WO2012098309A1 - Method for monitoring an exhaust line, and vehicle suitable for implementing said method - Google Patents

Abstract

The invention relates to a method for monitoring an exhaust line of a vehicle provided with an SCR system comprising a urea tank (10), characterised in that the method comprises the steps of: estimating the percentage of urea in the solid or liquid state in the urea tank (10) of the SCR system in accordance with the amount of time the vehicle has been parked; and determining the thermal power to be supplied in order to prime the SCR system according to the estimated percentage. The invention also relates to the associated vehicle. The invention makes it possible to save energy.

Description

 A METHOD FOR CONTROLLING AN EXHAUST LINE AND A VEHICLE ADAPTED FOR IMPLEMENTING SAID METHOD

The present invention claims the priority of the French application 1 150348 filed January 17, 201 1 whose content (text, drawings and claims) is here incorporated by reference.

[Ooo2] The invention relates to a method of controlling an exhaust line and the associated vehicle.

[OOO3] The emissions legislation for heavy vehicles and weight (in particular Euro 5 and Euro 6) provide inter alia a reduction of nitrogen oxides NO _x discharges into the atmosphere. To achieve this objective, SCR (Selective Catalytic Reduction) is known. It allows the reduction of nitrogen oxides by injection of a reducing agent, usually ammonia, into the exhaust line. This ammonia can come from the decomposition by thermolysis of a solution of an ammonia precursor whose concentration can be that of the eutectic. Such an ammonia precursor is generally a urea solution.

[ooo4] With the SCR process, the high clearance of _NOx produced in the engine during a combustion optimized efficiency are treated in engine output in a catalyst. This treatment requires the use of the reducing agent at a precise concentration level and in an extreme quality. The solution is precisely metered and injected into the exhaust stream where it is hydrolysed before converting nitrogen oxide (NO _x ) to nitrogen (N ₂ ) and water (H ₂ O).

[ooo5] To do this, the vehicles are generally equipped with a tank 10 containing an additive solution (urea generally), and a device for metering and injecting the desired amount of additive into the exhaust line. .

[Ooo6] Since the aqueous urea solution generally used for this purpose (eutectic at 32.5% by weight of urea) freezes at -1 1, 5 ° C, it is desirable to provide a heating device to liquefy the water. solution in order to be able to inject it into the exhaust line when starting in freezing conditions. In the state of the art, several systems have been provided for this purpose. Generally, these systems include heating devices involving either specific heating elements or a bypass of the engine cooling circuit (see for example WO 2006/064001). [ooo8] With regard to the use of specific heating elements, it is known to put inside the tank containing the urea solution, and possibly, on the lines (supply and return, the case urea, on the pump, the filter ... and other active elements of the system, heating resistive elements. For example, the application DE 2004 061 259 discloses a system using separate resistive elements for the reservoir, the pump, the dosing module and the feed and return lines of urea. temperature probes present on the tank, the pump and the dosing module and when one of these probes indicates a temperature below a given threshold value (generally the freezing temperature of the solution), all these resistances are activated so as to thaw the entire system. Such a strategy has several disadvantages.

[ooi o] Firstly, when starting a vehicle in cold weather (freezing), all the electrical devices (defrosting the windows, heating the passenger compartment, etc.) are generally started simultaneously, which causes a peak of electrical consumption which is then added that of the heating system SCR.

[ooi i] Then, it should be noted that some parts of an SCR system may sometimes contain urea solution and sometimes not (see for example the upper part of the tank and the lines in case they are purged). Therefore, heating them while they do not contain liquid unnecessarily consumes power and can further lead to the premature degradation of the resistive elements in these areas.

It is also known from FR-A-2 921 104 a method of heating an SCR system using resistive heating elements. However, none of the above systems applies a different heating depending on whether the urea of the tank is completely frozen or not.

There is therefore a need for a control method of a vehicle exhaust system provided with a SCR system consuming less energy.

For this, the invention provides a method of controlling a vehicle exhaust line provided with an SCR system. The system includes a urea tank. The method comprises a step of estimating the percentage of urea in the solid or liquid state in the urea tank of the SCR system according to the parking time of the vehicle. The method also includes a step of determining the thermal power to be provided to ensure the boot of the SCR system based on the estimated percentage.

[Ooi 6] According to a variant, the method further comprises a step of comparing the ambient temperature to a threshold temperature and triggering the determination step as soon as the temperature is below the threshold temperature.

According to one variant, the threshold temperature is -7 ° C.

[Ooi 8] According to one variant, the parking time is obtained by making the difference between the moment of the restart of the vehicle and the moment of stopping the vehicle. According to one variant, the estimation step also takes into account the level of urea in the tank.

According to a variant, the estimated percentage is different depending on whether the level is greater than a threshold value or less than this threshold value.

According to a variant, the estimation step is implemented by a computer, the computer taking into account the temperature of the SCR system during parking of the vehicle.

According to a variant, the estimation step is implemented by a computer, the computer assuming that the temperature of the SCR system is - 30 ° C while parking the vehicle. This allows the use of a method according to the invention especially in the context of vehicles that do not allow to know the outside temperature during parking.

According to one variant, the determination step is implemented by the use of mappings.

The invention also relates to a vehicle adapted to the implementation of the previously described method.

Other features and advantages of the invention will appear on reading the following detailed description of the embodiments of the invention, given by way of example only and with reference to the drawings which show:

• Figure 1, a SCR system boot scheme in the regulatory case, and

 FIG. 2, a diagram of an example of initiation of the SCR system according to the invention.

It is proposed to take into account the mass fraction of urea for priming the SCR system. Indeed, the regulatory phases are established for cold conditions that often do not correspond to the use that the user of the vehicle makes. According to the regulations, for a tank exposed for 7 days at -15 ° C (freezing state), whose filling level is 50%, the SCR system must be operational after 20 minutes of heating by a heating unit. Such a stress involves heating the urea of 100W for 20 minutes.

This is schematically shown in Figure 1 which is a boot scheme of the SCR system in the regulatory case. Figure 1 consists of two parts: the left part which is an illustration of the state of a urea tank of an SCR system just before heating to prime it and the right part which is an illustration of the state of the urea reservoir 10 just before the start of the SCR system.

On the left side, the urea tank 10 is shown in the state of chambering. The level of urea filling of this tank 10 is 50%. Urea has also been exposed to a temperature of -15 ° C for 2 days. In this case, the heating unit 12 included in the tank is inactive and the whole of the urea is frozen: 100% of the urea of the tank is in the solid state (tank completely hatched in the figure on the left ). In the case not shown where the tank 10 comprises thermal insulation means, the urea is completely frozen after 120 hours.

As explained above, this frozen urea will be heated by the heating unit 12 which is activated in the right part of Figure 1. The heating unit 12 is for example a heating resistor. In addition, the heating unit 12 produces 100W for 20 minutes to prime the SCR system. Part of the urea passes from the solid state to the liquid state (liquefaction) and becomes thus drawable.

However, the power of 100W for 20 minutes being used by default whatever the configuration of use of the vehicle, there are life situations in which a lower heating would start the SCR system of the vehicle.

This is schematically shown in Figure 2 which is a boot scheme of the SCR system in a non-regulatory case. Figure 2 also consists of two parts: the left side which is an illustration of the state of the urea tank just before heating to prime and the right side which is an illustration of the state of the tank urea just before starting the SCR system.

In this case, on the left side, it is the same tank 10 as Figure 1, but the experimental conditions vary. The level of urea filling of the tank 10 is still 50% but the urea has been exposed to a temperature of -30 ° C for 6 hours. In this situation, unlike in FIG. 1, only a portion of the urea of the urea reservoir has frozen. There is still a liquid portion in the reservoir 10. The reservoir 10 thus comprises a mixture of solid urea and liquid urea. As explained above, this frozen urea will be heated by the heating unit 12 which is activated in the right part of Figure 2. But, if the same amount of heating is applied, the proportion of liquid urea will be more important than in the case of Figure 1. This means that the SCR system could have been started with less heating. Taking into account the mass fraction or the percentage of urea in the liquid or solid state makes it possible to optimize the power used in the heating unit 12.

More specifically, it is proposed a control method of a vehicle exhaust line provided with an SCR system. The system includes a urea tank. The method comprises a step of estimating (by testing or modeling) the percentage of urea in the solid or liquid state in the urea tank of the SCR system according to the parking time of the vehicle. A simple way to know this time is to make the difference between the moment of the restart of the vehicle and the moment of stopping the vehicle. This step makes it possible to know the state of the urea in the tank 10 after a cold parking time. Indeed, the percentage of urea in the solid or liquid state depends on the amount of heat exchanged between the tank 10 and the outside. The longer the parking time, the greater the amount of heat exchanged and the greater the proportion of urea that has frozen.

The amount of heat can also be better estimated by taking into account the temperature of the SCR system during parking of the vehicle. This assumes the use of a dedicated sensor controlled by a computer. It may then be simpler for the calculator to carry out the estimation step by assuming that the temperature of the SCR system is -30 ° C during the parking of the vehicle, which corresponds to the worst case that a user is likely to have. to have to undergo.

The estimation step can further take into account the level of urea in the reservoir 10. The level of urea can be measured using a level gauge of the reservoir 10. Such a decision in account of the level of urea makes it possible to improve the estimate insofar as the percentage of liquid (respectively of solid) in urea depends both on the temperature and the amount of liquid to be solidified. The higher the urea level, the longer the solidification time of the whole urea.

As a simple example of taking into account the urea level in the estimation step, the percentage of urea in the solid or liquid state may be different depending on whether the level is greater than a value. threshold or lower than this threshold value. In Table 1 which is commented below, the threshold value is 3.6 L.

The method also comprises a step of determining the thermal power to be supplied to ensure the booting of the SCR system as a function of the estimated percentage. As explained with reference to the description of FIGS. 1 and 2, the method makes it possible to take into account the percentage of liquid or solid urea to determine the power to be supplied to the heating unit 12. This makes it possible to adapt the power for the different cases of the regulatory situation to the fair while ensuring the priming of the cold SCR system. When the urea is not completely frozen, it results in a decrease in the power or the activation time of the unit. This corresponds to an energy saving.

The determination step may be implemented by a computer, which may use the knowledge of maps. Table 1 below is an example of such a mapping for a tank 10 provided with thermal insulation. According to this example, in the estimation step, the level of urea in the tank 10 as well as the parking time of the vehicle are considered. The table gives, based on these data, an estimate of the mass fraction in the SCR tank (the first figure corresponds to the percentage of urea in the solid state and the second to the percentage in the liquid state) as well as the bring in to boot the SCR system. The values in the table are merely indicative. This is to illustrate the previously described method: SCR RESERVOIR WITH THERMAL INSULATION

Estimated time of estimation of the power to bring

Level

 Mass fraction parking in to prime the urea

 cold the tank 10 system SCR

<6 hours (30; 70) 50 W in 10 minutes

12 h <t <24h (50; 50) 70 W in 10 minutes

24 h <t <48 h (70; 30) 70 W in 20 minutes

> 3.6L

 48 h <t <72 h (80; 20) 100 W in 10 minutes

72 h <t <96 h (90; 10) 100 W in 15 minutes

96 h <t <120 h (100; 0) 100 W in 20 minutes

<6 hours (40; 60) 50 W in 10 minutes

12 h <t <24h (50; 50) 70 W in 10 minutes

24 h <t <48 h (70; 30) 70 W in 20 minutes

<3.6L

 48 h <t <72 h (100; 0) 100 W in 20 minutes

72 h <t <96 h (100; 0) 100 W in 20 minutes

96 h <t <120 h (100; 0) 100 W in 20 minutes

Table 1

Alternatively, the method further comprises a step of comparing the ambient temperature to a threshold temperature and the triggering of the determination step as soon as the temperature is below the threshold temperature noted T _seui |. When the temperature is higher than the threshold temperature, the heating of the tank 10 is not requested because it is in unnecessary effect of heating the tank 10 if the urea is already completely liquid. Since the freezing point of urea is -1 1, 5 ° C, it may be advantageous to fix

Tseuil at -7 ° C.

It is also proposed a vehicle adapted to the implementation of the method as described below. For the same reasons as above, this vehicle has a reduced energy consumption.

Claims

A method of controlling a vehicle exhaust line provided with an SCR system, the system comprising a tank (10) of urea, characterized in that the method comprises a step of:  estimating the percentage of urea in the solid or liquid state in the tank (10) of urea of the SCR system according to the parking time of the vehicle;  determination of the thermal power to be supplied to ensure the priming of the SCR system as a function of the estimated percentage. 2. The process according to claim 1, characterized in that the process further comprises a step of: - comparison of the ambient temperature with a threshold temperature (T _only ), - triggering the determination step as soon as the temperature is below the threshold temperature (T _seuN ) ,. 3. The method according to claim 2, characterized in that the threshold temperature (T _seuN ) is -7 ° C. 4. The method according to one of claims 1 to 3, characterized in that the parking time is obtained by making the difference between the moment of restarting the vehicle and the moment of stopping the vehicle. 5. The method according to one of claims 1 to 4, characterized in that the estimation step also takes into account the level of urea in the tank (10). 6. The method according to claim 5, characterized in that the estimate is different depending on whether the level is greater than a threshold value or less than this threshold value. 7. The method according to one of claims 1 to 6, characterized in that the estimation step is implemented by a computer, the computer taking into account the temperature of the SCR system during parking of the vehicle. 8. The method according to one of claims 1 to 6, characterized in that the estimation step is implemented by a computer, the calculator assuming that the temperature of the SCR system is -30 ° C during parking of the vehicle. 9. The method according to one of claims 1 to 8, characterized in that the determining step is implemented by the use of maps. 10. A vehicle comprising an exhaust line provided with an SCR system having a urea reservoir, characterized in that the vehicle comprises a computer, the computer being adapted to the implementation of the method according to one of the claims. 1 to 9.