Power plants – Internal combustion engine with treatment or handling of... – Having sensor or indicator of malfunction – unsafeness – or...
Reexamination Certificate
2002-02-13
2003-07-22
Denion, Thomas (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
Having sensor or indicator of malfunction, unsafeness, or...
C060S276000, C060S285000, C123S090150
Reexamination Certificate
active
06594987
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an apparatus for detecting a fault, i.e., leakage, in an exhaust system of an internal combustion engine.
2. Description of the Related Art
Three-way catalysts for simultaneously promoting the oxidation of incompletely burned hydrocarbons (HC) and carbon monoxide (CO) and the reduction of nitrogen oxides (NOx) formed by residual oxygen reacting with nitrogen in the air are used on internal combustion automotive engines to control exhaust emissions. To enhance the oxidation/reduction performance of the three-way catalyst, the air/fuel ratio (A/F), which indicates engine combustion state, must be controlled to within a very narrow range (called the window) centered on stoichiometry. To achieve this, in fuel injection control of an engine, an O
2
sensor (oxygen sensor) for detecting whether the air/fuel ratio is richer or leaner than stoichiometry from the residual oxygen concentration in exhaust gas is mounted as an air/fuel ratio sensor, and feedback control of the air/fuel ratio is performed to correct the amount of fuel based on the sensor output.
In such an air/fuel ratio feedback control system, the O
2
sensor for detecting the oxygen concentration is mounted as close as possible to the combustion chamber, that is, on the upstream side of the catalytic converter. There is also implemented a double O
2
sensor system in which a second O
2
sensor is mounted on the downstream side of the catalytic converter in order to compensate for variations in the output characteristic of the upstream O
2
sensor. That is, on the downstream side of the catalytic converter, the exhaust gas is thoroughly stirred, and its oxygen concentration is almost in equilibrium by the action of the three-way catalyst; as a result, the output of the downstream O
2
sensor changes little compared with the upstream O
2
sensor, and thus indicates whether the air/fuel mixture as a whole is on the rich side or lean side. In the double O
2
sensor system, sub air/fuel ratio feedback control is performed using the O
2
sensor mounted downstream of the catalyst in addition to the main air/fuel ratio feedback control performed using the O
2
sensor mounted upstream of the catalyst, and various constants used when calculating the air/fuel ratio correction coefficient in the main air/fuel ratio feedback control are corrected based on the output of the downstream O
2
sensor, or a second air/fuel ratio correction coefficient based on the output of the downstream O
2
sensor is introduced, thereby accommodating variations in the output characteristic of the upstream O
2
sensor and improving the accuracy of the air/fuel ratio control.
In such a double O
2
sensor system, if a fault such as an exhaust pipe crack occurs between the O
2
sensor upstream of the catalyst and the O
2
sensor downstream of the catalyst, outside air may be drawn into the exhaust pipe by exhaust pulsation, causing the downstream O
2
sensor to erroneously detect that the exhaust air/fuel ratio is lean. If this happens, the engine air/fuel ratio is erroneously controlled toward the richer side, and the purification performance of the catalyst degrades, resulting in increased HC and CO emissions. There are also cases where the O
2
sensor downstream of the catalyst is used to detect deterioration of the catalyst; in such cases, the above exhaust system fault can cause erroneous detection.
In view of this, Japanese Unexamined Patent Publication No. 8-210126 discloses a technique in which, when the main air/fuel ratio feedback control constant corrected based on the downstream O
2
sensor output reaches a predetermined guard value, the catalyst deterioration determining process is inhibited by determining the situation as being an exhaust system fault (exhaust pipe leakage).
This prior art technique attempts to detect an exhaust system fault from a tendency to lean that the output of the downstream O
2
sensor is showing, but the main air/fuel ratio feedback control constant corrected based on the downstream O
2
sensor output is not a parameter that always corresponds one for one to an exhaust system fault, because the constant is also affected by other factors such as the deteriorating tendency of the catalyst. Therefore, with the above prior art, it is difficult to detect an exhaust system fault reliably and quickly.
Recent years have also seen the development of an internal combustion engine in which air/fuel ratio is controlled so that the three-way catalyst can always provide a constant and stable purification performance. That is, the three-way catalyst has an O
2
storage capability and purifies the exhaust gas by adsorbing excessive oxygen when the exhaust gas is lean and by releasing necessary oxygen when the exhaust gas is rich, but such a capability is limited. To make effective use of the O
2
storage capability, therefore, it is important that the amount of oxygen stored in the catalyst be maintained at a prescribed level (for example, one-half the maximum oxygen storage amount) so as to be able to respond to the next change in the air/fuel ratio of the exhaust gas, whether it is a change to a rich state or a lean state. When the amount of oxygen is maintained in this manner, a consistent O
2
adsorption/desorption function can be achieved, ensuring a consistent oxidation/reduction performance of the catalyst.
In the internal combustion engine in which the O
2
storage amount is controlled to a constant level to maintain the purification performance of the catalyst as described above, a wide-range air/fuel ratio sensor capable of linearly detecting air/fuel ratio is used, for example, and feedback control (F/B control) is performed based on proportional-integral operations (PI operations). In such an O
2
storage amount constant control system, an O
2
sensor may also be installed on the downstream side of the catalyst in order to compensate for variations in the output characteristic of the wide-range air/fuel ratio sensor. In this case also, there arise the same problems as those described for the double O
2
sensor system.
It should also be recognized that the problem that, in the event of an automotive exhaust pipe fault, exhaust gases not purified by the catalyst are discharged into the atmosphere, or outside air is drawn into the exhaust pipe by exhaust pulsation, can also occur in an internal combustion engine equipped with only one air/fuel ratio sensor in the exhaust system.
SUMMARY OF THE INVENTION
The present invention has been devised in view of the above-outlined problems, and an object of the invention is to provide an apparatus that can reliably and quickly detect a fault in an exhaust system of an internal combustion engine.
To attain the above object, according to a first aspect of the present invention, there is provided an apparatus for detecting a fault in an exhaust system of an internal combustion engine, comprising: control means for providing a rich air/fuel ratio forcefully and continuously when detecting the presence or absence of a fault in the exhaust system; and determining means for determining that there is a fault in the exhaust system when a sensor mounted in the exhaust system does not produce an output that corresponds to the rich air/fuel ratio being provided under control of the control means. Since an exhaust system fault (leakage) is detected by forcefully enriching the air/fuel ratio, the apparatus of this invention can improve detection accuracy compared with an apparatus of the type that detects exhaust leakage during air/fuel ratio feedback control.
According to a second aspect of the present invention, there is provided an apparatus for detecting a fault in an exhaust system of an internal combustion engine, comprising: control means for providing a rich air/fuel ratio forcefully and continuously during engine idling when detecting the presence or absence of a fault in the exhaust system; and determining means for determining that there is a fault in the exhaust system when a sensor mounted in the e
Denion Thomas
Nguyen Tu M.
Oliff & Berridg,e PLC
Toyota Jidosha & Kabushiki Kaisha
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