JP2008223709A - Exhaust emission control system of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide technology of enabling suitable fuel addition irrespective of fuel property in an exhaust emission control system of an internal combustion engine equipped with a fuel addition valve for adding fuel to exhaust gas of the internal combustion. <P>SOLUTION: In the exhaust emission control system of the internal combustion engine equipped with the fuel addition valve for adding using fuel of the internal combustion engine to exhaust gas upstream of an exhaust emission control device, operation of the fuel addition valve is permitted on the condition that temperature of the exhaust emission control device is equal to or higher than a base temperature Tbase, and the base temperature Tbase is varied according to minimum evaporation temperature Tmin of fuel. According to the invention, the operation of the fuel addition valve is permitted only when fuel added from the fuel addition valve can evaporate, and the fuel added from the fuel addition valve does not attach to the fuel addition valve or the inner wall surface of an exhaust passage. As a result, clogging of the fuel addition valve and shortage of fuel supplied to the exhaust emission control device are inhibited. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification system for an internal combustion engine provided with a fuel addition valve for adding fuel of the internal combustion engine into exhaust gas.

2. Description of the Related Art Conventionally, a technique is known in which a fuel addition valve is attached to an exhaust passage of an internal combustion engine, and fuel of the internal combustion engine is supplied from the fuel addition valve to a particulate filter or a catalyst (see, for example, Patent Document 1).
Japanese Patent Laid-Open No. 2006-177311 JP 2006-177313 A

  By the way, as a fuel for an internal combustion engine, development of a heterogeneous fuel represented by a biofuel has been promoted. For this reason, it is expected that different types of fuel are mixed in the fuel of the internal combustion engine.

  However, different fuels have evaporative properties different from fossil fuels such as light oil and gasoline. For this reason, when a fuel containing a different type of fuel is added from the fuel addition valve, the added fuel may not evaporate and may accumulate on the fuel addition valve or the exhaust passage wall surface.

  The present invention has been made in view of the above circumstances, and an object of the present invention is to improve the properties of fuel in an exhaust purification system for an internal combustion engine including a fuel addition valve for adding fuel to the exhaust of the internal combustion engine. Regardless of this, the present invention is to provide a technique capable of suitably adding fuel.

  In order to solve the above-described problem, the present invention provides an exhaust purification system for an internal combustion engine including a fuel addition valve for adding fuel to exhaust gas upstream from an exhaust purification device. The operating condition of was changed.

  Specifically, the present invention relates to an exhaust purification device that is provided in an exhaust passage of an internal combustion engine and purifies exhaust, a fuel addition valve that adds fuel of the internal combustion engine into exhaust upstream of the exhaust purification device, and an exhaust purification device The acquisition means for acquiring the temperature of the engine, the permission means for permitting the operation of the fuel addition valve when the temperature acquired by the acquisition means is equal to or higher than the reference temperature, and the evaporability of the fuel actually used by the internal combustion engine And a changing means for changing the reference temperature according to the evaporability determined by the determining means.

  Here, the “temperature of the exhaust purification device” refers to the bed temperature of the catalyst provided in the exhaust purification device, the temperature of exhaust flowing into (or out of) the exhaust purification device, and the temperature of exhaust contacting the fuel addition valve. It is a concept that includes

  The operating conditions of the fuel addition valve are determined on the assumption that fossil fuels such as light oil and gasoline are used. For this reason, when different types of fuel are mixed in the fuel actually used by the internal combustion engine (hereinafter referred to as “used fuel”), the fuel added from the fuel addition valve cannot perform the desired function. There is also the possibility of inducing defects.

For example, a fuel containing a heterogeneous fuel and a fossil fuel (hereinafter referred to as “heterogeneous mixed fuel”) is less evaporative than a fuel containing only a fossil fuel (hereinafter referred to as “specified fuel”). . For this reason, when the fuel addition valve adds the heterogeneous mixed fuel, the added fuel is not completely evaporated and the deposit is easily generated.

  On the other hand, the exhaust gas purification system for an internal combustion engine according to the present invention permits the operation of the fuel addition valve on the condition that the temperature of the exhaust gas purification device is equal to or higher than the reference temperature, and according to the evaporability of the fuel used Change the reference temperature. That is, the exhaust gas purification system for an internal combustion engine according to the present invention changes the temperature range in which the operation of the fuel addition valve is permitted (hereinafter referred to as “operation temperature range”) according to the evaporability of the fuel used.

  According to this invention, even if the fuel used in the internal combustion engine is a heterogeneous mixed fuel, the fuel addition valve can be operated under conditions that allow the added fuel to evaporate. As a result, deposit generation can be suppressed.

  The changing unit according to the present invention may increase the reference temperature as the evaporability determined by the determining unit decreases. In this case, the lower the evaporability of the fuel, the higher the operating temperature range of the fuel addition valve. As a result, the added fuel is surely evaporated.

  In addition, the evaporability of fuel correlates with the ratio (content rate) of different types of fuel contained in the used fuel. For example, when the heterogeneous fuel is biofuel, the evaporability of the fuel used decreases as the biofuel content increases.

  Therefore, the discriminating means according to the present invention may discriminate the evaporability of the used fuel based on the different fuel content of the used fuel.

  ADVANTAGE OF THE INVENTION According to this invention, in the exhaust gas purification system of the internal combustion engine provided with the fuel addition valve which adds fuel in exhaust_gas | exhaustion, suitable fuel addition can be performed irrespective of the property of a fuel.

  Hereinafter, specific embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a diagram showing a schematic configuration of an exhaust gas purification system for an internal combustion engine according to the present invention. An internal combustion engine 1 shown in FIG. 1 is a compression ignition type internal combustion engine (diesel engine) having a plurality of cylinders 2.

  Gas (burned gas) combusted in each cylinder 2 of the internal combustion engine 1 is discharged to the exhaust manifold 3. Exhaust gas discharged to the exhaust manifold 3 is guided to the exhaust pipe 5 via the turbine housing 40 of the turbocharger 4.

  An exhaust purification device 6 is disposed in the middle of the exhaust pipe 5. The exhaust purification device 6 includes at least one of an NOx storage reduction catalyst, an oxidation catalyst, and a particulate filter, and purifies the exhaust gas flowing through the exhaust pipe 5.

  In addition, the internal combustion engine 1 includes a fuel addition valve 7 that adds fuel into the exhaust manifold 3. The fuel addition valve 7 communicates with the fuel tank 9 through the fuel supply pipe 8. A pump 10 that pumps the fuel in the fuel tank 9 to the fuel addition valve 7 is disposed in the middle of the fuel supply pipe 8.

The internal combustion engine 1 configured as described above is provided with an ECU 11. The ECU 11 is an electronic control unit including a CPU, a ROM, a RAM, a backup RAM, and the like.

  Various sensors such as a fuel pressure sensor 12, a first exhaust temperature sensor 13, a second exhaust temperature sensor 14, an air-fuel ratio sensor 15, a crank position sensor 16, and an air flow meter 17 are electrically connected to the ECU 11.

  The fuel pressure sensor 12 is a sensor that is attached to the fuel supply pipe 8 and measures the pressure (fuel pressure) in the fuel supply pipe 8. The first exhaust temperature sensor 13 is a sensor that is attached to the exhaust pipe 5 upstream from the exhaust purification device 6 and downstream from the turbine housing 40 and measures the temperature of the exhaust gas flowing into the exhaust purification device 6. The second exhaust temperature sensor 14 is a sensor that is attached to the exhaust pipe 5 downstream of the exhaust purification device 6 and measures the temperature of the exhaust gas flowing out from the exhaust purification device 6. The air-fuel ratio sensor 15 is a sensor that is attached to the exhaust pipe 5 downstream from the exhaust purification device 6 and measures the air-fuel ratio of the exhaust gas flowing out from the exhaust purification device 6.

  The ECU 11 performs fuel addition control for switching operation / non-operation of the fuel addition valve 7 based on the measurement values of the various sensors described above. For example, when the ECU 11 needs to reduce NOx stored in the exhaust purification device 6, oxidize PM collected in the exhaust purification device 6, or eliminate sulfur poisoning of the exhaust purification device 6, the fuel addition valve 7 is activated.

  At that time, the ECU 11 permits the operation of the fuel addition valve 7 on condition that the fuel added from the fuel addition valve 7 can evaporate. Specifically, the ECU 11 permits the operation of the fuel addition valve 7 on the condition that the temperature of the exhaust purification device 6 is equal to or higher than the reference temperature Tbase. The reference temperature Tbase is the lowest temperature at which the added fuel can evaporate (hereinafter referred to as “minimum evaporation temperature”).

  By the way, the reference temperature Tbase is a temperature determined on the assumption that the fuel used in the internal combustion engine 1 is a specified fuel (a fuel containing only light oil). For this reason, when the fuel used is a heterogeneous mixed fuel including light oil and biofuel (heterogeneous fuel), the reference temperature Tbase may become an inappropriate temperature.

  Biofuels are less evaporative than specified fuels. That is, the minimum evaporation temperature of the biofuel is higher than the minimum evaporation temperature of the specified fuel. For this reason, when the fuel addition valve 7 adds a different kind of mixed fuel, the added fuel cannot evaporate and the exhaust passage upstream of the fuel addition valve 7 and the exhaust purification device 6 (exhaust manifold 3, turbine housing 40, and exhaust pipe). 5) adheres to the inner wall surface.

  If the added fuel adheres to the fuel addition valve 7, the fuel addition valve 7 may be clogged. Further, if the added fuel adheres to the inner wall surface of the exhaust passage upstream of the exhaust purification device 6, the added fuel supplied to the exhaust purification device 6 is insufficient, so that the exhaust purification device 6 can exhibit the desired purification performance. It may disappear.

  In contrast, in the fuel addition control of this embodiment, the ECU 11 changes the reference temperature Tbase according to the evaporability of the fuel used.

  Specifically, the ECU 11 first obtains the biofuel content rate (in other words, biofuel concentration) of the used fuel. Since the biofuel has a characteristic that the kinematic viscosity is higher than that of the specified fuel, the biofuel content rate is obtained using the pressure of the fuel flowing through the fuel supply pipe 8 (measured value of the fuel pressure sensor 12) as a parameter. Also good. In addition, the method of calculating | requiring biofuel content rate is not restricted to an above-described method, Various conventionally well-known methods can be used.

  Next, the ECU 11 determines the evaporability of the fuel used using the biofuel content rate as a parameter. In this embodiment, the minimum evaporation temperature of the used fuel is used as a physical quantity indicating the evaporability of the used fuel.

  As shown in FIG. 2, the minimum evaporation temperature of the fuel used decreases as the biofuel content of the fuel used decreases, and increases as the biofuel content of the fuel used increases. Note that T0 in FIG. 2 is the minimum evaporation temperature of the specified fuel.

  Therefore, in this embodiment, the relationship between the minimum evaporation temperature and the biofuel content as shown in FIG. 2 is obtained experimentally in advance, and the relationship is mapped.

  The ECU 11 specifies the minimum evaporation temperature of the fuel used based on the biofuel content rate and the map shown in FIG. The ECU 11 updates the reference temperature Tbase with the specified minimum evaporation temperature (that is, sets the minimum evaporation temperature to the reference temperature Tbase).

  As described above, when the reference temperature Tbase is changed according to the minimum evaporation temperature of the fuel used, the operation of the fuel addition valve 7 is prohibited under a situation where the added fuel cannot be evaporated. That is, the operation of the fuel addition valve 7 is permitted only under a situation where the added fuel can evaporate.

  As a result, clogging of the fuel addition valve 7 or shortage of the added fuel supplied to the exhaust purification device 6 does not occur.

  Hereafter, the execution procedure of the fuel addition control in a present Example is demonstrated along the flowchart of FIG. FIG. 3 is a flowchart showing a fuel addition control routine. The fuel addition control routine is stored in advance in the ROM of the ECU 11 and is periodically executed by the ECU 11. In addition, when the ECU 11 executes the fuel addition control routine of FIG.

  In the fuel addition control routine, the ECU 11 first specifies the biofuel content L of the fuel used in S101.

  In S102, the ECU 11 determines whether or not the biofuel content L acquired in S101 is greater than zero. If an affirmative determination is made in S102 (L> 0), the ECU 11 regards the fuel used as a heterogeneous mixed fuel and proceeds to S103.

  In S103, the ECU 11 calculates a minimum evaporation temperature Tmin based on the biofuel content L obtained in S101 and the map shown in FIG.

  In S104, the ECU 11 sets the minimum evaporation temperature Tmin calculated in S103 to the reference temperature Tbase.

  If a negative determination is made in S102 (L = 0), the ECU 11 regards the fuel used as the specified fuel and proceeds to S105. In S105, the ECU 11 sets the minimum evaporation temperature T0 of the specified fuel to the reference temperature Tbase.

  After completing the process of S104 or S105, the ECU 11 proceeds to S106. In S106, the ECU 11 acquires the temperature Tcat of the exhaust purification device 6. Specifically, the ECU 11 acquires a measurement value of the first exhaust temperature sensor 13 or the second exhaust temperature sensor 14.

  In S107, the ECU 11 determines whether or not the temperature Tcat acquired in S106 is equal to or higher than the reference temperature Tbase set in S104 or S105.

  If an affirmative determination is made in S107 (Tcat ≧ Tbase), the ECU 11 proceeds to S108 and permits the operation of the fuel addition valve 7. That is, the ECU 11 permits fuel addition by the fuel addition valve 7.

  In this case, the ECU 11 adds fuel when it is necessary to reduce NOx occluded in the exhaust purification device 6, oxidize PM collected in the exhaust purification device 6, or eliminate sulfur poisoning of the exhaust purification device 6. It is possible to actuate the valve 7.

  On the other hand, when a negative determination is made in S107 (Tcat <Tbase), the ECU 11 proceeds to S109 and prohibits the operation of the fuel addition valve 7. That is, the ECU 11 prohibits fuel addition by the fuel addition valve 7.

  In this case, the ECU 11 may reduce the NOx stored in the exhaust purification device 6, oxidize the PM collected in the exhaust purification device 6, or eliminate sulfur poisoning of the exhaust purification device 6. The operation of the fuel addition valve 7 is refrained.

  When the ECU 11 executes the fuel addition control routine of FIG. 3 as described above, the operation of the fuel addition valve 7 is permitted only when the fuel added from the fuel addition valve 7 can evaporate. Therefore, the added fuel can reach the exhaust purification device 6 without adhering to the fuel addition valve 7 or the inner wall surface of the exhaust passage. As a result, the fuel addition valve 7 is not clogged, or the fuel supplied to the exhaust purification device 6 is not insufficient.

  In this embodiment, the example of obtaining the evaporability (minimum evaporating temperature) of the used fuel after obtaining the biofuel content of the used fuel has been described. However, the evaporability can be obtained without obtaining the biofuel content of the used fuel. (Minimum evaporation temperature) may be obtained.

  For example, the relationship between the pressure of the fuel flowing through the fuel supply pipe 8 and the minimum evaporation temperature may be previously mapped, and the minimum evaporation temperature may be obtained based on the map and the measured value of the fuel pressure sensor 12. .

It is a figure which shows schematic structure of the exhaust gas purification system of an internal combustion engine. It is a figure which shows the relationship between the biofuel content rate of use fuel, and minimum evaporation temperature. It is a flowchart which shows a fuel addition control routine.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 ... Internal combustion engine 2 ... Cylinder 3 ... Exhaust manifold 4 ... Turbocharger 5 ... Exhaust pipe 6 ... Exhaust gas purification device 7. .... Fuel addition valve 8 ... Fuel supply pipe 9 ... Fuel tank 10 ... Pump 11 ... ECU
12 .... Fuel pressure sensor 13 .... First exhaust temperature sensor 14 .... Second exhaust temperature sensor 15 .... Air-fuel ratio sensor 40 ...... Turbine housing

Claims (3)

An exhaust purification device that is provided in an exhaust passage of the internal combustion engine and purifies exhaust;
A fuel addition valve for adding the fuel of the internal combustion engine into the exhaust gas upstream of the exhaust purification device;
Obtaining means for obtaining the temperature of the exhaust purification device;
Permission means for permitting operation of the fuel addition valve when the temperature acquired by the acquisition means is equal to or higher than a reference temperature;
Discriminating means for discriminating the evaporability of fuel actually used by the internal combustion engine;
Changing means for changing the reference temperature according to the evaporability determined by the determining means;
An exhaust gas purification system for an internal combustion engine, comprising:   2. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the changing unit increases the reference temperature as the evaporability determined by the determining unit decreases.   3. The exhaust gas purification system for an internal combustion engine according to claim 1, wherein the discrimination means discriminates evaporability based on a different fuel content rate of fuel actually used by the internal combustion engine.

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