FR3077331A1 - METHOD FOR CONTROLLING ELECTRIC HEATING OF A SELECTIVE CATALYTIC REDUCTION SYSTEM OF THERMAL MOTOR - Google Patents

Abstract

The method is for the control of electric heating in an SCR system for the depollution of the exhaust gases emitted by a heat engine, the SCR system comprising a SCR catalyst mounted in an exhaust line of the heat engine and a heating device electrical circuit mounted upstream of an injector of the catalyst SCR, the method comprising the establishment of a heating control (CM) for the electric heating device, and the heating control being established so as to optimize at least one temperature ( T1, T2) in the SCR system. According to the invention, the method comprises first and second heating control modes, the first heating control mode (MOD_H) providing a heating control with hysteresis (CM_H) and the second heating control mode (MOD_D). providing a dynamic heating control (CM_D) according to an error (E) between the temperature to be optimized and a temperature setpoint (CT), and a selection (60, MOD_SEL) of a consolidated heating control (CMS) among the heating control with hysteresis and the dynamic heating control.

Description

The invention relates generally to the reduction of pollutant emissions of nitrogen oxides from a thermal engine vehicle equipped with a selective catalytic reduction system, known as SCR "Selective Catalytic Reduction" in English. More particularly, the invention relates to a method for controlling electric heating of an SCR system.

Vehicles with internal combustion engines are equipped with exhaust gas aftertreatment systems designed to reduce polluting emissions and comply with environmental standards. In the SCR system, the treatment of nitrogen oxides (NOx) emissions takes place in a specific catalyst, called the SCR catalyst, in which oxidation-reduction reactions take place leading to a selective reduction of nitrogen oxides in nitrogen and water. The reducing agent conventionally used is ammonia (NH3). The ammonia is obtained by dissociation of an aqueous urea solution, such as AdBlue (registered trademark), which is introduced into the exhaust gas line, upstream of the SCR catalyst, by the system injector SCR.

The conventional SCR system is dependent on the temperature of the exhaust gas which must be high enough to effectively reduce NOx emissions. At the level of the injector, the temperature must exceed a certain value so that the urea solution injected can decompose and release the ammonia necessary for the NOx reduction reactions. NOx reduction reactions in the SCR catalyst will only occur if the temperature is sufficient. Exhaust gas temperature conditions must therefore be satisfied upstream of the injector and in the SCR catalyst. This constraint on the exhaust gas temperature impacts the NOx reduction performance in certain vehicle life situations, such as when the engine is cold started and when driving at low speed. In order to overcome the above drawback, an electrically heated SCR system, called "eSCR", is used. The eSCR system enables optimum operating temperatures to be reached more quickly, thereby enabling increased efficiency in reducing NOx.

Patent application US2012 / 0173062A1 describes an SCR system in which an electric resistance heating device is installed upstream of the injector in the exhaust duct. This installation of the heating device is advantageous because the increase in the temperature of the exhaust gases by the device benefits both the release of ammonia at the injector and the NOx reduction reactions in the SCR catalyst.

The electrical supply of the heating device in SCR systems places significant demands on the vehicle's electrical supply network and on electrical energy stores, the durability of which can be impacted. Indeed, the electric power required to supply the heating resistor can be of the order of 1 kW or more.

It is desirable to propose an optimized method for controlling electric heating in an SCR system having a heating device installed upstream of the injector, so as to guarantee economical management of energy and reduce to the necessary minimum stresses on the vehicle's electrical power supply network and on electrical energy stores.

According to a first aspect, the invention relates to a method of controlling electric heating in an SCR system for the depollution of exhaust gases emitted by a heat engine, the SCR system comprising an SCR catalyst mounted in a line of exhaust of the heat engine and an electric heating device mounted upstream of an injector of the SCR catalyst, the method comprising the establishment of a heating control intended for the electric heating device, and the heating control being established so as to optimize at least one temperature in the SCR system. According to the invention, the method comprises first and second heating control modes, the first heating control mode providing a heating control with hysteresis and the second heating control mode providing a dynamic heating control as a function of '' an error between the temperature to be optimized and a temperature setpoint, and a selection of a consolidated heating command from the heating command with hysteresis and the dynamic heating command.

According to a particular characteristic, the consolidated heating control is selected by a control strategy of the SCR system.

According to another particular characteristic, the method also comprises a selection of the temperature to be optimized from a first temperature in an injection zone of the injector and a second temperature at the inlet of the SCR catalyst, for establishing the consolidated heating control.

According to yet another particular characteristic, the method also includes an invalidation of the consolidated heating control when an injection flow rate required by the control strategy of the SCR system is less than a minimum injection rate prefixed.

According to another embodiment, the method comprises a determination of a first consolidated heating command corresponding to a first temperature to be optimized in an injection zone of the injector and a second corresponding consolidated heating command at a second temperature to be optimized at the input of the SCR catalyst, and a selection of a final consolidated heating command equal to that of the first and second consolidated heating commands having the highest control level.

According to a particular characteristic, the method, in this other embodiment, also includes an invalidation of the final consolidated heating command when an injection flow required by the control strategy of the SCR system is less than a flow of minimum injection prefixed.

The invention also relates to a computer comprising a memory storing program instructions for implementing the method as briefly described above. According to a particular characteristic, the computer is the engine control computer of the vehicle.

The invention also relates to a vehicle with an internal combustion engine equipped with an SCR system for the depollution of the exhaust gases emitted by the internal combustion engine, the vehicle comprising a computer as defined above.

Other advantages and characteristics of the present invention will appear more clearly on reading the detailed description below of a particular embodiment of the invention, with reference to the accompanying drawings, in which:

- Fig. 1 partially shows an example of an SCR system comprising an SCR catalyst and a control computer comprising an on-board software module for implementing the method of the invention;

- Fig.2 is a block diagram showing a first embodiment of the method according to the invention; and

- Fig.3 is a block diagram showing a second embodiment of the method according to the invention.

Referring to Fig.1, an SCR 1 catalyst is inserted into an LE gas exhaust line from a heat engine (not shown) and treats the EG engine exhaust gases.

An aqueous urea solution injector 2 and an electric heating device 3, in the form of a heating resistor, are arranged in the LE gas exhaust line, upstream of the SCR catalyst 1.

The electrical supply of the heating resistor 3 is provided by an electrical supply unit 4, for example of the switching type, the IR output supply current of which is controlled by an electric heating control CM. The electric heating control CM is provided by an electric heating control module 5 implementing the method according to the invention.

The heating resistor 3 is located before the injector 2, in the direction of the flow of the EG gases, and is thus able to be able to heat the EG gases before they reach the injector 2 and the inlet of the SCR 1 catalyst.

A mixing device 20 is located at the inlet of the SCR catalyst 1 and ensures a homogeneous mixing of the aqueous solution of urea sprayed in the EG gases. NOx measurement probes, 10 and 11, are mounted in the LE exhaust line, respectively upstream and downstream of the catalyst 1 and are used by the control strategy of the SCR system.

Temperature sensors 12 and 13 are also provided for measuring the temperature of the exhaust gases EG at two measurement points of the exhaust line LE, namely, in an injection zone where the solution is injected aqueous urea and at the inlet of the SCR catalyst 1. In the exemplary embodiment shown in FIG. 1, the temperature sensor 12 is located near the injector 2 and provides a temperature measurement MT1 representative of a temperature T1 in the injection zone of the aqueous urea solution. The temperature sensor 13 is located at the inlet of the SCR catalyst 1 and provides a temperature measurement MT2 representative of a temperature T2 upstream of the SCR catalyst 1. It will be noted that, in other embodiments, the temperatures T1 and / or T2 can be estimated from one or more temperature measurements which will come from other measurement points in the LE line.

The method of the invention for controlling the electric heating of the SCR system uses the electric heating control module 5. The module 5 is an on-board software module which is installed in a memory MEM of an ECU computer and which participates in the control strategy of the SCR system. The electric heating control module 5 authorizes the implementation of the method according to the invention by the execution of program code instructions by a processor (not shown) of the ECU computer.

In this embodiment, described by way of example, the ECU computer is the engine control computer of the vehicle.

The temperature measurements MT1, MT2 and the electric heating control CM are exchanged between the sensors 12, 13, the electric heating control module 5 and the power supply unit 4 through an input port / output (not shown) of the ECU computer. As a variant, the measurements MT1, MT2 and the electric heating control CM may be exchanged through a CAN network of the vehicle to which the ECU computer, the temperature measurement sensors 12, 13 and the power supply unit 4 will be connected. .

With particular reference to the functional block diagram of FIG. 2, there is described below a first embodiment 5A of the electric heating control module implementing the method of the invention.

As shown in Fig.2, the electric heating control module 5A includes a temperature selection function F1A, a heating control function F2A and a heating control correction function F3A.

The electric heating control module 5A is designed to deliver an electric heating control CM for optimizing the temperature T1 in the injection zone of the aqueous urea solution or the temperature T2 at the inlet of the SCR catalyst 1. The temperature selection function F1 selects the temperature T1 or T2 to be optimized.

The F1A temperature selection function uses a selector 10 having two temperature inputs 11, 12, a temperature selection input 13 and a selected temperature output 14.

The temperature inputs 11 and 12 respectively receive the temperature measurements MT1 and MT2. The temperature selection input 13 receives a SELT command for selecting the temperature to be optimized. The SELT command is provided by the SCR system control strategy.

The selected temperature output 14 delivers a selected temperature measurement MTs, with MTs = MT1 or MTs = MT2 according to the binary state of the command SEL T. The selected temperature measurement MT _S is supplied as an input to the F2A heating control function.

The F2A heating control function includes two modes of heating control MODH and MODD. MODH mode provides a CM H hysteresis heating command obtained by an "all-or-nothing" command processing with hysteresis. The MOD D mode provides a dynamic heating command CM_D obtained by a dynamic command processing as a function of an error between the selected temperature measurement MT _S and a temperature setpoint. The two heating control modes MOD H and MOD D have the function of bringing the temperature T1 or T2, according to the selection command SEL T, to the optimal temperature defined by the control strategy of the SCR system. The optimum temperature desired is a temperature setpoint CT supplied to the MOD H and MOD D heating control modes. To obtain the optimum temperature desired, the control strategy of the SCR system can select one or the other of the control modes. MOD H, MOD D, depending in particular on different parameters, constraints and control objectives known from the strategy.

As shown in Fig.2, the MOD H hysteresis heating control mode essentially uses a hysteresis comparator 20 and a selector 30.

The hysteresis comparator 20 receives the selected temperature measurement MT _S at a temperature input 21 and delivers to an output 22 activation information EA of the heating control. High SH and SB low temperature thresholds are applied respectively to high threshold 23 and low threshold 24 inputs of the hysteresis comparator 20. The SH and SB temperature thresholds determine the operation of the hysteresis comparator 20 and are set by the strategy . Typically, the low temperature threshold SB is fixed substantially equal to the temperature setpoint CT. The heating control activation information EA switches to an active state as soon as the selected temperature measurement MT _S becomes lower than the temperature threshold SB and switches to an inactive state as soon as the selected temperature measurement MT _S becomes above the temperature threshold SH.

The EA heating control activation information is supplied to a selection input 31 of the selector 30 by the hysteresis comparator 20. The heating control level inputs 32 and 33 respectively receive high control levels NH and low NB. When the EA activation information = "active", the selector 30 delivers the hysteresis heating command CM H = NH by an output 34. When the EA activation information = "inactive", the selector 30 delivers the hysteresis heating control CM H = NB by output 34. Typically, percentages of 100% and 0% are assigned to the NH and NB control levels respectively, the NH = 100% control level being representative of a control of heating at full power, that is to say, with an IR heating current (see Fig. 1) of maximum intensity and the control level NB = 0% being representative of a zero heating command, c that is, with an IR heating current equal to zero.

As shown in Fig.2, the dynamic control mode MOD D essentially uses a subtractor 40 and a control map 50.

The subtractor 40 receives the temperature setpoint CT = SB at a positive input (+) and the selected temperature measurement MT _S at a negative input (-). The subtractor 40 calculates an error E between the selected temperature measurement MT _S and the temperature threshold SB. The error E delivered by the subtractor 40 is supplied at the input to the control map 50. The control map 50 provides at the output the dynamic heating control CM_D which, unlike the hysteresis heating control CM H, varies so continues between command level NB = 0% and command level NH = 100%. When the error E is positive, which means that the selected temperature measurement MT _S is less than the temperature setpoint CT, the control map 50 issues a command CM_D which evolves according to a predefined control law, typically with a level that decreases with error E. When error E is negative, which means that the selected temperature measurement MT _S is greater than the temperature setpoint CT, the command map 50 issues a command CM_D = NB = 0%.

A selector 60 is provided for selecting the heating command to be applied from the commands CM H and CM_D. The commands CM H and CM_D are applied respectively to command inputs 61 and 62 of the selector 60. A selection input 63 receives a MOD SEL selection command supplied by the strategy. The selected heating command CM _S , hereinafter designated the consolidated heating command, is delivered by an output 64 of the selector 60.

The heating control correction function F3A is provided to invalidate the consolidated heating control CM _S when the injection rate of aqueous urea solution required by the strategy is less than a minimum injection rate prefixed.

As shown in Fig.2, the F3A heating control correction function uses a comparator 70 and a selector 80.

The comparator 70 produces a SELN selection command from the comparison between an injection rate DI requested by the strategy and a minimum injection rate prefixed DImin below which it is considered that the injection is not not urgent. The DI injection rate and the minimum DImin injection rate. are supplied respectively to inputs 71 and 72 of comparator 70 which delivers the selection command SEL N by an output 73.

The consolidated heating command CM _S and an invalidation level NI = 0% are applied respectively to inputs 81 and 82 of the selector 80. The selection command SEL N is applied to a selection input 83 of the selector 80 The selector 80 delivers by an output 84 the heating control CM intended for the power supply unit 4 (FIG. 1). As long as the injection flow DI is at least equal to the minimum injection flow DImin, the selection command SEL N controls the selection of the heating command CM = CM _S. Otherwise, the SEL N selection command invalidates the heating command by selecting CM = NI = 0%.

A second embodiment 5B of the electric heating control module implementing the method of the invention is shown in Fig.3.

As shown in Fig.3, the electric heating control module 5B includes in particular two heating control functions F2B1 and F2B2 and a heating control correction function F3B. The heating control functions F2B1, F2B2, are each similar to the heating control function F2A of the module 5A and the heating control correction function F3B is similar to the heating control correction function F3A of the module 5A. A heating control selection function F4B is also provided in the electric heating control module 5B and is described below.

Unlike the electric heating control module 5A, the module 5B does not include at the input a temperature selection function, such as the function F1A of the module 5A. In module 5B, the temperature measurements MT1 and MT2 are processed in parallel by the heating control functions F2B1 and F2B2, respectively. The two heating control functions F2B1 and F2B2 each operate in a similar manner to the function F2A and issue heating commands CM_1 and CM_2 respectively. The heating commands CM_1 and CM_2 correspond respectively to the temperatures T1 and T2 to be optimized.

The command selection function F4B ensures a selection between the heating commands CM_1 and CM_2 and delivers a consolidated heating command CM12 _S. As in module 5A, the consolidated heating control, here CM12 _S , is supplied to the heating control correction function, here F3B, which delivers the heating control CM intended for the power supply unit 4 (Fig. .1).

As shown in Fig.3, the F4B command selection function uses a comparator 90 and a selector 100.

The comparator 90 produces a SELC selection command from the comparison between the heating commands CM_1 and CM_2. The heating commands CM_1 and CM_2 are supplied respectively to inputs 91 and 92 of the comparator 90 which delivers the selection command SEL C by an output 93. The comparison carried out in the comparator 90 makes it possible to determine the heating command having the level higher among the heating commands CM_1 and CM_2.

The heating commands CM_1 and CM_2 are applied respectively to inputs 101 and 102 of the selector 100. The selection command SEL C is applied to a selection input 103 of the selector 100 and controls the supply, by an output 104 of the selector 100, of the consolidated heating command CM12 _S equal to that having 5 the highest level among the commands CM_1 and CM_2. The consolidated heating control CM12 _S is then processed by the heating control correction function F3B which outputs the heating control CM intended for the power supply unit 4 (Fig.1).

Of course, the invention is not limited to the particular embodiments which have been described here by way of example. A person skilled in the art, depending on the applications of the invention, can make various modifications and variants which fall within the scope of the appended claims.

Claims (9)

1. Method for controlling electric heating in a selective catalytic reduction system, known as “SCR”, for the depollution of exhaust gases (EG) emitted by a heat engine, said SCR system comprising an SCR catalyst (1) mounted in an exhaust line (LE) of said heat engine and an electric heating device (3) mounted upstream of an injector (2) of said SCR catalyst (1), said method comprising the establishment of a heating control ( CM) intended for said electric heating device (3), said heating control (CM) being established so as to optimize at least one temperature (T1, T2) in said SCR system, characterized in that it comprises first and second heating control modes (MODH, MODD), said first heating control mode (MOD H) providing a heating control with hysteresis (CM H) and said second heating control mode (MOD D) providing a heating control dynamic (CM_D) e n function of an error (E) between said temperature to be optimized (T1, T2) and a temperature setpoint (CT), and a selection (60, MODSEL) of a consolidated heating command (CM _S ) from said command heating with hysteresis (CM H) and said dynamic heating control (CM_D). 2. Method according to claim 1, characterized in that said consolidated heating control (CM _S ) is selected (MOD SEL) by a control strategy of said SCR system. 3. Method according to claim 1 or 2, characterized in that it also comprises a selection (10) of said temperature to be optimized from a first temperature (T1) in an injection zone of said injector (2) and a second temperature (T2) at the input of said SCR catalyst (1), for the establishment of said consolidated heating control (CM _S ). 4. Method according to any one of claims 1 to 3, characterized in that it also comprises an invalidation (F3A) of said consolidated heating command (CM _S ) when an injection flow (DI) required by said control strategy of said SCR system is less than a minimum prefixed injection rate (DImin). 5. Method according to claim 1 or 2, characterized in that it comprises a determination (F2B1, F2B2) of a first consolidated heating command (CM_1) corresponding to a first temperature to be optimized (T1) in a zone of injection of said injector (2) and of a second consolidated heating command (CM_2) corresponding to a second temperature to be optimized (T2) at the input of said SCR catalyst (1), and a selection (90, 100) of a command for final consolidated heating (CM12 _S ) equal to that of said first and second consolidated heating commands (CM_1, CM_2) having the highest control level. 6. Method according to claim 5, characterized in that it also comprises an invalidation (F3B) of said final consolidated heating control (CM12 _S ) when an injection flow (DI) required by said control strategy of said system SCR is less than a prefixed minimum injection rate (DImin). 7. Computer (ECU) comprising a memory (MEM) storing program instructions for implementing the method according to any one of claims 1 to 6. 8. Computer according to claim 7, characterized in that said computer is the engine control computer (ECU) of a vehicle. 9. Vehicle with an internal combustion engine equipped with a selective catalytic reduction system for depolluting the exhaust gases emitted by said internal combustion engine, characterized in that it comprises a computer according to claim 7 or 8.