WO2013153298A1

WO2013153298A1 - System for metering a reducing agent for a device for removing pollutants from the exhaust gases of an engine

Info

Publication number: WO2013153298A1
Application number: PCT/FR2013/050322
Authority: WO
Inventors: Mathieu Artault; Mohamed Bozian
Original assignee: Peugeot Citroen Automobiles Sa
Priority date: 2012-03-13
Filing date: 2013-02-18
Publication date: 2013-10-17
Also published as: FR2988133A1; FR2988133B1

Abstract

The invention relates to a system (10) for metering a reducing agent (12) for a device (14) for removing pollutants from the exhaust gases of a combustion engine, comprising a tank (16) for storing the reducing agent (12), a device (32) for metering the reducing agent (12), which has an inlet connected to said tank (16) and an outlet connected to the pollutant-removal device (14), and which is designed to inject a predetermined amount of reducing agent (12) into the pollutant-removal device (14) according to a metering guideline, and a calculation unit (38) which cooperates with the metering device (32) and which determines said metering guideline, characterized in that the metering system (10) comprises a measuring device (42) which is connected to the metering device (32) so as to measure the amount of reducing agent (12) actually injected by the metering device (36), and which cooperates with the calculation unit (38) in order to correct the metering guideline on the basis of the calculated difference between the metering guideline and the measured amount of reducing agent (12).

Description

SYSTEM FOR DETERMINING A REDUCING AGENT FOR A DEVICE FOR DETERMINING THE EXHAUST GAINS OF AN INTERNAL COMBUSTION ENGINE

The invention relates to a dosing system for a reducing agent 5 for a device for cleaning up the exhaust gases of an internal combustion engine.

Internal combustion engines produce and emit toxic pollutants in the exhaust gases, in particular nitrogen oxides or NO _x and soot particles.

Emissions standards for motor vehicles impose on manufacturers maximum quantities of pollutants released into the atmosphere that must be lower and lower.

This is the reason why the exhaust line of an internal combustion engine is generally equipped with pollution control means. Among the pollution control means used, there is in particular known a depollution device which comprises a catalyst enabling a reduction to be achieved. selective catalytic, also known as SCR for Selective Catalytic Reduction in English terminology.

This depollution device is designed to remove nitrogen oxides by chemically reducing them with a reducing agent.

For this purpose, there is known a dosing system of a reducing agent which comprises a reservoir for the storage of the reducing agent, and a dosing device of the reducing agent.

The reducing agent is, for example, ammonia stored in the salt form solid state tank which is heated to gaseous state.

The metering device has an inlet duct connected to the tank and an outlet duct connected to the SCR depollution device.

The metering device is designed to inject a predetermined quantity of ammonia into the exhaust line, upstream of the depollution device SCR, according to a dosing instruction determined by a calculation unit.

The dosing set point is in particular determined as a function of the nitrogen oxide content measured in the exhaust gas at the outlet of the SCR depollution device. The metering device comprises an injection means which is able to occupy an open state in the injection means and which injects ammonia upstream of the SCR depollution device.

The amount of ammonia injected depends directly on the injection time and the flow rate of the injection means of the metering device.

Thus, the injection means occupies its open state for a determined period of time, as a function of the calculated dosing setpoint and the flow rate of the injection means.

A disadvantage of this type of metering device is its lack of precision over time.

Indeed, the metering device is designed to operate the entire life of the associated vehicle.

However, there is a dispersion of the amount of ammonia actually injected relative to the dosing setpoint and therefore with respect to the amount of injected reductant desired.

This dispersion can cause malfunctions of the SCR depollution device and the vehicle.

In the case of a sub-injection of ammonia, the SCR depollution device does not operate optimally and the driver of the vehicle is notified by a message indicating a pollution control problem.

Conversely, in the case of over-injection of ammonia, the ammonia reservoir may be exhausted before the normal maintenance step and the over-injection of ammonia may cause olfactory discomfort. driver.

In particular to overcome these drawbacks, the invention proposes a dosing system for a reducing agent for a device for cleaning up the exhaust gases of a combustion engine, of the type which comprises:

a reservoir for the storage of the reducing agent,

a device for dosing the reducing agent which has an inlet connected to said reservoir by an inlet duct and an outlet connected to the depollution device by an outlet duct, and which is designed to inject a predetermined quantity of reducing agent in the depollution device, according to a dosing instruction,

a calculation unit which cooperates with the metering device and which determines said metering instruction, characterized in that the metering system comprises a measuring device which is connected to the outlet duct of the metering device; dosing device, for measuring the quantity of reducing agent actually injected by the metering device, and which cooperates with the calculation unit in order to correct the dosing setpoint, as a function of the difference calculated between the dosing setpoint and the amount of reducing agent measured.

This characteristic makes it possible to calibrate the dosing system throughout its life, so that the metering device injects into the depollution device the quantity necessary and sufficient for the proper functioning of the depollution device.

According to another characteristic, the reducing agent is ammonia which supplies the metering device in the gaseous state, and the measuring device comprises:

a bottle containing a solution for dissolving the gaseous reducing agent,

a measurement pipe which connects the dosing device to the bottle, to supply the bottle with a reducing agent,

a means for measuring the hydrogen potential of the solution contained in the flask, for determining the quantity of reducing agent actually injected by the dosing device into the flask.

Such a measuring device makes it possible to measure in real time the quantity of reducing agent injected by the metering device.

In addition, the solution contained in the bottle for dissolving the reducing agent is water or any liquid for dissolving ammonia.

Water has the advantage of being inexpensive and available in quantity.

According to another characteristic, the metering device comprises an injection means which is able to occupy an open state in which the reducing agent is injected through the associated outlet duct, and a closed state, the cooperating injection means with a control means which controls the opening of the injection means during a determined opening time to inject a quantity of reducing agent into the pollution control device corresponding to the dosing setpoint.

In addition, the opening time of the injection means is determined at least as a function of the pressure upstream of the metering device and the pressure downstream of the metering device.

The injection means is a solenoid valve. In a complementary manner, the metering system comprises a three-way valve which is connected to the outlet duct of the metering device, to the measurement duct and to a depollution duct connected to the depollution device, the valve is controlled so as to occupy selectively a measurement state in which the reducing agent is injected into the measuring device, and a depollution state in which the reducing agent is injected into the pollution control device.

According to another characteristic, the reducing agent is stored in solid form in the storage tank, the storage tank comprising heating means which are designed to bring the reducing agent into a gaseous state.

In addition, the reservoir preferably comprises at least one main reserve cartridge and a secondary buffer cartridge which is connected to said main cartridge, each cartridge being equipped with a heating means for bringing the reducing agent to a gaseous state, the cartridge secondary having a capacity less than the capacity of the main cartridge to promote the temperature rise of the reducing agent.

The invention also relates to a vehicle equipped with such a system for dosing a reducing agent, and the method for implementing the system according to the invention.

Other features and advantages of the invention will appear on reading the detailed description which follows for the understanding of which reference will be made to the single appended figure which is a simplified diagram illustrating the dosing system according to the invention.

Diagrammatically in the single figure a dosing system 1 0 of a reducing agent 1 2 for a device 14 for removing pollution from the exhaust gases of a combustion engine (not shown), such as a motor of a vehicle automobile (not shown).

The depollution device 14 is of the so-called SCR type, which comprises a catalyst enabling a selective catalytic reduction by injection of the reducing agent 12 into the catalyst.

The reducing agent 12 is ammonia which is stored in solid form, here in salt form, in a tank 1 6.

The tank 1 6 is equipped with a first main cartridge 1 8a, a second main cartridge 1 8b and a secondary cartridge 20. The main cartridges 1 8a, 1 8b are arranged in a box 22 which is thermally insulated and which is fixed on the structure of the associated vehicle.

Each main cartridge 1 8a, 1 8b and the secondary cartridge 20, has a heating means 24a, 24b, 26 respectively, as a heating resistor, which is designed to warm the reducing agent 12 to bring it to a temperature. gaseous state.

The main cartridges 1 8a, 1 8b are two in order to reduce the temperature rise time of the reducing agent 12 and to increase the storage capacity of reducing agent.

The secondary cartridge 20 is connected to the two main cartridges 1 8a, 18b by a supply duct 28 which is equipped with a non-return valve 30.

The nonreturn valve 30 is designed to allow the passage of the reducing agent 1 2 only in one direction, namely from the main cartridges 1 8a, 18b, to the secondary cartridge 20.

The secondary cartridge 20 has a volume less than the volume of each of the main cartridges 18a, 18b to form a buffer reserve and to feed the dosing system 1 0 reducing agent 1 2 in the gaseous state quickly.

With reference to the single figure, the dosing system 1 0 comprises a device 32 for dosing the reducing agent 1 2.

The metering device 32 has an inlet which is connected to the supply duct 28 of the tank 1 6 via an inlet duct 34.

In addition, the metering device 32 has an outlet which is connected to the depollution device 14 by an outlet duct 36, so as to supply the decontamination device 14 with a reducing agent 12.

The metering device 32 is designed to inject a quantity of reducing agent 1 2 predetermined into the depollution device 14, according to a dosing instruction.

In a complementary manner, the dosing system 1 0 comprises a calculation unit 38 which cooperates with the metering device 32 and which determines said dosing instruction.

The dosing set point is determined to adjust the amount of reducing agent 1 2 as a function of the nitrogen oxide content measured in the gases. exhaust at the outlet of the depollution device 14, by means of a probe (not shown), for example.

The metering device 32 comprises a solenoid valve 40 forming injection means, which is able to occupy an open state in which the reducing agent 12 is injected through the associated outlet duct 36, and a closed state in which the device dosing 32 is closed.

The solenoid valve 40 is able to control the opening of the metering device 32 for a given time, to inject a quantity of reducing agent 12 into the decontamination device 32 which corresponds to the dosing setpoint.

The opening of the solenoid valve 40 is controlled by a control means (not shown) at a variable opening time and a fixed frequency which varies as a function of the rate of reducing agent 12 desired.

Indeed, over a given period of time, for example 500 milliseconds, the solenoid valve 40 occupies its open state for a variable time which is between 50 milliseconds and 500 milliseconds for example, depending on the flow rate and the amount of reducing agent 12 to inject.

In addition, the temperature of the reducing agent 1 2, the pressure upstream of the solenoid valve 40 and the pressure downstream of the solenoid valve are taken into account to determine the time and frequency of opening of the solenoid valve 40. .

According to another aspect, the metering system 1 0 comprises a measuring device 42 which is designed to measure the amount of reducing agent 12 actually injected by the metering device 32 into the outlet duct 36.

For this purpose, the measuring device 42 is equipped with a hermetic bottle 44 which is connected to the outlet duct 36 of the metering device 32 via a measuring duct 46.

The measurement duct 46 is designed to supply the bottle 44 with a gaseous reducing agent 12.

The vial 44 contains a solution 48 which makes it possible to dissolve the gaseous reducing agent, the solution 48 being here water.

Without limitation, the solution may be boric acid or any other solution capable of dissolving the reducing agent.

In addition, the measuring device 42 comprises measuring means

50 of the hydrogen potential, called pH, of the solution 48 contained in the vial 44, to determine the amount of reducing agent 1 2 actually injected by the metering device 32 into the vial 44.

The dissolution of the reducing agent 1 2, here ammonia, in a fluid, here water, forms OH ^" ions according to the following formula:

NH ₃ + H ₂ O> NH ₄ ⁺ + OH ^"

The formation of OH ions ^"leads the solution 48 to move from a neutral medium in a basic medium.

The more the amount of reducing agent 1 2 injected into the solution 48, the greater the hydrogen potential is basic, so that the measurement of the hydrogen potential makes it possible to measure the amount of reducing agent 1 2 injected into the vial 44, for a volume of solution 48 determined, according to the following law:

With:

- m ₍ NH3) for the amount of ammonia in grams per mol;

- k an acidity constant;

- pH the hydrogen potential.

The measuring device 42 transmits the measurement of the amount of reducing agent 1 2 to the calculation unit 38 which corrects if necessary the dosing instruction.

The new dosing setpoint is then transmitted to the dosing device 32, whereby the dosing device 32 injects a quantity of reducing agent 12 corresponding to the set point.

The dosing system 1 0 according to the invention is designed to selectively pass a depollution mode in which the metering device 32 injects the reducing agent 12 into the depollution device 14, in a calibration mode in which the metering device 32 injects the reducing agent 12 into the measuring device 42.

For this purpose, the metering system 1 0 comprises a three-way valve 52, of which a first channel is connected to the outlet duct 36 of the metering device 32, a second channel is connected to the measurement duct 46 of the measuring device 42, and a third channel is connected to a pollution control duct 54 which is itself connected to the depollution device 14.

The valve 52 is controlled so as to selectively occupy a measurement state in which the reducing agent 12 is injected from the metering device 32, to the bottle 44 of the measuring device 42, and a state of depollution in which the reducing agent 12 is injected from the metering device 32, to the depollution device 14.

The system is programmed to enter the calibration mode at a predetermined frequency, for example every 5000 kilometers.

When the dosing system 1 0 is in calibration mode, the amount of reducing agent 1 2 injected by the metering device 32 is measured by the measuring device 42 at different operating ranges of the metering device 32.

The measurement of the reducing agent 12 is carried out at different operating ranges, for example at low flow rate, medium flow rate and high flow rate.

The calculation unit 38 calculates the difference between the measurement made by the measuring device 42 and the reduction agent quantity instruction 12 given to the dosing device 32, for each operating range.

The setpoint is corrected, or calibrated, according to this difference.

However, it is possible to determine a dosing error tolerance for which the setpoint is not corrected, for example plus or minus ten percent difference between the measurement made and the setpoint.

The solution 48 contained in the bottle 42 is regularly replaced by an unsoiled solution, here water, at each maintenance intervention for example.

For this purpose, the bottle 44 should be replaced by a new bottle 44.

Similarly, the main cartridges 1 8a, 1 8b containing the reducing agent 1 2 are regularly replaced by new full cartridges, at a periodicity determined according to the autonomy of the metering system 10.

Advantageously, the metering system 1 0 is switched to calibration mode during favorable driving conditions (for example in fast city / motorway) in steps of 5000 km with a maximum tolerance of 1000 km).

The dosing system 1 0 according to the invention makes it possible to improve the accuracy of the amount of reducing agent 1 2 injected into the depollution device 14.

This advantage makes it possible to avoid the olfactory discomfort caused by an over-injection of reducing agent 1 2. In addition, an improvement in the injection precision makes it possible to avoid the anticipated change in the main reducing agent cartridges 18a, 18b 12 before the planned maintenance step, due to an over-injection of reducing agent 12.

Similarly, precisely controlling the amount of injected reducing agent 12 makes it possible to reduce the margin of error tolerance of the amount of reducing agent 12 in order to reduce the amount of reducing agent 12 embedded in the vehicle.

Claims

1. Dosing system (10) for a reducing agent (12) for a pollution control device (14) for the exhaust gases of a combustion engine, of the type comprising:

a reservoir (16) for storing the reducing agent (12),

a metering device (32) for the reducing agent (12) having an inlet connected to said reservoir (16) via an inlet duct (34) and an outlet connected to the depollution device (14) via a duct outlet (36), which is adapted to inject a predetermined quantity of reducing agent (12) into the depollution device (14), according to a dosing instruction,

- a calculation unit (38) which cooperates with the metering device (32) and which determines said metering instruction, characterized in that the metering system (10) comprises a measuring device (42) which is connected to the duct outlet (36) of the metering device (32), for measuring the amount of reducing agent (12) actually injected by the metering device (36), and cooperating with the computing unit (38) to correct the dosing setpoint, as a function of the difference calculated between the dosing setpoint and the amount of reducing agent (12) measured.

2. Dosing system (10) according to the preceding claim, characterized in that the reducing agent (12) is ammonia which feeds the metering device (32) in the gaseous state, and in that the device measuring device (42) comprises:

a bottle (44) containing a solution (48) for dissolving the gaseous reducing agent (12),

- a measuring duct (46) connecting the metering device (32) to the bottle (44), to supply the bottle (44) with reducing agent (12),

a means (50) for measuring the hydrogen potential of the solution (48) contained in the vial (44), to determine the quantity of reducing agent (12) actually injected by the metering device (32) into the vial ( 44).

3. Dosing system (10) according to the preceding claim, characterized in that the solution (48) contained in the bottle (44) for dissolving the reducing agent (12) is water.

4. Dosing system (10) according to one of the preceding claims, characterized in that the metering device (32) comprises an injection means (40) which is adapted to occupy an open state in which the reducing agent (12) is injected through the associated outlet duct, and a closed state, the injection means (40) cooperating with a control means which controls the opening of the injection means (40) for a period of time. determined opening for injecting a quantity of reducing agent (12) into the depollution device (14) corresponding to the dosing setpoint.

5. Dosing system (10) according to claim 4, characterized in that the opening time of the injection means (40) is determined at least as a function of the pressure upstream of the metering device (32) and the pressure downstream of the metering device (32).

6. dosing system (10) according to claims 4 or 5, characterized in that the injection means (40) is a solenoid valve.

7. Dosing system (10) according to one of the preceding claims, characterized in that it comprises a three-way valve (52) which is connected to the outlet duct (36) of the metering device (32), to the duct measuring device (46) and a depollution line (54) connected to the depollution device (14), and in that the valve (52) is controlled so as to selectively occupy a measurement state in which the reducing agent ( 12) is injected into the measuring device (42), and a depollution state in which the reducing agent (12) is injected into the depollution device (14).

The dosing system (10) according to one of the preceding claims, characterized in that the reducing agent (12) is stored in solid form in the storage tank (16), the storage tank (16) comprising heating means (24a, 24b, 26) which are adapted to bring the reducing agent (12) to a gaseous state.

9. dosing system (10) according to one of the preceding claims, characterized in that the reservoir (16) comprises at least one main cartridge (18a, 18b) reserve and a secondary cartridge (20) buffer which is connected to said main cartridge, each cartridge being equipped with a heating means (24a, 24b, 26) for bringing the reducing agent (12) to a gaseous state, the secondary cartridge (20) having a capacity less than the capacity of the cartridge main (24a, 24b) to promote the temperature rise of the reducing agent (12).

10. Vehicle equipped with a dosing system (10) of a reducing agent (12) according to one of the preceding claims.