KR20190126362A - How to control thickening in ignition controlled internal combustion engines - Google Patents

Abstract

The present invention proposes a method for adjusting the richness (r) of an ignition controlled internal combustion engine, which can limit the temperature of components constituting the exhaust circuit during operation at high loads. During operation near full load, the richness is adjusted to the first richness value R1 to precool the exhaust gas. When the temperature Q _ech of the exhaust gas reaches a first temperature threshold θ _{1 which} is lower than the second temperature threshold θ ₂ corresponding to the reliability limit of the parts, the richness value is the first richness value. The value of the exhaust gas is gradually increased from the value r ₁ to the second richness value r ₂ , for example, linearly, gradually, and at the second richness value r ₂ , the temperature of the exhaust gas is determined by the second temperature threshold ( θ ₂ ). When the temperature Q _ech of the exhaust gas reaches the second threshold value θ ₂ before the richness reaches the second richness value r ₂ , the richness is the second richness value ( r ₂ ) immediately.

Description

How to control thickening in ignition controlled internal combustion engines

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

In an ignition controlled internal combustion engine (operated by gasoline), more specifically in an internal combustion engine of an automobile, an air-fuel based on a collection of engine operating parameters including at least engine speed and torque required to drive the vehicle. It is a known practice to determine the richness of a mixture. The charge, or amount of air introduced into the engine, is in particular controlled by the opening of the engine butterfly valve, and the richness is controlled by adjusting the time during which fuel is injected into the engine according to the charge.

In order to enable a three-way catalytic converter type catalytic converter, mounted in an engine exhaust pipe, to remove contaminants from engine combustion gases, the enrichment of this engine is approximately the stoichiometric value at most engine operating points. The stoichiometric value, i.e., setting it to approximately 1 richness is known per se. For example, by using a closed-loop to control the thickening, through the use of an indication from at least one oxygen probe mounted at the inlet of the catalytic converter, the catalytic converter is a catalyst. It can be operated to reduce nitrogen oxides (NOx) generated in engine combustion gases and to oxidize unburned hydrocarbons (HC) and carbon monoxide (CO) in a catalytic window.

However, it is also known that near full load, the components making up the exhaust circuit of the engine can reach very high temperatures, which may reduce their mechanical strength and endanger vehicle reliability. When it is detected that a value of torque (or load) higher than a predetermined threshold is needed to drive the vehicle, the air-fuel mixture is generally rich, for example greater than 1.2, in order to limit the exhaust temperature. It is enriched by degrees.

The value of the richness set to obtain a given maximum temperature in the exhaust, for example a given exhaust manifold temperature or a given turbocharger turbine temperature (in the case of a supercharged engine), is determined by the speed and torque in the engine test bed. By keeping constant, it can be determined by prior testing performed in a stable mode. The richness value is actually set such that the exhaust gas temperature itself is equal to a given predetermined value, which is the temperature of the components of the engine's exhaust circuit after a certain period of time associated with the material's inertia.

It is known from the prior art that many methods for controlling the richness of an automobile and in these methods the richness increase to a value higher than 1 when the load of the engine reaches a value close to full load.

For example, patent document JP-S-6043144 discloses a method for setting a fuel injection time according to operating conditions of an engine, which aims to prevent the exhaust circuit from overheating. When a load above the threshold is detected, the temperature sensor measures the temperature of the exhaust gases, and the enrichment is increased after a predetermined delay, which is a decreasing function of the gas temperature.

The delay aims to prevent unnecessary overconsumption of fuel. Specifically, the components constituting the exhaust circuit have a specific heat capacity and, therefore, when the engine is operated at high loads, the heat derived from the exhaust gases does not immediately rise to the limit temperature in terms of reliability of the components. There is no need to increase thickening immediately as soon as a load is detected. Therefore, this property can be advantageously used to retard the increase in thickness without compromising the reliability of the engine, and in theory, fuel saving can be achieved.

However, this method is inaccurate because the temperature measured by the sensor after detection of high load does not accurately accurately represent the temperature of the components of the exhaust circuit of the engine at the same time. More specifically, the temperature of the components depends on the amount of heat supplied to the components before a high load is detected, and the higher the amount of thermal energy supplied to the components, the higher the temperature will be.

Thus, if the delay is reduced when the measured gas temperature is higher, although the temperature of the components of the exhaust circuit has not yet risen to the measured gas temperature value, it is necessary to correct the thickening at that particular time. In spite of this, there is a situation in which the thickening increases almost immediately.

Furthermore, from patent document US-A-5239965, a method for controlling the thickening is known, wherein the application of the increased thickening value is delayed, the length of the delay being dependent on the thermal state of the components of the exhaust circuit. The state is measured by dedicated measuring means.

More specifically, the detection of whether the engine load is above the high reference load (indicated by the acronym PMOTP1) serves to determine if the components of the exhaust circuit are in a high load thermal state. If the result of the test is positive, this means that the temperature of the components increases due to the heat from the exhaust gases and that the components can overheat if the thickening does not increase.

Under this high load condition, the value of the delay counter (expressed by the acronym COTPCY), which indicates the rate at which the temperatures of the components of the exhaust circuit increase as a result of heat from the gases, before the detection of the high load, is regularly Incrementally, the value of the counter is compared against a pre-calibrated reference delay threshold (expressed by the acronym QAOTP) according to the throughput of air passing through the engine. The delay threshold is a reduction function of throughput.

While the value of the counter is below the threshold, the components of the exhaust gases will not overheat within a very short period of time and no enrichment measures will be implemented. In contrast, when the value of the counter is above the threshold, the value of the counter is frozen at the value just beyond the threshold, and the thickness is immediately increased.

This method involves a large amount of work to calibrate the delay thresholds in advance. Moreover, only the throughput of air passing through the engine is considered to determine the delay thresholds. The inaccuracies of the adopted thresholds are the risk of exceeding the permissible temperature (if the threshold is set too high, which leads to too late enrichment) or excessive fuel consumption (if the threshold is set too low, this may cause the enrichment to proceed too quickly). Should be done).

In addition, patent document US-A-4400944 discloses a method for adjusting the richness which attempts to prevent thermal failure of the turbocharger of the engine, and more specifically, the engine has a very late ignition advance ( High turbocharger temperatures are recommended at high speeds and high loads when set to ignition advance.

According to that document, when the temperature of the exhaust gases passing through the turbocharger is below a predetermined target value (indicated by T1), and the temperature increases over time, the thickening is subject to open-loop control. Is adjusted by adding a fuel injection time correction to the injection time corresponding to the stoichiometric mixture. The correction depends on the difference between the temperature and the temperature target.

On the other hand, when the temperature is below the target value, the mixture is rich and the temperature decreases over time, the richness is adjusted by subtracting the fuel injection time correction value from the injection time corresponding to the stoichiometric mixture.

This method, in which the concentration can be varied, allows the temperature of the exhaust gas to be adjusted to the target value and does not require selecting a delay time to increase the concentration to a value greater than one. However, the method includes steps beyond the target, which can lead to loss of reliability of the components constituting the exhaust circuit, excessive consumption of fuel, and increased emissions of pollutants from the engine.

The present invention proposes to overcome the drawbacks of known methods for controlling thickening.

The present invention more specifically provides a richness, which can protect the engine exhaust circuit against excessive temperatures, is simple to implement, and can limit the overconsumption of fuel in the engine without significantly adversely affecting pollutant emissions. Suggest ways to adjust.

To this end, the present invention proposes a method for adjusting the richness of an ignition controlled internal combustion engine, the value of which is approximately a stoichiometric value when the engine is not operating near full load. It is set to a stoichiometric value, and is set to a value approximately higher than the stoichiometric value when the engine torque is above the torque threshold lower than the maximum engine torque.

When the torque is above the torque threshold, the method:

When the temperature value of the exhaust gas of the engine is below the first temperature threshold, the richness value is set to a first richness value that is higher than the stoichiometric value;

When the temperature value is above a second temperature threshold, the enrichment value is immediately set to a second enrichment value that is higher than the first enrichment value, wherein the second threshold is the first threshold. Higher than the value; And

When the temperature value is comprised between the first threshold value and the second threshold value, the richness value is gradually increased from the first richness value to the second richness value at most; It is characterized by.

Additional features and advantages of the invention will be apparent from one non-limiting embodiment of the accompanying drawings.
1 shows an example of an ignition controlled internal combustion engine suitable for the implementation of the method according to the invention;
2 is a flowchart of steps of a method for adjusting thickening according to one embodiment of the method.

1 shows an ignition controlled internal combustion engine (particularly operating in gasoline), more particularly in cross section through one cylinder 1 of the engine block. An intake circuit 2 and an exhaust circuit 3 communicate with the intake duct 4 and the exhaust duct 5 of the cylinder 1, respectively.

The intake circuit 2 includes, but is not limited to, a compressor 6 of a turbocharger 7, an air flow control valve, which is used to supercharge the engine from upstream to downstream in the direction in which air circulates. (8) or butterfly valve (8), and intake manifold (9) or splitter (9).

In this case, the engine is in the form of, but not limited to, an indirect injection engine: the fuel injector 10 is opened into the intake duct 4 by injecting gasoline into the intake duct 4. As an alternative not shown, the engine may be a direct injection type.

The cylinder head 11 of the engine is arranged above the cylinder 1. The cylinder head 11 houses an intake valve 12 used to open and close the intake duct 4 and an exhaust valve 13 used to open and close the exhaust duct 5. The cylinder 1 surrounds a piston 14 which can move in a reciprocating motion between a bottom dead center (BDC) position and a top dead center (TDC) position within a bore 15 of the cylinder 1, and the combustion chamber 16 is formed in a space defined between the piston 14 and the cylinder head 11. The spark plug 17 is mounted to the cylinder head 11, the electrode of which leads into the combustion chamber 16.

The exhaust circuit 3 is, but is not limited to, a turbocharger 7 mounted to the exhaust manifold 18, the compressor 6, and the shaft 20 common to the turbine, from upstream to downstream in the direction in which the combustion gas circulates. Turbine 19, and an apparatus 21 for removing contaminants from engine combustion gases, for example a three-way catalytic converter 21.

The temperature sensor 22 is mounted at the inlet of the turbine 19 in the exhaust circuit 3. The temperature sensor can measure the temperature value of the exhaust gas upstream of the turbine.

A richness sensor 23, or oxygen probe 23, is mounted upstream of the three-way catalytic converter 21 in the exhaust circuit 3 of the engine. The rich sensor may measure a value of the oxygen concentration of the engine exhaust gas.

In a manner known per se, the engine control unit (not shown) comprises at least one load in accordance with a collection of parameters indicative of the operation of the engine, including at least engine torque C and engine speed N. Determine the value of (or charge-air flow rate) Qair, the timing of fuel delivery relative to the injected fuel flow rate (Qfuel) and top dead center, and the value for ignition advance (AA) Means that can.

In a conventional manner, the control unit adjusts the charge by adjusting the opening of the butterfly valve 8 and / or through the opening of the turbine waste gate valve (or discharge valve) (not shown). Adjust the power of the turbine. The control unit adjusts the injection time Ti of the fuel injector 10, more specifically, the start-of-opening instant and the end-of-opening instant with respect to the top dead center. Thereby controlling the fuel flow rate Qfuel and the timing of injection of the fuel. The control unit adjusts the ignition advance AA by causing the spark to jump over the terminals of the electrodes of the spark plug 17 at a given angle in the engine cycle with respect to the top dead center of the cylinder 1.

Referring to FIG. 2, the method for adjusting the thickening according to the present invention may include the following steps, which are carried out by the engine control unit and have a constant time interval dt from the previous time point t _n . Repeated at each time point (t _{n + 1} ) separated by).

The method begins with step 100, during which the engine control unit determines the engine speed value N and torque reference value C required to drive the vehicle. The speed value may come from a sensor (not shown in FIG. 1) mounted at the end of the engine crankshaft, and the torque value may be estimated from the degree to which the driver presses the throttle pedal.

In a first test step 200, it is checked whether the engine torque is close to full load. In other words, it is checked whether the torque C is included between the torque threshold Cs and the maximum torque Cmax that is less than or equal to the maximum torque Cmax that the engine can generate. The torque threshold Cs and the maximum torque Cmax depend on the speed N. They limit the range of operating points, where the engine combustion gas (measured by sensor 22) upstream of the turbine, when the richness r of the air-fuel mixture is equal to one. temperature (θ _exh) is of wiil than the threshold value corresponding to a reliability threshold (limit reliability) (generally a temperature of approximately 950 ℃ to 980 ℃).

If the result of the test is negative, i.e. if the torque is not close to full load (ie, the torque is below the torque threshold Cs), the method proceeds to step 300, where the air-fuel mixture The richness r of is set to approximately stoichiometric richness (rich 1), and then starts again from step 100.

If contrary to the above, the method proceeds to step 400, where the concentration r corresponds to a slightly thicker mixture, for example a first enrichment value comprised between 1.00 and 1.05 ( r ₁ ).

Advantageously, the first enrichment value is substantially equal to 1.01 and the enrichment level is equal to 1.01 immediately so that the engine exhaust gas is immediately precooled without serious disturbances in the release of nitrogen oxides from the vehicle. It is set to a value. As an alternative, not shown, the first enrichment value may be substantially equal to 1.05, and setting the enrichment to the first enrichment value is incrementally, for example, from stoichiometric values. Up to a first enrichment value equal to 1.05 is achieved as a linear function of time.

The method continues with step 500 where the exhaust gas temperature θ _exh is measured using, for example, a temperature sensor 22. As an alternative not shown, the order of steps 400 and 500 may be reversed.

In step 600, the temperature θ _exh is compared with a first temperature threshold θ ₁ , for example approximately 900 ° C. If the temperature is below the first threshold, the method restarts at step 100. In other words, the richness continues to be set at the stoichiometric value. If the opposite is true, ie if the temperature is above the first threshold, the method continues with the further test step 700, where the temperature θ _exh is, for example, from about 950 ° C. to It is compared with a second temperature threshold θ ₂ at 980 ° C. and corresponding to the thermomechanical limit of the exhaust circuit. The method proposes not to exceed the second temperature threshold θ ₂ .

If the temperature θ _exh of the exhaust gas is above the second threshold θ ₂ , the method proceeds to step 800, where the richness is immediately set to the second richness value r ₂ . The second richness value r ₂ is higher than the first richness value r ₁ . The second richness value r ₂ is determined in such a way as to obtain a given maximum temperature of the components constituting the exhaust circuit, for example a given exhaust manifold temperature or a given turbocharger turbine temperature (in the case of a supercharged engine). . The second richness value r ₂ may be determined by a preliminary test performed in a stable mode in the engine test bed, ie keeping the speed and torque constant. The richness value is actually set in such a way that the exhaust gas temperature itself is equal to a given predetermined value, which is the temperature of the components of the engine's exhaust circuit after some time associated with the material's inertia.

For each given speed value N, there is a range of torques C near full load, for which the thickness needs to be actually increased to limit the temperature of the exhaust gas. Therefore, it is necessary to determine the second richness value r ₂ depending on the speed and the torque.

Otherwise, that is, if the temperature θ _exh of the exhaust gas is below the second threshold θ ₂ , the method continues with step 900, where the richness gradually increases, In other words, whenever the temperature of the exhaust gas is included between the first and second thresholds θ ₁ and θ ₂ , the second rich gas is repeated from the first richness value r ₁ at a time interval dt. The degree value r ₂ is increased.

Advantageously, the richness is increased as a linear function of time and at the same time is limited by the maximum value equal to the second richness value r ₂ , ie according to the equation below.

(Equation 1) r _{n + 1} = max (r ₂ ; r _n + k * (r ₂ -r ₁ ) * dt)

In this equation:

- r _{n + 1} represents the value calculated in FIG rich time t _{n + 1} of the method;

- r _n denotes a rich degree value calculated at the time t _n of the method;

k represents a positive constant coefficient representing the rate at which the thickening increases.

At the end of step 800 or 900, the method starts over from step 100. From the front, more specifically from the continuation of the steps 600 to 900, when the engine enters near full load, the temperature of the exhaust gas is continuously toward the values gradually approaching the second temperature threshold θ ₂ . You will understand that it starts to increase. As soon as the temperature reaches the first temperature threshold θ ₁ , which can be considered as a warning threshold, the increase in thickening begins. Although no delay is applied, the thickenings implemented are all below the second thickening value r ₂ , which corresponds to the stoichiometric limit of the exhaust circuit. Thus, as long as the rate of thickening (which is expressed as a positive constant coefficient k) is significantly slower, the temperature of the exhaust gas increases slowly, which generally means that the temperature of the components constituting the exhaust circuit keeps up with the temperature of the gas. Give time for This value can be determined by preliminary tests to take into account the inertia in the rise of the temperature of the components of the exhaust circuit, or empirically determined as a function of the values for the heat capacity of the materials.

In some particularly severe operating cycles, if the temperature of the exhaust gas nevertheless reaches a second temperature threshold θ ₂ before the richness reaches the second richness value r ₂ , the method As a conservative measure, it is anticipated to immediately increase the richness (r) to the second richness value (r ₂ ), which immediately prevents further increases in the temperature of the exhaust gases and constitutes the exhaust circuit. Does not allow the temperature of these to exceed the second temperature threshold θ ₂ , thereby ensuring the reliability of the components.

Claims (6)

A method for adjusting the richness (r) of an ignition controlled internal combustion engine,
The richness value is set to approximately stoichiometric value when the engine is not operating near full load, and the torque threshold value at which the engine torque C is lower than the maximum engine torque Cmax. is above the stoichiometric value when it is above the torque threshold (Cs),
When the torque C is above the torque threshold Cs, the method:
When the temperature value Q _exh of the exhaust gas of the engine is below the first temperature threshold θ ₁ , the richness value r is a first richness value r1 higher than the stoichiometric value. Set 400;
When the temperature value Q _exh is above the second temperature threshold θ ₂ , the enrichment value r immediately becomes a second enrichment value higher than the first enrichment value r ₁ ( r ₂ ), wherein the second threshold value θ ₂ is higher than the first threshold value θ ₁ ; And
When the temperature value Q _exh is included between the first threshold value θ ₁ and the second threshold value θ ₂ , the richness value is higher from the first richness value r ₁ . Gradually increasing to the second richness value (r ₂ ) (900). The method of claim 1,
The first enrichment value (r ₁ ) is comprised between 1.00 and 1.05. The method according to claim 1 or 2,
And wherein said first enrichment value r ₁ is substantially equal to 1.01. The method of claim 1, wherein
The second richness value r ₂ is set according to the engine speed N and the engine torque C, but at an operating point at which the engine is stabilized at the speed N and the torque C. And the second enrichment value r ₂ is set such that when operating the temperature Q _exh of the engine's exhaust gas is equal to the second temperature threshold θ ₂ . The method of claim 1, wherein
Wherein the second temperature threshold (θ ₂ ) is comprised between 950 ° C. and 980 ° C. The method of claim 1, wherein
The progressive increase in the richness value from the first richness value r ₁ to the second richness value r ₂ is a linear function of time.

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