Method for reducing pollutant emissions from a hybrid engine system

Abstract

This method for reducing pollutant emissions from a spark-ignition internal combustion engine (2) associated with at least one electric machine (15) capable of operating at least in generator mode, and capable of driving at least one drive wheel of a motor vehicle via a transmission system of a vehicle drive torque, comprises: a step of changing the gear ratio of a gearbox of said transmission system to a higher gear, said gear change step comprising a preliminary detection step and an engagement step; a step of adjusting the engine (2) comprising a fuel injection step and a fuel ignition step with optimal ignition advance; a step of controlling said electric machine (15) operating in generator mode which generates a resistive torque throughout the gear change. Figure for the abbreviation: Figure 1

Description

Description Title of the invention: Method for reducing polluting emissions of a hybrid motorization device Technical field

[0001] The invention relates to a method for reducing pollutant emissions from an engine internal combustion.

[0002] = It finds an advantageous application in a motor vehicle equipped with a spark-ignition engine associated with at least one electric machine. Previous techniques

[0003] A motor vehicle equipped with a combustion engine is generally equipped with a post-treatment system for polluting species in vehicle exhaust gases in order to reduce emissions of these polluting species.

[0004] — The aftertreatment system of a spark-ignition engine (of the func- operating in particular on gasoline) generally includes a three-way catalyst which carries out catalytic treatment of exhaust gases, such as for example oxidations of carbon monoxide and unburned hydrocarbons, and reductions nitrogen oxides. The treatment efficiency of different pollutant species depends on the amount of oxygen stored in the catalyst.

[0005] — When the amount of oxygen stored in the catalyst is close to zero, the oxidation efficiency of certain polluting species decreases. This is particularly true the case of unburned hydrocarbons and carbon monoxide.

[0006] — When the amount of stored oxygen is close to the maximum storage capacity in oxygen of the catalyst, the efficiency of reduction of polluting species, for example for nitrogen oxides, decreases.

[0007] — The amount of oxygen stored in the catalyst depends on the injection of a mixture air-fuel.

[0008] — In certain driving situations, for example when changing gears, ratio of a gearbox or a so-called foot lifting phase, the injection of fuel is automatically cut off to reduce fuel consumption and air is sent into the aftertreatment system. The amount of oxygen stored in the catalyst then increases, for example up to the maximum capacity value catalyst storage, and polluting species are no longer treated effectively, more particularly nitrogen oxides (NOx) comprising mainly nitric oxide and nitrogen dioxide.

[0009] — When resuming fuel injection, while the quantity of oxygen stored in the catalyst has reached the maximum oxygen storage capacity meaning that the catalyst is saturated with oxygen, a catalyst purge or oxygen load reduction strategy is generally carried out. The catalyst purge strategy includes increasing the richness of the injected air-fuel mixture to a richness greater than 1, i.e., increasing the proportion of fuel in the injected air-fuel mixture so that the proportion of fuel is greater than that present in the staichiometric air-fuel mixture, so as to rapidly decrease the amount of oxygen stored in the catalyst. However, the catalyst purge strategy significantly increases the vehicle's fuel consumption and causes a temporary but significant increase in NOx emissions. Indeed, during the period in which the catalyst is saturated with oxygen, the NOx treatment efficiency of the catalyst is very low, or even zero. It is known that the richness of the injected air-fuel mixture influences the quantity of oxygen stored in the catalyst. Thus, one solution to limit the increase in the quantity of oxygen stored in the catalyst, for example when changing gear in the gearbox, is to maintain the richness of the injected air-fuel mixture in stoichiometric proportions by delaying the fuel injection cut-off mentioned above so as not to saturate the catalyst with oxygen. The delay before the fuel injection cut-off is generally set at a predetermined and constant duration as described in the unpublished patent application FR 21 01 953. An improvement proposed in unpublished patent application FR 22 02 809 sets the delay before fuel injection cutoff to a duration dependent on the current maximum oxygen storage capacity of the catalyst. However, these strategies of delaying injection cut-off do not take into account the possible dispersion of gearbox shift times. For example, slow shifting leads to maximizing the oxygen loading of the catalyst. The solution described in the unpublished patent application FR 22 07 721 first proposes to cut off the fuel injection and then anticipate the resumption of fuel injection when the catalyst approaches oxygen saturation. However, these methods of cutting off the injection remain approximate as to the moment of stopping or resuming the injection, because the oxygen content of the catalyst is not known precisely. This imprecision creates in particular a risk of NOx pollution, as well as a risk of parasitic residual engine torque. Presentation of the invention In view of the above, the invention aims to strengthen the robustness of the processing of pollutant emissions, particularly NOx. The subject of the invention is a method for reducing pollutant emissions from a spark-ignition internal combustion engine associated with at least one electrical machine capable of operating at least in a generator mode, capable of driving at least one drive wheel of a motor vehicle via a system for transmitting a drive torque of the vehicle. The process includes: a step of changing a gear of a gearbox of said system transmission by a higher gear, said step of changing report including a preliminary step of detecting an order of changing the said ratio to the higher ratio and one step engagement of said higher gear corresponding to the end of the gear change; an engine adjustment step carried out after the detection of said command of change and comprising a fuel injection stage and a stage fuel ignition with a predetermined ignition advance which maximizes thermal torque produced by the engine; a step of controlling said electrical machine carried out in a manner concomitant with the engine adjustment step, said electric machine operates- operating according to a generator mode which generates a resistive torque (C_el) for the entire duration of the gear change. According to one characteristic, the quantity of fuel injected corresponds to a target value of unit richness. According to another feature, the quantity of fuel injected corresponds to a predetermined target value of oxygen stored in a three-way catalyst mounted in the engine exhaust. According to another feature, the engine adjustment step comprises a step of reducing the amount of air admitted into the engine to a minimum amount of air corresponding to a predetermined minimum pressure in an intake manifold of the engine. Advantageously, the resistive torque is representative of the work done by the electric machine to charge a battery. Preferably, the total effective torque, equal by definition to the sum of the thermal torque produced by the motor and the resistive torque generated by the electric machine, is slightly negative. For example, the total effective torque value allows the engine speed to be reduced to a target speed value (Neive) calculated based on the vehicle speed (Vreticuie) and a gearbox gear ratio (V 1000), according to the equation next: = Lixsherte (Eq.1) Noible FFE » in which the gear ratio (V 1000) is expressed in km / h per 1000 rpm. Preferably, the upshift step is performed when the engine speed reaches the target speed value (N;;pie)- According to another aspect, the invention also relates to a motorization device for a motor vehicle comprising an electronic control unit, a spark-ignition internal combustion engine and at least one electrical machine capable of operating at least in a generator mode, said motorization device being associated with a manual gearbox of a transmission system of said vehicle and implementing a method as described above. Brief description of the drawings Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which: [Fig.1] is a schematic view illustrating a motorization device according to the invention; [Fig.2] is a flowchart illustrating the different stages of a method for reducing pollutant emissions according to one embodiment of the invention; [Fig.3] illustrates the evolution of different parameters of the motorization device during the stages of the method according to the invention; Detailed description of at least one embodiment [Fig. 1] schematically illustrates a motorization device 1 according to the invention which can equip a vehicle, in particular a motor vehicle. It comprises a thermal engine 2, with internal combustion and spark ignition, which is presented here in a non-limiting manner in the form of a supercharged in-line four-cylinder engine. Of course, the engine can also be of the naturally aspirated type without departing from the scope of the invention. For its operation, such a heat engine 2 sucks in air in the direction of arrow F1 via an intake pipe 3, and discharges its exhaust gases via an exhaust pipe 4 in order to direct them towards a pollution control device 5. The pollution control device 5 comprises a three-way type catalyst 6. At the outlet of the pollution control device 12, the exhaust gases are discharged into the outside atmosphere in the direction of arrow F2. Engine 2 also consumes fuel, for example gasoline, a mixture of gasoline and ethanol, or even pure ethanol, which is brought to the engine using an injection system (not shown), for example a direct injection system which includes a fuel rail common to the cylinders and at least one fuel injector per cylinder capable of injecting the fuel directly into each of the cylinders. In the air intake duct 3, there can be found an air filter 8 which makes it possible to eliminate the dust contained in the air, a flow meter 9 which makes it possible to determine the mass flow of fresh air admitted into the engine 2, and an air intake flap 10, or butterfly valve 10 which makes it possible to regulate the flow admitted into the engine 2 by obstructing the intake duct 3 to a greater or lesser extent. In the case of a supercharged engine 2, the thermal engine 2 also comprises a turbocharger 11 whose compressor 12 is interposed in the intake duct 3 between the air filter 8 and the throttle body 10. In addition, it is possible for a temperature exchanger 13 to be arranged in the intake duct 3, between the compressor 12 and the throttle body 10, so as to cool the air compressed by the compressor 12. The compressor 12 is driven by the turbine 14 of the turbocharger 11, which is interposed in the exhaust pipe 4 between the engine 2 and the depollution device 5. In addition, the heat engine 2 may comprise one or more exhaust gas recirculation circuits at the intake (not shown), more particularly a so-called high-pressure EGR circuit and / or a low-pressure EGR circuit, EGR being the English acronym for “Exhaust Gas Recycling” or recycling of exhaust gases. The heat engine 2 may also have a variable valve timing with the acronym VVT for “Variable Valve Timing” in English. In a manner known per se, the heat engine 2 produces an engine torque, called thermal torque C_comb, which results from the combustion of a mixture of fresh air and fuel in quantities well defined by a computer of the engine 2. Recycled exhaust gases recycled to the intake can also be added to the fresh air. The motorization device 1 according to the invention also comprises an electrical machine 15 capable of operating at least in a generator mode. In generator mode, the electrical machine 15 is an alternator which supplies an electric current intended to be stored in a storage battery (not shown). In engine mode, on the contrary, it is powered by current previously stored in the storage battery and provides an engine torque which can be transmitted to the wheels of the vehicle, in addition to or in replacement of the torque supplied by the thermal engine 2. The electrical machine 15, for example an alternator-starter 15 separate from the flywheel inertia of the heat engine 2, and of which a rotary shaft 16 is coupled via transmission means 17 to a rotary shaft 18 of the heat engine 2, for example a crankshaft, is capable of operating in engine mode or in generator mode under the supervision of a control box 19. In generator mode, the electrical machine 15 is an alternator which supplies an electric current intended to be stored in a battery 20 of accumulators by taking a resistant electric torque C_el. In motor mode, the electric machine 15 is on the contrary powered by current previously stored in the battery 20 and it provides an electric torque which is added to that C_comb of the thermal engine 2 to be transmitted to the wheels of the vehicle. The motorization device 1 is associated with a transmission system (not shown) comprising in particular a manual gearbox, a differential axle and a transmission shaft making it possible to transmit to the wheels of the vehicle the torque supplied by the motorization device 1. A manual gearbox is a gearbox in which the gear changes are carried out at the initiative of the driver. Furthermore, the motorization device 1 comprises an electronic control unit 22 configured to control the different elements of the engine 2 from data collected by sensors at different locations of the engine. The electronic control unit 22 comprises a calculation module 23, a measurement module 24 and a control module 25. The control module 25 is for example capable of controlling the electric torque of the electric machine 15, the fuel injection system of the engine 2 and the opening and closing of the throttle body 10. The operating mode of the motorization device 1 is as follows: the driver pressing the accelerator pedal (not shown) of the vehicle is translated by an electronic control unit 21 into a torque setpoint C to be transmitted to the wheels of the vehicle. The torque C can then be obtained either in the form of thermal torque, or in the form of electric torque, or in the form of a combination of the two. In all cases, the value of the torque C is equal to the algebraic sum of the values ​​of the thermal torque C_comb and the electric torque C_el, the latter taking a positive value in motor mode and a negative value in generator mode of the electric machine 15, the electronic control unit 21 carrying out the distribution according to different parameters of the vehicle and / or of the motorization device 1. We will now describe with reference to figures 2 and 3 a method for reducing polluting emissions according to the invention. [Fig.2] illustrates the different stages of an emissions reduction process pollutants according to one embodiment of the invention, using a motorization device 1 as described previously. The reduction method begins with a step 30 of changing a gear of a gearbox of the vehicle transmission system to a higher gear, i.e. an upshift. Step 30 comprises a prior step 31 of detecting a command to change said gear to a higher gear and a step 38 of engaging the higher gear corresponding to the end of the gear change. The gear change command generally takes the form of actuation of the clutch pedal, which the electronic control unit is capable of detecting. It should be noted that in the case of manual gearboxes, the clutch remains open throughout the gear change. In a known manner, the electronic control unit 22 is capable of detecting that it is an acceleration phase based on several parameters such as the speed derivative and the depressing of the accelerator pedal. When the upshift command is detected, the method continues with a step 32 of controlling the electric machine and a concomitant step 33 of adjusting the engine. In step 32 of controlling the electric machine 15, the electronic control unit 22 regulates the operation of the electric machine 15 according to a generator mode which generates a resistive torque C_el for the entire duration of the gear change. Step 33 of tuning the engine 2 comprises a step 34 of fuel injection followed by a step of ignition of the injected fuel with a predetermined ignition advance which maximizes the thermal torque C_comb produced by the engine from the mass of air admitted into it. Fuel injection is maintained during gear changes, similar to the conventional nominal engine operating mode used outside of gear change phases. Preferably, the richness regulation continuously adjusts the quantity of fuel injected to produce, regardless of the mass of air admitted into the engine 2, a mixture of air and fuel according to stoichiometric proportions, i.e. at unit richness. The richness regulation is conventionally carried out in a closed loop on a unit setpoint value by adjusting the fuel injection from the indications of an oxygen sensor mounted upstream of the catalyst. Alternatively, it is possible to provide that the quantity of fuel injected corresponds to a predetermined target value of oxygen stored in a three-way catalyst mounted at the engine exhaust, as described for example in document FR — A1- 30 33 364. The ignition advance is not degraded and remains constantly on values optimal. Thus, engine 2 provides the maximum possible torque for the admitted air mass. Preferably, the air mass admitted into the engine 2 is reduced by closing the throttle body 10 so that the pressure in the intake manifold 3 reaches a predetermined minimum pressure value (step 36). In any case, the pressure in the intake manifold 3 should not be lower than said predetermined minimum pressure value, as this would cause a sharp increase in oil consumption. There therefore remains a residual air flow which generates with optimal advance a positive thermal torque C_comb, for example equal to +20 Nm. In the absence of the resistive electric torque C_el, the thermal torque C_comb would lead to a rapid and uncontrolled increase in rpm, while the driver wants to shift up a gear which requires the engine rpm to drop to a target rpm value N_target calculated as a function of the vehicle speed V eticue and a gearbox gear ratio V 1000, according to the following equation: Lsstiots (Eq.1) N cipie = FE , in which the gear ratio (V0) is expressed in km / h per 1000 rpm. The total effective torque C equal to the sum of the thermal torque C_comb produced by the engine and the resistive torque C_el generated by the electric machine is slightly negative, in order to ensure the controlled decrease in speed expected until the target speed N_target is reached (step 37) which allows the higher gear to be engaged in the best conditions. Thus, the electronic control unit controls the electric machine 15 so as to generate a resistive torque C_el greater in absolute value than the thermal torque C_comb produced by the engine 2. For example, C_el is equal to -25Nm and the total effective torque C is equal to -5Nm. The resistive electric torque C_el is representative of the work performed by the electric machine to charge the battery 20. The chemical energy of the fuel injected for the production of the thermal torque C_comb is therefore transformed into electrical energy and stored in the battery 20. Thus, fuel consumption can be reduced at other operating points, where the thermal torque of the engine 2 can be reduced thanks to the contribution of a positive electric torque generated by the electric machine 15 from the electrical energy stored in the battery 20. When the engine speed reaches the target speed N_target, the method continues with a step 38 of engaging the higher gear R+1, in which the electronic control unit 22 controls the operation of the engine 2 according to a setting classic nominal. Step 38 corresponds to the end of the gear change and is accompanied by the driver engaging the clutch. [Fig. 3] illustrates the evolution over time of different parameters of the motorization device 1 during a change of upward ratio from R to R+1 according to the invention. The proposed method allows to reduce pollutant emissions and consumption compared to the conventional methods mentioned above, because by keeping the injection activated during the gearbox gear change the level of oxygen stored in the catalyst remains constant and far from the saturation threshold. It is therefore not necessary to lower it when resuming acceleration. By avoiding the purging of catalyst 6, the proposed method avoids increases in NOx, particles and fuel consumption.

Claims

Claims

1. Method for reducing pollutant emissions from an engine (2) internal combustion with spark ignition associated with at least one electric machine (15) capable of operating in at least one mode generator, capable of driving at least one drive wheel of a vehicle au- automobile by means of a torque transmission system vehicle drive, characterized in that said method understand : a step of changing a gear in a gearbox said transmission system by a higher ratio, said gear change step including a step prior to detection of a change order of said report by the higher report and an engagement step of the said higher report corresponding to the end of the change of report; an engine adjustment step (2) performed after detection of said change command and comprising a step fuel injection and a fuel ignition stage with a predetermined ignition advance that maximizes a thermal torque (C_comb) produced by the motor (2); a step of controlling said electric machine (15) carried out concomitantly with the engine adjustment step (2), said electric machine (15) operating in a ge- mode generator which generates a resistive torque (C_el) throughout the duration of the gear change.

2. The method of claim 1, wherein the amount of fuel injected corresponds to a target value of unit richness.

3. Method according to claim 1, in which the quantity of fuel injected corresponds to a predetermined target value of stored oxygen in a three-way catalyst (6) mounted in the exhaust of the engine (2).

4. Method according to any one of the preceding claims, in wherein the engine adjustment step (2) comprises a reduction step from the quantity of air admitted into the engine (2) to a quantity of air minimum corresponding to a predetermined minimum pressure in a intake manifold (3) of engine (2).

5. A method according to any preceding claim, in which the resistive torque (C_el) is representative of the work carried out by the electric machine for charging a battery (20).

6. A method according to any preceding claim, in which the total effective torque (C) equal by definition to the sum of the thermal torque (C_comb) produced by the motor (2) and the torque resistor (C_el) generated by the electric machine (15) is slightly negative.

7. A method according to claim 6, wherein the value of the effective torque total (C) allows the engine speed (2) to be lowered to a value target speed (N;ipie) calculated based on vehicle speed (V vehicle) €t of a gearbox gear ratio (V 1000); according to the following equation: — Lrésisei (Eq.1) Noible RE EE NUE , in which the gear ratio (V100) is expressed in km / h for 1000 rpm.

8. The method of claim 7, wherein the engaging step of the higher gear is achieved when the engine speed (2) reaches the target diet value (N.ipie)-

9. Motorization device (1) of a motor vehicle comprising a electronic control unit (22), a combustion engine (2) internal spark ignition and at least one electric machine (15) able to operate at least in a generator mode, said device engine being associated with a manual gearbox of a transmission system of said vehicle and implementing a method according to any one of claims | to 8.

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