FR3073897A1 - METHOD OF REDUCING NITROGEN OXIDE EMISSIONS FROM A THERMAL ENGINE - Google Patents

Abstract

The invention relates primarily to a process for reducing emissions of nitrogen oxides in a motor vehicle with at least partly autonomous driving comprising a heat engine (1) and a pollution control system (3) associated to treat oxides of nitrogen. nitrogen contained in the exhaust gas, characterized in that said process comprises: - a step of determining a maximum amount of nitrogen oxides (QNOxmax) that can be treated by the pollution control system (3), and - a step of adaptation of the maximum torque (C_max_lim) achievable by the heat engine (1) as a function of the maximum quantity of nitrogen oxides that can be treated by the pollution control system (3) so as to reduce a quantity of oxides of nitrogen released into the atmosphere.

Description

The present invention relates to a method of reducing nitrogen oxide emissions from a thermal engine of a motor vehicle. The invention finds a particularly advantageous, but not exclusive, application in the field of motor vehicles with at least partially autonomous driving having a diesel type engine.

The exhaust gases from diesel engines contain polluting elements, which it is preferable to limit discharges into the atmosphere. These pollutants are mainly unburnt hydrocarbons (HC), nitrogen oxides NOx (nitrogen monoxide NO and nitrogen dioxide NO ₂ ), carbon oxides (including carbon monoxide CO), sulfur oxides ( SO ₂ ), and particles. These chemical elements, in particular nitrogen oxides, can be harmful to the environment and to health, and must be treated before their release into the atmosphere.

To this end, various pollution control devices are installed on the exhaust line, in order to treat the exhaust gases and thus reduce the polluting emissions of the vehicle using, in whole or in part, diesel as fuel. These pollution control devices, arranged along the exhaust line, typically include an oxidation catalyst, called Catox or DOC (acronym for Diesel Oxidation Catalyst in English), configured to oxidize certain constituents of the exhaust gases. In addition, a selective catalytic reduction device SCR (acronym for Selective Catalytic Reduction in English), makes it possible to reduce the quantity of nitrogen oxides. A particle filter is also used to trap particles contained in the exhaust gas, in particular in the form of soot.

The higher the engine torque required, the greater the quantity of air and fuel injected into the engine cylinders, which induces an increase in emissions of pollutants and in particular nitrogen oxides. The quantity of nitrogen oxides leaving the vehicle is equal to the quantity of nitrogen oxides leaving the engine minus the quantity of nitrogen oxides treated by the depollution system. The quantity of nitrogen oxides treated by the depollution system depends on several factors, such as the temperature of the system, the quantity of reducing agent available, etc. In certain living conditions, the system is therefore not not able to process all the nitrogen oxides emitted by the heat engine.

To limit the amount of nitrogen oxides emitted by the vehicle, it is necessary to limit the maximum torque achievable by the engine. However, this is not possible in the case of human-driven driving given the operational safety constraints which impose a certain availability of torque. The invention takes advantage of the at least partially autonomous driving of the motor vehicle to reduce nitrogen oxide emissions by suitable automatic piloting of the heat engine.

More specifically, the invention relates to a process for reducing emissions of nitrogen oxides in a motor vehicle driven at least in part autonomous comprising a heat engine and an associated depollution system for treating in particular oxides d nitrogen contained in the exhaust gas, characterized in that said method comprises:

a step of determining a maximum quantity of nitrogen oxides which can be treated by the depollution system, and

a step of adapting the maximum torque achievable by the heat engine as a function of the maximum quantity of nitrogen oxides which can be treated by the depollution system so as to reduce a quantity of nitrogen oxides discharged into the atmosphere.

The invention thus makes it possible, by adapting the maximum torque achievable by the heat engine, to reduce or even cancel the quantity of polluting particles discharged into the atmosphere. The invention also has an economic character, insofar as it requires for its implementation only an adaptation of the control instructions of the computers of the motor vehicle.

According to one implementation, the step of adapting the maximum torque achievable by the heat engine is implemented following a detection of a life situation without the need for significant torque.

According to one implementation, the life situation without the need for a large torque corresponds to a life situation in which no imminent danger which can justify a need for maximum torque is detected and / or a life situation in which the vehicle must reduce nitrogen oxide emissions to zero, in particular when detecting an arrival in built-up areas or when detecting a priority air zone.

According to one implementation, said method comprises a step of informing a heat engine control computer of a priority passage in an operating mode with torque limitation.

According to one implementation, the step of adapting the maximum torque achievable by the heat engine is carried out by adapting the settings of the heat engine, in particular by reducing an amount of fuel and / or an amount of air injected into of the engine cylinders.

According to one implementation, said method comprises a step of informing a torque produced by the heat engine which may be equal to or less than a setpoint torque.

According to one implementation, the maximum torque achievable by the heat engine corresponds to a maximum quantity of nitrogen oxides that can be treated by the pollution control system.

The invention also relates to a computer comprising a memory storing software instructions for the implementation of the method of reducing nitrogen oxides in a motor vehicle as defined above.

The invention further relates to a motor vehicle comprising a computer as defined above.

The invention will be better understood on reading the description which follows and on examining the figures which accompany it. These figures are given only by way of illustration but in no way limit the invention.

Figure 1 is a schematic representation of an exhaust line provided with a pollution control system fitted to a motor vehicle implementing the nitrogen oxide reduction process according to the present invention;

Figure 2 is a schematic representation of vehicle control and engine control implementing the method of reducing nitrogen oxide emissions according to the present invention;

Figure 3 is a graphical representation of the evolution of nitrogen oxide emissions as a function of the level of engine torque.

FIG. 1 shows a heat engine 1 of a fully or partially autonomous motor vehicle, so that the vehicle, more precisely its control computer, is able to request the heat engine to supply torque in order to drive forward the vehicle at a desired speed without driver intervention.

This engine 1 is associated with an exhaust line 2 consisting of a tube placed at the outlet of the engine 1 of the vehicle which allows the exhaust gases from the internal combustion of the engine to be removed. The line d exhaust 2 begins at the outlet of the combustion chambers of engine 1 by an exhaust manifold. This exhaust manifold makes it possible to collect the exhaust gases ejected from the combustion chambers of the engine 1 in order to bring them together in a conduit opening into the atmosphere.

Along the exhaust line 2, the gases undergo several pollution control treatments carried out by a pollution control system 3, so that at least partially extracted certain elements harmful to the environment. To this end, the depollution system 3 comprises a 4 Diesel oxidation catalyst (or DOC for Diesel Oxidation Catalyst) allowing the oxidation of nitrogen monoxide (NO) to nitrogen dioxide (NO ₂ ), monoxide of carbon (CO) to carbon dioxide (CO ₂ ), and hydrocarbons (HC) to carbon dioxide (CO ₂ ) and water.

A selective catalytic reduction system (or SCR system for Selective Catalytic Reduction in English) is suitable for injecting a reducing agent into the exhaust line 2 in order to transform the nitrogen oxides (NOx) released by the engine 1 in nitrogen and water. To this end, a reducing agent injector 6 is associated with a mixing box 7 intended to homogenize the mixture between the exhaust gases and the reducing agent before entering a catalyst 5 of the SCR system. The reducing agent advantageously takes the form of urea which decomposes into ammonia and carbon dioxide under the effect of heat.

A particle filter 8 based on a porous ceramic matrix makes it possible to trap solid or liquid particles consisting essentially of carbon-based soot, and / or oil droplets.

If necessary, it is possible to use a reduction catalyst 9 (or ASC for Ammonia Slip Catalyst in English) to remove excess ammonia from the exhaust gases.

A computer 10 provides in particular the control of the heat engine 1, as well as management of the various functional elements of the pollution control system 3. The engine control computer 10 is able to communicate with a vehicle control computer 11. These computers 10, 11 include a memory storing software instructions for implementing the method of reducing nitrogen oxides according to the present invention described below with reference to FIG. 2.

Taking into account life situations without the need for significant engine torque, as well as the nitrogen oxide treatment capacities of the vehicle exhaust gas depollution system 3, this process commands a reduction in engine torque. in order to emit a quantity of nitrogen oxides below a given threshold.

More specifically, the vehicle control module 100 11 manages a torque priority state. In the case where the torque is not subject to any particular constraint, a nominal operating mode 101 of the heat engine is implemented by the engine control.

10. Nominal adjustments 102 are then applied to the motor without torque limitation. The torque 103 supplied by the motor then corresponds to the setpoint torque C_cons.

When the vehicle control 11 detects a life situation without the need for significant torque, it informs the motor control 10 that the latter must go into torque limitation mode to reduce the emissions of nitrogen oxides.

Thus, following a detection 104 of a life situation in which the vehicle must reduce to zero the emissions of nitrogen oxides (zero emission mode), in particular during the detection of an arrival in built-up areas or when a priority air zone is detected, and / or when no imminent danger which can justify a need for maximum torque is detected (see block 105), the emission priority management module 106 informs the engine control 10 that it must trigger a torque-limiting operating mode 107.

The module 108 then determines a maximum quantity of nitrogen oxides QNOx_max that can be treated by the pollution control system 3. This maximum quantity of nitrogen oxides QNOx_max that can be treated depends on the temperature of the pollution control system 3 , in particular a temperature measured upstream and / or downstream and / or inside the SCR catalyst, of an amount of injectable reducing agent, and of an overall dimensioning of the pollution control system 3.

The module 109 calculates the maximum torque C_max_lim achievable by the heat engine 1 as a function of the maximum quantity of nitrogen oxides QNOx_max which can be treated by the depollution system 3 so as to minimize a quantity of oxides of nitrogen released to the atmosphere.

Figure 3 shows the evolution of nitrogen oxide emissions QNOx at the outlet of the engine 1 as a function of the engine torque Cmth. Advantageously, to obtain a zero emission mode, the maximum torque C_max_lim corresponds to the quantity of maximum nitrogen oxides QNOx_max that can be treated by the pollution control system 3.

In the case where the maximum achievable torque C_max_lim is greater than the setpoint torque C_cons, the nominal motor settings 102 are applied.

In the case where the maximum achievable torque C_max_lim is less than the setpoint torque C_cons, the module 110 modifies the settings of the heat engine 1 making it possible to reduce the engine torque to reduce the emissions of nitrogen oxides. The modification of the settings consists in particular in reducing an amount of fuel and / or an amount of air injected into the cylinders of the heat engine 1.

The engine control 10 then informs the vehicle control 11 of the torque produced by the heat engine 1 which may be equal to or less than the setpoint torque C_cons managed by the module 111.

According to a particular implementation, it is possible to determine the quantity of nitrogen oxides QNOx emitted at the output of the heat engine 1 using a speed / torque map indicating the quantity of oxides of nitrogen emitted depending on the operating point of the engine. This quantity of nitrogen oxides obtained can be corrected using correction maps taking into account in particular the operating conditions of the heat engine (temperature, etc.) to more precisely estimate the quantity of nitrogen oxides at the output of the heat engine 1.

This quantity of nitrogen oxides QNOx at the outlet of the heat engine is compared with the quantity of maximum nitrogen oxides QNOxmax that can be treated by the depollution system 3. In the case where this quantity of oxides d 'nitrogen QNOx is less than the maximum quantity of nitrogen oxides QNOx max which can be treated by the pollution control system 3, the maximum achievable torque C_max_lim is not modified and the setpoint torque C_cons is applied to the wheels.

In the case where this quantity of nitrogen oxides QNOx is greater than the maximum quantity of nitrogen oxides QNOx_max which can be treated by the pollution control system 5 3, the maximum achievable torque C_max_lim is reduced, so the torque applied to the wheels is less than the setpoint torque C_cons. The torque C_max_lim is reduced until it corresponds to the quantity of nitrogen oxides QNOx_max which can be treated by the depollution system 3.

Claims (9)

1. Method for reducing the emissions of nitrogen oxides in a motor vehicle with at least partially autonomous driving comprising a heat engine (1) and an associated depollution system (3) for treating in particular nitrogen oxides contained in the exhaust gas, characterized in that said method comprises: a step (108) of determining a maximum quantity of nitrogen oxides (QNOx_max) which can be treated by the depollution system (3), and - a step (109, 110) of adaptation of the maximum torque (C_max_lim) achievable by the heat engine (1) as a function of the maximum quantity of nitrogen oxides that can be treated by the depollution system (3) so to reduce the quantity of nitrogen oxides released into the atmosphere. 2. Method according to claim 1, characterized in that the step of adapting the maximum torque (C_max_lim) achievable by the heat engine (1) is implemented following a detection (104, 105) of a situation of life without the need for a significant couple. 3. Method according to claim 1 or 2, characterized in that the life situation without the need for significant torque corresponds to a life situation (105) in which no imminent danger which can justify a need for maximum torque is detected and / or a life situation (104) in which the vehicle must reduce nitrogen oxide emissions to zero, in particular when detecting an arrival in built-up areas or when detecting a priority air zone . 4. Method according to any one of claims 1 to 3, characterized in that it comprises an information step (106) of a control engine of the heat engine of a priority passage in a limited operating mode torque (107). 5. Method according to any one of claims 1 to 4, characterized in that the step of adapting the maximum torque (C_max_lim) achievable by the heat engine (1) is carried out by adapting settings of the heat engine (1) , in particular by reducing an amount of fuel and / or an amount of air injected into cylinders of the heat engine (1). 6. Method according to any one of claims 1 to 5, characterized in that it comprises a step of informing a torque produced by the heat engine (1) which may be equal to or less than a setpoint torque (C_cons ). 7. Method according to any one of claims 1 to 6, characterized in that the 5 maximum torque (C_max_lim) achievable by the heat engine (1) corresponds to a maximum quantity of nitrogen oxides (QNOX_max) that can be treated by the depollution system (3). 8. Computer (10, 11) comprising a memory storing software instructions for implementing the process for reducing nitrogen oxides in a vehicle 10 automobile as defined in any one of the preceding claims. 9. Motor vehicle comprising a computer (10, 11) as defined in claim 8.