Fuel injection system for internal combustion engine

Abstract

A fuel injection system for an internal combustion engine of the type so-called unit injector wherein the overflow of fuel under high pressure from a plunger chamber defines the fuel injection cut-off. In order to perform the sharp cut-off, an overflow passage is increased in cross sectional area, and in order to prevent the overflow from the plunger chamber while the fuel is being charged into it, a flow control means such as a spool type directional control valve is inserted into the overflow passage so that when the fuel is being charged into the plunger chamber the communication between the overflow passage and a fuel tank may be positively interrupted. In addition, in order to prevent the fuel recharge with the resulting secondary injection, a flow control means such as a solenoid operated directional control valve is inserted into a fuel supply line communicating between a fuel delivery source and the plunger chamber such that as long as the fuel injection continues or when the fuel injection is zto be completed, the communication between the plunger chamber and the fuel delivery source may be completely cut off.