Method for heating a catalytic converter in a hybrid drive vehicle

Abstract

This method for heating a three-way catalytic converter (13) mounted at the exhaust of a combustion engine (2) associated with a first electric machine capable of operating in a generator mode or in a motor mode, in which modes said electric machine participates in the drive torque of the vehicle, and associated with a second electric machine capable of operating at least in a generator mode, comprises: - a step of starting the vehicle in which a drive torque of the vehicle is required; and - a step of heating the catalytic converter (13) to a light-off temperature, in which the drive torque of the vehicle is produced entirely by the first electric machine. Said heating step comprises a step of adjusting the post-combustion of the engine (2) comprising a step of injecting fuel into at least one cylinder of the engine (2) around the top dead centre of combustion, followed by an ignition step around the bottom dead centre of exhaust.

Description

[0001] DESCRIPTION

[0002] TITLE: Method for heating a catalyst in a hybrid vehicle

[0003] Technical field

[0004] 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 relates to a hybrid motorization device capable of implementing such a method.

[0005] Previous techniques

[0006] Modern combustion engines, particularly those of motor vehicles which are subject to increasingly stringent anti-pollution standards, are equipped with various systems for post-treatment of polluting molecules emitted in the combustion gases of said engines, in order to limit the release of harmful species into the external atmosphere.

[0007] In spark-ignition type engines, particularly those running on petrol, three-way catalysts are known which are capable of treating unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) emitted in the engine combustion gases.

[0008] It is known that the efficiency of a post-treatment system depends on its temperature. By efficiency we mean the proportion of pollutant molecules of a given type that enter the system, that the said system manages to treat. The efficiency begins to reach acceptable values, for example between 50% and 90%, when the temperature of the catalyst is for example between approximately 250°C and 300°C. The efficiency of a catalyst is zero until the temperature reaches a value of around 150°C.

[0009] When starting a thermal engine, it is therefore necessary to take measures to ensure that the vehicle does not release too many polluting emissions into the outside atmosphere. We also know that the thermal engines of certain motor vehicles with so-called "hybrid" engines are associated with reversible electric machines that can operate in "motor" mode or in "generator" mode.

[0010] In these "hybrid" engines, delayed combustion is traditionally carried out inside the engine cylinders to heat the catalyst, thereby degrading combustion efficiency and increasing the engine's thermal losses. For example, it is common to use delayed ignition advance and to carry out a series of fuel injections with a final injection close to ignition.

[0011] However, the ignition under-advance remains limited by combustion instabilities which become unacceptable beyond approximately 15 crankshaft degrees. Indeed, increasingly erratic combustions generate significant torque variations from one cycle to another and result in significant engine speed instabilities which generate unacceptable increases in noise and vibrations.

[0012] Although the current process allows us to meet current anti-pollution standards, the future Euro7 standard is proving extremely strict.

[0013] Thus, to comply with the emission thresholds of future standards, the current catalyst heating strategy is not sufficient and it is necessary to couple 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 distributed throughout the post-treatment system before the engine actually starts.

[0014] Statement of the invention

[0015] The invention proposes to remedy the defects of known methods for initiating a thermal engine catalyst in a hybrid motorization device, that is to say in the case where the thermal engine is associated with at least one electric machine.

[0016] To this end, it proposes a method for heating a three-way catalyst mounted on 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 a generator mode or in a motor mode in which said first electric machine contributes to the driving torque of the vehicle, said engine being further associated with a second electric machine capable of operating at least in a generator mode, said method comprising:

[0017] - a vehicle starting step in which a vehicle drive torque is required; and

[0018] - a step of heating the catalyst to a predetermined minimum catalyst efficiency ignition temperature, in which the vehicle drive torque is entirely produced by the first electric machine operating in engine mode.

[0019] Said heating step comprises a step of adjusting the post-combustion of the engine comprising a step of injecting fuel into at least one cylinder of the engine around the combustion top dead center, followed by a step of igniting said injected fuel around the exhaust bottom dead center.

[0020] The post-combustion adjustment aims to improve the heating of the catalyst and corresponds to the adjustment of the operation of at least one cylinder of the thermal engine to transfer all the chemical energy contained in the fuel to the catalyst, eliminating the exchange of mechanical energy with the piston of the cylinder during the expansion phase and with the friction losses close.

[0021] Advantageously, the fuel injection step comprises a sequence of injections carried out around the top dead center of combustion.

[0022] According to an advantageous characteristic, the ignition of said injected fuel around the exhaust bottom dead center is carried out with several sparks. Preferably, said engine post-combustion adjustment step is applied to only a part of the engine cylinders or is applied to a sub-unit fraction of the engine cycles.

[0023] For example, the afterburner adjustment step is applied to all engine cylinders but only for every other engine cycle.

[0024] For example, the afterburner adjustment step is applied to a single cylinder.

[0025] According to another aspect, the invention also relates to a motor vehicle spark-ignition internal combustion engine implementing a method as described above.

[0026] Brief description of the drawings

[0027] 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:

[0028] [Fig 1] is a schematic plan view of a hybrid motorization device according to the prior art;

[0029] [Fig 2] is a schematic view of a heat engine according to the prior art;

[0030] [Fig 3] illustrates the injection and ignition signals in the compression and expansion phases of an engine cycle according to the prior art;

[0031] [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;

[0032] [Fig 5] is a flowchart illustrating the different stages of a method of heating a catalyst according to the invention;

[0033] [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;

[0034] [Fig 8] illustrates an engine afterburner setting according to one embodiment; and

[0035] [Fig 9] illustrates an engine afterburner adjustment according to another embodiment.

[0036] Detailed description of at least one embodiment

[0037] Figure 1 schematically illustrates a hybrid motorization device 1 known in itself, in particular mounted on a motor vehicle.

[0038] The hybrid motorization device 1 comprises a thermal engine 2 with internal combustion and spark ignition, a first electric machine 3 and a second electric machine 4.

[0039] The heat engine 2 produces an engine torque, which results from the combustion of a mixture of fresh air and fuel in quantities defined by a computer of the heat engine 2 not shown.

[0040] The electrical machines 3, 4 are capable of operating in “generator” mode under the supervision of a control box not shown. In addition, 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.

[0041] In “generator” mode, an electrical machine 3, 4 is an alternator which supplies an electric current intended to be stored in a battery of accumulators not shown.

[0042] In “motor” mode, the first electric machine 3 is on the contrary powered by current previously stored in the accumulator battery and provides engine torque which can be transmitted to the wheels of the vehicle, in addition to or replacing the torque provided by the thermal engine 2.

[0043] The motorization device 1 is associated with a transmission system 5 making it possible to transmit to the wheels 6 the torque supplied by the motorization device 1. The motorization device is adjusted in such a way that the torque which it supplies reaches a set torque value, or required torque, corresponding to the “driver's desire to accelerate”, materialized for example by a value of the depression of an accelerator pedal of the vehicle or the pressure exerted on said pedal.

[0044] The transmission system 5 comprises in particular a gearbox 7, a differential axle 8 and a transmission shaft 9. The gearbox is connected to the heat engine 2 and to the electric machines 3, 4 on the one hand, and on the other hand to the wheels 6 via the differential 8 and the transmission shaft 9.

[0045] Figure 2 illustrates the operation of the heat engine 2 of Figure 1. The heat engine 2 illustrated here is a supercharged in-line three-cylinder engine.

[0046] Such a heat engine 2 sucks in air in the direction of arrow E via an intake duct 10, and discharges its exhaust gases via an exhaust duct 11 in order to direct them towards a pollution control device 12. The pollution control device 12 comprises a three-way catalyst 13 and a particle filter 14.

[0047] At the outlet of the pollution control device 12, the exhaust gases are discharged into the outside atmosphere in the direction of the arrow S.

[0048] The engine also consumes fuel, for example gasoline, a mixture of gasoline and ethanol, or even pure ethanol, which is supplied to the engine by an injection system (not shown), for example a direct injection system which comprises 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 10, in a non-limiting manner, there may be found an air filter 15 which makes it possible to eliminate the dust contained in the air and an intake flap 16, or throttle body 16 which makes it possible to regulate the flow admitted into the engine 2 by more or less obstructing the intake duct 10.

[0049] In the case of a supercharged engine 2, the thermal engine 2 also comprises 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 for a temperature exchanger 19 to be arranged in the intake duct 10, between the compressor 18 and the throttle body 16 so as to cool the air compressed by the compressor 18.

[0050] The compressor 18 is driven by the turbine 20 of the turbocharger 17, which is interposed in the exhaust pipe 11 between the engine 2 and the pollution control device 12. In addition, and without detracting from the generality of the invention, 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 system with the acronym VVT for “Variable Valve Timing” in English.

[0051] The catalyst may 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.

[0052] Furthermore, the engine 2 comprises an electronic control unit 22 configured to control the various elements of the engine 2 from data collected by sensors at different locations of the engine.

[0053] The electronic control unit 22 comprises a calculation module 23, a measurement module 24 and a control module 25. The measurement module 24 is for example capable of receiving the temperature measurements from the temperature sensor 21.

[0054] The control module 25 is for example capable of controlling the fuel injection system and the opening and closing of the throttle body 16.

[0055] Typically, hybrid engines as described above require a catalyst heating phase when the thermal engine is started from cold. This catalyst heating phase lasts approximately 30 seconds and allows the catalyst temperature to be brought to a starting temperature at which it has a predefined minimum treatment efficiency.

[0056] During this phase, the torque supplied by the thermal engine 2 is not transmitted to the wheels and the vehicle's forward motion is ensured solely by the first electric machine 3. The torque supplied by the thermal engine 2 is transmitted to the second electric machine 4 in order to recharge the battery. The operating point conventionally used corresponds to a speed of 1300 rpm and a torque of 50 Nm, i.e. relatively low values.

[0057] The engine setting used in the catalyst warm-up phase is shown in Figures 3 and 4. The setting used in the catalyst warm-up phase differs from the nominal setting used outside the catalyst warm-up phase.

[0058] The PMB and TDC zones correspond respectively to the bottom dead center and the top dead center of a thermal engine 2. It should be noted that engine 2 operates according to a four-stroke cycle.

[0059] The engine adjustment consists of using a delayed ignition advance and carrying out a series of injections 26 including a final injection close to ignition 27. In the example illustrated, three injections 26 are carried out and ignition is carried out at approximately 15 crankshaft degrees with a single spark. For comparison, ignition according to the nominal adjustment occurs a few moments before TDC, in order to take into account the time required for combustion to develop. Figure 3 illustrates the injection and ignition signals in the compression and expansion phases, and Figure 4 illustrates the openings of the exhaust valves 28 and the intake valves 29 respectively in the exhaust and intake phases.

[0060] A method of heating a catalyst according to the invention will now be described with reference to Figures 5 to 7.

[0061] Figure 5 illustrates the different steps of a method 30 for heating the catalyst 13 according to an embodiment of the invention, using a motorization device 1 as described previously, in which the temperature T of the catalyst 13 is brought to an initiation temperature Ta at which it has a predefined minimum treatment efficiency. For example, the targeted efficiency may be of the order of 50%, and the corresponding initiation temperature may be close to 250°C.

[0062] The method is in particular implemented by means of a motorization device 1 comprising, as described previously, 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 further capable of operating in “motor” mode under the supervision of a control box.

[0063] The method 30 begins with a step 3 1 of starting the vehicle. This can be materialized by the fact that the driver switches on the ignition and requires a torque C to drive the vehicle, for example by pressing the accelerator pedal.

[0064] The method continues, iteratively, with a step 32 of measuring the temperature T of the catalyst 13, then with a step 33 of comparing said temperature T with a predefined ignition temperature Ta. The measurement of the temperature T of the catalyst 13 can be determined by the electronic control unit 22 using a temperature sensor 21 which equips the catalyst 13.

[0065] As long as the temperature T of the catalyst is lower than the ignition temperature Ta, the method continues with a step 34 of heating the catalyst 13 in which the torque C necessary for driving the vehicle is entirely provided by the first electric machine 3.

[0066] If the catalyst temperature T is not lower than the ignition temperature Ta, the method proceeds to step 38 of adjusting the engine to nominal operation.

[0067] At this step 34, the electronic control unit 22 controls the adjustment of at least one cylinder of the heat 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.

[0068] Step 34 comprises a step 35 of adjusting the post-combustion of the engine 2 comprising a step 36 of injecting fuel into at least one cylinder of the engine 2 around the combustion TDC, followed by a step 37 of igniting said injected fuel around the exhaust TDC. The combustion TDC is the moment of transition from a compression phase to an expansion phase and corresponds to the start of time three of a conventional four-stroke cycle. The exhaust TDC is the moment of transition from an expansion phase to an exhaust phase where the piston of an engine operating according to a conventional four-stroke cycle begins to rise just after the expansion phase.

[0069] The engine setting used in afterburner setting step 35 is illustrated in Figures 6 and 7.

[0070] Figure 6 illustrates the injection and ignition signals in the compression and expansion phases, and Figure 7 illustrates the openings of the exhaust valves and the intake valves respectively in the exhaust and intake phases.

[0071] This so-called "post-combustion" setting differs from the setting used in the prior art in the catalyst heating phase and illustrated in Figures 3 and 4.

[0072] Engine post-combustion tuning involves 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 exhaust BDC. The pressure and temperature conditions for ignition occurring around exhaust BDC are rather low compared to ignition occurring around combustion TDC.

[0073] It is therefore necessary to ensure sufficient combustion quality to ensure that the air-fuel mixture is as homogeneous as possible.

[0074] For this purpose, the fuel injection step 36 comprises a sequence of injections 40 carried out around the combustion TDC (figure 6). Indeed, it is at the combustion TDC that the aerodynamic speeds and intensities are the highest, making it possible to obtain ideal air-fuel homogenization.

[0075] It is also necessary to provide the highest possible ignition energy.

[0076] To this end, the electronic control unit 22 carries out in step 37 the ignition of the air-fuel mixture with several sparks 41 in the form of a spark train making it possible to increase the ignition energy and ensure the initiation of combustion (figure 6).

[0077] In the case of a thermal engine 2 having a variable distribution and like the classic adjustment in the heating phase of the catalyst, there is no crossing of the exhaust valves 42 and the intake valves 43 in the post-combustion adjustment to avoid the presence of burnt gases in the combustion chambers after combustion, in order to stabilize the combustion as much as possible (figure 7). In addition, in post-combustion any crossing of the exhaust valves and the intake valves must be eliminated at the risk of seeing ignited gases rise towards the intake and therefore of suffering problems of intake noise, or even reliability problems.

[0078] With the afterburner setting, engine 2 no longer provides torque and cannot meet its target rpm setting if the afterburner setting is applied to all cylinders and all cycles of engine 2.

[0079] It is therefore preferable to activate the afterburner setting only on certain cylinders or only in certain cycles (i.e. a subunit fraction) of the engine 2, the other cylinders or cycles of the engine operating either with a catalyst heating setting of the state of the art as described above, or with a nominal setting conventionally used outside the catalyst heating phase. In an embodiment illustrated in FIG. 8, the engine 2 has three cylinders and the afterburner is activated only on the second cylinder. The first and third cylinders provide a constant torque, while the second cylinder does not provide any torque. To simplify the presentation, we have neglected the friction and pumping losses of the second cylinder. These losses are in reality compensated by a torque provided by the second electric machine 4.

[0080] In another embodiment illustrated in Figure 9, the engine 2 is three-cylinder and the afterburner is activated on all three cylinders, at a rate of one engine cycle out of two.

[0081] Other combinations are possible while remaining within the scope of the invention.

Claims

CLAIMS 1. Method for heating a three-way catalyst (13) mounted at the exhaust of a spark-ignition internal combustion engine (2) capable of driving at least one drive wheel (6) of a motor vehicle, said engine (2) being associated with a first reversible electric machine (3) capable of operating in a generator mode or in a motor mode in which said electric machine (3) contributes to the driving torque (C) of the vehicle, said engine (2) being further associated with a second electric machine (4) capable of operating at least in a generator mode, said method comprising: - a vehicle starting step in which a vehicle drive torque (C) is required; and - a step of heating the catalyst (13) up to a predetermined minimum catalyst efficiency ignition temperature (Ta), in which the driving torque (C) of the vehicle is entirely produced by the first electric machine (3) operating in engine mode; characterized in that said heating step comprises a step of adjusting the post-combustion of the engine (2) comprising a step of injecting fuel into at least one cylinder of the engine (2) around the top dead center of combustion, followed by a step of igniting said injected fuel around the bottom dead center of exhaust.

2. Method according to claim 1 in which the injection step comprises a sequence of injections carried out around the top dead center of combustion.

3. Method according to claim 1 or 2, wherein the ignition of said injected fuel around the exhaust bottom dead center is carried out with several sparks.

4. Method according to any one of the preceding claims, in which said step of adjusting the afterburning of the engine (2) is applied to only a part of the cylinders of the engine. (2) or is applied to a subunit fraction of the engine cycles (2).

5. Method according to claim 4, in which the post-combustion adjustment step is applied to all the cylinders of the engine (2) but only for one engine cycle out of two.

6. The method of claim 4, wherein the afterburner adjustment step is applied to a single cylinder.

7. Internal combustion engine (2) with spark ignition for a motor vehicle implementing a method according to any one of claims 1 to 6.

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