JP2008255942A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To accurately detect the ammonia adsorption quantity of a NO<SB>x</SB>selective reduction catalyst. <P>SOLUTION: The NO<SB>x</SB>selective reduction catalyst 15 is arranged in an engine exhaust gas passage. Urea is supplied to the NO<SB>x</SB>selective reduction catalyst 15 and ammonia formed from the urea is adsorbed by the NO<SB>x</SB>selective reduction catalyst 15. NO<SB>x</SB>contained in exhaust gas is selectively reduced mainly by the adsorbed ammonia. Quantity of NO<SB>x</SB>discharged from the engine is increase by stopping recirculation of exhaust gas during engine idling operation, and ammonia adsorption quantity adsorbed by the NO<SB>x</SB>selective reduction catalyst 15 is detected from the NO<SB>x</SB>conversion rate of the NO<SB>x</SB>selective reduction catalyst 15. <P>COPYRIGHT: (C)2009,JPO&INPIT

Description

  The present invention relates to an exhaust emission control device for an internal combustion engine.

The _the NO _x selective reduction catalyst arranged in the engine exhaust passage, and supplies urea to _the NO _x selective reducing catalyst to adsorb the ammonia generated from the urea in _the NO _x selective reduction catalyst, the exhaust gas by the adsorbed ammonia An internal combustion engine that selectively reduces NO _x contained in the engine is known (see, for example, Patent Document 1). Estimating the amount of ammonia adsorbed on _the NO _x selective reduction catalyst when the way which is adapted to selectively reduce NO _x contained in the exhaust gas by the ammonia adsorbed in this manner in _the NO _x selective reduction catalyst It will be necessary.

So from the detection value of NO _x sensor when the steady operation state of the engine operating condition of the upstream and downstream sides respectively NO _x sensor arranged to the engine of the NO _x selective reduction catalyst in the above-mentioned internal combustion engine is constant seeking _the NO _x purification rate of _the NO _x selective reduction catalyst, and calculates the amount of adsorbed ammonia that is consumed for the reduction of NO _x in _the NO _x selective reduction catalyst from exhaust NO _x amount from the _the NO _x purification rate and the engine, The amount of adsorbed ammonia adsorbed on the NO _x selective catalyst is estimated from the amount of adsorbed ammonia consumed and the amount of urea supplied.
JP 2003-314256 A

Thus, in the internal combustion engine described above is estimated the amount of adsorbed ammonia seeking _the NO _x purification rate when the steady operation state of the engine where the engine operating state is constant in this case, the most constant operating state of the engine The steady operation state of the engine becomes idling operation. However, since most NOx from the engine during idling operation is not discharged it is difficult seek _the NO _x purification rate at the time of idling operation, thus there is a problem that it is difficult to estimate the amount of adsorbed ammonia.

According to the present invention in order to solve the above problems, the _the NO _x selective reduction catalyst arranged in the engine exhaust passage, ammonia _the NO _x selective reduction catalyst by supplying urea to _the NO _x selective reduction catalyst generated from the urea In the exhaust gas purification apparatus for an internal combustion engine that is selectively adsorbed by the adsorbed ammonia and selectively reduces NO _x contained in the exhaust gas, the amount of NO _x discharged from the engine during engine idling operation is reduced. increases, so that detecting the ammonia adsorption amount adsorbed by _the NO _x purification rate _the NO _x selective reduction catalyst by _the NO _x selective reduction catalyst in this case.

It is possible to detect the amount of adsorbed ammonia by increasing the amount of NO _x discharged from the engine when the engine is idling.

FIG. 1 shows an overall view of a compression ignition type internal combustion engine.
Referring to FIG. 1, 1 is an engine body, 2 is a combustion chamber of each cylinder, 3 is an electronically controlled fuel injection valve for injecting fuel into each combustion chamber 2, 4 is an intake manifold, and 5 is an exhaust manifold. Respectively. The intake manifold 4 is connected to the outlet of the compressor 7 a of the exhaust turbocharger 7 via the intake duct 6, and the inlet of the compressor 7 a is connected to the air cleaner 9 via the intake air amount detector 8. A throttle valve 10 driven by a step motor is disposed in the intake duct 6, and a cooling device 11 for cooling intake air flowing through the intake duct 6 is disposed around the intake duct 6. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 11, and the intake air is cooled by the engine cooling water.

On the other hand, the exhaust manifold 5 is connected to the inlet of the exhaust turbine 7 b of the exhaust turbocharger 7, and the outlet of the exhaust turbine 7 b is connected to the inlet of the oxidation catalyst 12. Downstream of the oxidation catalyst 12, a particulate filter 13 for collecting particulate matter contained in the exhaust gas is disposed adjacent to the oxidation catalyst 12, and the outlet of the particulate filter 13 passes through the exhaust pipe 14. To the inlet of the NO _x selective reduction catalyst 15. An oxidation catalyst 16 is connected to the outlet of the NO _x selective reduction catalyst 15.

A urea aqueous solution supply valve 17 is disposed in the exhaust pipe 14 upstream of the NO _x selective reduction catalyst 15, and this urea aqueous solution supply valve 17 is connected to a urea aqueous solution tank 20 via a supply pipe 18 and a supply pump 19. The urea aqueous solution stored in the urea aqueous solution tank 20 is injected into the exhaust gas flowing through the exhaust pipe 14 from the urea aqueous solution supply valve 17 by the supply pump 19, and ammonia ((NH ₂ ) ₂ CO + H ₂ O generated from urea. → 2NH ₃ + CO ₂ ), NO _x contained in the exhaust gas is reduced in the NO _x selective reduction catalyst 15.

  The exhaust manifold 5 and the intake manifold 4 are connected to each other via an exhaust gas recirculation (hereinafter referred to as EGR) passage 21, and an electronically controlled EGR control valve 22 is disposed in the EGR passage 21. A cooling device 23 for cooling the EGR gas flowing in the EGR passage 21 is disposed around the EGR passage 21. In the embodiment shown in FIG. 1, the engine cooling water is guided into the cooling device 23, and the EGR gas is cooled by the engine cooling water. On the other hand, each fuel injection valve 3 is connected to a common rail 25 via a fuel supply pipe 24, and this common rail 25 is connected to a fuel tank 27 via an electronically controlled fuel pump 26 with variable discharge amount. The fuel stored in the fuel tank 27 is supplied into the common rail 25 by the fuel pump 26, and the fuel supplied into the common rail 25 is supplied to the fuel injection valve 3 through each fuel supply pipe 24.

The electronic control unit 30 is composed of a digital computer, and is connected to each other by a bidirectional bus 31. A ROM (read only memory) 32, a RAM (random access memory) 33, a CPU (microprocessor) 34, an input port 35 and an output port 36 It comprises. The _the NO _x selective reducing catalyst 15 is attached a temperature sensor 28 for detecting the bed temperature of the NO _x selective reduction catalyst 15, further on the downstream side of the NO _x selective reduction catalyst 15 detects the concentration of NO _x in the exhaust gas A NO _x sensor 29 is arranged for this purpose. The output signals of these temperature sensors 28, NO _x sensor 29 and the intake air amount detector 8 via the AD converter 37 each corresponding input to the input port 35.

  On the other hand, a load sensor 41 that generates an output voltage proportional to the depression amount L of the accelerator pedal 40 is connected to the accelerator pedal 40, and the output voltage of the load sensor 41 is input to the input port 35 via the corresponding AD converter 37. Is done. Further, the input port 35 is connected to a crank angle sensor 42 that generates an output pulse every time the crankshaft rotates, for example, 15 °. On the other hand, the output port 36 is connected to the fuel injection valve 3, the step motor for driving the throttle valve 10, the urea aqueous solution supply valve 17, the supply pump 19, the EGR control valve 22, and the fuel pump 26 through corresponding drive circuits 38. .

The oxidation catalyst 12 carries a noble metal catalyst such as platinum, for example. The oxidation catalyst 12 functions to convert NO contained in the exhaust gas into NO ₂ and oxidize HC contained in the exhaust gas. . On the other hand, the particulate filter 13 may be a particulate filter that does not carry a catalyst, or a particulate filter that carries a noble metal catalyst such as platinum. The NO _x selective reduction catalyst 15 is composed of an ammonia adsorption type Fe zeolite having a high NO _x purification rate at a low temperature. The oxidation catalyst 16 carries a noble metal catalyst made of platinum, for example, and this oxidation catalyst 16 has an action of oxidizing ammonia leaked from the NO _x selective reduction catalyst 15.

FIG. 2 shows the ammonia adsorption amount to the NO _x selective reduction catalyst 15 in the saturated state, that is, the saturated adsorption amount Qt. The present invention has been adapted to selectively reduce NO _x contained in the exhaust gas by the ammonia adsorbed on _the NO _x selective reduction catalyst 15, the ammonia adsorbed the NO _x selective reduction catalyst 15 in this case It is known that the maximum NO _x purification rate can be obtained when the amount is saturated. Therefore, in the embodiment according to the present invention, the saturated adsorption amount Qt of ammonia is set as the target ammonia adsorption amount. As shown in FIG. 2, the target ammonia adsorption amount Qt is a function of the bed temperature TC of the NO _x selective reduction catalyst 15, and the target ammonia adsorption amount Qt decreases as the bed temperature TC increases. In the embodiment according to the present invention, the supply of urea is normally controlled so that the ammonia adsorption amount to the NO _x selective reduction catalyst 15 becomes the target ammonia adsorption amount Qt.

First, engine operation control that is normally performed will be described with reference to FIG. This operation control is executed by interruption every predetermined time.
Referring to FIG. 3, first, in step 50, fuel injection control from the fuel injection valve 3 is performed. Next, at step 51, EGR control for controlling the opening degree of the EGR control valve 22 to the target opening degree is performed. Then _the exhaust NO _x amount NOXA is calculated to be discharged per unit time from the combustion chamber 2 in step 52. The discharge amount of NO _x NOXA is stored in advance in the ROM32 in the function as a form of a map of the required torque TQ and the engine rotational speed N as shown in FIG. 4 (A).

Next, at step 53, the NO _x purification rate R in the NO _x selective reduction catalyst 15 is calculated. The NO _x purification rate R is a function of the bed temperature TC of the NO _x selective reduction catalyst 15 as shown in FIG. 4B, and further changes according to the exhaust gas amount, that is, the intake air amount Ga. The NO _x purification rate R is stored in advance in the ROM 32 in the form of a map as a function of the intake air amount Ga and the bed temperature TC of the NO _x selective reduction catalyst 15 as shown in FIG.

Next, at step 54, the amount of adsorbed ammonia ND consumed per unit time for reducing NO _x is calculated from the exhausted NO _x amount NOXA and the NO _x purification rate R. Next, at step 55, the supplied ammonia amount NI supplied per unit time in the form of urea is calculated. Next, at step 56, the ammonia adsorption amount ΣNH ₃ (ΣNH ₃ + NI−ND) of the NO _x selective reduction catalyst 15 is calculated. Next, at step 57, it is judged if this ammonia adsorption amount ΣNH ₃ is larger than the target ammonia adsorption amount Qt. When ΣNH ₃ <Qt, the routine proceeds to step 58 where urea is supplied, and when ΣNH ₃ ≧ Qt, the routine proceeds to step 59 where the urea supply is stopped.

Normally, the ammonia adsorption amount ΣNH ₃ is obtained as described above, and urea supply control is performed based on the ammonia adsorption amount ΣNH ₃ . This ammonia adsorption amount ΣNH ₃ is a calculated value, so it is sometimes necessary to check whether or not this ammonia adsorption amount ΣNH ₃ accurately represents the actual ammonia adsorption amount. Therefore, in the present invention, the ammonia adsorption amount is detected during the idling operation where the engine operating state is the most constant, and the ammonia adsorption amount ΣNH ₃ calculated based on the detected ammonia adsorption amount is checked.

Incidentally, in order to obtain the ammonia adsorption amount, it is necessary that a certain amount of NO _x is discharged from the engine. However, only a small amount of NO _x is discharged from the engine during idling. Therefore, in the present invention increases the amount of NO _x discharged from the engine during engine idling operation, the _the NO _x selective ammonia adsorption amount adsorbed by _the NO _x purification rate by the reduction catalyst 15 to _the NO _x selective reduction catalyst 15 at this time I try to detect it.

In this case, when the supply of EGR gas is stopped, the combustion temperature increases and the amount of NO _x exhausted from the engine increases, so that a sufficient amount of NO _x to detect the amount of adsorbed ammonia is detected even during idling. Discharged from. Therefore, in the embodiment according to the present invention, the supply of EGR gas is stopped during the engine idling operation, that is, the exhaust gas recirculation is stopped to increase the amount of NO _x discharged from the engine.

Now, when the engine operating state becomes a predetermined operating state with the supply of EGR gas stopped during idling operation, for example, the fuel injection amount becomes a predetermined injection amount, and the engine speed is predetermined. At the same engine speed, the amount of NO _x discharged from the engine becomes the same amount of NO _x . Thus _the exhaust NO _x from _the NO _x selective reduction catalyst 15 if found through experiments in advance the relationship between _the exhaust NO _x concentration from the ammonia adsorption amount and _the NO _x selective reduction catalyst 15 to _the NO _x selective reduction catalyst 15 at this time By detecting the concentration, it is possible to detect the amount of ammonia adsorbed on the NO _x selective reduction catalyst 15 from the above relationship.

Therefore, in the present invention, the ammonia adsorption amount to _the NO _x selective reduction catalyst 15 when the supply of the EGR gas becomes operating state operating conditions predetermined engine in a state of being stopped at the time of engine idling and NO _x selective reduction catalyst 15 stores in advance the relationship between the exhaust concentration of NO _x from when the operation state of the engine during the engine idling operation is in this predetermined operating condition by stopping the supply of the EGR gas NO detecting the emission concentration of NO _x from _x selective reduction catalyst 15, and to detect the ammonia adsorption amount adsorbed by the _the NO _x selective reduction catalyst 15 from the above relationship based on the detected exhaust NO _x concentration.

Incidentally in this case, the discharge concentration of NO _x from the engine during idling operation are approximately determined by the fuel injection amount, thus the fuel injection amount is beforehand in a state where the supply of the EGR gas is stopped during engine idling operation in this embodiment of the present invention relationship between the exhaust NO _x concentration from the ammonia adsorption amount and _the NO _x selective reduction catalyst 15 to _the NO _x selective reduction catalyst 15 when it is determined target value is stored in advance. In order to facilitate understanding of the present invention, a case where the bed temperature of the NO _x selective reduction catalyst 15 is equal to or lower than the ammonia desorption temperature will be described as an example.

FIG. 5A shows the amount of ammonia adsorbed on the NO _x selective reduction catalyst 15 and the NO when the fuel injection amount reaches a predetermined target value while the supply of EGR gas is stopped during engine idling operation. The relationship with the NO _x purification rate by the _x selective reduction catalyst 15 is shown. In FIG. 5A, TC _{1 to} TC ₄ indicate the bed temperature of the NO _x selective reduction catalyst 15, and this bed temperature has a relationship of TC ₁ <TC ₂ <TC ₃ <TC ₄ . Therefore, it can be seen from FIG. 5A that the NO _x purification rate increases as the ammonia adsorption amount increases, and increases as the bed temperature of the NO _x selective reduction catalyst 15 increases.

The discharge amount of NO _x from the engine when the fuel injection amount reaches the target value set in advance in a state in which the supply of the EGR gas at the time of engine idling operation is stopped is always a certain amount, therefore _the NO _x purification at this time _the exhaust NO _x concentration from the ammonia adsorption amount and _the NO _x selective reduction catalyst 15 to _the NO _x selective reduction catalyst 15 at this time because the less _the exhaust NO _x amount exhausted from _the NO _x selective reduction catalyst 15 the higher rate is The relationship with is as shown in FIG. That is, as can be seen from FIG. 5B, the exhausted NO _x concentration decreases as the ammonia adsorption amount increases, and decreases as the bed temperature of the NO _x selective reduction catalyst 15 increases.

Discharge concentration of NO _x from _the NO _x selective reduction catalyst 15 by NO _x sensor 29 in the embodiment according to the present invention is detected, FIG. 5 (B from bed temperature of the detected exhaust NO _x concentration and _the NO _x selective reduction catalyst 15 The amount of adsorbed ammonia is determined based on the relationship shown in FIG. For example, the detected exhaust NO _x concentration is a ND in FIG. 5 (B), the ammonia adsorption amount this time the bed temperature of the NO _x selective reduction catalyst 15 is assumed to be TC ₃ becomes NX. On the other hand, when the bed temperature of the NO _x selective reduction catalyst 15 is higher than the ammonia desorption temperature, the ammonia adsorption amount decreases, so the NO _x purification rate decreases, and the exhausted NO _x amount increases. Relationship between the exhaust NO _x concentration from the ammonia adsorption amount and _the NO _x selective reduction catalyst 15 to _the NO _x selective reduction catalyst 15 in every bed temperature is stored in advance in the ROM32 in the embodiment according to the present invention.

FIG. 6 shows an ammonia adsorption amount detection routine.
Referring to FIG. 6, first, at step 60, it is judged if the engine is idling. When it is during the idling operation, the routine proceeds to step 61, where it is judged if the fuel injection amount is a target value or not. When the fuel injection amount is the target value, the routine proceeds to step 62, where it is judged if the bed temperature TC of the NO _x selective reduction catalyst 15 is lower than the upper limit temperature TC ₀ at which ammonia cannot be adsorbed so much. When TC <TC _0, the routine proceeds to step 63.

In step 63, the EGR control valve 22 is fully closed, whereby the supply of EGR gas is stopped. Next, at step 64, the supply of urea from the urea aqueous solution supply valve 17 is stopped. Next, at step 65, the NO _x sensor 29 detects the exhaust NO _x concentration from the NO _x selective reduction catalyst 15. Then the ammonia adsorption amount is detected from the relationship stored in the ROM32 based on the detected concentration of NO _x in step 66. Next, at step 67, the ammonia adsorption amount ΣNH ₃ used in the operation control routine shown in FIG. That is, the ammonia adsorption amount calculated in the operation control routine shown in FIG. 3 is updated by the detected ammonia adsorption amount.

1 is an overall view of a compression ignition type internal combustion engine. It is a figure which shows the saturated adsorption amount Qt of ammonia. It is a flowchart for controlling operation of an engine. It is a diagram showing a map or the like of the discharge amount of NO _x NOXA. Is a diagram showing the relationships of the exhaust NO _x concentration from the ammonia adsorption amount and _the NO _x selective reduction catalyst to _the NO _x selective reduction catalyst. It is a flowchart for detecting the ammonia adsorption amount.

Explanation of symbols

4 Intake manifold 5 Exhaust manifold 7 Exhaust turbocharger 12, 16 Oxidation catalyst 13 Particulate filter 15 NO _x selective reduction catalyst 17 Urea aqueous solution supply valve 29 NO _x sensor

Claims (6)

The _the NO _x selective reduction catalyst arranged in the engine exhaust passage, to supply urea to the _the NO _x selective reduction catalyst and ammonia generated from the urea is adsorbed on _the NO _x selective reduction catalyst, mainly by the adsorbed ammonia In an exhaust gas purification apparatus for an internal combustion engine that selectively reduces NO _x contained in exhaust gas, the amount of NO _x discharged from the engine during engine idling operation is increased, and the NO _x selective reduction catalyst at this time An exhaust purification device for an internal combustion engine that detects an ammonia adsorption amount adsorbed on a NO _x selective reduction catalyst from a NO _x purification rate. An exhaust purification system of an internal combustion engine according to claim 1, _the amount of NO _x discharged from the engine is made to increase by stopping the recirculation of the exhaust gas during the engine idling operation. From the ammonia adsorption amount to _the NO _x selective reduction catalyst and _the NO _x selective reduction catalyst when the exhaust gas recirculation during engine idling operation becomes operating state operating conditions predetermined engine in the stopped state _the exhaust NO _x concentration is stored in advance the relationship between, from _the NO _x selective reduction catalyst by stopping the recirculation of exhaust gas when the engine operating state at the time of engine idling operation becomes operation state that is determined the advance is the exhaust NO _x concentration detected, the internal combustion engine according to claim 2, ammonia adsorption amount adsorbed by the _the NO _x selective reduction catalyst from the relationship based on the detected the exhaust NO _x concentration was is detected exhaust purification apparatus.   The exhaust purification device for an internal combustion engine according to claim 3, wherein the operating state of the engine is a fuel injection amount, and the predetermined operating state is a target injection amount. _The NO _x selective reduction exhaust purification system of an internal combustion engine according to NO _x claim 3 in which the sensor is arranged to detect the exhaust NO _x concentration from _the NO _x selective reduction catalyst downstream of the catalyst in the engine exhaust passage. A calculation means for calculating an ammonia adsorption amount adsorbed on the NO _x selective reduction catalyst is provided, and the ammonia adsorption amount calculated by the calculation means is updated by the detected ammonia adsorption amount. An exhaust gas purification apparatus for an internal combustion engine as described.

Images