WO2024079298A1

WO2024079298A1 - Method for heating a catalytic converter in a hybrid drive vehicle

Info

Publication number: WO2024079298A1
Application number: PCT/EP2023/078435
Authority: WO
Inventors: Bertrand Fasolo
Original assignee: New H Powertrain Holding, S.L.U
Priority date: 2022-10-13
Filing date: 2023-10-12
Publication date: 2024-04-18
Also published as: FR3140910A1

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

DESCRIPTION

TITLE: Process for heating a catalyst in a hybrid motorized vehicle

Technical area

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 process.

Previous techniques

Modern combustion engines, more particularly those of motor vehicles which are subject to increasingly strict 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 releases of harmful species into the outside atmosphere.

On spark ignition type engines operating in particular on gasoline, three-way catalysts are known in particular which are capable of treating unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). emitted in the engine combustion gases.

It is known that the efficiency of a post-treatment system depends on its temperature. By efficiency, we mean the proportion of polluting molecules of a given type which enter the system, which 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 effectiveness of a catalyst is zero until the temperature has reached a value of around 150°C.

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 heat engines of certain motor vehicles with so-called “hybrid” engines are associated with reversible electrical machines that can operate in “engine” mode or “generator” mode.

In these “hybrid” engines, conventionally delayed combustion is carried out inside the engine cylinders to heat the catalyst, so as to degrade the combustion efficiency and increase the thermal losses of the engine. For example, it is common to use a delayed ignition advance and perform a series of fuel injections with a final injection close to ignition.

However, the ignition underadvance remains limited by combustion instabilities which become unacceptable beyond approximately 15 crankshaft degrees. Indeed, increasingly erratic combustion generates significant differences in torque from one cycle to another and results in strong regime instabilities which generate unacceptable increases in noise and vibrations.

Although the current process makes it possible to meet current anti-pollution standards, the future Euro7 standard is extremely severe.

Thus, to meet the emission thresholds of future standards, the current catalyst heating strategy is not sufficient and it is necessary to couple it with complex and expensive 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 starting of the engine.

Presentation of the invention

The invention proposes to remedy the defects of known methods of priming a heat 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.

For this purpose, it proposes a method of heating a three-way catalyst mounted at the exhaust of a spark-ignition internal combustion engine capable of driving at least one driving 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 participates in the driving torque of the vehicle, said motor being further associated with a second electric machine capable of operating at least in a generator mode, said process comprising:

- a vehicle starting step in which a vehicle drive torque is required; And

- a step of heating the catalyst up to a predetermined minimum efficiency priming temperature of the catalyst, in which the driving torque of the vehicle is entirely produced by the first electric machine operating in motor mode.

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

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 heat 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 frictional losses.

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

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

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

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 method as described above.

Brief description of the drawings

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:

[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 process for heating a catalyst 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 a cycle of the engine according to the invention;

[Fig 8] illustrates a post-combustion adjustment of the engine according to one embodiment; And

[Fig 9] illustrates an engine post-combustion adjustment according to another embodiment.

Detailed presentation of at least one embodiment

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

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.

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 calculator of the heat engine 2 not shown.

The electrical machines 3, 4 are able to operate in “generator” mode under the supervision of a control box not shown. In addition, at least the first electric machine 3 is able to operate in “motor” mode. In other words, the first electric machine is reversible. However, it is not essential to the implementation of the method according to the invention that the second electric machine 4 is able to operate in “motor” mode.

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

In “motor” mode, the first electric machine 3 is on the contrary powered by current previously stored in the accumulator 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 thermal engine 2.

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 it provides reaches a torque value setpoint, 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.

The transmission system 5 includes in particular a gearbox 7, a differential bridge 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 goes to the wheels 6 via the differential 8 and the transmission shaft 9.

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

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

At the outlet of the pollution control device 12, the exhaust gases are evacuated into the external atmosphere in the direction of the arrow S.

The engine also consumes fuel, for example gasoline, a mixture of gasoline and ethanol, or even pure ethanol, which is brought to the engine using an injection system (not shown), by example a direct injection system which comprises a supply 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 pipe 10, in a non-limiting manner, we can find an air filter 15 which makes it possible to eliminate 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 obstructing the intake pipe 10 to a greater or lesser extent.

Concerning a supercharged engine 2, the thermal engine 2 also comprises a turbocharger 17 whose compressor 18 is interposed in the intake pipe 10 between the air filter 15 and the throttle body 16. In addition, it It is possible that a temperature exchanger 19 is arranged in the inlet pipe 10, between the compressor 18 and the throttle body 16 so as 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 pipe 11 between the engine 2 and the pollution control device 12. In addition and without harming the generality of the invention, the engine thermal 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 thermal engine 2 can also have a variable distribution with the acronym VVT for “Variable Valve Timing” in English.

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 engine 2 comprises an electronic control unit 22 configured to control the different elements of the engine 2 from data collected by sensors at different locations of the engine.

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

Conventionally, hybrid engines as described above require a heating phase of the catalyst during a cold start of the thermal engine. This phase of heating the catalyst lasts approximately 30 seconds and makes it possible to bring the temperature of the catalyst up to a priming temperature at which it has a predefined minimum treatment efficiency.

During this phase, the torque provided by the heat engine 2 is not transmitted to the wheels and the advancement of the vehicle is ensured solely by the first electric machine 3. The torque provided by the heat engine 2 is transmitted to the second electric machine 4 to recharge the battery. The conventionally used operating point corresponds to a speed of 1300 rpm and a torque of 50 Nm, i.e. relatively low values.

The engine setting used in the catalyst heating phase is shown in Figures 3 and 4. The setting used in the catalyst heating phase differs from the nominal setting used outside of the catalyst heating phase.

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

Adjusting the engine 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 achieved at approximately 15 crankshaft degrees with a single spark. For comparison, ignition according to the nominal setting occurs a few moments before TDC, in order to take into account the time necessary 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 phases. and admission.

We will now describe with reference to Figures 5 to 7 a process 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 one embodiment of the invention, using a motorization device 1 as described previously, in which the temperature T of the catalyst 13 is brought up to at a starting 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.

The method is in particular implemented by means of a motorization device 1 comprising, as previously described, 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 electric machine 3 is also capable of operating in “motor” mode under the supervision of a control box.

The method 30 begins with a step 31 of starting the vehicle. It can materialize 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.

The process continues, iteratively, with a step 32 of measuring the temperature T of the catalyst 13, then by a step 33 of comparing said temperature T with a predefined initiation 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.

As long as the temperature T of the catalyst is lower than the initiation temperature Ta, the process continues with a step 34 of heating the catalyst 13 in which the torque C necessary to the drive of the vehicle is entirely provided by the first electric machine 3.

If the temperature T of the catalyst is not lower than the priming temperature Ta, the process goes to step 38 of adjusting the engine to nominal operation.

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.

Step 34 comprises a step 35 of post-combustion adjustment 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 fuel injected around the exhaust BDC. Combustion TDC is the moment of transition from a compression phase to an expansion phase and corresponds to the start of stroke three of a conventional four-stroke cycle. Exhaust BDC is the moment of transition from an expansion phase to an exhaust phase where the piston of an engine operating on a conventional four-stroke cycle begins to rise just after the expansion phase.

The engine adjustment used in afterburner adjustment step 35 is illustrated in Figures 6 and 7.

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 expansion phases. ' admission.

This so-called “post-combustion” adjustment differs from the adjustment used in the prior art in the catalyst heating phase and illustrated in Figures 3 and 4.

The post-combustion adjustment of the engine consists of burning the air-fuel charge very late in the engine cycle with ignition carried out at the end of the expansion phase before the opening of the exhaust valves, i.e. around the BDC of exhaust. The pressure and temperature conditions of an ignition carried out around the exhaust BDC are rather low in comparison to an ignition carried out around the combustion TDC.

It is therefore necessary to guarantee sufficient quality of combustion to ensure that the air-fuel mixture is as homogeneous as possible.

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 TDC of combustion that the aerodynamic speeds and intensities are the highest, making it possible to obtain ideal air-fuel homogenization.

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

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 train of sparks making it possible to increase the ignition energy and ensure the initiation of combustion (figure 6).

In the case of a heat 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 setting to avoid the presence of burnt gases in the combustion chambers after combustion, in order to stabilize 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 rising towards the intake and therefore experiencing intake noise problems, or even problems. reliability.

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

It is therefore preferable to activate the post-combustion adjustment 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 catalyst heating setting of the state of the art as described previously, or with a nominal setting conventionally used outside the catalyst heating phase. In one embodiment illustrated in Figure 8, the engine 2 has three cylinders and the post-combustion is activated only on the second cylinder. The first and third cylinders provide constant torque, while the second cylinder provides no torque. To simplify the presentation we have neglected the losses by friction and by pumping of the second cylinder. These losses are in reality compensated by a torque supplied by the second electrical machine 4.

In another embodiment illustrated in Figure 9, the engine 2 has three cylinders and the post-combustion is activated on all three cylinders, at the rate of one engine cycle out of two.

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

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 driving wheel (6) of a motor vehicle, said motor (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) participates in the torque (C) driving the vehicle, said motor ( 2) being further associated with a second electrical machine (4) capable of operating at least in a generator mode, said method comprising:

- a vehicle starting step in which a driving torque (C) of the vehicle is required; And

- a step of heating the catalyst (13) up to a starting temperature (Ta) of minimum predetermined catalyst efficiency, in which the driving torque (C) of the vehicle is entirely produced by the first electric machine (3) operating in motor mode; characterized in that said heating step comprises a step of post-combustion adjustment 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 by a step of igniting said fuel injected around the exhaust bottom dead center.

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, in which the ignition of said fuel injected around the exhaust bottom dead center is carried out with several sparks.

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

5. Method according to claim 4, wherein the post-combustion adjustment step is applied to all the cylinders of the engine (2) but only for every other engine cycle.

6. Method according to claim 4, wherein the post-combustion adjustment step is applied to a single cylinder.

7. Motor vehicle spark-ignition internal combustion engine (2) implementing a method according to any one of claims 1 to 6.