The present invention relates to a system for controlling the injection of fuel for a two-cycle engine with a direct fuel injection system, and more particularly to a system for controlling the injection timing in accordance with operating conditions of the engine.
There are various methods for supplying fuel to a two-cycle engine. In a method where fuel is mixed with air to make a combustible mixture and the mixture is supplied to a cylinder of the engine, a part of the fuel escapes from the cylinder through an exhaust port during the scavenging of the cylinder. In order to prevent fuel from escaping through the exhaust port, a method in which air alone is delivered to the cylinder and fuel is injected directly to the cylinder by an injector is proposed.
Japanese Patent Application Laid-Open 62-113819 discloses a two-cycle engine in which first and second scavenge passages are provided. The first scavenge passage is provided with a first throttle valve and a fuel injector to supply a combustible mixture to a cylinder of the engine. The second scavenge passage is provided for supplying air. The quantity of fuel is calculated in accordance with engine speed and a signal from an air-flow meter. The cylinder is scavenged by air, then supplied with the combustible mixture. In the system, fresh air must be quickly delivered from first and second scavenge passages to perform the scavenging. Accordingly, the structure of the control system becomes complicated. Thus, it is preferable to employ a direct fuel injection system for directly injecting fuel to the cylinder.
Japanese Patent Application Laid-Open Nos. 57-203821 and 60-501963 disclose direct fuel injection systems where each fuel injector is mounted in the cylinder of the engine. A quantity of fuel dependent on engine operating conditions is injected to form a combustible mixture in the cylinder.
In the direct fuel injection system, the fuel is injected after the exhaust port is closed in a compression stroke. Since the pressure in the cylinder changes during the compression stroke, the penetration, distribution and atomization of the fuel spray inevitably varies in dependency on the timing and duration of the fuel injection. Accordingly, it is preferable to change the time condition, in order to form a proper combustible mixture and to burn the mixture in accordance with engine operating conditions. For example, in a heavy engine load range, the duration of fuel injection is increased to produce large engine power. To the contrary, in a light engine load range, a stratified charge is preferable for burning a mixture without misfiring.
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