Method for controlling a motor vehicle powertrain incorporating an internal combustion and spark ignition engine and associated control system

Abstract

A method for controlling a powertrain comprising a spark-ignition internal combustion engine (102), the method comprising the following steps: a) determining a fuel dilution ratio of the oil, b) determining a maximum difference between a torque generated by one of the cylinders and an average torque (Cmoy) generated by all the cylinders, c) determining an oil temperature, and d) implementing compensation for torque dispersions between the cylinders, step d) being activated when the following conditions are met: - the fuel dilution ratio of the oil determined in step a) is greater than a predetermined threshold value, - the maximum torque difference determined in step b) is greater than a predetermined threshold value (x), and - the oil temperature determined in step c) is greater than a predetermined threshold value. Figure for abstract: Fig 4

Description

Title of the invention: Method for controlling a motor vehicle powertrain incorporating an internal combustion and spark ignition engine and associated control system

[0001] The present invention relates, in general, to the control of the richness of an internal combustion and spark ignition engine of a motor vehicle and, more particularly, to the control of the richness of an internal combustion and spark ignition engine of a motor vehicle in the presence of engine crankcase gases, known as "blow-by" gases.

[0002] More specifically, the invention relates to a method for controlling a powertrain incorporating an internal combustion and spark ignition engine, to a control system intended to implement such a method, as well as to a motor vehicle incorporating such a control system.

[0003] In an effort to reduce polluting emissions, automobile manufacturers are required to equip motor vehicles with an on-board diagnostic device, known as an “OBD” device, an acronym for the English term “On-Board Diagnosis”, and intended for monitoring the operating condition of the engine.

[0004] In order to meet the new pollutant emission requirements, the OBD device must, in particular, include an on-board diagnosis of cylinder imbalance, known as "Cylinder imbalance". The latter consists of detecting torque balance problems between the different cylinders of the engine which may lead to the emission limits being exceeded.

[0005] Conventionally, spark-ignition engines are equipped with a proportional type oxygen sensor, mounted on the engine exhaust and upstream of a three-way catalyst, and making it possible to measure the oxygen content of the exhaust gases.

[0006] This control of the oxygen content makes it possible to monitor the richness of the engine, adjusted in a closed loop to a set value which is generally equal to 1, i.e. a stoichiometric richness of the air and fuel mixture which makes it possible to ensure the optimal decomposition of the three pollutants CO, HC and NOx. The set value is adjusted by modifying the duration of injection of the fuel by the injectors, i.e. by modifying the duration of opening of the injectors.

[0007] However, this richness adjustment is an average richness adjustment, the duration of fuel injection by the different fuel injectors being the same in all cylinders of the engine.

[0008] Consequently, when one of the fuel injectors is malfunctioning, for example partially blocked, it injects a much lower quantity of fuel than the expected quantity corresponding to the commanded opening duration, the average richness of the cylinders is unbalanced. This results in the cylinder on which less fuel is injected being "lean", i.e. the richness is less than 1, and the other cylinders being "rich", i.e. the richness is greater than 1, resulting in higher pollutant emissions at the exhaust.

[0009] The OBD diagnostic device's "Cylinder imbalance" diagnosis allows the detection of malfunctions in engine components, such as fuel injectors. The detection of a component malfunction is called "Good Detection" and allows the correction of parameter imbalances such as the resulting richness.

[0010] In the case where the OBD diagnostic device manages to highlight that an injector is delivering too little fuel, it is known to rebalance the richness of the engine cylinders by specifically increasing the injection duration of the malfunctioning injector, that is to say by adopting a distinct injection duration compared to the other functional cylinders.

[0011] In certain cases, the richness between the cylinders can be very dispersed without this resulting from a malfunction of an engine component.

[0012] In particular, crankcase gases, known as blow-by gases, generated in the cylinder block of an internal combustion engine are likely to disturb the richness.

[0013] [Fig.l] represents an existing powertrain 1 comprising an internal combustion and spark ignition engine 2, an air intake circuit 3 and an exhaust circuit 4.

[0014] The engine 2 comprises three cylinders C1, C2 and C3, and a fuel supply circuit, not visible, comprising fuel injectors each of which is capable of injecting fuel into one of the three cylinders C1, C2 and C3.

[0015] The air intake circuit 3 comprises an intake manifold 5 supplying air to the cylinders.

[0016] Engine 2 is supercharged by compressor C of a turbocharger 6.

[0017] The exhaust circuit 4 comprises an exhaust manifold 7, a turbine T of the turbocharger 6, a treatment device 8 and a proportional oxygen sensor R.

[0018] The treatment device 8 comprises a three-way catalyst which, continuously, oxidizes the unburned hydrocarbons HC and the carbon monoxide CO and reduces the nitrogen oxides NOx which are present in the exhaust gases. The treatment device further comprises here a particulate filter which makes it possible to store the fine particles emitted by the engine and then burn them when the stock reaches a threshold. The proportional oxygen sensor R is mounted at the inlet of the three-way catalyst, and allows the richness of the air and fuel mixture to be regulated to a set value, in a closed loop, by adjusting the injection duration of all the injectors to the same value.

[0019] The powertrain 1 incorporates an OBD diagnostic device.

[0020] As illustrated in [Fig.2], during its operation, the engine 2 generates leaks of unburned combustion gases which escape beyond the segments of the pistons of the cylinders C1, C2 and C3, penetrating into the cylinder housing 9, above an oil bath 10 for lubricating the engine 2. The oil bath 10 then gradually becomes loaded with fuel.

[0021] The blow-by gases, part of which has evaporated from the oil bath 10, rise to the level of the cylinder head 11 where they are freed from the oil using a decanter, before being readmitted via a recirculation circuit 12 into the air intake circuit 3 of the engine 2. The blow-by gases are admitted at a point P of the air intake circuit 3 located on the intake manifold 5.

[0022] The blow-by gas recirculation circuit 12 is connected to the intake manifold 5 of the air intake circuit 3, which supplies fresh air to each of the cylinders of the engine 2, so as to minimize flow dispersions between the cylinders. However, given the architectural constraints and the internal aerodynamics of the intake manifold 5, this distribution is generally not ideal so that design-related blow-by flow dispersions form between the cylinders.

[0023] When fuel evaporated from the oil bath is readmitted via the blow-by gas recirculation circuit 12, the richness is regulated via the oxygen sensor R so that the average richness Rmoy of the cylinders returns to a value equal to 1. This results in an individual richness of each cylinder which is highly dispersed between the cylinders.

[0024] Figures 3A and 3B, representing, respectively, the torque and richness dispersions generated by the presence of blow-by gases in the three cylinders C1, C2 and C3 of the engine 2, show the consequences of a low flow rate of blow-by gas on the first cylinder C1 where the richness is less than 1 and of a high flow rate on the second and third cylinders C2 and C3 where the richness is greater than 1.

[0025] The dispersions of richness have a direct consequence on the torque generated by each of the cylinders, which will deviate in the same way from an average torque Cmoy generated individually by each of the cylinders in the absence of blow-by gas and failure of components of the engine 2.

[0026] However, conventionally, the OBD cylinder imbalance diagnostic device is activated based on torque dispersion information. In particular, the OBD diagnosis is activated when the torque of one of the cylinders deviates from the average torque Cmoy by a predetermined deviation e, in percentage %, beyond which it is considered that the level of exhaust emissions becomes critical, as is the case of the first and third cylinders Cl and C3 in [Fig.3B].

[0027] Such activation of the OBD diagnosis linked to the presence of blow-by gas in the cylinders of the engine 2 is problematic since it leads to a “False Detection”, that is to say to an activation which is not linked to a faulty component.

[0028] The invention therefore aims to remedy these drawbacks and to propose a solution making it possible to detect at low cost torque dispersions due to the presence of blow-by gas in the cylinder block of an internal combustion and spark ignition engine, in order to be able to distinguish such a dispersion from a torque dispersion due to a failure of an engine component.

[0029] There is therefore proposed a method for controlling a powertrain comprising an internal combustion and spark ignition engine incorporating a plurality of cylinders and a cylinder block containing oil, an air intake circuit into the cylinders, a blow-by gas recirculation circuit from the cylinder block connected to the air intake circuit, and a circuit for supplying fuel to the cylinders, the method comprising the following steps:

[0030] a) determining a dilution rate of the oil by the fuel,

[0031] b) determining a maximum difference between a maximum torque generated by one of the cylinders and an average torque generated by all the cylinders,

[0032] c) determining an oil temperature, and

[0033] d) implementing compensation for torque dispersions between the cylinders, step d) being activated when the following conditions are met:

[0034] - the dilution rate of the oil by the fuel determined in step a) is greater than a predetermined threshold value,

[0035] - the maximum torque deviation determined in step b) is greater than a threshold value predetermined, and

[0036] - the oil temperature determined in step c) is higher than a threshold value predetermined.

[0037] Preferably, step d) comprises adjusting the quantity of fuel injected into at least one of the cylinders to rebalance the richness between the cylinders.

[0038] Advantageously, the adjustment of the quantity of fuel can be achieved by increasing the duration of fuel injection in the cylinders where the richness of the air and fuel mixture is less than a set value, preferably the set value being equal to 1.

[0039] Preferably, the adjustment of the fuel quantity is carried out from a model as a function of the maximum deviation of the maximum torque of the cylinders and the torque average generated by all the cylinders.

[0040] Preferably, the powertrain further comprises a device for diagnosing failure of a component of the engine, the predetermined threshold value of the maximum torque deviation being less than a predetermined threshold value of a maximum torque deviation from the average torque generated by all the cylinders from which the device for diagnosing failure of a component of the engine is activated.

[0041] Preferably, the predetermined threshold value of oil temperature is between 40 and 50°C.

[0042] In one embodiment, the oil temperature value determined in step c) may be a value calculated from a model.

[0043] Preferably, the value of the oil dilution rate determined in step a) by the fuel is a value calculated from a model.

[0044] The invention also relates to a system for controlling a powertrain comprising an internal combustion and spark ignition engine incorporating a plurality of cylinders and a cylinder block containing oil, an air intake circuit into the cylinders, a blow-by gas recirculation circuit from the cylinder block connected to the air intake circuit, and a circuit for supplying fuel to the cylinders, the control system comprising a control device capable of:

[0045] - determine a dilution rate of the oil by the fuel,

[0046] - determine a maximum difference between a maximum torque generated by one of the cylinders and an average torque generated by all the cylinders,

[0047] - determine an oil temperature, and

[0048] - implement compensation for torque dispersions between the cylinders when the following conditions are met:

[0049] - the dilution rate of the oil by the determined fuel is greater than a value predetermined threshold,

[0050] - the maximum torque deviation determined is greater than a predetermined threshold value, And

[0051] - the determined oil temperature is higher than a predetermined threshold value finished.

[0052] Preferably, the control device is capable of adjusting the quantity of fuel injected into at least one of the cylinders to rebalance the richness between the cylinders.

[0053] Advantageously, the control device may be able to adjust the quantity of fuel from a model as a function of the maximum deviation of the maximum torque of the cylinders and the average torque generated by all of the cylinders.

[0054] Advantageously, the control device can be configured to adjust the quantity of fuel injected by increasing the duration of fuel injection in the cylinders where the richness of the air and fuel mixture is less than a set value, preferably the set value being equal to 1.

[0055] Advantageously, the control system may comprise an oil temperature sensor intended to measure the temperature of the oil present in the cylinder block.

[0056] Advantageously, the control device may comprise a model adapted to calculate the temperature of the oil present in the cylinder block.

[0057] Advantageously, the control device may comprise a model adapted to calculate the maximum torque deviation.

[0058] Advantageously, the control device may comprise a model adapted to calculate the dilution rate of the oil by the fuel.

[0059] Preferably, the powertrain further comprises a device for diagnosing failure of a component of the engine, the predetermined threshold value of the maximum rate of torque dispersion between the cylinders being less than a predetermined threshold value of the rate of torque dispersion between the cylinders from which the device for diagnosing failure of a component of the engine is activated.

[0060] The invention also relates to a motor vehicle comprising:

[0061] a spark-ignition internal combustion engine comprising a plurality of cylinders, a cylinder crankcase containing oil, an air intake circuit into the cylinders, a blow-by gas recirculation circuit from the cylinder crankcase connected to the air intake circuit, and a fuel supply circuit for the cylinders, and

[0062] a control system as previously described. Brief description of the drawings

[0063] Other aims, advantages and characteristics will emerge from the description which follows, given purely for illustrative purposes and with reference to the appended drawings in which:

[0064] [Fig. 1] is a motor vehicle powertrain incorporating a spark-ignition internal combustion engine according to the prior art.

[0065] [Fig.2] represents a blow-by gas recirculation circuit of the motor vehicle powertrain of [Fig.l].

[0066] [Fig.3A] and [Fig.3B] represent, respectively, the richness and the torque of each of the three cylinders of the engine of [Fig.l].

[0067] [Fig.4] illustrates a motor vehicle powertrain incorporating a spark-ignition internal combustion engine according to one embodiment of the invention.

[0068] [Fig.5] is a flowchart illustrating a method for controlling an internal combustion and spark ignition engine according to an embodiment of the invention.

[0069] [Fig.6A] and [Fig.6B] represent, respectively, the richness and the torque of each of the three cylinders of the engine of [Fig.4] dispersed by the presence of blow-by gas.

[0070] [Fig.7A] and [Fig.7B] represent, respectively, the richness and the torque of each of the three cylinders of the engine of [Fig.4] after compensation for the torque dispersions between the cylinders from a control method according to the invention. Detailed description

[0071] In what follows, the limits of a domain of values ​​are included in this domain, in particular in the expression “between”.

[0072] Furthermore, the expression "at least one" used in the present description is equivalent to the expression "one or more".

[0073] [Fig. 4] illustrates a motor vehicle powertrain 101 comprising an internal combustion and spark ignition engine 102, an air intake circuit 103 and an exhaust circuit 104.

[0074] The illustrated engine 102 comprises three cylinders C1, C2 and C3, and a fuel supply circuit, not shown, comprising fuel injectors each of which is capable of injecting fuel into one of the three cylinders C1, C2 and C3.

[0075] The air intake circuit 103 comprises an air inlet A, an air filter F, the compressor C of a turbocharger 106, a cooler RG of the intake gases supercharged by the compressor C, a throttle body B and an intake manifold 105 supplying fresh air to the cylinders C1, C2 and C3.

[0076] The engine 102 also comprises a cylinder block 109 surmounted by a cylinder head, not visible, and an oil bath 110 for lubricating the engine 102 in the cylinder block 109.

[0077] The exhaust circuit 104 comprises an exhaust manifold 107, a turbine T of the turbocharger 106, a treatment device 108 and a proportional oxygen sensor R.

[0078] The treatment device 108 illustrated comprises a three-way catalyst 114 which oxidizes the unburned hydrocarbons HC and the carbon monoxide CO and which reduces the nitrogen oxides NOx present in the exhaust gases. It further comprises here a particulate filter 113 which makes it possible to store the fine particles emitted by the engine 102 and to burn them when the stock reaches a threshold. The proportional oxygen sensor R is mounted at the inlet of the three-way catalyst 114 and makes it possible to regulate the richness RCi of the air and fuel mixture introduced into the cylinders C1, C2 and C3 on a set value, in a closed loop, by adjusting the injection duration of all the in- fuel injectors on the same value.

[0079] The powertrain 101 further comprises a blow-by gas recirculation circuit 112 connecting the cylinder block 109 to the air intake circuit 103 of the engine 102. The blow-by gases are admitted at a point P of the air intake manifold 105 located on the intake manifold 105.

[0080] The powertrain 101 further incorporates a control system for controlling the powertrain 101.

[0081] The control system comprises a control device 115 capable of:

[0082] determine the dilution rate of the oil in the oil bath 110 with fuel,

[0083] determine a maximum difference, expressed as a percentage %, between a maximum torque generated by one of the cylinders C1, C2, C3 and an average torque Cmoy generated by all of the cylinders C1, C2, C3,

[0084] determine an oil temperature Th of the oil bath 110, and

[0085] implement compensation for torque dispersions between cylinders C1, C2, C3 when the following conditions are met:

[0086] - the dilution rate of the oil by the determined fuel is greater than a value predetermined threshold,

[0087] - the maximum torque deviation determined is greater than a predetermined threshold value x, and

[0088] - the determined oil temperature Th is higher than a predetermined threshold value finished.

[0089] Preferably, the control system further integrates a fault diagnosis device 116 of a component of the engine 102, such as a fuel injector.

[0090] The fault diagnosis device 116, or OBD diagnostic device, is intended to detect torque balance problems between the different cylinders C1, C2, C3 of the engine 102 likely to lead to the pollutant emission limits being exceeded.

[0091] With reference to [Fig.5], the invention also relates to a method for controlling the powertrain 101 comprising the following steps:

[0092] a) determining the dilution rate of the oil in the oil bath 110 with fuel,

[0093] b) determining a maximum difference between the torque generated by one of the cylinders C1, C2, C3 and the average torque Cmoy generated by all the cylinders,

[0094] c) determining the oil temperature Th of the oil bath 110, and

[0095] d) implementing compensation for torque dispersions between cylinders C1, C2, C3, step d) being activated when the following conditions are met:

[0096] the dilution rate of the oil by the fuel determined in step a) is greater than a predetermined threshold value,

[0097] the maximum torque deviation determined in step b) is greater than a predetermined threshold value x, and

[0098] the oil temperature Th determined in step c) is greater than a predetermined threshold value.

[0099] The control method is implemented by the control system which incorporates all the hardware and software means for implementing this control method.

[0100] The dilution rate of the oil by the fuel determined in step a) is advantageously a value calculated from a model.

[0101] For example, the dilution rate of the oil by the fuel can be determined from a model as described in document EP2520785.

[0102] Preferably, the predetermined threshold value of the dilution rate of the oil by the fuel is less than or equal to 10%.

[0103] In step b), the individual torque generated by each of the cylinders C1, C2, C3 is determined so as to identify the cylinder whose rate of variation between its individual torque and the average torque Cmoy generated by all the cylinders is the greatest compared to the other cylinders C1, C2, C3.

[0104] The individual torque generated by each of the cylinders C1, C2, C3 and therefore the maximum torque deviation can be calculated.

[0105] The control system may comprise a torque meter intended for determining the individual torque generated by each of the cylinders C1, C2, C3 and connected to the control device 115.

[0106] Advantageously, the maximum torque deviation can be determined from a method known as a “software torque meter”, as described in document FR2757945 or document FR2818740, based on the use of a torque meter and on the analysis of the instantaneous speed of the engine 102, and which makes it possible to know the individual torque developed in a cylinder over a combustion cycle.

[0107] Preferably, the predetermined threshold value x of the maximum torque dispersion deviation is greater than or equal to 5%.

[0108] In one embodiment, the oil temperature value determined in step c) may be a value calculated from a model.

[0109] Advantageously, the control device 115 of the control system is capable of determining the value of the temperature of the oil in the oil bath 110 from a model.

[0110] Alternatively, the oil temperature value determined in step c) may be a value measured from a temperature sensor.

[0111] The control system may comprise a temperature measurement sensor connected to the control device 115 and intended for determining, in step c), the value of the temperature of the oil in the oil bath 110 in the cylinder block 109.

[0112] The predetermined threshold value of oil temperature is preferably between 40 and 50°C. Beyond this range of values, the fuel present in the oil evaporates.

[0113] Preferably, steps a), b) and c) are carried out simultaneously.

[0114] Furthermore, the three aforementioned conditions are cumulative so that the implementation of the compensation of the torque dispersion between the cylinders C1, C2, C3 in step d) is only activated when the three conditions are met.

[0115] Preferably, steps a), b), c) and d) are carried out continuously during operation of the engine 102 so as to regulate, in a closed loop, the dispersions of richness and therefore of torques between the cylinders C1, C2, C3.

[0116] Figures 6A and 6B represent, respectively, the richness and the torque generated individually by each of the three cylinders C1, C2 and C3 of the engine 102 at a time t.

[0117] It can be seen that the admission of blow-by gas into the air intake circuit 103 disturbs the richness of the air and fuel mixture so that the torque difference Displ, Disp3 of the first and third cylinders C1 and C3 is greater than the predetermined threshold value x.

[0118] In the third cylinder C3, a maximum torque deviation is generated compared to the average torque Cmoy.

[0119] When, cumulatively to the determination of the maximum torque deviation greater than the predetermined threshold value x, the dilution rate of the oil by the fuel and the oil temperature Th are greater than their predetermined threshold value, a situation of disturbance of the richness of the cylinders C1, C2, C3 by the presence of blow-by gas is identified.

[0120] The control device 115 then triggers the implementation of compensation for torque dispersions between the cylinders.

[0121] Advantageously, the quantity of fuel Qinj_i injected into each of the cylinders C1, C2, C3 is adjusted using a model based on the maximum torque difference determined and the average torque Cmoy generated by all the cylinders.

[0122] Preferably, the set value of the richness of the air and fuel mixture in each of the cylinders C1, C2, C3 is equal to 1. The coefficients before disturbance are therefore preferably fixed at a value equal to 1.

[0123] The control device 115 applies coefficients Fac_Qinj_i to each of the quantities of fuel Qinj_i to be injected to rebalance the richness between the cylinders so that each of the cylinders returns to the set value which, in the example illustrated, is equal to 1.

[0124] For example, when a cylinder lacks torque, such as the first cylinder C1, the quantity injected on this cylinder C1 is increased, and when a cylinder generates too much torque, such as the third cylinder C3, the quantity injected on this cylinder C3 is reduced in order to reduce the maximum torque difference in the cylinders C1, C2, C3.

[0125] In this regard, the control device 115 is advantageously connected to the fuel injectors in the cylinders C1, C2, C3 in order to control the adjustment of the quantity of fuel.

[0126] Advantageously, the activation of the fault diagnosis device 116 is also based on the torque dispersion information, calculated for example by the torque meter.

[0127] Advantageously, the fault diagnosis device 116 of a component of the engine 102 is activated when the maximum torque deviation, relative to the average torque generated by all the cylinders, is greater than a predetermined threshold value e.

[0128] The predetermined threshold value x of the maximum difference between the torque generated by one of the cylinders and the average torque Cmoy generated by all the cylinders, determining the activation of step d) is less than the predetermined threshold value e of the maximum torque difference triggering the activation of the fault diagnosis device 116.

[0129] After compensation for the torque dispersions in step d), we will therefore return to a compliant situation as presented in FIGS. 7A and 7B, avoiding a critical emission quantity of pollutants and avoiding false detection of the fault diagnosis device 116.

[0130] Advantageously, the control method comprises a step of deactivating step d) when at least one of the conditions for activating step d) is no longer met.

[0131] The coefficients Fac_Qinj_i are all reset to 1 by the control device 115.

[0132] Such a control method makes it possible, at low cost, to detect a dispersion of torque between the plurality of cylinders C1, C2, C3 of the engine 102 due to the presence of blow-by gas in the cylinder block 109 of the engine 102 so as to prevent false detection of failure of an engine component by the failure diagnostic device 116 and avoid unjustified maintenance and replacement of the components concerned.

Claims

Claims

1. Method for controlling a powertrain comprising a spark-ignition internal combustion engine (102) incorporating a plurality of cylinders (C1, C2, C3) and a cylinder block (109) containing oil, an air intake circuit (103) in the cylinders, a blow-by gas recirculation circuit (112) coming from the cylinder block connected to the air intake circuit, and a circuit for supplying the cylinders with fuel, the method comprising the following steps: a) determining a dilution rate of the oil by the fuel, b) determining a maximum difference between a torque generated by one of the cylinders and an average torque (Cmoy) generated by all the cylinders, c) determining an oil temperature, and d) implementing compensation for torque dispersions between the cylinders,step d) being activated when the following conditions are met: - the dilution rate of the oil by the fuel determined in step a) is greater than a predetermined threshold value, - the maximum torque deviation determined in step b) is greater than a predetermined threshold value (x), and - the oil temperature (Th) determined in step c) is greater than a predetermined threshold value.,

2. A method according to claim 1, wherein step d) comprises adjusting the quantity of fuel injected into at least one of the cylinders to rebalance the richness between the cylinders.

3. A method according to claim 2, wherein the adjustment of the fuel quantity is achieved by increasing the duration of fuel injection into the cylinders where the richness of the air and fuel mixture is lower than a set value, preferably the set value being equal to 1.

4. Method according to claim 2 or 3, in which the adjustment of the quantity of fuel is carried out from a model as a function of the maximum deviation of the torque of the cylinders and the average torque (Cmoy) generated by all the cylinders (Cl, C2, C3).

5. A method according to any preceding claim, wherein the powertrain further comprises a device for fault diagnosis (116) of a component of the engine (102), the predetermined threshold value (x) of the maximum torque deviation being less than a predetermined threshold value (e) of a maximum torque deviation from the average torque (Cmoy) generated by all the cylinders from which the fault diagnosis device (116) of a component of the engine (102) is activated.

6. A method according to any one of the claims, wherein the predetermined threshold oil temperature value is between 40 and 50°C.

7. A method according to any one of the claims, wherein the oil temperature value (Th) determined in step c) is a value calculated from a model.

8. A method according to any one of the claims, wherein the value of the oil dilution rate determined in step a) by the fuel is a value calculated from a model.

9. A system for controlling a powertrain comprising a spark-ignition internal combustion engine (102) incorporating a plurality of cylinders (C1, C2, C3) and a cylinder housing (109) containing oil, an air intake circuit (103) into the cylinders, a blow-by gas recirculation circuit (112) coming from the cylinder housing (109) connected to the air intake circuit (103), and a circuit for supplying the cylinders with fuel, the control system comprising a control device (115) capable of: - determining a dilution rate of the oil by the fuel, - determining a maximum difference between a torque generated by one of the cylinders and an average torque (Cmoy) generated by all the cylinders, - determining an oil temperature (Th), and - implementing compensation for torque dispersions between the cylinders (C1, C2,C3) when the following conditions are met: - the determined oil dilution rate by the fuel is greater than a predetermined threshold value, - the determined maximum torque deviation is greater than a predetermined threshold value (x), and - the determined oil temperature (Th) is greater than a predetermined threshold value.,

10. Motor vehicle comprising: a spark-ignition internal combustion engine (102) comprising a plurality of cylinders (C1, C2, C3), a cylinder housing (109) containing oil, an air intake circuit (103) into the cylinders, a blow-by gas recirculation circuit (112) coming from the cylinder housing (109) connected to the air intake circuit (103), and a fuel supply circuit for the cylinders, and a control system according to claim 9.

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