and then switches to standby. The pump 4 and the injector 6 are on standby.

In step C, the purge of the SCR system 1 is authorized at a time calculated according to reference no. 12. Reference no. 12 corresponds to an examination of the temperature at the exhaust, of the filling of the reservoir 2, or of the supply line 5, in order to calculate the time of authorization of the purge. In other words, the purge is authorized as a function of parameters of the SCR system 1 acquired based on the stopping of the engine. The purge can be authorized as a function of the filling level of the reservoir 2 of reducing agent 3, or of the filling of the supply line 5 upon stopping of the engine. If these components have no reducing agent 3, the control method does not proceed to the purge. The purge can also be authorized as a function of the conditions in the exhaust line 10 of the vehicle, for example, the temperature of the exhaust gases. This is particularly the case when the suction device is the injector 6 of the SCR system. The purge can then be activated when the temperature of the exhaust gases is sufficiently low so that the components (line 5, pump 4, sensors 7, 8) of the SCR system 1 are not damaged.

In step D, the pump 4 and the injector 6 are activated sequentially. The order of activation can be predetermined or can be selected at the time of the implementation of the method.

In step E, the pump 4 and the injector 6 have been activated, and the counting of the purge duration starts. The purge duration is estimated according to reference no. 13. Reference no. 13 corresponds to an examination of the pressure at the exhaust, of the capacity of the pump 4, or of the filling of the supply line 5, in order to estimate the purge duration. In other words, the purge duration (or timing) is determined as a function of parameters of the SCR system 1 and/or of the vehicle acquired before the activation of the purge. The purge duration can be determined as a function of the length of the supply line 5. In particular, the purge duration can be determined as a function of the filling state of the supply line 5 before the activation of the purge. The purge duration can also be a function of the pressure at the purge fluid suction device. In the case where the suction device is the injector 6, the purge duration can be a function of the pressure at the exhaust, that is to say at the injector 6 in the exhaust line 10. The pressure can be determined using a sensor in the vicinity of the injector 6, using a model associated with the sensors positioned in the exhaust line 10 a distance from the injector 10, or using a model of the engine of the vehicle. In the case where the suction device is a valve, the purge duration can be a function of the atmospheric pressure. The purge duration can also be a function of the capacity of the pump 4.

Step F takes place during the purge of the SCR system 1, and comprises performing the synthesis of the timing. This comprises updating the purge duration. The updating of the purge duration can be a function of the state of contact of the pump 4 with the air (or more generally the state of contact with the purge fluid) and potentially of pressure data at the output of the pump 4. In some pump technologies, the state of contact of the pump 4 with the air (or more generally with the purge fluid) can be determined using a measurement of the current consumed by the pump 4. Indeed, the resistance to suction of the purge fluid is different from that of the reducing agent. As a result, there is a difference in the consumption of the pump 4. These update data can be combined. The purge duration can be updated on the basis of other parameters of the SCR 1 system and/or of the vehicle, such as the pressure in the supply line 5.

In one embodiment, the method additionally includes the determination of the consistency between two of the three pieces of data, which are the purge duration, the measurement of the current consumed by the pump 4, and the measurement of the pressure at the outlet of the pump 4. On the basis of these parameters, a diagnosis of the state of operation of the elements of the SCR system 1 can be carried out. For example, if, after the elapse of the maximum estimated purge duration, the pressure corresponds to that of the air, but the current of the pump 4 is high, one can deduce therefrom that the purge has failed (due to the pump 4 or due to a blocked suction device; other causes are possible; they depend on the choice of components of the SCR system).

In step G, the pump 4 and the injector 6 are deactivated sequentially. The deactivation order can be predetermined, or selected at the time of the implementation of the method.

In step H, the controller, the pump 4, and the injector 6 are on standby. The method can include the calculation of the filling state of the supply line 5 throughout the entire purge, and the recording in step H of the filling state of the line 5 as soon as the purge is deactivated. A deactivation may be due to the fact that the purge duration has reached its end. Alternatively, the deactivation can be an abrupt interruption of the purge before the end of the purge duration. The abrupt interruption of the purge can occur following the introduction of the contact key by a user of the vehicle, a restart of the engine of the vehicle, a shortened duration of the power latch phase, or because of a dysfunction of one of the actuators performing the purge. In the case of an abrupt interruption of the purge, the method proceeds directly to step H, regardless of what the ongoing step of the method is.

The recorded filling state can be used for the implementation of a subsequent priming procedure allowing the filling of the SCR system 1 with the reducing agent 3.

In step I, once all the previous operations have been carried out, the controller deactivates the maintenance of the engine in the power latch phase.

The method has been described for the example of a purge carried out by suctioning of the exhaust gases by the injector 6. However, the method is also appropriate for a purge carried out by suctioning of air by means of a valve. When the suction device is a valve, steps A, B, D and F to I remain identical to those described above. In step C, the purge of the SCR system 1 is authorized at a time which is calculated according to reference no. 12. Reference no. 12 corresponds to an examination of the filling of the reservoir 2, or of the supply line 5, in order to calculate the time of authorization of the purge. In other words, the purge can be authorized as a function of the filling level of the reservoir 2 of reducing agent 3, or of the filling of the supply line 5, acquired on the basis of the stopping of the engine. The purge authorization is not obtained on the basis of the conditions in the exhaust line 10 of the vehicle. In step E, the purge duration is estimated according to reference no. 13. Reference no. 13 corresponds to an examination of the atmospheric pressure, of the capacity of the pump 4, or of the filling of the supply line 5, in order to estimate the purge duration (or timing). In other words, the purge duration can be a function of the filling state of the supply line 5, or of the atmospheric pressure acquired before the activation of the purge.

The invention further relates to a selective catalytic reduction system 1 for a vehicle, that includes a controller that uses the method according to the invention. The SCR system according to the invention has the above-described characteristics.

The invention further relates to a vehicle that includes a catalytic reduction system according to the invention.