1. Field of the Invention
The present invention relates to an intake device of an internal combustion engine.
2. Description of the Related Art
In order to create a swirl motion in the combustion chamber when the engine is operating under a light load and to obtain a high volumetric efficiency when the engine is operating under a heavy load at a high speed, it is well known, to equip each cylinder in an engine with a pair of intake valves, and to arrange a fuel injection in an intake passage. The intake passage is divided into two branch intake passages at a position downstream of the fuel injector, and these branch intake passages are connected to the combustion chamber via the corresponding intake valves. A control valve which is closed when the engine is operating under a light load is arranged in one of the branch intake passages (See Japanese Unexamined Patent Publication (Kokai) No. 57-70914). In the above arrangement, when the engine is operating under a light load, and since the control valve is closed, air is fed into the combustion chamber from only one of the branch intake passages, thus creating a swirl motion in the combustion chamber. Conversely, when the engine is operating under a heavy load, and since the control valve is open, air is fed to the combustion chamber from both branch intake passages, and a high volumetric efficiency can be obtained. However, since the fuel injector is arranged upstream of the control valve, some of the fuel injected from the fuel injector when the control valve is closed adheres to the control valve. Therefore, since all of the fuel injected from the fuel injector is not instantaneously fed into the combustion chamber, a good accelerating operation cannot be obtained.
Also, since a swirl motion is created in the combustion chamber when the engine is operating under a light load, the burning velocity of the air-fuel mixture in the combustion chamber can be improved. However, in the above arrangement, ignitability is neglected.
Also, well known is an engine in which each cylinder is equipped with a pair of intake valves and a pair of independently arranged intake passages. A control valve which is closed when the engine is operating under a light load is arranged in one of the intake passages. The intake passages are interconnected via a connecting hole at a position downstream of the control valve, and the fuel injector is arranged in the connecting hole (See Japanese Unexamined Patent Publication No. 57-105534). In this engine, when the engine is operating under a heavy load, and since the control valve is open, air is fed to the combustion chamber from both intake passages, and a high volumetric efficiency can be obtained. In addition, since the fuel injector is arranged downstream of the control valve, there is no danger that fuel injected from the fuel injector will adhere to the control valve.
However, in this engine, since the intake passages are interconnected at a position downstream of the control valve, air is fed to the combustion chamber from both intake passages even if the control valve is closed when the engine is operating under a light load. As a result, the velocity of the air flowing into the combustion chamber is inevitably reduced, and, since it is difficult to create a strong swirl motion in the combustion chamber, it is impossible to sufficiently increase the burning velocity of the air-fuel mixture in the combustion chamber. In this engine, also ignitability is neglected.