JPH03121240A - Exhaust emission purifying catalyst failure diagnosing method - Google Patents

Abstract

PURPOSE:To enable precise diagnosis on the degradation of a catalyst by judging the failure of the catalyst when the actual catalyst temperature is lower than the specified catalyst temperature read according to the operating state, referring to a map indicating the relation of the catalyst temperature to air-fuel ratios and engine speed. CONSTITUTION:A device for discharging exhaust gas from an engine out to atmospheric air after removing harmful elements by a catalyzing device 1 is provided with an air fuel ratio sensor 2, and engine speed sensor 3, a water temperature sensor 4 and a catalyst temperature sensor 5, and the output signals of these sensors are inputted into a catalyst failure diagnosis unit 6. In this unit 6, the relation of the catalyst temperature to the air-fuel ratio and engine speed is made into a map and stored in an electronic module in advance. When the engine is in a temperature range indicating its normal state after the completion of warming-up, the corresponding catalyst temperature To is read from the air-fuel ratio and engine speed referring to the above-mentioned map, and compared with the actual catalyst temperature Tcat. In case of Tcat<To, the catalyst is judged to be in failure.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a method for diagnosing a failure of an exhaust gas purification catalyst for an internal combustion engine.

[Conventional technology]

Harmful components in the exhaust gas of internal combustion engines, especially automobiles, are detected by combining the 0N-OFF type 02 sensor that can detect the stoichiometric air-fuel ratio with a catalyst supporting platinum, palladium, rhodium, etc., and feeding back the O2 sensor signal to adjust the air-fuel ratio. The air-fuel ratio was controlled to approximately the stoichiometric air-fuel ratio to maximize the purification ability of the catalyst.

[Problem to be solved by the invention]

The above-mentioned conventional technology does not take into account countermeasures against the case where the catalyst deteriorates or breaks down and harmful exhaust gas is released into the atmosphere without treatment, resulting in the problem of environmental pollution.

The present invention is aimed at diagnosing and warning of catalyst deterioration and failure, and is intended to minimize environmental pollution.

[Means to solve the problem]

In order to achieve the above objective, we focus on the change in reaction heat generated during the reaction of harmful components on the catalyst, detect the exhaust gas temperature immediately after passing through the catalyst, compare it with a predetermined value, and if it is lower than the predetermined value, The diagnosis was that the reaction was insufficient, that is, the catalyst had failed, and an alarm was issued. In this case, the temperature of the exhaust gas entering the catalytic converter is an important factor, but if the air-fuel ratio and rotational speed are specified in a steady state of operation after the engine has been warmed up, the temperature of the exhaust gas will be approximately constant. Since it is a value, we decided to take in the signals from the air-fuel ratio sensor and rotation speed sensor to estimate the exhaust gas temperature.

On the other hand, the air-fuel ratio and rotational speed also serve as a measure of the amount flowing into the catalyst, indicating the amount of substances reacting on the catalyst. Therefore, we experimentally determined the exhaust gas temperature after passing through the catalyst when the air-fuel ratio and rotational speed were varied, and created a map. This map is created through various experiments from when the catalyst is new to each stage of deterioration, and the standard map is the map when the purification ability of the catalyst is reduced to a value equivalent to 70% of the initial value, which is diagnosed as a failure. , stored in the unit that performs catalyst failure diagnosis, and when the engine is in a steady state, reads the air-fuel ratio and rotational speed, reads the catalyst temperature as a reference for comparison from the stored map, and calculates the temperature from the actual temperature sensor. It was decided to perform a failure diagnosis by comparing the temperature with the temperature, and to issue an alarm such as turning on a lamp in the event of a failure.

〔Example〕

An embodiment of the present invention will be described below.

Figure 1 shows sensors for diagnosing catalyst failure.

This is an example of a system including a failure diagnosis unit.

When the exhaust gas from the engine 8 passes through the catalyst device 1,
- Harmful components such as carbon oxides (CO), unburned hydrogen carbides (HC), and nitrogen oxides (NOx) are
, Hz O+ N 2 , 02, etc., and are released into the atmosphere as harmless components. An air-fuel ratio sensor 2 that detects the air-fuel ratio in exhaust gas is installed in front of the catalyst device 1.

On the other hand, in order to know when the engine has warmed up and is in a steady operating state, a water temperature sensor 4 that detects the engine cooling water temperature and a rotational speed sensor 3 that detects the engine rotational speed are respectively installed. A catalyst temperature sensor 5 for detecting the reaction state of the catalyst is attached to the catalyst device 1 or to the exhaust pipe immediately after it.

Here, the air-fuel ratio sensor 2 determines the air-fuel ratio from the amount of oxygen or combustible substances (Co, HC, H2, etc.) in the exhaust gas, and generally there is a limit current type sensor. In some cases, an electromotive force method may be used.

The rotation speed sensor 3 may use a signal from a crank angle sensor or the like, and in some cases may use a signal from a vehicle speed sensor.

FIG. 2 shows an example of the relationship between the gas temperature input to the catalyst and the purification rate (η), and curve I shows the initial state. The reaction initiation temperature is approximately 300℃, and 370℃ for 100% reaction.
or more is required. As the catalyst deteriorates, the curves become as shown in (1) and (2), the rising edge of the temperature-purification rate curve shifts to the high temperature side and the slope becomes gentler, and the purification rate does not reach 100% even at 600°C. Also, if it deteriorates to the state of ■, 60
Even at 0°C, the purification rate does not reach 70%.

FIG. 3 is an example showing the relationship between the purification rate η and the catalyst temperature when the catalyst inlet temperature is constant. The catalyst temperature T car increases in proportion to the purification rate.

Figure 4 shows that when the engine is operating in a steady state, 1. For example, the water temperature is 70' to 90°C, and the exhaust gas temperature is 400°C to 6.
This is an example in which the catalyst temperature was experimentally determined from the air-fuel ratio (A/F) and the rotation speed (N) when the temperature was approximately 50°C. Here, if the reduction in purification rate that is considered to be a failure of the catalyst is determined to be, for example, 30% from the initial stage, then the data shown in Figure 4 is obtained from the deteriorated catalyst, and based on that, the A/F for failure diagnosis is determined. -N-T
A CaT map is created and stored as a standard map in the catalyst failure diagnosis unit 6 shown in FIG.

FIG. 5 shows the flow of failure diagnosis. First, the water temperature (Tw) is detected from the water temperature sensor 4 at a predetermined value a = b (for example, a
= 70°C, b = 90°C),
If OK, use the stored standard map A/F-N based on the signals of the air-fuel ratio sensor 2 and rotation speed sensor 3.
Read T cat from T cat. This Tea
r is a value corresponding to, for example, To in FIG. Next, if the actual temperature Tear<To by the catalyst temperature sensor 5, it is determined that the purification rate of the catalyst has fallen below the value determined to indicate a failure, and a lamp is turned on to notify the failure.

As a result of the above, it has become possible to diagnose failures of catalysts that have an important effect on environmental pollution.

〔Effect of the invention〕

According to the present invention, since catalyst failure can be diagnosed, deterioration of the catalyst can be known, and the time to replace it with a new one becomes clear, which is effective in preventing environmental pollution.

[Brief explanation of drawings]

Figure 1 is a diagram showing a system including sensors and failure diagnosis unit 1 to perform catalyst failure diagnosis, Figure 2 is a diagram showing the relationship between the gas temperature at the catalyst inlet and the purification rate, and Figure 3 is a diagram showing the relationship between the gas temperature at the catalyst inlet and the purification rate. Figure 4 is a diagram showing the relationship between purification rate and catalyst temperature under a certain condition. Figure 4 is a diagram showing an example of experimentally determining catalyst temperature from the air-fuel ratio and rotational speed when the engine is operating in a steady state. Figure 5 is a flow diagram of failure diagnosis. DESCRIPTION OF SYMBOLS 1... Catalyst device, 2... Air-fuel ratio sensor, 3... Rotation speed sensor, 4... Water temperature sensor, Catalyst temperature sensor, 6... Catalyst failure diagnosis unit, 7... Failure warning lamp. 25 S.〉P i Otsu 431 qOqri 4 Fig. 2 3 4 S 1 Otsu 7 3 Science

Claims (1)

[Claims] 1. At least a catalyst device that purifies the exhaust gas of an internal combustion engine, an air-fuel ratio sensor that detects the air-fuel ratio from the amount of oxygen or combustible material in the exhaust gas, a rotation speed sensor that detects the engine speed, an engine cooling water temperature sensor, and a catalyst. When diagnosing a failure in a catalyst failure diagnosis unit that includes a temperature sensor and an electronic module that captures, stores, compares and outputs signals from each sensor, a map of the relationship between catalyst temperature and air-fuel ratio and rotational speed is stored in the electronic module in advance. When the coolant temperature sensor is within the temperature range that indicates that the engine has completed warm-up and is in a steady state, read out the corresponding catalyst temperature from the stored map based on the air-fuel ratio and rotational speed, and calculate the actual temperature. A catalyst failure diagnosis method for exhaust purification characterized by diagnosing catalyst failure by comparing the temperature with the temperature measured by a catalyst temperature sensor and issuing an alarm.