JP2002543322A - Method for controlling richness of air / fuel mixture gas of an internal combustion engine that discharges exhaust gas to an exhaust line provided with a hydrocarbon trap - Google Patents

Abstract

(57) [Summary] Exhaust gas successively passes through a hydrocarbon trap (3) and a catalyst pot (4) for treating exhaust gas, and the fuel richness of the air-fuel mixture gas is reduced by the engine (1). Closed loop control to a predetermined richness setting is provided by a signal delivered from an oxygen probe (5) located in an exhaust line (2) between the gas and a hydrocarbon trap (3). According to the present invention, a) it is detected by estimation that the hydrocarbon trap (3) is operating during salting out hydrocarbons into the exhaust line (2), and In some cases, the set value of the richness in the closed loop control of the richness is reduced. In the step a), the amount of fuel (MHC) contained in the trap (3) is estimated, and the amount of fuel is positive, and the temperature (T _p ) of the trap (3) is equal to the predetermined temperature (T _p ). _s ) If not, the trap (3) detects that the hydrocarbons are operating during salting out.

Description

DETAILED DESCRIPTION OF THE INVENTION

The present invention relates to a method for controlling the richness of an air-fuel mixture gas of an internal combustion engine. The present invention is particularly applicable to an internal combustion engine that applies exhaust gas to an internal combustion engine where the exhaust gas flows into an exhaust line that successively passes through a trap for hydrocarbons and a pot of catalyst for treating the exhaust gas. Regarding the richness control method, the richness of the fuel of the mixed gas is determined by a signal sent from a probe of oxygen disposed in an exhaust line between the internal combustion engine and the hydrocarbon trap. Is controlled in a closed loop.

FIG. 1 shows an internal combustion engine 1 arranged in the above environment. The exhaust gas of the engine passes through the exhaust line 2 while passing successively through the hydrocarbon trap 3 and the pot 4 of the catalyst for exhaust gas treatment. The catalyst pot 4 oxidizes incompletely combusted hydrocarbons and carbon monoxide contained in exhaust gas, for example, to convert harmful chemicals into less harmful chemicals and further into harmless chemicals (nitrogen). And it is a "three-function" type capable of reducing nitrogen oxides contained in exhaust gas.

[0003] Pots of catalysts of this type do not properly handle incompletely combusted hydrocarbons in exhaust gases when they do not reach a sufficiently elevated predetermined temperature on the order of about 300 ° C. Are known. Such a temperature is not instantaneously reached when starting a cold engine. Furthermore, during such a start-up, the air / fuel mixture supplied to the engine is enriched in fuel, so that the exhaust gas of the engine contains more hydrocarbons.

[0006] Therefore, it has been proposed to arrange a hydrocarbon trap between the engine and the pot in order to take in hydrocarbons at the above-mentioned temperature or lower and avoid passing through the pot 4. When the temperature in the trap 3 reaches about 200 ° C., the trap 3 releases the trapped hydrocarbons into the exhaust line 2, that is, “salts out”. The hydrocarbons released into the exhaust line 2 are released into the atmosphere after being reduced in the next pot 4 to a chemical substance consisting mostly of carbon dioxide and water.

Further, when such a pot is used, very precise adjustment of the richness of the fuel of the air-fuel mixture gas supplied to the engine is required. It is known that it works with good efficiency only in a "window" with a richness centered on the richness corresponding to a mixed gas.

This adjustment is generally determined by the time t t of opening the fuel injector to the cylinder of the engine._i(Figure
(Not shown). Opening time t of the fuel injector _i Is generally referred to as "injection time". This adjustment is commonly called a lambda probe.
Signal from an oxygen probe that responds to the concentration of oxygen in the exhaust gas.
To use. This oxygen concentration depends on the fuel-rich air-fuel mixture supplied to the engine.
It turns out that it is possible to follow the changes in the nesting of stoichiometric values of Ness
I have. The signal sent from the probe 5 is therefore "rich" or "
Between the "high level" and the "low level" representing the gas mixture called "poor"
Rocks. "

[0007] The computer uses this information to adjust the injection time. When the computer senses the poor gas mixture, the injection time is increased until the oxygen probe output again transitions to a level representing a rich gas mixture. In this way, the output of the probe is always "rocking". In order to obtain an accurate adjustment of the richness, a certain oscillation frequency is required.

When a hydrocarbon trap such as the trap 3 is disposed in the exhaust line 2,
A probe 5 needs to be provided between the engine 1 and the trap 3. Because,
When an oxygen probe is arranged downstream of the trap 3, the frequency of the oscillation is too small in order to effectively incorporate the transmitted information into the closed loop control calculation of the fuel richness of the air-fuel mixture gas. Because.

This control is generally carried out by a computer 6 programmed accordingly for this. The computer 6 also performs complete general management of the engine and controls other functional parameters of the engine, for example the advance of the ignition timing of the air / fuel mixture.

In the position shown in FIG. 1, the probe 5 cannot sense the salting out of hydrocarbons, which increases the hydrocarbon concentration of the exhaust gas, by the trap 3 located downstream of the probe, The composition of the exhaust gas with increased hydrocarbon concentration results in the exhaust resulting from combustion of the engine with a rich air-fuel mixture of the fuel contained in the "window", wherein the function of the pot 4 is no longer optimal. Does not support gas.

[0011] The present invention relates to an internal combustion engine suitable for maintaining the optimal functioning of a catalyst pot for treating engine exhaust gases during periods when hydrocarbons are being salted out by the trapping of hydrocarbons. It is an object of the present invention to provide a method for controlling the richness of an air / fuel mixture gas.

This object of the invention and other objects which will become apparent from reading the following description are: a control method of the type described in the introduction to the detailed description of the invention, comprising the steps of: It is detected by estimation that the hydrocarbon is in the operating state during salting out into the line. B) When the hydrocarbon trap is in the operating state during the salting out, the richness of the closed loop control of the richness is reduced. This is achieved by a control method characterized by decreasing the set value.

As will be explained in more detail below, the increase in hydrocarbons present in the exhaust gas due to salting out of the hydrocarbons contained in the hydrocarbon traps is thus offset,
The effective function of the pot of catalyst located downstream of the hydrocarbon trap is maintained.

According to another feature of the method of the present invention, in the step a), the amount of fuel contained in the hydrocarbon trap is estimated, and the amount of fuel is positive, and When the temperature of the trap is equal to or higher than a predetermined temperature, it is detected that the trap is in an operating state during salting out hydrocarbons. When the temperature of the trap is equal to or lower than the predetermined temperature, the amount of fuel stored in the trap is determined by the following model of the current value (MHC _i ) of the amount: MHC _i = MHC _i−1 + ΔMHC And ΔMHC = K ₁ · K ₂ · DGE (1) Here, K ₁ and K ₂ are estimated using coefficients, and DGE is estimated using the exhaust gas flow rate.

When the temperature of the trap is equal to or higher than the predetermined temperature, the estimated value of the amount of fuel in the trap is decreased in proportion to the flow rate of the exhaust gas.

According to still another feature of the method of the present invention, in the step b), the richness set value of the closed loop control of the richness of the air / fuel mixture supplied to the engine is set to the value of the richness. Intervening in the calculation of the fuel injection time to the engine, the richness loop correction factor is varied and reduced. In particular, the proportional correction of the correction factor is varied so as to adjust the air / fuel mixture to a "poor" mixture.

Other features and advantages of the present invention will become apparent from reading the following description and studying the accompanying drawings.

As shown below, in the first stage of the method according to the invention, the operating condition of the trap 3 for incompletely combusted hydrocarbons is that the hydrocarbons are being salted out into the exhaust line 2. Is detected by estimation. For this purpose, on the one hand, whether the trap 3 contains hydrocarbons and, on the other hand, the temperature of this trap, the hydrocarbons trapped in the trap 3 are salted out into the exhaust line 2. It is necessary to determine if the temperature has been raised to a sufficient level to allow

According to the invention, the temperature of the trap 3 can be known by means of a temperature sensor 7 which sends a signal representing this temperature to a computer, or by a model which makes it possible to calculate this temperature.

For example, a model of the trap temperature T _pi at instant i can take the following form: T _pi = T _{p (i−1)} + F (T _pstab −T _{p (i−1)} ) where T _pstab is the value of the operation at a sufficiently long and stable engine speed where the temperature of the trap does not change significantly. The temperature of the trap at the end, F, is a filter coefficient that is a function of the exhaust gas flow rate DGE.

As a variant, starting from the temperature T _ap of the exhaust gas at the outlet of the trap, obtained using a sensor or a model, T _pi may be derived by the following relation: T _pi = T _api ± offset where offset is a function of the exhaust gas flow rate DGE.

According to the present invention, the computer 6 executes an estimation method described in detail below.
In order to be properly programmed. For example, traps can be used to remove incompletely burned hydrocarbons.
If you start while the engine is cold,
At the current sampling instant i.
Hydrocarbon mass MHC_iTrack changes. MHC_i= MHC_i-1+ ΔMHC and ΔMHC = K₁・ K₂・ DGE (1) Here, K₁Is a constant factor, for example, the temperature of the trap
Constant from the plot using the amount of hydrocarbons stored in the tap, K ₂ Is equal to 1 when the engine is running at richness 1 and runs at richness 1 or higher.
The coefficient is 1 or more during operation, and 1 or less during operation with richness 1 or less.
As is known, it is obtained from the computer 6 using the suction pressure and the rotation speed of the engine.
Is the flow rate of the exhaust gas.

[0023] This model is immediately applied exceeds the temperature T _s to the temperature T _p of the trap 3 is predetermined is stopped. The temperature T _s is the temperature above which the accumulated hydrocarbons are salted out into the exhaust line, so that the salted out hydrocarbons are added to the incompletely burned hydrocarbons in the engine, This is the temperature that flows into the pot 4 of the catalyst.

Next, the mass MHC _i is decremented by successive decrements proportional to the exhaust gas flow rate DGE, and the change in the amount of hydrocarbons stored in the trap is subsequently tracked.

Therefore, the flow rate DHC of the hydrocarbon salted out from the trap 3 into the exhaust line 2 is equal to the following equation. DHC _i = MHC _i −MHC _i−1 (2) When the engine is stopped, the computer stores and saves the latest calculated value of the MHC. This value becomes the initial value MHC ₀ of the MHC in the new calculation of the MHC according to the model (1) at the time of the next start of the engine.

Thus, the model used in the method according to the invention provides an instantaneous indication of whether and how much hydrocarbons have been salted out by traps in the exhaust line 2. be able to.

Now, in accordance with the present invention, how this information is used to maintain the total amount of hydrocarbon passing into the pot 4 corresponding to that defined by the "window" referred to above. Is explained.

According to the present invention, when the trap 3 salts out hydrocarbons into the exhaust line 2, the duration of the injection time t _i calculated by the computer 6 is changed to change the air flowing into the engine. Reduce the richness of the fuel mixture.

This calculation intervenes in the model of the injection time t _i , for example in the following manner. t _i = A + F · (P + P ₀ ) where A, F and P ₀ are coefficients, and P is the suction pressure of the engine 1.

The coefficient F is particularly formed of a set of multiplication terms such as the following equation.

[0031] _{F = (1 + F 1/} 256) (1 + F 2/256) ···· (1 + ALPHA CL / 256) _Here, F _{1, F} 2, · · ·, etc., scale, air temperature, water ALPHA CL is a correction coefficient that acts when the computer 6 executes a closed loop control of the richness of the air-fuel mixture gas supplied to the engine, which is called a “richness control loop”. is there.

In this case, in order to maintain the fuel richness of the air-fuel mixture gas at 1 in accordance with the variation of the signal generated from the oxygen probe 5, the conventional coefficient ALPHA CL is theoretically set as shown in FIG. Can be changed as shown in FIG.

Similarly, when the probe 5 detects a transition from “rich” to “poor” or “poor” to “rich” of the gas mixture, the correction introduces a new variation in the signal generated by the probe 5. Until it does, ALPHA CL first receives a “proportional correction” CP,
Then, the "integral correction" CI is received, and the same is repeated thereafter.

In this way, since the area of the range between the curve representing ALPHA CL and the time axis located on both sides of the time axis is exactly balanced, richness having an average value equal to 1 is theoretically obtained. .

In practice, known oxygen probes differ slightly depending on whether they transition from a rich gas mixture to a poor gas mixture or, conversely, from a poor gas mixture to a rich gas mixture. It can be seen that the timing of the fluctuation and the richness when the output of the probe fluctuates are not exactly equal to one. This deviation causes a particular probe to perform control around richness slightly above or below one, with sufficient correction later. Conventionally, this phenomenon is corrected by changing the proportional correction CP so that the above-mentioned area restores the balance.

According to the present invention, when the trap 3 salts out incompletely combusted hydrocarbons into the exhaust line, as shown in FIG. 3, the value of the proportional correction CP applied to the ALPHA CL is changed. By changing it, the set value of the richness nominally equal to 1 in the control executed by the computer 6 is reduced. This operation consists in increasing the absolute value of the proportional correction when the probe 5 detects a rich mixed gas, and decreasing the absolute value of the proportional correction when the probe 5 detects a poor mixed gas.

In practice, the nominal value of the proportional correction CP is changed by adding or subtracting an “offset” O. The offset O is added to or subtracted from the absolute value of the correction factor, respectively, depending on whether the gas mixture is rich or poor.

This “offset” has the effect of increasing the area under the time axis located between the curve representing ALPHA CL and the time axis, compared to the corresponding area on the time axis. Is clear from FIG. In this way, the calculation based on this adjustment is included to artificially reduce the set value of the richness.

According to the present invention, the reduction in the amount of fuel injected into the engine thus obtained is
Offsetting the amount of fuel salted out of the trap 3 in the exhaust line 2 and thus guaranteeing the hydrocarbon content of the engine exhaust gas the effective treatment of the hydrocarbons contained in this gas. To maintain within the appropriate limits allowed for the pot of catalyst.

As seen above, this “offset” O corrects for deviations in the richness set point on the side of the poor or rich gas mixture, due to the unique characteristics of the oxygen probe used. Can be added to the other required.

According to another feature of the invention, the offset O is advantageously a function of the flow rate DHC of hydrocarbons salted out of the trap 3, which flow rate is given by the relation (
It can be known from the computer 6 by 2).

The present invention satisfies the above objectives, and advantageously, is normally present around an internal combustion engine connected to an exhaust line provided with a trap for hydrocarbons and a pot of catalyst for treating exhaust gases. It is now evident that it can be achieved without using material means other than the ones.

[Brief description of the drawings]

FIG. 1 shows the arrangement of an apparatus for carrying out the method according to the invention, which is described in particular at the beginning of the detailed description of the invention.

FIG. 2 is a graph useful for explaining the method according to the invention.

FIG. 3 is a graph useful for explaining the method according to the present invention.

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Claims (10)

[Claims] 1. An internal combustion engine air system in which exhaust gas flows into an exhaust line (2) in which said exhaust gas passes successively through a hydrocarbon trap (3) and a catalyst pot (4) for treating the exhaust gas. A method for controlling the richness of the fuel gas mixture, wherein the richness of the fuel of the air / fuel gas mixture is controlled by the exhaust line (2) between the engine (1) and the hydrocarbon trap (3); A method for controlling the richness of an air-fuel mixture of an internal combustion engine, wherein the richness is controlled to a predetermined richness set value by a signal transmitted from an oxygen probe (5) disposed therein. A hydrogen trap (3) is presumably detected to be operating during salting out hydrocarbons into said exhaust line (2); b) said hydrocarbon traps (3) When in the operating state of the salt 析中 is
A method for controlling the richness of an air / fuel mixture gas of an internal combustion engine, wherein the set value of the richness in the closed loop control of the richness is reduced. 2. In the step a), the amount of fuel (MHC) contained in the hydrocarbon trap (3) is estimated, and if the amount of fuel is positive and the hydrocarbon trap (3) is If the temperature (T _p ) is equal to or higher than the predetermined temperature (T _s ), it is detected that the hydrocarbon trap (3) is in an operating state during salting out hydrocarbons. The method for controlling the richness of an air / fuel mixture gas of an internal combustion engine according to claim 1. 3. When the temperature of the hydrocarbon trap (3) is equal to or lower than the predetermined temperature (T _s ), the amount (MHC) of the fuel is changed to the current value (MHC _i ) of the amount. The following model: MHC _i = MHC _i−1 + ΔMHC and ΔMHC = K ₁ · K ₂ · DGE where K ₁ and K ₂ are coefficients, and DGE is the flow rate of exhaust gas. 3. The method according to claim 2, wherein the richness control of the air / fuel mixture gas of the internal combustion engine is performed. 4. The internal combustion engine according to claim 3, wherein one of the coefficients (K ₂ ) is a function of the richness of the air / fuel mixture supplied to the engine (1). A richness control method for air / fuel mixture gas. 5. When the temperature (T _p ) of the trap (3) is equal to or higher than the predetermined temperature (T _s ), an estimated value (MHC) of the amount of the fuel in the trap (3) is calculated. 5. The method according to claim 3, wherein the exhaust gas is decremented in proportion to the flow rate (DGE) of the exhaust gas. 6. When the operation of the engine (1) is stopped, the amount of the fuel in the trap (3) is reduced for initial setting of the calculation of the amount of the fuel at the next start of the engine. The method according to any one of claims 3 to 5, wherein the estimated value is stored. 7. In the step (b), a set value of the richness of the closed loop control of the richness of the air / fuel mixture gas supplied to the engine is calculated by calculating a fuel injection time (t _i ) to the engine. Intervening with the correction factor of the richness control loop (
7. The method for controlling richness of an air-fuel mixture gas of an internal combustion engine according to any one of claims 1 to 6, wherein ALPHA CL is changed and reduced. 8. The method according to claim 7, wherein the proportional correction (CP) of the correction coefficient (ALPHA CL) is changed so as to adjust the air / fuel mixed gas to a poor mixed gas. A method for controlling richness of an air / fuel mixture gas of an internal combustion engine. 9. The operation of changing the proportional correction (CP) includes adding an offset (O) to the absolute value of the proportional correction (CP) depending on whether the mixed gas is rich or poor. 9. The method for controlling richness of an air-fuel mixture gas of an internal combustion engine according to claim 8, wherein the method further comprises subtracting an offset (O) from an absolute value of the proportional correction (CP). 10. The air / fuel mixture of an internal combustion engine according to claim 9, wherein the offset (O) is a function of a hydrocarbon flow rate (DHC) of the trap (3). Richness control method.