Pilot injection system for fuel injection pump

Claim 1

A pilot injection system for a fuel injection pump, which has a pump chamber and supplies a pressurized fuel in the pump chamber to a combustion chamber of an internal combustion engine through an injection nozzle, comprising: a casing attached to the fuel injection pump, the inside of the casing communicating with the pump chamber of the pump; a partition wall provided in the casing and dividing the pump chamber and the inside of the casing in a liquid-tight manner; a movable wall disposed in the casing and dividing the inside of the casing between a fuel-spill chamber, situated closer to the pump chamber and connected to a low pressure, and a holding chamber situated farther from the pump chamber; a valve unit for controlling the connection between the pump chamber and the fuel-spill chamber, the valve unit including a valve hole formed in the partition wall and connecting the pump chamber and the fuel-spill chamber, the valve hole having a seat surface facing the pump chamber, a valve plug adapted to be seated on the seat surface, thereby closing the valve hole, a coupling rod attached to the valve plug, extending through the valve hole into the fuel-spill chamber, and coupled to the movable wall, and a coil spring located between the movable wall and the partition wall and pressing the movable wall toward the holding chamber, whereby the valve plug is seated on the seat surface of the valve hole, by means of the movable wall and the coupling rod, urged by the coil spring, the coupling rod including means for adjusting a distance between the valve plug and the movable wall; and actuator means disposed in the holding chamber of the casing for operating the valve plug, the actuator including a stack of piezoelectric elements, coupled to the movable wall and capable of extending or contracting in accordance with a voltage applied to each piezoelectric element, so that the valve plug may be lifted from the seat surface of the valve hole, against the urging force of the coil spring, through the medium of the movable wall and the rod, when the stack extends, whereby the adjusting means and the coil spring provide both a predeterminable preload on the piezoelectric elements and a predeterminable sealing force on the valve plug.