JP2010190203A - 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 detecting the abnormality of air fuel ratio sensors without increasing emission. <P>SOLUTION: The exhaust emission control device for the internal combustion engine 10 includes an adsorption catalyst 40 provided in the exhaust passage 20 of the internal combustion engine 10 and O<SB>2</SB>sensors 60A, 60B each provided at least downstream of the adsorption catalyst 40 in the exhaust passage 20 and serving as the air fuel ratio sensor having a built-in heater. Before start of the internal combustion engine 10, the heaters are operated to activate the O<SB>2</SB>sensors 60A, 60B, and based on the detection signals of the O<SB>2</SB>sensors 60A, 60B with respect to the exhaust gas at start of the internal combustion engine 10, the abnormality of the O<SB>2</SB>sensors 60A, 60B is detected. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to an exhaust purification device provided in an exhaust passage of an internal combustion engine.

  In order to purify the exhaust gas discharged from the internal combustion engine, an exhaust purification device incorporating an adsorption purification catalyst is provided in the exhaust passage of the internal combustion engine. In order to keep the exhaust gas purification rate above a certain level, it is necessary to detect abnormality of the adsorption purification catalyst. For this reason, oxygen sensors and air-fuel ratio sensors are provided upstream and downstream of the adsorption purification catalyst, and abnormality diagnosis is performed using detection signals of these sensors (for example, Patent Documents 1 to 3, for example). Etc.).

  When an oxygen sensor is used to diagnose an abnormality of the adsorption purification catalyst, the adsorption / desorption performance and oxygen storage capacity of the adsorption purification catalyst are estimated by detecting the rich / lean atmosphere upstream and downstream of the adsorption purification catalyst. Then, the adsorption purification catalyst is monitored. In this case, it is necessary to detect whether the oxygen sensor is operating normally. For this purpose, for example, a gas having a rich air-fuel ratio is temporarily allowed to flow through the exhaust passage, and it is detected whether an output corresponding to the oxygen sensor can be obtained.

JP 2006-016974 A JP-A-2005-240729 JP 1999-190244 A

  By the way, if a rich gas having a rich air-fuel ratio is caused to flow through the exhaust passage, hydrocarbons (HC) are discharged to the outside. That is, in order to detect an abnormality of the oxygen sensor, it is necessary to actively control the air-fuel ratio, so that there is a problem that the emission discharged to the outside increases.

  The present invention has been made in view of the above problems, and an object of the present invention is to provide an exhaust purification device for an internal combustion engine that can detect an abnormality of an air-fuel ratio sensor without increasing emissions.

  An exhaust gas purification apparatus for an internal combustion engine according to the present invention includes an adsorption catalyst provided in an exhaust passage of the internal combustion engine, an air-fuel ratio sensor provided at least downstream of the adsorption catalyst in the exhaust passage, and including a heater, Before starting the internal combustion engine, the heater is activated to activate the air-fuel ratio sensor, and the abnormality of the air-fuel ratio sensor is detected based on the detection signal of the air-fuel ratio sensor with respect to the exhaust gas at the start of the internal combustion engine. And an abnormality detection means.

  According to the present invention, the air-fuel ratio of the exhaust gas at the start or immediately after the start of the internal combustion engine from which the gas with rich air-fuel ratio is discharged is detected by the air-fuel ratio sensor, and the abnormality of the air-fuel ratio sensor is detected using this detection signal. Therefore, the abnormality of the air-fuel ratio sensor can be detected while suppressing emissions.

1 is a configuration diagram illustrating an example of an internal combustion engine to which the present invention is applied. It is a graph which shows an example of the output of each sensor provided in the exhaust passage of an internal-combustion engine. It is a flowchart which shows an example of the abnormality detection process of the sensor which concerns on one Embodiment of this invention.

  Hereinafter, a preferred embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 is a schematic configuration diagram showing an example of an internal combustion engine system to which an exhaust emission control device according to an embodiment of the present invention is applied.

This internal combustion engine system includes an internal combustion engine 10, an exhaust passage 20 connected to the exhaust system of the internal combustion engine body 10, a three-way catalyst 30 and an adsorption catalyst 40 provided in this exhaust passage 20 in order from the upstream side, and an adsorption O ₂ sensors 60A, 60B as air-fuel ratio sensors provided upstream and downstream of the catalyst 40, an A / F sensor 70 provided upstream of the three-way catalyst 30, and a vehicle door A door courtesy switch 80 and an electronic control unit (hereinafter referred to as ECU) 100 are included.

  The internal combustion engine 10 generates power by burning a fuel / air mixture in a combustion chamber (not shown) and reciprocating a piston in the combustion chamber. Moreover, it is a multi-cylinder engine for vehicles (for example, 4-cylinder gasoline engine).

  The three-way catalyst 30 is a well-known device that purifies substances such as NOx, HC, and CO in exhaust gas by reduction and oxidation, and is efficient in the vicinity of the stoichiometric air-fuel ratio where gasoline and oxygen are completely combusted and oxygen does not remain. Reduction and oxidation are performed.

  The adsorption catalyst 40 has a function of adsorbing and oxidizing a substance such as HC that has passed without being purified by the three-way catalyst 30.

The O ₂ sensors 60A and 60B detect the air-fuel ratio of the exhaust gas upstream and downstream of the adsorption catalyst 40 and detect the detection signal in order to detect the adsorption and oxidation performance of the adsorption catalyst 40 and judge its deterioration. Output to the ECU 100. The O ₂ sensors 60A and 60B have a built-in heater. When the heater is energized, the O ₂ sensors 60A and 60B are heated and activated, and the air-fuel ratio can be detected.

  The A / F sensor 70 detects the air-fuel ratio of the exhaust gas and controls the air-fuel ratio of the internal combustion engine 10 and outputs a detection signal to the ECU 100.

  Door courtesy switch 80 detects the opening and closing of the door of the vehicle and outputs a detection signal to ECU 100.

The ECU 100 includes, for example, a backup memory such as a central processing unit (CPU), a read only memory (ROM), a random access memory (RAM), and an electronically erasable and programmable read only memory (EEPROM), an A / D converter, a buffer, and the like. The input interface circuit includes a hardware including an output interface circuit including a drive circuit and the like, and necessary software. The ECU 100 is configured to be able to control an ignition plug, a fuel injection valve, a throttle valve, and the like provided for each cylinder of the internal combustion engine 10, and controls the ignition timing, air-fuel ratio, and fuel injection timing by controlling them. To do. Furthermore, as described above, the ECU 100 determines the deterioration of the adsorption catalyst 40 based on the signals from the O ₂ sensors 60A and 60B. When determining the deterioration of the adsorption catalyst 40, an abnormality detection process for the O ₂ sensors 60A and 60B is executed as described later.

FIG. 2 is a graph showing an example of the vehicle speed, the engine speed, the outputs of the O ₂ sensors 60A and 60B, and the output of the A / F sensor 70 when the internal combustion engine 10 is started. As shown in FIG. 2, when the internal combustion engine 10 is started, the ECU 100 controls the air-fuel ratio of the air-fuel mixture supplied to the internal combustion engine 10 to an air-fuel ratio richer than the stoichiometric air-fuel ratio. As a result, the engine speed exceeds a predetermined speed. At this time, rich signals indicating that the air-fuel ratio is rich are output from the outputs of the O ₂ sensors 60A and 60B and the A / F sensor 70. Thereafter, the ECU 100 controls the air-fuel ratio of the air-fuel mixture to an air-fuel ratio that is leaner than the stoichiometric air-fuel ratio. Thereby, a rich constant rotational speed is maintained. At this time, a lean signal indicating that the air-fuel ratio is lean is output from the outputs of the O ₂ sensors 60A and 60B and the A / F sensor 70.

In the present invention, the abnormality of the O ₂ sensors 60A and 60B is detected by utilizing the change in the air-fuel ratio at the start of the internal combustion engine 10 and immediately after the start as shown in FIG.

FIG. 3 is a flowchart showing an example of an abnormality detection process of the O ₂ sensors 60A and 60B by the ECU 100. The processing routine shown in FIG. 3 is executed, for example, every predetermined time. In addition, even when the internal combustion engine 10 is not driven, some functions of the ECU 100 are operated by the battery.

  First, based on a signal from the door courtesy switch 80, it is determined whether or not the vehicle door has been opened (step S1). If the door of the vehicle has not been opened, the process ends.

  If it is determined that the vehicle door has been opened, all the functions of the ECU 100 are activated (step S2).

  Next, it is determined whether the engine coolant temperature is lower than a predetermined temperature Ta and the difference between the engine coolant temperature and the intake air temperature is smaller than a predetermined temperature Tb (step S3). This process is for determining whether the internal combustion engine 10 is in a cold state or is already in a warm-up state. If it can be determined whether the internal combustion engine 10 is in a cold state, parameters other than these can be used for the determination.

  If it is determined in step S3 that the engine is already warmed up, the internal combustion engine 10 is started (step S16), and the process is terminated. If it is determined in step S3 that the internal combustion engine 10 is in a cold state, the estimated temperature α of the three-way catalyst 30 and the estimated temperature β of the adsorption catalyst 40 at the end of the previous trip, and the time from the end of the previous trip. It is determined whether the product of the elapsed time coefficient K corresponding to the time elapsed until the start of this time is lower than the predetermined temperatures Td and Te (step S4). That is, it is determined whether the temperatures of the three-way catalyst 30 and the adsorption catalyst 40 at the end of the previous trip have sufficiently decreased by the time of the current start.

If it is determined in step S4 that the temperatures of the three-way catalyst 30 and the adsorption catalyst 40 have not sufficiently decreased by the time of the current start, the internal combustion engine 10 is started (step S16), and the process is terminated. . If it is determined that the temperatures of the three-way catalyst 30 and the adsorption catalyst 40 have sufficiently decreased by the time of the current start, is the estimated temperature β of the adsorption catalyst 40 at the end of the previous trip lower than the predetermined temperature Tf? Is determined (step S5). That is, it is determined whether the temperature of the adsorption catalyst 40 at the end of the previous trip has increased to a state where HC can be adsorbed and purified. If the temperature of the adsorption catalyst 40 at the end of the previous trip has not increased to a state where HC can be adsorbed and purified, the abnormality determination of the O ₂ sensor is not performed and the internal combustion engine 10 is started (step S16). ), The process is terminated. Thereby, the electric power required for the heating process (preheating) of the O ₂ sensor described later is reduced.

If it is determined in step S5 that the temperature of the adsorption catalyst 40 at the end of the previous trip has not increased to a state where HC can be adsorbed and purified, preheating of the O ₂ sensors 60A and 60B is executed (step 6). Thereafter, the engine is started (step S7). In addition to the O ₂ sensors 60A and 60B, the A / F sensor 70 is also preheated.

Next, it is determined whether the signal from the A / F sensor 70 is smaller than the predetermined value V1 (step S8). In other words, the O ₂ sensor 60B on the downstream side of the adsorption catalyst 40 is checked based on the signal from the A / F sensor 70 that can reliably detect the rich signal when the engine is started. That is, if the signal from the A / F sensor 70 is smaller than the predetermined value V1, it is determined that the O ₂ sensor 60B can reliably detect the rich signal.

In step S8, when the signal from the A / F sensor 70 is larger than the predetermined value V1, it is determined that the O ₂ sensor 60B cannot detect the rich signal, and the process is terminated. O ₂ sensor 60B is when it is determined that can be reliably detected rich signal, the output of the O ₂ sensor 60B determines greater than a predetermined value X1 (step S9). That is, it is determined whether the output of the O ₂ sensor 60B is at a rich level. At this time, it may be simultaneously determined whether the output of the upstream O ₂ sensor 60A is at a rich level.

In step S9, when the output of the O ₂ sensor 60B has not reached the rich level, it is determined that the rich output abnormality of the O ₂ sensor 60B is present (step S15). At this time, when the output of the O ₂ sensor 60B reaches the rich level and the output of the O ₂ sensor 60A does not reach the rich level, it is determined that the rich output abnormality of the O ₂ sensor 60A has occurred. If none of the outputs of the O ₂ sensors 60A and 60B reach the rich level, the abnormality determination is suspended and the process of step S10 is executed.

In step S9, when both the outputs of the O ₂ sensors 60A and 60B reach the rich level, it is determined whether the fuel supplied to the internal combustion engine 10 is heavy fuel (step S10). If it is determined that the fuel is heavy fuel with low volatility, the process is terminated and the abnormality determination of the O ₂ sensor is not executed. If it is determined that the fuel is normal rather than heavy fuel with low volatility, the A / F sensor is used during the first idling (FI) after engine start, as shown in FIG. Based on the output of 70, the target air-fuel ratio is set to a predetermined value R that is lean (step S11).

Next, it is determined whether the outputs of the O ₂ sensors 60A and 60B during the first idling after the engine start are lower than a predetermined value X2 (step S12). That is, it is determined whether both the outputs of the O ₂ sensors 60A and 60B are inverted from the rich level to the lean level.

In step S12 determines, when the O ₂ sensor 60A, both of the output of 60B inverted from the rich level in the lean level, O ₂ sensor 60A, and 60B are operating normally (step S13). O ₂ when the sensor 60A, the output of 60B is not inverted, it is determined that the O ₂ sensor 60A, lean output abnormality of the sensor not reversed out of the 60B (step S14).

10 ... engine 20 ... exhaust passage 30 ... three-way catalyst 40 ... adsorber 60A, 60B ... O ₂ sensor 70 ... A / F sensor 80 ... courtesy switch 100 ... ECU

Claims (1)

An adsorption catalyst provided in an exhaust passage of the internal combustion engine;
An air-fuel ratio sensor provided at least downstream of the adsorption catalyst in the exhaust passage and incorporating a heater;
Before starting the internal combustion engine, the heater is activated to activate the air-fuel ratio sensor, and the abnormality of the air-fuel ratio sensor is detected based on the detection signal of the air-fuel ratio sensor with respect to the exhaust gas at the start of the internal combustion engine An exhaust gas purifying device for an internal combustion engine, comprising:

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