FR2890412A1 - METHOD FOR INTRODUCING A REACTIVE AGENT IN THE EXHAUST GAS ZONE OF A COMBUSTION ENGINE AND DEVICE FOR IMPLEMENTING THE METHOD - Google Patents

Abstract

Process for introducing a reactive agent into an exhaust gas zone (13) of a combustion engine (10) in which the reagent-reactive agent of the reactive agent (p_Rea) is dosed by a dosing device of the reagent (14), the assay of the reagent being predefined according to a signal of the reagent (S_Rea). The difference (dp) between the pressure of the reactive agent (p_Rea) and the pressure of the exhaust gas (p_abg) is determined and the signal of the reactive agent (S_Rea) is influenced as a function of this pressure difference ( dp).

Description

Field of the invention

  The present invention relates to a method for introducing a reactive agent into an exhaust zone of a combustion engine wherein the reagent-reactive agent of the reactive agent is dosed by an agent dosing device. reagent, the dosage of the reactive agent being pre-defined according to a signal of the reactive agent.

  The invention also relates to a device for implementing this method.

  State of the art DE 199 03 439 A1 discloses a method and a device for managing a combustion engine whose exhaust gas zone is equipped with a catalyst SCR (Selective Catalytic Reduction Catalyst) reducing to nitrogen the oxides of nitrogen from the exhaust gases of the combustion engine using a reactive agent. The dosage of the reactive agent is preferably according to the operating parameters of the combustion engine, such as, for example, its speed of rotation and the quantity of fuel injected. In addition, the dosage is preferably based on the characteristics of the exhaust gas, such as, for example, the temperature of the exhaust gas or the operating temperature of the SCR catalyst.

  As reactive agent, for example, ammonia is used as reducing agent. This ammonia is obtained from an aqueous solution of urea. The dosage of the reagent or the raw materials of the reagent must be carefully done. Too low a dosage results in an incomplete reduction of the nitrogen oxides in the SCR catalyst. Too high a dosage leads to slipping of reagent, that is to say on the one hand to an unnecessarily high consumption of reagent and secondly to an unpleasant odor release according to the composition of the reagent agent .

  DE 101 39 142 A1 describes a system for treating the exhaust gases of a combustion engine also using an SCR catalyst to reduce NOx nitrogen oxide emissions. The ammonia is obtained by a hydrolysis catalyst upstream of the SCR catalyst from an aqueous solution of urea. The hydrolysis catalyst converts the urea contained in the aqueous solution of urea into ammonia and carbon dioxide. To ensure an accurate dosage, it is intended to determine the concentration of the aqueous solution of urea. The aqueous solution of urea must be pressurized with a pump and a metering valve sets a predetermined flow rate.

  The setting of the reference flow rate or the amount of dosing can be done according to the teaching of document EP 1 024 254 A2 from an operating parameter of the combustion engine, for example the quantity of fuel to be injected and / or its rotational speed and if necessary at least one characteristic of the exhaust gas, for example the temperature of the exhaust gas.

  DE 10 2004 031 624 A1 (previously unpublished) describes a method of managing an SCR catalyst used to clean the exhaust gases of a combustion engine; according to this method, the level of the reactive agent filling of the SCR catalyst is controlled or regulated according to a predetermined storage-age set value. The precise predefinition of the storage set point ensures that in the non-stationary states of the internal combustion engine, a sufficient quantity of reactive agent is available to eliminate as much as possible the raw emissions of oxides. NOx nitrogen from the combustion engine and on the other hand reduce the slip of reactive agent to a minimum, or even completely avoid it.

  The level of reactive agent filling of the SCR catalyst is determined by means of a catalyst model taking into account the mass flow rate of nitrogen oxides NOx entering the SCR catalyst, the mass flow rate of NOx nitrogen oxides. leaving the catalyst SCR, the catalyst temperature and optionally the slip of the reagent. The maximum possible filling level of the reactive agent of the SCR catalyst depends in particular on the operating temperature of the SCR catalyst which is maximum for the low operating temperatures and decreases as the operating temperature increases. The efficiency of the SCR catalyst depends on the catalytic activity which is low at low temperatures and goes through a maximum when the temperature increases to fall again when the operating temperature continues to increase.

  Document DE 100 65 125 A1 partially describes the calculation of a measurement of the temperature of the exhaust gas using the rotation speed of the combustion engine as well as the air signal captured in an intake zone of air from the combustion engine.

  OBJECT OF THE INVENTION The object of the present invention is to develop a process for introducing a reactive agent into the zone of the exhaust gases of a combustion engine as well as a device for carrying out this process. , allowing an exact dosage of the reagent.

  DESCRIPTION AND ADVANTAGES OF THE INVENTION To this end, the invention relates to a process of the type defined above, characterized in that the difference between the pressure of the reactive agent and the pressure of the exhaust gas is determined, and the signal of the reactive agent is influenced as a function of this pressure difference.

  The process according to the invention makes it possible to take account of the pressure conditions in the zone of the exhaust gases for the purpose of measurement and which are taken into account to influence the signal of the reactive agent as a function of the difference between the pressure. of the reactive agent and the pressure of the exhaust gas.

  The reactant signal is influenced by acting on or correcting the characteristic curve of the reagent dosage device; this curve is the relationship between the reactant signal and the reagent dosage amount.

  This makes it possible to modify the quantity dosed as a function of the pressure difference obtained. The action on the assay by the reactive agent signal allows a faster reaction to a possible variation of the pressure difference with respect, for example, to a pressure-fixing action of the reactive agent.

  The method according to the invention allows an exact dosage of the reactive agent thus avoiding any uneconomic overdose or underdosing which would result in insufficient cleaning of the exhaust gas.

  According to one development, the reactant signal is influenced as a function of the difference in pressures so that the amount of reagent dosed is at least approximately independent of the pressure difference. This measure ensures that the actually dosed amount of reagent corresponds to the predetermined amount of reagent. Dosage errors are avoided. This allows not only minimal consumption of reagent but also optimum cleaning.

  According to a development, the pressure of the reactive agent is measured. Instead of a measurement, it is also possible to calculate the pressure of the exhaust gases according to at least one operating parameter of the combustion engine. The exhaust gas pressure can also be calculated based on a back pressure that occurs upstream of the exhaust gas treatment device installed behind the reagent introduction zone. The pressure produced at the exhaust gas treatment device is preferably seized. Another development provides a pressure difference sensor which detects the difference between the pressure of the reactive agent and that of the exhaust gas.

  Another characteristic provides for influencing the reactive agent signal according to at least one operating parameter of the combustion engine and / or as a function of at least one characteristic of the exhaust gases. This makes it possible to set the quantity of reagent agent to be dosed according to the available quantities. As operating variables or operating parameters of the combustion engine, it is possible, for example, to use the rotation speed (speed), the air flow rate in the intake zone of the combustion engine and / or the load of the combustion engine. As parameters or characteristics of the exhaust gas, the exhaust gas temperature, which influences the catalytic effect of the catalyst installed in the exhaust zone of the combustion engine, is used, according to the agent reagent for converting the troublesome components of the exhaust gases as well as, where appropriate, also the reagent agent storage capacity.

  The reactant signal can be deduced from the corrected reagent base signal with a correction signal formed from the pressure difference.

  It is a development that the reactive agent signal is a switching signal for timed control of the reagent dosage device and the duration of the pulse and / or the duration of the repetition period of the pulse of the switching signal. The switching signal fixes, for example, a mean opening section of a valve or valve. The switching signal can be provided by a simple circuit with respect to an analog signal and in particular with a very low power loss.

  The device according to the invention for introducing a reactive agent into the exhaust gas zone of a combustion engine provides a control apparatus for carrying out the method. In particular, the control apparatus comprises a pulse width modulator which provides the reactive agent signal as a switching signal.

  A development of the device of the invention is characterized in that downstream of the reactive agent introduction zone, an exhaust gas treatment device is envisaged.

  The exhaust gas treatment device preferably comprises at least one catalyst, for example an SCR catalyst which requires the reactive agent to convert at least one disturbing component of the exhaust gases.

  In addition or alternatively, the exhaust gas treatment device comprises a particulate filter. The reactive agent may be provided in this case to provide a temperature increase necessary for the regeneration operation of the particulate filter.

  Another development of the device of the invention, pre-sees a reactive agent pressure sensor to capture the reagent agent pressure and optionally an exhaust gas pressure sensor or a pressure difference sensor of exhaust gas to capture the pressure of the exhaust gas.

  The exhaust gas pressure difference sensor measures the pressure difference at the exhaust gas treatment device, which difference influences the exhaust gas pressure upstream of the exhaust gas treatment device if the exhaust gas treatment device comprises a particulate filter.

  Drawings The present invention will be described hereinafter in more detail with the aid of an embodiment shown in the accompanying drawing in which: The single figure shows the technical environment of the method of the invention with a block diagram of the control unit. DESCRIPTION OF THE EMBODIMENT OF THE INVENTION The single figure shows a combustion engine 10 whose intake zone 11 comprises an air detection means 12 and the zone of the exhaust gases 13 a metering device of the reactive agent 14, an exhaust gas temperature sensor 15, an exhaust gas pressure sensor 16 and an exhaust gas treatment device 17.

  Downstream of the combustion engine 10, there is an exhaust gas flow ms_abg and an emission of NOx nitrogen oxides crude ms NOx. In the exhaust gas zone 13, in particular the reagent introduction zone 18, there is an exhaust gas pressure p_abg and a temperature of the exhaust gas te_abg.

  The air sensing means 12 provides the control apparatus 20 with an air signal ms _L; the combustion engine 10 provides a rotational speed signal n; the exhaust gas temperature sensor 15 provides a measurement signal of the exhaust gas temperature te_abg_mess and the exhaust gas pressure sensor 16, a signal for measuring the exhaust gas pressure p_abg_mess.

  The control apparatus 20 includes a signal determining means 29 which receives the set value of the torque Md_Soll, the air signal ms_L and the rotational speed signal n to supply the fuel signal m_K, the pressure calculated exhaust gas p_abg_mod and calculated exhaust gas temperature te_abg_mod.

  The control apparatus 20 supplies to a fuel delivery device 21 associated with the combustion engine 10 the fuel signal m_K, the reagent dosing device 14 provides the signal of the reagent S_Rea, the reagent pressure upstream of the reagent dosing device 14 is detected by the reagent pressure sensor 22 which provides the pressure of the reagent p_Rea to the controller 20.

  The control apparatus 20 includes NOx nitrogen oxide raw emission determination means 30 which receives the rotational speed signal n, the fuel signal m_K and the air signal ms_L to provide the raw emission of nitrogen oxides NOx, calculated ms_NOx_mod.

  The raw emission of nitrogen oxides NOx, calculated ms_NOx_mod is given by a characteristic curve element 31 which provides the base signal of the reactive agent GS_Rea for a means for fixing the reactive agent signal 32.

  The reagent agent signal attachment means 32 provides a corrected reactive agent signal S_Rea_korr for the pulse width modulator 33; the latter gives the signal of the reactive agent S_Rea.

  The signal of the reagent S_Rea is a modulated pulse width signal with level 0 or level 1; the duration of the pulse tiD and the duration of the repetition period of the pulse tiP are variably set.

  A difference determining means 34 provides the pressure difference dp between the pressure of the reactive agent p_Rea and the pressure of the exhaust gas p_abg; the difference signal dp is supplied to a correction means 35 which determines a first correction signal K1 and supplies it to the means for fixing the reactive agent signal 32. The temperature of the exhaust gas te_abg is supplied to a means of correction. correction of the exhaust gas temperature 36 which determines a second correction signal K2 and also provides it to the fixing means of the reactive agent signal 32.

  The invention is implemented as follows: The signal determining means 29 in the control unit 20 determines the fuel signal m_K at least from the set value of the torque Md_Soll deduced for example from the position of the pedal accelerator (this pedal is not shown in detail) installed in the vehicle not shown, equipped with the combustion engine 10. It is preferably taken into account in addition to the ms air signal L. Where appropriate, it can be use the rotational speed signal n which is, for example, a measurement of the rotational speed of the combustion engine 10 and / or a measurement of the rotation angle of the combustion engine shaft 10.

  The fuel signal m_K supplied by the signal determination means 20 sets the instant and the fuel dose for the various cylinders of the combustion engine 10.

  The fuel used by the combustion engine 10 generates an exhaust gas flow ms_abg which contains a higher or lower level, annoying emissions depending on the operating point of the combustion engine 10.

  In order to eliminate as much as possible the emission of crude nitrogen oxides NOx, ms_NOx, an exhaust gas treatment device 17 comprising, for example, at least one catalyst and / or a particulate filter is provided. For example, an SCR catalyst or an NOx nitrogen oxide storage catalyst may be provided. In the following, reference will be made in particular to an SCR catalyst which maintains the reaction of reducing the emission of crude nitrogen oxides NOx, ms_NOx with a reagent introduced metered in the zone of the exhaust gas. 13 by the dosing device of the reagent 14 is provided internally if necessary by the engine.

  Instead of the reactive agent, it is also possible to provide a raw material. In the case of ammonia as a reactive agent, an aqueous solution of urea or, for example, ammonium carbamate can be used instead of ammonia as raw material. The assay is done using the signal of the reactive agent S_Rea; in the example presented, this signal is provided by the reagent dosing device 14.

  After the start of the process according to the invention, the base signal of the reactive agent GS_Rea is fixed according to the raw emission of nitrogen oxides NOx, calculated ms_NOx_mod. The characteristic curve element 31 contains the functional relation between the raw emission of nitrogen oxides NOx, calculated ms_NOx_mod and the opening section of the metering valve of the dosing device of the reactive agent 14. This relationship corresponds to the characteristic curve of the valve or valve.

  Since there is no correction signal K1, K2, the reagent agent signal attachment means 32 transmits the base signal of the reagent agent GS_Rea as a signal of the reactive agent S_Rea corrected the pulse width modulator 33; it sets the signal of the reactive agent S_Rea as a modulated pulse width switching signal of the pulse duration tiD and of the duration of the pulse repetition period tiP to supply this signal to the dis-positive dosing of the reagent 14.

  The working ratio of the modulated pulse width S_Rea reagent signal gives a mean value corresponding to the opening section of the reagent dosing device valve 14. In place of a valve or valve, it is also possible to use another component for the dosing device of the reactive agent 14 which provides at least a mean time, a reagent dosage dependent on the signal of the reactive agent S_Rea.

  When determining the emission of crude nitrogen oxides NOx, ms NOx in the means of determination of the raw emissions of nitrogen oxides NOx 30, at least the air signal ms_L and of a measure of the load of the combustion engine 10. As a measure of the load, in the exemplary embodiment shown, the fuel signal m_K is used as a measure of the load, it is also possible to use the setpoint value of the torque Md_Soll. In addition, the speed signal n can be taken into account.

  The dosing device of the reactive agent 14 doses a quantity of reactive agent in the zone of the exhaust gas 13; this quantity depends on the one hand on the signal of the reagent S_Rea and on the other hand on the pressure of the reagent p_Rea; this pressure is detected by the pressure sensor of the reagent 22 to be supplied to the control apparatus 20. The pressure of the reagent p_Rea corresponds for example to 4 bar.

  The exhaust gas pressure p_abg in the exhaust gas zone 13 depends on the operating conditions of the combustion engine 10. When the combustion engine 10 is operating at an idle speed, there is an exhaust gas pressure p_abg which is for example of the order of 10 to 50 mbar; for a higher load of the combustion engine 10, the exhaust gas pressure p_abg in the case of a combustion engine with suction can be for example between 50 and 400 mbar; in the case of a supercharged combustion engine, the exhaust gas pressure p_abg can be up to 800 mbar. These are average values and one can briefly have a maximum pressure of up to 2 bars.

  If necessary, there is a pressure difference at the exhaust gas treatment device 17 and which can also be taken into account. Such a pressure difference occurs in the case where the exhaust gas treatment device 17 is equipped with a particulate filter. The pressure difference is preferably determined using a differential pressure sensor or an absolute pressure sensor not shown.

  Although the exhaust gas pressure p_abg is on average much lower than the pressure of the reactive agent p_Rea, the differences between the setpoint dosage and the actual dosage have been found in series tests. the reactive agent. The difference in pressure dp can have a significant influence on the flow of reagent in the reagent 14 dosing device. In addition, the pressure difference dp can influence the sputtering of the reagent in the reaction zone. reactive agent introduction 18 in particular affecting the size of sprayed droplets. The spraying or size of the droplets has an influence on the conversion of, for example, an aqueous solution of urea to ammonia which constitutes the effective reactive agent and / or an influence on the storage or conversion in the treatment device. exhaust gas 17 which is optionally equipped with a catalyst SCR.

  Therefore, it is intended according to the invention to determine the pressure difference dp between the pressure of the reactive agent p_Rea and the pressure of the exhaust gas p_abg and to influence the signal of the reactive agent S_Rea in function of this pressure difference dp.

  Advantageously, the exhaust gas pressure p_abg captured is at least approximately a measure of the pressure of the exhaust gas p_abg prevailing in the reagent introduction zone 18.

  According to one development, there is a separate determination of the pressure of the reagent p_Rea and the pressure of the exhaust gas p_abg to form the pressure difference dp.

  The exhaust gas pressure p_abg can be measured using an exhaust pressure sensor 16 installed for example in the exhaust zone 13 which provides the pressure measurement signal. exhaust gas p_abg_mess and transmits this signal to the control unit 20.

  Alternatively or additionally, it is possible to calculate the pressure of the exhaust gas p_abg. The signal determining means 29 can determine the calculated exhaust gas pressure p_abg_mod for example from the load of the combustion engine 10 and the air signal ms_L. The set value of the torque Md_Soll or the fuel signal m_K can be used as a measure of the load of the combustion engine 10.

  Another possibility of calculating the exhaust gas pressure p_abg uses the exhaust gas vein ms_abg which can also be calculated. The calculation of the exhaust gas vein ms_abg mainly uses the air signal ms_L taking into account, if necessary, also the load of the combustion engine 10 represented for example the setpoint value of the torque Md_Soll or the fuel signal m_K .

  If necessary, the difference in pressure can be taken into account in the exhaust gas treatment device 17, which is measured, for example, by means of a pressure differential sensor (not shown). Depending on the reference pressure, the ambient air pressure can be taken into account.

  Since the exhaust flow rate signal ms_abg is measured on the basis of a mass flow of the exhaust gas, the exhaust gas temperature te_abg can be taken into account to determine the pressure of the exhaust gases. escape p_abg.

  The temperature of the exhaust gas te_abg can be measured by means of an exhaust gas temperature sensor 15 installed in the exhaust gas zone 13 which supplies the control unit 20 with the measurement signal. the temperature of the exhaust gas te_abg_mess.

  Alternatively or in addition, the signal determining means 29 can provide the calculated exhaust gas temperature te_abg_mod which is also determined based in particular on the ms_L air signal and on the load of the combustion engine 10; the load of the combustion engine 10 is again represented, for example, by the setpoint value of the torque Md Soli or the fuel signal m_K.

  The difference determining means 34 provides the difference between the pressure of the reactive agent p_Rea and the pressure of the exhaust gas p_abg and provides as a result the pressure difference dp. This pressure difference is transmitted to the correction determining means 35.

  According to another development, the pressure difference dp is measured using a pressure difference sensor. In this case, the exhaust gas pressure sensor 16 and the pressure sensor of the reactive agent 22 are joined by construction into a single pressure difference sensor 16, 22.

  The correction determining means 35 comprises, for example, a characteristic curve or a table of the functional relationship between the pressure difference dp and the resulting correction value K1 obtained experimentally or by calipers. Calculations can be based on the Bernoulli equation; the first flow rate is the reactant flow rate at the outlet of the reagent dosing device 14 and the second flow rate is the exhaust gas flow rate ms_abg. The pressure correction required for the calculation of the pressure of the reactive agent p_Rea may assume that the reactive agent is incompressible, that it has no friction and that the flow conditions are quasi-stationary.

  The first correction signal K1 influences the base signal of the reactive agent GS_Rea in the reagent agent signal setting means 32 providing as a result the corrected reactive agent signal S_Rea_Korr.

  According to a development, there is provided an exhaust gas temperature correction means 36 which determines the second correction signal K2 as a function of at least the temperature of the exhaust gas te_abg and provides the information by means of for fixing the reagent agent signal 32.

  The temperature of the exhaust gas may be considered at least approximately as a measure of the temperature of the exhaust gas treatment device 17 or the SCR catalyst equipping the exhaust gas treatment device 17.

  The second correction signal K2 makes it possible to correct the signal of the reactive agent S_Rea in particular as a function of at least one measurement of the temperature of the exhaust gas treatment device 17 since the yield of, for example, the SCR catalyst and the capa -Reactive agent storage capacity depend on the temperature. Storage capacity is highest at low temperatures and decreases as temperature increases. On the other hand, the yield is low at low temperatures, for example below 150.degree. C., and increases with temperature and has a maximum, for example, at 250.degree. C., and then decreases again as the temperature increases.

  Since the temperature of the exhaust gas treatment device 17 can be increased, this temperature of the exhaust gas treatment device 17 can be detected by means of a sensor. a non-detailed temperature which is at least part of the exhaust gas treatment device 17 or is installed between a component of the exhaust gas treatment device 17 or downstream of the exhaust gas treatment device 17.

Claims (14)

  A method for introducing a reagent into an exhaust gas zone (13) of a combustion engine (10) wherein the reactive agent reactive agent (p_Rea) is dosed by a assaying the reagent (14), wherein the assay of the reagent is predefined according to a signal of the reagent (S_Rea), characterized in that the difference (dp) between the pressure of the reactive agent (p_Rea) and the pressure of the exhaust gas (p_abg) and the signal of the reactive agent (S_Rea) is influenced as a function of this pressure difference (dp).   2) Process according to claim 1, characterized in that the signal of the reactive agent (S_Rea) is influenced as a function of the pressure difference (dp) so that the metered quantity of reagent is at least approximately independent of the pressure difference (dp).   3) Process according to claim 1, characterized in that the pressure difference (dp) is determined by a difference determination means (34) from the pressure of the reagent ( p_Rea), seized separately and the exhaust gas pressure (p_abg).   4) Process according to claim 1, characterized in that the pressure of the reactive agent (p_Rea) is measured.   5) Method according to claim 1, characterized in that the exhaust gas pressure (p_abg) is calculated according to at least one operating parameter (Md_Soll, ms L, n) of the combustion engine (10) .   6) Process according to claim 5, characterized in that, in determining the exhaust gas pressure (p_abg), account is also taken of a pressure difference produced in an exhaust gas treatment device (17) downstream of the reagent introduction zone (18).   7) Method according to claim 1, characterized in that the signal of the reactive agent S_Rea is influenced as a function of at least one operating parameter (Md_Soll, ms L, n) of the combustion engine (10) and / or according to at least one characteristic (p_abg, te_abg) of the exhaust gas.   8) Method according to claim 1, characterized in that the signal of the reactive agent (S_Rea) is provided from the base signal of the reactive agent (GS_Rea) which is corrected with a correction signal ( K1) obtained from the pressure difference (dp).   9) Process according to claim 1, characterized in that the signal of the reactive agent (S_Rea) is a switching signal for controlling the reagent dosing device (14) in a controlled manner, the duration of the the pulse (tiD) and / or the duration of the re-petition period of the pulse (tiP) can be varied.   10) Device for introducing a reactive agent into an exhaust gas zone (13) of a combustion engine (10), characterized by a control apparatus (20) for carrying out the process according to the invention any of the preceding claims 1 to 9.   11) Apparatus according to claim 10, characterized in that the control apparatus (20) comprises a pulse width modulator (33) which provides the signal of the reagent (S_Rea).   12) Device according to claim 10, characterized by an exhaust gas treatment device (17) downstream of the reagent introduction zone (18).   13) Device according to claim 12, characterized in that the exhaust gas treatment device (17) comprises at least one catalyst and / or a particulate filter.   14) Device according to claim 10, characterized by a pressure difference sensor (16, 22) for determining the pressure difference (dp).