Internal-combustion engines – Charge forming device – Including exhaust gas condition responsive means
Reexamination Certificate
2004-02-05
2004-11-23
Kwon, John T. (Department: 3747)
Internal-combustion engines
Charge forming device
Including exhaust gas condition responsive means
C123S681000, C123S699000, C123S399000
Reexamination Certificate
active
06820603
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a control system and control method for an internal combustion engine equipped with a nitrogen-enriching device in an intake passage for enriching nitrogen in intake air, and an engine control unit.
2. Description of the Related Art
Conventionally, a control system for an internal combustion engine, of the above-mentioned kind, has been disclosed e.g. in Japanese Laid-Open Patent Publication (Kokai) No. H08-254161 (FIG. 1). This control system is applied e.g. to diesel engines, and includes a gas separation device disposed in a branch passage branching from an intake passage. This gas separation device separates incoming intake air (outside air) into nitrogen and oxygen-enriched air by a separation membrane provided in its housing. At an upstream portion of the intake passage, there is disposed a compressor of a turbocharger that supercharges the intake air so as to cause the intake air to pass through the separation membrane. The gas separation device has a nitrogen outlet connected to an intake port via the branch passage, and an oxygen-enriched air outlet connected to cylinders via an oxygen supply passage having an oxygen storage tank interposed therein. A cylinder head of each cylinder has a gas injection valve for injecting oxygen-enriched air into the cylinder. At a location downstream of a branching point where the branch passage branches from the intake passage, there is disposed a butterfly valve. Further, an exhaust gas recirculation (EGR) passage is connected to the branch passage at a location downstream of the gas separation device. In the exhaust gas recirculation passage, there is provided an EGR valve for controlling the amount of EGR gas.
In the control system described above, in a low-load operating region of the engine, for example, the degree of opening of the butterfly valve is controlled such that part of the intake air flows into the branch passage, and the EGR valve is opened, while stopping the operation of the gas injection valves. As a result, nitrogen separated by the gas separation device in the branch passage is supplied to the cylinders, together with outside air through the intake passage, so that the oxygen content of the intake air supplied to the cylinders is reduced as a whole, which provides practical EGR effects. Further, the intake air is depressurized due to pressure loss caused during passing of the intake air through the gas separation device, which promotes recirculation of the EGR gas, so that it is possible to provide proper EGR effects, thereby suppressing generation of NOx.
It is also conventionally known that in a low-load operating condition of a gasoline engine, for example, lean-burn operation is carried out in which the air-fuel ratio of an air-fuel mixture is controlled to be an extremely larger value than the stoichiometric air-fuel ratio in order to improve fuel economy (as disclosed e.g. in the publication of Japanese Patent No. 2817106). The effect of improving fuel economy by this lean-burn operation is achieved through reduction of heat loss by an increase of the working fluid and the improvement of combustion efficiency by reduction of pumping loss, and as shown in FIG. 9, when the air-fuel ratio is approximately 21.0, the brake specific fuel consumption BSFC is minimized, whereby the best fuel economy can be achieved.
However, in the lean-burn operation described above, although fuel economy is improved, NOx in exhaust gases cannot be reduced sufficiently by a three-way catalyst generally used as an emission reduction device. This is because in lean-burn operation, the air-fuel ratio of an air-fuel mixture is higher than the stoichiometric air-fuel ratio, so that a large amount of superfluous oxygen remains unburnt in the exhaust gases, whereas the three-way catalyst exhibits its highest performance for reducing CO, HC and NOx, under a condition where oxygen density is substantially zero.
To solve this problem, conventionally, as a substitute for the three-way catalyst, there have been proposed the following emission reduction devices: (1) a catalyst of a type that stores NOx during lean-burn operation and reduces NOx during stoichiometric combustion executed at the stoichiometric air-fuel ratio; (2) a catalyst of a type capable of reducing NOx even when superfluous oxygen exists. However, these catalysts are both more expensive than the three-way catalyst. Further, in the case of the first type, when storage of NOx reaches saturation, lean-burn operation has to be interrupted so as to prevent NOx from being emitted, and hence the effect of improving fuel economy by lean-burn operation cannot be fully obtained. On the other hand, the second type is not capable of achieving excellent emission control since its NOx reduction rate is low when superfluous oxygen exists, which prevents this type from becoming commercially practical.
Since the problem of NOx reduction in lean-burn operation results from the existence of superfluous oxygen as described above, it is effective to make use of the gas separation device disclosed in Japanese Laid-Open Patent Publication (Kokai) No. 8-254161 (FIG. 1 of the publication), to supply nitrogen from the gas separation device to the engine during lean-burn operation. In this control system, however, since the butterfly valve is opened only to allow part of intake air to flow into the gas separation device, for supply of nitrogen, the amount of intake air that actually flows into the gas separation device cannot be gasped accurately. Further, a gas separation device of this kind has the characteristic that its separation performance varies with the boost pressure and the temperature of intake air, which makes the degree of separation between nitrogen and oxygen-enriched air unknown, and the separation performance is degraded due to insufficiency of boost pressure e.g. at the start of the turbocharger. Consequently, the above control system cannot accurately control the actual amount of nitrogen in intake air supplied to the cylinders of the engine, i.e. the actual amount or concentration of oxygen, and therefor superfluous oxygen inevitably remains in exhaust gases. As a result, the emission-reducing potential of the three-way catalyst cannot be fully exploited, which also makes it impossible to achieve excellent exhaust emission control.
Further, in this control system, in low-load operation, EGR is carried out simultaneously with supply of nitrogen. For this reason, CO2 with a high specific heat is increased by combustion, causing increased heat loss. As a result, combustion efficiency is reduced, which makes it impossible to sufficiently obtain the effect of improving fuel economy by lean-burn operation. Moreover, CO in the EGR gas can cause carbon clogging and generation of smoke.
SUMMARY OF THE INVENTION
It is an object of the present invention to provide a control system and control method for an internal combustion engine and an engine control unit which are capable of meeting a driver's demand of torque, and achieving high combustion efficiency and high emission reducing performance by a three-way catalyst in lean-burn operation in a compatible manner.
To attain the above object, in a first aspect of the present invention, there is provided a control system for an internal combustion engine including a throttle valve and a nitrogen-enriching device that enriches nitrogen in intake air, both disposed in an intake passage, and an emission reduction device disposed in an exhaust passage, for reducing exhaust emissions,
the control system comprising:
an oxygen concentration sensor provided in the exhaust passage, for detecting oxygen concentration in exhaust gases;
control amount-setting means for setting a control amount indicative of one of a mass of oxygen supplied to a combustion chamber of the engine and a fuel injection amount, such that the detected oxygen concentration becomes equal to an oxygen concentration corresponding to stoichiometric combustion;
operating condition-detecting m
Iwamoto Jun
Ogihara Hidemi
Takahashi Hitoshi
Yasui Yuji
Arent Fox PLLC.
Honda Motor Co. Ltd.
Kwon John T.
LandOfFree
Control system and control method for internal combustion... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Control system and control method for internal combustion..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Control system and control method for internal combustion... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3342500