Single solenoid unit injector

Abstract

A fuel injector (10) is provided for each cylinder of an internal combustion engine, the injector including an electronically operated control valve (146) disposed between supply passage 42 and a timing chamber (98) to control the admission of fuel into and out of the timing chamber. A primary pumping plunger (62) and a secondary plunger (90) are axially spaced within the central bore of the injection body, and a normally closed injection nozzle (14) is situated at one end of the injector body. A mechanical linkage (27, 28, 30) associated with the camshaft of the engine drives the primary pumping plunger (62) against the bias of a main spring (18). The timing chamber (98) is defined between the plungers (62, 90) and a metering chamber (128) is defined between the secondary plunger (90) and the nozzle (14). An electronic control unit (52) responds to engine operating conditions, and delivers a timing and metering signal to the control valve (146) to close the valve and seal the timing chamber for a controlled period of time. The sealed timing chamber forms a hydraulic link, so that the plungers (62, 90) move in concert during the injection and metering phases of the cycle of operation. When the signal from the ECU is terminated, the control valve opens, and breaks the link so that the primary plunger (62) moves independently of the secondary plunger (90) which is biased in a set position by a spring (96) after termination of the control signal. The timing function can be adjusted by the ECU relative to any preselected position of the crankshaft to optimize engine performance, while the metering function is achieved in a proportionate manner relative to the degree of camshaft rotation. A cam (22), having a linear portion, controls the mechanical linkage, and thus the primary pumping plunger (62), to produce the proportional metering function.