Method for reducing pollutant emissions of hybrid drive system

Abstract

The invention relates to a method for reducing the pollutant emissions of a controlled ignition internal combustion engine (2) associated with at least one electric machine (15) capable of operating at least in generator mode, the electric machine (15) being capable of driving at least one drive wheel of a motor vehicle via a system for transmitting a drive torque of the motor vehicle, the method comprises: a step of changing a transmission ratio of a gearbox of the transmission system to a higher transmission ratio, the step of changing the transmission ratio comprising a pre-detection step and an engagement step; a step of adjusting the engine (2), comprising a step of injecting the fuel and a step of igniting the fuel in advance with an optimal ignition; a step of controlling the electric machine (15) to operate in a generator mode in which a counteracting torque is generated throughout the duration of the transmission ratio change.

Description

Field of the Invention

[0001] The present invention generally relates to reducing the pollutant emissions of internal combustion engines.

[0002] Advantageous applications are found in motor vehicles equipped with a spark ignition engine associated with at least one electric machine. Background Art

[0003] Motor vehicles equipped with a combustion engine are generally equipped with a system for post - treating the pollutants in the vehicle's exhaust gases in order to reduce the emissions of these pollutants.

[0004] The post - treatment system of a spark ignition engine (especially of the type operating with gasoline) generally includes a three - way catalyst for catalytically treating the exhaust gases (e.g., oxidation of carbon monoxide and unburned hydrocarbons, and reduction of nitrogen oxides). The treatment efficiency of different pollutants depends on the amount of oxygen stored in the catalyst.

[0005] When the amount of oxygen stored in the catalyst approaches zero, the oxidation efficiency of some pollutants decreases. This is especially true for unburned hydrocarbons and carbon monoxide.

[0006] When the stored amount of oxygen approaches the maximum oxygen storage capacity of the catalyst, the reduction efficiency of pollutants (such as nitrogen oxides) decreases.

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

[0008] In certain driving situations, such as during gear shifting of the gearbox or during a phase called lift - off (during which the driver completely lifts the foot from the accelerator pedal), the fuel injection is automatically cut off to reduce fuel consumption, and air is sent to the post - treatment system. Then, the amount of oxygen stored in the catalyst increases, for example, up to the maximum storage capacity value of the catalyst, and pollutants (more particularly nitrogen oxides (NOx) mainly including nitric oxide and nitrogen dioxide) are no longer effectively treated.

[0009] When fuel injection is resumed, when the amount of oxygen stored in the catalyst reaches OSC (meaning the catalyst is saturated with oxygen), a strategy for purifying or reducing the oxygen load of the catalyst is usually adopted. The catalyst purification 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 such that the proportion of fuel is greater than the proportion of fuel in the stoichiometric air - fuel mixture, thereby rapidly reducing the amount of oxygen stored in the catalyst. However, the catalyst purification strategy significantly increases the fuel consumption and NOx emissions of the vehicle. In fact, during the period when the catalyst is saturated with oxygen, the NOx treatment efficiency of the catalyst is very low, even zero.

[0010] It is well known that the richness of the injected air-fuel mixture affects the amount of oxygen stored in the catalyst. Thus, for example when changing the gear ratio, a solution to limit the increase in the amount of oxygen stored in the catalyst is to maintain the richness of the injected air-fuel mixture at stoichiometry by delaying the aforementioned fuel injection cut-off so that the catalyst is not saturated with oxygen. As described in the unpublished patent application FR 21 01 953, the delay before cutting off the fuel injection is generally set to a predetermined constant duration.

[0011] The improvement proposed in the unpublished patent application FR 22 02 809 sets the delay before the fuel injection is cut off to a duration that depends on the maximum current oxygen storage capacity of the catalyst.

[0012] However, these strategies for cutting off the delayed injection do not take into account the possible spread in the gearshift time of the gearbox ratio. For example, a slow passage causes the oxygen load of the catalyst to be maximized.

[0013] The solution described in the unpublished patent application FR 22 07 721 first proposes to cut off the fuel injection and then predict the resumption of fuel injection when the catalyst approaches oxygen saturation.

[0014] However, since the oxygen content of the catalyst is not precisely known, these methods of cutting off the injection still approximate when to stop or resume injection. This inaccuracy particularly gives rise to the risk of NOx pollution, as well as the risk of parasitic residual engine torque. Summary of the Invention

[0015] In view of the above, the present invention aims to enhance the robustness of the treatment of pollutant emissions (especially NOx).

[0016] The present invention relates to a method for reducing pollutant emissions of 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 the vehicle via a system for transmitting the driving torque of the motor vehicle.

[0017] The method comprises:

[0018] - a stage of changing the gear of the gearbox of the transmission system to a higher gear, the gear change stage comprising a previous stage of detecting a command to change the gear to a higher gear and a stage of engaging the higher gear corresponding to the end of the gear change;

[0019] - A phase of performing engine regulation after detecting the change command, including a fuel injection phase and a fuel ignition phase with a predetermined ignition advance that maximizes the thermal torque generated by the engine;

[0020] - A phase of controlling the electric machine that is simultaneous with the phase of regulating the motor, and the electric machine operates in a generator mode that generates a resistive torque (C_el) during the entire gear change process.

[0021] According to one feature, the amount of fuel injected corresponds to a target value of unit concentration.

[0022] According to another feature, the amount of fuel injected corresponds to a predetermined target value of the oxygen stored in the three-way catalyst installed at the exhaust pipe of the engine.

[0023] According to another feature, the phase of regulating the engine includes a phase of reducing the amount of air entering the engine to a minimum air amount corresponding to a predetermined minimum pressure in the intake manifold of the engine.

[0024] Advantageously, the resistive torque represents the work done by the electric machine to charge the battery.

[0025] Preferably, the total effective torque, which is defined as the sum of the thermal torque generated by the motor and the resistive torque generated by the electric machine, is slightly negative.

[0026] For example, according to the following manner, the value of the total effective torque enables the engine speed to be reduced to a target speed value (N vehicle ), which is calculated based on the vehicle speed (V 1000 ) and the gear ratio of the transmission (V target ):

[0027] (Equation 1),

[0028] where the gear ratio (V 1000 ) is expressed in km / h per 1000 rpm.

[0029] Preferably, when the engine speed reaches the target speed value (N target ), the phase of engaging the higher gear is performed.

[0030] According to another aspect, the present invention also relates to a motorization device for a motor vehicle, including: an electronic control unit, a spark-ignition internal combustion engine, and at least one electric machine capable of operating at least in a generator mode, and the motorization device is associated with a manual transmission of the vehicle's transmission system and implements the above method. Description of the Drawings

[0031] Other objects, features and advantages of the present invention will become apparent upon reading the following description given by way of non-limiting example only and with reference to the accompanying drawings, in which:

[0032] Figure 1 is a schematic view showing a motorized device according to the present invention;

[0033] Figure 2 is a flowchart showing different stages of a method for reducing pollution emissions according to an embodiment of the present invention;

[0034] Figure 3 shows the evolution of different parameters of the motorized device during the stages of the method according to the present invention. Detailed Description

[0035] Figure 1 Schematically shows a motorized device 1 according to the present invention that can be assembled to a vehicle (in particular a motor vehicle). The motorized device 1 includes a thermal engine 2 with internal combustion and controlled ignition, which is in the form of a supercharged in-line four-cylinder engine here in a non-limiting manner. Of course, the motor can also be naturally aspirated without departing from the scope of the present invention.

[0036] For its operation, such a thermal engine 2 sucks in air through an intake pipe 3 in the direction of arrow F1 and discharges its exhaust gases through an exhaust pipe 4 in order to direct the exhaust gases to a decontamination device 5. The pollution control device 5 includes a catalyst 6 of the three-way type.

[0037] At the outlet of the decontamination device 12, the exhaust gases are discharged into the external atmosphere in the direction of arrow F2.

[0038] The engine 2 also consumes fuel (such as gasoline, a mixture of gasoline and ethanol, or even pure ethanol), and the fuel is supplied to the engine through an injection system (not shown) (such as a direct injection system, which includes a feed rail shared by the cylinders and at least one fuel injector for each cylinder capable of directly injecting fuel into each cylinder).

[0039] In the intake pipe 3, there can be: an air filter 8, which can remove the dust contained in the air; a flowmeter 9, which can determine the mass flow rate of the fresh air entering the engine 2; and an intake flap 10 or a throttle body 10, which can regulate the flow entering the engine 2 by more or less blocking the intake pipe 3.

[0040] In the case of a supercharged engine 2, the thermal engine 2 also includes a turbocharger 11, whose compressor 12 is placed in the intake pipe 3 between the air filter 8 and the throttle housing 10. In addition, a temperature exchanger 13 can be arranged in the intake pipe 3 and between the compressor 12 and the throttle housing 10 in order to cool the air compressed by the compressor 12.

[0041] The compressor 12 is driven by a turbine 14 of a turbocharger 11 in an exhaust pipe 4 placed between the engine 2 and the decontamination device 5. In addition, the heat engine 2 may include one or more intake exhaust gas recirculation circuits (not shown), more specifically, a so-called high-pressure EGR circuit and / or a low-pressure EGR circuit, where EGR is the acronym for "Exhaust Gas Recycling". The heat engine 2 may also have variable valve timing (VVT) distribution.

[0042] In a manner known per se, the heat engine 2 generates an engine torque (referred to as the thermal torque C_comb), which is generated by the combustion of a mixture of fresh air and fuel in a well-defined quantity by the computer of the engine 2. Recirculated exhaust gas recirculated to the intake pipe may also be added to the fresh air.

[0043] The motorized device 1 according to the invention further includes an electric machine 15 capable of operating at least in generator mode. In generator mode, the electric machine 15 is an alternator that provides an electric current for storage in a battery (not shown). Conversely, in motor mode, it is powered by an electric current pre-stored in the battery and provides a motor torque that can be transmitted to the vehicle's wheels, as a supplement or alternative to the torque provided by the heat engine 2.

[0044] The rotating shaft 16 of the electric machine 15 (such as an alternator-starter 15 separated from the flywheel of the heat engine 2) is coupled to the rotating shaft 18 (such as a crankshaft) of the heat engine 2 via a transmission 17, and the electric machine 15 is capable of operating in engine mode or generator mode under the supervision of a control box 19.

[0045] In generator mode, the electric machine 15 is an alternator that supplies an electric current intended for storage in the battery 20 by applying a resistive electric torque C_el.

[0046] In motor mode, the electric machine 15 is, on the contrary, powered by an electric current pre-stored in the battery 20, and the electric machine 15 provides an electric torque that is added to the C_comb of the heat engine 2 to be transmitted to the vehicle's wheels.

[0047] The motorized device 1 is associated with a transmission system (not shown) that particularly includes a manual gearbox, a differential shaft, and a drive shaft, such that the torque provided by the motorized device 1 can be transmitted to the vehicle's wheels. The manual gearbox is a gearbox in which gear shifting is actively performed by the driver.

[0048] In addition, the engine is equipped with a control system 1 including an electronic control unit 22 configured to control various elements of the internal combustion engine 2 based on data collected by sensors at different positions on the engine.

[0049] The electronic control unit 22 includes a calculation module 23, a measurement module 24, and a control module 25.

[0050] The control module 25 is capable of controlling, for example, the electric torque of the electric machine 15, the fuel injection system of the engine 2, and the opening and closing of the butterfly housing 10.

[0051] The operating mode of the motorized device 1 is as follows: The depression of the accelerator pedal (not shown) of the vehicle by the driver is converted by the electronic control unit 21 into a torque setpoint C to be transmitted to the vehicle's wheels. Then, the torque C can be obtained in the form of thermal torque, in the form of electric torque, or in the form of a combination of both. 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 being positive in motor mode and negative in generator mode of the electric machine 15, and the electronic control unit 21 performs the distribution based on different parameters of the vehicle and / or the motorized device 1.

[0052] Now, reference will be made to Figure 2 and Figure 3 describe a method for reducing pollutant emissions according to the present invention.

[0053] Figure 2 The different stages of a method for reducing pollutant emissions using the motorized device 1 as described above according to an embodiment of the present invention are shown.

[0054] The reduction method starts at stage 30 of changing the gear ratio of the gearbox of the vehicle transmission system to a higher gear ratio (i.e., upshifting). Stage 30 includes a previous stage 31 of detecting a command to change the transmission ratio to a higher ratio and a stage 38 of engaging the higher gear ratio corresponding to the end of the transmission ratio change. The shift control is generally achieved by the actuation of the clutch pedal that can be detected by the electronic control unit. It should be noted that in the case of a manual transmission, the clutch remains open throughout the shifting process. In a known manner, the electronic control unit 22 can detect whether it is an acceleration stage from a plurality of parameters such as the derivative of speed and the depression of the accelerator pedal.

[0055] When a upshift command is detected, the method continues to stage 32 of controlling the electric machine and stage 33 of regulating the accompanying motor.

[0056] In stage 32 of controlling the electric machine 15, the electronic control unit 22 regulates the operation of the electric machine 15 according to the generator mode that generates a resistance torque C_el throughout the shifting duration.

[0057] The phase 33 of adjusting the engine 2 includes a phase 34 of injecting fuel, which is followed by a phase of igniting the injected fuel with a predetermined ignition advance that maximizes the thermal torque C_comb generated by the engine from the air mass entering it.

[0058] During the gearshift process, the fuel injection is maintained in the same way as in the conventional rated operating mode of the engine used outside the gearshift phase.

[0059] Preferably, the richness adjustment continuously adjusts the amount of fuel injected to achieve a mixture of air and fuel according to the stoichiometric ratio (i.e., at unit richness), regardless of the air mass entering the engine 2. Generally, the richness adjustment is carried out in a closed loop at a unit set value by adjusting the fuel injection based on the indication of an oxygen sensor installed upstream of the catalyst. Alternatively, as described in document FR-A1-30 33 364, the amount of fuel injected can be made to correspond to a predetermined target value of the oxygen stored in the three-way catalyst installed in the engine exhaust pipe.

[0060] The ignition advance does not degrade and always remains at the optimum value. Thus, the engine 2 provides the maximum possible torque for the air mass entering it.

[0061] Preferably, the air mass entering 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 (phase 36). In any case, the pressure in the intake manifold 3 should not be lower than the said predetermined minimum pressure value, as this would lead to a significant increase in fuel consumption.

[0062] Thus, there still remains a residual air flow that generates a positive thermal torque C_comb (e.g., equal to +20 Nm) with optimum advance.

[0063] In the absence of a resisting electric torque C_el, the thermal torque C_comb would cause a rapid and uncontrolled increase in speed, while the driver wishes to switch to a higher gear, which requires the engine speed to be reduced to a target speed value N_target calculated based on the vehicle speed V vehicle and the gear ratio V 1000 according to the following formula:

[0064] Equation 1

[0065] where the gear ratio (V 1000 ) is expressed in km / h per 1000 rpm.

[0066] The total effective torque C, which is equal to the sum of the thermal torque C_comb generated by the motor and the opposing torque C_el generated by the electric machine, is slightly negative in order to ensure the expected controlled speed reduction until the target speed N_target is reached (phase 37), which makes it possible to engage the higher gear under optimal conditions. Thus, the electronic control unit controls the electric machine 15 in order to generate an opposing torque C_el whose absolute value is greater than the thermal torque C_comb generated by the motor 2. For example, C_el is equal to -25 Nm and the total effective torque C is equal to -5 Nm.

[0067] The opposing 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 used to generate the thermal torque C_comb is converted 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 by providing a positive electric torque generated by the electric machine 15 from the electrical energy stored in the battery 20.

[0068] When the engine speed reaches the target speed N_target, the method continues with phase 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 conventional rated setting. Phase 38 corresponds to the end of the gear shift and is accompanied by the driver's engagement of the clutch.

[0069] Figure 3 Shows the evolution over time of the different parameters of the motorized device 1 during an upshift from R to R+1 according to the invention.

[0070] Compared with the above conventional method, the proposed method makes it possible to reduce pollutant emissions and consumption because, by keeping the injection activated during the change of the gear ratio, the oxygen level stored in the catalyst remains constant and far from the saturation threshold. Thus, there is no need to reduce the oxygen level during a new acceleration. By avoiding the purification catalyst 6, the proposed method avoids an increase in NOx, particulate matter and fuel consumption.

Claims

1. A method for reducing the pollutant emissions of a spark-ignition internal combustion engine (2), said spark-ignition internal combustion engine (2) being associated with at least one electric machine (15) capable of operating at least in generator mode, said electric machine (15) being capable of driving at least one driving wheel of the vehicle via a system for transmitting the driving torque of the motor vehicle, characterized in that, the method comprises: - a phase of changing the gear of the gearbox of the transmission system to a higher gear, said gear change phase comprising a previous phase of detecting a command to change the gear to a higher gear and a phase of engaging said higher gear corresponding to the end of the gear change; - a phase of performing engine (2) regulation after detecting said change command, comprising a fuel injection phase and a fuel ignition phase with a predetermined ignition advance that maximizes the thermal torque (C_comb) generated by the engine (2); - a phase of controlling the electric machine (15) simultaneous with the phase of regulating the engine (2), said electric machine (15) operating in generator mode generating a resistance torque (C_el) throughout the gear change.

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

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

4. The method according to any one of the preceding claims, wherein, the phase of regulating the engine (2) comprises a phase of reducing the amount of air entering the engine (2) to a minimum air amount corresponding to a predetermined minimum pressure in the intake manifold (3) of the engine (2).

5. The method according to any one of the preceding claims, wherein, said resistance torque (C_el) represents the work performed by the electric machine to charge the battery (20).

6. The method according to any one of the preceding claims, wherein, the total effective torque (C), which is defined as the sum of the thermal torque (C_comb) generated by the engine (2) and the resistance torque (C_el) generated by the electric machine (15), is slightly negative.

7. The method according to claim 6, wherein, According to the following formula, the value of the total effective torque (C) enables the engine speed (2) to be reduced to a target speed value (N vehicle ) calculated based on the speed (V 1000 ) of the vehicle and the gear ratio (V target ) of the transmission: (Formula 1), wherein the gear ratio (V 1000 ) is expressed in km / h per 1000 rpm.

8. The method according to claim 7, wherein, When the rotational speed of the engine (2) reaches the target speed value (N target ), the stage of engaging the higher gear is executed.

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, said motorization device being associated with the manual gearbox of the vehicle's transmission system and implementing the method according to any one of claims 1 to 8.

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