Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2001-08-10
2002-10-15
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000
Reexamination Certificate
active
06463735
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an apparatus for detecting deterioration of a catalyst which is used for purifying exhaust gas and is employed in an exhaust gas purifying system.
In an exhaust gas purifying system of an automobile manufactured in recent years, two catalysts, that is, an upstream-side catalyst and a downstream-side catalyst, are installed in series on an exhaust pipe in order to increase an exhaust gas purifying rate as disclosed in JP-A-6-294342. Two air-fuel ratio sensors (oxygen sensors) may be provided on the upstream and downstream sides of the upstream-side catalyst respectively. In addition, an air-fuel ratio sensor (an oxygen sensor) may be provided on the downstream side of the downstream-side catalyst.
Existence or non-existence of the deteriorating state of the upstream-side catalyst is diagnosed in such dual-catalyst exhaust gas purifying system by detecting ratios of attributes of an output generated by the upstream-side air-fuel ratio sensor of the upstream-side catalyst to attributes of an output generated by the downstream-side air-fuel ratio sensor of the upstream-side catalyst in the same way as the conventional one-catalyst exhaust gas purifying system. The attributes of an output include the frequency and the amplitude of the output.
In order to detect the deteriorating state of the upstream-side catalyst with a high degree of precision, it is necessary to forcibly switch an air-fuel ratio control condition to a condition suitable for a diagnosis of the deteriorating state of the upstream-side catalyst so as to make an effect of the deteriorating state of the upstream-side catalyst noticeably appear in the variation of a signal output of the downstream-side air-fuel ratio sensor of the upstream-side catalyst. In consequence, the exhaust gas purifying rate of upstream-side catalyst during the period of time to diagnose the deteriorating state of the upstream-side catalyst decreases. Thus, the quantity of an unpurified gas component passing through the upstream-side catalyst tends to increase. As a result, the quantity of an unpurified gas component which must be removed by the downstream-side catalyst also increases as well.
However, since the air-fuel ratio control condition is forcibly switched to a condition suitable for a diagnosis of the deteriorating state of the upstream-side catalyst during the period of time to diagnose the deteriorating state of the upstream-side catalyst, the air-fuel ratio of exhaust gas entering the downstream-side catalyst tends to depart from the most efficient purifying range of the downstream-side catalyst. The purifying range is a range of the air-fuel ratio for which the exhaust gas purifying rate is high. Thus, the exhaust gas purifying rate of downstream-side catalyst during the period of time to diagnose the deteriorating state of the upstream-side catalyst tends to decrease in spite of the fact that the quantity of an unpurified gas component passing through the upstream-side catalyst tends to increase. As a result, it is likely that exhaust emission is worsened during the period of time to diagnose the deteriorating state of the upstream-side catalyst.
SUMMARY OF THE INVENTION
It is thus an object of the present invention addressing the problems to provide an apparatus for detecting the deteriorating state of an upstream-side catalyst for purifying exhaust gas by diagnosing the deteriorating state of the upstream-side catalyst without worsening exhaust emission.
In order to achieve the object, the present invention provides an apparatus for detecting the deteriorating state of one of a plurality of catalysts installed on an exhaust pipe of an internal combustion engine and used for purifying exhaust gas. Specifically, the catalysts include an upstream-side catalyst and a downstream-side catalyst. Two air-fuel ratio sensors are provided on the upstream and downstream sides of the upstream-side catalyst respectively. In addition, an air-fuel ratio sensor is provided on the downstream side of the downstream-side catalyst. The air-fuel ratio sensors are each used for detecting the air-fuel ratio of exhaust gas, that is, for determining whether the air-fuel ratio has a value on the rich or lean side with respect to the stoichiometric air-fuel ratio. The existence or the non-existence of the deteriorating state of the upstream-side catalyst is determined on the basis of at least a signal output of the downstream-side air-fuel ratio sensor of the upstream-side catalyst. At that time, the air-fuel ratio is controlled to take a signal output of the downstream-side air-fuel ratio sensor of the downstream-side catalyst into a predetermined range during the period of time to diagnose the deteriorating state of the upstream-side catalyst.
The signal output of the downstream-side air-fuel ratio sensor of the downstream-side catalyst is a parameter reflecting the air-fuel ratio of exhaust gas passing through the downstream-side catalyst. Thus, if the air-fuel ratio is controlled to take a signal output of the downstream-side air-fuel ratio sensor of the downstream-side catalyst into the predetermined range, the air-fuel ratio of exhaust gas passing through the downstream-side catalyst can be adjusted to a value within the most efficient purifying range of the downstream-side catalyst. Thus, even if the exhaust gas purifying rate of upstream-side catalyst during the period of time to diagnose the deteriorating state of the upstream-side catalyst decreases, causing the quantity of an unpurified gas component passing through the downstream-side catalyst to rise, the unpurified gas can be purified by the downstream-side catalyst with a high degree of efficiency. As a result, while the existence or non-existence of the deteriorating state of the upstream-side catalyst is being determined with a high degree of precision, exhaust emission can be prevented from becoming worse.
Alternatively, the deteriorating state of the upstream-side catalyst can be diagnosed during a period of time in which a signal output of the downstream-side air-fuel ratio sensor of the downstream-side catalyst has a value in the predetermined range. The deteriorating state of the upstream-side catalyst can be diagnosed during a period of time in which the air-fuel ratio of exhaust gas passing through the downstream-side catalyst has a value within the most efficient purifying range of the downstream-side catalyst.
REFERENCES:
patent: 5579637 (1996-12-01), Yamashita et al.
patent: 5740676 (1998-04-01), Agustin et al.
patent: 5845489 (1998-12-01), Dohta et al.
patent: 6003309 (1999-12-01), Agustin et al.
patent: 6253541 (2001-07-01), Sullivan et al.
patent: 6256981 (2001-07-01), Sullivan et al.
patent: 6321529 (2001-11-01), Mueller et al.
patent: 6330795 (2001-12-01), Takaku et al.
patent: 6-10738 (1994-01-01), None
patent: 6-294342 (1994-10-01), None
Morinaga Shujiro
Nakayama Masaaki
Yamaguchi Masahiko
Yoshiume Naoki
Denion Thomas
Denso Corporation
Tran Diem
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