Method for calculating the dilution ratio of a fuel in the oil of a spark-ignition internal combustion engine associated with at least one electrical machine

Abstract

This method for calculating the dilution ratio of a fuel in the oil of a spark-ignition internal combustion engine (2) capable of driving at least one wheel of the motor vehicle, said engine (2) being associated with at least one electric machine, comprises the steps of: - calculating a change (ΔM) in the mass of fuel diluted in an oil bath (14) of the engine (2) by a time integral of the difference between a first quantity of fuel (Q_in) added to the oil bath and a second quantity of fuel (Q_out) removed by evaporation, - updating a stored value of the mass of diluted fuel (M_fuel_oil) as a function of the calculated change (ΔM), - calculating the dilution ratio (Td) as a function of the ratio between the updated mass of diluted fuel (M_fuel_oil) and a mass of oil (M_oil) in the oil bath. Figure for the abbreviation: Figure 2

Description

Title of the invention: Method for calculating a dilution rate of a fuel in an oil of a spark-ignition internal combustion engine associated with at least one electric machine Technical field

[0001] The invention relates to a method for estimating oil dilution applied to hybrid gasoline or equivalent engines in which a heat engine is combined with reversible electric machines. It also relates to a spark-ignition internal combustion engine capable of implementing such a method. Prior art

[0002] Many modern engines are equipped with exhaust gas treatment devices, which operate sequentially. Most diesel engines, for example, are equipped with a particulate filter. In normal operation, these devices trap pollutants but do not treat them. Periodically, when a parameter representative of the quantity of accumulated pollutants reaches a predefined value, a so-called regeneration phase is triggered by an engine computer, during which the engine settings are modified to treat and eliminate the pollutants.

[0003] In a known manner, regeneration is generally obtained by supplying fuel to the device, for example by late post-injections into the engine cylinders. Thus, quantities of fuel are injected into each cylinder long enough after the top dead center of combustion of the cylinder so that they do not participate in the combustion. These quantities of fuel are evacuated from the engine, during the exhaust time of the cylinder in question, to the gas treatment device to regenerate it, that is to say to purge it of accumulated pollutants.

[0004] However, a fraction of the fuel injected during the regeneration phases penetrates into the oil, in particular through the gaps between the cylinder block and the pistons, and it is diluted in the oil.

[0005] The dilution, that is to say the rate of fuel contained in the oil, thus increases each time a regeneration phase is triggered.

[0006] To avoid engine reliability problems, such as premature wear of the cylinder block barrels or crankshaft bearings, a maximum dilution threshold of around 10% should never be exceeded, because such dilution greatly reduces the viscosity of the oil and therefore its lubricating power.

[0007] For diesel engines equipped with a particulate filter, it is known to use a Oil control system or OCS for "OU Control System" in English, embedded in an engine computer, which estimates the dilution level of the oil bath and alerts the driver that an oil change is necessary as soon as the maximum dilution threshold is reached. Calibrating such a system is long and expensive because it requires numerous laboratory tests using samples from the oil bath.

[0008] For non-hybrid gasoline engines, although dilution may appear after cold starts and then during the heating phase of the three-way catalysts, it disappears quickly under the effect of evaporation, as soon as the oil bath is hot, and the dilution never reaches the maximum threshold. In addition, when non-hybrid gasoline engines are equipped with particulate filters, active regenerations, i.e. induced regenerations of the filter, are rare and do not cause significant dilutions, because the driving conditions are sufficient to cause spontaneous combustion of the particles accumulated in the filters.

[0009] However, dilution becomes problematic for hybrid gasoline or equivalent engines covered by the invention, i.e. engines which combine a thermal engine running on gasoline (or with a mixture of gasoline and ethanol, or even pure ethanol) with at least one electric machine which can operate in engine mode.

[0010] Indeed, these engines often keep the thermal engine off, because we generally seek to minimize its use to reduce fuel consumption in favor of the vehicle moving forward alone using the electric machine(s).

[0011] Thus, in critical cases such as a succession of short journeys in town in a cold environment, for example at 0°C, the heat engine generally does not reach a minimum temperature of the order of 40-50°C necessary to be able to evacuate by evaporation the gasoline accumulated in the oil bath. In addition, it is usual in cold ambient conditions to take calories from the heat engine to heat the passenger compartment, which cools the engine even more. Under these conditions, the dilution level can increase until it exceeds the maximum acceptable threshold in terms of engine reliability.

[0012] In order to ensure engine reliability, it is possible either to set oil change intervals in advance or to use an OCS type system to estimate the dilution ratio and alert the driver of the need to carry out an oil change.

[0013] However, these solutions have serious drawbacks. For example, oil change intervals set in advance generate additional maintenance costs, because oil changes are carried out even if they are not really necessary. For example, the calibration of OCS type systems known from the prior art is a long and expensive procedure as indicated previously. Statement of the invention

[0014] The invention proposes to remedy the aforementioned drawbacks by aiming at a method for calculating a fuel dilution rate based on a simple, precise and robust calculation model of the dilution, applied to hybrid engines comprising a spark-ignition internal combustion engine associated with at least one electric machine capable of operating in a motor mode.

[0015] The subject of the invention is a method for calculating a dilution rate of a fuel in an oil of a spark-ignition internal combustion engine capable of driving at least one drive wheel of a motor vehicle, said engine being associated with at least one electrical machine capable of operating in a motor mode in which said electrical machine contributes to the drive torque of the vehicle.

[0016] The method comprises steps of: - calculation of a variation in a mass of fuel diluted in an engine oil bath by a time integral of the difference between a first quantity of fuel which is added to the oil bath and a second quantity of fuel which is subtracted from it by evaporation, - updating a stored value of the mass of fuel diluted in the engine oil bath according to the calculated variation, and - calculation of the dilution ratio based on the ratio between the updated mass of fuel diluted in the engine oil bath and a mass of oil in the engine oil bath.

[0017] Such a method makes it possible to know precisely the dilution ratio in the engine, thus avoiding endangering the reliability of the engine or unnecessarily increasing the maintenance costs of the engine. In addition, such a method is easy to implement, since it does not require prior calibration.

[0018] Advantageously, the first quantity of fuel which is added to the oil bath is obtained by a fuel balance from a flow rate of injected fuel and a flow rate of burned fuel which is found in the exhaust. Such a fuel balance represents a simple, precise and robust method of estimating the first quantity of fuel which is added to the oil bath.

[0019] For example, the flow rate of burnt fuel which ends up in the exhaust is equal to the product between a richness measured at the exhaust and a ratio between an intake air flow rate and the value of the combustion power of the engine fuel.

[0020] Advantageously, the second quantity of fuel which evaporates is obtained from an evaporation model in which the evaporation rate of the fuel is proportional to its instantaneous concentration. Such an evaporation model represents a simple and effective estimation method.

[0021] Preferably, a measurement of the temperature of an engine coolant is used to calculate the second quantity of fuel that evaporates. This is because the temperature of the coolant is closer to the temperature of the fuel evaporation surface than the temperature of the core oil that is conventionally used.

[0022] In addition, the method further comprises a step of transmitting an alert message when the calculated dilution ratio exceeds a predetermined threshold value representative of a risk to the reliability of the engine. Such a step promotes the protection of the engine.

[0023] For example, the method further comprises a prior step of initializing the mass of fuel diluted in the engine oil bath either to a zero value if the oil is new, or to a value previously stored in an engine computer otherwise. Such a method allows continuous monitoring of the dilution and promotes engine protection.

[0024] According to one characteristic, the time integral is calculated with a time step of predetermined duration.

[0025] According to another aspect, the invention relates to a motor vehicle equipped with a spark-ignition internal combustion engine capable of driving at least one drive wheel of the motor vehicle, the engine being associated with at least one electric machine capable of operating in a motor mode in which the electric machine contributes to the drive torque of the vehicle.

[0026] The engine is provided with means of: - calculation of a variation in a mass of fuel diluted in an engine oil bath by a time integral of the difference between a first quantity of fuel which is added to the oil bath and a second quantity of fuel which is subtracted from it by evaporation, - updating a stored value of the mass of fuel diluted in the engine oil bath according to the calculated variation, and - calculation of a dilution ratio based on the ratio between the updated mass of fuel diluted in the engine oil bath and a mass of oil in the engine oil bath. Brief description of the drawings

[0027] Other aims, characteristics and advantages of the invention will appear on reading the following description, given solely by way of non-limiting example, and made with reference to the appended drawings in which:

[0028] [Fig.l] is a schematic plan view of a hybrid gasoline engine device capable of implementing a method according to the invention;

[0029] [Fig.2] schematically illustrates a heat engine of the hybrid motorization device of [Fig.l]; and

[0030] [Fig.3] is a flowchart of a method for calculating a dilution rate of a fuel in an oil of the engine of [Fig.2] according to an embodiment of the invention. Detailed description of at least one embodiment

[0031] [Fig.l] schematically illustrates a hybrid motorization device 1 known in itself, in particular mounted on a motor vehicle.

[0032] The hybrid motorization device 1 comprises a thermal engine 2 with internal combustion and controlled ignition, associated with at least one electric machine, here, a first electric machine 3 and a second electric machine 4.

[0033] The heat engine 2 produces engine torque, which results from the combustion of a mixture of fresh air and fuel. The fuel is gasoline, a mixture of gasoline and ethanol, or even pure ethanol.

[0034] The electrical machines 3, 4 are capable of operating in “generator” mode under the supervision of a control box not shown. Furthermore, at least the first electrical machine 3 is capable of operating in “motor” mode. In other words, the first electrical machine is reversible. However, it is not essential for implementing the method according to the invention that the second electrical machine 4 be capable of operating in “motor” mode.

[0035] In “generator” mode, an electrical machine 3, 4 is an alternator which supplies an electric current intended to be stored in a storage battery not shown.

[0036] In “motor” mode, the first electric machine 3 is on the contrary powered by current previously stored in the accumulator battery and provides engine torque which can be transmitted to the wheels of the vehicle, in addition to or replacing the torque provided by the thermal engine 2.

[0037] The motorization device 1 is associated with a transmission system 5 making it possible to transmit to the wheels 6 the torque supplied by the motorization device 1. The motorization device 1 is adjusted in such a way that the torque which it supplies reaches a set torque value, or required torque, corresponding to the “driver's desire to accelerate”, materialized for example by a value of the depression of an accelerator pedal of the vehicle or the pressure exerted on said pedal.

[0038] The transmission system 5 comprises in particular a gearbox 7, a differential axle 8 and a transmission shaft 9. The gearbox is connected to the engine thermal 2 and to the electrical machines 3, 4 on the one hand, and on the other hand to the wheels 6 via the differential 8 and the transmission shaft 9.

[0039] The engine 2 comprises an engine control computer 10 configured to control the different elements of the thermal engine 2 from data collected by sensors at different locations of the engine 2.

[0040] [Fig.2] illustrates in a simplified manner the heat engine 2 of [Fig.l]. Such an engine is suitable for implementing a method for calculating a fuel dilution rate in an oil bath of the engine according to the invention.

[0041] The thermal engine 2 is here a three-cylinder in-line engine comprising one injector 11 per cylinder. The engine comprises a top engine 12 comprising a cylinder head and a cylinder block, the bottom of which is closed by an oil sump 13. The oil sump 13 contains an oil bath 14 for lubricating the engine 2 and which also collects crankcase gases, also known as “blow-by” gases.

[0042] During operation of the engine, a portion Q_in of the fuel injected Q_inj by the injectors 11 passes from the top of the engine into the oil sump 13, thus increasing the mass of fuel M_fuel_oil present in the oil bath 14 of the engine 2.

[0043] Conversely, a portion Q_out of the fuel present in the oil bath 14 is removed therefrom by evaporation through a degassing circuit 15 of the oil sump 13 opening into an air intake circuit 16, downstream of an intake flap or throttle body 17.

[0044] The air intake circuit 16 comprises, upstream of the throttle body 17, a flow meter 18 configured to measure the intake air flow rate Q_air. Alternatively, the flow rate can be estimated from the pressure and temperature in an intake manifold of the engine, not shown, and from a filling model.

[0045] The engine 2 comprises an exhaust circuit 19 for the burnt gases provided with a probe 20 adapted to measure the richness Ri_exh at the exhaust. For example, the measurement of the richness Ri_exh allows the computer 10 to adjust in a closed loop the richness of the air-fuel mixture to a set value, generally unitary, by adjusting the quantity of fuel injected.

[0046] The engine 2 may have other specific features depending on the configurations, without departing from the scope of the invention. For example, the engine may be of the supercharged type. For example, the engine may be equipped with one or more partial exhaust gas recirculation circuits at the intake.

[0047] [Fig. 3] illustrates a flowchart of a method for calculating a dilution rate Td of fuel in the oil of the engine 2 according to an exemplary implementation of the invention.

[0048] The method begins with a preliminary step 21 of initializing the mass of fuel in the engine oil M_fuel_oil to a zero value if the oil is new, or to a value previously stored in the computer 10 of engine 2 otherwise.

[0049] The method continues with a step 22 of calculating a variation AM of a mass of fuel diluted in the oil bath 14 of the engine 2. The computer 10 calculates the variation AM by a time integral of the difference between a first quantity of fuel Q_in which is added to the oil bath 14 and a second quantity of fuel Q_out which is subtracted from it by evaporation.

[0050] Preferably, the time integral is calculated with a time step dt of predetermined duration, for example of the order of 100 milliseconds.

[0051] The first quantity of fuel Q_in is obtained by a fuel balance from an injected fuel flow rate Q_inj and a burnt fuel flow rate found in the exhaust Q_exh. In other words, the flow rate of the fuel introduced into the oil 14 is the difference between the fuel flow rate found in the exhaust and the injected fuel flow rate.

[0052] Preferably, the value of the injected fuel flow rate Q_inj is directly available in the computer 10.

[0053] The value of the flow rate of burnt fuel which is found at the exhaust Q_exh is equal to the product between the richness Ri_exh measured at the exhaust by the probe 20 and a ratio between the intake air flow rate Q_air and the value of the combustion power Ks of the fuel of the engine 2.

[0054] By comburivorous power of a fuel is meant the ratio between the quantity of air and the corresponding mass of fuel for complete combustion. This ratio is also called mass stoichiometric relationship.

[0055] The second quantity of fuel Q_out is obtained from an evaporation model in which the evaporation rate of the fuel is proportional to its instantaneous concentration.

[0056] For example, fuel evaporation is modeled by a first-order kinetic law, in which the fuel evaporation rate is equal to the opposite of the product between a rate parameter k of the evaporation reaction and the instantaneous value of the dilution.

[0057] In a known manner, the speed parameter k of such a reaction depends on the evaporation temperature T and the activation energy Ea of the reaction, i.e. the enthalpy of vaporization of the fuel according to the following equation:

[0058] k = k^W

[0059] In which: - k0 is a predetermined speed constant, - R denotes the ideal gas constant, and - T denotes a value representative of the evaporation temperature of the fuel.

[0060] The activation energy or evaporation enthalpy Ea is a function that depends on the composition of the fuel, more precisely on the proportion of heavy hydrocarbons contained in the fuel. This proportion increases over time, with the lightest hydrocarbons evaporating first.

[0061] It should be noted that the time step dt for calculating the integral is chosen to be small enough so that the evaporation enthalpy Ea can be considered constant. For example, it can be considered that the variation in the evaporation enthalpy Ea is negligible over a period of a few minutes.

[0062] Advantageously, the representative value of the fuel evaporation temperature T is not the core oil temperature as it is conventionally measured or estimated on engines, but rather the temperature of the coolant, called water temperature, circulating in the engine 2. This temperature is in fact closer to the temperature of the fuel evaporation surface. It can be measured by a sensor, not shown in the figures.

[0063] The method continues with a step 23 of updating a value stored in a memory of the computer 10 of the mass of diluted fuel M_fuel_oil in the oil bath 14 of the engine 2 as a function of the calculated variation AM.

[0064] The computer 10 then proceeds to calculate the dilution ratio Td as a function of the ratio between the updated mass M_fuel_oil of fuel diluted in the oil bath 14 of the engine and the mass of oil M_oil of the oil bath 14 of the engine 2 (step 24). Preferably, the mass of oil M_oil of the oil bath 14 of the engine 2 is available in the computer 10. For example, the engine 2 is provided with means for measuring the mass of oil M_oil of the oil bath 14 adapted to transmit the value of M_oil to the computer 10.

[0065] The method further comprises a step 25 of issuing an alert message when the calculated dilution rate Td exceeds a predetermined threshold value representative of a risk to the reliability of the engine 2. For example, an alert may be issued on the dashboard of the motor vehicle to alert the driver that the threshold value has been exceeded.

Claims

Claims

1. Method for calculating a dilution rate (Td) of a fuel in an oil of a spark-ignition internal combustion engine (2) capable of driving at least one drive wheel (6) of a motor vehicle, said engine (2) being associated with at least one electric machine (3) capable of operating according to a motor mode in which said electric machine (3) contributes to the drive torque of the vehicle, characterized in that said method comprises steps of: - calculating a variation (AM) of a mass of fuel diluted in an oil bath (14) of the engine (2) by a time integral of the difference between a first quantity of fuel (Q_in) which is added to the oil bath (14) and a second quantity of fuel (Q_out) which is subtracted therefrom by evaporation, - updating a stored value of the mass of diluted fuel (M_fuel_oil) in the oil bath (14) of the engine (2) as a function of the variation (AM) calculated,and - calculating the dilution ratio (Td) as a function of the ratio between the updated mass of diluted fuel (M_fuel_oil) in the oil bath (14) of the engine and a mass of oil (M_oil) in the oil bath (14) of the engine (2).,

2. Method according to claim 1, in which the first quantity of fuel (Q_in) which is added to the oil bath (14) is obtained by a fuel balance from a flow rate of injected fuel (Q_inj) and a flow rate of burned fuel which ends up in the exhaust (Q_exh).

3. Method according to claim 2, in which the flow rate of burnt fuel which ends up at the exhaust (Q_exh) is equal to the product between a richness (Ri_exh) measured at the exhaust and a ratio between an intake air flow rate (Q_air) and the value of the comburivorous power (Ks) of the fuel of the engine (2).

4. A method according to any one of claims 1 to 3, wherein the second quantity of fuel (Q_out) which evaporates is obtained from an evaporation model in which the evaporation rate of the fuel is proportional to its instantaneous concentration.

5. A method according to any one of claims 1 to 4, wherein uses a measurement of the temperature of an engine coolant (2) to calculate the second quantity of fuel (Q_out) that evaporates.

6. Method according to any one of claims 1 to 5, further comprising a step of transmitting an alert message when the calculated dilution rate (Td) exceeds a predetermined threshold value representative of a risk to the reliability of the engine (2).

7. Method according to any one of claims 1 to 6, further comprising a prior step of initializing the mass of diluted fuel (M_fuel_oil) in the oil bath (14) of the engine (2) either to a zero value if the oil is new, or to a value previously stored in a computer (10) of the engine (2) otherwise.

8. Method according to any one of claims 1 to 7, in which the time integral is calculated with a time step (dt) of predetermined duration.

9. Motor vehicle equipped with a spark-ignition internal combustion engine (2) capable of driving at least one drive wheel (6) of said motor vehicle, said engine (2) being associated with at least one electric machine (3) capable of operating according to a motor mode in which said electric machine (3) contributes to the driving torque of the vehicle, characterized in that said engine (2) is equipped with means for: - calculating a variation (AM) of a mass of diluted fuel (M_fuel_oil) in an oil bath (14) of the engine (2) by a time integral of the difference between a first quantity (Q_in) of fuel which is added to the oil bath (14) and a second quantity of fuel (Q_out) which is subtracted therefrom by evaporation, - updating a stored value of the mass of diluted fuel (M_fuel_oil) in the oil bath (14) of the engine (2) as a function of the calculated variation (AM),and - calculating a dilution ratio (Td) as a function of the ratio between the updated mass of diluted fuel (M_fuel_oil) in the oil bath (14) of the engine (2) and a mass of oil (M_oil) of the oil bath (14) of the engine (2),

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