Power plants – Internal combustion engine with treatment or handling of... – By means producing a chemical reaction of a component of the...
Reexamination Certificate
2002-08-28
2004-05-04
Tran, Binh (Department: 3748)
Power plants
Internal combustion engine with treatment or handling of...
By means producing a chemical reaction of a component of the...
C060S284000, C060S286000, C060S292000, C060S324000, C123S299000, C123S300000
Reexamination Certificate
active
06729123
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to an exhaust gas purifying device for an in-cylinder injection spark ignition type internal combustion engine, and more particularly, to techniques of improving the exhaust gas purifying efficiency to enhance the effect of reducing the emission quantity of harmful matter contained in exhaust gas.
2. Description of the Related Art
As one of techniques for reducing harmful matter (including not only unburned matter such as HC, CO, and H
2
but smoke, NO
x
, etc.) contained in exhaust gas, there has been known an exhaust gas purifying technique utilizing reaction with the aid of catalyst.
This exhaust gas purifying technique is, however, disadvantageous in that unburned matter such as HC is discharged into the atmosphere before the catalyst is activated. The disadvantage can pose a grave problem because the quantity of harmful matter discharged before the catalyst is activated occasionally accounts for 90% of the total emission quantity during cold-mode operation.
To solve the problem, a two-stage combustion technique (or two-stage injection technique) for an in-cylinder injection spark ignition type internal combustion engine has been proposed. According to this technique, fuel injection is carried out in two stages, that is, a main injection (with the air/fuel ratio so set as to provide an ultra-lean mixture) and an auxiliary injection which is performed in or after the expansion stroke to cause oxygen remaining after a main combustion (stratified combustion) following the main injection to react with unburned fuel of the auxiliary injection in an exhaust system (including parts of the engine from the combustion chamber to the catalytic converter), thereby reducing harmful matter and quickening the activation of the catalyst.
There has also been proposed a technique of accelerating the reaction by increasing the exhaust pressure (by restraining the exhaust gas flow) and thereby quickening the activation of the catalyst in cold mode, as disclosed in Unexamined Japanese Patent Publications (KOKAI) No. 3-117611 and No. 4-183921, for example.
Further, a combination of these techniques also has been developed wherein the two-stage combustion is carried out while at the same time the exhaust pressure is increased, to quicken the activation of the catalyst in cold mode.
In the case where the two-stage combustion is performed, however, although the reaction in the exhaust system can be drastically accelerated and the catalyst can be activated quickly, a problem arises in that the auxiliary injection leads to a correspondingly lower fuel efficiency because the fuel injected in the auxiliary injection does not directly contribute to the production of engine torque.
Also, in the case of the two-stage combustion, the air/fuel ratio needs to be controlled such that the air/fuel mixture burned in the main combustion following the main injection should be ultra-lean. There is naturally a limit to the engine torque that can be produced, and if the exhaust pressure is increased, the exhaust resistance also increases, making it difficult even to maintain the limit. Such a limit on the engine torque is undesirable because the driver's demand for acceleration may fail to be satisfied.
SUMMARY OF THE INVENTION
An object of the present invention is to provide an exhaust gas purifying device for an in-cylinder injection spark ignition type internal combustion engine, which device is capable of minimizing lowering of the fuel efficiency even during cold-mode operation, and improving the exhaust gas purifying efficiency to restrain the emission quantity of harmful matter while at the same time ensuring acceleration performance.
To achieve the object, the present invention provides an exhaust gas purifying device for an in-cylinder injection spark ignition type internal combustion engine including an injection valve for injecting fuel directly into a combustion chamber, fuel injection control means for controlling the injection of fuel by the injection valve, and air/fuel ratio control means for controlling burn air/fuel ratio. The exhaust gas purifying device comprises a catalytic converter arranged in an exhaust passage for purifying harmful matter in exhaust gas, catalyst activation determining means for determining an activated state of the catalytic converter, compression-stroke slight-lean operation means for causing the air/fuel ratio control means to control the burn air/fuel ratio to produce a slight lean air/fuel mixture equivalent to or slightly leaner than a stoichiometric air/fuel mixture and also causing the fuel injection control means to inject fuel in a compression stroke, to thereby carry out a compression-stroke slight-lean operation, and exhaust gas flow control means for restraining an exhaust gas flow in the exhaust passage, wherein when it is judged by the catalyst activation determining means that the catalytic converter is not in the activated state, the compression-stroke slight-lean operation is performed by the compression-stroke slight-lean operation means and also the exhaust gas flow in the exhaust passage is restrained by the exhaust gas flow control means.
It has been thought hitherto that in the case of an in-cylinder injection spark ignition type internal combustion engine, if fuel is injected in the compression stroke, the spark plug is likely to be wetted because fuel is injected in the vicinity of the spark plug. As a result of experiments conducted by the applicant hereof, however, it was found that when fuel was injected in the compression stroke especially while the engine was in a cold state, the injected fuel actually showed a satisfactory spray pattern with less wetting of the spark plug. It was also found that a large quantity of CO (carbon monoxide) was produced while at the same time ensuring the engine torque. In accordance with the findings, when the engine is in a cold state, the compression-stroke slight-lean operation is carried out wherein the burn air/fuel ratio is so controlled as to produce a slight lean air/fuel mixture equivalent to or slightly leaner than the stoichiometric air/fuel mixture and fuel is injected in the compression stroke, thereby to discharge CO into the exhaust passage as unburned matter together with the residual oxygen (O
2
), and also the exhaust gas flow is restrained at the same time.
Consequently, while the engine is in a cold state and the catalytic converter is not yet activated, the exhaust gas can be made to contain a large quantity of CO as unburned matter along with O
2
, without carrying out the auxiliary injection of the two-stage combustion. CO reacts with O
2
more easily than HC, so that the reaction in the exhaust system is further accelerated also with the aid of the exhaust gas flow restraining effect. It is therefore possible to improve the exhaust gas purifying efficiency with the air/fuel mixture as a whole set to a slightly lean mixture to restrain the fuel efficiency from lowering while at the same time ensuring the engine torque, and also to quicken the activation of the catalytic converter.
The exhaust gas purifying device of the present invention may further comprise exhaust port ambient temperature detecting means for detecting temperature of or ambient temperature of an exhaust port extending from the combustion chamber to the exhaust passage. When it is judged by the catalyst activation determining means that the catalytic converter is not in the activated state and also the temperature or ambient temperature of the exhaust port detected by the exhaust port ambient temperature detecting means is higher than or equal to a predetermined temperature, the compression-stroke slight-lean operation is carried out and also the exhaust gas flow is restrained.
The experiments conducted by the applicant hereof confirmed that the reaction of CO in the exhaust system was accelerated inside the exhaust port into which the exhaust gas flows directly from the combustion chamber. The rate of the reaction increases with increa
Kawashima Kazuhito
Tamura Yasuki
Birch & Stewart Kolasch & Birch, LLP
Mitsubishi Jidosha Kogyo Kabushiki Kaisha
Tran Binh
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