Method for heating catalytic converters in hybrid-powered vehicles - Patent Application 20070122997

Abstract

The method for heating a three-way catalytic converter (13) mounted on an exhaust of a heat engine (2) associated with a first electric machine capable of operating in a generator mode or a motor mode in which the first electric machine contributes to a driving torque of the vehicle, and associated with a second electric machine capable of operating at least in a generator mode, comprises the steps of starting a vehicle requiring driving torque for the vehicle, and heating the catalytic converter (13) to an ignition temperature, wherein the driving torque for the vehicle is generated entirely by the first electric machine. The heating step comprises a step of adjusting aftercombustion of the engine (2), comprising the step of injecting fuel into at least one cylinder of the engine (2) near top dead center of combustion, followed by the step of igniting the fuel near bottom dead center of exhaust.

Description

[Technical Field]

[0001] The present invention relates to a method for heating a three-way catalytic converter installed in the exhaust line of a spark-ignition internal combustion engine, and also to a hybrid motorization system in which the method can be implemented. [Background technology]

[0002] Modern internal combustion engines, especially those used in motor vehicles subject to increasingly stringent pollution control standards, are equipped with various systems for after-treating the polluting molecules emitted in the combustion gases of these engines in order to limit the emission of harmful species into the outside air.

[0003] Three-way catalytic converters are known, in particular from spark-ignition engines that run on petrol, and are capable of treating unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx) emitted in the combustion gases of the engine.

[0004] It is well known that the efficiency of an aftertreatment system depends on its temperature. Efficiency refers to the percentage of a given type of pollutant molecule that enters the system that the system can treat. When the catalytic converter temperature reaches, for example, about 250°C to 300°C, the efficiency starts to reach acceptable values, for example, 50% to 90%. Until the temperature reaches values ​​of the order of 150°C, the efficiency of the catalytic converter is zero.

[0005] Therefore, steps must be taken to ensure that the vehicle does not emit excessive pollutants into the outside air when the heat engine starts.

[0006] We also know that in some so-called "hybrid" motorized vehicles, the heat engine is combined with a reversible electric machine that can operate in either "motor" mode or "generator" mode.

[0007] These "hybrid" powertrains typically delay combustion within the engine's cylinders to heat the catalytic converter, thereby reducing combustion efficiency and increasing engine heat loss. For example, it is common to perform a sequence of fuel injections with spark retard and final injection near spark.

[0008] However, below-advance spark remains limited by combustion instability, which becomes unacceptable above about 15 degrees of crankshaft angle. Increased combustion instability results in large torque differences from one cycle to the next, significant speed instability, and an unacceptable increase in noise and vibration.

[0009] While current methods are able to meet current pollution control standards, the future Euro 7 standards will be extremely strict.

[0010] Therefore, to comply with the emission thresholds of future standards, current strategies for heating catalytic converters are insufficient and need to be combined with technical solutions such as complex and expensive electrically heated catalytic converters (EHCs), potentially combined with exhaust injection systems to dissipate the heat generated upstream by the EHC throughout the aftertreatment system before the engine is actually started. Summary of the Invention

[0011] The present invention proposes to overcome the drawbacks of known methods of firing a heat engine catalytic converter in a hybrid motorization system, i.e. when the heat engine is associated with at least one electric machine.

[0012] To this end, the present invention proposes a method for heating a three-way catalytic converter mounted in the exhaust of a spark-ignition internal combustion engine capable of driving at least one drive wheel of a motor vehicle, the engine being associated with a first reversible electric machine capable of operating in generator mode or motor mode, in which the first electric machine contributes to vehicle drive torque, and the engine being associated with a second electric machine capable of operating at least in generator mode, the method comprising the steps of starting the vehicle, where vehicle drive torque is required, and heating the catalytic converter to a predetermined minimum catalytic converter efficiency light-off temperature, the vehicle drive torque being generated overall by the first electric machine operating in motor mode.

[0013] The heating step includes a post-combustion conditioning step of the engine, which includes the steps of injecting fuel into at least one cylinder of the engine near top dead center of combustion, followed by igniting the injected fuel near bottom dead center of exhaust.

[0014] Post-combustion adjustment corresponds to adjusting the operation of at least one cylinder of the heat engine in order to improve the heating of the catalytic converter and to transfer all the chemical energy contained in the fuel to the catalytic converter, eliminating the exchange of mechanical energy with the piston of the cylinder within the limits of friction losses during the expansion phase.

[0015] Advantageously, the fuel injection step comprises a series of injections carried out near top dead centre of combustion.

[0016] According to an advantageous feature, the ignition of the fuel injected near the exhaust bottom dead center is carried out by multiple sparks.

[0017] Preferably, the engine post-combustion conditioning step is applied to only a portion of the engine's cylinders, or over less than one unit of an engine cycle.

[0018] For example, a post-combustion tuning step may be applied to all cylinders of an engine, but only for one engine cycle out of two.

[0019] For example, the post-combustion tuning step is applied to a single cylinder.

[0020] According to another aspect, the invention also relates to a spark-ignition internal combustion engine for a motor vehicle using the method described above. [Brief explanation of the drawings]

[0021] [Figure 1] 1 is a schematic plan view of a hybrid powertrain in the prior art; [Figure 2] 1 is a schematic diagram of a heat engine in the prior art; [Figure 3] 1 shows injection and ignition signals during the compression and expansion phases of a prior art engine cycle. [Figure 4] 2 shows the exhaust and intake valve openings during the exhaust and intake phases, respectively, of an engine cycle according to the prior art; [Figure 5] 2 is a flow chart illustrating the various steps of a catalytic converter heating method according to the present invention. [Figure 6] 3 shows injection and ignition signals during the compression and expansion phases of an engine cycle according to the present invention; [Figure 7] 3 shows the exhaust and intake valve openings during the exhaust and intake phases, respectively, of an engine cycle according to the present invention. [Figure 8] 1 illustrates engine post-combustion tuning in one embodiment. [Figure 9] 4 shows post-combustion tuning of the engine in a further embodiment; DETAILED DESCRIPTION OF THE INVENTION

[0022] Other objects, features and advantages of the present invention will become apparent from the following description, given purely by way of non-limiting example and made with reference to the accompanying drawings, in which:

[0023] A detailed description of at least one method of implementation FIG. 1 provides a schematic diagram of a hybrid motorization device 1 known per se, in particular mounted on a motor vehicle.

[0024] The hybrid power plant 1 comprises a spark ignition internal combustion heat engine 2, a first electric machine 3 and a second electric machine 4.

[0025] The heat engine 2 produces engine torque resulting from the combustion of a mixture of fresh air and fuel in amounts determined by the heat engine 2 computer (not shown).

[0026] The electric machines 3, 4 can be operated in "generator" mode under the supervision of a control box (not shown). Furthermore, at least the first electric machine 3 can be operated in "motor" mode. In other words, the first electric machine is reversible. On the other hand, it is not essential for the implementation of the method according to the present invention that the second electric machine 4 can be operated in "motor" mode.

[0027] In "generator" mode, the electric machines 3, 4 are alternators that provide current for storage in a storage battery, not shown.

[0028] In "motor" mode, the first electric machine 3 is powered by current previously stored in the storage battery and provides a drive 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.

[0029] The motorization device 1 is associated with a transmission system 5, which allows the torque provided by the motorization device 1 to be transmitted to the wheels 6. The motorization device is adjusted so that the torque it provides reaches a set torque value or a required torque corresponding to the "driver's intention to accelerate", e.g., represented by the value of the depression of the accelerator pedal of the vehicle or the pressure applied to said pedal.

[0030] The transmission system 5 comprises a gearbox 7, a differential 8 and a drive shaft 9. The gearbox is connected to the heat engine 2 and the electric machines 3, 4 on the one hand and to the wheels 6 via the differential 8 and the drive shaft 9 on the other hand.

[0031] Figure 2 shows the operation of the heat engine 2 shown in Figure 1. The heat engine 2 shown here is a supercharged in-line three-cylinder engine.

[0032] The heat engine 2 draws air in the direction of arrow E through an intake manifold 10 and discharges exhaust gases through an exhaust manifold 11 for directing the exhaust gases towards a pollution control device 12. The pollution control device 12 includes a three-way catalytic converter 13 and a particulate filter 14.

[0033] Upon exiting pollution control device 12, the exhaust gases are discharged in the direction of arrow S into the ambient atmosphere.

[0034] The engine also consumes fuel, for example petroleum, a petroleum-ethanol mixture 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.

[0035] The intake pipe 10 may have an air filter 15 that removes dust particles from the air, and an intake flap (throttle body) 16 or a throttle box (throttle body) 16 that adjusts the flow introduced into the engine 2 by slightly blocking the intake pipe 10.

[0036] In the case of a supercharged engine (engine) 2, the heat engine 2 also has a turbocharger 17, whose compressor 18 is interposed in the intake manifold 10 between the air filter 15 and the throttle body 16. Furthermore, a temperature exchanger 19 may be arranged in the intake manifold 10 between the compressor 18 and the throttle body 16 for cooling the air compressed by the compressor 18.

[0037] The compressor 18 is driven by a turbine 20 of a turbocharger 17, which is interposed in the exhaust pipe 11 between the engine 2 and the pollution control device 12. Furthermore, and without affecting the generality of the invention, the heat engine 2 may be equipped with one or more exhaust gas recirculation circuits (not shown), more particularly a high-pressure EGR circuit and / or a low-pressure EGR circuit, EGR being an abbreviation for "Exhaust Gas Recycling". The heat engine 2 may have variable valve timing (VVT).

[0038] The catalytic converter may be fitted 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 catalytic converter itself, measured by a temperature sensor 21 .

[0039] Furthermore, the motor (engine) 2 comprises an electronic control unit 22 configured to control various elements of the motor 2 based on data collected by sensors at different points of the engine.

[0040] The electronic control unit 22 comprises a calculation module 23 , a measurement module 24 and a control module 25 .

[0041] The measurement module 24 may receive temperature measurements from, for example, the temperature sensor 21 .

[0042] The control module 25 may, for example, control the fuel injection system and the opening and closing of the throttle body 16 .

[0043] Typically, the hybrid motorizations mentioned above require a catalytic converter heating phase during a cold start of the engine, which lasts approximately 30 seconds and allows the catalytic converter temperature to reach the specified minimum efficiency light-off temperature.

[0044] During this phase, the torque provided by the heat engine 2 is not transferred to the wheels and the vehicle is driven forward exclusively by the first electric machine 3. The torque provided by the heat engine 2 is transferred to the second electric machine 4 to recharge the battery. Conventionally used operating points correspond to a speed of 1300 rpm and a torque of 50 Nm, i.e. relatively low values.

[0045] The engine adjustments used during the catalytic converter heating phase are shown in Figures 3 and 4. The adjustments used during the catalytic converter heating phase are different from the nominal adjustments used outside the catalytic converter heating phase.

[0046] The BDC region and the TDC region correspond to the bottom dead center and the top dead center, respectively, of the thermal engine 2. The engine 2 operates on a four-stroke cycle.

[0047] Engine tuning consists of performing a series of injections 26 with spark retard and a final injection near spark 27. In the example shown, three injections 26 are performed, ignited by a single spark at approximately 15 degrees relative to the crankshaft. By comparison, the nominal tuned spark is slightly before TDC to allow for the delay required for combustion to progress.

[0048] FIG. 3 shows the injection and ignition signals in the compression and expansion phases, and FIG. 4 shows the openings of the exhaust valve 28 and the intake valve 29 in the exhaust and intake phases, respectively.

[0049] Now, with reference to Figures 5 to 7, a method for heating a catalytic converter according to the present invention will be described.

[0050] 5 illustrates various steps of a method 30 for heating a catalytic converter 13 according to one embodiment of the present invention using the powertrain 1 described above, where the temperature T of the catalytic converter 13 is set to a light-off temperature Ta for a specified minimum process efficiency. For example, the target efficiency may be on the order of 50%, with a corresponding light-off temperature near 250°C.

[0051] The method is particularly implemented by a motorization device 1 comprising, as previously described, a heat engine 2 associated with electric machines 3, 4, which can operate in "generator" mode, of which at least the first electric machine 3 can also operate in "motor" mode under the supervision of a control box.

[0052] The method 30 begins with starting the vehicle at step 31. This may take the form of the driver turning on the ignition and requesting torque C to drive the vehicle, for example by depressing the accelerator pedal.

[0053] The method continues by iterating step 32 of measuring the temperature T of the catalytic converter 13, followed by step 33 of comparing said temperature T with a predetermined ignition temperature Ta. The measured temperature T of the catalytic converter 13 can be determined by the electronic control unit 22 using a temperature sensor 21 attached to the catalytic converter 13.

[0054] As long as the temperature T of the catalytic converter is below the ignition temperature Ta, the method continues with a step 34 of heating the catalytic converter 13, during which the torque C required for driving the vehicle is provided entirely by the first electric machine 3.

[0055] If the catalytic converter temperature T is greater than or equal to the ignition temperature Ta, the method proceeds to step 38 of adjusting the motor for nominal operation.

[0056] In 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 catalytic converter 13 by eliminating the exchange of mechanical energy with the piston during the expansion phase.

[0057] Step 34 comprises a step 35 of modulating after-combustion of engine 2, comprising a step 36 of injecting fuel into at least one cylinder of engine 2 near combustion TDC, followed by a step 37 of igniting the injected fuel near exhaust BDC. Combustion TDC is the moment of transition from the compression phase to the expansion phase, which corresponds to the start of stroke 3 in a conventional four-stroke cycle. Exhaust BDC is the moment of transition from the expansion phase to the exhaust phase when the piston of an engine operating on a conventional four-stroke cycle starts to rise just after the expansion phase.

[0058] The engine adjustments used in post-combustion adjustment step 35 are shown in FIGS.

[0059] FIG. 6 shows the injection and ignition signals in the compression and expansion stages, and FIG. 7 shows the openings of the exhaust and intake valves in the exhaust and intake stages, respectively.

[0060] This so-called "afterburn" adjustment is different from the adjustment used in the prior art of the catalytic converter heating stage shown in FIGS.

[0061] Late combustion tuning of the engine consists of burning the air-fuel input very late in the engine cycle, with ignition occurring at the end of the expansion phase before the exhaust valve opens, i.e., near the exhaust BDC.

[0062] The pressure and temperature conditions for sparks performed near the exhaust BDC are lower than those for sparks performed near the combustion TDC.

[0063] To ensure a sufficiently high quality of combustion, it is therefore necessary to ensure that the air-fuel mixture is as homogeneous as possible.

[0064] To this end, the fuel injection step 36 comprises a series of injections 40 performed near the combustion TDC (FIG. 6), where aerodynamic speed and intensity are highest and ideal air-fuel homogenization can be achieved.

[0065] It is also necessary to provide the maximum possible ignition energy.

[0066] To this end, in step 37, the electronic control unit 22 ignites the air-fuel mixture by means of a plurality of sparks 41 in the form of a spark train that increases the ignition energy and initiates combustion (FIG. 6).

[0067] In the case of a heat engine 2 using variable valve timing and following the example of conventional regulation in the catalytic converter heating phase, in order to stabilize the combustion as much as possible, there is no overlap of the exhaust valve 42 and the intake valve 43 in the post-combustion regulation so that there is no burnt gas in the combustion chamber after combustion (Figure 7). Furthermore, during post-combustion, there is a risk that ignited gases will rise towards the intake side, causing intake noise problems and even reliability problems, so the overlap of the exhaust valve and the intake valve must be eliminated.

[0068] With post-combustion tuning, if post-combustion tuning is applied to all cylinders and all cycles of engine 2, engine 2 will not output torque and will not be able to meet its target speed setting.

[0069] Therefore, it is preferable to operate post-combustion tuning only in certain cylinders or in certain cycles (i.e., less than one unit) of engine 2, while other cylinders or cycles of the engine are operating at either the current catalytic converter heating tuning described above or the nominal tuning conventionally used outside the catalytic converter heating stage.

[0070] In the embodiment shown in Figure 8, the engine 2 has three cylinders and after-combustion is activated only for the second cylinder. The second cylinder provides no torque, while the first and third cylinders provide constant torque. For simplicity, friction and pumping losses in the second cylinder are ignored. These losses are in fact compensated for by the torque provided by the second electric machine 4.

[0071] In another embodiment shown in FIG. 9, the engine 2 has three cylinders and after-combustion is activated for all three cylinders at a rate of one in every two engine cycles.

[0072] Other combinations are possible and are within the scope of the present invention.

Claims

1. 1. A method of heating a three-way catalytic converter (13) mounted in the exhaust of a spark-ignition internal combustion engine (2) suitable for driving at least one drive wheel (6) of a motor vehicle, the 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 the electric machine (3) contributes to a drive torque (C) of the vehicle, and the engine (2) being further associated with a second electric machine (4) capable of operating in at least a generator mode, the method comprising: a vehicle starting step in which a vehicle driving torque (C) is required; heating the catalytic converter (13) to a predetermined minimum catalytic converter efficiency light-off temperature (Ta), wherein the drive torque (C) of the vehicle is generated entirely by the first reversible electric machine (3) operating in motor mode; Equipped with The heating step comprises the step of injecting fuel into at least one cylinder of the engine near top dead center of combustion, followed by the step of igniting the injected fuel near bottom dead center of exhaust.

2. The method of claim 1 , wherein the injecting step comprises a series of injections performed near top dead center of combustion.

3. 3. The method according to claim 1, wherein the ignition of the fuel injected near the exhaust bottom dead center is performed by multiple sparks.

4. 4. The method according to claim 1, wherein the step of post-combustion tuning of the engine (2) is applied to only a portion of the cylinders of the engine (2) or over less than one unit of a cycle of the engine (2).

5. 5. The method of claim 4, wherein the step of post-combustion tuning is applied to all cylinders of the engine (2) but only in one engine cycle out of two.

6. The method of claim 4 , wherein the step of post-combustion tuning is applied to a single cylinder.

7. A spark-ignition internal combustion engine (2) for a motor vehicle using a method according to any one of claims 1 to 6.

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