Method for controlling an internal combustion engine

Abstract

The invention relates to a method for controlling an internal combustion engine (1) comprising: - a combustion chamber, - a fresh air intake line (20) into the combustion chamber, - an exhaust line (80) for burnt gases from the combustion chamber, which is equipped with a catalytic converter (82), - a fuel injection circuit (60) into the combustion chamber, which includes a fuel tank (61), and - a fuel vapor discharge line (50) originating in the fuel tank and terminating in the exhaust line, and which includes a fuel vapor storage tank (51) and a fuel vapor flow control valve (52). According to the invention, when the internal combustion engine is started and fuel injection into the combustion chamber is suspended, the control valve is opened. Figure for the abstract: Fig. 1

Description

Title of the invention: Method for controlling an internal combustion engine Technical field of the invention

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

[0002] It relates more particularly to an internal combustion engine comprising: - a combustion chamber, - a fresh air intake line into the combustion chamber, - an exhaust line for burnt gases outside the combustion chamber, which is equipped with a catalytic converter, - a fuel injection circuit in the combustion chamber, which includes a fuel tank, and - a fuel vapor evacuation line, which originates in the fuel tank and opens into the exhaust line, upstream of the catalytic converter, and which includes a fuel vapor storage tank (canister) and a fuel vapor flow control valve.

[0003] The invention relates mainly to a method of controlling such an internal combustion engine.

[0004] It finds a particularly advantageous application in spark-ignition engines. State of the art

[0005] A spark-ignition engine operates by admitting a mixture of air and fuel (the intake mixture). The amount of air admitted is generally regulated according to the degree to which the accelerator pedal is depressed. The amount of fuel is generally regulated so that the air-fuel ratio of the intake mixture is equal to 1, which ensures complete combustion of the intake mixture in the engine cylinders.

[0006] Technical solutions are currently being sought, within an increasingly restrictive legislative framework and with a view to preserving the environment, to improve the operation of internal combustion engines, in particular to reduce the level of pollutants contained in the exhaust gases released by the engines into the atmosphere.

[0007] To reduce these polluting emissions, a spark-ignition engine generally includes, in its exhaust system, a three-way catalyst in which three main chemical reactions take place in order to transform carbon monoxide into carbon (CO), unburned fuel (HC hydrocarbons) and nitrogen oxides (NOx) into non-polluting compounds with no effect on health.

[0008] These reactions take place in the presence of oxygen. It is known that if the catalyst contains too little oxygen, the treatment of carbon monoxide and hydrocarbons will be ineffective. Conversely, if it contains too much oxygen, the treatment of nitrogen oxides will be impaired.

[0009] However, a catalyst naturally becomes oxygen-rich when oxygen-containing gases pass through it. The idea is then to regulate the flow rate of oxygen contained in the exhaust gases so that the amount of oxygen adsorbed by the catalyst is equal to a setpoint value. This setpoint is derived from a compromise such that the three aforementioned chemical reactions proceed as efficiently as possible.

[0010] To this end, document FR3033364 proposes determining the intake air-fuel ratio using a sensor placed in the exhaust line, upstream of the catalytic converter, and controlling the fuel injection to regulate this ratio to a setpoint value. This setpoint value is itself calculated to regulate the amount of oxygen in the catalytic converter to the setpoint value.

[0011] This solution is effective in many situations but it proves to be ineffective in the so-called "lifting off the accelerator" phases of the driver, i.e. in the event of deceleration or manual shifting of a gear ratio.

[0012] In these phases, with fuel injection interrupted, the richness of the intake mixture falls to 0, so that it is no longer possible to apply the aforementioned regulation processes.

[0013] However, if fuel injection is interrupted during these deceleration phases, air continues to pass through the cylinders and reach the catalytic converter, which then becomes oxygenated. It is not possible to completely stop the flow of air through the engine without generating strong vacuums in the cylinders, which would lead to oil consumption.

[0014] Consequently, when the regulation processes resume, the treatment of nitrogen oxides is no longer effective due to the excessive presence of oxygen in the catalyst. To reduce the duration during which this treatment is ineffective, this document FR3033364 proposes, at the moment when both regulation processes resume, to increase the richness of the intake mixture so that a large quantity of unburned hydrocarbons reaches the catalyst and burns the excess oxygen.

[0015] This solution is not as efficient as desired for two reasons. The first reason is that the combustion of excess oxygen takes time, so nitrogen oxide emissions into the atmosphere are still observed at each phase of Lifting off the accelerator. The second reason is that it consumes fuel. Presentation of the invention

[0016] In order to remedy the aforementioned drawbacks of the prior art, the present invention proposes to use the fuel vapors which have been adsorbed by the fuel vapor storage tank (well known under the Anglo-Saxon term "canister") by blowing them into the catalytic converter at each phase of lifting off the accelerator to regulate the amount of oxygen stored by the catalytic converter.

[0017] More particularly, the invention proposes a method for controlling an internal combustion engine as defined in the introduction, according to which, when the internal combustion engine is started and the fuel injection into the combustion chamber is suspended (in the deceleration phase), the regulating valve is opened.

[0018] Preferably, when the internal combustion engine is started and fuel injection into the combustion chamber is suspended, it is planned to regulate the opening of the control valve so that the richness of the gases entering the catalytic converter remains substantially equal to 1.

[0019] Preferably, when the internal combustion engine is started and fuel is regularly injected into the combustion chamber, steps are provided for determining a richness value of the gases entering the combustion chamber, and for controlling fuel injectors of the injection circuit so as to regulate the determined richness value to a calculated richness setpoint value.

[0020] Preferably also, said richness setpoint value is calculated so as to regulate the amount of oxygen contained in the catalytic converter to a predetermined storage setpoint value.

[0021] Advantageously, the internal combustion engine includes forcing means adapted to force the circulation of fuel vapors in the exhaust line when the regulating valve is open.

[0022] In a first embodiment, the forcing means comprise a narrowing of the cross-section of the exhaust line, into which the discharge line opens.

[0023] In another embodiment, the forcing means comprise a tube which is located in a section of the exhaust line, which occupies only a part of the section of said section, which has internally a convergent-divergent shape in the direction of flow of the burnt gases, and into which the exhaust line opens.

[0024] In yet another embodiment, the forcing means comprise a fuel vapor suction pump.

[0025] Preferably, the exhaust line includes a richness sensor located between, on one side, the point of junction of the exhaust line with the waste line, and, on the other, the catalytic converter.

[0026] Of course, the various features, variants, and embodiments of the invention can be combined with one another in various ways, provided they are not incompatible or mutually exclusive. Detailed description of the invention

[0027] The following description with regard to the attached drawings, given by way of non-limiting examples, will make it clear what the invention consists of and how it can be carried out.

[0028] On the attached drawings:

[0029] [Fig.1] is a schematic view of an internal combustion engine according to the invention;

[0030] [Fig.2] is a detail view of area II of [Fig.1];

[0031] [Fig.3] is a view representing an alternative embodiment of zone II of [Fig.1]

[0032] [Fig.4] is a schematic view of an alternative embodiment of the motor Internal combustion of the [Fig. 1]; and

[0033] [Fig.5] is a graph illustrating the variations in parameters of the internal combustion engine of [Fig.1], during a transient phase of lifting the foot off the accelerator.

[0034] In the description, the terms "upstream" and "downstream" will be used according to the direction of gas flow, from the point of fresh air intake in the atmosphere to the exit of the burned gases into the atmosphere.

[0035] In [Fig.1], a part of an internal combustion engine 1 intended for example to equip a motor vehicle has been schematically represented.

[0036] The internal combustion engine 1 comprises an engine block 10 equipped with a crankshaft and pistons (not shown) respectively housed in cylinders 11. These cylinders, for example three in number, delimit with their pistons a combustion chamber.

[0037] The internal combustion engine is of the spark-ignition type (gasoline, LPG, etc.). Consequently, it includes an ignition circuit which notably includes spark plugs, each opening into a cylinder 11 so as to be able to generate a spark of ignition of a combustion mixture.

[0038] Upstream of the cylinders 11, the internal combustion engine 1 has an intake line 20 which draws fresh air from the atmosphere and opens into an air distributor 25 arranged to distribute the fresh air to each of the cylinders 11 of the block- engine 10. This intake line 20 includes, in the direction of the flow of fresh air, an air filter (not shown) and an intake valve 21 which allows the flow of fresh air flowing into the air distributor 25 to be regulated. Typically, this intake valve 21 is of the butterfly type.

[0039] At the outlet of the cylinders 11, the internal combustion engine 1 includes an exhaust line 80 extending from an exhaust manifold 81, into which the gases previously burned in the cylinders 11 flow, to an exhaust silencer (not shown) allowing the burnt gases to expand before being released into the atmosphere. It also includes, in the direction of the flow of the burnt gases, a catalyst 82 followed by a particulate filter 83.

[0040] The catalyst 82 is here described as "three-way" in the sense that it is designed to, on the one hand, oxidize unburned hydrocarbons and carbon monoxide contained in the burnt gases, and on the other hand, reduce nitrogen oxides.

[0041] It could be foreseen whether the engine is supercharged or not.

[0042] It could also be provided that it includes or does not include one or more lines for partial recirculation of the exhaust gases at the intake (commonly called EGR lines), originating in the exhaust line 80 and opening into the intake line 20.

[0043] The internal combustion engine 1 also includes a fuel injection line 60 into the cylinders 11. This injection line includes an injection pump (not shown) arranged to draw fuel from a reservoir 61 in order to deliver it under pressure into the cylinders 11 via fuel injectors (not shown).

[0044] The fuel consists mainly of hydrocarbons.

[0045] As clearly shown in [Fig.1], the tank 61 has a fuel filling conduit 62.

[0046] This tank 61 is therefore designed to store a variable quantity of fuel, which gradually decreases when the engine is running, so that there is generally a volume of air above the fuel level. This volume of air is filled with fuel vapors.

[0047] To prevent these vapors from being dangerously compressed, for example when the vehicle is in the sun, an evacuation line 50 for these vapors is provided which originates in the tank 61.

[0048] To prevent these vapors from being released into the atmosphere, which would cause air pollution, this exhaust line 50 includes a volatile hydrocarbon adsorber, which constitutes a fuel vapor storage tank, commonly called a canister 51, and it opens into the exhaust line 80, upstream of the catalyst 82.

[0049] Conventionally, this canister 51 contains activated carbon capable of adsorbing hydrocarbon molecules suspended in the gases contained inside the tank 61.

[0050] According to the invention, the exhaust line 50 includes a regulating valve 52 for regulating the flow of gas circulating in this line. This valve allows these gases to be injected into the exhaust line 80 only when conditions require it, and at an appropriate flow rate.

[0051] When this regulating valve 52 is opened, it is necessary that the gases be drawn from the canister 51 to the exhaust line 80.

[0052] To ensure this gas circulation forcing function, three distinct embodiments can be considered.

[0053] In a first embodiment illustrated in Figures 1 and 2, the exhaust line 80 may locally have a reduced cross-section forming a convergent-divergent throat 84. In this embodiment, the exhaust line 50 opens at the midpoint of this throat 84, where its cross-section is at its narrowest. Consequently, the Venturi effect generated by the circulation of the exhaust gases in the exhaust line 80 (arrow F1) creates a suction effect on the gases contained in the exhaust line 50 (arrow F2).

[0054] It will be noted in this mode that the smallest section of the neck 84 corresponds to the nominal section of the exhaust line 80, so that the neck does not hinder the circulation of the burnt gases.

[0055] In a second embodiment illustrated in [Fig. 3], the exhaust line 50 can be provided to internally house a section of tube 85 which also forms an internally convergent-divergent throat. In this variant, the exhaust line 50 opens inside the section of tube 85, and this section of tube 85 occupies only a portion of the cross-section of the exhaust line 80. Here again, the Venturi effect will create the desired suction.

[0056] In a third embodiment illustrated in [Fig.4], it can be foreseen that the exhaust line 80 does not have a particular shape at the point of its junction with the evacuation line 50.

[0057] On the other hand, the evacuation line 50 includes a pump 59 allowing gases to be drawn through the canister 51 so that they become charged with hydrocarbons and are then discharged into the exhaust line 80.

[0058] In all these embodiments, as shown in figures 1 and 4 in dotted lines, it would also be conceivable that the evacuation line 50 includes a branch 53 which connects the canister 51 with the inlet line 20.

[0059] In this event, this bypass 53 will be equipped with its own regulating valve 54 in order to be able to discharge the hydrocarbons stored in the canister 51, as appropriate, to the intake line 20 or to the exhaust line 80, depending on the point engine operation.

[0060] As shown in [Fig.1], to control the various components of the internal combustion engine 1, a computer is provided comprising a processor (CPU), a memory and a data input and output interface.

[0061] Thanks to this interface, the computer is adapted to receive input signals from different sensors.

[0062] Among these sensors, one or more sensors are provided in particular to measure or evaluate the richness of the intake mixture (namely the mixture of gas and fuel admitted into the cylinders 11).

[0063] In this regard, it should be recalled that the concept of richness is defined by the ratio between the "effective proportion of fuel in the gases" and the "stoichiometric proportion of fuel in the gases".

[0064] The concept of "proportion of fuel in the gases" corresponds more precisely to the ratio between the mass of fuel and the mass of air.

[0065] Here, this richness measurement function is fulfilled by an oxygen sensor 86 provided in the exhaust line 80, upstream of the catalyst 82 and downstream of the junction zone of the exhaust line 80 with the waste line 50.

[0066] Also thanks to its interface, the computer is adapted to transmit output signals to the various components of the engine, in particular to the regulating valve 52, the fuel injectors, and the intake valve 21.

[0067] Thanks to its memory, the computer stores a computer application, consisting of computer programs including instructions whose execution by the processor allows the implementation by the computer of the process described below.

[0068] Conventionally, when the engine is started, fresh air taken from the atmosphere through the intake line 20 is filtered by the air filter, possibly compressed by the compressor (if the engine is equipped with a turbocharger for engine boosting), and then burned in the cylinders 11.

[0069] Upon exiting the cylinders 11, the burnt gases are possibly expanded in the turbocharger turbine, treated in the catalyst 82, filtered in the particulate filter 83, then expanded in the exhaust silencer before being released into the atmosphere.

[0070] In parallel, the computer is programmed to determine a load value requested from the internal combustion engine 1.

[0071] This load corresponds overall to the energy that the motor must supply.

[0072] In this case, the computer more precisely acquires the position of (or the effort exercised on) the vehicle's accelerator pedal.

[0073] It then deduces a setpoint position to be transmitted to the inlet valve 21 so that the inlet line 20 draws in a flow of fresh air corresponding to the charge requested.

[0074] As a general rule (i.e., outside the deceleration phases defined below), the computer maintains the control valve 52 in the closed position and controls the fuel injectors according to the method described in document FR3033364, using a dual control loop in which: - The value of the intake mixture richness is evaluated using oxygen sensor 86, - the quantity of fuel injected into each cylinder 11 in each cycle is determined so as to regulate the value of the mixture evaluated against a setpoint value of mixture CONS, and - this CONS richness setpoint value is itself calculated in such a way as to regulate the quantity of oxygen contained in the catalyst 82 on a storage setpoint value OSt.

[0075] This Ost storage setting is less than the total OSC storage capacity of the catalyst 82 and it ensures good treatment of nitrogen oxides, unburned hydrocarbons and nitrogen monoxide in the catalyst 82.

[0076] According to the invention, during the phases of lifting the foot off the accelerator, the computer is programmed to control the regulating valve 52, the intake valve 21 and the fuel injectors differently.

[0077] A deceleration phase will be defined here as a time interval during which fuel injection into cylinders 11 is temporarily suspended without the engine stopping. In practice, such a phase corresponds to a gear change in a manual transmission or a vehicle deceleration phase. During such a phase, no pressure is applied to the accelerator pedal.

[0078] To implement the invention, the computer implements in a loop, at regular time steps, a multi-step process.

[0079] The first step consists of acquiring the engine operating point to detect any phase of lifting the foot.

[0080] For this purpose, the computer acquires, for example, the position of the accelerator pedal, or the quantity of fuel injected into the engine, or any other related parameter.

[0081] When it detects that the engine is in such a phase, the computer suspends the double control loop described above.

[0082] This double loop can no longer be used since, with fuel injection suspended, the richness of the intake mixture is zero.

[0083] The computer is then programmed, in a second step, to place the intake valve 21 in the closed position. In this position, the closure of the intake line 20 is only partial, so that the flow of fresh air circulating at through cylinders 11 and opening into the exhaust line 80 is then minimum but not zero.

[0084] In order to prevent the catalyst 82 from becoming too heavily charged with oxygen, the computer is programmed, during a third step, to command the opening of the regulating valve 51. Thus, gases from the canister 51 are blown into the exhaust line 80, upstream of the catalyst 82.

[0085] It should be noted that in the embodiment illustrated in [Fig.4], the computer is programmed to simultaneously control the pump 59 in the started state during the entire foot lift phase.

[0086] From then on, the fresh air circulating in the exhaust line 80 and the volatile hydrocarbons from the canister 51 mix and enter the catalyst 82, where they react together and cause an exothermic reaction.

[0087] This reaction provides several advantages.

[0088] First of all, it allows the catalyst 82 to be kept at a high temperature, so that if the driver accelerates strongly afterwards, this catalyst remains able to treat the polluting elements of the burnt gases.

[0089] Above all, it prevents a large amount of oxygen from being stored in the catalyst 82 and prevents the treatment of unburned hydrocarbons when the driver accelerates again.

[0090] The idea here is to keep the amount of oxygen stored in the catalyst 82 constant.

[0091] For this purpose, during the deceleration phase, the computer acquires the value measured by the oxygen sensor 86, which allows it to determine the richness of the gases entering the catalyst 82.

[0092] Therefore, during this phase of lifting off the accelerator, the computer can control the position of the regulating valve 52 so that the richness measured using this probe is maintained equal to 1, which allows all the oxygen and hydrocarbons to react together and be burned in the catalyst 52, so that the amount of oxygen in the catalyst does not change.

[0093] This regulation can be achieved in various ways. For example, a proportional-integral type regulator can be used.

[0094] As soon as the lifting phase is over, the double regulation described above can resume.

[0095] In [Fig.5], the variations of different engine parameters during a foot-lifting phase are shown as a function of time t.

[0096] Curve Cl illustrates the rate of depressment of the accelerator pedal. It can be observed that this rate varies in steps and is zero between two instants t1 and t2 which delimit the phase of lifting the foot.

[0097] Curve C2 illustrates the gas flow rate in the exhaust line 82. It is therefore low but not zero during the deceleration phase. During this phase, the gases are highly oxygen-rich.

[0098] Curve C3 illustrates the gas richness measured at the inlet of the catalyst 82 using the oxygen probe 86. It can be seen that thanks to the opening of the regulating valve 52, the hydrocarbons from the canister 51 make it possible to maintain this richness substantially equal to 1 during the deceleration phase.

[0099] In this way, as shown by curve C4, the amount of oxygen stored in the catalyst does not vary during the lifting phase.

[0100] Finally, curve C5 shows the evolution of the temperature of catalyst 82, which increases slightly during this phase.

[0101] The present invention is in no way limited to the embodiments described and represented, but a person skilled in the art will be able to make any variation in accordance with the invention.

[0102] For example, if the vehicle speed is regulated autonomously by the computer, without intervention from the driver (for example via a cruise control), the load will be deduced not from the position of the accelerator pedal but from a speed setpoint calculated by the computer.

Claims

Demands

1. Internal combustion engine (1) comprising: - a combustion chamber, - a fresh air intake line (20) into the combustion chamber, - an exhaust line (80) for burnt gases out of the combustion chamber which is equipped with a catalytic converter (82), - a fuel injection circuit (60) into the combustion chamber, which includes a fuel tank (61), - a fuel vapor outlet line (50) originating in the fuel tank (61) and terminating in the exhaust line (80), upstream of the catalytic converter (82), and which includes a fuel vapor storage tank (51) and a fuel vapor flow control valve (52), and - a control unit programmed to implement a control method according to which, when the internal combustion engine (1) is started and fuel injection into the combustion chamber is suspended,It is planned to open the regulating valve (52), characterized in that it provides forcing means adapted to force the circulation of fuel vapors in the exhaust line (50) when the regulating valve (52) is open, which forcing means comprising a tube (85) which is located in a section of the exhaust line (80), which occupies only a part of the cross-section of said section, which has internally a convergent-divergent shape in the direction of flow of the burnt gases, and into which the exhaust line (50) opens.

2. Internal combustion engine (1) according to claim 1, wherein the forcing means comprise a fuel vapor suction pump (59).

3. Internal combustion engine (1) according to any one of claims 1 and 2, wherein the exhaust line (80) has a mixture sensor (86) located between, on one side, the point of junction of the exhaust line (80) with the outlet line (50), and, on the other, the catalytic converter (82).

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