Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2003-09-17
2004-12-28
Tran, Binh Q. (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000, C060S292000, C060S297000
Reexamination Certificate
active
06834497
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to an exhaust gas purifying device for an engine, and, more specifically, to an exhaust gas purifying device for an engine to remove NOx from exhaust gas of the engine.
An exhaust gas purifying device for an engine that performs a lean burn operation is known. Such a device is equipped with a NOx trap catalyst including a NOx trap material to absorb NOx during a state of high oxygen concentration in the exhaust gas and release the absorbed NOx during a state of low oxygen concentration in the exhaust gas. The NOx absorption capacity of the NOx tarp material is limited. Accordingly, in this exhaust gas purifying device, when the amount of NOx absorbed in the NOx tarp material reaches a saturation amount, a purifying control (so called, rich-spike control) is performed which changes an engine operating condition from the lean burn operation to an operation with a stoichiometric air-fuel ratio or the like to lower the concentration of oxygen in the exhaust gas. This control causes the NOx trap material to release NOx absorbed and to reduce and thereby purify the released NOx with a catalytic metal included in the NOx trap catalyst.
As a device for conducting a diagnosis of deterioration for this kind of NOx trap catalyst, Japanese Patent Laid-Open Publication No. 2000-337131 proposes a device making use of a peak value of an output of the NOx sensor during the rich-spike control. In this device, the deterioration is determined such that the lower the peak value of the NOx sensor at a transitional stage to a rich side becomes, the more NOx trap capacity of the NOx trap material has reduced, that is, the NOx trap catalyst has deteriorated.
The NOx trap catalyst, in general, includes a catalytic metal (noble metal) for oxidizing NOx and an O2 storage material for absorbing oxygen. However, the deterioration diagnosis device described in the above patent publication may not diagnose the deterioration of the reduction capacity of the catalytic metals or deterioration of O2 storage capacity of the O2 storage material.
Further, when the rich-spike control is executed, the following reactions occur sequentially: O2 release from the O2 storage material; oxidization of an exhaust gas composition by the released O2; NOx release from the NOx trap material; and reduction of the released NOx by the catalytic metal. However, if the air-fuel ratio of the exhaust gas is changed rapidly toward a rich side during NOx release, as performed in the deterioration diagnosis device described in the above publication, results of some reactions described above adversely affect or are mixed up with the output value of the NOx sensor due to an output delay of the NOx sensor or the like. Accordingly, a state of these reactions is not detected appropriately, so that each of deteriorations of O2 storage capacity of the O2 storage material (deterioration of O2 storage material) and reduction capacity of the catalytic metal (deterioration of catalytic metal) can not be diagnosed accurately.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above-described problems, and an object of the present invention is to provide an exhaust gas purifying device for an engine that performs the diagnosis function of diagnosing accurately each of deterioration of O2 storage capacity of an O2 storage material and NOx reduction capacity of a catalytic metal, which are included in a NOx trap catalyst.
In order to achieve the above-described object, the first aspect of the present invention provides an exhaust gas purifying device for an engine, comprising a NOx trap catalyst disposed in an exhaust gas passage of the engine including a NOx trap material to absorb NOx while oxygen of an exhaust gas is in high concentration and release the absorbed NOx while oxygen is in low concentration, a catalytic metal to purify the NOx released from the NOx trap material, and an O2 storage material to absorb O2 while oxygen of the exhaust gas is in high concentration and release the absorbed O2 while oxygen is in low concentration, a NOx sensor disposed in the exhaust gas passage downstream of the NOx trap catalyst, NOx absorbed amount calculating section for calculating the amount of NOx absorbed in the NOx trap catalyst, NOx release controlling section for lowering the concentration of oxygen of the exhaust gas in the exhaust gas passage so as to cause the NOx trap catalyst to release NOx absorbed when the amount of the NOx absorbed in the NOx trap catalyst reaches a specified amount, operating condition detecting section for detecting an operating condition of the engine, determination section for determining whether a specified diagnosis condition to diagnose the NOx trap catalyst is satisfied or not, according to the engine operating condition detected by the operating condition detecting section, detecting section for detecting whether or not O2 release from the O2 storage material caused by oxygen concentration lowering of the exhaust gas in the exhaust gas passage by the NOx release controlling section has terminated, diagnosing section for diagnosing a degree of deterioration of respective capacities of the O2 storage material and the catalytic metal that are included in the NOx trap catalyst when the specified diagnosis condition is satisfied, the diagnosing section diagnosing a degree of deterioration of O2 storage capacity of the O2 storage material according to output values of the NOx sensor that are generated during a term from the beginning of the oxygen concentration lowering of the NOx release controlling section until a termination of the O2 release from the O2 storage material, the diagnosing section diagnosing a degree of deterioration of NOx reduction capacity of the catalytic metal according to an output value of the NOx sensor that is generated after the termination of the O2 release from the O2 storage material, wherein the NOx release controlling section is configured such that a speed of lowering oxygen concentration thereby when the specified diagnosis condition is satisfied is slower than that when the specified diagnosis condition is not satisfied.
According to the exhaust gas purifying device for an engine of the first aspect of the invention, each of deterioration of O2 storage capacity of the O2 storage material and NOx reduction capacity of the catalytic metal, which are included in the NOx trap catalyst, can be diagnosed accurately, during a control (rich-spike control) for NOx release from the NOx trap catalyst for lowering the concentration of oxygen of the exhaust gas in the exhaust gas passage.
The second aspect of the present invention provides the exhaust gas purifying device of an engine of the first aspect of the invention, wherein the detecting section comprise an O2 sensor disposed in the exhaust gas passage downstream of the NOx trap catalyst, and O2 release termination determining section for determining that the O2 release from the O2 storage material has terminated when an output value of the O2 sensor indicates a value equivalent to a stoichiometric air-fuel ratio of the exhaust gas.
The third aspect of the present invention provides the exhaust gas purifying device of an engine of the first aspect of the invention, wherein the diagnosing section is configured so as to diagnose that O2 storage capacity of the O2 storage material included in the NOx trap catalyst has deteriorated when an integrated value of output values of the NOx sensor with respect to time during a term from the beginning of the oxygen concentration lowering of the NOx release controlling section until a termination of the O2 release from the O2 storage material is smaller than a first threshold value.
The fourth aspect of the present invention provides the exhaust gas purifying device of an engine of the first aspect of the invention, wherein the diagnosing section is configured so as to diagnose that O2 storage capacity of the O2 storage material included in the NOx trap catalyst has deteriorated when a value that is gained by dividing a d
Kuroki Masayuki
Miyoshi Seiji
Takami Akihide
Yamada Hiroshi
Mazda Motor Corporation
Studebaker Donald R.
Tran Binh Q.
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