Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
2002-10-08
2004-08-10
Denion, Thomas (Department: 3748)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090160, C123S090170, C123S090180
Reexamination Certificate
active
06772720
ABSTRACT:
CROSS REFERENCE TO RELATED APPLICATION
This application is based upon, claims the benefit of priority of, and incorporates by reference the contents of prior Japanese Patent Application No. 2001-315828 filed Oct. 12, 2001.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a valve opening and valve closing timing control device for use in internal combustion engines.
2. Description of the Related Art
Generally, governmental requirements with respect to hazardous gas emissions from internal combustion engines have become increasingly tough in recent years. To reduce the emission of hazardous gases, a variety of technologies are now under development. When a catalytic converter is inactive, for example, during a cold start of an internal combustion engine, a lot of hazardous gases are discharged. It is known that the three-way catalyst, which is a popular material for catalytic converters, exhibits its highest performance when it is in an active state and the air-to-fuel ratio is maintained at its theoretical value. However, since the catalytic converter is not activated at cold start, the hazardous gases produced by combustion are not decomposed and are discharged, as combusted, into the atmosphere, this results in a poor quality of exhaust gas being discharged into the atmosphere.
Japanese Unexamined Patent Application Publication No. Hei. 11-336574 discloses a technology for reducing hydrocarbon (HC) gases which are part of the hazardous gases. It converts post-combustion gas, after being discharged to the exhaust line, back to the cylinder of the internal combustion engine by controlling the duration of the time that both intake and exhaust valves are open at the same time, which is called the valve overlap.
It is possible to burn the unburned HCs in the post-combustion gas and thereby reduce HC emissions by recirculating the post-combustion gas, once it is discharged to the exhaust line, back into the cylinder. If a lot of post-combustion gas is returned to the cylinder, however, the state of combustion becomes unstable because of the increased ratio of the post-combustion gas to the pre-combustion gas. The technique disclosed in Japanese Unexamined Patent Application Publication No. Hei. 11-336574 sets the valve overlap at a value below a predetermined level in order to prevent the amount of post-combustion gas being recirculated to the cylinder from increasing. Then, since the period of time that both intake and exhaust valves are open is shortened, the amount of recirculated gas can be properly limited to avoid the above problem.
Note that the amount of combustion gas that will be returned is determined by the degree of valve overlap and pressure difference between the intake line and the exhaust line. If the pressure in the intake line does not differ much from that in the exhaust line, a sufficient amount of exhaust gas is not returned to the cylinder. As a result, the effect of burning yet-burned HCs is not fully achieved.
This is particularly a problem during engine starting. At the moment the engine is started, the engine has not reached its idle speed, and therefore the pressure in the intake line is not low enough to pull post-combustion gas back into the cylinder. It then becomes impossible to take in a sufficient amount of post-combustion gas during engine starting by the technology disclosed in Japanese Unexamined Patent Application Publication No. Hei. 11-336574 that introduces combustion gas back into the cylinder by retarding the closure of the exhaust valve by controlling valve overlap. Particularly during cold start, unburned HCs are discharged into the air as they are because the catalytic converter has not yet been activated.
Part of the fuel injected during a cold start is not involved in combustion, and does not burn well in the cylinder but adheres to the cylinder wall. This is because fuel is not sprayed into the cylinder very well upon cold start, compared with that sprayed during normal engine operation. Since the fuel lodged onto the cylinder walls is less exposed to air, it is further less involved in combustion. Such unburned HC adhering to the cylinder wall is scraped up by the piston and discharged into the exhaust line when the exhaust valve opens. This HC is referred to as quench HC.
SUMMARY OF THE INVENTION
An object of the present invention is therefore to provide a valve timing control device for internal combustion engines in order to reduce the emissions of unburned HC.
Another object of the invention is to provide a valve timing control device that can reduce the amount of unburned HC discharged into the exhaust line including during a cold start.
According to a first aspect of the present invention, a valve timing control device for an internal combustion engine includes an exhaust valve control means for controlling at least a close timing of an exhaust valve installed in an internal combustion engine and a first engine condition detection means for detecting or estimating a condition of the internal combustion engine. The exhaust valve control means advances or retards the exhaust valve close timing from an intake top dead center based on the engine condition detected or estimated by the engine condition detection means.
It then becomes possible to retain post-combustion gas in the combustion chamber by advancing the close timing of the exhaust valve when the first engine condition detection means detects an engine condition under which a sufficient amount of post-combustion gas cannot be returned to the combustion chamber. If the post-combustion gas is retained in the combustion chamber, it becomes possible that unburned hydrocarbons in the combustion gas (hereafter called unburned HCs) will be involved in combustion during the next combustion round. Therefore, hazardous gas emissions are reduced. Meanwhile, when a sufficient amount of post-combustion gas can be recirculated into the combustion chamber by retarding the exhaust valve close timing, it becomes possible to reduce unburned HC emissions by reintroducing the unburned HCs in combustion. The above approach can accomplish the first goal of reducing emissions by cutting unburned HC.
According to a second aspect of the present invention, the first engine condition detection means detects or estimates pressure in an intake line or a parameter related to pressure as the operation condition of the internal combustion engine. The exhaust valve control means advances the exhaust value close timing from intake top dead center when the pressure or parameter detected or estimated by the first engine condition detection means is larger than a predetermined value while retarding the exhaust value close timing from the intake top dead center when the pressure or parameter detected or estimated by the first engine condition detection means is smaller than a predetermined value.
Then it becomes possible to advance or retard exhaust valve closure based on the pressure in the intake line or a parameter related to the pressure. Specifically, when the pressure difference between the intake line and the exhaust line is small, the close timing of the exhaust valve is advanced to confine the post-combustion gas in the combustion chamber to burn the unburned HC. On the other hand, when the pressure difference between the intake line and the exhaust line is large, the combustion gas discharged in the exhaust line can be recirculated to the combustion chamber. Then the unburned HC is consumed in combustion, thereby reducing emissions. The above configuration can also accomplish the first goal of reducing emissions by cutting unburned HC.
According to a third aspect of the present invention, the valve timing control device may further include a second engine condition detection means for detecting the condition of the internal combustion engine. The second engine condition detection means estimates an amount of wet fuel adhering to the intake line and/or an amount of unburned hydrocarbons adhering to a cylinder wall of the internal combustion engine. The wet fuel
Denso Corporation
Nixon & Vanderhye P.C.
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