Internal combustion engine and method for controlling such an engine

Abstract

The present invention corresponds to an internal combustion engine (1) comprising a combustion chamber, a fuel injection circuit (60), an intake line (20) for fresh gases equipped with at least one intake valve, an exhaust line (80) for combustion gases equipped with at least one exhaust valve and a catalytic converter (83), a variable valve lift system, and a computer (100). More specifically, the present invention comprises a method for controlling such an engine, comprising obtaining operating parameters for the engine and determining a nominal set point for controlling the variable lift system as a function of said parameters. According to the present invention, the objective is to correct said nominal set point in order to open the intake valve earlier and / or close the exhaust valve later when the amount of oxygen in the catalytic converter is below a certain oxygen threshold and when pressure permits.

Description

[Technical Field]

[0001] The present invention generally relates to motor vehicles equipped with internal combustion engines.

[0002] In particular, the present invention provides A combustion chamber; a fuel injection circuit in the combustion chamber; an intake line for fresh gas into the combustion chamber, the intake line being equipped with at least one intake valve; an exhaust line for combustion gases outside the combustion chamber, the exhaust line being equipped with at least one exhaust valve and a catalytic converter; a variable lift system for the intake valves and / or the exhaust valves; a computer adapted to control the variable lift system; The present invention relates to an internal combustion engine equipped with the same.

[0003] The present invention includes a method of control for such an engine. [Background technology]

[0004] In an increasingly restrictive legal framework and with environmental protection in mind, technical solutions are required to improve the performance of ICEs and, in particular, to reduce the amount of pollutants emitted into the atmosphere.

[0005] To reduce polluting emissions, spark-ignition ICEs are typically configured with a three-way catalytic converter in the exhaust line to oxidize at least a portion of the unburned hydrocarbons (HC) and carbon monoxide (CO) and reduce at least a portion of the nitrogen oxides (NOx) contained in the combustion gases of the ICE.

[0006] There are several known methods and devices for adjusting fuel richness with the goal of improving catalytic converter efficiency.

[0007] As an example, one well-known method uses a control loop with an oxygen probe (or lambda probe) mounted in the exhaust line upstream of the catalytic converter. The output voltage of this probe is subtracted from a setpoint voltage that corresponds approximately to a richness value equal to 1. The error signal is then compared to zero using a binary comparator. Thus, if the setpoint voltage is higher than the sensor's output voltage, more fuel is added by a regulator, typically a proportional-integral (PI) controller. Conversely, if the setpoint voltage is lower than the sensor's output voltage, the amount of fuel is reduced. The resulting mixture richness then oscillates around the stoichiometric value.

[0008] In this way, the catalytic converter operates within its "catalytic window," which means that the catalytic converter is capable of carrying out both the oxidation and reduction reactions described above.

[0009] Note that when a catalytic converter is operating outside its catalytic window and near oxygen saturation, this disfavors nitrogen oxide reduction but favors carbon monoxide oxidation. Conversely, when the catalytic converter is devoid of oxygen, this disfavors carbon monoxide oxidation but favors nitrogen oxide reduction.

[0010] Therefore, the amount of oxygen stored in the catalytic converter is a very important parameter to ensure good simultaneous treatment of the three pollutants mentioned above. This means that it is important to maintain a stable amount of oxygen in the catalytic converter to ensure optimal pollution removal. This is one of the reasons why richness is adjusted to a value close to 1.

[0011] However, under certain conditions, this richness may be temporarily adjusted around a different value. Typically, at high loads, for example on the highway, the richness may be increased to a value slightly higher than 1, for example 1.002, to help reduce nitrogen oxide emissions (these emissions are tightly regulated) even if it means penalizing carbon monoxide emissions.

[0012] However, we realize that this situation cannot continue as long as we would like, as the catalytic converter will gradually become oxygen-starved and eventually be unable to oxidize the carbon monoxide and unburned hydrocarbons. Summary of the Invention

[0013] To solve the aforementioned problems of the current art, the present invention proposes a solution to keep the oxygen level in the catalytic converter at an optimum value even when the richness set point is higher than 1.

[0014] More particularly, the invention proposes a method for controlling an engine such as defined in the introduction, comprising the following steps: - obtaining at least one engine operating parameter (usually its speed, its load and required torque), the amount of oxygen stored in the catalytic converter and the pressure difference between the pressure of the fresh gases in the intake line and the pressure of the burnt gases in the exhaust line; determining a nominal control set point for the variable lift system as a function of the operating parameters; Correcting the nominal set points to open the intake valve earlier and / or close the exhaust valve later when the amount of oxygen is below a certain oxygen threshold and when the pressure difference is above a certain pressure threshold. Includes:

[0015] Therefore, according to the present invention, when the amount of oxygen is reduced in the catalytic converter, which risks making the catalytic converter unable to oxidize carbon monoxide and unburned hydrocarbons, the computer controls the variable valve lift system to create a scavenging effect in the combustion chamber.

[0016] This effect consists in circulating fresh gas from the intake line to the exhaust line without burning it in the cylinders, taking advantage of the moment when all valves are open simultaneously, thus introducing fresh oxygen-containing gas into the catalytic converter, which allows the amount of oxygen stored in the catalytic converter to increase.

[0017] Other advantageous and non-limiting features of the method for control of the present invention, taken individually or in all technically possible combinations, are the following: In the obtaining step, the computer calculates a richness value of the combustion gases, in the determining step, the computer determines a nominal set point for controlling the fuel injection circuit according to the richness value, and in the correcting step, the computer controls the fuel injection circuit according to a corrected set point different from the nominal set point so as to maintain a specific richness of the mixture of fresh gas and fuel entering the combustion chamber equal to the determined target value; the correction set point is determined in an open loop based on the total flow rate of fresh gases entering the combustion chamber and the flow rate of scavenging fresh gases passing uncombusted in the combustion chamber from the intake line to the exhaust line; The pressure threshold is equal to zero, determining a nominal control set point for the variable lift system as a function of engine speed and engine load parameters; The oxygen threshold is a predetermined constant, In the acquisition phase, the computer acquires the torque demand that the engine must produce, in the determination phase, the computer determines a nominal set point for controlling the general intake valve according to the torque demand, and in the correction phase, it attempts to correct the nominal set point for controlling the general intake valve by advancing the opening of the intake valve and / or delaying the closing of the exhaust valve.

[0018] The present invention provides A combustion chamber; a fuel injection circuit in the combustion chamber; an intake line for fresh gas into the combustion chamber, the intake line being equipped with at least one intake valve; an exhaust line for combustion gases from the combustion chamber, the exhaust line being equipped with at least one exhaust valve and a catalytic converter; a variable lift system for the intake valves and / or the exhaust valves; a computer adapted to control a variable lift system and programmed to carry out the method of controlling as described above; An internal combustion engine comprising:

[0019] Preferably, the intake line includes a fresh gas compressor.

[0020] Other features, variations and various embodiments of the invention may be associated with one another in various combinations, provided they are not mutually inconsistent or mutually exclusive.

[0021] The following description, given by way of non-limiting example with reference to the accompanying drawings, clearly explains what the invention consists of and how it can be put into practice. [Brief explanation of the drawings]

[0022] [Figure 1] 1 is a schematic diagram of an internal combustion engine in which the method for controlling according to the invention can be implemented; [Figure 2] FIG. 2 is a schematic cross-sectional view of the engine block of the internal combustion engine of FIG. 1. [Figure 3] FIG. 1 shows the main steps of the method for control proposed in the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0023] In the description, the terms "upstream" and "downstream" are used depending on the direction of gas flow from the point where fresh air is taken in from the atmosphere to the exhaust of the combustion gases into the atmosphere.

[0024] 1 is a schematic diagram of an internal combustion engine 1 of a motor vehicle, which comprises an engine block 10 defining combustion chambers formed by cylinders 11. Here there are four cylinders 11, although fewer (e.g., two) or more (e.g., four, six, or eight) may be used.

[0025] Upstream of the cylinders 11, the internal combustion engine 1 is provided with an intake line 20 which draws in fresh air from the atmosphere and opens into an air distributor 25 designed to distribute the fresh air to each of the four cylinders 11 of the engine block 10.

[0026] This intake line 20 is provided, in the direction of fresh air flow, with an air filter 21 for filtering the fresh air taken in from the atmosphere, a compressor 22 for compressing the fresh air filtered by the air filter 21, a main air cooler 23 for cooling this compressed fresh air, and a general inlet valve (intake valve) 24 (also known as a "throttle body") that makes it possible to regulate the flow rate of fresh air to the air distributor 25.

[0027] At the outlet of the cylinders 11, the internal combustion engine 1 comprises an exhaust line 80 extending from an exhaust manifold 81, through which the gases previously combusted in the cylinders 11 flow into an exhaust silencer 87, allowing the combustion gases to be purified before being discharged into the atmosphere. In the direction of the combustion gas flow, the internal combustion engine 1 further comprises a turbine 82 which drives a compressor 22 and a catalytic converter 83 which treats the combustion gases. Alternatively, the compressor 22 may be driven by other means, for example by an electric motor. Another variant, although not preferred, would be to design the intake line without a compressor 22.

[0028] Here, the engine does not have any gas recirculation lines. Alternatively, the engine may include a recirculation line for the combustion gases from the exhaust line to the intake line at high or low pressure, better known as an EGR line. The engine may also include additional pollution control devices.

[0029] The internal combustion engine 1 also includes a fuel injection circuit 60 , which comprises an injection pump 62 that takes fuel from a tank 61 for supplying fuel under pressure into injectors 64 from a common rail 63 .

[0030] To control the various components of the ICE 1, in particular the intake valves 24 and the injectors 64, a computer 100 is provided which comprises a processor (CPU), random access memory (RAM), read only memory (ROM), an analog-to-digital converter (A / D) and various input and output interfaces.

[0031] Through the input interface, the computer 100 can receive input signals from various sensors relating to the operating parameters of the engine.

[0032] In particular, the computer 100 is suitable for receiving a signal corresponding to the depression angle α of the accelerator pedal 30 or the pressure applied to this accelerator pedal 30. The computer 100 may also receive the rpm of the engine and its load.

[0033] The computer 100 is also designed to receive a signal relating to the richness λ of the air-fuel mixture injected into the combustion chamber. This signal is transmitted by a dioxygen probe (oxygen sensor) 40 in the exhaust line 80, upstream of the catalytic converter 83.

[0034] The computer 100 is capable of generating output signals for each of the engine's operating stages using mappings that are pre-configured for the test bench and stored in ROM.

[0035] Finally, the computer 100 may send output signals through an output interface to various engine components, particularly the intake valves 24 and the injectors 64.

[0036] FIG. 2 provides a cross-sectional view of the engine block 10 of the internal combustion engine 1 in FIG.

[0037] This engine block 10 has four main parts including a cylinder block 10C, an oil pan 10D fixed to the bottom of the cylinder block 10C to store oil for lubricating various engine components, a cylinder head 10B fixed to the cylinder block 10C, and a cylinder head cover 10A that covers the cylinder head 10B.

[0038] FIG. 2 shows the interior of one of the cylinders 11 of the engine block 10.

[0039] The cylinder 11 has rotational symmetry about a vertical axis A1 here and houses a cylindrical piston 14 which rotates about the axis A1, whereby the piston 14 is adapted to slide within the cylinder 11 along the axis A1 in an alternating linear (or reciprocating) motion.

[0040] The piston 14 has a peripheral skirt transversely perforated by two openings for receiving a pin against which the upper end of the connecting rod 13 is engaged, the lower end of which is connected to the crankshaft 12 (also called the "engine shaft") through an eccentric connection.

[0041] The reciprocating linear motion of the piston 14 therefore enables the crankshaft 12 of the internal combustion engine 1 to rotate about its longitudinal axis, referred to as the engine axis A2.

[0042] FIG. 2 also shows the end of one of the fuel injectors 64 that opens directly into the cylinder 11 (referred to as "direct injection").

[0043] The engine, now a spark ignition engine, also includes a spark plug (not visible) located near this injector 64 .

[0044] For the intake of fresh air into the cylinders 11, the cylinder head 10B is pierced by one (or two) intake ducts 16A extending from the air distributor 25 to intake openings 15A on the underside of the cylinder head opposite the cylinders 11.

[0045] For exhausting the combustion gases outside the cylinder 11, the cylinder head 10B is perforated by one (or two) exhaust ducts 16B which start at the exhaust opening 15B on the underside of the cylinder 11 facing the cylinder 11 near the intake opening 15A and open into the exhaust manifold 81.

[0046] To regulate the flow of fresh air to and burned gases from each cylinder 11, the cylinder head 10B houses intake valves 17A and exhaust valves 17B, the flared ends of which close the intake openings 15A and exhaust openings 15B of the fresh air intake duct 16A and the burned gas exhaust duct 16B.

[0047] The cylinder head 10B also houses a distributor adapted to control the position of these intake valves 17A and exhaust valves 17B, so that the internal combustion engine operates according to four thermodynamic cycles called intake, compression, power and exhaust cycles.

[0048] These distributors are of the variable type (VVT systems, for "variable valve timing"), so they make it possible to shift the opening and / or closing moments of the intake valves 17A and / or exhaust valves 17B relative to the top dead center (i.e., relative to the moment when the piston 14 reaches the highest point in the cylinder 11). In other words, the computer 100 can vary the opening and / or closing moments of at least one of the valves.

[0049] These distributors are, for example: two camshafts 18A, 18B rotatably mounted in the cylinder head 10B, carrying cams 19A, 19B arranged to periodically press the intake valves 17A and exhaust valves 17B so that each valve "rises" regularly, in order to periodically generate the passage of fresh air or burnt gases through the intake opening 15A and exhaust opening 15B; a timing chain (not shown) that rotates the crankshaft 12 via two pinions coupled to the two camshafts 18A and 18B, respectively; a control system (not shown) that allows each of these two pinions to be angularly offset by a few degrees in one direction or the other relative to the camshaft that supports it; Includes:

[0050] Control systems of this kind are well known to those skilled in the art and are not the object of the present invention, so they will not be described in more detail here.

[0051] It should be remembered that the camshaft phase shift is considered to be zero if complete closing of exhaust valve 17B (of the illustrated cylinder 11) occurs at the exact moment that intake valve 17A begins to open while piston 14 is at top dead center between the exhaust and intake cycles.

[0052] The phase shift, measured in degrees, corresponds to the angle between, on the one hand, the angular position of the camshaft when the piston 14 is at top dead center between the exhaust and intake cycles, and, on the other hand, the angular position that this camshaft would have if the phase shift were zero.

[0053] This phase shift can, in particular, create a "scavenging effect" by opening intake valve 17A while exhaust valve 17B is not yet closed (between the exhaust and intake cycles). Fresh gas circulating in intake line 20 can thus be delivered directly into exhaust line 80 without first being combusted in cylinder 11.

[0054] When the engine is started, fresh air is drawn in from the atmosphere by the intake line 20, filtered by the air filter 21, compressed by the compressor 22, cooled by the main air cooler 23, and then combusted in the cylinders 11.

[0055] As the combustion gases leave the cylinder 11, they are expanded in a turbine 82, treated by a catalytic converter 83, and then expanded again in an exhaust silencer 87 before being released to the atmosphere.

[0056] The camshafts 18A, 18B are then controlled to maintain a phase shift of approximately zero, although at certain operating phases, the phase shift is adjusted to a non-zero value, for example, to create a recirculation of burned gases from the exhaust to the intake (referred to as internal EGR) or to utilize a scavenging effect.

[0057] In practice, the phase shift set point sent to the control system is derived from the engine's operating point, i.e., its speed and load. This set point is then considered "nominal" and is determined independently of the amount of oxygen stored in catalytic converter 83.

[0058] According to the invention, the computer 100 is programmed to execute a method for controlling the engine 1 in a recursive manner, ie in loops and at regular intervals.

[0059] This control method comprises several main steps, which are illustrated in FIG.

[0060] The first step E0 is to obtain the desired torque request, which corresponds to the torque that the driver wants the engine 1 to produce.

[0061] This demand can be calculated, for example, by taking into account the engine speed and the accelerator pedal 30 angle α (received via angular velocity and position sensors connected to the computer 100).

[0062] It can also be calculated differently, especially if the vehicle is driven (partially) autonomously.

[0063] In a second step E2, the computer 100 uses this torque demand and the engine operating point to derive control commands for the components of the engine 1. These set points are calculated to regulate the fresh air flow rate and the fuel flow rate to desired values.

[0064] In practice, the computer 100 determines the phase shift set point as a function of the operating point of the engine 1, taking into account the boost pressure and the camshaft phase shift, and determines the control set point of the intake valve 24 as a function of torque demand.

[0065] The flow rate of fuel is adjusted so that the richness λ of the mixture (oxygen and fuel) entering the cylinder 11 is maintained at a target value, typically equal to 1.

[0066] To do so, the computer 100 employs a feedback loop that takes into account measurements from, for example, the oxygen sensor 40 .

[0067] This feedback loop operates at a target value C, which is equal to 1 here. λ As an input, the feedback loop then receives a setpoint value for the flow rate of fuel to be injected over the time that the injector 64 is open during each cycle, setpoint T i Output.

[0068] A regulator (e.g., PID) is used to determine the ratio between the measured richness λ and the target value C λ The difference ε between these values ​​allows a correction value Tc to be determined for the operating time of the injector 64.

[0069] Therefore, the operating time setpoint T is then sent to the injector 64. i is the ratio of the correction value Tc to the predetermined value t (taking into account the operating point of the engine, i.e., its speed and load). i is equal to the sum of

[0070] This feedback loop therefore allows the amount of fuel injected to be adjusted depending on the position of the intake valve 24.

[0071] Furthermore, at high loads and constant speeds, the target value C λ may be increased, for example, here equal to 1.002.

[0072] In a third step E4, the computer 100 calculates the current value of the amount of oxygen in the catalytic converter 83. This amount of oxygen is commonly referred to as the OS (oxygen storage).

[0073] There are a variety of possible calculation methods that can be used.

[0074] Typically, those used are those described in French patent no. 3033364, which are based on the following formula:

number

[0075] In this equation, the variables are defined as follows:

[0076] Q exh indicates the flow rate of the combustion gas (for example, equal to the sum of the flow rates of the intake air and the fresh gas circulating in the fuel line).

[0077] R λ indicates the richness (measured by the dioxygen probe (oxygen sensor) 40) upstream of the catalytic converter 83.

[0078] τ O2 indicates the oxygen concentration in air (approximately 0.23, or 23%).

[0079] OS init is the lower limit of integration at time t init, which represents the amount of oxygen stored in catalytic converter 83. This amount is initially set to a predetermined value corresponding, for example, to oxygen saturation of catalytic converter 83. The lower limit of the integral function then corresponds to the moment at which catalytic converter 83 is known to be saturated with oxygen. This is usually the case when fuel injection is interrupted for a sufficiently long time, especially when the driver fully lifts his foot off the accelerator pedal. This value can be predetermined by prior testing.

[0080] OS denotes the amount of oxygen stored at the current instant t.

[0081] In a fourth step E6, the computer 100 calculates the current value of the amount of oxygen in the catalytic converter 83 using a predetermined threshold value, which corresponds to the value below which the catalytic converter is considered to be unable to treat carbon monoxide and unburned hydrocarbons to a sufficient extent.

[0082] As long as this current value OS remains above the threshold value, which means that sufficient oxygen is maintained in the catalytic converter 83, the method resumes the first stage E0. The phase shift of the camshaft is therefore maintained equal to the nominal phase shift (determined taking into account the operating point of the engine).

[0083] It is understood that if the richness of the mixture is adjusted to a value slightly higher than 1 to ensure good treatment of the nitrogen oxides, and if this adjustment continues for a long enough time, the catalytic converter 83 will gradually become oxygen-starved and will risk being unable to oxidize carbon monoxide CO (or unburned hydrocarbon molecules).

[0084] Thus, if the current value OS of the amount of oxygen stored in the catalytic converter 83 is below the threshold value, the method continues with a fifth step E8.

[0085] From this stage onwards, the aim is to inject more oxygen into the catalytic converter 83 so that it can store enough oxygen to treat the carbon monoxide whilst still respecting the torque setpoint. The idea here is to use the scavenging effect.

[0086] It will be appreciated that this is only feasible provided that the inlet pressure is higher than the exhaust pressure.

[0087] Thus, in step E8, the computer 100 determines the intake and exhaust pressures, which may be based on measurements from pressure sensors located in the air distributor 25 and in the exhaust manifold 81. Alternatively, these two pressures may be calculated taking into account the operating point of the engine.

[0088] Then, in step E10, the computer 100 determines whether the exhaust pressure is less than the intake pressure.

[0089] If this determination is negative, which means that no scavenging effect can be generated, the method resumes the first stage E0. The phase shift of the camshaft is therefore maintained equal to the nominal phase shift (determined taking into account the engine operating point), and the amount of dioxygen stored in the catalytic converter continues to decrease or, conversely, increase, for example, due to the foot-up phase and interruption of fuel injection.

[0090] On the other hand, if the pressure in the exhaust is less than the pressure in the intake, the method continues with step E12 and attempts to modify the nominal engine settings calculated in step E2 in order to take advantage of the scavenging effect and re-establish oxygen conservation in the catalytic converter 83.

[0091] To do this, computer 100 may delay the closing of exhaust valve 17B and / or advance the opening of intake valve 17A so that there is a moment when these valves are simultaneously open.

[0092] It is understood that in this situation, the dioxygen probe (oxygen sensor) 40 will record a richness of less than 1. This measured richness will not be equal to the richness of the mixture introduced into the combustion chamber.

[0093] The idea is then to adjust the engine (without measuring) so that richness in the combustion chamber is maintained equal to 1 on each cycle, producing the required engine torque demand while reducing pollutant emissions as much as possible.

[0094] To do this, the computer 100: the total flow rate of fresh gas introduced into the cylinder (measured using a flow meter or by calculation); The flow rate of scavenging fresh gas (which travels from the intake section to the exhaust section without being burned in the combustion chamber) is calculated from the measured combustion gas flow rate and the oxygen concentration measured by the oxygen sensor. Get.

[0095] The flow rate of fresh combustion gases in the cylinder can then be derived from the difference between these two values, and the fuel flow rate can then be adjusted in an open loop, for example, at a rate of 1 gram of fuel per 14.7 g of fresh gases if the target value is equal to 1.

[0096] The computer can therefore inject the correct amount of fuel so that the richness of the combustion mixture in the cylinder 11 is maintained equal to the target value and the torque produced is equal to the required torque demand.

[0097] In this situation where the camshaft phase shift differs from the nominal phase shift, the amount of oxygen introduced into catalytic converter 83 increases rapidly, thereby allowing the oxygen reserves to be recharged. This phase shift is maintained until the calculated value for the amount of stored dioxygen is higher than a threshold value (greater than or equal to the threshold value previously mentioned).

[0098] Naturally, the production of the scavenging effect can be interrupted earlier, in particular when the pressure at the intake becomes less than the pressure at the exhaust.

[0099] The present invention is not limited in any way to the methods described and illustrated, and a person skilled in the art will know how to carry out any modifications thereof in accordance with the present invention.

[0100] Typically, variable valve lift systems cannot control all of the engine valves, but can control only the intake valves or only the exhaust valves, or the valves (intake or exhaust) for only some of the engine cylinders.

[0101] According to another variation of the present invention, computer 100 can be programmed to produce a scavenging effect only when the intake pressure is higher than the exhaust pressure by a non-zero and predetermined difference.

Claims

1. A method for controlling an internal combustion engine (1), the internal combustion engine (1) comprising: A combustion chamber; a fuel injection circuit (60) in the combustion chamber; an intake line (20) for fresh gases into the combustion chamber, the intake line (20) being equipped with at least one intake valve (17A); an exhaust line (80) for combustion gases from said combustion chamber, said exhaust line (80) being equipped with at least one exhaust valve (17B) and a catalytic converter (83); a variable lift system for the intake valve (17A) and / or the exhaust valve (17B); a computer (100) adapted to control the variable lift system; Equipped with The method of controlling comprises the steps of obtaining at least one operating parameter of the engine (1) and determining a nominal set point for controlling the variable lift system as a function of the operating parameter; The obtaining step obtains the amount of oxygen stored in the catalytic converter (83) and the pressure difference between the pressure of the fresh gas in the intake line (20) and the pressure of the combustion gas in the exhaust line (80), The method of controlling includes a corrective step relative to the nominal set point to open the intake valve (17A) earlier and / or close the exhaust valve (17B) later when the amount of oxygen is below a certain oxygen threshold and when the pressure difference is higher than a certain pressure threshold.

2. In the acquisition step, the computer acquires a richness value of the combustion gas, In the determining step, the computer determines a nominal control set point for the fuel injection circuit (60) as a function of the richness value; 2. The method of claim 1, wherein in the corrective step, the computer controls the fuel injection circuit (60) according to a corrective set point different from the nominal set point so as to maintain a specific richness of the mixture of fresh gas and fuel introduced into the combustion chamber equal to a determined target value.

3. 3. The method of controlling according to claim 2, wherein the correction set point is determined in an open loop based on a total flow rate of fresh gases introduced into the combustion chamber and a flow rate of scavenged fresh gases traveling uncombusted in the combustion chamber from the intake line (20) to the exhaust line (80).

4. 4. Method of controlling according to any one of claims 1 to 3, wherein the pressure threshold is equal to zero.

5. 5. A method of controlling according to any one of claims 1 to 4, wherein the nominal control set point of the variable lift system is determined as a function of engine (1) speed and engine (1) load parameters.

6. 6. The method of claim 1, wherein the oxygen threshold is a predetermined constant.

7. In the obtaining step, the computer obtains the torque demand that the engine (1) must produce, In the determining step, the computer determines a nominal set point for controlling a general intake valve (24) in response to the torque demand; 7. The method of claim 1, wherein in the correction phase, the objective is to correct the nominal control set point of the general intake valve (24) by advancing the opening of the intake valve (17A) and / or delaying the closing of the exhaust valve (17B).

8. An internal combustion engine (1), A combustion chamber; a fuel injection circuit (60) in the combustion chamber; an intake line (20) for fresh gases into the combustion chamber, the intake line (20) being equipped with at least one intake valve (17A); an exhaust line (80) for combustion gases from said combustion chamber, said exhaust line (80) being equipped with at least one exhaust valve (17B) and a catalytic converter (83); a variable lift system for the intake valve (17A) and / or the exhaust valve (17B); a computer (100) adapted to control the variable lift system and programmed to carry out the control method according to claims 1 to 7; An institution (1) that has:

9. An engine (1) according to claim 8, wherein the intake line (20) comprises a fresh gas compressor (22).

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