JP4645471B2 - Sulfur poisoning recovery control device - Google Patents

Description

  The present invention relates to a sulfur poisoning recovery control device.

A technique is known in which an NOx storage reduction catalyst (hereinafter simply referred to as a NOx catalyst) is disposed in an exhaust passage of an internal combustion engine. This NOx catalyst occludes NOx in the exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reduces the NOx occluded when the oxygen concentration of the inflowing exhaust gas decreases and a reducing agent is present.

  By the way, the NOx catalyst also stores the sulfur component contained in the fuel by the same mechanism as NOx. The sulfur component occluded in this way is less likely to be released than NOx and accumulates in the NOx catalyst. This is called sulfur poisoning. Since the NOx purification rate of the NOx catalyst is reduced by this sulfur poisoning, it is necessary to perform a sulfur poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This sulfur poisoning recovery process is performed by causing the NOx catalyst to have a high temperature and exhaust gas with a reduced oxygen concentration to flow through the NOx catalyst.

Even in an internal combustion engine that uses a mixture of a plurality of fuels, NOx is contained in the exhaust gas, so an exhaust reduction NOx catalyst may be provided in the exhaust passage (see, for example, Patent Document 1).
). Even in such a case, if the mixed fuel contains a sulfur component, sulfur poisoning of the NOx storage reduction catalyst occurs.

  By the way, in an internal combustion engine that uses a mixture of a plurality of fuels, the combustion state changes depending on the fuel mixing ratio, so the ignition timing or the like may change depending on the fuel mixing ratio. Thereby, the temperature of the exhaust gas changes.

Here, when performing the sulfur poisoning recovery process, the temperature of the NOx catalyst must be raised, but the NOx catalyst does not become hot depending on the operating state of the internal combustion engine. Therefore, the sulfur poisoning recovery process is performed in a predetermined operating state in which the NOx catalyst can be brought to a high temperature. However, since the sulfur poisoning recovery process cannot be performed unless the operating state is capable of raising the temperature of the NOx catalyst, the NOx purification rate of the NOx catalyst may decrease if this state continues for a long time.
Japanese Patent No. 2692311 JP-A-3-124965

When a plurality of fuels are mixed and used, the temperature of the exhaust gas changes depending on the mixing ratio of the fuel, so that the operating state in which the NOx catalyst can be heated may change. On the other hand, if the sulfur poisoning recovery can be performed in the widest possible operating range, the NOx purification rate can be improved.

  The present invention has been made in view of the above-described problems, and an object of the present invention is to provide a technique capable of performing sulfur poisoning recovery processing in a wider operation region in the sulfur poisoning recovery control device. To do.

In order to achieve the above object, the sulfur poisoning recovery control apparatus according to the present invention employs the following means. That is, the sulfur poisoning recovery control device according to the present invention is:
A sulfur poisoning recovery control device for performing sulfur poisoning recovery processing when the sulfur poisoning amount of an NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine using a mixture of a plurality of fuels exceeds a predetermined amount. ,
Fuel concentration detecting means for detecting the concentration of a predetermined type of fuel in the fuel supplied to the internal combustion engine;
Based on the concentration detected by the fuel concentration detection means, sulfur poisoning recovery area determination means for determining an operation area in which the sulfur poisoning recovery processing is performed,
It is characterized by comprising.

The internal combustion engine uses a mixture of a plurality of fuels as a mixed fuel. The burning speed, burning temperature, or ignition timing of each fuel in the mixed fuel may be different. Therefore, the exhaust temperature may vary depending on the fuel mixing ratio. Then, the operating state in which the temperature of the NOx storage reduction catalyst can be raised to the temperature required for recovery of sulfur poisoning varies depending on the fuel mixing ratio.

  Therefore, the sulfur poisoning recovery area determining means determines an operation area in which the sulfur poisoning recovery process is performed based on the concentration detected by the fuel concentration detecting means. Here, the operation region is divided based on, for example, the engine speed and the engine load. The sulfur poisoning recovery process can be performed at a lower speed or a lower load as the ratio of the fuel that increases the exhaust temperature increases. As a result, the operating range in which the sulfur poisoning recovery process can be performed is widened, so that it is possible to suppress a reduction in the NOx purification rate resulting from the inability to perform the sulfur poisoning recovery process.

In the present invention, the internal combustion engine uses a mixture of a plurality of fuels including at least alcohol,
The fuel concentration detection means detects the concentration of alcohol in the fuel supplied to the internal combustion engine,
The sulfur poisoning recovery region determining means extends the operating region in which the sulfur poisoning recovery processing is performed to a low rotation side or a low load side of the internal combustion engine as the alcohol concentration detected by the fuel concentration detecting means is higher. Can do.

  Since alcohol burns faster than gasoline or the like, the ignition timing is generally retarded as the alcohol concentration increases. Thus, when the same torque is generated in the internal combustion engine, the temperature of the exhaust becomes higher as the alcohol concentration is higher. Therefore, as the alcohol concentration is higher, the sulfur poisoning recovery process can be performed at a lower rotation or load.

  Moreover, since the occurrence of knocking is suppressed as the alcohol concentration increases, operation with a high load becomes possible. And in the area | region where the driving | operation with high load was attained, sulfur poisoning recovery processing can also be performed. That is, as the alcohol concentration increases, the sulfur poisoning recovery process can be performed even at a higher load.

According to the present invention, the sulfur poisoning recovery process can be performed in a wider operating range. Thereby, since the opportunity to perform sulfur poisoning recovery processing can be increased, the NOx purification rate can be improved.

  Hereinafter, specific embodiments of the sulfur poisoning recovery control apparatus according to the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram illustrating a schematic configuration of an internal combustion engine 1 to which a sulfur poisoning recovery control apparatus according to the present embodiment is applied, and an intake system and an exhaust system thereof. An internal combustion engine 1 shown in FIG. 1 is a water-cooled four-cycle engine. The internal combustion engine 1 can use a mixed fuel in which gasoline and alcohol are mixed at an arbitrary ratio. The internal combustion engine 1 can be burned in a homogeneous lean or stratified lean.

  An intake passage 3 that leads to the combustion chamber 2 is connected to the internal combustion engine 1. An air flow meter 4 for measuring the intake air amount of the internal combustion engine 1 is attached in the middle of the intake passage 3. A throttle 5 is provided in the intake passage 3 closer to the internal combustion engine 1 than the air flow meter 4. A throttle opening sensor 51 that outputs a signal corresponding to the opening of the throttle 5 is attached to the throttle 5. The load on the internal combustion engine 1 can be detected from the output signal of the throttle opening sensor 51. Then, the amount of fuel supplied to the internal combustion engine 1 is calculated based on the output signal from the air flow meter 4 or the throttle opening sensor 51.

  A fuel injection valve 6 that injects fuel into the intake passage 3 is attached to the intake passage 3 closer to the internal combustion engine 1 than the throttle 5. A fuel supply pipe 61 is connected to the fuel injection valve 6, and fuel flows in the fuel supply pipe 61. Further, an alcohol concentration sensor 62 for detecting the alcohol concentration of the fuel flowing through the fuel supply pipe 61 is attached to the fuel supply pipe 61. In this embodiment, the alcohol concentration sensor 62 corresponds to the fuel concentration detecting means in the present invention.

On the other hand, an exhaust passage 7 leading to the combustion chamber 2 is connected to the internal combustion engine 1. An occlusion reduction type NOx catalyst (hereinafter simply referred to as NOx catalyst) 8 is provided in the middle of the exhaust passage 7. The NOx catalyst 8 has a function of storing NOx in exhaust when the oxygen concentration of the inflowing exhaust gas is high, and reducing NOx stored when the oxygen concentration of the inflowing exhaust gas is reduced and a reducing agent is present. Have. An air-fuel ratio sensor 9 that outputs an electric signal corresponding to the air-fuel ratio of the exhaust gas flowing through the exhaust passage 7 is attached to the exhaust passage 7 upstream of the NOx catalyst 8.

  The internal combustion engine 1 configured as described above is provided with an ECU 10 that is an electronic control unit for controlling the internal combustion engine 1. The ECU 10 controls the operation state of the internal combustion engine 1 according to the operation conditions of the internal combustion engine 1 and the request of the driver. In addition to the above sensors, the ECU 10 is connected to a crank position sensor 11 that outputs a signal corresponding to the engine speed via electric wiring, and the output signals of these sensors are input. On the other hand, the fuel injection valve 6 is connected to the ECU 10 through electric wiring, and the fuel injection valve 6 is controlled by the ECU 10.

By the way, the NOx catalyst 8 stores the sulfur component contained in gasoline by the same mechanism as NOx. The sulfur component occluded in this manner is less likely to be released than NOx and is accumulated in the NOx catalyst 8. This is called sulfur poisoning. Since the NOx purification rate in the NOx catalyst 8 is reduced by this sulfur poisoning, it is necessary to perform a sulfur poisoning recovery process for recovering from sulfur poisoning at an appropriate time. This sulfur poisoning recovery process is performed by causing the NOx catalyst 8 to have a high temperature and the exhaust gas with a reduced oxygen concentration to flow through the NOx catalyst 8. In the sulfur poisoning recovery process, the ECU 10
The air-fuel ratio of the exhaust gas flowing into the NOx catalyst 8 is temporarily set to a predetermined target rich air-fuel ratio. The sulfur component is released from the NOx catalyst 8 as the temperature of the NOx catalyst 8 rises. Thereby, it becomes possible to recover the sulfur poisoning of the NOx catalyst 8.

Here, the higher the concentration of alcohol in the mixed fuel, the higher the combustion speed, and therefore the ignition timing is retarded, so the temperature of the exhaust becomes higher. Therefore, the sulfur poisoning recovery process can be performed at a lower rotation or a lower load. Further, since the occurrence of knocking is suppressed as the alcohol concentration increases, the internal combustion engine 1 can be operated at a higher load. Therefore, the sulfur poisoning recovery process can be performed with a higher load. These relationships are shown in FIG.

  FIG. 2 is a diagram showing the relationship between the engine speed, the engine load, and the operation region in which the sulfur poisoning recovery process can be performed for each alcohol concentration. Solid lines (1) and (11) indicate when the alcohol concentration is 0%, that is, gasoline only, alternate long and short dash lines (2) and (12) indicate when the alcohol concentration is 50%, and dashed lines (3) and (11) (13) indicates when the alcohol concentration is 100%. Also, the upwardly convex lines (1), (2) and (3) indicate the maximum loads at the respective engine speeds, and the downwardly convex lines (11), (12) and (13) are respectively The lower limit of the engine load at which the sulfur poisoning recovery process can be performed at the engine speed is shown.

  That is, when the alcohol concentration is 0%, the operation region in which the sulfur poisoning recovery process is possible is occupied by the side having a lower load than the line (1) and the side having a higher load than the line (11), that is, an oblique line. It is an area. In addition, the operation region in which the sulfur poisoning recovery process is possible when the alcohol concentration is 50% is a side where the load is lower than the line (2) and a side where the load is higher than the line (12). Furthermore, the operation region in which the sulfur poisoning recovery process is possible when the alcohol concentration is 100% is a side where the load is lower than the line (3) and a side where the load is higher than the line (13).

  Thus, the higher the alcohol concentration, the wider the operating range in which the poisoning recovery process can be performed. The engine load in FIG. 2 may be a fuel injection amount.

Therefore, in this embodiment, the operation region where the sulfur poisoning recovery process of the NOx catalyst 8 is performed is changed according to the alcohol concentration in the mixed fuel.

  Next, the flow of the sulfur poisoning recovery process according to the present embodiment will be described. FIG. 3 is a flowchart showing a flow of the sulfur poisoning recovery process according to the present embodiment. This routine is repeatedly executed every predetermined time.

  In step S101, the alcohol concentration is read. In this step, the alcohol concentration of the fuel is detected by the alcohol concentration sensor 62, and the value is stored in the ECU 10. Instead of using the alcohol concentration sensor 62, the alcohol concentration may be estimated from a feedback value at the time of feedback control of the fuel supply amount based on the air-fuel ratio detected by the air-fuel ratio sensor 9.

  In step S102, the sulfur poisoning amount is integrated based on the alcohol concentration. The sulfur poisoning amount is obtained by performing correction according to the alcohol concentration with reference to the case where fuel of 100% gasoline is supplied. The formula for calculating the integrated value S (n + 1) is as follows.

  S (n + 1) = F × R × T × K × KAL + S (n)

  Where F is the fuel injection amount per revolution of the internal combustion engine 1, R is the engine speed per unit time, T is the elapsed time from the previous integration time to the current integration time, K is a coefficient, KAL is the alcohol concentration coefficient, S (N) is an integrated value of the sulfur poisoning amount obtained during the previous treatment. The alcohol concentration coefficient KAL is a value for correcting the sulfur poisoning amount in accordance with the alcohol concentration. Since alcohol does not contain a sulfur component, the alcohol concentration coefficient KAL is obtained by the following equation.

  KAL = (100-AL) / 100

  However, AL is alcohol concentration (%).

  The fuel injection amount F can be obtained from a command value for the ECU 10 to open the fuel injection valve 6. Further, the fuel injection amount F may be obtained based on the intake air amount obtained by the air flow meter 4 or the throttle opening obtained by the throttle opening sensor 51. The engine speed R can be obtained from the crank position sensor 11. The elapsed time T can be obtained by integrating the time from when the previous flow is executed until the current flow is executed. The coefficient K is, for example, the concentration (%) of the sulfur component in gasoline, and is obtained in advance by experiments or the like. Further, when other correction is necessary, the correction is performed by the coefficient K.

Thus, by integrating the sulfur poisoning amount, the amount of the sulfur component stored in the NOx catalyst 8 can be obtained.

In step S103, it is determined whether or not the sulfur poisoning recovery operation state is performed without performing the sulfur poisoning recovery process. That is, it is determined whether or not the temperature of the NOx catalyst 8 has risen to a temperature at which sulfur poisoning recovery can be performed, and the exhaust air-fuel ratio is rich. Depending on the operating state of the internal combustion engine 1, sulfur poisoning is recovered without performing the sulfur poisoning recovery process. In such a case, the sulfur poisoning recovery process is not performed. Thereby, deterioration of fuel consumption and thermal deterioration of the NOx catalyst 8 can be suppressed. If an affirmative determination is made in step S103, the process proceeds to step S107, whereas if a negative determination is made, the process proceeds to step S104.

In step S104, it is determined whether or not the integrated value S (n + 1) of the sulfur poisoning amount is a predetermined amount or more. The predetermined amount is set in advance as a value that requires a sulfur poisoning recovery process. That is, in this step, it is determined whether the sulfur poisoning recovery process of the NOx catalyst 8 is necessary. If an affirmative determination is made in step S104, the process proceeds to step S105, whereas if a negative determination is made, this routine is temporarily terminated.

  In step S105, it is determined whether the fuel injection amount is equal to or greater than a threshold value. In this step, it is determined whether or not it is an operating region in which the sulfur poisoning recovery process can be performed based on the engine speed, the alcohol concentration, and the fuel injection amount.

  FIG. 4 is a diagram showing the relationship among the engine speed, the alcohol concentration, and the fuel injection amount threshold.

The engine speed obtained by the crank position sensor 11 and the alcohol concentration obtained by the alcohol concentration sensor 62 are substituted into FIG. 4 to obtain a fuel injection amount (mm ³ / st) threshold value. The threshold value of the fuel injection amount is a fuel amount injected from the fuel injection valve 6 and is a lower limit value of the fuel injection amount that enables the sulfur poisoning recovery process. If the fuel injection amount is larger than this threshold, the exhaust gas temperature is required for the sulfur poisoning recovery process, and the sulfur poisoning recovery process can be performed. In the operation region where the sulfur poisoning recovery process cannot be performed, the threshold value of the fuel injection amount is set to a value (for example, 1000) that is not possible.

  By the way, since the calorific value of alcohol per unit volume is smaller than that of gasoline, it is necessary to increase the fuel injection amount as the alcohol concentration increases when the same torque is to be generated. However, in FIG. 4, for easy understanding, it is conceptually shown without considering the increase in the fuel injection amount according to the alcohol concentration. Actually, the fuel injection amount is corrected according to the alcohol concentration. Thus, the threshold value after correcting the fuel injection amount in accordance with the alcohol concentration may be mapped as shown in FIG.

  In this embodiment, the ECU 10 that performs the process of step S105 corresponds to the sulfur poisoning recovery region determination means in the present invention.

  In step S106, a sulfur poisoning recovery process is executed. As described above, the sulfur poisoning recovery process is performed with the air-fuel ratio of the exhaust gas being rich while keeping the NOx catalyst 8 at a high temperature.

  In step S107, the integrated value S (n + 1) of the sulfur poisoning amount is set to zero. Further, when the sulfur poisoning recovery process is stopped halfway, the integrated value S (n + 1) of the sulfur poisoning amount may be reduced by the amount recovered. Thereafter, this routine is temporarily terminated.

In this way, the higher the alcohol concentration in the mixed fuel, the wider the operating range in which the sulfur poisoning recovery process is performed. That is, when only gasoline is supplied, it is possible to increase the chances of performing the sulfur poisoning recovery process as compared with applying the region where the sulfur poisoning recovery process is possible as it is, so that the reduction in the NOx purification rate is suppressed. be able to. In addition, even when the alcohol concentration in the mixed fuel changes due to refueling, it is possible to obtain an operating region in which sulfur poisoning recovery processing can be performed each time. Even when other types of fuel are mixed, the sulfur poisoning recovery process can be performed in a wider operation region by obtaining the map shown in FIG. 4 in the same manner.

As described above, according to the present embodiment, the sulfur poisoning recovery process of the NOx catalyst 8 can be performed in a wider operation region, so that the NOx purification rate can be improved.

It is a figure which shows schematic structure of the internal combustion engine to which the sulfur poisoning recovery control apparatus which concerns on an Example is applied, and its intake system and exhaust system. It is the figure which showed the relationship between the engine speed, an engine load, and the driving | operation area | region which can perform the sulfur poisoning recovery process for every alcohol concentration. It is the flowchart which showed the flow of the sulfur poisoning recovery process which concerns on an Example. It is the figure which showed the relationship between an engine speed, alcohol concentration, and the threshold value of fuel injection amount.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Internal combustion engine 2 Combustion chamber 3 Intake passage 4 Air flow meter 5 Throttle 6 Fuel injection valve 7 Exhaust passage 8 Occlusion reduction type NOx catalyst 9 Air-fuel ratio sensor 10 ECU
11 Crank position sensor 51 Throttle opening sensor 61 Fuel supply pipe 62 Alcohol concentration sensor

Claims (2)

A sulfur poisoning recovery control device for performing sulfur poisoning recovery processing when a sulfur poisoning amount of an NOx storage reduction catalyst provided in an exhaust passage of an internal combustion engine using a mixture of a plurality of fuels exceeds a predetermined amount. ,
Fuel concentration detecting means for detecting the concentration of a predetermined type of fuel in the fuel supplied to the internal combustion engine;
Based on the concentration detected by the fuel concentration detection means, sulfur poisoning recovery area determination means for determining an operation area in which the sulfur poisoning recovery processing is performed,
A sulfur poisoning recovery control device comprising: The internal combustion engine uses a mixture of a plurality of fuels including at least alcohol,
The fuel concentration detection means detects the concentration of alcohol in the fuel supplied to the internal combustion engine,
The sulfur poisoning recovery region determining means extends the operating region in which the sulfur poisoning recovery processing is performed to a low rotation side or a low load side of the internal combustion engine as the alcohol concentration detected by the fuel concentration detecting means is higher. The sulfur poisoning recovery control device according to claim 1.

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