The present invention relates generally to intake structures for internal combustion engines, and more particularly, to a vane which is incorporated in the intake passage of internal combustion engines for producing advantageous swirl in the combustion chambers of the engine during operation.
In the field of internal combustion engines, it is known that, if the intake gas induced into a combustion chamber is provided with a swirling motion, the resulting turbulence assists the propagation of flame in the combustion chamber increasing the speed of flame propagation, thereby improving the performance of the engine. In addition, the anti-knock and driving characteristics of the engine, and the quality of the exhaust emissions thereof, are improved.
Conventionally, the inlet port of an internal combustion engine, especially a gasoline engine, is formed so as to minimize the resistance to the flow of intake gases and thereby increase the volumetric efficiency and maximum output power of the engine at high load operation. When such an internal combustion engine is operating at high load, although the flow or suction resistance of the inlet port is low, sufficient turbulence and swirl is caused in the combustion chamber for the flame propagation speed to be kept at an acceptable level.
However, during low and medium load operation, in which the amount of inlet gases is relatively low, a good level of swirl and turbulence of the inlet gases does not occur, due to the low flow resistance of the inlet port, and because the velocity of the inlet gas entering the combustion chamber from the inlet port is low. Thus combustion speed is sometimes not high enough, and, especially if the engine is operating in a lean mixture condition, or is provided with a substantial quantity of exhaust gas recirculation, good operating performance of the engine may be lost.
Conventionally, it has been realized that the generation of swirl in the cylinder is strongly affected by the direction of entry of inlet gases thereinto, and their degree of swirling as they enter. Therefore, in the past, various types of inlet ports have been proposed, with a view to enhancing swirl. One of these has been the so-called helical port, which is provided with a helical surface leading to the valve seating surface and extending helically around the axis of the valve seating surface. This type of port imparts a swirling action to the inlet gases before they pass the inlet valve.
However, there is a significant disadvantage in the performance of such a helical inlet port, which limits the usefulness thereof. If the helical surface is provided as a long and deep helix, so that it imparts a very strong swirling action to the inlet gases, then, at high load operation, when a large volume of inlet gases is required to be passed by the inlet port, the volumetric efficiency of the engine will be degraded, and thus its maximum output power will suffer, due to the increase of the resistance of the inlet passage to the flow of inlet gases. On the other hand, if the helical surface is provided as a short and shallow helix, so that it imparts a rather weak swirling action to the inlet gases, it will not function well at low load operation of the engine. Accordingly, such a helical port has not fully met the need for generating swirl in intake gases.
The present invention results from the realization that, if the flow of inlet gases is specifically directed to the start of the helical surface of a helical inlet port during low and medium load operation of the engine, without greatly increasing flow resistance of the inlet port to inlet gases, swirl and turbulence in the combustion chamber would be advantageously improved, and combustion speed would be increased, without sacrificing engine output power.
It is, therefore, an object of the present invention to provide an apparatus in the inlet passage of an internal combustion engine by which the mixture gas is directed to the start of the helical surface of a helical inlet port, particularly during low and medium load operation of the engine, without greatly increasing flow resistance of the inlet passage.