Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Patent
1997-01-30
1998-01-06
Wolfe, Willis R.
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
123571, 123569, F02D 4114, F02M 2507
Patent
active
057043400
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an excess air rate detecting apparatus and an excess air rate control apparatus for an engine, used in a fuel supply system or exhaust emission control device of an automotive diesel engine and the like.
BACKGROUND ART
Principal harmful exhaust components emitted from of a diesel engine include NOx that is produced by combustion at high temperature, besides black smoke, unburned HC, etc., which are attributable to uneven distribution of a fuel injected into a cylinder or some other causes. A reduction catalyst, such as the one used in a gasoline engine, cannot be used as NOx reducing means for the diesel engine, since it contains extra oxygen, so that retardation of fuel injection timing (timing retardation) and water jet are being investigated. However, the former entails lowering of outputs or worsening of fuel efficiency, inevitably causing increase of CO and HC. The latter involves problems of installation of a water jet system and water tank, inclusion of water in lubricating oil, etc. Therefore, an exhaust gas recirculation (EGR) system, in which exhaust gas, an inert material, is recirculated as an EGR gas to a combustion chamber, is being put to practical use, since it has a relatively simple construction and is less susceptible to the aforesaid harmful influences.
In an EGR system for a diesel engine, if the recirculation quantity (hereinafter referred to as EGR quantity) of the EGR gas becomes excessive, the delivery of smoke or HC suddenly increases as the excess air rate lowers, and the fuel efficiency deteriorates. Besides, engine oil is deteriorated by inclusion of free carbon or particulates, so that lowering of the engine durability or the like occurs. In order to reduce NOx while minimizing these troubles, therefore, it is advisable to use an electronic control device for detecting the excess air rate to effect feedback control of the EGR quantity or to keep the excess air rate within an appropriate range even during transient operation or the like, to say nothing of steady-state operation.
In general, methods for detecting the excess air rate include a method using a CO.sub.2 analyzer and a method using a linear air-fuel ratio sensor (hereinafter referred to as LAFS).
As is generally known, however, the CO.sub.2 analyzer is large-sized and heavy in weight, so that it is not practical for vehicular use, although it can be used for a bench test or the like. As known EGR apparatuses equipped with the LAFS, on the other hand, there are ones described in Jpn. Pat. Appln. KOKAI Publication Nos. 55-7964 and 63-201356. In the former EGR apparatus, the LAFS is attached to an exhaust system, and an EGR valve is actuated in its opening direction when the output current of the LAFS is higher than a given threshold value, and in contrast with this, in its closing direction when the output current is lower. In the latter EGR apparatus, an EGR valve is actuated with reference to a control map for the EGR quantity, while the EGR valve opening degree (control map) is corrected by means of the LAFS that is attached to an exhaust system, which control map is determined as a function of the lever opening degree (accelerator opening degree) of a fuel injection pump and the engine rotation speed.
Nevertheless, those EGR apparatuses equipped with the LAFS for the feedback control of the EGR quantity have the following problems.
Since the LAFS is attached to the exhaust system, for example, a delay in transfer is caused before the exhaust gas reaches the LAFS even though the excess air rate actually changes. Since the LAFS is designed so as to output a current corresponding to the excess air rate, based on the principle of an oxygen concentration cell, and that the exhaust gas reaches the elements through a protective tube, moreover, the response to change of the excess air rate is low itself. At the time of acceleration or deceleration such that the excess air rate suddenly changes, therefore, a delay (normally tens of strokes) is caused before the LAFS detec
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Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Wolfe Willis R.
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