JP2003041991A - Catalyst deterioration diagnosing device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To accurately diagnose deterioration of a catalyst by a simple and convenient composition. SOLUTION: When fuel injection is restarted (S2) from a state of a maximum quantity of oxygen adsorbed in a catalyst by a fuel cut (S1), an oxygen deficient state is provided by incrementally correcting a fuel injection quantity (S3) so that the adsorbed oxygen is consumed. When a predetermined time has passed from a fuel injection restart (S4) and an air-fuel ratio sensor provided in a downstream side of the catalyst detects a rich air-fuel ratio (S5 and S6), it is determined that the oxygen quantity adsorbed by the catalyst in a fuel cut state is low and it is determined that deterioration accompanying reduction of a maximum absorbing oxygen quantity has occurred (S8).

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an engine catalyst deterioration diagnosing device, and more particularly to a device for diagnosing deterioration of a catalyst having an oxygen adsorption capacity based on a decrease in the oxygen adsorption capacity.

[0002]

2. Description of the Related Art Conventionally, as a device for diagnosing the deterioration of a three-way catalyst having an oxygen adsorption capacity (oxygen storage capacity), an air-fuel ratio feedback control based on the output of an air-fuel ratio sensor provided on the downstream side of the catalyst is performed. An apparatus for diagnosing the deterioration of the three-way catalyst (decrease in oxygen adsorption capacity) based on the output cycle of the air-fuel ratio sensor at this time is known (JP-A-7-247830 and JP-A-10-).
061427).

[0003]

By the way, as described above, in the configuration in which the deterioration diagnosis is performed based on the output cycle of the air-fuel ratio sensor on the downstream side of the catalyst, the fluctuation cycle of the exhaust air-fuel ratio on the upstream side and the downstream side of the catalyst. Is a condition for diagnosis, but it is difficult to accurately determine the stable state of the fluctuation cycle, and it is difficult to accurately determine the fluctuation cycle of the output of the air-fuel ratio sensor, Further, there is a problem that it is difficult to adapt the threshold value for making the deterioration determination.

The present invention has been made in view of the above problems, and an object thereof is to provide an engine catalyst deterioration diagnosing device capable of diagnosing catalyst deterioration (decrease in oxygen adsorption capacity) accurately with a simple structure. To do.

[0005]

Therefore, the invention according to claim 1 is an apparatus having a capability of adsorbing oxygen, and diagnosing deterioration of a catalyst interposed in an exhaust pipe of an engine. From the state where the amount is estimated to be the maximum, the combustion in the air-fuel mixture richer than the stoichiometric air-fuel ratio is started, and the change in the exhaust air-fuel ratio on the catalyst downstream side from the start of combustion in the rich air-fuel mixture. The deterioration of the catalyst is diagnosed based on the above.

According to this structure, the oxygen adsorbed on the catalyst is desorbed and used for the oxidation treatment when the exhaust gas with a rich air-fuel ratio (exhaust gas with insufficient oxygen) is introduced into the catalyst. , When the rich air-fuel mixture is burned from the state where the maximum amount of oxygen is adsorbed, the adsorbed oxygen amount gradually decreases, and when the adsorbed oxygen amount that compensates the oxygen shortage disappears, the exhaust air-fuel ratio on the downstream side of the catalyst becomes It comes to indicate a rich state.

Here, when the maximum amount of oxygen that can be adsorbed decreases due to deterioration of the catalyst, the exhaust air-fuel ratio on the downstream side of the catalyst becomes richer as quickly as possible, and the deterioration of the catalyst is estimated based on this. Will be done. According to the second aspect of the invention, the state in which the fuel supply to the engine is stopped is detected as the state in which the amount of adsorbed oxygen in the catalyst is estimated to be maximum.

According to this structure, when the fuel supply to the engine is stopped, the atmosphere is introduced into the catalyst as it is, and the maximum amount of oxygen is adsorbed by the catalyst. According to a third aspect of the present invention, there is provided a device for diagnosing deterioration of a catalyst which is provided in an exhaust pipe of an engine and which has an oxygen adsorbing capacity, and is arranged on the downstream side of the catalyst based on the oxygen concentration in the exhaust gas. Equipped with an air-fuel ratio sensor that detects the air-fuel ratio,
When the fuel supply is restarted from the stopped state of the fuel supply to the engine, the air-fuel ratio of the combustion mixture is made richer than the stoichiometric air-fuel ratio, and the rich air-fuel ratio is shorter than the reference time by the air-fuel ratio sensor. The deterioration of the catalyst is diagnosed based on whether or not it is detected.

According to this structure, the combustion with the rich air-fuel mixture is started from the state where the fuel supply to the engine is stopped and the maximum amount of oxygen is adsorbed on the catalyst, and the rich air-fuel ratio is set to the air downstream of the catalyst. If the time until it is detected by the fuel ratio sensor is shorter than the reference time, it means that the amount of oxygen adsorbed by the catalyst when the fuel supply was stopped is less than in the initial state. Then, the deterioration of the catalyst is determined.

[0010]

According to the first aspect of the present invention, it is judged based on the exhaust air-fuel ratio on the downstream side of the catalyst that the maximum oxygen amount adsorbed on the catalyst has been consumed for purifying the rich exhaust gas. Since the deterioration state in which the maximum adsorbed oxygen amount is decreased is diagnosed, there is an effect that the deterioration of the catalyst can be accurately diagnosed with a simple configuration.

According to the second aspect of the present invention, there is an effect that the state in which the catalyst adsorbs the maximum amount of oxygen can be accurately determined and the deterioration diagnosis can be performed with high accuracy. According to the third aspect of the present invention, the state in which the catalyst adsorbs the maximum amount of oxygen is accurately determined, and the maximum adsorbed oxygen amount is consumed for purification of the rich exhaust gas.
Since the deterioration state in which the maximum adsorbed oxygen amount is reduced is diagnosed based on the exhaust air-fuel ratio on the downstream side of the catalyst, the deterioration of the catalyst can be diagnosed with a simple configuration and high accuracy.

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described below. FIG. 1 is a system configuration diagram of an engine in the embodiment. In FIG. 1, air is sucked into a combustion chamber of each cylinder of an engine 1 mounted on a vehicle through an air cleaner 2, an intake passage 3, and an electronically controlled throttle valve 4 which is driven to open and close by a motor.

An electromagnetic fuel injection valve 5 for directly injecting fuel (gasoline) is provided in the combustion chamber of each cylinder, and the fuel mixture injected into the combustion chamber by the fuel injected from the fuel injection valve 5 and the intake air. Is formed. The fuel injection valve 5 is
The injection pulse signal output from the control unit 20 energizes the solenoid to open the valve and injects the fuel whose pressure is adjusted to a predetermined pressure.

The mixture formed in the combustion chamber is ignited by the spark plug 6.
Is ignited and burned. The engine 1 is not limited to the above direct cylinder injection type gasoline engine, but may be an engine configured to inject fuel into the intake port. Exhaust from the engine 1 is exhausted from the exhaust passage 7,
A catalyst 8 for purifying exhaust gas is interposed in the exhaust passage 7.

The catalyst 8 is a three-way catalyst having an oxygen adsorption capacity (oxygen storage capacity), and is harmful to the exhaust gas.
It oxidizes carbon monoxide CO and hydrocarbons HC which are components, and reduces nitrogen oxide NOx to convert them into harmless carbon dioxide, water vapor and nitrogen. And
The purification performance by the three-way catalyst 8 is highest when the exhaust air-fuel ratio is the stoichiometric air-fuel ratio, and when the exhaust air-fuel ratio is lean and the amount of oxygen is excessive, the oxidizing action becomes active but the reducing action becomes inactive. Conversely, when the exhaust air-fuel ratio is rich and the amount of oxygen is small, the oxidizing action becomes inactive but the reducing action becomes active.

However, since the three-way catalyst 8 has an ability to adsorb oxygen (oxygen storage effect), when the exhaust air-fuel ratio becomes temporarily rich, the oxygen adsorbed up to that time is used, On the contrary, when the exhaust air-fuel ratio temporarily becomes lean, the exhaust purification performance can be maintained by adsorbing excess oxygen. The control unit 20 includes a microcomputer including a CPU, a ROM, a RAM, an A / D converter, an input / output interface, and the like. The control unit 20 receives input signals from various sensors, performs arithmetic processing based on these signals, and performs electronic processing. The opening degree of the controllable throttle valve 4, the injection amount / injection timing by the fuel injection valve 5, and the ignition timing by the spark plug 6 are controlled.

As the various sensors, a crank angle sensor 21 for detecting the crank angle of the engine 1 and a cam sensor 22 for extracting a cylinder discrimination signal from the cam shaft are provided, and the engine rotation based on the signals from the crank angle sensor 21 is provided. The speed Ne is calculated. Besides this, the intake passage 3
The air flow meter 23 for detecting the intake air amount Q on the upstream side of the throttle valve 4, the accelerator sensor 24 for detecting the depression amount APS of the accelerator pedal, and the opening T of the throttle valve 4.
A throttle sensor 25 for detecting VO, a water temperature sensor 26 for detecting a cooling water temperature Tw of the engine 1, and upstream and downstream sides of the catalyst 8 for detecting the exhaust air-fuel ratio based on the oxygen concentration in the exhaust gas. 1, 2nd air-fuel ratio sensors 27a and 27b, vehicle speed sensor 28 for detecting vehicle speed VSP
Etc. are provided.

Further, the control unit 20 is
It has a function of diagnosing the deterioration of the catalyst 8, and the details of the deterioration diagnosis will be described with reference to the flowchart of FIG. In the flowchart of FIG. 2, in step S1, it is determined whether or not a so-called fuel cut state in which fuel injection (fuel supply) by the fuel injection valve 5 is stopped.

The fuel cut is performed, for example, in a deceleration operation state in which the accelerator is fully closed and the engine rotation speed is equal to or higher than a predetermined rotation speed. In the fuel cut state, the fuel does not burn in the cylinder and the atmosphere flows in the exhaust passage 7, so that the maximum amount of oxygen is adsorbed by the catalyst 8. When the fuel cut state is determined in step S1, the process proceeds to step S2, and it is determined whether fuel injection is restarted from the fuel cut state.

When it is determined in step S2 that the fuel injection is restarted, the process proceeds to step S3, in which the fuel injection amount by the fuel injection valve 5 after the injection is restarted is forcibly increased by a predetermined ratio to achieve a predetermined rich mixture. Make settings to create energy. In step S4, it is determined whether or not a predetermined time has elapsed since the injection was restarted.

The predetermined time period is set as a time period during which the exhaust air-fuel ratio on the downstream side of the catalyst 8 maintains a substantially stoichiometric air-fuel ratio when the catalyst 8 is normal and the maximum adsorbed oxygen amount is equal to or more than the predetermined amount. When the air-fuel mixture richer than the stoichiometric air-fuel ratio is burned, the exhaust gas introduced into the catalyst 8 becomes insufficient in oxygen,
The oxygen adsorbed on the catalyst 8 will be used for the oxidation treatment of exhaust harmful components, and while the adsorbed oxygen remains on the catalyst 8, the exhaust air-fuel ratio on the downstream side of the catalyst 8 will be near the stoichiometric air-fuel ratio. Will be maintained.

Therefore, when the catalyst 8 is normal, in other words, when the maximum adsorbed oxygen amount in the catalyst 8 substantially maintains the value in the initial state, the time when all the adsorbed oxygen in the catalyst 8 is consumed is taken as a reference. As the time, the predetermined time is set as a time shorter than the reference time. Therefore, if the catalyst 8 is normal and the initial maximum amount of adsorbed oxygen is substantially maintained, the adsorbed oxygen should remain on the catalyst 8 when the predetermined time has elapsed. If the adsorbed oxygen has already been exhausted at the time of, the amount of adsorbed oxygen in the fuel cut state was small, so it can be determined that the adsorbed oxygen has disappeared earlier than in the normal state.

When it is determined in step S4 that the predetermined time has elapsed after the fuel injection is restarted, the process proceeds to step S5, and the detection result by the air-fuel ratio sensor 27b at that time is read. Then, in step S6, the detection result by the air-fuel ratio sensor 27b read in step S5, that is, the catalyst 8
It is determined whether or not the exhaust air-fuel ratio on the downstream side of is near the stoichiometric air-fuel ratio.

When it is determined in step S6 that the exhaust air-fuel ratio on the downstream side of the catalyst 8 is near the stoichiometric air-fuel ratio,
Although the rich air-fuel mixture is burned, the adsorbed oxygen still remains in the catalyst 8, so it can be determined that the exhaust air-fuel ratio on the downstream side of the catalyst 8 is maintained near the stoichiometric air-fuel ratio. Therefore, when it is determined in step S6 that the exhaust air-fuel ratio on the downstream side of the catalyst 8 is close to the stoichiometric air-fuel ratio, the process proceeds to step S7, and the normal state of the catalyst 8 in which the maximum adsorbed oxygen amount is a predetermined amount or more. To judge.

On the other hand, when it is judged in step S6 that the exhaust air-fuel ratio on the downstream side of the catalyst 8 exceeds the stoichiometric air-fuel ratio and is rich, the oxygen adsorbed on the catalyst 8 is exhausted and the rich air-fuel mixture is exhausted. Since it is no longer possible to make up for the lack of oxygen due to, it is determined that the exhaust air-fuel ratio on the downstream side of the catalyst 8 has become rich. As mentioned above, exhausted oxygen is exhausted faster than normal.
It can be judged that this is because the amount of oxygen adsorbed in the fuel cut state was smaller than that in the normal state, and thus it is estimated that the oxygen adsorption capacity is deteriorated due to deterioration.

Therefore, when it is determined in step S6 that the exhaust air-fuel ratio on the downstream side of the catalyst 8 is rich above the stoichiometric air-fuel ratio, the routine proceeds to step S8, in which the maximum adsorbed oxygen amount is reduced. The deterioration state of No. 8 is determined. When the deterioration state is determined, the diagnosis result is stored, and a countermeasure such as issuing a warning is executed.

In step S9, the correction for increasing the fuel injection amount is stopped. It should be noted that depending on the exhaust flow rate from the restart of injection after the fuel cut state to the elapse of the predetermined time,
Since the speed at which the oxygen adsorbed by the catalyst 8 is consumed changes, the predetermined time may be changed according to the exhaust gas flow rate. Further, after waiting for the elapse of the time required for the integrated value of the exhaust flow rate after the restart of injection to reach a predetermined value, the catalyst 8
It is also possible to adopt a configuration in which the exhaust air-fuel ratio on the downstream side is judged.

Further, by setting the idle operation state after the deceleration fuel cut state as the diagnostic condition, there is no large variation in the exhaust gas flow rate, and it is possible to omit setting the diagnostic timing according to the exhaust gas flow rate. Further, the time until the rich air-fuel ratio is detected is measured by the air-fuel ratio sensor 27b on the downstream side of the catalyst, and when the measurement result is shorter than the reference time in the normal state by a predetermined time or more, the catalyst 8 You may make it determine a deterioration.

[Brief description of drawings]

FIG. 1 is a system configuration diagram of an engine according to an embodiment.

FIG. 2 is a flowchart showing a catalyst deterioration diagnosis according to the embodiment.

[Explanation of symbols]

1 ... engine 4 ... Throttle valve 5 ... Fuel injection valve 6 ... Spark plug 8 ... Catalyst 20 ... Control unit 21 ... Crank angle sensor 23 ... Air flow meter 27a, 27b ... Air-fuel ratio sensor

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F02D 45/00 314 F02D 45/00 314Z // G01M 15/00 G01M 15/00 Z F term (reference) 2G087 AA27 BB28 CC19 EE17 3G084 AA03 BA05 BA13 BA15 BA17 BA24 CA03 CA06 DA10 DA27 EA11 EB01 EB11 EC01 FA05 FA07 FA10 FA20 FA30 FA33 FA39 3G091 AA02 AA17 AA24 EA02 EA01 EA01 EA01 EA01 EA02 EA01 EA02 BB01 CB02 CB08 CB02 CB02 CB02 CB02 CB02 CB02 CB02 CB03 CB03 CB02 CB02 CB02 CB02 CB02 CB03 CB03 CB03 CB02 CB02 CB03 CB03 EA31 EA34 EA36 EA39 FA05 FA19 FB12 HA36 HA37 HA42 3G301 HA01 HA04 HA06 JA15 JA25 JA26 JB09 LA03 LB04 MA01 MA11 MA18 NE01 NE06 NE13 PA01B PD01B PD08A PD08B PD09A PD09B PE01B PE03B PE08B PF01B PF03B

Claims (3)

[Claims] 1. A device for diagnosing deterioration of a catalyst interposed in an exhaust pipe of an engine, which has an oxygen adsorbing ability, and which is estimated to have a maximum adsorbed oxygen amount in the catalyst. , Starting combustion in a mixture richer than the stoichiometric air-fuel ratio, and diagnosing deterioration of the catalyst based on a change in the exhaust air-fuel ratio on the downstream side of the catalyst from the start of combustion in the rich mixture. Characteristic engine catalyst deterioration diagnosis device. 2. The engine according to claim 1, wherein a state in which fuel supply to the engine is stopped is detected as a state in which the amount of adsorbed oxygen in the catalyst is estimated to be maximum. Catalyst deterioration diagnosis device. 3. A device for diagnosing deterioration of a catalyst interposed in an exhaust pipe of an engine, which has an oxygen adsorbing capacity, wherein an air-fuel ratio is provided on the downstream side of the catalyst based on an oxygen concentration in exhaust gas. An air-fuel ratio sensor for detecting is provided, and when the fuel supply is restarted from the state where the fuel supply to the engine is stopped, the air-fuel ratio of the combustion mixture is made richer than the stoichiometric air-fuel ratio, and the rich air-fuel ratio is longer than the reference time. A catalyst deterioration diagnosing device for an engine, wherein deterioration of the catalyst is diagnosed based on whether or not it is detected by the air-fuel ratio sensor in a short time.