Method for correcting the richness of an air / fuel mixture supplying an internal combustion engine

Abstract

The present invention relates to a method for correcting the richness of an air / fuel mixture supplying an internal combustion engine (1) in the period between the engine (1) being started and an oxygen sensor (6) positioned in an exhaust line (2) of the engine (1) reaching its operating temperature, which involves determining a richness setpoint (Cr) and, based on this setpoint (Cr), a quantity of fuel to inject into the engine (1), measuring, when the engine (1) is started, a temperature (T) representative of the thermal state of the engine (1), heating the oxygen sensor (6), characterised in that it involves determining, depending on the value of this representative temperature (T), a correction factor (Fcr) to be applied to the quantity of fuel to be injected, and applying this correction factor (Fcr) until the oxygen sensor (6) has reached its operating temperature.

Description

[0001] The present invention relates to the field of internal combustion engines. More particularly, the subject of the invention is a method for correcting the richness of an air and fuel mixture supplying an internal combustion engine in the period between starting the engine and reaching the operating temperature of an oxygen sensor positioned in an exhaust line of the engine.

[0002] The depollution of internal combustion engines requires increasingly precise richness regulation in order to meet increasingly stringent standards. These internal combustion engines are equipped with an exhaust system that integrates one or more depollution components such as a catalyst or a particulate filter and a richness sensor.

[0003] The control system associated with internal combustion engines includes a richness regulation based on measurements obtained by a probe called a lambda probe or oxygen sensor, present in the exhaust line. This probe measures the oxygen content of the burnt gases resulting from combustion.

[0004] However, the richness regulation is not active until this sensor has reached its operating temperature. However, a large part of the pollutants are produced during the first seconds following the start of a cold internal combustion engine and one of the reasons which explains these high emissions is the lack of control of the richness of the air / fuel mixture during this phase when the lambda sensor is not active.

[0005] Document FR-A-3 052 189 describes a method for recalibrating the behavior models of actuators of air intake and fuel injection lines of a motor vehicle internal combustion engine. The engine is equipped with controlled actuators.

[0006] The recalibration of the behavior models is done simultaneously for the actuators of the air intake and fuel injection lines at at least one operating point of the engine solely as a function of an air flow in each cylinder and a richness setpoint.

[0007] For camshaft timing and variable intake or exhaust valve lift actuators, the retiming is done according to a difference between an actual flow measurement and a model estimating the flow in each cylinder.

[0008] For an injector actuator, the recalibration is done according to a difference between an actual richness measurement and the richness setpoint.

[0009] However, this document does not provide any information on controlling the richness of the air / fuel mixture during a cold start of the internal combustion engine during which the richness sensor in the exhaust gases is inoperative.

[0010] Documents US2011010035A1 and JPH01219327 A also disclose methods for correcting the richness of an air and fuel mixture supplying an internal combustion engine in the period between starting the engine and reaching an operating temperature of an oxygen sensor positioned in an exhaust line of the engine.

[0011] Consequently, the problem underlying the invention is to correct the richness of the air / fuel mixture of a cold internal combustion engine when a richness sensor, present in the exhaust line of this engine, is inoperative because it has not yet reached its operating temperature, which does not allow the richness regulation loop to be activated.

[0012] To achieve this objective, the invention provides a method for correcting the richness of an air and fuel mixture supplying an internal combustion engine in the period between starting the engine and reaching the operating temperature of an oxygen sensor positioned in an exhaust line of the engine, in which: a richness setpoint is determined, and from this setpoint a quantity of fuel to be injected into the internal combustion engine, a temperature representative of the thermal state of the engine is measured at engine start, the oxygen sensor is heated, the time elapsed between the last engine stop and the start of start is calculated and the process is activated if this time is greater than a determined engine stop duration threshold for which the engine is considered to be sufficiently cooled, and if the process is activated, a corrective factor to be applied to the quantity of fuel to be injected determined from the richness setpoint is determined, and this corrective factor is applied until the oxygen sensor has reached its operating temperature,the corrective factor being determined from a map establishing this factor as a function of the temperature representative of the thermal state of the engine, , characterized in that: the temperature representative of the thermal state of the engine measured during start-up is stored, the time elapsed between the start of start-up and the oxygen sensor reaching its operating temperature is measured, and when the oxygen sensor has reached its operating temperature, a current corrective factor is determined from the difference between the richness setpoint and the richness determined from the measurement of the oxygen sensor, and the existing corrective factor associated with the measured temperature is replaced in the map by this current corrective factor, the replacement of the corrective factor being authorized only if the time elapsed between the start of the start and the oxygen sensor reaching its operating temperature is greater than a threshold of duration of operation of the oxygen sensor.

[0013] The technical effect is to obtain an adjustment of the actual richness of an air and fuel mixture supplying an internal combustion engine according to the thermal state of the engine when the richness regulation is inactive.

[0014] Various additional features may be provided, alone or in combination: According to one embodiment, the engine shutdown duration threshold determined for which the engine is considered to be sufficiently cooled is greater than one hour.

[0015] According to one embodiment, the mapping comprises several corrective factors, each of these factors establishing the correction for a determined range of the temperature representative of the thermal state of the engine.

[0016] According to one embodiment, the temperature representative of the thermal state of the engine is the engine coolant or the lubricating oil.

[0017] The invention also relates to an engine control unit, characterized in that it comprises the means of acquisition, of processing by software instructions stored in a memory as well as the control means required for implementing the method according to any one of the variants previously described.

[0018] The invention also relates to a vehicle comprising an internal combustion engine connected to an exhaust line equipped with an oxygen sensor, and comprising such an engine control unit.

[0019] Other features and advantages will appear on reading the following description of a particular, non-limiting embodiment of the invention, given with reference to the figures in which: [ Fig 1 ] shows a flowchart of the method for correcting the richness of the air / fuel mixture supplying an internal combustion engine according to the present invention. Fig 2 ] illustrates an example of mapping establishing the richness correction factor as a function of a temperature range representative of the thermal state of the engine.

[0020] There figure 1 shows an engine control unit 7 responsible for the operation of an internal combustion engine 1 opening onto an exhaust line 2 for evacuating exhaust gases from the internal combustion engine 1. The present invention is intended more particularly for a spark-ignition internal combustion engine, in particular fueled by gasoline or containing gasoline. The present invention can also be applied to a compression-ignition engine. The internal combustion engine can be integrated into a motor vehicle. The control unit 7 comprises the means of acquisition, processing by software instructions stored in a memory as well as the control means required for implementing the method of the invention detailed later.

[0021] The internal combustion engine 1 comprises actuators 3 managing the air loop such as for example an air metering butterfly valve and actuators 4 managing a fuel supply system. The exhaust line 2 comprises a pollution control system 5 and an oxygen sensor 6, which is operational only when it reaches a minimum operating temperature.

[0022] The engine control unit 7 comprises an air loop control module 8. The air loop control module 8 sends an intake air setpoint to the air loop actuators 3 of the internal combustion engine 1 and a fuel setpoint to the fuel supply system actuators 4 of the internal combustion engine 1.

[0023] The engine control unit 7 also comprises an adaptation module comprising an adaptive air loop sub-module 11 and an adaptive fuel injection model sub-module 10 in the engine 1.

[0024] The adaptive air loop sub-module 11 communicates with the air loop actuators 3 of the engine 1 and the adaptive fuel injection pattern sub-module 10 in the engine 1 communicates with the fuel system actuators 4 of the engine 1.

[0025] The engine control unit 7 also includes a richness regulation module 13 of the air / fuel mixture, a selector 9 which can alternate between a first position when the oxygen sensor 6 present in the exhaust line 2 is operational (position of the cursor of the selector 9 shown in dotted lines on the figure 1 ) and a second position when the oxygen sensor 6 is not operational (position of the selector cursor 9 shown in solid line on the figure 1 ).

[0026] The engine control unit 7 also includes a module for determining a richness setpoint 14 of the air / fuel mixture. This module communicates with the actuators of the fuel supply system 4 of the engine 1 by sending a richness setpoint, Cr, of the air / fuel mixture to the actuators of the fuel supply system 4 of the engine 1. This richness setpoint, Cr, makes it possible to determine a quantity of fuel to be injected.

[0027] The selector 9 communicates with the actuators of the fuel supply system 4 of the engine 1 by also sending a corrective factor, Fcr, for the richness of the air / fuel mixture to the actuators of the fuel supply system 4 of the engine 1. Depending on the position of the selector 9, the corrective factor, Fcr, for the richness of the air / fuel mixture will come from the richness regulation module 13 (first position) or from the richness correction module 12 (second position). This corrective factor, Fcr, makes it possible to modify the quantity of fuel to be injected determined from the richness setpoint, Cr.

[0028] The engine control unit 7 also comprises a richness correction module 12 which will be detailed later in more detail for the implementation of the method of the invention for correcting the richness of the air / fuel mixture supplying the engine 1 during start-up, during the phase where the oxygen sensor 6 is not operational.

[0029] The richness correction method according to the invention takes place when the internal combustion engine 1 is started, between the instant of start and the subsequent instant when the oxygen sensor has reached its operating temperature, which makes it operational and then allows the richness regulation module 13 to be activated.

[0030] Thus, during a start, the module 14 determines a richness setpoint, Cr, and the heating of the oxygen sensor is activated. However, as long as the oxygen sensor 6 is not operational, the selector 9 is positioned in its second position. A richness correction factor, Fcr, is then provided by the richness correction module 12.

[0031] In this case, a temperature T representative of the thermal state of the engine 1 is measured. This temperature T can be that of the coolant or the engine lubricating oil. This temperature T is supplied to the richness correction module 12 which determines, as a function of the value of this temperature representative of the thermal state of the engine 1, the corrective factor, Fcr, to be applied to the quantity of fuel to be injected determined from the richness setpoint Cr.

[0032] This corrective factor, Fcr, determined by the richness correction module 12 is applied until the oxygen sensor 6 has reached its operating temperature. When the oxygen sensor 6 reaches its operating temperature, the selector 9 switches to its first position and the corrective factor Fcr to be applied to the quantity of fuel to be injected determined by the richness setpoint Cr is now supplied by the richness regulation module 13 which receives the measurement from the oxygen sensor 6.

[0033] For reasons of speed and simplicity of calculation, it is possible to determine the corrective factor, Fcr, from a map establishing this factor as a function of the measured temperature T.

[0034] As illustrated by the figure 2 , we can predict a mapping including several corrective factors (Fcr1 to Fcr5 on the figure 2 ) each of these factors establishing the richness correction for a given temperature range of the parameter representing the thermal state of engine 1. The precision of determining the correction factor is further improved, which is crucial during the starting phase of engine 1.

[0035] In the example illustrated in figure 2 if the temperature T is lower than a minimum temperature T1, the richness correction factor Fcr1 is selected. If the temperature T is in the temperature range respectively between T1 and T2, or between T2 and T3, or between T3 and T4, the selected richness correction factor will be respectively Fc2, Fc3, Fc4. Finally, if the temperature T is higher than the maximum temperature T4, the richness correction factor Fcr5 is selected.

[0036] It is possible to provide for conditioning the restitution of the richness correction factor, Fcr, by the richness correction module 12 on the time elapsed between the last shutdown of engine 1 and the start of starting. During this time, the vehicle and therefore engine 1 are subject only to the outside temperature. While engine 1 is stopped, the engine 1 cools down and its temperature tends towards the outside temperature if the time elapsed between the last shutdown of engine 1 and the start of starting is sufficiently long.

[0037] In this case, the correction process is activated if the time elapsed between the last shutdown of engine 1 and the start of the start is greater than a determined engine shutdown duration threshold, a duration threshold for which the engine is considered to be sufficiently cooled. This engine shutdown duration for which the engine is considered to be sufficiently cooled can be a duration greater than 1 hour.

[0038] If the time elapsed between the last stop of engine 1 and the start of the start is less than this time, a correction factor equal to 1 (neutral) can be applied.

[0039] It can also be provided that the correction module 12 can update the mapping through learning, which allows regular adjustment of the wealth correction factor.

[0040] In this case, the temperature T representative of the thermal state of the engine (1) is stored, measured during start-up. Then, when the oxygen sensor 6 has reached its operating temperature, the richness regulation module then being active, a current corrective factor is determined from the difference between the richness setpoint Cr and the richness determined from the measurement of the oxygen sensor 6, and the existing corrective factor associated with the measured temperature T is replaced in the map by this current corrective factor.

[0041] It is possible to condition this learning of the corrective factor by the richness correction module 12 on the time taken by the probe to be operational and on the time elapsed between the last shutdown of engine 1 and the start of the start. In this case, the time elapsed between the start of the start and the oxygen probe 6 reaching its operating temperature is measured and the time elapsed between the last shutdown of engine 1 and the start of the start is calculated.

[0042] Thus, if the time elapsed between the start of the start and the oxygen sensor 6 reaching its operating temperature is greater than a start-up time threshold and if the time elapsed between the last shutdown of engine 1 and the start of the start is greater than a determined engine shutdown time threshold, then the corrective factor existing in the map is replaced.

[0043] The operating time threshold can be between a few seconds, for example 5 seconds, and a few minutes, for example 5 minutes, while the engine shutdown time threshold is greater than 1 hour. Indeed, it takes a few seconds to heat the probe 6 if drying the line is not necessary, while it takes a few minutes if it is necessary to wait until the line is dry, in the case where the probe 6 can break upon contact with liquid water during its heating.

[0044] The learning function allows the richness to be brought closer to the desired value engine by engine and therefore helps reduce pollutant emissions.

[0045] The invention makes it possible to reset the richness of the air / fuel mixture when cold and only when cold, when the richness regulation is not activated because the oxygen sensor is not operational. The invention therefore makes it possible to reduce pollutant emissions during this phase when the richness regulation is not activated. The invention, not being based on a physical model, is generalizable to all systems and makes it possible to reset any dispersion which could lead to a richness difference.

Claims

1. Method for correcting the richness of an air and fuel mixture supplying an internal combustion engine (1) in the period between starting the engine (1) and reaching the operating temperature of an oxygen sensor (6) positioned in an exhaust line (2) of the engine (1), in which: - is determined, and from this setpoint (Cr) a quantity of fuel to be injected into the internal combustion engine (1), - when starting the engine (1), a temperature (T) representative of the thermal state of the engine (1) is measured, - the oxygen sensor (6) is heated, - is calculated and the process is activated if this time is greater than an engine stop time threshold. determined for which the engine is considered to be sufficiently cooled, and if the process is activated, - we determine according to the value of this representative temperature (T) of the thermal state of the engine (1), a corrective factor (Fcr) to be applied to the quantity of fuel to be injected determined from the richness setpoint (Cr) and we apply this factor corrective factor (Fcr) until the oxygen sensor (6) has reached its operating temperature, the corrective factor (Fcr) being determined from a map establishing this factor as a function of the temperature (T) representative of the thermal state of the engine (1), characterized in that: - the temperature (T) representative of the thermal state of the engine (1) measured during start-up is stored, - we measure the time elapsed between the start of the startup and the probe reaching oxygen (6) from its operating temperature, and when the oxygen sensor (6) has reached its operating temperature, - is determined from the difference between the richness setpoint (Cr) and the richness determined from the measurement of the oxygen sensor (6), - replaced by this current corrective factor, the replacement of the corrective factor (Fcr) being authorized only if the time elapsed between the start of the startup and the probe reaching oxygen (6) of its operating temperature is greater than a threshold of duration of operation of the oxygen sensor (6).

2. Method according to claim 1, characterized in that the determined engine shutdown duration threshold for which the engine is considered to be sufficiently cooled is greater than one hour.

3. Method according to claim 1 or 2, characterized in that the mapping comprises several corrective factors (Fcr1, Fcr2, Fcr3, Fcr4, Fcr5), each of these factors establishing the correction for a determined range of the temperature (T) representative of the thermal state of the engine (1).

4. Method according to any one of the preceding claims, characterized in that the temperature (T) representative of the thermal state of the engine (1) is the engine coolant or the lubricating oil.

5. Engine control unit (7), characterized in that it comprises the means of acquisition, processing by software instructions stored in a memory as well as the control means required for implementing the method according to any one of the preceding claims.

6. Vehicle comprising an internal combustion engine (1) connected to an exhaust line (2) equipped with an oxygen sensor (6), characterized in that it comprises an engine control unit (7) according to the preceding claim.

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