JP2006022753A - Exhaust emission control device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device of an internal combustion engine, improving the drivability and fuel economy by acceleration the temperature rising rate of a catalyst. <P>SOLUTION: Ni(nickel) is carried on the catalyst of a three way catalytic converter 19 interposed in an exhaust pipe 18, and in regeneration from S (sulfur) poisoning in the catalyst of the three way catalytic converter 19, periodic rich to lean operation is repeated until the catalyst reaches a target set temperature by an exhaust emission air-fuel ratio forced changing means, and when it reaches the target set temperature, rich operation is performed for a predetermined time. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to an exhaust gas purification apparatus for an internal combustion engine such as an automobile, and more specifically, can effectively increase the temperature increase rate of a catalyst that is interposed in an exhaust system to purify and reduce harmful substances in the exhaust gas. The present invention relates to an exhaust gas purification device that can be used.

  In general, an exhaust system of an internal combustion engine (engine) for an automobile is provided with, for example, an underfloor catalytic converter (UCC) located under the floor of a vehicle. In this underfloor catalytic converter, the underfloor catalytic converter is mainly built in the catalytic converter. A three-way catalyst purifies and reduces HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) in the exhaust gas. In recent years, a vehicle including a three-way catalyst in an underfloor catalytic converter and a NOx occlusion catalyst (NOx trap catalyst) that occludes NOx in an oxidizing atmosphere and releases and reduces the occluded NOx in a reducing atmosphere has been put into practical use. Yes.

  Furthermore, recently, in addition to the underfloor catalytic converter, a pre-stage catalytic converter (MCC, FCC) is additionally provided in the exhaust manifold that is susceptible to high-temperature combustion gas from the engine or immediately after the exhaust manifold in order to activate the catalyst early. In this way, an exhaust gas purification device that can exhibit high exhaust purification performance even immediately after the cold start of the engine has been developed and put into practical use.

JP-A-10-317946

  By the way, in the exhaust gas purifying apparatus described above, there is a problem that S (sulfur, sulfur content) contained in the fuel adheres to the catalyst and deteriorates the catalyst function by inhibiting NOx adhesion to the catalyst. The degree of deactivation of the catalyst mainly depends on the amount of S passing through the catalyst. The amount of deposition increases with the travel distance, and the poisoning deterioration proceeds. However, the exhaust gas air-fuel ratio rich operating condition where the catalyst is exposed to high temperature Then, it is known that S is eliminated and the catalyst performance is recovered.

  However, in a layout in which it is relatively difficult to drive the catalyst under high temperatures while the vehicle is running (for example, an underfloor catalytic converter of a gasoline vehicle), generally known temperature increase control such as ignition retard is not only effective, but also drivability and fuel efficiency There was a problem that the deterioration of was large. Also, high temperatures are desired in DPF (diesel particulate filter) regeneration processing control of diesel vehicles having low exhaust gas temperatures, but only a method that relies on fuel control such as post-injection causes a significant deterioration in fuel consumption. There was also a point.

  In Patent Document 1, the odor is suppressed by adding Ni or NiO to the NOx storage catalyst, and the air-fuel ratio control is not performed so that Ni or NiO contributes to the temperature increase. Therefore, the ignition timing retard or the like is performed to raise the temperature of the catalyst as in the conventional case, and it still takes time to raise the temperature, resulting in a problem of deterioration in drivability and fuel consumption.

  SUMMARY OF THE INVENTION An object of the present invention is to provide an exhaust gas purifying apparatus for an internal combustion engine that can improve drivability and fuel consumption by increasing the rate of temperature rise of the catalyst.

  In order to achieve the above object, an invention according to claim 1 is an exhaust gas purification device that activates or regenerates a catalyst provided in an exhaust passage of an internal combustion engine by raising the temperature thereof. A transition metal capable of promoting temperature rise, catalyst temperature calculating means for detecting or estimating the temperature of the catalyst, exhaust gas air-fuel ratio adjusting means capable of switching the exhaust gas air-fuel ratio upstream of the catalyst to lean and rich, and A catalyst temperature rise determining means for determining whether the catalyst is inactive or needing regeneration and determining the temperature rise of the catalyst; and a first temperature rise state calculating means for calculating a temperature rise state of the catalyst when the exhaust gas air-fuel ratio is lean; The temperature rise state calculated by the second temperature rise state calculation means for calculating the temperature rise state of the catalyst when the exhaust gas air-fuel ratio is rich and the temperature rise state calculated by the first temperature rise state calculation means become the first predetermined state. The exhaust gas air-fuel ratio And an exhaust gas air-fuel ratio forcibly changing means for changing the exhaust gas air-fuel ratio to lean when the temperature rise state calculated by the second temperature rise state calculation means becomes the second predetermined state. Features.

  The invention according to claim 2 is characterized in that the transition metal is Ni.

  According to a third aspect of the present invention, the exhaust gas air-fuel ratio forcibly changing means repeats a periodic rich → lean operation until the catalyst reaches a target set temperature via the exhaust gas air-fuel ratio adjusting means, When the set temperature is reached, rich operation is performed for a predetermined time.

  According to the first aspect of the present invention, in the catalyst supporting the transition metal that can promote the temperature rise of the catalyst, the phenomenon that the bed temperature rapidly rises at the moment when the exhaust gas air-fuel ratio switches from rich to lean is obtained. Since the temperature of the fuel cell is raised quickly, the fuel consumption can be minimized in the regeneration process of the catalyst and the DPF function without impairing drivability. In addition, since the operating conditions capable of regeneration are expanded, the deterioration of exhaust emission can be minimized.

  According to the invention of claim 2, the oxidation reaction with the surplus reducing substance present on the catalyst is promoted, and the phenomenon that the bed temperature rapidly increases at the moment when the exhaust gas air-fuel ratio is switched from the rich operation to the lean operation is more remarkable. Is obtained.

  According to invention of Claim 3, it can transfer to the regeneration process control of a catalyst and a DPF function promptly and reliably.

  Hereinafter, an exhaust gas purifying apparatus for an internal combustion engine according to the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram of an exhaust gas purifying apparatus for an internal combustion engine showing an embodiment of the present invention, FIG. 2 is a flowchart of temperature increase control processing, FIG. 3 is a graph showing an image of temperature increase control, and FIG. Similarly, FIG. 5 is a graph showing the catalyst temperature history, FIG. 5 is a graph showing a comparison of the temperature characteristics of the Ni carrying amount, and FIG. 6 is a graph showing a comparison of the HC purification performance with respect to the Ni carrying amount.

  As shown in FIG. 1, as an internal combustion engine body (hereinafter simply referred to as an engine) 1, for example, by switching a fuel injection mode, fuel injection in an intake stroke (intake stroke injection) and fuel injection in a compression stroke (compression) An in-cylinder spark-ignition gasoline engine capable of performing stroke injection) is employed. This in-cylinder injection type engine 1 can easily realize an operation at a lean air-fuel ratio (lean operation) in addition to an operation at a stoichiometric air-fuel ratio (stoichio) or an operation at a rich air-fuel ratio (rich operation). is there.

  An electromagnetic fuel injection valve 4 is attached to the cylinder head 2 of the engine 1 together with a spark plug 3 for each cylinder, so that fuel can be directly injected into the combustion chamber. An ignition coil 5 that outputs a high voltage is connected to the spark plug 3. Further, a fuel supply device (not shown) having a fuel tank is connected to the fuel injection valve 4 via a fuel pipe 6. More specifically, the fuel supply device is provided with a low pressure fuel pump and a high pressure fuel pump, whereby fuel in the fuel tank is supplied to the fuel injection valve 4 at a low fuel pressure or a high fuel pressure. Can be injected from the fuel injection valve 4 into the combustion chamber at a desired fuel pressure.

  An intake port 7 is formed in the cylinder head 2 in a substantially upright direction for each cylinder, and one end of an intake manifold 8 is connected so as to communicate with each intake port 7. Further, an exhaust port 9 is formed in the cylinder head 2 in a substantially horizontal direction for each cylinder, and one end of an exhaust manifold 10 is connected to communicate with each exhaust port 9. In the figure, 11 is an intake valve for opening and closing the intake port 7, and 12 is an exhaust valve for opening and closing the exhaust port 9.

  The in-cylinder injection type engine 1 is already known, and therefore, the detailed description of the configuration is omitted. As shown in the figure, the intake manifold 8 is provided with an electromagnetic throttle valve 13 for adjusting the amount of intake air and a throttle position sensor (TPS) 14 for detecting the opening th of the throttle valve 13. Further, an air flow sensor 16 for measuring an intake air amount is interposed in an intake pipe (intake passage) 15 connected to the intake manifold 8. As the air flow sensor 16, a Karman vortex air flow sensor is used. In the figure, 17 is an air cleaner.

On the other hand, an exhaust pipe (exhaust passage) 18 is connected to the exhaust manifold 10, and a three-way catalytic converter 19 serving as a UCC is interposed in the exhaust pipe 18. The three-way catalytic converter 19 includes an HC selective oxidation function, an oxygen storage function (O ₂ Storage Component: OSC), and a CO storage function (CO Storage Component (COSC).

  In this embodiment, Ni (nickel) or an oxide of Ni is supported as a transition metal capable of promoting the temperature rise of the catalyst in the noble metal support layer (or may be divided into layers) of the three-way catalytic converter 19. . In addition, an exhaust temperature sensor (catalyst temperature calculation means) 20 is interposed in the exhaust pipe 18 directly below the three-way catalytic converter 19.

  The vehicle is provided with an ECU (electronic control unit) 21 having an input / output device, a storage device (ROM, RAM, nonvolatile RAM, etc.), a central processing unit (CPU), a timer counter, and the like. Overall control including 1 is performed. That is, various sensors such as a crank angle sensor 22 and an accelerator position sensor 23 are connected to the input side of the ECU 21 in addition to the throttle position sensor 14, the airflow sensor 16, and the exhaust temperature sensor 20 described above. Detection information from is input.

  On the other hand, the ignition plug 3, the fuel injection valve 4, the throttle valve 13, and the like are connected to the output side of the ECU 21 through the ignition coil 5 described above. The ignition plug 3, the fuel injection valve 4, the throttle valve 13, and the like. Are respectively output optimum values such as ignition timing, fuel injection amount, throttle opening th and the like calculated based on detection information from various sensors. Thus, ignition is performed at an appropriate timing by the spark plug 3, and an appropriate amount of fuel is injected from the fuel injection valve 4 at an appropriate timing so that a predetermined air-fuel ratio (A / F) is obtained.

  Actually, the ECU 21 obtains the target in-cylinder pressure corresponding to the engine load, that is, the target average effective pressure Pe, based on the accelerator opening information from the accelerator position sensor 23 and the engine rotational speed information from the crank angle sensor 22. Further, the fuel injection mode is determined from a map (not shown) according to the target average effective pressure Pe and the engine rotational speed Ne. For example, when the target average effective pressure Pe and the engine rotational speed Ne are both small, the fuel injection mode is set to the compression stroke injection mode, and fuel is injected in the compression stroke, while the target average effective pressure Pe increases, or the engine When the rotational speed Ne increases, the fuel injection mode is changed to the intake stroke injection mode, and fuel is injected in the intake stroke. Then, a target air-fuel ratio (target A / F) as a control target is set from the target average effective pressure Pe and the engine rotational speed Ne, and an appropriate amount of fuel injection is determined based on this target A / F ( Exhaust gas air-fuel ratio adjusting means).

  In the present embodiment, the ECU 21 executes the catalyst temperature increase control according to the image shown in FIG. 3 in the regeneration process control from the S poisoning of the catalyst in the three-way catalytic converter 19. That is, the periodic rich → lean operation is repeated until the catalyst reaches the target set temperature (650 ° C. to 700 ° C.), and when the target set temperature is reached, the rich operation (regeneration processing operation) is performed for a predetermined time (exhaust gas). Air-fuel ratio forced change means).

The temperature increase control will be described in detail based on the flowchart shown in FIG.
First, when the conditions for starting the temperature increase control to execute the regeneration process control of the catalyst in the three-way catalytic converter 19 are met based on the travel distance, the operation time, the catalyst temperature history, the detected value by the NOx sensor, etc. (determining the catalyst temperature increase) Means), the operation mode is switched to the rich operation mode (λ (excess air ratio) <1) in step P1.

  Next, in step P2, it is determined whether or not the catalyst has reached the target temperature by the exhaust temperature sensor 20, and if it is already possible at this time, a regeneration processing operation (continuous rich operation) is performed in step P7, and a predetermined period ( After the elapse of time, the temperature raising control is terminated.

  On the other hand, if the answer is NO in Step P2, it is determined in Step P3 whether or not the temperature increase rate is equal to or less than a predetermined value 1 (temperature increase rate per unit time in rich operation) (second temperature increase state calculation means). If NO, return to Step P2. On the other hand, if it is possible (second predetermined state), the operation mode is switched to the lean operation mode (λ (excess air ratio)> 1) in step P4. Note that it is possible to quickly determine a decrease in temperature rise efficiency due to the rich operation by switching at the temperature increase rate.

  Next, in step P5, it is determined whether or not the catalyst has reached the target temperature by the exhaust temperature sensor 20. If yes at this time, an immediate regeneration processing operation (rich operation) is performed in step P7, and a predetermined period (time) is reached. ) After the elapse, the temperature raising control is finished.

  On the other hand, if NO in step P5, it is determined in step P6 whether or not the temperature increase rate is equal to or greater than a predetermined value 2 (temperature increase rate per unit time in lean operation) (first temperature increase state calculation means). If NO, return to Step P2. On the other hand, if yes (first predetermined state), the process returns to Step P5. The predetermined value 1 and the predetermined value 2 of the temperature increase rate may be equal, but the predetermined value 1 may not be equal to the predetermined value 2 according to the temperature increase characteristic in the rich operation and the temperature increase characteristic in the lean operation. For example, the temperature increase rate in the lean operation is abrupt compared to the rich operation. Therefore, if the predetermined value 1 <predetermined value 2 is satisfied, a temperature decrease due to a delay in switching from the lean operation to the rich operation can be suppressed.

  In this way, by combining the three-way catalytic converter 19 supporting Ni (nickel) or Ni oxide with fuel control (forcibly changing the air-fuel ratio), the catalyst heating rate is increased (the target temperature arrival time is shortened). In the catalyst regeneration process, fuel consumption can be minimized and fuel consumption can be improved.

  In addition, as understood from the graph showing the catalyst temperature history in FIG. 4, the present inventors are centered at the moment when the air-fuel ratio (A / F) is switched from rich to lean in the Ni-supported catalyst ( It was confirmed that the (Bed) temperature increased rapidly (in contrast, the inlet (Inlet) temperature decreased). This is because Ni or Ni oxides are sometimes used as NOx catalysts and are also known to have an OSC function, which promotes the oxidation reaction with surplus reducing substances present on the catalyst. It is thought to be caused by.

  Further, as can be seen from the graph showing the comparison of the temperature characteristics of the Ni carrying amount in FIG. 5, the present inventors increase the temperature as the Ni carrying amount increases, but conversely, the Ni carrying amount in FIG. As can be seen from the graph showing the comparison of the HC purification performance against the HC, it has been confirmed that the HC purification performance deteriorates. Incidentally, A (x1) in FIGS. 5 and 6 is about 11 g / l (NiO amount).

  Thus, in the regeneration process of the catalyst, the temperature of the catalyst is raised at an early stage by the temperature rise control by the fuel control instead of the ignition retard or the like, so that the fuel consumption can be minimized without impairing the drivability. In addition, since the operating conditions capable of regeneration are expanded, the deterioration of exhaust emission can be minimized.

  In the above embodiment, the three-way catalytic converter 19 is described as an example, but the present invention can also be applied to a NOx trap catalyst. Of course, as the transition metal capable of promoting the temperature rise, a substance such as Mn (manganese) other than Ni or an oxide of Ni may be used. Further, the S regeneration is forcibly performed by the temperature rise control by the ECU 21, but in a gasoline MPI (multipoint injection) vehicle or lean burn vehicle, if the catalyst carries Ni or an oxide of Ni, Depending on the driving state, S regeneration may occur naturally. Further, according to the present invention, the above-described temperature rise control is performed by supporting Ni or Ni oxide on a coated DPF (diesel particulate filter) of a diesel vehicle or an oxidation catalyst (pre-stage catalyst) in the case of an oxidation catalyst + DPF. It can be applied to the case where PM (particulate matter) regeneration is performed in combination.

1 is a schematic configuration diagram of an exhaust gas purification device for an internal combustion engine showing an embodiment of the present invention. It is a flowchart of temperature rising control processing similarly. It is a graph which similarly shows the image of temperature rising control. It is a graph which similarly shows a catalyst temperature history. It is a graph which shows the comparison of the temperature characteristic of Ni carrying amount. It is a graph which shows the comparison of the HC purification performance with respect to Ni carrying amount.

Explanation of symbols

  1 engine, 2 cylinder head, 3 spark plug, 4 fuel injection valve, 5 ignition coil, 6 fuel pipe, 7 intake port, 8 intake manifold, 9 exhaust port, 10 exhaust manifold, 11 intake valve, 12 exhaust valve, 13 throttle Valve, 14 Throttle position sensor, 15 Intake pipe, 16 Air flow sensor, 17 Air cleaner, 18 Exhaust pipe, 19 Three-way catalytic converter, 20 Exhaust temperature sensor, 21 ECU (electronic control unit), 22 Crank angle sensor, 23 Accelerator position Sensor.

Claims (3)

In an exhaust gas purification device that is activated or regenerated by raising the temperature of a catalyst provided in an exhaust passage of an internal combustion engine,
A transition metal supported on the catalyst and capable of promoting the temperature rise of the catalyst;
A catalyst temperature calculating means for detecting or estimating the temperature of the catalyst;
Exhaust gas air-fuel ratio adjusting means capable of switching the exhaust gas air-fuel ratio upstream of the catalyst between lean and rich;
A catalyst temperature increase determining means for determining whether the catalyst is inactive or needing regeneration and determining a temperature increase of the catalyst; and a first temperature increase state calculating means for calculating a temperature increase state of the catalyst when the exhaust gas air-fuel ratio is lean When,
Second temperature rise state calculating means for calculating a temperature rise state of the catalyst when the exhaust gas air-fuel ratio is rich;
When the temperature rise state calculated by the first temperature rise state calculation means becomes the first predetermined state, the exhaust gas air-fuel ratio is changed to rich, and the temperature rise state calculated by the second temperature rise state calculation means Exhaust gas air-fuel ratio forcibly changing means for changing the exhaust gas air-fuel ratio to lean when the engine reaches the second predetermined state;
An exhaust gas purification device for an internal combustion engine, comprising:   The exhaust gas purifying device for an internal combustion engine according to claim 1, wherein the transition metal is Ni.   The exhaust gas air-fuel ratio forcibly changing means repeats the periodic rich → lean operation until the catalyst reaches the target set temperature via the exhaust gas air-fuel ratio adjusting means, and when the target set temperature is reached, the rich for a predetermined time. The exhaust gas purification device for an internal combustion engine according to claim 1 or 2, wherein the operation is performed.

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