Method for heating a catalyst in a hybrid vehicle
Patent Information
- Application Number
- FR2022010533
- Authority / Receiving Office
- FR · FR
- Patent Type
- Patents
- Current Assignee / Owner
- Filing Date
- 2022-10-13
- Publication Date
- 2026-09-11
- Estimated Expiration
- 2042-10-13
AI Technical Summary
Current catalyst heating strategies in hybrid engines are insufficient to meet the stringent Euro7 emission standards, leading to increased noise, vibrations, and inefficiencies due to erratic combustion and complex, expensive solutions like electrically heated catalysts are required.
A method involving post-combustion adjustment in hybrid engines, where fuel is injected around the top dead center and ignited at the bottom dead center to heat the catalyst efficiently, using a sequence of injections and multiple sparks to transfer chemical energy directly to the catalyst, avoiding mechanical energy exchange.
This approach effectively heats the catalyst to the required temperature, enhancing efficiency and reducing emissions, meeting future emission standards without complex additional systems.
Smart Images
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Abstract
Description
Description Title of the invention: Method for heating a catalyst in a hybrid engine vehicle technical field
[0001] = The invention relates to a method for heating a three-way catalyst integrated into the Exhaust line of a spark-ignition internal combustion engine. It also concerns a hybrid engine system capable of implementing such process. Previous techniques
[0002] Modern combustion engines, particularly those of vehicles, Vehicles that are subject to increasingly stringent anti-pollution standards are equipped with various post-treatment systems for polluting molecules emitted in the combustion gases from said engines, in order to limit the release of harmful species into the outside atmosphere.
[0003] — On spark-ignition type engines running in particular on gasoline, We are particularly familiar with three-way catalysts which are capable of treating hydro- unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) emitted in the engine's combustion gases.
[0004] It is known that the efficiency of a post-processing system depends on its temp- operature. By efficiency, we mean the proportion of polluting molecules of a type Given that the system is able to process the input data, the system's efficiency is also a factor. begins to reach acceptable values, for example between 50% and 90%, when the catalyst temperature is, for example, between approximately Between 250°C and 300°C, the effectiveness of a catalyst is zero as long as the temperature has not reached reaches a value of around 150°C.
[0005] — When starting a heat engine, it is therefore necessary to take measures that the vehicle does not release too many polluting emissions into the outside atmosphere.
[0006] It is also known that the internal combustion engines of certain motor vehicles So-called "hybrid" engines are associated with reversible electric machines. which can operate in "engine" mode or in "generator" mode.
[0007] — In these "hybrid" engines, combustion conventionally takes place delayed inside the engine cylinders to heat the catalyst, in a way to degrade combustion efficiency and increase engine heat losses. For example, it is common to use a retarded ignition advance and to proceed to a series of fuel injections with a final injection close to ignition.
[0008] — However, the ignition timing under-advance remains limited by instabilities of combustion becomes unacceptable beyond approximately 15 degrees of crankshaft rotation. Indeed, increasingly erratic combustion generates significant torque variations from one cycle to another, resulting in severe engine speed instabilities that lead to unacceptable increases in noise and vibration. Although the current process meets current anti-pollution standards, the future Euro7 standard is proving to be extremely stringent. Thus, to meet the emission thresholds of future standards, the current strategy of heating the catalyst is not sufficient and it is necessary to combine it with complex and costly technical solutions such as an electrically heated catalyst (EHC) potentially added to an exhaust air injection system allowing the heat produced upstream by the EHC to be diffused throughout the post-treatment system before the actual start of the engine. Description of the invention The invention proposes to remedy the defects of known methods of priming a catalyst of a thermal engine in a hybrid motorization device, that is to say in the case where the thermal engine is associated with at least one electric machine. It proposes for this purpose a method for heating a three-way catalyst mounted at the exhaust of a spark-ignition internal combustion engine capable of driving at least one drive wheel of a motor vehicle, said engine being associated with a first reversible electric machine capable of operating in generator mode or in motor mode in which said first electric machine contributes to the vehicle's drive torque, said engine being further associated with a second electric machine capable of operating at least in generator mode, said method comprising: - a vehicle start-up stage in which vehicle drive torque is required; and - a stage of heating the catalyst to a predetermined minimum catalyst efficiency start-up temperature, in which the vehicle drive torque is entirely produced by the first electric machine operating in motor mode. Said heating stage includes an engine afterburner adjustment stage comprising a fuel injection stage into at least one engine cylinder around the top dead center of combustion, followed by an ignition stage of said injected fuel around the bottom dead center of exhaust. Post-combustion tuning aims to improve catalyst heating and involves adjusting the operation of at least one cylinder of the internal combustion engine to transfer all the chemical energy contained in the fuel to the catalyst. by eliminating the exchange of mechanical energy with the cylinder piston during the expansion phase and with respect to friction losses. Advantageously, the fuel injection stage includes a sequence of injections carried out around the top dead center of combustion. According to an advantageous feature, the ignition of said fuel injected around the bottom dead center of the exhaust is achieved with several sparks. Preferably, said engine afterburner adjustment step is applied to only a portion of the engine cylinders or is applied to a subunit fraction of the engine cycles. For example, the afterburner adjustment step is applied to all engine cylinders but only for one out of every two engine cycles. For example, the afterburner adjustment step is applied to a single cylinder. According to another aspect, the invention also relates to a spark-ignition internal combustion engine for a motor vehicle implementing a process as described above. Brief description of the drawings Other objects, features and advantages of the invention will become apparent from the following description, given solely by way of non-limiting example, and made with reference to the accompanying drawings in which: [Fig.1] is a schematic plan view of a hybrid motorization device according to the prior art: [Fig.2] is a schematic view of a heat engine according to the prior art; [Fig.3] illustrates the injection and ignition signals in the compression and expansion phases of an engine cycle according to the prior art; [Fig.4] illustrates the openings of the exhaust and intake valves respectively in the exhaust and intake phases of an engine cycle according to the prior art; [Fig.5] is a flowchart illustrating the different stages of a catalyst heating process according to the invention; [Fig.6] illustrates the injection and ignition signals in the compression and expansion phases of an engine cycle according to the invention; [Fig.7] illustrates the openings of the exhaust and intake valves respectively in the exhaust and intake phases of an engine cycle according to the invention; [Fig. 8] illustrates an engine afterburner setting according to one implementation method; and [Fig.9] illustrates an engine afterburner setting according to another mode of re- lisation. Detailed description of at least one embodiment Figure [Fig.1] schematically illustrates a known hybrid motorization device 1, notably mounted on a motor vehicle. The hybrid drive system 1 includes a spark-ignition internal combustion engine 2, a first electric machine 3 and a second electric machine 4. The internal combustion engine 2 produces engine torque, which results from the combustion of a mixture of fresh air and fuel in quantities defined by an internal combustion engine 2 computer not shown. The electrical machines 3 and 4 are capable of operating in "generator" mode under the supervision of a control unit (not shown). Furthermore, at least the first electrical machine 3 is capable of operating in "motor" mode. In other words, the first electrical machine is reversible. However, it is not essential for the implementation of the method according to the invention that the second electrical machine 4 be capable of operating in "motor" mode. In "generator" mode, an electrical machine 3, 4 is an alternator that provides an electric current intended to be stored in a battery of accumulators not shown. In "motor" mode, the first electric machine 3 is instead powered by current previously stored in the battery and provides a motor torque which can be transmitted to the wheels of the vehicle, in addition to or in replacement of the torque provided by the internal combustion engine 2. The drive unit 1 is associated with a transmission system 5 which transmits the torque supplied by the drive unit 1 to the wheels 6. The drive unit is adjusted so that the torque it supplies reaches a setpoint torque value, or required torque, corresponding to the "driver's desire to accelerate", materialized for example by a value of the depressment of a vehicle's accelerator pedal or the pressure exerted on said pedal. The transmission system 5 includes in particular a gearbox 7, a differential 8 and a drive shaft 9. The gearbox is connected to the internal combustion engine 2 and the electric machines 3, 4 on the one hand, and on the other hand to the wheels 6 via the differential 8 and the drive shaft 9. Figure 2 illustrates the operation of the internal combustion engine 2 from Figure 1. The internal combustion engine 2 shown here is a supercharged three-cylinder in-line engine. Such a heat engine 2 draws in air in the direction of arrow E through an intake duct 10, and expels its exhaust gases through an exhaust duct 11 in order to direct them to a pollution control device 12. The pollution control device 12 includes a three-way catalyst 13 and a particulate filter 14. At the outlet of the pollution control device 12, the exhaust gases are released into the outside atmosphere in the direction of arrow S. The engine also consumes fuel, for example gasoline, a mixture of gasoline and ethanol, or even pure ethanol, which is supplied to the engine via an injection system (not shown), for example a direct injection system which has a common fuel rail for the cylinders and at least one fuel injector per cylinder capable of injecting fuel directly into each of the cylinders. In the air intake duct 10, by way of non-limiting information, one can find an air filter 15 which allows the removal of dust contained in the air and an intake flap 16, or throttle body 16 which allows the flow admitted into the engine 2 to be regulated by more or less obstructing the intake duct 10. As it is a supercharged engine 2, the internal combustion engine 2 also includes a turbocharger 17 whose compressor 18 is interposed in the intake duct 10 between the air filter 15 and the throttle body 16. In addition, it is possible that a heat exchanger 19 is disposed in the intake duct 10, between the compressor 18 and the throttle body 16 in order to cool the air compressed by the compressor 18. The compressor 18 is driven by the turbine 20 of the turbocharger 17, which is interposed in the exhaust duct 11 between the engine 2 and the emissions control device 12. Furthermore, and without prejudice to the generality of the invention, the internal combustion engine 2 may include one or more exhaust gas recirculation circuits at the intake (not shown), more particularly a high-pressure EGR circuit and / or a low-pressure EGR circuit, EGR being the English acronym for "Exhaust Gas Recycling." The internal combustion engine 2 may also be equipped with variable valve timing (VVT). The catalyst can be equipped with means for determining a parameter representative of the temperature T of the exhaust gases passing through it, for example the temperature T of the catalyst itself, measured by a temperature sensor 21. Furthermore, the motor 2 includes an electronic control unit 22 configured to control the various elements of the motor 2 from data collected by sensors at different locations in the motor. The electronic control unit 22 comprises a calculation module 23, a measurement module 24 and a control module 25. The measuring module 24, for example, is suitable for receiving temperature measurements outputs from temperature sensor 21. The control module 25 is, for example, capable of controlling the fuel injection system and the opening and closing of the throttle body 16. Typically, hybrid powertrains as described above require a catalyst warm-up phase during a cold start of the internal combustion engine. This catalyst warm-up phase lasts approximately 30 seconds and allows the catalyst temperature to reach a predetermined minimum treatment efficiency. During this phase, the torque supplied by the internal combustion engine 2 is not transmitted to the wheels, and the vehicle's forward motion is ensured solely by the first electric motor 3. The torque supplied by the internal combustion engine 2 is transmitted to the second electric motor 4 in order to recharge the battery. The typically used operating point corresponds to an engine speed of 1300 rpm and a torque of 50 Nm, which are relatively low values. The engine setting used in the catalyst heating phase is illustrated in Figures 3 and 4. The setting used in the catalyst heating phase differs from the nominal setting used outside the catalyst heating phase. The PMB and TMH zones correspond respectively to the bottom dead center and top dead center of a heat engine 2. It should be noted that engine 2 operates according to a four-stroke cycle. The engine tuning involves using a retarded ignition advance and a series of injections 26, including a final injection close to the ignition point 27. In the illustrated example, three injections 26 are performed, and ignition occurs at approximately 15 degrees of crankshaft rotation with a single spark. By comparison, ignition according to the nominal setting occurs a few moments before top dead center (TDC) to account for the time required for combustion to develop. Fig. 3 illustrates the injection and ignition signals in the compression and expansion phases, and Fig. 4 illustrates the openings of the exhaust valves 28 and the intake valves 29 respectively in the exhaust and intake phases. We will now describe, with reference to figures 5 to 7, a method for heating a catalyst according to the invention. Figure 5 illustrates the different stages of a process 30 for heating the catalyst 13 according to an embodiment of the invention, using a motorization device 1 as described above, in which the temperature T of the catalyst 13 is brought to a starting temperature Ta at which it has a predefined minimum treatment efficiency. For example, the target efficiency may be on the order of 50%, and the corresponding ignition temperature can be close to 250°C. The process is in particular implemented by means of a motorization device 1 comprising, as described above, a heat engine 2 associated with electrical machines 3, 4 which are capable of operating in "generator" mode and of which at least the first electrical machine 3 is also capable of operating in "motor" mode under the supervision of a control box. The process 30 begins with a step 31 of starting the vehicle. This can be materialized by the driver switching on the ignition and requiring a torque C to drive the vehicle, for example by pressing the accelerator pedal. The process continues iteratively with a step 32 of measuring the temperature T of the catalyst 13, followed by a step 33 of comparing said temperature T with a predefined initiation temperature Ta. The temperature T of the catalyst 13 can be determined by the electronic control unit 22 using a temperature sensor 21 fitted to the catalyst 13. As long as the temperature T of the catalyst is below the initiation temperature Ta, the process continues with a step 34 of heating the catalyst 13 in which the torque C required to drive the vehicle is entirely supplied by the first electric machine 3. If the catalyst temperature T is not lower than the ignition temperature Ta, the process proceeds to step 38 of engine adjustment to nominal operation. At this stage 34, the electronic control unit 22 controls the setting of at least one cylinder of the internal combustion engine so as to transfer all the chemical energy contained in the fuel to the catalyst 13 by eliminating the exchange of mechanical energy with the piston during the expansion phase. Step 34 includes a step 35 for adjusting the afterburner of engine 2, comprising a step 36 for injecting fuel into at least one cylinder of engine 2 around the combustion TDC, followed by a step 37 for igniting said injected fuel around the exhaust BDC. The combustion TDC is the point at which the engine transitions from a compression stroke to an expansion stroke and corresponds to the beginning of stroke three of a conventional four-stroke cycle. The exhaust BDC is the point at which the engine transitions from an expansion stroke to an exhaust stroke, where the piston of an engine operating on a conventional four-stroke cycle begins its upward movement immediately after the expansion stroke. The engine setting used in step 35 of the afterburner setting is illustrated in figures 6 and 7. Figure 6 illustrates the injection and ignition signals during the compression and expansion phases, and Figure 7 illustrates the openings of the exhaust and intake valves respectively during the exhaust and admission. This so-called "post-combustion" setting differs from the setting used in the prior art during the catalyst heating phase and illustrated in figures 3 and 4. The engine post-combustion setting consists of burning the air-fuel charge very late in the engine cycle with ignition occurring at the end of the expansion phase before the exhaust valves open, i.e. around the exhaust BDC. The pressure and temperature conditions of an ignition carried out around the exhaust BDC are rather low compared to an ignition carried out around the combustion TDC. Therefore, to guarantee sufficient combustion quality, it is necessary to ensure that the air-fuel mixture is as homogeneous as possible. To this end, fuel injection step 36 comprises a sequence of 40 injections performed around the combustion TDC ([Fig. 6]). Indeed, it is at the combustion TDC that aerodynamic speeds and intensities are highest, allowing for ideal air-fuel homogenization. It is also necessary to provide the highest possible ignition energy. To this end, the electronic control unit 22 achieves in step 37 the ignition of the air-fuel mixture with several sparks 41 in the form of a spark train to increase the ignition energy and ensure the initiation of combustion ( [Fig.6]). In the case of a heat engine 2 with variable valve timing, and similar to the conventional setting during the catalyst warm-up phase, there is no overlap between the exhaust valves 42 and the intake valves 43 in the post-combustion setting to prevent the presence of burnt gases in the combustion chambers after combustion, thus stabilizes combustion as much as possible ([Fig. 7]). Furthermore, during post-combustion, any overlap between the exhaust and intake valves must be eliminated to avoid the risk of flaming gases flowing back into the intake manifold, which can lead to intake noise problems and even reliability issues. With the afterburner setting, engine 2 no longer provides torque and cannot maintain its target RPM if the afterburner setting is applied to all cylinders and all cycles of engine 2. It is therefore preferable to activate the afterburner setting only on certain cylinders or only in certain cycles (i.e., a sub-unit fraction) of engine 2, the other cylinders or engine cycles operating either with a prior art catalyst heating setting as described above, or with a nominal setting used conventionally outside the catalyst heating phase. talyzer. In an embodiment illustrated in [Fig. 8], the engine 2 has three cylinders, and afterburning is activated only on the second cylinder. The first and third cylinders provide constant torque, while the second cylinder provides no torque. For simplicity, we have neglected friction and pumping losses in the second cylinder. These losses are actually compensated by torque supplied by the second electric machine 4. In another embodiment illustrated in [Fig.9], the engine 2 has three cylinders and afterburning is activated on all three cylinders, at a rate of one engine cycle out of two. Other combinations are possible while remaining within the scope of the invention.
Claims
Claims
1. A method of heating a three-way catalyst (13) mounted on the exhaust of an internal combustion engine (2) with ignition controlled capable of driving at least one drive wheel (6) of a vehicle automobile, said engine (2) being associated with a first machine electric (3) reversible capable of operating in generator mode or according to a motor mode in which said electric machine (3) participates in the torque (C) of the vehicle drive, said engine (2) being further associated with a second electric machine (4) capable of operate at least in a generator mode, said method including: a vehicle starting stage in which a torque vehicle drive (C) is required; and a step of heating the catalyst (13) to a tem- minimum catalyst efficiency ignition temperature (Ta) predetermined, in which the drive torque (C) of the vehicle is entirely produced by the first machine electric (3) operating in motor mode; characterized in that said heating step comprises a step of engine afterburner adjustment (2) comprising a step fuel injection into at least one cylinder of the engine (2) around from the top dead center of combustion, followed by an ignition step of said fuel injected at about exhaust bottom dead center.
2. The method of claim 1 wherein the injecting step includes a sequence of injections carried out around top dead center of combustion.
3. A method according to claim | or 2, wherein the ignition of said fuel injected around the exhaust bottom dead center is made with several sparks.
4. A method according to any preceding claim, in wherein said engine post-combustion adjustment step (2) is applied to only part of the engine cylinders (2) or is applied to a subunit fraction of the cycles of the engine (2).
5. The method of claim 4, wherein the post-adjusting step combustion is applied to all cylinders of the engine (2) but only for every other engine cycle.
6. The method of claim 4, wherein the post-adjusting step combustion is applied to a single cylinder.
7. Internal combustion engine (2) with spark ignition for a vehicle au- automobile implementing a method according to any one of the re- claims | at 6.