Method for reducing polluting emissions from hybrid drive systems

Abstract

A method for reducing polluting emissions of 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 system for transmitting drive torque of the vehicle, comprises: a step of changing the gear ratio of a gearbox of the transmission system to a higher gear ratio, the step of changing the gear ratio comprising a pre-detection step and an actuation step; a step of adjusting the engine (2) comprising a fuel injection step and a fuel ignition step at an optimal ignition advance angle; and a step of controlling the electric machine (15) operating in generator mode to generate a resistance torque throughout the duration of the gear change.

Description

[Technical Field]

[0001] The present invention relates generally to the reduction of polluting emissions from internal combustion engines. The invention finds advantageous application in motor vehicles equipped with a spark ignition engine associated with at least one electric machine. [Background technology]

[0002] Motor vehicles equipped with combustion engines are generally equipped with systems for the aftertreatment of polluting species in the exhaust gases of the vehicle in order to reduce the emission of these polluting species.

[0003] Aftertreatment systems for spark ignition engines (particularly those that run on gasoline) generally include a three-way catalyst for catalytic treatment of the exhaust gases, e.g., oxidation of carbon monoxide and unburned hydrocarbons and reduction of nitrogen oxides. The efficiency of treatment of various pollutant species depends on the amount of oxygen stored in the catalyst.

[0004] As the amount of oxygen stored in the catalyst approaches zero, the efficiency of oxidation of some polluting species decreases, particularly in the case of unburned hydrocarbons and carbon monoxide.

[0005] As the amount of stored oxygen approaches the maximum oxygen storage capacity of the catalyst, the efficiency of reducing polluting species, such as nitrogen oxides, decreases.

[0006] The amount of oxygen stored in the catalyst depends on the amount of injected air-fuel mixture.

[0007] In certain driving situations, for example during gear shifting or when the driver fully lifts his foot off the accelerator pedal, known as foot lifting, fuel injection is automatically interrupted and air is sent to the aftertreatment system to reduce fuel consumption. The amount of oxygen stored in the catalyst then increases, for example up to the catalyst's maximum storage capacity, and polluting species, more specifically nitrogen oxides (NOx), essentially consisting of nitric oxide and nitrogen dioxide, are no longer efficiently treated.

[0008] When fuel injection is resumed, the amount of oxygen stored in the catalyst reaches OSC, which means the catalyst is saturated with oxygen, and a strategy is usually implemented to purge or reduce the oxygen load of the catalyst. The catalyst purge strategy involves 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 a stoichiometric air-fuel mixture, in order to rapidly reduce the amount of oxygen stored in the catalyst. However, the catalyst purge strategy significantly increases the vehicle's fuel consumption and NOx emissions. In fact, during the period when the catalyst is saturated with oxygen, the catalyst's NOx treatment efficiency is very low or may even be zero.

[0009] It is known that the richness of the injected air-fuel mixture affects the amount of oxygen stored in the catalyst. Thus, for example, a means of limiting the increase in the amount of oxygen stored in the catalyst when changing gear ratios is to maintain the richness of the injected air-fuel mixture at stoichiometric proportions by delaying the interruption of fuel injection as described above, so as not to saturate the catalyst with oxygen. The delay before interrupting fuel injection is generally set to a predetermined and fixed duration, as described in unpublished French patent application No. 2 101 953.

[0010] An improvement proposed in unpublished French patent application No. 2 202 809 is to set the delay before fuel injection is interrupted to a duration that depends on the current maximum oxygen storage capacity of the catalyst.

[0011] Nevertheless, these injection interruption delay strategies do not take into account possible variations in gearbox ratio shift times, e.g., a slower pass would maximize oxygen loading of the catalyst.

[0012] The solution described in unpublished French patent application No. 2 207 721 proposes first interrupting fuel injection and then predicting its resumption when the catalyst approaches oxygen saturation.

[0013] However, because the oxygen content of the catalyst is not known precisely, these injection interruptions leave uncertainty as to when injection will be stopped or restarted. This imprecision creates, among other things, risks of NOx pollution and of parasitic residual engine torque. Summary of the Invention

[0014] In view of the above, the present invention aims to enhance the robustness of the treatment of polluting emissions, particularly NOx.

[0015] The present invention relates to a method for reducing polluting emissions from a spark-ignition internal combustion engine associated with at least one electric machine capable of operating in at least one generator mode, the electric machine being capable of driving at least one drive wheel of a motor vehicle via a system for transmitting drive torque of the vehicle.

[0016] The method is: - changing a gear of a gearbox of a transmission system to a higher gear, the gear changing step comprising a preceding step of detecting a gear change command by a higher gear and a step of actuating said higher gear corresponding to the end of the gear change; a stage of engine adjustments carried out after the detection of the change command, comprising a fuel injection stage and a fuel ignition stage at a predetermined spark advance angle that maximizes the thermal torque generated by the engine; a step of controlling the electric machine, performed simultaneously with the step of adjusting the motor, the electric machine operating in generator mode to generate a resistive torque (C_el) throughout the duration of the gear change; Equipped with.

[0017] According to one feature, the amount of injected fuel corresponds to a target value of unit richness.

[0018] 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 exhaust of the engine.

[0019] According to another feature, the step of adjusting the engine comprises reducing the amount of air introduced into the engine to a minimum amount of air corresponding to a predetermined minimum pressure in the intake manifold of the engine.

[0020] Advantageously, the resistive torque represents the work done by the electric machine to charge the battery.

[0021] Preferably, the total effective torque, which by definition is equal to the sum of the thermal torque produced by the motor and the resistive torque produced by the electric machine, is slightly negative.

[0022] For example, the value of the total effective torque is calculated using the following formula:

number

[0023] Preferably, the step of activating the higher gear is performed when the engine speed reaches a target speed value (N target ) is reached.

[0024] According to another aspect, the present 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 electric machine capable of operating at least in generator mode, the motorization device being associated with a manual gearbox of the transmission system of the vehicle to perform the above-mentioned method.

[0025] Other objects, features and advantages of the present invention will become apparent on reading the following description, given purely by way of non-limiting example and made with reference to the accompanying drawings, in which: [Brief explanation of the drawings]

[0026] [Figure 1] 1 is a schematic diagram showing a motorized device according to the present invention; [Figure 2] 3 is a flow chart illustrating various steps in a method for reducing polluting emissions, according to an embodiment of the present invention. [Figure 3] 3 shows the progression of various parameters of the motorized device during the steps of the method according to the invention; DETAILED DESCRIPTION OF THE INVENTION

[0027] Detailed Description of At Least One Embodiment 1 shows a schematic representation of a motorization system 1 according to the invention, suitable for use in a vehicle, in particular a motor vehicle. The motorization system 1 comprises a heat engine 2 with internal combustion and controlled ignition, here in the form of a non-limiting supercharged in-line four-cylinder engine. Naturally, the motor may also be of the naturally aspirated type without departing from the scope of the invention.

[0028] In operation, the heat engine 2 draws air in the direction of the arrow F1 through an intake pipe 3 and expels its exhaust gases through an exhaust pipe 4 in order to direct them to a depollution device 5. The pollution control device 5 includes a catalyst 6 of the three-way type.

[0029] At the outlet of the decontamination device 5, the exhaust gases are discharged to the outside air in the direction of arrow F2.

[0030] The engine 2 also consumes fuel, for example gasoline, a mixture of gasoline and ethanol or pure ethanol, which is supplied to the engine by an injection system (not shown), for example by a direct injection system comprising a supply rail common to the cylinders and at least one fuel injector per cylinder capable of injecting fuel directly into each of the cylinders.

[0031] The intake pipe 3 may have an air filter 8 that makes it possible to remove dust contained in the air, a flow meter 9 that makes it possible to determine the mass flow rate of fresh air introduced into the engine 2, and an intake flap 10 or throttle box 10 that makes it possible to adjust the flow rate introduced into the engine 2 by slightly blocking the intake pipe 3.

[0032] In the case of a supercharged engine 2, the heat engine 2 also comprises a turbocharger 11, the compressor 12 of which is interposed in the intake manifold 3 between the air filter 8 and the throttle housing 10. Furthermore, it is also possible to arrange a temperature exchanger 13 in the intake manifold 3 between the compressor 12 and the throttle housing 10 in order to cool the air compressed by the compressor 12.

[0033] The compressor 12 is driven by a turbine 14 of a turbocharger 11, which is interposed in the exhaust pipe 4 between the engine 2 and the depollution device 5. Furthermore, the heat engine 2 may be equipped with one or more intake and exhaust gas recirculation circuits (not shown), more particularly so-called high-pressure and / or low-pressure EGR circuits, EGR being an abbreviation for "Exhaust Gas Recycling". The heat engine 2 may also have a variable valve timing (VVT) distributor.

[0034] The heat engine 2 generates, in a manner known per se, an engine torque, called thermal torque C_comb, resulting from the combustion of a mixture of fresh air and fuel in an amount appropriately defined by the computer of the engine 2. Recirculated exhaust gases, which are recirculated to the intake side, may also be added to the fresh air.

[0035] The motorization device 1 according to the invention also comprises an electric machine 15 operable at least in generator mode. In generator mode, the electric machine 15 is an alternator providing a current intended to be stored in an accumulator battery (not shown), whereas in motor mode it is powered by a current previously stored in the accumulator battery and provides a motor torque that can be transmitted to the wheels of the vehicle in addition to or instead of the torque provided by the heat engine 2.

[0036] An electric machine 15, e.g. an alternator starter 15, independent of the flywheel of the heat engine 2, can operate in engine mode or in generator mode under the supervision of a control box 19, and its rotary shaft 16 is coupled to a rotary shaft 18, e.g. a crankshaft, of the heat engine 2 via a transmission means 17.

[0037] In generator mode, the electric machine 15 is an alternator that takes on a resistive electric torque C_el and supplies a current intended to be stored in the accumulator battery 20 .

[0038] In motor mode, the electric machine 15 is instead powered by the current previously stored in the battery 20 and provides an electric torque that is added to the thermal torque C_comb of its heat engine 2 that is transmitted to the wheels of the vehicle.

[0039] The motorized 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 the torque provided by the motorized device 1 to the wheels of the vehicle. A manual gearbox is a gearbox in which shifting is initiated by the driver.

[0040] Furthermore, the engine is equipped with a control system 1 comprising an electronic control unit 22 configured to control various elements of the internal combustion engine 2 based on data collected by sensors at various locations on the engine.

[0041] The electronic control unit 22 comprises a calculation module 23 , a measurement module 24 and a control module 25 .

[0042] The control module 25 may, for example, control the electrical torque of the electric machine 15 , the fuel injection system of the engine 2 , and the opening and closing of the butterfly housing 10 .

[0043] The mode of operation of the motorization device 1 is as follows: the driver's depression of the vehicle's accelerator pedal (not shown) is converted by the electronic control unit 22 into a torque setpoint C that is transmitted to the vehicle's wheels. The torque C can then be obtained either in the form of a thermal torque, an electric torque, or 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, which is positive in the motor mode of the electric machine 15 and negative in the generator mode, and the electronic control unit 22 performs the distribution depending on various parameters of the vehicle and / or the motorization device 1.

[0044] The method for reducing polluting emissions according to the present invention will now be described with reference to FIGS.

[0045] FIG. 2 shows various stages of a method for reducing polluting emissions according to an embodiment of the invention using a motorized device 1 as described above.

[0046] The reduction method begins with a step 30 of changing the gear ratio of the gearbox of the vehicle transmission system to a higher gear ratio, i.e., an upshift. Step 30 comprises a pre-step 31 of detecting a command to change the ratio to a higher ratio, and a step 38 of activating the higher ratio, corresponding to the end of the ratio change. The gear change control is generally realized by actuation of the clutch pedal, which can be detected by the electronic control unit. In the case of a manual gearbox, the clutch remains open for the entire duration of the gear change. The electronic control unit 22 can detect the acceleration phase by several parameters, such as the speed derivative and the accelerator pedal depression, in a known manner.

[0047] If an upshift command is detected, the method continues with step 32 of controlling the electric machine 15 and step 33 of adjusting the associated motor.

[0048] In the stage 32 of controlling the electric machine 15, the electronic control unit 22 regulates the operation of the electric machine 15 in generator mode producing a resistive torque C_el throughout the duration of the gear change.

[0049] The stage 33 of adjusting the engine 2 comprises a stage 34 of injecting fuel, followed by a stage of igniting the injected fuel at a predetermined spark advance angle that maximizes the thermal torque C_comb generated by the engine from the mass of air introduced therein.

[0050] Fuel injection is maintained during gear changes in the same manner as in the conventional mode of nominal operation of the engine used outside the gear change phase.

[0051] Preferably, the richness adjustment continuously adjusts the amount of injected fuel to achieve a stoichiometric air-fuel mixture, i.e., unit richness, regardless of the mass of air introduced into the engine 2. The richness adjustment is conventionally performed in a closed loop relative to a unit setpoint by adjusting the fuel injection according to the readings of an oxygen sensor mounted upstream of the catalyst. Alternatively, as described, for example, in patent application FR 3 033 364, the amount of injected fuel can be defined to correspond to a predetermined target value of oxygen stored in a three-way catalyst mounted in the exhaust of the engine.

[0052] The spark advance is not reduced but remains constant at the optimum value, so that the engine 2 provides the maximum possible torque for the mass of air introduced.

[0053] Preferably, the mass of air admitted to the engine 2 is reduced by closing the throttle housing 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 fall below said predetermined minimum pressure value, as this may cause excessive oil consumption.

[0054] Thus, there remains a residual airflow which generates a positive thermal torque C_comb equal to, for example, +20 Nm at the optimum advance angle.

[0055] In the absence of the resistive electric torque C_el, the driver would want to shift into a higher gear, but the thermal torque C_comb would result in a sudden and uncontrolled increase in speed, which is expressed as follows:

number

[0056] The total effective torque C, which is equal to the sum of the thermal torque C_comb generated by the motor and the resistive torque C_el generated by the electric machine, is slightly negative (step 37) to ensure control of the expected speed drop until the target speed N_target is reached, which makes it possible to operate a higher gear under best conditions. The electronic control unit therefore controls the electric machine 15 to generate a resistive torque C_el of greater absolute value than the thermal torque C_comb generated by the motor 2 (heat engine 2). For example, C_el is equal to -25 Nm and the total effective torque C is equal to -5 Nm.

[0057] The resistive electric torque C_el represents the work done by the electric machine to charge the battery 20. Thus, the chemical energy of the injected fuel for generating the thermal torque C_comb is converted into electrical energy and stored in the battery 20. Therefore, fuel consumption can be reduced at other operating points and the thermal torque of the engine 2 can be reduced by providing a positive electric torque generated by the electric machine 15 from the electrical energy stored in the battery 20.

[0058] When the engine speed reaches the target speed N_target, the method continues with step 38, which activates higher gear R+1, and the electronic control unit 22 controls the operation of the engine 2 according to the conventional nominal settings. Step 38 corresponds to the end of the gear change and involves the actuation of the clutch by the driver.

[0059] FIG. 3 shows the progression over time of various parameters of the motorization device 1 during an upward ratio change from R to R+1 according to the invention.

[0060] The proposed method can reduce pollutant emissions and consumption compared to the conventional method described above. This is because by maintaining active injection during gear ratio changes, the level of oxygen stored in the catalyst remains constant and far away from the saturation threshold, and therefore does not need to be reduced during re-acceleration. The proposed method avoids purging the catalyst 6, thereby avoiding increases in NOx, particulates and fuel consumption.

Claims

1. 1. A method for reducing polluting emissions of a spark-ignition internal combustion engine (2) associated with at least one electric machine (15) capable of driving at least one drive wheel of a motor vehicle via a system for transmitting drive torque of the vehicle and capable of operating at least in generator mode, comprising: a gear changing step of changing a gear of a gearbox of a transmission system to a higher gear, the gear changing step comprising a preceding step of detecting a command to change said gear by said higher gear, and a step of activating said higher gear corresponding to the end of said gear change; a stage of adjusting the engine (2) performed after detecting the change command, comprising a fuel injection stage and a fuel ignition stage at a predetermined spark advance angle that maximizes the thermal torque (C_comb) generated by the engine (2); a step of controlling the electric machine (15), performed simultaneously with the step of adjusting the engine (2), the electric machine (15) operating in generator mode to generate a resisting torque (C_el) throughout the duration of the gear change; A method for providing the above.

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

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

4. 4. The method according to claim 1, wherein the step of adjusting the engine (2) comprises reducing the amount of air introduced into the engine (2) to a minimum amount of air corresponding to a predetermined minimum pressure in the intake manifold (3) of the engine (2).

5. The method of any one of claims 1 to 4, wherein the resistive torque (C_el) represents the work done by the electric machine to charge a battery (20).

6. 6. The method according to any one of claims 1 to 5, wherein the total effective torque (C), which by definition is equal to the sum of the thermal torque (C_comb) generated by the engine (2) and the resistive torque (C_el) generated by the electric machine (15), is slightly negative.

7. The value of the total effective torque (C) is calculated using the following formula: [Equation 3] (Formula 1) According to the above, the speed of the engine (2) is calculated based on the speed of the vehicle (V ｖｅｈｉｃｌｅ ) and the gear ratio of the gearbox (V １０００ ) is calculated as a function of the target speed value (N ｔａｒｇｅｔ ) The gear ratio (V １０００ 7. The method of claim 6, wherein the speed is expressed in km / h per 1000 rpm.

8. The step of operating the higher gear is performed when the speed of the engine (2) reaches the target speed value (N ｔａｒｇｅｔ 8. The method of claim 7, wherein the method is executed when

9. A motorization device (1) for a motor vehicle comprising an electronic control unit (22), a spark ignition internal combustion engine (2) and at least one electric machine (15) capable of operating at least in generator mode, the motorization device (1) being associated with a manual gearbox of a transmission system of the vehicle and adapted to perform the method according to any one of claims 1 to 8.

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