The present invention relates to an internal combustion engine, and specifically to an internal combustion engine in which fuel is injected into an intake air passage.
There have been proposed internal combustion engines having a plurality of engine cylinders and a fuel injector disposed in an intake air passage communicated with each engine cylinder. In the conventional arts, generally, for the purpose of facilitating atomization of fuel, the fuel is injected toward a valve head of an intake valve at an engine exhaust stroke. Further, for the purpose of improving an air-fuel mixture generation, there has been proposed a fuel injector capable of atomizing fuel to particles having a relatively small particle diameter. Japanese Patent Application First Publication No. 2000-38974 discloses an improved fuel injector for atomizing fuel to fine particles.
U.S. Pat. No. 5,113,833 discloses a fuel injector capable of generating an atomized fuel having a particle diameter of 80-90 xcexcm. A fuel injection timing of the fuel injector is set to an engine intake stroke when a temperature of an engine cooling water is low, and is shifted from the engine intake stroke to an engine exhaust stroke as the engine cooling water temperature increases. The related art contemplates preventing the fuel from adhering to a peripheral wall of the intake air passage and flowing down therealong into the engine cylinder upon injecting the fuel at the engine exhaust stroke in a cool state of the engine.
Japanese Patent Application First Publication No. 2000-313672 discloses an internal combustion engine in which an intake valve made of ceramic is utilized.
When the fuel is injected toward the intake valve head at the engine exhaust stroke, atomization of the fuel is facilitated. However, heat required for vaporizing the fuel injected, namely, latent heat of vaporization of the fuel injected, is taken from the intake valve head. There is a demand to positively take the latent heat of vaporization of the injected fuel from the intake air in the intake air passage and reduce a temperature of the intake air flowing into the engine cylinder to thereby suppress an engine knock.
In the internal combustion engine of U.S. Pat. No. 5,113,833, the fuel injection timing of the fuel injector is set to the intake stroke when the engine is in a cool state, namely, the temperature of the engine cooling water is low. When the engine is warmed up, the fuel injection timing is shifted from the intake stroke to the exhaust stroke. At this time, latent heat of vaporization of the fuel injected to the intake valve is mainly taken from the intake valve. Therefore, a temperature of the intake air in the intake air passage cannot be reduced. In addition, the related art aims at improving the air-fuel mixture generation in the cool state of the engine by setting the fuel injection timing to the intake stroke. It is not suggested by the related art to positively take the latent heat of vaporization of the injected fuel from the intake air in an engine operating range in which knocking occurs, in order to reduce the temperature of the intake air in the intake air passage.
Further, the ceramic intake valve as described in Japanese Patent Application First Publication No. 2000-313672 has an effect of thermal insulation. However, merely application of the ceramic intake valve to internal combustion engines will fail to take latent heat of vaporization of the injected fuel from an intake air in an intake air passage and sufficiently reduce a temperature of the intake air.
An object of the present invention is to provide an internal combustion engine capable of reducing a temperature of an intake air in an intake air passage to thereby suppress knocking.
According to one aspect of the present invention, there is provided an internal combustion engine, comprising:
a combustion chamber;
an intake air passage communicated with the combustion chamber;
an intake valve having a thermal insulator at an air-exposure portion thereof which is opposed to the intake air passage, the intake valve being operative to establish fluid communication between the combustion chamber and the intake air passage and prevent the fluid communication therebetween;
a fuel injector operative to inject an amount of fuel toward the air-exposure portion of the intake valve at a fuel injection timing, the fuel injector being disposed within the intake air passage; and
a controller in communication with the fuel injector and programmed to set the fuel injection timing of the fuel injector to an engine intake stroke.
According to a further aspect of the present invention, there is provided an internal combustion engine, comprising:
a combustion chamber;
an intake air passage communicated with the combustion chamber;
an intake valve having a thermal insulator at an air-exposure portion thereof which is opposed to the intake air passage, the intake valve being operative to establish fluid communication between the combustion chamber and the intake air passage and prevent the fluid communication therebetween;
a fuel injector operative to inject an amount of fuel toward the air-exposure portion of the intake valve at a fuel injection timing, the fuel injector being disposed within the intake air passage; and
control means, in communication with the fuel injector, for setting the fuel injection timing of the fuel injector to an engine intake stroke on the basis of an engine load.
According to another aspect of the present invention, there is provided a method of controlling fuel injection for knock suppression in an internal combustion engine which has an intake air passage, an intake valve having an air-exposure portion opposed to the intake air passage, and a fuel injector adapted to inject an amount of fuel toward the air-exposure portion of the intake valve, the method comprising:
determining whether or not the engine operates in a warmed-up state;
determining whether or not the engine operates in a knock range under condition that the engine operates in the warmed-up state; and
setting a fuel injection timing at which the fuel injector injects the amount of fuel, to an engine intake stroke when it is determined that the engine operates in the knock range.