Internal-combustion engines – Poppet valve operating mechanism – With means for varying timing
Reexamination Certificate
1999-08-20
2001-05-22
Walberg, Teresa (Department: 3742)
Internal-combustion engines
Poppet valve operating mechanism
With means for varying timing
C123S090160, C123S090170
Reexamination Certificate
active
06234123
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a four-cycle internal combustion engine and a valve timing control method thereof, and more specifically relates to those which can be used preferably for an automobile gasoline engine.
Japanese Patent Application Laid-Open No. 7-332141 discloses a compression ignition gasoline engine in which a premixed gas is compression-ignited and burned so that lean combustion and low-NOx exhaustion are attempted.
Japanese Patent Application Laid-Open No. 5-321702 discloses a valve control apparatus of an internal combustion engine in which valve timing of inlet/exhaust valves is controlled in a low engine speed area and a gas is allowed to remain in a cylinder so that exhaust efficiency and fuel consumption are improved.
SUMMARY OF THE INVENTION
According to the studies by the present inventors, in order to improve thermal efficiency of a four-cycle internal combustion engine, a fuel-air mixture is made to be lean so that a pump loss is reduced, and a ratio of specific heat of the fuel-air mixture is set to be large so that a theoretical thermal efficiency is improved.
However, in a gasoline engine, since the combustion due to spark ignition and flame propagation becomes unstable, to be lean in the fuel-air mixture is limited naturally. Moreover, at the time of the lean combustion, a catalyst for purifying an exhaust gas has a tendency to be incapable of performing a purifying function, particularly a NOx reducing function, as much as the time of combustion in stoichiometry.
Meanwhile, in a diesel engine, the extremely lean combustion can be executed, but its soot is occasionally exhausted, and a catalyst for purifying an exhaust gas can not be activated effectively.
Further, particularly in the gasoline engine, when the combustion is executed by the compression-ignition, the lean combustion and low NOx exhaustion can be intended, but the phenomenon of the compression-ignition using a premixed gas is greatly influenced by its air fuel ratio. Namely, knocking tends to occur on the rich side in its lean area, and misfire tends to occur on the lean side in its lean area, and thus an air fuel ratio range where the satisfactory operation of the engine is possible is limited inevitably. In other words, a load range where the satisfactory operation is possible tends to be limited.
In addition, even if the low NOx exhaustion is realized by the combustion of the compression ignition using the premixed gas, since EGR is not executed, substantially whole the premixed gas is exhausted as the exhaust gas, and thus such a constitution provides room to be improved in the point that the thermal efficiency is improved by efficiently utilizing its fuel.
In addition, in a case where valve timing of inlet and exhaust valves is controlled suitably in the low engine speed area and a burned gas is allowed to remain in the cylinder so that the exhaust efficiency and fuel consumption are improved, knocking tends to occur and its combustion tends to become unstable. As a result, the load range where the operation is sufficiently possible is limited.
The present invention has been achieved with such points in view, and it therefore is an object of the present invention to realize uniform premixture compression-ignited combustion, which exhibits high thermal efficiency and low NOx exhaust in a wide load range of a four-cycle internal combustion engine, and improved thermal efficiency by effectively utilizing a fuel by means of re-combustion of unburned HC in the four-cycle internal combustion engine, and therefore to attain the four-cycle internal combustion engine with high thermal efficiency and clean exhaust.
Namely, the present invention has a constitution such that valve timing of the inlet and exhaust valves is switched correspondingly when high load and low load are put on the internal combustion engine, and the valve timing is controlled variably according to the load at the time of low load, and a large quantity of residual gas in a cylinder is utilized effectively as a heat source.
More concretely, a four-cycle internal combustion engine of the present invention includes: a combustion chamber; an igniter igniting a fuel-air mixture in the combustion chamber; a piston changing a capacity of the combustion chamber; an inlet valve opening/closing the combustion chamber; an exhaust valve opening/closing the combustion chamber; an adjustable valve mechanism switching valve timing of the inlet valve and switching that of the exhaust valve; and a controller controlling the igniter and the adjustable valve mechanism. Here when a high load is put on the four-cycle internal combustion engine, the controller sets the valve timing of the exhaust valve in the adjustable valve mechanism so that the exhaust valve is closed around a top dead center of the piston, and ignites the fuel-air mixture around a compression top dead center of the piston by using the igniter. Meanwhile when a low load is put on the four-cycle internal combustion engine, the controller sets the valve timing of the exhaust valve in the adjustable valve mechanism so that valve closing timing of the exhaust valve advances before the top dead center of the piston as a load put on the four-cycle internal combustion engine becomes lower, and compression-ignites the fuel-air mixture without using the igniter.
According to such a structure, when the low load is put on the four-cycle internal combustion engine, the valve closing time of the exhaust valve advances and the exhaust valve is closed in the middle of the exhaust process before the piston top dead center. For this reason, a burned gas of high temperature whose quantity corresponds to the cylinder capacity at this time remains in the combustion chamber so as to be capable of being used as a ignition source in the next cycle. That is, a new gas sucked in the next cycle is agitated and mixed with the residual burned gas and thus the uniform fuel-air mixture of high temperature is formed. And the uniform fuel-air mixture of high temperature is compressed so that the compression ignition of the lean fuel-air mixture can be realized around the piston top dead center.
At this time, since the fuel-air mixture is self-ignited and burned due to such high temperature/high pressure atmosphere, the ignition does not require the igniter. Meanwhile, so-called flame propagation, which is observed in conventional spark-ignited combustion, does not exist, and thus a local high-temperature portion due to the flame propagation does not exist. Further, a burned gas portion after the flame surface is passed is not compressed and does not have high temperature due to the flame propagation. Still further, since so-called internal EGR with large quantity is executed, oxygen density of the fuel-air mixture is lowered. Therefore, NOx exhaust can be suppressed to an extremely small quantity.
In addition, soot is not generated because the partial rich area does not exist in the fuel-air mixture. Further, extremely lean combustion can be realized by the compression self-ignition, and unburned HC, which is normally exhausted and disposed, can be burned and recovered effectively by a large quantity of the internal EGR. As a result, the thermal efficiency can be improved.
In particular, the advance of the valve closing time of the exhaust valve at the time of the low load is controlled according to the load, and the advance degree of the valve closing time of the exhaust valve is increased on the low load side in the low load area so that the quantity of the residual burned gas is increased. Meanwhile the advance degree of the valve closing time of the exhaust valve is reduced on the high load side in the low load area so that the quantity of the residual burned gas is reduced. As a result, in the lower load state, namely in the state that the fuel-air mixture is more lean, the temperature of the fuel-air mixture can be effectively heightened by increasing the internal EGR. For this reason, the compression self-ignited combustion can be executed securely for the lean
Iiyama Akihiro
Masuda Tsuyoshi
Noda Toru
Dahbour Fadi H.
Foley & Lardner
Nissan Motor Co,. Ltd.
Walberg Teresa
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