The present invention relates to a system for controlling the injection of fuel for a two-cycle engine with a direct fuel injection system.
There are various methods for supplying fuel to the 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 at 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 No. 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 scavenging. Accordingly, the structure and control system of the engine are complicated. Thus, it is preferable to employ a direct fuel injection system for directly injecting fuel to the cylinder.
In addition, a part of intake air escapes inevitably from the cylinder at scavenging without forming the combustion mixture. Since the quantity of intake air detected by the air-flow meter includes the escaping air, the air-fuel ratio of the mixture cannot be accurately controlled.
Consequently, it is necessary to determine the quantity of fuel based on the quantity of intake air in the cylinder excluding the quantity of air discharged from the cylinder.
In order to obtain the quantity of air excluding the quantity of discharged air based on the quantity of air detected by the air-flow meter, a complicated system having a memory and calculator is necessary.