JP2023182629A - Method for adjusting richness in controlled-ignition internal combustion engine - Google Patents

Abstract

To provide a method for adjusting richness in a controlled-ignition internal combustion engine, which can limit the temperature of parts constituting an exhaust circuit during operation at a high load.SOLUTION: During operation in the vicinity of a full load, richness is adjusted to a first richness value (r1) in order to pre-cool exhaust gases. When a temperature (θe ch) of the exhaust gases reaches a first temperature threshold (θ1), which is lower than a second temperature threshold (θ2) corresponding to a reliability limit of 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 (θe ch) of the exhaust gases reaches the second threshold (θ2) before the richness reaches the second richness value (r2), the richness is immediately adjusted to the second richness value (r2).SELECTED DRAWING: Figure 2

Description

The present invention relates to a method for adjusting the richness of an air-fuel mixture in an internal combustion engine of the ignition-controlled type (in particular gasoline-fueled). The invention is advantageous for application in the automotive field.

In internal combustion engines of the ignition-controlled type (gasoline-fueled), especially those of automobiles, the richness of the mixture is determined based on a set of engine operating parameters, including at least the engine speed and torque required for the operation of the vehicle. It is known to do. The supercharging air or amount of air that the engine can take in is specifically regulated by the opening of the engine butterfly valve, and the richness is adjusted depending on the supercharging air by adjusting the time for injecting fuel into the engine.

For example, a three-way catalytic converter type catalytic converter located in the engine's exhaust pipe can remove pollutants from the engine's combustion gases for most engine operating points. It is known to set the richness near the theoretical mixture value, that is, near the richness of 1. For example, a catalytic converter can be operated within its catalytic window by using closed-loop control that adjusts richness through the use of indications from at least one oxygen probe mounted at the inlet of the catalytic converter; Catalytic converters reduce nitrogen oxides (NOx) produced in engine combustion gases and can oxidize unburned hydrocarbons (HC) and carbon monoxide (CO).

However, near full load, the components that make up the engine's exhaust circuit can reach extremely high temperatures, which can impair their mechanical strength and reduce vehicle reliability. Are known. If it is detected that a torque (or load) value exceeding a predetermined threshold is required to operate the vehicle, the mixture is adjusted to a value greater than 1.20 as a whole in order to limit the exhaust temperature. Enriched with richness value etc.

The richness value set to obtain a given maximum temperature in the exhaust pipe, such as a given exhaust manifold temperature or a given turbocharger turbine temperature (in case of a supercharged engine), in stable mode, i.e. , can be determined by preliminary tests performed on an engine test bed by keeping speed and torque constant. The richness value is actually set so that the exhaust gas temperature itself is equal to the given predetermined value. This value results in that of the components of the engine's exhaust circuit after a certain period of time, which is related to the inertia of the material.

Numerous methods are known from the prior art for adjusting the richness of a motor vehicle, increasing the richness to a value higher than 1 when the load on the engine reaches a value near full load.

For example, Japanese Publication No. JP-S-6043144 discloses a method of setting fuel injection time according to engine operating conditions with the aim of avoiding overheating of the exhaust circuit. Upon detecting a load above a threshold, a temperature sensor measures the temperature of the exhaust gas and increases the richness after a predetermined delay that decreases depending on the gas temperature.

This delay is intended to avoid unnecessary overconsumption of fuel. Specifically, there is no need to immediately increase the richness as soon as a high load is detected. This is because the components that make up the exhaust circuit have a certain heat capacity and therefore, even when the engine is operating at high loads, the heat caused by the exhaust gases will limit the temperature in terms of their reliability. This is because it does not rise immediately. Therefore, this characteristic can be used advantageously in slowing richness increases to achieve theoretical fuel economy without compromising engine reliability.

However, this method is not accurate because the temperature measured by the sensor after detection of a high load does not accurately represent the temperature of the components of the engine's exhaust circuit at that same moment. More specifically, the temperature of the component is determined by the amount of heat imparted to the component before a high load is detected, and the greater the amount of thermal energy imparted to the component, the higher this temperature will be.

Therefore, if the measured gas temperature is high, and the delay is reduced, the temperature of the components of the exhaust circuit has not risen to the measured gas temperature value and it is necessary to change the richness at that particular moment. There may be situations in which richness is increased almost immediately even in the absence of Fuel consumption is therefore unnecessarily worsened.

From United States Publication No. US-A-5239965, the richness is determined by the length of which the application of the increased richness value is delayed by a delay determined by the thermal conditions of the components of the exhaust circuit, measured by dedicated measuring means. Methods of adjustment are also known.

More specifically, it is detected whether the engine load exceeds a high reference load (denoted by the acronym PMOTP1), which determines whether components of the exhaust circuit are under high load thermal conditions. shared with. If the test result is positive, this means that the temperature of the component is increasing due to heat from the exhaust gases, and if the richness is not increased, the component may overheat.

Under these high load conditions, the value of the delay counter (designated by the acronym COTPCY), which indicates that the temperature of the exhaust circuit components has increased as a result of heat from the gas, before the high load is detected. The ratio, , is incremented periodically and the value of this counter is compared to a reference delay threshold (designated by the acronym QAOTP) that is pre-calibrated according to the throughput of air through the engine. This delay threshold decreases depending on throughput.

As long as the value of the counter is below the threshold value, it is assumed that the components of the exhaust gas will not overheat in a very short period of time and no enrichment measurements are performed. On the other hand, when the value of the counter exceeds the threshold, the value of the counter is fixed at the value at the exact moment when the threshold is crossed, and the richness is immediately increased.

Such a method entails a lot of effort in pre-calibrating the delay threshold. Moreover, to fix them, only the throughput of air through the engine is taken into account. Inaccuracy of the applied thresholds means that there is a risk of exceeding acceptable temperatures (if the thresholds are set too high, enrichment will be delayed too much) or excessive fuel consumption (if the thresholds are set too low) , this results in the enrichment being done immediately).

From United States Publication No. US-A-4400944, it is known that the turbocharger of an engine, especially at high speeds and loads, is Methods of adjusting richness seeking to avoid thermal failures are also known.

According to these documents, if the temperature of the exhaust gas passing through the turbocharger is below a predetermined target value (designated T1) and this temperature increases over time, the richness is adjusted using open-loop control. and adds to the injection time a fuel injection time correction determined by the difference between the temperature and the temperature target, which corresponds to the stoichiometric mixture.

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

Such a method with variable richness allows the temperature of the exhaust gas to be adjusted to the target value and does not require the selection of a delay time to increase the richness to a value greater than one. However, this has the potential to exceed targets, impair the reliability of exhaust circuit components, consume too much fuel, and increase pollutant emissions from the engine.

The present invention presents how to overcome the shortcomings of existing methods of adjusting richness.

This is, among other things, a richness adjustment method that can protect the engine exhaust circuit from excessive temperatures, is easy to implement, and limits the overconsumption of fuel by the engine without highlighting the undesirable effects of pollutant emissions. is aimed at presenting.

To that end, the invention presents a method for adjusting the richness of a spark-controlled internal combustion engine. The richness value is set near the stoichiometric mixture value unless the engine is operating near full load, and is set near a value higher than the stoichiometric mixture value when the engine torque exceeds a torque threshold that is less than or equal to the maximum engine torque. be done.

In this method, when the torque exceeds the torque threshold,
- the richness value is set to a first richness value higher than the stoichiometric mixture value when the temperature value of the engine exhaust gas is less than a first temperature threshold;
- as soon as the temperature value exceeds a second temperature threshold that is higher than the first threshold, the richness value is set to a second richness value that is higher than the first richness value;
- the richness value gradually increases from the first richness value up to a second richness value when the temperature value is between a first threshold value and a second threshold value; shall be.

Further features and advantages of the invention will become apparent from reading the non-limiting embodiments thereof with reference to the accompanying drawings in which: FIG.

FIG. 1 shows an example of an ignition-controlled internal combustion engine suitable for implementing the method according to the invention. FIG. 2 is a flow diagram of the steps of a method for adjusting richness, according to one embodiment of the method.

FIG. 1 shows an internal combustion engine of the ignition-controlled type (in particular gasoline-fueled), more specifically a cross-sectional view through one cylinder 1 of an engine block. The intake circuit 2 and the exhaust circuit 3 communicate with an intake duct 4 and an exhaust duct 5 of the cylinder 1, respectively.

The intake circuit 2 includes, without limitation, from upstream to downstream, in the direction in which air circulates, a compressor 6 of a turbocharger 7 used for supercharging the engine, an air flow control valve 8 or a butterfly valve 8, and an intake circuit. A manifold 9 or a splitter 9 is included.

In this example, the engine is, without limitation, in the form of an indirect injection engine, with a fuel injector 10 opening into the intake duct 4 to inject gasoline into the duct 4. Although not shown, the engine may alternatively be of the direct injection type.

A cylinder head 11 of the engine is located above the cylinder 1. The cylinder head 11 accommodates 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 that is movable 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 . A combustion chamber 16 is formed within a space defined between the piston 14 and the cylinder head 11. A spark plug 17 is mounted on the cylinder head 11, and its electrode communicates with the inside of the combustion chamber 16.

The exhaust circuit 3 includes, without limitation, from upstream to downstream, in the direction in which the combustion gases circulate, an exhaust manifold 18 and a turbine 19 mounted on a common shaft 20 with the compressor 6 of the turbocharger 7 . a device 21, such as a three-way catalytic converter 21, that removes pollutants from engine combustion gases.

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

The richness sensor 23 or oxygen probe 23 is placed in the exhaust circuit 3 of the engine upstream of the three-way catalytic converter 21. This sensor can measure the oxygen concentration value of the engine exhaust gas.

In a known manner, for example, an engine control unit (not shown) determines the value of the load (or charge air flow rate) Qair, the value of the flow rate of the injected fuel Qfuel and the timing of supplying the fuel with respect to top dead center; and a value of the ignition advance angle AA in response to a set of parameters indicative of engine operation, including at least engine torque C and engine speed N.

In a conventional manner, the control unit adjusts the power of the turbine through the opening of the butterfly valve 8 and/or the opening of the turbine wastegate (or exhaust) valve (not shown). Adjust supercharging air Qair. The control unit adjusts the fuel flow rate Qfuel and the timing of its injection by adjusting the injection time Ti of the injector 10, more specifically the moment when it starts opening and the moment when it ends opening with respect to top dead center. The control unit adjusts the ignition advance angle AA by sending a spark between 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.

With reference to FIG. 2, the method for adjusting the richness according to the invention is carried out by the engine control unit, repeated at every instant t _n+1 after the previous instant t _n , at regular time intervals dt. It may include the following steps:

The method begins at step 100. Here, the engine control unit determines the engine speed value N and the torque reference value C required for the operation of the vehicle. The speed value may be from a sensor (not shown in FIG. 1) mounted on the end of the engine's crankshaft, and the torque value may be subtracted from the amount of throttle pedal depression by the driver. It's good to be there.

In a first test step 200, it is checked whether the engine torque is near full load. In other words, it is checked whether the torque C is between the maximum torque Cmax and a torque threshold Cs 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 are determined by the speed N. These are such that when the richness r of the mixture is equal to 1, the temperature θ _exh of the combustion gases of the engine (measured by sensor 22) upstream of the turbine is within the reliability limit (typically 950°C to 980°C). Define a range of operating points at which a threshold corresponding to a temperature of the order of degrees Celsius) may be exceeded.

If the result of the test is negative, ie, the torque is not near full load (in other words, less than the torque threshold Cs), the method proceeds to step 300. Here, the richness r of the air-fuel mixture is set near the theoretical mixture richness (richness of 1). The method then resumes at step 100.

If the opposite is true, the method proceeds to step 400. Here, the richness r is set to a first richness value _r1 , which corresponds to a slightly richer air-fuel mixture, such as a richness between 1.00 and 1.05.

Preferably, the first richness value is substantially equal to 1.01, such that the richness immediately This first richness value is set equal to 1.01. Although not shown, the first richness value may alternatively be substantially equal to 1.05. Setting the richness to this first richness value is achieved progressively, for example linearly over time, from the theoretical mixture value to a first richness value substantially equal to 1.05.

The method continues at step 500. Here, the exhaust gas temperature θ _exh is measured using a temperature sensor 22 or the like. Although not shown, the order of steps 400 and 500 may alternatively be reversed.

In a test step 600, the temperature θ _exh is compared to a first temperature threshold θ ₁ , such as a temperature on the order of 900°C. If the temperature is below the first threshold, the method resumes at step 100. In other words, the richness remains set to the theoretical mixture value. If the opposite is true, ie, the temperature exceeds a first threshold, the method further continues to test step 700. Here, the temperature θ _exh is compared to a second temperature threshold θ ₂ , which corresponds to the thermomechanical limit of the exhaust circuit, such as a temperature on the order of 950° to 980°C. The method provides that this second temperature threshold θ ₂ is not exceeded.

When the exhaust gas temperature θ _exh exceeds the second threshold θ ₂ , the method proceeds to step 800 . Here, the richness is immediately set to the second richness value _r2 . This second richness value _r2 is higher than the first richness value _r1 . Decisions are made in such a way as to obtain a given maximum temperature of the components making up the exhaust circuit, such as 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 performing preliminary tests on an engine test bed in stable mode, ie with constant speed and torque. The richness value is actually set so that the exhaust gas temperature itself is equal to the given predetermined value. This value results in that of the components of the exhaust circuit 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 range of torque C around full load where the richness must actually be increased in order to limit the exhaust gas temperature. Therefore, it is necessary to determine a second richness value r ₂ that depends on speed and torque.

If this is not the case, ie if the exhaust gas temperature θ _exh is less than the second threshold θ ₂ , the method proceeds to step 900 . Here, the richness is gradually increased, that is, each time the temperature of the exhaust gas is between the first threshold value θ ₁ and the second threshold value θ ₂ , the first from a richness value r ₁ up to a second richness value r ₂ .

Preferably, the richness is increased linearly with time and at the same time limited by a maximum value equal to the second richness value _r2 , i.e. according to a formula of the following type:

(Formula 1) r _n+1 = max (r ₂ ; r _n +k×(r ₂ − r ₁ )×dt),

In this formula,
- r _n+1 denotes the richness value calculated at moment t _n+1 of the method;
- r _n denotes the richness value calculated at instant t _n of the method;
- k indicates a positive constant coefficient indicating the rate at which richness increases.

At the end of step 800 or step 900, the method resumes at step 100. From the foregoing, in particular, from the successive steps 600 to 900, when the engine is under a condition near full load, the temperature of the exhaust gas increases continuously to a value approaching the second temperature threshold _θ2 . You'll see how to get started. As soon as the temperature reaches a first temperature threshold θ ₁ , which may be considered as an alarm threshold, the richness begins to increase. No delays are applied and all implemented richnesses are less than a second richness value _r2 , which corresponds to the thermomechanical limit of the exhaust circuit. The temperature of the exhaust gas therefore rises slowly. Overall, this gives the temperature of the components making up the exhaust circuit time to catch up with the temperature of the gas, as long as the rate of increase in richness (represented by the positive constant factor k) is fairly low. This value can be determined by prior testing or empirically depending on the value of the heat capacity of the material, in order to take into account the inertia in temperature rise of the components of the exhaust circuit.

Particularly in the case where, in a particular severe driving cycle, the temperature of the exhaust gas still reaches the second temperature threshold θ ₂ before the richness reaches the second richness value r ₂ , this method is conservative. As a simple action, we expect to immediately increase the richness r to this second richness value _r2 . This immediately prevents the temperature of the exhaust gases from increasing further and ensures that the temperature of the components making up the exhaust circuit does not exceed the second temperature threshold θ ₂ and thus guarantees their reliability.

Claims (6)

A method for adjusting richness (r) of an ignition-controlled internal combustion engine, wherein the richness value is set near a stoichiometric mixture value unless the engine is operating near full load, and the richness value is set near a stoichiometric mixture value, and the engine torque (C ) exceeds a torque threshold (Cs) lower than the maximum engine torque (Cmax), is set near a value higher than the theoretical mixture value,
When the torque (C) exceeds the torque threshold (Cs),
- if the temperature value (θ _exh ) of the exhaust gas of the engine is less than a first temperature threshold (θ ₁ ), the richness value (r) is a first richness value (r) higher than the theoretical mixture value; a step (400) set to ₁ );
- if the temperature value (θ _exh ) exceeds a second temperature threshold (θ ₂ ) which is higher than the first threshold (θ ₁ ), the richness value (r) is lower than the first richness value (r ₁ ) immediately setting (800) to a higher second richness value ( _r2 );
- if the temperature value (θ _exh ) is between the first threshold (θ ₁ ) and the second threshold (θ ₂ ), the richness value is equal to or less than the first richness value (r _{1 )} ; ) up to the second richness value (r ₂ ) (900).
Method. 2. The method of claim 1, wherein the first richness value ( _r1 ) is between 1.00 and 1.05. 3. A method according to claim 1 or 2, wherein the first richness value ( _r1 ) is substantially equal to 1.01. The second richness value (r ₂ ) is determined by the temperature (θ The method according to any one of claims 1 to 3, wherein _exh ) is set according to the speed (N) and the torque (C) to be equal to the second temperature threshold (θ ₂ ). . A method according to any one of claims 1 to 4, wherein the second temperature threshold (θ ₂ ) is between 950°C and 980°C. 4. The gradual increase in richness (r) from the first richness value (r ₁ ) up to the second richness value (r ₂ ) is a linear increase in time. The method according to any one of 1 to 5.

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