KR20100064184A - Diagnosing method and apparatus of catalyst deterioration of a car - Google Patents

Abstract

PURPOSE: A diagnostic method for catalyst degradation ratio of a vehicle is provided to accurately measure catalyst degradation ratio regardless of the motion area of a vehicle and combustion conditions. CONSTITUTION: A diagnostic method for catalyst degradation ratio of a vehicle comprises following steps. Catalyst degradation ratio is diagnosed using the purge fuel amount of accumulated catalyst(11) sprayed on a catalyst purge region. The purge fuel amount of accumulated catalyst and the catalyst degradation ratio are in inverse proportion. A diagnostic apparatus for catalyst degradation ratio of a vehicle comprises a downstream oxygen sensor and an electronic control unit. The downstream oxygen sensor is installed behind catalyst. The electronic control unit controls the air-fuel ratio of an engine using the output of the downstream oxygen sensor.

Description

Diagnosis method and apparatus of catalyst deterioration of a car

The present invention relates to a method for diagnosing catalyst deterioration of an automobile, and more particularly, to a method and apparatus for diagnosing deterioration of a catalyst using a catalyst purge function of a gasoline engine.

Internal combustion engines, including gasoline engines, which are currently used as automotive prime movers, burn fuel in a cylinder and use thermal energy generated at this time as power.

Therefore, the exhaust gas emitted from the automobile contains harmful components such as nitrogen oxides (NOx) resulting from combustion, carbon monoxide (CO) or hydrocarbons (HC) due to incomplete combustion. The air pollution caused by these exhaust gases is a big social problem today, and countermeasures have been taken.

As part of the countermeasure against such exhaust gas, automobiles are equipped with a catalyst for purifying harmful components in the exhaust gas. When the exhaust gas is rich, the catalyst releases the adsorbed oxygen to oxidize harmful substances in the exhaust gas, thereby reducing the exhaust gas.

The basic method for determining the normal operation of the catalyst is to use the characteristic of the oxygen storage capacity (OSC) of the catalyst.

1 is a diagram illustrating a general catalyst deterioration diagnostic apparatus.

The catalyst deterioration diagnosis device is installed in front of the catalyst 11 and is located upstream of the oxygen sensor 12 for detecting the oxygen concentration contained in the exhaust gas discharged from the combustion chamber, and behind the catalyst 11. By using the signals of the downstream oxygen sensor 13 and the upstream oxygen sensor 12 and the downstream oxygen sensor 13 which detect the oxygen concentration contained in the exhaust gas purified by the catalyst 11. An electronic control unit 14 for calculating the degree of catalyst deterioration is provided.

In addition, precise air-fuel ratio control is required in order to improve the purification efficiency of the catalyst. The electronic control unit 14 analyzes signals output from the upstream oxygen sensor 12 and the downstream oxygen sensor 13 to determine the current fuel amount. After determining whether it is Lean or Rich, the air-fuel ratio is controlled accordingly.

The electronic control unit 14 outputs the output values of the upstream oxygen sensor 12 installed in front of the catalyst and the downstream oxygen sensor 13 installed in the rear of the catalyst in the driving region that satisfies the diagnostic criteria among the partial load driving conditions of the vehicle. The degree of deterioration of the catalyst is calculated by comparison over a constant cycle. The biggest parameter of the catalyst deterioration diagnosis in the past is the stability of the output value of the downstream oxygen sensor 13.

2 is a diagram illustrating a correlation of an output signal of a downstream oxygen sensor according to a degree of catalyst deterioration.

In other words, as the degree of catalyst deterioration increases, the oxygen storage capacity (OSC) of the catalyst decreases, and the stability of the output value of the downstream oxygen sensor decreases.

However, this conventional catalyst deterioration diagnostic method is difficult to accurately diagnose the catalyst deterioration due to the influence of air-fuel ratio trim learning. This air-fuel ratio trim learning is to reduce the emission test deviation according to the degree of catalyst deterioration. The air-fuel ratio trim learning changes the target air-fuel ratio by the operating region of the engine, and thus the output value of the downstream oxygen sensor is affected. Will receive. That is, the stability of the output value of the downstream oxygen sensor shows a large deviation for each operating region of the engine.

The conventional catalyst deterioration diagnosis method may cause a customer complaint by diagnosing a normal catalyst in a deteriorated state and lighting an engine warning light, and causing a violation of IN USE regulations by diagnosing a deteriorated catalyst as normal. There is this.

SUMMARY OF THE INVENTION An object of the present invention is to provide a method for accurately measuring the degree of deterioration of a catalyst without being influenced by a difference in a vehicle driving area or a combustion environment.

The method for diagnosing catalyst deterioration of a vehicle according to the present invention for achieving the above object is characterized by diagnosing the catalyst deterioration using the accumulated amount of catalyst purge fuel injected in the catalyst purge section.

In addition, the apparatus for diagnosing catalyst deterioration of a vehicle according to the present invention uses a downstream oxygen sensor installed behind the catalyst and an output value of the downstream oxygen sensor to control the air-fuel ratio of the engine and to accumulate the catalyst injected into the catalyst purge section. And an electronic control unit for diagnosing deterioration of the catalyst using the amount of purge fuel.

According to the present invention, the catalyst purge logic is used to calculate the oxygen storage capacity (OSC) of the catalyst and to measure the degree of deterioration of the catalyst. There is a measurable effect.

Hereinafter, a method for diagnosing catalyst deterioration of a vehicle according to the present invention will be described in detail with reference to the accompanying drawings.

3 is a view illustrating a catalyst purge function to be utilized in the present invention, and describes a process of controlling the air-fuel ratio by using a signal output from the downstream oxygen sensor.

Since the air-fuel ratio is rich when the output value of the downstream oxygen sensor is (I) (III) in FIG. 3 (a), the electronic control unit is supplied to the engine as shown in (I) (III) in FIG. Control the injector to reduce the fuel level. On the other hand, in the electronic control unit, when the fuel is cut off and the output value of the downstream oxygen sensor is shown as (II) in FIG. 3 (a), the air-fuel ratio is lean. Control the injector to increase the amount of fuel supplied to the engine.

Here, as shown in Figure 3 (b), there is a P-JUMP section that changes rapidly when the fuel amount is switched to the (I)-> (II) and (II)-> (III) section, (II) When switching to section (III), the electronic control unit performs a catalyst purge function that delays P-JUMP by injecting a rich fuel amount over a theoretical air-fuel ratio for a predetermined time.

That is, when fuel is cut off in the section (II) of FIG. 3 (a), a large amount of air enters the catalyst. After that, the downstream oxygen sensor starts to run as shown in (III) of FIG. 3 (a). Even if the signal is output, the catalyst remains in a lean state, whereby nitrogen oxide (NOx), an air pollutant, can be easily generated. Therefore, the fuel is leaned by rich injection of a predetermined amount of fuel at a time when the fuel is cut off and supplied again ((II)-> (III) in FIG. 3 (b)). A catalytic converter purge function that converts richly to reduce the incidence of NOx. The amount of catalyst purge fuel injected into the catalyst purge section in which the catalyst purge function is performed is proportional to the amount of oxygen stored in the catalyst. The present invention uses this amount of catalyst purge fuel to diagnose catalyst degradation.

4 is a graph showing the catalyst purge section according to the degree of catalyst deterioration.

In the case of a normal catalyst having a low degree of catalyst deterioration, the oxygen storage capacity (OSC) is excellent and the amount of oxygen stored in the catalyst during the fuel cut period is high. Therefore, the amount of catalyst purge fuel for removing oxygen stored in the catalyst after the fuel cut (fuel cut) is large.

On the other hand, as the catalyst deteriorates, the oxygen storage capacity (OSC) of the catalyst is reduced, and the amount of oxygen that can be stored in the catalyst during the fuel cut period is also reduced. As a result, the amount of catalyst purge fuel carried out to remove oxygen stored in the catalyst after the fuel cut is also reduced.

5 is an operation flowchart illustrating a method for diagnosing catalytic degradation of a vehicle according to an exemplary embodiment of the present invention.

When the coolant temperature and the catalyst temperature respectively exceed the set value (S51), it is determined whether the catalyst purge function is performed when the fuel is cut and the fuel cutoff time exceeds the set time (S53).

When the catalyst purge function is performed, the injection fuel amount of the catalyst purge section is calculated and accumulated (S54). When the catalyst purge function is terminated (S55), the accumulated catalyst purge fuel amount is applied to the catalyst diagnosis table to calculate a catalyst diagnosis index (S56). That is, when the accumulated amount of catalyst purge fuel injected into the catalyst purge section is smaller than the preset value, it is determined that the catalyst is deteriorated.

1 is a view showing a general catalyst degradation diagnostic apparatus,

2 is a view showing a correlation of the output signal of the downstream oxygen sensor according to the degree of catalyst degradation;

3 is a view illustrating a catalyst purge function to be utilized in the present invention;

4 is a graph showing a catalyst purge section according to a degree of catalyst deterioration,

5 is a flowchart illustrating a method for diagnosing catalytic degradation of a vehicle according to an exemplary embodiment of the present invention.

Claims (3)

In a method for diagnosing catalyst deterioration of an automobile, A method for diagnosing catalyst deterioration of a vehicle, characterized by diagnosing the degree of catalyst deterioration using a cumulative amount of catalyst purge fuel injected in a catalyst purge section. The method for diagnosing catalyst deterioration of a vehicle according to claim 1, wherein the cumulative amount of catalyst purge fuel is inversely proportional to catalyst deterioration. A downstream oxygen sensor mounted behind the catalyst, The catalyst of an automobile comprising an electronic control unit for controlling the air-fuel ratio of the engine by using the output value of the downstream oxygen sensor and diagnosing the degree of degradation of the catalyst by using the accumulated amount of catalyst purge fuel injected in the catalyst purge section. Degradation degree diagnostic device.

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