WO2018167406A1

WO2018167406A1 - Method for adjusting richness in a controlled-ignition internal combustion engine

Info

Publication number: WO2018167406A1
Application number: PCT/FR2018/050558
Authority: WO
Inventors: David ISSARTEL
Original assignee: Renault S.A.S
Priority date: 2017-03-16
Filing date: 2018-03-09
Publication date: 2018-09-20
Also published as: RU2752657C2; JP7575873B2; EP3596326B1; FR3064030A1; JP2023182629A; KR20190126362A; JP2020510160A; RU2019132476A; RU2019132476A3; FR3064030B1; EP3596326A1

Abstract

The invention proposes a method for adjusting richness (r) in a controlled-ignition internal combustion engine, capable of limiting the temperature of the parts constituting the exhaust circuit during operation at high load. During operation at close to full load, the richness is adjusted to a first richness value (r1) in order to pre-cool the exhaust gases. When the temperature of the exhaust gases (θech) reaches a first temperature threshold (θ1), which is lower than a second temperature threshold (θ2) corresponding to a reliability limit of the parts, the richness value is gradually increased, for example linearly, from the first richness value (r1) to, at a maximum, a second richness value (r2), at which the temperature of the exhaust gases is equal to the second temperature threshold (θ2). If the temperature of the exhaust gases (θech) reaches said second threshold (θ2) before the richness has reached the second richness value (r2), the richness is immediately adjusted to said second richness value (r2).

Description

METHOD OF ADJUSTING WEEK IN A COMBUSTION ENGINE

INTERNAL IGNITION CONTROL

TECHNICAL FIELD OF THE INVENTION

The invention relates to a method for controlling the richness of the air-fuel mixture in an internal combustion engine of the spark ignition type (operating in particular with gasoline). It finds an advantageous application in the automotive field.

STATE OF THE ART

In internal combustion engines of the spark-ignition type (operating on gasoline), more particularly those of motor vehicles, it is known to determine the richness of the air-fuel mixture as a function of a set of engine operating parameters. comprising at least the engine speed and the torque required for driving the vehicle. The load, or amount of air admitted into the engine, is adjusted in particular by the degree of opening of a throttle body of the engine, and the richness is adjusted according to said load by adjusting the fuel injection time in the engine.

It is known in itself to adjust the value of richness of such an engine around the stoichiometric value, that is to say around the wealth 1, on most points of operation of the engine, so as to allow the cleaning of the combustion gases of the engine by a catalyst of the three-way type mounted at the exhaust of the engine. For example by regulating the closed-loop richness by using the indications of at least one oxygen sensor mounted at the inlet of the catalyst, said catalyst is operated in its catalytic window, in which it reduces the oxides of nitrogen (NOx) produced in the engine's combustion gases, and it oxidizes unburnt hydrocarbons (HC) and carbon monoxide (CO).

However, it is also known that in the vicinity of the full load, the parts that make up the exhaust system of the engine can reach very high temperatures that can reduce their mechanical strength and jeopardize the reliability of the vehicle. To limit the temperature at the exhaust, the air-fuel mixture is generally enriched, for example at values of richness which may be greater than 1, 20, when it is detected that a value of torque (or load) above a predetermined threshold is required for driving the vehicle.

The value of richness to be adjusted to obtain a given maximum exhaust temperature, for example a given exhaust manifold temperature value or a temperature value of a given turbocharger turbine (in the case of a supercharged engine ), can be determined by prior tests performed on the engine bench in stabilized mode, that is to say, by maintaining constant speed and torque. In fact, the value of the richness is regulated so that the temperature of the exhaust gas itself is equal to a given predetermined value, this value becoming that of the components of the exhaust system of the engine after a certain lapse of time which is related to the inertia of matter.

Several methods of adjusting the richness of a motor vehicle engine are known from the state of the art in which the richness is increased to a value greater than 1 when the engine load reaches a value close to the full load.

For example, the publication JP-S-6043144 discloses a method of adjusting the fuel injection time, according to the operating conditions of an engine, which is intended to prevent the exhaust system from overheating. When a load greater than a threshold is detected, a temperature sensor measures the temperature of the exhaust gas, and the richness is increased after a predetermined delay time which is a decreasing function of said gas temperature.

The delay is to avoid unnecessary fuel consumption. Indeed, it is not necessary to increase the wealth immediately as soon as a high load is detected, because the parts that make up the exhaust system have a certain heat capacity and are therefore not instantly brought to temperatures below 20 ° C. limits for their reliability by the heat coming from the exhaust gases when the engine is running at high load. This property can thus be used to delay the increase in wealth without jeopardizing the reliability of the engine, which in principle saves fuel.

However, this method is imprecise because the temperature measured by the sensor after the detection of a high load does not correctly represent the temperature of the parts of the engine exhaust circuit at the same time. More specifically, the temperature of the parts depends on the amount of heat that has been supplied to said parts before the high load is detected, and it is all the higher a high amount of heat energy has been supplied to said parts.

Thus, if the delay time is decreased when the measured gas temperature is higher, a situation can be encountered in which the wealth is increased almost immediately, although the temperature of the exhaust system parts has not yet increased. up to the value of the measured gas temperature, so it is not necessary to change the wealth at that time. Fuel consumption is therefore unnecessarily degraded.

Also known from US-A-5239965 a wealth control method in which the application of an increased value of the richness during a delay time is delayed, which is a function of the thermal conditions of the parts of the circuit. exhaust, said conditions being measured by dedicated measuring means.

Specifically, it is detected whether the engine load is greater than a high reference load (designated by the acronym PMOTP1), which is used to determine if the exhaust system parts are in high load thermal conditions. If the test is positive, it indicates that the temperature of the parts increases because of the heat coming from the exhaust gases, and that the parts can be brought to overheat in the absence of an increase of the richness.

Under these conditions of high load, the value of a delay counter (designated by the acronym COTPCY) is regularly incremented, which represents the proportions in which the temperature of the parts of the exhaust circuit has been high, because of the heat of the gases, before the detection of the high load, and comparing the value of said counter with a reference delay threshold (designated by the acronym QAOTP), which is pre-calibrated according to the air flow in the engine. The delay threshold is a decreasing function of the flow rate.

As long as the value of the meter is below the threshold, it is considered that the parts of the exhaust circuit will not overheat in the very near future, and no enrichment measurement is implemented. On the other hand, when the value of the counter is greater than the threshold, the value of the counter is fixed on the value which it takes at the precise moment when the threshold is exceeded, and one immediately increases the wealth.

Such a method requires an important work of pre-calibration of the delay thresholds. In addition, only the air flow in the motor is taken into account to fix them. The inaccuracies on the selected thresholds result either in a risk of Exceeding the permissible temperature (if the threshold is too high, leading to an enrichment that is too late), or fuel consumption too high (case of too low a threshold, which leads to an enrichment too early).

US-A-4400944 discloses a method of adjusting the wealth which aims to prevent thermal malfunctions of the turbocharger of an engine, particularly at high speed and high load where the engine is adjusted with a feedrate to the engine. ignition very delayed, which promotes high temperatures of the turbocharger.

According to this document, when the temperature of the exhaust gas passing through the turbocharger is lower than a predetermined target value (designated by T1), and said temperature increases over time, the richness is set in open loop, adding a correction of fuel injection time at the injection time corresponding to a stoichiometric mixture, the correction being a function of the difference between the temperature and the temperature target.

On the other hand, when the temperature is lower than the target, the mixture is rich, and the temperature decreases over time, the richness is adjusted by subtracting a fuel injection time correction at the corresponding injection time to the stoichiometric mixture.

Such a method, in which the richness is variable, makes it possible to control the temperature of the exhaust gases on a target value, and does not require any work of choice of a delay time to increase the wealth to a value greater than 1. But it includes phases in which the target is exceeded, which can lead to loss of reliability of the components of the exhaust system, overconsumption of fuel and an increase in pollutant emissions of the engine.

SUMMARY OF THE INVENTION

The invention proposes to remedy the defects of the known methods of adjusting the richness.

It is more particularly to provide a wealth control method capable of protecting the exhaust system of the engine against excessive temperatures which is simple to implement, and which limits the overconsumption of engine fuel without significantly degrading pollutant emissions.

It proposes for this a method of adjusting the richness of a motor to internal combustion with positive ignition, the value of the richness being regulated around the stoichiometric value when the engine is not operating near the full load, and around a value higher than the stoichiometric value when the engine torque is higher at a torque threshold less than or equal to the maximum torque of the engine.

The method is characterized in that it comprises, when said torque is greater than said torque threshold:

A step during which said value of richness is set to a first value of richness greater than the stoichiometric value, when a value of temperature of the engine exhaust gases is lower than a first temperature threshold;

A step during which said value of richness is immediately set to a second value of richness greater than the first value of richness, when said value of temperature is greater than a second temperature threshold, said second temperature threshold being higher than first threshold; and,

A step during which said richness value is progressively increased from the first richness value to the maximum the second richness value, when said temperature value is between said first threshold and said second threshold.

BRIEF DESCRIPTION OF THE FIGURES

Other characteristics and advantages of the invention will appear on reading a non-limiting embodiment thereof, with reference to the appended drawings in which:

FIG. 1 represents an example of a spark ignition internal combustion engine capable of implementing the method according to the invention; and,

FIG. 2 is a flowchart of the steps of the wealth adjustment method according to one embodiment of the invention.

DETAILED DESCRIPTION OF THE FIGURES FIG. 1 shows an internal combustion engine of the type shown in FIG. controlled ignition (operating in particular with gasoline), more specifically a section of a cylinder 1 of the engine block. An intake circuit 2 and an exhaust circuit 3 communicate respectively with an intake duct 4 and an exhaust duct 5 of the cylinder 1.

The intake circuit 2 comprises, in a nonlimiting manner, from upstream to downstream in the direction of air circulation, the compressor 6 of a turbocharger 7 of the supercharger of the engine, an air flow control valve 8 , or throttle body 8, and an intake manifold 9, or distributor 9.

Here, the engine is non-limiting in the form of an indirect injection engine: a fuel injector 10 opens into the intake duct 4 so as to inject gasoline into said duct 4. As a variant not shown, the engine can be direct injection type.

The cylinder 1 is capped by a cylinder head 11 of the engine. The cylinder head 11 houses an intake valve 12 which serves to open and close the intake duct 4 and an exhaust valve 13 which serves to open and close the exhaust duct 5. The cylinder 1 encloses a piston 14 adapted to move within a bore 15 of the cylinder 1 alternatively between a position of bottom dead center (PMB) and top dead center (TDC), and a combustion chamber 16 is formed in the defined space between the piston 14 and the cylinder head 11. A spark plug 17 is mounted on the cylinder head 11, the electrodes of which open into the combustion chamber 16.

The exhaust circuit 3 includes, in a non-limiting manner, from upstream to downstream in the direction of circulation of the combustion gases, an exhaust manifold 18, the turbine 19 of the turbocharger 7, which is mounted on a shaft 20 common to the engine. compressor 6 and the turbine, and a device 21 for cleaning the combustion gases of the engine, for example a three-way catalyst 21.

A temperature sensor 22 is mounted in the exhaust circuit 3 at the inlet of the turbine 19. It is able to measure the value of the temperature of the exhaust gas upstream of the turbine.

A richness sensor 23, or oxygen sensor 23, is mounted in the exhaust circuit 3 of the engine, upstream of the three-way catalyst 21. It is able to measure the value of the oxygen concentration in the combustion gases of the engine. engine.

In a manner known per se, an engine calculator (not shown) comprises means capable of determining at least one load value (or airflow) Qair, a value of injected fuel flow Qcarb and of the flow rate phasing. fuel with respect to the top dead center, as well as a value of ignition advance AA according to a set of parameters representative of the operation of the engine, comprising at least the torque C and the engine speed N.

Typically, the computer adjusts the Qair load by adjusting the degree of opening of the throttle body 8 and / or the power of the turbine via the degree of opening of a discharge valve to the exhaust of the turbine, also called waste-gate valve (not shown). It regulates the fuel flow Qcarb and the timing of its injection by adjusting the injection time Ti of the injector 10, more precisely the opening start time and the opening end instant, relative to the top dead center. It adjusts the advance ignition AA by sparking a spark across the electrodes of the spark plug 17 at a given angle of the engine cycle relative to the top dead center of the cylinder 1.

With reference to FIG. 2, a wealth control method according to the invention may comprise the following steps, implemented by the engine computer and performed iteratively at each instant t _n + i separated from the previous instant t _n by a step of time dt constant:

The process begins with a step 100 during which the engine computer determines a value of engine speed N and torque setpoint C required for driving the vehicle. The speed value can come from a sensor (not shown in FIG. 1) mounted at the end of the crankshaft of the engine, and the value of torque can be deduced from the value of the depression of the acceleration pedal of the vehicle by the driver.

In the first test step 200, it is checked whether the motor torque is close to full load or not. In other words, it is checked whether the torque C is between a torque threshold Cs which is less than or equal to the maximum torque Cmax that can develop the engine, and the maximum torque Cmax. The torque threshold Cs and the maximum torque Cmax depend on the speed N. They delimit a range of operating points in which, if the richness r of the air-fuel mixture was equal to 1, the temperature θech of the combustion gases of the engine in upstream of the turbine (measured by the sensor 22) would be greater than a threshold that corresponds to a reliability limit (typically a temperature of the order of 950 ° C to 980 ° C).

If the test is negative, ie if the torque is not close to the full load (in other words if it is below the torque threshold Cs), then the process goes to step 300 in which the richness r of the air - fuel mixture is set around the stoichiometric richness (richness 1), then it resumes in step 100. In the opposite case, the process points to a step 400 in which the richness r is set to a first richness value r ₁ corresponding to a slightly rich mixture, for example a richness of between 1.00 and 1.05.

Preferably, the first value of richness is substantially equal to 1, 01, so as to allow immediate pre-cooling of the engine exhaust without significantly degrading the emissions of nitrogen oxides of the vehicle, and the wealth is set immediately to this first richness value equal to 1.01. As a variant not shown, the first value of richness may be substantially equal to 1.05, the adjustment of the richness at this first value of richness being carried out progressively, for example in a linear manner as a function of time from the stoichiometric value up to said first richness value substantially equal to 1.05.

The process is continued by a step 500 in which the temperature of the exhaust gas θ _ech is measured, for example by means of the temperature sensor 22. As a variant, not shown, the order of the steps 400 and 500 can be reversed.

In the test step 600, said temperature θ _ech is compared with a first temperature threshold θ ₁ , for example a temperature of the order of 900 ° C. If said temperature is lower than said first threshold, the process resumes at step 100. In other words, the richness remains set to the stoichiometric value. In the opposite case, ie if the temperature is higher than the first threshold, the process continues with a new test step 700, in which the temperature is compared with a second temperature threshold θ2, for example of the order of 950 ° C. at 980 ° C, and corresponding to the thermomechanical resistance limit of the exhaust circuit. The method proposes not to exceed this second temperature threshold θ2.

If the temperature of the exhaust gas θ _ech is greater than the second threshold θ2, the process is directed to a step 800 in which the wealth is immediately set to a second value of richesser ₂ . This second value of richesser ₂ is greater than the first value of richness n. It is determined so as to obtain a given maximum temperature of the parts making up the exhaust circuit, for example a given exhaust manifold temperature value or a temperature value of a given turbocharger turbine (in the case of a supercharged engine). The second value of richness r ₂ can be determined by prior tests carried out on the engine bench in stabilized mode, that is to say by keeping the speed and the torque constant. We are actually setting the value of the richness so that the temperature of the exhaust gas itself is equal to a given predetermined value, this value becoming that of the components of the exhaust system of the engine after a certain period of time which is related to the inertia of the material.

For each given speed value N, there is a torque range C, close to the full load, on which the wealth must actually be increased so that the temperature of the exhaust gas is limited. It is therefore necessary to determine the second value of richness r ₂ as a function of the speed and the torque.

In the opposite case, ie if the temperature of the exhaust gas θ _ech is lower than the second threshold 82, the process continues with a step 900 in which the richness is increased progressively, that is to say by successive iterations to each time step dt each time the temperature of the exhaust gas is between the first and the second threshold 81, 82, from the first value of richness n to the maximum of the second value of richness r ₂ .

Preferably, the ratio is increased linearly over time, while being limited by a maximum value equal to the second ratio value r _2, that is to say according to an equation of the type

(Equ.1) r _{n + 1} = max (r ₂ ; r _n + k * (r ₂ - n) * dt), equation in which:

- r _{n + 1} denotes the value of richness calculated at time t _{n + 1} of the process;

- r _n denotes the value of richness calculated at time tn of the process; and,

k denotes a positive constant coefficient, which is representative of the rate of increase of the richness.

At the end of step 800 or step 900, the method then resumes in step 100. It is understood from the foregoing, and more particularly from the succession of steps 600 to 900, that when the motor enters under conditions close to full load, the temperature of the exhaust gas starts to increase continuously towards values which are approaching more and more the second temperature threshold 82. As soon as the temperature reaches the first temperature threshold 81, which can be considered as a warning threshold, we begin to increase the wealth. No delay time is applied, but the resources used are all less than the second wealth value r ₂ which corresponds to the limit thermomechanical exhaust system. There is therefore a slowed increase in the temperature of the exhaust gas, which generally leaves time for the temperature of the parts making up the exhaust circuit to catch up with the temperature of the gases, since the speed of increase of the (represented by the positive constant coefficient k) is quite small. This value can be determined by preliminary tests to take into account the inertia of temperature rise of the parts of the exhaust system or empirically according to the values of the heat capacities of their materials.

In the case where, on certain particularly severe running cycles, the temperature of the exhaust gas nevertheless reaches the second temperature threshold θ2 before the wealth has reached the second richness value, the method provisionally provides for an immediate increase in the temperature. richness r up to this second value of richness which instantly prevents the temperature of the exhaust gas from increasing even more and does not allow the temperature of the parts making up the exhaust circuit to exceed the second temperature threshold θ2, which makes it possible to guarantee their reliability.

Claims

1. A method for adjusting the richness (r) of a spark ignition internal combustion engine, the value of the richness being adjusted around the stoichiometric value when the engine is not operating in the vicinity of the full load, and around a value higher than the stoichiometric value when the engine torque (C) is greater than a torque threshold (Cs) lower than the maximum torque (Cmax) of the engine,

CHARACTERIZED IN THAT it comprises, when said torque (C) is greater than said torque threshold (Cs):

A step (400) during which said value of richness (r) is set to a first value (n) of richness greater than the stoichiometric value, when a temperature value (θ _ech ) of the exhaust gases of the motor is below a first temperature threshold (θι);

A step (800) during which said value of richness (r) is immediately set to a second value (Γ2) of richness greater than the first richness value (n), when said value of temperature (6och) is greater than at a second temperature threshold (θ2), said second threshold (θ2) being greater than said first threshold (θ1); and,

A step (900) during which said wealth value is progressively increased from the first richness value (n) to the maximum the second richness value (r ₂ ), when said temperature value (9ech) is included between said first threshold (θ1) and said second threshold (θ2).

The method of claim 1, wherein the first richness value (n) is between 1.00 and 1.05.

3. The method of claim 1 or 2, wherein the first richness value (n) is substantially equal to 1, 01.

4. Method according to any one of the preceding claims, wherein the second richness value (r ₂ ) is adjusted according to the speed (N) and the torque (C) of the engine so that the temperature (θ _ech ) of the the engine exhaust gas is equal to the second temperature threshold (θ2) when the engine is operating at a stabilized operating point regime (N) and said torque (C).

The process of any preceding claim, wherein the second temperature threshold (θ2) is from 950 ° C to 980 ° C.

6. A method according to any one of the preceding claims, wherein the progressive increase of the wealth (r) from the first richness value (n) to the maximum the second richness value (r ₂ ) is a linear increase. according to the time.