JP2005240729A - Exhaust emission control device for internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust emission control device for an internal combustion engine capable of determining whether or not purification performance of a HC trapping catalyst is deteriorated when rich spike is performed. <P>SOLUTION: This exhaust emission control device for the internal combustion engine is provided with a NOx trapping catalyst arranged in an exhaust system of the engine and capable of trapping nitrogen oxides (NOx) in exhaust gas and with the HC trapping catalyst arranged in the downstream side of the NOx trapping catalyst, trapping hydrocarbon (HC) discharged during cooling-down of the engine and eliminating and purifying trapping HC after the exhaust gas temperature is increased. When trapping amount of the NOx trapping catalyst is increased, the rich spike is performed such that an air fuel ratio of the exhaust gas becomes rich, and the NOx trapping catalyst eliminates and purifies the trapping NOx. The exhaust emission control device is provided with a purification performance determination means for determining whether or not the purification performance of the HC trapping catalyst is deteriorated when rich spike is performed (Step S140). <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

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

2. Description of the Related Art Conventionally, there has been known an exhaust purification device that includes an NOx trap catalyst and an HC trap catalyst in an exhaust system to purify exhaust (for example, Patent Document 1). This NOx trap catalyst comprises a NOx adsorbent capable of trapping nitrogen oxide (hereinafter referred to as “NOx”) in exhaust gas, and a three-way catalyst capable of reducing the NOx when the trapped NOx is desorbed. It is a combination. The NOx trap catalyst desorbs and purifies trapped NOx when exhaust air rich in air-fuel ratio flows. The HC trap catalyst includes an HC adsorbent that adsorbs (traps) HC when the catalyst temperature is low and desorbs HC when the catalyst temperature is high, and a three-way catalyst that is activated to oxidize HC when the catalyst temperature is high. Is a combination.
JP-A-6-193433

  Incidentally, since the NOx trap catalyst has a limited amount of NOx adsorbed, it is necessary to desorb and purify NOx when the amount of adsorption increases. Therefore, conventionally, the air-fuel ratio of the exhaust gas is made rich, and NOx is purified by a reducing agent (HC, CO, etc.) contained in the exhaust gas. At this time, the reducing agent is sufficient if the HC contained in the exhaust gas just reacts with NOx and is consumed so that HC does not flow downstream of the NOx trap catalyst. If the exhaust gas can be made richer when the rich spike is performed, NOx can be purified more efficiently, but there is a problem that the inflowing reducing agent is not processed and is released into the atmosphere.

  The inventors of the present invention have conducted research sincerely, and in an exhaust purification device having an NOx trap catalyst and an HC trap catalyst in the exhaust system, the exhaust gas is richer than before when the purification performance of the HC trap catalyst has not deteriorated. I found out that it is possible.

  The present invention has been made paying attention to such a viewpoint, and provides an exhaust purification device for an internal combustion engine that can determine whether or not the purification performance of the HC trap catalyst has deteriorated when performing a rich spike. The purpose is to do.

  The present invention solves the above problems by the following means. In addition, in order to make an understanding easy, although the code | symbol corresponding to embodiment of this invention is attached | subjected, it is not limited to this.

  The present invention is arranged in an exhaust system of an engine and is arranged downstream of the NOx trap catalyst (21) capable of trapping nitrogen oxide (NOx) in the exhaust, and the NOx trap catalyst (21). An HC trap catalyst (22) that traps exhausted hydrocarbon (HC) and desorbs and purifies the trapped HC when the exhaust gas temperature rises, and the NOx trap catalyst (21) has a large trap amount An exhaust gas purification apparatus for an internal combustion engine that depletes and purifies NOx trapped by a NOx trap catalyst by performing a rich spike so that the air-fuel ratio of exhaust becomes rich when And a purification performance deterioration determining means (step S140) for determining whether or not the purification performance of the HC trap catalyst is deteriorated. .

  According to the present invention, it is possible to accurately determine whether or not the desorption purification performance of the HC trap catalyst is deteriorated by detecting a change in the oxygen concentration at the outlet of the HC trap catalyst when a rich spike is performed. It became.

  Hereinafter, embodiments of the present invention will be described in more detail with reference to the drawings.

  First, a basic concept will be described in order to facilitate understanding of the present invention.

  In order to purify nitrogen oxides (hereinafter referred to as “NOx”) contained in the exhaust gas of an internal combustion engine, a NOx trap catalyst capable of adsorbing (trapping) NOx may be provided in the exhaust system. This NOx trap catalyst is a combination of a NOx adsorbent capable of adsorbing (trapping) NOx and a three-way catalyst capable of purifying when trapped NOx is desorbed. By the way, since this NOx trap catalyst has a limited amount of NOx that can be adsorbed, it is necessary to desorb and purify NOx when the amount of adsorption increases. Therefore, conventionally, a rich spike is performed so that an appropriate amount of reducing agent (such as HC) to react with NOx is included in the exhaust gas, and NOx is purified by the reducing agent.

  Further, an HC trap catalyst capable of adsorbing (trapping) hydrocarbons (Hydro Carbon; hereinafter referred to as “HC”) may be provided in the exhaust system. This HC trap catalyst is composed of an HC adsorbent that adsorbs (traps) HC when the catalyst temperature is low and desorbs HC when the catalyst temperature is high, and a three-way catalyst that is activated and oxidizes HC when the catalyst temperature is high. Is a combination. According to such an HC trap catalyst, HC is trapped when the catalyst temperature is low, and is oxidized to CO 2 and H 2 O while desorbing the trapped HC when the catalyst temperature is high.

  As a result of earnest research on the exhaust gas purification method, the present inventors have found that when a NOx trap catalyst is arranged in the exhaust system and an HC trap catalyst is arranged downstream thereof, HC flows out of the NOx trap catalyst. Since the HC that has flowed out can be further purified by the HC trap catalyst, for example, the rich spike that is performed when the NOx trap catalyst is regenerated can be controlled to a richer state than when there is no HC trap catalyst. And gained knowledge. Thus, the NOx desorption purification in the NOx trap catalyst can be quickly performed by making the rich spike more rich than the conventional rich spike.

  However, in order to carry out such a rich spike in a richer state than in the past, it is necessary that the purification performance of the HC trap catalyst has not deteriorated. Therefore, whether or not the HC trap catalyst is deteriorated is determined as follows. That is, an air-fuel ratio sensor is provided at the inlet of the HC trap catalyst, and an O2 sensor is provided at the outlet. Normally, the air-fuel ratio at the inlet of the HC trap catalyst is lean, but when the NOx trap catalyst is regenerated, a rich spike is performed to make the exhaust air-fuel ratio rich. Then, the output signal of the O2 sensor at the outlet of the HC trap catalyst increases as the desorption purification function of the HC trap catalyst deteriorates (in FIG. 1, the signal value changes from a broken line to a thick solid line).

  Therefore, when the NOx trap catalyst is regenerated and a rich spike is performed to make the exhaust air-fuel ratio rich, the output signal of the O2 sensor is small if the desorption purification function of the HC trap catalyst is not deteriorated (see FIG. 2 (A)), the output signal of the O2 sensor increases as it deteriorates (FIG. 2B). Based on this, it is possible to determine the deterioration of the desorption purification function of the HC trap catalyst.

  In the following, a specific system to which the above basic concept is applied will be described.

  FIG. 3 is a configuration diagram of a system showing an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention, which is configured by taking a diesel engine using light oil as an example.

  In FIG. 3, 1 indicates a diesel engine (hereinafter simply referred to as an engine), and 3 indicates an exhaust passage of the engine 1.

  An exhaust outlet passage 3a constituting an upstream portion of the exhaust passage 3 of the engine 1 is connected to a turbine 3b of a supercharger, and a NOx trap catalyst 21 and an HC trap catalyst 22 are arranged in series downstream thereof. ing. An air-fuel ratio sensor 37 serving as an actual air-fuel ratio detection unit is provided at the inlet of the NOx trap catalyst 21. The air-fuel ratio sensor 37 detects the oxygen concentration in the exhaust gas using, for example, an oxygen ion conductive solid electrolyte, and obtains the air-fuel ratio from the oxygen concentration.

As an exhaust gas recirculation device, an EGR passage 4 for recirculating a part of the exhaust gas is provided between the intake collector 2c and the exhaust outlet passage 3a of the intake passage 2, and the opening is opened by a stepping motor. The intake passage 2 is provided with an air cleaner 2a at an upstream position, and an air flow meter 7 serving as intake air amount detection means is provided on the outlet side thereof. A turbocharger compressor 2b is arranged downstream of the air flow overnight 7, and an intake throttle valve that is opened and closed by an actuator (for example, a stepping motor type) between the compressor 2b and the intake collector 2c. 6 is interposed.

  The fuel supply system of the engine 1 includes a fuel tank 60 that stores diesel oil as diesel fuel, a fuel supply passage 16 that supplies fuel to the fuel injection device 10 of the engine 1, and a fuel supply device 16 of the engine 1. And a fuel return passage 19 for returning the return fuel (spill fuel) to the fuel tank 60.

  The fuel injection device 10 of the engine 1 is a known common rail type fuel injection device, and generally includes a supply pump 11, a common rail (accumulation chamber) 14, and a fuel injection valve 15 provided for each cylinder. After the fuel pressurized by the supply pump 11 is temporarily stored in the common rail 14 via the fuel supply passage 12, the high-pressure fuel in the common rail 14 is distributed to the fuel injection valves 15 of each cylinder.

  The common rail 14 is provided with a pressure sensor 34 and a temperature sensor 35 in order to detect the pressure and temperature of the fuel in the common rail 14. Further, in order to control the fuel pressure in the common rail 14, a part of the fuel discharged from the supply pump 11 is returned to the fuel supply passage 16 via the overflow passage 17 having the one-way valve 18. Yes. Specifically, a pressure control valve 13 that changes the flow passage area of the overflow passage 17 is provided, and the pressure control valve 13 changes the flow passage area of the overflow passage 17 in accordance with a duty signal from the engine control unit 30. Thereby, the substantial fuel discharge amount from the supply pump 11 to the common rail 14 is adjusted, and the fuel pressure in the common rail 14 is controlled.

  The fuel injection valve 15 is an electronic injection valve that is opened and closed by an ON-OFF signal from the engine control unit 30, and injects fuel into the combustion chamber by the ON signal and stops injection by the OFF signal. The fuel injection amount increases as the period of the ON signal applied to the fuel injection valve 15 increases, and the fuel injection amount increases as the fuel pressure of the common rail 14 increases.

  A water temperature sensor 31 for detecting the cooling water temperature is attached to an appropriate position of the engine 1 as representative of the temperature of the internal combustion engine.

  Further, an air-fuel ratio sensor 39 for detecting the air-fuel ratio is provided at the inlet of the HC trap catalyst 22, and an O2 sensor 40 for detecting the oxygen concentration is provided at the outlet.

  The engine control unit 30 includes a signal (Qa) from the air flow meter 7 that detects the intake air amount, a signal from the water temperature sensor 31 (cooling water temperature Tw), and a signal from the crank angle sensor 32 for crank angle detection (of the engine speed Ne). Basic crank angle signal), cylinder discrimination crank angle sensor 33 signal (cylinder discrimination signal Cyl), pressure sensor 34 signal for detecting fuel pressure in common rail 14 (common rail pressure PCR), temperature sensor for detecting fuel temperature 35 (fuel temperature TF), an accelerator opening sensor 36 signal (accelerator opening (load) L) for detecting an accelerator pedal depression amount corresponding to a load, an air-fuel ratio sensor 37 signal (O2), an air-fuel ratio A signal (O2) from the sensor 39 and a signal (O2) from the O2 sensor 40 are input.

  Next, the deterioration determination of the HC trap catalyst will be described with reference to the block of FIG.

  First, the temperature of the HC trap catalyst is detected (# 11), and the air-fuel ratio before and after the HC trap catalyst is detected (# 12). Based on these, it is determined whether or not the HC trap catalyst can adsorb or purify HC when the rich spike is performed (# 13), and the deterioration of the HC trap catalyst is determined (# 14).

  Subsequently, the deterioration determination of the HC trap catalyst will be described in more detail based on the flowchart of FIG.

  In step S110, it is determined whether or not the NOx trap amount ΣNOx in the NOx trap catalyst 21 exceeds the reference value ΣNOxc.

  In step S120, a rich spike is performed so that the air-fuel ratio at the inlet of the HC trap catalyst (the air-fuel ratio of the exhaust gas flowing through the NOx trap catalyst 21) becomes rich.

  In step S130, it is determined whether or not the change amount VO2out of the detection value of the O2 sensor at the outlet of the HC trap catalyst is larger than the reference value VO2outc. If it is larger, that is, the state shown in FIG. 2B, it can be determined that the HC trap catalyst 22 is in a deteriorated state (step S140). The reference value VO2outc is set by conducting an experiment in advance.

  According to this embodiment, when rich spike is performed, it is possible to accurately determine whether or not the desorption purification performance of the HC trap catalyst has deteriorated by detecting a change in the oxygen concentration at the outlet of the HC trap catalyst. It came to be.

  The present invention is not limited to the embodiment described above, and various modifications and changes can be made within the scope of the technical idea, and it is obvious that these are equivalent to the present invention.

  For example, in the above embodiment, the change in the oxygen concentration downstream of the HC trap catalyst is detected by the O2 sensor, but may be detected by an air-fuel ratio sensor, for example.

It is a figure which shows the output signal of O2 sensor of the HC trap catalyst exit when rich spike is implemented. It is the figure which divided and showed the output signal of the O2 sensor of the HC trap catalyst exit when rich spike was implemented before and after catalyst deterioration. 1 is a configuration diagram of a system showing an embodiment of an exhaust gas purification apparatus for an internal combustion engine according to the present invention. It is a block diagram explaining deterioration determination of HC trap catalyst. It is a flowchart explaining deterioration determination of the HC trap catalyst.

Explanation of symbols

1 Engine 21 NOx trap catalyst 22 HC trap catalyst 40 O2 sensor (outlet oxygen concentration detection means)
Step S140: Purification performance deterioration judging means

Claims (6)

A NOx trap catalyst which is disposed in the exhaust system of the engine and can trap nitrogen oxide (hereinafter referred to as “NOx”) in the exhaust;
An HC trap catalyst disposed downstream of the NOx trap catalyst, traps hydrocarbons (hereinafter referred to as “HC”) discharged when the engine is cold, and desorbs and purifies trapped HC when the exhaust temperature rises; ,
With
Exhaust gas purification of an internal combustion engine that desorbs and purifies NOx trapped by the NOx trap catalyst by performing a rich spike so that the air-fuel ratio of the exhaust gas becomes rich when the trap amount of the NOx trap catalyst increases A device,
A purification performance deterioration determining means for determining whether or not the purification performance of the HC trap catalyst is deteriorated when the rich spike is performed;
An exhaust emission control device for an internal combustion engine. An outlet oxygen change detecting means for detecting a change in oxygen concentration at the outlet of the HC trap catalyst;
The purification performance deterioration determining means determines whether or not the purification performance of the HC trap catalyst is deteriorated based on a change in oxygen concentration at the outlet of the HC trap catalyst.
The exhaust emission control device for an internal combustion engine according to claim 1. The purification performance deterioration determining means determines the deterioration of the purification performance of the HC trap catalyst when the oxygen concentration at the outlet of the HC trap catalyst is larger than a preset reference value;
The exhaust emission control device for an internal combustion engine according to claim 2. The outlet oxygen change detection means is an air-fuel ratio sensor.
The exhaust emission control device for an internal combustion engine according to claim 2 or claim 3, wherein The outlet oxygen change detection means is an O2 sensor.
The exhaust emission control device for an internal combustion engine according to claim 2 or claim 3, wherein The purification performance deterioration determining means determines the HC purification performance of the HC trap catalyst at the time of rich spike, and determines the purification performance deterioration of the HC trap catalyst based on the determination result.
The exhaust emission control device for an internal combustion engine according to any one of claims 1 to 5, wherein:

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