Pressure time controlled unit injector

Abstract

A fuel injector is provided for each cylinder of an internal combustion engine, the injector including an electronically operated control valve disposed between supply passage and a timing chamber to control the admission of fuel into and out of the timing chamber. A primary pumping piston and a secondary floating piston are axially spaced within the central bore of the injection body, and a normally closed injection nozzle is situated at one end of the injector body. A mechanical linkage associated with the camshaft of the engine drives the primary pumping piston against the bias of a main spring. The timing chamber is defined between the pistons and a metering chamber is defined between the secondary piston and the nozzle. An electronic control unit responds to engine operating conditions, and delivers a signal to the control valve to close the valve and seal the timing chamber for a controlled period of time to form a hydraulic link so that the pistons 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 piston moves independently of the second piston. The timing function can be adjusted by the ECU relative to any preselected position of the crankshaft to optimize engine performance. The metering function is controlled by the pressure drop across a restricting orifice in the passageway feeding fuel to the metering chamber. The flow rate through the metering orifice is proportional to the square root of the pressure drop across the orifice.