Power plants – Internal combustion engine with treatment or handling of... – Methods
Reexamination Certificate
2000-05-04
2001-10-02
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Methods
C060S276000, C060S277000, C060S297000
Reexamination Certificate
active
06295807
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purifying catalyst deterioration detecting system for detecting the deterioration, if any, of a catalyst which is disposed in the exhaust system of an internal combustion engine for purifying the engine exhaust gas.
2. Related Art
In order to prevent a vehicular exhaust gas purifying system from being run with the catalyst deteriorated so as to have a lower exhaust gas purifying ability, a catalyst deterioration detecting system for detecting the deterioration of the catalyst (as disclosed in Japanese Patent Laid-Open Publication No. 2-136538 or 3-253714, for example). These catalyst deterioration detecting systems are made to detect the deterioration of the catalyst from a reduction in the exhaust gas purifying ability after the catalyst is warmed up to an activation temperature (generally 300 to 400° C. or higher).
Before the catalyst is warmed up to the activation temperature after an engine start, even the normal catalyst has a low exhaust gas purifying ability; however, the deteriorated catalyst has a much lower exhaust gas purifying ability, and thus increases to increase noxious contents (or emissions) in the exhaust gas. According to both of the aforementioned catalyst deterioration detecting methods of the prior art, however, the deterioration of the catalyst is detected from the drop in the exhaust gas purifying ability after the activation of the catalyst, thereby making the catalyst deterioration detection difficult while considering the emission increasing degree before the catalyst activation. The increase in the emissions before the catalyst activation may erroneously determine that the catalyst which is to be intrinsically determined deteriorated is not deteriorated.
If the engine is started cold, the activation of the catalyst proceeds from the inflow (or upstream) side of the exhaust gas as the time elapses after the cold-start, until the entire catalyst is finally activated. Generally, the catalyst is given some surplus in its entire capacity so that it can achieve, even if deteriorated more or less once entirely activated, a purification factor approximate to that of a new one thereby to reduce the difference in the purification factor between the deteriorated and new catalysts. As the activation of the catalyst proceeds the better, it becomes more difficult to discriminate between (i.e., to detect the catalyst deterioration) the deteriorated and new catalysts. As a result, when the deterioration of the catalyst is detected from the drop in the exhaust gas purifying ability after the catalyst activation, the emission increase before the catalyst activation may determine no deterioration of the catalyst, which should be intrinsically determined to be deteriorated.
SUMMARY OF THE INVENTION
The present invention has been conceived by considering such background and has an object to provide an exhaust gas purifying catalyst deterioration detecting system which can perform a catalyst deterioration detection while considering the emission increase before the catalyst activation thereby to improve the catalyst deterioration detecting accuracy.
In order to achieve this object, according to a first aspect of the present invention, noting that the amount of gas component to be purified in the catalyst (as will be called the “amount of purified gas component”) changes with the deterioration degree of the catalyst, the amount of purified gas component till the catalyst reaches a predetermined temperature after a start of an internal combustion engine is calculated, so that the deterioration of the catalyst is detected on the basis of the amount of purified gas component. As a result, it is possible to detect the catalyst deterioration highly accurately while considering the emission increase before the catalyst activation.
Preferably, at the time of detecting the deterioration of the catalyst, consideration is taken into not only the amount of purified gas component but also the data of the fluctuation of the gas component flowing into the catalyst till the catalyst reaches a predetermined temperature. This is because the amount of purified gas component is influenced by the fluctuation of the gas component flowing into the catalyst, so that a highly accurate catalyst deterioration detection excluding the influences of the fluctuation of the gas component flowing into the catalyst can be achieved by performing the catalyst deterioration detection while considering the fluctuation of the gas component flowing into the catalyst.
Preferably, the amount of purified gas component is calculated on the basis of the air/fuel ratio of the exhaust gas downstream of the catalyst. This is because the air/fuel ratio of the exhaust gas downstream of the catalyst is a parameter reflecting the amount of purified gas component.
Preferably, the data of the fluctuation of the gas component flowing into the catalyst is accurately determined by calculating the data of the fluctuation of the gas component flowing into the catalyst on the basis of the air/fuel ratio of the exhaust gas flowing into the catalyst and the flow rate of the exhaust gas.
Preferably, the catalyst deterioration detection is inhibited till the catalyst temperature reaches a deterioration detection starting temperature lower than the aforementioned predetermined level. With the catalyst temperature failing to reach the deterioration detection starting temperature, specifically, the temperature of the sensor for detecting the air/fuel ratio downstream of the catalyst is so low that the sensor output is not stabilized. As a result, the catalyst deterioration detecting accuracy is prevented from dropping by inhibiting the catalyst deterioration detection for that period.
Preferably, the catalyst deterioration detection is inhibited when the catalyst temperature at the start of the internal combustion engine is higher than a predetermined level. According to this catalyst deterioration detecting method, the catalyst deterioration is detected from the amount of purified gas component in the course (e.g., the catalyst temperature ranging from 150 to 550° C.) of the activation of the catalyst. As a result, when the catalyst temperature at the engine start far exceeds the lower level of 150° C., for example, the amount of purified gas component will deviate to lower the detection accuracy of the catalyst deterioration. Therefore, the accuracy drop of the catalyst deterioration detection is prevented by inhibiting the catalyst deterioration detection when the catalyst temperature at the engine start is higher than the predetermined level.
Preferably, noting that the catalyst is warmed up with the exhaust heat, the exhaust temperature is estimated on the basis of the running state of the engine so that the catalyst temperature is estimated on the basis of the exhaust temperature. As a result, the temperature sensor for detecting the catalyst temperature can be eliminated to meet the demand for reducing the cost for parts.
Preferably, the catalyst deterioration detection is inhibited till a predetermined period is elapsed after the start of the air/fuel ratio feedback control. Thus, the catalyst deterioration detection can be started after stabilization of the air/fuel ratio feedback, to improve the catalyst deterioration detecting accuracy better. Here, the “predetermined period” for inhibiting the catalyst deterioration detection is one necessary for the air/fuel ratio feedback to be stabled after the start of the air/fuel ratio feedback control. This period may be exemplified either by the period which is elapsed after the start of the air/fuel ratio feedback control or by the period for which the output of the air/fuel ratio sensor to cross the threshold value at first after the start of the air/fuel ratio feedback control.
According to a second aspect of the present invention, in a system including an air/fuel ratio sensor and an oxygen sensor upstream and downstream of the catalyst for purifying the exhaust gas, the satura
Douta Hisayo
Mukai Yasuo
Nakayama Masaaki
Denion Thomas
Denso Corporation
Nixon & Vanderhye PC
Tran Binh
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